240 10 13229 https://digitalcollections.lakeheadu.ca/files/original/1596d2e3228c258cd2151bf57792baf5.pdf adc222c122cfc2f81dda355b3c92682c PDF Text Text a THIRTY-SEVENTH THIRTY-SEVENTH ANNUAL ANNUAL INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY oenp4iáoh/e — - PROCEEDINGS: PROCEEDINGS: PART PART 11 - ABSTRACTS MAY 1-4, MAY 1-4, 1991 1991 EAU CLAIRE, CLAIRE,WISCONSIN �U Committee, 37th Annual Meeting Organization committee, Meeting ILSG, ILSG, 1991 1991 Chairman: Paul General C hPaul E. E Myers Mvers PHONE: 715-836-3713 PHONE; 715-836-3713 Editor: Luff! S. Chan Geology Department Department Geology Li University of Wisconsin Eau Claire, Claire. WI 547024004 S4702.4004 I VOLUME 37 PROCEEDINGS VOLUMEJiZ PROCEEDINGS U (Includes Meeting Program) Program) ABSTRACTS (Includes PART I: ABSTRACTS 2: FIELD TRIPS PART 2: Referenceto to material material in this follow the example Refereace this volume volume should follow example below. below. Morey, Glen Glen B., and Southwick, Southwick, David David L., L,, 1991, Manganese mineralization mineralization in early Many, 1991, Mangame early Proterozoic iron-formation of the Emily District, Cayuna Range, east-central Pm€erowi r o i i - f i ' o n of Emily District, Cquna Range, east-central Minnesota, (abst.j; Institute 37th Annual Minnesota, [tabst.]; Instituteon enLake LukeSuperior SuperiorGeology Geology Proceedings, 37th Meeting, Eau Claire, part 1, p. 75-76. Meeting, EM Ctairv,WI, WI, 1991; v.v. 37, part 75-76. Published and Distributed Published Distributed by: by: I I I U Institute on Institute on Lake Lake Superior SuperiorGeology Geology M.G. Mudrey, Jr., Jr., Secretary/Treasurer M.G. Secretary/Treasurer Geologicaland and Natural Natural History Survey Wisconsin Geological Survey 3817 Mineral Mineral Point Road 3817 WI 53705 53705 Madison, WI Li Li PURCHASE OF PROCEEDINGS PURC&iSE PROCEEDIh'GS VOLUMES Copies Copies of of the the 37th 37th ILSG ILSG Proceedings Proceedings(Part (Part I,I, Abstracts Abstractsand and Part Part II, H, Field Field Trips) Trips) may may be be purchased purchased during during $5.00 (US) each. each. the meeting for $5.00 Payable to the institute Instituteon onLake LakeSuperior SuperiorGeology Geology Issues of Proceedings and 1,and Field Guidebook, Guidebook, Part and Abstracts, Abstracts, Part Part 1, Part 2. 2. from from this this and previous meetings may be ordered from: I I I G. Mndrey, Mudrey, Jr. Michael G. Address, See above PHONE: PHONE: 608-263-1705 608-263-1705 The cost of $6.00 U.S. US. Orders Orders will will be filled tilled while supplies of each part isis$6.00 supplies last, last. All All volumes volumes back back to to 1955 1955 are are rom the available for for photocopying photocopyingaatt the the prevailing prevailingrate rate f from the Michigan Michigan Technological TechnologicalUniversity UniversityLibrary Librarythrough through Mr. M.S. MS. Spence, Spence, Archivist. Archivist. Phone Phone906-487-2505. 906487-250s. I 1 L �a 37th Annual Institute on Lake SuperiorGeology Proceed iii gs Ray Wachs Civic center Eati Claire1 VisconSin May 1-4, 1991 Orqaizized kv Mvcrs. I.Jniversitv of \Visconsin-1 ZIU Claire i ..s. i ;fliLNitV of Wise' )nsin—Lau Claire Volume 37 Part 1 Abstracts �TABLE OF OF CONTENTS CONTENTS Institutes on on Lake Lake Superior Superior Geology Geology to to1991 1991 L L L Constitution Constitution of the the Institute Institute on on Lake Lake Superior Superior Geology Geology ii ii By-Laws By-Laws of the Institute Institute on on Lake Lake Superior Superior Geology Geology iii iii Goldich Medal Medal Guidelines Guidelines iv Student Travel Travel Award Award \v Board of of Directors Directors vi vi L Local Local Committee Committee vi vi rL Student Paper Paper Award Committee Committee vi [ Goldich Goldich Medal Recipient Recipient vii Banquet Speaker Speaker viii L Acknowledgements viii Goldich Medal Medal Committee Committee l vi V. Report of the the 36th 36th Annual Annual Institute Institute Report of the Chairs Chairs of ix L Calendar of Events Events xi [ Programs Programs Poster Papers Papers Xiii xiii I XV I L L L L L L Abstracts Abstracts 1 �INSTITUTES ON INSTITUTES ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE INSTITUTENUMBER NUMBER 11 2 3 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 DATE PLACE 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Minneapolis, Minneapolis, MN MN Houghton, MI Houghton, MI East East Lansing, Lansing, MI MI Duluth, Duluth, MN Minneapolis, MN Minneapolis, MN Madison, WI Madison, WI Port Arthur, Arthur, Ont. Port Ont. (Thunder (Thunder Bay) Bay) Houghton, Houghton, MI MI Duluth, MN Duluth, Ishpeining, Ishpeming, MI MI St. St. Paul, Paul, MN MN Sault Sault Ste. Ste. Marie, Marie, MI MI East East Lansing, Lansing, MI MI Superior, Superior, WI WI Oshkosh, Oshkosh, WI WI Thunder Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, MN Houghton, Houghton, MI MI Madison, Madison, WI WI Sault Sault Ste. Ste. Marie, Marie, Ont. Ont. .,: Marquette, Marquette, MI MI :c, St. St. Paul, Paul, MN MN Thunder Thunder Bay, Bay, Ont. Ont. ., . ~ , Milwaukee, Milwaukee, WI WI Duluth, Duluth, MN MN Eau Eau Claire, Claire, WI WI :. .,,i East East Lansing, Lansing, MI MI .,International International Falls, Falls, MN MN Houghton, Houghton,MI MI Wausau, Wausau, WI WI Kenora, Kenora,Ont. Ont. Wisconsin Wisconsin Rapids, Rapids',WI WI Wawa, Wawa,Ont. Ont. Marquette, Marquette, MI MI Duluth, Duluth, MN MN Thunder Thunder Bay, Bay,Ont. Ont. Eau Eau Claire, Claire, WI WI 1 �CONSTITUTION SUPERIOR GEOLOGY OFINSTITUTE INSTITUTEON O NLAKE LAKE SUPERIOR GEOLOGY CONSTITUTIONOF ArticleI I Article Name kb!!s The Thename nameofofthe theorganization organizationshall shallbe bethe the'Institute "Instituteon onLake LakeSuperior SuperiorGeology. Geology". Article ArticlcIII1 Objectives The T h eobjectives objectivesofofthis thisorganization organizationare: are: region exchange A.A.ToTo provide providea ameans meanswhereby wherebygeologists geologistsininthe theGreat GreatLakes Lakes regionmay may exchangeideas ideasand and scientific scientificdata. data. B.B.ToTo promote better understanding ofofthe geology promote better understanding the geologyofofthe theLake LakeSuperior Superiorregion. region. C.C.ToTo plan and conduct geological plan and conduct geologicalfield fieldtrips. trips. Article ArticleIII I11 aaus Status No Nopart partofofthe theincome incomeofofthe theorganization organizationshall shallinure inuretot othe thebenefit benefitofofany anymember memberororindividual. individual. tnInthe theevent eventofofdissolution dissolutionthe theassets assetsof ofthe theorganization organizationshall shallbe b edistributed distributedtoto (some (sometax taxfree freeorganization). organization). (To (Toavoid avoidFederal Federaland andState Stateincome incometaxes, taxes, the the organization organization should should be be not not only only scientiflc "scientific" oro reducational, "educational",but butalso alsonon-profit".) "non-profit".) Minn. 290.01, Minn.Stat. Stat.Anno. Anno. 290.01.subd. subd.4 4 Minn. 290.05(9) Minn.Stat. Stat.Anno. Anno. 290.05(9) 1954 501(c)(3) 1954Internal IntcrnalRevenue RevenueCode C d cs.s.50I(c)(3) Article ArticleIV IV Membership Membership The Themembership membershipof ofthe theorganization organization shall shall consist consist of of the the board board of of directorsdirectors. Any Anygeologist geologist interested interestedshall shallbe b epermitted permittedtotoattend attendand andparticipate participateininand andvote voteatatthe theannual annualmeetings. meetin&% ArticleVV Article Meetings The year, preferably preferably during during the the month month of of April. April. The T h eorganization organizationshall shallmeet meet once once aa year, T h eplace placeand and exact exactdate dateofofeach eachmeeting meetingwill willbe bedesginated desginatcdby bythe theboard boardofofdirectors. directors. ArticlcVI VI Article Directors The and T h eboard boardofofdirectors directorsshall shallconsist consistofofthe theChairman, Chairman,Secretary-Treasurer, Sccreta~y-Treasurer, andthe the last last three three past pastChairman; Chairman;but butififthe theboard boardshould shouldatatany anytime timeconsist consistofoffewer fewerthan thanfive fivepersons, persons, by byrcaon rcaon vacancies ofofunwillingness unwillingnessororinability inabilityofofany anyofofthe theabove abovepersons personstotoserve serveas asdirectors, directors,the the vacancieson on the theboard boardmay maybe b efilled filledbybythe theannual annualmeeting meetingso soas asto t obring bringthe themembership membershipof ofthe theboard boardup up tot ofive fivemembers. members. ArticleVII VII Article Officers ixGQxs The and T h eofficers officersofofthis thisorganization organizationshall shallbeb ea aChairman Chairman andSecretary-Treasurer. Secretary-Treasurer. A. A.The T hChairman e Chairmanshall shallbeb eelected electedeach eachyear year by bythe theboard board ofofdirectors, directors, who who shall shallgive givedue due consideration considerationtotothe thewishes wishes of of any any group group that that may may be b e promoting promotingthe thenext nextannual annualmeeting. meeting. His Histerm termofofoffice officeasasChairman Chairmanwilt willterminate terminateatathe t theclose closeofofthe theannual annualmeeting meetingover overwhich which he shall have been appointed. appointed. He hepresides presides or orwhen when his hissuccessor successor shall have been H ewill willthen thenserve serve for foraa period threeyears yearsas asaa member member of of the theboard boardofofdirectors. directors. periodofofthree B. T hSecretary-Treasurer e Secretary-Treasurershall shallbe beelected elected at a t the the annual annual meeting. meeting. His Histerm termofofoffice office shall shall B.The be betwo twoyears yearsoro runtil untilhis hissuccessor successorshall shallhave havebeen beenappointed. appointed. Article VIII VIII Article Amendments Afwdnwm This Thisconstitution constitutionmay maybe b eamended amended by by aamajority majorityvote voteofofthose thosepersons personswho whoare arepersonally personally present present at, at, participating participatingin, in,and andvoting votingat atany anyannual annualmeeting meetingof ofthe theorganization. organization. II �BY-LAWS Duties of of the .Duties the Officers Officers and and Directors Directors A. .4 It It shall shall be be the the duty duty of of the the Annual Annual Chairman Chairman to; to: 1.. 1 2. 2 3. 3. Preside Preside at at the the annual annual meeting. meeting. Appoint all committees needed for for the the organization organization of Appoint all committees needed of the the annual annual meeting. meeting. Assume complete complete responsibility responsibilityfor for the the organization organization and and financing financing of of the the Assume annual meeting annual meeting over over which which he he presides. presides. It It shall shall be be the the duty duty of of the the Secretary-Treasurer Secretary-Treasurer to: to: B. B. 1. 1. 2. 2. 3. 3. Keep Keep accurate accurate attendance attendance records records of of alt all annual annual meetings. meetings. Keep accurate records of all meetings of, Keep accurate records of all meetings of, and and correspondence correspondence between, between, the the board board of of directors. directors. Hold Hold all all funds funds that that may may accrue accrue as as profits profits from from annual annual meetings meetings or or field field trips and and to to make make these these funds funds available available for for the the organization organization and and operation operation trips of future as required. of future meetings meetings as required. C. of the the board board of of directors directors to annual meetings C. It I t shall :shall be be the the duty duty of to plan plan locations locations of of annual meetings and to and to advise advise on on the theorganization organizationand andfinancing financingof of all allmeetings. meetings. II. Duties and and Expenses F.mensas 1. 1. 2. ill. There shall shall be be no . There no regular regular membership membership dues. dues. , Registration fees for the Registration fees for the annual annual meetings meetings shall shall be be determined determined by by the the Chairman Chairman is strongly recommended that in consultation in consultation with with the the board board of of directors, directors. it It is strongly recommended that these be encourage attendance attendanceof of graduate graduatestudents. students. these be kept kept at at aa minimum minimum to to encourage Rules of Order The rules The rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shall govern govern this this organization organization in in all all cases cases to to which which they they are are applicable. applicable. IV. Amendments . . . . , ~ ::~.. . . These by-laws maybe be amended amended by by aa majority vote of of those who are are These by-laws may majority vote those persons persons who personally present present at, at, participating participatingin, in,and and voting voting aatt any any annual annual meeting meeting of of the personally the with the the constitution constitution organization; provided that such modifications shall not conflict with as presently adopted or as or subsequently subsequently amended, amended. Ill iii �Award Guidelines Guidelines Award SAM GOLDICH GOLDICH MEDAL SAM MEDAL Preamble The Institute Geology was born born on or or around around1955, 1955, as as documented documented by by The Institute on o n Lake Lake Superior Geology the fact that the meeting will will be be held held in 1981. 1981. The TheInstitutes Institutes are are exemplary exemplary the 27th 27th annual annual meeting in their theircontinuing continuingobjectives objectives of of dealing dealing with with those those aspects aspects of of geology geology that that are are related related geographically to to Lake Lake Superior; Superior;of ofencouraging encouragingthe thediscussion discussion of ofsubjects subjects and and sponsoring sponsoring field trips tripswhich whichwill willbring bringtogether togethergeologists geologistsfrom fromacademia, academia, government government surveys, surveys, and and industry; and of maintaining an exceedingly exceedinglyinformal informal but but highly highly effective effective mode mode of of operation. operation. During the the membership membership of of the the Institute Institute (that geologists During the course course of of its its existence existence the (that is, is, those those geologists an interest interest in in the the objectives objectives of of the the I.LS.G. I.L.S.G.by byattending) attending)has hasbecome become aware aware who indicate an of the colleagues of the fact factthat thatcertain certainofoftheir their colleagueshave have made made particularly particularly noteworthy noteworthy and and meritorious meritoriouscontributions contributionsto tothe theimprovement improvementof ofunderstanding understanding of of"Lake "LakeSuperior" Superior"geology geology and its mineral and mineral deposits. deposits. The exemplary award was wasmade madeby byI.L.S.G. I.L.S.G.toto Sam Sam Goldich Goldich in in 1979 for his 1979 for his many many exemplary award contributions to 50 years. years. contributions to the the geology geology of the the region region extending extending over over about about 50 . Award Guidelines Award G .u ~ d a 1) The T h emedal medalshall shallbe beawarded awarded annually annually by the LL.S.G. I.L.S.G. Board of of Directors Directors to to aa geologist geologist whose name is associated associatedwith withaasubstantial substantialsustained sustainedinterest interestin, in,or oraamajor majorcontribution contribution to, the geology geology of the the Lake Lake Superior Superior region. region. appoint the the Nominating Nominating Committee. Committee. The initial 2) The TheBoard Board of ofDirectors, Directors, LL.S.G. I.L.S.G. shall appoint appointment will will be one for two, and appointment be of of three three members, members, one to serve serve for for three three years, years, one and one for one year, year, the the member memberwith with the the briefest briefest incumbency incumbencytotobe bechairman. chairman.After After the the one first year the the Board Board of of Directors Directorsshall shallappoint appointat a teach each spring springmeeting meeting one one new new member who will will serve serve for forthree threeyears. years. In the the thrid thrid year year this this member member shall shall be be the the chairman. chairman. The Committee should reflect reflect the main fields Committee membership membership should fields of of interest interest and and geographic geographic distribution of of I.LS.G. I.L.S.G. membership. membership. 3) By 1, the Goldich make its its Goldich Medal 3) By November November 1, Medal Nominating Nominating Committee Committee shall make recommendationto to the the Chairman of the Board of, Directors Directors who will then inform the recommendation card of who will then inform the .z.:,: , ..~ . , ~ . ~ , . Board of the the nominee. nominee. 4) The nominee of of the the Committee, Committee,will will inform inform 4) TheBoard Board of ofDirectors Directors normally normally will willaccept accept the nominee the medalist and will will have the medalist immediately, immediately, and have one one medal medal engraved engraved appropriately appropriately for presentation of the Institute. presentation aatt the next meeting meeting of 5) It It is 5) is recommended recommended that that the the Institute Instituteset set aside aside annually annually from fromwhatever whatever sources, sources, such such funds as as will will be be required required to to support support the the continuing continuingcosts costs of of this this award. award. April 4, April 4, 1981 1981 J. Kalliokoski, Chairman J. Chairman Bill Cannon Cannon Fred Kehlenbeck Glenn Morey Glenn Greg Mursky iv �STUDENT TRAVEL TRAVEL AWARD STUDENT AWARD l'hc I080 1986 Board Board of 4)1Directors Directorsestablished establishedthe theI.L.S.G. 1.LS.G. Student Student Travel Travel Award I'hc Award totosLIl)I)orL siipport sttideiit participation s~iidcnt participationat atthe the annual annual Institutes. Institutes. The Theawards awardswill willbe bemade made from fromaa special special fund fund intended to to help defray some some of of the the direct direct travel set up up for set for this this purpose. purpose. This award is intended travel costs to to the Institute costs Institute and and includes includes aa waiver waiver of ofregistration registrationfees, fees,but butexcludes excludesexpenses expenses for for meals, lodging, lodging, and and field field trip trip registration. The meals, Thenumber numberof ofawards awardsand and value are determined by the annual Chairman in in consultation consultation with with the the Secretary-Treasurer Secretary-Treasurerand and will willbe be announced announced at the annual annual banquet. banquet. The following The following general general criteria criteria will will be be considered considered by by the the annual annual Chairman, Chairman, who who is is responsible for the responsible the selection: selection: 1)) The graduate) student student 1 Theapplicants applicantsmust must have have active resident (undergraduate or graduate) status at at the time of the status the Institute, Institute, certified certified by by the the department department head. head. 2) 2) Students Studentswho who are are the the senior senior author author on on either either an an oral oral or or poster poster paper paper will will be be given favored favored consideration. consideration. It is 3) It 3) is desirable desirable for for two twoor ormore morestudents students to tojointly jointlyrequest requesttravel travelassistance. assistance. 4) In priority will will be 4) In general, general, priority be given given to to those those in in the the Institute Institute region region who who are arc farthest away. away. 5) Each made in in writing, writing, to 5) Eachtravel travelaward awardrequest request shall shall be be made to the the annual annual Chairman, Chairman, with an or other significant significant details. with an explanation explanationof of need, need, possible author status or details. Successfulapplicants applicantswill willreceive receivetheir theirawards awardsatatthe thetime timeof of registration registrationfor for the the Meeting. Successful V �BOARD BOARDOF OFDIRECTORS DIRECTORS 1991 P. P.E. E.Myers Myers(with (withL.L.S.S.Chan) Chan) 1991 Department Departmentof ofGeology, Geology,University Universityof ofWisconsin, Wisconsin,Eau Eau Claire. Claire,Wisconsin Wisconsin 54701 54701 1990 1990 H. M.H. M.Kehlenbeck Kehlenbeck Department Departmentof ofGeology, Geology,Lakehead LakeheadUniversity, University,Thunder Thunder Bay, Bay,Ontario Ontario P7B P7B 5El 5E1 1989 1989 R.W. W.Ojakangas Ojakangas(with (withJ.J.C.C . Green Greenand andT.T.B.B.Holst) Hoist) Department 55812 Universityof ofMinnesota, Minnesota,Duluth, Duluth,Minnesota Minnesota 55812 Departmentof ofGeology, Geology,University ft. 1988 J. D. D.Hughes Hughesand andK. K.J. J.Schulz) Schulz) 1988 J.J. S. S.Klasner Klasner(with (withJ. Department Departmentof ofGeology, Geology,Western WesternIllinois IllinoisUniversity, University,Macomb, Macomb,lilnois Illnois 61455 61455 Secretary-Treasurer Secretary-Treasurer M. M.G. G.Mudrey, Mudrey,Jr. Jr. Wisconsin WisconsinGeological Geologicaland andNatural Natural History HistorySurvey, Survey,3817 3817Mineral Mineral Point Point Road, Road,Madison, Madison,WI WI 53705 53705 LOCAL LOCALCOMMITTEE COMMITTEE P. E. E.Myers Myers General GeneralChairman Chairman L. S. S.Chan Chan Program Program and and Abstract Abstract Editor Editor and and Field Field Trip Trip Guidebook Guidebook Editor Editor P. L. ft. P. Willis Registration RegistrationCoordinator Coordinator STUDENT STUDENT PAPER PAPERAWARD AWARD CoMMITTEE COMMITTEE 1991 1991 J.' S. S. Klasner, Klasner, Chairman Chairman Western Western Illinois IllinoisUniversity, University,Macomb, Macomb,Illinois Illinois GOLDICH MEDAL COMMITTEE COMMITTEE1990-91 1990-91 GOLDICH MEDAL M. M. C. G.Mudrey, Mudrey,Jr. Jr. Wisconsin Wisconsin Geologic Geologic and and Natural Natural History HistorySurvey, Survey, Madison, Madison,WI WI F. W. W. Cambray Cambray F. Dept. Dept. of of Geological GeologicalSciences, Sciences,Michigan MichiganState State University, University,East East Lansing, Lansing,MI MI H. H. H. Halls Halls H. Dept. Dept. of of Geology, Geology,Erindall Erindall College, College,Mississauga, Mississauga, Ont. Ont. LSL L5L 1CO 1CO j j '1 vi U j �Biographical Biographical Sketch Sketch of WILLIAM J. HINZE HINZE WILLIAM J. 1991 1991 Goldich Goldich Medal Medal Recipient Recipient William WilliamJ.J. Hinze Iiinzebegan beganhis hisearth-science earth-sciencecareer careeratatthe theUniversity Universityof ofWisconsin, Wisconsin,where wherein in1951 1951 he he received received aa bachelor bachelor of science science in geology. gwlogy. From From1954 1954to to1955 1955he he served served in inthe the U.S. US. Anny Army Corps of Engineers at their Research and Development Laboratory, after which he returned to the Corps of Engineers at their Research and Development Laboratory, University of Wisconsin, receiving his doctorate in geology and physics in 1957. From 1956 University of Wisconsin, receiving doctorate gwlogy From 1956to to 1958 & Laughlin Steel Steel Company. In In1958 1958he hejoined joined 1958 he he worked worked as as aa staff staff geophysicist geophysicist for for Jones Jones & the thefaculty facultyof of the the department departmentof of geology gwlogy at atMichigan Michigan State State University. University, where where he he held appointments appointments of full professor. professor. InIn1972 1972he hetook tookhis hispresent presentpost postas asprofessor pmfessorof ofgeophysics gwphysics in inthe the of assistant assistant to to full Department of Earth and Atmospheric Sciences Sciences atat Purdue PurdueUniversity. University. In In 1985 he he served served as as aa visiting visiting professor professorat atthe the University Universityof of Lausanne Lausannein inSwitzerland. Switzerland. In Hinzehas hasmade mademany manysignificant significantand andlasting lastingcontributions contributionsto to In the the course course of ofhis hiscareer careerHinze potential-field potential-field geophysics. In Inaddition additionto to numerous numerous abstracts abstracts and and technical technical reports, he avenges averages several truly remarkable severalformal formalpapers papers per per year, year. either eitheras as chief chief author author or or as as co-author—a w-authorremarkable record rewrd if his fonnidable duties are considered. formidable professional professional duties considered. For For instance, instance, from from 1975 1975 to 1982 1982 he he was was chairman chairman of of the the U.S. US. National National Magnetic Magnetic Anomaly Anomaly Map Map Committee, Committee, and and from from 1985 1985to 1989 1989he cowchaired Magnetic Anomaly Regional chairedthe the North North American AmericanMagnetic Anomaly Map Map Committee. Committee. He Heedited editedThe TheUtility Utilityof ofRegional Gravity and which was was published published by by the the Society Society of ofExploration Exploration and Magnetic Magnetic Anomaly Anomaly Maps, Maps, which Geophysicists Geophysicists in in 1985. 1985. From From1986 1986to to1988 1988he heco-chaired w-chaired the theU.S. US. National National Science Science Foundation's joint U.S./Indian Lineaments: Their U.S./hdian workshop workshop "Regional "Regional Geophysical Lineaments: Their Tectonic and Economic Significance" Significance"and and co-edited co-editedthe the workshop workshopvolume, volume,which whichwas waspublished publishedby by the theGeological GeologicalSociety Society of of India M i a in in 1989. 1989. Since Since1985 1985he hehas hasdealt dealtwith withproblems problemsconcerning concerning the distribution distribution and archiving of task, has has served in of geophysical gwphysical data data for for the the worldwide worldwide scientific scientificcommunity community and, related to this task, various various posts posts with with the the U.S. U.S. Geodynamics Geodynamics Committee, Committee, the International International Lithospheric Commission, and has and the the National National Academy Academy of of Science/National Sciendational Research Research Council. Council. From From1988 1988to tothe thepresent presenthe hehas served served as as aa consultant consultantto to and and member memberof of the the Advisory Advisory Committee Committee on on Nuclear Nuclear Waste Waste of of the the Nuclear Nuclear Regulatory Regulatory Commission. He Hehas hasserved servedfrom from1986 1986both both as as aa member member and and vice-chainnan vice-chairman of of the the board of directors directors of of Deep Deep Observation Observation and and Sampling Sampling of the the Earth's Earth's Continental Continental Crust, Crust, Inc. Inc. (DOSECC), and as aa co-chairman (DOSECC), and co-chairman of of the the Potential Potential Fields Fields Committee Committee of the the Great Great Lakes Lakes International Program on Crustal Evolution Evolution (GLIMPCE). (GLIMPCE). He He has has been been aa member member of of the theU.S. US. Geodynamics Geodynamics Committee Committee of the National Academy of Science/National ScienceJNational Research Council since 1989. 1989. During Hinze has has been at at the forefront of geophysical gwphysical research During his long long and and successful successful career career Hinze in in the the Lake Lake Superior Superiorregion region and and the the surrounding surrounding Midcontinent. His Hisdoctoral doctoralresearch, research,aagravity gravity investigation investigationof of the the Baraboo Bamboo Syncline Syncline region, region, which which was was published published in in the the Journal Journalof ofGeology Geologyin in 1959, gravity studies studies of of its its time. time. His 1959, was one of the most innovative gravity His 1960 1960 Economic Economic Geology paper paper on on the the gravity gravity method method in in iron-ore iron-oreexploration, exploration, which which was was largely largely based based on on his his experiences experiences with Jones & Laughlin Steel Company, became a classic work among explorationists; Jones & Laughlin Steel Company, became a classic work among explorationists; aa slightly slightly revised version reappeared Exploration Geophysicists' volumes on mining reappeared in in 1966 1966in in the Society Society of Exploration geophysics. Duringthe the1960s 1960sHinze Hinzewas wasthe theprincipal principalinvestigator investigatorof of several severalmajor major aeromagnetic aeromagnetic gwphysics. During and gravity the Upper Upper Peninsula Peninsula of of Michigan, Michigan,and and the the Michigan Michigan gravity studies studies of of the the western western Great Great Lakes, Lakes,the Basin. The Theaeromagnetic aeromagneticstudies studiesover overLake LakeSuperior Superiorcomplemented complemented the seismic seismic investigations of vii �the and in in 1966 the results results were were published published with with the the Lake Lake Superior Superior Experiment, Experiment, and 1966 the the seismic seismicstudies studies in in the frequently cited The Earth Beneath the Continents (American Geophysical Union Geophysical the frequently cited The Earth Beneath the Continents (American Geophysical Union Geophysical Monograph 10). In1982 1982R.J. R.J.Wold Woldand andhe heco-edited co-editedGeology Geologyand andTectonics Tectonicsof ofthe theLake Lake Superior Superior Monograph 10). In Basin today the Basin (Geological (GeologicalSociety Societyof of America America Memoir Memoir 156). 156). which which remains remains today the definitive definitive reference reference on Lake on Lake Superior Superior geology geology and and geophysics. geophysics. In Inrecognition recognitionof of his hiscontributions contributionsto toMidcontinent Midcontinent geology, he geology, he was was awarded awardedan an honorary honorary membership membership in in the the Michigan Michigan Basin Basin Geological Geological Society Society in in 1986. 1986. Today Hinzemaintains maintainshis his high high profile profilein in geophysical geophysical studies studies of of the theLake LakeSuperior Superiorregion. region. Today Hinze Since the mid-1970s he has been a leading investigator of Mideontinent seismicity Since the mid-1970s he has been a leading investigator of Midcontinent seismicityand andits itsprobable probable relationship relationshipto to basement basement structure. structure. Through Throughhis hisinvolvement involvementwith with DOSECC DOSECCand andother otheragencies, agencies,he be has been a leading pioponnent of deep scientific drilling in the Lake Superior region. has been a leading pmponnent of deep scientific drilling in the Lake Superior region. He He and and his his students students are are presently presentlyconducting conductingcombined combined studies studiesof of seismic-reflection, seismic-reflection, gravity, gravity, and and magnetic magnetic data data to to investigate investigate crusthi crustal structure structure beneath beneath Lake Lake Superior. Superior, aa task task that that epitomizes epitomizesthe thestrong strong generalist characterizeshis his career. career. generalist approach approachthat that characterizes Perhaps Perhaps Bill Bill Hinze's Hinze's greatest greatest legacy legacy is is his his students. students. Through Throughorganizational organizationalskills skillsthat thatare are unsurpassed he has has inspired unsurpassed and and an an enthusiasm enthusiasm for for his his work work that that is is contagious, contagious, he inspired many many to to learn learn and and achieve they were were capable. capable. The achieve far far beyond beyond what what they they thought thought they The careers careers of of many many successful successful geophysicists worldwide proudly bear his imprint. geophysicists worldwide proudly bear his imprint. His is is truly truly aa career carter that His thathas has made made aa difference. difference. VAL W. W. CHANDLER CHA1'DLS VAL Minnesota Geological Minnesota Geological Survey Survey ~ >' Ban quet Speaker Speaker Banquet Paul IC. Sims,US. U.S. Geological Geological Survey, Survey,Denver. Denver,Colorado, Colorado,will willbe bethe the speaker speaker at the K. Sims, the Annual AnnualILSG ILSG Banquet in Ray Wachs Banquet Wachs Civic Center (Rm (Rm A) A) at at8:30 8:30pm pm on onThursday, Thursday,May May 2, 2, 1991. 1991. His topic topic will be 'Archean and Overview.' He "Archean and Early Early Proterozoic Proterozoic Geology Geology of the Lake Superior Superior Region Region -- An An Overview." He will will be Morey of of the the Minnesota Minnesota Geological GeologicalSurvey. Survey. introduced by Glen Morcy - Acknowledgements Acknowledgements We greatly appreciate the enthusiastic enthusiastic and vital vital assistance assistance of the the many many UW-Eau UW-Eau Claire Clairegeology geology student drivers, volunteered student drivers, registration helpers, helpers, projectionists, projectionists,and gofers. We also thank those who volunteercd to serve serve as as session session chairs, speakers, and authors; their dedication to to the the philosophy philosophy of ofthe theILSG ILSG isis conspicuous. conspicuous. viii viii �36th 36th ANNUAL ANNUAL INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Thunder underBay, Bay, Ontario Ontario 1990 1990 The 36th annual meetinggof Geology of the theInstitute Instituteon onLake LakeSuperior Sup Geol was held from Bay, Ontario. Ontario. The from May May 9 9 through May 12 12 in Thunder Bay, The meeting meeting was was hosted by Lakehead Bay. Manfred Lakehead University, University, Thunder Bay. Manfred M. M. Kehlenbeck Kehlenbeck served as General Chairman, Chairman, Graham Graham Borradaile Borradaile edited edited the the Field FieldTrip TripGuidebook, Guidebook,and andPhilip Philip W. W. Fralick Fralick assisted assisted with the the program programorganization. organization. .. ..;. ~.. ... . , . , ' ,:-7--. <,.* <<A . ,:. . ,. The and banquet banquet were were held held at at 'the the Airlane Motor Hotel on The technical technical sessions and on Thursday, May 11. A A total total of of 191 191geologists geologists registered for the the Thursday, May 10 and Friday, May meeting. meeting. Thirty-five Thirty-five oral oral and and twenty twenty poster papers papers were were presented presented on on aa wide wide variety variety of of subjects subjects pertinent to to the thegeology geology of of the the Lake LakeSuperior SuperiorRegion. Region. Three Three of of the the four four field field trips trips were were held held as as both both prepre- and and postpost- meeting meeting trips trips on on May respectively. The The fourth field trip trip was was held held on on May May 1 12. 9 and May 12 12 respectively. 2. Richard May 9 Sutcliffe of the the Ontario led 2 trips to the des Dies mes area Sutcliffe of Ontario Geological Geological Survey Survey led the L.ac Lac des area to to exposures of of mafic intrusions, intrusions, PGE PGE mineralization mineralization and and granitoid granitoid rocks. rocks. Graham Graham Borradaile Borradaile of of Lakehead field trips trips to to examine examinethe thegeology geology of of the the Lakehead University University led led 22field Shebandowan Shebandowan and Quetico Quetico subprovinces. subprovinces. Two Two trips led by Maurice Lavigue and John Scott Scott of the Ministry Ministry of Northern Development Development and Mines offered insigbt insight on base metal mineralization in the belt. The the Shebandowan Shebandowan greenstone belt. Thefinal finalfield fieldtrip tripwas wasled ledby bySteve Steve Kissin Kissin of Lakehead University University and focused on granitoid-related mineral deposits in the western Superior totalofof187 187geologists geologists registered registered for for the the seven seven field field Superior region. AAtotal excursions. excursions. To To transport transport the the entire entiregroup groupto torelatively relatively isolated areas required a total of 10 vans and 3 large buses. buses. In 10 vans Inaddition additionto tothe thetrip tripleaders, leaders,the thefollowing following members members of the Geology Department acted acted as asvan van drivers: drivers: P. Fralick, Frali M. Kehlenbeck, S. Kissin, D. Nicol, R. Viitala. Viitala. i... Nicol, S. S. Spivak, Spivak, B. Seemayer and it. : A total of on May 10. Manfred of 140 140 people attended the annual annual banquet b Kehienbeck Kehlenbeck presented presented the the 1990 1990Goldich Goldich Medal Medal to to Ken KenCard Cardof ofthe theGeological GeologicalSurvey Survey of of Canada for his many significant contributions to the geological understanding of Canada for his many significant contributions to the geological understanding of the the rocks in the Great Great Lakes Lakes Region. Region. J.J. J.J.Brummer, Brummer,M.G. M.G. Mudrey Mudrey and and F.W. F.W. Cambray Cambray served on the the Goldich Goldich Medal Medal Committee. Committee. Dedication Dedicationof of the the1990 1990I.LS.G. I.L.S.G. publication publication to to H.L. H.L. James James in in recognition recognition of of his his life-time life-time achievements achievements as a geologist in the Lake Lake Superior area area was was presented presented by by Mike Mudrey. Mudrey. After After numerous numerousunsatisfactory unsatisfactory replies to inquiring we were were delighted delighted to to have Herr inquiring participants during the day-long day-long program, we Doktor Doktor Professor Professor Wolfgang Wolfgang Gottlieb Gottlieb von von Schlunimerklutz Schlummerklutz (a.k.a. (a.k.a. Richard Ojakangas), Ojakangas), Direktor Institut filer fuer Welt Welt Probleme entertain all assembled Direktor of of the the Wissenschaftliche Wissenschaftliche Institut with with his presentation of recent research on the origin origin of Panzerenkotklotzen. His His meticulous research research and and marvellous marvellous illustrations illustrations made made aalasting lastingimpression. impression. Recognition of the importance importance of student student participation in the the meetings meetings of the the Institute led to the continued financial support of 16 student contributors in 1 1990. 16 in 990. Funds Institute to the continued financial for this waiver of of registration fees were drawn equally from the this assistance assistance which includes waiver two treasuries of the Institute. AAtotal totalofof$2,060.00 $2,060.00was spent in 1990. Four Four awards awards were ix �presented for the best oral oral and and poster poster papers papers by students for a total of $600.00. The recipients of the 1990 Best Student Paper Paper Awards Awardswere: were: Stephen D. Geerts, Natural 1990 Best Resources Research of Research Institute, Institute, Duluth, Duluth, MN.; MN.;Joseph Joseph D. D. Jablinski, Jablinski, University of Minnesota, Falls; and David R. Koehler, Koehler,University University of of Wisconsin, Wisconsin, River Falls, Minnesota, Duluth; Duluth; Steven Steven R. B. Saja, Michigan Technological Technological University, University,Houghton. Houghton J. J. Kiasner, Klasner, W. W. Kangas and D. Southwick served served on the Best Student Student Paper Paper Committee. Committee. The I.LS.G. 4.. The ~a~ 4 Themeeting meeting was was attended by J. I.L.S.G. Board Board of of Directors Directors met on on May Kalliokoski, M. Kehienbeck, J. Klasner, Lung Chan, M. Lavigne, P. Myers, M. Mudrey, Kehlenbeck, R. Ojakangas, Ojakangas, R. R. Sage, Sage,and andM. M.Smyk. Smyk. The The following following items items were were discussed: discussed: (1) (2) (3) (4) (5) (6) - The 1991 meeting meeting will be at at Eau Eau Claire, Claire, WI WI - Paul Myers as General The site site for for the the 1991 Chairman. Chairman. Voted to to accept accept Henry Henry Halls Halls on on the the Goldich Goldich Medal Medal Committee Committee to replace replace J.J. Brummer Bmmmer whose term term has has expired. expired. To continue papers. Funds continue the practice practice of of travel travel support for students presenting papers. Funds to be drawn drawn equally equally from the ILSG treasuries in the United States States and and Canada. Canada. The treasurer's report wasreceived. received. The balance balance in in the General report by by J. J. Kalliokoski Kalliokoski was account as as of of March March 27, 27,1990 1990 was $8,463.75. The Goldich Medal Fund contained $911.76. Fourteen Medals Medals are are in in care care of of G.B. G.B. Morey. Morey. Since Sincethe the 1990 1990meeting meeting was held in Thunder changing. Consequently, Thunder Bay Bay the the account account was was actively actively changing. Consequently, no meaningful statement could be made. M. M.Kehlenbeck, Kehlenbeck,however, however, assured the the Board that that all allexpenses expenses would would be met met and and that that no nodeficits deficitswould would be be incurred. incurred. Offers to host future future meetings meetings of the Institute Institute were received received from the Ministry Ministry of Northern Development Development and and Mines Mines (Marathon, (Marathon,Ontario), Ontario),Michigan Michigan Technological Technological University, and the the Minnesota MinnesotaGeological GeologicalSurvey. Survey. Alter After many many years years of of service, service, Joe Joe Kalliokoski Kalliokoski tendered tendered his his resignation resignation as asSecretarySecretaryTreasurer of the Institute. Joe has not only been carrying out the duties Institute. Joe has not only been carrying out the duties of of this this office, but has been of the Institute been very very active in many aspects of the functioning of Institute and has a sustained sustained record of contributions. contributions. His His sage sage advise has been a great help and comfort chairmen in in the the past. past. Voted comfort to many general chairmen Voted to to ask ask Mike Mike Mudrey to assume the the office office of of Secretary-Treasurer. Secretary-Treasurer. I wish wish to thank all those who dedicated their time and and expertise expertise to to make make the the 1990 1990 meeting meeting aa success. success. Respectfully submitted, submitted, M.M. Kehlenbeck M.M. x �CALENDAR OF EVENTS CALENDAR TUESDAY, APRIL APRIL 30 TUESDAY, Civic - Civic 3:00-5:00 p.m. p.m. 300-500 Early Registration Registrationfor forField FieldTrips Trips#1 #1 and and #2 #2 Participants Participants Early Center Inn Inn (CCI) Center (CCI) Lobby Lobby FIELD TRIP TRIP #1 #1 FIELD P.K. Sims, Sims, and and J.S. J.S. Kiasner Mountain shear Klasner (Leaders) (Leaders) "The "The Mountain shear zone zone - aa P.K. post-Penokean discrete ductile deformation zone" deformation 5:00p.m. for A Antigo (Park Inn) Inn) 5 0 0 p.m. Two Two vans veins depart for ntis (Park p.m., Park Park Inn, Pre-Field 8:30 p.m., Pre-Field Trip TripConference CoIfference - WEDNESDAY, MAY 11 FIELD TRIP TRIP #1 #1 FIELD 8:00 a.m. for the 8:00 a.m. Vans Vansdepart depart from from Park ParkInn, Inn,Antigo, Antis, for the mountain mountain area. area. Vans Vans by about about9:00 9:00p.m. p.m. return to CCI by FIELD TRIP TRIP #2 #2 FIELD L.S. Chan, L.S. Chan, P.E. P.E. Myers, Myers, and and R.L. R.L. Hay, Hay, (Leaders): (Leaders): "Features "Features and and contact in western significance of of the significance thePrecambrian-Cambrian Precambrian-Cambrian contact Wisconsin" Wisconsin" Pre-trip Seminar 8:00 a.m. Pre-mp Seminar CCI, CCI, Farwell Farwell Rm. Rm. a.m. Vans from CCI 8:20 a.m. Vans depart from CCI Lobby Lobby 2:00-5:00 p.m. 4:00-8:00 p.m. 8:00-11:00 p.m. Staff, CCI CCI Gibson Room Pre-Conference Planning Planning Session -- Staff, Pre-Conference Registration and Registration and check-in check-in for for pre-registrants, pre-registrants,Civic Civic Center Center Inn Inn Lobby Lobby Informal Get.together and Cash Informal Get-together and Cash Bar Bar Music by: by: Bill BillJordan Jordan Jazz Jazz Quintet Music THURSDAY, MAY 2 7:15 a.m - Civic Center Center Inn Inn (CCI) Lobby, Civic Registration - Lobby, (CCI) TECHNICAL SESSION TECHNICAL SESSION All Technical Technical Sessions Sessions are are in Room Center (RWCC); Poster Poster Sessions All Room C, Ray Wachs Civic Center in Rooms D B and of oral oral papers in RWCC RWCC Rooms and E. E. Schedules Schedules of papers are are shown shown on on pages pages xiii xiii and and xiv. xiv. a.m. Contributors should have posters up by 9:00 9:00 a.m. 8:00 a.m. 8:00 Introduction and Paul Myers, and Lorry Larry Introduction andWelcome: Welcome: Paul Myers,Conference Conference Chairman, and Claire Eau Claire Schnack, Chancellor, Schnewk, Chancellor, University University of Wisconsin - Eau 8:20-10:00 a.m. 8:20-10:OO Morning Session Chairs: R.W. Ojakangas Morning Session#1. #I. Chairs: R.W. Ojakangasand andA.B. A.B. Dkkas Dickas 10:00 1 0:OO a.m. a.m. 10:20-11:50 a.m. a,m. 10:20-11:50 - COFFEE BREAK COFFEE BREAK Morning Session G.L. Morning Session#2. #2.Chairs: Chairs: G.L.LaBerge LaBergeand andK. If.Schultz Schultz xi �NOON-2:00 p.m. BOARD Farwell BOARD LUNCHEON LUNCHEONAN]) ANDANNUAL ANNUALMEETING: MEETING: FanvellRoom, Room,CCI CCI 12:30-1:30 p.m. POSTER #1 - Authors POSTER SESSION SESSION #1 Authors present present (Poster (Posterpapers, papers,p.p. xv) xv) 1:40-3:00 p.m. Afternoon Chairs: V.W. AfternoonSession Session#1.#1. Chairs: V.WChandler .Chandlerand andG.B. G.B.Morey Morq - - COFFEE COFFEE BREAK BREAK -- Remove Remove Poster Papers Papers 3:00 p.m. 3:20-4:50 p.m. Afternoon MM. Kehienbeck AfternoonSession Session#2. #2.Chairs: Chairs: MM. &hienbeck and andC.C.Craddock Craddock 6:00-7:30 p.m. CASH CASH BAR: BAR: RWCC RWCC ROOM ROOMAA 7:30-10:00 p.m. ANNUAL ILSG ILSG BANQUET BANQUET -- RWCC RWCC Rooms A and B B -- Presentation to WJ. WJ.Hinze, Hinze,Purdue PurdueUniversity University Presentation of of the the Goldich Goldich Medal Medal to by V.W. Chandler V.W. Chandler Speaker: K. Sims, Sims,"Archean "Archean and and Early Early Proterozoic ProterozoicGeology Geology of the Speaker: Paul Paul K. introduced by Lake Superior An Overview"; introduced by G.B. G.B. Morey. Morey. SuperiorRegion Region -- An -- FRIDAY, 1991 FRIDAY, MAY MAY 3, 3,1991 8:00 p.m. Registration 8:00 a.m.-3:30 a.m.-330 p.m. Registrationand andSale SaleofofExtra ExtraProceedings ProceedingsVolumes Volumes 8:20 a.m. Morning Chairs: M.M. G. GMudrey, and MorningSession Session#1. #l. Chairs: . Mudrey,Jr.Jr. and7'.T.A.A.DeMatties DeMatties COFFEE COFFEEBREAK BREAK 10:00 a.m. 10:20-11:30 a.m. Morning G.W. Adams Chairs: G.W. A d a mand andBA. BA.Brown Brown MorningSession Session#2. #2.Chairs: 12:30-1:30 p.m. POSTER SESSION SESSION #2 -- Authors Authors present (poster (poster papers, papers, p. p. xvi) xvi) 1:40-2:40 p.m. Afternoon Chairs: W.S. #l. Chairs: W.S.Cordua Corduaand and M. M. Jirsa AfternoonSession Session#1. 2:40 p.m. Student Student Award Award Presentation, John Klasner Klasner -- - COFFEE Remove Poster Papers Papers COFFEEBREAK BREAK -- Remove 3:00 p.m. 3:20-4:30 p.m. Afternoon J. J. Kaliokoski AfternoonSession Session#2. #2.Chairs: Chairs: SalioImskiand a dJ. .C. C.Green Green 7:00-8:30 p.m. Pre-Trip Pre-Trip #3 #3Seminar, Seminar,CCI, CCI,Farwell Farwell Room, Room, M.G. M.G. Mudrey, Jr. and and B.A. B.A. Brown Brown SATURDAY, MAY 4, 1991 4,1991 FIELD TRIP #3 (Leaders), "Proterozoic Mudrey, Mudrey, Jr., and and B.A. BA. Brown Brown (Leaders), "Proterozoic volcanogenic massive sulfide deposits of northwestern northwestern Wisconsin' Wisconsin" 8:00 a.m. Bus departs from from front front entrance of of CCI M.G. xli xii �PROGRAM -- DAY 1, THURSDAY, THURSDAY, MAY 2, 1991 2,1991 L Atil hors Ii Inc 8:20 AM L 8:40 AM AM 8:40 L 9:00 AIvI 9:00 AM I 1 9:40 AM 10:20 AM 10:40 AM 11:00 AM AM 11:00 1 1 Read, William William F. F. Anderson, 1 Anderson, Raymond It. R 1 I 11:20 AM L Morey, G.B. G.B. and D.L Morev. D.L. Southwick Bachman, R.L. 11:40 AM 11:50 AM L 1:40 PM 1 The Relationship of of Topography Topography and and Gravity over over the the Lake Superior The Superior Swell:Evidence Evidencefor foraa Keweenaw Keweenaw Hot Hot SDOI Spot Swell: Aeromagnetic Surveying SurveyingProgram ProgramininMinnesota: Minnesota:Past Pastand and Future Future 1 Acromagnetic Physical Volcanology of the Footwall Rocks at the Winston Lake Massive Sulfide Deposit Geology & & Petrography Petrography of of the the Amnicon Amnicon Pluton, Pluton, Douglas Douglas County, County. Geology I COFFEE BREAK Wisconsin isc cons in 1 COFFEE BREAK Product of 1 The Neda Iron Iron Formation Formation -- AA Product of Vulcanism? Vulcanism? 1 1 1 The Amoco MG. The M.G.Eischeid Eischcid Oil Oil Test: Test: 4200 4200 Meters Meters of of Clastic Clashc Rocks of Midcontinent Rift Rift System Midcontinent System Manganese Mineralization MineralizationininEarlv EarlyProterozoic ProterozoicIron-Formation Iron-Formation of of the the Mansanese Emily District, Cuyuna Range, East-Central Minnesota The Homestake Mine: An Early Proterozoic Iron-Formation Hosted Gold Deposit CONCLUDING REMARKS BY SESSION CHAIRS END OF MORNING SESSION Laberge, Gene L. Early Proterozoic Rocks in the Monico, Wisconsin Area: Implications Magmatic Terrane Terranc on the Wisconsin Wisconsin Magmatic Isoclinal Slump Slump Folds Folds in in the the Lower Pokegama Ouartzite: Isoclinal Quartzite: Evidence Evidence for Seismicity Seismicityand and Slope Slope Instability InstabilityDuring During Deposition Deposition of of the for Animikie Group Group Animikie Continuous Strike-Slip Strike-SlipFault-En Fault-En Echelon Echelon Fracture Fracture Arrays in in Deformed Archean Rocks: for Fault Propagation Deformed Rocks: Implications for Mechanics 2:00 2 0 0 PM Hemming, S., S., G.N. GN. Hanson, Hemming, S.M. McLennan, and W.D. S.M. Sharp Sharp 2:20 2 2 0 PM Craddock, John John P. and 'Craddock, Andrew Moshoian Moshoian 2:40 PM 240 J Jerde, e r d e , Eric A A Evolution in in the Midcontinent Rift: Evidence Magmatic Evolution Evidence from from HypabyssalRocks Rocksof of the the North North Shore of Lake Superior Hypabyssal Superior COFFEE BREAK Cambray, F. William and Kazuya Fujita Cambray, F. Camhray, F. William William and Glenn Scott Scott Collision Induced Induced Ripoffs, Ripoffs, Ancient Ancient and and Modern: Modern: The The Midcontinent Collision Midcontinent Rift System and the the Red Red Sea-Gulf of Aden Rift System and Sea-Gulf of Aden Compared Compared A Late Keweenawan Thrust ? Marquette Keweenawan Thrust Marquette County, County,Michigan Michigan 'Manson, M.L. "Manson, M.L and H.C. Halls Halls Canibray, F. William Cambray, William and Joseph J. 1.Maneuso Mancuso 4:40 PM 4:40 The Geology and Geophysics of Major Post-Keweenawan Post-Keweenawan Faults in the Eastern Lake Superior Region the Detachment Faulting Faulting and and the Origin of the Asymmetric Detachment Asymmetric Depositional Pattern of of the Marquette Pattern Marquetie Trough CONCLUDING REMARKS REMARKS BY BY SESSION CHAIRS CONCLUDING 4:50 4 5 0 AM AM END O OFF AFTERNOON SESSION END SESSION L L The Wisconsin Gravity Minimum: Source & Implications POSTER SESSION 12 30 PM__J L 11 tie j Perspectives Osterberg, Steven A. and Ian R. Morrison Dickas, AJbert B. B. and and M.G. MG. Dickas, Albert Mudrey, Mudrev. Jr ..Jr. 9:20 AM 10:00 AM AM 10:00 Allen, David J. and William J. Hinze AJlen, David David J., 1., William 1 L. "Allen, Hinze, Hinze. and William William F. F. Cannon Chandler, Val W. 3:00 3 0 0 PM PM 3:20 3 2 0 PM 3:40 3 4 0 PM PM 4:00 4 0 0 PM 4:20 PM 4:20 XIII xiii �1991 PROGRAM -- DAY R DAY 2, FRIDAY, MAY MAY 3, 3,1991 I — Authors 'runt- Title — A.M.: A.M.: SYMPOSIUM ON O N MINERAL RESOURCES POTENTIAL OF O F NORTHERN NORTHERN WiSCONSIN WISCONSIN 8:20 8:20 Mv! AM 1 8:40 840 AM AM TA. and I DeMatties, DeMatties, T.A. and W.F. W.F. 1 DeMatties, TA. and MG. DeMatties, T.A M.G. Mudrw. Mudrey, Jr. 1 Hanson, Hanson., Jay Jav.C. C. 9:20 920 AM AM 1 9:40 940AIM AM I Bend, A Lower Proterozoic, Copper- and Gold-Enriched 1 Ground Geophysical Leading to the Bend Geophysical Bend Copper-Gold Coppcr.Gold - to .. . . Surveys Leading Discovery The The Lynne Lynne Massive Massive Sulfide Sulfide Deposit, Deposit, Oneida OneidaCounty, County,Wisconsin Wisconsin 1 Volcanogenic Volcanogenic Massive-Sulfide ~Deposit e b i int Taylor Taylor County, County,Wisconsin Wisconsin Rowell Rowell 9:00 900 AM AM Kennedy, Lawrence P., Teresa A. Harding, A Hardina. John A A.Schaff, Schaff, and Anne ~ n n M. e kZielinski Zielinski . Counts'. of the Flambeau Deposit, 1 Geology and Mineralogy Mineralogy of Deposit, Oneida Oneida County. 1 Thresher, Thresher, Jr., Jr.. J.J. Wisconsin .. I 10:00 10:00AM AM 10:20 AM la20 1 1 1 Mudrey, Jr., Jr., M.G. M.G. and and B.A. BA. Mudrey, Brown 10:40 la40 AM Brown, Bruce, A. A 11:00AM 11:00 AM I. Evans, Thomas J. 1 COFFEE BREAK BREAK Platinum Group Group Element Element Potential Potential of of Keweenawan Keweenawan Intrusive Intrusive Rock Rock in Wisconsin Wisconsin Nonmetallic Mineral Resources Resources and and Minor Metals Potential of Nonmetallic Mineral of Northern Wisconsin Wisconsin Regulating Metallic Mineral Development Development in in Wisconsin Wisconsin CONCLUDING REMARKS REMARKS BY BY SESSION SESSION CHAIRS CHAIRS 11:20 11:20 AM 11:TOAM 11:30 .... .AM .- . Geological Setting of of the Early Proterozoic BaseBase- and and Precious Precious Metal-Rich Metal-Rich Metavolcanic Meiavolcanic Belt Belt of of Wisconsin Wisconsin I END O MORNING SESSION -~ - OF - -F MORNING -~ - SESSION ~ POSTER SESSION SESSION 1230 1230PM PM Klasner. John S. and P.K. P.K. Sims Sims Klasner, 1:40 1:40PM Backthrusting in the Felch-Calunict I Thick-Skinned Thick-skinned back thrust in^ in Fclch-Calumcl Troughs Trouch* Region, Ki;Wn, - with the Southern Alps Northern Michigan Michigan -- A comparison with Alps 2:00 2:00 PM PM 2:20 2:20 PM PM A Preliminary Preliminary Study of Rejuvenated Movement Movement Along Along aa Precambrian Fault, Fault. St. St.Croix CroixCounty, Counlv. Wisconsin Wisconsin Middleton, Michael D. D. J.D., Jr., J.B. Paces, 1 Miller, J.D., Paces, J I Geochronology of of the the Duluth Complex: A Progress Report Geochronolo&y Complex: A and RE. R.E. Zartman Zartman STUDENT AWARD PRESENTATION 2:40 240 PM PM 1 300PM PM 3:00 3:20 PM 320 pM 3:40 340 PM 4:00 4:00 PM I Seifert, Karl E., Zell F. E. Peterman, and Scott ScoU E. Thieben Thieben I COFFEE BREAK The Nature Nature and and Source Source of of Midcontinent Midcontinent Rift Igneous Rocks Windom, Kenneth E., E, W.R. Windom, Kenneth W.R. Van Schmus, Schmus, Karl E. Seifert, Seifert, E.T. Wallin, Wallin. and R.R. Anderson Archean and Proterozoic Proterozoic Tectono-Magmatic Tectono-Magmatic Activity Activity Along the in Northwestern Northwestern Iowa, Iowa, Southern Margin of the Superior Superior Province Province in USA Chan, Lung Lung S. S. Paleomagnetism of of Central Dike Swarm: Palmmagnetism Central Wisconsin Wisconsin Dike Swarm: Constraints Constraints on on Thermomechanical Model of Midcontinent Rift CONCLUDING REMARKS BY SESSION CHAIRS 4:20 PM 4:30 PM J j J Li END OF AFTERNOON SESSION Li Student Contribution 'Student Contribution xiv -J J �POSTER SESSION DAY 1, THURSDAY, MAY MAY 2,1991, 2, 1991, DAY 12:30 PM PM -- 1:30 1:30 PM, PM, ROOMS ROOMS D D& &E E,,RW CWIC 12:30 CIVIC CENTER CENTER Brehm, Daniel J., C. Patrick Ervin, M.G. Brown, & & M.G. Mudrey, Mudrey, Jr., Jr., B.A. B.A. Brown, M. L. Czechanski Czechanski M.L. Wisconsin: 1990 COGEOMAP Program Program Wisconsin: 1990 COGEOMAP Brown, B.A. and R.S. Maass Preliminary Bedrock Geology Map of Eau Claire County, Extension of Gravity Filed Coverage in East-Central Wisconsin *Dahl, Linda Linda J.J. and and Susan E. E. Brink *Dahl, I PreliminaryDrill Drill Core Core Study Studyof ofTwo TwoHoles HolesDrilled Drilledon on the the Preliminary Cuyuna Iron Iron Range Range and and Emily Emily Manganiferous Manganiferous Iron Iron Formation Formation Cuyuna District of of Minnesota Minnesota District *Mariano, J.J. and W.J. 'Mariano, W.J. Hinze Geophysical Investigations Investigationsofofthe the Midcontinent Midcontinent Rift in Geophysical Eastern Lake Superior Using Variable Magnetization Magnetization Eastern 1 Modeling 11 Modeling Nicholson, S.W., SW., K.J. Ki. Schulz, Nicholson, Schulz, W.F. W.F. Cannon, and and L.G. Cannon, L.G. Woodruff Woodruff Keweenawan The Porcupine Porcupine Mountains The Mountains Area, Area, Michigan Michigan - aa Keweenawan Central Volcano? Central Volcano? Reichhoff, J.A., J.A., S.A. S.A. Hauck, Hauck, and and D.L. DL. Reichhoff, Southwick Lithogeochemistry and and Geological Geological Mapping Mapping in in the the Vermilion Lilhogwchemistry Vermilion Minnesota, as as an an Aid Aid to Mineral Greenstone Bely, Bely, Minnesota, Exploration Exploration Severson, Mark 3. J. and Steven Steven A. A. Hauck Correlation of of Igneous Igneous Units Units at at the the Minnamax Deposit. NE NE Correlation Minnamax Deposit, Minnesota Teskey, D. Three-Dimensional Modelling Modelling of of the the Magnetic Anomaly Anomaly Three-Dimensional Lake Superior Central Lake Turnock, AC., A.C., D.C. D.C. Kamineni, Kamineni, and R. McGregor McGregor Chemistry and and Metamorphism Metamorphism of of an Archean Pillow Chemistry Pillow Basalt Welsh, James James L. L. and and Jayne Reichhoff Welsh, 1I 1 Geochemistry of of Archean Archean Rocks Rocks form form the the Virginia Virginia Horn area: Geochemistry Preliminary Interpretations Interpretations Preliminary Witthuhn, Kathleen 'Witthuhn, Stress Analysis Analysis of of the the Midcontinent Midcontinent Rift in Michigan Stress Michigan and Minnesota Zanko, L., Zanko, L., A. A. Gokee, Gokee, B. B. Dewey, Dewey, S. S. Hauck, and J. Pastor Geostatistical and and GIS GIS Evaluation of Biochemical Geostatistical Biochemical and Ecological Data Data From From Three Three Mineralized Mineralized Sites Sites (Au (Au & & Cu-NiCu-NiEcological PGE), Northeastern PGEt. Northeastern Minnesota: Minnesota: Implications Irn~licationsfor for Mineral Mineral in ~Exploration x ~ l & a t i oin n a Boreal Forest Student Contribution *Student xv I �POSTER POSTER SESSION SESSION DAY 2, 2, FRIDAY, MAY 33,, 1991 DAY PM-1:30 PM, PM, RROOMS D& &E E,,RW CIVIC RW C M C CENTER CENTER 112:30 2 3 0 PM-1:30 OOMS D Campbell, Frederick Frederick K. Campbell, The Feasibility of of Recovering Recovering Metals Metals From From aa Hazardous Waste Site; A A Brief Case Study Waste Geerts, Stephen D. Geeris, D. Horizons Geology of of Platinum Platinum Group Element-Enriched Element-Enriched Horizons Geology Prospect, St. St. Louis within the Dunka Copper-Nickel Prospect, within the Dunka Road Road Copper-Nickel Louis County, Minnesota Green, John C., Ed. Ed. Venzke, Venzke, Green, John C., and Tom Lawler and Lawler Drift Pebble Pebble Lithology Lithology of of the the Tomahawk Tomahawk Road Road Area, Area, Lake Lake Drift County, Minnesota, Minnesota, Used Used to to Help Help Infer Infer Local Bedrock County, Local Bedrock Heine, John John J., Tom A. Heine, A. Toth, Steven A. A. Hauck, and Steven George W. Shurr George Shurr Geology of of the the Meridian Meridian Aggregates AggregatesQuarry Quany and and the Gwlogy Surrounding Area, Area, St. St. Cloud, A Study of the Surrounding Cloud, Minnesota: Minnesota: A Study of the Bedrock Influences Influences on on the the Pre-Late Pre-Late Creiaceous Cretaceous Weathering Weathering Bedrock Profile Hinz, Peter Peter Hinz, Industrial Minerals Minerals of of Northwestern Northwestern Ontario Ontario Industrial Hinz, Pete1 Peter Hinz, Exploration and and Mining Activityin in Northwestern Northwestern Ontario Ontario Exploration Mining Activity TMJohnson, JamesS., S.,Denise Denise A. 'Johnson, James Stavish, Mary Mary K. Tozer, and Slavish, Surface Expression Expression of of Major Major Bedrock Bedrock Structural Structural Features Surface George W. Schurr Morrison, Ian R. R. Pick Lake Pick Lake Zinc-Copper-Silver Zinc-Copper-Silver Deposit Deposit Thompson, M.D., Thompson, M.D., L.D. L.D. McGinnis, M.G. MG. Mudrey, McGinnis, Mudrey, Jr., Jr., and CA'. C.P. Ervin Midcontinent Rift Rift Structure Structure Interpreted Interpreted From From the the Midcontinent GNtJArgonne Seismic Seismic Data Data Set Set GNIIArgonne Toth, Toth. Thomas Thomas A., A.. John John 3. I. Heine, & Steven A. A.1-lauck Hauck Regional Stratigraphic Stratigraphic Model Model of of Late Late Cretaceous Sediments Regional Sediments and their their Relationship with the Underlying and Underlying Pre-Late Cretaceous Weathering Weathering Profile Profile along along the the Minnesota Minnesota River River Cretaceous Valley, Minnesota Minnesota Valley, Woodzick, Thomas Thomas L., Gary Woodzick, P. Murdock, and Douglas E. Pride A Study Study of of Thematic Thematic Mapper Mapper Lineaments A Lineaments in Northwest Nevada J U 1 J U *Student Contribution Contribution "'Student J xvi U J �L L C [ L L [ ABSTRACTS ABSTRACTS xvii �Wisconsin Gravity Gravity Minimum: Source and Im~lications Implications The Wisconsin Source and '' and William William J. Hinze, D David David J. J. Allen and Department of Earth and Atmospheric Sciences, University, West Lafayette, Indiana Purdue University, The 1) attains its its most most negative The Wisconsin Wisconsin Gravity Gravity Minimum Minimum (Fig. (Fig. 1) negative values values of 1.5 Ga Ga Wolf Wolf River River Batholith, Batholith, but but extends extends approximately -95 approximately -95 milliGals milliGals over the outcrop of the 1.5 discordantly across the the Archean 1.9-1.8 Ga Penokean discordantly across Archean Marshfield Marshfield Terrane, Terrane. the 1.9-1.8 Penokean PembinePembineWausau Wausau Terrane, Terrane, and the the 1.76 1.76Ga Gaanorogenic anorogenic rhyolite-epizonal rhyolite-epizonal granite granite terrane terrane of of southern southern Wisconsin. The edges that the edges of of the the minimum minimum are arecharacterized characterized by by sharp sharp gradients gradients indicating indicating that source trend of of the anomaly source of the the anomaly anomaly lies lies atat shallow shallow depths. depths. The north-northeast north-northeast trend anomaly is discordant with the east-west discordant with east-west Penokean Penokean structural structural grain grain in in Wisconsin, Wisconsin, suggesting suggesting that that the the source of the source of the anomaly anomaly may may be be younger younger than than 1.8 Ga. Ga. Thus, Thus, we we propose propose that that the the entire entire Wisconsin Gravity Minimum Minimum is produced produced by by the Wolf River Batholith. Wisconsin Gravity Batholith. Although Although the the batholith batholith outcrops only in in northeast northeast Wisconsin, Wisconsin, the anomaly anomaly suggests suggests that itit lies lies buried buried beneath beneath aa thin thin outcrops cover cover of older older Precambrian Precambrian roof roof rocks rocks and and early earlyPaleozoic Paleozoic sedimentary sedimentary rocks rocks throughout throughout a substantial portion of Wisconsin. Wisconsin. Forward modeling modeling of gravity Forward gravity data along along several several profiles profiles across across the the Wisconsin Wisconsin Gravity Gravity Minimum South and and west of the Minimum supports supports the buried buried Wolf Wolf River RiverBatholith Batholith hypothesis. hypothesis. South west of the its its outcrop, the Wolf River River Batholith Batholith may may be be buried buried beneath beneath approximately approximately 44 km outcrop, the Wolf km of older older Precambrian rock, and and the batholith 10 and 15 15 km km (Allen, (Allen, 1990). 1990). Precambrian rock, batholith extends extends to depths between between 10 Figure Figure 22 is is an an interpreted geologic cross-section based on a gravity model along along a based on gravity model northwest-southeast northwest-southeast profile (Fig. (Fig. 1). 1). In northern northern Wisconsin, Wisconsin, the the negative negative gravity gravity anomaly anomaly is produced produced by by the the density density contrast contrast between between the the granitic granitic rocks rocks of of the theWolf WolfRiver RiverBatholith Batholith and the the 1.76 the denser denser Penokean Penokean and and Archean Archean rocks. rocks. In southern southern Wisconsin, Wisconsin, however, however, the 1.76 Ga anorogenic rhyolites-epizonalgranites granites and and Baraboo Baraboo quartzites quartzites have have densities densities similar similar to to that iinorogenic rhyolites-epizonal of the Wolf River Batholith; thus, the source of the gravity anomaly in southern Wisconsin the Wolf River Batholith; thus, the source of the gravity anomaly in southern Wisconsin is the density between the the Wolf Wolf River and the the denser, pre-l.76 Ga rocks the density contrast contrast between River Batholith Batholith and denser, pre-1.76 rocks which underlie the anorogenic granites, rhyolites, and quartzites. The lower crustal structure underlie the anorogenic granites, rhyolites, and quartzites. crustal structure shown shown in Figure Figure 2 was was obtained obtained by by projecting projecting aa crustal crustal model model based based on on aacombined combined seismic seismic reflection-gravity interpretationalong alongGLIMPCE GLIMPCEline lineHH in in Lake reflection-gravity interpretation Lake Michigan Michigan (Cannon (Cannon et et al., 1991) As shown in Figure 1991) west along along geophysical-anomaly geophysical-anomaly strike strike into intoWisconsin. Wisconsin. As shown in Figure 2, the the lower crustal structure does does not not significantly contribute contribute to to the the Wisconsin Wisconsin Gravity Gravity Minimum. Minimum. The emplacement of the emplacement of the Wolf Wolf River River Batholith Batholith may may have have been been controlled controlled by by prepreexisting the Eau existing structures. structures. For example, example, the Eau Pleine Pleine Shear Shear Zone, Zone, a 1.8 1.8 Ga Ga suture suture between between the the Pembine-Wausau Terraneand and the the Marshfield Terrane, has Pembine-Wausau Terrane Marshfield Terrane, has been been identified identified beneath beneath Lake Lake Michigan and projects the most negative portion of Michigan (Cannon (Cannon et et al., al., 1991) 1991) and projects through through the most negative portion of the the Wisconsin Gravity Minimum Minimum where where the Wolf River Batholith Wisconsin Gravity Batholith is thickest thickest (Fig. (Fig. 2). 2). The shear zone may have have acted acted as as aaconduit conduit along alongwhich which magma magma was was preferentially preferentially transported transported at 1.5 1.5 Ga. outcrops north northof of the the shear shear zone, zone, but but is is buried Ga. Also, Also, the Wolf Wolf River River Batholith Batholith outcrops buried to the the south. The northern portion of the batholith may have been uplifted relative to the southern south. northern of the batholith may have been uplifted relative to the southern portion portion at aa later later time timeduring duringshear shear zone zonereactivation. reactivation. Alternatively, the batholith batholith originally originally may have been emplaced to shallower levels in the Pembine-Wausau Terrane than have been emplaced to shallower levels in the Pembine-Wausau Terrane than in in the the Marshfield Marshfield Terrane. Terrane. The southeast southeast margin margin of of the theWisconsin Wisconsin Gravity Gravity Minimum Minimum closely closely approximates approximates a I �prominent magnetic magnetic boundary boundary which which separates separates aa positive positive anomaly anomaly to to the northwest prominent northwest from aa negative anomaly to the magnetic boundary, boundary, herein herein called called the the negative anomaly the southeast southeast (Fig. (Fig. 2). This magnetic Winnebago magnetic anomaly, anomaly, continues continues northeast northeast beyond beyond the the Wisconsin Wisconsin Gravity Gravity Minimum, Minimum, of the edge suggesting that it is not suggesting not the the magnetic magnetic signature signature of edge of of the the batholith, batholith, but but instead instead reflects reflects a pre-1.5 pre-1.5 Ga Ga structure structure which which controlled controlled the location location of the the southeast southeast margin margin of of the the Wolf River Batholith. Batholith. with the Wisconsin The general general correlation correlation of the the Wisconsin Wisconsin Gravity Minimum Minimum with Wisconsin Arch Since the Wolf River Batholith is suggests a possible genetic relationship. possible genetic relationship. Since Wolf River Batholith less dense dense than than the surrounding surrounding rocks, rocks, it may may have have been been intermittently intermittently uplifted uplifted over over the the past past 1.5 1.5 Ga in in response to buoyancy forces. buoyancy 60 -.4 50 40 30 20 -j 10 0 —10 —20 j —30 —40 —50 J —60 —70 —80 —90 J —100 F-I 0 0 - - 50 50 100 100 150 150 200 200 J 250 250 I Scale 1 : Kilometers Kilometers Figure 1: Figure 1: Bouguer gravity anomaly anomaly map map of of the Wisconsin Bouguer gravity Wisconsin area area based based on on four four kilometer kilometer gridded data. The Theline lineindicates indicatesthe theprofile profileshown shown in Figure 2. j J 2 U �_______ ____________________________ __________________ 0NW SE 2 0 ..... . . . -0 o m -. . .... _J . . . .......: :: :: a ; C . o0 .: .: 3 : ;. i—. .;-.. .:.. >- ..... ..... . . ....-.. . ............ - .: ... .-. ...... .. .. .. ...:.. '. . ..:. . -0 LI) Mi -. '0 .... .... ....... ..... .. .. . . . . . . . •. -0 --. .. 0 a — In_ - . -.- .-- -. cn o OR ...... -----------------— ........ Lrrzcr t r r c Or c ~oLOWZA r L O WCAUST ~~ m u s t MaGNETIC M A G N E T I C£NOSAL.Y ANOMALY I I SO 50 00 100 100 PRENTICE 200 250 200 250 DISTANCE DISTANCE (KM) (KM) WAUSAU WAUPACA — +I . J' I I 150 ISO •_• -. 'vj7 gfJ • A / PEMBINE-WAtJSAU TERRA. / 400 350 350 £1CRANITC 3açnQrsn\+ \ ' 300 300 SILW7U*LE _ANOROCtN1C FELSIC ROCKS..r - , ' — — -10 L__'__J I ' N FAULT MARS1ELDTERRANE , / / ICLEINE / / / / / " \ 1SHEARZONE N SUPERIOR,,I,...,I •I / /N N N/N / / / / / \ , / CRATON ..I..("S. ' ' ' / , ' , — -40 ', / / •1 N LAG ABA J -, I — 20 I N N N N S. .. I N N , .1 N S. N N — — N 'N N N N S. N •M... N N . • ' • • . - N \ — — • • S. — • • \ — • UPPER M&E . - 50 Fiaure 2: 2: Bouguer Bouguer gravity gravity and and total total intensity intensity magnetic magnetic anomaly anomaly profiles profiles and and related related geologic geologic Figure showing major major crustal crustal units units and and terranes. terranes. The dashed dashed line line indicates indicatesthe thegravitational gravitational model showing effect 20 km. See SeeFigure Figure1 1for forthe thelocation locationof ofthe theprofile. profile. effect of of density density variations variations beneath beneath 20km. REFERENCES REFERENCES CITED CITED implications, unpub. unpub. M. M. S. S. Allen, D. D. J., J., 1990, 1990,The TheWisconsin Wisconsin gravity gravity minimum: minimum: source source and and implications. Thesis, Thesis, Purdue PurdueUniv., Univ., W. W. Lafayette, Lafayette, IN, IN, 183 183p. p. Cannon, W. F., Lee, Lee, M. M. W., W., Hinze, Hinze. W. W.J., J., Schulz, Schulz, K. J., J., and and Green, Green, A. A. C., G., 1991, 1991.Deep Deep crustal crustal structure of of the the Precambrian Precambrian basement basement beneath beneath northern northern Lake LakeMichigan, Michigan,midcontinent midcontinent North 207-2 10. 19,207-210. North America: America:Geology Geology19, —as �The Relationship of Topography and Gravity over the Lake Superior Swell: Evidence for a Keweenaw Hot Spot? David J. Allen, William J. J. Hinze, Hinze, Department Department of of Earth Earthand andAtmospheric AtmosphericSciences, Sciences, Purdue University, IN, and andWilliam WilliamF.F.Cannon, Cannon,USGS, USGS,Reston, Reston,VA VA Purdue University, West West Lafayette, Lafayette, IN, The The Lake Lake Superior Superior Swell Swell (Dutch, (Dutch, 1981) 1981) is is a a broad broad topographic topographic dome dome surrounding the Lake Superior Basin, the location of the most intense 1.1 Ga Lake Superior Basin, location of the most intense 1.1Ga Keweenawan rifting rifting activity. activity. Centered Keweenawan Centered on on Lake Lake Superior is a radial drainage drainage pattern pattern of of approximately approximately 1000 1000 km km diameter. diameter. Within Within this this area, area, streams streams flow flow radially radially outward outward from from the the relatively relatively small small inward-directed inward-directed drainage drainage system system of of the the Lake Lake Superior Basin (Figure 1). In addition, recent analysis of the regional gravity Basin (Figure 1). regional gravity and and topographic data indicates indicates that that aabroad broadnegative negativegravity gravityanomaly anomalyisisalso alsocentered centeredon on Lake Superior and is related to isostatic compensation of the Lake Superior Swell. is related to isostatic compensation of the Lake Superior Swell. The regional negative anomaly is defined by determining average gravity as a function of radial distance 1). As function distance from from aa central central point point in inLake LakeSuperior Superior (Figure (Figure 1). shown shown in in Figure Figure 2, 2, the theaverage averagegravity gravitydecreases, decreases, in inan anapproximately approximately linear linear manner, from a radial km, the the gravity gravity manner, from radial distance distance of of 650 650 km to to 300 300 km. Within Within300 300 km, anomalies produced by anomalies by the the Midcontinent Midcontinent Rift Rift obscure obscure the the regional regional anomaly, anomaly, while while km, the the average gravity is influenced by remote features unrelated to the beyond 650 km, the Lake Superior Swell. of topographic data indicates Lake Swell. Analysis Analysis of topographic data indicates that the the average average topography varies in an an inverse inverse manner manner to tothe thegravity gravity(Figure (Figure2). 2). Furthermore, the between average gravity relationship between gravity and and average average topography topography (Figure (Figure3) 3) suggests suggests that the that the Lake Lake Superior Superior Swell Swell is is in in approximate approximate isostatic isostatic equilibrium equilibrium (for aa fully fully -112 mGals/km). compensated topographic mCals/km). topographic load load of of density density2.67 2.67 g/cm3, slope slope == -112 Recently, has been been proposed that Recently, itit has that aa mantle mantle plume plume (the (theKeweenaw Keweenaw hot spot) spot) is related to to the the origin origin of of the the 1.1 1.1Ga Ga rifting rifting and and igneous igneous event event which which led led to to the thelarge large volume of basalts and the the short shorttime timespan spanof oftheir theireruption eruption(Hutchinson (Hutchinsonetetal., al.,1990; 1990; Nicholson and and Shirey, Shirey,1990). 1990). We propose that the the drainage drainage pattern, pattern, the the topographic topographic dome, and the negative gravity anomaly may still reflect the short-lived the negative gravity anomaly may still reflect the short-livedKeweenaw Keweenaw hot spot. spot. The persistence of the topographic related to a The persistence of topographic dome must be be isostatically isostatically related fundamental change change imprinted imprinted on on the lithosphere fundamental lithosphere by the the mantle mantle plume. plume. For a u s t which has has example, the Lake Superior Swell may be supported isostatically isostatically by a crust Beneath the Lake been thickened by the been the addition additionof ofKeweenawan Keweenawan basaltic basaltic rocks. rocks. Lake for example, example, the the crust crust thickens thickens by by as much as 15 km. km. The Superior Basin, Basin, for The negative negative gravity anomaly, anomaly, however, however, extends extends well well beyond beyond the theLake LakeSuperior SuperiorBasin, Basin, suggesting suggesting that the the crust crust may may have have been been thickened thickened (to (to aa lesser lesser degree) degree) over a much much broader broader area, well beyond beyond the outcrop of the the rift rift rocks. rocks. The Theobserved observed gravity gravity anomaly anomaly may may (of approximate approximate magnitude magnitude 11 be accounted for by a gradual gradual thickening thickening of of the the crust a u s t (of km) from from 650 650 km to to 300 300 km km radial radialdistance distance(Allen, (Allen,1990). 1990). The source of of the gravity anomaly, alternatively, may be a density contrast in contrast'in the mantle related to basalts. The to the the extraction extraction of of the the Keweenawan basalts. The depleted depleted upper upper mantle rocks are expected to be less dense (by at most 0.10 g/cm3) than undepleted 0.10 g/cm3) undepleted rocks due to the rocks due the removal removal of of the dense dense phase phase garnet garnet and/or an an increase increase in the the ratio (Boyd (Boyd and andMcCallister, McCallister, 1976; 1976; Oxburgh and Parmentier, Parmentier, 1977). 1977). The The MgO/FeO ratio 4 I - �negative negative gravity gravityanomaly anomalymay maybe beaccounted accountedfor forby by an an upper upper mantle mantlewhich whichbecomes becomes increasingly increasingly depleted depleted toward toward the the center center of of the theLake Lake Superior Superior Swell. Swell. Again, this this suggests suggests that that the theupper uppermantle mantlewas wasdisturbed disturbed over over aa region region much much broader broader than than the the outcrop outcropof of the therift riftrocks. rocks. 100 75 40 75 40 Figure ofofcentral North America 1:Map Mapofofpart part central North Americashowing showingmajor majordrainage drainagesystems. systems. Figure1: Arrows of stream streamflow. flow. Shaded Shadedareas areasare arecovered coveredby byPhanerozoic Phanerozoic Arrows denote denotedirection directionof platform platform sedimentary sedimentaryrocks; rocks;unshaded unshaded areas areasare areexposed exposedPrecambrian Precambrian rocks rocks of of the the Canadian ofthe theMidcontinent Midcontinent CanadianShield. Shield. Heavy Heavydashed dashedline lineshows showsapproximate approximateaxis axisof Rift Rift (MCR). (MCR). Short Shortdashed dashedline lineisisoutline outlineofofpresent presentLake LakeSuperior Superiordrainage drainagebasin. basin. Circle 1000km km diameter. diameter. Cross Crossin inLake LakeSuperior Superiorindicates indicatesposition position of ofcentral central Circleisis1000 point pointused usedininthe theradial radialaveraging averaginganalysis. analysis. 5 �-4 0 AVERAGE AVERAGE GRAVITY GRAVITY AND ANDAVERAGE AVERAGETOPOGRAPHY TOPOGRAPHY VERSUS VERSUS RADIAL RADIALDISTANCE DISTANCE CENTRAL POINT AT AT 47.97 47.97 N. p4, 888.39W CENTRAL POINT 8.39 W I • AVERAGE AVfRAGf GRAVITY GRAVITY VERSUS VERSUSAVERAGE AVERAGETOPOGRAPHY TOPOGRAPHY FOR FOR RADIAL DISTANCES DISTANCES FROM FROM 300 3 0 0KM KMTO TO 650 6 5 0KM KU SLOPE SLOPE= —114 -114 MGALS/KM. UCALS/KU. YIWT Y 1 N k —9 - 9 MOALS. MGALS. R= R = —0,963 -0.963 0 I I I )C 0 x —I 0 I •o C/) I LI I I -J 0 Ix I Lii >-I C. I I 'C > Cr 0 'C Cr . C S I x 0 In S •I • S S 00 00 - I- j >- > 'C', Cr 4 o' . J IS •GRI ITt '<CLEVATION 100 0 • I 'C C 0>o p1 - j Ui xx IC1 I IC 1 Cr I 200 I I -1- 300 400 500 600 700 0 800 RADIAL DISTANCE (NM) 0 00' 0 250 250 360 300 3 TOPOGRAPHY TOPOGRAPHY (M) (M) Figure Figure 3: 3: Average Averagegravity gravityvs. vs.average average topography topographyfor forradial radialdistance distancebetween between 300 300 km km and and650 650km. km. j j REFERENCES REFERENCESCITED CITED Allen, Allen, D. D. J., J., 1990, 1990, The Wisconsin Wisconsin gravity minimum: minimum: source source and andimplications, implications, unpub. M. S. S . Thesis, Thesis, Purdue PurdueUniv., Univ.,W. W.Lafayette, Lafayette,IN, IN,183 183p.p. unpub. M. Boyd, R., and and McCallister, McCallister, R. R. H., H., 1976, 1976, Densities Densities of of fertile fertile and andsterile sterile garnet garnet Boyd, F. F. R., J Figure Figure 2: 2: Average Averagegravity gravity and andaverage average topography topography vs. vs. radial radialdistance distancefrom from the the central central point point indicated indicatedininFigure Figure1.1. peridotites: 509-512. peridotites:Geophys. Geophys.Res. Res.Lett. Lett.3,3,509-512. I., 1981, 1981, Isostasy, Isostasy, epeirogeny, epeirogeny, and the the highland highland rim rimofofLake LakeSuperior: Superior: Z.2. Dutch, S. S. L, Dutch, Geomorph. N. F., Suppl.-Bd. 40, 27-41. Geomorph. N. F., Supp1.-Bd. 40,2741. R., White, White, R. R. S., S., Cannon, Cannon, W. W. F., F., and andSchulz, Schulz,K. K. J., J., 1990, 1990,Keweenaw Keweenaw Hutchinson, D. D.R., Hutchinson, hot hot spot: spot: geophysical geophysical evidence evidence for for aa 1.1 1.1 Ga Ga mantle mantle plume plumebeneath beneath the the RiftSystem: System:J.J.Geophys. Geophys.Res. Res.95(7), 95(7),10869-10884. 10869-10884. MidcontinentRift Midcontinent W., and andShirey, Shirey,S.S.B., B., 1990, 1990, Midcontinent Midcontinent Rift Rift volcanism volcanism in in the theLake Lake Nicholson, S. S. W., Nicholson, Superior region: region: Sr, Sr, Nd, Nd, and andPb Pbisotopic isotopicevidence evidencefor for aa mantle mantleplume plumeorigin: origin: Superior J.J. Geophys. Geophys.Res. Res.95(7), 95(7),10851-10868. 10851-10868. Oxburgh,E. E.R., R., and andParmentier, Parmentier,E.E.M., M., 1977, 1977,Compositional Compositional and anddensity densitystratification stratification Oxburgh, in oceanic lithosphere causes and andconsequences: consequences:J.J.Geol. Geol.Soc. Soc.London London133, 133, in oceanic lithosphere - causes 343-355. 343-355. - 6 J j Li �THE THEAMOCO AMOCO M.G. M.G. EISCHEID EISCHEID OIL OILTEST: TEST: 4200 1200METERS METERS OF OFCLASTIC CLASTIC ROCKS ROCKS OF OFMIDCONTINENT MIDCONTINENTRIFT RIFTSYSTEM SYSTEM , :, Raymond Raymond R. Anderson Anderson . i. Iowa Iowa Department Denartmentof of Natural Natural Resources Resources ' , . ~:..'- ,.::. .. . . . .. ... . ,., . Geological GeologicalSurvey Survey Bureau Bureau . .~. . . - . iowa IowaCity, City,Iowa Iowa52242 52242 - ,> , The rheM.G. M.G. Eischeid Eischeid#1 #1deep deeppetroleum petroleumtest testwell wellwas wasdrilled drilledby bvAmoco AmocoProduction Production Company A riland andOctober, October,1987, 1987,near nearthe thetown townof of Flalbur Halbu?(Carroll (CarrollCounty) County)in in Company between between fipril west-central west-centralIowa. Iowa. Theewell wellreached reachedaatotal totaldepth depthofof5355 5355mm(17,851 (17,851feet) feet)including including235 235 feet feetof of glacial dacial drift, drift. 130 130feet feetof of Cretaceous CretaceousDakota DakotaFormation, Formation.2392 2392 feet feet of of Paleozoic Paleozoic strata including Pennsylvanian through Cambrian units dominated by carbonates, 813 Â¥ feet of an unidentified sandstone unit ("Unit H"), and 14,085 feet of "Red Clastics" assigned to the Keweenawan Supergroup, before reaching t.d. 151 feet into a mafic dike in the crystalline basement. The well was primarily drilled by rock bit, with duplicate samples sets presently reposited at the geological surveys of Iowa and Nebraska. In addition to the cuttings, five short cores were taken (see Fig. 1 for intervals intervals cored) cored) totaling about 66 feet. Splits are reposited at the Iowa Geological Survey Bureau. A series of preliminary investigations of Eischeid rock samples and geophysical logs were conducted shortly after the release of the materials. These investigations included stratigraphic and petrographic studies, analysis of source rock potential, porosity studies, clay mineralogy analysis, fluid inclusion studies, integrated isotopic and fluid inclusion analysis of vein-filling minerals, and the determination of an age for the basal basal dike. dike. The results of these studies were published by the Iowa Geological Survey Bureau Bureau (Anderson, (Anderson,1990a). 1990a). Of Of particular particular interest interestin inthe theEischeid Eischeidwell wellwere werethe the14,000 14,000feet feetof ofKeweenawan Keweenawan "Red clasticsections sectionsin in the theMidcontinent MidcontinentRift Riftsystem system "Red Clastic" Clastic" strata, one one of of the thethickest thickestclastic (MRS) (MRS) strata strata ever ever examined. examined. The Thesix sixformations formationsinitially initially described described and and assigned assigned to the the Keweenawan b Witzke Witzke (1990) (1990) constitute constitute two groups groups temporarily temporarily named named the the Keweenawan Supergroup Supergrou by "Upper" C asticSequences" Sequences" (Figure (Figure 1). 1). "Upper"and and "Lower "Lower Red Re Clastic 8f. Unit Unit H H "Unit H" H" displays displa s a coarser average grain size and is less well-cemented than the rocks of underlying "Upper Red Clastic is more arkosic than the quartz Clastic Sequence", Se uence", and is uartz arenites arenites of of the theoverlying overlyingMt. Mt. Simon SimonFm. Fm. The Theunit unitwas wasdiscussed discussedby byMcKay McKay(1990) (1990)who who described described itit as asbeing beingdominated dominatedby bytwo twoprimary primarylithologies, lithologies, aa fine fine to tovery very coarse coarse arkosic arkosic sandstone siltstone. McKay sandstone and and aa micaceous, micaceous, shaley shaley to sandy sand&sil~tone. McKay reported trace trace amounts amounts of of rnicrobrecciated fragments observed observed in in all all units of microbrecciated lithic lithicfragments fragmentsin in "Unit "Unit H",,similar to fragments the the "Red "Red Clastic Clastic Sequences", Se uences", and interpreted the the fragments fragments as the products products of of structural structural movements along fault zones that pervasively cut the the MRS sequence. Grains movements d o n fault pervasively cut Grains with with similar similar lithologic fabrics are not observed in the Mt. Simon interval of the well and have not been been reported reported in insimilar similar age age rocks rocks in in the the region. region. Consequently Consequently these rocks are thought to to be be of of Proterozoic Proterozoicage ageand andthe themay may be be associated associated with the the "Upper "Upper Red Red Clastic Clastic Sequence". Sequence". "Upper "Upper Red Clastic ClasticSequence" Sequence* The units totalling is composed of three three informal informalunits totalling The "Upper "Up e r Red RedClastic ClasticSequence" Sequence".is 6895 6895 feet, and an?occupies occupies the the same same stratigraphic strati aphic position position as the the Bayfield Bayfield Group Group of of f Wisconsin which it is correlated. Both Bot groups groups are aredominated dominatedby by fluvial fluvial deposition, deposition, Wisconsin with which but display dis la different compositional compositional characteristics. characteristics. The The Bayfield Bayfield is more mature mature than than the and others others (1990 (1990) reported reported that the the underlying un er yin Oronto Oronto Group, Group, whereas whereas Ludvigson and wer Red Clastic Clastic "Upper Red Red Clastic Elastic Sequence" Sequence" is is less less mature mature than than its itsunderlying underlying "Lower Sequence". Sequence". An Anupward upwardincrease increasein inthe thevolcanic volcanicrock rock fragment fragment component componentof of "Upper "UpperRed Red s^ 4.0 7 7 �-J J Clastic Clastic Sequence" Se uence" sandstones sandstones may record the unroofing of basalts on the the nearby nearby central central horst horst (Anderson, (An erson, 1990b). 1990b). 5 "Lower "LowerRed Red Clastic ClasticSequence" Sequence"' ...-.vfi., The The "Lower "Lower Red Red Clastic ClasticSequence" Sequeii&enis is also dsb composed cbfflbosed of three three informal informalunits unitsand and totals 7190 feet of strata. thebasal basalclastic clasticsequence sequence in in the theEischeid Eischeidwell well and and bears bears strata. ItItisisthe many similarities to the Oronto Group with which whichititisiscorrelated. correlated. The similarities to Group of of Wisconsin Wisconsin with primary difference between between the two groups groups are the basal basal units: units: the the Copper Copper Harbor Harbor Conglomerate (Oronto (Oronto Gp) Gp)being beingdominated dominatedby by very very coarse coarse volcanic volcanic clasts, clasts, "Unit B' Bn ("Lower by quartz ("Lower Red Clastic Clastic Sequence") Sequence") )) being being dominated dominated by uartz sand grains. grains. These These differences differences can can be be explained explained by the relative positions of the Oronto ronto Gp Gp and and the theEischeid Eischeid well well in in the the MRS. MRS. The TheOronto OrontoGroup Groupisisdescribed describedfrom fromexposures exposureson onthe thecentral centralhorst. horst. Early in rift rift history histo the the horst horst area areawas was aa graben, graben, and and the theconglomerate conglomerate clasts class were were apparently apparent! eroded eroded from romvolcanic volcanic rocks rocks that capped capped the the footwalls footwallsof of the thegraben-bounding graben-bounding faults. The T eEischeid Eischeidwell well was was drilled drilled off off the the central central horst, horst, and and penetrated penetrated the thefluvial fluvial system s stem that drained the the rift-bounding nft-bounding Proterozoic terrane. These Thesefluvial fluvialsystems systems had their e i r headwaters headwatersin inthe thegranites ranitesand andgneisses gneisses that that dominate dominatethe thebasement basementof ofthe theregion, region, and t%equartz quartzsands sandsthat thatdominate dominate"Unit "UnitB". B". and were were the thesource sourceof ofthe The Themiddle middleunit unitininthe the"Lower "LowerRed RedClastic ClasticSequence", Sequence", Unit UnitC, C,isisalmost almost1500 1500feet feet thick thick and and displays displaysclose close lithologic lithologicand and sedimentological sedimentologicalsimilarity similarityto to the theNonesuch NonesuchShale Shale of the the Oronto OrontoGroup. Group.Both Bothare arecharacterized characterizedby bygray graytotoblack blacksiltstone siltstoneand andshales. shales. (1990) identified a number number of of sedimentary sedimentary structures structures that that they they Ludvigson and others (1990) interpreted interpretedasasevidence evidenceofofdeposition depositionininaalake lakeor orsimilar similarstanding standingbody body of of water. water. Calcite Calcite cements C".than than in in other other"Red "RedCla.stic" Clastic" strata strata in in cements and and vein vein fills fills are are more more abundant abundantin in "Unit "Unit C', the high angle angle tectonic tectonic dips dipsranging rangin from the Eischeid Eischeidwell, well, and and cored cored intervals intervals display display high from 65° 65O to to vertical vertical and and slightly sli htly overturned. overturned. Ludvigson Ludvigson and and Spry Spry (1990) (1990) described described calcite calcite veinlets and ault surfaces surfaceswith with rough rough facets facets indicating indicating reverse reverse faulting faulting during during the the and slickensided slickensided fault later, of later, compression compression phase phase of of rift rift development. development. The Thepresence presenceofofsuch suchaathick thicksequence sequenceof lake lake sediments sediments outside outside of of the the former formercentral centralgraben graben suggests suggests that the the lakes lakes that that formed formed in in the the MRS MRSwere werelarge, large,extending extendingwell well beyond beyond the thelimits limits of of the thegraben-bounding graben-boundingfaults. faults. Seismic as much as 15 miles Seismic interpretations interpretations suggest suggest they they may may have extended ext es beyond beyond the the graben graben(Anderson, (Anderson,1990c). 1990~). a ^ 7 J J J ! -4 Figure Figure1: 1 : Correlation Correlationof of Eischeid EischeidRed RedClastics Clasti with with the theKeweenawan Keweenawan Supergroup Supergroup mean mean 1 1 1 framewoñ framework ,-Eischeid ,Eischeid - composhion composition ?? QF17L4 Q,F,,L, — 1 Unit UnitHH g. Q ~ F , , L , unit Keweenawan Supergroup J Q76F17L7 Unit G G Chequarnegon SS 0 QJnL9 Q&LB Unit UnitFF QeviI Island SS 6 % Q5SL13 QAGL,~ UnitE Unit E OrientaSs 0m Q75F1L UnitD FredaFm QF24L3 Unit C Nonesuch Fm a. (1) a. a C) Cl) o 0 8 -J QVFI2L1 Unit B ci. a. 0 —I C 0 Copper Harbor Fm 0 �Eischeid Petroleum Potential Potential Eischeid Petroleum Although of liquid liquid petroleum petroleum were Although no no shows shows of were encountered encounteredduring duringthe thedrilling drillingof of the the Eischeid well, trace trace amounts of methane Eischeid well, amounts of methane and and ethane ethane were were detected, detected, and and rare rare a intergi-anular black residues residues (suggestive of oil oil movement) inter anular black su estive of movement) were were observed observedin inthe the"Lower "Lower Red Red Clastic astic Sequence". Sequence". The Thedark ar shales shalesand andsiltstones siltstonesin inthe thelower lowersequence se uencewere wereshown shown by Palacas and and others others (1990) to once once have been organic-rich potential by Palacas (1990) to have been organic-rich p t e n t i a petroleum troleum source source !i S8 rocks, but are rocks, but are presently presently overmature. overmature. Methane Methane clathrates clathrates were were identified icfcntified in in fluid fluid inclusions in calcite and Spry who suggested suggested that that petroleum petroleum inclusions in calcite veins veins by by Ludvigson Ludvigson and S ry (1990) 1990) who was mobile mobile durin during the the compression compression phase phase of of MRS was istory. On On the the basis basis of of comparisons corn arisons S history. between between fluid fluid inclusions inc usions ans ans isotope isotope data data from from vein-filling vein-filling calcites calcites in in the the rift-flanking rift-flanking basins oil test) basins (Eischeid (Eischeid oil test) and and faults faults bounding boundin central central horsts horsts (Ludvigson (Ludvigson and and Anderson, Anderson, 1986), Ludvigson and and Sp Spry (1990) (1990)su suggested that such such fluid fluidwould wouldbe be transported transported towards towards 1986 ,Ludvigson ested that the may still still be be trapped the flanks anks of of the the rift. rift. TThis h i s petroleum petro eum may trapped on on the the flanks flanks of of the the Midcontinent MidcontinentRift Rift System. System. ^ .. &h as A The The M.G. M.G. Eischeid Eischeid #1 #1 well well offers offers aa great eat potential potentialto toincrease increaseour ourunderstandin understandin of the the development developmentof of the theMidcontinent MidcontinentRift Ri tSystem Systemand andthe theclastic clasticstrata strataassociated associated wit wit f F, it. it. Also, Also, the the rocks rocks encountered encountered in in the the well well demonstrated demonstrated that that large largevolumes volumes of of petroleum petroleum was was probably probably generated general from organic-rich units and may still be trapped ed within within the the structure. structure. References Anderson, The Amoco M.G. Eischeid Eischeid #1 #1 deep Anderson, R.R., R.R., 1990a, 1990a. The Amoco M.G. deeppetroleum petroleum test, test, Carroll CarrollCounty, County, Iowa. Iowa. Iowa Iowa Department 185 p.p. Departmentof ofNatural NaturalResources. Resources,Geological GeologicalSurvey SurveyBureau, Bureau,Special SpecialReport ReportSeries SeriesNo.2, No. 2,185 Ludvigson Ludvigson G.A. G.A. and and Anderson, Anderson. R.R., R.R., 1986, 1986,The The Douglas DouglasFault Fault atatAmnicon AmniconFalls FallsState StatePark, Park,Wisconsin: Wisconsin: Brittle Keweenawan Rocks. in Keweenawan Rocks. Proceedings Proceedings of of the the 32nd 32nd Annual Annual Meeting, Meeting, institute Institute Brittle cataclastic cataclastic textures textures in of of Lake SuperiorGeology, Wisconsin Geological Geological and NaturalHistory HistorySurvey, 50-51. Lake Superior Geology,Wisconsin and Natural Survey,pp.SO-Si. * the following references are * all all of of the following references are in in Anderson, Anderson,1990a 1990a** ** ** ** Anderson, R.R., 1990b, Review of current current studies studies of of Proterozoic eview of Proterozoic rocks rocks in in the the Amoco Amoco M.G. M.G. Eischeid #1 petroleum petroleumtest well. Carroll County, Iowa. Iowa. p.p.175-184. 175-184. testwell, Can-oilCounty, Anderson, data over Anderson, R.R., R.R., 1990c, 1990~.Interpretation Interpretation of of geophysical geophysical data over the the Midcontinent Midcontinent Rift Rift System System in in the the area area of of the #\petroleum petroleumtest, test,Carroll CarrollCounty, County,Iowa. Iowa.p.p.27-38. 27-38. the M.G. M.G. Eischeid E i i c i d *1 Ludvigson, G.L., (3.L., McKay, McKay, R.M., R.M., and and Andersoo, Anderson, R.R, R.R., 1990, 1990,Petrology Petrologyof of Keweenawan Keweenawan sedimentary sedimentaryrocks rocks in in the the M.G. M.G. Eiscbeid Eischeid #1 #1drillhole. drillhole.p.p.77-112. 77-112. Ludvigson, G.L., G.L., and Spry, P.G., Tectonic and paleahydrologic paleobydrologic significance carbonate veinlets P.G., 1990, 1990,Tectonic significance of carbonate veinlets in the Keweenawan sedimentary rocks Eischeid #l #1 drillhole. rocks of the Amoco MX3. M.G. Eischeid drillhole. p.p.153-168. 153168. Kewcenawan sedimentary McKay Regional aspects aspectsof of the the Mt. Mt. Simon Simon Formation Formation and and the the placement McKay R.M., R.M., 1990, 1990, Regional placement of of the the Mt. MI. SimonSimon pre-Mt. pre-Mt. Simon Simon sedimentary sedimentarycontact contact in in the the Amoco Amoco M.G. Eischeid Eischeid #1 #Idrillhole. drillhole.p. p.59-66. 59-66. , Palacas, J.W, Daws, M.J.,and and Anderson, Anderson, R.R., Rit, 1990, Palacas. J.G., J.G., Sebmoker, Schmoker, J.W., Daws. T.A., T.A., Pawlewicz, Pawlewicz, MJ., 1990,Petroleum Petroleum source-rock #1 well, well, source-rock assessment assessment of Middle Proterozoic (Keweenawan) (Kcweenawan) sedimentary sedimentary rocks, Eiscbeid #1 Carroll CarrollCounty, County,Iowa. Iowa.P.P.119-134. 119-134. Witzke, BJ., 1990, 1990, General General stratigraphy stratigraphy of of the the Phanerozoic Phanerowic and and Keweenawan Kcweenawan sequences sequences in in the the area area of of the the WWte, BJ., M.G. Eischeid #1drillhole, drillhole,Carroll CarrollCounty, County,Iowa. Iowa.P. P.39-58. 39-58. Eischeid#1 99 I �THE THEHOMESTAKE HOMESTAKEMINE MINE AN AN EARLY EARLY PROTEROZOIC PROTEROZOICIRON-FORMATION IRON-FORMATIONHOSTED HOSTEDGOLD GOLDDEPOSIT DEPOSIT R.L. R.L.Bachman Bachman District DistrictGeologist Geologist Homestake HomestakeMining MiningCompany Company Lead, Lead,South SouthDakota Dakota mine in the the northern northern Black Black Hills Hills of of South South Dakota, Dakota, USA USA isis the thelargest largest ironironformation-hosted hasprOduced produced 1,126 1,126tonnes tonnes (36.2 (36.2million million oz.) oz.)ofofgold goldfrom from formation-hosted gold gold deposit deposit known, known, and andhas The deposit was In 1990 the mine produced 12 tonnes of gold. million tonnes of ore milled. In 1990 the mine produced 12 tonnes of gold. The deposit was 130 130 million tomes of ore milled. discovered in 1876, 1876,and and the themine minehas hasoperated operated continuously continuously to to the the present present day. Gold Goldore oreisiscurrently currently discovered in mined 2,438meters. meters.Gold Goldisisthe theprincipal principalcommodity commodityproduced producedalong alongwith withaaminor minorsilver silver mined for fordepths depthsto to2,438 by-product. 5:l;base basemetal metalcontent contentisisnegligible. negligible. by-product. The Thegold/silver goldlsilverratio ratioaverages averages5:1; J j The The Homestake Homestake The Thedeposit deposit lies lies within within the theEarly EarlyProterozoic Proterozoiccore coreof ofthe theBlack BlackHills Hillsuplift, uplift,which whichrepresents represents the the southern rocks.Tectonism Tectonismand andthermal thermalactivity activityassociated associatedwith with southern most most exposure exposureof of Trans-Hudson Trans-Hudson orogen orogenrocks. the the Trans-Hudson Trans-Hudson event event occurred occurred as as aaresult resultofofthe thecollision collisionofofWyoming Wyomingand andSuperior SuperiorCratons Cratons contemporaneous contemporaneouswith with the the Penokean Penokean orogen. orogen. Proterozoic Proterozoicgold goldmetallization metallizationisisinterpreted interpretedtotobe beaa result result of of an an evolved, evolved,long longlived livedtecto-thermal tecto-thermalprocess processthat thatrelied reliedon onplate platescale scaleshear shearzones zonesasasfluid fluidconduits conduits asfluid fluidmobilizers. mobilizers. and zones zones of of high high geothermal geothermalgradient gradientas and Gold Gold ore orebodies bodiesatatHomestake Homestakeare arehosted hostedalmost almostexclusively exclusivelyby by the theEarly Early Proterozoic ProterozoicHomestake Homestake Formation, (15toto35% 35%total totalFe) Fe)consisting consistingofofsiderite sideritephyllite phylliteand/or and/orgrunerite gruneriteschist. schist. Formation,an aniron-formation iron-formation(15 The Theunderlying underlying Poorman Poorman Formation Formationisiscomposed composedof ofan anupper uppersequence sequenceofofsericite sericiteto.biotite-dominant to-biotite-dominant carbonate-quartz carbonate-quartz and graphitic graphiticphyllites phyllitesand andaalower lowervoluminous voluminoussequence sequenceofofhornblende-plagioclase hornblende-plagioclase schist schist of of tholeiitic tholeiitic affinity. affinity.The Theoverlying overlyingEllison EllisonFormation Formationconsists consistsofofsericite-quartz sericite-quartzphyllite phyllite@elitic (pelitic and and tuffaceous tuffaceous strata) strata) interbedded interbeddedwith with quartzite. quartzite. Strata Stratathat thatcontain containthe theHomestake Homestakedeposit depositwere werecomplexly complexlydeformed deformedby byaaseries seriesisoclinal isoclinaland andsheath sheath fold fold events events that that are are synchronous synchronous with with extensive extensive ductile ductile and and ductile-brittle ductile-brittle shearing. Mine Minearea area rocks rocks have metamorphism; metamorphic intensity arnphibolitefacies facies metamorphism; intensity have been been subjected subjected to upper greenschist-lower greenschist-lower amphibolite 1.72Ga GaS-type S-typegranite granitenortheast northeast of ofthe themine minepost-dated post-dated increases to to the thenortheast. northeast. Intrusion Intrusion of aa 1.72 increases with late regional metamorphism, metamorphism, and and appears appears contemporaneous contemporaneous with late stage stagesemi-brittle semi-brittledeformation deformation regional (Bachman (Bachman et al., al., 1990). 1990). Individual Individual ore bodies bodies are arecontained contained within within plunging plunging synclinal synclinal fold fold structures structures ofofFlomestake Homestake Formation Formation known known as as ledges. ledges. Ten Tenofofthese thesestructures structureshave haveproduced producedgold goldfrom fromrelatively relativelyundeformed, undeformed, elongate elongate tabular zones of quartz, quartz, siderite, siderite,chlorite, chlorite, pyrrhotite, pyrrhotite,arsenopyrite, arsenopyrite,minor minor pyrite, pyrite, and and native native gold. gold. Ore Ore mineralization mineralization is is developed developed within within and and adjacent adjacentto todilated dilatedsegments segmentsof oflate-stage late-stageductileductilebrittle aL, 1990). folds and brittle shears (Caddey et al., 1990). These Theseshears shearsand andassociated associated ore ore bodies cross-cut earlier folds overprint metamorphic metamorphic fabric. fabric. overprint 10 J J j �I I I I I I I I I At At least least two two stages stagesof of mineral mineral alteration alterationare are observed, observed, one oneof of which which issynmetamorphic is synmetarnorphic and andappears appears to to predate predate gold goldmineralization, mineralization,and anda asecond secondsynchronous synchronouswith withgold goldmineralization. mineralization. The Thepre-gold pre-gold mineral alteration stage is represented by extensive potassium and carbonate mineral alteration stage is represented by extensive potassium and carbonate metasomatism. metasomatism. Ore-stage Ore-stage hydrothermal hydrothermal alteration alterationappears appearsretrogressive retrogressiveproducing producingextensive extensivechlorite chlorite and and siderite sideritereplacement replacement of of the Homestake Formation in and adjacent to the ore bodies. the Homestake Formation in and adjacent to the ore bodies. Timing Timingof ofgold goldmineralization mineralizationatatHomestalce, Homestake, even even though though not not dated dated directly, directly, isis regarded regarded as asearly early Proterozoic. Proterozoic. Dating Datingofofzircon zirconfrom fromtuffaceous tuffaceoussediments sedimentswithin withinthe theEllison EllisonFormation Formation gave gave an an age ageof of 1.97 1.97 Ga Ga(Redden (Reddenetetal., al.,1990) 1990)and andprovide provideananapproximate approximateage agefor forHomestaice HomestakeFormation Formationdeposition. deposition. The The approximate approximate age ageof ofregional regionalmetamorphism metamorphism and and major majorregional regionalductile ductiledeformation deformationisis1.84 1.84 Ga Ga (Zartman (Zartmanand andStem, Stem,1967). 1967).The TheCrook CrookMountain MountainGranite Graniteand andassociated associateddeformation deformationat at1.72 1.72Ga Gaappears appears to topost-date post-dategold goldmineralization. mineralization. ItItisisinterpreted interpretedthat thatgold goldwas wasintroduced introducedafter afterpeak peakmetamorphism metamorphism (1.84 Ga) and prior to granite emplacement (1.72 Ga) by epigenetic processes. (1.84 Ga) and prior to granite emplacement (1.72 Ga) by epigenetic processes. I 1 REFERENCES REFERENCES Bachman, Crook Bachman, R.L., R.L., Campbell, Campbell, T.l., T.J.,and andSneyd, Sneyd,D.S., D.S.,1991, 1991, CrookMountain Mountaingranite graniteand andits itsrelation relation toto Early EarlyProterozoic Proterozoicgold goldmineralization mineralizationatatthe theHomestalce Homestake mine, mine, northern northern Black Black Hills, Hills, SD: SD: Geol GwlSoc. Soc. America, America, Abstracts Abstracts with with Programs, Programs, v. v. 22, 22, no. no. 6,6,p.2. p.2. Caddey, S.W., Bachman, R.L., Campbell, T.J., The Homestalce Caddey, S.W., Bachman, R.L., Campbell, T.J., Reid, Reid,R.R., R.R.,Otto, Otto,R.P., R.P.,1990, 1990, The Homestakegold gold mine, an Early Proterozoic iron-formation hosted gold deposit, Lawrence County, mine, an Early Proterozoic iron-formation hosted gold deposit, Lawrence County,South SouthDakota: Dakota: U.S. U.S.Geol GeolSurvey SurveyBull. Bull. 1857-3 1857-1(in (inpress). press). Redden, DeWitt, 1990, U-Th-Pb geochronology Redden, J.A., J.A., Peterman, Petennan,Z.E., Z.E.,Zartman, Zartman,R.E., R.E.,and and DeWitt,E.,E. , 1990, U-Th-Pb geochronologyand and preliminary preliminaryinterpretation interpretationofofPrecambrian Precambriantectonic tectonicevents eventsin inthe theBlack BlackHills, Hills,South SouthDakota: Dakota:(3eol. Gwl. Assoc. Assoc.Canada CanadaSpec. Spec.Paper Paperononthe theTrans-Hudson Trans-HudsonOrogen Orogen(in (inpress). press). Zartman, R.E., and Stem, T.W., 1967, Isotopic age and geologic relationships Little Elic Zartman, R.E., and Stem, T.W., 1967, Isotopic age and gwlogic relationshipsofofthe the Little Elk Granite, northern Black Hills, South Dakota; U.S. Geol. Survey Prof. Paper 575-D, Granite, northern Black Hills, South Dakota; U.S. Geol. Survey Prof. Paper 575-D, p.p.D157D157Dl 63. Ill �EXTENSION OF GRAVITY FILED COVERAGE IN EAST-CENTRAL WISCONSIN: 1990 COGEOMAP PROGRAM Daniel Daniel J. J. Brehm, Brehm, C. C. Patrick Patrick Ervin, Ervin, Dept. Dept:of of Geology, Geology, Northern Northern Illinois University, University, DeKalb, DeKalb, IL IL 60115 60115 M.G. M.G. Mudrey, Mudrey, Jr., Jr., B.A. B.A. Brown, Brown, M.L. M.L. Czechanski, Czechanski, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 3817 Mineral Mineral Point Point Rd. Rd., Madison, Madison, WI WI 53705 53705 Illinois J • During During the the summer summer of of 1990, 1990, approximately approximately 4800 4800 additional additional measurements of of the the earth's earth's gravity gravity field field were were made made in in an an area area measurements 44 && 45 45 degrees degrees latitude latitude and and by 88 88 & 90 degrees degrees bounded by by 44 bounded & 90 longitude. longitude. Most Most stations stations are are located located at at surveyed surveyed elevation elevation points points posted posted on on USGS USGS topographic topographic sheets sheets and and are are spaced spaced one one mile mile apart, apart, except except where where access access was was limited. limited. Northern Northern Illinois Illinois University's Lacoste-Romberg LaCoste-Romberggravity gravity meter meter G409 G409 was wasused. used. Data .University's Data are are tied tied to to the the State State of of Wisconsin Wisconsin Primary Primary Gravity Gravity Base Base Station Station Network (Ervin, (Ervin, 1983), 1983), which which is is in in turn turn tied tied to to the the International International Network Gravity Gravity Standardization StandardizationNetworlc-1971 Network-1971 (DMAAC, (DMAAC,1974). 1974). Normally Normally accepted accepted field field and and processing processing procedures procedures were were used. used. These These data data have have been been combined combined with with earlier earlier data data to to produce produce aa much much more more detailed tailed Bouguer Bouguer gravity gravity anomaly anomaly map. map. The The northwest northwest section section of of the the area area is is underlain underlain by by primarily primarily Proterozoic Proterozoic and and Late Late Archean Archean rocks, rocks,comprised comprisedof ofqüartzite, quartzite, granite, granite, rhyolite, rhyolite, granodiorite, granodiorite,gneiss, gneiss, metavolcanics, metavolcanics, and and metasediments. metasediments. This This variability variability is is reflected reflected in in the the complex complex character character of of the the Bouguer Bouguer gravity gravity anomalies. anomalies. The The north-central north-central part part of of the the region region contains contains the the southern southe part which is is part of of the the Middle Middle Proterozoic Proterozoic Wolf Wolf River River Batholith, Batholith, which composed with composed primarily primarily of of granitic granitic and and syenitic syenitic rocks, rocks, with inclusions inclusions of of quartz quartz monzonite, monzonite,anorthosite, anorthosite,and and gabbro. gabbro. The The greater greater homogeneity homogeneity of of the the Wolf Wolf River River Batholith Batholith produces produces aa smoother smoother Bouguer Bouguer gravity gravity field field than than exists exists in in the the northwest northwest section. section. The The southern southern and and eastern eastern areas areas of of the the map map largely largely overly overly Paleozoic Paleozoic sedimentary sedimentary rocks, rocks, possibly possibly underlain underlain at at depth depth by by an an extension extension of of the the Wolf Wolf River River Batholith Batholith (Allen, (Allen, 1990), 1990). resulting resulting in in aa Bouguer Bouguer gravity gravity field field dominated dominated by by longer longer wavelength wavelength anomalies anomalies than than in in the the rest rest of of the the survey surveyregion. region. REFERENCES REFERENCES Allen, Allen, D.J. D.J.,1990, 1990, The The Wisconsin Wisconsin Gravity Gravity Minimum: Source Source and and Implications, Implications,unpub. unpub. Ms MS thesis, thesis, Purdue Purdue Univ., Univ.,West West Lafayette, Lafayette, IN., IN., 183 183p. p. , Ervin, C.P.,1983, 1983,Wisconsin Wisconsin Gravity Gravity Base Base Station StationNetwork, Network,Wis. Wis Ervin, C.P., Geol. Geol. && Nat. Mat. Hist. Hist. Sun. S u m .Misc. Misc.Pap. Pap. 83-1, 83-1,43 43 p. p. - North North -j DMAAC, DMAAC, 1974, 1974, World World Relative Relative Gravity Gravity Reference Reference Network Network - America, DMAAC Ref. Ref. Pub. Pub. No. No. 25, 25,1974 1974Supplement. Supplement. America, DMAAC 12 J �I I I I i Nonmetallic Mineral Mineral Resources Minor Metals Metals Potential Potential Nonmetallic Resources and and Minor of Northern of Northern Wisconsin Wisconsin , .: .. Bruce nice A. A. Brown Brown Wisconsin Geological and Natural :nL and Natural History HistorySurvey Survey . . The Precambrian Precambrian terranes northern Wisconsin Wisconsin contain The terranes of of northern contain significant significant nonmetallic nmetallic mineral mineral resources resources and and have have the the potential potential for for other other metal metal deposits deposits in addition addition to to volcanic—hosted volcanic-hosted massive massive sulfides. sulfides. The The region region has has aa long long history stone and a variety of story as a producer of building and ornamental ornamental stone crushed stone crushed stone products. products. Other Other products products include include weathered weathered or or "rotten" "rotten" granite granite and clay clay from from weathered weathered crystalline crystalline rocks rocks and and glacial glacial deposits. deposits. Northern Northern Wisconsin contains contains potentially potentially economic Wisconsin economic occurrences occurrences of of industrial industrial minerals minerals (talc, graphite, graphite, marble,-kyanite, marble, kyanite, nepheline (talc, nepheline syenite, syenite, silica silica sand, sand. and and others) others) rare metals (molybdenum, Significant and rare (molybdenum, beryllium, beryllium, lithium, lithium, and and others). others). Significant deposits of deposits of iron iron are are also also present present but but are are not not currently currently economical economical to to produce. produce. In recent years, years, dimension dimension stone st-oneproduction production has has maintained maintained aa low low but but steady level steady level of of activity; activity; the the. crushed crushed stone stone industry industry has has grown grown significantly. significantly. This growth in response growing demand for ha? been been in response to a growing for high high quality quality railroad This growth has ballast and changing changing construction construction specifications specifications that that reQuire require higher higher quality aggregates aggregates for for base base course course and and asphalt asphalt paving paving mixtures. mixtures. Specialized Specialized metavolcanic rock operations produce crushed crushed metavolcanic rock for for roofing roofing granules granules and aggregates for 'aggregates for terrazzo terrazzo stone stoneand and synthetic syntheticgranite graniteproduction. production. metal potential Although base base and Although and precious precious metal potential has has attracted attracted much much attention attention recently, the recently, the nonmetallic nonmetallic minerals minerals have have long longbeen been and and will continue continue to to be be aa major economic economic resource . Important Important factors major resource of of northern northernWisconsin Wisconsin. factors are are aa good good transportation network and transportat ion network and Wisconsin's favorable favorable location location in in respect respect. to markets in The future future development in the markets theupper upperMidwest. Midwest. The development of of regulatory regulatoryframework framework on t:he the state for ure on stateand and local localLevel level will willhave have*important important implications inipl-i.cations forfut future deve 1 opmen t of hi s industry-. development of tthis industry. �j J J Preliminary Preliminary Bedrock Bedrock Geologic Geologic Map Map of of Eat, Eau Claire County, Claire County. Wisconsin Wisconsin J B.A. Brown Brown & B.A. & U.S. R.S. Maass Maass Wisconsin Geological and Wisconsin Geological and Natural Natural History HistorySurvey Survey Eau Claire Claire Cotwty is underlain Eau County is underlain by by rocks rocks ranging ranging froni from Early Early Proterozoic Proterozoic and and Archean Archean (?) ( ? ) to to Late Late Cambrian Cambrian age. age. Precambrian Precambrian rock rock is is exposed exposed in in scattered cattered outcrops outcrops along along the the Eau Eau Claire Claire River River and and tributaries tributaries in in northeastern northeastern Eau au Claire Claire County. County. The The Precambrian Precambrian consists consists of of aa suite suite of of amphibolites amphibolites and and granitic gneisses what is probably a a younger younger granitic gneisses of of possible possible Archean Archean age, age, and and what is probably sequence of inetavolcanic and metasedimentary metasedimentaryrocks rocksand andgranitic graniticintrusions intrusions of of equence of metavolcanic and probable Penokean Penokean (1850 maficdikes dikescut cut older older units probable (1850 Ma) Ma) age. age. Underformed Underfonned mafic unit.sand and may he as Kewanawan. asyoung youngasas Kewanawan. may be The Precambrian i.s i.s overlain overlain by Cambrianclastic clastic and The Precambrian by Upper Upper Cambrian and carbonate carbonate rocks Mound, and Trempealeau The Upper rocks of ofthe theElk Elk Mound,Tunnel TunnelCity, City, and TrempealeauGroups. Groups. The Upper Cambrian contains two sedimentary cycles. The lower lower cycle Cambrian contains two fining—upward fining-upward sedimentary cycles. The cycle consists of Mount that grades into the consists ofthe thebasal basal Mount Simon Simon sandstone sandstone that grades upward upward into the glauconitic sandy dolomite dolomite of of the the St. Lawrence Lawrence glauconitic Tunnel Tunnel City City Group Group and sandy Format ion. ion. Format Eau Claire County has no no historical historical record Eau Claire County has recordof ofmineral mineralproduction productionfrom from the Precambrian. Residual clay with thethe Cambrian/Precambrian the Precambrian. Residual clay is isassociated associated with Cambrian/Precambrian unconformity, and Wonewoc ion 1s is aa potential ica sand. andthe the WonewocFormat Formation potential source source of of sil silica sand. mconfotmi~y, The only Paleozoic Faleozoic unit unit potentially the St.St. Lawrence The only potentially suit-able suitable for foraggregate aggregateisi.s the Lawrence dolomite, whichis is present. present only on ridge ridge tops area nf in the thesouthwestern southwestern area of the the dolomite, which only on tops in county. Pleistocene county. Pleistocene alluvial alluvial deposits deposits along along the the Chippewa Chippewa and Eau Eau Claire Claire fers Principal aqui Rivers eriols. Principal Rivers are are the the primary primary source sourceof ofconstruction constructionmat materials. aqui'fers arc are the alluvial alluvial deposits deposits and and the the Mount Mount Simon Simon sandstone. sandstone. J J j 14 �I I fl 1 , Collision Induced Collision Induced Ripoffs, Ripoffs, Ancient and and Modern: Modern: The Mideontinent Rift System System and and the Red Sea—Gulf Midcontinent Rift Sea-Gulf of of Aden Aden compared. compared. - ' F. William Cambray F. William Cambray and and Kazuya Kazuya Fujita, Fujita, Dept. F p t . of of Geol. Geol. Sci., Sci., Michigan State State University, East MI 48824—1115; Michigan University, East Lansing MI 48824-1115; 517—355—4626) 517-355-4626) Slab pull is considered to major force force in in determining determining slab is considered to be a major the rate Irregular or the rate and and directions directions of of plate plate motion. motion. oblique convergence oblique convergence will will result result in in closure closure of of an an ocean ocean at at some some localities localities prior prior to to others. others. Once a portion portion of of the the subducting plate has subducting has sutured, sutured, the the plate plate will will slow slow down down or or stop. Adjacent, stop. Adjacent, unclosed unclosed sections sections of oceanic oceanic crust, crust, however, will however, will continue continue subduct subduct under under the the influence influence of of slab slab pull( fig.1.l). This may may result result in in tensional tensional stresses pull( fig.l.l). This stresses in in a portion portion the a the subducting subducting plate. plate. Since fractures fractures are are more likely t to likely o develop in in the the weaker, continental continental part of of the the subducting subducting plate, plate, aa fragment fragment of of the the plate plate may may be be detached detached along an intracontinental Opening along intracontinental rift rift system system (fig.1.2). (fig.1.2). of this of this rift rift system system would would be be limited limited to to a a small small ocean ocean basin continuing subduction close the the remaining remaining basin since since continuing subduction will close portion of Closure of portion of the the original original ocean ocean basin. basin. Closure of the the original ocean original ocean basin, could could then then result result in in compression compression in in ig.1.3). This sequence the rift rift system system (f(fig.1.3). sequence explains explains the the synchronous association extension and compression, compression, near synchronous association of of extension and the the subsequent subsequent deformation and deformation of of the the rift rift fill, fill, as as found found in many once once extensional extensional regions. regions. The Red Sea Sea is is a a modern example example of of this this process. process. Closure Tethys occurred occurred first the Mediterranean Mediterranean and of the Tethys first in the and left left a portion a portion of of the the African African plate, plate, with with attached attached oceanic oceanic crust, region. still subducting the Zagros crust, still subducting under under the Zagros region. Continuing slab slab pull pull in Continuing in this this region, region, combined combined with with the the restraint to induced the the detachment of the restraint to the the west, west, induced detachment of the Arabian Peninsula Peninsula along along the the Red Red Sea Sea and and Gulf Gulf of Arabian of Aden Aden Mid Continent Rift (fig.2). Extension in the Proterozoic Mid system of North America was coincident with the the Grenville Grenville The rift compressional event event to to the the south compressional south and and east. east. The rift experienced only limited limited opening opening which we suggest suggest was was due due to slab—pull slab-pull along an unclosed segment in the collision zone of the belt (fig.3). Grenville Orogenic zone of the Grenville (fig.3). Subsequently, the the entire entire collision collision zone zone closed closed and and the Subsequently, rift was pushed back into place giving rise to a complex complex pattern of of folds folds and and flower flower structures structures (fig.4). (fig.4). 15 �TURKEY GREECE BITLIS ARABIAN NORTH 1 /"ass? ' Early Miocene Fig. 2 Fig. 2 3. COMPLETE CLOS -I Fio 1 J Fig. 3 Fig. 3 j J 4 —4 Fig.4 4 Fig. 16 Cambray and F u j i t a (1991) Cambray and Fujita (1991) �DETACHMENT DETACHMENT FAULTING FAULTING AND AND THE THE ORIGIN ORIGIN OF OF THE THE ASYMMETRIC ASYMMETRIC DEPOSITIONAL DEPOSITIONAL PATTERN PATTERN OF OF THE THE MARQUETTE MARQUETTE TROUGH.F.wjlljam TROUGH.P.William Cambray, Dept Dept of of Cambray, Geological Sciences, Sciences, Michigan Michigan State State University, University, East East Lansing Lansing MI MI Geological 48824., Joseph Joseph J.Mancuso, J-Mancuso, Dept. Dept. of of Geology, Geology, Bowling Bowling Green Green State State 48824., University, Bowling Bowling Green, Green, OH OH 43403., 43403., and and Went Went Slitor, Slitor, C.C.I., c.c.I., University, 504, 504, Spruce Spruce Street, Street, Ishpeming, Ishpeming, MI MI 49849. 49849. L L L L L L The Marquette Marquette Trough Trough is is one one of of several several fault fault bound bound basins basins The set into into the the Archean Archean crust crust of of northern northern Michigan Michigan which which contain contain set tower Lower Proterozoic Proterozoic metasedimentary metaseditnentary rocks. rocks. The The pattern pattern is is interpreted interpreted as as deposition deposition in in rift rift basins basins associated associated with with the the development development of of aa passive passive margin margin prior prior to to the thePenokean PenokeanOrogeny. Orogeny. The by collision collision of of an an island island arc arc to to the the The orogeny orogeny was was triggered triggered by south. south. Deposition Deposition in in the the trough trough began began with with the the Siamo Siamo Formation Formation which consists consists of of alternating alternating layers layers of of pelite pelite and and arenite, arenite, the the which latter latter having having turbidite turbidite characteristics. characteristics. This was was followed followed by by aa thick thick sequence sequence of of banded banded iron iron formation, formation, the the Negaunee Negaunee BIF. BIF. The The iron iron formation formation is is interbedded interbedded with with clastic clastic lenses lenses which which thicken thicken and and become become more more frequent frequent towards towards the the southern southern margin margin suggesting suggesting provenance provenance from from this this direction, direction, sole sole marks marks indicating indicating aa turbidite turbidite origin origin have have been been found found at at the the base base of of these these layers. layers. The The clastic clastic lenses are are somewhat somewhat irregular irregular in in distribution distribution and and disappear disappear lenses rather rather abruptly abruptly to to the the north. north. Changes Changes in in the the pattern pattern of of clastics elastics is is often often associated associated with with faults. faults. This This pattern pattern is is similar similar to to asymmetric asymmetric fault fault basins basins which which have have been been describe describe in in relation relation to to major crustal crustal detachment detachment faults faults in in the the Cenozoic Cenozoic of of the the Western Western US US major (fig.l). (fig.1) The The overall overall stratigraphic stratigraphic pattern pattern suggests suggests that that such such aa detachment detachment may may be be present. present. On On the the south south side side the the stratigraphy stratiara~hvis is truncated truncated adjacent adjacent to to the the margin margin which which is is consistent consistent with with continual displacement during sedimentation whereas the continual displacement during sedimentation whereas the . succession succession is is more more continuous continuous across across the the margin margin of of the the trough trough (fig.l). The Palmer Gneiss is a candidate for the main detachment L L L (fig.1). The Palmer Gneiss is a candidate for the main detachment fault fault on on the the south south side, side. outcrops Outcrops of of the the gneiss gneiss close close to to the the contact contact with with the the Proterozoic Proterozoic rocks rocks are are broken broken and and contain contain chlorite, chlorite, this this lithology lithology passes passes into into aa banded banded gneiss gneiss to to the the south south near near the the Tilden Tilden Mine. Mine. The The banding banding consist consist of of normal normal gneissic gneissic texture texture interspersed interspersed with with mylonite. mylonite. This This association association is is similar similar to to the the description description of of detachment detachment surfaces surfaces in in the the western western US. US. The The chlorite chlorite rich rich material material represents represents the the high high level level breccia breccia which which formed formed in in the the brittle brittle zone zone and and the the banded banded mylonite mylonite is is the the deeper deeper ductile ductile portion portion of of the the detachment detachment fault. fault. The The two two were were brought brought together together by by aa large large normal normal displacement. displacement. The The Penokean Penokean orogeny Orogeny complicated complicated the the picture, picture, reactivating reactivating some some of of the the normal normal faults faults as as reverse reverse faults faults but but the the basic basic pattern pattern is isstill stillrecognizable recognizable (fig. (fig.2) 2). - 17 �MZXNNlsb 10 3HZ 11nn0uw4 Irnouz ñt%V1Wt3) put •Osnotnj4 (1661 N ______ ______ 8I MCqUHEXLIE M?HIDI UITH CLAStICS flNflflN CHOCOLflY CROUP $31LW13 A'IO3oN3 JflOIfD 2R3UU N I I I �A LATE LATE KEWEENAWAN KEWEENAWAN THRUST THRUST ?? MARQUETTE COUNTY, MICHIGAN. MICHIGAN. '.William Cambray Dept Dept of of Geological Geological Sciences, Sciences, Michigan State State F.Wulliam Cambray University, East Lansing Lansing Michigan 48824 48824 and Glenn Glenn Scott, Scott, Callahan Callahan University, East Mining Mining Co. Co. Marquette, Marquette, Michigan. Michigan. Records from a drill drill hole on on the the southern southern margin margin of of the the Records from ( Hole 1(30, ( Hole M30, sec. Quadrangle. sec. 17 17 T47N T47N R25W, R2SW, Sands Sands Quadrangle. Core Core made made available available by by CCI CCI Ishpeming.) describe a 'Cambrian 'Cambrian a clastic dike' occurring occurring at depth of of 360 360 feet. feet. The overlying overlying clastic dike' at a depth is deformed material is deformed and metamorphosed Proterozoic Kona and Kona Proterozoic Formation. 'dike' has is an an Formation. Re-examination Re—examination of of the the 'dike' has shown shown that that it is sorted unmetamorphosed quartz arenite arenite containing containing immature, poorly sorted fragments of the the Icona Kona Formation. similar to to fragments of Formation. The The lithology lithology is very similar the outcrops of the local local outcrops of Jacobsville Jacobsville Sandstone. Sandstone. Although Although the the Jacobsville has been described as Cambrian in the past it it is is now now widely believed believed to t o be be late late Keweenawan Keweenawan in in age. age. AA re—examination re-examination of of widely core reveals reveals that that the the sandstone sandstone bedding is is vertical and and the the the core fragments of of Kona Kona Formation Formation included included in in the the sandstone sandstone are are aligned aligned fragments parallel parallel to t o this this vertical vertical bedding. bedding. All All the exposures exposures in the the immediate region region are are Lower Lower Proterozoic Proterozoic rocks, rocks, mostly Kona Kona Formation. Formation. We We interpret interpret the pattern pattern observed observed in in the drill drill hole hole to to late Keweenawan Keweenawan thrust placing the Kona Formation Formation over over indicate a late the the Jacobsville Jacobsville (fig.2). (fig.2). During During the the Keweenawan Keweenawan widespread widespread rifting rifting produced clastic clastic filled filled basins basins throughout throughout the the Lake Lake Superior Superior region. Towards Towards the the end end of of the the period period the the Jacobsville Jacobsville Sandstone, Sandstone, and the the equivalent equivalent Bayfield Bayfield Group Group formed formed a widespread widespread blanket blanket over much much of of the the region. region. This This was was followed followed by by aa compressional compressional event rise to event which gave gave rise to thrust thrust faulting faulting on on the the Keweenaw Keweenaw Peninsula Peninsula and and several several reverse reverse faults faults in in the the Nidcontinent Midcontinent Rift Rift section of of Wisconsin Wisconsin and and Minnesota. Minnesota. Until now there there has has been been no no record event east east of the record of of this this late late compressional compressional event the Keweenaw Keweenaw Peninsula. Peninsula. The The sequence sequence of of events events proposed proposed is is as as follows. follows. 1) 1) Extensional tectonics tectonics associated associated with the opening opening of of the the Midcontinent Midcontinent Rift Rift System System produced produced aa rift basin basin above above the the Marquette Marouette Trough Trouqh which which filled filled with with sediment sediment derived derived from from the the surrounding Archean Basement the Proterozoic surounding k chean Basement and the ~roterozoic and netasediments metasediments (fig. (Ciq. 1) 1). The sediments sediments contain contain unweathered unweathered microcline microcline and and fragments fragments of mylonite mylonite from from the the gneisses. gneisses. Pelite Pelite lenses lenses mark mark the the bedding bedding surface surface and and compaction compaction structures structures are are clearly clearly visible. visible. Fragments Fragments of of the the Kona Kona Formation up up to to 55 centimeters centimeters long long by 2 2 centimeter centimeter wide wide are are aligned parallel parallel to to the the bedding. bedding. The The poor poor sorting sorting suggests suggests that that this this locality locality was was close close to to the the fault fault scarp. scarp. 2) The conpressional produced in a thrust close to compressional event produced to the the original and transported original rift rift margin margin and transported the the adjacent adjacent Kona Kona Formation over over the the Jacobsville Jacobsville basin, tilting the the sandstone sandstone to to its its present present vertical vertical position position in in the the process process (fig (fig2). 2). Marquette Trough Trough This pattern pattern of of deformation deformation in in the the late late Keweenawan Keweenawan is is not not surprising considering considering the the structures structures seen to the the west. If If it it is is more widespread widespread it it adds adds another another factor factor to t o be be considered considered when when attempting to t o unravel unravel the the structure structure of the the older older Proterozoic Proterozoic in in the the Great Great Lakes Lakes region. region. 19 �__ C N) LL. E' 1 Kona FM. coarse lenses . Jaoob!vllI! Sst. 1 rIg. 2 rig. I [J L._ CoMpresilenJi Pkn. BItting Pkr. L 1 Caribray and Scott 1991 LATE REWEEIIAWAN THRUSTING, MARQUETTE MICHIGAN __ __ _ CT r I __ L L �Hazardous The The Feasibility Feasibilityof ofRecovering RecoveringMetals MetalsFran Froma a HazardousWaste Waste Site Site Case AA (Brief) (Brief) CaseStudy Study Frederick -11 FrederickK.K.Campbell Minnesota Minnesota Pollution PollutionControl ControlAgency Agency 520 520Lafayette LafayetteRoad Road 55155 55155 St. St.Paul, Paul,Minnesota Minnesota The National Lead (NL))/Taracorp/Golden fTaracorp/C3olden Site (Site)isislocated located in in St. Site (Site) St.Louis Loui Park, Hennepin Park, HennepinCounty, County,Minnesota. Minnesota. The The Site Siteis isapproximately approximately 10 10 acres acres in insize size and ofofa asecondary secondarylead leadsmelter. smelter. The and is isthe theformer formersite site The Site Site is isincluded included in inthe the U.S. (NPL) U.S. Environmental EnvironmentalProtection ProtectionAgency's Agency's (EPA'S) (EPA's) National NationalPriorities PrioritiesList List(NPL) 5) and and is isalso alsopresent presenton onthe theMinnesota Minnesota Pollution PollutionControl ControlAgency's Agency's(MPCA' (MPCA'S) (PLP). Permanent (PLP). The The secondary secondarysmelter smelterwas was operated operatedbybyNL NL PermanentList Listof ofPriorities Priorities and lead,lead lead oxide oxide andTaracorp Taracorpbetween between 1940 1940 and and 1981, 1981,and andwas was used used to to reprocess reprocess lead, and trambatteries batteries and and scrap scrap into into various variouslead leadalloys. alloys. The The main main and lead leadsulfate sulfatefran solid by the the smelter smelterwas was slag slagfran from the the blast blast furnace furnacewhich whichwas was solidwaste wasteproduced produced by deposited deposited on—site on-sitebetween between 1940 1940arid and 1962. 1962. The the presence presence of ofthe thelead-bearing lead-bearingslag slag in constitutes aa potential potential threat threatto tothe thelocal localsurficial surficialand and in the thesub-surface subsurface constitutes bedrock and is isthe themain main reason reasonfor forthe the inclusion inclusion of of the theSite Siteon onthe the bedrock aquifers, aquifers,and NPL NPL and and the thePLP. PLP. The The slag, slag,which which is is aa major major component componentof of the thefill fillmaterials materialson onthe theSite, Site,is is heterogeneous ..etercqeneousin innature. nature. Limited Limited analytical analytical data indicate that the slag contains part per to 45,900 45,900 part per million million (4.5 (4.5percent) percent)lead. lead. Visual Visual inspection inspectxonof of contains up up to data indicate that the slag slag inin sane samples, while other sarriples slagsamples samples indicates indicatesaahigh highiron ironcontent content some samples, while other sanples cubic yards yardsof of fill fill have 16,000 cubic have a a high high lead lead(galena) (galena)content. content. Approximately Approximately 16,000 materials arepresent presenton onthe the Site, Site,and and it it is isestimated estimated that that25 25toto90 90percent percent of of materials are the he fill fillisisslag. slag. redy for for the the Site Site is isan an asphalt asphalt "cap, "cap",installed installed in in 1988 1988 which which The current current remedy The was andthereby therebyprevent prevent was designed designed to toprevent preventinfiltration infiltrationof ofprecipitation precipitationand leaching The EPA EPA is is currently currentlyengaged engaged in in aa five-year five-year leaching of of lead lead fran fromthe theslag. slag. The review required by by the theSuperfund Suprfundprogram program (Cctnprehensive (Cmprehensive reviedof of the theSite, Site,which which is isrequired Environmental Compensation,and and Liability Liability Act Act (CERCIA)). (CERCLA)). This This review review Environmental Response, Response, Canpensation, and represented process process will willconsider consider the the status statusof ofthe theSite Site andthe therisks risks representedby bythe the hazardous materials (slag) (slag) that that retain hazardous materials remainon on the theSite. Site. In In this thiscontext, context,other otherrnre more permanent renedies remedies such such as as encapsulation, encapsulation,fixation fixationor orexcavation excavationand and ranoval ?33nOvalmay may permanent permanent EPA An alternative alternative permanent raredy remedy which which bythe the EPAand and the the MPCA. MPCA. An be considered consideredby be P.s) merits As)from from the the (Cd, therecovery recovery of of lead leadand andother othermetals metals(Cd, merits consideration considerationis isthe andeconomic economic barriers barriersmust mustbe beoverccne overcane in in order order to to Technical,regulatory regulatoryand slag. slag. Technical, recovery of of lead lead fran from the the slag slag aa feasible feasiblealternative. alternative. make the the recovery make Technical barriers to tothe the recovery recovery of of lead lead fran from the the slag slagrevolve revolve around around the the Technical barriers heterogeneous natureofofthe theslag slag and andthe thevariable variable iron, iron, lead and silica silicacontent content iieterogeneousnature lead and Environmental Technology of theslag. slag. The The U.S. U.S. Bureau Bureau of ofMines, Mines,through throughits its Environmental Technology of the has investigated investigated the the possibility Research Program, Program, has possibilityof ofrecovering recoveringlead leadfrom frommill mill Research such as as an tailings Missouri. tailingsinin Missouri. Approaches Ap~roachessuch an air airsparged spar- hydrocyclone wra=ycloneshow s h promise andmay may also also permit permit recovery recovery of of lead leadfrom from slag. slag. Another Another technique, technique, promiseand by the theEPA EPA in inits its utilizingaa flame flame reactor reactor process, process, has has been been evaluated evaluated by utilizing Superfund Superfund Innovate InnovateTechnology Technology Evaluation Evaluation (SITh) (SITE)Program. Program. 21 �J I Regulatory barriers to Regulatory barriers tothe therecovery recovery of of lead lead fran from the the slag slag are are related related to tothe the involvanent TheResource Resource Conservation Conservationand and involvement of of tvo twomajor major statutory statutoryauthorities. authorities. The Recovery Act (m) (ICRA)and and CEIWmay may both regulate this type rredial activity activity Recovery Act CERCIA both regulate this type of of remedial of of hazardous waste and andcleanup cleanupstandards standardsare arecauplex complex Definitions hazardous waste at atthe theSite. Site. Definitions issues context and inin order to to make inthis this context andmust mast be be clarified clarified order makerecovery recovery of oflead lead issues in frau permanent remedy. fromthe theslag slaga afeasible feasible permanent raedy. 1Econcniic barriers to to the the recovery of lead lead from fran the Econdc barriers recovery of the slag slag at at the the Site Siteare are similar those that axe faced during thethe cievelopnent ofofan shilartoto those that axe faced during -1-nt anore oredeposit. deposit. The The costs of the costsfor forexcavation, excavation,rancval removaland and transportation transprtatim of the slag slag to toaasmelter melter will will prob&1y given the volume, andand heterogeneous besubstantial substantial given the volume,distribution distribution heterogeneousnature nature probablybe The metallurgical metallurgicalproblans problems in inseparating separating the thelead lead fran fromthe the of thematerial. material. The ofthe incentive for thistype typeof of slag be significant. significant. The The econanic economic incentive forconç'leting completing this slagmay may be permanent raTedial action action is is the developnent permanent remedial theprospect prospect of ofindustr±al/camercial industrial/commercial development of ofthe the Site. Site. I 1- J J J Li Li LI Li J 22 �PALEOMAGNETISM OF CENTRAL WISCONSIN DIKE DIKE SWARM: SWARM: CONSTRAINTS ON THERMOMECHANICAL MODEL MODEL OF MIDCONTINENT RIFT Lung S. C/ian Lung Chan Department of Department of Geology Geology Eau Claire University of Wisconsin - Eau Five mafic mafic dikes dikes in incentral central Wisconsin Wisconsinwere weresampled sampledfor forpaleomagnetic paleomagneticdeterminations. determinations. The The palwpoles paleopoles Five obtained reveals obtained reveals more more than than one one dike dikeintrusion intrusion episode. episode. The Thepreliminary preliminary paleomagnetic palwmagnetic results results can can be divided into two groups. The mafic dikes dikes in in Marathon Marathon City, City, Big BigFalls FallsPark, Park,and and Little Little Falls Falls Park Park Eau Claire County yield yield aa cluster cluster of of palmpoles paleopoles that that lie lie near near the the 11.1 Ga paleomagnetic paleomagnetic pole pole of of the the .1 Ga in Eau North American craton. The paleopoles North American craton. palwpoles of the the dikes dikes in in Lake Lake Wissota Wissota and and Jim Jim Falls Falls in in Chippewa Chippewa County are about 1.0 Ga. Ga. The Thelack lackof ofintermediate intermediatepoles polesimplies impliesepisodic episodicdike dikeintrusions. intrusions. Similarly, Similarly, about 1.0 and volcanic volcanicunits unitsin inthe the Lake Lake Superior Superior area area also show show an an episodic episodic nature. nature. Keweenawan dike swarms and The determination determination of the to our The the intrusion intrusion ages ages is is conducive to our understanding understanding of the the thermomechanical thennomechanical state of is located located about about 200 200 km km from from the the rift rift axis. The axis. The state of the the midcontjnent midcontinent rift. rift. The The dike dike swarm swarm is recurrence of dike at such recurrence dike intrusion intrusion activities activities at such aa far fardistance distance from from the therift riftaxis axisimplies impliesoscillation oscillation between strong strong tensile stress during the intrusive stress between intrusive stages and weak tensile or compressional compressional stress during the inter-intrusive likely resulted resulted from from fluctuation fluctuation in in magmatic magmatic inter-intrusive stages. Such variation in stress likely along the rift axis. activity along axis. 23 �AEROMAGNETIC SURVEYING PROGRAM IN MINNESOTA: PAST AND FUTURE PERSPECTIVES PERSPECTIVES CHANDLER, VAL VAL W., W., Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul.MN MN 55114 55114 The high-resolution aemmagnetic Minnesota Geological The high-resolution aemmagnetic surveying surveying program pmgram of the Minnesota Geological Survey Survey(MGS), (MGS),,\ which began in 1979 1979with support support from from the Legislative Legislative Commission Commission on on Minnesota Minnesota Resources (LCMR). (LCMR), will be completed completed in in 1991. 1991. InInaddition additiontotothe theLCMR-sponsored LCMR-sponsoreddata, data,data datahave havebeen beencontributed contributedby bythe theU.S. U.S. Geological Geological Survey Survey and and the the Geological GeologicalSurvey Survey of Canada Canada for for north-central Minnesota and by USX Corporation Corporation for for southwestern Minnesota When Whencomplete, complete,the thestatewide statewideaemmagnetic aemmagneticdata database basewill will be be the the only one one of its its kind kind in in North America America to to encompass encompass aa relatively relatively large large area area with with such such detail. detail. All Allsurveying surveyingto to date has maintained nearly the same specifications, the key ones being close flight-line spacing (400—500 date has maintained nearly the same specifications,the key ones being close flight-line spacing (400-500 meters). In the present present survey meters) and low low terrain terrain clearance clearance(150—200 (150-200 meters). survey over over southeastern southeasternMinnesota, Minnesota, some spacing, owing to burial-related some data data can can be be flown flownatat10(X)-meter 1000-meter spacing, burial-related smoothing smoothingof of anomalies anomaliesfrom from Paleozoic strata. Paleozoic I The The data, data, which which have have already alreadyserved served aa broad bmad spectrum spectiurnof of economic economicand andscientific scientificinterests, interests,are are available available as as 1:24,000-scale 1:24,000-scale contour contour maps, amps.1:250,000-scale 1:250,000-scalecontour contour and and color colormaps, maps, and and as as digital digital tapes of flight-line and gridded data. flight-line gridded data. test drilling drillinghas hasled ledto toseveral severalmajor majorrevisions revisionsof ofthe the Use of the aeromagnetic aeromagneticdata data in in conjunction conjunctionwith with test Precambrian Precambrian geology geology of of Minnesota, Minnesota, most most of of which which lies lies concealed concealed beneath beneath aa thick thick mantle mantle of Pleistocene Pleistocene glacial materials. Inverse andPoisson Poisson analysis analysis of gravity and Inversemodeling modelingof ofaeroinagnetic aeromagneticanomalies anomaliesand magnetic data have assisted significantly in a recent reinterpretation of the Early magnetic data have assisted significantly in a recent reinterpretation of the EarlyProterozoic ProterozoicPenokean Penokean I orogen in east-central Minnesota. Aemmagnetic the omgen Aemmagneticdata data have have been been consistently consistently used in interpreting the , partially exposed Archean greenstone-granite greenstone-granite tenane terrane of of north-central north-central Minnesota. Minnesota. Derivative-enhanced Derivative-enhanced aeromagnetic and gravity data part of of interpret the geology geology of the poorly poorly exposed central part aeromagnetic data have have been used to interpret Protcrozoic Duluth Complex of northeastern Minnesota. In Innorthern northernand and central central Minnesota, Minnesota, the Middle Proterozoic aeromagnetic data are being used to investigate a major major dike dike swarm swann of Early Protemzoic Pmterozoic age. The aeromagnetic The Minnesota Geological Geological Survey plans further interpretive wo& in the Archean greenstone-granite Survey farther work in the Archean greenstone-granite terrane of northwestern and the the Middle Middle Proterozoic Archean gneiss gneissterrane terrene of of southwestern southwesternMinnesota, Minnesota,and northwestern Minnesota, Minnesota,the the Archean Duluth Complex. Complex. I, Looking aeromagnetic surveying remain. remain. In Looking to the future, future, several several major tasks tasks related to aeromagnetic In a recent workshop hosted workshop hosted by the theMOS MGS and and sponsored sponsored by by the the L.CMR, LCMR, several recommendations were made for future geophysical geophysical woit workininthe thestate. state.Among Amongthe therecommendations recommendationspertinent pertinenttotoaeromagnetic aemmagneticsurveying surveying were (1)10 (1) to accelerate accelerateprocessing processingand andinterpretation interpretationof ofaeromagnetic aeromagneticdata dataininconjunction conjunctionwith withtest testdrilling drillingand and geologic (2) to to make make the the digital digital aeromagnetic aeromagnetic data data available available in in more more diverse diverse media than presently geologic mapping; mapping; (2) available, available, with with emphasis emphasison on PC-based PC-basedtechnology; technology;and and(3) (3)to toexpand expandthe theMGS MGSphysical-property physical-propertydata database base on Minnesota's Minnesota's bedrock and glacial sediments. The TheMGS MGS plans plans to to pursue pursue these these recommendations recommendations aggressively. I aggressively. itgion, much In the broader perspective of the Midcontinent region, much remains remains to to be be done. In Inmost mostareas areasthe the ' aeromagnetic coverage aemmagnetic coverage is is simply simplyinadequate, inadequate,especially especiallywith with regard regardto toflight-line flight-linespacing spacingversus versusdepth depthto to basement. The Thetremendous tremendoussuccess successofofthe theaemmagnetic aemmagneticsurveying surveyingprogram pmgramininMinnesota Minnesotapresents presentsaastrong strong incentive the Midcontinent Midcontinentregion regionto topursue pursuesimilar similarprograms. programs. incentive for for other other state state or or federal federal agencies agencies woiking workingin inthe 24 j I —j �CONTINUOUS STRIKE-SLIP CONTINUOUS STRIKE-SLIP FAULT-EN FAULT-EN ECHELON ECHELON FRACTURE FRACTURE ARRAYS IN DEFORMED DEFORMED ARCHEAN ARCHEAN ROCXS: ROCKS: IMPLICATIONS IMPLICATIONS FOR FOR FAULT FAULT PROPAGATION PROPAGATION b CHAN IC $ MECHANICS I John Craddock and John P. P. craddock and Andrew Andrew Moshoian, Moshoian, Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN MN 55105 55105 Abstract AbsmaGL A A regional regional strike—slip strike-slip and and en en echelon echelon fracture fracture array array (orientation: dimensions in 90) is observed in three dimensions in (orientation: N—B, N-S, 90) Archean Archean rocks rocks in in northern northern Minnesota, Minnesota, northern northern Michigan, Michigan, and and western western Wisconsin. Wisconsin. Distinct Distinct fault fault planes planes (Mode (Mode I) I) change change along strike strike into into single single or or conjugate conjugate en echelon echelon fracture fracture arrays arrays (Mode (Mode II) 11) resulting resulting in in an an undulating undulating fault fault trace trace with with an an average average amplitude amplitudeof of—5 -5cm cmand andwavelength wavelengthofof—1-1in. m. Both Both dextral dextral and and sinistral sinistral displacements displacements are are found found in in the the same same outcrop, outcrop, and and fault fault displacements displacements change change along along strike. strike. Brittle Brittle en en echelon echelon shear shear sense sense indicators indicators generally generally compliment compliment the the observed observed fault fault displacement, displacement, but but not not always. always. Mode and II I1 fractures fractures cut cut and and cross—cut cross-cut each each other other and and Mode II and are are thus thus contemporaneous contemporaneous features, features, indicating indicating that that the the Mode Mode I extensional fractures I extensional fractures became became strike—slip strike-slip faults faults where where initially macimum principal principal compressive compressive stress stress (0-1) (Cl) was initially the the maximum was parallel parallel to to the the strike-slip strike-slip fault. fault. Mode Mode II I1 en en echelon echelon sets sets can can be be used used as as shear shear sense sense indicators indicators for for the the strike—slip strike-slip faults faults however, however, displacements displacements along along individual individual Mode II I1 fracture fracture planes planes are are opposite opposite that that of of the the strike—slip strike-slipfault. fault. The The undulating undulating fault fault planes planes resulted resulted from from the the interaction interaction between between propagating propagating Mode Mode II fractures fractures and and Mode Mode II I1 en en echelon echelon shear shear fracture fracture pods, pods, both both of of which which are are three three dimensionally dimensionally continuous continuous and and locally locally out—of—phase. out-of-phase. Timing Timing constraints constraints on on these these fault fault systems, systems, which which are are regionally regionally distributed distributed in in Archean post-2.6 Archean rocks rocks of of the the Great Great Lakes Lakes region, region, indicate indicate aa post—2.6 13? and pre-1.1 pre-1.l BY BY age BY and age for for this this deformation. deformation. 25 �PRELIMINARY DRILL DRILL CORE CORE STUDY STUDY OF OF TWO TWO HOLES HOLES DRILLED DRILLED ON ON THE THE CUYUNA CUYUNA IRON IRON RANGE AND EMILY EMILY MANGANIFEROUS MANGANIFEROUS IRON IRON FORMATION FORMATION DISTRICT DISTRICT OF OF MINNESOTA MINNESOTA J. DAHL DAHL and and SUSAN SUSAN E. E. BRINK, BRINK, Twin Twin Cities Cities Research Research Center, Center, U.S. U.S. Bureau Bureau of of LINDA J. Mines, 5629 Minnehaha Avenue Avenue South, South, Minneapolis, Minneapolis, MN 55417 Mines, 5629 Minnehaha MN 55417 Two diamond diamond drill drilled core holes holes were were recently recently completed completed in in manganiferous manganiferous iron iron Two ed core Central Minnesota--one on the Cuyuna formations in in Central Cuyuna Range Range and and one in in the the Emily Emily The purposes purposes for drilling were were first drill core core for for geologic geologic District. District. The for drilling first to t o obtain obtain drill characterization and to conduct conduct characterization and whole whole core core leaching leaching experiments, experiments, and and subsequently subsequentlyto geophysical logging hydrologic flow testing. This geophysical logging and and hydrologic flow testing. This drilling drilling program program was was costcostBureau of Mines shared by shared by the the U.S. U.S. Bureau Mines and and the the University University of of Minnesota-Mineral Minnesota-Mineral Resources Research Research Center Center under under a Resources a Bureau Bureau Cooperative Cooperative Agreement Agreement and and is is part part of of the Bureau's situ mining the Bureau's ongoing ongoing research research on on in in situ mining of o f critical critical and and strategic strategic minerals. gathered from these two holes will minerals. The information information gathered will be used used in in the the mining techniques techniques can evaluation of o f whether whether or or not not in in situ mining can be be utilized to to recover manganese from from the the manganiferous manganiferous iron iron formations formations in in Central Central Minnesota. Minnesota. the use In In situ situ mining mining involves involves the use of of fluids fluids to t o remotely remotely solubilize solubilize and and mobilize target metals in ore deposit mobilize target metals in an an ore deposit and and transport transport them them to to the the surface surface via via recovery wells where recovery wells where the the fluids fluids can can be be directly directly processed processed for for metal metal recovery. recovery. The success success of of an an in in situ situ mining operation operation depends depends to t o aa large large degree degree on on whether whether the target ore minerals can be selectively dissolved and and whether the dissolved transported to target metal can can be be transported to the the production production wells wells via via fluid fluid flow flow channels. channels. physical the inherent The degree degree of of sulccess success is by the The is governed governed by inherent chemical chemical and and physical characteristics of the ore body characteristics of body such such as as the the types types of o f ore ore minerals, minerals, types types and and kinetics of ore abundance abundance of reactive reactive gangue gangue minerals, minerals, kinetics ore and and gangue gangue mineral mineral dissolution, ore dissolution, ore zone zone permeability, permeability, proximity proximity of of ore ore minerals minerals to to the the fluid fluid path, path, and groundwater groundwater flow flpw characteristics characteristics in in both both saturated saturated and and unsaturated unsaturated deposits. deposits. the relationships At the microscale, microscale, the relationships between between the the ore ore and and gangue gangue minerals, minerals, Low target particularly particularly texture and composition, composition, are are very very important. important. Low target metal metal solution cannot cannot contact if the leach recoveries will will occur occur if leach solution contact the target target ore ore example, minerals regardless regardless of of how how well well the the leach leach chemistry chemistry is is optimized. optimized. For example, target ore minerals may be encapsulated by by unreactive unreactive gangue gangue or or short short circuiting circuiting and as joints may occur of leach fluid fluid may occur due due to structural controls controls such such as joints and clay swelling Also, may be microfractures. microfractures. Also, fluid fluid pathways pathways may be plugged plugged by by clay swelling or or accumulation of of mobilized particles. particles. This type type of of information information obtained obtained through through a petrographic petrographic study study of of preleach preleach and and postleach postleach ore ore samples samples provides provides valuable valuable guidance in in predicting in in situ situ mining metal metal recoveries recoveries and and the the feasibility feasibility of of in situ situ mining for aa prospective in prospective ore ore body. body. Bureau research research is is providing providing new new insights insights into into predicting predicting in in situ situ mining mining Potential problems and metal recoveries. metal recoveries. Potential and constraints constraints are are being being identified identified and and research, modeled before before field field leach leach mining tests are initiated. As part of this research, conducting a geologic geologic characterization characterization study the Bureau is conducting study of of the the drill core core from from stratigraphy, gangue the Cuyuna Range Range and and Emily Emily District District which which includes: includes: stratigraphy, gangue and and ore mineralogy, mineralogy, textural textural relationships, re1 ationships, assays, assays, detailed detailed whole whole rock rock chemical chemical analyses of selected selected samples, samples, permeability and porosity, porosity, fracture analysis, analysis, and and characterization magnetic susceptibility. susceptibility. AA combination of laboratory geologic characterization techniques are are being being used techniques used on whole core core samples samples to t o determine determine ore/gangue ore/gangue and and These techniques structural structural relationships relationships of of preleach preleach and and postleach postleach material. material. These techniques scanning electron include petrographic petrographic analysis analysis of of polished include polished thin thin sections, sections, scanning electron microscope imaging, electron microscope electron microprobe analyses, analyses, and and X-ray X-ray diffraction. diffraction. 26 �Hole Hole G-1 G-1 from from the the Cuyuna Cuyuna Range Range was was drilled drilled on on the the National National Steel Steel Corporation's Corporation's former former Gloria Gloria underground underground mine site site near near Ironton, Ironton, MN, located in in the the northwest northwest 1/4 1/4 of of the the southeast southeast 1/4 1/4 of of the the southeast southeast 1/4 1/4 of of Section Section 28, 28, Township Township 47N, 47N, Range Range 29W, 29W, Crow Crow Wing Wing County. County. This This hole hole was was drilled drilled to t o aa depth depth (along (along the the incline) incline) of 1200 1200 ft ft at at an an inclination inclination of of 55 55 degrees degrees to to the the northnorthnorthwest. northwest. Hole Hole E-1 E-1 was was drilled drilled on on public public land land near near Emily, Emily, MN, MN, and and located located in in the the southeast southeast 1/4 1/4 of of the the southwest southwest 1/4 1/4 of o f the the northwest northwest 1/4 1/4 of of Section Section 21, 21, Township Township 138N, 138N, Range Range 26W, 26W, Crow Crow Wing Wing County. County. This This hole hole was was vertically vertically drilled drilled to t o aa depth depth of of 787 787 ft. ft. The The following following descriptions descriptions of the stratigraphy stratigraphy from each each hole hole are are based based Detailed solely upon upon hand hand sample sample observations. observations. Detailed petrographic petrographic analyses analyses are are solely currently currently ongoing. ongoing. HOLE HOLE G-1 G-I Depth, ft (along (along the the incline) incline) Deoth, ft Glacial 85 Glacial surficial surficial material material 00 -85 - 202 202 Rabbit Rabbit lake Lake Formation Formation -- Dark Dark to to medium-dark medium-dark gray gray carbonaceous carbonaceous argillite, 1-2% marcasite marcasite and and pyrite, pyrite, argillite, locally locally mineralized mineralized with with << 1-2% contains which are are variably variably contains minor minor 0.2-mm to 15-cm thick clastic beds which hematitic. hematitic. - 1167 1167 Trommald Trommald Iron Iron Formation Formation 85 85 - 202 202 - - 438 438 Thick-bedded Thick-bedded facies facies -- Massive Massive and and mottled appearing appearing beds beds (2-5 up to to 1.5 1.5 m) m) of of intermixed intermixed goethite, goethite, limonite, and (2-5 cm and up hematite with (< 11 mm mm with locally occurring thin-bedded thin-bedded clastics clastics (< thick) Manganese mineralimineralithick) and and massive to thin-bedded thin-bedded chert. chert. Manganese zation zation begins begins at at 243 243 ft. ft. 438 q38 -- 659 659 Mixed thick- and and thin-bedded facies facies -- Massive Massive to to mottled mottled to to thin-bedded thin-bedded iron iron formation formation consisting consisting of of interbedded interbedded goethite, goethite, limonite, limonite, hematite, hematite, and and manganese manganese oxides oxides with with minor minor locallylocallyoccurring occurring argillized argillized clastics clastics and and oolitic oolitic chert. chert. 659 1167 659 -- 1167 Thin-bedded Thin-bedded facies facies - Oxidized Oxidized interval interval (659-922 (659-922 ft) ft) consists consists cm thick) of alternating alternating thin beds (0.2-5 (0.2-5 mm and and up up to to 11 cm thick) of of hematitic/goethitic iron formation, argillizedclastics,chert, hematitic/goethiticironformation,argillizedclastics,chert, and and magnetite. magnetite. The transition transition from from oxidized oxidized to to reduced reduced iron iron formation 922-943 ft. formation occurs occurs from from922-943 ft. Reduced iron iron formation formation (943(9431167 consists of of very very fine-grained, fine-grained, thinly-bedded thinly-bedded (0.5mm 1167 ft) consists (0.5 mm 22 cm cm thick) alternating dark to t o light light gray gray to to dark dark greenish greenish cm) 3.5 cm) gray gray bands. bands. The The unit unit contains contains minor minor thin thin (0.5 (0.5 mm mm -- 3.5 chert chert and and clastic clastic interbeds. interbeds. Magnetite Magnetite beds beds are are partially partially oxidized ft. oxidized to to hematite hematite above above 913 913 ft. 202 202 - - - - 1167 1200 Mahnomen Mahnomen Formation Formation - Medium to to light light gray, gray, massive massive to to weakly weakly bedded, bedded, 1167 -- 1200 sericite-quartz sericite-quartz semischist with are are 0.25-1 0.25-1 mm mm in in diameter. diameter. 1% 7%dark dark mafic mafic porphyroblasts porphyroblasts that that Hole G-1 G-1 was was drilled drilled along along cross cross section section A-A" A-A" on on Plate Plate 33 described described in in "Geology Cuyuna North Range, Minnesota" G e o l o g y and Ore Deposits of the Cuyuna Minnesota" by by Robert Robert Gordon Gordon Schmidt, U.S. U.S. Geological Geological Survey Survey Professional Professional Paper Paper 407, 407, 1963, 1963, 96 9 6 pp. pp. Schmidt Schmidt suggested that Trommald Iron that the contact between the Trommald Iron Formation Formation and and the the underlying 27 �Mahnomen Mahnomen Formation Formationwas was folded. folded. Using Using this this interpretation, interpretation,hole hole 6-1 G-l should should have have contacted contactedthe theMahnomen MahnomenFormation Formationat atapproximately approximately760 760ftftdepth depthalong alongaa65-degree 65-degree incline. incline. Hole Hole 6-1 G-l located located the the contact contact between between these these two two formations formations at at 1167 1167 ft ft which which is is approximately approximately 400 400 ft ft lower lower than than proposed proposed by by Schmidt, Schmidt,thereby thereby proving proving that that the the proposed proposedfold foldisisnot notpresent. present. Also, Also, the the oxidized oxidized zone zonein in the the upper upper part part of 800 ft ft below below bedrock bedrock surface) surface) of the the Trommald Trommald Formation Formation extends extends deeper deeper (about (about 800 than than previously nreviouslv described described by bv Schmidt. Schmidt. HOLE E-1 Deoth. ft ft Depth, -- 169 00 169 Glacial Glacial surficial surficial material material 169 169 - - 321 321 Ferruginous Ferruainous graywacke aravwacke -- Light Light to to medium-gray, medium-gray,well-bedded well-bedded(1-5 (1-5mm) mm) clastics elastics consist consistof of fine finesiltsilt-to to medium medium sand-sized sand-sizedgrains grainsofofquartz, quartz, argillized araill ized feldspar, feldsoar. and and disseminated disseminatedhematite hematiteininaa clay-rich clay-richmatrix. matrix. Irregular, irregular, mottled-appearing mottled-appearingiron iron oxide oxide staining staining loosely loosely follows follows bedding bedding and and fractures fracturesin in 1I mm mm to to 55 cm cm bands. bands. Argillization Argillization varies varies from from slight slight at at the the top top of of the the bedrock bedrock (221-305 (221-305ft) ft) to to extreme extreme at at the the bottom bottom of of the the unit unit (310-321 (310-321ft). ft). 321 - 437 437 - 437 Cherty Chertv iron iron formation formation -- Consists Consists of ot massive massive white white chert chert with wiin disdisseminated seminated clots clots (1-5 (1-5 mm diameter) diameter) of of hematite hematite and and goethite goethite interinterbedded bedded with with predominantly predominantly massive massive to to thinly thinly bedded bedded hematitic hematitic iron iron formation. formation. Towards Towards the the top top of of the the unit, unit, the the chert chert is is thinly thinly and and irregularly irregularly bedded bedded (321-328 (321-328ft). ft). Thin, Thin, argillized argillized clastic clastic beds beds (1-10 ft (1-10 mm) are are interbedded interbedded with with iron iron formation formation from from 337-350 337-350ft. - 734 734 Manganiferous Manaaniferous iron iron formation formation -- From From 437-584 437-584 ft, ft, the the unit unit consists consists of of hematitic, hematitic, manganiferous, manganiferous, thin-bedded thin-beddedto to massive massive iron iron formation formationwith with minor minor oolitic oolitic to to massive massive chert chert interbeds. interbeds. Manganese Manganese oxides oxides occur occur in in zones zones intermixed intermixed with with hematite hematite and and as as beds beds and and irregular irregular lenses lenses (1 (1 mm mm -- 33 cm cm thick). thick). From From 584-734 584-734 ft. ft, the the unit unit consists consists of of thin thin to to thickly 10 cm) cm) interbedded interbedded hematitic hematitic and and goethitic goethitic iron iron thickly (1 (1 mm mm -- 10 formation, formation, chert, chert, and and manganese manganese oxide-rich oxide-richbeds beds with with intervals intervalswhere where iron iron formation, formation, chert, chert, or or manganese manganese oxides oxides predominate. predominate. 734 734 J - 761 761 Manganiferous Manqaniferous chert chert - Oolitic Oolitic granule-rich granule-richchert. chert. Sooty Sooty manganese manganese - - oxides and the the matrix matrix as as irregular irregular vuggy vuggy oxides locally locally replace replace oolites oolites and patches. patches. AA medium medium grey, grey, massive massive chert chert bed bed (80 (80cm cm thick) thick) occurs occurs at at 765 ft. ft. 765 761 761 22 - ,, - Argillized, Argillized, finely finely bedded bedded (1 (1 mm mm -cm) of cml, slate slate consists consists of mediummedium- to to fine-grained fine-drained clastics elastics with with - - ~disseminated magnetite octahedra. disseminated hematite hematite pseudomorphs pseudomorphs after aftermagnetite octahedra Localized Localized iron-oxide iron-oxidestaining staining generally generally follows followsbedding. bedding. - 763 763 Argillized Araillized thin-bedded thin-bedded slate slate - - 767 767 Manganiferous Manaaniferous chert chert -- Same Same as as 734-761 734-761 ft. ft. 763 763 - 767 767 - - 787 787 - Argillized Araillized thin-bedded thin-bedded slate slate - Same Same as as 761-763 761-763 ft. ft. The The stratigraphy stratigraphy of hole hole E-1 E-1 identified identified that that the the dip dip of of the the sedimentary sedimentary The information information from from this this hole hole was was layers layers in in this this area area flatten flatten to to the the north. north. The added added to to the the geologic geologic database database of of holes holes previously previously drilled drilled (approximately (approximate1y 40 40 years stratigraphy of of the the Emily Emily district. district. years ago) ago) to to further further define define the the stratigraphy 28 j ~~ j �GEOLOGIC SETTING OF THE THE EARLY PROTEROZOIC PROTEROZOIC BASE- AND PRECIOUS-METAL-RICH PRECIOUS-METAL-RICH METAVOLCANIC BELT OF WISCONSIN I . 3 Theodore A. A. DeMatties, Ernest K. K. Lehmann & & Associates, Inc., Inc., 430 430 First Avenue North, 55401 North, Minneapolis, Minneapolis, Minnesota Minnesota 55401 I M.G. M.G. Mudrey, Jr., Jr., Wisconsin Geological Geological and Natural History Survey, 3812 Mineral Point Road, Road, Madison, Wisconsin 53705 Wisconsin 53705 .. , Since the the late late 1960s, 1960s, measured measured and and inferred inferred resources resources of ofF . .. . Since massive—sulfide over 100 million short tons of volcanogenic volcanogenic massive-sulfide' The mineralization mineralization have have been been discovered discovered in in northern northern Wisconsin. Wisconsin. -%he largest deposit, deposit, near Crandon, was identified by Exxon Minerals and contains approximately 75 75 million short short tons of ore ore averaging averaging most recent discovery 5% zinc, 1.1% 1.1% copper, copper, and and 0.4% 0.4% lead. lead. The most was made by Noranda Exploration Inc. at Lynne, Exploration Inc. at Lynne, in in Oneida Oneida County. County. One of o f their discovery holes holes contained contained a a 128—foot 128-foot intercept intercept Significant copper, and 2.95% grading 22.7% 22.7% zinc, zinc, 0.64% 0.64% copper, 2.95% lead. lead. Significant precious metal values are are associated associated with with many of o f the the known known deposits. deposits. "... . t d I The deposits occur within the the Early Proterozoic Proterozoic Penokean Penokean belt (1850—1900 fold belt (1850-1900 Ma) which has been divided by Greenberg Greenberg and and Brown (1983) (1983) into into two two major terranes: terranes: the the northern northern terrane terrane supported by a supra—crustal supra-crustal sequence sequence deposited on the the Archean ~rchean basement (Sims' (Sims' Continental Continental Margin Margin assemblage; assemblage; Sims Sims and and others, others 1989) and and a southern terrane composed of volcanogenic rock and 1989) and This southern terrane, Early Proterozoic granite intrusives. granite intrusives. This southern terrane, the the Terrane (also (also known known as as the the Wisconsin Wisconsin Penokean Penokean Wisconsin Maginatic Magmatic Terrane by a an volcanic belt) , is is characterized volcanic belt), characterized by n island—arc island-arc basin basin assemblage containing abundant calc—alkaline metavolcanic units calc-alkaline units Sims and associated lesser amounts of metasedimentary rock. rock. Sims and and others (1989) (1989) have further further divided the the Wisconsin Magnetic Magnetic Terrane Terrane into two volcanic volcanic arc arc terranes on on the the basis basis oof lithology and and f lithology structure; they include the northern Pembine—Wausau terrane structure; they include the northern Pembine-Wausau terrane and and 1 29 a �J the the Marshfield Marshfield terrane terrane to to the the south. south. The The three three terranes terranes are are believed believed to to be be separated separated from from one one another another by by major major paleosuture paleosuture zones zones (Niagara Fault, Eau Eau Pleine PleineShear ShearZone) Zone). (Niagara Fault, 1 1 The The Pembine—Wausau Pembine-Wausau arc arc sequence sequence is is the the focus focus of of base— base- and and precious—metal precious-metal exploration exploration activity activity that that has has resulted resulted in in the the discovery discovery of of aa number number of of massive—sulfide massive-sulfide deposits deposits and and occuroccurrences. rences. The The dominant dominant volcanic volcanic complex complex in in this this terrane, terrane, based based on on regional regional gravity gravity and and magnetic magnetic data, data, has has been been referred referred to to 1 informally informally as as the the "Ladysmith—Rhinelander "Ladysmith-Rhinelandergreenstone greenstone belt". belt". At At 1 its its western western end, end, the the complex complex can can be be further further subdivided subdivided into into three three major major regional regional units, units, based based on on geophysics geophysicsand and known known lithology. lithology. They They include include aa central central volcanic—arc volcanic-arc sequence sequence that that defines defines the the structural structural core core of of the the complex, complex, aa marginal marginal back—arc back-arc basin basin sequence, sequence, and and aa number number of of major major felsic felsic centers centers (DeMatties, (DeMatties, 1989). 1989). These These units units may may correlate correlate with with LaBerge LaBerge and and Myers' Myers' (1984) (1984) amphibole—greenschist amphibole-greenschist succession succession in in the the Wausau Wausau and and Eau Eau Claire Clail areas. areas. Within geologi( Within this this geologic geologic framework, framework, three three distinct distinct geologic environments (1) environments appear appear to to host host massive—sulfide massive-sulfide mineralization: mineralization: (1) syngenetic syngenetic strata—bound strata-bound and and stratiform stratiform sulfide sulfide mineralization mineralization J J within, within, along along the the flanks flanks of, of, or or near near the the stratigraphic stratigraphic top top of of the the felsic felsic centers; centers; syngenetic syngenetic strata—bound strata-bound and and stratiform stratiform massive—sulfide massive-sulfide mineralization mineralization associated associated with with cherty cherty magnetic magnetic 1 iron-formation iron-formation and and located located in in the the main main volcanic volcanic arc arc sequence; sequence; and and epigenetic epigenetic stringer—sulfide stringer-sulfide mineralization mineralization and and syngenetic syngenetic 1 strata—bound strata-bound and and stratiform stratiform massive—sulfide massive-sulfide mineralization mineralization - * associated associated with with mafic mafic piles piles within within the the back—arc back-arc basin basin sequence. sequence. Based Based on on our our present present knowledge knowledge of of the the region, region, the the three three defined defined host host environments environments and and their their association association with with meta-argillite meta-argillite formations formations appear appear to to be be major major regional regional features features controlling controlling the the localization localization of of metal—bearing metal-bearing massive—sulfide massive-sulfide mineralization mineralization in in I 30 j j �.. ~ . . . the the western part of thee complex. complex. Other Other host host environments environments will will undoubtedly undoubtedly be be identified identified as as exploration exploration continues continues in in the the complex. Â¥ complex. References: References: DeMatties, A., 1989, 1989, AA proposed proposed geologic geologic framework framework for for DeMatties, Theodore Theodore A., massive massive sulfide sulfide deposits deposits in in the the Wisconsin Wisconsin Penokean Penokean volcanic volcanic belt: belt: Economic v. 84, 84, p. p. 946—952. 946-952. Economic Geology, Geology, v. , 1960, 1960, The The Ritchie Ritchie Creek Creek Main Main Zone: Zone: AA Lower Lower Proterozoic Proterozoic copper—gold copper-gold volcanogenic volcanogenic massive massive sulfide sulfide deposit deposit in in northern northern Wisconsin: Wisconsin: Economic Economic Geology Geology v. v. 85, 85, p. p. 1908—1916. 1908-1916. Sins, Sims, P.R., P.K., Van Van Schmus, Schmus, W.R., W.R., Schulz, Schulz, R.J., K.J., and and Peterman, Peterman, Z.E., Z.E., 1989, 1989, Tectono—stratigraphic Tectono-stratigraphic evolution evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatic terranes terranes of of the thePenokean Penokean Orogen: Orogen: Canadian Canadian Journal v. 26, Journal Earth Earth Science, Science, v. 26, p. p. 2145—2158. 2145-2158. Mudrey, Mudrey, M.G., M.G., Jr., Jr., Evans, Evans, T.J., T.J., Babcock, Babcock, R.C., R.C., Cummings, Cummings, M.L., M.L., Jr., Jr., Eisenbrey, Eisenbrey, E.H., E.H., and and LaBerge, LaBerge, G.L., G.L., 1991, 1991, Case Case history history of of metallic metallic mineral mineral exploration exploration in in Wisconsin Wisconsin 1955—1990: 1955-1990: AIME, AIME, Case Case' Histories Histories of of Mineral Mineral Discoveries, Discoveries, v. v. 3, 3, p. p. 117—132. 117-132. I LaBerge, LaBerge, C.L., G.L., and and Myers, Myers, P.E., P.E., 1984, 1984, Two Two Early Early Proterozoic Proterozoic successions successions in in central central Wisconsin Wisconsin and and their their tectonic tectonic significance: significance: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 95, 95, p. p. 246-253. 246-253. 31 �I ONTARIO ONTARIO :.. à Ironwood / I I I I ,. . Iron District Phillips .- THORNAPPLE Ladysmilh FLAMBEAU \LVI4N? Rhinelander / 5'1 I RITCHIE _*._______ BENDI '_# — Eau Claire -, . Somo Area of regional geologic map I . Thunder Bay —. tMe c/ford Ladysmith District PELJCAN RIVER (j Chicago ' IZ'CRANDON WOLF— — RIVER Wausau s S Crandon District Â¥ Population center center Population Major massive-sulfide massive-sulfide Major deposit or or occurrence occurrence deposit Wisconsin massive-sulfide districts districts (1 Wisconsin , massive-sulfide I Green Bay• 50 mites miles 50 I___________1 ' , ,.. ,.- . . . .~ .. , . ' ~ .- . 50km 50km ' '-I Index Map Map of of Wisconsin WisconsinMineral MineralDistricts Districts ~ U U U Li Li U J -J 32 �° LrLrsJ metadiolite and metasyenite I ments, and cherty iron tormation I PPEWA CLEAR CREEK metavolcanic flows and subvolcanic intrusives PROSPECT Regional geologic map Pmv I Pms — graphitic, sulfide-bearing meta-argitlites \ Pmvl — dominantly intermediate to matic . Pvs — dominantly tutlaceous metasediments; includes metagraywacke, reworked metatufis, and associated chemical metasediments Back-Arc Basin Sequence Metagabbro, altered ultramatic intrusives, syenodiorile S.. AY E R .\'#" metavolcanic tlows and interbedded metatufts and tultaceous metasediments Piv — dominantly intermediate to matic ± \ Pmv — mafic 10 ultramafic volcanicintrusive complex; includes metavolcanic flows, interitow tufts and sedi- Main Volcanic Arc Sequence Lower Proterozoic Metavolcanic and Related flocks CH £55 2 .2 Metagranite, quartz metadiorite, Lower Proterozoic (?) intrusive Rock Units Pb:Hj Lower Proterozoic Barron Ouartzite :.J units locally covering basement metavolcanic units not shown Undifferentiated Cambrian sandstone lormations; thin (.c SOft) sandstone Sedimentary Rock Units —— , — Contact, based on airborne magnetic data __________ Q • 0 I 0 POSct \\ L N / -J ziV — / \\ C (2'.i' Pb 4 9 LYNNE PROSPECT 5km I Sniies Reverse and normal magnetized mafic dikes (Keweenawan age) Deposit with defined reserves \\\\\ \\\' A Shear zone —— Projected or interred fauft — Nv — dominantly telsic melavolcanic tutls/lapilli metatults (lilhicicrystal), cherly metalults, and associated chemical metasediments (metachert) Feisic Center(s) END PROJECT,'Ce, Au) - ____ ______ __ ___ Eflflflrrflflflrcrrnrr-rrr—', �J BEND, BEND, A A LOWER LOWER PROTEROZOIC, PROTEROZOIC, COPPERCOPPER-AND ANDGOLD-ENRICHED GOLD-ENRICHED ,. VOLCANOGENIC VOLCANOGENIC MASSIVE-SULFIDE MASSIVE-SULFIDE DEPOSIT DEPOSIT IN IN TAYLOR COUNTY, WISCONSIN TAYLOR COUNTY. WISCONSIN Theodore F. Rowell, A. DeMatties DeMatties and andWilliam William F. Rowell. Ernest ErnestK. K .Lehmann Lehrnann&& Theodore A. Associates, 430 Associates, Inc., Inc. , 430First FirstAvenue AvenueNorth, North,Minneapolis, Minneapolis,Minnesota Minnesota 55401 55401 Exploration and 1991 by the Exploration work work conducted conducted between between 1976 1976 and 1991 by the Jump Jump River River Venture (Wisconsin Mineral Resources Incorporated and Chevron USA Joint Joint Venture (Wisconsin Mineral Resources Incorporated and Chevron USA Inc.) economic Inc.)has hasidentified identifieda potentially a potentially economiccopper—gold copper-gold deposit deposit within within the the Chequamegon Chequarnegon National National Forest Forest in in Taylor TaylorCounty. County,Wisconsin. Wisconsin. Geophysical Geophysical follow-up and evaluation by diamond drilling (over 30,000 feet follow-up and evaluation by diamond drilling (over 30,000 feet in in 25 2 5 holes) holes) of of the aa single-line AEM (INPUT) anomaly identified in 1977-78 resulted in (INPUT) anomaly identified in 1977-78 resulted in the single-line AEM discovery volcanogenic discovery of ofthe theBend Bend volcanogenicmassive—sulfide rnassive-sulfide deposit. deposit. Geologically the project project area area lies part of Geologically the lies within within the the west—central west-central part of the the Ladysmith—Rhinelander VolcanicComplex, Complex,aa member memberofof the the Lower Ladysrnith-Rhinelander Volcanic Lower Proterozoic Proterozoic Penokeari Penokean volcanic volcanic belt belt of of northern northernWisconsin. Wisconsin. The The copper—gold copper-gold mineralization mineralizatk (up to 2000 feet). occurs an upright, occurs within within an upright, steeply steeply dipping, dipping, thick thick (up to 2000 f e e t ) , and and relatively undistrubed felsic sequence dominated by rhyolite—rhyodacite relatively undistrubed felsic sequence dominated by rhyolite-rhyodacite flows, flow flow breccias, and flow breccias, and fine fine to to coarse coarse pyroclastic pyroclastic tuffs t u f f sand andsubordinate subordinatesedimensedimensection iis A t depth, depth,this thisflow—pyroclastic flow-pyroclastic section s intercalated Intercalated with with or or tary tary rocks. rocks. At which intruded intruded by by aathick thick(nearly (nearly1000 1000 feet) feet)series seriesofofsilicic silicicrhyolite rhyoliteflows flows which The felsic succession or center The felsic succession or center has has may may be be part p a r t of of aa larger largerdomal domal structure. structure. developed developed along along the the flanks flanks of ofaalarger largervolcanic volcaniccomplex. complex. J I U LI Ore Ore reserves reserves are a r e hosted hosted by by an an altered altered quartz quartz crystal crystal rhyolite rhyolite tuff tuff (quartz—sericite schist) and (quartz-sericite schist) andhave havebeen beendi'C'ided divided into intoa acopper—rich copper-rich hanging-wall hanging-wall horizon and aa gold-rich (HW1 and =old-richfootwall footwall(FW) (FW) zone. zone. horizon (HW) Two to semimassive semimassive igreazer (greater than (50-YU%) to tnan TWOstacked stacked stratiform stratiformmassive massive(50—90%) 30%) sulfidelenses lenses(the (theupper upper lens lens and and the the middle lens) at at or middle lens) o r near near the the 30%) sulfide stratigraphic tuff constitute thethe hanging—wall stratigraphic top top of of the t h equartz quartzcrystal crystal tuff constitute hanging-wall over 40 feet true thickness to over 40 feet t r u e thickness and and These lenses lenses range rangefrom from55 to horizon. horizon. These 34 J J j �containmostly mostlyfinefine-totovery very fine-grained, fine-grained, granular, granular. pyrite pyrite with contain with varying varying amountsofofinterstitial interstitial chalcopyrite ± tetrahedrite tetrahedrite 2± bornite bornite ±  gold gold amounts chalcopyrite 2 tellurides. Gangue include quartz, and sericite. sericite. tellurides. Gangue minerals minerals include quartz, carbonate carbonate (calcite) (calcite),• and Petrographic analysis analysisindicates indicatesthat thatthe the majority majorityof of the the pyrite pyrite grains Petrographic grains contain contain very fine inclusions of of chalcopyrite and bornite. bornite. Individual Individual very fine to tosubmicroscopic submicroscopic inclusions chalcopyrite and beds within within the and unaltered unaltered quartzquartzbeds the lens lens may may be be fragment-bearing fragment-bearing (altered (altered and crystal tuff vague to to well—developed crystal t u f ffragments) fragments)and andexhibit exhibit vague well-developed bedding/laminabeddingllaminations. tions. Sedimentaryfeatures features such such aas observed in in Sedimentary s graded graded bedding bedding have have been been observed drill core, origin. drill core, suggesting suggesting a a syngenetic syngenetic origin. Both lenses lenses extend extend to Both to subcrop subcrop, and are are overlain overlain by by about 120 feet feet of of glacial glacial moraine. moraine. and about 120 Near the the subcrop Near subcrop there is evidence of oxidation and supergene enrichment. Supergene there i s evidence of oxidation and supergene enrichment. Supergene minerals minerals include and bornite. bornite. include chalcocite chalcocite and Each lens iis serniconformable, Each lens s partially partially underlain underlain stratigraphically stratigraphicallyby bya a semiconformable, poorly developed stockwork—stringerororstringer stringer like like zone consisting of of fine poorly developed stockwork-stringer zone consisting fine cross-cutting chalcopyrite chalcopyriteanastomasing anastomasing cross-cutting chalcopyrite veinlets veinlets and/or andlor pyrite pyrite± 2chalcopyrite veinlets-veins andlor and/or fine fine pyrite veinlets-veins pyrite matrix matrix supporting supporting altered altered (silicified) (silicified)medium medium to coarse—sized, subrounded—subangular quartz crystal tuff fragments. to coarse-sized, subrounded-subangular quartz crystal tuff fragments. Locally wispy wispy chalcopyrite chalcopyrite stringers Locally s t r i n g e r s may may overprint overprintbedded bedded massive massive sulfides. sulfides. The stockwork by weak weak to to strong The stockwork stringer s t r i n g e rmineralization mineralization may may be be accompanied accompanied by strong No silicification and silicification and generally generally weak, weak, wispy wispy chlorite chlorite alteration. alteration. N o well—developed well-developed Locally these zones may carry carry alteration pipe to date. alteration pipe has has been been recognized recognized to date. Locally these zones may ore—grade gold gold values ore-grade values.- Both lenses enveloped by by aa pyritic 30% Both lenses aare r e enveloped pyritic stockwork stockwork sulfide sulfidehalo halo(up (uptoto 30% sulfides) which extends throughout the stratigraphic upper portions of the sulfides) which extends throughout the stratigraphic upper portions of the The stockwork crystal tuff The stockwork crystal tuff unit unitand andalong alongstrike strikean anundetermined undetermined distance. distance. halo consists consists of of ppyrite halo y r i t e disseminations, disseminations, bands, bands, laminations, laminations, discontinuous discontinuous cross—cutting and parallel (to foliation and bedding) veinlets cross-cutting and parallel (to foliation and bedding) veinlets and and is isassociated associate" Stockwork—stringer mineralization mineralization with widespread pervasive sericitization. with widespread pervasive sericitization. Stockwork-stringer developedstratigraphically stratigraphically below below both both lenses lenses grades grades both both vertically vertically and developed and laterally into laterally into the the halo. halo. The footwall The footwall gold gold zone zone is i s comprised comprised of of at at least leasttwo twostratiform stratiformore—grade ore-grade (plus 0.1 0.1 oz/ton) ranging from from less less than than 10 10 feet feet to to over (plus ozlton) gold gold assay assay subzones subzones ranging over 35 �designated as as the 20 feet true 20 feet true thickness. thickness. One One designated the "tuck Yuck under" undern subzone subzone is is stratigraphically belowthe the upper upper lens and stratigraphically below and hosted hosted by by stockwork stockwork sulfides. sulfides. A second occurs within, within, above above and and along second occurs along strike strike of of aa thin thinlower lower massive massive sulfide sulfide lens (or 600—foot (or group groupofoflenses) lenses)below belowthe the 600-foot elevation. elevation. Both Both assay assay subzones subzones Primary Cu, Cu, As, appear appear to to have have continuity continuity along along strike strike and and down down dip. dip. Primary A s , Bi, Bi, and Sb Sb dispersion dispersion patterns developed developed in the the stockwork stockwork halo halo indicate a geochemical continuitybetween betweenthe the lower lower sulfide sulfide lens lens and geochemical continuity and the the lower lower gold gold zone zone drilling is is needed and at depth. and suggest suggest that that it it may may widen widen at depth. Additional Additional drilling needed to to gold tellurides tellurides present present include fully delineate delineate these gold gold subzones, subzones. Hypogene Hypogene gold include calaverite calaverite (AuTe), (AuTe) , petzite petzite (Ag3AuTe2), (Ag3AuTe2), and and krennerite krennerite (AuAgTe4). (AuAgTe4). J J Widespread goldvalues valuesgreater greater than than 0.01 0 . 0 1 oz/ton ozlton have have been been found found Widespread gold Higher values throughout throughout the the stockwork stockwork sulfide sulfide halo. halo. Higher values can can form form poorly poorly developed strataform assay assay subzones subzones of of limited limited down downdip dipor or lateral lateral extent. extent. developed strataform The and geochemical geochemicaldata dataobtained obtainedthus thusfar far indicate indicate that that the The geologic geologic and the deposit exhibits zoningpatterns, patterns, Bend Bend deposit exhibits characteristic characteristichypogene hypogenecopper—gold copper-gold zoning i.e. by several several i.e. development development of of copper-rich copper-rich massive-sulfide massive-sulfide lenses lenses accompanied accompanied by The isopach isopach data data indicate indicate that that the parallel gold subzones. prominent parallel subzones. The the locus locus of of the the sulfide sulfide systems systems was was both both within within and andalong alongaapaleotopographic paleotopographic high high The massive— developed by aa thickening thickeningofof the the quartz quartz crystal developed by crystal tuff tuff unit. unit. The massivesulfide tends to to be be more fragment-bearing and and disrupted disrupted near sulfide mineralization mineralization tends more fragment-bearing near the margins, where generally well—developed the top top of of the thepile pilethan thantoward towarditsits margins, where generally well-developed The sulfide is believed to be sulfide system system is believed to be laminations and beds beds are are evident. laminations and evident. The be the plunging This may may be the result resultof ofpaleotopographic paleotopographic plunging in two two directions. directions. This control on sulfide control sulfide deposition. deposition. J J The of tetrahedrite of the The presence presence of tetrahedrite explains explains the the unusual unusual geochemistry geochemistry of the mineralization whichincludes includes anomalous anomalousconcentrations concentrationsofofarsenic, arsenic, bismuth, mineralization which bismuth, of tellurium high owing Concentrations of tellurium are are also also anomalously anomalously high owing to to and antimony. antimony. Concentrations the the tellurides tellurides present. present. A reserve base A geologic geologic reserve base estimate estimate as asof ofMarch March 1,1,1991, 1991,ofofdrill—indicated drill-indicated 2.77% and -inferred short tons tons of and -inferred reserves reserves includes includes approximately approximately 2.2 2.2 million million short of 2.77% oz/ton gold, copper, 0.05 copper, 0.05 ozlton gold, and and 0.43 0.43 oz/ton ozlton silver silver in in the the stratigraphically stratigraphically J j 36 �I I I upper upper hanging-wall hanging-wall copper-rich copper-rich horizon horizon and and an an additional additional 1.5 1.5 million million short short tons of 0.14 oz/ton tons of 0.14 ozlton gold, gold, 0.26% 0.26% copper, copper, and and 0.11 0.11 az/ton ozlton silver silver in inthe thefootwall footwa gold gold subzones. subzones. Exploration Exploration for for additional additional reserves reservesisi scontinuing continuingdown—plunge down-plunge and and along strikee of unit; at of the the productive productive mineralized mineralized unit; at least least five five high-priority high-priority hysical-geologic targets f a r , two geophysical-geologic targets have have been been identified identified thus thus far, two of of which which have hav been partially drill tested. �j j J ONTARIO Marquelle Iron Area of regional geoiogic map , Somo / • 'S IHORNAPPLE Ladysmfth FLAMBEAU -A 1 Chicago 5ti S (RITCHIE 1CREEK' BENDS '.1 Med!ord . Eat, C/afro J • Crystal Fafl's District Phillips — River Wausau Crandon District S  I' i Population Population center center 7yMajor massive-sutfide Major massive-sulfide I deposit deposit or or occurrence occurrence I (j(-,Wisconsin Wisconsin massive-sulfide massive-sulfidedistricts districts - Ladysmith District &j - 50 50 miles miles ' 50km 50km -A j . ' ! Index IndexMap Mapof ofWisconsin WisconsinMineral MineralDistricts Districts j j J J -I j J j j j J �e -doffllnmnlyintermafale @ mafc ,4( - CH -:-: I Pvs PROSPECT (LLSCHOOLHOUSE '-' '#t .. '\ Feisic Center(s) Felslc Cenler(s) ' i;II''—,., • Regional geologic map Pmvj>.. .—' .— R ' 4., .4 / 0 o ••_2' Pnwf 'fl ' I - -J 2 — (Zn,Pb,Cu,Au) 0 J a PROSPECT I SPIRIT "ini" / i' ø'fl Pvszv W\ RIVE' E C PAA9)/ LYNNE PROSPECT 5km Smiles (Keweenawan age) netized mac dikes Reverse and normal mag- Deposit with with delinetlfflserves defined reserves Deposit PR0SPECT.\\4 • Prospecti P THUNDER A 0 .7,c-y-- .—. j PROJECT(cu,Aa) ..... .-, I •'#J\ \pmv - -, cherly netatutfs, chew metalulls,and and assoassociated chemical chemical nietasedidated mewedments (metactiert) (metachen) ments Pfv — dominantly felsic metavolcanic tuffs/tapilli metatuffs (lithiclcrystat), maatufls (rihiislal), "' //_7 I cD , '?': ;"'—_.-' (','.'—\)--_ p FM -<,f4 Pry , J\\\\',1/X'-\__' c.')-7-Vc, '/\ V\'A Pmv Pms—graphitic. graphitic,sullide-bearing sulfide'ang meta-argillites Pms mela-amilites -dominantly int6fmediate to msftc kanic flows and.subvokanicinlwsives - Pvs — dominantly tuffaceous metasediments: includes metagraywacke. reworked metatuffs, and associated chemical rnetasediments t,'I\\\' (',','''' ',IJK PbLC Pvs PPEWA /<i ::Css: \J-\-.cy --: I AWYER it\'f S /5-g' "'a' .., ......... ....,....... ..... .. . CLEAR CREEK tufts and and mffaceous tuffaceous metasediments tuffs malasediments niotsvolcsnicflows and intertwddcdmela- I N ments, and cherty iron menls. anddÈit ironformation formation canic flows, interflowlullsand inteiflow tufts and sedic@.Bows. sedi. intrusive complex; includes metavol- 'p\N Pmv — mafic toto uftramafrc Pmv mnk ultramaticvolcanicvolcanic- intiusive complex: includesmetavo!- Main Volcanic Arc Sequence Metagabbro, altered ultramafic intnjsives, syenodiorite Back-Arc Basin Back-Arc Basin Sequence Sequenn .4.4 . Lower Proterozoic Metavolcanic and Related Rocks metadiorite and rnetasyenite Metagranite, quartz metadiorite, Lower Proterozoic (7) IntrusIve Rock Units Shear zone — — Projected or inferred fauft . ,... units locally covering basement metavoicanic units not shown magnetic data Contact, based on airborne Lower Proterozoic Barron Ouartzite Undifferentiated Cambhan sandstone formations; thin (<50 It) sandstone —— ri r ci r— ci r- r r— r r— ci r- rT r— r Sedimentary Rock Units —— g L 2' 2 2 C r r—i �L__ a 0 LL. I - I L_. -1000 0 1400 €LE ASL L. 016 WSW < " LL_ I 1990-1991 drillholes 1986-1989 drillhales L_ L L.. 0 = WeakJy mineralized 90-4 LL LWEI SEA ENE 7.4, 5.6 5.2 90-4 0.10 0.10 5.7' [LL I FW FW NW HW HW FW FW NW FW FW FW FW FW EW FW HW NW FW HW FW MARCH MARCH1991 1991 I Longitudinal Longitudinal Projection Projection of of Mineralization, Mineralization,Bend Bend Project Project - Taylor Taylor County, County, Wisconsin Wisconsin L 1.12 0.02 0.02 0.38 0.01 0.03 0.06 0.01 0.05 0.02 0.22 0.02 0.29 0.089 0.089 (cut) (cut) 0.35 0.35 0.190 0.190 (uncut) (umut) 0.139 0.10 0.139 0.10 0.085 0.055 0.041 0.038 0.058 0.052 0.067 0.041 0.093 0.072 0.476 0.058 0.023 0.024 0.119 0.35 0.09 0.13 0.068 0.091 0.61 1.51 Ag Ag ozfton oznon 0.076 ozlton oznon Au Au FW FW . Footwail Footwallzone zone 1.87 1.87 1.28 0.20 0.04 2.46 61.4' 5.1' 16.5' 11.9' 69.5' 0.01 5.2' 6.1' 0.02 0.11 0.13 (71') 0.10 0.09 0.08 0.08 2.22 3.88 0.10 2.66 5.98 0.90 % % Cu Cu 29.9' HW HW- Hanging Hangingwail wall zone zone 91-8 91-7 90-6 - 21.8' 90-3 90-5 14.7' 12.3' 90-2 21.1' 40.7' (14.1') (26.6) True True Thickness Thlcknese 90-1 DDH# DOH# Assay AssayData Data �S. ID COOS Albert B. Dickas, Professor of Geology/Extension, University o f Wisconsin-Superior, Superlor, Wlsconsln 54880 M. G. Mudrey, 3r.< Wisconsin Geological and Natural History Survey, Madlson Wisconsin, 53705 N ZWWt H ID lID' p.00 DIN ft i (DH H C rfi-'1D Di ftH • '< (0 (DID Dii- rtC N a'< a N ft o H ID OOW o om a DiW nj'a rtID'< (:1 Nt OlD Di ON'l CDI P0 ftC 01 DiiID tOW ID'—Oft (tHctfrt,P1 ft Di l-.m CD fti-r 1 mDiC OIft (A rtctH m— N HWIDN H, i-i,ftC awo Di p.m o 1 OH (D0W0 H tQQ,i- (DID <: Hi-ft X rt (D (A p.pa.fl) The Amnicon intrusion is chemical1 structurally, and petrographically similar t o $he otikr ma or K=weenawan intrusive suite? assoc4ated with the Mldcontinen? &ift ln t h e western Lake Su erlor reglon, t h e Duluth Igneous Sulte t o the north and the ~ e y l e nIntruslye Suite t o the east (Table 1), and probabl represents a mxnor, high-level differentiated gabbroic bozy. t • tt(fl ID F--tOPN'Q I IDrtIDCN H (AID(AH0ft IDOOCO ijDirtCOCH, r14<CO10013'<001 OH XHrtUM W1NtNHC HCD'<WHHItH"ft' DItOrtID WU<N IDHHHt'ftID IDQaH"HIDHID DH"l-C H'<H"H"IDPftD p-C) ctW HOIC I OflO'O0 NQi OCt Qi' ( '0 oDIrtID O HHIOD) OH (D'< 00 a frtt<rtO WC (D0 (DH P•ID IDIDNHO<C ctaHH"ftaftDiftON C IDDiftCtftC'N CHND10H"OCOQ)< DIN '.ONN H.IDNrbYP< —' WDlWDitNNftON I-c. IDOWft N (DD)tHDiUIftIDDi rt0 Nt H QADIDWO CnaftmIDft<D' ID (AfflH,H,HWIDIDft00)00" :HOOH"0NNt0Di 0 N H"0HDiOPIDO 1Y ID NOHH OO(DWDiftHNItDi IDOftlDCO ft1 ft IDOID0'<O IDH-ct<(DtO OW frfI ID DftrtHH"Di HNIACIO ti-QIDHOIDQ4IHDIH" CN0ffl 01 IDtrnrCooJDHDO (DX HID 0' 0DiNIftC DiO-NrH"H"0NC '<CDt QlI t1 rrp'rt0flQi —'cta FCC 0Di0Q' IDftWLOIH ftrF flhrtOf 0 r1<H"C (DIDNXD 0 N'i mi-'-o (DID CC O0IDHOCOHfflID ui—.DiDi IDP.0J-COtOtO WO Ja aft p-DiNlft NiQthb tOImO)_h ftI ft Di CD • N t D)IDOWNO WNt'<C 1ft HO'NftftDl'<N ftQ WOO • (I) N itO 0) N '< <N Oft p0) M 0 10 H- (0 ft 'H O0 tOC ID N ID 0" * OH 0 ft 'OH, OCO 010 C1N (0 COft01 0 HOCID ftD)rt 0) HQHCDO ftmnIHmwC 0) pi N odaoO aCO id tQtft UH.ftftclH ft WH-OH 00 CO N HID N 0>0 rUfl ftHID 0 HO o\° COt D)tDI mtDrt tID tH<I-rtD <ftW—OW O HQlF-'ft jp DIDN rQ10rhQHCHft OO '<HaIDfrtlCtIDt0'< F-4J0 D cC,-'.DlOft(DdCOH" IDWftID (DCOOO Oo\0WAH (OHHCO ftIDW >fta-tt<ftWDOH"i- X(DC H"OftHnHDit dO' ID 0 bH" 0' N HifitO 0 0 (DO -ma otCCHrtO ct0OCO NftO tftN ftCftctCDtON ODiH"WDiNO ft OWOFH,OH"NH 0HNH ft O i-CA tQ o\°O (DO Di 100 OH"H '<ftQ• OftID NWH" COCOIDO CO NHWCO IDIDIDO it l0It(AOIDDiH"IDft ma '<H"WIDO) WOO HX OIOID t 0) CO ID 10 ttOP 0< CA 0) d - 0 ft CO N , O 01 tV DIH"D' dOft HNDIP-P-ffl COlt - CO ft d-'i11 aIDwH, ft i-CaoH" OH" ptflU)ØH"DIW ft aCNJOCAH"d HQi d 0N fflftWH-dQi01O HDIU1O 0)0 0 OftD) ID PHOOdM <Na '<H"rt IJIDID CDI Oft (0 O tttUft LQIDO)OPIDH i-W(D'< WWHID-0< NftO C dNO< IDuCd0DiQi0 H" Qi (ANt OO ONIDCO (DdIUNitNZ CIDH"ID N011CCO H-H-ftH,Qj ftaart-4ID> O'1Di aftWO adOltftft (DO OIDH"CQJO ID CIDP&OCACO CO ctdoH"rt- QIDQi H IDCOCO O SN a.p.ft ID'< 0 DI P-P• 01< H, COtD :10 00 OH (AID C P•0 N -O I 010< 'C N 0 ft CO H" H Di C N ft Dl z 0 'C ft H- (51 N ID C H. :1 C - 0 CU) P. 03:1 aft QiODID :1 0) P1 H"< H IN 0' 0 H. tO H 0 P'OWC-'Oft 0)0 pCDDid0iDi cHOP' aaNN iC hl,W0 (DftDIOmS<ft itNiDifi t OH-H oDi H0 C IDftftl 1.51:1 OD'H"ID<' H"Q)H ti HoaID (AID CCC (A—4HH" —10 1101 tb'IDOCOi OlD CO wd 10 ft0 - • The s ~ a l l ,sill-like Amnicon kntruskon located,southeast of S u erlor &Douglas Count ) , Wlsconsln, identifled by D+ckas avd otEers (i9 9 and ~ e n g e y (1970), has noy been mapped 1n detcll The Amnlcon biuton exceeds 6 square km. ln outcrop area and 1s named for exposures alon the bank of the Amnicon River in sec. ?t is poorly exposed in sec 31 and 3'2, 32, T. 48 N., R. 12 W. T. 48 N., R. 12 w., and sec. 5 and 6 T. 47 N - , R. i2 w. ( ~ i g u r e 1). N? contact? were observed, and the qutcrop ext9nt c o ~ n c ~ d e s roxlmatel wlth the map ed magnetlc signature (Dlckas and. Field relagions lndlcate lntruslve contact wlth :&?ers, 1969y surrounding ckengwatana basalt and interbedded volcaniclastic units is well constrained t o the north, and moderately The southern margin appears t o constra+ned t o the east and west. be a chllled contact. (U ft HOODS H CO cOD N C cit H OiOCW OW rtt' ID rP)rtH Ii Z em uDaHtOP1 wOdCrtt'- -MDIftC 0J 0 ID 00 '-,,O CD Hi-HID NPN 0 p)WH.CCHDIH NIDNO F-t PrFID tIDIDH(Q0DiNC CdftCCO<frDi <0 00 (DID D'COftN(DN A C$DiH"ct ft HtCCO H H" WNciDNftftIDftH<ID P1 HID ftN ON ftWONO OOHa>NNCA 0'ODH"ft OWt-0rtO t HIDN0CCOIDID DiCO dCOH"d 1< ON CCAXZ it H-ftID 00 ourtC(ACDiCD tDiH-0HQiH" ci-aai-"Wt p•lo'fl m P- 00) -ZCO HZO0cl'< ID0ID0'H,DI WP-d -OZ CIDWHDi0N '<Oft ii (DC 0 a AOH.NH C H"bl NH" 'CNCOft Di-ftDi IDHO) tO a0'NW (DWFtIDH 1 HN DiD) P• HCOt o0-.NffltftDift0 H p-HDi0 NOH H za• ft:i mtdO IDl-'1WD fttlrr'lOft ftwui 0I'tQ HHWHNIDX 0CC DIN HIDCdtoftO 0WN OW a)Dio0tmD' WrtIDHDiH,w0N (A çtI In ::rO alt 000 H-IDN(tID ID aIDtO O'(D d Z0 i Cs—' OW ft. DiH"COIDCO ct(AHNCN OOCI-N rtW Fl (DO P• H< tO C'00(0 0) a H tDHft H" tOftH•¼oHOftO HIDLqOi-CD'<H0tWH' 10Dl C'Q 0 0 CAftHn<Di tOOtN H-l• (ON O ft ID00Q0 'jIQID p. OH 0CMCH 0 ID (D OftHIDOID 00 O 0k- OHICOOOIC (DF-'Hi- •HO H0 Di H —fti-COftQi O C)ID CftNJWC tQH C4 ND) H0W fti-'ct CwCO0-'rhODiN 0. i-CO CrtWHI N P-CA OC'<ID OH 0 tomWft (0 HftoamCftID 10- (D'<N NOD'H 0C' Dim < ft.Q'iift n0DiHtn0HIDft NftIDHNftSCP0P ftDiC'< QiC 0 H(DDIP DiIDmCH-C HIDawH" H N ftrt rtftDiNW0DCOON (Am IDMCO ftDJID O ID'<CD(D,Qft '<(Od N •t5 NIDDiW0Wft0 - CCPP N IDZOID OC ft am ftIDNftHftN o iIDIDftHID ft (DIlDiOt N i-ID -• 0 OH"COO • Dio'o)ab(DPCD)XIDO H.orMtOIDOH"aCOH"Nrt -"DIDNIDID dON OiCi artifi ftHi HOC> wWOtID CH, OtmN mH-Nomm0ft rtWN OQi O(DtOd l--d1QQi 0.Dft ftWCO(D i—ID H DIDlftDiOH" DitODlOO1 D)iNftDi amDioIDDirnC HH,CDi C OW IDIDfti ,-'-O (Od xftDidIDDaCODi '-CD NO ND)FiDift NH"IDi14<O (1 rtHrfN CA d NCO 0) QiOHW CO (A FC a—< iID CHOP-H" IDIBO I 0Ci ID' awC(DNDiID00 -CO H"0 '—'0 WDi'OIUIDft DiooaOCOftrittO 0> DaftCOrtONO iDWO i-'IDP•ftID N H rt(DrtO H- ON -t -.- 0 ctIDCO HH,tt mct O DiffltftonmWaOWJO HH 0 d - IC Z H C 0 n [A C) C 0 C 0 Z - C t1 t Z 0 Zn 0 Z (AZ HH 0 (DPI CS "1 0 'C Z 0 0 H P1 •d C Z :ri F< 0 t' 0 rrnrrrrnrr-flrcrnr-r-r SEOLOGY AND PETROGRAPHY OF THE AMNICON PLUTON, DOUGLAS COUNTY, WISCONSIN �Ni • •%%_,•_ I ENTA SANDSTONE I I Falls1 N OR1ENTA I mile SANDSTONE -Illgl,'.ay 2 cIIENGWAANA VOLCANICS ' - -jitE::: -1 PLUTON 4, fc CIIENGWATANA - Areal Areal distribution distribution of of the the Amnicon Amnicon Pluton Pluton and and its its relation or relation to to regional, regional, Middle Middle Proterozoic Proterozoic (Keweenawan) (Keweenawan) geology geology of the Nidcontinent Midcontinent Rift Rift System System within within Douglas Douglas County, County, Wisconsin. Wisconsin. the Figure 1. 1. Figure 0 61K SE 5000 Feet +80 NW tall Bayf.eliI Norito J .Amnicon Norm .80 48N-ISW E_48N-12W Ilicloway 5)— I .t —— HIgt.ny2andSS GIo.cioolCuaar* gS N - I S. 1W1 — p BAYFIELD.OR0NTOU') CLASTICS R.tl0..OII Dii, 3-to SE 42 -j j j Li 2 Stc t'vr 4S0-t( neLine diagram diagram interpretation interpretation of of the the upper upper two two and ar one2. Line Figure 2. Figure as as half half seconds seconds of of reflection reflection seismology, seismology, magnetics, magnetics, and and gravity grak in. collected 2-53 and and 53, 53, Douglas Douglas County, County, Wisconsin. Wisc collected along along highways highways 2—53 Display Display presented here here courtesy courtesy of of Halliburton Halliburton Geophysical Geophysical Services, Inc., Inc., Texas. Texas. Services, -j j J -j �O1C F1(D tZ na_ pj n-tm <o PflJP) HQJCD ¼00DN p. DN It'D t', C - DQa HD 0) tO) E-'WD IF-'tQ 0) Q 0 • CD D' 0 D CD tO P• (0 O' c t-. CDI-'D N N D (0 rt- P• 0 N CD it NJ1t't 0300 CD 01 0 CD N CD ct DO OH, U'-O 100 OH CDO 0(0 a -'D' .- O1S 0— D CD C (0 rt Hi 0 0 - 'C it it N f----'- DDO 10DN 0010 D10P- I-'-f-- H(O }-IDO DCDCD NO' itOD 'IDO' 0 Z-'< - 0100 Df--H P-CN rtNrl- 0)rt(0 NH CD WND 10(DH zj—J CO-a (tH C U - - • t <P '<H- OCD ftC-" HDO) 0)0 I-'- tQb' H--t OON 100 0)0 ODE'- D f-00 '-C -tOfl OHO CIOCO 0 D F-'o C-ct NIflO rto,Z NJ :— J 0-kb Z0 N1 •-0• Yrt- - (0 - In 1<0 uDw O0)rt HHCD OtOD CDCtO 000) CD OH HCDOJ NHD CDtOO tDP- CO)tO OINCD O'N CD0) ZCHi O'iOO 010 -tOt rtDF-'- WORD' D10 HD (tH D0 rtCrt 0100) HCOH CD CD ifiDi '-0 rtrh 0 0)ht,0) H NO-C it 01'< :t:QCW- HH •-OW DCD f-tOrt (0 D 00- 0001 WN F-'-O, 10 m D U Table 1. Chemical anal ses of the two etrographic phases within the Amnicon Flvton, witg comparison of the Amnicon trqctolice phase with slmllar phases from the Mellen and Duluth lntruslves. D 1!) D D' (OCt <CDk p-ftC YIP- CHW NO0 ctrtffl P-OD DOD' Nt Yrt ctO HOD CDP- COt OF-"O) DN N D'O 0) (OCt DD(0 CDctO HhtO H Z ct moC D CDO0 N rtk-rt N OtO 01 00 N,OW (1) fflrtH 0) D)H-O) 't NDH (BOO) HçtQ 10 DO ito DH PH" CDT'(D f-i H '— b'CDa_ DCDD D DCDD 'U 'C 0<0 OP-fl Ifi DittO) ' CD N-< 0—]'- D'03 HO 01kb C. CD C\ A IlitIl 111111 I_I H D 0 P• (0 DC D'NJN flout 0 'U 0 0) '0 1 HH .N 0 • tbHHU1-3O3HHH01 H HHA —]IOONJHO1000IH-] '0 U) '— - — NJ —' it C H C C - C-' — CD H H CD ND GO 000-U)H0001NJ0H N H OHHNJOWHU3-J H-I WINJU1ANJUNJO1aW'-) HC-'D (00 0) D' H HU (DD rtD P.tS 0 H U 0 N H -' —s CD 0, —]HouNJooaHow D '0 < I-'- H01rt UlOtO03HO '—3 MQD(OHH-I-'- 0)WAG\NJkbHNJtOU0)A 0000 0 H 01 H CD' (FHOONJ0000NJOO 01 ONflJ 0 OONJNJ NDit tOIOONJO0)000DI-"0 rt-O' it wpNJcokbHHo1A--J Of-tO ZC'C '0(00 'UN CD N 1< 'U 0 D 0' '.0 N frtü-'H, DD O—'O t-'-CDP- P+'-P Hi OO 0 10 CD (0 'C H WCW 0)0010 D 0' 0 C it Hr'Q rhO DND ONJOJDOJ —]DHD Ow tOHrtDit (OHCD W NDNHN CD0)CDP) WCDtt tON 0)OCDDCD (t—HN H D CDt H1tP CDNOI'lO NOW0)(0 OClfltflLO NJ 'tot—"d U --- I fflN 010 I-'-W • DC -GD rHO tOO o'CD'.Q Qiçtk H OdD ND< 0 10 P-WI-'- 003 10—] 'CC P-kb (OtON H -- X- ZOrt HD 00 fl)Q.i. -'•QD CD H CD••C 0) 0 N C q t< 'ci- o- OdD -mm CD ,--'cr to 0)0 t000) -0 0 H 0—C N •D- '--'f--NJ (0 ct (OH O'D NJ (0 N 01 %% kbtrt ot-NZ U) D p•- NH 0D P-0) 0) '<010 F--i— - NJr CD CD , 0- H - D- CD- <H • m Uff)O— (Z: (A tllDtCD 0)'--'bit CD ic WDD C U f-cict References: Dickas, A. B. et al., 1969 Relationships of regional magnetics to the bedrock geolo y of the South Range Quadrangle, Douglas CoUnCY Wlsconsln: ~gstracts,15th Inst. Lake Super lor Geology, p . 12-i4. N •—CDqaa_ rp ro'x rtH • HDD N- H-OH . '<c OOD '—'--'CD NOH Omit mztr 'ci WCD Green, J. C., 1972 North Shore volcanic Group, in Sims,.P. K. Ieds), Geology of Minnesota: A centennial and More G. B. M. ~cliwartzvolume), Minnesota Geological survey, p. volume 294-332Klewin, K. W. 1987< The petrology and zeochemistry,o the Keweenawan potato Rlver Intryion, nort ern W+scqnsIn; un ubllshed Ph. D. dissertation, Northern Illlno~sUn~versity, 357 p . Mengel, J. T., 1970 Geology of the western Lake Superior region, privately printed, $6 p. Tabet, D. E., and Mangham, J. R., 1978, The geology of the eastern,Mellen Intrusive Complex, Wisconsin: Geosclence Wisconsin, v. 3, p. 1-19. Weiblen, P. W., 1982, Keweenawan intrusive igneous rocks in R J. Wold and W. J. Hinze (eds): Geology and tectonics of &he Lake Superlor Basln, Geol. SOC. America Memolr 156, p. 57-82. C. CD OOP- rrrrrrrrr----r Amnicon Mellen (1) Duluth (2) Oxide ( 8 ) Troctol~te Granophyre (3) sio2 : . .-.,.,, 50.4 69-8-71. 47.7 Ti02. $ . 1.8 0.3- 0. 1.3 A1203 18.3 11-7-12. 18.4 FeO 9.9 4.3- 5. 10.6 MnO 0.2 0-1- 0.1 0.1 0.2 5.1 0.3- 0.8 6.1 5.3 9.9 2.0- 1.7 9.9 11 2 3.2 Na20 3.2- 3.5 2.9 2.4 K20 0.6 4.1- 4.1 0.6 0.5 P205 0.4 0.1-<O. 1 0.2 0.2 LO1 0.8 1.9- 0.9 Totals 100.6 97.8-100.7 99-8 97.8 n Potato River Intrusion (1) Possible Earent ma ma ~ o m p o s ~ t i oof Eastern ellem 1n?rusLve SuLte) (Klewln 1987, p. 152) (2) bossible parent ma ma composition of ~ o r t hShore Volcanic Group (Green, 19727 '(3) Percentage range of two analyses of granophyre phase - - �REGULATING REGULATING METALLIC HETALLIC MINERAL HINEPAL DEVELOPMENT DEVELOPHENT IN IN WISCONSIN WISCONSIN I Thomas Thomas J. Evans, Evans, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey 1 I Despite Despite the the significant significant potential potential for for metallic metallic mineral mineral deposits deposits in in the the Ladysmith/Rhinelander Ladysmith/Rhinelander volcanic volcanic complex complex of of northern northern Wisconsin, Wisconsin, only only one one mining mining project project has has received received permits permits for foractual actualmineral mineral development. development. In In part, part, the the regulatory regulatory framework framework for for metallic metallic mining mining has has been been responsible responsible for for the the slow slow pace pace of of mine mine development. development. The The statutes statutes and and administrative administrative rules rules governing governing metallic metallic mineral mineral development development in in Wisconsin Wisconsin form form aa comprehensive, comprehensive,broad-based broad-based regulatory regulatory framework. framework. In In addition addition to to extensive extensive environmental environmental regulations regulations focusing focusing on on groundwater, groundwater, surface surface water, water, air, air, water-supply water-supplywells, wells, and and wastewater wastewater discharge discharge activities, activities, Wisconsin Wisconsin has has adopted adopted aa net net proceeds proceeds tax tax on on the the occupation occupation of of metalliferous metalliferous mineral mineral mining. mining. " The The regulations regulations affecting affecting metallic metallic mining mining in in Wisconsin Wisconsin include include aa thorough thorough assessment assessment of of environmental environmental impacts impacts and, and, together together with with the the extensive extensive permitting permitting requirements, requirements,result result in in aa lengthy lengthy process process from from mineral mineral discovery discovery to to eventual eventual mine mine start-up. start-up. However, However, the the process process does does provide provide aa mechanism mechanism that that will will lead lead to to positive positive decisions decisions on on the the necessary necessary permits, permits, as as long long as as the the environmental environmental standards standards can can be be addressed. addressed. I I I; The The net net proceeds proceeds tax tax provides provides aa reasonable reasonable tax tax basis basis for for mineral mineral development. This tax, often misunderstood or mischaracterized development. This tax, often misunderstood or mischaracterized by by the the mining mining industry in the early years after its adéption in 1977, was modified industry in the early years after its adoption in 1977, was modified in in 1981 1981 to to clarify clarify and and expand expand certain certain allowable allowable deductions deductions and and to to reduce reduce the the overall overall tax tax rate rate so so that that it it was was more more closely closely tied tied to to the the profitability profitability of of mining mining ventures. ventures. Although Although the the tax tax is is an an added added burden burdenor or "cost "costof of doing doing business" business"in in Wisconsin, Wisconsin, it it does does not not have have aa significant significantimpact impacton on the the overall overallpotential potential for for mining mining in in Wisconsin. Wisconsin. The The modified modified net net proceeds proceeds tax, tax,aa "workable" "workable"mine-permitting mine-permittingprocess, process,and and recent recent decisions decisions that that favor favor mineral mineral leasing leasingcreate create aa positive positive climate climatefor for mining; mining; however, however, the the small small but but vociferous vociferousanti-mining anti-miningactivity activity and and recent recent 1 legislation legislation that that would would severely severely limit limit mining mining in in the the state state do do much much to to obscure obscure that that positive positive climate. climate. It It is is important important to to remember remember the the "upside" "upside"when when you you are are 1 up up to to your your ears ears in in the the "downside". "downsiden. I 44 �GEOLOGY OF HORIZONS OF PLATINUM PLATINUM GROUP GROUP ELEMENT ELEMENT -- ENRICHED ENRICHED HORIZ WITHIN WITHIN THE DUNKA DUNKA ROAD ROAD COPPER-NICKEL PROSPECT PROSPECT ST. LOUIS ST. LOUIS COUNTY, COUNTY, MINNESOTA MINNESOTA Stephen 0. Geerts Geerts Stephen D. Natural a t u r a l Resources Resources Research Research Institute, Institute, University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth The Dunka Dunka Road Road Cu-Ni Cu-Ni prospect p r o s p e c t is i s located l o c a t e d within w i t h i n what is i s informally informally known W.), which is W., R. R. 13 W.), i s part part known as as the t h e Partridge P a r t r i d g e River R i v e r intrusion i n t r u s i o n (T. (T. 60 60 W., of of the t h e Duluth D u l u t h Complex, Complex, 1.1 1.1 b.y. b.y. (Keweenawan) (Keweenawan) in i n age age (Figure ( F i g u r e 1). 1 ) . Seven Seven major lithologic 1 i t h o l o g i c units, u n i t s , along a l o n g with w i t h several s e v e r a l internal i n t e r n a l ultramafic u l t r a m a f i c subunits, s u b u n i t s , have have been been identified i d e n t i f i e d and and are a r e correlatable c o r r e l a t a b l e over o v e r the t h e deposit. d e p o s i t . The ultramafic u l t r a m a f i c subunits subunits (layers of p picrite uniform tthicknesses are ( l a y e r s of i c r i t e tto o ddunite), u n i t e ) , eexhibit x h i b i t rrelative e l a t i v e uniform h i c k n e s s e s and a re present p r e s e n t at a t the t h e same same relative r e l a t i v e position p o s i t i o n within w i t h i n the t h e major m a j o r lithologic l i t h o l o g i c units. units. The The major m a j o r lithologic l i t h o l o g i c units u n i t s are a r e the t h e same as ddelineated e l i n e a t e d by Severson and Hauck (1990), Unit I, a finefine(1990), and upward upward from from the t h e basal basal contact c o n t a c t are a r e (Figure ( F i g u r e 2): 2): U n i t I, to anorthositic pyroxene t o coarse-grained sulfide-bearing a t r o c t o l i t e ttoo pyroxene c o a r s e - g r a i n e d sulfide-bearing n o r t h o s i t i c troctolite troctolite with and ft. tthick) hick) w i t h aassociated s s o c i a t e d uultramafic l t r a m a f i c llayers a y e r s 1(a), I ( a ) , 1(b), 1 (b), and t r o c t o l i t e (450 (450 ft. 1(c); Unit medium- to pyroxene I(c); U n i t II, 11, aa mediumt o coarse-grained c o a r s e - g r a i n e d ttroctolite r o c t o l i t e ttoo pyroxene troctolite Unit ft. thick) t h i c k ) with w i t h aa basal ultramafic u l t r a m a f i c layer l a y e r 11(a); II(a); U n i t III, 111, t r o c t o l i t e (200 (200 ft. aa fine-grained, m o t t l e d textured t e x t u r e d troctolitic a n o r t h o s i t e to anorthositic f i n e - g r a i n e d , mottled t r o c t o l i t i c anorthosite t o anorthositic troctolite Unit anorthositic f t . thick); thick); U n i t IV, I V , aa coarse-grained coarse-grained a northositic t r o c t o l i t e (200 (200 ft. troctolite coarse-grained t r o c t o l i t e to t o pyroxene pyroxene troctolite t r o c t o l i t e (400 (400 ft. ft. thick); t h i c k ) ; Unit U n i t V, V, a c oarse-grained anorthositic coarse-grained ft. thick); a n o r t h o s i t i c troctolite t r o c t o l i t e (300 (300 ft. t h i c k ) ; Unit U n i t VI, V I , aa finef i n e - tto o c oarse-grained troctolitic f t . thick) t h i c k ) with w i t h basal ultramafic ultramafic t r o c t o l i t i c anorthosite a n o r t h o s i t e to t o troctolite t r o c t o l i t e (400 (400 ft. layer V I I , aa coarse-grained c o a r s e - g r a i n e d troctolitic t r o c t o l i t i c anorthosite a n o r t h o s i t e to to l a y e r VI(a); V I ( a ) ; and Unit U n i t VII, anorthositic ft. t thick) basal uultramafic h i c k ) wwith i t h basal l t r a m a f i c layer l a y e r VII(a). VII(a). a n o r t h o s i t i c troctolite t r o c t o l i t e(400.4(400+ ft. Most I. The The sulfide sulfide Most sulfide s u l f i d e mineralization m i n e r a l i z a t i o n occurs occurs within w i t h i n Unit U n i t I. mineralization m i n e r a l i z a t i o n is i s both b o t h interstitial i n t e r s t i t i a l and and widespread, widespread, but b u t variable v a r i a b l e in i n modal percentage percentage (rare ( r a r e to t o 5%), 5%), continuity, c o n t i n u i t y , and thickness t h i c k n e s s (few (few inches i n c h e s to t o tens t e n s of of feet). Sulfide feet). S u l f i d e mineralization m i n e r a l i z a t i o n is i s generally g e n e r a l l y related r e l a t e d with w i t h proximity p r o x i m i t y to: to: hornfels Virginia i n c l u s i o n s , basal basal contact c o n t a c t with w i t h the t h e ffootwall ootwall V i r g i n i a Formation, and and h o r n f e l s inclusions, some of I. Primary P r i m a r y sulfide sulfide o f the t h e internal i n t e r n a l ultramafic u l t r a m a f i c layers l a y e r s within w i t h i n Unit U n i t I. mineralization pyrrhotite, and cubani cubanit. te. m i n e r a l i z a t i o n includes chalcopyrite, p e n t l a n d i t e and i n c l u d e s chalcopyrite, y r r h o t i t e , ppentlandite Minor M i n o r amounts amounts of o f bornite, b o r n i t e , native n a t i v e copper, copper, talnakhite t a l n a k h i t e and and mackinawite m a c k i n a w i t e or or valleriite v a l l e r i i t e have have also a l s o been been identified i d e n t i f i e d in i n preliminary p r e l i m i n a r y petrographic petrographic observations. Pt+Pd values observations. v a l u e s range ranae from f r o m 100 100 to t o >2400 >2400 ppb ~ o over bo v e r 10 10 foot foot intervals, i n t e r v a l s , and and these t h e s e occur o c c u r as as iisolated s o l a t e d values v a l u e s or o r along a l o n g stratigraphic stratigraphic horizons h o r i z o n s in i n the t h e upper upper 3/4 3/4 of of Unit U n i t I. I. Several Several Cu/PGE-enriched Cu/PGE-enriched horizons h o r i z o n s have have been been identified, i d e n t i f i e d , and and occur laterally The most l a t e r a l l y throughout t h r o u g h o u t the t h e prospect. prospect. most continuous c o n t i n u o u s horizon, h o r i z o n , (RED (RED Horizon) H o r i z o n ) is i s found found directly d i r e c t l y beneath beneath ultramafic u l t r a m a f i c layer l a y e r 11(a), I I ( a ) , within w i t h i n the the uppermost uppermost portion p o r t i o n of of Unit U n i t I. I. This T h i s horizon h o r i z o n ranges ranges from from 10 10 to t o 30 30 feet f e e t thick thick and Two other and contains c o n t a i n s average average values v a l u e s of o f 0.65% 0.65% Cu Cu and and 1200 1200 ppb ppb Pt+Pd. Pt+Pd. other horizons, h o r i z o n s , (ORANGE (ORANGE Horizon H o r i z o n and and YELLOW YELLOW Horizon) H o r i z o n ) occur o c c u r roughly r o u g h l y at a t 100 100 and and 200 200 feet f e e t beneath beneath Red Red Horizon, Horizon, respectively. r e s p e c t i v e l y . These These are a r e less l e s s continuous c o n t i n u o u s horizons horizons that t h a t range range from from 10 10 to t o 50 50 feet f e e t thick t h i c k and and contain c o n t a i n average average values v a l u e s of o f 0.70% 0.70% Cu Cu and Only Pt+Pd. Only one one PGE-enriched PGE-enriched horizon h o r i z o n has has been been identified identified and 1000 1000 ppb ppb Pt+Pd. outside Unit Horizon), I. It I t occurs in in U n i t VVII (MAGENTA H o r i z o n ) , directly d i r e c t l y beneath beneath o u t s i d e of o f Unit U n i t I. ultramafic i t has has been been identified i d e n t i f i e d in i n only o n l y six s i x drill drill u l t r a m a f i c layer l a y e r VII(a). V I I ( a ) . Although A l t h o u g h it holes i t ranges ranges from f r o m 10 10 to t o 30 30 feet f e e t thick t h i c k and and contains c o n t a i n s average average h o l e s to t o date, date. it values values of o f 0.90% 0.90% Cu Cu and and 1875 1875 ppb ppb Pt+Pd. Pt+Pd. 45 �j. The Cu/PGE-enriched The predominant predominant hhost o s t rock r o c k for f o these r these Cu/PGE-enriched horizons horizons iiss coarse-grained which may may eexhibit coarse-grained a anorthositic n o r t h o s i t i c t troctolite, r o c t o l i t e , which xhibit some ubtle some ssubtle minor a1 alteration. The a1 alteration t e r a t i o n . The t e r a t i o nassemblage assemblage ffracturing r a c t u r i n g accompanied accompanied wwith i t h minor within serpentine, uuralite w i t h i n these these mineralized m i n e r a l i z e d zones zones i is s serpentine, r a l i t eand and saussurite. saussurite. TThis his type of throughoutt the type o f alteration a l t e r a t i o assemblage n assemblage has has also a l s o been been observed observed throughout h e eentire ntire prospect, but with Although the prospect, b u t is i s not n o talways always associated associated w i t h mineralization. m i n e r a l i z a t i o n . Although the majority m a j o r i t y of o f sulfide s u l f i d emineralization m i n e r a l i z a t i o nisi sbelieved b e l i e v e dtot obebeprimary, primary, mineralized mineralized zonest that f r a c t u r e d / a l t e r e dzones zonescan cancontain c o n t a i nsecondary secondary zones h a t are a r e intersected i n t e r s e c t e dby by fractured/altered sulfides Themmajority s u l f i d e s and and textures, t e x t u r e s , suggesting suggesting local l o c a lenrichment. enrichment. The a j o r i t y ooff the the sulfide (5 mm) and and commonly rimmed (5 mm) commonly rimmedby bysecondary secondary s u l f i d eitself i t s eisl f coarse-grained i s coarse-grained red-brown red-brown bbiotite. i o t i t e . IIlmenite l m e n i t e occurs occurs in i n two two habits h a b i t s within w i t h i nthese these zones, zones, as euhedral host rock, rock, and and as as ""bleb-like" euhedral tto o subhedral subhedral llaths a t h s throughout throughout t the h e host bleb-like" black shiny ddroplets within This second b l a c k shiny roplets w i t h i n the t h e sulfides. s u l f i d e s . This second i ilmenite l m e n i t e habit h a b i t has has only o n l y been been i identified d e n t i f i e d in i nsulfide s u l f i d ezones zones that t h a tare areenriched enriched in i nPd Pd and/or and/or Pt. Pt. References: Morton, P., A., 1987, PGE, Au and and Ag Ag contents contents of o f Cu-Ni Cu-Ni P., and and Hauck, Hauck, S. A., base o off tthe Duluth Complex, nnortheastern ssulfides u l f i d e s found at a t the t h e base h e Duluth ortheastern Minnesota: Natural ResearchI nInstitute, N a t u r a l Resources Resources Research s t i t u t e , Technical Technical Report Report NRRI/GMIN-TR-87-04, 85 pp. NRRI/GMIN-TR-67-04, 85 Morton, 1989, Precious Precious metals metals i in Morton, P., P., and and Hauck, Hauck, S. S. A., A., 1989, n the t h e copper-nickel copper-nickel Minn. Geol. ddeposits e p o s i t s of o f the t h eDuluth D u l u t hComplex: Complex: Minn. Geol. Survey, Survey, IInf. n f . Circ. C i r c . 30, 30. pp. 47-48. 47-48. pp. Severson, M. M. J., J., and S. A., 1990, Geology, geochemistry, and and and Hauck, S. A., stratigraphy of a portion of Partridge River s t r a t i g-r a p. h -y o f a p o r t i o n o f the the P artridge R i v e r IIntrusion, ntrusion, northeastern Natural n o r t h e a s t e r n Minnesota: ~innesota: N a t u r a l Resources RResearch e s e a r c h ~Institute, nstitute; Technical Report, NRRI/GMIN-TR-89-11, Duluth, Minnesota, Report, NRRI/GMIN-TR-89-11, Duluth, Minnesota, 240 240 pp. pp. _1 j = tMIT VII -J UNIT VI IMIT V CENERAUZED IGNEOUS GENERALIZED IGNEOUS $TRATCRAPHIC COLUMN STRATIGRAPHIC COLUMN UNIT IV UNIT fil I_____I UNIT UNIT I — —K — 111 UNIT I Insow ..,.— r_AL_.r 'H * qRNIA FOlIaTiON BIWASIC ON-FOlMAT1ON IIGC II WOAL C flc PRNIIGL PlYtI INTmITD a a,cn. zn oa s,.n—c a,... 1' j -A 46 �DRIFT PEBBLE LITUOLOGY DRIFT LITHOLOGY OF OF THE THETOMAHAWK TOMAHAWK ROAD ROAD AREA, AREA, LAKE COUNTY, MINNESOTA, MINNESOTA. USED TO HELP HELP INFER INFER LOCAL LOCAL BEDROCK BEDROCK John John C. C. Green, Green,Univ. Univ. of ofMinnesota, Minnesota,Duluth; Duluth;Ed. Ed.Venzke Venzke&&Tom TomLawler, Lawler,D.N.R. D.N.R. 1-libbing Hibbii Abstract In In 1989 1989 a multi-media, regional, geochemical geochemical orientation and andreconnaissance rewmaissance survey surveywas was completed completed for for a portion portion of of Lake Lake County, County, Minnesota. The Theresults resultsofofthis thissurvey surveysuggest suggestthat that three threeanomalous anomalouslocalities localities exist exist across also concluded that that the thegeochemical geochemicalsurvey survey reflects bedrock lithologies, lithologies, despite across the the project project area, area. It was also variable gladal glacial overburden overburden thickness thickness of of several several deposit deposit types types and and aacomplex wmplex depositional depositional history, history, (Buchheit (Buchheit et et al,, p. 1). 1). These These results were related to scale, "Geologic 'Geologic al., 1989, p. to the the geology geology as mapped by by Green on on the the 1:250,000 1:250,000 scale, Map of Harbors Sheet', of Minnesota, Minnesota, Two Harbors Sheet",(1982) (1982) but but the thecomplex complex pattern pattern of of geochemical geochemical results results made obvious obvious the need need for for aa more moredetailed detailedgeologic geologicmap mapto toassess assessthis thisrelationship. relationship. Traditional Traditional geologic geologic maps are are aa reflection reflectionof ofthe thequantity quantityand andquality qualityof ofavailable availablegeologic geologic information, information, which did not not provide computer which did provide the the needed needed detail. detail. Improved Improvedquality qualityof ofgeophysical geophysical surveys surveys and and sophisticated sophisticated computer enhancement techniques now provide provide the the means means to generate inferred geologic geologic maps. maps. For techniques now For accuracy accuracy and detail detail these maps provided in in Minnesota Minnesota by by an maps require require high high resolution resolution aeromagnetic aeromagnetic and and regional regional gravity gravity surveys, surveys, provided aeromagnetic survey survey funded funded by by the Legislative Commission on on Minnesota Minnesota Resources Resources (LCMR) (LCMR) and aa gravity Legislative Commission gravity survey by the the Minnesota Minnesota Geologic GeologicSurvey Survey(MGS). (MGS). Geologic interpretations interpretations made from remote measurements survey by measurements of properties are nseudo-Qeoloic mans. mans. of physical physical properties are known known as as pseudo-eeolo-ic As the practicality practicalityof ofthese these maps, maps,the theDepartment Department of ofNatural NaturalResources Resources (DNR) (DNR) contracted contracted A s a pilot test of the with private consultants to to interpret interpret geophysical geophysicaldata dataand andmake makemaps mapsinintwo twoareas. areas. One of the areas selected private consultants selected was was a four four township township block in the McDougal Lakes Lakes Area of of Lake Lake County, County, in the interior interior of of the the Duluth DuluthComplex, Complex, aa Proterozoic intrusivecomplex. complex. This This area was mapped by Robert Robert J. Ferderer, Proterozoiclayered layered maCic mafic intrusive Ferderer, Eagan, Eagan, Minnesota. Minnesota. Ferderer's Ferderer's pseudo-geologic pseudo-geologic map is much much more more detailed detailed than than its itspredecessor predecessor The TheTwo TwoHarbors Harborsgeologic geologicmap. map. Lithologic Lithologic units and structural features features are areconfirmed confirmed by by verification verification procedures procedures wherever wherever tested. In addition addition to to lithologic lithologic units and structural features features this this map map has hasthree threedimensional dimensional aspects aspects shown shown by depth to to magnetic magnetic source forward modeling modeling profiles. profiles. A portion of this map in the pebble count area is shown on source calculations and forward Plate Plate 3. 3. In feet deep, and there are In this this area area glacial glacial cover cover is is 00 to to 65 65 feet are some some outcrops, outcrops, but prior prior to to this this program program there drill holes, holes, with with there were were only only three three drill drillholes. holes. To T overify verifythe thepseudo-geologic pseudo-geologicmap mapititwas wastested testedwith: with: 1) Six drill lithologic loggingusing usingassays assaysand andthin thinsection sectionstudies; studies; 2) 2) Geophysical Geophysicalmeasurements measurementson onthe thecore; core; 3) 3) Ground lithologic logging geophysical traverses over overselected selected features: features;and and 4) till and and outcroo outcrop studies studies that that relate 4 ) Pebble Pebble counts wunts of glacial olacial till geophysical traverses lithologic observations to to geophysical geophysicalparameters. parameters. The h h & g k observations The pebble pebble count, count, thin thin section, outcrop studies, and drill core logging were done by, logging were by, or under the the direction direction of, of,John John C. C.Green Green(University (Universityof of Minnesota Minnesota - Duluth). The glacial drift Theu -nebble sed 1 countine technique used by byGreen Greenand andVenake Venzke(1990) ( 1 W )was was to to determine determineififglacial drih pebble pebble composition drift-covered areas. areas. A can be used to determine the the lithology litholoey of ofthe the underlying underlying bedrock in drift-covered A strip strip of of composition can sections sections was chosen along the the Tomahawk Tomahawk Road Roadwhere, &here,with withadditional addLtioLa1outcrop outcropmapping mappingand anddrill drillhole holelogging, log&& an an improved improved geologic geologic map could be made made to t oevaluate evaluatethe theresults resultsof ofthe thepebble pebblecounts wuntsand andthe thepseudo-geologic pseudo-geologic map. Although hole coverage. coverage. Bedrock Although some some contacts contacts are are poorly poorly constrained constrained due to gaps in outcrop and drill hole units gabbro and and troctolite troctolite of of the Bald Bald Eagle Eagle Intrusion, Intrusion, and and one one or two troctolite units of anorthosite, olivine olivine gabbro troctolite units were m a p ~ e dBased .Basedon oncounts countsofofthe the50 50largest largestpebbles nebblesinineach eachsample, sample.four fourlithologic litholodcdrift driftunits unitswere weremapped: maoned: were mapped. 1) 1) Troctolitic; ~roct&tic; 2) Transition Transition Zone; 3) 3) Anorthositic; ~northositic;and and 4) 4) Mixed Mixed Volcanic ~ o l & n i c(Plate 5). 5). In type, In general, the the most most abundant abundant pebble pebble type type in in these these samples samples corresponds corresponds to to the the underlying underlying bedrock rvoc. suggesting that this technique can be useful for"remotely for 'remotely sensing' types in in coveredareas. covered areas. However, suggesting that technique can sensing" bedrock bedrock types owe&; in the drift is dominated byby llthologies (Archean, the eastern eastern 1/4 1/4ofofthe thearea areathe the drift is dominated lithologies (Archean,Animikie, Animikie,Keweenawan Keweenawanlavas, lavas, granophyre) 10's of km) kin) from from the the E E,,ENE, ENE, or ESE. This granophyrc) that that have have been been transported for for long long distances (several 10' s of This must have been carried bedrock). Elsewhere clearly not not basal basal till till (directly (directly overlying bedrock). Elsewhere carried by by the Superior SuperiorLobe Lobeand andisisclearly in the 1 the study study area, area. ice transport transoort has has produced oroduced some some gradations madations or or transition transition zones zones in the drift pebble nebble assemblages, assemblaees. compared bedrock contacts. here) was wasprimarily compared to t othe thebedrock contacts.-,Also, since sinceglacial glacialtransport transportin inthe theRainy RainyLobe Lobe(dominant (dominanthere) roughly bedrock contact contact fanorthosite (anorthositeyvstroctolite), rouehly ~-a r a l l eto l the main bedrock troctoliteVthe thepebble nebbleassemblage assemblaeeat atany anvsample sarnole site site - . parallel may the technique will be may have have come come largely largely from from aa few fewkm km up-ice. ~ ~ - i c eThus . thetechnique'wiU be most most successful successful when the drift driftisis - .. 47 47 �1 relatively thin thin and to exclude the existence existenceof ofan anupper upper drift drift sheet that is is relatively and its its stratigraphy stratigraphy is is known known well well enough enough to exclude the sheet that not in in contact contact with with local localbedrock, bedrock,and and where where rock rock boundaries boundaries are arc at at large large angles angles to to ice ice transport transport direction, direction, not (Green and and Venzke Venzke 1990). 1990). Comparing results with with Fcrdcrcr's Fcrdcrer's map there is aa corrclativc correlative relationship relationship between between the the west west Comparing geochemical results contact area of of his his lb2 sb2unit unit and and high high geochemical geochemicalassays. assays.Th This unitisi5similar similarininareal arealextent extentto to the the dg dg unit unit on on is unit contact area thc Harbors Sheet. Sheet. Anomalous correlate with Ferderer's the Two Two Harbors Anomalous geochemical geochemical values values also correlate Fcrderer's fault faultzones. zones. Buchheit, R.L., R.L., Malmquist, "GlacialDrift Drift Geochemistry for Strategic Minerals; K.L. and and Niebuhr, Nicbuhr, J.R., J.R., 1989, 1989, "Glacial Geochemistry for Strategic Minerals; Buchhcit, Malmquist, K.L. Duluth Complex, Lake County, Minnesota",Minnesota MinnesotaDcpt. Dept.ofof Natural Natural Resources, Divisionof of Resources, Division Duluth Complex, Lake County, Minnesota", Minerals, Report 262. Minerals, 262. Green J.C. J.C. and and Vcnzke, Venzke, EA., ES., 1990, Lithology of of the Road Area, Area, Lake Green 1990, "DriFt "Drift Pebble Pebble Lithology the Tomahawk Tomahawk Road Lake County, County, Minnesota: Can Can itit be be Used Used to to Infer infer Local Dept. of Division Minnesota: Local Bedrock?", Bedrock?". Minnesota Minnesota Dent. of Natural Natural Resources, Resources, Division of Minerals, Minerals, part of of Report Report 290. 290. -I j J J * 00 ::::: a - J 'a. a... .-..t... ot 1" I. Plot. 3. "op of Outcrop. one Dclii Hal.. a,,d 'hair R.lolion.hlp I, ha A..o'aootI.c l'.l.rp..Iol,or. •dap *t (1*09) I C*O •t (AV.,fl. - 'no —-—"-.0-I. —.•ofral,_fl•!t'o — oo •'.I— .4 a.—. ' —. OOq S.. a_a.,, — V.. S.'! (aDI—a. .4 V.. w Ca.!" S.'—— •—'.°. •a" a' I.. a'.., V.' SO! .,, J J ,'w—......, •.•..,..a' •t. 593 t.. .v..l•, -I H j 1" Plate S. Wop of Sompl.. She—in2 the.. £saign.'a.n? IC Glacial Drill Unit.. CO So tao..... ISIC 48 1s9 �I I I I I I I I I I I I I I I - I I GROUND GROUND GEOPHYSICAL GEOPHYSICAL SURVEYS SURVEYS LEADING LEADING TO TO THE THE BEND COPPER-GOLD DISCOVERY BEND COPPER-GOLD DISCOVERY Jay Associates, Inc., Inc., Jay C. C. Hanson, Hanson,Ernest ErnestKK*. Lehmann Lehmann & & Associates, North, Minneapolis, Minnesota 55401 North, Minneapolis, Minnesota 55401 SUMMARY SUMMARY ' ' . . . . ,..,.,< 430 430 First First Avenue Avenue ,. . ... .~,.. ,~ The The initial initial ground ground geophysical geophysical surveys surveyswere were intended intendedto tofollow follow up up aa1977 1977 INPUT airborne electromagnetic (AEM) anomaly located in the Chequamegon INPUT airborne electromagnetic (AEM) anomaly located in the Chequamegon National Forest in • Wisconsin. National Forest in Taylor TaylorCounty County, Wisconsin. The The anomaly anomaly was was delineated delineated on on only only one one flight flight line. line. The The ground ground geophysics geophysics consisted consistedof ofhorizontal-loop horizontal-loop frequency electrornagnetics (HLEM) and total-field magnetics frequency electromagnetics (HLEM) and total-field magnetics profiling. profiling. Five Five north—south surveylines, lines, spaced spaced 400 400 feet feet apart, apart, were north-south survey were placed placed over over the the anomaly. on two of the anomaly. A A strong strong nonrnagnetic nonmagnetic conductor conductor was was encountered encountered on two of the central central lines, lines, suggesting suggesting the t h eoccurrence occurrenceof of aasteeply steeplydipping dippingmassive massive sulfide sulfide lens with short strike length. Subsequent drilling, which began with two lens with short strike length. Subsequent drilling, which began with two cored holes drilled on each of the surveylines, lines, verified verified tthe cored holes drilled on each of theanomalous anomalous HLEM HLEM survey he conductive source conductive source as as being being due duetotomassive massivechalcopyrite chalcopyritemineralization. mineralization. Assays The Assays of of core core samples samples indicated indicated the thepresence presenceofofore—grade ore-grade gold gold as a swell. well. The importance of ground geophysical follow-up over single-line or poorly defined importance of ground geophysical follow-up over single-line or poorly defined AEM anomaliescannot cannot be be overestimated. AEM anomalies overestimated. INTRODUCTION INTRODUCTION North—central Wisconsinhas has been been aa focal North-central Wisconsin focal point point for formassive—sulfide massive-sulfide exploration exploration since Copper initiated initiated aa large in the since Kennecott Kennecott Copper large exploration exploration program program in the late late led to 1950s. 1950s. They They were were originally originally led to the t h e area area because because of of favorable favorable outcrops outcrops (primarily (primarily in in Rusk Rusk County), County),new newvolcanogenic volcanogenicmodels, models,and andimproved improvedAEM AEM surveys in in particular particular were for the systems. The AEM AEM surveys systems. The were responsible responsible for the initial initial discoveries Flambeaudeposit depositand. and, to to aa major extent, the discoveries of of the the economic economic Flambeau major extent, the Further subeconomic Thornapple deposit, deposit, both subeconomic Thornapple both located located near near Ladysmith. Ladysmith. Further to to the the east, AEM exploration programs by the Central Wisconsin Joint Venture (Getty east, AEM exploration programs by the Central Wisconsin Joint Venture (Getty Minerals and Ernest • Noranda, Minerals and Ernest K. K .Lehmann Lehmann&&Associates) Associates). Noranda, and and Exxon Exxon led led to to the mid— the discoveries discoveries at a t Ritchie Ritchie Creek, Creek. Pelican Pelican River, River,and andCrandon Crandonininthe the mid- to to More recently, an exploration program funded by the Jump River late—1970s. late-1970s. More recently, an exploration program funded by the Jump River Joint Venture Resources), although Joint Venture (Chevron (ChevronUSA USA and andWisconsin Wisconsin Mineral Mineral Resources), although flown much earlier earlier by by the joint venture led to flown much the Getty-Lehmann Getty-Lehmann joint venture (CWJV), (CWJV), led to the the 49 �geophysical discovery of geophysical discovery of the the Bend Bend massive massive sulfide sulfide in in1986. 1986. In In 1990, 1990, Noranda Noranda announced its discovery Lynne deposit, discovery of of the thezinc—rich zinc-rich Lynne deposit, also also originally originally announced its delineated AEM. This delineated with withAEM. This paper paper will will discuss discuss the the sequence sequence of of geophysical geophysical events events that thatultimately ultimately led ledtotothe theBend Bendcopper—gold copper-gold discovery. discovery. DISCUSSION DISCUSSION The Forest in The Bend Bend deposit deposit is i s located located in in the theChequamegon Chequamegon National National Forest in Taylor Taylor County, 1 2 miles miles northwest northwest of of Medford. Medford. The airborne County, about about 12 airborneanomaly anomaly may may have at least have been been recognized recognized at least as as early earlyas as1974 1974when when National National Lead Lead Industries Industries conducted an AEM (INPUT)survey survey over over the the area. However, However, no no ground AEM (INPUT) conducted an follow-up was done, done, probably probably because because of of the the poor follow-up was poor quality quality of of the theanomaly. anomaly. At about the survey over the same same time, time, Kerr-McGee AEM survey over Kerr-McGee Corporation Corporation also flew flew an AEM the area area but, b u t , again, again,did didnot notperform performground groundgeophysics. geophysics. Later, in AMAX and in 1977, 1977,adjacent adjacent surveys surveyswere wereflown flownsimultaneously simultaneously by byAMAX AMAXobtained obtained CWJV. surveys detected CWJV. Both Both surveys detected the the Bend Bend massive massive sulfide. sulfide. AMAX prospecting permitsinin the the area area but, prospecting permits but, because because of of difficulties difficulties in in securing securing aa land land position, pursue exploration position, did did not not 'pursue exploration efforts efforts and and left left the the area area in in1978. 1978. The Getty—Lehmann jointventure venturedissolved dissolved in in 1983 when Getty ceased Getty-Lehmann joint 1983 when ceased mineral mineral Chevron Resources, Resources, which whichalso alsohad hadan aninterest interest in in the the exploration operations. operations. Chevron joint partner and joint venture, venture, became became the the major major partner and continued continued the the exploration exploration work work I t s ground ground geophysical geophysical program program began began through (JRJV). Its through a new new joint joint venture (JRJV). with andground groundmagnetics magneticssurveys surveys in in February, with HLEM HLEM and February, 1986, 1986. Five geophysicallines, lines, each each approximately approximately 5000 5000feet feet long, long, were were Five north—south north-south geophysical magnetics were were run run with positioned Ground magnetics with aa GeoGeoAEM anomaly. anomaly. Ground positioned over the the AiM No o metries at 50m e t r i c ~proton proton precession precession magnetometer magnetometer at 50- and and 100-foot 100-foot intervals. intervals. N residual could be be discerned discerned in in the residual anomaly anomaly could the vicinity vicinity of of the theAEM AEM response. response. MaxMin II HLEM HL.EM profilingwas wasalso alsoundertaken. undertaken. profiling MaxMin I1 A constant A constant600—foot 600-foot separation was was maintained maintainedbetween betweenthe the transmitter transmitter coil coil and and receiver separation receiver coil, coil, In-phase and and quadquadresulting in in aa penetration penetration depth depth of of about about 300-400 300-400 feet. feet. In-phase - rature components ofthe the vertical vertical secondary secondary field field were were recorded recorded for for three three rature components of The 444 444 Hertz Hertz data data are are shown shown in in profile profile frequencies atat100—foot intervals. The 100-foot intervals. A strong strong bedrock form in Figure 1. bedrock conductor conductor (up (up to to 93 93 mhos) mhos) was was defined defined form in 1. A The first first and 8W 8Wand andformed formedthe thebasis basis for for the the initial drilling. 4W and drilling. The on lines 4W on 50 -J �% PrIn..rp 10J .5J oJ 5J I0 SOUTH SOUTH FIGURE FIGURE11 2OOi. In— Phase In-Phase 0 200fl. ————. Out-of- Phase -.-. . HLEM HLEM Coil CoilSeparation Seporotlon • 600 600Feet Feet - --- NORTH NORTH LOO L4W L8W LI2W L 14W r— r- r r n r r— r— r— r BEND MAXMIN PROFILES PROFILES -444 444HZ HZ BEND MAXMIN r r r. r r ri r �two two holes, holes, drilled drilled in inOctober October1986, 1986,were werecollared collaredon onlines lines4W 4 W and and8W 8W and and intersected intersected aa thick thick massive-sulfide massive-sulfide conductor, conductor, now now known known as the the Bend Bend deposit. deposit. To copperTo date, date, 25 25 cored coredholes holes have havedelineated delineated 3.7 3.7 million million tons tons of of coppergold gold mineralization mineralization in two two zones. zones. Depending Depending on permit permit requirements, requirements, mining mining operations operations could could begin begin as as early early as a s1995. 1995. J j In In order order to toinvestigate investigatethe thepossibility possibilityofofthe theoccurrence occurrenceofofdeep deepmineralization mineralization along EM-37survey survey was was performed. Large— Largealong strike, strike,a large—loop a large-looptime—domain time-domain EM-37 loop systemsare are often often used used for exploring deep ore deposits. loop electromagnetic electromagnetic systems exploring deep deposits. At survey lines lines were were added, added, east east and and west of the At Bend, Bend, several several additional additional survey west of the original five-line with thethe EM—37 five-line grid, grid,and andsurveyed surveyed with EM-37 system. system. The The data data indicate both east east and indicate deep deep conductors conductors both and west west of of the the Bend Bend deposit, deposit, very very nearly nearly on strike strikewith with the theknown knownmineralization. mineralization. At At this this time time drilling drilling has has not not confirmed the results resultsofofthe the EM-37 survey. confirmed EM—37 survey. was detected detected by by aa single ItIt is is important important to to note note that thatthe theBend BendAEM AEM anomaly anomaly was single line spacing spacing used used during during the flight flight line line during during the the 1977 1977 survey. survey. The The nominal nominal line the high—amplitude survey was Considering that thatthe the high-amplitudeHLEM HLEM 114 mile mile (1320 (1320 feet). feet). Considering was 1/4 anomaly hasaashort short strike strike length length at at the feet), itit is anomaly has the subcrop subcrop (400+ (400+ feet), is fortunate fortunate If the the flight flight line line had had been been displaced displaced that the the deposit deposit was was detected detected at all. all. If slightly slightly to to the the east east or o rwest, west,the theresponse responsewould wouldhave havebeen been greatly greatlydiminishdiminishcomplicate ed, reducing reducing its its attractiveness attractiveness as asan anexploration exploration target. target. To complicate matters, conductors are are located locatedtoto the the north, north, northmatters, several several other other formational formational conductors northof these One of these was was drilled drilled shortly shortly after after the the initial initial east, and and southwest. southwest. One Several discovery of Bend and found to discovery of Bend and to be be conductive conductive graphitic graphitic argillite. argillite. Several holes, too responses along along strike strike with too shallow shallow to to test testthe theweak weakEM—37 EM-37 responses with the Bend conductor, were Bend conductor, were drilled drilled and and found found to to contain contain little little or or no no sulfide sulfide the geologic section containing containingthe the host host felsic felsic tuff tuff However, the geologic section mineralization. However, unit persists. Geophysical worki sis continuing continuingalong alongthe the Bend Bend volcanic volcanictrend trend in in aan n attempt attempt to to Geophysical work drilling southwest of Bend Bend has has shown that the locate locate sister sister orebodies. orebodies. Recent Recent drilling southwest of shown that the felsic tuff host host rock rock does feet at at least. felsic tuff does strike strike for for several several thousand thousand feet least. Ground Small geophysical worktotothe the northeast northeast suggests suggests similar similartrends trends in in that that area. geophysical work area. Small volcanogenic massive-sulfidedeposits depositssuch suchaas Bend usually usually occur occur in in clusters volcanogenic massive-sulfide s Bend clusters and undoubtedly result result in and continued continued exploration exploration will will undoubtedly in additional additional discoveries. discoveries. 52 j �CONCLUSION CONCLUSION Innorth-central north-central Wisconsin, Wisconsin, it is likely likely that that most massive-sulfide deposits will In it is most massive—sulfide deposits will be small, small, averaging averaging only only aa few fewmillion milliontons tons and will be geophysically expressbe and will be geophysically expressedas asshort—strike—length short-strike-length anomalies. anomalies. This may be a result of (1) primary ed This may be a result of (1) primary sulfide deposition, deposition, (2) ( 2 )structural structural complications. ( 3 ) conductive overburden, sulfide complications, (3) conductive overburden, ( 4 ) depth depth of ofburial, burial,and/or a n d l o r(5) ( 5flight—line ) flight-line orientation and location. There(4) orientation and location. ThereAEM surveys surveys should should be be flown flown with with 118-mile (660 feet) spacing. All fore.most most AEM fore, l/8-mile (660 feet) spacing. All single-line anomalies anomalies and subtle anomalies anomalies should should be be investigated with approsingle—line and subtle investigated with appro— priateground groundtechniques, techniques, ifi fpossible. possible. pilate El ,,-Over theyears yearsseveral severalAEM AEMexploration exploration programs were undertaken in o r Over the programs were undertaken in or For various reasons the Bend For various reasons the Bend AEM anomaly anomaly was not investigated. not recognized for i t s importance, not well AEM was not investigated, not recognized for its importance, not well defined or, o r , perhaps, perhaps, not not detected detected at at all. all. Whatever the reason, the discovery defined Whatever the reason, the discovery illustrates the need for persistence and thoroughness in in exploration, exploration, even if illustrates the need for persistence and thoroughness even if an area area has has been been looked looked at at before. before. Weak or poorly defined AEM anomalies or an Weak or poorly defined AEM anomalies or anomalies without direct magnetic magnetic support support should should always always be be considered considered for for anomalies without direct f u r t h e revaluation evaluation ififgeologic geologicconditions conditions warrant. warrant. further -^around the Bend Bend area area by bydifferent different companies. around the companies. 53 �GEOLOGY OF THE MERIDIAN AGGREGATES QUARRY AND AN0 THE SURROUNDING AREA, ST. ST CLOUD, MINNESOTA: MINNESOTA: A STUDY OF THE BEDROCK INFLUENCES ON THE PRE-LATE PRE-LATE CRETACEOUS WEATHERING CRETACEOUS WEATHERING PROFILE. PROFILE. John A. Hauck John J. Heine, Heine, Tom A. A. lath, Toth, and Steven A. Natural Natural Resources Resources Research Research Institute Institute of Minnesota-Duluth Duluth, MN 55811 Minnesota-Duluth Duluth, 55811 University George W. W. Shurr Shurr . . rtment of of Earth Department Earth Sciences Science St. Cloud State St. Cloud, Mn. State University University Mn. 56301 56301 The The Meridian Meridian Aggregates Aggregates Quarry Quarry in in St. St. Cloud, Cloud, Minnesota Minnesota contains contains aa complex complex group group of of metamorphic metamorphic and and igneous igneous rocks. rocks. Residual clays clays overlie overlie the the bedrock bedrock in in some some areas areas of of the the quarry. quarry. The The focus focus of of the the study study is is to t o relate relate the the composition composition and and physical physical characteristics characteristics of of the the parent rocks to the overlying residual clay 1:1200, in in clay deposits. deposits. The quarry has has been mapped at at aa scale scale of of 1:1200, order order to to give give sufficient sufficient control control of of the the geology geology and and structural structural characteristics. This information has been characteristics. information has been linked linked with with information information from from regional studies studies to t o better better understand understand the controls controls on clay distribution in in the the St. St. Cloud Cloud area. area. Because Because the the composition composition of of the the parent parent rock rock is is a critical factor factor in in the the composition composition of of the the clays clays that form during weathering, detailed mapping of of the rock Five major rock types rock types types in in the the quarry quarry was was critical. critical. Five major types have have been been mapped: 1) 1) aa dark metamorphic metamorphic rock rock type, type, 2) 2) gray gray reformatory reformatory granite, granite, 3) 3) St. St. Cloud Granite, 4) mafic mafic dikes, dikes, and and 5) 5) a porphyritic porphyritic rhyolite rhyolite dike. dike. The The Granite, 4) dominate rock rock type type in in the the quarry quarry is is the the dark dark gray gray metamorphic. metamorphic. All All of of the the rock i n the the western quarry wall wall where residual clays clays have have rock types types can can be be found found in developed developed on on them. them. The The most most important important physical physical characteristic characteristic related related to t o the the formation formation of of the the residual residual clays clays is is the the presence presence of of faults faults throughout throughout the the quarry. quarry. Many of of the the residual residual clay clay occurrences occurrences in in the the St. St. Cloud Cloud area area are are found found in in linear linear bedrock bedrock lows. lows. Work Work in in the the Meridian Meridian Aggregates Aggregates Quarry Quarry shows shows that that the the residual residual clays clays are are found found in in bedrock bedrock lows lows along along fault fault traces. traces. This This conclusion conclusion is is based based on bedrock bedrock and and drill drill hole hole information information from from the the quarry. quarry. In the quarry quarry area, area, glacial glacial deposits deposits rest rest directly directly on on bedrock bedrock or or the the residuum. residuum. Any Any overlying overlying residual other areas residual clays that may have developed developed in in other areas of the quarry, would would have been removed prior to or during glaciation, leaving pockets of of residuum residuum in bedrock bedrock lows. out1 ined lows. Three Three major major structural structural features features in in the the quarry were were outlined by mapping: 1) an an east-west east-west trending trending fault fault zone zone on on the the north north wall wall of the the mapping: 1) quarry; 2) a central, central, northeast northeast trending trending fault fault zone; zone; and 3) 3) a western, western, quarry; 2) northwest northwest trending trending fault fault zone. zone. The The deepest clay clay formation formation in in the the quarry quarry is is associated the the northwest northwest fault fault zone. zone. Drill Drill hole hole information, information, provided provided by by Meridian Aggregates Aggregates outlines the extension extension of this zone outside the the active active quarry quarry area. area. In addition, addition, the the drill drill hole hole information information locates locates the the deepest deepest clay clay development development near near where where the the northwest northwest fault fault zone zone an an the the east-west east-west fault fault zone zone are are thought thought to t o intersect. intersect. Other northwestern trending, residual residual clay clay filled filled bedrock bedrock lows, lows, have have been been identified identified to to the the northeast northeast and and southwest, southwest, which which correspond correspond with with linear linear features features visible visible on on high high altitude altitude photos. photos. 54 j J j j �The residual sidual clay clay deposits deposits ininthe theMeridian Meridian Aggregates Aggregates Quarry Quarry vary vary in in grade rade both both vertically vertically and and horizontally. horizontally. The residual residual clays clays vary vary from from The kaolinite-rich aolinite-rich to t o chiorite-illite-rich chlorite-illite-rich horizontally. horizontally. This This variation variation in in clay clay grade rade appears appears to to be be controlled controlled by by the the distribution distribution of o f the the bedrock bedrock composition. omposition. The The kaolinite-rich kaolinite-rich residual residual clays clays are are located located above above the the St. St. Cloud loud Granite Granite and and the theporphyritic porphyriticrhyolite rhyolitedike. dike. The The amount amount of of chlorite chlorite and and illite llite increases increases in in the the dark dark metamorphic metamorphic rocks rocks and and the the gray gray reformatory reformatory granite, ranite. and and is is dominate dominateininthe theresidual residual material material above abovethe themafic mafic dikes. dikes. The The depth epth of of weathering weathering also alsovaries varieshorizontally, horizontally, and and is is controlled controlled by by the the northwest orthwest trending trendingfault faultzone. zone. The The residual residual clays d a y s are are deepest deepest in in the the center center off the the fault fault zone, zone, and and thin thin to to the thenorth north and and south, south, away away form form the the fault fault zone. zone. The +hornblende he vertical vertical variation variationisisincrease increasequartz quartzfeldspar, feldspar,and andbiotite, biotite, ±hornblende with with depth depth in in residuum residuum above above the the granitic granitic and and metamorphic metamorphic rocks. rocks. The The increase increase in in these these minerals minerals is is consistent consistent with with decreasing decreasing chemical chemical weathering weathering effects effects with with depth. depth. 55 �Isoclinal IsoclinalSlump-folds Slump-foldsininthe theLower LowerPokegarna Pokegama Ouartzite: Quartzite: Evidence Evidence for for Seismicity Seismicilyand andSlope Slope Instability InstabilityDuring DuringDeposition Depositionof ofthe theAnimikie AnimikieGroup Group Hemming, Hemming. S.; S.; Hanson, Hanson,G.N.: G.N.; McLennan, McLennan.S.M.; S.M.; Sharp. Sharp,W.D., W.D., State StateUniversity Universityof ofNew NewYork Yorkat atStony Ston Brook, Brook. Stony Stony Brook, Brook, NY NY 11794 11794 The basement of of the the Superior The Early EarlyProterozoic ProterozoicPokegama PokegamaQuartzlte Quartziteoverlies overlies Archean basement Superior Province Provincein in the Minnesota. Its constrained by is constrained by geologic geologic the northwestern northwesternpart partof ofthe theAnimikie Animikie Basin, Basin, Minnesota. Its age age is relationships [I ,2,3] and and Pb Pbisotope isotopedata data on on detrital detrital and cross-cutting cross-cutting quartz quartz [4] [4] as asbetween between2.17 2.17 relationships[1,2,3] and 1.95 Ga. The depositional environment of the very fine grained, lower Pokegama and 1.95 Ga. The depositional environment of the very fine grained, lower PokegamaOuartzite Quartzitehas ha been on the the nature nature of of crossbedding crossbedding in in the the sandy sandy middle middle Pokegama Pokegama beeninterpreted Interpretedas as tidal tidal flat, flat. based on Quartzite to the the better better exposed exposed Palms Formation in Quartzite and and suggested suggestedcorrelation correlationand and similarity similarity to Palms Formation in Wisconsin Wisconsin[51. [5]. The Thesoft softsediment sedimentdeformation deformationwe we recognize recognizein in the the lower lower Pokegama, Pokegama. mostly mostly tight tight to t isociinal isoclinalfolds foldsand and refolded refoldedfolds, folds, may may provide provideimportant importantinformation informationconcerning concerningtectonic tectonicactivity activityinil the theAnimikie AnimikieBasin Basinduring duringthis thistime timeinterval. interval Abundant olds can can be be found found In inthe the only onlywell-exposed well-exposedoutcrop outcrop in in the the lower lower Abundant evidence evidence for for slump-f slump-folds north of of Eveleth, Eveieth, MN. MN. The Pokegama PokegamaQuartzite Quartzite(Figs. (Figs.1-6). 1-6). ItIt is is located located immediately immediately north The outcrop outcropis is approximately approximately500 500ftftlong longand and5-8 5-8ftft high. high. ItIt is is characterized characterized by by interbedded interbeddedsiltstones siltstonesand andargillites argillites with thick). Folding with numerous numerousthin, thin, fine fine sandstone sandstone layers layers (up to several inches thick). Foldingisisgenerally generallyvery very tight tight to toisoclinal, Isoclinal,and andrecumbent recumbent(Fig. (Fig.7), 7).and and these these characteristics characteristics are suggested suggested by by Farrel Farrel and Eaton Eaton [6] [6] to toindicate: indicate: 1) 1) long longdistant distanttransport transportof ofthe theslumps slumpsand and 2) 2) a a southeasterly southeasterlypaleoslope, paleoslope,consistent consistentwith withprevious previousinterpretations interpretationsof ofshoreline shorelineposition position15.7][5,7]. Figures from field field photographs, photographs, of of some someof ofthe thefold foldnoses. noses. These Figures1-6 1-6 are line drawings, from These folds folds addition to correspond correspondto totype type33refolded refoldedfolds, folds,defined definedby byRamsay Ramsay[8,6,9]. [8,6,9]. In In addition to the the numerous numerous isoclinal isoclinalfold fold noses, noses,shear shearsurfaces surfacesand and at at least least one one sheath fold indicate indicate substantial substantialhorizontal horizontal displacement displacement[6.10]. [6,10]. The The Pokegama PokegamaQuartzite, Quartzite,as aswell well as as the the Biwabik BIwabik and and Gunflint Gunflint Iron-formations, Iron-formations,are arehere hereinterpreted interpreted to tohave havebeen beendeposited depositedin inaa tectonically tectonicallyactive active basin. basin. This Thisinterpretation interpretationisisbased basedon: on: 1) evidence for for soft-sediment deformation in in the the lower lower Pokegama Pokegama Quartzite Quartzite (this (this study); study): 1) evidence soft-sediment deformation 2) deformation, observed observed in the Biwabik Iron-formation: 2) evidence evidence for soft-sediment deformation, in the Wwabik iron-formation; 3) 3) presence presenceof of early early brecciation brecciatton[11] [ l l ] and andisoclinal isoclinalfolds foldsin inthe the Gunflint Gunflint Iron-formation Iron-formationin inOntario: Ontario; 4) great just below below the the contact contact with with the the Biwabik, in the easterr eastern great variation variation in in facies of the Pokegama just Mesabi comm., 1990): Mesabi district district (Ron (Ron Graver, Graver, per. comm.. 1990); and and 5) and Wwabik Biwabik Iron-formation Iron-formation across a of the the Pokegama Quartzite and 5) sudden sudden change change in in thickness thickness of presumed presumedfault fault in inthe theeastern easternMesabi Mesabidistrict district[12). [12]. Strike-slip Strike-slip faulting faulting in in the the region region north northof of the the Animikie Animikie Basin Basin at about 1.95 1.95 Ga has been been documented documents by of pseudotachylite pseudotachylitein inthe the Rainy RainyLake-Sein Lake-SeinRiver River fault fau by Peterman Petermanand and Day Day [13] [I31using usingRb-Sr Rb-Sr dating dating of system. They associated with with one of the Early Theyinterpret interpretthe thefaulting faultingto tobe be aa result result of stresses associated Early Proterozoic, the Penokean. Penokean,as asdescribed described by by Hoffman Hoffman [14]. [14]. The Proterozoic, circum-Superior circum-Superiororogens, orwens. including including the The shales and turbidites turbidites of the Virginia and Thompson Formations, which form the upper part of the of Thompson Formations, which form the Animikie deposited in foreland basin associated associated with the Animlkie Group, Group, are are interpreted Interpretedto l o have have been been deposited In a foreland Penokean Orogen [1]. Penokean Oroaen 111. Understanding Understandinathe thetectonic tectonicsetting seninaof of the the Animikie Animikie Basin Basin prior prior to to turbidite turbidite deposition depositionclearly clearlyhas has important importantimplications implicationsfor for understanding understandingthe the Early Early Proterozoic Proterozoichistory historyin inthe the Great Lakes Region. The location of the Animikie Basin across the Great Lakes tectonic zone 1151, Great Lakes Region. The location of the Animikie Basin across the Great Lakes tectonic zone 1151, and between the the Superior Superior Province Province and and the the and the location location of of Penokean Penokeanmagmatism magmatism generally between - - 56 .. - J - .J j �MinnesotaRiver River Valley Province Province makes makes the sedimentary rocks rocks within withinthe the Aninilkle AnImIMebasin bask)important Important Minnesota the sedimentary for ofofthe forevaluating evaluatingthe thenature natureand andlocation location thepre-Penolce,an pra-Penokeancontinental continentalmargin. margin. An Anoblique oblique extenstonalsetting, setting,either eitherdrtven drivenby byor orassociated associatedwith, wfth,strike strikesup slipfaulting faultingIsIssuggested suggestedas as aa woiidng working extensional model modelfor forearly eaW Animikie Anhlkle Group Group deposition. deposition. Such Suchaasetting settingcould couldbe beassociated associatedwfth withthe thepassive passive margin ofaaback backarc arcbasin basin(such (suchas asseen seenbetween betweenJapan Japanand andChina, China,and and consistent consistentwith withthe the marginside sideof Interpretationof of Van Van Schmus Schmus [161 (161 and The time time Interval Interval for fortectonic tectonicactMty activity interpretation and Southwick Southwlck et ata/. at (11). [1)). The during duringdeposition depositionofdthe thePokegama PokegamaOuartzite Quartzitemay maybe beconstrained constrainedbetween between2.17 2.17 and and1.95 1.35 Ga. Ga. The The 1.95 Pb-Pb age Is is from from quartz gash gash veins veins in Inthe the upper upper Pokagama Pokegama Quartzite. Quartzite. Additional Additional age Ga Pb-Pb age 1.95 Ga constraintsfor for pseudotach,lltes pseudotachylitesand andquartz quartzveins veinsin Inthe thebasement basement and and sedimentary sedimentary rocks rocks of of the the constraints region, region. in Inconjunction conjunctionwith withan anunderstanding understandingof of their their kinematic kinematic significance, significance, may may lead lead ltoo important Important further onthe theearly earlyevolution evolutionofofthe theAnimikie AnimikleBasin. Basin ' furtherconstraints constraintson References: MN Geol. 37; [2) References: (1) (11Southwlck, Southwick, D.L D Letat, eta/..1988. 1988, MN Geol.Sur., Sur.,Report Re&; ofofInvestigations lnve Southwlck, Day. Southwick.0.L, D.L.and and Day,W.C.. W.C.. 1983, 1983.Can. Can.Jour. Jour.Earth EarthSci..v.20.p.622; Scl.,v.20,p.622; (31 [3] Hanson, G.N., and Malhotra, Geot. Soc. Soc. America Bull.. Bull., v.82.p.1107v.82.p.1107: 141 [4) Hemming Hemming et R., 1971, 1971. Ged. et al, at.,1990, 1990.EOS, EOS. Malhotra. R., v.71 .p.654;151 (51Ojakangas, Ojakangas.R.W..1983. R.W..1983. Geol. Geol. Soc. Soc. America America Mom. Mem. 160. 160. p.49; p.49; [6] (61Farrel, Farrel,S.G., S.G., and and v71p.654; Eaton, [7) Morey, Eaton.5,1987, S..1987.Geoi. Ged.Soc. Soc.Spec. Spec.Pub, Pub.no no29; 28; [71 Morey,G.B.,1972, GA.1972,MN MNGeol. Geol.Sur. Sur.Centennial CentennialVol; Vol: [SI Folding and 181Ramsay, Ramsay. J.G.,1967, J.G..1967. Folding and Fracturing Fracturingof of Rocks. Rocks. McGraw-Hill, McGraw-Hill.New NewYork; York;[9) (91Rarnsay, Ramsay,J.G., J.G.. and andHuber, Huber,M.i., M.I.. 1987, 1987.The The Techniques Techniques of of Modem ModemStructural StructuralGeology, Geology.v.2, v.2.Folds Foldsand andFractures. Fractures, Academic J.R.L, 1982, AcademicPress; Press;110) [lo) Allen, Alien. J.R.L. 1982. Sedimentary Sedimentary Structures, Structures. Their Their Character Characterand andPhysical Physical Basis, Franklin, J.M. Basis, 0ev. Dev. in in Sod Sed. 306, 306. Elsevier; Elsevier; till (11) Franklin, J.M.eta!, era/,1972, 1972.IGC IGCField FieldExcursion Excursion034; C34;[12) [I21 Gundersen, and Gundersen.J.N., J.N.. and andSchwartz, Schwartz,G.M.,1952, G.M.,1%2. MN MNGod. Geol.Sur. Sur.Bull. Bull.43; 43;(Peterman, [Peterman.Z.E. Z.E. andDay, Day,W, W., 1989. Geology. Geology. v.17,p.1089; v.17.p.1089; [14) (14)Hoffman, Hoffman.P.F., P.F.. 1988, 1888.Ann. Ann. Rev. Rev.Earth Earthand andPlan. Plan.Sd, Scl.v.16,p. v.16.p.543; 543; [15) Sims, Van ims.P,K P.Ketetai.. al..1980, 1980,Geol. Ged.Soc. Soc.America AmericaBull., Bull..v.91,p.690; v.91.p.690; [16) [I61 VanSchrnus, Schmus,1976, 1976.Phd. PM. Trans. .R. R.Soc. Soc.Lond..v280,p.605. Lond..v280.p.605. - —E:c — 'a. C - - - -a a Fig. of converging converging fold Fig.11Relatively Relatively large large area of fold features. features. HeartHeartshaped asas shapedsand sandbody bodyand andelongate elongaterefolded refoldedfold foldare areInterpreted Interpreted type type33refolded refoldedfolds foldsofofRamsey Ramsay[81. (81. Note Notethe thefanning fanningcleavage cleavageinin the theargiilfte, argillite. between betweenthe the refolded refolded folds. folds. Hammer Hammerfor forscale. scale. 57 �Fig. 3 Fold Fold nose nose with with several sandy sandy layers layers that that are are thickened thickened in Fi9.3 pair of of fold fold noses. noses. Hinge one (labeled) clearly visible visible on on Fig. 2 AA pair the and thinned thinnedto toboudinaged boudinagedon onthe thelimbs. limbs. The The box box possible to tell if the nose on the right the nose noseto to the theleft. left. It is not possible right the hinge and the approximate location location of Fig. left of drawing. Non..... Fig. 4. N< drawn on this figure is the is refolded. Note Notescale scale bar bar at lower left scale bar at lower left of drawing. — Fig. 44 Detail Detail of of Fig. Fig.3.3. Note thinning to separation limbs separation of the limbs and thickening thickening in the hinge of the sandier layer. in — J - ——a— C— — ----t=_ -. — — --—s— —,-— — — = —4 a -2CM - Recumbentisoclinal isoclinalfold. fold. Lower limb is thinned thinned and Fig. 66 Recumbent quite disrupted. disrupted. Note bedding is quite Notescale scale bar bar at lower lower left left of drawing. drawing. 58 j Fig. 55 An An early earlytight tight fold fold refolded refolded by by a a later later tight tight recumbant recumbant ffold. Fig. Note scale scale bar bar at at lower lowerof ofdrawing. drawing: Note Fig. Stereoplot of of fold fold hinges in in the the Lower LowerPokqama. Pokegama. The ~ i g7, Stereoplot plane representing the approximate attitude of bedding at th6 the @ane the approximate attiiude of bedding outcrop is also plotted (1]. outcrop is plotted [I]. �Magmatic Evolution in in the Magmatic Evolution the Midcontinent Midcontinent Rift: Rift: Evidence Evidence from from Hypabyssal Rocks Rocks of of the the North North Shore Shore of of Lake superior Lake Superior Hypabyssal Eric A. Jerde Jerde Department Angeles, CA 90024 Earth arid and Space Sciences, Sciences, University of California, Los Angeles, 90024 Department of Earth The hypabyssal dikes dikes and sills sills of northeastern northeastern Minnesota associated with the 1.1 1.1 Ga Midcontinent Rift are aa suite suite of rocks rocks distinct distinct from from the the flows flows of the the North North Shore ShoreVolcanic Volcanic Midcontinent Rift are provide valuable are far far less less significant significant volumetrically, volurnetrically, they provide valuable Group, and although although the the dikes dikes are information about processes operating operating during during rifting. In general, general, the diabase diabase is is ophitic, ophitic, with with pyroxenes pyroxenes 1-3 1-3 cm cm across across containing containing varying varying plagioclase and olivine chadacrysts. Exsolution are amounts of enclosed plagioclase Exsolution features featuresin in pyroxene pyroxene are common, but do not dominate the grain population. In In aa few samples, samples, coarse coarse symplectites symplectites are are present, with blebby oxides within the pyroxene. Some Someof of these these symplectites symplectitesdisplay display exsolution lamellac Thisisisevidence evidencethat that the the oxides oxides and and pyroxene pyroxeneformed formed lamellae in the pyroxene. This comagmatically, and not not simply simply as an alteration of a pre-existing phase phase such as olivine comagrnatically, and olivine since since exsolution features are unlikely to form in alteration products. exsolution features are unlikely to form in alteration products. Plagioclase as laths laths and and fragments fragments formed during rapid cooling, cooling, Plagioclase is is present mainly mainly as although a small number of phenocrysts phenociysts are usually seen. These are not large These are not large (usually (usually <2 mm), and many display display prominent pits pits and and dusty regions, interpreted as resorption features resulting resulting from from rapid decompression. decompression. Such Suchan anorigin originhas hasbeen been suggested suggestedfor forsimilar similarfeatures featuresin in plagioclase the Rio Rio Grande Granderift rift (Lipman, (Lipman,1969), 1969),and and the the southern southernRocky RockyMountains Mountains plagioclase from from the (Doe et al., aL, 1969). Plagioclase compositions compositions range rangefrom fromlaths lathsand andchill chillfragments fragmentsofofAns<,.;, An5n, to phenocryst cores coresup upto toAnon. An. The Thephenoczysts phenocrystsoften oftenhave have rims rimsof of the the "chill" composition, and a few are are complexly complexly zoned. zoned. Olivine up to to 33mm, rnm,and andoccasional occasional Olivine occurrs occwrs as as fine fine disseminated disseminated grains, grains, glomerociysts glomerocrystsup up to to 1 1cm. cm. It is generally generally unzoned, unzoned,with withcompositions compositionsmainly mainlybetween betweenFom Fo and " oikocrysts up Fop. Oxides PoTT). Oxidesmake makeup upaafew fewpercent percentof ofall allsamples, samples, most most being <1 mm across. Both Both ilmenite ilmenite and spinel phases are present, and most grains display some oxyexsolution features. thermometiy (Table 1) performed performed on on plagioclase plagioclase and and pyroxene pyroxene gave gave crystallization Mineral thermometry of 1000 1000-- 1150°C. 1150°COxides Oxidesyielded yieldedtemperatures temperaturesbetween between 850°C 850eCand 1000°C, 1000°C temperatures of and oxygen fugacities QEM buffer, buffer, which are consistent fugacities approximately one one log unit below the QFM with results from the Portage Lake klcanics Volcanics (Paces, (Paces, 1988). Oxide Oxide phases phases re-equilibrate re-equilibrate rapidly with aa cooling cooling liquid, liquid, and thus the temperatures obtained for the oxides are probably best interpreted as as near-solidus temperatures. The Theoxygen oxygenfugacities fugacitiesindicated indicatedare areconsistent consistent (1990) for the evolution of the Sonju Lake intnision, intrusion, also with the modelling by Miller et al. (1990) which QFM. which produced produced the the best best results resultswhen when using using oxygen oxygenfugacities fugacitiesone onelog logunit unitbelow belowQEM. The The chilled chilled margins were were analyzed analyzed by INAA INAA and microprobe microprobe fused bead techniques techniques for chemistry. Modelling bulk chemistry. Modellingof offractionation fractionationwas was done done using the CHAOS program (a more 59 �gdms core qthna core gene core C) Cl a 2 + 4 3 + 4 5 + . + 6 7 . 0 + 8 13 9 10 11 I3RD fract. (I atm) 12 Silver Ray intrusions 47th Avenue Sill Lester River Sill BRD C LL L. L... —15.0 860 plagiociase —13.0 961 I Cl Là C Là S 2 • -o 6 7 8 9 l0 II 12 0 000 I' 0° oa° 0 a C 0 4 5 6 sj a • 8 MgO (%) 7 9 10 1,111 L1 0 .0 0 Iii 1! 12 BRD.5..2-.5 BRD.5-o..5 I3RD 0-0-0 Thisstudy Otlierdikes 13 - - 3 4 5 6 8 tVlgO (%) 7 9 10 II 12 Dingnim showing I-aim models and hypabyssal rocks. ('Other dikes" from Green et al., 1987) 3 0 00 'I' 1,1,1,1 0 • L_ [ hypahyssal rocks. L L L_ Fig. 3. Diagram showing possible frnciionnlion pnlhs for nil 1. 0 __ Fig. S 6 MgO (%) Eli Cl a 1150 ± 50 Fig. 2. Dingtnm showing hypabyssal material matching I-atm model. (Silver Ray intnisions from Shank. 1990; 1. Miller, pers. Comm.; 47th Avenue SiU from K. Seifert, pert Comm. 5 6 7 S 9 10 11 12 —14.8 10 —12.3 9 11 1o2 12 7 853 990 1- Oxide 1000 (1150 9 5kb) 1050 ± 50 1100 ± 50 "gdm&' — groundmaea 1138 1126 1066 1192 1245 1236 1064 1015 1009 1065 a3oTtJ 1194 1156 1211 1192 dfl Pyrox.n. geoth.riaom.ter results. Piagiociaee Mineral Temperatures in °C. P—S CL—i HP—i BR—i P.R—i SB—i tsijtj& Tale i. LJ L LL. r 0 __ L �recent version of TRACEFOR TRACE.FOR described described by Nielsen, 1988a,b). 1988a,b). One Oneatmosphere atmospheremodelling modelling (Fig. 1) 1) shows shows that the the majority majority of of the thehypabyssal hypabyssalrocks rocksformed formedatatmoderate moderatepressures pressureswhere where the onset of pyroxene crystallization pyroxene stability stability at atdepth. depth. This crystallization is earlier due to greater pyroxene earlier earlier ciysta]iization crystallization results results in in the the earlier earlier depletion depletion of Ca, Ca, leading to the offset of the data from the model trend. trend. A Anumber numberof ofhypabyssal hypabyssalrocks rocksshow showevidence evidenceof fractionation fractionation at near surface surface levels levels (Fig. 2), 2), falling falling on on the the model model trend. trend. It is possible through polybaric fractionation It is possible through polybaric fractionationto torelate relateall allof of the the varied varied hypabyssal hypabyssal rocks rocksto to aa single primary parent, the high-Al "primitive olivine tholeiites," which are a common single primary parent, the high-A1 "primitive divine tholeiites," which are a common composition compositionamong among the the volcanic volcanic rocks rocks associated associated with with the Midcontinent Rift. In In such suchaa scenario, sw&ho, aa primitive primitiveolivine olivinetholeiite tholeiitemagma magmacrystallizes crystallizesol+plag+pyx ol+plag+pyxatatdepth depth(—10 (-10 kb?), kb?), driving the composition to lower Ca and Mg (BRD in Fig. 3). Continued fractionation driving composition to lower (BRD Continued fractionation at depth depth could could lead lead to to compositions compositionssimilar similarto tothe theSonju byMiller Milleretetal. al. SonjuLake Lakeparent parentproposed proposedby (1990). (1990). IfIfaathe themagma magmaofofBRD BRDcomposition compositionisisinjected injectedtotoananintermediate intermediatedepth depth(—3-5 (-3-5 kb?), kb?), the the crystallizing crystallizing assemblage assemblagewould would lose lose pyroxene pyroxenedue due to to shrinkage shrinkage of the pyroxene stability field, field, and and the the ol+plag ol+plagcrystallization crystallizationwould wouldcarry canythe theliquids liquidsto tolower lowerMg Mg(point (pointBBin inFig. Fig.3), 3), where againcrystallize, crystallize,and andthe the liquid liquid compositions compositions then then migrate migrate down down in in where pyroxene pyroxene would would again Ca, along the trend trend seen seen by by many many of the the hypabyssal hypabyssal rocks rocks (toward (toward C in Fig. 3). IfIfsome some liquids surface regions, regions, pyroxene pyroxene liquids of BRD BRD composition compositionwere were actually actually injected injectedto to near near surface crystallization crystallization could could be be delayed delayedeven evenfurther, further,and andthe theliquids liquidswould would follow followthe thetrend trend shown shownin in the modelling for 1-atm 1-atm pressure (toward D in Fig. 3). Sills Sills such such as as the Lester River and 47th 47th Avenue are in this group, as are the Silver Silver Bay intrusions. In Inreality, reality, there there can can of of course coursebe be many cross cross trends, but the the overall overall picture picture of multi-level multi-level fractionation fractionation is apparent. The The resorption resorption features featuresseen seenin in the the plagioclase; plagioclase;evidence evidencefor forevolution evolutionat at various variouslevels levelsin in the crust, are consistent process. The Thechemical chemical consistent with the chemistry, which suggests the same process. similarity alsoevidence evidencefor for lateral communication among among similarity among among samples samplesof of the the entire entiresuite suiteisis also chambers chambers for for great great distances distances along along the the rift. rift. These Thesetwo twoprocesses processeshave havebeen beeninferred inferredfor forthe the Mid-Atlantic rift in Iceland, which indicates that some modem rift processes were occurring Mid-Atlantic in Iceland, which indicates that some modem rift processes were occurringatat 1.1 Ga. Ga. References: References: Doe, Doe, B.R., Lipman, Lipman, P.W., P.W., Hedge, Hedge, C.E., C.E., and and Kurasawa, Kurasawa,II. H.(1969). (1969).Contributions Contributionsto to Mineralogy and Petrology, 2 1, 142-156. 142-156. Green, J.C., J.C., Bornhorst, Bornhorst, Ti., T.J., Chandler, Chandler,V.W., V.W., Mudrey, Mudrey, M.G.J., M.G.J., Meyers, Meyers, P.E., P.E., Pesonen, Pesonen, L.J. and Wilband, J.T. (1987) In: Mafic dyke swarms (Halls, R.B. and and Wilband, J.T. (1987) In: Mafic dyke swarms (Halls, R.B. andFahrig, Fahrig,W.F., W.F., ed.), 289-302. cd.).Geological GeologicalAssociation Associationof of Canada CanadaSpecial SpecialPaper Paper34, 34,289-302. Lipman, America Bulletin,80, 80, 1343-1354. Lipman, P.W. P.W.(1969). (1969). Geological GeologicalSociety Society of ofArnericaBulletin, 1343-1354. Miller, J.D., Jr., Schaap, B.D. and Chandler, V.W. (1990). 36th Miller, J.D., Jr., Schaap, B.D. and Chandler, V.W. (1990). 36thAnnual AnnualInstitute Instituteon onLake Lake Superior Geology, 66-68. Superior 66-68. Nielsen, R.L. (l988a) Acta, 552, (1988a)Geochimica GeochimicaaetCosmochimica CosmochimicaAda, 2, 27-38. Nielsen, R.L. (1988b) Computers and Geosciences, 14, 15-35. (1988b) Computers Geosciences, 1 4, 15-35. Paces, University, Houghton, Houghton, 413p. 4l3p. Paces, J.B. (1988) (1988) Ph.D. Ph.D. dissertation, dissertation,Michigan MichiganTechnological Technological University, Shank, S.G. (1990) M.S. thesis, University of Minnesota, Minneapolis, l3Op. thesis. University Minnesota, Minneapolis, 130p. 61 �SURFACE EXPRESSION EXPRESSION OF SURFACE OF MAJOR MAJOR BEDROCK BEDROCK STRUCTURAL FEATURES FEATURES JamesS.S. Johnson, Johnson,Denise DeniseA.A. Slavish, Stavish, Mary James Mary K. K. Tozer, Tozer, and and George George W. W. Shurr Shurr Departmentofof Earth Earth Sciences, Sciences, St. St. Cloud State University, University, St. Department Cloud State St.Cloud, Cloud,MN MN 56301 56301 Continental lithosphere lithosphere in in Minnesota subdividedinto intoaaseries seriesoof strucContinental Minnesota isissubdivided f structural blocks plate tural blocksbounded bounded by by fault faultzones zonesthat thatare arecomponents components of o f Precambrian Precambrian plate margins. Major Major fault fault zones basement zones in in the thecrystalline crystalline basement have have expression expression in in landfonns For example, example, in in western landforms and and surface surface sediments. sediments. For western Minnesota, Minnesota, the the Great Great Lakes TectonicZone Zoneisislocated locatedatat the the southern southernlimit limit of Lakes Tectonic of the theLake Lake Agassiz Agassiz plain; plain; and in in southwestern Minnesota, faults faults bounding the Fulda Pipestone structural structural and southwestern Minnesota, bounding the Fulda and and Pipestone basins (Southwick (Southwick and and Mossler, Mossier, 1984) 1984) correspond correspond with the theend end moraine moraine complex complex on on basins Equivalence of of basement structure the southwestern southwestern margin margin of of the theDes Des Moines Moines lobe. lobe. Equivalence basement structure and surface surface features featureswill will be in three Agassiz beach beach and be described described in three other other areas: areas: 1) Agassiz area in Minnesota, 2) 2) Swanville Swanville spillway spillway area area in in central centralMinnesota, Minnesota, area in northwestern northwestern Minnesota, and 3) north north of and 3) of Lake Lake Mille Mille Lacs. Lacs. complexatat the the margins margins ooff the In northwestern northwestern Minnesota, Minnesota, the beach beach complex the Lake Lake Northwest— Agassiz plain forms to the Agassiz plain forms aa broad broad arc arc opening opening to the south south and and east. east. NorthwestArchean trending faults faultsininthethe Archeanbasement basement generally generally converge converge toward toward the curve curve of of the arc parallel the Near Greenbush, MN, Greenbush, MN, the arc and and parallel the sides sides of of the thearc arc ofofbeach beach ridges. ridges. Near sharp variations variations in in the sharp the elevation elevation of ofthe thebeach-ridge beach-ridge crest, crest, mark mark the the position position of gradients associated with the the Vermillion In of large largeareomagnetic areomagnetic gradients associated with Vermillion Fault FaultZone. Zone. In central hasaa broad broadarc arc to to the central Minnesota, Minnesota, the the St. St. Croix Croixend endmoraine moraine complex complex has the west between the Serpent Serpent Lake Lakeand andMalmo Malmo structural discontinuities discontinuities mapped west between the structural mapped by by and McSwiggen (1988). On Onthe theinside inside of of the the arc Southwick, Morey, Morey,and McSwiggen (1988). arc of of the the end end moraine, several several eskers eskerstrend trend perpendicular perpendicularto to and andterminate terminateatat the the position position moraine, of the discontinuity. North North of of Lake Mille Lacs of the Malmo Malmo discontinuity. Lake Mille Lacs patterns patterns of o f lowland lowland peat peat and uplandtill till are geometry and upland are similar similartotothe the geometry of ofProterozoic Proterozoic thrust thrustduplexes. duplexes. Eskersin in this this vicinity generally located along steep Eskers vicinityare are generally located alongareas areasofof steepareomagnetic areomagnetic gradient and and trend trend parallel parallel to gradient to the thecontours. contours. Correspondenceo fofmajor majorstructural structural features Precambrian Correspondence featuresininthethe Precambrianbasement basement with geomorphic features and and surface surface sediments sedimentshelps helpsto to explain explain why linear geomorphic features why linear features on Landsat Landsat images images appear appear to to mark basementstructures. structures. Beach features mapped mapped on mark basement ridges, morainic and some someeskers eskers visible as linear morainic margins, margins, and areare allallvisible as Landsat Landsat linear features; eskers trending perpendicular perpendiculartotostructural structural features features are are not not easily easily eskers trending mapped obviouslinear linear features. features. Paleotectonic and mapped asasobvious and recent recentearth earthmovements movements along along the lithosphere 1 ithosphere block block boundaries boundaries influenced influenced patterns of o ferosion erosionand and deposition. As As aa consequence, consequence,patterns patternsofoferosion erosionand anddeposition deposition visible visible as as linear features imagesshow show fidelitywith with structures structures in in the linear features on on Landsat Landsat images fidelity the PrePrecambrian cambri an basement. basement. REFERENCES REFERENCES CITED CITED Southwick, D.L., D.L., and Mossler, J.H., Southwick, and Mossier, J.H., 1984, 1984, The The Sioux Sioux Quartzite and and subjacent subjacent regolith ininthe Basin, Minnesota, Minnesota, in in Southwick, D.L., regolith theCottonwood Cottonwood County County Basin, Southwick, D.L., ed., Shorter contributions to the geology of the Sioux Quartzite (Early ed., Shorter contributions to the geology of the Sioux Quartzite (Early Minnesota Geological Geological Survey Proterozoic), Southwestern Southwestern Minnesota: Minnesota: Minnesota Survey Report Report of Investigations Investigations 32, 32, p. p. 17—44. 17-44. Southwick, D.L., D.L., Morey, P.L., 1988, mapof of the Southwick, Morey, G.B., G.B., and and McSwiggen, McSwiggen, P.L., 1988, Geologic Geologic map Penokean Orogen, central and eastern Minnesota, and accompanying text: Penokean Orogen, central and eastern Minnesota, and accompanying text: Minnesota Geological Survey Report of Investigations 37, 25 p. Minnesota Geological Survey Report of Investigations 25 p. 62 J I �MASSIVE SULFIDE DEPOSIT, ONEIDA ONEIDA COUNTY, COUNTY, WISCONSIN WISCONSIN THE LYNNE MASSIVE SULFIDE DEPOSIT, Lawrence P. Lawrence P. Kennedy, Kennedy, Teresa Teresa A. A. Harding, Harding, John John N. N. Schaff, Schaff, & Anne N. M. Zielinski, Zielinski, Noranda Noranda Exploration, Ex~loration.Inc., Inc.. Rhinelander, Wisconsin The Lynne Lynne deposit ic-hosted, ZnThe deposit is is aa volcanicvolcanic-to tovolcanicl•ast volcaniclastic-hosted, Zn- Pb-Cu—Ag orebody located Proterozoic magmatic magmatic terrane terrane Pb-Cu-Ag orebody located in in the the early Proterozoic of northern Wisconsin. based on on the .of northern Wisconsin. A preliminary preliminary ore reserve, based first 39 holes in in an an open-pit open-pit mine design, is calculated at at 6.1 6.1 *Â¥firs million illion tons tons grading grading 7.14% 7.14% Zn, Zn, 0.34% 0.34% Cu, Cu, 1.89% 1.89% Pb, Pb, 3.09 opt opt Ag, Ag, and and hosted by by a gently-dipping 0.013 .013 opt opt Au. Au. The mineralization is hosted gently-dipping sequence of fragmental rhyolites, chiefly lapilli crystal tuffs, tuffs, sequence of fragmental rhyolites, chiefly lapilli to crystal and less abundant dacite to andesite flows, volcaniclastic and less abundant dacite to andesite flows, sandstones and relationships in the rhyolitic sandstones and siltstones. siltstones. Facies relationships rhyolitic pyroclastic rocks to the north (down-dip) yroclastic rocks to the north (down-dip) suggests proximity to aa volcanic constructional feature. tonalite intrudes and olcanic constructional feature. A footwall tonalite partly encloses encloses the lowermost part of the deposit, number of the lowermost part of deposit, and a number of subvertical, east— to southeast-trending faults disrupt subvertical, eastsoutheast-trending disrupt the downdip extension extension of mineralization. Many of of these these faults faults are are occupied occupied dip of mineralization. by feldspar-phyric, rhyolitic to basaltic dikes. b y feldspar-phyric, rhyolitic to basaltic dikes. The bulk of of the the Zn-Pb-Cu-Ag Zn-Pb-Cu-Ag mineralization mineralization occurs within aa sequence of chemical sedimentary rocks which thicken and coalesce coalesce ence chemical sedimentary in the central central part of the deposit. Lenses, lobes and stratiform of the deposit. stratiform bodies odies of massive to to semi-massive semi-massive sulfide sulfide are interbedded interbedded with laminated to disrupted carbonate conformable talc units, chert, onformable units, chert, laminated to carbonate rocks, and narrow narrow beds beds of of volcaniclastic volcaniclastic and and sedimentary sedimentary rocks. rocks. talcose rocks underlie of laminated, underlie and partly enclose lenses of laminated, The talcoserocks pyrrhotite—rich chert sphalerite-rich massive masEive sulfide, sulfide, and and also also pyrrhotite-rich chert and sphalerite-rich The talcose talcose host disseminated disseminated sphalerite, host sphalerite, pyrrhotite, pyrrhotite, and and galena. galena. The unit is overlain by thick beds beds of massive sulfide and lenticular lenticular masses of of carbonate and chert masses chert containing containing disseminated to bedded bedded aggregate thickness the sulfide-rich sulfide-rich sedimentary sedimentary sulfides. The aggregate sulfides. thickness of the rocks exceeds 325 feet the center center of the deposit; deposit; its its lenticular feet in in the lenticular rocks exceeds have formed formed as as a a nature and symmetry suggests suggests that that it it may have nature and symmetry with an undetermined hydrothermal mound, mound, with undetermined amount amount of replacement replacement mineralization. mineralization. Sphalerite is mineral, followed Sphalerite is the the most abundant abundant sulfide sulfide mineral, followed in in abundance pyrite, and chalcopyrite. chalcopyrite. galena, pyrite, abundance by pyrrhotite, pyrrhotite, galena, native silver, silver, Tetrahedrite (var. freibergite) polybasite, native freibergite) or or polybasite, Tetrahedrite (var. pyrargyrite, electrum, and native also economically economically are also pyrargyrite, electrum, native gold are important minerals. minerals. The sulfide sulfide distribution distribution and metal metal zonation zonation is important is similar to the zoning similar zoning documented documented in in other other volcanogenic volcanogenic massive sulfide deposits. deposits. Chalcopyrite Chalcopyrite and pyrrhotite pyrrhotite are are most most abundant abundant in sulfide talcose unit, whereas silver silver minerals and galena are the lowermost talcose unit, whereas are concentrated concentrated in in diopside-rich diopside-rich cherts cherts and and cherty beds in in the the upper upper Calc-silicate minerals, minerals, including part of of the the deposit. deposit. Calc-silicate including diopside, diopside, ferrosalite, garnet, garnet, tremolite, widespread; most ferrosalite, tremolite, and epidote, epidote, are widespread; of these minerals formed as a result of decarbonation reactions reactions during the emplacement emplacement of footwall tonalite, perhaps during tonalite, or perhaps during of the footwall the late stages stages of of hydrothermal hydrothermal activity. activity. 63 �- j THICK-SKINNED BACKTHRUSTING IN THE BACKTHRUSTING IN FELCH-CALUMET FELCH-CALUMET TROUGHS TROUGHSREGION, REGION,NORTHERN NORTHERNMICHIGAN-MICHIGAN-A A COMPARISON COMPARISON WITH WITH THE T H ESOUTHERN SOUTHERNALPS ALPS J JOHN S. S. KLASNER, KLASNER, Department Department of ofGeology, Geology, Western Western Illinois Illinois University, University, and and U.S. U.S. Geological 61455and andP. P.K. K. SIMS, SIMS, U.S. U.S. Geological Geological Survey, Survey, MS MS 905, 90q GeologicalSurvey, Survey, Macomb, Macomb,Illinois Illinois61455 Box Federal Center, Box 25046, Federal Center,Denver, Denver,Colorado Colorado80225-0046 80225-0046 j The The Felch Felch and and Calumet Calumet troughs troughs region region is is on on the the south south edge edge of of the the Superior Superior craton. craton. Rocks 1850 Rocks of of the the Wisconsin Wisconsin magmatic magmatic terranes terraneswere were accreted accreted to tothe thecraton cratonapproximately approximately1850 Ma deformation and and metamorphism metamorphism Ma along along the the north-verging north-verging Niagara Niagara fault, fault, causing causing complex deformation of of Archean Archean basement basement and and Early EarlyProterozoic Proterozoic strata strata on onthe theforeland. foreland. In In the the study study area, area, deformation deformationisischaracterized characterizedby bythick-skinned, thick-skinned,south-verging south-vergingbackthrusting backthrusting and and backfolding backfolding opposite on the the continental continental foreland. foreland. That opposite the the overall overall sense sense of of north-verging north-verging deformation deformation on That near-recumbent near-recumbent minor minor folds foldswith withaccompanying accompanying axial-planar axial-planar subhorizontal subhorizontal foliation foliation are are evident evident in in both both Archean Archeanand andEarly EarlyProterozoic Proterozoicrocks rockssuggests suggeststhe the presence presence of ofcrystallinecrystallin'-cored cored nappes, nappes, such such as as that that of of the theCarney CarneyLake Lakeblock. block. Deep Deeptectonic tectoniclevels levelsare areexposed exposedin inthe theFelch Felchand andCalumet Calumettroughs troughsregion, region, indicating indicating major major involvement involvement of Archean Archean rocks rocks in the deformation. Both Bothinvolvement involvement of basement basement and and the existence existence of of backthrusts backthrusts are arecommon common in in younger younger orogens, orogens, such as in the southern southern Alps. Alps. Comparing 1850Ma Ma Penokean Penokean orogen orogen in in northern northern Michigan Michigan with with a section section Comparing aa section section of of the the1850 in common features. features. Proceeding in the the 30 30 Ma southern Alpine Alpine orogen orogen reveals reveals several common Proceeding inward from by the from the the continental continental margin, margin, both both orogens orogens have have 1) 1)accreted accreted oceanic oceanic crust crust as as shown shown by the presence presence of of ophiolite; ophiolite; 2) 2)aazone zoneofofthick-skinned, thick-skinned,complex complex deformation deformation with with associated associated backthrusting and backfolding; 3) aa master backthrusting and backfolding; 3) master thrust thrust along along which which strata strata were were tectonically tectonically transported 4) inboard inboard of of the the basement basement arch, arch, deformation that transported over over a basement arch; arch; and and 4) is of basement basement rocks. rocks. The is mainly mainly thin skinned, skinned, but also also involves involves some thrusting thrusting of TheAlpine Alpine orogen multiply deformed deformed nappes, whereas whereas deep deep erosion of the the Penokean orogen consists consists of multiply Penokean orogen orogen the minor minor recumbent recumbent folds folds and and aa makes recognition recognition of of nappes nappesdifficult. difficult. Nevertheless, Nevertheless, the subhorizontal subhorizontal foliation foliation in in the the Felch Felch and and Calumet Calumet troughs troughs area area are are structures structures similar similar to to those those in a'=" in the the Alps, Alps, and and their theirpresence presencestrongly stronglysuggests suggests that that nappes, nappes, now now mostly mostly eroded, eroded, may may also exist exist in the the Penokean Penokean orogen orogenof ofnorthern northernMichigan. Michigan. J j j J j j K:\PKS\ABS\NorMich (3-22-91) -j 64 -J �EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS IN IN THE THE MONICO, MONICO, WISCONSIN WISCONSIN AREA: AREA: IMPLICATIONS IMPLICATIONS ON THE WISCONSIN MAGMATIC MAGMATIC TERRANE TERRANE L. GENE L . LABERGE, Geology Dept., Dept., UW—Oshkosh, UW-Oshkosh, Oshkosh, WI 54901 54901 The Wisconsin magmatic terrane terrane is is a a major east—trending east-trending belt belt of Early Proterozoic volcanic and plutonic plutonic rocks rocks in in the the Lake Lake Superior Superior region. region. The The Monico area area is is a a "window" "window" into into the the Early Early Proterozoic rocks through the the Pleistocene Pleistocene deposits that that blanket blanket most of northern Wisconsin, and, therefore, therefore, may afford afford an an opportunity to determine the the relationships relationships between major units units within the the volcanic volcanic belt. belt. This paper presents preliminary data from a project funded by a Faculty Development Grant from from UWOshkosh, with support from from the the Wisconsin Wisconsin Geological Geological Survey, Survey, and and the U.S. U.S. Geological Geological Survey. Survey. Similar to other parts parts of of the the Wisconsin Wisconsin magmatic magmatic terrane, terrane, at at least two distinctly different sequences sequences of rocks rocks are are present present in in Monico area. the Monico area. One sequence, sequence, exposed exposed mainly north north of of Highway Highway 8, consists mainly of amphibolite—facies amphibolite-facies gneissic gneissic rocks rocks with with little preservation of lithology :ittle of primary features. features. The dominant lithology a foliated granitoid gneiss with abundant mafic blocks. is a Numerous segmented segmented mafic mafic dikes dikes are are also also present. present. The other 8, other sequence, sequence, exposed exposed mainly mainly south south of of Highway Highway 8, consists of several mafic to felsic felsic successions successions of of greenschist— greenschistfacies volcanic rocks with subordinate volcanogenic sedimentary f a d e s volcanic sedimentary rocks. rocks. The repetitions repetitions in in successions successions may may be be due due to to aa combination of tight folding folding and and faulting. faulting. Several large large metadiabase dikes and and the the "Jennings "Jennings granite" granite" intrude intrude the the volcanic volcanic successions. Although pillow basalts, debris flows, successions. flows, and flow— flowbanded rhyolite and and felsic breccias are dominant in in the the Monico Monica banded area, drill cores to the the east east and and west west of of the the area area of of outcrop outcrop This suggests contain higher proportions of of sedimentary sedimentary rocks. rocks. This Suggests Monica area that rocks in the Monico area may may represent represent aa volcanic volcanic center center (a (a By contrast, the volcanic island?) island?) within the the magmatic magmatic terrane. terrane. By areas with abundant sedimentary sedimentary rocks rocks may may represent represent intra—arc intra-arc or or back—arc back-arc basins basins between between volcanic volcanic centers. centers. The two major sequences of rocks in the map area are presumably in fault contact, and it is is probable that the gneissic rocks represent uplifted, deeper deeper levels levels of of volcanogenic volcanogenic rocks rocks that were formed during earlier stages stages of of subduction subduction within within aa mature By contrast, contrast, the mature island island arc. arc: By the greenschist—facies greenschist-facies rocks rocks may may The represent later products of the the general general subduction subduction event. event. The fault separating the two rock sequences sequences may be the the result result of of deformation during docking of of the the magmatic magmatic terrane terrane with with rocks rocks of of the Superior Superior Craton Craton to to the the north. north. Thus, the rocks exposed in in the the Wisconsin inagmatic terrane may may represent represent various various tectonic tectonic slices magmatic terrane mature island arc and associated of a mature associated intra—arc intra-arc and and back—arc back-arc basins. basins. 65 �L - Sketch of hypothetical east-west (longitudinal) section along the LJ L L L L of volcanic centers along the island arc. Wisconsin magmatic terrane showing various stages of development L LL LL �The T h e Geology and a n d Geophysics Geophysics of major majorpost-Keweenawan post-Keweenawan faults in faults in the the eastern eastern Lake Lake Superior Superior region region Manson, M.L. M.L. and H.C. Manson, a n d Halls, Halls, H.C. Department of of Geology, University of Department Geology, University of Toronto, Toronto, Erindale Erindale campus, campus, 3359 Mississauga MississaugaRd., Rd., Mississauga, Mississauga,Ontario Ontario L5L L5L 1C6 1C6 The eastern outline eastern Lake Superior Superior shoreline shoreline has has aa characteristic saw-tooth outline primarily occupied are primarily occupied by by Middle MiddleKeweenawan Keweenawan volcanics in which which promontories promontories are of the of the l.lGa l.lGaMidcontinent MidcontinentRift RiftofofNorth NorthAmerica America(MCR), (MCR),and andembayments embayments by by This pattern generatedby bymajor major ENE ENE Upper Keweenawan clastics. elastics. This pattern appears appears to be generated to to WSW WSW faults, faults, some some of of which which are arerelated related totoArchean Archean structures structures within within the the southern Superior Province. Province. At Mamainse southern Superior Mamainse Point, Point, more more than than 5km of of volcanics volcanics are are bound against sandstones sandstonestotothe thesouth south by by aa fault that in new Ontario bound against that appears, appears, in Ontario Geological Survey aeromagnetic data, to extend inland along the southern Survey aeromagnetic data, to extend inland along the southern margin greenstone belt. belt. The The Montreal Montreal River fault, of the the adjacent adjacent greenstone fault, possibly possibly related related to to the the Kapuskasing structure, defines defines the the northern Kapuskasing structure, northern margin margin of ofthese these greenstones greenstones and and extends into into rift rift straw extends strata underlying underlying eastern eastern Lake Lake Superior Superior in in GSC-GLIMPCE GSC-GLIMPCE aeromagneticdata. data.At At Havilland Havilland Bay. aeromagnetic Bay, aa 500m 500m thick thicksuccession succession of Jacobsville Jacobsville sandstonehas hasbeen beenupturned upturnedand and folded folded against against aa little-recognised little-recognised fault fault exposed sandstone exposed directly alongside directly alongside Highway Highway 17. 17.Further Furthereast-west east-west faults faultshave have been been observed observed bounding Keweenawan bounding Keweenawan strata strata in the the Goulais Goulais Bay Bay area area and and at at Grindstone Grindstone Point. Point. Whilst the exact nature of these faults is unclear, significant the exact nature of these faults is unclear, significant vertical vertical displacements across acrossthe theMamainse MamainsePoint Point and and Havilland Havilland Bay Bay faults is suggested displacements suggested potential field data from detailed gravity profiles profiles collected collected during during 1990. 1990. Regional Regional potential indicate the lateral extent of of many many of ofthe thefaults faultsand andsuggest suggest broad structural units normal to the rift rift axis. axis. This Thiscontrasts contrasts with withpost-Keweenawan post-Keweenawan faults in in the the western western lake region which which are parallel to to the lake region are generally generally parallel the axis of the the rift. rift. The Thechange change in in structural structural style from west west to east east is highlighted in in the the centre centre of the lake, where aa series of of arcuate arcuatefault fault segments segmentsappear appeartotolink link the the Isle Isle Royale Royale and and Michipicoten Michipicoten series 1991). Sampling Island faults via via Superior Shoal (Teskey et at, Superior Shoal (Teskey et al., 1991). Sampling with with aa submersible has has revealed revealed aa complex complex structure for Keweenawan volcanics exposed for Keweenawan volcanics exposed at the possibly involving involving drag (Manson and and at the Shoal, Shoal, possibly drag folding folding and and block block rotations rotations (Manson Halls, 1991). 1991). Constraintson on the the sense senseand andtiming timing of of the faults will will have Constraints the eastern eastern faults have relevance to models models describing describing the the closure closureof of the the MCR, MCR, possibly requiring a relevance to possibly requiring Grenville influence, quantifying Grenville influence, and and offer offer aamethod methodfor for quantifyingpost-Keweenawan post-Keweenawan deformation within deformation within the the southern southern Superior Superior Province. Province. Manson, M.L., and Manson, and Halls, H.C., H.C., 1991, 1991, An An investigation investigation of ofSuperior Superior Shoal, Shoal, central central press, CJ.E.S. Lake Superior, with a manned submersible, in with a manned submersible, in press, C.J.E.S. Teskey, D.J., D.J., Thomas, Thomas, M.D., M.D., Gibb, R.A., Teskey, R.A., Dods, Dods, S.D., S.D., Kucks, Kucks, R.P., R.P., Chandler, Chandler, K., Phillips, V.W., Fadaie, Fadaie, K., Phillips, J.D., J.D., 1991, 1991, High High resolution resolution aeromagnetic aeromagnetic survey EOS, V.72, V.72, No.8 of Lake Superior, Superior, EOS, 67 �-j OF THE MWCONTINENT GEOPHYSICAL GEOPHYSICAL INVESTIGATIONS INVESTIGATIONS OF MIDCONTINENT RIFT IN INEASTERN EASTERN LAKE LAKE SUPERIOR SUPERIOR USING USING VARIABLE VARIABLE MAGNETIZATION MODELING MARIANO, J. AND HINZE, W.J. (Dept. MARIANO, J. (Dept. of of Earth Earth and andAtmospheric Atmospheric Sciences,Purdue Sciences.Purdue Univ., Univ., West West Lafayette, Lafayette, IN. IN. 47907 47907 Magnetic Magnetic anomalies anomalies over eastern Lake Superior are very useful in tracing tracing the the subsurface subsurface extent extent and and geometry geometry of of the the Keweenawan Keweenawan volcanic volcanic rocks rocks of of the the Midcontinent Midcontinent Rift. Rift. In In 1987, 1987, aa high high J J resolution surveywas wasflown flownover overLake Lake Superior Superiorasas'part part of of the resolution aeromagnetic aeromagnetic survey the Great Great Lakes Lakes Multidisciplinary Multidisciplinary Program on Crustal Crustal Evolution. Evolution. In In order order to to take take full full advantage advantage of of these these new new data, data, improved improved quantitative quantitative magnetic magnetic modeling modeling techniques techniques have been developed and and applied applied to to the the volcanic volcanic rocks. rocks. The TheKeweenawan Keweenawan basalts basalts have have retained retained aa strong strong remanent remanent magnetization magnetization derived derived when when they they cooled cooled through through the the Curie Curie point point isotherm isotherm of ofmagnetite. magnetite. Post-depostional Post-depostional structural structural deformation of these rocks rocks has has rotated rotated the the remanent remanent magnetization magnetization vector vector resulting resulting in in aa spatially spatially varying varying direction direction and and intensity intensity of of magnetization magnetization, when when vectorially vectorially added added to to the the vector. An induced induced magnetization magnetization vector. An algorithm algorithm to toaccomodate accomodate these these variations variations in in magnetization magnetization has and tested has been been formulated formulated and tested and and has has been been applied applied to to the the volcanic volcanic rocks rocks of of eastern eastern Lake Lake J Superior. Superior. The which is is based The magnetic magnetic modeling modeling procedure, procedure, which based on on the the equivalent equivalent point point source source concept, concept, is is termed termed the the equivalent equivalent point point dipole &pole (EPD) (EPD) method, method, and and calculates calculates the the magnetic magnetic response response of aa given given volume volume of of anomalous anomalous magnetization magnetization by summing the magnetic fields fields due due to to a series of point point dipoles dipoles of of specified specified spacing spacing contained containedwithin withinthe thevolume. volume. This This approach allows allows the to vary the direction direction and magnitude magnitude of magnetization magnetization to vary freely freely over an an anomalous anomalous unit. unit. The The accuracy and speed of this calculation are directly dependent on the point dipole spacing. accuracy speed of this calculation are directly dependent on the point dipole spacing. The The optimum calculation time, time, but but still results optimum spacing spacing minimizes minimizes calculation results in in acceptable acceptable calculation calculation error. error. Given Given the the simplicity simplicity of the the dipole dipole calculation calculation and and the the speed speed of of modern modern computing computingfacilities, facilities,this this is is fortunately fortunately not not aa problem. problem. In Ingeneral, general,aadipole dipole spacing spacingequal equal to to one one tenth tenth the thedistance distancebetween between the plane and and the the point point dipoles dipoles yields yieldserrors errorsless lessthan thanone onepercent. percent. Figure 11 shows the observation observation plane shows comparisons of the comparisons of the EPD EPD calculation calculation with with the the conventional conventional method method of ofanomaly anomalycalculation calculation (Tal\vani (Talwani and and Heirtzler,1964). Heirtzler.1964). The to profiles The EPD EPD method method has has been been applied applied on on aa two two dimensional dimensional basis basis to profiles that that have have been been studied with the gravity and seismic reflection methods in eastern Lake Superior. These studied with the gravity and seismic reflection methods in eastern Lake Superior. These profiles profiles include recentlyreleased releasedseismic seismicreflection reflectionsections sections with of TWYI' TWTT as as well well as as include recently with upup toto88ss of previously availableGLIMPCE GLIMPCEdata datawith withupuptoto 16 ss of previously available of T\V1T. TWTT. On On these these sections, sections, the the Keweenawan basalts are are clearly clearly imaged imaged as as aa series Keweenawan basalts series of of strong, strong, laterally laterally continuous continuous reflections reflections with with dips generally generally ranging from -30 -30 to to ±30 +30degrees. degrees. Extensive Extensive paleomagnetic paleomagnetic studies studies in in the the Lake region indicate indicate that that the both aa normal Lake Superior Superior region the basalts basalts possess possess both normal and and reversed reversed remanent remanenl Assuming magnetization to the the induced induced component. component. Assuming original original magnetization component component in in addittion addittion to horizontality of the the basalt basalt flows, flows, the the apparent apparent dips dips derived derived from from the the seismic seismic reflection reflection sections sections are vector back back to to the the horizontal in the are used used to to rotate rotate the the remanent remanent magnetization magnetization vector horizontal in the plane plane of of the the profile. The rotated remanent vector is then added to an induced magnetization vector, resulting The rotated remanent vector is then added to an induced magnetization vector, resulting in in aa spatially spatially varying varying direction and and magnitude magnitude of of total total magnetization. magnetization. Modeling results indicate that the Modeling results indicate that the consideration consideration of of variable variable magnetization magnetization will will provide provide basalts. much much greater greater confidence confidence in in the the structural structural interpretations of of the theKeweenawan Keweenawan basalts. Preliminary models in in eastern Lake Superior suggest that a large volume volume of of reversely reversely polarized polarized rocks is is necessary to account account for the observed aeromagnetic anomalies. 68 J J �(a) s 020 .0 4!o 50 DISTANCE (1(M) N 0 iS 50 50 50 50 10 a 2C S = —S S C 10 o 20 50 40 50 DISTANCE (1(M) 70 (b) s z 50 '00 N — 0° ¶0 20 I'S 10 0 — 50 40 50 DISTANCE (1(M) 60 70 60 90 '00 5'O *o 100 100 0• - " 0 20 t'o.'oiot'o7'0 40 DISTANCE (1(M) 70 .o I Figure Figure 1.1. (a) (a) The The magnetic anomaly due to combined induced and remanent magnetization calculated calculated by by the the EPD EPD method method (dashed) (dashed) and andthe theTalwani Talwani and and Heirtzler Heirtzler method method (solid). (solid).Note Notethat that these these are are essentially essentially coincident coincident over over the the entire entire length length of of the the profile. profile. The Thetotal totalmagnetization magnetization vector vector in in the the plane plane of ofthe theprofile profileisisshown shownfor forevery everyfifth fifthdipole. dipole. (b) (b) The Themagnetic magneticanomaly anomalydue due to to combined combined induced induced and and remanent remanentmagnetization magnetization with with aagradational gradational rotation rotation of of the the remanent remaneni vector vector using using the the EPD EPD method method (dashed) (dashed) and andwith withhomogeneous homogeneous magnetization magnetization using using the the Talwani Talwani and A single singlehorizontal horizontalplane plane of of total total magnetization magnetization vectors vectors isisshown shown. and Heirtzler Heirtzler method method (solid). (solid). A The The induced induced and and remanent remanent magnetization magnetization vectors vectors and and the the disturbance disturbance of the the remanent remanent vector vector are are and the compatible compatible with with conditions conditions in in the the Lake Lake Superior Superior region region and the volcanic volcanic rocks rocks of of the the Midcontinent Rift. Rift. Mideontinent Reference Reference . , . Talwani, Talwani, M. M. and and Heinzler, Heirtzler. J;, 1..1964, 1964,Computation Computation of of magnetic magnetic anomalies anomalies caused caused by by twotwoMineral Industries, dimensional structures of arbitrary shape. IN: Computers in the dimensional structures of arbitrary shape. IN: Computers Mineral Industries, 1. 1. Stanford Stanford Univ. Publ. Publ. Geol. Sci., Sci.. 90): 9(1): 464-480 69 69 �A MOVEMENT ALONG A PRELIMINARY PRELIMINARYSTUDY STUDY OF OF REJUVENATED REJUVENATED MOVEMENT ALONG A FAULT,ST. St CROIX A PRECAMBRIAN PRECAMBRIAN FAULT, CROIXCOUNTY, COUNTY, WISCONSIN WISCONSIN Michael MichaelI). D.Middleton, Middleton,Department DepartmentofofPlant Plantand andEarth EarthScience, Science, University University of of Wisconsin-River Wisconsin-River Falls, Falls, River RiverFalls, Falls,WI WI54022 54022 The The eastern eastern margin margin of of the the Midcontinent Midcontinent Rift Rift system is marked by by the the Hastings-Lake Hastings-Lake Owen fault in western western Wisconsin. Wisconsin. Precambrian Precambrian displacement displacementalong along this this high high angle anglefault faulthas hasbeen beenestimated estimatedatatapproximately approximately3,000 3,000m. m.(Craddock, (Craddock,1972) 1972) based upon upon geophysical geophysical evidence. A A number number of of workers workers have have suggested suggested that that the the Hastings-Lake Owen fault was reactivated in the of the late late Cambrian, Cambrian, causing causing thinning thinning of the the Cambrian Cambrian section and an an unconformity unconforrnity between the the Cambrian Cambrian and and Ordovician Ordovician sequences sequences in in Minnesota Minnesota (Morey (Moreyand andRensink, Rensink,1969; 1969;Cavaleri, Cavaleri, et. et. al., al., 1987). 1987).Evidence Evidence from aa number number of of exposures exposuresin inSt. St.Croix Croix County, County, Wisconsin Wisconsin supports supportsthese theseviews, views, and further further refines refines the the timing timing and andamount amountof ofpost-Precambrian post-Precambrian movement movement along along the the fault. fault. The The surface surfaceexpression expression of of the the Hastings-Lake Hastings-Lake Owen Owen fault faultin inSt. St.Croix Croix County Countyisis aa series series of low escarpments with a northeast northeast trend trend formed formed by by differential differential erosion erosion of of the softer Cambrian sandstones to the west which have been displaced upward upward against more resistant Ordoviaan Ordovician dolomites to to the the east. east. A A quarry quarry along along this this trend trend cut cut into into dolomites dolomites of of the the Lower Lower Ordovician Ordoviaan Prairie Prairie du du Chien Chien Group Groupshows showsevidence evidence of this displacement. In In sharp sharpcontrast contrastto tothe therelatively relatively flat-lying flat-lying bedrock units in this this region, the sttata strata in the the quarry quarry dip dipapproximately approximately 20° 20' to the east. These These strata strata dip downthrown side, side, and and these these dips dips were were most most probably probably dip away away from the fault on its downthrown caused by drag. The Thedisplacement displacementof of the the Cambrian Cambrian sandstones sandstonesagainst against Lower Lower Ordovician Ordovician dolomites and the drag drag folding folding within within the the dolomites dolomites both both demonstrate demonstrate post-Early Ordovician Ordovician movement movement along along the the fault. fault. In In addition, addition, features features within within the the dolomite itself provide evidence for movement of the the fault fault in in the theEarly EarlyOrdovician Ordovician during deposition of the sediments. The The beds beds in in the thequarry quarrythicken thicken away awayfrom from the the fault, with lower strata showing higher higher dips than those above. above. Sharply Sharply truncated stromatolite stromatolite beds, thick thick dolomitic dolomitic conglomerates, conglomerates, erosional relief relief along contacts, contacts, and and mudcracks mudaacks all attest to to periodic erosion and and exposure exposure of of the the sea sea floor floor during during deposition of the Prairie du Chien Group at this site, perhaps due due to to recurrent recurrent small small movements along the fault. fault. 70 �The The amount amountof of Post-Precambrian Post-Precambrian displacement displacementalong along the the Hastings-Lake Hastings-Lake Owen Owen fault fault in in this thisregion region can canbe bedetermined determinedat atexposures exposuresin in the thevicinity vicinity of of Hudson, Hudson, Wisconsin. Wisconsin. Cambrian Cambriansandstones sandstoneshave havebeen beendisplaced displacedupward upwardapproximately approximately85-100 85-100 m. the Cottage Grove fault which m. against against Ordovician Ordoviaan strata strata along along the the fault. fault. Along Along the Cottage Grove fault which parallels parallels the the Hastings-Lake Hastings-Lake Owen fault to to the the northwest, northwest, displacement displacement is is even even greater, greater, approximately approximately115-125 115-125 m. The Theevidence evidencegathered gatheredin inSt. St.Croix Croix County County demonstrates demonstrates later later recurrent recurrentmovements movements and andgreater greaterPost-Precambrian Post-Precambrian displacement displacement than than has has previously previously been been reported reported for for the the Precambrian Precambrian faults in in this this region. region. References ReferencesCited Cited Cavaleri, The Geology Geology of of the Cavaleri, M., M., Mossier, Mossier, J.H. J.H. and andWebers, Webers,G.F., G.F., 1987, 1987, The the St. St. Croix Croix River River Valley, in Balaban, N.H., Ed., Field Trip Trip Guidebook Guidebookfor for the the Upper Upper Mississippi Mississippi Valley, in Balaban, N.H., Ed., Field Valley, MinnesotaGeological Geological Survey, Survey, Valley, Minnesota, Minnesota, Iowa Iowa and and Wisconsin. Wisconsin.Minnesota Guidebook GuidebookSeries Series#15, #15,p. p.23-43. 23-43. Craddock, and Southeastern Southeastern Craddock, C., C., 1972. 1972. Keweenawan Keweenawan Geology Geology of East-central and Minnesota, Eds, Geology Geology of of Minnesota: Minnesota: AA P.K. and and Morey, Morey, G.B., G.B., Eds, Minnesota, in in Sims, Sims, P.K. Centennial MinnesotaGeological GeologicalSurvey, Survey,p.p.416-424. 416-424. Centennial Volume. Volume.Minnesota Morey, and Rensink, 1969. Rejuvenated Rejuvenated Precambrian Precambrian faults faults as as aa cause Morey, C.B. G.B. and Rensink, D.C., D.G., 1969. cause of of Paleozoic structures in Minnesota. Annals of the the Institute Institute of Paleozoic structures in southeastern southeastern Minnesota. Annals of of Lake Lake Superior Superior Geology. Geology. 15th, 15th,Wisconsin Wisconsin State State University, University, Dept. Dept. Ceol., Geol., Oshkosh, Oshkosh,WI, WI,May May8-9. 8-9. 71 �GEOCHRONOLOGY GEOCHRONOLOGYOF OFTHE THEDULUTH DULUTHCOMPLEX: COMPLEX:AAPROGRESS PROGRESSREPORT REPORT MILLER, MILLER, .ID., J.D., JR., JR., Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAve., Ave., St. St. Paul, Paul, MN MN 55114 55114and and LB. J.B.Paces Pacesand andR.E. R.E. Zartman, Zarunan,U.S. U.S. Geological GeologicalSurvey, Survey.Box Box25046, 25046,MS MS963, 963,Denver DenverFederal Federal Center, Center, Denver, Denver, CO CO80225 80225 Recent Recenthigh-precision high-precisiondating datingofofvolcanic volcanicrocks rocksassociated associatedwith withthe theMidcontinent MidcontinentRift Rifthave havecontributed contributed much muchtoward towardunderstanding understandingthe thetiming, timing,duration, duration,and andtectonomagmatic tectonomagmaticevolution evolution of the the Li-Ga 1.1-Garifting riftingevent. event. However, However, similar similargeochronological geochmnologicalcontrol control for for associated associated plutonic plutonic rocks rocks is not yet yet available. available. The Theprimary primary objective innortheastnonheastobjectiveof ofthe thepresent presentstudy studyisistotodate dateindividual individualgabbroic gabbroicintrusions intrusionswithin withinthe theDuluth DuluthComplex Complexin ern em Minnesota Minnesotausing using high-precision high-precision U-Pb U-Pb techniques techniques (1) (1) to to determine determine the the temporal temporal range of of intrusive intrusive activity activity within within several severalwell-studied well-studiedareas areasof of the thecomplex, complex,as aswell wellas asbetween betweenthese theseintrusions intrusions and and the the overlying overlying volcanic volcanic rocks, rocks,and and(2) (2)tototest testmodels, models,which whichhave havepreviously previouslybeen beenbased basedonongeologic geologicmapping mappingand andgeophysical geophysicalinterpreinterpretation, tation,for forthe theemplacement emplacementofofthe theDuluth DuluthComplex. Complex. The Duluth Complex is large, The Duluth Complex is large,composite compositemafic maficintrusive intrusivesupersuite, supersuite,which whichwas wasemplaced emplacedatatshallow shallow depths (<7 km) beneath a comagmatic edifice of plateau basalt during the development depths (<7 km) beneath a comagmatic edifice of plateau basalt during the development of of the the Midcontinent Midcontinent Rift Rift (Fig. (Fig.I). 1).Multiple Multipleintrusions intrusionswere werealso alsoemplaced emplacedhigher higherinto intothe thevolcanic volcanicpile, pile,with withthe themost mostvoluminous voluminousof of these thesebeing beingthe theBeaver BeaverBay BayComplex. Complex.The TheDuluth DuluthComplex Complexisiscomposed composedofofseveral severallithologieally lithologicallydistinctive distinctive rock Morey,1980). 1980).The Theoldest oldestintrusive intrusive rockseries, series,previously previouslyinterpreted interpretedto tobe betemporally temporallydistinct distinct(Weiblen (Weiblen&&Morey, rocks rocksare areaalayered layeredsuite suiteof ofgabbroic gabbmiccumulates cumulatesin in the thenorthern northern area, area, termed termed Nathan's layered layered series series (Fig. I). 1). Their Theirevolved evolvedcompositions compositionsand and reversed reversed magnetic magneticpolarity polarity suggest suggestthat that these these rocks rocks may may be be similar similar in in age ageto to the the nearby nearby Logan Logan sills sills(1109 (1 109±Â22 Ma; Ma, Davis Davis & & Sutcliffe, Sutcliffe,1985). 1985). These Thesegabbros gabbrosare areintruded intrudedby by aastructurally structurally complicated complicatedsuite suiteof of dominantly dominantlyplagioclase plagioclasecumulates, cumulates,termed termedthe theanorthositic anorthositic series series (Fig. (Fig. I), 1).which whichoccur occur throughout plagioclasecrystal crystalmushes mushes(Miller (Miller & &Weiblen, Weiblen, throughoutthe thecomplex complex and andare arethought thoughttotohave haveintruded intrudedasasplagioclase 1990). 1990). Anorthositic Anorthositicseries seriesrocks rocksare areintruded intrudedthroughout throughoutthe thecomplex complexby bylayered layeredintrusions inbusionsofofiroctolitic troctolitictoto gabbroic gabbroiccumulates, cumulates,collectively collectively termed termed the thetroctolitic troctoliticseries. series.The Theapparent apparenttruncation truncationofofaeromagnetic aeromagneticpatterns patterns related relatedtotoSE.dipping SE-dippinglayering layeringininintrusions intrusionsalong alongthe theunexposed unexposedwestern westernmargin marginof ofthe theDuluth DuluthComplex Complex(Fig. (Fig. 1) 1)led led Miller Milleret etal. al.(1990) (1990)totospeculate speculatethat thattroctolitic troctoliticseries seriesintrusions intrusionsyoung youngtotothe thesouth southasasaaresult resultofofsuccessuccessive siveintrusive intrusiveoverplating. overplating. AAfelsic felsicseries seriesalso alsocomprises comprisesaasignificant significantportion portionof ofthe theDuluth DuluthComplex Complex (Fig. (Fig.I)1) but geochronologicstudy. study. butwas wasnot notincluded includedininthis thisgeochronologic Differentiated Differentiatedsamples samplesfrom fromseven sevenmafic maficintrusive intrusivebodies bodieswere werechosen chosen that, that,based basedon on geologic geologicand andgeogeophysical physical evidence, evidence,span span the the temporal temporal and and spatial spatial(areal (arealand andstratigraphic) stratigraphic)limits limitsof of intrusive intrusiveactivity activity in in the the Duluth Duluth Complex (Table (Table 1; 1; Fig. 1). 1). Between Between30 30and and40kg 40 kgofofrock rockwas wasprocessed processedfor foreach eachsample sampleyielding yieldingclear clear zircon (± baddeleyite) grains lacking obvious cores or rims. Air-abrasion and hand-picking yielded crack-and and zircon ( baddeleyite) grains lacking obvious cores or rims. Air-abrasion and hand-picking yieldedcrackinclusion-free inclusion-free grains, grains,which which were were analyzed analyzed individually individually or or as as2-5 2-5grain grainaggregates aggregates weighing weighing 30 30 to to 150 150jig. ug. UU contents 200 to to 1000 1000ppm, ppm, and most most fractions fractions are are less less than 1.5% 1.5% discordant. Preliminary Preliminary ages agesfor for contents range range from from 200 five five of of these these samples samples are are reported in Table 1. 1. The Thetwo twoanorthositie anorthositicsamples samples(FCI, (FC1,AS3) AS3)plus plusone onetroctolitic troctolitic series level. Fractions series ferrogabbro ferrogabbro (Dl) (Dl) yield yieldidentical identical ages agesat at the the95% 95%confidence confidencelevel. Fractionsfrom fromall allthree threerocks rocksreregressed gressed together together result result in in an an age age of of 1099.1 1099.1±Â0.6 0.6 Ma Ma with with aa lower lower intercept intercept age of-I of -1±Â40 40Ma Ma(MSWD (MSWD== 1.3), 1.3). The aswell wellas asthe thehypabyssal hypabyssalferrodiorite ferrodiorite from from the the Beaver Beaver Bay Bay ComThe troetolitic troctolitic series series olivine olivine gabbro gabbm (P02), (PG2).as plex plex (SBG2), (SBG2). yield yield younger younger ages ages of of1096.1 1096.1±Â0.8 0.8and and1095S 1095.9±Â0.5 0.5Ma, Ma,respectively, respectively,which whichare areclearly clearlyresolved resolved from from the older older ferrogabbro ferrogabbm and anorthosite dates. Although Although additional additional analyses are required before final age determinations determinations are are made, made, the thefollowing followinghave havebeen beenestablished: established: - Although Although the the onset onset of of igneous igneous activity activity as as represented by Nathan's layered layered series has not yet been deter— mined, mined, the the bulk bulk of of the the Duluth Duluth Complex Complex and and associated associated hypabyssal hypabyssal intrusions intrusions were emplaced between 1099 Thisfurther furthersupports supportsprevious previousobservations observationsthat thatvolumetrically volmetricallymost mostKeweenawan Keweenawan 1099 and 1096 1096 Ma. This igneous Ma (Davis (Davis & & Sutcliffe, Sutcliffe,1985; 1985;Davis Davis& & igneous activity activity occurred occurred over over aa time time span span between between 1099 1099and and 1094 1094Ma Paces, Paces, 1990; 1990; Van Van Schmus Schmus et a!., a]., 1990). Since Sinceparts pansof ofthe theDuluth Duluth Complex Complex are are older older than than the the normalnormalpolarity rocksmay may represent represent aa means means of of sampling sampling polarity lavas lavas exposed exposed along along rift rift margins, margins, these these intrusive intrusiverocks magmas that are are more more deeply deeplyburied buried within within the the central central rift rift graben. graben. magmas associated associated with lavas lavas that — The The relative relativeages ages of of intrusive intrusiverocks rocks based based on ontheir theirmagnetic magneticpolarity polaritymust must be be viewed viewed with with considerable considerable caution. caution. Although Althoughall allof ofthe theanalyzed analyzedrocks rockspossess possessnormal normalmagnetic magnetic polarity, polarity, three three of the the intrusive intrusive bodies bodies have have emplacement emplacement ages ages of 1099 1099Ma, Ma, older older than than the the major majorR-N R-N magnetic magnetic reversal reversal placed placed at at about about I09L6 1097.6±Â3.7 3.7 Ma Ma (Fig. (Fig. 1;1;Davis Davis & & Sutcliffe, Sutcliffe, 1985). 1985). This Thisdisparity disparityisislikely likely related related to to the the slow slow cooling cooling of of - • 72 �1I 90 CANADA r___aiScRIPTloN or MAP UNITS Middle ProlerpzO,c (Keoae enasyan Superoroupi Sedsmentary Rocks (Baylield & Oronto Groups) • shale and Ieldspalhic ID quartz Ose sandslone nlrusive Rocacs l,ncludes Duluth COmoleal R - granod.oriI.c IC graniI.c bc I5 domnaruly subvolcanc malic rocks dominanbly Irootolilic rocks !-dom, nanlly gabbro.c rocks Xc -dorn.nanlty anorlh ostIbc rocks • need lroclob,t,c so goat crc rocks abundant Volcan.c Rocks North Shore Volcan,c Gtou:SoleyI,c basall beat caIn some anoes!te shyol,be. and nt ertlom seo,men lacy C;. Early P.ocarn,n!r lAnjrnrk.p O'puol arolillIe and greyvacke Rove S V!n.r.a nrc ran lornlat!crr re 0° cl p a;-.. &ctlarn lyerm,ll,cn dIstrict ntaas.ae to OnelSs.c. yr anItIc 504; IIC 1 ;kS locally micat,tsc metacoboan,; and metased.me-:a -' 'sty banded ron bornOatcI] sno.r.n SYMBOLS -— .;.WISCONSIN .• . —. Aopron,malo geolog.c corrtaCI. dariec .srre,r ,nberred Irom geopnysscal data Large-scale laull 20 40 20 30 4CM. —u ing samples samples collected collected for for U-Pb isotope analyses. Figure 1. 1. Generalized geology of northeastern Minnesota show showing Complex and and related related intrusions zircons from from Duluth 0 uluth Complex Table 1. 1. Preliminary Preliminary U-Pb U-Pb ages for zircons Sample Sample Rock Series Series T-R-Sec. T-R-Sec. Rock Type Upper Intercept Age (Ma) (Ma) i2a ±2a Age error error No. of of No. analyses analyses Lower Intercept Intercept Lower Age (Ma) (Ma) i±2a Age 2a error error Dll D PG2 A53 AS3 FCI FC1 NLS5 LLG2 LLG2 Troctolitic Troctolitic Anorthositic Anorthositic Anorthositic Nathan's L.S. L.S. Beaver Bay Complex Complex Beaver Bay Complex Complex 49-15-1 59-12-8 49-14-6 61-8-10 64-2-2 56-7-6 fen-ogabbro ferrogabbm olivine gabbro olivine gabbroic anorthosite gabbmic gabbroic anorthosite anorthosite gabbroic olivine gabbro gabbro olivine fenogabbro ferrogabbro 1099.0  ± 0.8 1099.0 1096.1 i ± 0.8 0.8 1096.1 1098.9* 1098.9. 1099.2  ± 1.7 1099.2 in progress in progress 3 3 3 3 1 4 --22 ± i 441 1 O** 56-7-29 ferrodiorite ferrodiorite 1095.9  ± 0.5 0.5 1095.9 44 ±7 5 SBG2 SBG2 0" O* .2rnpb,206pbage agefrom from single single analysis analysis *2CTPb/2çÈ **Regression forced forced through through 0 0 Ma lower intercept due due to clustering clustering of of data data near near concordia concordia 73 �these these plutonic plutonic rocks racksbetween betweenzircon zirconcrystallization crystallizationtemperatures temperatures(—900°C) (-90O0C) and the the Curie Curie point point of of the theFe-Ti Fe-Ti oxides oxides (c590°-350°C). (c59O0-350T). — - The The similar similar ages ages of anorthositic anonhositicseries seriesrocks rocks(AS3 (AS3 & &PC!) FC1)taken takenfrom fromwidely widely separate separateareas areasof of the the complex occurredas asaarestricted restrictedtemporal temporalevent eventthroughout throughout complex suggest suggestthat that the the emplacement emplacementof ofthese theserocks rocksoccurred the Duluth Complex around 1099 1099 Ma. This Thisisisconsistent consistentwith withtheir theirunique uniquepetrogenesis petrogenesis(Miller (Miller & & Weiblen, Weiblen, 1990). 1990). — - The The essentially essentially identical identical 1099-Ma 1099-Ma age age of of anorthositic anorthositicand and troctolitic troctolitic rocks at Duluth (AS3 & Dl), Dl), while while not contradicting contradicting field relations relations indicating that the the anorthositic rocks are older, does lead to the speculation that the thought. At the petrogenesis of these these two two series series may may be be more more closely closely linked linked than previously thought Atthe the very least, least, itit implies implies that that the the types typesof of parent parentmagmas magmas that that gave gave rise rise to to these these two two rock rock series series were were either either very very closely closely related related or or were weregenerated generatedby bymechanisms mechanismsthat thatwere werevery very nearly nearly synchronous. synchronous. - Speculation Speculation (Miller et al., 1990) 1990)that that the the troctolitic troctolitic series seriesintrusions intrusions along the western margin young to — the south is strongly strongly contradicted contradicted by by the the distinctly distinctly younger younger age age of the the troctolitic series sample from the northwest (Kawishiwi) part of the complex (PG2; 1096 compared to to the sample at at Duluth Duluth (Dl; 1099 1096 Ma) compared 1099 Ma). Given & Hauck, Hauck, 1990), 1990).itit Giventhe thecomplexity complexityof ofintrusive intrusiverelationships relationshipsininthe theKawishiwi Kawishiwi area area(Severson (Severson & seems seems likely that that troctolitic troctolitic series seriesrocks rocksof ofvarious variousages agesmay mayexist existininthis thisregion. region. - The The similarity similarity of of 1096-Ma 1096-Maages ages between between the theKawishiwi-area Kawishiwi-area olivine olivinegabbro gabbm (PG2) (PG2)and and the the ferrogabbro ferrogabbro — (SBG2) representing the youngest intrusive unit of the hypabyssal Beaver Bay Complex (Miller, (SBG2) representing the youngest intrusive unit of the hypabyssal Beaver Bay Complex (Miller,1988) 1988) implies implies that magmas magmas were were simultaneously simultaneously emplaced emplacedat at several severalstratigraphic stratigraphiclevels levels within within the thevolcanic volcanicpile, pile, at least late in the the intrusive intrusive history. Dating Datingof ofthe theLax LaxLake Lakegabbro, gabbro,which which mapping shows to be among the earliest earliest intrusions intrusionsin in the the Beaver BeaverBay BayComplex Complex(Miller, (Miller,1988), 1988).will willdetermine determinewhether whetherintrusive intrusiveactivity activity in this hypabyssal hypabyssal environment environment began began as asearly earlyas asititdid didininthe thedeeper deeperDuluth DuluthComplex. Complex. In summary, high-precision dates generated by this this study study place very important constraints on the timing and emplacement emplacement mechanisms mechanisms for for the the Duluth Duluth Complex Complexand andrelated related intrusions, intrusions. as aswell well as asproviding providingadditional additional data bearing on the broader evolution evolution of of the the Midcontinent Midcontinent Rift. Rift. These Thesepreliminary preliminary results resultsgive givecause causetotorethink rethink previously proposed concepts concepts hypothesized hypothesized from from field, field,geochemical, geochemical,and and geophysical geophysical data, data, and and offer offerincentives incentives for for further furtherintegration integration of of these thesedata datatoward towardbetter betterunderstanding understandingofofrift riftprocesses. processes. REFERENCES REFERENCES CITED CITED Davis, D. W., & & Paces, Paces, 1. J. B., B.. 1990, 1990,Time Time resolution resolution of of geologic geologicevents eventson on the theKeweenawan KeweenawanPeninsula Peninsulaand and implications EarthPlan. Plan. Sci. Sci.Letters, Letters,v.v.97, 97,p.p.54-64. 54-64. implications for for development development of the the Midcontinent Midcontinent Rift system: Earth R.H., 1985, Nipigon plate plate and andnorthern northemLake Lake Superior: Superior: Geol. Davis, Davis, D.W., D.W., & Sutcliffe, R.H., 1985, U-Pb ages from the Nipigon Soc. Am. Bull., v. v.96, Am. Bull., 96,p. p. 1572-1579. 1572-1579. Miller, J.D., J.D., Jr., 1988, 1988, Geologic Geologic map of the the Silver SilverBay Bay and and Split Split Rock Rock Point NE quadrangles, quadrangles. Lake County, Minnesota: Minn. Minn. Geol. Geol.Surv. Surv.Misc. Misc.Map MapM-65, M-65,scale scale1:24,000. 1:24,000. Miller, J.D., Cambray,F.W., F.W., 1990, 1990,Style Styleof ofemplacement emplacementof ofthe theDuluth Duluth J.D., Jr, Jr, Chandler, Chandler, V.W., V.W., Southwick, Southwick,D.L., D.L., &&Cambray, Complex: Am. Abstr. Abstr. with with Programs, Programs, v. v. 22, 22, p. A369. A369. Complex: Geol. Geol. Soc. Soc. Am. Miller, J.D., J.D., Jr., & & Weiblen, P.W., P.W., 1990, 1990,Anorthositic Anorthositic rocks of of the the Duluth Complex: examples examplesof ofrocks rocksformed formed from plagioclase crystal mush: mush: J.J. Petrol., Peml., v. v. 31, 31,p.p. 295-339. 295-339. Palmer, H.C., & Davis, Davis, D.W., D.W., 1987, 1987,Paleomagnetism Palmmagnetismand andU-Pb U-Pb geochronology geochronology of of volcanic volcanic rocks rocksfrom from H.C., & Michipicoten Island, Lake Superior, Canada: precise calibration of the Keweenawan polar precise calibration of the Keweenawan polar wander wander track: track: Precambrian Res., Res., v. v.37, 37, p. p. 151-171. 151-171. Severson, & Hauck, Hauck, S.A., S.A., 1990, 1990,Geology, Geology,geochemistry, geochemistry,and and siratigraphy stratigraphy of of aaportion portionof ofthe thePartridge Partridge Severson, M.J., M.J., & River intrusion: Duluth, Duluth,Univ. Univ.ofofMinn., Minn.,Nat. Nat.Resources ResourcesResearch ResearchInst. Inst. Tech. Tech. Report ReportNRRJ/GMIN-TR-89NRRVGMlN-TR-8911,236 11,236p. p. Van Schmus, W.R., W.R., Martin, M.W., M.W., Sprowl, D.R.. D.R., Geissman, J., J., & Berendsen, Berendsen, P., P., 1990. 1990, Age, Age, Nd Nd and Pb isotopic composition, and magnetic of the the 1100 1100Ma Ma Midcontinent MidcontinentRift: Rift: magnetic polarity polarity for for subsurface subsurfacesamples samplesof Geol. Geol. Soc. Soc. Am. Am. Abstr. Abstr. with with Programs, Programs, v. v. 22, 22, p. p. A174. A174. P.W. and and Morey, Morey, G.B., 0.8., 1980, Weiblen, P.W. 1980,AAsummary summary of of the the stratigraphy, stratigraphy, petrology, and structure of the Duluth Complex: Am Am J.J. Sci., Sci., v. v. 220-A, 280-A, p. p. 88-133. 88-133. 74 �MANGANESE MINERALIZATION IIN EARLY PROTEROZOIC PROTEROZOIC IRON-FORMATION MANGANESE MINERALIZATION N EARLY IRON-FORMATION OF OF THE THE EMILY EMILYDISTRICT, DISTRICT,CUYUNA CUYUNARANGE, RANGE, EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA MOREY, D.L. L.Southwick, Southwick,Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642 University Avenue, St. Paul, MOREY, G.E., G.B., and and 0. Minnesota Minnesota 55114 55 114 Early EailyProterozoic Pmtemwicstrata strata of of the the Emily Emily district district at at the far far northern end of the Cuyuna Iron Range Range define define the (Southwick and others, 1988). As [hesouthwestern southwestern closure closure of the Animikie Aniiikie basin in east-central Minnesota (Southwick A such, Anitnikie Gmup Group of the such, the the rocks rocks of of the the Emily Emily district are correlative with strata of the well known Animikie Mesabi Mesabi range. range. However, However.unlike unlikethe themonodlinal monoclinalnature natureof ofthe theMesabi Mesabirange, range,strata stratain inthe theEmily Emilydistrict districtare are thrown thrown into inw aa series series of of broad, broad, open, open. eastward-plunging folds with near-vertical axial planes. Geometric Geometric relationships relationships imply imply that that the the basal basal contact contact of of the the Animikie ~ ~ m i kGroup Groupoverlies i e overlies an an unconformity unconfo&ty cut cutonto ontoolder older folded rocksof of the the North North range ranee (Chandler (Chandler and Malek, Malek. 1991). 1991). That Thatunconformity unconformitvmarks marksthe theboundary boundary folded rocks between between twice-deformed twice-deformedrocks rocks of of the the Penokean Penokean fold-and-thrust fold-and-thrustbelt belt and and the the once-deformed onc&efonned rocks rocksof of the the Animilde Animikiebasin basinOn On the the Mesabi Mesabi range, range, the the Animikie Animikie Group Gmup consists consists of a lower lower quartz arenitic arenitic sequence sequence (Pokegama (Pokegama Quartzite). Quartzite), an an intermediate intermediateiron-rich iron-rich sequence sequence(Biwabik (BiwabikIron IronFormation), Formation),and andan anupper upperblack-shale— black-shalegraywacke graywacke sequence sequence (Virginia (Virginia Formation). In Inthe the Emily Emily district, district,however, however. the the stratigraphic stratigraphic position position of of the the Biwabik Biwabik is is occupied occupied by by several several lenticular lenticular units units of iron-formation iron-formation intercalated within both PokegarnaPokegama- and Virginia-like Virginia-likematerials. materials. The area—can be dividei divided The main main iron-formation iron-formationof the Emily district—termed districtÑterme Unit A of the Ruth Lake areaÑca into epiclastic lithotope into seven seven lithotopes lithotopes (Fig. 1). 1). They Theyare are(1) (1)an anepiclastic lithotopeof of quartz-rich quartz-rich siltstone siltstone and and shale; shale; (2) (2) aa mixed lithotope;(3) (3) an an oolitic oolitic and and pisolitic pisolitic lithotope; lithotope; (4) (4) a ihick-bedded thick-bedded lithotope mixed epiclastic—jaspery-chert epiclastic-jaspery-chertlithowpe; lithotope of o cherry (5) aa mixed mixed thickthick- and and thin-bedded thin-beddedlithotope lithowpecharacterized characterizedby bythick thick cherty or or granular granular iron-formation; iron-fonnation; (5) intervals intervalsof of slaty slaty or or nongranular nongranular iron-formation; iron-formation; (6) (6) aa thin-bedded thin-bedded lithotope lithowpe consisting consisting of of laminae laminae to w very very thin lithotope. In nongranulai iron-formation; and (7) a ferruginous chert lithowpe. thin beds beds of of nongranular In general. general,lithotopes lithotopes 1, I. 2, 2. and the oxide (hematite) and have textural textural attributes attributes indicative of lhe (hematite) facies facies of of ironironand 33 contain contain primary ~rimarvhematite and formation. contrast. lithotope and has has textural attributes formation. In Incontra& lithowpe 66 contains contains appreciable appreciable carbonates or silicates and indicative carbonate facies of iron-formation. iron-formation. Lithotopes Lithotopes44 and and 55are areinterlayered interlayeredand andcontain contain indicative of the carbonate mixtures silicates, and thus were deposited in generally similar similar mixtures of of oxides oxides (hematite-magnetite) (hematite-magnetite)and silicates, sedimentological affected by by currents currentsand and at atdepths depthsintermediate intermediatebetween betweenoxides oxide: sedimenwlogicalregimes regimes in in waters watersvariably variablyaffected and of lithotope lithotope 77 isis uncertain. uncertain. It Irisis aa thin-bedded and carbonate carbonate facies. The Thesedimentological sediienwlogical significance of thin-bedded laminated laminated unit deposited in a deeper water regime as evidenced by a stratigraphic position transitional between between thin-bedded thin-bedded iron-formation iron-formation and overlying overlying p r i m w hematite. hematite. - - black shale; yet it contains primary Sedimentological Sedimentologicalparameters parameters imply imply that that Unit Unit A A was was deposited deposited during duringtwo twotransgressive-regressive uan&ressive-regressive cycles water 10 to the the north north and and east. east. Well-rounded Well-rounded grains grains cycles in in aa basin basin with with a strandline strandline to w the west and deeper wakr of lithotopes 1-5. imply that of the sedimentation of terrigenous temeenous quartz, auartz. which which persist nersist throughout ihroughout liihownes 1-5. much sedimentation occurred &curred relatively relativelyclose closeto w the the strandline. strandline. Although Although Unit unit A A in in the the Emily Emily district district has has many many mineralogical, mineralogical. textural, textural. and and chemical chemicalattributes attributes indicative of indicative of "ordinary" "ordinary" iron-formation, iron-formation. it locally locallv contains remains manganese manganese oxides oxides in in amounts amounts 10 10to to 100 100times times greater of 0.6 to Formation (Morey and greater than than the the norm normof w 0.8 percent in the Biwabik Biwabik Iron ~ronkormation and Morey, Money,1990). 1990). Manganese Manganese oxides oxides occur occur principally principally in in lithotopes 1-5 1-5 as disseminated grains, grains, as thin ihin pods or or lenses, lenses, and and as a layers layers as as thick thick as as 1.5 1.5 meters meters that typically typically contain wntain about about 10 10percent Mn; some some contain wntain as as much much as as20-30 20-30 percent percent Mn. Manganese Manganeseoxides oxidesare areparticularly particularly abundant abundant near Ruth Lake where two laterally persistent zones to the the 10-50 percent range. Both w 18 18 meters thick have manganese tenors enriched to Both zones zone zones about about 15 15 to more stratigraphic positions positions occupied occupied by by the the oolitic-pisolitic oolitic-pisoliticlithotope. lithotope. They Contain contain or less less coincide coincide with stratieraphic more or various psiomelane and and quanz. quartz. Goethite Goethite and and various proportions proponions of psilomelane and cryptomelane. cryptomelane, as well as hematite and manganite may be locally locallv abundant abundant-where wherethey theyoccur, occur. they they are are secondary secondary phases phases that that formed formed during during aa maneanite mav be " period period of of intense intense chemical chemical weathering weathering that modified modified these rocks rocks in in Late Late Jurassic ~ u k s ior or c Early Early Cretaceous Cretaceoustime. time. 75 75 �The origin. They Themanganese manganese oxides oxides are are most most likely epigenetic eqigenetic in origin. They are are confined to the porous and permeable permeablepails pansof ofUnit UnitA; A,rocks rockswith withthe thegreatest greatestprimary primary porosity—such porosity~suchas as quartz q u m arenitic areniticrocks rocksin inthe the epiclastic lithotope and the oolitic-pisolitic lithotope-.-.-have the most manganese. Morey and others (1991) others (1991) epiclastic lithotope and the oolitic-pisolitic lithotopeÑhav the most manganese. have have suggested suggested that that the themanganese manganesewas was deposited deposited by by aa refluxing refluxing process process involving involving reducing reducingsolutions solutionsthat that leached North range. range. The the Nonh Themanganese manganese was was subsequently subsequently precipitated precipitated leached manganese manganese from older older rocks mcks of the where depositional basin just where the the reducing reducing solutions solutionscame came into into contact contact with oxidizing oxidizing conditions in the depositional below themanganese manganesemust musthave havebeen beenprecipitated precipitatedearly earlyin inthe the below the the sediment-water sediment-water interface. interface. Much Muchof ofthe diagenetic porn spaces normally normally filled with silica the iron-formation, iron-formation, because because texturally it occupies pore diagenetichistory history of of the cement. cement. Mesozoic redistributionof ofmanganese. manganese. The The abundance of of Mesozoic weathering weathering of the rocks mcks caused some redistribution manganese theRuth RuthLake Lakearea areain inthe theEmily Emilydistrict districtaa potential potential target target for for in-situ in-situ mining mining techniques techniques manganesemakes makesthe currently and the theMineral MineralResources ResourcesResearch ResearchCenter Centerofofthe the currentlybeing beingdeveloped developedby by the theU.S. U.S. Bureau Bureauof ofMines Minesand University University of of Minnesota. Minnesota. l'his Diversification Thisproject projectwas wassupported supportedin in part pan by by the the basic basic research component of the Minerals Diversification Program, theMinerals Minerals Cooniinating CoordinatingCommittee Committeefor for the theMinnesota Minnesota State State Legislature. Legislature. Program, administered administeredby by the REFERENCES REFERENCES CITED CITED Chandler, Chandler, V.W., V.W.,and and Malek, Malek, K.C., 1991, 1991,Moving-window Poisson analysis of gravity and magnetic data from the Penokean orogen, east-central p.p.123—132. 123-132. from the Penokean omgen, east-centralMinnesota: Minnesota:Geophysics, Geophysics,v.v.56,56, Morey, Morey, G.B., G.B., and and Morey, Morey, P.R., 1990, 1990, Major Major and minor minorelement elementchemistry chemistryof of the the Biwabik BiwabikIron IronFormation Formation and and associated associatedrocks, rocks,Minnesota, Minnesota,ininAIME, AIME,Minnesota MinnesotaSection, Section,163rd 163rdAnnual AnnualMeeting, Meeting,and andMining Mining Symposium, Symposium,51st, 5lst. 1990. 1990, Proceedings: Proceedings: University University of Minnesota, Minnesota, Duluth, Duluth, Continuing Continuing Education Education and and Extension, p.p.259—287. Extension,Center Centerfor forProfessional ProfessionalDevelopment, Development, 259-287. Morey, Morey, G.B., G.B., Southwick, Southwick, D.L., and and Schonler, Schottler, S.P., S.P., 1991, 1991,Manganiferous zones in the Early Early Proterozoic Proterozoic iron-formation Range, east-central east-centralMinnesota: Minnesota: Minnesota iron-formation in in the Emily district of the Cuyuna Iron Range, Geological 42 p.p. Geological Survey SurveyReport Reportof of Investigations Investigations39, 39.42 Southwick, Southwick, D.L., D.L., Morey, Morey. G.B., G.B., and and McSwiggen, McSwiggen, P.L. 1988, 1988,Geologic Geologic map (scale 1:250,000) 1:250,000) of of the the Penokean text: Minnesota Penokean orogen, omgen, central central and eastern Minnesota, and accompanying text: Minnesota Geological GeologicalSurvey Survey Report 25 p.. Invesligations37, 37.25 p.,11p1. pi. Reportof of Investigations w E Back ramp platform litholopes Ramp hMrashett basin wave ag.Iated Solo.. fa,.weaiher wave base Low energy e,alor. 050 ,a1wy flyer ood ,.se 00a1s Figure Figure 1. 1. Schematic Schematicprofile profile of of lithotopes lithotopes in the Emily district. No No vertical vertical or or horizontal scale scale intended. intended. Environmental Phanerozoic limestone-shale sequences. Environmental nomenclature nomenclature is is typical of that used in Phanemzoic sequences. 76 �PICK LAKE ZINC—COPPER—SILVER ZINC-COPPER-SILVER DEPOSIT DEPOSIT IAN R P.. MORRISON, MINNOVA MINNOVA INC. INC. The Pick Lake massive sulphide The sulphide deposit is is situated situated 20 20 kin east of of Thunder Thunder Bay, Ontario Ion east north of Schreiber, Schreiber, 145 145 kin and km from Minnova's Ninnova's Winston Winston Lake Lake mine. mine. nd 1.5 1.5 1cm The deposit occurs 1000 meters stratigraphically below The of the Winston Lake Lake deposit deposit at the the the base of of a sequence sequence of calc—alkalic volcanics and sediments. calc-alkalic sediments. First indications of the deposit came in 1984 when Minnova drill tested a weakly the within a zone mineralized horizon horizon zone of strong hydrothermal alteration. Drill hole hole WL-9 WL—9 intersected 0 0.3 meters of massiv massive alteration. .3 meters clastic of altered pyrrhotite within a thick sequence a thick sequence clasti weakly sediments and intentiediate sediments intermediate to to felsic ash which was weak1 mineralized with zinc. zinc. Subsequent drilling down dip led to t the discovery of thin but high high grade grade massive massive suiphides. sulphides. Exploration Exploration drilling has continued to systematically test the Pick Lake deposit at depth and has defined a steeply plunging sheet with a strike length of 400 meters, dip length of less than 22 1400 meters but an average of 1400 average thickness thickness less than meters. In 1990, drill hole WL—67 meters. WL-67 intersected 13.4 13.4 meters of of massive sulphides grading 2.6% 2.6% Cu, 26.0% 26.0% Zn and 106 106 g/t Ag at at a a vertical depth of 1050 1050 meters. meters. Drilling to to date at Pick Pick Lake totals 27,000 36 holes. holes. 27,000 meters meters over over 36 — — - — — — - - Core and poster poster display: display: regional geological map of N. regional N. W. W. Ontario geological map of the Winston Lake property geological the 1:2000 section (Pick 1:2000 composite section (Pick Lake Lake stratigraphy) stratigraph 1:2000 1:2000 longitudinal section section (Pick (Pick Lake Lake deposit) deposit) surface surface geology map of the the Anderson showing showing (Pick (Pick Lake) Lake) core representative of the fringe mineralization mineralization core core representative of thin massive suiphides core sulphides massive massive sulphide intersection intersection WL—67 WL-67 sample sample suite of Pick Pick Lake Lake stratigraphy stratigraphy 77 �PLATINUM GROUP PLATINUM GROUP ELEMENT ELEMENT POTENTIAL POTENTIAL OF OF KEWEENAWAN INTRUSIVE INTRUSIVE ROCK IN WISCONSIN KEWEENAWAN H.G. Jr., Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 M.G. Itudrey. Hudrey, Jr., Mineral Point Mineral Point Road, Road, Madison, Madison, Wisconsin Wisconsin 53705, 53705, and and Bruce Bruce A. A. Brown, Brown, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 3817 Mineral Point Mineral Point Road, Road, Madison, Madison. Wisconsin Wisconsin 53705 53705 ABSTRACT ABSTRACT > Whole Intrusion, Sawyer Whole rock rock analyses analyses of of platinum platinum in in the the Round Round Lake Lake Intrusion, County, County, Wisconsin Wisconsin discloses discloses platinum platinum enrichment enrichment with with increasing increasing iron iron and and titanium accompanied titanium accompanied by by decreasing decreasing paladium. paladium. Anomalous chromium and and vavanadium nadium also also correlate correlate with with iron iron and and titanium. titanium. The Round Lake Intrusion Intrusion is is known known only from boreholes and geophysgeophysical data. It is at least 88 km long long and 22 2 2 km wide and is inferred to to exextend to a depth of of 1400 1400 mm (Roder, (Roder, 19773; 19773; Stuhr, Stuhr, 1976). 1976). Diabasic olivine olivine gabbro and troctolite occur at at the the margin of an an oxide-rich core of of the the trough-shaped intrusion. Dominant trough-shaped Dominant minerals are olivine, plagioclase and and titanomagnetite in titanomagnetite in various various proportions. proportions. In the core of of the the intrusion, intrusion, olivine olivine and and plagioclase plagioclase crystallized crystallized early early and and iron-titanium iron-titanium oxides oxides cryscrystallized tallized late. late. The core of of the the intrusion intrusion consists of a magnetitite unit unit of 12 to to 26 26 percent clusters clusters of of oxide oxide and and silicates, silicates, 9-15 9-15 percent percent olivine, 2-10 2-10 percent percent plagioclase, plagioclase, 54 54 to to 72 72 percent percent titanomagnetite titanomagnetite and and less than An50;; titanomagnetite titanomagnetite less than 3 3 percent percent ilmenite. ilmenite. Plagioclase is An averages Usp50 contains 1.3 1.3 percent percent VV on. 0. 50~ommercial Commercial poaverages Mt Mt U s p and contains potential of the Re vanadium-rich ecause ilmenite-ulvospinel vanadium-rich core core is is limited limited because ilmenite-ulvospinel intergrowths are are narrow, narrow, and and ultra-fine ultra-fine grinding grinding would would be required for for beneficiation. However, However, added beneficiation. added values from from platinum group elements may alter alter the the economics. economics. Pt ppb RL-Ol-O316 RL-01-0316 RL-05-O557 RL-05-0557 RL-Ol-0324 RL-01-0324 RL-09-1190 RL-09-1190 RL-09-1179 RL-09-1179 RL- 01-0184 RL-01-0184 RL-05-0320 RL-05-0320 RL-02-0078 RL-02-0078 RL-10-0386 RL-10-0386 ' diabase <5 ,.. ,, , <. . C5 diabase dibase 7 dibase ~ 7 * .,. - . diabase 8 diabase 8 magnetite/troctolite 11 11 lower magnetite/troctolite lower rnagnetite/troctolite lower magnetite/troctolite 30 30 Magnetite/troctolite 75 Magnetite/troctolite 75 magnetitite 106 magnetitite 106 magnetitite 116 116 magnetitite magnetitite 120 magnetitite 120 ,- PcI Co Cr V ppb ppm ppm ppm 38 103 41 35 28 29 54 105 155 142 189 35 94 50 408 478 391 609 1050 na na na >2000 1 3 3 4 1 5 170 349 790 541 2420 2530 2820 Stuhr, Stuhr, S.W., S.W., 1976, 1976, Geology of of the the Round Round Lake Lake Intrusion, Intrusion, Sawyer Sawyer County, County, Wisconsin: unpublished unpublished M.S. M.S. thesis, thesis, University University of of Wisconsin-Madison, Wisconsin-Madison, 148 148 p. P. 7Q 78 IntruRoder, D.L., 1973, 1973, The petrology petrology and and chemistry chemistry of of the the Round Round Lake Lake Intrusion, sion. Northwest Wisconsin: unpublished unpublished H.S M.S. thesis, University of of Wisconsin-Madison, Wisconsin-Madison, 115 115 p. p. U j �The The Porcupine P orcupine Mountains M ountains Michigan aarea, rea, M ichigan vvolcano? olcano? -- aa Keweenawan K eweenawan I central central ." byY b S.W. Nicholson.K.J. K.). Schulz. Schulz, W.F. W.F. Cannon. and L.G. L.G. Woodruff S.W. Nicholson. Cannon, and Woodruff U.S. VA. 22092 Survey, National Center -- MS MS 954, 954, Reston, Reston, VA. 22092 U S . Geological Geological Survey, National Center Although to the system is mostly mostly basaltic Although magmatism magmatism related related to the Midcontinent Midcontinent rift rift system basaltic composition, intermediate and about 10 of the the composition, intermediate and felsic felsic rocks rocks comprise comprise about 1 0 ttoo 15% 15% of volcanic region. Locally, and felsic volcanic section section iinn the the Lake Lake Superior Superior region. Locally, intermediate intermediate and felsic rocks dominate the Porcupine area of rocks dominate the the volcanic volcanic suite, suite. as as they they do d o in in the Porcupine Mountains Mountains area of northern Michigan. Michigan. The Porcupine Mountains Mountains area area iiss aanomalous northern T h e Porcupine n o m a l o u s in the the Midcontinent rift rift system system not not only of felsic Midcontinent only because because of of its its abundance abundance of felsic rocks rocks but but also also because of of the coincidence of of two low and -- aa gravity gravity low because the coincidence two geophysical geophysical anomalies anomalies and aa magnetic low -- superimposed broader magnetic In addition, 1). magnetic low -superimposed on on a broader magnetic high high (Fig. (Fig. 1). addition, the abundant abundant rhyolite rhyolite and rocks form partial ring ring ooff topographic the and intermediate intermediate rocks form aa partial topographic highlands making making up the structurally complex complex and felsic and apparently apparently folded highlands t h e structurally folded felsic volcanic pile. For clarity, clarity, the the entire entire area area underlain by the the elliptical elliptical broad broad volcanic pile. For underlain by magnetic high the corresponding corresponding topographic topographic highlands) highlands) will will be called the the magnetic high (and (and the be called Porcupine Mountains Within this vvolcanic Porcupine M o u n t a i n s volcanic v o l c a n i c center. center. Within this o l c a n i c ccenter, e n t e r , the the Mountains themselves themselves make make up highlands, Porcupine PPorcupine o r c u p i n e Mountains up tthe h e northern northern highlands. Porcupine Peak forms forms the the western western highlands, and the the hills hills around around the firetower Bergland firctowcr Peak highlands, and the Bergland the southeastern southeastern highlands make up highlands (Fig. Earlier workers that this this make up the (Fig. 1). 1). Earlier workers suggested suggested that area is is aa remanent remanent of of an Icelandic-style central central volcanic (White, 1972; 1972; area an Icelandic-style volcanic complex complex (White. Green, Kopydlowski, 1983), but evidence supporting this suggestion has has 1983). but evidence supporting this suggestion Green, 1977; 1977; Kopydlowski. been largely To mapping, geochemical, this hypothesis, hypothesis, mapping. geochemical, been largely undocumented. undocumented. T o evaluate evaluate this isotopic, and and geophysical geophysical studies studies were were recently recently undertaken Porcupine isotopic, undertaken in tthe h e Porcupine Mountains area. area. Mountains Preliminary results of of mapping studies indicate indicate many Preliminary results mapping and and geophysical geophysical studies many similarities between Icelandic Icelandic central central volcanoes the inferred inferred Porcupinc Porcupine volcanoes and the similarities between Mountains center. For Porcupine Mountains Mountains volcanic volcanic center. For instance, instance, the the Porcupine Mountains center center formed formed at the rift zone 40km kmwide, wide,comparable comparable in in size size at the edge edge of of an an active active rift zone and and is is about about 30 30 to to 40 to Icelandic Icelandic central central volcanoes. volcanoes. Earlier that an accumulation accumulation to Earlier workers workers recognized recognized that felsic and intermediate of rocks, called the the 'unnamed" lensof felsic intermediate rocks, "unnamed" formation, formation, formed formed a lensshaped body body underlain underlain by the the northwest-dipping Lake shaped northwest-dipping basalts basalts of of the t h e Portage Portage Lake Volcanics (Fig. 1). The "unnamed' formation formation iiss being formally formally named named the Volcanics (Fig. 1). T h e "unnamed" the Porcupine Volcanics review). This formation Porcupine Volcanics (Cannon (Cannon and and Nicholson, Nicholson, in review). This formation is is more more than thins away than 2 2 km km thick thick at its its thickest thickest but but thins away from from the the Porcupine Porcupine Mountains Mountains area. area. The T h e thickness t h i c k n e s s ooff the t h e overlying o v e r l y i n g Copper C o p p e r Harbor H a r b o r Conglomerate C o n g l o m e r a t e decreases decreases substantially over the Porcupine Porcupine Volcanics. substantially o v e r the Volcanics. Recent mapping mapping hhas the southern southern highlands highlands Recent a s shown shown that that much much rhyolite rhyolite in the occurs as flows of intermediate occurs a s subvolcanic subvolcanic bbodies o d i e s that that intrude intrude flows intermediate composition. composition. These rhyolites porphyritic, containing both quartz quartz and feldspar These rhyolites are a r e commonly commonly porphyritic, containing both feldspar phenocrysts. Near the Porcupine Volcanics southern highlands, highlands. hcnocrysts. Near the top top of o f the the Porcupine Volcanics in the the southern ann extrusive small feldspar feldspar phenocrysts. In extrusive rhyolite rhyolite body contains contains mostly mostly small phenocrysts. In contrast, rhyolite bodies bodies in the northern highlands highlands are extrusive flows. ntrast, most most rhyolite the northern a r e extrusive flows. However, typically massive massive aphyric aphyrie flows flows oor owever. these these rhyolites rhyolites are a r e typically r they they may may contain contain only Understanding the u a r t z phenocrysts. phenocrysts. Understanding t h e cchemical hemical nly ssparse p a r s e feldspar f e l d s p a r ±Â qquartz relationships among rhyolite bodies in the Porcupine Porcupine Volcanics awaits the relationships among the t h e rhyolite Volcanics awaits the results of of detailed geochemical studies. results detailed geochemical studies. Gravity modeling modeling across across the center requires Gravity the Porcupine Porcupine Mountains Mountains volcanic volcanic center requires the the presence stock to felsic stock presence ooff a felsic t o account for the low low gravity anomaly beneath the the 79 �Portage Lake Volcanics Magnetic high (ft j_. Strike and dip /0 Gravity (in mgals) II Magnetic low GEOPHYSICAL ANOMALIES 1Vpl1I a km 10 sedimentary rocks x -la w n n 3 C V Z-C: C 0) m Â¥*- 4-1 *<-xu .P- w'n Â¥*->0) sm 0Q C m E c 0 0 I-<->-= w m 0 .- .- - \ Â¥I-' - 0 3 C.£m Â¥*- 0 a%- 0 s %-Â¥I0 0-7 C> > W -c Â¥*- .- s- c-0 C -3 C. 0 u I . part of the upper location of Porcupine Mountains volcanic center in the northwestern Volcanics coincide with an peninsula of Michigan. -a C m w .- cr s - 0 % wQ- 0 Â¥IC w w-c: u Â¥*- I à .- - L_ L I m L. L W C (L- c±i L_ C 0 Lt 0 I Â¥! L... .- CL The topographic highlands of the Porcupine low and gravity low anomalies coincide and elliptical magnetically high anomaly. Smaller magnetic are superimposed on the middle of the magnetic high. FIG. 1: Map showing -S.-' 5 1 Keweenawan Lillill Porcupine Voicanics [Vs EXPLANATION GEOLOGIC UNITS ____ m LC[ 0 _ w =, (0 �A felsic volcanic also is is consistent volcanic center center (Kiasner (Kiasner and and Jones. Jones. 1989). 1989). A felsic stock stock also consistent with with inference of the The the coincident coincident low low magnetic magnetic anomaly anomaly (King, (King, 1987). T h e geophysical geophysical inference of the aa felsic felsic stock stock lying lying beneath beneath the the volcanic volcanic center center supports supports the the comparison comparison with with the Icelandic model of of aa central Icelandic model central volcano volcano overlying overlying aa shallow shallow magma magma chamber. chamber. interpretation in Numerous Numerous faults faults and and apparent apparent folding folding complicate complicate structural structural interpretation in highlands (in the Porcupine For this area. For example, example. in in the northern northern highlands (in the Porcupine Mountains Mountains Statee Wilderness Wilderness Area). Area). a a change change in in the the dip dip of of volcanic volcanic units units from from south south ttoo north north However, detailed detailed mapping led Hubbard (1975) 5 ) to to propose propose an an anticline. anticline. However. mapping indicates indicates that some individual ual stratigraphic stratigraphic units units cannot cannot be be traced traced across across the the proposed proposed fold. fold. different An n alternative alternative model model for for the the structure structure of of the the northern northern highlands highlands is i s that that different flow-dome (1-3 km rhyolite bodies may may represent represent individual individual small small (1-3 km wide) wide) flow-dome complexes, still intact, exes. some some with with carapace carapace breccias breccias still intact, and and possibly possibly localized localized along along aa Similar major caldera-bounding een c a l d e r a - b o u n d i n g fault. fault. S i m i l a r flow-dome f l o w - d o m e ccomplexes o m p l e x e s hhave a v e bbeen (Macdonald eett al.. in Iceland Iceland (Macdonald documented ented in in the the Torfajokull Torfajokull volcanic complex complex in al.. coincident the coincident area of 1990). Thus, Thus, we we suggest suggest that the elliptical area of highlands highlands and and the shape of of the volcanic shield, shield, although the original original shape geophysical sical anomalies anomalies reflect the the volcanic although it has been been somewhat somewhat modified modified by by post-rift post-rift compressional compressional deformation. deformation. share many The T h e Porcupine Porcupine Mountains Mountains volcanic volcanic center center appears appears ttoo share many similarities similarities off the with ith Icelandic-style Icelandic-style central volcanoes, but but aa more more complete complete understanding understanding o the structures along area e a will will require require careful careful interpretation interpretation of of structures a l o n g nearby nearby seismic seismic structural units of stratigraphic reflection flection profiles, profiles, detailed detailed correlation correlation of stratigraphic u n i t s and and structural isotopic aand of chemical, analysis nalysis within within the t h e center, center. and and careful careful analysis analysis of c h e m i c a l , isotopic nd volcanological data. ., : 7 data. References R eferences of stratigraphic stratigraphic Revisions in review, and and Nicholson, Nicholson, S.W., S.W.. in review, Revisions of northern Michigan. Michigan. Supergroup of of northern Keweenawan Supergroup nomenclature nomenclature within tthe h e Keweenawan U.S. Geological U.S. Geological Survey, Survey, Bulletin Bulletin 1970-A. 1970-A. region. Keweenawan plateau Green, 1977, Keweenawan plateau volcanism volcanism in in the the Lake Lake Superior Superior region. reen. J.C., 1977. p. 407-422. Geological Association Association of of Canada, Geological Canada. Special Special Paper Paper 16, 16, p. 407-422. Carp River Geology Hubbard, 1975, ubbard, 11.A., H.A., 1975, Geology of of Porcupine Porcupine Mountains Mountains in in Carp River and and White White v. 3. 3, U.S. Geological Pine quadrangles, Pine quadrangles, Michigan. Michigan. U.S. Geological Survey, Survey, Journal Journal of o f Research, Research, v. p. 519-528. quadrangle. River 1° Iron River Aeromagnetic map map of King, King, E.R., E.R., 1987, 1987. Aeromagnetic of the the Iron 10 xx 2° 20 q uadrangle. Miscellaneous Survey, Geological Wisconsin. U.S. G Michigan and Michigan and Wisconsin. eological S urvey, M iscellaneous Inverstigations Inverstigalions Series, Series, 1-1360-F. I-1360-F, 1:250,000. anomaly map map and Bouger gravity Klasner, J.S., 1989, J.S., and Klasner. and Jones, Jones. W.J., 1989, Bouger gravity anomaly and geologic geologic and Wisconsin. Wisconsin. Michigan and quadrangle, Michigan interpretation of of the Iron River the Iron River 10 10 xx 20 quadrangle, J-1360-E. Series. Miscellaneous G e o l o g i c a l Survey, Survey, M i s c e l l a n e o u s Ilnverstigations nverstigations S e r i e s . I-1360-E. U.S. Geological Cannon, Cannon, W.F., W.F.. 1:250,000. . 1:250,000. The Kopydlowski, opydlowski. P.J., 1983. Oak Bluff Bluff Volcanics. central P.J.. 1983, The Oak Volcanics. aa Middle Middle Keweenawan Keweenawan central thesis, unpublished M.S. M.S. thesis. region. Michigan. Mountains region, volcano; Porcupine Mountains Michigan. unpublished Michigan Michigan Technological Technological University. Houghton. Houghton. 88 8 8 pp. 1990. Macdonald, R., McGarvie, McGarvie, D.W., D.W.. Pinkerton, Pinkerton, H., H., Smith, Smith. R.L., R.L., and and Palacz, Palacz. Z.A., Z.A.. 1990. Macdonald, R., I. Petrogenetic evolution of o f tthe h e Torfajokull Torfajokull volcanic v o l c a n i c ccomplex. o m p l e x , IIceland c e l a n d I. 31, p. Journal of of Petrology. Relationship between the Relationship between the magma magma types. types. Journal Petrology, v. v. 31, p. 429-459. 429459. Quarterly eastern Iceland. volcano, eastern Walker, The alker, G.P.L., G.P.L.. 1963, 1963. The Breiddalur Breiddalur central central volcano. Iceland. Quarterly 119. p. p. 29-63. Journal Journal of the the Geological Geological Society Society of of London. London, v. v. 119, 29-63. White, hite. W.S., W.S.. 1972, 1972, The T h e base base of ofthe theUpper UpperKeweenawan, Keweenawan, Michigan Michigan and and Wisconsin. Wisconsin. U.S U S .Geological .Geological Survey Survey Bulletin Bulletin 1354-F, 1354-F. 23 2 3 pp. pp. 81 �PHYSICAL PHYSICALVOLCANOLOGY VOLCANOLOGY OF OF THE THEFOOTWALL FOOTWALL ROCKS AT ROCKS AT THE WINSTON LAKE LAKE MASSIVE SULFIDE DEPOSIT Steven A. A. Osterberg Osterberg Steven Geology Dept., Dept., Economic Economic Volcanological Volcanological Research Lab. Lab. 55812 University of of Minnesota—Duluth, Minnesota-Duluth, Duluth, MN 55812 Ian R. R. Morrison, Morrison, P7C lE7 Minnova, Inc., Thunder Thunder Bay, Bay, Ontario Ontario P7C 1E7 Footwall Footwall racks rocks at at the the Winston Winston Lake Lake massive massive sulfide sulfide deposit deposit consist of amphibolite grade, sequence consist of an amphibolite grade, hydrothermal].y—altered hydrothermally-altered sequence north—south trending of north-south trending volcanic volcanic and and volcaniclastic. volcaniclastic rocks. Geological mapping, drill drill core, core, and and petrographic petrographic studies studies allow allow dedeanalysis of of the stratitailed subdivision and volcanological volcanological analysis graphy. graphy. Thick (100—325m), to felsic felsic (100-325m), massive massive to to poorly—bedded poorly-bedded tuafic mafic to Thick volcaniclastic rocks rocks form form the the base base of the stratigraphy and are are bounded to the the west west by by granitic granitic intrusive intrusive rocks. rocks. Intercalated and suggest suggest the felsic pyroclastic rocks form marker horizons horizons and deposits thicken thicken southward. southward. The clastic rocks by l00—850m rocks are are overlain overlain to the east by 100-850m of interlayered felsic and maf Ic lava flows which, in general, interlayered felsic and mafic lava flows which, general, thicken southward. constitute 80% of the southward. Felsic flows, which constitute the succession, are quartz—feldspar—phyric, and rarely succession, quartz-feldspar-phyric, massive, massive, and rarely flow—banded and flow-banded and brecciated. brecciated. Mafic lava flows vary from massive to well-pillowed, and and aphyric aphyric to to feldspar-phyric. feldspar-phyric. Local mafic mafic and felsic dikes dikes are present near are present near the the south end of the sequence and are are thought thought to to represent represent feeders feeders to to the the lava lava flows. flows. is 75-200m thick Immediately above the lava flows a 75-200m Immediately above the lava flows is a thick sequence of pyroclastic Pumice-bearsequence pyroclastic and and volcaniclastic volcaniclastic rocks. rocks. Pumice—bearing to the north ing felsic felsic pyroclastic pyroclastic rocks predominate predominate to north with with The pyroclastic pumice size and content increasing northward. size and content increasing northward. rocks interfinger rocks interfinger to to the the south south with mafic-felsic volcaniclastic rocks. The volcaniclastic rocks. volcaniclastic rocks are locally locally transected transected by aa laterally limited (100—125n), but thick (150m), laterally (100-125m), (150m), succession of The maf mafic rocks are aphyric mafic lava flows, sills, and dikes. aphyric maf ic lava flows, sills, and ic rocks are thought to fill an axial trough, and to represent a feeder comfill an axial trough, and plex to to lavas lavas higher higher in in the the section. section. The flows vary from from maspeperites and sive to pillowed; peperites and cm—scale cm-scale sheet sheet flows are locally locally well-developed. The Winston Lake Lake Horizon Horizon caps caps the the footwall footwall sequence sequence and and mafic—felsic consists of 3—4 3-4 interlayered interlayered mafic lava lava flows and mafic-felsic volcaniclastic rocks rocks and and cherty cherty tuffs. tuffs. The lavas lavas are are aphyric, aphyric, laterally extensive southward. Vo].laterally extensive (>2km), (>2km), and and thicken thicken (2-BOrn) (2-80m) southward. Volcaniclastic rocks thickness and are caniclastic rocks and and tuffs tuffs vary vary from from l-20m 1-2Om in thickness are massive, to well-laminated. well—laminated. massive to The stratigraphy stratigraphy at Winston Winston Lake Lake developed developed with with cyclic cyclic accumulation of volcaniclastic accumulation volcaniclastic and volcanic volcanic rocks; lava flows flows In contrast, contrast, rift—related southward were derived from from aa rift-related southward source. In felsic pyroclastic pyroclastic rocks felsic rocks appear appear to to have have been derived from from an an unrelated northward northward source. source. The lack lack of hydrovolcanic or vesivesicular deposits volcanism prevailed suggests deep water cular deposits suggests water volcanism prevailed at at Winston Winston Lake. Lake. 82 �-- THE THE NEDA NEDA IRON IRON FORMATION FORMATTON—— AA PRODUCT PRODUCT OF OFVOLCANISM? VULCANISM? William Alexander St., Appleton, WI W i l l F. F. Read, Read, 1905 1905 14. N. Alexander WI 54911 54911 The Neda iron formation crops out along the east, south, and southwest flanks of the It lies at the top of the upper Ordovician Maguoketa shale and is Wisconsin Arch (Fig. 1). It reaches a maximum The formation is discontinuous. overlain by Silurian Mayville dolomite. thickness of about 12 meters. Downdip. sway from the arch, its extent is not well known. The Neda is characterized by an abundance of oblate spheroidal structures not more than These have generally been described as ooids, implying that they about 2 mm in diameter. originated by wave and current action on the aea floor. Near the village of Neda in eastern Wisconsin. the type locality, the formation was Two types of ore were fonnerly mined in small open cuts and shallow underground workings. in "soft recognized: &&gnized: "soft ore.' ore," in in which which the the "ooids" "ooids" are are weakly weakly cemented cemented together, together, and a "hard ore, Ore xt is is generally generally not not which which they they are are well well cemented. cemented. Hard ~ard ore Occurs occurs as as aa capping capping on on the the soft soft ore. ore. It more more than than aa meter meter thick. thick. My formation are based mainly on petrographic My ideas i d concerning i n c o m i n g the the origin origin of of the the Neda Neda formation Lakeside examination of 0 0 aa few r e thin h " sections i o n of Of hard hard ore ore from from the thetype locality. localit". Lakeside 70 7 0 was was used to 5y attach the rock to the slide. This cement, unlike epoxies, does not gelatinize in acids. soaking the section for several days in strong (6N) nitric acid I got rid of most of the hematite Removal of these ingredients did and linonite which makes an untreated section largely opaque. It appears that the iron oxide minerals are finely disseminated not leave holes in the section. through the host materi•ala in which they occur. Fig. Fig. 11 outcrop Outcrop of of Ordovician—Silurian ordovician-silurian boundary boundary in in parts parts of of Minmesota, HinnÇÈot Iowa, on down—dip aide Iowa, Illinois, Illinois, and and Wisconsin. wimconsin. Dots ~ o t sare o n the &--dip side of the the line. line. Areas Nçd formation formation is is exposed exposed are are stippled. stippled. The Ordovician—Silurian Ordovician-Silurian Ar-as where wh-r- Neda boundary Devonien; boundary is is overlain overlain in in places plat-s by by post—Siluriem post-Silurian sedisenta: sediments: 0 D — m vonian; C — carboniferous. Carbonirxrous. Geology, Geology, except except Weds ~ e d aareas, areas. from from U.S. U.S. Geological Geological Survey, Survey, Geologic Map Map of of the the United United States, States, 1/250,000, 1~250,000,1932. 1932. Geologic - - 0' 0-, �work has been done On thin sections of the Heda so far as I an aware, very little have contented oxides have been removed. Most workers formation from which most of the iron A rather detailed study of polished surfaces or acetateinpeels. themselves with the examination Neda was published 1934 by Hawley and Beavan (1). of the mineralogy of the Neda formation at mixture material obtained from a mining company —— presumably athem They worked mainly withThin crushed lisonite by soaking in a fragments were clearedexamined of hematite and of hard and of softnitric ore. and hydrochloric by transmitted light under a acid, then combination a mineral by petrographic methods was petrographic microscope. If the identification of checked it by powder X—ray diffraction. uncertain, and the mineral seemed important, they "ooids" alone are so varied and complex that it is not In the hard ore from Neda, the am convinced, however, that they were not formed easy to draw conclusions about their origin. I ooids in the usual sense of the term. It seems to by sedimentary processes and are therefore not volcanic origin. A volcanic me more likely that they are miniature accretionary lapilli of abundant transported origin is suggested by Hawley and Beavan's observation that 'the most They also obser-ved that the lava." fragments in the ore are rough, angular grains of scoriaceous I found to brown volcanic glass. cleared of iron oxides, im a "dirty, green lava, when of in ooids." They are not what I take to be volcanic glass mainly as nuclei fragments really glass Or some amorphous or open to question whether they are acoriaceous and it is crystalline material which may have been derived from glass. submicroscopically Hawley and meavan reject the idea that Where did this glass come from and how old is it? active when the Neda formation was deposited. They came from nearby volcanoes which were it from which the glassy fragments Were prefer a precambrian source to the "west or northwest" objection to a nearby, contemporary source I is transported by streams or marine currents. Their is recognized in this part of North America." that "as yet no igneous activity of such age The youngest their proposed alternative, think there is a much sore serious objection toaxis of the Wisconsin Arch) and northwest (the Precambrian volcanics to the west (along with only a very small percentage of whatever glsaa may present take Superior region) are Keweenawan. volcanics is likely to have escaped originally have been present in the Keweenawan Even if we assume that there was more devitrification as early as OrdovicisnSilurian time. fragments of it remain then than there is now, how could transported fleas in the geweenawan velsasics in the source area, alteration was actively apparently unaltered in the rieds formation while,formation, glassy fragments should be abundant progressing? one may also ask why, in the Neda more abundsnt in the source while fragments of crystalline lava, which certainly would have been Igneous activity of Pa,leozoic or later age may not have been recognized in area, are miasinq. in Hawley and meavan's day but now we have the the area where the Neds formation was deposited take Ellen kimberlite to remind us that there has, in fact, been post—Keweenawan volcanic Whether it extended down into the area where the Made was activity south of Lake Superior. deposited remains to be seen. Most of the •'ooids" in my thin sections show a thick costing of slightly anisotropic say be material surrounding any nucleus that may be visible. This, together with the nucleus, In "ooids" which lack a visible nucleus, the core consists regarded as the "core" of the "ooid." There is evidence Most of it is pale green or brown. entirely of the nearly isotropic material. Both varieties show imperfect green. that the brown variety was formed by oxidation of thevisible —— otherwise around what may be taken concentric lamination around the nucleus, if one is Light passing The laminae are most clearly ylsible XN. roughly as the center of the core. long dimensions of the laminae (and also, of course, at through them is polarized parallel to the guess in otherwise stra,n is that this is a result of My right angles to the long dimensions) . look as if they may betheparticles inclusions which isotropic material. There are abundant small long parallel to of volcanic ash, also platy or lath—shaped crystals which are elongatadin alternate shells around dimensions of the laminae. The material which forms cores also occurs the cores, material as was The same question may be asked concerning this slightly anisotropic core is it glass or some amorphous or sumicroscopically asked about certain nuclei in the "ooids': of which many shell fragments identified the material crystalline material? Hawley and seavan According to Ross and Kerr (2) , halloysite is a they observed consisted as halloysite. If the green or brown core submicroscopically crystalline clay mineral related to kaolinite. been weathered. The material which I observed is halloysite, it has presumably material I suggest that the material forming cores in weathered may very well have been volcanic glass. but composed of the same material, the "ooids" I observed, and shells separated from the cores lava onto nuclei which, in some cases, tiny droplets of liquid were formed by the accretion ofThe of droplets. I think, spread out over the rounded surface Thus are visible; in others, not. the previously accreted material which had had time to harden or become extremely viscous. imperfect lamellae were formed. Alternating with the shells of green or brown core material are shells composed of It is generally completely isotropic but may material which is transparent and colorless. The refractive showing low birefrimgence. contain very small, nearly equidimenaional crystalsthan the mean refractive index of core index I found to be close to 1.54. a little lower Scattered reflected present in it. commonlyclear material look tomato—red XN. material, opaque patches of iron oxide minerals are light from these patches makes a good deal of the adjoining in transparent, colorless shells as Hawley and Beavan identified the material which they found about 1.54They too found that it has a refractive index of colorless opal. transparent shells seems to have The mode of deposition, or emplacement, of the large Some of these shells were originally composed Of relatively been rather extraordinary. projecting from the - Euhedral outlines of these crystals may be seen In one case which I observed a shell of of thews inner and/or outer surfaces of shells composed euhedral crystal of the same material is present in crystals, mow paeudomorphs. this core type pinches out and a single, isolated. the shell was growing material a short distance beyond its tip. I see this as evidence that the direction of growth toward the isolated crystal, which is in line with it. What controlled lameliae in adjacent core is uncertain. Transparent, colorless sheila roughly perallel theof the core and of the "ooid' as This means that they also parallel the outer tension surfaces material, developed in core material of Possibly more or less evenly spaced zones of a whole. 84 �If these zones of tension were been entirely Composed. expected that they whic4 the "oojd" sees originally to have due to shrinksge as a result of etier cooling or dehydration it is to be would parallel the outer surface of the "ooid." crystals and show no pseudOmorphs of antecedent Many of the colorless, transparent shellscrystalline some ehells of this from the This other. were preeusably amorphous or sumnicroscopically each with of many very thin shells in contact start. type are clearly composites madeup a crack, which opened, was filled, and then reopened several may be the result of deposition in tines. idea, L. embraced by other workers, that the oblateness of the The I am doubtful about theis due to sediments. compreçsion under the load of overlying masses of "ooids" in the Neda formation structures a few cm in diameter which appear to be depositioflal surface, picking up soft ore contains cylindrical which rolled down an inclined flattened tangentially. material, mud—like in consistency, "Ooida" in these structures are If so. the additional material as they progressed. deposited. place before overlying sediments were indicating that the flattening took while the "ooids" were still soft and most likely cause of the flattening would be rapid rotation known as airborne. spheroidal bodies 1-10 mm in diameter surrounded by Kimberlites and kimberlitic ejects contain nucleus—Usually a sineral grain——is "pelletal lspilli." In these, some kind of a The latter often exhibits a poorly defined very fine—grained. optically unresolvable, material. lath—shaped sinerals with their long dimensions concentric structure and contains platy or parallel to the surface of the is present; otherwise This does parallel to the concentric layering, if thisthese bodies as quenched lava droplets. clement (3) originally explained lapillus. i attribute the concentric structure in concentric structure, however. suggested that accretion may also not eccouflt for their later to accretion, clement (4) lapilli it is not clear core material of Neda "ooids' of kisberliteS. concentric etructure in pelletsi of Neda ooids and also be responsible for the to account for the oblatenesssomehow initieted after whether the rapid rotation postulated numerous pellets1 lepilli was in progress during accretion or was accretion had ended, of pelletsl lapllli I do not features of Neda "ooids" with those produced the weda formation was In comparing certain volcanic activity which, in my opinion, mean to imply that the This is not an impossibility. the same as, or similar to, that which produces kimberlites. however. Many "ooids" in the Neda hard ore show evidence of deformation after the rlgld clear This caused solidified. shells had been emplaced but before core material had completely the fragments. accompanied by flowage of clear layers and displacement of by a later fragmentation of the of landing; (2) impact causes of deformation are (1) shock"ooids" material, Possible(3) and matrix; (4) compression viscous flow of the accumulated core volume of an 'ooid" core after landing; arrival Where deformation decreased the under the load of overlying sediments, was squeezed out into the surrounding matrix, ieces of pre—existing material have observed fragments of fossils, sand grains. Wd support the concept of a Many workers "ooids" serving, as nuclei in Neda ooids - — these occurrences sppear to volcanic crater near - L L. - a sedimentary origin, rather than a volcanic one. I suggest, however, that that normal marine intervals of quiescence, by sea water and AccretionarY lapilli will sea level may be filled, during be deposited in it. sediments containing the remains of organisms may of these Fragments when en eruption occurs. crater well as outside of, the fall inside, as be blown aloft by a subsequent L. lapilli, the sediments, and hard parts of organisms all may eruption. does not see likely, to me, that the Neda formation was deposited under water. as I propose, an aquatic land -- land which, to allow for occasional coaling. I think that deposition took place on It If temperature 'ooids" and the matrix was due to high the fluidity of core environment material in of deposition is ruled out because it would have caused rapid far above sea level. the crster of the source volcano, was not flooding I of sections. It surrounding "ooida" in my thin have looked et a good deal of the matrix by which may be bits of volcanic glass replaced contains many angular fragments, mostly opaque, fragments they saw were Hawley and Beavan saw a lot of these, too. However, the They are iron oxides. kinds. many of so by high temperature in scoriaceous; the ones I saw are not. There are other inclusions material, kept imbedded in what appears to have been fluid or plastic (?) replacement seems to have occurred, After hardening, a good deal of deuteric main purpose here is my opinion. description and interpretation of the matrix, My shall not attempt furthervolcanic origin, and I think it is sufficiently promoted by to promote the theory of consideration of the ooids" alone. Rr nmxN cr5 (1) (2) (3) (4) Ore of and A. P. Besvan. 1934. "Mineralogy and Genesis of the Mayville Iron American Mineralogist. vol. 19. p. 493—514. Wisconsin. "Halloyaite arid Allophane." U, s. Geological Survey, Ross. c. S., and P. F. Ierr. 1934. Profeapional Paper la5—G. p. 135—148, "Icisberlites fros the Mao Pipe, L.esOtho." Lesotho Kimberlites. Clement. C. R. • 1973. p. 110—121. Study of Some Major Icilaberlite Pipes in the Clement, c, IL, 1982. "A conparative Geological Ph.D. thesis. univ. of cspe Town. Northern cape and orange Free State." Hawley. .7. E., 85 �LITHOGEOCHEMISTRYAND ANDGEOLOGICAL GEOLOGICALMAPPING MAPPINGININ THE THE VERMILION VERMILION GREENSTONE BELT, LITHOGEOCHEMISTRY GREENSTONE BELT, MINNESOTA, AS AS AN MINNESOTA, AN AID AIDTO TOMINERAL MINERALEXPLORATION EXPLORATION Reichhoff, J.A., J.A., Hauck, Hauck, S.A. S.A. Reichhoff, Natural Resources ResearchInstitute Institute Natural Resources Research University ofofMinnesota-Duluth University Minnesota-Duluth Duluth, MN MN 55811 55811 Duluth, Southwick, D.L. Southwick, D.L. Minnesota Geological Survey Minnesota Survey 2642 University University Avenue 2642 Avenue St. Paul, Paul,MN MN 55114 55114 The Vermilion Vermilion greenstone greenstonebelt belt in northern tectonic The northern Minnesota Minnesota is aa complex complex tectonic assemblageofoflate late Archean volcanic and andsedimentary sedimentaryrocks rocksthat thatconsists consists of the assemblage Archean volcanic the where oreore has classic Vermilion Vermilion district, district, whereiron iron hasbeen beenmined mined for for more more than than a century, and its subsurface theglacial glacial cover. Several cycles and its subsurface extensions extensions to the the west west beneath beneath the cover. Several other than than iron iron have occurredinin the the belt of mineral mineral exploration exploration for forcommodities commodities other have occurred over the years, generally the most most intensive intensive of over generally without withoutsuccess; success; perhaps perhaps the of these these has has been in in the recognition that the the last lastdecade, decade, following the thegeneral general recognition the Vermilion Vermilion greenstonebelt belt isistectonically a part of the productive Shebandowan-Wawagreenstone tectonically a part of very the very productive Shebandowan-WawaAbitibi subprovince To assist assist industry with the Abitibi subprovinceofo fthe t h eSuperior Superiorprovince provinceofofCanada. Canada. To the difficult task of of conducting this poorly exposed difficult task conductingexploration explorationinin this poorly exposedregion regionofofMinnesota, Minnesota, the State has regional mapping mappingprojects projectsaimed aimedatatproviding providing the the geological, geological, has conducted conducted regional frameworkrequired requiredfor for mineral mineral potential geophysical, and and geochemical geochemical framework potentialassessment assessment and and The lithogeochemistry lithogeochemistry and andmapping mappingproject projectdescribed described here here is is strategic planning. planning. The within the Vermilion Vermilion designed to provide regional data on rock compositions compositions within greenstone be1 belt. greenstone t. Recent geological geological mapping, Recent mapping, supported supported by by detailed detailedaeromagnetic aeromagnetic mapping mapping and and shallow drilling in poorly exposed areas, has led to the recognition at least shallow drilling in poorly exposed areas, has led to the recognition ofof at three volcanic-sedimentary cycles in the belt. These Theseare: are: (1) volcanic-sedimentary cycles the Vermilion Vermilion greenstone greenstone belt. dominantly calc-alkaline calc-alkaline sequence aa dominantly sequence that that includes includesrocks rockssouth southofo fthe theMud MudCreek Creek and and Wolf Lake Lakefaults faults in the Vermilion district and the Bear BearRiver Riverfault fault in Vermilion district and southeast southeast oof f the dominantlytholeiitic tholeiitic sequence that includes northeast Itasca (2) aa dominantly sequence that includes rocks rocks northeast Itasca County; County; (2) a mixed volcanic sequence north and northwest of these faults; and (3) north and northwest of these faults; and (3) a mixed volcanic sequence (calc(calcalkaline and tholeiitic) ofofunknown stratotectonicaffinity affinity (in the and tholeiitic) unknown stratotectonic the "Virginia "Virginia horn") horn") that lies south of sequence (1) and is separated from it by intrusive granitic rocks lies south of sequence (1) and is separated from it by intrusive granitic rocks of the batholith. the Giants Giants Range Range batholith. Approximately 280 rock rock samples havebeen beencollected collectedfrom fromthese thesethree three volcanic Approximately 280 samples have sequences and analyzed for major elements, minor elements, and trace elements sequences and analyzed for major elements, minor elements, and elements (70 (70 Thesedata dataform formanan analyticallyconsistent consistentset set that that characterizes elements total). These elements total). analytically comparisons, facilitates comparisons, and facilitates the lithogeochemistry of the volcanic volcanicsequences sequences and Thedata data also also provide provide the correlations and correlations and petrochemical petrochemical interpretations of o fthem. them. The statistical background metal statistical background on on the the distribution distributionof of metalbackground background concentrations, concentrations, and and pathfinder elemental associations in in the pathfinder elemental associations the rocks rocks that isisnecessary necessary for formeaningful meaningful interpretation ofofthe have interpretation themore morethan than6,200 6,200 partial partialrock rockanalyses analysesthat that haveaccumulated accumulatec over the past andexploration explorationactivities activities in the the Vermilion Vermilior over past century century from from academic academic and greenstone be1 belt. greenstone t. Productsoof the lithogeochemistry lithogeochemistryproject projectwill will be: be: (1) (1) aa generalized generalized regional Products f the the central part shows geologic map map oof f the part ofofthe theVermilion Vermiliongreenstone greenstone belt beltthat that showssample sample locations for 70-elementrock rockanalyses; analyses;(2) (2)a acomputer computer file(electronic) (electronic) locations forthe the280 280 new new 70-element file file (electronic) (electronic) of data; (3) (3) aa computer of the the new new analytical analytical data; computer file of the the archival archival provides report that describes methodologies and analytical data; and (4) (4) a report that describes methodologies and provide: interpretations. 86 . U j J �THE NATURE NATURE AND SOURCE SOURCE OF MIDCONTINENT RIFT IGNEOUS ROCKS IGNEOUS ROCKS !1(ailT. Seçfrt1, ZeOT!E. fPetennan2 ant Scott tE. 'Thieben3 (Departmentof of ~geological a' A i4tmospfieric Sciences, lown LowaState State University, 'University,S^mes, Thnes Ifi IA ' 'Department e o l o tV w ~ f k T Sciences, V 2 500111 5001 fBrancfi S. geolbgica4TSurvey, yesleral Center, (Denver, Co 'Branch of Isotope Isotope,geology, (geology,V. 11.5. QeohgicdSurvey, '(Denver D e n w fahraf~enter, 'Denver, CO 80225 8022.5 (Department of geologicalsciences, 'University of Texps, J.ustin, 'IX 78712 Trace element and Nd-Sr isotopic data Midcontinent Nd-Sr isotopic data indicate indicate that the Keweenawan Midcontinent igneous rocks rocks originated originated from from both both mantle and crustal crustal sources sources with with mafic maficrocks rocks being being Rift igneous from the the mantle and and more more felsic felsic rocks rocks being being derived derived from fromthe the crust. crust. The Mineral derived from the occurrence of interlayed interlayed mafic mafic and and Lake intrusions near Mellen, Wisconsin, illustrate the intrusions with with mixed The bimodal felsic intrusions mixed mantle mantle and and crustal crustal origins. origins. The bimodal source source of igneous rocks explains the bimodal bimodal compositional distribution distribution of these Midcontinent Rift igneous and other other flood flood basalt province province rocks. rocks. and 1984; Dosso, Nd-Sr isotopic data for Midcontinent Midcontinent Rift Rift igneous rocks (Brannon, 1984; 1984; Paces and and Ben, Bell, 1989) 1989) plot in three largely separate fields on an Nd-Sr(T) 1984; Nd-Sr(T) diagram diagram with T ==1100 The three fields 1100Ma, Ma,suggesting suggestinglimited with limitedmixing mixingand andcontamination. contamination. The fields represent aa mafic mafic rock rock mantle field field surrounding surrounding Nd-Sr Nd-Sr values values of of zero, zero, and and lower lower and and represent fields for for more felsic felsic rocks. rocks. The mafic rocks rocks plot plot in the the field field upper crustal fields The Mineral Mineral Lake mafic by other Midcontinent rocks indicating an an origin origin from from slightly slightly depleted depleted defined by Midcontinent Rift mafic rocks or near chondritic mantle. mantle. The The Mineral Mineral Lake Lake felsic felsic rocks fall close to the crustal crustal fields felsic rocks. rocks. Some defined by other Midcontinent Midcontinent Rift felsic Some mixing mixing is indicated indicated by by the narrow narrow connecting the mafic isthmus connecting mafic mantle mantle field with with the the more more felsic felsic lower lower crustal crustal field. field. Spider diagrams Spider diagrams of of trace trace element element data data for for the the Mineral Mineral Lake Lake mafic mafic rocks rocks relative relative to to field for flood basalts at., 1984) 1984) indicates that the mafic mafic the calculated field basalts (Thompson (Thompson et al., rocks, and perhaps other Keweenawan mafic mafic rocks, rocks, are are contaminated. contaminated. Consequently, the Mineral Lake mafic rocks are derived derived from slightly depleted depleted mantle mantle contaminated contaminatedwith with material. Similar crustal material. Similar plots plots for for the the Mineral MineralLake Lake felsic rocks rocks indicates indicates they are are similar similar to felsic rocks mixed mantle mantle and and crustal crustal origin origin on on the the basis basis of of isotopic isotopicevidence evidence rocks with aa mixed (Thompson et et al., The felsic felsic melts melts were were probably generated by by heat 1984). The probably generated heat from from (Thompson al., 1984). upwelling mantle mantle melts melts of of the the type type which produced upwelling produced the the mafic mafic intrusion intrusion and and followed followed channels opened by by earlier earlier fast moving moving mafic mafic magmas. magmas. REFERENCES Brannon, J. J. C. C. (1 (1984) flows of the Keweenawan North 984) Geochemistry of successive lava flows Shore Volcanic Group. Ph.D. dissertation, Washington Group. Ph.D. dissertation, Washington University, University, St. Louis. 87 �Dosso, L. (1984) (1984) The nature of of the the Precambrian Precambrian subcontinental subcontinental mantle. mantle. Isotopic Isotopic study study (strontium, (strontium, lead, neodymium) neodymium) of of the the Keweenawan Keweenawan volcanism of the north north shore shore of of Lake Lake Superior. Ph.D. Ph.D. dissertation, dissertation, University University of of Minnesota, Minnesota, Minneapolis. Minneapolis. Paces, J. B. Paces, J. B. and and Bell, Bell, K. K.(1989) (1989)Non-depleted Non-depletedsub-continental sub-continental mantle beneath the Superior Superior Province Province of the Canadian Canadian Shield: Shield: Nd-Sr Nd-Sr isotopic isotopic and and trace traceelement element evidence Rift basalts. basalts. Geoch. Geoch. Cosmoch. Cosmoch.Acta, Acta, 53, 53, 2023-2035. 2023-2035. evidence from from Midcontinent MidcontinentRift Thompson, R. A., Hendry, G. 0. LL.and R. N., N., Morrison, M. A,, andParry, Parry,S. S. J. J.(1984) (1984)An Anassessment assessment of and mantle in magma genesis: an elemental approach. approach. of the the relative relative roles of crust and Phil. Trans. Trans. Roy. Soc. London LondonA, A, 310, 310, 549-590. 549-590. J J j Ij -A -A -A 88 -j �CORRELATION OF CORRELATION OF IGNEOUS IGNEOUS UNITS AT THE MINNAMAX MINNAMAX DEPOSIT, NE MINNESOTA DEPOSIT, NE Mark J. J. Severson Severson A. Hauck Steven A. Natural Inst. N a t u r a l Resources Resources Research Research Inst. University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth The Minnamax Minnamax Cu-Ni situated within The Cu-Ni Deposit D e p o s i t (Babbitt ( B a b b i t t Deposit) D e p o s i t ) is is s ituated w i t h i n what has been informally been i n f o r m a l l y rreferred e f e r r e d tto o as as the t h e Partridge P a r t r i d g e River R i v e r intrusion i n t r u s i o n of o f the t h e Duluth Duluth Within are Complex (1.1 (1.1 Ga), Ga), northeastern n o r t h e a s t e r n Minnesota Minnesota (Figure ( F i g u r e 1). 1). W i t h i n tthe h e ddeposit eposit a re a wide vvariety types, and and hhornfelsed u l t r a m a f i c , and and ffootwall o o t w a l l rrock o c k types, o r n f e l sed a r i e t y of o f ttroctolitic, r o c t o l it i c , ultramafic, Many sspecific iinclusions n c l u s i o n s (both igneous(?)). p e c i f i c rrock t y p e s are ( b o t h sedimentary and and igneous(fl). Many o c k types are holes and can can grossly be ccategorized ccorrelative o r r e l a t i v e between between drill drill h o l e s and g r o s s l y be a t e g o r i z e d iinto n t o seven subhorizontal s u b h o r i z o n t a l troctolitic t r o c t o l i t i c units, u n i t s , three t h r e e types types of o f hornfelsed h o r n f e l s e d inclusions, i n c l u s i o n s , and and aa late late Also are units within ccross-cutting r o s s - c u t t i n g pegmatitic p e g m a t i t i c phase. phase. A l s o present present a r e ccorrelative orrelative u nits w i t h i n the the by detailed These correlative ffootwall o o t w a l l rrocks. ocks. These c o r r e l a t i v e rock r o c k units u n i t s were were iidentified d e n t i f i e d by detailed off 61 d drill holes are pportrayed on n nine rossrrelogging elogging o rill h o l e s (117,605' (117,605' of o f core) c o r e ) and are o r t r a y e d on i n e ccrosssections s e c t i o n s through t h r o u g h various v a r i o u s portions p o r t i o n s of o f the t h e deposit. deposit. off tthe att tthe Dunka Road Road Cu-Ni Cu-Ni DDeposit Most o h e rrock o c k uunits n i t s ddefined efined a h e Dunka e p o s i t ((located l o c a t e d tto o by Severson (1990) a are tthe h e immediate immediate SW of o f Minnamax) Minnamax) by Severson and and Hauck Hauck (1990) r e present p r e s e n t aatt Minnamax. However, However, the overall somewhat more more ccomplicated p i c t u r e at omplicated the o v e r a l l picture a t Minnamax is i s somewhat 1) ppinch-out and i n c h - o u t and tthan h a n Dunka Road Road due due to t o rock r o c k type t y p e changes changes that t h a t are a r e manifest m a n i f e s t by: by: 1) reappearance of specific marker-bed units, off reappearance of s p e c i f i c marker-bed u n i t s , 2) 2 ) ddown-strike o w n - s t r i k e ggradational r a d a t i o n a l changes o extent of some extremely horizons, uultramafic ltramafic h o r i z o n s , 33)) e x t r e m e l y limited l i m i t e d aareal real e x t e n t of some uultramafic ltramafic horizons, 4) g gradational r a d a t i o n a l changes changes in i n the t h e troctolitic t r o c t o l i t i c rock r o c k types t y p e s between between any any h o r i z o n s , and 4) some areas areas a pparticular marker hhorizon may ""disappear" two d drill two holes. r i l l holes. IIn n some a r t i c u l a r marker o r i z o n may d i s a p p e a r " and marker h horizon, may ""disappear" be rreplaced e p l a c e d by aanother n o t h e r marker o r i z o n , which in i n tturn, u r n , may d i s a p p e a r " llaterally. aterally. of tthese difficulties, of seven horizontal IIn n sspite p i t e of h e s e llocal ocal d i f f i c u l t i e s , aa gross g r o s s stratigraphy s t r a t i g r a p h y of horizontal are off (from bottom 2) a r e present p r e s e n t at a t Minnamax and cconsist onsist o (from b o t t o m tto o igneous uunits n i t s (Figure ( F i g u r e 2) augite heterogeneous, ssulfide-bearing Unit ulfide-bearing a u g i t e ttroctolite r o c t o l i t e and ttroctolite roctolite ttop): op): U n i t II - heterogeneous, with homogeneous ttroctolites with w i t h abundant sedimentary inclusions; i n c l u s i o n s ; Unit U n i t II I 1 -- homogeneous roctolites w ith a mottled present basal p picrite horizon SW Minnamax); Minnamax); Unit U n i t III 111 -- m ottled basal icrite h o r i z o n (II ( I 1 iis s p r e s e n t only o n l y in i n SW with augite anorthositic a n o r t h o s i t i c ttroctolite r o c t o l i t e tto o a u g i t e ttroctolite roctolite w i t h ccharacteristic h a r a c t e r i s t i c oolivine livine I oikocrysts o i k o c r y s t s (III (111 is i s present p r e s e n t mainly m a i n l y in i n SW S W Minnamax Minnamax and and is i s enveloped enveloped by by Unit Unit I tto o of NE); Unit mixed ttroctolite I V - mixed r o c t o l i t e and augite a u g i t e ttroctolite r o c t o l i t e (at ( a t tthe h e base or o r top t o p of tthe h e NE); U n i t IV Unit different U n i t IV I V in i n two d i f f e r e n t areas) areas) with w i t h aa basal basal ultramafic u l t r a m a f i c horizon h o r i z o n ("± ( "  ppicrite"); icrite"); anorthositic with Unit homogeneous a U n i t VV -- homogeneous n o r t h o s i t i c troctolite t r o c t o l i t e (gradational ( g r a d a t i o n a l contact contact w i t h Unit U n i t IV); IV); with basal ultramafic Units V I I -- homogeneous ttroctolites roctolites w i t h basal u l t r a m a f i c horizons horizons and U n i t s VVII and VII (more abundant abundant and tthicker (more h i c k e r ultramafic u l t r a m a f i c horizons h o r i z o n s in i n the t h e Bathtub B a t h t u b cross-section). cross-section). Specific horizons drill hole 2): : S p e c i f i c marker h o r i z o n s utilized u t i l i z e d in in d rill h o l e ccorrelations o r r e l a t i o n s iinclude n c l u d e ((Figure F i g u r e 2) "pocket p picrite", Unit and Unit U n i t III, 111, "± " picrite", p i c r i t e " , "pocket i c r i t e " , ttop o p ooff U n i t IIV V ((augite a u g i t e ttroctolite), r o c t o l i t e ) , and The ttroctolitic are commonly c cut tthe h e base of o f Units U n i t s VI V I and and VII. VII. The r o c t o l i t i c rrock o c k uunits nits a r e commonly u t by granophyric veins, bodies, and and p pegmatitic pyroxenite tthin hin g ranophyric v e i n s , hybrid h y b r i d hornblendite h o r n b l e n d i t e bodies, egmatitic p yroxenite Chlorine-rich drops which which c coat bodies (OUI (OUI -oxide - o x i d e ultramafic u l t r a m a f i c intrusions). intrusions). C h l o r i n e - r i c h drops o a t the the ccore o r e surface s u r f a c e are a r e common in i n the t h e OUI OUI and and ultramafic u l t r a m a f i c horizons. horizons. Several e enigmatic Units att I I a n i g m a t i c hornfelsed h o r n f e l s e d inclusions i n c l u s i o n s are a r e present p r e s e n t in in U n i t s VVII and VVII I) ggranular gabbro These are r a n u l a r gabbro a r e grouped grouped in i n two two categories c a t e g o r i e s which which include: i n c l u d e : 1) Minnamax. These tto o olivine o l i v i n e gabbro gabbro which which contain c o n t a i n crude crude ovoid-shaped ovoid-shaped plagioclase-filled p l a g i o c l a s e - f i l l e d zones zones granular oxide-rich olivine gabbro which which also and 2) g ranular o xide-rich o l i v i n e gabbro a l s o contains contains ((vesicles?), v e s i c l e s ? ) , and The llater plagioclase-filled hercynite). p l a g i o c l a s e - f i l l e d ovoids o v o i d s and and modally m o d a l l y bedded bedded magnetite (± ( h e r c y n i t e ) . The ater inclusion megascopically i n c l u s i o n ttype ype m e g a s c o p i c a l l y resembles resembles the t h e material m a t e r i a l present p r e s e n t within w i t h i n the t h e Colvin Colvin While these these two two iinclusion Creek ""Hornfels" area ((Smiles Creek H o r n f e l s " area 5 m i l e s SW SW of o f Minnamax). Minnamax). While n c l u s i o n ttypes ypes are exact nnature remains unknown. unknown. a r e rreadily e a d i l y ccorrelative o r r e l a t i v e between between drill d r i l l holes, holes, ttheir h e i r exact a t u r e remains - - 89 �j Interestingly, modally magnetiteisisalso alsopresent presentinin picritic picritic horizons modally bedded bedded magnetite horizons which occur occurat at the the same stratigraphic levels as which same stratigraphic as the the second second inclusion type. type. Anotherenigmatic enigmaticrock rocktype typeisis present present within within the the lower of the Another lower 50-100' 50-100' of the Virginia Formation This rock with the rocks. This Formation footwall rocks. rock is is generally generally concordant concordant with overall bedding trend, exhibits bedding trend, exhibits aa gradational(?) gradational(?) contact contact with with the thesurrounding surrounding sedimentaryrocks, rocks,and andgenerally generallyexhibits exhibits aa granoblastic sedimentary granoblastic texture; texture;the themassive massive sulfide ore sulfide ore is is restricted restrictedtotothe therock rocktypes typesabove above this this horizon. horizon. Preliminary petrography and andgeochemistry geochemistryindicate indicatethat that this petrography thishorizon horizoncontains containshornblende hornblende and and olivine (serpentinized), Cl contents (up (up to 1300 ppm) andand highhigh MGMGNumbers olivine (serpentinized),high high C1 contents to 1300 ppm) Numbers (10-20) whichare aresimilar similar to values (10-20) which values within within ultramafic ultramafic horizons, horizons, and and high high Cr Cr ppm)which whichare are much muchhigher higherthan than anything anything sampled within the contents (800-2300 (800-2300 ppm) sampled within overlying troctolitic troctolitic rocks. dateinfer infer that overlying rocks. These These date that this thishorizon horizonmay may represent represent either (chilled material?) or aa either aa metamorphosed early Keweenawan sill sill (chilled metamorphosed mafic flow within VirginiaFormation Formation- ---further further study on this this study on metamorphosed mafic flow within thethe Virginia horizon is is pending. pending. Severson, M.J., S.A., 1990, J., and and Hauck, Hauck, S.A., 1990, Geology, Geology, geochemistry, geochemistry, and and stratigraphy stratigraphy Severson, M. of a portion of the Partridge River intrusion, northeastern of a portion of the Partridge River intrusion, northeasternMinnesota: Minnesota: Natural Resources ResearchInstitute, Institute, Technical NRRI/GMIN-TR-89-11, Resources Research TechnicalReport, Report, NRRWGMIN-TR-89-11, Duluth, Minnesota, 240 p. p. Minnesota, 240 j j 11 <? LEGEND Â¥ -È PRTS- OUTLINES AREA OF PARTRIDGE RIVER TROCTOLITE SERIES PRGC - PARTRIDGE RIVER GABBRO COMPLEX Cu-Nl Dewails MINNAMAX DUNKA ROAD VETLEGS VYMAN CREEK - - MMAX - DR -- WL VC W t S tOU1) SECTION 17 17 LONGEAR LE LONGNOSE LN 22 SECTION ZS SKU0 SK -- J j j U j J CEOLIC MAP THE PARTRIDGE rIGURE GENERAL GEOLOGIC MAPorOF THE PARTRIDGERIVER RIVERft4TRUSIDN INTRUSION FIGURE 1I- GENERAL J 90 �'C 'e I II IV - / - - FOOTWALL / / v . I FOOTWALL I1 Ill .I V v ----- -- - - - DUNKA ROAD 15 MILES MILES k LOCAL BOY / TIGER BOY MINNAMAX/BABBIT SOUTHERN EDGE r rirt I ntrL45lon, uttranaf u ~ t r n n oc t i emtrusien, * - n,.nrpn-ti,n,I rr'n+n rt H 'rnl n MnI:r,4 Mn rrk 1 Qq [3 El Ni El R t L I Z El U I GENERALIZED! Strike—Length correLationoof najor Igneous Strike-length correlation f major Igneous units units within within the t h e basaL basal 3000 3000 fFt. t . of o f the t h e Partridge Partridge River River intrusion. intrusion. / -1- r- r ITt PARTRIDGE P A R T R I D G E RIVER R I V E R INTRUSIEN INTRUSION r- n aug!te troctolite, -troctolite, IiI1 = troctolite Sulflde-beorlng au@@ t r o c t o l l t ewth wlthp;crl-te plcrlteLoyers layers etc., etc. II = SutFide—becring northostic Ill Ill == 'Mottled' 'Mottled' onorthositic anorthosltlc troctotite, troctollte, IV I V==uugrte auQltetroctoUte, trOctoUte, VV = onorthosltlc oide VII == nnorthositic troctofltp, onorthositic troctoUte t r o c t o l l t e to t oou9ite a u v t etroctoUte, troctollte, OW DUI = oxide troctolrte, VI V I 8& VII UNITS' UNITSv FIGURE IGURE 2: 2: FOOTWALL -- ^ LONGNOSE) LONGEAR SECTION V1) 'v i r— WYMAN CREEK - Ià I in r r COOfl w+ -0" odd bdd nodal hdd �- THREE-DIMENSIONAL THREE-DIMENSIONALMODELLING MODELLINGOF OFTHE THEMAGNETIC MAGNETICANOMALY ANOMALY CENTRAL LAKE SUPERIOR CENTRAL SUPERIOR D. D. TeskeyY ABSTRACT ABSTRACT Two Two and and one-half one-half dimensional dimensional modelling modelling of the the central central portion portion of of Lake Lake Superior Superior has has been been carried carried out out using using the thehigh high resolution resolution aeromagnetic aeromagneticdata datacollected collectedby by the theGSC's GSC's Oueenair Queenairaircraft aircraftinin1987 1987 for for the theGreat GreatLakes LakesInternational InternationalMultidisciplinary MultidisciplinaryProgram Program on on Crustal CrustalEvolution Evolution(GLLMPCE). (GLIMPCE). Individual 2.5dimensional dimensional models modelsfor forprofiles profilesspaced spacedapproximately approximately10 10km km apart apartcan canbe becombined combined Individual2.5 using dimensional models. models. These Thesemodels modelsindicate indicate up up to to40 40km km of of using trigonal trigonal surfaces surfaces to to produce produce 33dimensional volcanic with the lower members volcanic flows, flows, with members having having reversed reversed magnetization, magnetization,similar similar to to the thelower lowerOsler Osier group. seismic group. These Thesemodels modelstend tendtotoagree agreewith withthe theinterpretation interpretationofofthethe seismicprofiles profilesshot shotinin1986 1986asas part part of ofthe theGLIMPCE GLIMPCEprogram. program. j J J j J 92 �MIDCONTINENT RIFT RIFT STRUCTURE MIDCONTINENT STRUCTURE INTERPRETED INTERPRETED FROM FROM THE GNI/ARCONNE GNI/ARGONNE SEISMIC SEISMIC DATA DATA SET SET M.D. L.D. McGinnis McGinnis M.D. Thompson Thompson && L.D. Argonne Argonne National National Laboratory Laboratory Argonne, IL 60439 60439 Argonne, IL M.G. M.G. Mudrey, Mudrey, Jr. Jr. Wis. Nat. Hist. Surv.. Sun., 3817 3817 Mineral Mineral Point Point Rd. Rd. Wis. Geol. Geol. & Mat. Madison, Madison, WI WI 53706 53706 C.?. C.P. Ervin Ervin Dept. Dept. of of Geology, Geology, Northern Northern Illinois Illinois Univ. Univ. DeKalb, 60115 DeKalb, IL IL 60115 Midcontinent rift rift structure structure is is interpreted interpreted from 2500 km of of Midcontinent orthogonally-oriented orthogonally-orientedseismic seismic profiles profiles located located in in Lake Superior Superior to to have have evolved evolved in in the the following following sequence: sequence: A) Localized Localized volcanic-filled al., 1990) and volcanic-filled basins basins first first developed developed (Hinze (Hinze et al., and later later coalesced coalesced to to form form the the main main axial axial rift riftbasin. basin. Volcanic Volcanic flows suggesting flows extruded extruded at at this this time time are are constant constant in in thickness, thickness, suggesting that that the the major major component component of of rift rift subsidence subsidence began began after after development development of of the the primary primary axial axialbasin. basin. B) The main main rift rift stage stage involved involved crustal crustal extension, extension, subsidence, subsidence,and and rapid rapid lava lava extrusion. extrusion. Lava Lava flows flows interpreted interpreted as as Portage Portage Lake Lake and and Osler Osier equivalents equivalents exhibit a pronounced fanning geometry towards exhibit a pronounced fanning geometry towards the the rift's rift's axis, axis, indicating extrusion into a rapidly subsiding basin. indicating extrusion into a rapidly subsiding basin. C) Volcanic Volcanic cessation cessation is is marked marked by by aa region-wide region-wide mixed mixed sediment-volcanic sediment-volcanic facies sequence from fades that that separates separates a lower, lower, dominantly dominantly volcanic sequence from an an upper upper sedimentary sedimentary series. series. D) D) Post-volcanic Post-volcanicsedimentary sedimentary basins basins developed, developed,reaching reachingthicknesses thicknessesofof7 71cm, km, or or more. more. E) Sediment Sediment basin ional event basin development development was was interrupted interruptedby byaacompress compressional event that that reactivated reactivated the the normal normal boundary boundary faults, faults, producing producing high-angle high-angle reverse reverse and and thrust thrust faults. faults. Faulting Faulting and and folding folding involved involved all all of of the the volcanics volcanics and and the the older older Oronto Oronto group group sediments. sediments. F) A F) A regional youngest regional unconformity unconformity developed developed and and is is overlain overlain by the youngest Keweenaw-age Keweenaw-agesediments. sediments. The clearly The geometry geometry and and location location of of several several major faults is clearly detailed detailed by by the the seismic seismic data data set. set. A southeast southeast extension extension of of the the Keweenaw Keweenaw Fault Fault from from the the Keweenaw Keweenaw Peninsula Peninsula is is strongly strongly corroborated. The Douglas Douglas Fault Fault must must parallel parallel the the southern southern corroborated. The shoreline, Keweenaw shoreline, juxtaposing juxtaposing its its southern southern dip dip against against the the Keweenaw Fault's Fault's northward northward dip, dip, and and probably probably dies dies out out near near the the Porcupine Porcupine Mountains. Mountains. Ebinger Ebinger (1989) (1989) described described a similar similar fault geometry in in the the Western Western Rift Rift System System of of East East Africa. Africa. AA shear shear fault fault or or accommodation accommodation zone zone is is imaged imaged on on the the northeast northeast side side of of White White Ridge, Ridge, which which acts acts to to separate separate aa dominantly dominantly thrust thrust fault fault regime regime to to the northeast from the high-angle reverse faults observed the northeast from the high-angle reverse faults observed on on White White Ridge. Ridge. Synthesis Synthesis of of the the structural structural features features imaged imaged by the the seismic seismic profiles profiles suggests suggests that that crustal crustal shortening shortening was was directed directed NW-SE NW-SE in in western western Lake Lake Superior Superior and and NE-SW NE-SWin in the the eastern easternlake. lake. AA net net N-S N-S 93 �-J component component of of crustal crustal shortening, shortening,as as argued argued by by Cambray Cambray (1988), (1988). could could explain explain the the fault fault and and fold fold geometries geometries observed throughout throughout the The Keweenaw Keweenaw Volcanics Volcanics behaved behaved as as aa single single "thrust" "thrust" the lake. lake. The sheet between sheet in in the the western western lake, lake, overriding overriding aa basal basal decollement decollement between Animikie Animikie and and pre-Portage pre-PortageLake Lake Volcanic Volcanic units. units. Tilted, Tilted, folded, folded, and and uplifted uplifted volcanic volcanic units units imaged imaged in in the the eastern eastern lake lake also also support support this this "thrust" "thrust" sheet sheet interpretation. interpretation. J REFERENCES REFERENCES CITED CITED Cambray, Caubray, F.W., F.W., 1988, 1988, AA Tectonic Tectonic Model Model for for the the Mid-continent Mid-continent Rift Rift System: Abstract Volume, 34th Institute on Lake System: Abstract Volume, 34th Institute on Lake Superior Superior Geology, Geology, Marquette, Marquette, MI, MI, p. p. 17. 17. Ebinger, Ebinger, C.J., C.J., 1989, 1989, Geometric Geometric and and Kinematic Kinematic Development Development of of Border Border Faults Faults and and Accommodation Accommodation Zones, Zones. Kivu-Rusizi Kivu-RusiziRift, Rift, Africa, Africa, TECTONICS, TECTONICS, v.8, v.8, no.1, no.1, pp. pp. 117-134. 117-134. J Hinze, , L.W. Hinze,W.J. W.J., L.W. Braile, Braile, and and V.W. V.W. Chandler, Chandler, 1990, 1990, AA Geophysical Geophysical U Profile Profile of of the the Southern Southern Margin Margin of of the the Midcontinent Midcontinent Rift Rift System System in in Western Western Lake Lake Superior, Superior, TECTONICS, TECTONICS, v.9, v.9, no.2, no.2, pp. pp. 303-310. 303-310. J j -3 j U j 1 U U U 94 J �REGIONAL REGIONAL STRATIGRAPHIC MODEL MODEL OF OF LATE LATECRETACEOUS CRETACEOUS SEDIMENTS SEDIMENTS AND AND THEIR THEIR RELATIONSHIP WITH WITH THE THEUNDERLYING UNDERLYINGPRE-LATE PRE-LATECRETACEOUS CRETACEOUS WEATHERING WEATHERING PROFILE PROFILE ALONG THE THE MINNESOTA RIVER VALLEY, ALONG MINNESOTA RIVER VALLEY, MINNESOTA. MINNESOTA. ThomasA.A.Toth, Toth, John Heine, and Thomas John J. Home, and Steven Steven A. A. Hauck Hauck ResearchInstitute Institute Natural Resources Resources Research University ofo fMinnesota-Duluth University Minnesota-Duluth Duluth, Duluth, MN 55811 MN 55811 The presence of pre-Late The presence of pre-Late Cretaceous Cretaceous residual residual kaolin kaolin deposits, deposits, and kaolinitic kaol ini tic Cretaceous Cretaceous non-marine non-marine and marine sediments sediments in in southwestern Minnesota Minnesota is is well welldocumented. documented. Current Falls, Current work work in in the thearea areafrom fromRedwood Redwood Falls, Mn. is being the detailed detailed regional Mn. to Fairfax, Fairfax,Mn. Mn. is being conducted conducted to understand understand the regional stratigraphic relationships pre-Late Cretaceous relationshipsofofthethe pre-Late Cretaceousresiduum residuum and and Late Late Cretaceous sedimentsthat that are are found found on on both both sides Cretaceous sediments sides of of the theMinnesota Minnesota River River valley. val 1 ey. in grade, grade, both both vertically The residual residual deposits deposits vary vary greatly greatly in vertically and and horizontally, from from kaolinite-rich kaolinite-rich to parent rocks to grus. grus. The The parent rocks for these these residual of factors residual deposits deposits consists consists of ofgranites granitesand andgneisses. gneisses. AA number number of influence the grade gradeof of this this residual These factors factors can influence the residual material. material. These can be be grouped grouped into into three threegroups: groups: 1)1)composition composition of ofthe theparent parent rock, rock,2)2)chemical chemical weathering weathering effects, effects, and and 3) 3) physical influences. influences. Presently, Presently, some some of these residual residual of these deposits are portland cement, and are used used in inthe theproduction productionofof portland cement, andmay maysoon soonbe be used used as filler ininlivestock as filler livestockfeed. feed. Overlying the pre-Late residual deposits Overlying pre-Late Cretaceous Cretaceous residual deposits is is aasequence sequence of kaolinites, siltstones, kaol inites, composed of kaolmnitic kaol initic sandstones, sandstones, siltstones, mudstones andlignite. lignite. These These sediments sedimentsare arediscontinuous, discontinuous, commonly commonly filling mudstones and filling topographic low areas areasin in the residual Secondarykaolinites kaolinites are topographic low residual deposits. deposits. Secondary are white to to light pisolitic. Near Near The The top of white lightbrown brown in in color, color,and and commonly commonly pisolitic. ofsome some sections kaolinites, aa pisolite sections of secondary secondary kaolinites, pisolitebench bench ofofiron-cemented iron-cemented material material is River valley, the kaolinites appear is present. present. In the the Minnesota Minnesota River thesecondary secondary kaolinites appear Late Cretaceous and overbank to occur occur in in Late Cretaceous stream stream channel channel and overbank deposits. deposits. The secondary kaolinitic material is presently presently being secondary kaolinitic material is being mined mined for use in the manufacture face-brick. manufacture ofof face-brick. secondary Late Cretaceous sedimentsoverlie overlie residual deposits, and Cretaceous sediments residual and and secondary secondary deposits, and are lignites, sandstones sandstones and shales, lignites, are composed composed oof f non-marine non-marine and and marine marine shales, and siltstones. Some the shale shale units ininthis Some o fofthe thissequence sequence are are considered considered to to be be ball significant. The ball clays, ball clays, clays,and and are are the themost most economically economically significant. The ball clays, which which are kaolinite in contain organic organic material, which are dominantly dominantly kaolinite in composition composition contain impart thethe sediments. impart aa light light gray gray totoblack blackcolor colortoto sediments.This Thispackage package of of Late Late Cretaceous sediments is is wide-spread Currently, Cretaceous sediments wide-spread ininsouthwestern southwestern Minnesota. Minnesota. Currently, the ball manufacture ball clays claysare areused used ininface-brick face-brick manufactureininMinnesota. Minnesota. Pleistocene glaciation and eroded erodedparts partsor or all all glaciationhas hassubsequently subsequently scoured scoured and of the sequence,resulting resultinginindeposition depositionof of aa thick thick blanket the Late Late Cretaceous Cretaceous sequence, blanket of till andandoutwash deposits cover cover till outwash material material ofo fvarying varyingthickness. thickness. Glacial deposits much the study study area, area, leaving the best for study along the the walls much ofof the best exposures exposures for study along of Rivervalley valley and andtributaries. tributaries. of the the Minnesota Minnesota River 95 �Initial observations concerning the stratigraphic model Initial Minnesota River valley andFairfax Fairfax include: Minnesota River valleybetween between North North Redwood Redwood and .; : , .>..*>., .:, .,.. , . I . 1 I I I I for the the The grade gradeof of the the primary 1. The primary kaolinite kaolinite isisdependent dependent upon upon the type type parent material. parent Thedegree degreeofofweathering weatheringofofthe thebedrock bedrock primarykaolinite kaolinite is The totoa aprimary This inconsistency inconsistencyisiseither eitherthe theresult resultoof differential inconsistent. This f differential removalbybyglacial glacial activity activity ororreflects thethe Late Cretaceous removal reflects Late Cretaceoustopography topography of the area. the area. 2. 3. The Thesecondary secondarykaol kaolinite is discontinuous andvariable variable in thickness 3. inite is discontinuous and thickness across the study area. across the area. 4. grain size 4. There is aa change change inin grain size and and texture texture ofofthe thesecondary secondary kaolinite from kaolinite from east east to to west. west. 5. Evidenceofoffluvial fluvial deposition includesthe thequartz, quartz, kaol kaolinitic5. Evidence deposition includes initicsupportedconglomerate conglomeratefound found thebase baseofofthe the secondary secondarykaolinite. kaolinite. supported atatthe Elevations of the Elevations the pisolite pisolitebench benchare areconsistent consistentalong alongCrow Crow Creek Creek andcan canbebeused used a time lineififthe thethick thick pisolitic pisolitic bench and as as a time line bench isisindeed indeed the result of laterization event. the ofthe thesame same laterization event. 6. 6. Cretaceous non-marine and marine marine shales rarely 7. The Late Cretaceous non-marine and shales are rarely preserved. Sedimentary structures and stratigraphic marker marker are are lacking. 8. 8. 1 I provide a fossils that would provide fossils 9. Organic Organic remains remainsare arefound foundininthe theform formofof carbonized carbonizedimprints imprints in in the 9. whichform formthe thelignitic lignitic material. Theseimprints imprints are are the shale, which material. These the Tree branches branches and and trunks trunks formed remainsofof leafs leafs and thin twigs. Tree remains and thin formed the nucleus for siliceous concretions with the woody material material since nucleus removed. removed. Theseobservations observationsare arebeing beingincorporated incorporatedinto into aa stratigraphic These stratigraphicmodel model for the the Minnesota River valley valley area. for theLate LateCretaceous Cretaceous sequence sequence inin the Minnesota River area. I I j I J J j J J 96 -J �I I I I I I I I I I I I CHEMISTRY CHEMISTRY AND AND METAMORPHISM METAMORPHISM OF OF AN AN ARCHEAN ARCHEAN PILLOW PILLOW BASALT BASALT Turriock A.C.(2), D.C. Turriock A. C. ( 2 ) , Karnineni Kamineni D. C. (l),MoGregor (1),McGregor H. R . (1) (I) (1) ( 1 ) AECL AECL Research, Research, Whiteshell Whiteshell Laboratory, Laboratory. Pinawa, Pinawa, Manitoba, Manitoba, ROE ROE lLO, 1L0, Canada. Canada. (2) ( 2 ) Geological Geological Sciences, S c i e n c e s , University U n i v e r s i t y of of Manitoba, Manitoba, Winnipeg, Winnipeg, R3T R3T 2N2, 2N2, Canada. Canada. Abstract Abstract In I n southeastern s o u t h e a s t e r n Manitoba, Manitoba, on on the t h e western western edge edge of of the t h e Superior Superior River greenstone Bird Province is aa r o v i n c e of of Archean Archean age, age, the t h e Bird River g r e e n s t o n e belt b e l t is Pillow basalts are rocks. of supracrustal small mall sub—province sub-province of s u p r a c r u s t a l rocks. P i l l o w b a s a l t s are aa lower stratigraphic ower s t r a t i g r a p h i c formation, formation, approx. approx. 22 km km thick, t h i c k , in i n aa sequence sequence olastic and volcanics felsic mafic and bimodal of of bimodal mafic and f e l s i c v o l c a n i c s and c l a s t i c metametasedimentary edimentary rooks. rocks. Two Two samples samples of of basalt b a s a l t have have been been analysed analysed (both ( b o t h core c o r e and and rim), rim), The dyke. cross—cutting plus a basalt, sheared plus The l u s aa sheared b a s a l t , p l u s a c r o s s - c u t t i n g dyke. basalt, are sheared the and compositions of the pillow cores, ompositions of t h e p i l l o w c o r e s , and t h e s h e a r e d b a s a l t , are Archean to other similar irnilar to other Archean tholeiites t h o l e i i t e s of of diverse d i v e r s e volcanic volcanic They arid to modern pillow tholeiites. formations, ormations, and t o modem p i l l o w t h o l e i i t e s . They have have flat f l a t EEl REE They are enriched in Nb-Zr-V they plot as E—MORB. patterns, and They are enriched a t t e r n s , and i n Nb-Zr-Y t h e y p l o t as E-MORB. in n C02 CO2 and and Sr S r compared compared to t o rims. rims. The rims of the pillows The r i m s of t h e p i l l o w s are a r e darker d a r k e r (abundance (abundance of of hornblende) hornblende) They are porphyroblasts. corranon garnet and contain and c o n t a i n common g a r n e t p o r p h y r o b l a s t s . They are enriched e n r i c h e d in in They also have Ca, Mn compared to cores. Fe+3, Fe, Mg, e+3, Fe, Mg, C a , Mn compared t o c o r e s . They a l s o have flat f l a t REE REE patterns, i n Nb-Zr-V Nb-Zr-Y and and Ti-Zr-V Ti-Zr-Y they t h e y plot p l o t outside o u t s i d e the t h e field field a t t e r n s , but b u t in of igneous rooks due to enrichment in Y. f igneous rocks due t o enrichment i n Y. The cross—cutting c r o s s - c u t t i n g dyke dyke is is an an andesite a n d e s i t e which which has h a s not n o t been been subject u b j e c t to t o the t h e alteration a l t e r a t i o n seen seenira i n the t h e rims r i m s of of the t h e pillow p i l l o w basalt. basalt. is distinct d i s t i n c t from from that t h a t of of the t h e pillow p i l l o w basalt, b a s a l t , as as magma is Its I t s primary primary magma shown shown by by enrichment enrichment in i n light l i g h t REE, REE, decreasing d e c r e a s i n g from from La La to t o Dy. DY. The The formations formations are a r e steeply s t e e p l y dipping, d i p p i n g , and and show show post-folding post-folding The shear s h e a r zones. zones. The alteration a l t e r a t i o n of of pillow p i l l o w rims r i m sisi sprercietarnorphic, premetamorphic, arid sheared basalt nd ddid i d nnot o t aaffect f f e c t tthe h e sheared b a s a l t or o r the t h e late l a t e dyke. dyke. During During cummington ite have overgrown ende and 1 sm, hornbl rnetamorph ~et.amorphisrri, hornblende arid cummingtonite have overgrown tthe h e 52 52 interpreted is This foliation 01 i a t i o n (main (main folding f o l d i n g event). event). This i s i n t e r p r e t e d as as indicating bathcii i t h i e probably from from tthe h e adjacent ad ~ a c t i n tbathoiit.hc i n d i c a t i n g that t h a t heat h e a t flow, flow, probably intrusion, i n t r u s i o n , continued continued after a f t e rdeformation. deformatio 97 I �Geochemistry Archean Rocks from the the Virginia Virginia Horn Horn area: area: Geochemistryof ofArehean Interpretations Preliminary Interpretations James JamesL. L.Welsh Welsh Department of Department ofGeology Geology Gustavus Gustavus Adoiphus Adolphus College College St. Peter, St. Peter, MN 56082 56082 Jayne Reichhoff Jape Reichhoff Natural Resource Resource Research Institute Institute University of Minnesota, Duluth Duluth Archean supracrustal rocks Archean supracrustal rocks exposed exposed in the the anticlinal anticlinal core core of of the the Virginia Virginia Horn Horn structure of the Mesabi Iron Range of northeastern Minnesota comprise a structure of the Mesabi Iron Range of northeastern Minnesota comprise a sequence of of folded foldedmetavolcanic metavolcanicand andmetasedimentary metasedimentary units, units, some some and and perhaps which are are tectonically tectonically stacked, stacked, and and into into which which are are intruded intruded a series all of of which series of small felsicporphyry porphyrybodies. bodies. A A major major through-going through-goingstructure, structure, the Pike gold-bearing felsic River faultlshear fault/shear system cuts this sequence. River sequence. Chemical Chemical analyses analyses for for major major and minor elements have been obtained for a suite of 66 samples representing suite of representing all all principal lithologies. lithologies. Metavolcanic rocks rocks of of the the area are Metavolcanic areprincipally principallyflows, flows,some some pillowed, pillowed, with with subordinate intercalated fragmental units. Major Majorelement elementanalyses analysesof of these these rocks rocks show them them to to range range in composition compositionfrom frombasalt basalt to to dacite, dacite, with with basalt basalt and andesite predominating. The major and minor element data suggest that that these predominating. these rocks rocks are are grouped into two two distinct distinct geochemical geochemical suites. suites. The The basaltic basaltic rocks rocks show show tholeiitic affinities and have flat lIFE REE patterns; patterns;the theandesitic andesiticand anddacitic daciticrocks rockshave havecaiccalcalkaline affinities and are REF. Rocks Rocks in in the the are somewhat somewhat enriched in the light REE. Gilbert and McKinley McKinleyareas areas appear appear to be tholeiitic, while those those in in the Biwabik Biwabik area are are calc-alkaline. The The nature natureof of the thefield Held expression expression of the transition between between these two suites is not yet clear, though though the the Pike River Fault may play a role. The felsic porphyries porphyries plot plot in in aa very very tight tight cluster around 70% Si02 and Na20 70% Si02 and 8% 8%Na20 +1(20. These rocks would appear to be more silicic than other dacite porphyries + K20. These rocks would appear to be more silicic dacite from the Vermilion District. These Vermilion District. These rocks rocks have have undergone undergonesericite-carbonate sericite-carbonate silicification. With alteration and the high 5i02 Si02values values might might suggest suggest secondary secondary silicification. of occasional occasional quartz quartz veins, however, there appears appears to be be little little the exception of however, there petrographic evidence for for secondary silicification. silicification. Likewise, the the consistent consistent 5102 S102 values of of the the various various samples samples would wouldseem seemtotorule ruleout out silica silicaintroduction. introduction. Perhaps the higher Si02 Si02 values, as as occur occur in these intrusives, might might be aa clue clue as as to to why why these bodies are auriferous, while similar-appearing similar-appearing dacitic dacitic bodies bodies with lower lower 5i02 Si02 contents contents elsewhere elsewhere in the the Vermilion District are are not. not. Greywackes range range from 55-70% 55-70%Si02, Si02, the the majority plotting as as "dacites", "dacitesn, suggesting possible derivation from the the calc-alkaline calc-alkaline portions portionsof of the thevolcanic volcanicpile. pile. The composition compositionofofthese these greywackes greywackes is is consistent consistent with greywackes throughout the Vermilion Vermilion District. 98 �ARCHEAN AND PROTEROZOIC PROTEROZOIC TECTONO-MAGMATIC TECTONO-MAGMATIC ACTIVITY ALONG THE ThE SOUTHERN SOUTHERN MARGIN OF THE THE SUPERIOR PROVINCE IN NORTHWESTERN IOWA, PROVINCE IN NORTHWESTERN IOWA, USA USA Kenneth B. E. Windom', W. W. R. R.Van VanSchmus2, Schmus2,Karl Karl B. E.SeiferO, Seifert', B. E. T. T. Wallin2, Wallin2,and R. R. R. R.Anderson3 Anderson3 Iowa State State University, University, Ames, IA ..24 'Department of of GeolQgical Geological and Atmospheric Sciences, Iowa IA 50010 50010 . 2Department 'Department of Geology, University of of Kansas, Kansas, Lawrence, Lawrence, KS KS 66046 66046 3Geological Survey Bureau, Bureau, Iowa Iowa Department Department of of Natural Natural Resources, Resources, Iowa Iowa City, City, IA 52242 'Geological Survey 52242 A A Precambrian Precambrian igneous igneous complex complex of layered layered ultramafic and mafic rocks occurs occurs within within the the basement of northwestern meters of of Phanerozoic Phanerowicsediments. sediments. northwestern Iowa Iowa beneath beneath approximately approximately 300 meters This layered layered series series has has been been named named the the Otter OtterCreek Creek complex. complex. It is is marked marked by by aa circular circular magnetic anomaly,one one of of several several that that lie lie north north and and west west of of an an inferred inferred suture that that has been magnetic anomaly, postulated Superior Province Province and and an an Early Proterozoic postulated as the boundary between between the Archean Archean Superior Proterozoic terrane. terrane. The layered layered series series is is tilted tilted steeply steeply to the the northwest; northwest; rocks rocks representing representing the upper upper portion of the by erosion or tectonic the original original magma magma chamber chamber have have been removed removed by tectonic processes. processes. A A block of banded iron formation, formation, itself itself intruded intruded by by lamprophyre lamprophyre dikes, dikes, isis contained contained within within the the layered sequence. fonnation/lamprophyre block has has undergone high-temperature igh-temperature sequence. The iron iron formation/lamprophyre metamorphism followed by a retrograde retrograde event. event. The banded iron formation formation was deposited deposited in a supracrustal supracrustal environment, then intruded incorporated into into a mafic magma by the the lamprophyre. lamprophyre. This assemblage assemblage was apparently apparently incorporated magma that that subsequently crystallized crystallized to to form form the the layered layered complex. complex. Radiometric dating of of the layered rocks subsequently and the lamprophyre, Ga and an NdISm isotopes, isotopes, yields yields an isochron of approximately 2.9 Ga lamprophyre, using using Nd/Sm of zero to slightly negative values. The lamprophyre and layered complex fall value eNd value zero to slightly negative The lamprophyre and layered complex fall on on the the same isochron and thus appear to be be essentially essentiallycoeval. coeval. Archean lamprophyre has been reported reported from the Superior Superior Province as having having been formed formed during during the closing stages of the the various various in both subprovinces. subprovinces. Trace element abundances abundances in both the lamprophyre lamprophyre and layered complex complex are are consistent with derivation from a primitive to partially depleted mantle and thus support the consistent with derivation from a primitive to partially depleted mantle and thus support the isotopic isotopic evidence. evidence. The alteration, similar to that seen The entire entire layered complex complex has undergone low-temperature alteration, We interpret the the high-temperature high-temperature rocks from fromArchean Archeangreenstone greenstone belts. belts. We in other other mafic mafic rocks metamorphism experiencedby by the the iron formation and lamprophyre to have occurred during metamorphism experienced formation and lamprophyre to during incorporation of these lithologies as incorporation into the mafic magma magma and the retrograde retrograde metamorphism metamorphism of resulting from the the same same event event that that produced prograde paragenesis of low-temperature minerals in the layered complex. complex. Although Althoughmost mostprimary primary phases phases were were replaced replaced with with secondary secondary phases phases istribution such as serpentine, chlorite, chlorite, uralitic uralitic amphibole, epidote, epidote, and albite, major cchemical redistribution does not appear to to have have affected affected these these rocks A younger Archean quartz monzodiorite gneiss gneiss occurs occurs near near the the layered layered complex, complex, but the known. The originally crystallized crystallized contact relations are not known. Themagma magma from which the monzodiorite originally 99 �formed formedatatapproximately approximately 2523 2523 Ma Ma(Van (Van Schmus Schmus et et al., al.,1987). 1987). AAmantle mantleseparation separationage ageofof2.9 2.9 Ga Gahas hasbeen beendetermined determinedfor forthis thisrock, rock,indicating indicatingthat thatititcould couldhave haveformed formedby bypartial partialmelting melting of of material materialderived derivedfrom fromthe thesame samemantle mantlerocks rocksthat thatproduced producedthe theOtter OtterCreek Creeklayered layeredcomplex. complex. Tectonic Tectonicuplift uplifttilted tiltedthe thelayered layeredigneous igneousbody bodyand andthe thequartz quartzmonzodiorite monzodioriteand andexposed exposedthem them erosion. totoerosion. Felsic F d s i cvolcanism volcanismoccurred occurredata tapproximately approximately1775 1775Ma Ma(Wallin (Wallinand andVan VanSchmus, Schmus.1988) 1988) and volcanics andcovered coveredthe theexposed exposedrocks. rocks. These These volcanicsyield yielda adepleted depletedmantle mantleseparation separationage ageof of2.7 2.7 Ga. area rsimilar in in age and stratigraphic position rhyolites Ga.They They e similar age and stratigraphic positiontoto rhyolitesfound foundinincentral centralWisconsin Wisconsin (Smith, (Smith, 1978; 1978;Van VanSchmus, Schmus, 1978), 1978),but buthave havebeen beenmore morestrongly stronglyaltered alteredthan thanthe theWisconsin Wisconsin rhyolites, rhyolites,being beingdepleted depletedininLILE LILEwhich whichresulted resultedinina acomposition compositionequivalent equivalent totokeratophyre. keratophyre. These PenokeanOrogeny Orogeny Thesevolcanics volcanicsmay mayhave haveformed formedininthe thewaning waningstages stagesof ofthe the1850-1900 1850-1900Ma MaPenokean oro rthey theymay maybe berelated relatedtotothe theproposed proposed1750 1750Ma MaCentral CentralPlains PlainsOrogeny Orogeny(Bickford (Bickford et etal., al.,1986) 1986) Analysis Analysis of ofthe thecombined combineddata dataindicates indicatesthe thepresence presenceofofprimitive primitivetotoslightly slightlydepleted depleted mantle mantlematerial materialto tothe thesouthern southern margin marginof ofthe theSuperior SuperiorCraton Craton at at approximately approximately 2.9 Ga. Ga. Varying Varying degrees degreesof ofpartial partialmelting meltingofofthis thismantle mantleproduced producedlamprophyric lamprophyricdikes dikesand andcontemporaneous contemporaneous mafic maficmagma magmabodies, bodies,including includingone onewhich whichcrystallized crystallizedtotoform formthe theOtter OtterCreek Creeklayered layeredcomplex. complex. The entire complex subsequently underwent low-temperature alteration, resulting The entire complex subsequently underwent low-temperature alteration, resultingmainly mainlyininthe the formation formationof ofhydrous hydrousminerals. minerals. Subsequent Subsequenttectono-magmatic tectono-magmaticactivity activityinvolving involvingpartial partialmelting melting ofofrocks rocksderived derivedfrom fromthe the2.9 2.9Ga Gamantle mantlesource sourceoccurred occurredininthis thisregion regionatatapproximately approximately2.5 2.5Ga Ga and and1.75 1.75Ga Garesulting resultingininaaquartz quartzmonzodiorite monzodioritepiutonic plutonicrock rockand andfelsic felsicvolcanics, volcanics, respectively. respectively. REFERENCES REFERENCES Bickford, Zeitz, history M.E., E., Van VanSchmus, Schmus, W. W.It, R.,and and Zeitz,1986. 1986.Proterozoic Proterozoic historyofofthe themidcontinent midcontinent =&ford, M. region region of of North North America. America. Geology, Geology,14:492-496. 14:492-496. Field Precambrian rhyolites rhyolitesand andgranites granitesininsouth-central south-centralWisconsin: Wisconsin: Field Smith, E. E. I.I. 1978. 1978. Precambrian Smith, relations relationsand andgeochemistry. geochemistry. Geological Geological Society Society of of America America bulletin, bulletin, 89:875-890. 89:875-890. Van southern Van Schmus, Schmus, W. W. R. R.1978. 1978.Geochronology Geochronologyofofthe the southernWisconsin Wisconsinrhyolites rhyolitesand and granites. granites. Geosciences Geosciences Wisconsin, Wisconsin, 2:19-24. 2: 19-24. Early and andmiddle middleProterozoic Proterozoic Van W. R., Bickford, Bickford, M. M. E., E., and and Zeitz, Zeitz, I.I. 1987. 1987. Early Van Schmus, Schmus, W. provinces InternationalLithosphere Lithosphere Program. Program. Edited Editedby by provincesin inthe the central central United United States. States. InInInternational A. A. Kröner. Kroner.American AmericanGeophysical GeophysicalUnion UnionGeodynamics GeodynamicsSeries, Series,17:43-68. 17:43-68. , . theArcheanArcheanGeochronological studies studies of of the Wallin, E. E. T., T.,and andVan VanSchmus, Schmus, W. W. R. R.1988. 1988. Geochronological Wallin, Geological Society of America Proterozoic transition, north-central United States. , , ..Proterozoic transition, north-central Un Programs, "Abstracts ~ b s t r a c twith with s Programs, 20:131. 20: 131. Li j — J J 100 -4 �I STRUCTURAL STRUCTURAL ANALYSIS ANALYSIS OF OFTHE THEMIDCONTINENT MIDCONTINENT RIFT RIFT BASED BASED ON ON SLICKENSIDE ANALYSIS SLICKENSIDE ANALYSIS Kathleen Kathleen Witthuhn, Witthuhn, University University of of Minnesota Minnesota I I I I I. I I I I I I ABSTRACT ABSTRACT ,a& Midcdri*l"e"* Rift Rif Midcontinent ,.,.,. . . ,,^i . The is a 1.11 billion billion year year feature feature which which has hasbeen been defined primarily by geophysical studies. Many studies have exned primarily by geophysical studies. Many studies have examined amined the the rift rift from from aapetrologic petrologic view view but butfew fewhave haveexamined examined the the structural structural geology geology in in any anydetail. detail. This This study study examines examines the thestructural structural .: aspects aspects of of the the rift, rift, elucidates elucidates the the directions directions of of opening opening and andclosing, closing, and and constrains constrains the the timing timing of ofthe thesystem, system,by byutilizing utilizingpaleostress paleostress stratigraphy. Preliminary field work in Minnesota, stratigraphy. Preliminary field work in Minnesota, Canada, Canada, and and the the Upper Penninsula of Michigan has yielded data on fault and joint Upper Penninsula of Michigan has yielded data on fault and joint populations, populations from from which which stress stresstensors tensorswere werecalculated. calculated. ClassifiClassification of faults and cation of faults and establishment establishment of of the the sense sense of of movement movement was was accomplished slickensides,recrystallization recrystallization on on the the fault fault accomplished by by analyzing analyzing slickensides, plane, plane, and and Reidel Reidelfractures fracturesas asprimary primarymovement movementindicators. indicators. Faults Faults with with opposite opposite sense sense ofofmovement movement(dextral (dextral vs. vs. sinistral, sinistral, normal normal vs. vs. reverse) reverse) have have similar similar attitudes attitudes indicating indicating aa 1800 180Âreversal reversal of of stress stress direction. direction. This This study study proposes proposes the the direction direction of of opening opening and and closing closing of of the the rift rift was was constrained constrained by by the thegeometry geometry of of the thefault faultsystems systems and andby by simUar directions of of the similar directions the far far field fieldstresses. stre .. 101 �j A A STUDY OF THEMATIC THEMATICMAPPER MAPPERLINEAMENTS LINEAMENTSIN INNORTHWEST NORTHWESTNEVADA NEVADA Woodzick, Thomas L., Orbital Orbital Technologies Technologies Corporation, Corporation, Madison, Madison, WI WI Murdock, OH Murdock, Gary P., P., Battelle Memorial Memorial Institute, Institute, Columbus, Columbus, OH Pride, Douglas E., The The Ohio OhioState StateUniversity, University, Columbus, OH Analysts were able to identify Analysts of the the 1970's 1970's were identify major linear patterns (>250km long) long) such such as the as the Midas Trench and Rye Rye Patch lineaments lineaments in the area between Reno and Winnemucca J J J on single-band Landsat-1 Landsat-] images and relate them them to to the the geomorphology geomorphology and structure structure of of the the Basin Basin and and Range Range province. province. Multiband Thematic Mapper (TM) data data with with an animproved improved (30m) resolution provide provide an an opportunity opportunity to to re-examine the area area in terms terms of of the the spatial spatial (30m) resolution re-examine the distribution numerous shorter distribution of its numerous shorterlinear linearfeatures, features.68,000 68,000lineament lineamentsegments segmentswere wereinitially initially interpreted scale interpreted (primarily (primarily from fromthe thedeeply deeplyincised incisedand andshadowed shadowedranges) ranges)onona 1:100,000 a 1:100,000 scale — band-234 Subsequentreprocessing reprocessingof of the thedata datawith with an anintensity-hue-saturation intensity-hue-saturation band-234 TM image. Subsequent (IHS) transformation transformation and and edge-enhancement edge-enhancement enabled enabledanother another36,000 36,000 lineament lineament segments segments to be interpreted basins. Digitization interpreted from fromthe thetopographically topographically subdued subdued intervening intervening basins. Digitization of the x-y coordinates of of the lineament endpoints x-y coordinates endpointswas was accomplished accomplished at aa digitizing digitizing tablet, using using aa puck puck with with a head-tail head-tail audio audio prompt prompt and andaadomain-clearing domain-clearing technique technique to to accommodate accommodate lineament clusters. lineament clusters. Once digitized, TM lineament lineament set became became amenable amenable to to visualization, visualization, Once digitized, the TM manipulation, and analysis as well with other otherspatially spatially manipulation, and well as as coregistration coregistration and and integration integration with addressable aeromagnetics,known knownmining miningactivity, activity, and and Digital DigitalElevation Elevation addressable data datasets setssuch suchasasaeromagnetics, Model with a geographic information informationsystem system(GIs). (GIS). The The via processing processing with Model (DEM) (DEM) datadata --- via results of such treatments treatments with the PANACEA GIshave have been been the thefocus focus of of presentations presentationsby by PANACEA 015 Murdock, Pride, Woodzick Woodzick and and others others at meetings in in both both Canada Canada and the United States. States. Selected examples from this body of of work work (e.g., (e.g., lineament lineament intersection intersection enhancement enhancement and and comparison willbe bediscussed discussedwith with respect respectto totheir theirsignificance significance comparison of TM/DEM TM/DEM lineament lineamentsets) sets)will for mineral and in light by the the next next mineral exploration exploration and light of of the theadvanced advanced capabilities capabilities offered by generation of of orbital orbital monitoring monitoringsystems systems such such as as RADARSAT RADARSATand and Eos. Eos. 102 j �GEOSTATISTICAL GEOSTATISTICAL AND AND 615 G I S EVALUATION EVALUATION OF OF BIOGEOCHEMICAL BIOGEOCHEMICAL AND AND ECOLOGICAL ECOLOGICAL DATA DATA FROM FROM Cu-Ni-PGE), NORTHEASTERN NORTHEASTERN MINNESOTA: MINNESOTA: THREE MINERALIZED MINERALIZED SITES SITES (Au (Au && Cu-Ni-PGE), THREE IMPLICATIONS IMPLICATIONS FOR FOR MINERAL MINERAL EXPLORATION EXPLORATION IN IN AA BOREAL BOREAL FOREST FOREST L. L. Zanko, A. A. Gokee, Gokee, B. B. Dewey, Dewey, S. S. Hauck, Hauck, and J. J. Pastor Natural Natural Resources Resources Research Research Institute Institute University University of of Minnesota, Minnesota, Duluth Duluth Duluth, Minnesota Duluth, Minnesota 55811 55811 Detailed biogeochemical biogeochemical and and ecological ecological studies studies of vegetation vegetation were were conducted conducted in in the the boreal boreal forest forest of of northeastern northeastern Minnesota. Minnesota. These These studies studies were were implemented implemented over over three three mineralized mineralized sites: sites: 1) 1) Raspberry Archean Rasoberrv Prospect: Prosoect: Archean (2.7 (2.7 Ga) Ga) gold gold mineralization mineralization in in the the Shagawa Shear Shear Zone Zone (SSZ), (SSZ), Vermilion Vermilion greenstone belt, belt, 5 miles west of of Ely, Ely, Minnesota; Minnesota; 2) 2) Spruce Spruce Road Road (SR): (SRI: 3) 3) South South Filson Filson Creek Creek (SFC): fSFC1: the the Duluth Duluth Complex. Complex. basal basal Cu-Ni Cu-Ni mineralization mineralization of of the the Duluth Duluth Complex; Complex; "cloud Cu-Ni-PGE mineralization mineralization of "cloud zone" zone" Cu-Ni-PGE of The The two two Keweenawan Keweenawan age age (1.1 (1.1 Ga) Ga) Duluth Duluth Complex Complex sites sites are are 15 15 miles southeast southeast of of Ely. Ely. The The SR SR site site consists consists of of low low grade grade Cu-Ni Cu-Ni sulfide sulfide mineralization mineralization at at the basal SEC site has discreet, of the the Duluth Complex, Complex, whereas the SFC basal contact of fracture-controlled fracture-controlled secondary secondary Cu-Ni-PGM Cu-Ni-PGM "cloud "cloud zone" zone" mineralization. mineralization. Glacial Glacial overburden overburden thickness thickness at at the the three three sites sites varies varies from from 0-40 0 - 4 0 ft. ft. Over 1300 vegetation vegetation samples samples were were collected collected from from 17 17 plant plant species species Over 1300 Sampling took took place over over two two weeks weeks in in late late August August and and early early September September of of both both years. years. Tissue samples samples (1100) (1100) submitted for INAA and and DCP DCP analysis analysis included included leaves, leaves, twigs, twigs, for multi-element multi-element INAA needles, and and outer outer bark. bark. Analysis of 500 500 vegetation vegetation samples samples from from the Raspberry Raspberry site in in 1989 1989 during during 1989 1989 and and iggo 1990 at at the the three three sites. sites. shows Abies balsamea tremuloides (quaking shows Abies balsamea (balsam (balsam fir) fir) twigs, twigs, Pop'ilus Popu7us tremuloides (quaking aspen) aspen) leaves, leaves, Corylus Cory7us cornuta cornuta (beaked (beaked hazel) hazel) leaves leaves and and twigs, twigs, Acer Acer spicatum spicatum (mountain maple) maple) twigs, and macrophyllus (large-leaved aster) leaves and Aster macrophy7lus leaves contain anomalous anomalous gold gold values. values. Many Many of the gold anomalies anomalies in in vegetation vegetation overlie aa zone zone of of sericite-iron sericite-iron carbonate carbonate alteration alteration associated associated with the the SSZ. A. balsamea balsamea twigs twigs recollected recollected in in 1990 1990 verify verify the the gold gold anomaly. anomaly. SSZ. At the two Cu-Ni sites, A. balsamea (twigs), 600 tissue samples from A. (twigs), sites, 600 Picea ana (black twigs and bark), bark), Pinus banksiana (jack (jack pine pine Picea marl mariana (black spruce spruce -- twigs calyculata bark), bark), Ledunigroenlandicum Ledum groenlandicum (labrador (labrador tea tea -- twigs), twi'gs), Chan,aedaphne Chamaedaphne ca7ycu7ata (leatherleaf twigs), Alnus Ainus crispa crispa (green (green alder alder -- twigs twigs and leaves), Alnus Alnus (leatherleaf - twigs), rugosa (speckled (speckled alder alder -- twigs twigs and and leaves), leaves), and A. A. macrophyllQs macrophy77us (leaves) (leaves) were were analyzed analyzed for for base base and and precious precious metals. metals. Anomalous Anomalous levels levels of of Ni, Ni, Co, Co, Au, Au, P.. mariarza balsamea (twigs), and A. and Pd Pd were were found found in in A. (twigs), P mariana (twigs), L. L. groenlandicum A. inacraphyllus macrophyllus (leaves). (leaves). These These anomalies anomalies appear appear groenlandicum (twigs), (twigs), and andA. to t o correspond correspond closely closely to to the the bedrock bedrock mineralization. mineralization. Bacillus cereus cereus spore spore counts counts and and other measures of microbial activity activity in soils were used as bioindicators bioindicators of of natural metal enrichments. enrichments. S. 6. cereus cereus counts, total mineralization, and total carbon carbon and and nitrogen, nitrogen mineralization, and pH analyses analyses were done on the ft. intervals across acrossthe A horizon horizon of of soils soils collected at 200 ft. each 6. cereus cereus counts counts ranged ranged from from 1,000 1,000 to t o 576,000 576,000 spores/gm spores/gm soil, soil, each site. site. B. - - 103 �..%. matching spatial ofsoil soilmetal metal anomalies. Initial results indieate matching spatial variation variation of anomalies. resultsore indicate that 8. cereus counts can be an effective indicator Initial of concealed bodies that B. cereus counts can be an effective indicator of concealed ore bodies in northern Minnesota. The effectiveness effectiveness of other soil soil properties as in northern Minnesota. The of other properties as biogeochemical prospecting tools is being evaluated. biogeochemical prospecting tools is being evaluated. Ecological characterization characterization consisted consisted of of identification and Ecological identification and quantification of tree, shrub, and herbal species present within 550 tree and herb plots and 1100 shrub plots. Geostatistical interpretation of the tree, shrub, and herb data will be used to map the various plant communities U at each site as well as the spatial distribution of metals. A geographical information system (GIS) will be used to determine what spatial relationships exist between the geochemical, geological, ecological, and geographical data. The ecological, nutrient uptake, geostatistical, and GIS studies are being used to better characterize and identify variables that affect metal uptake and concentration by boreal forest vegetation over metallic mineralization. j J J J j U Li 104 J J � https://digitalcollections.lakeheadu.ca/files/original/01407a8326f54b05f39f8f88362f45fc.pdf 31ba8d1a4cc4815ebcb8fbf8d66c44bf PDF Text Text r IT I THIRTY-SEVENTH THIRTY-SEVENTHANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY I I I I I I I I I I I I, TI t: r1 PART22 --FIELD FIELDTRIPS TRIPS PROCEEDINGS: PROCEEDINGS: PART MAY MAY1-4, 1-4,1991 1991 EAU EAUCLAIRE, CLAIRE,WISCONSIN WISCONSIN �Organization Committee, Committee, 37th Annual Annual Meeting Meeting ILSG, ILSG, 1991 1991 General Chairman: Chairman: Paul E. General E. Myers Myers PHONE: 715-836-3713 715-836-3713 Editor: Lung L u w S. Chan Geology Department Geology Department University of Wisconsin Wisconsin Eau Claire, WI 54702-4004 54702-4004 PROCEEDINGS VOLUME PROCEEDINGS VOLUME 37 37 PART I: ABSTRACTS ABSTRACTS(Includes (Includes Meeting Meeting Program) Program) PART 2: 2: FIELD TRIPS TRIPS Reference to to material material in Reference inthis thisvolume volumeshould shouldfollow follow the thee.rample examplebelow. below. Morey, Glen Glen B., B., and South wick,David David L., L., 1991, 1991, Manganese Manganese mineralization mineralization in in early Moray, Southwick, Proterozoic iron-formation of the Emily District, Cayuna Range, east-central Proterozoic iron-formation of the Emily Cayuna Range, east-central Minnesota, [abst.]; [abst.]; Institute on Proceedings, 37th 37th Annual Annual on Lake Lake Superior Superior Geology Geology Proceedings, Meeting, Eau Claire, WI, 1991; v. 37, pan 1, p. 75-76. Meeting, Eau WI, v. 37, part I, 75-76. Published and Distributed Distributed by: by: Institute on Lake Superior Institute on Lake SuperiorGeology Geology M.G. Mudrey, Mudrey, Jr., Jr., Secretary/Treasurer M.G. Secretary/Treasurer Wisconsin Geological Geological and and Natural History History Survey Survey Mineral Point Road 3817 Mineral Madison, WI 53705 53705 ***********see** PURCHASE OF PROCEEDINGS PROCEEDINGS VOLUMES VOLUMES Abstracts and and Part II, Trips) may (luring Proceedings (Part I,I, Abstracts Copies of the 37th ILSG Proceedings 11, Field Field Trips) may be be purchased purchased diiriiig the the meeting for for $5.04) $5.00 (US) each. Payable 1'ayal)le to the Institute Institute on onLake LakeSuperior SuperiorGeology Geology Proceedings and and Abstracts, Abstracts, Part Part 1,1, and Field Guidebook, Part 2, Issues of Proceedings 2, from from this this and andprevious previousiiieetiiu,s meetings may be ordered from: from: may he Michael G. Mudrey, .Ir. Jr. See above above PHONE: Address, See PHONE: 608-263-1705 608-263-1705 l'he cost of Orders will he filled while supplies last. All (955 a are The of each each part is $6.00 $6.00 U.S. U S . Orders will be All volumes volumes hack buck to 1955 rt available photocopyingat atthe theprevailing prevailingrate ratefrom fromthe theMichigan MichiganTechnological TechnologicalUniversity UniversityLibrary library through wailiible for photocopying lhriiuflh MS.Spence, Spence,Archivist. Archivist.Phone Phone906.487-2505. 906-487-2505. Mr. MS. �37th Annual Institute on Lake SuperiorGeology Procee:d.ings L . . Ray Wachs Civic Center L Eñu Claire, Wisconsin May 1-4,. 1991 Organized by P.U. Myers, University of Wisconsin-Eau Clairc LS. Chan, Ulniversity of Wi.sconsin-Eau Claire Volume 37 Part 2 Field Trips �TABLE OF OF CONTENTS CONTENTS Calender of Events Events Field Trip 11 - "The Mountain Shear Zone 'The Zone - aa Post Post Penokean Penokean Discrete Ductile Ductile Deformation DeformationZone" Zone" iii iii Field Trip 2 and Significance of the "Features and the PrecambrjanPrecambrianCambrian Contact in in Western Western Wisconsin" Wisconsin" 33 Field Trip 33 "Proterozoic Volcanogenic Volcanogenic Massive Sulfide Proterozoic Sulfide Deposits of Northwestern Northwestern Wisconsin" Wisconsin" 57 �CALENDAR OF EVENTS EVENTS TUESDAY, APRIL APRIL 30 30 - 3:00-5:00 p.m. p.m. 3:OO-500 Early Registration Registrationfor forField FieldTrips Trips#1 #1 and and #2 #2 Participants Civic Early Participants - Civic Center Inn (CCI) Lobby Lobby FIELD TRIP # #1 FIELD 1 P.K. P.K. Sims, and J.S. J.S. Kiasner Klasner (Leaders) (Leaders) "The "The Mountain Mountain shear shearzone zone -- aa post-Penokean discrete discrete ductile ductile deformation deformationzone" zone" 5:00 p.m. Two for Antigo Antigo (Park Inn) 500 p.m. Two vans depart for Inn) 8:30 p.m., p.m., Park Inn, Pre-Field Trip Conference Inn, Pre-Field Trip Conference WEDNESDAY, MAY 11 TRIP #1 #1 FIELD 'I'iUP 8:00 a.m. a.m. Vans Vansdepart departfrom from Park Park Inn, Inn,etntigo, Antigo, for for the mountain mountain area. area. Vans Vans return to CCI by about 9:00 p.m. return to CCZ by about 9:00 p.m. FIELD TRIP #2 L.S. Chan, L.S. Chan, P.E. P.E. Myers, Myers, and R.L. R.L. Hay, Hay, (Leaders): (Leaders): "Features "Features and and contact in western significance significance of the Precambrian-Cambrian Precambrian-Cambrian contact in Wisconsin" Wisconsin" 8:00 a.m. a.m. Pre-trip Pre-trip Seminar 8:00 Seminar CCI, CCZ, Farwell Farwell Rm. Rm. 8:20 a.m. Vans depart from CCI Lobby Vans depart CCZ Lobby 2:00-5:00 p.m. Pre-Conference Planning Session Pre-Conference Planning Session - Staff, Room Staff, CCI Gibson Room 4:00-8:00 p.m. Registration and and check-in check-in for pre-registrants, pre-registrants,Civic Civic Center Center Inn Inn Lobby Lobby 8:00-11:00 p.m. - Informal Get-together Get-together and Cash Cash Bar Bar by: Bill Bill Jordan Jordan Jazz Quintet Music by: THURSDAY, THURSDAY. MAY MAY 22 7:15 a.m - Registration Lobby, Civic Civic Center Center Inn (CCI) (CCI) Registration - Lobby, TECHNICAL SESSION SESSION All Technical Sessions are in Room All Room C, C, Ray Ray Wachs Wachs Civic Civic Center Center (RWCC); (RWCC); Poster Poster Sessions Sessions in RWCC Rooms D and E. Schedules of oral papers are shown on pages xiii and xiv. in RWCC Rooms D and Schedules of oral shown pages xiv. Contributors Contributors should should have have posters postersup upby by 9:00 9:00 a.m. a.m. 8:00 a.m. Introduction and Paul Myers, Paul Myers,Conference ConferenceChairman, Chairman, and Larry Larry Introduction andWelcome: Welcome: - Schnack, Schnack, Chancellor, Chancellor,University Universityof of Wisconsin wsconsin - Eau Claire 8:20-10:00 8:20-10:OO a.m. 10:00 a.m. a.m. 10:OO 10:20-11:50 10:20-11:50 a.m. Morning Chairs: R.W. MorningSession Session#1. #l. Chairs: R.W.Ojakangas Ojakangasand andA.B. A.B. Dickas Dickas COFFEE COFFEE BREAK BREAK Morning G.L. Chairs: G.L.LaBerge LaBergeand andK.K.Schultz Schultz MorningSession Session#2; #2;Chairs: �11 L -- L NOON-2:00 p.m. BOARD BOARD LUNCHEON LUNCHEONAND ANDANNUAL ANNUALMEETING: MEETING:Farwell FarwellRoom, Room. CCI CCI 12:30-1:30 p.m. POSTER SESSION SESSION #1 - Authors Authors present (Poster (Posterpapers, papers,p.p.xv) xvl 1:40-3:00 p.m. Afternoon Chairs: V.W. AfternoonSession Session#1. #l. Chairs: V.W.Chandler Chandlerand and(jB. G.B.Morey Morey - -- COFFEE BREAK BREAK -- Remove Remove Poster Papers Papers 3:00 p.m. U 3:20-4:50 p.m. Afternoon M.M. AfternoonSession Session#2. #2.Chairs: Chairs: M.M.Kehienbeck Kehlenheckand andC.C.Craddock Craddock 6:00-7:30 p.m. CASH BAR: RWCC ROOM ROOMAA 7:30-10:00 p.m. ANNUAL ANNUAL ILSG ILSG BANQUET BANQUET-- RWCC RWCC Rooms A and and BB - U Presentation Presentation of of the the Goldich Goldich Medal Medal to to W.J. WJ. Hinze, Hinze, Purdue Purdue University University Chandler by by V.W. V.W. Chandler [ Speaker: K. Sims, Sims,"Archean "Archeanand andEarly EarlyProterozoic ProterozoicGeology Geologyof of the the Speaker: Paul PaulK. introduced by G.B. Lake Lake Superior Superior Region Region -- An An Overview"; Overview"; introduced G.B. Morey. - [ IL FRIDAY, MAY 3, 3,1991 1991 p.m. 8:00 8:00 a.m.-3:30 a.m.-330 p.m. Registration Registrationand andSale Saleof ofExtra ExtraProceedings ProceedingsVolumes Volumes 8:20 a.m. Morning Chairs: M.M. G. G. Mudrey, A.A.DeMatties #l. Chairs: Mudrey,Jr.Jr.and andT.T. DeMatties MorningSession Session#1. COFFEE COFFEE BREAK BREAK 10:00 a.m. L L [ 10:20-11:30 a.m. Morning G.W. MorningSession Session#2. #2.Chairs: Chairs: G.W.Adams Adamsand andBA. BA.Brown Brown 12:30-1:30 p.m. POSTER SESSION #2 -- Authors Authors present (poster (poster papers, papers, p. p. xvi) xvi) 1:40-2:40 p.m. Afternoon Session W.S. #l.Chairs: Afternoon Session#1. Chairs: W.S.Cordua Corduaand and M. M. Jirsa 2:40 p.m. Student Award Award Presentation, John Klasner Klasner - -- COFFEE COFFEE BREAK BREAK -- Remove Remove Poster Papers 3:00 p.m. 3:20.4:30 p.m. Afternoon J. J. Kaliokoski Afternoon Session Session#2. #2.Chairs: Chairs: Kaliokoskiand andJ.J.C. C.Green Green 7:00-8:30 p.m. Pre-Trip Pre-Trip #3 Seminar, Seminar,CCI, CCI,Farwell Farwell Room, Room, M.G. M.G. Mudrey, Jr. and WA. B.A. Brown Brown L SATURDAY, MAY 4, 1991 1991 SATURDAY, FIELD TRIP #3 Mudrey, Mudrey, Jr., and and B.A. Brown Brown (Leaders), (Leaders), "Proterozoic "Proterozoic volcanogenic massive sulfide deposits of northwestern northwesternWisconsin Wisconsin" from front front entrance of CCI 8:00 a.m. Bus departv departs from M.G. ii II �WEDNESDAY, MAY 1, 1991 FIELD TRIP #1 and J.S. J.S. KJasner Klasner (Leaders) (Leaders) P.K. Sims, and - "The "The Mountain shear shear zone zone - a post-Penokean post-Penokean discrete ductile ductile deformation deformationzone" zone" discrete HI iii �MOUNTAIN SHEAR ZONE, ZONE, OCONTO OCONTOCOUNTY, COUNTY, WISCONSIN-WISCONSIN-A POST-PENOKEAN DISCRETE DUCTILE DEFORMATION DEFORMATION ZONE ZONE P. K. Sims, Sirns, U.S. U.S. Geological Geological Survey Survey Denver Box 25046, MS MS 905, 905, Denver Federal Center Denver, CO 80225 80225 Klasner, Department Department of of Geology Geology John S. Kiasner, Western Illinois University and U.S. Geological U.S. Geological Survey Survey Macomb, IL 61455 61455 Warren C. Day, U.S. U.S. Geological Geological Survey Survey Box 25046, 25046, MS MS 905, 905, Denver Denver Federal Federal Center Center Denver, CO 80225 Denver. 80225 E. Peterman, Peterman, U.S. U.S. Geological GeologicalSurvey Survey Zell E. Box 25046, MS 963, Denver Federal Box 25046, MS 963, Denver Federal Center Center Denver, CO 80225 80225 of Institute on Field trip, 37th Annual Meeting of Lake Superior Superior Geology, Geology, Eau Eau Claire, Claire,Wisconsin Wisconsin May 1, 1, 1991 1991 iv �CONTENTS CONTENTS Page Page Introduction . . . . . . . . . . Penokean orogen . . . . . . . . . . . penokean Rock units units, Mountain area . . . Rock Outside O u t s i d e of o f sshear h e a r zzone one . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waupee Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waupeevolcanics Mafic lava flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mafic Felsic volcanic volcanic rocks and and minor minor interbedded interhedded mafic volcanic rocks Felsic Granodiorite Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shear zone . . . . . . . . . . . . . . . . . . \Vaupee Waupee Vblcanics Volcanics . . . . . . . Amphibole schist schist . . . . . . . . . . . . . . . . . . Quartz diorite schist schist . . . . . . . . . . . . . . . Interlayered biotite biotite and and amphibole amphihole schist schist . . . Biotite schist . . . . . . . . . . . . . . . . . . . . Biotite-amphihole schist Biotite-amphibole schist . . . . . . . . Amphibole schist schist . . . . . . . . . . . . . Magnetite-rich sch ist . . . schist Granite gneiss . . . . . . . . . . . . . Baldwin Baldwin Conglomerate . . . . . . . Hines Quartz Diorite Diorite . . . . . Regional structure . . . . . . . . . . . . . . . . . Shear zone . . . . . . . . . . . . . . . . . . Mesoscopic structure structure . . . . . . Mesoscopic Microscopic structure . . . . . Kinematic analysis . . . . . . . . Geoharometry Geobarometry and geothermometry . . . Conclusions Conclusions . . . . . . . . . . . . . . . . . . Regional significance significance . . . . . . . . . . . Acknowledgments . . . . . . References cited . . . . . . . Field stops and road log Field log . . . . 1 I . L L L L V 2 2 2 3 . 3 4 4 4 5 D 6 6 7 7 7 9 9 l0 10 10 11 11 12 12 13 14 14 16 �INTRODUCTION INTRODUCTION by Sims Simsand and M.G. M.G. Mudrey, Mudrey,Jr. Jr. revealed revealed the the existence existence of of aa Reconnaissance mapping in 1980 by belt of remarkably well exposed mylonitic rocks near Mountain in Oconto County, Wisconsin. belt of remarkably well exposed mylonitic rocks near Mountain in Oconto County, Wisconsin. Subsequently, the mylonitic mylonitic rocks rockswere were systematically systematicallymapped mappedtotodetermine determine their their relation relation to Subsequently, the to the the regional deformation (Sims, 1989), and Kiasner made detailed structural studies of critical outcrops regional deformation (Sims, 1989). and Klasner made detailed structural studies of critical outcrops to to determine determine the the sequence sequenceof of deformational defonnational events events and and the the sense sense and and direction direction of of movement movement within within the the shear shear zone zone (Sims (Sims and and others, others, 1990). 1990). The Mountain shear shear zone zone is is aa discrete discrete ductile ductile deformation deformation zone zoneas as much much as as 1.5 1.5 km wide that post-dates Early Early Proterozoic Proterozoic regional regional deformation deformationof of the the Penokean Penokean orogeny. orogeny. A post-dates A body body of of quartz quartz diorite, formally named named the the Hines Hines Quartz Quartz Diorite, Diorite, that that was was intruded intruded into into the the shear diorite, formally shear zone zone at at about about the close of the shearing event has a U-Pb zircon concordia intercept age of 1,812.7± 3.6 Ma (Sims the shearing event has a U-Pb zircon concordia intercept age of 1,812.723.6 Ma (Sims and others, 1990), which places placesaafirm firmminimum minimumage ageon onthe thetime time of ofshearing. shearing. The Mountain shear 1990), which zone and other E. shear zones in N.55°-60° 55'-60 E. in the the Wisconsin Wisconsin magmatic terranes terranes record record aasignificant significant zone otherN. episode of ductile deformation that that probably probably resulted resultedfrom fromaa collision collision of unknown rocks to the south of the area after of after the the Penokean Penokeanorogeny. orogeny. PENOKEAN OROGEN Ma Penokean Penokean orogen orogen developed developed as as an embayment in the southern The 1,990-1,835 1,990-1,835 Ma southern margin margin of the Archean Superior craton. Rocks of the orogen are exposed in Wisconsin, northern Michigan, Superior Rocks of the orogen are exposed in Wisconsin, northern Michigan, and Minnesota Minnesota (Cannon, (Cannon,1973; 1973;Morey, Morey,1973; 1973; Sims Sims and and Peterman, Peterman,1983). 1983). The orogen orogen consists consists of of two twodistinct distinctlithologic lithologic domains domains (fig. (fig. I): northern deformed deformed 1): a northern continental margin assemblage overlying an Archean basement; and a southern assemblage of island southern continental an Archean basement; arcs, the Wisconsin magmatic terranes (Sims and others, 1989). The northern rocks include Wisconsin magmatic terranes (Sims and others, 1989). northern include the Marquette (Cannon and and Gair, Marquette Range Range Supergroup Supergroup in Michigan Michigan and Wisconsin Wisconsin (Cannon Gair, 1970), which Mille Lacs Lacs Groups Groups in in Minnesota Minnesota (Morey, (Morey, 1983), 1983), and and comprise comprise aa correlates with the Animikie and Mille south-facing continental-margin assemblage. They consist of a lower rifted passive-margin sequence They consist rifted passive-margin sequence overstepped northward by a synorogenic foredeep sequence (Barovich and others, 1989; Southwick northward by a synorogenic foredeep sequence (Barovich and others, 1989; Southwick and others, 1988). 1988). Early EarlyProterozoic Proterozoicregional regional deformation deformation involved involved northward-directed thrusting and related folding folding of the supracrustal supracrustal rocks rocks and and produced produced metamorphism metamorphism and basement gneiss gneiss domes caused by crustal thickening (Sims and Peterman, 1983; HoIm and others, 1988; Attoh thickening Peterman, 1983; Holm others, 1988; Attoh and and Klasner, 1989). Klasner, 1989). The Thesouthern southernmagmatic magmatic terranes terranesconsist consistofofEarly EarlyProterozoic Proterozoiccalc-alkaline calc-alkaline and and tholeiitic volcanic and caic-alkaline calc-alkaline plutonic rocks rocks (Sims (Sims and and others, others,1989). 1989). The Niagara Niagara fault zone zone separates separates the thesouth-facing south-facing continental continental margin margin assemblage assemblage and the the oceanic arc terranes in Wisconsin and Michigan (fig. 1). It is a broadly arcuate, terranes in Wisconsin and Michigan (fig. 1). is arcuate, convex-northward convex-northward of ductile shears as system of as much as as 10 10 km wide that contains contains flattened flattened steeply steeplydipping dippingrocks rockshaving having dominantly down-dip down-dip stretch stretch lineations lineations (Larue and Ueng, Ueng, 1985; 1985; Sedlock Sedlock and and Larue, Larue,1985). 1985). It dominantly contains a dismembered ophiolite and has has been been interpreted interpreted as asaapaleosuture paleosuturezone zone(Schulz, (Schuiz,1987) 1987) between the two terranes, which were juxtaposed at about 1,860 Ma (Sims and others, 1985). two terranes, which were at about 1,860 Ma (Sims and others, 1985). rocks and and related related intrusive rockssouth south of of the the Niagara Niagara fault fault are are part part of of the The oceanic arc rocks intrusive rocks Pemhine-Wausau terrane of the Pembine-Wausau terrane the Wisconsin Wisconsin magmatic magmatic terranes (Sims (Sims and and others, others,1989). 1989). The The to 1,889 1,889Ma. Ma. The The granitoid rocks are mainly granodiorite granodiorite and tonalite; metavolcanic rocks are 1,860 to tonalite; post-tectonic. Sims they range in age from from 1,760 1,760 to 1,870 1,870 Ma, with with the younger group being post-tectonic. Simsand and others (1989) have proposed that that the the Penokean Penokeanorogeny orogenyterminated terminatedbetween between1,835 1,835Ma Maand and1,840 1,840 �Ma, when when the the Marshfield Marshfield terrane (see was sutured sutured to the Pembine-Wausau Pembine-Wausau terrane along the (see fig. 1) was Eau Pleine shear zone. shear zone. ROCK UNITS, AREA UNITS, MOUNTAIN MOUNTAIN AREA The Mountain shear zone zone is in in the the eastern eastern part part of of the the Pembine-Wausau Pembine-Wausauterrane. terrane. The major rock units exposed within within and and adjacent adjacent to the Mountain shear zone are metavolcanic Mountain shear zone are metavolcanic rocks rocks and and sedimentary rocks, assigned to to the the Waupee Volcanics, granodiorite granodiorite and minor related volcanogenic sedimentary mylonitized equivalent equivalent in the the shear zone--granite gneiss (unit Xgn, fig. fig. 2)--and 2)--and the the Hines Hines Quartz its mylonitized Diorite. The sheared metavolcanic rocks (units Xwi and Xwa, fig. 2) and the granite The sheared metavolcanic rocks (units Xwi and Xwa, fig. 2) granite gneiss gneiss are overlain along the northern margin of the shear zone by a metaconglomerate, named the overlain along the shear zone the Baldwin Baldwin Conglomerate. These These rocks rocks are are Early Early Proterozoic Proterozoic in age. They They are are intruded intruded by by and and occur occur as a roof pendant in in anorogenic anorogenic rocks rocks of of the theMiddle MiddleProterozoic Proterozoic(—1.47 (- 1.47 Ga) Ga) Wolf Wolf River River batholith. batholith. The stratigraphic stratigraphic nomenclature nomenclature used used in in this this report report was was adopted adoptedearlier earlier(Sims, (Sims,1989), 19891,and and isis based largely on previously proposed proposed geologic names. names. Mancuso Mancuso (1957) (1957) assigned the the name name Waupee Waupee to the the metavolcanic metavolcanic rocks exposed exposed in in this this and and adjacent adjacent areas areas to the east Volcanics to east because because of of typical typical exposures near Waupee Creek, and this formal designation is retained herein. exposures near and this formal designation is retained herein. Lahr (1972) (1972) renamed this unit the the Waupee Waupee Formation, Formation, but but the the earlier earlier nomenclature nomenclature appropriately appropriately emphasizes emphasizes affinity of of the the rocks. rocks. Mancuso Baldwin Conglomerate the volcanic affinity Mancuso (1957) (1957) also proposed the the name name Baldwin for the Baldwin Creek, Creek, which whichisisaccepted accepted herein. herein. Lahr the metaconglomerate metaconglomerateexposed exposed in in the thevicinity vicinity of Baldwin (1972) assigned assigned the the undeformed quartz diorite exposed in section 12, T. 31 N., R. 16 E., east of the 16 the quartz diorite exposed in section 12, T. 31 N., village of Mountain (see Sims, 1989), to the Hines Quartz Diorite because of its exposures village of Mountain Sims, 1989), to the Hines exposures near Hines Creek. Mancuso (1957) (1957) had had included Creek. Previously, Previously, Mancuso included these rocks rocks in in his his "Macauley "Macauley Granite.t Granite." Although Lahr (1972) correctly correctly renamed renamed the granitoid rocks "Macauley Gneiss,' neither of these Although "Macauley Gneiss," terms are are used used herein herein because becausethey theyeach eachinclude includesubstantial substantialamounts amountsof of metavolcanic metavolcanic rocks rocks as as well well as granitoid rocks. rocks. within the the Mountain shear zone differ profoundly profoundly in in structure structure and to some Because the rocks within extent in mineralogy mineralogy and degree of metamorphism from those outside of it, it, the the rocks rocks within within and outside of the shear zone are described separately below. Slightly to moderately deformed shear zone are described separately below. Slightly to moderately deformed rocks rocks (D1) of of the the Waupee Waupee Volcanics and and the intrusive granodiorite granodiorite were converted (D,) converted to to mylonitic mylonitic schists and gneisses within within the the shear shear zone (D2). gneisses (D,). The The undeformed undeformed Hines Hines Quartz QuartzDiorite Dioritewas wasemplaced emplaced within within the shear zone at or or near near the theend endofofthe theductile ductiledeformation. deformation. Outside or of Shear Zone Zone Waupee Volcanics Volcanics Within the map map area area (fig. (fig. 2), 2), the theWaupee WaupeeVolcanics Volcanics is is divided divided into into four four mappable mappable units. units. Outside of the the shear shearzone, zone, ititconsists consists of of aaunit unitofofmafic maficlava lava flows flows (unit (unit Xwm, Xwm, fig. 2) and a unit unit of of rocks (unit (unit Xwf). Xwf). Sheared correlative predominantly felsic volcanic rocks correlative rocks within the shear shear zone zone are: are: (1) amphibole schists (unit (unit Xwa) and (2) (2) interlayered interlayered quartz-biotite quartz-biotite and and amphibole amphibole schist schist (unit (unit Xwi), respectively. A A body body of quartz quartz diorite dioriteschist schist(unit (unitXwq), Xwq),presumably presumably aasubvolcanic subvolcanic intrusion, intrusion, Xwi), respectively. occurs within the shear zone. Chemical Chemicalcompositions compositionsof of two two representative representative rocks rocksare arelisted listedinintal)IC table 1. 1. 2 �Mafic lava Mafic lava flows flows This rock unit southeast of of the shear unit (Xwm, (Xwm, fig. 2) is is dominantly dominantly exposed exposed southeast shear zone, zone, and is is of dark-gray, dark-gray, fine-grained fine-grained porphyriticlava porphyritic lava flows flowsthat thatare arehighly highlyaltered. altered. The rocks composed mainly of are generally generally massive and unfoliated to to weakly weakly foliated but locally locally have a distinct distinct compositional compositional layering visible on weathered surfaces. Possible relicts of pillow rinds can seenatatplaces. places. The The layering visible on weathered surfaces. Possible relicts of pillow rinds can bebeseen lavas are metamorphosed to togreenschist greenschist facies. facies. lavas In the occur as stubby the least least altered alteredrocks, rocks,plagioclase plagioclase megacrysts megacrysts occur stubby laths with broad albite albite twinning and as aggregates of randomly oriented stubby laths. The twinning and aggregates of randomly oriented stubby laths. The plagioclase plagioclase is altered altered variably variably sericite, and and calcite. calcite. The to epidote/clinozoisite, epidote/clinozoisite, sericite, Themafic mafic minerals minerals are are completely completely altered to to palepaleand skeletal opaque green actinolite and, and, locally, locally, to sphene, sphene, which which shows incipient crystallization, and oxides. Quartz as anhedral, anhedral, strained, sutured grains. oxides. Quartz generally generally is absent, but in two sections occurs as Biotite is dark brown. brown. Felsic volcanic volcanic rocks rocks and minor minor interbedded interbedded mafic mafic volcanic volcanic rocks This rock rock unit unit (Xwf (Xwf,fig. fig.2) 2)isismainly mainlyexposed exposedin in sections sections44 and and5, 5, T. T. 31 31 N., R. 17 17F. E.(see (seeSims, Sims, 1989). felsic tuff, intercalated metasedimentary 1989). It consists of massive to layered metamorphosed felsic rocks, and and generally generally thin thin interbedded interbedded layers layers of of mafic mafic tuff. tuff. The rocks rocks, rocks have a penetrative cleavage cleavage (Si) and, at (S,) at least least locally, locally, are arefolded folded(F1). (F,). The felsic granular rock rock of felsic tuff tuff isis aalight-gray, light-gray, fine.grained, fine-grained, inequigranular, inequigranular, xenomorphic xenomorphic granular composition. ItIt isiscut general dacitic composition. cut by by widespread widespread narrow narrow shears shears but but lacks lacks mylonitic mylonitic textures. Plagioclase occurs occurs mainly mainlyas as anhedral anhedral grains grains generally generallyless lessthan than 0.3 0.3 mm mm in in diameter, but Plagioclase locally forms forms phenocrysts phenocrystsas as much much as as 1.5 mm in diameter. locally 1.5 mm diameter. It is is poorly poorly twinned. twinned. Some Somegrains grains contain abundant rounded quartz inclusions. inclusions. Quartz Quartz grains grains are are anhedral, anhedral, clear, and approximately grains. Stubby brown brown to pale-red biotite is preferentially orientated the same size as the plagioclase grains. orientated in the (Si) foliation and is intergrown with about equal amounts of muscovite. The biotite (S,) is intergrown equal amounts of muscovite. The biotiteisislocally locally altered to chlorite. sphene, opaque opaque oxides, allanite, and zircon are altered chlorite. Sparse, Sparse, poorly crystallized crystallized sphene, oxides, allanite, are accessory minerals. minerals. The The sedimentary sedimentary rocks rocks are are mediummedium-to todark-gray, dark-gray,fine-grained, fine-grained, thinly thinly layered, foliated rocks rocks composed of plagioclase, quartz, and biotite and, locally, either garnet or cummingtonite. Good composed of plagioclase, quartz, and biotite and, locally, either garnet or cummingtonite. Good N., R. R. 17 E., F., on on the ridges just just north of Bear exposures can be seen in the center center of of section section 5, 5, T. 31 N., Paw road, west of Waupee Creek Creek (stop (stop5,5,fig. fig. 8). 8). Granodiorite fig. 2) 2) that that have an average composition of granodiorite granodiorite Porphyritic granitoid rocks (unit Xg, fig. (table 2; 2; fig. fig. 3) 3) intrude the metavolcanic rocks on the southeast side of the Mountain metavolcanic rocks on the southeast side of the Mountain shear zone. T. 31 N., N., R. R. 17 E., E., but but extend into sec. 5 (see Sims, They are are most most extensively extensively exposed in section 7, T. 1989). The 1989). The granodiorite granodiorite intrudes intrudesthe thesurrounding surroundingmetavolcanic metavolcanicrocks rocks lit-par-lit, lit-par-lit, to form migmatite, migmatite, and contains of them them (mainly amphibolite) that that are and contains moderate to abundant abundant elliptical elliptical inclusions inclusions of (mainly amphibolite) F. The oriented N. consistently oriented N. 1Oo3O 10'-30' E. Thegranodiorite granodioriteextends extendsnorthward northward into into the the shear shearzone, zone, where where The chemical itit has has been been deformed deformed into into aagneiss, gneiss, termed termed granite granite gneiss gneiss (unit (unit Xgn, Xgn, fig. fig. 2). chemical 2). odiorite (number composition of of one sample of granodiorite composition (number 35-85) 35-85) is is given given in in table table 1.1. 3 �The characterized by The granodiorite granodiorite isisaa pinkish-gray, pinkish-gray, generally generally massive, medium-grained rock characterized by light-gray or pinkish-gray pinkish-gray subhedral microdine light-gray microche porphyrocrysts porphyrocrysts (—1 (-1 cm crn long) and and pink pink plagioclase plagioclase phenocrysts as 1.5 1.5 cm cm long) long) in in aa finer finergrained, grained,essentially essentiallyequigranular equigranulargroundmass groundmass of of phenocrysts (as much as feldspar, quartz, feldspar, quartz, hornblende, hornblende, and biotite. biotite. The mafic mafic minerals minerals typically typically form clusters clusters between between feldspar grains. Adjacent Adjacent to to the the southeast southeast margin margin of of the the shear shear zone zone (fig. (fig. 2), 2), the the rock rock feldspar and quartz grains. is partly deformed into into protomylonite, protomylonite, but itit lacks lacks a penetrative penetrative structure. structure. Plagioclase (oligoclase) occurs as blocky blockyto tolath-shaped, lath-shaped, subhedral subhedral crystals crystals that that have have CarlsbadCarlsbadPlagioclase (oligodase) albite and, less commonly, peridline twins. twins. A weak but distinct commonly, pericline distinct concentric concentric normal zoning zoning can be distinguished in a few sections. sections. Myrmekite Myrmekite commonly commonly occurs adjacent to microcline. Phenocrysts Phenocrysts IPcore-mantle core-mantle aggregates aggregates and and type type TIP IIP structures; Hanmer, Hanmer, locally structure (type (type IP locally have have aa mortar structure 1982) that comprise intragranular, intragranular, fine-grained fine-grained recrystallized recrystallizedplagiodase. plagioclase. Adjacent Adjacent to to the shear 1982) that plagioclase contains abundant abundant tiny tiny rounded rounded inclusions inclusions of of quartz. quartz. zone, the plagioclase Quartz generally occurs as sutured grains grains that that are aresomewhat somewhatcrackled crackled and andshow showundulose undulose extinction. extinction. Most Most quartz quartzisisinterstitial interstitialbut butsome someforms formsanastomosing anastomosing aggregates aggregates as as much much as as 55 mm long. long. Microcline commonly commonlyoccurs occursas as phenocrysts phenocrysts that that have undulose Microcline undulose extinction extinction and and contain contain inclusions of of mynnekitic myrmekitic plagioclase plagioclaseand and quartz. quartz. At At places, places, elliptical elliptical quartz grains grains and and aggregates aggregates of grains are clustered near near grain grain margins. margins. Type TypeTM IM mantle mantle aggregates aggregates and and type type TIM IIM structures (Hanmer, (Hanmer, 1982) 1982) are are present present locally. locally. Judged Judgedfrom fromits itsmorphology, morphology, microcline behaved more brittlely plagioclase to In aa thin thin section, section, from from the the center center than associated plagioclase to the the strain strain related related to the shearing. In of section 77 (fig. 8), for example, plagioclase has been partly reduced to fine-grained intragranular (fig. plagioclase fine-grained intragranular and mantle mantle aggregates, aggregates, whereas whereas nearby nearby microcline microcline is only strained and crackled. Not Notuncommonly, uncommonly, shears shears transect transect microcline microclinemegacrysts. megacrysts. The dark-green to tobluish-green, bluish-green,poikilitic poikilitichornblende hornblendecommonly commonly0.5 0.5 The principal principal mafic mafic mineral mineral isis dark-green to to 1 mm in diameter. diameter. It is is partly partly intergrown intergrown with biotite of of approximately approximately the same same grain grain size, size, probably is is aa primary primary mineral, mineral, but but also also isis partly partlyaltered altered to to biotite. biotite. The which probably The secondary secondary biotite biotite and and associated reaction products-magnetite, products--magnetite, sphene, and epidote--tend to to form ill-defined pseudomorphs after after hornblende. pseudomorphs hornblende. The Thesecondary secondary biotite biotite isis much much finer finer grained grained than than the theoriginal original biotite. The Theaccessory accessoryminerals minerals are aremainly mainly zircon, zircon, apatite, and and altered altered allanite. allanite. Shear Shear Zone Zone Waupee Waupee Volcanics Volcanics Amphibole schist schist Xwa (inside (inside shear zone) superficially (outside Mafic rocks in unit Xwa superficially resemble those in unit Xwm (outside shear zone) shear zone) in in being beingdark-gray dark-grayporphyritic porphyriticlavas, lavas,but but they theyare arevariably variablymylonitized mylonitized and andfoliated, foliated,less less slightly higher metamorphic grade (lower amphibolite facies). An exception exception isis altered, and and have have aa slightly facies). An the mafic rocks in the extreme northeastern northeasternpart partofofthe theshear shearzone, zone,west westofofNelligan NelliganLake Lake(see (seeSims, Sims, The chemical 1989), highly altered and and bleached bleached and anddefinitely definitelygreenschist greenschist facies. facies. chemical 1989), which which are are highly is listed listed in in table table 1.1. composition of a representative representative sample sampleof of amphibole-facies amphibole-facies lava lava is 4 �Plagioclase sparse anhedral Plagioclase occurs as sparse anhedralporphyroclasts porphyroclastsas asmuch much as as 55 mm in diameter, but mainly has been recrystallized to finer finer grained grained aggregates. aggregates. Core-mantle aggregates has recrystallized to aggregates (Hanmer, 1982) are common. common. Quartz Quartz grains grains are are sparse. sparse. The amphibole is either a green green or or aa bluish-green bluish-green hornblende; the latter latter appears to replace the ihe former. former. The Thehornblende hornblendecommonly commonlycontains containsoriented orientedblebs blebs of of magnetite. Olive-green Olive-greento tobrown brown biotite and and associated associated sphene spheneisislocally locally associated with the hornblende and and appears appears to to be be mainly mainly an alteration Skeletal opaque opaque oxides occur in aa few alteration product product of it. it. Skeletal oxides occur few sections. sections. Zircon Zircon is a sparse sparse accessory accessory mineral. Quartz Quartz diorite diorite schist schist Quartz diorite diorite schist schist isis aadark-gray, dark-gray, speckled, speckled, medium-grained medium-grained metamorphosed rock that that intrudes the amphibole schist in section 33, T. 32 N., R. 17., and presumably is a subvolcanic body. intrudes the amphibole schist in section 33, T. 32 N., R. 17., and presumably is a subvolcanic body. It It has has aaconspicuous conspicuousfoliation foliation and andlineation lineationexpressed expressedby byaligned alignedhornblende hornblendeaggregates. aggregates. This structure structure isis modified modified by by local local mylonitic mylonitic structures, structures, characterized by by grain-size grain-sue reduction through through recrystallization. (table 3), 3), the rock recrystallization. Narrow Narrow mylonitic mylonitic shears are arecommon. common. Compositionally Compositionally (table rock overlaps overlaps that of of the the Hines Hines Quartz QuartzDiorite Dioritebut butititdiffers differsfrom from ititininmegascopic megascopic appearance appearance and and by by being deformed. deformed. Plagioelase (An-) occurs occurs as as concentrically concentrically zoned, zoned, elongate elongate subhedral subhedral crystals crystals having having Plagioclase (An15.) combined Carlsbad-albite Carlsbad-albite twins twins and and pericline pericline twins. twins. It is is partly partly recrystallized recrystallized to IP IP core-mantle core-mantle aggregates (Hanmer, (Hanmer, 1982) 1982) and fine-grained intragranular aggregates (mortar structure). In Inshears, shears, aggregates recrystallized recrystallized plagioclase plagioclase is is intergrown intergrown with with recrystallized recrystallized hornblende. hornblende. Hornblende Hornblende isis altered altered to tovarying varying degrees. The Theleast leastaltered, altered,possibly possibly original original hornblende, is medium strongly poikilitic and medium to to dark dark green. green. ItItisisintergrown intergrownwith with aa bluish-green bluish-green hornblende hornblende that that isisstrongly is probably an alteration product of the green hornblende. Locally, Locally, either of the hornblendes have a partial partial rim rim of of aa secondary secondary fibrous fibrous pale-green pale-green actinolitic actinolitic hornblende or actinolite. Recrystallized Recrystallized hornblende grained and and dark green. green. Much hornblende in in mylonitic mylonitic shears is fine grained Much of of the the original(?) original(?) hornblende hornblende is is replaced replaced by by pseudomorphs pseudomorphsof offine-grained fine-grainedsecondary secondarygrayish-olive grayish-olive to to brown brown biotite. biotite. Quartz Quartz grains grains are areinterstitial interstitialand andparagenetically paragenetically late. late. The Thegrains grainshave haveundulose unduloseextinction extinction and indiameter diameter that that retain retain the approximate outline and are are recrystallized recrystallized to sutured sutured grains —0.5-0.8mm -0.5-0.8 mm in of rnrn in in of the the original original 3-4-mm-diameter 3-4-mm-diameter grains. The Theaccessory accessoryminerals minerals are arezircon, zircon, as asmuch much as as 0.15 0.15 mm diameter, diameter, apatite, apatite, and and altered alteredallanite. allanite. The 2) isis interpreted interpreted as asaacoeval, coeval,subvolcanic subvolcanic intrusive intrusive The quartz quartz diorite dioriteschist schist(unit (unitXwq, Xwq, fig. fig. 2) rock associated with the metamorphosed porphyritic lava flows (units Xwm and Xwa). rock associated with the metamorphosed porphyritic lava flows (units Xwm Xwa). Interlayered biotite biotite and and amphibole amphibole schist schist Interlayered Interlayered biotite biotite and andamphibole amphiboleschist schist(fig. (fig. 4; 4; table table 4) is is the the most most abundant abundant rock rock unit unit in in the the Mountain Mountainshear shearzone zone(unit (unitXwi, Xwi,fig. fig.2). 2).The Therocks rocksare aredark-gray dark-graytotopinkish-gray, pinkish-gray,generally generallyfine fine grained grained schists, schists, which which can be be designated designated primarily primarily as asbiotite, biotite,biotite-amphihole, biotite-amphibole, and andamphibole amphibole schist. schist. More Morerestricted restrictedrock rocktypes typesinclude includecummingtonite-bearing cummingtonite-bearingschist, schist,gedrite-bearing gedrite-bearingschist, schist,and and magnetite-rich schist; none none of these magnetite-rich schist; these units units were were mapped mapped separately separately(Sims, (Sims, 1989), 1989), and and only only the the magnetite-rich are representative of of the the major major magnetite-rich schist schist is is discussed discussed following. following. The modes in in table table 44 are rock rock types; types; the the cummingtonite-, curnmingtonite-,gedrite-, gedrite-, and and magnetite-rich magnetite-rich schists schists are are generally generally too too fine fine grained grained 5 �for accurate accurate modal modal analysis. analysis. The metamorphic grade of of the the rocks rocks isismainly mainly lower lower amphibolite amphibolite facies. The rocks are grossly equivalent to the interbedded felsic and mafic volcanic rock The rocks are grossly equivalent to the interbedded felsic and mafic volcanic rock unit unit (Xwf) (Xwf) outside the shear zone, and represent strongly deformed variants of the volcanic rocks within the shear zone, and represent strongly deformed of the volcanic within shear zone. The Theschists schists are areintruded intruded by by granite granite gneiss gneiss and, adjacent to the the main main body body of granite gneiss, by dikes of pink leucogranite gneiss that are part of the granite gneiss body. gneiss, by dikes of pink leucogranite gneiss that are part of the granite gneiss body. Biotite schist Biotite schist is the the dominant dominant rock rock type type in in the theinterlayered interlayered schist schist unit unit (Xwi). (Xwi). It consists consists Biotite schist principally of plagioclase and quartz and contains variable amounts of K-feldspar and biotite; itit is principally of plagioclase and quartz is gradational into biotite-amphibole gradational biotite-amphibole schist schist and and cummingtonite-, cummingtonite-, gedrite-, and and magnetite-bearing magnetite-bearing schists. schists. Plagioclase, the most most abundant occurs as as anhedral 4), occurs anhedral to to subhedral subhedral Plagioclase, the abundant mineral mineral (table (table 4), porphyroclasts as much as 2 mm in diameter, and as smaller, recrystallized grains (oligoclase) porphyroclasts mrn in diameter, and as smaller, recrystallized grains (oligoclase) as as mantle aggregates and intragranular aggregates aggregates (Hanmer, 1982). 1982). Combined Combined Carlsbad-twinning Carlsbad-twinning in porphyroclasts is is partly partly obliterated obliterated by bystrain. strain. Locally, Locally,the theporphyroclasts porphyroclastsare areantiperthite. antiperthite. The the porphyroclasts recrystallized, is intragranular plagioclase untwinned or weakly twinned. generally weakly twinned. The recrystallized, intragranular plagioclase generally is untwinned porphyroclasts commonly contain small rounded blebs of quartz; the recrystallized porphyroclasts commonly recrystallized grains lack quartz are generally weaklytoto moderately moderatelyaltered altered to to sericite, sericite, and and (or) blebs. The porphyroclasts porphyroclasts are generally weakly (or) epidote/clinozoisite and and calcite. calcite. Quartz commonly of sutured grains, reciystallized as lensoid lensoid aggregates aggregates of grains, which which in part part commonly is recrystallized express a foliation; grains are generally larger than the express foliation; the recrystallized recrystallized grains generally somewhat somewhat larger the associated associated plagioclase. Many recrystallized plagioclase. Many quartz quartz aggregates aggregates contain contain inclusions inclusions of of recrystallized recrystallized plagioclase plagioclase and biotite, of the quartz occurred biotite, indicating indicating that recrystallization recrystallization of occurred after grain grain size-reduction size-reduction of plagioclase and biotite. Biotite is various shades of olive brown, and for the most part occurs occurs in in shears shearsin in association association with recrystallized plagioclase, plagioclase, K-feldspar, K-feldspar,and and minor minor quartz. quartz. This with This biotite biotitecommonly commonly isis obliquely obliquely oriented to the strike of the shears. In relatively unsheared rocks, the biotite retains its oriented strike of the shears. relatively unsheared rocks, its original original with sphene. grain size and orientation; orientation; commonly, commonly, this biotite biotite isis associated associated closely closely with is sparse sparse or absent in most K-feldspar is most of of the the biotite biotite schist. schist. It occurs as interstitial twinned twinned microcline grains, grains, rare rare microcine porphyroclasts, and as recrystallized, very fine grained material microcline porphyroclasts, as recrystallized, very fine grained in shears and core-mantle core-mantle aggregates. aggregates. Accessory Accessory minerals minerals are are zircon, zircon, apatite, apatite, opaque opaqueoxides, oxides, and and allanite (altered). Riotite-amyhil,ole schist Biotite-amohibole This rock type differs mainly from biotite schist schist in containing containing aa few few percent percent of ofamphibole. amphibole. The amphiboles are mainly mainly hornblende or related related actinolitic actinolitic hornblende hornblende or or actinolite, actinolite, but but include include colorless clinoamphiboles, mainly cummingtonite(?). The hornblende is a green or bluish-green colorless clinoamphiboles, mainly cummingtonite(?). green or bluish-green variety, which which locally locally isis variably variably altered altered to actinolitic hornblende hornblende or actinolite. actinolite. It is commonly commonly intergrown with with biotite, biotite, and occurs as both original intergrown original crystals crystals and as as recrystallized recrystallized hornblende hornblende with with K-feldspar and and quartz quartz in shears. The associated biotite, plagioclase, plagioclase, and locally, K-feldspar Theclinoamphibole clinoamphiboleisis relatively widespread widespread as a minor component of of the the rocks. rocks. ItItisistypically typically colorless, acicular or bladed, angle of of tos-15'. 10 0l50. Tentatively, and has a high relief and an extinction extinction angle Tentatively, the the mineral mineral is is identified identified as cummingtonite. cummingtonite. 6 �Amphibole schist schist Amohibole Amphibole schist is interlayered. with the the biotite biotite and as Amphibole schist is interlayered with and biotite-amphibole biotite-amphibole schists, schists, mainly mainly as subordinate discrete compositional layers a meter or more thick. Contacts with the biotite-bearing subordinate discrete compositional layers a meter or more thick. Contacts with the biotite-bearing schists are are sharp. schists sharp. The Theschist schistisisdark darkgray, gray,fine finetotomedium mediumgrained, grained,generally generallyequigranular, equigranular, and and strongly foliated. It ranges from massive and homogeneous to a thinly layered strongly foliated. It ranges from massive and homogeneous to a thinly layered rock. rock. It It is is dominantly of of lower dominantly lower amphibolite amphibolite facies facies metamorphic metamorphic grade. grade. The rocks The rocks are are mainly mainly composed composed of of amphibole amphibole and and plagioclase plagioclase (table (table 4) 4) but but locally locally contain contain as as much as 10 percent quartz and (or) magnetite and sparse biotite. Epidote and chlorite are the the much as 10 percent quartz and (or) magnetite and sparse biotite. Epidote and chlorite are principal alteration minerals. The principal Theamphibole amphibolevaries varieswidely widely from green hornblende hornblende to tobluish-green bluish-green hornblende, or actinolitic hornblende, to pale-green actinolite, reflecting a decrease in metamorphic grade from lower amphibolite to actinolite ca. 0.1-0.3 0.1-0.3 actinolite facies. facies. Plagioclase Plagioclaseisis partly partly recrystallized recrystallized to to ca. mm-diameter grains, which are finer grained than the associated amphibole. Quartz mm-diameter grains, which are finer grained than the associated amphibole. Quartz is an an interstitial mineral. Magnetite Magnetiteisisdisseminated disseminatedthrough throughthe therocks rocksasassmall smallsubhedral subhedralcrystals. crystals. Magnetite-rich schist Magnetite-rich schist 20 modal modal percent percent of magnetite is exposed on Magnetite-bearing schist containing as much as 20 of the broad hill in the SEI/4 the southwest southwest side of SE1/4 of of section section 6, 6, T. T. 31 31 N., N., R. 17 17 E. and on the the lower lower immediately to to the the west west (fig. (fig.8). 8).The The magnetite magnetite units units trend trend northeastward but their and smaller hills immediately their lateral extent and length have not been delineated. The magnetic rocks are interlayered lateral extent length not been delineated. magnetic rocks interlayered with with biotite-amphibole schist and and amphibole amphibole schist. schist. principal lithotypes lithotypes contain contain uncommon uncommonamounts amountsof ofmagnetite: magnetite: (1) Two principal (I) actinolite-magnetite actinolite-magnetite schist and and (2) cummingtonitecummingtonite- or or grunerite(?)-magnetite grunerite(?)-magnetite schist. schist. Although both of these rock types are compositionaUy compositionally layered, the magnetite is disseminated disseminated through them, them, apparently indiscriminantly, indicating indicating that that the the magnetite is a metamorphic mineral formed by the breakdown indiscrirninantly, of iron-rich of iron-rich silicate silicate minerals minerals that that were were redistributed redistributed during during the theductile-brittle ductile-brittle deformation deformation accompanying the the shearing. shearing. Possibly the protolith protolith had had aa higher higher iron iron content content than than most most of of the the other other accompanying Possibly the volcanic rocks rocks in the interlayered schist unit. schist unit. Granite Granite gneiss gneiss Granitic Granitic gneiss ranging in composition from tonalite to granodiorite granodiorite(table (table5; 5;fig. fig. 3) is a major fig. 2). 2). It crops out in the western part of section constituent of the Mountain shear shear zone zone (unit (unit Xgn, Xgn, fig. 5S and the eastern eastern part part of of section section 6, 6,T. T. 31 31 N., N.,R. R.17 17 E. E. (fig. (fig. 8), within an area area of of about about 11km2, km2, and forms spectacular, spectacular, nearly nearly continuous continuous exposures exposureson onseveral severalhills hillsininthis thisarea. area. The gneiss gneiss contains local rafts of amphibolite. from other felsic rocks in the shear amphibolite. It is distinguished distinguished from shear zone zone mainly mainly in in being coarser grained and and lighter lighter in in color. color. The gneiss isis megascopically medium-grained rock characterized megascopically a light-gray, light-gray, generally medium-grained characterized by by narrow, discontinuous, commonly intersecting intersecting dark-gray dark-gray mafic-rich mafic-rich zones zones and by coarse, lensoid narrow, discontinuous, commonly lensoid zones are seen to quartz aggregates. aggregates. In thin thin section, section, the dark-gray dark-gray zones to be be ductile ductile shear shear zones zones (S-C (S-C structures; Lister and and Snoke, Snoke, 1984) 1984) composed composed mainly mainly of fine-grained (commonly (commonly less than 0.2 0.2 mm in diameter) biotite, biotite, rare rarehornblende, hornblende, plagioclase, plagioclase, and and microcline microcline that that have have formed formedby bygrain-size grain-size protomylonite, but but in part part they are reduction of the original minerals. Overall, Overall, the rocks rocks are are mainly protomylonite, orthomylonite, orthomylonite, as defined by by Wise and others others (1984). (1984). 7 �Plagioclase (oligoclase) is It occurs is typically typically bimodal. bimodal. It occurs as as (1) (1) sub-rectangular sub-rectangular to to lath-like lath-like porphyroclasts 1-5 with somewhat somewhat finer finer grained, grained, anhedral, anhedral, nearly nearly equigranular equigranular porphyroclasts 1-5mm mm across associated with (—0.5-1mm mmdiameter) diameter) and (2) as plagioclase (-0.5-1 as fine-grained, fine-grained, recrystallized, recrystallized, intragranular intragranularplagioclase plagiodase less than than 0.2 0.2 mm mm in indiameter. diameter. Both the commonly less the porphyroclasts porphyrodasts and the the associated associated intragranular intragranular plagioclase are periclinelaws, laws, are twinned twinned according according to to the thecombined combinedCarlsbad-albite Carlsbad-albitelaws, laws,and andlocally, locally,pericline and at places have a small amount of patch antiperthite; in a few sections, quartz blebs at have small of antiperthite; in a few sections, quartz blebs are arevisible. visible. are present in Rarely, K-feldspar blebs are in the the plagioclase. The Therecrystallized recrystallizedplagioclase plagioclaseoccurs occurs as astype type IP IP mantle aggregates aggregates (Hanmer, (Hanmer,1982), 1982),intragranular intragranularplagioclase plagioclasethat that at atplaces places completely completely obliterates obliterates the original grains, and and as fine-grained fme-grained material material in in narrow narrow shear shear zones zones that that transects all the original It is minerals except except biotite. The recrystallized plagioclase generally is untwinned. The recrystallized plagioclase generally is untwinned. It is typically typically less less altered by by weathering than the the original original grains. grains. Quartz is recrystallized of coalesced, coalesced, sutured sutured and and strained grains that are recrystallized into aggregates aggregates of are Quartz distinctly coarser grained than the associated recrystallized plagioclase, distinctly coarser grained the associated recrystallized plagioclase, microcline, microcline, and biotite. biotite. Typically,the the aggregates aggregatesare are lensoid, lensoid,as as much much as as 44 or 55 mm mm in in length, length, and andconsist consist of of several several Typically, individualgrains grains0.3 0.3toto 11mm mminindiameter. diameter. Some quartz is crackled crackled by by late late brittle brittle fractures. fractures. The individual The aggregates locally locally contain contain considerable considerable plagioclase plagioclaseand and are are transected by late aggregates late shears shearsfilled filled with with recrystallized biotite, biotite, plagioclase, plagioclase,and andmicrocline. microcline. The The quartz quartz lenses lenses impart impart a foliation to the rock, recrystallized which is conspicuous conspicuous on on weathered weathered surfaces surfaces because because the the quartz stands out in relief. which sparse. ItIt occurs Microcline generally is sparse. occursmainly mainly as as interstitial interstitialgrains grains between between plagioclase plagioclase and and quartz and as recrystallized fine-grained (—0.2-0.3 mm in diameter) material intergrown with and as recrystallized fine-grained (-0.2-0.3 mm in material intergrown with plagioclase and biotite in in narrow narrow shears. shears. Biotite is is grayish olive to greenish greenish brown brown and and occurs occursentirely entirelyas asclots dotsof ofvery very fine fine(0.1-0.2 (0.1-0.2 mm) mm) Biotite grain size that are nearly confined to narrow shears--the Cand S-surfaces of Berthé and others are nearly confined to narrow shears-the C- and S-surfaces Berth6 and others (1979) and and Lister and intergrown with withrecrystallized recrystallized (1979) and Snoke Snoke (1984). (1984). The biotite biotite generally generally isisintergrown plagioclase and microcline, and commonly is oriented obliquely to the the S-surfaces S-surfaces (foliation), (foliation), thus thus indicating a unidirectional movement movement along along the theS-surfaces S-surfaces(Simpson, (Simpson, 1986). 1986). With Withfew fewexceptions, exceptions, the biotite is is closely closely associated with epidote, sphene, and magnetite, magnetite, suggesting suggesting that itit probably probably isis secondary after after hornblende. hornblende. Sparse secondary Sparsegarnet garnet isisassociated associated with with biotite biotite in in one one section. section. Amphibole is is uncommon uncommonin in the the granite granite gneiss. gneiss. Where present, it is a dark-green Amphibole dark-green or darkdarkIn two sections, it is in late shears bluish-green hornblende that is intergrown with biotite. is intergrown sections, it shears and and bluish-green hornblende by prograde metamorphism. metamorphism. Possible Possible pseudomorphs pseudomorphs of an appears to have have formed from from biotite biotite by original hornblende consist of epidote, biotite, biotite, sphene, sphene, magnetite, magnetite, quartz quartzand, and,locally, locally, hornblende. hornblende. minerals include zircon, zircon, apatite, apatite, and allanite (altered). Accessory minerals The chemical composition of 3 samples of granite gneiss is given in table 1. 1. is the the granodiorite granodiorite (fig. (fig.2). 2). The granodiorite borders the The protolith of the granitic gneiss is southeast margin of the shear shear zone, zone, strikes strikes into into it, it, and was incorporated into into the the shear shearzone, zone, where where it was deformed and metamorphosed under under conditions conditions of of the the lower lower amphibolite amphibolite facies facies during the the ductile shearing. shearing. The Thedeformation deformationwas wasaccompanied accompanied by by pronounced pronounced mineralogic mineralogic changes changes in the the amounts amounts of modal quartz and amphibole. amphibole. Comparison Comparison of of modal modal analyses analyses of of the the granitic granitic gneiss gneiss 5) and and the granodiorite (table 2) indicate indicate that the the gneiss gneiss contains about 15 15 percent more more (table 5) quartz than the the protolith and and has has much much less amphibole. The The apparent apparent decrease decrease in in K-feldspar K-feldspar in in the gneiss, as as indicated indicated by by modal data, probably results from original variations variations in in the amount of of KKgneiss, feldspar in the granodiorite, granodiorite, and and thus thus almost almost certainly certainly isis aa sampling sampling problem. 8 �The The increase increase in in modal modal quartz quartz in in the thegneiss gneiss (fig. (fig. 3) over over the the protolith protolith appears appears to to be be related related to to metamorphic metamorphicreactions reactionsaccompanying accompanyingthe the deformation. deformation. Specifically, Specifically,the the increase increasein in quartz quartzfrom from an an average average of of about about 21 21 percent percent in in the thegranodiorite granodiorite to to an anaverage average of of more more than than 36 36percent percent in inthe the gneiss is attributed to the separation of silica from plagioclase during recrystallization. Relatively gneiss is attributed to the separation of silica from plagioclase during recrystallization. Relatively undeformed undeformed plagioclase plagioclase in in the the granodiorite granodiorite appears appearshomogeneous homogeneous in in thin thin section, section, whereas whereas in in the the partly partly deformed deformedrocks, rocks, plagioclase plagiodase contains contains abundant abundant tiny tiny inclusions inclusions of of quartz. quartz. Within Within the theshear shear zone zoneitself, itself, the theplagioclase plagioclase appears appears to to lack lack tiny tiny quartz quartz blebs, blebs, but instead instead contains contains larger, larger, generally generally rounded inclusions of quartz or coalesced groups of inclusions sufficiently large to be rounded inclusions of quartz or coalesced groups of inclusions sufficiently large be counted counted modally. Quantitative estimates of the amount of quartz clearly associated with modally. Quantitative estimates the amount of quartz clearly associated withparticular particular plagioclase plagioclase grains have not been been determined, determined, but but we we suggest suggest that that the the aggregate aggregate amount amountofofsilica silica derived of the plagioclase plagioclase isis on on the the order order of 10 percent, to account recrystallization of derived from from recrystaffization account for the increase increase of of modal modalquartz quartzininthe thegranite granitegneiss. gneiss.Chemical Chemicalanalyses analyses (table (table 1) 1)also alsoshow showhigher higher 5i02 SiO, values in the shear zone. The processes involved in the release of silica from plagioclase during values in the shear zone. The processes involved in the release of silica from plagioclase during progressive progressive deformation deformation are are presumed presumed totobe, be.first, first,exsolution exsolutionof ofsilica silica as as aasubsolidus subsolidus reaction reaction during duringinitial initialrecrystallization recrystallizationof ofplagioclase plagioclaseand, and, second, second, the the migration migration and andcoalescence coalescence of of individual individual quartz quartzblebs blebsinto intolarger largergrains grainsduring duringductile ductile deformation deformation of of the therock. rock. Inasmuch Inasmuchasasthe thequartz auartzwas was relatively more mobile than the associated plagioclase (and microcline) in the stress field, relatively more mobilethan the associated plagioclase (and microcline) the stress field, itit differentially differentially flowed flowed into into lensoid lensoid masses masses oriented orientedperpendicular perpendiculartotothe themajor majoraxis axisofofstress. stress. Baldwin Baldwin Conglomerate Conglomerate The Baldwin Conglomerate Conglomerate (unit (unit Xb, Xb,fig. fig. 2) 2) isis aa lens-shaped lens-shaped metaconglomerate metaconglomerate unit unit about about TheBaldwin 2.3 2.3 km km long long and andaamaximum maximumof of150 150m m wide wide that thatisisexposed exposedlocally locally along the northwest northwest margin margin of of the theshear shearzone. zone. ItItunconformably unconformablyoverlies overlies metavolcanic metavolcanic rocks and granite granite gneiss gneiss within within the the shear shear zone HagerRhyolite Rhyolite(Lahr, (Lahr,1972). 1972). zoneand andisistruncated truncated and andintruded intrudedon onthe thenorth northby bythe theHager The Themetaconglomerate metaconglomerate has has relict relict sedimentary sedimentary layering layering and possible possible scour scour features features and and contains gneiss, and and quartzite. quartzite. All containssubrounded subroundedtotosubangular All but but the the subangularclasts clastsof of metavolcanic metavolcanic rocks, gneiss, quartzite quartziteare areofoflocal localderivation; derivation;the thequartzite quartziteclasts clastsprobably probablywere werederived derived from from the the more moredistal distal quartzite quartzite bodies bodies exposed exposed at at McCaslin McCaslin Mountain Mountain and and Thunder Thunder Mountain, Mountain, 20 20 km km and and1010 km, km, respectively, respectively,north northofofthe theMountain Mountainshear shearzone zone(Sims, (Sims,1990; 1990;Sims Simsand andPeterman, Peterman, 1988). 1988). Clasts Clastsof of the theHines HinesQuartz QuartzDiorite Diorite(unit (unitXh, Xh,fig. fig.2)2)have havenot notbeen beenreported reportedininthe themetaconglomerate metaconglomerate (Lahr, (Lahr, 1972). medium-grained 1972). The Thematrix matrixisisa gray, a gray,finefine-toto medium-grainedrock rockcontaining containingquartz, quartz,feldspar, feldspar,biotite, biotite, muscovite, and hornblende. A weak foliation exists that is approximately parallel to the bedding. muscovite, and hornblende. A weak foliation exists that is approximately parallel to the bedding. Hines HinesQuartz QuartzDiorite Diorite The fig. TheHines HinesQuartz QuartzDiorite Diorite(unit (unitXh, Xh, fig.2)2)occurs occursmainly mainlyasasa alenticular lenticularintrusive intrusivebody bodyabout about 33km long and 0.4-0.5 km wide in the southwestern part of the Mountain shear km long and 0.4-0.5 km wide in the southwestern part of the Mountain shearzone. zone. Except Exceptfor for exposures exposureson onhills hillsininthe theSWI/4 31N., N., R.R.1616E.E.(see (seeSims, Sims,1989), 1989),outcrops outcropsare aresmall small SW1/4section section12, 12,T.T.31 and intrudes adjacent anddispersed. dispersed.The Thequartz quartzdiorite diorite intrudes adjacentmetavolcanic metavolcanicrocks rocksand andcontains containslocal, local,small small inclusions of them. It is intruded to the southwest by the Belongia Granite inclusions of them. It is intruded to the southwest by the Belongia Granite(unit (unitYwb, Ywb,fig. fig.2) 2)of ofthe the Wolf 1972).which whichisisnot notdiscussed discussedininthis thisreport. report. WolfRiver Riverbatholith batholith(Lahr, (Lahr,1972), The virtuallyundeformed, undeformed,indicating indicatingthat thatititwas wasintruded intrudedinto intoand andalong alongthe the Thequartz quartzdiorite dioriteisisvirtually shear meter-thickdike dikeininthe theSE1/4NWI/4 SE1/4NW1/4section section7,7,T.T.31 31N., N.,R.R. shearzone zoneas asthe theshearing shearingwaned. waned. AAmeter-thick 17 17E. E.(fig. (fig. 8)is 8) isintruded intrudedalong along the the 2S,foliation. foliation. ItIthas hasa aU-Pb U-Pbzircon zirconage ageofof1,812.7±3.6 1,812.723.6Ma Ma(Sims (Sims and andothers, others,1990). 1990). 9 �The The rock rock isisdark darkgray, gray,locally locally slightly slightly mottled, mottled, massive, massive, and and medium medium grained. grained. Primary Primary subophitic textures are by plagioclase plagioclase laths, laths, but but the theprimary primarymafic maficmineral--apparently mineral-apparently subophitic textures are retained retained by clinopyroxene--is so highly highlyaltered altered to to aa pale-green pale-green amphibole amphibole (actinolitic (actinolitic hornblende), hornblende), actinolite, actinolite, clinopyroxene--is so biotite, and opaque oxides and locally chlorite that its primary texture is largely obliterated. biotite, and opaque oxides and locally chlorite that its primary texture is largely obliterated. Although little little deformed, Although deformed, the the quartz quartzdiorite dioriteisiscut cutby bylocal localmylonitic mylonltic shears. shears. Plagioclase(Ann4), (An), thethe major mineral (table Plagioclase major mineral (table3),3),isisweakly weaklyaltered, altered, has has aa moderate moderate concentric concentric zoning, is tabular tabular to lath-shaped, and is twinned according to to the the combined Carlsbad-albite and the pericline laws. mm long. long. Quartz laws. Crystals Crystalsare aretypically typically2-4 2-4 mm Quartz isis interstitial, interstitial, somewhat somewhat strained, and and highly variable variable modally (table 3). 3). The as an an alteration alteration mineral The biotite biotite associated associated with with clinopyroxene clinopyroxene as mineral is dark dark reddish reddish brown. brown. Elsewhere in the rock, the biotite is dark yellowish brown, and is always associated with opaque Elsewhere rock, the biotite is dark yellowish brown, and is always oxides. Cummingtonite Cummingtoniteisis aa local local alteration alteration product product of of actinolitic actinolitichornblende, hornblende, occurring occurring as as colorless colorless needles Apatite, zircon, zircon, and and allanite needles extending extending outward outward from from the theactinolitic actinolitichornblende. hornblende. Apatite, allanite are common accessory accessory minerals. REGIONAL STRUCTURE REGIONAL STRUCTURE The rocks rocks southeast southeast of the the shear shear zone zone have have aasingle singlepenetrative penetrative structure structure (cleavage (cleavage or or schistosity, S) that is interpreted as the regional foliation. It is generally subparallel to layering and schistosity, S,) that is interpreted as the regional foliation. It is generally subparallel to layering pillow structures (Se) but locally is is crosscutting. crosscutting. The structure (So) but structure is is expressed expressed by by sub-planar sub-planar fractures, fractures, biotite sheets, sheets, and flattened clasts. s1 occurs both in the aligned biotite S, occurs the metamorphic metamorphic and and granitoid granitoid rocks. rocks. Flattened mafic volcanicinclusions inclusionsininthe thegranodiorite granodioriteare areoriented orientedparallel paralleltotoS,.S1.S,1 is Flattened mafic volcanic is oriented northward and dips steeply; within within the the map area, the strike ranges from about N. N. 150 15 W. W. to N. N. 25 ' E. (fig. 5). SHEAR ZONE The Mountain Mountain shear zone zone sharply sharply truncates truncates and and isis distinctly distinctly younger younger than the the regional regional foliation () and foliation (S,) and resulted resulted from a ductile ductile shear shear deformation deformation (D2) (D,) that was superimposed superimposed on the regional D2 structures structures are modified regional foliation foliation (fig. (fig. 2; table table 6). 6). D, modified locally locally by two two younger younger ductile ductile deformation which do do not not appreciably appreciabty affect the distribution of the DJ, which the rocks, rocks, and and deformation events events (D3 (D3 and D4), still younger younger kink kink bands formed by brittle deformation (Sims and others, 1990; Fk, table 6). (Sims others, 1990; F,,, Mesoscopic Structure Structure Mesoscopic 55, E. E. and and isis ito 1 to2.5 2.5km kmwide. wide.S2 S, foliation foliationwithin within the the shear shear The shear zone strikes about N. 55 average strike strike of of N. N.55" 55' E. dip. Northwest-oriented E. and a moderately moderately steep southeast dip. Northwest-oriented zone has an average of the shear S-surfaces within within the the shear zone are local local relicts of S,,/S,. The southeastern margin margin of zone--the abrupt. Jt zone-the transition transition between between mylonitic mylonitic and and non-mylonitic non-mylonitic rocks--is abrupt. It is is composed of narrow zones of mylonitic mylonitic rocks rocks that that clearly clearlytruncate truncateS, S structures (as can be seen at stop 2). The Thetransition transition zone is 100 wide. The 100 m or less wide. The boundary boundary is is aa zone zone of of deformation deformation and and differential differential displacement displacement of the without apparent separation. the walls walls accomplished by ductile flow, flow, without separation. The shear zone is truncated on on the the north north and andnortheast northeastends endsby by the theyounger youngerHagen Hagen Rhyolite, Rhyolite, and on 1.47 Ga Wolf Wolf River River batholith, batholith, on the the southwest southwest end end by by granitic granitic rocks rocks (unit (unit Ywb, Ywb, fig. fig. 2) of the 1.47 which had had little or or no tectonic effect on the rocks in the shear zone. Accordingly, which Accordingly, neither the the full full width nor the termination width termination of of the the shear shearzone zoneisisknown. known. 10 �The The dominant dominant structures structures in the the shear shear zone zone are arerelated related totoD2 D, and andconsist consist mainly mainly of of an an SSsurface (S2) (S,) resulting from tectonic tectonic layering and and aa mylonitic mylonitic foliation; foliation; aa stretching stretchinglineation lineation(L2), (L,), expressed by elongate elongate clasts, clasts, rodding, rodding,and andbiotite biotitestreaks, streaks;and andrare rare folds folds of of S, 2 surfaces expressed by surfaces (L2). (L,).The The resulting structure is an L-S tectonite (Ramsay, 1980). The younger ductile structures (D3, D4) that structure is an L-S tectonite (Ramsay, 1980). The younger ductile structures (D3,D,) that are modi' the are superposed superposed on on the the older older structures structures (table (table 6) 6) do do not not appreciably appreciably modify thegeometry geometry of of the the rocks. rocks. In S consists In the the granitoid granitoidrocks, rocks, which which were were relatively relatively isotropic initially, initially, S, consists dominantly of thin anastomosing, commonly commonly sigmoidal sigmoidalbiotite-rich biotite-richzones zonesand and oriented, oriented, flattened flattened aggregates of quartz (S-C (S-C structure); structure); aa related related lineation lineation isis given given by by streaked streaked biotite biotite aggregates aggregates and and quartz quartz rods, rods, composed of of fine-grained fine-grained recrystallized recrystallized aggregates of quartz. In Instrongly stronglyanisotropic anisotropicrocks, rocks,such suchas as bedded tuff, locallyexpressed expressed by by brecciated brecciated and and boudinaged, boudinaged, hard hard (siliceous) (siliceous) layers layers that that have have tuff, 2S,isislocally been has been been tectonically deformed deformed into been tightly tightlyfolded foldedso sothat thatSO/S1 S,,/Sl has into parallelism parallelismwith withS2. S? Elsewhere, Elsewhere, segments of S0/S1 surfaces have not been completely transposed. In layered felsic-mafic In layered felsic-maficrocks rocks(unit (unit segments of So/Slsurfaces have not been Xwa, fig. 2) 2) in the Xwa, fig. the northeastern northeastern part part of ofthe theshear shearzone, zone,the thefelsic felsiclayers layerscommonly commonly have have aa conspicuous 2 foliation biotite that that obliterates S, conspicuous S, foliation expressed expressed by by recrystallized recrystallized biotite S,, whereas whereas the themafic mafic layers 2 foliation layers have have only only a weak S, foliation generally generally expressed expressed by aligned hornblende or chlorite. In Inthese these rocks, rocks, SSocommonly commonlyisis not not appreciably appreciably reoriented reoriented or ortransposed. transposed.The Thefelsic-mafic felsic-maficlayer layercontacts contactsmay may show a slightly zig-zag, sawtooth sawtooth (chevron (chevron fold) fold) pattern pattern similar slightly zigzag, similar to to that thatformed formedby byaaslip slipcleavage. cleavage. F2 are not common, but have F, folds are have been been observed observed at ataafew few localities, localities, especially especially in interlayered interlayered felsic-malic volcanic rocks. The folds generally plunge gently to moderately northeast or felsic-mafic rocks. The folds northeast orsouthwest. southwest. Microscopic Microscopic Structure Structure The The mylonitic mylonitic rocks in the the shear shear zone zoneare arecharacterized characterizedby byrecrystallization recrystallization as asindicated indicated by by conspicuous grain-size reduction. Biotite and quartz are entirely, or nearly entirely, recrystallized, conspicuous reduction. Biotite and quartz are entirely, or nearly entirely, recrystallized, whereas and microcline, whichwere were harder harder than than the whereas plagioclase plagioclase and microcline, which the matrix, matrix, were were only onlypartly partly recrystallized. (1984), the the rocks rocks are aremainly mainly recrystallized. According According to the the classification classification of Wise and others others (1984), protomylonite protomylonite or ororthomylonite. orthomylonite. Biotite Biotite occurs occurs in in irregular, irregular,anastomosing anastomosing trains, trains,commonly commonly associated with recrystallized plagioclase and, locally, microcline. Both the biotite associated with and, locally, microcline. Both the biotite and feldspar are are very mm diameter). Quartz very fine fine grained grained (—0.2 (-0.2 mm Quartzisisrecrystallized recrystallizedinto intooriented orientedlenses lensesororrods, rods,which which are are coarse-grained coarse-grained aggregates aggregates of of individual individual sutured grains <0.5 <0.5 mm mm in in diameter; diameter; commonly, commonly, itit contains inclusions of plagioclase and biotite and, locally, sphene and amphibole. Plagioclase contains inclusions plagioclase biotite and, locally, sphene and amphibole. Plagioclase commonly mm in in diameter diameter and and commonlyisis only only partly recrystallized, recrystallized, itit occurs occurs as as porphyroclasts porphyroclasts as asmuch much as as55 mm commonly has mantles 1982)ofoffine-grained fine-grained(—0.1-0.2 (-0.1-0.2 mm) mm) IPstructures; structures;Hanmer, Hanmer,1982) commonly has mantles (type (type IP plagioclase. plagioclase. Also, Also,fine-grained fine-grainedrecrystallized recrystallizedplagioclase plagioclaseoccurs occurs as as veinlets (shears) (shears) that thattraverse traversethe the rocks. rocks. Kinematic KinematicAnalysis Analysis The The sense sense of of movement movement during during the theF2 F, shear shear deformation deformation has has been been determined determinedfrom fromS-C S-C fabrics fabrics (Berthe (Berth6and andothers, others,1979; 1979;Lister Listerand andSnoke, Snoke,1984) 1984)ininthe themylonitic myloniticgranite granitegneiss gneiss(unit (unitXgn, Xgn, fig. fig. 2), orientation orientation of of stretch stretchfabrics fabrics (long (long axes axes of of strain strain ellipsoids), ellipsoids), and and other otherfield field data datasuch suchasas described described by by Simpson Simpson (1986). (1986). S-C S-Cmylonite mylonitefabrics fabrics(fig. (fig. 6) 6) in in granite granitegneiss gneissfrom from several severallocalities localities show show that the the southeast southeastblock block of of the the Mountain Mountain shear shear zone zoneisisupthrown upthrown relative relative to to the thenorthwest northwest block. block. Stretch Stretchfabrics, fabrics,as asindicated indicated by by the theorientation orientation of ofthe thelong long(X) (X)axes axesof ofstrain strainellipses, ellipses,also also suggest (La,)plunge plungesteeply steeplysouth south suggest the the same same sense sense of of movement. movement. Stereoplots Stereoplotsshow showthat thatstretch stretchaxes axes(Lb) to to east. east.This Thissteeply steeplyplunging plungingstretch stretchfabric fabricisispossibly possibly caused caused by by aa simple simple shear shearcouple couplehaving having aa 11 �dip than the dip shallower dip dip of of the the stretch stretchaxis, axis,as as shown shown on on figure figure 7. 7. Stereoplots at some some localities localities indicate stretch fabric, fabric, whereas whereas aa stereoplot stereoplot at one locality indicates indicates a steep indicate a steep steep easterly easterly Lzb La, stretch Thisdifference difference in in orientation orientationofofstretch stretchfabrics fabricssuggests suggestsaa varying varying sense sense southerly stretch fabric. fabric. This movement of of the shear couple along the length of of the shear zone. of movement Field data suggest suggest that the the sense sense of of movement movement in in the the horizontal horizontal plane plane was was generally dextral (right lateral). At Atthe themap mapscale scale(fig. (fig.2), 2), Si S, foliation foliation appears appearsto to have have been been rotated rotatedclockwise clockwisetoward toward parallelism with granodiorite with the shear zone, which is consistent consistent with with dextral dextral movement. movement. Also, the granodiorite body (unit Xg, dextrally in in the the shear zone as granitic displaced dextrally granitic gneiss (unit Xgn). Xgn). In body (unit Xg, fig. fig. 2) is displaced is supported supported also alsoby by measured measuredaxes axes addition, S-C fabrics suggest dextral movement. Such Such movement movement is of extension extension (L2b) as well as by computed ellipsoid axes; these axes plunge toward the east-southeast (La,) as well as by computed ellipsoid axes; these axes plunge toward the east-southeast that the upthrust southeast block block had had a dextral component component of of quadrant of stereoplots, indicating indicating that movement in the horizontal plane, as as shown shown on on figure figure77 (Sims (Simsand andothers, others, 1990). 1990). On the other movement in horizontal plane, hand, the different horizontal horizontal shear sense from place the variation in in orientation orientationof ofL2b hnsuggests aa different place to to place along the shear zone. GEOBAROMETRY GEOBAROMETRY AND GEOTI-IERMOMETRY GEOTHERMOMETRY The regional regional D1 Dl deformation deformation textures textures and and associated associated M1 M, metamorphic metamorphic minerals minerals were were overprinted in the shear zone by shear-induced D2 fabrics and M2 metamorphic mineral assemblages overprinted in the shear zone by shear-induced D2 metamorphic mineral Hornblendegeobarometry geobarometryof of granitoid granitoid rocks rocks and and metabasalt metabasalt indicates indicates (Day and others, in press). Hornblende M, pressure pressure of of about about 4.5±1 4.5  1Kbar Kbarwas waselevated elevatedduring duringM2 M, to to approximately approximately 6.0±1 6.01 1 that the the regional regional M1 Kbar both within and adjacent to the shear shear zone. Garnet-biotite Garnet-biotitegeothermometry geothermometryindicates indicatesthat thatM1 MI ranged from 5850 585 * to 615 °C, "C,but but that that M2 M2 equilibrium temperatures may may have increased to as as much much as 654 654 C. Inasmuch Inasmuch as as garnet garnet is is rare rare both both outside outside and and inside inside the shear zone, the estimated peak Two-feldspar geothermometry indicates that inside inside M2 thermal thermal conditions conditions are are only approximate. approximate. Two-feldspar the shear shear zone zonethe thefeldspars feldsparsunderwent underwentcontinuous continuoussubsolidus subsolidusreequilibration reequilibration from from peak peakNI2 M, conditions (574 (574 'C C atat6.0 temperatures (280 (280 * 0C at 6.0 6.0Kbar). Kbar). These data Cat conditions 6.0Kbar) Kbar)down down to to very very low low temperatures indicate that both both pressure pressureand andtemperature temperatureincreased increasedduring duringshear-induced shear-inducedM2 M2recrystallization recrystallization within the Mountain shear within shear zone. zone. CONCLUSIONS within the the Mountain shear zone are Rocks within are L-S L-S tectonites tectonites that that fit fit with with the the classic classic definition of aa shear The shear is shearzone zone(Ramsay, (Ramsay,1980). 1980). The is aa local local (discrete) (discrete) linear linear zone zone of of high high ductile ductile deformation. Neither Neither the thewidth width nor nor the thelength length are areknown, known, but we presume that the shear zone had parallel sides prior to to emplacement emplacement of of the theWolf Wolf River River batholith. batholith. In this area, area, the the batholith batholith was was ernplaced passively. passively. emplaced Ramsay classifiedshear shearzones zonesaccording accordingtototheir theirdisplacement displacementfields. fields. The The Mountain Rarnsay (1980) classified shear zone appears to fit best Ramsay's (1980) type (iii) classification; that is, it is a heterogeneous heterogeneous appears to fit best Ramsay's (1980) type (iii) classification; heterogeneous volume volume change. change. Ramsay and Graham (1970) noted simple shear with accompanying heterogeneous that most most deformation from from natural natural orogenic orogenic processes lead to states states of heterogeneous strain, and Ramsay (1980, (1980,p.p. 89) 89) noted noted that "the of practically all shear shear zones zones is is that of Ramsay "the basic basic component component of practically all of heterogeneous simple shear shear .. . . made made up of aa number number of of elements elementsshowing showing homogeneous homogeneous simple simple shear.' The shear." TheMountain Mountainshear shearzone zonehas hasthe thefollowing following features that fit these criteria. . . 12 �(1) Deformation Deformation within within the the shear shearzone zonewas was not not uniform; uniform; domains domainsof ofrelatively relatively low low strain, pre-F2 features features are high strain, strain, where where the country rocks have where pre-F, are preserved, as as well as domains of high been mylonitized, are present. been mylonitized, are present. (2) The nature, nature, magnitude, magnitude, and and orientation orientation of of displacement displacement varies both across and along the shear by the the variation in (a) the shear zone, zone, as as suggested suggested by variation in (a) shape shape of of the the strain strain ellipsoids ellipsoids at at different different localities, (b) percentage percentage of flattening and stretching among the outcrops where strain analyses of flattening and stretching among the outcrops where strain analyseswere were carried out (Sims and others, 1990), pattern along the shear zone; the orientation 1990), and (c) movement pattern orientation out (Sims of the maximum principal shortening direction apparently rotated from nearly nearly west in the northern northern part of the exposed shear zone to north-northwest at at its its southwestern southwestern exposed segment, as indicated by the orientation (La,). orientationofofdeformed deformedclasts clasts(L2b). (3) L-S tectonites of the shear shear zone zone appear appear to tohave haveformed formedprimarily primarily by by plane plane strain, strain, as as indicated by the Flinn Flinn K K values values (Flinn, (Flinn, 1962) 1962) at attwo two localities, localities, which are are very very close close to to 1,1,the thevalue value for plane strain strain (Sims (Sims and others, others, 1990). 1990). Rocks Rocksatatanother anotherlocality, locality,however, however, have have aa K K value value of of 2.4, 2.4, indicating that they lie in the field of apparent constriction. the field of apparent constriction. (4) The The magnitude of both flattening and stretching increases from the southeast margin of the shear zone toward toward the interior. interior. (5) Finally, Roy (1977) (1977) has pointed out that that mylonites mylonites within shear shear zones zones develop develop in in stages stages and that that this this development developmentisisaccompanied accompanied by by chemical chemical mobility. Chemical Chemical mobility mobility is suggested in the Mountain shear shear zone zone by by an apparent apparent substantial substantialgain gain in modal quartz quartz and and some some increase increase in in Si02 SiO, (table 1) of the granodiorite gneiss (unit Xgn) within it, as compared to undeformed granodiorite 1) the granodiorite gneiss within compared undeformed (unit Xg), but this this apparent apparent gain gain has hasnot notbeen beenconfirmed confirmedby by quantitative quantitativechemical chemical studies. studies. REGIONAL SIGNIFICANCE SIGNIFICANCE Prior to the the study study of of the the Mountain Mountain shear shearzone zone(Sims (Sims and and others, others, 1990), 1990), major major northeastnortheasttrending shears shears in in the the Wisconsin Wisconsin magmatic terranes terranes were were known known to have formed subsequent subsequent to to the the main regional regional deformation in the Penokean Penokean orogen orogen (Sims (Sims and Peterman, Peterman, 1983, 1983, p. 8), but data data on on the precise timing were lacking. lacking. The The fortunate fortunate existence existence of of a datable datable intrusive intrusive rock (Hines (Hines Quartz Quartz Diorite, 1,812.7±3.6 1.812.723.6 Ma) within within the the Mountain Mountain shear shearzone, zone,which whichwas was emplaced emplaced during duringthe thewaning waning stages of the ductile deformation deformation and and thus thusestablishes establishes aa firm firm younger limit for the the shearing, provides a benchmark basis. Thus, it can be presumed now that the benchmark for the time of shearing on a regional basis. steep Jump River and Athens shear zones (fig. 1) as (Sims 5O0-60' E. trend (Sims River and Athens shear zones (fig. 1) as well well as others of of N. N. 50°-60 Ma. A and others, 1989) 1989) have comparable ages of about 1,815 1,815 Ma. A deformed deformed intrusive intrusive rock rock within within the the Athens shear zone, age of Athens zone, which which has aa crystallization crystallization age of 1,832±9 1,83229 Ma (Sims (Sims and others, others, 1989), 1989), is is consistent with with this this interpretation interpretation that that the shearing 1,840Ma. Ma. The consistent shearing post-dates post-dates 1,840 The recognition recognition of aa 35m.y. my. after after the themain maincontinent-arc continent-arccollisional collisionalevent event(—1,860 (- 1,860 major ductile ductile deformation deformationevent event25 25toto35 Ma; Sims and others, 1985) along the Niagara fault zone indicates the complexity and tong duration 1985) along the fault zone indicates the complexity and long duration of tectonic events in the the Penokean Penokean orogen orogen and and the theneed needtotoidentify identifyspecific specificevents, events, perhaps perhaps by by names to them, such as has been done in the Wopmay orogen in the Northwest Territories Territories assigning names Bowring, 1984). 1984). ItIt seems seemsimprobable improbable that thatthe the—1,815 (Hoffman and and Bowring, 1,815 Ma ductile deformation deformation could could be aa late late tectonic tectonic episode episode related related to tothe thecollision collision that thatsutured suturedthe theWisconsin Wisconsin magmatic magmatic (arc) (arc) terranes to the the continental continental margin margin at at about about 1,860 1,860 Ma. Ma. Instead, Instead,we wesuggest suggestthat thatthe the—1,815 -1,815 Ma Ma ductile deformation resulted from a continent-continent ductile deformation probably probably resulted continent-continent or continent-arc continent-arc collision collision far removed from northern Wisconsin, probably to to the the south south or or southeast. southeast. AA possible removed Wisconsin, probably possible candidate candidate was was accretion of the Central Central Plains Plains orogen (Sims and Peterman, 1986) 1986) to the North American continent. - 13 �ACKNOWLEDGMENTS ACKNOWLEDGMENTS K.J. G.L. LaBerge, LaBerge, and and Bruce Bruce Brasaede Brasaemle assisted assisted in the geologic mapping mapping of of the K.J. Schulz, Schuk, G.L. Mountain area 1985-86. areainin1985-86. REFERENCES REFERENCES CITED CITED Attoh, Kodjopo, Kodjopo, and and Kiasner, Klasner, J.S., J.S., 1989, 1989, Tectonic Tectonic implications implications of metamorphism metamorphism and andgravity gravityfield field in the 11-933. the Penokean Penokean orogen orogenofofnorthern northernMichigan: Michigan:Tectonics, Tectonics,v.v.8,8,p.p.9 911-933. 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Geological Survey Survey Bulletin Bulletin 1904-H, deformation: Geological Flinn, Flinn, D., 1962, 1962, On folding during three-dimensional three-dimensionaldeformation: GeologicalSociety Societyof of London London Quarterly Quarterly Journal, Journal,v.v.118, 118,p.p.385-433. 385-433. Hanmer, Hanmer, Simon, Simon, 1982, 1982, Microstructure Microstructure and and geochemistry geochemistry of of plagioclase plagioclase and microcline microcline in in naturally naturally deformed granite: Journal of Structural Geology, v. 4, p. 197-2 13. deformed granite: Journal of Structural Geology, v. 4, p. 197-213. Hoffman, P.F., Short-lived 1.9 1.9 Ga Ga continental continental margin and its P.F., and and Bowring, Bowring, S.A., S.A., 1984, 1984, Short-lived its destruction, destruction, Wopmay orogen, northeast Canada: 12,p.p.68-72. 68-72. Canada: Geology, Geology,v.v.12, Holm, D.K., D.K., Hoist, Hoist, T.B., T.B., and and Ellis, Ellis,M., M.,1988, 1988,Oblique Obliquesubduction, subduction,footwall footwalldeformation, deformation, and and Hoim, imbrication--a imbrication-a model for the Penokean orogeny in east-central Minnesota: Geological GeologicalSociety Society of America 100,p.p.1811-1818. 1811-1818. AmericaBulletin, Bulletin,v.v.100, Lahr, M.M., of a greenstone M.M., 1972, 1972, Precambrian geology geology of greenstone belt belt in in Oconto OcontoCounty, County,Wisconsin Wisconsin and and geochemistry of the the Waupee Waupee metavolcanics: metavolcanics: Madison, Madison,University UniversityofofWisconsin, Wisconsin, M.S. M.S. thesis, thesis, 62 p. Larue, D.K., 1985, Florence-Niagara Florence-Niagara terrane--an terrane-an Early Early Proterozoic Proterozoic accretionary accretionary D.K., and and Ueng, Ueng, W.L., W.L., 1985, complex, Lake 96,p.p.1179-1187. 1179-1187. Lake Superior Superior region, region,U.S.A.: U.S.A.: Geological GeologicalSociety SocietyofofAmerica, America,v.v.96, Lister, mylonites: Journal Journal of Lister, G.S., G.S., and and Snoke, Snoke, A.W., A.W., 1984, 1984, S-C mylonites: of Structural Structural Geology, Geology, v.6, v. 6,p.617-638. p. 617-638. Mancuso, JJ., J.J., 1957, 1957, Geology Geology and mineralization mineralization of the the Mountain Mountain area, area,Wisconsin: Wisconsin: Madison, Madison; Mancuso, University of 32 p. p. of Wisconsin, Wisconsin, M.S. M.S. thesis, thesis, 32 Morey, Stratigraphic framework framework of of Middle Middle Precambrian Precambrian rocks in Minnesota, in G.M. 1973, Stratigraphic G.M. Morey, G.B., G.B., 1973, Young, ed., ed., Huronian Huronian stratigraphy stratigraphy and andsedimentation: sedimentation: Geological Association of Canada, Special 12,p.p.211-249. 21 1-249. Special Paper Paper12, Animikie basin, Lake Superior Superior region, region, U.S.A., U.S.A., in in Trendall, Trendall, A.F., A.F., and and Morris, Morris, R.C., R.C., 1983, Animikie basin, Lake 1983, ______ 13-68. Iron-formation--facts and problems: Elsevier ElsevierScience SciencePublishers, Publishers, Amsterdam, Amsterdam, p.p. 13-68. Iron-formation--facts Ramsay, J.G., 1980, 1980, Shear zone geometry--a review: review: Journal JournalofofStructural StructuralGeology, Geology,v.v.2,2,p.p.83-99. 83-99. Ramsay, J.G., J.G., and Graham, R.H., Strain variations variations in in shear shear belts: belts: Canadian R.H., 1970, 1970, Strain Canadian Journal Journal of of Earth Earth Sciences, 7,p. p. 786-813. 786-813. Sciences, v. v. 7, 14 - �Roy, S., S., 1977, 1977,Mylonite Mylonitemicrostructures microstructures and and their theft bearing bearing on development developmentof of mylonites--an mylonites-an example example from deformed deformed trondhjemites trondhjemites of of the the Bergen Bergenarc arcregion, region, SW SW Norway: Norway: Geological GeologicalMagazine, Magazine, v. 114, 114, p. 445-458. 445-458. 1987, AnEarly EarlyProterozoic Proterozoic ophiolite ophiolite in in the the Penokean Penokean Orogen: Geological K.J., Schulz, Schuiz, 1987, An GeologicalAssociation Association of Canada Program and Abstracts, v. 12, p. 87. Canada Program and Abstracts, v. 12, p. 87. Sedlock, R.L., R.L., and and Larue, D.K., Fold axes axes oblique oblique to to the regional plunge and D.K., 1985, Fold and Proterozoic Proterozoic Sedlock, terrane accretion terrane accretion in in the the southern southern Lake Lake Superior Superiorregion: region: Precambrian PrecambrianResearch, Research,v.v.30, 30,p. p. 249249262. Journal of Simpson, Carol, Carol, 1986, Determination of movement Simpson, 1986, Determination movement sense in in mylonites: mylonites: Journal of Geological Geological Education, v. Education, v. 34, 34, p. p. 246-261. 246-261. P.K., 1989, 1989, Geologic Geologic map map of of Proterozoic rocks near Mountain, Sims, P.K., Mountain,Oconto OcontoCounty, County,Wisconsin: Wisconsin: U.S. 1:24,000. U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsSeries SeriesMap Map1-1903, 1-1903,scale scale1:24,000. 10 1990, Geologic Geologicmap map of of Precambrian rocks of of Iron 1990, Precambrian rocks Iron Mountain Mountain and andEscanaba Escanaba 1%'' quadrangles, northeastern Wisconsin and northwestern Michigan: U.S. Geological Survey quadrangles, Wisconsin northwestern Michigan: US. Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsSeries SeriesMap Map1-2056, 1-2056,scale scale1:250,000. 1:250,000. Sims, P.K., P.K., Klasner, Klasner, J.S., J.S., and and Peterman, Sims, Peterman, Z.E., Z.E., 1990, 1990, The Mountain Mountain shear shear zone, zone, northeastern northeastern Wisconsin, U.S.A.--A discrete ductile deformation zone within the Early Proterozoic Wisconsin, USA.--A discrete ductile deformation zone within Early Proterozoic Penokean 1904-4p. p. A1-A15. A1-A15. Penokean orogen: orogen: U.S. U.S.Geological GeologicalSurvey SurveyBulletin Bulletin1904-A, Sims, P.K., P.K., and and Peterman, Peterman, Z.E., 1983, Evolution of of Penokean Penokean foldbelt, foldbelt, Lake Lake Superior Superior region, region, and Sims, 1983, Evolution its tectonic of the Great Medaris, L.G., L.G., Jr., ed., ed., Early Proterozoic Proterozoic geology geology of Great tectonic environment, in Medaris, Lakes region: Geological Society of America Memoir 160, p. 3-14. Geological Society of America Memoir 160, p. 3-14. 1986,Early EarlyProterozoic Proterozoic Central Central Plains orogen-A orogen--A major major buried buried structure structure in the north-central north-central United States: Geology, Geology,v.v.14, 14,p.p.488-491. 488-491. 1988,The The Mountain Mountain shear shear zone--Relevance zone--Relevancetotoage age of of quartzite quartzite at McCaslin 1988, McCaslin and Thunder northeastern Wisconsin: Thirty-fourth meeting, Institute Institute on Lake Lake Superior Superior Mountains, northeastern Thirty-fourth annual meeting. Geology, Marquette, Michigan, p. 97-99. Marquette, Michigan, p. 97-99. .K.,Peterman, and Schulz, Schuiz, K.J., K.J., 1985, Dunbar gneiss-granitoid gneiss-granitoid dome--Implications dome--Implicationsfor for Sims, P P.K., Peterman, Z.E., and Geological Society Society of America Proterozoic tectonic Proterozoic tectonic evolution evolution of of northern northern Wisconsin: Wisconsin: Geological America 96, p. p. 1101-1112. 1101-1112. Bulletin, v. 96, Sims, P.K., Van Schmus, Schmus, W.R., W.R., Schulz, Schuiz, K.J., K.J., and Peterman, Peterman, Z.E., Z.E., 1989, 1989,Tectonostratigraphic Tectonostratigraphic Sims, P.K., evolution of the EarLy Proterozoic Wisconsin Wisconsinmagmatic magmaticterranes terranes of of the Penokean orogen: Early Proterozoic orogen: Canadian Journal Canadian Journal of ofEarth EarthSciences, Sciences,v.v.26, 26,p.p.2145-2158. 2145-2158. D.L., Morey, G.B., and Southwick, D.L., and McSwiggen, McSwiggen, P.L., P.L., 1988, 1988, Geologic map (scale (scale 1:250,000) 1:250,000) of the the Minnesota Penokean orogen, central and eastern Minnesota, and accompanying text: Penokean orogen, and eastern Minnesota, and accompanying text: Minnesota Geological Survey Report of 25 p. 37,25 of Investigations Investigations 37, Wise, D.U., D.U., and others, 1984, Fault-related rocks: Suggestions Wise, 1984, Fault-related Suggestionsfor for terminology: terminology: Geology, Geology,v.v. 12, 12,p. p. 39 1-394. 391-394. - �HELD STOPS FIELD STOPSAND AND ROAD ROAD LOG LOG FIELD STOPS ARE SHOWN ON FIGURE 88 STOP 11 Riverview road, 0.7 0.7 mi mleast east of of County County Highway Highway(Co. (Co.hy.) hy.)W. W. Park Park in in open space at Riverview road, junction. Walk road junction. Walk east east 0.1 0.1 mi mi through through woods to prominent knob. knob. Massive to pillowed pillowed porphyritic porphyriticbasalt. basalt. Pillows Pillows are are about 11ft thick and 2 ft long; they they Massive trend N. 500 50' W., W., dip steep, and top to southwest. southwest. Outcrops Outcropsare aretypical typical of of Xwm Xwm unit (Sims, 1989); 1989); they they are are outside the shear shear zone. zone. of Waupee Volcanics (Sims, Drive west west on on Riverview road to to Co. Co. hy. hy. W; W; turn left (southwest) Drive Riverview road (southwest) on hy. hy. W and and mi; turn left left (east) on Bear Paw road and proceed for 1.1 1.3 mi; 1.1 mi; mi; park on proceed for 1.3 north side of road. STOP STOP 22 This outcrop area extends extends westward westward for about 0.2 0.2 ml. mi. It contains contains dominantly dominantly felsic felsic volcanic rocks rocks (Xwf, (Xwf, fig. fig.2;2;Sims, Sims,1989) 1989)that thatare are intruded intruded on the west volcanic west by by porphyritic (Xg, fig. fig.2). 2). The outcrops are outside the shear zone. granodiorite (Xg, unit; a crude The most easterly easterly outcrops outcrops are are aalayered layered biotite-garnet biotite-garnet s.chist schist of Xwf Xwf unit; crude layering is is expressed expressedby bygarnet-rich garnet.richzones. zones.Numerous Numerousflattened flattenedclasts clastsare arepresent. present. S, 1 layering foliation is subparallel subparallel to to layering layering (So); (Se);ititisisoriented oriented N. N. 28' 280 E., E., 78' 780 NW. NW. (fig. (fig. 9). 9). A A foliation ft-wide zone zone of of folding foldingdeforms deformsS,.5r Axial planes planes to to these folds trend trend N. 70' 700 E. and 3 ft-wide 820 SE. This correspondsto to S2 s2inside insidethe theshear shearzone. zone. The dip 82' Thisorientation orientation roughly roughly corresponds folded zone is interpreted to folded zone to be be aasmall smalldomain domain of ofF2 F2deformation deformation that that developed developed outside the shear shear zone. zone. Westward, narrow dikes dikes of of granodiorite-tonalite granodiorite-tonaliteand andpink pink aplite aplite of of Xg Xg unit unit cut cut the Westward, narrow schist. The The westernmost westernmost outcrops outcrops are aredominantly dominantly porphyritic porphyritic granitoid granitoid rocks rocks (Xg unit, fig. 2) 2) that that contain inclusions of of amphibolite amphibolite and and biotite biotite schist. schist. The granitoid rocks are fig. are nearly massive. massive. Return to Bear Paw road. road. Proceed of 0.4 0.4 mi. mi. Walk Proceed west west for a distance of Walk north about Return 0.05 mi ml to outcrop outcrop of of aa pink pink granite granite gneiss. gneiss. STOP 3 cut by by pink pinkaplitic apliticgranite; granite; these these rocks rocks are are within within the The granite granite gneiss gneiss (Xgn, fig. fig. 2) is cut Mountain zone. The Mountain shear zone. Thegranite granite gneiss gneiss has has aa prominent prominent 2S2foliation foliationexpressed expressed by by 86 SE aligned E., 86' SE(fig. (fig. 10). 10). The Thesoutheastern southeastern aligned biotite sheets that is is oriented oriented N. N. 530 53- E., margin of of the shear zone lies margin lies in the northeast-trending northeast-trending valley valley to the east of Stop Stop 3. Return to Bear Paw Paw road. Proceed Proceedwest weston onthis thisroad roadtotojunction junction with with County County Highway Highway W. road. Park W. Turn Turn right right (northeast) (northeast) on onHighway Highway W and proceed to Riverview Riverview road. Park on on Riverviewroad road and and walk walk southwest southwest on on Highway HighwayW Wfor for aa distance distance of of 0.35 0.35 mi. mi. Walk Riverview Walk southeastward onto mylonitic granite granite gneiss. gneiss. onto outcrops outcropsof ofmylonitic STOP STOP 44 These outcrops These outcrops of of granite granite gneiss gneiss (mylonite) (mylonite) (Xgn, (Xgn, fig. fig. 2) 2) have havewell-defined well-defined S-C S-C structures (Berthé 1984). C is a foliation oriented (Berth6 and others, others, 1979; 1979; Lister and Snoke 1984). subparallelto to the the southeastern southeastern boundary boundaryofofthe theshear shearzone. zone. The relation subparallel relation of S (an oblique foliation) to C indicates that the southeast block of the shear zone is upthrown 16 �relative to to the block. The relative the northwest northwest block. The sense sense of of movement movement in in the the horizontal horizontal plane plane was was generally, but not everywhere, dextral. The stretching lineation (X finite strain generally, but not everywhere, dextral. The stretching lineation (X finite strain axis), axis), as indicated deformed clasts, clasts, plunges plungessteeply steeplysouth southto to east; east; itit is is subparallel subparallel to to the the as indicated by by deformed intersection of intersection of SS and and C. C. Return to Riverview road. road. Proceed Return Proceed southwestward southwestward on on County County Highway Highway W to junction with Bear Paw road, and continue southwest on Highway W for a distance distance of of 1.3 1.3 mi. and continue southwest on Highway W Park in low area, near house house on on northwest northwest side side of of road, road, and and walk walk southwestward southwestward on Highway W Wfor for 0.1 0.1mi. mi. Proceed northwestward to outcrops in the County Highway the woods. woods. STOP STOP 55 These outcrops outcrops are within the shear These shear zone zone and and are aredominantly dominantly felsic felsic biotite biotite schist schist of of (fig. 2). 2). The foliation that that has been folded into a S, foliation unit Xwi Xwi (fig. The schist schist has a prominent prominent S2 (fig. 11). 11). The series of east-southeast plunging plunging folds (F3) (F,) (fig. The axes axes of of these these folds foldshave, have, in in turn, been folded by younger north-trending folds (F4). The axes and axial planes turn, folded younger north-trending folds (F4). axial associated with F4 cannot cannot be be measured on these these outcrops. outcrops. these outcrops, outcrops,the theS2 2 foliation is expressed by by brecciated and boudinaged siliceous siliceous In these layers that are generally parallel to At surfaces places, however, S/S are generally S,. places, however, So/S, surfaces (siliceous layers) are are not transposed parallel parallel to to s2 The occurrence layers) not completely completely transposed S,. The occurrence of isolated isolated domains in which the older SO/S1 foliation is preserved is characteristic of the mylonite domains older S,,/S, foliation is preserved is characteristic of (shear) zone as as aa whole. whole. Return to parking area. Proceed nil to road Proceedwest weston onHighway Highway W for a distance distance of of 1.4 1.4 mi junction junction on left. Proceed Proceed on onthis thisroad roadinto intothe thevillage village of of Mountain Mountain and and to to Wisconsin Wisconsin Highway 32-64. 32-64. Turn left (southeast) on and proceed southward for Highway on Highway Highway 32-64 32-64 and a distance of 0.9 0.9 mi to to low low outcrop outcrop on on north north side sideofofhighway highway in in borrow borrow pit. pit. STOP STOP 66 This outcrop is the Hines Quartz Diorite (unit This (unit Xh, Xh, fig. fig. 2) (named by by Lahr, 1972), 1972), a late-to post-tectonic rock intruded intruded into the Mountain late-to post-tectonic rock Mountain shear shear zone. zone. (It has not not been been noted outside the shear zone). The TheHines HinesQuartz QuartzDiorite Dioritehas hasaaU-Pb U-Pbzircon zirconconcordia concordia intercept age age of of 1,812.7±3.6 1,812.723.6 Ma (Sims (Sims and othets, others, 1990). 1990). km wide wide that that The Hines Quartz Quartz Diorite Dioriteisisaalensoid lensoid body body about about 33 km km long long and and 0.4-0.5 0.4-0.5 km S, foliation; itit is is virtually undeformed, undeformed, although although locally locally was intruded subparallel subparallel to to the theS2 cut by by mylonitic mylonitic shears, shears, and and therefore therefore it establishes a minimum age for the Mountain Mountain shear zone. zone. The Thequartz quartzdiorite dioriteisisdark darkgray, gray,slightly slightlymottled, mottled, massive, massive, and and medium medium grained. Primary plagioclase (Ans4) (An35) laths, grained. Primary subophitic subophitic textures are retained by plagioclase laths, but the the altered to amphibole, primary mafic mineral--probably mineral-probably clinopyroxene--is clinopyroxene--is highly highly altered amphibole, hiotite, biotite, and locally chlorite. chlorite. The The amphibole amphibole is is mainly mainly actinolitic hornblende and actinolite, hut but includes cummingtonite. Noie: AAfacies Note: faciesof ofthe theanorogenic anorogenicBelongia Belongia Granite Granite(unit (unitYwb, Ywb, fig. fig. 2) 2) of of the the 1.47 1.47 Ga Ga Wolf River batholith is exposed on the low knob on the southwest side of Highway Wolf is the low knob on the southwest side of Highway 32 32 This intrusive intrusive rock rock truncates truncates the southwest margin of of the Mountain and 64. 64. This southwest margin Mountain shear shear 4 zone. I This concludes the field trip, but, an additional but, an additional stop stopisisdescribed described below below because because of of its its significancetotothe thegeology geoto' of significance of aa broader broader region. region. To Toreach reach Stop Stop 7, 7, return to to Mountain, Mountain, 17 �then proceed W; turn right (east) and proceed to to County County Highway Highway W; and proceed proceed on onHighway Highway W for a distance of 2 mi. Outcrop Outcropon onleft left(north) (north)side sideofofHighway HighwayW Wisisstop stop7.7. STOP 7 The Baldwin Conglomerate (unit Xb, fig. fig. 2) 2)is is exposed on the south-facing slope of the hill. hill. The Baldwin Conglomerate is a lensoid unit about about 2.3 2.3 km km long long and aa maximum maximum of of 150 150 (sec. 6, 6, T. T. 31 31 N., N., R. R. 17 17 E.) E.) along along the the northwest northwest margin m wide that is exposed locally (sec. of the Mountain shear within the shear zone and shear zone. ItItoverlies overliesmetavolcanic metavolcanic rocks within is truncated and intruded (by dikes) on the north by the Hager and intruded (by dikes) on the north by the HagerRhyolite Rhyolite(Ywh, (Ywh, fig. fig. 2) of the Wolf of Wolf River batholith batholith (Lahr, 1972). 1972). The Theconglomerate conglomerate has has relict relict sedimentary sedimentary layering and possible scour features and contains contains subrounded subrounded to to subangular subangularclasts clasts of of metavolcanic rocks, rocks, granite granite gneiss, gneiss, and and quartzite quartzite (as (as much much as as 25 25 cm cm in in diameter). diameter). All All but the quartzite from the shear zone of the but quartzite clasts clasts are are derived derived locally locally from zone itself. itself. Clasts of Hines Quartz Diorite have not been reported in the conglomerate (Lahr, (Lahr, 1972). 1972). The matrix of the conglomerate is is a gray, gray, fine- to medium-grained rock rock containing containing quartz, quartz, feldspar, biotite, muscovite, feldspar, muscovite, and hornblende of a proximal source. E., 78' 780 NW. It is interpreted The The conglomerate conglomerate has has a foliation foliation that that is is oriented oriented N. N. 66 66ÂE., 2 foliation as S, foliationinasmuch inasmuchas asititisisparallel paralleltotoS2 S, in in the the mylonitic mylonitic rocks of the shear shear zone. zone. The source of the quartzite was the quartzite now exposed quartzite clasts clasts almost almost certainly was exposed at McCaslin and Thunder Mountains, less than 20 km to the north north (Sims (Sims and and Peterman, Peterman, Sims, 1990). 1990). Thus, Thus, inasmuch inasmuch as as the Baldwin Baldwin Conglomerate Conglomerate was deformed deformed during 1988; Sims, during the ductile deformation along the Mountain shear zone, and prior to to emplacement emplacement of of the Hines Quartz Diorite, the quartzite clasts and their parent rocks are older than clasts and than 1,812 Ma, Ma, the the age age of of the Hines Quartz Diorite. 1,812 Diorite. 18 �'C I: ij I IT L I) El [ IT: Table 1--Chemical analyses of selected rocks in Mountain area, Wisconsin : ii r >n 18.90 17.70 2.69 7.30 99.87 0.04 0.03 1.48 4.77 7.35 3.29 2.28 0.73 0.25 0.16 49.00 51.80 9 Nb w o m m 1.32 w 0.086 00 M Peacbck 99.85 100.09 0.056 2.43 0.129 0.46 0.161 0.18 363 440 658 511 541 0.270 0.36 2.735 0.05 0 '0- 00 M O O u 0.248 0.37 402 4 97 7 6 2 8 42 93 115 165 18 27 8 48 195 54 22 22 148 12 35 2 47 175 70 431 22 168 17 299 99.69 3,62 2.34 0.18 0.05 0.04 0.45 0.03 0.09 2.21 0.55 73.20 13.00 0.83 3.10 130-85A 14 -I o'? Q O M 0.041 2.95 377 1 27 9 346 1.33 0.167 711 7 91 15 208 35 99.77 7.52 2.68 2.97 0.65 0.23 0.05 0.40 0.02 0.01 1.64 2.89 17.40 0.21 63.10 50.10 19.00 0.90 10.80 4.57 9.68 2.64 0.64 0.70 0.17 0.19 0.99 0.02 0.05 153-85 150-85 100.45 ("I 396 99.49 0.41 2.39 6.48 0.02 0.05 0.02 0.29 0.06 0.02 0.22 12.40 0.61 1.52 75.60 129-85A - f \ o m IM- - K/Rb Rb/Sr Zr Y 48 555 21 92 99.59 100.77 0.23 0.09 0.04 0.68 0.01 0.04 2.22 3.60 2.50 0.19 0.05 0.05 0.58 0.04 0.15 0.50 72.70 13.20 0.89 3.18 39-85 (weight percent) Minor elements (parts per million) by X-ray fluorescence 0.02 0.01 0.19 1.28 0.01 1.15 0.29 0.05 0.02 0.66 0.10 0.16 5.52 2.79 1.33 1.09 3.40 1.47 2.19 3.44 10.90 69.30 14.20 0.98 3.14 35-85 1.00 72.40 14.50 0.31 2.19 27-85 1.69 2.00 9.54 3.54 23-85B 20-85 W i n - M m ^- in M m Rb Sr Sum CO2 H20+ H20- MnO P205 MgO CaO Na20 K20 Ti02 FeO Fe203 203 Si02 Sample No. M alor oxides [Major oxide analyses by A. Bartel, E. Brandt, S. Roof, J. Taggart, and K. Stewart. FeO, 1120, and CO2 by F. Brandt and S. Roof. Minor element analyses by K. Barovich, K. Futa, and Z. Petermani 1] I1 4 u in cs*i. o* r �C N) cliii :riiii r' 20-85 23-85B 27-85 35-85 39-85 129-85A 130-85A 150-85 153-85 i - ci riiuii i r r:r: ii n flT Amphibolite (unit Xwa), SW1/4 SW1/4 sec. Amphibolite sec. 33, 33, T. 32 N., R. R. 17 17 E. E. Porphyritic mafic mafic metavolcanic metavolcanicrock rock(unit (unit Xwm), Xwm),NE1/4 NE1/4 NW1/4 NWI/4 sec. 4, T. 31 N., R. 17 Porphyritic N., R. 17 E. Feisic metavolcanic rock (unit SW1/4 NW1/4, NWI/4, sec. Felsic (unit Xwf), Xwf), SW1/4 sec. 4, 4, 1. T. 31 31 N., N., R. R. 17 17 E. E. N., R. 17 F. Porphyritic granodiorite granodiorire (unit Xg), Xg), NE1/4 NE1/4 SW1/4, sec. Porphyritic sec. 5, T. T. 31 N., E. Granitic gneiss (unit Xgn), NE1/4 SW1/4, SW1/4, sec. sec. 5, 5, T. T. 31 N., R. 17 17 E. Granitic gneiss (unit Xgn), Xgn), SW1/4 NW1/4, NW1/4, sec. sec. 5, 5,T. T.31 31 N., N., R. R.17 17E. E. Granitic gneiss (unit Xgn), NW1/4 NW1/4 NW1/4, sec. 5, T. 31 N., R. 17 sec. 5, T. 17 F. E. Hines Quartz Diorite Diorite (unit (unit Xh), Xh), NW1/4 NW1/4 NW1/4, NW1/4, sec. sec. 13, 13,T. T. 31 31 N., N., R. R.16 16 F. E. Intermediate metatuff metatuff (unit (unit Xwi), Xwi), SEI/4 SE1/4 SW1/4, SW1/4, sec. sec. 1,1,T. T.31 31 N., N., R. R. 16 16 E. E. Table Table 1 (continued) fl F �I Table 2.-Approximate 2.--Approximate modes modes of of granodiorite granodiorite Table Constituent 101 101 60B 60B 35 35 112 112 Plagioclase Plagioclase 42.8 49.5 40.7 Quartz 18.2 15 15 K-feldspar 24.6 17,5 Biotite 8.8 Hornblende 1.8 Alteration minerals minerals 3.3 3.3 Accessory minerals 0.5 I I 101 101 60B 60B 35 35 112 112 165 165 34A 34A 34B 34B 10 10 7.5 Tr. 0.5 0.5 165 165 34A 34A 34B Average 44.8 51.8' 51.8 55.2 55.2 23.3 47.5 47.5 37.6 14.6 14.6 18.2 18.2 21.6 21.6 35.2 35.2 21 21 15.4 20.6 11 40 16 5.4 10.6 9 7 1.4 7.5 9.8 9.8 99 0 6 00 7.3 7.3 0.1 0.8 Tr. 2.1 Tr Tr.. 5.7 Tr. 0.2 Sample localities Sample localities NE1/4 N.,R. 17 17 E. NE1/4 SW1/4 sec. 7, T. 31 N., SE1/4 SWI/4 SW1/4 sec. sec. 5, 5, T. T. 31 31 N., N., R. 17 17 E. NE1/4 SWI/4 NE1/4 SW1/4 sec. sec. 5, 5, T. T. 31 31 N., N., R. R. 17 17 B. E. NW1/4 SEI/4 NW1/4 SE1/4 sec. sec.7, 7, T. T. 31 31 N., N., R. R. 17 17 E. SE1/4 NE1/4 NE1/4 sec. sec.7,7, T. T. 31 31 N., N., R. R. 17 17E. E. NE1/4 SW1/4 SW1/4sec. sec.5, 5,T. T.31 31N., N., R. R. 17 17B. E. Same as 34A. Pink Pink leucogranite leucogranite that that cuts cuts granodiorite. granodiorite. 21 1.5 1.5 Tr. Tr. Â¥) j) 0.1 ) 0.1 22 �Table 3.--Approximate 3.--Approximate modes of Quartz Diorite Diorite Table of Hines Quartz and and quartz quartz diorite diorite of of the theamphibole amphiboleschist schist unit unit Hines Quartz Quartz Diorite Diorite Quartz diorite diorite Quartz Constituent Constituent 147 147 150 150 134 134 172 172 Plagioclase 47.7 54.2 65.6 48.8 Quartz Quartz 32.6 2 9.7 22.6 0 0 0 12.4 0.9 5.6 12.2 Amphibole Amphibole 6.3 141.7 18.4 15.8 Alteration Alterationminerals minerals 0.1 0.1 Tr. Tr. Accessory Accessory minerals minerals 0.9 0.9 K-feldspar Biotjte Biotite 1.2 1.2 'Includes Includesrelicts relictsofofclinopyroxene. clinopyroxene. Sample Samplelocalities localities 147 147 150 150 134 134 172 172 Roadcut, NEI/4 NE1/4 NW1/4 NW1/4 sec. sec. 14, 14, T.31 ~ . 3N., N., 1 R. R. 16 16E. E. Roadcut, Outcrop, NWI/4 NW1/4NW1/4 NW1/4sec. sec.13, 13,T. T.31 31N., N., R. R. 16 16E. E. Outcrop, Outcrop,SE1/4 SE1/4NW1/4 NW1/4sec. sec.33, 33,T. T.32 32N., N., R. R.17 17E. E. Outcrop, Outcrop, NE1/4 NE1/4 SEI/4 SE1/4sec. sec.33, 33,T. T.32 32N., N., R. R.17 17E. E. Outcrop, 22 Tr. Tr. 0.7 0.7 0 0.4 0.2 �N) 0 0.8 0 00 Tr.r T Tr. Tr. Tr. Tr. Amphibole Amphibole Muscovite Muscovite Epidote/clinozoisite Epidote/clinozoisite Sphene Sphene Chlorite Chlorite Calcite Magnetite Magnetite 141-1 88 79 76 199 64 12 13 2 0.5 0.5 TI. Ir. 0.2 0.2 0.2 0.2 Tr. Tr. 0.5 0.5 Tr. Tr. 00 4 4 0.6 0.6 47.8 47.8 46.2 46.2 12 12 64 64 0.2 0.2 Tr. Ir. Tr. Tr. 00 00 0.2 0.2 0.3 0.3 00 1.8 1.8 8.3 8.3 38.7 38.7 50.5 50.5 Plagioclase has abundant tiny tiny quartz quartz droplets. Plagioclase droplets. 0.2 0.2 /jt4'!.i/,i.. T. 31 31 N., N., R. R. 17 NE1/4 sec. sec. 5, 17 E. E. 5, T. NW1/4 NE1/4 sec. 5, 31 N., R. R. 17 17 E. NW1/4 NE1/4 NE1/4 sec. 5, T. 31 NW1/4 sec. 6, 31 N., Ft. R. 17 17 E. E. SW1/4 NE1/4 NE1/4 sec. 6, T. 31 31 N., 16 E. sec. 1, R. 16 SE1/4 SW1/4 SW1/4 sec. 1, T. 31 N., R. E. sec. 7, T. T. 31 31 N., R. 17 17 E. NE1/4 NW1/4 NW1/4sec. 17 E. sec. 7, 7, T. 31 N., R. 17 NW1/4 NW1/4 NW1/4 sec. sec. 7, N., R. R. 17 17 E. E. SW1/4 SW1/4 SWl/4 sec. 7, T. 31 N., 0 17 cmT. N I 11?J .JLI'. 31 N., ''.1! R. 17 E. NE1/4 NE1/4 scc. 5, Included with biotite in mode. ' Included mode. I Accessory Accessory minerals minerals Calcite .8 4.9 4.9 Biotite Biotite 22 41.2 41.2 Quartz K-feldspar K-feldspar 50.8 50.8 Plagioclase Plagioclase 13 13 0.4 0.4 Ir. Tr. 0.1 0.1 0 0 0 0 44.2 44.2 0.1 0.1 2.4 2.4 00 0.6 0.6 3.5 3.5 47.7 47.7 199 199 of 01 Ir. TI. 1 1 Tr. Tr. 00 Tr. Tr. 0.5 Tr. Tr. 0 0 5.8 5.8 2.1 2.1 37.3 37.3 53.3 53.3 It. Tr. It. Tr. 00 0I 11 Tr. Tr. 00 2.5 2.5 8.5 8.5 10 10 37 37 41 41 3 3.5 3.5 00 Tr. Tr, 22 00 13 13 00 41.5 41.5 '42 '42 It. 6 Tr. 0 1 Tr. 5 28 0 29 31 0.2 0.2 It. Tr. Ti. TI. Tr. Tr. 0.3 0.3 Tr. Tr. 0 0 Tr. Tr. 11.5 11.5 00 37.5 37.5 50.5 50.5 -- 0.5 Tr. TI. It. Tr. Tr. Tr. 1 1 Tr. Tr. 00 00 37 37 00 21.5 40 40 It. Tr. It. Tr. It. TI. Tr. Tr. 1 1 It. Tr. Tr. Tr. 00 15 15 10 10 22.5 22.5 51.5 51.5 173 173 91 91 It. Tr. (0 (0 It. TI. 0.2 0.2 0.3 0.3 It. Tr. 22 0 68.5 0 0 1 25 Tr.. Tr Tr. Tr. 164 164 991l 18 18 167 167 168 168 170 170 173 173 r— N., RI sec. 7, Rl 17 17 E. NE1/4 NE1/4 NE1/4 sec. 7, T. 31 N., sec. 7, R. 17 E. E. NE1/4 NEI/4 NE1/4sec. 7, T. 31 N., Ft. SW1/4 NW1/4 W 1 / 4 sec. sec. 27, 27, T. 32 32 N., Ft. R. 17 E. sec. 33, R. 17 17,E. E. NE1/4 SEI/4 SE1/4sec. 33, T. 32 N., R. 31 N., R. 16 E. SE1/4 SE1/4 sec. 12, T. N., 16 E. 12, SEI/4 SEI/4 sec. T. 32 32 N., N., Ft. SW1/4 SW1/4sec. sec. 33, R. 17 E. 33, T. SWI/4 SW1/4 T. N., R. 17 sec. 7, T. 31 N., 17 E. E. NW1/4 SW1/4 NWI/4 SWI/4 sec. 7, Tr. Tr. 22 Ir. Tr. It. Tr. It. Tr. 22 00 64 64 0 00 Tr, TI. 32 32 schist Amphibole schist 18 164 18 164 3 I Tr. Tr. Tr. T 37 3 31.5 31 27.5 L_J Amphibole is clinoamphibole, probably probably cummingtonite. cummingtonite. Amphibole is aa clinoamphibole, Ti. Tr. 00 Tr. Tr. Sample localities Sample localities It. Tr. Ir. Tr. 00 0 0 0 0.8 0 7.2 21.7 23.6 46.7 170 170 interlayered Diotite biotite and amphibole schist interiaycreu schist Ii_] biotite-amphibole schist Biotite and biotite-aniphibole 76 79 88 141-1 167 168 76 79 88 141-1 167 168 Table i aoie 4--Approximate 4.--~pproximaiemodes moucs ' t1 r: Ei L ii r' ti 11 t_J 111_I �39.0 10.6 6.0 6.0 00 0.2 0.2 . Quartz Quartz Microcline Microcline Biotite Biotite Hornb!ende Hornblende Alteration minerals minerals a>. Accessory minerals 129-85B 129-85B 130-85A 130-85A 130-85B 130-85B 39 39 46 46 50 50 44.2 Plagioclase Plagioclase 0.7 0.3 u.5 0n 8.4 8.4 0 41.2 49.4 46 46 t_.. 1.0 1.O 1.3 0.5 0 8.4 8.4 1.5 40.4 48.2 50 50 tj tj r: F I 0.7 0.7 0.1 0fi 12.0 12.0 1.0 32.2 54.0 85B 85B 129129- . 1.O 1.0 0.5 0.5 00 6.5 6.5 8.0 37.0 47.0 85B 85B 130130- 55 55 Tr. Tr. 1.2 1.2 129-85A 129-85A 18-1 18-1 44 44 40A 40A 45B 45B 0.5 0.5 2.0 2.0 Tr. Tr. 0.7 0.7 00 5.4 19.0 30.5 44.4 45B fl1 Tr. Tr. 0.3 0.3 0 6.5 6.5 8.7 36.1 48.4 44 44 Tr.. Tr 0.9 U 0 , 10.77 10 0 30.7 57.7 18-1 18-1 fl 0.4 0.4 1.0 1.1) 0 1.1 11 30.9 37.1 29.5 85A 129129- 0.4 0.6 0.2 8.2 5.9 35.9 48.8 Average Average NEI/4 NE1/4 SE1/4 SE1/4sec. sec.6,6,T. T.31N., 31N, R. R. 17E. 17E. NWI/4 NEI/4 sec. 5, T. 31N., R. 17E. NW1/4 NE1/4 sec. 5, T. 31N.. R.17E. SE 1/4 NW1/4 NW1/4 sec. T. 31N., 31N., R. 17E. 17E. SE1/4 sec. 5, 5, T. NWI/4 R. 17E. 17E. NW1/4 NEI/4 NE1/4sec. sec.5,5,T. T.31N., 31N, R. R. 17E. 17E. NW1/4 SWI/4 SW1/4 sec. sec.33, 33,T., T., 32N., 32N, R. NW1/4 Same Same as as 129-85B, 129-85B, Leucogranite Leucogranite gneiss. gneiss. 0.7 0.7 .o 1.0 1 15.0 15.0 1.3 34.4 46.1 40A 40A 3.4 3.4 9.4 38.3 46.7 55 55 Sample Sample localities localities 0.4 0.4 u. I 0.1 0n 8.2 8.2 5.0 35.3 51.0 13013085A 85A Table 5.--Approximate 5.--Approximate modes of granite granite gneiss gneiss LJ i; R. 17E. SW1/4 sec. 5, T. T. 31N., 31N., R. 17E. NW1/4 SW1/4 sec. 5, T. R. 17E. T. 31N., R. 17E. SW1/4 NE1/4 31N., SWI/4 NEI/4 5, T. T. 31N., 31N, R. R. 17E. 17E. NW1/4 sec. 5, SE1/4 NW1/4 17E. SW1/4 T. 31W., 31N, R. 17E. SW1/4 NW1/4 NWI/4 sec. 5, T. sec. 5, T. R. 17E. R. 17E. SW1/4 NW1/4 T. 31N, 31W., SWI/4 NWI/4 Same as 130-85A. Same as 130-85A. Tr. Tr 39 39 ;i 11i:t j Constituent .._j �N) U, ( F1 F4 F3 F2 F 2 F1 Deposition Event EJ rr L_il I Uj [fl r r r' r c L3 Fold axes axes Kink bands L1 S L4b Lineations Shears Shears L4a Fold axes axes Foliation S3 Foliation L2b '2a Fold axes Long axes of strained clasts clasts Stretched S2 S Regional foliation Regional ~Flattened l a t t e n e dclasts clasts Foliation Foliation S Symbol Bedding, pillow structures pillow structures intrusive contacts contacts Structural element Variously oriented kink bands Variously oriented and fold axes associated with kink bands Fabric is poorly developed Appears to fold fold F3 F3 Seen as fold fold axes on S, surface Geometric element. element. Not Geometric Not generally observed Stretched clasts that lie in lie in S2 plane 2 plane Tectonic layering, mylonitic foliation in granitic gneiss foliation (unit Xgn) Folds of of S,2 Folds Best observed observed south of shear shear but present in isolated zone, but isolated within shear zone outcrops within Primarily is layering between Primarily felsic and and mafic rocks felsic Explanation r Late-state brittle deformation. Not systematically studied. Number of events not not known. known. Shears are parallel to to cross cross faults faults . Rarely observed. observed. Yielded Rarely Yielded a northnorthwest-trending northwest-trending fabric Late folding folding that that created aa westwestnorthwest-trending fabric northwest-trending Foliation associated with with simple simple shear due to relative relative upthrow upthrow 4,formed by from southeast. L2a fold of S1 and S. fold of S, and Sw '2b bbcaused caused by simple simple shear associated by associated with with upthrow Flattened clasts suggest regional regional compression Original depositional and intrusive Original feature Nature of event 6--Sequence of events, structural elements, elements, and and nature of events in the Mountain Table 6.--Sequence Mountain shear shear zone zone [C ti L I (J �91° 88° 89° 9Qs /'T NSIN 460 J 1 I. . .. ... HI 1 50 KILOMETERS 50 KILOMETERS 00 EXPLANATION EXPLANATION • Middle Proterozotc Proterozoic lKeweenacsanl IKeweenawanI mafic mafic igneous igneom rocks of Midconttneni and sedimentary sedimentary rocks Midcontinent rift nf!system w-~~113001,200 Mal 11.000-1200 Mil ,* ,. .-..*\ :- • - -- Contact Contac, High angle angle fault High WISCONSIN MAGMATIC MAGMArlc TERRANES WISCONSIN TERHANES Meiauolcatiic and granilnid Meiavolcanic granttoid rocks rocks in in Pernbine'Wausau Pembme-Wausau rterrane e 11.760-1.880 Ma1 1.7601.880 Ma) Metavolcanic and qranttoid rocks in t m Marshiteld Marshheid terrane 8mane Metavoicanic qmnitmd rocks 1.835 1.8W 1,890 Ma) 11.835 Mal 0 LI CONTINENTAL-MARGIN CONTINENTAL MARGIN ASSEMBLAGE ASSEMBLAGE Marquette Range Range Supergroup Superyroup (1.820 1.820-2.100 Ma) and and Marquene 2.100 Mat gneiss.granite, granite, and and greenstone greenstone (2.600-3.550 )2,600.3,550 Ma1 Ma) gneiss. Sedimetuary rocks of Paleozoic Sedimentary Paleozoi~age age Anorngentc rocks 11.4701.510 1,4701510 Ma) A r o y e n i c igneous rocks Mai ________ 7 Gnetss 2.800 Ma) Gneiss in Marshfield Marshheld errane wrrane f12.800 Mat Thrust fault Thrus . o_r _,, ,, Shear zone y \^ y a Shear zone A Athens EE Eau Pleme Pleine Eau J.i Jump River Jump RIWF MM Mountain Mountain Michigan. the Lake Superior region, region, northern northern Wisconsin and Michigan. Figure 1. Generalized Generalizedgeologic geologic map map of of the the eastern part of the location of the Note the location the Mountain Mountain shear shear zone. zone. 26 �L L EXPLANATION MIDDLE PROTEROZOIC PROTEROZOIC (1600.900 (1600900 Ma) MIDDLE Belongia Granite oof Btlongia Granite f Wolf River River baiholith batholith Ywu N1480 1-1480 Ma) Ma1 __________ L V wh [ [ U.' z 0 5..' Lx. C U.' x L ______ Hager Rhyolite Rhyolite EARLY PROTEROZOIC PROTEROZOIC Xh Hines Quartz Dtorite Quartz Diorite Xb Baldwin Conglomerate Baldwin Conglomerate Granite gneits—Defortned gneiss-Deformed and and metamorphosed granodiorite metamorphosed granodlorite Blotite schist Biotite schist and and amphibole amphibole schist schist Interlayered Interlayered *n. Xwi _________ Xwq Quartz dionte Quartz diorite schist schist X Wa Amphibole schist schist with with thin layers Amphibole layersooff felsic schist lelsic schist ___________ d 9 Granodiorlie—Equivalent to to unit Xgn Xgn shear zone zone kin n ghem WAUPEE VOLCANICS VOLCANICS WAUPEE _______ Xwni Dominantly felsic volcanic rocks rocks Dominantly felsic volcanic Mafic lava lava flows (lows Mafic - Trace ooff S, foliation foliation Trace 4 Trace of of S9 foliation foliation Trace Southeastem boundary ol of shear  Southeastern shear zone zone Figure 2. Geologic Geologicmap mapof o fthe theMountain Mountainshear shearzone zoneand andvicinity, vicinity. Oconto OcontoCounty. County, Wisconsin Wisconsin 27 �QUARTZ QUARTZ A EXPLANATION S A a. Granite gneiss; gneiss; ®, Average Average Granite Granodiorite; Granodiorite; A, Average Field of of granodiorite granodiorite Field Field of of granite granite gneiss Field b a A 8 K-FELDSPAR PLAGIOCLASE Figure FigUre3. 3. Quartz-K-feldspar-plagioclase Quarlz-K-feldspar-plagioclase diagram diagram showing showing modal modal composition composition of of samples samples from from the the granitic granitic gneiss gneiss and and granodiorite granodioriteUnits units a 1' A K-FELDSPAR C 8 PLAGIOCLASE Figure 4. Quartz-K-feldspar-plagioclasediagram diagram showing modal composition of samples samples from interlayered interiayered biotite biotite 4. Quartz-K-feldspar-plagioclase and amphibole amphibole schist schisl unit and 28 �Figure 5. Contoured, Contoured,equal-area e ual areaprojection projectionof of 68 68 poles poles to to foliation foliationoutside outside of shear shear zone. zone. Contours Contours are 1. 3.5.and and FigureS. are 1.3.5, percent.The t h egreat greatcircle circle(N. (N.8°8"E., E.,90C) 90') isisthe thecalculated calculatedmean meanof of Si jfoliation foliation 77percent, NW / C clast r I€ I II4l ii It iiiI1IiII 'In II''''' I''''' e g 1 o i i 2 Figure ol01granitic 9neiss 6 Photograph Phoiograpn granitic gneissslab slabshowing showingS-C S Cfabric fabricviewed viewedparallel raileltotothe theshear shearzone zonefrom fromthe menortheast. northeast Figure6. The adjacent totothe showndiagrammatically daqrammatica~adlacent thephotograph. photograph The Thelong longaxis axis Thedirection directionofofrelative relativemovement movementisisshown ofofthe stretched clast lies within the S plane me siretched clast lies within the S olane 29 �Shear zone Shear zone Figure7.7.Block Blockdiagram diagramshowing showingrelationship relationshipofofstrained strainedclasts clasts(strain (strainellipsoids) ellipsoids) to simple shear envelope. Note Figure to simple shear shear zone envelope. Note that the stretch (long) axis of the clasts (LZh) dip more steeply than the that the strelch (long) axis of the clasts (L2b) dip more steeply than the shear zone 30 �E"D — r I I! I-'- -.\'.- - N'. ' v14 I o' ! IFL?F'I,i / —— •:- ::M(lulliI - / r' ' F\ - - j -- - I H - ,',> —. ) '1 5 - ,. I I I In ci::' Aj - I / -' - - :' C, I - - <_1H • • _:. -' I ' I -' L I LFORESTI ,:' -, - 2-" 2, — F T (I - I F - C / —- ) 32 I - 8• .. - IIop:, I? ) ', — r'' i i: 9( ' :------, KT — 31 I V'-' ;\ I •.q.L•: :s::.I. IwLo9901?1 i5.-/IecJ IF • I / R. 17E. r.. (} L _"' —.- ft 16E, I: Y-"N I:C 5 1 NATIoNAJ4I '[I - I - 2/F?? __________________ r FIgure 8, Map of part ol Mountain 71/2-minute quadrangle showing tied stops F I 17 N _____ c: tI • - H j - 0 -'• ______ I,0 2 1>'".•J's. '9010 - :I1 r: "0, [] "04 —1230' SLUnchstop(afterstopa) 1 -5 - --5- I -I I I 1 H )Jl'ot/Irlr -. --— t �NW Figure Figure9. 9. Contoured Contouredequal-area equal-areaprojection projectionof of 33 33 poles poles to to 1Stfoliation. foliation.Contours Contoursare are1,1,16, 16,20 20percent. percent.The Thegreat greatcircle circle isisthe Sifoliation foliation thecalculated calculatedmean meanof ofSi N N N 53° E, 86° SE Figure 43 poles poles to to S2 2 foliation. Figure 10. 10. Contoured Contouredequal-area equal-areaprojection of 43 foliation.Contours Contours are 1, 1, 1020,3040 "120, 30 40percent. percent.The Thegreat great circle 2 foliation foliation circleis is Ihe the calculated calculated mean of 89 N Figure Contoured equal-area projection ofof 5050 poles totoS2 foliation. Poles S2 loliationContours Contodrsare are2,6, 2. 6. and1212percent; percent;50 50points pointstoto Figureii.11. Contoured equal area Prolcction and (1-3)(contours (mntoursare are2,2.10, 10.20, 20.30, 30, and40 40percent). percent)A,A.girdle giroledefined defined tolaed longaxes axesofofdeformed oeformedclasts ciasts(L3) long and bybyfolded tol~ation (F3 toldsl. maximum mncenuabon lineanons represcntod dot 2S2 foliation (F3 folds); 9.Bmaximum concentration ofoflineations represented bybydot 32 �WEDNESDAY, MAY MAY 1, 1,1991 WEDNESDAY, 1991 FIELD FIELD TRIP #2 L.S. L.S. Chan, Chan,P.E. P.E. Myers, Myers, and andR.L. R.L.Hay Hay (Leaders) (Leaders) "Features "Featuresand andsignificance significanceof of the the Precambrian-Cambrian Precambrian-Cambriancontact contactininwestern westernWisconsin" Wisconsin" 33 �Field Field Trip #2 Precambrian-Cambrian Precambrian-CambrianBoundary BoundaryininWest-Central West-CentralWisconsin Wisconsin Lung. Lung. S. S. Chan, Chan,Paul Paul E. E.Myers, Myers, and andRichard Richard L. L. Hay Hay INTRODUCTION INTRODUCTION Geologists the stratigraphic stratigraphic record. record. Recent Recent Geologists have have realized realized long long ago ago the the predominance predominance of of gaps in the developments in event stratigraphy and the introduction of the idea of 'catastrophic uniformitarianism' developments in event stratigraphy and the introduction of the idea of 'catastrophic uniformitarianism' to togeology geologyhave have called called for for increasing increasing effort efforton onthe thestudy studyof ofgeologic geologicgaps gaps and and boundaries boundaries[Ager, [Ager, 1981]. 19811. The The Precambrian-Cambrian Precambrian-Cambrian boundary boundary is aa very very big topic. topic. It represents represents aa time time when when dolomite dolomite accumulation accumulation and and stromatolite stromatolite formation formation decreased, decreased; when when red red biogenic biogenic limestone limestone and and phosphorite phosphorite deposits increased, and when living organisms abruptly became skeletalized deposits increased, and when living organisms abruptly became skeletalized [Rozanov, [Rozanov, 1984]. 19841.Most Most studies studies of of the thePrecambrian-Cambrian Precambrian-Cambrian (PC-C) (P6-6)boundary boundary are areconcerned concernedwith withits itsstratigraphic stratigraphic aspects, aspects, as as exemplified exemplified by the objectives of the Working Working Group Group on on the thePC-C PC-6Boundary Boundary (JUGS) (IUGS)[Crowe [Croweand and Brasier, Brasier, 1989]. 19891. Consequently, the major controversies about the PC-C PC-6 boundary are focused upon uponits its biostratigraphic biostratigraphic definition definition and and geochronometry. geochronometry. In In the the mid-continent, mid-continent, the thePC-C PC-Âboundary boundary is is generally represented represented by by aagap gapalmost almost 500 500 my. my. long. long. In Inmost most areas, areas, the the 0.9-1.1 0.9-1.1 Ga Ga Keweenawan Keweenawan Event Event that that affected affected most most of of the theMid-continent Mid-continentrepresents representsthe thelast lastgeological geologicalrecord recordininthe thePrecambrian. Precambrian.AAfew few intracratonic intracratonicbasins basins formed formed near near Lake Lake Superior Superior while while most most of the the mid-continent mid-continent remained remained emergent emergent above above the thesea-level sea-levelduring duringthis thisvast vast interval interval of of time. time. The Theabsence absenceof of continuous continuousstratigraphic stratigraphicsections sections across the PC-C boundary has perhaps limited the potential usefulness of the area for studying across the PC- boundary has perhaps limited the potential usefulness of the area for studying the the major major events events and and phenomena phenomena atatthe theboundary. boundary.The Thenon-stratigraphic non-stratigraphic aspects aspects of of the thePC-C PC-? contact, contact, however, however, still still present present many many geological geological problems that may be important for the the understanding understanding of of the the geological geological processes processes and andhistory history of ofthe theboundary. boundary. One Oneofofthe theproblems problemsisisthe theage ageand andmanner mannerof ofthe thepeneplanation peneplanation process. process. The ThePC-C PC-âunconformity unconformity in in west-central west-central Wisconsin Wisconsin is represented by a gentle gentle surface surface with with regional regional dip less less than than 1°. lo.The The smooth smooth morphology morphology of of the thePC-C PC-6contact contactpresumably presumablyresulted resulted from fromprolonged prolongedweathering weatheringand and peneplanation. peneplanation.The Thegeology geologyofofthe thesurface, surface,however, however,isishighly highlyvariable. variable.Precambrian Precambriancrystalline crystallinerocks rocks below below the theunconformity unconformity are are weathered weathered totoaathick thicksaprolite saproliteininsome some areas, areas, but but may may be beunweathered unweathered or orpartially partially weathered weathered in in others. others. The Theformation formation and and condition condition of of the thePrecambrian Precambriansurface, surface, the theage age of ofthe thesaprolitization, saprolitization,the thespatial spatialvariations variationsininthe thedegree degreeofofweathering weatheringof ofthe thePrecambrian Precambrianbasement, basement, and andpossible possiblepre-transgression pre-transgression uplift uplift of of the themid-continent, mid-continent, are areamong among the theproblems problemsawaiting awaitingfurther further examination. examination. The Thealteration alterationprofile profiledeveloped developed on onPrecambrian Precambrian rocks rocks by by weathering weathering prior prior to to the theMt. Mt.Simon Simon Sandstone potassic diagenesis diagenesis over a wide wide area area of of the themid-continent mid-continent [Duffin, [Duffin, Sandstonehas hasbeen beenmodified modifiedby by potassic 1989]. 19891.The Theauthigenic authigenicpotassic potassicminerals mineralsare areK-feldspar K-feldsparand andillite-rich illite-richmixed-layer mixed-layerillite-smectite illite-smectite(ItS). (11s). The TheK-feldspar K-feldsparoccurs occursprincipally principally as asaareplacement replacementofofprimary primaryigneous igneousfeldspar, feldspar,and andthe theI/S 11smay may be be chiefly chieflyaareaction reactionproduct productofofkaolinite kaolinitewith withpotassic potassicfluids. fluids. Potassic Potassic alteration alteration of ofgranite graniteisisexhibited exhibited atatStop StopI 1(Chippewa (ChippewaFalls) Falls)and andStops Stops3 3and and4 4(Neillsville). (Neillsville).Authigenic AuthigenicK-feldspar K-feldsparisisalso alsowidespread widespread ininthe theMt. Mt.Simon SimonSandstone, Sandstone,and andauthigenic authigenicK-feldspar K-feldsparfrom fromthe theIllinois IllinoisBasin Basinhas hasgiven givenaaK-Ar K-Ardate date of of394±6 39426Ma Ma[Duffin [Duffinetetal., al.,1989]. 19891.Dates Datesofof390-400 390-400Ma Ma have have been been obtained obtained from fromthe theauthigenic authigenic K-feldspar 19881,suggesting suggesting aawidespread widespread K-feldspar of of Ordovician Ordovician tuffs tuffs of ofMinnesota Minnesotaand andIowa Iowa[Hay [HayetetaL, al.,1988], K-feldspar K-feldspar episode episode in in the theearly earlyDevonian. Devonian. Basinal Basinal brines brines have have been been postulated postulatedfor forthe theK-feldspar K-feldspar episode, and oxygen-isotopic data suggest that the K-feldspar formed at elevated episode, and oxygen-isotopic suggest the K-feldspar formed at elevated temperatures. temperatures. Illitization Illitizationepisodes episodesatat350-375 350-375Ma Ma(late (lateDevonian-early Devonian-earlyMississippian) Mississippian)and and250-275 250-275Ma Ma (Permian) (Permian) have havebeen beendocumented documentedbybyK-Ar K-Ardating datingofofI/S 11sininOrdovician Ordoviciantuffs tuffsand andthe theMt. Mt.Simon SimonSandstone Sandstone[Hay [Hay al.,1988; 1988,Duffin Duffinetetal.,al.,19891. 19891. etetal., 34 34 �The important implications for for the the lead-zinc lead-zincmineralization mineralizationin inthe theUpper Upper The K-feldspar event event may have important Valley.Lead Lead isotope isotope data for some Upper Mississippi Mississippi Valley. some Upper Mississippi Valley ores reveal Pb-leaching Pb-leaching event event early Devonian Devonian time [Doe al., 1983]. 19831. The similar age of the potassic diagenesis suggests at possibly early [Doe et et al., link between between the hydrothermal a possible possible link hydrothermal event and the the Pb-Zn Pb-Zn mineralization. mineralization. Duffin Duffin et et al. al. [1989] [I9891 suggested that the fluids in the basal sandstone aquifers could have interacted with the Precambrian the fluids basal Precambrian basement and the paleosols. paleosols. The The nature of the Precambrian-Cambrian granitic basement Precambrian-Cambrian surface, thickness and distribution of of the the paleosols, and the the fracture pattern pattern of the distribution paleosols, and the PG-C PG-6 surface surface could could have have played played an important role in guiding the fluid flow and in the ore mineralization. guiding ore mineralization. Late Proterozoic Proterozoic to to Late LateCambrian Cambrian also also represents represents aatime time of of substantial substantial latitudinal latitudinal migration migration and and climatic changesofof the the paleocontinent. Paleomagneticevidence evidenceshows showsthat thatthe thecenter center of of the climatic changes paleocontinent. Paleomagnetic paleocontinent must must be located at high latitudes latitudes during during the the Late Proterozoic and at equator paleocontinent equator during during the Late Cambrian [e.g. Irving, 1979; Van der Voo, 1981J. Late Keweenawan age glacial deposits Late Cambrian [e.g. living, 1979; der Voo, 19811. Late Keweenawan age glacial deposits in in Lake Superior area are also evidence of continental are also evidence of continental glaciation glaciation during the late Proterozoic Proterozoic [Murray, [Murray, was relatively relativelyquiet quiet in in this this part part of the 19551. Despite the large large horizontal horizontal motions, motions, tectonic tectonic activity activity was 1955]. paleocontinent and and was was represented representedmainly mainly by by formations formations of gentle arches arches and and highlands. highlands. Why Why was was there such a long manage long interval of apparent apparent lack lack of tectonogenesis? tectonogenesis? How did paleozoic formations manage to maintain an almost perfect horizontality? What was was the the geometry geometry of of the the epeirogenic epeirogenic blocks? blocks? How did the drastic climatic changes changes and continental glaciation affect the morphological did morphological development of the Precambrian and the paleosols? paleosols? We We may may have to resolve resolve to to geophysical geophysical means to to answer answer Precambrian surface surface ancj some of these questions. However, field observations can can undoubtedly undoubtedly provide provide important important constraints and tests on on geophysical geophysical models and and hypotheses. hypotheses. We have outlined above several questions related to the the Precambrian-Cambrian Precambrian-Cambrian unconformity unconformity in the mid-continent. The traditional traditional focus focusof of the the Institute mid-continent. The Institute on Lake Lake Superior Superior Geology Geology has has been been geology and and ore ore mineralization. mineralization. ItIt isisour our hope hope that this field trip to the PC-C Precambrian geology PG- boundary outcrops in western Wisconsin and encourage research outcrops Wisconsin could could promote promote discussion discussion and research on on Paleozoic Paleozoic geology of of the Lake Superior geology Superior region. region. PRECAMBRIAN TERRANES TERRANES Numerous papers papers on the Precambrian of the the Lake Superior region have been published Numerous Precambrian geology of published in recent years. The correlation of the Precambrian rock sequences in in the Lake Superior area is years. The is best summarized in three U.S.G.S. Denison et al. U.S.G.S. professional papers by Morey and Van Schmus Schmus [1988], Denison summarized [1984], and and Harrison and Peterman Peterman [1984]. [1984]. The The most most comprehensive descriptions descriptions of of the thePrecambrian Precambrian outcrops in west-central Wisconsin Wisconsin are are given given in in two two field field trip trip guidebooks guidebooks by by Myers Myers et e tat. al.[1980] [I9801and and Maass and Sims Sims et al. [1989] Maass and Van v a n Schmus Schmus [1980]. [1980]. LaBerge and Myers Myers [1984], [1984], and [I9891 presented two two different syntheses on the the Precambrian Precambrian magmatic magmatic terranes terranes in in west-central west-central Wisconsin. Wisconsin. - identifed two LaBerge and and Myers Myers [19841 [I9841 identified two major major Based on structure structure and and metamorphic metamorphic facies, facies, LaBerge Proterozoic metamorphic sequences in in west-central west-central Wisconsin: Wisconsin: a younger younger greenschist greenschist facies facies caiccalcalkaline sequence showing northeasterly trending fold-axes alkaline fold-axes and an older amphibolite-facies amphibolite-facies quartzfeldspathic gneiss and and amphibolites. amphibolites. The The spatial extents of the feldspathic gneiss the two two Proterozoic Proterozoicsuccessions successionsroughly roughly coincide with with the the tectonostratigraphic terranes postulated et at. The latter model, al. [1989]. [1989]. The model, coincide tectonostratigraphic terranes postulated by Sims Sims et however, contends contends that the two early Proterozoic Proterozoic terranes are separate separate entities. The The Eau Eau Pleine Pleine Shear Shear Zone between between Ladysmith Ladysmith and Mosinee that separates separates the the Marshfield Marshfield tectonostratigraphic terrane terrane inin the south from Terrane in in the north from the the Pembine-Wausau Pembine-Wausau Terrane north probably probably represents the paleosuture paleosuture between the two Terrane supposedly contains maGc matic to two terranes terranes [Sims [Sims et et a!., al., 1989]. 19891. The Marshfield Terrane supposedly contains [elsie volcanicsequences sequencesthat that formed formedon on an an Archean Archean basement. basement. All All the the field field stops stops on on this this trip are felsic volcanic located in the the Marshuield Marshfield Terrane. 35 �South South of of the thetown townNeillsville Neillsville near near the theBlack BlackRfrer, River,Precambrian Precambrianbedrock bedrock consists consists primarily primarily of Archean 19741. Archean gneissic gneissic rocks and early early Proterozoic metamorphic metamorphic and and plutonic plutonic rocks rocks [Myers [Myers et et al., al., 1974]. At At Lake LakeArbutus Arbutusnear nearHatfield, Hatfield,the thesub-Cambrian sub-Cambrianconsists consistsof of high high grade grade metamorphic metamorphic rocks rocks or or gneiss gneiss and and migmatite migmatite (Stop (Stop 5). 5). The The principal principal rock rock types types are are an an interlayered interlayered sequence sequence of of quartzo-feldspathic quartzo-feldspathic gneiss Schmiis, 1980]. 19801. Uranium-lead dating dating on on two two gneiss gneiss gneiss and and amphibolite amphibolite complex complex [Maass maass and and Van Van Schmus, specimens specimens has has yielded yielded ages agesof of 2.5 2 5 and and 2.8 2.8 Ga Ga [Sims [Sims et et al., al., 1989]. 19891. No Archean rocks are known north north of In the theChippewa ChippewaValley Valley area, area,layered layered amphibolite amphibolite and and feldspathic feldspathic gneiss gneiss form the the core core ofNeillsville. Neillsville. In of Recent zircon dating of the the eastward eastward plunging plunging Penokean Penokeanorogen orogen[Myers [Myerset et al., al., 19801. 19801. Recent dating has has yielded yielded an an age of 1835±10 m.y. [Sims et aL, 1989]. age of 1835±1m.y. [Sims et al., 19891. In In both both Archean Archean and andProterozoic Proterozoicrocks, rocks,cataclasis cataclasis played played a major major role in in the the metamorphism metamorphism and and deformation deformation throughout throughoutthe theregion. region.At Atleast leasttwo twogenerations generationsofoffold folddeformation deformationand andshearing shearing can can be observed in the Archean feldspathic gneiss exposed below Lake Arbutus Dam be observed in the Archean feldspathic gneiss exposed below Lake Arbutus Dam [Maass [Maass and and Van Van Schmus, 19801. In In the theChippewa Chippewaamphibolite amphibolitecomplex, complex,cataclasis cataclasis is is manifested manifested by by development development of of Schmus, 1980]. interlensing interlensingfoliation, foliation,transposition transpositionofoforiginally originallydiscordant discordant structures structuressuch suchas asdikes dikes and and xenoliths, xenoliths,and and transposition The amphibolite terrane transposition of offold foldfragments fragments into intotectonic tectonicxenoliths xenoliths [Myers [Myers et et al., al., 19801. 19801. The isis flanked provinces that that are less deformed and metamorphosed. the flanked by by volcanic-sedimentary provinces the nature nature of of the thecontact contactbetween betweenthe theamphibolite amphiboliteterrane terraneand andthe thevolcanic-sedimentary volcanic-sedimentaryterrane terraneisisuncertain. uncertain. Both Both the theArchean Archeanand andProterozoic Proterozoicterranes terraneswere weresynkinematically synkinematicallyintruded intrudedby bytonalitic tonaliticand andgabbro gabbro plutons plutons between between1880 1880and and1820 1820m.y. my. [Sims [Simset etal., al., 1989]. 19891.In In many many locations, locations, such such as as Lake LakeWissota, Wissota, Little Little Falls, Falls, and and Neillsville, Neillsville, rocks that belong belong to to the the amphibolite amphibolite complex complex are present present in ingenerally generally foliated plutons as xenoliths. foliated plutons as xenoliths. Late LatePrecambrian Precambriandikes dikes of of the theKeweenawan Keweenawan age agecut cutall allthe theother otherrocks rockswith withstrong strongdiscordance. discordance. Most Most Keweenawan-age Keweenawan-age dikes dikes have have an an ENE ENEstrike. strike.Prolonged Prolongedpre-intrusion pre-intrusionerosion erosionisisevident evidentsince since the themafic maficdikes dikes often oftencontain containchilled chilledmargins margins indicative indicative of intrusion at shallow depth and high thermal thermal gradient 19801. Two Two sets of dike dike orientation orientation can can be beobserved. observed. gradientacross across the thedike dikemargins margins[Myers [Myerset etal., al., 1980]. Paleomagnetic Paleomagneticresults resultsfrom fromcentral centralWisconsin Wisconsindike dikeswarms swarmsreveal reveal episodic episodic dike dike intrusions intrusions during duringthe the Keweenawan Proceedings]. Keweenawan event event [Chan, [Chan,Part Part11ofofProceedings]. PRECAMBRIAN-CAMBRIAN PRECAMBRIAN-CAMBRIAN UNCONFORMITY UNCONFORMITY The ThePC-C PC-â boundary boundary isisrepresented representedby byaahighly highlyvariable variable surface surface in in the themid-continent mid-continent area. area. The The morphotectonic characteristics of basement surface in the Midwest were described by Rudman et morphotectonic characteristics of basement surface in the Midwest were described by Rudman etal. al. [1965] surface forms [I9651and and Thwaites Thwaites[1980]. [1980].In west-central Wisconsin, Wisconsin, the the PC-C PC-€surfa forms an an extensive planation planation surface degree.Archean Areheaniron ironformations formationsand andProterozoic Proterozoicquartzites quartzites surfacewith withaaregional regional dip dip of of less less than than I1degree. form formisolated isolatedmonadnocks monadnocks on onthe thepeneplain. peneplain.Some Someofofthese thesemonadnocks monadnockswere wereseveral several hundred hundred feet feet ininelevation. elevation.The Thepeneplain peneplainwas wasmantled mantledbybyaalayer layerofofpaleosols paleosolsasasmuch muchasasseveral severalhundred hundredfeet feetthick thick [Cummings 19801.In Insome someareas, areas,Cambrian Cambrianrocks rocks directly directly rest rest upon upon barren, barren,moderately moderately [Cummingsand andScrivner, Scrivner,1980]. weathered weatheredPrecambrian Precambrianformations. formations. Considering Considering the the low low paleolatitude paleolatitude of of the thecontinent continentduring duringthe theCambrian, Cambrian, deep deepweathering weathering of of the the Precambrian Precambrian surface surfacemust must have haveoccurred occurredbefore beforethe theUpper UpperCambrian Cambriandeposition. deposition.The ThePrecambrian Precambrian basement, basement,however, however,shows showsvariable variable degree degreeof of weathering. weathering. Where WhereCambrian Cambrian formations formations are areinincontact contact with with Precambrian Precambrian plutonic plutonic rocks, rocks, the thePrecambrian Precambrian basement basement isisgenerally generallydeeply deeply saprolitized saprolitized toto kaolinite-rich 1980;Stop Stop1]. 11.In InNeillsville, Neillsville,for for example, example,spheroids spheroidsover over kaolinite-richsoils soils[Cummings [Cummingsand andScrivner, Scrivner,1980; 66mmacross acrossdeveloped developed in in weathered weatheredgranites; granites;Mt. Mt. Simon Simon sandstone sandstone and and conglomerate conglomeratetill fill the thewedges wedges among amongthe thespheroids spheroids[Stops [Stops33&&4]. 41. In Insome someareas areassuch suchas asBig BigFalls Falls in in Eau Eau Claire Claire County Countyor orRock Rock Dam 21,qambrian Cambriansandstones sandstonesrest rest upon upon Proterozoic Proterozoicamphiholite amphiboliteand and Dam ininJackson JacksonCounty CountyIStop [Stop2], metarhyolites that are only partially weathered. In the Jackson County Iron Mine, Upper Cambrian metarhyolites that are only partially weathered. In the Jackson County Iron Mine, Upper Cambrian Mt. deposited Mt.Simon Simonand andEau EauClaire Claireformations formationsare arerepresggted representedby byangular angularbreccia brecciaand andsandstones sandstonesdeposited �on on the theslopes slopesof of the theiron ironformation formationmonadnock monadnock [Stop [Stop7]. 71. The The variable variable degree degree of of weathering weathering of the the PC-C PC-â contact contact has has raised raised questions questions about the the timing timing of the PC-surfacewas was already already a gentle gentle and and smooth smooth the planation planation process. process. ItItisisunquestionable unquestionable that thatthe thePC-surface surface surface with with isolated isolated monadnocks monadnocks by by Late LateCambrian Cambrian time. time. The Thechilled chilledmargins margins of mafic mafic dikes indicate prolonged prolonged erosion erosion even even during during the theProterozoic Proterozoic time. time. The Therelatively relativelyunweathered unweathered Precambrian Precambrian outcrops in some localities, however, suggest relatively immature weathering or intense outcrops in some localities, relatively immature weathering or intense erosion and removal removal of weathered material material during during the the transgression transgression event. event. Budel Budel [1957] [I957 presented aa model model on on the theformation formationofofpeneplains peneplainswhich whichconsists consistsof of two twoconcurrently concurrentlyactive active leveling leveling surfaces: surfaces: an an exposed exposed wash wash surface at the top top of of the the deep deepsaprolite saproliteand andaaburied buried basal basal surface surface of of weathering at the the bottom bottom in contact with unweathered bedrock. The limited weathering in some sub-Cambrian profiles suggests in contact with unweathered bedrock. The limited weathering in some sub-Cambrian profiles suggests aa very very late-stage late-stage development of the peneplain peneplain or or aa rapid rapiddenudation denudationof ofthe thewash washsurface surfaceshprtly shortly before before the the deposition deposition of of the the Mt. Mt. Simon Simon Sandstone. Sandstone. The latter latter theory theory points points to to the thepossibility possibility of Cambrian Cambrian uplift or or eustatic eustatic movement movement before before the theDreisbachian Dreisbachian transgression. transgression. UPPER UPPERCAMBRIAN CAMBRIAN MOUNT MOUNTSIMON SIMONFORMATION FORMATION The The sediment sediment above abovethe theunconformity unconformity consists consists largely largely of Upper Cambrian Cambrian Mt. Mt. Simon Simon formation formation deposited deposited on onthe themid-continent mid-continentregion regionof ofNorth NorthAmerica Americaduring duringthe theDreisbachian Dreisbachian transgression. transgression.The The Mount Mount Simon Simon formation formation isis aafine-coarse-grained, fine-coarse-grained, poorly poorly sorted, sorted, quartz quartz arenite arenite with with aalocal localbasal basal conglomerate. conglomerate. In Inthe theUpper UpperMississippi MississippiValley, Valley, the thethickness thicknessof of the theformation formationvaries variesfrom from180 180toto40 40 meters. meters. Lochman-Balk Lochman-Balk [1971] [I9711 gave aa summary summary on the the Cambrian Cambrian paleogeography paleogeography and andpaleoecology paleoecology of of the theNorth NorthAmerica Americacraton. craton.Previous Previousstudies studiesbybyThwaites Thwaites[1923], [1923],Ostrom Ostrom[1964, [l%4,1966, 1 x 6 , 1967], 19671, Asthana Asthana [1969], [1%9], and and Ostrom Ostrom [19881 [I9881 have outlined outlined the the general generalstratigraphy stratigraphy and andpaleodepositional paleodepositional environment environment of ofthe thelocal localsequences sequencesininwest-central west-centralWisconsin. Wisconsin. - In In the theChippewa Chippewa Valley Valley area, area, the the lower lower part part of of the theMount MountSimon Simonformation formation isis aacoarse-grained. coarse-grained, thick-bedded sandstones. The The relief relief of the thick-bedded quartz sandstone and and conglomeratic conglomeratic sandstones. the deposition deposition was was probably The presence presence of of trace tracefossils fossils probablyvery very shallow; sedimentary channels are less than 11 meter deep. The (rusophycus?), (rusophycus?), and planar planar and and bipolar bipolar cross-bedding cross-bedding suggest suggest aa littoral littoral or orshallow shallowmarine marine tidal tidalflat flat environment environment of deposition deposition for the lower lower part of the the formation. formation. The upper part part of of the theMt. Mt. Simon Simon formation formationcontains containsfeldspathic feldspathicsandstone sandstonewith withsmall-scale small-scaleripple ripplebedding, bedding,brachiopod brachiopodfragments, fragments,and and worm worm trails trails (planolites). (planolites). Iron-oxide Iron-oxide concretions concretions are arecommonly commonly present. Some Some concretions concretions are areas aslarge large as as1.5 1.5 cm cm in in diameter. diameter. The Thegrain grainsize sizedata dataobtained obtainedby byAsthana Asthana[1969] [1%9] indicate indicatean anunimodal unimodalgrain grainsize size in in the thelower lowerpart partofofMt. Mt.Simon, Simon,aabimodal bimodaldistribution distribution in in the the middle middle and and the the upper upper parts. parts. The Thegrain grain size fining upward upward sequence. sequence.The The upper upper part part of the size distribution distribution shows shows a generally generally fining the formation formation represents subtidalshallow shallowmarine marinedeposition. deposition. The Thepresence presenceofof10-20 10-20mm mmdiameter diameteriron-oxide iron-oxide represents aasubtidal concretions concretions and andhorizontal horizontalworm worm trails trails suggest suggest a much much broader transgression transgression toward the top top of of Mt. Mt. Simon Simon Formation. Formation. Presence Presence of of brachiopods brachiopods and and ripple ripple bedding bedding in in the the upper upper part part of of Mt. Mt.Simon Simon Formation Formationisisdiagnostic diagnostic of of aashallow-marine shallow-marine subtidal subtidal deposition, deposition, probably probably above the the wave wave base base atat aa depth depthofof10-15 10-15m. m. The Thepart partofofthe thesection sectioncontaining containingiron-oxide iron-oxideconcretions concretionsmay mayrepresent representa aslightly slightly deeper deeperwater waterthan thanthe thesandstones sandstonescontaining containingbrachiopod brachiopodfragments. fragments. There Thereare areaafew fewquestions questionsconcerning concerning the theorigin origin and and source source of of the thedetrital detritalgrains grainsand andthe the age age of ol' the thediagenesis. diagenesis. Asthana Asthana [1968] [I9681 reported reported aalarge largerange rangeininK-feldspar K-feldspar content contentininthe theformation. formation.Qi Qiand and Chan Chan have have also alsoidentified identified several several lithotypes lithotypes in in the the formation formation [Suppl. [Suppl. notes notes ininthis thisfield field guidej. guide]. The The age age of of the thepotassic potassicdiagenesis diagenesis in in the theMt. Mt.Simon Simonformation formation in in Wisconsin Wisconsin is is still still uncertain. uncertain. Further Further mineralogical and stable isotope mineralogical and isotope studies studies will will be conducive conducive to our understanding understanding of of the the sediment sediment source, source,the thediagenetic diageneticenvironment, environment, and and the theregional regionaltectonics tectonics atatthe thetime timeofofdeposition. deposition. 37 �I Field Field Trip Trip 2: 2: Route Route Map Map and andStop StopDescriptions Descriptions Eagleton I 'limFal Tilde 'I .1 _ ___ STOP iJ4" LYE fl° * :P'J --___ Icona / Fall ) Cre - I 7 IWillard] ___ r RJ'E t2r( — o r usselI r / — eon Falls 121 ________ ef 'L 4STOP4 Faircj,Id TThb ":ii 5 Gran vile orth leld, cr — 32! ork Al rnacente. 'i1 -' - \?iatfl&d 7 Eli. " n I Price ,- indepen / / Eleva L t - — so0 Loyal ugusta jF — ] I N- — ___ H T Grenwood - L Bracke C:.., STOP 2 '- 1 // _- Irni I — 91 Ei1t$çn : iii — 'l - frhcrp LINE _Lfl-iNYL -- - ______ — — —— SEaL, TATE PARK oDwaF I - STOP 5 STOP. H eha a I -5 1./ :I — rcadia — / 20 st r4oAR I — Fork (t0 • Era in N 1L1J P I 38 ALLL_, BLAO+L STATE NORTH �STOP 1: GEOLOGY OF OF IRVINE IRVINEPARK, PARK, CHIPPEWA CHIPPEWA FALLS, FALLS, WISCONSIN Location: NW1/4 NW1/4 SW1/4 Section Section 31 31 T29N T29N R8W, R8W; Chippewa Chippewa Falls Falls 15' Quadrangle Location: Quadrangle Summary of of Features: Features: Mt. Simon Simon basal conglomerate on o n Precambrian saprolitized saprolitized granite Summary is Middle trondhjemite showing Middle Proterozoic Proterozoic biotite trondhjemite showing spheroidal spheroidal and saprolitic saprolitic weathering weathering is unconformably overlain overlain by by feldspathic feldspathicconglomerate conglomerateand andsandstone sandstoneof of the the Mt. Mt. Simon Simon Sandstone Sandstone of of unconformably Late Cambrian age. The The configuration configuration of of the thePrecambrian Precambriansurface surfacewas was mapped mappedby by Thwaites Thwaites [1957]. [1957]. 19871. The Precambrian-Cambrian Precambrian-Cambrianunconformity unconformityatatIrvine I ~ nPark Park e isisdescribed describedinindetail detailby byOstrom Ostrom[1978, [1978,1987]. The Precambrian composedofofaadeeply deeplysaprolitized saprolitizedtrondhjemite. trondhjemite.Myers MyersetetaL al. Precambrian at at Irvine I ~ nPark Park e isiscomposed [1980] reported that the [I9801 reported the trondhjemite trondhjemiteat atIrvine IrvinePark Parkisis probably probably part part of of aa larger larger granitic granitic pluton which occupies Valley between between Eau Eau Claire Claire and and Jim Jim Falls Falls and and that it is is part part of of aa complex complex occupies the Chippewa Chippewa Valley WNW-trending granite-amphibolite complex of Middle Proterozoic age. The trondhjemite WNW-trending granite-amphibolite complex of Middle Proterozoic age. The trondhjemite at at Chippewa [I9801 at 1,840±15 1,840515m.y. m.y. Chippewa Falls was dated by Van Schmus Schmus [1980] Saprolite is aa "soft, 'soft, earthy, clarrich, clay-rich,thoroughly thoroughly decomposed decomposed rock rock formed formed ininplace placeby bychemical chemical [AOl, 1972]. 19721. ItIt is is characteristic of areas areas of prolonged prolonged weathering of igneous and metamorphic rocks" [AGI, tropical Saprolites in in thc the tropical to subtropical weathering weathering on a granitoid granitoid bedrock bedrock surface of low low relief. relief. Saprolites Piedmont of United States attain aa thickness thickness of over over 100 100 rn. m. The saprolite at at this this outcrop outcrop Piedmont Province of contains high high clay clay content. content. The feldspar contains feldspar and quartz grains grains tend to to be bequite quiteequidimensional equidimensional and and possess sharp edges edges and corners. The saprolite altered upward upward until until at the possess sharp saprolite becomes becomes increasingly increasingly altered the N 7 (I I / 39 A �unconformity. unconformity. It It isis composed composed mostly mostly of quartz, quartz, clay clay minerals and chlorite. Was the the saprolite saproliteformed formed before before or orafter afterdeposition depositionofofMt. Mt.Simon SimonSandstone? Sandstone?Evidence Evidencesuggests suggests that that most most of of the theweathering weathering and and saprolitization saprolitization preceded preceded Mt. Mt. Simon Simon Sandstone Sandstone deposition, deposition, although although there thereisis also also evidence of later modification. modification. A A comparison comparison of of the theclay claymineralogy, mineralogy, heavy heavy mineralogy, mineralogy, and clast clast texture texture classification classification in the the saprolite saprolite and andoverlying overlying sandstone sandstone reveals reveals aa strong strong provenance provenance relationship relationship between between the thetwo twounits. units. Cummings indicated that that most most of the clasts Cummings and Scrivner Scrivner [1980] [I9801 indicated clasts over 1.0 1.0 mm mm in in the the saprolite saprolite are are composite whereas the coarser size fraction in the composite grains grains composed composed of quartz and and K-feldspar, K-feldspar, whereas the Mt. Mt. Simon Simon Sandstone Sandstone isis composed composed predominantly predominantly of of quartz quartzgrains. grains. The Theclay clayminerals, minerals,according according to to Cummings [1980], are 80-90% kaolinite and 10-20% 10-20% illite and vermiculite, and maroon maroon Cummings and Scrivner Scrivner [1980], color color of of the thesaprolite saprolite atatthis thislocality locality isisaaresult resultofofmore morerecent recentweathering weatheringofofchlorite. chlorite.Reddish Reddish spheroids spheroids of of altered altered trondhjemite trondhjemite are arefound foundininthe thelower lowerpart partofofthe thesaprolite. saprolite.Plagioclase Plagioclaseand and part part of of the themicrocline microclineare arereplaced replacedby byK-feldspar K-feldsparand andlesser lesserphyllosilicate. phyllosilicate. This This isis an an excellent excellent example example of the theregional regionalpotassic potassicalteration alterationofofPrecambrian Precambrianrocks rocksbelow belowthe theSub-Cambrian Sub-Cambrianunconformity. unconformity. The TheMt. Mt.Simon SimonSandstone Sandstonethickens thickensfrom fromabout about35 35mmatatChippewa ChippewaFalls Fallstotoabout about270 270 m m in in southern southern Wisconsin Wisconsin [Asthana, 1969]. 19691. The Thenorthernmost northernmost exposures exposures of of this this formation formation are are near near Ladysmith Ladysmithand and Conrath, Conrath, Wisconsin, Wisconsin, and and probably probably represent represent the theapproximate approximateoriginal originallimit limit of of Mt. Mt. Simon Simon deposition deposition in in this thisregion. region. Ostrom Ostrom [1964], [1964], in in aadetailed detailedregional regional synthesis synthesis of of the theCambrian Cambrian stratigraphy stratigraphy of of Wisconsin [1964], concluded that the Mt. Simon Sandstone formed in that the Mt. Simon Sandstone formed in aa marine marine littoral littoral and and nearshore nearshore Wisconsin 119641, shelf shelf environment environmentby bya aslowly slowlytransgressing transgressing sea, sea, which which migrated migrated S&NW SE-NW over over aa deeply deeply eroded eroded Precambrian Precambriansurface. surface. ItIthas hasbeen beensuggested suggestedthat thatthe thebasal basalconglomeratic conglomeratic sandstones sandstonesof of the theCambrian Cambrian sequence sequencewere werebest bestinterpreted interpretedasassubtidal subtidalshelf shelforortidal-channel tidal-channeldeposits. deposits. The TheMt. Mt. Simon-Eau Simon-EauClaire Claire sequence sequence was was regarded regarded as asprogradational. progradational. Driese Driese [1979], [1979], based based on on sedimentary sedimentary structures structures and and paleontological evidence, argued that the Mt. Simon Sandstone is "largely progradational, shoalingpaleontological evidence, argued that the Mt. Simon Sandstone is "largely progradational, shoalingand andfining-upward fining-upward tidal tidal sequence." sequence." According According to to Driese Driese [1979] [I9791the the sandstones sandstones atatIrving IrvingPark Parkbelong belong to tothe thelower lowerand andmiddle middleunits unitsofofthe theMt. Mt.Simon SimonSandstone. Sandstone. Asthana 18%feldspar feldspar of of which which 81% 81% isis Asthana [1969] [I9691 showed showed that that the theMt. Mt.Simon SimonSandstone Sandstone averages averages 18% K-feldspar; K-feldspar; the feldspar feldspar content ranges ranges from from 2.85 2.85 to to 40.07% 40.07% and and that that its itsabundance abundance decreases decreases generally generallyupward upward in in the theformation. formation.Authigenic Authigenicorthoclase orthoclaseoccurs occurscommonly commonly as as rhombic rhombicovergrowths overgrowths on ondetrital detritalgrains. grains.AApetrographic petrographicdescription description of ofseveral severalspecimens specimens of of the theMt. Mt.Simon Simonformation formationisis given 11.Cummings Cummingsand andScrivner Scrivner[1980] [I9801compared compared givenin inthe thesupplementary supplementarysection section[Qi [Qiand andChan, Chan,Suppl. Suppl.1]. the themineralogy mineralogyand and texture textureof ofthe theMt. Mt.Simon SimonSandstone SandstoneatatIrvine IrvinePark Parkwith withthe theunderlying underlyingsaprolite, saprolite, and andconcluded concludedthat thatthe thesilt siltand andclay clayfractions fractionsofofboth bothshow showconsiderable considerablesimilarities. similarities.The Thesaprolitized saprolitized trondhjemite trondhjemitecould couldhave havebeen beenaasource sourceofofclasts clastsfor forthe theMt. Mt.Simon SimonSandstone. Sandstone.The Thecoarser coarserfractions fractions of the Mt. Simon Formation are devoid of the composite quartz-feldspar grains characteristic of the Mt. Simon Formation are devoid of the composite quartz-feldspar grains characteristicof ofthe the underlying abundant epidote epidote and and garnet not found underlying saprolite. saprolite. The sandstone sandstone also contains contains abundant found in in the the underlying underlying saprolite. saprolite. These These minerals, minerals, however, however, are abundant abundant in in the theamphibolites amphiholites nearby nearby (e.g. (e.g. Jim Jim Falls) Falls)and andcould couldhave havebeen beenderived derivedfrom fromthem. them. Based Based on onthe thework workofofmany manygeologists, geologists, ititappears appearsthat thatthe thePrecambrian Precambrianbasement basement was was deeply deeply weathered weatheredtotoform forma asaprolite saproliteininLate LatePrecambrian Precambriantime time(between (between900 900and and500 500m.y.). m.y.). The Thesaprolite saprolite was was locally locally preserved preserved during during slow slow transgression transgression of the the Late LateCambrian Cambrian seas seasand anddeposition depositiono1 ofthe the saprolite saproliteresulted resulted inintheir theirincorporation incorporationasasinterstitial interstitial materials materials in in the the Mt. Mt. Simon Simon Sandstone. Sandstone. With With more morerecent recentexposure exposureofofthe thelower lowerPaleozoic Paleozoicformations formationsto toground groundwater watercirculation, circulation, some some alteration alteration ofofchlorite chloritetotoiron ironoxides oxidesoccurred. occurred. 40 �\PVNE r. PARK PAPK C •ictYQ CT, CWPPEWA FALLS FALLS Ct-\tPPEWA C I -g 1^ . C 0 6 —I Cl) 7; .t--.tr. F r e s h , spheroidally spheroidally Fresh, weathered w e a t h e r e d pink p i n k granite granite 1840 1840 Ma Ka "gruss' + Duncan Cr. of Duncan Cr. rcNNFoRMITY Red and green saprolite (paleo— so 1?) Fresh granite I—I SIGNIFICANCE Corners C o r n e r s weather weather SIGNIFICANCE first first If If this t h i s granite granite is is composed composed of 30% quartz, quartz, 70% 75%feldspar, feldspar, which which weathered toclay c l a ywhich wtaich was was washed -bed weathered to away away (sedimentary (sedimentary "winowi.ng"). "winowing"). calcalrelatively relatively culate culate the t h ethiciciess thickness of of granite granite fresh f r e s hrock rock needed needed to to produce produce the t h e approx. appmx. 600' 600' of ofPa.leozoic Paleoznic quartz quartzsandstones sandstonesfound found in in the theregion regionsouthwest southwest of of Eau Eau Claire. Chire. of a C —4 0 v-I C) —I I) horizontal joint SPHEROIDALWEATHERI WEATHERING SPHEROIDAL MG unconformity at Fig. 1. 1. Precambrian-Cambrian Precambrian-Cambrian unconformity at Irvine IrvinePark. Park. Fig. 41 �STOP2:2:PRECAMBRI PRECAMBRIAN-CAMBRIAN CONTACT A T ROCK DAM, HAY C R E E K STOP -CAMBRIAN CONTACT AT ROCK DAM, HAY CREEK Location:Hay H a yCreek, Creek,0.15 0.15mile miledownstream downstream from Rock Dam; SE 114 NW 114 Sec 15 Location: from Rock Dam; SE 1/4 NW 1/4 Sec 15 T26N R4W; Fairchild 15' Quadrangle T26N R4W; Fairchild 15' Quadrangle Summary of of Features: Features: Mt. Mt. Simon basal conglomerate on partly weathered Summary Simon basal conglomerate on partly weathered Precambrian rnetarhyolite Precambrian metarhyolite ConglomeraticMt. Mt.Simon SimonSandstone Sandstoneoverlies overlies unconformably Penokean-age metamorphic rocks. Conglomeratic unconformably Penokean-age rocks. [I9801 contended contendedthat thatthe thePrecambrian Precambrian unit is a metarhyo1ite:a felsicmetamorphic mylonite containing Myersete taL al.[19801 Myers unit is a metarhyolite:a felsic mylonite containing lenticularclusters clustersofofstrained strainedquartz quartzinin a very fine matrix of K-feldspar, quartz and muscovite. In thin lenticular a very fine matrix of K-feldspar, quartz and muscovite. In thin 1.0-2.5 mm long, with a coarse-grained core that grades section, the clusters of strained quartzare are1.0-2.5 section, the clusters of strained quartz mm long, with a coarse-grained core that grades 57%,quartz, 35%. muscovite, outwardinto intoa afine-grained fine-grainedmatrix. matrix.Estimated Estimatedcomposition composition is:K-feldspar K-feldspar outward is: quartz,crops 57%,phyllite muscovite, 35%,out 3%, magnetite 2%, and biotite, 1% [Myers et al., 19801. A muscovite-rich near the 3%, magnetite 2%, and biotite, 1% [Myers et al., 1980]. A muscovite-rich phyllite crops out near theis of Rock Dam. The rock is composed of K-feldspar, quartz, and muscovite. The foliation base base of Rock Dam. The rock is composed of K-feldspar, quartz, and muscovite. The foliation is N87W, 85N. 85N. Complementary Complementary joint joint sets sets atatNI8W, N18W,73E 73Eand and N77E. SS account for the bloc@ N87W, N77E, 8S account for the blocky appearance of the outcrops. appearance of the outcrops. Thebasal basalMt. Mt.Simon Simonisis a conglomeratic layer containing large pebbles of vein quartz and The a conglomeratic containing pebbles veinthequartz and metarhyolite. Some thepebbles pebbles are over alayer foot across. The large contact surfaceofwith underlying inetarhyolite. Some ofofthe are over a foot across. The contact surface with the underlying metarhyolite shows shows aalocal localrelief reliefofofabout about5 5 meters. The Precambrian rocks do not appear to be metarhyolite meters. The Precambrian rocks do not appear to be deeplyweathered weatheredininthis thisparticular particular outcrop. deeply outcrop. 'I ;sI 1/ - - -- L t TtfT, — -z \ i/Il 24 k / / - J104- — I / -_ -,ooer1 lIT 29 -. - - -. 25 -7 t -l\ -- H - 7 ------I -. '-- - - - - - -< -v f;c 42 �STOPS STOPS 33 & & 4: 4: SPHEROIDAL SPHEROIDALWEATHEIW4G WEATHERING IN NEILLSVILLE NEILLSVLLLE GRANITE GRANITE QUARRIES QUARRIES Location: Location: Stop S t o p 33 NW N W1/4 114NW N W1/4 114SEC SEC20 20T24N T 2 4 NR2W; R2W,Neillsville Neillsville 15' 15' Quadrangle Quadrangle Stop SE1/4 114SW S W1/4 114 SEC SEC 10 10 T24N T 2 4 N R2W; R 2 W ; Neillsville Neillsville 15' Quadrangle S t o p 44 SE Summary ThePrecambrian-Cambrian Precambrian-Cambrian boundary boundary displays displays a spectacular spectacular S u m m a r y of Features: The spheroidal weathering features in the Neillsville granite in two quarries spheroidal weathering features in t h e Neillsville in two quarries in in the the Neillsville Neillsville area. area. I The River Valley, Valley, isis aa Penokean Penokean pluton. A The NeilIsville Neillsville granite, located in the Black River A description description of of its petrography petrography and andcomposition composition isisgiven given by by Maass Maass and and Van Van Schmus Schmus[1980]. [1980]. Zircon Zircondating datingyields yields an an age the age age is is about 40 Ma older age 1875±25 1875±2 m.y. m.y. [Sims [Sims eett al., al., 1989]; 19891; the older than than other othersimilar similar Penokean Penokean plutons plutons in in the thearea. area.The Thegranite graniteisiscomposed composedofofsubequal subequalamounts amountsofofquartz, quartz,microcline, microcline, and and plagioclase plagioclase (An (An 26-28); 26-28); and and approximately approximately 2% biotite [Maass [Maass and Van Van Schmus, Schmus, 1980]. 19801. Fresh Fresh rock rock isis gray gray and altered altered rock rock isis pink, pink, both both because because of of pyrite pyrite weathering weatherins to to ferric ferric oxide oxide and and replacement replacement of of igneous feldspar by authigenic K-feldspar. A strong set of lineation trends N4SE and plunging 820 by authigenic K-feldspar. of lineation trends N45E and plunging 82O pervades pervades the granite. granite. The Thegranite granitecontains contains xenoliths xenoliths of mica mica schists schists which which display display at least least three three generations generations of of deformation. deformation. Two Two sets sets of crenulation form an oblique angle of about 30°. 30". A third third set of as the lineation in the granite. The northern of lineation lineation aligns aligns in the same same direction direction as lineation in northern end end of of the the quarry is a mixture of granite and granodiorite which contain similar structures. The nature of the quarry is a mixture of granite and granodiorite which contain similar structures. The of the contact contact between between the thetwo twounits unitsisisunknown. unknown. I r ejuvrue Mounds • . - I - . '5 - /O(j — _________ - J' 'O3 - - .6 - lB h ry 111 s - —= —. -—, 4PneVIeCr- :-- H - STOP4APr --r': -IV_AIL L 24 —- STOP3 19 ',.I1 - H 43 pJ N 2OJ ., '-I - Th\BMw8S -— 1,icliitv 00 —, - / -. — —— 79 I - - -: - - — h.r ihilije / 12 - 'e ' _6. ' £evai. I tI, / - ______________ '._-14 - / ' I._ K 21 H H- 2 �The granite isis exposed exposed in in several several old old quarries quarries atat Stop Stop 4. 4. In the The Neillsville Neillsville granite the largest largest quarry, the the sandstone sandstone on top top of ofthe thePQ-C PC-Âboundary boundary isisabout about10 10meters metersthick thickand andoverlain overlainby byrecent recentglacial glacial outwash. outwash. The spheroidally spheroidally weathered granite granite isis spectacularly spectacularly exposed exposed in this this quarry. The The PC-Q PC-â boundary meter across. across. The The granite granite boundary is is at at about about 1070' 1070'elevation. elevation. The The spheroids spheroids are are sometimes sometimes over 66 meter is over is identical identical to those those found found atatStop Stop3.3.Relatively Relativelyunweathered unweathered corestones corestonesranging ranging from from 11 m to over 66 m m have have been been isolated isolated by by zones zones of of intense intenseweathering weathering where where grus erus formed. formed. The The granite eranite shows shows a foliation foliation that that strikes strikesN45W ~ 4and and 5dips dips 30°SW. ~ 3WSW. A sub-planar s ~ b - ~ l a nfabric fabricin a r in the the grus strikes hN58W 5 8 and and ~ dips dips 16E[Nelson, [Nelson,19801. 19801. 16E In Inboth bothquarries, quarries,the thePrecambrian Precambriansurface surfaceweathers weathersinto intoaaclay-rich clay-richspheroidally spheroidally weathered weathered pinkish pinkish granite. and conglomerate conglomeratecan canbe be found found on on top top of of and and in in the the wedges wedges between between the the granite. Sandstone Sandstone and weathering weatheringspheroids. spheroids.The Thegranite/Mt. granitemt.Simon Simonunconformity unconformityhas hasaafew fewfeet feetofofrelief, relief,which whichfollows followsthe the tops tops of of the thegranite granitespheroidS, spheroids,and andcoarse coarsematerial materialhas hasfilled filled the thewedges wedges between between the thespheroids. spheroids. The The clasts clasts in in the thebasal basal conglomerate conglomerate are areentirely entirelyquartz quartzpebbles. pebbles. AAdacite dacitedike dikecut cutacross acrossthe theNeillsville Neillsville granite granite in in the thenorthern northernend endofofthe thequarry. quarry.The Thedike dikeisiscomposed composedofofquartz, quartz,oligoclase, oligoclase,biotite biotite and and minor recrystallization textures textures are arenearly nearly identical identical to to those those minor microcline. microcline. Microscopic deformation and and recrystallization in The weathering in the the granite graniteand andgranodiorite granodiorite[Maass [Maassand andVan VanSchmus, Schmus,19801. 19801. The weathering sequence sequencefor forminerals minerals in the theNeillsville Neillsville Granite Granitedetermined determinedby byNelson Nelson[1980, [1980,unpubl. unpubl. work] work] suggests suggests that that plagioclase plagioclase in in the the in saprolite saproliteisisweathered weatheredinto intoa aclay. clay.Biotite Biotitemica micaisissimilarly similarlyweathered weatheredby byhydrolysis hydrolysis to tochlorite. chlorite.IlliteIlliterich richI/S US of of diagenetic diagenetic origin origin is the the principal principal clay clay mineral mineral in the saprolite at Stop Stop 3. 3. Here HereK-feldspar K-feldspar replaces in pink pink bodies bodies of of granite granite within replaces primary primary microcline microcline and plagioclase plagioclase in within the saprolite. saprolite. In In the the quarry quarry at at Stop Stop4,4,exfoliation exfoliation sheets sheetsofofthe thespheroids spheroidsconsist consistlargely largely of of authigenic authigenic K-feldspar, K-feldspar, and and primary preprimary igneous igneous textures textures have have been beenlargely largely obliterated obliterated by by diagenetic diagenetic alteration alteration superimposed superimposedon on preMt. Simon weathering. Potassic alteration extends to the quarry floor in fractured area, —10 m below Mt. Simon alteration extends to the quarry floor in fractured area, -10 below the thesub-Cambrian sub-Cambrianunconformity. unconformity. The at the two before the deposition The weathering weathering and and saprolitization saprolitization at two outcrops outcrops occurred occurred before deposition of the the Mount Mount Simon Simon Sandstone. Sandstone. Uplift and erosion occurred after the the plutonic plutonic emplacement. The time of the theuplift upliftisisuncertain. uncertain. The Thepresence presenceofofcorestones corestonesnot notentirely entirelyconverted convertedtotogrus grussuggests suggestseither eitheranan immature immature weathering, weathering, which which implies aa short duration between the exposure exposure of of the thesurface surfaceand andthe the Dreisbachian Dreisbachian transgression, transgression, or denudation denudation of of substantial substantial portion portion of of the thesaprolite saproliteby byerosion, erosion,which which may may suggest suggest a pre-transgression pre-transgression uplift that led led to to rapid rapid erosion erosion of ofthe theweathered weatheredprofile. profile. 44 �w p-Il 1 P CD = CD CD p-f-) CD p ri- a 0- 1 9. CD (I) Fig. 3 Spheroidal weathering features in Neillsville quarry. 1 a -c 0) CD Z CD C — 00) C CD CD C B C a NJ C) U) :31 t r'r:r :r - f' r F Fig. 2 Basal conglomerate of Mount Simon Sandstone in Neillsville quarry. �.1 u-- - 1 7) Neillsville Granite-Sandstone Contact i—i 3 sKt'4ci'-iS •&or. pt.wkjrttpks. fl r r r' r"i — Z r- r steeply steeply west-plunging west-plunging lineation lineation weathered (75°) is spheroidally (75') is spheroidally weathered in 5-10 cm cm in concentric concentric layers layers 5-10 thick. The outermost rinds are thick. The outermost rinds are bleached; bleached; inner inner ones ones are are ironironquartz Cross-bedded stained. stained. Cross-bedded quartz sandstone sandstone of of the the Mt. Mt. Simon SimonFm. Em. deposited in the depression was was deposited in the depression between between the the spheroids. spheroids. (A) (A) and and SW-dipping surface (B) a steep, (B) a steep, SW-dipping surface of of one one spheroid spheroid isisoverlain overlain by by Mt. Simon Sandstone at (C). Mt. Simon Sandstone at (C). The The sandstone sandstone isis overlain overlain by by orange-brown cobble orange-brown cobble till till on on the the south south side side of of the the exposure. exposure. The The directly overlies till till directly overlies weathered weathered granite granite to to the the north. north. P€ Pâ granite granitegneiss gneisswith withstrong, strong, r- �STOP 5: 5: LAKE LAKEARBUTUS ARBUTUS DAM DAM Location: SE Location: SE 1/4 114 SEC SEC 3 T22N R3W, Hatfield 7½" 7%" Quadrangle Summary ooff Features: Weathered Summary Weathered Mt. Mt.Simon Simon Sandstone Sandstoneoverlying overlying Archean Archean gneisses. gneisses. In the on top of the Hatfield Hatfield and andLake LakeArbutus Arbutusarea, area,glacial glacial outwash outwash generally generally overlies overlies directly directly on ol' Precambrian rocks. Archean rocks are well exposed below the Uike Arbutus Dam. The Archean Precambrian rocks. Archean rocks well exposed below the Lake Arbutus Dam. The Archean rocks are interlayered interlayered scquence sequenceof of quartzo-feldspathic quartzo-feldspathicgneiss, gneiss, amphibole amphibole gneiss, and metarhyolite that that formed about 2.8 Thefeldspathic feldspathicgneiss gneissshows showsaagneissic gneissic 2.8 Ga G aago ago[Van [VanSchmus Schmusand andMaass, Maass,1980J. 19801.The microcline [Van [Van banding ranges from 0.1 to 3cm 3 cm thick thick and and contains contains principally principally quartz, plagioclase and microcline Schmus and Maass, 1980]. The rocks underwent at least two generations of fold deformation; the 19801. The generations of fold deformation; thefirst first one produced produced aa foliation foliationwhich which was was refolded refolded about aboutan aneasterly easterlyfold foldaxis axisplunging plunging atatabout about400. 40". were sheared to dikes intrude the gneissic The metavolcanics metavolcanics were to form form aa phyllonite. phyllonite. Several mafic dikes gneissic and a strong foliation, indicative of a probable phyllonites. Some Some of of the dikes phyllonites. dikes show astrong probable synkinematic synkinernatic origin origin. The boundary between the ft. the Mt. Mt. Simon Simon Sandstone and the Archean rocks rocks is present about about 400 400 ft. south of the covered by by talus, talus, but but could could be he located the Dam. Dam. The Theboundary, boundary, however, however, is is presently presently covered located to within within 15 feet. The upper 20 feet of of the the Archean Archean rocks rocks are are partially partially weathered. weathered. A A 6-10' 6-10' section of exposed oonn a talus Mt. Simon Simon is is exposed talus slope slope above above the the Archean Archean metavolcanics. metavolcanics. The sandstone sandstone is is deeply deeply weathered and crumbles easily in hand specimens, hut relict sedimentary structures like lamination and crumbles easily in hand specimens, but relict sedimentary structures like lamination On the lake side of the Lake Lake Arhutus Arbutus Dam, Dam,Mt. Mt.Simon Simon sandstone sandstone and cross bedding are still visible. visible. On is exposed at water level. is exposed level. ii STOP 6: HALLS HALLS CREEK 1/4 SEC 19 Location: NW SE 114 N W 1/4 114 SE 19 T22N R3W Summary ooff Features: Mt. Mt. Simon Simon conglomeritic conglomeritic sandstone over over Precambrian Precambrianmetavolcanics metavolcanics boundary isis exposed exposedalong alongaameander meanderabout about300' 300'from fromHwy H' E. E.The Theboundary boundary isis located located The PC-C PG- boundary at about 2' 2' above above the thewater waterlevel leveland andmay may be be covered covered by by aa thin thin layer layer of of gravel gravel and and talus. talus. The The Mt. Mt. Simon basal layer is a conglomeratic Simon basal conglomeratic sandstone. sandstone. The Precambrian Precambrian is is aa weathered weathered metavolcanics metavolcanics of ol' unknown age age (Proterozoic?). (Proterozoic?). The weathered weathered rocks rocks do do not not appear to contain unknown contain iron iron oxide. oxide. STOP 47 �STOP IN JACKSON JACKSON COUNTY IRON STOP 7: 7: PRECAMBRIAN-CAMBRIAN SURFACE IN IRON MINE MINE ! Location: Location: NE NE 1/4 114SE SE1/4 114SEC SEC15 15T21N T21NR3W; R3W,U.S.G.S. U.S.G.S. 1:50,000 150,000 Jackson County County Map Map I I Summary of o f Features: Features: Precambrian Precambrianiron ironformation formationand andquartz quartzfelldspathic feldspathicgneiss gneiss overlain overlain by Upper Upper Cambrian CambrianEau EauClaire Claireformation formationcontaining containing aa basal basalbreccia brecciakiyer. layer. The Jackson miles east east of of Black Black River River Falls Falls was was an an open pit pit Jackson County County Iron Iron Mine Mine located located about about 66 miles taconite operation active during the early eighties. The ore body is a lens-shaped 915 mx 550 m body operation active during the early eighties. The ore body is a lens-shaped 915 m x 550 m body [Jones, [Jones, 1977, 1977, Unpublished Unpublished work]. work]. The primary primary ore mineral is inagnetite magnetite residing residing in in Archean Archean iron iron formation which is embodied in quartz-feldspàthic schist and and gneiss. gneiss. The The iron formation quartz-feldspathic schist formation is is composed almost entirely entirely of of quartz, quartz, magnetite, magnetite, cummingtonite-grunerite, cummingtonite-grunerite, biotite, biotite, garnet, garnet,calcite, calcite,ferroactinolite, ferroactinolite, Ca-rich hornblende. hornblende, sphene, sphene, apatite, apatite,pyrite, pyrite, and and K-feldspar. K-feldspar. The The iron-formation iron-formationisishighly highly deformed deformed and exhibits prominent compositional bands ranging from a few mm to several meters. exhibits prominent compositional bands ranging from a few mm to several meters. The The compositionaL bands often often formed isoclinal isoclinal folds foldsand andwere weretransposed transposed along along foliation. foliation. The The iron mound compositional bands has 200 ft. St. of ofwater. water. has been been completely completely excavated excavated and the the open open pit pit isis at at present present filled filled with with over over 200 Fragments Fragments of the the iron iron formation formation could could be be found found on the the slopes slopes of the the pit. pit. The T h erocks rockssurrounding surrounding the the iron mound are upper greenschist-amphibolite facies metamorphic rocks. The principal rock types are are upper greenschist-amphibolite facies metamorphic rocks. The principal rock types arc quartz-biotite-plagioclase schist, mica-garnet-staurolite mica-garnet-staurolite schist. quartz-biotite-plagioclase schist, schist, mica-chlorite-andalusite mica-chlorite-andalusite schist, schist, and amphibolite wide are are present. present. amphibolite gneiss. gneiss. Quartz Quartzveins veinsover over11 ftft wide The The contact contactbetwcen betweenthe theArchean Archeanand andPaleozoic Paleozoicformation formation isis an an undulatory undulatorysurface. surface. The TheArchean Archean rocks are generally weathered. The depth of the weathered zone varies from 6 to 50 meters, probably rocks are generally weathered. The depth of the weathered zone varies from 6 to 50 meters, probably controlled controlled by by fracture fracturepatterns patterns[Jones. [Jones,1977]. 19771.The The Paleozoic Paleozoic rock immediately above the the unconformity uncontbrmity is is a framework-support framework-supportbreccia breccia containing containingangular angular to tosubangular subangularfragments fragmentsofofiron ironformation, formation,schists, schists, and and quartz quartz pebbles. pebbles. Fragments Fragments from from the the iron iron formation formation are aretabular tabularininshape shapeand andoccasionally occasionally imbricated. of them them over over 1/2 m in in diameter, diameter, tend to concentrate 112m concentrate in in certain certain imbricated. Quartz fragments, fragments, some of levels. siltstoneand and shale shale can can be be found levels. Upper Cambrian Cambrian glauconitic glauconitic siltstone found above above the thebreccia breccialayer. layer. Mudcracks, Mudcracks, iron concretions, concretions, and and worm worm trails trails are commonly commonly present in in the theargillaceous argillaceous layers. layers. The The rock rock isis lithological lithological similar similar to the the Eau Eau Claire Claire formation formation which which overlies overlies stratigraphically stratigraphically the Mount Mount Simon Simon Sandstone. Sandstone. The during the the late Proterozoic The iron iron formation formation probably probably formed formed a monadnock monadnock during Proterozoic time. time. The The basal basal breccia deposit on on the slopes and base base of the monadnock. breccia layer layer represents represents a slump deposit slopes and monadnock. Since Since the Eau Eau Claire formation is in direct contact with the iron formation, this particular outcrop Claire formation is in direct contact with iron formation, this particular outcrop was was probably probably located located at at aa relatively relatively high high part part of of the theslope. slope. I- Leus L F L T1TI . Rr-4q; • ii! i / ——- — A •: •Pôrrij - STOP 7 - - MIMNG BIar' RAILROAD I Jackson Countyt • Taibgs dp -* N*\ DuPy\ l!BR0cKWAY/ Mine Oun 48 >, •—•' - RERVA11ON �a '0 r FIG. 1 CJa&s, •'qiij n •1 Margin of Ri ,n, Toic Schist ''.1., Iron Formation 50 Hongingwall Schist El and Footwall Schist + + Diobosic Intrusives Granitic Unit METERS nfer,ed Contact — Known Contact + JACKSON COUNTY IRON MINE r' Cflf1 -17 r: r: r: r r Modified from Jackson County Iron Company Mine Mop August 1977 rr �REFERENCES REFERENCES CITED CITED AmericanGeological GeologicalInstitute, Institute,1972, 1972,Glossary Glossaryof of Geology. Geology. American States, States, U.S.G.S. U.S.G.S. Prof. Prof. Paper Paper1241-F., 1241-F.,31 31p.p. Murray, Murray,R.C., R.C., 1955, 1955,Late LateKeweenawan Keweenawanor orEarly EarlyCambrian Cambrian glaciation glaciation in Upper Upper Michigan, Michigan, Bull. Bull. Geol. G a l . Soc. Soc. Amer., Amer., 66, 66,341-344. 341-344. Myers, Myers, P.E., P.E., M.L. 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Kolata, Kolata, J.C. J.C. Matthews, Matthew, and and Hay, R.L., J.P. Morton, Morton, 1988, 1988,Episodic Episodic potassic potassic diagenesis diagenesis of of J.P. Ordoviciantuffs tuffs in in the the Mississippi Mississippi Valley area, area. Geology, Geology, Ordovician 16, 743-747. 743-747. 16, Harrison J.E., J.E., and Z.E. Z.E. Peterman, Peterman, 1984, 1984, Introduction Introduction to to Harrison correlation of of Precambrian Precambrian rock rock sequences, sequences,U.S.G.S. U.S.G.S. correlation 1241-A,7p. Paper 1241-A, Prof. Paper 7p. Irving, E., E., 1979, 1979, Paleopoles and paleolatitudes paleolatitudes of of North North Irving, America and and speculations speculations about about displaced displaced terranes, terranes, America Sci.,16, 16,669-694, 669-694,1979. 1979. Can. J.J. Earth EarthSci., Can. D., 1977, 1977,Geology Geology of of the the Jackson Jackson County County Iron Iron Jones, 0., Jones, Mine, Unpublished Unpublishedreport, report,copy copyavailable available upon upon request. request. Mine, Twoearly earlyProterozoic Proterozoic LaBerge, G.L., P.E. Myers, Myers, Two Lal3erge, G.L., and P.E. successions in central Wisconsin Wisconsin and their tectonic tectonic successions in ccntral and their significance, Bull. ~ u l lGeol. Geol. . Soc. Amer., Amer., 95, 95,246-253. 246-253. significance, Soc. 1971. The of Lochman-Balk, C., C., 1971, The Cambrian of the craton of United States, States,in in 1-lolland, Holland, C.H. of the United C.H. (ed), Cambrian of the New New World, World,Wiley-Interscience, Wiley-Interscience,London, London,79-168. 79-168. R.S. and W.R. W.R. Van Van Schmus, Schmus, 1980, 1980. Precambrian Precambrian Maass, It.S. tectonic history history of the the Black Black River River Valley, Valley, 26th 26th Inst. Inst. tectonic Lake Superior Superior Geology, Geology, Field Eau Claire, Claire, Lake Field Trip Trip 2, Eau Wisconsin. Wisconsin. Schmus. 1988, 1988, Correlation Morey, G.B.. G.B., and W.R. Van Schmus, Correlation of United Precambrian Rocks Rocks of of the the lake lakeSuperior Superiorregion, region, United Precambrian Precambrian Precambrian Geology Geology of the theChippewa ChippewaValley, Valley, 26th 26th Inst. Inst. Lake Lake Superior SuperiorGeology, Geology, Field Field Trip Trip 1,1,Eau Eau Claire, Claire, Wisconsin. Wisconsin. Nelson, P., P., 1980, 1980, Petrography Petrography and weathering weathering of of the the Nelson, Neillsville Granite, Unpublished report available Neillsville Granite, available upon upon request. request. O~trom, 1966, 1966, Cambrian Cambrian stratigraphy stratigraphy in in western Ostrom, Wisconsin, Guidebook Guidebook to to the the Michigan Michigan Basin Basin Wisconsin, Geological Society 1966 Annual Geological Society Annual Field Field Conference: Conference: W.G.N.S. 79p. W.G.N.S. Info. Cir. Cir. 7,7,79p. Ostrom, M.E., M.E., 1978, 1978,Irvine Irvine Park: Park: Precambrian/Paleozoic Precambrian/Paleozoic Ostrom, unconformity unconformity at at Chippewa Chippewa Falls, Falls, Wisconsin: W.G.N.H.S. W.G.N.H.S. Outcrop Outcrop Description ~ e s c r i ~ t iCH29N/08W/31. oCH29N/08W/31. n Ostrom, ME., M.E., 1987, 1987,Precambrian/Paleozoic PrecambrianPaleowic unconformity unconformity Ostrom, at Chippewa Chippewa Falls, Falls, Wisconsin, Wisconsin, W.G.N.H.S. W.G.N.H.S. outcrop outcrop Description TR TR 24N/08W/18. 24Nl08W118. Ostrom, Ostrom. M.E., M.E., 1988, 1988,Cambro-Ordovician Cambro-Ordovician Field Guide to to Western Wisconsin, Field tour by by representatives representatives of of Wisconsin, Field Amoco Ammo Production Production Co. Co. Ostrom, Guildbook,for for CambroCambroOstrom, M.E., M.E., 1970, 1970, Fieldtrip Fieldtrip Guildbook Ordovician Ordovician Geology Geology of Western Western Wisconsin, Wisconsin, W.G.N.S. W.G.N.S. Information Circular 11, 131p. lSlp. Rozanov, A.Y., A.Y., 1984, 1984, The The Precambrian-Cambrian Precambrian-Cambrian Rozanov, boundary in in Siberia, Siberia,Episodes, Episodes,7,7,20-24. 20-24. AJ., C.H. C.H. Summerson, Summerson, and and W.J. WJ. Hinze, Hinze, 1965, 1965, Rudman, A.J., Geology of basement Geology of basement in in Midwestern Midwestern United United States, States, Bull. A.AY.G., A.A.P.G., 49, 49, 894-904. 894-904. Bull. Sims, P.K., Schmus, K.J. KJ. Schulz, Schulz. and Z.E. Sims, P.K., W.R. W.R. Van Schmus, and Z.E. Peterman, 1989, 1989,Tectonostratigraphic Tectonostratigraphicevolution evolutionof of early early Peterman, Proterozoic Wisconsin magmatic Proterozoic Wisconsin magmatic terranes of the the Penokean Orogen, Orogen, Can. Can. J., J., Earth EarthSci., Sci.,26, 26,2145-2158. 2145-2158. Thwiites, P.E., and others, others, 1980, of buried 1980, Map Map of Thwaites, Precambrian Precambrian of Wisconsin, Wisconsin, W.G.N.S. W.G.N.S. Sheet. Van of North Van der der Voo, Voo, It., R., 1981, 1981, Paleomagnetisni Paleornagnetism of North America: America: A A brief briefreview, review, in in McElhinny, McElhinny,M.W. M.W. and and D.A. D.A. Valencio Valencio (eds.), Paleoreconstruction Paleoreconstruction of the the Continents, Continents, Geodynamicser.2,A.G.U.. Washington,D.C., D.C.,167-176. 167-176. Geodynamic ser. 2, A.G.U., Washington, Van Schmus, Schmus, WIt., W.R., Chronology Chronology of igneous igneous rocks rocks associated with the Penokean Penokeanorogeny orogenyininWisconsin, Wisconsin,inin Selected Studies of of Archean Archean gneisses gneisses and Lower Lower Selected Studies Proterozoic Proterozoic rocks rocks of of Southern Southern Canadian CanadianShield, Shield, in Morey, G.B., I lanson (eds.), Morey, and G.N. G.N. Hanson Spec. (cds.), GSA Spec. G.B., and Paper Paper 182, 182,159-168. 159-168. c, 50 �SUPPLEMENT PEThOGRAPHIC CIIARACTERISTICS SUPPLEMENT1: 1: NOTES ON PETROGRAPHIC CHARACTERISTICSOF OF THE THE MOUNT MOUNT SIMON FORMATION, EAU CLAIRE, WISCONSIN SIMON FORMATION, EAU CLAIRE, WISCONSIN Authors: Qi Qi Zhu Z h u (Visiting (Visiting Scholar Scholar from from Chongqing Chongqing Petroleum College, College, China) and and Lung S. Chan (University at Eau Claire) (University of Wisconsin Wisconsin at I I We We have have conducted conducted aa petrographic petrographicstudy studyon onMt. Mt. Simon Simon Sandstone Sandstone samples samples collected collected from from the thetype typ locality of of the formation in Eau Eau Claire. Claire. Nineteen Nineteen specimens specimens were collected at at different different stratigraphic stratigraphi levels levels of the formation. Based on on the the petrographic petrographicobservation, observation,we wehave have identified identified the thefollowing followingtypes type of lithologies lithologies in the the formation. formation. The Theapproximate approximate levels levels of of the thespecimens specimens and andthe themineralogical mineralogica ! abundance abundance are areshown shownininFig. Fig. S1.1. Sl.1. Type I.I. Coarse-Fine Coarse-Fine Conglomeratic Conglomeratic quartz sandstone (MS-I, (MS-1, Plate Plate 1). 1). I The The conglomerate conglomerate consists consists of 20% 20% quartz quartz pebbles pebbles and and 80% 80% quartz quartzcobbles. cobbles. Magnetic Magnetic grains grains are are occasionally present. present. The quartz grains show high high degree of rounding and maturity. maturity. About 10% 10% of of the the grains grains display display dissolved dissolved edges. Individual Individual quartz quartz shows shows wavy wavy extinction indicating a source source from fro metamorphic rocks. About 20% polycrystallineand and quartz-vein quartz-vein fragments. fragments 20% of of the thedetrital detritalgrains grainsare arepolycrystalline All the the quartz quartzgrains grains are areclear clearand andstructureless, structureless,with withfew fewimpurity impurity inclusions. inclusions. Cementing material materia consists mostly of matrix material material with with 80% silt (0.1 -- 0.05 mostly of 0.05 mm) and 20% euhedral euhedral potash potash feldspar feldspa or or irregular irregular feldspar feldspar or or kaolinite. kaolinite. Both Both detrital detrital grains grains and and cementing cementing matrix matrix are are very very well sorted. 1t I The Thepetrographic petrographiccharacteristics characteristicsofofthe thesandstone sandstonesuggest suggestaashoaling shoalingdeposition depositionwith withmultiple multiplecycles cycle of erosion. potas erosion. Original Original or or primary primary cementing cementing materials materials are replaced replaced entirely entirely by by authigenic authigenic potash feldspars. feldspars. The matrix matrix material material suggests suggests a multiple multiple cycle cycle of deposition, deposition, indicating indicating strong wave wave or oi current motion motion and and active active pore pore current current flow flow during during the the deposition. deposition. 1 Type II. 11. e.g. e.g. MS-2. MS-2. Quartz sandstone. sandstone. I , 1 This This type type of of quartz quartz sandstone sandstone contains contains about about 60% 60%medium-fine medium-fine grained grained sand sand and and 40% 40% medium mediu grained grained sand and and minute minute amount amountof of silt silt size size particles. particles. The The sand is is 95% quartz and about about 5% 5%feldspar. feldspar The are The quartz quartz grains grains are areclean cleanand andmonocrystalline; monocrystalline;polycrystalline polycrystalline quartz and impurity impurity inclusions ar absent. The quartz quartz sands sands are are subrounded subrounded to tosubangular subangular and and moderately moderately sorted. sorted. The The fetdspars feldspars are ar mostly minerals that develop around a detrital mostly authigenic minerals detrital core core of of microcline microcline or or plagioclase. plagioclase. Most of o the Some of of the authigenic feldspars feldspars tend tend to form suturethe authigenic authigenic feldspars feldspars show euhedral form. form. Some type intergrowth pattern patterninininterstitial interstitialspaces spacesamong among the the quartz quartz grains. grains. Many feldspars develop aroun type around detrital detrital feldspar feldspar grains. grains. Detrital Detrital feldspars feldspars are arenormally normally not not stained, stained,microcline microcline in in composition composition while whil authigenic twinning isisobserved observedin insome someof of the the detrital feldspar authigenic feldspar are are well well stained. Plagioclase twinning grains. grains. The orientation orientation in in the theauthigenic authigenicfeldspar feldspar often often makes makes aa10-12° 10-12" angle angle with with the the twinning twinnin orientation veins and orientationof of the thedetrital detritalcore. core. Fragmentsof Fragments ofquartz quartzveins and granites granites are are present present in in minute minute amount. The The same Thecementing cementingmaterial materialalso alsocontains containssmall smallquantity quantity of of silica. silica. The same lithological characteristics are ar 7, 8, 8, 11, 11, 12, 13, 14, and these specimens 4,5, present in in MS-3, MS-3, 4, present 5, 7, and 15 (Plate 2). Feldspar composition in these ranges ranges from from 55 to to 15%, 15%,and andnormally normally not notexceeding exceeding10%. 10%. 51 �Type III. IIL Volcaniclastic-like Volcaniclastic-like feldspathic quartz sandstone This This type type of of quartz quartz sandstone sandstonediffers differs from from Types I and II IIin in that thatmorphology morphology and and composition composition of of the the feldspars. feldspars. This This type type of of quartz quartzsandstone sandstonecontains contains40-60% 40-60%feldspar feldsparand andshows showsaa strong strongdissolution dissolution of of the thecrystal crystaledges. edges. InInMS-b MS-10 collected at about 15 15 m m from the the base base of of the theMt. Mt.Simon Simon Formation, Formation, mica to mica grains grains present in in matrix matrix material material seem seem to to show show aa preferred preferredorientation, orientation,which which may be due to strong current flow through the interstitial pore spaces during or after the deposition. We suggest that strong current flow through the interstitial pore spaces during or after the deposition. We suggest that the the presence presence of of aa strong strong interstitial interstitial pore pore current current may may be an an important important factor factor in in the the formation formation of of authigenic authigenicfeldspar. feldspar. MS-9 (Plate (Plate3) 3) MS-9 This contains 50% 50% feldspar feldspar and and 50% 50% quartz quartz. About About 20% This specimen specimen contains 20% of the the quartz quartz grains grains are are subrounded, subrounded,30-40% 30-40%subangular subangularand and40% 40%show showdissolution dissolution edges. edges. The The dissolution dissolution grains grains show bonebonelike, like, curve curve or or sharp sharp shards. shards. Feldspar Feldspar grains grains are are mostly mostly fine fine sand sand size, size, and and in in the theforms formsofofsingle single crystals. euhedral and and form form intergrowths. intergrowths. Many form around crystals. Most of the feldspars feldspars are subhedral to euhedral aa core core grain grain of of dissolved dissolved residue and enlarge around the core. Other Other feldspars feldspars do not not indicate indicate aa core core grain. grain. Cementing Cementing material material are areinconspicuous. inconspicuous. The Thefeldspars feldspars basically basically form the interstitial interstitial materials. materials. MS-b MS-10 The of this this specimen The lithological lithological characteristics characteristics of specimen are similar similar to that that of ofMS-9. MS-9. Feldspar Feldspar grains grains constitute constitute about about 50% 50% of of the thespecimen. specimen.ItItcontains containsabout about10% 10%ofofcoarse-grains coarse-grains pebble-size pebble-size detrital detrital quartz quartz fragments fragments with with good good degree degree of of rounding rounding and and uniform uniform composition, composition, and about about 2% 2% sericite sericite mica mica fragments. fragments. Type Type IV. IV. Feldspathic Feldspathic Quartz Quartz Siltstone Siltstone MS-19 MS-19 This specimen specimen contains contains 80% 80% quartz, quartz, about about15% 15%irregular-shaped irregular-shaped quartz quartzgrains grainsshowing showing strong strong This dissolution dissolution edges edges and and 20% 20% feldspar feldspar with with or or without without aa detrital detrital core. core. Quartz Quartz grains grainsare aresubrounded subroundedtoto subangular subangularand andmoderately moderatelysorted. sorted.Cementing Cementingmaterials materialsare aremostly mostlyiron-rich iron-rich mineral mineral or orsericite sericitemicas micas in in interstitial interstitial pores. pores. MS-18 MS-18 This with 70% 70% quartz and >25% feldspar. feldspar. Sericite Sericite and and This specimen specimen contains contains 80% 80% silt and 15% 15% fine tine silt with ferric ferricmineral mineral are arepresent presentatatabout about2-3%. 2-3%.Quartz Quartzgrains grainsare aremostly mostlysubrounded subroundedtotosubangular subangularand andwell well sorted. The Thefeldspars feldsparsare aremostly mostlysecondary secondarypore porefiller, filler,crystal crystalforms forms are areless lesswell well developed developed as asMS-S MS-8 sorted. or orMS-9 MS-9 and and are aresimilar similar to tokaolinite kaolinite cement. cement. Part Part of ofthe thefeldspars feldsparsare areauthigenic authigenicand andauthigenic authigenic overgrowth. and MS-10. MS-b. overgrowth. Feldspar Feldspar abundance abundance is also lower than in MS-9 and Based on on the thepetrographic petrographicobservations, observations, the theMt. Mt. Simon Simon formation formation in in Eau Eau Claire Claire can can be be divided divided into Based several several zones. zones. The The basal basal layer layer of of the theMt. Mt.Simon Simon Sandstone Sandstone isis represented represented by by aaconglomerate conglomerate and and coarse coarse sandstone sandstone layers. layers. The The dominance dominance of of rounded rounded quartz quartzsand sand indicates indicates high high degree degree of of maturity. maturity. ItItisisalso also evident evident that that the thesandstone sandstoneunderwent underwentmultiple multiplecycles cyclesof of erosion erosion and anddeposition. deposition. The Thedetrital detrital quartz grains and quartz cement show corroded edges that resembles quartz that formed in a volcanic quartz grains and quartz cement show corroded edges that resembles quartz that formed in a volcanic setting. setting. ItItisis questionable questionable whether whetherthe thecementing cementingmaterial materialrepresents representsthe theprimary primaryoriginal originalcementing cementing medium. medium. The Theclay claycontent contentininthe theconglomerate conglomerateisisvery verysmall, small,suggesting suggestingaasecond secondcycle cyclecementation cementation process. process. The TheMt. Mt.Simon SimonFormation Formationcontains containsseveral severalbeds bedsthat thatare areenriched enrichedininfeldspathic feldspathiccomposition. composition.Based Based 52 52 �on on the theform formand andcrystallinity, crystallinity, the potash feldspars feldspars are are authigenic a u t h i g e ~ in c nature. About About 50% 50% of the the quartz quart grains, derived there there though normal transportatio~ transportation grains, on the other other hand, hand, are are terrigenous temgenous detrital detrital grains derived means. means. The Theother otherquartz quartzgrains, grains,however, however,exhibit exhibitdissolved dissolvededges edgesand andform formirregular irregularshards. shards.This Thisform forr of quartz bears similarities to quartz that forms in a volcaniclastic environment. quartz bears similarities to quartz that forms in a volcaniclastic environment. The The authigenic authigenic feldspar feldspar crystals crystals and their their formation formation conditions conditions present present aacomplicated complicated problem. problem Some grains. Others Others do do not contain any core and Some of of the the feldspars feldspars contain contain aa core core of of dissolved dissolved feldspar grains. am are are entirely entirely authigenic authigenic in in origin. origin. Some of the the core core grains grains contain contain obvious obvious twins, others do not. Some Somi of of the thecore coregrains grainsare arepossibly possiblydissolved dissolvedquartz, quartz,with with brainline brainline structures. structures.Some Someauthigenic authigenicfeldspars feldspar simply simply follow the forms of existing existing detrital quartz quartz and andfeldspar feldspar grains grains or orfill-in fill-in cracks cracks and andveins veinsinii existing existinggrains. grains. 1 I Most Most of of the the authigenic authigenic feldspars feldspars are are euhedral euhedral to to subhedral. subhedral. When When the the growth growth condition condition is is confined confine1 by by surrounding surrounding quartz quartz grains, grains, the thefeldspar feldspar may may !form form dog-teeth dog-teeth like like crystal crystal edges. The source of o feldspars, questions. First, the source feldspars, morphology and authigenesis authigenesis have presented some interesting questions. sourci of of the thefeldspar feldspar has has been beenan anenigma. enigma. The Thedepositional depositional medium medium and and water water conditions conditions at at the the time time of o deposition deposition also represent problems problems for for understanding understanding the origin of the Mt. Mt. Simon Simon Formation. Formation. The Thi high high percentage percentage of of feldspar feldspar in in particular particular beds beds of of the theformation formation may may be be indicative indicative of of the thefollowing follow in^ conditions. conditions. (1) (1)The Thetransported transporteddebris debrismay maycontain containsubstantial substantialamount amountofofvolcanic volcanicquartz quartzfragments, fragments as (2) During During the the early early deposition deposition of the the Mt. Mt. Simon Simoi as suggested suggested by the forms forms of the the quartz quartz grains. grains. (2) sandstone, sandstone, there theremight mighthave have been beenvolcanic volcanic eruptions eruptions in in aanearby nearbyarea. area.The Thedeposit depositsurely surelycontains contain quartz quartz grains grains sufficiently sufficiently washed and eroded eroded by by ocean ocean waves. waves. The The primary primary cementing cementing material material may ma' contain volcaniclastic volcaniclastic material being eliminated eliminated during redeposition. The eroded erode! contain material that that were were being during the the redeposition. primary primary cement might be enriched in potassium feldspar and constituted the source of the the authigenic authigenii feldspar feldspar in the the Mt. Mt. Simon Simon Formation. Formation. (3) (3)The Theobserved observed dissolution dissolution of of quartz quartz isisprobably probably related relate! genetically event at the to the theformation formationof ofthe theauthigenic authigenicfeldspars feldsparsand andmay mayimply imply an volcaniclastic event tht -genetically to time time of of the thedeposition. deposition. 53 �Type Type LI. Sandstone Sandstone Conglomeratic Conglomeratic MS-i. MS-1. Sig. 4x1" Sig. 4xiO Type II. 11. Quartz QuartzSandstone Sandstone Type MS-3 MS-3 Sig. lOxlO 10x10 Sig. Type III. 111. Volcaniclastic-like Volcaniclastic-like Type feldspathic sandstone fe]dspathic sandstone MS-9 MS-9 10x10 Ri. lOxiO * 54 �Fig. S1.1 Grain Fig. Sl.1 Grain Composition Composition of of Mt. Mt. Simon Simon Sandstones Sandstones based based on on 500 500 points points I Level Level zo EAU 250 EAu CLAIRE FORMATEON FORMATION - 2: © Ct z (/D 2: C I Specimen Specimen DMQ I DSQ 3.2 3.2 1.2 1.2 MS-i MS-1 44.4 32.2 32.2 MS-2 MS-2 68.6 3.8 3.8 MS-3 MS-3 MS-4 MS-s MS-5 MS-7 MS-7 MS-9 MS-9 64.6 2.2 55.8 65.2 00 DO DM AKF PITY C) 11.2 0.8 0 0 0.8 0.8 0.2 7.4 20.2 5.6 0 - 25 0 1.4 Lit 2.4 0.2 2.8 3.0 0.8 0.8 00 29.4 0.2 2.4 6.8 0.4 2.0 1.6 1.6 2.4 2.4 24.8 1.6 2.0 2.0 1.6 Oh 0.6 65.2 2.8 1.0 1.0 10.2 4.0 0.8 4.0 4.0 2.4 2.4 2.4 2.6 2.2 24.0 26.6 43.6 6.6 0.2 MS-b MS-10 MS-Il MS-11 33.6 8.0 1.8 1.8 11.6 2.2 1.8 1.8 36.6 4.0 - 60.7 6.5 6.5 2.7 0.4 2 2.8 9.0 0.4 3.7 3.7 2.2 22 3.0 69.6 4.5 4.5 0 17.7 MS-12 MS-12 11.4 4.0 0.4 MS-13 MS-13 58.6 &4 6.4 5.8 5.8 23.6 1.2 1.4 1.4 2.0 0.4 1.0 MS-14 MS-14 61.4 8.6 8.6 6.0 13.0 5.0 1.4 1.4 3.0 0.6 1.6 MS-IS MS-15 61.1 &8 8.8 0 72.2 2.5 10.8 10.8 3.7 3.7 2.7 0.3 0.3 0.6 0.6 4.7 MS-16 MS-17 MS-17 MS-Is MS-18 9.1 0 0 -MS-19 P4; DPQ DPQ - - a -- 60.0 3.6 5.6 50.3 6.0 6.0 54.0, 3.3 -- 12.9 0.2 7.4 13 6.4 9.9 0.5 0.5 2.5 6.7 6.7 4.3 0.9 lM 13.6 10.6 4.3 4.3 13.6 0 1.0 7.6 3.6 2.7 - 25.9 0 2.0 DMQ Deirital monocrystalline quartz; DPQ -- Detrital DMQ -- Detrital monocrystalline quartz; Detrital polycrystallinc polycrystalhnc quartz, quartz: Strained quartz; QO -- Quartz overgrowth; DO -- Detrital Detrital orthoclase: SQ -- Strained SQ orthoclasu. DM -- Detrital Detrital microcline; AK K-feldspar; AK .- Authigenic Authigenic K-feldspar; PRY 0 PHY - Phyllosilicate; Phyllosilicate; 0 - Others. Others. 55 �Supplementary SupplementaryNotes Notes 2. 2. Mineralogical Mineralogical data datafor fordiagenetically diagenetically altered altered paleosols paleosols at at Stops Stops 1, 1, 3, 3, & & 44 Analysis Analysis done done by by Richard Richard L. L. Hay Hay Irvine Irvine Park Park / / \ , / / U A — ¼ - s_ L 5c. prc).4.. 1st 1stNejjlsvjlle Neillsville Quarry Quarry(Stop (Stop3)3) A (Altered) Granite , 7 /. Fresh Oligoclase PC / Q 35 24 Mr 14 8 Pc 47 0 Mc 3 5 K.F 0 52 l'h 0 10 B / /1'1 / — ÷K — -p. A • Covcre — Microeline Graniie F. '-KR — 3 (Altered) Q 43 43 Mr 40 C) Pc 12 0 Mc 5 5 KF 0 49 0 3 'C I 2nd 2ndNeillsville Neillsville Quarry Quarry(Stop (Stop4)4) Cc Granite Gnciss (Altered) Q 24 13 Mr 51 31 Pc 18 0 Mc —1 —1 1cF 0 53 Ph 0 2 -G. e "(0 m oQ- Quartz - Quartz Mr Mr- Microcline - Microcline l'cI'c- Plagioclase - Plagioclase Mc -~ k a Mc- Mica KF KT- Authigenic - AuthigenicK-feldspar K-feldspar Ph AuthigenicPhyllosilicate Phyllosilicate 1'h- -Authigenic Saprolite & gruss [i< Granite Granite&tegranite granitegneiss gneiss 56 56 C �1991 SATURDAY, MAY MAY 4, 4, 1991 SATU1mAY, FIELD TRIP #3 #3 M.G. Mudrey, Jr., Jr., and andB.A. B.A. Brown (Leaders) (Leaders) Proterozoic "Proterozoicvolcanogenic volcanogenic massive massive sulfide sulfide deposits of northwestern northwesternWisconsin" Wisconsin" 57 �L [ PROTEROZOIC VOLCANOGENIC PROTEROZOIC VOLCANOGENIC MASSIVE MASSIVE SULFIDE SULFIDE I I [ 1 WISCONSIN DEPOSITS OF NORTHWESTERN WISCONSIN M.G. Jr., and and B.A. LA. Brown M.G. Mudrey, Mudrey, Jr., Brown Wisconsin Geological and Wisconsin Geological and Natural Natural History History Survey, Survey, Madison, Madison, WI WI L INTRODUCTION: INTRODUCTION: [ Field trip trip 3 Field 3 represents represents aa departure departure from from the the usual usual format format followed followed by by previous Institute The emphasis previous Institute field field trips. trips. The emphasis is is on on massive massive sulfide sulfide L mineralization, and particularly particularly on on the the Flambeau, Flambeau, Lynne, Lynne, and and Bend Bend deposits. deposits. mineralization, and The regional geology The regional geology has has been been covered covered in in previous previous Institute Institute field field guides guides [ 4 1984, 1986) and regional geology (1980, 1984, and in in several several papers papers about about the the regional geology (Sims (Sims and an I [ others 1990, Greenberg others 1990, Greenberg and and Brown, Brown, 1983). 1983). Because Because time time is is limited, limited, we we will will 1 depart depart from from tradition tradition and and not not visit visit any any outcrops. outcrops. We will will proceed proceed directly directly to to L where we Hawkins, where Hawkins, we will will examine examine core core from from the the Bend Bend and and Lynne Lynne deposits, deposits, guided by personnel Lehman and E. K. Lehman and Associates Associates and and Noranda. Noranda. personnel from from E. Then we we will Then will to to Ladysmith, where Ladysmith, where we we will will examine examine core core from from the the Flambeau Flambeau Deposit, Deposit, guided guided by L personnel of the Mining Co. personnel of the Flainbeau Flambeau Mining Co. The The following following notes, notes, based largely largely on on papers papers by by DeMatties DeMatties (1989) (1989) and and Mudrey Mudrey and and others others (1991), (1991). are are intended intended to to C provide brief outline provide a brief outline of of the the geology, geology, mineralization, mineralization, and and exploration exploration history, history, and and will will be be supplemented supplemented by by reprints reprints provided provided to to trip trip participants. participants. ii L E GEOLOGIC FRAMEWORK: GEOLOGIC FRAMEWORK: The Penokean Penokean orogen in northern Wisconsin consists of consists two distinct of two distinct The orogen in northern Wisconsin terranes. The northern oxideterranes. The northern terrane terrane contains contains platform platform sediment, sediment,including including oxide- L facies iron iron formation, facies formation, turbidite, turbidite, and and minor minor tholeiitic tholeiitic volcanic volcanic units units deposited on deposited on an an Archean Archean continental continentalmargin. margin. The The northern northern terrane terrane extends extends east east This into Michigan Michigan and and west west across across the the Midcontinent Midcontinent Rift Rift into into Minnesota. Minnesota. This 1 terrane terrane has has historically historically been been aa major major producer producer of of iron iron but but is is not not known known to to 1 contain major contain major massive massive sulfide sulfide deposits. deposits. The southern known only only in in Wisconsin, Wisconsin, represents represents an island island arc The southern terrane, terrane, known 58 \geology\sulfide ,bab �L. volcanic terrane terrane accreted accretedto to the the Superior Superior Craton Cratonduring during the the Penokean Penokean orogeny volcanic orogeny L HA). (1850MA). (1850 [ This terrane, the Penokean Volcanic Belt of Greenberg and Brown This terrane, the Penokean Volcanic Belt of Greenberg and irown i (1983) or or Wisconsin WisconsinMagmatic Magmatic Terrane Terrane of ofSims Sims(1987), (1987). consists consistsof ofcalc-alkaline calc-alkaline (1983) volcanicrock rockand andvolcanogenic volcanogenicsedimentary sedimentaryrock. rock. The Penokean arc terrane, in volcanic The Penokean arc terrane, in contrast to to the the continental continentalmargin margin terrane, contains significant massive contrast terrane, contains significant massive sulfidemineralization. mineralization. To date. seven deposits totalling nearly 100 million sulfide To date, seven deposits totalling nearly 100 million L tons have been discovered, including the 60 million ton Crandon deposit. tons have been discovered, including the 60 million ton Crandon deposit. MASSIVE SULFIDE SULFIDEDEPOSITS DEPOSITS MASSIVE L DeMatties (1989) (1989) recognized recognizedtwo two mineralized mineralized districts in the western DeMatties districts in the western L area of the volcanic belt, the Ladysmith district centered on the Flambeau area of the volcanic belt, the Ladysmith district centered on the Flambeau deposit in in Rusk Rusk County County and andthe the Somo Somo district district to the east in Price, Lincoln. deposit to the east in Price, Lincoln, [ L and Taylor TaylorCounties. Counties. The massive sulfide deposits belong to the Cu-Zn group and The massive sulfide deposits belong to the Cu-Zn group of Franklin Franklinand andothers others(1981) (1981) and andrepresent represent at least three district host of at least three district host environments. environments, L . . The first first environment environmentis isexemplified exemplifiedby by the theFlambeau Flambeau and Ritchie Creek The and Ritchie Creek main zone zonedeposits, deposits,and andconsists consistsof of syngenetic strata-bound and stratiform main syngenetic strata-bound and stratiform mineralization associated with felsic volcanic centers. This association is mineralization associated with felsic volcanic centers. L This association is typical of of many many of ofthe theclassic classic deposits deposits in inthe the Canadian Canadian Superior Province. typical Superior Province. The felsic-hosted felsic-hosteddeposits depositsconsist consistof oftabular tabular to lenticular layers of massivi The to lenticular layers of massive L r to semi-massive semi-massivesulfide, sulfide,enveloped envelopedby by a disseminated sulfide halo with no to a disseminated sulfide halo with no I distinctly recognizable recognizablealteration alterationpipe. pipe. distinctly The mineralization is copper I (chalcopyrite) rich and associated with quartz-sericite + amphibole or 1I The mineralization is copper (chalcopyrite) rich and associated with quarcz-sericite ± amphibole or L I chlorite-carbonatealteration. alteration. chlorite-carbonate Host rock in this environment is commonly felsic crystal tuff (quartz- Host rock in this environment is commonly felsic crystal tuff (quartz- L sericite schist). schist). sericite Cherty tuff and metachert commonly occur interbedded with Cherty tuff and metachert commonly occur interbedded with Disseminated sulfide of the or stratigraphically stratigraphicallyabove abovethe thehost hosttuff. tuff. or Disseminated sulfide of the 1 footwall grade upward into massive sulfide, which is commonly in sharp contact footwall grade upward into massive sulfide, which is commonly in sharp contact L with the the hanging hangingwall wallrock. rock. Primary jointing may be present in these deposits with Primary jointing may be present in these deposits \ I \geology\sulfide bab . 59 �with zinc with zinc enrichment enrichment occurring occurring stratigraphically stratigraphically above above the the copper copper rich rich ore. ore. Precious metals Precious metals may may be be uniformly uniformly distributed distributed through through the the massive massive sulfides sulfides or or occur as occur as assay assay zones zones throughout throughout the the sulfide sulfidehalo. halo. DeMatties DeMatties (1988) (1988) reported reported that gold gold appears appears to to be be locally locally enriched enriched in in the the Ritchie Ritchie Creek Creek ore ore body body near near crosscutting faults crosscutting faults that that have have been been intruded intruded by by mafic-intermediate mafic-intermediate dikes. dikes. L The second second environment The environment described described by DeMatties DeMatties (1989) (1989) is is that that of of syngenetic strata-bound syngenetic strata-boundand and stratiform stratiform massive massive sulfides sulfides associated associated with with cherty cherty L magnetic The Thornapple magnetic iron iron formation formation within within the the main main volcanic volcanic arc arc sequence. sequence. The Thornapple deposit north north of The deposit deposit of Ladysmith Ladysmith is is an an example example of of this this type. type. The deposit consists consists 1 of lenses of lenses of of copper copper and and zinc zinc bearing bearing pyrite-pyrrhotite pyrite-pyrrhotite in in quartz-amphibole quartz-amphibole L The mineralized mineralized schist, which is is interpreted interpreted to to have have been been aa mafic mafic tuff. tuff. The schist, which lenses grade Thornapple lenses grade laterally laterally into into cherty cherty magnetic magnetic iron iron formation. formation. The Thornapple L deposit is not associated associated with a center but is located deposit a felsic felsic center located in in predominantly mafic rocks rocks of of the the volcanic volcanic arc arc sequence. sequence. Zoning Zoning is is also also evident evident within within the the Thornapple deposit, Thornapple deposit, with with sphalerite sphalerite enriched enriched in in the the upper upper ore ore lenses. lenses. Some Some stringer and stringer and disseminated disseminated sulfide sulfide occurs occurs stratigraphically stratigraphically below below the the main main chalcoyrite-bearing chalcoyrite-bearinglens. lens. L Limited information Limited information suggests suggests that that there there are are precious metals precious metals (0.029 (0.029oz/ton oz/ton Au) Au) in in this this deposit depositas as well. well. DeMatties' third DeMatties' third type type comprises comprises epigenetic epigenetic stringer stringer sulfide sulfide mineralization and mineralization and syngenetic syngenetic stata-bound stata-boundand and stratiform stratiform massive massive sulfide sulfide at at or or [ near near the the top top of of mafic mafic volcanic volcanic piles piles within within back back arc arc basin basin sequences. sequences. The The itivela zone zone on on the the Ritchie Ritchie Creek Creek prospect prospect occurs at the contact contact between between Kivela L massive mafic mafic to flows and and overlying overlying cherty cherty tuff tuff and and volcanogenic volcanogenic massive to izntermediate intermediate flows metasedimentary rock. sulfide halo halo is is developed developed in in the the flows flows and and is is metasedimentary rock. A sulfide associated associated with with intense intense quartz-sericite quartz-sericitealtertion. altertion. The halo grades grades into into an an alteration veinlets of of pyrite-pyrrhotite pyrite-pyrrhotite chalcopyrite chalcopyrite ±2 alteration pipe pipe of of stringers stringers and and veinlets quartz quartz in in brecciated brecciated and and altered altered country countryrock. rock. L The environments of mineralizaton DeMatties environments of mineralizaton described described by DeMattiesby (1989) provide (1989) provide The 60 \geology\sulfide .bab �F? the basis for the for aa geological geological model model to to guide guide exploration exploration in in the the western western part part of of the volcanic volcanic belt. the belt. AA similar similar stratigraphic stratigraphic model model has has yet yet to to be developed developed for for eastern part of known deposits the eastern of the the belt, belt, although although known deposits such such as as Crandon, Crandon, 1 1 I Pelican, Pelican, and and sulfides in barren sulfides in Marinette County occur in in similar host rock 1 [ I settings. settings. [ L The lithologic lithologic similarity, similarity, similar similar tectonic tectonic setting, setting, and and presence presence The of of mineralization throughout the the belt belt suggests suggests aa potential potential for for more more mineralization throughout 1 discoveries (Mudrey and and Kalliokoski, Kalliokoski, in in press; press; Mudrey, Mudrey, 1979; 1979; and and Mudrey Mudrey and and discoveries (Mudrey 1 others, 1991. others, 1991. ; I iI I I EXPLORATION AN!) EXPLORATION AND DEVELOPMENT DEVELOPMENT HISTORY HISTORY [ I Thehistory history of The of exploration exploration in the Penokean belt up up to to 1976 1976 is is1 Penokean volcanic volcanic belt suimnarized summarized in detail detailby byMudrey Mudrey and others others (1991). (1991). An was the the in An important important factor factor was existence of aa good existence good database database from from early early surveys surveys of ofthe theWisconsin Wisconsin Geological Geological L and Natural Hisory Survey Survey in which C.E. and in which C.E. Dutton recognized the the presence of Dutton recognized of "greenstone beltn 'greenstone assemblages and and hints of mineralization mineralization similar similar to that that of of 1 belt" assemblages hints of i massive sulfide sulfide bearing bearing Archean Archean terranes terranes of of Canada. Canada. Although exploration exploration of of1 [ the terrane began the in the the 1950s, 1950s. real real progress progress was made only only after after the began in I 1I successful application of of ground ground and and airborne airborne geophysics geophysics allowed allowed conductive conductive successful application L anomalies to anomalies to be identified identified beneath beneath the the thick thick glacial glacial overburden. overburden. The The result result1 has has been been aa series series of of significant significant discoveries, discoveries, from from the the announcement announcement of of the the L Flambeau deposit in in 1968 1968 and and Crandon Crandon in in 1976 1976 down down to to the the Lynne Lynne and and Bend Bend Flambeau deposit I I [ i projects of projects of the the 1990s. 1990s. I With the the permitting permitting of of the the Flambeau Flambeau deposit deposit in in early early 1991 1991 and and with with [ startup scheduled startup scheduled for for the the summer summer of of 1991, 1991, the the Penokean Penokean terrane terrane may may finally finally become become aa producing producing district. district. I 61 \geology\sulfide bab . ii �REFERENCES: REFERENCES: DeMatties, DeMatties, T.A., T.A., 1989 1989 aa proposed proposed geologic geologic framework framework for for massive massive sulfide sulfide deposits in the Wisconsin Penokean Volcanic Belt, Economic deposits in the Wisconsin Penokean Volcanic Belt, Economic Geology, Geology, Vol. Vol. 84, p. 946-952. 84, p. 946-952. Greenberg, Greenberg, J.K., J.K., and and Brown, Brown, B.A., B.A.,1983. 1983. Lower Lower Proterozoic Proterozoic volcanic volcanic rocks rocks and and their setting in the southern Lake Superior district. In Early In Early their setting in the southern Lake Superior district. Proterozoic Medaris, Edited by by L.G. L.G. Medaris, Proterozoic geology geology of of the the Great Great Lakes Lakes region. region. Edited Jr. Geological Society of America, Memoir 160, pp. 67-84. Jr. Geological Society of America, Memoir 160, pp. 67-84. Mudrey, Mudrey, M.G., M.G., 1979. 1979. The The massive massive sulfide sulfide occurrences occurrences in in Wisconsin: Wisconsin: Wisconsin Wisconsin Geol. Nat. History Misc. Paper 79-2, 2Op. Geol. Nat. History Misc. Paper 79-2, 20p. Mudrey, M.G., M.G., Jr., Jr.,Evans, Evans,T.J. T.J. Babcock, Babcock,R.C., R.C., Jr., Jr.,Cummings, Cummings,M.L., M.L., Jr. Jr. Mudrey, Eisenbrey, Eisenbrey, E.H., E.H., and and LaBerge, LaBerge, G.L., G.L., 1991, 1991,31. 31. Case Case history history of of metallic metallic mineral in V.F. V.F. Hollister, Hollister, ed., ed., mineral exploration exploration in in Wisconsin, Wisconsin,1955 1955 to to 1991, 1991,in I Case Case histories histories of of mineral mineral discoveries, discoveries,volume volume 3, 3, porphyry porphyry copper, copper, molybdenum, molybdenum, and and gold gold deposits, deposits,volcanogenic volcanogenic deposits deposits (massive (massive sulfides), sulfides), and and deposits deposits in in layered layeredrock: rock: Society Society of of Mining, Mining, Metallurgy Metallurgy and and Exploration, Exploration, Inc. Inc. (SMNE), (SMME) , 272 272p. p. Mudrey, J., in in press, press, "Metallogeny, "Metallogeny,Lake Lake Superior Superior Mudrey, M.G., M.G., Jr. Jr. and and Kalliokoski, Kalliokoski,J., Region," Precambrian of the U.S., Chap. 2, P.K. P.K, Sims, S h , ed., ed., Decade Decade of of Region," Precambrian of the U.S., Chap. 2, North North American American Geology, Geology, Geological Geological Society Society of of America, America, Boulder, Boulder, CO. CO. Sims, Sims, P.K. P.K., 1987, 1987, Metallogeny Metallogeny of of Archean Archean and and Proterozoic Proterozoic terranes terranes in in the the Great Great Lakes Lakes region: region: U.S. U.S. Geol. Geol. Survey Survey Bull. Bull. 1694, 1694,p. p. 55-74. 55-74. , Schmus,W.R.., W.R., Schulz. and Peterman, Peteman, Z.E., Z.E., 1989, 1989, TectonoTectonoSims, P.K., P.K.,Van Van Schmus, Sims, Schulz, K.J., K.J., and stratigraphic stratigraphic evolution evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatic terranes terranes of of the the Penokean PenokeanOrogen. Orogen. Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, Vol. V O ~ 26, .26,p. p. 2145-2158. 2145-2158. 62 \geology\sulfide .bab � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1991 Description An account of the resource Institute on Lake Superior Geology. Eau Claire, Wisconsin. May 1-4, 1991. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1991 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/6f4ce8e493668b59ee17a019748a7712.pdf 2891383c5858fd84a92605ce6ea24145 PDF Text Text INSTITUTE UTE ON ON •L A KE SUPERIOR S UPERIOR GEOLOGY G EOLOGY PROCEEDINGS PROCEEDINGS MEETING 338TH8 ANNUAL ANNUAL ~ ~ MEETING MAY 1992 MAY6-9, 6-9,1992 HELD AT AT HURLEY, WISCONSIN HURLEY, WISCONSIN VOLUME 38 PART MAY PROGRAM & ABSTRACTS �ORGANIZING COMMITTEE 38TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY General General Chairman: Chairman: Albert Albert B. B. Dickas, Dickas, University University of of Wisconsin-Superior Wisconsin-Superior Program Program Chairman Chairman and and Proceedings ProceedingsEditor: Editor: Bruce Bruce A. A. Brown, Brown, Wisconsin Wisconsin Geological Geologicaland and Natural Natural History History Survey Survey Volume 38 consists consists of Part Program and and Abstracts Abstracts Part 1: 1:Program Part 2: Field Trip Guidebook Guidebook Published Published and distributed distributed by Institute Institute on on Lake Lake Superior SuperiorGeology Geology M.G. Mudrey, Mudrey, Jr., Secretary-Treasurer Secretary-Treasurer do c/oWisconsin WisconsinGeological Geologicaland andNatural Natural History HistorySurvey Survey 3817 38 17 Mineral Point Road Road Madison, Madison, Wisconsin Wisconsin 53705-5100 53705-5100 ISSN ISSN 1042-9964 1042-9964 �INSTITUTE ON INSTITUTE - L A K E m SUPERIOR S UPERIOR GEOLOGY G EOLOGY uLAK ER I PROCEEDINGS 38m ANNUAL MEETING MAY 6-9, 1992 HURLEY, WIscoNsIN ORGANIZED BY ALBERT B. DIcKAs, UMvERsnY Oi WISCONSIN-SUPERIOR BRUCE A. BROWN, WISCONSIN GEoi.ooIcAL AND NATURAL HISTORY SURVEY VOLUME 38 MAY 1992 PART 1 PROGRAM & ABSTRACTS �CONTENTS Institutes Instituteson onLake LakeSuperior SuperiorGeology Geologytoto1991 1991 i1 Constitution Constitutionof ofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology iiii By-Laws By-Lawsof ofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology iii iii GoldichMedal MedalGuidelines Guidelines Goldich iv v StudentTravel TravelAward Award Student V Boardof ofDirectors Directors Board Vi vi LocalCommittee Committee Local vi vi Student StudentPaper PaperAward AwardCommittee Committee vi vi GoldichMedal MedalCommittee Committee Goldich V1 GoldichMedal MedalRecipient Recipient Goldich VU vii BanquetSpeaker Speaker Banquet Viii Vlll Reportof of the theChair Chairof ofthe the37th 37thAnnual AnnualInstitute Institute Report ix ix Calendarof of Events Events and andProgram Program Calendar xi xi Abstracts Abstracts 1 vi ... 1 �INSTITUTES ON LAKE SUPERIOR GEOLOGY Institute Number Institute Date 1 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Place Place Minneapolis, MN Minneapolis, Houghton, MI East Lansing, MI Duluth, MN Minneapolis, MN Madison, WI Port Arthur, Ont. (Thunder (Thunder Bay) Houghton, MI Duluth, MN Ishpeming, MI Ishperning, St. Paul, MN MN Sault Ste. Marie, MI East Lansing, MI Superior, WI Oshkosh,WI Oshkosh, WI Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, MN Houghton,MI Houghton, MI Madison, WI Sault Ste. Marie, Ont. Ont. Marquette, MI St. Paul, MN Thunder Bay, Ont. Milwaukee, WI Duluth, MN Eau Claire, WI East Lansing, MI International Falls, MN Houghton,MI MI Houghton, Wausau,WI Wausau, WI Kenora, Ont. Wisconsin Rapids, WI Wawa, Ont. Ont. Marquette, MI Duluth, MN ThunderBay,Ont. Thunder Bay, Ont. Eau Claire, WI WI Hurley,WI Hurley, WI �____________ CONSTITUFION OF INSTITUTE INSTI1VIt ON CONSTITUTION OF ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Articlc Art icic I I Name EaEX ArticlcIII1 Article Qbiedivc~ Objectives Theobjectives objediw of ofthis thisorganization organizationare: are: The Thename n a eofofthe theorganization organhationshall shallbe bcthe the"Institute -Instituteon onLake LakeSuperior SuperiorGeology". Gdogf. The A. provide a means whereby A.ToTo provide a means wherebygeologists gdogistsininthe theGreat GreatLakes Lakesregion regionmay mayexchange exchangeideas ideasand and scientific scientificdata. data. B. promote understanding B. ToTo promotebetter bctter understandingofofthe thegeology geologyofofthc thcLake LakeSuperior Superiorregion. region. C. plan conduct C. ToTo planand and condudgeological geologicalfield fieldtrips. trips. ArticleIII I11 Artide Status Sl.iu No Nopart partofofthe theincome incomeof of the the organization organization shall shall inure inure to to the thebenefit benefit of of any any member member or orindividual. individual. In Inthe theevent eventofofdissolution dissolution the the assets assets of of the the organization organization shall shall be be distributed distributed to to (sometax taxfree freeorganization). organization). (some (To (To avoid avoidFederal Fcdcraland andState Stateincome incomctaxes, taxes,the thcorganization organintionshould shouldbebenot notonly only'scientific" 'scientificor or'cducational, "cducationaY,but butalso also"non.profit".) %on-profito.) Minn.Stat. Stat.Anno. Anno.290.01, 290.01, subd. SUM.44 Minn. Minn. Minn.Stat. Stat.Anno. Anno.290.05(9) 290.05(9) 1954 Revenue 1954 Internal ln~crnd RcwnucCode C d cs.s.501(c)(3) 501(c)(3) IV ArticleIV Artidc members hi^ Membership The Themembership membership of of the theorganization organization shall consist of the board board of of directors. directors. Any Anygeologist geologist interested interested shall shall be be permitted pcrmittcd to to attend attend and andparticipate participateininand andvote voteatatthe thcannual annualmeetings. meeting<. ArliclcVV Article Mcetinsq Meetings The Theorganization organizationshall shall meet meet once once a year, preferably prekrably during the month month of April. The Thcplace placeand and exact e n c t date dateof ofeach cachmeeting meetingwill will be desginatcd desginatcd by the thc board board of of directors. directors. Ar~iclcVI VI Article Directors Directors The Theboard boardofofdirectors directorsshall shallconsist consist of the the Chairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and and the the last last three thrcc past pastChairman; Chairman;but butififthe theboard boardshould shouldatatany anytime timeconsist consistof offewer fewerthan thanfive fivepersons, persons, by by rcaon rcaon of of the above persons asdirectors, directors,the thevacancies vacancieson on of unwillingness unwillingnessor or inability inability of any of persons to toserve serveas the so as theboard boardmay maybe befilled filled by by the annual a ~ u ameeting l as to to bring bring the the membership membership of of the the board board up up tofive fivemembers. members. to Arlicle VII 0fficcrs Officcrs Theofficers officersof of this thisorganization organization shall be aa Chairman Chairmanand andSecretary-Treasurer. Secretary-Treasurer. The A. The T%e Chairmanshall shallbebeelected electedeach cachyear yearby bythe theboard boardofofdirectors, dircctors,who whoshall shallgive givedue due A. Chairman considerationto tothe thewishes wishes of of any group that that may may be bepromoting promotingthe thenext nextannual annualmeeting. mecting. consideration asChairman Chairmanwill will terminate terminateatatthe theclose doseofofthe theannual annualmeeting meetingover overwhich which Histerm termofofoffice ofice as His he shall have have been been appointed. appointed. He his successor successor shall Hewill will then then serve serve for for aa he presides presides or or when when his as aa member member of of the the board board of of directors. directors. period of of three three years years as period B. B. The TheSecretary-Treasurer Secretary-Treasurershall shall be be elected elected at at the theannual annualmeeting. meeting. His Histerm termofofoffice oficcshall shall be two two years years or oruntil until his his successor successor shall have have been appointed. appointed. be Article VIII WII Article -Amendmen& Amendments Thisconstitution constitution may may be amended amended by aa majority majority vote vote of ofthose thosepersons personswho whoare arepersonally personally This present at, at,participating participatingin, in, and and voting voting at at any any annual annualmeeting metingof ofthe theorganization. organization. present �BY-LAWS 'BY-JAWS I. Duties of of the the Officers Officers and and Directors Directors Duties A It It shall shall be be the the duty duty of of the the Annual Annual Chairman Chairmanto: to: A. 1. 1. 2. 2. 3. 3. B. B. Preside at the the annual annual meeting. meeting. Appoint committees needed for the organization organization of the annual meeting. Appoint all all committees meeting. Assume for the organization Assume complete responsibility for organization and financing financing of of the the annual meeting meeting over over which which he presides. presides. It shall shall be be the the duty duty of of the theSecretary-Treasurer Secretary-Treasurerto: to: 1.. 1.. 2. 2. 3. 3. Keep Keep accurate accurate attendance attendance records records of of all allannual annualmeetings. meetings. Keep Keep accurate records records of all all meetings meetings of, of, and and correspondence correspondence between, between, the the board board of of directors. directors. Hold all funds funds that may may accrue as as profits profits from from annual annual meetings meetings or or field field trips and to make these funds available for the organization and operation operation of future future meetings meetings as as required. required. C. ItIt shall shall be the the duty of the board of directors to plan plan locations locations of annual meetings meetings C. and to to advise advise on on the theorganization organizationand andfinancing financingof ofall allmeetings. meetings. II. 11. Duties and and Expenses Expenses 1. 1. 2. 2. III. 111. There There shall shall be be no noregular regularmembership membershipdues. dues. Registration Registration fees for the annual meetings shall be determined by by the Chairman in consultation with the board of directors. It is strongly recommended consultation board of directors. is strongly recommended that that these be kept kept at at aaminimum minimum'to to encourage encourage attendance attendanceof of graduate graduatestudents. students. Order Rules of Order in all all The rules rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shallgovern govern this this organization organization in The to which which they they are are applicable. applicable. cases to IV. IV. Amendmenu Amendments These by-laws bylaws may majority vote of those those persons persons who who are are may be be amended amended by by aa majority vote of personally present meeting of personally present at, at, participating participatingin, in,and and voting voting at at any any annual annual meeting of the organization;provided provided that that such such modifications modifications shall shall not not conflict conflict with the the constitution constitution organization; as presently presently adopted adopted or orsubsequently subsequentlyamended. amended. as iii III �Award Guidelines Guidelines SAM SAM GOLDICH GOLDICH MEDAL MEDAL Preamble Preamlde as documented documented by by The Institute Institute on on Lake LakeSuperior SuperiorGeology Geology was was born born on on or oraround around1955, 1955, as The the fact fact that that the the27th 27th annual amual meeting meeting will be be held in in 1981. 1981. The The Institutes Institutes are are exemplary exemplary the in of dealing with with those aspects of in their their continuing continuing objectives objectives of of geology geology that are are related related geographically to Lake Lake Superior; Superior; of of encouraging encoumging the the discussion discussionof of subjects subjectsand andsponsoring sponsori~~g field will bring bring together togethergeologists geologists from from academia, academia,government governmentsurveys, surveys, and and field trips trips which which will industry; and of maintaining an exceedingly informal but highly effective mode of operation. industry; and of maintaining an operation. During During the the course course of of its its existence existence the membership membe'nhip of the Institute Institute (that (thatis, is,those thosegeologists geologists who who indicate indicate an an interest interest in in the the objectives objectives of the LLS.G. 1.LS.G. by by attending) attending) has has become become aware aware of the the fact factthat thatcertain certainofoftheir theircolleagues colleagueshave havemade madeparticularly particularlynoteworthy noteworthy and and meritorious contributions to the improvement of understanding of "Lake Superior" geology meritorious contributions to the improvement of understanding of Xake Superior" geology and and its itsmineral mineraldeposits. deposits. The exemplary award was was made made by by 1.LS.G. I.LS.G. to to Sam exemplary award Sam Goldich Goldich in in 1979 1979 for for his his many many contributions to 50 years. years. to the the geology geology of the region region extending over about about 50 Guidelines Award Guidelines 1) by the 1.LS.G. ILS.G. Board 1) The Themedal medalshall shallbe beawarded awarded annually annually by BoardofofDirectors Directorstotoaageologist geologist whose name is associated with with aa substantial substantialsustained sustained interest interest in, or a major contribution to, the the geology geology of of the the Lake Like Superior Superiorregion. region. 2) The TheBoard BoardofofDirectors, Directors,I.LS.G. 1.LS.G. shall shall appoint appoint the the Nominating Nominating Committee. The The initial initial appointment appointment will will be of three members, members, one to serve seme for for three threeyears, years, one onefor fortwo, two, and and one After the the one for for one one year, year, the the member member with with the briefest incumbency to be chairman. After first year the Board of Directors shall appoint at each spring meeting one new member spring seme for for three three years. years. In the the thrid thrid year year this this member member shall shall be be the thechairman. chairman. who will serve The Committee Committeemembership membership should reflect the main main fields fields of of interest interestand and geographic geographic of I.LS.G. 1.LS.G. membership. membership. distribution of 3) By By November November 1,1, the Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall shall make make its its recommendation to the the Chairman Chairman of of the the Board Board of of Directors Directorswho whowill will then then inform inform the the of the the nominee. nominee. Board of TheBoard BoardofofDirectors Directorsnormally normallywill will accept accept the the nominee nomineeof ofthe theCommittee, Committee,will will inform inform 4) The the medalist and will medalist immediately, immediately, and will have have one one medal medalengraved engraved appropriately appropriately for for presentation at at the the next next meeting meeting of the the Institute. Institute. 5) It is recommended recommended that the Institute Institute set set aside asideannually annuallyfrom fromwhatever whatever sources, sources, such such 5) as will will be required required to to support support the thecontinuing continuingcosts costs of ofthis thisaward. award. funds as April 4, 1981 1981 April 4, J. J. Kalliokoski, Kdliokoski, Chairman Chairman Bill Cannon Cannon Fred Kehlenbeck Kehlenbeck Glenn Morey Morey Greg Mursky Mursb iv �STUDENT TRAVEL TRAVEL AWARD -STUDENT AWARD the 1.LS.G. LLS.G. Stildcnt Student Travel Award ' l'hc 1 % ~l98ô 1080 Board of [)irectors Directors established established thc Aw:triI to t o s111~1~ot.t participation at fi11~1 sstudent t t ~ d ~participation t~t at the the annual Institutes. The Theawards awards will willbe bemade made from froniaaspecial spcci;d fund purpose. This set up u p for this purpose. This award award is intended to help help defray defray some of the direct direct travel travel costs to the Institute Institute and and includes includes aa waiver waiver of registration registration fees, fees*but but excludes excludes expenses for lodging,and and field fieldtrip tripregistration. registration. The The number number of of awards and value are are determined meals, lodging, by with the the Secretary-Treasurer Secretary-Treasurer and will will be be announced announced by the annual Chairman in consultation with at the annual annual banquet. banquet. The following following general general criteria criteria will will be be considered by the annual considered by amual Chairman, Chairman, who who isis responsible for the the selection: selection: 1) The resident (undergraduate (undergraduate or graduate) student Theapplicants applicantsmust must have active resident status at the the time time of of the the Institute, Institute, certified certified by by the the department department head. head. 2) Students Studentswho who are are the the senior senior author on either an oral oral or or poster poster paper paper will will be given favored consideration. consideration. 3) ItItisisdesirable desirablefor fortwo two or ormore more students studentsto tojointly jointly request request travel travel assistance. assistance. Ingeneral, general, priority priority will will be given given to those in in the the Institute Institute region region who who arc arc 4) In farthest farthest'away. away. 5) Each Eachtravel travelaward awardrequest request shall shall be be made made in in writing, writing*to the annual annual Chairman, Chairman, explanation of need, possible author status status or or other othersignificant significantdetails. details. with an explanation registration for the the Meeting. Meeting. Successful applicants applicants will willreceive receivetheir theirawards awardsatat the the time of registration V �BOARD OF DIRECTORS 1992 AlbertB.B.Dickas Dickas Albert University UniversityofofWisconsin-Superior, Wisconsin-Superior,Superior, Superior,Wisconsin Wisconsin54880 54880 1991 P.E.Myers Myers P.E. Department DepartmentofofGeology, Geology,University UniversityofofWisconsin, Wisconsin,Eau EauClaire, Claire,Wisconsin Wisconsin 54701 54701 M.M.Kehlenbeck Kehlenbeck 1990 M.M. Department DepartmentofofGeology, Geology,Lakehead LakeheadUniversity, University,Thunder ThunderBay, Bay,Ontario OntarioP7B P7B5E1 5El 1989 R.W.Ojakangas Ojakangas R.W. Department DepartmentofofGeology, Geology,University UniversityofofMinnesota, Minnesota,Duluth, Duluth,Minnesota Minnesota55812 55812 Secretary-Treasurer Secretary-Treasurer M.G.Mudrey, Muclrey,Jr.Jr. M.G. WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey Wisconsin 3817 Mineral Point Road, Madison, Wisconsin 53705 3817 Mineral Point Road, Madison, Wisconsin 53705 LOCAL COMMITTEE LOCAL COMM ~E A.B.Dickas Dickas A.B. General GeneralChairman, Chairman,University UniversityofofWisconsin-Superior, Wisconsin-Superior,Superior, Superior,Wisconsin Wisconsin 54880 54880 B.A. Brown Brown B.A. Proceedings ProceedingsEditor, Editor,Wisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey 3817Mineral MineralPoint PointRoad, Road,Madison, Madison,Wisconsin Wisconsin53705 53705 3817 STUDENT PAPER AWARD COMMITTEE 1992E STUDENT PAPER AWARD C O ~1992 PenelopeMorton Morton Penelope Chairman, Chairman,Department Departmentof ofGeology, Geology,University UniversityofofMinnesota, Minnesota,Duluth, Duluth,MinneMinnesota 55812 sota 55812 GOLDICH MEDAL COMMITTEE 1991-92 GOLDICH MEDAL C O ~1991-92 E F.W. Cambray Cambray(1992) (1992) F.W. Department Departmentof of Geological GeologicalSciences, Sciences,Michigan Michigan State StateUniversity, University, East East Lansing, Lansing, Michigan Michigan H.H.Halls Halls(1993) (1993) H.H. Department Departmentof of Geology, Geology,Erindall ErindallCollege, College,Mississauga, Mississauga, Ontario OntarioL5L L5L1CO 1CO R.D. Sage Sage(1994) (1994) R.D. Ontario OntarioGeological GeologicalSurvey, Survey,777 777Grenville GrenvilleStreet, Street,Toronto, Toronto,Ontario, Ontario,M7A M7A 1W4 lW4 vi �CiTATION CITATION Cannon, Goldich Goldich Medal Medal recipient, recipient, 1992 1992 W. F. Cannon, W. F. (Bill) Cannon richly richly deserves deserves this this highest highest honor honor of of the the Institute on Lake W. Lake Superior SuperiorGeology Geology because of his many outstanding outstanding contributions to geology and and mineral mineral deposits deposits of of the the Lake Superior Superior region. region. Bill received B.S. B.S. and and Ph.D. degrees from Syracuse Syracuse University and in between between sandwiched sandwiched in in an an M.S. degree degree from from Miami MiamiUniversity. University. He He was wasborn, born,raised, raised,and andstill stillremains remainsan aneasterner easterner at at heart, M.S. flat country of of the the Lake Superior and hence is ideally suited to work in the mostly flat Superior region. Bill joined joined the the U.S. U.S. Geological Geological Survey Surveyinin 1967. 1967. During During his his early early career with the USGS USGS he he was was Bill mainly a geologic mapper, mapper, who who slogged sloggedthrough through the the murky murky swamps swamps of of the the Upper Peninsula Peninsula in in his his L. L. Bean L. Bean rubber-soled rubber-soled shoes, and turned out out an anincredible incredible number number of ofhigh highquality qualitygeologic geologic These maps maps will will remain remain as as a legacy to his innate ability legacy to ability as aa mapper. mapper. In quadrangle maps. maps. These quadrangle addition, he was involved at various various times times with withiron iron and and manganese manganese resource resource studies studies on on a large involved at scale, and he continues today as an expert on worldwide manganese resources. From 1977 continues as an expert on From 1977toto1981, 1981, he coordinated lWOquadrangle, quadrangle, coordinated aa successful successful mineral mineral resource assessment assessment of the the Iron IronRiver River1°x2° Michigan-Wisconsin. Michigan-Wisconsin. days in in the field when he he was was named named Chief Chief of of the Branch of field terminated terminated in 1981, 1981, when These glory glory days of the USGS, Eastern Mineral Mineral Resources Resources and and then then (1984-88) (1984-88) Associate Chief Geologist of USGS, both of of which credit, while while Branch Branch Chief he hired hired several severaltop-flight, top-flight, younger younger which he served served ably. ably. To his credit, geologists, including our colleague colleague Klaus Klaus Schulz. Schulz. Chief Geologist, Geologist, he he conceived conceived and and master master minded a joint U.S.-Canadian While Associate Chief U.S.-Canadian deep deep with Alan Alan Green Green of the Geological of Canada as crustal study (GLIMPCE), in conjunction with Geological Survey of well as personnel personnel from numerous state and universities. universities. This state and and provincial surveys and This project focused focused and potential potential field investigations of of the the deep deep structure of the Midcontinent on seismic and MidcontinentRift Rift System, System, and it has Perhaps this project and has produced produced more more than than 50 50 papers papers and and abstracts. abstracts. Perhaps project with with its many many ramifications is the single most productive scientific scientificachievement achievementcarried carried out out in in the the Lake Superior Superior region in the post-World War II period. ItIt truly truly brought brought Keweenawan studies in the Lake Superior Superior region Bill is author or coauthor coauthor of of more more region out of the doldrums and into the forefront of science. science. Bill than 100 100 reports and and maps, maps, several severalof of which which concern the rift rift system. system. Conversations with him, Bill is a modest, generally quiet quiet guy guy who whonever neverpats patshimself himselfon onthe theback. back. Conversations about geology geology (or (or geophysics) geophysics) or sports sports at at Syracuse, Syracuse, however, however, are are always always lively, and he's whether about a stimulating guy He isisunique uniqueamong amongmy my guy to to be be with with in in the the field field or, or, after after work, work,in in the the local local bar. bar. He he drinks drinks aa manhattan manhattan before beforedinner, dinner,ififyou you know know what what that thatis. is. close acquaintances in that he know what Bill's middle initial (F.) stands for, but to many of his close associates it stands I don't know for aa fine, fine, fine finefellow. fellow. P. K. Sims Sims v" �BANQUET SPEAKER Duff Kerr, Kerr and Associates, Denver, Colorado, Colorado, will be the speaker speaker at at the Annual Annual ILSG ILSG Banquet. He will speak on: Industrial petroleum exploration of the Midcontinent Rift Frontier. tier. VIII �37TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY EAU CLAIRE, WISCONSIN, 1991 Meeting of the Institute on Lake Superior 1991 The 37th Annual Meeting Superior Geology met from from May May 1-4, 1-4,1991 in Eau Claire, Wisconsin-Eau Claire, Wisconsin. Wisconsin. The host for this meeting was the University of Wisconsin-Eau Claire. Paul Paul E. Myers Myers was the General Chairman. Lung Lung S. S. Chan Chan coordinated coordinated publications and field trips. The in two two parts: parts: Part I contains the The Proceedings Proceedings of this conference were published in abstracts, and Part II II contains conference field trips. contains field guides for the three conference Technical Center Inn, Inn, Eau Eau Claire. Claire. A A total total Technical sessions sessions and banquet were held in the Civic Center of 154 154 geologists geologists from from the Lake Lake Superior Superior region region registered, registered, and and 92 92 people people attended attended the the annual annual banquet. The technical sessions included 31 oral papers and 23 poster papers. A symposium The technical sessions included papers and 23 poster papers. symposium on the mineral resources comprised eight resources potential of northern Wisconsin comprised eight papers by geologists geologists from from the mining mining industry industry and and Wisconsin Wisconsin Geological Geological and and Natural History History Survey. Survey. (#1), led led by by Paul Paul K. K. Sims Sims and and John John S. S. Klasner, Kiasner, studied studied "The "The A pre-conference field trip (#I), Mountain shear zone-a zone—a post-Penokean discrete ductile ductile deformation deformation zone." zone." The The guidebook guidebookfor for this field trip was authored authored by P.K. Sims, Sirns, J.S. Kiasner, Klasner, W.C. Day, Day, and and Z.E. Z.E. Peterman. Peterman. A second second pre-conference pre-conferencefield field trip (#2) concentrated concentrated on the "Features "Features and and significance significance of the Precambrian-Cambrian contact in western western Wisconsin." Wisconsin." The trip, including stops The trip, including stops near near Wisconsin,was wasled ledby byLung Lung S. S. Chan Chan and and RichRichEau Claire, Black River River Falls, and Nefflsvffle, Neillsville, Wisconsin, ard L. Hay, with additional additional field field guide guide materials materials by Paul E. Myers. A post-conference post-conference field trip, entitled "Proterozoic volcanogenic massive massive sulfide sulfide deposits deposits of Northwestern Wisconsin," involved involved mainly mainly the the inspection inspection of cores cores from from the the Flambeau, Flambeau, Lynne, and Bend deposits Hawkins, deposits at Ladysmith and H a w h s , Wisconsin. Co-leaders Co-leaders for for this this trip trip were were M.G. Mudrey, Jr., and B.A. Brown, both of the Wisconsin Geological and Natural History History Survey. Survey. three field field trips. trips. Vans for the pre-conference pre-conference field A total of 87 people attended these three Squire, Tony Tony Jones, Jones, Zach Zach Kostalek, Kostalek, driven by undergraduate undergraduate geology geology students students Mike Mike Squire, trips were driven and Michelle Barnes from the University of Wisconsin-Eau Claire. Annual Banquet Banquet on May 2 was attended attended by 92 people. Val Val W. W. Chandler, Chandler,MinneMinneThe Annual sota Geological Survey, presented the 1991 1991 Goldich Medal to William Purdue UniverUniverWilliam J. Hinze, Purdue sity, for for his his many contributions as an educator and in geophysical geophysical studies of the Great Lakes region. The TheGoldich GoldichAward Award Committee Committee included included M.G. Mudrey, Jr., H.H. H.H. Halls, and F.W. F.W. Carnbray. The TheAnnual Annual Banquet Banquetspeaker speakerwas Paul K. Sims. His His topic topic was, was, "Archean "Archean and and Early Early Cambray. Proterozoic Geology of the Lake Superior Region-an Region—an Overview." Overview." Students travel travel awards awards totalling totalling $1080 $1080 were were presented presented to to five five students students giving giving papers: papers: Students Sidney Hemming, Matt Manson, James James Johnson, Johnson,Denise DeniseSlavish, Stavish,and andMary MaryTozer. Tozer. Three Three $150 David J. Allen, Alien, John John Mariano, Mariano, and and awards for best oral and poster papers went to to 3 students: David Michael D. Thompson. John Klasner, Klasner, John Gardener, Gardener, and William Cannon served on Thompson. John on the Best Best Student Paper Award Award Committee. Committee. The I.L.S.G. The meeting meeting was atI.L.S.G. Board of Directors met met in in Eau Eau Claire Claire on on May May 2. 2. The tended by M.G. Mudrey, Jr., M.M. Kehienbeck, Kehlenbeck, P.E. Myers, L.S. L.S. Chan, J. Klasner, Kiasner, R.W. Ojakangas, and A.B. Dickas. Ojakangas, The following items were were discussed: following items 1992meeting meeting will will be at Hurley, Wisconsin, on May 6-9. Co-hosts Co-hosts Thesite sitefor forthe the 1992 (1) The A.B. Dickas of University of of Wisconsin-Superior Wisconsin-Superior and B.A. for this conference are A.B. Brown of Wisconsin Geologicaland and Natural Natural History History Survey. Survey. Wisconsin Geological ix �(2) Treasurer's Report: (2) Wisconsin with with Bruce Brown Brown having a full Michigan account was transferred to Wisconsin power of attorney with M.G. Mudrey, Jr. Jr. $1000 $1000was was placed placed in ready ready checking checking account account and remainder (about $4000) was placed in a CD (Mt. Horeb). The Goldich account account was placed in a three-year CD, the rest in 6-month CDs total about $6800. Mudrey has old field trip guidebooks; proceedings are still at Houghton Tech. old Goldich Goldich medals. medals. Their present value is approximately Glen Morey still has old approximately $200. In In1988 1988there therewere were12 12medals, medals, then then valued valued at at $115 $1 15== $1380. (3) Procedures for limited limited student student travel assistance assistanceawards: awards: A motion was made (M.K.) (M.K.) to develop develop a form form for itemizing itemizing anticipated anticipated costs costs for for travel and lodging with total awards not exceeding $1000 (shared equally by Canadian U.S. treasuries) treasuries) and individual awards of no more than $200. This motion and U.S. motion was not not voted on. Another motion was made (J.K.) (J.K.) to provide assistance assistance to faculty in bringing students to institutes to a maximum maximum of of $50. $50. The motion The motion was amended amended to recommend recommend that that partial or total remission of fees may, at the discretion of the local committee, be used as an incentive for attracting students. The The motion passed. Lung Chan Chan and and I wish to thank those who generously donated donated time and and talents to to make make the 1991 1991 meeting a success. success. Respectfully submitted, submitted, P.E. Myers General Chairman, I.L.S.G., I.L.S.G., 1991 1991 x �CALENDAR OF EVENTS AND PROGRAM Wednesday,May May66 Wednesday, Field Trip Trip11 Early EarlyProterozoic Proterozoicand andArchean Archeanrock rockofofthe theGogebic GogebicRange. Range. Field Leaders: G.L. LaBerge, R.W. Ojakangas, and K. Licht Leaders: G.L. LaBerge, R.W. Ojakangas, and K. Licht Registrationand anddeparture, departure,Holiday HolidayInn Innlobby lobby am Registration 8:00 am 8:00 6:30 pm Return 6:30pm Return Field Trip Trip22 Evolution Evolutionof of the theKeweenawan Keweenawansedimentary sedimentarysequence. sequence. Field Leaders: M.G. Mudrey, Jr., and A.B. Dickas Leaders: M.G. Mudrey, Jr., and A.B. Dickas Registrationand anddeparture, departure,Holiday HolidayInn Innlobby lobby am Registration 8:00 am 8:00 6:30 pm Return 6:30pm Return 4:00-8:00 pm and check-in, check-in, Holiday HolidayInn Innlobby lobby 4:00—8:00 pm Registration Registration and 7:00-11:00 pm (cash bar)/Poster bar)/Poster session, session,Holiday Holiday Inn Inn Conference ConferenceRoom Room 7:00—11:00 pmIcebreaker Icebreaker (cash Thursday,May May77 Thursday, All technical technical sessions sessionsand andposter poster sessions sessionsare areininthe theConference ConferenceRoom Roomatatthe theHurley, Hurley,WisconWisconAll sin,Holiday HolidayInn. Inn. Contributors Contributorsshould shouldhave haveposters postersupupby bynoon, noon,Thursday, Thursday,May May7.7. sin, 7: 15am am 7:15 Registration,Holiday HolidayInn Inn lobby lobby Registration, ArcheanSession: Session:Frank FrankLuther, Luther,session session chair (8:30-9:50 am) am) Archean chair (8:30—9:50 TheodoreJ.J.Bornhorst, Bomhorst,Richard RichardT. T.Wilkin, Wilkin,and andRodney RodneyC. C.Johnson Johnson 8:30 am Theodore Temporalprogression progressionofofArchean Archeangranitoid granitoidrocks, rocks, Temporal Ishpeming greenstone belt and vicinity, Michigan Jshpeming greenstone belt and vicinity, Michigan 8:50 am A.C. Turnock Turnockand andD.C. D.C.Kamineni Karnineni A.C. Thermaland andregional regionalmetamorphism metamorphismin inArchean Archean basalt, basalt, Thermal Bird River Greenstone Belt, Manitoba, Canada Bird River Greenstone Belt, Manitoba, Canada 9:10 am BarbaraE. E.Seemayer Seemayerand andManfred ManfredM. M.Kehlenbeck Kehlenbeck Barbara Variations in metamorphic grade of metapelites along transects transects Variations in metamorphic grade of metapelites along acrossthe theQuetico QueticoSubprovince Subprovince across 9:30 am TerrenceJ.J. Boerboom Boerboomand andMark MarkA. A. Jirsa Jirsa Terrence Geology and andtectonic tectonicsetting setting of of the the Archean GiantsRange Range Batholirh; Batholith; Geology Archean Giants Western Wawa Subprovince, Minnesota Western Wawa Subprovince, Minnesota 9:50 am Coffee break break Coffee xi �Geophysics chair (10:10—11:50 GeophysicsSession: Session:C.C.Patrick PatrickErvin, Ervin,session session chair (10:10-11:50 am) am) 10:10 10: 10 am Daniel DanielJ.J.Brehm, Brehm,C.C.Patrick PatrickErvin, Ervin,and andJeffrey JeffreyK. K. Greenberg Greenberg Gravity Gravitymodel modelofofthe theWolf WolfRiver River Batholith Batholith 10:30 10:30 am Lung LungS.S.Chan, Chan,Zachary ZacharyKostalek, Kostalek,and andRichard RichardL. L. Hay Hay Isotope Isotope and andpaleomagnetic paleomagnetic dating datingof of weathered weatheredgranite granitebelow belowthe the Precambrian-Cambrian Precambrian-Cambriancontact contactininNeillsville, Neillsville,Wisconsin Wisconsin 10:50 10:50 am Stephen StephenA. A.Kissin, Kissin,Graham GrahamJ.J.Borradaile, Borradaile,Joe Joe D. D. Stewart, Stewart,William William A. A.Ross, Ross, andThomasz ThomaszWerner Werner and Magnetic Magnetic and and petrographic petrographic detection detectionof of heat heattreatment treatmentinin Gunflint Chert Gunflint Chert 11:10 am Timothy TimothyB.B.Hoist Hoistand andHaakon HaakonFossen Fossen 11:10 On Onthe theuse useof of paleocurrent paleocurrent indicators indicatorsinindeformed deformedrock rock 11:30 11:30 am am Michelle MichelleL.L.Barnes, Barnes,Georgia GeorgiaL. L.Osborn, Osborn,and andLung LungS. S.Chan Chan An An integrated integratedgravity gravityand andmagnetic magneticsurvey surveyofofthe theRock Rock Elm Elm structure, structure, westernWisconsin Wisconsin western 1l:5O am Lunchbreak break 11:50 am Lunch Institute Instituteon on Lake Lake Superior SuperiorGeology GeologyBoard Boardof of Directors DirectorsLuncheon Luncheon(by (by invitation) invitation) Posterson ondisplay display Posters Proterozoic W.W.Ojakangas, session chair ProterozoicSession SessionI:I:Richard Richard Ojakangas, session chair(2:00—3:20 (2:00-3:20 pm) pm) 2:OO pm pm Gene Gene L. L. LaBerge LaBerge 2:00 The The Early Early Proterozoic ProterozoicEmperor Emperorvolcanic volcaniccomplex: complex:Implications Implicationsfor for the the geology geology of the eastern eastern Gogebic Gogebic District, northern northernMichigan Michigan KathyLicht Lichtand andT.P. T.P. Flood Flood 2:20 pm pm Kathy 2:20 The from the The chemistry chemistry and and petrography petrography of ofmafic maficrocks rocks/rom the Early EarlyProterozoic ProterozoicEmperor Emperorvolcanic volcaniccomplex complexnear nearMarinesco, Marinesco,Michigan Michigan xii xii 2:40 pm pm 2:40 S.R. S.R. Hemming, Hemming, S.M. S.M. McLennan, McLennan,and andG.N. G.N. Hanson Hanson Provenance Provenanceofofthe theAnimikie Animikie Group, Group,NE NE Minnesota, Minnesota, basedon onNd Nd and and Pb Pbisotopes isotopes based 3:OO pm pm 3:00 Mark Mark E. E. Davidson Davidsonand andJohn JohnC. C. Palmquist Palmquist Implications Implicationsof of strain strainand andmagnetic magneticanisotrophy anisotrophystudies studiesfor for the the Penokean PenokeanOrogeny, Orogeny,Upper UpperMichigan Michigan 3:20pm pm 3:20 Coffee break break Coffee �Proterozoic ProterozoicSession SessionII:11:Bruce BruceA.A.Brown, Brown,session sessionchair chair(3:40—4:40 (3:40-4:40 pm) pm) 3:40 pm Richard W. Ojakangas Ojakangas and and Jukka Jukka S. S. Marmo Manno Early sequences of Early Proterozoic Proterozoicleptire leptite & & halleflinta halleflinta (tuff (tuff&& tuffite) tuffite) sequences southern southernFinland Finland reinterpreted reinterpretedas asshear shearzones: zones:Significance Significance to to Lake Superior Superior geology geology 4:00 pm M.G. M.G. Mudrey, Mudrey,Jr., Jr., and andB.A. B.A. Brown Brown Penokean from formational formational contacts Penokean structural structuraltrends trendsdefined defined from contacts and cleavage cleavageanalysis analysisalong alongthe theGogebic GogebicRange, Range,Wisconsin Wisconsin 4:20 pm Xinping XinpingYin Yin and andJames James A. A. Grant Grant Geochemistry Geochemistryof of the metadiabases metadiabases in in the the Republic Mine area, area, northern northernMichigan Michigan 4:40 pm End End of of technical technicalsessions sessionsfor for the the day day Posters Posters on on display display 6:00—7:00 pmMixer, Mixer, cash cash bar bar 6:00-7:00 pm 7:00-10:OOpm Annual Banquet Banquet 7:00-10:OOpm Annual Announcement Announcementof of 39th 39thAnnual Annual Meeting Meetinglocation, location,1993. 1993. Goldich F.Cannon Cannonby byPaul PaulK. K.Sims. Sims. GoldichAward Awardpresentation presentationto toWilliam WilliamF. Banquet Banquetspeaker: speaker:Duff Duff Kerr, Kerr, Kerr Kerrand andAssociates, Associates,Denver, Denver,Colorado; Colorado; IndustrialPetroleum PetroleumExploration Explorationof ofthe theMidcontinent Midcontinent Rift Frontier Industrial Frontier Friday, Friday,May May88 8:00 8:00 am am Registration, Registration,Holiday HolidayInn Innlobby lobby MidcontinentTectonics Tectonicsand andProcesses ProcessesSession SessionI:I:William WilliamJ.J.Hinze, Hinze,session sessionchair chair Midcontinent (8 :30-10:00 am) (8:30-1090 am) 8:30 am William F.Cannon Cannon WilliamF. Process Processrates ratesduring duringMidcontinent Midcontinent rfting: rifting: Clues Cluestotothe theorigin originofofthe theMidcontinent MidcontinentRift RiftSystem System 8:55 am J.D. J.D. Miller, Miller,Jr. Jr. The need for The need aa new new paradigm regarding regardingthe thepetrogenesis petrogenesis of of the theDuluth DuluthComplex Complex 9:20 am Albert AlbertB. B.Dickas Dickas Preliminary Preliminaryreport, report,geology geologyand andgeophysics geophysicsof of the the Terra/Patrick TerraIPatrick#7-22 #7-22 wildcat wildcathydrocarbon hydrocarbontest, test,Midcontinenr MidcontinentRift, Rift,Keystone KeystoneTownship, Township, Bayfield BayfieldCounty, County,Wisconsin Wisconsin xiii XIII �9:40 am am David J. Allen and Val W. Chandler of high-resolution high-resolution aeromagnetic aeromagnetic data for for investigating The utility of investigating the the Midcontinent Rift Rift in east-central east-central Minnesota 10:00 break 10:OO am Coffee break Midcontinent Tectonics II:A.B. A.B.Dickas, Dickas,session session chair chair Midcontinent Tectonicsand andProcesses ProcessesSession SessionII: (10:20—11:20 (10:20-11:20 am) am) 10:20 am am Pieter PieterBerendsen Berendsen Structure and composition composition of Keweenawan rift-related igneous igneous and Structure sedimentary rocks in Kansas 10:40 am am Kathleen 10:40 Kathleen M. M. Witthuhn Witthuhn A structural structural analysis MidcontinentRft analysis of the Midcontinent Rift in inMichigan, Michigan, fault array based on a fault arrayanalysis analysisutilizing utilizing slickensides 11:00 am John 11:OO am John C. C. Green Green Palisade Rhyolite, Minnesota. The Palisade Rhyolite, Lake County, County, Minnesota: rheoignimbrite in A cryptic rheoignimbrite in the North Shore Shore Volcanics Volcanics 11:20am am Lunch break 11:20 Posters on display Economic GeologySession SessionI:I:Lawrence LawrenceKennedy, Kennedy,session sessionchair chair(1:00—2:20 (1:00-2:20 pm) Economic Geology 1:00 pm Anthony J. Deevy Magino, the the making of aa mine 1:20 pm Susan E. Brink compositional study of aa managaniferous iron-formation, Textural and compositional managaniferous iron-formation, Emily District, deposition District, Cuyuna Range, with implications/or implications for original original deposition and in in situ leaching leaching of manganese manganese 1:40 pm G.B. Morey, Peter L. McSwiggen, and Jane M. Cleland G.B. of an an exhalative contribution to the manganese manganese mineralogy of Evidence of the Trommald Formation, Formation, Cuyuna Iron Iron Range, Range, east-central east-central Minnesota 2:00 pm Susan E. Brink petrology and geochemistry of the Spirit volcanogenic The petrology volcanogenic massive massive prospect, north-central north-central Wisconsin sulfide prospect, Wisconsin 2:20 pm break Coffee break Presentation Presentation of student student awards xiv �Economic chair EconomicGeology GeologySession SessionII:3.1Allan : AllanM.M.Johnson, Johnson,session session chair(2:40—3:40 (240-3:40 pm) pm) 2:40 pm Penelope PenelopeMorton Mortonand andStephen StephenD. D.Geerts Geerts High temperature hydrothermal alteration High temperature hydrothermal alterationassociated associated with with PGE PGEenrichment enrichmentofofCu-Ni Cu-Nisulfides, sulfides,Dunka DunkaRoad, Road,Duluth DuluthComplex, Complex, NE NE Minnesota Minnesota 3:00 pm Mark Mark J.J. Severson Severson Sulfide PGE mineralization Sulfide and andPGE mineralizationat at the the basal basal contact contactof ofthe the Minnamax Minnarnax deposit, deposit, Duluth Duluth Complex, Complex, NE Minnesota 3:20 pm Daniel Daniel N. N. Miller, Miller,Jr. Jr. Accessing Accessing the the Anaconda Anaconda Geological GeologicalDocuments DocumentsCollection Collection Minnesota Michigan -- Ontario Ontario Minnesota-Wisconsin -Wisconsin--Michigan 3:40 pm End Endofoftechnical technicalsessions sessions 5:00 pm Field departurefor for Marquette Marquette Field Trip Trip 4 departure Saturday, Saturday,May May99 Field Trip Trip 33 Geology GeologyofofKeweenawan Keweenawanrock rock near nearthe thePorcupine PorcupineMountains, Mountains, Ontonagon Ontonagonand andGogebic Gogebic Counties, Counties,Michigan. Michigan. Leaders: Leaders: W.F. W.F. Cannon, Cannon, S.S. S.S. Nicholson, Nicholson, C. C. Hedgman, Hedgman, L. Woodruff, Woodruff, and and K.J. Schulz Schulz Departurefrom fromHoliday ~ o l i dInn, Inn, a ~ Hurley Hurley 8:00 am Departure 4:30pm Return Return Field Trip Trip 4 Geology Field Marquette area, Geologyofofthe theGreat GreatLakes Lakestectonic tectonic zone zone in the Marquette area, Michigan—A Michigan-A late Archean Archean paleosuture. paleosuture. Leader: Leader: P.K. Sims Sims and and Z.E. Peterman Peterrnan 8:00 am am (Eastern (EasternDaylight Daylight Savings)—Departure SavingsbDeparture from from Ramada Ramada Inn, Inn, Marquette, Marquette,Michigan Michigan 4:30 4:30 pm pm (Eastern (Eastern Daylight Daylight Savings)—End SavingsbEnd of trip trip 6:00 6:00pm (Central (Central Daylight Daylight Savings)—Return SavingsbReturn to to Hurley Hurley xv �POSTER POSTER PRESENTATIONS PRESENTATIONS Archean Archean Frank Frank R. R. Luther Luther Magnetite Magnetite octahedra octahedrain inpillow basalt basalt near nearWawa, Wawa,Ontario Ontario Geophysics Geophysics C. Patrick Patrick Ervin, Ervin, M.G. M.G. Mudrey, Mudrey, Jr., Jr., B.A. B.A. Brown, Brown, and and M.L. M.L. Czechanski Czechanski 1991 program in 1991COGEOMAP COGEOMAP gravity mapping program in west-central west-central Wisconsin: Wisconsin: The Driftless Driftless Area Proterozoic Proterozoic Bradley Bradley Hellickson, Hellickson, Stanley Stanley Radzevicius, Radzevicius, and Garry Garry Anderson Anderson Petrology and structure of a rapakivi body from east-central Petrology and structure of a rapakivi body east-centralMinnesota Minnesota Daniel Daniel Holm, Holm, Timothy Timothy Hoist, Hoist, and and Daniel Daniel Lux Lux Thermochronologic Thermochronologicevidence evidencefor post-Penokean post-Penokeanunroofing unroofing in the the Lake Superior Superior region region in G.B. Morey Morey and and Terrence Terrence J. J. Boerboom Boerboom Rare Rare earth earthelement elementdistribution distribution patterns in in Early Early Proterozoic Proterozoiciron iron formations formations of of the the Penokean Penokean orogen, orogen, east-central east-centralMinnesota Andrew D. Moshoian, Moshoian, Karl Karl R. Wirth, Wirth, and and John John P. Craddock Craddock The Kenora-Kabetogama Kenora-Kabetogama dike trace element dike swarm: swarm: Results of trace element studies Midcontinent Midcontinenttectonics tectonics and and processes processes Albert Albert B. Dickas Dickas and and M.G. M.G. Mudrey, Mudrey, Jr. Jr. Precambrian Precambrianhydrocarbon hydrocarbonpotential potential of of the the western western Great GreatLakes Cheryl A. Hedgman Hedgman Cheryl Petrology and fades of Petrology and provenance of a conglomerate fades of the the Jacobsville Jacobsville Sandstone: Sandstone: Iron Iron to to Bergland, Bergland, Michigan R.J. Horton, Horton, R.J. R.J. Bisdorf, Bisdorf,and andR.P. R.P. Kucks Kucks Airborne geophysical geophysicalsurvey survey of of northwestern northwesternWisconsin Wisconsin Airborne William William F. Kean Kean and and John Feeney Magnetic studies studies of the Dresser-St. Croix Falls area, area,Polk Polk County, County,Wisconsin Wisconsin S.D. McDowell, K.L. Price, J. Huntoon, and T.J. T.J. Bornhorst Thermal modeling and illite/smectite geothermometry Thermal modeling and illitelsmectite geothermometry of of the the Precambrian PrecambrianOronto OrontoGroup, Group,Wisconsin Wisconsinand Michigan Michigan xvi xvi �Economic Economic geology geology P. Hinz and R.T. Lucas of industrial industrial minerals minerals in northwestern Ontario Exploration and mining activities of Stephen A. Kissin, Peter G. Harvey, Elizabeth A. Jennings, Samuel T. Spivak, Spivak, and Eric J. Mosley fluid inclusion, stable stable isotopic and and structural structural studies of the Alteration, fluid Bay District, District, Ontario Ontario Rabbit Mountain Silver Mine, Thunder Bay Peter L. McSwiggen, McSwiggen, G.B. G.B. Morey, and and Jane M. Cleland Cleland Acmite in the Trornrnald Trommald Formation Formation of of the the Cuyuna Iron Iron Range: Range: Revisited Acmite M.G. Mudrey, Jr., and A.B. Dickas Early Proterozoic Proterozoic metal-rich Geologic setting of the Early metal-richvolcanics volcanics of the upper Great Great Lakes region region Richard Patelke Richard Patelke and and Mark Mark Severson Severson Petrology Petrology and and origin originof ofthe thenorthern northernColvin ColvinCreek CreekBody, Body, Duluth Duluth Complex, Complex, NE Minnesota xvii �ABSTRACTS �The High-Resolution Aeromagnetic Aeromagnetic Data Data for for Investigating Investigating The Utility Utility of High-Resolution the Minnesota the Midcontinent MidcontinentRift Rift in in East,.Central East-CentralMinnesota David J. J. Allen Department Department of of Earth Earthand andAtmospheric AtmosphericSciences, Sciences, Purdue University, University, West Lafayette, Indiana 49707 49707 Val W. Chandler Minnesota Geological Survey, St. St. Paul, Paul, Minnesota 55114 55114 Geological Survey, Introduction Introduction Aeromagnetic data data are useful for delineating the structure structure of of the the Midcontinent Midcontinent Rift System (MCR). (MCR). Along Along the western western arm arm of of the theMCR, MCR, magnetic magnetic anomalies anomalies have have been used to and sedimentary to map map buried buried Keweenawan Keweenawan volcanic and sedimentary rocks rocks and and to to identify identify major structures, structures, including including basins basins and and faults faults(e.g., (e.g., Sims Simsand andZietz, Zietz,1967; 1967;King King and and Zietz, 1971). 1971). In In 1991, 1991,the theMinnesota MinnesotaGeological Geological Survey Survey (MGS) (MGS) completed a highhighresolution Minnesota (Chandler, (Chandler, 1991). Nearly all of resolution aeromagnetic aeromagnetic survey of Minnesota of the state state was surveyed with a terrain meters and a flight line separation terrain clearance clearance of of 150-200 150-200 meters of 400-500 meters. database, the only meters. This statewide statewide aeromagnetic aeromagnetic database, only one in North North America encompassingaa large large region region with with high resolution, America encompassing resolution, provides provides a new new opportunity opportunity to examine the the western western arm armof of the theMCR MCR in in detail. detail. A 213 meter meter data grid was generated generated from from the the aeromagnetic aeromagneticsurvey. survey. This data set contains contains detailed detailed information information about the the Precambrian Precambrian basement basementof of Minnesota Minnesota and and provides excellent images images of of the MCR, including the the Duluth Complex provides excellent MCR, including Complex and North North Shore Volcanic Group,aa large large portion portion of of the the St. Croix Horst, Horst, the Belle Plaine Fault, Fault, Volcanic Group, and the extreme extreme northern northern tip tip of of the Iowa Iowa Horst. To To take take full full advantage advantage of of these these data, data, new methods methods of of display display are are presently presently being beingdeveloped, developed, including including stereoscopic stereoscopic data presentation presentation and andimproved improved shaded shadedrelief relief techniques. techniques. Results Preliminary Results is aa magnetic magnetic Figure 11is present study studyfocuses focuses on the St. St. Croix Croix Horst (SCH). Figure The present Wisconsin. The MGS 213 m grid map of east-central Minnesota and adjacent Wisconsin. m data grid data from from an anolder olderUSGS USGS survey survey in in extreme extreme western westernWisconsin Wisconsin was merged with data 1967) and data from from the the DNAG DNAG 2 km magnetic magnetic grid, based on on aa (Sims and Zietz, 1967) (1966), for addition, the the Twin Twin survey by Patenaude (1966), for the the remainder remainder of of Wisconsin. Wisconsin. In addition, metropolitan region was not not included included in in the thehigh-resolution high-resolution aeromagnetic aeromagnetic Cities metropolitan area,the theMGS MGS 213 213 m m grid grid is is based based on on data dataacquired acquired by by the theUSGS USGS in in survey; in this area, As shown shown in Figure 1, 1, The specifications specifications for 1961. The for each each survey survey are are listed listed in in Table Table 1. As new high-resolution high-resolution data data clearly clearly portray portray features featureswhich which are arepoorly poorlyresolved resolved by by the new the older older USGS USGS surveys surveys and and completely completely absent absent in in the the DNAG DNAG 2 km data data grid. grid. the is an aninterpretive interpretivemap mapof ofthe theMCR MCR based based on on the theaeromagnetic aeromagneticdata. data. Figure 22 is underlain by by (essentially (essentiallynon-magnetic) non-magnetic) Keweenawan sedimentary rocks are are Areas underlain characterized by subdued subdued magnetic magnetic patterns, patterns, whereas whereas(magnetic) (magnetic)Keweenawan Keweenawan characterized anomalies, many many of of which which are are volcanic rocks rocks are are often associated with narrow linear anomalies, continuous for over over 50 50 km km along alongstrike. strike. Where continuous for Where the rift rocks rocks crop crop out, they strike strike parallel to is useful useful for for to the the trends trendsofofthe themagnetic magneticanomalies. anomalies. This correlation correlation is mapping packages and and delineating within the SCH. mapping volcanic volcanic packages delineating folds folds within SCH. In addition, addition, abrupt terminations terminations of of the the linear linearanomalies anomaliesare areuseful useful for for identifying identifying faults. faults. abrupt Several northeast-trending northeast-trending anomalies anomalies are areproduced produced by byKeweenawan Keweenawan dikes. dikes. Several o the rift axis (Figs. (Figs. 1-2). Within Within of the These dikes lie west of the MCR MCRand and strike strike parallel parallel tto the SCH, SCH, lineaments lineaments cut cut across across the the magnetic magnetic anomalies anomalies associated associated with with the thevolcanic volcanic the rocks. rocks. The lineaments lineaments do not not truncate truncate or orsignificantly significantly offset offset the themagnetic magnetic 33 �46 45 km km 0 I ——I 10 20 30 40 50 Figure 1: 1: Shaded Shaded relief relief presentation presentationofofmagnetic magnetic Figure datafor foreast-central east-central MN MN and and adjacent adjacentWI. WI. The The data sun illumination illumination isisfrom from the the northwest. northwest. sun 10 20 30 40 50 I— —I 0 Figure Figure2: 2: Interpretive Interpretivemap mapofofthe theMCR MCRbased basedon on aeromagnetic data. aeromagnetic data. Table Aeromagnetic Survey Survey Specifications Specifications (see (see Figure Figure1)1) Table1:1:Aeromagnetic Survey Survey A MGS,1991 1991 A MGS, l? Sims and Zietz,1967 1967 B Sims and Zietz, C USGS, 1961 C USGS, 1961 Patenaude,1966 1966 DD Patenaude, 44 Flight Fliehtline lineseoaration s e ~ a r a t i oand nanddirection direction North-South 500 North-South 200m mabove aboveground ground 500mm 200 East-West 500 (150 m) 500ftfl(150 m)above aboveground ground 11mile mile(1600 (1600m) m) East-West East-West 500 500ftft(150 (150m) m)above aboveground ground 11mile mile(1600 (1600m) m) East-West North-South North-South (900m) m)above abovesea sealevel level 66miles miles(9600 (9600m) m) 3000ftft(900 3000 Elevation Elevation �anomalies, suggesting that that they might be produced by dikes, faults of anomalies, suggesting produced by of minimal minimal displacement, or fracture zones within which which the magnetic character character of of the the volcanic volcanic rocks was altered. altered. The most prominent anomalies are' are associated with reverse faults prominent magnetic magnetic anomalies associated with along the margins of juxtapose volcanic volcanicand and sedimentary sedimentary rocks. rocks. Of of the SCH SCH which juxtapose particular interest interest is is the thePine PineFault. Fault.North Northofofthe thePre-Paleozoic Pre-PaleozoicTwin TwinCities Cities Basin, Basin, this to the east in this fault faultplaces places older older volcanic volcanic rocks to in contact contact with with younger younger sedimentary sedimentary rocks to the west. The rocks to The new new magnetic magnetic data indicate indicate that that the the Pine Pine Fault Faultcontinues continues northeast 46%, to to within within 20 20 km km of of the the Minnesota-Wisconsin Minnesota-Wisconsinborder border(Figs. (Figs.1-2). 1-2). northeastbeyond beyond46°N, Additional Problems Problem5 Thus far, the magnetic data data have have been been used used in in a qualitative the high-resolution high-resolution magnetic qualitative manner t o interpret the the structure structure of of the the SCH. SCH. Continued Continued efforts effortsto to enhance enhance the the manner to display of this this data images of of the the SCH SCH and and better better data set set will will hopefully result in improved images resolution of the structural structuralcomplexities complexities within the the rift's rift'svolcanic volcanic rocks. rocks. Magnetic modeling will will be be aa powerful powerful tool toolfor forquantifying quantifying interpretations interpretations of of the the SCH. AAmajor be to determine the sources sources of the continuous continuous linear major objective objective will will be magnetic with the magnetic anomalies anomalies associated associated with the rift's rift'svolcanic volcanic rocks. rocks. These anomalies anomalies might be produced produced by contrasts contrasts between between volcanic volcanic flows and interfiow interflow sedimentary sedimentary units, differences differences in magnetic magnetic properties properties between between adjacent adjacent packages packages of ofvolcanic volcanic rocks, or magnetic reversals. These hypotheses will be evaluated using magnetic evaluated using magnetic magnetic reversals. modeling in conjunction conjunction with magnetic properties measurements measurements of of volcanic volcanic rocks rocks from the the SCH. SCH. Magnetic modeling will will also be be usefid useful for investigating the the longer longer wavelength wavelength anomalies (not evident in the shaded relief presentation of Figure 1). Analytical anomalies evident shaded relief presentation of Figure 1). Analytical techniques which account account for for structural structural rotation of the remanent techniques which remanent magnetization magnetization vector vector (e.g., (e.g., Mariano Mariano and Hinze, Hinze, 1991), 19911, in in conjunction conjunction with with available available seismic seismic reflection data data and more reliable models models of the deeper deeper and gravity gravitymodeling, modeling, will lead to more structure of the SCH. structure of the SCH. The MGS data set set also provides an opportunity to examine other portions of the MCR. MCR. For For example, example, these data data may may lead lead to to an animproved improved understanding understanding of of the the St. Croix Croix and Iowa Iowa Horsts along the Belle Plaine Fault Fault in in between the St. transition between southeastern southeastern Minnesota. Minnesota. In addition, addition, the data data may may also also assist assist ininimproving improving interpretationsof of the theDuluth DuluthComplex Complex and North Shore Volcanic Volcanic Group. interpretations Group. Finally, the detail provided by the MGS survey suggests suggests that that aa similar MGS survey similar high-resolution high-resolution survey survey of of Wisconsin might of northwestern Wisconsin might be be extremely extremely useful useful for for investigating investigating the the nature of the the transition transition between between the thewestern westernarm armof of the the MCR MCR and the the Lake Lake Superior Superior Basin. REFERENCES REFERENCES Chandler, Chandler, V.W., V.W., 1991, Aeromagnetic Aeromagnetic anomaly of Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey anomaly map of State StateMap MapSeries SeriesS-17, S-17,scale scale1:500,000. 1:500,000. E.Rm7and Zietz, I., 1971, 1971, Aeromagnetic King, E.R., Aeromagnetic study study of ofthe the midcontinent midcontinent gravity gravity high of central United States: Am. Geol.Soc. States:Geol. SOC. Am. Bull., Bull., v. v. 82, 82*p. p. 2187-2208. 2187-2208. Mariano, J., and andHinze, Hinze7W.J., W.J., 1991, 19917Geophysical Geophysical investigations midcontinent rift in eastern eastern Manano, investigations of of the the midcontinent Superior using using variable variablemagnetization magnetization modeling, modeling, [abst.1; Labst.]; Institute Instituteon onLake LakeSuperior SuperiorGeology Geolo~ Lake Superior Annual Meeting, Meeting7Eau Eau Claire, Claire,WI, WI,1991; 1991; v. 37, part 1, p. 68-69. 68-69. Proceedings, 37th Annual part 1, Smith7 Patenaude, R.W., R.W., 1966, 1966, A Patenaude, A regional regional aeromagnetic aeromagnetic survey survey ofofWisconsin7 Wisconsin,ininSteinhart, Steinhart, J.S., J.S., and Smith, T.J., eds., eds., The Theearth earthbeneath beneaththe thecontinents: continents:American AmericanGeophysical GeophysicalUnion UnionGeophysical GeophysicalMonograph Monograph T.J., Series Series10, 10,p. p. 111-126. 111-126. Sims, P.K., P.K, and and Zietz, Zietz, I., I.,1967, 1967,Aeromagnetic Aeromagnetic and and inferred inferredPrecambrian Precambrianpaleogeologic paleogeologic map map of ofeasteastSims, central Minnesota Minnesota and andpart partofofWisconsin: Wisconsin: USGS USGS Geophysical Geophysical Investigations Map GP-563 [with text], central 66 p., scale scale 1:250,000. 1:250,000. 5 �AN ANINTEGRATED INTEGRATEDGRAVITY GRAVITYAND AND MAGNETIC MAGNETICSURVEY SURVEY OF'THE THEROCK ROCKELM ELMSTRUCTURE, STRUCTURE,WESTERN WESTERNWISCONSIN WISCONSIN OF Michelle MichelleL. L. Barnes, Barnes, Georgia Geop'a L. L. Osborn, Osbom, and andLung LungS.S.Chan Chan Department DepamentofofGeology Geologv University University of of Wisconsin-Eau Wucomin-Eau Claire, Claire, WI W 54701 54701 The TheRock RockElm Elm structure, structureylocated locatedininPierce PierceCounty, CountyyWisconsin, Wisconsin,isisan anapproximately approximately four fourmiles milesinindiameter, diameter,sub-circular sub-circularstructure structureof of uncertain uncertainorigin. origin.The Thestructure structurecontains contains Paleozoic Paleozoic strata strata tilted tilted away awayfrom fromaacentral centraldome domewhere wherebrecciated brecciatedrocks rocksare arepresent. present. Several Severalhypotheses hypothesesfor forthe theorigin originof of the the structure structurehave have been been suggested: suggested: 1) 1)meteorite meteoriteimpact impact (Cordua, (Corduay1985), 1985),2)2)volcanic volcanicactivity, activityyand and3)3)tectonic tectonicactivity. activity.Of Ofthe thethree, three,we welooked lookedmost most closely closelyat atthe thefirst firstone oneand andhave haveconducted conductedan anintegrated integratedgravimetric gravimetricand andmagnetic magneticsurvey survey determinethe theplausibility plausibilityofofthis thishypothesis. hypothesis. totodetermine Gravity LaCoste&&Romberg Romberggravity gravitymeter meteratatone one Gravitymeasurements measurementswere weretaken takenusing usinga aLaCoste mile miles.FreeFreemileintervals, intervalsymostly mostlyatatUSGS USGSelevation elevationmarkers, markersyover, over.an anarea area12 12miles d e sxx141 4miles. air airand andBouguer Bouguercorrections correctionswere wereapplied appliedto toall allmeasurements measurementsand andterrain terraincorrections correctionswere were applied was used to applied where where needed. needed. AA proton proton precession precession magnetometer magnetometer was' to measure measure the the ambient magnetic field and the vertical gradient of the field intensity in and around the ambient magnetic field and the vertical gradient of the field intensity in and around the structure. structure.Multiple Multiplemeasurements measurements were were taken taken atatstations stationspositioned positioned about aboutevery everyquarter quarter mile mile along along the thegrid grid pattern patterncreated createdby by the theroads roads in in the thearea. area. We 1 and 2) to We have have compared compared our our gravity gravity and magnetic magnetic results (Figures 1 to those thoseof of the theManson MansonImpact ImpactStructure StructureininIowa, Iowaywhich whichhas hasstrong strongmagnetic magneticanomalies anomaliesassociated associated with withits itsboundary boundary(Hartung (Hartungand andAnderson, Andersony1988). 1988).The TheRock Rock Elm Elm structure structure does doesnot notshow show significant significantmagnetic magnetic anomalies anomalies along along its its boundary boundary nor nor with with its itscentral centraldome. dome.The Thegravity gravity data dataalso alsodo donot notsupport supportthe thehypothesis hypothesisofofan animpact impactorigin. origin.AAnorthwest-southeast northwest-southeast trend trend in inthe thegravity gravityanomaly anomalycoincides coincideswith withthe theRiver RiverFalls Falls anticline anticlineand and the theLake LakeOwen OwenThrust Thst Fault Fault of ofthe theMid-Continent Mid-ContinentRift Rift System. System. We We have have also also computed computed gravity gravity and andmagnetic magnetic anomalies anomaliesof ofhypothetical hypotheticalimpact impactstructures structuresconstructed constructedfrom fromknown h o r ngeological geologicalconstraints. constraints. Thesimulated simulatedmodels modelsdo donot notresemble resemblethe thegeophysical geophysicalresults resultsobserved. observed. The References References CorduayW.S., W.S.y1985, 198SY RockElm Elm structure, structure,Pierce Pierce County, County, Wisconsin: Wisconsin: AApossible possible Cordua, Rock cryptoexplosion structure, structureyGeology, Geologyy13, 13 372-374. cryptoexplosion 372-374. Hartung, J.B., J.B., and andR.R. R.R. Anderson, Anderson, 1988, 1988 A Compilation Compilation of Information and Data Data Hartung, A onthe theManson MansonImpact ImpactStructure, Structure,LPI LPITechnical Technical Report Report Number Number 88-08. 88-08. on 6 �ROCK ROCK ELM, ELM, TOP TOP SENSOR SENSOR Contour Contour Interval, Interval, 500nT 500nT ROCK ELM, ROCK ELM, GRADIENT GRADIENT Contour Interval, Contour Interval, 200nT 200nT 1. Magnetic Magneticanomalies anomaliesof of the the Rock Rock Elm area. The circle represents approximate Figure 1. represents the approximate boundary of the structure. structure. GRAVITY GRAVIW ANOMALY ANOMALY AT AT ROCK ELM ROCK ELM Contour Interval, ContoatInterval, 2Ogu 20gu Figure Gravityanomaly anomalyof of the the Rock Rock Elm Elm area. The circle circle represents represents the the approximate approximate Figure 2. Gravity area. The 7 boundary of the structure. structure. 7 �rift-related Structure Stmctureand and composition composition of of Keweenawan Keweenawan rift-related igneous igneous and and sedimentary seamentaryrocks rocksin inKansas. Kansas. Pieter PieterBerendsen Berendsen Kansas KansasGeological GeologicalSurvey Survey During the last last decade decade a series series of of holes holes were were drilled into the the During Precambrian Precambrian basement. basement. Prominent Prominent among among these these are arethe theNoel NoelPoersch Poersch#1 #I , which which is the deepest deepest drill hole hole to to date in in Kansas Kansas at a t11,300 11,300feet, feet, and andtwo twoOZ OZ drill t o the the Poersch Poersch hole. hole. These These three three drill holes, holes, which which are ininclose closeproximity proximity to wells in Washington County, northeastern northeastern wells were were drilled drilledin in1984-85 1984-85by Texaco in Kansas 1).The TheFinn F i n#1-4 #1-4 and and the theFriederich Friederich #1-8 #l-8 in in Marshall Marshall and and Kansas (Figure (Figure 1). Riley respectively, are Riley counties respectively, are two two other wells with significant sigdicant penetrations penetrations into 1).Studies Studies of of well well cuttings cuttings and andsome some into the the Proterozoic Proterozoic basement (Figure (Figure 1). generated a lot of new data and made core from these and older drill holes core and older drill holes generated a lot of data and made itit possible to better interpret the nature of rift. possible better the nature of rift. Comparative petrographic studies of of representative representative outcrop outcrop samples samples from &om the the Lake Lake Superior Superior region region and and subsurface subsurface samples samples from from Kansas Kansas were were conducted. The mineralogical composition compositionand and the the heavy heavy mineral mineral content of of general stratigraphic correlations core and cuttings allow comparison and cuttings allow comparison and general stratigraphic correlations with with rocks rocks from from the outcrop belt in the Lake Superior Superior area. area. The The amount amount of of quartz, quartz, plagioglase plagioglase and K-feldspar, the amount and and nature natureof of rock rock fragments, fragments, the d ldiscriminating discriminatingfactors. factors. thetourmaline, tourmaline,zircon, zircon,and andepidote epidote content contentare areall Chemical the basalts and Chemical analysis of of the and gabbros gabbros encountered in the the four four drill holes in northeastern Kansas shows them to be alkalic to subalkalic northeastern Kansas shows to be alkalic to subalkalic (Figure 2). Baddeleyite from gabbro in the upper upper portion portion of of the the Poersch Poerschdrill drill (F'igure 2). hole of 1097.5 1097.5 3Ma hole yields a concordant concordant U-Pb age of 3Ma (Van Wan Schmus and and others, others, 1990). This This is essentially essentially the same age as published published data for for the the Lake Lake Superior Superior region, and indicates that thatno noage ageprogression progressiontook took place place along along this this arm of the rift. The lower 3874 feet in the Poersch drill hole penetrated aa arm of the rift. The lower 3874 Poersch predominantly which detrital monazite predominantly arkosic arkosic section section from which monazite and and zircon zircon were were recovered. ages of of these minerals range recovered. U-Pb provenance ages range from &om 1.7-1.8 1.7-1.8 Ga, Ga, 1.4-1.5Ga, From this itit 1.4-1.5Ga, and 1.1-1.2 Ga (Martin, Personal Communication). Communication). From appears appearsthat thatmost mostofofthe thearkosic arkosicsedimentary sedimentaryrocks rockswere werederived derivedproximally proximally from the adjacent rift margins, which consist of 1.7-1.8 Ga mostly granitic adjacent rift margins, which consist of 1.7-1.8 basement and and younger younger (1.45 (1.45 Ga) Ga) granitic granitic plutons. plutons. No No evidence evidence of of early early Proterozoic or Archaen Archaen detrital detrital minerals minerals was found, found,indicating indicatingthat that transport transport of sedimentary materials materials along the axis of the the rift from farther farther up north may may not have been significant. not have been significant. Core of the OZ drill hole has stable stable magnetic magnetic fiom gabbro gabbro of Core taken from remanence from shallow, shallow, reverse reverse to steep, remanence which which demagnetizes demagnetizes from steep, reverse reverse inclination inclination and and appears appears to todate datefrom fiomoriginal originalcooling cooling(Van (Van Schmus Schmus and and others, 1990). rocks that that 1990). This may be correlated with Lower Lower Keweenawan Keweenawan rocks occur below below the the R tto reversal. o N magnetic reversal. In I n the the Poersch Poersch drill drillhole holea apredominantly predominantlyvolcanic volcanic section, section, approximately 4580 foot foot thick thick overlies overlies the the mostly arkosic sedimentary rock section. Based on seismic from a COCORP line four four miles miles north of seismic evidence from COCORP line of the Poersch propose that that aa high-angle, (1991) propose high-angle, Poersch drill drill hole, hole, Woelk Woelk and Hinze Hinze (1991) west-dipping, reverse fault fault is responsible for the transposed order west-dipping, reverse responsible for order of of the the major rock packages. This This fault fault has has an approximate strike of N 40°E, 4 0 0 and and ~ ~ rock packages. dips steeply to shows that that a t o the west. west. Examination Examination of the seismic seismic profile profile shows 8 �steeply east-dipping reverse fault, having aa strike could strikeofofN400E, N~OOE, could also also be be responsible for the transposition. transposition. North-northeastand northwest-ternding faults dominate North-northeast- and northwest-ternding faults dominate the the structures associated with the rift in Kansas. Presently, a pattern pattern of structures of roughly rectangular rectangular structural structuralblocks, blocks,each eachhaving havingaanarrow narrowrange rangeof ofelevations elevationsabove above sea level, gives gives a characteristic characteristic appearance. appearance. Apparent Apparentcompound compound vertical vertical offset on faults faults can be as offset on as much much as as 2000 2000 feet. feet. Within Within the the Paleozoic Paleozoic era repeated reactivation repeated reactivation of earlier tectonic tectonic trends can can be be documented. documented. The The rift-related rocks rocks were subjected to magnitude and and number number of of times to which rift-related faulting in the Proterozoic Proterozoicisisunknown unknown The The last last major major adjustment adjustment on on faults faults occurred during the Pennsylvanian Ouachita orogeny. Preliminary studies in Ouachita Preliminary Kansas indicate of rocks rocksof ofwidely widely indicate that that sedimentary sedimentary and and igneous igneous suites suitesof differing ages may be be juxtaposed juxtaposed in in adjoining structural structural blocks. References: References: Martin, M.W., Department of University of of Kansas. Kansas. (Personal Martin, M.W., Department of Geology, Geology, University (Personal Communication) Communication) Martin, M.W., D.R.,Geissman, Geissman, J., J., and and Van Schmus, Schrnus, W.R., W.R., Martin, M.W., Sprowl, D.R., Berendsen, P., and Berendsen, P., 1990, 1990,Age, Nd and Pb isotopic composition, and magnetic polarity for subsurface samples of the the 1100 Ma Ma midcontinent midcontinent rift: [Abstract] [Abstract]Geological Geological Society Society of America, v. 22, no. 7, p. A174. Woelk, T.S., T.S., and and Hinze, Hinze, W.J., W.J., 1991, 1991, Model Modelofofthe themidcontinent midcontinentrift rift system system in in northeastern Kansas: northeastern Kansas:Geology, Geology,v. v. 19, 19,p. p. 277-280. 277-280. 9 �PRECAMBRIAN FSECAMEEIAN BEDROCK BEDROCK N miles 55 miles 00 t II IlL Ii I - HFZ HFZ Humboldt HumboldtFault FaultZone Zone fault fault , ----- inferred fault --inferred contact 00 ? ,'A ,'A: ! ' * km . 5 km . inferred fault — — — inferred contact Figure ininthe of F i ~1. 1-eBasement Basementstrticture sim~cture thevicinity ~cinity of the theFinn, l?in.n,Poersch Poerschand andFriedFriederich eri& drifl drill holes, holes, north-central n o r h x n t i d Kansas. Kansas. S 6 C z 2 0 40 40 44 44 52 52 48 48 56 56 60 60 SIC2 SIO2 Figure22Alkalies h a l i e svs vsSi02 SiOzdiagram diagramshowing sho&ng Keweenawan Kewemawan lavas and gabbrog. Figure gabbro. 10 �GEOLOGY AND AND TECTONIC SETTING SETTING OF OF THE THE ARCHEAN ARCHEAN GIANTS GIANTS GEOLOGY RANGE BATHOLITH; BATHOLITH;WESTERN WESTERNWAWA WAWASUBPROVINCE, SUBPROVINCE,MINNESOTA MINNESOTA RANGE BOERBOOM,Terrence TerrenceJ., J.,and andMark MarkA. A.Jirsa Jirsa BOERBOOM, MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul,MN MN55114-1057 55114-1057(612-627-4780) (612-6274780) Minnesota TheGiants GiantsRange Rangebatholith batholith(ORB) (GRB)isisaalarge largecomposite compositegranitoid granitoidbody body of of Late LateArchean Archean The agethat that intrudes intrudes supracrustal supracrustal rocks truncated by by the the age rocks of of the the Wawa Wawa subprovince. subprovince. It It isistruncated km to to ProterozoicDuluth DuluthComplex Complexatatits itseast eastend, end, and andextends extendswestward westward for formore more than than 200 200km Proterozoic north-central Minnesota, where it is deeply buried beneath Quaternary sediment. This north-central Minnesota, where it is deeply buried beneath Quaternary sediment. This studyisis based based on on detailed detailedoutcrop outcropmapping, mapping,and andto toaalesser lesserextent extenton ondrill drillcore coreand and study geophysical data in the westernmost exposed part of the batholith and several satellite geophysical data in the westernmost exposed part of the batholith and several satellite metasedimentaryrocks rocks plutons. The TheGRB GRBintrudes intrudescomplexely complexelydeformed deformedmetavolcanic metavolcanicand andmetasedimentary plutons. of the Lake Vermilion Formation. Two main periods of deformation have been identified of the Lake Vermilion Formation. Two main periods of deformation have been identified inthe thesupracrustal supracrustalrocks: rocks: aa Di D levent eventthat thatproduced producedlarge largescale, scale,locally locally recumbent recumbent folds folds but but in onlyaararely rarely preserved preservedcleavage; cleavage;and and aa D2 D2 that that produced produced NE-trending, NE-trending, upright upright folds folds and and only associated, steep axial planar cleavage. Mineral lineations and foliations that parallel F2 associated, steep axial planar cleavage. Mineral lineations and foliations that parallel F2 fold axes indicate that peak metamorphism (M2), which varies from greenschist to fold axes indicate that peak metamorphism (M2), which varies from greenschist to amphibolitefacies, facies, occurred occurred during during D2. D2. Field Fieldrelationships relationshipsshow showthat thatsome someportions portions of of the the amphibolite GRBare areolder olderthan thanD2 D2and andthe theassociated associatedM2 M2 metamorphism, metamorphism,and and others othersare areyounger. younger. ORB Localized structures that were generated after M2 and after plutonism are assigned toD3. D3. Localized structures that were generated after M2 and after plutonism are assigned to The GRB exposed in the study area consists of earlier, preto syn-D2, lineated and The ORB exposed in the study area consists of earlier, pre- to syn-D2, lineated and hornblende-bearinggranodiorite granodioriteand andmonzodiorite, monzodiorite,and andlater, later,muscovitemuscovite-and andbiotitebiotitehornblende-bearing bearing granite which was only slightly affected by D2 deformation. Several smaller, bearing granite which was only slightly affected by D2 deformation. Several smaller, ovoid plutons of petrochemically diverse alkalic a f f ~ t were y emplaced after peak ovoid plutons of petrochemically diverse alkalic affinity were emplaced after peak metamorphisminto intosupracrustal supracrustal rocks rocks adjacent adjacent to The best best exposed exposedexample example of of metamorphism to the the GFG3. ORB. The the earlier suite of rocks is the Britt granodiorite which occurs in and near a large antiform the earlier suite of rocks is the Britt granodiorite which occurs in and near a large antiform inthe thesouth southpart part of of the the map map area. area. The Therock rockisismetaluminous metaluminousand andI-type. I-type.The Theproportions proportionsof of in Rb, Y, Yb, Nb and Ta in the Britt granodiorite imply that it was emplaced in a volcanic arc. Rb, Y, Yb, Nb and Ta in the Britt granodiorite imply that it was emplaced in a volcanic arc. Thistectonic tectonicinference inferencealso alsois is supported supported by by major major element element data dataand anddiscrimination discriminationplots. plots. This The granodiorite is intruded by the Shannon Lake granite, a weakly to moderately foliated, The granodliorite is intruded by the Shannon Lake granite, a weakly to moderately foliated, multiphase,biotite-muscovite biotite-muscovitegranite. granite. Emplacement Emplacementof of the theShannon ShannonLake Lakegranite graniteclearly clearly multiphase, post-dated M2 in the area. However, weak NE-trending fabrics cross the trend of post-dated M2 in the area. However, weak NE-trending fabrics cross the trend of magmaticallyrelated relatedpegmatite pegmatiteand andaplite aplitedikes dikesthat that occur occurboth both in in the the granite graniteand andin in the the magmatically adjacent supracrustal rocks. Thus, some regional deformation occurred after intrusion. adjacent supracrustal rocks. Thus, some regional deformation occurred after intrusion. Geochemicaldiscrimination discriminationdiagrams diagramsfor forthe the Shannon ShannonLake Lake granite graniteplace place itit between between the the Geochemical island-arc and continental-collision classes of granitoids. Some plutons of alkalic rocks island-arc and continental-collision classes of granitoids. Some plutons of alkalic rocks (suchas asthe theIdington Idingtonpluton) pluton)are areintruded intrudedby by Shannon ShannonLake Lakegranite, granite,and andtherefore thereforeare are (such somewhat older than the Shannon Lake. However, the alkalic plutons and the Shannon somewhat older than the Shannon Lake. However, the alkalic plutons and the Shannon D2, and andmay may be be broadly broadlycontemporaneous. contemporaneous. Lakeare areboth bothpost-tectonic post-tectonicwith withrespect respectto toD2, Lake The Britt granodiorite and the Shannon Lake granite were emplaced beforeand andafter afterthe the The Britt granodiorite and the Shannon Lake granite were emplaced before D2 deformation, respectively. D2 is a transpressive deformational event of wide main main D2 deformation, respectively. D2 is a transpressive deformational event of wide begenerally generallycorrelated correlated across acrossthe the southern southern Superior SuperiorProvince. Province. regionalextent extentthat thatcan canbe regional High-precisionU-Pb U-Pbdating datinghas hasbeen beendone doneon onzircons zirconsfrom fromthese thesetwo tworock rockunits, units,and andthe the High-precision (R. Zartman, Zartman, U.S. U.S. preliminaryresults resultsindicate indicatethat that D2 D2ended ended between between 2674 2674 and and 2685 2685 Ma Ma (R. preliminary fullreport reportof of the the geochronologic geochronologicwork work will will GeologicalSurvey, Survey,pers. pers. communication). communication). AAfull Geological bepublished publishedsoon. soon. be Thisproject projectwas wassupported supportedininpart partby bythe theMineral MineralDiversification DiversificationProgram Programadministered administeredby bythe theMinerals Mnerals This CoordinatingCommittee Committeefor forthe theMinnesota MinnesotaState StateLegislature. Legislature. Coordinating 11 �TEMPORAL PROGRESSION OF ARCHEAN GRANITOID ROCKS, ISHPEMING GREENSTONE BELT AND VICINITY, MICHIGAN Theodore J. Borrthorst, Richard T. Wilkin1, and Rodney C. Johnson2 Department of Geological Engineering, Geology, and Geophysics, Michigan Technological University, Houghton, MI 49931 Granitoid rocks can now be integrated into the volcanic rock unit and structural framework of the Ishpeming greenstone belt and the development of the Great Lakes tectonic zone The Ishpeming greenstone belt is composed of more than 13,000 meters of mafic and felsic volcanic rocks erupted during active north-directed subduction about 2700 Ma. These volcanic rocks were intruded by a composite batholith of tonalite and granodiorite, and minor quartz monzonite and Since, the tonalite suite rocks granite (tonalite suite). (GLTZ; Sims, 1991). contain a penetrative foliation associated with recumbent folding (D1), this suite is pre- to early syn-deformation. Both the volcanic section of the greenstone belt and the tonalite suite formed during active north-directed subduction prior to collision along the GLTZ. Continental collision along the GLTZ resulted in progressive deformation of the volcanic-plutonic arc about 2700 Ma. Development of the magmatic arc ended with the onset of largescale north-directed recumbent folding (D1) that was followed by upright folding (D2) and development of shear zones (D3). A trondhjemite to granite suite occurs as intrusive stocks and plugs both interior and exterior to the volcanic section. Intra-belt stocks and rhyolite dikes are aligned subparallel to axes of F1 and F2 folds but cut by shear zones. The trondhjemite to granite suite is syn- to late-upright folding. A hornblendite-diorite-syenite suite occurs as scattered weakly foliated pipe-like to stock-sized bodies. While relative age with respect to the trondhjemite to granite suite is not established in the field, we interpret this suite as with large scale shear zones (D3) that define boundaries of lithostratigraphic blocks within the volcanic section. Both trondhjemite to granite and hornblenditediorite-syenite suites were emplaced during collision along the GLTZ. A late granite suite is found throughout the area and consists of massive rocks cutting foliated rocks. These rocks are the youngest Archean granitoid rocks and are posttectonic with respect to collision along the GLTZ. coeval 12 �In the the Canadian Canadian portion portion of of the the southern southern Superior Superior Province, Province, Sutcliffe (1991) Sutcliffe (1991) has identified identified aa temporal temporal progression progression of of granitoid granitoid rocks. rocks. A foliated foliated tonalite tonalite suite suite is is related related to to arc arc construction subduction. Syntectonic tonalite construction during during subduction. Syntectonic foliated foliatedtonalite was emplaced emplaced during during collision. collision. Granite to to granodiorite, granodiorite, Granite diorite diorite to to syenite syenite and and two-mica two-mica granite granite suites suites are are latelate- to to post-tectonic. Temporal progression post-tectonic. progression of Archean Archean granitoid granitoid rocks rocks in in the the Ishpeming Ishpeming greenstone greenstone belt belt and vicinity vicinity is is comparable comparable to to the the southern southern Superior Superior Province Province as as aa whole. whole. This partially funded Michigan Geological This research research was was partially funded by the the Michigan Geological Survey, Survey, U.S. Geological Geological Survey Survey (COGEOMAP), (COGEOMAP),and and Western Western Mining Mining Corporation Corporation (USA). (USA). REFERENCES REFERENCES CITED CITED Sims, P.K., P.K., 1991, 1991, Great Great Lakes Lakes tectonic tectonic zone zone in in Marquette Marquette area, area, Sims, Michigan Implications for for Archean Archean tectonics tectonics in in Michigan -- Implications Geological Survey Survey north-central United United States: U.S. Geological Bulletin Bulletin 1904-E, 1904-Elp. p. E1-E17. El-E17. Sutcliffe, R.H., R.H., 1991, 1991, Archean Archean plutonic plutonic rocks rocks in in the the southern southern Sutcliffe, Superior Superior Province: Province: Magrnatism Magmatism during arc-construction arc-construction and and arc-accretion: arc-accretion: Minnesota Minnesota Geological Geological Survey Survey Information 34, p. p. 16-22. 16-22. Information Circular Circular 34, 1 1 Present Present address: address: Department Department of of Geosciences, Geosciences, Pennsylvania Pennsylvania State State University, University, University University Park, Park, PA PA 16802 16802 2 Present (USA), Marquette, Present address: address: Western Western Mining Mining Corporation Corporation(USA), Marquette, MI MI 49855 49855 13 �Gravity Model of the Wolf River Batholith Daniel J. Brehm and C. Patrick Ervin, Dept. of Geology, Geology, Northern Northern Dekalb, IL Illinois University, DeKalb, IL 60115 60115 Jeffrey K. K. Greenberg, Wheaton College, College, Wheaton, Wheaton, IL IL 60187 60187 Recently acquired gravity data has more extensively extensively delineated the approximately -30 -30 mGal Bouguer Bouguer gravity gravity anomaly anomaly associated with the Wolf River Batholith, which outcrops outcrops in in northeast northeast Wisconsin. Wisconsin. This anomaly is is superimposed superimposed on on the the Wisconsin Gravity Gravity Minimum, Minimum, aa -60 -60 mGal mGal Bouguer Bouguer gravity gravity anomaly anomaly over the the Wisconsin Wisconsin Arch. Arch. The gravity field shortfield was upward continued to to eliminate eliminate shortwavelength, shallow shallow anomalies that that tend tend to to mask the the field field associated associated with with the the batholith. batholith. A second filter filter was applied applied to to minimize the affect of the Wisconsin Arch in the area minimize the affect &IL,,C .A~SCGGS~Z in the area associated associated with the the Wolf River River Batholith. Batholith. 7 1 - Modeling of the the filtered filtered gravity gravity field field indicates indicates that that the batholith has a variable thickness, averaging between between 1.5 1.5 and and 2 km thick. thick. This model supports the conclusions of Anderson Anderson (1980), who proposed on on the basis of of geochemical data, data, that the batholith was emplaced at relatively relatively shallow shallow depths depths (less (less than 4 km), and that it is fairly thin (less (less than than 55 km km thick). thick). The model also also suggests suggests that that the the batholith batholith does does not not extend extend far far past its its western, western, eastern, eastern, and and northern northern outcrops, outcrops, but but does does extend extend a considerable considerable distance distance in in the the subsurface subsurface beyond beyond its its southern southern boundary. boundary. Although the Wisconsin Gravity Minimum reaches reaches its its most most negative value over the batholith, batholith, the the Wolf River River Batholith Batholith is is not fully coincident with nor the the sole sole cause cause of of the the Wisconsin Wisconsin Minimum. Minimum. REFERENCES REFERENCES Anderson, J.L., J.L., 1980, 1980, Mineral Equilibria and Crystallization ~recambrianWolf River Conditions in in the Late Precambrian River Rapakivi Rapakivi Massif, isc cons in, Amer. Amer. Jr. Jr. Sci., Sci., v. v. 280, 280, p. p. 289—332. 289-332. Massif, Wisconsin, 14 �Textural Textural and and Compositional Compositional Study Study of of aa Manganiferous Manganiferous Iron-Formation, Iron-Formation, Emily Emily District, with Implications Implications for for Original District,Cuyuna Cuyuna Range, Range, with Original Deposition Deposition and and In Situ Situ Leaching of ofManganese Manganese Susan Brink, Geologist Susan E.E. Brink, Geologist U.S. Bureau Bureau of ofMines Mines The U.S. Bureau Bureau of of Mines Mines is is conducting conducting geologic geologic and and geochemical geochemical The U.S. characterization iron-formation of characterization studies studies on on drill drillcore corefrom fromthe themanganiferous manganiferous iron-formation of the Emily Cuyuna to determine whetherin in situ Emily District, District, CuyunaIron IronRange, Range, Minnesota Minnesota to determine whether situ izedtotorecover recoverhigh-grade high-grademanganese manganese solutions leach mining techniques can can be beutil utilized solutions from low-grade low-grademanganese manganese ore. ore. In this units of the manganese-oxide-bearing thisstudy, study,three threelithologic 1 i tho1 ogic units of the manganese-oxide-bearing ironironformation were and consist thinlybedded, bedded, chert-hematite formation wereidentified identified and consist of aa thinly chert-hematite ironironlaminated, fine-grained to thickly thicklybedded, bedded, granular, variably formation; a well laminated, granular, variably sandy, manganese-oxide-hematite-goethite manganese-oxide-hematite-goethiteiron-formation iron-formationthat that contains interbeds interbeds of manganese-oxide-bearing oolitic to and aabasal basal unit unitofof manganese-oxide-bearing oolitic tosandy sandy chert. chert. of chert; chert;and The of well-rounded, The presence presence of well-rounded, terrigenous quartz-sand-grains; quartz-sand-grains; hematitic hematitic and and manganese-oxide granules; a variety containingcombinations combinations manganese-oxide granules;and and a varietyof ofoolite-types oolite-types containing of suggest aa near of quartz, quartz, hematite, hematite, and and manganese-oxide manganese-oxide suggest near shore shore depositional depositional environment for the the granular granular subunits subunits of of the iron-formation. environment for iron-formation. The average assay assay grade <0.1 %% Mn, grade of the the three threeunits unitsis is <0.1 Mn,11.4 11.4%%Mn, Mn,and and 10.1 10.1 % % Mn, Mn, respectively. respectively. The The manganese manganese minerals minerals identified identified in in the the Emily Emily district district are are manganite, mangani te, crypton'ielane, hollandite, cryptomel ane, holl andi te, braunite, brauni te, and and 11 iithiophorite. thiophorite. Microscopic textural re1 ationshipsand and microanalysis microanalysis of the the composition composition Microscopic textural relationships of ore ore and and gangue gangue mineralogy situleach leach of mineralogyare areimportant importanttotothe the success successofof in in situ mining. mining. The The leach leach fluid fluidmust must be be able able to to access, access, selectively solubilize solubilize manganese, andand then transport it itutil izing the natural permeability permeabil ity of of the therock. rock. manganese, then transport utilizing Manganese mineralization is Manganese mineralization is strongest strongest in in the the granular granular facies of the the ironironfades of formation, formation, likely likely because because of of higher higher intergranular intergranular porosity porosity and and higher higher permeability permeability than than in in the the finely finely bedded bedded to to laminated laminated nongranular nongranular strata. strata. rep1replaced aced original chert granul ar Manganese-oxides commonly havehave Manganese-oxides commonly original chertmatrix matrixof of the granular fades. facies. Preliminary Prel imi nary experimental experimental data on on similar simi1 armanganiferous mangani ferous rocks to to date date have shown utions selectively dissolveMn Mn from from rocks rocks ininwhich which have shownthat that aqueous aqueousSO,-so1 SO-solutions selectively dissolve fine-grained and iron-oxidesare areintimately intimately mixed, mixed, as as in the fine-grainedmanganese-oxides manganese-oxides and iron-oxides the Emily rocks. rocks. Porosity/permeability Porosi ty/permeabi 1 i tydata dataononcore coresamples samples from from the theEmily Emilysuggest suggest thatleach leachsolutions solutions should morefavorably favorably access manganese-oxidesfrom fromthe themore more that should more access manganese-oxides granular strata of of the theiron-formation iron-formationthan than from from strata strata of ofwell-laminated, we1 1-1 aminated,very very granular fine-grained iron-formation iron-formation or chert. chert. 15 �The the Spirit The Petrology petrology and and Geochemistry Geochemi stry ofof the SpiritVolcanogenic Vol canogenic Massive Massive Sulfide Sulfide Prospect, Prospect, North-Central North-CentralWisconsin. Wisconsin. Susan Brink, Geologist* Geologist* Susan E.E. Brink, University UniversityofofMinnesota Minnesota The The Spirit Spiritzinc-lead-copper zinc-lead-coppervolcanogenic volcanogenic massive massive sulfide sulfide prospect prospect is is located massivesulfide sulfide district district ofof ananEarly Penokean located within withinthe theSomo Somo massive EarlyProterozoic Proterozoic Penokean volcanic-magmatic volcanic-magmatic terrane terrane in in north-central north-central Wisconsin. Wisconsin. A A petrographic petrographic and and geochemical studyofof the the lithologic was geochemical study lithologicpackage package that thathosts hoststhe thesulfide sulfide wasmade. made. Four majorinterbedded interbeddedrock rockunits unitswere wereidentified identifiedand andinclude includetholeiitic tholeiitic mafic Four major mafic and caic-alkaline felsic felsic volcaniclastic and calc-alkaline volcaniclastic pyroturbidites, pyroturbidites, felsic felsicfragment-rich fragment-rich According to data data from from trace traceelement el ement debris debri s flows, fl ows,and andminor mi normeta-carbonate. meta-carbonate. According discrimination the finely nature of discriminationdiagrams diagrams and and the finelybedded bedded nature of the the rocks, rocks,the thebimodal bimodal submarine volcanicswere wereerupted eruptedinin an an island-arc island-arc tectonic submarine volcanics tectonic setting settingand andwere were deposited distally from deposited subaqueously, subaqueously, distally from the the eruptive eruptivecenter, center,perhaps perhapsininaaback-arc back-arc basin. basin. Regional dynamothermal metamorphism produced isoclinally folded rocks in i socl i nal ly folded in dynamothermal metamorphi sm produced which the is well well foliated foliated(63°) (63') and and lineated. 1ineated. Prograde Prograde metamorphic metamorphic which the rock rock fabric fabric is mineral reachedthe thestaurolite-quartz staurolite-quartz subfacies mineral assemblages assemblages reached subfacies of ofthe thealmandinealmandineyields aa amphibolite metamorphism. amphi bol i te facies faciesof of metamorphism. Garnet-biotite Garnet-biotitegeothermometry geothermometry yields andsphal sphalerite-pyrrhotite-pyrite maximum temperature between 4100 410' and and 500° 500' CC and eri te-pyrrhotite-pyrite maximum temperature between geobaronietry indicates aa metamorphic pressure of of 55 kb. geobarometry indicates metamorphic pressure kb. The mainsul sulfide-bearing mineralized The main fide-bearing mineral ized horizon horizon is ischaracterized characterizedbybyenrichment enrichment of Ti, Ga, Sc and anddepletion depletion in in Si, Si, Na, of Fe, Fe, Cu, Cu, Pb, Pb, Z, Z,Mg, Mg, Mn, Mn, Ti, Ga, and and Sc Na, K, K, Rb, Rb, Sr, Sr,and and stratiform, stratabound sulfide lens (up 9.3m m thick) thick)isisdeveloped developed Ba. The The stratiform, stratabound sulfide (up to to 9.3 Ba. in schist which occurs below belowaachloritized chloritized mafic schist. The in aa muscovite-quartz muscovi te-quartz schist which occurs schist. The felsite occurring above the chloritized mafic schist contains quartz-pyrite felsite occurring above the chloritized mafic schist contains quartz-pyrite laminae (0.5 (0.5 cm cm thick) thick) with with low base base metal metal content. content. These These laminae laminae are are laminae solely on on the the rare earth Based solely earth interpreted as as being being aa hydrothermal hydrothermal exhalite. interpreted exhalite. Based element pattern of samples et al. felsic samplesand andthe themodel model proposed proposed by by Campbell Campbell et a1. element pattern of 33felsic (1984), laminae may 1 aminae maybe be genetically geneticallycapable capable (1984), the felsic fel sicunit unitwith withthe thequartz-pyrite quartz-pyrite of significant massive sulfide deposit. of hosting hosting an an economically economically significant massive sulfide deposit. *presently asaa geologist geologist at the the U.S U.S Bureau Bureau of of Mines, Mines, Twin Twin Cities Cities *Presently employed employed as Research Center, 5629 Minnehaha Minnehaha Ave. Mi nneapol is, Research Center, 5629 Ave. S., S., Minneapolis, MN 55417 55417 MN 16 �PROCESS PROCESS RATES RATES DURING MIDCONTINENT MIDCONTINENT RIFTING: CLUES CLUES TO TO THE THE ORIGIN ORIGIN OF OF THE THE MIDCONTINENT MIDCONTINENT RIFT RIFT SYSTEM SYSTEM William F. Cannon, U.S. U.S. Geological Survey, Survey, Reston, Reston, VA VA 22092 22092 Two developments developments in in recent recent years, the the acquisition acquisition of of deep deep seismic seismic reflection reflection profiles (Cannon (Cannon and others, 1990) 1990) and and the the determination determination of of aa precise geochronologic framework framework (Davis (Davis and Sutcliffe, Sutcliffe, 1985; 1985; Palmer Palmer and and Davis, Davis, 1987; Davis and Paces, 1990), make it possible to study quantitatively quantitatively processes related to to the the Midcontinent rift system system (MRS). (MRS). One step step in in these these studies is to estimate estimate rates rates of of processes. processes. This paper presents the the results results of of calculations which place considerable considerable constraint constraint on process some simple calculations process models models by comparison comparison to rates of younger and modern processes, helps and, by helps clarify clarify the the nature nature and and cause cause of of rifting. rifting. Subsidence Subsidence rate: Because numerous stratigraphic stratigraphic horizons horizons that that can can be be traced traced on on subsidence curves can be drawn. Figure seismic sections are precisely dated, subsidence Figure 1 shows a curve determined for the western Lake Superior region near near the the rift rift axis. Subsidence Subsidence accelerated accelerated for for the the 15 15 m.y. m.y. during which which the the voluminous voluminous basalts were erupted but then abruptly slowed slowed near the the end end of of volcanism volcanism and and continued at a slower slower rate for for at least several several tens tens of million million years years during during postrift sedimentation. sedimentation. The average subsidence subsidence rate rate during during volcanism volcanism was was about 1.3 1.3 mm/yr but may have exceeded 5 mm/yr during the the most rapid rapid subsidence subsidence toward the the close close of of volcanism. volcanism. During sedimentation, subsidence averaged only a few tenths tenths of of aa millimeter millimeter per per year year at at most. most. Macma Macnna generation aeneration rate: rate: For For the the entire entire rift rift II estimate estimate that that roughly roughly 2x106 2 x 1 0 ~km3 km3 of volcanic rocks rocks were were erupted. erupted. A comparable comparable amount of intrusive rock was probably emplaced within km3 within and and at at the the base base of of the the crust, crust, so so about about 4xl06 4x10~ km3 of of basaltic magma magma was3generated was generated in in about about 15 15 m.y. m.y. generation rate rate is is basaltic The magma generation 3 /yr. thus about about 0.25 0.25 km km /yr. thus Average eruption eruption rate rate was was about about 0.13 0.13 km3/yr. km3/yr. The eruption Eruption rate: Average eruption rate rate with time, time, but but that that is difficult difficult to to quantify quantify my have changed significantly with the older older flow sequences sequences which which because of incomplete incomplete preservation of the originally extended well beyond their their present present outcrop outcrop belts. belts. The Portage Portage Lake Volcanics, which probably erupted from a single center center near near the the end end of of Volcanics, volcanism, had an eruption eruption rate rate as as high high as as 0.2 0.2 km3/yr. k~n~/~r. Extension rate: Extension rate: A common common estimate estimate of the present extension across the rift in the Lake Superior region is about about 50 km. km. The The rift rift probably probably closed closed about 30 km during later compression, so so original original extension extension was was probably probably about about 80 80 km. km. Assuming that extension coeval, I calculated the extension extension extension and volcanism were coeval, rate averaged averaged 55 mm/yr. Com~arisonto to younger vounaer processes: processes: One of the most features of the the Comparison most striking features rift is the great volume volume of basalt produced in in aa relatively relatively short short time. time. The average eruption rate of 0.13 0.13 km3/yr is about about half half of of the the peak peak production production rate for Columbia River River basalts, basalts, which which maintained maintained that that rate rate for only only about 0.5 0.5 m.y., m .y., and about one—fourth one-fourth the average eruption rate of the Deccan basalts, probably the most rapidly erupted basalts of the Phanerozoic (Baksi, (Baksi, 1988). the However, the eruption rate for the Portage Lake Volcanics matched that of the Columbia River River basalts basalts and and was was half half that that of of the the Deccan. Deccan. Because basalts were Columbia probably being erupted from other centers synchronously synchronously with the Portage Lake, 17 17 �the the MRS, MRS, toward toward the the end end of of its its volcanic volcanic phase, phase, may may have have matched matched or or exceeded exceeded The eruption eruption rate rate for for the the Portage Portage Lake Lake the eruption eruption rate rate of of the the Deccan. Deccan. The the Volcanics Volcanics was was about about twice twice the the modern modern rate rate of of the the Hawaiian Hawaiian hotepot hotspot (Swanson (Swanson 1972), 1972), the the most vigorously vigorously erupting erupting volcanic volcanic center center of of the the modern modern earth. earth. There for the the volcanism volcanism of of the the MRS, MRS, and and There are are clearly clearly no no modern modern analogs analogs for only only rarely rarely in in earth earth history history have have continental continental flood flood basalts basalts been been erupted erupted at at rates comparable comparable to to the the MRS. MRS. On On the the modern modern earth, earth, the the only tectonic tectonic setting setting rates in in which basaltic magma is is generated generated at at rates rates comparable comparable to to the the MRS MRS is is ridge 2,000 2,000 km km long long (about (about the the length length of of the the MRS) MRS) midocean ridges. ridges. AA ridge midocean spreading spreading at at aa rate rate of of 55 cm/yr cm/yr produces produces about about 0.7 0.7 km3/yr km3/yr of of basaltic basaltic magma, magma, or or about 33 times times the the production production rate rate of of the the MRS. MRS. However, However, the the extension extension rate rate for for about the the MRS MRS is is an an order order of of magnitude magnitude less less than than such such aa ridge. ridge. The The MRS, MRS, therefore, therefore, was to 44 times times more more productive productive of of magma magma per per unit unit of of extension extension than than are are was 33 to modern midocean midocean ridges. ridges. modern These These relationships relationships require require that that the the mantle mantle beneath beneath the the MRS MRS was was much much hotter hotter than than mantle mantle beneath beneath modern modern midocean midocean ridges ridges in in order order for for great great volumes volumes of magma magma to to have have been been generated generated during during extension. extension. They They are are consistent consistent with with of origin origin of of the the MRS MRS magmatism magmatism in in response response to to the the arrival arrival of of the the head head of of aa new new mantle mantle plume plume beneath beneath the the region region at at about about 1.1 1.1 Ga. Ga. The The great great burst burst of of basaltic basaltic volcanism, volcanism, but but the the limited limited time time span span for for it it and and related related extension, extension, represents represents the the time time required required to to dissipate dissipate the the anomalous anomalous amount amount of of thermal thermal energy energy in in the the plume head. head. plume Postvolcanic sedimentation: sedimentation: Figure Figure 11 illustrates illustrates the the marked marked difference difference in in Postvolcanic subsidence subsidence rate rate during during volcanism volcanism from from that that during during later later sedimentation sedimentation and and implies implies that that the the sedimentary sedimentary rocks rocks of of the the Oronto Oronto Group Group and and younger younger sequences sequences were not not deposited deposited in in an an active active rift. rift. The The rate rate of of development development of of the the were sedimentary sedimentary basin basin is is consistent consistent with with the the rate rate of of subsidence subsidence caused caused by by decay decay of of the the rift-generated rift-generated thermal thermal anomaly anomaly in in the the mantle, mantle, augmented augmented by by isostatic isostatic compensation compensation of of loading loading by by the the sedimentary sedimentary fill, fill, and and does does not not require require postvolcanic extension. extension. Although Although thick thick accumulations accumulations of coarse, nearly nearly postvolcanic massive conglomerate, conglomerate, such such as as the the Copper Harbor Conglomerate, are generally massive assumed to to be be evidence evidence for for extensional extensional uplift uplift of of adjacent adjacent highlands, highlands, the the assumed sedimentation rate rate is is not not extreme extreme and and may may not not require require active active tectonism. tectonism. As As sedimentation indicated by ages ages of of underlying underlying Portage Portage Lake Lake Volcanics Volcanics and and interlayered interlayered flows indicated flows the accumulation accumulation rate rate of even even the the coarsest coarsest (Davis and Paces, 1990), the (Davis conglomerates was was about about 11 mm per per 5,000 5,000 yr. yr. The The continued continued supply supply of of coarse coarse conglomerates alluvium alluvium during during more more than than aa kilometer kilometer of of sedimentation sedimentation likewise likewise does does not not require require extension, extension, and and could could have been accomplished by isostatic isostatic renewal of original rift-flank rift-flank uplifts uplifts during during their their erosional erosional destruction. destruction. original References References Cited Cited Baksi, A.K. A.K. 1988, 1988, Estimation Estimation of lava extrusion and magma production rates of Baksi, two flood flood basalt basalt provinces: provinces: Journal Journal of of Geophysical Geophysical Research, Research, v. v. 93, 93, p. p. two 11809-11815. 11809—11815. Cannon, W.F., W.F., in in press, The Midcontinent rift in the Lake superior superior region with Cannon, emphasis emphasis on on its its geodynamic geodynamic evolution: evolution: Tectonophysics. Tectonophysics. Cannon, W.F., W.F., Green, Green, A.J., A.J., Hutchinson, Hutchinson, D.R., D.R., Lee, Lee, B. B. Milkereit, Milkereit, B., B., Behrendt, Behrendt, Cannon, J.C., Halls, Halls, H.C., H.C., Green Green J.C., J.C., Dickas, Dickas, A.B., A.B., Morey, Morey, G.B., G.B., Sutcliffe, Sutcliffe,R., R., J.C., 18 �and Spencer, C., C., 1990, 1990, The The North American Midcontinent rift rift beneath beneath Lake Lake Superior Superior from from GLIMPCE GLIMPCE seismic seismic reflection reflection profiling: Tectonics, Tectonics, V. v. 8, 8, p. p. 305—332. 305-332. Davis, D.W., J.B., 1990, 1990, Time Time resolution resolution of of geologic geologic events events on on the the D.W., and and Paces, Paces, J.B., Keweenaw Keweenaw Peninsula Peninsula and and implications implications for for the the development development of of the the Midcontinent rift rift system: system: Earth Earth and and Planetary Planetary Science Science Letters, Letters, v. v. 97, 97, p. p. 54—64. 54-64. Davis, D.W., D.W., and and Sutcliffe, Sutcliffe, R.H., R.H., 1985, 1985, U—Pb U-Pb ages ages from from the the Nipigon Nipigon plate plate and and northern northern Lake Lake Superior: Superior: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 96, 96, p. 1572—1579. 1572-1579. p. Palmer, H.C.,, and Davis, Davis, D.W., D.W., 1987, 1987, Paleomagnetism Paleomagnetism and and U-Pb U—Pb geochronology geochronology of H.C., and of Michipicoten Island——precise of the the Keweenawan Keweenawan polar polar wander Island~precisecalibration of track: Precambrian Precambrian Research, Research, v. v. 37, 37, p. p. 157—171. 157-171. Swanson, D.A., volcano: Science, v. D.A., 1972, 1972, Magma Magma supply supply rate rate at at Ki].auea Kilauea volcano: v. 175, 175, p. p. 169—172 ACE (MA) 1110 0 1090 1100 5 1080 1070 1060 1050 I 10 —' o z20 2 25 RIFlING RIFTING AND MAGMATISM MAGMATISM I I— Al Z i k SUBSIDENCEE AAND ND I SEDIMENTATION 1 Figure Figure 1. 1. Subsidence Subsidence curve curve for for the the axial axial region region of of the the Midcontinent Midcontinent rift rift beneath beneath Lake Lake Superior. Superior. Solid Solid circles circles identify identify stratigraphic stratigraphic horizons horizons for for which precise U-Pb radiometric ages are known (Cannon, in press). which precise U—Pb radiometric ages are known (Cannon, in press). 19 �ISOTOPE AND ISOTOPE AND PALEOMAGNETIC PALEOMAGNETIC DATING OF WEATHERED GRANITE GRANITE BELOW BELOW ThE IN NEILLSVILLE, WISCONSIN THEPRECAMBRIAN-CAMBRIAN PRECAMBRIAN-CAMBRIAN CONTACT IN Lung S. Chan Chan & & Zachary Zachary Kostalek Kostalek Department of Department of Geology Geology Universityofof Wisconsin-Eau Wisconsin-Eau Claire, Claire, Eau Eau Claire, WI University WI 54701 54701 Richard L. L. Hay Hay Department Departmentof of Geology Geology University of Illinois, Illinois, Urbana IL 61801 University of IL 61801 The Precambrian-Cambrian (PC-C) is represented represented by a nonconformity nonconformity (PC-C) contact in central Wisconsin is between the the Upper Upper Cambrian Cambrian Mount Mount Simon Simon Sandstone Sandstone and and the the late lateProterozoic Proterozoiccrystalline crystallinerocks. rocks. In Neillsville, the the section below the contact is a 3 m thick zone of of weathered weathered granites. granites. Petrographic Petrographic of the weathered weathered granite overprinted by diagenetic studies of granite show show that that the the pre-Mt. pre-Mt. Simon Simon paleosol is overprinted reactions with pore fluids from the Mt. Simon Sandstone [Hay and Liu, 1991]. The abundance in fluids Mt. and Liu, 19911. authigenic K-feldspar in in the the paleosol paleosol is is attributable attributable to widespread hydrological hydrological events that that occurred authigenic occurred in the Valley during during the mid- and late Paleozoic. Potassium-argon dating the Upper Upper Mississippi Mississippi Valley dating of of an an ilhitic clayand and authigenic authigenic K-feldspar in in the the altered granite illitic clay granite within within22 meters metersof of the thePC-C PC-Cin inNefflsville Neillsville yielded, respectively, respectively, 38529 385±9 Ma and 411±10 411±1Ma Ma ages. ages. These These ages are are compatible compatible with with previously previously reported ages of potassic diagenesis in the Upper Mississippi Valley [Hay et al., 1988; Lee Lee and ages of potassic diagenesis the Upper Mississippi Valley [Hay et al., values of of the illitic clay and K-feldspar are not in f i 1 8 0 values K-feldspar are in equilibrium, equilibrium, Aronson, 1991]. 19911. Measured Measured 6180 suggesting a probable probable higher higher diagenetic diagenetic temperature of the the K-feldspar K-feldspar than of the the illitization. illitization. have conducted a paleomagnetic study to to determine determine ififthe theweathered weathered granite granite was remagnetized We have during the diagenesis. block samples samples were were collected collected from from three three quarries in diagenesis. Eighteen Eighteen oriented oriented block Neillsville. At At least least four four 1" 1" diameter diameter xx 7/8" 7/8" length length specimens were were prepared prepared from from each each sample. sample. NRM NRM intensity measurements, measurements, thermal demagnetization, demagnetization, and alternating field field demagnetization demagnetization were were conducted at at the theInstitute InstituteofofGeomagnetism Geomagnetismand andRock Rock Magnetism Magnetism at at the theUniversity Universityof of Minnesota. Minnesota. progressively (Help from the UM UM Magnetics Group is gratefully acknowledged.) The samples were progressively 650° at 10°C 10° increments 80 demagnetized at temperatures up to 650°C incrementsand and in in alternating alternating fields up up to 80 milliteslas and 10 10 mT increments. Principal Principal component component analysis analysiswas wasconducted conducted to to delineate linear segments from from the the measurement results. For For samples samplesthat that do do not not yield linear segments, segments measurement results. segments, the magnetization step step before before aa substantial drop in NRM intensity isis used used as the magnetization substantial drop NRM intensity the representative representative direction. Orthogonal Orthogonal vector projections are used to help the component analysis. The acceptability of the results results from from individual individual blocks blocks is based on on the thefollowing followingcriteria: criteria: (1) stability stability of the magnetic magnetic component component upon demagnetization, demagnetization, of the the demagnetization demagnetization method as indicated by the the reduction reduction of NRM intensity NRM intensity (2) efficiency of during the demagnetization, demagnetization, and the same same sample. sample. (3) consistency consistency of magnetic components in specimens prepared from the Thennoremanent curves obtained from thermal demagnetization of the samples samples reveal reveal dominant dominant Thermoremanent 300-350°Cindicating blocking temperatures at about 300-350°C, indicatingilmenite ilmeniteor/and or/and aa titanomaghemite as the principal magnetic magnetic carriers. carriers. About 20% of the specimens do not yield stable NRM principal NRM components components and specimens consistent directions. unstable specimens from from three three blocks blocks do do not show consistent directions. The The large large number number of unstable samples reveals substantial weathering stable weathering effects. The magnetic magnetic components components obtained from the stable samples are present field. field. No No tilt correction correction are not randomly distributed, but but do not cluster about the present surface suggests no major major postpostbeen applied applied to to the the specimens; specimens; the the attitude attitudeof ofthe thePC-C PC-C contact contact surface has been 20 �Proterozoic tectonic rotation rotation of representative directions of the the sites. sites. The representative directions from the acceptable acceptable samples appear to form two general clusters, one with a southwesterly to westerly declination appear to form two general clusters, one with southwesterly declination and and aa second second one with with aa southeasterly southeasterlydeclination. declination. The The first first cluster cluster yields a mean direction direction at at D=263°, D=263', 1=50°, 1=50° and aa virtual 23°; the second cluster yields yields aa mean direction virtual geomagnetic geomagnetic pole at at 1469W, 146¡W23' ; the second cluster direction of D=140°, D=140°1=45°, 1=4S0,and aa pole pole at at125°E, 12S0E,9°. 9'. The two poles are compared to the the paleomagnetic paleomapetic poles poles of stable by Irving Irving [1977]. [1977]. The The first firstcomponent component can can be be interpreted interpreted as stable North North America compiled by as aa late late Proterozoic overprint, as indicated indicated by the the similarity similarity in in paleopole paleopole coordinates. coordinates. A A similar similar magnetic magnetic component in the the1.52 1.52Ga-old Ga-old syenite syenite in Wausau, eastern eastern Wisconsin, [Zich et al., 1986] 19861 component is present present in and in in Keweenawan-age Keweenawan-age mafic mafic dikes in central central Wisconsin Wisconsin [Chan, 1991]. 19911. The The presence presence of ofsimilar similar magnetic components implies aa widespread widespread remagnetization remagnetization event components in in these these rocks rocks plausibly implies event during during the late granite appears appears to be aa magentic component component in the Nefflsville Neillsville granite late Proterozoic. Proterozoic. The The second second magentic Cambrian-age remanent magnetism acquired acquired during Cambrian-ageoverprint, overprint, and and can can be interpreted interpreted as a chemical remanent during the latethe weathering weatheringand andformation formationof of the thepaleosol. paleosol. None None of the components components observed appears appears to to be be latePaleozoic age. Unfortunately, Silurian-Devoniansegment segmentof of the the apparent Unfortunately, the poorly constrained Silurian-Devonian polar wander wander path path ofofstable stableNorth NorthAmerica America renders rendersaaconclusive conclusivecomparison comparison impossible. impossible. Most Most Silurian-Devonian however, show showpaleopoles paleopoles at at high high latitudes latitudes of about 40°. 40° Silurian-Devonianpaleomagnetic results, however, The low latitude therefore, argues against a Devonian latitude of of the the paleopole paleopoleobtained obtainedfrom fromNefflsville, Neillsville, therefore, Devonian remagnetization. remagnetization. References References Chan, 1991, dike swarm: swarm: constraints constraints on thermomechanical 1991, Paleomagnetism Paleomagnetism of Central Central Wisconsin dike thermomechanical model of Midcontinent rift, Inst. Inst. Lake Lake Superior Superior Geology Geology Proc., Proc., 37th Annual Annual Meeting, Meeting, Eau Eau Midcontinent rift, Claire, WI, WI, 1991; 37, Pt. 1, 1, p. 23. Hay, R.L., M. Lee, Lee, D.R. D.R.Kolata, Kolata,J.C. J.C.Matthews, Matthews,and andJ.P. J.P.Morton, Morton, 1988, 1988, Episodic Episodic potassic potassic diagenesis diagenesis R.L., M. of Ordovician Ordovician tuffs tuffs in in the theMississippi MississippiValley area, Geology, 16, 16, 743-747. 743-747. 1991, Kaolinite was a precursor to diagenetic diagenetic K-feldspar K-feldspar of Paleozoic age in in Hay, R.L., R.L., and J. Liu, 1991, Hay, Wisconsin, Prog. and and Abstr. Clay Mineral. Wisconsin, Mineral. Soc. Soc. 28th 28th Ann. Ann. Meeting, Meeting, Houston, Houston, October 5-10, 1991, 1991, p. 70. 70. N. America America and displaced Irving, E., E., 1979, Paleopoles Paleopoles and paleolatitudes of N. Irving, and speculations about displaced terranes, terranes, Can. Can. J.J. Earth EarthSci., Sci., 16, 16,669-694. 669-694. the Lee, M., J.L. Aronson, Lee, M., and J.L. Aronson, 1991, Repetitive Repetitive occurrence occurrence of ofpotassic potassic diagenesis diagenesisin in the the region of the Upper Mississippi Valley (UMV) Mineral District: implications for a persistent paleoUpper Mississippi Valley (UMV) Mineral District: implications for a persistent hydrological setting settingfavorable favorablefor fordiagenesis, diagenesis,Prog. Prog. and andAbstr. Abstr. Clay Clay Mineral. Mineral. Soc. Soc. 28th 28thAnn. Ann. hydrological October 5-10, 1991, 1991, p. 98. 98. Meeting, Houston, October Zich, C., C., L.S. L.S. Chan, and P.E. P.E. Myers, Myers, 1986, 1986, Preliminary Preliminary paleomagnetic the Wausau Wausau Zich, paleomagnetic results results from the syenite complex, complex, central centralWisconsin, Wisconsin, EOS, EOS, Trans., syenite Trans., 67, 266. 21 �Implications of and Magnetic Magnetic Anisotropy Anisotropy Studies Studies for the the Penokean Penokean Implications of Strain and Upper Michigan Michigan Orogeny, Upper Davidson, John John C. C. Palmquist, Palmquist, Lawrence Lawrence University, Appleton WI, WI,54912 54912 Mark E. Davidson, This Thisstudy study applies appliesgeometric geometricstrain strain analysis analysisand and magnetic magnetic anisotropy anisotropy techniques techniquesto to the the Michigamme Michigamme Slate to to constrain constrain the the kinematics kinematics of of the thePenokean Penokean Orogeny. Orogeny. The The Michigamme MichigammeSlate Slate(Baraga (BaragaGroup, Group,Marquette MarquetteSupergroup) Supergroup)of of Upper UpperMichigan Michiganisispresent presentinin the of the the 1.88 Ga Penokean Penokean Orogeny. Orogeny. Our data the allochthon allochthon and parautochthon parautochthon of 1.88 Ga data was was collected collected within the allochthon on a 15 15 mile traverse traversefrom fromCovington, Covington,MI MIto tothe thesouth south along highway M-95. Early Early sedimentary sedimentary rocks of the Marquette Supergroup were were deposited deposited on on aa passive passive continental continental margin. Post Postpassive-margin passive-marginrifting riftingwas wasfollowed followedby by rapid rapidsubsidence subsidenceand andthe the deposition of turbidites turbidites from two two source source areas: areas: aa volcanic volcanic arc to the the south, south, and and aa deposition continental source to the north north (Barovich, (Barovich, 1989). 1989). These These turbidites are contained in the Michigamme Slate of Michigan and the correlative Thomson Thomson Formation Formation of of Minnesota. Minnesota. The The allochthon is characterized by tight upright upright to to overturned overturned folds folds with with steep steepaxial-plane axial-plane cleavage dipping 54° 5 4 to S6°W. S6'W. Iron-carbonate Iron-carbonate concretions concretions are are pancake-shaped, pancake-shaped, and and flattened in the plane of cleavage. The Theparautochthon parautochthon exhibits exhibits significantly significantly less less intense intense folding, extended ellipsoids ellipsoids on on the the cleavage cleavage plane. plane. The folding, and mineral grains form vertically extended The Michigamme of 53%, compared to to a (maximum) value value of of Michigamme Slate Slate exhibits exhibits a mean shortening of 64% for for the the Thomson Thomson Formation Formation (Hoist, (Holst,1985). 1985). Strain data measurements measurements from the 64% Michigamme Michigamme Slate Slate overlap overlap those those for for the the Thomson Thomson Formation Formation for for comparable comparablelocales localesin inthe the orogen (Figure (Figure 1). 1). Our Ourstrain straindata datashows showsthe the pancake pancakeshape shapeof of the the concretions, concretions,which which we we interpret as the result of of an an homogeneous homogeneouspure pureflattening flatteningstrain strain(x(x:: yy::z == 1.0: 1.0 :1.0 1.0 ::0.2). 0.2). In the northern area of the Thomson Formation, Formation, Holst Hoist (1985) (1985) finds finds xx : yy :: z = 1.5: 1.5 : 1.0: 1.0 : 0.2. 0.2. The TheThomson ThomsonFormation's Formation'sstrain strainellipsoid ellipsoidhas hasstrong strongvertical vertical extension extension accompanied accompanied by by flattening. flattening. Preliminary Preliminarymagnetic magnetic anisotropy anisotropy (ams) (am) axial axial orientation orientation values indicate indicate maximum maximum at at N20°W @55°. This N 2 0 T 055'. Thisisisnearly nearlyperpendicular perpendicular to to the the cleavage cleavage plane, and and hence hence the the maximum maximum extension extension found found through through our our strain strain analysis. The Theintermediate intermediateand and minimum minimumams amsdirections directions fall very close to the cleavage plane. plane. The The ams ams strain strain intensity intensity values were were found found to to be very minor when compared to the data from the concretions. concretions. As indicated in Figures 11 and 2, the the ams ams data data is is aa major major underestimation underestimation of the strain strain amount amount found found within the Michigamme Michigamme Slate. The Theams amsdata, data,shown shownmore more clearly clearly in in Figure Figure 2, can be seen to exhibit little indication strain: magnetic anisotropy does not appear appear to to correlate correlate with with conventional conventional strain strain of strain: anisotropy in either the Thomson or or Michigamme Michigamme Formations. Formations. We found good correlation with Davidson's ams values for the the Thomson Thomson Formation, but neither ams study exhibits exhibits correlation correlation with with the the strain strain observed observedthrough through conventional conventionalstrain strainanalysis. analysis. 22 �_____,1985; Davithori/Palmquist ams 0 Hoist strain analysis N L Davidzoxt/Pa1mqiist strain o D.M. Davidson ams Hoist's strain strain area area Davidson/P almLquist strain area 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 c2-c3 Figure Figure1: 1:Logarithmic Logarithmicdeformation deformationplot. plot. N '.4 cz-c3 Figure Figure2: 2: Logarithmic Logarithmicdeformation deformationplot plotshowing showingthe theams amsdata datapoints. points. References: References: Barovich, Barovich,K.M., K.M., et.al., et.al., 1989; 1989;Nd Nd isotopes isotopesand andthe theorigin originof of 1.9-1.7 1.9-1.7Ga GaPenokean Penokean continental continentalcrust crust of the Lake Superior region: Geological GeologicalSociety Society of of America America Bulletin, Bulletin, v. v. 101, 101,p. p. 333-338. 333-338. Borradaile, Borradaile,G.J., G.J., 1988; 1988;Magnetic Magnetic susceptibility, susceptibility, petrofabrics and strain: Tectonophysics, Tectonophysics, 156, 156, p. p. 1-20. 1-20. Davidson, Jr., Davidson,D.M. D~M. Jr., 1990; 1990;Magnetic Magneticsusceptibility susceptibilityanisotropy anisotropyand andstrain, strain,Thomson Thomson Formation Formation(Proterozoic), (Proterozoic),Minnesota: Minnesota: Institute Instituteon onLake LakeSuperior SuperiorGeology Geology Proceedings, Proceedings,Abstracts, Abstracts,v.v.36, 36,p.p.17-18. 17-18. Hoist, Hoist,T. T. B.,1989; B.,1989; The ThePenokean PenokeanOrogeny Orogenyin in Minnesota Minnesotaand and Upper UpperMichigan: Michigan:aa comparison comparisonof of the the structural structuralgeology geologyof ofthe theMichigamme Michigammeand and Thomson Thomson Formations: 35, Formations:Institute Instituteon onLake LakeSuperior SuperiorGeology GeologyProceedings, Proceedings,Abstracts, Abstracts,v. v. 35, p. 27-28. 27-28. p. _______, 1985;Implications Implicationsof of aa large large flattening flattening strain strain for for the origin origin of aa bedding-parallel bedding-parallel foliation ThomsonFormation, Formation,Minnesota: Minnesota:Journal Journal of foliation in in the the early Proterozoic Thomson of Structural StructuralGeology, Geology, v. v. 7, 7,p. p. 375-383. 375-383. 23 �MAGINO, THE THE MAKING OF A MINE MAGINO, Anthony Anthony J. J. Deevy Deevy Muscocho Muscocho Explorations Explorations Ltd. Ltd. Box 209 Box 209 Dubreuilville, Ontario 1BO Dubreuilville, Ontario POS POS 1BO ABSTRACT Gold Mine is Wawa, Ontario. The is located located 38 38 miles NE of of Wawa, Ontario. The Magino Gold There was limited limited gold gold production production in in the the late late thirties. thirties. The The present present operation operation was was officially officially opened opened in in October October 1988. 1988. It is a 700 700 ton ton per per decline accessed day decline accessed mine with ore ore coming coming from from several several small small blastblasthole hole and and shrinkage shrinkage stopes. stopes. The host for for the the gold gold is is the the Webb Lake Lake Granodiorite Granodiorite Stock Stock which which was was intruded intruded into into the the Coudreau Goudreau Deformation Deformation Zone. Zone. The The ENE ENE striking striking deformation zone zone overprints deformation overprints the the generaly generaly EW EW striking striking isoclinally isoclinally folded sedimentary rocks rocks which the east-end east-end of of folded volcanic and sedimentary which make up the Michipicoten Greenstone the Michipicoten Greenstone Belt. Belt. The The ore-shoots ore-shoots are are controlled controlled by by dilatancy associated dextral dilatancy associated with the the Goudreau Goudreau Deformation Deformation Zone. Zone. Shearing, bleaching and with the Shearing, and silicificatioon silicificatioon occured occured with the gold gold emplacement. emplacement. The history of of exploration exploration and and present present operation operation are are discussed. discussed. 24 �PRELIMINARY PRELIMINARY REPORT, GEOLOGY AND GEOPHYSICS OF THE TERRA/PATRICK TERRAJPATRICK #7-22 WILDCAT WILDCATHYDROCARBON HYDROCARBON TEST, TEST, MIDCONTINENT MIDCONTINENTRIFT, RIFT,KEYSTONE KEYSTONE TOWNSHIP, TOWNSHIP, BAYFIELD BAYFIELD COUNTY, COUNTY, WISCONSIN WISCONSIN Albert B. B. Dickas, Dickas, Department Department of of Geology, Geology, University University of of Wisconsin-Superior, Wisconsin-Superior,Superior, Superior, Wisconsin, 54880-2898 54880-2898 The Terra/Patrick TerraJPatrick #7-22 borehole, borehole, located located in in the the southwest southwest quarter, quarter, northeast northeastquarter, quarter, Section 22, Township 47 north, Range Range 6 west, is being being drilled drilled as as aajoint joint venture venture between Terra Energy, Energy, Inc. Inc. of of Traverse Traverse City, City, Michigan Michigan and and Patrick Patrick Petroleum Petroleum Company of Jackson, Michigan, Michigan, operating under a farmout arrangement arrangement from Amoco Amoco Production Company (USA). This well-site is situated approximately 5 miles northeast Production Company (USA). This well-site situated approximately 5 miles northeast of the Hazel Hazel Hills Hills site announced announced by byAmoco Amocoininthe theSpring Springofof1985. 1985.This This latter latter borehole borehole was never drilled because of a lack of existing exploration drilling legislation and the never because a lack of existing exploration drilling mid-1980's decline in crude mid-1980's decline crude oil oil value. value. The Terra/Patrick TerraIPatrick borehole was spudded spudded shortly shortly after after midnight, midnight,March March9, 9,1992. 1992. The The state-issued state-issued permit allows allows drilling to to 6000 6000 feet, with restrictions restrictions concerning concerning control controlof of mud chemistry additives, casing standards, and analyses analyses of cuttings. Extensive Extensiveand and involved public hearings were conducted in Bayfield Bayfield County prior to the the issuance issuance of of the drilling drilling permit. permit. This borehole, a central rift horst test, will be the fourth conducted conducted along alongthe the Midcontinent Midcontinent Rift Rift System System since since 1984. 1984. The The first first (Kansas, (Kansas,1984) 1984) drilled aa reversed reversed rift rift sequence sequence caused caused by by faulting. faulting. The Thesecond second(Iowa, (Iowa,1987) 1987) tested tested the the western, western, halt-graben half-graben flank of the the rift. rift. The The third, third, also also aa flank flank test, test, was was initiated initiated in in the the Upper UpperPeninsula Peninsulaof of Michigan All have have failed failed to to find hydrocarbon Michigan in in 1987. 1987. All hydrocarbonreserves. reserves. The Bayfield County (Chequamegon) (Chequamegon) prospect prospect isis seismically seismically identified identifiedas as aa large largefourfourway anticlinal structure caused caused by by drag folding along the hanging wall of the Douglas anticlinal structure Douglas fault fault (Fig. (Fig.I). I). The anticline, with an axis that parallels the strike of the Douglas Douglas fault, fault, extends over aa surface surface area area of of approximately approximately 37,000 37,000 acres (60 (60 square square miles) miles) and andhas has several thousand feet of structural closure. Reservoir Reservoir quality strata are being sought in all three units which comprise comprise the Oronto Oronto Group Group of of volcaniclastic volcaniclastic rocks--oldest rocks--oldestto to youngest, the Copper Copper Harbor, Harbor,Nonesuch, Nonesuch, and andFreda Fredaformations. formations. Depending upon upon the the final final drilling drilling outcome outcome (see (see note note below), below), additional additionalinformation informationwill will Depending be be available available at the time time of of presentation presentationof of this this report. report. At the time time this this abstract abstractwas was prepared prepared(March (March24, 24,1992), 1992), the subject subject borehole borehole was was drilling an injunction action, action, filed filed on behalf of drilling in in excess excess of of 3500 3500 feet. Simultaneously an the Lac Lac Courte Courte Oreilles Oreilles band band of of Chippewa Chippewa Indians, Indians, was in its third day of of testimony testimony in in the Dane Dane County County (Wisconsin) (Wisconsin) Circuit Circuit Court. Court. 25 �FIGURE1.1. FIGURE CHEQUAMEGONPLAY PLAY SCHEMATIC SCHEMATIC CHEQUAMEGON Ereda SS J- ... -. :::1orteae LktVotcaics BasalNonesuch NonesuchSand Sandand andCopper CopperHarbor HarborFm. Fm. RESERVOIR- - Basal RESERVOIR SOURCE- SOURCE NonesuchShale Shale Nonesuch SEAL- SEAL 26 NonesuchShale Shale Nonesuch 26 �PRECAMBRIAN PRECAMBRIAN HYDROCARBON HYDROCARBON POTENTIAL POTENTIAL OF OF THE THE WESTERN WESTERN GREAT GREAT LAKES LAKES Albert B. B. Dickas, Dickas, Department Department of of Geology, Geology, University University of Wisconsin-Superior, Superior WI, 54880, and Wl, 54880. and M. M. G. G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological Geologicaland andNatural NaturalHistory HistorySurvey, Survey,Madison, Madison,WI, Wl, 53705. 53705. Hydrocarbon Hydrocarbonshows showshave havebeen beenreported reportedininthe thewestern westernGreat GreatLakes Lakessince since1852. 1852. Occurrences Occurrences include include stained stained core, surface exposures, and indigenous shows shows in in mine mine roof roof strata. strata. All All emanate emanate from from aa single single source, source, the the Nonesuch NonesuchFormation Formation(maximum (maximumage age of Ga) of of the Oronto of 1.074 1.074 Ga) Oronto Group, Group, Keweenawan Keweenawan Supergroup, Supergroup, aa(Midcontinent) (Midcontinent)rift rift derived, derived, middle middle Proterozoic Proterozoic volcaniclastic sequence. Indirect Indirectage-dating age-dating(Rb-Sr) (Rb-Sr) indicates indicateslive live oil oil hosted hostedby bythe theNonesuch NonesuchFormation Formationhas hasa aminimum minimumage ageofof1.047 1.047Ga. Ga. Nonesuch NonesuchFormation Formation distribution distribution along along strike strike is is mapped mappedfor for 300 300km, km,from fromthe theUpper Upper Peninsula WI/Mn border. border. Borehole Peninsula of Michigan to within 30 km of the WIIMn Boreholestratigraphic stratigraphic studies studies suggest suggest lateral lateral deposition deposition into into rift rift flank flank basins. basins. Reflection Reflectioncorrelations correlationsindicate indicate source source rock rockthickness, thickness,measured measuredininoutcrop outcropas asmaximum maximum215 215 meters, meters, to to be betectonically tectonically controlled. controlled. Anticlinal, Anticlinal, drag dragfolding, folding,unconformity, unconformity, and andfault fault trap trap structural structural geometries geometries are are seismically seismically identified. Stratigraphic Stratigraphictrapping trappingmay maybe beassociated associatedwith withvarying varying depositional depositionalenvironments. environments. lntergranular Intergranularporosity porosityexceeds exceeds1313percent, percent,with withfracture fracture porosities porositiescommon. common. Recognizedanticlinal anticlinal closure is of aa scale scale defined defined by by seismic seismic profile profile spacing spacing Recognized approximating km, extending to to two-way-travel two-way-traveldepth depth of of 33 to to 44 seconds. Field approximating 88 to to 10 10 km, Field studies studies suggest suggestprimary primaryreservoirs reservoirs would would be bespatially/time spatiallyltimeassociated associated with with crustalcrustalextension, thermal events. events. Secondary Secondaryhydrocarbon hydrocarboncharges chargesinto intoaxial axial and and flank flank extension, domains domains may may have have been beencontrolled controlledby bysubstitution substitutionof ofcompression compressionfor forextension extension tectonics, causing causingstabilization stabilization of of oil oil and andgas gasaccumulations accumulationsprior priorto toinitiation initiationofof tectonics, Phanerozoic Phanerozoic time. Maturation Maturationanalyses analysesfavor favor gaseous gaseous over over liquid liquidreservoirs. reservoirs. 27 �t 4 m a . 0 Precambrian bedrock @ Phanerozoic bedrock m Boreholes . 1 . 5km Northwestthickening thickening • Northwest synriftcolumn column synrift (seismic) (seismic) i-r fl LI. ' Southeasterlythickening thickening • Southeasterly synriftcolumn column(core (coreand andseismic) seismic) synnft Non-fluorescing NonesuchFm. Fm. Nonesuch • 8 Non-fluorescing organicassemblage assemblage organic Lineargravity gravitytrend trend • d Unea Diffusegravity gravitytrend trend Diffuse Ouluthgabbro gabbrooutcrop outcrop Duluth Northerlythickening thickening , • Northerly synriftcolumn column synnft (outcropand andseismic) seismic) (outcrop fluorescingNonesuch NonesuchFm. Fm. • Fluorescing organicassemblage assemblage organic • ri-r I I l .U...L . a8 . -- \ Boundary Boundarycentral centralriftriftstructure structure Southerlythickening thickening Southerly synriftcolumn column synrift [\T xwn (seismic) (seismic) • down DisturbedOronto OrontoGroup Group Disturbed sequence sequence ' / Location of of hydrocarbon hydrocarbon test test boreholes boreholes Location drilled in Wisconsin through 1992. drilled in Wisconsin through 1992. 1 ~valuatio*criteria criteria Evaluation pertaining to the the pertaining to hydrocarbon (HC) hydrocarbon (HC) potential of of the the potential Lake Superior basin Lake Superior basin segment of the segment of the Midcontinent Rift Rift Midcontinent System. System. Reservoir Reservoir - Reservoir-quality Reservoir-qualitystrata stratawWiin withinCopper CopperHarbor Harbor Conglomerate, Nonesuch and Freda Conglomeratel Nonesuch and FredaFormations Formations - Oronto OrontoGroup Groupintergranular intergranularporosity porosityranges rangesfrom from7-15% 7-15Y0 - - I Passive Passive EvaluationCriteria Criteria Evaluation % '1 / Maturation Maturation Geothermalgradient gradientwithin withinnormal normaltotohigh highrange range - Geothermal Oilseeps seepsparaffinic, paraffinic,low lowininsulfur, sulfur,and and32° 32OAPI API - Oil - Migration Migration PrincipalProterozoic Proterozoicstructure structureininplace placeatattime timeofof - Principal migration primary migration by Earlyextension-phase extension-phasemigration migrationfollowed follow~d bylater later - - Early compression-phasemigration migration compression-phase Crudefound foundintergranular intergranularand andalong alongfractures fractures - Crude - 1 Active Active Each rift rift unit unit in Lake Lake Superior Superior basin. basin. Each Differentiation of Midcontinent rift in for HC potential must be individually evaluated individually evaluated for HC potential. Source Source NonesuchFormation: Formation:—1.074 -1 -074Ga Gaininage age --Nonesuch 1.5%, White Pine Mine, Michigan TOC averages 1 .WO, White Pine Mine, Michigan - TOC averages 1 Accommodation Accommodationstructure structure 1 1 1 , Structure - Two stage tectonic s-tr$tzage tectonichistory historycreated createdmultiple multiplestructure structure combinations combinations - - Structures Structuresinclude includefold, fold,fault, faultland andstratigraphic stratigraphictraps traps Seal seal - shale/ ill isis60/40 - Lake LakeSuperior Superiorregion regionrift riftclastic clasticinfinfill 60140 shale1 sandstone sandstoneratio ratio crystallization - Mineralization Mineralizationseals sealsformed formedby bycalcite calcite crystallization �1991 COGEOMAP COGEOMAP Gravity Gravity Mapping Mapping Program Program in in West-Central West-Central Wisconsin: Wisconsin: 1991 The The Driftless Driftless Area Area C. C. Patrick Patrick Ervin, ErvinI Dept. Dept. of of Geology, GeologyI Northern Northern Illinois Illinois University, Universityf DeKalb, DeKalb! IL IL 60178, 6O17af e-mail: e-mail: T6OCPE1@NIU.BITNET T6OCPEl@NIU.BITNET M.G. M.G. Mudrey, MudreyI Jr, JrI B.A. B.A. Brown, Brownf and and M.L. M.L. Czechanski, Czechanskif Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, SurveyI 3817 3817 Mineral Mineral Point Point Rd., Rd.! Madison, MadisonI WI WI 53705 53705 During During the the summer summer of of 1991, 19911 nominal nominal one-mile one-mile grid grid gravity gravity coverage 45 degrees degrees coverage was was extended extended to to an an area area bounded bounded by by 44 44 && 45 latitude latitude and and by by 90 90 and and 90.5 90.5 degrees degrees longitude. longitude. Stations Stations are are located 1:24000 located at at surveyed surveyed spot spot elevations elevations posted posted on on USGS USGS 1:24000 topographic topographic sheets. sheets. Northern Northern Illinois Illinois University's University's LaCosteLaCosteRomberg Romberg gravity gravity meter meter G409 G409 was was used. used. Data Data are are tied tied to to the the State State of of Wisconsin Wisconsin Primary Primary Gravity Gravity Base Base Station Station Network Network (Ervin, (Ervin! 1983), 1983)1 which which is i s in in turn turn tied tied to to the the International International Gravity Gravity Standardization Standardization Network-1971 Network-1971 (DMAAC, (DMAAC! 1974). 1974). Older Older data data have have been been merged merged with with these these data data to to yield yield aa much much more more detailed detailed representation representation of of the the Bouguer Bouguer gravity gravity anomaly anomaly field field than than was was previously previously available. available. The The northeast northeast half half of of the the area area is is underlain underlain by by glacial glacial deposits deposits that that are are in in turn turn underlain underlain by by Cambrian Cambrian sedimentary sedimentary rock, rock! primarily primarily sandstone, sandstoneI except except in in the the northeastern northeastern corner, cornerI where where lower rock! primarily primarily granite, granitef underlies underlies lower Proterozoic Proterozoic intrusive intrusive rock, the the till. till. The The southwestern southwestern half half of of the the survey survey area area extends extends into into the the driftless driftless area area and and is is dominated dominated by by the the Cambrian Cambrian sandstone sandstone that that is is covered covered by by the the glacial glacial deposits deposits in in the the northeast, northeastf although although lLower 1Lower Proterozoic Proterozoic and and uupper uUpper Archean Archean rock rock crop crop out out along along several several of of the the river river systems. systems. The The extreme extreme southwest southwest corner corner of of the the area area also also contains contains aa few few remnants remnants of of the the Ordovician OrdovicianPrairie Prairie du du Chien Chien dolomites. dolomites. Much Much of of the the area area is is covered covered by by marsh marsh and and swamp, swampIand and the the surface surface becomes becomes more more dissected dissected as as the the Mississippi Mississippi River River is is approached approached to to the the west. west. In In this this type type of of terrain, terrain, the the road road system system tends tends to to follow follow the the topography topography rather rather than than the the section section lines, linesI so so the the station station distribution distribution deviates deviates significantly significantly from from aa one-mile one-mile grid grid over over much much of of the the area. area. Access Access problems problems were were further further compounded compounded by by the the high high rainfall rainfall during during the the field field season season that that flooded flooded many many roads. roads. We We anticipate anticipate obtaining obtaining supplementary supplementary data data in in these these areas areas in in 1992. 1992. Due Due to to the the dissected dissected topography topography in in the the southwest, southwestI terrain terrain corrections corrections were were applied applied to to the the data. data. The The Bouguer Bouguer gravity gravity minimaf but but ascends ascends in in the the anomaly field field is is dominated dominated by by broad broad minima, anomaly southwest southwest to to values values above above -15 -15 mgals mgals and and in in the the northwest northwest to to over over -20 -20 mgals. mgals. The The field field descends descends below below -80 -80 mgals mgals in in an an east-west east-west trending trending minima minima located located in in the the southwestern southwestern corner corner of of Marathon Marathon County Marshfield. This This minima minima is is flanked flanked on on the the County and and west west of of Marshfield. 29 �north north by by aa fault fault that that separates separates if i f from from aa relatively relatively positive positive anomaly anomaly apparently apparently associated associated with with metamorphosed metamorphosed early early Proterozoic and Proterozoic mafic mafic to to ultramafic ultramafic intrusive intrusive rock rock (Mudrey (~udrey and others, othersf 1982). 1982). AA second second relatively relatively positive positive anomaly anomaly lies lies south south of of the the minima minima in in Wood Wood County. County. The The source source of of this this anomaly anomaly is is not not known. known. REFERENCES REFERENCES Ervin, Ervinf C.P., C.Paf1983, 1983f Wisconsin Wisconsin Gravity Gravity Base Base Station Station Network, Networkf Wis. wise Geol. Geol. and and Nat. Nat. Hist. Hist. Surv. Surv. Misc. Misc. Pap. Pap. 83—1, 83-lf43 43 p. p. DMAAC, North DMAACf 1974, 19741 World World Relative Relative Gravity Gravity Reference Reference Network Network -- North America, Americal DMAAC DMAAC Ref. Ref. Pub. Pub. No. No. 25, 25f 1974 1974 Supplement. Supplement. Mudrey, 1982, biucireyf M.G., bi.GefJr., J r e 1Brown, 8rownf B.A., E.A.~and an6 Greenberg, G r e e n ~ e r gJ.K., ,7.Kef ~ 1982f Bedrock Bedrock Geologic Geologic Map Map of of Wisconsin, Wisconsinf Wis. Wis. Geol. Geol. and and Nat. Nat. Hist. Hist. Surv., Surve1Madison, MadisonfWI. WI. 30 �THE PALISADE RHYOLITE, LAKE COUNTY, COUNTY, MINNESOTA: RHYOLITE, LAKE MINNESOTA: A CRYPTIC CRYPTIC RHEOIGNIMBRITE RHEOIGNIMBRITE IN THE NORTH NORTH SHORE SHORE VOLCANICS VOLCANICS C. Green Green John C. Geology Department, University of Minnesota Duluth Geology Department, The Palisade Palisaderhyolite, rhyolite, > 90 m thick, is one of the most easily easily accessible of the several The large rhyolite rhyolite flows flows in the NSVG. broken up up somewhat somewhat by by faulting, faulting, it large NSVG. Although Although itit has has been been broken can be traced with certainty for 18 km and possibly for 29 km northeast from Beaver can be traced with for 18 k m and possibly for 29 k m northeast from BeaverBay. Bay. In most outcrops it is massive massive and and porphyritic, porphyritic, with with a ffew e w percent percent of 18 quartz, quartz, alkali alkali feldspar, and oxidized and oxidized ferromagnesian ferromagnesian silicate phenocrysts. phenocrysts. Its groundmass groundmass is made made of fine-grained fine-grained feldspar and and flow-aligned flow-aligned tabular tabular quartz quartz paramorphs paramorphsafter afterprimary primarytridymite. tridymite. With alkali feldspar With aa flow flow breccia near near the the top top at lllgen City and folded folded flow-banding flow-banding near the top and bottom, ititlooks looks near the like an unusually and widespread widespread lava lava flow, flow, perhaps unusually large large and perhaps like other highly highly mobile, mobile, high-T high-T silicic lava flows recently silicic recently described described from from various various Tertiary Tertiary and and Mesozoic Mesozoic provinces. provinces. Close petrographic examination examinationofof the the base base and and top, top, however, Close petrographic however, indicates indicates that that the the Palisade rhyolite was was emplaced emplaced as asaahot hotpyroclastic pyroclasticflow flow that that completely welded to Palisade rhyolite t o the the base, base, Bothininthe thelaminated laminatedtop topbreccia brecciazone zoneand and in inthe the and flowed after after welding welding -- aa rheoignimbrite. Both basal meter only, only, thin sections reveal a groundmass groundmass of of welded glass shards. shards. Over basal meter Over aa narrow narrow transition zone of one one or two t w o meters metersabove above the the base base these these shards shards are completely deformed This transition zone until only until only aa fine, fine, planar planar flow flow lamination lamination isis present. present. This zone contains contains strong strong lineations that that show show the the direction direction of of flow after lineations after welding, welding, and and flow-folds, flow-folds, some some isoclinal, isoclinal, are are developed iin the overlying overlying zone. zone. This passes developed n the passes upward into the massive interior that makes makes up the great great bulk bulk of of the flow. the The Palisade Palisade rhyolite rhyolite illustrates illustrates the the necessity necessity of careful petrographic The petrographic as as well well as as field field examination of of the the tops tops and and bases bases of of felsic felsic flows flows in order examination order tto o interpret their origin origin correctly. 31 �Petrology of aa Conglomerate Conglomerate Pacies Facies of of the the Petrology and and Provenance Provenance of Jacobsville Ironwood to to Bergland, Bergland, Michigan Michigan Jacobsville Sandstone: Sandstone: Ironwood Cheryl Cheryl A. A. Hedgman, Hedgmant U.S. U.S. Geological Geological Survey, Surveyt Reston, Restont VA VA 22092 22092 West West of of Lake Lake Gogebic, Gogebict from from Ironwood Ironwood to to Bergland, Berglandt Mich., Michetthe the Late Late Proterozoic Proterozoic (Keweenawan) (Keweenawan) Jacobsville Jacobsville Sandstone Sandstone is is dominated dominated by by conglomerates conglomerates and and coarse coarse lithic lithic arenite arenite in in contrast contrast to to areas areas farther farther east east where where it it is is aa finer finer grained, grainedtsubinature submature to to mature, maturet quartzose, quartzoset feldspathic feldspathic and and lithic lithic arenite arenite with with minor minor shale, shalet siltsiltstone, stonet and and conglomerate conglomerate (Kalliokoski, (Kalliokoskit1982). 1982). This This paper paper presents presents data data indicating indicating aa southern southern source source for for these these western western conglomerates conglomerates and sandstonest which which is is consistent consistent with with aa current current theory theory and coarse coarse sandstones, of of active active thrust thrust faulting faulting south south of of the the Jacobsville Jacobsville along along the the Pelton Pelton Creek Creek fault fault (Cannon (Cannon and and others, otherst 1990; 1990; Sims, Simst 1990). 1990). The The conglomerate conglomerate is is clast-supported clast-supported and and poorly poorly sorted sorted with with aa Clay fills fills most most interstices interstices and and coats coats all all coarse sandy sandy matrix. matrix. Clay coarse grains. The The clasts clasts are are subrounded subrounded to well rounded and range in in grains. ironsize from from 3-15 3-15 cm. cm. Clast Clast lithologies lithologies are are predominantly predominantly ironsize formation ite from from Early Early Proterozoic Proterozoic units formation and and quartz quartzite units and and vein vein quartz quartz from from Archean Archean units. units. Only Only minor amounts amounts of of volcanic volcanic clasts clasts (probably (probably from Keweenawan Keweenawan units) units) are are present. present. Medium to TT1 and TT6 drill to very coarse coarse sandstone sandstone from the TTl cores, corest located located approximately approximately 16 16 km km east east of of Wakefield, Wakefield# were were studied. Two Two general general trends trends can can be seen: 1) 1) a decrease decrease upsection upsection studied. in in mafic and silicic silicic volcanic volcanic clasts clasts believed believed to to be be derived derived from from Keweenawan 2) an increase increase upsection in granitic clasts Keweenawan units units and 2) believed to to be be derived derived from from Archean Archean units. units. Iron—formation Iron-formation clasts clasts believed are rarely rarely seen seen in in the the sand-size fraction fraction making it difficult to to are distinguish distinguish sediment sediment contributed contributed by by Early Early Proterozoic Proterozoic units. units. These These trends trends indicate indicate initial initial erosion erosion through through aa cover cover of of Keweenawan Keweenawan rocks and presumably through Early Proterozoic rocks rocks into the the Archean Archean basement. basement. into Dips Dips within the the western portion of the Jacobsville Sandstone Sandstone range from from 34° 34O NN in range in the the lower lower part part of of the the section section to to 90 g o N in in the the upper upper part, part, excluding excluding areas areas where the the Jacobsville Jacobsville has has been been dragged up up on on the the Keweenaw Keweenaw fault. fault. In In contrast, contrastt most of of the the dragged Jacobsville east east of of Lake Lake Gogebic Gogebic is is relatively relatively flat flat lying. lying. The The Jacobsville fanning fanning nature nature of the the dips west of Lake Gogebic is consistent consistent with with sedimentation sedimentation on on aa fault fault block that that is is rotating rotating to to the the north. north. This This fault fault block rotation was caused by thrust faulting faulting along the fault the Keweenaw fault to the north and the Pelton Creek fault to the the south. south. Uplift and and erosion erosion of Keweenawan, Keweenawant Early Early Protero— Proteroto zoic this fault fault block zoic and Archean units along the southern end of this is the the source source of the conglomerates conglomerates and coarse sandstone in is in the the Jacobsville Sandstone Sandstone west west of of Lake Lake Gogebic. Gogebic. Jacobsville 32 �References References Cited Cited Cannon, Z . E . , and and Sims, Sims, P.K.,l990, P.K.,1990, Structural Structural and and Cannon, W.F., W.F., Peterman, Peterman, Z.E., isotopic isotopic evidence evidence for for Middle Middle Proterozoic Proterozoic thrust thrust faulting faulting of of Archean Archean and and Early Early Proterozoic Proterozoic rocks rocks near near the the Gogebic Gogebic Range, Range, abs. in Institute on Michigan and Wisconsin: Michigan and Wisconsin: abs. in Institute on Lake Lake Superior Superior Geology Geology Proceedings, Proceedings, V. v. 36, 36, p. p. 11—13. 11-13. Kalliokoski, Kalliokoski, J., J., 1982, 1982, Jacobsville Jacobsville Sandstone: Sandstone: in in R.J. R.J. Wold Wold and and Tectonics of the Lake W.J. W.J. Hinze, Hinze, eds., eds., Geology Geology and and Tectonics of the Lake Superior Superior Basin: Basin: Geological Geological Society Society of of America, America, Memoir Memoir 156, 156, p. 147—155. 147-155. p. Sims, Sims, P.K., P.K., 1990, 1990, Geologic Geologic map of of Precambrian Precambrian rocks, rocks, Marenisco, Marenisco, Thayer, Thayer, and and Watersmeet Watersmeet 15—minute 15-minute quadrangles, quadrangles, Gogebic Gogebic and and Ontonagon Ontonagon Counties, Counties, Michigan, Michigan, and and Vilas Vilas County, County, Wisconsin: Wisconsin: U.S. 1:62,500. U.S. Geological Geological Survey Survey Map Map 1—2093, 1-2093, scale scale 1:62,500. 33 �PETROLOGY OF A A RAPAKIVI BODYFROM FROMEAST-CENTRAL EAST-CENTRALMINNESOTA. MINNESOTA. PETROLOGY AND AND STRUCTURE STRUCTURE OF RAPAKIVIBODY HELLICKSON, Bradly, RADZEVICIUS, Stanley, ANDERSON, Garry,Dept. Dept. of HELLICKSON, Bradly, RADZEVICIUS, Stanley, ANDERSON, Garry, of Earth MNM56301-4498 E a r t h Sciences, Sciences, St. S t . Cloud CloudState S t a t eUniv., Univ.,St.SCloud, t . Cloud, N 56301-4498 AA 10 granitic 10 m. m. wide wide g r a n i t i c dike d i k elocated l o c a t e dini nthe t h eMeridian M e r i d i a nAggregate Aggregate quarryin q u a r r y ' i nWaite Waite Park, has an an east-west east-westsstrike Park, MN, MN, has t r i k e and and ddips i p s to t o the t h e south south at a t aasteep steepangle. angle. This T h i s tabular t a b u l a rbody body isi sbounded bounded on on the t h e north n o r t h and and south south sides sides by by nearly n e a r l y continucontinuous ous parallel p a r a l l e l basaltic b a s a l t i cdikes, dikes, and and isi scrosscut c r o s s c u t by by aa small small basaltic b a s a l t i cdike d i k e with with V a r i a b l e sized s i z e d basaltic b a s a l t i c xenoliths x e n o l i t h s are a r e found found within w i t h i n the t h e dike, dike, N60E sstrike. t r i k e . Variable aaN6OE The north n o r t h contact c o n t a c t of o f the t h e dike dike one of o f which which isi s 1 1ni.m. by by 10 10 m. m. ini ndimension. dimension. The one appears besstructural, with appears t to o be tructural, w i t h calcite-filled c a l c i t e - f i l l e dslickensided s l i c k e n s i d e dsurfaces s u r f a c e s within within t h e basalts b a s a l t snear near the t h e contact c o n t a c tand and mineralized m i n e r a l i z e d shears shears containing c o n t a i n i n g epidote e p i d o t e within within the m. The south south ccontact o n t a c t is i s undulatory u n d u l a t o r y with w i t haawave wave length l e n g t h of o f 55tot o1010m. t h e dike. d i k e . The the The The rapakivi r a p a k i v ibody body displays d i s p l a y saaporphyroblastic p o r p h y r o b l a s t i ctexture t e x t u rcomposed e composedofo fpotassium potassium feldspar by minor minor amounts amountso fofbbiotite f e l d s p a rand and quartz q u a r t zaccompanied accompanied by i o t i t e and and saussuritized saussuritized T e x t u r a l l ythe t h epotassium potassium feldspar f e l d s p a r grains g r a i n s at a tthe t h emargin marginare are p l a g i o c l a s e . Texturally plagioclase. (. 1-.5 cm), cm), do donot n o tdisplay d i s p l a yobvious obviousconcentric c o n c e n t r i claminations, l a m i n a t i o n s , and and are are small (.1-.5 small As the t h e center c e n t e r of.the o f . t h ebody bodyisi approached, s approached, the t h epotassium potassium feldspar feldspar anhedral. As anhedral. grains g r a i n s increase increaseini nsize s i z (.3—2.1 e (.3-2.1 cm), cm),become become subhedral subhedral to t o euhedral euhedral and and display display cores aare obvious concentric c o n c e n t r i c laminations. l a m i n a t i o n s . Often Often times times small small anhedral anhedral cores r e vvisible. isible. obvious An An aphanitic a p h a n i t i c matrix m a t r i xcomprises comprises 45-55 45-55 percent p e r c e n t of o f the t h eRapakivi Rapakivibody. body. The The matrix matrix consists c o n s i s t s of o fvermicular v e r m i c u l a r quartz q u a r t z either e i t h e rimming r rimminglarge l a r g epotassium potassium feldspar f e l d s p a r or or q u a r t z grains g r a i n s or o risi completely s completelynetworked networked with w i t hsmaller s m a l l e rpotassium potassium feldspar feldspar quartz g r a i n s forming forming aa granophyric granophyric texture. t e x t u r e . The The remainder remainder of o f the t h ematrix m a t r i xis icomposed s composed grains mm) sstrained t r a i n e d qquartz u a r t z ggrains, r a i n s , aaltered l t e r e d feldspar f e l d s p a r and and bbiotite. iotite. o f small small (less ( l e s sthan than .2.2mm) of Also present p r e s e n t are a r e accessory accessory mminerals i n e r a l s such asas a l lallanite, a n i t e , zzircon, i r c o n , eepidote, p i d o t e , chlorite chlorite Also such and calcite. c a l c i t e . The The llatter a t t e r three t h r e e are a r e confined c o n f i n e d to t o regions r e g i o n s of o f fracture f r a c t u r e or o rshear. shear. and Shearing is i sextremely extremelycommon common aat t aalll l scales scalesand andappears appears to t ohave haveplayed p l a y e da adominant dominant Shearing r o l eini nthe t h edevelopment development of o f this t h i sbody. body. Metasomatic Metasomatic aactivity c t i v i t y during d u r i n g the t h eshearing shearing role process may may have e a d to t o the t h edevelopment development of o fboth b o t hthe t h eobserved observedmineral m i n e r aassemblage l assemblage process have llead and the t h e Rapakivi Rapakivi ttexture e x t u r e displayed d i s p l a y e d iinn this t h i srock r o c kbody. body. and 34 �Provenance of the Animikie Group, Nd and and Pb isotopes Provenance Group, NE Minnesota, based on Nd S. R. Hemming, Hemming, S. S. M. M. McLennan, McLennan, and and G. G. N. Hanson, ESS, ESS, SUNY SUNY Stony Brook, NY Nd and Pb isotope data (Fig. 1, 1, Fig. 2) on samples from the Animikie Group in the northern margin margin of of the the Animikie Animikiebasin basin from from an an early early Mesabi Range reflect the progression of the northern near-shoreline facies near-shoreline facies with northern northern sources, sources, to a later relatively relatively deep-water facies with with sediments sediments derived from rising mountain ranges to to the the south southassociated associatedwith withthe thePenokean Penokeanorogen. orogen. Based Based on on derived facies analyses, the northern shoreline of the Animikie basin is interpreted to have been near the facies analyses, basin is interpreted to have been near the Pokegarna Quartzite Quartzite and and Biwabik Biwabik present northern northern margin of the basin during deposition of the Pokegarna Iron-formation by argillite argililte with with some some thin, thin, Iron-formation [1,2]. The Theoverlying overlying Virginia Virginia Formation is dominated by very fine [3]. Throughout infrequent,thin, thin,olive olive green greentuff tuff fine graywacke intervals [3]. Throughout the interval are infrequent, horizons. horizons. Lucente Lucenteand andMorey Morey[3] [3]interpret interpretthe thedeposition depositionof of the the Virginia Virginia Formation Formation to to have have been been dominantly dominantlyfrom frompelagic pelagicprocesses processes in in aa relatively relatively deep-water deep-water environment. in central Minnesota was studied studied by The petrogenesis of early Proterozoic mafic rocks in rocks are are arc-related. arc-related. The Pb and Nd isotopic isotopic Horan et al. [4], [4], who concluded that these rocks compositions associated granitic granitic plutonic plutonic compositionsof of these these mafic mafic rocks rocks are are the same as the geographically associated 1850Ma Mafor forthese theserocks rocksisisdominantly dominantly00to to -3, -3, with with depleted depleted mantle mantle model rocks [5]. [5]. The The CNd EN^ atat1850 model the sources for these rocks have evidence of a LREE Therefore ages of 2.1 to 2.4 Ga [4,5]. to 2.4 Ga [4,5]. Therefore rocks have evidence of enriched history LREE enriched enriched component [4,5]. [4,5]. The initial initial enriched history or or were were contaminated contaminated by an old, LREE isotope composition rocks precludes precludesthe the Superior Superior Pb isotope composition of the K-feldspars from the granitic rocks Province as as the thecontaminating contaminatingcomponent component[51. [51 Spencer [5] suggested that these are mantle mantle Province characteristics or that there is a contribution from the early Archean rocks of the Minnesota River characteristics the early Archean rocks of the Minnesota River of central central Minnesota Minnesota Valley terrane. The TheNd Nd isotopic isotopiccompositions compositions are included in the field of magmatic rocks in the general field of magmatic rocks in in Fig. 11 and and the the Pb Pb isotopic isotopic compositions compositions are included in Penokean magmatic rocks in Fig. 2. Van Penokean VanSchmus Schmusand andBickford Bickford[6] [6]and and Greenberg Greenberg and and Brown Brown that the early Proterozoic igneous rocks of the Wisconsin magmatic terrane are also [7] suggested [7] suggested Proterozoic also arc-related. The ThePb Pbisotopic isotopiccomposition compositionof ofearly earlyProterozoic Proterozoicrocks rocks from from Wisconsin Wisconsin [8] [8] are are included in rocks in in Fig. 2, and the the field field Nd isotopic included in the the general general field of Penokean magmatic rocks compositions at 1850Ma Ma [9] [9] are are shown in Fig. 1. compositions at 1850 1. = -10.5 at A silty unit of lower lower Pokegama Quartzite Quartzite from Midway, Minnesota has hasENd EN^ = 1850 Ma GaGa slope in in 2O7PbI2O4Pb 1850 Ma (Fig. (Fig.1)1)and and22whole wholerock rocksamples sampleslieliealong alonga 2.6 a 2.6 slope 2Wb1204Pb vs 206pb/204pbspace, space,consistent consistentwith withthe theinterpretations interpretationsof ofaaSuperior SuperiorProvince Provincesource source based based on 206PbPmPt) petrology [1] and whole wholerock rocksamples samples[lo]. [10]. Both Both Nd Nd (Fig. 1) and Pb [I] and Pb isotopes from quartz and petrology (Fig. 2) isotopes isotopesfrom fromthe theBiwabik BiwabikIron-formation Iron-formationappear appearto torecord recordaamixture mixture of of early early Proterozoic and of Gerlach et al. Proterozoic and Archean sources. This This is is consistent consistent with the Nd isotope data of [11]. [I 11. Two Twocore coresamples samplesfrom fromthe theupper upperslatey slatey member member (location (location22 of of the Mesabi Mesabi Deep Deep Drilling Drilling Project) from -6atat 1850 1850Ma Ma(Fig. (Fig.1). 1). The intermediate Project) from the the Biwabik Biwabik Iron-Formation have ENd EN^ ofof-6 intermediate slate from 1850Ma Maofof-3, in from the the MINTAC MINTAC mine, mine, which which Morey Morey [1] [I] interpreted as a tuff, has ENd EN,^ atat1850 -3, in the range rocks from fromcentral centralMinnesota. Minnesota. Ten Ten sedimentary sedimentary (he range of the the early Proterozoic igneous rocks samples samples from fromthe the Virginia Virginia Formation Formationfrom from location 2 of the Mesabi Deep Drilling Project Project have have Nd 1850Ma Maofof2.8 2.8and and3.2 3.2(Fig. (Fig. 1). 1). All EN^ at at1850 1850Ma Maofof-0.9 -0.9toto+0.3, +0.3,and andtwo twotuffs tuffshave haveENd EN^ atat1850 Virginia a 1.8 GaGa slope in 2O7PbI2O4Pb space(Fig. (Fig.2). 2). The The a 1.8 slope in 207PbPPb vs vs2O6Pb/2O4Pb 206Pb/204Pb space Virginiasamples sampleslielieclose closetoto data preclude substantial contributor contributorto tothe theVirginia VirginiaFormation. Formation. The preclude the the Superior Superior Province as a substantial early Penokean magmatic early Proterozoic Proterozoicsource source indicated indicated by the the data, which is suggested suggested to be the Penokean magmatic terrane to the the south south of of the Animikie Animikie basin, is consistent consistent with the evolution of the Animikie Animikie basin basin as a foredeep foredeepresulting resulting from from Penokean Penokean orogenesis orogenesis [12]. [12]. 35 �References: References:[1] [l]Morey, Morey,G.B., G.B.,1972, 1972,MN MNGeol. Geol.Sur. Sur.Centennial CentennialVol., Vol., p.p.204; 204; [2] [2] Ojakangas, Ojakangas,R.W., R.W., 1983, 1983, Geol. Geol. Soc. Soc. America AmericaMem. Mem. 160, 160, p. 49; 49; [3] [3] Lucente, Lucente, ME., M.E., and andMorey, Morey,G.B., G.B., 1983, 1983,MN MN Geol. Geol. Sur., Sur., Report Report of Investigations Investigations28; 28;[4] [4]Horan, Horan, M.F., M.F., Hanson, Hanson, G.N., G.N., and and Spencer, Spencer, K.J., K.J., 1986, 1986, Precambrian PrecambrianResearch, Research,v.v. 37, 37, p. p. 323; 323;[5] [5]Spencer, Spencer,K.J., K.J., 1987, 1987,unpublished unpublished Ph.D. Ph.D. thesis, thesis. SUNY SUNYStony Stony Brook; [6] [6] Van Van Schmus Schmusand and Bickford, J.K., and Brown, B.A., B.A., Bickford, 1981, 1981,in in Precambrian Precambrian Plate Plate Tectonics, Tectonics, Elsevier, p. 261; [7] Greenberg, J.K., 1983, P.K., and Delevaux, M.H., M.H., 1984, Economic 1983,GSA GSA Mem. Mem. 160, 160,p. 67; 67; [8] [8] Afifi, A., A., Doe, B.R., B.R., Sims, P.K., Geology, Geology,v.v.79, 79,p.p.338; 338;[9] [9]Barovich, Barovich,K.M., K.M., Patcheti, Patchett, P.J., P.J., Peterman, Peterman, Z.E., and Sims, P.K., P.K., 1989, 1989,GSA GSA Bul., E.J., and Mezger, K., Bul., v.v. 101, 101,p.p.333; 333;[10] [lo]Hemming, Hemming,S. S,McLennan, McLennan, S.M., S.M., Hanson, Hanson, G.N., Krogstad, E.J., K., 1990, (abs) EOS, v.71, v. 71,p.p.654; 654;[11] [ l l ]Gerlach, Gerlach, D.C., D.C., Shirey, Shirey, S.B., S.B., and and Carlson, Carlson, R.W., R.W., 1988, 1988, (abs) (abs) EOS EOS vol. vol. 69, P.L., 1988, MN MN Geol. Geol. Sur. Sur. Report Report of 69, p. 1515; 1515;[12] [12]Southwick, Southwick, D.L., Morey, Morey, G.B., G.B., and McSwiggen, P.L., Investigations Cosmochim. Acta, v. 50, p. Investigations37; 37;[13] [13]Shirey, Shirey, S.B., S.B., and and Hanson, Hanson, G.N., 1986, 1986, Geochim. et Cosmochii. 2631; 2631; [14] [14] Stile, Stille,P., P.,and andClauer, Clauer,N., N.,1986, 1986,Geochim. Geochim.etetCosmochim. Cosmochim.Acts, Acta,vol. vol. 50, 50,p.p.1141; 1141;[15] [15] Jacobsen, M.R., 1988, Geophys. Research Research Letters, v. v. 15, p. 393; [16] Gariepy, Jacobsen,S.B., S.B., and andPimentel-K.lose, Pimentel-Klose, M.R., Gariepy, C., and andAllegre, Allegre,C.J., C.J., 1985, 1985,Geochim. Geochim.et etCosmochim. Cosmochim. Acts, Acta, v. 49, p. 2371. 2371. 0.1 0.0 —0.1 —0.2 z —0.3 U) —0.4 WMT —0.5 —0.6 —15 central MN —10 0 —5 Nd 5 10 in the Mesabi Range. Fig. 11 Plot PlotofoffSm/Nd fSm@Jdvs. vs. eNd &N(I at at 1850 1850 Ma for samples of the Animikie Group in Fig. is the deviation of 1Nd/14Nd from fSmNd is Sm/Ndfrom fromCI CIchondrite chondriteand andCNd EN^ is deviation of 143Nd/^Nd fromCI CI fSm/Nd isthe the deviation deviation of Sm/Nd chondrite chondrite in in parts per 10,000. PP == Pokegaxna Pokegama Quartzite, B == Biwabik Biwabi Iron-formation, Iron-formation, and and V == Virginia Virginia Formation. M= Range Supergroup samples [9].additional For additional reference, the M= Marquette Marquette Range Supergroup samples [9]. For reference, the fields forfields late for late .. Archean central Minnesota Minnesota [4,5] and Archean Superior SuperiorProvince Province rocks rocks [13], [13], early Proterozoic plutonic rocks hfrom m central Wisconsin Wisconsin[9], [9],and andGunflint GunflintIron-formation Iron-formationfrom fromOntario Ontario[14,15] [14,15] are areshown. shown. 36 �65.0 14 16 18 20 22 24 26 28 30 32 34 36 38 40 60.0 55.0 CQ 50.0 C 45.0 C'2 40.0 35.0 17.5 17.0 16.5 C / tuffs (1774+/-62 Ma) 16.0 15.5 N C CQ 15.0 14.5 14.0 14 16 18 20 22 24 26 28 30 32 34 36 38 40 206 Pb/ 204 Pb Fig. 22 Pb Pbisotope isotopeconpositions conpositionsof ofsamples samplesfrom fromthe theAnimikie AnimikieGroup Groupin in the the Mesabi Mesabi Range. Range. The Thesame same Fig. symbolsapply applyasasininFig. Hg. 1.1. a)a)Plot Plotofof2O8Pbi2O4Pb 208PbWPb vsvs206PbPmPb. Growth curve is p=8, 4 with tics ticsatat symbols 2O6Pbf2O4Pb. Growth curve is j=8, ,4,,with 100Ma Ma intervals. intervals.b)b)Plot Plotofof2O7Pb/2O4Pb 207PbPMPb vs 206PbPaPb. Growth 8 with 100Ma Ma 100 vs 2O6Pb/2O4Pb. Growthcurve curveisispj=8 with tics tics at at 100 intervals.For Forreference, reference,fields fieldsincluding includingfeldspar feldsparand andwhole wholerocks rocksfor forlate lateArchean Archean latelate-totopostpostintervals. kinematicplutonic plutonicrocks rocksofofthe theSuperior SuperiorProvince[16] Province[16]and andearly earlyProterozoic Proterozoicplutonic plutonicrocks rocksof ofcentral central kinematic Minnesota[4,5], [4,5],and andfeldspar, feldspar,galena, galena,and andwhole wholerocks rocksfrom fromboth bothvolcanic volcanicand andplutonic plutonicrocks rocks Minnesota fromwisconsin(WMT) (WMT)[8] [8]are areshown. shown. fromWisconsin 37 �EXPLORATION EXPLORATION AND MINING MINING ACTIVITIES ACTIVITIES OF OF INDUSTRIAL INDUSTRIALMINERALS MINERALSIN IN NORTHWESTERN NORTHWESTERNONTARIO ONTARIO ....................................... Hinz, Hinz, P. P. and and Lucas, Lucas, R. R. T., T. , MINES MINES AND AND MINERALS M I NERALS DIVISION, D I V I SI ON, ONTARI 0 ONTARIO MINISTRY M I N I STRY OF OF NORTHERN NORTHERN DEVELOPMENT DEVELOPMENT AND AND MINES, MINES, THUNDER THUNDER BAY BAY ....................................... The The "Northwestern Northwestern Ontario O n t a r i o Industrial Industrial Minerals Minerals Program" Program" was was initiated, i n i t i a t e d , in in 1987, as aa province-wide 1987, a s part p a r t of of province-wide strategy s t r a t e g y to t o stimulate s t i m u l a t e development development of of Ontario' Ontario1ss industrial i n d u s t r i a l mineral mineral resources resources and and related r e l a t e d manufacturing manufacturing industries. industries. The Industrial The Industrial Minerals Program Minerals Program provides provides assistance a s s i s t a n c e to t o prospectors p r o s p e c t o r s and and industry i n d u s t r y by by conducting conducting property p r o p e r t y visits, visits, sample preparation, s amp1e preparation, analyses and analyses and discussion d i s c u s s i o n r e l a t i n g t o t h e industrial industrial mineral mineral industry. industry. relating to the There There are a r e over o v e r 50 50 industrial i n d u s t r i a l mineral mineral commodities known commodities known to t o occur occur within within Northwestern Ontario. Northwestern Ontario. Current Current production includes: production includes: two quarries two quarries producing almost producing almost 1,000,000 1,000,000 tons t o n s of of railway r a i l w a y ballast b a l l a s t material; m a t e r i a l ; two two granite granite dimension dimension stone s t o n e quarries quarries producing producing blocks blocks and and slabs s l a b s of of pink pink granite g r a n i t e for for use u s e as a s monument monument and and dimension dimension stone; s t o n e ; aa t h i r d dimension dimension stone s t o n e quarry q u a r r y will w i l l start start third production p r o d u c t i o n in i n April A p r i l 1992 1 9 9 2 and and produce produce rough blocks rough blocks and and slabs s l a b s of of green green granite; one quartz granite; one quartz q u a r r y which which quarry produced produced 17,000 17,000 tons t o n s of of crushed crushedquartz; quartz; and and one one quarry q u a r r y produced produced 8,000 8,000 tons t o n s of of crushed crushed diabase d i a b a s e for f o r use use in i n soil s o i l erosion erosion proj p r o jects. ects. 38 38 This This poster p o s t e r displays d i s p l a y s current c u r r e n tproducers, producers, sites s i t e s of of advanced advanced exploration e x p l o r a t i o n and and high high potential i n Âormation p o t e n t i a l areas. a r e a s . Detailed D e t a i l e d information on i s available a v a i l a b l e from from on all a l l the t h e properties p r o p e r t i e s is the Resident the Resident Geologists' G e o l o g i s t s t Office O f f i c e in in Thunder ThunderBay. Bay. �Exploration and prospecting is Exploration and prospecting is c u r r e n t l y under way t o e v a l u a t e currently under way to evaluate aa f o r their their number of properties number of properties for dimension s t o n e , g a r n e t , amethyst and dimension stone, garnet, amethyst and g r a p h i t e p o t e n t i a l . graphite potential. . . Northwestern Ontario includes the Northwestern Ontario includes the Resident G e o l o g i s t s t D i s t r i c t s of Resident Geologists' Districts of Kenora, Red Lake, Sioux Lookout, Kenora, Red Lake, Sioux Lookout, Thunder Bay, Bay, Beardmore-Geraldton, Beardmore-Geraldton, and Thunder and Schreiber-Hemlo. Schreiber-Hemlo. The The program is is program j o i n t l y funded funded by by the the jointly 1991 Northern O n t a rio 1991 Northern Ontario (NODA), Development Agreement Development Agreement (NODA), aa s u b s i d i a r y agreement t o t h e Economic subsidiary agreement to the Economic and Regional Development Development Agreement and Regional Agreement (ERDA) s i g n e d by t h e Governments of (ERDA) signed by the Governments of Canada and Ontario. Canada and Ontario. CANADA-ONTARIO CANADA-ONTARIO The project p r o j e c t is i s staffed s t a f f e d by by Peter P e t e r Hinz, Hinz, The G e o l o g i s t , and Robert Lucas, A s s i stant Geologist, and Robert Lucas, Assistant G e o l o g i s t . Geologist. 39 �Thermochronoiogic evidencefor for post-Penokean post-Penokeanunroofing unroofingininthe the Lake Superior Thermochronologic evidence Superior region. Daniel Daniel Hoim, Holm,Dept. Dept.of ofEarth Earthand andPlanetary PlanetarySciences, Sciences, Harvard Harvard University, Cambridge, Cambridge, MA MA 02138 02138 Timothy Hoist, Timothy Hoist,Department Departmentof ofGeology, Geology,University Universityof of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812 55812 Daniel Lux, Lux,Department Departmentof ofGeology, Geology,University University of of Maine, Maine, Orono, Orono, ME ME 04469 04469 Introduction. Determining Introduction. Determiningthe thetime, time,amount amountand andnature natureof ofunroofing unroofing of of rocks rocksdeeply deeply buried buried during collision is fundamental to an understanding of of the processes of lithospheric deformation. During the past decade, the construction construction of temperature-time temperature-time histories has become an increasingly important technique for assessing unroofing unroofing histories. histories. Because changes in the cooling history (shown as inflection points on temperature-time curves) are likely to be a reflection of tectonic tectonic events, events, these these data are extremely useful for discerning and and dating dating such such events events as as well well as as for for characterizing characterizing their their history of of ancient orogenic roots is thermal significance. Determining Determining the the post-collisional post-collisional cooling history due to thermal thermal overprinting overprintingassociated associatedwith withyounger youngerevents. events. Such Such has has been been the the commonly difficult due case in the the Precambrian Precambrianof ofMichigan Michiganand andWisconsin Wisconsinwhere where'events' 'events'dated datedatat—1630 -1630 Ma, Ma,—1330 -1330 Ma, and —1140 Mahave havemasked masked the the earlier earlier cooling cooling history Ma -1 140 Ma history of of rocks rocksinitially initiallyburied buriedduring duringthe the—1830—1860 -1830-1860 Ma Penokean orogeny. Here, we present 40ArP9Ar cooling ages from rocks metamorphosed during the Here, we present ^Ar/^Ar ages from rocks Penokean orogeny in east-central east-central Minnesota, an area apparently affected to a lesser extent by these later events. Proterozoic Lakes tectonic tectonic zone, an Archean crustal Proterozoic rocks in east-central east-central MN lie athwart the Great Lakes discontinuity along which alternating discontinuity alternating extensional and contractional events have occurred throughout throughout the Early and Middle Proterozoic. Denham Formation cover rocks (predominantly quartzite and Denham Formation (predominantly dolomite interbedded interbedded with with conglomerate and volcanic volcanic rocks) rocks) were dolomite conglomerate and were deposited deposited on on Archean Archean quartzofeldspathic basement basement (the McGrath quartzofeldspathic McGrath Gneiss) Gneiss) in in an anEarly EarlyProterozoic Proterozoic(2100—1900 (2100-1900 Ma) Ma) to amphibolite amphibolite facies during extensional basin. They Theywere were subsequently subsequently deformed and metamorphosed to Ma), having reached burial depths km. the Penokean Penokean orogeny orogeny(1860—1830 (1860-1830 Ma), depths in in excess excessof of21—25 21-25 km. Several rock rock forming forming 'events' 'events' following following the the Summary of of previous previousgeochronology*. geochronology*. Several Lake Superior Superiorregion. region. These include Penokean orogeny have been identified in the Lake include the formation formation of of a plutonic-volcanic Ma, intrusion intrusion of the Wolf River plutonic-volcanicterrane WIatat—1760 -1760 Ma, River terranein insouth-central south-centraland andnorthern northernWI Ma, and and magmatism magmatism associated with the Mid-continent Batholith at at —1469 -1469 Ma, Mid-continent Rift Rift System Systematat—1100 -1 100 Ma. In MN, post-orogenic granites U-Pb ages ages of of 1770 Ma Ma and and U-Pb U-Pb crystallization crystallization ages ages of of granites yield minimum U-Pb 1812±9 Ma. Ma. Initial 181239 Initial conventional conventional K/Ar K/Ar and and Rb/Sr chronologic data from eastern and central central MN MN were recomputed and summarized in Keighin Keighin et et al. al. (1972 (1972 Centennial CentennialVolume; Volume;MN MNGeol. Geol. Surv.). Surv.). K/Ar K/Ar biotite biotite and and muscovite muscoviteages agesfrom frombasement basementand andcover coverrocks rocks group groupinto intoages ageslargely largelyaround around—1730 -1730 Ma (7 ranging from Ma(6 (6ages agesranging ranging from from 1610-1650 1610—1650Ma). Ma). Rb/Sr dates dates ages ranging from1670—1770 1670-1770 Ma) and —1630 -1630 Ma include 1±18 Ma include errorchron errorchronages agesof of1746±86 17463336Ma Maand and174 1741k18 Maand andbiotite biotiteages agesininthe theinterval intervalofof1750—1740 1750-1740 Ma for the McGrath McGrath Gneiss. Gneiss. There have been several several studies studies using using both the Rb/Sr and Ar/Ar systematics systematics in the the regionally regionally equivalent equivalent rocks of MI and WI. The Theoldest oldestages, ages, generally generally preserved in a belt belt just south south of of MidMidcontinent Rift MaRbISr Rb/Srbiotite biotiteages agesand andone oneAr/Ar Ar/Arhornblende hornblendeplateau plateau age age of of Rift rocks, rocks, are are 1692—1750 1692-1750 Ma 1704 Ma. To Tothe thesouth, south,whole-rock whole-rock Rb/Sr Rb/Sr and and Ar/Ar Ar/Ar biotite ages are reset in response to a regionally regionally recognized but cryptic event at about 1630 1630 Ma. Younger Younger events events superimposed superimposed on on this this regional regional 1630 1630 Ma imprint, Rb/Srand andAr/Ar Ar/Arsystematics, systematics,occur occuratat—1330 -1330 Ma Maand and—1140 -1 140Ma. Ma. imprint,recognized recognizedininboth bothRb/Sr Results of Results of of this this study. study.AAcoarse-grained coarse-grainedamphibolite amphibolite schist schist was sampled at the type locality of the Denham Formation. Coarse well-developed foliation foliation at Coarseamphibole amphibole and and finer-grained finer-grained biotite form a well-developed this locality, the amphibole commonly containing large largeinclusions inclusionsofofplagioclase. plagioclase. A biotite separate of 1754k13 1754±13 Ma. Ma. A hornblende separate from from the the same sample gives a (DH-MN-4) gives a plateau age of plateau age of 1756±16 Ma, concordant with the biotite age. These two ages, 1756k16 with the biotite age. These two ages, from from minerals minerals with with highly discordant closure temperatures (—500°C and —300°C), indicate rapid cooling roughly highly discordant closure temperatures (-500° and -300°C) indicate cooling roughly60—100 60-100 Ma after after metamorphism metamorphism during during the the Penokean Penokean orogeny. orogeny. We observe consecutive increments observe that that of of the the first first 10 10 increments increments in the hornblende spectra, four consecutive increments (3—6) give concordant ages of —1615 Ma and have K/Ca ratios an order of magnitude greater than (3-6) give concordant ages of -1615 Ma and have K/Ca ratios an order of magnitude 40 �those of the plateau increments. In In addition, addition, these these same four increments, when subject to regression on the 15±9 Ma with the isotope-correlation isotope-correlation intercept plot, yield a concordant concordant intercept age age of of 16 1615k9 with an an 40ArP6Ar. These combined observations lead lead us us to to interpret interpret the "mini" "mini" plateau age age atmospheric initial ^Ar/^Ar. —1615Ma Maasasdating datingthe theplagioclase plagioclaseinclusions inclusionsininthe thehornblende. hornblende.The The younger younger age age is is consistent of -1615 with plagioclase having thaneither eitherbiotite biotiteororhornblende. homblende. These having a lower lower closure closure temperature (—230°C) (-230°C than Maevent eventrecognized recognizedin inMI MIand and WI WI also also affected data may indicate indicate that that the the regional regional low-grade low-grade —1630 -1630 Ma the rocks of east-central east-central MN, although although perhaps to a lesser extent. yields aa plateau plateau age age of of 1705k19 1705±19 Ma and Muscovite from the McGrath Gneiss (sample DH-MN-6) yields biotite (sample DH-MN-7) yields yields aa plateau plateau age ageof of 1702k12 1702±12Ma. Ma. The The concordant concordant mica mica ages indicate rapid cooling (from (from temperatures temperaturesabove above 350°C 350° to below 300°C) 300°Cof the gneiss at about about 1705 1705Ma. Ma. Discussion. Considering the high closure temperature for Ar diffusion in hornblende Discussion. Considering the high closure temperature for Ar diffusion in hornblende(—500°C) (-500°C and apparent lack of intrusions in this region it seems seems unlikely that the cover rock rock ages ages represent represent therefore interpreted interpreted as asrepresenting representingsimple simplecooling. cooling. Rapid cooling from thermal resetting, and are therefore 500°C to below below 300° 300°C is a strong indication of of tectonically driven uplift. In temperatures above 500° contrast, rocks cooled during isostatic rebound will have relatively slow uplift rates so that that mineral mineral pairs will will give give measurable measurableage agedifferences. differences. It has has long long been been observed observedthat thatcontinental continentalextension extension commonly commonly occurs occurs along alongpreviously previously overthickened crust crust with with a characteristic characteristic time time lag lag between between the the end end of of thrusting thrusting and the peak of overthickened of extension Ma.These Thesegeneralizations generalizationsseem seemtotoindicate indicatethat thatregions regions of of overthickened overthickened crust extension of of —30—100 -30-100 Ma. for post-collisional post-collisionalextension. extension. In the Precambrian Precambrian of of MN, MN, we observe create characteristics favorable for Maafter afterthe thePenokean Penokeancollisional collisional orogen orogen and was coeval coeval with that rapid cooling cooling began began roughly roughly 60—100 60-100 Ma with regional rhyolitic volcanism volcanism and and granite granite emplacement emplacementininMI MIand andWI. WI. Major regional rhyolitic Major cooling cooling occurred occurred dominantly MaRbISr Rb/Sr ages ages cited cited above dominantlyin inthe thetime-span time-span1755—1740 1755-1740 Ma as indicated by the 1740—1750 1740-1750 Ma for this considering the concordant this region. However, However,cooling coolingapparently apparentlycontinued continueduntil until—1700 -1700 Ma considering concordant 1705 1705 Ma basement basementmuscovite muscoviteand andbiotite biotiteages agespresented presentedhere hereasaswell wellasasthethe—1700—1750 -1700-1750 Rb/Sr RbISr biotite biotite and 1704 1704Ma Ma homblende hornblendeplateau plateau ages ages in in northernmost northernmost WI and MI. All of of these these observations observationsare, are, in ingeneral, general,characteristic characteristicof of Phanerozoic Phanerozoicextensional extensionalregimes regimes worldwide. Based Based on on these thesesimilarities, similarities, we we believe these data might best be explained by a major Ma. The The regional regional extent of this extensional episode in in the the Lake LakeSuperior Superiorregion regionatat—1750—1700 -1750-1700 Ma. this episode episode has largely largely been obscured obscured by later later disturbances disturbancesin both Rb/Sr RbISr and Ar/Ar ArIAr systematics systematicsin in much much of MI and WI. The Thelow-grade low-grade—1630 -1630 Ma event well recognized in those areas may have have also also affected affected the rocks of east-central 15±9 Ma east-centralMN MN (although (although to to aalesser lesserextent) extent)as assuggested suggestedby bythe the16 1615k9 Ma preferred preferred plagioclase age Ma clustering of K/Ar mineral ages. plagioclase ageand andthe the—1630 -1630 Ma Structures unroofmg of ancient compressional orogenic roots may be Structures associated associated with extensional unroofing deformational features features (e.g., (e.g., detachment detachment faults). faults). The difficult to recognize due to localization of deforrnational The of extensional structures difficult. paucity of exposure exposure in this region would also make identification of We do suggest suggest that late-stage late-stage anastomosing anastomosing shear shear zones which cross-cut the dominant dominant foliation foliationin in the the McGrath Gneiss Gneiss might might be be attributed attributed to to extension. extension. Also, a single isolated outcrop at the Denham McGrath theregional regionaleast-west east-west orientation orientation perhaps perhaps Formation type locality locality has has upright upright folds folds oriented oriented —90° -90' totothe reflecting rotation during extensional unroofing. unroofing. Detailed Detailed structural analysis of recently drilled core samples may may ultimately ultimately test test our explanation of the the cooling cooling ages ages by by allowing identification of samples explanation of identification of extensional extensionalstructures structures(or (or lack lack thereof) thereof) associated associated with tectonic tectonic unroofing. Conclusion. Cooling Coolingages agesprovide provideone onemethod methodfor fordifferentiating differentiating between between relatively relatively fast, fast, tectonically tectonically driven driven uplift (e.g., (e.g., via via post-collisional post-collisional extensional extensional unroofing) unroofing) and slow, slow, isostatic isostatic unroofing following following cessation cessation of of convergence. convergence. We Wesuggest suggestthat thatrapid rapidcooling coolingand andmagmatism magmatism30—100 30-100 unroofing Ma after unrecognized after burial burial associated associated with the the Penokean collisional orogeny may reflect a previously unrecognized post-tectonic unroofing event in the Lake Lake Superior Superior region, possibly analogous to to that that commonly commonly observed observed in in Phanerozoic Phanerozoicmobile mobilebelts beltsworldwide. worldwide. in this this section. section. We will make them available ** We regret not not having room to cite references in upon request. request. 41 �___________________________________ 1800 AGE AGE 1600 1 1 1800 lo .—I LJ McGrath Gnelss Gneiss (Biotite) McGrath (Blotite) I AGEAGE 16001600 ] DH-MN-7B • • 1400 Formation (Hornblende) Denham Formation DH-MN-4H Tg=1692Ma Tg=1728Ma Tp=1702±l2Ma Tp=1756±l6Ma 1400— 1400 I I %39Ar 0 b" EEl I I I I I I %39Ar 100 10 100 1800 1800 - McGrath Gneiss (Muscovite) McGrath Gneiss (Muscovite) AGE DH-MN-4H DH-MN-4H * 1614.6 ± 0.6 Ma plateau points r-i 'Nenham Formation (Plagloclase?) Denham Formation (Plagioclase?) I 160OU C,, DH-MN-6M Tg=l7OlMa Tp= 1705±19 Ma 1400 0 %39Ar - AGE 1 I & 36/40 100 I Formation (Biotite) (Blotite) Denham Formation 1600DH—MN-4B 0 Tg=1725Ma Tp = 1756 ± 15 Ma 1400 0 %39Ar Tg ==total total gas gas age age Tp == plateau plateauage age Hoim, Lux Holm, Hoist, Holst, and and Lux 42 100 �ON ON THE THE USE USEOF OFPALEOCURRENT PALEOCURRENTINDICATORS INDICATORSIN INDEFORMED DEFORMEDROCK ROCK HoIst, Holst, Timothy B., B., Department Department of Geology, Geology, University University of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812, 55812, and Fossen, Fossen, Haakon, Haakon, Department Department of Geology Geology and and Geophysics, Geophysics, University Universityof ofMinnesota, Minnesota,Minneapolis, Minneapolis,Minnesota Minnesota55455 55455 A A number numberof of sedimentary sedimentary structures structures have have long long been been used used as as indicators indicators of of current current direction at the time of deposition of the sediments that contain them. When the deposits direction at that contain them. When the deposits are there has has been beenpostpostare flat-lying flat-lyingand andundeformed undeformedthis thisisisaastraightforward straightfotwardprocess. process. IfIf there deposition deformation, including any displacement, rotation, tilting, folding, and finite deposition deformation, including any displacement, rotation, tilting, folding, and finite strain, strain, the the deformation deformation history history must must be be known known in in some some detail detail in inorder orderthat thatthe thebeds bedsmay may be to be valid. valid. This be restored restoredto their their original original position, for any paleocurrent data to This process process can be be far far from fromsimple. simple. can IfIf read read correctly correctly from from undeformed undeformedrocks, rocks, sedimentary sedimentarystructures structureswhich whichare arecurrent current indicators indicatorsyield yieldaa horizontal horizontalvector vector indicating indicatingthe the direction directionof of current current flow. This Thisvector vectormay may be deflected deflected from from its its original original position position by by many manytypes types of of deformational deformationalprocess. process. In In the the be general general case case the the deformation deformation history history may may involve involve several several episodes episodes of of deformation, deformation,each each of of which which may may have haveincluded includedone one or ormore moreofofthe theprocesses processesofofdisplacement, displacement,rotation, rotation, tilting, tilting, folding, folding, and finite strain. To Torestore restorethe the beds bedsto to correct correct onginal original position, position, aa series series of of deformation deformation inversions inversions needs needs to be performed. In Inpractice, practice, the the necessary necessaryinformation information to to perform perform these these inversions inversionsis is almost almost never never completely completely known. known. Finite Finite strain strain analysis analysis in in rocks rocks has has progressed progressed aa great great deal deal in in the the last last few few decades, decades, but suitablefinite finitestrain straindata data but still still many many rocks rocks are are not not amenable amenable to strain analysis. Even Evenifif suitable may may be be recovered, recovered, information information on strain path, path, necessary necessary if the the current current vector vector isisto tobe be restored to correct initial position, has proven to be extremely elusive. Veins and strainrestored to be extremely elusive. and shadow shadow fibers have have provided provided this information information in in some some situations, situations, with with results results showing showing evidence of non-coaxial strain histories sufficiently often so that if strain path information evidence of non-coaxial strain histories sufficiently often so that if strain path information is is lacking, lacking, paleocurrent paleocurrentdata datamay maybe beconsidered consideredsuspect. suspect. finite finite strain strain and and strain strain path path data data are are known, known, removal removal of these these effects effects by by deformation inversion may still leave the bedding bedding in aa position position other other than than original, original, and and effects also be be considered. considered. This is effects of folding, tilting, rotation and displacement must also is also also the starting point for consideration of rocks with with negligible negligible finite finite strain. strain. Ramsay (1961) Ramsay (1961) showed that the effects of strain and folding on sedimentary structures were the effects of strain and folding on sedimentary structures were more more profound profoundthan than had hadgenerally generally been beenappreciated, appreciated, and andoutlined outlinedaa technique techniquefor fordeformation deformation inversion inversion of folding folding once once effects effects of of finite finite strain strain had hadbeen beenremoved. removed. This This technique technique involves of the material involves rotation rotation of material about about an an axis axis perpendicular perpendicular to plunge plunge direction direction of of measurable measurable folds in the area, area, until until the fold fold axes axes are are horizontal, horizontal, and and then then rotation rotationof of the the in question question about strike to to restore restore to to horizontal. horizontal. This This is aarelatively relatively about the the strike bed in straightforward this procedure procedure straightforward technique, but will only result resultininaacorrect correct interpretation interpretationifif this is indeed indeed aa deformation deformationinversion. inversion. In In the general general case, this will will almost almost certainly certainly not not be be is true. true. Paleomagnetic Paleomagnetic studies studies in a number number of areas areas have have shown shown fairly fairly large large rotations, rotations, as as 140 degrees degrees during during displacement displacement deformation. deformation. In many many of these these areas, areas, finite finite much as 140 strain is is minimal, minimal, and the rocks rocks on an an outcrop outcrop scale appear nearly undeformed. undeformed. Early Early episodes of such rotation leave only a magnetic record in the rock, which may episodes of rotation magnetic record the rock, which may be be eliminated or or rendered rendered effectively effectively undecipherable undecipherable by by later later deformation deformation and/or andlor eliminated IfIf 43 �pateomagnetic data data are are not available, one can only assume assume that that no no metamorphism. metamorphism. If paleomagnetic when attempting attempting to to restore restore paleocurrent paleocurrent vectors. vectors. This such rotation has taken place when This often often may not be aa safe safe assumption. assumption. Even in areas without such displacement rotations, and with minimal finite strain, complications complications are certainly certainly possible. possible. In areas of plunging folds with a seemingly simple simple deformation history, history, it has has been been shown, shown, again again from from paleomagnetic paleomagnetic studies, studies, that that the the Using technique outlined in Ramsay technique outlined Ramsay (1961) is not not aa correct correct deformation deformation inversion. inversion. Using progressive demagnetization demagnetization techniques progressive techniques on on rocks rocks from from an an area area where where there there were were several several resetting, McClelland deformation history periods of magnetic resetting, McClelland Brown Brown (1983) (1983) found that the deformation history fold in the the Old Old Red Red Sandstone Sandstone in in Pembrokeshire Pembrokeshire involved involved marked marked changes changes of a particular fold in plunge (both (both steepening and gentling during deformation), deformation), and in plunge plunge direction direction during fold development, development, even even through nearly nearly 180 180 degrees degrees (opposite (opposite plunge plunge directions) directions) such as these during during one one stage. stage. Studies Studies such these show show that that when wheninformation information (from (from paleomagnetic studies) about fold or displacement displacement histories is is not not available, available, paleocurrent paleocurrent paleomagnetic data data should should be be considered consideredsuspect. suspect. In addition addition to errors errors in in orientation orientation of of aasingle singlecurrent current vector vector introduced introduced in in paleocurrent data from unknown or partially partially known deformation histories, problems problems may may sets, which are purely an artifact of the also arise because of apparent patterns in data sets, Depending on the deformation history, not the the original originalpaleocurrent paleocurrent pattern. pattern. Depending the deformation history, and not deformation deformation history and the the geometrical geometrical relationships relationships between between bedding, bedding, true true current current direction, and the various deformation components, deformation processes processes may create an apparent apparent single single cluster cluster of of paleocurrent paleocurrent vectors, vectors, an an apparent apparent bimodal, bimodal, bipolar bipolar distribution, or may even spread spread out to aa large large degree degree an an original original fairly fairly close closeclustering. clustering. As certain As certain of of these these patterns patterns are are generally generally taken taken as as being being indicative indicative of of particular particular environments of deposition, there are obvious obvious dangers involved involved in in placing placing much much faith faith in in studies of paleocurrent paleocurrent patterns deformed rock where information information necessary studies patterns in deformed necessary to perform perform a complete complete deformation deformation inversion inversion is is not not available. available. Many studies have shown that deformation histories of deformed, or or apparently apparently undeformed rock are much more complex than they appear appear to be. be. In general, detailed detailed detailed information information on deformation history in not attainable in in rocks. rocks. In the absence of detailed considered and complete information on deformation history, paleocurrent data must be considered suspect. Orientation Orientationerrors errorsintroduced introducedby by deformation deformation processes processes may may be be substantial, substantial, and and artificial patterns may be introduced introduced to a group group of data. data. REFERENCES REFERENCES McClelland Paleomagnetic studies of fold fold development development and and propagation McClelland Brown, E., 1983, Paleomagnetic McClelland Brown, Brown, E., E., and in the and the Pembrokeshire Pembrokeshire Old Old Red RedSandstone, Sandstone, & McClelland VandenBerg, J., eds., Paleomag Paleomagnetism of Orogenic Orogenic Belts: Belts: Tectonophysics, v. 98, netism of VandenBerg, J., s, 131-149. p. 131-149. Ramsay, J. J. G., G., 1961, 1961, The The effects effects of of folding folding upon upon the theorientation orientation ofofsedimentary sedimentary 84 -- 100. 100. structures: Journal Journal of of Geology, Geology, v. v. 69, 69, p. p. 84 44 �Airborne Survey of of Northwestern Northwestern Wisconsin. Wisconsin. Airborne Geophysical Geophysical Survey by by R.J. R.J. Horton, Hortonf R.J. R.J. Bisdorf, Bisdorf! and and R.P. R.P. Kucks Kucks USGS, USGS! Branch Branch of of Geophysics, Geophysicst MS MS 964, 964! Denver Denver Federal Federal Center. Center. In In 1988, 1988! the United United States States Geological Geological Survey Survey conducted conducted an an airborne geophysical geophysical survey survey over northwestern northwestern Wisconsin Wisconsin as as part part of of the the Great Great Lakes Lakes International International Multidisciplinary Multidisciplinary Program Program on on Crustal Crustal Evolution Evolution (GLIMPCE) (GLIMPCE) program. The The 6000 6000 line-kilometer line-kilometer survey survey covered covered portions portions of of Bayfield, Bayfield! Burnette, Burnettel Douglas, Douglas! and and Washburn Washburn counties. counties. The The survey direction was north-south! north-south, the spacing survey flight flight line line direction the flight flight line line spacing 800 800 meters, metersf and and the the survey survey altitude altitude 91 91 meters meters above above ground ground level. level. Magnetic Magnetic and and very very low low frequency frequency (VLF) (VLF) resistivity resistivity data data were were collected. collected. The The geology geology of of the the survey survey area area consists consists of of Precambrian Precambrian bedrock bedrock overlain overlain by by glacial glacial deposits. deposits. The The oldest oldest bedrock bedrock units units are are Middle Middle Keweenawan, Keweenawan! Chengwatana Chengwatana volcanic volcanic rocks rocks composed composed of of mafic mafic to to intermediate intermediate lavas lavas and and interbedded interbedded sedimentary sedimentary rocks. rocks. The The Upper Upper Keweenawan, Keweenawanf Copper Copper Harbor Harbor Conglomerate Conglomerate overlies overlies the the volcanic volcanic rocks. rocks. The The youngest youngest bedrock bedrock units, units! the the Upper Upper Keweenawan Keweenawan Bayfield Bayfield Group Group sandstones, sandstonesf are are juxtaposed juxtaposed against against the the Chengwatana Chengwatana volcanic volcanic rocks rocks by by the the Douglas Douglas fault. fault. Late Late Wisconsin Wisconsin to to Holocene Holocene glacial glacial deposits deposits consist consist of of alluvium, alluviumt peat, peat! lake lake silt, siltf clay, clay! ice—contact ice-contact and and outwash outwash sand sand and and gravel, gravel! and and clayey clayey to to loamy loamy ground ground moraine moraine and and till. till. These These glacial glacial deposits deposits range from from less less than 11 to to greater greater than than 100 100 feet feet thick. thick. The features on on the the aeromagnetic aeromagnetic map map (Figure (Figure1) 1) The most most obvious obvious features are are related related to to the the Ashland-Lake Ashland-Lake Superior Superior syncline. syncline. The The axis axis of of the the syncline through the center syncline strikes strikesnortheasterly northeasterlythroughthe centerof ofthe thesurvey surveyarea. area. The narrow, narrowf northeasterly—trending northeasterly-trending linear linear anomalies anomalies are are produce produce by by The dipping dipping volcanic volcanic rocks, rocksf upturned upturned along along the the northwest northwest and and southeast southeast limbs limbs of of the the syncline. syncline. The The Copper Copper Harbor Harbor Conglomerate Conglomerate occupies occupies the the center center of of the the syncline syncline where where aa relatively relatively deep deep and and flat-lying, flat-lying! magnetic magnetic basement basement produces produces the the broad—gradient broad-gradient magnetic magnetic anomaly. anomaly. In In the mapf the the Douglas Douglas fault, faultf has has brought brought the the the northern northern portion portion of of the the map, relatively relatively non—magnetic non-magnetic Bayfield BayfieldGroup Group sandstones sandstonesin in contact contact with with the the older, older! southeast—dipping, southeast-dipping! magnetic magnetic volcanic volcanic rocks. rocks. In In the the extreme extreme southern southern portion portion of of the the survey survey area, area! the the low—amplitude low-amplitude magnetic magnetic anomaly magnetic basement anomaly is is thought thought to to be be caused caused by by deep deep magnetic basement below below thick thick sedimentary sedimentary rocks. rocks. Unlike Unlike the the aeromagnetic aeromagnetic map, mapf the the VLF VLF apparent apparent resistivity resistivity map map (Figure 2) reflects reflects aa combination combination of of topographic, topographicf bedrock bedrock and and (Figure 2) surficial surficial geologic geologic features. features. Across Across the the northern northern portion portion of of the the survey survey area area low low resistivities resistivities are produced produced by by conductive conductive lake lake sediments sediments deposited deposited in in the the topographically-low topographically-low region region between between Lake Lake Superior Superior and and the the Douglas Douglas fault. fault. South South of of the the Douglas Douglas fault fault sand, sandf gravel, gravel! and and moraine moraine deposits deposits produce produce the the intermediate intermediate resistivities resistivities that that cover cover the the majority majority of of the thesurvey surveyarea. area. Small conductive conductive Small anomalies anomalies result result from from deposits deposits of of clay clay and and peat peat in in lakes lakes and and shallow shallow depressions. depressions. The The highly highly resistive resistive zones zones are are produced produced by by thick, thickfclay— clayfree free sand sand and and gravel gravel deposited deposited as as outwash outwash or or ice—contact ice-contact deposits. deposits. Subtle Subtle northeast—striking northeast-striking features features observed observed throughout the the survey survey area area reflect reflect the the direction direction and and resultant resultant deposits deposits of of southwesterly southwesterly glacial glacial advances advances and and the the influence influenceof of underlying underlying bedrock bedrockfeatures. features. 45 45 �CD N3 0 + Li, 0 Li, I (V 0 fl2 S CD 0 + CA3 N N rii N cJ, C C cJ, C rn C C C C C C C C N C N CC C CC ffl CN rn rn rn C C C C C C CCCCCCCC.fl C C C C C C C C rn r-4 CC C 0 a, 0 Li, Lighter ~ i m r1. e1. Gray-scale Gray-scale aeromagnetic aeromagneticmap map of of the the northwestern northwesternWisconsin Wisconsin survey surveyarea. area. Lighter Figure represent magnetic field field highs, darker shades of gray shades of gray represent magnetic field highsf darker shades of gray represent magnetic field shades of gray represent magnetic produced by dipping Chengwatafla linear, northeast-trending anomalies are ~ O W S . Narrow, Narrowf linearf northeast-trending anomalies are produced by dipping Chencpatana lows. produced by deep volcanic rocks. rocks. The The broad—gradient broad-gradient anomaly anomaly in in the the center center of of the the map map is is produced by deep volcanic Conglomerate. magnetic basement basement below below the the Copper Copper Harbor Harbor Conglomerate. magnetic �I l.A — t% c_fl — t, — (P1 I + + + + 0 luij 0,, '-1, Figure 2. 2. Gray—scale Gray-scale VLF VLF apparent apparent resistivity resistivitymap map of of the the northwestern northwesternWisconsin Wisconsinsurvey surveyarea. area. Figure Light shades shades of of gray gray represent represent high high resistivity resistivity areas, areas, dark dark shades shades of of gray gray represent represent low low resistivity resistivity areas. areas. Conductive conductive lake lake sediments sediments produce produce the the low low resistivity resistivity terrain terrain across across the northern portion the survey survey area. area. Sand, gravel gravel and moraine moraine deposits deposits produce produce the the northern portion of the Sand, intermediate that cover cover the the majority majority of of the the survey survey area. area. High resistivity resistivity intermediate resistivities resistivities that areas a r e a sare areproduced producedbybythick thickdeposits depositsofofclay—free clay-freesand sandand and gravel. gravel. �Magnetic Magnetic studies studies of of the the Dresser-St. Dresser-St. Croix Croix Falls Falls Area, Area, Polk Polk County, Wisconsin. Wisconsin. County, William F.Kean, Department Department of of William F.Kean, Wisconsin-Milwaukee, Wisconsin-Milwaukee, P.O. P.O. Box Box Geosciences, Geosciences, University University of of 413, Milwaukee, 413, Milwaukee, WI WI 53201 53201 John John Feeney, Feeney, Wisconsin Wisconsin Department Department of of Natural Natural Resources, Resources, 2300 2300 Martin Martin Luther Luther King, King, Jr. Jr. Drive, Drive, Milwaukee, Milwaukee, WI WI 53212 53212 The The ground ground magnetic magnetic study study by by Reich Reich (1989) (1989) and and the the paleomagnetic paleomagnetic study study by Feeney Feeney (1990) (1990) have have been been incorporated incorporated and and compared in the the Dresser—St. Dresser-St. Croix Croix Falls Falls area area compared to to the the bedrock bedrock map in by Cordua Cordua (1989). (1989). Paleomagnetic Paleomagnetic results results from from 11 11 locations locations give give by five five normal normal sites, sites, four four reversed reversed sites sites and and two two mixed mixed sites. sites. The The pole pole positions positions when when corrected corrected for for dip dip give give magnetic magnetic directions directions close close to to either either the the North North Shore Shore volcanics volcanics or or the the Gargantua Gargantua volcanics. The The remanent remanent intensities intensities and and susceptibilities susceptibilities are are volcanics. typically typically large, large, with with ratios ratios of of the the remanent remanent to to induced induced components components ranging ranging from from .4 . 4 to to 1.4. 1.4. This This implies implies that that remanent remanent intensities magnetic surveys intensities will strongly strongly influence influence land land magnetic surveys and and interpretations. The The land land magnetic magnetic surveys surveys by by Reich Reich (1989) (1989) interpretations. showed showed aa significant significant number number of of anomalies anomalies about about 1/4 1/4 to to 1/2 1/2 mile mile wide wide and and 300.0 300.0 gamma gamma to to 500.0 500.0 gamma gamma in in intensity. intensity. Preliminary Preliminary modelling modelling suggests suggests these these features features are are caused caused by by magnetic magnetic characteristics characteristics of of individual individual flows flows rather rather than than by by bedrock bedrock topography topography as as originally originally proposed. proposed. In In addition, addition, the the combined combined rock rock magnetic magnetic and and land land magnetic magnetic studies studies are are reasonably reasonably consistent consistent with (1989) and and could could be be used used to to extend extend the the with the the mapping mapping by by Cordua Cordua (1989) mapping mapping in in areas areas covered covered by by glacial glacial drift. drift. References References Cordua, S., 1989, 1989, A A Summary Summary of of the the Bedrock Bedrock Geology Geology of of the the Cordua, William S., Dresser—St. Dresser-St. Croix Croix Falls Falls area, area, Polk Polk County, County, Wisconsin Wisconsin and and Chisago County, County, Minnesota. Minnesota. 53rd Annual Field Chisago Annual Tri-State Tn-State Field Conference Guide Guide Book, Book, River River Falls, Falls, WI. WI. Conference Feeney, of Keweenawan Keweenawan Age Age Basalts Basalts of Feeney, John, John, 1990, 1990, Paleoinagnetism Paleomagnetism of the the Chengwatana Chengwatana Volcanic Volcanic Group Group in in Polk Polk County, County, Wisconsin. Wisconsin. Unpublished MS MS thesis, thesis, University University of of Wisconsin-Milwaukee, Wisconsin-Milwaukee, Unpublished 218 pp. pp. 218 Reich, Laura, Laura, 1989, 1989, Geomagnetic Geomagnetic Model of the the St. Croix Croix Horst Horst in in Reich, Polk County, County, Wisconsin. Wisconsin. Unpublished Unpublished MS MS thesis, thesis, University University Polk of Wisconsin-Milwaukee, 141 pp. pp. of Wisconsin-Milwaukee, 141 48 �MAGmTIC AND OF HEAT HEAT MAGNETIC AN]) PETROGRAPHIC DETECTION OF TREATMENT TREATMENT IN IN GUNFLINT G r n L I N ' TCHERT CrnRT Stephen Graham J. StephenA. A Kissin and Graham J. Borradaile, Borradaile,Department DepartmentofofGeology, Geology,Lakehead LakeheadUniversity, University, Thunder Thunder Bay, Bay, ON P7B P7B5E1; 5El;Joe JoeD.D.Stewart, Stewart,Department DepartmentofofAnthropology, Anthropology, Lakehead Mehead University, 5E1; William A. Ross, Ontario Ministry of Culture University, Thunder Bay, ON P7B P7B 5El; William A. Ontario Ministry of Culture and and Communications, 1825East EastArthur ArthurStreet, Street,Thunder ThunderBay, Bay,ON ON P7E 5N7; Communications, 1825 5N7; and and Tomasz Tomasz Werner, Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Bay, ON 5El. P7B 5E1. In the was the the material material of choice for the the Thunder Thunder Bay, Bay, Ontario Ontario area, area, "taconite" Yaconite" was manufacture of stone implements implements during during the the late late Paleo-Indian Paleo-Indianperiod periodCa. ca. 9000 9000 b.p. (Fox, (Fox, 1975; Dawson, Dawson, 1983). 1983). The "taconite" which occurs as stratabound Yaconite*'is an iron-bearing chert, which nodules and lenses of the local Gunflint lenses in calcareous calcareous and and siliceous siliceous siltstones of Gunflint Formation. Formation. Studies have indicated flaking indicated that heat heat treatment treatmentofofsiliceous siliceousmaterials materialsimproves improvestheir theirflaking characteristics, both in ethnographic characteristics, both ethnographic (Hester, (Hester, 1972; 1972; Mandeville, Mandeville, 1973) 1973) and experimental experimental investigations (Crabtree and and Butler, Butler, 1964, 1964, Mandeville and Flenniken, Flenniken, 1973; 1973; Flenniken Flenniken and and Garrison, the Thunder Bay area Garrison, 1975). 1975). The The possibility possibility that heat treatment treatment was employed in the technology has been suggested Dawson,1983), 1983),and andaamethod method of of detection of technology has suggested (Fox, 1975; 1975; Dawson, such treatment is is important important in in the thecontinuing continuingstudy study of of this this culture. culture. "Taconite" specimens specimens£ro from three three bedrock bedrock outcrops outcrops in in the Thunder Bay Bay area area were were heated at 2½hr. hr.and and allowed allowedtotocool cooltotoroom roomtemperature. temperature. Comparison at 425 425 and and 500°C 5OO0Cfor 2+ Comparison to unheated unheated specimens specimens revealed revealed some some color color differences differences attributable attributable to toheating; heating;however, however,the the mesoscopic and microscopic of the specimens did not permit microscopic heterogeneity of permit mineralogical mineralogical reflectance and microhardness microhardness techniques techniques to to be be usefully usefully employed. employed. Optical Optical microscopy microscopy using transmitted transmitted and andreflected reflectedlight lighton onpolished polishedthin thin sections sectionsrevealed revealeddistinctive distinctivedifferences differences in most specimens. specimens. The The most most pronounced pronounced effect effect of of heating heating was aa loss loss of of organic organic carbon, carbon, resulting and migration &om resulting in bleaching bleaching of most most carbon-rich carbon-rich specimens specimens and migration of carbon carbon from inclusions to grain boundaries boundaries and and cracks. inclusions to cracks. Decarbonation Decarbonation of siderite siderite with with production production of hematite isis also alsosignificant sigmficant in in carbonate-rich carbonate-richspecimens. specimens. hematite Non-destructive measurementofof magnetic magnetic properties properties revealed Non-destructive measurement revealed that that magnetic magnetic susceptibility, saturation isothermal isothermal remanent susceptibility, saturation remanent magnetization magnetization and and magnetic magnetichysteresis hysteresis changed as heating. Because Because the natural natural remanent remanent magnetism magnetism parameters all changed as a result of heating. (NRM) of of the the Gunflint Gunflint cherts cherts is is highly highly variable and unstable, this property is not aa useful useful parameter for heated £ro from unheated unheated material material although although itit has been used in for distinguishing distinguishing heated archeological work work in in Europe. Europe. Also, in the manufacture and Also, mechanical action and shock in M . We We took took ten ten specimens specimens of of the cherts cherts use of implements would wouldperturb perturb and and alter the m NRM. and broke them in two. two. One One part partwas was kept kept as as a2 control control sample sample and the other other half half heated. heated. aswell well as as the thehysteresis hysteresis after heating heatingas In this way, the the susceptibilitywas was measured measured before and after properties. Instead Insteadof ofusing using the the natural naturalmagnetization magnetization of of the the samples, samples, we compared their ability to retain a large large (saturation) (saturation)magnetization magnetization in an an inducting inducting field field of of 950 950 mT mT (9500 (9500 ability oersteds). This ( E M ) increased greatly as a result of of This isothermal isothermal remanent remanent magnetization magnetization (IRM) These parameters parameters alone alone allow allow one one to to distinguish distinguish between heating as did the susceptibility. These and the theunheated, unheated,control controlspecimens. specimens. cherts which which had had been heated and 49 �Hysteresis loops in unheated unheated materials materialsare arefrequently ikequently"wasp-waisted" "wasp-waisted because of the the presence of of two two magnetic magnetic minerals minerals (Jackson (Jackson et et al.. al., 1990). 1990). Heated Heated specimens specimenslose lose"wasp"waspin hysteresis hysteresis behavior are are variable. variable. waistedness", although the the changes changes in waistedness", Petrographic of Gun£lin Gunflint cherts cherts appear to provide a means by Petrographic and magnetic studies of which may be be detected. Magnetic which heat treatment in in the the manufacture manufacture of stone implements may Magnetic methods are are particularly attractive, attractive, as they are non-destructive so long as an artifact under investigation will will fit fit the the constraints constraints imposed imposedby bysample sampleholders holdersand andinstruments. instruments. Moreover, the as normal normalchert chertor orflint flintwith withmuch much the magnetic magnetic methods methods will will be applicable applicableto to samples samples such such as lower iron contents contents than than the thespecimens specimenswe we need. need. REFERENCES REFERENCES Crabtree, D.E. and Notes on onexperiments experimentsin inflint flintknapping: happing: 1. 1. heat B.R., 1964. 1964. Notes and Butler, Butler, B.R., treatment treatment of of silica silica materials: materids: Tebiwa, Tebiwa,v.v. 7,7,p. p.1-6. 1-6. Dawson, K.C.A., K.C.A.,1983. 1983. Cummins CumminsSite: Site: A late Paleo-Indian (Piano) (Plano) site site at at Thunder Thunder Bay, Bay, Ontario: Ontario 39,p.p.3-31. 3-31. OntarioArcheology, Archeology,v.v.39, altered novacuilte and Garrison, Garrison,E.G., E.G.,1975. 1975. Thermally Thermally altered novaculite and stone tool tool Flenniken, J.J. and manufacturing 1. 125-131. manufacturing techniques: Journal J o m a lofofField FieldArcheology, Archeology,v.v.2,2,p.p.125-13 ministry of Natural Natural W.A., 1975. 1975. The Paleo-Indian Paleo-Indian Lakehead M e h e a d Complex: Complex: Ontario ministry Fox, W.A., Resources Historic Historic Sites Sites Branch, Branch, Division of Parks, Research Report Report6,6,p.p.29-53. 29-53. evidence of of thermal thermal alteration of T.R.,1972. 1972. Ethnographic Ethnographic evidence of siliceous siliceous stone: stone: Hester, T.R., Tebiwa, v. v. 15, 15,p. p. 63-65. 63-65. Tebiwa, Jackson, M. Worm, H.-U. and and Banerjee, Banerjee, S.K., S.K, 1990. 1990. Fourier Fourieranalysis analysisofofdigital digitalhysteresis hysteresis data: rock rockmagnetic magneticapplications: applications: Physics Physics of of Earth Earthand andPlanetary PlanetaryInteriors, Interiors,v. v. 65, 65, p. 78-87. 78-87. p. Mandeville, M.D., 1973. 1973. A consideration of the thermal pretreatment consideration of pretreatment of of chert: chert: Plains Plains Mandeville, M.D., Anthropologist, 18,p.p.177-202. 177-202. Anthropologist,v.v. 18, Mandeville, M.D. and and Remiken, Flenniken, J.J., JJ., 1973. 1973. A comparison comparison of the the flaking flaking qualities qualities of Mandeville, M.D. Nehawka chert before and after thermal pretreatment: Plains Anthropologist, Nehawka before pretreatment: Plains Anthropologist, v. 19, 19, p. p. 146-148. 146-148. 50 �ALTERATION, FLUID INCLUSION, STABLE ISOTOPIC ISOTOPIC AND ALTERATION, FLUID STRUCTURAL STUDIES OF OF THE RABBIT MOUNTAIN SILVER MINJ3, MINE, STRUCTURAL STUDIES THUNDER THUNDER BAY BAY DISTRICT, ONTARIO ONTARIO Stephen A. Kissin, Peter G. Harvey, Elizabeth A. Jennings, Samuel T. Spivak Kissin, Peter Spivak and Eric J. Mosley, Department of Geology, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, ON ON P7B Mosley, Department P7B 5E1 5El The The Rabbit RabbitMountain MountainMine Minewas wasthe thefirst firstdiscovered discoveredof of aa number numberof of silver silvermines mines lying lying well inland of of Lake Superior. Total Total production production from from the the mine mine amounted amountedto toapproximately approximately 50,000 oz. oz. in the period during which which the the mine operated sporadically period 1882-1893, 1882-1893, during sporadically (Tanton, (Tanton, 1931). modest, the the discovery discoveiyof of the the Rabbit Rabbit Mountain Mine led 1931). Although Although production was modest, to additional e.g. Silver Silver Mountain, Mountain, Beaver, Beaver, Badger Badger and Porcupine, additionalsignificant sigdicant discoveries, discoveries, e.g. extending silver mining in in the the Thunder Bay District, following following depletion depletion and and closure of the famous Silver Islet Mine. Sporadic Sporadicactivities activities subsequent to the the main main period periodof ofmining mining did did not permitted underground not yield additional additionalproduction; production;however, however, in in 1967-1968, 1967-1968, dewatering permitted underground sampling sampling and and mapping. mapping. The The deposit depositconsists consists of of two two veins, no. 11vein, carrying most of the the ore, ore, and andno. no.22vein, vein, essentially with trace trace quantities of of sulfide sulfide minerals. minerals. Both veins strike at essentially aa barren system with about 230° withdips dipsofofS50 to 70' 70°northwest. northwest. The The no. no. 11 vein vein varies varies£ro from 11 to to 33 m in 230' with O to thickness, and no. 22 vein, outcropping vein, is is about about11m mthick. thick. outcropping about about 100 100northwest northwest of of no. no. 11vein, A few minor veins veins with withthe the same same attitudes attitudes outcrop outcrop between between no. no. 1 1vein veinand andno. no.22vein. vein. The veins veins are in in Rove Rove Formation Formation shales shales in in faults faults that thatoffset offsetcapping cappingLogan Logan diabase diabasesills. sills. Brecciation Brecciation and recementation recementationof of earlier earliervein vein deposits depositsby by later later deposits deposits is is observable observable in in the the field. field. The The ores ores contain contain acanthite acanthite (pseudomorphous (pseudomorphousafter after argentite), argentite),native nativesilver, silver, sphalerite, sphalerite, galena, pyrite wg-filling pyrite and andchalcopyrite. chalcopyrite. Gangue Gangue consists consists of quartz, quartz, including including aavug-fiuing amethystine variety, variety, calcite calciteand andgreen greenand andpurple purplefluorite. fluorite. Barite was reported by Tanton (1931) and earlier was not not encountered encounteredin inthis thisstudy. study. earlier workers, workers, but was of The veins and and their their narrow narrow alteration alteration zones zones (typically (typically 10 cm wide) The wide) cut cut the zone of contact metamorphosed shale, which developed microscopic-sized porphyroblasts of metamorphosed shale, which developed microscopic-sized porphyroblasts of andalusite in in response responseto tointrusion intrusionofofthe thediabase diabasesill, sill,Ca. ca. 13 13 m thick. The Theveins veinspinch pinchdown down andalusite to aafew centimetres width in the diabase and wallrock alteration is negligible. The few centimetres width in the diabase and wallrock alteration is negligible. The alteration zones zones in in the the shales shalesare areoften oftendelineated delineatedby bybleaching bleachingowing owing to to aaloss lossof of carbon, carbon, alteration which which is present in the unaltered shale. The Theonly only mineralogical mineralogical change noted is alteration of illite(1M) illite(1M) to to illite(2M). illite(2M). Studies of trace content content in in uniformly uniformly spaced spaced samples samples taken taken perpendicular to to no. no. 22 vein indicate apparent depletion depletion in in Cu Cu and and possible possible depletion depletion in in As As perpendicular in aa zone zone extending extending 55 ft from the vein. Within Within this this zone zone Zn, Zn,Pb, Pb, Co, Co,Ni Ni and andAg Agexhibit exhibit cases are below below the enrichment, and, although although concentrations apparent enrichment, concentrationsofofHg Hg in in most most cases ft.of of the the detectionlimit limit of of the the atomic atomicabsorption absorptionspectroscopy spectroscopytechnique techniqueemployed, employed,within within22ft. detection vein clear enrichment in Hg is present. vein clear enrichment in Hg is present. Fluid quartz, sphalerite sphalerite and purple purple fluorite fluorite indicate indicate the Fluid inclusions in calcite, quartz, the presence presence of two episodes of of ore deposition separated by a period of cooling, cooling, aa pattern pattern common to all 51 �Early calcite productive silver mines mines of of the inland calcite yielded yielded productive silver inland area area(Jennings, (Jennings, 1986). 1986). Early homogenization temperatures ranging ranging from from 125 6s0C, whereas whereas post-fracture post-fracture calcite calcite homogenization temperatures 125 to 65°C, homogenization temperatures lay lay in in the the90-100°C 90-100° range, sphalerite sphalerite in inthe the80-115°C 80-115°range range and one as compared compared to to 99.7OC 99.7°Cin in another. another. Two 308S° as Two adjacent adjacent one purple purple fluorite fluorite yielded yielded 308.5°C inclusions homogenized to liquid and inclusions in calcite homogenized and vapour vapour at atCa. ca. 100°C, 100°Cindicating boiling at -15.0°C near surface surface depths depths during during position. position. Final melting melting temperatures of of -15.7 -15.7 and and-15.0°C, corresponding to 19.4 19.4 and and 18.8 18.8equiv. equiv. wt.% wt.% NaC1, NaCl, respectively, respectively, were determined. determined. Initial Initial melting temperatures ininother melting otherdeposits depositssuggest suggestNaC1-CaC12 NaCl-CaC12 or or CaC12 CaC12 aqueous aqueous systems systems (Jennings, 1986), -50.6and and -35.6OC -35.6°Cwere wereobtained obtainedfrom fromthe the Rabbit Rabbit Mountain sphalerite 1986), -50.6 specimens. The Theformer formerisisin inagreement agreementwith withthe theeutectic eutecticfor forNaC1-CaC12-H20, NaCl-CaC12-H20,but the latter latter temperature C 0 2on onthe theNaC1NaCltemperatureisisdifficult difficultto to interpret, interpret,but butmay mayreflect reflectthe theeffect effectofofdissolved dissolvedCO2 CaCJ2-H20 system. Daughter Daughter minerals were not observed in fluid inclusions from Rabbit CaC12-H20system. Mountain Mountain specimens. specimens. Sulfur isotopic isotopicanalyses analysesyielded yielded6% 6S == -1.2, -1.2, + 3.5, 3.5, + + 9.3 9.3 and ++ 9.9 9.9 %o %o in in sphalerite and a galena 3S%osphalerite sphaleritegave gave&MS 6% = -9.3%0. wide galena grain grain paired paired with with the the ++3.5%o -9.3%o. The wide variation in &'S 6 ? 3 in in sphalerite sphaleriteisissuggestive suggestive of a lack lack of of isotopic isotopic equilibrium, equilibrium, possibly possibly as a result of precipitation from a solution undergoing undergoingoxidation. oxidation. The The isotopic isotopic temperature temperature from the sphalerite-galena sphalerite-galena pair pair isis -35.6°C, -35.6OC, an unreasonably unreasonably low low figure figure probably probably also also indicating indicating sequential deposition deposition from from aa solution solutionundergoing undergoing oxidation. oxidation. 1. 1. 2. 2. 3. 4. The results results lead lead to tothe thefollowing followingconclusions: conclusions: Ores were deposited Ores deposited at at low low pressure pressure from frommoderately moderately saline salinesolutions, solutions, which which experienced sporadic sporadic boiling. boiling. The lack sulfides and and the mild wallrock lack of of isotopic isotopic equilibrium equilibrium among sulfides mild nature of of walirock alteration suggest suggest relatively rapid deposition. Most Hg, found found in in minerals minerals Most metallic components components of of veins veins as as well well as as Ni, Ni, Co and Hg, (Franidin et al., 1986), seem seem to to have have been been added added to wallrock walirock elsewhere in the district (Franklin solutions. Cu and As, as well as carbon, carbon, alteration zones from the ore-depositing ore-depositing solutions. were depleted in in alteration alteration zones. zones. The process in in which whichthermal thermal highs highswere wereseparated separated The deposition depositionof of ores ores was a pulsatory process by a period period of of cooling cooling and and fracturing. fracturing. REFERENCES Smyk, M.C., M.C.,and and Scott, Scott, S.D., S.D., 1986. 1986. Silver Franklin, J.M., Kissin, S.A., S.A., Smyk, Silver deposits associated associated with Proterozoic rocks Jour. Earth Earth Sci., Sci., rocks of of the the Thunder Thunder Bay Bay District, District,Ontario: Ontario: Can. Jour. v. 23, p. 1576-1591. 1576-1591. Jennings, E.A., E.A., 1986. 1986. A survey Jennings, survey of the the Mainland Mainland and and Island Island Belts, Belts, Thunder Thunder Bay Bay silver silver Fluidinclusions, inclusions, mineralogy, mineralogy, and sulfur isotopes: Unpubi. Unpubl.M.Sc. M.Sc. district, Ontario: Fluid thesis, Lakehead M e h e a d University, University, 159 159 p. p. William and Port Port Arthur, Arthur, and and Thunder ThunderCape Capemap-areas, map-areas, Tanton, T.L., Tanton, T.L., 1931. 1931. Fort William Bay District, Ontario; Ontario; Geol. Geol.Surv. Sum. Can., Can., Mem. Mem. 167, 167,331 331 p. p. Thunder Bay 52 �THE EMPERORVOLCANIC VOLCANICCOMPLEX: COMPLEX: IMPLICATIONS THE EARLY EARLY PROTEROZOIC PROTEROZOIC EMPEROR IMPLICATIONSFOR FOR THE THE GEOLOGY GEOLOGY OF OF THE THE EASTERN EASTERNGOGEBIC GOGEBIC DISTRICT, DISTRICT, NORTHERN NORTHERN MICHIGAN MICHIGAN Gene Geology Dept., Dept., UW Oshkosh, Oshkosh, Gene L. LaBerge, LaBewe, Geology OshkoshI WI, Wl, and and U.S. U.S. Geological GeologicalSurvey Survey The Volcanic Complex constitutes a thick The Emperor Emperor Volcanic thick pile pile of of Early Early Proterozoic Proterozoic volcanic volcanic rocks and and sills sills in in the the sedimentary sedimentary sequence sequence on the eastern Gogebic Except for for aa rocks Gogebic range. range. Except number number of of diabase diabase dikes dikes and and sills, sills, igneous igneous rocks rocks are are scarce scarce on on the the western westernGogebic Gogebicrange. range. However, However, igneous igneous rocks rocks are abundant east of Wakefield, Mich., Mich., where wherethey theyreach reachaa thickness thickness of at at least least 2,000 2,000 m. m. Although Althoughthe thepresence presenceof ofvolcanic volcanic rocks rockson onthe theeastern eastern Gogebic range has been known for over 100 years (Irving and Van Hise, 1892), Gogebic range has been known for over 100 years (Irving and Van Hise, 18921, few few Irving and and Van Hise (1892) (1892) stated stated that thatthe the studies undertaken on on these these rocks. rocks. Irving studies have have been undertaken volcanic with the volcanic rocks rocks are are interbedded with the Ironwood Ironwood Iron lron formation, formation, an aninterpretation interpretation substantiated substantiated by by subsequent subsequent exploration exploration drilling drilling for for iron ironore ore in inthe thearea. area. Mapping (1973)documented Mapping by by Trent Trent (1973) documented the the distribution distribution of ofigneous igneousrocks rocksand andshowed showed some Dann(1978) (1978)showed showedthat thatthe thevolcanic volcanicrocks rocksrange rangeinin some of of the the Iithologies lithologies present. present. Dann composition prehnitecomposition from frombasalt basaltto todacite daciteand andthat thatthey theyhave havebeen beenmetamorphosed rnetamorphosed to t oprehnitepumpellyite pumpellyite or or to t o lower lowergreenschist greenschist facies. facies. Trace Traceelement elementstudies studiesby bySchulz Schulz(Sims (Simsand and others, others, 1990) 1990)indicate indicatethat thatthe thevolcanic volcanicrocks rocksare arebimodal bimodalrift-related rift-related tholeiites tholeiitesand and rhyolite. rhyolite. Geologic mapping mapping in in 1991 1991by byLaBerge LaBergeand and J. J. S. S. Klasner Klasnerindicates indicatesthat thatthe theEmperor Emperor Geologic Volcanic Volcanic Complex Complex consists consists of of aa variety variety of ofsubaqueous subaqueous mafic mafic and and felsic felsic volcanic volcanic rocks rocksand and sills. sills. Mafic Maficrocks rocksinclude includesills, sills, pillowed pillowedand andmassive massive flows--some flows--some with withcolumnar columnarjointing, jointing, and and extensive extensive hyaloclastites hyaloclastites and and pillow pillow breccias. breccias. Felsic Felsicrocks rocksinclude includemassive massivefelsite felsite breccias, lithic tuffs, tuffs, hyaloclastites, hyaloclastites,and andbreccia-hyaloclastite breccia-hyaloclastite debris debris flows. Kokelaar breccias, lithic Kokelaar (1986)states statesthat thathyaloclastites hyaloclastitesform formmainly mainlyininwater waterless lessthan than200 200mmdeep deepand and are aremore more (1986) abundant in inshallower shallower water. water. The Theabundance abundanceofofhyaloclastites hyaloclastites(Figure (Figure1)1)ininthe theEmperor Emperor abundant volcanics, therefore, therefore, suggests suggests extrusion in shallow Shallow water waterdeposition depositionisis volcanics, shallow water. water. Shallow further furtherindicated indicatedby bythin thininterbeds interbedsof ofoolitic ooliticiron ironformation. formation. The Emperor Emperor volcanic Ironwood Iron lron formation formation that that The volcanic rocks form a wedge wedge within the Ironwood (1973)shows showsthat thatthe the thickens eastward eastward from from Wakefield, Wakefield, Mich. Trent's Trent's mapping mapping (1973) thickens formationsare aretruncated truncatedby bymajor majorfaults faults(the (thePresque PresqueIsle lsleFault Faultand andthe theSunday SundayLake LakeFault) Fault) formations between Wakefield and Mareniso, Mich. between Wakefield and Mareniso, Mich. hyalo~lastites~ andinterbedded interbedded Thedistribution distributionofofvolcanic volcanicrocks, rocks,the theabundance abundanceofofhyaloclastites, The and ooliticiron ironformation formationindicate indicatethat thatthe theEmperor EmperorVolcanic VolcanicComplex Complexformed formedininshallow shallow water water oolitic basin subsiding subsiding markedly ttoo the the east east during during iron formation deposition. deposition. Truncation Truncationofof ininaabasin the theformation formationalong alongfaults faultsmay maybe beaa primary primary feature. feature. This Thissuggests suggests deposition depositionininaahalf half graben, perhaps perhaps during during continental continental rifting rifting(Figure (Figure2). 2). Deformation Deformationduring duringthe thePenokean Penokean graben, Orogeny resulted resultedin inthrusting thrusting(Klasner (Klasnerand and others, others, 1991) 1991)tot oproduce producethe thePresque PresqueIsle Isleand and Orogeny Sunday Lake Lake Faults and Rotation of of the the district districtduring during Sunday and the the present present distribution distribution of of rocks. rocks. Rotation Keweenawan Keweenawantilting tiltingproduced producedthe thepresent presentmap mappattern. pattern. 53 �References Cited Cited Dann, Dann, J. C., C., 1978, 1978, Major-element Major-element variation variation within withinthe theEmperor Emperor Igneous Igneous complex complex and and the the Hemlock and Badwater Badwater volcanic volcanic formations: formations: Houghton, Hemlock and Houghton, Michigan, Michigan, M.S. M.S. Thesis, Thesis, Michigan Technological Technological University, University, 199 p. Irving, R. D. and Van Hise, C. Series of of Michigan and Irving, C. R., R., 1892, 1892, The The Penokee Penokee Iron-Bearing Iron-Bearing Series Wisconsin: IXX, 534 p. Wisconsin: U.S. U.S. Geological Geological Survey Survey Monograph Monograph IXX, 534 p. Klasner, J. J. S., S., Ojakangas, Ojakangas, R. R.W., W., Schulz, Schulz, K. K. J., J., and LaBerge, LaBerge, G. G. L., L., 1991, Nature Klasner, Nature and Style of Deformation inthe theForeland Foreland of of the theEarly EarlyProterozoic Proterozoic Penokean Penokean Orogen Orogen Deformation in Northern Michigan: Michigan: U.S.G.S. 1904-K, 22 U.S.G.S. Bulletin 1904-K, 2 2 p. p. Northern Kokelaar, B. P., P., 1986, Magma-water Magma-water interactions interactions in in subaqueous subaqueous and emergent basaltic Kokelaar, B. volcanism: Bulletin vol. 48, 48, p. 275-289. volcanism: Bulletin of Volcanology, Volcanology, vol. Sims, P. P. K., K., Van Van Schmus, Schmus, W. W. R., R., Schulz, Schulz, K. K. J., J., and and Peterman, Peterman, 2. Z. E., E., 1990, 1990, Sims, Tectonostratigraphic evolution of of the the Early Early Proterozoic Proterozoic Wisconsin magmatic magmatic terranes of the Penokean Orogen: Canadian terranes Penokean Orogen: Canadian Journal of Earth Earth Sciences. Sciences. Trent, A., 1973, 1973,Geological GeologicalMap Mapofofthe theMareniso Marenisoand andWakefield WakefieldNE NEquadrangles, quadrangles, Trent, V. A., Gogebic County, Michigan: U.S. U.S. Geological GeologicalSurvey SurveyOpen-File Open-File Report. Report. Gogebic County, Figure 1. Figure 1. 54 Debris flow from from the Emperor Emperor volcanics. volcanics. Larger felsite f e l s i t e clasts clasts hyaloclastite (gray) iin n aa ffine ine h y a l o c l a s t i t e matrix. Paper clip c l i p is i s 33 cm. cm. �w L L L L L U U M - —-L- &././w £ Water W a t e r SSurface urface2 E T TYLER 4 / A 'II RAM SAY 41 A&q4V 44 V / PURITAN 7 // 7 Figure Figure 2a. 2a. Figure Figure 2b. 2b. / -J 7 / 1' I /7 / / BAD RIVER 'I- / 7 I I I Diagram showing showing hypothetical h y p o t h e t i c a l setting s e t t i n g of of the t h e Emperor Emperor Volcanics Volcanics Diagram s i l l s formed formed during during subsidence subsidence of of aa half h a l f graben graben that t h a t deepens deepens and sills and to t o the t h e east. east. S i m p l i f i e d sketch s k e t c h map map showing showing relationships r e l a t i o n s h i p s of of rocks rocks on onthe the Simplified eastern e a s t e r n Gogebic Gogebic range. range. Note Note that t h a t Emperor Emperor volcanics v o l c a n i c sand andsills sills are a r e truncated t r u n c a t e d by by major major faults. faults. 55 �THE CHEMISTRY AND PETROGRAPHY OF MAFIC ROCKS FROM THE EARLY PROTEROZOIC EMPEROR VOLCANIC PROTEROZOIC VOLCANIC COMPLEX COMPLEX NEAR MARINESCO, MARINESCO, MICHIGAN T. P., P., Geology Department, St. St. Norbert Licht, Kathy and Flood, T. College, DePere, WI 54115 54115 The Emperor Volcanic Complex (EVC) (EVC) is an Early Proterozoic Proterozoic sequence of mafic and felsic rocks located in the eastern Gogebic Range. Range. A portion of the EVC crops out near Marinesco, Michigan as massive basalts, pillow basalts, basalts, and and hyaloclastites. hyaloclastites. The The purpose of this this study was to characterize characterize the basalts and hyaloclastites petrographically and chemically in order to make inferences inferences regarding regarding the the formation formation and and alteration alteration of of these these rocks. rocks. The outcrop area of this study is located approximately 10 km north of Marinesco, Michigan and encompasses an area basalts approximately 600m approximately 600m by by 300m. 300m. The outcrop exposes pillow basalts that contain quench quench cracks cracks and and alteration alteration rims. rims. Pillows Pillows range range in in Hyaloclastite, which forms as the result size from 0.lm to 2in. size from O.lm to 2m. the of the interaction interaction of molten rock with seawater or saturated sediments, sediments, varies varies greatly greatly in in texture. texture. Fragments produced through through Some this interaction vary in size interaction vary in size from from aa few fewnun mm to to .5m. .5m. Some fragments contain alteration rims that are similar to pillow rinds. Some pillows included in the hyaloclastite appear rinds. virtually unaltered while others others are highly fractured fractured and and altered. altered. Petrographic Petrographic analysis analysis reveals that the various mafic rocks rocks are characterized by similar mineral assemblages including epidote, plagioclase, and chlorite, with lesser lesser amounts amounts of of Textures are calcite, quartz, and and amphibole. amphibole. Textures are variable. variable. Massive Massive and pillowed basalts are primarily composed composed of subhedral subhedral to to euhedral euhedral mostly mostly fine-grained fine-grained plagioclase, plagioclase, some some euhedral euhedral epidote, epidote, actinolite, and and sporadic sporadic pockets pockets of of quartz. quartz. chlorite, calcite, calcite, actinolite, Rinds on pillows are are comprised comprised mainly of plagioclase, plagioclase, some some chlorite and epidote, epidote, and vein fillings fillings of recrystallized recrystallized quartz. quartz. The hyaloclastite is is composed of angular angular basalt fragments fragments similar similar in texture to the massive basalt in a coarse to fine—grained fine-grained matrix that is is composed composed mainly of epidote, chlorite, chlorite, and and quartz. quartz. Epidote is medium to to coarse—grained coarse-grained and in in many samples samples epidote epidote "flowerettes" are ttflowerettes" are present. present. The chlorite chlorite is is mostly mostly amorphous. amorphous. The quartz is is usually fine-medium fine-medium grained grained and and recrystallized. recrystallized. Some flow structures structures occur occur around the the basalt fragments. fragments. Preliminary chemical chemical data indicates indicates that the the hyaloclastites hyaloclastites are similar ranges SiO, ranges similar in in composition composition to to the the massive massive basalts. basalts. Si02 from 57.2% 57.2% — 63.6%, MgO varies varies from from 2.8% 2.8% - 6.3%, 6.3%, Cr varies from 4oppm. Chemical 5lppm 63ppm and Cu varies from loppm lOppm - 40ppm. 51ppm - 63ppin composition of pillow rinds rinds tend to to be lower lower in in silica silica (54.4%) (54.4%) and higher higher in in Cu Cu (49ppm). (49ppm) - - - . 56 - �suggests The abundance of pillow lavas and hyaloclastites suggests intrusion into into water that extrusion onto the seafloor or shallow intrusion saturated sediments sediments occurred. occurred. The quenching of basaltic lava lava during eruption/intrusion eruption/intrusion resulted in the formation of hyaloclastites. Chemically, the basaltic fragments within the hyaloclastites. hyaloclastites show no greater degree of alteration than the the the exception exception basalts from which the fragments were derived, with the of the alteration alteration rims rims that that surround surround individual individual fragments. fragments. 57 �MAGNETITE MAGNETITE OCTAHEDRA OCTAHEDRA IN IN PILLOW PILLOW BASALT BASALT NEAR NEAR WAWA, WAWAfONTARIO ONTARIO by Frank Frank R. R. Luther, LutherfUW-Whitewater, UW-WhitewaterfWhitewater, Whitewater#WI WI by 53190 53190 Octahedral Octahedral magnetite magnetite crystals crystals in in Archean Archean pillow pillow basalt basalt found found south south of of the the Hwy. Hwy. 101 101 and and Lucy Lucy Pit Pit Road Road intersection intersection near near the the east east end end of of Wawa Wawa Lake Lake have have interested interested numerous numerous geologists geologists since since they they were were noted noted by by Ronald Ronald Sage Sage (Precambrian (Precambrian Geologist, Geologistf Ontario Ontario Geological Geological Survey) Survey) several several years yearsago. ago. Questions Questions related related to to these these crystals crystals include: include: (1) (1) are are they they of of igneous (2) are are the the crystals crystals evidence evidence igneous or or metamorphic metamorphic origin; origin; (2) bearing on on the the origin origin of of the the numerous numerous iron iron formations formations in in the the bearing region; region; and and (3) (3) given given that that pillow pillow basalt basalt is is voluminous voluminous in in the the Michipicoten Michipicoten greenstone greenstone belt, beltf why why are are the the crystals crystals confined confined to to the the rather rather small small area area southeast southeast of of Wawa Wawa Lake? Lake? Field Field studies studies by by the the author author and and Ronald Ronald Sage Sage have have shown shown that that the the magnetite magnetite octahedra octahedra are are confined confined to to an an area area of of about1 1km2 km2. There is is no no recognizable recognizable correlation correlation with with There about . pillow pillow selvages, selvagesf interiors, interiorsf amygdaloidal amygdaloidal zones, zonesf or or stratigraphic stratigraphic horizons; horizons; less less commonly commonly rnagnetite magnetite crystals crystals are are flows. The The magnetite magnetite crystals crystals present in in massive massive basalt basalt flows. present occur occur randomly randomly through through various various pillowed pillowed and and massive massive flows. flows. Petrographically, Petrographicallyf the the magnetite magnetite crystals crystals cut cut across across the the relict relict ophitic/subophitic ophitic/subophitic texture texture of of the the basalt basalt (now (nowalbite, albitef actinolitef epidote, epidotef chlorite, chloritef carbonate carbonate +/-pyrite, +/-pyritef actinolite, hematite). hematite). Preliminary Preliminary reflected reflected light light examination examination suggests suggests that that the the magnetite magnetite is is relatively relatively pure pure and and does does not not show show exsolution/oxidation. exsolution or or exsolution/oxidation. exsolution The above above evidence evidence shows shows the the magnetite magnetite octahedra octahedra to to be be The of metamorphic metamorphic origin; origin; presumably presumably the the crystals crystals were were of generated during during greenschist greenschist facies facies metamorphism metamorphism of of the the generated greenstone belt. belt. Frost Frost (1991) (1991) states states that that metamorphic metamorphic greenstone development of of magnetite magnetite in in metabasites metabasites is is somewhat somewhat unusual, unusualf development especially especially in in iron iron carbonate-rich carbonate-rich environments environments such such as as the the ankerite-siderite rich rich Michipicoten Michipicoten greenstone greenstone belt belt in in the the ankerite-siderite of Wawa. Wawa. One One can can conclude conclude that that the the isolated isolated area area vicinity of vicinity of magnetite magnetite porphyroblasts porphyroblasts was was not not subjected subjected to to the the of complete carbonate carbonate "soaking" "soaking" which which affected affected most most of of the the complete greenstone belt belt in in the the Wawa Wawa district; district; the the lesser lesser degree degree of of greenstone carbonation kept kept the the oxygen oxygen fugacity fugacity low low enough enough to to allow allow carbonation magnetite to to crystallization. crystallization. magnetite Reference: Reference: Frost, B.R., B . R S f1991, 1991f Magnetic Magnetic petrology: petrology: factors factors that that control control Frost, the occurrence occurrence of of magnetite magnetite in in crustal crustal rocks, rocksf in in Oxide Oxide the Minerals: petrologic petrologic and and magnetic magnetic significance, significance, D.H. D.H. Minerals: Lindsley Lindsley ed., e d e fMineralogical Society Society of of America America Reviews Reviews in Mineralogy Mineralogy 2j,5 , p. p. 489-506. 489-506. in 58 �THERMAL MODELING MODELING AND AND ILLITE/SMECTITE ILLITE/SMECTITE GEOTHERNOMETRY GEOTHEMOMETRY THERMAL OF OF THE THE PRECAMBRIAN PRECAMBRIAN ORONTO ORONTO GROUP, GROUPl WISCONSIN WISCONSIN AND AND MICHIGAN MICHIGAN K. L. L. PRICE, PRICEl J. J. HUNTOON, HUNTOONl AND AND T. T. J. J. BORNHORST BORNHORST S. D. D. MCDOWELL, MCDOWELLl K. S. Department Department of of Geological Geological Engineering, Engineeringl Geology, Geologyl and and Geophysics Geophysics Michigan Michigan Technological Technological University University Houghton, Houghtonl MI. MI. 49931 49931 The thermal history history of of Oronto Oronto Group Group sediments sediments in in the the White White The thermal Pine-Iron River syncline area has has been estimated Pine-Iron River syncline area estimated using using aa organic combination combination of illite/smectite (uS) (11s) geothermometry, geotherm~metry~ organic thermal one dimensional thermal maturity maturity indicators, indicatorsl and and one dimensional thermal thermal maturity data constrain modeling. Clay Clay and and organic organic maturity data are are used to constrain modeling. the the thermal thermal modeling, modelingl which which requires requires estimation estimation of of heat heat flow flow (including (including temporal temporal changes changes in in heat heat flow),  £ 1 0 time ~ time ) of of deposition deposition and erosion erosion of of sedimentary sedimentary rocks, rocksl and and lithology-dependent lithology-dependent thermal properties. properties. The The model model outputs outputs the the time-temperature time-temperature thermal history and and time-temperature time-temperature indices indices (TTI) (TTI) for for specified specified history positions I/S positions within within the the rock rock column, columnl and and estimates estimates I/S using Waples (1980, AAPG Bull., v. expandability using Waples (l98Ol AAPG Bullalv. 64, 64#p. p. 619) 619) expandability correlation correlation between between expandability expandabilityand and TTI. TTI. Model Model results results most most closely closely match match data data when when the the sediments sediments are are exposed exposed to to aa thermal thermal pulse pulse starting starting at at 1115 1115 Ma, Mal peaking peaking between between 1105 1105Ma Ma and and 1090 1090Ma, Mal and prodwing aa heating heating cycle cyc1.e of of roughly roughly 35 35 and ending ending by by 1080 1080 Ma, Mal producing Ma duration duration and and maximum maximum temperatures temperatures at at the the level level of of the the Nonesuch 110-125'~. Plausible Plausible total total thickness thickness for for Nonesuch Formation Formationof of110-125°C. the the Freda to 66 Km. Km. Freda Sandstone Sandstone range range from from 44 to Illite/smectite Illite/smectite geothermometry geothermometry (modified (modified from from Pollastro, Pollastrol 1990, 19901 SEPM SEPM Spec. Spec. Pub.) Pub.) has has been been carried carried out out on on clays clays from from the the Nonesuch and Freda drill holes holes in in Wisconsin Wisconsin Freda using using core core from from drill near near the the Michigan Michigan border border (DO-14, (D0-141DO-5), DO-5) from from the the White White PinePineIron and WPB-ll WPB-1, respectivelyl respectively, as Iron River River syncline syncline area area .(WP (WP and as well well as as samples samples from from the the mine mine itself), itself) and and from from aa series series of of drill drill holes holes extending extending northeast northeast to to the the vicinity vicinity of of Trimountain, TrimountainlMI. MI. Expandabilities Nonesuch Formation Formation range in the the Nonesuch range from from a maximum Expandabilities in of 25% 25% smectite smectite (Ri (Rl ordered) in the Iron Iron River Syncline Syncline area area to to values values of of <15% <15% smectite smectite (>R1 (>Rl ordered) ordered) in in Wisconsin Wisconsin and and <5% <5% To smectite (>R1 (>Rl ordered) ordered) at at White White Pine. Pine. To the the northeast northeast smectite expandabilities expandabilities decrease to to trace trace percentages, percentagesl and in in the the vicinity of of Winona Winona pure pure illite illite dominates dominates the the Nonesuch Nonesuch vicinity Formation. maximum Formation. Application Applicationof of I/S I/S geothermometry geothermometry indicates indicates maximum temperatures temperatures in in the the Nonesuch Nonesuch of of approximately approximately 115°C 115'~in in the the Iron Iron River at White Pine, River syncline, synclinel140°C 140'~ in in Wisconsin, Wisconsinl 160°C 160'~ at Pinel and and The most 190'~ near near Winona. Winona. most reliable reliable temperature temperature in the the 190°C smectite smectite to to illite illite sequence sequence is is that of the the change change in in ordering ordering Using from RO RO to to Ri Rl at at 100°C. 100'~. Using just just this this temperature temperature from constraint, above 100°C 100'~ everywhere in in constraintl temperatures temperatures were well above 59 �was reached at distances the Nonesuch Nonesuch Formation, Formationl and 100°C 1OO0c was distances contact of of at at least 300 m at White above the Freda-Nonesuch contact White Pine and 1120 1120 mm at at Winona. Winona. The data indicate indicate aa general general increase temperature northeast northeast toward toward the the Keweenaw Keweenaw Peninsula Peninsula increase in in temperature data also confirms confirms organic organic thermal native native copper copper district. district. The The data thermal maturity results results that indicate indicate maturities were higher higher in in the the relative to the the Iron Iron River River syncline syncline area area and and White Pine Pine area area relative increase increase westward westward into into Wisconsin Wisconsin from from the the area area of of the the syncline. syncline. The I/S I/S results results may also also be be used used to to estimate estimate geothermal geothermal gradients in gradients in the the drill drill holes. holes. In In the Winona area, areal aa gradient gradient of is estimated, estimatedl a value value identical identical to the the average average of SSOC/KXII 55°C/Km is gradient in the modern rift now forming the Salton Trough Salton Trough in in gradients are California. Higher Higher geothermal gradients are suggested suggested in in the the California. White white Pine Pine area, areal which, whichl coupled coupled with with lower lower I/S I/S temperatures temperatures imply decrease in thickness of the the Freda Freda Sandstone Sandstone to imply a decrease in the thickness to the the If true, this supports a Freda depocenter possibly off truel west. west. the Keweenaw Peninsula and in turn suggests suggests deeper erosion erosion of of rocks of the Keweenaw Keweenaw Peninsula Peninsula due to an increase increase in vertical in vertical rocks displacement along along the Keweenaw fault from Wisconsin to the displacement the There a relationship between deeper Keweenaw Peninsula. There may be a relationship between deeper Keweenaw Peninsula. burial burial near the the depocenter depocenter off the the Keweenaw Keweenaw Peninsula Peninsula and and native native copper copper deposits. deposits. The The results results of clay clay expandabilities expandabilities and and geothermometry geothermometry in in While both both expandabilities expandabilities the Wisconsin Wisconsin wells the wells are are anomalous. anomalous. While estimates in Nonesuch Formation Formation are are and temperature estimates and temperature in the the Nonesuch reasonable and with results reasonable and consistent consistent with results further further east, eastl the the change change with depth in the Freda Sandstone expandability with Sandstone there there is is in expandability transition from not. The transition from >80% >80% RO smectite smectite to to <20% <20% Ri Rl smectite smectite not. depth interval interval of of <125 <I25 m, m, a very very abrupt abrupt takes place over a depth versus depth profiles from relative to I/S versus depth profiles from transition transition relative to I/S In addition, both the highly expandable smectite elsewhere. In additionl the expandable smectite elsewhere. and and minor amounts amounts of of kaolinite kaolinite in in the the shallower shallower Freda Freda are are very very SEPM Spec. poorly crystalline. crystalline. Pollastro and Barker Barker (1986, (1986# SEPM Spec. investigated aa well well with a a similar similar expandability expandability Pub. 38) . investigated Pub. 38). profile that had undergone undergone erosion erosion and noted noted that that the the abrupt abrupt transition took place at The transition took at the top top of of overpressuring. overpressuring. The abruptness of the the clay clay transformation, transformationl coupled coupled with with the the poor poor crystallinity of the shallow shallow claysl clays, suggests retrograde retrograde crystallinity of the suggests alteration Freda Sandstone Sandstone after after diagenesis by alteration of of clays clays in the Freda circulating circulating low low temperature temperature waters, watersl perhaps perhaps during during deposition deposition of Bayfield Bayfield Group Group sediments. sediments. The fact fact that that clays clays in the the Nonesuch in the same wells appear to have preserved their Nonesuch same wells appear to have preserved their in turn turn indicates that the Nonesuch diagenetic character character in indicates that Nonesuch Formation here here is is aa permeability permeability barrier. barrier. It is also also quite quite reasonable reasonable to assume assume that that the Nonesuch Nonesuch Formation, Formationl during during diagenesis, depth at which which fluid pressures pressures first first diagenesisl might might mark mark the the depth hydrostatic pressures. exceeded hydrostatic pressures. 60 �ACMITE IN IN TIlE THETROMMALD TROMMALD FORMATION FORMATION OF OF THE THECUYUNA CUYUNA IRON IRON RANGE: RANGE: REVISITED REVISITED MCSWIGGEN, MCSWGGEN?Peter L., G.B. Morey, and Jane M. Cleland, Minnesota Geological Survey, Survey, 2642 2642 55 1 14 University Aveune, St. Paul, Minnesota 55114 In In the the process process of reevaluating possible protoliths protoliths for the the ferromanganese ferromanganese ores ores of the the Cuyuna Cuyuna North NaFesi206, that that was was first first North range, range, we we rediscovered rediscoveredthe theunusual unusual sodic sodicpyroxene pyroxeneacmite, acmite,NaFeSi2O6, described from the Trommald Trom maidFormation Formationby byGrout Grout(1946). (1946). Discovery occurred in a core obtained from the Memtt Merritt Number 2 mine (Sec. 33, T.47N.R29W) T.47N.R29W) where where two kinds of acmite were recognized; recognized; one one aa tea-green tea-green variety that occurs occurs in small small crosscutting veins veins and a second second tan tan to brown variety that occurs as disseminated grains in granules and as core grains in oolitic structures brown variety that occurs as purportedly rimmed by hematite and chert. The two acmite varieties was concentrated in a purportedly rimmed by hematite and The two acmite varieties was concentrated in alayer layer some 7.5 m (25 feet) thick that forms a marker some (25 forms a marker bed bed in in the the Merritt Memtt Number Number 22 and andFerro F m oMines. Mines. Both mines produced appreciable quantities of ferromanganese ferromanganese ore ore averaging averaging 12-14 12-14percent percent Mn. Mn. Therefore Therefore itit seems seems likely likely that that the the origin origin of of the the acmite acmiteisis significant significantto toaa better better understanding understandingof ofthe the origin origin of of the the protoliths protoliths to to the the ferromanganiferous ferromganiferousores. This seveml This investigation investigation focuses focuses on on compositional and and textural relationships of acmite acmite from from several different different settings. settings. Much Muchof ofthe theacmite acmiteoccurs occursas asfme-grained, fme-grained, tan tantotobrown brown material material in inbeds bedsor or lenses, rock. However lenses, with sharp contacts between it and the surrounding rock. However in in some some situations, situations, contacts contacts are are irregular irregular and the acmite is clearly secondary. Acmite Acmite also also occurs occurs as as rounded clasts clasts of either or as as intergrowths intergrowths with rhodonite rhodonite (MnSiO3). (MnSi&). These Theseclasts clasts either coarse coarse crystals, fine fine material, or commonly commonly form formcore coregrains grainsin in oolitic ooliticor or pisolitic-like pisolitic-like structures structureswhere wherethe therim rimmaterial materialisiseither either hematite hematite or or red-colored, cryptocrystalline acmite. However Howeverthese thesegrains grainsmay maynot notbe beof ofordinary ordinary sedimentary origin. Several areactually acmite acmite crystals crystals growing growing into into a Severalgrains grainsshow show that that the the cores cores are center center filled filled with quartz. Other Othercore coregrains grainshave havesecondary secondaryacmite acmitegrowths growths forming formingvariously variously shaped appendages on the rounded clasts. clasts. Acmite Acmite also also occurs occurs as zoned rims around around other kinds of core core grains, grains, including including Mn-oxides, qquartz, m , rhodonite, and rhodochrosite. The Theveined veinedacmite acmite described described by Grout Grout (1946) is is clearly secondary secondary in nature, whereas whereas many of the the other other textural relationships appear to be primary sedimentary structures. Compositionally, Compositionally, the theacmite acmitevaries varies from from approximately 95 mole% mole% NaFeSi2O6; NahSi206; the remainder is made up of other pyroxene approximately 80 80 to to 95 components, containing containing Ca Caand and Mn. Mn. Acmite/aegirine Acmitelaegirine is is a fairly common common mineral mineral series series in in sodium-rich sodium-rich igneous igneous rocks, rocks,but but itit also also occurs in blueschist-facies metamorphic rocks. The TheTrommald Trommald Formation, Formation, however, however?isisaa formation of sedimentary rocks that has been metamorphosed no higher than the upper greenschist facies. Thus ThusGrout Grout (1946) (1946) suggested suggested that that the the acmite acmite formed by a reaction between sodium-rich hypogene hydrothermal solutions and a mixture of chert and hematite. Experimental Experimental work work has has shown that acmite/aegirine can form over a wide range of P-T conditions. The acmitelaegirine can The upper upper stability stability limit limit of acmite 1200°C in in the the pressure pressure acmite as defmed by its its solidus occurs over a temperature range of 780°780°-1200 interval 11 to 10 10 kbars kbm (Bailey, 1969). The Thelower lowerstability stability limit limitfor foracmite acmitehas hasbeen been investigated investigated by by Likhoydov (1981). He Hehas hasshown shownthat thatacmite/aegirine acmitdaegirinecan canform formaccording according to tothe thereaction: reaction: 0.5 Fe203 + 2 Si02 + NaC1 + 0.5 H20 = NaFeSi2O6 + HC1 where the temperature of the reaction is very dependent on the pressure pressure and and on on the the concentration concentration of of NaCl in the solution (Fig. 1). seawater watercontains containsabout about0.5 0.5 molar molarNaC1, NaCl, Likhoydov's 1). Given Giventhat thatsea data suggest that acmite could easily form at temperatures of 200° 200°C or less at very low pressures. Acmite of possible authigenic origin have also been been reported reported from from from from the the Green Green River Formation Formation Utah (Milton and Eugster, 1959), 19591, and from Caithness, Scotland Scotland (Fortey (Fortey and and of Wyoming and Utah Michie, 1978). 1978). 61 �6kb 4kb 0.2 kb 1 kb 2 0.0 hematite hematite ±+ quartz 3000 4.00° 5(JØO Temperature T e m p t u r e (°C) (OC) Figure relative to hematite and quartz 1. Stability Stability of acmite acmite relative quartz Figure 1. (after (after Likhoydov, Likhoydov, 1981). 1981). This project is supported by the U.S. Mines—Selective Mining in Minnesota. U.S. Bureau of Mines-Selective Minnesota. REFERENCES CITED CITED Bailey, D.K., D.K., 1969, The stability stability of of acmite acmite in in the the presence presenceof of H20: H20: American AmericanJournal Journalof of Science, Science, V. 1-16. v. 267-A, p. 1-16. N.J., and Michie, U., U., 1978, Fortey, N.J., 1978, Aegirine of possible authigenic authigenic origin origin in in Middle Middle Devonian Devonian sediments in Caithness, Scotland: Mineralogical magazine,^. 42, p. 439-442. Mineralogical Magazine,v. Grout, F.F., F.F., 1946, 1946, Acmite occurrences on the Cuyuna Range: American AmericanMineralogist, Mineralogist,v. v.31, 31,p. p. 125-130. 125-130. G.G., 1981, 1981, Stability Stability of the aegirine-quartz-hematite aegirine-quartz-hematiteassociation, association,as as shown shownby by Likhoydov, G.G., data: Dokiady experimental data: DokladyAkad. Akad. Nauk. Nauk. SSSR, SSSR,v. v. 242, 242, p. p. 174-176. 174-176. H.P., 1959, Mineral assemblages of the Green River Formation, Formation, in Milton, C. and Eugster, H.P., Abelson P.H. P.H. ed., Researches Researches in in Geochemistry: Geochemistry: New York, John Wiley & Sons, p. 118-150. 118-150. 62 �ABSTRACT Accessing the the Anaconda Geological Geological Documents Documents Collection Collection Wisconsin -- Michigan Minnesota Michigan -- Ontario Ontario Minnesota -- Wisconsin Daniel Daniel N. N. Miller, Miller, Jr.1 Jr.' The International Archive of of Economic Economic Geology Geology is is a unique International Archive unique public repository and research facility available to research facility available to the the mining mining industry and industry and researchers. researchers. The central part of the the archive archive is is the the Anaconda Collection made made available Anaconda Geological Geological Documents Documents Collection available to to the the University University in 1987 1987 by by ARCO ARC0 Coal Coal Company. Company. It consists consists of 1.8 1.8 million documents documents and represents represents more than than 90 90 years years of of corporate corporate records and files files covering covering mineral mineral exploration exploration and mine mine development development records activities throughout throughout much much of of the United States States and 110 110 foreign foreign countries. countries. Others have described this this collection collection as as the the largest largest and most significant significant body of of economic economic geologic geologic data data in in the the world. world. The Anaconda Collection is a wealth of original unpublished geological material material compiled geological compiled by mining geologists, geologists, engineers, engineers, and and specialists specialists who followed followed the the original original policies policies prescribed prescribed by by Reno Reno Sales. Sales Sales establishedthe established the geological geological department H. Sales. department for for Anaconda Anaconda and was their their Chief Chief Geologist Geologist from from 1905 1905 until until he he retired retired in in 1954. 1954. Throughout his a highly Throughout his career, career, he he proved to to be be a highly competent competent administrator, organizer, organizer, and and long-range long-range planner planner who who expected expected the the administrator, staff to employ employ their their highest highest level level of of professional professional competence competence at at His all times. times. His direct, direct, systematic, systematic, analytical, and scientific scientific approach to to exploration played aa major role approach exploration played role in in the the company's company's efforts toward toward data data gathering gathering and record record keeping, keeping, coupled coupled with with peer efforts review files grew grew review of of all all work work performed. performed. As a a result, result, Anaconda's files over over the the years years and and became became the the envy envy of of the the industry. industry. 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Box Box 3924, 3924, University University Station Station Laramie, Laramie, WY 82071 82071 or call call (307) (307) 766 766 3704 3704 or or 766-6506 766-6506 or 64 �THE NEED NEED FOR FOR AANEW NEWPARADIGM PARADIGM REGARDING REGARDING THE THEPETROGENESIS PETROGENESIS OF THE THE DULUTH DULUTH COMPLEX COMPLEX MILLER, J.D., Ave., St. Paul, MN J.D., Jr., Minnesota Geological Survey, 2642 University Ave., 55114 55114 Recent Recent high-resolution high-resolution U-Pb U-Pb isotopic isotopic age age dates dates of zircons zircons from from Duluth Duluth Complex Complex intrusions rocks intrusions (Paces (Paces and and Miller, Miller, in prep.) indicate indicate that troctolitic and anorthositic anorthositic series series rocks have indistiguishable of about about 1099 (s.4-0.9) (±0.4-0.9)Ma Ma (Table (Table 1). 1). These indistiguishable crystallization ages of unexpected results results compel compel aa significant significantshift shift in in what what has has come come to to be be accepted acceptedas asthe thebasic basic paradigm of the Duluth Complex — that that itit is is predominantly composed composed of two two major major rock rock Complex series series which differ differ in parent magma types, types, emplacement emplacement styles, styles, crystallization crystallization histories, histories, and intrusive ages. With Withhis hiswork work in in the the Duluth Duluth area, area, Taylor Taylor (1964) (1964) was the first first to subdivide subdivide the the Duluth Duluth Complex Complex into into two two distinct distinctrock rock units units on on the the basis basis of of rock rock type, type, intrusive relationships, stratigraphic occurrence, and internal structure. At At Duluth, Duluth, anorthositic anorthositic gabbroic rocks occur occur as a multiple-intrusive, multiple-intrusive, structurally complicated, complicated, laminated (±olivinecumulates, cumulates, which which Taylor Taylor characterized characterizedas as an an laminated suite suite of plagioclase plagioclase (±olivine) igneous igneous breccia. AA4-km-thick, 4-km-thick,well-differentiated, well-differentiated,stratiform stratiform sequence sequence of troctolitic to ferrogabbroic rocks at Duluth and ferrogabbroic cumulates cumulates occurs occurs below the cap of anorthositic anorthositic rocks and has has been been termed termed the the layered layered series. series. Detailed revealed many of the characteristic Detailed mapping mapping elsewhere elsewherein in the complex complex revealed characteristic features features of the two rock suites defined defmed at Duluth. With With the the publication publication of the MGS Centennial Centennial Volume Volume in in 1972, 1972, which included included summaries summaries of this mapping, the terms anorthositic anorthositic series series and troctolitic series acquired a semi-formal status as a chronolithologic and troctolitic series acquired semi-formal status chronolithologic classification. The The genetic genetic implications implications of this this classification classificationwere were first incorporated incorporatedinto into aa petrologic petrologicmodel modelby by Weiblen Weiblen and and Morey Morey (1980) (1980) who postulated that the older anorthositic series was produced from quartz quartz tholeiitic tholeiitic basalt, aa composition composition common common among among early early rift rift lavas, lavas, by flotation flotation of from plagioclase chambers. They plagioclase and sinking sinking of mafic minerals in Duluth Complex chambers. They further further suggested tholeiite parent magma, suggested that that the rocks rocks of the troctolitic troctolitic series series formed from olivine tholeiite aa common emplacedand and common composition compositionamong amongyounger youngerrift rift lavas, lavas, which which had had been been emplaced fractionally fractionally crystallized crystallized in in chambers chambersbetween between the the anorthositic anorthositicseries series cap cap and and its its ultramafic ultramafic base. Most Mostrecently, recently,Miller Millerand andWeiblen Weiblen(1990) (1990)showed showedthat thatboth bothseries seriescould couldhave havebeen been produced produced from fromaa common commonprimary primary magma magma of of high-Al high-A1olivine olivine tholelite tholeiite composition composition and and suggested that the major difference difference between their parent magmas was the amount amount of suggested intratelluric plagioclase plagioclase crystals crystals which they contained contained upon emplacement emplacementinto into the the Duluth Duluth intratelluric Complex. They Theyconcluded concludedthat thatstructurally structurallycomplex complexanorthositic anorthositicrocks rocks were were formed formedfrom from gabbroic gabbroic magmas magmas charged charged with with as as much much as as 60% 60%plagioclase plagioclase creating creatingviscous viscouscrystal crystal mushes, whereas whereasthe the well-differentiated well-differentiatedtroctolitic troctolitic series series rocks rocks fractionally fractionally crystallized crystallized from from mushes, crystal-poor magmas. magmas. Miller Millerand andWeiblen Weiblenhypothesized hypothesizedthat thatcrystal crystalmushes musheswere wereproduced produced crystal-poor early in in the the evolution evolution of of the the Midcontinent Midcontinentrift rift when when magmas magmas tended tended to to pond pond in in lower lower crustal crustal early chambers plagioclase flotation. flotation. As chambers where high pressure would have promoted plagioclase As rifling rifting progressed, crustal crustal magma magma chambers chambers were were thought thought to to have have migrated migrated to to shallower shallowerdepths depths progressed, and and become become more more open open to to recharge recharge and and expulsion, expulsion, thereby thereby producing producing less less evolved evolvedand and less less crystalline magmas. The Theideas ideascommon commonto toboth both these these models, models, that that anorthositic anorthositic series series rocks crystalline were significantly significantly older older than than troctolitic troctolitic series series rocks and and that each each series series was related to to aa were particular stage stagein in the the tectonomagmatic tectonomagmaticevolution evolution of of the the rift, rift, were were not not based based on on definitive definitive particular Rather, they they were were constructs constructs that explained the observable differences evidence. Rather, differences in the internal structure, structure, modal modal mineralogy, mineralogy, cumulus cumulus texture, mode of crystallization, crystallization,and areal areal internal distribution distribution of the two series. ItItnow now appears appearsfrom from the the age age dates dates that the the anorthositic anorthositic and and troctolitic 1086 troctolitic rocks rocks evolved evolvedwithin withinaavery veryshort shorttime timeinterval intervalin inthe the22-million-year 22-million-year(1108(1108-1086 Ma) rift Ma) magmatic magmatichistory historyof ofthe theMidcontinent Midcontinentrift. Field evidence evidencefor for the the relative relative ages ages of of the the two two series series extends extends from from that that which which clearly clearly Field shows the the anorthositic anorthositicseries series to to be be the the older older to to that which would best be be classified classified as as shows 65 �ambiguous. ambiguous. In Inthe thedefinitive definitivecategory categoryare are1) 1)inclusions inclusions of anorthositic anorthositic rock in troctolitic/gabbroic troctoliticlgabbroicrocks rocks and and the the absence absence of the the reverse, reverse, and and 2) 2) sharp sharp intrusive intrusivecontacts, contacts, rarely rarely chilled, chilled,between between troctolitic/gabbroic troctolitic/gabbroic rocks rocks and and anorthositic anorthositic rocks. Not Notdefinitive definitiveare are contacts contacts between between troctolitic troctolitic and and anorthositic anorthositicrocks rocks described described as as obscure, obscure, ambiguous, ambiguous,or or hybrid Beltrame, 1974; Miller, 1986). Still Still hybrid zones zones of mixing (Taylor, (Taylor, 1964; Phinney, 1972; Beltrarne, other other evidence, evidence, such such as as the the presence presence of conformable conformable anorthositic anorthositic layers layers in stratiform stratiform troctolitic intrusions intrusions (Foose (Foose and and Cooper, Cooper, 1978; 1978;Bonnichsen, Bonnichsen, 1972; 1972; Phinney, Phinney, 1969), 1969),the the commonly commonly leucocratic leucocratic composition of many troctolitic troctolitic rocks, and the successive emplacement emplacement of of gradually gradually less less plagioclase-rich plagioclase-rich mushes mushes in in the the creation creationof of some someanorthositic anorthositic series series suites suites (Miller, (Miller, 1986), 1986), suggest suggest that the transition from anorthositic (crystal mush) to troctolitic (magma-dominated) (magma-dominated) magmatism was gradational. Whereas Whereas these these more more ambiguous field relations tended to be overlooked or dismissed as minor ambiguous field relations to overlooked dismissed as minor complications complications to to the the general general picture picture of two-stage two-stage magmatism, magmatism, they are are now seen seen as as being being consistent consistentwith with the the approximate approximatecontemporaneity contemporaneityimplied impliedby by the theage agedata. data. Under Under the the tighter tighter time time constraints constraints imposed imposed by by the the age age dates, dates, several severalnew new or or modified modified models models must must be be developed developed and and tested tested to to explain explain the petrogenesis petrogenesis of the anorthositic anorthositic and and troctolitic troctolitic series. Some Somepossibilities possibilities include: include : -the the two two series series represent represent a rapid progression from emplacement emplacement of plagioclaseplagioclase— enriched enrichedmushes mushesto to magma-dominated magma-dominatedintrusions intrusionsthat thatcould couldreflect reflectthe theevolutionary evolutionary stages stages of a lower lower crustal crustal staging staging chamber chamber from from which which progressively progressivelyless lesscrystal-rich crystal-rich magmas were tapped. Such be caused caused by flushing flushing of the staging Suchan an evolution evolution may may be chamber chamber brought brought on on by by frequent frequentrecharge recharge and andexpulsion. expulsion. —the -the two two series seriesrepresent represent the the products products of different different magma magma processes, processes, perhaps perhaps related related to crystallization shallow emplacement emplacement into crystallizationat at different different crustal crustal depths depths prior to shallow into the the Duluth Complex, which acted concurrently concunently on a common primary primary magma magma type. type. Polybaric Polybaric fractionation fractionation in multi-tiered staging staging chambers has been proposed to explain the compositional compositional range range observed observed in many Keweenawan hypabyssal and volcanic rocks (Klewin, (Klewin, 1989; 1989;Jerde, Jerde, 1991). 1991). -the the two two series series were were produced from from aa common common parent magma magma moderately moderately enriched enriched in in — plagioclase plagioclase crystals crystals by by flotation flotation or or flow concentration of the entrained plagioclase into the roof zone zone of the Duluth Duluth Complex, and subsequent subsequent fractional fractional crystallization crystallization of the the crystal-poor crystal-poor magma below the anorthositic cap. Such Suchaa model model has has been been used used to to explain explain the gabbroic gabbroic and and overlying overlying stratiform stratiform anorthositic anorthositic rocks of the Keweenawan Keweenawan Mineral Mineral Lake Lake intrusion intrusion of of the the Mellen Mellen Complex Complex in in Wisconsin Wisconsin(Olmsted, (Olmsted,1968) 1968)and andthe the plagioclase-rich plagioclase-rich upper upper parts parts of of the the Logan Logan Sills Sills in in northern northern Minnesota Minnesota (Phinney, (Phinney,1968). 1968). Although do not not refute the the possibility possibility that the anorthositic anorthositic Although the the results results of of the the age age dates dates do rocks rocks are are slightly slightly older older than than the the troctolitic/gabbroic troctoliticlgabbroicrocks, rocks, within the the resolution resolution of of the the dating dating (1.5 (1.5 Ma), Ma), the the very very similar similarcrystallization crystallization ages ages for for the two two suites suites strongly strongly suggests suggestsaa common Duluth Complex. Complex. Therefore, the twocommon petrogenesis over a large portion of the Duluth series series classification classification may may be be aa misleading misleading representation representation of the intrusive intrusive history history of the the complex complex and and should should perhaps be abandoned. With With more more high-resolution high-resolution dating dating of Duluth Complex Complex intrusions, intrusions, especially especially among among the the many many discrete discrete layered, layered, troctolitic/ troctolitic/ gabbroic gabbroic intrusions intrusions now now classified classified as as being being part part of the the troctolitic troctolitic series, series, the the two two series series chronolithologic further. Other chronolithologic classification classification may unravel still further. Other age age dates (Table (Table 1) 1) from this study study indicate indicate that that magma-dominated magma-dominated intrusions intrusions producing producing troctolitic/gabbroic troctoliticlgabbroic rocks preceded preceded and and postdated postdated the the 1099 1099 Ma event in other areas of the complex. Also, Also,the the multiple troctoliticl gabbroic and anorthositic rocks and the variety multiple intrusive intrusive nature nature of both troctolitic/ of contact contact relationships relationships observed observed between them imply extended and overlapping periods of both crystal mush and magma-dominated types of magmatism. magmatism. While Whilethe the validity validity of of the the series designations designations awaits geochronologic verification, an even more compelling reason awaits geochronologic verification, an even more compelling reason to to abandon abandon the the chronolithologic chronolithologicclassification classificationat at this this time time is is that that itit will will free free future futurepetrologic petrologic and field studies studies of the bias imposed imposed by its genetic genetic implications. implications. 66 �________ REFERENCES CITED CITED Beltrame, Beltrame, R.J., 1974, 1974,Field Field mapping mapping in in the the Duluth Duluth Complex: Complex: Gabbro Gabbro Lake Lake quadrangle, quadrangle, northern northern Minnesota: Minnesota Geological Geological Survey Open-file Open-file Report, 29 p. Bonnichsen, Bonnichsen, B., 1972, 1972, Southern Southern part of Duluth Complex, Complex, in Sims, Sims, P.K., P.K., and Morey, Morey, G.B., eds., eds., Geology Geology of Minnesota: AACentennial Centennialvolume: volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey,p.p. 361-387. 361-387. Foose, Foose, M.P., and and Cooper, Cooper, R.W., 1978, 1978, Preliminary geologic report on the Harris Lake area, northeastern Minnesota: U.S. 24 p. U.S.Geological GeologicalSurvey SurveyOpen-File Open-FileReport Report 78-385, 78-385,24 p. Jerde, Midcontinent Rift, Jerde, E.A., 1991, 1991,Geochemistry and petrology of hypabyssal rocks associated with the Midcontinent northeastern Ph.D. thesis, University of California, Los Angeles, Angeles, 305 305 p. northeastern Minnesota: Unpublished Unpublished Ph.D. Kiewin, K.W., 1989, Polybaric fractionation in an evolving continental rift: Evidence from the Klewin, 1989, rift: Evidence from the Keweenawan Keweenawan Midcontinent Midcontinent rift: Journal Journalof of Geology, Geology,v. v. 97, 97,p. p. 65-76. 65-76. Miller, J.D., Jr., 1986, 1986, The The geology and petrology of anorthositic rocks in the Duluth Complex, Snowbank Snowbank Lake Lake quadrangle, quadrangle, northeastern northeastern Minnesota: Unpublished Unpublished Ph.D. Ph.D. thesis, thesis,University Universityof of Minnesota, Minnesota, Minneapolis, Minneapolis, 280 280 p. p. Miller, J.D., Jr., and and Weiblen, Weiblen, P.W., P.W., 1990, 1990, Anorthositic rocks of the Duluth Complex: Examples Examplesof ofrocks rocks formed 39. formed from plagioclase plagioclase crystal mush: Journal Journalof ofPetrology, Petrology,v.v.31, 31,p.p.295-3 295-339. Olmsted, J.F., 1968, 1968,Petrology Petrology of of the the Mineral MineralLake Lake intrusion, intrusion, northwestern northwesternWisconsin, Wisconsin, in in Isachsen, Isachsen,Y.W., Y.W., Olmsted, LF., ed., The Science Service The origin origin of anorthosite anorthosite and related rocks: New York State Museum and Science Memoir Memoir 18, 18,p. p. 149-161. 149-161. Paces, J.B. and Miller, J.D., J.D., Jr., in prep., Precise U-Pb ages of Duluth Complex and related mafic intrusions, intrusions, northeastern northeastern Minnesota: Minnesota: Submitted Submitted to Journal Joumal of of Geophysical Geophysical Research Research 4/92. 4/92. Phinney, Phinney, W.C., W.C., 1968, 1968,Anorthosite Anorthositeoccurrences occurrencesin in Keweenawan Keweenawan rocks rocks of of northeastern northeastern Minnesota, Minnesota, in in Isachsen, Isachsen, Y.W., Y.W., ed., The The origin origin of anorthosite anorthosite and and related related rocks: New York York State StateMuseum Museumand and Science Science Service ServiceMemoir Memoir 18, 18,p. p. 135-147. 135-147. 1969, The Minnesota: Minnesota ,1969, The Duluth Complex in the Gabbro Lake quadrangle, Minnesota: Minnesota Geological Geological Survey 20 p. Survey Report Report of Investigations Investigations 9, 9,20 p. ,1972, 1972,Northwestern Northwestern part of Duluth Complex, in in Sims, Sims,P.K., P.K., and and Morey, Morey, G.B., G.B., eds., eds., Geology Geology of Minnesota: AACentennial Centennialvolume: volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey, p. 335-345. Taylor, Minnesota: Minnesota Taylor, R.B., 1964, 1964,Geology Geology of the Duluth gabbro complex near Duluth, Minnesota: Minnesota Geological 63 p. Geological Survey Survey Bulletin Bulletin 44, 44.63 Weiblen, Weiblen, P.W., and and Morey, Morey, G.B., G.B., 1980, 1980, A A summary summary of the the stratigraphy, stratigraphy, petrology, and and structure structure of the the Duluth Complex: American AmericanJournal Journalof of Science, Science,v. v. 280-A, 280-A, p. p. 88-133. 88-133. ------------------------ Table Table1.1.Summary Summaryof ofU-Pb U-Pbage agedates datesof of zircon zircon and and baddeleyite baddeleyite from from Duluth Duluth Complex Complex and and inprep.). prep.). related intrusive intrusiverocks rocks(from (fromPaces Pacesand andMiller, Miller,in related Samule Sample Rock Rock Unit Unit Location Location FC1 FCl Anorthositic Anorthositic Series Series Forest Forest Center Center AS3 AS3 Anorthositic Anorthositic Series Series Duluth Duluth area area 1099.2±0.4 1099.2k0.4 55 P02 PG2 Troctolitic Troctolitic Series Series Powerline Gabbro Gabbro Troctolitic Troctolitic Series Series upper upper layered layered series series Nathan's Lay. Series Series Basal Basalcontact contactUnit unit df Beaver Beaver Bay Bay Complex Complex Sonju Sonju Lake Intrusion Intrusion BeaverBayComplex Beaver Bay Complex Silver Silver Bay Intrusions Intrusions Dunka area Dunka R. area 1098.6±0.5 1098.6*0.5 88 Duluth Duluth area area 10993±0.3 1099.3k0.3 66 Gunflint Gunflint Trail Trail 1106.9k0.4 1106.9±0.4 55 Finland Finland 1096.1±0.5 1096.lkO.5 44 SilverBay Silver Bay 1095.8±1.1 1095.8kl. 1 66 Dl Dl NLS5 NLS5 SLI1 SLIl SBG2 SBG2 207m206?b age ace 207EhL206Pb 1099.0±0.3 1099.0k0.3 Analyses Analvses 55 67 �RARE EARTH ELEMENT ELEMENT DISTRIBUTION DISTRIBUTION PATTERNS IN EARLY EARLY PROTEROZOIC WON-FORMATIONS IRON-FORMATIONS OF THE PENOKEAN PENOKEAN OROGEN, EASTEASTCENTRAL MINNESOTA MINNESOTA Morey, G.B., G.B., and Terrence J. J. Boerboom, Minnesota Minnesota Geological Geological Survey, 2642 2642 University Paul, MN MN 55113 55 113 Avenue, St. Paul, Minnesota consists consists of of two two major components, components, an The Penokean orogen in east-central Minnesota allochthonous fold-and-thrust fold-and-thrust belt on the southeast allochthonous southeast and one or more more tectonic tectonic foredeeps foredeeps on on the the terranes northwest. The The fold-and-thrust fold-and-thrust belt consists consists of several discrete structural panels or krranes that have have small-scale small-scale features consistent with large-scale northwestbounded by cliscontinuities discontinuities that northwestnappes. Correlations panels are are impossible. impossible. The fold-and-thrust belt belt flanks flanks aa verging nappes. Correlations between the panels tectonic foredeep which extended to the Mesabi Mesabi range range in in northern northern Minnesota Minnesota and and the the Gunflint Gunflint range range in Ontario. Ontario. Although structural structural details are complicated, complicated, the orogen orogen also also can can be be divided divided into into an an early early extensional phase when sedimentary rocks, including iron-formation, iron-formation, were deposited deposited on a extensional southward-facing continental margin, and a subsequent subsequent compressional compressional phase when these and metamo~hosed metamorphosed and and when when one one or or more more northwardnorthwardcontinental-margin deposits were folded and migrating foredeep foredeep basins were partly filled fdled with iron-formation, iron-formation,as as well well as as detritus detritus derived derived from from both the north and the south. The The fact fact that that iron-formation iron-formationwas was deposited depositedduring during both both extensional extensional and compressional phases of the Penokean orogeny is is of considerable considerablesedimentological sedimentological significance. significance. persisted in in east-central east-centralMinnesota Minnesota from from approximately approximately 2200 2200 Extensional tectonic conditionspersisted m.y. m.y.. Bodies m.y. to about 1900 m.y.. Bodies of of iron-formation iron-formation deposited deposited during during that that interval interval include include those those in in range, the the Trommald Trommald Formation Formation of of the Cuyuna North range, Glen Township, the Cuyuna South range, Philbrook area. The and the Philbrmk The first frst two units units have sedimentological features indicative of "Algomatype" iron-formation, features indicative indicative of iron-formation,whereas whereas the latter two units have mineralogical features hydrothermal-fumarolic hydrothermal-fumarolicprocesses. m.y. to 1870 m.y. and iron1870 may. Compressional tectonic conditions persisted from about 1900 m.y. during that that time time are are assigned assigned to tothe theAnimikie AmmikieGroup. Group. They include the formations deposited during respectively, and the Biwabik and Gunflint Iron Formations of the Mesabi and Gunflint ranges, respectively, A of of the the Ruth Ruth Lake Lake area areain inthe theEmily Emilydistrict. district. These units units of of iron-formation iron-formation have have so-called unit A of "Iake "Lake Superior-type" iron-formations. sedimentological attributes indicative of of 95 95 REE REE analyses. analyses. In general, Algoma-type iron-formations have We report here the results of moderate REE abundances (La = =0. lx-0.9 xx 1986 0.1~-0.9 1986North North American American shale shale composite--NASC), composite-NASC), and and generally flat to somewhat are generally somewhat depleted depleted in the the heavy heavy elements elements (most (most La/Ybn M b n == 11 - 3). In addition, addition, iron-formation from Glen Township Township has consistently larger negative Ce anomalies anomalies (most CdCe*n Ce/Ce*n iron-formation = 0.65 = 0.65 -- 0.90), whereas iron-formation from the Cuyuna South Range has small negative to (Ce/Ce*n = 0.82 -- 1.04). Both units have positive Eu anomalies (most positive Ce anomalies (CdCe*n EuIEu*n Philbrook iron-formations EuEu*~ = 1.1 -- 1.5). 1.5). The Trommald Trommald and Philbrmk iron-formations have REE concentrations that = 0.1 x-lx are similar to the Algoma-type iron-formations ((La La = x- l x1986 1986NASC). Rocks Rocks associated associated Philbrook iron-formations iron-formations have with the Philbmk have generally generally flat flat REE RIB patterns patterns (most (most La/Ybn LdYbn == 0.7 -- 1.9) and consistent negative Ce anomalies (Ce/Ce*n = = 0.73 - 0.93). In contrast those from the Trommald 1 -3) HREE-depletedpatterns patterns(most (mostWYbn La/Yb = =1 3) and and both both positive and negative Ce Formation have HREE-depleted anomalies (Ce/Ce*n = = 0.58 -- 1-24], 1.24), relative to the 1986 NASC standard. Iron-formations of the wide range rangeof of REE REEabundances. abundances. In the the Biwabik Biwabik Iron lion Formation, slaty Animikie Group display aa wide = 0.5 x 1986 (La == 0.1 0.1 -- 0.5 1986 NASC) than the cherty units (Lan = units contain larger concentrations concentrations (La standard). The 0.09 - 0.1 x 1986 1986 NASC American shale standard). The slaty units are slightly HREE-depleted (most W La/Ybn Ybn = = 1.06 1-06-- 1.71), 1.71), whereas the cherty units have flat to slightly HREE-enriched slopes slopes = 0.75 - 1.18). In general both show very small, both positive and negative Ce Ce anomalies anomalies ( W b n= (La/Ybn (Ce/Ce*n = = 0.8 -- 1.6) and positive Eu anomalies anomalies (most (most EuIEu*n E u E u *= = ~ 1.2 -- 2.0). The Emily (Ce/Ce*n = 0.32 - 0.87) Formation, on the other hand, shows pronounced negative Ce anomalies (CdCe*n 68 �0.4 x - 2.0 x 1986 and higher total total REE REE(most (mostL.a L a = 0.4 1986 NASC, but have similar similar slopes slopes and and positve positve Eu Eu anomalies anomalies to the other foredeep iron-formations. Although small local differences exist, broad similarities in the REiE REE data imply that tectonic setting was not lbther the data imply that not particularly particularly important important in in iron-formation iron-formation sedimentationsedimentation. Rather the various units of iron-formation were deposited from from aa compositionally compositionally homogeneous homogeneous reservoir reservoir that persisted over at least 150 m.y. m.y. of of geologic geologictime. time. However the general lack of pronounced pronounced Ce anomalies and the presence of positive Eu anomalies implies that the reservoir reservoir was not simple "ocean watern, water", but rather had a "hydrothermal" component. "hydrothermalt' The project was supported in part by the U.S. U.S. Bureau of Mines Selective Mining Mining in Minnesota Minnesota Minerals Initiative and the Minnesota Minnesota Department Department of of Natural Natural Resources, Resources, Division Division of of Minerals, Public Geologic Sample Sample Program. 69 �EVIDENCE OF AN EXHALATIVE CONTRIBUTION TO THE EVIDENCE EXHALATWE CONTRIBUTION THE MANGANESE MANGANESE MINERALOGY OF OF THE TROMMALD FORMATION, CUYUNA CUYUNA IRON IRON RANGE, RANGE, EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA and Jane Jane M. M. Cleland, Minnesota Minnesota Geological Survey, 2642 Morey, G.B. Peter L. McSWIGGEN, and 55114 University Aveune, St. Paul, Minnesota 55 114 The The Trommald Trommald Formation Formation on the the Cuyuna Cuyuna North range range in east-central Minnesota Minnesota was a major major producer producer of iron iron ore for for 80 80 years. Between Betweendiscovery discoveryin in1904 1904and andclosing closingin in 1984, 1984,the therange range shipped more than 106 106 million tons, much of which which was was ferromanganese ferromanganeseore orethat that contained contained5-15 5-15 percent percent manganese. ItItisisthat that manganese manganesecomponent componentthat that sets sets the the Cuyuna Cuyuna range apart from fkom other Early iron-mining districts k l y Proterozoic iron-mining districts in the lake Superior Superior region. interpretations assumed that the ferromanganese ferromanganese ores Until very recently, most geologic interpretations ores were were formed through formed through the oxidation oxidation and and leaching leaching of a "green "green carbonate carbonateslate" slate" protolith protolith located locatedat at or or near near aa granular) and and thin-bedded thin-bedded (slaty, (slaty, non-granular) non-granular) ironirontransition between thick-bedded (cherty, granular) formation. These Thesetwo two lithofacies lithofacies were were thought to represent considerably different sedimentological regimes, the thin-bedded rocks deposited "deeper" water below wave base under mildly regimes, the deposited in "deeper" reducing conditions the thicker bedded rocks reducing conditions the thicker rocks deposited deposited near near or or above above wavebase wavebaseunder under oxidizing oxidizing conditions. In Inthat thatmodel, model, the the distribution distributionof of the the ferromanganese ferromanganeseores ores would would have have been controlled controlled by the configuration of the Trommald depositional basin. the pretectonic paleogeographic configuration paragenesis of the In an effort to better understand the paragenesis the ferromanganese ferromanganeseores, ores, we we reexamined reexamined core h m a hole drilled drilled on the property of the Merritt Number 2 mine in the northwestern part of core from been in storage since the the the North range. The The site site was was one one of four drilled in 1942 1942 and the core has been 1 950s. The The Menitt Merritt core core is is of of particular particular interest because because it intersects the entire Trommald Trommald 1950s. Formation carbonate slate." Formation in the the vicinity of unaltered "green carbonate We focus here on observations fiom from the thick-bedded upper part of the iron-formation. structures are an important component of the cherty rocks. rocks. They They were were thought thought by by Grout Grout Spherical stmctures (1946) jasper and (1946) to to be oolites oolites or or pisolites pisolites consisting consisting of jaspa and chert chert rims rims concentrically concentricallysurrounding surrounding cores acmite. In cores of quartz, feldspar, or acmite. In reality reality these these spheroids spheroids are far more complex than envisioned by Grout. The Thetypical typicalspheroid spheroidcontains containsaa clast clast at at its its center, center, surrounded surrounded by bands of lateral mineral growth. Both variety of of Both the the central central cores cores and and the associated associated rim material consist of aa variety minerals and/or hematite. hematite. Very minerals including acmite, rhodonite, rhodochrosite, Ba-feldspar, andor Very little little free k e quartz has been found; material previously thought to be jasper jasper consists mostly mostly of of rhodonite rhodomte or quartz acmite. acmite. Some spheroids Some spheroids have fairly simple simple mineralogical and textural textural attributes, attributes, but others others are are very very include: clasts complex. Some Someof the the observed complexities include: clasts of Ba-feldspar surrounded by rhodochrosite; rhodonite surrounded surrounded successively by hematite, Ba-feldspar and and ultimately ultimately rhodochrosite; rhodochrosite; rhodochrosite; clasts clasts of rhodonite rhodonite surrounded surrounded by rhodochrosite; rhodochrosite; clasts clasts of of acmite acmitesurrounded surroundedby by red red cherty-looking acmite; clasts of of rhodonite rhodonite surrounded by by red red cherty-looking cherty-looking rhodonite; rhodonite; clasts clasts of of cherty-looking Mn-oxide rhodochrosite surrounded Mn-oxide surrounded surrounded by acmite; acmite; clasts clasts of rhodochrosite surrounded by acmite; clasts of rhodochrosite rhodochrositesurrounded surrounded by hematite, hematite, which in in turn is is surrounded surrounded by rhodochrosite. rhodochrosite. Most of the minerals acmite which was ffirst by Grout ~ sdescribed described t Grout minerals described described above, other than acmite (1946), have not been been reported reported previously previouslyfrom fromthe theTrommald TrommaldFormation. Formation. Of particular interest is is (19461, the Ba-feldspar which also occurs in veins with rhodonite and carbonate, carbonate, and and as as a secondary secondary mineral surrounding grains grains of of stoichiometrically stoichiometricallypure pure K-feldspar. K-feldspar. The composition of the Bamined feldspar in these rocks varies from fiom about about 10 10to to 22 22 mole mole percent percent BaA12Si2O8. BaAl2Si2Og. been reported reported from from only only aa few few llocalities inthe theworld. world. Much of it is associated associated Ba-feldspar has been d i t i e s in deposits andor and/or Pb-Zn with deposits inferred to be of exhalative origin, including manganese deposits deposits. These These include includeBroken Broken Hill, Hill, New South South Wales Wales (Segnit, (Segnit, 1946), 19461,southern southern Grampian Grampian Highlands, Highlands, Scotland (Coats (Coats and others, 1984; Fortey and Beddoe-Stephens, 1982), 1982), central North 70 �Greenland (Jakobsen, 1990), 19901, Sweden (Bostrom and others, 1979; Lundstrom and Wadsten, 1979), Japan (Nakano, 19791, 1979), Wales Wales (Smith and others, 1949), Namibia Namibia (Vermaas, 1953), 19791, Japan 19531, and Greece (Reinecke, 1982). Stratiform Stratiform tourmalinites tourmalinites and barite veins also exist on the North range, hydrothermal component for the origin of these and are additional evidence for a fumarolic hydrothermal deposits. This project is supported by the U.S. U.S. Bureau of Mines-Selective Mines—Selective Mining in Minnesota. Minnesota. REFERENCES CITED CITED Boström, Bostrom, K., K., H. Rydell, and 0. 0.Joensuu, Joensuu,1979, 1979,Lângban—an LAngban-an exhalative sedimentary sedimentary deposit: Ecomonic Ecomonic Geology, Geology, v. 74, 74, p. 1002-1011. 1002-1011. J.S., N.J. NJ. Fortey, Coats, J.S., Fortey, N.J. N.J. Gallagher, and A. Grout, 1984, 1984, Stratiform barium Dalradian of of Scotland: Scotland: Economic enrichment in the Dalradian Economic Geology, Geology, v. 79, p. 1585-1595. 1585-1595. NJ., and Fortey, N.J:, and B. B. Beddoe-Stphens, Beddoe-Stphens, 1982, 1982,Barium Barium silicates silicatesin in stratabound stratabound Ba-Zn Ba-Zn mineralization in the Scottish Dalradian: Mineralogical Mineralogical Magazine, Magazine, v. 46, p. 63-72. p. F.F., 1946, Acmite Acmite occurrences occurrences on on the the Cuyuna Cuyunarange, range,Minesota: Minesota: American Grout, F.F., Mineralogist, Mineralogist, v. 31, 3 1, p. 125-130. 125-130. Jakobsen, U.H., 1990, 1990, A hydrated barium silicate silicate in umetamorphosed umetamorphosed sedimentary sedimentary rocks of central North Greenland. Mineralogical MineralogicalMagazine, Magazine,v. v. 54, 54, p. p. 81-89. 8 1-89. Lundström, Lundstrom, I., and T. Wadsten, 1979, 1979, Barium feldspar feldspar from Lillsjön, Lillsjon, southern southern Sweden: Sweden: 101, p. 229-232. 229-232. Geologiska Foreningens i Stockholm Forhandlingar, Forhandlingar, v. 101, barium microcline, microcine, hyalophane Nakano, S., 1979, Intergrowth of barium hyalophane and and albite albite in the the barium-containing alkali alkali feldspar feldspar from from the the Noda-Tamagawa Noda-Tamagawa mine, mine, Iwate Iwate Prefecture, Prefecture, Japan: Mineralogical Mineralogical Journal, Journal,v. v. 9, 9, p. p. 409-416. 409-416. Reinecke, Cymrite and celsian in manganese-rich metamorphic Reinecke, T., 1982, 1982, Cynxite metamorphicrocks rocks from from Andros Island/Greece: Contributions Contributionsto to Mineralogy Mineralogy and and Petrology, Petrology, v. 79, p. 333-336. 333-336. Segnit, E.R., E.R., 1946, 1946, Barium-feldspar from from Broken Broken Hill, Hill, New New South SouthWales: Wales: Mineralogical Magazine, v. 27, p. 166-174. Mineralogical 166-174. Smith, W.C., W.C., F.A. F.A. Bannister, and M.H. M.H. Hey, Hey, 1949, Cymrite, a new barium mineral from the Benallt manganese mine, mine, Rhiw, Rhiw, Carmvonshire: Carnarvonshire: Mineralogical 1. Magazine, v. 28, 28, p. p. 676-68 676-681. F.H.S., 1953, A new occurrence of of barium-feldspar barium-feldspar at Otjosondu, SouthVermaas, F.H.S., Africa, and an X-ray method for determining determining the composition of West Afica, hyalophan: American AmericanMineralogist, Mineralogist,v. v. 38, 38, p. 845-857. 845-857. 71 �HIGH TEMPERATURE TEMPERATURE HYDROTHERMAL ALTERATION ALTERATION OF Cu-Ni SULFIDES, ASSOCIATED WITH WITH PGE PGE ENRICHMENT ENRICHMENT OF SULFIDES, DUNKA ROAD, ROAD, DULUTH COMPLEX, COMPLEX, NE NE MINNESOTA Penelope Morton Morton and Stephen D. Geerts Penelope Geerts Department of Geology Geology University of Minnesota-Duluth Minnesota-Duluth Duluth, 5581 2 Duluth, MN, 55812 The Dunka Road Cu-Ni deposit deposit occurs occurs at at the base of of the Partridge River Intrusion Road Cu-Ni (PRT)within within the the 1.1 Ga Ga Duluth Duluth Complex. Complex. The The deposit deposit is approximately approximately 55 km by 1.25 km (PRT) km areal extent. extent. Relogging Relogging of of 80 80 drill drill holes holes has has identified identified seven seven major major lithologic lithologic units that in areal can be correlated correlated over over the the whole whole deposit deposit as as well well as as 27 km along along strike within within the thePRT PRT (Geerts, 1991; 1991; Severson (Geerts, Severson and and Hauck, Hauck, 1990). 1990). All All units units (I (I through through VII) VII) are are primarily primarily composed of troctolitic troctolitic anorthosite anorthositeto t opyroxene pyroxenetroctolite troctoliteand andininlesser lesseramounts, amounts, gabbroic gabbroic anorthosite and and olivine olivine gabbro. gabbro. Units Units 11,II, VI VI and VII have basal ultramafic units; and VII basal ultramafic units; other other anorthosite contacts between between units units have have been been interpreted interpreted on the basis basis of of other other mineralogical mineralogical and and textural differences (Figure 1). differences (Figure 1). About 90% 90% of of the the total totalsulfide sulfide mineralization mineralization occurs within Unit Unit I.I. It is interstitial and widespread, widespread,however howeveritit varies variesinin mode modefrom from rare rareup uptto and o 55% % and and it also also varies varies in in continuity and 0 cm tto m. Major and thickness from 110 o 1100 m. Major sulfide minerals minerals include include pyrrhotite, chalcopyrite, minor cubanite. cubanite. These are usually usually primary. primary. Minor amounts chalcopyrite, pentlandite and minor These are of bornite, bornite, native native copper, copper, sphalerite, sphalerite, galena, galena, pyrite, pyrite, talnakhite talnakhite and and mackinawite mackinawite or or valleriite occur throughout unit I and textures indicate that in most cases these minerals valleriite unit I and textures indicate that in most cases these minerals tend to t o replace replace the the primary primarymineral mineralassemblage. assemblage. Three CuIPGE Cu/PGE enriched enrichedhorizons horizonshave havebeen beenidentified identifiedwithin within unit II (Geerts, (Geerts, 1991), 19911, This horizon occurs of which whichhas hasbeen beencalled calledthe theRED RED horizon. horizon. horizon occurs the most most continuous continuous of directly ultramafic layer layer (lla, (Ila, Figure Figure 1) 1) in in the the uppermost portion of of unit directly beneath beneath ultramafic uppermost portion unit I.I. ItIt ranges from 33 tto averageCu Cucontent contentofof 0.57% 0.57% and and Pt Pt+Pd ranges from o 10 10 m m thick and and contains an average Pd recognized in in 887% contents of 991).1. It has been recognized of 986 986ppb ppb(Geerts, (Geerts,11991 7 % of the the holes holes logged. logged. Texturally than the the rest of unit Texturally this zone zone is is more more coarse-grained coarse-grained than unit I and contains more more secondary sulf ides that elsewhere in the section. For example bornite, pyrite, sphalerite, example bornite, sphalerite, secondary sulfides that elsewhere in the section. galena and native copper copper have have only only been recognized recognized in in the the enriched enriched zones, zones, in particular particular galena and the RED RED zone. both below Detailed logging, logging, both below and and above above the RED RED horizon horizon shows shows that the the predominant host rock, rock, anorthositic anorthositic troctolite, troctolite, exhibits predominant host exhibits subtle subtle fracturing fracturing and and alteration. alteration. Plagioclase has been been saussuritized, saussuritized,pyroxene pyroxeneisis now now greenish Plagioclase has greenish uralite uralite and and olivine olivine is abovethe the RED REDisisalso alsoserpentinized. serpentinized.The The majority majority of the ll(a) above the serpentinized. Olivine Olivine in inUnit Unit11(a) sulfide itself is sulfide is coarse-grained coarse-grained (5 mm) mm) and and commonly commonly rimmed by secondary secondary red-brown red-brown biotite. biotite. Plagioclase Plagioclaseboth bothinside insideand and outside outside of of this thiszone zone is is cumulus, cumulus, occurring occurringas asanhedral anhedral tabular tto crystals. The varies from from 2 to tto o subhedral, subhedral, tabular o lath-shaped lath-shaped crystals. The average average grainsize grainsize varies t o 66 mm throughout all the the troctolitic rocks throughout all rocks (Units (Units I-VII), 1-VII), however however within the the red red zone zone the the grainsize increases tto 4-10 1 0 mm. mm. grainsize increases o 4Plagioclase in in 50% 50% of of the samples throughout the section contains Plagioclase samples throughout contains reddish-black reddish-black Within the RED zone, where plagioclase is in contact needle-like inclusions. inclusions. the RED zone, where plagioclase is in contact with finefinegrained secondary sulfides (in particular bornite and remobilized remobilized chalcopyrite), chalcopyrite), the the needles needles are absent from the edges of the plagioclase. plagioclase. Where Where the the needles needles are are absent in a particular plagioclase crystal, crystal, the plagioclase plagioclase plagioclase shows undulatory undulatory extinction. extinction. These plagioclase plagioclase + I 72 �crystals are are interpreted interpreted to t o have have been been recrystallized recrystallized during during sulfide sulfide °remobilization'. "remobilization". crystals Microprobe analysis of plagioclase the zone zone plagioclase from from 18 1 8samples samplesfrom from within within and outside the generally An content varies varies from 60-65% whereas whereas within within the the recrystallized recrystallized show that generally o 75-90%. These compositions compositions of ofplagioclase plagioclase areas the the An An content content has been been increased increasedt to 75-90%. These are consistent alteration by by saline saline solutions solutions at temperatures in excess of 7 0 0 ~ ~ are consistent with with alteration at temperatures in excess of 700°C (Sassani and Shock, Shock, 1990). (Sassani and 1990). REFERENCES REFERENCES Geerts, S.A., 1991. Cu-Ni Geerts, S.A., 1991. Geology, Geology,Stratigraphy, Stratigraphy,and andmineralization mineralizationofofthe theDunka DunkaRoad RoadCu-Ni Northeastern Minnesota. Minnesota. Natural NaturalResources ResourcesResearch Research Institute InstituteTechnical Technical prospect, Northeastern Report, Duluth, Minnesota, NRRIITR-91-14, Duluth, Minnesota, 63 63 pp. pp. Report, NRRI/TR-91-14, Shock, E.L., E.L., 1990. 1990. Supercritical mass-transfer during during aqueous aqueous Sassani, Sassani, D.C., D.C., and and Shock, Supercritical mass-transfer alteration of of mafic mafic intrusive intrusive rocks. rocks. GSA Programwith with Abstracts, Abstracts, V. V. 22, 22, #7, #7, pp alteration GSA Program 213. Severson, M.J., M.J., and and Hauck, Hauck, S.A., S.A., 1990. Geology, Severson, Geology, geochemistry, geochemistry, and stratigraphy of aa portion of the portion the Partridge Partridge River River Intrusion, Intrusion, Northeastern Minnesota. Natural Northeastern Minnesota. Natural Resources Research Institute, Institute, Technical Resources Research Technical Report, Report, NRRI/GMIN-TR-89-1 NRRIlGMIN-TR-89- 1 1, Duluth, Duluth, Minnesota, Minnesota, 240 240 pp. pp. 73 �FIGURE FIGURE 1. 1. GENERALIZED GENERALIZED IGNEOUS IGNEOUS STRATIGRAPHIC STRATIGRAPHIC COLUMN COLUMN fl UNITUNIT VII"11 Anorthcitic Anorthositic Troctolite Troctolite — coarse—grained, basal uitramofic ultromafic layer coar3e-grained, basal layer Vll(a) Vll(a) - VIl(o) MAGENTA Horizon UNIT VI Troctotitic Trocto!itic Anorthosite Anorthosite to to Troctolite Tractolite — basal ultrornafic - fine— fine- to coarse—groined, coarse-gmined. basal uitramafic layer layer Vl(o) Vl(a) UNIT V Anorthositic Anort3ositic Troctolite Troctolite UNIT IV Anorthc'sitic Troctolite to Troctolite/Augite Anorthositic Troctolite Troctolite/Augite Troctolite Troctolite Vl(o) - — coarse—grained coarse-grained - — coarse—grained coarse-grained 11(a) UNIT III Troctolitic Troctolitic Anorthosite Anofthosite to t oAnorthositic Anorthositic Troctolite Troctolite — mottled olivine - fine—grained, fine-grained, mottied olivine texture texture UNIT Troctolite Troctolite to to Augite Augite Troctalite Troctolite — - medium— medium- to t o coarse—grained, coarse-grained, basal basal ultramofic ultramaficlayer layer11(a) ll(a) It 1(b) KO) RED Horizon GRANGE Horizon Horizoc ORANGE 1(a) l(a) UNIT UNIT I I YELLOW YELLOW Horizon Horizon Anorthositic Anorthositic Troctolite Troctdite to toAugite AugiteTroctolite Troctolite — - fine— fine- to to coarse—grained. coarse-grained. sulfide sulfide bearing, bearing, abundant abundant hornfe!s hornfels inclusions inclusions and ond local local ultramafic ultramaficlayers layers (a) [(a) and and1(b) l(b) VIRGINIA FORMATION {-I 74 BIWABIK BIWABIK IRON—FORMATION IRON-FORMATION SCALE (m) �THE THEKENORA KENORA-- KABETOGAMA KABETOGAMADIKE DIKE SWARM: SWRESULTS RESULTSOF O F TRACE TRACE ELEMENT ELEMENT STUDIES STUDIES Andrew AndrewD. D.Moshoian, Moshoian,Karl KarlR. R. Wirth Wirth and andJohn JohnP. P.Craddock Craddock Geology MN,55105 55105 GeologyDepartment, Department,Macalester MacalesterCollege, College,St. St.Paul, Paul,MN, The Kabetogamamafic mafic dikes dikescomprise comprise aa swarm swarmthat thatextends extendsfrom fromthe theMesabi MesabiIron Iron TheKenora Kenora-- Kabetogama Range, Range,Minnesota, Minnesota,northwest northwesttotoKenora, Kenora,Ontario, Ontario,aadistance distanceofofabout about300 300km km(Figure (Figure1). 1).AARb Rb--Sr Sr isochron isochronfor forthe thedikes dikesgives givesan anage ageofof2120±67 2120 k 67Ma Ma(Beck (Beckand and Murthy, Murthy,1982), 1982),suggesting suggestingthat thatdike dike emplacement emplacementmay mayhave haveoccurred occurredcontemporaneously contemporaneouslywith withEarly EarlyProterozoic Proterozoicextension extensionin inthe theAnimikie Animikie Basin in northeast northeast Minnesota KK dikes dikesstrike strike—N-S -N-S in Minnesota Basin of of the theLake LakeSuperior Superiorregion region(e.g., (e.g.,Morey, Morey,1983). 1983).The TheKK and -.E-W in west-central Minnesota and everywhere have vertical dips and cross-cut a variety and -E-W in west-central Minnesota and everywhere dips and cross-cut a varietyof of Archean parallel to Archean granite-greenstone granitegreenstone terranes. The The dikes are undeformed and are everywhere parallel to faultfaultfracture arrays in the country rock that are filled with epidote, quartz and calcite (Craddock and fracture arrays in the country rock that are filled with epidote, quartz and calcite (Craddock and Moshoian, are common commonalong along most of of these brittle brittle features Moshoian, 1991). 1991). Strike-slip Strike-slip offsets are featureswhich whichare areclosely closely spaced meter), regionally regionally distributed distributed and and appear genetically spaced(—1 (-1 meter), genetically related to the the evolution evohtionof of the theKK KK mafic maficdikes dikes(Penokean?). (Penokean?). Trace samples. The Trace element element concentrations concentrationswere determined determined for 12 samples. Theconcentrations concentrationsindicate indicate Southwick and and Day Day (1983) (1983) recognized many of significant geochemical geochemical variation between dikes. Southwick significant recognized that many the thedikes dikeshave been deuterically phases. Most Mostof the havebeen deutericallyaltered altered to secondary hydrous mineral mineral phases. of the incompatible incompatibleelements, elements,with withthe theexception exceptionof ofsome someof ofthe thealkali alkalielements, elements,are arewell well --correlated correlated suggesting suggestingthat thatthe thetrace traceelements elementsremained remainedrelatively relatively immobile immobile during this this alteration alterationepisode. episode. The The dikes dikescan canbe beseparated separatedinto intothree threedistinct distincttypes typeson onthe thebasis basisofoftheir theirRare RareEarth EarthElement Element(REE) (REE) patterns patterns(Figure (Figure2). 2). Group GroupI 1dikes dikeshave havehigh hightotal-REE total-REEconcentrations concentrations relative relative to Cl Cl Chondrite Chondrite(Sun (Sun andMcDonough, McDonough,1989) 1989)(samples (sampleslOa, lOa, lOb, lob, 13). Sample Sample lob, lob, which which is is located located near near Lake Lake Kabetogama, Kabetogama, isis and characterized 50. Rocks Rocks from from this this group groupalso alsohave haveaasignificant significant characterizedby byhigh high(La/Sm)cu= (L.a/Sm)a=1.67 1.67and andYbcn Ybm==50. negativeEu-anomalies, Eu-anomalies, suggesting suggestingthat thatplagioclase plagioclase fractionation has occurred. Group Group22dikes, dikes, negative represented (La/Sm)cn= 2.37, 2.37,but butwith withlow lowYba Yb ==10.76. 10.76. The Theslope slope representedby bysample sample1,1,are areLREE W E enriched with (La/SmIa= of of the theREE REE pattern patternof ofthis thissample sampleisisthe thesteepest steepestof of all all the the samples samplesanalyzed, analyzed, and andcrosses crossesthe thepatterns patterns ofofother 1,1,which MN,also alsoshows showsaapositive positiveEuEuotherdike dikerocks. rocks.Sample Sample whichisislocated locatedjust justwest westofofTower, Tower,MN, anomaly. 3 dikes (samples 4, 4,8,9,15,17,19,26,27) 8, 9, 15, 17, 19, 26, 27) show anomaly.Group Group 3 dikes (samples show nearly nearlyflat flatREE REE patterns, patterns,with with (La/Sm)a ranging ranging from 0.97(sample (sample04) 04)toto1.08 1-08(sample (sample 81, ranging from (sample (La/Sm)cu from 0.97 8), and and Ybm Th ranging from 1212 (sample 4)4)toto3131 (sample (sample8). 8).These Theserocks rockswere weretaken takenfrom fromvarious variouslocations locationsaround aroundnorthern northernMinnesota Minnesota(Figure (Figure1). 1). Figure Figure33isisaaspider-diagram spider-diagramofoftrace traceelement elementconcentrations concentrationsnormalized normalizedtotoNN-MORB -MORBwith with increasing increasingincompatibility incompatibilityfrom fromright right to to left. left. All Allof ofthe therocks rocks of of the the representative representative suite suiteshow show Ta/La progressiveenrichment enrichmentin inthe thehighly highlyincompatible incompatible elements. Most Most samples samples have normalized Ta/La progressive ratios> ratios >I 1except exceptfor forthose thoseininGroup GroupI 1(eg. (eg.sample samplelob). lob).Normalized NormalizedSrSrvalues valuesare arevariable variableasaswell, well,and and arelikely likelydue duetotoplagioclase plagioclasefractionation. fractionation.Group Group33dikes dikesare areenriched enrichedininBa Barelative relativeto tothose thoseof of Group Group are whichhave havehigher higherLa/Sm La/Smratios ratios(Figure (Figure4). 4).On Onmany manytectonic tectonicdiscriminant discriminantdiagrams diagrams(Figure (Figure5), 5),most most I1which dikesplot ploton onthe thefields fieldsofofMORB MORB(Group (Group3) 3)or or volcanic arcs (Group and 3). 3). Sample SampleI1(Group (Group2)2)isis dikes (Group 1 I and highly highlyenriched enrichedininTa Taand andplots plotsininthe thefield fieldofofwithin-plate within-platemagmas. magmas. Thetrace traceelement elementdata dataindicate indicatethat thatthe thedike dikesamples samplescan cannot notbe berelated relatedby bysimple simplecrystal crystal The fractionation. We interpret the data to indicate that the dike magmas fractionation. We interpret the data to indicate that the dike magmaswere werederived derivedfrom fromdifferent different mantle mantlesources, sources,or orthat thatthey theywere werevariably variablycontaminated contaminatedwith withcontinental continentalcrust crustororlithosphere, lithosphere,oror, ,oror both. both. 75 �Figure I Figure FigureCaptions Captions Figure Kabetogamadikes dikesininNorthern NorthernMinnesota h4innesotaand and Southern SouthernCanada. Canada. Figure11Map MapofofKenora Kenora--Kabetogama Locations Locationsof of selected selecteddikes dikesare are shown shown in italics. Modified Modifiedfrom fiom Southwick Southwickand andDay, Day,1983. 1983. Figure Figure22REE FUZEpatterns pattemsofofselected selecteddike dikesamples. samples. Figure Figure33Incompatible Incompatibletrace traceelement elementpatterns pattemsofofselected selecteddike dikesamples. samples. Figure Figure44Ba/La B a avs. vs.La/Sm LdSmdiagram diagramofofallallsamples samplesanalyzed analyzed Figure Th- -Ta Tadiagram diagramof ofall allsamples samplesanalyzed. analyzed. (From (FromWood Woodeteta!., al.,1979) 1979) Figure55H1/3 Hf/3--Th References References Beck, 1982.Rb Rb- -SrSrand andSm Sm- -Nd Ndisotopic isotopicstudies studiesof of Proterozoic Roterozoicmafic mafic dikes dikesinin Beck, W., W., and and Murthy, Murthy, V. R. 1982. northeasternMinnesota Minnesota(abstract). (abstract).Proceedings, Proceedings,28th 28thInstitute hstituteon onLake LakeSuperior SuperiorGeology, Geology,International International northeastern Falls, Falls.MN, MN.p.D.5.5. Craddock, P.'and k dA. A.D. D.Moshoian. Moshoian.1991, 1991,Continuous Continuousstrike strike- -slip slipfault fault- -en enechelon echelonfracture fracturearrays arraysinin craddock;J.J.P. implicationsfor forfault faultpropagation propagation mechanics (abstract). Proceedings, Proceedings,37th 37th deformedArchean Archeanrocks rocks: :implications deformed Institute EauClaire, Claire,WI, WI,p.p.25. 25. Instituteon onLake LakeSuperior SuperiorGeology, Geology,Eau Morey, Lower Proterozoic stratified 1983 Lower Proterozoic stratifiedrocks rocksand andthe thePenokean Penokeanorogeny orogenyinineast east- -central centralMinnesota. Minnesota. Morey,G. G.B.B.1983 Ed. Medaris,Jr.Jr.Geological GeologicalSociety SocietyofofAmerica, America,Memoir Memoir160. 160.p.p.97 97- -112. 112. Ed.L.L.G.G.Medaris, Southwick, Geology and petrology Southwick,D. D.L., L.,and andW. W.C.C.Day. Day.1983. 1983. Geology and petrologyofofProterozoic Proterozoicmafic maficdikes, dikes,north north- -central central Minnesota EarthSciences., Sciences.,20, 20,p.p.622 622- -638. 638. Minnesotaand andwestern westernOntario. Ontario.Canadian CanadianJournal JournalofofEarth Sun, Chemical andand isotopic systematics ofofoceanic Mcbnough.1989. 1989. Chemical isotopic systematics oceanicbasalts: basdts:implications implications Sun,S.S.S., S.,and andW. W.F.F.McDonough. formantle mantlecomposition compositionand and processes. In InMagmatism Magmatismin inthe the ocean ocean basins. Edited Editedby by Saunders, Saunders,A.A.D.D. and and for M. Society M.J.J.Norry. Norry.Geological Geological SocietySpecial SpecialPublication PublicationNo. No.42, 42, p.p.313 313- -345. 345. Wood, Wood,D. D.A., A.,J.J.L.L.Joron, Joron,and andM. M.Treuil. Treuil. 1979. 1979.AArere- -appraisal appraisalofofthe theuse useofoftrace traceelements elementstotoclassify classifyand and discriminatebetween betweenmagma magmaseries serieserupted eruptedinindifferent differenttectonic tectonic settings. settings. Earth Earthand andPlanetary PlanetaryScience Science discriminate Letters. Letters.45, 45,p.p.326 326- -336. 336. 76 76 �L) zC U z z 0 L) z 0 10 20 30 40 50 1 10 100 1000 1 Nd I I t S • S IS SmEu I I I I I I I I Th I 5' I 2 La/Sm 3 1c • Figure 4 - — YbLu Figure 2 I RARE EARTH ELEMENTS -\J — . LaCe I ''''''liii 11111 I 4 z U z0- C z z C Th 0.1 1 10 100 1000 Hf/ 3 Ta Figure 5 INCOMPATIBLE TRACE ELEMENTS CsRbBaTh U TaLa Ce Sr Nd HfSmEuYbLu �PENOKEAN STRUCTURAL TRENDS DEFINED DEFINED FROM FORNATIONAL CONTACTS AND PENOKEAN STRUCFORIVULTIONALI CONTACTS ANJ3 CLEAVAGE ANALYSIS ALONG THE GOGEBIC RANGE, WISCONSIN CLEAVAGE GOGEBIC RANGE, WISCONSIN MIJDREY, Jr., Jr., and and B.A. B.A. BROWN, BROWN, Wisconsin Wisconsin Geological Geological and and Natural Natural History History M.G. MUDREY, Survey, 3817 Survey, 3817 Mineral Point Point Road, Road, Madison, Madison, WI WI 53705 53705 ABSTRACT Structural Tyler Formation Structural reconstruction reconstruction of of the Paleoproterozoic Paleoproterozoic Tyler Formation by by rotating out the dip of Mesoproterozoic Keweenawan Keweenawan bedding orientation rotating of Mesoproterozoic orientation along along the Gogebic Range in northern Wisconsin suggests in northern suggests that that Paleoproterozoic Paleoproterozoic units units (Tyler (Tyler and earlier formations) formations) were were gently gently deformed deformed along along axes axes trending trending 04° 04O toward W. prior prior to deposition toward S. S. 79° 7g0 W. deposition of of Mesoproterozoic Mesoproterozoic quartzite quartzite (basal (basal Keweenawan Bessemer Keweenawan Bessemer Quartzite). Quartzite). This analysis analysis suggests suggests that that the the cleavage cleavage near near Hurley, Wisconsin, Wisconsin, is Hurley, is not a slaty cleavage, cleavage, but is is probably fracture fracture cleavage cleavage related to related to late late Keweenawan Keweenawan tectonism. tectonism. Keweenawan (Mesoproterozoic) Bessemer Quartzite Quartzite rests with The lower lower Keweenawan (Mesoproterozoic) Bessemer rests with slight slight angular angular discordance discordance on on the the Penokean Penokean Tyler Tyler Formation Formation (Paleoproterozoic). (Paleoproterozoic). All All the the units units generally generally dip dip at at 70° 70 to to the the northwest northwest (Montgomery, (Montgomery,1977). 1977). We have have rotated rotated the the bedding bedding of of Tyler Tyler units units immediate immediate below below the the Bessemer Bessemer contact contact back back to to the the pre-Bessemer pre-Bessemer position position using using the the bedding bedding orientation orientation of of the the Bessemer for western end of Gogebic, the Bessemer for rotation. rotation. At the the western of the the Gogebic, the Tyler Tyler dips dips approximately 15° east, the Tyler dips approximately approximately 15O to to the the northwest. northwest. In the east, approximately Analysis of 15° to the the southeast. 15O southeast. Analysis of these these localities localities on on steronets steronets and and computer computer structural rotation rotation programs suggests structural suggests a fold fold axis axis trending trending east-north-east east-north-eastand and plunging Rotation of plunging gently gently to to the the west-south-west. west-south-west. Rotation of the the cleavage cleavage in in the the Tyler Tyler to its presumed pre-Bessemer orientation results results in in a pre-Bessemer dip to to the the pre-Bessemer orientation pre-Bessemer dip south, which which we find understanding of south, find incompatible incompatible with our understanding of Penokean Penokean deformation deformat ion along along the the Gogebic Gogebic Range. Range. On the basis of reconstructed reconstructed thickness thickness of of post-Tyler strata along along the the post-Tyler strata Wisconsin-Michigan state Wisconsin-Michigan state line, line, the the recognition recognition of of well well developed developed slickensides slickensides planes, and minor, minor, centimeter-scale along the cleavage planes, centimeter-scale offset offset of of Freda Freda and and Tyler units units across across those those cleavage cleavage planes, planes, we we suggest suggest that that the the cleavage cleavage is is aa Tyler Keweenawan tectonism, fracture cleavage related to late late Keweenawan tectonism, that that Tyler Tyler and and Keweenawan sedimentary sections sections are are probably probably repeated, repeated, and and that that measured measured Keweenawan sedimentary thicknesses are thicknesses are too too great. great. Hotchkiss (1919) clearly clearly recognized recognized bedding bedding plane plane Hotchkiss (1919) faults near the base of the Ironwood Ironwood Iron-formation Iron-formation on on detailed detailed maps maps of of underground workings underground workings along along the the Gogebic Gogebic Range. Range. The The faults faults are are recognized recognized by by offsets offsets in in diabase diabase dikes dikes that that cut cut the the sedimentary sedimentary strata strata at at aa high high angle. angle. References Cited Hotchkiss, 1919, Geology of the Gogebic Hotchkiss, W.O., W.0., 1919, Gogebic Range Range and and its relation relation to to recent recent 501mining developments: developments: Engineering Engineering and and Mining Mining Journal, Journal, v. v. 108, 108, p. p. 443-452, 443-452,501mining 507, 507, 537-541, 537-541,577-582. 577-582. Montgomery, 1977, Deformation Montgomery, W.W., W.W., 1977, Deformation of the Tyler Tyler slate (Middle Precambrian) Precambrian) in northern northern Wisconsin Wisconsin and western Upper Upper Michigan: Michigan: unpub. unpub. M.S. M.S. thesis, thesis, University University of Wisconsin-Madison, 115 of Wisconsin-Madison, 115 p. p. �GEOLOGIC GEOLOGIC SETTING SETTING OF OF THE THE EARLY EARLY PROTEROZOIC PROTEROZOIC METAL-RICH METAL-RICH VOLCANICS VOLCANICS OF OF THE THE UPPER UPPER GREAT GREAT LAKES LAKES REGION REGION MtJDREY, M.G., Jr., MUDREY, M.G., Jr., Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 3817 Wisconsin Mineral Mineral Point Point Road, Road, Madison, Madison, WI WI 53705 53705 DICKAS, A.B., DICKAS, A.B., Division Division of of Sciences Sciences and and Mathematics, Mathematics, University University of of Wisconsin-Superior, Wisconsin-Superior,Superior, Superior,WI WI 54880. 54880. ABSTRACT ABSTRACT Since Since the the late late 1960s, 1960s, more than than 100 100 million million short short tons tons of of volcanogenic volcanogenic massive-sulfide massive-sulfide mineralization mineralization have have been been measured measured and and inferred inferred in in northern northern Wisconsin. Significant precious precious metal metal values values are are associated associated with with many many of of the the Wisconsin. Significant known known deposits. deposits. The The deposits deposits occur occur within within the the Early Early Proterozoic Proterozoic Penokean Penokean fold fold belt belt (1,850 (1,850-- 1,900 1,900 Ma), Ma), which which has has been been divided divided into into two two major major terranes: terranes: the the northern northern terrane, terrane, which which consists consists of of aa supra-crustal supra-crustalsequence sequence deposited deposited on on the the Archean Archean basement, basement, and and aa southern southern terrane, terrane, which which is is composed composed of of volcanogenic volcanogenic rock rock and and Early Early Proterozoic Proterozoic granite. granite. This This southern southern terrane, terrane, the the Wisconsin Wisconsin Magmatic Magmatic Terrane Terrane (also (also called called the the Wisconsin Wisconsin Penokean Penokean volcanic volcanic belt), belt), is is characterized characterized by by island-arc island-arcassemblages assemblages containing containing abundant abundant calc-alkaline calc-alkaline metavolcanic units units and and associated associated lesser lesseramounts amountsof ofmetasedinientary metasedimentary rock. rock. metavolcanic Within Within this this geologic geologic framework, framework, three three distinct distinct environments environments appear appear to to host host massive sulfide sulfide mineralization: mineralization: syngenetic syngenetic stratabound stratabound and and stratiform stratiform sulfide sulfide massive mineralization within, within, along along the the flanks flanks of, of, or mineralization near the stratigraphic top of or stratigraphic the the felsic felsic centers; centers; syngenetic syngenetic stratabound stratabound and and stratiform stratiform massive-sulfide massive-sulfide mineralization mineralization associated associated with with cherty cherty magnetic iron-formation iron-formation in in the main volcanic mineralization and volcanic arc arc sequence; sequence; and and epigenetic epigenetic stringer stringer sulfide sulfide mineralization syngenetic massive sulfide mineralization mineralization syngenetic stratabound stratabound and and stratiforin stratiform massive associated piles within within the associated with with niafic mafic piles the back-arc back-arc basin basin sequence. sequence. The The three three defined defined host host environments environments and and their their associated associated meta-argillite meta-argilliteformations formations appear appear to to be be major major regional regional features features controlling controlling the the localization localizationof of metal-bearing massive sulfide mineralization in the west part of the area. metal-bearing massive sulfide mineralization in the west part of the area. Other host host environments environments will will undoubtedly undoubtedly be identified identified as exploration exploration Other continues continues in in the the area. area. 79 �EARLY PROTEROZOIC PROTEROZOIC LEPTITE LEPTITE & HALLEFLINTA HALLEFLINTA(TUFF (TUFF&&TUFFITE) TUFFITE) EARLY SEQUENCES SEQUENCES OF SOUTHERN SOUTHERN FINLAND FINLANDREINTERPRETED REINTERPRETED AS SHEAR SHEAR ZONES: ZONES: SIGNIFICANCE SIGNIFICANCE TO TO LAKE LAKESUPERIOR SUPERIOR GEOLOGY GEOLOGY OJAKANGAS, W., Department of Geology, Geology, University of of Minnesota, Minnesota, Duluth, Duluth, OJAKANGAS, Richard Richard W., Duluth, Duluth, Minnesota Minnesota 55812; 5581 2;MARMO, MARMO,Jukka JukkaS., S.,Geological GeologicalSurvey SurveyofofFinland Finland SF-02150, 15,Finland Finland SF-02150, Espoo Espoo 15, Many Many Early Early Proterozoic Proterozoic volcanogenic volcanogenic sequences sequences in in southern southern Finland Finland and and adjacent adjacent (i.e., epiclastic epiclastic Sweden as bedded tuffs and Sweden have have long been been interpreted interpreted as bedded tuffs and "tuffites" "tuffites" (i.e., While volcanic sediments), and commonly have been called leptites and halleflintas. volcanic sediments), and commonly have been called leptites and halleflintas. While definitions Fennoscandinavia, definitions of of these these unfamiliar unfamiliar terms termsvary, vary,even evenin in Fennoscandinavia, leptites leptites and and halleflintas can can be be described as The halleflintas as fine-grained fine-grained quartzofeldspathic quartzofeldspathic metavolcanic rocks. The halleflintas the finer finer grained grained of of the the ttwo halleflintas are the w o (<0.25mm) à ‡ 0 . 2 5 m r nand andare are commonly commonly thinly thinly bedded bedded (<2.0 restudy of of several such units in in Finland ( ~ 2 .cm). cm). 0 AA restudy several such units Finlandhas hasprovided providedevidence evidence for foraa structural structural origin origin as as tectonic tectoniclayering layering(i.e., (i.e.,shear shearbands) bands) rather rather than thanas asprimary primarybedding. bedding. We We studied studied aa 11 km km wide widevertical verticalshear shear zone zone in in the the Tampere Tampere Schist Schist Belt Belt in in some some detail. Massive plagioclase porphyry was clearly the main protolith; in a zone about detail. Massive plagioclase porphyry was clearly main protolith; in a zone about ten ten meters wide there there is is aa gradual gradual transition transition from from unsheared unsheared plagioclase plagioclase porphyry to t o highly highly sheared and thinly thinly banded rock. Glassy sheared and banded rock. Glassy pseudotachylite, evidently the product product of of intense intense granulation andfusion fusiondue duet to frictional heat, heat, was was found found at at two granulation and o frictional t w o spots. spots. Kinematic Kinematic indicators indicators suggest suggest a a dominant dominant horizontal horizontal movement movement in in this this zone. zone. Color differences differences between between adjacent adjacent thin thin bands bands appear appear to t o reflect reflectcompositional compositionalchanges changesand andmay maybe belargely largely due due to t o metasomatism metasomatism by by sodium-, sodium-, potassium-, potassium-, magnesium-, magnesium-, silica-, silica-, and and calcium-bearing calcium-bearing solutions solutions rather rather than to t o original original compositions compositions of thin beds. beds. Silicification Silicificationappears appearsto t ohave have greenschist grade and amphibolite Subsequent process. been aa widespread widespread process. amphibolite and greenschist grade been metamorphism has produced produced skarns skarns and and other other metamorphic metamorphic rock rock types types in the metamorphism has the thinly thinly sequence. banded sequence. The The above above shear shear zone zone contains contains sulfide sulfide mineralization, mineralization, and and intensive intensive drilling drilling has has attempted that was attempted to t o locate locate sphalerite sphalerite mineralization mineralization that was originally originally spotted spotted in in large large mineralized glacial erratics. Drilling mineralized glacial Drilling has has resulted resulted in intercepts intercepts of of Zn-Pb-Ag Zn-Pb-Ag mineralization. mineralization. Elsewhere in the Tampere Schist Belt, gold gold has has been been discovered in shear shear zones; zones; in one one silicified shear shear zone, zone, 110 ppm ppm Au is is present. present. In (Orijarvi) Leptite Leptite Belt, Belt, three three In another another wide wide shear shear zone zone in in the the Southern Southern Finland Finland (Orijärvi) sulfide bodies mined out. out. Metsämonttu bodies have been mined Metsamonttuwas wasaaZn-Pb Zn-Pb deposit, deposit, Aijala Aijala was wasaaCuCuZn deposit, and deposit. The and Orijärvi Orijarvi was a Zn-Cu deposit. The significance significance of of shearing shearing in in the vicinity vicinity of the overlooked, and and while the ore bodies bodies were were logically logically interpreted the mines mines has has been overlooked, interpreted as as strata-bound Kuroko-type sulfides, we emphasize Kuroko-type volcanogenic volcanogenic sulfides, emphasize the possibilities possibilities of of an an epigenetic-metasomatic origin or a remobilization remobilization of primary volcanogenic volcanogenic sulfide in in this this zone of structurally-prepared structurally-prepared volcanogenic volcanogenic rock. rock. 80 �also visited leptite belts in We also in the Stockholm Stockholm area, area, and and made observations similar above. At are in in close close proximity proximity tto mine that that tto o those cited above. A t one one locality, locality, sheared sheared rocks are o aa mine has been been in in existence existencefor for centuries. centuries. Photographs Photographs in the literature on parts of leptite leptite belts belts that we were were not not yet yet able able to t o visit visit are are highly highly suggestive suggestive of of tectonic tectonic layering. layering. some "tuff "tuff sequences" zones? We Could some sequences" of of the theLake LakeSuperior Superior region region also also be be shear zones? are positive positive that that some some "thinly "thinly bedded sequencesofof mafic mafic and andfelsic felsic tuffs" tuffs" in are bedded sequences in Archean Archean terranes decades past past are, are, in reality, the result terranes that we we have have even even mapped mapped ourselves ourselves in decades result shearing. A reinspection of such "tuff of shearing. "tuff sequences" sequences" may may be be warranted, for for ititcould could make make additional terrane terrane worth worth prospecting for both gold and sulfide additional prospecting for sulfide deposits. 81 �PETROLOGY BODY, PETROLOGY AND AND ORIGIN ORIGIN OF OF THE NORTHERN COLVIN CREEK BODY, DULUTH DULUTH COMPLEX, COMPLEX, NE ME MINNESOTA MINNESOTA RICHARD RICHARD PATELKE PATELKE and andMARK MARK SEVERSON SEVERSON UNIVERSITY and UNIVERSITY OF OF MINNESOTA, MINNESOTA, DULUTH DULUTH and NATURAL RESOURCES RESEARCH RESEARCHINSTITUTE, INSTITUTE, DULUTH NATURAL RESOURCES DULUTH The The Colvin Colvin Creek Creek Body Body (CCB, (CCB, Colvin Colvin Creek Creek Hornfels Hornfels of of Bonnichsen Bonnichsen 1972, 1972, Tyson Tyson occurs within coarse—grained troctolite, anorthositic troctolite, and augite augite troctolite troctolite of of the the Partridge Partridge River River Intrusion Intrusion (PRI) (PRI)of of the the 1100 1100 m.y. m.y. Duluth Duluth Complex, km NN of of Duluth Duluth and and about about 13 13 km km ENE ENE Complex, NE NE Minnesota. Minnesota. It It is is located located about about 90 90 km of exposures of the basal contact of Hoyt Hoyt Lakes. Lakes. This This is is about about 55kin km SE from exposures contact of of the the Duluth Duluth Complex, Complex, the the CCS CCB is is estimated estimated to to be be about about 600—1200 600-1200 meters meters above above the the base base of of the the Complex. Complex. 1975) 1975) occurs within coarse-grained troctolite, anorthositic troctolite, and This his hornfels hornfels body body consists consists of of aa series series of fine—grained fine-grained to to medium—grained medium-grained units units of of basaltic basaltic composition composition and and aa coarser—grained coarser-grained gabbroic gabbroic unit. unit. In In the the finer— finergrained grained rocks rocks textures textures are are granoblastic granoblastic and and fabrics fabrics include include both both lava lava flow flow and and sedimentary sedimentary features. features. In In the the past past the the CCB CCB has has been been interpreted interpreted as as aa large large xenolith More recently recently it it has has been been suggested suggested that that it it is is of of xenolith of of Keweenawan Keweenawan basalt. basalt. More igneous igneous origin origin (Severson (Seversonand and Hauck Hauck1990). 1990). Field Field relations relations within within the the CCB CCB are are consistent consistent with with the the hypothesis hypothesis that that the the hornfels hornfels block block is is aa stratigraphic stratigraphic stack stack of of sediments sediments and and basalts, basalts, contact contact metamorphosed metamorphosed to to pyroxene-hornfels pyroxene-hornfels facies facies by by the the Duluth Duluth Complex. Complex. This This block block has has been been rotated rotated 70—90 70-90degrees degreesso sothat thataa cross—section cross-sectionis isnow nowexposed exposedat atthe thesurface. surface. Dips Dips are are now now to to the the north north and and most most indicators indicators give give aa northward northward topping toppingdirection. direction. Aside Aside from from the the rotation rotation there there is is little little definite definite kinematic evidence evidence of folding folding or or faulting, faulting, although although some some bedding bedding parallel parallel faults faults may may be be present, present, along along with with some some sigmoidal sigmoidal clots clots of of pyroxenes pyroxenes and and oxides. oxides. The The block block strikes strikes approximately approximately N6OE N60E along along aa length length of of 2400 2400 meters meters with with an an apparent apparent stratigraphic stratigraphic thickness thickness of 680 1.6 sq. sq. km. km. The The CCB CCB 680 meters. meters. The The hornfels hornfels block block has has an an areal areal extent extent of of about about 1.6 has has not not been been drilled drilled and and there there is is no no good good estimate estimate of of how how far far it it extends extends below below the the surface. surface. The The actual actual boundaries boundariesof of the the CCB CCB are are defined defined from from outcrop outcrop control control and and from from the the magnetic magnetic signature, signature, the the CCB CCB is is aa magnetic magnetic high high similar similar to to the the nearby nearby Powerline Powerline Gabbro. Gabbro. This This is is probably probably due due to to both both the the magnetite magnetite contained contained in in rocks rocks and and ubiquitous ubiquitous magnetite magnetite and and augite—magnetite augite-magnetite dikes, dikes, veins, veins, and and masses. masses. MAIN MAIN LITHOLOGIC LITHOLOGIC UNITS UNITS The The five five main main units units present present at at Colvin Colvin Creek Creek are are described described below below in in order order from from north north to to south south (youngest (youngestto to oldest). oldest). The The GOG GOG is is aa medium—grained medium-grained to to very very coarse—grained, coarse-grained, oxide oxide rich, rich, gabbro gabbroto to olivine gabbro. gabbro. It It contains contains some some areas areas of of modal modal layering, layering, and and has has anorthosite anorthosite olivine inclusions. Plagioclase inclusions. Plagioclasepercentage percentagevaries varies from from 50 50 to to 80% 80% in in the the unit unit itself itselfand and up 10-25%, up to to 85—90% 85-90% in in the the anorthosite anorthositeinclusions. inclusions. Olivine Olivine content contentranges rangesfrom from10—25%, augite 5—15%, 5-15%, and and oxides oxides 1-10%. 1-10%. This Thisis is clearly clearly an an igneous igneousunit, unit, similar similarto tothe the augite Powerline Gabbro Gabbro to to the the east, east, it Powerline it is is apparently apparently unmetamorphosed, unmetamorphosed, and and assumed assumed to to be younger younger than thanthe thebasaltic basaltic portion portionof ofthe the hornfels. hornfels. The The GOG GOG makes makesup up about about15% 15% be of of the the exposed exposed CCB. CCB. The The "Cross—Bedded "Cross-BeddedBelt' Belt"(XBB) (XBB)rocks rocks are are granoblastic, granoblastic, fine fineto to medium medium fine— finegrained, grained, have have aa dominant dominant mineralogy mineralogy of of plagioclase plagioclase (An (An 65—70), 65-70), aluminous aluminous pyroxene, pyroxene, magnetite, magnetite, ilmenite, ilmenite, with with traces traces to to aa few few percent percent of of olivine, olivine, orthopyroxene, orthopyroxene, cordierite, cordierite, biotite, biotite, and and covellite. covellite. There There are are millimeter millimeter to to centimeter scale, scale, high high angle angle cross-bed cross-bed sets, sets, defined defined by by modal modal layering layering with with centimeter pyroxene and and oxide oxidebases. bases. The pyroxene Thebed—sets bed-sets have have aa 25—40 25-40 centimeter centimeterthickness thicknessbut butare are not not traceable traceablefor for any any great great distance. distance. The The granoblastic granoblastictexture, texture,fine finegrain grainsize, size, cross-bedding, and cross—bedding, and the the stratigraphic stratigraphicthickness thickness of of about about 300 300 meters meters lead lead this this to to be interpreted interpreted as as aa metasedimentary metasedimentary unit. unit. This This unit unit makes makes up up about about 35% 35% of of the the be hornfels body. body. At At 300 300 meters, meters, the the thickness thickness of of the the XBB XBB unit unit is is about about the the same same hornfels stratigraphic thickness thickness as asthe thetotal totalofofKeweenawan Keweenawaninterf interflow sedimentary rock rock stratigraphic low sedimentary 82 �measured measured on on the the Lake Lake Superior Superior Shore. Shore. Ameboidal granoblastic, fine fine to to medium-grained, medium—grained, generally generally Ameboidal Augite Augite (AA), (AA), is is a granoblastic, massive unit. The the other other granoblastic granoblastic The mineralogy is is essentially the same as the units, plagioclase, and ilmenite +1— olivine. plagioclase, augite, augite, magnetite, magnetite, and ilmenite +/olivine. There There are are concentrations more or concentrations of of augite augite and and Fe—Ti Fe-Ti oxides occurring as small stringers more less perpendicular to material defining defining the the less perpendicular to bedding bedding and and rounded rounded clots clots of the same material bedding These bedding or or layering. layering. These parallel parallel layers layers of of augite augite and and Fe-Ti Fe-Ti oxide oxide concentrations are interpreted interpreted to be flow flow tops, tops, indicating indicating flows flows roughly roughly one one meter meters. Flow tops are actually actually only meter or or less Less thick thick up up to to as as much as as ten meters. only seen seen for a few unit has has pyroxenite pyroxenite zones few meters length length in in scattered scattered locations. This unit along veinlets (and (and along its its upper upper contact contact with with the the XBB XBB unit unit and and contains contains numerous numerous veinlets healed mixed with healed joints) joints) of of pyroxene pyroxene intimately intimately mixed with Fe-Ti Fe-Ti oxides. oxides. This This is is interpreted interpreted as as aa subaerial, subaerial, amygduloidal, amygduloidal, metavolcanic metavolcanic unit unit making making up up about about 15% 15% of the the CCB. CCB. Amygduloidal the AA AA and is very Amygduloidal Gabbro Gabbro (AMG), (AMG), is stratigraphically below the similar similar to to the the AA in in its its mineralogy mineralogy and granoblastic granoblastic texture. Here Here the the pyroxene pyroxene and oxide oxide concentrations concentrations are are less less regular, regular, and and there there are are concentrations concentrations of of plagioclase unit. This is also thought plagioclase occurring occurring as as small small clots clots throughout the unit. to be another 15% 15% of of the total be aa subaerial subaerial metavolcanic metavolcanic unit unit constituting constituting another total hornfels. hornfels. Colvin Creek (MCC), (MCC), at the base of the hornfels sequence, sequence, is a Massive Colvin massive massive rock rock of of roughly roughly the the same same mineralogy mineralogy and and composition composition as as the the metavolcanic metavolcanic containing plagioclase, plagioclase, augite, Fe—Ti Fe-Ti oxides, but areas of of units, containing but it also has areas high olivine olivine concentration. concentration. These These are are ophitic ophitic zones zones but but it it is is uncertain uncertain if if these these high original igneous igneous feature feature or or due due to to metamorphism. The MCC contains contains some some are an original small cavities and and has has plagioclase plagioclase clots similar to those in the AMG small cavities ANG unit, but lacks well well defined defined volcanic volcanic features. features. In aa few few locations locations there there are are large large plagioclase phenocrysts, phenocrysts, their their origin origin is is also also unclear. The contact with the AMG plagioclase unit unit above above is is gradational gradational over over about about 1-10 1-10 meters. meters. This This is is thought thought to to most most likely likely be aa thick thick lava lava flow flow or or near near surface surface sill. sill. This unit covers about be about 20% of the exposed exposed area area at at Colvin Colvin Creek. Creek. Whole rock rock geochemistry geochemistry indicates indicates that CCB rocks rocks are are similar similar to to Whole that the CCB Keweenawan igneous igneous rocks rocks and and selected selected interf interflow North Shore Shore Keweenawan low sediments of the North Volcanic Group, Group, but but are are not not strict strict analogues analogues for for any unit in the Keweenawan. Volcanic This work work has has been been supported supported by by the the UMD Graduate This Graduate School, School, UMD-NRRI, and and the the Coleraine Coleraine Minerals Minerals Research Research Laboratory. Laboratory. .................................................................. W., 1972, 1972, Southern Southern Part Of the Duluth Bonnichsen, W., Duluth Complex Complex in Sims, Sims, P.K., P.K., and Morey, G.B., G.B., editors, editors, Geology of Minnesota: Minnesota: A Centennial Centennial Volume: Volume: Minnesota Minnesota Geological Survey Survey pp. pp. 361-387. 361-387. Geological M. J., and and Hauck, Hauck, Steven Steven A., A., 1990, 1990, Geology Geology and and geochemistry geochemistry of of aa portion portion Severson, M.J., Severson, the the Partridge Partridge River River Intrusion: Intrusion: Natural Natural Resources Resources Research Research Institute— InstituteUniversity of of Minnesota, Minnesota, Duluth, Duluth, Technical Technical Report Report NRRI/GMIN-TR-89-ll. NRRI/GMIN-TR-89-11. University of of Tyson, R.M., R.M., 1976, 1976, Hornfelsed Hornfelsed Basalts Basalts in in the the Duluth Duluth Complex: Complex: M.S. M.S. Thesis, Thesis, Cornell Cornell Tyson, University, University, Ithaca, Ithaca, New New York, York, 85 85 pages. pages. 83 �. x )— 1- oog U) U) II 00 00 mo mo 4Q °o o Id -J uNorrEkENuI(o )ROCIOLUIC SIRICS '1 JL • EJ ivo [J DULUTIl COMPLEX 0 flJE1ERS 1000 FT — SWAMP CONTACT AREA OF OUTCROP CLEVtTI0N 7 9M ORIGINAL CAt) ARE) GiOI.OGY DY U J. SF'/EIVSON-•- URRI 1550 T.59N., R.13W. St. Louis County Minnesoto DULUTH COMPLEX NORTHERN COLVIN CREEK BODY 0 POWERLJNE GABBRO? �VARIATIONS VARIATIONS IN IN METAMORPHIC METAMORPHIC GRADE GRADE OF OF METAPELITES METAPELITES ALONG ALONG TRAMSECTS T W S E C T S ACROSS THE THE QUETICO QUETICO SUBPROVINCE SUBPROVINCE THUNDER THUNDER BAY, BAY, ONTARIO ONTARIO BARBARA BARBARA E. and MANFRED MANFRED 14. M. KEHLENBECK E. SEEMAYER SEEMAYER and DEPARTMENT DEPARTMENT OF OF GEOLOGY, GEOLOGY, LAKEHEAD LAKEHEAD UNIVERSITY, UNIVERSITY, THUNDER THUNDER BAY, BAY, ONTARIO ONTARIO The The Archean Archean rocks rocks of of the the western western Superior Superior province province of of the the Canadian Canadian Shield Shield have have been been subdivided subdividedinto into aa series series of of subprovinces. subprovinces. These These subprovinces subprovinces form form east—west east-west trending trending terranes terranes typified typified by by either either metavolcanic metavolcanic successions successions and granitic granitic intrusive intrusive rocks rocks as as represented represented by by the the Wawa Wawa and and Wabigoon Wabigoon subprovinces, subprovinces, or or by by metasedimentary metasedimentary gneisses gneisses and and migluatites migmatites characteristic of the the Quetico Quetico and and English English River River subprovinces. subprovinces. Many Many workers workers have have attempted attempted to to define define the the boundaries boundaries separating these subprovinces separating these subprovinces from from one one another. another. These These attempts attempts commonly commonly focus focus on on aa comparison comparison between between adjacent adjacent subprovinces subprovinceswith with regard lithological character, characterl orientation orientation of of structural structural regard to to lithological elements, elementslmetamorphic metamorphicgrade, gradelgeophysical geophysicalanomalies, anomaliesland and geochemical geochemical parameters. parameters. Although Although such such comparisons comparisons are are valuable valuable in in identifying identifying differences subprovincesl the the actual actual boundary boundary differences between between adjacent adjacent subprovinces, remains remains aa poorly poorly defined defined feature featurein in most most cases. cases. The The objective objective of of the the present present study study was was to to analyze analyze metamorphic metamorphic index index minerals minerals in in metapelites metapelites and and to to compare compare these these results results to to typomorphic analytical work work was was typomorphic mineral mineral assemblages. assemblages. Much Much of of the the analytical confined confined to to garnet garnet because because of of its its widespread widespread occurrence occurrence in in the the metapelites. metapelites. One Hitachi One hundred hundred thirty thirty two two garnets garnets were were analyzed analyzed using using aa Hitachi 570 Results 570 S.E.M. S.E.M. Results show show that that the the garnets garnets cover cover aa range range of of compositions compositions from from almandine almandine (54—92) ( 5 4 - 9 2 ) spessartine spessartine (1—33) (1-33) pyrope pyrope (2(225) 25) grossularite grossularite (0-17) (0-17) suggesting suggesting aa parent parent rock rock composition composition relatively relatively low low in in calcium calcium and and rich rich in in iron iron and and magnesium. magnesium. With With increasing increasing grade grade of of metamorphism metamorphism garnet garnet compositions compositions reflect MgO contents. CaOand andMnO MnO and and increasing increasingFeO FeOand andnMg0 contents. reflectdecreasing decreasingCaO Geobarometry Geobarometry using using the the equilibrium equilibrium assemblage assemblage garnet garnet ++ sillimanite sillimanite ++ plagioclase plagioclase ++ quartz quartz resulted resulted in in pressures pressures of of 55±k 1.5 1.5 Kbar. Kbar. Electron Electron microprobe microprobe analyses analyses of of twenty twenty samples samples containing containing biotite biotite and and garnet garnet showed showed temperature temperature ranges ranges from from 517°C 517OC in in metasedimentary rocks to to a maximum metasedimentary rocks maximum of of 714°C 714'C in in the the migmatite migmatite complex. complex. In In general, generallaa pattern pattern of of steadily steadily increasing increasing temperatures temperatures northward by a rather northward is is interrupted interrupted by rather sharp sharp drop drop north north of of the the highest grade rocks. highest grade rocks. The The widely widely held held view view that that the the metasedimentary metasedimentary terranes terranes of of the the western western Superior Superior province province possess possess aa symmetric symmetric distribution distribution of of metamorphic grades gradesfrom from low—grade low-grade rocks rocks near near the the margins margins to to higher higher metamorphic grade grade rocks rocks near near the the central central parts parts is is not not supported supported by by this this detailed detailed study study of of the the Quetico Quetico subprovince subprovincenorth northof ofThunder ThunderBay. Bay. It lowIt is is common common to to find find high-grade high-grade rocks rocks juxtaposed juxtaposed with with lowgrade grade schists schists near near the thesubprovince subprovincemargin. margin. The The variations variations in in metamorphic metamorphic grade grade are are not not only only profound profound in in transects transects across across the the regional regionalstrike strikeof of the the rocks rocksbut but also also occur occur parallel parallel to to the the strike. strike. The The latter latter variations variations are are particularly particularly well well demonstrated demonstrated near near the the 85 �southern gneisses and southern margin margin where where high high grade grade schists schists and and gneisses and low—grade low-grade slates 10 slates are are exposed exposed in in outcrops outcrops over over a a strike strike distance distance of of about about 10 . km. km The The variations variations in in metamorphic metamorphic grade grade throughout throughout the the Quetico Quetico subprovince subprovince between high—grade high-grade and and low—grade low-grade assemblages assemblages and and analyses, corresponding analysest contradict contradict aa simplistic corresponding mineral mineral simplistic distribution. distribution. An An explanation explanation for for this this pattern pattern of of distribution distribution lies lies to to some some extent in in the the evolution evolution of of the the Quetico Quetico terrane. terrane. Several Several models models invoking mobilist viewpoint viewpoint have have been presented presented in in the the invoking the the mobilist literature. literature. Based on on the the evidence evidence from from this this study, studyt we we conclude conclude that Archean crustal crustal that aa model model of of subduction—driven subduction-driven accretion accretion of of Archean elements elements best best explain explain the the field field and and laboratory laboratory data. data. The The Quetico Quetico terrane terrane represents represents an an accretionary accretionary prism prism composed composed primarily primarily of of detritus detritus shed shed southward southward from from the the Wabigoon Wabigoon island island arc arc and inicrocontinent terranes. The prism and microcontinent terranes. The prism comprises comprises quartzofeldspathic pelitic sediments. sediments. Southward Southward oblique oblique quartzofeldspathic and and pelitic accretion accretion of the the Wawa Wawa terrane terrane signalled signalled the the onset onset of of polyphase polyphase deformation, metamorphism, and regionalmetamorphisml and development developmentof of deformation, low low pressure pressure regional thrusts. thrusts. Northward dipping dipping thrusts thrusts and thrust thrust nappes nappes resulted resulted in in tectonic tectonic stacking stacking of of diverse diverse rock rock types types from from different different levels levels of of the the accretionary accretionary wedge. Continued Continued north—south north-south compression compression led led to to the sheetst and and the the the coaxial coaxial refolding refolding of of earlier earlier folds folds and and thrust thrust sheets, development sub-verticall east—west east-west striking striking development of of aa pervasive pervasive sub—vertical, schistosity. schistosity. Late Late north—south north-south dextral transpression transpression is is seen seen in in structures structures reflecting reflecting more more brittle brittle deformation deformationand and the the intrusion intrusionof of post-kinematic plutons near the post-kinematic plutons the southern southern margin. margin. This late late This intrusive intrusive activity activity produced produced contact contact metamorphic metamorphic effects effects which which overprint overprint the the regional regional metamorphism. metamorphism. At At the the present present level level of of erosion, erosion, the the pattern pattern of of distribution distribution of metamorphic metamorphic grade and and the the orientation orientation of of planar planar and and linear linear structures structures appears to correspond correspond to to the the proposed proposed evolutionary evolutionary model. model. The The boundaries boundaries between between the the Quetico Quetico subprovince subprovince and and adjacent adjacent volcanic terranes in in the area by this study volcanic terranes area covered covered by study are are best best described described as as products products of of aa complex complex fault—fold iault-fold geometry. geometry. In In the the area area studied studied there there appears appears to to be be no no distinct distinct line line of of demarcation demarcation between between subprovinces. subprovinces. 86 �THE BASAL CONTACT SULFIDE AND AN]) PGE MINERALIZATION AT THE OF THE THEMINNAMAX MINNAMAX DEPOSIT, DULUTH DULUTJ3 COMPLEX, NE NE MINNESOTA MINNESOTA OF Mark J. Severson Severson Natural Resources Research Institute Institute University of Minnesota, Minnesota, Duluth Duluth The Minnamax (Babbitt) Cu-Ni deposit, located within the Partridge Partridge River fiver Troctolite Troctoliteof of the Duluth Complex (1.1 Ga), Ga), northeastern northeastem Minnesota Minnesota (Fig (Fig 1), I), contains containsboth both troctolite-hosted troctolite-hosted disseminated disseminated ore and footwall-hosted footwall-hosted massive sulfide ore. This talk talk pertains pertains to to the the massive massive sulfide ore zone, which is restricted to a small portion portion of of the deposit, and is referred to as as the the Local bBoy y area. Detailed Detailedrelogging relogging of of 76 76 underground underground drill holes, along along with pertinent surface holes, has been completed within within the Local Local Boy Boy area area (from (from drifts drifts B, C, and and D). D). Relogging of of drill core indicates a highly undulatory nature nature of of the basal contact of the highly undulatory Duluth Complex with with the footwall footwall Virginia VirginiaFormation. Formation. Intrusive rocks of the the Complex Complex consist of augite troctolite, norite; all all exhibit exhibit gradational gradational contacts contacts with each other other and and all all troctolite, troctolite, troctolite, and and norite; may occur at any stratigraphic position position relative relativeto tothe theundulatory undulatorybasal basalcontact. contact. However, norite is the the most most common common rock rock type type adjacent adjacent to to sedimentary sedimentary homfels homfels inclusions inclusions and at at the the basal basal contact of the the magma. magma. The contact due to contamination contamination of Thespatial spatialconfiguration configuration of of the theintrusive intrusiverocks rocks indicates that the the troctolite, etc. was intruded as multiple pulses along along bedding bedding planes planes of of the indicates that multiple pulses Virginia Formation. Formation. The The Virginia Virginia Formation hosts the majority of the massive sulfide ores which are present within within hornfels homfels inclusions inclusions positioned positioned above the basal contact, and within within the the footwall footwallrocks rocksatat and and below the basal contact. Massive Massivesulfide sulfideore oreisisnot notas ascommon common within within the the intrusive intrusiverocks, rocks, and when present it is generally in close proximity to homfels inclusions. when present it is generally in close proximity to homfels inclusions. Megascopic ore ore textures are extremely varied, but all textures extremely varied, textures are indicative indicative of structural structural preparation preparation in the footwall footwall rocks. Overall, Overall,the themassive massivesulfide sulfideores oresare arespatially spatially distributed distributed in in aa spotty spotty manner manner in in an east-west (EW) direction direction that corresponds corresponds to aa major major EW-trending EW-trending anticline anticline present present within within east-west (EW) the the footwall footwall rocks. rocks. All these these factors factors suggest suggest that that an an immiscible immisciblesulfide sulfide melt melt was was injected injected into into the structurally structurally prepared footwall rocks along the anticlinal axis in aa "vein-like" "vein-like"setting. setting. At At some some later later period, period, the thefootwall-hosted footwall-hosted massive massive sulfide sulfide ore ore zone zone was was re-intruded re-intrudedby bymultiple multiplesills sills of the the troctolitic troctolitic rocks. rocks. The end end result result isis aadisjointed disjointed zone zone ofofmineralized mineralized inclusions inclusions and and mineralized footwall rocks separated by "barren" "barren" intrusive intrusive rocks. Sulfide textures that the sulfides textures indicate indicate that sulfides formed by cooling cooling of of aamonosulfide monosulfidesolid solid solution (MSS) followed followed by by limited limited replacement replacementatat very very low low temperatures. temperatures. Minerals Minerals contained contained within pyrrhotite, chalcopyrite, chalcopyrite, cubanite, cubanite, and and pentlandite. pentlandite. Locally within the sulfide ore are dominantly pyrrhotite, W l y present present are are maucherite, maucherite, sphalerite, sphalerite,bornite, bomite,talnakhite, talnakhite,mackinawite, mackinawite, and and an an unknown unlmown Cu-sulfide Cu-sulfide (ItCptt). ("Cpl'). Also Also present present in minor minor amounts amounts are are native native silver silver (both (both primary primary and andsecondary), secondary), parkerite, chalcocite, chalcocite,covellite, covellite,godlevskite, godlevskite, violarite, violarite,magnetite, magnetite,and andzincian zincianhercynite. hercynite. parkerite, Although no discrete PGE minerals were identified, analytical results results (from 1,050 1,050 drill drill core % Cu) Cu) core samples samples with with an an average averagesample sampleinterval interval of of 55 to to 10 feet long) of the high-grade (> (>11% massive sulfide ore ore confirms confirms the presence of several anomalous PGE Thesespot spotvalues values massive PGE values. These are are mainly mainly confined confined to an an EW-trending EW-trending zone that also roughly corresponds to to the the EW-trending EW-trending anticline (Fig 2). Maximum Maximumvalues valuesobtained obtained in in the the Local Local Boy Boy massive sulfide ores include: Pd Pd anticline = = 11,100 11,100ppb; ppb; Pt == 8,300 8,300ppb; ppb; Au == 10,900 10,900ppb; and Ag == 34 34 ppm. ppm. Underground Undergrounddrill drillhole hole 10198 probably metal-bearing drill hole found to to date datewithin within the the 10198 probably represents the best precious metal-bearing 87 �Complex. Within hole are are ten tenPd Pdvalues values>> 1 ppm, five Au Au values values > 11ppm, Within the the 300 300 foot foot long hole ppm, and three Pt values > 1 ppm. 1 ppm. and three Pt values origin of of the PGE mineralization mineralizationisistwofold. twofold. A primary origin is suggested by the The origin suggested by presence of maucherite presence maucherite grains which which contain contain extremely extremely fine-grained fine-grained myrmekitic native silver silver intergrowths (J)rimary intergrowths (primary silver). silver). Generally, drill holes that contain contain anomalous POE PGE values also also contain this silver-bearing type type of of maucherite. maucherite. Since contain Since maucherite maucherite appears appears to to have have formed formed early early in the paragenetic sequence, this suggests that silver (and PGEs) were scavenged from the sulfide sulfide by maucherite, and thus thus the PGEs PGEs are are related related to to aa primary primary (magmatic) (magmatic) process. process. However, melt by However, a hydrothermal origin for the PGEs is also hydrothermal origin also indicated. indicated. Anomalous Anomalous POE PGEvalues valuesare arecommonly commonly associated with with Cl-drop Cl-drop encrusted encrusted massive massivesulfide sulfidedrill drillcore. core. The spatial distribution of the Cldrop encrusted drill core also coincides with with the the EW-trending EW-trendinganticline anticline(Fig (Fig2). 2). Presence of the Boy area area were invaded by Cl-bearing solutions solutions that Cl-drops indicates that the rocks of the Local Boy may have been capable of transporting and concentrating PGEs. POEs. Therefore, Therefore, both both primary/magmatic prima.ry1magmatic (sulfides injected into a "vein-like" Vein-like" setting) and later secondary/hydrothermal processes processes appear appear to to have have been been factors in controlling POE secondarylhydrothermal PGE distribution in the Local Boy area. However, However,ititisisdifficult difficulttotoseparate separatethe theprimary primaryand andsecondary secondaryprocesses. processes. This is due due to to the the coincidence coincidence of of several several features features within within an an EW-trending EW-trending zone zone which which include: include: 1) anticline in the footwall rocks; 2) overall overall massive massive sulfide sulfide distribution; distribution; 3) 3) spatial spatial distribution distribution of anomalous POE values; spatial distribution distribution of of Cl-drop 4) spatial Cl-drop encrusted encrusted drill core. core. anomalous PGE values; and and 4) Reactivation of structures structures that controlled controlled the initial "vein-like" "vein-like" massive massive sulfide sulfidedistribution distributioncould could have been responsible responsible for for channeling channeling later later hydrothermal hydrothermal solutions. solutions. 88 �1 LEGEND Cu-Ni ~ e ~ o s i t s ' MINNAMAX DUNKA RDAD WETLEGS WYMAN CREEK SERPENTINE DUNKA PIT - - DR WL WC S DP Fe-Ti Deposits (OUO SECTION 17 LDNGEAR LONGNDSE SECTION 22 SKIBD WATER HEN - - 17 LE LN 22 SK WH 1: Figure 1: Locotion deposits within within tthe Figure Location of' o f Cu—Ni Cu-Ni deposits he Par'tridge Complex P a r t r i d g e River River Troctolite T r o c t o l i t e off o f the t h eDuluth Duluth Complex. * >2.0 p p m 1.0 - 2.0 p p m ANOMALOUS PRECIOUS METALS (Pt, Pd, o r A u ) 0.8 — - 1.0 1.0 ppm ppm Figure Figure 2: 2: Distribution anomalous precious precious metal metal values values and and Distribution of of anomalous Cl-drop core in the Local Local Boy Boy area, area, Cl—drop encrusted encrusted drill core in the Minnamax Minnamax deposit deposit 89 �THERMAL AND AND REGIONAL IN ARCHEAN BASALT, BASALT, THERMAL REGIONAL METAMORPHISM IN GREENSTONE BELT, MANITOBA, CANADA BIRD RIVER GREENSTONE Turnock A.C.(1), Turnock A.C.(l), Kamineni Kamineni D.C. D.C. (2), (2), (1) Geological Geological Sciences, Sciences, University University of of Manitoba, Manitoba, Winnipeg, 2N2, Canada. Canada. Winnipeg, MB, MB, R3T R3T 2N2, (2) AECL AECL Research, Research, Whiteshell Whiteshell Laboratory, Laboratory, Pinawa, MB, Pinawa, MB, ROE ROE 1LO, lL0, Canada. Canada. Abstract In southeastern southeastern Manitoba, on the the western edge In edge of the the Superior Superior Province (Archean), the Bird River greenstone belt is subsmall sub— Province (Archean), the Bird River greenstone belt is aa small Pillow basalts a lower lower province of of supracrustal supracrustal rocks. rocks. basalts are are a stratigraphic thick, overlain ic and stratigraphic formation, formation,approx. approx. 22km kmthick, overlainbybymaf mafic and felsic volcanics volcanics and and clastic clasticnieta—sedimentary meta-sedimentary rocks. rocks. Samples Samples from from felsic 3 localities localities are are described described with with chemical chemical and and mineral mineral analyses. analyses. and 2 have compositions similar other Archean # 1 2 have compositions to other Samples 1 Samples # tholeiites; their flat ratios of Nb-Zr-Y and tholeiites; flat REE patterns and ratios and TiTiThe exceptions exceptions are Zr—Y Zr-Y are are comparable comparable (with (with exceptions) exceptions) to to MORB. MORE. The are the Y, the selvedges selvedges of of the the pillows pillows of of Sample Sample #2, #2, which which are are enriched enriched in in Y, Fe+3, Fe, Fe+3, Mg, Ca, Mn compared compared to cores cores and and to to sample sample #1. #l. The The Fe, Mg, chemical anomalies anomalies are ascribed chemical ascribed to to diagenetic diagenetic or or hydrothermal hydrothermal alteration, Sample #3, #3, a cross-cutting cross-cutting dike, dike, alteration, possibly possibly syn-gentic. syn-gentic. Sample is an an meta-andesite. meta—andesite. steeply dipping dipping The formations are are folded, folded, faulted, faulted, and and steeply The formations D2), with with a regional foliation 52. (deformation D2), S2. There There are are postpostDuring metamorphism, metamorphism, hornblende, hornblende, garnet folding shear zones zones (D3). (D3). During garnet folding shear and cuinmingtonite have overgrown overgrown the the main S2 This cummingtonite have S2 foliation. foliation. This indicates that heat flow, flow, probably from the the adjacent adjacent batholithic batholithic intrusion, continued intrusion, continued after after deformation. deformation. This This thermal thermal recrystallrecrystallM3. The samples are in the aureole of a ization is called M3. a late— latetectonic batholith tectonic batholith of of granite granite and and granodiorite, granodiorite, the the Lac Lac du du Bonnet Bonnet (LDB) batholith. batholith. We interpret interpret that this this batholith batholith is is the the heat heat (LDB) source source for for M3 recrystallization. recrystallization. In samples samples #1 and 2 2 the the compositions compositions of of plagioclases plagioclases are are rich rich in In Ca and Al A1 (An 63 -- 91), 91), which is anomalous as compared compared to the compilation of of Spear Spear (1981). (1981). They are comparable comparable to to the the calcic calcic plagioclases the low-pressure low—pressure calcic schists schists (garnet—hornblende plagioclases of of the (garnet-hornblende zone) of of the the Panamint Panamint Mountains Mountains (Labotka (Labotka 1987). 1987). The hornblendes The hornblendes are rich rich in in tschermaks tschermaks molecule, molecule, especially especially #2 #2 selvedges. selvedges. We We interpret compositions as as the interpret these these compositions the result result of of the the enhanced enhanced instability instability of epidote epidote at at low low pressures pressures (andalusite (andalusite type type facies). facies). 1989)is the the An additional additional indicator indicator of low low pressures pressures (Yardley 1989)Is abundance of in samples samples #2 #2 and and 3, 3, this this is is caused by abundance of cunimingtonite cummingtonite in the the preference preference of of amphibole amphibole to to lower lower its its content content of of Al A1 at at low lowP. P. The selvedges of the pillows of sample sample 22 have have porphyroblastic porphyroblastic garnet, plus small small amounts amounts of of biotite. biotite. Temperatures of M3 are are thereby 600°C (range; thereby determined determined as as 565 565 -- 600° (range; additional error may may be be additional error 50 The garnet—hornblende garnet-hornblende geothermometer of Graham Graham && Powell Powell 50 O). The 608OC. (1984) gives 575 575 —- 608°C. The preservation preservation of cores of hornblende hornblende The of inclusions inclusions of biotite in in cores O ) . �indicates indicates that that M2 M2 biotite biotite was was aa reactant reactant that that was was used used up up by by the the M3 M3 recrystallization. recrystallization. metamorphic aureole late—tectonic granite in an an The thermal metamorphic aureole of a late-tectonic Archean greenstone belt may be outlined outlined by mapping the the appearance appearance of the garnet-hornblende garnet-hornblende assemblage assemblage (without (without chlorite, chlorite, as as pointed pointed in out by Labotka 1987) out by Labotka 1987) in the meta-basites. meta-basites. The ability ability of of amphiboles, garnet, plagioclase and epidote epidote to to react react in in the the postposttectonic thermal thermal aureole the late batholiths batholiths are the tectonic aureole indicates indicates that that the source of of advective advective heat. heat. It remains to be determined wether or Ptotal, in not there was a loss loss of of H20, H20, or or conditions conditions of PH2O pH20 << Ptotal, in this environment. environment. 91 �STRUCTURAL ANALYSIS ANALYSISOF OF THE THE MIDCONTINENT MIDCONTINENT RIFT RIFT IN A STRUCTURAL MICHIGAN, BASED ON A A FAULT FAULT ARRAY ARRAY ANALYSIS ANALYSIS UTILIZING SLICKENSIDES SLICKENSIDES Kathleen Kathleen M. M. Witthuhn Witthuhn Department of of Geology Department Geology and and Geophysics Geophysics University of Minnesota University Minnesota Minneapolis, Minneapolis, Minnesota Minnesota The Midcontinent Rift 1.1 billion billion year year old old crustal crustal structure structure which which has has The Midcontinent Rift is is a 1.1 Many studies been defined been defined primarily primarily by by geophysical geophysical studies. studies. Many studies have have examined the rift rift from examined the from a petrologic petrologic view view but but few few have have examined examined the the structural geology geology in in any Initial field work work in in Minnesota, Minnesota, Canada, Canada, structural any detail. detail. Initial and the Upper of Michigan yielded data data on on fault and Upper Peninsula Peninsula of Michigan yielded fault and joint joint populations, from which which scattered populations, from scattered stress stress tensors tensors were were calculated. calculated. Examinationofof nearly nearly 600 600 small small scale scale fault fault structures on both both of of the Examination structures on the synclinal limbs along along a transect synclinal limbs transect northwest northwest across across the the Lake Lake Superior Superior syncline, from from the the Keweenaw Peninsula to to Isle Royale syncline, Keweenaw Peninsula Royale in in Michigan, Michigan, was was more successful successfulinin isolating isolating two two consistent consistent stress stress fields fields for for each each limb limb of the more the syncline, that that would would satisfy satisfy criteria criteriafor for closing closingoff the syncline, theMidcontinent Midcontinent Rift Rift This study System. This study evaluates evaluates existing existing models models by by applying applying geometrical geometrical and and statistical methods methodstoto the the data data to determine determine the the kinematics kinematics of of the closing statistical closing of of the the Midcontinent Midcontinent Rift Rift System. System. The Keweenawan Portage Lake Lake Volcanics Volcanics (PLV) (PLV) form form aa broad The Keweenawan Portage broad anticline, anticline, with an an axis just causing the the lava lava flows flows west west of of with just west west of of Delaware, Delaware, Michigan, Michigan, causing Delaware of the the anticlinal anticlinal axis axis trend trend Delawaretoto trend trend northeast, northeast, while while those those east east of mainly A majority mainly east-west. east-west. A majority of the the small small scale scale fault fault orientation orientation data data collected on the east-west collected on east-west trending trending flows flows of of the the Keweenaw Keweenaw Peninsula Peninsula are are parallel with parallel with this this trend, trend, having having steeply steeplypitching pitchingslickensides, slickensides, indicating indicating dip-slip motion motion on on the the faults. dip-slip faults. However, However, there there are two two smaller smaller fault fault populationstrending trendingslightly slightlyeast eastand and west west of of north, populations north, with with low low angled angled slickenside orientations, suggesting slickenside orientations, suggesting strike slip slip motion. motion. All of the the fault fault All of orientations collected collected from from the the northeast orientations northeast trending trending PLV PLV are parallel parallel with with 92 �this this orientation orientation and and the the low low angled angled pitch pitch of ofthe theslickensides, slickensides, also, also,indicates indicates strike-slip 1). strike-slip motion motion along along these these faults faults (figure (figure 1). Figure Figure 1. 1. Diagram Diagramofofthe themajor majorfault faulttrends trendson onthe theKeweenaw KeweenawPeninsula Peninsula showing showing their their compatibility compatibilitywith with the thecomputed computedcompressive compressivetensor. tensor. y1 Fault data from Fault orientation orientation data from Isle Royale, Royale, on on the the north north limb limb of of the the Lake Lake Superior Superior syncline, syncline, exhibited exhibited two two shallowly shallowly dipping dipping populations, populations, one one trending trending northeast northeast and and the the other othernorthwest, northwest, with withslickenside slickenside lineations lineations suggesting suggesting mainly mainly strike slip slip motion motion along along the the faults. faults. The The quality quality of of fault fault sense sense criteria criteria was was excellent, excellent, with with fault fault slickenline slickenline growths growths allowing allowing for for incontrovertible incontrovertible macroscopic macroscopic determinations determinations of of fault fault motion. motion. Implimentation of a fault Implimentation of fault inversion inversion analysis analysis for for data data from fromthe theKeweenaw Keweenaw Peninsula Peninsula resulted resulted in aa southerly southerly compression, compression, while while that from from Isle Isle Royale Royale National National Park, Park, indicates indicates two two tensors, tensors, one one southerly southerly and and the the other other easteastsoutheasterly southeasterly compression. compression. These These tensors tensors are are compatible compatible with model of of with a model southerly southerly extension extension and and compression, compression, introduced introduced by Cambray Cambray and and Fugita Fugita (ILSG, (ILSG, 1991), 1991), with with the the central central portion portion ofofthe theMidcontinent Midcontinent Rift Riftcontaining containing more more material material to to be becompressed compressed than than the thesouthwestsouthwest- and and southeast southeast trending trending limbs limbs to to the thewest westand andeast, east,respectively. respectively. With With this this in in mind, mind, aa 93 �I southerly southerly compression compression would would lead lead to to an aneast-west east-west extrusion extrusion along alongthe the northern northern limb limb of of the the syncline, syncline, caused caused by by contact contact of of this thislimb limbwith withthe the Contact ofof arcuate arcuate shoreline shoreline ofofMinnesota Minnesotaand andOntario, Ontario,Canada, Canada,combined. combined. Contact this this sort sortwould would modify modify the thelocal localstress stressfield fieldaround around Isle IsleRoyale, Royale, on onthe the northern northern limb, limb, and and create create aamaximum maximum compressive compressive stress stress in in aamore more easterly direction. direction. easterly Theseconclusions conclusions are are confirmed confirmed by by examination examination of of the thetrend trend of of These slickensides, from from both both study study areas, areas, which which describes describes the the motion motion on on each each slickensides, 2). limb asascalculated calculated by by the thefault faultarray arrayanalysis analysisprogram program (figure (figure2). limb Figure2.2. Rose Rosediagram diagram of of the thetrend trendofof slickensides slickensideson on Figure normal normaland andreverse reversefaults faultson onIsle IsleRoyale Royale(a (aand andb) b) and andthe theKeweenaw KeweenawPeninsula, Peninsula,Michigan Michigan(C (cand andd). d). 94 �Geochemistry of the the Metadiabases in the Geochemistry of Metadiabases in the Republic Republic Mine Mine Area, Area, Northern Northern Michigan Michigan Xinping Xinping Yin Yin Department of Geology, Department of Geology, Bryn Bryn Mawr Mawr College, College, Bryn Bryn Mawr, Mawr, PA PA 19010 19010 James James A. A. Grant Grant Department of Geology, Department of Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812 55812 There There are are three three layers layers of of Precambrian Precambrian metamorphosed metamorphosed and and altered altered diabase within the the Negaunee iron formation diabase interlayered interlayered within Negaunee iron formation and and several several other other small small bodies bodies in in the the Goodrich Goodrich quartzite quartzite and and Precambrian Precambrian granitic granitic gneiss gneiss in in the Mine area, area, which which isis located at the the the Republic Republic Mine located at the core core of of the theRepublic Republic synclinoriumand andinin the the center syncline syncline in in the the Marquette Marquette synclinorium center of of the the regional regional Northern Michigan. All the metamorphic zones in diabases underwent metamorphic zones in Northern Michigan. diabases underwent extensive extensive regional regional pretectonic pretectonic hydrothermal hydrothermal alteration, alteration, metamorphism metamorphism and and deformation, and local local metasomatism, whichresulted resultedinin the deformation, and metasomatism, which the formation formation of of amphibolite, actinonite actinonite schist, schist, cummingtonite cummingtonite or o r grunerite schist, andalusite schist, muscovite schist and chlorite schist from the the center andalusite schist, muscovite schist and chlorite schist from center of of metadiabases metadiabases to to the contact contact between between the the metadiabases metadiabases and and the theNegaunee Negaunee iron and from from the iron formation, formation, and the limb limb to to keel keel of of the theRepublic Republic syncline. syncline. That That all these these rocks rocks are are formed formed from from same same protolith protolith is is suggested suggested by: by: 1). the t h e stratigraphically conformable conformable relationship between the the 1). metadiabases and Negaunee iron iron formation, formation, which which are are identical identical and and metadiabases and the the Negaunee uniform in the uniform in the whole whole area, area, 2). 2). the thegradual gradualtransition transition between between the the diabase diabase and amphibolite amphibolite outside Republic Mine, gradual change change of the the and outside of of the the Republic Mine, 3). 3). the gradual species and and volume volume of of minerals minerals and and the the mineral mineral assemblages assemblages from from the the species center of the the metadiabases metadiabases to to the the contact contact between between the the metadiabases metadiabases and and center the and from from the the limb limb to to the the iron iron formation formation and the keel keel of of the the syncline, syncline, 4). 4). the the relict amphibolite amphibolite bodies bodies in in different different zones, zones, 5). 5). the the existence existence of of relict relict minerals, such relict plagioclase plagioclase inin all the rock rock types, types, and and the the relict relict minerals, such as as the the relict all the andalusite andalusite in in the the muscovite muscovite schist schist and and chlorite-garnet schist, schist, 6). 6 ) . the the extensive relict textures, such the relict relict diabase diabase textures textures ininamphibolite amphibolite extensive relict textures, such as the and the the pseudomorph of amphibolite amphibolite from from pyroxene, pyroxene, 7).the 7).the gradual gradual decrease of Ca, Mg, decrease of Mg, Na, Na, Sr, Sr, V. V, Cr, Cr, Sc, Sc,Fe++, Fe++, Th, Th, and andYYcorresponding corresponding to to the the gradual increase of of Al, Al, Ti, Ti, K, K, P, H20, gradual increase H20, Nb, Nb,Zr, Zr, Rb, Rb, Ni, Ni, Ce, Ce, La, La, Fe+++, Fe+++, Mn, Mn, Si, Si, Co, Co, and and Ba Ba of of rock rock bulk bulkchemical chemical composition composition from from the the center center ofofmetadiabases metadiabases to the and the iron the contact contact between between the the metadiabases metadiabases and iron formation formation and and from from the 8). the gradual gradual decrease decrease of of the limb limb to to the the keel keelofofthe theRepublic Republicsyncline, syncline, 8). anorthite content inin the and the anorthite content the plagioclase plagioclase and the increase increase of of the the Al/Si, Al/Si, Al/Ca, Al/Ca, K/Na K/Na and and Fe/Mg Fe/Mg ratios ratios in in various various amphiboles amphiboles in in these these two twodirections. directions. 95 �The evidence The evidence above above together together with with the the structural structural analysis analysis suggest:1). suggest:!). before the regional hydrothermal alteration the extensive regional the decomposition metamorphism the diabase metamorphism ofof the diabase resulted resulted in in the decomposition of pyroxene pyroxene and in the and plagioclase plagioclase in the diabase diabase and and the the formation formation of of mafic mafictotoperaluminous peraluminous rocks through the leaching and sodium rocks through the leaching of of iron, iron, magnesium, magnesium, calcium calcium and sodium in the the diabases, 2). these diabases, these rocks rocks with with the different different chemical chemical compositions compositions are metamorphosed to amphibolite, actinonite actinonite schist, cummingtonite schist, schist, the second second episode episode of of andalusite and and muscovite muscovite schist, and and finally finally 3). the andalusite hydrothermal alteration resulted in the extensive alteration of these metamorphicrocks rocksand and in in the local metamorphic local metasomatism metasomatism at the the contact contact between between formation. These metadiabases and and Negaunee the metadiabases Negaunee iron iron formation. These conclusions conclusions are further supported by: by: 1). 1). the the zoning zoning of of the the garnet garnet in in chlorite chlorite schist, schist, which which further supported is defined the inner inner garnet garnet core; core; the middle altered altered garnet garnet ring ring with with defined by by the the middle garnet rim muscovite, biotite, quartz quartz and and chlorite; chlorite; and and the the outer garnet rim with with distinct overgrowths distinct overgrowths and and well-developed well-developed faces; faces; all three garnet zones zones are are three garnet then cut by by the thechlorite chloriteveins veinscontaining containing quartz quartz and and epidote, epidote, 2). then cut the existence at least least three three different different generation generation of of plagioclase: plagioclase: the relict existence of of at the relict plagioclase with anorthite content larger than 50, 50, the intergranural recrystallized and ithe plagioclase recrystallized plagioclase plagioclasewith with lower lower anorthite anorthite content, content, and the plagioclase (most albite) as as the inclusions in amphiboles; all of of these these plagioclase plagioclase underwent extensive sericitization, sericitization, 3). 3). the extensive sericitization of gradual decrease decrease of anorthite content center to andalusite, andalusite, 4). 4). the the gradual of anorthite content from from the the center the the edge edge of of the the relict relict plagioclase; plagioclase; and the increase increase of of the the Al/Si, Al/Si, Na/Ca, Na/Ca, and the 5). K/Na and Fe/Mg ratios center to the the edge edge of of the theamphiboles, amphiboles, 5). K/Na and Fe/Mg ratios from from the the center the the three three sample sample subspaces subspaces in the the cumulative cumulative possibility possibility diagram, diagram, in in the multi-peak curves of distribution pattens, and in the histogr ms for all the multi-peak curves of distribution pattens, and in the histogrtms for the elements, least three three geological geological processes, processes, 66). ) . the the Pearce Pearce elements, which which suggest suggest at at least elements which also also suggests suggests three three possible possible geological geological processes processes and and elements ratios ratios which the decomposition of amphiboles and and plagioclase plagioclase as major major mechanism mechanism for for the decomposition of amphiboles 7). the isocon analysis the regionally pretectonic pretectonic hydrothermal hydrothermal alteration, alteration, 7). the regionally the isocon analysis results which which indicate are at at least least three three major major isocons, isocons, which which are are results indicate that that there there are well demonstrated by two chemographic chemographic methods, suggesting at least least well demonstrated by two methods, thus thus suggesting three geologic processes. The detailed calculations to compare the chemical three geologic processes. The detailed calculations to compare the chemical composition and the the least compositionand and variation variationbetween betweenthe the various various rock rock types types and between adjacent rocks, and between altered metadiabase-amphibolite, metadiabase-amphibolite, between and between different the keel keel of of the the syncline syncline using using isocon isocon different sections sectionsfrom fromthe the limb limb to to the analysis method methodrevealed revealedthe thetotal total mass mass loss loss or or gain analysis gain for for whole whole rocks, rocks, and and the absolute and relative relative loss loss or gain for each elements, elements, which which also also absolute and for each supports the conclusions distinct reflections reflections along along supports conclusions discussed discussed above. above. 8). 8). the the distinct all the the element element concentration concentration curves occur not only from the muscovite curves occur not only from the muscovite schist to schist to the chlorite chlorite schist, schist, but also from from the the amphibole amphibole schist schist to the but also andalusite andalusite schist, schist, which which indicates indicatesthe the distinct distinct change change of of the physical physical and and chemical three different different geologic geologic processes. processes. chemical conditions conditions for for the three !' 96 �The degree degree of metamorphism and hydrothermal alteration is partially controlled by the structural structural position of the metadiabases. Comparedtoto the the relatively simple structures structureson on the the limb limb of the Compared relatively simple the syncline, syncline, numerous kinds of faults (especially the large-scaled axial faults which numerous kinds of faults (especially the large-scaled axial faults which cut cut the keel of of the the syncline), syncline), joints joints and and sliding sliding between between layers layers are are well developed in the developed in the keel. keel. These These structures structures are the the channels channels through through which which the the hydrothermal fluid has flown through and they mark the position where hydrothermal fluid has flown through and they mark the position where The the the most intensive intensive alteration of metadiabases happens. The comprehensive comprehensive analysis analysis of of the the above above information information also also suggests suggests that the fluid fluid flow flow direction direction runs runs from from the thecontact contact between between the themetadiabases metadiabases and and the iron formation to the center of the metadiabases and that the second the iron formation the center of the metadiabases and that the second episode episode of of hydrothermal hydrothermal activity activity is is aa result result hydrothermal hydrothermal alteration alteration and and local local metasomatism metasomatism rather rather than than ofofretrograde retrogrademetamorphism. metamorphism. References R eferences Cannon, Cannon, W.F., W.F., 1975, 1975, Bedrock Bedrock geologic geologic map of of the theRepublic Republic Quadrangle, Quadrangle, Marquette USGS, open-file Marquette County, County, Michigan: Michigan: USGS, open-file map, map, Scale Scale 1:24000 1:24000 Cannon, W.F., and Kiasner, Klasner, J.S., J.S., 1972, 1972, Guide Guide to to Penokean Penokean deformation deformation style style Cannon, W.F., and and of the and regional regional metamorphism metamorphism of the western western Marquette Marquette range, range, Michigan, In Field Michigan, In Field Trip Trip Guidebook, Guidebook, 18th 18th Ann. Ann. Inst, Inst, on on Lake Lake Superior Superior Geology, Geology, Houghton, Houghton, Michigan, Michigan, pp B1-B38 B 1-B38 Cleveland Cliff Iron Co. Cleveland Cliff Co. 1988. 1988. Republic Republic Open Open Pit Map, Map, Scale: Scale: 1:1200 1:1200 Frost, Parageneses in in the Frost, B.R., B.R., 1979, 1979, Metamorphism Metamorphism of iron-formation: iron-formation: Parageneses the system Fe-Si-C-O-H, Econ. Geol., Geol., V. P. 775-785 775-785 Fe-Si-C-0-H, Econ. V. 74, 74, P. Hasse, of the Hasse, C.S., C.S., 1982, 1982, Metamorphic Metamorphic petrology petrology of the Negaunee Negaunee Iron Iron Formation, Formation, Marquette Marquette district, district, northern northern Michigan: Michigan: Mineralogy, Mineralogy, metamorphic metamorphic reactions and phase equilibria, Econ. Geol., v. 77, 60-81 reactions and equilibria, Econ. Geol., 77, p. 60-8 1 Grant, J.A., J.A., 1986. 1986. The The isocon isocon diagram-A diagram-A simple simple solution solution ton ton Gresens' Gresens' Grant, equation alteration. Econ. Econ. Geol., Geol., v. 81, equation for metasomatic metasomatic alteration. 8 1, p. 1976-1982 1976-1982 Gresens, Gresens, R.L., R.L., 1967. 1967. Composition-volume Composition-volume relationships relationships of of metasomatism. Chem. Geol.., Geol.., V. V. 2, P. P. 47-55. 47-55. metasomatism. Chem. James, J.L., J.L., 1955. 1955. Zones Zones of of regional regional metamorphism metamorphism in the the Precambrian Precambrian of of James, northern 1465-1488. northern Michigan. Michigan. GSA GSA Bill., Bill., V.66, V.66, No. No. 12, 12, p. 1465-1488. Klasner, J.S., Klasner, J.S., 1978. 1978. Penokean Penokean deformation deformation and associated associated metamorphism metamorphism in in western Marquette Marquette district, district, northern northern Michigan, Michigan, GSA 89, the western GSA Bull., Bull., v. 89, p. 711-722. 71 1-722. p. 97 �the Proceedings of of this this meeting meetingmay maybe beordered ordered from from Issues of the M.G. Mudrey, Mudrey, Jr., Secretary-Treasurer Secretary-Treasurer do Wisconsin c/o WisconsinGeological Geologicaland and Natural Natural History History Survey Survey 38 17 Mineral Point Road 3817 53705-5100 Madison, Wisconsin 53705-5 100 Part 1: 1: Program and Abstracts: $7.00 U.S. Trip Guidebook: Guidebook: $7.00 $7.00 U.S. Part 2: Field Trip Orders filled while supplies last. Orders will will be filled last. All volumes back to 1955 are available for photocopying at the prevailing rate, from the Michigan Michigan Technological Technological University University Library, Library, through through Mr. Mr. M.S. M.S. Spence, Spence,Archivist. Archivist. Telephone Telephone (906) (906) 487-2505 487-2505 � https://digitalcollections.lakeheadu.ca/files/original/c5253427f96384daf3ddcc7f4512e8bf.pdf 105a711f529b6cdd5f7bf1c12a27cac1 PDF Text Text 7. �ORGANIZING COMMITTEE 38TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY General General Chairman: Albert B. Dickas, University University of Wisconsin-Superior Wisconsin-Superior Program Chairman and Proceedings Proceedings Editor: Bruce Brace A. Brown, Brown, Wisconsin Geological and Natural History Survey Survey Volume 38 consists of Part 1: 1: Program Program and and Abstracts Abstracts Part 2: Field Trip Guidebook Guidebook Published and distributed distributed by Institute on Lake Superior Superior Geology M.G. Mudrey, Jr., Secretary-Treasurer Secretary-Treasurer do c/oWisconsin WisconsinGeological Geologicaland and Natural Natural History History Survey Survey 3817 38 17 Mineral Point Road Madison, Wisconsin 53705-5100 53705-5100 ISSN 1042-9964 1042-9964 �INSTITUTE INSTITUTE ON ON •LAK E• SUPERIOR SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS 38m ANNUAL MEETING MAY 6-9,1992 HURLEY, WIscoNsJl4 ORGANIZED BY ALBERT B. DIcicAs, UNIvERsn'Y O WISCONSIN-SUPERIOR BRUCE A. BROWN, WISCONSIN GEOLOGICAL ANI) NATURAL HISTORY SURVEY VOLUME 38 PART 2 MAY 1992 FIELD TRIP GUIDEBOOK �CONTENTS CONTENTS Trip Trip1:1:Archean Archeanand andEarly EarlyProterozoic ProterozoicGeology Geologyofofthe theGogebic GogebicDistrict, District, Northern Michigan Michiganand andWisconsin Wisconsin Northern Leaders Leaders GeneL. L. LaBerge, LaBerge,University UniversityofofWisconsin—Oshkosh Wisconsin-Oshkosh Gene Richard W. W. Ojakangas, Ojakangas,University UniversityofofMinnesota—Duluth Minnesota-Duluth Richard J. Licht, Licht, St. St. Norbert Norbert College College Kathy J. Kathy Trip2: 2: Evolution Evolutionof of the theKeweenawan Keweenawan Sedimentary SedimentarySequence Sequence Trip Leaders Leaders Albert B. B.Dickas, Dickas,University UniversityofofWisconsin—Superior Wisconsin-Superior Albert M.G. M.G. Mudrey, Mudrcy,Jr., Jr., Wisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey Trip Supergroup Rocks near Trip3: 3: Geology Geology of Keweenawan Supergroup near the the Porcupine PorcupineMountains, Mountains, Ontonagonand andGogebic GogebicCounties, Counties,Michigan Michigan Ontonagon Leaders Leaders William WilliamF. F. Cannon, Cannon, Suzanne SuzanneW. W. Nicholson, Nicholson, Cheryl Cheryl A. A. Hedgman, Hedgman, Schulz, Laurel G. G. Woodruff, Woodruff,and andKlaus Klaus J.J. Schulz, Laurel U.S. Geological GeologicalSurvey, Survey,Reston, Reston, Virginia Virginia U.S. Trip4: 4: Geology Geology of the Great Great Lakes Lakes Tectonic Zone in the Marquette Trip Marquette Area, Michigan-A Late Late Archean Archean Paleosuture Paleosuture Michigan—A Leaders Leaders P.K. Sims Simsand andZ.E. Z.E. Peterman, Peterrnan,U.S. U.S.Geological GeologicalSurvey, Survey,Denver, Denver,Colorado Colorado P.K. 41 75 103 �ARC HEAN AND EARLY PROTEROZOIC GEOLOGY OF THE GOGEBIC DISTRICT, NORTHERN MICHIGAN AND WISCONSIN Gene L. LaBerge University Universityof ofWisconsin—Oshkosh Wisconsin-Oshkosh Richard W. Ojakangas Richard University Universityof ofMinnesota—Duluth Minnesota-Duluth WITH A CONTRIBUTION CONTRIBUTION FROM Kathy J. Licht St. Norbert College �This This field field trip trip is is the the outgrowth outgrowth of of numerous numerous student student field field trips trips led led by by the the authors authors over over the the past past quarter quartercentury. century. Most Most of of the the stop stop localities localities have have been been suggested suggested by by geologists geologists who who have have worked in in the the district. district. However, However, some some localities localities are are the the result result worked One of us (LaBerge) spent of our own studies in the area. of our own studies in the area. One of us (LaBerge) spent several 1991, supported supported by by the the several weeks weeks mapping mapping in in the the area area in in July, July, 1991, U.S. U.S. Geological Geological Survey, Survey, and and Ojakangas Ojakangas worked worked in in this this region region intermittently intermittently with with U.S. U.S. Geological Geological support support from from 1978 1978 until until 1990. 1990. 2 �EARLY EARLYPROTEROZOIC PROTEROZOICGEOLOGY GEOLOGYOF OFTHE THEGOGEBIC GOGEBICDISTRICT DISTRICT NORTHERN AND WISCONSIN WISCONSIN NORTHERNMICHIGAN MICHIGANAND INTRODUCTION The Gogebic Gogebic range range extends extendsfrom from Lake Lake Gogebic, Gogebic! Michigan, Michiganl The westward 128 km kmto tonear nearLake LakeNamekagon, NamekagonlWisconsin Wisconsin westward approximately approximately128 The major major structure structure in in the the area area is is aa north-facing north-facing 1). The (Figure1). (Figure and monocline monocline that that exposes exposes Archean Archean rocks rocks to to the the south south and and Middle Middle and -(~eweenawan Supergroup) rocks rocks to to the the north. north. Late Proterozoic Proterozoic (Keweenawan Late Supergroup) 7 SUPERIOR LAKE / — (C ( \000EBIC WAKEFIELD HURLE> LI. EN — - KiARENI3CO t • I. , + I + 4- 4- 0 10 5 4- 4- 4 + -f 4- 4- - -- vJ- . 4+ s LAX - cl SUE E I Ci -4- 20 KM EXPLANATION EXPLANATION MIDDLE PROTEROZOIC PROTEROZOIC MIDDLE - EARLY EARLY PROTEROZOIC PROTEROZOIC Volcanics and and volcanics sediments sediments I I Graywacke—slate Iron—Formation Iron-Formation ARCH EAN 1-4-4- 4! I m y ). vt.I Granitoids Volcanics Volcan ics 1. Generalized Generalized map map of of the the Gogebic Gogebic range, rangel showing showing the the Early Early Figure 1. Figure Proterozoic Proterozoic rocks rocks sandwiched sandwiched between between Archean Archean rocks rocks on on the south south and and Middle Middle Proterozoic Proterozoic Keweenawan Keweenawan Supergroup Supergroup the rocks on on the the north. north. (Adapted (Adapted from from Morey Morey and and others, others, rocks 1982) 1982) 33 �Early Early Proterozoic Proterozoic rocks rocks lie lie discordantly discordantly between between these these major major sequences. sequences. As As aa result result of of the the steep steep northerly northerly dip dip of of the the monocline tiltingl1 the the geological geological monocline (a (a consequence consequence of of Keweenawan Keweenawan tilting), the district is basically a stratigraphic cross-section. map of map of the district is basically a stratigraphic cross-section. The known The general general geology geology of the the Gogebic range has been known since (1892)1Van Van Hise Hise since the the pioneering pioneering work work of of Irving Irving and and Van Van Hise Hise (1892), and and Leith Leith (1911), (1911)1Hotchkiss Hotchkiss (1919), (1919),and and Aldrich Aldrich (1929). (1929). Although Although subsequent the subsequent studies studies have have done done much much to to "refine" I1refineIt the geological geological picture picture -- - and and much much still still remains remains to to be be done done -- - most most of the the early early interpretations interpretations have have withstood withstood the the test test of of time. time. The The broad-scale broad-scale geology geology of the the eastern eastern Gogebic district is is presented on on the Iron Iron River Quadrangle (Cannon, lo x 2° 2 ' Quadrangle (Cannonl1986). 1986) River 1° . STRATIGRAPHY The The Gogebic Gogebic range range contains contains excellent excellent exposures exposures of of rocks rocks that that range range in in age age from from Archean Archean (about (about 2,700 21700Ma) Ma) and and Early Early Proterozoic Proterozoic ProterozoictKeweenawantI (2,300 11900Ma), Ma), to to Middle and Late Protero~oic-~~Keweenawan~~(2#300-- 1,900 (1,200 (11200-- -600 -600 Ma). Ma). Stratigraphic Stratigraphic and and structural structural relationships relationships of of several several of of the the rock rock sequences sequences can can be be observed observed in in outcrops. outcrops. Thus,it 'Thuslitis is possible possible to to demonstrate demonstrate the the relationship relationship of of the the rock rock sequences sequences to to each each other. other. The The general general sequence sequence of of rock rock units units in in the the Gogebic Gogebic district district is is shown shown in in Figure Figure 2, Z1 aa diagrammatic diagrammatic longitudinal longitudinal section section along along the the Gogebic Gogebic range. range. w Keweenawan Keweenawan tr ofl E --- - Prit + + g Puritan * - - Figure Figure 2. 2. Idealized Idealized sketch sketch showing showing generalized generalized stratigraphic stratigraphic section section on on the the eastern eastern Gogebic Gogebic range. range. 4 �ARCHEA&N ROCKS ARCHEAN ROCKS Archean Archean rocks rocks in in the the Gogebic Gogebic range range are are variably variably deformed deformed and and metamorphosed greenstones and granitoid rocks typical metamorphosed greenstones and granitoid rocks typical of of Archean Archean greenstone-granite greenstone-graniteterranes terranes (or (orbelts), belts) and, and, indeed, indeedlare are an an The district district is is extension extension of of the the Wawa Wawa Greenstone Greenstone belt belt of of Canada. Canada. The near near the the southern southern margin margin of of the the Superior Superior Province Province of of the the Canadian Canadian Because this this fied fieldtrip tripis isconcerned concerned primarily primarily with with the the Shield. Because Shield. Early only aa brief brief description description of of the the Archean Archean Early Proterozoic Proterozoic rocks, rockslonly rocks is is presented presented here. here. rocks Archean volcanic volcanic rocks rocks are are exposed exposed in 'in aa belt belt Ramsay Formation. Formation. Archean Ramsay about about 55 km km wide wide and and 16 16 km km long long in in the the eastern eastern Gogebic Gogebic range range (Prinz and and others, othersl 1975). 1975). Schmidt Schmidt and and Hubbard Hubbard (1972) (1972) named named (Prinz volcanic volcanic and and sedimentary sedimentary rocks rocks in in the the Ramsay-Wakefield Ramsay-Wakefieldarea area as as the Ramsay Ramsay Formation. Formation. The The Ramsay Ramsay Formation Formation consists consists mainly mainly of of the pillowed, pillowedl fragmental, fragmentalland and massive massive basaltic basaltic rocks rocks in in the the eastern eastern part part of of the the area; area; however, howeverlfelsic felsic volcanic volcanic rocks rocks and and metametagraywackes graywackes are are dominant dominant to to the the west, westl near near the the Wisconsin Wisconsin border. border. Most Most of of the the rocks rocks have have been been metamorphosed metamorphosed to to greenschist greenschistfacies, faciesI Locallyl with with well-preserved well-preservedpillows pillows and and other other primary primary features. features. Locally, especially especially adjacent adjacent to to the the Puritan Puritan Quartz Quartz Monzonite, Monzonitelthe the rocks rocks have have been been metamorphosed metamorphosed to to amphibolite amphibolite facies, faciesland and few, fewlor or no, nol The Ramsay Ramsay Formation F o m t i o n may may be be the the primary features features are are preserved. preserved. The primary oldest rock rock unit unit in in the the Gogebic Gogebic range range proper, properl however, howeverl older older oldest gneisses 3#560Ma) Ma) are are exposed exposed in in the the Watersmeet Watersmeet area, areal some some gneisses (to (to3,560 30 km km southeast southeast (Sims (Simsand and others, othersl 1984). 1984) 30 . kritan Quartz Ouartz Monzonite. Monzonite. The The volcanic-sedimentary volcanic-sedimentarysequence sequence of of Puritan the Ramsay Ramsay Formation Formation has has been been intruded intruded by by large large granitoid granitoid masses masses the named the the Puritan Puritan batholith batholith (Schmidt (Schmidtand and Hubbard, Hubbardl1972). 1972). The The named Puritan Puritan Quartz Quartz Monzonite Monzonite exposed exposed in in the the central central and and western western Gogebic range range is is aa weakly-deformed weakly-deformedpost-tectonic post-tectonicpluton pluton that that Gogebic ranges ranges in in composition composition from from granite granite to to tonalite tonalite and and has has been been dated dated 2#735±& 16 to 2,735 16 Ma Ma (Sims (Simsand and others, othersl1984). 1984). to Granitoid rocks rocks are are also also extensively extensively exposed exposed in in the the Granitoid Marenisco area area on on the the eastern eastern end end of of the the Gogebic Gogebic range. range. Parts Parts of of Marenisco the granitoid granitoid has has prominent prominent gneissic gneissic banding banding and and associated associated the otherl more more extensive extensive phase, phasel is is aa weakly weakly amphibolite. The The other, amphibolite. deformed medium-grained medium-grainedgranite granitewith withwidely widelyscattered scatteredpeglnatite pegmatite deformed (Frittsl1969; 1969;Trent, Trentl1973) 1973) bodies (Fritts, bodies . The Archean Archean rocks rocks were were eroded eroded and and are are unconformably unconformably overlain overlain The by Early Early Proterozoic Proterozoic rocks rocks of of the the Marquette Marquette Range Range Supergroup. Supergroup. by Because the the Gogebic Gogebic range range is is aa north-dipping north-dipping monocline, monoclineI Early Early Because Proterozoic rocks rocks rest rest on on Archean Archean rocks rocks to to the the south south along along the the Proterozoic entire length length of of the the range. range. entire EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS EARLY At the the ends ends of of the the Gogebic Gogebic range range the the Archean Archean rocks rocks are are At unconformably overlain overlain by by rocks rocks of of the the Chocolay Chocolay Group Group of of the the unconformably 5 �Marquette Marquette Range Range Supergroup, SupergrouplSunday Sunday Quartzite Quartzite and and Bad Bad River River the eastern eastern end end and and only only Bad Bad River River Dolomite Dolomiteat at the the Dolomite Dolomite at at the Chocolay Group rocks are absent from the central western westernend. end. Chocolay Group rocks are absent from the central part and evidently evidently were were eroded eroded prior prior to to deposition deposition part of of the the range, rangeland of overlying units. of overlying units. The Sunday Sunday Quartzite Quartzite was was deposited deposited Sunday Ouartzite. Ouartzite. The Sunday unconformably uncon~ormablyon on Archean Archean rocks rocks (mostly (mostlythe the Ramsay Ramsay Formation), Formation) The basal basal no regolith regolith on on the the Archean Archean has has been been observed. observed. The however, howeverl no unit is is aa prominently prominently cross-bedded cross-beddedreddish reddish quartzite. quartzite. unit Conglomerate cm Conglomerate layers layers with with quartz quartz and and granite granite cobbles cobbles to to about about 88 cm Most of of the the are are present present within within the the lower lower part part of of the the formation. formation. Most formation formation is is aa gray gray vitreous vitreous quartzite quartzite in in which which cross-bedding cross-beddingis is common common and and current current ripple ripple marks marks are are well well developed developed in in places. places. According According to to Schmidt Schmidt (1973) (1973)the the Sunday Sunday Quartzite Quartzite is is present present only only on on the the eastern eastern end end of of the the range, rangelwhere where it it has has aa maximum maximum thickness thickness of about about 46 46m. m. One One of of the the type type localities localities of of the the Sunday Sunday of Quartzite Quartzite has has been been described described in in the the center center of of the the district district near near the the Newport Newport Mine Mine (Van (VanHise Hise and and Leith, LeithI1911) 1911) and and the the problem problem of of this locality" has this "lost lllost 10cality~~ has been been discussed discussed by by Schmidt Schmidt (1973) (1973). The Sunday Sunday Quartzite Quartzite grades grades upward upward into into the the Bad River River Dolomite. Dolomite. The Bad Bad River River Dolomite. Dolomite. The The transition transition is is marked marked by by interbedded interbedded Bad dolomite dolomite and and quartzite; quartzite; the the dolomite dolomite beds beds are are thicker thicker and and more more abundant abundant and and quartzite quartzite beds beds are are thinner thinner and and less less abundant abundant upward. upward. dolomite weathers weathers to to aa distinctive distinctive tan/brown tanlbrown color color and and The dolomite The contains contains abundant abundant layers layers and and irregular irregular patches patches of of gray gray to to black black chert. Stromatolitic Stromatolitic layers layers with with mounds mounds that that range range in in size size from from chert. about about 5-50 5-50 cm cm in in diameter diameter become become more more abundant abundant upward upward in in the the dolomite. Stromatolitic Stromatolitic units units tend tend to to be be prominently prominently silicified. silicified. dolomite. Maximum Maximum thickness thickness of of the the dolomite dolomite is is about about 120 120 m, ml but but in in most most areas it it is is considerably considerablyless. less. areas AA period period of of erosion erosion followed followed deposition deposition of of the the quartzite quartzite and and dolomite dolomite of of the the Chocolay Chocolay Group, Groupl removing removing the the Sunday Sunday Quartzite Quartzite and and Bad River River Dolomite Dolomite from from all all but but the the eastern eastern and and western western ends ends of of Bad the Gogebic Gogebic range. range. the Palms Formation Formation is is the the basal basal unit unit of of the the Palms Formation. Formation. The The Palms Palms Menominee Group Group of of the the Marquette Marquette Range Range Supergroup. Supergroup. It It rests rests Menomiaee unconformably on on the the Bad Bad River River Dolomite Dolomite and and Sunday Sunday Quartzite Quartzite on on unconformably rangel and and on on the the Puritan Puritan Quartz Quartz the east east and and west west ends ends of of the the range, the Monzonite and and Ramsay Ramsay Formation Formation in in the the central central part part of of the the range. range. Monzonite Little or or no no regolith regolith is is developed developed on on the the erosion erosion surface. surface. Little The Palms Palms Formation Formation is is about about 146 146 meters meters thick thick and and contains contains aa The basal mud-rich mud-rich unit, unitl aa central central interbedded interbedded mud-silt-sand mud-silt-sandunit, unitl basal and an an upper upper sand-rich sand-richunit unit (Ojakangas, (Ojakangas 1983). 1983) AA thin thin (usually (usually and less than than 33 mm thick) thick) conglomerate conglomerate occurs occurs locally locally at at the the base base of of less (Aldrich! 1929). 1929). The The Palms Palms grades grades abruptly abruptly upward upward the formation formation (Aldrich, the into the the Ironwood Ironwood Iron-formation. Iron-formation. Thin Thin (1-5 (1-5cm) cm) beds beds of of granular granular into iron-formationare are interbedded interbedded with with quartzite quartzite (Ojakangas, (Ojakangasl1983) 1983) iron-formation across aa thickness thickness of of 10 10 m. m. The The abundance abundance and and thickness thickness of of beds beds across of iron-formation iron-formationincreases increases upward with with a a corresponding corresponding decrease decrease of in detrital detrital beds. beds. Recent Recent studies studies by by Ojakangas Ojakangas (1983) (1983) indicate indicate in . 66 �that that the the Palms Palms Formation Fomtion may may have have been been deposited deposited by by tidal tidal currents sea currents in in aa transgressing transgressingsea(Figure (Figure3). 3j . Figure Sedimentational model model showing showing lateral lateral relationships relationships of of Figure 3. 3. Sedimentational the the siliciclastic siliciclastic tidal tidal facies, faciesI the the iron-formation iron-formation facies shelfI and and the the deeper-water deeper-waterturbidite-mud turbidite-mud facies on on the the shelf, facies. Thicknesses Thicknesses of of units units not not drawn drawn to to scale. scale. facies. (From Ojakangas, OjakangasI1983) 1983) . (From Ironwood Iron-Formation. Iron-Formation. The The transition transition from from the the Palms Palms Formation Formation Ironwood into into the the Ironwood Ironwood Iron-Formation Iron-Formationrecords records an an abrupt abrupt change change from from detrital to to chemical chemical sedimentation. sedimentation. Like Like other other iron-formations, iron-formationsI detrital the the Ironwood Ironwood contains contains little little detrital detrital material material even even though though it it is is 150-275mm thick. thick. 150-275 Although iron-formation iron-formationhas has aa simple simple composition composition ---- chert chert Although is extremely extremely varied varied in in appearance. appearance. Both Both and iron iron minerals minerals -- -- it is and the the chert chert and and the the iron iron minerals minerals are are varied varied in incolor. color. Although Although it it is is widely widely cited cited as as indicating indicating the the chemistry chemistry of of the the depositional depositional 1954)1 the the mineralogy mineralogy of of iron-formations iron-formationsis is environment (James, (JamesI1954), environment the product product of of the the depositional, depositionalI diagenetic, diageneticI metamorphic, metamorphicI and and to to the some extent, extentI the the weathering weathering environment environment that that the the rocks rocks have have some undergone. Still Still moderate moderate subsequent subsequent changes changes to to the the primary primary undergone. mineralogy do do not not usually usually reduce reduce our our ability ability to to infer infer primary primary mineralogy mineralogy. mineralogy. it Iron-formationshave have two two basic basic textural textural types. types. One One is is Iron-formations laminated with with layers layers of of chert chert about about 5-10 5-10 nun laminated mm thick alternating alternating with layers layers of of iron iron minerals minerals of of similar similar thickness. thickness. This This with laminated type type of of deposit deposit is. is comonly referred to to as as "slaty" 1lslatyll laminated commonly referred 4). It It has has aa grain grain size size and and bedding bedding iron-formation(Figure (Figure4). iron-formation characteristic of of siltstones siltstones (LaBerge, (LaBergeI1964, 19641 Dimroth, Dimroth! 1968). 1968). The The characteristic l1chertyI1 other textural textural type type of of iron-formation, iron-formationIreferred referred to to as as "cherty" other iron-formationIconsists consists of 1-10 1-10 cm cm thick thick layers layers containing containing fine fine iron-formation, (c2 mm) llgrainsn of chert with variable amounts of iron sand-size sand-size (<2 mm) "grains" chert with variable amounts iron minerals set in a chert matrix. These layers of llgranularll chert minerals set in a chert matrix. These layers of "granular" chert are extremely extremely variable variable in in thickness thickness over over short short distances, distancesI are commonly forming lenses (Figure 5). The cherty lenses are are The cherty lenses commonly forming lenses (Figure 5). 7 �_ Figure Figure 4. 4. Photo Photo of of thin-bedded thin-bedded (laminated) (laminated)iron iron formation formation with with some some thick-bedded thick-bedded(granular) (granular) layers. layers. Mt. Mt. Whittlesey, Whittlesey, nearMellen, near-Mellen,WI. WI. . ,: : * A. ' ;— — ,. ::::: : .,: ..— .vr : • . • '&. .• .. • . .. . ¶ , .- g_:L...' I .Figure Figure 5. 5. Photo Photo of of thick, thick, irregularly irregularly bedded, bedded, granular granular iron-formation. iron-formation. Mt. Mt. Whittlesey, Whittlesey, near nearMellen, Mellen, WI. WI 88 . �separated by 0.5-3 typically separated 0.5-3 cm layers layers of laminated laminated iron iron "Cherty" iron-formations have the grain size minerals. minerals. llChertyll iron-formations size and and bedding characteristics characteristics of of sandstones sandstones (Mengel, (Mengel, 1963; 1963; Dimroth Dimroth and and mineralogy of the minerals is Chauvel, Chauvel, 1973). 1973). The mineralogy the iron iron minerals is almost almost completely completely independent independent of of the the textural textural varieties varieties of of ironironironformation. (llchertyll) ironformation. Most geologists geologists agree agree that that granular granular ("cherty") formation formation represents represents shallow-water shallow-water deposition deposition and and laminated laminated ironironformation formation represents represents somewhat somewhat deeper deeper (quieter) (quieter)water water deposition. deposition. Several Superior region Several iron-formations iron-formations in in the the Lake Superior region have been subdivided into."members" on the basis of their been subdivided into."membersNon the their bedding Hotchkiss (1919) divided (textural) characteristics. characteristics. Hotchkiss (1919) divided the (textural) the Ironwood Ironwood Iron-formation Iron-formationinto into five five members. members. The -60 -60 m thick thick Plymouth Plymouth Member is is an an irregularly irregularly bedded bedded granular granular cherty cherty unit unit with a basal zone containing some detrital quartz quartz and and patches patches of zone containing overlying 46 46 m thick thick Yale Yale Member Member is is stromatolitic stromatolitic jasper. jasper. The overlying mainly an even-bedded (slaty) siderite-chert unit with a basal mainly an even-bedded (slaty) siderite-chert carbonaceous zone and a layer that is probably probably carbonaceous pyritic slate zone The succeeding Norrie Member is a 60 m thick unit m thick unit of of The succeeding Norrie Member is a 60 tuffaceous. tuffaceous. The Pence Member is The Pence Member is irregularly bedded cherty iron-formation. irregularly bedded cherty iron-formation. about 45 m of siderite-chert siderite-chert iron-formation, iron-formation, and the uppermost uppermost Anvil Anvil Member Member is is aa 15-60 15-60mm thick thick mixture mixture of of slaty slaty and and cherty cherty ironironThese members are continuous and uniform throughout formation. formation. These continuous uniform throughout However, they are are difficult difficult to the length of of the the range. range. However, to the 128 128 km length distinguish east of Wakefield, Michigan, where a thick distinguish east of Wakefield, Michigan, where a thick sequence sequence of volcanic rocks, 1973), is is rocks, the the Emperor Emperor Volcanic Complex Complex (Trent, (Trent, 1973), interbedded with interbedded with the the iron-formation. iron-formation. Gogebic range Iron ores. Iron ores. The iron iron ores ores on on the the Gogebic range were produced by chemical removal the chemical removal of of silica silica from from the the iron-formation. iron-formation. Dissolution of the Dissolution the silica silica required required the the removal removal of of nearly nearly 50 50 volume of the percent of the the original original volume the rock rock and and produced produced very very The ore ore consisted consisted mainly of earthy earthy goethite goethite porous orebodies. porous orebodies. The hematite; however, and hematite; however, in in open open spaces spaces produced produced by removal removal of of silica, botryoidal masses of silica, large large botryoidal of crystalline crystalline hematite hematite and and goethite were found, goethite found, as as well as as local local concentrations concentrations of of psilomelane psilomelane (romancheite), (romancheite), manganite, manganite, rhodochrosite, rhodochrosite, calcite, calcite, presence of manganocalcite, manganocalcite, barite, barite, gypsum, gypsum, and and marcasite. marcasite. The presence of iron iron ore ore cobbles cobbles in in Keweenawan Keweenawan rocks rocks in in the the district district suggests suggests that at least least some some of the the ore ore was was formed formed prior prior to to deposition deposition of of rocks of rocks of the the Keweenawan Keweenawan Supergroup. Supergroup. Nearly all all the the mines mines on on the the Gogebic Gogebic range range were were underground underground mines mines (Figures (Figures66 and and 7). 7). Mining Gogebic range on the the Gogebic range began began in in 1884 1884 and and ended ended in in 1967, 1967, when when the the underground mines could no longer open pit could no longer compete compete with the large large open taconite mines taconite mines elsewhere elsewhere in in the the world. world. Ore was taken taken by rail rail to to Ashland, Wisconsin, and Ashland, Wisconsin, and Escanaba, Escanaba, Michigan, from from where it was shipped to shipped to steel steel mills mills in in Indiana Indiana and and Ohio. Ohio. Emperor Volcanic Volcanic Complex. Emperor Complex. The The Emperor Emperor Volcanic Complex Complex constitutes a constitutes a thick thick pile pile of of volcanic volcanic rocks rocks and and sills sills in in the the sedimentary sequence sequence on the eastern Gogebic range where they sedimentary reach a thickness thickness of of at at least least 2,000 2,000 meters. meters. Although Although the the volcanic rocks been known volcanic rocks in in the the eastern eastern Gogebic Gogebic range range have have been known for for 100 1892), few studies have been few studies 100 years (Irving (Irving and Van Hise, 18921, undertaken undertaken on on these these rocks. rocks. Irving Irving and Van Hise (1892) (1892) stated stated 9 �___ GOGEBIC RANGE GOGEBIC RANGE GENERALIZED GEN E R A L I Z E D CROSS CROSS SECTION SECTION . (P. I b ... .0.. °o0 0.•. 0 :. .o;,; 0 ° . fl 0 :. - PLTMQJTII yap - ) --•------• ,O •- £pds,t - - \ \ \, / -- \ ./ . c \ —. \ /\ -<\ -. \/ / \ -, \, _y -':': — \ FORSATION —. — .' a \\ IlOH*Uc)O \ /,/\\ \\,S ,'—_-c' \ \ \ \ //,;/ " \ -: Poll I IOIUI.l l(P. __1__ _____:_.__ .. // 1.' \ 'a. ', •-' / /,'• // /1 '\/ \ Q.j U Y'\' \ç.\ — UUITI I NC, M G WE WK ST '31 // •0 0. ----------Q // 'I /1 \ \ \ \\ \ IAT ION . Figure 6. Schematic diagram showing showing the the occurrence occurrence of of iron iron (From Goldich orebodies on the orebodies the Gogebic Gogebic range. range. (From Goldich and Marsden, 1956) Marsden, 1956) Lake mine in in 1960. 1960. Note the the stockpile stockpile of of iron iron Figure 7. Sunday Lake ore in in the the upper upper left. left. Photo taken from from the the top top of of In Wakefield, Wakefield, Michigan. Michigan. Radio Tower Hill Hill In 10 �that that the the volcanic volcanic rocks rocks are are interbedded interbedded with with the the Ironwood Ironwood IronIronformation, formation, which which has has been been demonstrated demonstrated convincingly convincingly by by subsequent subsequent Mapping by by Trent Trent exploration or iron iron ore ore in exploration drilling drilling ffor in the the area. area. Mapping (1973) documented the distribution of igneous (1973) documented igneous rocks rocks and and showed showed some some of of the the lithologies lithologies present. present. Dann Dann (1978) (1978) showed showed that that the the volcanics dacite, and and that that volcanics range range in in composition composition from from basalt to to dacite, they have have been been metamorphosed metamorphosed only only to to prehnite-pumpellyite, or to to they prehnite-pumpellyite, or He also also elaborated elaborated on on the the possible possible lowest lowest greenschist greenschist facies. facies. He volcanic volcanic setting setting in in which which the the rocks rocks may may have have formed. formed. Trace Trace element studies by Schulz (Sims and others, 1990) element studies Schulz (Sims others, 1990) indicate indicate that that the the volcanic volcanic rocks rocks are are rift-related rift-relatedcontinental continental tholeiites. tholeiites. Reconnaissance Reconnaissance mapping in in 1991 1991 by LaBerge LaBerge and J. S. Klasner Klasner indicates that the Emperor Volcanic Complex indicates that the Emperor Volcanic Complex consists consists of of aa wide wide Both variety variety of of mainly mainly subaqueous subaqueous volcanic volcanic rocks rocks and and sills. sills. Both mafic mafic and and felsic felsic volcanics volcanics were were recognized. recognized. Mafic Mafic rocks rocks include include sills (such as the Wolf Mountain sill of Trent, 1973) sills (such as the Mountain sill Trent, 1973) pillowed pillowed and and massive massive flows, flows, some some with with columnar columnar jointing, jointing, and and extensive extensive Felsic hyaloclastites and pillow breccias (Figure 8). rocks hyaloclastites and pillow breccias (Figure 8). Felsic rocks include include hyaloclastites, hyaloclastites, massive massive felsite felsite breccias, breccias, and and units units comprised comprised of of felsite felsite breccia breccia with with 2-10 2-10 cm cm clasts clasts in in a a finer finer hyaloclastite 9). The The felsite felsite breccia breccia -hyaloclastite matrix matrix (Figure (Figure9). hyaloclastites may may be be debris debris flows flows from from aa subaqueous subaqueous felsic felsic dome. dome. hyaloclastites Although in the the Emperor Emperor Volcanic Volcanic Complex Complex with with Although there there are are zones zones in strong strong foliation, foliation, large large areas areas are are almost almost undeformed. undeformed. Because Because of of the metamorphic grade the low low metamorphic grade and and minimal deformation, deformation, primary primary features are are well-preserved. well-preserved. features The The relationship relationship between between volcanism volcanism and and iron-formation iron-formationhas has long (e.g., Van Van Hise Hise and and Leith, Leith, long been been debated, debated, with with some some advocates advocates (e.g., 1911) volcanic contributions 1911) arguing arguing in in favor favor of volcanic contributions of of iron, iron, and and others others (e.g., (e.g., James, James, 1954) 1954) contending contending that that there there is is no no genetic genetic relationship relationship between between volcanism volcanism and and iron-formation iron-formationdeposition. deposition. The The presence presence of of aa thick thick volcanic volcanic sequence sequence interbedded interbedded with with the the iron-formation iron-formationin in the the eastern eastern Gogebic Gogebic range range shows shows that that there there certainly certainly was was volcanism volcanism contemporaneous contemporaneous with with iron-formation iron-formation deposition deposition in in the the Lake Lake Superior Superior region. region. Therefore, Therefore, the the Gogebic Gogebic range range is is similar similar to to the the Hamersley Hamersley range range in in Western Western Australia Australia and and the the Proterozoic Proterozoic iron-formations iron-formationsin in South South Africa Africa where where numerous numerous volcanic ash layers layers are are interbedded interbedded with with the the iron-formations iron-formations volcanic ash (LaBerge, 1966a, 1966a, 196Gb). 1966b) (LaBerge, . Tyler and and Copps CORDS Formations. Formations. The The Ironwood Ironwood Iron-Formation, Iron-Formation, and Tyler locally the the Emperor Emperor Volcanic Complex, Complex, are overlain locally overlain by a 2,000 2,000 m graywacke-slatesequence. sequence. The The unit unit is is thickest thickest in in the the thick graywacke-slate thick western and and eastern eastern ends ends of the the range, range, and has been completely completely western removed by erosion erosion prior to to deposition deposition of the Keweenawan removed Keweenawan Supergroup in in an an area area near near Wakefield, Wakefield, Michigan. Michigan. Throughout Throughout most most Supergroup the range range the the unit is is called called the the Tyler Formation, however the of the Tyler Formation, however the correlative(?) portion at the eastern end of the range is called correlative(?) portion the eastern range is the Copps Copps Formation. Formation. The The Tyler Tyler Formation Formation is is correlated correlated with with the the the Michigamme Formation to the east, and with the Thomson, Rabbit Michigamme Formation to the east, and with the Thomson, Rabbit Lake, Virginia and and Rove Rove Formations Formations to to the the west and north in in Lake, Minnesota and and Ontario. Ontario. All these these units deposited Minnesota units were probably deposited in the the same same basin. basin. in 11 �Figure 8. Pillow Pillow breccia breccia in in Emperor Emperor Volcanic Volcanic Complex. Complex. Pillows Pillows and in aa hyaloclastite hyaloclastite matrix. matrix. and pillow pillow fragments fragments in Jackknife Jackknife is is on on aa pillow. pillow. Figure 9. 9. Felsic Felsic phase phase of of Emperor Emperor Volcanic Volcanic Complex. Complex. Felsite Felsite Figure clasts clasts in in aa finer finer hyaloclastite hyaloclastite matrix. matrix. Jackknife Jackknife is is 88 . cm. cm 12 �The The relationship relationship of of the the Tyler Tyler Formation Formation to to the the underlying underlying iron-formation is iron-formation is unclear. unclear. According to to Hotchkiss Hotchkiss (1919) (1919) the the basal unit of the the Tyler Tyler Formation Formation is is the the Pabst Pabst Member, Member, aa distinctive distinctive unit unit containing containing mainly mainly jasper jasper and and quartz quartz pebbles. pebbles. 10, from drill hole data (Atwater, Figure 10, (Atwater, 1938) 1938) shows shows the the relationship ironrelationship of the the conglomerate conglomerate to to the the underlying underlying ironHotchkiss (1919) relationships between formation. formation. Hotchkiss (1919) interprets the relationships Atwater the Tyler Tyler and the iron-formation to be unconformable. the iron-formation to be unconformable. Atwater (1938) did not believe* believe' that that aa major major unconformity unconformity separated separated the (1938) did the Schmidt and Hubbard (1972) Ironwood Ironwood and and Tyler. Tyler. Schmidt (1972) interpreted interpreted the the formations sedimentation to have been formations to be gradational and sedimentation continuous Gocrebic. However, However, Trent Trent (1973) (1973) stated stated continuous in in the the central central Gogebic. that that field field relationships relationships indicate indicate an an unconformity unconformity between between the the Schmidt (1980) Ironwood and Tyler Ironwood Tyler on on the the eastern eastern Gogebic. Gogebic. Schmidt (1980) summarizes summarizes the the field field evidence evidence pertaining pertaining to to the the Ironwood-Tyler Ironwood-Tyler contact contact as as well as as the the several several alternative alternative interpretations. interpretations. 1 ATLANTIC MINE NO 3 SHAfl D 0 HOI I 2 PLUMMER SHAF1 51H LEVEL CROSSCUI 3 PENCE NO 2 SHAFT AND 0 0 HOLE 4 MONTREAL NO 4 SHAFT 20TH I EVE1 ' ' 1 5 MONTREAL NO 4 SHAFI BTH LEVEL I I 1 l HOLE 6 OTTAWA 10TH LEVEL SHAFT CROSSCIII 7 GARY 19IH LEVEL NO 16 CROSSCUI 1) U HOLE 8 NORRIE 14TH AND 17TH LEVELS 9 AURORA E SHAFT 13TH LEVEL 10 PABS1 G SHAD I I BONNIL R2E Figure 10. Figure 10. 2 MRFS 0 &-\TJ I 0 H ~ I: ? I ~ N I A I XAI 3 ~IKIMETERS c .. vCRTICAL SCALE 1 >(L;Iu! n:ii Longitudinal section Longitudinal section through through part of of the the Gogebic Gogebic district, showing district, showing one one interpretation interpretation of of "Pabst Member" Membern of of the the relationship between the "Pabst relationship between the Tyler Formation and and the the Anvil and and Pence Pence Members Members of of Tyler Formation the the Ironwood Ironwood Iron-Formation. Iron-Formation. The upper slate is is aa upper slate layer layer of thin-bedded thin-bedded carbonate carbonate iron-formation, iron-formation,at at least least partly partly within within the the Anvil Anvil Member. Member. Compiled from measured in mines and and drill drill holes. holes. measured sections sections in Location sections given in map Ironwood Location of sections map of Ironwood Iron-Formation in in lower lower part part of of diagram. diagram. Modified Iron-Formation (1938,p. p. 163, 163, fig. fig. 2) 2) (From from Atwater from Atwater (1938, (From Schmidt, Schmidt, 1980) 1980) 13 �The The Tyler Tyler Formation Formation consists consists dominantly dominantly of of intercalated intercalated argillite argillite with with lesser lesser amounts amounts of of metasiltstone metasiltstone and and graywacke. graywacke. Graded sequences indicative Graded metagraywacke metagraywacke beds beds containing containingBouxna B o w sequences indicative of deposition by turbidity turbidity currents currents are common, common, but structureless structureless beds beds are are even even more more abundant abundant and and aa grain-flow grain-flow mechanism mechanism may may also also have have been been operative. operative. Sole Sole marks marks and and small-scale small-scale cross-bedding cross-bedding indicate westindicate a a paleocurrent paleocurrent trend trend from from east-southeast east-southeast to to westnorthwest northwest (Alwin, (Alwin,1976). 1976) . The The "average" "averagengraywacke graywacke of of the the Tyler Tyler consists consists of of 28 28 percent percent micaceous micaceous matrix matrix and and 72 72 percent percent framework framework grains grains (Alwin, (Alwin,1976). 1976). Of 73 percent percent are are monomono- and and polycrystalline polycrystalline Of the the framework framework grains, grains, 73 quartz quartz and and chert, chert, 10 10 percent percent are are plagioclase plagioclase (mostly (mostly altered altered plagioclase), plagioclase), and and 17 17 percent percent are are rock rock fragments, fragments, mainly mainly of of granitic granitic to to quartz quartz dioritic dioritic and and volcanic volcanic origin, origin, but but some some grains grains of sedimentary sedimentary and and metamorphic metamorphic origin origin also also are are present. present. Thus, Thus, the the "average" "averagev graywacke graywacke of of the the Tyler Tyler is is compositionally compositionally submature submature quartzose quartzose lithic lithic graywacke graywacke that that is is texturally immature immature as defined by by angular angular framework framework grains grains and and poor poor sorting. sorting. The The paleocurrent paleocurrent directions directions and and the the composition composition of of the the graywacke graywacke suggest suggest that that the the Tyler Tyler Formation Formation was was derived derived from from aa dominantly "graniticvsource source to to the the southeast. southeast. dominantly "granitic" MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC ROCKS ROCKS Following the Penokean orogeny, about about 1,860 Following the Penokean orogeny, 1,860 -- 1,830 1,830 Ma, Ma, the the Gogebic and the the rest Gogebic range range and restof ofthe theLake LakeSuperior Superior region region was was subjected subjected to to erosion erosion for fornearly nearly700 700 million million years. years. Erosion Erosion removed removed an an unknown unknown thickness thickness of of rocks rocks in in the the range, range, but but more more rock rock was example, at at was removed removed from from some some areas areas than than in in others. others. For For example, least preserved in least 2,000 2,000 meters of the the Tyler Tyler Formation Formation is is preserved in the the western western Gogebic, Gogebic, and and aa comparable comparable thickness thickness of of the the Copps Copps Formation Formation is is preserved preserved at at the the eastern eastern end end of of the the range. range. However, However, all Ironall of of the the Tyler, Tyler, and and some some of of the the underlying underlying Ironwood Ironwood IronFormation Formation as as well, well, was was removed removed in in the the eastern eastern Gogebic Gogebic where where the the range range experienced experienced more more folding. folding. The The erosion erosion interval interval presumably presumably ended ended with with the the onset onset of of the the Middle Middle Proterozoic Proterozoic Keweenawan Keweenawan rifting rifting event. event. Bessemer Bessemer Ouartzite. Ouartzite. In Gogebic range In most of of the the Gogebic range the the Bessemer Bessemer Quartzite, Quartzite, the the basal basal unit unit of of the the Keweenawan Keweenawan Supergroup, Supergroup, unconformably unconformably overlies overlies the the Tyler Tyler Formation. Formation. However, However, locally locally on on eastern part of of the the range range the the basal basal Keweenawan Keweenawan rests rests on on the the the eastern Ironwood Iron-Formation Iron-Formation or or the the Emperor Emperor Volcanic Volcanic Complex. Complex. The Ironwood The quartzite is is approximately approximately 100 100 mm thick, thick, has has channel channel cross-bedding cross-bedding quartzite and and is is aa relatively relatively mature mature quartz quartz sandstone sandstone (Ojakangas (Ojakangasand and Matsch, Matsch, 1982). 1982). The The Bessemer Bessemer Quartzite Quartzite evidently evidently originated originated in in a fluvial environment environment in in aa slight slight sag sag that that presaged presaged the the Keweenawan Keweenawan fluvial rifting rifting that that developed developed into into the the Midcontinent Rift System System (Ojakangas (Ojakangas and and Matsch, Matsch, 1982). 1982). 14 �Overlying the the Bessemer Bessemer Quartzite Quartzite is is aa thick thick Powder Mill Mill Group. Grouu. Overlying Powder sequence sequence of of mainly mainly basaltic basaltic lava lava flows flows that that formed formed during during the the Volcanic activity activity main main phase phase of of Keweenawan Keweenawan rifting rifting in in this this area. area. Volcanic (and Ma ago ago and and produced produced approximately 1,200 1,200 Ma (and rifting?) rifting?) began approximately hundreds hundreds of of lava lava flows flows that that have have an an aggregate aggregate thickness thicknessof ofmore more than 3,000 3,000m. m. The The lowermost lowermost basaltic basaltic lava lava flows flows that that overlie overlie the the than Bessemer Bessemer Quartzite Quartzite in in the the Bessemer, Bessemer,Michigan, Michigan,area areaare arepillowed, pillowed, suggesting either aa lake lake or or aa suggesting that that they they were were extruded extruded in in water, water, either fluvial system. fluvial system. Keweenawan Supergroup Supergroup volcanic volcanic rocks rocks are are overlain overlain Oronto Group. Group. Keweenawan Oronto by a thick sequence of mainly red clastic rocks in the Lake by a thick sequence of mainly red clastic rocks in the Lake Various representatives representatives of of this this sequence sequence are are Superior region. region. Various Superior The basal basal unit unit of of the the well exposed exposed north north of of the theGogebic Gogebicrange. range. The well Oronto the Copper Copper Harbor Harbor Conglomerate, Conglomerate, which which is is as as thick thick Oronto Group Group is is the The major lithology is red arkosic sandstone and The major lithology is red arkosic sandstone and as 2,000 2,000m. m. as siltstone with with numerous numerous conglomeratic conglomeratic horizons. horizons. The The Copper Copper siltstone Harbor Harbor Conglomerate Conglomerate probably probably represents represents alluvial alluvial fan fan deposits deposits formed formed near near aa rugged rugged source source area area along along the the south south side side of of Lake Lake Superior. Superior. The The Copper Copper Harbor Harbor Conglomerate Conglomerate is is overlain overlain by by the the Nonesuch Nonesuch Formation, Formation, aa 100 100 meter meter thick thick clastic clastic unit, unit, that that is is dominantly dominantly The Nonesuch Nonesuch was was probably probably gray to to black black carbonaceous carbonaceoussiltstone. siltstone. The gray deposited deposited in in aa lake lake developed developed on on the the subsiding subsiding pile pile of of volcanic volcanic (e.g., Suszek, Suszek,1991). 1991). In In rocks and and Copper Copper Harbor Harbor sediments sediments (e.g., rocks addition addition to to the the world world class class copper copper deposits deposits of of the the White White Pine Pine mine, mine, the the Nonesuch Nonesuch Formation Formation also also contains contains one one of of the the oldest oldest known occurrences occurrences of of petroleum. petroleum. known The Freda Freda Sandstone Sandstone of of the the Oronto Oronto Group Group consists consists of of The clastics, and and conformably conformably overlies overlies approximately 3,000 3,000 mm of of red red clastics, approximately the Nonesuch Nonesuch Formation. Formation. The The Freda Freda strata strata is is believed believed to to consist consist the of fluvial fluvial deposits deposits formed formed during during continued continued subsidence subsidence of of the the of Middle Proterozoic Proterozoic rift. rift. Middle KEWEENAWANTILTING TILTING KEWEENAWAN Following the the onset onset of of deposition deposition of of the the volcanic volcanic and and Following sedimentary rocks rocks along along the the Keweenawan Keweenawan Midcontinent Midcontinent Rift Rift System, System, sedimentary the south south side side of of the the rift, rift, including including the the Gogebic Gogebic district, district, was was the (65-90') to to the the north. north. tilted steeply steeply (659O0) tilted TECTONIC SEFING SETTING TECTONIC Early Proterozoic Proterozoic rocks rocks in in the the Gogebic Gogebic range range unconformably unconformably Early overlie Late Archean greenstone and granite of the Superior overlie Late Archean greenstone and granite the Superior L a m e (1981, 1983) suggested Province of the Canadian Shield. Province of the Canadian Shield. Larue (1981, 1983) suggested that the sedimentary rocks of the Lake Superior region (the that the sedimentary rocks the Lake Superior region (the Marquette Range Range Supergroup) Supergroup) were were deposited deposited in in aa number number of of grabengrabenMarquette like basins basins in in aa platformal platformal environment. environment. Sims Sims and and others others (1990) (1990) like 15 �proposed that that rocks rocks of of the the Marquette Marquette Range Range Supergroup Supergroup formed formed on on aa proposed rifted continental continental margin. margin. Break-up Break-upof of the the Archean Archean craton craton rifted resulted in in the the development development of of oceanic oceanic crust crust off off the the southern southern resulted margin of of the the Superior SuperiorProvince. Province. Therefore, Therefore, the the sedimentary sedimentary margin rocks were were deposited deposited during during aa rifting rifting stage stage that that developed developed into into aa rocks (1988) passive margin. Nd isotope studies by Gerlach and others passive margin. Nd isotope studies by Gerlach and others (1988) indicate that that iron-formations iron-formationsin in the the Lake Lake Superior Superior region region were were indicate deposited about 2,100 Ma. deposited about 2,100 Ma. concept of of aa rif rifted margin in in the the Lake Lake The concept The ted continental continental margin Superior region is probably best exemplified by the eastern Superior region is probably best exemplified by the eastern Gogebic range. range. As As discussed discussed earlier, earlier,the the stratigraphic stratigraphic Gogebic Wakefield, succession increases considerably in thickness east of of Wakefield, succession increases considerably in thickness east Michigan, and igneous rocks (volcanic rocks and sills) become aa Michigan, and igneous rocks (volcanic rocks and sills) become major component of the succession. The increase in thickness of major component of the succession. The increase in thickness of the sedimentary sequence and the influx of volcanic rocks is the sedimentary sequence and the influx of volcanic rocks is suggestive of of aa half half-graben near Wakefield Wakefield suggestive -graben structure structure with with a a hinge hinge near and a boundary fault (or faults) near Lake Gogebic. Emplacement and a boundary fault (or faults) near Lake Gogebic. Emplacement of basaltic basaltic sills sills (e.g., (e.g., the the Wolf Wolf Mountain Mountain sill sill of of Trent, Trent,1973) 1973) of and eruption of continental tholeiites (Sims, and others, 1990) and eruption of continental tholeiites (Sims, and others, 1990) The would be be characteristic characteristicof ofaarif rifted continental margin. margin. The would ted continental presence of the sills and volcanic rocks in the Ironwood Ironpresence of the sills and volcanic rocks in the Ironwood IronFormation as well as dramatic eastward thickening of the ironFormation as well as dramatic eastward thickening of the ironthat major major graben graben formation formation and and volcanism volcanism formation indicates indicates that formation occurred during deposition of the Ironwood Iron-Formation (Figure occurred during deposition of the Ironwood Iron-Formation (Figure 11). 11) Following the the rifting rifting and and passive passive margin margin stages, stages, aa phase phase of of Following convergent tectonics produced a volcanic island arc (the convergent tectonics produced a volcanic island arc (the Wisconsin magmatic magmatic terranes) terranes) that that collided collided with with the the Superior Superior Wisconsin Isotopic ages ages in inrocks rocksof ofthe thernagmatic magmatic terrane terrane range range craton. Isotopic craton. (Sims and others), and docking occurred 1.890 Ma to 1,840 Ma from from 1,890 Ma to 1,840 Ma (Sims and others), and docking occurred 1.860 Ma (Sims and others, 1990). Barovich and others about about 1,860 Ma (Sims and others, 1990). Barovich and others (1989) showed showed that that Nd Nd isotopes isotopes indicate indicate that that much much of of the the (1989) graywackes in the Michigamme Formation were derived from an Early Early graywackes in the Michigainme Formation were derived from an Proterozoic source. source. This This suggests suggests that that the the graywackes graywackes were were Proterozoic deposited in in aa foreland foreland basin basin during during docking docking of of the the island island arc arc on on deposited the margin margin of of the the Superior Superiorcraton. craton. the 16 16 Deformation and and metamorphism metamorphism of of rocks rocks of of the the Marquette Marquette Range Range Deformation Supergroup on the Gogebic range resulted from the collision of Supergroup on the Gogebic range resulted from the collision of the island arc with the margin of the Superior craton. This the island arc with the margin of the Superior craton. This collision fits fits very very well well with with aa foreland foreland basin basin model model as as developed developed collision Hoffman (1987) for the Early Proterozoic rocks that surround by by Hoffman (1987) for the Early Proterozoic rocks that surround Archean Superior Superior Province. Province. This the Archean This model model was was utilized utilized by by the Southwick and Morey (1991) to explain lithologic and structural Southwick and Morey (1991) to explain lithologic and structural relationships in in east-central east-centralMinnesota. Minnesota. AA similar similar foredeep foredeep relationships model, with associated southward subduction and collision of aa model, with associated southward subduction and collision of volcanic arc against the craton to the north was proposed by volcanic arc against the craton to the north was proposed by Ojakangas (in (inpress) press)to toexplain explainthe theorigin originofofthe theMichigainme Michigamme Ojakangas Formation of the Upper Peninsula of Michigan, as well as the the Formation of the Upper Peninsula of Michigan, as well as origin of the Copps and Tyler formations in the vicinity of the the origin of the Copps and Tyler formations in the vicinity of Gogebic range. In this model, the iron-formation was deposited Gogebic range. In this model, the iron-formation was deposited northwardon the the peripheral peripheral bulge bulge on on the the north north side side of of the the northwardon migrating foreland basin, whereas the aforementioned turbidite migrating foreland basin, whereas the aforementioned turbidite �sequences sequences were were deposited deposited in in the the deeper deeper axial axial parts parts of of the the basin. basin. This This would would require require that that the the Ironwood Ironwood Iron-Formation Iron-Formationand and the the overlying overlying Tyler Tyler Formation Formation have have aa gradational gradational and and conformable conformable relationship, relationship, and and that that they they were were deposited, deposited,at at least leastin inpart, part, tholeiitic volcanism volcanism contemporaneously. In In this this model, model, axial axial tholeiitic contemporaneously. (Hoffman, 1988) and hydrothermal activity activity in (Hoffman, 1988) in the the foredeep foredeep would would have provided the iron and silica that were precipitated have provided the iron and silica that were precipitated as as ironironformation formation on on the the shelf, shelf, as as upwelling upwelling brought brought the the solutions solutions to to aa favorable site site of of deposition. deposition. favorable Note Note that that the the foreland foreland basin basin model model provides provides an an alternative alternative interpretation interpretation for for the the Ironwood Ironwood and and the the intertonguing intertonguing Emperor Emperor Volcanic ted continental Volcanic Complex Complexcompared comparedwith withaarif rifted continental margin margin model. model. Obviously Obviously more more work work is is needed needed to to resolve resolve this this problem. problem. Deformation Deformation during during the the Penokean Penokean orogeny orogeny may may have have resulted resulted in in reactivation reactivation of of the the normal normal faults faults in in the the graben graben structures. structures. We We suggest suggest that that the the structure structure in in the the eastern eastern Gogebic Gogebic may may represent represent aa half-graben half-graben that that has has been been subjected subjected to to thrusting thrusting during during the the Penokean orogeny orogeny (Figure (Figure12). 12). Perhaps Perhaps significantly, significantly, erosion erosion Penokean prior prior to to deposition deposition of of the the Keweenawan Keweenawan Supergroup Supergroup cut cut deepest deepest into into the the Early Early Proterozoic Proterozoic sedimentary sedimentary sequence sequence in in the the central central Gogebic, where where the the proposed proposed thrust thrust faults faults are are present. present. Whereas Whereas Gogebic, over 2,000 2,000 mm of of the the Tyler Tyler Formation Formation remain remain on on the the western western Gogebic Gogebic over in Wisconsin, Wisconsin, and and aa similar similar thickness thickness of of Copps Copps Formation Formationis is in present at at the the eastern eastern end end of of the the range, range, erosion erosion removed removed all all of of present the Tyler Tyler and and part part of of the the iron-formation iron-formationeast east of of Wakefield. Wakefield. the Assuming that that erosion erosion cut cut down down to to aa relatively relativelyuniform uniform level, level, Assuming then the the central central Gogebic Gogebic may may have have been been uplifted uplifted at at least then least 2,000 2,000 mm more than than areas areas to to the the east east and and west. west. An An Archean Archean cored cored gneiss gneiss more dome is is present present near near Watersmeet Watersmeet about about 50 dome 50 km km to to the the east. east. That That area may may represent represent an an even even more more pronounced pronounced uplift. uplift. Therefore, area Therefore, rocks on on the the eastern eastern Gogebic Gogebic range range may may record record depositional depositional and and rocks deformationalevents events of of both both the therif rifted and convergent convergent deformational ted margin margin and tectonics during during the the Early Early Proterozoic Proterozoic in in the the Lake Lake Superior Superior tectonics region. region. 17 �w -- -- '---'---'——-— '- - E - tRON WOOD 4 —.-.—'.--— ___A._ Water Surface-7 - - EROR 4u , --- - -::,/_.-- — / M A vA I RAM SAY / / b A y I— 1-i • V V 18 Figure 11. Figure 11. pre-Penokean Diagram showing hypothetical pre-Penokean relationships on the eastern Gogebic relationships on the eastern Gogebic range. range. Figure Figure 12. 12. Simplified geologic map Gogebic Gogebic range. range. (Not (Not to of the eastern eastern part of of the the scale) scale) �STOP STOP DESCRIPTIONS DESCRIPTIONS Field Trip Gogebic Field 19 �Stop stow 1. 1. Tyler Wler Formation. Formation. Location: Location: Roadcuts Roadcuts at at junction junction of of U.S. U.S. Hwy. Hwy. 22 and and Hwy. Hwy. 51 51 north north of of Hurley, HurleyI WI WI Rocks Rocks exposed exposed at at this this locality locality are are representative representative of Tyler Formation, Formationlwhich which is is of the the upper upper part part of of the the Tyler about 21100meters meters thick thick here. here. It It thickens thickens westward westward to to about 2,100 about about 2,900 2#900meters meters in in Wisconsin Wisconsin and and thins thins eastward eastward to to zero Ramsay! where where it it was was entirely entirely removed removed by by zero east east of of Ramsay, erosion erosion prior prior to to deposition deposition of of Keweenawan Keweenawan strata. strata. The The Tyler Tyler is is unconformably unconformably overlain overlain by by the the Bessemer Bessemer Quartzite Quartzite and and aa substantial substantial thickness thickness of of Keweenawan Keweenawan volcanic volcanic rocks. rocks. The relationship of of the the Tyler Tyler to to the the underlying underlying The relationship Ironwood Ironwood Iron-Formation Iron-Formationis is uncertain uncertain because because of of poor poor outcrop. Atwater, outcrop. Most Most geologists geologists (e.g., (e.ge1 Atwater,1938) 1938) consider consider the the two two formations formations to to be be conformable conformable (Schmidt (Schmidt and and Hubbard, Hubbardl 1972); 1972); however, howeverl Aldrich Aldrich (1929) (1929)presents presents evidence evidence for for erosion erosion of of the the iron-formation iron-formationand and aa basal basal conglomerate conglomerate at at the the base base of of the the Tyler. Tyler. The The presence presence of of aa graywacke-slate graywacke-slatesequence sequence overlying overlying the the iron-formation iron-formation is is characteristic characteristic throughout throughout the the Lake Lake Superior Superior region region elsewhere on on the the western western Gogebic Gogebic range, rangeI the the As elsewhere As beds here here strike strikeeast-northeast, east-northeastl dip60°-75° 60'-75' northwest, northwestl beds dip block that that and top top to to the the northwest, northwest! part part of of aa large large block and was tilted tilted northward northward during during Keweenawan Keweenawan rifting rifting to to form form was aa large large north-facing north-facingmonocline. monocline. Schmidt Schmidt and and Hubbard Hubbard (1972) and and Kiasner Klasner and and others others (1991) (1991) pointed pointed out out that that (1972) cleavagelbedding relationships relationships in in these these (and (andother) other) the cleavage/bedding the outcrops outcrops are are unusual unusual and and may may be be of of tectonic tectonic significance. significance. As As shown shown in in the the accompanying accompanying diagrams diagrams 13) the (Figure 13), (Figure the graywacke-slate graywacke-slatewas was dipping dipping gently gently southward prior prior to to Keweenawan Keweenawan time. time. Because Because the the southward cleavage cleavage dips dips less less steeply steewlv than than the the bedding, beddingl rotation rotation of the the rocks rocks southward southward to to their their pre-Keweenawan pre-Keweenawansubsubof horizontal attitude attitude results results in in aa south-dipping south-dipping horizontal cleavage. cleavage. Cannon and and others others (1990) (1990)showed showed that that originally originally Cannon vertical Early Early Proterozoic Proterozoic diabase diabase dikes dikes in in the the Archean Archean vertical terrane to to the the south south of of the the Gogebic Gogebic range range now now have have aa terrane southward explained by by aa northward northward southwarddip. dip. This This dip dip is is explained rotationalong alongthe theeast east-northeast-trending Marenisco rotation -northeast - trending Marenisco faultlaa major major listric listric thermal thermal fault fault with with perhaps perhaps 10 10 km km fault, of of southward southward thrust thrust motion motion on onit. it. This This motion motion explains explains the present present steep steep northward northward dip dip of of the the major major monoclinal monoclinal the structure structure of of the the Gogebic Gogebic range. range. Alwin (1976) (1976)showed showed that that the the Tyler Tylerconsists consists Aiwin dominantly of of intercalcated intercalcated argillite argillite and and slate slate with with dominantly lesser amounts amounts of of siltstone siltstone and and graywacke. graywacke. Graded lesser Graded 20 �NORTH NORTH SOUTH SOUTH I Rocks o f Earlv Proterozo~c METERS 6OO METERS NORTH SOUTH B Figure Figure 13. 13. diagram and cross Generalized block diagram cross section section illustrating structural illustrating structural relationships relationships in in Ironwood, Ironwoodl Mich.-Hurley, Heavy dashed Mich.-Hurley, Wis., Wise1area. area. Heavy dashed line, linel A, Block diagram fault. Al diagram showing showing relationship relationship of of fault. pre-Keweenawan strata Midcontinent pre-Keweenawan strata to to rocks rocks of of Midcontinent foliation in in q Tyler Formation rift. rift. Note that that S1 S' foliation l e r Formation dips dips less less steeply steeply than than bedding. bedding. Modified from from B, Reconstructed Schmidt and Hubbard (1972). Schmidt and Hubbard (1972) Bl ~econstructed post-Penokean, post-Penokeanl pre-Keweenawan pre-Keweenawan position position of of the the Note gently south dipping strata shown strata shown in in A. A. Note gently south dipping S1 Sl foliation. foliation. Modified from from Schmidt Schmidt and Hubbard (From Klasner Klasner and and others, others! 1991) 1991) (1972). (From (1972). . 21 �graywacke sequences indicate indicate graywacke beds beds containing containing Bouina Bouma sequences marks and deposition deposition by turbidity turbidity currents. currents. Sole Sole marks and small-scale paleocurrent trend small-scale cross-beds cross-beds indicate indicate a a paleocurrent trend toward toward the the west-northwest. west-northwest. Framework Framework grains grains in in the the quartz and feldspar graywackes are quartz feldspar and and rock rock fragments fragments granitic, volcanic,and of graniticl volcaniclandmetamorphic metamorphic rocks. rocks. Therefore, Therefore, the the source source area area for for the the Tyler Tyler sediments sediments is is inf erred to to be be an an Archean Archean granitic-metarnorphic inferred granitic-metamorphic The Tyler (cratonic) source area (cratonic) source area to to the the southeast. southeast. The Tyler was was only slightly slightly metamorphosed to to sub-greenschist sub-greenschistfacies facies during during the the Penokean Penokean orogeny, orogenyl and and the the metamorphic metamorphic grade grade here was not changed during the Keweenawan here was not changed during the Keweenawan rifting. rifting. At this this exposure, exposurel note note graded graded graywacke graywacke beds beds topping NW, mud-chips mud-chips in topping NWl in some some beds, bedsl rare rare sole sole marks, marksl some soles, loading on some solesl flame flame structures, structuresl and and smallsmallassemblage of sedimentary scale cross-bedding. scale cross-bedding. The assemblage sedimentary structures structures indicates indicates a turbidity turbidity current current mechanism, mechanisml and and deposition on a submarine likely but but not not deposition submarine fan fan is is likely In the fan of essential. In fan model the "packets" npacketsll of graywacke graywacke essential. beds beds would would be be channel channel deposits deposits whereas whereas the the mudstones mudstones would would be be overbank overbank deposits. deposits. Continue east on Continue on U.S. Hwy 2 2 to to Golf Golf Club Club Road Road just just east east of of Ironwood. Thrn Ironwood. Turn right right (south) (south) on on Golf Club Road and proceed about miles south south to 1.1 miles to large large brick buildings buildings of of the the Newport Newport Mine. Mine. Walk Walk to to the the northeast northeast across across the the small small field field to to old old railroad railroad cuts, cutsl that that are are just just north north of of the the main main building building behind behind the the trees. trees. Caution: Caution: Area Area is is now now part part of of aa gravel gravel washing washing operation. operation. Stop 2. Sto~ 2. Newport mine (Archean/Early Proterozoic Old Nemort (ArcheanIEarlv Proterozoic Unconformity). Unconformitv) . The Palms Palms Formation Formation of the Menominee Group the Group of the Marquette Marquette Range Range Supergroup Supergroup rests rests upon upon the the 2,700 21700m.y. m.y. old Puritan Puritan Quartz Quartz Monzonite Monzonite (Schmidt, (Schmidtl1976). 1976). The The Marquette Range Marquette Range Supergroup Supergroup in in the the Gogebic Gogebic range range was was deposited on on aa moderately moderately flat flat erosion deposited erosion surface surface developed developed on on Archean Archean "granite" I1granitenand and greenstone. greenstone. steeply dipping dipping (to (to the the At this this locality, localityl the the steeply north) unconformable unconformable contact contact between between the the Palms Palms north) Formation is exposed exposed in in the the old old Formation and Archean granitoid granitoid is railroad cut. Small depressions in the the surface, surfacel as as can can railroad cut. depressions in be seen seen here, herel contain contain laminated laminated cherty cherty'material, some material, some granular and and somewhat somewhat resembles resembles ironironwhich is is granular of which formation. The mm in in diameter diameter formation. granules are are 0.5 to to 1.0 mm The granules and consist consist of of mixtures mixtures of of chert, chertI chlorite, chlorite, and and and calcite. There calcite. few phosphatic argillaceous There are also a few phosphatic argillaceous chips just just above above the the contact. contact. Note that that there there is is no no appreciable appreciable evidence evidence of of weathering weathering of of the the granite granite Palms. beneath the Palms. beneath the 22 �Red Red argillaceous argillaceous and and silty siltybeds beds of of the thelower lower member member of of the the Palms PalmsFormation Formationare areexposed exposedhere. here. They They contain contain wavy wavy bedding bedding and and small small mudcracks, mudcracksfand and have have been been interpreted interpreted as as upper upper tidal tidal flat flat deposits depositsof of aa transgressing transgressing sea sea(Ojakangas, (Ojakangas 1983). 19831 . cross it, it, and and continue continue north north approximately approximately Return Return to to U.S. U.S. Hwy. H w y . 2, cross on right, rightlbeyond beyond the the Kangas Kangas farm. farm. mile to 11 mile to rock rock knob knob on S t o3. ~3. Stop Contact Contact between between Bessemer Bessemer Ouartzite Ouartzite and and Powder PowderMill Mill Volcanics Vol canics This This exposure exposure is is approximately approximatelytwo twomiles milesnorth northof of and the the interval interval between between these these two two stops stops Stop Stop 2, and demonstrates demonstrates the the thickness thickness of of the the Early Early Proterozoic Proterozoic The exposure exposure shows shows the the contact contact sequencein inthis thisarea. area. The sequence between between the the basal basal Keweenawan Keweenawan Bessemer Bessemer Quartzite Quartzite and and the the Thus the the overlying overlying basalt basalt of of the thePowder PowderMill MillGroup. Group. Thus exposure exposure illustrates illustrates the the abrupt abrupt change change from from sedimentation sedimentationof of quartzose quartzose sandstone sandstoneto to flood floodbasalt basalt volcanism volcanism during during the the Middle Middle Proterozoic Proterozoic in in this this part part of of the Lake Lake Superior Superiorregion. region. Only Only the the lowermost lowermost basalt basalt the flows softl silty silty flows are are pillowed, pillowedl and and locally, locallyI the the soft, sediment sediment was was squeezed squeezed up up between between rubbly rubbly blocks blocks and and pillows. Some Some units units of of Bessemer-type Bessemer-typequartzite quartzite do do pillows. occur occur higher higher in inthe the flow flowsequence. sequence. These These features features indicate indicate that that volcanism volcanism here here was was initiated initiated in in aa sedimentary basinl overwhelmed overwhelmed sedimentation, sedimentationland and sedimentary basin, resulted resulted in in aa thick thick sequence sequenceof of subaerial subaerialflows. flows. Flows Flows just to to the the north north are aremassive. massive. just S t -o 4. ~4. Stop Ironwood Ironwood Iron-Formation Iron-Formationand and Ironwood-Tyler Ironwood-Tvler relationshi~s. (Modified (Modified from from Schmidt, Schmidtl1972) 1972) relationships. Location: Exposures Exposures on on the the east east and and west west banks banks of of the the Location: Black River River upstream upstream from from Hwy. H w y . 22 on on the the western western Black (NE ', XI SW, SWAl Sec. Sec. 12, 12, outskirts of of Ramsay, RamsaylMichigan. Michigan. (NE outskirts T.47N. R.46W.) R.46W. T.47N., The Ironwood Ironwood Iron-Formation Iron-Formationis is aa major major sedimentary sedimentary The Gogebic range, rangel and and is is the the source source rock rock for for all all of of the the Gogebic Unfortunatelylthe the ironironiron ores ores mined mined in in the the area. area. Unfortunately, iron formation is is very very poorly poorly exposed exposed on on the the eastern eastern formation Gogebic. Excellent Excellent exposures exposures of of the the Ironwood Ironwood IronIronGogebic. Formation are are present present on on Mt. Mt. Whittlesey, Whittleseylsoutheast southeast of of Formation Mellenl Wisconsin, Wisconsinl however, howeverl that that locality locality is is more more than than Mellen, 30 miles miles away, awayl and and will will not not be be visited visited on on this this trip. trip. 30 Schmidt and and Hubbard Hubbard (1972) (1972) described described several several Schmidt exposures along along the the Black Black River River at at this this locality locality that that exposures illustrate different different phases phases of of the the iron-formation iron-formationas as illustrate well as as possible possible stratigraphic stratigraphic relationships relationships between between well qler the Ironwood Ironwood Iron-Formation Iron-Formation and and the the overlying overlying Tyler the Formation. They They describe describe thin-bedded thin-bedded chert-carbonate chert-carbonate Formation. 23 23 �iron-formation Member of iron-formation at the the top top of the the Anvil Member of the the Ironwood Ironwood Iron-Formation Iron-Formation on on the the east east bank bank of of the the river river 600 upstream from bridge on 600 feet feet upstream from the the bridge on the the secondary secondary road road south of south of Hwy. Hwy. 2. 2. Granular Granular jasper jasper is is described from from test pits Sec. 121 12, T.47Na1 T.47N., R.46W. test pits in in the the SE(, SE%# SW1X, SWA1 Sec. R.46W. Schmidt Schmidt and and Hubbard Hubbard (1972) (1972) conclude conclude that that the the rocks rocks are are basically unmetamorphosed basically umetamorphosed examples examples of of the the ironironformation. Time formation. Time limitations limitations will will not not permit permit us us to to visit all of the localities described by Schmidt and the localities Hubbard (1972), and those interested in examining (1972)1 interested unaltered iron-formation unaltered iron-formationshould should consult consult their their 1972 1972 guidebook. guidebook. Schmidt Schmidt and and Hubbard Hubbard (1972) (1972) also also discussed discussed alternative alternative interpretations interpretations of the relationship between Tyler and the Tyler and Ironwood Ironwood Formations. Formations. The The contact contact is is (600 the Black Black River River 180 180 mm (600 exposed on the east bank of the ft.) roadl where where Schmidt Schmidt ft.) upstream from from the the secondary secondary road, and Hubbard (1972) (1972) interpreted interpreted the the contact contact to to be be and Hubbard gradational. gradational. We will examine examine only the exposure on the west bank of the Black River just just south south of Hwy. 22 where where aa lens lens of of carbonate iron-formation carbonate iron-formation and a a sulfide sulfide unit unit is is present present within the within the lower lower part part of of the the Tyler Tyler Formation. Formation. Although .ong the the stream stream exposure poor, there outcrops a1 along there are outcrops exposure is is poorl slatel massive bank consisting consisting of highly carbonaceous carbonaceous slate, sideritic pyrite/marcasite, and sideritic and concretionary(?) concretionary ( ? ) pyrite/marcasite, iron- formation. iron-formation. Stop 5. Radio Tower Radio Tower Hill Hill in in Wakefield. Wakefield. Palms Marmette Range RanqeSupercrroup Su~erqrouq Palms Formation Formation of of Marguette Location: Location: The The purposes of this this stop stop are are to to (1) (1) examine examine an excellent (2) an excellent exposure exposure of of the the Palms Palms Formation Formation and and (2) obtain obtain a a scenic scenic view view of of this this part part of of the the Gogebic Gogebic range, rangel and of the of the the Archean terrane terrane to to the the south, southl and the Keweenawan terrane Keweenawan terrane to to the the north. north. From hill, several From the the top top of the the hilll several abandoned abandoned iron iron mines mines can can be be seen seen in in the the lowland lowland immediately immediately to to the the thi north (refer (refer to to Figure Figure 7); 7); the the ridges ridges in in the north intermediate distance basalt of early early intermediate distance are are underlain underlain by basalt of Keweenawan (Middle Proterozoic) Proterozoic) age. age. The The lowland lowland in in Keweenawan (Middle the far far distance is underlain the late late Keweenawan Keweenawan distance is underlain by the Jacobsville Jacobsville Sandstone. Sandstone. The to the the south south overlooks overlooks Archean Archean terrane terrane The view to consisting of the the Ramsay Ramsay Formation Formation (mafic (mafic and and felsic felsic consisting metavolcanic rocks) rocks) and the the Puritan Puritan Quartz Monzonite metavolcanic and related related rocks rocks (—2,700 (-21700r n.y.1 which which constitute constitute aa m.y.), major batholith batholith more more than than 150 150 km km long. long. major area, the Palms Palms Formation unconformably Formation unconfombly In this areal overlies overlies the Archean Ramsay Formation Formation and is overlain overlain 24 �which conformably by by the the Ironwood IronwoodIron-Formation, Iron-Formation,which conformably underlies underlies the the low low area area north north of of the the hill hill and and also also southwest of of the thehill. hill. Low Low on on the the next next hill hill to to the the southwest Further east, rare rare Sunday Sunday Quartzite Quartziteis ispresent. present. Furthereast, east, east, the Palms Palms unconformably unconformably overlies overlies the the Bad Bad River River the Dolomite,and and has has aa thin thin phosphatic phosphatic conglomerate conglomerateat at its its Dolomite, with The Palms dips steeply northward, in accord base. The Palms dips steeply northward, in accord with base. the regional regional dip dip of of Proterozoic Proterozoic rocks rocks in in the the Gogebic Gogebic the This regional dip resulted mainly from range. This regional dip resulted mainly from range. toward the the northward northward tilting tilting during during Keweenawan Keweenawan time, time, toward axis of of the the (Keweenawan) (Keweenawan)Lake Lake Superior Superior syncline. syncline. The The axis Early deformed Early Proterozoic Proterozoic rocks rocks were were not not appreciably appreciably deformed (Penokean or metamorphosed metamorphosed during during the the tectonic tectonic event event (Penokean or that closed closed Early Early Proterozoic Proterozoic deposition, deposition,but but orogeny) that orogeny) the east-northeast at 20-25° 20-25' a few folds plunging to the east-northeast at a few folds plunging to have been been recognized. recognized. have Exposures Exposures of of the the Palms Palms Formation Formation at at this this locality locality are representative representative of of the the formation formation which which extends extends for for are Representative rock types 80 km to the west-southwest. Representative rock types 80 km to the west-southwest. well-exposed well-exposedat at the the top top of of the the hill hill include include the the upper upper part of of the the middle middle member member which which consists consists of of interbedded interbedded part argillite, argillite,siltstone, siltstone, and and sandstone, sandstone, and and the the transition transition to the the massive massive quartzite quartzite of of the the upper upper quartzite quartzitemember. member. to The middle middle member member is is thin thin bedded, bedded, with with beds beds generally generally The 2-10cm cm thick. thick. In In general, general, beds beds of of buff buff to to pink pink 2-10 siltstone and and white white sandstone siltstone sandstone alternate alternate with with buff, buff, red red or green green beds beds of of more more argillaceous argillaceous material; material;coarsecoarseor grained, grained, dark-red, dark-red,hematitic hematitic sandstone sandstone beds beds are are also also present. Most Most beds beds are are quite quite continuous continuousacross across the the present. outcrop but but "pinch "pinchand and swell" swellnirregularities irregularities impart impart aa outcrop waviness to to the the generally generally uniform uniform bedding. bedding. Lenticular Lenticular waviness beds of of sandstone, sandstone,commonly commonlycross-bedded, cross-bedded, arecommon. common. beds are Flaser bedding bedding is is present present locally locally where where the the mud mud supply supply Flaser was subordinate subordinateto to the thesand sandsupply. supply. Minor Minor cut-and-fill cut-and-fill was and soft-sediment soft-sedimentdeformation deformation structures structuresalso also are are and present. Symmetrical Symmetrical but but irregular irregular ripple ripple marks marks and and present. mud cracks, cracks,although although not not visible visible at at this this locality, locality,are are mud (Ojakangas,1983). 1983). present on on the the next next hill hill to to the the east east (Ojakangas, present Measurement Measurement of of 42 42 cross-beds cross-bedson on this this hill hill shows showsaa strong paleocurrent paleocurrent trend trend to to the the west west with with aa weaker weaker strong trend to to the theeast. east. Nearly Nearly 200 200 measurements measurements in inthe the trend formation as as aa whole whole accentuate accentuatethis thisbimodality. bimodality. formation Correction for for plunge, plunge, if if indeed indeed the the entire entire formation formation Correction has aa plunge plunge as as well well as as aa tilt, tilt, would has would rotate rotate the the major major and minor minor modes modes clockwise, clockwise, thus thus relocating relocatingthe themodes modes to to and the west-northwest west-northwestand and east-southeast, east-southeast,respectively. respectively. the General characteristics characteristics of of the the formation, formation, and and General especially the the bimodal bimodal cross-bedding cross-beddingpattern, pattern, the the especially bedding styles, styles, and and the the overall overall lithologies lithologies are are highly highly bedding suggestive of of deposition deposition in in aa tidal tidal environment. environment. suggestive Recall that that the the lower lower member member interpreted interpretedas asupper uppertidal tidal Recall 25 �flat, was was seen seen at at Stop Stop 2. 2. Here Here on on Radio Radio Tower Tower Hill, Hill, flat, the middle member is interpreted as middle tidal flat, the middle member is interpreted as middle tidal flat, and the cross-bedded quartz sand upper member is and the cross-bedded quartz sand upper member is interpreted as as lower lower tidal tidal flat flat or or subtidal subtidal (Ojakangas, (Ojakangas, interpreted 1983). 1983) Thin sections sections from from this this locality locality show show that that the the Thin sandstone beds beds are are feldspathic feldspathicquartzite. quartzite. Well-rounded Well-rounded sandstone unit quartz quartz grains grains and and feldspar feldspar (mostly (mostlyfresh freshKKunit feldspar) grains grains are are the the dominant dominant framework framework feldspar) constituents, with with chert chert grains grains aa poor poor third. third. Silica Silica constituents, illitic clay clay is is present present in in many many cement is is abundant abundant and and illitic cement samples as as minor minor to to abundant abundant matrix. matrix. Illite Illite is is also also samples the major major constituent constituent of of the the argillaceous argillaceous beds beds with with the chlorite locally locally prominent. prominent. The The coarser-grained, coarser-grained, chlorite hematitic sandstone beds are really thin beds beds of of ironironhematitic sandstone beds are really thin formation, consisting of granules of hematite, chert, formation, consisting of granules of hematite, chert, and iron iron silicates silicates in in addition addition to to the the common common quartz quartz and grains. grains. Deformation of of the the Palms Palms Formation Formation has has not not been been Deformation well studied. Basically, it is part of a large well studied. Basically, it is part of a large monocline in in which which folding folding is is rarely rarely seen seen except except at at monocline this locality. On the west flank of the hill, several this locality. On the west flank of the hill, several open, round-crested round-crestedfolds folds exhibit exhibit aa cleavage cleavage that that is is open, flatter than the bedding. The extent, origin, and age flatter than the bedding. The extent, origin, and age of these folds and their associated cleavage is not of these folds and their associated cleavage is not known, but but the the folds folds may may have have formed formed when when the the beds beds were were known, approximately flat-lying, presumably during the approximately flat-lying, presumably during the Penokean orogeny. orogeny. Alternatively, Alternatively, the the folding folding might might Penokean have been caused by drag along the Sunday Lake fault, aa have been caused by drag along the Sunday Lake fault, northwest-trending fault that passes just west of this northwest-trending fault that passes just west of this hill. hill. Stop 6. 6. Stop Archean Ramsay Ramsav Formation Formation (pillowed (pillowed meenstone) Archean reenstone) Location: Roadcut Roadcut along along U.S. U.S. Hwy. Hwy. Location: limits of Wakefield, about 2.5 mi. limits of Wakefield, about 2.5 mi. of Highways 2 and 28 in Wakefield. of Highways 2 and 28 in Wakefield. at eastern eastern city city 22 at SE of the junction SE of the junction Archean Ramsay Ramsay Formation Formation forms forms part part of of the the The Archean The Archean basement upon which the Early Proterozoic rocks Archean basement upon which the Early Proterozoic rocks Prinz and others (1975) were deposited. According to were deposited. According to Prinz and others (1975) metavolcanic rocks rocks of of Archean Archean age age extend extend eastward eastward for for metavolcanic approximately 15 km along the range in the vicinity of approximately 15 km along the range in the vicinity of Wakefield. They are intruded on the south and west by Wakefield. They are intruded on the south and west by the Puritan Puritan Quartz Quartz Monzonite, Monzonite, and and are are bounded bounded on on the the the east by gneissic rocks of the Puritan Quartz Monzonite. east by gneissic rocks of the Puritan Quartz Monzonite. They reported reported that that the the eastern eastern two-thirds two-thirdsof of the the belt belt They Archean rocks is mainly mafic to intermediate flows of of Archean rocks is mainly mafic to intermediate flows and pyroclastic rocks with sparse felsic volcanic and pyroclastic rocks with sparse felsic volcanic rocks. However, However, intermediate intermediate to to felsic felsic rocks rocks are are rocks. dominant in the western part of the belt. The rocks dominant in the western part of the belt. The rocks generally strike west to northwest (roughly parallel to generally strike west to northwest (roughly parallel to 26 �the the strike strike of of Early Early Proterozoic Proterozoic rocks) rocks) and and dip dip steeply steeply to to the the south. south. Pillows Pillows indicate indicate that that the the lava lava flows flows generally generally face face southward. southward. Prinz Prinz and and others others (1975) (1975)suggested suggested that that the the mafic mafic and felsic volcanics volcanics each each have have aa thickness thickness of of and the the felsic approximately approximately 3,000 3,000meters. meters. Metamorphic Metamorphic grade grade increases from greenschist facies increases from greenschist facies in in the the west west to to amphibolite amphibolite facies facies along along the the eastern eastern margin. margin. Rocks Rocks exposed exposed here here are are typical typical pillowed pillowed mafic mafic volcanic rocks that have been metamorphosed volcanic rocks that have been metamorphosed to to They are are composed composed of of fine-grained fine-grained greenschist fades. They greenschist facies. sodic plagioclase, quartz, epidote-zoisite, sodic plagioclase, quartz, epidote-zoisite,and and chlorite, chlorite, with with some some pale pale amphibole, amphibole, carbonate carbonate and and biotite biotite (Prinz (Prinzand and others, others, 1975). 1975). Pillows Pillows with with tops tops facing facing southward southward are are well-exposed well-exposed on on the the south south side side of of the the highway. highway. Take Take U.S. U.S. Hwy. Hwy. 22 east east of of Wakefield Wakefield city city limits limits about about two two miles miles to to Go to compressor station on pipeline and turn Go to compressor station on pipeline and turn Great Lakes Lakes Road. Road. Great left mile in in is is aa "Y"; "Yn; keep keep left (north) (north)on on gravel gravel road. road. About About 0.3 0- 3 mile Walk west west on on logging logging 1.5 miles miles to to end end of of road. road. Walk left and and go go about about 1.5 left road road ± 2 270 270 paces, paces, then then go go north north through through the the woods woods to to the the high high The outcrop outcrop is is an an escarpment escarpment along along SW SW side side of of hill hill in in the the hill. The hill. R.44W., (Wakefield NE 7%Minute %, Sec. Sec. 18, 18, T47N., R.44W., (Wakefield NE Minute SE (, SE Quadrangle.) Quadrangle.) Stop 7. Archean-Early Archean-Earlv Proterozoic Proterozoic unconformity. unconformitv. The The unconformity unconformity between between the the Archean Archean Ramsay Ramsay greenstone greenstone and and the the Early Early Proterozoic Proterozoic Sunday Sunday Quartzite Quartzite is is exposed exposed along along the the southwest southwest side side of of this this hill. hill. Note Note the the schistosity schistosity in in the the otherwise otherwise massive massive greenstone, greenstone, and and the the very very thin thin basal basal conglomerate. conglomerate. Just Just westward westward from from the the unconformity, unconformity, the the Sunday Sunday Quartzite Quartzite at at first first glance glance appears appears to to be be conglomeratic, conglomeratic, but but it it is is aa thin thin skin skin along along the the face face of of the the outcrop outcrop and and is is probably probably aa fault fault breccia. breccia. This This prominent prominent exposure exposure is is probably probably aa fault fault scarp. scarp. Moving Moving along along the the base base of of the the escarpment, escarpment, note note the the crosscross-bedding (some (some of of it it herringbone herringbone type, type, with with crosscross-bedding beds in in successive successive beds beds oriented oriented at at 180° 180' to to each each beds mudchip conglomerates, conglomerates, other), the the numerous numerous layers layers of of mudchip other), and mud-cracked mud-crackedhorizons. horizons. These These are are included included in in aa and series of stacked stacked tidal tidal channels channels to to about about 22 mm thick, thick, series each each starting starting with with aa mud-cracked mud-crackedhorizon. horizon. These These are are overlain by by aa cross-bedded cross-bedded unit unit that that includes includes overlain herringbone herringbone cross-beds, cross-beds, and and ends ends with with a a parallel-bedded parallel-bedded unit. At this this exposure, exposure, 41 41 cross-beds cross-beds yield a broad yield a unit. trimodal (but (but largely largely bimodal-bipolar) the trimodal bimodal-bipolar) pattern with the major mode mode to to the the northwest northwest and and aa less less prominent prominent mode mode major 27 �to to the the southeast. southeast. All All of of these these features features are are characteristic characteristic of of aa tidal tidal environment environment of of deposition deposition for for the the Sunday Sunday Quartzite. Quartzite. Thus Thus aa sandy sandy tidal tidal environment environment transgressed peneplained Archean Archean craton. craton. transgressed onto onto aa peneplained Continue Continue along along escarpment escarpment and and note note the the nature nature of of the the transition transition from from the the quartzite quartzite into into dolomite. dolomite. This This is is the the Bad Bad River River Dolomite. Dolomite. Note Note also also the the abundance abundance of of white black chert chert within within the the dolomite, dolomiteIand and the the white and and black Hanirnering Please! presence stromatolites. Hammering Please! presence of of stromatolites. Because Because the the vertical vertical facies facies give give the the horizontal horizontal facies facies relationships, relationshipsl it it seems seems that that the the carbonate carbonate was was deposited deposited seaward seaward of of the the terrigenous terrigenous sands sands that that are are now now the the Sunday Sunday Quartzite, Quartzitel and and this this carbonate carbonate environment environment then then transgressed transgressed over over the the quartz quartz sands sands as as the the sea sea transgressed transgressed northward. northward. Stop Stop 8. 8. Mafic Mafic phase. phase, Emperor Emperor Volcanics Volcanics (with (withcontribution contribution by by K. K. Licht) Licht) Location: NE'(, NE NE14• %, Sec. Sec. 24. 24, T.47N., T.47N., R.43W. R.43W. on Location: NE Forest Forest Service Semice Roads Roads 523 523 and and then then 8640 8640 approximately approximately 6.5 6.5 miles miles north north of of Marenisco, MareniscotMichigan. Michigan. Rocks Rocks exposed exposed on on this this hill hill illustrate illustrate several several varieties varieties of of the the mafic mafic phase phase of of the the Emperor Emperor Volcanic Volcanic Complex. Complex. The The Emperor Emperor Formation Formation is is at at least least 2,000 21000 meters thick thick in in this this area area but but thins thins rapidly rapidly to to the the west west meters and 10 miles miles to to the the west west in in the the and is is not not recognized recognized 10 Wakefield Wakefield area. area. The The volcanics volcanics are are truncated truncated on on the the east east by by major major faults. faults. Therefore, Thereforel the the volcanic volcanic rocks rocks form foxm an an eastward-thickening eastward-thickeningwedge wedge interbedded interbedded with with the the Ironwood Iron-Formation Iron-Formationand and the the wedge wedge is is truncated truncated by by Ironwood faults faults as as shown shown by by Trent's Trent's (1973) (1973)mapping. mapping. The Emperor Emperor Volcanic Volcanic Complex Complex consists consists of of aa mafic mafic The and and felsic felsic phase. phase. Dann D a m (1978) (1978)showed showed that that the the rocks rocks range range in in composition composition from from basalt basalt to to dacite. dacite. Mapping Mapping by by LaBerge and and J. J. S. S. Kiasner Klasner in in 1991 1991 indicates indicates that that the the LaBerge mafic phase phase Emperor Emperor volcanics volcanics are are the the products products of of mafic mainly subaqueous subaqueous eruptions, eruptionsland and include include massive massive and and mainly pillowed basalts, basaltsI pillow pillow breccias, breccias! hyaloclastites, hyaloclastitesland and pillowed debris debris flows. flows. Exposures near near the the base base at at the the north north end end of of the the Exposures hill are are pillowed pillowed basalt basalt with with little little or or no no interpillow interpillow hill hyaloclastite. hyaloclastite. Higher Higher on on the the hill hill and and in in the the cliffs cliffs along along the the western western side side of of the the hill, hilllsome some exposures exposures are are mainly hyaloclastite, hyaloclastitelothers others are are hyaloclastite hyaloclastite mainly containing containing pillows pillows and and pillow pillow fragments, fragmentsIand and some some exposures are are mainly mainly pillows pillows(Figure (Figure14). 14). exposures Figure 15 15 is is aa possible possible interpretation interpretationof of the the Figure rocks shallow rocks exposed exposedhere. here. Lava Lava fountaining fountaining in in aa shallow 28 �Pillow breccia with pillow fragments fragments in in a Jackknife is hyaloclastite cm long. long. hyaloclastite matrix. matrix. Jackknife is 88 cm Figure Figure 14. 14. ,. ,.t# - flSJ#%/% fS ..F — 'S1 fl - Water Surface Hyaloclastite formed by 4, shallow-water fountarning. ii 41 fr1-1 I_4 4 I ': 4 * a A. u 14 Ilebri S f (iw. ni p1 OW I,?It(. I I— end hyalocldst.itC. Pillows and pillow breccia i:. formed by flows into —_... • or onto hya1ocaSt1te / Li ) 4 .4 -. Li • •fr,.• 01 1ii Figure Figure 15. 15. ' iii t Sketch showing showing possible environment environment of of formation formation 8. of basalts exposed exposed at at Stop Stop 8. 29 �\ MARENISCO QUADRANGLE QUADRANGLE MICHIGAN—COGEBIC MICHIGAN-GOGEBlC CO. CO. 7.5 MINUTE MINUTE SERIES S E R I E S(TOPOGRAPHIC) (TOPOGRAPHIC) 30 NW4 5' QUADRANGLE N W ( 4 MARENtSOO MARE&!SCO 15' QGADRANGLE �subaqueous subaqueous environment environment may may have have produced produced aa Later eruptions eruptions may may have have resulted resulted hyaloclastitedome. dome. Later hyaloclastite in in emplacement emplacement of of pillow pillow lavas lavas onto onto (or (orinto) into) the the hyaloclastite. Additional Additional hyaloclastite hyaloclastite may may have have hyaloclastite. formed formed on on the the surface surfaceof of the the flow. flow. Pillows Pillows and and pillow pillow fragments fragments cascading cascading off off the the flow flow front front may may have have became became mixed mixed with withhyaloclastite. hyaloclastite. Debris Debris flows flowsof of hyaloclastite hyaloclastite and and pillow pillow breccia breccia may may also also have have been been formed. formed. Rocks Rocks collected collected from from this this stop stop were were analyzed analyzed in in Some textures textures thin-section thin-sectionand and by by chemical chemicalanalysis. analysis. Some and and unique unique findings findings will will be be described described in in the the following following paragraphs. paragraphs. Many Many pillows pillows within within the the hyaloclastite hyaloclastite contain contain reaction reaction rims rims around around the the outer outer margins margins and and along along quench quench cracks. The The thicknesses thicknesses of of these these rims rims vary vary from from aa few few cracks. millimeters millimeters to to aa few fewcentimeters. centimeters. The The reaction reaction rims rims are uniform highly highly altered altered are characterized characterized by by aa fairly fairly uniform basaltic texture with some remnant tabular basaltic texture with some remnant tabularplagioclase. plagioclase. Vein within the the reaction reaction rims rims contain contain Vein fillings, fillings) within chlorjte, recrystallized quartz, and chlorite) recrystallized quartz) andepidote. epidote. . Jasper Jasper occurs occurs sporadically sporadically and and tends tends to to be be "molded" between the pillows and in fractures l1mo1dedl1between the pillows and in fractureswithin within Si02 for for the the jasper jasper may may have have been been pillows. Source Source of of Si02 pillows. gelatinous gelatinous ooze ooze on on the the seafloor seafloor at at the the time time of of eruption. The The source source of of the the Fe Fe was was probably probably the the eruption. extruded basalt. basalt. extruded The The massive massive basalt basalt on on the the north north end end of of the the hill hill has Si02content contentofof62.48's. 62.48%. In In has an an abnormally abnormallyhigh highSi02 thin-section, thin-section)epidote, epidote) recrystallized recrystallized quartz, quartz)chlorite, chlorite) and and calcite calcite are are associated associated with with the thealtered alteredbasalt. basalt. The texture) but but The hyaloclastite hyaloclastite varies varies greatly greatly in in texture, varies little little in in composition. composition. The The included included basalt basalt varies fragments are are highly highly altered. altered. The fragments The hyaloclastite hyaloclastite matrix matrix is composed composed of of plagioclase, plagioclasel calcite, calcite)quartz, quartz)chlorite, chlorite) is amphiboleland and epidote. epidote. amphibole, 9. Stow 9. Stop Felsic phase. ~hase, Em~erorVolcanics Volcanics Felsic Emperor Location: Outcrop OutcropininSESE1A?4NE NE1,?4 Sec. Sec. 20, 20) T47N., T47N.) R.44W R.44W Location: 523 near Presque Presque Isle Isle River River on on Forest Forest Service Service Road Road 523 near approximately 66 miles miles north north of of Marenisco, MareniscoI Michigan. approximately Michigan. This exposure exposure contains contains rocks rocks representative representative of of This some varieties varieties of of the the felsic felsic phase phase of of the the Emperor Emperor some Volcanics. The The dominant dominant lithology lithology at at this this locality locality Volcanics. angular) tan, tan) 22 to to 10 10 cm, cml consists of of relatively relatively angular, consists monolithic clasts clasts of of microcrystalline microcrystalline felsite felsite in in aa monolithic 31 �Whereas the the small small finer hyaloclastite hyaloclastite matrix. matrix. Whereas finer hyaloclastite hyaloclastite fragments fragments typically typically have have aa whitish whitish alteration rind! the the larger larger felsite felsite clasts clasts generally generally alteration rind, lack lack alteration alterationrinds. rinds. Prinz Prinz and and others others (1975) (1975) stated stated that that the the felsite felsite clasts clasts as as well well as as the the matrix matrix have have aa In zones zones of of deformation deformation the the dacitic dacitic composition. composition. In hyaloclastite hyaloclastite matrix matrix tends tends to to be be strongly strongly foliated, foliated! whereas whereas the the felsite felsite clasts clasts tend tend to to show show little little deformation deformation (Figure (Figure16). 16). Some Some clasts clasts contain contain abundant abundant perlitic perlitic cracks, cracks! others others are are more more massive massive felsite. felsite. This This lithology lithology of of the the felsic felsic phase phase of of the the Emperor Emperor extends extends westward westward at at least least 55 km, k m l where where there there are are extensive extensive exposures 14 and and 23 23 north north of of Wolf Wolf Mountain. Mountain. exposures in in Secs. Secs. 14 In In addition addition to to the the variety variety of of rock rock exposed exposed here, here! Sec. Sec. 14 14 north north of of Wolf Wolf Mountain Mountain contains contains extensive extensive brecciated brecciated felsite Although felsite with with scattered scattered quartz quartz phenocrysts. phenocrysts. Although the the rock rock is is extensively extensively brecciated, brecciated, there there appears appears to to have have been been little little or or no no movement movement of of adjacent adjacent blocks blocks with with respect respect to to one one another. another. In In short, short! the the rock rock appears appears to to be be aa felsic felsic dome dome that that has has been been brecciated. brecciated. Surrounding Surrounding the the brecciated brecciated felsite felsite are are numerous numerous exposures exposures with with breccia breccia fragments fragments of of felsite felsite in in aa felsic felsic hyaloclastite matrix matrix (Figure (Figure17). 17). It It is is suggested suggested that that hyaloclastite the felsite felsite breccia breccia may may be be aa felsic felsic dome dome emplaced emplaced into into the felsic felsic hyaloclastite hyaloclastite produced produced by by an an earlier earlier eruption. eruption. Debris Debris flows flows off off the the dome dome may may have have resulted resulted in in more more widespread widespread units units of of the the felsite felsite breccia/hyaloclastite breccia/hyaloclastite as shown shown in in Figure Figure 18. 18. as 32 �Figure Figure 16. 16. Photo Photo of of sawed sawed slab slab of of Emperor Emperor Volcanics Volcanics from from Stop Stop 9. Larger, Larger, angular angular felsite felsite clasts clasts in in aa finer finer 9. grained, is grained, foliated foliated hyaloclastite hyaloclastite matrix. matrix. Slab Slab is 18 18 cm cm long. long. Figure 17. Figure 17. Photomicrograph Photomicrograph of hyaloclastite hyaloclastite from from Note phase of tie Emperor Volcanics. phase of the Emperor Volcanics. Note cracks cracks in in the the oval oval clast clast on on the the right right photo. mm. photo. Bar Bar scale scale is is 22 mm. the the felsic felsic the perlitic the perlitic side side of of 33 �Water Surface C a r a p a c e o f hyaloclastite formed (IuI-~ e aI rIl ~ ier Figure Figure18. 18. fountaininq. Sketch Sketch of of possible possible relationships relationships within within the the felsic felsic Highly fractured fractured phase phase of of the the Emperor EmperorVolcanics. ~olcanics. Highly felsite felsite blocks blocks become become dispersed dispersed in in finer finer grained grained felsic f aa felsic hyaloclastite hyaloclastitein indebris debrisflows flowsofoff subaqueous subaqueous lava lavadome. dome. Stop Stow 10. 10. Archean Archeanmetacrravwacke metaqrawacke Location: 2, about about 10.5 10.5 mi mi SE SE of of Location: Roadcuts Roadcuts on on Highway Highway 2, Marenisco, 'A, X , Sec. Sec. 30, 30, T. T. 46 46 N., N., R. R. 41 41W. W. (Thayer, (Thayer, Marenisco,SWSW MI MI 15' 15' quadrangle). quadrangle) . The metagraywacke metagraywacke in in these these roadcuts roadcutsis is part part of of aa The km wide wide and and 20 20 km km long. long. The The northeast-trendingbelt belt 44 km northeast-trending rocks rocks are are highly highly folded folded on on tight tight north-northeastnorth-northeasttrending km trending axes, axes, and and the the unit unit is is probably probably about about 11km thick. thick. The The graywacke graywacke is is aa fine-grained, fine-grained,thinthin-to to thick-bedded thick-beddedrock rock with with aa pervasive pervasive northeast-trending northeast-trending schistosity(S2) (S,) that that is is Penokean Penokean in in age; age; an an older older schistosity (Si)that that is is Archean Archean in in age age is is nearly nearly schistosity(Si) schistosity parallel parallel to tobedding. bedding. Graded Graded beds beds are are common, common,and andtops tops at at this this outcrop outcrop are areto tothe thesouth. south. Reversals Reversals of of grading grading indicate apart. indicate that that the the fold fold crests crests are are about about200 200mm apart. 34 �The The rocks rocks were were metamorphosed metamorphosed to to amphibolite amphibolitegrade grade during the the Archean Archean and and are are totally totally recrystallized; recrystallized;most most during of of the the garnet garnet was was retrograded retrogradedto to chlorite chlorite++ muscovite muscovite ++ epidote and and opaques opaques during during the the Penokean Penokeanorogeny orogeny(Sims (Sims epidote The nature of the original sediment and others, others,1984). 1984). . The nature of the originalsediment and is is unknown unknown because because of of the the thorough thorough recrystallization, recrystallization, but CIA indices (chemical indices but CIA indices (chemical indicesof of alteration) alteration) calculated calculated for for the the graywackes graywackes indicate indicatean anoriginal original immature detritus that had undergone little immature detritus that had undergone little if if any any weathering in the source area and could have weathering in the source area and could have been been immature immature volcaniclastics. volcaniclastics. The The area area was was mapped mapped by by Cannon Fritts (1969), Trent (1973), and Prinz (1981) . Cannon Fritts (1969), Trent (1973), and Prinz (1981) of (1986b) produced a structural and tectonic map (1986b) produced a structural and tectonic map of the the . region. region. Ma) Stoo11. 11. Watersmeet Watersmeet Gneiss Gneiss(3560 (3560Ma) Stor Location: Roadcuts Roadcuts on on Highway Highway 45, 45, about about 44 mi mi NN of of the the Location: This junction junctionis is on on the the junction and 45. 45. This junction of of Highways Highways 22 and Roadcut location location edge of of the the village village of of Watersmeet. Watersmeet. Roadcut SS edge is SSedge, edge,NENE'A, 1/, Sec. Sec. 4, 4,T. T. 46 46 N., N., R. R. 39 39 W. W. is (Watersmeet, (Watersmeet,MI, MI, 15' 15' quadrangle). quadrangle) . This This exposure exposure is is located located in in the the northern northern part part of of the the Watersmeet Watersmeet dome dome which which has has an an Archean Archean core coreabout about25 25 km km wide wide in inaaNNkm long long in in an an E-W E-Wdirection direction and and about about 88 km direction. The The dome dome is is considered considered to to be be aa mantled mantled SS direction. gneiss dome. dome. Sims Sims (1990) (1990) recognizes recognizes considerable considerable Early Early gneiss Proterozoic Proterozoic rocks rocks in in the the core core infolded infolded with with the the Archean. Deformation Deformation of of the the Archean Archean and and adjacent adjacent Early Early Archean. Proterozoic Proterozoic rocks rocks occurred occurred during during the the Penokean Penokeanorogeny. orogeny. The rocks rocks in in the the core core were were metamorphosed metamorphosed to to the the The amphibolite amphibolite fades, facies,aa15 15km-wide km-widezone zoneof of epidote epidote amphibolite amphibolite facies facies surrounds surrounds the the core, core, and and this this in in turn turn passes outward outward into into greenschist greenschistfacies. facies. (This (This is is the the passes Watersmeet metamorphic metamorphic node node of of James, James,1955). 1955). The The Early Early Watersmeet Proterozoic Proterozoic rocks rocks to to the the north north of of the the dome dome have have been been overturned toward toward the the northwest. northwest. This This area area was was studied studied overturned Peterman and and others others by Sims Sims and and others others(1984) (1984)and andPeterxnan by (1980). (1980) The gray gray gneiss gneiss is is aa tonalitic tonalitic augen augen gneiss gneiss about about The 3560 Ma Ma old old (zircon (zircondata) data) (Sims (Sims and others, 1984); 1984); it it and others, 3560 is aa medium-gray, medium-gray,mediummedium- to to coarse-grained, coarse-grained,biotitebiotiteis rich, irregularly irregularly layered layered rock rock with with plagioclase plagioclase augen. augen. rich, The alternating alternating layers layers are are feldspar-quartz-rich feldspar-quartz-richand and The biotite-rich. AA modal modal analysis analysis showed showed 48% 48% plagioclase, plagioclase, biotite-rich. 30% quartz, quartz, 8% 8% K-feldspar, K-feldspar,and and 13% 13%biotite. biotite. AA possible possible 30% protolith protolith was was dacitic dacitic volcanic volcanic rock rock (Sims (Simsand and others, others, 1984). In In this this exposure, exposure, biotite biotite leucogranite leucogranite veins veins 1984). Ma old old (Rb/Sr (Rb/Srand and U-Pb U-Pbmethods) methods) cut cut the the gneiss. gneiss. 2590 Ma 2590 Secondary whole-rock whole-rock and and mineral mineral isochrons isochrons give give ages ages of of Secondary Ma and and are are thought thought to to approximate approximate the the time time 1750 to to 1800 1800 Ma 1750 span of of the the Penokean Penokean event event in in this this area area (Sims (Sims and and span 35 �others, 1984) others, 1984). Whereas the Archean gneisses of of the the area area may may have have Whereas the Archean gneisses been folded folded three three times, times, the the cross-cutting cross-cutting Late Late Archean Archean leucogranite shows shows only a single leucogranite single foliation, foliation, that that of of the the Penokean Penokean event. event. gneiss is The gneiss is comparable comparable in in age age to to those those of of the the Minnesota Minnesota River River Valley, Valley, about about 3500 3500 Ma Ma old: old: these these are are parts parts of of the the ancient ancient gneiss gneiss terrane terrane that is is separated separated granite-greenstone terrane from the granite-greenstone terrane to to the the north north by by the the GLTZ, the GLTZ, the Great Great Lakes Lakes Tectonic Tectonic Zone Zone of of Sims Sims and and others others (1980). (1980) 36 �References Cited Cited References Aldrich, H. H. R., R., 1929, 1929, The The Geology Geology of of the the Gogebic Gogebic Iron Iron Range Range of of Aldrich, Wisconsin: Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey Wisconsin: Bulletin Bulletin 71, 71, 279 279 p. p. Allen, Allen, R. R. C., C., and and Barrett, Barrett, L. L. p., P., 1915, 1915, Contributions Contributions to to the the prepreCambrian Cambrian geology geology of of northern northern Michigan Michigan and and Wisconsin: Wisconsin: Michigan Michigan Geological Geological and and Biological Biological Survey, Survey, Publication Publication 18, 18, Geology Geology Series Series 15, 15, pp. pp. 65-139. 65-139. Aiwin, Tyler Alwin, B., 1976, 1976, Sedimentation Sedimentation of the Middle Precambrian Precambrian Tyler Formation Formation of of north north central central Wisconsin Wisconsin and and northwestern northwestern Master's Thesis, Thesis, Univ. Univ. of of Minnesota-Duluth, Minnesota-Duluth,200 200 Michigan: Master's Michigan: Pp. Bailey, Bailey, S. S. W. W. and and Tyler, Tyler, S. S. A., A., 1960, 1960, Clay Clay Minerals Minerals Associated Associated Economic with with the the Lake Lake Superior Superior iron iron ores: ores: Economic Geology, Geology, vol. vol. pp. 150-175. 150-175. 55, pp. 55, Barovich, Barovich, K. K. M., M., Patchett, Patchett, P. P. J., J., Peterman, Peterman, Z. Z. E., E., and and Sims, Sims, P. P. K., 1989, Origin of 1.9-1.7 Ga Penokean continental 1989, Origin of 1.9-1.7 Ga Penokean continental crust crust of of Geological Society Society of of America America the the Lake Lake Superior Superior region: region: Geological Bulletin, Bulletin, v. v. 101, 101, p. p. 333-338. 333-338. Cannon, Cannon, W. W. F., F., 1986, 1986, Bedrock Bedrock geologic geologic map map of of the the Iron Iron River River 10 1 ' x x 2° quadrangle, Michigan Michigan and Wisconsin; Wisconsin; 1:450,000: 2 ' quadrangle, 1:450,000: U.S. U.S. Geological Geological Survey Survey Map Map 1-1360-B. I-1360-B. Cannon, F., 1986b, 1986b, Structural Structural and and tectonic tectonic map of of the the Iron Iron Cannon, W. F., River 1° x 2° Quadrangle, Michigan and Wisconsin, ' x 2 ' Quadrangle, Michigan Wisconsin, 1:250,000: 1:250,000: River 1 U.S. Geological Geological Survey Survey Map Map I-1360-D. I-1360-D. Cannon, Cannon, W. F. F. and and Gair, Gair, J. E., 1970, 1970, A Revision Revision of of stratigraphic stratigraphic nomenclature nomenclature for for Middle Middle Precambrian Precambrian rocks rocks in in northern northern Michigan: Michigan: Geological Geological Society Society of of America America Bulletin Bulletin 81, 81,pp. pp. 2843-2846. 2 843-2846. Cannon, Cannon, W. F., F., Peterman, Peterman, Z. Z. E., and and Sims, Sims, P. P. K., 1990, 1990, Structural Structural and and isotopic isotopic evidence evidence for for middle middle Proterozoic Proterozoic thrust thrust faulting faulting of Archean Archean and and Early Early Proterozoic Proterozoic rocks rocks near near the the Gogebic Gogebic range, Michigan Michigan and and Wisconsin: Wisconsin: 36th 36th Annual Institute Institute on on range, Lake Superior Geology, Thunder Bay, Ontario, p. 11-13. Lake Superior Geology, Thunder Bay, Ontario, p. 11-13. Dann, variation within the Emperor Emperor Dann, J. C., C., 1978, 1978, Major-element Major-element variation Igneous Igneous complex complex and and the the Hemlock Hemlock and and Badwater Badwater Volcanic Volcanic formations: unpublished unpublished M.S. thesis, thesis, Michigan Michigan Technological Technological formations: University, 199 199 p. p. University, Dimroth, 1968, Sedimentary Sedimentary textures, textures, diagenesis, diagenesis, and and Dimroth, E., 1968, sedimentary environment environment of of certain certain Precambrian Precambrian ironstones: ironstones: sedimentary fur Geology Geology v. v. Paleontology, Paleontology, Abh. Abh. v. v. 130, 130,pp. pp. Neues Jahrbuch Jahrbuch für Neues 247-274. 247-274. 37 �Dimroth, E. E. and and Chauvel, Chauvel, J. J. J., J., 1973, 1973, Petrography Petrography of of the the Sokoman Sokoman Dimroth, Iron-formation in part of the central Labrador trough, Iron-formation in part of the central Labrador trough, Quebec, Canada: Canada: Geological Geological Society Societyof of America America Bulletin, Bulletin,v. v. Quebec, 84, p. 111-134. 84, p. 111-134. Fritts, C. C. E., E., 1969, 1969,Bedrock Bedrock geologic geologicmap map of of the the MareniscoMareniscoFritts, Watersmeet area, Gogebic and Ontonogan Counties, Michigan: Watersmeet area, Gogebic and Ontonogan Counties, Michigan: U.S. Geological Survey Miscellaneous Geologic Investigations U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-576, 1-576,scale: scale: 1:48,000. 1:48,000. Map Gerlach, D. D. C., C., Shirey, Shirey, S. S. B., B., and and Carison, Carlson, R. R. W., W., 1988, 1988,Nd Nd Gerlach, isotopes in Proterozoic iron-formations: Evidence for isotopes in Proterozoic iron-formations: Evidence for mixed-ageprovenance provenanceand and depositional depositionalvariability: variability: mixed-age Abstract,Am. Am. Geophys. Geophys. Union UnionTrans., Trans.,EOS, EOS,v. v.69. 69. Abstract, Goldich, S. S. S. S. and and Marsden, Marsden, R. R. W., W., 1956, 1956,Precambrian Precambrian of of Goldich, Northeastern Minnesota; Field Trip No. 1, Geological Society Northeastern Minnesota; Field Trip No. 1, Geological Society of America Annual Meeting, Minneapolis, MN. of America Annual Meeting, Minneapolis, MN. Hoffman, P. P. F., F., 1987, 1987,Early Early Proterozoic Proterozoic foredeeps, foredeeps,foredeep foredeep Hoffman, magmatism, and Superior-type iron-formations of the Canadian Canadian niagmatism, and Superior-type iron-formations of the Shield, Krnner, A., ed., Proterozoic lithosoheric Shield, in Krâner, A., ed., Proterozoic lithospheric Geodynamic Series, Series,American AmericanGeophysical ~ e o ~ h ~ k iUnion, cunion, al evolution: Geodynamic evolution: v. 17, pp. 85-98. v. 17, pp. 85-98. Penokean Foredeep?, Foredeep?, 34th 34th Hoffman,P. P. F., F., 1988, 1988,Animikie AnimikieGroup: Group: AA Penokean Hoffman, p. Annual Institute on Lake Superior Geology, Marquette, MI, Annual Institute on Lake Superior Geology, Marquette, MI, p. 40-41. 40-41. W. 0., O., 1919, 1919,Geology Geology of of the the Gogebic Gogebic Range: Range: Hotchkiss, W. Hotchkiss, Engineering and Mining Journal, vol. 108. Engineering and Mining Journal, vol. 108. Irving, R. R. D. D. and and Van Van Hise, Hise, 1892, 1892, The The Penokee Penokee Iron-Bearing Iron-Bearing Series Irving, Series U.S. Geological Survey Monograph Monograph of Michigan and Wisconsin: of Michigan and Wisconsin: U.S. Geological Survey 19, 534 534p. p. 19, James, H. H. L., L., 1954, 1954,Sedimentary Sedimentary Facies Faciesof of Iron-Formation: Iron-Formation: James, Economic Geology, vol. 49, p. 235-293. Economic Geology, vol. 49, p. 235-293. James, H. H. L., L., 1955, 1955,zones zones of of regional regional metamorphism metamorphism in in the James, the Precambrian of northern Michigan: Geological Society of Precambrian of northern Michigan: Geological Society of America ~ulletin, v. 66, p. 1455-1487. America Bulletin, v. 66, p. 1455-1487. Klasner, J. J. S., S. , Ojakangas, Ojakangas,R. R. W., W., Schulz, Schulz,K. K. J., J., and LaBerge, G . Kiasner, G.of 1991, Nature and Style of Deformation inand theLaBerge, Foreland L., L., 1991, Nature and Style of Deformation in the Foreland the Early Early Proterozoic ProterozoicPenokean PenokeanOrogen, Orogen,Northern NorthernMichigan: Michigan: of the U.S.G.S. Bulletin Bulletin1904-K, 1904-K,22 22 p. U.S.G.S. p. LaBerge, G. G. L., L., 1964, 1964,Development Development of of Magnetite Magnetite in in Iron-Formations LaBerge, Iron-Formations of the Lake Superior Region: Economic Geology, vol. 59, p. of the Lake Superior Region: Economic Geology, vol. 59, p. 1313-1342. 1313-1342. 38 38 LaBerge,G. G. L., L., l966a, l966a. Altered Altered Pyroclastic Pyroclastic Rocks Rocks in in IronLaBerge, IronFormation Hamersley Range, Western Australia: Economic Formation Hamersley Range, Western Australia: Economic Geology, vol. 61, p. 147-161. Geology, vol. 61, p. 147-161. �Pyroclastic Rocks Rocks in in South South African African LaBerge, LaBerge! G. G. L., L.! 1966b, 1966b1 Altered Altered Pyroclastic GeologyI vol. vol. 61, 611p. p. 572-581. 572-581. Iron-Formation: Economic Economic Geology, Iron-Formation: Larue, D. K., K.! 1981, 19811 The The Chocolay Chocolay Group, Group! Lake Lake Superior Superior region, region! Larue! D. U.S.A.: sedimentological sedimentological evidence evidence for for deposition deposition in in basinal basinal and platform settings on an early Proterozoic craton: and platform settings on an early Proterozoic craton: Geological Bulletin! vol. vol. 92, 92! p. p. 417-435. 417-435. Geological Society Society of of America America Bulletin, Larue, Larue! D. D. K., K.! 1983, 1983! Early Early Proterozoic Proterozoic tectonics tectonics of the the Lake Lake Tectonostratigraphic terranes terranes near near the the Superior region: region: Tectonostratigraphic Superior purported zone! in Medaris, Medaris! L. L. G., G e lJr., Jr.! Early Early purported collision collision zone, Geological Proterozoic Proterozoic geology geology of of the the Great Great Lakes Lakes region: region: Geological Society merica Memoir Society of America Memoir 160, 1601p. p. 33-47. 33-47. Mengel, Mengel! J. J. T., T.! Jr., Jr.! 1963, 1963! The The Cherts Cherts of of the the Lake Lake Superior Superior IronIronBearing Bearing formations: formations: Ph.D. Thesis, Thesis! University University of of Wisconsin. Wisconsin. Morey, Morey! G. G. B., B. Sims, Sims P. P. K., K. Cannon, Cannon! W. W. F., F. Mudrey, Mudrey! M. M. G., G. Jr., Jr. and and Southwick, D. L., L.! 1982, 1982! Geological Geological Map of the the Lake Lake Superior Superior Southwickl D. region: Minnesota, Minnesota! Wisconsin, Wisconsinl and and Northern Northern Michigan: Michigan: region: Minnesota Minnesota Geological Geological Survey Survey State State Map Map Series Series S-13. S-13. Ojakangas, Ojakangas! R. W., W.! 1983, 1983! Tidal Tidal deposits deposits in in the the Early Proterozoic Proterozoic basin basin of of the the Lake Lake Superior Superior region region -- the the Palms Palms and and Pokegama Pokegama Formations: Formations: Evidence Evidence for for sub-tidal sub-tidaldeposition deposition of of SuperiorSuperiortype banded iron-formation: iron-formation: jinEarly EarlyProterozoic Proterozoic Geology Geology of of type banded Geological the by L. G. Medaris), Geological the Great Great Lakes Lakes Region Region (edited (editerby G. Medaris) Society Society of of America America Memoir Memoir 160, 1601 p. p. 49-66. 49-66. Ojakangas, Ojakangas! R. W., W.! in in press, press! Sedimentology Sedimentology and and provenance provenance of of the the Early Proterozoic Proterozoic Michigaxnme Michigamme Formationl U.S. Early Formation, Michigan: Michigan: U.S. Geological Geological Survey Survey Bulletin Bulletin 1904-IL 1904-R. Ojakangas, Ojakangas! R. R. W. W. and and Matsch, Matsch! C. C. L., L.! 1982, 1982! Minnesota Minnesota Geology, Geologyl Univ. Univ. of of Minnesota Minnesota Press, Press! Minneapolis, Minneapolisl255 255 p. p. Peterman, Peterman! Z. Z. E., E e lZartman, Zartman! R. R. E., E e land and Sims, Sims! P. P. K., K.! 1980, 19801 Early Early Archean tonalitic gneiss gneiss from from northern northern Michigan! Michigan,U.S.A.! U.S.A., j Morey! G. G. B., B a 1and and Hanson, Hanson! G. G. N., N.! Selected Selected studies studies of of Archean Archean Morey, and lower lower Proterozoic Proterozoic rocks, rocksl southern southern Canadian Canadian Shield: Shield: and Geological Geological Society Society of of America America Special Special Paper Paper 182, 182! p. p. 125-134. 125-134. Prinz! W. W. C., C.! 1981, 19811 Geologic Geologic map map of of the the Gogebic Gogebic Range Range -Prinz, Watersmeet area, area! Gogebic Gogebic and and Ontonogan Ontonogan Counties, Countiesl Michigan: Michigan: Watersmeet Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsSeries Series U.S. Geological Map 1-1365, I-1365! scale scale 1:125,000. 1:1251000. Map Prinz! W. C., C.! Gair, Gairl J. J. E., E.! and andcannon! W. F., F.! 1975, 1975! "Greenstone: I1Greenstone: Prinz, Cannon, W. Field Trip Trip 2", 2If121st 21st Annual Annual Institute Institute on on Lake Lake Superior Superior Field Geologyl Marquette, Marquette! Michigan, Michigan! pp. pp. 41-85. 41-85. Geology, Schmidt! R. G e l1976, 1976! Geology of the Precambrian Precambrian W (Lower (Lower Schmidt, G., Countyl Michigan: Michigan: Precambrian) Rocks Rocks in in Western Western Gogebic Gogebic County, Precambrian) Geological Survey Survey Bulletin Bulletin 1407. 1407. U.S. Geological 39 �Schmidt, Schmidtl R. G., 1980, 19801 The The Marquette Range Supergroup Supergroup in in the the U.S. Gogebic Gogebic Iron Iron District, District, Michigan Michigan and and Wisconsin: Wisconsin: U.S. Geological Geological Survey Survey Bulletin Bulletin 1460, 14601 96 96 p. p. Schmidt, R. G and Hubbardl Hubbard, H. A A., Schmidtl v 11972, 19721 Penokean Penokean orogeny orogeny in in the the central and western Gogebic Gogebic region, Michigan and Wisconsin: regionl Michigan and Wisconsin: Field A, 19th Field Trip Trip Al 19th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Houghton, Geologyl Houghtonl MI, MIl p. p. A1-A27. Al-A27. Sims, Simsl P. P. K., K s 11990, 19901 Geologic Geologic map map of of Precambrian Precambrian Rock, Rockl Marenisco, Mareniscol Thayer, and Watersmeet 15 Minute Minute Quadrangles Gogebic and Thayerl Ontonagon Ontonagon Counties, Countiesl Michigan Michigan and and Vilas Vilas County, Countyl Wisconsin: Wisconsin: U.S. Geological U.S. Geological Survey Survey Miscellaneous Miscellaneous Investigation Investigation Map Map 1-2093. 1-2093. Sims, Z. E., E e l1976, 1976# Geology Geology and and Rb-Sr Rb-Sr ages ages of of Simsl P. P. K., K e 1Peterman, Petermanl Z. reactivated reactivated Precambrian Precambrian gneisses gneisses in in the the Marenisco-Watersmeet Marenisco-Watersmeet area, areal Northern Northern Michigan: Michigan: Journal Journal of of Research, Researchl U.S. U.S. Geological Survey, Geological Surveyl vol. vol. 4, pp. pp. 405-414. 405-414. Sims, Z. E., E e lPrinz, Prinzl W. C., C e 1and and Benedict, Benedictl F. F. C., Ce1 Simsl P. K., K a 1Peterman, Petermanl Z. 1984, Geology, Geology, geochemistry and age Archean and 1984# age of Archean and Early Early Proterozoic Proterozoic rocks rocks in in the the Marenisco-Watersmeet Marenisco-Watersmeetarea, areal northern northern U.S. Geological Michigan: Michigan: U.S. Geological Survey Survey Prof. Prof. Paper Paper 1292-A, 1292-Al41 41 p. p. Sims, Simsl P. K., K e 1Van Van Schmus, Schmusl W. R., Schulz, Schulzl K. K. J., J a 1and and Peterman, Peterman#Z. Z. E., Tectonostratigraphic evolution of the Early E e l1990, 19901 Tectonostratigraphic Proterozoic Penokean Proterozoic Wisconsin magmatic terranes of the Penokean Orogen: Orogen: Can. Jour. Jour. Earth Earth Sci. Sci. Southwick, D. L. and MoreyI Morey, G. B B., imbrication and a 1 1991, 19911 Tectonic imbrication Southwickl foredeep foredeep development development in in the the Penokean Penokean orogen, orogenl east-central east-central Minnesota-An Minnesota-An interpretation interpretation based on on regional regional geophysics geophysics and and results of U.S. Geological Geological Survey results of test test drilling: drilling: U.S. Survey Bulletin Bulletin 1904-C, 1904-Cl17 17 p. p. Suszekl T. T. J., J a 11991, 1991, Petrography Petrography and and sedimentation sedimentation of of the the Middle Middle Suszek, Proterozoic (Keweenawan) Nonesuch Formation, Formationl Western Lake Proterozoic (Keweenawan) Western Lake Superior region, region, Midcontinent Midcontinent Rift Rift System: System: unpublished unpublished M.S. M.S. Superior thesis, University University of thesisl of Minnesota, Minnesotal Duluth, Duluthl 198 198 p. p. e 1 1973, 19731 Geological Geological Map of of the the Marenisco Marenisco and and Wakefield Wakefield Trentl Trent, V. A A., NE quadrangles, quadranglesl Gogebic Gogebic County, Countyl Michigan: Michigan: U.S. U.S. Geological Geological Survey Open Open File File Report, Reportl scale scale 1:48,000. 1:481000. Survey Van Hisel C.R. C.R. and and Leith, Leithl C. C. K., K a 11911, 19111 Geology Geology of of the the Lake Lake Van Hise, Superior Superior Region: Region: U.S. Geological Survey Survey Monograph Monograph 52. 52. U.S. Geological 40 �KEWEENAWAN SEDIMENTARY ROCK OF THE THE SOUTH SHORE, LAKE SUPERIOR A.B. Dickas Dickas Department Department of of Geology, Geology, Wisconsin-Superior University of Wisconsin-Superior M.G. Mudrey, Mudrey, Jr. Jr. Wisconsin Wisconsin Geological and and Natural Natural History History Survey, Sumey, Madison, Wisconsin �INTRODUCTION The sedimentary sedimentary and igneous igneous rock composing composing the Precambrian Precambrian (Middle (Middle Proterozoic, Roterozoic, Keweenawan) section of the Lake Superior stratigraphic column column have have had had aa long long history history of of study. Almost six decades ago (19331, (1933), the geology of of the the "Lake "Lake Superior Region," Region," constituting Excursion C-4, was presented as Guidebook International Geological Geological Guidebook 27 of the XVI International Congress. The W. 0. 0. Hotchldss The field field guide guide for for this this excursion was prepared by W. Hotchlciss of of the the MichiMichigan College College of Mining Mining and and Technology Technology (now (now Michigan Michigan Technological TechnologicalUniversity) University)and andwas was purchased 25 cents. cents. purchased for for the the sum sum of of 25 In his introduction to that guidebook, guidebook, C. K. kLeith i t h (University (University of Wisconsin) stated: The The Lake Superior Superior region q i o n has been of special special interest to students of pre-Cambrian geology because it presents the largest and most varied pm-Cambrian pre-Cambrian succession succession that geology because has has been been definitely definitely worked worked out. Its Itscontent contentof ofvaluable valuableiron imnand andcopper copperores oreshas has made made possible possible more intensive intensive and detailed studies studies than have been accorded to extensive extensive pre-Cambrian pre-Cambrian areas elsewhere. The Thepre-Cambrian pre-Cambriansuccession successionnow now known known (in the Lake Superior Superior area) area) represents a greater mater thickness of sediments sedimentsand and aa larger larger time time than than all all the the post-Cambrian post-Cambrianof of North North America. America. It is k i t h , in a later section of this guidebook, presented the is interesting interesting to to note how Charles Charles Leith, Keweenawan Keweenawan sequence, sequence, now now known as as the the Midcontinent Midcontinent Rift Rift sequence: sequence: Keweenawan: Keweenawan: Next Next below below (the (the Cambrian) Cambrian)is is the the nonfossiliferous nonfossilifemusKeweenawan Keweenawan series, consisting of an immense mass, possibly 5 miles (8 km) thick, thick, of sandstone, sandstone, series, consisting an immense mass, miles intercalated shales shales and conglomerates, containing in its lower part large quantiwith intercalated ties of of extrusive extrusive lavas lavas and intrusive laccoliths and sills. In In degree degree of of metamorphism metamorphism ties is more more like like the the Cambrian Cambrian than the underlying Humnian It has has characterischaracterisitit is Huronian series. series. It tic reddish, reddish, yellowish, yellowish, and and purplish purplish colors colors and and carries cames various various evidences evidencesthat that itit was was tic essentially aa continental continental deposit deposit under semiarid conditions. Its Its lower lowerpart part isis tilted tiltedin in essentially marked unconformity unconformityto tothe theCambrian, Cambrian,but but its itsupper upperpart part lies liesnearly, nearly,ifif not notquite, quite, maiked in an an independent independent parallel to to the Cambrian. Cambrian. Obviously, Obviously,ititwas wasmainly mainlydeposited depositedin parallel basin before the incursion of the Upper Cambrian sea. Although the Keweenawan is sea. Although Keweenawan in the the sense senseof of preceding preceding the the Upper Upper Cambrian Cambrian transgression, transgression,having having pre-Cambrianin pre-Cambrian structural and and igneous igneousaffiliations affiliationswith with the the pre-Cambrian, pre-Cambrian, and and being being nonfossffiferous, nonfossiliferous, structural may be be Cambrian Cambrianin in the the sense sensethat thatitit was was being being formed formedatatthe thesame sametime timeas asMiddle Middle itit may and Lower Lower Cambrian Cambriansediments sedimentsin in distant distant Cambrian Cambrianseas. seas. and Today as as we we gather gather for for this this 38th 38th Institute Institute on on Lake Lake Superior SuperiorGeology Geologyfieldtrip, fieldtrip,comparisons comparisons Today 1933 form form distinct contrasts. In In1992, 1992,with with aasingular singularexception, exception,the the with conditions in 1933 copper mines mines are are closed closed and and the the massive massive iron iron ore ore fields fields have have fallen fallen under under different different economic economic copper Yet,aanew new era era of of evaluation evaluation and exploration has climates. Yet, has begun. begun. The Lake Superior Keweenawan section section is is widely widely recognized recognized as as one one of of the the fmest fmest extant extant examples examples of of continental continental Keweenawan rifting. The Theadvent adventofofindustrial industrialfield fieldevaluation evaluationof of the the hydrocarbon hydrocarbon potential potential of of these these rift rift rifting. indhctly facilitated facilitatedthe thecollection collectionof ofapproxiapproxistrata, beginning beginning in in 1983, 1983,has has directly directly and and indirectly strata, mately 4200 4200 km km of of seismic seismic reflection reflection data data in in the the Lake Superior Superior district dismct alone, alone, in in addition addition to to mately supportive supportive magnetic magnetic and and gravity gravity surveys. surveys. This new new period period of of exploration exploration within within the the Lake Lake Superior Superior region has altered altered our interpretation interpretation of This its geologic development, especially during Keweenawan time. m y of these updated geologic its geologic development, especially Keweenawan Many of these updated geologic 43 43 �relationships will be examined during the process of this field mp. trip. Our Our principal principal focus will be on the geology and geologic history of the youngest Precambrian rock in the region, the rifting,initiated initiatedcirca circa 1100 1100Ma. Ma. The The Keweenawan. This This rock rock is is a remnant of major continental rifting, resultant Midcontinent Midcontinent Rift System System trends trends from the Lake Superior Superior region to to as far far southwest southwest as as central central Kansas Kansas and and as as far far southeast southeastas as southern southernOhio. Ohio. As of this writing (March 2, 1992) has been been underway underway for for several weeks weeks for for 1992) site preparation has the Terra/Patrick TerraPamck #7-22 wildcat borehole, borehole, a test test of the the hydrocarbon hydrocarbon potential potentialof of the theWisconWisconsin section of the Midcontinent rift of national significance and interest. Located 47N, 22,47N, Locatedin in 22, this well well will will be be operated operated by by Terra Terra 6W, Keystone Township, Bayfield County, Wisconsin, this Energy, Energy, Ltd of Traverse Traverse City, Michigan, in partnership with Patrick Petroleum Company of arrangements with Amoco Ammo Production Production Company Company(USA), (USA), Jackson, Michigan, under farmout arrangements Houston, Texas. The The target target depth depth will be 6,000 feet, permitting a test of the oil or gas large dragdragpotential of the Oronto Oronto Group Group sequence sequence of sedimentary sedimentary rocks. The The structure structureis is aa large with north north closure closure against againstthe theDouglas Douglasreverse reversefault. fault. The The surface surface expression expression of of fold anticline with 60 square square miles. Available Available information information this structure structure extends over an area of approximately 60 on this state state record depth wildcat will be included in the 38th Institute on Lake Superior Geology Proceedings as an abstract abstract (Albert (Albert B. Dickas). The site of the TerraPatrick Terra/Patrick #7-22 borehole is approximately 6 miles miles north-northeast north-northeast of of an Oronto borehole Amoco M Production Oronto Group Group wildcat test W h o l e announced in 1985 by Ammo u c t i o n Company (USA). This bborehole, h o l e , planned for 13, 13,46N,7W, 46N,7W, and targeted for 15,000 feet, was never drilled for economic economic and and legislative legislative reasons. 44 �GEOLOGY GEOLOGYOF OF THE THEMIDCONTINENT MIDCONTINENTRIFT RIFTSYSTEM SYSTEMALONG ALONG THE THESOUTH SOUTH SHORE MICHIGAN SHORE OF OF LAKE LAKE SUPERIOR, SUPERIOR, WISCONSIN WISCONSIN AND MICHIGAN Reprinted from Dickas, Reprinted with with permission /rom Dickas, Albert B. (editor), (editor),1989, 1989, Lake Superior Superior basin basinsegment segment of the Midcontinent Rift Rjft System: System: Field Field trip trip guidebook guidebook T344.28th T344, 28th International International Geological Geological Congress, Congress. 62 62 pages. Introduction Introduction The The Midcontinent Midcontinent Rift Rift System System has been mapped over an axial length of in excess of 3,300 km. structure are contained krn.Portions Portionsofofthis thisPrecambrian Precambrian(Ca. (ca.1.1 1.1 Ga) extensional structure contained in in the the states states of of Kansas, Kansas, Nebraska, Nebraska, Iowa, Minnesota, Wisconsin, Michigan, and Ohio. This Thisreport report presents presents the geology of this rift system within the geographic region generally defined as northwestthe geology of this rift system within the geographic region generally defined as northwestern em Wisconsin Wisconsin and and the the adjacent adjacent upper upper peninsula peninsula of of Michigan. Michigan. Wisconsin Wisconsin Section Section The The Midcontinent MidcontinentRift Riftsequence sequenceof of Precambrian Precambriansedimentary sedimentarystrata stratain inthe thewestern westernLake Lake Superior Superior region region constitutes constitutes some some of of the the oldest oldest known known and and studied studied such such assemblages assemblagesin in the the United United states. states. These Theseunits unitswere wereinitially initiallydescribed describedby byHunt Hunt(1873), (1873),who whonamed namedthem themthe the Keweenaw Keweenaw Group Group after after the cupriferous cupriferous strata exposed along the Keweenaw Peninsula of Michigan. Thwaites Thwaites(1912) (1912)divided dividedthis this section sectioninto into the the Oronto Oronto (lower) (lower) and Bayfield (upper) (upper) groups (Fig. (Fig. 1). More More recently recently the the U. U. S. S. and and Ontario Ontario Geological Geological surveys surveys have have been been inforinforgroups mally termKeweenawan KeweenawanSupergroup. Supergroup. mally using usingthe theterm The outcrop outcrop belt belt of of the theOronto OrontoGroup Groupisis traced traced from from northwestern northwesternWisconsin Wisconsin east east and and northnorthThe east to to the the tip tip of of Keweenaw Keweenaw Point, Point, Michigan. The TheOronto OrontoGroup Groupcrops crops out out principally principally along along east Ashland syncine syncline(Fig. (Fig.2), 2),which whichisiscentrally centrally located located on the St. Croix horst. The TheAshland Ashland the Ashland the syncline is asymmetrical as the steeper dips are found within the southern limb. The horst is is syncline is asymmetrical steeper limb. The horst bounded by by the the reverse-throw reverse-throwDouglas Douglas and and Isle Isle Royale Royale faults faults to to the the north north and and the the Lake Lake bounded Owen and and Keweenaw faults to the south. While Whileseismic seismicinformation information suggests suggests the the presence presence Owen of Oronto Orontocomponents componentsin inthe theflanking flankingbasins, basins,deep deepdrilling drillinghas has yet yetto toconfirm confirmthis thisconjecture. conjecture. of (FredaSandstone) Sandstone)inin However,on on the thebasis basis of ofaadrag dragfold foldexposure exposureof of Oronto Orontotype typestrata strata(Freda However, Douglas County, County,Wisconsin, Wisconsin,White White(1966) (1966)supported supportedthe the concept conceptof of Oronto Orontostrata stratabeing being Douglas found north north of of the the Douglas Douglas fault. Alternately, Alternately,White White (1966) (1966) supported supported the possibility of found post-Oronto(Bayfield (BayfieldGroup) Group)inliers inliersbeing beingfound foundwithin withinthe thehorst horstposition positionas assuggested suggestedby by post-Oronto heavy heavy mineral mineralanalyses analysesconducted conductedby by Tyler Tyleretetal. al. (1940). (1940). The OrontoGroup Groupisis 40 40percent percent sandstone sandstoneand and 60 60 percent percent shale shale (Thiel, (Thiel, 1956) 1956) and and constitutes constitutes The Oronto aa maximum maximum 6,100 6,100 m m thick thick sequence sequence of reddish conglomerate, conglomerate, sandstone, and mudstone. ItIt shows rela-. shows aa general general upward upwardincrease increasein in maturity, maturity, from frompoorly poorly sorted sortedarkosic arkosicto toquartzose, quartzose,relatively tively well-sorted well-sortedsedimentary sedimentaryrocks. rocks. Much Muchofofthis thisgroup groupwas waslocally locallyderived derivedthrough through erosionof of Middle MiddleKeweenawan Keweenawanbasalts basaltsand andtransported transportedonly onlyaashort shortdistance distancetotoits itsdeposideposierosion tional tionalbasin. basin. 45 �The Thelowest lowestunit unitof of the theOronto OrontoGroup, Group, the the Copper CopperHarbor HarborConglomerate, Conglomerate, conformably conformablyoveroverlies liesbasement basementlavas lavasand andlocally locallyinterfingers interfingerswith with them them (White (White and and Wright, Wright, 1960). 1960). While While exposures exposurescan canregionally regionallyexceed exceed1,800 1,800m min in thickness, thickness,as asmuch muchasas 610 610 m m of of this this column column may may be be basic basic volcanics volcanics (Halls, (Halls, 1966). 1966). Overall Overallthis thisunit unitisisaafining-upward fining-upwardaccumulation accumulationof of brown brown to red,arkosic, arkosic,pebble pebble to to boulder boulder conglomerate, conglomerate,dominantly dominantlycomposed composedof of mafic maficto tofelsic felsic tored, volcanics, volcanics,with with lesser lesseramounts amountsof of rather rather coarse, coarse, cross-bedded, cross-bedded, graywacke graywackesandstone sandstone(Daniels, (Daniels, 1982). Within the sands, stratification is crude, shallow water flow regime structures 1982). Within the sands, stratification is crude, shallow water flow regime structuresare are common limited. Bedding Bedding plane plane dips dips range from from common and and lateral lateral correlations correlations for any distance are limited. ten degrees to overturned. The depositional regime of the conglomerate facies reflects a ten degrees to overturned. The depositional regime of the conglomerate facies a prograding, prograding,alluvial alluvialfan fan complex complex (Daniels, (Daniels,1982), 1982),while the sandstone sandstone units are are more more suggessuggestive tive of of shallow shallow water. water. AAlocalized localized"redder" "redder" arenaceous arenaceousfacies, facies,found found along along the the Keweenaw Keweenaw Peninsula, flood plain or or standing-water standing-waterdeposit deposit by White White and and Wright Wright Peninsula,has has been been classified classifiedas as aa flood (1960). (1960). The Thesame sameenvironment environmentisiselsewhere elsewherelocally locallysupported supportedby bythe thelimited limitedpresence presenceof of algal algal stromatolites stromatolitesin in the thevicinity vicinityof of Copper CopperHarbor, Harbor, Michigan, Michigan,the thelocation locationof ofthe thetype type section sectionof of this thisformation. formation. 11 — F'1a.n1 anit 'I' I. 'I' MuD—CO z -p si o rst M I D - C O NTI T I I'T NENT RIIF' F'T 2 —orst 2 'I' I. A. 'I' I C R. .A. P II Y T I M E S T R A T I G R A F H Y 3 u . r ' e nsu a 3 — tJ. P en xiiixisu. 1la. TIM 4 - L peninsula - —-- i... -- Iowa I Minn I 1 Wisc 11 Freda. Ss 1 NoneSuch Fm r 7 d -Val s , V A i "'I- "  ¥ 7 v ,.,"'I^^ 7 7 A ." V-01 s > < I >"4 i V < " , ^ >tans_> v > < - ' < A< 7 Mich Freda ss .. a! NoneSuch Tnor > St croik chenkwi. d pex1ins.iia. - rt, a g e, > l=>p ^ - 2 4 Lake \ ' A . < > J 7 < L,,7, VOlS', * VO-1 s + Q ffl , , I-. < 4 r v L grap hic terminology terminology and and time time relationships relationships of Upper FIGURE FIGURE 1: 1: Strati Stratigraphic Upper Keweenawan Keweenawan sedimentary sedimentary rocks permission of (1986), reprinted reprinted by by permission of the the rocks along along the the Midcontinent Midcontinent Rft RiftSystem System trend. trend. After Dickas (1986), American Association Association of of Petroleum Petroleum Geologists. Geologists. American 46 �In conformable and interfingering interfingering contact with the Copper Harbor Conglomerate Conglomerate is the the Formation, a hydrocarbon source rock Dickas, 1991) Nonesuch Formation, 1991) and the center center of industrial industrial interest focused on on the the Midcontinent Midcontinentrift riftsince sincethe theearly early1980's. 1980's. These strata are gray to distinguishable from enveloping grain size size ranges ranges black, easily distinguishable enveloping red to brown formations. The grain from medium sand to clay with with shale subordinate to to siltstone siltstone and and sandstone. sandstone. This unit is is the the from at least 140 m m in in northern northern Wisconsin Wisconsin to to a maxithinnest of the Oronto Group, ranging from mum 200 m in adjacent Michigan. Framework Frameworkcomposition composition emphasizes emphasizesmafic mafic rock rock fragfragments, with analysis showing ranges ranges of of 15 to to 30 30percent percent (Hite, (Hite, 1968). 1968). Of economic interest is the cupriferous nature of the basal 10 m of the Nonesuch Formation, especially in the cupriferous 10 White Pine, Michigan area where an estimated 11 million tones of of copper have been found (Cox et al., aL, 1973), predominantly predominantlyin inthe theform formof ofchalcocite chalcociteand andnative nativecopper. copper. The The variety variety of of sedimentary structures found in this formation have locally been employed employed as as supporting supporting environments. The best model appears to be that of evidences for a variety of depositional environments. reducing conditions conditions within a standing standing body of water (Hubbard, 1975), distinguished by frequent variations variations in water depths (Daniels, 1982), influenced by fluvial and deltaic associations (Barghoorn (Barghoom et al., 1965), 1965), and marked by periodic salinity levels exceeding that of Hieshima and and Pratt Pratt (1991) (1991) offer offer evidence evidencesupsupgypsum precipitation. Recently, Recently,however, however, Hieshima porting a marine embayment embayment environment. copper is found in direct lithologic The copper lithologic association association with finely finely disseminated disseminated carbonaceous carbonaceous 0.5% of of the the formation formationby byvolume. volume. Kelly and Nishioka (1985) believe matter which averages 0.5% copper copper precipitation was directly facilitated by the intimate presence of organic material. The organic organic matter, upon chemical extraction, shows remarkable structural features that have been preserved by a bituminization, rather rather than than aa carbonization, carbonization,process. process. This material is found both as matrix masses and as recognizable remains, such as bacteria cells, algal-like units and fungal hyphae, with volume distribution being concentrated in the finest grained Overall,individual individuallaminae laminaeare are alternately alternately rich and poor in organic components. strata. Overall, Moore et al. (1969), after thin-section analysis of the organic rich shale layers, concluded these units arc are characteristic of lake, swamp and tidal flat environments and that the majority of preserved preserved organic organic material material developed developedin in place. place. vugular also of interest because, at the White Pine mine, associated vugular The cupriferous zone is also porosity and fractures often are arc filled filled with small amounts amounts of solid solid and liquid liquid hydrocarbons. hydrocarbons. Analysis by Barghoom Barghoorn et al. (1965) indicates this Nonesuch crude oil contains higher concentrations of alkanes alkanes and and lower lower percentages percentagesof of aromatic aromaticss than an average crude crude oil, and and associated with Paleozoic production production in the the state state of of resembles the paraffinic crude commonly associated Pennsylvania. Further Furtheranalysis analysishas has indicated indicatedthe the oil oil is is indigenous indigenous to to its its host host rock rock (Eglinton (Eglinton et al., aL, 1964), is of organic origin (Moore et et al., al., 1969), and and was was formed formed under under mild mild formational temperature conditions (Barghoom environment is is also also (Barghoorn et et al., a!., 1965). A low thermal environment supported by Brown (197 I), who reported the presence of pink bornite and djurleite in (1971), reported presence of pink bornite and djurleite in the the Formation, minerals minerals which which cannot cannot exist exist above above respective respective ranges ranges of of 75 75 degree degreeCC Nonesuch Formation, and 95 degree C (167 (167 F F and 203 203 F). The Nonesuch crude presently represents one of the oldest known known liquid liquid hydrocarbon, hydrocarbon, being approximately 1,046 million years in age. This was determined for the Nonesuch host by approximately million years in age. using rubidium-strontium ratios. This date date is verified by the work of Ruiz et al. ratios. This a!. (1984), who obtained an age age of of 1,047 +I-35 cutting +1-35million millionyears years by by Rb-Sr Rb-Sr dating dating of of calcite calcite filled veins cutting 47 �acrossthe the cupriferous cupriferous shale shale of of the the Nonesuch Nonesuch Formation in the White As this this across White Pine Pine area. As calcite contains primary liquid oil inclusions, Kelly and Nishioka (1985) refer to this dateas as calcite contains primary liquid oil inclusions, Kelly and Nishioka (1985) refer to this date the time of oil entrapment and thus consider it as a minimum age for White Pine hydrocarthe time of oil entrapment and thus consider it as a minimum age for White Pine hydrocarbon. bon. The upper upper unit unit of of the the Oronto OrontoGroup, Group,the the Freda FredaSandstone, Sandstone,lies liesconformably conformablyover overthe theNoneNoneThe such Formation. The nature of the Freda Sandstone upper contact is not known for nowhere such Formation. The nature of the Freda Sandstone upper contact is not known for nowhere is this this formation formation found found in in exposed exposed (Myers, (Myers, 1971) 1971)or or drilled drilled contact contact with any any unit unit of of the the is Bayfield Group or its Michigan correlative, the Jacobsville Sandstone (Fig. 1). While listed Bayfield Group or its Michigan correlative, Jacobsville Sandstone While listed by Hite Hite (1968) (1968)as asexceeding exceeding3,660 3,660m min inthickness, thickness,only only1,500 1,500 m m is found found on on the the north north coast coast by of the Keweenaw Peninsula (Halls, 1966), near the type section at Freda, Michigan. The of the Keweenaw Peninsula (Halls, 1966), Michigan. The FredaSandstone Sandstoneisiscomposed composedof ofbasal, basal,subordinate subordinateconglomerate conglomeratefming-upward fining-upwardtotosandstone sandstone Freda color,aarepetition repetitionof ofthe theCopper CopperHarbor Harborred redto tobrown brownspectrum spectrumisisobserved, observed, andsiltstone. siltstone. InIncolor, and interrupted by spotty and laminar unoxidized zones (Daniels, 1982). With an analyzed maturity interrupted by spotty and laminar unoxidized zones (Daniels, 1982). With an analyzed maturity indexof of 0.63, 0.63, aafeldspar feldsparrange rangeof of 10 10to to24 24percent percent (Hite, (Hite,1968), 1968),and andthe thegrain grainshape shapebeing being index angular to sub-rounded, these sandstone units arc classed as immature. Daniels (1982) considers angular to sub-rounded, are immature. Daniels (1982) considers theaverage averagesand sandunit unitto tobe be aa fme-grained fine-grained feldspathic feldspathic lithic lithic arenite. arcnite. Sedimentary Sedimentarystructures structures the include cross-bedding, mud-cracks, graded beds, ripple marks, and a wide variation include cross-bedding, mud-cracks, graded beds, ripple marks, and a wide variation inin paleocurrentindicators. indicators. The Theimplied implieddepositional depositionalenvironment environmentranges rangesfrom fromfluvial fluvial(Daniels, (Daniels, paleocurrent 1982) to fluvial plain or tidal flat (Hamblin, 1961). 1982) to fluvial plain or tidal flat (Hamblin, 1961). Along the theeastern easternshore shoreof of Lake Lake Superior, Superior, in in the the Pt. Pt. Mamainse Mamainse region region of of Ontario, Ontario, aa 60 60m m Along section of gray sandstone is found unconformably overlying Keweenawan basalts. Work by section of gray sandstone is found unconformably overlying Keweenawan basalts. Work by Hamblin (1961) (1961)and and Annels Annels (1973) (1973)allows allows correlation correlation of of these these strata, strata, termed termed the the Mica Mica Bay Bay Hamblin sandstone, to the Freda sandstone and suggests a fluvial environment of deposition. sandstone, to the Freda sandstone and suggests a fluvial environment of deposition. Overallthe the Oronto OrontoGroup Groupcan can be be viewed viewed as as aa thick thick sequence sequence of of clastic clastic sedimentary sedimentary rocks rocks Overall that are stratigraphically unified by similar heavy mineral suites, an upward and distal dethat are stratigraphically unified by similar heavy mineral suites, an upward and distal dethree formations formations creasing in in grain grain size, size, and and an an upward upward increase increase in The three creasing in lithologic lithologic maturity. maturity. The of this group were derived from a common source of Keweenawan igneous material (Tyler of this group were derived from a common source of Keweenawan igneous material (Tyler et at., al., 1940). 1940).While Whileeach eachformation formationisisinterpreted interpretedin inlight lightof of slightly slightlydifferent differentdepositional depositional et environments, Elmore and Daniels (1980) view the group environment as a trangressiveenvironments, Elmore and Daniels (1980) view the group environment as a trangressiveregressivealluvial alluvialfan, fan,lacustrine lacustrineand andfluvial fluvialsystem systemthat that filled filledthe the developing developingMidcontinent Midcontinent regressive Rift basin during the final stages, and after cessation, of volcanic activities. Rift basin during the final stages, and after cessation, of volcanic activities. TheBayfield BayfieldGroup, Group,wherever whereverstudied, studied,isisfound foundto tobe be in in distinct distinct contrast contrast to to the the Oronto Oronto The Group. The TheBayfield Bayfieldsequence sequencedisplays displaysaahigher higherdegree degreeof of compositional compositionalmaturity maturityand and Group. structurallythe the bedding bedding is is more more commonly commonly subhorizontal. subhorizontal. In Interms termsof ofheavy heavyminerals mineralsthe the structurally tourmaline-zircon to epidote ratio is reversed in the Bayfield Group as compared to the Freda tourmaline-zircon to epidote ratio is reversed in the Bayfield Group as compared to the Freda and Nonesuch Nonesuch assemblages assemblages (Tyler (Tyler et et a!., al., 1940). 1940). There Thereisis aa question question as as to to the the type type of of contact contact and between these groups. Supporting an unconformable contact is the reported change in between these groups. Supporting an unconformable contact is the reported change in paleomagneticpole poleposition position(Du (DuBois, Bois,1962), 1962),the thechange changeinin accessory accessoryminerals minerals(Tyler (Tylereteta!., al., paleomagnetic 1940) and the immediate change from steep Oronto dips to low Bayfield dips (Morey and 1940) and the immediate change from steep Oronto dips to low Bayfleld dips (Morey and Ojakangas,1982). 1982).InInsupport supportof ofaaconformable conformablecontact, contact,or orone one of of minimal minimal hiatus, hiatus, is is the the lack lack Ojakangas, Orontoage age in in the the basal basal Orienta Orienta sandstone sandstone (Thwaites, (Thwaites, 1912), 1912), and and the the nature nature of of the the of clasts clasts of of Oronto of previously mentioned Freda Sandstone drag fold exposure in Douglas County, Wisconsin previously mentioned Freda Sandstone drag fold exposure in Douglas County, Wisconsin (Tyler et et at., al., 1940). 1940). From Fromaatectonic tectonicpoint pointof of view, view, Morey Morey and and Ojakangas Ojakangas (1982) (1982) state statethe the (Tyler 48 �______ 04 Isle Royale J•) Isle .o3rale1/ TI1iel P'a.u.lt .Superior ayfie 1 d a.sixi 3rx1clir1e - MI Jacosiile a.si ICe-we eu aw P'a.u. it I_i. Qre n P'a.tiit ..slilaxid sfilandSy-ricilne Sync line Basalt a.s a. it L1 Cla.st].os -Iiv-er F'ails $yucline l ] Ga.bbro u RIFT: I F T : NORTHERN N O R T H E R N SECTOR SECT-? OKm5O o Mi 25 OMi 25 FIGURE2:2:Midcontinent Midcontinent Rifi Systemtrend trendand andgeology geologyfrom fiomnorthwestern northwesternMinnesota Minnesotainto intothe the FIGURE Rift System Upper Michigan. Projection UpperPeninsula PeninsulaofofMichigan. ProjectionofofKeweenawan Keweenawangeology geology under underwestern westernLake L d eSuperior Superwr isis shown by hachured hachuredpatterns. patterns.From FromDickas D i c h(1986), (19861,reprinted reprintedby bypermission permissionofofthe theAmerican American shownby Association AssociationofofPetroleum PetroleumGeologists. Geologists. change changefrom fromOronto OrontototoBayfield Bayfield sedimentation sedimentationmarks marksaatransition transition from fkoman an extensional extensionalregime regime onecharacterized characterizedby byvertical verticaltectonic tectonicprocesses, pracessesyi.e., i.eaY theactivation activationof of the theSt. St.Croix Croixhorst horst totoone the by byuplifting upliftingof of4,600 4'600mm(Thiel, (Thiely1956). 1956). The Thetype typesection sectionfor forthis thisgroup p u pisisalong alongthe thesouthwestern southwesternshore shoreof ofLake LakeSuperior Superiorfrom fromthe the Apostle Islands to just east of Superior, Wisconsin. Reported group thicknesses Apostle Islands to just east of SuperioryWisconsin. Reported group thicknessesrange rangefrom fiomaa minimal minimal815 815mmininoutcrop outcrop(Craddock, (Craddocky1972), 1972)'totoaamaximum maximum2,100 2y100mmininthe thesubsurface subsurfaceasas suggested suggestedby byseismic seismicreview review(Mooney (Mmneyetetal., al.' 1970). 1970). Because Becauseofofthe therelative relativeuniformity uniformityinincomposition, composition,the thethree threeBayfield Bayfieldsandstones sandstonescan canbe bededescribedasasaaunit. unit.Thiel Thiel(l956) consideredthe theoverall overallcomposition compositiontotobebe99% 99%sandstone sandstoneand and1% 1% scribed (1956) considered shale. 80% shale.Peirographic PetrographicstudIed studiedbybyMyers Myers(1971) (1971)showed showedthat thatquartz q mconstitutes constitutesapproximately approximately80% ofofframework frameworkgrains. grains.The TheOrienta Orientaand andChequamegon Chequamegonsandstones sandstonesand andsiltstones siltstonesare arecommonly commonly red dinincolor colorand andfeldspathic feldspathicininmineralogy mineralogyand andcontain containlayers layersof of shale shaleand and conglomerate. conglomerate. The The Devil's Devil'sIsland Islandsandstone sandstoneisisbuff bufftotowhite whiteinincolor colorand andso soquartzose quartzoseas astotobe beclassified classifiedasasanan almost almostpure p morthoquartzite. o r t h o q d t e .An Anascending ascendingfluvial-lacustrine-fluvial fluvial-lacustrine-fluvialenvironment environmentofofdeposition depositionisis marks'and andaareturn return to tocross-bedding mss-bedding documentedby byrespectively, respectivelyytrough troughcross-bedding, mss-bedding' ripple ripplemarks, documented theChequarnagon ChequamagonSandstone Sandstone(Morey (Moreyand andOjakangas, Ojakangas,1982). 1982).Myers Myers(1971), (1971)'states statesthe the ininthe 49 �Bayfleld Keweenawan sediments Bayfield Group Group sedimentary sedimentary rocks rocks were derived mainly from older Keweenawan sediments and and probably represent the reworking of of Omnto Oronto Group Group units. units. Ojakangas O j h g a s and Morey (1982), (19821, however, believe the Bayfield were derived from an older granitic terrane. Bayfleld Group clastics we= 2), the basic structure of of Lake Lake Superior Superior is is aa continuation continuation of of West of the Thiel fault (Fig. 21, northwestern Wisconsin Midcontinent Rift Rift geology. geology. The Ashland syncline is projected offshore as as the Lake Superior syncline. Evidence Evidenceisislent lentby by northwest northwest dips dips of of Oronto OrontoGroup Group sedimentary sedimentary rocks along the Keweenaw Peninsula (Daniels, 1982) 1982) and the southeast dips in sedimentary rock of the same age which outcrop on the southwest shore of Isle Royale (Wolff and Huber, 1973). This This major major syncline syncline was was later later disrupted disrupted by reverse reverse faulting, faulting, forming forming the offshore offshore segment of the St. Croix horst (Fig. 2). Both Both the the Bayfield Ba*eld basin basin and andthe the St. Croix horst offshore extension are considered to be floored by Middle Keweenawan floored Middle Keweenawan Croix horst offshore extension are considered clastics clastics of the Oronto Oronto and/or Bayfield groups (Green, 1982). Thus, Thus, the the western western portion portion of of Lake Superior Superior is generally generally portrayed to to be immediately immediately underlain by Keweenawan Keweenawan Supergroup thickness (Ilinze (Hinzeet etal., al., 1982). 1982). Supergroupclastics clastics up to to 10 10km in thickness Michigan Michigan Section Section Keweenawan-age outcrops outcrops form the entirety entirety of the Keweenaw Peninsula jutting into into southsouthKeweenawan-age Thekeel keelof of this this peninsula peninsulais is formed formed of of Portage Portage Lake Lake Superior (Fig. 2). The central Lake Superior which all all Upper Upper Keweenawan Keweenawan sedimentary sedimenmy rocks rocksin inthe thearea arearest rest(Fig. (Fig.1). 1). volcanics, upon which Those outcrops outcropsnorth north and and northwest northwest of of the the Portage Portage Lake Lake Volcanics Volcanics form form the the classic classic Oronto Oronto Those Group. South South and and southeast southeastof of the the Portage Portage Lake Lake volcanic volcanic outcrop outcropbelt belt and andin in contact contactwith withthe the Group. Keweenaw fault fault is is found found aa thick thick sequence sequence of of northerly northerly dipping dipping clastics clastics named named the the Keweenaw Jacobsville JacobsvilleSandstone Sandstoneby by Lane Lane and and Seaman Seaman (1907) (1907) from from outcrops outcropsnear near Jacobsville, Jacobsville,located located near near the the southeast southeast base of the Keweenaw Peninsula. By By geologic geologic position these these outcrops outcrops appear to to be an an easterly easterly extension extension of the River Falls syncline. However, However, because because the the River River appear axtnot notinindirect directcontact contactdue duetotothe the Falls syncline synclineand andthe theJacobsvile Jacobsvillesandstone sandstoneoutcrops outcropsare Falls exposureof intervening interveningArchean Archeangranitoid granitoidrocks, rocks,this this area area of of Jacobsville Jacobsvillesandstone sandstonedeposition depositionisis exposure herein herein referred referred to to as as the the Jacobsville Jacobsvillebasin basin (Fig. (Fig. 2). 2). basin the the Jacobsville Jacobsvillesandstone sandstone has has aa maximum maximum thickness thickness of of 867 867m m by by drill drill hole hole In this basin measurement measurement (Kalliokoski, (Kalliokoski, 1982), 19821,but but on on the the Keweenaw Keweenaw Peninsula Peninsulaproper proper its its maximum maximum determined by geophysics to be approximately 3,000 m. The formation formationis is thickness has been determined m. The p~dominatelyquartzose quartzoseand andisis composed composedof of conglomerates, conglomerates, sandstones, sandstones, siltstones, siltstones,and and predominately shales, generally found found in repetitive upward-fining sequences. The The conglomerates conglomeratesare are generally generally basal, basal, up up to to 100 100m m in in thickness thickness and and contain contain clasts clasts composed composed of of iron iron formation, formation,vein vein quartz, volcanics, volcanics, and metamorphic rocks. The Thesandstones sandstonesare arefine fine to to coarse coarsegrained, grained, light light quartz, reddish reddish to to purple purpleto tomottled mottledcream-white cream-whitein in color colorand andcontain containstructures structuresranging rangingfrom fromcrosscrossbedding to oscillation oscillation and and current current ripple-marking. Shales Shalesand andmudstones mudstones appear appearto to be be in in the the The overall overall minority in terms of thickness and are found interbedded with laminated sands. The section section varies varies from from sub-arkose sub-arkose to to aa quartz quartz arenite, arenite, with with plagioclase plagioclasefound found more more commonly commonlyin in the the younger younger layers layers(Kalliokoski, (Kalliokoski,1982). 1982). The The Jacobsville Jacobsvillesandstone sandstonewas was derived derived from from highlands highlands situated situated to to the the southwest southwestand and southsoutheast fluvial, east of the the depositional depositional basin. The Thedetermined determinedenvironments environmentsof of deposition deposition include includefluvial, 50 �lacustrine, and alluvial fans. Because Because the the Jacobsville sandstone is nowhere found in direct dkct contact with either either the the Oronto Oronto or or Bayfield Bayfield Group Group formations, formations, its its exact exactrelationship relationshipwithin withinthe the Keweenawan Supergroup Supergroup is in some doubt. As As itit overlies overliesPortage Portage Lake Lake volcanics volcanics and and underlies the Late Cambrian Cambrian Munising Munising sandstone sandstone there seems seems little doubt doubt regarding regarding its its Keweenawan age. Considering Consideringthat thatTyler Tyleret et al. al. (1940) (1940)noted noted aa strong strong similarity similaritybetween between the the Jacobsvile JacobsvilleSandstone Sandstoneand andthe the Orienta Orientasandstone sandstone heavy heavy mineral suites and that Kalliokoski Kalliokoski (1982) (1982) related the Jacobsville Jacobsville Sandstone Sandstone to to the the Fond Fond du Lac Lac Formation Formation of Minnesota Minnesota on on the the basis of sediment, sediment, mineral, mineral, and and clay clay matrix comparison, comparison, most most workers workers today today consider consider the the Jacobsville Sandstone Sandstone to be a Michigan Michigan equivalent equivalent to the Bayfield Group Group of neighboring neighboring Wisconsin Wisconsin (Fig. (Fig. 1). 1). References References Annells, R. N., 1973, 1973,Proterozoic Proterozoic flood flood basalts basalts of eastern eastern Lake Lake Superior; Superior the the Keweenawan Keweenawan volcanic rocks rocks of the the Mamainse Mamainse Point Point area, area, Ontario: Ontario: Geological Geological Survey Survey of of Canada CanadaPaper Paper 72-10, 511p. 72- 10,5 Barghmm, E. S., W. G. Meinschein and J. W. Schopf, 1965, Paleobiology of a bcambrian Barghoorn, Precambrian shale: Science, Science, v. 148, 148, p. 461-472. Brown, A. C., C., 1971, 1971,Zoning Zoning in in the the White White Pine Pine copper copper deposit, deposit, Ontonagon Ontonagon County, County,Michigan: Michigan: Economic 543-573. Economic Geology, Geology,v. v. 66, 66, p. p. 543-573. Cox, D. P., R. G. Schmidt, Schmidt, J. D. Vine, H. Kirkemo, Kirkemo, E. B. Tourtelot Tomelot and and M. Fleisher, Fleisher, 1973, 1973, Copper, Copper, in Brobst, D. A. and and W. P. Pratt (eds.), United States mineral resources: U. S. Geological Geological Survey Survey Professional hfessional Paper Paper 820, 820, p. 163-195. 163-195. in Sims, Sims,P. P. K. K. and andG. G. B. B. Morey Morey(eds.): (eds.): Craddock, C., 1972, 1972,Regional Regionalgeologic geologic setting, setting,in Craddock, Geology of Minnesota: Minnesota: A A centennial centennialvolume, volume, Minnesota Minnesota Geological GeologicalSurvey, Survey,p. p. 281-291. 28 1-291. Geology Daniels, Daniels, P. A., 1982, 1982,Upper Upper Precambrian sedimentary rocks, Oronto Oronto Group, Michiganin Wold, Wold, R. R. J., and and W. J. Hinze Hinze (eds.), Geology and tectonics of the Lake Wisconsin, in Wisconsin, Superior Superiorbasin: basin: Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, 156,p. p. 107-133. 107-133. Dickas, A. A. B., B., 1987, 1987,Hydrocarbon Hydrocarbon potential of the Midcontinent Rift System, System, proceedings proceedings of Dickas, MidcontinentRift Rift System System Scientific ScientificDrilling Drilling Workshop, Workshop, Duluth, Duluth, Minn, Sept. 24-25, 24-25, Midcontinent 1987, 1987, p. 22-27. 22-27. DuBois, DuBois, P. M., M., 1962, 1962, Paleomagnetism Paleomagnetism and and correlation of Keweenawan rocks: Geological Survey 75 p. Surveyof of Canada CanadaBulletin, Bulletin,v.v. 71, 7 1,75 p. Eglinton, T. Beisky, Belsky, A. A. L. L. Burlengame Burlengame and and M. M. Calvin, Calvin, 1964, 1964,Hydrocarbons Hydrocarbons Eglinton, G., G., P. P. M. M. Scott, Scott,T. of biological 145, p. 263-264. biological origin origin from from aa one-billion one-billion year old sediment: Science, v. 145, Elmore, Elmore, R. R. D. D. and and P. P. A. A. Daniels, Daniels,Jr., Jr., 1980, 1980,Depositional Depositionalsystem system model model for for Upper Upper Keweenawan v. 61, 61, Keweenawan Oronto Oronto Group Group sediments, sediments,Northern Northern Peninsula, Peninsula,Michigan Michigan (abs): (abs): Eos, Eos, v. p. 1195. p.1195. 51 51 �Green, J. C., 1982, 1982, Geology Geology of the Keweenawan Keweenawan extrusive rocks, in Wold, Wold, R. J. and and W. W. J.J. Hinze Hinze (eds.), (eds.), Geology Geology and and tectonics tectonics of the Lake Superior Superior region: Geological Geological Society Society of of America America Memoir Memoir 156, 156,p. p. 47-55. 47-55. Halls, Halls, H. C., C., 1966, 1966,A A review review of of the the Keweenawan Keweenawan geology geology of of the the Lake LakeSuperior superiorregion, region,ininJ.J. S. Steinhart and T. J. Smith (eds.), The Earth beneath the continents: American Steinhart and Smith (eds.), The beneath the continents: AmericanGeoGeophysical physical Union Union Geophysical GeophysicalMonograph Monograph 10, 10,p. 5-27. 5-27. Hamblin, Hamblin, W. K., K., 1961, 1961,Micro-cross-lamination Micro-cross-lamination in in Upper Upper Keweenawan Keweenawan sediments sedimentsof of northern northern Michigan: v. 31, 3 1,p. p. 390-401. 390-401. Michigan: Journal Journal of of Sedimentary SedimentaryPetrology, Petrology, v. Hieshima, Hieshima, 0. G.B. B.and andL. L.M. M. Pratt, Pratt,1991, 1991,Sulfur/carbon Sulfur/carbonratios ratiosand and extractable extractableorganic organicmatter matter of the the Middle Middle Proterozoic Proterozoic Nonesuch Nonesuch Formation, Formation, North American American Midcontinent MidcontinentRift: Rift: Precambrian Precambrian Research, Research, v. v. 54, 54, p. p. 65-79. 65-79. Hinze, J., R. R. J.J. Wold Wold and and N. N. W. O'Hara, O'Hara, 1982, 1982,Gravity Gravity and and magnetic magneticanomaly anomalystudy study of of Hinze, W. W. J., Lake andW. W. J.J. Hinze Hinze(eds.), (eds.), Geology Geologyand andtectonics tectonicsof ofthe theLake Lake LakeSuperior, Superior,in in Wold, Wold, R. R. J.J. and Superior Superior basin: basin: Geological Geological Society Society of America America Memoir Memoir 156, 156, p. p. 203-22 203-221. 1. Hite, Hite, D. D. M., M., 1968, 1968,Sedimentology Sedimentologyof of the the Upper Upper Keweenawan Keweenawan sequence sequenceof of northern northernWisconWisconsin dissertation, University University of Wisconsin-Madison, Wisconsin-Madison,217 217 p. p. sin and and adjacent adjacent Michigan: Ph. D. dissertation, Hubbard, H. H. A., A., 1975, 1975,Geology Geology of of Porcupine PorcupineMountains Mountains in in Carp CarpRiver Riverand andWhite WhitePine Pine Hubbard, v. 3,3, p. p. 519-528. 519-528. quadrangles, Michigan: Michigan: U. U. S. S. Geological GeologicalSurvey SurveyJournal Joumal of of Research, Research,v. quadrangles, Hunt, T. T. S., S., 1873, 1873,The Thegeognostical geognosticalhistory historyofofmetals: metals:American AmericanInstitute Instituteof ofMining Miningand and Hunt, Engineering EngineeringTransactions, Transactions,v.v.1,I,P.P.33 331-345. 1-345. Kalliokoslci,J., J., 1982, 1982,Jacobsville JacobsvilleSandstone, Sandstone,in inWold, Wold,R. R. J.J.and andW. W. J.J.Hinze Hinze(eds.), (eds.),Geology Geology Kalliokoski, and and tectonics tectonics of of the the Lake Lake Superior Superiorbasin: basin: Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, 156,p. p. 147-155. 147-155. K.Nishioka, Nishioka,1985, 1985,Precambrian Recambrimoil oilinclusions inclusionsin inlate lateveins veinsand andthe therole role Kelly, W. W. C., C., and and 0. G.K. Kelly, of of hydrocarbons hydrocarbonson oncopper coppermineralization mineralizationatatWhite WhitePine, Pine,Michigan: Michigan:Geology, Geology,v.v.13, 13,p. p. 334-337. 334-337. Lane, A. C. C. and andA. A. E. E.Seaman, Seaman,1907, 1907,Notes Noteson onthe thegeological geologicalsection sectionofofMichigan, Michigan,part part1,1,the thePrePreLane, A. Ordovician: Ordovician:Journal Journalof ofGeology, Geology,v.v.15, 15,p.p.680-695. 680-695. Mooney, H.M., M.,P.P.R. R.Famham. Famham.S.S.H. H.Johnson, Johnson,G. G.Volz Volzand andC. C.Craddock, Craddock,1970, 1970,Seismic Seismicstudies studies Mooney,H. over the Midcontinent Gravity High in Minnesota and northwestern Wisconsin: Minnesota over the Midcontinent Gravity High in Minnesota and northwestern Wisconsin: Minnesota Geological 1911p. GeologicalSurvey SurveyReport Reportof ofInvestigations Investigations11, 11,19 p. Moore, Moore,L. L.R., R.,J.J.R. R. Moore Mooreand andE. E. Spinner, Spinner,1969, 1969,AA geomicrobiological geomicrobiological study study of of the the Precambrian Precambrian Nonesuch Shale: Proceedings of the Yorkshire Geological Society, v. 37, p. 35 1-394. Nonesuch Shale: Proceedings of the Yorhhire Geological Society, v. 37, p. 351-394. Morey, Morey, G. G. B. B. and andR. R. W. W. Ojakangas, Ojakangas,1982, 1982,Keweenawan Keweenawansedimentary sedimentaryrocks rocks of ofeastern easternMinnesota Minnesotaand and northwestern northwesternWisconsin, Wisconsin,in inR. R. J.J. Wold Woldand andW. W.J.J.Hinze Hime(eds.),Geology (eds.),Geologyand andtectonics tectonicsofofthe theLake Lake Superior Superiorbasin: basin:Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, 156,p.p. 135-146. 135-146. 52 52 �Myers, W. D., 1971, sedimentology and tectonic significance of the the Bayfield Group (Upper Myen, 1971, The sedimentology Keweenawan?), Wisconsin and Minnesota: Ph. D. dissertation, University of Wisconsin-Madison, 269 p. Ojakangas. pm-volcanic quartz sandstones and related Ojakangas, R. W. and G. B. Morey, 1982, 1982, Keweenawan pre-volcanic rocks of the Lake Superior Superior region, region, in Wold, R. J. and W. J. Hinze Hinze (eds.), Geology Geology and and tectonics tectonics of the Lake Superior Superior basin: Geological Geological Society Society of America Memoir 156, 156, p. 85-96. Ruiz, J., L. M. Jones and W. C. Kelly, 1984, 1984, Rubidium-strontium dating of ore deposits hosted by Rn-rich rocks, using calcite and other common Sr-bearing Sr-bearing minerals: Geology, Geology, v. 12, 12, p. 259-262. 259-262. Thiel, E. C., 1956, 1956, Correlation Correlation of gravity anomalies anomalies with the Keweenawan Keweenawan geology of Wisconsin Wisconsin and and Minnesota: Geological Ivhnesota: Geological Society Society of America Bulletin, v. 67, 67, p. 1079-1100. 1079-1100. Thwaites, Thwaites, F. T., 1912, 1912, Sandstones Sandstones of the Wisconsin shore shore of Lake Superior: Superior: Wisconsin Wisconsin Geological Geological Bulletin, 25,117 25, 117p. and Natural History Survey Bulletin, p. Tyler, S. A., R. W. Marsden, F. F. Gmut Grout and G. A. A. Thiel, 1940, Studies of of the the Lake Superior PrePrecambrian cambrian by accesory-mineral accesory-mineralmethods: Geological Geological Society Society of America Bulletin, Bulletin, v. 51, p. 142914291538. 1538. White, W. S S., ., 1966, 1966, Tectonics of the Keweenawan basin, western Lake Superior region: U. S. E-l to E-23. Geological Survey Professional Professional Paper 524-E, p. E-1 White, W. S., and J. C. Wright, 1960, White, 1960, Lithofacies Lithofacies of the Copper Copper Harbor Conglomerate, Conglomerate, northern noxthem Michigan: Michigan: U. S. S. Geological Geological Survey Survey Professional Pmfessional Paper Paper 400-B, W B , p. p. B-5 B-5 to to B-8. B-8. Wolff, R. G. and and N. K K Huber, Huber, 1973, 1973,The The Copper Copper Harbor Harbor Conglomerate Conglomerate (Middle Keweenawan) Keweenawan) on on Isle Royale, Michigan, and its its regional implications: U. S. Geological Geological Survey Survey Professional mfessional Paper Paper 754-B, p. to B-15. B-15. p. B-1 B-i to 53 �____ _____ CENTRAL RWf DEVELOPMENT CENTRAL NORTH NORTH AMERICAN CASE FOR SEGMENTED RIFT DEVELOPMENT Reprinted with with permission permission from Dickas, Dickas, A. B. Reprinted B. and and M. M. G. G. Mudrey, Mudrey,Jr, Jr. 1989, 1989, Abstracts, Abstracts, 28th InternationalGeological GeologicalCongress, Congress,vol. vol.1,1,p. p. 1-396 1-396toto1-397. 1-397. International The The Midcontinent MidcontinentRift Rift System System (MRS) (MRS) is is aa major Middle Proterozoic Proterozoic intracontinental, intracontinental, thermotectonic therrnotectonic structure structure that that has has been been traced by regional regional gravity gravity and and magnetic magnetic data, data, subsursubsurface face drilling, drilling, and and outcrop outcrop control over a length of 3,300 km in the central United States. In In the Lake outcrop is is known, known, this this structure structurewas was Lake Superior Superior region, region, the the only only area area in in which which MRS outcrop infilled by plateau lavas and sedimentary rock comprising Keweenawan Supergroup. Supergroup. infihled comprising the Keweenawan About 1140 rift. After 1140 Ma, basalt was extruded along the rift. After cessation cessation of of volcanic volcanic activity, activity, generally elastic, sedimentary rock rock was was deposited. deposited. Geophysical Geophysical analysis analysis in generally maturing upward, clastic, the 1950's 1950's (Thiel, (Thiel, 1956) 1956)suggested suggestedaa broad broad graben graben with a central horst separating separating wedgeshaped rocks. These shaped thick accumulations accumulations of low-density sedimentary rocks. These sedimentary sedimentary sections sections were identified by negative gravity anomalies. Since Sincethen, then, models models and and geologic geologic maps maps of of the the rift have been consistent in demonstrating an early developed symmetrical extensional have consistent demonstrating developed symmetrical extensional crustal crustal basin filled filled with with extrusive extrusiveand and volcaniclastic volcaniclastic rock, subsequently subsequently modified modified by by latelatephase compressional faulting forming the presently identified central horst (Fig. 2, previous phase compressional faulting forming the presently identified central horst (Fig. 2, previous paper). rN % 14 w IL NE MO KANSAS KS @ Gravity High High Gravity o ioo #11 o OH I io - 1 Gravity Low Low Gravity r///,2 Accommodation AccommodationStructure Structure FIGURE 3: 3: Gravity FIGURE Gravityexpression expressionofofthe theMidcontinent Midcontinent Rift System, R4ft System,showing showingthe thelocation location and and extent offirstofflrstorder rift riftzones. zones. order 54 Recent Recent acquisition acquisition of over over 4200 4200 km of onshore onshore and and offshore offshore reflection reflection seismic seismic data data and and analyanalysis sis of deep deep mineral mineral exploration exploration drill drill holes holes from from northern northern WisconWisconsin sin suggest suggest aa different differentgeometry geometry for the MRS. This geometry, for This geometry,as as proposed here, is similar similar to to strucstructures attributed attributed to to the Gregory Gregory rift rift in East Africa. Bosworth al. Bosworth et et al. (1986) (1986) suggest suggest the the Gregory Gregory rift rift structure structure formed formed through through the the development of deep, crustal, crustal, opposing detachment systems. As these detachments intersect at depth, depth, one one side side locks, locks, resulting resulting in in half-graben development. development. With lateral rift propagation, propagation, aa subresubrelateral gional gionalseries seriesof oftaphrogeosynclines taphrogeosynclines (haif-graben) (half-graben) are formed, formed, with adjacent adjacent grabens grabens displaying displaying igneous igneous and sedimentary sedimentary infill infill packages of opposing geometry. opposing geometry. The initial rift is thus unable unable to extend extend laterally laterally in uniform uniform strucstructural patterns but rather forms a linear linear pattern of individualized, individualized,en en echelon, asymmetric asymmetric basins, each each �history and and geometry geometry and each each separated by a type of cross-structure, cross-structure, with its own infihling infilling history generally referenced as "accommodation" faulting. faulting. On a regional regional basis, the fmal final structural configuration of a rift may also be dependent upon total extension developed at right angles to rift propagation. Schuepbach (1980) suggest Schuepbachand andVail Vail(1980) suggest that with such differential differential rift development, and even though structural extension along rift strike may be synchronous, basin formation and filling fifing could (1984) supcould be diachronous. Quenneil Quennell(1984) ported ported this this evolution evolution by by mapping mapping the the Dead Dead Sea Sea rift as divided divided into three three unique segments, segments,each each operating operating independently in geologic development. Viewed Viewed as as an an entirety, entirety, a rift may thus display first-order, representing coeval stages first-order, regional-size regional-size rift rift segments segments(Dickas, (Dickas,1986), 1986), representing stages of differing differingrift rift maturity. In Inturn, turn,these thesesegments segmentsmight mightbe be divided divided into into subregional-sized, subregional-sized, second-order second-order subbasins separated separatedby by "accommodation" "accommodation" faulting. faulting. Viewed Viewed from from the the perspective perspective of this this geometry, geometry, the the extent extent of the MRS is is here here interpreted interpreted to to be composed (1987). Clockcomposed of of five five first-order first-order rift rift segments, segments, termed termed "zones" by by Rosendahi Rosendahl(1987). Clockwise from are here named Kansas, Kansas, Iowa, from the the southwestern southwestern end end of the the MRS. MRS, these zones are Superior, identified on the basis of major major interrupinterrupSuperior, Mackinaw, Mackinaw, and Maumee (Fig. 3), and are identified tions tions in gravity gravity and and magnetic magnetic patterns, patterns, seismic seismic review, review, terrane terrane compositions, compositions, and and borehole borehole analysis. analysis. function of of overall overall rift rift extension, extension, zones zones may may be be further further divided divided Locally, and and developing developing as as aa function Locally, into into a series series of structurally structurallyindependent independent basins. These These second-order second-order sub-basins, sub-basins, termed termed by Rosendahi Rosendahl(1987), Withinthe theSupeSupe"units" by (1987), are separated by "accommodation" faulting. Within rior rior zone zone of of the the MRS, MRS, four four units units are are now now recognized recognized on on the the basis basis of of seismic seismicinterpretation, interpretation, interrupted geopotential geopotential trends, and core analysis. These These sub-basins sub-basinsare are here here named named the the interrupted These units appear appear to to have have underChisago, Brule, Ontonagon, and Manitou units units (Fig. (Fig. 4). 4). These similar history of structural structural development development during the early phase of MRS evolution. evolution. gone a similar On On the the basis basis of differential differential listric listric movements movements along along axial-oriented, axial-oriented,rift rift fault fault systems, systems,igneous igneous and and sedimentation sedimentationwedges wedges of alternating alternating isopach isopach patterns patterns distinguish distinguish juxtaposed zones. patterns of of these these wedge wedge geometries geometriesdiffer differ by by being being symmetrical symmetricalparallel, parallel, but but alteralterIsopach patterns nating asymmetrical asymmetrical perpendicular, perpendicular, to to the the MRS MRS axis. axis. nating In light light of this suggested suggested model, future future stratigraphic stratigraphic and and seismic seismic correlations correlations can no longer longer be be the framework frameworkof of aa symmetric symmetric rift rift model model existing existing along along the the entirety entiretyof of the the interpreted within the bedependent dependentupon upon consideration considerationof of isolated isolated igneous igneous MRS axis. axis. Instead, Instead,such suchcorrelations correlationsmust mustbe MRS and sedimentary sedimentary packages packages and isopach geometries created in response response to to first- and and second-order second-order and be directed directed to to basebasedegree of tectonic development. development. Exploration Explorationphilosophies, philosophies, whether whether they they be degree metal or hydrocarbon evaluation, must be constrained so as to recognize related regional and metal or hydrocarbon evaluation, must be constrained so as to recognize related regional and subregional subregional alterations alterationsin in structural structuralstyle. style. 55 �Central Structure (St. Croix Horst) SCHEMATIC SECTION FIGURE FIGURE4: 4:Structural Structuralrift riftunits unitscomposing composingthe theSuperior Superiorrift riftzone, zone,Midcontinent MidcontinentRift Rift System, System, as defined by accomodation accomodation structures structures(A.S.) (AS.) and isopach isopachthickening thickening trend, trend, References References 1986, A new look at Gregory's Rift: Rift: the the strucstrucBosworth, W., J. Lambiase, and R. Keisler, 1986, tural style 582-583. style of continental continental rifting: Eos, v. 67, p. 557, 557,582-583. Dickas, A.B., 1986, Seismologic analysis of arrested stage development A.B., 1986, development of the Midcontinent Rift, in M.G. Mudrey, Jr. (ed), Precambrian petroleum potential, Wisconsin and Michigan: Geoscience Wisconsin, Wisconsin Geological and Natural History Survey, v. 11, p. 45-52. Quennell, A.M., 1984, The western Arabia rift-system, in J.F. A.H.F. Robertson Robertson A.M., 1984, J.F. Dixon and A.H.F. Society Special Special (eds.), The geological geological evolution of the eastern Mediterranean: Geological Geological Society Publication 17, Publication 17, p. 775-788. Rosendahl, B.R.,11987, B.R.,11987, Architecture of continental special reference reference to to East EastAfrica: Africa: Rosendahi, continental rifts with special Annual Review Earth Earth and and Planetary Planetary Science ScienceLetters, Letters,v. v. 15, 15, p. 445-503. 1980, Evolution of outer highs on divergent divergent continental continental Schuepbach, M.A. M.A. and P.R. P.R. Vail, 1980, margins, in Continental Continental tectonics: tectonics: National Academy of Science, Science, 197 197 p. p. 56 1956, Correlation of gravity gravity anomalies anomalies with the Keweenawan geology geology of of WisconWisconThiel, E., 1956, sin and Minnesota: Geological Society of America Bulletin, v. 67, p. 1079-1100. 1079-1100. �LAKE FRONTIER LAKE SUPERIOR SUPERIORBASIN BASIN AS AS A HYDROCARBON FRONTIER Mod(fied from aa series of requested articles written by Albert Albert Dickas Dickasfor for the daily print print media Modified from of January, 1992, during site preparations preparations for the the Terra/Patrick TerrdPatrick#7-22, #7-22, of northwest Wisconsin,January, Bayjield County, County,Wisconsin Wisconsin exploratory exploratory wildcat. wildcat. Since Since the initial discovery of crude oil at a depth of 21.2 m beneath the rolling hills of Titusville, Titusville,Pennsylvania Pennsylvania in in 1859, 1859,hundreds hundreds of of thousands thousands of of boreholes boreholeshave havesought soughtthis this natural resource in the United States. Wisconsin Wisconsin has played a small role in this 133 133 year old "hydrocarbon revolution." Between 49 boreholes Between 1865 1865and and 1992, 1992,49 boreholes have sought economic volumes of oil oil or or gas gas in the the Badger state. Not Notone oneof ofthese thesewells wellshowever, however,has hasfound foundanyanything thing other other than than fresh fresh and and salt salt water. water. The The majority majority of of exploration exploration in in Wisconsin Wisconsin has has taken taken place place close close to to the the Lake LakeMichigan Michiganshoreshoreline (Fig. 5). 5). Here line between Milwaukee and Door County (Fig. Here the rocks form the western edge of the Michigan Michigan basin, basin, one one of of the the most most prolific prolific producers producers of of hydrocarbon hydrocarbonin in the theUnited UnitedStates. States. Unfortunately, Unfortunately, this this productivity productivity is is basically confined to the deeper deeper portions portions of the basin, and and not not along alongits its edges. edges. The Theremaining remainingarea areaof ofWisconsin Wisconsinhas haslong longbeen beenconsidered considerednon-producnon-productive because of the great geologic age and physical nature of much of its bedrock. tive because of the great geologic age and physical nature of much of its bedrock. In In the the early early 1980s, 1980s,pessimism pessimism turned turned to to guarded guarded optimism. optimism. Petroleum Petroleumgeologists geologistsbegan begantoto recognize recognize that that rocks rocks deposited deposited during during early early chapters chapters of earth earth history--the so so termed termed PrecamPrecambrian brian Eon--possesses, Eon--possesses, contrary contraryto to conventional conventionalwisdom, wisdom,those thoseseven sevento toeight eightcharacteristics characteristics necessary necessary for for the the development development of of an an oil oil or or gas field. field. Studies Studies suggested suggested these characteristics characteristics were often often contained containedwithin within rift rift structures, structures,formed formed by the the dissection dissection of pre-existent pre-existent conticontias Africa Africa is is presently presently being being torn tom into into portions along along the the African African Rift Rift Zone. Zone. nents, much as has been been known known for for 35 35 years years that that northwestern northwestern Wisconsin Wisconsin occupies occupies aa portion of of the the worldworldItIt has krn from from Kansas Kansas to to Ohio Ohio by way way of Lake Lake class Midcontinent Midcontinent Rift Rift System, System, extending extending3300 3300 km class Superior. With Withthe therecognized recognizedassociation associationof of ancient ancientrift rift rocks rocks with with economic economichydrocarbon hydrocarbon Superior. reserves, that that portion portion of of the theMidcontinent Midcontinentrift rift lying lyingbetween between the the upper upperpeninsula peninsulaof of Michigan Michigan reserves, and Kansas Kansas was was quietly quietly invaded invaded by the United States oil and gas industry. Initial Initialinterests interests and included Mobil, Mobil, Texaco, Texaco, Standard Standard of California, and Amoco, among others. Field Fieldcrews crews included 1980's and andspecial special "frontier "frontier region" region" analysis analysisteams teams of of geologeolobegan operating operating in the early early 1980's began gists, geophysicists, geophysicists, paleontologists, paleontologists, and geochemists were formed. Studies Studiesranged ranged from from gists, hand investigation investigationof of rock rock samples samplesto to sophisticated sophisticated computer computer reviews reviews of of newly newly collected collecteddata data hand pertaining pertainingto tothe theseismic, seismic,magnetic magneticand andgravity gravitycharacter characterof ofthe therift. rift. In 1984 1984Texaco Texacomade madethe thefirst firstmove moveby bydrilling, drilling,ininnortheast northeastKansas, Kansas,their their#1 #1Noel Noel Poersch Poersch In well 3444 m. m. InIncertain certainaspects aspectsthis thiswas wasaaguinea-pig guinea-pigborehole. borehole. well to to aa record record state statedepth depth of of 3444 Because Because the the rift rifthad had never never been been drilled drilledbeyond beyond normal normal water-well water-welldepths depthsof ofseveral severalhundreds hundreds of of feet, feet, industry industry was was probing probing into into the geologic darkness. Expectations Expectationswere were based based upon upon comparison comparisonof of Kansas Kansasdata datato tothe thenear-surface near-surfacegeology geologyof ofDouglas Douglasand andBayfield BayfieldCounties, Counties, Wisconsin, aa region region where rift rocks are exposed at the surface and The Wisconsin, and thus thus easy easy to to study. study. The Texacodrilling drilling plan plan envisioned envisionedseveral several thousands thousands of feet feet of sandstone sandstone and organic organic shale shale Texaco overlyingan an even even thicker thicker sequence sequence of layered layered lava. Under Underideal idealconditions conditionseither eitheroil oil or or gas gas overlying would have formed within the organic shales and subsequently moved upward into the would have formed within the organic shales and subsequently moved upward into the sandstones sandstones until until trapped trapped and andconcentrated concentratedinto into an an economic economic "pool." "pool." 57 �Drilling results were were not not released released until until mid-1988. mid-1988. This Drilling ceased in early 1985 1985 but detailed results three year delay made sense when information became becamepublic. public. The drill sequence sequence appeared reversed when compared to expectations, with lava and related igneous rock overlying overlying thick thick sandstone layers. Shale Shalewas was found found only only in trace trace amounts amounts and that shale present was not not possible. possible. The organic. Without Without organic organic shale shale an oil or gas field is not The Texaco Texaco well was classed as "dry and and abandoned" abandoned" and and exploration exploration geologists geologists began began to to reinterpret reinterpretthe the geologic geologic history of the Midcontinent Midcontinent rift. rift. Amoco Amoco Production Production Company Company was was the the second second major major player player to to enter enter the thesearch searchfor forPrecamPrecambrian-age rift hydrocarbon. Disenchanted Disenchantedby by the the Kansas Kansas results, results, Amoco Amoco geologists geologistschose chose west-central Iowa as their preferred drilling site. In 1987their their#1 #1Eischeid EischeidboreboreIn March March of of 1987 hole was set into operation and seven months later reached 5,441 m. m. reached a state state depth depth record record of of 5,441 This This borehole was shrouded in secrecy, protected by fence and guard. Under Underfavorable favorable weather weather conditions conditions a nearby hill was covered covered with curious curious observers observers and and industry industry scouts scouts and and skimpy reports were issued daily daiiy by the media. media. Even Even after after the the projected projected depth depth was was reached reached Amoco, Amoco, following following the lead established by Texaco in Kansas, maintained secrecy. With With the the release 1990 encouragement was given by the fact a normal release of information information in the spring spring of 1990 sequence of rock colunm column was drilled--shales were found found and they were organic. organic. The The high high risks risks associated associatedwith with the the oil oil and and gas gas business business is is largely largely attributed attributed to to the the fact fact that that while while the the proper proper conditions conditions for for an an economic economicreservoir reservoir are are often often found, found,the the sought soughtafter afterproduct productisisoften often absent. The Iowa venture was high risk in planning and execution and the end result was The Iowa venture was high risk planning and execution and the end result was labeled labeled "dry and and abandoned." The The third third borehole borehole to to test the Midcontinent rift was initiated in late 1987 and completed two months later. The Theoperator operatorwas wasagain again Amoco Amoco Production Production Company, Company, but now the geographic geographic site months finaltotal totaldepth depthwas was near the upper peninsula community community of Munising, Michigan. The Thefmal was near 2210 m. While Whilecomplete completeinformation informationhas has not not yet yet been released, it has been reported that all 2210 formations composing composing the the target Oronto Oronto Group Group were drilled--but not in the the normal three of the formations order order as as known known from fromWisconsin Wisconsingeology. geology. It is is interesting interesting to to note note this this borehole borehole is is located located in in aa region region of of historic, historic, little little known, known, exploraexploraIt In1865 1865the theOntonagon OntonagonPetroleum PetroleumCompany, Company, financed financed by by aa capital capital stock stock tion for crude oil. In $500,000, was was formed formed for for the the purpose purpose of "engaging in in and and carrying carryingon on the thebusibusioffering of $500,000, offering mining~petroleum."By ByDecember Decemberof of that that year yearthe the first first and and only only venture venture of of this this ness of mining---petroleum." company was was underway, underway, fueled fueledby by aa rapid rapid increase increase in in the the price price of of oil oil stock stockand and an an outbreak outbreak company While microfilm microfilm records indicate "two Thefinal finaldrilling drilling depth depth was was 38 m. While of "oil fever." The (of oil) oil) have have been been hoisted hoisted up," up," there there isis no no record record of of the the Ontonagon OntonagonPetroleum PetroleumComCombarrels (of pany pany beyond beyond the the year year of of its its incorporation. incorporation. Since Since 1929 1929 active active underground underground oil oil seeps seeps have have been been reported reported from from the the White White Pine Pine mine minein in Ontonagon County, County, Michigan. Analyses Analysesshows showsthis thiscrude crudeto tobe be very very similar similarchemically chemicallyto to Ontonagon high grade grade oil of Phanerozoic Phanerozoic age produced in the state of Pennsylvania. Radiometric Radiometricageagedating techniques techniques suggest suggestthe the White White Pine Pine product product may may be be the the oldest oldest known known crude crudeoil oilin inthe the dating Whilethese thesevolumes volumesare aremodest, modest,their theirpresence presencekeeps keeps alive alive the the possibility possibility of of "black "black world. While gold" gold" production productionin in northern northern Wisconsin. Wisconsin. 58 �As As of of early early March, March, 1992, 1992,site sitepreparation preparation was was underway underway for for the the fourth fourthtest testof ofthe thehydrocarhydrocarbon potential potential of of this this rift. rift. Located Located in in Bayfield Bayfield County, County, Wisconsin, Wisconsin, this this wildcat wildcat has has been been programmed programmed as as aa 1825 1825m m (6000 (6000ft.) ft.) test test of of the the Oronto Oronto Group Group in its position position overlying overlying the the central St. Croix horst. Available information on this TerraPatrick Terra/Patrick #7-22 borehole will be presented presented in in the the Proceedings Proceedings volume volume of this 38th meeting of the Institute on Lake Superior Superior Geology. Geology. 59 �60 Wisconsin. in degrees 75 and areas, River Isle Presque and Pine White the in grees de- 10 about to area Mountain Porcupine the in overturned from varies tude atti- Structural rn/km. 4 than more at basinward thickens Nonesuch the Park, State Isle Presque of east km 40 about area Pine White the In southwest. the area. to thins generally and thickness, in m 180 about averages Nonesuch The Pine White the in petroliferous is and material organic in rich is rock The dikes. clastic as such features dewatering and bedding graded show many and microscale, in common are alternations grain—size rhythmic Thin, thick. mm 1 than less laminae many with laminated evenly to massive—appearing from ranges bedding The color. in darkest the is rock grained finest The sandstone. medium to shale black to gray medium a is Nonesuch the Generally, quences. se- bed red overlying or underlying the than maturity compositional and tural tex- greater of generally and color in drab more is Nonesuch The Description: 1968 Hite, from (modified 1982) Daniels, and Jr. Daniels, P.A. and Jr. Mudrey, M.G. Authors: 1956). quadrangle, topographic 15—minute (Thomason Michigan County, Gogebic W., 45 R. N., 50 T. 30, and 19 Sec. River, Isle Presque the of Mouth Location: Formation Nonesuch — Park State Isle Presque Title: �Both The The Nonesuch Nonesuch possesses possesses aa great great variety variety of of sedimentary sedimentary features. features. Both Laminated stratifiLaminated stratifihorizontal stratification and cross stratification occur. horizontal stratification and cross stratification occur. irregular, and and ripple ripple stratifistratification lenticular, wavy or irregular, cation is is the the most most conmion; common; lenticular, 60 cm cm in in thickness, thickness, and and the the thicker thicker cation also also occur. occur. Units rarely exceed exceed 60 Units rarely cation beds are are coarser coarsersandstone sandstoneand and conglomerate. conglomerate. Alternating Alternatinglaminae laminae of of fine fine beds common. gray sandstone sandstoneand and black black shaley shaley ailtstone siltstoneless less then then 0.5 0.5 cm can thick thickare are common. gray The cross—stratification cross-stratification is is of of two two types, types, planar planar cross cross stratification stratification and and rib rib The and furrow. furrow. Both Both of of these these types types are are abundant abundant on on the thePresque Presque Isle IsleRiver River in in and Michigan. Shrinkage Shrinkage cracks cracks and and disturbed disturbed bedding bedding occur occur locally locallyand and sometimes sometimes Michigan. abundantly. Sediment Sediment and and current current transport transport data data support support aa dominant dominant flow flow abundantly. in the regime to tothe the west-southwest during during deposition deposition of of the theNonesuch Nonesuch in thePresque Presque regime west—southwest Islearea. area. Isle Discussion: The The sedimentary sedimentary structures indicate that that the the depositional depositional envienvistructures indicate Discussion: ronment ronment of of the the Nonesuch Nonesuch Formation Formation was that of of a standing standing body of of water, with with was at at least least high high perhaps significant significant variation variation in in water waterdepth. depth. Salinity Salinity was perhaps enough to to precipitate precipitate gypsum. gypsum. enough initial - The initial formation formation of of this this water water body body could could have have occurred occurred either either due due The to creating a closed topographic to subsidence subsidence along along the the rift, creating topographic low low that would as local local base level, or perhaps, more likely, the the disruption disruption of of rethen act act as then gionaldrainage drainagepattern pattern sometype type damming. gional bybysome ofof damming. 61 �Title: Parker Parker Creek Creek —- Oronto Oronto Group Group IR 47/O1E/30 47/01E/30 Location: Location: Approximately 300 300 a m upstream to to the the southeast southeast from from the the northwest northwest corner Sec. 30, 30, T. T. 47 47 N., N., H. R. 1 F., E., Iron Iron corner of of section section 30. 30. NWl/4, NW1/4, Sec. County, Wisconsin (Oronto (Oronto Bay Bay 77 1/2—minute 1/2-minute topographic topographic quadrangle, quadrangle, 1980). Author: Author: M.G. Mudrey, Mudrey, Jr. Jr. (modified (modified from from Myers, Myers, 1971 1971 and and Rosenberry, Rosenberry, 1924) 1924) M.G. Description: Description: Approximately Approximately 600 600 am of of continuous continuous exposure exposure from from the the last last Kewee— Keweenawan nawan lava lava flow, flow, through through the the Copper Copper Harbor Harbor and and Nonesuch Nonesuch Formations Formations into into the the lower of the the Freda Freda area area exposed exposed along along Parker Parker Creek Creek (also (also known known as as Davis Davis lower 300 300 in m of Creek). Creek). Because Because the the upper upper reaches reaches of of the the creek creek tend tend to to run run parallel parallel to to the the bedding, bedding, the the Copper Copper Harbor Harbor appears appears to to be be much much thicker thicker than than normal. normal. All E., 85 85degrees degreesNW. NW. There There are are aa All of of the the units units trend trend N. N. 60 60 degrees degrees F., few, very minor minor flexures flexures and and faults faults in in the the wall wall of of the the valley, valley, but but the the sec— secfew, very tion tion appears appears to to be be continuous continuous with with no no repetition repetition by by faulting. faulting. Approximately Approximately 200 200 mm of of Copper Copper Harbor Harbor Formation Formation are are exposed exposed in in the the upper upper reaches reaches of of the the creek. creek. The The unit appears appears to to consist consist of of five five main main conglomeritic conglomeritic zones 60 am in thickness, thickness, interbedded zones about about 30 30 to to 60 interbedded with coarse, coarse, sandy sandy 62 �conglomerate. Both Both lithologies lithologies are are clast—supported clast-supported conglomerate. conglomerate. The The Copper Copper conglomerate. Harbor is is relatively relativelytypical, typical, consisting consistingof of rounded rounded cobbles cobblesof of Keweenawan Keweenawan volvolHarbor canic canic rock rock and and granite graniteand and iron iron formation formationfrom from the the underlying underlyingEarly Early Protero— Proterozoicand and Archean Archeansuccession. succession. zoic About310 310inm of of Nonesuch Nonesuch Formation Formationis isexposed. exposed. The The Nonesuch Nonesuch consists consists of of About The lower lower several dark dark colored colored slate slate units, units, interbedded interbedded with with sandy sandyslate. slate. The several contact contact of of the the Nonesuch Nonesuch and and the the Copper Copper Harbor Harbor is is gradational gradationalin inthat thatthe the nonconglomerate asthe theupper upper nonconglomerateinterbeds interbeds become become finer finer grained grained and and more more abundant abundantas Bedding is is clearly clearly defined defined in in the the contact with with the theNonesuch Nonesuch isisapproached. approached. Bedding contact Nonesuch, Nonesuch, and and local local cross cross bedding bedding and and deformation deformation structures structures can can be be recogrecognized. The The upper upper contact contact of of the the Nonesuch Nonesuch with with the the Freda Freda is is also also gradational gradational nized. in that thatsand sand beds become more commonand and slate slatebeds beds less lessso. so. beds become more common in of the the Freda Freda Formation Formation is is aa thick The lower lower member member of thickbedded, bedded,fine— fine- to to The Local pebble Local pebble is strongly stained with iron. mediwgrained sandstone that is strongly stained with iron. medium—grained sandstone that The middle middle Member Member of of the the Freda Freda is is seen seenonly onlyat at the the zones are are common. common. The zones It is much better exposed in Spoon Creek It is much better exposed in Spoon Creek creek. northernmost outcrop in the creek. northernmost outcrop in the and very fine—grained sandsiltstone This member consists of siltstone and very fine-grained sandto the west. This member consists of to the west. stone with with occasional occasional shale shale and and cross—stratified cross-stratified fine—grained fine-grained sandstone sandstone stone to compared beds. Bedding is more pronounced in the middle member Bedding is more pronounced in the middle member compared to the the lower lower beds. member. The The upper upper member member of of the the Freda Freda is is best best seen seen at at the the mouth mouth of of the the member. The Montreal Montreal River River to tothe theeast, east, particularly particularlyat at Superior SuperiorFalls FallsininMichigan. Michigan. The upper member member consists consists of of thick thick bedding bedding units units of ofmicaceous micaceous siltstone, siltstone, very very upper fine—grained, fine-grained, laminated laminated sandstone sandstone with with abundant abundant scours scours and and and and current current direcdirection tion indicators, indicators, and and slightly slightly conglomeritic, conglomeritic, fine—grained fine-grained sandstone sandstone with with bedbedding poorly poorly developed. developed. The The White White River River location location is is probably probably in in the the upper upper memmemding ber. ber. Discussion: Clearly, Clearly, the the Oronto Oronto Group Group represents represents aa single single depositional depositional epiepiDiscussion: sode, the the individual individual formations formations representing representing various various environments environments within within that that sode, episode. All All of of the the units units appear appear to to be be gradational. gradational. The The Freda Freda appears appears to to episode. thicken from from its its type type locality locality near near Freda, Freda, Michigan, thicken Michigan, to to the the Montreal Montreal River River and west. west. The The Nonesuch, Nonesuch, conversely, conversely, appears appears to to thin thin toward toward the the west west from from and Presque Isle Isle State StatePark. Park. At At Copper Copper Falls Falls State State Park Park the the dominant dominant shale shale unit unit Presque the shale-bearing shale-bearing interval interval is thick; however, however, the appears to to be be less lessthan than2020inm thick; is appears thick. about140 140inm thick. about All along along the the Gogebic Gogebic Range, Range, the the Early Early and and Middle Middle Proterozoic Proterozoicunits units dip dip All northwest at at aa steep steepangle. angle. Reconstruction Reconstruction of of the the thickness thicknessof of the thesection section northwest results in in an an estimate estimate that that is is too too thick, thick, 20 20 km km of of section section from from Hurley Hurley to to results Lake Superior. Superior. In Keweenaw and and In Michigan Michigan this iseasy easyto tounderstand understand as as the the Keweenaw this is Lake associated faults faults clearly clearly repeat repeat parts parts of of the the section; section; however, however, in in Wisconsin Wisconsin associated because of of poor poor exposure, exposure, the the faults faults are are not not readily readilyrecognized. recognized. As As will will be be because seen and and discussed discussed at at White White River, River, there there is is at at least least one one major major anticline anticline seen known in in outcrop outcrop at at Marble Marble Point, Point, and and at at least syncline with with the the least one one major major syncline known Freda. AA more more reasonable reasonable estimate estimate for for the the total total thickness thickness of of the the Oronto Oronto Freda. km. Group would would be be 55 km. Group 63 �NE 25 0 Distance NE25 D i s t a n c e ffrom rom N E 2 5 tto o El/4 E 11425 25 == 1/2 112 mile mile ml conglomerate conglomerate Lo.QI sandy s a n d y conglomerate conglomerate sandstone •:.:1...sandstone sandstone s a n d s t o n e and a n d shale shale -.A. shale slate conglomerate ale glomerate ;hale late on glomerate andy conglomerate ate 0 E '/425 Sketch of o f geology geology in i n Parker Parker Creek Creek from from Rosenberry Rosenberry (1924). (1924). Sketch 64 �70 ::.'.) Silistone ona shole,grOy to block, alter- noting and laminated to 40 very thin bedoccasional •35 medium- to coorse-grained sandstone units 3 to 6" thick o few frne, thin- bedded sand(UNIT 4) 65 ---tones Unit 2 :=2-:- SttsIns. —--=. ded (1/4— I"); Ss, some Os -- lTt.oi alternating and ::_l laminated, with tUN IT 7) 90 alternating, some Unit I. irregular irregular bosal basal contocis, contocfs, generolly generally (UNIT 3) .;)5ac.irflobIW. 61 — sm.— to c.- grain— sole-morks Sandstone, Sandstone, blactc block medium— to coarsemedium- to coorsegroined. groined. some some Ss. blk., vTto c.—groined thin to thick 85 thick—bedded thick-bedded (UNIT ( U N I T 8) 8) bedded (UNIT 6 (UNIT I) 30 Stratigraphic Stratigraphic section section showing showing 100 100 feet of of typical typical Nonesuch Nonesuch Formation Formation (figure (figure 20 of of Rite, Hite, 1968). 1968). 20 Stratigraphic Stratigraphic section section showing showing 100 100 feet feet of of typical typical Lower Lower Freda Freda Formation Formation (figure (figure 30 30 of of Rite, Hite, 1968). 1968). 65 �Stratigraphic section showing Stratigraphic section showing 100 100 feet of typical typical Middle Freda Freda Formation Formation (figure 33 of of Hite, Hite, 1968). 1968). (figure 33 Siltstone, red micoceous and Siltstone, red rnicoceous,lOm- laminated, 1terbedded with irioted with sholes ond cross-bedded siltstones, inter— 21 70 C\ stratified (UNIT 3) I Sandstone, red very fine— to tine groined, 10mm— 65 oted,w,th 40 U. :.—• ... —.....- .: bedding which becomes more abundant upword in the section distorted bedding rn central 60 part of the unit. 6iltstone, red micaceous, irregular lam— motions with micro (ripple) cross—stab (UN IT 4) in upper part. interbedded St red, fine-grained (UNIT 2) _30 -:;.-: micro cross- — Sandstone, red fmne—groined, : 55 Sandstone, same as 95 Unit4,but sandstone, white to green, finegroined cross—bedded (UN I T 8) larger scale Cross—strata. —U.LNLL6)-. 90 Shale and fine silistone, brick red, micaceous, laminated. 85 interbedded coorse—grouned cross—bedded sandstone ocair 6 feet below the top of the unit (UNIT 5) 80 Sandstone red fine-groined, bedding poorly developed shale pebbles common in upper part (UNIT 7) laminated, rib and furrow StruClurC (UNIT I) Stratigraphic section feet ofFreda typical Upper Freda Formation Stratigraphic section showing showing 100 feet of 100 typical Upper Formation (figure 42 of Hite, 1968). (figure 42 of Hite, 1968). 66 �- Oronto Oronto Group Group Title: Title: Copper Copper Falls Falls State State Park Park — AS AS 45/02E/17B 45/02E/17B Location: Northwest of Mellen on Location: Northwest. of Mellen on Highway Highway 169. 169. SE1/4, SE1/4, Sec. Sec. 17, 17, T. T. 45 45 N., N., B. R. 22 E., E., Ashland Ashland County, County, Wisconsin. (Mellen (Mellen and and High High Bridge Bridge 77 1/2—minute 1/2-minute topographic topographic quadrangles, quadrangles, 1967 1967 and and 1984, 1984,respectively). respectively). Author: M.G. Mudrey, Mudrey, Jr. Jr. Author: M.G. Copper Falls Falls is is formed formed where where the the Bad Bad River River cuts cuts through through the the rereDescription: Description: Copper sistant ridge ridge of of Keweenawan Keweenawan lava lavaflows. flows. Downstream, Downstream, 0.6 0.6 km km from from Copper Copper Falls Falls sistant at the north, the the contact between basalt to the south and rhyolite to the north, Tyler Tyler Forks Forks River River joins joins the the Bad Bad River River at at Brownstone Brownstone Falls, Falls, which which occurs occurs at at the the contact contact between between basalt basalt to to the the south south and and rhyolite rhyolite to to the the north. north. The The conconglomerate of of the the Copper Harbor Formation is exposed in the lower glomerate gorge at lower gorge Devils Gate Gate about about 200 200 mm downstream downstream from from Brownstone Brownstone Falls. Falls. The Devils The conglomerate conglomerate is Montreal River is 129 129 m thick; thick; at the the Montreal River the the conglomerate conglomerate is is 515 515 mm thick. thick. NorthNorthwest Nonesuch Formation; west of of the the conglomerate conglomerate is is the the black shale shale of of the the Nonesuch Formation; northnorthwest west of of the the Nonesuch Nonesuch is is the the sandstone sandstone of of the the Freda Freda Formation. Formation. There There is is black black shale distributed distributedthrough through141 141inm of of section, section, but but only only2020inm are are considered considered shale Nonesuch Formation. Formation. Above the the interval interval with black shale, the sediment sediment is is red red Nonesuch shale, the shaley shaky arkose. arkose. 67 �The name Copper Copper Falls comes comes from a a small small copper copper prospmt prospect in a small small raravine working was south of of the the concession concession building. building. The working was begun by vine about 200 m south the Ashland Mining Company CompanyininAugust August1864 1864and andclosed closed in in February 1866. Copthe Ashland Mining 1866. Cop- per in quartzvein veininindiabase diabasewas was prospected. prospected. per in aa quartz reopened at the the turn turn of reopened at of the the century. century. Apparently the property Apparently the property was was Discussion: Discussion: Although faults faults complicate complicate the the local local geology, the the essentially essentially conformable relationship between the Oronto Group Group and Keweenawan conformable Keweenawanflows flows can can be seen. lowerparts parts of seen. The the Oronto Group, Group, the the Copper Harbor and the The lower of the theOronto Nonesuch, Nonesuch, are significantly significantly thinner thinner here here than than at at localities localities to to the the east. east. 68 �Title: Title: South South Fish F i s h Creek Creek Exposures Exposures in i n banks banks of of South South Fish F i s h Creek beneath bridge b r i d g e on on north—south north-south secondary m i l e s south south of of U. U. S. S. Highway Highway 22 on on the t h e east e a s t line l i n e of of the t h e SE-, SE*, secondary road road 1.2 1.2 miles SE, S E ~NE*, , NE*, Sec. Sec. 20, 20, T.47N., T.47N., R.5W., R.5W., Bayfield Bayfield County County (Moquah (Moquah 7.5 7.5 minute minute topographic topographic quadrangle, 1964). 1964). Location: Location: Author: Author: M. E. E. Ostrom Ostrom (modified (modified from from Myers, 1971) 1971) M. Exposures of of steeply—dipping steeply-dipping Freda Freda Sandstone Sandstone exhibit e x h i b i t the t h e lithologic lithologic Description: Exposures and mineralogic character c h a r a c t e r of of the t h e formation. formation. A description d e s c r i p t i o n of of the t h e strata s t r a t a downdownand is: stream from from the t h e bridge b r i d g e is: stream PRECAMBRIAN SYSTEM PRECAMBR IAN SYSTEM Keweenawan Keweenawan Series Series Oronto Group Group Oronto Freda Sandstone Sandstone Formation Formation (11.0 (11.0 feet) feet) 11.0' 11.0' Sandstone, grayish g r a y i s h red r e d to t o reddish r e d d i s h brown, brown, uniformly fine—grained, fine-grained, Sandstone, hard, h a r d , cross—bedded cross-bedded with w i t h parting p a r t i n g lineation. l i n e a t i o n . Much Much leaching. leaching. deformation. Current ripple r i p p l e marks found in in Penecontenporaneous deformation. float. float. 69 �BASE OF EXPOSURE Significance: Significance: Provides Provides evidence evidence of of environmental, environmental, geologic geologic and and structural structural history. Examine Examine lithology lithology and and mineralogy. mineralogy. What What do do they they signify? signify? What What direcdirechistory. tion tion is is the the top top of of the the beds? beds? Measure Measure dip dip and and strike strike of of beds. beds. What do do these these mean mean in in terms terms of of structural structural history? What What is is the the origin origin of of the the red red color? color? References: References: 70 From From what what direction direction did did the the sand sand come? come? Thwaites, Thwaites, 1912; 1912; Myers, Myers, 1971. 1971. �Chequamegon Formation Formation Title: U l e : Washburn Washburn Harbor Harbor --- Chequamegon BA 48104W/33 48/04W/33 Location: Outcrop on northside of J,ocatton~ of Washburn Harbor, Harbor! SW1/4, SW1/4, SEll SEl/ Sec. 33, T48N, R4W, Bayfield County, Wisconsin (Washburn 4 ! 33, T48Nr R4Wr Bayfield Countyf Wisconsin (Washburn 4, 7.5—minute quadrangle, 7.5-minute quadrangle! topographic, topographic! 1975). 1975). thor: M.G. Nudrey, Mudrey, Jr. Jr. (1992) (1992) Author: Description: Description: This low outcrop of Chequamegon sandstone of of the the Chequamegon sandstone Bayfield Group Group consists consists of of thick, thick, massively massively bedded, bedded! fine fine —- to Bayfield to medium-grained! grayish—red, grayish-red! quartzose quartzose sandstone. sandstone. The The grains grains medium-grained, are subangular subangular to to subrounded. subrounded. The bedding surfaces surfaces are are gritty gritty to coarse coarse grained, grained, but but are are thin thin and and discontinuous. discontinuous. Some Some bedding planes display scattered scattered small small quartz quartz pebbles. pebbles. Here! planes display Here, bedding dips gently to the southeast; southeast; however, at Big Rock Wayside Park Park at at the the east east quarter quarter corner corner of of Section Section 24, 24! T48N, T48Nf R5W, crossbedded R5Wf crossbedded sandstone sandstone dips dips 15 15 degress degress to to the the northwest, northwest! suggesting that that small, small! low-amplitude low-amplitude folds folds with with aa suggesting northeasterly northeasterly trend trend may may occur occur in in the the region. region. Discussion: The Chequamegon Qiscussion~ Chequamegon sandstone sandstone is is similar similar to to the the underlying Orienta sandstone, sandstone! which is found in fault contact �with with Keweenawan Keweenawan volcanics volcanics and and Oronto Oronto group group strata. strata. Bayfield Bayfield Group strata strata are are not not known known to to have high high dips, dipsI and and on on this this Group basis have have been been distinguished distinguished from from the the upper upper parts parts of of the the basis underlying underlying Freda Freda sandstone. sandstone. The The Douglas Douglas Fault Fault intervenes intervenes between between this this locality locality and and South South Fish Fish Creek Creek where where the the Oronto Oronto Group A petroleum petroleum Group dips dips south south at at aa high high angle angle to to the the south. south. A test test well well has has been been drilled drilled between between these these two two locations locations immediately immediately adjacent adjacent to to the the Douglas Douglas Fault. Fault. At At the the time time of of this this writing, writingI no no further further information informationwas was available. available. 72 �REFERENCES General geology, in Wisconsin Wisconsin Geological Aldrich, Aldrich, H.R., H.R., 1925, 1925,VI. VI. General geology, & Geological and and History Survey Natural History Survey Township Township Report Report T. T. 45 45 N., N., R. R. 22 W. W. (1924), (19241,p. p. 36—69. 36-69. Daniels, P.A., P.A., Jr., Jr., 1982, 1982, Upper Precambrian Precambrian sedimentary rocks: rocks: Oronto Oronto Group, Group, Daniels, Michigan—Wisconsin, in Wold, Wold, R.J., Michigan-Wisconsiny R.J., and and Hinze, Hinze, W.F., W.F., eds., eds., Geology Geology and and tectonics the Lake Superior basin: tectonics of the Lake Superior basin: Geological Geological Society Society of of America America Memoir 107—133. Memoir 156, 156,p. p. 107-133. Dickas, Comparative Precambrian Precambrian stratigraphy Dickasy A.B., 1986, 1986, Comparative stratigraphy and and structure structure along along the Mid—continent rift: the Mid-continent rift: American Association Association of of Petroleum Petroleum Geologists Geologists Bulletin, v. 70, 70, no, no, 3, 3, p. p. 227. 227. Bulletin, 1982, The sandstone architecture architecture of the Eckert, K.B., 1982, the Lake Lake Superior Superior region: region: Michigan Michigan State State University, University, Lansing, Lansing, unpublished unpublished Ph.D. Ph.D. dissertation, dissertation, 504 p. 504 p. Green, Keweenawan plateau plateau volcanism Green, J.C., 1977, 1977, Keweenawan volcanism in in the the Lake Lake Superior Superior region, region, Bara,dr, W.R.A., W.R.A., ed., Volcanic regimes in Bara&dr, regimes in Canada: Geological Geological Association .16, p p. 407—422. Association of of Canada Canada Special Special Paper Paper.16, . 407422. Hainblin,W.K., W.K., 1965, 1965, Basement Basement control control of of Keweenawan Keweenawan and and Cambrian Cambrian Hamblin, Association of of sedimentation American Association sedimentation in in the the Lake Lake Superior Superior region: region: American Petroleum Geologists Bulletin, 49,p. p. 950—959. 950-959. v.,49, Petroleum Geologists Bulletin, v. Hatch, J.R., and Morey, Morey, G.B., G.B., 1985, 1985, Hydrocarbon Hydrocarbon source source rock rock evaluation evaluation of of Hatchy J.R., Proterozoic Solor Church Church Formation, North American Mid-Continent Mid—Continent Middle Proterozoic Formation, North System, Rice County, County, Minnesota: Minnesota: American Association Association of Petroleum Rift System, Geologists Bulletin, v. 69, 69, no. no. 8, 8, p. p. 1208—1216. 1208-1216. Geologists Bulletin, v. Hite, D.M., 1968, 1968, Sedimentology of the Upper Keweenawan Keweenawan sequence sequence of northern Hite, D.M., University of Wisconsin, Madison, Wisconsin and Wisconsin and adjacent adjacent Michigan: Michigan: University of Wisconsin, Madison, unpublished Ph.D. thesis, p. thesis, 217 217 p. unpublished Hubbard, H. A., lW5, 1975, Keweenawan Keweenawan geology geology of of the the North North Ironwood, Ironwood, Ironwood Ironwood and and Hubbard, H.A., Little Girls Girls Point Point quadrangles, Little quadrangles, Gogebic Gogebic County, County, Michigan: Michigan: U.S. Geological Survey Geological Survey Open Open File File Report Report OF OF 75—152, 75-152, 23 23 p. p. or copper—bearing system, $J in Geology Irving, R.D., 1880, The The Keweenawan Keweenawan or Geology of of Irving, R.D., 1880, copper-bearing system, Wisconsin, p. p185, 205—206. Wisconsin, v. v. III., III., . 185, 205-206. frontier oil oil province: Kerr, S.D., Lee, C.K., C.K., and and Kerr, S.D., 1984, 1984, Midcontinent—a Midcontinent-a frontier province: Oil Oil Journal, August August 13, and Gas Gas Journal, 13,1984, 1984,p.p.144—150. 144-150. Superior regions region, U.S. A., and and its its Morey, G. B., 1978, in the G.B., 1978,Metamorphism Metamorphism in the Lake Lake Superior U.S.A., crustal evolution, evolution, in Fraser, J.A., and edseS relation to crustal Fraser, J.A., and Heywood, Heywood, W.W., W.W., eds., relation Metamorphism Metamorphism in in the the Canadian Canadian Shield: Shield: Geological Geological Survey Survey of of Canada Canada Paper Paper 78-10, p. 283—314. 283-314. 78—10, P. ., , Morey, and 0 Ojakangas, R.W.W., 1982,Keweenawan Keweenawan sedhentary sedimentary rocks rocks of Morey, G. I3B., and jakangas R. , 1982, eastern Minnesota and eastern Minnesota and northwestern northwestern Wisconsin, Wisconsin, in $J Wold, Wold, R.J., R.JeSand and Hinze, Hinzes W.F., W.F., eds., Geology Geology and and tectonics tectonics of of the the Lake Lake Superior Superior Basin: Basin: Geological Geological Society of 135-146. Society of America America Memoir Memoir 156, 156, p. p. 135—146. 73 �Mudrey, Mudrey, M.G., M.G., Jr., Jr., 1979, 1979, Geologic Geologic summary summary of of the theAshland Ashland 2° 20 quadrangle: quadrangle: Wisconsin WOFR Wisconsin Geological Geological and and Natural Natural History History Survey Survey Open—file Open-file Report Report WOFR 79—1, 79-1, 39 39 p. p. Myers, Myers, W.D., W.D., II, 11, 1971, 1971, The The sedimentology sedimentology and and tectonic tectonic significance significance of of the the Bayfield Bayfield Group Group (Upper (Upper Keweenawan?), Keweenawan?), Wisconsin Wisconsin and and Minnesota: Minnesota: University University of of Wisconsin, Wisconsin, Madison, Madison, unpublished unpublished Ph.D. Ph-D.thesis, thesis,269 269p. p. Ostrom, Ostrom, M.E., 1967, 1967, Paleozoic Paleozoic stratigraphic stratigraphicnomenclature nomenclatureof ofWisconsin: Wisconsin: Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey Information Information Circular Circular 8, 8, chart chart and and text. text. Ostrom, ME., and Ostrom, M.E., andSlaughter, Slaughter,A.E., A.E., 1967, 1967,Correlation Correlation problems problems of of the the Cambrian Cambrian and and OrdOvician Ordovician outcrop outcrop areas areas of of the the Northern Northern Peninsular Peninsular fsicJ [sic] of of Michigan: Michigan: Annual Annual Field Field Excursion, Excursion, Michigan Michigan Basin Basin Geological Geological Society, Society, p. 1—5. 1-5. p. Paull, Paull, R.K., R.K., and and Paull, Paull, R.A., R.A., 1980, 1980, Field Field Guide Guide to to Wisconsin Wisconsin and and Upper Upper Michigan: Kendall/Hunt Publishing Publishing Co., Co., Dubuque, Dubuque,Iowa, Iowa,260 260p. p. Michigan: Kendall/Hunt Rosenberry, Rosenberry, S.C., S.C., 1924, 1924,VI. VI. General General geology, geology,in: &: Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey Township Township Report Report T. T. 47 47N., N., R. R. 11 E. E. (1924), (1924), p. 17—28. 17-28. p. Thwaites, Thwaites, F.T., F.T., 1912, 1912, Sandstones Sandstones of of the the Wisconsin Wisconsin coast coast of of Lake Lake Superior: Superior: Wisconsin p. Wisconsin Geological Geological and and Natural Natural History History Survey Survey Bulletin Bulletin 25, 25, 117 117 p. Weiblen, Weiblen, P.W., P.W., and and Morey, Morey, G.B., G.B., 1980, 1980, A summary summary of of the the stratigraphy, stratigraphy, petrology and and structure structure of of the the Duluth Duluth Complex: Complex: American petrology American Journal Journal of of Science, Science, v. v. 280—A, 280-A, pt. pt. 1, 1, p. p. 88—133. 88-133. Wold, R.J., R.J., and and Hinze, Hinze, W.F., W.F., eds., eds., 1982, 1982, Geology Geology and and teconics teconics of of the the Lake Lake Wold, Superior Basin: Basin: Geological Geological Society Society of of America America Memoir Memoir 156, 156, 280 280 p. p. Superior 74 �GEOLOGY OF GEOLOGY OF KEWEENAWAN KEWEENAWAN SUPERGROUP ROCKS SUPERGROUP ROCKS NEAR THE NEAR PORCUPINE MOUNTAINS, PORCUPINE MOUNTAINS, GOGEBIC ONTONAGON & & GOGEBIC ONTONAGON COUNTIES, MICHIGAN COUNTIES, MICHIGAN William F. Cannon, Cannon, William Suzanne W. Nicholson, Nicholson, Suzanne Cheryl A. Hedgman, Laurel Laurel G. G.Woodruff, Woodruff, and Klaus J. Schulz U.S..Geological Geological Survey, U.S Survey, Reston, Reston, Virginia �5 5 5 LiL trip stops. 1r:-1 Figure 1. CONTOUR INTERVAL 50 FEET 0 0 10 ii Statute MiIe j Kilometers ________ �WAN SUPERGROUP SUPERGROUPROCKS ROCKSNEAR NEAR THE THE PORCUPINE PORCUPINE MOUNTAINS, MOUNTAINS, GEOLOGY OF KEWEENA WAN ONTONA GONAND AND GOGEBIC GOGEBIC COUNTIES. COUNTIES, MICHIGAN MICHIGAN ONTONAGON William F. Cannon, Suzanne W. W. Nicholson, Nicholson, Cheryl Cheryl A. A. Hedgman, Hedgman, Laurel LaurelG. G.Woodruff, Woodruff, and Cannon, Suzanne J. Schulz Klaus J. Schulz U.S. Geological Survey, Survey, Reston, Reston, VA U.S. INTRODUCTION INTRODUCTION This field trip trip examines examines the the geology geology of of rocks rocksof ofthe theKeweenawan KeweenawanSupergroup Supergroup(1 (1.1 .IGa) Gal and and related intrusive rocks rocks of of the Midcontinent rift rift system system (MRS) (MRS) in the western part of the the northern northern peninsula of of Michigan. The The combination combination of of stops stopsincludes includesall all formations formations of ofthe theKeweenawan Keweenawan Supergroup in in this this region. Examination Supergroup Examination of of all alldescribed described localities localitiesrequires requires more more than than aa single single day day and participants are are encouraged encouragedto to use usethis this guidebook guidebookon ontheir theirown own to to supplement the the localities that will will be be visited visited on on our one-day trip. Because Because of uncertainties uncertainties of weather, weather, road road conditions, conditions, and and remaining snow snow pack pack in in early earlyMay Mayininthis thisregion regionofofvery veryheavy heavysnowfall, snowfall,the thestops stopsthat thatwe we will will visit visit will will not not be be known known until until the the date date of of the the trip. trip. Stops Stopsare arenumbered numberedin in stratigraphic stratigraphic order, order, from from oldest oldest to youngest, youngest, not in the order in which they will will be be visited. GENERAL GENERALGEOLOGY GEOLOGY Supergroup is is aa very very thick thick sequence sequence of of volcanic and sedimentary rocks The Keweenawan Supergroup that was deposited deposited during and shortly shortly after after an an episode of continental continental rifting riftingat atabout about11.1 .IGa, Ga, when when formed within the the MRS formed the Proterozoic Proterozoic craton. The TheKeweenawan KeweenawanSupergroup Supergroup was was deposited deposited in in and and marginal to to rift rift graben graben and in a post-rift post-rift thermal thermal basin basin more or less centered on the axis of the the of the field trip (figs. 11 and former rift. In the area area of and 2), 21, the the Keweenawan Keweenawan stratigraphic section (fig. (fig. 3) 3) Quartzite)that thatis is overlain overlainby by aa great greatthickness thickness of of consists of a thin thin basal basal quartzite (Bessemer (Bessemer Quartzite) subaerial flood flood basalt flows and and felsite felsite flows (Powder subaerial and lesser lesser andesite and (Powder Mill MillGroup Groupand andPortage Portage Lake Volcanics). Volcanics). The progressively thicker thicker toward toward the rift Lake The volcanic section section becomes progressively riftaxis axisand and exceeds 20 20 km and others, others, 11988; 988; Cannon and others, exceeds km in in places places beneath beneath Lake Superior (Behrendt and 1 990). 1990). In the vicinity vicinity of of the thePorcupine Porcupine Mountains, Mountains, the the volcanic volcanic sequence sequence includes, at the the top, top, aa stratovolcano stratovolcano composed mostly of andesite andesite and rhyolite flows flows and and sub-volcanic sub-volcanic felsic felsic intrusions intrusions Volcanics). These (Porcupine Volcanics). These late late intermediate and felsic volcanic rocks rocks are are atypical atypical of of the theMRS MRSas as a whole and are limited to aa few few felsic felsic volcanic volcanic centers. centers. fluvial sedimentary sedimentary rocks rocks and and lesser lesser lacustrine lacustrine Conformably overlying the volcanic rocks rocks are are fluvial sedimentary rocks (Oronto (Oronto Group), which which are are as as much much as as 88 km km thick thickbeneath beneathLake LakeSuperior Superior(Cannon (Cannon and others, others, 11990) 990) and and at at least 5 km thick on shore in the field field trip trip area. area. Post-rift reverse faulting faulting has caused caused block block rotation rotation on a very large scale scale so so that that the Post-rift Keweenawan Supergroup Supergroupsection sectionisissteeply steeplytotovertically verticallydipping. dipping. More than 13 13 km km of of volcanic volcanic rocks and 5 km generally north-facing north-facing section. This km of of sedimentary sedimentary rocks rocks are exposed in a generally This thick section constituted at least half of the crustal enormously thick crustal thickness by by the the close close of of rifting riftingand and thus our field trip trip provides provides aa traverse through the upper half of the Middle Middle Proterozoic Proterozoic crust. The initial initial subsidence of the the MRS MRS is is recorded recorded by deposition deposition of of the theBessemer Bessemer Quartzite Quartzite(stop (stop 1), 1 ), a blanket of relatively relatively pure, fluvial fluvial quartzite quartzite as as much much as 100 100m mthick thick(Ojakangas (Ojakangasand and Morey, Morey, It formed in a broad basin, basin, more more or or less less centered centeredon onthe thesite Siteofofthe thefuture future deep deeprift. rift. The 1982). 1982). It The age of of deposition has an an upper upper bound boundof of about about 1109 1109 Ma, Ma, the age age of of the oldest overlying basalt age flows (Davis (Davis and Sutcliffe, 1985). 1985).Following Followingdeposition depositionofofthe theBessemer, Bessemer,the thearea areabecame became volcanivolcanias 15 km) of basalts and lesser andesites andesites and and rhyolites rhyolites cally active and a great thickness (as much as in only about 1155 m.y. m.y. The accumulated in The earliest earliest basalts basalts constitute constitutethe the Siemens Siemens Creek Creek Formation Formation of 975a) (stops (stops 11 and and 2). 2), which lies the Powder Mill Mill Group (Hubbard, 1 1975a) lies conformably conformably on on the the Bessemer Bessemer Quartzite. Soft flow (seen Quartzite. Softsediment sediment deformation deformation ofofthe theBessemer Bessemer by by the overriding overriding basal basalt flow (seen at flow is stop 1) 1) indicates a very short interval between the units. Locally, Locally, as at Stop stop 1, the basal flow is pillowed, but but all allsucceeding succeedingflows flowsare aresubaerial. subaerial. 77 �00 1 ,00730" 10G130 2 — •••_o___ o —- — 'KtOMETERS UE8 \' �________ EXPLANATION EXPLANATION Intrusive rock. rocks Intrusive O.bbrc or dleb...—grancphyn. ifitrunin. cOrgia000 I, f.rr.d f.I.la .tcob Volcanic and ..dimsntery rock. Jccob.vllla S.nd.ton.— •d end bran, f.ld.p.thln and aantoo.. scndstone. all (atcn.. nunglanut. O r o n l oGroup Group SAUGL— Ornate Fr.do Fcnn.tlc,,— r.d .cndst.n. end nu.,dsl,n. Noc.aoh Shale— gre—bl eat .llt.tone. shela. hoe needol000 Capper Herbs, Cnnqlansn.te— tears. nod—bins ..nglnr.te sad Ccpp.r Harbor Ccnglanr.te basalt ,m,H.r Bergland Grasp Perapie. Vclo.nlo. rhyollt. m..H.r— .phyr a to gaunt. and f.ldoper in abner 1.1 don... fleas end d.brl. floe. pitynlo rhy.lit* Poroopin. Voloeni.. basalt cod end., it. .e.,*.r thin °F ft... of and.. It. and miner tholelillo ba.clt ParIng. 1.1.. Vnl.noloe—nmotly nphltlo IlicleIltI. bdeelt floe.. naHasIt.. nhy.llt. utid intart lee t.ngla,arnt. nil,,, Po.dennsi II I I iii 1! Creep Fc.d.nniIl Creep (endlvld.d)— Thnl.iltic kooelt flea.. .nlncç II end.slt. end rhyc lit. anacin Leear Prat.ronuie cod Arch.., rack. (cndlvldad) Tr.ndofpronlnanl •.ran.gn.liu lin..n.nl. Mountainsarea area showing showing PorcupineMountains Figure Figure 2. 2, Generalized Generalizedgeologic geologicmap mapand andsection section of of the thePorcupine the location of field trip stops. the location of field trip stops. 79 �STOP j# 12a 12 Jocobsville Jocob,ville Sandstone Lj Sandstone Freda Sandstone Nonesuch Shale Copper Harbor Horbor Conglanerate Conglamrote rnmber) (bosoitk rnerther) (bosa; Porcupine Volcanic, Volcanics 1o I Portage Volcanics Portage Lake Volconic, 4 5 Kollander Kal lander Creek Formation 3 - 2 1 0 Sernena Siemens Creek Formation Bess-r Quartzite Bessner Quartzite KM Early Preterozoic Eorly Proterozoic rocks rocks Figure Stratigraphicsection sectionof ofKeweenawan Keweenawan Supergroup Supergroup rocks in the field field trip trip area area Figure 3. Stratigraphic showing the stratigraphic position of stops. Thicknesses are approximate average stratigraphic position of stops. Thicknesses are approximate average thicknesses for for the area. area. Some Some formation formation thicknesses thicknesses vary significantly significantlyacross across the the region. region. 80 �Overlying the Siemens Creek Formation Formationisisaathick thick section section of of more felsic felsic rocks Siemens Creek rocks (stop (stop 3) 3) of rhyodacite, rhyodacite, tra~hyandesite~ trachyandesite, andesite, andesite, and andbasalt. basalt. These rocks constitute constitute the composed of the Kallander Kallander Creek (Hubbardl 1975a). Powder Mill Mill volcanic volcanic rocks rocksare are Creek Formation Formation of of the the Powder Mill Group (Hubbard, 1 975a). The Powder distinguished from overlying overlying basalts basalts of similar similar character character largely on the the basis basis of of their theirreversed reversed to the normal polarity magnetic polarity as opposed to polarity of of younger younger units unitssuch suchas asthe thePortage PortageLake Lake Volcanics. In Michigan, Michiganl the Powder Mill Mill Group crops out in in aa belt belt that that isisseparated separated from from the the Volcanics by by the the Jacobsville Jacobsville Sandstone, Sandstone, which which lies with outcrop belt of the the overlying overlying Portage Portage Lake Volcanics subsurface, however, the Powder Mill Mill rocks. In the subsurfacef Mill and and angular unconformity unconformity on Powder Mill Lake probably probably form form a continuous Portage Lake continuousdepositional depositionalsequence. sequence. Supergroup range rangein incomposition compositionfrom from olivine olivine tholeiite tholeiite to Volcanic rocks of the Keweenawan Supergroup rhyolite. By high-Al olivine olivine tholeiite tholeiite (A1203 (Al2 03==15-19 wt%) followed by rhyolite. By far far the the dominant dominant rock type is high-A1 15-19 wt%) lesser high-Fe high-Fetholeiite tholeiite and and rocks rocks of of intermediate and and felsic felsic composition composition (Green, (Green, 1982; Brannon, lesser Brannon, 1984; Paces, Paces, 1988). 1988). The Theolivine olivinebasalts basaltscommonly commonly are are ophitic in in texture texture and and the the dominant dominant plagioclase. The most are geochemically geochemically similar similar to to phenocryst is plagioclase. most primitive primitive Keweenawan Keweenawan basalts are ridge basalts. basalts. However, primitive midocean ridge However, incompatible incompatible trace elements in most Keweenawan are enriched enriched compared comparedto to depleted depletedor or primitive primitive mantle. mantle. Radiogenic basalts are Radiogenic isotope isotope analyses analyses (Sr. (Sr, Nd, Pb) of of the the main stage stage high41 high-Al olivine olivine tholeiites tholeiites suggest suggest that that aa likely likely source source of of the voluminous and Pb) (Pacesand andBell, Bell,1989; 1989; Nicholson Nicholson and and Shirey, Shirey, 1990). 1990). basalts is a mantle plume (Paces Some of of the the oldest flowsl flows, such Some such as as those in in part part of of the the Siemens Siemens Creek Creek Formation, Formation, have distinctly different distinctly different chemical chemical compositions compositions than the younger basalts. These These basal basal rocks rocks are are transitransitional to weakly characterized by by low low A1203 A1203 content content and clinopyroxene weakly alkaline alkaline olivine basalts characterized phenocrysts. Locally, phenocrysts. Locally, in other parts of the rift, basal basal flows flows are are picritic picritic but but such such flows flows have havenot notbeen been identified in in this this area. area. Flows Lake Volcanics Volcanics north north of the Keweenaw Flows near the base of the exposed Portage Lake Keweenawfault fault were erupted at about 1096 near the the top top of the formation 1096 Ma Ma and those near formation at at about about 1094 1094Ma Ma(Davis (Davis and Paces, Paces, 1990). 1 990). Thus, Lake Volcanics, Volcanics, at at least 8 km in this Thusl the great thickness of Portage Portage Lake this area, areaf was erupted in only aa few few million millionyears. years. The Theestimated estimatederuption eruptionrate ratefor forPortage PortageLake LakeVolcanics Volcanicsinin the present eruption eruption rate the western western Lake Lake Superior region must have approximated the rate of of the the Hawaiian Hawaiian hot spot, spotl the the most mostvigorous vigorous volcanic volcanic center center of of the themodern modernearth earth(Cannon, (Cannonfin in press). press).Because Because synchronous volcanism volcanism occurred occurredalong alongthe theentire entiretrend trendofofthe therift, rift, the the rift rift system system as as a whole was was producing producing basalt at at aa rate rate unrivalled unrivalled by byany any modern modernanalog. analog. area of of the the Porcupine Porcupine Mountains Mountains contains contains aafelsic felsicto to andesitic andesitic volcanic volcanic center center that that The area became active late late in in the the volcanic volcanic history history of of the the regionl region, at at about about 1090 1090 Ma. The became active ThePorcupine Porcupine called the the "unnamed "unnamed formation") formation") (Cannon and and Nicholson, Nicholson, 1992) were erupted erupted Volcanics (previously called from from that that center center and and accumulated accumulated as much as 5 km of of andesite, andesite, rhyolite, rhyolite, and and basalt basalt in inaalarge large shield shield deposited on top of the the Portage Portage Lake Lake Volcanics lava field and centered near the Porcupine Mountains. The Thepresent presentarcuate arcuate shape shape of the the mountains mountains and and the the unusual unusual hook-shaped map pattern reflection of the of the Porcupine Porcupine Volcanics is partly a reflection the original original shape shape of the the volcanic volcanic shield. shield. The Porcupine Volcanics consists of aa sequence of subaerially deposited andesite, andesite, basalt, felsite, and quartz-porphyry quartz-porphyry lava flows, and and minor minor interbedded interbedded volcaniclastic volcaniclastic lithic lithic sandstone, sandstone, siltstone, 1 975b). The abundance siltstonel and and conglomerate (Hubbard, (Hubbardl 1975b). abundance of felsic rocks rocks and the predomipredominance of of andesite over basalt clearly distinguish the Porcupine Volcanics from the nance the underlying underlying Portage Lake LakeVolcanics. Volcanics. Felsite Felsite is is most most common common near nearthe thetop topof of the the formation formation where it it occurs occurs as Portage both flows flows and and domes domes (stops (stops 55 and and 6). 6). The major element chemistry of basalt, basalt, basaltic basaltic andesite, andesite, and and andesite andesite of of the thePorcupine Porcupine Volcanics and the Portage Volcanics are are very very similarl similar, but the Porcupine Portage Lake Volcanics Porcupine Volcanics are are distinctly distinctly enriched in rare earth elements WEE) (REE)and andTh Thcompared comparedtotothe thePortage PortageLake LakeVolcanics. Volcanics. The two two formations differ more profoundly in their rhyolite chemistry. Rhyolite Rhyolitethat that occurs occurs most mostcommonly commonly in the Portage Volcanics is is aphyric aphyric or or may may contain contain sparse sparse quartz quartz phenocrysts. phenocrysts. Rhyolites Rhyolitesof of the the Portage Lake Volcanics Portage Lake Lake Volcanics Volcanics on on Keweenaw Peninsula Peninsulahave havevery verylow low abundance abundance of of incompatible trace elements (such as as REE, REE,Zr, Zr,Y,Y,Hff Hf, and andThIl Th), whereas whereasthe the rhyolite rhyolite body body near near Bergland Bergland (stop (stop 41, 4), one one of of the few few rhyolite rhyolitebodies bodies with withthe thePortage PortageLake LakeVolcanics Volcanics in in the the Porcupine Porcupine Mountains Mountainsarea, area, has has moderate abundances of incompatible incompatible trace trace elements. elements. In contrast, the numerous rhyolite bodies in Volcanics range rangefrom fromrhyolites rhyolitesthat that are areaphyric aphyricto to those those with with abundant quartz andlor and/or the Porcupine Volcanics 81 81 �The thrust faulting faulting and and folding can be indirectly dated in the interval of approximately 1060 1060 and othersl others, 1984; Bornhorst and andothers, others, 1988; 1988; Cannon Cannonand andothers, others, 11990). to 1040 1040 Ma Ma (Ruiz (Ruiz and 990). The The cause of of the regional compression compressionisisnot not known known with certainty cause certainty but but isislikely likelylinked linkedininsome somemanner manner orogeny, which was in progress at that time. with the the Grenville Grenville orogeny, STOPS FIELD TRIP STOPS Stop .--BessemerQuartzite Quartziteand andbasalt basaltat at the the base base of of the the Powder Mill Mill Group Group Stop 11.--Bessemer A low east of of the county road (see (seefig. fig. 4) 4) shows quartzite of the low rock rock knob knob in in aa pasture pasture east upper part part of of the Bessemer Quartziteinincontact contactwith with the the overlying overlying basal basalbasalt basaltflow flow of of the the Powder Powder upper Bessemer Quartzite Mill Group. The 975a). Thebasalt basaltisisthe the lowermost lowermostflow flowofofthe theSiemens SiemensCreek CreekFormation Formation(Hubbard, (Hubbard,11975a). The Siemens Creekisiscomposed composedpredominantly predominantlyofofthin thinflows flows of of basalt and and minor minor andesite. andesite. Average Siemens Creek Average thickness of of flows is about 3 m, but the basal flow flow is about 50 m thick at this locality. Here, Here, the the basal flow flow is nonporphyritic holocrystalline. Unlike basal nonporphyritic and holocrystalline. Unlike some of the basal basal flows along along strike strike to to the the flows do west, these flows do not not contain contain clinopyroxene clinopyroxene phenocrysts. Chemical Chemical analyses analyses (table 1) of the flows are similar to the basal flows the younger younger high-alumina high-alumina main-stage basalts of the Portage Portage Lake Volcanics. The Creekflow flow is is pillowedl pillowed, which which is very very unusual for for basalts of the Volcanics. The basal basal Siemens Siemens Creek Supergroup, nearly all of which Keweenawan Supergroupl which are are subaerial. subaerial. In places, placesl stringers of the the quartzite quartzite been injected injected up up into into rubbly rubbly material material at at the the base baseof of the the flow, flow, indicating have been indicating that that the theBessemer Bessemer was was unconsolidated at the time of eruption. eruption. that dips here here are areabout about65O 65° N. N. Contrast Note that Contrast these these with with steeper steeper to slightly slightly overturned overturned dips at stops 2 and 3, higher in the Powder Mill section. This Thisupdip updipfanning fanningrelationship relationship commonly commonly Hubbard (1 (1975a) to propose that they they were were deposited deposited in in aa shown by the Powder Powder Mill Mill flows flows led ledHubbard basin that was centered centered south (updip) (updip) of the the present present outcrop outcrop belt belt and and the the volcanics volcanics originally originally thickened in that direction. direction. If that interpretation interpretationis is correct, correctDthere there must musthave havebeen been aa rapid rapid change change in in depocenters at the outset outset of of volcanism volcanism because because most most paleocurrent paleocurrent directions directionsin inthe theBessemer Bessemer are are northerly Morey, 1982). (Ojakangas and Morey, 1982). northerly (Ojakangas Stop 2.--Basalt 2.--Basalt flows flowsofofSiemens SiemensCreek CreekFormation Formation Roadcuts along along Powderhorn Road Road(fig. (fig.41, 4), which which follows the the valley valley of of Powder PowderMill MillCreek, Creek, provide a convenient cross section of the Powder Mill Mill Group in its its type type area area as defined by by Hubbard Hubbard 975a). At exposed and and at at stop stop 33 (1975a). At stop stop 22typical typicalbasalt basaltflows flowsofofthe theSiemens SiemensCreek Creek Formation Formation are exposed Creek Formation Formationcan canbe beseen. seen. Steeply Steeply north-dipping north-dipping basalt basalt flows flows of the the Kallander Creek the Siemens Siemens Creek Formationare arewell wellexposed exposedininoutcrops outcropson onthe thehill hillwest westof of the the road road and and in in low low roadcuts. The Creek Formation The meters or less thick. Commonly these these fine-grained flows have have basalt flows flows are thin, thin, typically a few meters thick. Commonly amygdaloidal and and rubbly rubbly flow flow tops, seen locally locally at at the the base base of of some flows. amygdaloidal topsl and and pipe vesicles can be seen show patchy alteration to to chlorite and and have have abundant abundantchlorite chloritein inthe the matrix, matrix. This The basalts show This relarelatively high high degree of metamorphism is typical of basalts basalts of the the Siemens Siemens Creek Formation and is one distinction between distinction betweenthem them and and less less metamorphosed metamorphosed basalt basalt of the the overlying overlyingPortage PortageLake Lake Volcanics. Volcanics. Some flows are porphyritic Some flows porphyritic with withsmall smallplagioclase plagioclase phenocrytsts. Stop 3.--Kallander Creek Creek Formation Formation About 2 km km north north of of stop stop2, 2, aaroad roadimprovement improvementproject projecthas has produced produced freshly freshly blasted blastedoutoutCreekFormation. Formation. Because Becauseall allflows flowsare aredipping dippingnearly nearly90 90° in in this this area, the crops in the Kallander Kallander Creek area, the passes up upthrough through about about 22 km km of of section, section, an impressive impressive pile pile of of basaltl basalt, yet yet this drive between stops passes erupted into into the the deepest deepestparts partsofofthe therift. rift. The is only 10% of the total thickness of basalt erupted The flows flows in in the Kallander Creek Formation Formationare arebasaltic basalticto toandesiticD andesitic,more morerarely rarelyrhyoliticl rhyolitic, and and generally generally aa few few Kallander Creek Creekisismore morefelsic felsicthan thanthe the Siemens SiemensCreek. Creek. At this this stop stop the the meters thick. Overall, Overall, the Kallander Creek flows include chloritized chloritized amygdular basalt, basalt, fine-grained fine-grained basalt basalt with with plagioclase phenocryts exposed flows stone"),non-porphyritic non-porphyriticandesite, andesite,andesite andesitewith with pla~ioclase plagioclasephenocrysts, phenocrysts, and tuff tuff (locally a TMdaisy -daisy stonew), breccias containing containing both both basalt basalt and andandesite andesitefragments. fragments. Although Although rhyolite occurs higher in the breccias formation, none flows are none is is exposed exposed here. The TheKallander Kallander Creek Creek flows are generally generally less metamorphosed than the Siemens Siemens Creek flows. 83 �asv c'RokFor 48N. 47N. Falls ° fPuritSch Figure4. 4. Location setting foi for stops 1, 2, and Figure Location and geologic setting and 3. 3. Geology Geologygeneralized generalized and modified from Hubbard (1975a). 975a). Note scale between between the the two two adjacent Note change change in scale quadrangles. quadrangles. 84 �TABLE 1: 1: CHEMICAL CHEMICALANALYSES ANALYSESFOR FORSOME SOMEVOLCANIC VOLCANICUNITS UNITSININTHE THEKEWEENAWAN KEWEENAWANSUPERGROUP SUPERGROUP TABLE ELEMENT ELEMENT 1 2 N=2 N=4 Si02 Si02 52.02 Ti02 Ti02 1.75 14.32 1.85 9.42 0.17 6.93 8.18 3.57 1.57 0.23 A1203 A1203 Fe203 Fe203 FeO FeO MnO Ph0 MgO MgO Cao CeO Na20 Na20 K20 K20 P205 SUM SUM Cr Cr Ni Ni Nb Nb Rb Rb Sr Sr Zr Y V La La Sm Sm Yb Hf Ta Ta Th Th 3 N=5 77.23 0.12 12.91 0.60 1.19 0.03 0.30 1.43 1.57 4.62 0.01 99.99 100.00 233 2.9 4 N=1 48.66 1.69 16.51 1.83 10.38 0.18 7.37 10.59 2.29 0.32 0.18 100.00 71.79 0.42 12.84 1.74 3.49 0.10 1.18 0.23 0.76 7.38 0.06 99.99 188 204 2.5 50 212 8 7 470 123 18 281 16 19.0 4.9 1.67 3.12 1.04 1.94 112 76.9 12.9 10.00 10.24 3.92 39.48 252 100 23 32 219 53 1130 103 273 27.3 94 20 35 1 11.6 4.0 2.08 2.65 0.58 1.04 <2 10.4 22.2 2.96 35.70 5 6 N=2 N=1 1 47.60 2.26 17.03 2.04 12.30 0.19 7.60 5.11 4.09 1.26 0.53 100.00 168 95.5 17 1.70 16.99 1.65 10.90 0.22 8.16 6.50 2.86 2.53 0.20 100.00 159 188 8.7 61 37.2 7.1 3.55 4.475 0.86 2.63 1 Average analysis of of Siemens Siemens Creek Creek basalts basalts Average analysis analysis of of rhyolite Average rhyolite from quarry quarry near near town town of of Bergland Bergland Average Average analysis of basalts basalts of of the thePortage PortageLake LakeVolcanics Volcanicsnorth northofofcrossroads crossroadsatatMerriweather Merriweathernear nearBergland Bergland Analysis Analysis of rhyolite rhyolite at at quarry quarry near near White White Pine Pinemine mine Average Average analysis of basalts basalts at at Lake Lake of of the theClouds Cloudsoverlook overlookininPorcupine PorcupineMountains MountainsWilderness Wilderness State StatePark Park analysis of basalts 6 Average Average analysis basalts of the the Portage Portage Lake LakeVolcanics Vofcanics on on Keweenaw Keweenaw Peninsula Peninsula 6 7 Average analysis analysis of of basalts basalts from from the thePorcupine PorcupineVolcanics Volcanics 7 Average 33 44 5 5 48.29 490 1 2 2 7 N=8 126 26 11.9 4.0 2.12 2.65 0.59 1.20 50.68 2.47 14.36 2.11 11.94 0.23 5.32 6.46 2.70 2.89 0.86 100.00 64 42 18 62 407 294 56 55.7 11.1 5.11 7.10 1.32 5.94 �Stop4.--Portage 4.--PortageLake LakeVolcanics Volcanics Stop This Thisstop stopillustrates illustratesrhyolite, rhyolite,basalt, basalt,and andinterfiow interflowsandstone sandstoneofofthe thePortage PortageLake LakeVolcanics. Volcanics. Exposures and quarry quarry along alongthe thenorth north side sideof of Michigan MichiganHighway Highway 28 28 (fig. (fig. 5). The The Exposures are in a roadcut and prominent expression prominentsouth-facing south-facingscarp scarpthat thatruns runsparallel paralleltotothe thehighway highwayusually usuallyisisthe thegeomorphic geomorphic expression ofofthe the Portage Lake theKeweenaw Keweenawfault, fault,but buthere herethe thefault faultlies liesmore morethan thana amile miletotothe thesouth, south,and and the Portage Lake Volcanics underlie the lowlands surrounding the north end of Lake Gogebic as well as the highlands Volcanics underlie the lowlands surrounding the north end of Lake Gogebic as well as the highlands northofofthe thescarp. scarp. north The are a thick thick pile of dominantly basaltic, subaerial flows, flows, with ThePortage Portage Lake Lake Volcanics are with lesser lesser rhyolites rhyolites and and interflow interflow sedimentary sedimentary rocks. At Atthis thislocality, locality,however, however,rhyolite rhyoliteisisthe thedominant dominant rock rocktype, type,although althoughgood goodexamples examplesof ofbasalt basaltare are in inthe theroadcut. roadcut.Another Anotherunusual unusualfeature featurehere hereisisthe the local localdevelopment development of of pillows pillowsalong along the the toe toe of of aaflow flowwhere whereititapparently apparentlyentered enteredaabody bodyof ofwater waterinin whichsandstone sandstonewas wasbeing beingdeposited. deposited. which The Thestratigraphy stratigraphy in inthe the quarry quarryarea area consists of an ophitic ophitic basalt basalt flow flow overlain overlain by by aa thin thin interinterflowsandstone sandstonetotosiltstone siltstonewhich whichininturn turnisisoverlain overlainby byan anamygdaloidal amygdaloidalbasalt. basalt.The Theamygdaloidal amygdaloidal flow basalt basaltexhibits exhibitswell welldeveloped developedpipe pipevesicles vesiclesatatroad roadlevel. level. Rhyolite Rhyoliteoverlies overliesthe theamygdaloidal amygdaloidalbasalt basalt and andisiswell wellexposed exposedin inthe the quarry quarry floor floor and and walls walls and and is is overlain overlain by by ophitic ophitic basalt basalt flows flows on onthe the hillside compositionally to to low Ti02 hillsideabove above the quarry. quarry. The Thebasalts basaltshere here are are identical compositionally Ti02basalts basaltson on 1). KeweenawPeninsula Peninsula(table (table1). Keweenaw ItItisisnot notclear clearwhether whetherthe therhyolite rhyoliteisisaasingle singleshallow shallow intrusive intrusivebody bodyor oraaseries series of of flows. flows. ItIt contains containsseveral severallenticular lenticular masses masses of of basalt basalt and and an an unusual unusual greenish sandstone. Are Arethese thesexenoliths xenoliths ininan anintrusion intrusionor ordiscontinuous discontinuousinterbeds? interbeds?Several Severalfeatures featuressuggestive suggestiveof of extrusive extrusiveorigin origincan canbe be Foldsare arepresent presentnear near the the contact contactof of the therhyolite rhyolitewith withthe theunderlying underlyingbasalt. basalt. In Inthe theupper upper noted. noted. Folds part partof ofthe thequarry, quarry, the therhyolite rhyoliteshows showswell-developed well-developed columnar columnar jointing, some some of of which whichisisbent, bent, following followingaaramp rampstructure structureininthe therhyolite. rhyolite.The Thepossibility possibilityofofaaseries seriesofofflows flowsisisenhanced enhancedby bythe the distribution distributionof ofspherulitic spheruliticrhyolite. rhyolite.Spherulites Spherulitesare arecommon commonthroughout throughoutthe thequarry quarrybut butare areconcenconcentrated tratednear nearthe the base base of of the the rhyolite, rhyolite, near near the the contact contactwith withaasedimentary sedimentary lens, lens, and and near near the the top top of of the thequarry. quarry.More Moremassive massiveororstony stonyrhyolite rhyoliteoccurs occursbetween betweenthe thespherulitic spheruliticzones. zones. Alteration Alterationrelated relatedto tocopper coppermineralization mineralizationis is widespread widespread in in the the quarry. quarry. Epidote EpidoteisisdissemidissemiSecondarycopper copperminerals mineralsare are nated anunusual unusualgreenish greenishcolor. color.Secondary natedin inmuch muchof of the therhyolite, rhyolite,giving givingititan abundant on on joint joint surfaces. surfaces. abundant Stop Stop5.-Porcupine 5.-Porcupine Volcanics: Volcanics:Rhyolite RhyoliteatatSummit SummitPeak Peak Summit one of of the highest Summit Peak Peak is the highest highest point point in in Porcupine Porcupine Mountains Park and one highest points points in in the the state. state. The Theobservation observationtower toweratatthe thesummit summitprovides providesaapanoramic panoramic view of of the the field field trip triparea area (fig. highlands are 6).ToTothe thesouth, south,the the highlands areunderlain underlainbybythe thePortage PortageLake LakeVolcanics Volcanicsand andPorcupine Porcupine (fig.6). Volcanics Volcanics along along the the main main monocline monocline of volcanic volcanic rocks rocks of of the the Keweenawan KeweenawanSupergroup. Supergroup. The The lowlands OrontoGroup Groupininthe theeasteastlowlandsimmediately immediatelyto to the thesoutheast southeastare are underlain underlain by by rocks rocks of of the the Oronto plunging plunging Iron IronRiver River syncline. syncline. Looking Lookingeast eastalong alongstrike, strike, the thesmelter smelteratatWhite WhitePine Pinecan canbe beseen seenin inthe the distance. distance. To Tothe thenorth, north,the theinterior interiorofofthe thepark parkextends extendsover overthe therugged ruggedtopography topography in in the the foreforeground ground to to Lake Lake Superior Superior in in the the distance. distance. The Theinterior interiorofofthe thepark parkisismaintained maintainedas asaawilderness wildernessarea area contains the the largest largest stand stand of of virgin virgintimber timberin inthe thestate. state. and access access is is only only by byhiking. hiking. ItItcontains and Most Mostof ofthe thepark parkinterior interiorisisunderlain underlainby byaathick thickunit unitofofrhyolite rhyolitecomposed composedofofaaseries seriesofof flows flowsand anddomes domestypified typifiedby bythe therocks rocksseen seenat atSummit Summitpeak. peak. Good Goodexposures exposuresof ofcoarse coarserhyolite rhyolite breccia the trail leading to to the summit and at at the overlook platform west of breccia are along the of the the summit. summit. Thisbreccia brecciaisisprobably probablythe thecarapace carapaceof of aarhyolite rhyolitedome. dome. This Excellent Excellent exposures exposures of typical typical intermediate intermediateand and felsic felsic units unitsofofthe thePorcupine PorcupineVolcanics Volcanicscan can be seen seen on the north north side side of the the hill hill (549 (549m melevation) elevation)near near the center of Sec. Sec. 31. 31. Take Takethe theBeaver Beaver be Creek Creek Trail about 0.5 mi mi from from the the Summit Summit Peak Peak parking lot. The Theunits unitsdip dipto tothe thesouth southand andinclude, include, in in stratigraphic stratigraphic order, order, sparse sparse outcrops outcrops of of intermediate intermediateto to mafic maficrocks rocksininthe thecreek creekbed, bed,overlain overlainby byaa vesicular vesicular siliceous siliceous andesite, andesite, which is is in in turn turn overlain overlain by by aacoarse coarse rhyolite rhyolite breccia breccia or or debris debris flow. flow. The in size size from from nearly nearly aa meter meterto to less lessthan than 11 cm. cm. The The breccia breccia is is The breccia breccia contains clasts ranging in clast clast supported supported and and some some clasts clasts are are subrounded. Overlying Overlyingthe thebreccia brecciaisisaamedium-grained medium-grainedbasalt basalt flow. flow. Capping Cappingthe thehill, hill,and andoverlying overlyingthe thebasalt, basalt, isisan anaphanitic aphanitic massive massive rhyolite that is is microspherulitic. microspherulitic. 86 �—H-- -j I, /1 —. SCALE1:25 1:25000 OW SCALE I 0 KILOM€TE 1 2 KILOMETERS 1 1000 1000 1 A — - 1 7 1000 + - - A 00 1000 1000 00 - .5.5 2000 .?OM- - METERS METERS 4000 3000 3000----4000 - - 2000 2000 1000 1000 00 1 MILES MILES -5000 5000 - 6000 6000 1000 7004 8000 8000 9000 WOO 10000 10!00 itt: I FEET CONTOUR INTERVAL INTERVAL55METERS METERS CONTOUR Figure 5. Location Locationand andgeologic geologic setting setting of ofstop stop4. 4.Geology Geologygeneralized generalizedfrom fromunpublished unpublished Figure compilation by by Walter Walter White. White. compilation 87 �88 (unpublished). mapping cooperative Survey Geological Corp./Michigan Range Copper from generalized Geology marked. well are all but shown, not are peak Summit on tower and platform observation and improvements, trail and road Recent 5. stop of setting geologic and Location 6. Figure METERS 5 INTERVAL CONTOUR FEET 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 Oa0 0 MILES 2000 1001) METERS 0 1 KILOMETERS 0 51N. R.44W. 1000 .5 1 �Stop Stop 6.--Porcupine Volcanics: Rhyolite Rhyolite quarry quarry near near White White Pine Pine here are are part part of of a small rhyolite body near the top The rocks exposed here top of of the thePorcupine Porcupine Volcanics. The beyond the the hill hill into into which the quarry is Volcanics. The body body probably probably does not extend much beyond is cut cut (fig. 7). The Thequarry quarryprovides providesaacross crosssection sectionthrough throughpart partof ofaasubaerial subaerialagglutinate agglutinatedeposit. deposit. form at vents by spatter of erupting magma and and buildup buildup of of mounds of of hotl hot, Agglutinate deposits form viscous material. material. The mound of erupted material materialeventually eventuallyflows flowsoutward outward under underits its own own weight weight resulting in large large flow flow folds such as seen seen in in this this quarry. quarry. The The near-vent near-vent nature of this deposit deposit is is deduced from the the presence presenceof of lithic lithic fragments fragments within within the the rhyolite, rhyolite, large flow flow folds and deduced from and stratification stratification of rhyolite rhyolite (light (light and dark units). At Atthe theedges edges of of agglutinate agglutinate deposits, deposits, flowage typically has has homogenized the the magma and and such such stratification stratification and and folding foldingare are generally generally not notpreserved. preserved. feldspar phenocrystsl phenocrysts, which which are are typically typically aligned parallel to to the The rhyolite here contains feldspar It is enriched substantially in such incompatible stratification incompatible trace trace elements elements as Zr, Ba, Ba, stratification and and foliation. It Hf, Hfl and and the the light light rare rareearth earth elements elements compared to the the rhyolite rhyolitein inthe thePortage PortageLake Lake Volcanics Volcanics near near Bergland (table 1). 1). These and sources sources for for the the two two Bergland (table These differences suggest different petrogenesis and rhyolites in spite of their physical physical proximity. proximity. Stop 7.--Basalt 7.--Basalt flows within withinthe theCopper CopperHarbor HarborConglomerate Conglomerate(Lake (Lake of the the Clouds Clouds overlook) overlook) Along the road road leading leading to Lake Lake of the the Clouds Clouds overlook overlook are several exposures of conglomerconglomerate of the Copper Conglomerate. To the north Copper Harbor Conglomerate. north is is aa good good view view of of Lake LakeSuperior Superior and and the the lowlowlands underlain underlain by by sedimentary sedimentaryrocks rocksofofthe theOronto OrontoGroup. Group. From From the the overlook overlook parking parking lotl lot, aa short short hike leads to to the overlook and a spectacular view of Lake Lake of the the Clouds Clouds and and the the Porcupine Porcupine MounMountains Wilderness State State Park. Park. The overlook is along the south escarpment of of a high ridge supported by a series of northdipping lava flows flows within the Copper Harbor Conglomerate (fig. 88). ) . The The low low area area south south of of the the ridge, ridgel within the Copper Conglomerate (fig. including Lake Lake of of the the Cloudsl Clouds, is underlain underlain by by sandstone sandstoneand andsiltstone siltstone and andaafew few basalt basalt flows flows which which Conglomerate. The higher regions farther farther south are are constitute the lower lower part part of of the the Copper Copper Harbor Conglomerate. by volcanic volcanic rocksl rocks, mostly rhyolite underlain by rhyolite of the the Porcupine Porcupine Volcanics. Toward surface shows shows a series series of of thin areal a large glaciated surface Toward the the east east end of the the overlook overlook area, basalt flowsl flows, which average a few meters thick. Individual flows can be readily identified by which average few can be identified by chilled chilled vesicular bases, in places containing inclusions of older flows, and by rubbly or vesicular tops. vesicular basesl in places containing inclusions of older flows, and by Abundant epidote alteration and and vesicle vesiclefillings fillingsalso alsoimpart impartaadistinctive distinctivegreenish greenishcast castto toflow flow margins. Hubbard the flows flows in as mostly andesite with with minor (1975b) described the in the Copper Copper Harbor as minor margins. Hubbard (1 basalt, but chemical analyses of two samples from this locality (table 1) indicate that they are basalt basaltl chemical analyses of two samples from this locality (table 1) indicate that similar to an an average basalt from the the Porcupine Porcupine Volcanics. Compared Comparedto toPortage PortageLake LakeVolcanics, Volcanics, these basalts are enriched in incompatible incompatible trace trace elements. Stop 8.--Upper part part of ofCopper CopperHarbor HarborConglomerate Conglomerateat atUnion UnionBay BayCampground Campground Good exposures of reddish sandstone containing containing thin conglomerate conglomerate beds are abundant along Superior at at this this locality locality (see (seefig. fig. 91. 9). The is noted noted for for The Copper Copper Harbor Conglomerate Conglomerate is the shore of Lake Superior volcanogenicconglomerates, conglomerates,which whichform formmost mostof of the the lower lower part part of the section coarse volcanogenic section throughout throughout much of its outcrop finer grained grained sandstones. sandstones. But, outcrop belt belt and which grade up into finer Butl north of the the Porcupine Mountains Mountains there there is is aa different different facies faciesrelationship. relationship. The lower part of the the formation formation isis lava flows; flows; conglomerate is very very subordinate. subordinate. These mostly sandstone, sandstonel siltstone and lava conglomerate is These rocks underlie south of the highway. The the high hills immediately south Thecoarse coarse conglomerate conglomerate facies is less abundant and is higher in the section. The Theexposures exposureshere here at at Union Union Bay Bay are near the base of the upper upper unit unit are probably probably about about 1,000 1,000 m above the the base base of of the the formation. formation. The and are The sandstones sandstones at at Union Union Bay Bay dip dip 10-20° to 10-20 to the the north. north.They Theyare arevolcanogenic volcanogenicand and quartz-poor. quartz-poor. They Theyshow showexcellent excellentexamples examples of of generally indicating indicating aa northeastward northeastwardcurrent currentvectorl vector, and and aa variety variety of of other trough cross bedding, bedding, generally sedimentary features features including including desiccation cracksl cracks, rip-up rip-up clasts, clasts, oscillation and current ripples, ripplesl and sedimentary swash marks. marks. Conglomerate north north of of the Porcupine The exposures of Copper Harbor Conglomerate Porcupine Mountains Mountains are are the the from the the source source highlands highlandsto tothe thesouth southof of any any part part of of the the unit unit on land. land. The farthest removed from The compared to to exposures exposuresfarther farther south south probably relative scarcity of thick units units of of coarse coarse conglomerate conglomerate compared 89 89 �ft 41 W. \/ - 2 /4 I /— ° -- 0 ' -- ( '— —---- _\__ \— Cdn9$,Wc3i:T2 k1 > 1. 50 N. / r: -- i 1 1 OCO 0 - w 2003 , - - 5 - 5 1 1MILE MILE 0 1000 H U H 1 SCALE 1:24000 1:24000 SCALE , w 3000 I 4000 —* — I - 00 5030 FEET 7000 6000 FEET I 1 KILOMETER 1 KILOMETER 4 CONTOUR CONTOURINTERVAL INTERVAL20 20FEET FEET Figure 7. 7.Location Locationand andgeologic geologicsetting settingofofstop stop6.6.Geology Geology generalizedfrom fromJohnson Johnsonand and Figure generalized White (1 969). White (1969). 90 �_______ R. 44 W. 51 N. KILOMETERS KILOMETERS 1 1 [ - - - H - MILES1 1 MILES .5 .5 .5.5 H 0 H 0 W 0 1 2 1I 0 2 3 H— k 1 1 SCALE 1:25000 1:25 000 SCALE 1 1CENTIMETER (2ENllMElE.RON ONTHE T I EMAP MAPREPIIESENTS REPRESENTS250 2%METERS MEIERSON ONTHE THEGROUND GROUND CONTOURINTERVAL INTERVAL 55METERS METERS CONTOUR Figure8.8.Location Location andgeologic geologicsetting settingofofstop stop7.7 Geology . Geologygeneralized generalizedfrom fromHubbard Hubbard Figure and (1 975b). (1 975b). 91 �R. 43 W. 51N. SCALE 1:24 000 — .5 — KILOMETERS 1 2 METERS 1000 2000 0 1000 0 .5 1 MILES 1000 0 1000 2000 3000 5000 4000 6000 7000 8000 9000 10000 FEET CONTOUR INTERVAL 5 METERS Figure9.9.Location Location andgeologic geologicsetting settingof ofstop stop8.8.Geology Geologygeneralized generalizedfrom fromHubbard Hubbard and Figure (1 975b). (1 975b). 92 �reflects the distal nature of these rocks and may may be be aa good good representative representativeof of much much of of the the Copper Copper Harbor beneath Lake Lake Superior. Superior. The unit here here shows shows aa crude coarsening-upward coarsening-upward trend as as opposed proximal parts parts of of the the unit. unit. This to the fining-upward trend typical of the more proximal This relationship relationship is is consistent with with northward northwardprograding progradingalluvial alluvialplain plain deposition. deposition. Several large large boulders boulders are are distributed distributed along the the beach and are are composed composed of conglomerate conglomerate typical of the lower lower part part of of the the formation formationelsewhere. elsewhere. These These conglomerates conglomerates contain contain almost excluexcluKeweenawan Supergroup Supergroupvolcanic volcanicrocks rockstypes typescommon commonininthe theregion. region. An An interestsively clasts of Keweenawan boulders. Although ing question is the source of these boulders. Althoughthe theCopper Copper Harbor Harbor does does contain contain some some conglomerate beds of this aspect aspect nearby, nearby, none none of of the thestreams streamsentering enteringLake LakeSuperior Superiornear nearhere here seem capable capableof of transporting transporting such such large largeboulders. boulders. Most have low low gradients, seem gradients, especially especially near the lakeshore, and and the the streambeds streambedsdo donot notcontain containsuch suchlarge largeboulders. boulders. No outcrops outcrops of coarse conglomlakeshore, erate would be expected nearby to the north north beneath beneath the lake; lake; so so ifif the theboulders bouldersare areglacial glacial erratics, erratics, they must perhaps from from the vicinity of must have have been transported for a long distance, distance, perhaps of Isle Isle Royale. Royale. Stop 9.--Nonesuch Shale Shale at at Bonanza Bonanza Falls Falls The most most complete exposure of the Nonesuch Nonesuch Shale in the region is along the Big Big Iron Iron River River BonanzaFalls, Falls,although althoughaccess accesstotoparts partsofofititisisdifficult difficult and and dangerous dangerousat at times times of of high water near Bonanza (see fig. fig. 10). 10). The TheNonesuch Nonesuchisisexposed exposed nearly nearly continuously in in aa gently gently southeast-dipping southeast-dipping section section Fallsto to the the sharp sharp bend bendin inthe the river river near nearthe the northeast northeast corner corner of of from just upstream upstream of Bonanza Bonanza Falls (1991) section 13. AAdetailed detailedmeasured measuredsection section is is presented presented by Suszek Suszek (1 991 ) and fig. fig. 11 11isisgeneralized generalized from that section. The Theexposed exposed rocks total 226 226 m m of of section, section, which which includes includes nearly nearly all of the Nonesuch, although neither the the upper nor lower contact Nonesuch, contact is is directly directlyexposed. exposed. The Nonesuch Shale Shale is is distinguished distinguished from from other other sedimentary units of the the Keweenawan Keweenawan by the the predominance of of gray, gray, green or or black, black, fine-grained fine-grained sediments. sediments. The Supergroup by TheBig BigIron IronRiver River predominanceof ofsiltstones siltstones and andfine finesandstones sandstonesover overtrue trueshales. shales. Many rocks show section has aa predominance trough cross asymmetrical ripples, ripples, rib rib and and furrow furrow structures, and cross bedding, symmetrical and asymmetrical and parting parting lineations. The shales, which which are most abundant lower in lineations. The finer-grained finer-grained rocks rocks include include well-laminated shales, in the section. The shaleyunits unitscommonly commonlyhave haveball balland and pillow pillowstructures structuresand andcalcareous calcareousconcretions. concretions. Theshaley The Nonesuch displays coarsening-upward at scales ranging from aa few coarsening-upward sequences at few meters meters to to the the entire entire thickness thickness of of the the unit. unit.On Ona asmaller smallerscale, scale,normally normallygraded gradedsequences sequences are are common common in in units from a few centimeters centimeters to aa few few meters meters thick. thick. concentrations of In the lower 10 10m m of of the thesection sectioncopper copper mineralization mineralizationcan can be be seen as concentrations chalcocite, bornite bedding planes. planes. The mineralization is is cogenetic cogenetic with the bornite and malachite along bedding the copper mineralization mineralizationat atthe the White White Pine PineMine Minewhere wherethe thedowndip downdip extension extension of of this unit major copper unit is is mined just just to to the the south south and and east. east. A good good exposure exposure of of the the mineralized mineralized base of the Nonesuch Nonesuch Shale and the top of of the theCopper Copper Harbor Conglomerate Conglomerate is is along alongthe the Little Little Iron Iron River River near nearthe thecenter centerof of the the SW SW 114, 1/4, Sec. 13, 13, but but It is an easy walk requires aa walk walk of about 1 mi south from Highway Highway 107. 107. It walk along along an an unmaintained unmaintained trail on the east bank of the river river for those those who who can can spend spend more time in the area. Remains Remains of of early early mining efforts for there, as as well well as as "ore" "ore" specimens from from old dumps. for native native silver silver can can be seen there, White Pine Mine Mine White The trip will will not not visit visitthe theWhite WhitePine Pine Mine; Mine; but butbecause because of the the importance importance of of this thisorebody, orebody, the following following brief briefsummary summary is is provided. provided. copper and andsilver silverfrom from aa very very large large strataform strataform orebody in the base of White Pine recovers copper Shale and and in in places places from from the upper few meters the Nonesuch Shale meters of of the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. Excellent summaries summariesof of the the geology geology and and origin origin of of the the orebody orebody are are provided provided by by White and Wright (1966), and others others(1 (1968), White (1 (1971), and Brown Brown(1 (1971). mostly of of (1966), Ensign Ensign and 9681, White 971 1, and 971 1. Ore, Ore, composed composed mostly copper, grades about about 1 .1%%Cu Cuand and99glt g/t Ag Ag over a mining height height chalcocite and lesser native copper, 1.1 typically about 5 m. m. Some Somebeds bedswithin withinthat thatinterval intervalconsistently consistentlycontain containgreater greater than than 3% 3%Cu. Cu. Reservesare areabout about200,000,000 200,000,000 tt of extractable ore. ore. Mining Mining of of the the gently gentlydipping dippingorebody orebody is is by by Reserves and pillar pillar method. method. The mine workings underlie about about 35 35 km2 km2 of of the low country room and country south south and and town of east of the town of White WhitePine. Pine. 93 �1 w - 1 7 4 - - i I 00 55 I + 1MILE MILE 00 47 7 I KILOMETER ; KILOMETER - CONTOUR CONTOUR INTERVAL INTERVAL 20 20FEET FEET Figure 10. 10. Location Locationand andgeologic geologicsetting settingof ofstop stop9.9.Geology Geologygeneralized generalizedfrom fromCopper Copper Figure Range Corp./Michigan CorpJMichiganGeological GeologicalSurvey Surveycooperative cooperativemapping mapping(unpublished). (unpublished). Range 94 �STRATIGRAPHIC SECTION SECTION OF NONESUCH NONESUCH SHALE SHALE AT AT BONANZA BONANZA FALLS FALLS STRATICRAPHIC Generalized from from Susiek Suszek (1991) (1991) Sandstone, Sandstone, siltstone, siltstone.rnudstone. mudstone. Fineto Fine— to coarse—grai ned. coarsening-upward coarsening—upward trend. coarse-grained, trend. 200— Reddish-brown increase in in top top 50 rn Reddish—brown units increase m of unit. unit. 8 3 SiItstone, sandstone. muastone. mustone. Fine— Siltstone. sandstone. Fine- to to medi.rn—grained, general general coarsening mediim-grained, ccarsening upward upward trend. trend Sndstcne. Sandstone, shale. shale. Coarse- to to fine— fine- grained. grained. Coarse— Fine— tornediun—grained. Sandstone. shale. Sandstone, shale. Fineto mediim-grained. CContains o n t a i n s some some red—brown red-brown units. units. oc Shale, sandstone. sandstone, mudstone. mudstone. Black B l a c k to to dark dark gray. gray. Lominites. Lcminites. trough trough cross c r o s s bedS, beds. and end undulatory undulatory bedding. Chioritic and henatitic Chloritic hematitic beds and and lenses. Calcareous concretions. lenses. concretions. Sandstone, siltstone. siltstone. mudstone. mudstone. Light to to dcrk dark gray wwith gray i t h some s o m e beds b e d s of of red red hematitic hematitic mudstone mudstone and siltstone. Fine—grained. Contains siltstone. Fine-grained. Contains carbonate lominite iominita units, ball boll and pillow pillow structures, and colcareous concretjons. structures, calcareous concretions. Fissil. shcie, Fissile shale. mmudstone, u d s t o n e , siltstone. siltstone. Block to Black to laninites with w i t h interbeds interbeds dark gray. Carbonate Carbonate lanintes of siltstone siltstone and and sandstone. sandstone. SSiltstone, i l t s t o n e , sandstone, sandstone. shale. shale. Fine—grained. Fine-grained. Dessication Dessication cracks, cracks, ball ball and pillow structures, floating floating clasts. clasts. Figure Measuredstratigraphic stratigraphicsection sectionof ofNonesuch Nonesuch Shale Shale along Big Iron River near Figure 11. Measured Falls, generalized from Suszek 991).1. Bonanza Falls, Suszek (1 (1991 95 �Copper Copper was introduced introduced to to the the Nonesuch Nonesuch Shale Shale mostly mostly during during early early diagenesis, diagenesis, probably probably by by upward upwardcirculating circulatingconnate connate water water which whichdissolved dissolvedcopper copper from from the the underlying underlyingredbeds. redbeds. Chalcocite, Chalcocite, largely of diagenetic diagenetic pyrite. pyrite. AAlater largely of of submicroscopic submicroscopic size, size, formed by the replacement of laterphase phaseofof others (in copper mineralization, documented by Mauk and others (1989) and Mauk and copper mineralization, Mauk (1989) and Mauk and others (inpress), press), introduced introduced native native copper, mostly mostly in in structurally structurallydisturbed disturbed zones. zones. This Thissecond secondstage stagemineralization mineralizationisis probably probably cogenetic with withthe theclassic classicnative nativecopper coppermineralization mineralizationof of the theKeweenawan KeweenawanSupergroup Supergroup basalts. basalts. Stop O.--Nonesuch Shale and Stop110.-Nonesuch and Freda Freda Sandstone Sandstoneat at Presque PresqueIsle IsleRiver River The The upper upper portion portionof ofthe theNonesuch NonesuchShale Shaleand andthe thebase baseof ofthe theFreda FredaSandstone Sandstoneare arewell well exposed exposed in in the the gorge gorge of of the thePresque Presque Isle Isle River River near its mouth mouth and and along the shore shore of of Lake Lake Superior Superior west west of of the theriver river(fig. (fig.12). 12).Continuous Continuousexposures exposuresalong alongthe thepicturesque picturesquegorge gorge of of the theriver riverextend extend from fromjust justupstream upstreamof ofNawadaha NawadahaFalls Falls to to the the lakeshore. lakeshore. Exposures Exposures continue continue in in bluffs bluffsalong alongthe the lakeshore for about about half half aamile milewest westof ofthe theriver rivermouth. mouth. In the the interest of of time, time, we will limit limit our our lakeshore for examination near the the river river mouth mouth and and aa short short distance to to the west along examination to exposures near along the the shore. shore. This This requires requires a round trip trip hike hike of of nearly nearly aa mile, mostly mostly on on well-maintained well-maintained trails trails and and stairways. stairways. The The rocks rocks exposed exposed here here are on the northeast northeast limb limb of of the the Presque Presque Isle Isle syncllne, syncline, aa gentle gentle 10ÂSW. SW.The TheNonesuch NonesuchShale Shalehere hereisis northwest-plungingfold. fold. Dips Dips range range from nearly nearly flat to to about about 100 northwest-plunging very for stop 9 on the Big Iron River Riverabout about30 30 km km to to the the east. east. The very similar similar to that described described for The lower lower part with copper part of of the thesection sectionin inthis thisarea area (not (notexposed) exposed) is is also also strongly strongly mineralized mineralized with copper and and contains contains aa fine-scale with the stratigraphy at the white fine-scale stratigraphy directly correlatable correlatable with White Pine Pine mine, mine, indicating indicating that thatsedimentary sedimentary conditions conditions were were very very uniform uniformover overthe theentire entireregion regionsurrounding surroundingthe the Porcupine Porcupine Mountains Mountainsduring duringNonesuch Nonesuchdeposition. deposition. The The upper upper part partof ofthe theNonesuch Nonesuchexposed exposedhere, here, as asdescribed describedin inmore moredetail detailby bySuszek Suszek (1991), consistsof offining-upward fining-upwardsequences sequencesand andlaminites laminitesinterbedded interbeddedwith withgraded gradedsandstones sandstonesand and (1991 1, consists siltstones. Most Mostrocks rocksare aredark darkgray graywith withaafew fewreddish reddishlenses lensesand and beds. beds. The upward to the through a zone in which The Nonesuch Nonesuch grades upward the Freda Freda Sandstone through which dark dark gray gray laminated siltstone and sandy mudstone mudstone is interbedded laminated and small-scale cross-bedded siltstone interbedded with withmediummediumto to coarse-grained coarse-grained reddish brown sandstone. The The upper upper contact contact of of the theNonesuch Nonesuchisisplaced placedwhere where the the reddish reddishsandstone sandstonebecomes becomes dominant. dominant. .-- Stop FredaSandstone Sandstonealong alongPresque Presque Isle IsleRiver River Stop 11.-11 Freda This This stop, stop, near near the the axis axis of of the thePresque Presque Isle Isle syncline (fig. 12), 121, shows showsreddish reddishcross crossbedded bedded sandstone typical of the lower lower part part of of the the Freda Freda Sandstone. Sandstone. The The gently gently southwest southwest dipping dipping beds beds exposed here are are probably probably 100-200 100-200 m above the the base base of of the the formation and slightly slightly higher higher stratistratigraphically than those seen seen at at stop stop 10. They They are are mostly mostly lithic lithic sandstone sandstone and and are somewhat somewhat micaceous in places. The The Freda Freda marks the return return to to fluvial fluvial redbed redbed deposition deposition following followingthe thelacustrine lacustrine deposition of of the theunderlying underlyingNonesuch NonesuchShale. Shale. deposition The The Freda Freda is a very thick unit unit in in much much of of the therift riftininthe theLake LakeSuperior Superiorregion regionand andisisvolumetvolumetrically the dominant unit unit of of the the post-rift post-riftsedimentary sedimentary fill. fill. Along Along the the Montreal Montreal River, River, about 30 30 km km to to the is even even thicker the west, west, about about 4,000 4,000 mmofofFreda Fredaare are exposed. exposed. Seismic Seismic sections sections indicate that itit is beneath the the Lake. Lake. beneath The generally becomes becomesfiner-grained finer-grainedand andmore moremature matureupward. upward. Excellent The Freda Freda Sandstone generally Excellent exposures of the upper part of the seen near nearthe the mouth mouth of of the Montreal the Freda Freda can be seen Montreal River, in in bluffs bluffs along the the lakeshore. lakeshore. along Stop 12.-12.- Jacobsville JacobsvilleSandstone Sandstone Stop The roadcut along the west side of the road is a fairly typical exposure of the the conglomerate conglomerate found abundantly in the Jacobsville Sandstone Sandstone in in this this region. region. Although Although exposures exposures are rare, rare, west of of Lake Gogebic the Jacobsville appears to be dominated by by conglomerate conglomerateand and coarse coarse sandstone sandstonein in contrast it is to mature quartzose, quartzose, feldspathic, feldspathic, and lithic is a submature to contrast to to areas areas farther east where it arenite with with minor minor shale, shale, siltstone, siltstone, and and conglomerate conglomerate layers (Kalliokoski, 1982). 1982). At strikes east eastand anddips dips9O 9° to to the the north, north, but only about 500 m At this this stop stop the the conglomerate conglomerate strikes to the the north north ititdips dips steeply steeply to the south south (62°) (62O)as as aa result result of drag drag along the Keweenaw The to Keweenaw fault. fault. The 96 96 �17 45W. R. 1 /' 20/ 12 —- Pres ue ..v / -, — $ - 'c — V I' / 1' — — I I — 7 — Presgue Isi State Campgro ere • 'Manido — 1 / 224 — /i/ ,/" \ —. I I -I I 3O(, I - ._ :i 'I _.. 'Z1CS, \fl I '0 / J l'\ '% ( 1 1--\ \ -__ L_._jr _2Li II — - y:.__i . 25 — —— —— — ——— — r MILES 1 MILESI - - - - I * - - - .5 .5 - - .5 .5 I LJ . I ____ J KILOMETERS1 1 KILOMETERS : — /iS awadaht ails 0 / 1 —i. j'I / 29 / 'T50 J 0 0 1 2 1 0 0 —1 1I SCALE 1:25 1:25 000 000 SCALE CENTIMETER ON ON ThE THEMAP MAP REPRESENTS 250 METERS ON THE GROUND 11CENW4ETER REPRESENTS 250 METERS ON ThE GROUND CONTOUR INTERVAL INTERVAL 55 METERS METERS CONTOUR Locationand and geologic geologic setting setting of of stops stops 10 10and and 11. 1 1. Geology Geologygeneralized generalized from from Figure 12. 12. Location Figure Copper Range CorpJMichigan Geological Survey cooperative mapping (unpublished). Copper Range Corp./Michigan Geological Survey cooperative mapping (unpublished). 97 �R. 45 W. 405 21 : ' . r_) 2 Portage Lake V canics - fflN AWAL - KE 12Jacob Gravel Pit - T. 48 N. lie Sandston r 28 (H -- 410 NH ' H H . H) omaston 500 500 H +-- / 0 2000 2000 METERS METERS 1000 1000 00 H H H H 1000 0 1000 ! , 2000 2000 — 1 1 1 ! 4000 4000 ! 6000 6000 FEET FEET SCALE 1:25 1:25 000 000 11 CENTIMETER CENTIMETER ON THE THE MAP MAP REPRESENTS REPRESENTS 250 METERS METERS ON ThE THEGROUND GROUND CONTOUR CONTOUR INTERVAL INTERVAL 5 METERS METERS Figure Figure 13. 13. Location Locationand andgeologic geologic setting setting of of stop stop12. 1 2.Geology Geologygeneralized generalized from from Copper Copper Range CorpJMichigan Geological Survey cooperative mapping (unpublished). Range Corp./Michigan Geological Survey cooperative mapping (unpublished). 98 �is poorly poorly consolidated and and weathers weathers to to a material that superficially conglomerate is superficially resembles resembles glacial till or or outwash, which covers covers most of the roadcut. From From time to time parts parts of this this material material slump till away to of fresh conglomerate to expose expose less less weathered conglomerate, conglomerate, and small exposures of conglomerate are usually exposed in the drainage drainage ditch ditch beside beside the road. road. conglomerate is is clast-supported. clast-supported. Coarse sandy matrix matrix surrounds pebbles. pebbles. Where The conglomerate Coarse sandy Where weathered, it is generally unconsolidated unconsolidatedbut buton onfresher freshersurfaces surfacesisisfairly fairlywell wellcemented. cemented. Clay fills weathered, interstices and and coats coats all all grains, grains. It It is uncertain whether the clay is a product of diagenetic diagenetic most interstices mechanicalinfiltration infiltration resulting resulting from from seepage seepageof of muddy muddy water water through coarse cement or is an early mechanical alluvium. are subrounded subroundedto to well well rounded, rounded, range rangein in size sizefrom from 3-1 3-10 cm, and consist mostly Clasts are 0 cm, mostly of of iron-formation (63-77%) iron-formation (63-77%)and and quartzite quartzite (8-20%) (8-20%) derived derived from from Early Early Proterozoic Proterozoic rocks rocks such such as as those those Range. Small amounts of altered rhyolite (1-5%) (1-5%) are are believed believed to be be now exposed in the Gogebic Range. from Keweenawan Keweenawan Supergroup Supergrouprocks. rocks. Vein Vein quartz quartz (9-1 (9-10%), litholoderived from 0%), chert (1%), (1%I, and other lithologies (1 % % or or less) less) derived derivedfrom from Archean Archean rocks rocks are are minor. minor. Several Several other conglomerate conglomerate outcrops outcropsto to the west have have similar compositions, compositions, but outcrops outcrops less less than 2 km km to to the thesoutheast southeastalong alongJackson Jackson Creek (shown by X on the map) are dominated dominated by by vein vein quartz quartz (73-82%) (73-82%) with Creek (shown with lesser lesser amounts amounts of of (11-13%) and iron-formation iron-formation (9-1 (9-12%). suggest that that most most of of the quartzite (1 1-13%) and 2%). These These clast lithologies suggest area to to the the south had been been stripped stripped of of Keweenawan Keweenawanvolcanics volcanicsby bythe the time time of of Jacobsville source area deposition. Although Althoughthe thesurface surfaceconsisted consistedmostly mostlyofofEarly EarlyProterozoic Proterozoicsedimentary sedimentaryrocks, rocks, the the presence of of large quantities of vein vein quartz quartz pebbles pebbles indicates indicates at at least leastsome some drainages drainageswere wereeroded eroded Archean crystalline crystalline rocks. down into into Archean In a few places appear to to be imbricated imbricated but but otherwise bedding within within places clasts found in in place appear conglomerate units units is is not not apparent. apparent. Clay nearly all all clasts clasts so so that that the the conglomerate Clay and iron coatings cover nearly clasts are are broken brokenopen. open. Many various lithologic types are not apparent unless clasts Many clasts clasts have have aa highly highly like desert desert varnish varnish and and some somehave havedistinctly distinctly striated striated shiny surface or patina that looks looks remarkably like surfaces of of unknown origin. origin. AAfew fewclasts clastshave havebeen beenfound foundthat thathave haveshapes shapes and and surface textures surfaces resembling ventifacts. east of of the the road, road, slightly higher in the section, the In the streambanks east the conglomerate conglomerate is is interinterwith coarse sandstone. sandstone. The are poorly poorly sorted, sorted, discontinuous discontinuous irregular layered with The sandstone sandstone layers are approximately 5-30 5-30 cm thick. The layers approximately Thesandstone sandstoneconsists consists of of subangular subangularto tosubrounded, subrounded, medium medium to coarse coarse sand (.25-2 mm) mm) and and gravel (2-30 (2-30 mm) mm) with with larger larger cobbles cobbles scattered scattered throughout. throughout. In thin thin section the sand is framework framework supported predominantly of of quartz and feldspar with with supported and composed predominantly minor lithic fragments, biotite, and and muscovite. muscovite. Pores Poresare are filled filled with withclay clayand andmany manygrains grainsare are coated coated with with iron iron minerals. minerals. 99 �CITED REFERENCES CITED Behrendt, J.C., Green, Green, A.G., A.G., Cannon, Cannon, W.F., W.F., Hutchinson, Hutchinson, D.R., D.R., Lee, Lee, M., M., Milkereit, B., Behrendt, J.C., B., Agena, W.F., C., 1988, Crustal structure of the Midcontinent Rift System-System-W.F., and Spencer, Spencer, C., Midcontinent Rift GLIMPCEdeep deepseismic seismicreflection reflectionprofiles: profiles:Geology, Geology,v.v.16, 16, p. p. 81 81-85. results from GLIMPCE -85. Bornhorst, T.J., T.J., Paces, J.B., Grant, Grant, N.K., N.K., Obradovich, Obradovich, J.D., J.D., and and Huber, Huber, N.K., N.K., 1988, Age of Bornhorst, Paces, J.B., mineralization, Keweenaw Keweenaw Peninsula, Peninsula, Michigan: Michigan: Economic native copper mineralization, Economic Geology, v. 61 9-625. 83, 83, p. 619-625. 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Petroleum Engineers, Green, J.C., 1982, rocks, in Wold, Wold, R.J., R.J., and and Hinze, Hinze, Green, J.C., 1982, Geology Geology of Keweenawan Keweenawan extrusive rocks, W.J., basin: Geological W.J., eds., eds., Geology Geology and tectonics of the Lake Lake Superior Superior basin: Geological Society of America Memoir 156, p. 47-55. 100 �______ Hinze, W.J., Braile, L.W., and Chandler, Chandler,V.W., V.W., 1990, 1990, A geophysical profile profile of the southern Hinze, W.J., Braile, L.W., v. 9, 9, of the Midcontinent Lake Superior: Superior: Tectonics, v. margin of Midcontinent Rift System in western Lake p. 303-310. 303-310. Hubbard, H.A., H.A., 11975a, 975a, Lower Keweenawan volcanic rocks of Michigan Hubbard, Michigan and and Wisconsin: Wisconsin: U.S. Geological Survey SurveyJournal Journalof of Research, Research,v.v.3,3, p. p. 529-541. 529-541. U.S. Geological 1 975b, Geology Geology of of Porcupine Mountains in Carp River and White Pine 1975b, Pine quadrangles, Michigan: Journal of of Research, Research,v.v.3, 3, p. P. 51 519-528. Michigan: U.S U.S Geological Geological Survey Journal 9-528. Johnson, R.F., White, W.S., R.F., and White, W.S., 1969, 1969,Preliminary Preliminaryreport report on on the the bedrock bedrockgeology geology and and deposits of of the the Matchwood quadrangle, quadrangle, Ontonagon OntonagonCounty, County,Michigan: Michigan: U.S. copper deposits Report, 31 31 p. Geological Survey Open-File Open-File Report, Kalliokoski, J., 1982, in Wold, Wold, R.J., R.J., and Hinze, Hinze, W.J., W.J., eds., Kalliokoski, J., 1982, Jacobsville Jacobsville Sandstone, Sandstone, in eds., Geology basin: Geological and tectonics of the Lake Lake Superior basin: Geological Society of America Memoir Memoir p. 147-1 147-156. 56. 156, p. King, °x2° quadrangle, King, E.R., E.R., 1987, Aeromagnetic Aeromagnetic map of the Iron Iron River River 11Ox2O quadrangle, Michigan Michiganand and l-1360F, Wisconsin: U.S. U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations Map 1-1 360F, scale scale 1:250,000. 1:250,000. Klasner, J.S., 1989, Klasner, J.S., 1989, Bouguer Bouguer gravity gravity anomaly anomaly map and geologic interpretation of the the Iron Iron °x2° quadrangle, Wisconsin: U.S. River 1 Ox2O quadrangle, Michigan and Wisconsin: U.S. Geological Geological Survey Survey Miscellaneous Investigations Investigations Map Map 1-1 I-i 360E, 360E, scale scale 11:250,000. :250,000. Mauk, J.L., Kelly, Mauk, J.L., Kelly, W.C., W.C., van van der der Pluijm, Pluijm, B.A., B.A., and and Seasor, Seasor, R.W., R.W., in in press, press, Relations Relations between between deformation and sediment-hosted copper mineralization: mineralization: evidence evidence from from the White deformation Pine portion of of the the Midcontinent rift rift system: system: Geology. Pine portion Geology. Mauk, J.L., Seasor, R.W., Kelly, Kelly, W.C., W.C., Andrews, Andrews, R.A., W.S., 1989, Mauk, J.L., Seasor, R.W., R.A., and and Nelson, W.S., 1989, The The White White Pine stratiform stratiform copper deposit, in in Margeson, Margeson, G.B., G.B., ed., ed., Precambrian Precambrian geology geology and and occurrences, Michigan's upper upper peninsula: peninsula: Society metal occurrences, Society of of Economic Economic Geologists Geologists field conference, conference, p. 143-153. 143-153. Nicholson, S.W., S.W., and and Shirey, Shirey, S.B., S.B., 1990, 1990, Midcontinent Nicholson, Midcontinentrift riftvolcanism volcanismin inthe the Lake Lake Superior Superior region--Sr. Nd Nd and and Pb Pbisotopic isotopicevidence evidencefor foraamantle mantleplume plumeorigin: origin: Journal Journal of of region--Sr, Geophysical Research, Research,v.v.95, 95,p. p. 10581 10581-10868. Geophysical -10868. Ojakangas, R.W., R.W., and and Morey, Morey, G.B., G.B., 1982, Keweenawan Ojakangas, Keweenawanpre-volcanic pre-volcanicquartz quartzsandstones sandstonesand and Superior region, region, in in Wold, Wold, R.J., R.J., and Hinze, Hinze, W.J., W.J., eds., related rocks of the Lake Superior eds., and tectonics tectonics of the Lake Superior Superior basin: basin: Geological Geology and Geological Society of America America Memoir 156, p. 85-96. 85-96. Paces, J.B., J.B., 1988, Magmatic characteristics Paces, Magmatic processes, processes, evolution evolution and mantle source characteristics contributing to basalts-Portage Lake Lake basalts, basalts, contributing to the the petrogenesis petrogenesis of Midcontinent Midcontinentrift riftbasalts--Portage Michigan: Houghton, Keweenaw Peninsula, Peninsula, Michigan: Houghton, Michigan Michigan Technological Technological University, University, Ph.D. dissertation, 413 p. Ph.D. p. Paces, J.B., J.B., and and Bell, Bell, K., K., 1989, Non-depleted the Superior Paces, Non-depleted sub-continental mantle beneath the of the Canadian Shield: Nd-Sr isotopic and trace element evidence from from Province of Canadian Shield: Midcontinent rift basalts: Geochimica CosmochimicaActa, Acta,v.v. 53, 53, p. p. 2023-2035. 2023-2035. Geochimica et Cosmochimica 101 �Ruiz, Ruiz, J., Jones, Jones, L.M., L.M., and and Kelly, Kelly, W.C., W.C., 1984, 1984,Rubidium-strontium Rubidium-strontiumdating dating of of ore ore deposits deposits hosted hostedby byRb-rich Rb-richrocks rocksusing usingcalcite calciteand andother othercommon commonSr-bearing Sr-bearingminerals: minerals: Geology, v. 12, 12, p. p. 259-262. 259-262. Geology, Suszek, Suszek, T.J., T.J., 1991, 1991,Petrography Petrographyand andsedimentation sedimentationof ofthe theMiddle MiddleProterozoic Proterozoic (Keweenawan) Formation, western Lake Superior Superior region, region, Midcontinent Midcontinent rift (Keweenawan) Nonesuch Formation, rift system: 98 p.p. system: Duluth, Duluth,University UniversityofofMinnesota-Duluth, Minnesota-Duluth,M.S. M.S.thesis, thesis,1198 White, paleohydrologicmodel modelfor formineralization mineralizationof ofthe theWhite WhitePine Pinecopper copper White, W.S., W.S., 1971, 1971,AApaleohydrologic deposit, Geology, v. v. 66, 66, p. 1-13. deposit, northern northern Michigan: Economic Economic Geology, 1-13. White, 966, Sulfide White, W.S., W.S., and andWright, Wright,J.C., J.C., 1 1966, Sulfidemineral mineralzoning zoningininthe thebasal basalNonesuch NonesuchShale, Shale, northern northern Michigan: Michigan: Economic EconomicGeology, Geology, v. 61, 61, p. p.1171-11 1171-1 190. 90. 102 �GEOLOGY OF ThE GREAT LAKES TECTONIC TECTONICZONE ZONE INTHE IN THE MARQUE TIE AREA, MARQUETTE AREA, MICHIGAN MCHIGANA ARCHEAN ALATE LATE ARCHEAN - PALEOSUTURE PALEOSUTURE P.K. P.K. Sims Sims and and Z.E. Z.E. Peterman Peterrnan U.S .Geological Geological Survey, Survey, Federal Federal Center, Center, U.S. Denver, Denver, Colorado Colorado �the geology geology of tectonic zone in the Guide to the of the the Great Lakes tectonic Marquette area, area, Michigan--A Michigan--A Late Archean paleosuture P.K. and Z.E. Peterman P.K. Sims and SUMMARY length The Great Lakes tectonic zone (GLTZ) is is an Archean crustal boundary of subcontinental length that separates a greenstone-granite terrane (southern part of of Superior Superior province of Canadian Shield) on on the the north north from a partly partly older older gneiss gneissterrane terrane on on the south., south. The TheGLTZ GLTZisisgenerally generally Shield) collision. The tectonic zone is paleosuture resulting resulting from continent-continent collision. interpreted as a paleosuture covered in most of the Lake covered Lake Superior Superior region region by by Proterozoic Proterozoic rocks rocks or orPleistocene Pleistoceneglacial glacialdeposits, deposits, and its position and and characteristics characteristics were were previously previously determined determined mainly mainlyby by geophysical geophysical data. data. Geologic mapping mappingin in the the Marquette, Marquette, Michigan Michigan area area provides provides for for the first time direct Geologic direct observations of of the structure. observations In the the Marquette Marquette area, area,the theGL1'Z GLTZisischaracterized characterized by by aa zone zone of of mylonite mylonite (orthomylonite) (orthomylonite) that that formed at brittle-ductile brittle-ductile transition transition conditions; conditions; this this was superposed on on previously previously deformed deformed rocks rocks of both the Archean Archean greenstone-granite greenstone-graniteterrane terraneand andthe theArchean Archeangneiss gneissterrane. terrane. The W. Foliation in the mylonite strikes about boundaries of the GLTZ GLTZ trend trend about aboutN. N. 600 60' W. N. 70' 70° W. W. and and dips dips steeply steeply southwest. southwest. A pronounced pronounced stretching lineation and tight fold hinges N. about42° 42' S. S. 430 43O E. The attitude attitude of of the the stretching stretching lineation (line (line of of tectonic tectonic transport), transport), plunge about of movement sense, indicate that collision together with asymmetric structures indicative of collision at at this this was oblique. oblique. This resulted in dextral-thrust locality was dextral-thrust shear along along the the boundary, boundary, northwestward northwestward vergence, and and probable probable overriding overriding of ofthe the greenstone-granite greenstone-graniteterrane terrane by by the the gneiss gneiss terrane. terrane. vergence, Transmittal of the dextral shear stress across a large area of of the the greenstone-granite greenstone-granite crust crust (Superior province) to the the north north may may have have formed formed the thenearly nearly east-west east-west foliation, foliation, upright upright folds, folds, and northwestdextralfaults faultsand andshear shearzones zones at at least least as as far north as the northwest- to east-west-trending east-west-trending dextral the Quetico fault, fault, in in southern southern Ontario, Ontario, a distance distance of of about about 250 250 krn. km. These structures in Superior province rocks are superposed on on older older recumbent recumbent folds. folds. angular bends bends that alternately trend As a whole, the GL1'Z GLTZ is characterized by systematic systematic angular trend westwestnorthwestward, as in in the the Marquette Marquette area, and northeastward. northeastward. This northwestward, as This zigzag zigzag pattern probably probably reflects relict irregularities in the continental margin (Superior province) province) composed composed of of greenstone-granite crust. crust. Late Archean convergence convergence along this margin resulted in aa variable variable greenstone-granite LateArchean trajectory of stress into the the greenstone-granite greenstone-granite crust crust and and probably probably in in along-strike along-strike diachroneity diachroneity of of orogeny. The orogeny. The major major deformation deformation resulted resulted from from oblique oblique compression compression at at promontories, promontories, which which which compressive compressivestress stresswas wasdirected directedinto intothe thecrust. crust. In addition to to acted as buttresses against which the dominant strike-slip faults faults also also formed, formed, such such as as the the dominant foliation, foliation, major brittle-ductile brittle-ductile to brittle strike-slip Vermilion fault fault system system in in northern northern Minnesota Minnesota and the Quetico and Rainy Vermilion Rainy Lake-Seine Lake-Seine River River faults in southern Ontario; these resulted from a more brittle continuum of the the transcurrent transcurrent shear caused by collision along the GLTZ. INTRODUCTION km The Great Lakes tectonic zone (GLTZ) is an Archean crustal boundary more than 1,000 1,000 krn long that separates a greenstone-granite terrane (southern part of Superior province) greenstone-granite terrane province) on the north from a gneiss gneiss terrane terrane on on the thesouth south(Sims (Sims and andothers, others,1980; 1980;Sims Sims and and Peterman, Peterman, 1981; 1981; Peterman, 1979). The The GLTZ GLTZisiscovered covered throughout throughout most of of the the Great GreatLakes Lakesregion region by by younger younger 105 �glacial deposits, deposits,but but recently recentlyitithas has been been delineated delineated and studied Proterozoic rocks or Pleistocene Pleistocene glacial in outcrop in an area area south southof of Marquette, Marquette,Michigan Michigan (fig. (fig. 1). 1). The The boundary boundary was was first first recognized recognized in in Minnesota Minnesota (Sims (Sims and andMorey, Morey,1973; 1973; Morey Morey and andSims, Sirns,1976) 1976) from regional geologic relations, relations, which which indicated indicated that that the two adjoining basement terranes terranes had had different geologic histories histories and probably had evolved separately. Regional evolved separately. Regional magnetic magnetic and and gravity gravity data were utilized to determine the the position position of of the the boundary. boundary. Later Later(Sims, (Sims,1980), 1980),the the boundary boundary approximately delineated delineated in the western part of was approximately of Upper UpperMichigan Michigan(Sims, (Sims, 1980; 1980; Sims and others, 1984) 1984) and northwestern Wisconsin (Sims and others, 1985), 1985), east of the the Middle Middle Proterozoic Midcontinent rift system, system, and itit was was inferred by by indirect indirect evidence evidence to to extend extend eastward through the Sudbury the Middle Middle Proterozoic Proterozoic Sudbury structure, where it is truncated by the Grenville tectonic zone (Sims (Sims and others, others, 1980). 1980). Recent geologic geologic mapping in the Sands Sands and and Palmer Palmer7½-minute 7%-minutequadrangles, quadrangles, Michigan Michigan (fig. (fig. 1), I), previously mapped mapped by by Gair Gair and Thaden (1968) (1968) and Gair (1975), (1975), has delineated this Archean outcrop for for the thefirst firsttime time(Sims, (Sims,1991). 1991). It is exposed exposed on the south side side of the the Early Early boundary in outcrop Proterozoic Proterozoic Marquette Marquette synclinorium, synclinorium, and its northwestern projection projection into the the trough trough coincides coincides with a major Early Early Proterozoic Proterozoic fault, fault,the the Richmond Richmondfault. fault. In the Marquette area, area, the the GLTZ GLTZisis wide that is overprinted krn wide overprinted on rocks of both the the greenstone-granite greenstone-granite a mylonite zone about 2 km terrane and Inthis this area, area,the theGL1'Z GLTZisisinterpreted interpreted as asaacontinentcontinentand the the Archean Archean gneiss terrane. In continent collision zone. The resulting in in dextral dextral wrench wrench shear shear on on the the collision zone. The collision collision was oblique, resulting 60ÂW.-trending the N. 60° W.-trending boundary boundary and and northwestward northwestward vergence vergence of of the the gneiss gneiss terrane terrane against the greenstone-granite terrane. The purpose of this field guide is to examine examine the exposed exposed GLTZ GLTZ in the context of of the regional geology, to to discuss discuss genetic geneticrelationships relationshipsbetween betweenconvergence convergencealong alongthe theboundary boundaryand and structural structural geology, features in the Archean rocks to the north, and to present present aa new new interpretation interpretation of of the theevolution evolution of the GLTZ throughout throughout the the Lake Lake Superior Superior region. region. GEOLOGIC GEOLOGIC SETI1NG SETTING in the Sands and Palmer moderately well exposed in The Great Great Lakes Lakes tectonic tectonic zone (GLTZ) (GLTZ) isis moderately 7%-minute quadrangles in Upper Upper Michigan Michigan (fig. (fig. 1). 1). It separates separates the thetwo two distinctive distinctive Archean 7½-minute terranes in the area. area. The Thenorthern northerngreenstone-granite greenstone-granite terrane terraneisiscomposed composed largely largely of Late granitoid rocks, rocks, with with subordinate subordinate approximately approximately coeval metavolcanic and Archean granitoid metasedimentary metasedimentary rocks rocks of of greenstone greenstone affinity. affinity. The layered rocks and most of the granitoid rocks were metamorphosed metamorphosed (mainly to greenschist greenschist facies) facies) and deformed during Late Archean orogeny. The southern southernArchean Archeangneiss gneissterrane terraneisiscomposed composedmainly mainlyof oflayered layered gneiss, gneiss, migmatite, migmatite, orogeny. The and amphibolite--rocks that are are distinct distinct from from those those in in the the greenstone-granite greenstone-granite terrane. terrane. Except amphibolite--rocks that Except post-tectonic, generally for late-tectonic to post-tectonic, generally small(?) small(?)granitoid granitoidbodies, bodies,the therocks rocksofofthe the terrane terrane are metamorphosed, metamorphosed, mainly to to amphibolite amphibolite facies. facies. The rocks exposed within within the two two terranes in Upper Michigan Michigan are are closely closely similar to those in Minnesota (Morey (Morey and and Sims, Sims, 1976; 1976; Sims and 1980), thus others, 1980), thus establishing establishingthe the identity identity of ofthe the GLTZ GL1'Z in in the the Marquette area. are overlain overlain in in the Marquette the Republic The Archean rocks in Michigan are Marquette synclinorium, synclinorium, the trough, River, Clark Clark Creek, Creek, and and Baraga Baraga basins basins by by shelf and foredeep deposits deposits of of trough, and the Dead River, Cannonand andGair, Gair,1970; 1970;Barovich Barovich the Early Proterozoic Proterozoic Marquette Marquette Range RangeSupergroup Supergroup(fig. (fig. 1;1;Cannon and others, 1989). 1989). 106 �Bayley(1897) (1897)introduced introducedthe thenames names"northern northerncomplex" complef for the Archean rocks rocks Van Hise and Bayley north of the Marquette synclinorium and southern complef for the Archean rocks south north synclinorium and "southern complex" for the Archean rocks south of the syndilnorium. synclinorium. relationships in A Late Archean age age for for the the GL1'Z GLTZisis now now established established by regional geologic relationships north-central United United States. States. The Archean rocks in in the the greenstone-granite greenstone-granite terrane terrane in in northern northern north-central Minnesota (Hudleston and others, 1988) and northernmost Michigan (fig. 1; Sims, 1991) are others, 1988) Michigan (fig. 1; Sirns, are mainly by by ductile ductileand and brittle brittle structures structures formed formed in in response to dextral dextral shear, shear, which which characterized mainly accords with with the the deformation deformation pattern pattern observed observed in in exposures exposures of ofthe the GLTZ GLTZ south of Marquette. west-trending steep foliation and upright These structures include a generally generally west-trending upright folds, folds, widespread indicative of dextral shear; the Z-shaped folds, and northwest- to west-trending dextral faults, indicative the (Johnson and Bomhorst, Bornhorst, 1991). structures are superposed on recumbent folds (Johnson 1991). In In contrast, contrast, Early Early Proterozoic Penokean Penokean deformation deformation in in the the Marquette Marquette area had little effect on the Archean Proterozoic basement (Cambray, 1984). Cambray (1984) (1984)proposed proposed that that the Penokean deformation was basement (Cambray, 1984). produced by by horizontal horizontal compression compressionthat thatwas wastransmitted transmittedfrom fromthe thebasement basement to to the folded folded cover cover produced rocks by narrow ductile shears in the basement. Readjustment of rigid basement blocks along rocks by narrow ductile shears in the basement. weaknesses,which whichresulted resultedininsome someshortening shorteningbut but not not folding folding of of the the these shears utilized old weaknesses, basement rocks. proposed a rocks. For Forthe theEarly EarlyProterozoic ProterozoicMarquette Marquettesyndlinorium, synclinorium, Cambray (1984) proposed nearly north-south compressional which initially initially produced produced reverse dip slip axis, which slip on on faults faults compressional axis, bounding the syncline and compressed the Early Proterozoic sedimentary rocks within the bounding and compressed the Early Proterozoic sedimentary within the syncline into into west-trending west-trending folds. folds. Subsequently, resistance resistance to this movement within the the trough trough resulted in sinistral sinistral strike strike slip slip motion and and the thedevelopment development of ofF2 F, folds folds with with northwest-trending northwest-trending axial surfaces and variable variable plunge. plunge. Gair and Thaden (1968) applied the the name "Compeau "Compeau Creek Creek Gneiss" Gneis? to both the (1968) applied the foliated foliated rocks of of the Archean Archean greenstone-granite greenstone-granite terrane terrane (northern complex) granitoid rocks complex) and the the layered layered gneisses and and massive massive intrusions intrusions of of the the gneiss gneiss terrane terrane (southern complex), gneisses complex), and subsequent investigators extended extended this this terminology terminologyto to the the western western parts parts of of the southern investigators southern complex complex (Cannon 1973). To apply this this name name to rocks in in both both Archean terranes, however, and Simmons, Simmons, 1973). however, is inappropriate, because the two two terranes terranes consist consist of of distinctive distinctive rock types of different origins. origins. Accordingly, in in this this guide guide informal informal lithologic lithologicnames namesare are used used to to describe the Accordingly, the crystalline crystalline rocks rocks in in the two terranes. ARCHEAN GREENSTONE-GRANITE TERRANE TERRANE greenstone-granite terrane terrane in the Marquette area The greenstone-granite area (fig. (fig. 1) 1) consists of a several thousandmeter-thick succession succession of metamorphosed metamorphosed subaqueous subaqueousmafic mafictotofelsic felsicflows, flows,pyroclastic pyroclastic rocks, rocks, volcanogenic sedimentary sedimentaryrocks rocksthat that is is intruded intruded by by small smallbodies bodies of of gabbro gabbro and ultramafic and volcanogenic rocks and by large plutons of granitoid rocks (Bornhorst, Johnson and Bornhorst, (Bornhorst, 1988; 1988; Johnson Bomhorst, 1991). 1991). The metamorphosed volcanic rocks rocks have have been been named named the the Ishpeming Ishpeming greenstone greenstone belt belt (Morgan and DeCristoforo, 1980); they represent represent the southwestern extension of of the Wawa 1980); they southwestern extension (Shebandowan) subprovince of of the the Superior province province of of Canada (Card and (Shebandowan) subprovince and Ciesielski, Ciesielski, 1986). 1986). volcanicrocks rocksadjacent adjacenttotoan an ultramafic ultramaficbody bodynorth northofofIshpeming Ishpemingare are host host to to the gold Felsic volcanic deposits of the the Ropes Ropes mine mine(Brozdowski (Brozdowski and and others, others,1986; 1986;Brozdowski, Brozdowski, 1988, 1988, 1989), and the ultramauic body bodyhosts hostsadditional additionalmineral mineralprospects prospects(Bodwell, (Bodwell,1972). 1972). Foliated Foliated tonalite from the ultramafic the 1978) in in the the greenstone-granite greenstone-granite terrane, terrane, has a U-Pb northern complex (Hammond, 1978) U-Pb zircon zircon age age of of 2,703±16 by Zell Zell E. Peterman), and associated rhyolite has aa U-Pb 2,7032 16 Ma (recalculated (recalculated by U-Pb zircon zircon age age byZeil ZellE. E. Peterman). Peterman). These ages are consistent with with more ± 69 Ma (recalculated of 2,780 2,780269 (recalculated by precise U-Pb ages in the Wawa subprovince in adjacent Canada (Corfu and Stott, Wawa subprovince in adjacent Canada Stott, 1986). 1986). 107 �Figure 1. 46°45 Xmsç MICH —- A 0 0 -r 5 5 •F )1f 8P30' 10 1''• Marc1uette IAKU SIJPURIOR 10 MILES 15 KILOMETERS (h' — Geologic map of part of Marquette 1°x2° quadrangle, Michigan. After Sims (1991). Palmer 7½-minute quadrangle is immediately west of Sands quadrangle. Marquette 7½-minute quadrangle is immediately north of Sands quadrangle. 880 00 �________ _________ CORRELATION CORREIATION OF O F MAP MAP UNITS Archean Archean terrane Greenstone-granite terrane Reany Creek Creek Formation Formation .- \ J Proterozotc Middle Unconformity Unconforrnity Granitoid rocks— Dominantly granodiorite lie but Granitoid rocks-bminantly grandiodteand andtonal tonalite Including granite; generally including generalb foliated foliated Mafic Mafic to felsic felsic flows flows and and pyrodastic pyrodasticrocks r o c kand and volcanogenic sedimentary rocks wkanogenic sedimentaq rocks Ultramafic Utramafiirocks rocks > 1-1'a m i i: Penokean orogeny Penokean orogeny deformation deformation and and metamorphism metamor~ism xm1L..... 1 +1 \\\\'' ) \ .\I. ,-!t~yt p W}Mzgy 1 1 Unconformity Unconforrnily Xmn Menominee Group J — Marquette Marquette Range Range Supergroup suwrgrOup Xc j granite and massive granite Contact Contact - J a A 1 . I Late Unconformity I -15 —15 kf5 J DESCRIPTION OF MAP UNITS DE!XRPTION UNnS Middle Mlddle Proterozoic Proierowic . Jacobsvllie Jacobsville Sandstone Sandstone Early Proterozoic Alkali granite 33 ±25 Alkali granite (1.7 (1,733 *25 Ma) Ma) ,, Marquette Range SUPWSTOUP Supergroup , Marquette j Vertical Bearing and lineation— Bearing andplunge plungeofof lineation-May Maybebecombined combinedwith with foliation symbol foliation symbol Direction Direction of stratigraphic tops tops --15 } Ahean y\.;;3,77, dip of foliation Strike and dip foliation Inclined Inclined 4— + I F, Transcurrent fault— Transcurrent fault-Showing Showingrelative relathhorizontal horizontalmovement m-mt A Thrust Thrustfault—Sawteeth fault-Swteeh on upthrown upthrownside side 50 Continent-continent collision ((=2,690 Cmtinentantinent colliskm ~ 2 , 6 9Ma) Ma) 0 South of North of ofGLTZ GLTZ South of GLTZ GLTZ North Gnelss terrane terrane Gneiss Greenstone-granitetterrane emne Greenstone-granite !'zá'_1 + _±I - - ".1 e:w;aJ , 4 1 - wuI Gneiss, migmatite, amphibolite—lncludes Gneiss, migmatite,and and amphibolide-Includes foliated foliated 7High-angie Wih-anglefault—Bar fault-& and andball ballon ondownthrown downthrownside side Chocolay Group I 3 Ago Early h dy Proterozolc Proterozoic I Unconformity unconformity Gneiss terrane terrane Tilden (Hammond, Granite near Tilden (Hammond, 1978) 1978) [\-.\' -"i Baraga Group Group Bearing of minor minor fold Bearins and plunge of fold MyloniteMylonlte— Dominantly Dominantly orthornylonite orthomyionite CRSZ Carp River shear zone CRFSZ Carp River Falls Falls shear zone zone DRSZ DRSZ Dead River River shear Dead shear zone zone GLTZ GLTZ tectonic zone Great Lakes tectonk zone GGT GGT R 217 Greenstone-granite terrane terrane Ropes mhse Ropes mhe J. Michigamme MkhlgammeFormation—Dominantly Fonnatbn-Domlmntlysiaty slatyrocks rocksIn Inlower lowerpart part 88' 89' Ciarksburg C l a h b u r g Volcanica Volcnnlcs Member Member of of Michigamme Mkhigamm Formation Fonnatbn Goodrich Quartzite G o d r i c h Quartzite 41' map Menominee Group, undlvlded, undivided, in trough Menominee Group, i n Republic Republic tmugh 1 Xmn 1 w 1 1 Xch Edge of Siamo Ajibik Quartzite, S i m o Slate and Ajibik Quartzite, undivided undivided L_ eozoicNç Negaunee Iron-formation Negaunee Iron-formatbn cover o o Cisocolay Chocolay Group, undivided undivided 4OKIWMETERS 46' INDEX MAP 4OMLIS �Granitoid Rocks Rocks The Late Archean granitoid granitoid rocks rocks in the the greenstone-granite greenstone-granite terrane terrane (fig. (fig. 1) 1)are aredominantly dominantly pink pink to grayish pink, pink, generally generally medium medium grained, grained, porphyritic, porphyritic,foliated, foliated,and and homogeneous homogeneous tonalite tonalite or granodiorite (Gair P. 18-23). xenoliths and and schlieren of of biotite (Gau and and Thaden, Thaden, 1968, 1968, p. 18-23). They contain xenoliths schist and amphibolite. amphibolite. In foliated granite is also a In the theSands Sandsquadrangle quadrangle(fig. (fig. 1), I), weakly foliated common rock rock type (table 1), I), but its age relation to the the tonalite-granodiorite tonalite-granodiorite was was not determined. determined. The bimodal composition of the granitoid rocks suggests, however, that that the the granite represents suggests, however, represents aa event. discrete magmatic event. The granitoid rocks of of the greenstone-granite greenstone-granite terrane terrane in the Marquette area area exposed exposed on on both both sides of the Marquette altered (table 1). Plagioclase Marquette synclinorium synclinorium are strongly altered Plagioclase (oligoclase) (oligoclase) is saussuritized and albite albite twinning twinning is largely obscured, and biotite is largely changed to to chlorite chlorite and opaque oxides (locallyrutile). rutile). The rocks are highly fractured and and fracture fracture surfaces are are highly fractured oxides (locally coated by chlorite and other propylitic minerals. Along the southern margin of the Marquette propylitic minerals. Along the southem margin of syndilnorium, the granitoid granitoidrocks rocksare are exceptionally exceptionallyrich richininquartz quartz(table (table1). 1). The granitoid rocks synclinorium, the in the Sands Sands quadrangle also are are protomylonites. protomylonites. The Theprotomylonite protomylonite isis characterized characterized by by recrystallization of quartz to shes and and localized localized shear-induced shear-induced recrystallization recrystallization of of to fine fine grain grain sizes plagioclase and potassium potassium feldspar feldspar to fie-grained fine-grained polycrystalline polycrystallineaggregates aggregates(type (type IP, 1P, llP, liP, 1M, lM, and 111M 1M structures of Hanmer, Hanmer,1982). 1982). The relative homogeneity of the foliated granitoid rocks, the occurrence of of sharp-walled sharp-walled the occurrence xenoliths, and and the general absence of a lithologic layering layering that that could represent relict xenoliths, relict sedimentary sedimentary or volcanic layering layering suggest suggestthat thatthe the granitoid granitoid rocks rocksof ofthe the greenstone-granite greenstone-granite terrane terrane are of magmatic origin. origin. Their pervasive foliation foliation is is attributed attributed to to deformation deformation subsequent subsequent to primary magmatic crystallization, as as discussed discussedfollowing. following. Structure The rocks in the greenstone-granite greenstone-granite terrane terrane (northern complex), complex),on onthe the north north side side of of the the GLTZ (fig. 1), I), record early recumbent recumbent folding folding (F1) (FJ of metavolcanic rocks of the Ishpeming Ishpeming greenstone greenstone (fig. Superposeddeformation deformation(D2) (D2)produced produced northwestnorthwest- to to west-trending west-trending upright, upright, upwardupward- and belt. Superposed An downward-facing 1991). An downward-facingfolds folds(F2) (F2)that thatare are Z-shaped Z-shaped in in plan plan view view (Johnson (Johnson and and Bomhorst, Bornhorst, 1991). axial plane The Z-symmetry Z-symmetry of of the theF2 F2folds folds is is consistent consistent with with plane foliation was developed during Fp F2. The their development dextral shear component. component. Associated development in a deformation deformation regime with a dextral Associated by D2. Younger, Younger, northwestnorthwest- to to west-trending west-trending faults, faults, some someof of granitoid rocks also were deformed by which have demonstrable demonstrable dextral dextral movement, movement, transect transect and and offset offset the the folded folded rocks. rocks. Commonly, which have Commonly, these faults faults separate separatedomains domainsof ofvolcanic volcanic rock rock that that have have opposite oppositestratigraphic stratigraphicfacing facingdirections. directions. of fig. fig. 1) 1) is is Foliation and lithologic layering layering in in the the vicinity vicinityofofthe the Ropes Ropes mine mine (R, (R, near center of puzzling with respect to the dominant regional structure. Here, foliation and lithologic layering with respect to Here, foliation and lithologic layering strike strike about aboutN. N.700 70' E. and are are nearly nearly vertical (Brozdowski, (Brozdowski, 1988, 1988,p.p.A-44). A-44). The published area (Negaunee (Negaunee SW SW quadrangle; quadrangle; Clark Clark and and others, others, geologic map map that that includes the Ropes mine area hte 1975) also also shows showsaa steep steep (stretch?) (stretch?) lineation that plunges southeastward in unit Wkf of the Late Archean Kitchi Schist (included in unit unit Wv Wv on on fig. fig. 1). 1). Possibly, the northeast-trending foliation Possibly, the large-scaleD2 D2Z-fold. Z-fold. the Ropes Ropes mine mine area arearepresents representsthe theeast-northeast-trending east-northeast-trendinglimb limbofofaalarge-scale in the 110 �greenstone-granite terrane terrane of of the the Marquette area Table 1. 1. Approximate Approximatemodal modal content content of of granitoid granitoid rocks rock in Archean greenstone-granite ['Fr., pr., trace; blank, absentj absent] Rock Rock Constituent Constituent Sample Sample number 136R l36R lilA 177A 17Th 177B 179A 179A 179B 179B 182A 18% 182B 182B 183A 183A 186A 186A 199 199 200 202 208 208 21LA 21lA 136-1 136-1 203 1 1 22 33 Plagioclase Plagioclase 37 37 35 35 60 60 66 54.5 54.5 48 52.5 52.5 38 54.5 36 36 56.5 60 60 39 39 41 41 273 27.5 33 33 61.2 58.5 58.5 50.6 50.6 Quartz Quartz 30 30 32.5 24 24 21.5 28.5 28.5 45 36 34 24 24 27.5 27.5 37.5 28 28 30 30 27 39 39 23 28 26 26 22.2 373 37.5 Potassium Potassium feldspar feldspar 30 31 31 10 10 5.5 2.5 00 24.5 14.5 14.5 31 31 33 11 30 24 32 32 373 37.5 3.8 12.8 1.4 1.4 Biotite Biotite Ti. Tr. Tr. Ti. Tr. Tr. 10 10 Ti. Tr. Tr. Tr. Ti. Tr. 0.2 Ti. Tr. 11 66 77 Ti. Tr. 66 4 Tr. Chlorite Chlorite 1.3 1.3 33 Epidote Epidote 0.5 Tr. Tr. 63 6.5 7 7 55 Ti. Tr. 10 10 0 Ti. Tr. Ti. Tr. Ti. Tr. Ti. Tr. 3 3 Ti. Tr. Tr. Tr. 88 Ti. Tr. Tr. Tr. 2.5 13 1.5 03 0.5 0.6 00 Ti. Tr. Sphene Sphene Opaque Opaque oxides oxides Tr. Tr. Accessory minerals minerals Tr. Tr. Ti. Tr. 0.2 Muscovite Muscovite Tr. Tr. Ti. Tr. Ti. Tr. Ti. Tr. 0.5 3.6 3.6 Ti. Tr. 0.5 4 Tr. Ti. Tr. 11 Tr. 0.5 Tr. Tr. Tr. Tr. 11 11 Ti. Tr. Tr. Tr. Tr. Ti. Tr. Tr. Tr. 1 1 Tr. Tr. 0.2 0.2 Tr. 'Fr. 23 2.5 23 2.5 Ti. Tr. 1.8 Ti. Tr. 0 0 Ti. Tr. Tr. Tr. Ti. Tr. 1.3 1.3 7 DESCRIPTIONS SAMPLE DESCRIF'TXONS 136R. corner of Pink, fineof biotite biotite schist. Sands W., 675 ft N. of the the SE. SE. corner of f i e - to to medium-grained, medium-grained,slightly slightly porphyritic, porphyritic, altered granite; granite; contains containswispy wispy inclusions of Sandsquadrangle, quadrangle,1,800 1,800 ft W., sec. 3, T. 47 N., R. 25 W. sec.3,T.47N.,R.ZW. lilA. T. 47 Pink, medium-grained, porphyritic, massive, massive,altered altered granite; granite; cut cut by by cldorite-coated chlorite-coatedfractures. fractures. Sands 5., 2 2,150 E. of of the the NW. corner of sec. sec. 16, T. medium-grained, porphyritic, Sands quadrangle, 775 ftft S., ,l50 ftft E. 47 N., N., R. 25W. 25 w. 17Th. Pink, porphyritic, massive, massive,altered altered granite. granite. Sands P i i fine-grained, fie-grained, porphyritic, Sands quadrangle. quadrangle. Same Samelocality localityas as177A. 177A. 179A. 26, Pinkish-gray, medium-grained, medium-grained,porphyritic, porphyritic,altered altered tonalite; tonalite;contains containsoriented oriented layers layersof ofbiotite biotite schist. schist. Palmer quadrangle, S., 2 250 W. of of the the NJ2. NE. corner of sec. 50 ftft W. see 26, quadrangle, 650 ft S., T. 47 N., N.,R. 26 26 W. w. 179B. 182A. foliated, altered altered tonalite. tonalite. Biotite Gray, medium-grained, foliated, Biotite is is fresh. Palmer Palmerquadrangle. quadrangle.Same Samelocality localityasas179A. 179A. W. Pinkish-gray, medium-grained medium-grained altered altered tonalite gneiss. gneiss. Sands quadrangle, 1,350 ft E., 100 ft N. of the SW. Sands quadrangle, 1,350 E., N. SW. coiner corner of of sec. sec. 31, 31, T. 47 N., R. 25 W. �182B. Pinkish-gray altered tonalite gneiss. Sands Piish-gray to medium-gray, medium-gray, altered Sands quadrangle. quadrangle. Same Samelocation locationasas182A. 182.4. 183A. Pinkish-gray, fine- to medium-grained Pinkish-gray, fmemedium-grained granite granite gneiss. gneiss. Sands Sandsquadrangle, quadrangle,675 675ftftN., N.,300 300ftftE.of E.of the theSW. SW.corner wrnerofofsec. sec.31, 31,T.T.47 47N., N.,R.R.2525 W. W. 186A. Pinkish-gray, medium-grained, altered altered grandorite granodiorite gneiss. Palmer Pinkish-gray, medium-grained, Palmerquadrangle, quadrangle,2,500 2,333ftftN., N., 2,200 2,200ftft E. E. of of the theSW. SW.corner wrnerofofsec. sec.36, 36,T. T.47 47N., N.,R.R.2626 W. W. 199. Pinkish-gray, medium-grained medium-grained granite granite gneiss. Sands Sandsquadrangle, quadrangle,1,000 1,000 ftft S., S.,2,000 2,000 ft W. of the the NE. NE. corner mrnerofofsec. sec.16, 16,T. T.46 46N., N., R. R.25 25W. W. 200. Pinkish-gray, fine- to to medium-grained medium-grained altered altered tonalite gneiss. gneiss. Sands N., 2,075 2,075 ftft E. E. of of the SW. SW. corner corner of of sec. sec. 9, T. T. 46 46 N., N.,R. 25 Piish-gray, fmeSands quadrangle, quadrangle, 775 ft N., 25 W. W. 202. Gray, fine-grained chlorite-coated fractures. fractures. Sands E. of of the SW. wrner corner of sec. 5, 5, T. T. 46 46 N., tine-grained biotite tonalite tonalite gneiss cut by chlorite-mated Sandsquadrangle, quadrangle, 850 850 ft N., N., 2,350 2,350 E. N.,R. R. 25 25 W. W. 208. Pink, medium-grained, 2,150 ftftN., N., 2,000 2,WO ftft W. W. of of the theSE. SE.corner wrnerofofsec. sec.8,8,T.T.46 46N., N.,R.R.2525 W. W. medium-grained, leucocratic leucocratic granite granite gneiss. gneiss. Sands Sandsquadrangle, quadrangle,2,150 211A. Pink, medium-grained, altered granite W. of of the SE. corner granite gneiss. Sands Sandsquadrangle, quadrangle,2,550 2,550 ft S., 150 ft W. wrner of of sec. sec. 7, T. 46 N., N.,R. 25 W. W. 136-1. Pink, medium- to coarse-grained, foliated foliated granite granite gneiss. gneiss. Fractures mated coated by chlorite. chlorite. Sands as136R. l36R. Sands quadrangle. Same Samelocation locationas 203. Pink, medium-grained, leucwratic leucocratic granite granite gneiss. gneiss. Sands 2,300 ftft W. W. of of the the SE. SE. wrner corner of sec. 5, T. 46 N., R. 25 W. Sands quadrangle, 200 ft N., N., 2,300 W. 1. Average of 14 samples of of foliated tonalite. Marquette Marquettequadrangle, quadrangle,north northofofthe theMarquette Marquettesyndlinorium syncborium(Gair (Gauand andThaden, Thaden,1968, 1968,table table6,6,no. no.1). 1). 2. Average of five samples of of foliated grandorite. granodiorite. Marquette Marquettequadrangle, quadrangle,north northofofthe theMarquette Marquettesynclinorium synclinorium(Gair (G& and andThaden, Thaden,1968, 1968,table table6,6,no. no.9). 9). 3. Average of 11 11 samples of quartz-rich, foliated tonalite. Sands Sandsquadrangle, quadrangle,south southof of the theMarquette Marquettesynclinorium syncborium (Gair (G& and andThaden, Thaden,1968, 1968, table table 6, 6, no. no. 6). 6). �The The steep, steep,northwestnorthwest- to to west-trending west-trending shear zones and faults in the the greenstone-granite greenstone-graniteterrane, terrane, as exposed in the northern complex, are tens tens of of meters meters to to aa few fewhundred hundred meters meters wide. wide. They are exposed in complex, are highly highly schistose zones characterized by an intense, intense, close-spaced close-spaced foliation, a steep steepstretching(?) stretching(?) ilneation, 1991). The faults are of lineation, and strong retrograde alteration (Johnson and Bornhorst, 1991). of both ductile and brittle-ductile types. Major structures include the Dead River shear zone both ductile types. Major structures include the Dead River shear zone (fig. 1, DRSZ) (Puffett, 1974), whichforms formsthe the northern northern boundary boundaty of of the Dead River 19741, which River basin; basin; the the Carp Carp River River shear shear zone zone (CRSZ), (CRSZ),east-northeast east-northeastof of the theRopes Ropesmine, mine,which which separates separates two two different different blocks of Archean volcanic rocks; rocks; and the Carp River River Falls Falls shear shear zone zone(CRFSZ), (CRFSZ),which whichforms forms the in this area. The the northern northern margin margin of of the the Marquette Marquettesynclinorium synclinorium in TheCarp CarpRiver RiverFalls Fallsshear shear zone is reported becut cutby byrelatively relatively undeformed undeformed mafic mafic dikes of presumed presumed Late Late Archean Archeanage, age, reported to tobe indicating an Archean age for the the shear shearzone zone(Baxter (Baxter and andBornhorst, Bornhorst,1988). 1988). In the the area areanorth northof ofthe thePalmer Palmerfault fault(fig. (fig. 1), I), foliated foliated and fractured Late Late Archean Archean granitoid granitoid rocks form partly fault-bounded domes surrounded by Early Proterozoic rocks of the Marquette rocks of Marquette Range Supergroup. The large Archean granitoid body in the Sugarloaf Mountain area, 88 km km The large Archean granitoid body the Sugarloaf north north of of Marquette, Marquette,isisalso alsoaadome; dome;foliation foliationin inadjacent adjacentmetavolcanic metavolcanic rocks rocks (Puffett, (Puffett,1974) 1974) dips dips gently to moderately moderately away away from the granite granite contact. contact. Late-Tectonic Late-Tectonic Conglomerate Conglomerate (Archean) (Archean) The is the the Reany Reany Creek Creek Formation Formation The youngest Archean unit in the greenstone-granite terrane is (Puffett, 1969; 1974). 1974). On the basis of a reinterpretation reinterpretation of of age age and and structural structuralrelationships, relationships, the the Reany Creek Formation is no longer included included as as part part of of the the C Chocolay Group or the Marquette h w l a y Group or the Range Supergroup Supergroup (Sims, 1991). ItIt isis aa heterogeneous heterogeneousbody body of of conglomerate, conglomerate, arkose, arkose,chloritic chloritic slate, slate, graywacke, graywacke, and and boulder-bearing boulder-bearingslate. slate. It It transects transectsstructures structuresin in the theolder oldervolcanic volcanicrocks, rocks, isis less deformed than than the themetamorphosed metamorphosedvolcanic volcanic rocks, rocks, and is bounded along along its its southern southern margin by the northwest-trending northwest-trending Dead River River shear shear zone zone (fig. (fig. 1). 1). Its age age has been uncertain uncertain (see Puffett, of basin basin fill,and and relationship relationship to to the Puffett, 1974), 19741, but its penetrative penetrative foliation, asymmetry asymmetry of Dead Dead River River shear shearzone zonestrongly strongly suggest suggest that itit developed developed concurrently concurrently with dextral shear along the similartoto"Timiskaming-type" "Timiskaming-typensequences, sequences, such such as as the theSeine Seine the Dead Dead River Rivershear shearzone. zone.ItItis issimilar Group, Group, in northern northern Ontario, Ontario,now now commonly commonly interpreted as forming in Archean analogs to modern modem pull-apart pull-apartbasins basins(Poulsen, (Poulsen,1986). 1986). fa ARCHEAN A R C H W GNEISS GNE3SS TERRANE TERRANE The Archean gneiss gneiss terrane terrane in the Marquette area (fig. 1) constitutes the the greater greater part of the southern complex, complex, as defined defined by by Van Hise Hise and andBayley Bayley (1897). (1897). ItItconsists consistsofofgneiss, gneiss,migmatite, migmatite, southern amphibolite, substantial amounts of and amphibolite, of deformed and undeformed granite pegmatite, and Cannon and and Simmons Simmons (1973) (1973) have have described described the the massive to weakly weakly foliated foliated granite granite plutons. plutons. Cannon as Late Late Archean. Archean. general rock types in much much of of the southern complex. complex. One rock has been dated as sample of of gray gneiss (called Compeau Creek Gneiss by Gair, 1975) 1975) collected in the A sample SEY&W% ofofsection SE¼SWV4 section36, 36,T.T.4747N., N.,R.R.27 27W. W.(Hammond, (Hammond,1978) 1978)has hasaaU-Pb U-Pb zircon zircon age age of of 2,779521 802576 Ma (recalculated (recalculated by Zell E. E. Peterman). Peterman). 2,779 ±21 Ma Ma and and a lower intercept age of 802±76 Gneiss Gneiss and and Associated Granitoid Granitoid Rocks Rocks Compositiondly layered, Compositionally layered, medium-grained medium-grainedgneiss gneissand andmigmatite migmatiteare are the the dominant rock types in the gneiss gneiss terrane in in the the Marquette Marquettearea. area.Layered Layeredfelsic felsicgneisses gneissesranging rangingin in composition composition from from the to granite granite predominate. predominate. Smaller Smalleramounts amountsof of massive massive to to layered layered amphIbolite amphibolite are tonalite to 113 �intercalated intercalated with with the the felsic felsic gneiss, but amphibolite constitutes layers several tens of meters thick thick at be seen seenon onthe thegeologic geologicmap map of of the thePalmer Palmer7½-minute 7%-minutequadrangle quadrangle(Gair, (Gair,1975, 1975, at places, places, as as can can be p1. 1), which whichisisimmediately immediatelywest westofofthe the Sands Sands quadrangle. quadrangle. The pi. I), The felsic felsic gneisses gneisses are are gray gray to to pinkish gray; typically, compositionallayering layeringisisexpressed expressedby bydifferent differentproportions proportions of of the the major typically, compositional silicate minerals, as plagioclase-quartz-biotite-microperthite,(2) (2) microperthitemicroperthiteas for for example, example, (1) (1) plagioclase-quartz-biotite-microperthite, quartz-plagioclase-biotite, and (3) biotite-quartz-plagioclase-microperthite. Textural differences quartz-plagioclase-biotite, and at layering. Pink aplitic granite and granite at places places emphasize the compositional compositional layering. granite pegmatite pegmatite commonly transect the gneiss and and amphibolite amphibolite and and locally locallyform formmigmatite. migmatite. Metasedimentary commonly transect rocks such as iron-formation, form layers in the felsic of the Republic felsic gneisses in the vicinity vicinity of trough (Cannon and Simmons, 1973); they were not observed in the Palmer and Sands and Simmons, they were not observed in the Palmer Marquette area. area. quadrangles, in the Marquette Pinkish-gray to pink, medium-grained, massive massive to weakly weakly foliated, foliated, homogeneous homogeneous granite granite (table (table 2) 2) intrudes intrudes the the gneisses gneisses in several places. places. Hammond Hammond (1978) (1978) delineated delineated aa body body of of massive massive granite granite about 44 km2 km2in areal areal extent extent south south of of Ishpeming Ishpeming (unit (unit Wgt, Wgt, fig. fig. 1), I), which which he he informally informally called the the "Tilden granite." granite." ItIt isisaagray porphyritic, and massive granite grayto topink, pink,medium-grained, medium-grained, locally locally porphyritic, that locally gneiss. ItIt isis cut locally contains oriented xenoliths of mafic gneiss. cut by by pink pink pegInatite pegmatite and andisishighly highly fractured. The Thefractures fractureshave haveslickensided slickensided surfaces and a thin coating of chlorite and other propylitic propylitic alteration minerals. minerals. U-Pb U-Pb isotopic isotopic data data on on aa sample sample of of the thegranite granitenear nearTilden Tilden (Hammond, 1978) 1978) indicate an age age of of 2,585±15 2,5855 15 Ma Ma (R.E. (R.E. Zartman, Zartman,oral oralcommun., commun.,1991). 1991). fig. 1) about about 2 km in diameter occurs about 3 A nearly nearly circular circular body body of alkali granite (unit Xga, fig. A km south of Humboldt (Schulz (Schuiz and others, 1988). The The granite graniteisislight light red red to tobrick brickred, red,generally generally massive, fineto medium-grained, and equigranular to hypidiomorphic granular. The granite massive, fine- to medium-grained, and equigranular to hypidiomorphic granular. granite is is the Arabian Arabian Shield Shield similar compositionally to Sn-W mineralized mineralized alkali feldspar feldspar granites of the (Jackson and Ramsay, Ramsay, 1986) 1986) and the the Nigerian Nigerian younger granite province province (Kinnaird (Kinnaird and and others, others, interpreted as a Thegranite granitehas hasaaRb-Sr Rb-Srwhole-rock whole-rockage ageofof1,733 1,733±525 25 Ma, which which is interpreted 1985). The crystallization crystallization age (Zell E. Peterman, Peterman, written written commun., commun., 1988); 1988); it is aa post-tectonic post-tectonic intrusion. intrusion. Structure Structure the gneiss gneiss terrane terrane (southern (southern complex) complex) form aa northwest-trending northwest-trending antiformal antiformal Archean gneisses in the structure by Paleozoic Paleozoic rocks rocks to to the theeast east(Sims, (Sims,1992). 1992). structure that that closes closes to to the thewest west and andisisoverlapped overlapped by An infolded belt of Early Proterozoic (Marquette Range Supergroup) rocks indents the Archean the Republic Republic trough (fig. 1). In Inthe thearea areawest westofofthe theRepublic Republictrough, trough,Taylor Taylor(1967) (1967) fold nose in the determined two two principal principal phases phases of of deformation: deformation: (1) (1)early, early,probably probablyflat-lying flat-lyingfolds foldswith withaxial axial determined trending northeastward, northeastward, and and(2) (2)younger youngerupright upright folds foldswith with steep steepnorthwest-trending northwest-trendingaxial axial planes trending surfaces. The Theyounger younger folds foldsmainly mainly control the the distribution distribution of of the the rock rock units. units. In the the Marquette Marquettearea, area,early earlygently gently inclined inclined to recumbent recumbent folds that trend trend northwestward northwestward and and plunge gently gently northward northward (fig. (fig.2) 2) are are the the dominant dominant structure in the gneisses. gneisses. These Thesefolds folds deform deform an older older foliation foliation (Si). (S,). Boudinage Boudinageaccompanied accompaniedthe thefolding; folding; the theboudins boudinsplunge plungesubparallel subparallelto to gently inclined inclined fold fold hinges. hinges. A later steep, northwest-oriented foliation, that that is axial planar planar to northwest-oriented foliation, northwest-trending folds, occurs at least locally, but but it does not significantly affect the significantly affect distribution of the rock stop 3. 3. rock units. These Theseyounger younger structures structures will will be examined at stop 114 �Table 2. Approximate Approximate modal modal content content of of granitoid granitoid rocks rocks in the the Archean Archean gneiss gneiss terrane terrane of the Marquette Marquette area area [Tr., trace; blank, absenti absent] Rock Constituent Constituent Sample Sample No. 153A 153A 146-88 146-88 11 226A 226B 226B Plagioclase Plagioclase 34.7 33.5 25 263 393 Quartz 28 23.8 25 38.2 32.7 Potassium feldspar 28 28 34.2 40 40 33.0 25.0 9 8.0 8.0 33 2.2 3 3 Biotite Biotite Chlorite Chlorite Muscovite Muscovite Tr. Tr. Tr. Tr. Tr. Tr. 22 Tr. Tr. Tr. Tr. Tr. Epidote Epidote Tr. Sphene Sphene Opaque Opaque oxides oxides Tr. Tr. Accessory minerals minerals 03 0.5 Tr. 0.3 Tr. DESCRU'TIONS SAMPLE DESCRIPTIONS 153A. Pinkish-gray, medium-grained, medium-grained, foliated foliated granite, granite, SE%NE!4 SE¼NE¼ of section T. 46 46 N., N., Pinkish-gray, section 7, T. R. 26 W. W. Biotite R. Biotiteisisweakly weakly altered. 146-88. "Tilden granite" granite"ofofHammond Hammond(1978). (1978). Quartz Quartz and biotite are recrystallized in Tilden shears; biotite is slightly altered to chlorite. 1. "Tilden granite" granite"of ofHammond Hammond (1978, (1978,p.p.63). 63). Potassium-feldspar Potassium-feldspar is microperthite. Tilden has concentric zoning. zoning. Highly Plagioclase has Highly fractured. fractured. 226A. Light-gray, mediuni-grained,foliated foliatedgranite. granite. Cut Cut by by fractures. fractures. Biotite Light-gray, medium-grained, Biotite isis highly highly N., R. 26 W. altered to chlorite. chlorite. Quarry, Quarry,SE¼SW½ SE%SW?hof of section section 21, T. 46 N., 226B. Pale-reddish-brown, mediuin-grained foliated foliated granite. granite. Cut Pale-reddish-brown, medium-grained Cut by by shears, shears,some somewith with mylonite. Biotite mylonite. Biotite is is highly highly altered to chlorite and calcite. Same Samelocality locality as as 226A. 226A. 115 �GREAT GREATLAKES LAKES TECTONIC TECTONIC ZONE ZONE is characterized characterized in in the the Marquette area The GLITZ GLTZ is area by by a mylonite mylonite zone about 22 km km wide that that has has The been been superposed superposedon onpreviously previously deformed deformed layered rocks and granitoid rocks of the the northern northern Archean Archean greenstone-granite greenstone-granite terrane terraneand andpreviously previously deformed rocks of the southern southern Archean Archean gneiss rocks of of the the two two terranes. terranes. The gneiss terrane. Therefore, Therefore,the themylonite mylonite overprints rocks The great great width width of this this shear shear zone zone and and the thepreponderance preponderanceof of mylonite mylonite distinguish distinguish it from the other, other, much much narrower narrower shear shear zones zones and and faults faults in in the the region. region. The Themylonite myloniteabruptly abruptlygrades gradesnorthward northward into into protomylonite and highly fractured and altered rocks along the northeast wall of the GLTZ protomylonite and highly GLTZ (fig. (fig. 3). 3). Boundaries Boundaries(walls) (walls) of of the theGLTZ GLTZare aresubparallel subparalleland andtrend trendN.N.55°-60° 55O-600 W., W., subparallel subparallel to to the the contact between the Archean greenstone-granite and gneiss terranes (fig. 3). Foliation in contact between the greenstone-granite gneiss terranes (fig. 3). Foliation the the 750 mylonite Thus,the thefoliation foliationstrikes strikes10°100mylonite has has an anaverage averageattitude attitudeofofN.N.7Q0 700W., W., 75O SW SW (fig. (fig. 4). Thus, 15° more westward westwardthan than the the trend trend of of the shear zone walls. walls. The 15O more The angular angular relationship relationshipbetween between the the orientation orientationof of the thefoliation foliationand andshear shearzone zoneboundaries boundariessuggests suggestsdextral dextralwrench wrench shear shearalong alongthe the walls 1986,fig. fig.2b). 2b). A A pronounced rodding (stretching) lineation in the walls (Simpson, 1986, the mylonite mylonite has has an average plunge of 42° and an average bearing of S. 43° E. an average plunge of 42' and an average bearing of S. 43O E. Hinges to the stretching lineation lineation (fig. (fig. 4). 4). The Hinges of tight to open open folds folds plunge subparallel to The folds folds have asymmetricalpatterns. patterns. Z-shaped folds have both symmetrical and asymmetrical folds are are most most common, common, but SSshaped and both both may may occur occur in in the the same outcrop area, as on the shaped folds coexist and the west west shore shore of of Powell covers outcrops outcrops and and prevented prevented determination of Powell Lake (fig. 3). Nearly Nearly pervasive pervasive lichen covers 0 t 0 • 0 + ++ + + ++ 0 + ++ + ++ + ++ Lower Lower hemisphere hemisphere Equal-areaprojection projectionof ofpoles polesto tofoliation, foliation,lineations, lineations, and and fold fold axes axes in gneisses of Figure 2. Equal-area Archean gneiss gneiss terrane. terrane. Archean 116 �fold symmetries symmetriesover overlarge largeparts partsof ofthe the GLTZ. GLTZ. Ridley have demonstrated demonstrated that fold Ridley and Casey (1989) (1989) have folds, with with axes axes subparallel subparallelto to the the maximum maximum extension extension direction direction (X finite strain strain symmetrical folds, axis), are produced by wrench shear, axis), shear, whereas whereas asymmetric asymmetric folds, with axes close to the the extension extension form in in a regime of of combined combinedwrench wrenchand andthrust thrustshear. shear. In wrench shear, because the direction, form fold axis does does not not lie lie initially initiallywithin withinthe theslip slipplane planeofofshear, shear,the the axis axisrotates rotates toward toward the the direction maximum extension extensionwith withthe theaddition addition of ofprogressive progressivestrain. strain. In of shear displacement and maximum combined wrench wrench and thrust shear, at high high strain strain the the fold fold axial axial plane and and both both limbs limbs approach approach parallelism with the the shear plane. plane. Ridley parallelism with Ridley (1986) (1986) has further shown that dextral wrench shear and sinistral wrench shear can result from strain inhomogeneity in in the same shear-parallel shear-parallel extension within a single deformation regime. deformation regime. Mylonite Mylonite The mylonite (1984), mylonite in the the GLTZ GLTZisismainly mainly orthomylonite, orthomylonite, as as defined defined by by Wise Wise and and others others(1984), inasmuch as as surviving survivingmegacrysts megacrystscompose compose10-20 10-20 percent rock. theterminology terminolor of of inasmuch percent of of thethe rock. InInthe Hanmer because the the porphyroclasts have Hanmer (1987), (1987), the the mylonites mylonites are are mainly mainly "heteroclastic" "heteroclastic" because mylonite having havingmore more uniform uniform textural variable size ranges, but include include "homoclastic" "homoclastic" mylonite characteristics. Ultramylonite Ultramyloniteisis absent absent except except on on aa scale scaleof of aa few few centimeters. centimeters. The mylonite typically typicallyhas has aa pronounced pronounced planar planar foliation foliation that that differs markedly markedly from from the the more irregular foliation in in rocks rocks outside outside the the GLTZ. GLTZ. In In this this respect, respect, the the mylonite mylonite fits the pattern of of most mylonite zones in comprising a "straight zone." zone." Quartz recrystallized into Quartz typically typically is recrystallized "ribbon quartz," quartz,"yielding yieldingaapronounced pronouncedrodding rodding (stretch) (stretch) lineation. lineation. The "ribbon Therelatively relatively stiff stiff minerals, minerals, recrystallized to to finer grain sizes, with the plagioclase and potassium feldspar, are generally recrystallized development of core-mantle structures (White, 1976) or type 1P IP and 1M 1M structures structures (Hanmer, (Hanmer, these structures structures form form oriented oriented aggregates aggregatesof ofquartz quartz and and feldspar feldspar that that produce a . 1982); 1982); these prominent stretch stretch lineation. lineation. Accompanying Accompanying biotite biotite is is mainly mainly recrystallized recrystallized in planar or irregular irregular shears. The Thequartz-poor quartz-pooramphibolite amphibolitein in the theGLTZ GLTZhas hasaaconspicuous conspicuous lineation lineation given given by elongate aggregates of of actinolite and and chlorite. chlorite. The in rocks rocks in in the GLTZ are The mafic mafic mineral assemblages in are upper greenschist greenschist facies, fades, indicating retrogressive alteration of amphibolite amphibolite to to actinolite actinoliteschist. schist. Interpretation The Great Lakes Lakes tectonic zone has been interpreted (Gibbs and others, 1984) 1984) as a paleosuture that juxtaposed juxtaposed the the Archean gneiss and greenstoneresulting from continent-continent coffision collision that greenstoneInthe theMarquette Marquettearea, area,the thestretching stretchinglineation, lineation, which which represents the line of granite terranes. In tectonic transport transport (Schackleton (Schackleton and and Ries, Ries,1984), 1984),indicates indicates that that collision collision was oblique, oblique, resulting resulting in in dextral wrench-thrust shear along the N. 60° W.-trendingboundary boundary (paleosuture). (paleosuture). Asymmetric 60ÂW.-trending Asymmetric structures, mainly microscopic, indicate indicate northwestward northwestwardvergence vergence and and probable probable overriding of the structures, Archean greenstone-granite greenstone-granite terrane terrane by by the the Archean Archean gneiss gneiss terrane. collisionwould wouldbe beexpected expectedtotoproduce producedextral dextralshear shearacross acrossaalarge largeregion regionnorth north of of The oblique collision of the area affected by by this dextral dextral transcurrent transcurrent shear is not the GLTZ GLTZ (fig. (fig. 5). 5). The extent of known, however, however,because because dextral dextral shear shear was was the the dominant mechanism of deformation definitely known, deformation throughout most of the Superior Superior province (Card, in press). Structures in the greenstone-granite greenstone-granite rocks of northern Minnesota (Wawa subprovince) are similar to to those those in in northern northern Michigan. Michigan. In northern Minnesota, remarkably similar Minnesota, deformed deformed and and metamorphosed sedimentary rocks of the the Vermilion Vermilion district district(Sims, (Sims,1976; 1976;Sims Sims and and metamorphosed volcanic and sedimentary 117 �_ 1r30. : = —. (n1 - 31 32 . , / \ 1 . / ) - N 6 \'\ 4 fl \ :.' / I SS I ... S ..•... 12 S ' \ $"za' I ,L '-S R.26W.I R.25W. lUtE I - o0 I I p 1 KILOMETER Figure Figure 3. 3. Structure Structuremap mapofofsouthwestern southwesternpart partofofSands Sands7½-minute 7%-minutequadrangle quadrangleshowing showing the the Great GreatLakes Lakestectonic tectoniczone. zone. Modified Modifiedfrom fromSims Sims(1991). (1991). 118 �________ _________ _______ D(PLANATION EXPLANATION Figure 3--Continued 1 Wsg Archean Greenstone-granite terrane tenane Biotite schist and and granitoid rocks [ e l Wggm I[ [wgn Mylonlte—Protollth MylonitÑProtolit dominantly dominantly granttoid granitoid rocks rocks but but includes includes blotite schist sdilst and biotite and amphlbolite amphibolite Gneiss terrane Gneiss, migrnatite, migmatite, and andamphibolite-includes amphibolitdncludeifoliated foliatedand and granite massive massive granite Mylonfte—Oomlnantly mylonitic Mylonite-Dominantly myloniticquartzofeldspathic quarlzofeldspathicgneiss gneiss wgmj [Â¥Wgm Silkified . Silicified rocks rocks :.'I... .. .. . --— — — Boundary between rocks of of greenstone-granite Boundary between rocks greenstone-granite terrane terrane . ------ 25 + - —ts F45 20 and gneiss gneiss terrane terrane within wIthin the Great and Great Lakes tectonic (GLTZ ) zone (GLTZ) Approximate outer limit limit of of orthomylonite orthomylonite in in Great Great Lakes tectonic zone Strike Strike and dip of foliation foliation Inclined Indined Vertical Bearing and and plunge plunge of of minor fold Bearing fold Bearing and andplunge plungeof olineation—May f lineation-Maybebe combinedwith with Bearing combined symbols Ioliatlon foliatton symbols + + + ++ +- 0 •. ++ . . Lower Lower hemisphere hemisphere 4. Equal-area Figure 4. Equal-areaprojection projection of of poles polesto to foliation foliation (crosses), (crosses), stretching stretching lineation (dots), (dots), and and fold hinges (open circles) in mylonite mylonite of of the the Great Lakes Lakes tectonic tectonic zone, zone, Sands Sands and and Palmer 7½-minute 7%-minute quadrangles, Marquette area, area, Michigan. Michigan. 119 �\ '' I 95° Complex continental-margin sequences Plutonic and volcanic rocks Middle Proterozoic Volcanic, sedimentary, and plutonlc rocks of Mldcontinent rift system (i.1,100 Ma) Early Proterozoic Turbid,tes overlying shelf deposits 96° 940 E 930 cover )" ,°. Rocks of gnelss terrane Rocks of greenstone-granite terrane (Sutienor province) ean EXPLANATION (ntad A 91° f No PalOoZOiC(o>,A>dI>c(1, 92° -, s 89° 89° A A Trace of Great Lakes tectonic zone I3LTZ) Thrust fault— Sawteeth on overthrust block — — — Trend of magnetic anomaly A movement I ± Transcurrent fault— Showing relative horizontal High-angle fault 4 owisconsin magmat(c terranes ,__a_rv•r r.a.cntyJ pFAULLII ,' ',a 900 Figure 5. Simplified tectonic map of the Lake Superior region showing Great Lakes tectonic zone and adjacent Archean terranes. After Sims (1991). Terminology of Early Proterozoic rocks modified from Southwick and Morey (1991). I 97° �Southwick, 1985)compose composean an east-trending east-trendingbelt belt between between higher higher grade grade rocks rocks of of the Late Archean Southwick, 1985) Archean Vermilion Granitic and the Giants Granitic Complex Complex (Quetico (Quetico subprovince, subprovince, fig. 5) (Southwick, 1972) and Giants Range batholith to the south. The Themeasured measuredstrain, strain,aacleavage, cleavage,upright upright folds, folds, and a mineral mineral lineation in this belt have been attributed to the the main" "main"phase phaseof ofdeformation deformation(D2) (D,) that thatfollowed followed an early nappe-forming event event (Dl) (D1) (Bauer, (Bauer, 1985). 1985). The nappes show little little evidence of of aa (D,) penetrative fabric (Hudleston, 1976). 1976). Hudleston and others others (1988) (1988) attributed attributed the the (D2) deformation to regional dextral transpression, transpression, as as the the strain pattern requires requires aa northeastnortheastsouthwestcomponent componentofofshortening shorteningininaddition additiontotoshear. shear. They They further further proposed proposed that that major major southwest dextral faults, such such as the Vermilion fault (fig. (fig. 5), 5), are are later, more brittle, expressions of this D2transpressive transpressive deformation resulted from from oblique oblique shear regime. They Theyconcluded concluded that that the theD2 compression between between the two more rigid crustal blocks blocks to to the the north (Quetico (Quetico subprovince) subprovince) and south (Giants Range batholith). A Asimilar similar tectonic tectonic regime regime has been recognized recognized in the the Rainy Rainy Lake area area (fig. (fig. 5; 5; Poulsen Poulsen and andothers, others,1980; 1980;Day Day and andSims, Sims,1984; 1984; Wood, Wood, 1980), 1980), where where early early recumbent folding by upright folding and dextral strike-slip folding was followed by strike-slip faulting. Recent precise isotopic analyses of of zircon, zircon,titanite, titanite, and and rutile rutile from the Rainy Lake area, area, Canada Canada (fig. 5; Davis and others, others, 1989), which lies lies between between the the Quetico Quetico and 1989), which and Wabigoon Wabigoon subprovinces, subprovinces, provided time time constraints constraints on on these these structural events. events. The have provided The major major deformation, deformation, including including nappe emplacement, emplacement, thrusting, and local doming, took place between 2,696 Ma and 2,692 Ma; followed shortly shortlyby bytranscurrent transcurrent faulting faulting and and simultaneous simultaneous deposition deposition of this deformation deformation was followed conglomerate/arenite (Timiskaming-type rocks, as as in in Seine Seine Group), Group), which which occurred occurred in in the the conglomerate/arenite (Tirniskaming-type rocks, 2,692-2,686Ma. Ma. Late (Algoman) granitic plutons were emplaced about 2,686 Ma, interval 2,692-2,686 and although some are older. InInthe theWawa Wawasubprovince, subprovince,west west of of Thunder Thunder Bay Bay (fig. (fig. 5), Corfu and found that that the D1 deformation occurred occurred during duringor or before before the the intrusion intrusion of of the Stott (1986) found Dl deformation Shebandowan Lake Lake pluton pluton at at 2,696± 2,696±2 Ma. Ma. Deformation Shebandowan Deformation D2 D2 in this area occurred between 2,689+3/-2 +3/-2 Ma Ma and and 2,684+ 2,684+6/-3 by Davis and others (1989) for 2,689 61-3 Ma, similar to the age age suggested suggested by D2 in the Rainy Lake wrench fault zone. These ages are compatible D, in Rainy Lake wrench fault zone. compatible with the less precise on rocks in in northern Minnesota and Michigan (Peterman, isotopic ages on (Peterman, 1979), 1979), and it seems seems probable that the the rocks rocks and and structures structuresthroughout throughout the the Wawa Wawa and and Quetico Quetico subprovinces subprovinces are approximately coeval coeval (Percival, (Percival, 1989). 1989). Although Although convergence convergencealong alongthe the GLTZ GLTZ undoubtedly was approximately probably occurred occurred in the approximate diachronous, collision probably approximate interval interval2,692-2,686 2,692-2,686 Ma (Davis and others, 1989), 1989), to yield the transcurrent transcurrentfaults faultsand andTimiskiming-type Timiskiming-typerocks. rocks. Kinematic Analysis Kinematic Analysis attitude of of the the stretching stretchinglineation lineation (line (line of of tectonic tectonic transport) transport) in in the themylonite mylonite exposed exposed south south The attitude of Marquette together micro-structures that that reveal reveal sense of of together with with asymmetric asymmetric meso- and micro-structures movement, indicate that that the theoblique obliquecollision collision resulted resulted in: in: (1) dextral-thrust shear along the the GLTZ, and and (2) (2) northwestward northwestward vergence and probable overriding of the Archean Archean greenstonegreenstonegranite terrane terrane by by the the Archean Archean gneiss gneiss terrane. terrane. Kinematic Kinematicindicators--rotated indicators--rotatedmica micagrains grainswithin within narrow compositional layers, asymmetric porphyroclasts porphyroclastswith withtails tails (o (a type; Simpson, 1986), and and asymmetric microfolds in in mylonitic myloniticlayering-demonstrate layering--demonstratenorthwestward northwestwardvergence. vergence. This information implies southward subduction of (Wawa of the the Archean Archean greenstone-granite greenstone-granite terrane terrane (Wawa subprovince) beneath beneath the Archean gneiss gneiss terrane terrane (fig. (fig. 1). 1). 121 �Evolution The northwest direction of tectonic transport during suturing of the Archean terranes, terranes, as as ascertained from the Marquette area, area, provides provides a means for determining the evolution evolution of the GL1'Z GLTZ and the variable trajectory of stress into the the Superior Superior province province crust. The GL1'Z bends that GLTZ in the Lake Lake Superior Superior region region is is characterized characterized by systematic angular bends alternately (fig.5). 5). Presumably this zigzag zigzag pattern pattern alternately trend northeastward and west-northwestward west-northwestward (fig. reflects relict relict irregularities irregularities in in the the margin margin of of the the Archean Archean greenstone-granite greenstone-graniteterrane terrane (or Superior reflects was aa continental margin before the province) crust, which was the convergence convergence and and coffision collision with the southern Archean gneiss terrane. gneiss terrane. segmentsof ofthe the GLTZ GLTZ have have different different The northeast-trending and west-northwest-trending west-northwest-trending segments structural styles. styles. Deformation Deformation along along the the northwest-trending northwest-trending segments of the GLTZ, GLTZ, as as by data data from the particularly shown by the Marquette Marquettesegment, segment,was wasprincipally principally caused caused by by dextral dextral transpression resulting from oblique oblique collision. coffision. Transmittal Transmittal of of this this transcurrent transcurrent shear into rocks rocks north of of the theGLTZ GLTZyielded yieldedaawidespread, widespread,pervasive pervasivewest-northwestwest-northwest- to towest-striking west-striking foliation, foliation, subparallel upright upright folds, and northwestnorthwest- to west-trending west-trending dextral dextral faults faults and and shear zones in the the Archean greenstone-granite terrane. northwest-trending segment segment of of the the GLTZ in northwestern Wisconsin The similarly-oriented northwest-trending Wisconsin has structural features in common common with withthe the Marquette Marquette segment. segment. Foliation and many structural and upright upright folds folds in low amphibolite-facies amphibolite-facies rocks rocksof of the the Archean Archean greenstone-granite greenstone-granite terrane terrane (unit (unit Wga, Wga, fig. fig. 4, Sims low and others, others, 1985) 1985) strike strike west-northwest and mineral lineations and fold hinges mainly plunge gently southeast. The gently southeast. The boundary boundary between the two terranes is not exposed exposed because of a glacial cover, but but is presumed presumed to lie along along the the south south edge edge of of unit unit Wga. Wga. Numerous northwest-trending cover, faults, some of of which which reactivated reactivatedin in Early EarlyProterozoic Proterozoictime, time,have havebeen been mapped mapped in in the dextral faults, area (Sims (Sims and and others, others,1985; 1985; fig. fig. 1). 1). Coffisionalong alongthe the northeast-trending northeast-trending segments segmentsofofthe the GLTZ, GLTZ, on on the the other hand, produced Collision northeast-trending structures structures of of apparently apparentlymore morerestricted restrictedareal areal extent. extent. In the northeastnortheast-trending northeastthe boundary is covered by Early trending Marenisco segment (fig. 5; Sims and others, 1984), the lithologic layering layering and and foliation foliation in rocks of Proterozoic sedimentary sedimentary and and volcanic volcanic rocks, however, lithologic Archean greenstone-granite greenstone-graniteterrane terrane near near the boundary boundary trend trend northeastward northeastward and are the adjacent Archean 45°-50° SW. These deformed into upright, moderately tight northeast-trending folds that plunge 45' -50' SW. subparallel to to the the covered covered Archean Archean GLTZ GLTZ boundary. boundary. Archean structures are presumably presumably subparallel metamorphism has been overprinted overprinted by by Early Proterozoic Penokean nodal nodal metamorphism metamorphism centered on on the theWatersmeet Watersmeet dome dome(Sims (Simsand andothers, others,1985; 1985;Sims, Sims, 1990); 1990); the presence of of relict relict garnet at aa few rocks of of the the greenstone-granite greenstone-granite terrane terrane near the boundary few places in the Archean rocks suggests that that these rocks were metamorphosed metamorphosed to to at least upper greenschist facies in Archean time. Similarly, Similarly, north-verging north-verging Penokean deformation in the the boundary boundary zone zone overprinted overprinted Archean Archean structures (Sims and others, 1984). plane S, 2 (Penokean) (Sims and 1984). An axial plane (Penokean) penetrative penetrative cleavage, cleavage, striking northeast SE., was was superposed superposed on on the previously previously folded folded rocks. rocks. Apparently northeast and and dipping dipping 45°-70° 45'-70' SE., Apparently the Archean rocks were not refolded, however, as aa result result of of the Penokean deformation. however, as In the northeast-trending segment of of the the GLTZ (fig. (fig. 5), 5), neither neither the terrane terrane boundary northeast-trending Minnesota segment nor adjacent Archean rocks on either side are exposed. These These rocks rocks are are covered covered in in west-central west-central by thick thick Quaternary glacial deposits deposits and and in in central central Minnesota by by Early Proterozoic Minnesota by sedimentary and volcanic rocks rocks of of the the Animikie Animikie basin basin (Southwick (Southwickand andothers, others, 1988). 1988). The GLTZ GLTZ 122 �has been investigated, computer-generated investigated, however, however, by a detailed detailed aeromagnetic aeromagneticsurvey, survey, by computer-generated the second second vertical vertical derivative derivative of of the the gravity gravity field, field, and and by by shallow shallow test drilling drilling (see (see mapping of the Southwick and Southwick and Sims, Sims,in inpress); press);the the boundary boundary has has been been located located rather rather accurately on on the basis of these data. The Thedrilling drillinghas hasshown shown that that the therocks rocks on on the thenorthwest northwestside sideare arevolcanogenic volcanogenic sedimentary and mafic to intermediate rocks,which whichare aremetamorphosed metamorphosed to to upper upper intermediate volcanic volcanic rocks, greenschist facies facies and and intruded by by Archean Archean tonalite (Southwick (Southwickand and Chandler, Chandler, 1983). 1983). These greenschist of the the Archean Archean greenstone-granite greenstone-granite terrane terrane in exposed exposed parts parts of of the Lake rocks are typical of region. A by COCORP COCORP Superior region. A seismic seismic reflection profile in central Minnesota acquired by (Consortium for Continental Reflection Profiling)has hasbeen been interpreted interpreted to indicate that the Reflection Profiling) the GL1'Z north-dipping tectonic tectonic feature feature (Gibbs and others, this area area isisaashallow shallow(—30°) (-30° north-dipping others, 1984). 1984). GLTZ in this In east-central Minnesota, the the GLTZ GLTZ isis covered covered by by Proterozoic Proterozoic rocks of the the Animikie Animikie basin. The structural structural style style in the the Proterozoic Proterozoiccover cover indicates indicates north-verging north-verging tectonism tectonism (Southwick (Southwick and others, others, 1988), 1988), and as in the Marenisco Marenisco segment, the Archean crustal crustal boundary had aa role role in in defining Penokean deformation. deformation. Deformation along both of the northeast-trending of the northeast-trending (Minnesota and Marenisco) segments of GL1'Z resulted mainly from northwest-southeast crustal shortening, probably dominantly by GLTZ resulted mainly from northwest-southeast crustal shortening, probably dominantly by flattening strain. The Thedirection directionofoftectonic tectonictransport transportduring duringconvergence convergencewas was virtually virtually perpendicular to the the juncture of of the the two two terranes terranes at at these theselocalities. localities. The origin of the the zigzag zigzag pattern of the the south south edge edge of of the the Superior Superiorprovince, province, now now marked marked by by the the GL1'Z, is uncertain. uncertain. The is one one of of a sequence GLTZ, The prevailing prevailing thought is that the Wawa subprovince is of stacked island arcs that formed from north north to south above north-dipping formed progressively progressively from subduction zones zones as as the the continental mass mass to to the south of the GLTZ GLTZ (i.e., (i.e., Archean gneiss terrane) terrane) migrated migrated to the the north north (Card, (Card,1990). 1990). With Withthis thisinterpretation, interpretation,possible possible modern modem analogs analogs of the Superior province are the convergent-plate boundaries of the western Pacific, as for Superior province are the convergent-plate of the western Pacific, as for example those of the the Indonesian Indonesian region region (Hamilton, (Hamilton,1979). 1979). The physical of the southern margin of the Superior physical resemblance of Superior province to the the AppalachianAppalachianOuachita Paleozoic orogenic belt (Thomas, 1977), however, suggests a possible alternative Paleozoic orogenic belt (Thomas, 1977), however, alternative margin. In this interpretation, the interpretation for the origin of the Superior margin. the Superior Superior margin margin. Two interpretations have been been made for the origin of the was a rifted continental margin. margin: (1) Paleozoic continental margin: (1)rift riftsegments segmentswere were offset offset by by transform transform faults, faults, as as suggested suggested by by 1983),or or (2) (2) intersections intersections between between active activerift rift arms arms at at triple junctions junctions (Rankin, Thomas (1977, (1977, 1983), with the 1976). Of these these two two suggestions, suggestions, the rift-transform mechanism seems the more more likely, with 5) and and the northwestern northwestern Minnesota and Marenisco Marenisco segments segmentsbeing being the the rifted rifted segments segments(fig. (fig. 5) Wisconsin and and Marquette segments being highly highlymodified modifiedtransform transformfaults. faults. Regardless of the Wisconsin the by which whichthe the zigzag zigzagArchean Archeancontinental continentalmargin marginoriginated, originated,the thesubsequent subsequent trace trace of of mechanism by the orogenic belt was probably probably inherited inherited from from the the shape shape of of the earlier margin. CONCLUDING CONCLUDING REMARKS REMARKS Convergence along the the irregularly shaped shaped margin margin of of the the Archean greenstone-granite greenstone-granite terrane terrane (GLTZ) resulted resulted in in aa variable variable trajectory trajectory of of stress stress into the the continental continentalcrust crust and and probably probably in in diachroneityofoforogeny. orogeny. Structural Structuraldata data from fromthe the Marquette Marquette area, in particular, as along-strike diachroneity well as as elsewhere elsewhere along alongthe the GLTZ, GLTZ, suggest suggestthat thatthe the major major direction direction of of tectonic tectonic transport transport was well northwestward. Accordingly, promontories such as those along the concave parts of the northwestward. Accordingly, promontories the Marquette and and Wisconsin Wisconsin segments of the GLTZ GLTZ (fig. (fig. 5), where the zone bends from a northeast orientation orientation to to aa northwest northwest one, one, must must have have projected projected as as buttresses buttressesagainst against which which 123 �compressive compressive stress was directed into the continental crust. Oblique Obliquecompression compression at atthese thesepoints points produced produced dextral dextral shear across across the region north of of the the suture, suture, probably probably at least least as as far far northward northward as km. This as the the Quetico Quetico fault fault (fig. (fig. 5), a distance distance of about 250 km. This shear shear imposed imposed aa roughly roughly easteastwest, west, steep steep structural structural fabric fabric on the the rocks rocks and, also as a late, more more brittle brittle expression expression of the the shear shear regime regime (Hudleston (Hudleston and andothers, others,1988), 1988),the thenorthwestnorthwest- to towest-trending west-trending dextral dextraltranscurrent transcurrentfaults. faults. Along Along the the Marenisco Mareniscoand andMinnesota Minnesotasegments segmentsof ofthe theGLTZ GLTZ(fig. (fig.5), 5),where whereconvergence convergencewas was more more perpendicular perpendicular to to the theancient ancientcontinental continentalmargin, margin, aanortheast-trending northeast-trendingstructural structuralfabric fabricwas was imposed imposed on on the therocks rocksimmediately immediately cratonward cratonward from from the thesuture. suture. We We suggest suggest that the the main main structural structural fabric fabric (D2) (D2) in rocks of the Archean greenstone-granite greenstone-granite terrane 5)resulted resulted terraneininthe thenorth-central north-centralUnited UnitedStates States(Wawa (Wawaand andQuetico Queticosubprovinces; subprovinces;fig. fig. 5) from along the the GLTZ. GL1'Z. The from the the coffision collision along The predominance of orthomylonite rather than ultramylonite ultramylonite and and the thenearly nearly pervasive pervasive retrogressive retrogressive alteration alteration (greenschist (greenschist facies) fades) in inrocks rocksof of the the greenstone-granite greenstone-granite terrane terranesuggest suggest that that the theexposed exposedcollision collision zone was developed at aa moderately level (at (at brittle-ductile brittle-ductile transition transition conditions). conditions). As discussed in a moderately shallow shallow crustal level previous report (Sims and others, 1980), the Archean structures previous report (Sims and others, 1980), structures in in this this regime regime also also played played aa strong strong role role in in subsequent subsequenttectonism, tectonism, especially especially in the the Early Early Proterozoic Proterozoic north-verging north-verging deformation. deformation. We We further further suggest suggest that the the late-tectonic late-tectonic granite bodies in the Archean gneiss terrane are are possibly related to the collision along the the GLTZ GLTZ and presumed presumed southward southward subduction. subduction. The possibly related collision along available available age data on these these granites granites are are compatible compatible with a presumed 2.69 2.69 Ga age for the coffision. collision. The The "Tilden "Tilden granite" granite" of Hammond (1978) (1978) in Michigan Michigan has a Late LateArchean Archeanage age (2,585±15 both the U-Pb and Rb-Sr Rb-Sr systems systemsare are disturbed. disturbed. In the (2,5852 15 Ma), although although both the Minnesota Minnesota River southwestern Minnesota, Minnesota, aa large large pluton pluton of of late-tectonic late-tectonic granite granite (Sacred (Sacred Heart River valley, in southwestern Granite) and a Rb-Sr age of Granite) has has aaPb-Pb Pb-Pb age ageof of about about2,605 2,605 Ma (Doe (Doe and and Delevaux, Delevaux, 1980) and about andand Delevaux (1980) have shown thatthat 207Pb-204Pb about 2.7 2.7 Ga Ga(Goldich (Goldichand andothers, others,1970). 1970).Doe Doe Delevaux (1980) have shown ^Pb-^Pb values in the Sacred Heart Heart Granite Graniteare arecharacteristic characteristicof of ensialic ensialic environments, environments, as contrasted with the the ensimatic ensirnatic (arc) (arc) granitoid granitoid bodies bodies in the the Superior Superior province (greenstone-granite terrane). with The The ensialic ensialic environment indicates that the Archean gneiss terrane had been cratonized cratonized prior prior to to emplacement of the Sacred Sacred Heart Granite. Granite. Precise emplacement of Precise ages ages are are required required to to test test the thehypothesis hypothesis that that the the Late Late Archean Archean granites granites south south of of the theGLTZ GLTZwere wereindeed indeed formed formedduring duringcontinent-continent continent-continent collision. collision. Cumulative Cumulative data on on the the Archean Archean Superior Superiorprovince province (see (see Hoffman, Hoffman, 1989, 1989, for review) review) indicate consists of of generally east trending belts that itit consists belts of of island island arc arc and related rocks that were assembled progressively from from north to south south (Card, (Card, in in press), press),before beforefmally finallycoffiding colliding with the Archean Ma. 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Wood, of the Hewitt Lake area, Wood, John, John, 1980, 1980, Geology of area, District District of of Kenora, Kenora,Patricia Patriciaportion: portion: Ontario OntarioGeological GeologicalSurvey, Survey,Report Report186, 186,122 122p. p. 130 �Field stops and road log Field stops stops shown shown on figure figure 66 Miles 0 0 3.8-6.3 Depart from from Ramada RamadaInn Inninindowntown downtown Marquette Marquetteon onMichigan Michiganhighway highway28 28 (M28) (M28) and proceed proceed west. west. of pillow pillowbasalt basaltalong alongM28. M28. Basalt Basaltcomprises comprisesaamajor majorpart part of of Numerous outcrops of Archean greenstone-granite terrane terrane (Wawa (Wawa subprovince) subprovince) in the the northern northern complex complex of Marquette Marquette district. district. Proterozoic rocks of Marquette Early Proterozoic Marquette syncline syncline lie to the the south southof ofhighway. highway. 7.2 Turn left (south) (south)from from M28 M28 onto ontoM35. M35. 10.8 M35 intersects Marquette County road road 480 480 (Co. (Co. 480). 480). Continue Continue south south on on M35. M35. 11.2 Outcrops Outcrops of Early Proterozoic Proterozoic Negaunee Negaunee Iron-formation. Iron-formation. 14.1 o'clock, Empire Empire iron iron mine mine waste waste rock. rock. Pass through Palmer. High dumps at 12 o'clock, 16.9 Turn right right (west) (west)on onCounty Countyhighway highway 565. 565. 18.1 At road road fork fork turn turnright rightonto ontoCounty Countyhighway highway 476. 476. 19.5 Stop 1. 1. Roadcut Roadcutinin"Tilden Tilden granite" granite" (Hammond, (Hammond, 1978). 1978). The "Tilden granite" granite" is aa pinkish-gray pinkish-gray to to pink, pink, medium-grained, medium-grained,locally locally porphyritic, porphyritic, massive to weakly weakly foliated, foliated, homogeneous homogeneous granite granite that that locally locally contains contains oriented oriented of mafic mafic gneiss. gneiss. It intrudes xenoliths of intrudes gneisses gneisses and in turn turn isis cut cut by by pink pink pegmatite. pegmatite. surfaces and a thin The granite is is highly fractured; the fractures have slickensided surfaces of chlorite chlorite and and other other propylitic propyliticalteration alterationminerals. minerals. The granite has a U-Pb coating of concordia intercept age of 2,585±15 Ma (R.E. Zartman, 2,585Â15 Zartman, oral oralcommun., commun., 1991). 1991). Chemically, the granite has characteristics of post-orogenic, within within plate plate granite on Chemically, the on Bornhorst, written written commun., commun., 1990), 1990), which is consistent consistent discrimination diagrams diagrams (T. Bornhorst, with its its post-tectonic post-tectonic field field relationships. relationships. Continue southwest Continue southwest on on Co. Co. 476. 476. 19.7 Turn around and return to to M35. M35. 22.4 Junction of Co. 476 and M35. M35. Proceed Proceed southeast southeaston onM35. M35. 23 gneiss terrane). terrane). Stop 2. High High roadcut roadcut on on M35 M35 in in Archean Archean gneiss (of Archean gneiss Road shoulder is narrow. Be Becareful. careful. Excellent outcrop outcrop of of layered layered gneiss gneiss(of (ofArchean Archeangneiss gneissterrane) terrane) on on the the northeast Excellent side of road. Amphibolite Amphibolite and and quartzofeldspathic quartzofeldspathic gneiss gneiss are are interlayered, and are by red pegmatite. Pegmatite cut by Pegmatite and and aplite aplite are areboudined boudined and andbrecciated; brecciated; boudins boudins 131 �plunge plunge parallel to to recumbent recumbent fold fold axes. axes. Tight Tightfolds foldswith with axial axial planar planar foliation foliation plunge 25' with a strike strike of of N. N. 50 5 ' W., W., as as does does aa mineral mineral lineation. lineation. plunge about about 25° This This outcrop outcrop is is typical typical of the gneiss of the Archean gneiss terrane, but amphibolite amphibolite is abundant here. Tight is uncommonly uncommonly abundant Tight recumbent recumbent folds folds that thatplunge plunge gently gently northward northward are are the the dominant dominant structures structures in in this this part part of of the thegneiss gneiss terrane. terrane. Return M35. Return to tovehicle vehicle and and continue continue southeast southeaston onM35. 23.7 M35 intersects private road road (Cleveland (ClevelandCliffs Cliffs Iron Iron Company). Company). 24.2 Stop 3. area. Outcrop 3. Low Low outcrop outcrop on on northeast northeast side of road in grassy grassy area. Outcrop has has been been covered covered by by loose sand sand and and isislichen lichen free. free. This outcrop contains contains northwest-trending northwest-trending folds folds with an an axial axial planar planar foliation foliationvisible visible 600 on polished polished surfaces surfaces that that strikes strikesN. N. 65° 65' W., W., and and dips dips 60' NE. NE. This structure structure is is superposed on recumbently folded folded gneiss, gneiss, and and therefore therefore is younger. younger. Thick Thick layers layers of felsic gneiss retain retain a dominant older older foliation foliation that that strikes strikesN. N. 250 25' W. W. The steep foliation and and associated associated folds foldsare are parallel parallel to to the the trend steep northwest-trending northwest-trending foliation of the (of Marquette district). district). Although the antiformal antiformal southern complex complex (of Although minor minor in in this this area, area, upright upright northwest-trending northwest-trending folds are the dominant dominant structures structures in in the theRepublic Republic area, 30 km km to to the thewest. west. area, 30 M35. Continue southeast southeast on on M35. Continue 132 24.3 Turn around around at atCommunity Community Club Club and and proceed proceed northwest northwest on on M35 M35 toward toward Palmer. Palmer. 24.9 M35 intersects private private road road (CCI). (CCI). Continue Continue north north on on M35 M35 to to intersection intersection with with 480. Co. 480. 32.3 Intersection of M35 and Co. 480. Turn Turn right right (east) (east) on onCo. Co.480. 480. 35.6 Turn right (south) on secondary road. road. Roads Roads for for remainder remainder of of field field excursion excursion are are unmarked; accordingly, we have have arbitrarily arbitrarily assigned assigned letter letter designations A through L accordingly, we L (see fig. 3) to specific segmentsas asan anaid aidininlocation. location. The main main road into area specific segments (road A) A) is is aa graded graded sandy sandy dirt road; other other roads roads followed followed on the trip are are not not and may may be be rutted rutted or orsoft, soft,requiring requiringsome somecare careinindriving. driving. graded and 39.6 Road A A crosses crosses Chicago Chicago and and Northwestern Northwestern railway railway near near Gentian. Gentian. 39.7 (B) and andcontinue continuesouthwest southwest on on B. B. road fork fork (B) Take right road 40.6 Junction with east-west east-west road road (C). (C). Proceed Proceed west west on on CC for for0.3 0.3 mi. mi. �40.9 40.9 Stop 4. Rock Rockknob knobnorth northside sideof of road road C. C. Stop This This outcrop outcrop isis typical typical of of the the Archean Archean greenstone-granite greenstone-granite terrane. terrane. ItIt consists consists of of granite granitegneiss gneiss (or (or foliated foliated granite) granite) that thatcontains containslenses lensesof ofbiotitic biotiticand andchioritic chloritic amphibolite. amphibolite. These Theserocks rocksare arecut cutby bygranite granitepegmatite pegmatiteand andaplite, aplite,which whichcrosscut crosscut the the foliation foliation in in the the granitoid granitoid rocks. rocks. Note Notethat thatcrosscutting crosscutting aplite aplite and and pegmatite pegmatite are are not 70ÂW. W.and anddips dips65° 65' Sw. SW. not sheared shearedout. out.Foliation Foliationstrikes strikesN.N.70° Although Although this outcrop lies near the the north north margin margin of of the theGreat GreatLakes Lakestectonic tectoniczone zone and although it has a foliation subparallel to that in the GL1'Z, the outcrop and and although it has a foliation subparallel the GLTZ, the outcrop and those those to tothe thewest-northwest west-northwest are areexcluded excluded from from the theGLTZ GLTZbecause becausethe thecrosscutting crosscutting pegmatite pegmatite and and aplite aplite are are not not sheared sheared out out and and the the rocks rocks are are protomylonite. protomylonite. The The northern northern boundary boundary isis placed placed at at the theabrupt abrupttransition transitionfrom from"straight-banded" "straight-banded" mylonite in the GL1'Z GLTZ to to rocks rocks that that retain retainrecognizable recognizable igneous igneous structures, structures, such such as as here. The Therocks rockstotothe thenorth northofofthe theGLTZ GLTZare areprotomylonite. protomylonite. Return Return totovehicle vehicleand andcontinue continuewest weston onCCfor for0.2 0.2mile. mile. 41.1 41.1 Intersection Intersection of roads C and D. Turn Turnleft left on onDDand andcontinue continuefor for0.4 0.4 mi. mi. 41.5 41.5 Stop 5. Outcrops Outcropsofofmilky milky quartz quartz and andaltered alteredArchean Archeanrocks rocksabout about50 50yards yardswest west of of Stop D. road D. road Milky Milky quartz and and silicified silicified country rock, such as those exposed here, here, characterize characterize the the hifis hills to the west. These Theseoutcrops outcrops comprise comprise the the most most eastern eastern exposed exposed part part of of aa quartz km long. The quartz 1.4 l un long. quartz body body quartz lense, oriented about about east-west, east-west, that is about 1.4 may may occupy a major tension fissure zone related to to dextral dextral wrench wrench shear shear within within the the GLTZ. GLTZ. Turn Turn around around and and proceed proceed north north on onDDtotointersection intersectionwith with C. C. Then Then follow follow C and D to to road road fork fork at atGentian Gentiancrossing. crossing. 42.8 42.8 sharply right from road B B onto onto road road E; E;continue continuesouth southfor for1.2 1.2ml. mi. Turn sharply 44 44 Road Road fork; fork; continue continue south south on on road road F. F. 44.35 44.35 Road fork (G), (G), then turn left at road Road fork; fork; continue south on right fork road fork fork onto onto H Hand and east on on H Hto tolocked lockedgate. gate. continue east 45.0 45.0 and walk walk on private road east east and and northeast northeast to towest west shore shoreof ofPowell Powell Lake Lake Park and (distance 0.3 mi). walk 0.3 mi). Walkisiseasy. easy. Stop Thisisisan anexceptionally exceptionally good good series series of of outcrops outcrops of of mylonite mylonite within the Stop 6. This GLTZ clean. The dominantly granite granite GLTZ because because they they are areperiodically periodically washed washed clean. Therock rockisisdominantly gneiss containing pods pods of of migmatized migmatized amphibolite amphiboliteand and hornblende hornblende schist. schist. The The protolith is is granite and and amphibolite amphibolite of the Archean greenstone-granite terrane. 133 �variable. A Foliation in the the gneiss gneiss strikes strikes about about N. N. 75° 75' W. W. and and dips dips 75° 75' SW., SW., but is variable. conspicuous stretching stretching lineation lineation plunges plunges uniformly uniformly about about550 55' and bears bears S. S. 45° 45' E. Both dextral and sinistral asymmetric folds plunge plunge subparallel subparallel to to the lineation; dextral folds predominate. predominate. Porphyroclasts Porphyroclasts are are common, common, but they they do do not not clearly clearly have internal monodlinic symmetly and and elongate elongate tails, tails, necessary necessary to to determine determine monoclinic symmetry 1986). movement sense sense (Simpson, (Simpson,1986). Return to parked vehicle at locked lockedgate. gate. Proceed Proceed west west on on road road H H to road fork vehicle at (distance 0.25 mi), then then turn right on H to 0.25 mi), to junction of of H H with with JJ (distance (distance0.15 0.15 mi). mi). 45.4 Junction of of roads roads H and J. Turn Junction Turnsharply sharply left left on on JJ and and continue continue for for 0.2 0.2 mi. mi. 45.6 45.6 Road fork. Continue Continueon onright rightfork fork(K) (K)for for0.1 0.1ml. mi. 45.7 45.7 northwest, a distance distance of about about 750 750 ft, to outcrops. outcrops. Park and walk on trail to northwest, Stop 7. Low Low outcrops outcropsof of pink pink mylonitic mylonitic gneiss with lenses of biotite schist. Protolith is considered to be felsic felsic gneiss gneissof ofArchean Archeangneiss gneissterrane. terrane. Foliation N. 750 75' W. and dips dips 65° 65' SW. A quartz quartzrodding rodding lineation lineationplunges plunges50° 50' and and strikes N. strikes SW. .A S. 45' 45°E. E. Note abundant ribbon ribbon quartz. quartz. This outcrop is in the southern part bears S. of the GLTZ. Return to road. Turn Turnaround aroundand andfollow follow roads K and J to road road fork fork with with H. Proceed south on H H to to junction junction (1.5 (1.5 mi). 46.2 Continue south on L. 47.3 Road L intersects power line. Park Parkand andwalk walk750 750ftft southwest southwest to tolow low outcrops outcrops along power line. Stop 8. Outcrops Outcropscomprise comprise pink pink granite granitegneiss gneiss with amphibolite layers and lenses, cut by Foliation strikes strikes N. 40° 40' W., by pink pink granite granite pegmatite. pegmatite. Foliation W., and and dips dips 80' 80°NE. NE. Rocks are not sheared. sheared. Two Twoparallel parallel diabase diabasedikes dikes cut cut the theArchean Archean gneiss. gneiss. These outcrops are are within the Archean gneiss terrane, a distance of about 0.65 0.65 km south of the south boundary boundary of the (3L1'Z. GLTZ. Thus, Thus, we have crossed from the Archean greenstone-granite terrane, through the GLTZ, into the the Archean Archean gneiss gneiss terrane terrane to to the the south south of of the the GLTZ. GLTZ. Suggest returning to Co. Co. 480 via End of field trip. Suggest via dirt roads L, G, F, E, and A. 134 �U) w -J In — U) w I 0— -0 Figure 6. Field Fieldtrip tripstops. stops.Marquette Marquetteand andmost mostofofMichigan Michiganhighway highway 28 are are just north north of of the the Figure map area. area. 135 �Issues of the Proceedings of this meeting may may be ordered ordered from from M.G. Mudrey, Mudrey Jr., M.G. Jr., Secretary-Treasurer Secretary-Treasurer do c/oWisconsin WisconsinGeological Geologicaland and Natural Natural History History Survey Survey 3817 38 17 Mineral Mineral Point Road Road Madison, Madison, Wisconsin Wisconsin 53705-5 53705-5100 100 1: Program and Abstracts: $7.00 U.S. Part 1: Part 2: Field Trip Guidebook: Guidebook: $7.00 U.S. Orders Orders will will be filled while supplies last. last. All volumes back to 1955 1955 are are available available for for photocopying photocopying at at the the prevailing prevailing rate, rate, from from the the Michigan Michigan Technological Technological University University Library, Library, through through Mr. Mr. M.S. M.S. Spence, Spence, Archivist. Archivist. Telephone Telephone (906) (906) 487-2505 487-2505 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1992 Description An account of the resource Institute on Lake Superior Geology. Hurley, Wisconsin. May 6-9, 1992. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1992 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/a357bd85b85ecf4d6d0697f4cc4a3867.pdf f15062cdc56fb94eb534f98788368468 PDF Text Text ��CONTENTS Institutes on Lake Superior Geology to 1993 Constitution of the Institute on Lake Superior Geology 11 By-Laws of the Institute on Lake Superior Geology lV Goldich Medal Guidelines v Student Travel Award Vi Board of Directors V11 Local Committee V11 Student Paper Award Committee V11 Goldich Medal Committee V11 Goldich Medal Recipient V11l Past Goldich Medal Recipients V11l Banquet Speaker V11l Report of the Chair of the 38th Annual Institute lX Calendar of Events and Program Xl Abstracts 1 �INSTITUTES ON LAKE SUPERIOR GEOLOGY Institute Number Date Place 1 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 Minneapolis, Minnesota Houghton, Michigan East Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Arthur, On tario Houghton, Michigan Duluth, Minnesota Ishpeming, :rvlichigan St. Paul, Minnesota Sault Ste. Mmie, Michigan East Lansing, Michigan Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Marquette, Michigan St. Paul, Minnesota Thunder Bay, Ontario Milwaukee, Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wawa, Ontario Marquette, Michigan Duluth, Minnesota Thunder Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 �CONSTITUTION OF INSTITUTE ON LAKE SUPERIOR GEOLOGY Article I Name The name of the organization shall be the "Institute on Lake Superior Geology". Article II Objectives The objectives of this organization are: A. To provide a means whereby geologists in the Great Lakes region may exchange ideas and scientific data. B. To promote better understanding of the geology of the Lake Superior region. C. To plan and conduct geological field trips. Article ill Status No part of the income of the organization shall inure to the benefit of any member or individual. In the event of dissolution the assets of the (some tax free organization). organization shall be distributed to (To avoid Federal and State income taxes, the organization should be not only "scientific" or "educational", but also "non-profit".) N1inn. Stat. Anno. 290.01, subd. 4 N1inn. Stat. Anno. 290.05(9) 1954 Internal Revenue Code s.501(c)(3) Article IV Membership The membership of the organization shall consist of the board of directors. Any geologist interested shall be permitted to attend and participate in and vote at the annual meetings. Article V Meetings The organization shall meet once a year, preferably during the month of April. The place and exact date of each meeting will be designated by the board of directors. Article VI Directors The board of directors shall consist of the Chairman, Secretary-Treasurer, and the last three past Chainnan; but if the board should at any time consist of fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be filled by the annual meeting so as to bring the membership of the board up to five members. ., II �Arricle VII Officers The officers of this organization shall be a Chairman and Secretary-Treasurer. A. The Chairman shall be elected each year by the board of directors, who shall give due consideration to the wishes of any group that may be promoting the next annual meeting. His term of office as Chairman will tenninate at the close of the annual meeting over which he presides or . when his successor shall have been appointed. He will then serve for a period of three years as a member of the board of directors. B. The Secretary-Treasurer shall be elected at the annual meeting. His term of office shall be two years or until his successor shall have been appointed. Article VITI Amendments This constitution may be amended by a majority vote of those persons who are personally present at, participating in, and voting at any annual meeting of the organization. 111 �BY-LAWS I. Duties of the Officers and Directors A. It shall be the duty of the Annual Chairman to: 1. 2. 3. B. It shall be the duty of the Secretary-Treasurer to: 1. 2. 3. C. II. Keep accurate attendance records of all annual meetings. Keep accurate records of all meetings of, and correspondence between, the board of directors. Hold all funds that may accrue as profits from annual meetings or field trips and to make these funds available for the organization and operation of future meetings as required. It shall be the duty of the board of directors to plan locations of annual meetings and to advise on the organization and financing of all meetings. Duties and Expenses 1. 2. III. Preside at the annual meeting. Appoint all committees needed for the organization of the annual meeting. Assume complete responsibility for the organization and fmancing of the annual meeting over which he presides. There shall be no regular membership dues. Registration fees for the annual meetings shall be detennined by the Chairman in consultation with the board of directors. It is strongly recommended that these be kept at a minimum to encourage attendance of graduate students. Rules of Order The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are applicable. IV. Amendments These by-laws may be amended by a majority vote of those persons who are personally present at, participating in, and voting at any annual meeting of the organization; provided that such modifications shall not conflict with the constitution as presently adopted or subsequently amended. IV �Award Guidelines SAM GOLDICH MEDAL Preamble The Institute on Lake Superior Geology was born on or around 1955, as documented by the fact that the 27th annual meeting will be held in 1981. The Institutes are exemplary in their continuing objectives of dealing with those aspects of geology that are related geographically to Lake Superior; of encouraging the discussion of subjects and sponsoring field trips which will bring together geologists from academia, government surveys, and industry; and of maintaining an exceedingly informal but highly effective mode of operation. During the course of its existence the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the LL.S.G. by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the improvement of understanding of "Lake Superior" geology and its mineral deposits. The exemplary award was made by LL.S.G. to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Award Guidelines 1) The medal shall be awarded annually by the LL.S.G. Board of Directors to a geologist whose name is associated with a substantial interest in, or a major contribution to, the geology of the Lake Superior region. 2) The Board of Directors, LL.S.G. shall appoint the Nominating Committee. The initial appointment will be of three members, one to serve for three years, one for two, and one for one year, the member with the briefest incumbency to be chairman. After the first year the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In the third year this member shall be the chairman. The Committee membership should reflect the main fields of interest and geographic distribution of LL.S.G. membership. 3) By November 1, the Goldich Medal Nominating Committee shall make its recommendation to the Chainnan of the Board of Directors who will then inform the Board of the nominee. 4) The Board of Directors normally will accept the nominee of the Committee, will inform the medalist immediately, and will have one medal engraved appropriately for presentation at the next meeting of the Institute. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. April 4, 1981 1. Kalliokoski, Chairman Bill Cannon Fred Kehlenbeck G.B. Morey Greg Mursky v �STUDENT TRAVEL AWARD The 1986 Board of Directors established the LL.S.G. Student Travel Award to support student participation at the annual Institutes. The awards will be made from a special fund set up for this purpose. This award is intended to help defray some of the direct travel costs to the Institute and includes a waiver ofregistration fees, but excludes expenses for meals, lodging, and field trip registration. The number of awards and value are determined by the annual Chairman in consultation with the Secretary-Treasurer and will be announced at the annual banquet. The following general criteria will be considered by the annual Chairman, who is responsible for the selection: 1) The applicants must have active resident (undergraduate or graduate) student status at the time of the Institute, certified by the department head. 2) Students who are the senior author on either an oral or poster paper will be given favored consideration. 3) It is desirable for two or more students to jointly request travel assistance. 4) In general, priority will be given to those in the Institute region who are farthest away. 5) Each travel award request shall be made in writing, to the annual Chairman, with an explanation of need, possible author status or other significant details. Successful applicants will receive their awards at the time of registration for the Meeting. VI ������This page intentionally left blank ����������������������������������������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/857b56a669d6b629e3610cd1383eaa73.pdf a8a6e46a4714c10523dfb417929437a2 PDF Text Text ������������������������������������������������������������������������������������������������������������������������������������������������������������������� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1993 Description An account of the resource Institute on Lake Superior Geology. Eveleth, Minnesota. May 5-8, 1993. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1993 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/686cdd7814f1ea17de0e13904c023eff.pdf f93685aadb30642819adb0efd3b82089 PDF Text Text S Proceedings Proceedings 40th 40th Annual Meeting May 11 11--14 14,1994 , 1994 Michigan MichiganTechnological Technological University University Houghton, Michigan Michigan Volume 40 Volume 40 Part abstracts Part 1—Program I-Program and ab Editors: horst and McDowell Editors:Theodore TheodoreI.J.Born Bornhorst and S. Douglas McDowell �40TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Volume 40 40 consists consists of of Volume Part 1: Part 1 : Program Program and and Abstracts Abstracts Self-guided geological geological field field trip trip to to the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan Part 2: Part 2 : Self-guided Part 3: Part 3: Volcanic Volcanicgeology geologyof of eastern eastern Isle Isle Royale, Royale, Michigan Michigan Fart 4: Part 4 : Michigan Michigankimberlites kimberlitesand anddiamond diamond exploration exploration techniques Part 5: Part 5 :Lessons Lessonsfrom frommining miningcase casehistories: histories: West West Menominee Menominee Range, Range, Michigan Michigan below: Reference to material in Volume 40, Part 1 should follow the example below: L.G., Cannon, W.F. W.F. and Back, J.M., J.M., 1994, Chalcocite mineralization in the Woodruff, L.G., Portage Lake volcanics, Keweenaw Peninsula, Peninsula, Michigan Michigan (abst.): (abst.): Institute Institute on on Lake Geology Proceedings, Proceedings,40th 40thAnnual AnnualMeeting, Meeting,Houghton, Houghton,MI MI 49931, 49931, v. v. 40, Superior Geology part 1, p. 77. 1, Published and distributed by Published Institute on Lake Superior Geology M.G. Mudrey, Jr., Jr., Secretary-Treasurer, I.L.S.G. I.L.S.G. M.G. 106 N 3rd Street 106 N Mt. Horeb, Horeb, Wisconsin Wisconsin 53572 ML ISSN 1042-9964 ISSN All volumes volumesare are available for for photocopying photocopying costs from from All Library Archives Archives Michigan Technological University Library Michigan Technological University Universityisisan anequal equalopportunity opportunityeducational educationalinsututiordequal institution/equalopportunity opportunity employer. Michigan �__ -- Institute on Lake Superior Instituteon SuperiorGeology Geology Proceedings Proceedings 40th Annual Meeting Meeting May 1994 May11—14, 11-14,1994 Michigan MichiganTechnological TechnologicalUniversity University Houghton, Michigan Michigan Volume Volume 40 40 Part Part 1—Program 1-Program and andabstracts abstracts Editors:Theodore Theodore3.J. Bornhorst Bornhorstand andS. S.Douglas Douglas McDowell Editors: McDowell Department Departmentof ofGeological GeologicalEngineering, Engineering,Geology, Geology, and andGeophysics Geophysics MichiganTechnological University, Michigan University, Houghton, Houghton, Michigan Michigan 49931-1295 49931-1295 �CONTENTS PART 1 PROGRAM AND AND ABSTRACTS ABSTRACTS PROGRAM ............................. i Constitution of the Institute on Lake Superior Geology .................... ii ... ilL By-Laws of the Institute Institute on on Lake Lake Superior Superior Geology Geology ....................... m Goldich Medal Guidelines Guidelines. ........................................ iv Institutes totes on Lake Superior Geology to 1994 1994 I I I I I I I ! I i I Goldich Medal Committee v Past Goldich Medalists v ..................................... v Banquet Speaker ............................................... vv Banquetspeaker Student Travel Award Award ...........................................vi Student Travel Award Application Form ............................... vi BoaM of Directors ............................................. vii BoardofDirectors Local Committees ............................................. vii LocalCommittees vii Report of the the Chair Chair of of the the 39th 39th Annual Annual Institute Institute ......................... ix 1994 Goldich Medal Recipient Program of of Events Events Abstracts Abstracts V ...............................................xi ......................... .......................... J 1 1 �INSTITUTE SUPERIOR GEOLOGY INSTITUTE ON ON LAKE SUPERIOR GEOLOGY INSTITUTE INSTITUTE NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 DATE DATE - PLACE CHAIRMAN CHAIRMAN 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1993 1994 1994 Minneapolis, Minnesota Houghton, Houghton, Michigan Michigan East Michigan East Lansing, Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Port Arthur, Arthur, Ontario Ontario Houghton, Houghton, Michigan Michigan Duluth, Duluth, Minnesota Minnesota Ishpeniing, Ishpeming, Michigan Michigan St. St. Paul, Paul, Minnesota Minnesota Sault Sault Ste. Ste. Marie, Marie,Michigan Michigan East Lansing, East Lansing, Michigan Michigan Superior, Superior, Wisconsin Wisconsin Oshkosh, Oshkosh, Wisconsin Wisconsin Thunder Bay, Bay, Ontario Ontario Duluth, Minnesota Minnesota Houghton, Houghton, Michigan Madison, Madison, Wisconsin Wisconsin Sault Sault Ste. Ste. Marie, Marie, Ontario Ontario Marquette, Marquetta, Michigan Michigan St. Paul, Paul, Minnesota Minnesota Thunder Thunder Bay, Bay, Ontario Ontario Milwaukee, Milwaukee, Wisconsin Wisconsin Duluth, Minnesota Minnesota Eau Eau Claire, Claire, Wisconsin Wisconsin East East Lansing, Lansing, Michigan Michigan International International Falls, Falls, Minnesota Minnesota Houghton, Houghton, Michigan Michigan Wausau, Wausau,Wisconsin Wisconsin Kenora, Ontario Ontario Wisconsin Wisconsin Rapids, Rapids, Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Marquette,Michigan Michigan Duluth, Minnesota Minnesota Thunder Thunder Bay, Bay, Ontario Ontario Eau Eau Claire, Claire,Wisconsin Wisconsin Hurley, Hurley, Wisconsin Wisconsin Eveleth, Minnesota Minnesota Houghthn, Houghton, Michigan Michigan C.E. Dutton C.E. A.I{. Snelgrove Snelgrove AK B.T. SandeftuSandefur B.T. R.W. Marsden Marsden R.W. E.N. Cameron & E.N. & R.A. R.A. Hoppin E.N. Cameron E.N. E.G. Pye E.G. LK Snelgrove A.K Snelgrove H. Lepp ~ P P H. A.T. Broderick AT. Pit Sims P.K. Sims& & Kit R.K.Hogberg Hogberg R.W. White White R.W. W.J. W.J. Hinze LB. A.B. Dickas Dickas G.L. LaBerge G.L. M.W. Bartley Bartley & E. Mercy M.W. D.M. Davidson D.M. J. Kaliokoski J. Kalliokoski M.E. Ostrom M.E. P.E. Giblin P.E. J.D. Hughes Hughes M. Walton M. M.M. Kehlenbeck Kehienbeck M.M. G. Mursky D.M. Davidson Davidson D.M. P.E. Myers W.C. W.C. Cambray D.L. Southwick D.h Southwick T.J. Bornhorst Bornhorst G.L. LaBerge G.L. LaBerge C.E. Blackburn C.E. J.K. Greenberg J.K. E.D. E.D. Frey & & R.P. Sage Sage J. S. Kiasner J. Klasner J.C. Green J.C. M.M. Kehlenbeck Kehienbeck M.M. P.E. Meyers P.E. LB. AB. Dickas Dickas IlL. D.h Southwick Southwick T.J. T.J. Bornhorst 1 �a- CONSTITUTION OF OF INSTITUTE ON CONSTITUTION LAKE SUPERIOR SUPERIOR GEOLOGY LAKE Article I Name The name of the organization shall be the "Institute on Lake Superior Geology". The name of the organization shall be the "Institute on Lake Superior Geology". Article I1 II Objectives Objectives The objectives objectives of ofthis this organization organization are: are: A. To A Toprovide provideaa means meanswhereby wherebygeologists geologists in the Great Great Lakes Lakes region region may may exchange ideas and scientific data. ideas data. B. To B. Topromote promote better better understanding understandingofofthe thegeology geology of the Lake Superior Superior region. region. C. To plan and conduct geological field trips. C. To plan conduct geological field trips. III Article I11 Status No part of the income income of ofthe the organization organization shall shall insure insure to to the the benefit of any any member member No part or individual. In the event of dissolution the assets of the organization shall be or individual. In the event of assets distributed to tax free organization). (some distributed (some tax organization). (To avoid avoidFederal Federaland and State State income taxes, taxes, the the organization should be not only (To or "educational, "educational, but but also "scientific" or also "non-profit".) "non-profit".) Minn, Stat. Anno, Minn. Anno. 290.01, 290.01, subd. 4 Minn, Stat. Mi. Stat. Anno. Anno. 290.05(9) 290.05(9) Internal Revenue 1954 Internal RevenueCode Codes.501(c)(3) s.501(cX3) W Article IV Membership The membership membership of ofthe the organization organization shall shall consist consistof ofthe theboard boardofofdirectors. directors. Any Any The geologistinterested interestedshall shallbe bepermitted permittedtotoattend attendand andparticipate participatein inand and vote voteaatt the the geologist annual meetings. Article V Meetings organization shall shallmeet meetonce onceaayear, yea; preferably preferably during duringthe the month month of ofApril. April. The The The organization by the the board of directors. directors, place and exact date of each meeting will be designated by Article VI Article Directors board of of directors directorsshall shall consist consistof ofthe theChairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and and the the The board fewerthan than last three past past Chairman; Chairman: but but if the the board should aatt any time consist of fewer by reason reason of unwillingness unwillingness or or inability inability of of &y any of of the the above persons persons to five persons, by as directors, the vacancies on on the the board may may be be filled filledby bythe the annual annual meeting serve as as to bring the membership the board up so as membership of tl+e up to to five members. Article VII Officers officersof ofthis thisorganization organizationshall shallbe beaa Chairman Chairman and and Secretary-Treasurer. The officers A. The A TheChairman Chairmanshall shallbe beelected electedeach eachyear yearby by the theboard board of of directors, who shall due consideration considerationto tothe the wishes wishes of ofany anygroup groupthat that may may be be promoting promotingthe the give due ' as 0Chairman terminate at at the next annual meeting. meeting. His Histerm termof ofoffice office as wwill ill terminate closeof ofthe theannual annual meeting meeting over which whichhe he presides presides or or when when his his successor shall shall close been appointed. appointed. He will then then serve for for aa period periodof ofthree threeyears yearsas as aa have been the board of directors. member of the B. The be elected electedat atthe the annual annualmeeting. meeting. His term term of of B. The Secretary-Treasurer Secretary-Treasurer shall be officeshall shallbe betwo twoyears years or or until until his his successor shall shall have have been appointed. office U �Article VIII Article VIII Amendments Amendments This constitution constitution may may be amended amended by by aa majority majorityvote vote of of those persons persons who who are are personally present at, participating in, and voting at any annual meeting at any annual meeting of of the participating in, and organization. organization. BY-LAWS BY-LAWS I. I. I Duties and Directors Duties of the the Officers Officers and Directors A. It A It shall shall be be the the duty dutyof of the theAnnual Annual Chairman Chairmanto: to: 1.. Preside 1 Preside at at the the annual annualmeeting. meeting. 2. Appoint all committees needed for for the the organization organization of the the annual 2. annualmeeting. meeting. 3. 3 . Assume Assume complete complete responsibility responsibilityfor the organization organization and and financing financingof of the the annual meeting annual meetingover over which which he he presides. presides. . . I B. It shall B. shall be the the duty dutyof of the the Secretary-Treasurer Secretary-Treasurer to: to: I 1.. Keep accurate accurate attendance 1 attendancerecords records of of all annual annual meetings. meetings. 2. Keep accurate accurate records 2. records of all meetings meetings of, of, and correspondence correspondence between, the the I board of directors. of directors. 3. Hold Hold all all funds fluidsthat thatmay mayaccrue accrueas asprofits profitsfrom from annual annualmeetings meetingsor orfield field trips trips of these funds funds available for the organization and operation of and to make these future future meetings as as required. I C. C. I I II. 1 1. Duties and and Expenses Expenses 1.. There shall 1 shall be no regular regular membership membership dues. for the annual meetings by the Chairman 2. Registration fees forthe meel& shall be determined by Chairman in consultation consultationwith with the theboard boardof ofdirectors. directors. It is is strongly strongly recommended that these a t aa minimum minimum to to encourage encourage attendance attendance of of graduate graduate students. students. these be kept at III. 111. Rules of Order Rules The rules contained Order shall govern this this organization in all The contained in Robert's Rules of Order cases to which they are are applicable. applicable. IV. Amendments Amendments These by-laws may may be be amended by by a majority vote of of those those persons persons who who are are These personally present present at, participating participating in, and voting aatt any annual annual meeting of the personally organization; that such rganization; provided that such modifications shall not conflict with the o constitution as constitution as presently presently adopted adopted or or subsequently subsequentlyamended. I I I It It shall shall be be the theduty dutyof ofthe theboard boardof of directors directorsto to plan planlocations locations of of annual annual meetings and to advise advise on the the organization organization and and financing financing of all meetings. meeting's. I I I I iii �Award Award Guidelines Guidelines SAM GOLDICH GOLDICH MEDAL SAM MEDAL Preamble Preamble The Institute Institute on was born born on on or or around around 1955, 1955, as as documented documentedby bythe the fact fact that that The on Lake Lake Superior Superior Geology Geology was the 27th annual meeting was held in 1981. The Institutes are exemplary in their continuing objectives the 27th annual meeting was held in 1981. The Institutes are exemplary in their continuing objectives of dealing with those that are to Lake of dealing with those aspects aspects of of geology geology that are related related geographically geographically to Lake Superior; Superior; of of encouraging the the discussion of subjects subjects and and sponsoring sponsoring field field trips trips which will bring bring together together geologists which will geologists encouraging discussion of from academia, academia, government government surveys, surveys,and and industry; industry; and and of maintaining an an exceedingly informal but but exceedingly informal from of maintaining highly effective operation. highly effective mode mode of of operation. During the the course of its its existence the membership of the the Institute existence the membership of Institute(that (thatis, is,those thosegeologists geologistswho who During course of indicate the LL.S.G. by attending) attending) has has become becomeaware awareof ofthe thefact factthat that indicate an an interest interest in inthe theobjectives objectives of of the I.L.S.G. by certain of of their their colleagues have made made particularly particularly noteworthy noteworthy and and meritorious meritorious contributions contributions to to the the certain colleagues have improvement of of understanding understanding of and its its mineral mineral deposits. deposits. improvement of "Lake "Lake Superior" Superior" geology geology and The exemplary exemplary award to Sam Sam Goldich in 1979 forhis his many many contributions contributions to to the the The award was was made made by by I.L.S.G. I.L.S.G. to Goldich in 1979 for geology of ofthe the region region extending over about 50 50 years. years. geology Award Guidelines Guidelines 1) of Directors Directors to to aa geologist geologist whose The medal shall be awarded awarded annually annually by by the theI.L.S.G. I.L.S.G. Board Board of name is associated with a substantial substantialinterest interestin, in,ororaamajor majorcontribution contributionto, to,the thegeology geology of of the the Lake Superior Superior region. region. 2) The Board The Board of of Directors, Directors, I.L.S.G. I.L.S.G. shall shall appoint appoint the theNominating NominatingCommittee. Committee. The The initial initial appointment will be of three members, one to serve for three years, one for two, and one appointment will members, one serve three years, one for two, and one for for one one year, the to be be chairman. chairman. After the the member member with the briefest incumbency to the first first year year the theBoard Board of Directors Directors shall shall appoint appoint at at each spring who will will serve serve for for three three of spring meeting one new member member who years. In the third year this member shall be the chairman. The Committee membership should In the third year this member shall be the chairman. The Committee membership should reflect the main fields interest and andgeographic geographicdistribution distributionof ofI.L.S.G. I.L.S.G. membership. membership. fields of interest 3) By November November 1, 1, the the Goldich Medal Nominating Nominating Committee Committee shall shall make its its recommendation to Goldich Medal the Chairman of the Board of Directors who will then inform the Board of Chairman of the Board of Directors who will then inform the Board of the thenominee. nominee. 4) The Board Board of of Directors Directors normally will accept the nominee nominee of the Committee, Committee, will inform the medalist immediately, and will have one medal medal engraved appropriately for for presentation presentation at at the the next meeting of the the Institute. 5) It is that die the Institute is recommended recommended that Instituteset setaside asideannually annuallyfrom fromwhatever whatever sources, sources, such such fhnds fundsas as will be be required to support the continuing costs of this award, the continuing costs this award. April 4, 4, 1981 1981 J. Kalliokoski, J. Kalliokoski, Chairman Bill Cannon Cannon Fred Fred Kehlenbeck Kehlenbeck GB. G.B. Morey Morey Greg Mursky iv �GOLDICH GOLDICH MEDAL MEDAL COMMIflEE COMMITTEE 1993-94 1993-94 RJ). R.D. Sage Sage (1994) (1994) Ontario Survey, Sudbury, Sudhury, Ontario Ontario Geological Geological Survey, Ontario Glen Glen Adams (1995) (1995) Crystal Crystal Exploration Exploration Inc., Inc., Crystal CrystalFalls, Falls,Michigan Michigan P.C. P.C. Morton (1996) (1996) Department Geolo', University Department of of Geology, Universityof ofMinnesota Minnesota Duluth, Duluth, Duluth, Duluth,Minnesota Minnesota , GOLDICH GOLDICH MEDALISTS MEDALISTS 1979 Samuel SamuelS.S.Goldich Goldich awarded 1980 not 1980 notawarded 1981 1981 Carl Carl E. E. Dutton, Dutton, Jr. Jr. 1982 1982 Ralph RalphW. W. Marsden Marsden 1983 1983 Burton BartonBoyum Boyum 1984 Richard RichardW. W. Ojakangas Ojakangas 1985 Paul PaulK. K.Sims Sims 1986 G.B. G.B. Morey Morey 1987 1987 Henry Henry H. H. Halls Halls 1988 1988 Walter S. S. White White 1989 Jorma Kalliokoski 1989 Jorma Kalliokoski 1990 Kenneth 1990 Kenneth C. C. Card 1991 William J. 1991 William J. Hinze ffinze 1992 William 1992 William F. F.Cannon 1993 Donald 1993 Donald W. W. Davis 1994 Cedric 1994 Cedric Iverson 1994 o&1icII I4fetatQecipieat Cetiric Celtic.Iverson BANQUET BANQUET SPEAKER Colorado Geoffrey GeoffreyS. S.Plumlee, Plumlee,U.S. U.S.Geological GeologicalSurvey, Survey, Denver, Denver, Colorado in Predicting Predicting The Crucial Crucial (but (but underutilized) underutilized)Role Roleof of the theEconomic EconomicGeologist Geologist in Effectsof of Mineral Mineral Resource Resource and Remediating Remediating the the Environmental Environmental Effects Development. Development. v �P STUDENT TRAVEL AWARD 1986 Board of Directors established the LL.S.G. Student Student Travel Travel Award Award to to support student student The participation at the annual Institutes. The awards will1be be made from aa special fund set up for this madefrom special fund purpose. This award is intended to help defray some of the the direct travel travel costs costs 60 to the the Institute Institute and and includes includes a waiver waiver of of registration registration fees, ftm, but but excludes excludes expenses expenses for meals, lodging, and field Geld trip trip The number by the registration. registration. The number ooff awards and end value value are determined determinsd by (be annual annualChairman Chairman in in .consultation with the Secretary-Treasurer be annoannouncedat at the the annual annual banquet. Secretary-Treasurer and will be banquetThe following general criteria will be considered by the annual Chairman, who is responsible for the selection: 1) 1) The applicants muç must have active mudent resident (tmdeqduate (undergraduate or orgraduate) graduate) staphat student sstatus t W q at at the time of the Institute, certified by the department head. (betimeofthelngtitute,certifiedbythçdepartmenthe& s. d are the 2) 2) Students Studentswho who are thesenior geniorauthor authoron oneither eitheran a oral n dor orposter posterpaper paperwill willbe be given given favored consideration. consideration. 3) 3) It students to It is is desirable desirable for for two or more mort stiidents to jointly j ~ ~ srequest b - t travel r a vassistance. assistance. e l 4) In general, priority will be given to those in the Institute region who are farthest away. 5) Each ~ a ctravel htravelaward a& request &wt shall (ballbe bt made nude in in writing, writing, to the annual annual Chairman, Chairman,with an explanation of need, possible author author status status or other significant details. details. Successful applicants will receive their their awards Successful appl@ntswi&receive awards at atthe thetime tineof ofregistration registrationfor forthe theMeeting. Meeting. ' INS11TUTE ON LAKE SUPERIOR GEOLOGY Student Travel Award Application Please print: Student Name: Date: Address: I certify that the above named person Is an active !ee1t student. Department Head . Typed Department Head Signature Date Educational Status: Are you the Senior Author of an oral or poster paper? Will any other students will be traveling with you? Yes No How many? Statement of Need: (It you need more room, please use the back of the page.) Other Significant Details: Please return to: vi �BOARD OF DIRECTORS 1994 Theodore Theodore J. J. Bornhorst, Bornhorst, Chairman Chairman Michigan Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 1993 David David L. Southwick Southwick Minnesota Geological Survey, St. St. Paul, Paul, Minnesota 55114 Geological Survey, 65114 I I 1992 Albert Albert B. B. Dickas Dickas Wisconsin-Superior, Superior, Superior, Wisconsin Wisconsin 54880 University of Wisconsin-Superior, 54880 1991 Paul t.Meyers Paul E Meyers Department University of Wisconsin, Wisconsin,Eau EauClaire, Claire,Wisconsin Wisconsin 54701 54701 Department of of Geology, Geology, University Secretary-Treasurer M.G. Jr. M.G. Mudrey, Jr. Wisconsin Geological Geologicaland andNatural Natural History Survey 3817 Mineral Point Road, Madison, Wisconsin Wisconsin 53705 COMMIFFEES LOCAL COMMITTEES GENERAL CHAIRMAN GENERAL CHAIRMAN Theodore J. J. Bornhorst I Department of Geological Geological Engineering, Geology Geology and Geophysics, Geophysics, Michigan Technological Technological University, Houghton, Michigan Michigan 49931 49931 I EDITORS PROGRAM AND ABSTRACTS EDITORS PROGRAM Theodore J. J. Bornhorst Bornhorst I I Department of Geological Geological Engineering, Geology Geology and Geophysics, Geophysics, Michigan Michigan Technological Technological University, Houghton, Michigan 49931 49931 Douglas McDowell S. S. Douglas McDoweU Department of of Geological Geological Engineering, Engineering, Geology Geology and Geophysics, Geophysics, Michigan Michigan Technological Technological University, Houghton, Michigan 49931 49931 TECHNICAL SESSIONS COMMITTEE TECHNICAL SESSIONS I I I J. Bornhorst Theodore J. Bornhorst Department of of Geological Geological Engineering, Engineering, Geology Geology and Geophysics, Geophysics, Michigan Michigan Technological Technological Michigan 49931 University, Houghton, Michigan 49931 A. Gere, Gere, Jr. Jr. Milton A. GeologiëalSurvey SurveyDivision, Division,Michigan MichiganDepartment DepartmentofofNatural NaturalResources, Resources,Marquette, Marquette, Geological Michigan 49855 vii vii I �LOCAL COMMITTEES COMMITTEES continued continued SBmENr PAPER STUDENT PAPER Co1nsnrrEE COMMITTEE MS M AGere, Gore,Jr. Jr.(Chair) (Chair) Geological Survey Survey Division, Division,Michigan MichiganDepartment Department ofNatural of Natural Resources, Marquette, Marquette, Michigan Michigan 49855 49856 S. Beske-Diehl Beske-DiehI Department of ofGeological Geological Engineering, Engineering,Geology Geology and andGeophysics, Geophysics,Michigan MichiganTechnological Technological 49931 University, Houghton, Michigan 49931 Klasner J.S. Klasner Geology,Western Western Illinois illinois University, University, Macomb, Macomb, Illinois Illinois 61455 Department of Geology, 61455 SESSION CHAIRS SR. Blaske AJLBbuke MWR, Incorporated, Incorporated, Lansing, Lansing, Michigan Michigan 48917 MWR, 48917 1 MS Gere, Jr. M.A. Gem. Jr. Division,Michigan Michigan~Department of Resources, Marquette, Michigan ~Geological & l o ~ i csurvey aSurvey l ~ivision, e p a r t m e nof t ~Natural a t u r a~esources, l ~arquette, ~ichigan 49855 J.D. Pasteris Pasteris Department of Earth Department Earth and andPlanetary PlanetarySciences, Sciences,Washington Washington University, University, St. St. Louis, Louis,Missouri Missouri 63130 J.M. Robertson Robertson Geologicaland andNatural Natural History Wisconsin 53705 Wisconsin Geological History Survey, Survey, Madison, Wisconsin 53705 D.M. Rossell D .M. Bossell Independent Geologist, Marquette, Michigan 49855 Independent Geologist, Marquette, 49856 I G.W. Scott G.W. Scott Company, Ishpeming, Ishpexning, Michigan Michigan 49849 Cliffs Mining Services Company, P..Sundeen Sundeen P Geological Survey Survey Division, Division,MMichigan Department of of Natural Natural Resources, Lansing, Geological ichigan Department Lansing,Michigan Michigan 48909 48909 1 L.G. Woodruff L .G. Woodruff U.S. Geological Survey, St Paul, Minnesota 55112 vii:i �39th Annual Annual Institute Institute on 39th on Lake Lake Superior SuperiorGeology Geology Eveleth, Eveleth, Minnesota Minnesota I in Eveleth, The 39th Annual Institute Instituteon onLake LakeSuperior SuperiorGeology Geology was was held May May 5-8, 1993 in Minnesota, under nearly perfect weather weather conditions. conditions. Co-hosts Co-hosts for the meeting meeting were the the Minnesota Minnesota Geological Survey,the the Minnesota Minnesota Department Department of Natural Natural Resources Division, and and the Geological Survey, Resources -- Minerals Division, Minnesota, GeologicalSociety. Society. David DavidL L.Southwick Southwickwas wasthe theGeneral GeneralChairman, Chairman, Jane Jane Cleland Range Geological Mesabi coordinated the the technical technical sessions sessions as as Program Program Chair, Chair, and and Mark Mark Jirsa Jima organized organized the the four four bus bus and and bag-lunch events as Field Trip Chairman. Proceedings Proceedingsof the 39th Institute Institutewere were published published in in two two Volume Part 11contains contains the the program program and abstract abstract of of papers given in the technical parts: Volume 39, Part bag-lunch May 66 and 7; P Part sessions on May art 22 contains contains the thefield fieldguides guides for for the the field field trips tripsconducted conductedMay May 5, 5, 6, 6, and 8. and8. and the annual The technical sessions and annual banquet banquet were were held held in inthe theHoliday Holiday Inn, Inn,Eveleth, Eveleth,Minnesota. Minnesota. A total total of of 182 182people peopleregistered registeredfor forthe themeeting meetingand and104 104attended attendedthe thebanquet. banquet. The technical A of 31 31 oral oral presentations presentations and 2211 posters. Field program consisted of Field trips trips11through through44(see (seebelow) below) program 77, attracted 60, 51, and 41 participants, respectively, demonstrating once onceagain againthat that the field attracted 77,60,51, respectively, demonstrating trips are are the the major major inducement inducement for for people people to attend attend ILSG. ILSG. A highlight of the annual annual banquet banquetwas wasthe thepresentation presentationofofthe theGoldich GoldichMedal Medalto toDonald DonaldW. W. Davis Davis of the the Royal Ontario Museum, Toronto, Toronto, in recognition of ofhis his outstanding outstanding contributions to to highhighof of Precambrian Precambrian rocks rocksand and events eventsin in the the Lake Lake Superior Superior area. area. The precision radiometric dating of The citation for Don Don was was read read by by Ken Ken Card, Card, who who also alsopresented presentedthe the medal medal on onbehalf behalf of ofthe the Institute. Institute. precision The banquet address banquet addresswas wasgiven givenby byRobert RobertZierenberg Zierenbergof of the theU.S. U.S. Geological Geological Survey, who was aa JOIJLJSSAC Distinguished Lecturer in 1993. His topic was "Implications JOIIUSSAC Distinguished Lecturer in 1993. was "Implications for massive massive sulfide sulfide genesis from ODP leg leg 139 drilling drilling in in Middle Middle Valley, Valley,northern northern Juan Juan de Fuca Ridge". de Fuca Eidge". Becausefield fieldtrips trips are are so so central central to to the the success and and survival survival of ofthe the Institute, Institute, the trips Because trips associated associated the 39th ILSG and their leaders are here specifically acknowledged. with 39th ILSG and their leaders are here specifically acknowledged. with Trip 1, 1993: Geology and taconite taconite mines mines of ofthe the Mesabi Mesabirange. range. Leaders Ronald G. Graber, 1, May 5, 1993: Geology and R.W. Ojakangas, Robert J. J. Waidler, Waidler, and andG.B. G.B. Morey. Morey. R.W. Trip 2, May 6, 1993: DNR DNR Core Library open house and core display. Leaders LeadersG.B. G.B. Morey, Morey, Mark J. Severson, Dennis P. Martin, Dale F. Cartwright, and Gary N. Meyer. J. Severson, Martin, Dale F. Cartwright, and Gary N. Meyer. Trip 3, 8, 1993: 1993: Geology Geology of of Archean Archean greenstone greenstone -- granite granite terrane terrane in in the theCook Cook to to Side Side Lake Lake 3, May May 8, area. Leaders Mark Jirsa, Terry Boerboom, and Peter McSwiggen. Leaders Mark Jirsa, Terry Boerboom, and Peter McSwiggen. Trip .4, 4, May May 8, 8, 1993: 1993: The Duluth Complex Complex at at Duluth. Duluth. Leaders Leaders James James D. D. Miller, Miller, Jr., John John C. C. Green, and Val W. Chandler. p Travel awards totalling totalling $1,120 $1,120 were made to students students Zaira Zaira Arias, Arias, Sidney SidneyHemming, Hemming, Nick Nick Van Wyck, and Hristo Stoynov to facilitate their participation in the Institute. Awards of $150 Travel and Hristo Stoynov to facilitate their participation in the Institute. Awards of $150 each Wyck, were made to Zaira Arias of Queens University and Michael Handke of Lawrence University University for student oral presentation and best student poster, respectively. best student oral presentation and best student poster, respectively. The Board of Directors of of the the Institute Institute on met in Eveleth, Minnesota on on Lake Lake Superior Superior Geology Geology met May 6, 1993. In attendance were M. M. Kehlenbeck, LB. Dickas, D.L. In attendance were M.M. Kehlenbeck, A.B. Dickas, D.L. Southwick, Southwick, T.J. Bornhorst, Bomhorst, M.G. Mudrey, Jr., and J.M. Robertson. Principal actions taken were: J.M. Robertson. Principal actions taken were: M.G. Mudrey, Jr., Michigan Technological TechnologicalUniversity Universitytotohost hostthe the40th 40thAnnual Annual Institute Institute in 1. An An offer offer from Michigan in Houghton, Michigan Michiganin in 1994 1994was wasaccepted acceptedwith withthanks. thanks. T.J. TJ. Bornhorst Bomhorst will will be Chairman. Chairman. Houghton, ix �. , 2. The (Southwick) agreed to explore upper management TheChairman Chairqn.(Southwick) 1.04with withupper managementofofthe theOntario OntarioGeological ~ e o l o ~ i &' Survey the possibility of oftheOGB the 005 hosting ILSG in Marathon, Ontario, or elsewhere in the hosting%i&G in.Mhtho&&tariO$ieelsewhere TO Province, in 1995. correspondence with Wood, OGS 1995.[Subsequent [Subsequentconversations conversationsand &correspondence withJohn John-Wood, OGS Director, Director, lead us to believe that a 1995 meeting in Marathon is likely). us to believe that a 1995 meetingin Marathon is likely). 3. It was decided that a mid-year conference-call meeting of the ILSG Board (in ILSGBoard {inOctober October or or November) could provide useful guidance for the chairman of the next annual meeting, and should meeting, andshould, become normal practice henceforth. The Secretary-Treasurer (Mudrey) was instructed to work with the 1994 chairman (Bornhorst) to arrange such a conference call in the of 1993. thefall faUof 1993. . - : , received 4. 4. The Theannual -ml report itpertofofthe dieTreasurer * ~ u r e r was wasreceived and Â¥aapproved. &OW. The Thecentral centralILSG VLSGaccounts accounts (investments 1993. (invettmentsand çnchecldng Aechingaccount) accotmt) showed showedaanet net-positive balance balanceofof$13,678.43 $13,678.43 as ~sof efMay May 6,6,1998. Details Detail* of of the the accounts account# may may be be obtained obtajnai from from the Secretary-Treasurer Secretary-Treasurerupon upon request. request. POST-MEETING POST-MEETINGNOTE: NOTE: The The on-site on-siteaccount account for for the the 39th 39thILSG ILSGatatEveleth, Eveleth,managed managedby bythe theMinnesota MinnesotaGeological GeologicalSurvey Survey through theProfessional ProfessionalDevelopment Developmentand andConference Confuenc*Services Servif* Office Office of of the the University Uniwr* of of throughthe Minnesota, closed in in September 1993 with with an an operating operating low loss of,$1,99$,27$~r of $1,991.27 forthe themeeting. meeting. The deficit wu was covered covered from fromthe thecentral central ILSG ILSGtreasury. treasury. As General Chairman of the Eveleth Af General Chairman o f Eveleth meeting, meeting. -. II am fill responsibility for am deeply deenlv chagrinned chaerinned by by this this financial financial mismanagement mismanaeementand and accept accent full res~oneibilitv for it, it. II have investigated the the sources and have thoroughly thoroughlyinvestigated the matter, matter,identified identifiedide sour%$of of unanticipated &anti&ated costs, costs,and informed the %tarySecretary-Treasurer of my sure Ted informed the surer and and next nextyear's year's Chainnan Chairmanof my findings. findings. II am amsure Ted Bornhorst from my errors errors and run aa meeting Bornhorst will profit f rom my meeting in in Houghton Houghton that thatfinishes finishesin inthe theblack. black. A* Respectfully submitted, David David L. L. Southwick Southwick General General Chairman, Chairman,39th 39thILSG ILSG x �I I I I I I I I I I I I I I I I I I PROGRAM PROGRAM �I a -— ______ CAT LENDAR OF EVENTS AND PROGRAM Wednesday, May May 11 8:00 aa.m. 8:00 m. I -- 5:00 p.m. p.m. Field Field Trips Trips 1 1 and and 22 5:00 I I U 5:00 p.m. p.m. 500 - Underground geology geologyofofthe theWhite WhitePine Pine and and Caledonia Caledonia Mines, Mines, Underground Ontonagon County, Michigan. Leaders: Staff White Pine Mine, Ontonagon County, Michigan. Leaders: Mine, Whiteman, R.W. Seasor and T.J. Bornhorst. R. R. Whiteman. R.W. Seasor and T.J. Bornhorst. 2. 2. Lessons from from mining mining case casehistories: histories: West Menominee Range, Range, Michigan. Leader: A.M. Johnson Michigan. Leader AM. - Registration - Second 8:00 p.m. Registration Second floor, Floor, Memorial MemorialUnion UnionBuilding Buildingon onthe the campus campus of of 8 :00 p.m. Michigan Technological University. Michigan Technological University. 7:00 p.m. -- 10i00 1000 p.m. p.m. Poster 7 :00 p.m. PosterSession Session and and cash cashbar barin inBallroom Ballroom B, B, Memorial Memorial Union Building (Authors at posters 7:30 p.m. 9:00 p.m.). (Authors a t 7:30 p.m. 9:00 p.m.). - I Thursday, May May 12 12 Thursday, I All technical technical sessions sessionsare are in in Ballroom Ballroom A, A,Memorial Memorial Union UnionBuilding Building All on the campus of Mwhigan Michigan Technological University on 4:30 p.m. 7:15 aa.m. m . -- 4 :30 p.m. I 11.. Registration -. Second Second Floor, Floor, Memorial MemorialUnion Union Building Building on on the the campus campus of of Registration Michigan Technological University. University. Michigan Technical Session JI - Resources Session Session Chairs: Chairs: J.M. Robertson and G.W. Technical G.W. Scott 1 8:10 a.m. 8:10 Opening.- 40th Annual Institute Opening Instituteon on Lake Lake Superior Superior Geology Geology T.J. Bornhorst, Bornhorst, General General Chairman Chairman T.J. I 8:15 aa.m. m. Welcome Address Address - President Curtis Curtis J. J. Tompkins, Tompkins, Michigan Michigan Technological Welcome University I 8:30 8 :30 aa.m. m. T.J. Bornhorst, T J. Forty years of Institutes on on Lake Superior SuperiorGeology Geology 88:50 5 0 aa.m. m. M.J. Lavigne, M.J. Archean rifts rifts and and gold: Examples Archean Examples from the central Shebandowan greenstone belt 99:10 :lO aa.m. m. and Beck, J.W. J.W. Lehmann, E.IC. E.K. and Birch Lake Lake prospect prospect . A A major major PGMprospect PGM prospect in in the the Duluth Complex The Birch Complex 9:30 a.m. F.H., Moray, Morey, G.B., G.B., McSwiggen, McSwiggen,P.h P.L.and and Cleland, Cleland, J.M. J.M. Melcher, F.H., origin oj fmanganese North On the origin, manganeseoxides oxides in in iron-formation iron-formationof the Cuyuna North Range, East-central East-central Minnesota - New New evidence evidencefrom fromthe the U.S. U.S.Bureau Bureau of of Range, Gloria drill drill site Mines Gloria I I • I I I - - - 9:50 am. CoffeeBreak Break Coffee xi' �f T à '* . Coffee Break Break Coffee 9:50 a.m. 9 50 a.m. Han, T.M. T.M. Genesis of ofhematite hematiteand and magnetite magnetite in in Precambrian Precambrian magnetite ironGenesis ironlow metamorphic metamorphicgrade. grade, Lake Lake Superior Superior D District, istrict,USA USA - AA formation of low microscopic observation observation microscopic 10:20 am. a.m. 10243 - 10:40 ajn. Pasteris, J.D., Harris, Pasteria, Harris, T.N., and and Sassani, Sassmi, D.C. D.C. Dual immiscibility of ofdominantly dominantly aqueous aqueousfluids fluids in in rocks rocks of ofthe the Dual southwestern footwall footwall of of the theDuluth Duluth CmnpteC, Complex,NE NEMinnesota Minnesota southwestern 11:00 am. a.m. 11-00 Pufahi, P. and Fralick, Pufahl, Fralick, P. Depositional controls onshallow shallowwater wateriron ironformation formation accumulation, accumulation, Depositional controls on (Jogebic Range, Wisconsin Gogebic Range,Wisconsin 11:20 am. a.m. 1130 Mine; G.C. (IC. Miner, possible metasomatic origin, origin for for the Longwise Longnose oxide-rich oxide-rich ultramafic ultramafic body A A metammatic 11:40 am. a.m. 11:40 Woodruft LG., L.G., Cannon, Cannon, W.F. WY. and and Back, J.M. J.M. Woodruff, Chalcocite mineralization in the Portage Lake Volcanics, Keweenaw Chaicocite mineralisation the Portage Volcanics, Keweenaw Peninsula, Michigan p.m. Optional and B, B, Memorial Memorial Union Union Building Building 12:00 noon noon -- 1:40 p.m. Optional Luncheon, Luncheon, Room Room 105A and 12AO stuff of of life: life: Provisiolung Provisioning the the early early miners" miners Speaker: Larry Lorry Lankton Lankton "The "The stuff - p.m. Board 100,Memorial MemorialUnion Union Building Building 12:00 noon - 1:40 1:40 p.m. Board of of Directors Directors Meeting, Room Boom 100, 1 2:00 noon (by invitation only) (by invitation - - Technical Session I UI - Fluids fluids and and Environment Environment Session SessionChairs ChairsTechnical A.R.Blaske Blaske and and P.C. P.C. Morton A.R. 1:40 p.m. Person, M. Person, oreformation formation within within continental continental Hydrologic mode& models of of sediment sediment - hosted hosted ore Hydmbgic rift basins 2:00 p.m. RB. and Suchoski, TA. White, R.B. Suchoski, T.J. Useof ofrunoffrunoff-and and sedimentantml sediment-control models modelsin in the the design design of of mine mine Use hydrologic controls 2:20 p.m. and Wessels, J.N. Lapakko, K.A. KA.and Release of ofadd acid and and trace metals from quartz-carbonate hosted gold mine Release tailings tailings 2:40 p.m. Loukola-Ruskeeniemi, K. Loukola-Ruskeeniemi, K. geochemistryoof Proterozoicblack blackshales shalesinineastern easternFinland: Finland: Environmental geochemistry f Proterozoic pilot study a pilot 3:00 p.m. Break Coffee Break 3:20 p.m. Eger, P. Wetland treatment treatment of of mine mine drainage drainage - an an alternative alternative to conventional conventional Wetland treatment or voodoo treatment? treatment voodoo treatment? xli �I * 3:40 p.m. 3:40 p.m. S.R Davis, S.R Metallic mineral mineral resources management at at Voyageurs Metallic resources and and ecosystem ecosystem management Voyageurs National Park. Park, Minnesota National Minnesota I 4:00 4:00 p.m. p.m. Johnson, AM. Johnson, AM. solutions for for muting mining related problems Geotechnical solutions I Room 105 A and B, Memorial 44:30 3 0 p.m. - 5:00 5:00 p.m. IGOP ZGCP Organizational OrganizationalMeeting Meeting -- Room Memorial Union Union Building Building I 6:00 6:00 p.m. - - - 7:00 p.m. p.m. Social Seaman Mineral Museum, ROO Social - Seaman Museum, Fifth Fifth Floor, Electrical Electrical Energy Energy Resources Center 6:30 p.m. -- 7;30 p.m. Cash Cashbar, bar,Ballrooms BallroomsAAand andB, B, Memorial Memorial Union Building - I 7:30 p.m. Annual 7:30 p.m. p.m. - 9:30 9:30 p.m. AnnualBanquet, Banquet,Ballroom BallroomA, A, Memorial MemorialUnion Union Building Building Speaker: GeoffreyS.&Plumlee Plumlee "The crucial crucial (but (but undenttilized) underutilized) role of the Speaker: Geoffrey economic geologistsin inpredicting predictingand and remedialing remediating the environmental economic geologists environmental effects mineral resource effectsooff mineral resource development" Friday, May Friday, May 13 13 Technical Session Session HI m --Regional Regional Geology Session Technical SessionChairs: Chairs:J.D. J.D.Pasteris Pasterisand andD.M. D.M.Rossell Rossell 8:30 a.m. S.A. and Fralick, P.W. P.W. Kissin, SA. Granitoid the Elliot ElliotLake Lakearea, area, Ontarin Ontario and and their relationship relationship to Gmnitoid rocks of the U-Th-REE bearing pegmatites U-Th-BEE 8:50 a.m. LaBerge, G.L. G.L. and Klasner, J.S. J.S. Merge, implications of ofEarly Early Proterozoic Proterozoiclithostratigraphy lithostratigraphy on on the the eastern eastern Tectonic implications Gogebicm Range, Northern Michigan e , Northern Michigan I 9:10 a.m. Kiasner, J.S. Klasner, J.S. and andLaBerge, Merge, G.L. G.L. Structural Northern Michigan Structuralevolution evolutionof ofthe theeastern easternGogebic Gogebic Range, Northern Michigan I 9:30 a.m. VanWyck, N., Johnson, Johnson, C. and VanWyck, N., and Gross, Gross,S. S. Archean crust in in the the Wausau-Pembine Wauaau-PembineTerrane; Terrane; continental continental underthrusting, or island island arc arcbasement? basement? underthrusting, I 9:50 a.m. Coffee Break Break I I I I I I 10:20 a.m. Uribe, R.D. Ri). Cambrian Mt. Mt. Simon Sandstone, Petrography and diagenesis diagenesis of the Upper Cambrian SE Minnesota 10:40 a.m. Kissin, and Fralick, Kissin, S.A. SA. and Fralick, P.W. P.W. Early the Anirnike AnimikeGroup, Group, Ontario Ontario and and Michigan, Early Proterozoic Proteromic volcanics volcanic8 ooff the Michigan. and their theirtectonic tectonicsignificance significance 11:00 a.m. Bennett, and Hatfield, KG. G., Born, P. and KG. Bennett, G., The stratigraphic stratigraphic significance dolostoneunit unit near near Sault Ste. significance of aa dolostone Ste. Marie, Marie, Ontario Ontario flu I �11:20 1120 a.m. a.m. VanWyck N., Medaris, Jr., .. Medaris, Jr..L.G. L.G.and andJohnson, Johnson,C.M. C.M. VanWyck N The Wolf River A-type magmatic event Wisconsin:UU/Pb and Sm/Nd Sm/Nd The WolfRiver A-type magmatic event ininWisconsin: / P b and constraints on timing and petrogenesis constraints on timing and petmgenesis 11:40 11:40 a.m. a.m. Smyk, Smyk, M.C. M.C. and and Schnieders, Schnieders,B.R. B.B. A geological geological Marathon: Marathon: The Therocks rocks of of the the North North Shore Shore of of Lake Superior Superior 12:00 12:OO p.m. p.m. -- 1:30 1:30 p.m. Optional OptionalLuncheon, Luncheon,Room Boom105 105AA and andB, B, Memorial MemorialUnion UnionBuilding Building Speaker: Stanley StanleyDyl Dyl "Minerals "Mineralsand and decorative decorative arts arts in inRussia" Russia" - Technical TechnicalSession SessionW IV- Mideontinental Midcontinental Rift Rift System System Session Session Chairs: Chairs: L.G. L.G. Woodruff Woodruff and and P. P. Sundeen Sundeen 1:30 p.m. p.m. Allen, D4., WJ.,Dickas, Dickas,A.B., AB., and and Mudrey, Mudrey, M.G., M.G., Jr. Jr. DJ., Hinze, Hinze,W.J., Geophysical investigations investigations of the Midcontinent rift system: AAnew new model model for for western western Lake Superior Superior and andnorthern northernWisconsin Wisconsin 1:50 150p.m. p.m. Palacas, Palacas, J.G. J.G.and and Burruss, Burruss,B.C. R.C. Preliminary Preliminarysource-rock source-rock and maturity maturity evaluation evaluationof of the the Precambrian Precambrian Nonesuch Formation in in the the Terra TerraPatrick Patrick#7.22 W-22borehole, borehole, Midcontinent rift system, Bayfield County, County,Wisconsin Wisconsin 2:10 2 1 0 p.m. p.m. Waggoner, Waggoner,T.D. T.D. Echo Echo Lake Gabbro, Gabbro,Houghton Houghton County, County, Michigan Michigan 3:00 p.m. p.m. 3:20 3:20 p.m. p.m. Boerboom, Boerboom, TA. TJ. Archean h h e a n crustal crustalxenoliths xenoliths in inaaKeweenawan Keweenawan hypabyssal hypabyssal sill, sill, northeastern northeastern ' Minnesota. Minnesota. White Whitewas was right! right! END END OF OFTECHNICAL TECHNICALSESSIONS SESSIONS Saturday, Saturday,May May14 14 8:00 8:00 a.m. a.m. -- 5:00 5:00 p.m. p.m. Field FieldTrips Trips33and and44 3. 3. Michigan Michigan kimberlites and diamond diamon exploration iloration techniques. Leaders: Leaders: S.M. S.M. Carison Carlson and and W. W. Floodatrand Floodstrand 4. 4. Geology Geology of the Keweenaw Keweenaw Peninsula, Peninsula, Michigan. Michigan. Leader: Bomhorst Leader: T.J. T J .Bornhorst Friday, Friday,May May13 13to toThursday, Thursday,May May19 19 Field Volcanic geology of Eastern Eastern Isle Royale, Michigan. Michigan. Leader: fieldTrip Trip55--Volcanic geology of Leader: W.I. W.I.Rose Rose xiv xiv '"•)•• .nfl,. �Poster Session 7:00 p.m. p.m. Wednesday, Wednesday, May May 11 11 to to 12.-00 12:00 noon noon Friday, Friday, May 7:00 May 13 13 SessionChair: Chair: M MA Jr. Session A Gere, Gere, Jr. Chenier, F. Chenier, P. Inventory of of the the Michigan Michigan Geological Survey Division's Division's Upper Upper Peninsula Peninsula significant Inventory Geological Survey significantwater waterwell well cuttings libtwy at at Escanaba. Escanaba cuttings library Frey, B. BA. Frey, A. Minnesota drill core examination and and assay assay Minnesota core examination Kean, W. Kean, W. Paleomo.gnetiszn ofaa 1500 1500 MA MA mafic mafic dike dike at at Waterloo, Paleornagnetism of Waterloo,Wisconsin Wisconsin Kropf, E.P., E.P., Wirth, Wirth, KR. KR. and Craddock, J.P. J.P. Kropf, New Archmn-hosted Archean-hosted pselidotechylite pseudotachylite occurrences, occurrences, western western Lake Lake Superior Superior region New region Lawler, T. Mineral potential evaluation, central Minnesota, phase II basic data Mineral potential evaluation, central Minnesota, phase basic data Leslie, M M., Wetzel,T., T.,Wirth, Wirth,K.R. Kit. and Craddock, J.P. J.P. .,Wetzel, Petrography and structure of the Keweenaw Chengwatana Petrography and structure of the Zfeweenaw ChengwatanaVolcanics Volcanics near near Dresser, Dresser, Wisconsin Wisconsin Luther, Luther, P.R. P.R. Petrology and whole rock rock W analyses of the the central central portion portion of a large Petrology and y s e s of large Early Early Proterozoic Proterozoic diabase diabase dike, dike, preliminary report Eastern Lake of the Woods, Ontario A Eastern Lake of the Woods, Ontario - Apreliminary report Miller, Jr., J.D., T.J., and Green, J J.C. J.D., Boerboom, Boerboom, T J.,Chandler, V.W. V.W. and .C. Geology of the "Greater" Beaver Bay Complex, Northeastern Minnesota Geology of the "Greater" Beaver Bay Complex.Northeastern Miller, Sr., Miller. S S.A -~ ------, -..r , S.A. Assessment of Spring Spring Creek Creek aquifer aquifer vulnerability vulnerability to pollution using Assessment of using DRASTIC, DRASTIC, water testing; testing, groundwater modeling, and historical records: a project of the MTU groundwater and historical a project of the MTU Regional Groundwater Education Education in inMichigan Michigan(GEM) (GEM Center Center ~ Nelson, S., Lawler, T., T., Lehr, Lehr, J.D., J.D., Theobald, P., P., Ryder, J., Sutley, S. S. and and Tripp, Tripp,R. R. Heavy mineral& minerals from glaciofitwial sediments in Minnesota from glactofluvial in Minnesota S.W., WooWoodruff, LG. L.G. and and Cannon, Cannon, W.F. Nicholson, S.W., W.F. Geochemistryof ofthe theHollander Kallander Creek Creek Volcanics, 1.1 1.1 da Ga Midcontinent Midcontinent rift rift system, Wisconsin and and Geochemistry Michigan Michigan BA. and Petrie, MA. Rogers, BA. MA Hydrogeologicinvestigations investigationsof ofpetroleum petroleumcontamination contaminationin in Karst, lGzrst,central centralUpper UpperPeninsula Peninsula of of Hydrogeoloeic Michigan Schmitz, M.D., M.D., Wirth, Wirth, KR. KR. and Craddock, Craddock, J.P. Origin of the Early Proterozoic Kenora-Kabetogama ma/ic dike swarm Origin, Praterozoic Kemra-Kabetogamamafic swarm W.T. and and Gere, MA, M.A., Jr. Jr. Swenor, W.T. Marquette, Michigan Michigan core and and sample repository Update on the the geological core repository - Marquette, - Update xv �Watkins, LW. Anorthosites: Igneous cumulate or metasomite White, R.B. and Wollensak, M.S. Biodegradation of environmental contaminants utilizing white rot fiengus Minnesota Department of Minnesota Department of Natural NaturalResources, Resources,Minerals MineralsDivision Division A compendium of mineral resource information, Minnesota A compendium of mineral resource information,east-central Minnesota Posters Abstracts Posters Without Without Abstracts Sage, R.P., Lightfoot, Lightfoot, P.C. P.C. and and Doherty, Sage, R.P., Doherty, W. W. Geochemist'y of cyclical bimodal basalt-rhyolite magmatism magmatism of of the the Archean Archean Wawa Belt, Geochemistry of cyclical bimodtd basalt-rhyolite Wawa Greenstone Greenstone B elt, Ontario: aapossible continental-arc setting possible continental-arc setting Sage, liP., Sage, R .P.,Lightfoot, Lightfoot, P.C. PC,and andDoherty, Doherty, W. W. Goechemical characteristics of granitoids from the the Michipicoten Michipicoten Greenstone GreenstoneBelt. Belt, Wawa Wawa Goedwmical characteristics of granitoidsfrom Subprovince, Superior Pmvince: Implications for source regions and tectonic evolution Subprovince, Superior M i n c e : Implications for source regions and tectonic evolution xvi �AR ST1{ACTS ABSTRACTS �GEOPHYSICAL GEOPHYSICAL INVESTIGATIONS OF OF THE THEMIDCONTINENT MIDCONTINENTRIFT RIFTSYSTEM: SYSTEM: A AND NORTHERN NORTHERN WISCONSIN WISCONSIN A NEW NEW MODEL MODELFOR FOR WESTERN WESTERN LAKE SUPERIOR AND ALLEN, J., Purdue Purdue University, West Lafayette, Lafayette, Indiana Indiana 47907 ALLEN, David David J., J., and and HINZE, HINZE,William William J., 47907 DICKAS, University of Wisconsin-Superior Wisconsin-Superior (Extension). Superior, Wisconsin 54880 DICKAS, Albert Albert B., B., University (Extension), Superior, 54880 MUDREY, M.G., Jr., Jr.,Wisconsin WisconsinGeological Geologicaland and Natural Natural History Survey, Madison, Wisconsin Wisconsin 53705 MUDREY, M.G., 53705 Seismic Seismic reflection data data are areof of enormous enormousvalue valuefor forinvestigating investigatingthe the1100 1100Ma Ma Midcontinent MidcontinentRift Rift System. Superior, together together with with proprietary proprietary data System. Recently released released eight-second eight-second proffles profiles from Lake Superior, datafrom from northwestern better understanding understanding of of the the western western Lake Lake Superior Superior and and northwestern Wisconsin, Wisconsin, have resulted in aa better Wisconsin Wisconsin segments segments of the the rift riftsystem. system. Combined Combined interpretation interpretation of of these these seismic profiles with gravity gravity data datareveals revealsseveral severalinteresting interestingstructural structuraland andstratigraphic stratigraphicfeatures, features,including includingtwo twopre-Keweenawan pre-Keweenawan ridges within the therift riftinterior, interior,the thetermination terminationof ofmajor majorreverse reverse faults, faults, aa flanking flanking sedimentary sedimentary basin basin ridges within located east of the St. Croix Horst, and, possibly, an Archean batholith buried beneath the rift. located east of the St. Croix Horst, and, possibly, an Archean batholith buried beneath the rift. Along Along the theLake LakeSuperior Superiorsyncline syndine(Fig. (Fig. 1), I), seismic seismic data data image image up up to to99km kmof of sedimentary sedimentaryrocks rocks(the (the majority majority of of which which are arelikely likelyOronto OrontoGroup Groupstrata) strata)and andup uptoto1818km kmofofvolcanic volcanicflows. flows. Along Alongthe theAshland Ashland syncline the Oronto synclinein in Wisconsin Wisconsin (Fig. (Fig. 1), I), the Oronto Group Groupisisas asthick thick as as44 km, km, and andthe theunderlying underlyingvolcanic volcanicflows flows have however, are separated separated have aa maximum maximumthickness thicknessof of 14 14km. The The Ashland Ashland and and Lake Lake Superior synclines, however, by by aa prominent prominentridge ridgethat thatwas wasfirst firsthypothesized hypothesizedby byWhite White(1966) (1966)on the basis of gravity gravity and and magnetic magnetic data. km) arevery verythin thin(<2 (4 km) and and pinch pinch out outin innorthern northernWisconsin, Wisconsin, data. Along AlongWhite's White'sRidge, Ridge, the thevolcanic volcanic strata strataare placing placing Oronto strata strata directly directlyon ontop topofofthe thepre-rift pre-riftbasement basement(Fig. (Fig.1). 1).Southeast Southeast of of Grand Grand Marais, Marais, Minnesota, the Lake Lake Superior Superior syncline syncline is deflected around around the the southern southernend endof of aasimilar similarridge ridge(Fig. (Fig.1). I). Stratigraphic White's Ridge Ridgeand andthe theGrand GrandMarais Mars Ridge Ridge remained remained topographically topographically Stratigraphic relations indicate that White's positive pinch out out gradually gradually onto the ridges, ridges, positive as as the the adjacent adjacent volcanic volcanic basins basins subsided. subsided. The The volcanic flows pinch with withno no evidence evidencefor forsubstantial substantialnormal normalfaulting. faulting. As the the Douglas Douglas Fault Fault (Fig. (Fig. 1) 1) approaches approaches Lake Lake Superior, it bends east and and follows follows the the southern southern margin margin of of White's White's Ridge. Ridge. Displacement across the fault gradually gradually decreases to the the east east until until the thefault faultisis replaced replaced by by aa fold foldnear nearthe theeastern easternmargin marginofofWhite's White'sRidge. Ridge. The The seismic seismic data also also indicate indicate that that the theIsle Isle Royale km southwest southwest of the the terminations terminations of the -40 km the Isle. Between the the Douglas Douglas Royale Fault Fault gradually graduallyterminates terminates—40 and forces resulted resulted in in folding foldingrather rather than than development development of and Isle Isle Royale Faults, late-stage rift compressional forces major major reverse reverse faulting. faulting. East sedimentary strata strata within withinan an East of the the Hastings HastingsFault Fault(Fig. (Fig. 1), I), seismic data image up to to 66 km of sedimentary asymmetric basin which is syndine. This basin is is is spatially spatiallyassociated associated with with the thePaleozoic Paleozoic River Falls syncline. characterized characterized by aa pronounced pronouncednegative negativegravity gravityanomaly anomalythat thatachieves achieves its its lowest lowest values valuesnear nearEmerald, Emerald, Wisconsin. Gravity modeling indicates indicates that that strata stratawithin within the theEmerald Emerald Basin Basin have a low low density density and andare are probably and Hincldey Hinckley sandstones sandstones probably correlated correlatedwith withthe theBayfield Bayfield Group Group of of Wisconsin and the Fond du Lac and of Minnesota. Interestingly, Interestingly, the northern margin of the the Emerald Emerald Basin Basin corresponds to the northern termination terminationof of the theHastings HastingsFault Faultand andthe thesouthern southerntermination terminationofofthe theLake LakeOwen OwenFault Fault(Fig. (Fig.1). 1).Although Although the the exact exact relation between between the the Hastings Hastingsand andLake Lake Owen Owen Faults Faults is is unclear, unclear, local gravity gravity and and magnetic magnetic characteristics areconsistent consistentwith with—10 -10 km kmof of left-lateral left-lateraloffset offsetalong alongaacross-fault. cross-fault. characteristicsare In In western western Lake Lake Superior, Superior, the rift's rift's igneous igneous and and sedimentary sedimentary rocks rocks cannot fully account for the the observed —30 observedgravity gravitysignature. signature.AAnortheast-striking, northeast-striking, -30 mGal mGal negative negative anomaly anomaly persists persistsafter afterthe theeffect effectof of the rocks is is removed removed from from the the observed observed gravity gravity field. field. The trend, amplitude, and gradients gradients of this the rift rift rocks anomaly anomaly suggest suggest that that itit may may be be produced producedby by aaburied buriedgranite granitebelt belt within withinthe the Archean Archean greenstone-granite greenstone-granite terrane liesbeneath beneaththe therift rift(Allen (Alienetetal., aL,1993). 1993). As shown shown in in Figure Figure 1, 1, the Douglas Douglas and andIsle IsleRoyate Royale terrane that that lies Faults terminate terminate as as they they approach approachthe the proposed proposedgranite granitebelt, belt, both both pre-Keweenawan pre-Keweenawan ridges ridges occur occur above this structure, structure, and andthe theSt. St. Croix M iHorst Horstterminates terminatesatatthe thesouthern southernmargin marginof of this thisfeature. feature.Therefore, Therefore, this this this Archean batholith might have acted as as aa buttress buttressthroughout throughoutthe thehistory historyof of development developmentof of the therift, rift, redirecting redirectingboth both the theearly earlytensional tensionalstresses stressesand andthe thelate latecompressional compressionalstresses. stresses. 1 �w Legend 48N Bayfield Group (Fond 00 0 I, + .4. 47N do Lac, Hi!Id.y. JacoSvdte SaMon.s( Oronto Group (Solo.' Q'*.th Foninj Volcanic Strata (Poflaga —. a, PayS.' Mt Noith aIa G,o.csi igneous intrusions fl.AShwMaftenConlax.s( Pie-Rift Pre-RlftRidge Rid (voSt <2 In, VSkI Archean Granite ArolMinGrMKe Ibtulad bensath r*I jocksi Rmrixlton-hitrode) Seismic SeismicProfile ProfileLocations Locations 46N 45N 0 50 100 150 200 250 km - Figure Figure1: 1:Geologic Geologic map map of of the the western western Lake Lake Superior Superior region based on on interpretation interpretationof of seismic seismicreflection reflection and andgravity gravitydata. data.Insert Insertshows showsthe thelocations locationsof ofthe theseismic seismicprofiles profiles used used in in this thisstudy study(e.g., (e.g., McGinnis McGinnis and Mudrey, Mudrey,1991; 1991;also alsorefer referto toacknowledgments). acknowledgments). Ref erçnces Allen, W.J., Alien,Dj., D.J.,I-line, Hinze, W.JDickas, .Dickas, , A.B., A.B.,and andMudrey, Mudrey,M.G., M.G.,Jr., Jr.,1993, 1993,An Anintegrated integratedseismic seismic reflection/three-dimensional reflection/thiee-dimensional gravity gravityinvestigation investigationofofthe theMidcontinent MidcontinentRift RiftSystem, System,USA: USA: western westernLake LakeSuperior Superiorregion region(abst): (abst):AAPG AAPG Hedberg Hedberg Research 1993. ResearchConference, Conference,Basement Basementand andBasins Basinsof ofEastern EasternNorth NorthAmerica, America,Ann AnnArbor, Arbor,MI, MI,November November10-13, 1043,1993. McGinnis, reflection profiling profiling and and tectonic evolution evolution of McGinnis,L.D., L.D., and andMudrey, Mudrey,M.G., M.G., Jr., Jr., 1991, 1991, Seismic reflection of the the Midcontinent Midcontinent Rift and Natural RiftininLake LakeSuperior: Superior:Wisconsin Wisconsin Geological Geological and Natural History HistorySurvey SurveyMiscellaneous MiscellaneousPaper Paper91-2. 91-2. White, the Keweenawan Keweenawan basin, White,W.S., WS., 1966, 1966,Tectonics Tectonicsof the basii western westernLake LakeSuperior Superiorregiorc region:USGS USGSProfessional ProfessionalPaper Paper524-E. 524E. - Acknowledgments Seismicprofiles profilesininWisconsin Wisconsinwere wereprovided provided to to the the authors authorscourtesy courtesyof ofTexaco Texaco Exploration Explorationand andProduction, Production,Inc. Inc. Seismic of of Denver, Denver, Colorado Coloradoand andAmoco AmocoProduction ProductionCompany Companyof of Houston, Houston,Texas. Texas. �I I I THE STRATIGRAPHIC SIGNIFICANCE SIGNIFICANCE OF OF A T HE STRATIGRAPHIC A MARIE, ONTARIO. S AULT STE. MARIE, ONTARIO. SAULT DOLOSTONE UNIT NEAR D OLOSTONE UNIT NEAR Bennett, G., MNDM, P.,, G. ,Mines Minesand andMinerals MineralsDivision, Division, MNDM, Born, Born, P. Bennett, G., Lake Superior University, Ottawa, K. G., C a r l e t o n University, Ottawa, Hatfield, H a t f i e l d , K. Lake S uperior Carleton State S t a t e University, University, Sault S a u l tSte. Ste.Marie, Marie,Michigan. Michigan. geological mapping iin Fenwick Township Township While undertaking g e o l o g i c a l mapping n Fenwick near Sault Ste. in 1986, Peter of tthe Marie Ontario i n 1986, P e t e r Born of he n e a r S a u l t Ste. While Ontario Geological 30 meter meter tthick Ontario Geological Survey, Survey, identified identified a a 30 hick unit, known dolostone-chert u n i t , llithologically i t h o l o g i c a l l y ddistinct i s t i n c t from known carbonate u units 1987). The The e t al., a l . , 1987). carbonate n i t s in i n Ontario Ontario (Born (Born et dolostone-chert dolostone-chert sequence directly and dolostone-chert d i r e c t l y overlies o v e r l i e s ffractured r a c t u r e d and sheared, green sheared, g r e e n and and maroon maroon siltstone s i l t s t o n e and and is i s overlain o v e r l a i n by by red red maroon laminated laminated siltstone tto o maroon s i l t s t o n e and sandstone. sandstone. The basal b a s a l one of tthe dolostone unit mainly of of iintercalated n i t cconsists o n s i s t s mainly ntercalated tthird h i r d of he d olostone u with minor rrecrystallized chert. Much Much of of tthe upper dolostone with e c r y s t a l l i z e d chert. h e upper portion unit dolostone made made up up llargely s aa cclastic l a s t i c dolostone argely p o r t i o n of of the the u n i t iis of of medium tto o coarse sand-sized sand-sized grains g r a i n s of of dolostone and quartz. O Oolitic quartz. o l i t i c dolostone is i s locally l o c a l l y present. present. Barite B a r i t e occurs as as as few iirregular r r e g u l a r replacement bodies bodies about midway in i n the the dolostone-chert d o l o s t o n e - c h e r t sequence. sequence. dolostone-chert-siltstone The d o l o s t o n e - c h e r t - s i l t s t o n e assemblage forms an 400 meter meter wide wide southeastward southeastward trending, trending, ssteeply approximately 400 teeply dipping, ffault-bounded block between between (Huronian) (Huronian) LLorrain dipping, ault-bounded block orrain metavolcanics tto Formation tto o tthe h e ssouth o u t h and Archean metavolcanics o the the north. A An altered dike north. n a l t e r e d mafic (diabase) (diabase) d i k e iintrudes n t r u d e s tthe he (Bennett et 1989; Bennett dolostone. (Bennett e t al. al. 1989; Bennett et e t al. al. 1993), 19931, The authors dolostone-chert assemblage a u t h o r s conclude tthat h a t tthe h e dolostone-chert represents a carbonate facies of f a c i e s of tthe h e Gordon Lake Formation represents of the Huronian Supergroup for the a) of t h e Supergroup f o r t h e following following reasons: reasons: ((a) The rred or maroon colored rocks are generally below ed o r colored rocks are g e n e r a l l y llacking a c k i n g below Cobalt Group of of tthe tthe h e Cobalt h e Huronian Supergroup (b) ( b ) The metamorphic grade of the assemblage is higher of metamorphic of t h e i s h i g h e r tthan h a n tthat h a t of the Keweenawan rocks on the east shore of Lake Superior. t h e Keweenawan rocks on t h e e a s t , s h o r e of Lake Superior. (c) (c) Jackson et (1992) have have rreported presence of of e t al. al. (1992) e p o r t e d tthe h e presence outheast dolostone iin n tthe h e Gordon Lake Formation about 60 km ssoutheast of Fenwick Fenwick Township. The previous1 previously proposed of Township. ((d) d ) The y proposed depositional of tthe d e p o s i t i o n a l environment of h e Gordon Lake Formation iis s consistant dolostonec o n s i s t a n t with features f e a t u r e s iin n tthe h e Fenwick Township dolostone1973). ssiltstone i l t s t o n e assemblage assemblage (Wood, (Wood, 1973). 3 �The The dolostone d o l o s t o n e of of Fenwick Fenwick Township Township closely c l o s e l y resembles resembles in i n terms terms of lithology and stratigraphic association, the Kona of l i t h o l o g y and s t r a t i g r a p h i c a s s o c i a t i o n , t h e Kona Dolomite Dolomite of of the t h e Marquette Marquette Range Range Supergroup Supergroup of of northern northern Michigan. The dolostone of Fenwick Township Michigan. The dolostone of Fenwick Towns h i p provides provides additional a d d i t i o n a l evidence evidence for f o r the t h e previously p r e v i o u s l y proposed proposed correlation correlation of Cobalt Group of the Huronian Supergroup of Cobalt Group of t h e Huronian Supergroup and and the t h e Chocolay Chocolay Group 1983) Group of of the t h e Marquette Marquette Range Range Supergroup Supergroup (Young, (Young, 1983) REFERENCES CITED REFERENCES CITED Leahy, E. 3., Melisek, 3., Bennett, G., Bennett, G., Leahy, E. J . , Melisek, J., Born, Born, P. P. and and 1989. Sault Ste. Marie Resident K. Hatfield, H a t f i e l d , K. 1989. S a u l t Ste. Marie Resident Geologist's Geologistf s District-1988; i n Report of A c t i v i t i e s 1988, Resident Misc. Paper Paper 142, 142, Resident Geologists, Geologists, Ont. Ont. Geol. Geol. Survey, Survey, Misc. 207-217. pp 207—217. District-1988; in Report of Activities 1988, Bennett, G . , Leahy, Leahy, Walmsley,J. Walmsley,J. Hailstone, Hailstone, M. M. (1993). (1993). Sault Sault Bennett, G., in Marie Resident Geologist' s District-1992; Ste. S t e . Marie Resident Geologisti s District-1992; in Report Report of of Activities A c t i v i t i e s 1992, 1992, Resident Resident Geologists, Geologists, Ont Ont Survey, Misc. Paper 161, Geol. p 207-232. Geol. Survey, Misc. Paper 161, p 207-232. 1987: Geology Geology of of tthe Havilland-Goulais Bay Born, P. 1987: h e Havilland-Goulais Bay Area, Area, Born, P. 0. Geol. Survey, Algoma; Ont. District of F. R. R. 5602, 5602, D i s t r i c t of Algoma; Ont. Geol. Survey, 0. F. 114p. 114p. with w i t h maps. maps. 1992. Jackson, Jackson, S.L. S. L. and and Henderson, Henderson, I. I. 1992. Geology Geology of of the the Area; in Summary of Field Aberdeen Area; i n Summary of F i e l d Work Work and and other o t h e r activities, a c t i v i t i e s , 1992; 1992; Ont. Ont. Geol. Geol. Survey, Survey, Misc. Misc. Paper Paper 160, 160, pp pp 47—52. 47-52. 1973: 1973: Stratigraphy S t r a t i g r a p h y and and depositional d e p o s i t i o n a l environments environments of of Huronian rocks of the Rawhide Lake-Flack upper upper Huronian rocks of t h e Rawhide Lake-Flack Lake Lake M. , ed. area, a r e a , Ontario, Ontario, ini Young, n Young, G. G.M., ed.,, Huronian Huronian Geol. stratigraphy s t r a t i g r a p h yand andsedimentation: sedimentation: Geol. Assoc. Assoc. of of Canada Special Canada S p e c i a l paper paper 12, 12, p. p. 73-95. 73-95. Wood, Wood, J. J. 1983: Tectono-sedimentaryh history of early 1983: Tectono-sedimentary i s t o r y of early the Proterozoic P r o t e r o z o i c rocks rocks of of t h e jorthern n o r t h e r nGreat GreatLakes Lakes region, region, Young, G.M. G. M. G. S. A. p. 15-32; 15-32; in i n G.S.A. p. Memoir Memoir 160, 160, Edited Edited by by L.G. L. G. Medaris, Medaris, Jr. Jr. 4 �I I ARCHEAN ARCHEANCRUSTAL CRUSTALXENOLITHS XENOLITHS IN INAAKEWEENAWAN KEWEENAWANHYPABYSSAL HYPABYSSAL SILL, SILL, NORTHEASTERIsI MINNESOTA. WHITE RIGHT! NORTHEASTEFW MINNESOTA. WHITEWAS WASRIGHT! BOERBOOM, Terrence J.,J., Minnesota University Avenue, Avenue, St. Paul, MN 55114 BOERBOOM, Terrence MinnesotaGeological Geological Survey, 2642 2642 University 55114 I I I I I I I I I I I I I I Recent Recent field field studies studieshave haveidentified identifiedabundant abundantxenoliths xenolithsof of Archean Archean crust crust in in the the earliest of several intrusions along the northeast-trending transition earliest of several intrusions along the northeast-trending transition zone zone between between the theupper upperportion portionofofthe theDuluth DuluthComplex Complexand andthe theBeaver BeaverBay BayComplex Complex in in northeastern (Boerboom and andMiller, Miller, 1994). 1994). This This inclusion-rich, inclusion-rich, highly highly northeasternMinnesota Minnesota(Boerboom contaminated, contaminated, mafic mafic hypabyssal hypabyssal intrusive intrusive unit, unit, informally informally termed termed the theShoepack Shoepack Lake redistributed by Lake inclusion-rich inclusion-rich ferrodiorite ferrodiorite(SLID), (SLID), has been widely redistributed by intrusion intrusion of granophyric granophyricand andanorthositic anorthositiccomponents componentsof ofthe theDuluth DuluthComplex, Complex,and andby bylater laterNENEtrending mafic dikes and sills related to both the Duluth and Beaver Bay Complexes. trending mafic dikes and sills related to both the Duluth and Beaver Bay Complexes. Most Mostoutcrops outcropsof ofSLID SLIDcontain containabundant abundantxenoliths xenolithsof ofKeweenawan Keweenawanfelsic felsic to tomafic mafic volcanic rocks, but at its northern extent nearly all xenoliths volcanic rocks, but at its northern extent nearly all xenoliths are areArchean Archeancrust. crust. Similar Similar but but unrelated unrelatedcontaminated contaminateddiabase diabasecontaining containingabundant abundantKeweenawan Keweenawan inclusions inclusions has has been been mapped mapped to tothe thesouth, south, and andisisinterpreted interpretedas asthe thefirst firstmagma magmapulse pulse of of the theBeaver BeaverRiver River Diabase Diabasedike dikeand andsill sillcomplex complexof of the theBeaver BeaverBay Bay Complex Complex (Miller (Miller and andothers, others,1989). 1989). Although Althoughthe theSLID SLIDisisclearly dearly older older than thanthe theBeaver BeaverRiver River Diabase, Diabase, ititsimilarly similarlyrepresents representsan aninitial initialpulse pulseof of magma magmarelated relatedto toincipient incipientconduit conduit opening. opening.These Theseearly, early,inclusion-rich inclusion-richphases phasesare areinferred inferredtotohave have'cleaned 'cleanedthe thepipes' pipes' and andcleared clearedthe theway wayfor forlater laterinclusion-free inclusion-freedikes dikesand andsills. sills. R7W , —VV—.. SS s 4Anorthositic Rocks R6W R5W •—--.t # . , -& .. & Approximate Approximatelocation location of study area of study area A NORTH SHORE VOLCANIC GROUP —------ , Shoepack ShoepackLake Lakeinclusioninclusionrich ferrodiorite(SLID) (SLID) richferrodiorite Archean Archeanxenoliths xenolithsininthe theSLID SLIDrange rangefrom fromsingle singledisaggregated disaggregatedquartz quartzcrystals crystalstoto outcrops 50mmacross, across,but butmost mostare arebetween between0.3 0.3and and11meter meterininsize. size. outcropsasaslarge largeasas50 Compositions Compositionsinclude includebiotite biotiteschist schistlocally locallycut cutby byfolded foldeddikelets dikeletsof ofgranite granitepegmatite, pegmatite, volcanogenic volcanogenicgraywacke graywackehaving havinggraded gradedbedding, bedding,pink pinkgranite, granite,pegmatite, pegmatite,and andgranitic granitic gneiss, monzodioritewith withlocally locallyabundant abundantlamprophyre lamprophyre gneiss,and andgranodiorite granodioritetotomonzodiorite inclusions—all ofArchean Archeanrocks rockswest westof ofthe theMidcontinent Midcontinentrift rift inclusions-all components compohentstypical typicalof system. Frozen amoeboid stringers of felsic material, trails of granular quartz grains, system. Frozen amoeboid stingers of felsic material, trails of granular quartz grains, and andsmall smallrock rockfragments fragmentsininvarious variousstates statesofofassimilation assimilationcommonly commonlyemanate emanatefrom from 5 �felsic inclusions. inclusions. The ferrodiorite host host rock rock ranges ranges from from dense dense black black to to pinkish pinkish gray gray fdsic variably assimilated assimilated xenoliths. due to variably .. The part of the SLID that contains Archean xenoliths' xenoliths overlies overlies aa northwestnorthwestwho postulated postulated a sub- ' White (1966), (19661,who trending gravity low, first first recognized by White Keweenawan ridge of Archean basement extending northwestward from the shoreline of Lake Superior. Geophysical modeling of this area by others supports White's interpretation of the negative gravity anomaly (Ferderer, 1982; Chandler, 1990; Allen and others, 1993). Geologic evidence other than Archean crustal xenoliths also supports White's interpretation. Multiple northeast-trending intrusive components of the Beaver Bay Complex form thick stacks of sheeted intrusions both northeast and southwest of the gravity low, but over the gravity low are pinched into narrow dike-like bodies (Miller and Chandler, in prep). This configuration suggests a buried control on their shapes. In addition, Jirsa's (1984) study of interflow sedimentary strata in the North Shore Volcanic Group has defined two sub-basins separated by a paleotopographic high that roughly corresponds to "White's basement high," and also to the necked zone of magmatic emplacement of the Beaver Bay Complex. Such a paleotopographic high implies that relative basement uplift occurred before or during deposition of the flow/interfiow sequences. Other areas of shallow crustal basement inferred from geophysical modeling underlie the Bayfield Peninsula in Wisconsin and an area southwest of Isle Royale (White, 1966; Allen and others, 1993). The Archean crustal xenoliths in northeastern Minnesota strongly support interpretations of of a pre- to syn-magmatic, high bl block geophysical interpretations syn-inagma^c, topographically nigh ock ofof older crustal rocks in northeastern Isle Royale and mtheastem Minnesota, Minnesota, and by.inference, inference, near Kovale and . " in h northern northern Wisconsin. isc cons in.' Field mapping mapping was program. wasfunded fundedin inpart partby bythe theUSGS-COGEOMAP USGS-C&BOMA~' .program. ,, REFERENCES CITED Allen, W.J.,Dickas, Dickas, A.B., A.B.,and andMudrey, Mudrey, M.G., M.G., Jr., Jr.,1993, 1993,Aa'lntegrktaf An integrated sdattfc seismic refteeUon/ reflection! ABen, D.J., Hinze, WJ., %. + three-dimensional gravity investigation rift system,system, USA: Western Western Lake three-dimensional gravity investigation of the Midcontinent Midcontinentrift Superior Region [abs.1: Basement Basement and and Basins of ofEastern EasternNo* North America,AAPG America, AAPG Hedberg Research Superior Regionbbs.1: --Research , Arbor, Michigan. : Conference, Ann Arbor, Michigan. Boerboom, T.J., Tj., and Geologicmap map of of the the Silver SilverIsland Island Lake, Lake, Wilson Wilson~ake.ind Lake, and western western andMiller, Miller, J.D., J.D., 1994, 1994, Geologic quadrangles, Cook and and Lake Counties, Counties, Minnesota: Minnesota Survey Toohey Lake quadrangles, Minnesota Geological Geelo&al Survey Miscellaneous (in prep.). MiscellaneousMap MapSeries, SerieÈscale scale 11:24,000 24,000 tin m.). Chandler, V.W., 1990, Geologic interpretation of gravity and magnetic data over the central part of the Duluth Comple; northeastern Minnesota: Economic Geology, v. 85, p. 816-829. Ferderer, R.J., 1982, Gravity and magnetic modelling bf the southern half of the Duluth Complex, northeastern Minnesota: Unpublished M.A. Thesis, Indiana University, Indiana, 99 p. Jirsa, M.A., 1984, Interfiow sedimentary rocks in the Keweenawan North Shore Volcanic Group, northeastern Minnesota: Minnesota Geological Survey Report of Investigations 30, 20 p. Miller, J.D., and Chandler, V.W., in prep, Geology, petrology, and tectonic significance of the Beaver Bay Complex, northeastern Minnesota: GSA Special Paper. Miller, J.D., Green, J.C., and Boerboom, T.J., 1989, Geologic map of the illgen City quadrangle, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-66, scale 1:24,000. White, W.S., 1966, Tectonics of the Keweenawan basin, western Lake Superior region: U. S. Geological Survey Professional Paper 524-E, 23 p. 6 �I p I FORTY FORTY YEARS YEARS OF OF INSTITUTES INSTITOTES ON OH LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY BORNHORST. Theodore J., Department BORNHORST, Theodore J., Department of of Geological Geological Engineering, Engineering, Geology Geology and and Geophysics, Geophysics, Michigan Michigan Technological Technological University, University, Houghton, ~ o u ~ h t o nMI MI , 49931 49931 The The Institute Institute on on Lake Lake Superior Superior Geology Geology (ILSG) (ILSG) began in in 1955 1955 with annual at locations locations annual meetings meetings held held in in April April or or May May of of each each year, year, at been held held at throughout throuahout the the Lake Lake Superior Suoerior region. region. Meetings Meetings have have been at 18 18 different locations, with 9 locations repeating (repeat interval different locations, with 9 locations repeating (repeat interval with time meeting locations around around 11 11 years). years). More More diversity diversity with time in in meeting locations is Over indicated indicated by by 66 single single locations locations occurring occurring in in the the last last 10 10 years. years. Over the 40 years of ILSG, there have been 30 chairmen; 9 have been the 40 ILSG, have been chairman chairman twice twice (repeat (repeat interval interval around around 11) 11) and and 21, 21, once. once. For For the the 55 from previous previous years years from from 1990 1990 to to 1994, 1994, all all chairmen chairmen have have been repeats repeats from years, years, indicating indicating less less diversity diversity with with time time in in annual chairmen. chairmen. The The ILSG ILSG was was founded founded to to bring bring together together geologists geologists from from academia, academia, government and industry industry to to discuss discuss the the geology of areas government surveys, surveys, and related Goldich Medal Medal related geographically geographically to Lake Superior Superior (see (see the Sam Goldich Award Award Guidelines). Guidelines). The The attendance attendance over over the the 40 40 years years of of ILSG, ILSG, estimated of 6000, clearly indicates indicates that that the the ILSG ILSG has has estimated to to be be in in excess excess of 6000, clearly years 1966 to met met its its objectives. objectives. Data on attendance is known for the years 1969, 1969, and and 1982 1982 to to present, present, and and suggest suggest aa cyclical cyclical pattern. pattern. The provides The number number of of abstracts abstracts published in proceedings volumes provides another measure of of the the success success of of the the ILSG ILSG in in bringing bringing another quantitative quantitative measure total number number of of abstracts abstracts over over the the 40 40 years years together together geologists. geologists. The total meetings, the number of of abstracts abstracts is is approximately approximately 1450. 1450. For For annual annual meetings, the number Overall, the ranges ranges from from 12 12 to to 60, 60, with with aa median median of of 31. 31. Overall, the number number of of abstracts dramatically abstracts gradually increased from 1955 to 1983, and then dramatically increased and has has stayed stayed higher higher than than in in earlier earlier years, years, increased in in 1984 1984 and although although slightly slightly declining declining from from 1985 1985 to to 1994. 1994. The total number of authors authors on on abstracts abstracts over over the the 40 40 years years is is approximately approximately 2450. 2450. For annual meetings, the with a a the number of authors ranges from 14 to 126, with median median of of 49. 49. Both Both the the number number of of abstracts abstracts and and number number of of authors, authors, documents geology of of the documents a significant volume of discussion on the geology Lake Lake Superior Superior area. area. The only available mix of academia, government government available means of analyzing the mix surveys, surveys, and and industry industry is is through through the the abstracts. abstracts. For every abstract, abstract, over the other author author the 40 40 years of ILSG, the senior author and every other was categorized categorized as as affiliated with either academia (includes (includes students) , government students), government surveys, surveys, or industry industry (includes (includes consultants) consultants). patterns are nearly nearly identical, using using The proportion and temporal patterns Published affiliation affiliation of either: senior senior author author only, only, or or all all authors. authors. Published contributions most of of the 40 contributions by academic geologists have dominated most year year history of of the the ILSG, ILSG, with a median of about 65 % of contributions each overall pattern in in the the proportion proportion of of academic academic each year. year. The overall contributions contributions is is one one of of aa gradual gradual increase increase from from around around 40 40 %% in in 1955, 1955, to to 80 80 % in in 1975, 1975, followed followed by aa decrease decrease to to about about 45 45 %% in in 1994. 1994. Government survey over the 40 Government survey contributions contributions have gradually increased over years of ILSG from around 20 % to around 35 %, %, with with a median median of of about about were much much Published 25 %. %. Published contributions contributions by industry geologists were 25 proportion greater in %. The proportion in the the first first 66 years years of of the the ILSG, ILSG, around around 25 25 %. of contributions fell to a lowfell around of near 0, while ofindustry industry contributions to1975 a low around 1975 of near 0, while at same timetime academic contributions peaked, and peaked, has since and has since atthe the same academic contributions 7 �The increased increased to to around around 10 10 %. %. The median median proportion proportion of of industry industry The contributions of ILSG contributions over over the the 40 40 years yearsof ILSGis is66%. %. The ILSG ILSG has has succeeded at bringing together a mix of geologists from succeeded at brin~ingtogether a mix of geologists from academia, academia, government government survey, survey,and and industry. industry. While While published published contributions contributions from from industry industry are are low, low, an an analysis analysis of of attendees, attendees, which which is is not not possible, possible, may may indicate indicate higher higher industry industry geologist geologist participation Rarticipation in in ILSG. ILSG. The The ILSG ILSG has has had had aa focus focus on on Precambrian Pmdombrian geology geology and and mineral mineral resources resources throughout Every abstract abstract was was categorized categorized as as throughout its its 40 40 year year history. history. Every related resources, basic basic geology, geology, geophysics, aeophysics, related to to either either resources, have dominated dominated glacial/environmental, glacial/environmental,or or other. other. Basic Basic geology geology topics topics have ILSG abstracts, with a median contribution of about 60 % over the 40 40 ILSG abstracts, wi-th a median contribution ot about 60 % over the Basic years. Basic geology geology contributions cmItributi0ns gradually gaxidually increased increased from from 1955 1955 to to years. 1972, The proportion proportion of of and have have since since fallen fallen to to around around 45 45 %. %. The 1972, and resource resource related related papers papers was was greatest greatest in in the the first first 55 years years of of the the ILSG, ILSG, at around 50 %, and since then it has remained variable at about 30 %% at around 50 %, and since then it has remained variable at about 30 (overall Geopbyics abstracts abstracts have remained remained (overall median median of ofabout about3030%)%.) . Geophysics consistent Glacial/environmental consistent with with aa median median of of 89%% contribution. contribution. Glacial/environmental topics teoics have have aa median median of at 22 %% contribution. contribution. As As the the 1994 1944 Chairman, Chairman, I I was was directed by the Board of Directors to increase the proportion of directed by the Board of Directors to increase the proportion of with the glacial/environmental glacial/environmentalcontributions. contributions. Solicitations, Solicitations, with the help help of of M. M. A. A. Gere, -re, Jr., Jr., resulted resulted in in aa dramatic dramatic increase increase of of glacial/environmental 20 %% for for 1994 1994 (by (by far far the the 40 40 glacial/environmental abstracts abstracts to to about about 20 year year high). high) . North What What is is the the future future of of the the ILSO? ILSG? The The role role of of geologists gedogists in in North The ILSG America ILSG has has America today today is is much much different different than than it it was was in in 1955. 1955. The changed It is is important important that that the the ILSG IIiSG look look changed over o w its its 40 40 year year history. history. It a lengthy to had& lengthy discussion discussion on on the the The Board Board of of Directors Directors had to its its future. future. The future of the annual annual board board meeting meeting in in 1993, 1993, and and will will continue continue future of ILSG ILSG at at the the in 1994. 1994. Can Can or or should should the the ILSG maintain its focus on the discussion discussion in the ILSG into Precambrian/resource Should the ILSG expand ~Z~an into d all all areas areas Precambrian/resourcegeology? geology? Should The critical question of geology of the Lake Superior region? is, of geology of the Lake Superior region? The critical question is, what of success? success? what changes ehangas must must the the ILSG ILSG undergo undergo to to insure insure 40 40 more more years years of II thank thank Mary Mary L. L. Larson Larson for for the the hours hours of of compilation compilation from from proceedings proceedings volumes volumes in in the the Michigan Michigan Technological Technological University University Library Library Archives. Archives. 8 �I U I INVENTORY DIVISION'S UPPER INVENTORY OF THE MICHIGAN GEOLOGICAL SURVEY DIVISION'S I Frank Frank Chenier, Chenier, District District Geologist; Geologist; Michigan Department Department of Natural I I I I I I I I I I I I I PENINSULA PENINSULA SIGNIFICANT SIGNIFICANT WATER WELL CUTTINGS LIBRARY AT ESCANABA ESCANABA Resources; Resources; Geological Geological Survey Survey Division; Escanaba, Escanaba, Michigan Michigan Drill Drill cuttings cuttings from from approximately approximately 570 570 selected selected water wells wells representing representing the the geology geology of of the the Upper Peninsula Peninsula are are maintained by the the Geological Geological Survey Survey Division of the Michigan Department Department of Natural Natural Resources Resources office office at at Escanaba. Escanaba. The collection collection includes includes rocks rocks of of precambrian precambrian and and paleozoic paleozoic age age and and overburden overburden samples. samples. Environmental Environmental and and groundwater groundwater conditions as well as potential mineral investigation of some some of mineral resources resources can can be assessed by the investigation these these cuttings. cuttings. In In addition, addition, the the office office maintains maintains aa library library of of available available water water well well logs logs for for the the entire entire U.P. U.P. All of of the the above above are are available available for for study study and and review. review. For more information information contact Frank Chenier at (906)786—2351. Frank Chenier at (906)786-2351. �METALLIC MINERAL METALLIC MINERAL RESOURCES RESOURCES AND AND ECOSYSTEM ECOSYSTEM MANAGEMENT MANAGEMENT AT AT VOYAGEURS NATIONAL PARK, MINNESOTA VOYAGEURS NATIONAL PARK, Davis, Steven R., R., U.S. Bureau Bureau of of Mines/IFOC, MinesIIFOC, Denver, Denver, CO CO 80225-0086 80225-0086 Under a Memorandum of Understanding with the the National the Under Memorandum of Understanding with National Park Park Service, Service, the IntermountainField FieldOperations OperationsCenter Centerofofthe the U.S. U.S. Bureau Intermountain Bureau of Mines Mines recently recently completed completed a hardrock mineral mineral study studyon on the the Voyageurs VoyageursNational NationalPark Parkarea areaofofnorth northcentral centralMinnesota. Minnesota.The The hardrock prompted by by proposed proposed changes in in the the State's Metallic Minerals Leasing Rules aimed aimed study was prompted at encouraging mineral mineral exploration exploration and and development. development. The announcement prompted a great deal The prompted by the Park's management might what aa likely likely mineral mineral development development might of uncertainty uncertainty by management staff as to what and what ramifications ramifications itit might might have have on on Park resources and operations. operations. encompass, and USBM study study includes includes aa comprehensive comprehensiveanalysis analysisofofthe the region's region's historical historical mining mining The USBM activities and and apparent apparent mineral mineral potential, potential, as as well as descriptive models models of of known known mines mines in in similar similar geologic tenanes. terranes. The geologic Thefinal finaldocuments, documents, aa Mineral MineralLand Land Assessment Assessment and Executive Summary, include socioeconomic socioeconomicimpact impactanalyses analysesofofaa typical typical mine and an applicable mine development, development, and applicable include managementplan planincorporating incorporatingan anecosystem-sensitive ecosystem-sensitiveapproach. approach. Included Included in in the the environmental management thta package is a series of resource management maps in both hard copy and GIS (digital) form, data in both hard copy and GIs (digital) form, allowing for site specific project and proposal proposal analysis analysis and management. management. This project is an opportunity to impart a better better understanding of what potential metallic mineral resources exist in the area, area, and the likely development and the development scenario scenario that might occur if these resources are identified resources identified and and developed. developed. The report also details details the the environmental environmental concerns concerns related to mineral developments and andcurrent current state-of-the-art state-of-the-artmitigation mitigationtechnologies. technologies. The project project therefore impart impart aa better understanding understanding of of mineral mineral development developmenton onthe thepart partof ofthe the Park Park should therefore Service personnel, and alleviate some of the concerns relative to disruptions of regional Service personnel, and alleviate some of concerns relative disruptions regional ecosystem integrity and balance. Objective Objective and and comprehensive comprehensive studies studiessuch suchas as these, these, tailored tailored ecosystem to the specific issues and management needs of the National Parks involved, should the specific issues and management needs National involved, should prove valuable to to the the P Park primary Bureau Bureau of of Mines Mines goals goals of of ark Service, and at the same time achieve primary valuable continuing resource evaluation and increased mineral awareness. increased mineral awareness. �a Wetland Wetland Treatment Treatment of of Mine Mine Drainage Drainage -an Alternative to Conventional Conventional Treatment or Voodoo Treatment? Paul Eger Minnesota Department of Natural Resources St. Paul, Minnesota I I I I I I I I I I I I Although wetlandshave havebeen been used used to to treat of this Although wetlands treat mine mine drainage drainage the application application of this technology has not always been successful. The type and size of wetland that is needed is technology has not always been successful. wetland that needed a function of the input drainage quality, the effluent requirements and and the the length length of of time time treatment treatment is required. required. of the 90% of both pilot pilot and full scale tests have demonstrated demonstrated that that from from 50 - 90% Results from both influent copper, nickel, cobalt and zinc can be removed from neutral mine drainage in free water influent Acid mine has been been treated in aa pilot surface wetlands. wetlands. Acid mine drainage drainage has treated in pilot system system representing representing a subsurface wetland. wetland. The pH of the drainage has generally been increased from influent values values the drainage generally and 7. Over between 4 and and 55 to effluent values between 6.5 and Over90% 90%of of the the influent influent copper, copper, nickel, cobalt and zinc have been removed. been removed. Although require much much less less maintenance maintenance than thanconventional conventional Although wetland treatment systems will require technology, plans for maintenance and replacement must be included for successful long term term technology, plans maintenance and replacement must be included for successful long treatment. treatment �MINNESOTA MINNESOTA DRILL DRILL CORE CORE EXAMINATION EXAMINATION AND AND ASSAY ASSAY FREY, PREY. Barry Barry A., A., Minnesota Minnesota Department Department of Natural Natural Resources, Resources, Division of Minerals, Minerals, 1525 1525 Third Avenue E., E., Ilibbing, MN 55746 Hibbii, MN 55746 Current work includes includes the new logging of 100 100 drill drill core core samples samples and assaying of 212 new new samples samples of existing DNR Drill Core Library existing DNR Library samples samples for most of which which no no modern modem descriptive descriptive logs logs and little little chemical data Samples are are from Central Minnesota, where rocks associated chemical data are are available. available. Samples Minnesota, where associated with the Penokean Orogen dominate dominate and and there are few Drill cores were were laid out and logged Penokean few outcrops. outcrops. Drill logged in a qualitative manner and then sampled in order to determine alteration, mineralization, and protoliths. qualitative order alteration, mineralization, and protoliths. The The entered into aa digital digital database databasefor for future futureGIS GISapplication. application. The fields and current descriptive logs were entered codes are listed elsewhere elsewhere on the poster. An Anexample example of of the thedatabase databaseprintouts printouts from from the the most most recent recent logging is also also shown. shown. Logging project has has verified verified or or expanded expandedthe theknowledge knowledgeofofthis thisProterozoic Proterozoicterrane. terrane. Three Three this project Logging for for this interesting features observed in this geologic setting are the presence of tourmaline, granitic granitic intrusive intrusive relationships, relationships, and the presence presence of of ultramafic ultramafic rocks. rocks. Grain mounts mounts taken while core core logging logging have have identified vein or stratiform tourmaline from several additional core samples. Amounts of tourmaline are identified vein or stratiform tourmaline from several additional core samples. Amounts of tourmaline are generally small. Where stratiform, the tourmaline is generally found with oxide, chert, silicate, or sulfide Where stratiform, the tourmaline is generally chert, silicate, or sulfide veinlets have been found in They hey have have chemical sediment. Granitic intrusives and veinlets in several severalplaces. places. T intruded phyllitic phyllitic schists, schists, metagabbro, metagabbro, and magnetite magnetite chert chert iron iron formation. formation. Some intruded Some(within (withinphyllitic phylliiic schist) schist) rocks while while others othersare aregood goodintrusives. intrusives. The may be sweated out from surrounding rocks The intrusives intrusives and veins may help to explain the recrystallized nature common with the quartz rich portions may to explain the recrystallized common with the rich portions of of these these iron iron magnetite, or Inplaces, places,this thisgranite graniteisisrelatively relatively fresh fresh with with assimilated magnetite, or itit may may be be extremely extremely formations. In altered with carbonate, when fresh, it appears to be carbonate, epidote, epidote, and and chlorite chlorite to tocreate createepidotites. epidotites. Even when be tectonized, with were with carbonate carbonate having having aaspatial spatialassociation. association. Four drill drill cores cores with with ultramafic ultramaf~c rocks were Chemistry subdivides subdividesthese thesebased basedon onrelative relativeabundances abundancesofofVVversus versusCr, Cr, Ni, Ni, and MgO logged. MgO logged. Chemistry by differences differencesin inmineralogy mineralogy and degree degree of of alteration. alteration. The contents, and logging by The more more magnesic magnesic rocks are more pervasively and destructively altered compared compared to to the vanadium vanadium rich rich rocks. *are areaalso alsounderwent underwentaaperiod(s) period(s)ofofpre-Pleistocene prePleistoceneweathering weathering before before being being The rocks rocks of of the thearea glacially scoured. These effects have been superimposed on the original rock types. Weathering effects These effects have been superimposed rock Weathering effects include limonitic, limonitic, red hematitic, and goethitic goethitic alteration alteration may may be include goethitic alteration, alteration, although some goethitic hydrothermal in in nature. nature. regionally There are are numerous numerous observed observed ore-mineral oremineral occurrences and alteration. Carbonate is regionally abundant within altered volcanics, as an iron formation component, as marble, and as minerals associated abundant within altered volcanics, as an iron formation component, as marble, and as minerals associated with most veins. Some Inassociation associationto to this, this, preliminary preliminary Someveins veinshave have associated associated skarn skarn and mineralogy. In examination of thin sections unexpected local occurrence sections indicated the unexpected occurrenceof ofbright brightblue-violet blue-violetpleochroic pleochroic sodic amphiboles associated with carbonate, epidote, zoisite alteration. Stratiform sulfides occur in numerous DDH's, as asdoes doesgraphitic graphiticargillite-phyllite argillite-phyllitewhich which isis often often These sulfides are typically pyrrhotite or pyrite, but lesser associated with the the stratiform stratiformsulfides sulfides . These sulfides are typically pyrrhotite or lesser chalcopyrite or or sphalerite sphalerite isis sometimes sometimes found. found. Sevn SevenDDH's DDH'salso alsohad hadtrace traceamounts amountsofofbornite. bornite. from the the latest latest logging logging occurred occurredin in K-1, K-i, BM-2, Possible visible sphalerite from BM-2, MLCH-7, MLCH-7, MLCH-5, MLCH-5, Drill core K-i MLCH-11, BM-i, CW-1, MLCH-9, T-665, MLCH-2, and C4 (see analytical results). BM-1, CW-1, MLCH-9, T-665, MLCH-2, and C4 (see analytical results). K-1 had the most most visible sphalerite, sphalerite, with withthe thechemical chemicaldata dataverifying veri'ing the sphalerite. Reddish-orange Reddish-orange siderite is also present and looks looks similar similar to to sphalerite. sphalerite. Analytical results for 212 212 new samples have been received from our contractor, contractor, Bondar-Clegg Bondar-Clegg & & Ltd. of Ottawa, Ontario. Forty package with with Company Ltd. Fortynine ninesamples samples were were analyzed analyzed using a 52 52 element package 163 samples samples analyzed analyzed using using aa 21 21 element elementpackage packageincluding includingAu, Au,Pt, Pt, and andPd. Pd. Some Someof of these these analyses analyses were were from drill from drill core core logged logged during during the the previous previous biennium. biennium. From the standpoint geology, there there are are many many significant significantassay assayresults. results. The standpoint of economic geology, The highest highest . 12 �Zn A 5 foot sample from from DDH DDH K-1 K-i had Zn values values to to date date have have come come from from the recent analyses. A had a Zn assay >>20000 20000ppm. ppm. AAsample samplefrom fromDDH DDHH12 H12had had aaZn Znvalue value of of 683 683 ppm. Beside BesideZn, Zn,these thesesamples samples had had anomalous Ag, Pb, Cu, Au, Pt, Pd, Cd, Mo, F, Sb, Hg; and separately, other elements. anomalous Ag, Pb, Cu, Au, Pt, Pd, Cd, Mo, F, Sb, Hg; and separately, other elements. The new analyses had had several Cu values over 600 600 ppm ppm from from DDH's DDH's H6, K-I, 17. Drill cores from values over K-1,and and B1-l Bl-117. several had anomalous anomalousAs As(to (to234 234ppm), ppm),Cd Cd(to (to134 134ppm), ppm),FF(to (to14.075 14,075 ppm), ppm), and Hg Hg several different areas had (to (to 428 428 ppb). ppb). The Thehighest highest Pb Pbvalues values (to (to762 762ppm) ppm) caine came from from the the unusual unusual association of MgO rich (to (to 24.54%) 24.54%) altered TC-101 and and TC-102. TC-102. These were also also high high in in Cr, Cr, N Ni, altered ultramafics in DDH TC-101 These samples were i,and Hg. The many places within The data data indicates indicates that thathydrothermal hydrothermal processes processes were active in in many within Central Central Minnesota, and and that thatthere theremay may be beaahigh highprobability probabilityfor forundiscovered undiscoveredeconomic economicmineralization. mineralization. 13 �GENESIS OF GENESIS OFHEMATITE HEMATITEAND ANDMAGNETITE MAGNETITE IN INPRECAMBRIAN PRECAMBRIANMACNETITE MAGNETITE IRON-FORMATION IRON-FORMATIONOF OF LOW LOW METAMORPHIC GRADE,LAKE LAKE SUPERIOR DISTRICT, USA USA - AA MICROSCOPIC MICROSCOPIC OBSERVATION GRADE. SUPERIOR DISTRICT, OBSERVATION METAMORPHIC HAN, T. T. M., M., Consulting Applied Mineralogist, Ishpeming, HI MI 49849 49849 HAD, metamorphic grade Precambrian Precambrian magnetite magnetite iron-formations iron-formations of of the Lake Lake The low metamorphic Superior District examined Superior examined in in this this study study were the the Biwabik of the Mesabi Range, the Ironwood Ironwood of of the the Gogebic Gogebic Range, Range, and and the Marquette Range. The the the Negaunee Negaunee of of the the Marquette flange. The banded type and Biwabik and Ironwood Ironwood iron-formations iron-formations consist consist of of both an evenly "banded irregularly wavy The Negaunee Negaunee iron-formation iron-formation is is exclusively exclusively the the an irregularly wavy banded banded type. type. The evenly banded type which which consists dominant subtypes, subtypes, i. e. e. carbonate-chert carbonate-chert evenlybandedtype consists of two dominant magnetite in the wavy wavy banded banded iron-formation and silicate-carbonate-chert. silicate-carbonate-chert. The magnetite hematite, iron coexists with hematite, iron carbonates, carbonates, layered layered iron-silicates iron-silicates and chert. The iron-formation has essentially the same mineral mineral assemblage assemblage but but is is evenly banded iron-formation generally free of hematite. number of of The study was done done by by microscopic examination of a substantial substantial number sections prepared from from these these iron-formations, iron-formations, polished sections from specimens collected from before is employed. employed. The The results before and after after an an induced induced oxidation oxidation procedure procedure is indicated that: that: (a) both the hematite hematite and and the the magnetite magnetite in these these (a) The origin of both indicated iron-formations is more complicated complicated than believed. (b) iron-formations is far farmore than previously previouslybelieved. (b) Some Some of the or developed developed shortly shortly hematite is probably aa product product of primary sedimentation, or deposition; and be a a result result of of authigenic authigenic growth growth generated generated after deposition; and some some of it may be from the the migration migration and and precipitation precipitationofofFe* Fe from from acidic acidic pore pore fluids fluids during during from diagenesis. (c) various hematites functioned functioned as "starting "starting points" points" responsible responsible diagenesis. (c) The varioushematites for the the development development of magnetite present present in the iron-formations. iron-formations. (d) for of most most of of the the magnetite in the (d) proceeds concurrently by replacing replacing the The magnetite development apparently proceeds concurrently by hematite on hematite on one one hand hand and and overgrowing overgrowing into into the the host host of of the the hematite hematite on on the the other. other. (e) More More than one stage (f) AA (e) stage of of overgrowth overgrowth is is evident evident on on some some magnetite. magnetite. (f) progressive change of of magnetite in some of the carbonate-chert progressive morphological change carbonate-chert subtype, i.e. it changes changes from clusters of lath-shaped lath-shaped pseudomorphs pseudomorphs to aggregates from clusters to aggregates subtype, (g) The The newly newly formed of anhedral grains and and finally finally to to coalesced coalesced octahedra. octahedra. (g) magnetite is believed to the solid solid diffusion diffusion of of Fe++ Fe++ magnetite is believed to be a product resulting from the the hematites. hematites. The The Fe* Fe is hematite toward the is generated generated from from the the reaction reaction between hematite metamorphism. and carbonaceous matter in in the iron-formation iron-formation during low grade metamorphism. hematites became became aa minor minor ore ore As a result, both the primary and diagenetic hematites mineral while magnetite became became a major ore ore mineral mineral in in the the Precambrian Precambrian ironironMuch of of the magnetite magnetite I in n the ironformation of the the Lake Lake Superior Superior District. District. Much formation currently furnace feed on on the the Hesabi Nesabi and and Marquette Marquette formation currently processed processed for for blast furnace enriched through process. Much of the the hematite hematite previously previously and and ranges was enriched through such a process. currently mined on the Mesabi, Mesabi, Gogebic Gogebic and and Marquette Marquette ranges ranges is is of of postmetamorphic postmetamorphic currently origin and represents represents an product of of the the magnetite, magnetite, iron iron carbonates carbonates and and origin an oxidation product layered iron-silicates. iron-silicates. These interpretations based on: on: (a) the morphological morphological character character and and the the These interpretations are are based mineral association of the magnetite; and (b) the morphologies, microstructures, mineral association of the magnetite; and morphologies, microstructures, impurities and and microtextural microtextural relationships relationships of of preexisting preexisting hematite hematite Inclusions inclusions in in impurities the existing magnetite. Many of these features are revealed after induced the existing magnetite. Many of these features revealed Induced oxidation. oxidation. 14 �I GEOTECHNICAL GEOTECHNICAL SOLUTIONS SOLUTIONS FOR MINING RELATED RELATED PROBLEMS PROBLEMS • Allan M. Johnson Johnson Department Mining Engineering Engineering Department of of Mining Technological University Michigan University Michigan Houghton, 49931 Houghton, MI 49931 ABSTRACT ABSTRACT Mining practices of the the 19th 19th and early early 20th 20th centuries centuries have have sometimes sometimes resulted in problems problems of current concern. These Theseproblems problemsinclude includeunsightly unsightly or or unsafe unsafe conditions conditions at the the mines mines and, and, in in some someinstances, instances, environmental environmentaldamage damage to varying degrees. Examples types can be found in all of the the older older iron iron ore oreand and Examples of problems of these types copper Michigan. More than 20 20 years years of of studies studies of problems problems on the the West copper mining districts in Michigan. Morethan types: Menominee Iron Iron Range Range in in Iron Iron County Countyhave haveidentified identified problems of the the following following types: Menominee 1) 1) 2) 2) 3) 3) 4) inadequately capped and sealed mine mine shafts shafts and raises; raises; the the threat threat of of surface surfacesubsidence subsidenceabove aboveshallow shallowmine minestopes; slopes; presently unacceptable disposal of mining waste rock; and presently unacceptable disposal mining waste rock; and mineralized mineralized and and acid add mine minedrainage. drainage. 4) These ,Thesestudies studies with with solutions solutions to problems of these these types typeshave have been reported reported in in the theliterature literature in published reports. One of these studies addressed a serious acid drainage problem at and in published One of these studies addressed a serious add drainage the the Dober Dober Mine Mine complex complex in in the theIron IronRiver RiverValley. Valley. and Here (pH2) 2)with withhigh highlevels levelsof ofdissolved dissolvedmetals metals (iron (ironand andaluminum) aluminum) Here acid acid waters waters (pH flowed Neutralizationof ofthe theacid add by by the theriver riverwaters waters caused caused insoluble insoluble flowed into the Iron River. Neutralization Fe boy) to precipitate, precipitate, turning turning the the waters watersyellow yellowbrown. brown. This Fe and and Al A1 hydroxides hydroxides (yellow boy) highly highly visible visible pollution affected the Iron River some seven miles to its confluence with the Brule south. Residents marks its its border border with with Wisconsin to the south. Residents of of both both states states Brule River, River, which which marks were affected. were affected. To studywas wasdone doneto toquantify quantify the the extent extent and and nature nature of of the the Toaddress address this this problem, problem, aastudy acid acid drainage. drainage. ItItwas wasdetermined determined that that aa huge huge teservoir feservoir of of acid acid water water was was present in the the underground was also alsolearned learned that that acid add waters waters flowed flowed from from the the Dober Dober underground mine minecomplex. complex. ItIt was Mine in response to groundwater inflow into the elevated western part of the mine Mine in response to groundwater inflow into the elevated western part of the minecomplex. complex. Calculations showed that that the the acid acid waters, waters, which which flowed flowedatatan anaverage avenge rate of 50 gpm, would Calculations showed would continue to impact the river system for at least 50 continue system for at least 50 years, years, at at which which time time the the mine minewould would have have been been sufficiently sufficiently flushed flushed of of the theacid. add. Bench scale tests tests of of methods methods to to neutralize neutralize the the acid add led led to to aaconceptual conceptualdesign design Bench and and pilot scale whereby mix with and whereby controlled amounts of river water would be diverted into the mine to mix neutralize treated drainage drainage from from the the mine mine was to to be be diverted diverted through through aa series series neutralizethe theacid. add. This This treated 15 �of downstream downstpm ponds adjacent to the the river in in which which settling settling would would remove remove the the metal metal returned to the the river. river. The precipitates. From From there there aa clear clear effluent effluent would be returned Thetest testresults results were promising and an engineering and economic assessment indicated the concept be were promising and an engineering and economic assessment indicated the concepttotobe precipitates. feasible. feasible. The acceptedand and supported supportedby bythe thelocal localcommunities communitiesand andthe theMichigan Michigan The plan plan was was accepted Department of Natural Resources. Ultimately it was funded through Act 307 (Michigan's Natural Ultimately it was funded through Act 307 (Michigan's "Superfund"), Act. The Thesystem systemwas wasbuilt builtand andbecame became "Superfund"), as the first first cleanup under the Act. operational in 1988. It is working as designed, with significant improvement operational in 1988. It is working as designed, with significant improvementto tothe theIron Ironand and Brule Brule River River system. system. References References 1986. 1986. Groundwater GroundwaterContamination ContaminationProblems Problems in in the theIron IronRiver RiverMining Mining District District of o Michigan (with (with David David M. M. Cregger). Cregger). Volume VolumeI,I,International InternationalSymposium Symposiumon onEnvironmental &-&onmental Geotechnology, in Environmental Environmental Geotechnology, Geotechnology, Hsai-Yang ~ s & - ~ Fang, a n ~ed., ed.,Envo EnvoPublishing Publishing Geotechnology, in Co., Co.,Bethlehem, Bethlehem, PA. PA. 1985. ControlAcid Acid Mine MineDrainage: Drainage: AAMichigan MichiganCase CaseHistory. History. 1985. AASynergetic SynergeticApproach ApproachtotoControl International 16-21. Printed PrintedininVolume VolumeII, 11,Mine Mine International Mine Water Assoc., Granada, Spain, Sept. 16-21. Water, ed., Talleres TalkiesGraficos GraficosARTE, ARTE, S.A., S.A., Maracena Maracena(Granada), (Granada),pp. pp. Water, R. R. Fernandez-Rubio, Pemandez-Rubio, ed., 695-708. 695-708. 1983. MineClosings. Closings. Invited Invited paper for for Session: Session: Water Water 1983. Hydrologic HydrologicConsiderations ConsiderationsininMine Resources SME-AIME Meeting, Meeting,Salt Salt Lake LakeCity, City,UT, UT,October October18-21, 18-21, Resources in in the the Western Western States, Slates,SME-AIME 1983. , 1983. Preprint -ria 83-365, 83-365, 55pp. pp.and andMining MiningEngineering, Eneineering,June June1984, 1984,pp. pp.644-648. 644-648. �PALEOMAGNETISM OF A A 1500 MA MA MAFIC MAFIC DIKE DIKE AT WATERLOO WATERLOO WISCONSIN KEAN, William, Department of Geosciences, Geosciences, University of KEAN, Milwaukee, P.O.Box P.O.Box 413 Milwaukee, Wisconsin- Milwaukee, 413 Milwaukee, Wi .53201 Wi. 53201 A recently quarry of of Waterloo Waterloo Quartzite A recently opened opened quarry Quartzite exposes exposes aa 1.5 1.5 meter thick cuts almost thick mafic dike that cuts almost vertically vertically through through dike is assumed assumed to be the the quartzite. The dike the same same age age as as a drill core core from the nearby nearby Portland mafic dike found found in drill Quarry, and dated at at 1450-1500 1450—1500 Ma Ma by by Ar/Ar Ar/Ar dating. The The dike studied for paleomagnetic analysis to aid in determining was paleomagnetic analysis in determining a more more reliable reliable paleopole paleopole position position for for the the 1500 Ma time a 1500 Ma time was frame frame for for central central North North 1\merica. America. the site site and and Twelve 2.54 2.54 cm cm diameter diameter cores cores were were drilled drilled from from the subjected to alternating field demagnetization demagnetization to lOOmT.,and 100mT.,and isothermal remanent remanent magnetism magnetism studies. Magnetite Magnetite saturation isothermal be the dominant dominant magnetic magnetic mineral.The mineral.The appears to be saturation direction of of Dec=308 Dec=308 deg.,Inc=-18.82 deg.,Inc=—18.82 deg. characteristic direction paleomagnetic pole pole of of 146 deg.E,18.66 deg.E,18.66 deg.N yields a paleomagnetic deg.N and an alpha 95 of 11 deg. deg. The The dike dike seems seems to cut across the folds folds in the quartzite so so no no structural structural corrections corrections have been made. of the Wolf Wolf River River Batholith Batholith (Hershberg, 1976), and Studies of (Hershberg, 1976), the Wausau Wausau Syenite Complex (Zich, Chan, and Myers (Zich, Chan, and Myers 1986) 1986) which are both dated at about 1500 1500 Ma indicate indicate posible Ma but show remagnetization at about 1100 Ma show aa component component results presented presented here. here. Also Also the magnetic similar to the results directions from the dike dike are significantly significantly different directions different from from Mercer 1984) those in the surrounding quartzite in surrounding quartzite ( Mercer 1984). ( References: References: E.L., 1976, Paleomagnetism Paleomagnetism of the Hershberg, E.L., the Wolf River M.S. Thesis,U.W.Madison, Thesis,U.W.Madison, 66 Batholith. M.S. 66 p. D.A., 1984, Paleomagnetism Paleomagnetism of the Baraboo Mercer, D.A., Mercer, M.S. Thesis, Thesis, U.W.Milwaukee, U.W.Milwaukee, 294 Quartzite. M.S. 294 p. Myers,P.,1986, Zich,C.,Chan,L.,and Myers, P., 1986, Preliminary Preliminary Zich,C.,Chan,L.,and Paleomagnetic results from the Wausau Syenite Syenite Complex, Central Central Wisconsin. Wisconsin. Eos,vol 67,p.266 17 �PROTEROZOIC VOLCANICS OF OF THE THE ANIMIKE ANIMIKEGROUP, GROUP, ONTARIO ONTARIO AND AND EARLY PROTEROZOIC MICHIGAN, AND THEIR TECFONIC SIGNIFICANCE MICHIGAN, AND TECTONIC SIGNIFICANCE KISSIN, Stephen Stephen A. A. and ERALICK, FRALICK, Philip Philip W., W., Dept. Dept. of of Geology, Geology, Lakehead Lakehead KISSIN, University, Thunder Bay, ON P7B SE1, Canada University, Thunder Bay, ON 5E1, Canada Although volcanic volcanicash ash components componentsare are found found in in the Early Although Early Proterozoic Proterozoic Animike Animike throughout the unitsare arerare. rare. The Gunflint Group throughout the Lake Lake Superior Superior region, volcanic units Gunflint Volcanics of Ontario and the have been been little studied in comparison of the Emporer Emporer Volcanics Volcanics of Michigan have formations, the the Gunflint Gunflint Formation Formationand and the the Ironwood Ironwood Iron Iron Formation, Formation, to associated iron formations, respectively. We report here the initial results of petrographic and geochemical work on on work respectively. here the initial results of petrographic units, together together with with data data on on the lapilli lapiui tuffs tufts of of the the Gunflint Gunifint Formation Formation. these units, The Gunflint Lavas occur conformably within within the the Gunflint Gunflint sedimentary rocks near Mink Mountain, Jean Jean Township, Township, Ontario. Ontario. The outcrop consists of ofthin thin bedded, bedded, The very limited outcrop Pillowedstructures structuresenveloped envelopedinin chert chert were were described by massive, aphanetic aphanetic basalt. Pillowed massive, described by (1960). The distinguished Goodwin (1960). Thebasalts basaltsare arevery veryfine-grained, fine-grained, with with few few microscopically distinguished features apart from plagioclase. Some units contain spherulites of microcrystalline quartz plagioclase. Some units contain spherulites microcrystallie quartz and K-feldspar that may be absorbed and recrystallized felsic lapilli. absorbed and recrystallized Emporer Volcanics The Emporer Volcanics are exposed in the Wakefield and Marenisco Quadrangles, Gogebic County, County, Michigan. Michigan. They have been described described most most recently recently by LaBerge LaBerge (1992), (1992), documented aasuite flows, hyaloclasites, hyaloclasites, and and pillow pillow who documented suiteof of mafic mafic sills, sills, massive and pillowed flows, breccias associated with felsic hyaloclasites, tufts, and breccias. The volcanics have been breccias associated with felsic hyaloclasites, tuffs, and breccias. The volcanics have been to be be interbedded interbedded with iron Irving and Van Hise (1892). known to iron formation formation since since the work of living Whole rock geochemistry reveals revealsthat that in in spite spiteof ofaarange rangein in major major element element chemistry, chemistry, the Gunflint Gunflint Volcanics Volcanics and mafic mafic Emporer Emporer Volcanics Volcanics have have indistinguishable indistinguishable chondritenormalized REE plots. The felsic Emporer Volcanics are somewhat depletedin inREEs, REEs,but but , REE plots. The felsic Volcanics are somewhat depleted relationship to to the the mafic mafic units units (Fig. (Fig. 1). 1). the plot indicates their probable close genetic relationship The classification classificationof ofthe thebasalts basaltsaccording accordingtotothe thetrace traceelement elementcontent contentof ofPearce Pearceand and + MgO MgO <c 20 wt wt Cann (1973) (1973) was was applied applied to samples fulfilling fulfillingthe the criterion criterion of of 12 12 < CaO CaO + Cam %, as well as to the Gunflint Volcanics, which are obviously basaltic but with low CaO %, the Gunflit Volcanics, which obviously basaltic but with low CaO + These affinities MgO. These samples plot in the the fields fields of of alkaline alkaline ocean-floor ocean-floor basalts. basalts. These MgO. suggest that that Gunfliit Gunflint Volcanics and and Mafic Emporer Emporer Volcanics may may have have formed in a backsuggest environment when when the the Penokean Penokean island island arcs, arcs,sutured sutured to to the the craton craton at 1860 ma ma arc spreading environment (Sims& et&aL. 1989),were were still still at at some some distance distance to to the south. (Sims , 1989), tuft beds are thickest and most numerous in the Kaministikwia The Gunflint lapilli tuff Kaministikwia near the apparent depositional edge of of the the unit unit. At tuff River gorge near At this this locality locality the lapilli tuff shalés. The beds are interbedded interbedded with carbonaceous carbonaceous shales. The lapilli lapilli are are mostly calcite-cemented and evidence of of sedimentary sedimentary reworking reworking(Shegelski, (Shegelski,1982). 1982).Although Althoughaagraded graded air-fall air-fallbed bed show evidence is present, the remaining beds may may have have been been accumulated accumulated by bysedimentation sedimentation shed shed from from the the Shield. The xenocrysts up up to to 2-3 2-3 rnm mm lapilli contain sanidine and quartz xenocrysts adjacent Archean Shield. The lapilli The Gunflint Volcanics in diameter, likely likely derived derived from from explosive explosive rhyolitic rhyolitic volcanism. volcanism. The Volcanics clearly are are not not viable viable sources sources for for these these constituents, constituents,and andthe the Emporer Emporer Volcanics are unlikely. unlikely. clearly The most likely source is a distal island arc, now highly metamorphosed in Penokean Penokean likely a distal island arc, now highly metamorphosed orogenic terrane. orogenic 18 �References References Goodwin, A.M., 1960, Gunflint Iron Iron Formation Goodwin, A.M., 1960, Gunflint Formation of the the Whitefish Whitefish Lake Lake area: Ontario Ontario Department of Mines, v. 69, Part 7, Department of Mines, v. 69,Part 7, p. p. 41-63. 41-63. Irving, living, R.D. and and Van Van Hise, Hise,C.R., C.R., 1892, 1892,The The Penokee Penokee iron-bearing iron-bearing series series of of Michigan Michigan and Wisconsin: U.S. Geological Survey Monograph 19, 534 Wisconsin: U.S. Geological Survey Monograph 19,534p. p. LaBerge, LaBerge, G.L, G.L,1992, 1992,The TheEarly EarlyProterozoic ProterozoicEmporer EmporerVolcanic VolcanicComplex: Complex:implications implicationsfor for the geology of the eastern Gogebic District, northern Michigan: Program the geology of the eastern Gogebic District, northern Michigan: Program & & Abstracts, Abstracts, Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology,38th 38th Annual AnnualMeeting, Meeting, p. p. 53-55. 53-55. Pearce, Pearce,J.A. JA.and andCairn, Cam,J.R., J.R., 1973, 1973,Tectonic Tectonicsetting settingof of basic basic volcanic volcanic rocks rocks determined determinedusing using trace traceelement elementanalyses: analyses:Earth Earthand andPlanetary PlanetaryScience ScienceLetters, Letters,v.v.19, 19,p. p. 290-300. 290-300. Shegeiski, R.J., 1982, The The Gunflit Gunflint Formation Formation in in the the Thunder Thunder Bay Bay area, area, j J.M. Shegelski, RJ., J.M.Franklin, Franklin, ed., Proterozoic Geology of the Northern Lake Superior area: Field Trip Trip 4, 4, ed., Proterozoic Geology the Northern Lake Superior area: Geological Association of Canada Mineralogical Geological Association of Canada - Mineralogical Association Association of Canada Canada Joint Joint Annual Meeting, p. 15-31. Annual Meeting, p. 15-31. Sims, W.R., Schulz, Schulz,KJ., KJ., and and Peterman, Z.E., Tectono-stratigraphic Sims,P.K., P.K., Van Schmus, W.R., Z.E., 1989, 1989,Tectono-stratigraphic evolution evolution of of the theEarly EarlyProterozoic ProterozoicWisconsin Wisconsin magmatic terranes of the the Penokean Penokean Orogen: Canadian Journal of Earth Sciences, v. 26, O of Earth ~ Sciences, v. 26, p. p. 2145-2158. 2145-2158. Orogen: Canadian J a I I 100 .-U I— I I I I I I I . It az 0 .— 10 - 1= = . C-) . 00 It —. '—S I I I La Ce Nd SmEu Tb I Yb Lu Fig. Fig.1.1.Chondrite-nornialized Chondrite-normalizedrare rareearth earthelement elementplot plotfor forAnimike AnimikeGroup Groupvolcanics. volcanics.Solid Solid lines dashedlines linesmafic - Emporer lines- Gunflint GunflintVolcanics; Volcanics; short dashed mafic EmporerVolcanics; Volcanics;long longdashed dashedlines linesfelsic felsicEmporer EmporerVolcanics. Volcanics. - - - 19 I �GRANITOID ROCKS OF OF THE EWOT GRANITOID ROCKS ELLIOTLAKE LAKEAREA, AREA,ONTARIO ONTARIOAND ANDTHEIR THEIR RELATIONSHIP RELATIONSHIP TO TO U-Th-REE U-Th-FUSE BEARING BEARING PEGMAITIES PEGMATITES KISSIN, A. arid and FRALICK, FRALICK, Philip PhilipW., W., Dept. Dept.ofofGeology, Geology,Lalcehead Lakehead KISSIN, Stephen StephenA. University, Thunder Bay, Bay, ON ON P7B P7B 5E1, 5E1, Canada Canada Archean Archeangranitoid granitoidrocks rocksintrusive intrusive into into metavolcanic metavolcanic terrane terrane form formthe thefootwall footwall of of the the Huronian Supergroup in the Quirke Syncline of the Elliot Lake Huronian Supergroup the Quirke Syncline the Elliot Lake area, area,Ontario. Ontario. These These granitoids granitoids have never been been studied studied in in detail, detail, attracting attracting little interest interest in in relation relation to to U-ThU-ThREE FUSEdeposits depositsof of the theElliot ElliotLake Lakearea areabecause becauseofoftheir theirlow lowlevels levelsof of radioactivity radioactivity (Robertson, (Robertson, 1981; Charbonneau, 1982). 1981; Charbonneau, 1982). Recent Recentdiscovery discoveryof of U-Th-REE U-Th-REE bearing bearingpegmatites pegmatites(Kissin (Kissinand and Fralick, 1991) in the north footwall of Quirke Syncline indicate that the granitoids merit Fralick, 1991) the north footwall of Quirke Syncline indicate that the granitoids merit investigation investigation as as parental parentalbodies bodiestotothe thepegmatites. pegmatites. The granitoid body at the Huronian The granitoid body at the Huronianfootwall footwall has hasbeen beeninformally informally named named the the Kindioganii Kindiogami River River Batholith Batholith(Breaks, (Breaks,1991). 1991). ItIt consists consists of pink to to brick brick red, red, equigranular equigranular biotite booksand andclots clotsofofbiothe biotite asas biotitegranite. granite.The Thegranite graniteisisuniformly uniformlycoarse-grained, coarse-grained,with withbooks the themain mainmafic maficmineral mineral(CI (CIc<10), 10).with withlessor lessormuscovite muscoviteand andaccessory accessoryhornblende, hornblende,sphene, sphene, and zircon. and zircon Analyses Analyses of of seven seven granite granitesamples samplesand andone oneassociated associatedaplite apliteyield yieldhigh highSi02 SiO2(70-77 (70-77 wt wt%), %), high highA12O3 A1203(12-14 wt %) %)and and low lowMgO, MgO, CaO, CaO,and andT102 TiO, (most (most << 11wt wt %). %). Total Totaliron iron as asFe2O3 Fe,03 is variable variable (1-4 (1-4 wt wt %), %), but but 1120 H20 (generally TheK20 K20isisusually usually (generally<c 11 wt%) is low. The greater thanNa20. Na;0. InIna aShand Shanddiagram diagram(Fig. (Fig.1),I),the thegranites granitesare aresubaluminous subaluminoustotoslightly slightly greaterthan peraluminous, peraluminous, whereas whereas associated associated pegmatites pegmatites are aremetaluminous metaluminous to toperaluminous. peraluminous. Some trace elements, notably Cs, Be, Sc, Ni and Cr are depleted, Some trace elements, notably Cs,Be, Sc,Ni and Cr are depleted,whereas whereasothers, others, notably Nbare areenriched enrichedrelative relativetotomost mostgranitoids. granitoids. Rare Rareearth earth notably Th, U, U, Zr, Zr, Ta, Ta,and andNb , elements elements exhibit exhibit aa roughly roughly linear linear trend trend of ofheavy heavy REE REEdepletion depletionand andslight slighttotonegligible negligible negative negative Eu Euanomalies anomaliesininaachondrite-normalized chondrite-normalizedplot plot(Fig. (Fig.2). 2). Application Maniarand andPiccoli Piccoli(1989) (1989)classifies classifiesthe the Applicationof ofthe thediscrimination discriminationcriteria criteriaofofMan.iar rocks rocksas aspost-orogenic post-orogenicgranitoids. granitoids. Although Althoughininthe theI-,I-,S-, S-,A-, A-,and andMM-classification classificationbased based on on petrographic petrographiccharacteristics characteristics(e.g., (e.g., Pitcher, Pitcher, 1983), 1983), the the rocks rocks have have the the general generalcharacteristics characteristics of al.,1987), 1987).they theydo donot notfulfil fulfilthe themore moredetailed detailed of A-type A-type (anorogethe) (anorogenic)granitoids granitoids(Whelan (Whelanetetal., . . . trace element discrimination criteria. Their parentage appears to be mixed, anorogenic with tion criteria. Their parentage appears to be mixed, anorogenic with trace element discrumna an anorogenic orogenictype typegranitoid. granitoid. The Thepegmatites pegmatitesthemselves themselvesexhibit exhibitaamixed mixedgeochemical geochemicalsignature signatureaccording accordingtotothe the criteria criteriaof ofèerny fiemy(1991a). (1991a). Although Althoughthey theybear bearmany manycharacteristics characteristicsof of rare-earth rare-earthpegmatites pegmatites of relative enrichment in Nb >> Ta, NYFfamily family of of rare-element rare-elementpegmatites pegmatites including including relative Ta, of the theNYF Zr, Zr,U, U,Th, Th,and andF,F,they theylack lackenrichment enrichmentin inY, Y,Sc Sc and and REE. FUSE. These Thesepegmatites pegmatitesseem seemtotofitfit into intothe themixed mixedfamily familyof of rare-element rare-elementpegmatites pegmatitesininwhich which NYF NYFcharacteristics characteristicsare arediluted diluted by by LOT LCTpegmatite pegmatiteattributes. attributes. The The bulk bulk compositions compositions lack lack the thesubaluminous subaluminous toto metaluminous of NYF pegmatites, and the metaluminous composition composition of pegmatites, and the associated associated granitoids granitoids of of this this pegmatite pegmatite group groupbear beara amixed mixedgeochemical geochemicalsignature. signature. Parental Parentalgranitoids granitoidsbear bearmany many characteristics characteristics of of anorogenic anorogenicgranites, granites, as asin inthe thecase caseofofKindiogami KindiogamiRiver RiverBatholith, Batholith,they they appear appeartransitional transitionaltotoother othertypes. types.ëerny fiemy(1991b) (1991b)has hassuggested suggestedthat thatsuch suchmixed mixedpegmatites pegmatites may may arise arisefrom: from: 1) 1)anatectic anatecticgranites granitesderived derived from from partially partially depleted depleted crust; crust; 2) 2) anatexis anatexis of of �both by both depleted depleted and andundepleted undepletedcrust, crust,or or3)3)ananNYF NY.Fmagma magmabecoming becomingcontaminated co assimilation of undepleted material. assimilation of undepteted material. Whatever Whatever the theultimate ultimatesource sourceof ofthe granites of the Kindiogami Batholith, they and their associated pegmatites are distinctive their associatedpegmatites are distinctiveand provide a plausible proximal source for detrital Huronian Supergroup. The pegmatite field detrital U, U,Th, Th, and andREE REEdeposits depositsininthe the associated associatedwith roof and proximal regions may have been largely removed by the effects of erosion. pegmatitic deposits in the Arabian Shield have been found to be both large erosion.Similar S and al., 1985). andof ofhigh highgrade grade(Jackson (Jacksonet£t-aL 1985). . \ References Breaks, F.W., 1991, Project Unit 91-10. Geology of the Rocky Island Lake - Lac aux Sables area, jjj Sunimaiy of field work and other activities: Ontario Geological Survey Miscellaneous Paper 157, p. 40-45. èerny, P., 1991; Rare-element granitic pegxnatites. Part I: Anatomy and internal evolution of pegmatite deposits: Geoscience Canada, v. 18, p. 49-67. ëerny, P., 1991b, Rare-element granitic pegmatites. Part II: Regional to global environments and petrogenesis: Geoscience Canada, v. 18, p. 68-81. Charboneneau, B.W., 1982, Radiometric study of three radioactive granites in the Canadian Shield: Elliot Lake, Ontario, Fort Smith and Fury and Hecla, N.W.T., j1 Uranium in granites: Geological Survey of Canada Paper 81-23, p. 91-99. Jackson, NJ., Drysdall, A.R., and Stoeser, D.G., 1985, Alkali granite-related Nb-Zr-REE-U- Th mineralization in the Arabian Shield, jg High heat production granites, hydrothermal circulation and ore genesis: London, The Institution of Mining and Metallurgy, p. 479-487. Kissin, S.A., and Fralick, P.W., 1991. A possible pegmatitic source for the Elliot Lake paleoplacer deposits: Program with Abstracts, Geological Association of CanadaMineralogical Association of Canada - Society of Economic Geologists, Joint Meeting, v. 16, p. A66. Mainar, P.D., and Piccoli, P.M., 1989, Tectonic discrimination of granitoids: Geological Society of America Bulletin, v. 101, p. 635-643. Pitcher, W.S., 1983, Granite type and tectonic environment, K. Hsu, ed., Mountain building processes: London, Academic Press, p. 1940. Robertson, J.A., 1981, The uranium deposits of Ontario - their distribution and classification: Ontario Geological Survey Miscellaneous Paper 86, 37 p. Whelan, J.B., Currie, K.L, and Chappell, B.W., 1987, A-type granites: geochemical characteristics, discrimination and p&rogenesis: Contributions to Mineralogy and v. 95, p. 407-419. Petrology, I I I I �it 1000 — 5 Ui I- 100 - cc C z0 0 0 0 cc NA 14 IC - 14A 13 II 12 I-——- I La Ce I SmEu Nd I I I Tb Yb Lu River Fig. 1. Chondrite-normalized rare earth element plot for granites of the Kindiogaini River Batholith of the Elliot Lake area. 18 I.- a 0 0c'.j [4 + o [2 c'J a z U) o Cu 08 C 06 06 08 10 + + [4 I6 /(CaO AlgOs CaO + Na20 NapO+ 1<20) KpO ) molar 41203 /( 2.. Shand (crosses) of of the the Elliot Lake area. area. Fig. 2 Fig. Shand diagram diagram for for granites granites (circles) and pegmatites (crosses) ' 22 �I p STRUCTURAL STRUCTURALEVCIUTION EVOLUTIONOF OFTHE "MEEASTERN EASTERNGOGEBIC GOGEBICRANGE RANGE NORTHERN NORTHERNMICHIGAN MICHIGAN John John S. 61455 S. Kiasner, Klasner,Department DepartmentofofGeology, Geology,Western WesternIllinois IllinoisUniversity, University, Macomb, Macomb, ILIL61455 and andU. U. S. S. Geological Geological Survey, Survey, and and Gene GeneL.L.LaBerge, LaBerge,Department DepartmentofofGeology, Geology,University Universityof of Wisconsin, Oshkosh, WI 54901 and U. S. Geological Survey Wisconsin, Oshkosh, Wl54901 and U. S. Geological Survey The range is is an an area area of of outcropping, outcropping,iron-bearing iron-bearingrocks rocks that that extends The eastern eastern Gogebic Gogebk range extends Lithostratigraphic some 100 km from northern Wisconsin to northern Michigan. some 100 km from northern Wisconsin to northern Michigan. Lithostratigraphic relationships relationships (LaBerge (LaBerge and and Klasner, Klasner, this this volume) volume) indicate indicate that that Early EarlyProterozoic Proterozoic(EP) (EP) volcanic volcanic and andsedimentary sedimentary rocks rocks of of the the Menominee Menominee Group Groupwere weredeposited depositedininaadeveloping, developing,fault-bounded fault-bounded trough trough in inthis thisregion, region,much muchlike like the the Marquette Marquette trough trough some some 180 180 km km to to the the east. east. Following Following this this extensional extensionalevent, event, EP EPstrata strataof of the the Copps Cows formation formation were were deposited deposited in inaa compressional compressional foreland foreland basin. basin. All All EP EPstrata stratawere werethen thensubjected subjectedto toatatleast leasttwo twopenetrative, penetrative,thin-skinned, thin-skinned, fault compressional events, and subsequently to a series of thick-skinned compressional events, and subsequently to a series of thick-skinned fault events events that that affected affected Much later, these deformed strata weretilted northward both Archean and EP strata. both Archean and EP strata. Much later, these deformed strata were tilted northwardduring during the the formation formationofofthe theMiddle MiddleProterozoic Proterozoic(MP)Midcontinent (MP)Midcontinent Rift Rift (Cannon (Cannon and and others, others. 1993). 1993). COMPRESSIONAL COMPRESSIONALEVENTS EVENTS underlying Archean D1 During this this initial initial event event most ER EP strata were detached from underlying Archean Dl - During basement, creating northeast-trending folds and north-verging, bedding-parallel shears basement, creating northeast-trending folds and north-verging, bedding-parallel shears in in the the supracrustal supracrustalsequence. sequence. D2 Dl folds folds in the the EP EPstrata stratawere werefurther further Da- - Both Boththe thebedding-parallel beddina-parallelshears shears and and Di deformed into a series of gently northeast-plunging folds that also appear to be detached deformed into a series of gently northeast-plunging folds that also appear to be detachedfrom from Archean inasmuchas as Dl Dj and and D2 D2 structures structures have have not not been been found found in in the the basement Archean basement basement inasmuch basementrocks. rocks. 0 3 - Folds Folds of of aa third third event, event, overprinting overprinting Di Dl and and D2 D 2were wereobserved observed ininaafew few places. places. These These folds folds may maybe berelated relatedto to later laterfaulting faultingassociated associated with with the the Presque Presque Isle Isle set set (see (see below). below). - - - The Copps Copps formation formationwas was deposited depositedin inangular angular unconformity unconformity on on underlying underlying EP EP strata, The (see in the the Cows Coppscontain containclasts clasts that that (see LaBerge and Klasner, Klasner, this volume). volume). Basal Basal conglomerates conglomerates in indicate ChocolayGroups Groups were were the the source. sourceevidence evidence implies implies that, indicate Menominee and Chocolay source. This source prior to to deposition depositionof of the the Copps, Copps, there must have been some uplift upliftofofpre-Copps pre-Coppsstrata, strata, prior Because the Copps strata and the underlying EP strata possibly as a forearc bulge. the underlying EP strata all all possess possess possibly as a forearc bulge. folds and axial planar foliation), we suggest the same same structural structuralpattern pattern(northeast-trending (northeast-trending planar foliation), suggest that the the structural structural evolution evolution of of the the whole whole ER EP stratigraphic stratigraphic sequence is the the result result of of aacontinuum continuum deformation that occurred after deposition of Copps of north-verging deformation that Copps of coaxial, coaxial, thin-skinned, thin-skinned, north-verging that strata. strata. FAULTEVENTS EVENTS FAULT Other of deformation in in the thp eastern eastern Gogebic Gogebiciron iron range range are found in in three Other manifestations manifestations of sets --the Lithe Presque Isle set, the Presque Isle set, and the Sunday Lake set. fault sets -the Little Presque Isle set, the Presque Isle set, and the Sunday Lake set. - Little Little Presque Presque Isle Isle fault set set -- Faults of of this thisnorth-northeast-trending north-northeast-trending set, set, fault especially as extensional extensional growth growth faults, faults, but they especially the the Little LittlePresque Presque Isle Islefault, fault, formed early as in were later later reactivated reactivatedin in Middle Proterozoic (MP) time. This continued movement resulted in truncation juxtapositionofof EP EP strata in the northeast-trending Wolf Mountain anticline anticline truncation and juxtaposition were against Archean occurs in in an en echelon pattern pattern along along the the southwest southwest Archean rocks. The juxtaposition occurs This interpretation is supported by magnetic extension of the Little Presque Isle fault. extension of the Little Presque Isle fault. This interpretation is supported by magneticdata. data. of the the Little LittlePresque PresqueIsle Isleset set cut cut the the unconformable unconformable contact contactbetween betweenMP MPKeweenawan Keweenawan and and Faults of underlying them. Faults underlying EP EP and andArchean Archean strata, also also indicating indicating late late MP MP movement movement on on-them. , �Presque Isle Isle fault faultset set- -The Thesouth-side-up, south-side-up,east-northeast-trending east-northeast-trending Presque Presque Isle Isle Group depositional depositionaltrough. trough. We suggest that, fault marks the southern southern edge of the Menominee Group Isle fault fault was was aa growth like the Little Little Presque Presque Isle fault, the Presque Presque Isle growth fault. fault. Other parallel parallel faults of the the Presque PresqueIsle Isleset set cross cross cut cut and and offset offset the the Little Little Presque Presque Isle Islefault fault near nearthe the core coreof of the the Wolf Mountain anticline, anticline, giving the the Little Presque Presque Isle Isle fault fault its its en echelon pattern in this Wolf region. region. - Sunday Lake fault Sunday Lake fault set set The south-side-up, south-side-up, left-lateral left-lateral Sunday Lake fault fault truncates the parallel faults faultsof of this this set set occur to the north, one at at truncates the Presque Presque Isle Isle fault. Several parallel where conspicuous conspicuous shearing the Copps Mine Mine exploration exploration prospect where shearing and associated associated mineralization is found. found. Formation of .the the Midoontinent Rift resulted resulted in in northward northwardtilting tilting (up (up to 70 degrees) Formation-of Midcontinent Rift degrees) of Archean, EP easterly tending the Archean, trendingaxis. axis. The Thenortheast-trending northeast-trending EPand and MP MP strata strata along an easterly depositional trough troughwas wasalso alsorotated rotatedso sothat that the the map mappattern pattern is a view looking lookingdown downthe the original original - the the Uttle LittlePresque Presque Isle Isle fault forming the northern northern edge of of the the trough trough and and keel of the trough -edge. During the Presque Isle fault forming the southern edge. During MP rotation, faults of the the Little Little offsetting the EP-MP Presque Isle Isle set were were reactivated, reactivated, offsetting EP-MP unconformity. unconformity. REFERENCES CITED CITED Cannon, W. F F., Z. E E., ., and and Sims, Sims, P. P. K., K., 1993, 1993, Crustal-scale thrusting and origin of Cannon, W. ., Peterman, Peterman, 2. cross section of the 35-kilometer-thick cross the Midcontinent Midcontinent rift the Montreal River River monocline monocline -- aa 35-kilometer-thick in northern Michigan: Tectonics, v. 12, p. 728-744. northern Michigan: Tectonics, v. 12, p. 728-744. - LaBerge, G. E., E., and and Kiasner, Klasner, J. J. S., S., 1994, 1994, Lithostratigraphic Lithostratigraptlirelations relations on on the the east eastGogebic GogebiiRange: Range: implications on tectonism in the Penokean Orogen: Orogen: Institute on Lake Lake Superior Superior Geology, Geology, this this volume. 24 �p NEW ARCHEAN-HOSTED ARCHEAN-HOSTED PSEUDOTACHYLITE OCCURRENCES, WESTERN WESTERN NEW PSEUDOTACHYLITE OCCURRENCES, LAKESUPERIOR SUPERIOR REGION REGION LAKE KROPF, Elizabeth P., WIRTH, WIRTH, Karl Karl R. R. and and CRADDOCK, CRADDOCK,John John P., P., Geology Geology KROPF, P., Dept., Macalester Dept., MacalesterCollege, College, St. St. Paul, Paul, MN M N 55105 55105 Pseudotachylite occurrences were were recently discovered discovered in in the the western Lake Superior region hosted in Falls, MN MN (Minnesota River Archeanrocks: rocks: 1) 1) Granite Falls, in aa variety variety of of Archean Valley terrane), 2) Deer Lake complex, MN (Wawa terrane), Valley terrane), Lake complex, MN (Wawa terrane), 3) Rossport, ONT ONT (Wawa terrane). terrane). All All of of these these pseudotachylites pseudotachylitesare areadjacent adjacentand and parallel parallel to to mafic (Wawa dike swarms, swarms, in contrast to the pseudotachylite dated and and described described by by Peterman Peterman pseudotachylite dated and Day (1989) along the the Rainy Rainy Lake Lake fault fault in in the the Wabigoon Wabigoonterrane terrane in in western western (1989) along Ontario. Granite Falls, Falls, MN MN Granite Pseudotachylite has been discovered crosscutting folded folded Archean Archean amphibolite-grade amphibolite-grade host rocks of of the the Minnesota MinnesotaRiver RiverValley Valleyterrane terrane(Himmelberg, (Himmelberg,1968; 1968; Bauer, Bauer, 1980) 1980) near Granite Falls, MN. The pseudotachylite is parallel to the regional foliation Falls, MN. The pseudotachylite is parallel to the regional (N70°E,75 75° N),isis<<2 cm in in width, can be traced m, and and contains (N70°E O N), 2 an traced in in outcrop outcrop for for —50 -50 m, "amygdules" of calcite (diameter: .5 cm; Fig. 1), calcite-quartz mixes, and plagioclase 'amygdules" of (diameter: an; Fig. I), calcite-pahz mixes, and plagioclase inclusions in calcite. Mafic Mafic dikes, which cross-cut cross-cut the Kenora-Kabetogama swarm (—2.2Ga), Ga),are arealso alsoparallel paralleltotothe thepseudotachylite pseudotachyliteare areaanumber numberof of calcite calcite veins. veins. The The (-2.2 outcrop is located 70 70 km km to the south of the boundary between the Wawa (north) terranes. The is and (south) terranes. and Minnesota Minnesota River River Valley Valley (south) The pseudotachylite pseudotachylite is compositionally layered along its margins and preserves some relict flow foliation compositionally layered along its margins and preserves some relict Dextral winged winged swirls defined by inclusions inclusions (Fig. (Fig. 2) 2) and and "amygdules" "amygdules" of calcite. calcite. Dextral porphyroclasts are present and preserve the displacement sense porphyroclasts the opposite opposite kinematic displacement of S-C S-C structures structures in the country calcite is is mechanically mechanically twinned twinned country rock. rock. The amygdule calcite 'of and preserves a horizontal shortening axis (magnitude: -0.74%) that is parallel (magnitude: -0.74%) that is parallel to of the pseudotachylite. Two Two phases phases of of calcite calciteveins veinsare are present, present, one set the strike of preserves twinning strains (shortening magnitude: -2.5%) identical those in in the magnitude: -2.5%) identical totothose calcite amygdules. amygdules. The The second second vein veinset set contains contains aa horizontal, horizontal, veinpseudotachylite calcite pseudotachyliteshortening perpendicular strain (magnitude: -2.4%). Inferred differential shortening strain (magnitude: -2.4%). Inferred differential stresses for the different twinning strains are and 200 MPa (calcite the are 66 66 MPa MPa (pseudotachylite) (pseudotachylite) and 200 MPa veins). Deer Lake MN Deer Lake Complex, Complex, M N This Archean ultramafic complex isis composed of interlayered This Archean ultramafic complex composed of interlayered gabbro, gabbro, peridotite and and pyroxenites pyroxenites (Jirsa, (Jirsa, 1990) 1990) in Itasca county. The Kenora-Kabetogama Kenora-Kabetogama mafic dikes (strike: (strike: N45OW) N45°W)crosscut crosscutthe thecomplex complexand, and,parallel paralleltotothe the dikes, dikes, are a mafic number zones which which are locally thin (1-5 (1-5 mm), mm), regularly-spiced regularly-spaced cataclastic cataclastic zones locally number of of thin mylonitic and contain contain some some pseudotachylite pseudotachylite material. material. Ross port, ONT Rossport, Archean granites granites and granodiorites along Lake Lake Superior Superiorare arecrosscut crosscutby by 22 thin thin Archean pseudotachylites(5 (5mm mm wide) wide) which which were were locally locallyinjected injectedininthe the country country rock. rock. pseudotachylites Maficdikes dikes of of unknown unknown age age are are adjacent adjacent and and parallel parallel to to the the pseudotachylite pseudotachylite veins Mafic (strike: N-S). (strike: 25 �Foliated Granite Falls Falls pseudotachylite pseudotachylite (width=2cm) with with calcite calcite amygdules. amygdules. Figure 1: Foliated Figure 2: 2: Close-up Close-upof of swirled swirledporphyroblast porphyroblastfrom fromFig. Fig.1.1.View Viewisis3.5X2.2 3.5X2.2 mm. REFERENCES REFERENCES Bauer, R.L., area, Minnesota River River R.L., 1980, Multiphase deformation deformation in in the. the,Granite Granite Falls-Montevideo Falls-Montevideo area, Valley: in in G G.B. Moreyand and G.N. G.N. Hanson Hanson (eds.), (eds.), Selected SelectedStudies StudiesofofArchean ArcheanGneisses Gneissesand and Lower Lower Valley: .B. Morey SpecialPaper Paper 182, 182,p.p. 1-17. Proterozoic Rocks, Southern Canadian Shield, C. G. S. A. Special 1-17. Himmelberg, Geology of of Precambrian Precambrian Rocks, Rocks, Granite Granite Falls-Montevideo Falls-Montevideoarea, area, southwestern southwestern Himmelberg, G.R., G.R., 1968, 1968,Geology Minnesota: Minnesota Minnesota Geological Survey Survey Publication SP-5. Minnesota: SP-5. M., 1992, 1992,Bedrock Bedrockgeologic geologicmap mapofofnortheastern northeasternItasca Itascacounty, county,MM: MN:Minnesota MinnesotaGeological Geological Survey Survey Jirsa, M., Map M-86. Map Peterman, Z. E. on Archean Archean faults faults in in the the western E. and andDay, Day,W., W., 1989, 1989,Early Proterozoic activity on Superior provinceevidence from pseudotachylite: Geology, v. 17, p. 1089-1092. Superior province- evidence from pseudotachylite: Geology, v. 17,p. 1089-1092. 26 �N I TECTONIC TECTONIC IMPLICATIONS OF EARLY PROTEROZOIC LITHOSTRATIGRAPHY ON P1 I 4 I I I I I . THE EASTERN EASTERN GOGEBIC GOGEBIC RANGE, NORTHERN NORTHERN MICHIGAN MICHIGAN GENE L. L.aBERGE, Department of Geology, UW Oshkosh, Oshkosh, WI LaBERGE, Department of Geology, U W Oshtosh, WI 54901 54901 and U.S. U.S.Geological Geological Survey Survey and JOHN JOHN S. KLASNER, KLASNER, Department Department of Geology, Geology, Western Illinois illinois University, Macomb, IL IL 61455 and U.S. Geological Geological Survey. Survey. Our recent mapping on the eastern Gogebic range reveals abrupt abrupt changes in stratigraphy stratigraphy and and structure that occur mainly mainly at at the newly discovered discovered Little Little Presque Presque Isle Isle fault east east of Wakefield, Michigan. Michigan. These Thesechanges changeshave have an animportant importanthearing bearing on on interpretations inteipretationson on history and and tectonic tectonic evolution evolutionof of this this part part of the Penokean orogen. depositional history In the the western western part of of the the map map area area (Figure (Figure1), I), the thePalms PalmsFormation Formationand andunderlying underlying Chocolay Group Group form form aa northdipping north-dipping stratigraphic stratigraphicsequence. sequence. These strata are not not exposed exposed Chocolay strata are east of of the Little Presque Isle fault, although immediately east although the the Palms Palms Formation Formation reappears reappears 10 10 Similarity in lithology of the Palms in the two areas suggests that it was km to the east. east. of areas deposited as a continuous continuous stratigraphic stratigraphic unit. Its absence in the 10 10 km Ioninterval interval is is probably probably aa of faulting (Klasner and LaBerge, this volume). consequence consequence The The Ironwood Iron-formation, which overlies the Palms Formation, Formation, shows shows abrupt abrupt changes within within the the map maparea. area. For For nearly nearly 100 100km Ion to to the thewest, west, ititconsists consists of of alternating alternating units iron-formation with with relatively relativelyuniform uniformthickness. thickness. However, east of granular and laminated iron-formation of the Little Little Presque Presque Isle Isle fault the the Ironwood appears to be be much much thicker, and and isiscomposed composed mainly of laminated iron-formation. There is is also also an an abrupt abrupt change change in the the Emperor Emperor Volcanic Volcanic Complex, which is is interbedded with the the iron iron formation, formation,across acrossthe theLittle LittlePresque PresqueIsle Islefault. fault. To the west, the interbedded with Emperor is mainly basalt flows and diabase sills. To the east, the volcanic rocksare aremainly mainly Emperor basalt flows and diabase sills. To the east, the volcanicrocks and felsic hyaloclastites hyaloclastites of of rift-related rift-related tholeiites. tholeiites. The mafic pillow breccias and Thecombined combined thickness of iron-formation and volcanic volcanic rocks changes abruptly across the Little Presque Presque Isle Isle fault. West meters. East Westof ofthe thefault, fault,the thethickness thickness is is about about 250-300 250-300 meters. East of of the thefault, fault, the the is much much greater but cannot be accurately measured thickness is measured because of structural complexities. complexities. We interpret these relationships to indicate that the Little Presque Isle fault was active during deposition of of the iron-formation. iron-formation. The area east east of of the theLittle LittlePresque Presque Isle Islefault fault appears appears during deposition The area to be aa remnant of a graben-like structure bounded by the Little Presque Isle and Presque remnant a graben-lie structure Little Presque Isle and Presque Isle Isle faults. faults. The change from granular to laminated laminated facies of iron-formation iron-formation suggests suggests a change change from shallow-water shallow-water deposition deposition in in the the west west to to deeper water deposition in a developing trough to the east. The rockswithin within the thepostulated postulated graben suggests suggests that Theincrease increaseininvolcanic volcanicrocks bounding faults may have served as channelways for the magmas. These relationships are bounding may have served as channelways for the magmas. interpreted to indicate indicate that rifting rifting occurred occurredduring duringiron-formation iron-formationdeposition. deposition. Older geological geological literature literature refers refers to a number of "ianges" south "ranges" south of of the theGogebic Gogebic Early Proterozoic Proterozoic iron-formation. iron-formation. These district district that contain Early These include the Marenisco, Turtle, Manitowish, Vieux Desert, Desert, and and Conover Conover "ranges" "ranges"of of Alien Allenand andBarrett, Barrett,(1915). (1915). They, and Manitowish, Vieux Dutton and Bradley (1970), and Prinz (1981) showed that these areas areas contain contain iron-formations iron-formations other sedimentary rocks interbedded with volcanic rocks. We suggest that these and sedimentary rocks with volcanic rocks. We suggest "ranges" 'ranges" may represent graben-like environments similar to that on the eastern eastern Gogebic Gogebic range. If so, these various "ranges" may represent a series of grabens formed on these "ranges" may series grabens formed the the rifted rifted range. continental margin that were intensely deformed during continental during later later convergent convergenttectonism. teetonism. I I 27 �In the eastern Gogebic range range the the Coops Copps Formation Formation of of the Baraga Group Group overlies overlies the the iron-formation and and other other rocks rocks with with marked marked unconformity unconformity(Figure (Figure 1). 1). A basal conglomerate A basal conglomerate with cobbles of of iron-formation, iron-formation, volcanic volcanic rocks rocks similar similar to to the the Emperor, Emperor, and Archean granitoids, as well as as complete complete removal of the the Menominee Menominee and Chocolay Group Group rocks rocks demonstrate the the unconformable unconformablerelationships. relationships. We We interpret interpret the the Copps Copps to to represent representaa demonstrate sequence of of turbiites turbidites deposited deposited in in aa foreland basin basin on eroded remnants of rocks rocks deposited deposited rifled passive margin. earlier on a rifted References Cited Allen, R.C., R.C., and of northern northern Alien, and Barrett, Barrett, L.P., L.P.,1915, 1915,Contributions Contributionsto to the the pre-Cambrian pre-Cambrian geology of Michigan and and Wisconsin: Wisconsin: Michigan Michigan Geol. Geol. and and Biol. Biol. Survey SurveyPub. Pub. 18, Geol. Geol. Ser. Ser. 15, Michigan p. 65-129 p. 65-129. Dutton, C.E., R.E., 1970, 1970,Lithologic, Lithologic,geophysical, geophysical, and and mineral mineral commodity commodity Dutton, C.E., and and Bradley, Bradley, R.E., maps of of Precambrian Precambrianrocks rocksininWisconsin. Wisconsin: U.S. U.S. Geol. Geol. Survey Survey Misc. Misc. Geol. Geol. Inv. mv. Map Map maps 1-631. 1-631. Klasner, J.S., J.S., and G.L., Klasner, and LaBerge, L-ge, G.L., 1994, 1994,Structural StructuralEvolution Evolution of of the the Eastern Eastern Gogebic Gogebic Range, Northern Michigan: 40th Institute on Lake Superior Geology, Abstracts and Northern Michigan: 40th Institute Abstracts and Proceedings, this this volume. W.C., 1981, Geologic Prinz, W.C., 1981, Geologic map map of the the Gogébic Gogebic Range-Watersmeet Rangewatersmeet area, Gogebic and Ontonagon Counties, Counties, Michigan, Michigan, Misc. Misc. Inv. mv. Series SeriesMap Map 1-1365 1-1365. Ontonagon Trent, V.A., V.A., 1973, Geological map of the Marenisco and Wakefield 1973, Geological map the Marenisco and Watefield NE quadrangle, Gogebic County, County,Michigan: Michigan: U.S. U.S. Geol. Survey File Report, Open Pile Report, scale 1:48,000. 1:48,000. Gogebic Survey Open LAKE -A- OGEBIC vs C) .ç S -, 55 ¶ V S $5 S si f 5_____ 5 5 Sc 0 () ç Figure 1. Figure 1. KM $ 1•I ,j Sketch nap mapofofthe the geology geology of of the Sketch the eastern easternGogebic Gogebic range range showing showing (Modified the major majorlithologic lithologic units units and and sstructural the t r u c t u r a l features. features. (Modified Trent, 1973, 1973, and and Prinz, Prinz, 1981.) ffrom r o m Trent, 1981.) 28 �U RELEASE HOSTED GOLD RELEASE OF ACID AND TRACE METALS FROM QUARTZ-CARBONATE HOSTED GOLD MINE TAILINGS TAILINGS fl LAPAKKO, K. A. A. and and WESSELS, WESSELS, 1. I. N., N., Division Divisionof of Minerals, Minerals, Department Department of of Natural Natural Resources, Resources,500 500 Lafayette Road, Box 45, St. St. Paul, Paul, Minnesota, Minnesota, 55155-4045. 55155-4045. Exploration for gold Exploration for gold (and (and other other non-ferrous non-ferrous minerals) minerals) is is presently presently occurring occurring in inMinnesota. Minnesota. Prior to mineral resource development, the potential mine wastes must be characterized wastes characterized and the the quantity quantity and and development, potential quality of drainage projected. This will be be used used to identilS' the types of drainage projected. T his infonnation information will identify the of mine mine waste waste management and drainage control required to protect protect the water water resources resourcesof of the thestate. state. Little information information characteristicsof, of, or or drainage quality qualityfrom, from, such such mining mining wastes. wastes. The has been compiled on the characteristics The lack lack of of management such information will inhibit the effectiveness and efficiency of drainage quality prediction and delay inhibit effectiveness efficiency of development of techniques to mitigate of this project was to development mitigate the the problems problems identified. identified. The objective objective of to characterize and determine release of acid and trace metals from tailings which are representative representative of characterize mining potential mining wastes wastes from from Minnesota. Minnesota. Ten tailings samples were from operating operating North North American American gold gold mines. mines. These sampleswere collected from Thesesamples samples of tailings tailings which which might might be generated provide the best best presently presently available available approximation approximation of generated ifif present present provide exploration belt exploration exploration site site in in Minnesota. Minnesota. The explorationled to development of a greenstone belt Thegeologic geologicsettings, settings, hydrothermal quartz-carbonate hosted hosteddeposits, deposits, from from which which the the gold mine tailings were hydrothermal quartz-carbonate were collected collected are are The gold tailings to a majority of those presently under exploration in Minnesota. similar a majority of those presently under exploration in Minnesota. gold tailings were were similar characterized and subjected to dissolution testing testing for 151 weeks to to examine the relationship between the solid-phase characteristics and release of acid and trace metals. fine, with 47% 47% to 97% 97% of each sample occurring occurring in the minus 270 mesh The samples were quite fine, fraction The and 26% 26% to 91 % in the minus 500 mesh fraction. The total sulfur contents, an indicator of acid 91% in the minus 500 mesh fraction. content, an indicator production potential, potential, ranged ranged from from 0.1% 0.1% to 7.63%. production 7.63%. The carbon dioxide dioxide content, indicator of neutralization potential, ranged from 0.61 0.61% % to 21.85%. 21.85%. Most Most of the the sulfur sulfurwas wasassociated associated with with pyrite pyrite and and pyrrhotite, pyrrhotite, with with iron ironsulfide sulfideminerals minerals constituting 0.58% 0.58% to 13.6% constituting 13.6% by by weight weight of of each eachsample. sample. Total calcium carbonate carbonate plus plus magnesium magnesium content varied varied from from 1.4% 1.4% to to 21 21%. %. Siderite Siderite was was present present in in appreciable appreciable amounts (14% (14% carbonate mineral content 31% and in minor minor amounts amounts (0.1 (0.1% and 31 % by weight) in two samples and % to 1.9%) 1.9%) in in seven seven samples. samples. Three samples contained contained ankerite ankerite(Lapakko, (Lapakko, 1992). 1992). The major rock forming minerals minerals were were quartz quartz (16%-44%), (16%-44%), feldspar (1 %-37%), mica (4%-24%), and chlorite (2%-21 %). feldspar %-37%), (4%-24%),and chlorite (2%-21%). wet-dry cycle dissolution test was conducted A wet-dry conducted on the the tailings tailings (Lapakko, (Lapakko, 1994). 1994). The 75-g 75-g reactors in in aacontrolled controlledtemperature temperature and andhumidity humidityroom, room, and rinsed rinsed samples (as received) were placed into reactors mL of of distilled water. The ThepH pHofofdrainage drainagefrom fromone onesample sample(T9) (T9) was was neutral neutral for for 120 120 weekly with 200 ml. after 122 weeks of dissolution, and reached reached 3.45 after 151 weeks. weeks, dropped below 6.0 122 151 weekly Nine samples drainage (generally at at or or above above pH pH 8) throughout throughout the the experiment. samples produced alkaline drainage Based of three of these Based on the composition of these samples and their rates of of iron ironsulfide sulfideand andcalcium calcium plus plus carbonate mineral dissolution (as indicated by the rates of sulfate, calcium, and magnesium magnesium dissolution (as indicated by the rates of sulfate, magnesium drainage), their after six sixto tofourteen fourteenyears. years. Based release in drainage), their drainage drainage could become acidic after Based on on similar similar data data analysis it was concluded that the six remaining samples, terminated after after 57 57 weeks weeks of of dissolution, dissolution,would would to produce alkaline to to neutral neutral drainage. drainage. For For the theestimates estimateson onthese these nine ninesamples, samples,assumptions assumptions continue to were required which lend uncertainty to the predictions. More accurate estimation requires More accurate estimation requiresadditional additional information on the formation of coatings on the surfaces of of sulfide and and carbonate carbonate minerals minerals present present in the waste. mine waste. mine A relationship rates and solid-phase sulfur sulfur wntent content of the samples was relationship between sulfate release rates determined by regression analysis. Samples which were inconsistent with the relationship defined, as well determined regression Samples which were inconsistent relationship as some "typical" as "typical"samples, samples, were were analyzed analyzed for for specific specific surface surface area (BET) and surface surface morphology morphology (SEM). (SEM). release rates rates were apparently apparently due due to to differences differences in in pyrite specific surface area The anomalous sulfate release 29 �resulting from from variations in pyrite There was was no apparent resulting variations in pyrite particle particle size size and and morphology. morphology. There apparent evidence evidence that something something other other than the the pyrite pyrite surface area was controlling the the rates of pyrite oxidation. oxidation. suggesting that (maximum concentrations concentrationsofof 140 140to to 4900 4900 pg/L) jigiL) were were observed observed Elevated arsenic concentrations (maximum T7, T8, and 19, contentsgreater greater than than 1000 1000 ppm. ppm. in drainage from solids T7, T9,which which had had solid-phase solid-phase arsenic contents A fourth sample (T6) had had a solid-phase arsenic arsenic content contentof of 1200 1200ppm, ppm,but butno noarsenic arsenic was was detected detected in in the the laboratory drainage. Elevated antimony concentrations (250 to 2800 jzglL) were observed observed in in drainage drainage laboratory draiinage. Elevated antimony concentrations to pg/L) were from T7, T7, T8, contentsofof20 20ppm, ppm,40 40 ppm, ppm, and and 290 from T8, and and T9, T9,with withsolid-phase solid-phase antimony antimony contents 290 ppm, ppm, in excess excess of of 700 700 pg/L j.tg/Lwwas observedin indrainage drainage respectively. AAmaximum maximum molybdenum molybdenum concentration in as observed from T9, which had aa solid-phase solid-phase molybdenum molybdenumcontent contentofof1100 1100ppm. ppm.Concentrations Concentrationsofofbarium, barium,copper, copper, nickel, and zinc were also occasionally detected in drainage from some samples. The concentrations nickel, occasionally detected in drainage from some samples. The concentrations ofof As, Cd, Cu, Mo, Mo, Ni, Ni, Pb, Pb,Sb, Sb,and andZn Znininthe thelaboratory laboratorywere wereininqualitative qualitative agreement agreement with that in the available, field field concentrations concentrationswere were 1 to 5 times field. In fourteen of twenty-five times those those in in the the field. twenty-five cases available, It was concluded that trace metal concentration in laboratory drainage was better suited as laboratory. laboratory. in laboratory drainage was better suited as an indicator of potential potential elevation in in the field, but not as aa quantitative measure. measure. quartz-carbonate hosted gold gold mines mines produced produced acid acid drainage, drainage, In summary, one one of the tailings from quartz-carbonate yielded the the potential potentialfor foracid aciddrainage drainagein insix sixtotofourteen fourteenyears yearsofofdissolution. dissolution. The The remaining remaining while three yielded six samples tested tested were were predicted predicted to to remain remainneutral. neutral. Trace Trace metal release from the tailings was variable, with arsenic, antimony, and molybdenum molybdenumhaving havingthe thehighest highestconcentrations concentrationsinindrainage. drainage. The The trace trace metal metal release was in qualitative agreement with field concentration concentration data. In: Achieving Achieving 1992, Characterization Characterization and Static Static Testing Testing of Ten Gold Mine Tailings: In: Lapakko, K. A, 1992, Potential Through Through Reclamation: Reclamation: Proceedings of the 1992 American AmericanSociety Societyfor forSurface SurfaceMining Mining Land Use Potential Reclamation Meeting, Meeting,Duluth, Duluth, MN, MN, June June 14-18, and Reclamation 14-18, 1992, p. 370-384. 370-384. Lapakko, K. K. A,, A., 1994, disposalof ofmine minewaste: waste: Laboratory Laboratory investigation: investigation: Presented Presented at at the the , Lapakko, 1994, Subaqueous disposal Land Reclamation Reclamation and and Mine Mine Drainage Drainage Conference Conferenceand andthe theThird Third International International Conference Conference International Land Abatement of of Acidic Acidic Drainage, Drainage, Pittsburgh, Pittsburgh, PA, PA, April 24-29, 24-29, 1994, 9 p. on the Abatement 30 �I I I I I. I I I I I ARCHEAN RIFTS AND SHEBANDOWAN ARCHEAN RIFTS AND GOLD: GOLD: EXAMPLES FROM THE CENTRAL SHEBANDOWAN GREENSTONE -. -- .- -. - BELT - -- LAVIGNE, Maurice J J., LAVIGNE, . , Ministry of of Northern Development and Mines, Suite South, Thunder Bay ON BOOS, 435 435 James James St. S t . South, Mines, S u i t e 8002, P7E 6E3 6E3 Shebandowan The discovery of of 41 4 1 gold occurrences in i n tthe h e central c e n t r a l Shebandowan Greenstone Belt B e l t in i n the t h e last l a s t 10 10 years years has led l e d to t o the t h e realization realization of a new of new gold gold belt. b e l t . The gold mineralization m i n e r a l i z a t i o n iis s sspatially p a t i a l l y (and (and in related i n some cases demonstrably), temporally temporally and and. genetically g e n e t i c a l l y related These assemblages assemblages occur occur as to t o ""Timiskaming" Timiskaming" ttype y p e assemblages. assemblages. These as Thesebbelts long narrowl ilinear belts. km) narrow near b e l t s . These e l t s contain contain long (75 (75 km) greywacke, iron conglomerate, greywacke, i r o n formation, formation, shoshonitic s h o s h o n i t i c pyroclastic pyroclastic and One area, particularly and alkalic a l k a l i c intrusive i n t r u s i v e rocks. rocks. area, p a r t i c u l a r l y rich r i c h in in iron known as a s the t h e Matawin IIron r o n Range and and i r o n formation formation and gold, gold, was known A t the the from tthis, h i s , the t h e term term Matawin Matawin Gold Gold Belt Belt was was dubbed. dubbed. At Stewart Stewart property, property, gold occurs within w i t h i n the t h e intrusive i n t r u s i v e breccia b r e c c i a of of a syenite mineralization s y e n i t e stock. stock. The m i n e r a l i z a t i o n is i s characterized c h a r a c t e r i z e d by by disseminated pyrite p y r i t e and and hematite hematite alteration. a l t e r a t i o n . Gold in i n the the Matawin Matawin Iron I r o n Range area a r e a consists c o n s i s t s of single s i n g l e ladder l a d d e r veins to t o more Att Gold Creek Creek complex vein v e i n arrangements arrangements iin n granodiorite g r a n o d i o r i t edykes. dykes. A South, occurs aas disseminateds usulfides South, tthe h e gold gold occurs s disseminated l f i d e s i in n ffelsic elsic volcanics. The ddelineation e l i n e a t i o n of late l a t e Archean rifts r i f t s serves s e r v e s as a s aa "first f i r s t sstep" t e p Mexploration e x p l o r a t i o n ccriteria. riteria. I 1 I I I 31 �EVALUATION, CENTRAL CENTRAL MINNESOTA. MINNESOTA, PHASE PHASE II BASIC BASIC DATA DATA MINERAL POTENTIAL EVALUATION, Department of of Natural Natural Resources, Resources, Division Divisionof ofMinerals, Minerals, 1525 15253rd 3rd LAWLER, Tom, Minnesota Minnesota Department Ave. E., ilibbing, Ave. Hibbing, Minnesota Minnesota 55746 The Minnesota Department Department of Natural Resources, Minerals Division, has completed a program using using contemporary methods methods to to begin begin to to evaluate evaluate the the mineral mineral potential potentialof ofaa large large part part of of Central Minnesota. Minnesota. contemporary This This project isis oriented orientedtoward toward identifying identifyingnonferrous nonferrous metallic metallic mineralization, mineralization, associated associated alteration or or lithologic units units and and structures permissive permissiveof of such such mineralization. mineralization. The purposes are: are: 1. 1. To To serve land use planning within the D .N.R.; 2. To D.N.R.; To encourage encourage private exploration through better data access, and; 3. To To serve servegovernment governmentagency agency planning of future future programs. Creating an 1. Defining Defining mineral an improved improved regional regional mineral potential potential evaluation evaluation was done done by: 1. units and and structures structures permissiveof permissive ofmineral mineraldeposits. deposits. 2. 2. Defining occurrences, or lithologic lithologicunits Defining basic bedrock lithologic maps, which lithologic locations from existing drill core. core. 3. Creating 1:62,500 1:62,500 scale inferred geologic maps, display supplemented by some display interpreted interpretedmineral mineral potential, potential, using usingavailable availablegeophysical geophysicaland and geologic geologicdata supplemented field work. and; 4. Re-evaluating Re-evaluating existing existing geochemical geochemical surveys using contemporaneous contemporaneous statistical field and; 4. analytical methods. methods. A contract was was completed completedby byDr. Dr. Don Don L. L. Shettel ShettelJr. Jr. and and Dr. Dr. Patrick O'Hara to interpret three three existing ground water water and lake sediment geochemical data sets using state of the art statistical sediment geochemical data sets using state of statistical and geochemical modeling methods. methods. From Fromthese these models models Drs. Drs. Shettel Sheneland and O'Hara O'Haraconstructed constructedanomaly anomaly maps maps for gold, gold, base base metals, metals, iron ironand and uranium. uranium. Contracts were were also completed completedby by Dr. Dr. Allan Spector Spector to to make make an inferred inferred geologic geologic map map of of the twenty township Shephard Area Area at a scale of 1:62,500 and a second twelve township map map extending extending this this area to the northeast. Dr. Dr.Spector's Spector'smaps mapsdisplay displaystructurally structurallydeformed, deformed,folded foldedand and faulted, faulted,greenstones greenstones with associated units and intrusives. An important aspect of of this this contract intrusives. An important aspect contract was was associated metasedimentary metasediientary units construction of of 1:62,500 scale maps displaying displaying several several high high m mineral potential areas as modeled from ineral potential areas as modeled geophysical characteristics characteristicsof ofknown knownmines mineslocated locatedininsimilar similarPrecambrian Precambrianterrains. terrains. These These models models are are primarily based on Dr. Spector's Some of of these these areas areas of of high mineral Spector's experience experience with with such such features. features. Some potential are coincident with anomalous geochemical geochemicalresults resultsdefined definedby byDrs. Drs. Shettel Shettel and and O'Hara. O'Hara. Geophysical measurements of density and magnetic susceptibility were made on selected logged samples for computer modeling of geologic features. features. Detailed Detailedmagnetic magnetic ground ground traverses traverses were were completed completed along roads using an A.T.V. A.T:V. or golf cart for for transportation. transportation. In summary resultsinclude: include: Improved definitionof definition ofgeologic geologicfeatures; features; Lithologic Lithologicunits units results - significant and features features permissive permissive of economic economic ore deposits; deposits; Detailed inferred geologic maps with definition of areas Detailed inferred geologic-maps definitionof Multi element geochemical anomalies with significant pathfinder element having- high mineral potential; Multi element geochemical anomalies with significant pathfinder element anomalies coincident with with favorable inferred geologic anomalies coincident geologic features. features. To test test the the inferred inferred geology, geology, in cooperation with the M.G.S., M.G.S., six and into bedrock bedrock six vertical vertical holes holes were were drilled drilled through glacial overburden and far enough to obtain hard bedrock samples. Hand lens examination of the core confirms inferred geologic fax hard bedrock samples. Hand lens of the core confirms inferred geologic bedrock bedrock maps maps in in most most of of the the drill drillholes holes and andprovides providesencouraging encouragingindications indications of mineral potential. 32 �I I I a • I The The Birch Lake Prospect Prospect -- AA Major PGM Prospect in the Duluth Complex by Ernest K. K. Lehmann Lehmann North Central Mineral Mineral Ventures Inc., Inc., Minneapolis, Minnesota and John W. W. Beck 3M Company, St. Paul, Minnesota 3M ABSTRACT I I I I I I I I I I I I I The (PGM) is The Birch Birch Lake Lake Platinum Group Metals Metals (PGM) Prospect is located within the the Duluth Complex on on the St. Louis/Lake County border border just east east of the the Dunka Taconite Mine of of LTV Steel Steel and about 10 miles south south of of Ely, Ely, Minnesota. Minnesota. The surface of the the area is marked by by aa humocky terrane terrane developed developed on on the surface surface of of the Complex Complex and covered with with aa thin thin ground ground morraine. morraine. The copper-nickel in the The area area was was originally explored for for copper-nickel 1950's 1950's and 60's 60's including drilling by Duval. Duval. These drill holes encountered encountered copper-nickel copper-nickel mineralization mineralization but but were not analyzed for for PGM5. PGMs. Resampling Resampling of of the drill core core in in the early 1980's 1980's by state agencies revealed ore and near ore concentrations of PGMs PGMs in This a program of of in two two holes. holes. This work work coincided with a program PGM exploration being carried out by by the the Beaver Beaver Bay Bay Joint Joint Venture Venture and and its Subsequent drilling 1991 was its partners. partners. drilling in 1988 1988 through through 1991 carried carried out by by the the venture. venture. The PGH Lake occurs within the the PGM prospect at Birch Birch Lake South Kawishiwi intrusive, a part the Complex. Kawishiwi intrusive, a of the Duluth Complex. Mineralization the the Mineralization is is confined to to aa unit near the base of the intrusive intrusive which consists of of aa copper-nickel copper-nickel sulphide sulphide rich rich olivene olivene troctolite is iron oxide troctolite zone zone and and is associated with iron rich troctolites. troctolites. These These units units dip dip at at shallow shallow angles angles to to the the east. east. The area area drilled drilled is is on the the south south flank flank of aa strong oval oval magnetic anomaly mineralized anomaly which is believed to be the the same depth as the mineralized zone; the rocks above above the the minerilized mineralized zone zone typically typically have a low magnetic This magnetic susceptibility. susceptibility. This magnetic magnetic anomaly may indicate indicate increased increased sulphide sulphide and/or and/or iron iron oxide oxide content content at at its its center, center, giving giving aa strong strong suggestion suggestion of of better potential potential for for enconomic mineralization mineralization on on this this as as yet yet untested untested target. target. The The mineralized mineralized zone zone is is characterized characterized by by serpentinization serpentinization and of a and saussuritization saussuritization and and the the occurrence occurrence of a high chlorine chlorine content content which causes a unique rusting of the rocks on exposure to air. air. The The PGM PGM values are are associated associated with copper copper and nickel. �Pt:Pd Ratios ios of o Rat d are are in in the t:he range range of of 1:1 1:l to to 1:2, rather rather than than ratios of 1:3 ratios 1:3 to 1:4 1:4 characteristic characteristic of the the Minnamax, Minnamax, Inco Inco and and Dunka Road copper-nickel deposits which contain only accessory Dunka Road copper-nickel deposits which contain only accessory amounts The mineralogy of amounts of of POMs. PGMs. The mineralogy of the the PGMs PGMs at at Birch Birch Lake Lake is is poorly known known though though complex complex platinum-palladium-bjsmuth-telluride platinum-palladium-bismuth-telluride sulphosalts sulphosalts have have been been identified. identified. The The deposit deposit is is believed believed to to have formed formed in in aa trough trough in in the the base base of the the complex, complex, perhaps perhaps caused by faulting faulting which which permitted chlorine chlorine rich rich solutions solutions to to caused by deposit and deposit and enrich enrich PGMs PGMs in in the the zone zone of of pre-existing pre-existing copper-nickel copper-nickel sulphide sulphide mineralization. mineralization. Considering Considering the the substantial substantial thickness thickness of of the the mineralized mineralized zone zone and and its its possible possible major major areal areal extent, extent, the the potential potential exists exists for a world class PGM deposit mineable by large scale highly for a world class PGM deposit mineable by large scale highly mechanized Initial investigations the mechanized methods. methods. Initial investigations suggest suggest the a bulk possibility of making sulphide concentrate for sale possibility of making a bulk sulphide concentrate for sale to to existing Preliminary existing smelters smelters in in Canada Canada or or Europe. Europe. Preliminary economic economic analysis suggests that that at least hole contains analysis suggests at least one one drill drill hole contains mineralization of economic grade at current prices under mineralization of economic grade at current prices under such such aa scenario. Further drilling of the deposit is planned to test scenario. Further drilling of the deposit is planned to test its its economic potential. economic potential. �I p PETROCRAPHY AND STRUCTURE OF THE KEWEENAW CHENCWATANA NEAR DRESSER, WISCONSIN VOLCANICS LESLIE, Magnus, Wetzel, Todd, Wirth, Karl, R. and Craddock, John P., Geology Dept., Macalester College, St. Paul, MM 55105 Dresser Trap Rock quarry provides a unique look at 6 flows of the Chengwatana volcanic group (Age: —1.1 Ga) which range in thickness from 10 to 70+ meters. The flows are basaltic diabases whose primary mineralogy consists mainly of unzoned plagioclase (An 45-50) and augite with lesser amounts of illmenite and hornblende. The P 1 1 1 . . No modal olivine or olivine alteration products exist in these samples, but previous chemical analysis indicates that the flows are olivine normative (Cavaleri et al., 1987).The Theflows flowsstrike strikeNNNE anddip dip 13-20W. 13-20°W,Flow Flowbottoms bottomstend tendtotobebeaphyric aphyric and and 1987). N E and rapidly coarsen into subophitic or intergranular intergranular textures. textures. The centers of of the flows coarseness in in proportion proportion to the thickness are understandably more coarse, with the coarseness of the flow. Flow centers contained in the quarry exhibit two textures. The most of contained in are intergrowth termed "luster-mottled" common texture is an ophitic ophitic pyroxene-plag. intergrowth 'luster-mottled" due to the spoiled appearance of the rocks on exposed faces. A few flow centers the spotted appearance of the rocks on exposed with 1-2 an cm plagiodase plagioclaselaths laths in in aa mediummediumexhibit a plagioclase-phyric texture often with grained groundmass. Flow Flow tops are are fine grained and all have amygdules filled with fine amygdules chlorite, epidote, epidote, quark quartz and calcite. alteration mineralization, primarily chlorite, Major and trace element analysis (INAA and XRF) is being conducted across across the the Major and XRF) is being conducted stratigraphy from flow stratigraphy from Dresser west to the the Taylor's Falls area to: 1) delineate differentiation trends across the successive successive Chengwatana Chengwatanaflows flowsand, and, 2) 2) characterize characterize of the Keweenawan rift. the Chengwatana sequence in the overall stratigraphy of exposed in in the quarry were erupted episodically, with with the exception The flows exposed of the fifth/sixth fifth/sixth flow of interflow of flow boundary boundary which which exhibits exhibits a remarkable example of sedimentation of the This surface surface sedimentation the flowtop flowtopbreccia breccia type type as as described described by by Jirsa Jirsa (1984). This represents the deposition of fluvial sediments over over the the rough rough brecaated, brecciated, top top of of flow flow five and is composed of of angular angularfragments fragments of of subjacent subjacent flows and fine grained, cross-bedded sand. on the western wall of of cross-bedded sand.The The fluvial fluvial sediments sediments are well exposed on meters before before tapering tapering off off the quarry, where where they they reach reach aa maximum maximum thickness thickness of of 5-8 meters on either side of the central paleochannels. side of the central paleochannels. lava flows in in the quarry have undergone undergone very very low low to to low-grade low-grade The lava metamorphism, as well as hydrous alteration. The flows contain significant as hydrous alteration. The of epidote, chlorite, chlorite, and of the flow tops having become amounts of and actinolite; actinolite; many of epidosite. The plagioclase present in significantly altered samples has has been been The plagiodase in altered samples converted to albite albite indicating indicating metamorphism in the low grade grade albite-actinolitealbite-actinolitechlorite fades. facies. Hydrothermal Hydrothermal alteration has has caused caused the the alteration alteration of of pyroxenes pyroxenes to to uralite, variant of of hornblende; hornblende; and the dominant epidotization uralite, a semi-fibrous variant overprint exhibited in in nearly nearly every every sample. sample. Previous Previous studies studies have have indicated indicated aa depth depth of burial of at krn and andtemperatures temperaturesapproaching approaching440°C 440T(Cordua, (Cordua,1989). 1989). at least least 22 km The outcrop structures in the volcanic flows are straightforward and include the following features: 3 systematic joint sets (N-S. 90°; E-W, 90°; N-S, 45°E), and a conjugate thrust fault pair (N-S. 45°E and N-S, 35°W) which are not crosscut by the 35 �(older) joint surfaces are commonly commonlyfilled filledwith withcalcite calciteand/or and/or quartz (older) joints. All the the joint which has has been been plastically plastically deformed. deformed. Both Both vertical vertical joint sets commonly preserve preserve sub-horizontal striations with dextral stepping directions (and minute offsets). a1 striations with dextral stepping directions minute offsets). The east-dipping thrust thrust faults faults are are quite quite numerous, numerous, whereas only one west-dipping thrust fault has been observed which is preserved as a .5 m width quartz quartz zone. Within this gouge zone we have observed epidote-filled echelon fractures, fractures, striated striated and idote-filled en echelon stepped chlorite-quartz-epidote, S-C structures, and late-stage syntaxial structures, and late-stage syntaxial calcite calcite fillings. All of these kinematic indicators documenthangingwall hangingwallmotion motionas as up up and and tors document to the east; this fault displacement also offsets the other thrust faults (N-S, 45°E) and offsets thrust faults (N-S, 45OE) and is interpreted as being younger. The gouge gezone zone isis composed composed of of quartz+chlorite÷ quartz+chlorite+ epidote+adularia÷calcite÷hematite (+opaques) and represents a green schist ques) and represents schist metamorphic assemblage ("400?C,r4 kb) that is is similar similarto to the themetamorphic metamorphicgrade gradein in. the host volcanic rocks. Calcite and quartz joint and and fault quartz are are abundant abundant as as secondary secondary minerals filling joint surfaces, faces, and and contain contain mechanical mechanical twins twins or or deformation deformation lamellae, which allowed allowed us us to characterize characterize the the state stateof of stresè stressin in these these rocks rocks after after mineralization. Quartz Quartz containing deformation lamellae was observed only associated associatedwith with the the thrust thrust faul fault erved only gouge zone whereas twinning was observed in all phases of calcite. These in all phases of calcite. These deformation lamellae bracket the differential (calcite) tial stress magnitudes as as >10 >10 MPa (calate) and >50 MPa (quartz), respectively. Twinning in calcite allows for a detailed and >50 respectively. calate allows for a detailed strain analysis analysis with the the caveat caveat that that the the age ageof of the the calcite calate is not known. Our results results include include strain analyses of calcite fillings in joints and thrust st faults; calcite amygdules were rare: joint set I (N-S. 900; sub-horizontal shortening II1(E-W, N45OE), joint tening trend: trend: N45°E), joint set 1 90°; shortening trend: N5°E), thrust fault I (N-S. 45°E; shortening trend and plunge: (N-S, 45OE; shortening trend plunge: N90°E, 40°), thrust fault II (N-S, (N-S, 45OE; 45°F; shortening shortening trend trend and and plunge: plunge:N4°E, N4OE,70°F). 70°E) These complex twinning strains are best interpreted reted as representing regional stress and strain field changes over a long time periodd(e.g., (e.g., joint-filling joint-filling deformation, then thrusting), rather than as variations in the stress field within the area of I1square stress square km.. A regional regional interpretation interpretation of of these these thrust thrust faults, faults, in conjunction with the detailed flow of thrust faulting flow stratigraphy, stratigraphy,is is in in progress progress to to characterize characterize the extent of faulting along the Keweenaw-Lake Keweenaw-Lake Owen-Hasting Owen-Hastingfault fault(Middleton, (Middleton,1991; 1991;McGovern McGovernetetal., al.,1993). 1993). REFERENCES REFERENCES Cavaleri, The Geology Geology of the Cavaleri, M., M., Mossier, Mossier, J. J. H. H.and andWebers, Webers, C. G.F., F., 1987, 1987, The the St. Croix Crow River Valley: Minnesota Geological Survey, Guidebook Series #15, p. 2343. Minnesota Geological Survey, Guidebook Series 23-43. Cordua, area, Wisconsin and and Minnesota: Cordua,W., W., 1989, 1989, Bedrock Bedrock geology geology of of the theDresser-St.Croix Dresser-St-CrowFalls area, Minnesota: 53rd Annual Tri-State field Conference Guidebook, River Falls, WI. 53rd Annual Tri-State field Conference Guidebook, River Falls, WI. Jirsa, A., 1984, 1984, Interflow Interfiow sedimentary sedimentary rocks in the Keweenawan North North Shore Volcanic Volcanic Group, Group, Jiisa,M. M.A., northeastern Minnesota: Minnesota Geological Survey Report of Investigations 30. northeastern Minnesota: Minnesota Geological Survey Report Investigations McGovern, M.G., Craddock, J.P.,,Webers, G.F., G.E. 1993, Evidencefor forlatePaleozoic latePaleozoicdisplacement displacement of of the the 1993, Evidence Keweenawan Keweenawanthrust thrustfault faultfrom fromfolded foldedPaleozoic Paleozoicoutliers outliers in in Michigan's Upper Upper Peninsula: Peninsula:39th 39th Annual AnnualProceedings Proceedingsofofthe theLake LakeSuperior SuperiorInstitute, Institute,p.p.56-57. 56-57. Middleton, M.D., 1991, A preliminary study study of of rejuvinated rejuvinated movement movementalong alongaa Precambrian Precambrianfault, fault.St. St. Croix county, WI: 37th Annual Institute LakeSuperior SuperiorGeology, Geology,p.p.70-71. 70-71. Instituteon onLake 3.6 �Environmental geochemistry of Proterozoic black shales in eastern Finland: a pilot study LOUKOLA-RUSKEENIEMI, Kristi, Geological Survey of Finland, FIN-02150 Espoo, Finland The Precambrian geology of Finland is comparable in many aspects to that of the Lake Superior region. In particular, both areas contain black shales and the environmental geochemistry of these may be direcUy compared because of similarities in climate. Thick (20-400 m) formations of 5- and C-rich black schists occur in eastern Finland (black schist = metamorphosed black shale). Median concentrations of both graphitic carbon and sulfur are 6-9%. These black schists are spatially associated with the disrupted remnants of 1.96-1.97 Ga ophiolites, occurring over 250 km of strike length along a probable former rift zone in the Kainuu and Outokumpu areas. The thickest black schist formations occur at Talvivaara, where 300 Mt of black schist with Ni+Cu+Zn > 0.8% are present. The Talvivaara deposit is syngenetic in origin and the main part of the contained metals were precipitated in organicrich mud during deposition. The primary fine-grained spheroidal pyrite (<0.01 mm) contains 0.3-0.4% Ni which has, during recrystallization, been incorporated in pynhotite and pentlandite. The deposit has undergone amphibolite facies metamorphism and tectonic deformation. The deposit included Mn-rich horizons and up to 17% interlayered black calc-silicate rocks. The Ni-Cu-Zn-rich black schist is easily weathered when in contact with surface waters. The background concentrations of the black schist area have been compared with those of different bedrock, namely the Late Archean granite gneiss areas adjacent to the Talvivaara area. The Hg concentrations of pike (a large northern predatory fish) seem to correlate with bedrock geochemical characteristics: Lake Hg in pike (ppm) of black schists Distribution of schists Kolmisoppi Jormasjärvi Alanne 0.96 0.76 0.33 Abundant Hg-rich schists in mica schist Black schist interlayers in No black black schists schists Average in 67 Finnish forest lakes 0.56 (Verta, 1990) Chemical concentrations of stream and lake waters, ground water and stream and lake sediments axe compared. Spring water results of pilot sampling committed in August 1993 (n = number of samples): Black schist area Cu Zn Ni Co Pb Cd Mn Al > > > > > SO4 > pH C n 4.08 97.3 69.90 3.33 0.15 > 0.25 > 183 Granite gneiss area 031 1.08 4.17 0.65 0.20 0.31 - 6.39 0.96 0.41 0.64 <0.02 38.5 244. - 90.4 272. 7.3 1.0 - 1.7 4.8 12 5.2 - 1.7 > 390 - 4 Sampling is continuing this year, but these results already indicate that the natural background values are dependent on bedrock geochemical characteristics in the Talvivaara area. The bedrock at Talvivaara contains anomalous Cu, Zn, Ni, Co and Mn. elevated Cd and Hg, but in most places not elevated Pb concentrations, which can also be seen in the chemical composition of spring waters. 37 �PETROLOGY ANALYSES OF PETROLOGY AND WHOLE ROCK ANALYSES OF THE THE CENTRAL CENTRAL PORTION PORTION OF OF A LARGE LARGE EARLY PROTEROZOIC PROTEROZOIC DIABASE DIABASE DIKE, DIKE, EASTERN EASTERN LAKE LAKE OF OF THE THE WOODS, WOODS, ONTARIO ONTARIO -- AA PRELIMINARY PRELIMINARY REPORT REPORT by Frank Frank R. R. Luther, Luther, Geology Geology Program, Program,tJW-Whitewater, UW-whitewater, Whitewater, whitewater, WI WI 53190 53190 The study, part of the The dike under study, the 2100 2100 m.y. KenoraKenoraKabetogama Kabetogama (Southwick (Southwick and Day, Day, 1983) 1983) dike dike swarm, swarm, extends extends at at least least 60 60 km km from from the the Pipestone-Cameron Pipestone-Cameron Fault Fault on on the the northwest northwest through Whitefish Bay and through the the center of Whitefish and Kakagi Kakagi Lake Lake to to southern southern Godson informally named named the the Whitefish Whitefish BayBay Godson Township; it is informally Kakagi Kakagi Lake Lake (WBKL) (WBKL) dike dike in in this this report. report. The The objective objective of of this this study was to use field observations observations as as well as as mineral and and rock rock chemistry chemistry to to constrain constrain the the intrusive intrusive history history of of the the dike. dike. In Whitefish Bay the WBKL WBKL dike dike is is 70-80 70-80 m wide with well-developed well-developed chill chill borders borders in in contact contact with with the the Archean Archean granitic granitic country country rocks; rocks; no no chill chill borders borders were were observed observed within within the the dike. dike. The The intrusive intrusive contact contact with with the the granite granite is is irregular irregular with with apophyses apophyses of basalt at at the the mesoscopic mesoscopic scale scale while while the the regional strike strike and dip is constant constant at 1400 vertical over over the the area area studied. studied. Igneous Igneous layering layering characterized characterized by by modal modal variation variation in in plagioclase, plagioclase, pyroxene, pyroxene, and and magnetic magnetic opaques opaques is is noticeable noticeable between 10 10 and 30 30 m from from the the dike dike border. The The layering is often often distorted distorted and/or and/or truncated. truncated. The The massive massive central part of the dike dike is is a low—quartz-content low-quartz-content diorite diorite which which contains contains small small well-developed well-developed cross-cutting cross-cutting mafic mafic pegmatites. pegmatites. Microscopically, Microscopically, the the chill chill border border is is characterized characterized by by altered phenocrysts (up (up to to about about 11 mm mm in in diameter) diameter) of of pyroxene, pyroxene, unaltered unaltered to to partly altered altered phenocrysts phenocrysts of of zoned zoned plagioclase plagioclase (an6o-70), smaller opaque (anso-70), and smal-ler opaque minerals minerals in in aa brown-green brown-green cryptocrystalline groundmass cryptocrystalline groundmass of of devitrified devitrified tachylite. tachylite. The The groundmass groundmass contains contains xenocrysts xenocrysts of of quartz quartz and and K-feldspar K-feldspar indicating indicating interaction interaction with with the the country country rocks. rocks. Proceeding Proceeding into into the dike, the the interior interior of the dike, the grain grain size size gradually gradually coarsens coarsens (over (over about about 55 m) m) to to 3-7 3-7 mm. mm. In In the the center center of of the the dike, dike, (1) (1) vapor-phase vapor-phase alteration alteration of of plagioclase plagioclase and and pyroxene pyroxene is is severe, severe, (2) (2) the the plagioclase plagioclase shows shows complex complex oscillatory oscillatory zoning zoning and, and, (3) (3) up up to to 10% 10% quartz quartz is is present present along along with with micrographic micrographic to to symplectic symplectic intergrowths intergrowths of of quartz quartz and and feldspar. feldspar. Whole-rock Whole-rock chemical chemical analyses analyses (by (by XRAL) XRAL) presented presented below below show show the the dike dike margin samples samples to to be be chemically chemically very very similar similar both both to to one one another another and and to to the the N-i N-1 dikes dikes analyses analyses of of earlier earlier workers. workers. Sample from aa plagioclase plagioclase layer layer shows shows predictably predictably higher higher Al, Al, Sample 55 from Ca, from the the dike dike center center Ca, and and Na Na and and lower lower Mg Mg and and Fe. Fe. Sample Sample 66 from shows shows higher Si, Si, Al, and Na and and lower lower Ca, Ca, Mg, Mg, Fe, Fe, and and Ti Ti as as well as a higher LOt indicative of a more felsic composition well as a higher LO1 indicative of a more felsic composition and and of of more more vapor-phase vapor-phase alteration. alteration. 38 �spl Spl no: no: 1 1 49.3 49.3 3102 SI02 AL2 03 12.5 ALaOs 12.5 CAO CAO MOO MGO NA2 0 MA20 1(2 K2 00 9.28 9.28 6.12 6.12 1.72 1.72 0.28 0.28 FE2 03 16.5 FEaOa 0.21 0.21 MNO MNO TI 02 TI02 P205 P205 LO LO1I TOTAL TOTAL 2.15 0.21 0.21 1.80 1.80 100.1 100.1 55 2 2 3 3 44 47.8 47.8 13.0 13.0 10.1 10.1 5.45 5.45 1.88 1.88 0.26 0.26 18.0 18.0 0.24 0.24 2.30 2.30 0.24 0.24 0.75 0.75 48.5 12.7 8.65 5.52 1.96 0.32 18.0 0.25 2.24 0.22 1.70 48.4 12.8 9.66 5.42 2.01 0.37 17.7 0.25 2.22 0.21 1.10 100.1 100.1 100.1 48.8 16.0 9.64 4.30 2.31 0.59 14.9 0.21 1.96 0.20 1.35 100.3 100.2 6 6 54.1 15.4 6.91 1.82 3.24 0.78 13.9 0.20 1.49 0.47 1.95 100.4 77 47.9 12.5 8.26 5.57 2.68 0.84 17.0 0.25 2.16 0.22 1.65 99.11 - from FRL. element data data available from bc ations and Samples Samples - locations and minor element FRL. contact. 1. 1. LW87-1—la, LW87-1-la, diabase 11 cm from west contact. diabase 0. LW87-1-lb, diabase 2. 2. LW87-1-lb, 0.33 mm from wes westt contact. contact. lmm from west contact. 3. LW87-1-lc, LW87-1-lc, diabase 1 contact. diabase 3 3mm from west contact. 4. 4. LW87—1—le, LW87-1-le, diabase contact. as e -rich diabase from 5. 5.LW87—1—2a, LW87-1-2a, plagioci plagioclase-rich from the the layered layered diabase. diabase. ily altered quartz diabase from mid-dike. 6. 6. LW87—4—3, LW87-4-3, deuterica deuterically 7. 7. LW87—4—llc, LW87-4-llc, diabase 3 cm from from east east contact. contact. The The WBKL dike was a major feeder feeder to to early early Proterozoic Proterozoic The distorted and truncated truncated igneous igneous layering layering atory-zoned plagioclase record a complex and the he oscill and oscillatory-zoned complex history history causing of intrusion/extrusion, quiescence, and back-flow causing the crystallized distortion, distortion, re-melting, re-melting, and/or erosion erosion of of the crystallized border of of the the dike. dike. The increase in in quart quartzz in the dike extrusion proceeded. interior shows magmatic evolution as lava lava extrusion proceeded. eted as deuteric Alteration of the dike interior is interpr interpreted because of of (1) (1) stronger stronger alteration in in the the interior, (2) the egmatites, and presence of (3) a lack of of of the the mafic ppegmatites, and (3) hydrothermal alteration alteration cross-cutting the the margin of the the dike. dike. Many of of these these observations observations and conclusions support those of Southwick Southwick and and Day Day (1983). (1983). flood basalts. flood basalts. I I I I I I I REFERENCE Southwick, Southwick, D.L., D.L., and and Day, Day, W.C., W.C., 1983, 1983, Proterozoic Proterozoic mafic dikes, north-central Geology and petrology of of Minnesota and western 622—638. Ontario. Ontario. Can. Can. 3. J. of Earth Sciences Sciences 20, 622-638. a, 39 �ON THE ON THE ORIGIN ORIGIN OF OFMANGANESE MANGANESE OXIDES OXIDES IN IN IRON-FORMATION IRON-FORMATION OF OF THE THE CUYUNA NORTH NORTH RANGE, CUYUNA RANGE, EAST-CENTRAL EAST-CENTRAL MINNESOTAMINNESOTA- NEW NEW EVIDENCE EVIDENCE FROM THE U.S. U.S. BUREAU BUREAU OF MINES GLORIA GLORIA DRILL SITE MELCHER, Frank H H.; G.B.; McSWIOGEN, McSWIGGEN, Peter Peter LU; CLELAND, M., MELCHER, .,MOREY, G.B.; .;C L E L W . Jane M., Geological Survey, 2642University 2642 University Avenue, Avenue, St. Paul, Minnesota Geological Paul, MN 55113 55113 The Tronimald Formation on the Cuyuna North Range is unique in that it contains the highest reported manganese values of any Early Proterozoic iron-formation in the world, and as such is the largest resource of this metal in the United States. Traditionally, the Trommald has been divided into a lower thin-bedded facies containing Fe-Mn-Mg-Ca carbonates, Fe silicates, magnetite and chert, and an upper thick-bedded facies composed of granular chert, hematite, magnetite, manganese hydroxides, and minor silicates and carbonates (Schmidt, 1963). Near the Merritt mine, uncommon Na-, Mn- and Ba-rich silicates indicative of hydrothermal fumarolic processes occur near the contact between thin- and thick-bedded rocks (Morey and others, 1992). To further elucidate the complex history of the manganese oxides and to investigate the possibility of their in ! situ leaching, the U.S. Bureau of Mines drilled a long inclined core at the Gloria mine, approximately 1.5 km to the northeast of the Merritt site (Dahl, 1992). That core was drilled to an inclined depth of 366 m (304.8 m below the surface) and intersected a complete section of Trommald Formation (true thickness of 168 m) as well as short intervals of the overlying Rabbit Lake and underlying Mahnomen Formations. DahI and others (1992) divided the Trommald into an upper oxidized interval separated from a lower unoxidized interval by an oxidation boundary at a depth of 234 m below the surface. The oxidized part was further subdivided into a thin-bedded facies, a mixed thin- and thick-bedded facies, and a thick-bedded facies. In that scheme, the thickbedded and part of the thin-bedded facies were thought to have been oxidized and leached during subsequent ore-forming events. We observe that some of the thin-bedded rocks contain primary hematite and are chemically akin to thick-bedded rocks. The core is presently being investigated at the Minnesota Geological Survey in terms of mineralogy and geochemistry, and some preliminary results are presented here. The Mahnomen Formation consists of sericite-biotite quartzite interlayered with thin layers or lenses of toumialinite. Beds of chlorite-bearing oxide (hematite) iron-formation mark the base of the Trommald Formation. They are overlain by approximately 40 m of thin-bedded strata containing abundant carbonates, silicates and magnetite. Features indicative of syndepositional reworking, possibly under shallow-water conditions, include granule-rich layers, breccias, and pebble-size conglomerate. The silicate-carbonate iron-formation also contains considerable sulfides (pyrite, pyrrhotite, chalcopyrite, arsenopyrite), commonly in irregular, discordant, composite veins—along with quartz, carbonates, and stilpnomelane— in stratiform layers and lenses, or as inclusions in intercalated beds of chert. The sulfides are typically replaced by magnetite, which in turn is martitized. Mafic tuffaceous material, as well as tourmaline-bearing sericite schist, is intercalated with the iron-rich strata. Preliminary data imply that the silicate-carbonate ironformation is poor in Mn (<2 wt.% MnO) which is at variance with similar rocks from the Merritt site. In turn, there are higher contents of Ca, P, and S observed in the thin-bedded facies of the Gloria Gloria mine. mine. A transitional interval of approximately 4 m separates thin-bedded silicate-carbonate ironformation below from thin-bedded oxide iron-formation above. Individual laminae contain chert, primary hematite, stilpnomelane, and limonite. Carbonates are rare, and magnetite where present is martitized. Individual layers of nearly monomineralic chert are interlayered throughout. A highly brecciated interval contains interealations of argillized shale or tuffitic sediments. Manganese-rich layers first appear in thin-bedded oxide iron-formation about 75 in (true thickness) above the Mahnomen Formation. These massive, concordant hematite-goethite-Mn-oxide-bearing intervals as much as 4 in thick are partly enveloped by brecciated oxides, and have maximum MnO (total) 40 �I I values of 12 0.2. The latter is similar to the Mn-Fe ratios in values 12 wt.% and Mn-Fe ratios of about 0.2. unoxidized thin-bedded rocks at the Merritt site. unoxidized Memtt site. Mn values increase markedly about 110 wt.% for for about 110 m above the base, and stay above above 5 wt.% 55 m (true thickness). As such this zone straddles the boundary between thin-bedded (true thickness). As such this zone straddles the boundary between thin-bedded and overlying thick-bedded strata. strata. Mn-oxide-rich Mn-oxide-rich layers layers in in thin-bedded thin-bedded strata have brecciated or "gnarled ore" textures and are conformably interlayered with intervals of decomposed iron"gnarled are conformably with formation containing containing abundant secondary limonite. Mn-oxide-rich layers in thick-bedded strata are are interlayered conformably with thick beds of admixed chert having a relict micronodular texture, interlayered conformably beds admixed micronodular texture, and with secondary limonite. The layers typically occur as brecciated rubble zones that exhibit exhibit numerous discordant textural features. Manganese minerals minerals include include manganite, manganite, cryptomelane, cryptomelane,and and pyrolusite (Dahl, 1992). Whole-rock Whole-rock assays over 1.5-m intervals show that Mn-rich layers in 1.5-m intervals show that Mn-rich layers in thick-bedded strata contain as much as 50 wt.% wt.% MnO, MnO, and and MnFe Mn/Fe in in places places>> 1. 1. The The zones zones also also have have elevated elevated Ca, Ca, Mg (attributed (attributed to secondary secondary carbonates), and P values and are enriched in Ba (as much as Pb, Sr, Ag, and As. as 1.8 %), Pb, The of thick-bedded, thick-bedded, oxide oxide iron-formation iron-formation The uppermost 12 12 m of Trommald Formation consists of where p primary hematite is abundant but where manganese oxides are lacking. Mn-Fe ratios are are r* manganese oxides are lacking. Mn-Fe ratios generally less than 0.01. The overlying Rabbit Lake Formation differs considerably; beds of overlying considerably; beds of sulfide (pyrite) iron-formation are intercalated with thick beds of oxide iron-formation, intercalated with beds of oxide iron-formation, iron-formation carbonaceous carbonaceous shale, and and thin layers layers of tuffaceous tuffaceous material. The The sulfide sulfide iron-formation iron-formation (35.7 (35.7 wt.% wt.% Fe203, (31 ppb), As, Cu, Co, Ni, Pb, Sr, V. V, Mo, and Se Fe203, 26% 5) S) contains elevated values of Au (31 (230 (230 ppm). PP~). Several Trommald Formation in the Gloria drill core are unique, and it seems to Several features features in the Trommald be special importance that no direct correlation correlation can be made with the well-documented drill core be of special mine. Granular fabrics, fabrics, extensive extensivesynsedimentary synsedimentarydeformation deformationtextures, textures, and and of the nearby ~Merritt e m tmine. t Granular extensive sulfide documented for the first time in the thiin-bedded thin-bedded facies of extensive sulfide mineralization mineralization have been documented relationships among the various iron iron and manganese oxides the Trommald Formation. Paragenetic relationships oxidation events events in in the the upper upper part part of of the the are difficult to interpret because of several superimposed oxidation Trommald Formation. Formation. However, However, we we have have found no evidence that the major major elements elements were were redistributed on on aa scale scale larger larger than than tens tens of ofmeters. meters.Therefore Therefore the the manganese manganese oxides, oxides, significantly redistributed along with other other enriched enriched elements, elements, seem seem likely to be synsedimentary precipitates derived from a hydrothennally the hydrothenually influenced influenced source source of uncertain uncertain affinity affinity and redistributed on a small scale to form the present present enriched enriched zones. zones. ' I I I I I REFERENCES CITED REFERENCES CITED Dahi, of Minnesota manganese manganesedeposits depositsfor forininsitu situmining: mining:Skillings' SUllings' Dahl, L., L., 1992, 1992, Characterization of Mining D. 4-9. Minine Review, v. 81, 81. no. 41, 41. p. Dahl, Brink, S.E., R.L., Tuzinski, brink. s.E.. Blake, lake.^.^.. Tuzinski. P.A., P.A.. and and Adamson, Adamson. N.R., N.R.. . 1992, 1992. Dahl. L.J., - . Site - characterization characterization of Minnesota manganese deposits to evaluate the potential for in situ leach mining: Littleton, Colorado, Inc., Annual Colorado, Society for Mining, Metallurgy, and Exploration, . Meeting, Meeting, Phoenix. Phoenix. Morey, G.B., P.L. and Cleland, J.M., 1992, Evidence of of an exhalative contribution G.B., McSwiggen, P.L. to the the manganese manganese mineralogy mineralogy of the the Trommald Trommald Formation, Formation, Cuyuna Cuyuna iron iron range, range, east-central east-central Minnesota: Institute on Lake Minnesota: Institute Lake Superior Superior Geology, Geology, 38th 38th Annual, Annual, Hurley, Hurley,Wisconsin, Wisconsin, Proceedings, 1. 70-71. Proceedings, part part I,1,p.p.70-7 Schmidt, R.G., R.G., 1963, Geology and ore deposits of the the Cuyuna Cuyuna North North range range Minnesota: Minnesota: U.S. U.S. Geological Survey Professional Paper, 407, 96 p. 407.96 Survey Professional - I ' I I I I �GEOLOGY NORTFIEASTERN MINNESOTA MThNESOTA GEOLOGY OF OF THE THE "GREAThR" "GREATER" BEAVER BEAVER BAY BAY COMPLEX, NORTHEASTERN J. J. D. D. Miller, Miller, Jr., Jr., T.J. TJ.Boerboom, Boerboom,V.W. V.W. Chandler, Chandler,Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642 University UniversityAve., Ave., St. St.Paul, Paul, MN MN 55114, 55114, and and J.C. University of of MinnesotaÑDduth Minnesota—Duluth,Duluth, Duluth,MN MN 55812 55812 J.C. Green, Green. Dept. DepL of of Geology, Geology, University The the USGS's The Minnesota MinnesotaGeological Geological Survey Surveyrecently recently completed completed an 8-year mapping project, supported in part by the COGEOMAP intrusions of the COGEOMAP program, program, whose whosemain main objectives objectiveswere were to to delineate delineate the the multiple multiple subvolcanic intrusions the Middle Middle Proterozoic BC) ofof northeastern northeasternMinnesota Minnesotaand andtotocharacterize characterizeits itstransition transitioninto intothe themore more Proterozoic Beaver Bay Complex (BBQ plutonic (DC). These been accomplished accomplished and and the the the Duluth Complex 0. These objectives have largely been plutonic environment environmentof the results results are are set set forth forthin in the theform formof of three three1:24,000-scale l:24,000-scale geologic geologicmaps maps (Miller, (Miller,1988; 1988; Miller, Miller. Green Green and andBoerboom, Boerboom. 1989; Miller, Green, Green, Boerboom, and Chandler, 1993). 1993), the imminent imminent publication publicationof of two twoothers others (Miller, (Miller, Boerboom, Boerboom, and andMiller, Miller,ininprep.), prep.), and andan anopen-file open-filemap map of of the theLittle LittleMarais Marais quadrangle, quadrangle, also also in in and Jerde, in prep.; Boerboom Boerboomand preparation. These maps,which whichwe wepresent presentininour ourposter posteras asaa mosaic mosaiccompilation, compilation, include include all all or or parts parts of of eleven eleven 7.5' Thesemaps, quadrangles 440-square-mile-area Fig. (Fig. 1). Although has been historically historically called called the quadranglesand and cover cover aa440-square-mile-area Although this this area area covers covers what what has BBC of aemmagnetic aeromagnetic data over BBC (Grout (Grout and and Schartz, Schartz, 1939), 1939). reconnaissance reconnaissancemapping mapping to the east and interpretation of covered needfor foran an expanded expanded definition definition of of the the BBC. BBC. covered areas areasto to the thewest west suggest suggestthe theneed Twelve major intrusive (lithodemic) units were identified within the area of the the BBC, BBC, which which represent represent at at Twelve major intrusive (lithodemic) units were identified the mapped area least central part part of the North North Shore Shore least six six major emplacement emplacementevents events of mafic to less common felsic magmas into the central Volcanic events reflects reflects the the composite compositenature natureof of Volcanic Group. Gmup. This Thisnumerical numericaldisparity disparitybetween between map map units and intrusive events some of correlating units over over such suchan anextensive extensivearea. area. Because Because of of these these correlation correlation the uncertainties uncertainties of some events events and and the problems, it and northern northern pam. parts.The Thesouthern southern BBC BBC contains, contains,in in it is is convenient convenient to to subdivide subdivide the the BBC into southern and order Lax Lake gabbro gabbro and the diorite; the the separate separate but but correlative(?) k l a t i v @ ? ) Blesner Lake diorire: order of successive successive emplacement, emplacement,the LaxLuke the Finland abase sill, and and Finland Radar RadarStation Stationgranophyre; eranonhvre:the thelayered layeredmafic maficSonju SoniuLake Lukeintrusion, intrusion.the the Victor VicforHead di diahme . -. ..dl . - ihp. -theextensive with its -mrthosite anorthosite inclusions inclusions and and composite composite bodies bodies of of the the extensivedikes dikesand andsills silkof ofBeaver BeaverRiver ~ i v ediabase diabase r ferrogabbroic Silver Bay intrusions. intrusions.Although Althoughthe theBeaver BeaverRiver River diabase diabaseand and its its composite composite intrusions intrusionscan can be be traced fermgabbmic throughout north of of about about 47%' 47°30'latitude. latitude. From oldest oldest totoyoungest, throughout the the BBC, a distinct distinct suite suite of intrusions intrusions occurs north youngest, the Lake inclusion-rich inclusion-rich &rife diorite (see (see Bcerboom, Boerboom, this volume), the Cabin thenorthern northern BBC BBC units units are arethe the Shoepack ShoepackLuke Cabin Creek porphyritic ferrogabbro, the porphyritic diorite, dorife,the theUpper UpperManitou ManitouRiver Rivergabbro, gabbro,the theWilson WilsonLake ferrogabbro, theHoughtaling HoughtalingCreek Creektroctolite, rrocfolite, and Beaver River diabase, diabase, together intrusions. The River gabbro and again, again, the theBeaverRiver together with several composite intrusions. The Upper UpperManitou ManiwuRiver gabbro is Lake gabbro/Blesner is probably probably correlative correlativewith with the the Lax LaxLake gabbrolBlesnerLake diorite dorite units units of of the the southern southernBBC, BBC, because becauseall allare are irregular internal smicture, structure, are strongly strongly altered, altered,and andhave haveaasimilar similarrange rangeofofrock rocktypes. types. A A possible possible irregular in form, lack internal comagmatic keelcomagmatic relationship relationshipbetween the the Houghtaling Creek Creek troctolite, troctolile, a 2- to 3-km-wide, northeast-trending, keelshaped Lake intrusion, a well-differentiated, well-differentiated, 1-km-thick, sheet-like shaped intrusion, intrusion, and and the the lower lower section section of of the the Sonju Late body, isissuggested olivine-plagioclasecumulates. cumulates. More texturesand and compositions of their olivine-plagioclase suggestedby bythe thesimilar similartextures discussion discussionof of petrologic petrologic and andtectonomagmatic tectonomagmatic relationships relationshipsof of the the BBC BBC are are given given in in Miller Miller and and Chandler Chandler(in (in review). review). General (heBeaver BeaverBay Bay and andDuluth Dduth complexes complexes are are the the shape, shape,cumulate cumulatecharacter, character,and and Generalcriteria criteriathat that distinguish distinguishthe environment environmentof of emplacement emplacement of individual mafic intrusions. Whereas Whereas DC intrusions are typically thick tabular bodies rocks, BBC intrusions tend be thinner (c2km) (<2km) bodiesof of mostly mostly mafic mafic cumulates cumulatesemplaced emplaced adjacent adjacentto to other other intrusive rocks, sheet-like sheet-likebodies bodies or ordikes dikesof of typically typically non-cumulate non-cumulate mafic mafic rocks that commonly are in contact with volcanic country rock. betweenBBC BBCand andDC DCininthe themap maparea areaisisaa northeast-trending, northeast-trending,55- to to 8-km-wide 8-km-wide transition zone rock. The Theboundary boundarybetween bounded bounded by the the Houghialing HoughfalingCreek Creek troctolite frocfolile totothe thesoutheast southeastand andby by gabbroie gabbmicanorthosites anorthositesof of the the DC DC to to the the northwest. zoneisisaacomplex, complex,heterogeneous heterogeneousmixture mixtureof of DC DCand andBBC BBCrock rock types, types, from fromoldest oldestto to northwest. Within Withinthis thiszone youngest, rock, (2) highly contaminated mafic mafie intrusions youngest, (1) strongly strongly metamorphosed metamorphosed to to partially remelted remelted volcanic rock, of inclusion-rich diorite, diorite, (3) plutons, (4) (4) plagioclase-phyric plagioclase-phyric mafic mafie intrusions, intrusions,and and (3) large granopyhyre plutons, of Shoepack Lake inclusion-rich (5) ferro gabbro - Plagioclase Plagioclase phenocryst (5)mafic mafii dikes dikesand andlayered layeredcumulates cumulatesof ofthe theWilson WilsonLake Lakeferrogabbro phenocryst compositions compositions and textures Creek porphyritic &rite diorite are textures and and the theferrodioritic fermdiorificmatrix matrix composition composition of the CabIn Cabin Creekporphyritic are consistent consistent with its its being aa hypabyssal gabbroic anorthositic anorthositie locks. rocks. If the deeper DC gabbmii If so, this would imply that DC DCand andBBC BBC hypabyssal equivalent equivalent of the magmatism magmatismwere, were, in part, part, contemporaneous. Recently Recentlyacquired acquiredU-Pb U-Pbages ages (Paces (Pacesand Miller, 1993) 1993) bracket DC and BBC Lake BBC magmatism magmatism between between 1099 1099Ma, the the age age of of DC gabbroic anorthosite, and 1096 1096 Ma, the age of the Sonju Lake intrusion intrusion and andaaSilver SilverBay Bay intrusion, intrusion,but butdo donot not reveal reveal whether whether the themagmatism magmatism overlapped. overlapped. ItIt is is apparent apparentfrom from Figure Figure11that thatan anextensive extensiveband bandof of subvolcanic subvolcanicintrusions intrusions occurs occursin in the the North North Shore ShoreVolcanic Volcanic Group toGrand GrandPortage. Portage. Although Althoughthese theseintrusions intrusionsfit fitthe thegeneral generalcriteria criteriadistinguishing distinguishingthem themfrom from Gmupfrom from Duluth Duhithto the band should be considered considered part of the the Duluth DuIuth Complex, Complex, itit will willrequire require more more work work to to determine detennme how much of this tend BEC. between Torte Tofte and and Grand Grand BBC. Miller Millerand andChandler Chandler(in finreview) review)suggest suggestthat (hatthe the intrusive intrusive rocks near the lakeshore between Marais Marais be beincluded includedininthe theBBC BBC(eastern (easternBBC, BBC,Fig. Fig.1). 1).The Themain mainintrusive intrusiveunit unitthere thereisisanorthosite-bearing anorthosite-bearingdiabase diabase which signature directly to toBeaver BeaverRiver Riverdiabase diabasein inthe thenorthern northernBBC. BBC. Another be traced (racedby by its its aeromagnetic aemmagnetic signature which can can be phase porphyry, aaplagioclase-phyric Cabin Creek phaseisisthe theLeveaux Leveauzporphyry, plagioclase-phyricdiorite dioritethat thatisis very similar similar to the Cabin Creek porphyritic diorite diorileof of the the northern northernBBC. BBC. More Moremust mustbe belearned learnedof ofthe thewell-exposed well-exposedbut but incompletely incompletelymapped mapped subvolcanic subvolcanic intrusions too should should be be included included in in the the BBC. BBC. West intrusionsfarther farther northeast northeast of of the the project project area area to determine determine whether they too West -. . 42 �I southwest of of the the study study area, area,thick thick glacial glacial cover makes interpretation and southwest interpretation tenuous. tenuous. However, However, aemmagnetic aeromagnetic data integrated with shallow in a large area area covering integrated shallow drilling drilling and and rare tare outcrop in ig. 1) covering the central central Duluth Duluth Complex Complex (CDC, (CDC, F Fig. 1) suggest BBC-like sheeted intrusions. These suggest the presence of BBC-like Theseintrusions, intrusions, informally informally termed the Cloquet Cloquet Lake Lake layered series, seem to be enclosed merge, in part, part, with the the Houghlalimg Houghtaling Creek troctolite. enclosed in volcanic rock and seem to merge, troctolite. A A preliminary 1:100,000-scale 1: 100,000-scalegeologic geologicmap mapofofriris thisarea areawi will alsobebeshown shownatatthe theposter postersession. session. Very Verylittle littleisis ll also known of of the hypbyssal hypabyssal rocks rocks tentatively tentalively mapped mappedfarther farthersouthwest. southwest. REFERENCES CITED REFERENCES CITED Boerboom, T.B, and and Miller, Miller, J.D.. J.D., Jr.. Jr., in preparation. preparation, Geologic Geologicmap mapof of the theWilson WilsonLake Lakeand andparts partsof of the the Silver Silver Island Island Lake Lake Boerboom, T.B. and Toohey Lake quadrangles: Minnesota Minnesota Geological Survey Misc. Map Series, scale scale 1:24,000. 124,000. F.F. Schwartz, G.M., G.M., 1939, The The geology of of the anorthosites of of the Minnesota Minnesota coast coast of of Lake Superior: Superior: Grout, F .F. and SchwarU, Minnesota Geological Geological Survey Survey Bulletin Bulletin 28, 28, 119 119 p. Miller, J.D., J.D., Jr., the Split Split Rock Rock Point Point NE NE and and Silver Silver Bay Bay quadrangles, Lake County. County, Minnesota: Minnesota; Jr.. 1988, 1988, Geologic map of of the Minnesota Geological Survey M Misc. isc. Map Series, M-68, M-68. scale scale 1:24,000. 1:24,000. Miller, J.D., J.D., Jr., Jr., Green, JC., J.C., and andBoerboom, Boerboom, T.B., T.B.. 1989. 1989,Geologic Geologic map of the the IlIgen City quadrangle, quadrangle. Lake County, Comity, Minnesota: Misc. Minnesota: Minnesota Geological Survey M i . Map Series, Series, M-69, M-69, scale 1:24,000. 1:24,000. Miller, J.D., J.D., Jr.. Jr., Green, V.W., Geologic map map of of the Finland and Doyle Lake Green,J.C., J.C., Boerboom, Boeiboom. T.B., T.B., and Chandler, Chandler, V .W.,1993, Geologic quadrangles, Misc. Map Series. Series, M-73, scale quadrangles. Lake County, County. Minnesota: Minnesota; Minnesota Geological Survey Misc. scale 1:24,000. 1:24.000. Miller, Miller, J.D., J.D., Jr., Jr, Boerboom, Boeiboom. T.W, T.B., and and Jerde, Jerie. E.A., E.A., in in preparation. preparation, Geologic map of the the Cramer CraniCT and and Cabin CabinLake Lakequadrangles: quadrangles: Minnesota Misc. Map Series, scale M i i t a Geological Survey Misc. scale 1:24,000. 1:24,000. Miller, J.D.. J.D., Jr. and and Chandler, Chandler, V.W., V.W., in in review, review. Geology, Geology, petrology petrology and tectonic significance of the the Beaver BeaverBay Bay Complex, Complex. Miller. Minnesota: Geological Society of America Special Paper. Paper. northeastern Minnesota; Paces, J.B. and Miller. Miller, J.D., Paces. J.B. J.D., Jr., Jr.. 1993, 1993. Precise Precise U-Pb ages of Duluth Duluth Complex and related mafic intrusions, intrusions. northeastern Geochronological insiits insights to physical, paleomagnetic, and and lectonomagmatic tectonomagmatic processes Minnesota: Geochronological physical. petrogenetic, petrogenetic. paImmagnetic, processes associated with the the 1.1 1.1Ga Ga Midcontinent Midcontinent rift rift system: system: Journal Journal of of Geophysical Geophysical Research, Research v. 98, 98, p. 13,997-14.013. p. 13,997-14,013. wen I' t I Ik — C p 16 :1K Eastern r 7— BI3C MIDDLE PROTEROZOIC (Keweenawan Supergroup) J: SEDIMENTARY Rocgs S Bayfield and Oronto Gps INTRUSIVEROOCS Subvolcanic maflc rocks md. Beaver Bay Complex Duluth Complex (Z) /• Geologic Map Coverage 50 0 Kilometers Southern BBC M-68 - Silver Bay/Split Rock NE M-69 - fllgenCfty M-72 - Doyle Lake/Finland LM - Little Marais (in prep.) Northern BBC C-CL - Cramer/Cabin Lake (in prep.) S-W-T - Silver Island Lake/Wilson Lake/Toohey Lake (in prep.) CDC - Central Duluth Complex and western BBC? Figure of Figure 1. 1. Generalized Generalizedgeology geology of northeastern northeasternMinnesota showing showing the location of maps covering Complex. Solid covering the Beaver Beaver Bay Complex. Solid outlines outlines show show areas areasof of 124,000 124.000 geologic maps (published (publishedMGS MGS Miscellaneous Miscellaneous Map Series are indicated indicated by by MMnumber). number). Dashed Dashed outline shows the the central central Duluth Duluth Complex Complex study area area for which geologicmap mapis isin inpreparation preparation. which aa 1:100,000 1:100/100 geologic Granitoid rocks Gabbroic cumulates Troctolitic cumulates C....) Anorthositic cumulates Early gabbroic rock 41111m) Logan sills VolcArqlc Rocxs (2) Schroeder Basalts = PLV C) NSVG - Normal polarity €2) NSVG - Reversed polarity LOWER PROTEROZOIC (Animikie Group) Creywacke, shale 41 Iron—formation ARCHEAN Granite-Greenstone terrane =Graniteree ens tone terrane 43 �ASSESSMENT OF SPRING CREEK CREEKAQUIFERVULNER AQUIFER VULNERABILITY TO POLLUTION USINGDRASTIC, DRASTIC. WATER WATER ASSESSMENTOF -LUTION USING TESTING, MODELING, AND AND HISTORICAL TESTING, GROUNDWATER GROUNDWATER MODELING, HISTORICAL RECORDS: RECORDS: AA PROJECT PROJECT OF THE THE MTU MTU REGIONAL GROUNDWATER EDUCATION EDUCATION IN IN MICHIGAN MICHIGAN(GEM) (GEM)CENTER CENTER MILLER, MILLER, Scott Scott A.. A., Sr., Sf., School School of of Forestry Forestry and and Wood Products, Michigan Michigan Technological University, University, Houghton, MI 295 MI 49931-1 49931-1295 The Spring Creek weilfield wellfield supplies supplies approximately one-half of the public drinking water water supply supply for the City of Ironwood and Erwin Township in Michigan and and the City of Hurley, Wisconsin. Wisconsin. The origin of E. E. coil colicontamination wntamination in in two two of ofthe thewells wellswas wasinvestigated investigated by by the theMichigan Michigan Technological University Regional Regional Groundwater Groundwater Education Education in in Michigan Michigan (GEM) (GEM) Center. Center. ARC/ INFO and ERDASgeographicinformation ERDASlgeographic informationsystems systems(GIS) (GIS)aided aideddata dataanalysis analysisand andpresentation. presentation. aquifer vu1nerabilitymap.-implemented vulnerabilitymapçimplemented on ARCIINFO A DRASTIC aquifer ARCIINFO GIS, GIs, was created created to provide provide a regional perspective on relative vulnerability of aquifers to pollutants originating at the ground perspective relative vulnerability of aquifers to pollutants originating at theground surface. The seven seven DRASTIC DRASTIC parameters parameters are are Depth Depth to to water, water, Recharge, Aquifer type, Soil, Soil, surface. Topography (slope), (slope), Impact of the vadose zone, and hydraulic Conductivity. Potential sources vadose zone, and hydraulic Conductivity. Potential sources of pollution were mapped to identify areas of particular particular concern. concern. Surface Surfacewater water testing testing estabestablished the presence of FL coil and fetal streptococci in Spring Creek and septic effluent pollution E. coli and fecal streptococci septic effluent pollution records providprovidin a wetland at the headwaters. Michigan Department of Public Health (MDPH) records ed clear evidence of aa close hydraulic connection between Spring Creek and the upper close hydraulic connection the upper Spring Spring Creek aquifer. Groundwater quality quality declined declined when when mine mine wastewater wastewater entered entered the the creek and Creek and improved when the wastewater was diverted. MODFLOW 2-D modeling demonstrated that was diverted. MODFLOW 2-D modeling demonstrated that aa improved when pumping well well located located close close to to a creek in hydraulic to the aquifer can draw creek hydraulic connection connection to pumping water into the well. water of F. The presence presence of E. coil colt and and fecal fecalstreptococci streptococci in in Spring Spring Creek Creek at at the the wellfield wellfield isis apparently apparently contamination in the upstream wetland. wetland. Fecal wliforms coliforms and streptococci independent of sewage wntamination streptococci 3/4 mile mile downstream of the wetland. wetland. Wildlife and livestock along the were barely detectable 314 for indicator indicator organisms organisms reaching reaching the the wellifeld. wellfield. creek can account for -1 aquifer may may draw draw a significant amount amount of of creek water. Wells screened in the upper unconfined unconfined aquifer Preventing wntamination contamination of of Spring Spring Creek Creek.is therefore a priority. The DRASTIC is The DRASTIC map mapindicates indicates :high risk riskof the wellfield wellfield is at relatively 'high of contamination contamination by vertical vertical movement movement into into the the aquifer aquifer from the ground surface. An active rail line along the creek valley and over the aquifer is rail line over the aquifer is cause cause confined aquifer is is an an option, option, but but this this water water has a higher for concern. Drawing from the deeper ~nfined~aquifer used only when when mixed with softer water from concentration of dissolved solids and is presently used the upper aquifer. Drilling Drilling wells farther away away from from Spring Spring Creek Creek or or into intoaquifers aquifersnot not closely closely connected with with surface water is recommended. Should the MDPH designate the water entering recommended. as surface water, a treatment plant will be needed. needed. The best long-term option the affected wells as is to develop aa welihead protection plan that includes an alternative wellhead that includes alternative water water source. source, 44 �A A POSSIBLE POSSIBLE METASOMATIC METASOMATIC ORIGIN FOR THE THE LONGNOSE LONGNOSE OXIDE-RICH OXIDE-RICH ULTRAMAFIC BODY ULTRAMAFIC BODY MINER, MINER,Owendolyn GwendolynC., C., Department Departmentof of Earth Earth and and Planetary Planetary Sciences, Sciences, Washington Washington University, University, St. Louis, MO 63130 63130 The TheLongnose Longnosebody bodyisisaatitanifemus titanifemusoxide-rich oxide-richultramafic ultramafic body body hosted hosted by by the the Partridge Partridge River intrusion of the troctolite series of the Duluth Complex. The body is located Complex. The is located 83 83 km north of River intrusion of the troctolite series Duluth 30,T. T. 59 59N., N., R. R 13 13W. W.ItItlies liesalong alongthe the trace trace of aa normal normal fault faultthat that cuts cuts two two Duluth in insection section30, other oxide-rich ultramaflc bodies, the Longear and 'Section 17' (Fig. 1). This fault offsets This other oxiderich ultramafic the Longear and 'Section 17' (Fig. sedimentary units, bringing bringing the the Biwabik Biwabik Iron Iron sedimentarystratigraphy, stratigraphy, but not the the Partridge River igneous units, Formation into contact with the Virginia Formation (Severson, 1988). Formation into contact with the Virginia Formation (Severson, 1988). Linscheid funnel, 760 760 m m long, long, up up Linscheid(1991) (1991)described describedthe theLongnose Longnosebody body as as an asymmetrical asymmetrical funnel, to 490 m wide, and with a maximum thickness of 167 m. The body is gradationally zoned inward and of 167 m. The is zoned inwanl to 490 m from oxide dunite, dunite, which hosts discordant discordant from an an oxide oxideclinopyroxenite clinopyroxemte to to an an oxide oxide peridotite peridotite to an oxide massive oxide zones (>80% oxides). In many cases, olivine is completely replaced by serpentineserpentineIn many cases, is completely replaced by massive oxide zones (>80% group minerals. The ilmenite-to-magnetite ratios vary among the distinct units within the group minerals. The ilmenite-to-magnetite ratios vary among distinct units Longnose is the the dominant dominant oxide m mineral. ineral. Longnoseand andwithin withinthe the massive massive oxide oxideunit unit itself, but ilmenite is Most magnetite grains show exsolution lamellae of spinelss and ilmenite. Secondary hydrous Most magnetite grains show cxsolution lamellac. spinelss and ilmenite. hydrous mineral to zones of intense fractures. mineral assemblages assemblagesoccur occur in in all all rock rock types types and and are not limited to There of the theLongnose Longnosebody. body. if Longnose Thereare aremany many questions questions regarding the origin of If the Longnose body is an source of of the the low-Sic, low-Si02,high-Fe-Ti high-Fe-Timelt? melt? If if it is not an intrusion, intrusion, an intrusion, intrusion, what is the source does crystal mush or after does itit represent representigneous igneousmaterial material that that was was reworked while still aa crystal crystallization or solidified material, fluids fluids must must crystallization was was complete? complete? Whether Whetherthere therewas was aa crystal mush or have been present present in in the the reworked areas. What Whatare are the the composition and origin of these fluids? Although concentration of platinum-group Althoughthe theLongnose Longnose body body has has no no known known appreciable appreciable concentration platinum-group elements, Bushveld. Both elements, itit resembles resembles the the platinifemus platinifemus dunite dunite pipes of the Bushveld. Both the thepipes pipes of the the Bushveld cores, which which host host massive massive oxide oxide zones, zones, Bushveld and and the the Longnose Longnose body consist of Fe-rich dunite cores, and and marginal marginal pymxenitic pyroxenitk and and gabbroic gabbmic rocks. rocks. The Thecomposition compositionof of olivine olivine from from the the Bushveld Bushveld pipes pipes ranges from Fow Fo93 to toFFog4; theLongnose, Longnose,it itranges ranges FoototoFofi6 Fo (Linscheid, frfrom om Fogo (Linscheid, 1991). 1991). w ; ininthe Schiffries Driekop pipe in the Bushveld formed by infiltration Schifflies(1982) (1982)suggested suggestedthat the the Driekop metasomatism, of which which is the the formation of a metasomatism, one oneof of the the most most important important characteristics of monomineralic monomineralicrock rock such such as as dunite (Korzhinskii, (Korzhinskii, 1970). The The Longnose Longnose body body has has aa conspicuous conspicuous dunite is in in turn turnsurrounded surrounded by byttoctolitic troctoliticrocks. rocks. In dunite core, core, which which grades grades outward to pyroxenite and is this Longnose body and this context, context, itit seems seemsreasonable reasonable to to suggest suggest aa metasomatic metasomatic model for the Longnose and to to exnlore possible nossible lines of evidence. explore lines evidence. r _____ _Ñ_. _ _ of ._ _ In the with noritic noritic host rocks and produced the Driekop Driekop pipe, pipe, metasomatizing metasomatizing fluids fluids reacted with olivine-rich rocks (Schiffries, (Schif&ies, 1982). Schiffries' Schif&ies'model modelisis that that fluids fluids passed passed through through the the troctolitic troctolitic olivine-rich rocks rocks removing appropriate to produce producedunite. dunite. These components were were rocks removing appropriate components in order to transferred occurrence of such transferred to to secondary minerals. In Inthe theLongnose Longnosebody, body, the occurrence such secondary minerals clinopyroxene indicate indicate the presence of a minerals as as chlorite, chlorite, serpentine, serpentine, amphibole, amphibole, and and Ti-rich clinopyroxene fluid fluid that that transported transportedat atleast least calcium, calcium, iron, iron,titanium, titanium, and and water. if were involved, then how howwere weretheir theireffects effectsconcentrated concentratedin inone one If metasomatizing metasomadzing fluids fluids woe area? fault that that connects connects three three oxide-rich, oxide-rich, area? One Onepossible possibleanswer answerlies liesin in the theexistence existenceof aa normal fault ultramafic Formation, which could could be be aa Onone oneside sideof of this thisfault faultis is the the Biwabik Iron Formation, ultramafic bodies. On wide actinolite actinolite source of of Fc-rich Fe-rich fluids. fluids. Also, has noted notedthe thepresence presenceofof<2 cm wide Also,Linscheid (1991) has Q cm veins in the Longnose body. body. In from area.surrounding surrounding the Longnose In the drill core f rom the Longnose body there the area All of these ffractures could are are numerous numerousmillimeter-scale mdkmem-scale fractures fractmaand andcross-cutting mss-cuttiug features. featunx. A ll ofthese ractu~ could ~ serve as conduits conduitsfor forpercolating percolating fluids. serve as Present on: possible possible correlation of ilmenite-toihnemte-toPresent research research on on the the Longnose Longnose body is focused on: magnetite rock type within the body, electron microprobe microprobe magnetite ratios ratios with with respect respect to rock type and and spatial position within -~ .à ...‘. ~ . 45 �S analyses on exsolved and unexsolved ilmenite and magnetite grains to provide T-f02 esfintnes of the formation and reequilibration conditions in the Longnose body, and electron microprobe analyses of secondary minerals to place temperature and compositional constraints on the possible metasomatizing fluids. Fig. 1. Location of three oxide-rich ultramafic bodies along the trace of a normal fault (after Severson, 1988). Oxide-richultr-c bodies Virginia Formation 0 Duluth Complex N t REFERENCES CIT ED Korzhinskii, D.S., 1970, The theory of metasomatic zoning: London, Oxford Univ. Press, 162 p. Linscheid, E.K., 1991, The petrography of the Longnose peridotite deposit and its relationship to utelithithtomplexflinpubL MS. thesis, UidMinn., Duluth, MN. d SchifiSts, CM, 1982, The peirogenesis of a plañniferous dunite pipe in the nskweA. Cotr\er Infiltration metasomatism by a chloride solution: Ecoa GeoL, v. 77, p. 1439-1453. Severson, 1sf., 1988, Geology and structure of a portion of the Partridge River intrusion: A progress report: Natural Resources Research Institute, Univ. Minn., Duluth, Tech. Rept., NRRI/GMIN-TR-88-08, 78 p. 46 �HEAVY MINERALS FROM GLACIOFLUVIAL GLACIOPLUVIAL SEDIMENTS SEDIMENTS IN MINNESOTA MINNESOTA M i o t a Department Department NELSON, Sherry (prepared abstract), LAWLER, Tom and LEHR, J.D., Minnesota of Natural Resources, Division of Minerals, 1525 3rd Avenue E., Hibbing, of Natural Resources. of Minerals. Avenue E.. Hibbh. Minnesota M i t a , 55746; THEOBALD, Paul, RYDER, Jean, SUTLEY, Stephen andTRIPP, TRIPP, Richard, Richard, U.S. U.S. '55746;THEOBALD,P~U~,RYDBR, Jean, SUTLEY, Stephenand Geological Survey, Survey, Branch Branch of of Geochemistry, M .S. 973, 973, Eox Geochemistry, M.S. Box 25046, Federal Federal Center, Center, Geological 80225-0046 Denver, Colorado Colorado 80225-0046 A study which which analyzed analyzed the theheavy-mineral heavy.-Qiinei'alfraction fraction of ofnortheastern northeasternprovenance provenanceglaciofluvial glaciofluvial sediments sediments was conducted by by the the Minnesota Minnesota D Department of Natural Resources, Division of Minerals, in cooperation cooperation epartment of,NaQ@ Resources,Diykiiof Minerals, in U.S. Colorado. Eighty-eight samples samples were were with the u .S.GGeological eo~ogicalSurvey, SurveyBranch ,Branchofof Geochemistry,&Denver, m ~ r ,Colorado. , collected from from ggravel pits across a broad area of Minnesota, sieved to pass separated (sp r a d pitsacrossa Minnesota,,sieved pass. 0.83mm, 0.83mqseparated (sp gr gr collected —2.85) into three heavy-mineral fractions and then examined geochemically and mineralogically. -2.85) into threeheavy-m+ral fractions amj then .&m@ed geochemically and mineralogidy. .. A summary of the o fsample sample preparation preparation and and analysis, analysis, the the s.ymmy of the sampling samplingstrategy, strategy, the the methods of geological characteristics of of the samples, and the samples,and the geochemical geochemical and mineralogical mineralogical data for for the theheavyheavymineralconcentrate and &the paramagnetic paramagneticand &nonmagnetic nonmagnetic heavy-mineral fractions is ispres.&ntedin Openmineral presented in Open- concentrate file and others, file Report Remit 284 284 (Nelson ( N e wMri often. 1992). 1993. The geochemical and mineralogical data were analyzed by statistical techniques including basic statistics, correlations, histograms, and multivariate factor analysis of the individual data sets and by glacial the data s&. sets. Spatial geochemical and mineralogical data a and glacial lobe within thedata Spatialdata dataplots plots portraying portrayingthe thegeochemical nd .. the statistical results were prepared. prepared.: Fairly strong evidence of :the the local derivation derivation of aa significant significant fraction of of the the heavy heavy minerals, minerals,, particularly fraction, areindietfted are indicated in in the thespatial spatialdataplots. data plots.. Many of the patterns particularly those those iin nthe nonmagnetic fractian, Manyof variation in the geochemical mineralogical data define discrete clusters of samples definediscrete clsamples with with similar similar of variaf~on in&e geochemical and @uip&~&gieal The platinum group, with fire assay gold values, forms an anomaly which is characteristics. characteristics. platinum group,' fire assay gold valyes, an anomaly which is most most enriched along and southwest of the contact of the Duluth Complex. High concentrations consistently ~igh'concentrations . P , of andalusite or sillimanite occurred only in samples straddling the contact of the theintrusive intrusiveDuluth Duluth Complex with the adjoining metasediments. Several results show samples rich in in precious, base base metals, metals, and/or associated multi-element associations clustering along and just to the justto thewest westof of the theMississippi MississippiRiver. River. Three "hot spots" were identified: 1) sample number 23960 is enriched in elements and mbnlsusually minerals usually extremely differentiated granites, 2) sample number 23935 his has extreln6:characteristics extreme characteristics that associated with exf&e$differentiatedgrani~. 2)samplebnumber deposits, and 3) sample number typical would be attributed attributed to base metal metaldeposW,and 3)shple number 23908 23908 has values which exhibit exhibittypical anomalous characteristics for the platinum group assemblage. Many of the discrete clusters defined for @platinum group assemblage. Many of the' discrete clusters definedinin would the results exhibit characteristics expected from bedrock results exhibit characteristics expected bedrock in the thevicinity. vicinity. The results results also also show show strong geochemical and mineralogical evidence mineralization in (tadmineralogical evidence for mineralionin several areas previously f + ~ r * @ s~ not known (mownto to be mineralized.. . . surprisingly A report an interpretation of the results from A reportthat that will will present present.an interpret&g-of the,&ults fromthe thegeochemical gepdwnhl and and mineralogical min@ogicd the statistical data analysis, and the resultant spatial data plots is being prepared pl@,,b being prepared as as aacooperative cooperative data, +$a. analysis,& the resultant effort by a team of scientists the DNR and the This report will be available in July mm of from the DNR@ die USGS. This report w i l l be available 4 July 1994 1994 data, from the DNR, Division of Minerals, Hibbing, Minpesota. from the DNR,~ i v i s i o nof 'M , iee&, Hibbing, M i*. ~ *.. , . . . . . ,. ' ~~ Reference: ~ : , . .. . ,. L., Sutley, S .J., and Tripp, R.B., 1992, Chemical and mineralogical analyses and geological .,. Nelson, S. S.L., Sutley;SJ., characteristics of heavy minerals from glaciofluvial sediments in Minnesota; test and pilot study . .., data: Minnesota Department of Natural Resources Open-file Report 284, lOOp. A cooperative project with the U.S. Department of the Interior, Geological Survey, Denver, Colorado. . . 47 P �Geochemistry of the Geochemistry the Kallander Kallander Creek Creek Volcanics, Volcanics, 1.1 Ga Midcontinent Rift System, Wisconsin and Wisconsin and Michigan Michigan S.W. Nicholson,1 L.G. L.G. Woodruff,2 Woodruff? and and W.F. W.F. Cannon1:1 Cannon1: uSGS, S.W. USGS, National National 2 2280Woodale Woodale Dr., Dr., Mounds Mounds View, Center MS 954, Reston V VA A 22092; 22092; USGS, USGS, 2280 View, Center MN MN 55112 55112 (KCV)isisthe theyounger youngerofoftwo twounits units that that compose the The Kallander Creek Volcanics Volcanics (KCV) Powdermill Group, the earliest volcanic rocks to be erupted from the Powdermill the earliest volcanic erupted from the 1.1 1.1Ga in Wisconsin Wisconsin and and Michigan. Michigan. The system (MRS) (MRS)in The older older volcanic volcanic Midcontinent rift system rocks in the Powdermill Group are the Siemens Creek Volcanics (about 1.5 km the Powdermill Group are the Siemens Creek Volcanics (about 1.5 km dominated by high-alumina flood basalts which were probably thick), dominated probably fissure fissure fed. fed. KCV overlieithe-Siemens+Creek overliethe:SiemensCreek Volcanics Volcanics and are are composed composed of of aa sequence sequence of of The KCV andesite,and The KCV rhyolite'2-4-km-thick.~The KCV has been postulated to to be be the the basalt, andesite, andrhyolite'2-41cm-thick. partly eroded Ma erodedremnant remnantof ofaacentral centralvolcano volcanoerupted eruptedbetween betweenabout about1108 1108and and1102 1102Ma (Cannon and others, 1993). 1993). The outcrop outcrop belt extends more than 100 100 km along strike, but the the true true extent extent of of the the formation formation is unknown because it is overlain by younger rocks at both both ends. ends. The basalts basalts and of the the KCV KCV have average 5i02, S i a , P205, and and FeO FeO and basaltic basaltic andesites andesitesof contents somewhat higher than for the underlying underlying basalts basalts of the the Siemens Siemens Creek Lake Volcanics and Porcupine Porcupine Volcanics and the overlying overlying basalts basalts of the fee Portage Portage Lake Volcanics, whereas whereas MgO MgO and and CaO CaO contents contentsare are somewhat somewhatlower. lower. The most striking Volcanics, striking characteristic of of the KCV KCV is is the the high high average T Ti02 characteristic i e content (about 3.5 wt %) %) compared Portage Lake Volcanics to that that of of the theSiemens SiemensCreek CreekVolcanics Volcanics (about (about1.5-2.5 1.5-2.5 wt %), %), Portage 1.7-2.7 wt wt %), %),and and Porcupine Porcupine Volcanics Volcanics(about (about2.2 2.2wt wt%). %). There There appear appear to be (about 1.7-2.7 5i02 content from basalt through the intermediate no large compositional gaps in Si02 intermediate of the KCV. KCV. Average trace element compositions of and more more felsic felsic volcanic rocks of Kallander Creek basalts and basaltic andesites and basaltic andesites show show significant significant differences differences in Lake, and comparison to average average basalt basalt compositions compositions of the the Siemens Creek, Portage Lake, KCV have lower contents contents of compatible trace trace elements elements Porcupine Volcanics. Volcanics. The The KCV such as Cr and and Ni Ni and andhigher highercontents contentsof of incompatible incompatibletrace traceelements elementssuch suchas asNb, Nb,Y, Y, REE, Hf, and Th than many other basalts, except for a few individual flows in both REE, Hf, and Th than basalk, for a few individual the Porcupine PorcupineVolcanics Volcanics and•the and the basalSiemens basal SiemensCreek CreekVolcanics. Volcanics. In detail, distinctive trace element characteristics make it possible to recognize distinctivetrace-element two suites suites of volcanic rocks within the Kallander Creek Volcanics. Volcanics. Both Both suites suites range from basalt to intermediate rocks ançl rhyolite and are indistinguishable in and rhyolite and are major element composition. The Thelowermost lowermost1.5 1.5 km km of of the theKCV KCV consist consist of of basalt basalt with minor andesite and rhyolite, all of which have steep straight REE patterns andesite and rhyolite, all of which have steep straight REE patterns (basalts and andesites andesites have have (Ce/Yb)= (Ce/YbIn=8.0-10.6; 8.0-10.6; rhyolites rhyolites have have (Ce/Yb)= (Ce/YbIn=11.2-11.4). 11.2-11.4). The upper part of the Kallander Creek contains all three rock types as well, but part of the Kallander Creek contains as REE patterns are much less steep steep and and LLandesites dominate. The Theslopes slopesof of these these REF shaped (basalts and andesites have (Ce/Yb)= 2.9-5.8; rhyolites have (Ce/Yb)= 3.4shaped (basalts (Ce/Yb)n= 2.9-5.8; rhyolites have (Ce/Yb)n= 3.4 7.7). Similar distinctions between the upper and lower suites 7.7). suites can be made made by using using ratios. For of basalts and andesites other trace element ratios. For example, the lower group of 48 �have Y/Nb= 0.8 and Ta/Th= Ta/Th' 0.6, 0.6, whereas whereas the upper group group of basalts and andesites have Y/NbY/Nb= 2.0 2.0 and and Ta/Th= Ta/Th 0.3. 0.3. This work, in conjunction with with previously previously gathered gathered Nd Nd and Pb isotopic data, data, documents fluctuations in magma sources and eruptive style during development development of the MRS in Wisconsin Wisconsinand and Michigan. Michigan. Volcanism Volcanismbegan beganwith with the the eruption eruption of of a MRS in thin discontinuous group of basalts that contain clinopyroxene phenocrysts and are discontinuous group of basalts that contain clinopyroxene generally rich in incompatible Ti02. These These rocks form the incompatible trace elements, including TiO2. basal unit of the Siemens Creek Volcanics and are postulated to unit of the Siemens Volcanics and are postulated be fissure-fed flood basalts derived by small degrees of of partial partial melting meltingwithin withinthe themantle mantleplume plume that that led led to the development of the MRS (Nicholson and Shirey, 1992). Overlying this basal Shirey, 1992). Overlying the development of the MRS unit, most flood basalts, basalts, which which are poorer most of of the the Siemens Siemens Creek Creek Volcanics Volcanics comprise flood in incompatible trace element abundances and and which which were were most probably derived from plume melts probably augmented by the addition of of melts from another source, possibly subcontinental lithosphere (Nicholson and subcontinental lithosphere (Nicholson and Shirey, Shirey, 1992). 1992). The lower lower unit unit of of the the Kallander Kallander Creek Creek Volcanics Volcanics is broadly similar in incompatible trace element contents contents to the basal Siemens SiemensCreek Creekunit unit and, and, thus, thus, may be the result of of an additional additional small small degree degree of partial melting from deep within the plume. However, the major element However, the major element compositions compositions and low compatible compatible trace element content of of the lower KCV suggest that that this this batch batch of of melt melt underwent underwent some KCV suggest fractionation before before eruption. eruption. The upper Kallander Creek unit, with its The upper Kallander its abundance abundance of rocks, is is most most similar similar to to the younger Porcupine of intermediate and and felsic felsic volcanic rocks, Porcupine Volcanics, which is is considered a broad central volcano at the top top of of the the volcanic volcanic Volcanics, which section (Nicholson and others, others, 1991). 1991). By By analogy with the the Porcupine PorcupineVolcanics, Volcanics, the upper upper KCV KCV is most likely derived by mixing of crustal and mantle melts. (Note, the isotopic isotopic analyses needed to to constrain constrain hypotheses hypotheses for for the the origin origin of of the the KCV KCV are are in in preparation). Overlying Overlyingthe theKallander KallanderCreek Creek Volcanics Volcanics are the Portage Lake highalumina alumina fissure-fed flood basalts, most probably derived by shallow melting within the 1990), and and finally finally by by the thePorcupine PorcupineVolcanics. Volcanics. the plume plume(Nicholson (Nicholsonand andShirey, Shiiey,1990), Cannon, R.E., Peterman, Z.E., Z.E., and Davis, Davis, D.W., D.W., Cannon, W.F., W.F., Nicholson, S.W., S.W., Zartman, R.E., 1993, The Kallander Creek Volcanics--A remnant of the Keweenawan central The Kallander Creek Volcanics-A of Keweenawan central volcano centered centerednear nearMellen, Mellen,Wisconsin Wisconsin[abs.]: Labs.]: Institute on Lake Superior Superior Geology, Proceedings, v. 39, Geology, Proceedings, v. 39, p. p. 20-21. 20-21. Nicholson, L.G.,1991, 1991, The The Nicholson, S.W., S.W., Schulz, Schulz, K.J., K.J., Cannon, W.F., W.F., and and Woodruff, Woodruff,L.G., Porcupine Mountains area, Michigan--A Keweenawan central volcano? Porcupine Mountains area, Michigan~AKeweenawan central volcano? [abs.]: [abs.]: Institute 79-81. Instituteon onLake LakeSuperior SuperiorGeology, Geology, Proceedings, Proceedings, v. v. 37, 37, p. 79-81. Nicholson, S.W., 1990,Midcontinent Midcontinentrift riftvolcanism volcanism in in the Lake S.W., and Shirey, S.B., S.B., 1990, Superior Superior region: region: Sr, Nd, and and Pb Pb isotopic isotopic evidence evidence for a mantle mantle plume plume origin: origin: Journal p. 10851-10868. 10851-10868. Journalof of Geophysical GeophysicalResearch, Research,v. v. 95, 95, p. 1992, Nd 1.1Ga Ga Midcontinent Midcontinent ,1992, Nd and andPb Pbisotopic isotopicevolution evolutionof of basalts basalts of of the the1.1 rift: rift: evidence evidence for aa region-wide region-wide model model for for plume-lithosphere-asthenosphere plume-lithosphere-asthenosphere interaction 7 p. p. interaction[abs.]: [abs.]: U.S. U.S. Geological Geological Survey SurveyOpen-File Open-FileReport Report92-525, 92-525,7 49 �Geochemistry of the Kallander Creek Volcanics, 1.1 Ga Midcontinent Rift System, Wisconsin and Michigan S.W. Nicholson,1 L.G. Woodruff,2 and W.F. Cannon1:1 USGS,Nationa National 0x1': USGS, 2 Center MS 954, Reston VA 22092; USGS, 2280 Woodale Dr., Mounds View, ' MN 55112 The Kallander Creek Volcanics (KCV) is the younger of two units that compose the Powdermill Group, the earliest volcanic rocks to be erupted from the 1.1 Ga Midcontinent rift system (MRS) in Wisconsin and Michigan. The older volcanic rocks in the Powdermill Group are the Siemens Creek Volcanics (about 1.5 1cm thick), dominated by high-alumina flood basalts which were probably fissure fed. The KCV overliethe-SiemenszCreelc,Volcanics and are composed of a sequence of basalt, andesite; and: rhyolite:24km thick;. The KCV has been postulated to be the partly eroded remnant of a central volcano erupted between about 1108 and 1102 Ma (Cannon and others, 1993). extends more more than than 100 100 kkm along strike, strike, 1993). The outcrop belt extends m along but the true extent of the formation is unknown because it is overlain by younger rocks at both ends. The basalts and basaltic andesites of the KCV have average Si02, P205, and FeO contents somewhat higher than for the underlying basalts of the Siemens Creek Volcanics and the overlying basalts of the Portage Lake Volcanics and Porcupine Volcanics, whereas MgO and CaO contents are somewhat lower. The most striking characteristic of the KCV is the high average Ti02 content (about 3.5 wt %) compared to that of the Siemens Creek Volcanics (about 1.5-2.5 wt %), Portage Lake Volcanics Porcupine Volcanics (about 2.2 wt wt %). There appear appear to be (about 1.7-2.7 wt wt %), %), and Porcupine %). There no large in S5i02 from basalt basalt through through the intermediate i a content from arge compositional gaps in and more felsic volcanic rocks rocks of of the the KCV. KCV. Average Average trace trace element element compositions compositions oof Kallander in and basaltic andesites show significant differences in ander Creek basalts and comparison to average basalt compositions of the Siemens Creek, Portage Lake, and Porcupine Volcanics. The KCV have lower contents of compatible trace elements such as Cr and Ni and higher contents of incompatible trace elements such as Nb, Y, REE, Hf, and Th than many other basalts, except for a few individual flows in both the Porcupine Volcanics .and the basal Siemens Creek Volcanics. In detail, distinctive trace element characteristics make it possible to recognize two suites of volcanic rocks within the Kallander Creek Volcanics. Both suites range from basalt to intermediate rocks ançl rhyolite and are indistinguishable in major element composition. The lowermost 1.5 km of the KCV consist of basalt with minor andesite and rhyolite, all of which have steep straight REE patterns (basalts and andesites have (CeIYb)8= 8.0-10.6; rhyolites have (CeIYb)n= 11.241.4). The upper part of the Kallander Creek contains all three rock types as well, but andesites dominate. The slopes, of these REF patterns are much less steep and Lshaped (basalts and andesites have (Ce/Yb)= 2.9-5.8; rhyolites have (Ce/Yb)n= 3.4 7.7). Similar distinctions between the upper and lower suites can be made by using other trace element ratios. For example, the lower group of basalts and andesites 50 �whereasthe theupper uppergroup group of of basalts basalts and and andesites andesites have Y/Nb= 0.8 0.8 and Ta/Th=' Ta/Th= 00.6, .6,whereas have Y/Nb= Y/Nb= 2.0 and Ta/Th= 0.3. 2.0 and Ta/Th= 0.3. with previously previously gathered gathered Nd Nd and and Pb isotopic data, This work, in conjunction conjunction with documents fluctuations in in magma magma sources sources and and eruptive eruptive style style during during development of the MRS in Wisconsin Wisconsinand and Michigan. Michigan. Volcanism Volcanismbegan beganwith with the the eruption eruption of of a of MRS in thin discontinuous group of basalts that contain dinopyroxene clinopyroxene phenocrysts phenocrystsand and are are TiC2. These rocks form the generally rich in incompatible trace elements, including Ti02. basal unit of the Siemens Creek Volcanics and are postulated the Siemens Volcanics and are postulated to be fissure-fed flood of partial partial melting meltingwithin withinthe themantle mantleplume plume that that led led basalts derived by small degrees of and Shirey, Shirey, 1992). 1992). Overlying this basal to the development development of of the the MRS MRS (Nicholson and unit, most of the Siemens Creek Volcanics comprise flood basalts,which which are are poorer poorer the Siemens Volcanics comprise flood basalts, element abundances abundances and and which which were were most most probably derived in incompatible trace element from plume melts probably. augmented by the addition of melts from another probably augmented-by,the addition of melts from 1992). source, possibly mssiblv subcontinental subcontinental lithosphere lithosohere (Nicholson (Nicholson and and Shirey, Shirev. 1992). The lower unit of the Kallander Creek Volcanics is broadly similar in he &it the Kallander creek ~ilcanicsis broadly similar in. incompatible trace trace element element contents contentsto to the the basal basalSiemens SiemensCreek Creekunit unitand, and,thus, thus, may may incompatible be the result of an additional small degree of partial melting from deep within the of an additional of melting from deep plume. However, plume. However,the themajor major element element compositions compositions and low compatible compatible trace element content of the lower KCV suggest that this batch of melt underwent some KCV suggest that this batch of melt fractionation before before eruption. eruption. The upper Kallander Creek Creek unit, unit, with with its abundance of intermediate and felsic volcanic rocks, is most similar to the younger rocks, is most similar to the younger Porcupine and felsic Volcanics, which isis considered considered aa broad broad central central volcano volcanoat at the the top top of of the volcanic Volcanics, which section (Nicholson and others, 1991). By analogy with the Porcupine Volcanics, the 1991). By analogy with Volcanics, the of crustal and and mantle melts. (Note, the upper KCV KCV is most likely derived by mixing of of the KCV are in in isotopic analyses needed to constrain hypotheses for the origin of KCV are preparation). Overlying preparation). Overlyingthe theKallander KallanderCreek Creek Volcanics Volcanics are the Portage Lake highbasalts, most most probably probablyderived derived by by shallow shallow melting melting within within alumina fissure-fed flood basalts, the plume 1990), and finally by the Porcupine Porcupine Volcanics. Volcanics. plume (Nicholson (Nicholson and andShirey, Shirey, 1990), Zartman, R.E., Peterman, Peterman, Z.E., Z.E., and and Davis, D.W., D.W., Cannon, W.F., W.F., Nicholson, S.W., S.W., Zartman, 1993, The Kallander Creek Volcanics--A remnantofofthe the Keweenawan Keweenawan central central 1993, Volcanics~Aremnant volcano centered near Mellen, Wisconsin [abs.]: Institute on Lake Superior centered near Mellen, Wisconsin [abs.]: Institute 39,p. Geology, Proceedings, v. 39, p. 20-21. 20-21. Nicholson, S.W., Schulz, K.J., Cannon, W.F., and and Woodruff, L.G., L.G., 1991, The The S.W., K.J., Cannon, W.F., Porcupine Mountains Mountains area, area, Michigan--A Michigan-A Keweenawan central volcano? [abs.]: [abs.]: Institute on Lake Superior Geology, Proàeedings, v. 37, 79-81. Institute on Lake Superior Geology, Proceedings, 37, p. 79-81. Nicholson, S.W., 1990,Midcontinent Midcontinentrift riftvolcanism volcanism in in the Lake S.W., and Shirey, S.B., S.B., 1990, Superior region: Sr, Nd, and Pb isotopic evidence for for a mantle plume plume origin: origin: Journal 95,p. 10851-10868. Journal of of Geophysical GeophysicalResearch, Research, v. 95, p. 10851-10868. 1992, Nd and Pb of basalts basalts of of the the 1.1 Ga Midcontinent Midcontinent ,1992, Pb isotopic isotopic evolution of 1.1 Ga rift: evidence for a region-wide rift: region-wide model for plume-lithosphere-asthenosphere plume-lithosphere-asthenosphere interaction [abs.]: 7 p. 92-525,7 [abs.]: U.S. U.S. Geological Survey Open-File Report 92-525, interaction p. 51 �EXPLORATION AND MINING MINING ACTIVITY EXPLORATI ON AND ACT1 VI TY IN I NNORTHWESTERN NORTHWESTERN ONTARIO ONTARI 0 0' MarkS.,S., Ministry Ministry of 0' BRIEN, BRIEN, Mark of Northern NorthernDevelopment Development and and Mines, Mines, Suite B002, 435 James St. South, Thunder Bay ON P7E 6E3 Suite 435 James St. South, Thunder Bay ON P7E 6E3 The The mineral mineral' sector s e c t o r in i n Ontario Ontario provided provided an an estimated estimated 18,244 18,244 direct jobs and produced products with a total Canadian dollar d i r e c t jobs and produced products with a t o t a l Canadian dollar value billion $5. 1 b i l l i o n in i n 1993. 1993. value of of $5. Four Canada iin were from Four of of the t h e top t o p gold gold producers producers iin n Canada n 1993 were from northwestern Ontario: Williams Mine (492,251 oz), Golden Giant northwestern Ontario: Williams Mine (492,251 o z ) , Golden Giant Mine oz) and and tthe Mine (422,528 (422,528 oz), oz), Campbell Campbell Mine Mine (300,472 (300,472 oz) h e David David Bell Bell Mine (215, 188 oz). Mine (215,188 0 2 ) . This mines and and advanced advanced This poster p o s t e r displays displays the t h e producing producing mines mineral exploration projects in the northwestern portion of the the mineral e x p l o r a t i o n p r o j e c t s i n t h e northwestern p o r t i o n of Province of Ontario. The base map is a collage of the Bedrock Province of Ontario. The base map i s a c o l l a g e of t h e Bedrock Geology Geology Map Map of of Ontario. Ontario. Currently tthere h e r e aare r e 7 producing gold mines, 2 base metal mines, 1 platinum group mines, 2 base metal mines, 1 platinum group metal metal mine, mine, 66 quarries, 2 peat moss producers, 5 amethyst mines and 99 amethyst q u a r r i e s , 2 p e a t moss producers, 5 amethyst mines and amethyst producers in the region employing approximately 2700 people. producers i n t h e region employing approximately 2700 people. Quarry crushed dimension stone, stone, I1 crushed Quarry producers producers consist c o n s i s t of of 22 dimension granite, 1 quartz, 1 diabase and 1 soapstone producer. There quartz, 1 diabase and 1 soapstone producer. granite, are also 5 projects in the advanced exploration stage. a r e a l s o 5 p r o j e c t s i n t h e advanced exploration s t a g e . Representative of Northwestern Ontarioaare on display. display. Representative samples samples of Northwestern Ontario r e on A statistical summary booklet that tabulates regional data A s t a t i s t i c a l summary booklet t h a t t a b u l a t e s r e g i o n a l d ata such as reserves, grades, location, ownership and development is a s reserves, grades, location, is available free of charge. Many other free brochures are also a v a i l a b l e f r e e of charge. o t h e r f r e e brochures a r e a l s o available. available. 52 �PRELIMINARY SOURCE-ROCK EVALUATION OF PRELIMINARY SOURCE-ROCK AND AND MATURITY MATURITY EVALUATION OFTHE THE PRECAMBRIAN PRECAMBRIAN NONESUCH NONESUCHFORMATION FORMATIONIN INTHE THETERRA TERRAPATRICK PATRICK#7-22 #7-22 BOREHOLE, MIDCONTINENT BAYFIELDCOUNTY. COUNTY, WISCONSIN WISCONSIN RIFTSYSTEM, SYSTEM. BAYFIELD BOREHOLE. MIDCONTINENTRIFT' - James G. and and BURRUSS, C., U.S.~Geological PALACAS, James BURRUSS, ~Robert o b e rC., t U.S. e o l o ~ i c aSurvey, l ' s u r vBox e~, Denver, CO 25046, MS971, Denver, CO80225 80225 A wildcat wildcat well, westofofAshland, Ashland, Wisconsin, Wisconsin, was well,Terra TerraPatrick Patrick#7-22, #7-22, about about88ml mi(13 (131cm) km) west recently drilled drilled to Proterozoic Keweenawan Keweenawan to test test the the petroleum petroleum potential potential of Middle Proterozoic rocks in the Midcontinent pyrolysis analysis analysis was was performed performed on MidcontinentRift Rift System. Rock-Eval Rock-Eva1 pyrolysis m) section section of of the the Nonesuch Nonesuch 25 samples, 22 of which were were from from the the 436-foot 436-foot (133 m) Formation. (3m) m)interval. interval. Total organic organic Formation. Each Eachsample samplewas wasaacomposite compositeof of aa 10-foot 10-foot (3 carbon and averaged wt. % % and averagedabout about0.1 0.1 carbon (TOC) (TOO content content ranged rangedfrom fromessentially essentiallyzero zeroto to0.44 0.44 wt. %. The above values, however however should should be be considered consideredminimum. minimum. Although wt. %. Although special special' care was taken to remove drilling mud contaminants contaminants and larger larger sized sized chips chips of reddish reddish brown brown (oxidized) (oxidized)caved caved particles, particles, variable variable amounts amounts of the oxidized, oxidized, caved caved material material remained in dilution effects. This in the the samples, samples, causing causing in in some some cases serious dilution This is is remained illustrated by analysis illustrated analysis of a duplicate sample that was high-graded by meticulously individual dark-gray, fine-grained fine-grained particle. particle. The results results showed an picking out each individual relatively thin increase in 0.44 wt. wt. %. %. It is possible that relatively thin (about (about0.5-2 0.5-2 ft; increase inTOC TOCfrom from0.1 0.1toto0.44 0.2-0.6 m) m) organic-rich organic-rich silty shales that have have TOC of of from from 1.0 to to 2.5 2.5wt. wt. %, %,which which have have 0.2-0.6 been analyzed analyzed by others in nearby mineral exploration coreholes and outcrops, are also and others of oxidized oxidized caved caved materials materials and present but but completely completely masked masked by a combination of thicker, very organic lean, indigenous indigenous rock units. units. We speculate speculate that the average average TOC content may wt. % % but but certainly certainly not not higher higher than than0.5 0.5wt. wt.%. %. content may be be as ashigh highas as0.4 0.4 wt. Of the 25 samples analyzed only 3 gave gave reliable reliableTmax Tmaxvalues. values. These ranged from 436°C to to 441° 441°Cand and averaged averaged 438T, 438°C,maturity maturity values values indicative indicative of of the the early phase phase of 436OC of oil generation for Type II kerogen. This maturity ranking is consistent with maturity I1 ranking maturity generation for values obtained by previous previous workers. workers. values obtained for for comparable comparable Nonesuch rocks by In conclusion, the maturation maturation level favorable for oil level for the Nonesuch is favorable generation but generation but the the source-rock source-rock potential for this particular drillhole sample set, based content, is is rated rated poor poor to to at atbest bestfair. fair. On On the the other other hand, hand, as shown on the solely on TOC content, mud log, ppm by volume, and mud log, the the presence presence of of methane methane gas, gas, averaging averaging about about 1,000 1,000 ppm and throughout most of the Nonesuch lesser volumes of ethane to butane gases occurring throughout Formation indicates Formation indicates some some hydrocarbon hydrocarbon potential. potential. 53 �DUAL IMMISCIBILITY IN ROCKS ROCKS OF OF THE THE DUAL IMMISCIBILITY OF OF DOMINANTLY DOMINANTLY AQUEOUS AQUEOUS FLUIDS FLUIDS IN SOUTHWESTERN FOOTWALL OF THE DULUTH COMPLEX, NE MINNESOTA SOUTHWESTERN FOOTWALL OF THE DULUTH COMPLEX, NE MINNESOTA Jill Dill; HARRIS, N.; SASSANI, David C., C., Dept. Dept. Earth & & Planetary PASTERIS, Jill HARRIS, Teresa N.; Sciences, Washington Washington University, University, Campus CampusBox Box1169, 1169,St. St.Louis, Louis,MO MO 63130-4899 63130-4899 Sciences, Microthermometric and and Raman Raman microprobe microprobe analyses analyses were were made madeon on about about 150 150 fluid fluid inclusions inclusions Microthermometric in 6 rock sections from drillhole FHL-2, which sampled the Fish Lake area of the Duluth in 6 rock sections from drillhole FHL-2, which sampled the Fish Lake area of the Duluth Complex 25 25 k km of Duluth. Duluth. The in quartz quartz and Complex m northwest of The inclusions, inclusions, which were investigated in apatite grains grains in in troctolitic troctolitic to only of of aqueous aqueous fluid fluid (vapor (vapor bubble bubble in in apatite to gabbroic gabbroic rocks, rocks, consist consist only liquids-solidphase), phase),aasingle singlevolatile volatilephase phase(CH<±Nd02) (CH4NgCO2), or both aqueous and volatile liqu&solii phases. This This work work isisfocussed focussedon onthe theaqueous aaueous inclusions, inclusions. which contain 0 to 48 wt. % % total total ohases. dissolved salts with CaCI2/(NaCI + CaCl2) weight ratios ranging up to 0.9. Homogenization dissolved salts with CaClJ(NaC1 + weight ratios ranging up to 0.9. Homogenization temperatures of of the the aaueous aqueous Inclusions inclusions ranae range from 100° to 400° 400°C (see (see fiaures). figures). temoeratures 100Âto vs. total total dissolved dissolved salt salt suggest that The attached attached plots plots of of homogenization homogenization temperature temperature vs. different rocks rocks encountered fluids of different compositions and and that that individual individual rocks rocks interacted interacted with more than one fluid during their history. Most of the rocks that were investigated with more than one fluid during their history. Most of the rocks that were investigated have have mineral assemblaaes assemblages that that indicate their interaction with with aa fluid fluid chase, phase, for for instance, instance, mats mats of of olivine, and and ~ K-feldspar replacing plagioclase; chlorite and amphibole replacing pyroxene and olivine, - f e l d s ~replacing & pkgioclase; of the fluid inclusions quartz and and (earlymany of inclusions lie lie along along secondary trails in (late-crystallizing) quartz and late-crystallizing) apatite. temperature, and and CaCIJ(NaCI CaClS(NaCl + The ranges in in values values of of salinity, salinity, homogenization homogenization temperature, Gaol2) ratio indicate the complexity CaCL) complexity of the the igneous, igneous, magmatic-hydrothermal, magmatic-hydrothermal, and postpostprocesses that that interacted interacted in these rocks; rocks; our group and and others others have have provided provided magmatic processes evidence of of both strong magmatic and sedimentarylmetasedimentary sedimentary/metasedimentarycomponents componentsin inthe the aqueous and and volatile volatile fluids. fluids. Thus, aqueous Thus, the the data dataon on the the accompanying accompanying figures could be interpreted as representing such a diverse array of fluid fluid sources and timings as to defy their tracking. We believe that aa more more reasonable reasonable alternative alternative model is that many of the inclusions inclusions were trapped when when the system was in a field of two coexisting fluids, fluids, i.i.e., a field of fluid e., a field of immiscibility. There in the the general general chemical immiscibility. There are are two two possible possible regions regions of such immiscibility in system H20-(C-0-H-N) H20-(C-O-H-N) gases-salt: gases-salt: brine-brine immiscibility at at high high temperatures temperaturesand andbrinebrinesystem In the the inclusion inclusion parameters parameters (see vapor at lower temperatures temperatures (Bowers (Bowers and and Helgeson, Helgeson, 1983). In figures), the the main main lines of evidence for an the bimodal distribution in figures), an immiscibility immiscibility model are the salinity, lack of correlation correlation between (Tb) and and either either salinity salinity or salinity, between homogenization homogenization temperature (Th) composition, differences differences in Th Tb between pairs of adjacent inclusions (particularly those composition, extremes in salinity), salinity), and pairing of high salinity with with low low gas gas content in mixed representing extremes aqueous-volatile inclusions. alone does does not not account accountfor forall allof of the the above above A model of brine-brine immiscibility alone features, however, however, in in that that salinity salinity and and density density do do not not co-vary; co-vary;in infact, fact,all allbut butaafew few of of the the features, homogenize to to the liquid. liquid. In fri other otherwords, words,there thereisisaalack lackof of evidence evidencefor for aqueous inclusions homogenize the one-step segregation of the system at high temperature into a coexisting saline brine and high saline Further refinement refinement of of an an immiscibility model fluid. Further a lower-density, much less saline aqueous fluid. aqueous inclusions inclusions that that is required to explain the formation formation of coexisting coexisting liquid-dominated aqueous have similar liquid:vapor Iiquid:vapor ratios ratios but widely ranging salinities and CaClJ(NaCI + Ca012) but ranging salinities and CaCLJNaCI + CaCI,) ratios. could have have occurred occurred in in two two stages, stages,initially initiallyby bythe thesegregation segregationofofC-0-H-N 0-0-H-N Immiscibility could from brine brine and subsequently subsequently by by the the segregation segregationof oftwo twobrine-like brine-likefluids. fluids. This model volatiles from requires that the bimodal distributions noted noted in in the the figures figures do not of dual immiscibility requires bimodal salinity distributions not just reflect sampling statistics and that the physical parameters, such as wetting properties, of just physical parameters, such as wetting and physically physically within within the the the immiscible fluids precluded them from interacting chemically and C~CU �¶ I d I n extensive fracture system extensive fracture system in in the the rocks. rocks. Dual immiscibility requires much more stringent stringent geological geological conditions conditionsthan thandoes does oneone chemical reactivity step, brine-brine immiscibility. The The physical physicalproperties properties (e.g., (e.g., fractures) and chemical (e.g., (e.g., susceptibility to hydration) hydration) of the Duluth Duluth rocks, rocks, as as well well as as the the rift riftenvironment environmentof ofthe the Complex, were critical in the development of dual episodes of fluid immiscibility. critical in the development of dual episodes of fluid immiscibility. In In the the first first stage some combination combination of of factors factors moved moved the the bulk bulk composition composition of of the thelatelatestage of immiscibility, immiscibility, some stage, magmatic-hydrothermal magmatic-hydrothermalfluid into into the the field field of of liquid liquid ++ vapor; multiple episodes of physical physical segregation segregation of brine brine and and volatiles volatiles probably probably occurred, occurred, enhanced enhanced by by the the periodic periodicdrops drops in pressure during rifting. This depletion in volatiles moved the aqueous component of the pressureduring rifting. depletion involatiles moved component of the ' original Hp-salt "binary", original bulk fluid toward the Kid-salt "binary",eventually eventuallyinducing inducingthe the second second stage stage of of immiscibility. Two Twocoexisting coexistingbrines brinesdeveloped, developed, with withcontrasting contrastingsalinities salinitiesand anddensities. densities. IfIf these two aqueous aqueous fluids fluids remained remainedphysically physicallysegregated segregated within the fracture system system of of the the host rocks during isobaric cooling (e.g., system evolution at fixed depth) or isothermal host rocks during isobaric cooling (e.g., system evolution at fixed depth) or isothermal increase in in pressure pressure (e.g., (e.g., change change from from hydrostatic hydrostatic to lithostatic lithostatic pressure pressure after after rifting), rifting), then then both Trappingof ofthese thesefluids fluidswould would produce producetwo two populations populations both fluids would increase in density. Trapping of liquid-dominated liquiddominated brines brines with contrasting salinities, like those seen in the figures figures below. below. Severat distinctive petrologic features of drillhole FHL-2 and many other portions Several FHL-2 other portions of of the the Duluth Complex can be explained explained by a mobile, mobile, high-salinity high-salinity brine that interacted interacted with the the melt melt and pegmatoidal and host rock during during subsolidus ccooling: onilig: pegmatoidal zones, zones, the the gradational gradational nature nature of the the contacts between 990), between inferred inferredigneous igneousstratigraphic stratigraphic zones zones (Severson (Seversonand andHauck, Hauck,11990), enrichment in anorthite content in in the rims rims of of plagioclase plagioclase grains, bulk-rock bulk-rock concentrations concentrations of of up to 3200 and Saini-Eidukat, 1991), and iron-rich compositions of 3200 ppm pprn chlorine chlorine (Dahlberg (Dahlberg and Saini-Eiukat 19911. and iron-rich comoositions of .. pyroxenes pyroxenesand andolivines. olivines. . sr — aA 450 N MX sA A a 350 250 atsA A • S a a —I — .gA 200 a 150 100 — %o a — e S • A" S 35c -1 50 t — I8aS 40C1' A a 300 I— lsaniplole4lll — I S S —— SOC 25c a. — 200 — U S__I.. 150 100 50 - 5go Sathty: wt% toS salts 15 - lo — Semplel847l ample 18471 N sanplele474 Sample18474 — San1p1e184751 Sample 18475 a 18476 0 18488 = - Sanple18521 A sample Sampte18476 c.Sample Sample16486 Homogenization vs. total salinity for foi ailS Homogenization temperature vs. aà 6 samples samples investigated investigatedin in this (hisstudy. study. "so 4s 40 as .tio so i5 io SaI.itr wt%tt sa4ts . . Homogenization HomogeTOaton vs. total salinity salinity in intwo two of of the the samples at the the left. left Note sampbs shown at Notethe thebimodal bimodal distribution insalinity. salinity. All All inclusions inclusionsinin distributionin both bothdiagrams diagrams homogenize homogenizeto tothe theliquid (quidphase. phase. I I 55 I �HYDROLOGIC HYDROLOGICMODELS MODELS OF OF SEDIMENT-HOSTED SEDIMENT-flOSTEDORE OREFORMATION FORMATIONW1TIIIN WITHIN CONTINENTAL CONTINENTALRIFT RIFTBASINS BASINS PERSON, PERSON, M., M., Dept DeptGeology Geologyand andGeophysics, Geophysics,The TheUniversity Universityof ofMinnesota, Minnesota,310 310 Pillsbury Pisbury Aye, Ave, SE, SE, Minneapolis, Minneapolis,MN MN 55455 55455 Much Much attention attention has recently recently been been placed placed on on the theinterrelationship interrelationship between between compressional tectonics and the paleohydrology of sedimentary compressional tectonics paleohydrology sedimentary basins (Bethke (Bethke and Marshak, Marshak, 1990; 1990; Oliver, Oliver, 1992; 1992; and and Sverjensky Sverjensky and and Garven, Garven, 1992). 1992). These These studies studieshave have proposed that during orogenic events, uplift of the land surface and tectonic shortening proposed that during orogenic events, uplift of the land surface and tectonic shortening can can induce quantifies of of induceregional regional subsurface subsurface flow flow systems systems capable capable of transporting significant significant quantities heat and fluid mass over hundreds of kilometers. Such transient flow events, which remain heat and fluid mass over hundreds of kilometers. Such transient flow events, which remain active active until until erosional erosional processes processes incise incise the the landscape landscape (Garven (Garven and and Freeze, Freeze,1984a,b) 1984a,b) or or compressional stresses wane (Ge and Garven, 1992), are thought to have formed compressional stresses wane (Ge and Garven, 1992), are thought to have formedeconomic economic metal edges of foreland and intracratonic metalore oredeposits depositsand andpetroleum petroleum accumulations accumulations at at the edges intracratonic sag basins (Garven, 1989 and Garven et al., 1993). To sag basins (Garven, 1989 and Garven et al., 1993). To date, date, however, however, little littleattention attentionhas has been been given giventotounderstanding understanding the the interrelationship interrelationship between between extensional extensionaltectonic tectonic events events and and the the paleohydrology palcohydrology of of continental continental rift systems systems (Person (Person and Garven, 1992, 1992, 1994). 1994). This This study attempts to fill this gap by presenting a series of generic mathematical study attempts to fill this gap by presenting a series of generic mathematicalmodels models of of hydrothermal within actively actively rifting rifting basins. The numerical numerical experiments experiments illustrate illustrate hydrothennalfluid fluidflow flow within the the important important control control of of permeability permeability and water table table configuration configuration in determining determining which driving—force on fluid motion (compaction, density, or topography) will dominate driving-force on fluid motion (compaction, density, dominate during during basin evolution. The idealized models also help to infer the role of groundwater basin evolution. The idealized models also help to infer the role of groundwaterflow flowin in the the formation of sediment—hosted, hydrothermal ore deposits within continental rift basins. formation of sediment-hosted, hydrothermal continental rift basins. The The unique unique stratigraphic stratigraphic relations, relations, heat heat flow flow and and tectonic tectonic conditions conditions associated associated with with continental rifts warrants quantitative analysis. continental rifts warrants quantitative analysis. Assuming rift basin basin subsidence subsidenceand and basal basal heat heat flow flow can can be berepresented representedusing using aa Assumingthat thatrift 'standard' 'standard'geodynamic geodynamicmodel model (Gamer (Garnerand and Turcotte, Turcotte,1986), 1986).two twodistinct distinctgroundwater moundwaterflow flow systems systems evolve evolve within within continental continental rifts rifts during during basin basin evolution. evolution. During ~ k r i the nthe~initial initial (stretching) (stretching)phase phaseof of rifting lifting(Fig. (Fig. la), la),subsidence subsidenceisisaccommodated accommodatedby byfault faultblock blockmotion, motion, and andaatopography-driven topography-drivengroundwater groundwaterflow flowsystem systemdevelops developswithin withinthe thepermeable permeablealluvial alluvial fan fandeposits. deposits.Within Within the theless lesspermeable permeable lacustrine lacustrine facies facies located located in in the the center center of of the the basin, basin, compaction-driven compaction-driven groundwater groundwater flow dominates. dominates. Here, Here, the thecompacting compactinglacustrine lacustrine sediments sedimentsfocus focuspore porefluids fluidslaterally laterally from fromthe the basin basin center center into into the the alluvial alluvial fan fan deposits deposits due due totothe therelatively relativelylarge largepermeability permeabilitycontrast contrastbetween betweenthe thetwo twodepositional depositionalenvironments. environments. Thermal Thermalanomalies anomaliesresulting resulting from from convective convective heat heat transfer transfer are are restricted restricted to to alluvial alluvialfan fan facies faciesnear nearthe thebasin basin framing framingfault. fault. During During the the thermal thermal cooling cooling (flexural) (flexural) stage stage of of basin basin development development(Fig. (Fig. ib), lb),laterally laterallyextensive extensiveon-lap on-lap facies faciesare are deposited, deposited, and and density-driven density-driven groundwater groundwater flow flow dominates dominates in in the thepermeable permeablealluvial alluvial fan fan deposits depositswhile whilecompactioncompactiondriven drivenflow flowcontinues continueswithin withinthe thelacustrine lacustrineand andon—lap on-lap facies. facies. The Thepresence presenceof ofaapermeable permeable aquifer resulted in long-range fluid transport to the aquiferwithin withinthe theon—lap on-lap hfacies i e s resulted the edge ed e of of the the basin. During both stages of basin evolution Darcy flow rates varied from l0 10-1 basin. During both of basin evolution Darcy flow rates varied from 10- to to 10-1 m/y. between the lacustrine and alluvial fan deposits respectively. The observed m/y. between the lacustrine and alluvial fan deposits The observedpresence presence of ofore oremineralization mineralization within within alluvial alluvial fan deposits deposits at the edges of of some some continental continental rift rift systems, RiftBasin Basin of of Angola, Angola, supports supportsthe thefindings findingsof of this thisstudy. study. systems,such suchas asthe theCretaceous CretaceousRift �I REFERENCES REFERENCES Bethke, C.and andS.S.Marshak, Marshak,1990, 1990,Brine Brinemigration migrationacross acrossNorth North Americt America:the theplate platetectonics tectonicsof ofgroundwater groundwater Bethke,C. hydrology, AnnualReviews ReviewsofofEarth Earthand andPlanetary PlanetarySciences, Sciences,v. v. 18, 18,p.p.287—315. 287-3 15. hydrology.Annual Garner, Garner,D.L., DL..and andD.L. D.L.Turcotte, Turcotte.1986, 1986.The Thethermal thermaland andmechanical mechanicalevolution evolutionof ofthe theAnadarko Anadarkobasin, basin, Tectonophysics, v. 107, p. 1-24. Tectonophysics, v. 107, p. 1-24. Garven, Gwen,G., G.. and andR.A. RA. Freeze, Freeze,1984a, 1984a.Theoretical Theoreticalanalysis analysisof ofthe therole roleof of groundwater groundwaterflow flowin in the thegenesis genesisof of stratabound oredeposits: deposits:1.I.Mathematical Mathematicaland andnumerical numerical model, model, American American Journal Journal of of Science, Science,v.v. strataboundore 284, 124. 284,p.p.1085-1 1085-1124. Garven, G., and R.A, Freeze, Garven, G., and RA. Breeze,19Mb, 1984b.Theoretical Theoreticalanalysis analysisofofthe (herole roleof ofgroundwater groundwaterflow flowin in the thegenesis genesisof of stratabound strataboundore oredeposits: deposits:2.2Quantitative Quantitativeresults, results,American AmericanJournal Journalof ofScience, Science. v. v. 284, 284,p.p. 112411241156. 11% ----. Garven, Garven,0., G.,1989, 1989.Hydrogeologic Hydrogeologicmodel modelfor forthe theformation formationofofthe thegiant giantoil oilsands sandsdeposit depositof ofthe theWestern Western Canadian Canadiansedimentary sedimentarybasin, basin,American AmericanJournal Journalof ofScience, Science,v.289, v. 289,p.p.105-166. 105-166. Garven, Garven,0., G.,Ge, Ge,S.,S.,M.M.Person, Person,and and1).D.Sverjenski, Sverjenski,1993. 1993,The Thegenesis genesisof of stratabound stratabound ore oredeposits depositsin in the the Midcontinent MidcontinentBasins BasinsofofNorth NorthAmerica: America:I.I.The Therole roleofofregional regionalgroundwater gmundwaterflow. flow.American AmericanJournal Journal ofofScience, Juneissue. issue. Science,June Ge, S. and 0. Garven, Hydromechanica] Ge, S. and G. Garven,1992, 1992, Hydromechanicalmodeling modelingofoftectonically tectonicallydriven drivengroundwater groundwaterflow flowwith with application to the Arkoma Foreland basin, Journal of application to the ArkomPoreland basin, Journal ofGeophysical GeophysicalResearch, Research,v.v.97, 97,p.p.9119—9144. 9119-9144. Oliver, Oliver,J.,J.,1992, 1992,The Thespots spotsand andstains stainsofofplate platetectonics: tectonics:Earth EarthScience ScienceReviews, Reviews,v.v. 32, 32,p.p.77—106. 77-106. Person, 1992, Person,M. M.and and0.G.Garven, G-, 1992,Hydrologic Hydrologicconstraints constraintson onpetroleum petroleum generation generationwithin withincontinental continentalrift rift basins: Theory and application theRhine RhineGraben, Graben.American AmericanAssociation Association of of Petroleum Petroleum basins: Theory and applicationtotothe Geologists GeologistsBulletin, Bulletin,v.v.76, 76,p.p.468—488. 468-488. Person, AAsensitivity Person,M. M.and andG.G.Garven, Garven,1994, 1994, sensitivitystudy studyofofthe thedriving drivingforces forceson onfluid fluidflow flowduring duringcontinental continental rift riftbasin basinevolution, evolution.Geological GeologicalSociety SocietyofofAmerica AmericaBulletin, Bulletin,v.v.104, 104,p.p. Sverjensky, Tracing D.A. A.and and0.G.Garven, Garven,1992, 1992, Tracinggreat greatfluid fluidmigrations, migrations.Nature, Nature,v.356, v. 356, 481-482. Sverjensky,I). p.p.481—482. + + B + ++ + Not Not totoscale scale + LEGEND R-3Crystalline CrystallineBasement Basement [;E] Pie—Rift Pre-Rift .. Basal BasalAquifer Aquifer , ., ~. Figure Figure1.1. - - Alluvial Lacustrine AlluvialFan Fanand andLacustrine Deposits (Initial Stage of Rifting) Depos@ (~nitial~tageof ~ifting) Carbonate Aquifer ,. , , . (Thermal/Flexural (Thermal/Fle~.~tate.,of ~ ~ f t -i n o ) State of Rifling) Conceptual Conceptualmodel modelofofgroundwater groundwaterflow flowsystem systemduring duringinitial initialand andflexural flexural stages stagesofofcontinental continentalrift riftevolution. evolution.Arrows Arrowsdepict devictdirection directionofofgroundwater moundwater motion topography—, motiondue duetoto topography-, density—, density-, and and compaction compactiondriven drivenflow flowsystems. systems. Two distinct groundwater flow systems Two distinct groundwater flow systemscan canform formwithin withincontinental continentalrifts riftsdue due totochanges changesinintectonic, tectonic,thermal, thermal,and andhydrologic hydrologicboundary boundaryconditions conditionsduring during basin basinevolution. evolution. 5J �z 0 H oz t11 Plcn -S 09 0 or z nm nI.t c-fl rn 0 0 0 M C) DEPOSITIONAL CONTROLS ON SHALLOW WATER IRON FORMATION ACCUMULATION, GOGEBIC RANGE, WISCONSIN. PUFAHL, Peir and FRALICK, Philip, Dept of Geology, Lakehead University Thunder Bay, ONT P7B 5E1, Canada. 0 liji LZo -I > I I r° I o -< SLATY IRON FORMATION -n t)III C) P1 c ot.z OZrfl SMALL GRAINSTONE LENSES AND WAVY BEDDING ('1 côr GRAINSTONE LENSES a zrn Cflg t - -I ci Well exposed, glacially polished iron formation outcrops near the town of Mellen, Wisconsin. There units form a portion of the western Gogebic iron range which strikes eastwest through the area. Iron formation exposure of this calibre is unusual in the LakeSuperior region and provides an opportunity to investigate physical and chemical sedimentary controls on accumulation of this type of sediment SLUMPS �I • I I I A 40 x 40 40 m m section section of of hon ironformation formationcomposed composed of of trough troughcross-stratified cross-stratified chert grainsxonesand and parallel parallel laminated laminated slaty slaty iron iron formation formation was was mapped mapped in detail (Figure 1). grainstones (Figure 1). The units. The The sequence sequence is is composed composed of three three distinct stratiographic stratiographic units. Thefirst firstcomprises comprises 12 12m m of parallel laminated slaty iron formation with small chert lenses appearing at the bottom laminated slaty formation the bottom of the is a 15 succession of of large trough the section. section The second second is 15 in m thick succession trough cross-stratified cross-stratified grainstone 10-12min. . The The third thirdunit unitlies liesimmediately immediatelyabove above grainstone lenses, lenses, some some extending extending laterally laterally 10-12 the m of ofslaty slatyiron ironformation formation. Paleocurrent Paleocurrent data data the grainstone grainstonesuccession succession and is composed of 88 m is dominantly unidirectional from the north. Slaty iron formation is dominated by parallel laminated laminated beds beds 2-5 2-5mm mm in in thickness. thickness. In regions where slaty iron formation coexists with small grainstone lenses the characteristic In regions where slaty iron formation grainstone characteristic wavybedding. bedding. Ripple Ripple lamination is present present in in the the lowest lowest parallel lamination lamination gives rise to wavy stratigraphic unit. Many beds are both physically and chemically graded. Variations graded. Variations in in the the stratigraphic Many beds are both physically distribution of Al, Mn, beds and and throughout the entire distribution Mn,Fe and Mg are seen seen within individual beds entire span section. Mineralogically span of the section Mineralogically the dominant dominant phases are are hematite, hematite, magnetite magnetite and andchert chert with minor amounts of greenalite, apatite apatite and and manganese manganese oxide. oxide. The trough cross-stratified chert chert grainstone lenses are composed of rounded chert and hematite ranging in in size size from from 0.1 0.1 to 2 mm. Many Many chert chertgrains grains are are coated coated with with hematitegrains grains ranging hematite, suggesting rolling by bottom currents through hon-rich muds. A few of the largest A few hematite, suggesting by bottom currents through iron-rich cores composed composed of of ilmenite. ihuenite. The hematite grains possess possess cores Thematrix matrix isisdominately dominately chert chert & & with traces of stilpnomelane. Lenses range from 2 to 40 cm thick and may extend calcite stilpnomelane. Lenses range from 2 to 40 cm thick and may extend laterally 00.70 15m. a The laterally .70 toto 15 Thesmallest smallestgrainstone grainstonelenses lenses appear at at the the base base of of the the section section calcite within slaty iron formationformation. The largest lenses are found in the succession of trough The largest lenses are found in the succession of troughcrosscrossare common at at the 1-3cm in length, are stratified grainstones. Ripups Ripups of of slaty slaty iron iron formation, formation, 1-3 of the stratified (30cm cm thick, 8-11 8-11m wide) at the top top of of the the succession. succession. base the largest largest lenses lenses (30 by aa coarsening coarseningupwards upwards sequence sequencein inwhich which muddy muddy shelf The section section is characterized characterizedby pass through ripple laminated fine sand into a succession of cross-stratified deposits through ripple laminated fine sand into a succession of cross-stratifieddunes. dunes. deposits of offshore offshorebars. bars. The This sequence is characteristic of The thin thin ripple ripple lamination lamination in in slaty slaty iron iron formation in the lowermost slaty unit may represent sands moved by storm produced the lowermost slaty may represent sands moved by storm produced currents. The alsoindicative indicative of of storm storm currents. Thedominantly dominantlyunidirectional unidirectional paleocurrent paleocurrent pattern pattern isisalso enhanced currents. Slumping is suggested throughout the sequence by the presence of of currents. Slumping is suggested throughout the sequence by extensive convolute bedded slaty iron formation. formation. bar complex the Upper Upper Cretaceous The offshore offshore bar complex composing the Cretaceous Sussex Sussex Sandstone Sandstone in the the The is similar similar to to the chemical sedimentary sedimentaiy succession described Powder River Basin, Wyoming is above. The Thesedimentological sedimentologicalcontrols controlsforming forming the the carbonate carbonatesequence sequencein inWyoming Wyoming should therefore closely sedimentation on present during therefore closely parallel parallel those those governing governing sedimentation on the the shallow shallow shelf present hon formation. deposition of the slaty and cherty iron formation The Theoffshore offshorebar barsequence sequenceininWyoming Wyoming claystonethrough through interbedded interbedded sandstone sandstone and also grades gradationally from silty claystone and claystone to sandstone and contains a sequence of sedimentary structures similar similar to to that that present in also the hon alsodemonstrates demonstratesan anasymmetrical asymmetricaldistribution distribution ironformation. formation. The TheSussex Sussexsandstone sandstonealso facies resulting resulting in aa steeper steeperdepositional depositionalslope slopewhich which endured enduredhigher higherdepositional depositional of fades energies, and underwent periodic slumping probably similar to observed in the energies, and underwent periodic slumping probably similar to that observed the of Proterozoic bar Proterozoic bar succession. succession. �FIYDROGEOLOGICINVESTIGATIONS INVESTIGATIONS OF HYDROGEOLOGIC OF PETROLEUM PETROLEUM CONTAMINATION CONTAMINATION IINNKARST, KARST, CENTRAL CENTRAL UPPER UPPER PENINSULA PENINSULA OF OF MICHIGAN MICHIGAN Beth A. A. Rogers, MalcolmPPirnie Engineers, E. Lansing, Beth Rogers, Malcolm i r n i e En ineers, E. Lansing, MI MI Mark A.A. Petrie, Petrie, Department Mark Department of o f Natural Natura Resources, Resources, Marquette, Marquette, MI MI ? BACKGROUND BACKGROUND Hydrogeologic Hydrogeolo i c iinvest4ations n v e s t i ations have havebeen beenconducted conducted iinn response r e s onse to t o ffuel uel Upper Michigan contaminattono of contamination f rresidential e s i d e n t i a water water supply su p l y wells w e l l s iinn aa small Upper Michigan community(due (due An i initial cannot be be disclosed). disclosed An nitial community t o tol i tlitigation, i g a t i o n , the the location l o c a i o ncannot investigation i n v e s t i g a t i o nidentified i d e n t i f i esome d somepossible possiblesources sourcesand and poorly p o o r l ydefined d e f i n e hydrogeology. hydrogeolo y. A subsequenti ninvestigation thesource sourcei didentification A subsequent v e s t i g a t i o n r erefined f i n e d the e n t i f i c a t i o n and and provided provided bbetter et e r definition of othe d e f i n i t i o nofo fthe thevertical v e r t i c aand l andhorizontal horizontalextent extent f t hcontaminant e contaminantplumes. plumes. 9! ? J. f GEOLOGIC GEOLOGIC SETTING SETTING The ssite basin, near The i t e lies t i e son onthe theNorthwest Northwest edge edge ooff the Michigan Michigan basin, near the contact contact between the Michigan Basin Paleozoic sediments and the Precambrian between the Paleozoic sediments and the Precambrianmetamorphics metamorphics medium ooff the the Canadian Canadian Shield. Shield. AAtt the the surface surfaceare areWisconsinan-aged Wisconsinan-a ed tthin, h i n medium textured gglacial (ground moraine) textured l a c i a l tills t i 1 1s ground moraine)(Farrand (Farrand and and Bell, Be11, 1982). 1982). Underlying ~ n d e r f y i the nthe ~ drift Middle a gray, d r i f tisi the s the MiddleOrdovician O r ovicianTrenton Trenton Group; Grou ; a gray, brown, brown, oorr buff b u f f colored, colored, t i ngray grayshale shalepartings, partings,sometimes sometimes ffine i n e grained, rained, limestone limestone or o r dolomite, dolomite, with w i t h thin with calcite ffossiliferous, o s s i i f e r o u s fractured, fractured, vuggy vuggy w i t h some some c a l c i t e ccrystals r y s t a l s or pyrite in vugs fOstrom anddaughter, Slaughter,1967, 1967,SSinclair, Vanlier, 1963). Underlying the Ostrom and i n c l a i r , 1960 1960 and and Vanlier, Trenton Group (estimated to be at least 250 feet jrenton Group (estimated t o be a t l e a s t 250 f e e t t hthick i c k i in n this area) are the Black River River Limestone, the Prairie Chienformation formationand the Late Cambrian Black Limestone, the P r a i r i edu duChien Munising Sandstone Sandstone(Sinclair, (Sinclair, 1960 andVan1 Vanlier, 1960 and i e r , 1963). 19631. Regional groundwater groundwater flow Munisin is to the Southeast, generally parallel to the dip of the bedrock structure. i s t o t e Southeast, generally p a r a l l e l t o the d i p o f the bedrock structure. A ? R a DISCUSSION DISCUSSION Surficial light brown till: l i gbrown, h t brown, brownororeddish-brown, r reddish-brown, S u r f i c i a l deposits deposits are are gglacial l a c i a l till: fine to medium clayey sand, sandy clay or clayey silt, with t r a c e tot osome some fine fine f i n e t o medium clayey sand, sandy c l a y o r claye s i l t , w i t h trace gravel, ran ranging from33t oto 99 ffeet Gravel tto o coarse coarse gravel i n g from e e t tthick. hic Gravel percentage percentage increases increases with w i t h depth; depth; cobbles cobbfes of o bedrock bedrock are incorporated incorporated just j u s tabove above the the bedrock bedrock surface. surface. I. ? The bedrocki is The bedrock s ffairly a i r l yhomogeneous homogeneous t otoaat t lleast e a s t 60 60 feet f e e t below be1ow ground round level level 1 (bgl), (bgl), the the total t o t a ldepth de t h of o f investigation. investigation. It Itisi sgrayish-brown grayish-brown to t o buff bu f dolomite, dolomite, microcrystalline, m i c r o c r y s t a l l ine, fractured fractured with w i t h some some ddissolution i s s o l u t i o n features, features, containing containing few few to to somevugs vugsand and few some (<2"t hthick) zonesoor bedsooff shaley shaley dolomite dolomite to some few t otosome t h ithin n (<2" i c k ) zones r beds to shale, generally depthoof 20f feet bgl. The shale, generally occurring below below aa depth f 20 e e t bgl The vugs commonly commonly are are are ffilled ffilled i l l e dwith w i t h calcite c a l c i t ecrystals c r y s t a l s or o rpyrite, p y r i t e , fractured, fractured, which which often o f t e n are i l l e d with with reddish-browns silty Pleaser refer reddish-brown i l t y clay. Please e f e r tto o the the core core and and ddrill r i l log l l o for g f oMW-hOD. r MU-1100. . Groundwater flowisis strongly strong1y influenced influenced by by the thesecondary secondary permeability permeabil it y Groundwater flow (fractures). Thede depth the 40 40 monitor monitor wwells fractures). The t h t to o groundwater roundwater i nin the e l l s (Figure (Figure 1) 1)ranges ranges from 0.5 0.5 tto from o 29 29 ffeet e e t bgl, g1, with w i t ha acorrespondin9 corresponding range range in i n ground ground surface elevations of only 18.5 Waterl levels of 18.5 feet. Water e v e l s ffluctuate l u c t u a t ewidely widelywith w i t hseasonal seasonal changes, changes, with w i t h as as 1 muchas as18.25 18.25ffeet much e e t noted from from May May tto o September September i in n one one well, MW-HID. MW-111D. weref rfrustrating IInitial n i t i aattempts l attemptstot ocontour contourthe thegroundwater groundwater eelevation l e v a t i o n data were ustrating (Figs. 2 & It was respondingddifferently & 3). 3). It was apparent apparent tthat h a t several several wells w e l l s were were responding ifferently (Figs. so well hydrographsoof ttoo changing chan i n conditions, conditions, so w e l l hydrographs f eelevation l e v a t i o n versus versus time time were were prepared 4-61. In I n the the hydrographs h drographs iitt is i sobvious obvious that t h a tsome some wells w e l l s do do not not pre arer? (Figs. ?igs. 4-6). reflect concertwwith the m majority r e f e c t changing c!I anging groundwater groundwater e elevations evations i ninconcert i t h the a j o r i t y of o f the the wells. These "anomal "anomalous" wells probablyare arescreened screenedi nin zones zoneshydraul hydraulically we11s These ousn we1 1s probably i c a l ly from the the rrest They were were not iisolated s o l a t e d from e s t of o f the the aquifer. aquifer. They n o t used used iinn subsequent subsequent ?. r 60 �interpretation, in i potentiometric surface i n t e r p r e t a t i o n ,resulting resulting n potentiometric surfacemaps maps (Figs. (Figs. 77&& 8) that t h a t agree agree well with (Figs. 9 & w i t hthe theobserved observed contamination contamination plumes plumes (Figs. & 10). 10). A groundwaterhigh highi is found aatt the Western edge thestudy study area, area, roughly roughly A groundwater s found Western ed e o of f the corresponding bedrockand andtopographic topographichigh, high,wwith groundwaterflowing flowingooff correspondin tto o a bedrock i t groundwater f f the the 1 i high South(Fig. (Fig. 7). This high high iiss not high ttoo the the North, orth, East East and and South 7). This n o t reflected r e f l e c t e ddeeper deeper in the regional regional flow i n the the aquifer, aquifer, where where groundwater groundwater f follows o lows the f l o w to t o the t h eSoutheast Southeast (Fig. 8). Horizontal Horizontal hydraulic hydraulic gradients gradients vary vary around around t this h i s high, high, from from 0.022 0.022 to to 0.028 ft/ft tot othe East ft/ft 0.015 ft/ft ft/fttot the o the Eastand and0.026 0.026 - 0.031 0.031 ft/ft theNorth, North 0.012 0.012 -- 0.015 to the South, wwith nonoseasonal Althought the i t h llittle i t t l etot o seasonal fluctuations. f l u c t u a t i o n s . Although h e vvertical ertical hydraulic gradient contamination the deep ittle contaminationwas was found found in in'the deep wells: gradient isi sdownward, downward, 1little 1 detection of of aa single singlecompound, compound, aatt ttrace r a c e levels, levels, on ononly onlyone onesampling sampling date date each each in i n 22 of o fthe the1212deep deep wells, wells, and and one one of o f those those detections detections was was not n o t repeated repeated iin n aa duplicate duplicatesample. sample. A A total t o t a l ofo 24 f 24slug slugtests t e s t swere wereperformd erformedon on14 14moni2tor moni$or wwells e l l s (8 8 shallow). shallow). Hydrauli cm/s, with c o n d u c t i v i t i e range s rangefrom from1.37x10 1.37~10 to t o 4.25x10 4.25~10' cm/s, w i t an an average average Hydraul conductivities of A A 24-hour 24-hour constant constant rrate a t e pumping ~ u m p i n g ttest e s t yielded y i e l d e dcomparable comparable o f 1x10 1x10" cm/s. cm/s. hydraulic cm/s, wwit hydraulic conductivity conductivity values values ooff 2.35x104 2.35~10' ttoo 1.52x10 1.52~10' cm/s, i t h aa Transmissivity of 1.92 to 12.4 m2/day and Storage Coefficient of 1.O6x10 o T r a n s m i y i v i t y o f 1.92 t o 12.4 m /day and Storage C o e f f i c i e n t o f 1.06~10" tto k is 1.26x103 and the the larger 1.26~10' (the (thesmaller smallernumbers numbers are from from MW-6 MW-6 and l a r g e rfrom fromMW-112D). MW-112D). A markedseasonal seasonalf l ufluctuation plumesi is evident. The The A marked c t u a t i o n iin n the contaminant contaminant plumes s evident. plumes reach aa maximum maximum thespring spring (Fig. 9) 9) when when snow snow mmelt e l t and and heavy heavy rrains ains plumes reach i ninthe flush Later iinn the 10), f l u s h residual residual contaminants contaminants i into n t o the the aquifer. aquifer. Later t h e year year (Fig. (Fig. lo), lesser sizes, tto lesser recharge recharge i is s rreflected e f l e c t e d in i n the the greatly g r e a t l yreduced reduced plume plume sizes, o the the point point where evident. Since knownl eleaking where ddiscrete i s c r e t e sources sources become become evident. Since aalll l known a k i n g ffuel u e l storage storage tanks have beenremoved, removed,these thesecontaminant contaminantsources sources probablyare aree ieither residual have been probably t h e r residual fuel epikarst, f u e l in i n the the drift d r i f or t oin r isediments n sediments filling f i l l i n the g the epi karst,or oLNAPL r LNAPL trapped trapped in in fractures fractures above above the high high water water table. table. CONCLUSIONS CONCLUSIONS Carbonate young regimes Carbonate hydrogeology, hydrogeology, even even in i n young regimes such such as as tthe h e rrecently ecently glaciated influenced byby karst l a c i a t e d Midwest, Midwest, often o f t e n isi sstrongly s t r o n 1y influenced k a r development s t developmentwhich whichmay may I be It isi ssuggested i n rock rock cores. cores. It suggested that, t h a t iiff e so so subtle as as to t o be be unnoticeable unnoticeab e in potentiometric flow maps prove difficult potentiometric f l o w ma s prove d i f f i c u l t tto o interpret, i n t e r p r e t , innovative innovativedata data handling hand\ i n g </ techniques techniques may may be be needed. nee ed. REFERENCES REFERENCES CITED CITED Farrand, W.R. W.R. and and D.L. D.L. Bell, off Northern B e l l , 1982, Map Hap ooff Quaternary Quaternary Geology Geology o Northern Michigan, Departmentoof Natural Resources, Resources,Geological Geological Survey SurveyDivision, Division, Michigan, Michigan Department f Natural Lansing, Lansing, Michigan. Michigan. Ostrom, M.E. andA.E. A.E. Slau Slaughter, Ostrom, M. E. and hter, 1967, 1967, Correlation CorrelationProblems Problems of o f the theCambrian Cambrian and and Ordovician Areas, northern Northern Peninsula Peninsula ooff Nichigan, Michigan, Michigan Basin Society, Society, Ordovician Outcrop Areas, June, June, 1967. 1967. Sinclair, the Groundwater Resourcesoof Delta Sincl a i r , W.C., W .C., 1960, 1960, Reconnaissance Reconnaissance o of f the Groundwater Resources f D elta County, Geological Survey County, Michigan, Michigan, Michigan Michigan Department Department of o f Conservation, Conservation, Geological Survey Division, Division, Lansing, Lansing,Michigan, Michigan,Progress ProgressReport ReportNumber Number 24. 24. Vanlier, Resourcesoof Van1 i e r , K.E., K. E., 1963, 1963, Reconnaissance Reconnaissance oof f the Ground-Water Ground-Water Resources f Alger County, County, Michigan, Michigan, Michigan Michigan Department Department of o f Conservation, Geological Geological Survey Division, Division, Lansing, Lansing, Michigan, Michigan, Water Water Investigation I n v e s t i g a t i o n 1. 1. 61 �ORIGIN MAFIC DIKE ORIGIN OF OFTHE THEEARLY EARLYPROTEROZOIC PROTEROZOICKENORA-KABETOGAMA KENORA-KABETOGAMA MAFIC DIKE SWARM SWARM SCHMITZ, Mark D., WJRTH, Karl R., CRADDOCK, John P., Geology Department, Macalester SCHMTIZ, Mark D., WIRTH, Karl R., CRADDOCK, John P., Geology Department, Macalester College, College, St. Paul, Minnesota Minnesota 55105 St. Paul, 55105 The dike swarm swarm intrudes over over90.00 90,O km2 km2 of of northern Minnesota Minnesota and southern southern The Early Early Proterozoic Proterozoic Kenora-Kabetogama Kenm-Kabetogama dike Ontario. Dikeswere weresampled sampledfrom fromoutcrops outcropsthroughout throughoutthe theexposed exposedeastern easternportion portion of of the the swarm, swarm, from from the the Mesabi Mesabi Ontario. Dikes Iron Range, north to Kenora, Ontario. Samples from dikes buried beneath glacial cover in noithwestern Minnesota Iron Range, north to Kenora, Ontario. Samples born dikes buried beneath glacial cover in northwestern Minnesota were were obtained obtained from from drill drill core. Mne. The Theswarm swannisiscomposed composedof ofthousands thousandsof ofdikes, dikes, ranging ranging from from 1-120 1-120rn m wide, wide, some someof of which can be traced for over 100 km. Pllyric basalt at the quenched margins of the dikes coarsens to diabase and which be traced fot over 100 km. Phyric basalt at the quenched margins of the dikes coarsens to diabase and gabbro gabbro in in the the cores cores of of large large dikes dikes (>20 (a20 m m in in width). width). Rare Rarecomposite compositedikes dikes are are composed composed of of aa similar siniilarmarginal marginal basalt basalt and have medial felsic granodiorite intrusions. Dike margins are porphyritic, with plagioclase, pyroxene, and and have medial felac granodiotite intrusions. Dike margins are porphyritic, with plagioclase, pyroxene, andrare line Fe-Ti pyroxene, magnetite, %Ti oxide oxidephenocrysts phenocrystsin inaagroundmass groundmassof ofplagioclase plagicclasemicrolites, mictolites,pyroxene, magnetite, and and green green hydrous hydroussilicates; silicates; the of the primary primary inintruded magma. Alteration themargins marginsare are believed believed to tobest best represent represent the thecomposition composition of magma. Alteration within within dikes dikes is isvariable, variable, and and isisbelieved believedto tohave havebeen beenlargely largelydeuteric deutericin innature. nature.ItItwas wasnot notaccompanied accompaniedby bysignificant significantchemical chemical compositional compositionalchanges, changes,and andmobilization mobilizationof ofelements elementswas wasrestricted restrictedto toK, K,Rb, Rb, Sr, St,Ba, Ba,Ca, Ca,and andMn. Mn. All basalts following following aa tholeiitic All dikes dikesof of the theKK KKswarm swarmare arecomposed composedof ofFe-rich Fe-richquartz quartz normative normative basalts tholeiitic trend trend on on the AFM diagram. Dike margin rocks have nearly constant silica contents and exhibit a wide range in magnesium the AFM diagram. Dike margin rocks have nearly constant silicacontents and exhibit a wide range in magnesium index rocks. Coherent index (Mg/Mg+Fe), (Mg/Mg+Fe), typical typical of of continental continental tholeiitic tholeiitic rocks. Coherent trends tends of of Mg Mg depletion depletion and and Ti, Ti, PPenrichment enrichment with differentiation are seen on major element bivariate diagrams. Our data set shows a distinct grouping with differentiation are seen on major element bivariate diagrams. Our data set shows a distinct grouping of of samples samples into intohigh highMg-low Mg-lowTi, Ti,and andlow lowMg-high Mg-highTi Tigroups, groups,similar similartotothat thatseen seenby by Southwick Southwickand and Day Day (1983). (1983). Trace Traceelement elementanalyses analysesof ofthe thedikes dikeshave havebeen beenstudied studiedtotobetter betterconstrain constrain the thetrends trendsin inboth bothwithin-dike within-dikeand and inter-dike intet-dike variation. variation. Most Mostgabbro gabbrocore corerocks rockscan canbebesuccessfully successfullymodelled modelled from from their their basaltic basaltic margins margins using using major major element element mixing mixing and andtrace traceelement elementfractionation fractionationmodels. models. In In the thecomposite compositedikes, dikes, the theextremely extremelydifferentiated differentiated granodiorite granodioriteportions portionshave havetrace traceelement elementpatterns patternsexhibiting exhibitingboth both fractionation fractionation and contamination contamination processes. processes. Large Large negative Ta anomalies, and highly enriched incompatible elements including Th, require an upper crustal component Th,requirean crustal negative Ta anomalies, and highly enriched incompatibleelements of of contamination contaminationin inaddition additionto toextreme extremedifferentiation differentiationto toproduce produce the the granodiorites(Figure granodiorites(Figure 1). The Thenegative negativeTi, Ti,P,P, Zr, Sr, and Ba anomalies in the extended trace element patterns of these felsic samples are due to large degrees of Zr, Sr, and Ba anomalies in the extended trace element are due fractionation amphibole, fractionationincluding includingaccessory accessoryphases phasesofofapatite, apatite,zircon,ilmenite, zin-onÂ¥ilffldte amphibok,and and potassic potassicfeldspar. feldspar. Inter-dike variation has been studied using analyses from the margins of dikes. Margin (he dikes. Margin rocks rocksfall fallalong alongtwo two Intet-dike variation has teen studied using analyses distinct distinctarrays arraysin inplots plotsof ofcompatible compatibleelements elements(Ni, (Mi,Cr, Cr,Co) Co)versus versusZr Zr(Figure (Figure 2). 2). These Thesetwo twotrends trendscorrespond correspondtotothe the groupings based on major element chemistry. REE patterns of both groups are essentially parallel over large groupings on major element chemistry. REE patterns of both groups are essentially parallel over large variations variations in HFSE HPSE (Zr= (Zr=48-162 48-162 ppm). ppm). Both Bothgroups groupsofofdikes dikeshave haveflat flatMORE-like MORB-likechondrite.normalized chondrite-normalizedREE REE patterns [e.g. (La/Sm)CN= 0.86-1.07] with absolute abundances of 15 to 6th chondrite. The total absolute REE patterns 1e.g. (La/Sm)cN= 0.86-1.071 abundances of 15 to 60x chondtite. The total absolute RBE abundance abundanceisisclearly clearlycorrelated correlatedwith with the thehigh high and and low-Zr low-Zr groups (Figure (Fiime 3). AA distinctive distinctivedifference differencein in the the slopes slopesof of the HREE is the basis of Figure 4, which divides the high-Zr group into two subgroups; these two subgroups are the HREE is the basis of Figure 4, which divides the high-Zr group into two subgroups; two subgroups are believed believedto torepresent representdifferent differentmagma magmaseries seriesand andpossible possibledifferences differencesin in source. Within Withineach eachsubgroup, subgroup,the theREE REEand and extended extended trace (raceelement element patterns patterns suggest suggest aa fractionation Sactionation series. Eu Euanomalies anomaliesbecome becomeprogressively progressivelylarger larger with with increasing increasing enrichment, enrichment, suggesting suggesting fractionation fsaclionationof of plagioclase, plagioclase. consistent consistent with with major majorelement elementmodelling modellingand and petrographic petrographicevidence. evidence. Patterns Patternswithin withinthe thelow-Zr low-Zrgroup groupdodonot notillustrate illustrateaaclear cleardifferentiation differentiationsequence, sequence,but butshare share similarities similaritieswith withboth bothhigh-Zr high-Zrgroups. groups. Extended Extendedtrace daceelement elementpatterns patternsof ofthe diedike dikemargin marginsamples samplesare are well well correlated correlated with with the the exception exceptionof of the the highly highly incompatible incompatible mobile alkali elements, Cs, Rb. Rb, K, K,and to some some extent Ba. Ba. Low Lowabundances abundancesof ofthe thehighly highly incompatible incompatibleelements elementsare aresimilar similarto toMORE MORBand andindicate indicateaa depleted depletedsource. source. Little Littleevidence evidenceof ofcrustal crustalcontamination contamination isisseen, (0.47.0.85) ratios. Samples seen,as asindicated indicatedby byminor minorTa-anomalies, Ta-anomalies,and andlow low(TlilLa)CN (Th/La)cN (0.47-0.85) Samplesof of KK KKdikes dikesplot plotininthe the N-MORB N-MORB field fieldof ofFigure Figure1,1,with withvery veryfew fewsamples samplespulled pulled along along aa vector vector of of crustal crustal contamination. contamination. This Thisdiagram diagram illustrates illustratesthe thedistinct distinctcomposition compositionofofdikes dikesnear nearTower, Tower,MN, MN.and andthose thosefound foundinindrill drillcore corefrom fromnorthwestern nonhwesternMN. MN. 62 �A dike near Tower, MN with a trend and field characteristics similar to those of the KK swarm is seen to have a very different face element chemistry. It has enriched, OIB-like REE and extended trace element pattterns, and plots within the OrB field of the Hf13-Th-Ta diagram. It also shows a low degree of crustal contamination. The Tower dike represents a melt from a different magma source not observed elsewhere in the KK swarm, and might be related to a different magmatic event (i.e. Keweenawan Rift). While the thousands of NW-trending dikes observed in northwestern MN by aeromagnetics have been previously assumed to be of KK affinity, the six samples of four drill cores analyzed have trace element patterns that are distinct from the rest of the KK swarm (Figure 3). Two of the dikes sampled appear to have reversed polarity aeromagnetic signatures. The three samples from these "reversed" dikes have similar REE and extended flee element patterns: highly enriched in incompatible elements, similar to OIB, with large negative Ta and P anomalies suggesting crustal contamination. The other two dikes have "normal" polarity. Samples from one dike have OIB like patterns highly enriched in incompatibles and show signs of extreme cuistal contamination. A sample from the other "normal" dike is highly. altered,. but has a distinctJlat trace element pattern similar to MORB. These dikes from northwestern MN might berepresentatives of one or more different dike swarms. Conversely, they might be part of the Kenora-Kabetogama swarm, with their different compositions a function of extreme crustal contamination, or the tapping of different mantle sources. Reference: Southwick, D.L., and Day W.C., 1983, Geology and petrology of Proterozoic mafic dikes, northcentral Minnesota and western Ontario: Canadian Journal of Earth Sciences, v. 20, p. 622-638. Figure 1 Hf /3 Figure 2 Th Zr 1000 Towcrdjk, 1k Bewnce *11 o,.t NonF till Ce 4nur drill Cat Graaoditt.. --—,- I a 13 High Zirtonium Basalts Is Low Zireonlun' fla..lt. 1410 1.2 I.' 1 I I LaCe Figure 3 I Nd J..l SmEu REE I Th II Yb Lu 40 Pa Low Ziivonium Basalts 60 80 100 120 Zr 140 160 180 Figure 4 63 �I r THE ROCKS GEOLOGICAL MARATHON: MARATHON: THE ROCKS OF OF THE THENORTH NORTH SHORE SHOREOF OFLAKE LAKE AA GEOLOGICAL I SUPERIOR SUPERIOR SMYK, MarkC.,C., and SCHNIEDERS, BernieR.,R.,Ontario Ontario Geological SMYK, Mark SCHNIEDERS, Bernie Geological Survey, Survey, Ministry MinistryofofNorthern NorthernDevelopment Development and and Mines, Mines, Suite Suite B002, B002, 435 435 James James St. St. South, South, Thunder Thunder Bay, Bay, ON, ON, P7E P7E 6E3 6E3 i s underlain underlain by by aa variety v a r i e t y of of Lake Superior Superior is The north north shore shore of of Lake The Precambrian Precambrian rocks rocks and and hosts hosts numerous numerous economic economicmineral mineraldeposits. deposits. The hosted by by the t h e Town Town of of The 41st 4 1 s t Institute I n s t i t u t e on on Lake Lake Superior Superior Geology, Geology, hosted Marathon exceptionally varied varied Marathon in i n 1995, 1995, will w i l l highlight highlight the t h earea' area1s exceptionally geology. geology. Neoarchean Neoarchean greenstone greenstone belts b e l t s and and granitoid granitoid plutons plutons of of the t h e Wawa Wawa The supracrustal subprovirice underlie most The supracrustal rocks rocks subprovince underlie most of of the the region. region. (2.77 (2.77 to t o 2.70 2.70 Ga) Ga) consist c o n s i s t of of komatiitic komatiitic to t o tholeiitic t h o l e i i t i c basalt, basalt, caic-alkalic c a l c - a l k a l i c basalt b a s a l t to t o rhyolite, rhyolite, clastic c l a s t i c sedimentary sedimentary rocks rocks and and i r o n formation. formation. They They have have been been tectonically t e c t o n i c a l l y juxtaposed, juxtaposed, deformed deformed iron and and intruded intruded by by massive massive to t o gneissic gneissic granite, granite, granodiorite granodiorite and and tonalite. t o n a l i t e . Greenstone Greenstone belt b e l t rocks rocks host host the t h e gold gold. deposits deposits at a t Hemlo Hemlo (Field the (Field Trip Trip 1), I), t h e volcanogenic volcanogenic massive massive sulphide sulphide (VMS) (VMS) deposits deposits at a t Manitouwadge Manitouwadge (Field ( F i e l d Trip Trip 2) 2 ) and and the t h e VMS VMS and and gold gold deposits deposits of of The Wawa Wawa the 3). The t h e Winston Winston Lake Lake and and Schreiber Schreiber area area (Field (FieldTrip Trip3). subprovince subprovince was was amalgamated amalgamated with with the t h e accretionary accretionary prism prism rocks rocks of of the t h e Quetico Quetico subprovince subprovince to t o the t h e north north during during late l a t e Neoarchean Neoarchean plate plate convergence convergence and and crustal c r u s t a l transpression. transpression. Paleoproterozoic Paleoproterozoic sedimentary sedimentary rocks rocks are a r e represented represented by by the the Gunflint Ga) and Rove Gunflint (2. ( 2 . 11 Ga) Rove formations formations of of the t h e Animikie Admikle Group. Group. Mesoproterozoic, Mesoproterozoic, pre—Keweenawan pre-Keweenawan rocks rocks consist consist dominantly dominantly of of red-bed of the t h e Sibley Sibley Group Group(1.34 (1.34 Ga). Ga). red-bed sedimentary sedimentary rocks rocks of The The development development of of the t h e Midcontinent Midcontinent rift r i f t (1.11 (1. 11 to t o 1.09 1.09 Ga) Ga) resulted r e s u l t e d in i n the t h e deposition deposition of of Keweenawan Keweenawan lavas lavas and and sedimentary sedimentary rocks rocks of of the t h e Osler Osler Group, Group, now now exposed exposed on on offshore offshore islands. islands. Associated Associated intrusive i n t r u s i v e rocks rocks include include the t h e Prairie P r a i r i e Lake Lake carbonatite, carbonatite, diatremes, K i l l a l a Lake Lake and and Coldwell Coldwell alkalic a l k a l i c complexes, complexes, diatremes, the t h e Killala (Field 4 ) and and tholeiitic t h o l e i i t i c diabase diabase sills s i l l s and anddikes. dikes. The The (Field Trip Trip 4) Coldwell Coldwell complex, complex, the t h e largest l a r g e s t alkalic a l k a l i c complex complex in i n North North America, America, consists consists of of three t h r e e intrusive i n t r u s i v e centres centres of of gabbroic gabbroic to t o syenitic syenitic magmatism. magmatism. Significant S i g n i f i c a n t deposits deposits of of copper-nickel-PGE, copper-nickel-PGE, rare r a r e metals metals associated with (T, Zr, Z r , Be) Be) and and rare-earth rare-earth elemei±ts demerits aare r e associated with these these (Y, intrusive i n t r u s i v e rocks. rocks. The ( F i e l d Trip Trip 5) 5) are a r e aa crucible c r u c i b l e of of geologic geologic The Slate S l a t e Islands Islands (Field The majority majority of of the t h e islands i s l a n d s are a r e underlain underlain by by Neoarchean Neoarchean activity. a c t i v i t y . The supracrustal supracrustal rocks rocks which which are a r e unconformably unconformably overlain overlain by by Paleoproterozoic Keweenawan Paleoproterozoic Animikie Animikie Group Group sedimentary sedimentary rocks. rocks. Keweenawan Osler Group basalts and diabase comprise the Mesoproterozoic, Osler Group basal ts and diabase comprise t h e Mesoproterozoic, Perhaps the t h e most most unique unique aspect aspect of of Midcontinent Midcontinent rift r i f t assemblage. assemblage. Perhaps the islands' geology is the extensive development of shatter t h e islands1 geology i s t h e extensive development of s h a t t e r cones, cones, which which have have been been alternatively a l t e r n a t i v e l y ascribed ascribed to t o hypervelocity hypervelocity meteorite meteorite impact impact and and endogenic, endogenic, volcanic volcanic activity. activity. I 1 , I I I 64 �UPDATE ON THE GEOLOGICAL GEOLOGICAL CORE CORE MARQUETTE, MICHIGAN MICHIGAN AND SAMPLE SAMPLE REPOSITORY REPOSITORY - MARQUETTE. - I I WWilliam i l l lam 1. T. Swenor, Swenor, Geological Technician Technician Milton A. Gere, Jr., Regional Regional Geologist Geologist Milton A. &re, Jr.. Geological Survey Survey Division, Division, Michigan RegionI I,,Marquette, Geological Michigan DNR, DNR, Region Marquette, MI MI The Michigan Michigan DNR' DNR's GeologicalSurvey SurveyDivision Division (GSD) maintains the Geological The s Geological (GSD) maintains Geological Core Coreand andSample Sample This "Rock Library" collection collection of currently "Rock Library* o fcore coreand and samples samples currently Repository aatt Marquette, Marquette, Michigan. Michigan. This represents36 36oof the83 83counties countIesi ninthe the state: state; however, theMajority majority ooff the materials are from however, the from represents f the the western one-half of the Upper Peninsula. Thus, Precambrian agedrocks rocks are are lmore represented western one-half o f the Upper Peninsula. Thus, Precambrian aged o r e represented than the Paleozoic materials. than Paleozoic aged aged materials. As ooff the end ooff 1993, Repositorycollection collection contains As 1993, the the Geological Geological Core Core and and Sample Sample Repository contains778 778 complete complete feet, filling drill from195 195 holes holes ddrill r i l lhole holecores cores totaling totaling 236,436 236,436 feet, f i l l i n g17,135 17,135 boxes; boxes: d r i l lcuttings cuttingsfrom representing 64,154 64,154feet feet ooff ddrilling contained abbreviated representing rilling containedini 507 n 507boxes; boxes; 386 386holes holes represented represented by abbreviated core from from 131,855 131,855feet feetoof f ddrilling, r i l l i n g ,held heldin i1,907 n 1,907boxes; boxes:174 174boxes boxes of o fmiscellaneous miscellaneous materials core overburdend drilling assay pulps, pulps, etc.) soils, overburden etc.) (chip samples, samples, soils, r i l l i n g materials, materials, outcrop outcropsamples, samples, assay Including 4,498 4,498feet feet ooff represented overburden Thisgives givesaacollection collectiont total including represented overburden d rdrilling. i l l i n g . This o t a l of o f 1,404 1,404 feet (82.75 (82.75miles) miles)oof alll l contained ddrill r i l lholes holesrepresenting representing 436,943 436,943 feet f ddrilling r i l l i n gplus plusother othersamples, samples, a contained in 19,723 boxes of materials. i n 19,723 boxes o f Thecore coreand andsample sample collectioncontinues continues grow better represent The collection t otogrow i ninanan e feffort f o r t t to o better represent the geology geology ooff the state. Materials are submitted to the Repository from a number of sources: 1) As partial are submitted t o the Repository from a number o f sources: 1) As a-apartial requiremento foff ufulfilling various state state requirement l f i l 1ingstate statemetallic metal 1i and c andnon-metallic non-roetall i cmineral mineral leases; leases; 2) 2) From Frcia various sponsoredprojects: projects;3)3) Through Throughcompany company donations of single holes large collections;4)4) sponsored donations o f single holes on on up up t o to large collections; Fromother otherstate state and agencies, such such as as the the US. U.S. Bureau Mines. From and federal government government agencies, Bureau ooff Mines. 146holes holestotaling totaling 34,639 34,639feet feetoof addedt otothe thecollection. collection. IIn n 1993, 1993, 146 f ddrilling r i l l i n gini n3,677 3,677 boxes boxes were were added Muchoof Exploration, Inc. Inc. Much f the core core was was donated donated by by Western Western Mining Corporation Corporation and and Resource Resource Exploration, Besidesthe themany many Shaled drilling, as the Western Syncline, or or Besides d rdrill i l l holes holes of o f Nonesuch Nonesuch Shale r i l l i n g , known known as Western Syncline, PresqueI sIsle deposit, Resource Exploration, Inc. Inc. donated boxesooff outcrop Presque l e deposit. Resource Exploration, donated 125 125 boxes outcrop samples, samples, ssoil oil samples,assay assaypulps, pulps,splits, splits, etc. along results from work iinn the samples, alongwith withhundreds hundreds of o f assay assay results from previous previous work U.P. This aalll l helps useful. U .P. This helps our our collection collectionbe bemore more useful. I I I I I I I SomeCore Core and sample materials on-loan several universities ffor Additionally, SOM and sample materials areare on-loan t o to several universities o r research. research. Additionally, material iiss reviewed on-site or or borrowed short tern term studies studies periodically periodically by material reviewed on-site borrowed f ofor r short by consultants, consultants, exploration and academiaand andindividuals. individuals. and mining mining companies, companies, academia TheRepository Repositoryi sisalso alsothe the storage storagessite DataCollection. Collection. The i t e for f o r the theG.5.D.'s 6.s.D.'~ Metallic MetallicMine MineMap Hap and and Data During 1993, 1993, the the balance balanceooff the inventoried was During inventoriedcollection collection wasmoved moved from fron Lansing Lansing ttoo Marquette. Harquette. Additionally, we several years we obtained obtained a collection collectionofo M.A. f M.A. Hanna's Hanna's Michigan Michigan materials and and several years ago ago we also received receivedaalarge large collection collection ofo fUSX andcross crosssections, sections, etc. etc. These These w e also USX (U.S. (U.S. Steel) Steel) mine nine maps maps and materials assist with andthe themine minesubsidence subsidence potentiali nInspecific specific materials with understanding understanding ooff the geology geology and potential areasoof thestate, state, thus thus they they also also are are an anaid aidt to the public public safety. safety. areas f the o the Thef facility thethe corecore andand cuttings, by appointment ononweekdays The a c i l i t yisi sopen ooenfor forvisitors v i s i t o rto s study t o study cuttings, by a~wintntent weekdays between8:30 8:30a.m a.m. and4:W 4:00p.p.m., Eastern tine. time. Some Somesampling samplingcan canbebearranged arrangedf ofor onaa case-bycase-bybetween . and m., Eastern r on case basis. Copies Copiesoof dataderived derivedfro from thestudy studyo of thecollection collection are are ttoo be be case f data m the f the be submitted submitted tto o be madepart parto of thepublic public record recordf for For information informationor or an an appointment, appointment,c acall made f the o r future use. use. For l l BBill ill SwenorororMMilt Swenor i l t Gere &?re at a t 906-228-6561. 906-228-6561. maintainsa11 all we1 well1 logs and thousandso fofselected selectedwe11 wellcuttings cuttingsf for Additionally, the theGSD GSD maintains and thousands o r ooili l and and gas wells wells In Waterwell wellrecords recordsf ofor the entire entire state are gas i n Lansing. Lansing. Water r the are also also kept kept in i nLansing Lansing by by the GSD. information. Copies Copiesoof Peninsula, Region RegionII,,water BSD. Call 517-334-6907 517-334-6907 f ofor r information. f aall l l Upper Upper Peninsula, water well records and andselected selectedwell wellcuttings cuttings are maintained maintainedby bythe theBGSD theDNR' DNR's office near near records SD at at the s D i sDistrict t r i c t 3 3Office information. Escanaba. Call Frank Frank Chenier Chenier aatt 906-786-2351 906-786-2351 f for o r more more information. 65 �GOLD POSSIBILITIES INI MICHIGAN' SS lATE ARCHEAN HENLCCK GOLD POSSIBILITIES N MICHIGAN' LATE ARCHEAN HEMLOCKFORMATION, FORMATION, AND THE PAINT RIVER GROUP IS STILL A USEFUL STRATIGRAPHIC AND THE PAINT RIVER GROUP IS STILL A USEFUL STRATIGRAPHICTERM. TERM. TROW, Jim,Department DepartmentofofGeological GeologicalSciences, Sciences, Michigan MichiganState State University, TROW, Jim, University, East lansing, Michigan 4882k East lansing, Michigan 48824 Almost everyoneseems seemst oto believe believe that Formation is is Proterozoic. that the theHemlock Hemlock Formation Froterozoic. Almost everyone However, However, aa late late Archean Archean age age for f o r the the Hemlock Hemlock is is suggested suggested by by Francis Francis Pettijohn's Pettijohn's field mapping (1951, USGS OF) of T.42N., R.30W., Dickinson County, f i e l d mapping (1951, USGS OF) of T,42N., R.30W., Dickinson County, by by Dave Dave Paddock's Paddock's gravity gravity survey survey (1982, (1982, MSU MSU MS MS Thesis) Thesis) of of the the Iron Iron River-Crystal River-Crystal Falls Falls Basin by Jim Jim Basin showing showing tthat h a t the the Hemlock Hemlock and and the the Badwater Badwater both both underlie underlie the the Basin, Basin, by mow's 1st Symposium) using U USGS aeromagnetic datat oto-trace trace three Trow's (1989, (1989, NGS MGS 1st symposium) using SGS aerorcagnetic data three magnetic horizons (Mansfield the Hemlock, Hemlock,East EastKKiernan magnetic horizons (Mansfield member member ofofthe i e m SSill, i l l , and and Skunk Creek I-F) from Iron County S and E along strike into the late Archean Skunk Creek I-F) from Iron County S and. E along s t r i k e into the lateArchean Dickinson GroupSix-Mile Six-Nilelake lake and and Solberg Solberg strata strata inInDickinson Dickinson Group Dickinson County, County, and and.by by Warren Beck's and Rama Murthy's (1991, USGS Bl904—I) recent Hemlock Nd Warren Beck's and Kama Murthy's (1991, USGS 31904-1) recent Hemlock Nd errorerrorchron chron with with an an age age of of 2.7 2.7 ±? 0.5 0.5 Ga. Ga. To reconstruct palinspastically To reconstruct palinspastically to t o an an early early Penokean Penokeanpattern, pattern, the theAinasa Amasa Oval and related domes are translated back 5 miles 55W along the Bush Oval and related, domes a r e t r a n s l a t e d back 5 miles SSW along the Bush lake lake Fault, f a u l t , and and rotated rotated back back 60 60 counterclockwise counterclockwise to t o appear appear tot obebealmost ahnostE-W E-w Archean endofofthe the gneissic gneissic core AnasaOval Oval Archean trends trends.• The The now—northern now-northern end coreof ofthe theAmasa appears to andDave Dave Wen-long Ueng Ueng and appears t o have have originated originated near near present present Iron IronRiver. River. lien-long larue v. 7, similar rotation. rotation. Iarue (1988, (1988, Tectonics, Tectonics, v. 7, no. no. 3) 3) envisaged envisaged aa somewhat somewhat similar At the Iron Iron placergold gold.panned panned from from the Iron River River aatt Iron A t the the turn turn of of the thecentury, century,placer River if traced River led lednowhere nowherewhen when traced tracedNW NW upstream. upstream. However, tracedNE MEup—ice up-ice in in However, if the Pleistocene (with SW SWglacial glacialmotion) motion)itit leads the IangJade -lade Pleistocene Lobe Lobe (with leads back back to t o the the northern Hemlock northern half halfofofthe the Hemlockofofthe theAinasa Anasa Oval. Oval. Bill B i l lCannon's Cannon's 10 1 xx 22 Iron Iron River Map 1-1360-A)shows showsairborne airborne EEM anomaliesinin this River Quadrangle Quadrangle(1985, (1985,USGS USGS M ap I-1360-A) M anomalies area thethe Amasa area and and in Inthe thesouthern southernhalf h a lof f of AmasaOval, Oval,which whichWarren Warren Peterson's Peterson's 10x 1 x 22 Iron 1—1360—a) suggests occuri ninthe the area area of *on River RiverQuadrangle Quadrangle(1985, (1985,USGS USGS Nap Map I-1360-C) suggests occur of W and NW NWglacial-motion glacial-motion vectors vectors of W and. of the theGreen GreenBay BayLobe. Lobe. If Sims (1992, USGS I f the theHemlock Hemlock isisArchean, Archean,then thenPaul Paul Sims (1992, USGSMap Map 1-2185) 1-2185) cannot cannot use supposed correlation correlation with use its itssupposed withthe theProterozoic ProterozoicBadwater Badwater Greenstones Greenstones to to justify thethe Paint River Group with thethe Michigamme justifycorrelating correlating Paint River Group with Michigwme Formation, Formation, aallthough the latter plausible forf Marquette County, though the lattercorrelation correlationis is plausible o r Marquette County,where where ClarksClarksburg equalBadwater, Eadwater,and andthe theBBijiki equal the the Riverton i j i k i I-F I-F may may equal Riverton I-F. I-F. HowHowburg may may equal ever, ever, that t h a tcorrelation correlationdoes doesnot notsquare squarewith w i t hobservations observations to tothe thesouth southwhere where an an almost WSW canbeIetraced traced W S W within w i t h i n the the almost complete complete Marquette Marquette Supergroup Supergroup section sectioncan Calumet Calunet Though Trough (and (and its its westward westwaxd extension) extension) from from the the Randville Randville Dolomite Dolomite at a t the the Calumet Calumet Iron Iron Mine, Mine, sec. sec. 8. 8. T.klN., T.&lN., R.28., R.28., Dickinson Dickinson County, County, stratigraphically stratigraphically upward Wisconsin, holes and and exposures exposures of of Paint upward to t o Commonwealth, Commonwealth, Wisconsin, d rdrill i l l holes Faint River River Group sequenceexposes exposesnonoHemlock, Hemlock, Group rocks rocks.• This This conformable conformable sequence asasi lillustrated l u s t r a t e d in In the stratigraphic column. Michigamme the accompanying accompanying strat$graphic column. Here, Here, the thethick thick Michigamme gradedgradedbedded graywackiesunderlie underlie the the Badwater Badwatel'and andthe theeentire bedded graywackies n t i r e Paint Faint River River Group, Group, as as suggested H a lJames James(1958, (1958,USGS USGSP314-C). ~314-c). suggestedby byHal This T h i s north/south north/south stratigraphic stratigraphio dilemma dilemma may nay be be reconciledby reconciled by seimentology: sedimentology: If If Marquette Marguette Supergroup Supergroup sedimentary sedimentary basin basin development development migrated migrated northward, northward., as as the Penokean orogeny soon thereafter rolled northward, then the appropriate the Penokean orogeny soon thereafter r o l l e d northnard., then the appropriate environment Michigamme in Iron Ironand and environment for f o rthe thethick thick Michiganae graded-bedded graded-bedded graywackes graynackes in Dickinson Counties may have occurred in Baraga "time", whereas that environDickinson Counties may have occurred In Baraga "time", whereas that environment maynot nothave haveexisted, existeduuntil late int River "time" nearnear lakelake Nichigamme, ment may n t i l late Faint River "time" Michigamme, in Marquette County. This involves merely fine tuning excellent Survey work. i n l&rguette County. This Involves merely fine tuning excellent Surveywork. The meatand andpotatoes potatoesbottom bottoml iline of this this paper A Along-unrecognized The meat n e of paper is isthis: this: long-unrecognized Archean greenstone bbelt probably contains gold. Archean greenstone e l t (Hemlock) gr em lock) probably gold. Let's L e t ' s go go: thiso 66 �I I I I I I I I I I I I I I I I I I Pre-KeweenawanRocks RocksIninIron Iron and and Dickinson Dickinson Counties, Counties, Michigan, N. Pre-~eweenawan Michigan,by byJim J i mThow, Trow, M . S. 5. U. U. Iron County Dickinson . Dickinson County Iron County - .1 Fortune lakes Slate $1 Fortune Lakes Slate 0 > ft Hiaatha Graywacke Hiverton Iron—Formation Dunn Creek Slate (with Wauseca Pyritic Member) '4 +' 51 —4 I ' Badwater Greens tone Jflebigamme • 0 •-1 Granite, Diorite, Granite, Diorite, Pegnatite fegmatite lie tagabbro Metagabhro Intrusive IntrusivePeavy PeavyPond PondComplex Complex Badwater Gre en tone Formation Nichigamme Formation Vulcan Vulcan Iron-Formation Iron-Formation Felch Formation Felch Formation 63 à Felch Formation Formation Felch (quartz-mica schist, (quartz-mica schist, garnetm e t grunerite schist, quartzite, grunerite schist, quartzite, fe1dsthic quartz-mica feldsmthic quartz-flea schist schist greenschist of his Iameys DickinsonkENXXXXXXfl4.Ealus greenschist of h i s Dicfclnson suIameyls1961 1961FF310 PP33.0 p.p.131— 131Horizon?* 133 ainfaibolite) Group) amitibolite) ~ roup) Horizon?* Raudvifle Dolomite Randville Dolomite BanilvllleDolOBite Banilville Doldte (slate, graywacke, - ft9 (slate, g r a y n a ~ hquartzite, quartrib, 0 Â¥ arkose plus Bayiey' 2 = yivs B ~ Y ~ sY1959 1959 's ° B1077 B1077 p. p. 14—i? magnetic 11-17 -tic se ;; , g Sturgeon Quartzite Quartzite Sturgeon -. u 0 Pem Fern Creek 28 Creek Formation Foniation ° Sturgeon Quartmite Sturgeon Quartnit8 Fern Creek Formation Fern Creek Fomation some arkose) arkose) (including some (including f% lciernan ~ S i lSills l sanda other n d Metagabbros Metagabbros ; I o ~ A 0 c fletagabbro (Aiqfaibolite) (Mjtiboflte) Hetagabla-o 8 — S.d >4' ?2 41.1;, ^M Unnamed Graywa eke ?=? ?? Fence Graynaeke Fence Lake Strata in SE Baxaga Co. IalceStrataInSl3BaxagaCo. 0 Gneissic Granite Gneissic Granite and Banded Gray Gneiss A 4 G4 0--I id -0 .a S An8sa—Fence River Iron—FormagAm6a-Fence River Iron-Fonnations tions s-at -'-4 $4 't 51051 Formation (inciuang Hemlock Formtion (including p1 Mansfield IronBird and Mansfield Bird and IronFormations) & h i Formations) 'd .p o d 4' Quartz-Sericite--Magnetite Z rI cdN Quartz-sericite-Vagaetite ' Schist, Skunk Skunk Creek Creek IronIronO'd-.-I Schist, 0 TI.—I 2 Formation, and andPorphyritic Porjyritic El —143--4 (3 Fen-nation, *> 8 51 Red Felsite 0 Bed Felslte g " g-'-I 2(0 .C $-i >3 Magnetic low low nay My be be East Magnetic East or Porphyritic Porphyritic Ph 014 Branch Arkose Branch Arkose or Red Red Granite Granite - Nargeson IkCgeSOII Creek Gneiss Gneiss of of Aiinsa Oval Asaaa.Oval I, + ^2 .-I ! 4 5 4 IL I Unnamed Graywacke (see Janes, James Unnamed Graywacke (See 1961, PP310, PP31O,p.p. 25.) 25.) 1961, ! Grunerite Zone in Six-Mile 0) Grunerite Zone In Six-Mile 0, lake -1' Amphibolite Six-Nile lake Amphibolite Six-Bile lake Anphilollte 40 C ss Onl a .J -d 5 051 0 % o 2 Solberg Schist (inclmling (including S o l k g Schist Skunk Creek Creek Iron Iron Formation) Skunk Formation) ; I ! * i I East Branch East Branch Arkose Ark- 4, Red Granite Gneiss of R e d Granite Norway lake area Noruaybke- - *Outsidearea area discussed, discussed, Quinnesec Quinnesec Fornation Formation overlies overlies Randvifle Â¥Outsid BanAvllleDolomite Dolomite in Wisconsin (mow), and overlies in Wisconsin in InMenominee Henodnee River R i v e r ESE SSS from tram Pembine Pemblne ( Trow), aod narbles, on W, W, N,N, and and.EEsides sides of marhies. arkosites, arkoeites, quartzites, qusu-kites, and and schists schists on Duntar Duntar gneiss dome dome (Schulz, (Schuiz, 1982, 1982, Inst. Inst. on onL. L.Superior SuperiorGeo1ogy Geology, pp.- 43) 43) 6-7 �PETROGRAPHY OF THE THE UPPER PETROGRAPHY AND DIAGENESIS DIAGENESIS OF UPPERCAMBRIAN CAMBRIAN MT. MT. SIMON SIMON SANDSTONE, SE MINNESOTA. SANDSTONE, SE MINNESOTA. URIBE, URIBE, Ruben Ruben D., D., Department Department of of Geology, Geology, University University of of Minnesota— MinnesotaDuluth, Duluth, MN 55812. Duluth, Duluth, MN 55812. The The Mt. Simon Simon Sandstone Sandstone is is the the lowermost lowermost formation formation of of the the Dresbachian Dresbachian The stage . stage (Upper (UpperCambrian) Cambrian). The unit unit rests rests unconformably unconformably on on aa wide wide variety variety of of Precambrian Precambrian rocks rocks in in southeastern southeastern Minnesota. Minnesota. Its Its average average thickness thickness is is about about 260 260 feet. feet. The The Mt. Mt. Simon Simon Sandstone Sandstone is is dominantly dominantly aa medium—to (Q954F41L05) white medium-to fine—grained fine-grainedquartz quartzsandstone sandstone white to togray, gray, noticeable featureof of(Q95.4F,.iLo.5) the unit unit is is with with sporadic sporadic thin thin shale shalebeds. beds. A A noticeable feature the The presence presence of the of authigenic feldspar. The the abundance abundance of authigenic potassium potassium feldspar. of mineralization of authigenic authigenic feldspar feldspar may be correlated correlated with mineralization of midcontinent midcontinent Mississippi Mississippi Valley—type Valley-type lead—zinc lead-zinc deposits. deposits. Petrography microprobe analysis Petrography and and microprobe analysis were used used to to identify identify the the framework framework and and matrix matrix constituents constituents of of the the Mt. Simon Simon Sandstone Sandstone and and to to determine determine the the diagenetic diagenetic textures, textures, paragenetic paragenetic sequence sequence and and chemical chemical composition total of of 95 95 thin thin sections sections were were composition of of authigenic authigenic minerals. minerals. AA total All studied - All studied and and point point counted counted with with 600 600points pointson oneach each(Table (Table1)1). samples samples were were from from drill drill holes. holes. The The sandstone sandstone has has undergone undergone aa varied varied diagenetic diagenetic history, history, which which includes includes precipitation precipitation and and dissolution dissolution of of authigenic authigenic minerals, minerals, Potassium dissolution dissolution of of unstable unstable detrital detrital grains, grains, and and compaction. compaction. Potassium feldspar feldspar is is the the most most common common authigenic authigenic mineral mineral in in the the Mt. Mt. Simon Simon Sandstone. Sandstone. The The feldspar feldspar is is present present in in almost almost all all the the samples samples as as euhedral euhedral to to subhedral subhedral overgrowths overgrowths on on detrital detrital grains, grains, ranging ranging from from 0.2 0.2 to The overgrowths overgrowths are are not not to 23.5 23.5 volume volume percent percent in in the the thin thin sections. sections. The in in optical optical continuity continuity with with the the detrital detrital cores, cores, and and are are usually usually pure pure orthoclase orthoclase in in composition, composition, as as evidenced evidenced by by electron electron microprobe microprobe detrital quartz contacts and and analysis. Quartz cement cement is is present along detrital analysis. Quartz Authigenic dolomite in dolomite in very very few few cases cases as as distinct distinct overgrowths. overgrowths. Authigenic exhibits two rhombic*exhibits two different different textures: textures: 1) 1) Euhedral, sand—sized sand-sized rhombic— shaped shaped crystals crystals with with considerable considerable zonation zonation showing showing iron—rich iron-rich (red) (red) and and iron—poor iron-poor (clear) (clear) dolomite, dolomite, and and 2) 2) Rhombic Rhombic fine—grained fine-grained subhedral subhedral crystals illitic matrix. matrix. Poikilotopic calcite is found in a crystals replacing replacing illitic few few samples samples partially partially replacing replacing detrital detrital and and authigenic authigenic minerals. minerals. Calcite Calcite is is also also present present as as isolated isolated patches patches filling filling pore pore spaces. spaces. Two texturally Kaolinite Kaolinite cement cement is is present present in in nearly nearly all all samples. samples. Two texturally well—crystallized vermicular vermicular different different types types of of kaolinite kaolinite occur: occur: 1) 1) Well-crystallized aggregates Micron-sized particles particles finely aggregates in in pore spaces spaces and 2) Micron-sized laminated laminated around around detrital detrital grains, grains, displaying displaying aa wavy—looking wavy-looking pattern pattern Other secondary parallel to the stratification. parallel to the stratification. secondary authigenic authigenic minerals minerals found found in in the the unit unit include include hematite, hematite, pyrite pyrite and and leucoxene, leucoxene, present present as as grain grain coatings coatings and and pore pore fillings. fillings. The The total total average average porosity porosity for for all all the the samples samples taken taken from from the the Mt. Mt. Simon Simon Sandstone Sandstone is is 15.5 15.5 percent; part of of it it is is secondary secondary porosity porosity which which is is evidenced evidenced by by dissolution dissolution of of cements cements and and labile labile detrital detrital grains grains throughout throughout the the unit. unit. The The final final objective objective of of this this study study is to describe the paragenetic sequence seauence of of the the authigenic authiaenic minerals. minerals. This part of the the study study is is presently in progress. �I HIA Bi 8Q9 SCH&KANV669 TOTAVE • I I P NUMBER OF SAMPLES 21 18 18 22 COMMON• 593 628 51.2 62.7 66,5 60.51 POLYCRYSTALLINE 2.0 1.6 31 0.6 41 2.30 VEIN(?) ,i 1.9 1.0 2.1 1.17 227 6503 1.4 1.4 1.0 1O . 0.1 0.3 1A2 1.42 0.34 0.34 1.05 1.05 2.81 16 QUARTZ g v MULTICYCLE FELDSPAR H TOTAL QTI 61.4 653 615 ORTHOCLASE ORTHOCLASE 2.2 2.2 1.9 1.9 0.5 0.5 MICROCLINE 1.0 1.0 MICROCLINF. PLAGIOCLASE F'LAGIOCLASE 0.5 0.5 0.3 0 3 3.1 3.1 TOTALFELDSJ'AR 17 54 I SEDIMENTARY MuscoviTE ... ILLI'rIC(')CLAY CEMENT CEMENT 0.4 •' 0.12 0.07 0.6 t22 0.4 0.4 0.3 :. 0.3!.. .: 0.1 0.12 0.1 0.03 1.6 37 14. 1.0 1.55 256 435 4.35 QUARTZ 3.9 1.9 2.7 1.9 2.4 PELDSPAR FELDSPAR 9,7 9.7 5.0 5.0 0.8 0.8 3.2 3.2 3.1 3.1 DOLOMITE 1.3 DOLOMITE 1.3 CALCITE 0.1 CALCITE 0.1 2.9 2.9 4.6 4.6 33.66 0.7 0.7 KAOLINITE KAOUNITE FOSSILS GLAUCONITE PORES : 1.3 1.3 LEUCOXENE 1.4 COLLOPI-IANE .. pyRIm REPLACED 0.4 . .FELDSPAR (F) CLASSIFICATION CLASSIFICATION (Q) FELDSPAR (F) LITHICS (L) UTHICS 0.9 0.9 1.28 1.28 0.1 0.1 0.08 1.78 1.78 0.08 0.4 0.4 1.3 1.3 HEMATITE HEMATITE • 1.59 1.59 0.4 0.4 8.3 8.3 0.5 0.5 PYRITE PYMTE QUARTZ I 18 00 0.6 :. SIDERITE S IDERITE . I .:. :; 0.3 0.6 0.6 . MICA MICA I I . METAMORPHIC TOTALROCKFRAIJ MATRIX ' 0.1 1.0 1.O 2.6 LOS : . BIOTITE I I• 643 ' 0.6 01 PLUTONIC ROCK FRAO. ... : • 4.1 4.1 0.27 . 02 0.2 . 1.4 02 . . 0.34 034 1.09 1.09 0,7 0.59 0.2 007 0.63 0.6 2.6 15:9 182 13.0 14.5 16.0 ISM 943 92.2 77.66 98.1 0.9 0.9 0.3 0.3 1.0 1.0 95.7 3.8 3.8 0.5 0.5 97.0 2.4 2.4 0.6 0.6 95.42 4.12 4.12 0.46 0.46 5.7 5.7 Table!: Petrographic Tablel: Petrographic summary summary for for the the Mt. Simon Simon Sandstone, Sandstone, based based on on 95 thin sections from 5 drill holes in southeastern 95 thin sections southeastern Drill hole locations Minnesota. Minnesota. Drill locations are are listed listed below. below. Northern Natural Northern Natural Gas Gas Hollandale 1-A 1—A (H1A) (=A) Hollandale sec.7,T.103N,R.19W. SE1/4SW1/4 sec.7,T. SE1/4SWI/4 1 0 3 ~ ,19W. ~. Freeborn Countv County Freeborn . - New Jersey New Jersev Zinc Zinc B—i B-1 sec.25,T.104N.,R.9W. NW1J4SW1/4 sec. NW1/4~~1/4 25,T. l04N., R. 9W. Fillmore Countv County Fillmore Pan Ocean Ocean Oil, Pan Oil, Ltd. Ltd. SQ—9 SQ-9 SE1/4SW1/4 sec.l,T.lO4N.,R.32W. SE1/4SW1/4 sec.1,~.104~. ,R.32W. County Martin County Minneqasco KAM-1 RAN—i Minnegasco sWl/45W1/4 sec.4,T.1081,4.,R.22W. SW1/4SW1/4 sec.4,T.108N..R.22W. Waseca County Waseca County Minnegasco SCE-1 SCH—1 Minnegasco NW1/4NE1/4 sec.6,T.lO8N.,R.22W. NW1/4NE1/4 sec.6.T.lOEN..R.22W. Waseca County County Northern Northern Natural Natural Gas Gas Vermillion 66—9 66-9 (V66—9) (v66-9) Vennillion W1/4NW1/4 sec.ll,T.ll4N.,R.lBW. W1/4NW1/4 sec.l1,~~.114N. ,R.lEW. Dakota Dakota county county 6-9 �WAGGONER1 WAGGONER. ECHO ECHO LAKE LAKE GABBRO, GABBRO, HOUGHTON HOUGHTON COUNTY, COUNTY, MICHIGAN MICHIGAN IL, Cliffs Mining Services T. D., Cliffs Mining Services Co., Co.. Ishpeming, Ishpeming, MI MI ff1. 49849 49849 The Jacobsville sandstone The Jacobsville sandstone between between Lake Lake Gogebic Gogebic and and Keweenaw Keweenaw Bay Bay has has long long been been thought thought to to cover cover the the Powder Powder Mill Mill Group Group (extrusive (extrusive volcanics) volcanics) which which form form the the southeastern southeastern flank flank of of Midcontinent Midcontinent Rift Rift Basin. Basin. The The relative relative magnetic magnetic and and gravity gravity highs highs were were interpreted interpreted as as fault fault blocks blocks of of the the Group Group at at shallow shallow burial. burial. Jacobsville Jacobsville thicknesses thicknesses range range from from 00 to to +3600 +3600 feet feet based based on on outcrop outcrop and and drilling information. Further geophysical data suggest thickness in excess of Further geophysical data suggest thickness in excess of drilling information. 9000 9000 feet feet in in some some areas. areas. Based Based on on the the geological geological interpretation interpretation and and seeking seeking knowledge knowledge of of the the copper copper potential potential in in the the lower lower flow flow units, units, an an exploration exploration hole hole was was completed completed in in 1975. was collared collared 990'N. 990'N, 1480'W 1975. The The hole, hole, Echo Echo Lake Lake ff1, #l, was 1480'W of of the the SE SE corner comer of of Section Section 22, 22, T49N, T49N, R37W, R37W, Houghton Houghton Co., Co., Michigan. Michigan. Collar Collar elevation elevation was was +1375' +1375'. The The hole hole encountered encountered 95 95 feet feet of of glacial glacial till till followed followed by by 805 805 feet feet of of JacobsJacobsville At 900 900 feet, feet, the the hole hole entered entered weathered weathered olivine olivine gabbro gabbro for for ville sandstone. sandstone. At 20 20 feet feet and and was was terminated terminated at at 1315 1315 feet feet in in fresh fresh olivine olivine gabbro. gabbro. Minor Minor zones zones of of more more basic basic rock rock approaching approaching aa picrite picrite are are present. present. Shattering Shattering normal normal to to the the vertical vertical hole hole is is evident evident in in both both core core and and thin thin section, section, affecting affecting both both labradorite labradorite and and olivine. olivine. Serpentinization Serpentinization of of the the olivine Specific gravity gravity of of the the gabbro gabbro ranges ranges olivine along along the the fractures fractures is is common. common. Specific from Magnetite occurs occurs as as thin thin (mm) (mm) bands bands normal normal to to core core angle angle from 2.94 2.94 to to 3.11. 3.11. Magnetite in and the the magnetic magnetic iron iron content content at at 10251 1025' measured measured in the the upper upper part part of of the the hole, hole, and 4.3%. 4.3%. The The core core was was devoid devoid of of sulfides sulfides and and the the Pt/Pd Pt/Pd analysis analysis did did not not exceed exceed background. background. Both Both the the magnetic magnetic and and gravity gravity signature signature can can be be reinterpreted reinterpreted as as an an elongate elongate plutonic plutonic body body similar similar in in shape shape to to the the Mellen Mellen Gabbro Gabbro and and possibly possibly with with a It can can also also be be postulated postulated that that at at depth depth near near the the a granophyric granophyric component. component. It lower lower Proterozoic Proterozoic contact, contact, base base metals metals may may occur. occur. 70 �ANORTHOSITES: E., ANORTHOSITES:IGNEOUS IGNEOUSCUMMULATE CUMMULATEOR ORMETASOMITE? METASOMITE?ROGERS, ROGERS, Michael Michael E., WATKINS, Ivan W., W., Department WATKINS, Ivan Department of Earth Sciences, St. St. Cloud Cloud State State University, Universi St. Cloud, MN. St. Cloud, MN. 56301. 56301. Paradigms problems and and interpreting interpreting data within the Paradigms are are guide guide lines lines or rules used for solving problems wi confines of of that paradigm. Paradigms and Paradigms are are an anintegral integral part part of of any any scientific scientific discipline, an geology is no different. The The prevalent paradigm paradigm of of today today is is that that the the anorthosites anorthositesof of the the Duluth Complex along the north shore of Minnesota are igneous cummulates. Why? Well, they, Duluth Complex along the north shore of Minnesota are igneous cununulates. Why? Well, have have an anobvious obviousigneous igneoustexture texture and andbesides, besides, they they are arenot not associated associated with with metamorphic metamorphicrocks rocks like the slates and greenstones near Virginia and Ely Minnesota(Phinney, 1966, like the slates and greenstones near Virginia and Ely Minnesota(Phinney, 1966, p. 142). 142). Plagioclase magma simply floated towards the top Plagioclase crystals from the gabbroic magma top of the the intrusion, intrusion, settled to the bottom, or sometimes both (Phinney, 1966, p. 135). Besides accumulating Besides accumulating as settled to the bottom, or sometimes both (Phinney, 1966, phenocrysts in magmatic chambers, anorthosites are also observed phenocrysts in magmatic chambers,anorthosites are also observed as asinclusions inclusions within within dikes, dikes, sills, and flows. Where present, nearly all of these inclusions are rounded (Phinney, 1966, p. sills, and flows. Where present, nearly all of these inclusions are rounded (Phinney,1966, p. 135). as lenticular lenticularmasses masseswithin withinthe thesurrounding surrounding gabbro. gabbro. Temperature Temperature 135). Anorthosites Anorthosites also also occur as estimates ratios samples and and suggest that estimatesfor for anorthosites anorthosites are are based on 018/016 018/01*' ratios from several samples most anorthosites crystallized under conditions of about 1000° to 1100°C with most anorthosites crystallized under conditions of about 1000" to 1100'C with a water fugacity between between500 500bars baretoto2000 2000bars bars(Isachsen, (Isachsen,1966, 1966,p. p. 439). 439). Study and sampling was done at the large disused Study and sampling was done at the large disusedanorthosite anorthositequarries quarriesatatCarlton CarltonPeak Peak(SE (SB of NE 1/4 of Sec 20, R4W, T59N). At this site anorthosite dominates the quarry but 1/4 1/4 of NE 1/4 of Sec 20, R4W, T59N). At this site anorthosite dominates quarry but is is spotted spottedwith withhundreds hundredsof of gabbroic gabbroic inclusions. inclusions. When Whenviewed viewed from from the the proper proper orientation orientation these these gabbroic spots appear as elongate lenses which are oriented parallel to one another. of gabbroic spots appear which are oriented parallel to one another. Many of these spots can be found with a deep red rim of hematite surrounding them. These samples are surrounding These samples are these spots can extremely dipped in extremely friable friable and needed to be dipped in epoxy epoxy glue in order to cut, polish and thin section. Without this epoxy, the samples simply could not have been thin sectioned. Air bubbles rising Without this from fractures thin section from fracturesin inthe thegabbroic gabbroic spots spots as as well well as as plucking plucking of the entire thin section sample was a common occurrence. Obviously, these samples are highly fractured. The gabbro Obviously, these samples The gabbrospots spots common themselves are the most severely fractured/friable and in many cases themselves erely fractured/friable and in many cases these these spots spots are are parallel parallel to to major fractures within the samples. In In lL'._.1JC addition addition to to this, this, several rounded spots spots had visible 'tails 1) which which are are "tails" to them them (Fig. (Fig. 1) identified structure identified by Carol Carol Simpson as shear structure geometries 250). Another geometries(Simpson, (Simpson,1986, 1986, p. 250). Another feature is the the feature worth worth note note in this this paper paper is apparent apparentgrain grainof of the the rock rock which, which, when when broken, broken runs runssubparallel subparallelto to the the gabbro gabbro spots spots and and not n FIGURE 1: Gabbro spot showing diagnostic along along the shortest shortest path path as as would would be be tail, expected. expected. tail,aatypical typicalshear shearstructure structureshape. shape. IfIf the thelarge largescale scale features features and and hand hand samples sampleswere weresuggestive suggestiveof of shear shearzone zone genesis, genesis, then the thin The first first step step was was to to thin thin section section the the anorthosite anorthosit itself, thin section section evidence evidence is overwhelming. The without withoutthe thegabbro gabbrospots. spots. The Thefirst firststriking strikingthing thingabout aboutthe theanorthosites anorthositesof of this thisarea area is isthat even even they they are are highly fractured. Most Most fracture fracture fills are chlorite, chlorite, yet yet there there are are many more that have haveplagioclase plagioclase as asaafracture fracturefill fill itself. itself. Also Alsocbmmon cbmmonin inthe theanorthosites anorthositesare areplagioclase plagioclase crystals rounded and crystals that that have have both both very very typical typical angular angular crystal crystal faces and very atypical rounded and curved curvedcrystal crystal faces. faces. Both Both of of these these features features can be found within the same crystals. Where Where the the crystal crystalfaces faces are are smoothly smoothly rounded rounded the thecrystal crystal h-' boundary boundaryappears appearsvery veryfuzzy. fuzzy.Upon Uponcloser closer examination, examination,one onecan cansee seeaaseries seriesof of fractures fractures that aresubparallel subparallel to to the the crystal crystal face. face. Also Also that are present presentwithin withinthe theanorthosite anorthositethin thinsections sectionsare are several severalexamples examplesof of shear shear structures. structures. One Onesuch such feature nlaeioclasecrystal, crystal, roundedand and featureisisaaplagioclase , . rounded FIGURE2:2: & l a s e ' ~ o r p h y r o ~ t with exhibiting FIGURE exhibitingtails, as an aninclusion inclusion within within another ano plagioclase tail another plag ta! inside Inside another plogcrystal. clystal. plagioclasecrystal crystal(Fig. (Fig. 2). Moving Movingfrom fromthe - - &,as .. 71 �anorthosite can see see an an interesthe interesting trend. trend. Many anorthositeto tothe thegabbroic eabbroicspot spotinclusions, inclusions, one one can Manvof of the spots in the anorthosite are highly fractured while others are more massive. the spots in the anorthositeare highly fractured while others are &e massive. Beginning with the the more more massive massive samples samples (which (which still needed to be epoxied for for thin thin sectioning) sectioning) one can observe plagioclase and pyroxenes. The pyroxene has been slightly to moderately one can observe plagioclase and The pyroxene has been slightly to moderately altered altered along along it's it's fractures fracturesand and exhibits exhibits aa vermicular vermicular texture at these points. The Themain main alteration minerals are chlorite and hematite. Within many anhedral pyroxenes Within many anhedralpyrbxenesare are perfectly perfectly alteration rounded plagioclase crystals. Within many anhedral plagioclase crystals there are rounded pyroxene crystals which are highly altered to chlorite and hematite. Several more pyroxenes show an almost perfect textbook quality porphyroclast with tails. P1 B v1any of the more circular and rounded pyroxenes have curious fracture patterns which change direction and ior.c circle around the pyroxene crystals(Fig. 3). Moving to the more fractured spots, the pyroxertes appear much more heavily altered. Within many of these heavily FIGURE 3: Circuldr fracture patterns altered pyroxenes are more circular plagioclases. .rounded pyroxenes. surrounding And And within G&in these theseplagiocl plagi ses aiy chlocitr "' ure surrounding rounded pyroxene&. fills (Fig. 4). fills encased encased within withinpig. 4). Moving Moving to tethe the.' '' most highly fractured material within most highly fractured material within the the pro, 3 anorthosites, can hardly anorthosites, one onecan' hardlyrecognize recognizethe the altered altered ro, fl B pyroxenes round pyroxenesanymore. anymore.Many Manystifi stillencase enca~e'lound;:C-L,!.;+& t.f5 plagioclase chlorite and plagiiklase,with withchlorite and hematite hematite present. pres&t.''' l-ie.^c.ia ll .. As other two spot As with with the tHeothertwo spotsamples samplesthere thereare arethe the ". rounded patterns, roundedpyroxenes, pyroxenes,circular circularfracture fracturepatterns, rounded crystal faces, chlorite rounded plag pl&guy&d f-, ddoritefracture fracturefills, &,7jpyroxenes FIGURE pyroxenesaltered alteredentirely entirelyto to chlorite, chlorite, and and more more FIGURE 4:4: Rounded piag wi shear pyroxene. pwxerle. Note Notethe ttiechlorite <shteittefracture ftticfuiiefills. His. shear structure structurepatterns. patterns. The The question questionthat thatneeds needstotobe beasked askednow nowis;is;ififthis thisisiftruly trulyan anigneous igneouscumn-tulate, cummulate,can canthese these things thingsbe be present? present? And Andthe flieanswer answerisisunequivocally unequivocally"No". "No". Phinney Phinneyhad haddifficulty difficultyconstructing constructing aa theory of anorthosite anorthosite in in northeastern northeastern Minnesota. An theorythat thatcould couldexplain explainall all four four occurrences occurrences of An igneous made in in the field field and and in in the lab. lab. The north north igneous model model just does does not agree agree with observations observationsmade shore rocks. As pbbro gabbro was was sheared sheared and and ground ground up shoreanorthosites anorthositesare aremetamorphosed metamorphosed gabbroic gabbroic rocks. up water fluxremoved removed and anddeposited depositedminerals mineralsuntil untilan analmost almost plag plag pure pure composition composition waterflux recrystallized certainly recrystaffizedfrom from it. it. The Thelenses lensesand androunded itoundedinclusions i~lusions certainlyfit fit this (hismodel. modeLMany Many anorthosite oneis is not not looking looking. anorthositebodies bodiesdo donot notexhibit exhibitshear sheargeometries. geometries. However, However,ifif one perpendicular structures. Additionally, perpendiculartotothe thesense 'senseof of shear, shear, one one cannot cannot observe the shear structures. Additionally, preliminary we have have conducted conducted supports supports aa metasomtic metasomatic environment. environment. For For preliminarygeochemical geochemical evidence evidencewe those theirparadigm paradigmand andcannot cannotaccept acceptthe theobservations observationsthemselves, themselves, thosewho whoare arerestricted restrictedby bytheir then be added to the thereare aredozens dozensof of ad ad hoc's hoe's which which can be the cummulate cummulate theory. However, However,the the then there more exceptionsthere thereare are to to aa rule r6teor or theory, theory, the Ideless less and and less less^that that theory theory is is capable capable of of making making moreexceptions predictions. cannot theorvcannot cannotmake makepredictions, oredictions,ititisisuseless. useless. IfIf aaparadigm ~aradlem cannotallow allow oredictinns.IfIfaatheory someone then that someoneto to problem problemsolve &ve accurately, accurately;then that paradigm paradigmisisalso alsouseless. deless.The Thereal realgenesis genesisof of the the north by no nomeans means resolved resolved by this this paper. paper. What Whatcannot cannotbe bedenied, denied, northshore shoreanorthosites anorthositesisisby however, inability of however, isisthe theinability of the the cummulate cummulatemodel model to to hold up upeven even under undercommon commonobservational observational techniques. timefor foranother anotherparadigm. paradigm. techniques. ItItisistime REFERENCES REFERENCES Jsachsen, bachsen,Yngvar, ~ n ~ v W., a r ,1966, 1966, ~ . , Origin Originof of anorthosite anorthotiiteand and related relatedrocks rocks- aa summarization: York Museum and Science ScienceService, Service,Memoir Memoir18, 18,p.435-445. p.435-445. summarization:New New Yo&State State Museum and %&a '.-c ,. a U - Phinney, Phinney,William WilliamC., C., 1966, 1966, Anorthosite Anorthositeoccurrences occurrencesin in Keweenawan Keweenawanrocks rocksof of Northeastern Memoir 18, NortheasternMinnesota: Minnesota:New NewYork YorkState StateMuseum Museumand andScience ScienceService, Service,'Memoir 18,p.135-147. p.135-147. Simpson, Simpson,Carol, Carol,1986, 1986, Determination Determinationof of movement movement sense sensein inmylonites: Journal Journalof of Geologic Education, v.34, 246. GeologicEducation, v.34,p.p.246. Â¥iv 72 �AND SEDIMENT-CONTROL MODELS USE OF RUNOFF- AND IN THE DESIGN OF MINE IN THE DESIGN MINE HYDROLOGIC HYDROLOGIC CONTROLS CONTROLS Richard Richard B. White, P.E. P.E. Principal Hydrologist Hydrologist and and Thomas J. Suchoski Suchoski Senior Hydrotogist Hydrologist EarthFax Engineering, Inc. Midvale, Utah Utah and Bath, Michigan Michigan ABSTRACT ABSTRACT I I  I I I at mine surface facilities facilities is an important aspect Control of of runoff and erosion at Control of environmental protection. Regulations regarding the installation environmental Regulations regarding installation and maintenance maintenance 5 of runoff- and and sediment-control sediment-control facilities at at coal coal mines mines have have been been in in place place over over 115 years since since implementation implementation of of the Surface Mining Control and Reclamation Act Act of years of 1977. Similar Similarlaws lawsgoverning governingenvironmental environmentalcontrols controls at at mineral mineral mines mines are currently considered on being considered on aa Federal Federal level. Several models have been developed developed for for the the design of runoffrunoff- and andsedimentsedimentcontrol facilities at mining and industrial operations. These models range from control facilities at mining and industrial operations. These models range from simple simple analytical and empirical approaches approaches to to detailed detailed computer computer codes. codes. Models'have Modelshavebeen been to estimate rainfall-runoff rainfall-runoff relations, sediment yield, yield, the the erosion potential of developed to streamflow, and the sedimentation characteristics characteristics of of control structures. channelized streamflow, structures. These models will be reviewed, along with examples of their implementation. These models will reviewed, with of implementation. 7.3 �BIODEGRADATION OF BIODEGRADATION OF ENVIRONMENTAL CONTAMINANTS CONTAMINANTS UTILIZING WHITE UTILIZING WHITE ROT ROT FUNGUS FUNGUS Richard B. White, Richard White, P.E. P.E. Hydrologist Principal Hydrologist and and Mark S. Wollensak Wollensak Project Project Geologist Geologist EarthFax Engineering, Inc. Inc. Midvale, Utah Utah and and Bath. Bath, Michigan Michigan ABSTRACT ABSTRACT . White rot rot fungi fungiare areaacommon, common,naturally-occurring naturally-occurringclass class of ofwood-degrading wood-degrading fungi that 980s thatevolved evolvedto todegrade degradelignin. lignin. Extensive Extensiveresearch researchconducted conducted since since early 11980s has shown shown that many utilized by by the the fungi for has many of of the thesame same mechanisms mechanisms utilized for lignin lignin degradation also also promote the degradation the degradation degradation of ofseveral severalcarbon-based carbon-based environmental environmental contaminants include polycyclic aromatic hydrocarbons, contaminants. These These contaminants include polycyclic aromatic hydrocarbons, pesticides, pesticides, herbicides, herbicides, wood preservatives, preservatives, chlorinated chlorinated solvents, solvents, PCBs, PCBs, explosives, explosives, cyanide, dyes, dyes, and others. cyanide, The utilize an extra-cellular, free-radical, non-specific mode of degradation degradation hef fungi utilize anextra-cellular, which allows them to degrade both soluble and insoluble contaminants, whether they which allows them to deorade and insoluble contaminants. whether thev absorbed or orin insolution. solution. The secreted by the fungi fungi include are absorbed The extra-cellular extra-cellular substance substance secreted include several enzymes enzymes (which (which catalyze batalyze the the initial oxidation several oxidation of of contaminant contaminant molecules), molecules), hydrogen ions (to maintain maintain a slightly slightly acidic charge balance hydrogen acidicpH), pH), electrons electrons(to (to maintain maintainaa charge balance and to reduce contaminants through the breaking of chemical bonds), and hydrogen contaminants through the breaking of chemical andhydrogen (a highly highly effective effective oxidizer). peroxide (a oxidizer). In addition, the fungi fungi secrete secrete veratyl veratyl alcohol alcohol (a (a free-radical mediator mediator which which catalyzes reductions) and oxalate (an organic acid which which free-radical is a highly effective reductant). Application of Application of white whiterot rotfungi fungifor forthe theremediation remediationof ofcontaminated contaminatedsoils soilsinvolves involves fungal-inoculated substrates with with the mixing fungal-inoculated the soil. The Thematerials materialsare are moistened during mixing to to provide which is conducive mixing provide an environment environment which conducive to fungal fungal growth. growth. The The soil/substrate soillsubstrate mixture mixture is is then then placed placedin in aa biocell biocell and and aerated to promote promote contaminant contaminant degradation. Case degradation. Case histories historiesof of bench-scale bench-scale tests tests and and field field applications applications are are presented. presented. 74 �MAKING THE MOST OF IT: COMBINING COMBINING FIELD, FIELD,MICROSCOPIC MICROSCOPIC AND AND BIBLIOGRAPIIIC BIBLIOGRAPHIC FINDINGS TO INTERPRET SHOWINGS AROUND LAKE SUPERIOR INTERPRET SHOWINGS LAKE WILSON, Graham C.: C.: Turnstone Geological Geological Services ServicesLtd, Ltd,P.O. P.O. Box Box 130, 130, Station Station "B", "B", Toronto, Toronto, Ontario, Ontario, CANADA CANADA M5T 2T3 and and IsoTrace IsoTrace Laboratory, Laboratory, University University of Toronto, Toronto, 60 60 St. St. George George Street, Toronto, (e-mail:gcw@quartz.geology.utoronto.ca). gcw@quartz.geology.utoronto.ca). Tomnto, Ontario, Ontario, CANADA CANADAM5S M5S1A7 1A7(e-mail: Electronic Electronic Education: Education: A project has manner for research and learning has been been initiated initiated to present present geological geological information in an accessible accessible manner purposes, to produce produce a PCPCmultimedia educational educational software software tailored tailored to a broad audience. The eventual aim is to purposes, using using multimedia compatible product product on on CD-ROM, CD-ROM, with a wide range of data data enclosed within a "shell" structure of menu options, options, help screens and and indices. indices. The Theinformation informationto to be be offered offered in inthis thissystem systemcan canbe bedivided dividedinto intofour fourelements: elements: help screens annotated entries, database, with with = 1. 1. A bibliographic database, ~ 330,000 0 , 0 0 0annotated entries, 2. 2. An image image bank, with hundreds of colour colour photographs and other figures, 3. AAbook and bookononcomputer computerdatabases databasesininEarth Earthand andenvironmental environmentalscience science applications, and 4. AAsetset ofof "tutorials" illustrating "tutorials" illustratingselected selectedthemes, themes,one oneexample examplebeing beingthe thegeology geology of of the theSuperior Superior region. region. • .1 The Lake Superior Tutorial: Tutorial: The Lake Superior region provides excellent examples examples of of many many facets facets of of Archean Archeanand andProterozoic Proterozoicgeology. geology. A A partial partial The Lake Superior region provides excellent listing includes banded banded iron iron formations, formations, metavolcanic metavolcanic rocks, rocks, mafic-ultramafic mafic-ultramafic and and alkaline alkaline intrusions, intrusions, and and deposits deposits listing includes metamorphism, Products of progressive deformation, metamorphism, of copper, silver, silver, gold gold and and platinum platinum group group elements (PGE). Products the emplacement of minor intrusions intrusions and veins, hydrothermal hydrothermal alteration mineralizing events can can all be examined alteration and mineralizing km of of the the shore) shore) have have been beenintegrated integratedinto into in the the field. field. Selected Selected features features of Superior Superior geology ((in in an area within 100 km a sequential "tutorial" presentation. sequential "tutorial" presentation. . tutorial comprises comprises30 30 frames, frames, each each consisting consistingofofan an image image (with (with aa brief brief caption) caption) or or a short The Superior Superior tutorial paragraph of text. The viewer can browse through the screens, which are analogous to a slide show. If further can which analogous to a slide show. If paragraph information is is required, required, a second screen screen can can be revealed revealed with an explanatory explanatory paragraph, paragraph, and and perhaps perhaps aa selection selection of references. The visual approach, combined with a "layered" access to information, is designed to hold appeal references. combined with a access to information, is designed to hold appeal for both casual and specialized viewers, and will hopefully promote worthwhile discussion! discussion! Follow-up Follow-up queries queries can can be addressed to a database which (in old-style terms) functions as a cross-linked card index. Areas referred to in addressed a database (in cross-linked card in the tutorial, proceeding anticlockwise around the lake from Sault Ste. Marie, are as follows: tutorial, proceeding anticlockwise around the lake from Sault Ste. Marie, 1. The Wawa area 1. area 2. The TheHemlo Hemlogold gold camp camp 3. The Coldwell alkaline The Coldwdl alkalinecomplex complex belt 4. Iron formations and gold in the Beardmore-Geraldton belt The North Shore of Superior 5. 5. Islet: native silver 6. Silver Islet: 6. Lac des Iles: 7. 7. Hes: PGE PGE in in mafic-ultramafic mafic-ultramafic rocks Kakabeka Falls 8. 8. Falls 9. The TheDuluth Dulathcomplex complex 10. Keweenaw Keweenaw Copper Copper Country Country and Pet rography: Field Geology and Petrography: The site site selection is dictated more more by the availability of of materials than by by a any systematic aim aimto todefine defmethe the "top "top ten" ten" ny systematic features of the regional geology. geology. In the Lake Superior tutorial, tutorial, deposits of of three three native nativeelements elements(Au, (Au,Ag Agand andCu) Cu) are included, while volcanogenic massive sulphides suiphides are are omitted. omitted. In the wider context context of of the CD-ROM project, project, this is compensated for by by the use of examples examples from other other parts parts of of the world. The initial selection is is divided divided roughly roughly compensated for 2:1 between field items (outcrops, landscape features) and photoniicrographs of rocks and ores. photomicrographs of 2:l 75 �Bibliographic Bibliographic Database: Database: Although it is anticipated Oat that image fileswill will fill fill80-90% 80-90% of of the thecapacity capacityof ofthe theCD-ROM, CD-ROM, the the driving driving force force behind behind MINLIB database database (Wilson,11991), and to to present present it it in the project project is is to tomake makeavailable available the theheavily-annotated heavily-annotated MINLffi 991), and in conjunction with a review of the use of computer databases in the Earth sciences sciences ((coincident, in part, part, with Wilson, c o i n c i i , in 11992a,b). 992a,b). MINLIB is not designed to to compete with with major databases databases such such as as GeoRef, GeoRef, which have broader thematic rhematic and systematic systematic coverage, coverage, nor to to supplant supplantmaterial material compiled compiled by by regional regionalsurveys surveys (including (including mineral mineral deposit deposit inventories assessment files) files) and and other geographically specializedpublications publications(e.g., (e.g., Sheahan, Sheahan, 1 1984). inventories and assessment geographically special'& 984). ItIt is intended to cover a broad range of topics, topics, but but with withclear clearemphasis emphasis on on aspects aspects of of economic economic geology, mineralogy, mineralogy, petrology and keywords <up (up to 30 lines and structural $tructuralgeology. geology. A A relatively relativelyintensive intensive selection selection of ,keywords lines per per record) record) facilitate facilitate recovery of robject subject matter. matter. Within Withinthe the cmrent currentcontents contents(-28,000 (=28,000 records), recovery of articles articles with with diverse combinations of records), there features in the Lake Superior region. Examples there is is significant significantcoverage coverage for for many many geological geological features Examples include the Wawa subprovince (230 references), the Keweenawan<110), Keweenawan (110), the Gunflint iron iron formation00). formation (50), (he the Hemlo gold camp camp (200), (200), subprovince (230 the (80), the Duluth complex complex ( (120), the Lac des des lies Iles complex complex and and the Silver Silver Islet mine mine (20), (20),the the Coldwell ColdweU complex (80). 120), and the associated PGE mineralization (80). (80). la In terms of the the cumulative literature, coverage of these subjects varies from sketchy to substantial. Available m material is weighted towards towards recent recent articles articles (MINUB (MINLIB was was initiated initiated in in 1983, 1983, and aterial isW1ghted only only 18% 18% of of records recordsconcern concernitems items published pubrished prior to to that thatyear). year). While the thrust "hard-rock" geologists thrust of MINLIB MINLIB will will appeal appeal especially to economic and "hard-rock' geologists and mineralogists, several hundred "popular" "popular*articles articles are are included, included, and and ititisishoped hoped that that these, these, in inconjunction conjunctionwith with the the image image bank bank and and several hundred tutorials, will be of high-school students, rockfaounds, rockhounds, and toothers to others interested in extending their of broad broad appeal appeal to tdhigh-school knowledge of of die the natural world. world. The wider for the wider audience audierd-for the tutorial tutorial approach and the supporting imageiy imagery may in every every 40 40 records). records). This includes books on on local local appreciate material in in the "popular" category of of the the database database (o (= 11 in appreciatematerial This includes mining exampleswould wouldbe beBan-, Barr, 1988; 1988; Lefolfi, Lefolii, 1987; 1987;Smith, Smith,11986), certainfield fieldguides guides(e.g., (e.g., Pye, Pye, mining history (recent examples 986). certain 1968) and articles in non-technical publications such as Canadian Geographic and National Geographic. 1968)and publications such as Canadian Geogquhk and National Geographic. References: References: .BARR,E., BARR.E., 1988, 1988, Silver Silver Islet, Islet, Striking Striking iitt Rich Rich in in Lake Lake Superior. Superior. Natural Natural Heritage/Natural HeritagdNatural IHistory, i i i r y , Toronto, 159pp. 159pp. LEPOLII,K., Ltd, Toronto, LEFOULK.. 1987, 1987, Claims: Claims: Adventures Adventures in the Gold Trade. Key Porter Potter Books Ltd. Toronto. 264pp. 264BD. Lake and east to Lake Superior. Ontario Dept. Dept. of Mines PYE,E.G., PYJ3.E.O.. 1968, 1968,Geology Geologyand and Scenery: Scenery: Rainy Rainy Lake Mmes Geol. Guide 1, 118pp. ll8pp. Book 1, of Mi-Continent Mid-ContinentBasement BasementU.S.A. U.S.A. Geol.Soc.America Geol.Soc.America Microform SHEAIIAN,P., 1984, Geological Bibliography of SHEAHAN.P., 15, 56pp. 56pp. Publication 15, SMITH,P., SM1TH.P.. 1986, Harvest from the Rock. Rock. Macmillan of Canada, Toronto, Toronto, 346pp. 346pp. WILSON,G.C., 1991, mineral exploration. exploration. Geol.Assoc.Canada Geol.Assoc.Canada WILS0N.G.C.. 1991,MINLIB: MINUS: aacomputer computerdatabase database emphasizing emphasizing mineralogy and mineral Prog.w.Abs. 16. 16, Toronto, 133. / Mineral.Assoc.Canada Mineral.Assoc.Canada Prog.w.Abs. database management management systems. systems. In 'Mineral Databases'(Smith,D.G.W. (Smith,D.G.W. and and WILSON.G.C., 1992a, Databases Databases and and database WILS0N.G.C.. 1992a. In 'M Mineral Databases' Congress, Kyoto, Kyoto, Japan, Japan, sponsored by by the Ozawa,T., editors), Workshop at the 0zawa.T.. editors). Workshop the 29th 29th International International Geological Congress, Mineralogical Association, l83pp., 31pp. 3lpp. International Mineralogical International Association, 183pp.. WILSON,G.C., Ibid., 38pp. WILS0N.G.C.. 1992b, 1992b.Bibliographic Bibliographic databases. /Aid., 38pp. �CHALCOCITE MiNERALIZATION MINERALIZATION IN IN THE THEPORTAGE PORTAGELAKE LAKEVOLCANICS,, VOLCANICS, PENINSULA, MICHIGAN KEWEENAW PENINSULA, MICHIGAN KEWEENAW Laurel 0. Woodruff1, woodruff1, William William F. F.Cannon2, ~ a n n o nJudith Judith ~ , M. M. Back2 ~ a c k ~ Laurel G. U.S. Geological Survey; 'St. Pad, MN, 2Reston, VA U.S. Geological Survey; 1st Paul, MN, 2~eston,VA Seven chalcocite chalcocite deposits deposits occur occur in in the the Michigan Michigan copper copper district district in in the the western western part part of of the the Seven Peninsula of Michigan, a region better known for native copper mineralization. Upper Peninsula of Michigan, a region better known for native copper mineralization. The The chalcocite deposits, mostly discovered discovered in in the the 1970's. 1970's, ran range in tonnage from 0.1 0.1 to to 4.5 4.5 million Upper e in metric tons, and most have average grades from 2.5% to 3.0% Cu. The chalcocite deposits metric tons, and most have average grades from 2.5% to .O% Cu. The chalcocite depositsare are within the the 1.0 1.0 Ga Ga Portage Portage Lake Lake Volcanics Volcanics near near the the northeast northeast tip tip of of the theKeweenaw KeweenawPeninsula, Peninsula, restricted 13 km, km, stratigraphically stratigraphically below below the the Bohemia Bohemia Conglomerate Conglomerate and and just just restricted to an an area area 22 km km by. by 13 within to above the Keweenaw fault (Figure 1). the Keweenaw fault (Figure 1). On copper.mineralization mineralizationin inthe the Keweenaw Keweenaw Peninsula Peninsula can can be be subdivided On aa regional regional scale. scale copper subdivided into three three types types or ordistricts, each with a characteristic style of mineralization: (1) native copper districts, a style of mineralization: in fissure fissure deposits (2) native native copper in lode deposits in both basalt and and conglomerates, deposits in basalt, (2) and (3) chalcocite in basalt. The chalcocite district is along strike and stratigraphically basalt The chalcocite district is along strike and stratigraphically lower than the native copper native copper lode lode district district and and is is directly directly stratigraphically stratigraphically below the native native copper fissure district (Figure 1). Although these three districts are adjacent to one another, there Although these three districts are adjacent there is little district (Rgure overlap, suggesting that the three styles of mineralization are interrelated and part of regional overlap, suggesting that the three styles of mineralization are interrelated and part of aa regional mineralizing system. system. We We have have attempted attempted to to define define the mineralizing mineralizing process for the chalcocite deposits and to determine determine the genetic genetic connection between chalcocite mineralization and native copper mineralization. mineralization. In all predominant sulfide sulfide is is chalcocite. chalcocite. In all the the chalcocite chalcocite deposits, the predominant In most, most, bornite bomite in in trace amounts is the only other sulfide. One exception is the Mt. Bohemia deposit amounts sulfide. One exception is the M t Bohemia deposit which contains chalcocite pyrite-chalcopyrite-bomitechalcocite in addition addition to to aareplacement replacementsequence sequenceofofpyrite-chalcopyrite-bornitechalcocite, in which Fe-sulfides were replaced by successively more Cu-rich Cu-rich sulfides chalcocite, Fe-sulfides sulfides (Robertson, The chalcocite deposits occur in fragmental tops of basalt flows in much the same 1975). chalcocite same style style 1975). as native copper copper lode deposits. Chalcocite Chalcociteoccurs occursas as an an amygdule amygdulemineral, mineral, as as open-space open-spacefillings fillings disseminated in in altered altered basalt, basalt, and and in in veinlets veinlets cutting cutting basalt. basalt. Related around basalt fragments, disseminated Related alteration minerals include epidote, quartz, hematite, hematite, pumpellyite, pumpellyite, chlorite, albite, albite, K-feldspar, K-feldspar, laumontite, and laumontite, and titanite. titanite. 3345 values 0%o, ranging ranging from from 8% values for chalcocite from six of the the deposits deposits are all less than 0%, Although basalts in the rift are sulfur-poor because of degassing -0.1% to -21%. -0.1%0 -21%0. Although basalts in are sulfur-poor because degassing during during eruption, sulfur and copper copper were were derived derived by by hydrothermal hydrothermal alteration of the underlying underlying volcanic volcanic Individual deposits have a section during burial metamorphism .downdip from the deposits. during burial metamorphism downdip deposits. roughly correlated correlated with with the the tonnage tonnage of of copper copper ore in the deposit: deposit: 6% which isis roughly restricted range of oMS the largest deposit has the highest 345 values (-0. 1% to -4.2%o) and the smallest deposit has the the highest S^S values (-0.1%0 to -4.2%) deposit to -6.6%o). This correlation can be interpreted as indicating that chalcocite l5.6%o can chalcocite was was lowest ((-15.6% -6.6%). This deposited during progressive oxidation of a mineralizing fluid, which probably carried a limited limited amount of sulfur and/or copper copper chloride. chloride. sulfur along along with with abundant abundant copper copper complexed complexed as as bisulfide biisulfide and/or Because of the large isotopic fractionation between sulfide sulfide and and sulfate, sulfate, oxidation oxidation of of sulfide sulfide in in the the M8• sulfide becoming increasingly increasingly isotopically isotopically depleted depleted in ^S. fluid would result in residual aqueous sulfide veinlets in in one deposit, which have the further indicated by late native copper-bearing copper-bearing veinlets This is further most depleted values of any samples from that deposit, indicating.that indicating that most of the the sulfide sade had had been oxidized oxidized before before the the deposition deposition of the the veinlets, but the copper copper remained remained in in solution. solution. with lower sulfur isotope values is consistent consistent with with aa The lower tonnage tonnage of deposits with diminution of the due to the progressive the ability ability of the the fluid fluid to precipitate precipitate copper copper dsulfide slueil progressiveoxidation oxidation diminution The fluid. of the the mineralizing mineralizing fluid. After all sulfur was stripped from the fluids by oxidation, oxidation, abundant abundant $ p I 77 �* dissolved dissolvedcopper copperremained remainedininmsidual residualfluids fluidsand andwas wasavailable availablefor fordeposition depositionasasnative nativecopper. copper. We Webelieve believethat thatchalcocite chalcocitemineralization mineralizationconsumed consumedthe thelimited limitedsupply supplyofofsulfur sulfurininthe theregional regional system systemasasa aprecursor precursortotonative nativecopper copperdeposition. deposition. Negative Negativesulfur sulfurisotope isotopevalues valuesfor forchalcocite chalcociteoccur occurthroughout throughoutthe theKeweenaw Keweenawdistrict, district,asas evidenced -9.4% forfor chalcocite ininveins evidencedby by345 6% values valuesofof-ó.7% -6.7%to to-9.4%0 chalcocite veinscutting cuttingthetheBaltic Balticnative native copper copperlode lode(Livnat, (Uvnat,1983), 1983).and andsecond-stage second-stagechalcocite chalcocitemineralization mineralizationatatthe theWhite WhitePine Pinedeposit deposit (Mauk 1992),showing showingthat thatoxidation oxidationof of sulfide-bearing sulfide-bearingfluids fluids was was widespread. widespread. The The (Maukand andothers, others,1992), zonal theKeweenaw KeweenawPeninsula Peninsulasuggests suggeststhat thatother otherchalcocite chalcocite zonalarrangement arrangementofofdeposit deposittypes typeson onthe deposits depositsmight .might . bebefound foundelsewhere elsewhereininthe theKeweenaw Keweenawvolcanic volcanicsection, section,peripheral peripheraltotonative nativecopper copper mineralization. mineralization. References ReferencesCited Cited Livnat, Livnat,A., A.,1983, 1983,Metamorphism Metamorphismand andcopper coppermineralization mineralizationofofthe thePortage PortageLake LakeLava LavaSeries, Series, northern northernMichigan: Michigan:unpublished unpublishedPh.D. Ph.D,Dissertation, Dissertation,University UniversityofofMichigan, Michigan,Ann AnnArbor, Arbor. 292 p. 292 p. Mauk, Mauk,J.L., J.L,Brown, Brown,A.C., A.C.,Seasor, Seasor,R.W., R.W., and andEldridge, Eldridge,C.S., C.S.,1992, 1992,Geology Geologyand andstable stableisotope isotope and andorganic organicgeochemistry geochemistryofofthe theWhite WhitePine Pinesediment-hosted sediment-hostedstratiform stratiformcopper copperdeposits, deposits,inin Bomhorst, Bornhoist,Ti. T.J.(ad.), (ed.),Keweenawan Keweenawancopper copperdeposits depositsofofwestern westernUpper UpperMichigan: Michiian:Soc. Soc.Econ. Econ. Geol. 13,p.p.63-98. 63-98. Geol.Guidebook, Guidebook,v.v.13, Robertson, Robertson,J.M., J.M., 1975, 1975,Geology Geologyand andmineralogy mineralogyofofsome somecopper coppersulfide sulfidedeposits depositsnear nearMount Mount Bohemia, Econ.Geol., Geol.,v.v.70, 70,p.p.1202-1224. 1202-1224. Bohemia,Keweenaw KeweenawCounty, County,Michigan: Michigan:Econ. l u 10 KILOMETERS o 1: JV Copper tiahor Congbmemte 0 Portage M e Volcanics Generalized geologic geologic map map of ofthe theKeweenaw KeweenawPeninsula, Peninsula,Michigan. Michigan. Region Region of of Figure 1.1. Generalized Figure chalcocite mineralization contains seven small, high-grade chalcocite deposits. chalcocite mineralization contains seven small, high-grade chalcocite deposits. 78 �Archean Archeancrust crustininthe theWausau-Pembine Wausau-Pembiie Terrane; Terrane; Continental Continental underthrusting, underthrusting, or o r island island arc arc basement? basement? Nicholas NicholasVan VanWyck, Wyck,Clark ClarkJohnson, Johnson,and andStuart StuartGross. Gross.Department Departmentof of Geology Geologyand and Geophysics, Geophysics, University of Wisconsin, Madison WI, 53706 University of Wisconsin, Madison WI, 53706 Conventional ConventionalU/Pb UIPband andsingle singlezircon zirconevaporation evaporationdata dataon on zircons zircons from from aa strongly strongly deformed deformed gneiss 20km kmsouth southof ofthe themapped mappedtrace traceof of the theNiagara Niagara Fault Fault (N45.78286°, (N45.78286', W88.68963°), W88.68963"), gneisslocated located20 within the Wausau-Pembine Terrane (Sims et al. 1989), yield a simple concordia plot with an an within the Wausau-Pembhe Terrane (Simset al. 1989). yield a simple concordia plot with zircon evaporations upper 2604Ma, Ma,and andaalower lowerintercept interceptage ageof of 590 590 Ma. Ma. Single Single zircon evaporations upperintercept interceptage ageofof2604 from ages at at 2610 2610 Ma. Ma. Together threeseparate separategrains grainsall allgive five single singleplateau plateau Pb/Pb Pb/Pb ages Together these these data data fromthree indicate a crystallization age of 26 10±7 Ma. indicate a c q k d l i i o n age of ?.61&7 Ma. . 45 45 40 40 0 GrainAT=1620 Grain A T-1720 OrainAT=1720 3535 • GrainBl=1600 5 - 3300 5 2525 C) 3 ? 3'2 20 ^ 1515 10 10 5 5 00 V77)1m1 I 2 5 ( 0 2580 2 5 1 0 2600 2 6 0 0 2620 % 2 0 22640 6 à ‡ 22660 6 6 0 22680 6 1 0 22700 70 (Ma) Pb2°'/Pb2°6 Age pbm/Pb^ Age (Ma) 2560 8 9 tO II 12 The TheNd Ndwhole wholerock rockisotope isotopecomposition composition(TDM= (TDM=2.99 2.99Ga Gaand andE(T)Xa1 &om=-2.5) -2.5) isis typical typical of of true true Archean basement. Feldspar common Pb (6/4=16.08, 7/4=15.76), similarly indicate an old age Archean basement. Feldspar common Pb (6/4=16.08,714=15.76), for this sample. The high 7/4 ratio is in good agreement with the proposed end-member model for this sample. The high 714 ratio is in good agreement with the lower lowercrust crustrequired requiredfor forthe thePenokean Penokeanmixing mixing model model described described by Van Wyck and Johnson Johnson (1993) (1993) and into feldspars. One andrequires requiresremobalization rtkobaliition of of Archean Archean lead l&into One possible interpretation interpretation of the feldspar Pbdata dataisisthat thatthe thestrong stronggneissic meissicfabric fabricand and outcrop outcrop scale scale folding folding are are related relatedto to aa feldsoarPb Penokean high grade metamorphic and fabric forming event, and therefore may be of use therefore use in in ~enokeanhigh grade metamorphicand fabric forming event, deciphering Alternatively, the the relatively relatively simple simple decipheringthe thePenokean Penokean kinematic kinematic history of this area. Alternatively, zircon zirconsystematics systematicsand andlack lackof ofaaPenokean Penokeanlower lowerintercept intercept age age argues argues against against a high high grade grade Penokean metamorphism, and in turn suggests that feldspar lead was not a closed system closed systemduring during ~enoke&metamorphism, and in turn suggests that feldspar lead was the thePenokean. Penokean.Under Underthis thisscenario, scenario,the thestructures structuresrecorded recordedat at this this outcrop outcrop could could be PrePen okean. Penokean. Collectively Collectivelythese thesedata dataargue argue for for the the presence presence of Archean crust within the Wausau-Pembine terrane. Thisisisthe thefirst firstreported reportedpresence presenceofofcrust crustof ofthis thisage ageininwhat whathas hasbeen been previously previously terrane. This thought to be a juvenile package of rocks; this leads to the following possible interpretations: interpretations: thought to be a juvenile package of rocks, this leads to a) a) The TheSuperior Superiorprovince province isis underthrust underthrust at at least least 20 20 km to the south, as has been implied by the gravity gravity data data of of Attoh Attoh and and Klasner Klasner (1989). This Thiscrust crustisisnow nowexposed exposedas asaa basement basement culmination, culmination, and one would predict that structures such as the Dunbar Gneiss Dome, along strike to the east, and one would predict that structures such as the timing and mechanism for the exposure these may be similarly similarly cored by Archean crust. The The timing and mechanism for the exposure of of these 7.9 �I deeper deepercrustal crustallevels levelsare areunknown, unknown,but butanalogies analogieswith withdeep deepcrustal crustalexposures exposuresproduced producedby by extensional extensionaltectonics tectonicsare areappealing. appealing. b) ageisisfrom frombasement basementtotothe theWausau-Pembine Wausau-Pembiieterrane, tenane,which whichhas hasbeen been b) Alternatively, Alternatively,this thisage previously previouslythought thought to toconsist consistof of juvenile juvenile crust crustformed formedininan anisland islandarc arc environment. environment. In In either eithercase, case, the the feldspar feldsparcommon commonPb Pband and 143Nd/1Nd 143~d/1% ratio ratiomeasured measuredininthis thissample sampleoffers offersan an appealing appealingexplanation explanationfor forthe thehigh highPb2071204 Pb207/204signatures signaturesof of galenas galenasand and feldspar feldsparleads leadsreported reported for thisregion, region,as aswell wellasasthe thereported reportedtrend trendofofincreasingly increasinglynegative negativeENd eNdvalues for Penokean Penokean forthis intnisives verses distance from the Superior Province. On account of intrusives verses distance from the Superior Province. On account of the the absence absenceof of reported reportedold old crust crustin in the theWausau-Pembine Wausau-Pembiieterrane, terrane,Barovich Barovichetetal., al.,(1989) (1989) have havesuggested suggestedthat thatmantle mantle contamination eNdPenokean Penokean contaminationby bySuperior SuperiorProvince Provincederived derivedsediments sedimentsexplained explainedthe thelow lowENd intrusives in the northern Waasau-Pembine Wausau-Pembinetenane. terrane. Mother Anotherexplanation explanationisis now now possible; that of of interaction interaction with with pre-existing pre-existingolder oldercrust, oust, rather ratherthan thanaa large largescale scale mantle mantle contamination contamination process. process. References: References: Attoh, K., and and Kiasner, Klasner,J.J. S., S., 1989, 1989,Tectonic Tectonicimplications implicationsof of metamorphism metamorphism and and gravity gravity field fieldin in Attoh, K., the v.8, the Penokean Penokean orogen orogen of of northern northern Michigan: Tectonics, v. 8,p.911-933. p. 911-933. Barovich,Karin E; Sims,Paul Sims,Paul K K (1989): (1989): Nd Nd isotopes Barovich,Karin M; M, Patchett,P PatchekP Jonathan; Jonathan; Peterman,Zell Petennan.ZeU E; isotopes and and the origin of 1.9-1.7 Ga Penokean continental crust of the Lake Superior region. GSAB the origin of 1.9-1.7 Ga Penokean continental crust of the Lake GSAB 101(3), 101(3), 333-338. 333-338. Sims, Sims, P. K., K., Van, Van, S. S.W. W.R., R..Schulz, Schulz,K. K.J.,I..and andPeterman, Petennan,Z.Z.E., E.,1989, 1989,Tectonostratigraphic Tectonostratigraphic evolution of the early Proterozoic Wisconsin magmatic terranes of the evolution of the early Proterozoic Wisconsin magmatic terranes of the Penokean PenokeanOrogen: Orogen:Can CanJ.J. Ear. Ear. Sci. Sci. v. 26, 26, p. p. 2145-2158. 2145-2158. Van Van Wyck, Wyck, N. and and Johnson, Johnson,C. C. M. M. 1993, 1993,Lead Lead isotopes isotopesand and the the Penokean Orogeny: Omgeny: Crustal Crystal growth growth revisited. revisited. GSA GSA Abs Abs v. v. 25, 25, p.A236 p.A236 Zircon data Zircon age age data Zircon Zircon fraction fraction fQQ75gj ((10-75p IOO-75is 1W75p lOO-75ps 100-75p LM2Abd LM2 AM LM2Abd LM2 AM 206/204 206/204 Meas. Meas. 206*1238 206*/238 5398 5398 0.396274 0.396274 5096 5096 0.400454 0.400454 4124 4124 0.398362 0.398362 6476 0.431821 0.431821 6476 4834 4834 0.403347 0.403347 207*1235 207*/235 8.86105 8.86105 8.95252 8.95252 8.89045 8.89045 9.9453 9.9453 9.06484 9.06484 207*/206* 207*/206* * 0.162177 0.162177 0.16214 0.16214 0.161862 0.161862 0.167037 0.167037 0.162997 0.162997 207*/206* 207*/206* 206*/238 206*/238 207*/235 M7*/235 Age Age (Ma) (Ma) Age Age (Ma) (Ma) 2151.86 2151.86 2323.8 2323.8 2478.48 2478.48 2171.13 2171.13 2333.17 2333.17 2478.11 2478.11 2161.49 2K1.49 2326.82 2326.82 2475.21 2475.21 2313.92 2313.92 2429.72 2429.72 2528.17 2528.17 2184.43 2184.43 2344.57 2344.57 2486.99 2486.99 Age Age (Ma) (Ma) 80 �S I N I I I I The TheWolf Wolf River RiverA-type A-type Magniatic MagmaticEvent Eventin inWisconsin: Wisconsin: U/Pb UIPb and andSm/Nd S d N d Constraints Constraintson on Timing Timing and andPetrogenesis Petrogenesis Nicholas L. Gordon Gordon Medaris MedarisJr., and and Clark Clark M. Johnson, Johnson, Department Department of Geology Geology and and Nicholas Van Van Wyck, Wyck,L. Geophysics, Geophysics,University Universityof ofWisconsin, Wisconsin,Madison MadisonWI, WI,53706 53706 A U/Pb U/Pbzircon zircon age ageand and l43Nd/WNd ^~d/~4"^ ratio ratio have have been been determined determined for for syenite syenite from from the the Stettin Stettinintrusive intrusive A complex, complex,and andaaU/Pb UPbzircon zirconage, age,for forPrecambrian Precambrianbasement basement from from aa borehole borehole at at Oshkosh. Oshkosh. The Thedata dataindicate indicate that thatduration durationof of Early EarlyMesoproterozoic MesoproterozoicA-type A-type magmatism magmatismin in Wisconsin Wisconsin may may have have been been on on the the order orderof of 80 80 m.y. my. and and that that various variousproportions proportions of mantle mantle and and crustal crustal components components are are incorporated incorporated in in different different lithologies lithologies of of the the Wolf Wolf River Riverpetrologic petrologicprovince. province. Abundant and inclusion inclusion free free zircons zircons were separated from from aa pyroxene pyroxene syenite syenite Abundant euhedral, euhedral,diamagnetic diamagnetic and collected collectedat at an an abandoned abandonedquarry quarry in in the the south south central central part pan of the Stettin Stettin complex. Fractions Fractions 1,2 1.2 and and 33 were were unabraded mg ((typically unabraded and and the the sample sample size size was was approximately 1 mg typically 20-30 grains). Fractions Fractions44and and66were were identical identical to to 11 through through 33 except exceptthat that they they were were abraded for for over over 24 hours. Fraction Fraction55was wasaasingle singlezircon zircon crystal, 200 lie. gg. Abraded Abradedand andunabraded unabradedzircon zirconfractions fractions crystal, also also abraded, abraded, which weighed approximately 200 together Ma, which is is interpreted interpreted as the crystallization crystallization age age of the the Stettin Stettin together give give concordia concordiaages agesof of 1565+3-5 1565+3-5 Ma, syenite. syenite. , Diamagnetic, replicate analyses analyses were Diamagnetic, euhedral euhedral zircons zircons from fromthe the Oshkosh Oshkosh borehole have been abraded and replicate performed performed over over aa one one year year period. Fractions Fractions1,2 1.2and and33were wereless lessthan than0.5 0.5mg mgsample samplesize sizeand andwere wereabraded abraded for andare aredifficult difficultto tointerpret. interpret. Although for 15 15 hours. All Allfractions, fractions,except except for for 1, 1, do not lie on concordia and Although three three fractions fractions(1,2, (1,2,and and 5) 5) give give consistent consistentPb206IU238 Pb2061U238ages of approximately 1471 Ma, it is more likely that these zircons have experienced lead loss approximately 1475 that these zircons have experienced lead loss from from a slightly older age of approximately 1475 Ma, which is well 15 Ma within error errorof of the thepreviously previouslypublished publishedage agefor forthe theWolf WolfRiver Riverof of1485± 1485±1 Ma (Van Schmus Schmuset et al al well within 1975). An Anadditional additionalcomplication complicationmaybe maybezircon zirconinheritance. inheritance.Fractions Fractions44and and55were wereanalyzed analyzedone oneyear year later later and and are are 11 mg mg sized sized samples. samples. One Onezircon zirconpopulation populationisisdark darkbrown brownin incolor, color,inincomparison comparisontotothe the majority majority of zircon zircon grains, grains, which which were were clear clear to light colored. Fraction Fraction44has hashad hadthe thedarker darkergrains grainsremoved removed shows approximately 10% shows no no indication indicationof of inheritance. inheritance. Fraction Fraction 5, 5. which contained contained approximately 10%dark brown grains, does does show show an an inheritance inheritance component. component. Unfortunately Unfortunatelythe thedata datacan cannot notresolve resolvewhether whetherititisisArchean Archeanor or Penokean Penokean inherited inheritedzircons, zircons,which whichwill willrequire requiredetailed detailedsingle singlezircon zirconanalysis. analysis. 02Th oses Oshkosh borehole &277 0.264 (LOTS 0.2 $1 0273 0.254 0.254 0.271 vaso 0.250 oasa 0246 0È 3.0 3.0 354 3.1 rPbp3sU 3JW 3S6 a70 a74 20TPbrIJ "Wll 81 �Stettin pyroxene syenite are slightly REE concentrations for Stettin slightly lower than those for Wolf River adamellite adamellite and momnite, monzonite, but the chondite-normalii chondite-normalized REE patterns are similar, with LREE eenrichment ~ c h m e nand t 4.90, and == 1.31). &ox& C(T)xal for relatively flat flat HREE HREE(for (for syenite, syenite,(CeiTb)CN (Ce/Tb)a = = 4.90. and (Th/Yb)CN (Tb/Yb)cN for syenite syenite is +2.9, derivation from a mildly depleted subcmstal subcrustal lithospheric lithosphenc source, suggesting derivation source, in contrast contrast to to Wolf River River NdT (Nelson, 1991). 1991), indicating significant granitic rocks, in which epsilon N ~ ranges T from -0.3 to -4.0 (Nelson, amounts of crustal contributions. contributions. Nd model complex and and Wolf Wolf River River also differ for the Stettin complex model ages also batholith, being 1.65 1.65 Ga Ga and 1.9 1.9 to to 2.1 Ga, respectively. respectively. 1000 0 v s -. 3(0 E Avenge VW River Jioo a lm =E u c 0 6 l0 La ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu nepheline syenite, isotopically Geochemical differences between the Stettin complex (syenite and nepheliie depleted) and the Wolf River batholith (predominantly adamellite, isotopically enriched) reflect River batholith (predominantly adamellite, enriched) reflect evolving evolving compositions due to increasing mantle-crust interactions in an A-type igneous cycle. The Wolf magma compositions of the the Stettin complex at River magmatic event was initiated by mantle upwelling (plume?) and generation of 1565 Ma Ma by by partial partial melting melting of of mildly mildly depleted depleted lithosphere. lithosphere. Later mantle-derived melts Later melts were were contaminated contaminated with crustal (quartz syenite and granite) at 1517 1517 Ma (Van Schmus, Schmus, crostal material material to form form the Wausau complex complex (quartz Thermalmaturation, maturation, magma magma ponding, ponding, and crustal crustal anatexis culminated at 1485 1485Ma (Van pers. comm.). Thermal Schmus Schmus et et al., 1975) 1975)in in production production of of the the voluminous voluminousWolf Wolf River Riverbatholith. batholith. Mesoproterozoic A-type magmatism that affected much of North America Amenca was diachronous, The Early Mesoprotemzoic diihronous, beginning in Wisconsin and ending in Labrador and the southwestern Cordillera Cordillera 115 and 135 M.y. later, beginniig 135 M.y. respectively (Anderson, (Anderson, 1983). The Stettin complex, which so far is the oldest dated intrusion in this this The Stettin complex, dated intrusion in contipental-scale magmatic event. igneous suite, is thus the harbinger of a major, continental-scale References References ll, Cullers Anderson JL, CutlersRL RL(1978) (1978)Geochemistry Geochemistryand andevolution evolutionof of the the Wolf Wolf River River Batholith, a late late Precambrian U.S.A: Precamb Res 7,287-324. 7, 287-324. Precambrianrapakivi rapakivi massif in North Wisconsin, U.SA Anderson J JL anorogenic granite granite plutonism plutonismof of North North America. America. Geol Geol Soc Soc Am Mem L (1983) (1983) Proterozoic Proterozoic anomgenic Anderson 161:133-152. Nelson, B. K., growth near near the Archean craton: craton: the isotopic record from K, (1991) (1991) Proterozoic Proterozoic continental growth anorogenic granites Wisconsin: Eos 544. Eos 72, 72,544. anomgenic granites in Wisconsin: Schmus,WR; Medaris,LG; Medaris,LG; BanksJO Banks,PO (1975) Geology and and age age of of the the Wolf Wolf River River batholith, batholith, Wisconsin: Wisconsin: Van Schnnis,WR; GSABuII 86, 907-9 14. GSABdl86,W-914. 82 �A COMPENDIUM OF MINERAL RESOURCE INFORMATION, EAST-CENTRAL MINNESOTA Minnesota Department of Natural Resources, Division of Minerals, 1525 3rd Ave. E., Flibbing, Minnesota 55746 The administration of state-owned lands includes the management of those lands for mineral resources. The Minnesota Department of Natural Resources Minerals Division administers state-owned mineral rights for the benefit of schools, the university, local units of government and the public. As a part of this responsibility, the Minerals Division has maintained mineral resource records and information. This compendium of minerals information for east-central Minnesota is provided by the Minerals Division for all people who work in the field of land management, both within various levels of government and outside government. It is intended to serve as a guide to available information, by providing maps showing the location of known mineral resources and the geographic extent of information sources, and listing a knowledgeable contact person for each theme. Further, it is intended to document the presence of some known subeconomic mineral resources, which may have a higher value in the future, and therefore should be considered in current planning. It does not contain a map of speculative resource locations for all commodities, because that would require a complex evaluation and presentation. This compendium is intended to be a starting point for all who need or want access to mineral resource information in east-central Minnesota. Three mineral commodities are currently being extracted in east-central Minnesota - peat for horticultural applications, aggregate for construction purposes, and dimension stone for buildings or monuments. There have been over 70 years of mining of two other mineral commodities - iron and manganese, from from Crew Crow Wing County and adjacent Moreover, large large quantities quantitiesof of iron iron and manganese, adjacent areas. Moreow, manganese resources are still present here, having been identified by past drilling. vnawsctsw(tillpraittthere,kavtagbeteidentitiediiyoftdrilUng. that mining for for the the W above five axamodities, commodities,as aswell wellas as other other mincralg, minerals, bIt is reasonable reuoaable to aassume i ~ a a e&at e five be propotad proposed in in (be the future future in in this this rtgion. region. The setting tuggeitt suggests that thatother otherplausible plausibleminerals minerals could be The geologic geologic sctt&is could iach^ include iJdustTid industrialmiiMTdi minerals<ç suchu asgnphite, graphite,p garnet oroli^ otherlbiwivet. abrasives,barite. barite,berylberyllium,ghmphse; phosphate; 'could mt or minerals such suchas as gold, gold, tilver, silver, coppar, copper, lead, lead, zinc, zinc, bismuth, bismuth,chromium, chromium,platinum, platinum,nickel, nickel,or or or metallic metallic mineralf rare earth metals. There are known mineral occurrences for almost all of these commodities, but not in ran meld*. There amknown mineral occmreneti for abBOM ill thege commodities, but not in sufficient, known known quantitiesfor forextraction. extraction. As As aa result, these these "other* "other minerals mineralsare are referred referred to to here here as as sufficient, speculativemi+cal mineral(dowcfs, resources,wfaidi whichwould wouldW have be dueovered discoveredininlarger larger qmatity quantityand and quality quality to to specdative e toto be evaluation initiates such suchdevelopment developmentevituation, evaluation,primarily primarily warrant development w ~  ¥ work. w o rThe The k private private sector sector iiritiites spurred by by market market denumd demand inthe in the form formof of favorable favorablecoianodity commodityprices. prices. All All futun futuredevelopment developmentproposals proposals spurred would be be gubject subject to the compendium of law review and and permitting permitting would compendium of law applicable applicable to the environmental environmental review process. The study area (see the first map) covers the part of Minnesota that very nearly corresponds to Minnesota's Department of Natural Resources administrative region III. Our study area differs from DNR Region III boundaries in that we use county boundaries for the border with two minor exceptions. Because most of our minerals databases contain county designations, it was more practical to use entire county boundaries as much as possible. The two exceptions are small areas within Itasca and Anoka counties, which were included to accommodate the entirety of DNR Region III. The minerals information in this compendium is presented primarily in the form of maps, and is organized around seven general themes: State-Owned Lands and Mineral Leasing, Peat, Industrial Minerals, Sand and Gravel, Iron Ore and Manganese, Other Speculative Minerals, and Mineral Exploration Data (see Table 1). A common package is presented for each theme, and contains an explanation, a bibliography or digital database reference, and a set of index maps. No part of the package was intended to stand alone. The explanation defines what is included in the theme, describes it and the maps, and summarizes the information. Each bibliography was created from those references judged most helpful. The maps for 83 �three three themes themes were were created created from fromexisting existingdigital digitaldatabases1 databases, and do not have bibliographies (see Table Table I). 1). A specialist with extensive knowledge of each theme has written the explanation, created the bibliography, A specialist withextensive knowledgeof each written the explanation, created the bibliography, and and designed designed the the theme theme maps. maps. ItIt was was not not practical practical to toillustrate illustrateall all of of the the references references on onall allthe themaps. maps. The The following following maps maps were were created created by by overlaying overlayingmineral mineral resource resourcedata data on onaabase basemap mapassembled assembled from the Information System System (MLMIS) (MLMIS) 100 100database. database. MLMIS is aa gridthe Minnesota Land Land Management Management Information gridcell based database of Minnesota's natural resources, public land survey, and ownership. The database cell based Minnesota's resources, land survey, and ownership. The database was was designed designed for use use with with EPPL7, EPPL7,aaraster-based raster-basedGIS CISpackage packagedeveloped developed by by the theLand LandManagement Management Information Information Center, Center, Minnesota Minnesota Office Office of of Planning. Planning. The captured from The data data for for MLMIS MLMIS were werecaptured frommaps maps ranging ranging in in scale scale from from 1:24,000 1:24,000 to to 1:1,000,000 1:1,000,000 through grid-overlay techniques and digitizing. MLMIS was designed to be used in regional through grid-overlay techniques and digitizing. MLMIS was designed to used in regionaland and statewide planning, planning, not not for site specific work, and isis divided into two databases, divided into two databases, based on on cell cell size: size: MLMIS4O 100 The The cell cell size sizeof ofMLMIS4O MLMIS40 is is 40 40 acres acres and and isis available available as as statewide statewidefiles. files. MLMIS40 and andMLMIS MLMIS100. The size of 100 is approximately 2.5 Thecell cellsize ofMLMIS MLMIS100 2.5 acres acres(the (thelength lengthof of each eachside sideof ofthe thecell cellisis100 100meters) meters) and 100 isis available and is is the the spatially spatiallycorrected correctedversion versionof ofMLMIS4O. MLMIS40. MLMIS MLMIS100 available as as county county files filesand andenables enables the user to better match geographically referenced data from other sources. the user to better match geographically referenced data from other sources. For 100 toto For this thisstudy studyof ofeast-central east-centralMinnesota, Minnesota,staff staffused usedthe thepublic publicland landsurvey surveyfiles filesofofMLMIS MLMIS100 map map their their 'occurrence" "occurrence"data datathat thatwere werestored storedinintabular tabulardatabase databaseformats formatsas astownship, township,range, range,section, section,and and sometimes forty. The references were mapped through digitizing the reference boundaries or by matching sometimes forty. The references were mapped through digitizing the reference boundaries or by matching the 100 files. andsections sectionscovered coveredby bythe thereferences referenceswith withthe theMLMIS MLMIS100 files. the township, township, range, range,.and , . . .. ~ . > .. ~ , . .. .. ~ ', , ~ # . , . ~ . . .. .. , . , , . ,:.,~. . . ~ ~ . . . . ,. , ; . . ~ .. , ., .. 84 � https://digitalcollections.lakeheadu.ca/files/original/39759c212b92a75f106d8045c6c295a3.pdf b89931cafd8d01019fb19c3187acf300 PDF Text Text tL&&Ntat By: By: Theodore TheodoreA J. Bornhorst Bornhorstand andWilliam WilliamI.I.Rose Rose Institute Instituteon onLake LakeSuperior Superior Geology Geology Proceedings Proceedings Volume 40, Part 2 �Proceedings Proceedings Volume 40, Volume 40, Part Part 22 FIRSTPRINTING—MAY PRINTING-MAY 1994 1994 SECOND PRINTING—SEPTEMBER PRINTING-SEPTEMBER 1994 SECOND 1994 FIRST Publisher Publisher Institute Instituteon onLake Lake Superior Superior Geology Geology Distributor Distributor TheodoreJ. J. Bornhorst Bornhorst Theodore do c/oDepartment DepartmentofofGeological GeologicalEngineering, Engineering,Geology, Geology, and andGeophysics Geophysics MichiganTechnological Technological University University Michigan Townsend Drive Drive 1400Townsend 1400 Houghton, Houghton, Michigan Michigan49931-1 49931-1295 295 ISSN 1042-9964 ISSN 1042-9964 Volume 3, 4, and Volume 40 40consists consists of ofParts Pam 1, 1, 2, 2,3,4, and 5. 5. Reference Volume 40, 40, Part Part22should shouldfollow follow the the example below: below: Reference to Volume Bornhorst, 1. J. and and Rose, Rose,W. W.I.,I.,1994, 1994, Self-guided Self-guided geological geologicalfield field trip trip to to the T. J. the Keweenaw Peninsula, Michigan: Institute on Lake Superior Geology Proceedings, Keweenaw Peninsula, Michigan: Institute on Lake Superior Geology Proceedings, 40th 40thAnnual AnnualMeeting, Meeting,Houghton, Houghton,Ml, 40, part part2, 2, 185 185p. p. MI,v.v. 40, �1 PREFACE PREFACE In 1983 1983 we, with the help of Jim Jim Paces, put together together a "Field Guide to the Geology Geology of the the Keweenaw Keweenaw Annual Institute Institute on on Lake Lake Superior Superior Geology Peninsula, Michigan" Michigan" (Bornhorst (Bornhorst and others, 1983) for the 29th Annual Technological University Universityon onMay May11-14, 11-14,1983. 1983. At At that that time, time, we considered that that "It is held at Michigan Technological presumptuous for for us us to put together together a book book which which is based based mainly mainly on on the work of others," presumptuous others," but we did "because hundreds of people come to the Keweenaw Keweenaw each year to look look at at geological geological features features and andmany many 1983guide guide was was aa smashing smashing success and after 10 and 1/2 112 years a total of them ask us for advice." The The 1983 and others. others. At the time we completed the 1983 guide, we expected of 1850 copies were sold to geologists and to revise However,this this did did not not happen happen for for a variety revise and and update update the the guide guidethrough through new new editions. editions. However, variety of reasons, especially the fact that the 1983 reasons, 1983 version was done with a typewriter before word processing on computers became became popular. popular. Due Due to to the the sheer sheermagnitude magnitude of changes changes made to the 1983 1983 guide, guide, including including increasing the the number number of of stops stops from from 24 24 to to 56, 56, this this guide guide is is being published published an all new introduction and increasing Geology. The 40th Annual Annual Institute on Lake Superior Superior Geology. The Institute Institute on on Lake Lake as a new new publication publication for the 40th Geology meeting meeting in in May May 1994 is the deadline deadline forcing forcing completion completion of of this this guide, guide, which which will be Superior Geology published under the Institute on Lake Superior Superior Geology name, as would probably have been appropriate appropriate for the 1983 guide. guide. the 1983 We have 1983 guide. guide. The text, figure figure have designed designed this guide guide to to make make revisions revisions much much easier easier than than the the 1983 captions, etc. are computerized. Maps make revisions revisions easier. easier. We really do expect Maps have have been produced to make and we we get get the the momentum momentumto toadd addnew newstops. stops. We welcome your to revise this guide as mistakes are found and comments comments and and suggestions. suggestions. contributed a mountain 150 years ago, dozens of geologists have contributed Starting with Douglass Houghton almost 150 information on on the the Keweenaw Keweenaw Peninsula. Peninsula. We have faithfully of geological information faithfully tried to transmit transmit the the ideas ideas are doing doing serious serious geological geological within this mountain of information. However, However, this this guide guide is is for for people people who who are field trips. trips. �U ACKNOWLEDGMENTS ACKNOWLEDGMENTS Mary Mary Larson, Larson, an anundergraduate undergraduatestudent studentin inScientific Scientificand andTechnical TechnicalCommunication Communicationwith withaageology geologyminor, minor, played thetext textofofthis thisguide; guide;editing, editing,assembling, assembling,and andwriting writingaafew fewsegments. segments. She She played a key key role roleininthe undertook undertook this project both both as as aawork workstudy studystudent studentand and for foraascientific scientificand andtechnical technicalcommunications communications class. class. Her Hereffort effortisissincerely sincerelyappreciated. appreciated.Jane JaneCookman, Cookman,ananundergraduate undergraduateininGeology, Geology,prepared preparedmany many Laurie, Gail and Ellen of the the maps maps in in the the road road log. log. Finally, the senior senior author author (Bomhorst), thanks Laurie, Ellen for for of tolerating the extra hours at the office officeneeded needed to to complete complete this this guide. guide. to DEDICATION DEDICATION "Self-guided geological field trip to the the Keweenaw Keweenaw Peninsula, Michigan" the late late This "Self-guided Michigan" is dedicated to the mapping in in the theKeweenaw KeweenawPeninsula. Peninsula. Walter S. S. White, White, who who spent spent much much of of his his life lifedoing doinggeologic geologicmapping Walter �Proceedings Proceedings Volume Volume 40, Part Part 22 Institute on Institute on Lake Lake Superior Superior Geology Geology trip to the Self-guided Self-guided geological field trip Keweenaw Peninsula, Peninsula, Michigan Keweenaw Michigan Bornhorst and By: By: Theodore Theodore J. J. Bornhorst and William WilliamI.I.Rose Rose Department Departmentof ofGeological GeologicalEngineering, Engineering,Geology, Geology,and andGeophysics Geophysics Michigan University, Houghton, Houghton, Michigan Michigan 49931-1 295 Michigan Technological University, 49931-1295 for Published for 40th 40th Annual Meeting Meeting Institute on Lake Superior Geology Institute on Lake Geology Houghton, Houghton, Michigan Michigan May 11—14, 1994 May ll-I4,1994 ISSN 1042-9964 1042-9964 ISSN Cover photoÑClif photo—Cliff Mine Minedrca circaearly early 1900s. 1900s. Photo from from Mlii Photo MTUArchives Archivesand andCopper CopperCountry CountryHistorical HistoricalCollections; Collections;Donor DonorTony TonyVranesich. Vranesich. �U' TABLE OF TABLE OF CONTENTS CONTENTS && PREFACE PREFACE i ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS ii ii DEDICATION DEDICATION iiii USING THIS THIS GUIDE GUIDE iv iv LIST LIST OF OF STOPS STOPS vi LIST OF OF MAPS MAPS xii xii LIST OF OF FIGURES FIGURES XV LIST LIST OF OFTABLES TABLES INDEX TO TO GEOLOGY GEOLOGY ON ON MAPS MAPS GEOLOGY GEOLOGY OF OF THE THEKEWEENAW KEWEENAWPENINSULA PENINSULA MAIN ROAD LOG LOG AND AND STOP STOPDESCRIPTION DESCRIPTION - xviii xviii xix xix 1 1 33 33 LEG A A - REDRIDGE REDRIDGE 117 117 LEG B -- OWL OWL CREEK CREEK 124 1% LEG C C -- HORSESHOE HORSESHOE HARBOR HARBOR 128 LEG D D -- EASTSIDE EASTSWE OF OF THE THEKEWEENAW KEWEENAWPENINSULA PENINSULA 132 LEG E E-932 - 932CREEK CREEK 144 LEG LEG FF -- FIVE FIVE MILE MILE POINT POINT 149 LEG LEG G G -- COPPER COPPER CITY CITY 155 LEG LEG H H -- MCLAIN MCLAIN STATE STATE PARK PARK 158 LEGI-L'ANSE LEG I - L'ANSE 172 REFERENCES REFERENCES 178 �iv USING 11118 THIS GUIDE GUIDE A NUMBER NUMBER OF STOPS ARE ON PRIVATE PRIVATE LAND. LAND. PLEASE PLEASE RESPECT RESPECT PRIVATE PRIVATE PROPERTY. PROPERTY. PROBLEMS OF ACCESS ARE MINIMAL, BUT THIS CAN QUICKLY CHANGE IF EVERYONE PROBLEMS MINIMAL, BUT THIS CAN QUICKLY CHANGE IF EVERYONE DOES NOT USE DOES USE LOW LOWPROFILE PROFILEOUTDOOR OUTDOOR PRINCIPLES PRINCIPLES AND AND ASK ASK PERMISSION PERMISSION WHEN WHEN POSSIBLE. OLD MINEROCK ROCK PILES PILESARE AREHAZARDOUS, HAZARDOUS, SO SO COMMON COMMON SENSE SENSE MUST MUST BE BE POSSIBLE. OLD MINE APPLIED. APPLIED. for geologists and and geology geologystudents. students. It begins with with an an introductory introductory description description with with This guide is designed for figures and tables. The Theroad roadlog logconsists consistsof ofaamain main log logwith withsequentially sequentiallynumbered numbered stops, stops, maps, maps, figures, figures, and tables (sequence (sequence for for figures figures and and tables tables continues continues from from introductory introductory description) description)followed followedby by separate separate legs. Each leg has separate sequentially numbered stops, maps, figures, and tables (leg numbers has separate sequentially numbered stops, maps, figures, (leg numbers are are by the letter of the leg). preceded by leg). 240 m or I" 2000 ft) scale Ml maps have north to the top. top. Most All Most maps maps are are 1:24,000 1:24,000 (1 cm = 240 1" == 2000 scale (Figure (Figure 1689.6 m or 3/8 I (5280 ft)). Several maps and I are 1:168960 cm = lb). maps in Legs D are 1:168960 (1 = 1689.6 318" = 1 mile (5280 ft)). Dots ib). follow the road traveled for the main main road log, log, and and open open circles circles are are used used for for the the legs. legs. The field trip stops stops are are grouped grouped below below in in topics topics to to assist assist in in design design of of your your field fieldtrip. trip. TOPIC TOPIC Glacial Glacial 2, 3. 7, 16, 29, 33, A2, F2, Hi, H2, H3, H4, H5, H7, H9 Rift-flanking Rift-flanking clastic clastic sedimentary sedimentary rocks rocks 10, 11, 12, 12, D5, El, El,11 I1 Rift-filling dominantly clastic clastic sedimentary rocks Rift-filling dominantly igneous igneous rocks rocks 12, 22, 22, 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,28, 28,A1, Al, A3, A3, Cl, Cl, Fl, Fl, H6, H8 1, 4, 6, 8, 14, 15, 16, 18, 19, 20, 21, 30, 31, Bi, Dl, El, F3, Gi Native Copper Copper Deposits Deposits 5. 8, Scenic Scenic 7, 16, 25, D4, D6 9, 13, 15, 16, 17, 18, 28, 30, 32, 34, 81 We encourage you to be imaginative and make make up up your your own own subset subsetof of stops. stops. To visit all the stops stops listed based in this guide would take at least five days. We We have have designed designed several trips with different emphasis based on about 10 10 stops per day. Stops Stopsare arelisted listedininapproximate approximateorder order of of visiting. visiting. One-day trip with emphasis Oneday emphasis glacial glacial features features A2, A2, 7, 33, 33, Hi, HI,H2, H2,113, H3, H4, H4, H5, H5, H7, H7, H9 H9(requires (requires special specialpermission) permission) One-day coverage of of rift rift geology geology in in the theHoughton/Calumet HoughtonlCalumetarea area Oneday trip with broad coverage Al, A3, 4, 5, 6, 6, A1, A3. H8, H8, 10, 10, 12, 12, 13, 13, 15, 15, 16 16 �V One-thy One-day trip tripwith withemphasis emphasison onmineral mineraldeposits deposits 5, 8, 8, 13, 13, 15, 15, 16, 16, 17, 17, 18, 18, 30, 30, El El 4, 5, One-day trip trip with with emphasis emphasison onigneous igneousgeology geology One-day 4, 6, 31, El, El, Gl 6, 15, 15, 16, 16, 18, 19, 20, 31, G1 One-thy One-day trip tripwith withbroad broadcoverage coverageof ofgeology geologyand andscenery scenery 4, 7, 10, 10, 12, 12, 13, 13, 15, 15, 16, 16, 18, 18, 24, 24, 25, 25, 27 27 One-thy One-day trip tripwith withscenic scenicoverview overviewand andgeology geology 7, 16, 22, 24, 24, 25.28, 25, 28,Cl, Cl, D4, 04, D6 06 16, 21, 22, Two-day trip with with broad broad coverage coverage of of geology geology and and scenery scenery 4, 5, 10, 10, 12, 12, 13, 13, 15, 15, 16, 16, 18, 18, 20, 20, 21, 21, 22, 22, 25, 25, 28, 30, 30, Cl, Cl, H8, H8, A3 A3 so many excellent stops we almost don't We are are not not sure surewhich which stops stops There are so don't like to make suggestions. We are the most popular, but our guess is the following: 4, 7, 10, 12, 15, 16, 18, 21, 25, and 27. following: 4, If you use this guide, we would really really like like to to hear hearabout aboutyour yourexperience. experience. What Whatstops stopsdid didyou youlike? like? What like? etc. etc. Piease mail. With your your comments comments and and Please drop a letter letter or or postcard postcard in in the the mail. stops you don't like? suggestions we èan make this guide better. can make this guide better. suggestions �vi LIST LIST OF OF STOPS STOPS The The following following list of stops stops can can be be used to to help help you you design design your your The self—guided self-guided geological geological field field trip trip to to the the Keweenaw Keweenaw Peninsula. Peninsula. The The appropriate maps for location location of of stops stops are are shown shown in in Figure Figure 1A. 1A. The appropriate maps for each stop stop and and trip trip route route are are located located in in Figure Figure lB. IB. We hope hope you you enjoy enjoy seeing seeing the the Keweenaw Keweenaw and and its its geology. geology. STOP STOP APPROPRIATE APPROPRIATE MAP PAGE PAGE STOP DESCRIPTION STOP DESCRIPTION MAIN ROAD ROAD LOG LOG 1 (2) 33 seventh Street, Seventh Street, City City of of Houghton Houghton (Portage Lake Volcanics (Portage Lake Volcanics [PLy]) [PLV]) 2 (2) 34 Boughton Houghton grooves)) grooves 3 (2) 36 Hurontown (glacially caned basalt) (glacially carved basalt) 4 (3) 39 South Range Quarry South Quarry Volcanics Volcanics [PLy]) [PLV]) 5 (3) 42 (native Baltic Mine Shaft No. 33 (native Baltic Mine Shaft copper deposit within Portage Lake Lake Volcanics [PLy]) Volcanics [PLV]) 6 (2) 43 city of Sheldon Avenue, Avenue, City of Houghton Houghton (Portage Lake Volcanics (Portage Lake Volcanics [PLy]) [PLV]) 7 (4) 44 Overlook Keweenaw Waterway Overlook 8 (4) 48 Quincy Mine Adit Mit Quincy Mine Volcanics [PLy]) Volcanics [PLVI) 9 (4) 53 Quincy Quincy Mine Mine Rock Rock Piles Piles (native (native copper deposit within Portage Lake Lake Volcanics [PLy]) [PLV]) Volcanics 10 (6) 56 M-26 M-26 near near Sandstone) Sandstone) 11 (7) 59 Hungarian Falls Hungarian Falls (Keweenaw (KeweenawFault) Fault) 12 (8) 64 Natural Wall Ravine Ravine (Keweenaw Natural (KeweenawFault) Fault) 13 (9) 68 wolverine Mine Shaft No. 22 (native Wolverine (native copper deposit within Portage Portage Lake Lake Volcanics [PLy]) Volcanics [PLV]) 14 (9) 74 Scales Creek creek (Portage Lake Volcanics Volcanics Scales (Portage Lake [PLVI) r PLVI ) water water tower tower Tamarack Tamarack (glacial (glacial (Portage Lake (Portage Lake (Portage Lake (Portage Lake (Jacobsville (Jacobsville �vii LIST OF LIST OF STOPS STOPS (Cont'd.) (Cont'd.) STOP STOP PAGE APPROPRIATE APPROPRIATE PAGE MAP MAP STOP STOP DESCRIPTION DESCRIPTION 15 15 (9) (9) 74 74 Allouez ~llouez(conglomerate (conglomerate in in Portage Portage Lake Volcanics [PLy]) Lake Volcanics [PLV]) 16 16 (9) (9) 75 75 Bumbletown Bumbletown Hill (Allouez (Allouez Gap Gap Fault Fault and and Portage Portage Lake Lake Volcanics) ~olcanics) 17 17 (11) (11) 82 82 Cliff Cliff Nine Mine (native (native copper copper vein vein deposit) deposit) 18 18 (12) (12) 83 83 Phoenix vein phoenix Mine (native (native copper copper vein deposit deposit and and Portage Portage Lake ~ a kvolcanics Volcanics e [PLy]) [PLVI) 19 19 (12) 87 87 Eagle Eagle River River (Portage (PortageLake Lake Volcanics Volcanics [PLy]) [PLVI) 20 20 (12) 89 89 M-26, M-26, Eagle Eagle River River (Portage (Portage Lake Lake volcanics Volcanics [PLy]) [PLVI) 21 21 (12) 89 89 Eagle Eagle River River Falls Falls (contact (contactof of Portage Portage Lake Lake Volcanics Volcanics and and Copper Copper Harbor Harbor Conglomerate) Conglomerate) 22 (14) 90 90 Eagle Eagle Harbor Harbor Lighthouse Lighthouse (Lake (Lake Shore Shore Traps) Traps) 23 (16) 93 93 Silver Silver River River (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) 24 (16) 96 96 Esrey Esrey Park Park (Lake (LakeShore Shore Traps) Traps) 25 (17) 98 98 Brockway Brockway Mountain Mountain Viewpoint Viewpoint 26 (17) 100 100 Hebard (Copper Harbor Harbor Hebard Park park (Copper Conglomerate) Conglomerate) 27 (17) 100 100 Dan's Dan's Point Point (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) 28 (18) 104 104 Fort Fort Wilkins Wilkins State State Park Park (native (native copper copper veins veins within within Copper Copper Harbor Harbor Conglomerate) Conglomerate) 29 (20) 105 105 Mandan Mandan (Mandan (Mandanesker) esker) 30 (21) 105 105 Delaware Delaware Mine Mine (native (nativecopper copper deposit deposit within within Portage Portage Lake Lake Volcanics Volcanics [PLy]) [PLVI) �LIST LIST OF OF STOPS STOPS (Cont'd.) (Cont'd.) STOP STOP APPROPRIATE APPROPRIATE MAP MAP 31 31 (21) 32 32 (10) PAGE PAGE 110 STOP STOP DESCRIPTION DESCRIPTION US-41 near Delaware Delaware (Portage (Portage Lake Lake US-41 Volcanics Volcanics [PLy]) [PLV]) 113 Mohawk Mine (native (native copper copper deposit deposit within within Portage Portage Lake Lake Volcanics Volcanics [PLy]) [PLVI) 33 33 (24) 114 Calumet Calumet (glacial (glacialgrooves) grooves) 34 34 (24) 116 Osceola Osceola Mine (native (native copper copper deposit deposit within within Portage Portage Lake Lake Volcanics Volcanics r [PLy]) PLVI ) LEG LEG A Redridge Al A1 (A2) 117 Houghton Houghton Canal Canal Road Road (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) A2 A2 (A2) 117 Cole's Cole's Creek Creek (glacial (glacial sediments) sediments) A3 A3 (AS) 120 Redridge Cliffs Cliffs (Freda (FredaSandstone) Sandstone) 124 124 Owl Owl Creek Creek [PLy] [PLV] and LEG LEG BB Owl Owl Creek Creek El Bl (B2) (B2) (Portage Lake volcanics (Portage Lake Volcanics Copper Falls Copper Falls Mine) Mine) LEG C Horseshoe Horseshoe Harbor Harbor Cl Cl (C2) (C2) 131 131 Horseshoe Horseshoe Harbor Harbor (Copper (CopperHarborS Harbor Conglomerate) Conglomerate) LEG Peninsula LEG DD Eastside Eastside of of the the 1(eweenaw Keweenaw Peninsula Dl Dl (D2) (D2 132 132 Mount Mount Bohemia Bohemia (diorite (diorite stock stock within within the Portage Lake Volcanics the Portage Lake Volcanics [PLy]) [PLV]) D2 D2 (Dl) (Dl) 136 136 Bete beach from Bete Grise Grise (white (white sand sand beach from Jacobsville Sandstone) Jacobsville Sandstone) D3 D3 (02) (D2) 137 137 Haven Haven Park Park (Portage (Portage Lake Lake Volcanics Volcanics [PLy] near the [PLV] near the Keweenaw Keweenaw Fault) Fault) D4 D4 (Dl) (Dl) 139 139 South South Point point (view (view of of the the tip tip of of the the Keweenaw Keweenaw Peninsula) Peninsula) DS D5 (Dl) (Dl) 139 139 Eastern Eastern Keweenaw Keweenaw Peninsula Peninsula (Jacobsville (Jacobsville Sandstone) Sandstone) �-- ix LIST LIST OF OF STOPS STOPS (Cont'd.) (C0nt8d.) APPROPRIATE APPROPRIATE PAGE PAGE MAP MAP STOP STOP D6 D6 (D3) (D3) STOP STOP DESCRIPTION DESCRIPTION 141 141 Gay Gay (stamp (stamp sands) sands) 144 144 932 932 creek Creek (Keweenaw (KeweenawFault) Fault) LEG LEG EE 932 932 creek Creek El El (E2) (E2) LEG LEG FF Five Five Mile Mile Point Point Fl Fl (Fl) (Fl) 149 149 W.C. W.C. Verde ~ e r d eRoadside ~oadsidePark Park (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) F2 (F3) 149 Allouez Allouez Gap Gap (kettles) (kettles) F3 (F3) 153 North North of of Abmeek Ahmeek (Portage (PortageLake Lake Volcanics [PLy]) Volcanics [PLV]) 155 155 copper Copper City City Rhyolite ~hyolite(Portage (Portage Lake Lake Volcanics [PLy)) Volcanics [PLV]) LEG LEG GG Copper Copper City City Gl Gl (Gi) (GI) LEG LEG HH Mctain McLain State State Park Park Hl HI (Hl) (HI) 158 158 Red Red Jacket ~acket(glacial (glacialsand sand and and H2 (Hl) 158 West West Tamarack Tamarack (glacial (glacialgravEls) gravels) H3 (H2) 161 Cloverland Clwerland Road Road (Washburn (WashburnStage. Stage beach beachridges) ridges) H4 (H4) 161 Lake Lake Annie Annie (glacial (glaciallake lake baymouth baymouth gravel) gravel ) bar) bar ) H5 (H3) 161 Sand Sand Ridges Ridges M-203 M-203 (Nipissing (Nipissingbeach beach ridges) ridges) (H3) 165 McLain McLain State State Park Park (Freda (FredaSandstone) Sandstone) (H5) 165 Till Till along along M—203 M-203 (till) (till) H8 (H6) 168 Hancock Rancock Campground campground(Nonesuch (NonesuchShale) Shale) H9 (136) 168 Superior Superior Sand Sand and and Gravel Gravel (glaciofluvial (glaciofluvialsediments) sediments) 174 174 L'Anse L'Anse Red Red Rocks Rocks (Jacobsville (Jacobsville H6 137 . LEG LEG II L'Anse L'Anse fl I1 (12) (12) Sandstone) Sandstone) �Figure Route and Stop Map I 4> Route Number iF 2P Kilometers 3P A..... Leg Route and Stop Number �15 13 Figure 1B: Index Index of 1:24,000 1:24,000 Scale Scale Maps Maps El F2 F3 H2 H 'Vt I C' AS 'V 3 See Map Ii I Region Covered Covered Region A6 1 LI Q 1p 2Q Kilometers 3 byMap MapNumber Number by Main Route Route and and Main Stop Number Number Stop See Map 12 ......' Leg Route Route and and Leg Stop Number Number Stop �xli LIST OF MAPS LIST MAPS MAP MAP 1 MAP 2 MAP MAP 33 MAP 4 MAP 55 MAP MAP 66 MAP 77 MAP 88 MAP MAP 9 1 34 34 35 35 40 40 45 54 55 60 60 63 67 MP 10 MAP 10 77 77 MAP MAP 11 11 83 83 MAP 12 MAP 12 84 84 MAP 13 MAP 13 91 91 MAP MAP 14 14 92. 92 MAP 15 MAP 15 94 94 MAP 16 MAP 16 95 95 MAP MAP 17 17 99 99 MAP 18 MAP 18 101 101 MAP MAP 19 19 106 106 MAP 20 MAP 20 107 107 MAP 21 MAP 21 108 MAP 22 MAP 22 111 Ill MAP 23 MAP 23 112 112 MAP MAP 24 24 115 115 �Xlii UST LISTOF OFMAPS MAPS (Cont'd.) (Cont'd.) MAP MAP Al A1 118 MAP MAP A2 A2 119 MAP MAP A3 A3 121 MAP MAP A4 A4 122 MAP MAP AS A5 123 MAP MAP 81 Bl 125 MAP MAP 82 B2 126 MAP MAP Cl Cl 129 MAP •C2 C2 130 MAP MAP Dl Dl 133 MAP MAP D2 D2 134 MAP MAP D3 D3 142 MAP MAP El El 145 MAP MAP E2 E2 146 MAP MAP Fl Fl 150 MAP fl MAP F2 151 MAP fl MAP F3 152 MAP MAP Cii Gl 156 MAP MAP HI HI 159 MAP MAP H2 H2 162 MAP MAP 113 H3 163 MAP MAP H4 H4 164 MAP MAP H5 H5 166 �xiv LIST OF MAPS (Cont'd.) MAP 1-16 H6 169 MAP Ii MAP I1 173 MAP MAP 12 12 175 �xv LIST OF OF FIGURES FIGURES &?&FPage Index map of route, route, stops stops and and 1:24,000 1:24,000 scale scale maps. maps. x Figure 2: Figure 2: Location of the Keweenaw Keweenaw Peninsula native copper district 22 Figure 3: Figure Geology of the Lake Lake Superior Superior segment segment of of the the Mideontinent Midcontinent rift rift system. system. 33 progression of major geologic events of the North Temporal progression American rift system. system. 55 Map showing showing the Midcontient rift system system in relation relation to to the the (GFTZ). Grenville front front tectonic tectonic zone zone (GVFZ). 6 6 Figure Figure 6: 6: Geologic map of the the Keweenaw Keweenaw Peninsula. Peninsula. 7 Figure 7: Figure 7: Geologic map and stratigraphic stratigraphic column of the central central Keweenaw Keweenaw Peninsula. Peninsula. 88 Columnar stratigraphic section of the Keweenaw Fault in the the Calumet-Mohawk area. Calumet-Mohawk area. 9 9 Figure Figure 1: 1: Figure 4: Figure Figure 5: 5: Figure 8: Figure 8: Generalized stratigraphic section of the Portage Lake Volcanics from Victoria to Copper Harbor. Harbor. 13 13 Schematic cartoon of the depositional environment of the Copper Copper Harbor Harbor Conglomerate. Conglomerate. 15 15 Figure 11: Figure 11: Faults and minor minor folds folds in in the thecentral centralKeweenaw Keweenaw Peninsula. Peninsula. 17 17 Figure 12: Figure 12: Paragenesis of secondary minerals in flow top top deposits deposits and and veins, veins, and conglomerate conglomerate deposits. deposits. 21 21 Distribution of amygduleamygdule- and vein-filling minerals in the Calumet Calumet cross section of of the PLV. PLy. 22 22 Figure Figure 14: 14: Speculative Speculative ice-marginal positions positions during during the the Wisconsin Wisconsin ice iceretreat. retreat. 28 28 Figure 15: 15: Enlarged view of ice-marginal ice-marginal positions during the Wisconsin Wisconsin ice ice retreat. 29 Figure Figure 16; 16: End moraine moraine of of the the Keweenaw Keweenaw Bay Bay Lobe Lobe glacier. glacier. 30 30 Figure 17: Figure 17: Keweenaw Bay lobe glacier and position of glacial glacial Lake Lake Duluth. Duluth. 30 Figure 18: Figure 18: Physiographic divisions of the the central central Keweenaw Keweenaw Peninsula. Peninsula. 31 31 Figure 9: Figure 9: Figure Figure 10: 10: Figure 13: Figure 13: �xvi xvi LIST LIST OF OF FIGURES FIGURES (Cont'd.) (Cont'd.) Figure Figure 19: 19: High level level drainage drainagethrough through the the Portage PortageGap. Gap. 31 Figure Figure 20: 20: Geologic Geologic profile of the the South South Range Range Quarry. Quarry. 38 Figure 21: 21: Cross section on MAP MAP2. 2. section A-A' on 41 Figure Figure 22: 22: View View from from Portage Portage overlook overlookfacing facing south. south. 46 Figure Figure 23: 23: The The Quincy Quincy Mine Mine location. location. 49 Figure 24: 24; Sketch Sketch map map of of the theQuincy Quincyand andHancock Hancock Mines. Mines. 50 Figure 25: 25: Geologic Geologic cross cross section section for for Maps Maps H6, H6, 4, 4,and and5.5. 51 Figure 26: 26: Contoured Pb and and Sn Sn in in Torch TorchLake. Lake. Contoured concentrations concentrations of Pb 57 Figure 27: 27: Relationships Relationships of of Jacobsville JacohsvilleSandstone. Sandstone. 58 Figure Figure 28: 28: Geologic sketch sketch map map of of the the Hungarian Hungarian Falls Palls area. area. 61 Figure Figure 29: 29: Geologic Geologic sketch sketch map map of of the the Natural Natural Wall Wall Ravine. Ravine. 65 Figure Figure 30: 30: Geologic map map and and cross cross section, section. Wolverine Wolverine Mine, and and vicinity. vicinity. 69 Figure Figure 31: 31: Thickness to Mandan. Mandan. Thickness of the the Kearsarge Kearsarge flow flow (top) (top) from from Isle Isle Royale Royale to 70 Figure Figure 32: 32: Paragenesis Paragenesis of of secondary secondaryminerals mineralsin inthe theKearsarge Kearsargeamygdaloid. amygdaloid. 71 Figure Figure 33: 33: Cross Cross section section of of Kearsarge Kearsargeamygdaloid amygdaloid showing showing the banding banding of of mineral mineral assemblage. assemblage. 72 Figure Figure 34: 34. Thickness Thickness of of the the Kingston Kingston Conglomerate Conglomerate at at the the Kingston Kingston Mine. Mine. 78 Figure Figure 35: 35: Outcrop Outcrop map mapof ofthe theAllouez-Bumbletown Allouez-BumbletownHill Hillarea. area. 79 Figure Figure 36: 36: Physiographic Physiographic and and glacial glacial features features of of the the Allouez Allouez Gap. Gap. 80 Figure Figure 37: 37: Map betweenSeneca Senecaand andthe the Map and andsection sectionof ofthe theGreenstone Greenstoneflow flowbetween Cliff Cliff Mine. Mine. 81 Figure Figure 38: 38: Map Mapand andsection sectionof ofthe theGreenstone Greenstoneflow flownear nearPhoenix. Phoenix. 86 Figure Figure 39: 39: Stratigraphy Stratigraphyof of the thePortage PortageLake LakeVolcanics Volcanicsabove abovethe theGreenstone Greenstone Flow. Flow. 88 Stratigraphic Stratigraphiccolumn column of of the theLake LakeShore ShoreTraps. Traps. 97 Figure Figure 40: 40: �xvii LIST OF OF FIGURES (Cont'd.) (Cont'd.) Measured stratigraphic stratigraphic sections from Horseshoe Harbor and Dan's Point. 103 Figure Dl: Figure Geologic map showing andesitic dikes near Mount Bohemia. 135 Figure Figure D2: D2: Geologic sketch map of part of of the the Keweenaw Keweenaw Fault Fault in in the the vicinity vicinity ofDeerLake. of Deer Lake. 138 Geologic Geologic map showing the location of rhyolites on the eastern eastern tip tip of the the Keweenaw KeweenawPeninsula. Peninsula. 140 Figure El: Figure El: Location of of the the region region of of chalcocite chalcocitemineralization. mineralization. 147 Figure Flgure Hi: HI: Physiographic and glacial glacial features features west of of Calumet. Calumet. 160 Figure 112: H2: Results Results of of gravity gravitymeasurements measurements across across Bear Bear Lake. Lake. 167 Figure H3: H3: Geologic section section through through the the Hancock Hancock "fairground" "fairground"tezrace terrace glacial glacial deposit. deposit. 170 Physiography and glacial glacial features features of the northern northern part part of of Portage Portage Lake. Lake. 171 Geologic Anse redrocks. L'Anse redrocks. Geologic sketch sketch map map and and cross cross section section of of L' 177 Figure 41: 41: Figure D3: D3: Figure 114: H4: Figure Flgure Ii: 11: �xviii LIST LIST OF OF TABLES TABLES Avenge Averageand andrepresentative representativegeochemical geochemical data data for for least least altered altered lavas lavas of the Volcanics. the Portage PortageLake LakeVolcanics. 12 Table Table 2: 2: Stages in the theLake LakeSuperior SuperiorBasin. Basin. Stages of of glacial glacial lakes lakes in 27 Table Table 3: 3: Major-element composition composition of the the Kearsarge Kearsargeflow. flow. 69 Table Table 4: 4: Volume Volume percent percent amygdule amygdule minerals minerals from from mapped mapped assemblages assemblages shown in Figure 33. shown in Figure 33. 72 Table 5: 5: Avenge Averagemajor-element major-elementcomposition compositionof of the theScales ScalesCreek Creekflow. flow. 79 Table 6: 6: Avenge Averagecomposition compositionofofthe theGreenstone GreenstoneFlow. How. 87 Table Table El: El: Chemical Chemical composition composition of of intrusive intrusiveplug plug on on932 932Creek. Creek. 148 Table 01: Gl: Chemical Chemical types types of of rhyolites PLV. rhyolites within within the the PLV. 157 Table Table 1:1: �xix XIX INDEX TO TO GEOLOGY GEOLOGY ON ON MAPS MAPS Map No. Quadrangle Quadrangle Reference Reference 1 MTLJ MTU Campus Map Map White, 1956; Hase, 1973 1973 2 Chassell Chassell White, 1956 1956 3 South Range, Chassell White and Wright, 1956; White, 1956 1956 4 Chassell, Hancock White, 1956; 1956; Cornwall Cornwall and and Wright, Wright, 1956a 1956a 5 Chassell, Hancock White, 1956; 1956; Cornwall Cornwall and and Wright, Wright, 1956a 1956a 6 Laurium 956b Cornwall and Wright, Wright, I1956b 7 Laurium Cornwall and Wright, 956b Wright, 11956b 8 Laurium Cornwall and Wright, 1956b 1956b 9 Ahmeek White and others, others, 1953 1953 10 Mohawk Davidson and others, 1955 1955 11 Mohawk Davidson and others, others, 1955 1955 12 Phoenix Phoenix Cornwall, 1954a 1954a 13 Eagle Harbor Cornwall and Wright, 1954 1954 14 Eagle Harbor Cornwall and Wright, 1954 1954 15 Delaware Delaware Cornwall, 954b Cornwall,11954b 16 Delaware Delaware Cornwall, I1954b 954b Cornwall, 17 Lake Medora Cornwall, 954c Cornwall,11954c 18 Lake Medora, Fort Fort Wilkins Wilkins 954c; Cornwall, 1955 Cornwall, I1954; 1955 19 Lake Medora Cornwall, 1954c 1954c 20 Delaware Delaware Cornwall, 1954b 1954b 21 Delaware Cornwall, 1954b 1954b 22 Eagle Harbor Harbor Cornwall and Wright, 1954 1954 �xx 23 Eagle Eagle Harbor Harbor Cornwall Cornwall and Wright, Wright, 1954; 1954;'Cornwall, Cornwall, 1954a 1954a 24 Laurium Laurium Cornwall Cornwall and andWright, Wright,19561, 1956b Al Chassell Chassell White, White, 1956 1956 A2 Chassel1,Hancock Chassell,Hancock White, White, 1956; 1956; Cornwall Cornwall and and Wright, Wright, 1956a 1956a A3 Oskar Oskar Cornwall Cornwall and and Wright, 1956a; 1956a; White White and and Wright, 1956 1956 A4 Oskar White, White, 1968 1968 AS Beacon Hill Hill White, White, 1968 1968 B1 Eagle Harbor Cornwall and Wright, Wright, 1954 1954 B2 Eagle Harbor Harbor Cornwall and Wright, 1954 1954 Cl Fort Wilkins, Lake Medora Medora Wilkins, Lake Cornwall, 1954c; 1954~;Cornwall, Cornwall, 1955 1955 C2 Fort Fort Wilkins Wilkins Cornwall, Cornwall. 1955 1955 Dl Michigan Michigan DNR-Keweenaw DNR-Keweenaw and and Houghton Houghton Counties Counties White, White, 1968 1968 D2 Delaware Delaware Cornwall, 954b Cornwall,11954b D3 Gay Gay White, 1968 1968 El Eagle Harbor Harbor Eagle Cornwall and Wright, 1954 1954 E2 Eagle Harbor, Harbor, Bruneau Bmflea~Creek Creek Eagle Wright and 954b and Cornwall, Cornwall, I1954b Fl Phoenix Phoenix Cornwall, Cornwall, 1954a 1954a F2 Phoenix,Mohawk,Ahmeek Ph0enix.Mohawk.Ahmee.k Cornwall, 1954a 1954a;Davidson Davidson and andothers, others, 1955; White and and others, others, 1953 1953 p3 Ahmeek White and others, others. 1953 1953 01 Ahmeek,Mohawk White and others, others, 1953; 1953; Davidson Davidson and and others, 1955 1955 Hi Laurium Cornwall and and Wright, 1956b; C~rnwall 1956b; Hughes, Hughes, I1963 963 H2 Hancock, Hancock. Muggen Creek Creek Cornwall and Wright, 1956a 1956a �xxi Cornwall and Wright, Cornwall Wright, 1956á; 1956a; Warren, Warren, 1981 1981 H3 Hancock H4 Hancock Hancock H5 Hancock, Oskar Oskar Cornwall and Wright, 1956a 1956a H6 Hancock Hancock Cornwall and Wright, 1956a 1956a Ii I1 Michigan DNR-Houghton County County White, 1968 1968 ¶2 12 Michigan DNR-Baraga County County White, 1968 1968 �Geology 1 GEOLOGY OF TilE THEKEWEENAW KEWEENAW PENINSULA, PENINSULA,MICHIGAN MICHIGAN INTRODUCTION INTRODUCTION The Keweenaw Keweenaw Peninsula Peninsula is located located on the the margin margin of of Lake LakeSuperior. Superior. The geology geology of the the Keweenaw Peninsula consists consists of of two two quite quite distinct distinct episodes. episodes. The bedrock is composed of consolidated between about about 1100 and and 1000 million million years yearsago ago (Ma) (Ma) as as part part of of the Midcontinent rift rocks deposited deposited between Midcontinent rift system of North America. The bedrock is overlain by unconsolidated glacial sediments deposited during system The bedrock is overlain by unconsolidated the past 2 million glaciation of of North North America. America. The million years years as as part part of of Pleistocene Pleistocene continental glaciation The field field trip trip glacial materials. materials. Because the cultural history of the Keweenaw contains stops to view both bedrock and glacial Peninsula is so dominated by the mining of native copper from the bedrock, more emphasis is placed on on the geology of the bedrock. the bedrock. BEDROCK GEOLOGY GEOLOGY This Peninsula was was taken taken from from aa combination combination This description description of the bedrock geology of the Keweenaw Peninsula of Bornhorst (in press). press), Bornhorst Bornhorst (1992), and Bomhorst and others (1983) (1983) without without specific specific citation citation or or quotation. quotation. Midcontlnent Midcontinent Rift Rift System System is on on the the margin of the Lake Superior segment of the Midcontinent rift The Keweenaw Peninsula is from Kansas Kansas to Lake Superior system. The Midcontinent system. %dcontinent rift system system extends northeasterly northeasterly from Superior and and then then southeasterly through lower Michigan (Fig. 2). It was formed at about 1100 Ma by extensional thinning lower Michigan (Fig. 2). crustal block. block. Present day crystal crustal thickness in the Lake Superior region of the rigid Precambrian Superior crustal between 40 and 50 km, km. which is thicker than adjacent areas (Halls, 1982). 1982). is between Beneath Lake Superior the rift is filled with more than 25 km of volcanic volcanic rocks, including including about about 10 km of Portage Portage Lake Volcanics Volcanics (PLy) (PLV) (Fig. (Fig. 2) 2) (Cannon (Cannon and and others, others, 1989; 1989; Hinzc Hinze and others, others, 1990; 1990; Cannon, 1992). The ThePLy, PLV,with withaatotal totalthickness thicknessofofabout about55km kmofofrift-filling rift-fillingvolcanic volcanicrocks, rocks, isisexposed exposed on the Keweenaw Peninsula. Large in response response to to a period period of rifting Large volumes volumes of magma magma were extruded in over an asthenospheric mantle plume (Hutchinson and others, 1990). Rift magmatism extended from 1109 asthenospheric (Hutchiinson and others, 1990). to 1087 1087 (Davis and Paces, 1990; 1990; Paces and Miller, 1993). The ThePLV PLVof ofthe theKeweenaw KeweenawPeninsula Peninsulaerupted erupted during a 2 to 3 million year span of time, time, at about about 1095 1095 Ma Ma (Davis (Davisand andPaces, Paces,1990). 1990). It It is part of a vast association of igneous rocks of similar similar age, including the Duluth Gabbro 3). Gahbro (Fig. 3). the rift-filling volcanic rocks, rocks, A thick succession of rift-filling clastic sedimentary rocks overlie the by volcanism, volcanism, to to one onedominated dominatedby bysedimentation. sedimentation. While and represent a change from a period dominated by magmatic activity continued as thermal anomaly anomaly of the the magmatic activity waned, waned, subsidence subsidenceofofthe the rift rift basin basin continued as the thermal asthenospheric plume decayed (Cannon and Hinze, 1992; Hutchinson Hutchinson and and others, others, 1990). A total thickness total thickness km of ofrift-filling rift-filling clastic clastic sedimentary sedimentary rocks exist beneath to 88 km of up to beneath the the center of Lake Superior, with with a maximum exposed thickness in the western Upper Peninsula of Michigan, of 6 km (Fig. 2) (Cannon, 1992; 1992; Cannon and others, 1989). 1989). These Theseclastic clasticsedimentary sedimentaryrocks rocks are are dominated dominated by by red-colored red-colored conglomerates conglomerates Conglomerate) and red-colored sandstones (Freda Sandstone), with aa thin thin intervening intervening gray (Copper Harbor Conglomerate) to black black shale shale (Nonesuch (Nonesuch Shale). Late Lateininthe thethermal thermalsubsidence subsidence phase phase of of the the rift. rift. Cannon Cannon and andothers others (1989) and Hinze and and others others (1990) (1990) propose propose that that mature mature red-colored red-colored sandstones sandstones (Jacobsville Sandstone) Sandstone) basin. The is poorly poorly constrained, constrained, was deposited across the entire basin. The age age of these rift-filling sedimentary strata is but is likely between about 1085 1085 and and 1060 1060Ma. Ma. �2 Geology Geology A . B B GLIMPCE GLIMPCE Line A Shoreline Slate && Islands, 3000 Superior Shod. shot ~uitou Shore {. en ra'r F—I?.,. - 3 5:.8 10- Lower ~rotnowic? At Yu At Faultblocks or introsivu I 151 EXPLANATION EXPLANATION Yj YjJaoobsville JacobtvillcSandstone Sandstone(Middle (MiddleProterozoic) Proterozoic) Yb Bayfield Group (Middle Yb Bayfield Group (MiddleProterozoic) Proterozoic) Yo Yo Ozonto OrontoGroup Group(Middle (MiddleProterozoic) Prokrowic) Lake (Middle Yp Pflge Portage LakVolcanics cVolcinio, (MiddleProtezozoic) Proterozoic) Yu rocks older older Yu Undivided UndividedMiddle Middle Proterozoic Protauwicrocks than thanPortage PortageLake LakeVolcanics Volcanics Ag GnSss Gneiss(Archean) (Archean) Figure 2: 2: (a) Location Location of the the Keweenaw Keweenaw Peninsula native copper district within the North North American American Midcontinent rift system system((from Bomhorst,ininpress). press). The large black area contains from Bornhorst, contains all major major Midcontinent rift areas contain contain minor minor deposits. deposits. (b) (b)Interpretative Interpretativecross-section cross-sectionacross acrossthe the deposits, the two smaller smaller areas deposits, Cannon and and others others (1989) (1989) from from Superior segment segment of the Midcontinent Midcontinent rift system by Cannon Lake Superior A. seismic-reflection seismic-reflection profile Line A. �Geology A fanas B NMddgan ?JWMto,idn Th— NE MI wow AWg nBe ROpuwk, 1100 Figure3: 3: (a) (a) Geology Geology of of the theLake LakeSuperior Superiorsegment segmentof ofthe theMidcontinent Midcontinentrift riftsystem system (from (from Paces Pacesand and Figure igneous rock Miller, U-Pbdates datesaxe arelisted listed below belowabbreviated abbreviatedmajor major igneous rock units: units: Miller, 1993). 1993).High Highprecision precisionU-Pb BBC, BBC,Beaver BeaverBay Bay Complex; Complex;CCD, CCD, Canton CarltonCounty County dikes; dikes; CC, CC, Coldwell ColdwellComplex; Complex;LS, LS,Logan Logansills; sills; LST, LST, Lake Lake Shore ShoreTraps; Traps; MPF, MPF, Mamainse Mamainse Point Point Formation; Formation; MBD, MBD, Marquette-Baraga Marquette-Baragadikes; dikes;MC, MC, NSVG. North Shore Volcanic Mellen Intrusive Complex; MW, Michipicoten Island Formation; Mellen Intrusive Complex; MIF, Michipicoten Island Formation; NSVG, North Shore Volcanic Group; Group; PIll, PRI, Pigeon PigeonRiver Riverintrusives; intrusives;PLV, PLV,Portage PortageLake LakeVolcanics; Volcanics; PMG, PMG, Powder PowderMill MillGroup; Group; for igneous rock PD, PD, Pukaskwa Pukaskwa dikes; dikes; OVG, OVG, Osler Osier Group. Group. (b) (b)Absolute Absoluteage agecorrelation correlation for igneous rock units units of of the the Midcontinent Midcontinent rift rift system system(from (fromPaces Pacesand andMiller, Miller, 1993). 1993). 3 �4 occiogy The last phase of the Midcontinent Midcontinent rift rift system was characterized by a transformation of original original normal faults faults into into reverse reverse faults faults(Fig. (Fig.22and and4). 4). The Keweenaw graben bounding normal Keweenaw Fault is now a lowlow- to to high-angle reverse fault, but originally was a major graben bounding growth fault (Cannon and others, high-angle reverse was bounding growth fault and 1989). The The Keweenaw Keweenaw Fault Fault has has several several kilometers kilometers of of reverse reverse displacement displacement which caused steepening of already tilted strata (due to syn-depositional downwarpage). downwarpage). Faults, fractures, and broad open folds within developed in in response response to to this compressional event (White, (White, rift-filling strata of the Keweenaw Peninsula developed 1968; Butler and Burbank, km of ofred-colored red-colored shallow shallow dipping dippingsandstone sandstone(Jacobsville (Jacobsville Burbank, 1929). 1929). Over 33 km movement along along the the Keweenaw Keweenaw Fault Fault in in a riftSandstone) was deposited during and after active reverse movement flanking basin (Fig. 2 and 4). Cannon Cannonand and others others(1993) (1993) have have determined that high-angle reverse reverse faulting faulting ± 20 Ma, based on reset Rb-Sr biotite ages within older Precambrian basement rocks occurred about 1060 1060 + near the the Michigan-Wisconsin Michigan-Wisconsin border. border. The timing and probable probable cause of this this compressional compressional event is is continental collision continental collision along along the the Grenville Grenville front front (Fig. (Fig. 5) 5) (Cannon, (Cannon, 1994; 1994;Cannon and Hinze, Hinze, 1992; 1992; Hoffman, Hoffman, 1989). This Thisregional regionalcompression compression phase phase may have started as early as 1080 1080 Ma (Cannon, 1994), 1994), and was likely completed by 1040 1040 Ma, Ma, based on thermal models (Price (Price and McDowell, 1993; 1993; Price Price and and others, others, in in review). review). The rocks of of the the Midcontinent Midcontinent rift rift system system were were subsequently subsequently overlain by Paleozoic Paleozoic sedimentary sedimentary with the Michigan basin. An rocks associated associated with Michigan basin. Anisolated isolatedoutlier outlier of ofOrdovician Ordovician limestone limestone at at Limestone Limestone Mountain Mountain and Sherman Sherman Hill Hill occurs occurs about about 35 35 km krn south of Houghton, and is underlain by rift-flanking rift-flanking basin filling Jacobsville Sandstone. Sandstone. The largely atectonic. atectonic. The The Paleozoic Paleozoic geologic geologic processes were largely ThePaleozoic Paleozoic rocks were removed removed by by erosion erosion from from the the Keweenaw Keweenaw Peninsula. Peninsula. The present present day day landscape landscape of of the theKeweenaw Keweenaw Peninsula Peninsula isisstrongly strongly influenced influencedby byPleistocene Pleistocene glaciation, especially by by features features associated associated with with withdrawal withdrawalofof the the Wisconsin Wisconsin ice ice sheet about 15-8 glaciation, especially 15-8 thousand years years ago. ago. Bedrock Stratigraphy of of the the Keweenaw Keweenaw Peninsula volcanic rocks rocks and clastic The bedrock of the the Keweenaw Keweenaw Peninsula is composed composed of subaerial volcanic sedimentary rocks of the Keweenawan Supergroup(Fig. (Fig.6). 6). The volcanic and sedimentary rocks on the Keweenawan Supergroup northwest side of the Keweenaw moderately toward toward Lake Lake Superior (Fig. (Fig. 7) and Keweenaw Peninsula generally dip moderately include the PLV, PLy, Copper Harbor Conglomerate, Nonesuch Shale and the Freda Sandstone (Fig. 8). The Copper Harbor Nonesuch Shale and the Freda Sandstone (Fig. 8). The Jacobsville Sandstone, which which fills fills a rift-filling rift-filling basin basin on on the southeast side of much of the Jacobsville Sandstone, the Keweenaw Keweenaw Peninsula, Fault. The Peninsula, is in fault contact with the PLV along the Keweenaw Keweenaw Fault. The Jacobsville Jacobsville Sandstone Sandstone is younger than the Freda Sandstone and related to to aa late phase phase of of regional regional compression. compression. The bedrock strata are unconformably capped capped by Pleistocene Pleistocene glacial glacial deposits. deposits. Portage Portage Lake LakeVolcanics Volcanics (PLV) (PLV) The Portage Portage Lake Lake Volcanics are composed of a succession of more than 200 200 individual individual subaerial subaerial tholeiitic basaltic basaltic lava lava flows flows with with aa total thicknessofof 2500 2500 to to 5200 tholeiitic total exposed exposed thickness 5200 m on on the the Keweenaw Keweenaw Peninsula, with with the base truncated Peninsula, truncated by the the Keweenaw Keweenaw Fault (Butler (Butler and Burbank, Burbank, 1929; 1929; Huber, Huber, 1975; 1975; volcanic and and subvolcanic subvolcanic rocks rocks comprise compriseless less than than 1 volume % of the White, 1968) (Fig. 9). Rhyolitic volcanic PLV. Dikes PLV. Dikesof ofintermediate intermediatecomposition composition cut cut the the exposed exposed volcanic volcanic pile, but are as as aa whole whole uncommon. uncommon. A diorite stock intrudes the base of the PLV at Mt. Bohemia. Bohemia. Interfiow reddish-colored conglomerate Interflow conglomerateand and sandstone sandstone units total total less less than than 55 volume % of the PLV (Merk and Jirsa, 1982), 1982). but increase in abundance toward the top of the formation. These Theserift-filling rift-filling volcanic volcanic rocks are comparable to the rift zones of East Africa and Iceland (Nicholson, (Nicholson, 1992; 1992; Basaltic Volcanism Study Project, 1981; Chase and Gilmer, 1973; Green, 1977 1977 and 1982; 1982; White 1960 1960 and 1972). Lavas Lavas flowed flowed away away from from feeders feeders along along the the axis axis of of the the rift rift zone. During Duringintervals intervalsof ofquiescence, quiescence,sediments sediments were were transported from the edges toward the center of the �Native CopperMineralization Mineralization __..,.Native Copper Regional Regional Compression Compression Thermal Subsidence Subsidence Thermal Plume-Induced Plume-induced Rifting Rifting / \Reverse Faulting and and Sedimentation Sedimentation Faulting -- P Clastic Sedimentation ÑÑÈ¥Cl Sedimentation Maginatism ~ ~ l wu BBasaltic a s a l tMagmatism ic -— —Is -S Sedmentaty I I I I I I I —— I 1110 1100 1090 1080 1070 1060 1050 1040 Ma Rocks 0 0 Volcanic Rocks Pte-Keweenawan basement cross-sections Midcontinent rift Temporal progression geologic events the North North American mnenciiit mtucununeni n n system. s y ~ ~ i t t Schematic ~i.~ciiiaub . i-WW-ao-uuna of m progression of of major major geologic events of the Figure 4: 4: Temporal cnzstal sag sag filled with volcanic rocks is followed by extension, development of the rift development fromcannon rift from Cannon and others others(1989). (1989). (a) (a) An An initial initial broad crustal faults and eruption of large (b) After After volcanism volcanism which results in normal growth faults large volumes of plume-induced basalt into the central central graben. graben. (b) wanes, thermal subsidence continues with with the the basin basin progressively progressively filled filled with withclastic clasticsediments. sediments. (c) The last last phase phase of of development development of of the the rift is regional compression which which inverts inverts original original graben graben bounding bounding faults faults into intoreverse reversefaults. faults. This results in the uplift of buried rift strata, erosion, and exposure of the PLV in the the Keweenaw Keweenaw Peninsula. Compression Compressiongenerated generatedfaults/fracwres faults/fracturesprovided provided for forupward upward movement movement and focussing of ore fluids into permeable and porous tops of basalt lava flows and interflow sedimentary rocks within the Portage Lake Volcanics (Figure and caption entirely from Bomhorst, Bornhorst, in press). press). I U' ut �6 Geology B 40 --7' $1 D / :Z0 E 0 Figure 5: (a) Map showing showing the the Midcontinent Midcontinent rift system in relationship relationship to the the Grenville Grenville front font tectonic tectonic Compression along along the the Grenville Grenville front was toward (GFTZ) (from (from Cannon. Cannon, 1994). 1994). Compression toward the the zone (GFTZ) (b) Cross sections of the Midcontinent rift rift system system of locations given in (a) northwest. (b) the Midcontinent (a) (from (from northwest. Cannon, 1994). 1994). �88° KEY [MI ri1 ri-w El 3*cthnWeS Iicolxvillc StiaolU Fnda Swddons I n Naiesidt NonesuchMiii. State El 1 Ilaiboc Congicuixale Copper OperHtltot-iloroenIt Porcupine VoiceS Porcupine Val, 1 FI Posge it VMcSa Powder Mill Gicup IYiI Mallen lnhuuive Caipin Major Fault ? 2 Kilometers Figures 7 and 11 (from Bornhorst, 1992). Figure Figure 6: 6: Geologic Geologicmap mapofofthe theKeweenaw Keweenaw Peninsula. Peninsula. The Thebox box shows shows the the location location of of Figures 7 and 11 (from Bomhorst, 1992). I '-a -J �8 Gcology Sandstone Upto 1 m m + Freda Sandstone ujl10360011+ Figure 7: Figure 7: Geologic Geologicmap mapand andstratigraphic stratigraphiccolumn columnof of the thecentral centralKeweenaw Keweenaw Peninsula Peninsula showing attitude of bedding, major faults and fractures, and major native copper deposits (modified from White, Stratigraphic nomenclature nomenclature of of Cannon Cannon and Nicholson 1968; from Bornhorst, Bomhorst, 1992). 1992). Stratigraphic Nicholson (1992). native copper deposits deposits (total (total production production of of refined refined copper) copper) are are marked marked by by numerals: numerals: 1. Major native (1,922 million million kg), kg), 2. 2. Kearsarge Kearsarge flow flow top (1,029 million kg), Calumet and Hecla Conglomerate (1,922 kg), 4. Pewabic flow tops tops (490 million million kg), kg), 5. Osceola flow top 3. Baltic flow top (839 million kg), (263 million million kg), kg), and 6. Isle Royale flow top (155 million million kg). kg). Total Total district district production production equals equals million kg kg of refined refined copper. copper. Location 5,013 million Location given given in Figure Figure 2. �Geology 9 a b FREDA SANDSTONE SANDSTONE Lava unit unit AND COPPER HARBOR HARBOR NONESUCH SHALE NONESUCH SHALE CONGLOMERATE CONGLOMERATE cl Lava unit unit PORTAGE LAKE LAKE LAVA LAVA SERIES SERIES Lava unit unit C b Figure 8: Figure 8:Columnar Columnarstradgraphic stratigraphicsection sectionnorthwest northwestof ofthe theKeweenaw Keweenaw Fault Fault in the Calumet-Mohawk Calumet-Mohawk area and others, others, 1953). 1953). (from White and �10 Geology :Hao conglomerate (No. 17) i —? Ashbed flow %Searsarge flow Wolverine sandstone sandstone (No. 9) PP West conclomerate conglomerate Pewabic West (No. 16) IÑ POC - Old Old Colony Colony sandstone (unnumbered) Greenstone flow Allouez conglomerate conglomerate (No. 15) Portage Lake Lake Volcanics de Houghton Houghton conglomerate conglomerate (No. 14) 14) (No. pi PC Scales Creek flow Iroquois Iroquois flow flow -calumet •Calumet and and Hecla Hecla conglomerate conglomerate (No. 13) 13) Osceola flow Kingston conglomerate conglomerate 12) (No. 12) pcc I 1 Copper city City flow copper &St. St. Louis Louis conglomerate conglomerate (No.6) (No. 6) Figure Figure 88 contInued. continued. �(ISogy Geology 11 11 Hecla Conglomerate at rift. AAcomplex comptexsub-mature sub-mature caliche caliche soil soil profile profile within within the the interfiow interflow Calumet and Hecia the Centennial Mine suggests a temperate temperate or tropical tropical climate (Kalliokoski and Welch, 1985). 1985). Basalts of the PLV are are relatively primitive, magnesia-rich, high-alumina olivine olivine tholeiites tholeiites and and are are (Paces. 1988). 1988). Olivine by primitive olivine typically aphyric (Paces, Olivine tholeiites tholeiites are the most abundant, followed by tholeiites, with lesser amounts of quartz tholeiites, and iron-rich iron-rich olivine olivine tholeiites tholeiites (Table (Table 1). Also Also shown shown in Table 1, 1, are the minor minor amounts amounts of of basaltic basaltic andesite, andesite, andesite, dacite, and rhyolite that interfinger interfinger with with stratigraphywithin withinthe thebasalts basalts isis cyclical cyclical with with minor and the basalts. basalts. Geochemical Geochemical stratigraphy and major major cycles cycles more primitive primitive compositions. compositions. Basaltic magmas were apparently superimposed on an overall trend toward more derived by partial melting of relatively shallow, sub-continental upper mantle, mantle, with younger basalts being primitive, with with little or or no contamination contaminationby by crustal crustalmaterial material(Paces (Pacesand andBell, Bell,1989). 1989). The overall more primitive, compositional trend toward younger, less contaminated primitive primitive magmas magmas can can be be explained by repeated eruption at the rift axis that gradually crust through dike injection and magma eruption gradually modified the continental cmst which magmas must pass, and by progressive crustal thinning, thinning, which which provided provided more more efficient transport which intracrustal chambers. chambers. Model calculations show that major of magmas to the surface without residence in intracmstal geochemical cycles are due to fractional crystallization and replenishment in large magma chambers near cycles and and silicic rocks result from the crust/mantle crust/mantle interface (Paces, (Paces, 1988). 1988). Minor Minor cycles from closed closed system system crystallization in in small small magma magma chambers chamberswithin withinthe thecrust. crust. Eruption in an oxidizing fractional crystallization oxidizing subaerial subaerial ic), that created environment resulted in degassing degassing of of volatiles, volatiles, particularly particularly SO2 SO, (Cornwall, 195 1951~). created aa sulfursulfurdeficient environment which favored the later later deposition deposition of native native copper. copper. Primary magmatic differentiation differentiation has long long been been recognized recognized within within tholeiitic tholeiitic flows flows(Broderick, (Broderick, 1935; Broderick Broderiek and Hohl, 1935; andb). b). For example, the Greenstone 1935; Cornwall, 1951 1951aa and Greenstone Flow, Flow, the the thickest thickest individual flow in the formation (Fig. 9), 9). is chemically stratified due to internal differentiation (Cornwall, 195 ib; Longo, Longo, 1983). The rocks was was also also effected effected by by deuteric deuteric 1951b; Thepresent-day present-day composition composition of the the volcanic volcanic rocks or diagenic alteration of olivine and glass to hydrous minerals, the most important of which is chlorite. chlorite. used 8D 3D and 6'o Livnat and others (1976) used 8"O totoshow showthat thatthe thebasalts basaltshave haveundergone undergoneextensive extensiveisotopic isotopic exchange with low-temperature meteoric waters waters prior priorto tometamorphism/hydrothennal metamorphism/hydrothermalmineralization. mineralization. After After exchange emplacement, the low-pressure emplacement, the volcanic volcanic pile pile was subjected subjected to extensive extensive low-temperature, low-temperature, low-pressure hydrothermal/metamorphicalteration alteration(see (seeFig. Fig.10). 10). The PLV on the Keweenaw Peninsula are a classic hydrothedmetamorphic alteration minerals. minerals. Penetrative deformation did not locality of abundant and widespread low temperature alteration accompany the the metamorphic episode, and and primary primary textures textures are are preserved preserved even even in the most accompany metamorphic episode, most intensely intensely recrystallized areas. areas. has an average avenge total A typical subaerial lava flow has total thickness thickness of about about 10 10to to 20 20 m m(range (rangefrom from11 to 450 m), and consists consists of of aa massive massive (vesicle-free) (vesicle-free) interior capped by a vesicular flow top (Paces, 1988; 1988; White, 1960). A few of of the the thicker thicker flows flows and and interfiow interflow sedimentary sedimentary rocks can be traced traced laterally laterally along along strike for up to about flows have have much much less less continuity continuityininstrike strikedirection. direction. The about 90 kin, km,although although many many flows Scales Creek, Kearsarge, and Greenstone Flows Rows are are the the best best documented documented laterally continuous flows flows (Fig. with the Greenstone Flow able able to be correlated to Isle Royale Royale (Huber, (Huber, 1975; 1975; Longo, Longo, 1982). 1982). The 9), with Greenstone Flow correlated to The 9). uppermost 55 to 20% uppermost 20% of of most most individual individual lava lava flows flows isis vesicular, vesicular, with with between between 55 and and50% 50%vesicles. vesicles. Because flow tops in Because vesicles vesicles are commonly commonly filled filled with secondary secondary minerals, minerals, flow in local local terminology terminology are are amygdaloids, and brecciated flow tops are fragmental amygdaloids. amygdaloids. White White (1968) (1968) estimated estimated that 21% 21% of of the lava flows in the PLV are fragmental amygdaloids amygdaloids(brecciated). (brecciated). The The Copper Copper City City Flow Flow (Fig. (Fig. 9) is the dated 1096 + ± 1.8 My and the Greenstone flow is 1094 2 ± 1.5 My My (Davis and Paces, Paces, 1990). 1990). Based Greenstone Bow (Davis and Based on data, Paces and Bell (1989) inferred that the PLV was erupted empted in about 2-3 million million years, years, which which these data. represents a rate that is is similar similar to to younger younger rift rift and and flood flood basalt basalt sequences. sequences. Interflow sedimentary sedimentary rocks, rocks,with withthicknesses thicknessesfrom fromaafew fewcm cmup up to to about about 40 40 m, m, are important Interflow stratigraphic markers markers in in an otherwise succession of of basalt basalt lava flows. stratigraphic otherwise monotonous monotonous succession flows. In drill drill core, core, �12 Table Table 1: 1: Avenge Average and andrepresentative representative geochemical geochemical data Portage Lake Lake data for for least least altered altered lavas lavas of the Portage Volcanics (from (from Paces, Paces, 1988). 1988). Tholeiites Tholeiiteswere weregrouped groupedby by Ni Nicontent. content. Volcanics POT POT Ni(ppm) 400-300 QT1 QT1 QT2 QT2 300-250 250-200 n=5 n=9 S102 47.82 47.34 48.03 A1203 15.89 9.77 12.44 10.58 15.27 11.82 11.69 10.24 15.32 2.04 0.19 0.98 0.98 0.16 0.16 0.14 0.14 2.10 0.22 Fe01 MgO CaO Na20 K20 'PlO2 P2O3 pzos MnO MnO PPM PPM Ni Ni Cu Cu Zr Zr FeO, FeO, POT POT n=14 1232 9.85 10.16 2.25 0.33 LOT IOT FOT FOT AND AND DAC DAC RHY RHY 200-100 100-15 n=8 n=6 n=l n=1 n=1 48.55 15.12 12.86 9.06 9.65 2.31 0.42 49.94 56.39 68.44 77.89 13.28 14.91 7.78 13.78 9.87 15.17 12.77 1.11 5.52 5.10 3.94 2.27 1.14 1.40 2.34 2.34 0.36 0.36 0.24 0.24 1.13 1.13 135 1.35 1.60 1.60 0.19 0.19 0.15 0.16 0.22 0.22 0.16 0.25 0.25 0.18 0.18 6.64 2.91 1.43 1.83 1.83 1.00 1.00 0.30 0.30 172 172 86 86 54 54 10 10 51 51 231 23 1 73 73 126 126 85 85 101 101 126 126 212 212 55 430 430 326 326 37 37 279 279 78 78 total Fe as as FeO FeO total Fe Primitive Primitive olivine olivinetholeiite tholeiite OT1 OT1 Olivine Olivine tholelite tholeiite 0T2 OT2 Olivine Olivine tholeiite tholeiite LOT IOT Intermediate 'Intermediateolivine olivinetholeiite tholeiite FOT Iron-rich olivine olivine and andquartz quartztholeiites tholeiites FOT Iron-rich AND Andesite AND Andesite DAC Dacite DAC Dacite Rhyolite RHY RHY Rhyolite 4.46 4.74 3.86 0.51 0.51 0.19 0.19 0.08 0.08 77 13 13 573 573 0.17 0.01 3.67 4.28 0.08 0.08 0.01 0.01 0.01 0.01 55 61 61 145 145 �13 .I U 6 I q&, I oa a Meters 3OO 0 300 6OO 9W l8 Upper Limit of Epidote in Flows UpperLimit LimitofofQuartz QoaniininFlows Flows Upper Lower Limit of Prehnite in Flows ExceptionallyThick ThickLava Lavaflows Flows Exceptionally LocationofofMine Minewithin within Location StratigraphicSection Section Siratigiaphic \ "'--d - '.-...* ' ww 3 6 L Figure9:9:Generalized Generalizedstratigraphic stratigraphicsection sectionof ofthe thePortage PortageLake LakeVolcanics Volcanicsfrom fromVictoria VictoriatotoCopper CopperHarbor Harbor Figure Bornhorst, 1992). Location of the (modified (modifiedfrom fromStoiber Stoiberand andDavidson; Davidson;1959, 1959,from from Bomhorst, 1992). Location of themajor majornative native copper areshown showninincontext context with with the themajor majorstratigraphic stratigraphicmarker marker horizons horizons and and with with copper mines mines are stratigraphic stratigraphiclimits limitsof ofassociated associatedamygduleamygdule-and andvein-filling vein-fillingminerals. minerals. See SeeFigure Figure22for forlocation location ofVictoria Victoriaand andCopper CopperHarbor. Hartor. of �14 Geology horizon to to be recognized, even where sedimentary sedimentary material in an underlying basalt flow top allows the horizon Interfiow sedimentary sedimentary rocks rocks are dominated by well-lithified the bed itself itself isis missing missing (White, (White, 1968). 1968). Interflow well-lithified pebble-to-boulder conglomerate with lesser amounts of interbedded sandstone and occasional significant pebble-to-boulder thicknesses of siltstone and shale. shale. Conglomerates Conglomerates are characterized characterized by by sub-rounded-to-angular sub-rounded-to-angular pebbles-to-boulders pebbles-to-boulders Clast lithologies are predominantly felsic, although although in detail, (pebbles typical) in aa sandy (pebbles typical) sandy matrix. matrix. Clast lithologies predominantly felsic, detail, considerable variation variation exists exists within within and and between specific beds, beds, reflecting reflecting diversity diversity in source considerable between specific source terrane, terrane. beds as as alluvial fan fan deposits deposits laid laid down down on essentially White (1968) interprets most interflow sedimentary beds toward the center of the rift basin now under Lake flat-lying lava flows by streams flowing toward Lake Superior. Superior. The sediment interbeds, in all but the uppermost part part of of the PLV, PLy, have been given names and have been given names and are are shown shown 8 and 9). on the maps included included in this this self-guided self-guided geological field trip (Fig. (Fig. 8 9). Copper Rarbor Harbor Conglomerate Conglomerate The Copper Copper Harbor interfingers with the PLV (Fig. Harbor Conglomerate Conglomerate conformably overlies overlies and locally interfingers 6.7, 8). It is aa red-brown red-brown basinward-thickening basinward-thickening wedge of volcanogenic clastic sediments that varies 6, 7, and 8). in thickness from about 100 to 1800 m, in, and fmes fines distally distally and and upsection, upsection, reflecting a waning sediment supply due to progressive erosion erosion of of the source area (Elmore, (Elmore, 1984). Sandstones Sandstones are are lithic lithic graywackes, graywackes, and conglomerates are composed of volcanic conglomerates are composed of volcanic clasts clasts with with aa ratio ratio ofofmafic-to-intermediate mafic-to-intermediate + + siicic silicic composition composition of about about 2:1 21 (Daniels, 1982). 1982). Daniels Daniels(1982) (1982)and and Elmore Elmore(1984) (1984)have have interpreted interpretedthe theCopper Copper Harbor Congloñierate Conglomerate as a fining fining upward upward prograding progradiig alluvial fan complex complex (Fig. (Fig. 10). 10). The prevailing prevailing climate was likely arid with seasonal high rainfall rainfall (Elmore, (Elmore, 1983; 1983; Kalliokoski, Kalliokoski, 1986). 1986). Algal stromatolites, stromatolites, which formed in shallow, medial fan lakes and possibly abandoned channels on the alluvial fan surface, surface, occur in the upper upper part part of of the theCopper CopperHarbor HarborConglomerate Conglomerate (Elmore, (Elmore, 1983). 1983). The middle portion of of the the Copper Copper Harbor Harbor Conglomerate Conglomerate (northeast (northeast of Calumet) Calumet) includes includes aa successionofof lava lava flows flows known known collectively collectivelyasasthe the Lake Lake Shore Shore Traps Traps (Lane, (Lane, 1911) 1911) (Fig. (Fig. 7, 7, see succession thickness of of the the Lake Lake Shore Shore Traps Traps is is 600 m near the tip of stratigraphic column). The maximum exposed thickness Peninsula, where where the unit unit is composed of 31 lava flows and one the Keweenaw Keweenaw Peninsula, one interfiow interflow conglomerate (Diehl and Haig, in press). The composition of the Lake Shore Traps is more variable (Diehl and Haig, The composition of the Lake Shore Traps more variable than the the PLV; PLV; ranging from Fe-rich olivine tholeiites at the base, to to Fe-rich Fe-rich olivine-bearing olivine-bearing tholeiitic basaltic andesites, andesites, to tholeütic tholeiitic andesites andesites at the top (Paces and Bornhorst, 1985). Geochemical stratigraphic relationships can be explained replenishment, and and wall rock explained by aa combination combination of fractional fractional crystallization, parental magma replenishment, assimilation. Davis and Paces (1990) report a U-Pb age on zircon of 1087 ± 1.6 Ma for the Davis and Paces (1990) 1087 + 1.6 for the Lake Lake Shore Shore Traps. Traps. Nonesuch Shale of 215 m, is a succession of siltstones; shales; The Nonesuch Shale, with a maximum thickness of carbonate laminates; laminates; and minor sandstones sandstones with low-to-moderate low-to-moderate amounts amounts of total carbon, carbon, that that overlie overlieand and interfmger with the Copper interfinger Copper Harbor Harbor Conglomerate Conglomerate (Fig. 7 and and 8). 8). Elmore and others (1989) (1989) recognize recognize three genetic genetic assemblages: assemblages: marginal marginal lacustrine lacustrine (sandflat-mudflat (sandflat-mudflat complex), complex), lacustrine lacustrine (progressively (progressively In the lacustrine assemblage, bottom conditions of shallowing perennial perennial lake), lake), and andlacustrine-to-fluvial. lacustrine-to-fluvial. the lake were were anoxic; anoxic, but but became became oxic oxic as as the the lake lakeshallowed. shallowed. Copper sulfides and native copper copper in in economic quantities are hosted by the the Nonesuch Nonesuch Shale Shale at at the the White White Pine Pine Mine Mine (Mauk (Mauk and and others, others,1992). 1992). Freda Sandstone Sandstone The Freda Sandstone Sandstone is is aacyclic cyclicsuccession successionof ofred-brown red-brown ferruginous ferruginoussandstone, sandstone, siltstone, siltstone, and and mudstone overlying and gradational gradational with with the Nonesuch Nonesuch Shale Shale (Fig. (Fig. 77 and 8). B). The The exposed exposed thickness thickness of of �Geology 15 BASINWARD— BASINWARD FINE GRAINED CHANNEL FILL a FLOOD PLAIN DEPOSITS Figure 10: 10:Schematic Schematiccartoon cartoonofofthe thedepositional depositionalenvironment environmentofofthe theCopper CopperHarbor HarborConglomerate Conglomeratewith with Figure coalescing coalescingalluvial alluvialfans, fans,braided braidedstream stream and and flood flood plain plain deposits, deposits,and and shallow shallow ephemeral ephemeral lakes lakes or or abandoned 1982). abandoned stream streamchannels channelscontaining containimg strornatolitic stromatolitic deposits deposits (from (fromDaniels, Daniels. 1982). �16 the Freda Sandstone is greater than than 3700 3700 m m as as the the top top is is not not exposed. exposed. It is is dominantly dominantly fluvial in origin, with greater compositional maturity than the Copper Harbor Conglomerate (Daniels, 1982). Jacobsville Sandstone Sandstone The Jacobsvile Jacobsville Sandstone Sandstone isisaared-to-bleached red-to-bleached white whitecoarse-to-fme-grained coarse-to-fine-grained feldspathic feldspathic and and quartzose sandstone sandstone with varying varying amounts amounts of of siltstone, siltstone,shale, shale,and andconglomerate. conglomerate. It is is in in unconformable unconformable contact with Early Proterozoic and Archean rocks to the east, and is in fault fault contact contact with with the the PLY PLV along along the Keweenaw Fault on the southeast side of the Keweenaw Peninsula. Peninsula. Some Some active active reverse reverse movement movement (Kalliokoski, 1988; 1988; Hedgman, along the fault occurred during deposition of at least part of the formation (Kalliokoski, 1992). completely devoid of igneous igneous rocks and and were were 1992). The Jacobsville strata, over 3,000 m thick, are completely deposited in in a rift flanking basin basin (Kalliokoski, (Kalliokoski, 1982). 1982). The rock has been quarried fluvially deposited quarried extensively and was used as aa building building stone stone in in many many buildings buildings in the the Copper Copper Country Country and throughout throughout the the midwest. midwest. Structure Structureof of the theKeweenaw Keweenaw Peninsula Peninsula The Keweenaw strata dip moderately northwesterly northwesterly toward toward the the center center of of the the rift (Lake Superior), toward the the top top of of the the section section (Fig. (Fig. 7). 7). Angular and their dip angles decrease toward Angular divergence in dip from from the the to the the base base of of the PLV PLY of about 20° 200, is due to syn-depositional top of the Copper Harbor Conglomerate to downwarping before before deposition deposition of of the Nonesuch similar amount amount of of synsyndownwarping Nonesuch Shale (White, (White, 1968). 1968). A similar depositional downwarping downwarpingoccurred occurredduring duringdeposition depositionofofthe the Nonesuch Nonesuch Shale Shale and and uppermost uppermost Freda Freda depositional Sandstone. The Sandstone. Theremaining remaining tilting tilting of of the the beds beds occurred occurred during during reverse reverse movement along the Keweenaw Fault. Bedding 5' in most areas, except near the Keweenaw Keweenaw Fault. Beddingin inthe theJacobsville JacobsvilleSandstone Sandstonedips dips less less than than 50 Fault, where dips steepen to vertical in response to drag along the fault. Fault, Dips of specific horizons horizons tend to steepen 200 20' to 300 30' along strike from northeast to southwest of the major area of native copper deposits, deposits, yielding yielding aa gently gently twisted twistedsurface surface(Fig. (Fig.7;7;White, White,1968). 1968). The strike strike of area northern end end of this twist. bedding changes to a more east-west orientation at the northern anticines, with Broad open synclines and anticlines, with wavelengths wavelengths of around 10 10 km and various various orientations, orientations, dip (Fig. (Fig. 11). 11). Faults with displacement and mineralized tension tension breaks breaks are superimposed on the regional dip Burbank, 1929). 1929). These are common near the crests of anticlines (Butler and Burbank, These post-depositional post-depositional folds are likely related to the Keweenaw Keweenaw Fault Fault (White, (White, 1968). 1968). Faults Faults The Keweenaw Fault is the major major fault fault in in the the Keweenaw Keweenaw Peninsula. Peninsula. It is is aa lowlow- to to high-angle high-angle reverse fault which marks the border of the main rift-filling volcanic and sedimentary rocks with riftwhich the main rift-filling volcanic sedimentary flanking sedimentary sedimentary rocks. The TheKeweenaw KeweenawFault Faultwas was originally originally aa graben-bounding graben-bounding normal normalfault faultthat, that, late late transformed into into aa high-angle high-angle reverse reversefault fault(Cannon (Cannonand andothers, others,1989). 1989). The in the history of the rift, was transformed reverse movement is possibly related to Grenvillian Grenvillian compression (Cannon, 1994). Fault strikes strikes more more or or less less parallel parallelto to the the bedding bedding of of the the PLV PLV (Fig. (Fig. 6 and 7). The Keweenaw Keweenaw Fault 7). Measured dips dips of the fault fault plane plane range range from from 70° 70' to to 20°14 20% and are generally sub-parallel to dips of the PLV (Butler and Burbank, Burbank, 1929). The TheKeweenaw Keweenaw Fault Fault is is not not aa single single fault, fault, and and in in places places branches branches diverge diverge from the the main mainfault fault (Butler (Butler and and Burbank, Burbank, 1929). 1929). Where Whereexposed, exposed,the the Keweenaw Keweenaw Fault Fault isis up to 0.8 km from denoted by up to 4 m m of gouge gouge of of red red clay-to-breccia (Brojanigo, (Brojanigo, 1984). 1984). Basalt Basaltflows flowswithin withinseveral severallOOs 100s of meters of the fault fault are are broken and and brecciated; brecciated; with fractures fractures filled filled with with calcite, calcite, laumontite, laumontite,and and chlorite. chlorite. In mines opened near near the the fault, fault,many many fractures fractures subparallel subparallel to to bedding bedding include include fillings fillings of of native native copper. copper. The St. Louis deposit, the target of aa recent recent evaluation, evaluation, consists of shear-controlled native copper within a fault, about 150 main Keweenaw Fault (it has potential open pit reserves 150 m m from, from, and and subparallel subparallel to, the main �Geology 17 flgure U: and minor folds Figure 11:Faults Faults and minor foldsininthe thecentral centralKeweenaw KeweenawPeninsula Peninsula(modified (modified from White, 1968; from Bornhorst, listed in in Figure Figure 7. 7. Location Major mines and symbols listed Location given in Figure 2. Bomhorst, 1992). Major �18 18 Geology Geology of 8 million tons, grading grading 0.8 0.8 % %copper; copper;Northern Northern Miner, Miner, 1990). 1990). Several reverse Several reverse faults, faults, including the Hancock and Isle Royale Faults, cut the PLV PLV at at higher higher angles angles to bedding of 200 m and bedding than the the Keweenaw Keweenaw Fault, Fault, with with horizontal horizontal displacement of and 50 50m, m,respectively respectively (Butler and Burbank, 1929). High-angle High-angle faults faults striking striking north-to-northwest north-to-northwest are common in the area area of of the the of aa regional regional anticlinal anticlinal (twist) (twist) structure structure(Fig. (Fig.7). 7). Displacement major native copper deposits near the crest of Displacement along these faults varies varies from from none none (tension (tensionfractures) fractures)totoaround around100 100mm(Butler (Butlerand andBurbank, Burbank,1929). 1929). A along copper-- well known known for for masses of native copper weighing number of small tabular vein deposits of native coppermany tons, but not economically important because of the limited dimensions-are dimensions--are localized along these cross fractures just just beneath the thickest thickest basalt basalt flow flow in in the the district, district, the the Greenstone GreenstoneRow. flow, Flow Flowtops topsand and adjacent to these veins (Butler and Burbank, 1929). conglomerates are mineralized adjacent 1929). PLy, numerous Throughout the PLV, numerous faults faults or slips slips exist parallel to the strike and dip dip of of the the beds, beds, but but of displacement displacement isis impossible impossibleto to determine. determine. Such these are often difficult to recognize and the amount of Such common on on the top of of conglomerate beds, beds, which which are are perhaps perhaps aa better faults, denoted by clay gouge, are common slip zone than between basalts (Butler and Burbank, 1929). At At the the Delaware Delaware Mine, Mine, red red clay clayfault faultgouge gouge is aa minimum minimum of of 20 20 cm cmthick thickatatthe thecontact contactbetween betweenthe theAllouez AllouezConglomerate Conglomerate and and the the overlying overlying flow, and Greenstone How, and isis composed composed of of vermiculite vermiculite and and smectite smectite with minor calcite (Schleiss, 1986). 1986). Mineralization and Alteration Alteration of a dormant billion-dollarcopper coppermining miningdistrict. district. From From 1845 to The Peninsula is the location location of dormant billiondollar 1968 the mines of the the Keweenaw Keweenaw native native copper copper district district produced produced about 11 11 billion billion pounds pounds of of refmed refined copper (Weege and Pollack, 1971). Small Smallpersistent persistent quantifies quantities of native silver (less than 0.1%; White, accompany the the native native copper. copper. The 1968) accompany The major major ore ore producing producing horizons horizons are geographically geographically restricted to a 45 km-long belt within the PLV in the Keweenaw Peninsula (Fig. 2 and 9). A A close closerelationship relationshipin inboth both mineralization and and alteration alteration in in the the PLV PLV (Fig. 12 and 13). time and space exists between native copper mineralization 13). The native copper copper deposits deposits of the Keweenaw Peninsula are unique in the geological record, except of the for similar similar occurences occurences on aa much much smaller smaller scale. scale. The The uniqueness uniqueness of the deposit deposit has has confounded confounded conventional wisdom conventional wisdom from from the the beginning beginning of exploration (Krause, (Krause, 1992) 1992) when Douglass Houghton Houghton believed believed that the native copper found in in float float and and vein vein occurences occurences at at the the surface surface reflected reflected supergene supergene alteration alteration of of a sulfide ore. Today, Today,even evenafter afterextensive extensivemining, mining,there thereisisstill stillno no agreement agreementamong among experts expertsabout aboutexactly exactly how the deposits deposits formed. formed. Nature of of Ore Ore Bodies Bodies Native copper copper occurs occurs in in brecciated brecciated and and amygdaloidal amygdaloidal flow tops (58.5% (58.5% of of production), production), interfiow interflow production), and and cross cross vein vein systems systems (about (about 2% 2% of of production) production) (Fig. (Fig. 77 and conglomerate beds (39.5% of production), 9). The Thefour fourlargest largestdeposits depositsin inthe thedistrict districtproduced produced 85% 85% of the S5 billion kg total total district production at an average grade of about 2%. about 2%. Lava Flow Tops Tops Brecciated flow tops (fragmental amygdaloid) Brecciated amygdaloid) are much more common hosts for native native copper copper unbrecciated amygdaloidal amygdaloidal flow tops (White, (White, 1968). 1968). Flow top deposits deposits than unbrecciated between aa deposits are between footwall of barren basalt in the massive interior of the same flow and a hanging wall of barren basalt in the succeeding flow tops tops grade downward and laterally to succeeding flow. flow. Deposits in brecciated amygdaloidal flow to amygdaloidal basalt with low or barren ore grades. Both Both distribution distributionof brecciated brecciated flow flow top top and and contained contained amygdaloidal native copper is Usually native native copper copperisis more more abundant abundantnear nearthe the top top and and bottom bottom of of the is irregular. irregular. Usually �Geology 19 brecciated interval interval of of the flow top, but in in exceptionally exceptionally rich ore shoots, the entire brecciated flow top contains significant significant copper (White, (White, 1968). 1968). In some cases, rich rich ore shoots are located located in tongues tongues of brecciated flow top within massive basalt (Weege and Schillinger, Schillinger, 1962). In In general, general,stope stopeheights heightsare are from 3 to 55 m. m. For Formajor majorore orebodies, bodies,the thestrilce strike length length ranges ranges from 1.5 1.5 to 11 11 kin, km,with with dip dip length length from from to 2.6 2.6 km (Butler and Burbank, Burbanlc,1929; 1929;White, White,1968). 1968). Ore Ore shoots shoots have have aa wide wide variety variety of of shapes, some 1.5 to are elongate elongate with with widths widths of of 30 30 to to 150 m, and lengths from 50 50 m to around are lengths from around 600 m with with aa preferred preferred orientation, preferred orientation orientation (White, (White, 1968). Autointrusive are irregular with no preferred Autointrusive bodies bodies orientation, whereas whereas others others are are in in the the in the flow top can can localize localize ore ore shoots shoots (Weege (Weege and Pollack, 1971), and a number of deposits deposits are tops of, or just below, exceptionally thick flows (Butler (Butter and and Bin-bank, Burbank, 1929; White, White, 1968). White White (1968) (1968) bedding slip in adjacent layers, resulting resulting in more fracturing. suggested that thicker flows concentrate bedding Conglomerates Conglomerates interfiow conglomerate PLY (<5%), they host Although interflow conglomerate beds make up only a small volume of the PLV comparatively large amounts districtproduction). production). Deposits occur as lenticular (-40% ofofdistrict lenticular comparatively amounts of native native copper copper (—40% beds with a hanging wall of massive basalt and a footwall of lava flow top, which commonly hanging of massive footwall lava which commonly contains bands (0.5 (0.5 to to 55 m m thick), and rich rich sand and silt. Usually Usually native native copper copper is is concentrated concentrated along stratigraphic bands bands tend to jump from from one one stratigraphic stratigraphic position to another within the same conglomerate (Weege and others., 1972). Within others., Within the the Kingston Kingston Conglomerate Conglomerate (Fig. (Fig. 9) ore can occur throughout the 12 12 in m bed, bed, but tends to be concentrated in three zones: footwall (43% of the copper), hanging wall (33% of the copper), concentrated three zones: footwall (43% copper), hanging wall (33% of the copper), and intermediate (24% of the the copper) copper) (Weege (Weege and and others, others, 1972). 1972). Hecla Conglomerate Conglomerate (Fig. (Fig. 9). 9), the the largest largest single single native native copper copper Native copper ore in the Calumet and Hecla of 1.9 1.9 billion billion kg kg along alongaa strike strikelength lengthof of4.9 4.9km, kin,and and 2.8 km down-dip), down-dip), lode in the district (production (production of occurs where the bed thickens from less than 11 m to up to to 66 m m(Butler (Butlerand and Burbank, Burbank, 1929; 1929;Weege Weege and and others., 1972). Ore Oregrades gradesininthe theCalumet Calumetand andHecla HeclaConglomerate Conglomeratedecrease decrease significantly significantlywith with depth, depth, as as the width of the conglomerate that is, is, essentially essentially the the same amount conglomerate unit greater than 1.5 m thick increases; that of copper is distributed throughout a greater volume volume of ofconglomerate conglomerate(Butler (Butlerand andBurbank, Burbank,1929). 1929). Highest grades occur where where up-dip up-dip moving moving ore ore fluids fluids were were focused focused by by the tapering, lenticular nature nature of of the grades occur tapering, lenticular conglomerate 1929). The Thehighest highestgrade gradeore orein in the the Calumet Calumetand and Hecla HeclaConglomerate Conglomerate conglomerate (Butler and Burbank, 1929). are filled filled with with tends to be where relatively little little fme fine interstitial interstitial material material exists, or where interstitial interstitial spaces spaces are coarse sand or small pebbles (Weege (Weege and others., 1972). 1972). Localization of native native copper copper ore in beds is dependent Localization of in conglomerate conglomerate beds dependent on on sedimentary sedimentary and and environmental factors, factors, such such as as grain grain size and the the latter controlled the bedrock bedrock paleotopography; paleotopography; the controlled the environmental in the the thickness thickness of of conglomerate. conglomerate. location of paleostreams and variations variations in Veins Although the first first mines mines in in the the district district were developed developed on veins veins which tend to cut cut bedding bedding at at high high slight economic economic importance importance in the district. district. Distribution of native copper in angles, vein deposits are of slight veins lodes,but but tend tend to to be be richest veins is more more erratic erratic than either flow flow top or conglomerate conglomerate lodes, richest at or near near well-oxidized flow tops (Butler and Burbank, Burbank, 1929). Native Native copper copper can can occur occur as asboth both intersections with well-oxidized finely disseminated, and and as masses weighing weighing many many tons tons in in the the same same vein. vein. Row Howtops topsand andconglomerates conglomerates are mineralized adjacent to veins. Veins Veinshosting hostingnative native copper copper also also exist within stratabound stratabound lode deposits deposits (Broderick, (Broderick, 1931). 1931). Ore and and Gangue Gangue Minerals Minerals Native copper copper represents metallic minerals mined orebodies orebodies of Native represents over over 99% 99% of of the metallic minerals in in the the mined of the �20 20 Geology Keweenaw 0.1%; White, White, 1968) accompany Keweenaw Peninsula. Persistent Persistentsmall smallquantities quantitiesof of native native silver silver (less than 0.1%; 1968) kcompany the native copper. Most Mostofofthe thenative nativecopper coppercarries carriesaasmall smallamount amountof of arsenic arsenicin in solid solidsolution solution(less (lessthan than arsenic, typically less than 0.2%; 0.2%; Broderick, Broderick, 1929). Copper-nickel 0.5% arsenic in total copper + silver silver ++ arsenic, Copper-nickel arsenides, and Davidson, Davidson, 1959), occur in veins that arsenides, particularly particularly common in the Kearsarge deposit (Stoiber and are paragenetically late (Butler and and Burbank, Burbank, 1929; 1929; Moore, Moore, 1971). 1971). Within paragenetically late Within the the native native copper copper deposits, deposits, late, occurs as small veins veins cutting flow flow top deposits, and as coatings on chalcocite, also paragenetically late, joints with with calcite calcitein in conglomerate conglomeratedeposits deposits (White, (White, 1968). 1968). Several Several copper sulfide sulfide deposits deposits occur in flow tops near the base of the PLV within the Keweenaw Keweenaw Peninsula in association Peninsula association with mafic mafic intrusive intrusive rocks rocks (Broderick (Broderick and others., others., 1946; 1946; Robertson, Robertson, 1975). 1975). Chalcocite is the principal Chalcocite principal ore mineral with rare, paragenetically late, native copper (Woodruff and others., Wilkin and and Bornhorst, Bornhorst, unpublished unpublisheddata). data). One deposit is now the target 1992; Wilkin target of of possible possible new new mining mining activity, with probable probable reserves of of 3.1 3.1 million million tons, tons, grading grading 2.95% 2.95%copper copper(Northern (NorthernMiner, Miner,1990). 1990). The relationship between between these these copper copper sulfide sulfide deposits deposits and and the the native native copper copper deposits deposits is is conjecture, conjecture, and and is relationship more at at Stop El. El. discussed more and interflow interflow sedimentary sedimentary rocks were were altered altered pervasively pervasively by hydrothermal hydrothermal fluids, fluids, Flow tops and producing low-temperature low-temperature metamorphic metamorphicmineral mineralassemblages assemblages(Fig. (Fig.12 12and and13). 13). The The minerals occur as amygdule and vein fiffings, and as whole rock rock replacements replacements in in the the most most permeable penneable units. Intensity and fillings, and degree of alteration alteration varies as as aa function function of of position position within within individual individual flows, flows, position position in in the the volcanic volcanicpile, pile, and proximity to cross-cutting cross-cutting fractures. While Whileflow flowtops topsare areintensively intensively altered, altered,massive massive interiors interiorsof oflava lava flows are much less less altered, altered, and hydrothermal alteration is limited to the vicinity of faults faults and fractures. fractures. Some original igneous igneous minerals minerals are present in the massive interiors of flows, but secondary secondary minerals exist in all flows regardless of their thickness (Scofield, (Scofield, 1976; Paces, Paces, 1988). 1988). The The geochemical geochemical composition of many flow interiors interiors are are only slightly modified modified by secondary hydrothermal processes, and and represent represent original original igneous composition. of lava composition. Thus, Thus, the interiors interiors of lava flows flows acted acted as as aquicludes aquicludes with with respect respect to to the the paleohydrothermal system. paleohydrothermal A close close relationship relationship in in time time exists exists between between native native copper copper mineralization mineralization and and secondary secondaryminerals minerals formed during during alteration alteration of the the PLY, PLV, although although individual individual deposits deposits may not exactly exactly follow follow the the district-wide district-wide paragenesis (Fig. 12). 12). Metamorphic Metamorphiczoning zoningbased based on on distribution distribution of amygdule-filling amygdule-filling minerals, equivalent equivalent to zeolite and prehnite-pumpellyite prehnite-pumpellyite facies, varies vertically (Fig. 13) and laterally laterally (Fig. 9) within the PLV. PLY. through most of the stratigraphic On the tip of of the the Keweenaw Keweenaw Peninsula Peninsula (Fig. 6), 6). zeolite minerals exist through section with epidote appearing only in the basal basal 750 750 m m (Cornwall, (Cornwall, 1955; 1955;Cornwall Cornwall and and White, White, 1955), 1955), into the the PLV. PLY. The indicating lower metamorphic grades extend deeper into The major major native native copper copper mines mines are areall all within a section within section containing containing epidote, and near the the appearance appearance of quartz quartz (Fig. (Fig. 9; 9; Stoiber Stoiberand andDavidson, Davidson, 1959). AAdetailed 1959). detailedstudy study by byStoiber Stoiberand andDavidson Davidson (1959) (1959) of of the theKearsarge Kearsarge deposit deposit shows shows that that native native mineral zones zones although although aa general correlation copper is much more irregularly distributed than secondary mineral exists between between grade and the the variation variation of of quartz quartz and and microcline microcline (see (see Stop Stop 13). 13). Broderick (1929) and PLY dip shallowly toward Livnat (1983) showed that the metamorphic mineral zones (isograds) within the PLV Lake Superior, compared to the volcanic volcanic strata strata which which dip moderately, moderately, implying that the volcanic volcanic units units were tilted prior to to metamorphism metamorphism and and associated associated native native copper copper mineralization. mineralization. Age Constraints for for Native Native Copper Copper Deposits Deposits Native copper found in both both stratabound stratabound lodes and in veins veins is is accompanied accompanied by the the same samegangue gangue minerals minerals (Butler and and Burbank, Burbank, 1929; 1929;Broderick, Broderick, 1931; 1931;White, White,1968), 1968).indicating indicatingcontemporaneous contemporaneous epigenetic deposition. Native Nativecopper coppermineralization mineralization isisyounger youngerthan than the theCopper CopperHarbor HarborConglomerate, Conglomerate, calcite and and native native copper. copper. White (1968) interpreted the age of native native copper copper which hosts rare veins of calcite mineralization as after after deposition deposition of of much much or or all of mineralization as of the the Freda Freda Sandstone, Sandstone, and and has has an anundetermined undetermined �Geology A Flow Top Top Deposits Deposits and and Veins Veins Flow K-Feldspar — Pu—I— Coppa Datolile Silver Qunt Saicite Ctm Anaild Sulphidcs (npaSe) Launiontite Suiphatca (bathe, anhydrite, gypsum r- r e- nfln — 21 ConglomerateDeposits Deposits Ccmglomerate —- - LIS TitHe -p — ——p e -a - Relative RelativeAge Age Abundant AbuiKtuit RelativeAge Age Relative Not Notabqmdat dnnitt B widespread Widespread Minerals Minerals albite, albite, calcite, calcite, chlorite, chlorite, epidote, hematite, laumontite, laumontite, native native copper, copper, prehnite, prehnite, puxapellyite, pumpellyite, quartz, quartz, sphene sphene Locally Locally Important Important Minerals Minerals anaicixne, analcime, ankerite, ankerite, arsenides, arsenides, chabazite, chabazite, chalcedony, chalcedony, clay clay minerals, minerals, ilver, natrolite, datolite, datolite, heulandite, heulandite, native native ssilver, natrolite, orthoclase/microcline, orthoclase/microcline, thompsoni t e sulfates, suif ides, sericite, sericite, sulfates, sulfides, thompsonite Rare Rare Minerals Minerals apophyllite, apophyllite, atacamite, atacamite, bowlingite, bowlingite, brucite, brucite, chlorastrolite, chlorastrolite, chrysocolla, chrysocolla, cuprite, cuprite, faujasite, faujasite, fluorite, fluorite, powellite, powellite, serpentine, serpentine, stilbite, tenorite, tourmaline, whitneyite, wairakiite stilbite, tenorite, tourmaline, whitneyite, wairakiite secondary minerals Figure Figure12: 12: (a) (a) Paragenesis of secondary minerals inin flow flow top top deposits deposits and and veins, veins, and and conglomerate conglomerate List of of secondary secondary deposits fromRuder Butlerand andBurbank, Burbank,1929; 1929;from fromBornhorst, Bornhorst,1992). 1992). (b) (b) List deposits (modified (modifiedfrom minerals fromButler Butler minerals within within the the Portage Portage Lake Lake Volcanics Volcanics of of the theKeweenaw KeweenawPeninsula Peninsula(compiled (compiledfrom and and Burbank, Burbank, 1929; 1929; Stoiber Stoiberand and Davidson, Davidson, 1959; 1959;Jolly Jolly and and Smith, Smith,1972). 1972). �22 22 Geology Geology Calumet CalumetSection Section MetamorphicZones and Temperature Estimates ofLivnat(1983) of Livnat (1983) Top of Portage Lake Volcanica A I Native Copper M i i NativeCoppaMifles % of District %ofDislrict IWQoincy 38%C&H 38%C&B 5% Osceola 0sceola 5% 21%KeÈrs* % Kearsarge 21 3%IsleRoyç 3%IsleR I -- I I I i B ----- Epidote &quartz present 1 I I I I __2600C a c Dppearance ofof common isa appearance common . IauntonÜte laumontite Cc -awe Disappearance Disappearanceofofferrian f&mI preimite I I 17% Baltic 17%Baltic KeweenawFault Fault Kewetuw -- - I D IM .c32SOCNOadiflOlitt Figure Figure13: 13:Distribution Distributionofofamygduleamygdule-and andvein-filling vein-fillingminerals mineralsininthe theCalumet Calumetcross crosssection sectionof ofthe thePLV PLV (compiled 1983;Stoiber Stoiberand andDavidson, Davidson,1959; 1959;from fromBornhorst, Bornhoist,1992). 1992). Vertical Vertical (compiled from from Livnat, 1983; distribution distributionof ofsecondary secondaryminerals mineralsisissimilar similarthroughout throughoutthe thearea areaof ofthe themajor majornative nativecopper coppermines mines listed listedon onthe thevertical verticalstratigraphic stratipphic column column(see (see Fig. Fig.77and and99for formine minelocations). locations). �23 minor amounts amounts of of native copper at the relationship with respect to the Jacobsville Jacobsville Sandstone--although Sandstone-although minor the bottom of aa 1,100 bottom 1,100mmdrill drillhole holewithin withinthe theJacobsville JacobsvilleSandstone Sandstone near near Rice RiceLake Lake(Weege, (Weege,personal personal communication) suggests suggeststhat that mineralization mineralizationpost postdates datesdeposition depositionofofatat least least some some of the Jacobsville communication) Jacobsville (1929, 1931), Butler and Burbank (1929), Broderick and and others (1946), Sandstone. Sandstone. Broderick (1929, (1929). Broderick (1946). White White (1968), Weege and others (1972) and other geologists, pointed out the close connection between (1968). geologists, have pointed mineralization and and deformation deformationrelated relatedtotothe theKeweenaw KeweenawFault. Fault. At the White Pine Mine, native copper mineralization Mauk and evidence for two distinct episodes of copper copper mineralization: and others others (1992 (1992 and this volume) show evidence mineralization: 1) main stage copper copper sulfides sulfides and and subordinate subordinate native copper copper formed during diagenesis of of the the Nonesuch Nonesuch Shale, and 2) second stage stage native copper copper and and subordinate subordinatecopper copper sulfide sulfide synchronous synchronouswith with thrust thrust faulting. faulting. are interpreted as contemporaneous withthe the Keweenaw KeweenawFault, Fault, leading leading to to the interpreted as contemporaneous with the thrust faults faults are The thrust interpretation by by Mauk Mauk and and others (1992) (1992) that that second second stage stage copper copper at at White White Pine Pine Mine Mine is is related to the interpretation Peninsula. Based native copper deposits of the Keweenaw Peninsula. Based on on field field relations relations native native copper copper mineralization mineralization is younger than deposition of rift-filling volcanic and sedimentary rocks, and likely synchronous deposition rift-filling ahd sedimentary likely synchronous with with reverse faulting and earliest deposition deposition of of rift-flanking rift-flanking sedimentary sedimentary rocks. Bornhorst and others Bornhorst others (1988) (1988) used used the theRb-Sr Rb-Srmethod methodon onamygdule-fihling amygdule-filling microcline; microcline; calcite; calcite; epidote; and and chlorite to determine determine the the absolute absolute age age of of mineralization mineralizationas asbetween between1060 1060and and 1047 1047Ma Ma (+ (± epidote; — 20 Ma), which is similar similar to an an approximate approximate age age of Keweenaw Keweenaw reverse reverse faulting faulting of 1060 1060Ma Ma (Cannon (Cannonand and and radiometric radiometric dating dating suggest suggest an an age of native others., 1993). 1993). Thus, both field relationships and native copper copper mineralization of about 1060 1060 to 1050 1050 Ma, some some 30 30 Ma Ma after after rift-filling rift-filling volcanism, volcanism, but but contemporaneous contemporaneous with reverse faulting along the Keweenaw Fault (Fig. 4). faulting along the Keweenaw Fault (Fig. 4). - Genetic Model For Native Native Copper Copper Deposits Deposits Genetic models for the the native native copper copper deposits deposits of of the the Keweenaw Keweenaw Peninsula Peninsula call call upon upon epigenetic epigenetic ore-bearing fluids related to either either magmatic (Broderick, 1929; Butler and Burbank, 1929; 1929; Broderick and others, 1946) or burial burial metamorphic metamorphic processes (Stoiber and Davidson, 1959; White, 1968; 1968; Jolly, 1974). 1974). does not not exist exist against against either either hypothesis. hypothesis. The localization of native copper deposits Conclusive evidence does in the Keweenaw Keweenaw Peninsula may may favor favor aa magmatic magmatic hypothesis, hypothesis, but but the the widespread widespread distribution distribution of of native native regional ore ore fluids fluids related related to burial metamorphic copper in Keweenawan basalts argues for widespread regional processes. The Theage ageof of mineralization mineralizationsome some30 30Ma Maafter after most most Keweenawan Keweenawanmagmatic magmatic activity activity also alsosuggests suggests for ore ore genesis. genesis. Stable isotope data are consistent with burial direct magmatic processes are not important for metamorphism, but but cannot rule out Although evidence evidence is not metamorphism, out magmatic magmatic hypotheses hypotheses (Livnat, Gvnat, 1983). 1983). Although not cumulative arguments arguments favor favor formation formationof of ore ore fluids fluids during during burial burial metamorphism metamorphism of of the rift conclusive, cumulative rocks. rocks. The source of native copper is possibly possibly the rift-filling rift-filling basalts. basalts. Dissolution of only a few ppm ppm of of copper from the over 18 18 km km of of basalt basalt in in the therift riftduring duringburial burial metamorphism metamorphism yields yields more more than than adequate adequate amounts of copper (White, 1968). Copper Coppermay may have have been been initially initially tied up in in Fe-Ti Fe-Ti oxides oxides (Cornwall (Cornwall and Rose, 1957) 1957) with subsequent subsequent oxidation oxidation releasing copper during burial metamorphism of the lava flows flows in the deep parts of the volcanic pile within the rift (Jolly, 1974). In this way, burial metamorphism 1974). In this way, burial metamorphismof ofriftriftfilling basalts at temperatures of 300°C 300° to 500°C 500° could result result in the the generation generation of of aa Cu-rich Cu-rich ore orefluid. fluid. Stable isotope data on on secondary secondary minerals minerals indicate indicate that that burial-derived burial-derived fluids fluids probably probably were were modified modified evaporated intermontane meteoric water (Kelly, personal communication; Livnat, 1983). Cornwall that the ore fluids Cornwall (1956) suggested suggested that fluids had had much much lower lower sulfur sulfurcontent contentthan thanmagmatic magmatic hydrothermal fluids, as copper sulfides are uncommon. uncommon. Degassing Degassing of sulfur sulfur from from subaerial subaerial erupted erupted lava lava flows would result in low low residual residual sulfur sulhr contents, and burial metamorphism of this low sulfur source rock would yield a low low sulfur sulfur ore ore fluid. fluid. fluid Fluid inclusion inclusion studies studies suggest suggest the ore ore fluids fluids were were Ca-Na Ca-Na brines brines (5 (5 to 10 10 weight weight % % salinity) salinity) (Livnat, &inat, 1983). 1983). Copper Copperwas was likely likely transported transported as aa chloride chloride complex, complex, and its its �24 oeoiogy abundance in the ore fluids could have been as high as 2,000 ppm, based on assumed amounts of copper and water derived from metamorphism and thermodynamic thermodynamic solubility solubiity of copper (Jolly, 1974). However, However, fluids extracted from inclusions in alteration contained less than than about 200 ppm alteration minerals minerals contained ppm Cu Cu (Livnat, (Livnat, 1983). 1983). Temperature Temperature history models (McDowell and others, 1992; 1992; Price and and McDowell, McDoweU, 1993; 1993;Price Priceand and others, in review) predict that the PLV in the center of the rift was likely dehydrated as as much much as 10 10 to m.y. prior prior to ore deposition. migrated toward toward the the edge edge of of the filled 15 m.y. deposition. These These fluids fluids could could have slowly migrated rift, where millions of years after after their generation they were available to be tapped and focused into orebearing horizons. Alternatively, Alternatively,temperatures temperatures of buried buried basalt on on the the flanks flanks of of the therift riftwere weresufficiently sufficiently high to have been the source of ore-bearing fluids. fluids. A A sufficient sufficient mass mass of copper exists exists in basalt strata strata on the flanks of the rift, present ( 4 0 ) km beneath the present rift, thus thus the ore ore fluids fluids need to be tapped only some few (<10) ore horizons. horizons. The fundamental fundamental control on the movement movement of ore fluids fluids to to sites sitesof ofdeposition depositionisispermeability. permeability. Primary permeability includes brecciated and vesicular lava flow tops tops and and interfiow interflow sedimentary sedimentaryrocks rocks separated by variably variably impermeable impermeable massive massive flow flow interiors. interiors. Thus, the vertical section consisted of of thin thin by thin aquicludes. aquifers separated by aquicludes. Overlapping Overlapping of successive successive lava flows and minor minor unconformities suggests that simple up-dip movement of of ore ore fluids fluids was was not not likely. lIkely. Secondary Secondary permeability provided by the network of faults/fractures faults/fracturesproduced produced during during late late compression compression (reverse (reverse movement movement along along the the Keweenaw Keweenaw of ore fluids. Since the turn turn of Fault) integrated the plumbing system, allowing for upward upward movement of the century, it was was clear clear that that faults faults played played a major major role in in localization localization of many of the the native native copper copper minerals indicate indicate that that faults and fractures deposits. Fault brecciated deposits. brecciated and re-cemented re-cemented alteration alteration minerals fractures were were principal pathways for ore ore fluids, fluids, and and that that faulting faulting was was synchronous synchronous with with mineralization. mineralization. For the Baltic (20%of of district districtproduction), production), Broderick Broderick (1931) (1931) Baltic and and Isle Isle Royale Royale flow flow top top deposits deposits (20% that ore fluids moved upward along faults until until intersecting intersecting with with the the permeable permeable flow flow tops tops at concluded that Mass, and Adventure the ore deposition stratigraphic interval. A A similar similar situation situation exists for the Caledonia, Mass, Mines near the town of Mass Mass (Fig. (Fig. 9). 9). There, native copper is hosted in flow flow tops tops in in close closeassociation association with abundant faults and fractures (Bornhorst (Bornhorst and and Whiteman, Whiteman, 1992). 1992). Faulting Faulting occurred occurred before, during, and after deposition of native copper. Many Many faults faults host host native copper, some even, with quite high grades. interiors of of lava flows in areas where they they are cut by faults. Native copper occurs in the massive interiors faults. For mines near Mass, it is likely that faults were the principal pathways for transport of ore fluids to the flow likely flow tops. The Allouez Gap Fault Fault (Fig. (Fig. 7) 7) cuts cuts the thevolcanic volcanic succession succession and and connects connects with with the theKeweenaw Keweenaw Fault. Almost Almostevery everypermeable permeable horizon horizon near near the the Allouez Allouez Gap Fault contains above average amounts of there so many many mineralized mineralizedhorizons. horizons. R.J. R.J. Weege, former native copper; nowhere else in the district, are there company report that the Allouez chief geologist of C & &H H Mining Mining Company, Company, suggested in an unpublished company Allouez Gap Fault was the single single most most important important fluid pathway in the district, perhaps linking 60% of the the district district production. The production. Thelargest largestflow flow top topdeposit depositin inthe thedistrict districtoccurs occurswhere where the the Allouez Allouez Gap GapFault Fault bisects bisects the the of the Kearsarge Kearsarge How Flow along along its its 55 55 km km strike strike length length(see (seeStop Stop 13). 13). Higher grades and thickest segment of occui northeast of the fault, where fractures parallel parallel to to the the fault faultare aremore moreabundant. abundant. The small production occur Kingston Kingston deposit (9 million kg of of copper) copper) is is also also bisected bisected by by the the Allouez Allouez Gap Gap Fault. Fault. Ore grade and and outward from the fault, degree of alteration lead Weege and others (1972) to conclude that fluids moved outward TheHoughton Houghtonand andAllouez AllouezConglomerate Conglomerate deposits deposits (50 (50 million million kg kg of of copper) copper) are are near near rather than up-dip. The the Allouez Gap Fault, Fault, with with local local faults faults and and the the conglomerates conglomerates themselves themselves connected directly with the Allouez Gap Fault. The million kg kg of of copper) is Thegiant giantCalumet Calumetand and Hecla HeclaConglomerate Conglomerate deposit (1900 million a few The axis axis of the ore body few km km west west of of the the Allouez Allouez Gap Gap Fault. Fault. The body trends at depth toward the fault fault �ooiogy 25 (Weege and others, 1972) 1972) which is consistent with ore fluid movement up the fault and then up-dip along the penneable conglomerate. permeable conglomerate. The Thedeposit deposithas hasaahigher highergrade gradeup-dip, up-dip,where wherehydrothermal hydrothermal fluids fluidswere were focused by lateral lateral (strike (strike direction) direction) thinning thinning of of the the permeable permeable conglomerate conglomerate(Butler (Butler and and Burbank, Burbank,1929). 1929). Within the Allouez Allouez Gap Gap Fault Fault zone, zone, brecciated brecciated and and recemented recemented native native copper copper and and alteration alteration minerals minerals (Butler and Burbank, indicate that that movement movement along along the the fault fault occurred occurred before, before, during, during, and and after (Butler Burbank, 1929) indicate deposition of native native copper. copper. Northeast of the major major native copper district, small vein deposits are localized localized just beneath beneath the the thickest basalt flow in in the the district, district, the theGreenstone Greenstone Flow, Flow, with with permeable permeable flow flow tops tops and and conglomerates conglomerates to these these veins. veins. AA reasonable mineralized adjacent to reasonable model model is is one one in in which which hydrothermal hydrothermal fluids fluids moved moved up up along cross fractures until stopped by the impermeable massive interior interior of of the Greenstone Flow. Broderick and others others (1946) noted that the Keweenaw Fault would make an ideal conduit conduit for for ore ore fluids. Although Althoughno nodeposits depositsare arelocated locatedalong alongthe the main main fault fault itself, itself, fluid fluid movement movement along along the the Keweenaw Keweenaw Fault and adjacent rocks is indicated by highly altered rocks and by several small native copper deposits deposits along nearby subparallel subparallel branch faults. faults. It is is likely likely that the Keweenaw Keweenaw Fault was an important factor in the paleohydrologic system with intersecting intersecting subsidiary faults faults or or permeable permeable stratigraphic stratigraphic horizons, horizons, such such as flow top or conglomerates, providing secondary secondary conduits. conduits. Like the Keweenaw Fault, in other districts main faults are often not or or little little mineralized (Sibson, (Sibson, 1987). NW-SE NW-SE directed directedregional regionalcompression compression(Fig. (Fig. under tight tight compression, compression, 2 and 5) 5) could could have have caused caused the the generally generally NE-trending NE-trending Keweenaw Fault to be under whereas perpendicular structures would be under dilation stress and more more open open for forfluid fluidmovement. movement. The intersection of major subsidiary faults with locally locally thick thick permeable horizons horizons is is a key factor in localization localization of ore. ore. Faults may have have behaved behaved as as valves valves and and become become highly highly permeable permeable pathways pathways immediately postfailure postfailure (Sibson (Sibson and and others., others., 1988; Sibson, Sibson, 1990) 1990) with with periodic periodic upward upward movement movement of of immediately hotter, sulfur-poor, burial metamorphic metamorphic fluids into into permeable permeable horizons. horizons. Fluid flow in small small fractures fractures of lava flows (e.g., Turcotte, 1989) may have have also been an cutting the massive massive interior interior of (e.g., Deloule Deloule and Turcotte, 1989) may an mechanism for for the the upward transport of of ore fluids. White important mechanism upward transport White (1968) (1968) suggested suggested that that permeability permeability than primary primarypermeability permeabilityfor forthe themovement movementofofore orefluids. fluids. At At the due to fracturing was more important than horizon of ore deposition, deposition, fluid pressures pressures were likely greater than hydrostatic, but less than lithostatic (e.g., (e.g., Powley, 1990). The Thepressure pressure was was dependent dependent on the height of rocks above the horizon of ore deposition ("mountains' maintainedby bycompressional compressionaluplift uplift rather ratherthan than stratigraphic stratigraphicdepth. depth. ("mountains" in in section sectionccininFig. Fig.4)4)maintained Mixing of ore ore fluids fluids channeled channeled upward upward through through faults and fractures fractures with with cooler, cooler, more more dilute dilute resident fluids may have been an an important important mechanism mechanism for precipitation precipitation of native copper. copper. Oxygen Oxygen isotope isotope for less data on quartz, quartz. data for calcite shows about a 10 10 per mu mil spread at a given stratigraphic depth, and for about 5 per SI the spread is about mil(Livnat, &mat, 1983). 1983).This Thisspread spreadcould couldbe beinterpreted interpreted as as due due to to fluid fluid mixing. mixing. deposition resulted resulted from from mixing mixing of of Wells (1925) and Richards and Spooner (1986) suggest that copper deposition precipitation of of native native copper copper fluids of different salinities and sources. The The needed reducing conditions for precipitation seems to rule out mixing of ore fluids with with oxidized oxidized groundwaters. groundwaters. The oxidation of magnetite to hematite and the prograde prograde metamorphic metamorphic reaction reaction of pumpellyite pumpellyite to epidote occurred along along with native native copper copper deposition, and also could have provided reducing conditions needed for the deposition of native copper (Jolly, 1974). Reduction Reductionof of the theore orefluids fluidsduring during deposition deposition of native native copper would have yielded copper sulfides if sulfur was present in the fluids, confirming the low sulfur character of ore fluids. Overall, a combination of fluid mixing; fluid-rock interaction; and cooling may may have caused precipitation of native copper. copper. The onset phase late late in in the the history of the rift onset of aa compressional compressional phase history of rift provided provided a network network of faults/fractures that integrated integrated the the plumbing plumbing system system and and allowed allowed for for easier easier and more faults/fractures that more rapid rapid upward upward movement of fluids. Major Majorfaults faultswere were principal principal pathways for focussing of ore fluids where they intersect �26 Geology Midcontinent rift rift system system does does not not seem unusual unusual in either igneous locally thick permeable permeable strata. strata. The Midcontinent igneous activity or in geothermal gradient, gradient, as as compared compared to to other otherrifts rifts(Hutchinson (Hutchinsonand andothers, others,1990). 1990). Low grade burial metamorphism/alteration throughout the world, yet native copper metamorphismlalterationof mafic mafic volcanics is observed throughout copper ore ore deposits of the Keweenaw Peninsula are are unique. unique. Major Major compressional faulting late in the history of the Midcontinent distinguishes it from other flood flood basalt basalt provinces. provinces. The superposition deformation Midcontinent rift distinguishes superposition of this deformation event on temporally temporally available available "burial" "burial" metamorphic fluids being generated via the thermal pulse pulse related related in the genetic model of the native copper deposits. to rifting, may have provided the critical component in The thick section of basalts in the the rift rift and and aahigh highgeothermal geothermal gradient gradient may have have also also played played aa role role (Nicholson and others, in the genesis The (Nicholson and others, 1992), 1992). albeit albeit secondary, secondary, in genesis of of the the native native copper copperdeposits. deposits. The localization localization of large large native copper copper deposits deposits within within the the Keweenaw Keweenaw Peninsula may may be be controlled controlledby by several several factors, including favorable geometric geometric orientation orientationwithin withinthe theregional regionalcompression compressionstress stressfield; field; abundant faults, fractures, and broad open folds as compared with with other areas areas of of the rift; and coincidence of flow tops and conglomerates, conglomerates,which which are are thickest thickest in in the Keweenaw Keweenaw Peninsula, Peninsula, with with abundant abundant faults faultsand and fractures. fractures. Since much of the the Midcontinent Midcontinent rift system system is buried, buried, perhaps perhaps another area of native native copper copper deposits deposits remains hidden. Despite deposits of the Keweenaw Keweenaw Peninsula, Despite over over 100 100years years of research research on the native copper copper deposits Peninsula, there there remains many unanswered questions, questions, from from aa small small to to a large scale. many unanswered scale. While our ow understanding understanding of this this district district slowly slowly improves, improves, the the exact exact reasons reasons for for the large native copper deposits in the Keweenaw Peninsula Peninsula will likely remain speculative speculative for for years years to to come. come. GLACIAL GEOLOGY GEOLOGY Over the past two million Peninsula has has been been effected effected by by four stages of million years the Keweenaw Keweenaw Peninsula continental glaciation. Each Eachsubsequent subsequentglacial glacialadvance advancesignificantly significantly modified modified or or obliterated obliterated the the effects effects of previous previous glaciations glaciations except except for major bedrock basins (Warren, 1981). Glacial Glacial features features of the Keweenaw Keweenaw Peninsula are related to advance and retreat of of glaciers glaciers of of the the Wisconsin Wisconsin Stage Stage (the (the most most recent recent stage stage of of glaciation). glaciation). During During the maximum maximum extent extent of Wisconsin glaciation, an ice sheet extended as far south south as as central central Illinois and Ohio (Fig. 14). The covered by by up up to to 3000 m m of of ice during Theentire entireKeweenaw Keweenaw Peninsula was covered the maximum glaciation glaciation (Sugden, (Sugden, 1977). 1977). The source source area area of of the the ice sheet sheet was was in in the vicinity of James Bay (Fig. 14). The when the ice sheet TheKeweenaw Keweenaw Peninsula Peninsula tended to deflect the flow of ice, especially when was thinner during advance advance and retreat, and caused two major lobes of the ice sheet (Warren, 1981) 1981) (Fig. (Pig. 15). The TheKeweenaw Keweenaw Bay Bay lobe lobe made made the the final final advance and retreat of the ice sheet about 13,000 years ago. An end moraine (a linear mound of till) marks the the llimit of this this lobe lobe (Fig. (Fig. 16). The i t of The Keweenaw Keweenaw Bay lobe lobe moved from east to west in the vicinity of Houghton, whereas farther further south, it moved southward (Warren, 1981). 1981). As the ice ice sheet sheet retreated retreated (melted back), the very large volumes of water filled the Lake Superior basin, turning it into a glacial features allows allows various various stages stages of of glacial glacial lakes within within the glacial lake. lake. Shoreline features Lake Superior Superior basin to be recognized. The TheDuluth DuluthGlacial Glacial Lake Lake was was the the longest longest lived lived of of the the glacial glacial lakes lakes (Regis, 1993) Bay Lobe Lobe (Fig. (Fig. 17). There 1993) and was bordered on the east by the Keweenaw Keweenaw Bay Thereare arenumerous numerous post-Duluth Superior basin, with 10 stages recognized recognized in the the western western Lake Lake post-Duluth Glacial Glacial Lake Lake Stages Stages of the Lake Superior Superior basin (Table 2). The levels of the glacial lakes depended on the position of the ice front, outlets, The levels of the glacial lakes and crustal rebound (Regis, 1993). 1993). Isostatic Isostaticrebound reboundafter afterglacial glacial retreat retreat causes causes the the shoreline shorelineof of the the glacial glacial lakes to tilt Hughes (1963) (1963) documented documented 55 post-Duluth shorelines in in the post-Duluth shorelines tilt southward southward (Wanen, (Warren,1981). 1981). Hughes western side of the the Keweenaw Keweenaw Peninsula, Peninsula, and since none of them extend north of Allouez Gap (Fig. 18; 18; 1981). The in that that position position (Warren, 1981). The lack lack of of shoreline shoreline features features in the the see Stop 16) the ice ice front front was was in eastern Keweenaw Peninsula indicates that that this this area was still occupied occupied by by glacial ice (Clark and others, �- Geology 27 27 Farrand, 1960). Table Table 2: 2: Stages Stagesofofglacial glaciallakes lakesininthe theLake LakeSuperior Superiorbasin basim(from (from Farrand, 1960). Ian S Isle .fl sabavit a.lt fla.tta at Ga . . !lmtia St 1. fl) S --- *11_n S a_.n - l I 61* 631 633 *100 I.tflttta La 3ta5 51* 561 3S00 Sorts. 590 613 a 651 app., matNst-Stao mow I..,.' Isp à ‘ à r Ñ 691 w 712 112 750 733 nt 7-TI 771 77* 319 S 905 909 Snttou MBHltMi Ms.hbvfl v.hbwm NOCV&t H w h north of isle 8500 72* 819 a*T 3*7 9*9 949 1022 1092 104* lo** 1087 Ion 813 PottI slore i.e boner • Po.t—flldsn to. (linen I. to 1.n.V ?totanla - border l 3 Iarq.sstte-St*tfloa— 9*1 M.b.r17° s.ntu.s) 905 1 1123 ulishIridSe HlihferldU 1131 1131 1167 ~uft-~lll~tll 3,ib-Dtsliath 1178 117à 122* 1 .2'24 121* DUI,Itb m luu 1236 a is. .hs.t — tat of lard. (2) — 'WithS of InC 670 IsSaamc ..-—— 32n 611 *ljon flfl.sS,t ----—-•- IeoO 4 1269 1292 ir 10.220 IsrIp V. ideps mint �28 28 ~eology 52 4.. 44. — •4_ —_.— — __s•, LZOSO 4O .—7—h.P. — —a—.—, t77 . t - Sr North America WISCONSINICE ICERETREAT RETREATfrom fromceital central North America.Note Notemajor malorice resurge. surge.ororreadvance. readvance.InIn WISCONSIN theLake LakeSuperior Sunenorbasin basin(from (fromV.VK.KPrest, Rest.1969, 1969.Geological GeologcalSurvey SurveyofofCanada CanadaMap Map1257A). 1257Al the (Fia 46) Figure 14: 14: Speculative Speculative ice-marginal ice-marginal positions positions during during the the Wisconsin Wisconsin ice ice retreat retreatfrom fromcentral centralNorth North Figure Huber,1975; 1975;Prest, Prest,1969). 1969). America(from (fromHuber, America �Peninsula. Keweenaw ice major the Note the over pattern withdrawal and basin Superior Lake the in readvance view Enlarged 15: Figure 1969). Prest, (from retreat ice Wisconsin the during positions ice-marginal of Gedogy �30 Geology o o Miles Kilometers 50 80 Figure Figure16: 16: End End moraine moraineof ofthe theKeweenaw KeweenawBay Bay lobe lobeglacier glacier(from (fromKalliokoski, Kalliokoski,1976; 1976;Warren, Warren,1981). 1981). / — I, / / j_ I LAKE DULUTH — KEWEENAW BAY LOBE "1 'I t1 // —— /7' /' C, Figure Figure 17: 17:Keweenaw KeweenawBay Baylobe lobeglacier glacierand andposition positionof ofglacial glacialLake LakeDuluth Duluthatatthe the1250 1250foot footelevation elevation (from (from Warren, Warren, 1981). 1981). �Geology 31 (from Hughes, 1963). Figure Figure18: 18:Physiographic Physiographicdivisions divisionsofofthe thecentral centralKeweenaw KeweenawPeninsula Peninsula (from Hughes, 1963). LAKE WASH BURN Figure Figure19: 19:High Highlevel leveldrainage drainagethrough throughthe thePortage PortageGap Gapduring duringthe theLake LakeWashburn Washbwnstage stageof ofthe theLake Lake Superior Superiorbasin basin(from (fromWarren, Warren,1981). 1981). �32 1994). As 1994). As the thewater waterlevel leveldropped droppedfrom from its itsLake LakeDuluth Duluth high, high, water water drained drained through through the the Portage PortageGap Gap (Fig. 19). Warren Warren(1981) (1981)provides provides evidence evidence of this this drainage drainage in the form form of of terraces terraces and and water-scoured water-scoured surfaces. A2). After the surfaces. The Huron Creek Channel is the the drainage drainage through through Portage Gap (see Map Map A2). Wisconsin glacier retreated from the Lake Superior Superior basin, the level of water water receded receded to to the the level levelof of Lake Lake Superior. Superior. Many glacial features are evident evident in in the the Keweenaw Keweenaw Peninsula, Peninsula, both both erosional erosional and anddepositional. depositional. features are bedrock surfaces surfaces(very (very common common in in the the Keweenaw KeweenawPeninsula), Peninsula), Erosional glacial glacial features features include includesmoothed smoothed bedrock grooves, striations, and chatter marks. Depositional features include sediments directly deposited from Depositional features include the melting glacier (till) and those sediments deposited by glacial meltwaters. meltwaters. Various Varioustypes typesof ofmoraines moraines (accumulation (accumulation of glacial deposits) are made of till. Although Although an an end end moraine moraine is is present present in in the the Keweenaw Keweenaw by hummocky, boulder-rich estimated 80% of the Keweenaw Peninsula is covered by 16). an estimated Peninsula (Fig. 16), glacial sediment ground moraine (Hughes, 1963). Glacial deposits of water-laid sediment Glacial deposits of water-laid origin origin include: include: outwash, outwash, eskers, deltas, kames, channel deposits, deposits, and more (Regis, (Regis, 1993). 1993). �MainRoadLog 33 MAIN ROAD LOG AND STOP STOP DESCRIPTIONS Reminder. The Reminder. Thenotes notes throughout throughout all all the the logs logs on on the the bedrock bedrock of of the the Keweenaw Keweenaw Peninsula Peninsula were compiled from Bornhorst (in press), Bornhorst (1992), and Bornhorst and others (1983) without specific citation or (in quotation to these particular particular references. references. Seaman Mineral located on the campus of The Seaman MineralMuseum, Museum,The TheMineralogical MineralogicalMuseum Museum of Michigan, Michigan, is located Michigan Technological University University (see (see campus campus map map on on back back cover coverpage). page). The museum has the world's Peninsula native native copper copperdistrict. district. We highly finest display of minerals from the Keweenaw Keweenaw Peninsula highly recommend recommend Plan to spend at least two hours in the a visit visit to to the the museum museum either either before before or after after your your field field trip. trip. Plan museum (Map 1). 1). CUMULATIVE from previous entry) CUMULATIVE MILEAGE (mileage from MAPII MAP 0.0 Assemble at at the the Memorial Memorial Union Union Building Building on on the the campus campus of of Michigan MichiganTechnological TechnologicalUniversity. University. Begin the field trip from the circular drive located on the northeast side of the Memorial field trip from the circular drive located on the northeast side of the MemorialUnion Union Building. The TheMichigan MichiganTech Techcampus campusisis located located on on aa kame kame terrace terrace to to the the south southof of Portage PortageLake. Lake. Turn right out of the the circle circle drive. drive. 0.05 Turn left. left. 0.1 0.1 Immediately after, alter, turn turn right on Townsend Townsend DriveAJS-41. Drive/US-41. The Quincy Quincy Mine Mine can can be be seen on the skyline ridge. ridge. 0.45 Left turn on Agate Agate Street, Street, and up the steep hill on the south south side side of of the the Portage Portage Lake Lake channel. channel. We are are climbing climbing off the the kame kame terrace to an area of scattered bedrock outcrops of the PLV covered covered by varying varying thicknesses thicknesses of of glacial glacial sediments. sediments. MAP 22 right on on Seventh Seventh Street. Street. 0.7 Turn right 0.9 STOP 1: 1:Seventh SeventhStreet, Street,City CityofofHoughton Houghton(Portage (PortageLake LakeVolcanics Volcanics[PLY]) [PLV) This stop is marked by a prominent ridge of ophitic basalt; an outcrop of the Scales Creek Flow. Plow. ItItisisone oneofofthe thegreat greatKeweenawan Keweenawanlava lavaflows flowswhich which can can be be traced traced continuously continuously for for aa strike strike length of more than than 160 160km km along along the thePeninsula. Peninsula. It is about 70 m thick, has an anamygdaloidal amygdaloidal top which is typically typically not resistent resistent to to erosion, erosion, and and aa prominent, prominent, ridge-forming, ridge-forming, ophitic ophitic massive interior. The Theridge ridgeatatthis thissite sitecan canbe befollowed followed down down hill hill all all the the way way to to Shelden Shelden Avenue, Avenue, where where it is covered by glacial glacial deposits, deposits, and can be traced across the valley where it passes beneath the Ripley School, a prominent brick building across Portage Lake. This Thisbearing, bearing,about aboutN30°E, N30"E, isis the the of the PLV, PLY, which which dip dip about about 50 50°to tothe the NW. NW. Another regional strike of Another clue to the attitude attitude of the the rock is given by the Quincy @ncy #2 shaft shaft house on the horizon, which heads up an inclined shaft. It It is down-dip down-dip along the amygdaloidal amygdaloidal ore bodies of lava flows flows and over over 2000 2000 m m higher higher in in the the PLY PLV section. the PLV PLV section Baltic and Mohawk, section. Throughout Throughout the section between between Baltic Mohawk, most amygdaloid amvedaloid and conglomerate zones are effected by conglomerate zones by well well developed developed zeolite zeolite and andprehnite-pumpeilyite prehnite-pum&ilyite facies facies metamorphism and by widely variable native native Cu Cu mineralization. mineralization. At this site the amygdaloids amvgdaloids just iust below the Scales below Scales Creek c A k Flow Flow are arestrongly stronglymineralized. mineralized. One mine, the the Shelden ~ h e l d eColumbian, ~~~olumbian, operated just a few hundred meters to the east in the the early early 1900's. This Thissame samehorizon horizonisisexploited exploited by aa series series of of shafts shaftscalled calledIsle IsleRoyale RoyaleMines Mines (see (seemileage mileage 3.75 3.75 for fordescription), description), for for several several kilometers to the SW. SW. �___ __________________________ A tc1Vl'r' p ;I 4;9c.s Bedrock •(ThV4' tJ a - I Mineral floor) Geology k.wnnaw W.tnw.y Po,rtage Lake floor) • • 4* •= - 12 1 r- - 'kC!_ rA Lrfl Lake ()R -, c",' r -A,-VoIcanlcs L.'.f .r - 'N /f IFSId p 'flA fl thYTh it. -' ' , Pthr1'X' %.ç4S% - - - —- - - -— - ('C 7 e V an s one Michigan mchnoiogical univ.rslty tioughton, Michigan 49031-1295 nw-° J - ,,Sh.rmanFl*Id - / aco 32 2 1 4 r / — Au. S.Mcia 7 EoincSEoq9yR..OtJItslCsotSc 42 FacIHhI..Mng.olsotStOrtOl 1EcELe1. 49 WnSMeIOfl.OIRSSOWC•S - - 12 Mln.r.lsdMMflslEflQlflllIlfl9 II Poqnt,yhnSlllolS ol od Rnntcli 34 MsoiodiL UnIon - — I p Coid Hall Food S•Mc• .aI.IO1.ImIIOO sod &tudsnl C' 1ItF C:$t! / 3' I z: P Pwklr.g Lol & €C 9 -. — Hmw P utq 'a4 iQ Q' R K1w1fl* RUWth Cnls', (7 kA 1.1.11 BuIlding, Hsncock Poitag. LS• Gall Coui HO.JØIIOO Y' �M1I0ROSdLOS Map3 35 �36 MathRoadLog Portage Lake valley is the the most most obvious obvious geomorphological geomorphological feature, and its origin origin was was formed in in a fault zone typical of that thoroughly investigated by Warren Warren (1981). (1981). The valley valley formed that which crosscuts 200 m m deep deep crosscuts the Keweenawan stratigraphy elsewhere. A A bedrock bedrock valley valley more more than than 200 formed along the fault as aa result result of stream stream superposition superposition through a cover cover of flat-lying flat-lying sediments. sediments. This valley, like others on the Keweenaw Peninsula, Peninsula, was was deepened deepened and and widened widened by by glacial glacial erosion erosion in a fashion of New New York State. State. The fashion similar to the Finger Lake region of The complex complex glacial glacial deposits, deposits, terraces; varved varved clays; clays; and and gravels, gravels, were were the result of the pattern consisting of moraines; terraces; pattern of of ice ice retreat from the region, which which had profound and and complex complex effects on on the the drainage drainagepatterns. patterns. 1.0 Turn Turn left left on on Portage Portage Street. Street. 1.15 Grand Portage Mine rock piles 1.15 piles on on the the left. left. 1.35 We (used for Walktoward toward the the metal metal triangular triangular structure (used arenear nearthe theHoughton Houghton water water tower. tower. Walk 1.35 Weare surveys) on the left side side of of Portage PortageStreet Street(east). (east). STOP 2: 2: Houghton Houghtonwater watertower tower(glacial (glacialgrooves) grooves) with a number of parallel The exposed basalt has a glacially glacially smoothed smoothed surface with parallel glacial glacial grooves that trend about N65%, N65°E, which is consistent with with Stop Stop 3. 3. The The grooves grooves near near the the tower tower are are about 10 10 cm deep deep and and 15 15cm cm wide. wide. At this stop, the Scales Scales Creek Ridge (flow) is exposed higher on the south slope of the the Lake'valley. valley. To ridge, many Portage Lake To the the east east of of the the prominent prominent ridge, many mine mine openings openings from the series Adams Township Township takes takes its its water supply from mines lower in in the the of Isle Royale Royale shafts shafts exist. exist. Adam stratigraphic section which are now filled with with water, water, and and is the the source of of water for Hancock and several other other towns. Using Usingwater waterfrom from mines mines for for drinking drinking is is only only possible possible because because the local local rocks rocks break down in oxidizing surface are almost completely completely devoid of any minerals, such as pyrite, that break surface to produce produce acid acid waters. waters. The lack of acid and groundwaters to acid waters waters keeps most ore ore and and gangue gangue minerals in in the rocks and and remain remain immobile. immobile. Therefore, Therefore, the the water waterfrom fromthe themine mineisof isof drinking drinking quality. quality. Avenue. Across 1.45 Turn right on Sharon Avenue. Across Sharon Sharon Avenue is the City of Houghton Houghton fire station. station. 1.45 1.95 Turn left 1.95 left at at the the flashing flashing light light on on Main Main Street, Street, heading heading into into Hurontown. Hurontown. 2.2 Turn right on on Frederick Frederick Street. Street. 2.25 On arelow lowexposures exposures of of basalt. basalt. 2.25 Onthe theleft leftside sideofofthe theroad roadjust justbefore beforeHuron HuronStreet Streetare STOP 3: STOP 3:Hurontown Hurontown(glacially (glaciallycarved carvedbasalt) basalt) The small of glacially glacially carved and smoothed small knobs of basalt represent excellent examples of basalt within the Keweenaw Peninsula. The are asymmetric asymmetric with a gentle, smooth slope Keweenaw Peninsula. The knobs knobs are on one side and a steep, irregular side opposite. opposite. This This morphology is that of a roches moutonnees, formed by glacial glacial abrasion abrasion on on the the gentle gentle smooth smooth slope slope with plucking steepening steepening the the opposite opposite side side as ice ice moves moves over the ridge. Glacial Glacialgrooves groovesand and the the roches roches moutonnees moutonnees indicate ice movement from N60°E. N60% Return to Main Main Street. Street. �MainRoadLag 37 2.35 Turn right on Main Main Street Streettoward toward Dodgeville. Dodgeville. 3.0 3.0 Charter Township of Portage water tower on the right. 3.55 3.55 Entering Dodgeville. On On the the right right side side of the road is one of the prominent Isle Royale Mine rock piles. piles. Dodgeville. At 3.75 3.75 Center of Dodgeville. At this this time time (May, (May, 1994), 1994), the Isle Royale Mine rock piles from Shaft No. 4 and 5 are are visible visible on on the the right right side side of of the the road road (west), (west), but these these piles of of mine mine rocks rocks are are slowly slowly being removed as crushed rock. The Themine mine rocks rocks are are relatively relatively inert, inert, containing containingno no acid acid generating generating minerals such as pyrite. pyrite. Native mineral in in the rocks, rocks, is stable in Native copper, copper, the the dominant dominant metallic mineral environment. Further, the surface surface oxidizing environment. Further, the the mine mine rocks rocks contain contain only only background background levels levels of of pollutants such as Pb. mine rocks rocks can can beused be used as ordinary crushed stone. stone. These Pb. Thus, these mine ordinary crushed These mine rocks rocks are areoff off limits limits to tocollecting. collecting. Rocks from these Isle Royale Mine rock piles are scattered throughout the City of Houghton Houghton for for purposes and and to to minimize minimizeerosion. erosion. While the rock rock piles piles themselves themselves are are off off limits limits for for decorative purposes collecting, excellent excellent specimens specimenscan canbe be gathered gatheredfrom from the the public public right-of-way right-of-wayinin the the City of collecting, Houghton. AAdescription description of of the theIsle IsleRoyale RoyaleMine Mine isisprovided provided as as aageneral general background. background. worked the the top top of of the the Isle Isle Royale Royale Plow. Flow. Production from the Isle Royale The Isle Royale Mine worked Amygdaloid beganinin 1855, 1855,and andthe themine mineclosed closedinin1948. 1948. A A total total of of about 160 million million kg kg of Amygdaloid began refined copper and Pollack, Pollack, 1971). 1971). The Arcadian Mine (see copper was was removed from this mine (Weege and (see Map 4) may may also also work work the the Isle Isle Royale Royale Amygdaloid. Amygdaloid. The Isle Royale plow flow varies but is about 22 to 46 m thick and lies just below varies in in thickness, thickness, hut below the Flow discussed in Stop 1. The Scales Creek How Theflow flow dips dipsabout about50 50to to 60° 60Âto to the the northwest northwest (Fig. (Fig. 20), 20). fragmental zone; banded with a gentle fold accounting for the curvature, and is characterized by a fragmental amygdaloid; aa foot foot inclusion inclusion zone; zone; and and aa massive massive main main trap. trap. The amygdaloid; The fragmental fragmental zone zone consists consists of irregular fragments of amygdaloid and fme-grained basalt ranging ranging from from small grains to tabular fine-grained basalt blocks several several meters in long direction. The Thevesicles vesiclesand andspaces spacesbetween between the the fragments fragmentsare arefilled filled minerals. The with secondary minerals. The banded handed amygdaloid amygdaloid is is an an unbroken unbroken rock rock body body over overconsiderable considerable area with amygdules abundant at certain horizons, horizons, giving giving this this zone zone aa handed banded appearance. appearance. Below Below the fragmental fragmental zone, or or banded amygdaloid, is the foot inclusion zone which is indefinite patches or inclusions of amygdaloid basalt. The Thefoot footinclusion inclusion zone zone grades grades into into massive massive basalt basalt practically practically devoid of amygdules amygdules (summarized (summarized from from Butler and and Burbank, Burbank, 1929). 1929). rock piles piles from from four shafts of of the Isle Royale Mine and made Stoiber (unpublished data) studied rock the following estimate estimate of the the percentage percentage of alteration alteration minerals: minerals: quartz, 26-59%; 26-59%; calcite, 5-39%; 5-39%; prehnite, 6-32%; 6-32%; pumpellyite, pumpellyite, 1-17%; 1-17%;epidote, epidote, 1-10%; 1-10%;sericite, sericite, 0-12%; chlorite, chlorite, 0-3%; 0-3%; K-feldspar, K-feldspar, 0-trace. Good Good specimens of alteration minerals, and and less commonly native copper, copper, can be 0-trace. specimens of alteration minerals, commonly native be collected from from the the mine mine rock rock throughout throughoutthe the Houghton Houghton area. area. 4.25 junction to the Green Green Acres Acres Road. Road. Thrn Turn right. 4.25 The junction 4.6 4.6 former Isle Isle Royale RoyaleShaft ShaftNo. No.6.6. As of 1994, the once large mine On the left is the location of the former rock pile is nearly nearly gone. gone. 5.45 The junction junction of of M-26 M-26 at the Copper Copper Country CountryMall. Mall. Make a left turn. 5.45 �U) 00 I A Harbor Copper Harbor Conglomerate A' ISLE ISLE ROVALE ROYALE NO. 2 SHAFT I Keweenaw fault 'ooq 100V 500' 5.w Sea Sea leveL level -500' -500' -bOO' -1000' -1500' -1500' -2000' -2000' P o r t a g e Lake L a k e Volcanics Volcanics Portage Jacobsvllle Jacobsville Sandstone Sandstone Figure 20: 20: Cross Cross section section A-A' on onMap Map 22(from (fromWhite, White, 1956). 1956). Abbreviations Abbreviationsare areas asfollows followsfor forthe the Portage Portage Lake Lake Volcanics Volcanics (P) and its its subunits: subunits: Figure (pp). Greenstone Greenstone flow flow (pg), (pg), Allouez Allouez Conglomerate Conglomerate (pa), (pa). Calumet Calumetand andHecla HeclaConglomerate Conglomerate(pe), (pc), Kingston Kingston Pewabic West Conglomerate (pp), Conglomerate (pkc). Wolverine Sandstone flow (psc), (psc), Bohemia Bohemia Conglomerate (pkc), National National Sandstone Sandstone (pn), (pn), Kearsarge Kearsarge flow flow (pk), (pk), Wolverine Sandstone (pw). (pw), Scales Creek flow Conglomerate (pb), St. Louis Louis Conglomerate Conglomerate (ps), (ps), Baltic Baltic Conglomerate Conglomerate(pbc), (pbc),and andUnnamed UnnamedConglomerate Conglomerate(pu). (pu). �Main Mtia Road Hoed Log Log 39 39 MAP3 MAP 3 7 .05 Atlantic Mine is on the the right. right. Continue Continue on M-26. M-26. 7.05 An outcrop of PLV is on the the right. right. 7.8 7.8 8.4 8.4 Turn right onto a dirt dm road road about about 200 m m before before the sign sign that that says: says: South South Range Range Village Village Limit. Limit. 150 m (a church is on the left) to an open open "parking" "parking" area on the the right, right, just before before Proceed about 150 of the open area is a path which which goes up a steep steep slope slope the road goes up hill. hill. At the far end end of open area 4. through a notch up the hill another another 60 meters to Stop 4. STOP 4: STOP 4: South SouthRange RangeQuarry Quarry(Portage (PortageLake LakeVolcanics Volcanics [PLY]) [PLV]) Volcanic textures and structures structures typical of moderate-to-thick subaerial suhaerial lava lava flows flowswithin within the PLV are well well exposed exposed in this old quarry. quarry. As Asone onetraverses traversesup-section upsection into intoand andthrough throughthe the quarry (Fig. 21), one crosses m thick thick interfiow interflow conglomerate conglomerate bed exposed in the the path, path, crosses over a 44m overlain by an 18 flow top top is exposed just just as you enter the 18m m thick thick Java lava flow (the amygdaloidal flow quarry itself), followed by a complete complete section through a 42 42 m thick thick ophitic ophitic basalt basalt flow flow (the (thebulk bulk lowermost 17 17 m m of of the the overlying overlying ophitic ophitic lava lava flow flow (at (at the the of the quarry walls), walls), and finally, the lowermost northwest middle of of the PLVs' northwest end of of the the quarry). quarry). The quarry is positioned positioned in about about the middle PLVs' lava flows N45°E (subparallel (subparallel to to the the stratigraphic section. section. Locally, Locally, lava flows strike strike approximately approximately N45% northwetem shoreline toward the center of the rift (Lake (Lake northwestern shorelineof of the the Keweenaw Keweenaw Peninsula) and dip toward Superior) at about 60°. 60". In Inthe thecross crosssection section of of the thePLV PLVthrough through this this area, area, all alldips dipsare areabout about60°. 60'. Dips in the the sedimentary sedimentary section section overlying the PLV to the the NW NW flattens flattens to to subhorizontal subhorizontal on on the the shoreline of the the Keweenaw Keweenaw Peninsula. Peninsula. sedimentary beds beds provide provide critical stratigraphic markers Laterally continuous interfiow interflow sedimentary within an an otherwise otherwise uniform uniform volcanic volcanicpile pile(PLV). (PLy). The within The unit unit exposed exposed below the quarry has been correlated with with the the National National Sandstone, Sandstone,aamarker markerbed bedininthe theMass-Rockland Mass-Rocldandarea. area. This marker correlated silicic-withis aamassively massively bedded, bedded,pebble-cobble pebble-cobble framework framework conglomerate, conglomerate, composed composed of silicic-withsubordinate mafic, mafic, volcanic subangular-to-subroundedclasts, clasts,within withinaa matrix mathx of poorly-sorted subordinate volcanic subangular-to-subrounded poorly-sorted medium-to-coarse sand of similar similar composition. composition. aremainly mainly olivine olivine tholeiites tholeiites erupted erupted as as thick. thick, The basalts in this this portion portion of of the the PLV PLV are ponded subaerial lava sheets. The Theprincipal principal lava lava flow flow exposed exposed in the quarry walls illustrates illustrates many in cross cross section. section. The top and of the volcanological features observable in and bottom of of this this lava lava flow flow of aphanitic aphanitic chilled chilled basalt. basalt. It are exposed at the two ends of the quarry and consist of It was was deposited deposited underlying lava directly on top of the underlying lava flow, flow, so its base occurs where amygdules amygdules disappear disappear abruptly abruptly brecciated slightly by by in the top of the underlying flow. The The upper upper surface surface of the main flow was brecciated movement of of lava after the formation movement formation of an upper upper crust, crust, but but rapidly rapidly grades grades downward downward to to an an unbrecciated, highly highly vesicular flow top. Note the variation unbrecciated, top. Note variation in vesicle vesicle size size and anddistribution distribution downward in the flow. The Theflow flowtop topbreccia breccia(locally (locally called called fragmental fragmental amygdaloid) is laterally flow. Slow discontinuous for this flow. Slow cooling cooling of of the the lava lava flow flow caused solidification toward the flow interior at a rate which allowed interior allowed development of subophitic suhophitic to ophitic textures (large oikocrysts of clinopyroxene enclosing framework of An-rich plagioclase plagioclase and and intergranular intergranular olivine). The clinopyroxene enclosing a felted framework The constitutes about about two-thirds two-thirds of of the flow. Before Before resulting massive, non-vesicular non-vesicular flow interior constitutes fmal final solidification, solidification, small small amounts amounts of volatile-rich, volatile-rich, differentiated differentiatedresidual residual liquid liquid were were concentrated concentrated in thin discontinuous zones and and lenses. lenses. Many discontinuous zones Many of of these these are are subparallel subparallel to the the bottom bottom and and top top surfaces of of the the flow. flow. A zone consists consistsof of aa 44 cm cm to 1.3 1.3 m core of vesicular vesicular surfaces A typical typical pegmatoid pegmatoid zone surrounded by by aa 44 to 9 cm border zone at at the the top top and and bottom. bottom. The basalt surrounded border zone The vesicular vesicular core of the pegmatoid zones clinopyroxene and zones contains contains coarse coarse laths laths of Ab-rich plagioclase, prisms of Fe-rich cl'iopyroxene �Main Road Log 4 per H bor Conglom . r'ç;r 21 Ii a cobsville San dstone I -.' sJztt —7 MAP 3 �Main Road Log RX ax conglomerate bed S. QUARR 41 Meters 15 0 I Brecciated Brecciated Basil! Basalt Amygdaloidal Amygdaloidal Bmit Bnslt II Massive Massive Buih Basalt *5x5 xxx. Pegmatite Pegmañte Layers Layers Figure21: 21:Geologic Geologic profile theSouth SouthRange Rangequarry quarryalong alongthe thenortheast northeastwall wall(modified (modifiedfrom fromCornwall, Comwall, Figure profile ofofthe in 1951; 1951; White, White, 1971b; 1971b; from Bornhorst, Bomhorst, 1992). 1992). Location Location of of the the quarry quarryisisshown shown inMap Map13, 13,Sec. Sec. 17,T54N, T54N.R34W. R34W. 17. �42 ukoadLog minerals such suchas asapatite apatiteand andzircon. zircon. The border zone abundant Fe-Ti oxides, as well as accessory minerals abundant is composed of aa medium-to-coarse medium-to-coarse grained aggregate aggregate of albite/oligoclase, albiteloligoclase, augite, ilmenite, ilmenite, and and magnetite. Pegmatoid magnetite. Pegmatoid zones zones toward toward the top of the the flow flow are are more more vesicular. vesicular. Zircons extracted within thick thick PLV basalt flows have yielded high-precision (e.g., from pegmatoids pegmatoids within high-precision U-Pb dates (e.g., Davis and Paces, 1990). Numerous Numerous thin thin pegmatoids pegmatoids are exposed exposed in the quarry quarry walls, walls, as as well well as as in the glacially-polished glacially-polished surfaces above and to the north of of the the quarry. quarry. observed within the the vesicular vesicular flow flow The effects of regional regional hydrothermal alteration can be observed Vesicles are are filled with a variety variety of of secondary secondary minerals minerals including including and pegmatoid pegmatoid zones. zones. Vesicles top and pumpellyite. chlorite chlorite and andtraces tracesof ofnative nativecopper. copper. Pseudomorphic Pseudomorphic quartz, epidote, prehnite, calcite, pumpellyite, replacement of of basalt by in the theprehnite-pumpellyite prehnite-pumpellyite facies facies replacement by fine-grained fine-grained secondary secondary minerals minerals in pale bluish green) is most (epidote, olive green; pumpellyite, pumpellyite, pale most intense intense where where permeability permeability was was highest. The massive interior of the flow is only a little altered except in the vicinity of selected highest. The massive interior of flow vicinity fractures. Alteration along the interior fractures is characterized by a green-to-red fractures. green-to-red cherty cherty rock, rock, pseudomorphicreplacement replacementofofthe thebasalt. basalt. The massive interior interior was representing nearly complete pseudomorphic Fracturing during during late a relatively relatively impermeable impermeable horizon horizon in in the thepaleohydrologic paleohydrologic system. system. Fracturing late compression (reverse provided limited limited pathways pathways for upward upward compression (reverse movement movement along the Keweenaw Fault) provided movement of ore ore fluids. fluids. Outside series of glacially grooved outcrops outcrops in in which which Outside of the Quarry Quarry and to the north are a series the exposures of the pegmatitic zones are spectacular. the pegmatitic zones are spectacular. 8.7 8.7 Return from Stop 4. 4. Take turn on on M-26, M-26, going going into the town of South Range. Return Takeaaright right turn 9.2 At the stop stop sign sign in in South South Range, Range, take take aa left leftturn. turn. 9.4 Turn right at the the church, church, immediately immediately followed by a left turn (the (the whole road jogs to to the theleft). left). 9.5 9.5 Entering the town of of Baltic. Baltic. 9.6 Turn right. right. 10.0 10.0 The main road tams concrete turns to the left, but go to the right on a small paved road, driving past a coiicrete building toward some some very very large large mine mine rock rock piles. piles. 10.2 STOP 5: Baltic BalticMine MineShaft ShaftNo. No.3 3(native (nativecopper copperdeposit depositwithin withinPortage Portage Lake Lake Volcanics [PLy]) [PLV]) STOP 5: The Baltic, Champion, and Trimountain Mines worked worked the the Baltic Baltic How top Champion, and Trimountain Mines top deposit. deposit. Native copper is irregularly through the the flow flow top, ranging from minute irregularly distributed through minute specks specks to to masses weighing weighing several several tons. tons. The producer in the Keweenaw native masses The Baltic Baltic Mine, third largest producer copper district, opened about 1898. 1898, while the remaining two mines which worked this flow flow top top production from from the the Baltic Baltic Mine Mine was was about about 840 million opened in 1902. 1902. Total production million kg of refined refined copper. The km along along strike, strike, and and to the the 38th 38th level level (1000 (1000 m) m) Theamygdaloid amygdaloidwas was mined mined for for about about 77 km Mine. The and had had an an average avenge stoping width width of of 55 to to 8 m. in the Baltic Mine. The lode lode dips dips 70°NW 70¡N and of the Baltic Flow The massive interior of How is ophitic and varies considerably in thickness The flow top is with a thickness of 17 m or from about about 50 50 to 70 m. m. The flow top breccia breccia with thickness of or more more where where from mineralized, to less less than 11 m m of ofvesicular vesicular to tomassive massive basalt basalt where where unmined. unmined. The abundant abundant mineralized, to minerals associated with copper are quartz, quartz, pumpellyite, pumpellyite,epidote, epidote,and andcarbonate. carbonate. Paragenetically late copper rare chalcopyrite chalcopyrite are are unusually unusually abundant abundant copper sulfldes, sulfides, chalcocite, chalcocite, some bornite, bomite, and rare �MSRoa4I.og 43 compared to the district as a whole. The Thesulfides sulfidesoccur occurin in fissures fissuresassociated associated with with carbonate carbonatethat that of the rock dip 75° 75' to 90°, 90°and strike strike nearly nearly parallel parallel with the lode. lode. Most Most of rock pile at this stop stop is is amygdaloidal basalt, with the following estimated percentages of amygdule-filling minerals: amygdaloidal basalt, with following estimated percentages amygdule-filling minerals: calcite, 91%; 91%; quartz, Stoiber, unpublished calcite, quartz, 5%; epidote, epidote, 3%; 3%; chlorite, chlorite, 1% 1% (R.E. (R.E. Stoiber, unpublished data). data). Paragenetically, epidote Paragenetically, epidote and chlorite chlorite are early; calcite, calcite, quartz, and native native copper copper are are intermediate; intermediate; Excellent specimens of while copper sullides sulfides and and carbonates carbonates are are late late (Fig. (Fig. 12 12Introduction). Introduction). Excellent chalcocite can be found on this this rock rock pile, pile, along along with with native native copper. copper. Butler two distinct Butler and Burbank Burbank (1929) (1929) recognized recognized two distinct periods periods of alteration alteration within within the the Keweenaw Peninsula native copper district. district. The earliest alteration was oxidation, causing the development of of hematite, which in turn, turn, produced produced reddened reddened basalt. basalt. This oxidation oxidation could could development hematite, which alter eruption. The essentially represent deuteric alteration shortly after The second second period period of of alteration alterationwas was probably after the flows had had been been tilted. tilted. This probably This period period was was complex and resulted in deposition of native copper. copper. It is is divisible divisible into into three three substages: substages: 1) an an early early stage stage of of deposition deposition of of epidote, epidote, pumpellyite quartz, quartz, calcite, calcite, most most of of the native pumpellyite native copper and minor prehnite, alkali feldspar, and laumontite; 2) an intermediate by the development intermediate stage stage characterized characterized by development of of sericite sericite with with quartz, quartz, calcite, anhydrite, gypsum and minor barite; and 3) a fmal final stage of copper copper sulfides sulfides and and arsenical arsenical copper accompanied by calcite, quartz, chlorite, chlorite, and and specular hematite occurring in copper accompanied by calcite, sericite, quartz, numerous veinlets. veinlets. 10.4 10.4 Retrace route route through through Baltic. Baltic. 10.9 10.9 At the stop stop sign sign in in Baltic, Baltic, turn turn left left to to go go back back in in the thedirection direction of of South SouthRange. Range. 11.1 11.1 Turn right, immediately followed at the church by a left left turn. turn. 11.3 In the center 11.3 center of of South South Range, Range, take aa right right turn turn off off M-26. M-26. 11.8 11.8 Passing the South Range Quarry, Stop 4. MAP22 MAP 14.75 On On the theright rightisisthe theGreen GreenAcres AcresRoad RoadtotoDodgeville Dodgeville that thatwe wepreviously previously followed. followed. 15.6 15.6 Stoplight Stoplight at Sharon Avenue. Continue Continuestraight straightahead. ahead. 16.05 The junction. This This road road is used in Leg A -- Houghton Houghton Canal Road. Road. 16.05 The Canal Canal Road junction. 16.5 16.5 Between the Junction of of M-26 M-26 and and US-41, US-41, stay stay right right and and continue continue ahead ahead on on US-41 US-41 (Marquette) (Marquette) past the gas stations stations on on the the right. right. 16.95 An Anexcellent excellentoutcrop outcropof ofbasalt basaltwith with exposed exposed vesicular vesicular flow flow top (amygdaloid) (amygdaloid) on both sides sides of the road. Move road. Move to to the the far far left left lane. lane. 17.1 17.1 Make a left U-turn back onto US-41, going Stay going one one way way back back through through the the City City of of Houghton. Houghton. Stay in the left lane. lane. 17.2 17.2 Turn off US-41 into into the the Burger Burger King King parking parking lot. lot. STOP STOP 6: Shelden SheldenAvenue, Avenue,City CityofofHoughton Houghton(Portage (PortageLake LakeVolcanics Volcanics [PLVI) [PLY) West of the restaurant, massive restaurant, an unbrecciated amygdaloidal amygdaloidal flow top with an underlying massive �44 MsmkoadLog south along along the the highway). highway). The flow top is strongly interior interior is well exposed (also to the south strongly altered ainygdule minerals characteristic characteristicof ofthe theprehnite-pumpellyite prehnite-pumpellyitefacies. fades. The with amygdule The green green color color is is due due to the abundance of epidote. The Themassive massive flow flow interior interior below below the the altered altered flow flow top, top, isis essentially essentially unaltered except where thin pegmatoid zones cross it. Pegmatoid zones are discussed at Stop Stop 4. 4. This stop is an an alternate alternate to to the the South South Range Range Quarry Quarry Stop Stop 4. 17.65 Turn Turnright righton onUS-41/M-26 US41/M-26and andcross crossthe thePortage PortageLake LakeLift LiftBridge Bridgeinto intoHancock. Hancock. The bridge was built in 1957, 1957, and and isis designed designed to to accommodate accommodate Great Lakes ore boats, whose whose captains prefer the Keweenaw Keweenaw Waterway route (Portage Lake) to rounding rounding Keweenaw Keweenaw point point in in stormy weather. The Thepresent present bridge bridge abuts abuts the the Hancock side of the canal at approximately approximately the site of the old old Quincy Quincy Mill, Mill, where where the the tramway tramway descended Quincy Hill from the mines. MAP 4 on US-41 US41 into into Hancock. Hancock. 17.9 17.9 Turn left on Turn right, immediately followed followed by by US-41 US-41 going going to to the left, but go straight at 17.4. 17.4. 18.1 18.1 18.25 Bear Bear to to the the left left on on White White Street. Street. 18.75 The Thejunction junction between between White WhiteStreet Streetand and Lincoln Lincoln Drive Drive which which is is US-41; US-41; turn turn right. right. The fenced fenced ground ground near this locality surrounds surrounds an area of caved ground, which is thought thought to to be be of the Hancock Hancock Mine. Mine. The related to shallow stopes of The detection detection and distribution of such openings mines had had shallow workings, is a problem of considerable considerable concern to local authorities since many mines since since towns towns grew grew up adjacent adjacent to mines, mines, and and since since maps maps of ofthe theunderground underground workings workings are are incomplete and/or andtor inaccurate. inaccurate. Turn off US-41 US41 to the right to to the overlook overlook of the Keweenaw Keweenaw Waterway or Portage Lake, which 19.05 Turn 19.05 is Stop Stop 7. 7. STOP 7: Keweenaw Keweenaw Waterway Waterway Overlook Overlook This overlook, near the crest of Quincy Quiicy Hill, allows a broad overview overview of the the Keweenaw Keweenaw Waterway. From From east eastto towest west(left (leftto toright), right),the the features features which which can can be be seen seen are are (Fig. (Fig. 22): 22): 1) 1) KeweenawBay, Bay,the theknobby knobbyterrain terrainofofthe theHuron HuronMountains. Mountains. The On the skyline across Keweenaw mountains are underlain by Archean gneisses and granites of the Michigan portion of of the the Wawa subprovince subprovince of the Superior Superior Province of Canada. Canada. 2) 2) In the foreground, foreground, the flat topography is characteristic of areas of Jacobsville Jacobsville Sandstone, Sandstone, which has typical dips of less than 100. The Jacobsville extends from the Keweenaw which dips of less than 10". Keweenaw waterway at at the the east east end end of of the theMTU MTh campus, across Keweenaw Fault, which crosses the waterway Bay, and to the north of of the the Huron Huron Mountains. Mountains. 3) 3) basalt lava flows Within the town of Houghton, several ridges of resistent massive interior basalt can be traced downhill. The most prominent ridge is the Scales Creek downhill. The most prominent the Scales Creek Row Flow horizon, horizon, where Stop 1 was made. made. The Theattitude attitude of of the thePortage Portage Lake Lake Flows Flows and and the the alteration alteration of of resistent flow interiors and interfiow tesistent interflow conglomerates with less resistant tops, tops, makes makes site site investigation work critical for for some some construction construction projects. projects. Investigations are are necessary necessary to accurately determine determine depths depths to to bedrock, bedrock,and and to to make make hydrologic hydrologicinterpretations. interpretations. For �Map5 Mmii Road Log 45 MAP �0a I £ Figure Figure22: 22:View Viewfrom fromPortage Portageoverlook overlookfacing facingsouth south(from (fromBornhorst Bornhorst and and others, others, 1983). 1983). Notable Notablefeatures featuresinclude: include: 1)1)Huron Huron Mountains, Mountains, 2) 2) FlatFlatlying 3A) Scales Scales Creek Creek flow Flowridge, ridge,3B) 3B)Michigan MichiganTechnological TechnologicalUniversity University Student StudentDevelopment Development Complex, Complex, 4A) 4A) lying Jacobsville Jacobsville terrain, 3A) Bluff Houghton water tower at Isle Royale Shaft #1, 4B) Isle Royale mine rock pile #4, 4C) Isle Royale mine rock pile #5, 4D) Wheelkate Houghton tower Isle #I, #4,4C) #5,4D) Wheelkate Bluff (Trimountain), (Trimountain), 5) Highway M-26, 6) Contact between the Portage Lake Lake Volcanics Volcanics and and the the Copper Copper Harbor Harbor Conglomerate, Conglomerate, 7) 7) Houghton Houghton County Courthouse, Courthouse, 8) 8) Quincy Quincy Smelter, Smelter, 9) 9)Michigan MichiganTechnological TechnologicalUniversity Universitymain maincampus. campus. County �MainRoadLog 47 example, site investigations of of the extensive area south of the the main main campus, campus, where where the the Michigan overlook) is now located, Michigan Tech Student Student Development Complex (visible (visible from the overlook) located, provided the focus of several several Master's theses theses for for students students in in Geological Geological Engineering Engineering at at Michigan Tech (Stevens, 1971; Hase, 1973). A general map, showing the detailed Michigan Tech (Stevens, 1971; Hase, 1973). general map, showing the detailed bedrock geology of the City of Houghton (Holcomb, (Holcomb, 1975) is used used by by developers in the area. area. 4) 4) On the the skyline skyline directly directly on the the opposite opposite side of the the waterway, waterway, and beginning beginning at the the Houghton water tower (black, orange and and yellow), yellow), is a series waste-rock piles Houghton series of of mine minewaste-rock piles from the Isle Isle Royale Mine (flow top deposit) deposit) that extend into the distance along along the the strike strike of the PLy. PLV. The Theknob knobononthe theskyline skylineisisWheelkate WheelkateBluff Bluff near nearSouth SouthRange, Range, just just south south of Stop 4, which is one of several resistant bedrock highs. which is one of several resistant bedrock 55)) To the north north of of the the divided divided state state Highway Highway 26, are are glacial-fluvial glacial-fluvial deposits. 6) 6) To the right, extends across across the the upper upper contact contact of of the the PLV PLV to the Copper right, the waterway waterway extends Harbor Conglomerate, Leg A follows Conglomerate, Nonesuch Nonesuch Shale, and and Freda FredaSandstone. Sandstone. Leg follows the the Houghton side of the waterway waterway with stops observing the Copper Harbor Conglomerate Conglomerate (along the waterway), waterway), and the Freda Freda Sandstone Sandstone (along the Lake Lake Superior Superiorshoreline shorelineatat Redridge). Redridge). This, and other other major major bedrock valleys in the area, were formed by stream stream superposition superposition as the tilted tilted Keweenawan as ancient ancient rivers eroded through flat-lying Paleozoic rocks and into the strata. The valleys strata. valleys were were greatly greatly deepened deepened by glacial glacial erosion erosion during during the the Pleistocene. Pleistocene. During a pause in the retreat of the Keweenaw Bay sub-lobe at the end of the Wisconsin glaciation, a waterway was established that allowed eastward eastward drainage across the peninsula glaciation, toward toward lower lower lake lake levels to the east. First, First,drainage drainageoccurred occurredin in the the Portage PortageGap Gap(between (between Houghton and Hancock) while a tongue of ice remained in what is now western western Portage Portage Lake. As Asthe theice iceretreated retreatedfurther, further,the thevalley valley now now occupied occupied by by Portage Portage Lake Lake was was formed formed by the eastward eastward drainage drainage of successively successively lower proglacial lakes in western Lake Superior. Torch Lake was formed by a trapped block of ice which later melted in place to to form form the the lake lake basin basin (Warren, (Warren,1981). 1981). The Keweenaw was named named after after an an Indian Indian word word for for portage portage route. route. Dredging, Keweenaw Peninsula was Dredging, completed completed in in 1873, 1873, was necessary necessary at both the northern and southern ends, to make Portage Portage Lake accessible accessible to to Lake LakeSuperior Superiorshipping. shipping. Houghton was named for Douglass Douglass Houghton, Houghton, the geologist geologist who sparked sparked the the Michigan Michigan boom by by publishing publishing his his Michigan Michigan State State Geologist GeologistReport Reportin in 1841. 1841. The copper mining boom The town was seWed in 1852 and is the site of several historic buildings, the most important settled 1852 the site of several historic buildings, the most important of which which is is the theHoughton Houghton County County Courthouse Courthouse (1887). (1887). It's aa prominent prominent yellow yellow brick brick Sandstone facing facingand andaa copper copper roof roof that that sits sits on on the hill above building with Jacobsville Sandstone the main part of town. town. Hancock was settled in 1859. Across Across the the road road and and just slightly slightly uphill is the the Quincy Quincy Hill Hill (1871), the the Quiincy Quincy Mine Minemanager's manager'shouse. house. The Quincy No. No. 6 Mine shaft house House (1871). (flow top top deposit) deposit) dominates dominatesthe theskyline skylinebehind behindthe theviewpoint. viewpoint. A A map map of the Quincy (flow Quiincy operations in its heyday No. 2 shaft operations in heyday is given given in in Figure Figure 23. 23. The inclined inclined No. shaft descends at nearly a 45' 45° angle, angle, more more than than 33 km km (1.7 (1.7 km km vertical) vertical) below belowthe the surface. surface. The surface nearly surface projection of the area mined mined is shaded shaded on on Map Map 4. 4. �48 MainkoadLog Main Road Log 19.05 19.05 Turn right, back onto US-41 going up the hill. 19.5 19.5 A prominent outcrop of basalt basalt with with glacial glacial grooves. grooves. 19.6 19.6 Turn right to Stop Stop 8. 8. 19.7 19.7 Quincy Steam Steam Hoist. We're in in the thecenter centerof of the the Quincy Quincy Mine Mine area area at at Shaft Shaft No. 66 and and the the Quincy Quincy Steam Steam Hoist Hoist (Fig. (Fig. 23). 23). The Quincy Hoist is the largest Quiincy Steam Hoist largest steam mine mine hoist in the the world. world. This great great machine, machine, by Bruno Nordberg Nordberg and and installed installedinin 1920, 1920,could couldlift liftaa 10 10ton ton ore ore load load at at aa rate rate of of more invented by than 1000 1000 m per minute. The Thehoist hoist isisstill stillin in pristine pristine condition condition and aa full full museum museum of of the the Quincy Quincy Mine is maintained Mine maintained inside the building building as well. well. The hoist can be visited visited during during the the summer summer months for an admission charge. Tours months admission charge. Tours of of the the Quincy Quincy Mine Mine Adit, Adit, connecting connecting with the Quincy Quincy workings, start at the hoist and is operated by the Quincy Mine Hoist Association. workings, start hoist and is operated by the Quincy Mine Hoist Association. For an an admission charge, charge, vans vans shuttle visitors to the admission the underground underground workings, workings, where excellent excellent crosscrosscopper-mineralizedrock rockcan canbe be observed. observed. The Quincy Mining sections of lava flows with native copper-mineralized Mining Company earned earned the the name name "Old "Old Reliable" Reliable"because becauseititpaid paiddividends dividendsso soregularly. regularly. Lankton and Company Hyde (1982) provide an an outstanding historicalaccount accountofof the the Quincy Quincy Mining Mining Company. Company. The Hyde (1982) provide outstanding historical The below as Stop 8. geology of the Quincy Mine and connecting adit is described below STOP 8: Quincy STOP QuincyMine MineAdit Adit(Portage (PortageLake LakeVolcanics Volcanics [PLV]) [PLV]) Mine Adit connects connects with with the the Quincy Quincy Mine Mine (Pig. (Fig. 24) 24) and and is owned by the The Quincy Mine Association. The Quincy Mine Hoist Association. The Michigan Michigan Tech Mine (the (the mine adit) description is revised from Bornhorst Bomhorst and McDowell (1992) and Bomhorst and others. (1986). (1986). once aa drainage drainagetunnel tunnelfor forthe theQuiincy QuincyMine. Mine. Michigan Tech The Quincy Mine Adit was once students in Mining Engineering expandedthe the adit adit (since (since 1976) to to its present size. students Engineering expanded size. The adit adit intersects old workings of the Quincy Mine, one of the major producers in the district with 10% 10% production. The adit is 700 m in length; 5 x 5 m of total district production. m in in cross-section; cross-section; and leads to the No. 5 shaft shaft area area on the the seventh seventh level of the the Quincy Quincy Mine, where it divides into into several several drifts drifts that are used for for mining mining and and rock rock mechanics mechanics research and teaching (Figs. 24). Exposed at this site 4) are are site of the the Keweenaw Keweenaw Peninsula native copper district (Figs. 2 and 4) of basaltic flows, flows, aa long, high high open stope follows two classic aspects: 1) in an inclined sequence of a major and 2) an oblique major horizon horizon of of mineralized mineralized flow tops (Pewabic); (Pewabic); and oblique fault fault (Hancock (Hancock Fault) Fault) limit for for the the Pewabic Pewabic orebody. orebody. A offsets the basalts and forms the southwestern limit A segment segmentof of this this fault was mineralized and mined at the Hancock Mine, where about 365 m of the fault was mineralized and mined Hancock Mine, where about 365 the fault was opened down to the 12th 12th level (300 m vertical). This Thisfault faultmay may have have been been aa feeder feederthrough through which which the mineralizing mineralizing solutions reached the favorable Pewabic Flow tops. The Quincy Mine began operations on the Pewabic Row Flow tops in 1856 and ended in 1967. 1967. along aa series flow tops tops by by 8 shafts--on The mine was developed developed along series of parallel parallel flow shafts-on 85 levels--to levels-to a vertical depth of 1675 1675 m. The Theorebodies orebodiesdecrease decrease in in dip dipfrom from55° 55' atatthe thesurface, surface,toto350 35' at at the the bottom levels (Fig. (Fig. 25). 25). By 330 million millionkg kgof ofcopper copperand and22xx lo9 io By 1925, 1925, the mine had sold about 330 106oz) oz) silver. silver. Production to 1968 g (71 x 10' 1968 totaled 490 million kg of copper, ranking it fourth fourth in in the district. The Pewabic flows at the Quincy Mine are relatively thin and are difficult to follow, The Pewabic Flows at the Quincy Mine are relatively thin and are difficult to follow, been mapped mapped in in detail detail (Butler (Butlerand andBurbank, Burbank,1929). 1929). The flows are unless the top of the flow has been porphyritic with with large large feldspar feldspar phenocrysts, phenocrysts, and and some some of of the thicker flows texturally distinctly porphyritic flows �QUINCY MINE LOCATION HOUSIING AND COMMUNITY STRUCTURES C0 k920 C asaa. Ø.ttVWS& J trJ /mica-*are 4 CW*3 Clericsamaence a Mint ~ i n eqpa ~fflcs w tstEg If *#vdot Qtgt', It C,u,qIic tht,rh and ATtSfl Q ~ a-t l w t i e . ~ w t i o n d ~ n e a c ~ m -- KS a ]Jame,MeaqetSnIö7WOfV a m H-Svaqv and Company franklui ismrv —a 6.ffwwMychSHmaenos #4 franklin id,oo UfwMmilctWot 7. cacwra/wnence 15 ~ wt~ftSMI&1 w ~ s n  iotc(; ¥ ~ c h&&tU ool;/rantti a AbmY ~MU- W itÇPwaHicSchoo aw,bE; 3G'Ot a tfumcwÂ¥3cfwo 1!It tt cr ! t..._ a.n' — — _.•_ — a, I .1 S Figure Figure23: 23:The TheQuincy QuincyMine Minelocation location(from (fromLankton Lanktonand andHyde, Hyde,1982). 1982). �A B '.7 C I °—" I I-,, I I :• : C, Figure Hancock Mines Mines (from (from Bomhorst Bornhorst and andothers, others,1986). 1986). The TheQuincy Quincy Mine Mine workings follow follow several Figure 24: (a) (a)Sketch Sketch map map of of the the Quincy Quincy and the Hancock several parallel Fault. The parallel flow flow tops tops (Pewabic). (Pewabic). These These flow flowtops tops are are not not mineralized mineralized south south of the the Hancock Hancock Fault. TheHancock Hancock Mine Mineoperated operated on the Hancock projectionsofofmine mineworkings workingstotothe thehorizontal. horizontal. The TheQuincy Quincy Mine Mine Adit Adit (MTU (MTUMine Mineon onfigure) figure) Hancock Fault. Stippled Stippledpattern pattern represents represents projections provides to the Allouez Conglomerate, N-S provides access access to Conglomerate, the Hancock Fault, Fault, and and open open stopes stopes of the Pewabic Pewabic deposit. deposit. Same Samescale scalefor formap mapand andN-S of the the adit adit at at A' A' (from section. (b) (b) Geology Geology of the Quincy Mine Adit Adit with withthe the portal-to-A portal-to-A section section joining the the remainder remainder of (from Bornhorst Bornhorst and and section. others, others, 1986). 1986). The Theold oldstopes stopeson onthe the Pewabic Pewabic deposit depositextend extend only onlyshort shortdistances distances southwest southwest of the the No. No. 55shaft; shaft;mineralization mineralization terminates terminates at the Hancock Fault such such that neither the fault nor the the southern southern portion of of the the Pewabic Pewabic flow flowtops topscontain contain significant significant native native copper. copper. The The deposit. B, C, and F refer stopes in the the vicinity of shaft follow followan anamygdaloid amygdaloid200 200mmstratigraphically stratigraphicallyabove abovethe the Pewabic Pewabic deposit. B, C,and F refer to to stopes in of the the No. No. 77shaft thick flows flowsininthe the adit. adit. thick I �Harbor geologic relationships of the Keweenaw Peninsula. The Portage Lake Volcanics are overlain successively by the Copper Harbor with the younger Conglomerate, the Nonesuch Shale, and the Freda Sandstone. The Portage Lake Volcanics are in fault (reverse) contact Hancock Conglomerate for the Portage Lake Volcanics (p) are as follows: Jacobsville Sandstone (see Fig. 2 Introduction). Abbreviations Hecla Conglomerate (pc), (phc), Pewabic West Conglomerate (pp), Greenstone flow (pg), Allouez Conglomerate (pa), Cahimet and (ps). Kingston Conglomerate (pkc), Kearsarge flow (pk), Scales Creek fbi (psc), Bohemia Conglomerate (pb), St. Louis Conglomerate section illustrates the general FIgure 25: Geological cross section from B to B' on Map H6, B' to B" on Map 4, B" to B" on Map 5. This cross Con9lomerate Copper "0. • .xcq .1007 .S.s lent SW B", Ut -S �52 MzinRoadI.og have an ophitic ophitic texture. The Theflow flowtops tops are arc characterized characterized (Butler (Butler and Burbank, 1929) 1929) by cavernous cavernous zones or layers 1 to 1.5 and coalescing coalescing vesicles. vesicles. Layers can form zones 1.5 m thick, thick, large gas cavities, and for 3 to 30 m, and a series of such openings provided an almost continuous connected openings for path for the flow of mineralizing hydrothermal hydrothermalsolutions. solutions. Where coalescing is is well developed in Amygdaloid, there there may may be be 22 to to 10 layers. layers. There the Pewabic Amygdaloid, There is is every every gradation gradation from from coalesced coalesced tendency to to collect collect in layers. Brecciated layers of vesicles, to those that show only a moderate tendency Brecciated of the Pewabic Pewabic Flows flows as they flow tops are not characteristic characteristic of they are are for for other other flow flow top topdeposits. deposits. calcite are abundant cavity- and amygdule-filling amygdule-fluing secondary Quartz and calcite secondary minerals, minerals, with with pumpeilyite pumpellyite and epidote less abundant. Chlorite Chlorite is is present present in amygdules in the base of the flows, except near is present veins veins where where it is is replaced replaced by by quartz quartz or or calcite. calcite. Prehnite Prehnite is present but not not common, common, and and laumontite is mostly confined to to veins. veins. Datolite Datolite was reported from upper levels of the mine, mine, but but through the the mine, mine, dipping dipping at at high high angles. angles. The not lower levels. Several Severalprominent prominent veins extend through The veins are mostly mostly filled with with calcite, calcite, laumontite, quartz, and epidote and are similar similar to to minerals minerals found in the the flow flow tops tops (Butler (Butlerand andBurbank, Burbank, 1929). 1929). These veins probably probably help integrate integrate the the paleohydrologic system for the movement of ore fluids. The adit adit exposes exposes 12 12lava lavaflows flowsbeneath beneath the the Allouez AllouezConglomerate, Conglomerate, dipping dipping about about 50° 50' northwest, northwest, with several several thick flows noted on Figure 24. The The Greenstone GreenstoneFlow, How, which which lies liesdirectly directly above above the Allouez Conglomerate, can be traced for 50 km northeast--where it is 430 m thick--and to Isle Royale on Lake Superior, 100 100 km north. An An excellent excellentexample example of of aa clay clay gouge gougeassociated associated with a bedding plane fault of unknown displacement occurs at the top of the with a bedding plane fault of unknown displacement occurs at the top of the Allouez Allouez Conglomerate. Conglomerate. Such Suchfaults faultsare arefound foundthroughout throughoutthe the district, district, especially especially on on the the top top of conglomerate conglomerate beds. beds. Pewabic How flow tops At the Quincy Mine, the Pewabic tops are about about 100 100 m m stratigraphically stratigraphically (120 m horizontally) above the Allouez Conglomerate. Conglomerate. About About 12 12 lava lava flows flows occur occur in in this this interval interval in in the the Flows are barren barren at this location on on the south side of the Hancock Fault. adit, but the Pewabic Rows Above Above the the Allouez Allouez Conglomerate, 14 14 more lava flows occur before the Hancock Fault is reached; reached; about 425 m from the entrance. The Hancock Fault is marked by a distinctive clay gouge The Hancock Fault is marked a distinctive clay gouge(almost (almost corrensite) and a green corrensite-rich, brecciated brecciated alteration alteration zone zone adjacent adjacent to to thegouge. the, gouge. The pure comnsite) fault is best exposed in the the small small drift drift leading leading to the the No. No. 77shaft shaftarea, area, where wheresmall smallexploratory exploratory stopes were made in a flow top that occurs 200 m stratigraphically stratigraphically above the Pewabic lode on the Fault. No southwest side of the Hancock Fault. No native native copper-rich copper-rich flow tops occur at at the the stratigraphic stratigraphic position of the Michigan Tech Tech adit adit southwest southwest of of the theHancock HancockFault. Fault. In the flow tops of the adit, amygdule-filling minerals include quartz; calcite; pumpellyite; epidote; chlorite; laumontite; laumontite; and and native copper. Rimmed Rimmedamygdules amygdulessuggest suggestearly early prehnite prehnite and and chlorite, chlorite, followed followed by by quartz, quartz, then then chlorite, and lastly calcite (Bumgarner, (Bumgarner, 1980). 1980). Some of the Pewabic lode has been mined by students so they can run experiments. experiments. The The ore ore grade grade is is about about 1.75% 1.75%copper. Return to the the main main road. mad. 19.85 Turn Turnright right on onUS-41. US-41. MAP4 MAP 4 21.05 Turn arc some someof of the the Quincy Quincy 21.05 Turnright righton onArcadian ArcadianRoad. Road.On Onthe theleft leftside, side,immediately immediatelyafter afterthe theturn, turn, are Mine rock piles, nearest to Shaft No. No. 1. This This is is Stop Stop 9. Please Pleaserespect respectprivate private property property signs signs and and stay within the public right-of-way. within the public right-of-way. STOP (native STOP9: 9:Quincy QuincyMine MineRock RockPiles Piles (nativecopper copperdeposit depositwithin withinPortage PortageLake LakeVolcanics Volcanics[PLV]) [PLV]) Refer Stop 88 for for aadescription description of of the theQuincy Quincy Mine, Mine, which which worked worked the the Pewabic Pewabic Refer to Stop �MainRo.dLog 53 Amygdaloid. In the Amygdaloid. the Pewabic, Pewabic, quartz quartz is is the the most most abundant abundant secondary secondary mineral mineral associated associated with with native copper, but calcite is also abundant. Pumpellyite, Pumpellyite, epidote, epidote, and chlorite chlorite are are common common but but prehnite is present. Laumontite not abundant and prehnite Laumontite and datolite are common in upper levels but not lower levels. levels. However, the majority majority of of the the rock However, the rock at at this this stop stop is amygdaloidal-to-massive amygdaloidal-to-massive basalt. basalt. with lesser amounts of of pumpellyite pumpellyite followed by Secondary minerals are mostly quartz and calcite with epidote. Paragenetically, Paragenetically, epidote epidote and and pumpellyite pumpellyite seem to be early, whereas quartz; calcite; and native copper formed later. copper formed later. MAP 55 operations, 20.5 Entering Pewabic, another one of the communities that sprung up around the Quincy operations, 20.5 with Several ethnically and owned owned by bythe thecompany. company. Several ethnically distinct distinct with most most of of the the houses houses built built and neighborhoods existed 'on the hill" in the early 1900's. In all, more than 6,000 people lived neighborhoods existed "on the early 1900's. In all, more than 6,000 people lived on on the hill in in 1905. 1905. 21.45 Thereisisaa"Y "Y" theroad; road,take takethe theright righthand handbranch, branch,which whichisisessentially essentiallyaastraight straightroad, road, with with 21.45 There ininthe a sign saying Arcadian Scenic View. sign saying Arcadian Scenic View. 21.7 Passing a radio tower on the right, we are now crossing the Scales Creek Flow Row at at the the top top of of the the small ridge (see Map 5). The just below the Scales Creek TheArcadian Arcadian Mine Mine worked worked an amygdaloid just Flow. The Row. Theamygdaloid amygdaloidmay may correlate correlate with with the the Isle Isle Royale Royale Amygdaloid Arnygdaloid discussed at Stop Stop 2. 2. North of the road is Shaft North Shaft No. I1of ofthe theArcadian Arcadian Mine. Mine. Stoiber Stoiber(unpublished (unpublisheddata) data) studied studiedthe the rock pile from from Shaft Shaft No. No. 11and andestimated estimatedthe thepercentages percentagesof of non-metallic non-metallic secondary secondary minerals: minerals: calcite, 43%; prehnite, prehnite, 25%; 25%; quartz, quartz, 16%: 16%: K-feldspar, K-feldspar, 8%; 8%; epidote, epidote, 6%; 6%;pumpdllyite, pumpellyite, 1%; 1%;chlorite, chlorite, 1%; and laumontite, trace. 22.4 To the right right of the the road road you you can can see see the the largest largest part part of of Portage Portage Lake, Keweenaw Keweenaw Bay, and the Huron Mountains. Much Much of of the thefield fieldof ofview viewisisbasically basically flat-lying flat-lyingJacobsville Jacobsville terrane. terrane. 22.6 The road turns turns to to the the right right and and changes changes to togravel. gravel. 22.8 We're descending We're descendingoff off the the Portage Portage Lake Lake Volcanic Volcanic Series Series by crossing crossingthe the Keweenaw Keweenaw Fault Fault and and onto onto Jacobsville Sandstone. Jacobsville Sandstone. 24.0 We are are descending descending the hill and have a view view of of the the Isle Isle Royale Royale sands sands across across Portage Portage Lake Lake in in Houghton; they are tailings from the Isle Isle Royale Royale Mine. 24.15 The 24.15 Thejunction junction with with M-26; M-26; take take aa left leftturn turn atat the the Portage Portage Lake Lake Coal Coal Dock. Dock. 24.6 24.6 Entering Dollar Bay on M-26. MAP66 MAP cross-bedded redbeds redbeds of of the the Jacobsville Jacobsvilie Sandstone Sandstone on on the the left side of 26.2 26.2 An exposure of flat-lying cross-bedded the road (northwest (northwest side). side). 26.9 Mason. Mason Entering the small town of Mason. Mason was was the site site of company housing for the Quincy Mill operations from from 1890. 1890. 27.5 which is is stuck stuck in in tailings tailings in in Torch TorchLake. Lake. This is On the right side of the road is an old dredge which by the the Quiincy Quincy Mill Mill in in 1955 and used until the C&H dredge #1, built in 1913, 1913, which was bought by 1967. 1967. �p 54 Main Roll Log �55 Main Road ¼ / 4't( ., ,,/ ,tG r ,' - ,, - p.- -St.-- S I, II II S Is Cl) / I — 5-- p -' C NEt4P-9A TICN8I EXPLORATION S 41012 / / IT-'-'. / NA?? A H Nt4L5Q NAL3 I uiney Mill S \14— 41 - I 5— •.c,_\_-,_ UI 1 ---, — — -, - —'l- — ______/_\_ — I -. - .- - / 1/ —-. - '1\ 1stc$ 0 'V — C, --\E -: - - Cr Map5 '*1- 40 7 / / 602 jF I' 1' -7 - :--. —IL 1* c) • II Ii j7 c==_v 26 W;; 7 'I 4 1.- 4 — / fi / 7' 56$ - z — I —'' 7—- —,Vf'_-— - ,'t:/ #—) - - - - - /_ t- -L MAP —N �56 56 ~ a l ~i o a d~ o g You may pull to the right of the mad road and view the dredge at your leisure. This Thisisisthe theTorch TorchLake Lake Superfund Site. The Superfund Site. The site site was was used used as as aa giant giant tailings tailings pond for both the Calumet Calumet & Hecla and Quincy operations. operations. Torch Quincy Torch Lake has been more than 20% filled with stamp sands from both the and conglomerate conglomerateore orebodies bodiesofofthe thedistrict. district. The The relatively relatively inert inert stamp stamp sands sands have have aa amygdaloid and stronger aesthetic impact than a chemical one. On stamp sands, much stronger sands, little little vegetation vegetation grows, grows, and and ponds, toxic toxic levels levels of of Cu Cu may may be be found. found. Other on the surface of poorly drained ponds, Othertrace traceelements elements that may be be elevated elevated and and of of environmental environmental concern include Cr, As, and Ag. In the 11970s, 970s, tumorous tumorous sauger saugercaught caughtby byfishermen fishermenininTorch TorchLake Lakewere werethe the focal focal point point of In concern, and and the the site was was eventually eventually designated designatedas asaa superfund superfund site. site. No cause environmental concern, cause for for defmitively determined, determined, and and sauger, sauger, which which live live in in murky murky water, water, are are no no longer longer the tumor was ever definitively found in Torch Lake, which is less turbid now than it was when tailings tailings was was entering entering itit regularly. regularly. One interesting result of the environmental studies on the lake, was the observation of environmental studies on the lake, was the observation of a bottom enriched in in Sn Sn and and Pb. Pb. These sediment plume in the lake (Fig. 26) which was highly enriched Theseenrichments enrichments due to to mill mill wastes wastes are not part of the the geochemistry geochemistry of native Cu deposits, and are believed to be due which date to the post war era era (1945-68) when electrical wastes from a large part of the the midwest midwest were channeled through the Calumet & & Hecla Hecla mill mill at at Tamarack. Tamarack. 27.7 Mill, built built in in 1890 to accommodate Now we pass the remains of the main buildings of the Quincy Mill, steam stamps. The mill mill was was required required when the the Quincy Quiincy operation operation expanded expanded to to the the Pewabic Pewab'ic Lode. Lode. 28.0 Along the road road on on the the left leftare aremore moreoutcrops outcropsof offlat-lying flat-lyingJacobsville JacobsvilleSandstone. Sandstone. STOP 10: M-26 STOP M-26near nearTamarack Tamarack(Jacobsville (JacobsvilleSandstone) Sandstone) Jacobsvile Sandstone and quartzose quartwse sandstones, sandstones, The Jacobsville Sandstoneisis aa fluvial fluvialsuccession succession of of feldspathic feldspathic and conglomerates, siltstones, siltstones, and and shales shales up up to 1,000 1,000 m thick (Fig. (Fig. 27) 27) Filling filling a rift-flanking rift-flanking basin basin conglomerates, 1982). There or cross-cutting cross-cutting dikes. dikes. The (Kalliokoski, 1982). There are are no no interbedded interbedded lava flows or The age age of of the the Jacobsville is inferred of geologic geologic evidence evidencetotobe beabout about1070 1070toto1030 1030m.y. m.y.old. old. The infened on the basis of Jacobsville Sandstone Sandstone is in fault contact contact with the PLV along the Keweenaw Fault on the the southeast southeast along the fault side of the theKeweenaw Keweenaw Peninsula. Peninsula. Some active movement movement along fault occurred occurred during during deposition of of at least deposition least part part of ofthe theJacobsville JacobsvilleSandstone Sandstone(Kalliokoski, (Kalliokoski, 1988; 1988; Hedgman, Hedgman, 1992). 1992). Ancient current current directions directions in in the the Keweenaw Peninsulaare are to to the northeast Ancient Keweenaw Peninsula northeast and east, east, which which northeast of of Keweenaw Keweenaw Bay Bay (Fig. (Fig. 21b). 21b). West suggests transport to deeper parts of a basin located northeast West and current current directions directionssuggest suggestanother anotherdeep deeppart parttotothe thebasin. basin. East East of of of Lake Gogebic, thickness and Calumet, near the Keweenaw Fault (Stop 12), the Jacobsville contains boulders boulders of of Calumet, Keweenaw Fault Jacobsville Sandstone contains basalt--which suggests suggestsaa topographic topographichigh highininthe thePLV PLVnorth northofof the the fault fault during during this this period period of of basalt--which Jacobsville sedimentation—due to reverse movement along the Keweenaw fault. sedimentation-due to reverse movement along Keweenaw fault. Jacobsville Jacobsville sedimentation sedimentation was was the the last last event event associated associated with the the development development of the the Mid-continent Mid-continentrift rift system system by a long period of cratonic stability. in the Keweenaw Keweenaw Peninsula and was preceded by stability. Lithology of sandstones varies from subarkose sandstones of the Jacobsville Jacobsville Sandstone varies subarkose to quartz sublithic arenite. arenite. There arenite. Grain Grain size size varies varies from from fine fine There are are some some beds of arkose and quartz arenite. to coarse. coarse. Quartz grains show show evidence evidence of of volcanic volcanic and and metamorphic metamorphic origin. origin. Microcline is unaltered- to to highly-altered. highly-altered. Other Other clasts clasts include: include: volcanic volcanic relatively unaltered and plagioclase is unalteredrocks, schist, muscovite, and chlorite. Sandstone schist, shale, shale, and the the minerals: minerals: epidote, biotite, muscovite, Sandstonevaries varies in color from red to aa cream-white color. The cream-white or purplish-red purplish-red color. The color color depends depends on the the alteration alteration of of ferromagnesian minerals and and the the amount amount of of iron oxide ferromagnesian minerals oxide deposited deposited as rims rims on on feldspar feldspargrains. grains. Ripple marked bedding surfaces and cross-bedding common in in some localities. Sandstones Sandstones cross-bedding are common are fluvial, fluvial, and and conglomerates conglomerates probably probably represent represent alluvial alluvial fan fan deposits deposits (summarized (summarized from from �MeinRoadLog 57 TORCH TORCHLAKE LAKESEDIMENT SEDIMENT pprn ANOMALIES IN INppm ANOMALIES Figure26: 26: Contoured Contouredconcentrations concentrationsof of Pb Pband andSn Snininsediment sedimentand andstamp stampsand sand in inTorch TorchLake Lakeand and Figure vicinity (fromRose Roseand andothers. others,1986). 1986). vicinity(from �58 MsinRowlLng A B >I Current Directions Km. C Figure ofofJacobsville Figure27: 27:Relationships Relationships JacobsvilleSandstone Sandstone(from (fromKalliokoski, Kalliokoski,1982). 1982).A.A.Thickness ThicknessofofJacobsvilte Jacobsville Current directions Sandstone '+'. B.B. Current directionsininthetheJacobsville Jacobsville Sandstone with with minimum minimum thickness thickness denoted denoted by '+'. C. Location Location of of possible possible source source areas areas of ofiron ironformation formationand andofofstaurolitic staurolitic Sandstone. C. Sandstone. metasedimentaiy clasts. �MainRoidLfl Main Road Log 59 Kalliokoski, Kalliokoski, 1982). 1982). The outcrop at this stop (Stop 10), lo), about 120 120 m long long and and 33 m mhigh, high,displays displaysfeatures features characteristic of the fluvial Jacobsville Sandstone. At the northeast end of the outcrop, the characteristic At the northeast end of the outcrop, thesection section exposes red shale and red-brown at the the level level of of the the highway. highway. They are red-brown siltstone at are overlain overlain by by two two fining-upward sequences of conglomerate conglomerate and red, red-brown, red-brown, and and white white crossbedded crossbeddedsandstone. sandstone. The lower conglomerate bed is is planar planar and and can can be be traced traced 30 m to the southwest, along with the conglomerate bed underlying shale and siltstone. Farther to the southwest, underlying shale Farther to the southwest, the the section section is is almost almost entirely entirely crossbedded crossbedded red sandstone, sandstone, in beds 0.2 0.2 m m toto1.0 1.0mmthick, thick,some someofofwhich whicharearecontorted, contorted,conspicuously conspicuously crossbedded, and color mottled. Crossbeds Crossbedsshow showaanortheasterly northeasterly transport transportdirection. direction. The sandstone consists of almost equal parts of rounded-to-subrounded quartz, feldspars, feldspars, and lithic fragments. fragments. Clasts in the the lower lowerconglomerate conglomerate are arepredominately predominately subangular, subangular, felsic felsic volcanic in composition, entire section section can be be rocks. The entire volcanic composition, with with subordinate subordinate mafic mafic volcanic volcanic rocks. interpreted as a shaly flood plain sequence overlain overlain by by sandy sandy fluvial fluvial deposits. deposits. The interpreted The Jacobsville Jacobsville Sandstone fills a rift-flanking basin southeast of the the rift rift proper. proper. At this stop, the character of the Jacobsville Sandstone can be compared and contrasted to Jacobsville that will be seen at Stop 11 11 and Stop 12. 12. 28.3 28.3 On the right right is is Torch Torch Lake. Lake. 28.7 have been been revegetated. The Enter Tamarack City. On On the theright right side side of the road are tailings which have The Hecla Company Mines Mines and of the Calumet tailings are part of the mill operation of the Calumet & Hecia region, which have have major major mills mills located located atatTamarack Tamarackand andHubbell. Hubbell. 29.15 On 29.15 Onthe theleft leftside sideofofthe theroad roadare arethe thefootings footingsfrom fromone oneof of the theTamarack Tamarack Mills. Mills. MAP 7 are the the remains remains of a steam steam stamp stamp mill. 29.6 On the right side of the road are 29.7 Turn left, going up the hill toward 9. Follow toward Stop 9. Follow the the paved paved road road which which jogs a little little to to the the left left and goes up the hill. hill. 29.85 Cross 29.85 Crossthe theold oldCopper CopperRange Rangerailroad railroadgrade. grade. 30.0 30.0 Hungarian Falls. Falls. This is A sign indicating the Hungarian is the the lower lower part of the the falls, falls, continue continue going up the the hill, straight ahead. 30.25 30.25 The Thejunction junction of ofaafour-wheel four-wheeldrive driveroad road isisto tothe theleft. left. Stop here and walk toward the the Tamarack Tamarack Reservoir/Hungarian Falls upper part, where excellent exposures of Jacobsville Sandstone are Reservoir/Hungarian Falls upper part, where exposures of found near the the Keweenaw Keweenaw Fault. Fault. STOP 11: STOP 11: Hungarian HungarianFalls Falls(Keweenaw (Keweenaw Fault) Fault) Hungarian Falls is located near the the Keweenaw Keweenaw Fault Fault (Fig. (Fig. 28). 28). The The Keweenaw Keweenaw Fault is is a reverse fault that juxtaposes older PLV and the the younger younger Jacobsviile Inthis thislocality, locality, Jacobsville Sandstone. In presumably dips dips at at a high angle to the west, the Keweenaw Keweenaw Fault presumably west, similar similar to that that illustrated illustrated in in Figure 25. At Atthe thesurthee, surface,the theKeweenaw KeweenawFault Fault varies varies from from aa single singlefault fault plane plane to to aa more more complex complex fault zone, such 5.85). The such as as described near Lac La Belle (Leg D, mileage 5.85). Thestructural structuralrelationship relationship of beds near the fault also varies from steepened dips to folds. In In general, general, the the dip dip of of the the PLV PLVand and �60 MOIDROa4LOg Map8 — I I I I I I I 1 I Map6 �Main Log ~mRo.d ~ o ~do g 6161 Tamarack reservoir metal grat Jacobsville Jacobsvilie 100 sandstone sandstone feet z— D fault fails basalt Conglomerate Figure Figure28: 28:Geologic Geologicsketch sketchmap mapofofthe theHungarian HungarianFalls Fallsarea area(unpublished (unpublishedmap mapby byJ.M. J.M.Robertson, Robertson.1973, 1973. Basalt and conglomerate are part of the pan of the Portage Pomge Lake Lake from Bomhorst Bomhorstand andothers, others.1983). 1983). Basalt and conglomerate from Volcanics. Volcanics.Note Notethat thatnorth northisistoward towardthe theleft left margin marginof ofthe thepage. page. �62 62 zinRoadI.og Main Road Log Jacobsville Sandstone steepen appropriately as one one approaches approaches the the fault. fault. Falls, the fault contact causes very At Hungarian Falls, very little deformation of the Jacobsville Jacobsville Sandstone, which is only tilted slightly. To the west of the fault, at this site, the Portage Sandstone, which is only tilted slightly. the west of the fault, at this site, the Portagelake lake Volcanics are are unusually unusually shallow shallow dipping. dipping. If not viewed viewed in the context context of of many many other otherlocalities, localities, the fault fault might not be be recognized recognized as as such such aa profound profound feature feature and could could appear appear as as aaconformable conformable contact. The Thecontrast contrastbetween between the the fault fault exposure here at Hungarian Falls and that at the Natural Wall, Stop 12 12 (the (the next next stop), stop), isis striking, striking, and and illustrates illustrates the structural structural variability variability of rocks rocks along along this major major feature. feature. PLY near the Keweenaw Fault at Hungarian Falls consists of basaltic lava The PLV lava flows flows with with interbedded conglomerate. Interbedded sediments make up a small part of the stratigraphic section interbedded interbedded sediments make up small stratigraphic However, here here and and at a arefound foundas asrelatively relatively thin, thin,widely widely separated separated beds. beds. However, of the PLY PLV and and are within the the PLV PLY are either number of other localities in the Keweenaw Peninsula, conglomerates within near, or at, at, the the fault faultcontact. contact. along the the stream to to the upper and lower falls, allows examination Walking downstream, along of good of good exposures exposures of of Jacobsville Jacobsville Sandstone Sandstone with with cross cross bedding; bedding; interbedded interbedded shaly shaly and and conglomeratic horizons; and many typical typical arkosic arkosic redbed sedimentary sedimentary rocks. rocks. 30.25 Go 30.25 Goback back to tothe thecars carsand andgo goback back down down the the hill hill to to Tamarack Tamarack City. 30.8 Stop sign. Stamp Stampmill mill remains remains are are straight straight ahead. Turn Turn left left on on M-26. M-26. 30.9 Entering Hubbell. 31.5 On the right are the Calumet Calumet & & Hecla Hecla Mill buildings that are now being used for small small industries. industries. Torch Lake is still still on on the the right right with with many many of of the the tailings tailings in in the the lake. lake. 32.4 Entering the town of Lake Linden. The The Houghton Houghton County Historical Museum is on the right side of the road. The Thebuilding building(1917) (1917)was wasdonated donatedby bythe theC&H C&H(Calumet (Calumetand and Hecla) Hecla)Company Companyto tothe the Houghton County County Historical HistoricalSociety Societyinin1963. 1963. Among the best best displays displays are are scale models models of Houghton Among the underground mines and a rich rich photographic photographic record of the the boom boom copper copper days. days. 33.2 Turn right on on Ninth Ninth Street Street (the (the so-called so-called Bootjack Bootjack Road) Road) in in Lake Lake Linden. Linden. 33.35 Turn Turnleft lefttwo twoblocks blocksafter after 32.2. 32.2. Follow Followthe thesigns signsto to the the Lakes Lakes Drive-In Drive-in Theater. This ThisisisGregory Gregory Street. Street. MAP 88 cemetery. The road heads north along the Trap 34.3 On the left side of the road is the Lake Linden cemetery. Rock River Valley. On the left side of the road, On the left side of the road,atatthe thetop topof ofthe thesteep steepslope, slope,isisthe theKeweenaw Keweenaw right side side of of the theroad, road,isisflat-lying flat-lyingJacobsville Jacobsville terrane. terrane. The Trap Rock Rock River River Fault. Fault. On the right follows follows another another of of the the glacially glacially eroded, eroded, deep deep bedrock bedrock valleys valleys described described by by Warren Wamn (1981). (1981). 35.5 35.5 Pavement ends. 35.6 The gravel road bears to the right. right. 35.9 Cross over the the Trap Trap Rock Rock River. River. Cross a bridge over �Main Road Log 63 MAP �64 M-i" i Log 36.0 at the the Trap TrapRock RockSchoothouse. Schoolhouse. Turn left left at Thrn 36.0 36.0 Cross the Trap Rock River River again. again. 36.7 36.7 Turn left on another dirt road that begins to go go up up hill. hill. 37.1 37.1 railroad grade grade of of the the Copper Copper Range RangeRailway. Railway. Access Access to the Natural Cross the railroad Natural Wall Ravine for this railroad railroad mapping purposes can be gained by walking a couple hundred yards to the left along this and then then walking walking up up the the stream stream valley. valley. The traverse begins in grade until the first major valley, and Jacobsville Sandstone, crosses the Keweenaw Fault, and ends in the PLV at the head of the stream As the road valley. As road parallels parallels the stream stream valley valley a few few hundred hundred meters meters to to the the north, north, it is is recommended that one return via overland and the road. 37.2 37.2 Poor exposures of flat-lying conglomerate beds within within the the Jacobsville Jacobsville Sandstone Sandstone are are on on the left conglomerate beds side of the the road. road. 37.4 path on the left side of the road, about 200 m, for an overlook Stop here and follow a path overlook of the The bottom of the ravine provides an excellent traverse Natural Wall Wall Ravine. Ravine. bottom the ravine provides an excellent traverse across across the the Keweenaw Fault. Fault. To Keweenaw To gain gain access access to to the the bottom bottom of the the ravine, ravine, go back down the road road 0.3 0.3 miles miles to mileage mileage 36.1. 36.1. STOP STOP 12: 12: Natural NaturalWall WallRavine Ravine(Keweenaw (KeweenawFault) Fault) about 200 200 m m south south of of the the gravel gravel road road at the top of aa steep There is a ravine ravine overlook overlook about steep slope. and just just east of the Keweenaw Fault (Fig. 29). 29). This locality is in Jacobsville Sandstone and The Natural Wall is is aa vertical verticalbed bed of of resistant resistant trough-bedded trough-bedded sandstone sandstone that forms forms an an erosional erosional wall on the south The Jacobsville Sandstoneinin this this area consists wall south side side of of the the ravine. ravine. The Jacobsville Sandstone consists of conglomerate; sandstone; and shaly horizons, possibly accumulating accumulating as the lower portion portion of of the the formation dragged along the Keweenaw Fault. Fault. The The attitudes attitudes of beds beds in in the the creek creek bottom bottom change change from flat-lying, about 1 km to the east east of of the the fault; fault; to to east-dipping; eastdipping; and finally to vertical, vertical, and then the beds are folded as the Keweenaw Fault is approached. approached. West West of the the fault fault the the PLV PLV dip dip to to The latest movement on the Keweenaw Fault is reverse, but the fault the WNW at 35-40°. WNW at 35-40'. movement on the Keweenaw Fault is reverse, but the nonnal growth fault on the southeast originated as a major normal southeast margin of the Midcontinent rift system (Cannon and others, 1990). Deposition Deposition of of the the Jacobsville Jacobsville Sandstone Sandstone was controlled by the same same compressional the Keweenaw KeweenawFault. Fault. Also at this locality, the Jacobsville compressional tectonism that produced the Sandstone contains abundant boulder boulder sized clasts of felsic and mafic mafic volcanic volcanic rocks, rocks, similar similarto to Keweenawan volcanic rocks. rocks. The Keweenawan volcanic The Keweenawan Keweenawan volcanic rocks were exposed and undergoing undergoing as a result of uplift along the erosion during Jacobsville sedimentation as the Keweenaw Keweenaw Fault. Fault. 38.95 The Thebeginning beginningof of pavement; pavement; we we air areentering enteringthe thetown town of ofLaurium. Laurium. 39.7 39.7 Turn left, followed immediately by by a right turn at the next stop stop sign sign on on School School Street. Street. 39.8 The junction of School Street and Calumet Avenue, Avenue, which which isisUS-41. US-41. Turn right. This ThisisisCalumet, Calumet, Michigan, the center center of of the Michigan Copper District, District,and andthe the site site of of the Calumet Michigan, the Michigan Copper Calumet & Hecla Hecla headquarters. the Calumet Conglomerate load load in in the early headquarters. Here, Edwin Hurlbut discovered discovered the Calumet Conglomerate early 1860's, which was ore body body in in the the whole whole district. district. Greater Calumet was to to become the most important ore (including (including Red Jacket, Jacket, Blue Blue Jacket, Jacket, Yellow Yellow Jacket, Jacket, Laurium Laurium and and Rambaultown) Rambaultown) had had aa population population �___ Math Log 65 Portage Lake Volcanics aKeweenaw a aa a aa Fault a aa u Natural Wall Jacobsville Sandstone .1? 1 1 = \\i t CALUMET CALUMET 11111111 I AND AND I I I I I I "i/' (\ -I It I I ^i\ SCALE SCALE In In thousands thousands of of feet feet HECLA HECLA U' 1 m I . 2 0 9 + I. I. I I GRAPE GRADE I. 111111. 1983). Note Figure 29: 29: Geologic Geologicsketch sketchmap mapof ofthe theNatural Natural Wall Wall Ravine Ravine (from (from Bornhorst and others, 1983). Note Figure that north is toward toward the the right right margin margin of the the page. page. north is �66 MainRotdLfl of 33,000 in 1910. Among Amongthe the many many historic historic buildings, buildings, are the Calumet Theater (1900) and the Community Library Library Building Building (1898). (1898). Immediately behind behind the Calumet High School and C&H Community the blue water tower is the the surface surface location location of the great great Calumet Calumet & Hecla Hecla Conglomerate, Conglomerate, the "Mother Lode" Lode" of of the the district and the the principal ore body body where where more more than than one one third third of all "Mother district and principal ore all Michigan copper was mined. mined. Excavations of a cross section of this great ore body is planned as Excavations body part of the the new new Keweenaw Keweenaw National National Historic Historic Park. Park. MAP 9 41.0 Entering Centennial. Centennial. 41.3 On the left side of the road you can see No. 6. After see the Centennial Mine Shaft No. Afterclosing closingin in1968, 1968, this mine was 1970's by Homestake, but the operation was dewatered dewatered in in the the midmid-1970's Homestake, but operation has has since since been been abandoned. Nos. 3 and 6 worked worked the the Calumet and and Hecla Hecla Conglomerate. Conglomerate. The The Centennial Mine Shaft Nos. The ore ore body lies up-dip and northeast from the main ore body body in the C&H Conglomerate mined by the Calumet and Hecla Mine in the Calumet area. area. The The C&H C&H Conglomerate Conglomerate yielded about 1.9 billion kg of mfmed refined copper, the the largest largest lode in the the district, district, and is is over over one-third one-third of of the the total total production production from the Keweenaw district (total (total district district production productionofofabout about 55 billion billion kg). kg). The Keweenaw native copper district The C&H lode had the highest grade in in the the district district of of 2.85% 2.85% Cu Cu per per ton ton of rock treated highest average average grade treated (Weege and Pollack, Pollack, 1971). 1971). The Calumet and Hecla Conglomerate can can be be followed followedalong alongstrike strikefor formore morethan than65 65kkm. rn. Along most of this length, most length, it is less than about 11 m thick. In the Calumet Calumet area, area, it averages over 3 m with depth. depth. The thick and tends to thicken with Thebed bed consists consists of of north north trending, trending, thicker thicker and and thinner thinner channels. At the Centennial Mine Shaft Nos. Nos. 3 and 6, thickness is often less zones representing channels. than 3 m channel. The m and and the the C&H C&H Conglomerate Conglomerate was deposited in a tributary stream channel. The pebbles pebbles in the the conglomerate conglomerate at at Centennial Centennial are are almost almost all allquartz-feldspar quartz-feldspar phenocrystic phenocrystic rhyolite. The pebbles pebbles in the the main main channel channel conglomerate conglomerate are are quite quite a varied suite of rhyolite and granophyre, granophyre, with with phenocrystic rhyolite. rhyolite. Main and tributary channel conglomerates conglomerates tend tend to to be some quartz-feldspar phenocrystic coarser and contain less fine material material where where it's it's thicker. Outside Outside of of the the 1.5 1.5m m thickness thickness contours, contours, the bed is usually shaly shaly or sandy. sandy. At AtCentennial, Centennial,copper coppermineralization mineralization tends tends to to occur occur in in bands bands with with the bed, bed, and and the the intensity intensity is is related related to to the the type typeand andamount amount of ofinterstitial interstitial material material and and or barriers. bathers. Higher location of pinch-outs or Higher grade grade areas areas are related to conglomerate with coarse sand or small when pebbles pebbles and and sand grains are quartzsmall pebbles pebbles as as interstitial interstitial material, material, especially especially when quartzfeldspar phenocrystic rhyolite. Evidence Evidence also alsostrongly strongly suggests suggests that that the the mineralized mineralizedareas areasfollow follow the axis of stream stream channels and grade grade is highest highest adjacent to the 1.5 1.5 m m thickness thickness contour, contour, where where bed increases greatly greatly in in thickness thickness down-dip. down-dip. These pinch-outs localized ore the conglomerate bed deposition from mineralizing solutions that were were migrating migratingup-dip. up-dip. Sedimentological Sedimentological relationships deposition relationships are important in in exploring exploring the the conglomerate conglomerate ore bodies bodies (summarized (summarized from Weege Weege and and Pollack, Pollack, 197 1). 1971). 41.6 41.6 Entering Kearsarge, Kearsarge, Michigan. 42.1 42.1 A stone boat on the right right side side of of the the road. road. 42.3 mm onto Water Street, just Turright n right onto Water Street, justbefore beforethe theWolverine WolverineMarket. Market. Continue Continuestraight straight ahead on the 42.3 main paved road. road. 42.5 right and and Park along along the road and walk about about 100 100 m to the north. Mine rock piles are on both the right left sides of the road. Keep Keeptotothe theleft leftside; side;the theones oneson onthe theright rightside sideof ofthe theroad road(south)—on (south)-on the �Map 10 Map MthaRoMtOS MAr 6') �68 MainRoadLog dangerous because of bad ground. other side of some some old old buildings—are buildings-are dangerous ground. Mining in this area area was very shallow (Shaft No. No. 3). BEWARE: THEPATHWAYS PATHWAYS because because these these are are OLD OLD BEWARE:STAY STAYON ONTHE mined areas. STOP 13: STOP 13: Wolverine WolverineMine MineShaft ShaftNo. No.2 2(native (nativecopper copperdeposit depositwithin withinPortage Portage Lake Lake Volcanics Volcanics [PLVII) [PLW) Flow top deposit was was worked worked by by the Wolverine Mme Mine and seven The Kearsarge Flow seven other other Kearsarge, North North Kearsarge, Kearsarge, Ahmeek, Ahmeek, Allouez, Allouez, Mohawk, Mohawk, and and Seneca mines: Centennial, South Kearsarge, (Fig. 30). Production Production of of copper copper from from the the Kearsarge Kearsarge Row Flow top top began began in in 1887 1887and and stopped stoppedin in 1967. 1967. About 1026 1026 million kg of refined copper copper were produced at an average average grade grade of 1.05% 1.05% Cu, Cu, making making the Kearsarge deposit deposit the the largest largest flow flow top top deposit deposit and and the second largest largest ore producer in the the Underground workings workingsare are continuous continuousfor formore morethan than 12 km km and extend down-dip as district. district. Underground much as 2,500 m. The TheKearsarge Kearsarge deposit deposit is is one one of the best documented orebodies in the district (Stoiber and Davidson, 1959; 1959; Butler and Burbank, 1929). 1929). The Kearsarge Flow flow has has been been recognized recognized for for aa distance distance of of about about 55 55 km along strike. strike. It lies directly Sandstoneand and dips dips between between35 35 and and 40" 40° N NW directly above above the Wolverine Wolverine Sandstone W (Fig. (Fig. 30). 30). Stratigraphic and textural relationships make this flow easily easily recognized. recognized. It has an an amygdaloid amygddoid top that ranges from near zero up to 10 m in thickness. In the productive area, the flow top is from zero up to 10 m in thickness. productive area, a brecciá. breccia. Individual Individualfragments fragmentsare aregenerally generally less less than than 15 15cm cm in in greatest greatestdimension, dimension, and and contain contain numerous small amygdules. amygdules. The flow numerous small flow top breccia breccia makes up the uppermost uppermost part of the the flow, flow, grading amygdules abundant abundant at certain horizons. grading downward downward into into layered cellular cellular amygdaloid, with amygdules This zone grades grades downward, first, into a zone of fewer and larger amygdules with fewer layered (Table 3). 3). Just structures, and then into massive basalt (Table Just below the flow top is a distinct plagioclase plagioclase porphyritic porphyritic basalt. The Theabundance abundanceand andsize sizeof of the theplagioclase plagioclase phenocrysts phenocrysts in in this this zone zone isisvariable, variable, but they can can make make up up a large percentage percentageofofthe therock, rock,and andcan canbe beup uptoto2.5 2.5cm cm in in length. length. This but zone is probably during in in situ crystallization of the flow. zone probably the result result of of plagioclase plagioclase floating floating during crystallization of flow. can be be found found on on this this rock rock pile. pile. The Specimens with abundant plagioclase phenocrysts can The porphyritic porphyritic zone grades downward into massive aphyric basalt. The Thetop topof of the theKearsarge KearsargeFlow Flowin. in the the mined mined area has an average average thickness of around 2 m. The basalt in the Kearsarge Flow flow is well by two types of well oxidized and has been affected by alteration: albitization albitization and and pumpellyitization. pumpellyitization, Albitized Albitized basalt basalt is about about 60% euhedral euhedral albite laths set in Pumpellyitized basalt basalt consists of finein aafine-grained fine-grainedtotocryptocrystalline cryptocrystalliinegroundmass. groundmass. Pumpellyitized fmegrained pumpellyite pseudomorphically replacing plagioclase. pseudomorphically replacing plagioclase. The amygdule amygdule and interfragmental space-filling gangue minerals in the Kearsarge deposit are generally (in order of most most to to least least abundant): abundant): calcite, epidote, K-feldspar, quartz, and lesser lesser amounts of chlorite, chlorite, prehnite, prehnite, pumpellyite, pumpellyite, laumontite, laumontite, and and sericite. sericite. Native copper is closely closely associated with the secondary amygdule minerals (Stoiber and and Davidson, Davidson, 1959). The Thesecondary secondary assemblages vary both temporally spatially within mineral assemblages temporally and spatially within the productive area. area. Paragenétically, chlorite; epidote; epidote; microclime; microcline; and and prehnite prehnite are are early-formed early-formed minerals, minerals, and and the Paragenetically, chlorite; latest-formed minerals are are quartz; quartz; native native copper; copper; calcite; calcite; and and chlorite latest-formed minerals chlorite (Fig. (Fig. 31). 31). A zonal zonal stratabound arrangement of amygdule minerals minerals in in the Kearsarge deposit is seen in the Ahmeek in the Ahmeek (Fig. 32 and Table Table 4). 4). The to bedding bedding but but irregularly Shaft No. 3 (Fig. The zones are approximately parallel to distributed laterally. the bottom to the top of laterally. From From the bottom to of the the flow flow top, top, are arefive fivemajor majormineral mineral ± calcite 2 ± microcline, assemblages: 1) chlorite 2 microclime, 2) quartz-epidote, 3) calcite-epidote, 4) calcitemicrocline + ± epidote, and and 5) 5) chlorite-calcite chlorite-calcite ± +microcline. microcline. The Thelast lastassemblage assemblage is is found found in in the the �Mrnnaoasl.og 69 A' A nil. 4000 It a Figure 30: Geologic Geologicmap mapand andcross crosssection sectionshowing showingthe theKearsarge KearsargeFlow, How,Wolverine WolverineMine, Mine,and andvicinity vicinity Figure 30: (modified from from White White and and others, 1953; from Bornhorst and others, 1983). 1953; from Bomhorst and others, 1983). Stop Stop 13 is the the mine rock rock pile. pile. Abbreviations are Wolverine Wolverine Mine Mine Shaft No. No. 2 mine are as as follows: Iroquois flow (pi); Hecia Conglomerate Conglomerate (pc); Osceola Osceola flow flow (po); (po); Kingston Kingston Conglomerate Conglomerate (pkc); (pkc); Calumet Calumet and and Hecla Wolverine Sandstone (pw); Old Colony Sandstone Sandstone (poe); (poc); St. St. Louis Louis Conglomerate Conglomerate(ps). (ps). Si02 sio; Table 3: 3: Major-element Major-elementcomposition compositionofof the the Kearsarge Kemarge Table Davidson, flow (from Stoiber and flow (from Stoiber and Davidson, 1959). 1959). This is is aaweighted weighted average avenge exclusive of the This the close thus 12 feet feet and thus represents represents a close top 12 of approximation approximationtoto the the original composition of theflow. the flow. A1203 *lz03 Fe203* Fe203* MgO MgO CaO CaO Na20 Na20 K20 K20 Ti02 Ti09 P205 p205 Mno HZ@+ H20— H20CO2 '32 Total T otal ppm Cu Cu Weight Percent 48.55 48.55 16.51 16.51 11.54 6.68 9.44 9.44 2. 82 2.82 0.58 0.58 1.49 0.18 0.16 2.06 0.63 0.15 100.79 90 �70 MtnRosdLOg =m SW sw ME NE Producbve 90 9 0'- jMes1 Thickncss60 meters 30 30 Top of Wolverine TopSandstone Sandstone of Wolverine H 1iez 4s- -I aI S.- u -, / a, "s Â¥ C C ea M 9 N "s s .a 5I N. N / N. / N \ 1 , / , N \ N N 4— N / SOUTH So.rrH 'CENTENNIAL KEARSARGE — -r OF AHMEEK 6 — — — c— MINING a k?1 Vexy high grade copperore Vqhighgnde-are - limit quat Upper limitof of quartz — e Upper d d N 5 WOLVERINE KEARSARGE — SENECA MOHAWK ALLOUEZ A LLOW wRm N N 0 600 I I 1200 + I SCALE SCALE metess meters Lower limit lint of of micncine microcliae — — * Lower — Figure 31: Figure 31: Thickness Thicknessofofthe theKearsarge Kearsargeflow flow(top) (top)from fromIsle IsleRoyale Royaleto toMandan Mandan(south (south of of Copper Copper Harbor) Harbor) of the showing location location of showing the productive productive area area (modified (modified from from Butler Butler and and Burbank, Burbank, 1929; 1929; from from Bornhorst, 1992) (see (see Fig. Fig. 77 and and 99 for for location). location). The The mined Kearsarge flow top (largest flow top Bomhorst, deposit, with 1026 deposit, 1026 million kg of refined copper production) is is bisected bisected by the the Allouez Allouez Gap Gap Fault Fault (bottom) with the high (bottom) with high grade grade copper copper zone zone northeast northeast of of the thefault faultassociated associatedwith withabundant abundant faults and fractures. fractures. Distribution subparallel faults Distribution of of amygdule-filling amygdule-filling quartz quartz (over (over 10% 10% on on hatchured hatchured aniygdule-filling K-feldspar/microclie K-feldspar/microcline (absent below line) roughly correlates correlates with native side) and amygdule-filling copper (modified (modified from Stoiber and Davidson, Davidson, 1959; from Bornhorst, Bomhorst, 1992). 1992). Amygdule-filling Arnygdule-filling present throughout throughout the the mine. mine. The TheKearsarge Kearsarge flow flow dips dipsabout about 350 35' to 40° 40 calcite and epidote are present northwest and all data projected to a horizontal plane. �MainkoadLog CHLORITE CHLORITE 71 11111110 IIIOIIIIIIIIVV MICROCLINE MICROCLINE Pr•hnlti Prehnlte H e m a tflt• lte Mimi EPIDO E P I D OTE TE P u m p e l.IyIt. /ylte Pump OILIllIIIIIIIIllIIIji. Quartz Quartz Serlclte Ssrlclt• N a t l v e Copper Copper Nativi CALCITE CALCITE Early Early TIME TIME Late Late Figure Figure32: 32:Paragenesis Paragenesisofofsecondary secondaryminerals mineralsininthe theKearsarge KearsargeAmygdaloid Amygdaloidat atthe the Wolverine WolverineMine Mine Shaft Shaft No. (from Bornhorst Bomhorst and others, 1988). The Therelationships relationships are are based based on on aa megascopic megascopic and and thin thin No. 22 (from section study of samples from the the Shaft No. No. 22 mine mine rock rock pile. pile. Compare Compare to district-wide district-wide synthesis synthesis of 12. of paragenesis paragenesisgiven given in inFigure Figure12. �i jnRoadLOg 72 sanH SOUTH — —.. çttt —— p ctte-.ciWott .::::tt Th - WORTH — we. — caftftrwadoM 7< — Footwal m-cwtetcta. SCALE SCALE 0 M m M " 00 aA 10 10 20 20 30 feat 30 feet cupp— copper Contact between Kea,sav. amygdaoW d ovemrp flow bottae, Figure Figure 33: 33: Cross Cross section section of of the theKearsarge Kearsarge Amygdaloid Amygdaloid showing showing the the banding banding of of amygdule amygdule mineral mineral assemblages, Ahmeek Mine, 35th level, 399 to 500 feet south of the Kearsarge Flow (modified Mine, south of the Kearsarge Row (modified from Stoiber Stoiber and and Davidson, Davidson, 1959; 1959:from fromBornhorst, Bornhorst. 1992). 1992). Data from the back back and and walls walls are are to aa horizontal horizontalplane. plane. In In one one mapped mapped locality, locality, Stoiber Stoiber and and Davidson Davidson (1959) (1959) found found aa projected to Arnygdulemineralogy mineralogy of of the the various various zones zones are are given given in in Table Table 44 laumontite-quartz-calcite zone. zone. Amygdule below. shown in in Figure Table Table 4: 4: Volume Volumepercent percentofofaxnygdule amygduleminerals mineralsfrom frommapped mapped assemblages assemblages shown Rgure 33 33 (from (from Stoiber and and Davidson. Davidson, 1959). 1959). Stoiber Mineral Mineral Assemblage Assemblage Band Band Chlorite Chlorite Chlorite— ChloriteMicrocline— MicroclineCalcite Calcite Microcline— MicroclineCalcite Calcite Quartz— QuartzEpidote Epidote CalciteCalcite— Epidote Epidote 0 0 0—1 90—96 00 00 87 87 12 12 0 trace trace Volume Volume Percent Percent kuydule Amydule Filling Filling Chlorite Chlorite Microcline Microcline Calcite Calcite Epidote Epidote Pumpellyite Quartz Quartz 100 100 00 69—74 69-74 15—25 15-25 0—5 0-5 0—1 0-1 0—6 0-6 0—5 0-5 1 2 00 trace trace 00 00 0—3 45—82 0—47 5—10 0—trace 0—8 2 4—9 2 11 1. �MiukoadLog 73 hanging wall wall comer corner in in Fig. Fig. 32). 32). The base of the overlying flow (north hanging The zoning may be be explained explained by deposition of secondary from a hydrothermal solution moving moving along along a permeable secondary minerals minerals from hydrothermal solution channel. Chlorite along the the outer limits of of the Chlorite and and microcline microcliie would would have been deposited first, along solution channel; channel; followed followedby byquartz quartzand and epidote epidoteinin the the center center of of the channel; solution channel; and finally, finally, deposition of calcite This observation is consistent deposition of calcite in in the theremaining remaining openings. openings. This observation is consistent with with the the paragenetic relationshipsseen seen in in individual individual samples. samples. No strict paragenetic relationships strict correlation correlation exists between the stratabound zoning and the grade of native-copper mineralization (Stoiber and Davidson, 1959). 1959). and grade grade of of copper copper mineralization mineralizationvary varywith withdepth. depth. The quartz The amygdule minerals and less than 10% at shallower content is considerably less shallower depths, and generally averages about 15% 15% An irregular irregularincrease increase in quartz content occurs within the quartz zone with within the quartz zone. An increasing depth. depth. The increasing The amount amount of of native native copper copper present present is much much more more irregular irregular than than the the depth depth zones. The variation of the mineral zones. The richest richest copper copper ore ore appears to follow the boundary for >10% >lo% The lower quartz. The lower limit limit of of microcline microcline may may also mark mark the the limit limit ofofsignificant significantcopper copper mineralization. On mineralization. Onaaregional regionalscale, scale,the theKearsarge KearsargeFlow Flow lies lieswithin within the the quartz quartzand andprehnite prehnitezones. zones. Detailed data suggests that quartzand prehnite-free 'islands' are present within the regional present within regional Detailed data suggests that quartz- and prehnite-free "islands" zones. zones. Microcline, calcite, calcite, chlorite, and epidote separated from amygdules amygdules from from rocks rocks collected collected off of this rock pile were used by Bornhorst and others (1988) to provide an absolute age of this rock pile were used by Bomhorst provide microcline, calcite, calcite, and and epidote epidote all allprecipitated precipitated simultaneously simultaneously with with mineral precipitation. precipitation. The Themicrocline, such as inclusions inclusions of of native copper and crossnative copper, as indicated by textural evidence such the Rb-Sr Rb-Sr method method to to these suggests an an age of cutting veinlets. veinlets. Application Application ofof the these minerals minerals suggests of mineralization of between 1060 and 1047 m.y. (+1— 20 m.y.). These results are consistent with m.y.). These results are consistent mineralization of between 1060 and 1047 my. (+Iother data rift system. system. data from from the the Midcontinent Midcontinentrift - The Allouez Gap Fault bisects bisects the the thickest thickest segment segmentof of the the Kearsarge KearsargeFlow flow along its 55 Higher grade grade and and production production occur occur northeast northeast of of the the fault where km strike length length (Fig. (Fig. 33). 33). Higher where fractures parallel to the fault are more abundant. abundant. Within the Allouez Gap Fault zone, early epidote fractures and quartz were brecciated and recemented by by more calcite; quartz; and native copper. Finally, Finally, after another major episode episode of brecciation, the fault zone was recemented with calcite; quartz; and lesser laumontite are clear clear indications indications that that movement movementalong along lesser laumontite (Butler (Butler and Burbank, 1929). The The data dataare and after deposition of native native copper. copper. The the fault occurred before, before, during, during, and deposition of Thefault faultapparently apparently flow top. top. The provided ore fluids to the permeable permeable flow Thecoincidence coincidence of of the the fault fault with with the therelatively relatively thick flow top resulted resulted in in the the second second largest largest deposit deposit in in the the district. district. Mine Shaft Shaft No. No. 22 rock rock pile, pile, you you will will have the opportunity to see a At the Wolverine Mine opportunity to variety of mineral assemblages and and their theft paragenetic parageneticrelationships. relationships. For For the Shaft Nos. Nos. 11 and 22 rock rock piles piles as as aawhole, whole,Stoiber Stoiber(unpublished (unpublished data) data) estimated estimated the the following following percentage percentage of amygdaloidal minerals: calcite, 51%; microcline, prehnite, 1%; and quartz, microcliie, 38%; epidote, 10%; prehnite, quartz, trace. In Inthe thevicinity vicinityof ofthe theShaft ShaftNos. Nos. 22and and33rock rock piles, piles, one onecan can find find outcrops outcrops of of the the Kearsarge Kearsarge flow copper can can be found in specimens from this rock pile. This, and other Plow interior. interior. Native copper other Kearsarge Mine Mine rock rock piles, piles, illustrate illustrate the the complexity complexity of of flow flow top ore bodies Kearsarge bodies in in the the Keweenaw Keweenaw Peninsula Peninsula native native copper copper district. district. 42.5 Continue on the same road and and in in the the same same direction direction as as before before (east), (east), away away from fromKearsarge. Kearsarge. 43.1 43.1 right. We are now now in in the the vicinity vicinity of of Scales Scales Creek, which is Stop at the din dirt road junction junction to the right. We are Flow. This the type section of the Scales Creek Plow. This is is the the same same flow flow seen seen at at Stop Stop 1, 1,about about 22 22 km km to to the south, in Houghton. south, Houghton. �74 MainRoadL.og STOP 14: STOP 14: Scales ScalesCreek Creek(Portage (PortageLake LakeVolcanics Volcanics[PLVfl [PLY) This stop stop provides an opportunity to view the Scales Creek Flow, a regionally extensive extensive basaltic flow. It has been traced for more more than 30 30 km km along along strike strike in in the the Keweenaw Keweenaw Peninsula. Peninsula. Outcrops of the Scales Creek Flow can be seen on both sides of the main main road road and and along along Scales Scales Creek, just just north and paralleling paralleling the the road. road. This flow was studied, from drill cores northeast of This flow was studied, here, by Scofield characteristically ophitic, ophitic, with an amygdaloidal amygdaloidal Scofield (1976). (1976). The The Scales Scales Creek Flow is characteristically top and base, and a massive massive interior. The Themassive massive interior interior is, is, for for the the most most part, part, geochemically geochemically unaltered unaltered (Table 5), with with the thefollowing followingestimated estimated modes: modes: plagioclase, plagioclase, 40%; 40%; pyroxene, pyroxene, 48%; 48%; opaque oxides. 2%. Primary plagioclase; pyroxene; and opaque oxides can be olivine, 10%; 10%; and oxides, Primary plagioclase; chlorite. Although found, but but olivine olivine isis pseudomorphically pseudomorphically replaced replaced by by talc; talc; serpentine; serpentine; and/or andlor chlorite. Although the massive massive interior of the the flow flow contains contains both both primary primary and and secondary secondary minerals, minerals, it remained remained aa for water water flowing flowing away away from from fractures fracturesthat thatcut cut the the interior. interior. The chemically closed system except for The massive nature of the the interior interior inhibited inhibited movement movement of of hydrothermal hydrothermal fluids. fluids. In the amygdaloidal amygdaloidal are present; all have by a suite flow top, no primary primary minerals minerals are present; all have been been replaced replaced by suite of of secondary secondary alteration products. Plagioclase is now albite with some some replacement by sericite, sericite, chlorite, chlorite, and and clinopyroxeneisis replaced replaced by by chlorite; chlorite; olivine olivine is is replaced replaced by by chlorite, epidote and pumpellyite; clinopyroxene pumpellyite; and opaque oxides are altered to hematite and sphene sphene (Scofield, (Scofield, 1976). 1976). 43.1 43.1 Turn around and retrace the route back to US-41. US41 43.7 Passing the Wolverine Mine rock piles (Stop 11). 11). 43.9 Turn right on US-41 US41 at at Wolverine Wolverine Market. Market. 45.2 Entering the Village of Allonez. Allouez. We We have have an an excellent excellent view of the southeast side of a prominent ridge. This ridge is held held up up by by the theGreenstone Greenstone Flow, Flow, which which isis the the thickest, thickest,and andvolumetrically, volumetrically, flow within within the the PLV. PLV. It will largest single flow will be seen seen at Stop 16. 16. 45.4 Turn left on aa paved just before a gas station. paved road road called called Bumbletown Bumbletown Road, just station, 45.6 Stay on the the main main paved paved road, road, bearing bearingright. right. the road 45.75 the right right at at the the dirt dirt road. road. Walk Walk the road to the the mine mine rock rock piles piles of of the theAllouez Allouez 45.75 Park on the Conglomerate Mine. Conglomerate Mine. STOP 15: STOP 15: Allouez Allouez(conglomerate (conglomerateininPortage PortageLake LakeVolcanics Volcanics[PLY]) [PLV]) The rock piles here are are from from the the Allouez Allouez Conglomerate Conglomerate Mine, which operated operated from from 1869 1869 to 1892 about 1.2 1.2 million million kg kg of of copper. copper. The one of of a 1892 and and produced produced about The Allouez Allouez Conglomerate Conglomerate isis one horizons within within the the PLV PLV (Fig. 9). These sedimentary small number of interfiow interflow sedimentary sedimentary horizons sedimentary horizons are important important for stratigraphic correlations within the otherwise otherwise monotonous pile of basalt horizons stratigraphiccorrelations basalt This bed bed can be traced lava flows of the the PLY. PLV. This traced along along strike from the tip of of the theKeweenaw Keweenaw Peninsula west and south, to at least the Mass area, aa strike length length of of more more than than 120 120 km. km. It It is is one one of the of the most mostcontinuous continuous sedimentary sedimentary horizons horizons in in the theKeweenaw Keweenaw Peninsula. Peninsula. The Allouez Allouez Conglomerate is exposed in underground workings at Stop 8--Quincy Mine Adit, Hancock--and in underground workings at Stop Stop 30--the 30Ñth Delaware Delaware Mine. It is is stratigraphically stratigraphically just below the the Greenstone Flow, the thickest flow in the PLY--prominent PLV-prominent in the northern half of the the Keweenaw Keweenaw Peninsula. Like Likeother otherirnerflow interflow conglomerate conglomerate beds within within the PLY, PLV, the the Allouez AUouez Conglomerate Conglomerate consists conglomerate with lesser amounts amounts of of sandstone sandstoneand andsiltstone. siltstone. These red-colored consists of mostly conglomerate �MainkoadLog Mill Rod Log 75 75 clastic clastic sedimentary sedimentary rocks rocks where where deposited deposited in aa terrestrial terrestrial alluvial alluvial fan fan environment environment with with dominant dominant transport of sediment sediment from the margins margins of the rift, rift, toward toward the the center center (current (current center center of of Lake Lake Superior) Superior) during during aa hiatus hiatus of ofvolcanic volcanicactivity. activity. The The rock rock piles piles from from the the Allouez Allouez Conglomerate Conglomerateillustrate illustrate features of interfiow interflow sedimentary sedimentary beds conglomerate. The largest beds of the PLy. PLV.The Therock rockpiles pilesprovide providean an excellent excellent view of "clean" conglomerate. boulders in this conglomerate conglomerate are about 65 cm in diameter, diameter, and the median median size is about 8 cm. cm. A A pebble pebble count count of of boulders boulders more more than 20 20 cm cm across across gave the following results: mafic rock, mostly amygdaloidal, 16%;quartz quartzporphyry, porphyry, 36%; 36%;feldspar feldsparporphyry, porphyry, 11%; 11%;and and granophyre, granophyre,37% 37%(White, (White, amygdaloidal,16%; 197 lb). The 1971b). Theheterogeneity heterogeneityof ofthis thisassortment assortmentsuggests suggestsaa less less restricted restricted source sourceterrane terranethan than the theone one that supplied the Kingston and Houghton Conglomerates in this area. For example, the Kingston Conglomerates in this area. For example, the Kingston that supplied the ~ i n ~ s t o n is made made up up almost almost entirely entirely of fragments fragments of quartz-feldspar porphyry, but bedded red sandstone sandstonecan can also be be found found in in some somespecimens. specimens. Little evidence evidence of native copper mineralization Occasionally, Little mineralization is is present present in in this this rock rock pile. pile. Occasionally, one can find find aaspecimen specimen with with native native copper copper filling filling the the void void space space between between clasts clasts and and grains. grains. Calcite and arethe thedominant dominantpore-filling pore-filling secondary secondary minerals. minerals. In slabs, and chlorite chloriteare slabs, almost almost every every feldspar is associated feldspar phenocryst phenocryst is associated with with a tiny tiny speck speck ofofnative nativecopper copper(Kalliokoski, (Kalliokoski,personal personal communication, 1988). Thin are calcite, calcite, full full of of Thin black black veinlets veinlets cutting the Allouez Conglomerate are chalcocite dust. Supergene Supergenealteration alterationresulting resulting from fromthe the downward downward percolation percolationof of groundwater groundwaterisis rare in in Keweenawan Keweenawan native native copper copper deposits deposits of of the theKeweenaw KeweenawPeninsula. Peninsula. Here however, however, the the effects effects of of supergene supergene alteration alteration is quite visible visible as chrysocolla; chrysocolla; malachite; and cuprite cuprite are are present present in in numerous numerous samples. samples. 45.75 Continue Continueon onthe themain mainpaved pavedroad roadtotothe thetop topofofBumbletown BumbletownHill. Hill. 46.1 46.1 right on on Cedar CedarStreet. Street. Turn right 46.3 46.3 The top top of of Bumbletown Bumbletown Hill near the communication towers. The hill hill isis visible visible to to the thenorthwest northwest The towers. The while traveling traveling from from Calumet Calumet to to Allouez. Allouez. STOP STOP16: 16:Bumbletown BumbletownHill Hill(Allouez (AllouezGap GapFault) Fault) Bumbletown Hill is located on the southwest side of the Allouez Allouez Gap, Gap, aa north-trending north-trending valley. The valley follows the Allouez Gap Fault, a zone of faults and fractures, along valley. The valley follows the Allouez Gap Fault, a zone of faults and fractures, along which which the the PLV swings from from about about N35°E N35'E PLV and and Keweenaw Keweenaw Fault are offset. At At this this gap, gap, the the strike strike of of the the PLV swings to to N50°E. N50T. From this location on a clear day, day, Isle Royale may be seen--80 s e e n 4 0 km to the northwest--and the Bay--60km km to to the the southeast. southeast. The seen beyond beyond Keweenaw Keweenaw Bay-60 The land land the Huron Huron Mountains Mountains may be seen slopes very gradually to the northwest toward Lake Superior, as it does throughout most of the length of the Keweenaw Peninsula. The The southeast southeast flank of the Keweenaw Peninsula has a steeper slope at the skyline, the line line of of the the Keweenaw Fault. The skyline, following following approximately approximately the Keweenaw Fault. Thelow-lying low-lying plain between between the the fault fault and and Keweenaw Keweenaw Bay. Bay, isis underlain underlain by by flat-lying flat-lying Jacobsville Jacobsville Sandstone. Sandstone. northeast along along the the strike strike of of the the PLV, PLy, one can see the cuesta form of the Looking northeast the ridge ridge upheld by the Greenstone How. flow. At Bumbletown Hill, this flow is only 85 m thick, but it thickens At Bumbletown Hill, this flow is only 85 m thick, but it thickens than 400 m at the near near end of of the cuesta cuesta ridge. ridge. To abruptly to more than To the the right right of of the the Greenstone Greenstone ridge, the more more distant distant hills hills are are formed formed by by lava lava flows flows lower lower in in the thesection. section. �76 76 l.ainao.dIog ~ a i n~ o a d ~og - The Allouez Gap Fault follows the SE trending valley, near the relatively new headframe. headframe. The Almost every permeable horizon horizon near near the the Allouez Allouez Gap Gap Fault Fault contains contains above above average average amounts amounts of of native copper; nowhere else in the district are are there there so so many many mineralized mineralizedbeds. beds. About 60% 60% of the district production can be linked to the fault as a primary primary pathway pathway for for ore ore fluids. fluids. The district The fault fault bisects bisects the Kearsarge deposit, deposit, which which isis the the second secondlargest largestproducer producerininthe thedistrict district(Fig. (Fig.32). 32). The The line line of of rock piles demarking its location is a little more than than 1500 m m southeast southeast of of Bumbletown Bumbletown Hill. Hill. The The large "new" headframe, 2000 m m east east of of the the hilltop, hilltop, is is the the Kingston Kingston Mine. Mine. This headframe, 2000 This small small deposit deposit produced 9 million kg of of copper copper (1963-1968), (1963-1968). and is bisected bisected by the the Allouez Allouez Gap Gap Fault Fault (Fig. (Fig. 34). 34). About About 1200 m of the the hilltop hilltop is is aa deposit, deposit, at at N65°E, N65¡Ewhich which produced produced 15 million million kg of copper copper (1944-1964) from from the the Houghton HoughtonConglomerate Conglomerateand andthe theIroquois IroquoisFlow Howtop. top. The rock piles (1944-1964) piles just below the hill top at in the theAllouez AUouez Conglomerate Conglomerate which which produced 34 at Stop Stop 15 15are arefrom from mines mines in million kg of copper. copper. The outcrops on the top and upper slopes of of Bumbletown Bumbletown Hill Hill represent represent aa series series of of basalt basalt porphyritic. They range up and andesite flows; some flows are slightly porphyritic. up to to 20 20 m m in in thickness, thickness,and and and lithologically lithologically similar similar to to those those whose tops were as a group group are are stratigraphically stratigraphically equivalent and mined at the Quincy Mine, just just north north of Hancock. mined Hancock. Unlike Unlike the the basaltic basaltic flows flows found found below below the the Houghton Conglomerate, these flows have little lateral/strike direction continuity. Two flows Houghton Conglomerate, these flows have little lateral/strike direction continuity. Two flows 1971b). pinch out on the top of of Bumbletown Bumbletown Hill (Fig. 35) (White, 1971b). layers which which Some of the exposed flow tops on Bumbletown Hill are slabby pahoehoe layers have experienced runout of much of the mass of the lava flows. lava The Greenstone Flow is exposed Greenstone Flow exposed in a series series of of outcrops outcrops 160-300 160-300 m southeast southeast of of the the top isis exposed exposedatat the the end end of of a private roadway hilltop. Its thick amygdaloidal southhilltop. amygdaloidal top roadway 200 m southsoutheast of the hilltop. Columnar Columnarfine-grained fine-grained basalt basalt and and ophitic ophitic basalt basalt can can be be seen seen in in exposures exposures farther down the slope. slope. Allouez Allouez Gap Gap is is an an important important physiographic feature feature of the the Keweenaw Keweenaw Peninsula Peninsula (Fig. (Fig. 18). 18). It contains the largest accumulation of glacial sediments north of Portage Lake. The gap is accumulation of glacial sediments north of Portage Lake. is the the lowest elevation elevation that cuts cuts across across the peninsula between Portage Lake and the tip of the peninsula peninsula (Regis, 1983). AAnumber numberof of kettles kettlesalong along aa northwest northwest trend trend occur occur within within the gap gap (Fig. (Fig. 36). 36). Retrace the 1. the route routeback backtotoUS-4 US-41. 47.2 At the the junction with with US-41, US-41, turn turn left leftand andcross crossinto intoKeweenaw Keweenaw County Countyfrom fromHoughton HoughtonCounty. County. 48.1 48.1 Entering Ahmeek. Ahmeek. junction to Cliff Drive. Turn Turnleft left on onCliff Cliff Drive. Drive. 48.4 The junction MAP 10 10 mad. We near the the base base of of 48.65 Passing PassingSeneca SenecaLake Lake on on the right side of the mad. We are are driving driving along strike, near the Greenstone Flow. Along Alongthe the road road are are several several small outcrops of basalt, mostly on the left side of the road. road. 51.7 At this point, the Greenstone Flow abruptly thickens thickens to to nearly nearly400 400m m(Fig. (Fig.37). 37). It dips northward at about 25° center of of the the Midcontinent Midcontinentrift. rift. This lava flow can be traced along much 25' toward the center of the Keweenaw and has been stratigraphically and geochemically geochemicaily correlated with a similar unit on Isle Royale, 90 km away, on the other side of the rift. Thus, Thus, the the areal areal extent extentof of this this great greatflow flow km2,and its volume volume is is on on the the order orderof of 800-1500 800-1500km3, km3,according to White White (1960) (1960) exceeds 5000 5000 km2, �10 MSRoadLog 77 MAP 10 �. 7878 ~ a i n~ o a d~ o g MainRoadLog LEGEND 0 0 80 Melen 165 250 330 - 500 750 loo0 Feet Contour Interval 5 feet 250 m i OVERBURDEN MINED OUT AREAS 1 SHAFTS AND LEVELS HORIZONTAL PLAN MAP Figure ofof thethe Kingston Figure34: 34:Thickness Thickness KingstonConglomerate Conglomerateatatthe theKingston KingstonMine Mineshowing showingthe thebisecting bisectingAllouez Allouez 1972; from Bornhorst, 1992). Ore ends abruptly Gap Fault (modified from Weege and others, Gap Fault (modified from Weege and others, 1972; from Bornhorst, 1992). Ore ends abruptlyatat the thethickness thicknesspinch-down pinch-downon onthe thesouthwest southwestend endofofthe thedeposit depositwith withsome someofofthe thehighest highestgrades gradesinin edge of the orebody is gradational. the themine minenext nexttotothe thepinch-down pinch-downwhereas whereasthe theeastern eastern edge of the orebody is gradational.The The 400. bottom bottomlevel levelisis350 350mmdeep deepon onthe theincline inclineatat 40'. �MainRoedLog 79 OSt £0 LA AMYGDALOID 00 I--I 2000 2000FEET FEET 1000 1000 -- I I I I I Figure Figure35: 35:Outcrop Outcropmap mapofofthetheAllouez-Bumbletown Allouez-BumbletownHill Hillarea area(from (fromWhite, White,1971b). 1971b). Table5: 5: Avenge Averagecomposition compositionof ofthree threesamples samplesfrom fromthe themassive massive part part of of the theScales ScalesCreek Creekflow flow(from (from Table Scofield,1976). 1976). Scofield, weight Weight Percent Percent Ssio2 i02 47.57 47.57 20 10 16. 16.10 3 Fe203* Fe203* 12.54 12.54 MgO MI30 7.67 7.67 CaO CaO 10.00 10.00 Na20 Na20 2.24 2.24 K20 K2 0.29 0.29 Ti0, Ti02 Total Total 1.43 1.43 97.84 97.84 �80 MainRoudLog SL1F'St 0 sano OW4ES —1 I o5jTHI%; b- • —.Iloo•. - 1 — GREENs ro,sj - . .,—-_.. ot-ra•941! -=-. ——_GAP 2'--.::.. -' 876' -- -— 4.. -. - -- Figure36: 36:Physiographic Figure Physiographicand and glacial glacial features featuresof ofAllouez AllouezGap Gap (from (fromHughes. Hughes,1963). 1963). �RoadLog Thickness Thickness (feet) (feet) 81 Top 'op of Flow Flow Vesiculated Flow Flow Top Top / / / // // / / / / /,.1 / / // f / / /'• A;z.: columnar Jointed Jointed EM: Columnar Melanophyre 285 UOp: uop: Upper Upper Ophite Ophite 225 Pg 3rd Pg: 3rd Pegmatoid Pegmatoid Zone Zone / /// / / // :; / / tPgt// /UOpSJ/o/ / / 680 / i Ø?Pi' EM / t 'IV! / 'ii' I/I 1/ /___._ 1 /// /i Ii / / SCALE I; ityille — Sub—ophite Pg: 2nd Pegtnatoid Zone Z sub—opizite Pg: 1st Peginatoid Zone LOpE Lower Lower Ophite Lop: Ophite Vertical Scale: 1"=200' 1"200' Vertical Scale: Figure 37: Figure 37: Geologic Geologicsketch sketchmap mapand andstratigraphic stratigraphicsection sectionshowing showingvertical vertical zones zones within within the the Oreenstone Greenstone (fromLongo, 1983). 1983). flow between Seneca and the Cliff Mine (from �82 hflRoadLog composite Roza Ron flow and Longo (1983). It rivals the composite How (Columbia (Columbia R.) as as the the largest largest known lava flow on Earth. The TheGreenstone GreenstoneFlow Flowtypically typically shows showsspectacularly spectacularlydeveloped developedpegmatites, pegmatites,ophitic ophitic horizons, and columnar jointed jointed areas. areas. The flow near The pegmatoid pegmatoid zone within the Greenstone Flow near this this (Fig. 37). 37), and and the ophitic ophitic zones zones are are relatively relativelyunaltered. unaltered. Longo (1983) location is unusually thick (Fig. (1983) has shown that the composition of these zones are remarkably constant and demonstrated the great chemical chemical similarity similarity of the composition of the Isle Royale and Keweenaw ophitic exposures exposures of the the Greenstone Plow. Flow. The flow at The rapid rapid thickening thickening of the Greenstone Greenstone Flow at this this point point was was suggested suggested by White (pers. comm., comm., 1982) 1982) to to be be caused caused by by the separation of the the upper upper part part of the flow separation of flow into into multiple flow units, multiple flow units, which which appear to be be separate separate flows. flows. To the the north, north, the flow may may be aa continuous, single flow unit, while to the south, it may have been made made up of of many many flow flowunits. units. MAP 10 10 and and 11 11 52.1 52.1 Crossing the the Gratiot Gtatiot River. River. MAP MAP 11 11 side of of the prominent ridge which which isis held held up up by the 52.7 are now now driving driving on on the the southeast southeast side prominent ridge the 52.7 We are Greenstone Flow. Flow. 54.6 54.6 This is the the site site of ofthe theCliff CliffMine, Mine,which which was was the the first firstmine mine ininthe thedistrict, district,and andoperated operated discontinuously from from 1845 1845 to to 1887. 1887. The discontinuously The rock rock piles piles and and old old footings footings for for the the mine mine building building are are mainly on the left side of the road and the town site, of which little remains, remains, is on the right side side of the road. road. STOP 17: STOP 17: Cliff Cliff Mine Mine (native (nativecopper coppervein vein deposit) deposit) (see cover photo) photo) The Cliff Mine worked the Cliff Fissure from 1845 1845 to 1887, and produced a total total of about about 38 million lbs. portion lies under under the Greenstone Greenstone Flow. Flow. The Ibs. of of refined refined copper; the productive portion The Cliff Fissure is nearly at right angles to to the the attitude attitudeof ofbedding beddingand anddips dipssteeply steeplytotothe theeast. east. Most of the mineralization mineralization was confined to the fissure, although some amygdaloids were mineralized (summarized from Butler and Burhank, Burbank, 1929). Many Many large large masses masses of of native native copper copper were were mined mined from the Cliff Cliff Mine and and larger larger masses weighed weighed up to 100 100 tons. One Onelarge large100 100ton, ton mass masscould could not be blasted, so pieces (Clarke, (Clarke, 1976). Among so it had to be cut by hand into smaller pieces Among the the fissures, fissures, the Cliff was the most productive of silver. In Inaddition additionto to native native copper copperand and silver, silver,the the Cliff CliffMine Mine produced the the following following minerals (not (not in order of abundance): calcite, epidote, chlorite, laumóntite, laumontite, prefinite, clatolite, thomsonite, chlorastrolite, chiorastrolite, galena, galena, apophyllite, apophyllite, adularia, gypsum, sphalerite, prehnite, datolite, thomsonite, sphalerite, pyrite, and surface surfaceoxidation oxidation minerals. minerals. sometimes shows shows quite quite The Greenstone Flow at this locality is mainly ophitic basalt and sometimes developed coarse coarse columnar columnarjointing. jointing. The Greenstone Flow is described in more detail well developed Greenstone How detail at at mileage 50.7. The junction of of US-411M-26. US-41/M-26. Turn Turn left left(north). (north). MAP 12 12 55.5 Entering Phoenix. Phoenix. 55.2 56.6 Turn just before (0.1 (0.1 mile) mile)the thejunction junctionbetween betweenUS-41 US-4land andM-26. M-26. It is about T urn left on a dirt dirt road just 100 m from the paved road road to the base of the Phoenix Mine rock rock pile pile which which is is Stop 14. �Map 12 Map MtoRLsg MAP 83 �84 itin Road Loz Map 11 1. �MainRo*diog 85 STOP 18: copper STOP 18: Phoenix PhoenixMine Mine(native (native coppervein veindeposit depositand andPortage PortageLake Lake Volcanics Volcanics [PLy]) [PLV]) The Phoenix Mine worked worked numerous numerous veins veins below belowthe theGreenstone GreenstoneFlow. Flow. Like the Cliff Mine discussed Mine was was one of the earlier discussed at Stop 17, the Phoenix Mine earlier mines mines in the the district district and and operated off off and and on on from from 1849 1849to to 1917. 1917. The vein was worked worked to to a vertical vertical depth depth of of about 300 operated m, with varied (average grade grade around around 1.5%). 1.5%). Since the vein cuts thin lava flow m, varied grade (average flow tops, tops, no no mining was done on adjacent mineralized flow flow tops. tops. The Phoenix Mine produced a total of about milling 17 million Burbank, 1929). 1929). It also also worked worked the the Ashbed Ashbed million lbs. Ibs. of of refmed refined copper copper (Butler (Butler and and Burbank, Amygdaloid where where itit is mineralized, mineralized, in in the the vicinity vicinity of of vein vein copper copper occurrences. occurrences. The Amygdaloid The Phoenix Phoenix Mine rock pile Mine pile is notable notable for for halfbreeds halfbreeds (native (native copper copper plus plus native nativesilver), silver),spectacularly, spectacularly, and chlorastrolitic pumpellyite pumpellyite (Michigan (Michigan"greenstone"). "greenstone"). Listed below are are crystallized analcite and some other minerals that have been reported in the Phoenix Mine area (Clarke, 1974a): some other minerals that have been reported the Phoenix Mine area (Clarke, 1974a): pumpellyite, chlorite, chlorite, natrolite, natrolite, and andapophyllute. apophyllite. To look at the Greenstone flow you Greenstone Plow you must must climb climb over the rock pile and then pass one one of of zones just just above above the the shaft. shaft. Proceed the fissure zones Proceed ahead and climb to the base of the the steep steep cliffs, cliffs, which are composed of a portion of the Greenstone flow, an which composed of portion of the the massive massive flow flow interior interior of Greenstone Flow, an representing the the greatest greatest single single outpouring outpouring of of enormous lava flow over 400 m thick, and perhaps representing Earth. lava on Earth. ophitic zone zone occurs occursnear nearthe thebase baseofofthe theGreenstone GreenstoneFlow Flow(Fig. (Fig.38). 38). By A very coarse ophitic along the the cliff, the pegmatoid; pegmatoid; subophitic; subophitic;and and ophitic ophitic zones zones can can all all be following the exposures along observed. From Fromthe thetop topof of the theGreenstone Greenstone Ridge, Ridge, there is aa view view of of the the strike strike of of this this great great flow flow and of the town site of Phoenix, which had a population of 1,000 from 1877-1887. the town site of Phoenix, which had a population of 1,000 from 1877-1887. The Greenstone Flow has been identified for a distance of 90 km along the length length of of the the Keweenaw Peninsula, as well as throughout the length of Isle Royale, 90 km northwest northwest on on the the Keweenaw Peninsula, 90 km opposite limb of the Lake line. The extent is 5000 km2 with with volume volume of of 800 to to 1500 1500 opposite Lake Superior Superior Sync Syncline. km3 (Longo, Very slow slow solidification solidification of this great mass of magma magma allowed allowed (Longo, 1983; White, White, 1960). 1960). Very resulting in in aa massive, ophitic zone at the base of of the the extensive in-situ magmatic differentiation, resulting flow; an overlying overlying zone of intercalated subophitic and pegmatoidal layers; an upper ophitic zone; and aa fine-grained, 195laa and ii). b). The lower lower ophitic ophitic zone zone fine-grained, vesicular vesicular flow flow top top (Cornwall, (Cornwall, 1951 low enough enough to to allow allow growth growth of of clinopyroxene cinopyroxene oikocrysts experienced rates of undercooling low oikocrysts up to 5 cm in in diameter. diameter. the Greenstone GreenstoneFlow flow magma is more evolved than typical The geochemical composition of the olivine tholeiites; tholeütes; which constitute the greatest volume volume of ofthe thePLV. PLy. Primitive Primitiveolivine olivine tholeiite tholeiite and and quartz tholeiite occur between between the the Greenstone GreenstonePlow Flowand andthe thetop topof ofthe thePLV. PLV. Generally, magmas with time time during the Midcontinent rift become more primitive and less crustally crustally contaminated contaminated with changes in in magmatic magmaticand andtectonic tectonicprocesses. processes. A model of magmatic and development, reflecting changes rift evolution based on on PLV PLV data data involves involves primitive primitive parental parental magma magma modification modification by complex, complex, open-system fractional crystallization crystallization in in large reservoirs reservoirs at at the base of the thinned thinned crust crust (Paces, (Paces, 1988). The Theresulting resultingolivine olivinetholeiite tholeiitemagma magma is is either either erupted at the surface or supplied supplied to to smaller smaller chambers at higher evolved tholeiites and silicic higher levels levels where where further farther crystallization crystallization produces produces evolved rocks. rocks. differentiation of of the the Greenstone Greenstone Flow flow was described The chemistry and petrology of differentiation described in papers by Cornwall Cornwall(1951a. (1951a. 1951b). 1951b). �86 86 Main ill Road ~ o a Log d~ o g Thickness Thickness (feet) (feet) u Ii Iii Ill Top Top of of Flow Plow M l : Melanophyric Melanophyric Zone Zone Ml: IJOp: Upper Ophite Ophite UOp: Upper Pg: Pg: Pegniatoid Pegmatoid Lenses Lenses with intercalated i n t e r c a l a t e d lenses lenses with of Of ophites o p h i t e s and and sub—ophites sub-ophites -Sub-ophite Sub-ophite -Pg:Peginatoid PegmatoidZone Zone Pg: Sub—ophite -Pg: Zone ....—Pg: Pegmatoid Zone PHOENIX / 7 Lop: LOP: Lower Lower Ophite Ophite SCALE SCALE 00 -Sub—ophite Sub-ophite - Pegmatoid Zone Zone —Pg:Pg: Pegntatoid Imul. 1 mil. Bottom off Flow Bottom o Flow V e r t i c a l Scale: S c a l e : l"—200' 1"-200' Vertical Figure Figure38: 38:Geologic Geologicsketch sketchmap mapand andstratigraphic stratigraphicsection sectionshowing showingzonation zonation of of the the Greenstone Greenstoneflow flow near near Michigan (from (fromLongo. Longo, 1983). 1983). Phoenix, Michigan �~ a i Road n~ o rLog ~i o t 87 6: Avenge Table 6: Averagecomposition compositionofofthe theGreenstone GreenstoneFlow Flow (Longo, (Longo, 1983). 1983). Si02 SiO, A1203 A1203 FeO' MgO Mgo CaO CaO Na20 Na,O K20 K@ Ti02 TiO, P205 p 205 wt.% 46.7 15.1 15.1 12.8 12.8 7.8 7.8 9.9 9.9 2.1 2.1 0.4 0.4 1.2 1.2 0.14 0.14 Ba Cr Cu La Mn Ni Rb Sc Sn Sr Y Zn Zr rrn 104 214 66 11 1680 186 S 28 6 259 14 84 92 'Total TotalFe Feas asFeO. FeO. 56.8 Thm Turn left left on on M-26 M-26 toward toward Eagle Eagle River. Cross CrossCentral CentralCreek Creek and and begin begin to to drive driveperpendicular perpendicularto to strike and cross the the Greenstone Greenstone Flow. Flow. 56.9 56.9 At ~t 9:00 9:00(on (on the the left), left), the the Phoenix Phoenix rock rock piles piles and and cliffs cliffs of of the the Greenstone GreenstoneFlow Flow are arereadily readilyvisible. visible. 57.1 57.1 Cross Cross Eagle Eagle River. River. 57.2 57.2 Outcrops the left left of of the the road. road. Exceptionally coarse ophitic texture, Outcrops of the Greenstone Flow are to the individual pyroxenes with individual pyroxenes up to 5 cm can be found on these exposures, which represent represent the the slower slower cooling middle middle of of the the flow. flow. 57.6 There is a pull-out on the right right hand hand side side of of the the road. road, flows Flowsabove abovethe the Greenstone Greenstone flow Flowcan canbe be Eagle River. River. The seen along Eagle The river river is is about about 25 25 m m from from the side side of the the road road and and in in this this locality, locality, there are many deep pools. You You can can follow follow the the river river downstream from here all the way to Eagle River, looking at many many flow flow contacts. contacts. This This can't can't be bedone done in in the thehigh high water water periods periods of of spring. spring. At Stop 19, 19, just up the the road, road, one one can can begin begin aa traverse traverse along along Eagle River. 57.9 57.9 Pull over over at at aa poorly poorly maintained maintained dirt dirt road road pull-out pull-out on the the right. right. At this locality, locality, Eagle River River crosses the Ashbed. There is a very sharp bend in Eagle River north of the Ashbed Flow. There is a very sharp River north of the Ashbed Flow. From here it is is possible possible to to begin begin aatraverse traverse along along Eagle Eagle River River either either upstream upstream or ordownstream. downstream. STOP 19: Eagle STOP EagleRiver River(Portage (PortageLake LakeVolcanics Volcanics[PLV]) [PLV]) Eagle River, Jacobs Creek, and Owl Creek each make excellent stream traverses of the PLY. PLV. At ~t this thispoint, point,approximately approximatelyatatthe the Ashbed, Ashbed, aa traverse traverse along the stream north to Eagle River observations of of the the upper upper stratigraphy stratigraphyofofthe thePLV. PLy. The allows excellent observations The Ashbed Ashbed isisdescribed described at at Stop 20. Stop 20. Eagle River River traverses traverses the the section section shown shown in in Figure Figure 39; along the traverse, you see: Eagle see: 1) 1) excellent sections sections through through individual lava flows flows showing tops, and and massive excellent individual lava showing amygdaloidal amygddoidal tops, massive melaphyric, glomeroporphyritic, glomeroporphyritic,ororophitic ophiticflow flowinteriors; interiors;2)2) the the best best section melaphyric, section of entablature entablature jointed basalt in the Keweenaw Peninsula, Peninsula, which which can can be be reached overland by walking columnar jointed �88 88 ~ i m aid LMaiDROSI.Sg COPPER COPPBHARBOR CONGLOMERATE CONGL —I of Copper Sitor ,t—,,eiete Dø.liic fl.-s mans flow pqmstutic DØatic flo.t ffi 'tow cnirwlitic .ofiyrtv thief rboss sJ'fltfy Ila,.tl00r,l,ntic aM ophitic conglomerate (No. 17) Mj,bed amygdlo,dfl'd IrwISPAYflt. - I MSn'tm; thtwr -' uloa.ropflqd* ed pegtn.tittc 0_f_s Finr.mS nwIsoNnt. pomtrit'c Gacat.roPofDiiwitic ISO., Glonwrmofdhnttielk- .umr(hiltion* Upoer chill son, Pme'ttMnne Greenstone flow Â¥Greenston flow PORTAGE PORTAGE LAKE LAKE LAVA LAVA SERIES SERIES lo- • Optsitic bewail — I Figure Figure39: 39:Stratigraphy Stratigraphyofofthe thePortage PortageLake LakeVolcanics Volcanicsabove abovethe theGreenstone Greenstoneflow flowininthe thevicinity vicinityofofEagle Eagle River and and Phoenix, Phoenix, Michigan Michigan (from (fromCornwall Cornwall and and Wright, Wright, 1954). 1954). �MainRoadI.og Main Road Log 89 89 a few hundred meters of sediments with with the the lava flows, which meters downstream; and 3) interbedding of becomes more prevalent prevalent up up section. section. If you decide to take this traverse, traverse, it's best to to just resign resign yourself to wet feet. The traverse is not advisable in the spring because of high water. yourself The traverse is not advisable in the spring because water. 58.0 Pull over opposite to the outcrops on the left side side of the the road. road. STOP STOP 20: 20: M-26, M-26,Eagle EagleRiver River(Portage (PortageLake LakeVolcanics Volcanics[PLV]) [PLV]) horizon that can can be traced traced over a distance of almost 25 The Ashbed is a very distinctive horizon km tan in outcrop outcrop and drill drill holes. ItItisisthe thevesicular vesicularzone zonebelow below the theHancock HancockConglomerate Conglomerate(Fig. (Fig. 39 39 and Map 12). The TheAshbed Ashbed isisexposed exposed on on the the SE SEend end of of the the outcrop outcrop (away (away from from Lake Lake Superior), Superior), and is is overlain overlain on on the the NW NW end end by by the the massive massive interior interior of of the the overlying overlying basalt lava lava flow flow dipping dipping Lake Superior). Superior). The about 225°NW 5 W (toward Lake The weathered outcrop outcrop has a rubbly appearance, appearance, but in in the the water-washed low exposures exposures in the the drainage drainage ditch ditch alongside alongside the the road, road, 55 to to 15 cm diameter diameter clasts clasts basalt set in aa fine of vesicular vesicular basalt fine matrix matrix isis clearly clearly visible. visible. The clasts are subrounded, subrounded, and in in general, the Ashbed is a jumble of of vesicular vesicular basalt basalt fragments fragments and an an interstitial interstitial brown-to-gray, brown-to-gray, matrix. The fine-grained matrix. Thesecondary secondary minerals minerals filling filling the the void void spaces spaces are are calcite, calcite,quartz, quartz, chlorite, chlorite, of Cu Cu (White, (White, 1971b). 1971b). Small mines were and minor epidote. Some Some vesicles vesicles contain minute flecks of places, from from Atlantic Atlantic Mine Mine (near (near Stop Stop 3) 3) to Owl Creek (Stop found along this horizon in many places, Bi). Bl). The Ashbed includes includes rocks rocks characterized characterized as pyroclastic, and those interpreted interpreted by Johnson Johnson On Eagle Eagle River, River, the Ashbed Ashbed is only only the the pyroclastic pyroclastic horizon horizon and (1985) as as hyaloclastite. hyaloclastite. On stratigraphically separate separate is is another another horizon horizon consisting consistingof of aa pillowed pillowed lava lava sequence overlain overlain by by stratigraphically The pillows are about hyaloclastite (Johnson, 1985). 1985). The pillows are about 50 cm in in diameter diameter with with red red oxidized oxidized margins. 58.3 58.3 Go downhill toward Lake Lake Superior. Superior, which which is is visible visible at at the the treeline. treeline. 58.6 The Evergreen Cemetery on the the left left was was established established in in 1843. 1843. 58.9 River. On Leg FF -- Five Mile Point Entering Eagle River. On the the left left is is the road to Five Mile Point (begin Leg The stone monument is a memorial Houghton who who was was the the first State here). The monument is memorial to Douglass Douglass Houghton Geologist of Michigan. He Hedid didpioneering pioneering geologic geologic studies studies in the Keweenaw Peninsula. In In1845, 1845, he drowned off Eagle River. drowned off Eagle River. 59.1 59.1 Cross Eagle River on the Eagle River Bridge. Park ParkNE NEof of the thebridge. bridge. Eagle River Falls Falls STOP 21: 21: Eagle Conglomerate) Conglomerate) (contact of Portage (contact of Portage Lake Lake Volcanics Volcanics and and Copper Copper Harbor Harbor between the the top top of of the the PLV PLV and and the base of the Copper The falls occur at the contact between Copper Harbor Conglomerate. There are some spectacular potholes potholesthat thathave havedeveloped developedon onthis thisface. face. Ifif the water is low, low, like like itit is is sometimes sometimes in the summer, summer, you can see ropy surfaces on flows at the top of the the PLV PLV which which indicate indicate the flow was erupted from a vent to the north (the center of the the dips about 30 30° NNW. NNW. The rift now under under Lake Lake Superior). Superior). The contact dips Thecontact contactrelationships relationships suggest very very little erosion between between the the flow flow and deposition of the conglomerate beds of the suggest deposition of conglomerate beds the Conglomerate. Under Copper Harbor Conglomerate. Under the the bridge, one can get a good view of the lithology of of the the lower part of consists of of mostly lower of the theCopper CopperHarbor HarborConglomerate. Conglomerate. It It consists mostly rhyolite rhyolite pebble pebble conglomerates, but includes many sandstone and even some shale shale beds. beds. �90 itoñ Follow Follow M-26 with a sharp sharp left turn, just after after the the bridge. bridge. 59.2 59.2 Sharp right turn. 13 MAP 13 62.15 Jacobs JacobsCreek CreekFalls. Falls.From Fromthis thispoint, point,one onecan canbegin begin aatraverse traverse up up Jacobs Jacobs Creek Creek that ends near the Arnold Mine on the Garden City Road. There are excellent exposures of the upper part of of the the Arnold Mine Garden City Road. There are excellent PLV along Jacobs PLV Jacobs Creek. Creek. For those who who are are hardy, hardy, the the stream stream offers offers virtually virtually continuous continuous through thin thin pahoehoe pahoehoe flows, flows,especially especiallyininthe thefirs firstseveral severalhundred hundredmeters. meters. This is a exposures through steep and rough traverse, traverse, and and should should not not be be attempted attempted in in high high water waterperiods. periods. 64.0 64.0 level Great Sand Bay. bay.The m esand WIU dunes uunca at at the US<- road i,&el are areremains remains of of the the Lake LakeNipissing Nipissing Stage Stageof of the the Lake Superior Superior Basin. Basin. Cat Harbor. The TheLake LakeShore ShoreTraps Traps form form the the offshore offshore ridge, they are mafic to intermediate lava flows within the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. MAP 14 14 the Eagle Eagle Harbor Harbor Store. Store. 66.9 Turn right by the 66.9 65.0 M-26 makes makes aa sharp sharp bend bend to to the the right. right. Continue straight toward the Eagle Harbor Harbor Lighthouse. Lighthouse. 66.95 M-26 67.0 sharp left left to to the the lighthouse. lighthouse. Make a sharp 67.1 The Eagle Eagle Harbor Harbor Lighthouse Lighthouse parking parking lot. lot. STOP 22: Eagle EagleHarbor HarborLighthouse Lighthouse(Lake (LakeShore ShoreTraps) Traps) PLEASE DO NOT USE TillS SITE. USE ROCK HAMMERS AT THIS SITE. The Eagle Harbor Harbor Lighthouse Lighthouse is maintained maintained as aa museum museum by by the theKeweenaw Keweemw County County Historical HistoricalSociety. Society.AAlighthouse lighthousebegan began operation operation here here in in 1851, 1851, four four years prior to the completion completion Harbor Lighthouse. Lighthouse. The of the Soo S w Locks, and two years after the Copper Harbor The current current building was constructed in 1871, and and the light was was automated automated in in 1980. 1980. The constructed in The position position of the the lighthouse; lighthouse; the shape of the harbor; harbor; and and the the many many islands islands and and shallow shallow rocks along the shore shore facing facing the the big big lake lake (climb the wooden steps northwest of the lighthouse for the best view) are controlled controlled by the Lake Lake Shore Traps. The Thetraps trapsare areaaseries seriesof ofresistant resistant basaltic basaltic lava lava flows flows that that occurs occurs within within the the Copper Copper from Harbor Conglomerate Conglomerate and which outcrop along the Keweenaw shore shore for for more more than than 14 141cm, km, from Harbor. These m.y., about 7 m.y. Great Sand Bay to Agate Harbor. These lavas are dated at 1087 1087 m.y., m.y. younger than the PLy, the PLV, and andtogether togetherwith withthe theMichipicoten Michipicoten Island IslandFormation, Formation, represent represent the the youngest youngest Keweenawan igneous rocks known (Paces (Paces and and Miller, Miller, 1993). 1993). Start Start at the west end of the parking lot, about 25 m from the Maritime Museum. AA small small Lake Shore Shore Traps Traps are are cut cut by by aa number number of of small small veins veins ravine occurs here because the well-exposed Lake up to about 2.5 cm wide, in a zone about 30 cm wide trending N-S, perpendicular to the shoreline. about cm wide, in zone about 30 wide trending perpendicular to the shoreline. although bedding bedding is not The Lake Shore Shore Traps Traps are are dipping dipping about about 25°N 25% toward toward Lake Superior, although obvious. Prominent Prominentjoints joints ininthe themassive massiveinteriors interiorsof offlows flowssometimes sometimesapproximate approximatethe the attitude attitude of bedding. From Fromthe theparking parkinglot lottoward toward Lake LakeSuperior, Superior, aa massive massive interior interior of aa flow flow isis visible, visible, and grades into a vesicular-to-brecciated vesicular-to-brecciated flow top at the lakeshore. Further Furtherwest, west, just just beyond beyondthe the fence, is a ridge of massive basalt which is the interior of the overlying lava flow. More flows ridge of massive flow. More flows are visible visible along along the shoreline, shoreline, and east east of of the the lighthouse lighthouse provides provides an excellent excellent view view of of Eagle Eagle �G.ct '.0 �r - 62 — : ff , trit a," ;Yg() \ • j—' v C L_ - cope.. - - f -u ' 977.)) ' ()/J)J -'C - A4 - : / : —— '7 rDor uLe !-> "HARBOR s - bOf N —' - 7- - - iv 6to v "C - A --- C J 4 p )M44k ' I / A ot 1W V elate ff - /' JL) _rç J kf Boat Ramp ....VrT iv . VoIcanic :• at Stop 22 Con9lomerate2 Y 'Copper- Harbor I/I :4 ? MQthfl4 B14 " r Lake Superior pS ____ �Roa4 Log Main RoatI Log 93 93 Harbor and outcrops of the Lake Shore Shore Traps. Lake Shore Shore Traps Traps is is generally generally The amygdaloidal amygdaloidal mineralization and alteration seen in the Lake PLy, but mineralization calcite; chrysocolla; lower grade zeolite facies than the PLV, mineralization includes zeolites; calcite, chlorite; datolite; and abundant chlorite; abundant agate. agate. The flows have have segregation segregation cylinders cylinders and and numerous numerous sandstone dikes, and also have numerous mineralized slickenside surfaces that could reflect the subsidence of the rift rift sequence. sequence. At the Lake Lake Breeze Breeze Resort, Resort, just south south of of the the lighthouse lighthouse (PLEASE, (PLEASE, ask ask permission, permission, and and NO HAMMERS), the point that projects into the harbor has an exposure of beautifully preserved pahoehoe surfaces. Return to M-26. M-26. 67.25 Turn Turnleft leftand andfollow followM-26 M-26along alongEagle EagleHarbor. Harbor. 67.4 67.4 junction of M-26 and and Garden GardenCity CityRoad. Road. Stay on on M-26. M-26. The Owl Creek Leg (Leg B) begins The junction here. 67.5 67.5 The harbor at Eagle Harbor Harbor is controlled controlled by the occurrence occurrence of units which are called called the the Lake Lake Shore Traps. These PLy, is of Thesebasalt basalt flows flows are a member of the PLV, is interbedded with conglomerates of the Copper Copper Harbor Harbor Conglomerate, Conglomerate, and typically typically fonn form resistant resistant ridges. ridges. There are are excellent excellent exposures of the Lake Shore Shore Traps that occur at the Eagle Harbor Lighthouse, continue along the shore through Grand Grand Marais Harbor, Harbor, into into Agate Agate Harbor, Harbor, and and eastward eastward through through Copper CopperHarbor. Harbor. 68.25 The 68.25 Thejunction junction to to the theleft leftgoes goesto tothe theEagle Eagle Harbor Harbor Marina. Continue Continueahead ahead on on M-26. M-26. MAP 15 15 Marais Harbor. Hèbor. On rand Marais Onthe theright righthand hand side, side,you you can can see seethe the offshore offshore islands islands and and 69.4 69.4 A view of Grand by the the occurrence occurrenceof ofthe theLake LakeShore ShoreTraps. Traps. We are driving along a ridges which are controlled by conglomerate conglomerate ridge. ridge. 70.0 70.0 of Lake Lake Bailey Bailey on on the theright right side sideof ofthis thisconglomerate conglomerateridge. ridge. The The road passes along the shores of tend to to be be held up up by the conglomerates, and ridges throughout the Copper Harbor Conglomerate tend the valleys valleys are are underlain underlain by the the more more easily easily eroded eroded sandy sandy and and shaly shaly members members within within the the is Mount Mount Lookout. Lookout. The conglomerate. On Onthe the opposite oppositeside side of Lake Lake Bailey (on the right), is The contact contact between the the Copper Conglomerateand andthe the PLV PLV runs runs through through the the back back side of Mt. between Copper Harbor Harbor Conglomerate Mt. Lookout. Lookout. 70.15 On areexposures exposuresof ofthe thesandstone sandstonemembers members of of the the Copper Copper Harbor Harbor Onthe theleft leftside sideofofthe theroad roadthere thereare Conglomerate. Conglomerate. MAP 16 16 71.55 Crossing Crossing Silver Silver River. Pull Pullover over for for Stop Stop 23. STOP 23: Silver SilverRiver River(Copper (CopperHarbor HarborConglomerate) Conglomerate) This stop consists of excellent exposures, exposures, here here at Silver River and 0.1 0.1 miles east of the the Junction of M-26 with the Brockway Brockway Mountain road, on the left side of the the road. road. The Copper Harbor Conglomerate is is well well exposed exposedin inthis thisarea areaalong alongthe theSilver SilverRiver. River. At Eagle River Falls (Stop 21). 21), one had had the opportunity to look look at at the the basal basal beds of the Copper Eagle opportunity to Copper �___ gCJ C' rtJ. --TraP9 Lake Superior C- _r.Laj. - - .rr ) nr-rc4 -';7 tVVZ& rç G - -- A '(I e øpP (\ rr -F — — :'—L'-- ,, Tt' I naL' Lake - ç\,I - 2 —- — _: ie-'- -- - /1 -_ (I - - - I - - ç-- -- \t _-n— - —- -r - Portage take Vo canics -. - —c----4 2—' •. -. — 0 — 2J - ' -—- 1. )fl Cs— ,—North '1 it 3 —_ — -- - '15t± p:s. •/ çfl..r GreeflSt0 'roo( — 1' — -a—• v1 - _Ic—C-'4' t'- _) ( - 1 J — c0-ajioo 'c I — - / - 1001 -- —s," _rooo—- ——poo 110 — g2 — '-I / 9rj5ECongIomerate AG — _i (; I. fYif( -:Ty\ iC° - 1 FION.." • -(ç-- \\ 0 �>1 P — �96 MaiD Road Log Harbor Conglomerate. Now, Now, we we are arestratigraphically stratigraphically in the more central central part of of the the formation, formation, just below lava flow interbeds of the the Lake Lake Shore ShoreTraps. Traps. At Stop 26 and and 27, 27, one one will will get get the the interbeds of opportunity to look at the upper part part of the foymation. foymation. The The lithology lithology of the the sediments sediments here can be compared to to those those of of other otherstops. stops. Exposures provide a strike section within the Copper Exposures along the Brockway Mountain mad pmvide Harbor Conglomerate, allowing allowingone onewalking walkingalong along the the outcrop outcropto to observe observelateral lateralfacies facieschanges. changes. The The First large large exposure exposure on the the west end is is about about 55 m m high, high, and and at at the the base base isis aared redcolored, colored,very very fme-to-medium grained sandstone, sandstone,about about3.5 3.5m m thick, thick, overlain overlainby by massive massiveconglomerate. conglomerate. The fine-to-medium grained conglomerate clast-supportedwith with mostly mostlypebbles, pebbles,and andoccasional occasionalboulders bouldersup uptoto 20 20 cm in conglomerate is clast-supported diameter. The Thepebbles pebblestend tendtotobe becomposed composedof of subequal subequalamounts amounts of of mafic mafic and and felsic felsiclithologies, lithologies, tend to be be rhyolite rhyolite or or granophyre. granophyre. The conglomerates of of the the Copper Copper Harbor whereas the boulders tend Conglomerate are part of an alluvial fan complex complex with with sediments sediments being beingshed shedoff offof of the the flanks flanks of of the rift rift into into the thecenter, center,i.e., i.e., toward towardLake LakeSuperior. Superior. 71.65 The Thejunction junction totoBrockway BrockwayMountain Mountain Drive. Drive. We Weare aregoing goingto tocome come back back to to this this point, point, but but we we are are going to first take a side trip to Esrey Park. Park. Go Goto tothe theleft lefton on M-26. M-26. 72.15 We arenow nowatatthe theshore shoreofofLake LakeSuperior, Superior,where where there there are are dipping lava flows of the Lake Shore Shore Weare Traps. The Themad madfollows followsthe theshore shoreapproximately approximately parallel to the strike strike of the the lava lava flows. flows. 72.45 Pull 72.45 &ll left left into into Esrey Esrey Park. Park. STOP 24: Esrey STOP 24. Esrey Park Park(Lake (LakeShore ShoreTraps) Traps) The basalts cropping out at Esrey Park occur within the Copper Harbor Conglomerate, Conglomerate, some 800-1000 800-1000 m m above above the the PLV. PLy. They Theyare areaapart partof ofaasuccession succession of of Fe-rich Fe-rich olivine olivine tholeiite, tholeiite, basaltic andesite, andesite, and andesite andesite lava flows known collectively as the Lake Shore Traps (an informal member within the Copper Harbor Conglomerate) Conglomerate) (Fig. (Fig. 40). 40). This succession succession is thickest thickest at at the the tip tip and thins toward the east (on Manitou Island) of the Keweenaw Peninsula Peninsula (approximately (approximately 600 600 m), m), (on Manitou Island) pinch out near Calumet (a total strike length and toward the west-southwest, where the lava flows pinch lava flows flows vary vary in in thickness thickness fmm from about about44 to to 40 m and of about about90 901cm). km). Individual Individual lava and exhibit exhibit volcanologicalfeatures featuressimilar similartotoflood floodbasalts basaltsofofthe thePLV. PLy. The volcanological Thelowermost lowermostmafic mafic flows flows were were deposited as ponded sheets while upper andesite flows may have formed a low, positive deposited as ponded while upper andesite flows may formed a low, positive topographic feature such as a shield shield volcano. volcano. Magmatic variation variation within within lava lava flows flows at at the tip of the Magmatic the Keweenaw Keweenaw Peninsula imply that fractional crystallization of of plagioclase, cliopyroxene, clinopyroxene, olivine, olivine,Fe-Ti Fe-Ti oxide, oxide, apatite, apatite, and and zircon played an an important role in the of the played important role the petrogenesis petrogenesis of the Lake Lake Shore Shore Trap Trap magmas magmas (Paces (Paces and and Bornhorst, 1985). ~omhorst, 1985). Additional Additionalprocesses processes of of parental parental magma magma replenishment replenishment and and possible possible wall wall rock rock assimilation however, however,are arerequired requiredtotoexplain explaingeochemical-stratigraphic geochemical-stratigraphicrelationships. relationships. is aa massive flow flow interior of fineThe large outcrop outcrop between the parking lot and the shore is grained, Fe-rich olivine tholeiitic basalt. The Theflows flows strike strikeparallel parallel to to the the shoreline shorelineand and dip dip20-30° 20-30' toward the lake. The Theupper upperportion portion of of this this flow flow isisnot notexposed, exposed, but but the the top topof ofthe theunderlying underlying of the the large outcrop. outcrop. Because basalt flow can be seen at the shoreline on either side of Because of of its its higher higher the degree degree of of metamorphism/alteration metamorphism/alteration in in the the Lake Lake stratigraphic level within the rift-fill sequence, the Shore Traps Traps is is much lower than than in in the PLy. Zeolite facies metamorphism, as opposed to Shore much lower PLV. Zeolite metamorphism, as deposited chalcedony; chalcedony; laumontite; laumontite; analcite; prehnite-pumpellyite, affected affectedthe the flow top and deposited analcite; calcite; calcite; and smectite in amygdules. amygdules. Massive Massive flow flow interiors interiors of the Lake Shore Traps often retain relict �Main Reed Log FredaSandstone Sandstone Freda and and Nomwdl Sink Nonesuch Shale 97 SAMPLED UNITS m 600 outer outer LST ILST IBVBS 11ev.. 500 400 Copper Harbor Harbor Conglomerate w 7= flows middle middle LST lava. 300- I d iow LST LST 200— mlddi. LST laVal eves 100-S PortageLake Lake Portage Volcanlcs Volcanics lower ? lava Jnows 0— (a) (a) Traps Figure columnofofthe the Lake Shore Figure 40: 40: Stratigraphic Stratigraphic column Lake Shore Traps[LST] [LST]from fromthe theeastern easterntip tipofofthe theKeweenaw Keweenaw Peninsula (from DieM and Haig, in press). Peninsula (from Diehl and Haig, in press). �- 98 olivine the PLV, PLy, where olivine and glassy, intersertal mesostatis in contrast to the where both both olivine olivineand and intersertal intersertal replaced by by Mg-Fe Mg-Fe phyllosilicates. phyllosiicates. glass are invariably replaced 100m m east east From the east end of the large basalt ridge next to the parking lot, walk about 100 along the the shore to see along see the the flow flow top top of of the theunderlying underlying flow. flow. This well exposed exposed flow top is is basalt, typical typical of of aapahoehoe pahoehoeflow flowtop. top. The vesicles are are partially partially filled filled with with composed of vesicular basalt, laumontite, chlorite, calcite, calcite, and quartz. quartz. 72.55 Turn 72.55 Turnaround aroundand andhead headback backtoward toward the the junction junction of of Brockway Brockway Mountain Drive. 73.35 Take Takeaasharp sharpleft leftturn turnonto ontothe theBrockway BrockwayMountain Mountain Drive, Drive, more more exposures exposures of of the the Copper Copper Harbor Harbor Conglomerate described describedatat Stop Stop 23, 23, can can be be seen. seen. We Conglomerate We will will drive drive for for several several kilometers kilometers along along aa conglomerate ridge ridge with with many many conglomerate conglomerateexposures. exposures. In In spring spring and and fall fall a very diverse hawk migration occurs along this ridge. The Theridge ridge summit summitallows allows very very close close observations observationsbecause because the the birds often follow the ridge ridge top. top. MAP 17 17 78.35 At Atthe thesummit summitofofBrockway BrockwayMountain, Mountain, take take aa right right turn turn in a short distance, to the observation site. STOP 25: Brockway BrockwayMountain MountainViewpoint Viewpoint This high conglomerate conglomerate ridge reaches an elevation of over 400 m, with with excellent excellent views views of the ridge and valley topography of the northern shore of of the the Keweenaw Keweenaw Peninsula. Peninsula. Underfoot, Underfoot, the Copper Harbor Harbor Conglomerate Conglomerate dips dipsabout about200 20' to to the north. north. To the west, the Lake Shore Shore Traps Traps form island chains on a prominent ridge in the vicinity of Agate Harbor and Esrey Park. Copper Copper Harbor Harbor Conglomerate Conglomerate is found in the drowned valleys and along the outer outer ridge ridge jutting into into Agate Agate Harbor Harbor and projecting into a smaller smaller island island chain. chain. The reefs of the the Lake Lake Shore Shore Traps Traps and and Copper Copper Harbor Conglomerate Conglomeratealong along the the Keweenaw' Keweenaw'ss north north shore are are the the site siteof of numerous numerousshipwrecks. shipwrecks. topographicallylow low valley valley Lake Bailey (with (with the small small island) and Lake Upsom occupy a topographically on a finer-grained finer-grained clastic clastic horizon horizon within within the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. Just to the south of Lake Lake Bailey, Bailey, is is the the conglomerate conglomerate ridge of Mt. Mt. Lookout, Lookout, marking marking the the contact between the Copper Harbor Conglomerate Conglomerate and and the the PLV. PLy. The inland directly south, south, isis Lake Lake Medora, Medora,and andjust just before before the the lake lake is a The inland lake almost almost directly prominent ridge which marks the stratigraphic position position of of the Greenstone How. flow. In the distance, distance, farther to the south south across across Lake Medora, is Mount Bohemia, a dioritic dioritic stock-sized intrusion. To the southwest, southwest, a distant distant ridge ridge with with white white buildings buildings on itit marks marks Gratiot Gratiot Mountain, Mountain, which is underlain by andesitic dikes and small rhyolite bodies that cut the PLV. To the east are the communities communitiesof ofCopper CopperHarbor Harborand andLake LakeFanny FannyHooe, bee, both both of of which which occupy the same stratigraphic horizon as as Lake Lake Bailey. Bailey. Copper Harbor was a boom town in 1843, Copper 1843, following the initial discovery of native copper copper in in the the Keweenaw KeweenawPeninsula. Peninsula. In 1844 1844 Fort Wilkins was built on the shores of Lake Fanny Hooe; it is now a state park. The Thelighthouse lighthousewas wasbuilt builtinin 1866. 1866. �____j Stop 27 r------ -- - - Copper ri -- - Harbor jj •_•. — .0 -- IT ,1 t— - - -",' _L -- — pp /V -- zcT>TT1 ReTaTC --7 -.. CS Traps -_— -- — I - C—--tfl-fl - Trap - '-'t_±i_ISc 1c1i2 TIk - nr-c - —— £ —- - - Shr Conglomerate Lake — Lake Th -—— -c---z--T c - 26 ..___ — asi;zID Luke ____ ___ Lake Superior - - - ---I-- —— ,_jI - _I — -- — - — -- er / 4'<---—--c-----*--- -B-0 - —'-'? - <---- —, ) C -- - - -' Th I 44, \ C -ç or a9e Lake volca '- — c—±cc �100 Harbor, lies lies East Ridge, To the To the east east on on the skyline, skyline, beyond beyond Copper Copper Harbor, Ridge, aa prominent prominent conglomerate hill. To the the north on the the skyline skyline 65 km away, is Isle Isle Royale, Royale, which is visible visible on aa clear clear day. day. The skyline of Isle Royale is formed formed by the the Oreenstone Greenstone Flow, as it is is on on the thePeninsula. Peninsula. Follow the road downhill downhill toward Copper Harbor. 78.35 Turn Turntotothe theright rightand andfollow followthe theroad roadstraight straightahead aheadtoward toward Copper Copper Harbor, Harbor, going going downhill downhill and and which has excellent views views all the way down. continuing along the ridge which MAP IS 18 pull-out on the right right hand hand side of the the road road that that gives gives an an excellent excellent view of of Copper Copper 81.9 81.9 There is a pull-out Harbor and Lake Fanny Hooe. Copper Copper Harbor Harbor is is controlled controlled by the occurrence of the Lake Shore Shore Traps. Porters Island, Island, are areunderlain underlainby bylava lavaflows. flows. From the Traps. The Theislands islands offshore, offshore, including including Porters to excellent excellent exposures of the Lake Copper Harbor Marina, with a small boat, you can have access to There are exposures of the Copper Shore Traps along the edges of Copper Harbor. of Copper Harbor Harbor edges of Copper Harbor. Conglomerate along the road road descending descending into into Copper Copper Harbor. Harbor. M-26, turn left. 83.0 At the junction at M-26, MAP 17 17 past the the blowhole blowholecalled calledthe theDevil's Devil's Washtub. Washtub. If you you 84.7 We come to the shore of the lake again, past stop here by the right right side side of of the the mad road and andtake take aashort shortwalk walkalong alongthe theconglomerate conglomeratealong along the the shore, you come to wave washed exposures of the conglomerate at the Devil's Devil's Washtub. Washtub. (This (Thisisis PRIVATE PROPERTY.) PROPERTY.) 85.25 On Onthe theleft leftisisaapublic publicaccess accessto tothe thelake lake shore shore and and exposures exposures of the Copper Harbor Conglomerate. 85.55 Pull 85.55 Pullover overon onthe theright rightatatthe theKeweenaw KeweenawCounty County Park. Park. STOP 26: Hlebard STOP HebardPark Park(Copper (CopperHarbor HarborConglomerate) Conglomerate) Excellent exposures exposures of of the Copper are exposed exposed at at this public Excellent Copper Harbor Conglomerate Conglomerate are public locality. At Atthis thispoint, point,the theCopper CopperHarbor HarborConglomerate Conglomerate is is stratigraphically stratigraphicallyabove above the the Lake Lake Shore Shore Traps. See SeeStop Stop27 27for forfurther furtherdescription descriptionofofthe theCopper CopperHarbor HarborConglomerate. Conglomerate. 86.35 Pull 86.35 Pullover overto tothe theright rightatatthe thegift gift shop. shop. The Thenext nextstop stopisisPRIVATE PRIVATE PROPERTY. PROPERTY. Ask Askpermission permission at the gift gift shop. shop. DO DONOT NOTUSE USEROCK ROCKHAMMERS HAMMERS AT AT THIS THIS STOP. STOP. STOP Harbor STOP 27: Dan's Dan'sPoint Point(Copper (Copper HarborConglomerate) Conglomerate) Walk about 20 m to the shore shore of of Lake Lake Superior, Superior, to look look at the the lithology lithology of of the the Copper Copper Harbor Conglomerate and an occurrence of stromatolites in in wave wave washed washed exposures. exposures. Please Please do do outcrop, specimens specimens can can be be found found on on the pebble beach. not remove stromatolites from the outcrop, The Copper Harbor Conglomerate ranges ranges from 490 m thick near the Wisconsin Wisconsin border, border, to about about 1310 1310 m m ininthe theKewesnaw KeweenawPeninsula. Peninsula. As aa whole, whole, the the formation formation is is aared-brown, red-brown, basinward-thickeningwedge wedgeofof fluvial fluvial siliciclastic siiciclastic conglomerates and sandstones that was basinward-thickening conglomerates and sandstones that was deposited in the rift basin after flood basalt volcanism volcanism (PLV). (PLV). The The Dan's Dan's Point Point outcrop outcrop shows shows a proportion of lithologies lithologies that is characteristic of the upper two-thirds two-thirds of the formation. Directly PLy, is Directly above, above, and locally interfingering interfingering with the lava flows of the PLV, is aa thin-to-thick thin-to-thick �Lake Superior ore• Copper * HAYS (PIt,st.URGH 6 £XPLORATION Lake -— arbor • . I /- V • ... —--. —V. . ,.• /.- . _/ .-..... I 0 -. �102 102 ?,bin Road Mtin Rend Log Los bedded, bedded, coarse coarse basal basal conglomerate conglomeratefacies facies consisting consisting of well-rounded, well-rounded, poorly sorted sorted clasts clasts of of mauicmaiicThese, and the higher conglomerates, generally are clastto-silicic volcanic rock rock fragments. fragments. These, higher conglomerates, generally supported and show a ratio of supported of mafic-to-silicic mafic-to-silicic intermediate clasts of about 2:1 21 (Elmore, (Elmore, 1984). 1984). The sandstones lithic graywackes which The sandstones are are predominantly predominantly red-brown, red-brown, subangular-to-angular subangular-to-angular lithic exhibit current-ripples; current-ripples; foreset and trough-cross beds; and parting lineations. lineations. Minor shale and and siltstone interbeds show desiccation features. In the conglomerate and coarse sandstones, show desiccation features. the conglomerate and coarse sandstones, the the abundant calcite cement probably abundant probably was deposited as vadose vadose carbonate carbonate or or caliche calicbe(Kalliokoski, (Kalliokoski, by this In the theupper upper two-thirds two-thirds of of the the formation formation on the Keweenaw Peninsula, represented by 1986). In are more more abundant. abundant. There outcrop, sandstone interbeds are There are are also also laminated laminated cryptoalgal cryptoalgal carbonate carbonate horizons occurring laterally-linked stromatolites, stromatolites, that are draped draped over over cobbles, cobbles, as as laterally-linked laterally-linked horizons occurring as laterally-linked contorted layers in mudstone-siltstone mudstone-siltstone and as as poorly developed developed mats mats in coarse coarse sandstone sandstone(Elmore, (Elmore, 1983). 1983). of the Copper Harbor Conglomerate has been interpreted The depositional environment of interpreted as a prograding braided stream and sheet prograding alluvial alluvial fan complex (Fig. 10) 10) with proximal-to-distal proximal-to-distal braided alluvial fans fans and and sand sand flats flats (Elmore, (Elmore, 1984). 1984). The region flood facies on coalesced coalesced alluvial region was was nearly nearly equatorial in geographic probably arid arid with with aa seasonal seasonal rainfall rainfall pattern equatorial geographic position and the climate was probably conducive conducive to flashy streams streams and to to the the development development of of vadose vadose carbonate carbonate(Kalliokoski, (Kalliokoski, 1986). 1986). and ooid ooid lenses lenses formed formed in in shallow, medial medial fan fan lakes and possibly Isolated cryptoalgal carbonate and which received received very very little sediment (Elmore, 1983). abandoned or low-water stream channels which 1983). section of of the Copper Harbor Harbor Conglomerate Conglomerate exposed exposed atat Dan's Dan's Point The stratigraphic section and sandstones sandstones (Fig. (Fig. 41). 41). Clast-supported consists of about 30 m of interbedded interbedded conglomerates and Clast-supported beds consist consist of of rounded, rounded, cobblecobble- to to boulder-sized boulder-sized clasts clasts with with a matrix of coarse conglomerate beds coarse grains cemented cemented with with carbonate carbonateand andiron ironoxide. oxide. Clasts are sand-sized subangular grains are predominantly of siicic of silicicvolcanics, volcanics,with withsubordinate subordinatebasalt; basalt; pyroclastic; pyroclastic; plutonic; plutonic; and and metamorphic metamorphic lithic lithic exposed section section exhibit exhibit crossbeds, crossbeds, current current fragments. Several Severalfmer finergrained grained interbeds interbeds higher in the exposed Jineations, current ripples, parting lineation, and reduction spots. lineations, spots. In particular, one should note note that represent vadose carbonate or paleocaliche. the calcite-rich zones that paleocaliche, and the white white stromatolite stromatolite Along one one of these calcite zones, algal growth occurred during a (genus Colleria) Colleria)horizons. horizons. Along occurred during period of depositional quiescence quiescenceand and was was halted halted by by an influx of silty period silty material material followed followed by by renewed conglomerate conglomerate deposition. deposition. , Several Conglomerate occur Several sites sites for for public access access to the lakeshore and the Copper Harbor Conglomerate occur for up to about of Dan's for about 0.6 miles miles west west of Dan's Point. Point. We Wewill will retrace retrace our our route route back back toward toward the Brockway Mountain Drive junction. 86.35 Turn 86.35 Turnaround aroundand andgo goback backtoward toward Copper Copper Harbor Harbor on on M-26. M-26. MAP 18 18 Mountain Drive. Drive. To the the left left isis aajunction junction to tothe theCopper CopperHarbor Harbor 89.7 At the junction junction of Erockway Brockway Mountain Marina. Continue Continuestraight straightahead aheadon onM-26 M-26totoCopper CopperHarbor. Harbor. 90.15 The 90.15 Thejunction junction between between M-26 M-26 and and US-41 US-41 in in Copper Copper Harbor. Continue Continue straight straight ahead ahead toward toward Fort Fort Wilkins Wilkins State State Park. Park. Copper Harbor was suddenly suddenly a boom town in 1843, 1843, following the discovery of copper in the the vicinity. Porter's Porter's Island Islandwas wasthe thesite siteof of the the first firstgovernment government land office and in 1844, Fort Wilkins (Stop 28) was built on on the the shores shores of of Lake LakeFanny Fanny Hooe, Hooe, to toprotect protectthe theminers minersfrom frompotentially potentially hostile Indians. The Thelighthouse lighthouse was was built built in in 1866. 1866. �MainRoadLog A 103 0 B .r t ct9j e.P. , a T,o.4, as beinq Ib*u,IS i......a... Wove a,d cnt nppt oos a 4? :n U-.-- n r— .— tLcuj o3.93J a t, °_Oo .1 B Slrrt. a Ooids Figure41: 41: (a) (a) Measured Measuredstratigraphic stratigraphicsections sections from from Horseshoe Harbor (B) and Dan's Point Point (D) (D)with with Figure current direction rose diagrams. diagrams. (b) (b)Schematic Schematiccartoon cartoonof ofthe thedepositional depositional environment environmentwhich which fostered growth of of stromatolites stromatolites in in temporarily temporarily abandoned abandoned medial-fan medial-fan stream channels channels (from (from fostered growth Elmore,.1981). 1981). Elmore,, �104 91.6 MäiRog Entrance to Fort Wilkins WillcinsState StatePark. Park. There There isis aa fee fee to to enter enterthe the state statepark. park. The entrance pass is Park, visited visited at at Stop Stop H6 H6 on on the the McLain McLainLeg. Leg. Upon entrance also valid for McLain State Park, entrance into into the the park park store. The park, pull into the parking lot and proceed to the The Fort Fort has has many many excellent excellentexhibits exhibits illustrating the mining history history of of the the Keweenaw Keweenaw Peninsula. Peninsula. STOP 28: Fort (native copper veins STOP FortWilkins WikinsState StatePark Park (native copper veinswithin withinCopper CopperHarbor HarborConglomerate) Conglomerate) Fort Wilkins is now a state park park with with camping campingfacilities facilitiesand andaamuseum. museum. Much exploration Port of the fort, and there are shafts and exploration pits activity took place in the immediate vicinity of Hoot and all along the land land between between Lake Fanny Fanny Hooe and the the Harbor, Harbor, mostly mostly from from exploration exploration in the the of the park store, several pits provide evidence of early mining 1843-1846 period. Just north north park store, several activity by European settlers. The ThePittsburgh Pittsburgh and and Boston Boston Mining Mining Company Company operated operated here here In in the the 1840's on aa vein vein of of native native copper copper within within the the Copper Copper Harbor Harbor Conglomerate, Conglomerate, the the vein vein was was reported reported to be up to 0.3 0.3 m m wide. wide. This Thisventure venturewas wasnot notprofitable. profitable. In 1853, thereafter, mining mining activity activity took took place place south south of of the fort 1853, and for for several several decades thereafter, in a series the Clark Clark Mine. Mine. The series of workings called the The mineralization is of the fissure and amygdaloid adularia, microcline, microcline,chlorite, chlorite, type and consists consists of of prehnite, prehnite, epidote, epidote, analcite, analcite, quartz, quartz, laumontite, laumontite, adularia, datolite, calcite, and several copper minerals including chalcocite, cuprite, and tenorite as several chalcocite, cuprite, and tenorite as well as native copper. Agates Agatesare areconspicuous conspicuous in in vesicular vesicular basalt of the Lake Lake Shore Shore Traps Traps here, here, and and the the area is well known known for for datolite datolite collecting. collecting. An occurrence of manganese minerals minerals in in aa fissure accounts for for the name of Manganese manganese minerals found here Lake, south of Lake Fanny Hooe (refer to Map The here were were south of Lake Fanny Hooe (refer to Map ).). The pyrolusite, manganite, braunite, and orientite. Pine tract represents represents aa part part of the pyrolusite, orientite. The Estivant Estivant Pine Clark Mine Mine lands which were were deeded deeded to to the the C&G C&G Company Company in in 1942, 1942, and and are now a nature nature Clark lands which the Upper Upper Peninsula. Peninsula. preserve, containing the last virgin pine tracts in the Opposite Fort Wilkins Wilkins on on one one of of the Park trails trails that crossed US-41, is a view Opposite Fort crossed US-41, view of of the the Lighthouse. Near the point of the lighthouse on the shore facing the big lake, is Copper Harbor Lighthouse. is rock". The the sight of the famous "green rock. The "green "green rock" is a vein seen by early voyagers and was described by by Douglass Douglass Houghton; Houghton;ititisis one one of of the localities that focused focused early early interest interest in in the described localities that Houghton himself himself may may have have never never really really understood understood the the uniqueness uniqueness of of the Copper Country. Country. Houghton district, as the conventional wisdom then, was that it was the surficial alteration of a sulfide ore. 1993). But Houghton promoted the district well (Krause, 1993). Horseshoe Harbor has has excellent of the Copper Horseshoe Harbor excellent exposures exposures of Copper Harbor Harbor Conglomerate Conglomerate and and interbedded algal stromatolites can can be be reached reached via via the the Horseshoe Horseshoe Harbor HarborLeg. Leg. Keweenaw Point, East Bluff, and other dirt road road other points points of interest interest can be reached reached by continuing continuing on the unmarked unmarked dirt which goes eastward from the end of US-4 US-41I and are discussed in the Horseshoe Harbor Leg. 91.7 Retrace the the route back toward Entrance to Fort Entrance Fort Wilkins Wilkins State State Park. Park. Retrace toward Copper Copper Harbor. Harbor. The Horseshoe Harbor Leg Leg begins begins here. here. 93.15 The Turnleft lefton on US-41, US-41, south south out out of of Copper Copper Harbor. Harbor. 93.15 Thejunction junction of ofM-26 M-26 and andUS-41. US-41. Turn 94.25 Nice Niceexposures exposuresofofthe theCopper CopperHarbor HarborConglomerate Conglomerate are to the left of the road as we are going up the hill. hill. 94.6 Entrance to the Keweenaw Mountain Lodge Lodge and and Golf Golf Course. Course. During Keweenaw Mountain During the the Great Great Depression Depression of of rate in in Keweenaw KeweenawCounty Countywas wasaround around70 70toto 80%. 80%. Keweenaw the 1930's, the the unemployment unemployment rate Keweenaw �MainkoadLog Mill Rod Log 105 105 County's Boani County's Board of of Trustees Trusteessubmitted submitted aa proposal proposal to the Civil Works Administration Administration (C.W.A.) and programs. Most became one of the first work projects within the Federal programs. Most of of the the present present buildings buildings were completed on the 167 acre site in 1935 with with Federal Federal funds. funds. Revenue from operations Revenue operations have new cottages cottages (after (after aa report report by by J.J. W. W. Jackson). Jackson). The lodge allowed several new lodge has has accommodations accommodations and an excellent excellent atmosphere atmosphere for for eating. eating. MAP 19 19 side of of the the road. road. 97.5 Lake Medora on the right side MAP 20 100.35 junction on on the the left left goes goes to to Mandan. Mandan. Mandan now is only a few 100.35 The junction Mandan now few houses, houses, but it had 300 residents in 1910. Continue Continueahead ahead on on US-41. US-41. 100.6 The mad 100.6 road to to the the left is is the the entrance entrance to the outer portion of the Keweenaw Peninsula, all on poorly maintained dirt roads. roads. To Tovisit visitMount Mount Houghton Houghton and and Keweenaw Keweenaw Point, you may exit here. side of of the the road road is is aa swamp swamp lying lying east east of of aa north-south north-south trending trending esker. esker. 100.8 On the left hand side 100.8 park here. here. Proceed Proceed on on foot foot to to view view the the esker. esker. on the the right. right. Pull over and park 100.9 A small road on 100.9 STOP 29: Mandan Mandan(Mandan (Mandanesker) esker) featured in many geological lab exercises, exercises, is is clearly visible on Map The Mandan esker, featured as a north-south trending topographic topographic ridge ridgewith withup upto to25 25m mof ofrelief relieffrom fromnear nearClear ClearLake. Lake. The ridge is composed composed of coarse coarse Pleistocene Pleistocene sand and gravel, and was deposited by glacial glacial meitwater meltwater flowing in a subglacial tunnel. The esker sediments are not exposed along the road, but subglacial tunnel. The esker sediments are not exposed road, but can can be be viewed by walking viewed by walking along along the ridge ridge toward toward the south to an an old old railroad railroad cut cut (Regis (Regispersonal personal communication, communication, 1992). 1992). This stop is best in the fall fall or or spring spring due due to to the the dense densefoliage. foliage. MAP 21 MAP 21 junction of the road to Lac 1. The Eastside Keweenaw 103.4 The junction La Belle. Belle. Continue Continueahead aheadon onUS-4 US-41. 103.4 Lac La Peninsula Leg begins here here and and ends endsin in Lake LakeLinden. Linden. 104.05 The dirt Delaware Mine. Mine. Turn 104.05 dirt road to the right goes to Stop 30 at the Delaware Turn right on the dirt road and follow the signs to the Delaware Mine. signs to the Delaware Mine. 104.2 STOP Mine (native copper deposit 104.2 STOP30: 30:Delaware Delaware Mine (native copper depositwithin withinPortage PortageLake LakeVolcanics Volcanics [PLV]) [PLV]) The Delaware Mine is open to to tours tours during during the the summer summer months. months. At this stop, one one has the the opportunity look atat the the rock rock piles piles from from the the Delaware DelawareMine Mineand andtoto visit visit (for (for aa fee) the opportunity toto look underground workings. workings. The workings is is at Stop 8. The other other opportunity opportunity to visit underground underground workings The Delaware Delaware Mine is aa typical typical vein vein deposit deposit situated situated below below the the Greenstone Greenstone Flow. Flow. It operated from 1848 to 1887, of about 3.5 3.5 million million kg kg of refined copper 1887, with a total production production of (Butler and Burbank, Bill-bank, 1929). 1929). Overall, Overall, it was not not aaprofitable profitable venture. venture. The early and major major production was from a native production native copper-bearing copper-bearing vein, the Stoughtenburgh Stoughtenburgh Vein, which was mined mined section was was below for 265 for 265 m on on strike, strike, to aa depth depth of of 330 330 m. m. The productive productive section below the Allouez Allouez Conglomerate. Three shafts were opened Conglomerate. opened in 1881 1881 to mine mine copper copper from from the the adjacent adjacent Allouez Allouez Conglomerate. The Delaware Conglomerate. Delaware Mine Mine was first first known known as as the theNorthwest Northwest Mine. Mine. The current current accessible mine was mapped and and described described by Schleiss Schleiss (1986). (1986). Two thin crosscuts on on the the first-level first-level drift. drift. They thin basalt flows are exposed exposed in two crosscuts They strike strike E-W and dip dip 25°N. 25W. The Theflows flowshave havefme-grained fine-grainedmassive massive interiors interiors and and amygdaloidal amygdaloidal flow flow tops, tops, �-o 0 Is) V -ii) -JT: -Th - Y r-JTT ) V 4r 'I--- - •__ / 15_ — *iS _5 0pL 14 ' -— - - JU -- —z-"U/' I N - -- - — /____- - . - f__f - 1Th- \\ \ ) ,5)--- N) C——. V UJ' / J[ 'i2 -I --.--+- C- cT. / /rr0! S __iJ ,-K / 1—' -t_ , -- I - i f7' --C - 4. ___r ___&etnst4 C -a 0* a., C �_ ____ ___ _______ MainRciadLog C Stop 29... -CUtWL / "\ l'cç " 107 -- / H44ç' f; *Nj iqe * )W >+tc Mandan' If )d' — ç ? ) ' cr r2cKrcSE?4T e b' Ctcrrt4, 'I ftP: 4r:: —/ °°J ((/ 'Fr Th z —_2::N)\ _2 : — -r I .-.. ,.j---t.Bohemia c N— C %— ' ) -- / J a c ob s I MAP 2C �______ ________________ '-T'-"4t-9 = H?E- t—-- ci DLR CL —— _iia'—---' r _\ \>-\ ''0O.( -C' —--i—r-= 51(_ I r- —: ——r- cL3'—'4( I 0 — pbC- " ( -— —— -- -S ¶i5i!St L - — / — -— — v ::- t \__ *00 '— \K -, _xc r t1D)lp a- 1s) 0 -, - p —- _- H - /Stop 30; —' Dela : — '5 — >.-..___ C - - — Zt -Tt5 &r>_c-2-J 4— - ___ a>— •- -- V r-__ - - -— - —----'-- 22 "Stop31 JZ/68 S N ) - / N 'c't Jf I'.) [ I \c' ea 2Cr-i !v 1'__ 1,'c— çto'H X I 0 00 I �MainRo.dLng 109 with amygdules predominantly filled with calcite. A A weathered weathered zone zone on on the the top top of of the theuppermost uppermost of the two basalt flows is overlain by the Allouez Conglomerate. The Allouez Allouez is the only unit Allouez Conglomerate. along the first-level, m thick; thick; is is composed composed of first-level, and and currently currently is is the the only only accessible accessiblelevel. level. It is 88 m rounded-to-subangular rounded-to-subangular clasts clasts up to 30 30 cm in diameter; composed of rhyolite, granophyre, and and rare rare by a matrix matrix of of sand. sand. There basalt; and is supported by There is is an an interbedded interbedded lens of fine- to mediummediumsandstone and is overlain by the Greenstone Flow, which crops out up the bluff above grained red sandstone above the mine, but is is not not exposed exposed in in the the mine. mine. The principal accessible portion portion of of the the Stoughtenburgh StoughtenburghVein Veinisisabout about 35 35 cm cm wide. wide. Here, Here, as in all all veins veins in in the the mine, mine, calcite calcite is the the main filling. The Theparagenetic paragenetic sequence sequenceisis minor minorquartz, quartz, microcine, and by minor microcline, and muscovite; muscovite; followed followed by minor native copper copper and abundant abundant calcite; in turn, turn, the epigenetic minerals consist of followed by minor minor chalcocite. chalcocite. In the Allouez Conglomerate, the the interstices between between matrix and calcite with minor amounts of quartz and microcline filling the clasts, and sporadic sporadic native native copper copper within within the the matrix. matrix. The only faults in the mine are bedding plane faults, at the upper and lower contacts of the conglomerate. wall is denoted denoted by by more more than than 18 cm cm of of clay fault conglomerate. The fault in the the hanging hanging wall gouge (vermiculite (vermiculite and and smectite) smectite) with with introduced introducedcalcite. calcite. The footwall bedding bedding plane fault is denoted by a 2 to 55 cm cm thick layer layer of gouge, gouge, consisting of chlorite chlorite with lesser amounts amounts of calcite; calcite; microcline; quartz; and native copper. copper. The microcliine; The amount of displacement along these faults is unknown. In the first-level drift of the the Delaware Delaware Mine there are a large large number number of of parallelparallel- to to sub-parallel sub-parallel fractures, filled with calcite. calcite. The The fractures, fractures, known as tension fractures, can be subdivided into a major northwest-striking set set and and aa minor minornortheast-striking northeast-strikingset. set. A model model for for the theDelaware Delawarefissure fissurevein-conglomerate vein-conglomerate lode lode mineralization mineralization begins begins with with copper copper bearing fluids along along permeable permeable flow flow tops tops and and conglomerates. conglomerates. Faults and and fractures fractures produced during the paleohydrologic paleohydrologic produced duringlate late compression--reverse compression--reverseKeweenaw Keweenaw fault faultmotion—integrated motion-integrated the system and allowed allowed effective effective movement movement of ore ore fluids. fluids. The steeply steeply dipping dipping tension tension fractures fractures (veins) were efficient pathways pathways for for fluid fluid movement. movement. The fluids migrated upward and The fluids migrated upward and laterally laterally through these open fractures and were diverted beneath the thick, unfaulted, massive interior of Flow so that the Greenstone Greenstone Row that fluids fluids moved moved laterally laterally from from the the fractures fractures into into the theAllouez Allouez were deposited, deposited, probably probably in in response response to to a combination of fluid Conglomerate. Ore minerals minerals were combination of Conglomerate. mixing; cooling of the the solution; solution; and and fluid fluid wall-rock wall-rock reactions. reactions. The Delaware Mine rock pile, as with other vein deposits deposits in the Keweenaw, Keweenaw, is is aa notable notable locality for datolite. Also Alsoincluded includedin inreports reportsabout aboutthe the rock rock pile pile are are these these minerals: minerals: chlorastrolite, chlorastrolite, prehnite, calcite, laumontite, analcite, chlorite, epidote, native copper and native native silver silver (Clarke, (Clarke, 1975; Zelenka, 1978). 1978). 1. Left turn on IJS-4 US-411 and continue ahead towani toward 104.35 The The junction of of the theDelaware DelawareMine Mineand andIJS-4 US-41. Phoenix. right side side of of the the road. road. Massive basalt on the east end of 104.45 Exposures of basalts of the PLV on the right the outcrop is N30°W. The The orientation orientation of of these these fractures fractures is cut cut by by several several fracture fracture zones zones trending N30W. is similar similar to to those those in in the the Delaware Delaware Mine. Mine. The fractures fractures contain containminor minoramounts amountsof ofnative nativecopper. copper. 104.8 104.8 Pull over over on on the the right right hand hand (north) (north) side side of of the the road road just before before the the outcrops. outcrops, �110 t.4aiuadI.og near STOP 31:US-41 US-41 nearDelaware Delaware(Portage (PortageLake LakeVolcanics Volcanics[PLY]) [PLV]) STOP 31 of basalt basalt lava lava flows flows within within the thePLV PLYcan canbe be observed observedatatthis thislocality. locality. The The character of strike of the flows is about E-W here, roughly parallel to the orientation of the road, thus you are are half of the 55 m looking at aa strike-parallel strike-parallelsection. section. The lower half m high high outcrop outcrop face face consists consists of of appearance. In the center of the the outcrop, outcrop, a large large egg-shaped egg-shaped mass mass vesicular basalt with a rubbly appearance. by vesicular vesicular basalt. basalt. The vesicles of more dense basalt is surrounded by vesicles dominantly are filled with calcite, prehnite, prehnite. and and chlorite. chlorite. The calcite, The character character of this flow top represents a pahoehoe flow with brecciation. This limited brecciation. This isis overlain overlain by by flne-grained fine-grained massive basalt with subvertical joints of the higherflow. flow. The contact contact between betweenthese thesetwo twoflows flowsisisirregular. irregular. Note that next stratigraphically stratigraphically higher no sediment sediment exists exists between between these these flows. flows. The lack of sediment sediment between between flows is aa common common rapid rate rate of of extrusion. extrusion. Where sediment horizons exist, the temporal feature, and is indicative of a rapid composition of of the the basalts basalts often often suggest suggestthe theend endof of aa cycle, cycle, and and is is consistent consistent with with aa hiatus hiatus in composition arestratigraphically stratigraphicallybelow below the the Greenstone Greenstone Flow. Flow. volcanic activity. The Theflows flowsatatthis thislocality localityare MAP 22 22 107.0 Ahead are cliffs of the Greenstone Flow. The The road road nears nears the the basal basal contact contact of of the the flow. flow. Greenstone Flow. 107.0 108.3 exposure of one one of of the the flows flowsbeneath beneath the theGreenstone Greenstone Flow. How. 108.3 An exposure Ridge in inthe thebackground. background. In the foreground is is the ghost 109.1 To the right, one can see the Greenstone Ridge 109.1 town of Central and its associated rock piles. ofcentral and its associated rock piles. ahead on on US-41. US-41. The road 109.45 A junction of paved paved roads roads to to the the right right and and left. left. Continue ahead mad to the left goes to Gratiot 932 Creek. The Theroad road to tothe the right right goes goes toward toward the the Gratiot Lake and is the start start of Leg E -- 932 ghost town of of Central Central and and the the Central Centralrock rock piles. piles. nearly at right angles to bedding and dipping The Central Mine worked a fissure vein striking nearly dipping to the the east. The produced about 52 52 million million Ibs. lbs. of of 1854 to 1898 and produced steeply to The mine mine operated operated from 1854 copper. The Thefissure fissureextends extendsfrom from just below below the Greenstone Greenstone Flow to the Kearsarge Conglomerate. offsets the the vein vein to to the the west, west, and and below below .this this it is not A strike strike fault at the Kearsarge Conglomerate offsets mineralized. mineralized. by Cornish immigrants. immigrants. Although Although the area area was was The town of Central was settled in 1854 mainly by mostly mostly abandoned abandoned after the mine closed, closed, the descendants descendants of these these immigrants, immigrants, now living living all all across the country, hold hold a yearly yearly reunion reunion in in July July at at the the town town site. site. Later immigrant groups to the copper mining towns included: included: Italian, German, Croatian, and Finnish people. MAP 23 110.8 A junction of a road right. Continue 110.8 mad to the right. Continue ahead on US-41. The The road road to to the the right right connects connects with Leg B -Owl -Owl Creek, Creek, at at mileage mileage 60.3. 60.3. 111.9 of the the ENE ENEstriking striking Greenstone Greenstone Flow How holding holding up up the theprominent prominent ridge. ridge. 11 1.9 Another view of flow ridge. 112.6 112.6 Again another another excellent view of the Greenstone How ridge. MAP 11 11 113.4 The junction junction of M-26 and US41 US-41 at Phoenix. Phoenix. Continue Continue ahead on US-41. For Foran analternate alternate route route 113.4 to Ahmeek with two stops, go to Leg F F -- Five Mile Point. Point. This leg begins near the settlement of Eagle River. River. 113.5 On the right is the road 113.5 road toward Stop 18. 18. Continue Continueon on US-41. US-41. �N) -I I a. �112 Maini Log �MSiDROIdLog 113 the Eagle EagleRiver. River. 113.8 Cross the West Branch of the 113.8 Bear left left on US-41. Another excellent excellent view of the the junction of US-41 US-41. Another US41 and and Cliff Drive. Bear 114.9 The junction Greenstone Row flow ridge. ridge. the small park park and and the the snow snow 'thermometer" "thermometer" showing showing the amount amount of snowfall snowfall in the On the left is a small 116.2 On 116.2 Keweenaw Peninsula. Peninsula. Gratiot River. River. 117.7 117.7 Cross Gratiot MAP 10 10 in the 1980's. 118.6 The open site on the left 118.6 left was a lumber lumber mill which which closed in 119.4 119.4 Entering Mohawk. Mohawk. side of the the road road are are mine mine rock rock piles piles from from the the Mohawk Mohawk Mine. 119.5 On the left side 119.5 119.7 119.7 Turn left on 3rd 3rd Street Street in in Mohawk Mohawk and and proceed proceed past past the the school school toward toward the the Keweenaw Keweenaw County County garage. garage. the rock rock piles piles of of the theMohawk Mohawk Mine. Mine. 119.8 Park at the 119.8 STOP 32: copper deposit STOP 32: Mohawk MohawkMine Mine(native (native copper depositwithin withinPortage PortageLake LakeVolcanics Volcanics(PLY]) [PLV]) flow top Mine and seven other other mines: mines: The Kearsarge Flow top deposit deposit was worked by the Mohawk Mine North Kearsarge, Kearsarge, Ahmeek, Ahmeek, Mohawk, Mohawk, and and Seneca. Seneca. The Centennial, South Kearsarge, Wolverine, North The along about 3 km of strike length of the ore Mohawk Mine consisted of 6 different shafts along ore body. body. The Mohawk was opened in 1902 1902 with with production production ending in 1967 1967 from from the the Kearsarge Kearsarge deposit. deposit. of refmed copper from from the Kearsarge Flow top top was was 1026 Total production production of refined copper Kearsarge Flow 1026 million kg. The The Kearsarge deposit deposit isis described describedinindetail detailatatStop Stop 13. 13. The rock piles at this locality are from the No. shaft. R. E. E. Stoiber Stoiber made made the the following following estimate estimate of of the the percentages percentages of of the the.secondary secondary No. 3 shaft. prehnite, 1%; epidote, 1%; and quartz, minerals: minerals: calcite, 73%; K-feldspar (red and pink), 24%; prehnite, trace. The TheMohawk MohawkMine Mineisisnotable notablefor forthe theoccurrence occurrence of of veins veinscontaining containing Cu-Ni Cu-Ni arsenides. arsenides. Return to to US-41. US-41. 119.9 Turn left left on on US-41 US41 toward toward Calumet. Calumet. 119.9 the skyline skyline with the four towers on it is Bumbletow' Bumbletow' Hill, the location of Stop 16. 120.6 120.6 The hill on the MAP 99 andCliff Cliff Drive Drive (Cliff (Cliff Drive Drive was was followed followed earlier earlier in in the field trip) just junction of 1.15-41 US41 and 121.3 121.3 The junction before Ahmeek. Ahmeek. - junction of US41 US-41 and and the the road road from from Five Five Mile MilePoint. Point. This is the end of Leg F - Five Mile 121.6 The junction Mile 121.6 Point. Point. City. This 122.4 122.4 The road to the left goes to Copper City. This is is the start start of Leg G -- Copper City. City. 122.5 122.5 Enter Houghton County. County. 122.55 The road to the right 122.55 right goes goes to Stops Stops 15 15 and 16. 16. Continue Continueon onUS-41. US-41. �114 114 MainRotdLOg Main Road Log goes to Stops Stops 13 13 and and 14. 14. 123.8 The road on the left goes 123.8 124.8 Settlement of Centennial. Centennial. 124.8 edge of of CalumetLaurium. Calumet/Laurium. This is the start 125.45 The The junction of of US-41 US41 and M-203 on the north edge start of Leg Park, an an alternate alternate route route back back to to Hancock. Hancock. Continue ahead on US-41. McLain State Park, US-41. H -- McLain MAP 24 Caluinet on on Red Red Jacket Jacket Street. Street. After 126.15 Turn Turn right right at at the the flashing flashing light light toward the center of Calumet After the the turn turn to Calumet" Calumet" sign signand andaalarge largepiece pieceofoffloat floatcopper. copper. Float copper is on the left, is the "Welcome to masses of native copper copper plucked by glaciers from veins and lodes during the latest latest Pleistocene Pleistocene glaciation. Later, Later,the themasses massesof of native native copper copper were were deposited deposited with with other other sediments sediments as as the the glaciers glaciers retreated, about 10,000 10,000 years ago. Float Float copper copper of of varying varying sizes sizesare arestill stillbeing being found foundby by farmers fanners and during construction of buildings. On the right and ahead, are basalt block buildings that On the right and ahead, are basalt block buildings that were were headquarters of the Calumet and Hecla Consolidated Consolidated Copper Copper Company, Company, which which was the the former headquarters largest mining company company in the the Keweenaw Keweenaw Peninsula. Peninsula. one-way toward toward the the school school and andwater watertower. tower. Straight 126.2 Turn right on Mine Street, going one-way Straight ahead is 126.2 the historic downtown Calumet, Calumet, which whichisis part part of of the the Keweenaw KeweenawNational NationalHistorical HistoricalPark. Park. The C&H Mining Mining Coppertown Museum is 0.2 miles ahead on the left, and offers an overview of the C&H Company. old stack stack is is visible visible at at 2:00. 200. 126.3 126.3 The Calumet school is on the left. An old 126.4 At9:00, 9:00,about about100 100m mbeyond beyond the the tower, tower, isis an an old oldstone stonebuilding building 126.4 The water tower is on the left. At which houses 200 km of locatable by Gordon Peterson. Peterson. The locatable drill core owned by The fenced fencedarea areaatat7:00, 7:00, is the location of the the Red Jacket Headframe, it sits above the Calumet and Hecla ConglomerateConglomeratehosted native copper deposit--the largest single deposit in the Keweenaw Peninsula. 126.45 Just at at the the end end of of an an old oldsandstone sandstone building, building, turn left on the gravel gravel road entrance to the school school lot. Park 50 m m ahead ahead on the right to a low low outcrop. outcrop. parking lot. Park on on the theright right and and walk walk about about 50 STOP 33: Calumet Calumet(glacial (glacialgrooves) grooves) Basalt of the PLV is exposed in this low, glacially smoothed outcrop. outcrop. This This stop stop provides provides well-developed glacial glacialgrooves. grooves. The grooves are oriented an opportunity to observe exceptionally well-developed crest-to-crest spacing spacing of of about about25 25cm cmand andamplitude amplitudeofof33toto55cm. cm. Mineralized about E-W with a crest-to-crest segregation cylinders cylinders in in the the lava flow flow are resistant to the glacier, so flow direction vectors are resistant to spectacularly shown. spectacularly shown. Turn 126.5 T 126.5 urn around and return return to Mine Street Street and turn left left (one-way). (one-way). Turnright rightonto ontoChurch Church Street. Street. The ThePeterson Peterson Funeral Funeral Home Home is is on on the the left. left. 126.6 Stop sign. Turn 126.6 1. Turn 126.65 A stop stop sign sign at at the the junction junction with with USA US-41. Turn right right toward toward Hancock. Hancock. 126.95 Flashing light again. Continue Continuestraight straight ahead ahead this this time. time. Calumet. The The Osceola Osceola Mine Shaft No. 13 13 can be seen seen on the the right right side side of of the the 127.9 Southern edge of Calumet. 127.9 road behind the the Holiday Holiday gas gas station. station. �Map 9MamRoadLog Stop 3 Os, - - 4 �116 128.0 128.0 MainkoadLog Turn right right on on Millionaire MillionaireStreet Street just just beyond beyond the the Holiday Holiday gas gasstation. station. 128.15 Turn Turnleft left onto ontoChurch Church Street, Street, just just before before the the old old mine mine headframe. headframe. four-way junction, junction, continue continue straight straightahead. ahead, 128.5 A four-way 128.5 the road road and and walk walk to the rock piles on the right side of the 128.6 PUll Pull over alongside the the road road (northwest). (northwest). 128.6 STOP copper STOP34: 34: Osceola OsceolaMine Mine(native (native copperdeposit depositwithin withinPortage PortageLake LakeVolcanics Volcanics [PLy]) [PLV]) The Amygdaloid in inthe theCalumet Calumetarea. area. Production from The Osceola Osceola Mine worked the Osceola Amygdaloid the the Osceola Osceola Amygdaloid Amygdaloid began began in in 1879 1879and and continued continued until until 1920, 1920, when when mining mining activity activity stopped. stopped. The continued until until 1968. AA total The mine mine reopened reopened in 1925 1925 and and production production continued totalofofabout about600 600million million lbs Ibs of of refmed refined copper copper was was removed removed from this mine, mine, which which ranks ranks fifth in production production in the the Keweenaw native copper copper district. district. The amygdaloid amygdaloid was developed for about four miles miles along along strike and to a depth depth of of 1372 1372m m along along incline incline (823 (823 m m vertically) vertically) (summarized from Weege and Pollack, 1971). 1971). is ophitic ophitic basalt and varies in The Osceola Flow Row is in thickness thickness from from 11 11 to to 64 64 m. m. The thickest part of the productive. The the flow, flow, near Calumet, has been the most productive. The Osceola Osceola Row Flow has has been been traced traced from the Cliff Mine to the Arcadian Mine. In Inthe theCalumet Calumetarea, area, the the flow flow strikes strikesN35°E N35-E and and dips dips around around 37°NW. 3 7 W . The The top top of of the the flow flow is is a well developed fragmental amygdaloid consisting of well oxidized, reddish, annular fragments of of vesicular lava which which typically range in size from from aa few few cm up to to 30 30 cm cm in in diameter. diameter. The Thelode loderanged ranged ininthickness thickness from from 30 30 cm cm up up to toand andsometimes sometimes greater than 18 m. Amygdules Amygdules and and the the voids voids in in the the brecciated brecciated flow flow top top are are filled filled mostly mostly with with calcite, epidote, native copper. copper. Quartz epidote, K-feldspar, chlorite, and native Quartz is present in certain areas and also minor amounts amounts of of prehnite, prehnite, pumpellyite, pumpellyite, laumontite, laumontite, and analcite analcite are are found. found. The fragmental fragmental amygdaloid by sill-like layers of dense basalt, which amygdaloid is frequently interrupted interrupted by sill-like layers which may may have have been been emplaced by injection of lava from the interior interior of the the flow flow into into the the solidified, solidified, brecciated brecciated crust. crust. The dense basalt basalt layers layers provided provided bathers barriers to to the themovement movement of of mineralizing mineralizing solutions. solutions. Native Native copper in the small masses masses up up to an inch in diameter, the Osceola Osceola ranges ranges from disseminated-todisseminated-to- small diameter, to to large masses weighing ;Butler and weighing hundreds of lbs. Ibs. (summarized (summarizedfrom fromWeege Weegeand andPollack, Pollack,1971 1971;Butler and Burbank, 1929). 1929). Burbank, The The Osceola Osceola Shaft Shaft No. 66 is is at at the the southwest southwest end of the ore ore body, and was the the richest richest part part of the deposit. AAbather barrierzone zoneisisbelieved believedtotohave havefunnelled funnelledmineralizing mineralizingsolutions solutionsmoving movingup-dip, up-dip, resulting resulting in the the high highcopper coppercontents. contents. Textures Textures and colors, colors, characteristic characteristic of of fragmental fragmental amygdaloid, can be seen in this rock pile. An Anestimate estimatewas wasmade made by by Stoiber Stoiber(unpublished (unpublisheddata) data) of the the percentages percentages of of the thesecondary secondaryminerals: minerals: calcite, calcite, 59%; 59%; microcline, microcline, 29%; 29%; prehnite, prehnite, 4%; 4%; epidote, 1%; 1%;quartz, quartz, 1%; 1%;and and chlorite, chlorite, 5%. 5%. Pumpellyite, Pumpellyite, laumontite, native copper, and and the the minerals listed above can be of the basalt in the vicinity of be found found on on this thisrock rock pile. pile. Bleaching Bleaching of be seen seen in in individual individual specimens. specimens. native copper can be Retrace Retrace the route back to US-41. Turn Turn right right on on US-41 US-41 to return to Hancock/Houghton or turn left to return Park, at M-203 M-203 on on the the far end of return to to Calumet Calumet for for the the junction of of Leg Leg H H -- McLain McLain State Park, Calumet. Calumet. OF MAIN ROAD ROAD LOG END OF �lap 117 LEG A A REDRIDGE LEG REDRIDGE Mileage Mileage Al MAP A1 of the the Memorial Memorial Union Building from the circular drive located on the northeast side of 0.0 0.0 Begin Leg A from on the campus campus of of Michigan Michigan Technological Technological University. 0.05 0.05 Turn left. left. 0.1 0.1 Immediately 1. The Quincy Mine can be seen on the the Immediately after, after, turn turnright righton onTownsend TownsendDriveIUS-4 Drive~US-41. skyline ridge. Continue Continueon onUS-41 US-41through throughHoughton. Houghton. 0.7 On the left is is Burger Burger King King and and Stop Stop 6. 6, in Houghton. Houghton. 0.85 The stop light light in 1.15 1.15 Intersection, follow follow M-26 M-26 toward toward Ontonogan. Ontonogan. Turn right on on Canal Canal Road. Road. 1.7 1.7 MAP A2 Al: Houghton HoughtonCanal CanalRoad Road(Copper (CopperHarbor HarborConglomerate) Conglomerate) 2.5 Stop Al: exposed along along the the south south side side of of the road. It is mostly Copper Harbor Conglomerate isis exposed mostly and basalt basalt red-brown conglomerate conglomerate composed composed of of clasts clastsofofrhyolite rhyolite(—50%), (-SO%), granophyre granophyre (—40%), (-40%), and (—10%) with typical diameters of about 1 cm and maximum diameter of 40 cm. Clasts are matrix (-10%) with typical diameters of about 1 cm and maximum diameter of 40 cm. Clasts are supported with occasional 45 cm cm thick, thick, discontinuous discontinuous lenses of of clast-supported clast-supported conglomerate, conglomerate, cemented with with sparry sparry calcite calcite (possibly (possiblypaleocaliche). paleocaliche). Conglomerate Conglomeratebeds bedson onthe the order order of of 11 m cemented alternate with with 15 to to 25 cm thick thick beds beds of of very very fine to coarse red-brown red-brown sandstone. sandstone. Such thick alternate lithologies are typical of the Copper Copper Harbor Conglomerate, Conglomerate, which was deposited in alluvial alluvial fans. fans. Stratigraphicposition positionofof the the Copper The attitude The attitude of bedding bedding is N20°E, N20"E, .% 939W. '3 Stratigraphic Copper Harbor Harbor Conglomerate is shown in Figures 2, 6, and 25. Continue on the Houghton Houghton Canal Canal Road. Road. 3.75 Pleistocene glacial fluvial sand and gravel at Cole's Creek. Creek. Stop A2: Cole's Cole'sCreek Creek(glacial (glacialsediments) sediments) Pleistocene glacial glacial sediments sediments cover cover much much of of the A variable thickness of unconsolidated unconsolidated Pleistocene bedrock of the Keweenaw Peninsula. The Keweenaw Peninsula. The Keweenaw Keweenaw Peninsula Peninsula has probably been modified modified by by During maximum glaciation, the entire all of the major glacial episodes of the Pleistocene. of the major glacial episodes of the Pleistocene. entire Keweenaw Peninsula Peninsulaisisbelieved believedtotohave havebeen beenoverridden overriddenbybyaround around3000 3000mmofofice. ice. The final Keweenaw glacial advance and stillstand over the Keweenaw Peninsula was was made made by by the Keweenaw Keweenaw Peninsula Keweenaw Bay Lobe, marked by an an end end moraine moraine of of the the Wisconsin Wisconsin Stage Stage (Fig. (Fig. 15) 15)(Warren, (Warren, 1981). 1981). channel cut cut by by drainage drainage through through the the Portage Portage Gap Gap area, area, is the The earliest recognized recognized channel the southward flow flow of of water. water. Huron Channel Channel (Map (Map ).). The channel is waterworn bedrock due to aa southward Since there is no delta at the southern end of this channel, perhaps the source of water water was aa large large had time time to to settle before before the the water water was removed. removed. The lake where glacial sediments sediments had Thedrainage drainage pattern through the Portage Gap is shown shown in in Pig. Fig. IS. 18. �00 �-D /lr. / kr4t2/ + —A ,, - ,'tc,°...9) ZPL%H n=.. 882' r) k iitc i 'V. - $O'?qNE Delta Kamed C' TANTO * —1 3 4, p I Stop 5/ çt e'Jk V. V V2 I)'E,.d' 'j[ CITY'\\ II FF.. 4 •.pAWC Al �120 120 Legs Legs part of of a delta kame, kame, is just just west west of of the the Huron Huron Creek Creek Channel. Channel. The This locality, part The sands sands and gravels in this dissected dissected ridge show strong evidence of being deposited by a braided stream, stream, closely associated with aa glacier. Extreme variations variations in in grain grain size size and and sorting occur within glacier. Extreme within a distance of of a few meters, differing flow flow regimes regimes during during deposition. deposition. Poorly- to distance meters, which suggests differing well-worked cobble-to-pebble gravels are also well-worked unconsolidated unconsolidated sands sands predominate, predominate, but poorly sorted cobble-to-pebble present. The Thegravel gravellenses lensesmay maybe beseen seennear nearthe thetop topand andbottom bottomof ofthe theexposure, exposure,and andnumerous numerous are present. present. Toward the left side of the cut, individual resistant bedding in cut-and-fill structures are the sands is visible. the visible. On Onthe theright rightside sideof ofthe thecut, cut,contorted contorted bedding bedding within within the sand sand layers layers is visible. This Thisdeformation deformation isis aaresult resultof ofpost-depositional post-depositional slumping slumping of of the the unconsolidated unconsolidated sands. sands. MAP A3 MAP A3 5.85 Turn left (west) (west) toward Redridge Redridge and Freda. Freda. 5.85 MAP A4 A4 9.45 The road curves to the left. left. 9.45 MAP A5 11.55 The Thesettlement settlementof of Redridge. Redridge. 11.85 just past the guardrail. the main 11.85 Turn Turn right right toward toward Lake Lake Superior, Superior, just guardrail. Follow Follow the main dirt road road to to Lake Lake Superior by either either foot or or auto. auto. 12.25 Stop 12.25 Stop A3: A3: Redridge RedridgeCliffs Cliffs(Freda (FredaSandstone) Sandstone) At the edge edge of of Lake Lake Superior, Superior, is aa large large area area of of gray-to-black gray-to-black "stamp" "stamp" sands. The sands sands were produced during processing processingofof the the native native copper copper ores ores shipped shippedby by train train to a mill mill here here were produced during (Redridge). (Redridge). The The steel steel structure structure on the opposite opposite side of the paved road at the turnoff, is an an old old which provided provided water water for for the the mill. mill. The dam which The old old smoke smoke stack stack is the principal principal ruins of the mill mill here. The Thestamp stampsands sandswere were deposited deposited in in Lake Lake Superior Superior as tailings from the mill. Since Sincepyrite pyrite and other virtually absent absent in the ores of of the the Keweenaw Keweenaw other potential acid- producing minerals minerals are virtually these sands sands do not yield acid drainage. The are Peninsula, these The elemental elemental constituents constituents of of the the sands sands are relatively insoluble, insoluble, except exceptunder underacid acidconditions. conditions. Thus, without contained in minerals that are relatively acid waters, the constituents locked in in place. place. This minimizes the environmental. environmental impact of constituents are locked these sands. Walk Walk to, to, and andalong, along,the the beach beach to to the the red-colored red-colored cliffs. During Duringthe thewalk, walk, you you can can see sections of the stamp stamp sands sands cut cut by by wave wave action. action. Freda Sandstone Sandstone isis well well exposed exposed in in aa 20 meter meter high high wave-cut wave-cut cliff cliff on on the the shoreline of of Freda fme sandstone-to-siltstone. Sub-parallel Lake Superior, Superior, and is composed of red very fine Sub-parallel to bedding, bedding, about 20 to 40 40 cm cm thick, thick, red color color alternates alternates with 3 to 5 cm thick of gray color (reduced) without striking differences differences in grain Mica is readily striking grain size. size. Mica readily visible visible on on bedding bedding plane plane surfaces. surfaces. The The lithologies exposedare are typical typical of of the which was was deposited deposited in in a fluvial the Freda Freda Sandstone, Sandstone, which fluvial lithologies exposed environment. toward Lake Superior, about N-S strike, environment. Bedding Bedding dips shallowly toward strike, and and 5°W 5 W dip. dip. N38°W and and dipping dipping 88W. 88W. Prominent joints in this exposure are spaced about 2.5 m apart, striking N38W subvertical gray gray zones zones follow followthe thejoints. joints. This is one of many spots along the shore Irregular subvertical shore of Lake Superior where canoes offer an an excellent way wayto to see seethe the geology. geology. If you launch here (don't go if the surf surf isis up), up), paddle paddle westward westward to to Freda Freda for for spectacular spectacular sandstone sandstone cliffs. cliffs. End of Leg A -- Retrace route to Houghton. Houghton. �lags — ——— II - C I, Si MAP A3 �122 Map A3 Map MAP A4 �Map A4 123 .)4Jo Jt2 •0 0 4) 0 U) MAP A5 �124 124 Legs LEG B OWL OWL CREEK CREEK MAP MAP BBI1 d at the head head of the the bay. bay. •AtEagle EagleHarbor, Harbor,M-26. M-26. Turn right on Garden City Roa Road 0.0 At 1.05 Them dirtroad, road,just just aafew fewhundred hundred meters meters up up 1.05 Thereisisaadirt dirtroad roadthat thatgoes goes off off to to the the left. left. From Fromthis thisdirt hill, you can begin a traverse hill. traverse upstream on Eliza Creek to get to the exposures of the Portage Portage Lake Lake Lava Flows of this this region. region. Creek. You 1.15 You can can also also begin begin aa traverse traverse upstream upstream on Eliza Elua Creek from here. 1.15 Crossing Eliza Creek. MAP B2 to the the right rightgoes goesdownhill. downhill. If you follow this road several hundred meters, meters, you will 2.5 The road to 2.5 reach the 30-mile 30-mile stamp stamp sands; sands; which are the tailings tailings from the the Copper Copper Falls Falls mining mining operation. operation. From this stamp sand, you can gain access to the bottom of Owl Creek, and can begin a 22 to to 33 hour traverse upstream to the bridge along this road. road, IfIf you you continue continue upstream upstream beyond beyond the the bridge, bridge, you will reach aa poor poor rock rock pile pile along along Owl Owl Creek from the Copper Falls mining operation. By By climbing out of the creek bed, to the east, one can reach reach a dirt road road which which will will come out on the main road at mileage 2.7 just ahead. ahead. 2.6 Road to the left goes goes uphill to to the the rock rock piles of the the Copper Copper Falls Falls Mine, Mine, which which isis part part of of Stop StopBB1l described below. Bi: Owl Lake STOP Bl: OwlCreek Creek(Portage (Portage LakeVolcanics Volcanicsand andCopper Copper Falls Falls Mine) Owl Creek Creek is another of of the the streams streams that that cuts cuts across acrossthe the upper upperpart partof of the the PLV. PLY. The The traverse begins downstream, where where the the base base of of the the Copper Harbor Harbor Conglomerate Conglomerate and and top top of of the PLY interfinger. interfmger. Excellent PLV Excellentexposures exposuresof of interbedded conglomerate/sandstone conglomerate/sandstoneand lava flows along as several several well well exposed exposed amygdaloidal amygdaloidal flows. flows. the bed and sides sides of Owl Owl Creek Creek are are visible, visible, as as well well as The Copper Falls Mining Company worked several fissures fissures and and the the Ashbed Amygdaloid. refmed copper from the The mine operated operated from 1847 1847 to 1893, 1893, producing about 18 million lbs. of refined Ashbed Amygdaloid, Amygdaloid, and and about about 99 million million Ibs. lbs. from fissures; mostly the the Owl Creek Ashbed fissures; mostly Creek Fissure. Fissure. Row that Copper Falls was the only mine in the north end of the district above the Greenstone Flow that paid dividends, but was not a profitable venture (summarized from Butler and Burbank, 1929). was not a profitable venture (summarized from Butler and Burbank, 1929). The The Owl Owl Creek Creek vein vein starts starts near the base of the the Copper Copper Harbor Harbor Conglomerate Conglomerateand and extends extends through the Portage Lake Volcanic Series, probably probablyinto intothe the Greenstone GreenstoneFlow. Flow. The vein Volcanic Series, vein was was productive only in the vicinity of the Ashbed Amygdaloid (described also at Stop 20). The productive only vicinity of the Ashbed Amygdaloid (described Stop 20). The Ashbed Ashbed Rows Flows are are porphyritic porphyritic and and scoriaceous, scoriaceous, with with aa notable notable clastic clasticcomponent. component. In some some localities, pebbles and boulders of amygdaloid amygdaloid are are set set in in aa sandy sandy matrix. matrix. Johnson (1985) studied the Ashbed exposed upstream upstream of of the the road road on on Owl Owl Creek. Creek. Here the Ashbed of a broken Ashbed consists of pillowed lava breccia (hyaloclastite). The hyaloclastite contains angular fragments of (hyaloclastite). The hyaloclastite contains angular fragments of vesicular vesicular basalt ranging in size size from from ash-sized ash-sized to blocks. The Thelarger largerfragments fragmentsoften oftenhave havedistinct distinctrinds, rinds, whereas smaller fragments fragments are are finely finely fractured, fractured,like likeperlitic perlitictexture. texture. This horizon horizon is interpreted whereas as subaqueously subaqueously emplaced. emplaced. It is the the only only documented documented subaqueous-emplaced subaqueous-emplaced volcanic horizon within the PLV of of the the Keweenaw Keweenaw Peninsula Peninsula (see (see also also Stop Stop20). 20). The mineralization of the similar to to that mineralization of the Ashbed Ashbed Amygdaloid Amygdaloid is is similar that found found in in other other amygdaloids in the Keweenaw Peninsula. Peninsula. At At the the Copper Copper Falls Mine, the the following following are are the the more more abundant minerals: calcite, quartz, quartz, epidote, epidote, and and pumpellyite. pumpellyite. Datolite is abundant abundant in the the Ashbed Ashbed �-L 03 -D N V - £7, - r cope \, a b Boat Ramp -It,-- - - 4<e— -2 a I H) 4 erat 0 4 + : : 1-: 1" - -pi 0 - 7jJ%c- '—2-c 2 , cofl9 sN-:s't 0 hg rs - 09to, t- %(i c4 -:task - - 1*AsA H £AQLEHARBOR —/ — J-- 'Y21u - -2 — , tCopper Harbor Conqiomerate rY ( pj e(-;C -, f't..CJ cr'719J :4 4 C0n° JatHarbor. ,- Lake Superior ' -rapS ___ l.A 1-.) ¾• �_______ ______________ •HMj606 pot0 ci 4.'Trtt-!i'i - — — 4._ /. cy or Harbor CongIomerate 0 . . 4-.t 0 — / 7. - I.. ,_J-, t__a_a.____..__—r+ ( 4- -C- —I ft k_Si rcV '9fl4'29'yT I -" C -- �ten 127 127 near fissures, such as Owl Creek. Creek. Native toward the the top part of the Native copper copper was more abundant toward deposit. Also Alsoreported reported in in the theCopper Copper Fails Falls area area are are these these minerals: minerals: laumontite, laumontite, prehnite, native silver, silver, adularia, adularia, analcime, analcime, apophyllite, apophyllite, faujasite, faujasite,natrolite, natrolite,and and stilbite stilbite (summarized (summarized from fromButler Butlerand and Burbank, 1929; Clarke, Clarke, 1974b). I 974b). The in the the The Copper Copper Pails Falls Mine Mine is is stratigraphically stratigraphically the highest highest in Keweenaw native copper district, and is near the top of the pumpellyite zone (see Figs. 88 and and 12 12 in the Introduction). Introduction). 2.7 Cross Cross Owl Owl Creek. Creek. 3.0 A dirt town site of of Copper Copper Falls. Falls. Copper dirt road that slants to the left goes to the old town Copper Pails Falls was there are a handful settled in about 1846, settled 1846, and had aa population population of 500 500 in 1877. Today, Today, there handful of of residents. residents. 3.7 park with with aa tower. tower. From On the right is a roadside park From the the top top of of this this tower, tower, there there is is an an excellent excellent view of Isle Royale on a clear day. You Youcan canalso alsosee seesome someofofthe theridge-vailey ridge-valley topography, topography, due due to the dipping lava flows and conglomerates in this part of the section. flows and conglomerates the section. 4.4 The junction junction of a dirt road on the right. right. Continue paved road. road. Prom Continue ahead on the paved From this this road, road, aa short distance to the west, there is access to Jacobs Creek, the site of the Arnold Mine, along the Ashbed Amygdaloid. Amygdaloid. This is the end Ashbed end of of aa traverse traverse one one can can make make across across the upper upper part part of of the the PLY. ItItisisrecommended PLV. recommendedto tobegin begin the thetraverse traverseat at the the lower lower end end of of Jacobs Jacobs Creek, where where itit crosses crosses M-26. This Thisisisaavery verytough toughtraverse traversewith with many many steep steep and and dangerous dangerous points within it. Excellent Jacobs Creek. Creek. At exposures of many individual lava flows are along Jacobs At the the Arnold Arnold Mine, Mine, one one of of the the nearly conformable massive massive dikes is exposed in the streaxnbed. Geologic traverses made along streambed. Geologic traverses made along 1),and and Jacobs JacobsCreek Creekallow allowone oneto to look look in in detail at Eagle River (Stop 19), 19), Owl Creek (Stop B Bl), lateral variations in the upper part of the the PLY. PLV. 4.6 Cross Jacobs Jacobs Creek. Creek. END OF LEG B - Continue ahead on the paved road to reach US-41, or turn around and retpm return to to Eagle Eagle Harbor. �__ 128 128 ~ev LEG C HORSESHOE HORSESHOEHARBOR HARBOR MAP C1 Cl Leg C at the entrance Park, east of Copper Harbor. Continue Continueahead ahead entrance to Fort Wilkins State Park. 0.0 Start Lee -. Harbor. to the east east (away (away from from Copper Copper Harbor.) Harbor.) 0.15 On Harbor. The Onthe theleft leftisisaatrail trailfor foraccess accessto tothe theshoreline shoreline of Copper Harbor. The basalt flows of the Lake Shore Traps are exposed along- the lakeshore. lakeshore. MAPC2 MAP C2 1.05 1.05 The end of the paved road. This This isis the the end end of of US-41, US-41, which goes south from here all the way to Florida. Continue maintained gravel gravel road. road. The the southern tip of Florida. Continue ahead on the poorly maintained The road road isis easily traversed with aa regular regular passenger passenger car. 1.5 1.5 At the ridge ridge crest. crest. 1.65 1.65 On the right, right, aa ridge ridge of ofCopper CopperHarbor HarborConglomerate Conglomerate isis visible. visible. which goes goes steeply steeply downhill. downhill. This dirt 1.95 1.95 The crest of a ridge with a dirt road on the left, which dirt road goes to Horseshoe Horseshoe Harbor. ItItisisnot notrecommended recommended that that you drive drive this road with a regular passenger passenger car. Park and proceed on foot along the dirt road toward Horseshoe Harbor. proceed on foot along the din road toward Horseshoe Harbor. you can gain access to the If you continue continue on the main main road road (straight (straight ahead), you the region region around around Point (it is private private land). land). Of greatest geologic interest is the the region region around around High High Rock Rock Keweenaw Point Bay, accessible by four-wheel drive vehicles. vehicles. North of the end of the road, the Lake Shore Traps North of the the the Lake Shore Traps are exposed in in a series series of of rocky rocky wave-washed wave-washed outcrops outcrops that that allow allow examination examination of of the the are exposed physical/solidification physical/solidification features of Keweenawan Keweenawan lava flows. Walking Distance (A typical typical pace--2 pace-2 steps--is steps--is about 55 ft.) ft.) FEET FEET (Approximate) The parked parked cars cars on on the the gravel gravel road road isis at at the the crest crest of of the theridge. ridge. This ridge is supported by by tilted tilted 0 0 walking downhill downhill (it (it is is steep) on the beds of of Copper CopperHarbor Harbor Conglomerate. Conglomerate. Begin Begin walking the poorly poorly maintained dirt mad. 1750 AAglacially glaciallypolished polishedoutcrop outcropof ofbasalts basaltsof of the the Lake Lake Shore Shore Traps. Traps. 2700 On Onthe theleft leftisisa aridge ridgeofofbasalt basaltofofthe theLake LakeShore ShoreTraps, Traps,which whichare area asequence sequenceofofmafic-tomafic-tointermediate lava lava flows flows within within the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. The Lake Shore Traps are intermediate are described more at Stop 24. Continue Continueon on the the main main road. road. 2850 Copper bed. Just CopperHarbor HarborConglomerate Conglomerateoutcrops outcrops on the left and in the road bed. Justahead, ahead, the the basalt basalt of of seen in in the the road mad bed. bed. We the Lake Shore Traps are seen We are are now now near the upper contact of the Lake Shore Traps and conglomerates conglomerates of the the Copper Copper Harbor HarborConglomerate. Conglomerate. 3000 3000 Lake Shore Shore Traps Traps basalt basalt outcrops outcrops in in the the road mad bed. bed. 4000 Lake LakeShore ShoreTraps Trapsbasalt basaltoutcrops outcropson on the the left. left. 5300 Several pullouts for autos are 5300 are on the right. right. �___ _ ___ __ ______ Lake Superior àIHarbor — ____ _____ _____ ________ ________ _____ ____ ________ Pode. CopperHaruo Lighthouse V . —•• a me — rate - ci Copper 3F32 Copper Hero0 C . 1;*.t S S e Fa - h557/j1000 Lake 620 k1> L': 3 / ENA'W Lake !zz?j !U_flw)) SSclKSfl) !T... ,-D C -I / zV Es p3I :N I 'I Lake f SE SON C) Â¥ F0 ll H 2 -L L . - 4Jk$. L Mud-, -' .. \ aI .. Hooe C - Fiow '\ 1)PL o rafl JtiL-ji L* 603 ' - > Lake b HAYS (Psi — -. 6z=p A ci / 620?. 5erHarbor 1 e -- a I )o Sit È ��~eo Legs 131 131 Harbor is is on on the the left. left. Follow 5375 Follow that that trail trail downhill. downhill. 5375 The major trail to Horseshoe Harbor Reset Distances Distances At the dirt dirt road road and and the thetrail trailtotoHorseshoe HorseshoeHarbor, Harbor,going goingdownhill. downhill. 0 60 60 450 450 Horseshoe Harbor Harbor isis aa part of the Horseshoe Harbor the Michigan Michigan Chapter of The The Nature Nature Harbor sign. sign. Horseshoe Conservancy. Please do not collect rocks. Please do not collect rocks. Copper Harbor Conglomerate outcrops in the the path. path. 1350 Horseshoe Harbor beach. Proceed Proceed left left (north) (north) toward toward the rock ridges along along the Lake Lake Superior Superior 1350 At Horseshoe It is recommended to walk along the shoreline. Follow the prominent ridge to the left (west). shoreline. Follow the prominent ridge the left (west). lowland just just landward landwardof ofthe theridge ridge(south). (south). Stop Stop Cl Cl is at the lowland the far far west west end end of of this this ridge, ridge, where where excellent exposures exposures of stromatolites. stromatolites. there are excellent Stop Cl: Harbor Cl: Horseshoe HorseshoeHarbor Harbor(Copper (Copper HarborConglomerate) Conglomerate) PLEASE DO NOT REMOVE REMOVE ROCKS The Copper Harbor Conglomerate at the the east end on Horseshoe Harbor is composed of Conglomerate at red clast-supported conglomerate with with aa 5 m thick bed of clast-supported conglomerate of shale, shale, sandstone, sandstone, conglomerate, conglomerate, and and stromatolite (Fig. 41). The Theconglomerate conglomerateisiscomposed composedof of pebble-to-cobble, pebble-to-cobble, well-rounded well-rounded clasts dominated by rhyolite and corresponds corresponds to conglomerate conglomerate facies as described described by by Elmore Elmore (1984). (1984). These conglomerates are interpreted as as an an alluvial alluvial fan fan deposit deposit shed shed toward toward the the center center of of the rift. The stromatolites stromatolites are are associated associated with with conglomerate, conglomerate, trough trough cross-stratified cross-stratified sandstone, sandstone, and and conglomerate-mudstone (Elmore, (Elmore, 1983). 1983). The The stromatolites, stromatolites, Collenia undosa undosa species species (Cornwall, (Cornwall, 1955), intermittently found found from fromhere hereto toDan's Dan's Point Point (Stop (Stop 27). 27). Elmore (1983) describes the 1955). are intermittently various forms of stromatolites, including laterally linked bedded, oncolites, and and poorly developed forms oncolites, mats. The Thetypical typicalstromatolite stromatoliteisisaahemispheroid, hemispheroid,about about 15 15cm cm thick thick and and up up to to40 40cm cminindiameter, diameter, Contorted stromatolites stromatolitesmay maybe be due due to soft and isis often often draped draped over overcobbles. cobbles. Contorted soft sediment sediment deformation deformation during during compaction. compaction. Ooids, Ooids,oncolites, oncolites,and and intra intraclast clast limestone limestone(stromatolite (stromatoliteand and oolite oolite fragments) occur within within stromatolites. stromatolites. The The stromatolites stromatolites are cryptalgal deposits in abandoned abandoned stream channels (Fig. 41). Horseshoe Harbor is worth the time to visit for its beautiful scenery alone. The Theexposures exposures of stromatolites stromatolites are are the the best best of ofthe theKeweenaw KeweenawPeninsula. Peninsula. END OF LEG C -- Return to the vehicles vehicles and and proceed proceed back back to to Copper CopperHarbor. Harbor. �132 LEG I) D EAST SIDE SIDE OF OF THE THEKEWEENAW KEWEENAW PENINSULA PEN1NSTIT.A MAP Dl junction of the road to Lac La Belle. Belle. Turn Turn left left and and go go down down hill hill toward toward Mt. Mt. Bohemia. Bohemia. 0.0 The junction MAP D2 D2 On basalt of of the the PLy. These On the left left side side of of the the road road isis aalarge largeoutcrop outcrop of of amygdaloidal amygdaloidal basalt PLV. These 3.5 exposures are flows in the lower part of the formation, formation, below the Scales Creek Flow. 3.9 Ad dirt road turning turning off offthe themain mainroad roadtotothe theleft. left.This ThisisisSTOP STOPDDl at Mt. Mt. Bohemia. Bohemia. It is about about irt road l at a one half mile mile walk walk up up this this road mad to to the the summit summit of of Mt. Mt. Bohemia; Bohemia; the the road road isisaafour-wheel four-wheel drive drive vehicle vehicle road. road. STOP (diorite STOP Dl: Dl:Mount MountBohemia Bohemia (dioritestock stockwithin withinthe thePortage PortageLake LakeVolcanics Volcanics [PLV]) [PLV]) Walk the road to the summit Mount Bohemia. Bohemia. The summit of Mount The road road crosses crosses flows flows of of the the PLY. PLV. The diorite and granophyre intrusive complex crops crops out out to to the the southeast southeast of of the the summit. summit. Intrusive Intrusive stocks are not common in the Keweenaw Peninsula, most occur in the lower part of the PLV and are rhyolitic in composition. composition. Mount Mount Bohemia Bohemia is the only only occurrence occurrence of a diorite diorite stock stock in in the the Keweenaw Keweenaw Peninsula. Peninsula. An intrusive stock of of diorite diorite and and granophyre granophyrecrops cropsout out on on the the south south slope slope of of Mount An intrusive stock Bohemia Dl). The ~ o h e m i a(Map Dl). Themajority majorityofofthe theMount MountBohemia Bohemiastock stockisisan analtered, altered,massive, massive,mediummediumto coarse-grained, coarse-grained, miarolitic miarolitic diorite. The Thepre-alteration pre-alteration mineral mineralassemblage assemblageconsists consistsof of 45 45to to50% 50% sodic plagioclase, plagioclase, 30 30 to 50% mafic and hornblende), and up up to 3% sodic mafic minerals minerals (augite (augite and hornblende), and 3% quartz quartz the stock, stock, and and in small (Sikkila, 1984). 1984). Magnetite Magnetite is found throughout throughout the small areas areas exceeds exceeds 15%. 15%. Apatite and sphene are also present present in in trace trace amounts. amounts. The southeast portion of the stock consists of quartz diorite 30% quartz, quartz, 7% biotite, and of diorite with with approximately approximately 60% sodic plagioclase, plagioclase, 30% and 3% 3% The central major central core core isis aafinefine-totocoarse-grained, coarse-grained,niiarolitic miaroliticgranophyre. granophyre. The major quartz. quartz. The constituents of of the granophyre constituents granophyre are sodic sdc plagioclase, plagioclase, quartz, and granophyric granophyric intergrowths intergrowths of quartz and feldspar quartz feldspar with with lesser lesser amounts amounts of of orthoclase, orthoclase,sericite, sericite, hornblende, hornblende, apatite, apatite, sphene, sphene, magnetite, and chlorite. Miarolitic Miaroliticcavities cavitiesare are lined lined with with quartz, quartz, albite, albite, calcite, calcite, chalcopyrite, chalcopyrite, and chalcocite chalcocite (Cornwall, (Cornwall, 1954). 1954). The diorite and granophyre at Mt. Bohemia intrude basaltic lava flows of the lower lower part part PLY. The at the the contact. contact. The intrusive body is cut by of the PLV. Thebasalts basalts are are slightly slightly metamorphosed at north-northwest. This fissure is mineralized with with copper the Lac La Belle Fissure which trends north-northwest. sulfides, mostly chalcopyrite and bomite bornite with a gangue of calcite, chlorite, and quartz (Juilland, (Juilland, 1965). 1965). The stock stock has hasbeen beenmoderately-to-strongly moderately-to-strongly altered. altered. Secondary potassium feldspar is is observable throughout throughout the the stock. Hand Hand specimens specimens have have the themisleading misleading appearance appearance of of syenite, syenite, because of the potassium feldspar and secondary fine-grained fine-grained hematite hematiteafter aftermagnetite. magnetite. Alteration products include serpentine (after mafics), epidote (after plagioclase plagioclase and mafics), calcite (after plagioclase), actinolite (after pyroxene), plagioclase), and and chlorite (after mafics). pyroxene), sericite (after plagioclase), Sildcila (1984) (1984) reports reports aa correlation correlation between between alteration alteration and and the the cross-cutting Lac La Belle Sikkila Belle Fissure, Fissure, indicating a preferential channeling of of hydrothermal hydrothermal fluids. fluids. Secondary geochemical variations in geochemical with respect respectto tothe the fissure. fissure. The grade of alteration of of the Mount Mount the stock also tend to correlate with PLY. Actinolite Bohemia stock is higher than the surrounding PLV. Actinolite has has not not been been observed observed within within the the PLY. PLV. Both Boththe thegrade gradeand andcharacter characterof of alteration alteration may may have been the result of a local hydrothermal system related to the stock stock itself, rather than to the regional hydrothermal hydrothemal system, which which produced produced �.0 (1 cm = Stop 06 1689.6 m or 3/8" = SCALE 1:168960 1 mile) Stop D5 Ia. ��A Isp Drill Hole "mmnlnm ~m~gdoloids ond dike projected to 1300'elevotion a preliminary Calumet General Generalgeology geology and anddrill drillhole holelocations locations in inthe theMount MountBohemia Bohemiaarea area(modified (modifiedfrom from a prcldnary Calumet and andHecla HedaMining MiningCompany Companymap). map). B MINERAL Chlorlle Chlorite Epidote Epidote Quart2 Cuartz Secondary secondary minerals minerals VesicteVesicle- FractureFracturefillings inindike dikematrix matrix fillings fillings fillinQS 00 0  . Calcite c01cite Sericite 5cr/cite Pumpellyile Pumpelfy/te Microcline Microci/ne Hematite Hematite - - 0 — 00 — 00 Sa  G0 Sa S0 00 S0 - a - Â¥Mino -- — — G0 .common •Â 00 — Copper Copper suit/des suffices NoliveCopper Copper Native 0 a G 00 Pyrite P/rite .• . 0 00 00 00 00 ORafe -Absent Nonpyrogenic Nonpyroeenic Minerals Minerals in in the theDikes Dikes D C MINERAL Henna! lie I ——— Set/cite Epidot. Spbo/erit. —— —?— ——— Co/c/I. Hematite (fall) Suit/fls —— ——— -7— — —-— —— Pink bonnie Purple born/ic —— Ougrtz Mic,odllne Supergene - Cho/capynte Go/coo Galena ——— Hydrothermal —— Pyrit. CA/op/i. Pam pe/ly/te Pyrogenic Deuteric —________ 9/penile 0/up/cit. Cho/cocite —__________ Hematite II — Cove//it. Paragenetic sequence of secondary minerals in the dikes. Paragenesis opaque minerals in dikes Paragenesis ofofopaque minerals in dikes and and flow flo tops Bohemia. tops at Mount Bohemia. FigureDl: Dl:Geologic Geologic mapshowing showingandesitic andesiticdikes dikesnear nearMount MountBohemia Bohemiaand andoccurrence occurrenceand and patagenesis paragenesis Figure map minerals in in the the dikes dikes(from (fromRobertson, Robertson, 1975). 1975). of secondary secondary and and opaque opaque ininemls of �136 En' Mount Bohemia Bohemia stock stock aa bears resemblance resemblance to to a porphyry copper native copper deposits. deposits. Mount system. the the Andesitic dikes are found in the vicinity of Mt. Bohemia Bohemia (Fig. 35a), 35a), and average about of the the PLV. PLy. Two 5 m in thickness. thickness. The The dikes dikes intrude flows of Twoflow flowtops topsare areshown shown in in Figure Figure35a 35a as alpha and beta. The carry copper sulfides. sulfides. Copper sulfates Thedikes dikesand and amygdaloidal amygdaloidal flow tops carry sulfides in other and native copper copper is the other parts parts of of the the district district are are found found typically typically as fracture fracture fillings, and dominant ore mineral of the Keweenaw Keweenaw Peninsula. Peninsula. A variety of secondary and opaque minerals secondary found in in the dikes dikes and and flow flow tops tops (Fig. (Fig. Dl). Dl). Copper allylate. late. The are found Coppersulfides sulfides are are paragenetic paragenetically copper and and sulfur in in this occurrence occurrence isis believed believedto to be be of of direct direct magmatic magmaticorigin. origin. The atypical copper atypical copper sulfide mineralized flow tops and dikes also may have been related to the magma magma source source that produced the Mount Bohemia stock and andesite dikes, rather than the regional hydrothermal hydrothermal system (Robertson, (Robertson, 1975). 1975). 4.3 4.3 At the turnoff turnoff to Mt. Bohemia. Bohemia. Go Gostraight straightahead ahead(south) (south) toward toward Lac Lac La La Belle, Belle, down down hill. hill. 4.7 4.7 A junction junction of of roads roads at at Lac Lac La La Belle. Belle. Turn right (west) (west) along along the the shore shoreof ofLac LacLa LaBelle. Belle. For the stop at Bete Grise, turn left and continue until the Bete Grise sand beach. Map Dl, there To Bete Grise, turn left. left. (See Map there is is no no mileage mileage logged logged to Bete Grise and back) Stop D2: Bete stop BeteGris.e Grise(white (whitesand sandbeach beachfrom fromJacobsville JacobsvilleSandstone) Sandstone) The white sand beach is derived from Jacobsville Sandstone and is typical of beaches beaches on on whereas on on the the west west side, side, the beaches are often of the east side side of of the the Keweenaw Keweenaw Peninsula, whereas of Conglomerate. Black sand beaches on the Keweenaw Peninsula pebbles from the Copper Harbor Conglomerate. are crushed mine rock derived derived from from milling milling of of native native copper copper ores. ores. Bete Grise is located on the shore of of Keweenaw XeweenawBay Bay on onthe theKeweenaw KeweenawFault. Fault. Along the shoreline, east of of the point shoreline, east point where where the road road reaches reaches the shore, shore, are are several several exposures exposures of the the Keweenaw Fault which crosses crosses onon- and and off-shore off-shore several severaltimes. times. A canoe or small boat is a good way to visit visit these these areas. areas. Also to the east, east, are are several several of of the the rhyolite rhyolite bodies bodies which which are arechiefly chiefly found in the lower part part of of the the PLV. PLy. Three found Threetenths tenths of of aamile milenorth north of of Bete BeteGrise, Grise, aafour-wheel four-wheel of the the paved pavedroad roadto toSmith's Smith's Fisheries. Fisheries. The road mad intersects the Bare Hill drive road continues east of body, which which is is aa shallow shallow intrusive. intrusive. Beyond the end of of the road at Smith's Fisheries, a Rhyolite body, to the the mouth mouth of of the the Montreal MontrealRiver. River. From here, one trail continues eastward along the shore to one may may traverse up river to several falls--over fine outcrops of basaltic flows, ash flow tuffs, and a rhyolite several falls~over dome--or continue along the shore to the the Fish Fish Cove Coverhyolite, rhyolite, aacompositionally compositionallyzoned zoned shallow shallow intrusive (Bornhorst, 1975). Inland, Inland, and and not not far far from from Bete Bete Grise, Grise, is is the the Mt. Mt. Houghton Houghton Rhyolite, Rhyolite, an extrusive rhyolite dome with prominent flow flow banding banding and and block block and and ash ash flow flow deposits on its flanks. Mt. Houghton is best approached from the Mandan Road (Map 20). Mt. Houghton is best approached Mandan Road (Map 20). See See Stop Stop D4 D4 (this (this leg), for for more more on on rhyolites. rhyolites. lthyolites make make up up less less than than 1% 1% of of the the mass mass of of the the PLV, PLy, as Rhy&es as seen seen in in outcrops outcrops on on the the Keweenaw. Considerable Considerabletextural textural variety variety of rhyolites rhyolites are found, including intrusive and extrusive rhyolite and even small small ignimbrites. The Theabundance abundanceand andvariety variety of of rhyolitic rhyoliticboulders bouldersand andcobbles cobbles interfiow conglomerates conglomerates however, within the interflow however, demands demands that a large number of rhyolitic source areas source areas must underlie the Jacobsville, south and east of the the Keweenaw Keweenaw Fault. Return to the junction at Lac La Belle. Belle. �Legs 137 MAPD2 MAP D2 Behind, described at at Stop Stop Dl. Dl. Behiid, is an excellent view of Mount Bohemia &scriW 5.1 5.2 Pull over over to the the right right at at Haven Haven Park. Park. Stop D 3 Haven Haven Park Park(Portage (PortageLake LakeVolcanics VolcanicsIIPLV] PLVI near near the the Keweenaw Keweenaw Fault) Fault) Stop 1)3: The exposures provide an an excellent excellent view view of of the PLV adjacent to the exposures at the waterfalls waterfalls provide Keweenaw Fault. At locality, Keweenaw Fault. At this thi~s locahty, the the Keweenaw Keweenaw Fault is is oriented oriented subparallel to the slope slope face face (and the road), and is less than 100 m to the south (toward (toward L Lac La Belle) of of the exposures at the ac La waterfalls. In Inaddition, addition,in in this thisgeneral general area area several several faults faults cut the PLV nearly perpendicular perpendicular to the Keweenaw Fault. Basalt at the base of the falls is overlain by conglomerate, and in turn, turn, overlain overlain Basalt at the base of the falls is overlain by and in by basalt. basalt. The conglomerate conglomerate is unnamed unnamed (Cornwall, (Cornwall, 1954) and is is an aninterfiow inteflow sedimentary sedimentary horizon within within the the PLV. PLY. Conglomerate expozed base base of of the the Conglomerate beds are common at, or near, the exposed PLY Fault. The PLV close to the Keweenaw Keweenaw Fault. The rocks rocks of of the the PLV PLV here, here, and and elsewhere elsewhere adjacent adjacent to the the Keweenaw Fault, are typically typically quite quite fractured fractured and and altered. altered. The basalt basalt is is cut cut by by closely closelyspaced spaced Keweenaw Fault, fractures that trend to probable to the fractures that trend subparallel subparallel and perpendicular perpendicular to probable bedding beddiig (subparallel (subparallel to the Keweenaw Fault) that yield 1 to 2 cm rectangular pieces pieces of of basalt. basalt. The The rock rock is is quite quite altered, altered,with with a lot cm wide, wide, and and aa dominant dominant orientation orientation subparallel subparallel to the Keweenaw Fault. lot of veinlets veinlets up up to to 11cm Secondary minerals include laumontite, calcite, chlorite, and hematite. The grade of Secondary minerals include laumontite, calcite, chlorite, and hematite. of regional regional within the thePLV PLV (see (seeFig. Fig. in Introduction), with the highest grades alteration varies systematically within lower in the PLY. lower PLV. Paragenetically Parageneticallylate latelower lower grade grade assemblages assemblages are are superimposed superimposed on higher higher where suff~cient sufficient porosity porosity and andpermeability permeabilitystill stillexits, exits,such suchasasatatthis thisstop. stop. The alteration grades where minerals here, and at other locations near the Keweenaw Fault, are characterized characterized by low grade grade and and late minerals such as laumontite. laumontite. Some Somelocalities 1ocaIitieshave haveabundant abundanthigher highergrade gradeassemblages assemblagesnear near assemblages. This the fault, with clear superimposed superimposed lower grade assemblages. This suggests suggests that that the the Keweenaw Keweenaw Fault was hydrothermalfluids. fluids. was aa long-lived long-Iived conduit conduit of ofhydrothermal Continue west on the the paved paved road. road. 5.3 altered basalt basalt of of the the PLV PLY is is exposed exposed on on the the right right side of the road, Highly fractured and altered road. 5.85 Thk locality, locd~ty,and the remaining remainiig localities on this kg, leg, are are River Side Park at Little Gratiot River. This of the the Keweenaw Keweenaw Fault, Fault, with with the the principal principal bedrock bedrock being behg Jacobsville JacobsvilleSandstone. Sandstone. south and east of juxtaposed against the PLV by the Keweenaw The Jacobsville Sandstone is the typical rock unit juxtaposed Fault. Fault. However, at the west end of Lac La Belle, However, Belle, in the the vicinity vicinity of Deer Deer Lake, Lake, the the rocks rocks south south of of the the Keweenaw Fault are are Portage Portage Lake Lake Basalts Basalts(Fig. (Fig.D2). D2). These Keweenaw Fault These basalts may represent the lowest The area has stratigraphic horizons horizons exposed exposed in in the stratigraphic the PLY. PLV. The has been been studied studied by by geological geological and and geophysical geophysicalmethods methods by DeGraff (1976), (1976). whose whose model for the development development of this IS unusual unusual feature feature is shown graphically in Fig. 36. ItIt isisyet yet another another example example of the deformation along the high-angle Fault. A reverse Keweenaw Keweenaw Fault. A traverse traverse down down the the Little L'lttle Gratiot Gratiot River from the Lac La La Belle-Gay Belle-Gay Road crosses tilted body body of of the PLV was cmsses many outcrops outcrops of the the basalts. basalts. The fault-bounded, fault-bounded, tilted defined by a dense profiles and a few key key drillholes. The dense array of magnetic magnetic and gravity profiles Theattitude attitude of the beds was altered by the faulting, but the the rocks, rocks, like like the the rest rest of of the the PLV, PLy, have altered by faulting, but have normal n o d of polarity. magnetic . Dll MAP D Lac La La Belle. Belle. 7.4 End of Lac �\ 41 * Bchent N N S S S I Basalt, and sandstones in a block south of the fault are oxposed and overturned. posed and dip to the sooth. Basalts and sandstones in a block south of the fault are ex- basalt and sandstone. Classical fault contact between Sandstone stilt exposed north of thu Keweenaw Fault. Figure D2:• Geologic sketch map of part of the Keweenaw Fault in the vicinity of Deer Lake, where the Portage Lake Volcanics are found south of the Keweenaw Fault. At right, schematic cross sections show stages in the development of the Keweenaw Fault at Deer Lake as envisioned by DeGraff (1976). p = PLy, J = Jacobsville. IT- RI,.' \ 'Litu. orstIot Jacobsvllls Ssndslons I iji P Porlag. Lske Volosolca I To Dswsr. N Prior to faulting. -I �Le12 9.4 9.4 Behind, is a view of of Mount Mount Bohemia. Bohemia. 10.5 10.5 Along the shore shore of of Lake Lake Superior. Superior. 11.7 11.7 At South South Point. J39 D4: South SouthPoint Point(view (viewofofthe thetiptipofofthe theKeweenaw KeweenawPeninsula) Peninsula) Stop Dk South Point, being on the southern southem end of Bete Grise Bay. Bay, provides an excellent excellent view view of of the tip of the the Keweenaw Keweenaw Peninsula--visible Peninsula-visible on the far right (northeast) (Fig. D3). to the shoreline, is Fish Cove Knob, At 1:00, l:W, facing perpendicular perpendicular to Knob, aa rhyolite rhyolite intrusive intrusive PLY (Bornhorst, (Bomhorst. 1975). The body into the base of the PLV The rhyolites at Fish Cove Knob contain sparse spme phenocrysts of feldspar feldspar and quartz. light-colored bare bare rock rockbluff bluffwhich whichisispart partof ofthe theBare BareHill HillRhyolite. Rhyolite. Bare At 12:00, is a light-colored Hill consists of several several sills sills of ofrhyolite, rhyolite, containing containingsparse sparse phenoczysts phenocrysts of feldspar feldspar and and quartz quartz (Cornwall, 1954). (Comwall, 1954). to the shoreline, 10:00, facing perpendicular perpendicular to shoreline, is Mount Houghton, Houghton, a rhyolite dome At 10:00, within the lower section of of the the FTV. PLy. Rhyolite complex withii RhyoliteatatMount MountHoughton Houghton isis aphyric aphyric with with wellwellbeds of of conglomerate, conglomerate, interclated interclatedwith withbasal& basalts of of the the PLV, PLy, are developed flow foliation. Several beds are detritus shed off off the the rhyolite rhyolite dome. dome. The Superior shorehe shoreline from south of Mount Houghton The Keweenaw Fault Fault follows the Lake Superior to Keweenaw Keweenaw Point. Point. Rhyolite intrusive intrusive and and extrusive below the Bohemia Rhyolite extrusive rocks m k s occur occur stratigraphically stratigraphically below Bohemia Conglomerate Conglomerate (Fig. D3). The TheBohemia BohemiaConglomerate Conglomerate is stratigraphically in the lower part of the PLY. KeweenawanNorth North Shore ShoreYolcanic Volcanic Group Group contains contains frequent rhyolites, similar PLV. The Theolder olderKeweenawan to the the proportion proportion found in the lower PLY PLV (Green, 1982). 1982). Nicholson Nicholson(1992) (1992)proposed proposed Iceland Icelandas as a modem volcanological analog for rhyolites within the Midcontinent rift system. Within-rift modem voIcanological for rhyolites within the Midcontinent system. central central volcanic volcanic complexes complexes in in Iceland Iceland are arelocalized localizedaccumulations accumulations ofofbasalts-to-rhyolites, basalts-to-rhyolites, by basalts erupted surrounded by empted from from fissures fissures (Walker, (Walker, 1966). 1966). The distal part of of these these central central volcanoes may be a good good model model for for rhyolites rhyolites within within the PLY. PLV. 12.7 12.7 the left. left. Point Isabelle is on the Sandstone on on the the shoreline extend from from here to the 13.0 Good Good exposures of Jacobsville Jacobsville Sandstone shoreline extend the roadside roads& 13,O pullover. The TheJacobsville JacobsvilleSandstone Sandstoneyields yields excellent excellentlight-colored light-colored sand sand beaches. beaches. 13.3 13.3 The roadside pullover is on on the the left. left. 15.1 15.1 are on the left. Excellent low exposures of Jacobsville Jacohsville Sandstone are STOP STOP D5: D5:Eastern EasternKeweenaw KeweenawPeninsula Peninsula(Jacobsville (JacohsvilleSandstone) Sandstone) is well well exposed exposedalong alongthe theLake LakeSuperior Superiorshore shoreatatthis thislocation. location. The The Jacobsville Sandstone is character of the Jacobsville Sandstone illustrated here is typical of many exposures elsewhere. the Jacobsville Sandstone illustrated is typical of many exposures elsewhere. are red-colored with characteristic characteristiccircular circular white white Here, the mediumm d ~ u mto - coarse-grained coarse-grained sandstones sandstones are �140 I2 30 25 35 25 50 35 35 ---------__-I__ a Mt. Mt.Houghton Houghton 30 - oNGLOMT - - - - - - - - Montreal River 25 25 50 A- -\ . Keystone Point Fish Cove -- Fish FishCove Coveknob knob EXPLANATION EXPLANATION .... jJacobsviIle Sandstone ~acobsville Sandstone Copper Harbor Conglomerate Copper Harbor Conglomerate :.:.:./ . . . . PortageLake b k e Volcanics Volcanlcs Portage ~ o w - l basalts basalts i ~ ~ D:iLow—TiO2 High—TiO2 basalts and ......./; . .. .. . . . . . . . . . .. .. .. .. .. .. .. .. . . . . . . . . . .. .. .. .. .. .. . . . .. .. .. .. .. .. . . , . . . . . . . . . . . . . : .. . . . .. .. .. . . . . . . . . . . . :.q 0 0 i 0 MILES 55 MILES w 0 55 KILOMETERS KILOMFERS -- —— andesitic flows Bohemiaconglomerate conglomerate Bohemia ! Strike and Strike anddip dip Horizontalbed bed ee 3 Horizontal Individual rhyolite clasticbodies bodies aa Individual rhyolite or or ciastic Figure FigureD3: D3Geologic Geologicmap mapshowing showingthe thelocation locationofofrhyolites rhyoliteson on the the eastern eastern tip tip of of the the Keweenaw Keweenaw Peninsula Peninsula (from 1992). (from Nicholson, Nicholson,1992). �141 reduction spots up to about 2.5 2.5 cm in diameter. diameter. Well Well developed developed white reduced zones of variable thickness thickness are are subparallel subparallel to to bedding. bedd'mg. Some Somezones zoneswithin withimthe thesandstones sandstonesshow showcross-bedding cross-beddingand and others others contain contain mud chips. For Foraafurther furtherdescription descriptionof of the the Jacobsville Jacobsville Sandstone, Sandstone, refer refer to to Stop Stop 10. 10. 17.5 17.5 Burnette Park is on on the the left. left. ItIt has has lakeshore lakeshore exposures exposures of Jacobsville Jacobsville Sandstone with a sand sand beach. Well-developed visible in in the the sandstone sandstoneexposed exposedhere. here. On a clear day Welldeveloped cross bedding bedd'mg is visible the Huron Huron Mountains Mountains are are visible visible across acrossthe theKeweenaw Keweenaw Bay. Bay. 18.3 18.3 Outcrops Outcrops of of Jacobsville Jacobsville Sandstone Sandstone along along the the Keweenaw Keweenaw Bay/Lake BayLake Superior Superiorshoreline. shoreline. 19.0 19.0 The road gees to Betsy. Betsy. Continue Continueahead. ahead. road to the the right right goes 23.6 23.6 is on on the theright. right. Hermit Bay is 25.2 25.2 Cross the Tobacco Tobacco River at its mouth mouth with Lake Superior. Superior. The TheHuron Huron Mountains Mountains are are visible visible across Bay on a clear day. The across Keweenaw Bay The black black sand sand beach beach is aa result result of of longshore longshore drift of of the the basalt mine mine tailings tailings dumped dumped into into Lake Lake Superior Superior from 1902 1902 to to 1932. 1932. Road access access to to the the Gay Gay Stamp Stamp Sands. Sands. Continue Continueon onthe thepaved pavedroad. road. MAP D3 MAPD3 smokestack is on on the the left. left. 26.0 The Gay smokestack 26.0 25.9 25.9 Stop D6: 96: Gay Gay(stamp (stampsands) sands) Walk Walk toward toward the the stack stack and Lake Superior. This Thisvantage vantagepoint pointprovides providesan anexcellent excellentview view of Lake Superior Superior and Keweenaw Keweenaw Bay. On Onaaclear clearday, day,the theHuron HuronMountains Mountainsare areclearly clearlyvisible visible consist of of a core the horizon horizon across acrossKeweenaw Keweenaw Bay. Bay. The Huron Mountains Mountains consist core of of Archean Archean on the granitoid rocks, unconformably unconformab~yoverlain by Early Early Proterozoic Proterozoic deformed deformed and andmetamorphosed metamorphosed sedimentary rocks. Keweenaw Keweenaw Bay Bay however, however, isisunderlain underlain by by Jacobsville Jacobsville Sandstone Sandstonewith with Early Early Proterozoic metasedimentary rocks cropping out out on the opposite shore of Keweenaw Bay (Stop metasedimentary rocks II). 11).The Thenearly nearlyflat-lying flat-lyingJacobsville JacobsvilleSandstone Sandstoneextends extends from from the Keweenaw Keweenaw Fault contact with the PLy, PLV, about about 88km kmN/NW, NNW, totothe theopposite oppositeside sideofofKeweenaw Keweenaw Bay, Bay, about about 35 35 km. km. The The Jacobsville Sandstone Sandstone fills aa rift-flanking rifi-flanking basin. basin. The Gay Stamp Sands are visible in the foreground. The Stamp Sands The sands sands accrued accmed from from the the Mohawk Mohawk and Wolverine Wolverine Mills as as tons tons of of crushed cmshed rock rock were were milled milled to to extract extract the the copper copper they they contained. contained. The twin twin mills mills began began processing processing in 1902, 1902, with with the Wolverine Wolverine Mill working until 1922 1922 and and the the Mohawk Mohawk Mill Mill running running until until 1932. 1932. Both companies proximity companies began their their processing plants in the town of Gay because of the proximity of water-covered areas in which they could dispose of of their their tailings. tailings. Lumbering was previously Lumbering was previously the main occupation occupation of the the town, town, also also because of the the accessibility to the Bay, which they used to to float their logs logs to to the the larger larger shipping shippingareas. areas. Conveyor Conveyor belts belts were were used used to to transport transport the the sands sands away away from from the the plants, plants, and and water waterwas wasused used to transport transport them them even even further furtherinto intoKeweenaw Keweenaw Bay. Bay. obtained at at mileage mileage 25.9. 25.9. If you Access can be obtained you walk walk along along the beach, beach, you you can can see seean an stratified beds beds and cross cutting erosion scarp of the the stamp stamp sands. sands. Within the accumulation, accumulation, stratfied cutting �CA) ci a-Zt"A.- t. ,— .— ._ • - -4• Ct 0 S - -- — - I- - a.— 4 .1- — * -I .C,4 1* A 4_-e — e 0 - ._a-..t__; :4;;ve.:.s. 4. - — -e -•- 4-- .ot I �143 evident layers-as the the slurry slurry found found new directions directions in in its its progress progress toward toward Keweenaw KeweenawBay—am Bay-are evident. layers--as NOTE: NOTE:When Whenapproaching approachingthe theedge edgeof of the the sands sandsfacing facing the bay, do not go too close to the edge because because the the cliff cliff face facecould couldgive give way. way. Erosion of the shoreline current caused caused the the toe toe of of the fan to shoreline and a right lateral longshore current be be dispersed dispersedsouth southtoward towardTraverse Traverse Point Point and and beyond. Accumulations Accumulations at at Traverse Traverse Point are are the cause now. At cause of of the the tombolo tombolo that that connects the island to the mainland mainland now. At that thatpoint, point, some someof ofthe the sands were diverted into the middle of Keweenaw Bay. but but the majority Keweenaw Bay, majority of the sand sand was was kept kept along the shore shore by by wave wave refraction, refraction, to to be be deposited deposited further farther south. south. Continue Continueahead. ahead. 26.1 26.1 left turn turn in in Gay Gay on onMain MainStreet. Street. Take aa left sharp right right turn. turn. 26.3 Leave Gay with aa sharp 26.3 MAP Dl Dl the left left goes goes to to Big Big Traverse Traverse Bay Bay (about (about 1.5 1.5 miles). miles). 30.0 The road to the 30.0 30.8 30.8 The road bends bends right, right, then then left. left. 35.0 35.0 Gently Gently rolling rolling farm farm land. land. 36.4 36.4 The view ahead is of that follows follows the the trace trace of of the the Keweenaw KeweenawFault. Fault. At the of aa topographic topographic slope that Jacobsville top of of the the slope, slope, the thePLV PLVare areexposed. exposed. The slope slope face to here here isis underlain underlain by by Jacobsville Sandstone. The Theroad roadgoes goesdownhill downhillinto intothe theTraprock TraprockValley. Valley. 36.7 36.7 left at at the thestop stopsign signtoward towardLake LakeLinden. Linden. Turn left 37.6 37.6 The The slope slope related related to to the theKeweenaw Keweenaw Fault Fault isisagain again visible visible on onthe theright. right. 38.1 38.1 At the the stop stopsign, sign,turn turn right right toward toward Lake Lake Linden, Linden, and and immediately immediately cross the Traprock Traprock River River near near the the mouth mouth with with Portage Portage Lake. Lake. Left, Left,the theroad roadgoes goestotoJacobsville Jacobsvillevia viaDreamland. Dreamland. 38.6 38.6 Gregory Street Street is is on on the the left, left, which which goes goes to to the the Natural Wall Wall in in the the main main road road log log at at mileage mileage37.4. 37.4. 38.7 38.7 The junction junction of 9th Street with with M-26 M-26 in in Lake Lake Linden. Linden. Turn left on M-26 to return return to Houghton, floughton, or right right to to go goto toCalumet/Laurium. Calumet/Laurium. END OF OFLEG LEG1) D END �144 - LEG E 932 932 CREEK CREEK MAP E Ell Leg E at the junction of US-41 US41 and Gratiot Lake Road. North North of of US-41 US41isisthe theCentral CentralMine. Mine. 0.0 0.0 Start Lee Proceed immediately after after the the junction junction on on the the left, left, there are ~ r o c e e don o nthe paved paved Gratiot Lake Road, immediately stamp sands from the Central Mine. Mine. The The copper copper content content of the the sands sands restricts restricts plant growth. growth. 1.3 1.3 The road traverses section across traverses nearly nearly perpendicular perpendicularto to strike, strike,and andgoes goesdown downsection across the thePLY. PLV. with 2.65 The entrance to an an abandoned abandoned Calumet Calumet Air Force Station is on on the the left. left. Continue ahead with slow, gradual descent. descent. MAP E2 E2 onthe thesouth southside sideof of the the Keweenaw Keweenaw Fault Fault and and underlain underlain by by flatflat4.1 4.1 Gratiot Lake is visible ahead. ItItisison Jacobsville Sandstone Sandstonebedrock. bedrock. We are on the tilted lava flows of the PLY. lying Jacobsville PLV. building. The 4.25 Pull over to the side of the road. Walk Walk along along the the road road toward an A-frame building. The slope slope ahead along along the the paved paved road road isis the thetopographic topographicexpression expression of of the theKeweenaw Keweenaw Fault. Fault. Walking Distance (A typical typical pace--2 steps--is steps-is about 55 feet.) feet.) Feet (Approximate) (Approximate) dirt road is to the east. Junction of the paved road and the d irt road 0 A-Frame building. Bear 180 A-Frame 180 Bearright right (N70°E) (N70¡Ealong along the now forested forested road. 280 280 Now you are are going going downhill. downhill. 880 880 N50°E Continue N 5 W over a berm on an abandoned abandoned road. 1000 right. 1000 Outcrops are on the right. first part of of Stop El. El. Proceed ahead another 25 ft. to 932 1150 The outcrops on the right are the fist 1150 932 Creek and go upstream slightly slightly to to some some outcrops outcrops adjacent adjacent to to the the Keweenaw Keweenaw Fault. Fault. Stop El: El: 932 932Creek Creek(Keweenaw (KeweenawFault) Fault) The outcrops on on the the right right side sideof of the theroad road consists consistsof of altered alteredand andfractured fracturedbasa.lts basalts of of the the PLV intruded by a plug of basaltic andesite (Table (Table El). El). The Thefme-grained fine-grained texture texture suggest suggest that that this this The basaltic plug is highly plug plug was was shallowly shallowly emplaced. emplaced. The basaltic andesite andesite plug highly altered altered and and contains contains disseminated chalcocite. chalcocite. This This locality is at at the base of the PLY, PLV, near the Keweenaw Fault. Rhyolite Rhyoliteextrusive extrusiveand and intrusive rocks, and mafic-to-intermediate intrusiverocks rocksare are much much more more common common in in the intrusive rocks, matic-to-intermediate intrusive the stratigraphically lower part of the PLV (Fig. El). The mafic-to-intermediate intrusive rocks are stratigraphically lower part of the PLV (Fig. El). The mafic-to-intermediate intrusive rocks are known to contain copper sulfides (Broderick and others, others, 1946), 1946), (Fig. (Fig.El). El). Deposits (Broderick and Depositsdiscovered discovered to date (there (there are are 7) contain contain 0.1 to 4.5 4.5 million million tons of ore, with 2.5 to 3.0% Cu as as chalcocite chalcocite in amygdules; and and disseminations disseminations(Woodruff (Woodruffand andothers, others,1994). 1994). Most Most of of the the sulfur in the vienlets; amygdules; basalts during subaerial subaerial eruptions. eruptions. Mineralizing basalts of the PLV was lost by degassing during Mineralizing fluids fluids generated generated PLY should be be low low in in sulfur. sulfur. Woodruff and others (1994) suggest that that the the little from within the PLV �___ Begin -': 0— " \ I 9 I] St V7 t- c (_ t ' ,- ' t Ilfr ( — 025 ,A -' ç C12-.J 3 032 & - '4 t1f j..S .s - 3 *: .tI 3t MAP �0 S E .0 743 "V. B 0 (SR 1 a MAP E �Lap Leo a 147 EXPLANATION Jacobwllle Sandstone Freda Sandatone Nonefuch Formation Copper Harbor Conglomerah Portage b k e Volcanics a a n 0 in context context with with the geology Figure El: El: Location Location of the region region of of chalcocite chalcocite mineralization mineralization in geology ooff the the Keweenaw Peninsula (from Woodruff and and others, others,1994). 1994). �148 by progressive oxidation during chalcocite available sulfur sulfut was stripped from mineralizing fluids by deposition, but but dissolved copper copper remained remained in in residual residual fluids, fluids, allowing allowing for for deposition deposition of of native deposition, copper. The Therelationship relationshipbetween between the the chalcocite chalcocite and and native native copper copper is is uncertain. uncertain. Jacobsville Sandstoneisis exposed exposedinin932 932 Creek Creekjust just below below the the road. road. A A short shortdistance distance Jacobsville Sandstone upstream, the beds in the Jacobsville upstream, Jacobsville Sandstone are nearly vertical, making highly fractured and Keweenaw Fault Fault (a (a reverse fault), is altered basalts of the PLV visible in the creek bottom. The Keweenaw poorly exposed here, here, just just as it is elsewhere. Beds of the Jacobsville Sandstone are dragged dragged into into Beds of the Jacobsville Sandstone are the attitude attitude of the a near-vertical near-vertical position position by reverse reverse motion motion along along the the fault. fault. Downstream, Downstream, the the Jacobsville dip. The Keweenaw Fault was initially Jacobsville Sandstone Sandstoneshallows shallows to to the typical, less than 100 10' dip. normal fault fault along along the the edge rift system. system. During a graben-bounding graben-bounding normal edge of of the theMidcontinent Midcontinent rift Fault was was inverted inverted into into aa high-angle high-angle reverse reverse fault. fault. compression, at about 1060 1060 Ma, the Keweenaw Fault El: Chemical Table El: Chemical composition composition of the the intrusive intrusive plug on on 932 932 Creek Creek near near Gratiot Gratiot Lake. Lake. It is a median of 3 analyses. The probably due due to to 1420. $0. Unpublished Unpublished data data of of Bornhorst. Bomhorst. median Thelow lowtotal total isisprobably WT% Si02 A1203 Fe203 MgO CaO Na20 1(20 Ti02 P205 MnO CuS 53.61 14.48 8.69 2.93 8.54 4.71 0.77 1.30 0.54 0.13 0.32 Cr Ni Rb Sc Sr Zn Zr PPM 42 14 14 30 30 20 65 145 145 351 35 1 96.02 96.02 END OF LEG B E -- RETRACE ROUTE BACK TO CARS AND AND TO TO (15-41. US-41. �~ee Legs 149 149 LEG F FIVE FIVEMILE MILEPOINT POINT MAP Fl Fl MAP Just west of Eagle River, start Lee Leg on the the paved paved road roadto toFive FiveMile MilePoint. Point. Make a left turn on 0.0 Just 0.0 - FF on the road to to Five ~ i vMile Mile e Point. Point. the right side of of the the road road for for some some distance, distance, there are sand dunes from a past past high high stand stand of of the Lake Nipissing Stage of the Lake Superior basin. Ahead the road bends left. Lake Superior basin. Ahead 0.5 0.5 On On 0.8 0.8 Ahead, Ahead, aa view view of of Five FiveMile MilePoint. Point. 1.5 1.5 An An excellent excellent view view of of Lake Lake Superior Superior at at 3:00, 3:00,with with sand sanddunes dunesalong alongthe theroad. road. 1.8 1.8 Cross the Silver Silver River. Sand Sanddunes dunescontinue continuealongside alongsidethe the mad. road. 2.2 Pull Pull over over on on the the right right side side of of the theroad road into intothe theroadside roadside park. park. Stop Harbor Stop Fl: Fl:W.C. W.C.Verde VerdeRoadside RoadsidePark Park(Copper (Copper HarborConglomerate) Conglomerate) The The road is is at at the the level level of sand sand dunes dunes from from the Lake Lake Nipissing Nipissing Stage Stage of the the Lake Lake Superior Superior basin. The Theunconsolidated unconsolidatedHolocene Holocene sands sands rest rest unconformably unconformably on Precambrian Precambrian Copper Harbor Conglomerate exposed at the lake shore here. At Atthe theLake LakeSuperior Superiorshoreline, shoreline,one onecan canobserve observe the Copper both ways from here along the shoreline for Copper Harbor Harbor Conglomerate, Conglomerate, which continues both 0.5km km west west and and 2.5 2.5km km east. east. It interfingers interfingers with, and overlies, the PLV (Fig. 6), 6). and and at at about 0.5 this point, with interclated interclated red red sandstone. The point, itit is is composed composed of of pebble-to-cobble pebble-to-cobble conglomerate with The Copper Copper Harbor Harbor Conglomerate Conglomerateis in the subsurface subsurface under Lake Superior and crops out again on Isle (Fig. 2). 2). Royale (Fig. MAPF2 MAP F2 the right right side side of the the road road is is aa mm-off turn-off to to the the Five Five Mile Mile Point Point lighthouse. lighthouse. You You must must get 3.8 On the 3.8 permission to enter this area. In Inthe thefront frontyard yard of of the thelighthouse, lighthouse, is is aa thin thin lava lava flow flow of of the theLake Lake Shore Shore Traps Traps with with the theCopper CopperHarbor HarborConglomerate Conglomerateabove above and andbelow belowit.it. Seven Mile Point beach beach mm-off turn-off on the right right side side of of the the road. road. Along Along this beach beach are are many many exposures exposures of of the the Copper CopperHarbor HarborConglomerate. Conglomerate. P3 MAP F3 Cross the the Gratiot Gratiot River. River. 9.5 9.5 Cross 4.1 4.1 Ahmeek Cemetary Cemetary is is on on the the left. left. 10.45 Ahmeek Turnright rightatatthe thesouth southend endofofthe thecemetary. cemetery. 10.55 mm over to to the the right. right. 10.65 Pull over 10.65 Stop F2: F2:Allouez AllouezGap Gap(kettles) (kettles) Stop This This locality locality is is just northeast northeast of the the Allouez Allouez Gap, the lowest lowest bedrock bedrock gap gap between between the the tip rip of the 17). This gap lead lead to to aaconcentration concentration of of the Keweenaw Keweenaw Peninsula Peninsula and and Portage Portage Lake Lake (Fig. (Fig. 17). outwash from the retreating Wisconsin glacier. glacier. A A fan fan of of outwash outwash extends extends northwest northwest to to the the level level 6). Northwest Northwest of of the the gap, gap, the the outwash outwash is is pitted pitted and and channeled channeled glacial Lake Nipissing (Fig. (Fig. 3 of glacial 36). �apF2 �151 65O— 2 Lake Shore T �ca I-,' Is) m �~ess Legs 153 153 with 14 trend (Regis, (Regis,1993) 1993)(Fig. (Fig.36 36). On the left, at the the 867 867 foot foot 14 kettles kettles along a northwest northwest trend ). On elevation, of a kettle. kettle. Ahead, elevation, is is aa shallow shallow depression depression representative of Ahead, aa few few tenths tenths of of aa mile mileon onthe the right, 816foot footelevation. elevation. ItIt isis to tothe thenorthwest northwest right, are are more more depressions. depressions. The Thebest best kettle kettle isis at atthe the816 near near the the edge edge of of MAP MAPP3 F3and andhas has aadiameter diameter of of 100 100m mand andaadepth depthof ofabout about25 25mm(Regis, (Regis,1993). 1993). Ahead 0.1 0.1 miles on the the right, right, is is the the former former Calumet Calumet landfill in a kettle. kettle. 10.75 Turn Turnright righton onthe thepaved pavedroad madtoward towardAhmeek. Ahmeek. 11.25 11.25 Outcrops Outcropsof of basalt basalt are areon onthe theleft leftside sideof ofthe theroad. road Stop Lake Stop F3: F3:North NorthofofAhmeek Ahmeek(Portage (Portage LakeVolcanics Volcanics[PLV]) [PLV]) A A thin thin basalt basalt flow flow of of the the PLy, PLV,just justabove abovethe theGreenstone GreenstoneFlow, Flow,forms formsan anoutcrop outcropwhich which displays well-developed well-developed columnar columnar jointing. jointing. The Greenstone Greenstone Plow itself itself shows showsspectacular spectacular columnar columnar jointing in some some areas, areas, most notably, along the palisades shown on Isle Isle Royale, Royale, where where columns 22 m or or more more in in diameter diameter are found. In Inaafew fewareas, areas,the thecolonnade/entablature colonnade/entablaturejointing pattern described in the Columbia River River flood flood basalts, basalts, is is well-developed well-developedininthe theGreenstone. Greenstone. On the the Keweenaw, Keweenaw, columnar columnar jointed exposures in thin flow sequences are rare, probably because the underlying horizons were not water-saturated when when covered covered by by the next lava flow. 11.5 At the the stop stopsign, sign,go gostraight straightahead. ahead. 11.6 Another Another stop stop sign. sign. Turn Turnleft, left,and andafter afterone oneblock, block,turn turnright. right. 12.8 Turn right, in front front of of aa church. church. Join US41 by by turning turning right, and immediately immediately following, is a stop sign in Join US-41 Directly ahead about 11:00, the Kingston Mine; shallow mine that worked the 11:00, is Kingston Mine; a shallow worked right. Directly ahead at right. Kingston Conglomerate. Conglomerate. This mine mine is is said said to tobe bethe theonly onlysignificant significant nativenative- copper copper deposit deposit in the the region region that that was was not not discovered Inc. discovered and worked worked initially initially by by the theCopper CopperCulture CultureIndians. Indians. Calumet Calumet and Hecla, Inc. discovered 1962and andisisdescribed describedby by Weege Weegeand andothers others discovereditit via viadiamond diamonddrilling drillingby by Randy Randy Weege Weegein in1962 (1972). (1972).Production Productionfrom from1965 1965toto1974, 1974,totalled totalled 900,000 900,000kg kg of of copper copper from from about about 90,000 90,000tonnes tonnes ore. of ore. The original original lava lava surface surfaceon onwhich whichan aninterfiow interflowconglomerate conglomeratewas wasdeposited, deposited,had hadnumerous numerous primary irregularities. As Asthis thissurface surfacerotated rotated slowly slowly through through the horizontal horizontal during filling of the the rift rift basin, basin, some some of of the the depressions depressions on on the the surface surface formed formed shallow shallow ponds and drainages for low low velocity streams, in which fine-grained sediments were were deposited. deposited. Only after tine-grained sediments after further farther rotation of of the surface were stream gradients sufficient to transport coarser gravels, and to deposit them as surface were stream transport gravels, and to of the sheets. The deposition deposition of the sediment sediment was was sufficiently sufficiently slow, slow, and the the climate climate prograding sheets. sufficiently sufficiently warm warm and and moist, moist, so so that that calcium calcium carbonate accumulated in the sediment in horizontal horizontal zones, as caliche. .3 to thick. The Kingston Mine is located in one of these interflow conglomerates; aa bed bed 00.3 to 30 m thick, and traceable for 100 100 km along strike. Depressions Depressions on the footwall lava surface, exposed in the in thickness thickness mine, have fillings of reddish shale and siltstone, which which measure measure as as much much as 15 m in 100 m in in diameter. diameter. This Thisunit unit isisoverlain overlain by by about about 10 10 to to 15 15 m m of of massive massive to to faintly faintly and 30 to 100 bedded, distinctly cmss-bedded, cross-bedded, and and graded-bedded graded-beddedconglomerate conglomerateand andminor minor sandstone. sandstone. Where original lava lava surface surface was was topographically topographically higher, the conglomerate conglomerate rests directly directly on aa basalt basalt the original footwall. footwall. �154 within the the PLy, In comparison comparison with other other conglomerates conglomerates within PLV,the theKingston KingstonConglomerate Conglomerate shows shows several unusual characteristics. For For example, example, the clasts clasts are are composed composed almost entirely of aa single single porphyritic rhyolite. rhyolite. Also, lithology: dark red to reddish-brown quartz and feldspar porphyritic Also, the the clasts clastshave have a high angularity and small average size (about (about 88 mm), mm), with with the the largest largest pebbles pebbles being about being about 10 10 Thematrix, matrix,generally generally40 40to to 60% 60%of of the the sediment sedimentby by volume, volume, consists consists of fme-grained fine-grained cm in size. The chlorite, martite, quartz, feldspar, chlorite, martite, specular specular hematite, hematite, and caliche-derived caliche-derived calcite cement cement quartz, feldspar, (Kalliokoski, 1986). Where Wherethe the calcite calcitecontent content is is low, low, the the cement cementisisquartz. quartz. Fluvial planarplanar- and and cross-beds cross-bedsare are shown shownby by variations variationsinin grain grain size size and and color, color, and in the the Fluvial abundance of of matrix, composed composed of of dark dark chlorite chlorite and and calcite calcite cement. cement. Parts Parts of of the the conglomerate conglomerate that are poorly matrix) appear appear to to have dis-aggregated poorly bedded bedded and and contain contain little littlematrix matrix (—20% (-20% matrix) dis-aggregated in in situ. In some large samples, calcite and dark chlorite occur in different parts of beds. Calcite (as In some large samples, calcite and parts of beds. Calcite (as caliche) may have precipitated precipitated along zones with larger clasts; less matrix; and and probable probable greater greater horizontal transmissivity, but not not in zones with abundant transmissivity, but abundant clay (chlorite) (chlorite) in in which which permeability permeability might have been less. The Thesource sourceof of the theconglomerate conglomeratewas was aa proximal, proximal, southerly southerly located located upland upland porphyritic rhyolite rhyolite from from which which the the sediment sediment was waterwith friable, unweathered quartz-feldspar porphyritic transported with minimal minimal abrasion abrasion and and sorting. sorting. Mining was done on on four four levels levels along along two two segments segments of the the Kingston Kingston Conglomerate, Conglomerate, with 1000 1000 anirregularly irregularly distributed, distributed, fmefmem in total length length (Fig. (Fig. 34). 34). Native Nativecopper copperisisco-extensive co-extensive with with an grained hematite hematite pigmentation pigmentation and and kaohite kaolinite alteration. alteration. A grained A hematite hematite pigmentation pigmentation in in feldspar feldspar phenoerysts produced produced the the reddish reddishcolor colorininthe theconglomerate. conglomerate. In In places, places, the the rock rock has has lost its red phenocrysts color due to the the hydrothennal hydrothermal leaching of iron. The Themineralization mineralization decreases decreases gradually gradually along along strike, where the the conglomerate conglomeratethins thins or or contains containsepidote. epidote. Native copper Native copper occurs within within the the conglomerate conglomerate as generally generally continuous continuous zones zones of of mineable mineable (43% of the mined mined copper) copper) and and hanging hanging wall wall (33%); (33%); thicknesses and grades along the footwall (43% occursalong alongthe thecentral centralportions portions of of the conglomerate. normally, minor mineralization (—10%) (-10%) occurs Weege and others others (1972) (1972) describes describes several several empirical empirical relationships relationships between ore ore distribution distribution and and One important important ore ore control control is is considered consideredto to be be the thickness thickness of the the conglomerate lithology. lithology. One conglomerate: there is little or no ore where where the the thickness thicknessisisless lessthan than10 10m. m. Another Mother possibility conglomerate: that represents a control over permeability: permeability: where where the the base base of of the theconglomerate conglomerateisis"muddy"--as "muddy"--as occur nearby nearby at at higher higher in a basal depression--ore depression-ore may be absent along this basal zone, but it may occur stratigraphic levels in the the conglomerate. conglomerate. Permeability of of the host conglomerate is the fundamental control on on the distribution of native Permeability fundamental control native Allouez Gap Gap Fault Fault (Fig. (Fig.34). 34). The conglomerate copper. The TheKingston Kingston deposit deposit is bisected by the Allouez itself. At is well mineralized in the fault zone itself. At the thesouthwest southwest end end of of the the mine, mine, the the conglomerate conglomerate thins and ore grade is the best best in in the the mine. mine. The Thethinned thinnedconglomerate conglomeratecould could have have provided provided an an excellent barrier to ore ore fluid fluid movement, movement, if mineralizing mineralizing solutions moved parallel to strike strike rather rather than simply up-dip up-dip (Weege and and others, others, 1972). 1972). These These data are consistent with the Allouez Gap principal pathway for ore fluid, moving outward from the fault into the conglomerate. Fault as a principal END OF LEG F �Lep 155 LEG G G COPPER LEG COPPER CiTY CITY MAP G1 01 MAP 0.0 Start at the junction paved road road to to Copper Copper City City in in Allouez. Allouez. This mile junction of US-41 US41 and the paved This isis0.1 0.1 mile northeast of the Houghton Houghton and and Keweenaw Keweenaw County County line, line, just inside insideKeweenaw KeweenawCounty. County. 0.65 Enter Copper City. City. 0.8 left, goes goes toward toward the the Kingston Kingston Mine, continue continue straight straight ahead. Ahmeek Street, on the left, 0.85 0.85 At the the stop stop sign, sign,continue continue straight straightahead. ahead. 1.05 AAsharp 1.05 sharpbend bend inin the the road road to to the the right. right. junction, continue straight straight ahead ahead toward towardLake LakeLinden. Linden. The road to the 1.15 At the junction, the left left goes goes to toGay. Gay. Asharpbendinroadtotheleft 1.25 A sharp bend in road to the left. 1.7 1.7 Going downhill. downhill. At the the skyline, skyline, the the low, low,smooth smoothterrane terrane(underlain (underlain by by relatively relatively flat-lying flat-lying basalts of of the the PLY. PLV. Jacobsville Sandstone) Sandstone) is is visible. visible. We are driving on the tilted basalts 1.75 AAroad roadsign signon on the the right. right. 1.8 1.8 An open field on on the the right. right. 1.9 Park and and walk walk to Stop GI. A dirt path on the right. right. Park 01. STOP Gi: Gl: Copper CopperCity CityRhyolite Rhyolite(Portage (PortageLake LakeVolcanics Volcanics [PLy]) [PLY) Walk along the dirt about 170 dirt road/path roadlpath parallel parallel to the tree tree line, line, about about 70 70m, m,then thenwaljc walkabout 170 m toward the tree tree line (N45°W). (N45¡W)Small Smalllow-lying low-lyingscattered scatteredoutcrops outcrops and and float float rhyolite rhyolite occur occurhere, here, and can be be found found elsewhere elsewhere further further west west within within the tree tree covered covered area. area. The Copper City rhyolite is poorly exposed throughout throughout the the body. body. The The rhyolite rhyolite isiswhite white on weathered surfaces and red-brown on fresh broken surfaces, it is fine-grained with abundant is fine-grained with abundant phenocrysts of quartz. Since Sinceexposures exposures are are of of poor quality, it is not known whether this body of rhyolite is intrusive intrusive or or extrusive, extrusive, although although the published published geologic geologic map shows shows contacts contacts as as crosscrosscutting; cutting; making making the body body more more likely likely intrusive intrusive(subvolcanic) (subvolcanic) (Davidson (Davidson and and others, others, 1955). 1955). Stratigraphically, thisbody bodyisis within within the the lower lower part part of of the PLY Stratigraphically, this PLV exposed exposed on on the the Keweenaw Keweenaw Peninsula, Bodies of rhyolite are much more Peninsula, and below below the the Bohemia BohemiaConglomerate Conglomerate (Fig. (Fig. ).). Bodies common in the lower stratigraphic section section of of the thePLV, PLy, although still volumehically volumetrically minor. minor. Just downhill from here, the PLY PLV are are truncated truncated by the the Keweenaw Keweenaw Fault. Fault. Recently, Nicholson (1992), as summarized below, below, has has recognized recognized two two chemical chemical types types of of rhyolite (TableGl). 01). Type rhyolite in the the Keweenaw Keweenaw Peninsula: Types Types II and 11 11(Table Type II rhyolites rhyolites contain containbetween between percent SiO,), Si02), and fall near the border 71 to 76 weight percent Si02 SiO, (generally less than 75 weight percent between peraluminous peraluminous and and metalurninous, metaluminous,with with less less than than 2 %%normative between normativecorundum. corundum. The peraluminous character of some Type II rhyolites may may be be due due to to alteration. alteration. Type Type H I1 rhyolites rhyolites have greater than 75 weight percent SiOy Si02, and and are are slightly slightly peraluminous. peraluminous. High High contents contents of of Th and Rb 11rhyolites rhyolitesfrom humType TypeI.I. The rhyolites of the PLV PLV are are part part of of a bimodal basaltdistinguish Type II �PiP �~eo 157 157 rhyolite rhyolite association, association, typical typical of of extensional extensional tectonic tectonic settings settings such as the Midcontinent Midcontinent rift rift system. system. Type rhyolites of of the thePLV PLVare aresimilar similartotomoderate-silica moderate-silica rhyolites rhyolites from other areas, areas, such such as as Type IIrhyolites Iceland, association. Type II II rhyolites of the PLY PLV are are similar similar to to aa Iceland, with with bimodal bimodal basalt-rhyolite basalt-rhyolite association. select subset subsetofofhigh-silica high-silicarhyolites, rhyolites,termed termedtopaz topazrhyolites. rhyolites. Topaz Topaz rhyolites rhyolites are are notable notable for for select enriched lithophile elements, sometimes to economic levels. The Copper City rhyolite is the only enriched lithophie elements, sometimes The Copper City rhyolite is the only recognized PLy, the IIrhyolite rhyolite within the PLV, theother otherrhyolites rhyolites are are all all Type Type I. Overall, Overall,the thesetting setting recognized Type TypeU of thePLY PLVisiscomparable comparabletotoIceland Iceland(Nicholson, (Nicholson,1992). 1992). of basalt basaltand andrhyolite rhyoliteininthe Table Table (31. Gl. Chemical ChemicalTypes Typesof ofRhyolites Rhyoliteswithin within the the PLV PLV(from (fromNicholson. Nicholson, 1992). 1992). Type TypeUII Major Type TypeII Major N=4 1 oxides: N=3 N=31 N=4 oxides: 75.74 SiO, 73.84 73.84 75.74 Sb2 0.05 0.12 TiO, 0.12 0.05 Ti02 13.28 A 1 A 13.65 13.65 13.28 A1203 0.44 F a 0.66 0.66 0.44 Fe203 0.87 1.32 FeO 1.32 0.87 FeO 0.04 MnO 0.03 0.04 MnO 0.03 0.14 MgO 0.23 0.14 MgO 0.23 1.38 0.25 CaO 0.25 1.38 CaO 2.48 N%0 3.23 3.23 2.48 Na20 6.64 5.60 6.64 5.60 K,O 1(20 0.02 0.03 P A 0.03 0.02 P205 100.04 Total 100.00 100.00 100.04 Trace Trace elements: elements: Nb 41 41 Nb Rb 112 Sr 55 Zr 240 Y 56 La 30.3 6.57 Sm Yb 5.55 Hf 7.53 2.91 Ta Th 15.09 End of of Leg Leg(3 G-- Retrace Retrace route route to to US-41. US-41. End 51 51 465 28 144 74 12.0 6.9 7.68 6.3 4.9 63.0 �158 STATE LEG II H McI,AIN M~LAIN STATE PARK PARK MAP HI Hi The junction junction of US-41M-26 US-4i/M-26 and M-203, Calumet. Turn M-203, at the edge of Calumet. Turn right right on on M-203. M-203. 0 0.55 The Village Limit of Calumet. Continue Continuestraight straight ahead. ahead. 1.0 Turn right just west of an open open playing field (on the right side, after the turn.) 1.1 Turn right. 1.2 Turn building. On Turn left left just before before a red sandstone sandstone block building. On the the left left isis the the concrete concretecapped cappedRed Red Jacket Jacket Mine. 1.3 At a sand and gravel pit. Hi: Red Stop HI: RedJacket Jacket(glacial (glacialsand sandand andgravel) gravel) The Pleistocene sands and and gravels gravels at at this locality Pleistocene sands locality are are interpreted interpreted as deposited deposited in in perforation kames and crevasse fillings. The deposits show both cross-bedding and channeling, perforation fillings. The deposits show both cross-bedding channeling, due to the glacial-fluvial sediments sediments being deposited in perforations and crevasses in the ice. These These deposits, and the esker to the north of here (Fig. HI, Hi, location location B), are characteristic of the glacial ice margin (summarized (summarized from from Regis, Regis, 1993). 1993). Retrace route and M-203. and return return to to M-203. 1.6 At the junction of of M-203, M-203, turn turn right--away right~awayfrom from Calumet. Calumet. 1.95 Turn right, onto 1.95 onto Tamarack Tamarack Waterworks Waterworks Road. Road. 2.25 The road road bends bends left. left. Superior on the horizon horizon is excellent. 2.45 At the crest of the West Tamarack Moraine, the view of Lake Superior excellent. 2.5 Pull over to the the right. right. Stop 112: H2: West Tamarack Tamarack(glacial (glacialgravels) gravels) The West Tamarack Moraine is composed composed of of cobbles-to-boulders cobbles-to-bouldersin inaa sand sand matrix. matrix. This This moraine extends for about 10 withaawidth widthofofabout about1.5 1.5km kmin in the the south, south, several several 100 m in km,with 10 1cm, the north (Fig. Hi), HI), and and aathickness thickness of of around around 20 20 m. m. The Thenorth-south north-southtrending trending West West Tamarack Tamarack Moraine has a gender gentler west west slope, slope, which which is is interpreted by Hughes Hughes (1963) (1963) as indicating indicating underwater underwater deposition, except at the the extreme extreme north north end end (summarized (summarized from from Regis, Regis, 1993). 1993). Retrace route and and return return to toM-203. M-203. 3.05 Turn right on 3.05 on M-203. M-203. 4.0 Lakeview Cemetery is on the right. right. �~ e o MapH2 159 MAP Hi �a ec. 4- - 7., --S a- 4 - A-. a-, - -flair. -. -: - ?iC; t it—. a-.. --'4:.' JL V 4. 24.. I. I Figure Hi: Physiographic and glacial features west of Calumet (from Hughes. I 963). A. West Tamarack moraine, subaerial portion; B. esker. C. sand plain; D. boulder ridge; E. delia kame; F. Centennial hill; G. Tamarack hill; H. Swedetown hilt. I t -a — - .-, __fl.r. - �Legs 161 junction at the road to the Calumet Waterworks Park. Park. Continue 4.3 4.3 The junction Continue on on M-203. M-203. MAP H2 H2 Road. The Theroad road goes goes uphill. uphill. 6.0 Turn left onto Cloverland Road. 6.35 Pull over, alongside alongside the the road. road. Stop 113: H3: Cloverland CloverlandRoad Road(Washburn (WashburnStage Stagebeach beachridges) ridges) This stop stop is is at at the the elevation elevation of of the the Washburn Washburn Stage Stage of of the the Lake Lake Superior Superiorbasin basin (Table (Table2). 2). beach ridges ridges about about 1.5 1.5 m m high high in in the open field. Here, one can view a pair of NE-SW NE-SW trending beach The two ridges are only only about about 11 m m apart apart and and their theirassociated associated sediment sediment is is well well sorted sorted medium medium sand. The Theelevation elevationatatthis thisglacial glaciallake lakestage stagevaried varied between between 1040 1040 to 1051 1051ft, ft, which which is is about about 440 440 ft above the present-day elevation of of Lake Lake Superior. Superior. The Washburn Stage has the most traceable features, next to to the the Nipissing Nipissing Stage Stage (summarized (summarized from from Regis, Regis, 1993). 1993). Return to to M-203. M-203. 6.7 6.7 Turn left onto onto M-203. M-203. 9.2 The road to the right is Lakeshore Lakeshore Drive, which goes goes to the the Calumet Calumet Township Township Waterworks WaterworksPark. Park. The road to the left is Sale Road, which goes to the Bear Lake Rhyolite and Stop H4. The Bear Salo which goes to the Bear Lake Rhyolite and Stop H4. Lake Rhyolite cuts the Freda Sandstone bedrock, bedrock, and and is is the the youngest youngest known igneous activity in Peninsula. The Bear Lake Rhyolite of 1054  ± 34 my. m.y. years old, the Keweenaw Keweenaw Peninsula. Rhyolite is a minimum minimum of based on a KJAr (White, 1968). 1968). The mileage to H4 is not logged, but just follow the KIAr age date (White, directions given in the the stop stop description, description, H4. H4. Continue on M-203 M-203 toward towardStop Stop115. H5. Stop H4: Lake LakeAnnie Annie(glacial (glaciallake lakebaymouth baymouth bar) bar) Directions to Lake Annie Stop (not logged): Turn left onto Salo Road and continue due south for where the the road road bends bends sharp sharp right right (west). (west). At about 1.0 miles from the turnoff, where about 1.5 1.5 miles, miles, turn turn left left (south). Continue straight ahead (south) and at about 4.35 miles there is a "Y' in the road, stay (south). Continue straight (south) and at about 4.35 miles there is a "Y" right. On right. Onthe theleft, left,atatabout about5.3 5.3miles, miles,isisaasand sandand andgravel gravelpit, pit,MAP MAP114. H4. The Pleistocene glacial sediments at this stop represent a baymouth bar, related to either the Shoreline V V or Washburn Washburn glacial glacial lake lake stage stage (Table (Table2). 2). This ridge is composed of sand with gravel. Near little gravel. Near the theeast eastedge edgeof of the thepit, pit, the thesand sandisiscapped capped by by till till(summarized (summarized from from Regis, Regis, 1993). 1993). MAP H3 H3 9.9 Sand ridges on the right, at the east east end of of McLain McLain State Park. Stop 11$: H5: Sand SandRidges RidgesM-203 M-203(Nipissing (Nipissing beach beach ridges) ridges) beach sand sand ridges ridges are are related related to Glacial Lake Nipissing, These subaqueous beach Nipissing, which was 10 m above above the the current current level level of of Lake LakeSuperior--approximately Superior--approximately 4,000 to 5,000 5,000 years years ago. ago. about 10 but sometimes are more The Nipissing Stage features are usually close to those of Lake Superior, but prominent. prominent. the Nipissing Nipissing stage, one The north end of Portage Lake opened into two channels during the �—— -D '-S lc'olc t.J 0' �_ ______ _____ Legs It S11 Ii eQ2 Stop H5flf-S ELEYAT MA$ 163 '-' Stop H6 IJ )75(U? gfL7a7 S' t:kar Lake GravitY Traver_.J J Rhyolite 4 ,628 \' COAST ' GUARD \\a;srA o BM t:c . 5; ,, U J 'Cl Map H4 MAP H3 �MAP �~eo Legs 165 165 was the the Bear Bear Lake Lake Channel. Channel. The was the current channel, channel, the other was The two two were were separated separated by an an island. Sand Sandclosed closedoff off both both channds channels(the (thecurrent-day current-day channel channel was was dredged dredged by the Army Army Corps Corps filled in the Bear Lake of Engineers for ship traffic), and eventually eventually filled Lake channel channel described described below below (summarized from Regis, 1993). Regis, 1993). 10.1 10.1 Bear Lake is on the left left side side of the the road. mad. Cross Crosson ontop topofofthe thefilled filledglacial glacialBear BearLake Lakechannel. channel. The Bear Lake Lake Channel Channel (Map H3) represents a deep bedrock valley, and is an an extension extension of of the the Keweenaw Waterway. Waterway. The Waterway was dredged dredged to to the west of McLain Keweenaw Waterway was McLain Park because because the the distance was less, but also because the Bear Lake Channel is a much more profound feature, with than 600 ft to bedrock. bedrock. The and similar similar bedrock bedrock valleys, valleys, is shown by more than The definition definition of this, this, and gravity data. One such traverse, plotted on the map, is displayed as Figure One such traverse, plotted on the map, is displayed as Figure H2. H2. 11.0 11.0 Turn right at the the entrance entrance to to McLain McLain State Park and the other other edge edge of of the the Bear Bear Lake LakeChannel. Channel. Camping facilities are located here. here. You can park on on the the side side of of M-203 M-203 opposite opposite to to the the entrance entrance and and wallc walk into the park, or or pay pay the the (the same same park park sticker stickerisis valid validfor forStop Stop28). 28). Enter the park and stop vehicle fee at the entrance (the stop at the main open area. Walk Walktoward toward Lake Lake Superior Superior and and the children's play play equipment. equipment. Stop Stop 116: H6: McLain McLain State StatePark Park(Freda (FredaSandstone) Sandstone) the shore of of Lake Superior, depending depending upon upon the level Freda Sandstone is exposed along the and slabs of Freda can be found of the the lake. lake. Blocks Blocks and Freda Sandstone Sandstone can found along along the the beach beach however, however, regardless of the lake lake level. level. It consists of red colored interbedded fme fine sandstone and siltstone, siltstone, and the red color reduced zones zones and and spots. spots. The Freda Sandstone color is interrupted by white reduced Sandstone was the last rift-filling clastic clastic sediment, sediment, and and was was deposited deposited in in aafluvial fluvialenvironment. environment. M-203. The The road road to to the the right right is is to to the the Coast Coast Guard Guard Station; Station; the road to the left is is 11.8 Continue on M-203. 11.8 the Bear Lake Lake Road, Road, the the location location of of gravity gravity traverse. traverse. 12.8 12.8 The access access road to to Lily Lily Pond. Pond. Lobe, a great mass of glacial ice which At this point, the end moraine moraine of the Keweenaw Keweenaw Lobe, great mass which was Wisconsin glaciation, glaciation,isiscrossed crossed(Fig. (Fig. 16). 16). The regional distribution of stabilized here during the Wisconsin this moraine in Figure Figure 15. 15. The moraine is plotted plotted in The positions positions of lobes as they retreated retreated at the end of the Wisconsin period are are shown shown in in Figure Figure 14. 14. MAP H5 H5 High Point Road, continue continue ahead ahead on on M-203. M-203. 16.1 16.1 17.85 Exposures Exposures on on aa vertical vertical road road cut. cut. Stop 117: Stop H7: Till along M-203 (till) (till) The 5 S m high vertical face exposes exposes aa matrix-supported matrix-supportedsediment: sediment:diamict. diamict. It is a hard and compact till with cobbles set in a fme matrix. Carbonate Carbonate cement cement causes the hard character, and is likely an older older till till (summarized (summarized by Regis, Regis, 1993). 1993). 17.95 AAhigh highcut cutofofglaciofluvial glaciofluvialsediment sedimenton on the theleft. left. �MAP �Legs ten 167 167 BEAR BEAR LAKE LAKE 9 8 7 0 0 6 5 I I I 4 6 — I 8 I I IC 12 I 14 0 x IC — I 0 0 -2 -3 C 200 S Figure112: H2: Results Results of of gravity gravitymeasuxements measurements across the Bear Lake Lake traverse traverse plotted plotted in in Map MapH3 H3(from (from Figure Warren, Warren. 1981). 1981).At Atthe thetop topisisthe theBouguer Bougueranomaly anomalywith withregional regionaltrend. trend. InInthe themiddle middlediagram, diagram. the the regional regional trend trend isis subtracted subtracted to to get getthe thesolid solidline linewhich whichisiscompared compared with with the themodelled modelled difference topography QC's). The bottom diagram is the model of the valley and the density topography (X's). The bottom diagram is the model of the valley and the density differenceof of bedrock(Freda (FredaSandstone) Sandstone)and andthe thevalley valleyfill. fill. thebedrock the �168 Hancock City limit. limit. MAP H6 H6 Creek are are exposures exposures of of Freda Swedetown Creek. Creek. To the northeast northeast along Swedetown Swedetown Creek 18.7 Cross Swedetown 18.7 Sandstone. Sandstone. 18.6 18.6 19.05 Hancock and Superior Superior Sand Sand and and Gravel Gravel is is on on the the left left (Stop HancockCampground Campgroundisison onthe theright right(Stop (Stop118), H8), and H9). STOP STOP 118: H8: Hancock Hancock Campground Campground(Nonesuch (NonesuchShale) Shale) paved road road to to the the boat boat launch. launch. Tell the attendant attendant you you are aregoing goingto tolook lookatatrocks. rocks. On Follow the paved the shore exposed. An shore of Portage Lake, the Nonesuch Shale is exposed. An abandoned abandoned quarry is is located located NE NE of the boat launch. launch. The Nonesuch is stratigraphically stratigraphically between the Copper Harbor Harbor Conglomerate Conglomerate and and Frecla Freda Sandstone (Fig. (Pig. 5). Nonesuch crops crops out around around the the margin margin of of the the quarry quarry and and lakeshore lakeshore at at this stop. It The Nonesuch is aa fmefine-totomedium-grained, medium-grained,gray-to-reddish gray-to-reddish brown brown sandstone sandstone with with subordinate subordinateinterbedded, interbedded, reddish-brown laminated siltstone and shale 956a). The attitude of reddish-brown shale (Cornwall (Cornwall and andWright, Wright,1 1956a). bedding is about N30?3, As a whole, the Nonesuch Shale consists primarily of siltstone siltstone N30°E, 25W. 25W. As amounts of of sandstone, sandstone,deposited depositedininaalacustrine lacustrineenvironment. environment. It It can and shale, with subordinate amounts from the formations above and and below below by by its generally be distinguished distinguished from formations above generally grayish grayish color. Most Most Nonesuch is aa rippled, rippled, laminated laminated siltstone siltstone with with reddish-gray reddish-gray partings. partings. Lithologically, siltstones siltstones composed of of around around 30 30 to 40 % rock fragments and 60 and sandstones of the Nonesuch Nonesuch are composed 60 to to 70 % mineral grains. The Therock rockfragments fragmentsare are mostly mostly volcanic volcanic with with a 2:1 2:1 ratio ratio of of mafic-to-silicic mafic-to-silicic (Daniels, 1982). 1982). The + intermediate intermediate composition composition (Daniels, The Nonesuch Nonesuch Shale at Hancock Hancock Campground is + some 60 60 km km northeast northeast of of the the thicker thicker section section near near White White Pine, Pine, and and likely likely represents representslacustrine-tolacustrine-tofluvial facies (Elmore and others, 1989). The Thedip dipof of the the underlying underlyingCopper CopperHarbor HarborConglomerate Conglomerate at Stop Al A1isis39W % 93' and andoverlying overlyingFreda FredaSandstone Sandstoneatatthe theLake LakeSuperior Superior shoreline shoreline at at Stop Stop A3 A3 is is SW. 5 T . This Thisshallowing shallowingofofdip dipup-section up-section isis typical typical of of the the rift-filling rift-filling strata, and is mostly mostly due to syn-depositional syndepositional down warping of the the rift-filling rift-filling strata. strata. Stop 119: H9: Superior SuperiorSand Sandand andGravel Gravel(glaciofluvial (glaciofluvialsediments) sediments) YOU MUST MUST GET GET PERMISSION PERMISSION TO TO ENTER ENTER THIS THISLOCATION. LOCATION. Sand and gravel terraces occur all along the Portage Gap, but most are less that 1.5 1.5 km krn long, and are are related to ice ice margin margin features. The TheFairground Fairground Terrace, Terrace,being being mined mined here, here, consists consists of three zones and H4). 114). Massive lacustrine sand sand is is overlain overlain (in channels) by a poorly zones (Fig. (Fig. 113 H3 and pinkish color. color. The sorted gravel with a pinkish The pink color is the result of a significant amount of silt and clay. Some Atthe thetop, top, the the coarse, coarse, purplish purplish gravels gravels Sometill tillisisincluded included in in the the poorly poorly sorted sorted gravel. At lack the pinkish color, and was likely deposited deposited in in a deltaic environment. environment. The Michigan The Michigan Tech Tech Terrace formed at at the the same sametime. time. The glaciofluvial glaciofluvial sediments formed during the last glacial retreat, about 8,000 years ago. Glacial ice was abutted against the Keweenaw Keweenaw Fault slope from the east for aa protracted protracted period period of time, with a tongue of ice in the Portage Gap. The Thepost-Duluth post-DuIuth glacial glacial lake lake drained drained eastward through the Gap (summarized (summarized from Regis, 1993). 1993). END OF OF LEG LEGHH -- CONTINUE ON M-203 INTO END INTO HANCOCK. HANCOCK. �169 I H6 MAP H6 I �170 Isgs Figure Figure113: H3: Geologic Geologicsection sectionthrough throughthe the Hancock Hancock "Fairground" "Fairground"terrace terrace glacial glacial deposit deposit(from (fromHughes, Hughes, 1963). 1963). �Legs a 171 a-'-' O. rj-, -. ap3t-4E -t - Figure FigureH4: H4:Physiography Physiographyand andglacial glacialfeatures featuresofofthe thenorthern northernpart partofofPortage PortageLake Lake(from (fromHughes, Hughes,1963). 1963). �172 t.cgs LEG I L'ANSE Ii MAP I1 on the the campus campusof ofMichigan MichiganTechnological TechnologicalUniversity. University. The Begin at the Memorial Union Building on 0.0 Begin by the PLV PLY (see MAP 1). 1). campus is built on glacial glacial sediments underlain by 0.1 Turn left (east) onto US-41. US-41. NOTE: NOTE:Stay Stay on on US-41 US-41 all the way to Stop Stop Ii. 11. 0.6 The middle of Wadsworth Dormitory Dormitory overlies overliesthe the Keweenaw KeweenawFault. Fault. As you follow US-41 past the dorm, and will will continue dorm, the the underlying underlying bedrock bedrock is now now Jacobsville Jacobsville Sandstone, Sandstone, and continue to be be Jacobsville Sandstone all the way #I. way to to Stop Stop#1. 0.7 East entrance/access entrancelaccess road to the Michigan Tech campus. 1.2 On the left is a view of Isle Royale Sands and and the the Portage PortageWaterway. Waterway. The dark-colored sands are basalt flow flow top lodes were processed crushed basalt. basalt. The native copper mineralized mineralized basalt processed by stamp stamp mills primarily along the margin of Portage Lake, Lake, Torch Torch Lake, Lake, and and Lake Lake Superior. Superior. In those those days, days, the waste crushed water. Fortunately, crashed basalt was dumped into the adjacent water. Fortunately, the native native copper copper ore ore deposits of the any, acid-generating acid-generating sulfide sulfideminerals--such minerals--such the Keweenaw Keweenaw Peninsula Peninsula contain contain little, little, ifif any, as pyrite--so pyrite-so that the actual rock waste is as inert inert in in the the surface surface environment environment as natural rock exposures. exposures. 2.7 On the left left is is an an excellent excellent view view of of Portage Portage Lake. Lake. 6.8 Enter Chassel. Chassel. 9.0 Crossing the Sturgeon Sturgeon River River and and its itsassociated associatedsloughs. sloughs. The Sturgeon River discharges discharges into Portage Lake, Lake, forming forming aa bid's bird's foot delta. delta. The are an an excellent excellent wildlife wildlife area area where where a Thesloughs sloughs are It is a recommended canoe launching spot. diverse list of birds nest. of birds nest. a recommended launching 12.7 The rolling rolling terrane terrane here here isis glacially glacially carved carved from from the theunderlying underlying Jacobsville Jacobsville Sandstone, Sandstone, and veneered with a variable thickness of glacial glacial sediment. sediment. 15.6 Yiewing Viewing Keweenaw Bay of Lake Lake Superior. Superior. 20.5 Grover Diilman, Pullover is is on on the left toward Keweenaw Bay of Lake Dillman, Baraga Cliff, Roadside Pullover the fenced in area is a 21 m high exposure Superior. Behind Behind the fenced in area is a 21 m high exposure of of Jacobsville Jacobsville Sandstone. These These L'Anse. exposures can be seen from the Keweenaw Keweenaw Bay shoreline in L'Anse. 21.8 Enter Keweenaw Bay Bay Indian Indian Reservation. Reservation. 22.3 An excellent view view across across Keweenaw KeweenawBay. Bay. At the 10:00 position position is a good view of the western Archean core composed of granitoid rocks end of the Huron Mountains. This Thisarea areaconsists consists of an Archean unconformably overlainby by early early Proterozoic sedimentaryrocks rocks of of the unconfonnably overlain Proterozoic sedimentary the Marquette Marquette Range Range Supergroup Supergroup (Klasner (Klasner and and others, others, 1991). 1991). 24.3 A good view of L'Anse black sand beaches are made of the same L'Anse across across Keweenaw Keweenaw Bay. The black crushed basalt mine rock as the Isle Royale Sands near Houghton. The Thebedrock bedrock here, here, Jacobsville Jacobsville Sandstone, Sandstone, yields yields white white sand sand beaches. beaches. �SCALE 1:168960 (1 cm = 1689.6 in or 3/8' =1 mile) AP �174 174 ten MAY12 MAP I2 26.8 Entering Baraga. 27.3 10:00 position position is aa view view across across The US41 and M-35; M-35; stay stay on on US-41. US-41. At At the 10:00 The junction junction of US-41 Keweenaw with L'Anse L'Anse Red Rocks cliff cliff exposures exposures (Stop (Stop 11) Ii) in the Keweenaw Bay with the background. background. 28.7 Baraga State State Park. Park. 29.1 The head of of Keweenaw Keweenaw Bay. Bay. 29.4 L'Anse L'Anse Red Red Rocks Rocks are arevisible visible straight straight ahead. ahead. 30.1 Pull over over to to the the side side of of the the road--being road-being careful careful of of traffic. traffic. It is recommended recommended that you turn around of the guardrail on the pebble and pull over on this end (the downhill end, near Lake Superior) of beach. Walk toward the the tree tree line (there is a path) to begin beach. Walk along along the the Keweenaw Keweenaw Bay shoreline shoreline toward Stop #1, which is the unconformity between the early Proterozoic Michigamme Michigamme Formation Formation of of the Marquette Range Supergroup (cleaved slate) and the the Jacobsville Jacobsville Sandstone. Sandstone. After viewing the lower part, you may either climb the steep steep bank to the the highway, highway, or or retrace retrace the the path path and and emerge emerge by the cars, where where you you can can cross cross the the street street and and proceed proceed to to walk walk along along the the cliff cliff onto the highway by exposures of the the Jacobsville Jacobsville Sandstone. Sandstone. BE EXTRA EXTRA CAREFUL CAREFUL OF OF TRAFFIC!! TRAFFIC!! Ii:1:L'Anse Stop 1 L'AnseRed RedRocks Rocks(Jacobsville (JacobsvilleSandstone) Sandstone) In the the Lake Lake Superior Superior syncline syncline portion portion of the the Midcontinent Midcontinent rift zone, zone, the the Jacobsville Jacobsville Sandstone Sandstone is aa thick thick (+900 (+900m) m) redbed redbed sequence sequenceof of fluvial fluvialsandstones; sandstones;conglomerates; conglomerates; siltstones; siltstones; and shales, cutting dykes. dykes. On shales, completely devoid of lava flows and cross cutting On the the north and and south south sides sides of Lake Superior, the formation occurs as inward-dipping, fault-bounded depositional wedges. Lake Superior, the formation occurs as inward-dipping, fault-bounded depositional wedges. These are are separated separated by regional regional reverse faults faults from from the strata strata that are are more more axial axial on on the the inner innerside side of the basin, the PLy, PLV, and andthe theOronto Orontoand and Bayfield Bayfield Groups Groups of similar similar red sandstones. sandstones. consists of arkose, The sandstone sandstone lithology lithology consists arkose, subarkose, subarkose, quartz, sub-lithic sub-lithic arenite, arenite, and and massive sandstone-shale sandstone-shalesequences sequencesrepresenting representing point point quartzite. Locally, Locally,there there are well developed massive bar-overbank facies, and in drill cores, there are several hundreds of meters of upward fining beds, of fluvial, fluvial,possibly possiblybraided, braided,stream streamdeposits. deposits. The The cement 55 to 30 cm thick, which is characteristic of varies from from authigenic clay to calcite and zeolite. Conglomerates Conglomerateswith with clasts clasts of of Lower LowerProterozoic Proterozoic extensive, particularly west and east and Archean lithologies, are locally abundant and laterally extensive, of Lake Gogebic. In places, places, there are also also clasts clasts derived derived from Keweenawan volcanic rocks. Jacobsville sedimentation was preceded preceded by by volcanic quiescence; quiescence; cratonic stability; and sedimentation was weathering, so that chemically resistant debris such as quartz weathering, so chemically resistant debris as quartz and andiron-formation iron-formation became became concentrated in in the source areas. Erosion Erosionwas wasinitIated initiated by by late late Keweenawan Keweenawan warping, warping, perhaps perhaps accompanied Vigorous marginal accompanied by movement movement along along the the Keweenaw Keweenaw Fault. Fault. Vigorous marginal fluvial systems systems developed on the south side by ridges of iron-formation. The side from from uplands dominated by Theresistant resistant debris was deposited in alluvial fans. Later Later sediments sediments were also also derived from a Keweenawan age terrane. On basaltic and felsic volcanic terrane. On burial, burial, the thesandstone sandstone underwent underwent low-grade low-grade alteration alteration so so that microcline-plagioclase-kaolinite-montmorillonite that the the present matrix mineralogy changes from microclhe-plagioclase-kaol'inite-montmorillonite near the surface, surface, to to microcline-montmorillonite-illite microcline-montmorillonite-illite(chlorite) (chlorite) at at depth. depth. At the top of the the cliff is is aa locally fabricated sheet copper statue of Bishop Fredric Baraga �SCALE 1:168960 (1 cm = 1689.6 m or 3/8" = 1 mile) MAP �176 12gz (1797-1868); a Roman Roman Catholic priest born in Yugoslavia, Yugoslavia, who worked among the Indians and early white settlers. settlers. The 20 m highway on on the shoreline) and upper m section, section, divided divided into lower (below the highway parts (above highway), shows shows many many of of the the characteristics characteristicsofofthis thisfluvial fluvialredbed redbedformation. formation. The sandstone rests on Lower Formation Slate Slate which which displays a reddish Lower Proterozoic Proterozoic Michigamme Michiganune Formation reddish discoloration along joints, joints, possibly possibly denoting denoting pre-Jacobsville pre-Jacobsvilleweathering. weathering. At the inner edge of the slate outcrop, under under the the overhang, overhang, there thereare areparallel parallelstriations striationson onthe thesurface surfaceofofthe theslate. slate. These striations striationswere interpreted interpreted by Murry Murry (1955) (1955) as as having having been produced by pre-Jacobsville pre-Jacobsville glaciation, glaciation, and by Kalliokoski Kalliokoski (1982), as produced produced by aa more more recent recent lakeward lakeward sliding sliding of of the theJacobsville Jacobsville Sandstone on top of of the the regionally regionally inclined inclined slate slatesurface surface (Fig. (Fig. 11). 11). At the base of of the the Jacobsviile, Jacobsville, the the wide wide variety variety of of clasts clasts in in the thepolymictic polymictic framework framework conglomerate and metamorphic metamorphic Archean Archean and and Lower Lower conglomerate resemble lithologies in igneous, sedimentary, and Proterozoic rocks that outcrop some tens of of kilometers kilometers to the the south southand andsouthwest. southwest. Note the the pebbles of vein quartz and iron-formation. iron-formation. The abundance of pebbles The sandstone sandstone immediately immediately above above the the conglomerate display foresets and troughs. conglomerate foresets and troughs. The upper part of of the theJacobsville Jacobsville section, section, above above the the level level of of the thehighway, highway,consists consists predominantly of fmepredominantly fine- to to medium-grained medium-grained reddish reddish brown-to-tan brown-to-tan feldspathic-to-sublithic feldspathic-to-sublithic quartz quartz sandstone, with minor minor red silty ranges from well-bedded sandstone, with silty shale shale (east, (east, left). left). The sandstone ranges well-bedded to massive. Some Somebeds beds are areup up to toI1mmthick thickand andshow showconspicuous conspicuousforesets foresetsoverlain overlain by by planar planar beds beds layers of of quartz pebble pebble lag lag conglomerate. conglomerate. Some surfaces are current ripple and thin, continuous layers marked. AAconvoluted convolutedsandstone sandstonebed bed above above aa planar planar bedding surface suggests suggests that sedimentation was on a slope. slope. END OF LEG II RETRACE ROUTE TO HOUGHTON - RETRACE HOUGHTON - �A scsia - -, W w ,vast LAfl ~Izgse o 177 177 LI I 5— A' u.s. B fl 1.1.; A Dik. ..ta.g rs-rwn Ijasntnd; w.11.ert.4i erSbs4L 114 4 (a ia.c1s.t.. 1a.p—.eM IkiMrPM... b—Maj (a. ad, n. fI.l—ts.t*.d, ..fl—..rt.d; U—.l. tn..—b.441; .1 1..cS.1.t; .s(tis .n—fl beddtfl nfl... .1 i.cnnl dnp.s .tlyi.( i.t.sL. .Si.. tt s L.Ai ..ttMd net...., flw.bM v.U.ercMI lnp—...i. cn..SddL.t; .a.t Near b4dI; .fla (tic rifl.. — Sn tanlad .ithS. Sst.r..1; d. .,k — i.a.cl..t.i •h—l lain •eantt. - .....-"'-.- lai..t.d te sMy 24.1 d1.41s ii.. tf 1.1.1 2.d-m w aU—iteM snesbiddia *54 ..,,-...—gLSL, . >, . " . , - , " .&cSU&,flI.-ncy -u-.-u $.arb.dd.4i SS,.aULC —. •i IflSI '0I0—. -1Ul, r*-1 .ini..; MUM* .-là IS te k. tSS.k1 In. .nI Figure Ii: Figure 11:(a) (a)Geologic Geologicsketch sketchmap mapand andcross-section cross-sectionof L'Anse redrocks (from 1962 1962 Michigan College College Sandstone is equivalent and Technology, Technology, NSF NSF Summer SummerConference Conferenceguidebook). guidebook). Sandstone equivalent to to the the of Mining and Jacobsville Sandstone, slate is equivalent to the Michigamme Formation, the the Early Early Proterozoic Proterozoic Michigammc the Jacobsville Strañgraphic section of the Jacobsville Sandstone (b) Stratigraphic Sandstone at at contact is an an angular angularunconformity. unconformity. (b) L'Anse Redrocks L'Anse Redrocks (from (fromAble. 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Thesis): Thesis): Michigan MichiganTechnological TechnologicalUniversity, University, Houghton, Houghton, l98p. 198p. (M.S. Mauk, Mauk,J.L., J.L., Brown, Brown,A.C., A.C., Seasor, Seasor,R.W., R.W., and and Eldridge, Eldridge,C.S., C.S., 1992, 1992,Geology Geology and and geochemistry geochemistry of of the the White White Pine Pinesediment-hosted sediment-hostedstratiform stratiformcopper copperdeposit. deposit,Michigan. Michigan. McDowell, McDowell, S.D., S.D., Price, Price, K.L., K.L., Huntoon, Huntoon,J., J., and and Bornhorst, Bomhorst, 1.1., T.J., 1992, 1992, Thermal modeling modeling and and illite/smectite illitekmectite geothermometry geothermometryof of the the Precambrian Precambrian Oronto Oronto Group, Group, Wisconsin Wisconsin and Michigan Michigan (abs.): (abs.): 38th 38th Annual Annual Institute on on Lake LakeSuperior SuperiorGeology Geology Program Program and and Abstracts, Abstracts, v. v. 38, 38, P. p. 59-60. 59-60. Institute Merk, Merk. G.P.. 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Northern Northern Miner, Miner, 1990, 1990,Great Great Lakes Lakes hits hits high high grade grade zones zones with with iritill infill drilling: drilling: Northern Miner, v. v. 76, 76, no. no. 32, p. 3. 3. 32, p. Paces, Paces, J.B., J.B., 1988, 1988,Magmatic Magmatic processes, processes, evolution evolution and and mantle mantle source sourcecharacteristics characteristics contributing contributingto tothe the petrogenesisof of Midcontinent Midcontinentrift rift basalts: basalts: Portage Portage Lake Volcanics, Keweenaw Keweenaw Peninsula, Michigan petrogenesis Michigan Dissertation): Michigan Michigan Technological University, Houghton, 413p. (Ph.D. Dissertation): 4l3p. Paces, Paces, J.B., and and Bell, Bell, K., K., 1989, 1989,Non-depleted Non-depleted sub-continental subcontinental mantle mantle beneath beneath the the Superior SuperiorProvince Provinceof of the the Canadian Shield: Shield: Nd-Sr Nd-Sr isotopic isotopic and and trace trace element element evidence evidence from from Midcontinent Midcontinent rift rift basalts: basalts: Canadian Geochemica et Cosmochimica Cosmochiica Acta, v. v. 53, 53, p. p. 2023-2035. 2023-2035. Geochemica Paces, J.B., J.B., and and Bornhorst, Bornhorst, T.J., 1985, 1985, Geology and geochemistry of lava flows within the Copper Harbor Paces, Conglomerate, Keweenaw Keweenaw Peninsula, Peninsula, Michigan: Michigan: 31st Annual Institute on Lake Lake Superior SuperiorGeology Geology Conglomerate, Proceedings, Kenora, Kenora, Ontario, Ontario, p. p. 71-72. 71-72. 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D.E., 1990, 1990,Pressures Pressures and and hydrogeology hydrogeology in in petroleum petroleum basins: basins: Earth Science Powley, D.E., 215-226. 215-226. �_________ 184 184 Prest, Prest, iteruencc* ~ef- - - V.K., 1969, 1969, Retreat Retreat of of Wisconsin and recent ice in North America: America: Geological Survey of Canada Canada Map Map 1257A. 1257A. Price, K.L., K.L., Huntoon, Huntoon, J.E., J.E., and and McDowell, McDowell, S.D., S.D., in review, review, Thermal Thermal history of the the 1.1 1.1 Ga GaNonesuch Nonesuch Fonnation, Formation, North North American American Midcontinent Midwntinent tilt rift at atWhite WhitePine, Pine, Michigan: Michigan: American American Association Association of of Petroleum Geologists Geologists Bulletin. Bulletin. Petroleum Price, McDoweIl,S.D., S.D.,1993, 1993,ilhite/smectite nlitefsmectite geothermometry geothermometryof of the the Proterozoic ProterozoicOronto OmntoGroup, Group, Price, K.L., K.L., and andMcDowell, Midcontinent rift system: Clays and Clay Minerals, v. 41, p. 134-147. system: and Clay Minerals, v. 41, p. 134-147. Regis, R., 1993, 1993, Field Field guide guide totothe theglacial glacialgeology geologyofofthe thecentral centralKeweenaw KeweenawPeninsula, Peninsula,Michigan Michigan (unpublished (unpublished class classreport): report): Michigan MichiganTechnological TechnologicalUniversity, University,Z3p. 23p. Spooner, E.T.C., 1986, 1986, Native copper deposition by mixing of high temperature, temperature, high Richards, J.P., and Spooner, salinity fluids fluids of of possible possible magmatic magmatic association association with with cool cooldilute dilutegroundwaters, groundwaters, Keweenaw Keweenaw salinity 18, p. p. 730. 730. Peninsula, Michigan: Geological Society of America Abstracts with Programs, v. 18, Robertson, J.M., J.M., 1975, 1975, Geology and mineralogy mineralogy of some some copper sulfide sulfide deposits deposits near Mount Mount Bohemia, Bohemia, Keweenaw County, County, Michigan: Michigan: Economic Economic Geology, Geology, v. v. 70, 70,p.p. 1202-1224. 1202-1224. Rose, W.1., Bornhorst, T.J., Ti., Chesner, W.I., Bomhorst, Chesner, C.A., C.A., Leddy, Leddy, D.G., D.G., Lodise, Lodise, L., L., and andSymonds, Symonds,R.B., R.B., 1986, 1986,Heavy Heavy metals metals in in sediments sedimentsand and mining mining wastes of Torch Lake, Michigan: unpublished report, pp. 119-151. 119-151. Schleiss, W.A., W.A., 1986, A study study of of vein vein mineralization mineralization and wall rock alteration at the the Delaware Delaware mine, mine, Keweenaw Keweenaw County, County, Michigan Michigan(M.S. (M.S. Thesis): Thesis): Michigan MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton,86p. 86p. Scofield, N., 1976, 1976,Mineral Mineral chemistry chemistry applied applied to to interrelated interrelated albitization, albitization, pumpellyitization pumpellyitization and native native copper redistribution redistribution in in some some Portage PortageLake Lakebasalts, basalts,Michigan Michigan(Ph.D. (Ph.D. Dissertation): Dissertation):Michigan Michigan Technological TechnologicalUniversity, University,Houghton, Houghton,144p. 144p. Sibson, Sibson, R.H., R.H., 1987, 1987,Earthquake Earthquake rupturing mpturing as as aamineralizing mineralizing agent agent in in hydrothermal hydrothermalsystems: systems: Geology, Geology,v.v. 15, p. 701-704. 701-704. 15, , 1990, 1990, Conditions Conditions for fault-valve fault-valve behaviour: behaviour: Geological Geological Society London Special Special Society of London Publication No. 54, 54, p. p. 14-28. 14-28. Sibson, Sibson, R.H., Robert, Robert, F., F., and andPoulsen, Poulsen,K.H., K.H., 1988, 1988,High-angle High-angle reverse reversefaults, faults,fluid-pressure fluid-pressurecycling, cycling,and and mesothermal gold-quartz deposits: Geology, Geology, v. v. 16, 16,p. p. 551-555. 551-555. Sikkila, K, 1984, Petrographic Petrographic and geochemical geochemical study Mount Bohemia Bohemia Stock, Stock, Portage Portage Lake Lake Sildcila, K, 1984, study of of the Mount Volcanics, Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan (abst.); (abst.); Institute Institute on Lake Lake Superior Superior Geology Geology Volcanics, Proceedings, 30th Annual Meeting, Meeting, Wausau, Wausau, WI, WI, v. v. 30, pan part 1, p. 72. Stoiber, R.E., R.E., and Davidson, zoning in the Portage Davidson, E.S., E.S., 1959, 1959, Amygdule Amygdule mineral mineral zoning Portage Lake Lake Lava Lava Series, Series, Michigan copper district: Economic Geology, v. 54, p. 1250-1277, 1250-1277, 1444-1460. 1444-1460. Sugden, D.E., 1977, of the morphology, dynamics and and thermal thermal characteristics characteristics of of the Sugden, D.E., 1977, Reconstruction Reconstruction of morphology, dynamics Laurentide ice sheet at its its maximum: maximum: Arctic and Alpine Res., Res., v. 9, p. 21-47. 21-47. Walker, G.P.L., G.P.L., 1966, 1966, Acid Acid volcanic volcanic rocks rocks in in Iceland: Iceland: Bulletin Bulletin Volcanologique, Volcanologique, v. 29, 29, p. p. 375-402. 375-402. �__________ _________ 185 981, The bedrock topography Warren, E.J., EJ., I1981, topography of the the Keweenaw Keweenaw Peninsula, Peninsula,Michigan Michigan (Ph.D. (Ph.D. Dissertation): Dissertation): Houghton, 169p. l69p. Michigan Technological University, Houghton, Weege, R.J., and Pollack, J.P., J.P., 1971. 1971, Recent developments in native-copper district of Michigan: Society of Economic Geologists Field Conference, Michigan Copper District, September 30 -- October October 2, 1971, p. 18-43. 18-43. Weege, R.J., RI., Pollock, Weege, Pollock, 1.?., J.P., and andthe theCalumet CalumetDivision Division Geological Geological Staff; Staff, 1972, 1972, The geology geology of of two two new new mines in the native copper district: Economic Geology, v. 67, p. 622-633. the native copper district: Economic Geology, v. 67, p. 622-633. Weege, R.J., Weege, R.J., and Schillinger, Schilliiger, A.W., A.W., 1962, 1962, Footwall mineralization in Osceola amygdaloid, Michigan native copper copper district: district: A.LM.E. A.I.M.E. Transactions, Transactions, v. 223. 223, p. p. 344-350. 344-350. Wells, R.C., 1925, 1925, Chemistry of deposition of native copper from ascending solutions: U.S. US. Geological Survey 71p. Survey Bulletin 778, 778, 71p. White, W.S., 1956, Chassell Quadrangle, Michigan: U.S. U.S. Geological Survey Mineral 1956, Geologic Geologic map of the Chassell Investigations MF 43. 43. Investigations Field Studies Map MF lavas of Lake Superior, , 1960, Keweenawan lavas Superior, an example example of of flood floodbasalts: basalts:American American 1960, The Keweenawan Journal of Science, v. v. 258A, 258A, p. p. 367-374. 367-374. J.D., ed., Ore , 1968, 1968, The native-copper deposits of northern Michigan: in Ridge, J.D., Ore Deposits Depositsof of 1933-1967 (the (the Graton Graton Sales Sales volume): volume): American American Institute Institute of of Mining, Mining, the United United States, States, 1933-1967 Metallurgical, and Petroleum Engineering, New York, Yo& p. p. 303-325. 303-325. - - 197 lb. Field 1971b. Field Trip Trip A-2 A-2 -- Houghton Houghton to to Calumet Calumet via via South South Range Range quarry quarry and and Eagle Eagle River: River: Society of Economic Economic Geologists. Copper District, Society Geologists, Guidebook Guidebook for Field Conference, Michigan Copper District, Sept. Sept. 30-Oct. 2, 1971. p. 68-75. 1971, p. 68-75. . . flood basalts basalts and continental rifting: rifting: Geological Society of America , 1972, 1972, Keweenawan Keweenawan flood America Abstracts with Programs, v. 4, p. p. 732-734. 732-734. R.W., 1953, Bedrock geology geology of of the Ahmeek quadrangle, White, W.S., Cornwall, H.R., H.R., and Swanson, R.W., GQ 27. 27. Michigan: U.S. US. Geological Survey Geologic Quadrangle Maps of the United States States Map Map GQ White, W.S. and Wright, White, Wright, J.C., J.C., 1956, 1956, Geologic Geologic map map of of the theSouth SouthRange Rangequadrangle, quadrangle,Michigan: Michigan: U.S. U.S. Geological Survey Mineral Investigations Field Studies Map MF 48. L.G., CannOn, W.F., and and Back, Back, J.M., J.M., 1994, mineralization in in the Portage Lake Woodruff, L.G., Cannon, W.F., 1994, Chalcocite mineralization Lake Volcanics Michigan (abst.): (abst.): Institute Institute on Lake Volcanics of the the Midcontinent Midcontinent rift, Keweenaw Keweenaw Peninsula, Peninsula, Michigan Lake Superior Geology Proceedings, Proceedings, 40th 40th Annual Annual Meeting, Meeting, Houghton, Houghton,MI, MI,v.v. 40, 40, part part 1, p. 77-78. Wright, J.C., Bruneau Creek quadrangle, quadrangle. Michigan: Michigan: US. U.S. J.C., and Cornwall, H.R., 1954b, 1954b. Geologic map of the Bmneau Geological Geological Survey Survey Geologic Quadrangle Maps of the United United States. States. �ES. IA: Figure Figure 1A: Route and Stop Stop Map Map 5. 1 'V Fridi South Rings t N Main Main Route Route and and I Q 'p Stop 2p Kilometers Kilometers 3p Number Leg Route and Stop Number �Figure 1B: Index of 1:24,000 Scale Maps 99 See Map Ii A69 Region Covered by Map Number Route and Number See Map Kilometers Leg Route and 5...-. Stop Number � https://digitalcollections.lakeheadu.ca/files/original/6317c926bcd52ad1b187aba51adabc6d.pdf 8a601acd41fe6d8e5c84adeeb20f41b3 PDF Text Text Proceedings 40th Annual Meeting May 11-14,1994 Michigan Technological University Houghton, Michigan Volume 40 Part 3-Volcanic geology of eastern Isle Royale, Michigan By: William I. Rose i I �40TH ANNuAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Volume 40 consists of Part 1: Program and Abstracts Part 2: Self-guided geological field trip to the Keweenaw Peninsula, Michigan Part 3: Volcanic geology of eastern Isle Royale, Michigan Part 4: Michigan kimberlites and diamond exploration techniques Part 5: Lessons from mining case histories: West Menominee Range, Michigan Reference to material in Volume 40, Part 1 should follow the example below: Woodruff, L.G., Cannon, W.F. and Back, J.M., 1994, Chalcocite mineralization in the Portage Lake volcanics, Keweenaw Peninsula, Michigan Cabst.): Institute on Lake Superior Geology Proceedings, 40th Annual Meeting, Houghton, MI 49931, v. 40, part 1, p. 77. Published and distributed by Institute on Lake Superior Geology M.G. Mudrey, Jr., Secretary-Treasurer, LL.S.G. 106 N 3rd Street Mt. Horeb, Wisconsin 53572 ISSN 1042-9964 All volumes are available for photocopying costs from Michigan Technological University Library Archives J J Michigan Technological University is an equal opportunity educational institution/equal opportunity employer. J �Institute on Lake Superior Geology Proceedings 40th Annual Meeting May 11-14,1994 Michigan Technological University Houghton, Michigan Volume 40 Part 3-Volcanic geology of eastern Isle Royale, Michigan By: William I. Rose Department of Geological Engineering, Geology, and Geophysics Michigan Technological University, Houghton, Michigan 49931-1295 �Table of Contents Preface 1 Introduction 2 Background and Key References 2 The First Day Grand Portage, I\IIN The Isle Royale Fault Washington Harbor Windigo The N Side of Isle Royale: The Hill Point Flow McCargoe Cove The Amygdaloid Channel The Palisades: The Greenstone Flow Blake Point , '" Rock Harbor The Second Day: An OveNiew Day Mount Franklin The Mount Ojibway Tower Daisy Farm Campground Edison's Fishery and The Lighthouse Mott Island Boreal Research Center. Davidson Island The Third Day: A Good Look at the Greenstone Flow Blake Point Porter's Island Red Rock Point Tobin Harbor Lookout Louise The Fourth Day 4: Scoville Point Rock Harbor Scoville Point The Fifth Day Raspberry Island The W Part of the SE Shore: Vesicle Cylinders The Central Part of the SE Shore: Slickenside Surfaces The E Part of the SE Shore: Pegmatoid Zones 12 12 12 12 15 19 23 23 23 26 27 29 29 29 29 29 30 .31 32 32 33 33 34 34 36 36 36 38 38 .38 .40 .40 �The Sixth Day: Back to the Mainland Conglomerate Bay Chippewa Harbor Malone Bay: The Copper Harbor Conglomerate SW Isle Royale: The Glacial Deposits Washington Harbor: The End of Our Trip .43 43 43 .43 .46 .46 Acknowledgments 50 References 50 �Preface (or why people don't go to Isle Royale) Isle Royale has very few visitors, especially considering that it is a national park and is, for many people, within a couple of days travel. This lack of tourism can be explained partially by the park's island location and by the fact that a trip to Isle Royale seems to require a deeper commitment, of both time and money, than other vacations might require. The very people whom you would most expect to want to visit Isle Royale don't go. When you compare the popularity of various national parks, the public's avoidance of Isle Royale is obvious, perhaps even more obvious to me because of my position. As a professor at Michigan Technological University for more than 20 years, I have had direct contact with hundreds of students, many of them geology majors, who are committed to the outdoors and to field experiences. However, very few of these students go to the park, even though they live in Houghton, MI, which is the home of the Ranger III, one of the principal transporters of visitors to and from Isle Royale. Likewise, many of the geologists I have known have visited all of the geological sites around Lake Superior and the other Great Lakes, but only a few of them have been to Isle Royale. This is a remarkable contradiction, something I'm at a loss to explain. It seems to attest to America's addiction to the automobile; maybe people just can't stomach the thought of being separated from their car for a few days! At any rate, I hope that this guidebook will encourage more geologists, as well as other people, to visit the park. Besides the fact that Isle Royale has outstanding geological sites, a trip there can be made at moderate expense, and the park offers comfortable facilities and logistics that most geologists would find agreeable. I recommend taking a week to visit (September is the very best time) and renting a motor boat from the park concession to allow access to the many wavewashed outcrops. Prepared in cooperation with the Keweenaw Volcano ObselVatory, Michigan Technological University, Houghton, Michigan 1 �Introduction .40 This guidebook is meant to be used with The Geologic Story ofIsle Royale National Park by N. King Huber (1983) and does not try to duplicate what occurs in that volume. Instead, the goal is to focus on the volcanic geology that can be observed in the wave-washed shorelines of the Rock Harbor area, emphasizing the physical volcanology of basaltic lava flows. The field trip described here offers the participant a chance to see excellent exposures of large and thick, tholeiitic lavas and to observe the combination of physical features that are associated with slow solidification and segregation. 30- 20 AIL FLOWS N - 224 x -lo.9m 10 MEIAPHYRIC FLOWS N-86 x· S.3m o Background and Key References 10 Huber's work offers a complete background to this trip. It includes a bedrock geological map (Huber 1973) and United States Geological Survey (USGS) Professional Papers on the Portage Lake Volcanics (PLV) (Huber 1973a), the Copper Harbor Conglomerate (CHC) (Wolff and Huber 1973), and the glacial and postglacial geology (Huber 1973b). Since 1973, when Huber's work was published by the USGS, there have been a number of further studies published that are important to the context of Isle Royale. Here, I will cite those that pertain to the Keweenaw section of the Midcontinent rift and to solidification of lavas in particular for those who wish to read more of the current literature. A detailed study of the composition of the lavas of the PLV, as determined by study of a complete section on the Keweenaw Peninsula, was completed by Paces (1988). In this study, Paces provides a general description of the flows with respect to texture and thickness (Figure 1); chemical composition (Table 1); mineral chemistry (Figure 2); and petrography (Table 2), which is described in the following: o 10 l Ll SUBOPmTICFLOWS _ N-SS x -lL6m U ~f."I-l""""--'~--'~--'--"""""--"""""-"'" OPmTICFLOWS N - S2 x·332m 0.1(,': "'Iar," o 20 40 60 i 80 100 ", 120 I ' 140 TIllCKNESS (m) Figure 1: Histograms ofPLV lava flow thickness (Paces 1988). N=number of lava flows; X=geometric mean thickness in meters. The coarsely-ophitic Greenstone flow is not shown. Textural categories are based on macroscopic observations. phenocrysts or microphenocrysts ofplagioclase, and sometimes olivine. Textures that developed within the coarsest portion ofdifferent lava flows range from fine-grained intergranular through subophitic and ophitic. This same range in textures can be observed in individual, thick lava flows which grade from intergranular chilled flow margins to a coarsely ophiticflow interior. True quench textures (Lofgren 1980)"including skeletal, dendritic or spherulitic olivine and pyroxene, have not been observed in PLV basalts. PLV lava flows do not preserve evidence ofan extensive pre-eruptive crystallization history. Chilled margins are generally aphanite. Occasionally, lavas contain minor amounts (usually less than 1%) ofsmall euhedral phenocrysts ofplagioclase (often with melt inclusion-rich cores) and sometimes olivine. When present, both of these phases commonly exhibit glomeroporphyritic tendencies. Neither the plagioclase nor olivine phenocrysts show obvious evidence ofdisequilibrium with the PLV lava flows display a relatively limited number oftextures based on the relationships between dominant mineralogical constituents. These components originally included groundmass plagioclase, olivine, clinopyroxene, iron-titanium oxide, volcanic glass or mesostasis, occasional 2 �= . . . . .z;z' POT Ni(ppI) SiOz Alt33 feet MgO cao NazO ICzO TiOz PzOs MnO on 400-300 na5 300-250 47.82 15.89 9.77 12.44 10.58 2.04 0.19 0.98 0.16 0.14 aaaaaa____aa*-=a OT2 DAC RHY D581297 83JP-7 85MH-' na6 47.34 15.27 11.82 11.69 10.24 2.10 0.22 1.13 0.19 0.16 48.03 15.32 12.32 9.85 10.16 2.25 0.33 1.35 0.22 0.16 48.55 15.12 12.86 9.06 9.65 2.31 0.42 1.60 0.25 0.18 49.94 13.28 14.91 7.78 6.64 2.91 1.43 2.34 0.36 0.24 56.39 13.78 9.87 5.52 5.10 3.94 2.27 1.83 1.00 0.30 68.44 15.17 4.46 1.14 1.40 4.74 3.86 0.51 0.19 0.08 77.89 12.77 1.11 0.17 0.01 3.67 4.28 0.08 0.01 0.01 305 203 1365 431 113 1804 54 126 106 30 245 31 212 14 514 263 59 6 627 7 13 81 62 879 0 5 105 5 61 25 129 36 35 145 68 1127 13.4 30.6 4.50 1.51 0.88 2.46 0.38 0.66 3.11 1.31 30.62 54.4 139.0 14.00 3.44 2.77 9.41 1.39 2.64 16.13 10.32 11.43 39.9 96.2 8.57 0.95 1.97 6.70 1.00 3.52 7.29 16.30 2.73 189 Mn eu 1090 326 37 230 260 1316 27'9 51 2n 64 80 Rb Sr Y Zr Nb Ba 12 358 20 78 4 108 6 253 20 6 154 255 213 1250 231 73 7'9 5 267 20 101 7 200 La Ce 6.7 15.0 2.49 0.96 0.46 .. 1.47 0.21 0.43 1.74 0.55 24.86 8.2 18.4 3.13 1.14 0.61 1.7'9 0.27 0.48 2.09 0.77 28.19 10.5 23.7 3.74 1.33 0.71 2.00 0.30 0.55 2.57 0.97 28.25 Eu Tb Yb Lu Ta Hf Th Sc sses naB 286 8~ 1n 86 85 8 283 23 126 8 265 100-15 AHO ...-a. 200-100 V Snl FOT = 250-200 na14 na9 Cr Ni lOT - 25.8 58.7 7.91 2.12 1.58 4.43 0.64 1.14 5.n 3.39 34.61 16 2282 10 5 146 51 335 47 430 28 757 48.6 117.2 13.78 3.84 2.51 6.94 1.04 1.77 10.44 5.94 21.06 88 45 573 55 Table 1: Average major and trace element compositions for eight groups ofPLV lavas (paces 1988). Tholeiites were grouped by their Ni concentrations with criteria listed in the first row and the number of samples in each group in the second row. POT=primitive olivine tholeiite; OT1=olivine tholeiite 1; OT2=olivine tholeiite 2; IOT=intennediate olivine tholeiite; FOT=Fe-rich olivine tholeiite; AND=andesite; DAC=dacite; and RHY=rhyolite. The last three columns are individual analyses. Oxides are given in weight percent, trace elements in ppm. 3 �I PLV.... I PLt-em I I 11111111 I I I III 1111111111 II I IUIII • II nail.... I III••• ' I III NSVG I I 1M lUll 111111 I 1111111 !YUill 60 40 I liquid. Except for rounded plagioclase cores, both olivine and plagioclase phenocrysts are in apparent textural equilibrium with the liquid. Slightly porphyritic lavas frequently exhibit serrate textures. The dominant textural element in all lavas is the framework ofgroundmass plagioclase laths. This framework is a randomly-oriented, felt-like structure ofinterlocking euhedral to subhedral laths. Rarely, the partial alignment oflaths forms crude trachytic fabric, indicating movement of magma after at least partial crystallization. The second most prominent textural element is defined by clinopyroxene crystals and their relationships to the plagioclase lathframework. In all cases, clinopyroxene has clearly crystallized later than olivine and plagioclase. Clinopyroxene crystals exhibit intergranular to ophitic textures depending both on the size ofthe clinopyroxene crystals as well as the size ofthe plagioclase laths. Melaphyricflows and chilledflow margins contain small, blocky clinopyroxene crystals intergranular to the plagioclase framework. In many (but not all) thickerflows, clinopyroxene grains begin to enclose subophitically, and eventually ophitically, plagioclase and olivine crystals as the massiveflow interior is approached. The boundary between PLAGIOCLASE 80 %An CLINOPYROXENE PLY II 111 I .11 III I NJvG 1I11UI.11lIl IlflllllnllDUOU'1 I 111 I III II I I I I I 0.70 0.60 II 0.80 mg' OLIVINE I PLY I NSVG I ~ I I I 11111111111 I 1 II liD III I Dl111 ~ ~ ~. Figure 2: Compositions ofminerals in PLV primitive olivine tholeiites compared to those available from North Shore Volcanic Group primitive olivine tholeiites (Paces 1988). Each line represents a single analysis. The North Shore Volcanic Group data was taken from BVSP (1981) and Brannon (1984). PLV plagioclase compositions are sub-divided into groundmass (PLV-gm) and phenocryst (PLV-p) crystals. Olivine Basalts N-8 Groundmass Plagioclase Clinopyroxene Olivine Fe-Ti Oxides Glass Vesicles Phenocrysts Plag ± Olv Basaltic-andesites N-3 Typical Range Typical Range 41 23 18 4 10 4 (39-56) (19-29) (11-19) (2-13) (4-11) (1-9) 53 18 (50-55) (16-22) 7 19 3 (6-10) (15-25) (1-10) <1 «1-9) <I <1 Table 2: Petrographic modes, in volume percent, ofrepresentative PLVolivine basalts and basaltic andesites (Paces 1988). Model analyses are based on SOO-spot point counts on a 0.6 x 1.2 mm grid. 4 �Vesicles are particularly well preserved in thinner flows which quenched rapidly; however, they are observable in some thicker flow interiors as well. subophitic and ophitic textures is gradational and is exceeded when a significant number ofplagioclase laths are completely enclosed by the surrounding clinopyroxene oikocrysts. Absolute size of the oikocryst is not definitive: a large clinopyroxene grain may only subophitically enclose large groundmass plagioclase laths, however the same sized grain may ophitically enclose plagioclase laths ofsmaller dimensions. Thus, over half, 60-70% (volume basis), ofmost PLV lavaflows are typically composed ofa plagioclase lath framework with loosely packed clinopyroxene oikocrysts. The remaining interstitial space within the plagioclase framework and between oikocrysts is filled with variable proportions ofintergranularolivine, iron-titanium oxides, and intersertal volcanic "glass. " Evidence ofgas exsolution is preserved in some flow interiors as vesicular cavities ofellipsoidal to highly irregular shapes. Diktytaxitic textures, however, are not apparent. --Paces 1988 Two conclusions emerge from Paces work: (I) the lavas are compositionally similar throughout the section and generally are high magnesium, olivine tholeiites; and (2) the flows range from less than 10 m (33 ft.) to more than 100 m (330 ft.) thick, and the thicker ones are more likely to have ophitic textures. Paces and Miller (1993) have recently published a summary of age information on the igneous rocks of the Midcontinent rift (Figures 3 and 4), which shows that the PLV represents one of the last events of the approximately 25 million year period of rift magmatism. Lane (1911) describes the first recognition of the mirror image geology and lithological similarity ~@ Volcanicroclcs ICNEOUS . . Plutonic roclca ROCXS ~ Hypabyssal rocks Ontario Y '" A1lcaline intrusions Diabase dikes :I( :I( Ontario * 100 1 ISO I Scale Figure 3: Generalized middle Proterozoic geology ofthe Lake Superior region (Paces and Miller 1993). Major igneous units are abbreviated as follows: DC=Duluth Complex; NLS=Nathan's layered series; BBC=Beaver Bay Complex; NSVG=North Shore Volcanic Group; CCD=Carlton County dikes; PRI=Pigeon River intrusions; LS=Logan sills; OVG=Osier Group; CC=Coldwell Complex; PD=Pukaskwa dikes; MIF=Michipicoten Island Formation; MPF=Mamainse Point Formation; MBD=Marquette-Baraga dikes; PLV=Portage Lake Volcanics; LST=Lake Shore traps; PMG=Powder Mill Group; MC=Mellen Intrusive Complex. Volcanic units are differentiated on the basis of remnant magnetic polarity (N=normally polarized; R=reversely polarized). Major graben-bounding faults are shown as heavy, labeled lines. 5 �NMichigan Thunder Bay KLJnsas NW WISconsin MpigonBay NE Minnesota E Ontario Magnetic Polarity 1090 ~ N 1100 <t: 1110 Figure 4: Generalized stratigraphic correlations and absoLute age determinations for Midcontinent rift rocks exposed in the Lake Superior region and subsurface Kansas (Paces and Miller 1993, modified after Green 1982). Unit abbreviations are the same as in Figure 3, with additions: SB=Schroeder basalts, and GC=Great Conglomerate. Episodicity of volcanism is schematically portrayed by the amplitude of jagged curves, implying eruptive frequency and volume increasing toward the right. Major intrusive events are indicated by vertically ruled polygons, and major episodes of clastic sedimentation are denoted by horizontally ruled areas. The boundary of the major reverse-to-normal magnetic polarity switch is placed between 1099 and 1100 Ma, but it is uncertain at a level of 23 million years. lONG ANO DAVIDSON TOMkEIEFF 119401 SPRY 119621 SYVANSQN 119671 119811 VESICULAR -,. FLOW TOP COLONNAOf PSEUOOCOLUMNAA IUPPERI 'ON' COLONNADE ENTABlATUAE ENTAIlLATUAE ENTABLATURE ENTA81A TURE CURVICOLUMNAA ZONE COLONNADE IlOWEAt COlONNADE 8ASAlOR COLONNADE LOWER COLONNADE PtltOW PAlAGOHITE P4ll0W APPROXIMATE VERTICAl. SCALE METERS FEET ':jt; -,2 T03m ~ COMPlEX lONE "CPS108·'188 Figure 5: Typical intraflow structures present in Grande Ronde Basaltflows (Long and Wood 1986). Fractures are represented in a stylized manner, and fracture widths are not to scale. 6 �------~~:) 0 ~ -- JO ~ / c[~ N SHORELlN~ I~~:~~S .- AG I ~.z::!~~ -u•• < LljE G I ;"' I ~=;-;:=.=:A! BSlgG~,::...i4:t- ~-';-'!=: .~4.i·. 5.3klllfJ·· ....~~ ' 30,00 ' -:~. -- s,•. \r:.. S~H~r;:rR ""':- ~'7GE ~~I 20PO I I I Shot IOpO Points. MANITOU, IS. I -!!\;:;f~~?;/'~~"rr'''~, 'S~.t.>~... ~... .-' <?9r';;:;'~1~J ._ ~', ..._::,kU ':.", SHORELINE I JS ~: ;"'~' ;: -::: ..;;'?!£J"ff --..,..' e!l/oa:.p,· ... , " \~",- ~'~6~'" "':6~:·,,· .. ,'.. Sedinil\llts i • •;,'1 :-.'. "l1' '.'""",''"'--~~, Bl;VlJt~..,j' 1J.'~ -;.. ."""pfV·: \:~-: 'I ...'I. Vol'anl~sL.'.· '~', ~ ':"~ ,;\\~"'".:."JC~·,,;-:.~~~~~~~ ~>.;o-~--:.:.. ""~'-<'-' :,~, ':'~."''? .~~~ ,_, .. -46. "j "'.1' '.. '~1~';- \1.. ".~"" '•• _, l'p1:iV~ . ~ 3 I- I- 10 10 15 -i'.1=~~~"':'':::;: ",_ca.:;_:-"i . ".' . .::::; •. I ~._- .-;::...:..~ - .... :-~ ~ ~ .- ":'.:'. -'- - ~... t~·.~~!-># - CHANGE IN SIlOT POINT , SPACING 3000 ....... .. _-- . ~: ~;~:~.>. ~. .;., :.,,: .,. ... ,. ~~ s..... ... ~ .. .r-~, ~"~~ -.-.,' ,. ..... ~ -l, I \ . ''''-'''1. .:t>., . ' . ....... _~~1'.} ': .", ',~ ....... - ""1\".... , ~ l .... ...... .~-~~.~? . I- 1000 Shot Poln" 2000 ... "F .. 15 -:-=~~~~ :, ' ::..,." .. ... . - ': .: !.;::.~ .~-: ... '" ",:.~:: I- 10 10 ~~". ~""'''~'''''''.'' ." .~ .::,0~: -="7'"":":;. ~. ~ . :; '0. .~. : c' .~. -,,~. "., ;, ~. ,;jt~:,:i;~n . ;- 15 ~.- 20 LINE A. MIGRATED Figure 6: Top: Interpreted reflection profile along line A showing the subsurface geology beneath central Lake Superior (Cannon et al. 1989). Bottom: Migrated seismic reflection profile along line A (Cannon et al. 1989). Vertical scale is seconds of two-way travel time. Vertical exaggeration is 1: 1 for average velocity of 6 kIn/s. S AG �.. ;:: 10 \0 ~. -: ' . "__ ,"7·'.'· "'- 15 ,!'..... _.- 00 ... ~.~;-':'.~ - • 500 -.' .W ';-. .... .~._.::~:::' .... 15 \.4":".".; ~;'4' ..•__ .;~ ~. .:-::'."~':";;;~':f~"I~~~~~'_.~. ",~, .~. ''',.' ..," Shot 1500 POi.., 1000 .. , . , 0 . . :~.;I.i~:Ij>~:i!~~~~ 5 3 ;:: .... 10 10 .':' } ·}-15 '5 LINE C, MIGRATED o \0 Figure 7: Top: Interpreted reflection profile along line C, showing subsurface structure beneath W Lake Superior (Cannon et al. 1989). Inferred subsurface units are projected updip to their exposed extensions on land in N Michigan and Minnesota. Bottom: Migrated seismic reflection profile along line C (Cannon et al. 1989). Velocity/depth profiles determined from refraction surveys were used to calculate depths to reflectors. M=approximate location of Moho; AG=Archean Gneiss; PLV=Portage Lake Volcanics; pPLV=pre-Portage Lake Volcanics; NSV=North Shore Volcanics Group; OG=Oronto Group; BS=Bayfield Group; and AnG=Animikie Group. Vertical scale is seconds of two-way travel time. Vertical exaggeration is 1: 1 for average velocity of 6 kmIs. �of the PLV and the CHC on both sides of the syncline and further suggests that the great lava flow of the Keweenaw Peninsula and the large flow of Isle Royale are the same. Huber (1973a) strongly supports Lane's correlations. Longo (1984), after extensive field mapping and sampling at Isle Royale and the Keweenaw, gives field observations and geochemical data that strongly confirmed the correlation of the Greenstone flow. This correlation means that the Greenstone flow is one of the earth's largest lava flows; according to Longo (1984), it has an aggregate volume of 1650 km3 (396 mP), comparable to the Roza flow of the Columbia River Flood basalts, which is estimated to be 1500 km3 (360 mP) by Swanson et aI. (1975). The areal extent of the Roza, 40,000 km2 (15,450 mi2), is much larger than the Greenstone flow, 5000 km 2 (1930 mi 2), a comparison which results from the ponding of the Greenstone within the rift basin. Thus, the solidification of the Greenstone flow is a kind of magma ocean experiment, the likes of which is rare on this planet. Studies of the formation of columns in lavas are also important to the appreciation of the Isle Royale occurrences. The recognition of the role of water infiltration in the formation of certain kinds of entablature jointing (Figure 5) in the Columbia River Flood basalts by Long and Wood (1986) was an important insight, as was the detailed work on column formation by DeGraff and Aydin (1993) and DeGraff et al. (1989). The work by Goff (1977) provides information on vesicle cylinders in lavas for the Isle Royale occurrences. Green's (1989) paper on the physical volcanology of the North Shore Volcanics gives a valuable comparison with rocks associated closely in time and space with the Isle Royale PLV. The GLIMPCE results (Cannon et aI. 1989) provide confirmation of the rift basin synclinal geometry and allow a more accurate picture of the rift to be developed (Figures 6 and 7). The discussion by Cannon (1994) of evidence that suggests a relationship between the Grenville event and the closing of the Keweenaw rift contributes to the understanding of the rift episode (Figure 8). The consideration of implied tilting of ancient shore- , ' . . ' " . ., : \ ' . . \ . . \ .. ""',',,,,',:,' ... ,' ... , , ' " : \ , .... " , ' ... " ... " I .... ' , .., ' ' " ' : , ' : , ' .... ' , : , ...." : ... " , , , ... , "", I c ,, ' ... \ ' ... \ , . \ , ... , ... \ , ..., , , , , "" , , , ,' ... ,' .. , ... ,,"" "",",'" ,",,", \ , ,; ... ,: ... ,;" ' .. ,':',' ""\~""~""":'"'': ...' , , E Figure 8: (a-e) Schematic depiction ofdevelopment of the Midcontinent rift (Cannon 1994). (a) Lower Keweenawan, broad crustal sag and eruption ofwidespread plateau basalts. Low-angle normal faults and shear zones develop in Archean crust, producing some crustal thinning. Some normal faulting occurs near rift axis but is subordinate to sagging. (b) Middle Keweenawan, early rift valley stage. Continued extension and thinning of crust results in development of a central graben and rift valley by a combination of normal faulting and continued sagging. Volcanism is mostly confined to the rift valley. (c) Middle Keweenawan, late rift valley stage. Central graben expands and deepens. Rotation of basement blocks causes asymmetrical shape. Very thick volcanic accumulations are in the graben, and little or no volcanic flows spread outside the graben. The Archean crust nearly separates by extension on low-angle faults. (d) Upper Keweenawan, thermal collapse and sedimentation stage. Extension and volcanism end. Both the central graben and surrounding areas subside by thermal collapse, and a thick (as much as 10 km) basin develops and is filled with clastic sediments. (e) Upper Keweenawan, tectonic inversion stage. The central graben is uplifted. Original graben-bounding normal faults are transposed to high-angle reverse faults. Rocks of the central graben are thrust up several km or more. Thin sequences (up to 2 km thick) of clastic rocks (not shown) are deposited unconformably on deformed volcanic and sedimentary rocks. 9 �(a) 10 6 4 2 050 60 70 § ~ 'il ::c Tune (years) Composition (wt" Oi) Time (years) Composition (WL% Oi) 100 100 80 80 60 60 40 40 " " " ;,,,,,,,,, ,;,;,;,;,:E~~.ti~~ . .;';' 20 0 " , .... """"", " ,',',',",'...',FIoor layer;',','../ ,......',"...',..., ..., ... ~ " " " " " " , ... " , ... , , , , , , , , ... , "..... , ... ""...... , "" ...""" " ... , , ... ... "" ...... ,,,, ,,, ... ... , "... , ... 0 20 80 90 100 40 80 60 (e) 20 o L..-...L.-.1_..L----L----' 50 60 70 80 90 100 Composilion (wl.% Di) Time (years) Figure 9: History ofsolidification and final compositional profile in lava lakes ofinitial composition DiSoAn20 and 0 initial temperature equal to the liquidus temperature of 1352 C (Worster and Huppert 1993). The curves labelled he' hi, and h f show the interfaces between the crust and the mushy layer, the mushy layer and the melt, and the melt and the floor layer, respectively. lines around the Great Lakes by Clark et al. (1994) is clearly important to understanding Isle Royale, with its abundant evidence of tilted shorelines. The processes that operate during the solidification of tabular magma bodies are reviewed by Marsh et al. (1991). Worster and Huppert (1993) present models developed to predict the patterns of solidification in time and space (Figures 9 and 10); fundamental work to understand solidification in other kinds of materials has been done and is pre- sented by Hellawell et al. (1993). The literature lacks lucid explanations about ophitic texture and its origin. Longo (1984) infers the following: An ophitic texture is produced by large augite crystals enclosing, either partially or totally, unoriented laths ofplagioclase. A qualitative explanationfor ophitic texture, as with all igneous textures, involves fusion entropy relationships coupled with growth rates and nucleation rates (Carmichael et 10 �AIR OR WATER ) c al. 1974). While the magma was cooling slowly, initially abundant plagioclase nuclei grew relatively slowly and were enveloped by faster growing, but less abundant clinopyroxene nuclei. The slower cooling rates offlow interiors typically allow clinopyroxenes (in this study augite ±pigeonite) to grow to larger diameters. In other words, crystals tend to increase in size awayfrom the flow margins. The crystal networkformed by the simultaneous crystallization ofaugite and plagioclase inhibits crystal settling in the flow after extrusion. The ophitic texture imparts a mottled and knobby surface to the weathered outcrop. On the freshly broken surface, clinopyroxene cleavage faces are clearly visible. --Longo 1984 Figure 10: Schematic diagram ofa lava lake that is being cooled at its surface by contact with the cold air or water above it and also cooled by conductive heat transfer to the country rock beneath (Worster and Huppert 1993). A crust of composite solid grows downward from the roof where the temperature, T b' is constant. A mushy layer separates the composite solid from the molten lava, which is convecting vigorously. Internal crystallization, which occurs as a result of the interaction of convection with the kinetic undercooling at the interface with the mushy layer, forms a solid layer near the floor of the lake. A sketch of the temperature field is indicated on the diagram. The full environmental significance of ophitic texture is important for understanding the Isle Royale exposures. We need to know how the rates of crystallization and heat loss work together to produce the jointing, segregation, and textural patterns that are observed. The works cited above, along with others referenced in this guide, contribute more information to our understanding of the geology of Isle Royale. All of these works are valuable as supplements to this field guide. 11 �The First Day Grand Portage, MN Our trip begins at Grand Portage, a national monument and reconstructed fort that commemorates the fur trade era, which began in the sixteenth century and reached a peak in the later part of the eighteenth century. The fort was built in 1778 and abandoned in 1803. Figure 11, from the National Monument, describes the geography of the fur trade and the significance of this site. From Grand Portage we will travel E and eventually go all the way around Isle Royale in a clockwise fashion (Figure 12). The Isle Royale Fault Between the Minnesota shoreline and Isle Royale, the strike of Keweenawan rocks, known as the North Shore Volcanics in Minnesota (1109-1100 Ma), changes from E-W to about N 55° E, where the PLV formation (1096-1094 Ma; Figure 13) at Isle Royale begins. This discontinuity could be partially related to the Isle Royale Fault (Figure 6), which the Voyageur crosses between Grand Portage and Isle Royale. This is a thrust fault, apparently associated with the inversion of the Midcontinent rift and was detected in the GLIMPCE profile collected on a NS line E of the Keweenaw Peninsula (Figures 6 and 7). It is thought to extend W to at least the SW end of Isle Royale, where Isle Royale is mantled with a much thicker portion of glacial till and the glacial features are much more prominent (Huber 1983; see pp. 20-21 and 41-54). Washington Harbor From Grand Portage, we will take the Voy- ::rmirl~~:··'.L.........__ _ ...- ..·t··}------I-~-·j·._ _ . --J •• ••' L- .J. .-n-... .I.__ .~ .___ __ --" -"" ~ --;"0' __ ~-~ ~ SCALE: IN .. ,<r ._--~- .14,_ ~ ~ 't£T SECTION OF THE ClifT min'! in 1850. CLIFF MINE Rketl'h fly A. H. MNlche. nft"f Fnsf"f & Whitnpy. 12 �4; The Great Carrying Place Only three water passages to the Northwest are scored into the broad rock lace 01 the Laurentian Shield which forms the weslern shore of Lake Superior. They are the rivers known loday as the St. Louis, Ihe Kaminlstiqula, and Ihe Pigeon. The last of these Is navigable excepllor a few kilomelers at lis mouth, but a narrow, muddy trail links the lake wllh the navigable walers of the Pigeon. Indians had used this trail lor ages belore the first European explorer, a Frenchman, recorded II In 1722. The French explorers, who continued to search for an easy pauage to the weslern sea, and the French missIonaries, who sought converts In the wilderness, gave the trail Its name-"Le Grande Portage," The Great Carrying Place. It remained, however, lor the Highland Scots and their partners In the North West Company to give Grand Porlage Its place In history as the vltatllnk In a network 01 waterways that nurtured the fur trade empire. ..... w The lur trade of Norlh America developed in the 16th cenlury between French fishermen and Indians along Ihe banks of Newfoundland and the mainland coast. Furs gathered by the French for sale In Europe soon became the cash crop of New France. When fur.bearing animals, partiCUlarly beaver, became scarce, the French traders searched westward. Blocked to the north by the British lur domain 01 the Hudson's Bay Company, the French traders were forced over a long water and land route Irom Montreal through Ihe Onawa River and the Great Lakes 10 Grand Portagegateway to the unlapped lur riches 01 the Northwest. Under British auspices aller 1763, the route over the Grand Portage was Inherlled by independent traders who tounded the North West Company. Theirs was a lur trade empire based primarily on the exporlation 01 beaver lur to supply the particular lasles 01 European fashion. Beaver pelts, Irom which Ihe linest qualily fell hals were made, were In tremendous demand. In July the post at Grand Porlage was the scene 01 the North West Company's annual rendezvous. From the east came canoe loads 01 trade goods Irom the warehouses In Montreal destined for the Interior. From the northwestern outposts came wintering traders wllh loads of furs en route to Montreal. Though II was Ihe North West Company's most Important Inland trading cenler, Ihe Grand Portage post was short-lived; II was founded about 1778 and abandoned In 1803 when the North West Company moved north to avoid American laxation and established the post of Fort William. The buildings at Grand Portage were lellto the elements and quickly disappeared. Traffic along Ihe porlage trail dwlndledj then II, too, disappeared. . 0' o For al least 200 yaars Ihe In· dian birch-bark canoe served as the main transport In the fur trade. The biggest ones, the "canol du maitre," trav~ eled Ihe Great Lakes on the Montrealers' route to Grand Porlege. They were usually , about 11 melers (36 leet) In lenglh and could hold up to 3.5 metric tons (4 tons' 01 cargo, plus e crew of 8 to 16 men. The north canoes or "canot du nord,"' used on the narrow water courses of the northwest were somewhat smaller, about 8 meters (26 leal) In length. From Montreal Ihe raule of the fur trade swept westward lor nearly 5,000 kllome,ers (aboul 3,000 miles) over a network of rivers and lakes, linked by portages In those places where travel by canoe was Impossible. The far northern terminus was Fort Chipewyan on Lake Athabaska. At the peak at the trade hundreds of tons of pelts and trade goods were paddled and portaged each season along this waterway. The short season between break-up and freeze-up of the lee spurred the voyageurs In their dash to Grand Portage, In 5 months they had to cross half a continent and return. In early Mayas soon as the Ice broke up, brigades at lake canoes, laden with several tons of cargo, moved out from Lachine, lust above Montreal at the mouth of the Ottawa River. Eight weeks and 36 portages laler they glided into Grand Porlage Bay. In the north· west. crews of seasoned voyageurs, the "homme du nord." waited for the ice to break up. usually around May 15. Then Athabas\(a brigades, burdened with furs, began traveling down from the fur country to rendezvous in mid-July wilh traders at Rainy Lake and Grand Portage Return lourneys had to gel underway by August 1 10 Bilow narlhmen to be In Chlpewyan and voyageurs In Monlreel by October. Figure 11: Description of the geog raphy of the fur trade in relation to Grand Portage, MN (Grand Portage National Monument 1986). St. Lawfen �/ Figure 12: Shaded reliefmap ofIsle Royale National Park, MI (Huber 1973b). The map was modified to include locations that will be visited during this field trip. Scoville Point Tobin Harbor .... Daisy Farm Campground +:'- .. ~ ~MaJO".Bay 'a,~"9to" Ha..""",. N /' "'" 1 o Windigo o 1 2 3 4 I I I I 5 I I I I I I I 1 2 3 4 5 6 6 I I II 7 8 7 8 9 I I I I I I I I 10 MILES I 9 10 11 12 13 14 t5 16 KILOMETERS �STRAT. HEIGHT (km) ~ ~ ~_ ::l:~ LAJ(£ '" 9 t o ~0 SHORE TRAPS (1087.2 z 1.6 Ma) u u ... 0 ~ ." ;'" -1 GREENSTONE FLOW (1094.0 z IS Mil) <I) U :s0~ -2 ~ -3 ~ r..l 0 ... COPPER CITY FLOW <0( Ill: 0 c. (1096.2 -4 WSittL.-. z nong flow (pm) outcrops S of McGinty Cove, and the Scoville Point flow (psp) outcrops near Middle Point on the S side of Grace Harbor. Figure 16 shows the variations in thickness of the PLV. The thickest flows in this area are the Washington Island flow (pwi) and the Grace Island flow (pgi). Both of these flows occur only locally, from the end of Washington Island to a point between Windigo and Sugar Mountain, a distance of about 14.5 km (9 rni) along strike. The lava flows here dip at 15-20° SE, an attitude that is similar almost everywhere on Isle Royale. Vertical N-S trending fractures, with little offset, cut across the bedrock strata near Washington Harbor. Huber (1983) interprets these as structures related to the warping of the Lake Superior Syncline. S of Grace Harbor, the bedrock of the island is buried by till. 1.8 Mil) Windigo KEWEENAW FAULT Figure 13: Conceptual diagram ofPortage Lake Volcanics showing ages (from unpublished data of Paces). ageur E to Washington Harbor and Windigo (Figure 14), about 35 km (22 mi) offshore. (The keys, to the maps that are shown in Figures 14, 17-21,23, 28,34, and 35, are shown in Figure 15a and b). The bedrock geology of the Washington and Grace Harbor areas includes four large flows that continue all the way to the other end of the island. The Greenstone flow (pg) crosses the center of Washington Island and outcrops in several places SSE of Windigo. The Tobin Harbor flow (pth) outcrops at South Rock, SW of Washington Island. The Mi- Horse whim. The Windigo area was the site of the last serious mining on Isle Royale, from 1890 to 1892. After failure and closure of mines further E, the Wendigo Copper Company (renamed from the Isle Royale Land Corporation) founded a mining venture on 8000 acres of land at Washington Harbor, under the leadership of Jacob Houghton, who was the brother of Douglass Houghton. The town site was named Ghyllbank and was located near the present site known as Windigo. The mine site, about 2 km (1.25 mi) inland to the NE, was named Wendigo. People built roads all around the Wend ofIsle Royale, and 135 people lived at the mine site. The company did diamond drill exploration, as well as extensive trenching. In 1892, the miners gave up Sketch by A. H. :\Ieuche. after F05ter & Whitney. 15 �tr. Cove ~ ':I:: j~':~/""" ........ ~ \..; ~ '< tr. ~ '<' Figure 14: Geologic map of the S end of Isle Royale (Huber 1973). 16 j �~ 0 C) Copper 0 0 Harbor 0 o Conglomerate 0 0 Named lava flows: ~ 0 o 0 0 0 0 I I 0 rT ~.~.o'.·o,o 0"'·0_0 QoO Scoville Point Flow (porphyrite) (psp) Edwards Island Flow (trap) (pei) -I ( Unnamed rock sequences: ~ Numerous thin ophitic flows with as many as seven interbedded sandstone and conglomerate units (see fig. 17 for details) Several thin ophitic flows I Conglomerate-known from drill records Middle Point Flow (porphyrite) ++ Long Island Flow (trap) (plil Several thin ophitic flows I Sandstone-known from drill records Tobin Harbor Flow (porphyrite) Washington Island Flow (ophite) Tuff-breccia Greenstone Flow (ophite) Conglomerate-known from drill records Grace Island Flow (porphyrite) ~c;> • c • 0 0.0 • 0 • Sequence of thin to thick (more than 100 ftl flows chiefly ophitic, with one or more sedimentary units suggested by drill data Tuff-breccia Minong Flow (trap) (pm) I o Huginnin Flow (porphyrite) Hill Point Flow (ophite) (ph) \ ......... ..... 0 I 0 I 0 ... Sequence of thin to thick flows, chiefly ophitic, with one or more sedimentary units suggested by drill data 0 I , _ / ...... I " 11 r T-{ I r One or more ophitic flows present locally (php) Sequence of thin to moderately thick flows, chiefly ophitic. Several sedimentary units and a felsite indicated by drill records o· Breccia Amygdaloid Island Flow (trap) (pai) I Lava flows, chiefly ophitic Figure 15: (a) Key to maps shown in Figures 14, 17-21,23,28,34, and 35 (Huber 1973). This is a schematic columnar section of the PLVon Isle Royale; not drawn to scale. 17 �Figure 15: (b) Marked reliefmap, showing which sections ofthe map are enlarged in Figures 14, 17-21,23, 28,34, and 35 (modified from Huber 1973b). N 36 f-' ClO o I 1 I 2 I 3 I 4 I 5 I 6 I 7 I 8 I 9 I 10 MILES I �w_.... on,~ .... ~~-/l[~ l~ f;f~ P_I"~ 'SLEL J~OYAlE ~r ~ I ~.D =--- ~ .= . C ~ o~_ c:=-----? ~ _ ~ 1~MILES INDEX MAP SHOWING LOCATION OF DRILL HOLES AND INDIVIDUAL CROSS SECTIONS USED IN CONSTRUCTING LONGITUDINAL SECTION --i _ _ au"L-__-.:.:p'-----t-- II Bee of Gr"""one Flow t F,- _of _ GREENSTONE Edwwd> I".... ~ - ~. FLOW --- ---.----~ hned.,dIItum ~ i ----~--if'-=-t---=-----+------I----+----+------+---t------=::::i--"""'---- e.. of M<nona Flow '0 FEET 2000 r SCALE lOOO~ o o 5 MILES Figure 16: Longitudinal stratigraphic section showing variations in thickness ofthe PLVon Isle Royale (Huber 1973a). and left. When mining stopped, the company tried to sell land to tourists and resort owners (Rakestraw 1965). ophitic flow, which forms imposing cliffs along the shore from Hugginin Cove all the way to Todd Harbor, a distance of about 24 km (15 mi) (Figures 1719). This flow also makes up the majority of shoreline from Pickerel Cove all the way to Hill Point itself, at the Wend of Five Finger Bay, about 64 km (40 mi) from Windigo. The tilted strata along the shore make the shoreline steep, and the prevailing winds from the NNW can make conditions treacherous for small boats. The Hill Point flow is a coarse-grained, ophitic unit with augite oikocrysts of 2 cm (0.8 in) or more. The N Side of Isle Royale: The Hill Point Flow From Windigo and Washington Harbor, we will take the Voyageur first N and then E along the N side of Isle Royale. With the flows dipping toward the SE, moving toward the N side ofthe island takes us further into the PLV section, until we reach the horizon of the Hill Point flow (php). This is an 19 ��------------------- .< < ,,~ ~ <t '<cO < ;:.""' .:3'" ....... t < Ct:: ....... V:: -Figure 18: Geologic map, showing Lake Desor to Todd Harbor (Huber 1973). This map shows the portion of Isle Royale that is just NE of the portion shown in Figure 17 (see Figure 15b). " �J' ,GoG t 0 .« «. ." .z: <! to ,,-" c' ,'b ," 2'" ,0 r:.:te" c:r:,' o • "tJ (;;'0 tl· (\:" ~'" \\'\t .~.,.~Iif '~IJ [llb\\ vr 4<11t ;'II,;;;" . ce Figu;e 19: '-.J <;) [.~:! "'..'". Ge~logic map, showing Todd Harbor to McCargoe Cove (Huber 1973). This map shows the portion of fc Isle Royale that is just NE of the portion shown in Figure 18 (see Figure ISb). b t:' I~ ~ �The vertical fractures are superimposed across the dipping strata and are noticeable throughout the entire flow. From the W area of the flow to the E area, the fractures gradually begin to change from N-S to more N-E trending. According to Longo (1984), the Hill Point flow may correlate with a large flow on the Keweenaw Peninsula, the Scales Creek ophite, which extends all along the Keweenaw Peninsula for more than 160 km (100 mi) of strike length, and right through Houghton, which is about 110 km (68 mi) SSE of Hugginin Cove. McCargoe Cove At the midpoint of the island is McCargoe Cove (Figure 19), which is a fiord-like, 3.2 km (2 mi) long inlet that follows a large fracture zone, trending N 30· E to a campground site located along an ancient Native American portage route and near another mine, the Minong Mine. Native Americans left hundreds of ancient pits as relics of mining over centuries at this site, and in 1874 three companies were formed in Detroit to exploit the potential here. They built a dock and a warehouse and started to build a railroad. Some large masses of copper were successfully mined, and the community here grew for several years in spite of difficult winter conditions. But mining did not last beyond 1885 (Rakestraw 1965). The Amygdaloid Channel From McCargoe Cove, we will continue to the NE (Figures 20 and 21), passing through the Amygdaloid Channel. Amygdaloid Island is composed of the oldest lavas of the PLV on Isle Royale and is supported by a large flow, the Amygdaloid Island flow (pai), which is a fine-grained basalt (termed "trap"). At the Wend of Amygdaloid Island is the National Park Service (NPS) ranger station near Kjaringa Kjeft. Crystal Cove is 3.2 km (2 mi) E of the station, which was, beginning in 1906, a private residence and fishery. As we travel through the Amygdaloid Channel, the drowned ridge and valley topography of Isle Royale will become very visible, with more resistent lava flows holding up linear islands. Shipwrecks are numerous on the many "reefs" found all around the NE end of Isle Royale. Opposite of Crystal Cove on the S side of Amygdaloid Island is Belle Isle, which is a beautiful campground, accessible only by boat and canoe, located on the site of a resort that operated in the 1920s, serving the grand lake steamers of that period. The Palisades: The Greenstone Flow From this point, we will head toward the tip of Isle Royale to Blake Point (Figures 21 and 22), moving up in the stratigraphic succession. We will first cross the Hill Point flow (php) at Hill Point, then the Minong flow (pm) near Locke Point, and finally the Greenstone flow (pg) at the Palisades. The Greenstone flow is perhaps the earth's largest lava flow. The following are comments by Longo (1984): Similarities in the stratigraphic sequence of Isle Royale and the Keweenaw Peninsula ofMichigan were recognized by numerous workers prior to 1851. The first thorough study ofboth areas, conducted by Lane (1893, 1911), resulted in the correlations ofspecific rock units. One unit in particular, due to its persistence as a prominent ridge on both Isle Royale and the Keweenaw Peninsula, became Lane's most convincing evidence for a correlation across this section ofthe Lake Superior syncline. Lane (1893) states, "The backbone ridge thus agrees in every way with the great corresponding ridge on the Keweenaw Point. " Outcrop and drill core data by Lane (1893) reveal this unit as a single immense, differentiated lava flow. Lane (1893) refers to the flow as "the Greenstone, the 'backbone' and biggest ophite ofall, with the bed at its base we correlate as the Allouez Conglomerate. " The Greenstone's great thickness and differentiated nature led some workers to consider it as an intrusive sill (Seaman and Seaman 1944; Van Hise and Leith 1911). However, convincing data have proven this unit to be a lavaflow (Lane 1893,1911; Butler and Burbank 1929; Broderick 1935, 1946; Cornwall 1951), and henceforth known as the Greenstone flow. Huber (1973a) confirms the similarities ofthe Greenstoneflow on Isle Royale and the Keweenaw Peninsula, and he supported the correlation. --Longo 1984 The columnar character of the exposure seen at 23 �---------------- - ( -'? \ ~~~1 I •• ~. Figure 20: Geologic ""'P. showing Amygdaloid lskmd to Five Finger Bay (Huber 1973). lion of ble RnYale thau, ju'! ME of the po,""On Mown in Figure 19 (""" Pigore ISh). ~~ <:;Q'§!! ;,r'b o"- ~ Q:-0- "fo ��GEOLOGY OF THE GSF BLAKE POINT, ISLE ROY ALE, MICHIGAN T67N R33W Blake POlllt B o Pyr.et... Uc. Br.ccia. O*her fl.-• ••••••• Mel.. phy.. e Contact Figure 22: The geology ofthe Greenstonefiow at Blake Point on Isle Royale (Longo 1984). the Palisades is interpreted by Longo (1984) as a colonnade, following the terminology ofTomkeieff (1940). The cliffs are formed in the lower part of the great lava flow, which is 122 m (400 ft.) thick at the Palisades. The unit that comprises the cliffs is called the lower ophite and is about 30 m (98 ft.) thick. The rude columns are typically a few meters in diameter, and the rock is a coarse ophite with large pyroxenes enclosing many tiny plagioclases. The pyroxene oikocrysts increase in size from the bottom until they reach about 1.5 cm (0.6 in) in diameter near the top of the lower ophite. The lower ophite commonly forms steep anti-dip slopes on the N side of the Greenstone ridge (Huber 1973a). We will return to the Palisades and will also walk around to Blake Point later in the trip to look at this exposure more carefully. Blake Point As we take the Voyageur around Blake Point, we will see that the layers of the Greenstone flow are clearly delineated (Figures 21 and 22). Under the navigation light at the water line is the contact between the lower ophite and the pegmatoid (or pegmatitic) zone, about 23 m (75 ft.) thick. The pegmatoid represents the flow interior and has a texture that is strikingly different from the ophite, consisting of a mat of interlocking plagioclase laths as long as 2 cm (0.8 in) each. The pegmatoid is a bit less resistant to weathering, causing an indentation of the shoreline S of the light that marks the pegmatoid zone. Farther S, a cliff face with columns marks the beginning of a third layer of the Greenstone flow, the upper ophite. Like the Palisades, this part is also marked by colonnade columnar jointing. We will 26 �have an opportunity to examine this location on the ground later in the trip. The uppermost parts of the Greenstone flow consist of an entablature jointed part, which is locally prominent, and a fragmental flow top with abundant agates. The flow top is not well exposed because it erodes much more readily than the interior. Around the point, we will pass between Third Island and North Government Island. On the N side of Edwards Island, exposures of entablature style columnar jointing are spectacular in the Edwards Island flow (pei). N of Edwards Island are exposures of the Long Island flow (pH), recognized by characteristic blue agate amygdules. Both of these flows can be traced along Tobin Harbor and through scattered outcrops as far as 50 km (31 mi) to a point near Hay Bay (Huber 1973). Rock Harbor Heading SW to Rock Harbor (Figure 23), we will pass Scoville Point, which is the site of the Scoville Point flow (psp), a porphyritic basalt with fine, equant, millimeter-sized plagioclases. This flow extends all the way across Isle Royale and is very resistant to erosion, forming shoreline exposures and topographic highs. We will see this flow on numerous occasions throughout the next several days. Rock Harbor is the National Park's main visitor center and the location of the only hotel on Isle Royale, Rock Harbor Lodge. Upon arrival, we will be taken by a smaller boat to Three Mile Campground about 5 km (3.1 mi) farther SW. 27 ��The Second Day: An Overview a fire tower. Now it is used for monitoring acid rain, along with other environmental monitoring. We can climb the tower stairs for full views of the surroundings, both to the Nand S. Day Mount Franklin The day begins with a morning hike. We will take the Mount Franklin Trail, which begins 0.3 km (0.2 mi) W of Three Mile Campground (Figure 23). The trail immediately climbs a ridge supported by the Scoville Point flow (psp), then levels off and descends. We will cross a boardwalk over a swamp and arrive at a valley where there is a junction with the Tobin Harbor Trail, 0.8 km (0.5 mi) from Three Mile Campground. We will continue on the Mount Franklin Trail, straight ahead, crossing the Tobin Creek swamp and then climbing a ridge underlain by the Tobin Harbor flow (pth). From here we will descend to cross another swamp and then begin the 300 ft. ascent of the Greenstone ridge. The entire swamp and ascent is underlain by the great Greenstone flow (pg). At the top of the ridge there is a junction with the Greenstone Ridge Trail, which we will take left to go about 0.5 km (0.3 mi) to Mount Franklin, elevation 330 m (l080 ft.). Here there is a good view of the N side of the island, including Five Finger Bay, Lane Cove, and Amygdaloid Island, as well as of the Canadian Shoreline, including the Logan Sills and the Sleeping Giant. The Greenstone flow is indeed the backbone of the island, forming the most prominent ridge all along; only at Blake Point, however, is a reasonably complete section through the flow exposed. The contact between the pegmatoid and the lower ophite units of the Greenstone is mainly located near the crest of the Greenstone ridge. The lower ophite underlies the N slope, which is a steep, anti-dip slope, and the pegmatoid armors the gentler dip slope to the S. Daisy Farm Campground From the tower we will descend to the Daisy Farm Campground via the Mount Ojibway Trail. We will go down from the ridge to the first level spot and then begin to rise over a smaller ridge. The beginning of this small ridge is the approximate location of the top of the Greenstone flow; the ridge top and the dip slope to the S is underlain by the Tobin Harbor flow (pth). At the base of this ridge we will cross a swamp fed by Tobin Creek. Then we will ascend Ransom Hill, which has the Long Island flow (pli) on its anti-dip (N) side and the Edwards Island flow (pei) on its dip slope (S) side, where there is some entablature jointing. From Ransom Hill, the trail descends to Daisy Farm Campground. Daisy Farm is located on the site of an old mining community, called Ransom, which was founded in 1847 with the clearing of land and the construction of a smelter. The mining prospects dimmed quickly, however, and the mining activity ended only two years later in 1849. Then, in 1866 all the buildings burned down. In later years, the place was the site of a sawmill, a garden that supplied vegetables to Rock Harbor Lodge, and a Civilian Conservation Corps (CCC) camp, which was a foundation for youth employment, developed by Roosevelt during the depression (Rakestraw 1965). Edison's Fishery and The Lighthouse From Daisy Farm we will travel by boat across Rock Harbor to Edison's Fishery. The fishery itself is a restored camp that is occupied each summer by a retired Lake Superior fisherman and his family; this man is employed by the park to interpret what life was like here during the heyday of Isle Royale Fishing camps, from before the establishment of the park in 1936 until the sea lamprey invasion of the 1950s. The lavas that underlie the site of the fishery and the lighthouse are a sequence of 45-50 ophitic flows (Figure 24), which occur between the Scov- The Mount Ojibway Tower From this point, still following the same trail, we will descend sharply to a wooded area and level off for about 0.4 km (0.25 mi) before climbing again. We will then reach the ridge crest and follow it for another 3.2 km (2 mi), with occasional outstanding views, to the Mount Ojibway tower. This structure was built in 1962 and was used initially as 29 �o 0 0. 0 =- Projechd position of EXPLANATION ille Point flow (psp) and the overlying CHC. As we walk around the point we will see several flow tops exposed, good examples of cellular amygdaloids. This is an excellent place to find greenstone, a nodular, compact form of pumpellyite that is prized as a semi-precious gemstone (Huber 1983, see pp 589). The geological purpose of stopping here is to look at the flow sections along the wave-washed shoreline, following it from this point to Tonkin Bay (no relation to the Gulf of Tonkin!). We can also look at the amygdule mineral suite, which can be found on the pebble beaches. The amygdules of Isle Royale's flows contain a variety of secondary minerals, listed alphabetically (by Huber) as barite, calcite, chlorite, copper, datolite, epidote, laumontite, natrolite, prehnite, pumpellyite (chlorastrolite or greenstone), quartz (agate), and thomsonite (see Table 3 for information about each). The prehnite is unusual in that it contains disseminated native copper inclusions and has a pink color, which has caused some to confuse it with thomsonite (Huber 1969). Overall, the assemblage is zeolite facies and prehnite-pumpellyite facies, representing a slightly lower grade than much of the Keweenaw Peninsula area. This may partially explain the lower abundances of native copper on Isle Royale than the amount found on the Keweenaw Peninsula. [2] .. 0··.....".. - e-200-25Oft 25-30 ft .. end p-~ 1»14Oft 10ft ~ 160-170 ft 25-30 ft 60-70 ft 25-3Oft 1()().110ft 1().15 ft 60-70 it 25·30ft 17().l80ft 15-20 ft 200ft Mott Island Figure 24: Columnar section of upper part of Portage From the lighthouse, we will return to the fishery and take the boat across the Middle Island Pas- Lake Volcanics showing distribution of sedimentary units in the Chippewa Harbor area (Huber 1973). All the ophitic flow zones consist of multiple flows. Mineral Formula Hardness Color Notes Barite Calcite Chlorite Copper Datolite Epidote Laumontite Natrolite Prehnite Pumpellyite Quartz Thomsonite BaS04 CaC03 (Mg,Fe)sAl 2Si 30 lO (OH)g Cu HCaBSiOs Ca2(AI,FehSip,iOH) CaAI2Si40'2·4H20 Na2A12Si301O.2H20 Ca2AI2SiPlO(OHh Ca2MgAI 2Si 30'1 (OHhH 20 Si02 NaCa2AIsSis02o·6H20 2.5-3.5 3 2-2.5 2.5-3 5-5.5 6-7 3.5-4 5-5.5 6-6.5 5.5 7 5-5.5 white white olive - dk green copper white, various pistachio white, red-yel colorless It green-pink green colorless, varied pink vein occurrences vy common, veins, amygdules very common rare, veins, amygdules porcelaineous, opaque crystalline, amygdules amygdules radiating fibers, amygdules radiating fibers, amygdules mosaic, segmented pattern agate amygdules radiating amygdu1es Table 3: Characteristics ofsecondary minerals at Isle Royale. 30 �sage to Mott Island (about 3.2 km (2 mi) NE). We will stop here to visit one of the best exposures of sedimentary units within the PLV, found at the SW end of the island, facing East Caribou Island near the park headquarters complex. There are seven such units mapped by Huber (1973) in the Chippewa Harbor area. Most of them are remarkably constant in thickness and lithology throughout their lateral extents, which are 65 km (40 mi) or more. Paces (1988) reports the following about interflow sediments in the PLV: top of the underlying lava flow top indicating a more-or-less constant and relatively short repose period between eruptions. The infrequent presence of sedimentary beds between lava flows may indicate occasional hiatuses in magma extrusion, which allowedfor alluvialfans to transgress out towards the center ofthe basin. Conversely, interflow sedimentary horizons may mark briefperiods of increased depositional rates possibly related to episodic normal faulting and basin subsidence. --Paces 1988 The pebble conglomerate unit at Mott Island is thicker than most, about 12 m (40 ft.). The pebbles are essentially all of volcanic rock, with mafic varieties about twice as abundant as felsic ones. The sandstones are very feldspathic, plagioclase being most abundant. Fine-grained hematite is ubiquitous. The rocks have scour and fill structure, suggesting an origin in braided stream environments. Desiccation cracks and raindrop impressions have also been noted. Paleocurrent data suggest transport to the SE, similar to the CHC (Huber 1973a). Occasionally, lava flows are separated by intervening sheets and lenses of terrigenous clastic sediment. Twenty two major interflow sedimentary horizons occur scattered throughout the PLV section and are described by Butler and Burbank (1929), White (1952), and Merk and Jirsa (1982). lnterflow sedimentary beds vary in thickness from less than 1 cm (0.4 in) thick fine-grained siltstones filling fractures between flow top fragments to coarse boulder conglomerates over 100 m (330ft.) thick locally. Typically, interflow sediments are poorly sorted, lithologically immature conglomerates and sandstones derivedfrom a nearby volcanic source of some reliefand deposited in an alluvial fan-type environment (Merk and Jirsa 1982). Transportation was generally from the SE to Nl¥, orfrom basin margins towards the center ofthe subsiding graben (White 1952). Although the interflow sediments are volumetrically insignificant within the PLV (3% of the total lithologic volume) (Merk and Jirsa 1982; White 1971), they form distinct and relatively continuous stratigraphic marker horizons within an otherwise monotonous volcanic pile. The occurrence ofoccasional interflow sediments implies that rates oflava flow extrusion, sedimentation, and/or tectonic subsidence were not constant during the formation of the PLV. White (1960) shows that a subsidence-depositional equilibrium was established so that both lava flows and sediments were deposited on near-horizontal surfaces. Most lava flows were deposited directly on Boreal Research Center, Davidson Island Next, we will go by boat for a brief stop at Davidson Island, opposite Three Mile Campground. On this island is the Boreal Research Center, a residence for researchers at Isle Royale. After stopping at the dock in front of the center, we will walk around this small island, visiting another exposure of the epiclastic sedimentary rocks and an exposure of a columnar jointed, ophitic flow on the SE comer of the island. The wave-washed shoreline has exposed a surface perpendicular to the columns, which are 2-3 m (6-10 ft.) across. We will see many exposures of large columns like these in the next few days, as they seem to be a regular feature of ophitic flows at Isle Royale. We will then return to Three Mile Campground for dinner. 31 �The Third Day: A Good Look at the Greenstone Flow Blake Point Weather pennitting, this is a day to visit one of the most dramatic places on Isle Royale, Blake Point (Figure 21). The shoreline around Blake Point offers the best view of the Greenstone flow, better than any other sites at Isle Royale or the Keweenaw Peninsula. On the way to Merrit Lane, the starting point of our Blake Point walk, we will pass several islands that have interesting wave-washed exposures of lava flows. Among the sites we may see from the boat are: the SE sides of Heron, Shaw, and Smithwick Islands, where there are exposures of calcite veins and columnar jointed surfaces like the one we visited at Davidson Island; the SE side of Raspberry Island, which we will visit on the fifth day and which has many interesting features of the ophitic flows; and the NW side of Edwards Island, which has good exposures of entablature columnar joints in the Edwards Island flow (pei). The boat will let us off at the Merrit Lane Campground for our walk to Blake Point. We will follow the shoreline from Merrit Lane around the point, remaining close to the wave-washed rocks, yet trying to keep our feet dry. Most of the walk is on the upper ophite unit of the Greenstone flow. (The entablature part of the Greenstone and its flow top is underneath Merrit Lane, and we will see parts of this from the boat later). The upper ophite exhibits a rude columnar structure all along the walk, with the columns perpendicular to the bedding. The size of the oikocrysts increases from top to bottom. After rounding the comer, we will cut through the bushes to descend a cliff that marks the lower anti-dip face ofthe upper ophite. At the base of this cliff, we will see wave-washed exposures of the pegmatoid, here about 23 m (75 ft.) thick. The contact here appears to be quite sharp, although Huber (1973a) says it is frequently gradational. The following description of the pegmatoid is from Longo (1984): Lacroix (1928, 1929) coins the term ''pegmatitoide" to describe the coarse-grained zones consid- ered to represent the final stages ofdifferentiation in basaltic lavas ofFrance. The lavas ofMichigan's Copper Country show similar differentiates for which Lane (1893) applies the term "doleritic." Cornwall (1951) adopts the textural term "pegmatite" from the usage ofButler and Burbank (1929). He changed the confusing "doleritic" term to "pegmatitic facies, " and subsequently described such units in the Greenstone flow, Big Trap, and several other large flows within the PLVon the Keweenaw Peninsula. For the present study, the term "pegmatoid zone" from Lindsley et al. (1971) is adopted to encompass the portion ofthe Greenstoneflow with numerous en echelon, lens-shaped pegmatoids, associated granophyric phases, and subophitic layers. Texturally, pegmatoids are coarse grained when compared to ophitic zones. Coarse plagioclase laths dominate with interstitial, subhedral clinopyroxene and abundant interstitial to somewhat poikilitic magnetite and ilmenite. Consequently, the pegmatoids are strongly magnetic compared to ophitic units. This suggests that a higher titaniferous magnetite/ilmenite ratio for magmatoids than for ophites. Visual inspection generally reveals a greater overall opaque (oxide) concentration in the pegmatoids. Subophitic layers are often found hosting the en echelon pegmatoids. These layers, like pegmatoids, are strongly magnetic and very coarse grained stratiform features, but contain less abundant, smaller sized pyroxene. The contacts between pegmatoids and subophitic units are usually sharp, although instances ofgradational contacts have been observed. Subophitic layers grade into the ophites and seem to occupy the greatest volume of the pegmatoid zone. They have been observed to pinch out within pegmatoid units and may not be continuous planar features throughout the flow. Perhaps pegmatoid units are not only lens-shaped but also flattened amoeboid-like features interfingering with subophitic layers. The frequency ofpegmatoids and subophitic layers increases proportionally with increasing flow thicknesses. Both vary in thickness and shape and typically occur in the upper halfofa lava flow. Pegmatoids have also been observed as autointrusions, such as in the entablature on Isle Royale and the upper ophite on the Keweenaw Peninsula. The stratiform pegmatoids are usually found armoring the tops ofcliffs formed ofthe lower ophite. The ex- 32 �tension ofweak vertical joint patterns into the pegmatoid (forming crude large columns) suggests that pegmatoids may be part of the colonnade. In most cases pegmatoid zones separate a basal colonnade from an upper colonnade. Pegmatoids are not unique to thickflows ofthe PLV. Lindsley et at. (1971) assert that three ofthe thicker flows from the Picture Gorge Basalt contained pegmatoid lenses. Santin (1969) discusses the presence ofpegmatoids in horizontal basalts of the Lanzarote and Fuerteventura Islands in the Canadian Archipelago. --Longo 1984 The pegmatoid underlies the low shoreline and also the area under the light tower. A section of the Greenstone flow is exposed on Passage Island, a 2 km (1.2 mi) long island that can be seen about 4 km (2.5 mi) offshore from Blake Point. Around the corner from the tower and vertically down about 4 m (13 ft.) is the contact with the lower ophite (which is too difficult for us to reach safely). Longo (1984) describes the contact as a gradation over about 1 m of thickness. From here, we will return by the same route to Merrit Lane. Weather permitting, we will travel around the point in the boat to examine the lower ophite cliffs along the Palisades. The columns exposed on the anti-dip slope are up to several meters across. The base of the Greenstone flow is not exposed here. Porter's Island Upon returning to Merrit Lane, we will head S to Porter's Island, which includes exposures of a fragmental rock that Huber (1973a) interprets as pyroclastic. However, according to Longo (1984), these exposures may represent a fragmental top of the flow. The breccia unit, which is about 1-5 m (3.3-16.4 ft.) thick, contains rounded and semirounded fragments of the Greenstone flow set in a finer matrix that has amoeboid-shaped, agate amygdules. Longo did an extensive perographic study but could not find any evidence of shards or pumice. He did, however, find bow-tie spherulitic plagioclases in the matrix, which suggests an undercooled texture for the basaltic material there. This unit occurs at the top of the Greenstone flow along about 15 km (9.3 mi) of strike length (approximately to Mt Ojibway), according to Huber's map. Similar units are found at the top of the Greenstone flow on the Keweenaw Peninsula (Longo 1984). Figure 25 shows an old drawing of a cross section through Lake Superior, including Isle Royale and the Keweenaw peninsula. Red Rock Point At Red Rock Point, we will pass excellent examples of entablature jointing of the upper part of the Greenstone flow. The basalt of the entablature is Figure 25: An older drawing ofa cross section through Lake Superior, from the Huron Mountains to Port Arthur (Lane 1911). 33 �melaphyre, very fine grained. The curvicolumnar nature of a few of the columns resembles some of the Columbia River basalt descriptions (Figure 5). Long and Wood (1986) suggest that entablature jointing results when extensive floods that are created from deranged drainages cause dramatic quenches of solidifying flood basalts. Around the comer of Red Rock Point is an autointrusion of the Greenstone's entablature zone by material that is apparently from the pegmatoid zone. Longo (1984) describes the feature: develops as the crust of a partly solidified flow founders and causes the upward escape of the flow's fluid interior (Figure 26). Below the water level at Red Rock Point is an occurrence of coarse grained granophyric rock, which can be found in beach cobbles and boulders and may occur within the Greenstone flow itself. Tobin Harbor Continuing to the SW along Tobin Harbor, we will pass Newman Island. Opposite this island on the N shoreline ofTobin Harbor are outcroppings of the volcanic breccia that may represent the fragmental top of the Greenstone flow. We will continue SW to Hidden Lake dock. A large autointrusive dike was found intruding (N 20° W, 65° E) the columnar-jointed melaphyre at Red Rock Point. Despite an apparent lack of aplites, the dike is texturally similar to the stratiform pegmatoid. It is composed ofrandomly oriented, euhedral plagioclase laths with interstitial, subhedral augite and pigeonite (no poikilitic textures occur). The plagioclase laths are immense by comparison to the microlites ofa typical ophitic unit. Three characteristic features of the dike are: (1) the abundant plagioclase phenocrysts (up to 1 cm (0.4 in)), (2) a blue-green hue from plagioclase altered to chlorite in the dike, and (3) alignment of plagioclase laths parallel to the dike contact, forming an igneous lamination. Amygdules are more abundant along the dike contact also. The process ofautointrusion is similar to the mechanisms ofpegmatoidformation, except that after the residual liquid is pressed out of the hosting crystal mesh, the differentiated magma is squeezed up into the vertical tensional fractures. Lookout Louise From Hidden Lake to Lookout Louise, we will hike about 1.6 km (l mi) long and 85 m(280ft.) up. We will begin on the Tobin Harbor flow, but after passing the lake we will on the Greenstone flow, following a dip slope up to Lookout Louise. At about the halfway point, the trail passes Monument Rock (Figure 27), an individual column from the colonnade of the upper ophite that is exposed as an erosional remnant. Huber (1983, see especially pp 47-55) suggests that Monument Rock was formed by wave cut shoreline processes along a former "raised" shoreline, which he associates with glacial Lake Minong, about 10 Ka. From Lookout Louise we will look over the steep anti-dip slope of the lower ophite and see Five Finger Bay, Duncan Narrows, and Amygdaloid Island. The plan is to return from Lookout Louise to Hidden Lake and take the boat back to Three Mile Campground for the night. --Longo 1984 Longo (1984) interprets the auto intrusion to be related to a sag flowout structure, described by McKee and Stradling (1970) as: a large structure that Figure 26: Idealized cross section ofa sag jlowout structure (McKee and Stradling 1970). Following erosion, the dikes commonly remain as topographic highs in a circular pattern around the central sag area. 34 �AcKeonanlith. 37Y.]XOadway N.T MONUMENT ROCK (NORTH EAST VIEW) ISLE ROYALE. Figure 27: An old drawing ofthe NE view ofMonument Rock on Isle Royale (Foster and Whitney 1851). 35 �The Fourth Day 4: Scoville Point lodge lie ancient mine pits, attributed to Native Americans who occupied this area from about 2500 BC during the period of the Nipissing stage. The mining was apparently informal and quite limited in anyone place, but there are more than 1000 such pits all over Isle Royale according to Rakestraw (1965). Rock Harbor For part of this day's trip we will walk on the rocky dip slope of the Scoville Point flow (psp), facing Rock Harbor along the shore. Huber (1973) describes the basalt of this flow as containing "fine, equant, millimeter sized, plagioclase crystals distributed uniformly through a fine grained matrix." He says the thickness is 30-60 m (l00-200 ft.). There are not many features that can be seen in outcrop, but the flow is very resistant to erosion and buttresses the shoreline. At Suzy's Cave, about 1.8 km (1.1 mi) E of Three Mile Campground along the Nipissing shoreline, waves cut a sea arch at a contact between two lava flows about four thousand years ago, selectively eroding the region of the flow top. After passing Suzy's Cave, the trail to Snug Harbor, where the Rock Harbor Lodge is located, parallels the shore of Rock Harbor and lies on thin ophitic flows, which are stratigraphically below the Scoville Point flow. At Snug Harbor (Figure 28), the Scoville Point flow crops out only within the recessed part of the harbor, and the point where the Americas Dock is located is underlain by ophitic flows above the Scoville Point flow. We will take the Stoll Trail, which goes along the shore of Rock Harbor. Along here, we will see Nipissing shorelines and outcrops of the Scoville Point flow. Also, we will be able to see the ophitic flows above and below the Scoville Point flow along the way. About 0.8 km (0.5 mi) from the Scoville Point As we near the Scoville Point, the Scoville Point flow dominates the shoreline and has steep smooth exposures. At the point itself, we will look at the excellent exposures of the Scoville Point flow, the ophitic flows below it, and the Edwards Island flow (pei), which underlies the companion point located just to the NW of Scoville Point. There is a good exposure of cellular amygdaloid in one of the ophitic flows and the Edwards Island flow shows well developed entablature jointing. We will return to the lodge and to Three Mile Campground via the Tobin Harbor Trail, which is easier to hike. It stays near the shore of Tobin Harbor, mostly atop the Edwards Island flow. Just NE of the Rock Harbor Lodge on the return trail is the site of the Smithwick Mine remains; this mine was discovered in 1843 and actually operated in 1847 and 1848. The work done here mostly consisted of exploratory shafts and excavations, and it is unclear whether or not much ore was found (Rakestraw 1965). From Rock Harbor Lodge we return to Three Mile Campground via the Tobin Harbor Trail. 36 ��The Fifth Day Raspberry Island We will go by boat to Raspberry Island (Figure 28), about 0.5 km (0.3 mi) SE of Rock Harbor Lodge, and spend the entire day looking at a remarkable set of exposures nearby that provide an impression of some of the solidification features of an ophitic flow (approximately 20-30 m thick). Raspberry Island, which is one of many small islands along the S side of Rock Harbor, is a sequence of three ophitic flows dipping 15° SE. The uppermost of these flows is extensively exposed on a wave-washed dip slope along the SE shore. This shoreline receives strong storm waves and, therefore, has extensive wave-washed exposures about 1 km (0.6 mi) long. These expose the flow interior, although neither the top nor the base of the flow is clearly exposed. A loop trail goes around the W half of the island, marked by informative signs about the unique ecosystem of this island, which features frequent fog and damp, moss-rich swamps. Among the unusual plants is the pitcher plant (Sarracenia puerperia), which is an insectivorous plant that flourishes in the swamp along the loop trail. First, we will visit the most W point of the island, where the regional attitude of the lava flows is seen in the view along strike toward Smithwick Island across the Smithwick Channel. The point facing the channel on Raspberry Island is underlain by the oldest of the three flows on Raspberry Island. We will walk on a dip slope that shows some of the jointing pattern we observed on the SE sides of Davidson and Smithwick Islands. Next, we will head to the SE corner of the island to observe some rude columns in the uppermost Raspberry Island flow. The W Part of the SE Shore: Vesicle Cylinders We will next move out to the wave-washed SE shore, where there are two zones of exposures of vesicle cylinders. Paces (1988) describes vesicle cylinders (Goff 1977) in the PLV: Vesicle pipes are elongated, tube-like struc- tures, 10-30 cm (4-12 in) in diameter and 0.5-2 m (1.6-6.6 ft.) in length, containing somewhat coarser and more prismatic crystals compared to the adjacent groundmass. They are oriented vertically and occur predominantly in the bottom halfofthe flow. The origins and dynamic behavior of vesicle cylinders are poorly understood; however they appear to represent an accumulation ofexsolved magmatic gas bubbles which migrate upwards through the magma during the period when the cooling magma behaves as a Bingham plastic (i.e., possesses afinite yield strength, Walker 1987). --Paces 1988 Here at Raspberry Island, exposures of vesicle cylinders show a regular spacing between them, 13 m (3-10 ft.) apart, and a marked variety of textures; some were evidently preserved almost as voids, while others are filled with material that closely resembles vesicular pegmatoid. An interesting aspect of the exposures here is the relationship between the ophitic textures of the flow and the vesicle cylinders: The grain size of oikocrysts seems to be influenced by the proximity to the vesicle cylinder. Vesicle cylinders are found mainly in only two areas along this shoreline. This may reflect their restricted occurrence in a thin part (less than a few meters thick) ofthis flow. Based on limited field examination, this thin part seems to be in the lower part of the flow. The comparisons between this occurrence and written descriptions, one by Paces (1988) of the PLV on the Keweenaw (Figure 29) and one by Marsh et al. (1991) of solidification in sheet-like basaltic bodies (Figure 30), are illuminating. Both descriptions show the vesicle cylinders as developing in the upper part of the lower capture front of a solidifying body and continuing upward to the liquid zone. This suggests that the segregations formed during solidification--when the region around the cylinders was mushy. The vertical movement of the cylinders was accommodated by the positive thermal gradient and by more fluid material that overlay the mush region. The process forming the cylinders could possibly be common to the solidifying process of a wide variety of materials, such as metals, aqueous solu38 �c 8 A SMOOTII (PAHOEIIOEI BRECCIATED (F1lAGMEHTAL) UPPF.II CIlIUED MARGIN Ili,hI, OokIjud ..i'h Ahu_Ti.,V......... VOLA·III.!! EXSOI.UT1ON FROM COOUIf() WAClMA AND UPWAIIO MIGRATION Of PEGMATOlDLAYERS VESICla ..... ~~'~"OH ~""'······11,!ilill'f!/r·~~- . OH,..•••• LOWEll CIllUED IoIAROII" ..i'h Pipe Vaic\cs W \0 D 4!!/!!////!f!/f!!j! Figure 29: (a-c) Illustration of the development of volcanic rock textures and flow structures typical in sub-aerially erupted PLV flood lavas (Paces 1988). Unstippled areas within the cooling lava flow interior represent molten material. (a) Ponded lava flow after emplacement. (b) Partially solidified. (c) Solidification near complete. (d) Illustration of a portion of four successive lava flows summarizing the hydrodynamic characteristics of the volcanic pile. Very high permeability is present in interflow sediments and in highly vesicular and/or brecciated flow tops (heavy stippling). Permeability decreases gradually as the degree of vesicularity diminishes (light stippling) towards the center of the flow. Massive interiors of thicker flows (unpatterned) are largely impermeable to migrating ground water and secondary hydrothermal fluids. Lava flows were originally deposited in a near-horizontal orientation and have been subsequently tilted by both depositional and compressive tectonic mechanisms. �(al --- ---'Roof bulk liquid boundary layer (d) Rock=-- I~.I!!II Capture front~ is 'iJ ill1ll ---- FQQI Ro2L--::.. Temperature Crystals Figure 30: Conceptual diagram, showing residual fluids forming lenses in the Shonkin Sag and the schematic temperature and grain size relationships at the time oftheir formation (Marsh 1991, personal com- Figure 31: Schematic representation ofboundary layer perturbation leading to plume and channel formation (Hellawell et al. 1993). Note that the entrainment of bulk liquid must first accelerate the dendritic growth front locally, while the release of solute-rich liquid from below causes subsequent melting, in the order of (a to e). munication). This is comparable to the observed relationship of vesicle cylinders and pegmatoids on Raspberry Island. tions, and organic mixtures; this process is described as channel convection in partly solidified systems (Hellawell et al. 1993). In experiments with aqueous solutions, Hellawell et al. (1993) present observations of plumes that formed above the channels and extended into the liquid zone above (Figure 31). The Central Part of the SE Shore: Slickenside Surfaces Featured conspicuously along the E shore of Raspberry Island are slickenside surfaces. A study of the fault slickenfibers allowed Witthuhn (1993) to use geometrical and statistical methods to define the kinematics of the closing of the rift. In Witthuhn's study, Raspberry and Edwards Islands offered one of the largest populations of measurements (Figure 32). The measurements revealed two consistent stress fields, for each limb of the syncline, that would satisfy the conditions envisioned for the opening and closing of the Midcontinent rift. Most ofthe faults on Isle Royale, including both normal and reverse faults, trend NE. This suggests that the reverse faults represent reactivated normal faults. The orientation of reverse faults at Isle Royale differs significantly from the predomi- nately N-S trending structures measured in the PLV on the Keweenaw Peninsula (Figure 33). The EPart of the SE Shore: Pegmatoid Zones About two-thirds of the way along the shore of Raspberry Island, the exposures that occur are stratigraphically higher in the flow. Here the flow has a laminar structure that consists of fractures that are parallel to the bedding and spaced about 0.5-3 cm (0.2-1.2 in) apart. Within this part of the flow, vesicle cylinders are not seen, but small pegmatoid lenses occur. Paces (1988) describes what these lenses look like: Pegmatoid horizons are similar to vesicle cylinders in that they consist ofgas-rich, coarsely crystalline, granophyric material. However, they occur as discontinuous lenses and layers, typically 10 em (4 in) to several meters thick, and are usually located between the flow top and most massive portion ofthe flow interior. Pegmatoids are best developed in thicker flows that have cooled slowly enough to allow in situ differentiation (Cornwall 1951; Lindsley et al. 1971). This material represents the last remaining volatile-rich liquid, which is injected into fractures oriented sub-parallel to the upper flow surface. Both vesicle cylinders and pegmatoid layers contain significant void space in 40 �a) Mon EAST AND WEST CARIBOU INNER lULL, OUTER HILL AND DAVIDSON Equal Area +:..... = RASPBERRY AND EDWARDS STOKLEY BAY, TOOKER, SHAW AND SMITHWICK ISLANDS Figure 32: Left: Equal area rose diagrams of the trend of slickensides on (a) normal and (b) reverse faults on Isle Royale (Witthuhn 1993). Notice the similar trends that define the resolved shear stress on the faults. Right: Rose diagrams ofthe trends of slickensides on reverse faults measured on islands along the SE shoreline of Isle Royale (Witthuhn 1993). �tJ e::-. _ -~ / Figure 33: Compression directions deducedfrom slickenlines on reverse faults from the island groupings along the SE shoreline ofIsle Royale (Witthuhn 1993). Identification of circles from left to right: (1) West and East Caribou islands; (2) Mott island; (3) Inner Hill, Outer Hill, and Davidson islands; (4) Tooker, Shaw, and Smithwick islands and Stokley Bay peninsula; and (5) Raspberry and Edwards islands. the form ofvesicles and gas pockets and contribute to the permeability of the lava flows. history; also, the vesicle cylinder zones and the pegmatoid zones may represent comparable and complementary features that formed at about the same time. (A Master's student at Northern Illinois University, Matt Wollert, has begun a study on the origin of pegmatoid layers in thick Keweenawan lavas. Suggestions for Matt that result from our trip here are very welcome.) After examination and discussion of these outstanding exposures, we will return to Three Mile Campground for the night. We need to be well-prepared for departure because we must leave very early for Snug Harbor in the morning. --Paces 1988 The origin of the pegmatoids is possibly related to the process by which the vesicle cylinders were formed. However, for the pegmatoid origin, the rise of material in channels is limited by the thermal gradient and by the associated solidification that happens above the zone of pegmatoids, so the material is blocked and accumulates in lensoid layers (Figure 30). It is possible that this flow has frozen a snapshot of what was happening late in the solidification 42 �The Sixth Day: Back to the Mainland We will leave early to get to Snug Harbor in time for the departure of the Voyageur for our return to Grand Portage. The route will be via Chippewa Harbor, Malone Bay, and Windigo, so we will complete a circumnavigation of Isle Royale. Conglomerate Bay The first leg of the trip is SW along Rock Harbor to Daisy Farm Campground, and then past the Isle Royale Lighthouse and Tonkin Bay to Conglomerate Bay (Figure 20). Conglomerate Bay is named for one of the interflow sediments that crops out halfway along the inlet. On the edge of this bay was the site of the Saginaw Mine, which was a very brief mining effort with two shafts and a winze from 1877 to 1879. The regular 15" dip of the PLV strata is disrupted in this part of Isle Royale with a system of steep and curved faults. This causes the more SE parts to be offset progressively upward, as though the regular subsidence of the rift basin was disrupted in this place. Chippewa Harbor The entire region of Middle Island Passage to Siskiwit Lake consists mainly of the ophitic flows and their intervening sedimentary units (Figure 24). At Chippewa Harbor, we will see exposures of these flows and the sedimentary units, and near the dock is an outcrop of the interflow conglomerate. The harbor is the site of a fishing camp and is now a favored campsite. The beaches S of Chippewa Harbor are some of the best for finding Isle Royale greenstones (see "Greenstone Beach" on Figure 34 and Huber 1983, pp 58-9). Malone Bay: The Copper Harbor Conglomerate We will take the boat to Malone Bay (Figure 35), the site of exposures of the conglomerate beds of the CHe. On our way, we will pass Schooner, Hat, and Ross Islands, which are all underlain by sandstone of the CHe. This formation is described by Wolff and Huber (1973): The CRC at Isle Royale is the N limb counterpart of the type CRC exposed on the S limb ofthe Lake Superior syncline on the Keweenaw Peninsula. In both areas, the formation, which is ofmiddle Keweenawan age, overlies the middle Keweenawan PLVand is largely derivedfrom older Keweenawan volcanic source terranes that shed debris into the subsiding Lake Superior basin from opposite sides; for Isle Royale, the source terrane would have been the North Shore Volcanic Group in Minnesota. The deposits appear to be piedmont fan deposits and flood-plain deposits formed under a combination of fluvial and lacustrine conditions. Various sedimentary features at Isle Royale indicate that the sediments were transported generally E, with a range in direction from NE to SE. The formation also increases in thickness and in textural and compositional maturity in this direction; it varies from a boulder conglomerate, through a mixture ofcobble and pebble conglomerates and sandstone, to sandstone alone. This clastic wedge thickens within a distance of 32 km (20 mi) from a minimum of460 m (/,500 ft.) to more than 1830 m (6,000 ft.) between stratigraphic marker horizons; the top of the formation is nowhere exposed, however, and the total thickness probably is considerably greater. The clastic materials in the formation are predominantly derived from older Keweenawan volcanic rocks. Felsic varieties are slightly dominant over mafic varieties. Metamorphic rocks are minor components, and clasts ofintrusive igneous rocks appear to be absent. The overall local composition ofthe formation, chiefly reflecting degree of sediment maturity, is closely related to grain size; rocks ofsimilar grain size have the same composition throughout the formation. Calcite cement is ubiquitous; in the conglomerate and coarse-grained sandstone, it commonly amounts to about 15 percent. As the textures become finer, rock fragments and calcite cement decrease in abundance, whereas quartz, feldspar, and opaque mineral percentages increase. Thefelsic and many ofthe mafic Keweenawan rock types that occur as clasts in the CRC are not known to occur as flows within the PLVon the island. Most ofthe rock types, however, are known to occur as flows in the North Shore Volcanic Group, which is stratigraphically lower than the PLVand 43 �...~ -.>,,;:/;:<; ~~:...",,<::; <r'- ," ,I.) ,s- .~·I ~ ~'t' ~. ,{' Q �--- /' " c c -J:.~"'-' ,::~ // " Q) V:;, ;;L ~_.; �is present in the direction from which the clastic debris was transported. Several lines ofevidence suggest the presence ofan unconformity between the North Shore Volcanic Group and the PLV. Such an unconformity would facilitate the erosion of the North Shore Volcanic Group and the deposition of the erosional debris basinward on top ofthe PLV. The situation would be analogous to that on the S side of the Lake Superior syncline. There, many clasts in the CRC appear to have been derivedfrom the lowermost Keweenawan volcanic terrane, the volcanic rocks ofthe South Trap Range which underlie the PLV. --Wolff and Huber 1973 We will move along shorelines underlain by the CHC all the way to Grace Harbor, passing Menangerie Island, Long Island, Point Houghton (Figure 35), McCormick Reef, Long Point, the Head, Rainbow Point, and Cumberland Reef (figure 36). Figure 37 shows the variation of sediment lithology across the section, and Figure 38 shows sediment disposal patterns measured by Wolff and Huber (1973). SW Isle Royale: The Glacial Deposits It is in this SW section of Isle Royale (Figure 36) that the thickness of glacial deposits is the greatest. The glacial setting is summarized by Huber (1973b): Isle Royale was overridden by glacial ice during each ofthe four major glaciations ofthe Pleistocene Epoch, and each successive glaciation essentially obliterated all direct evidence ofpreceding glaciations on the island. In the waning phase ofthe last major glaciation, the Wisconsin Glaciation, the frontal ice margin retreated N from at least the greater part ofthe Lake Superior basin, then readvanced into the basin during Valders time, about 11,000 years ago. We can attribute to the Valders ice the final aspect ofglaciation at Isle Royale, including both erosional and depositional features. It is impossible to estimate the quantity ofglacial debris or other surficial materials that might have been present at Isle Royale prior to the Valders readvance, but the readvancing ice appears to have removed most of what might have been present, as judged by the thin surficial cover on the E two-thirds of the island today. During the Valders retreat, a series oflakes formed in the Lake Superior basin infront ofthe retreating ice margin. The retreating ice opened successively lower outlets, and thus the general trend oflake elevations is downward. Distinct lake stages reflect periods ofrelative stability during which well-defined shoreline features developed. The ice front forming the N margin ofthe earlier lakes probably remained S ofIsle Royale until about the time ofglacial Lake Beaver Bay, when it retreated to a position straddling Isle Royale W of Lake Desor. Abundant deposits ofglacial debris were left upon the newly deglaciated Wend ofthe island, and the ice front remained stable long enough to build a complex of ice-margin deposits across the island. Shorelines formed by the glacial lake associated with this ice frontarefound on the Wpartofthe island about 61 m (200 ft.) above present Lake Superior. Subsequent renewed and complete retreat of the ice margin from Isle Royale was rapid enough that only a minor amount ofglacial debris was deposited on the central and E parts of the island. When the ice margin reached the N edge ofthe Lake Superior basin, Lake Minong was formed, and the entire basin was filled for the first time since the Valders advance. Lake Minong marked a relatively stable episode in the history of the basin, and its beaches are among the best developed ofthe abandoned shoreline features on Isle Royale. Lake Minong beaches and later lower beaches are best developed on the SW end of Isle Royale, where abundant glacial debris provided easily worked materials for beach construction. --Huber 1973b The discussion about changing shoreline levels in Huber (1983, see pp 41-55) is important to understand the geomorphology we will be seeing, and if you are a field trip participant, you should particularly read the discussion of shorelines at Rainbow Cove, which includes clear exposures of both Nipissing and Minong shorelines (Huber 1983, see pp 52-3). Washington Harbor: The End of Our Trip Rounding the Cumberland Reef we will arrive once again at Washington Harbor, where we began on the first day. You have now seen Isle Royale from all sides. 46 �{\ EXPLANATION \-- \ I l ... ---'- Ar@a with exteMive glacial debt'is, in part reworked or eo'Vered by alluvium ~\1~~~&11 Iu-margin depofllts FO'f"'7IU'd at i.e. ~rg\" dun"" paWl". ' It "trt'Gt 01 glocill{ 1,t« Glacial striation SMwiftQ dh,(:~ <J!u, _Ute""C Drumlin (crag-and·taU type) Sltbwi", dirfftion Q/ it, """"""",,,t Abandoned IlhoreUne of 1\.<:\.\ ot' po8tal~t.l take "tuh"' 1m 14" ftM fJ/ .A!>Nfw of N '11 1 ~ 1 .- ~ Pol",t IloUBhton -..,J CumberlAnd Point 2 I 0 I 2 '" I ! 2 0 I I 2 4 I I 6 I 6 ~_,_ CONTOUR INTERVAL 100 FEET ~Q'IO' 89"00' Figure 36: Map shoWing the glacial features and abandoned shorelines ofSW Isle Royale (Huber 1973b). �Composition of lIel-y fine grained sandstones, very coarse grained ,~andstones, and pebble conglomerates taken f 1"01/1 the measured section on Houghton Ridge (Specimen numbers indicate relative lH,siliou with lowest number lowest in seclion. See plate I for loeations] Very fine grained sandstunes Specimen No. MV .................... FV .................... SF MF::::::::::::::::::: UQ .................... UnQ .................. PQ PF :::::::::::::::::::: PIF .................... 0 Ca ::::::::::'.:::-:':::::: Other ................ 4 6 0.3 .9 4.2 .0 46.2 21.6 .6 4.3 6.6 6.6 6.1 3.2 0.6 .6 .3 .0 39.7 16.2 .6 16.6 8,4 6.8 6.8 4.6 • Pebhle conglomerates 11 13 28 12 15 18 22 24 27 6 0.9 .9 .0 .3 42.3 18.8 .6 12.9 6.2 8.1 6.6 4.6 Trace 0.9 Trace .0 0.9 .6 .0 0.0 .0 .0 .0 28.1 11.9 .0 22.9 20.6 6.6 4.6 6,4 30.7 31.8 .0 .6 4.8 4.8 .3 1.6 9.0 6.1 9,4 .9 36.9 :18.8 .9 35.5 31.7 .6 2.3 3.9 1.9 .9 .9 6.4 1.3 16.3 .3 35.6 33.6 .9 23.9 24.2 1.6 .6 4.6 2.9 1.6 3.9 10.0 7.1 17.1 2.6 21.7 39.6 22.7 43.7 .9 .9 1.9 .9 1.3 7.1 2.9 1.3 14.8 1.6 36.6 24.2 .0 23.3 6.6 6.2 1.9 3.6 Trace 32.4 23.2 .9 18.6 6.1 6.8 8,4 3.2 MOTE.-Abbreviations: mafic volcanic rock fragments I"" V• felsic volcanic rock fragments SF. sedimentary rock fragments (shale and sandstones) MF. metamorphic rock fragments M V. Very coarse grathe1 sandstones 7 Trace 3.5 1.6 .6 1.6 11.6 2.3 1.3 .9 Trace 4.6 1.3 .6 .9 6.8 6.2 9.7 .9 UQ. unslrnined quartz grains UnQ. undulatory quartz grains PQ. PF. Ilnlycryslalline quartz "Tuins l)()tRssium feldspar RrninR Trace .3 1.6 1.9 1.3 4.6 2.3 1.6 22.3 2.9 PIF. o. 16 30 31 32 34.3 39.9 .3 .3 2.9 .6 1.9 .6 6.9 1.6 9.8 1.9 28.2 37.2 1.9 1.3 4.2 1.3 .6 1.6 1.9 .9 19.0 1.9 22.9 21.9 3.6 1.3 6.1 3.6 1.3 2.9 2.9 8.1 23.3 2.3 29,4 34.6 .3 Trace 4.2 1.3 .9 1.9 4.6 7.1 14.2 1.6 ploRioelase grains 0llsque grains Cn. Calcite cement Olhenl epidote. pyroxene. zeoHtes SECTION EXPLANATION I·.hhl.. n)ftl'ktm.... t. r~- ~ o .....i ........ ndo1<'HW ~ n,....,..iMd .. lldaltiofl. .......'um·cr.in.,f •• nohton. s..~~;~ ~i';:~: ~:':::~::'~t;:: I::'::: for'fOfti..,..,,,,,ottabl.4 SISJ(IIVIT Figure 37: The variation ofsediment lithology across Houghton ridge (Wolff and Huber 1973). 48 �it ., it ."it'it .., ..,., Q, '" it " .., 0, " '" .., '" ",' it it .., '" <0 <0it .., "'",'" '" ~~~:S! SIS[(I!VIT BA}' 1"-'>" ( ~ 1.0 . , CD N=38 M=135" S=40 ~ / "-~ ii- 25"..21\: 4iJ' CD N=I04 M=I02" 8=28 g> /!j~- <::> ~ N M S Direction (arrow) or trend (line) of paleocurrent movement obtained by averaging all meaSlII'ements tallen within the township section near which it is plotted. Numhers indicate the number of measurements that each symbol represents Composite of direction measurements taken mainly along the shoreline in townships indicated. N, number of measurements; M, mean direction; S, stanclal'd deviation. Measurements at west end of Siskiwit Bay not included ='-.. 0 0 N=105 M=67" .'>=33 ~ EXPLANATION --is , 17 =2 tv I 0 I 1 2 MILES I Figure 38: Sediment dispersal patterns in the Copper Harbor Conglomerate on Isle Royale (Wolff and Huber 1973). N=19 M=82" 5=23 �Acknowledgments The opportunity to write a detailed guide to Isle Royale and to lead a field trip comes from the cooperation of many people. I would like to thank Jack Oeltke of Isle Royale National Park for enabling a group to stay together at a campground during a field trip. Kim Alexander of National Park Concessions was helpful to us by providing the support of the Sandy, even though it was very early in the regular season. King Huber provided us with a complete set of his many publications about Isle Royale and also with lots of cheerful encouragement. Jim Paces, Tony Longo, and Rick Wunderman provided me with a lot of insight on the volcanic geology of Isle Royale. Kate Witthuhn suppLied some unpublished data. Discussions with Bruce Marsh and Angus Hellawell about solidification helped me to understand a little better what may have been going on inside Isle Royale's lava flows. Dave Schneider planned the food and logistics for the trip. Finally, Libby Titus did all the work of putting this field guide together: revisions, layout design, and copy-editing--everything but the fun parts! References Basalt Volcanism Study Project, 1981, Basaltic volcanism on the terrestrial planets, Pergamon Press, Inc., New York, 1286 pp. Brannon, J.C. 1984, Geochemistry of successive lava flows ofthe Keweenawan North Shore Volcanic Group, Ph.D. dissertation, Washington University, St. Louis, MO, 312 pp. Broderick, T.M., 1935, Differentiation in lavas of the Michigan Keweenawan, Geo!. Soc. Am. Bull., v. 46, pp.503-58. Broderick, T.M., Hohl, C.D., and Eidemiller, H.N., 1946, Recent contributions to the geology of the Michigan copper district, Econ. Geol., v. 41, pp. 675-725. Butler, B.S. and Burbank, W.S., 1929, The copper deposits of Michigan, u.s.G.s. Prof Pap., No. 144, 238 pp. Cannon, W.F., 1994, Closing of the Midcontinent rift: a far-field effect of Grenvillian compression, Geo!., v. 22, pp. 155-8. Cannon, W.E et aI., 1989, The North American Midcontinent rift beneath Lake Superior from GLIMPCE seismic reflection profiling, Tectonics, v. 8, pp. 30532. Carmichael, r.S.E., Turner, EJ., and Verhoogen, J., 1974, Igneous Petrology, McGraw-Hili, New York. Clark, J.A, Hendriks, M., Timmermans, T.J., Struck, C., and Hilverda, K.J., 1994, Glacial isostatic deformation of the Great Lakes region, Geol. Soc. Am. Bull., v. 106, pp. 19-31. Cornwall, H.R., 1951, Differentiation in lavas ofthe Keweenawan series and the origin of the copper deposits of Michigan, Geo!. Soc. Am. Bull., v. 62, pp. 159-202. DeGraff, J.M. and Aydin, A, 1993, Effect of thermal regime on growth increment and spacing of contractionjoints in basaltic lava, J. Geoph. Res., v. 98, pp. 6411-30. DeGraff, J.M., Long, P.E., and Aydin, A, 1989, Use of joint-growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows, J. Vole. and Geotherm. Res., v. 38, pp. 309-24. Foster, J.W. and Whitney, J.D., 1851, Report on the geology ofthe Lake Superior land district, Washington, DC, AB. Hamilton, 400 pp. Goff, F.E., 1977, Vesicle cylinders in vapor-differentiated basalt flows, Ph.D. dissertation, University of California, Santa Cruz, CA, 83 pp. Grand Portage National Monument, 1986, Grand Portage, National Park Service, U.S. Department of the Interior, GPO: 1986--491-414/20056. Green, J.C., 1982, Geology of Keweenawan extrusive rocks, Geo. Soc. Am. Mem., v. 156,47-55. Green, J.C., 1989, Physical volcanology of mid-proterozoic plateau lavas: the Keweenawan North Shore Volcanic Group, Minnesota, Geol. Soc. Am. Bull., v. 101, pp. 486-500. Hellawell, A, Sarazin, J.R., and Steube, R.S., 1993, Channel convection in partly solidified systems, Phil. Trans. R. Soc. Land., v. 345, pp. 507-44. Huber, N.K., 1969, Pink copper-bearing prehnite from Isle Royale National Park, Michigan, U.S.G.s. Prof Pap., No. 650-D, pp. D63-8. Huber, N.K., 1973, Geologic map of Isle Royale National Park, Keweenaw County, Michigan, u.s. G. S. Map, No. 1-796. Huber, N.K., 1973a, The Portage Lake Volcanics (middle Keweenawan) on Isle Royale, Michigan, U.S.G.S. Prof Pap., No. 754C, 32 pp. Huber, N.K, 1973b, Glacial and postglacial geologic history of Isle Royale National Park, Michigan, U.S.G.S. Prof Pap., No. 754-A, 15 pp. Huber, N.K., 1983, The Geologic Story ofIsle Royale National Park, U.S.G.S. Bull., No. 1309,66 pp. Lacroix, A, 1928, Les Pegmatitoides des Roches Volcaniques a Facies Basaltiques, Ac. Sci. Paris Comptes Rendus, v. 187, pp. 321-6. Lacroix, A, 1929, Les Pegmatitoides des Roches Volcaniques a Facies Basaltiques: A Propos de Celles du Wei-Tchang, Bull. Geol. Soc. China, v. 8, pp. 45-9. Lane, AC., 1893, Geological report on Isle Royale, Michigan, Geol. Surv. ofMichigan, v. 6., pp. 1-265. 50 �Lane, A.C., 1911, The Keweenaw series of Michigan, Michigan Ceo!. and Bio!. Surv. Pub. 6, Geol. Ser. 4, v. 2, 983 pp. Lindsley, D.H., Smith, D., and Haggerty, S.E., 1971, Petrography and mineral chemistry of a differentiated flow of Picture Gorge Basalt near Spray, Oregon, Carnegie Inst. of Washington, Yearbook 69, pp. 264-85. Lofgren. G.E., 1980, Experimental studies on the dynamic crystallization of silicate melts, Physics of Magmatic Processes (ed. RB. Hargraves), Princeton Univ. Press, Princeton, NJ, pp. 487-551. Long, P.E. and Wood, BJ., 1986, Structures, textures and cooling histories of Columbia River basalt flows, Ceo!. Soc. Am. Bull., v. 97, pp. 1144-55. Longo, A.A., 1984, A correlation for a middle Keweenawanflood basalt: the Creenstoneflow, IsLe Royale and Keweenaw Peninsula, Michigan, M.S. thesis, Michigan Technological University, Houghton, MI, 198 pp. Marsh, B.D., Gunnarsson, B., Congdon, R., and Carmody, R., 1991, Hawaiian basalt and Icelandic rhyolite: indicators of differentiation and partial melting, Ceologische Rundschau, 80/2, pp. 481510. McKee, B. and Stradling, D., 1970, The sag flowout: a newly described volcanic structure, Ceol. Soc. Am. Bull., v. 81, pp. 2035-44. Merk, G.P. and Jirsa, M.A., 1982, Provenance and tectonic significance of the Keweenawan interflow sedimentary rocks, Ceo!. Soc. Am. Mem., v. 156, pp. 97-105. Paces, J.B., 1988, Magmatic processes, evolution and mantle source characteristics contributing to the petrogenesis ofMidcontinent rift basalts: Portage Lake Volcanics, Keweenaw Peninsula, Michigan, Ph.D. Dissertation, Michigan Technological University, Houghton, MI, 413 pp. Paces, J.B. and Miller, J. D., Jr., 1993, Precise U-Pb ages of Dullish complex and related mafic intrusions, northeastern Minnesota: geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent rift system, J. Ceoph. Res., v. 98, pp. 13,997-14,013. Rakestraw, L., 1965, Historic mining on Isle Royale, reprinted in Borealis Isle Royale, Natural History Association, Houghton, MI. Santin, S.F., 1969, Pegmatitoides in the horizontal basalts of the Lanzarote and Fuerteventura Islands, Series I, Bull. Vole., v. 33, pp. 989-1007. Seaman, A.E. and Seaman, W.A., 1944, Geological column Lake Superior Region in general: Michigan Ceol. Surv. Div., Progress Report No. 10. Swanson, D.A., Wright, T.L., and Helz, RT., 1975, Linear vent systems (and estimated rates of magma production and eruption) for the Yakima basalt of the Columbia plateau, Am. J. Sci., v. 275, pp. 877-905. Tomkeieff, S.I., 1940, The basalt lavas of Giants Causeway district of Northem Ireland: Bull. VoLe., v. 6, pp. 90-143. Van Hise, c.R. and Leith, C.K., 1911, The geology of the Lake Superior region, U.S.G.S. Mon., No. 52, 381 pp. Walker, G.P.L., 1987, Pipe vesicles in Hawaiian basaltic lavas: their origin and potential paleoslope indicators, Ceol., v. 14, pp. 84-7. White, W.S., 1952, Imbrication and initial dip in a Keweenawan conglomerate bed, J. Sed. Pet., v. 22, pp. 189-99. White, W.S., 1960, The Keweenawan lavas of Lake Superior: an example of flood basalts, Am. J. Sci., v. 258-A, pp. 367-74. White, W.S., 1971, Geologic setting of the Michigan copper district, In Cuidebookfor FieLd Conference. Michigan Copper District, Sept. 30 - Oct. 2, (ed. W.S. White), Soc. Econ. Geol., Michigan Technological University, Houghton, MI, pp. 3-17. Witthuhn, K., 1993, A structural analysis ofthe Midcontinent rift in Michigan based on a fauLt array analysis utilizing slickensides, M.S. thesis, University of Minnesota, 129 pp. Wolff, RG. and Huber, N.K., 1973, The Copper Harbor Conglomerate (middle Keweenawan) on Isle Royale, Michigan, and its regional implications, U.S.C.S. Prof Pap., No. 754-B, 15 pp. Worster, M.G. and Huppert, H.E., 1993, The crystallization of lava lakes, J. Ceoph. Res., v. 98, pp. 15,891901. 51 � https://digitalcollections.lakeheadu.ca/files/original/5de63f9a5707ef8cb802fbb18d52081c.pdf 89db5e131bf5b0c588a042ee4d5d53b1 PDF Text Text I < I Proceedings Proceedings Annual Meeting Meeting 40th Annual May 11-14,1994 11-14, 1994 May Michigan Michigan Technological University Houghton, Michigan Michigan Volume 40 Part4—Michigan kimberlites and diamond exploration techniques By: By: Shawn Shawn M. M.Car/son Carlson and and Wayde Wayde Floodstrand Floodstrand �Institute Institute on on Lake Lake Superior SuperiorGeology Geology Proceedings 40th Annual Meeting Meeting May 11—14, 1994 May 11-14,1994 Michigan Technological University Michigan University Houghton, Houghton, Michigan Michigan Volume Volume 40 40 4—Michigan kimberlites and diamond exploration techniques Part 4-Michigan techniques By: Shawn Shawn M. M. Car/son' Carlsonland andWayde WaydeF/oodstrand2 Floodstrand2 Ashton Michigan 49920 49920 Ashton Mining Miningof ofCanada CanadaInc., Inc., Crystal Crystal Falls, Falls, Michigan 2Crystal CrystalExploration Exploration Inc., Inc., Crystal Crystal Falls, Falls,Michigan Michigan 49920 49920 �CONTENTS PART PART4 MICHIGAN MICHIGANKIMBERLITES KIMBERLITES AND AND DIAMOND DIAMOND EXPLORATION TECHNIQUES Introduction Introduction .................................................. 1 1 Road Log Stopi StoplA Stop2 Stop3 3 3 6 8 9 ........................................ Field Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fieldsamples Acknowledgements Acknowledgements ............................................ References References . . . . . . . Kimberlite Bulk Samples Samples 10 10 11 11 14 14 15 Figures Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure2 F i p r e 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Figure3 Figure3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Figure 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Figure4 Figurel Figure1 Figure 5 Figure5 Figure 6 Figure6 .................................................. .................................................. 12 12 13 13 �INTRODUCHON During the the past past 150 150years, years, atatleast least17 17purported purporteddiamond diamonddiscoveries discoverieswere were made made ininWisconsin, W~sconsin,with with additional Peninsula of of Michigan Michigan and and other midwestem midwestern states. The The accidental additional finds in the hLower w e r Peninsula accidental discovery discovery of a kimberlite pipe in Iron county, Michigan in 1971 suggested suggested the these diamonds the possibility that these diamonds might might have have been derived derived from source bodies closer closer than than northern northernOntario, Ontario,and and several several diamond diamond exploration companies initiated sampling programs to assess assessthe thediamond diamondpotential potentialof of the theUpper UpperPeninsula Peninsulaof of Michigan, Michigan, as aswell well as as adjacent adjacent Great Great Lake Lake States. States. To To date, date, more more than than 20 20 kimberlites kimberlites have havebeen beendiscovered discoveredininMichigan. Michigan.These Thesepost-Ordovician post-Ordovician intrusions intrusions range between 11and 20 acres, and follow aa crude crude northwest trend through through Iron, Iron, Dickinson Dickinson and and Menominee Menominee counties counties from from Crystal Crystal Falls Falls to Hermansville. Hermansville. Age dates dates have have been been obtained obtained for for several several of of these thesekimberlites, kimberlites, placing the intrusions years before present, the the youngest youngest in the the state placingthe intrusionsbetween betweenapproximately approximately186 186and and209 209 million years state (Jarvis, While none none of ofthe thebodies bodies discovered discovered so far have been been proven to be be economic, economic, there there is abundant abundant (Jamis, 1993). While evidence evidence to to suggest suggestthat thatmany manyundiscovered undiscoveredkimberlites kimberlitesexist existininthe theGreat GreatLakes Lakesregion. region.Some Someof of these thesebodies bodies may may be be the the source sourceof of the thelarge largehistorical historicaldiamonds diamondsfound foundininglacial glacialand andalluvial alluvial sediments sediments throughout throughout the the midwestern United States. midwestem United States. In In November November1991, 1991,Dia Met Minerals Minerals Ltd. M.announced announcedthe thediscovery discoveryofof81 81diamonds diamondsinin59 59kilograms kilogramsof of drill drill core Territories. This This release set off the core from from a kimberlite in the Lac I a c de Gras region of Canada's Northwest Temtories. largest in the the history of North America, and diamonds are currently the most largest claim-staking claim-staking frenzy in most exciting exciting exploration exploration is also progressing in the United States, explorationcommodity commodity in Canada. Diamond exploration States, with ongoing economic Arkansas, Colorado continuing efforts economicevaluations evaluationsof of several bodies bodies in in Arkansas, Coloradoand and Montana, Montana,in in addition addition to continuing efforts in the theLake LakeSuperior Superiorregion. region. This This field field trip trip is is designed designed as asaaprofessional professionalprospecting prospectingcourse, course,and andwill willfamiliarize familiarize participants participants with with the the science includiig the the dynamics dynamicsof ofkimberlite kimberliteemplacement, emplacement,relative relativeimportance importanceofof science of of diamond diamond exploration, exploration, including glaciation, collection and and processing processing techniques. techniques. While While most most emphasis emphasis has has been placed on the glaciation, and sample collection Michigan Michigan kimberlites and exploration exploration in the the midwest, midwest, kimberlite kimberlite and and lamproite lamproite rock rock samples samplesfrom frommany many worldwide will be be presented presented for examination, and a brief worldwide localities will brief update update of of current currentdiamond diamondexploration exploration activities throughout North America will be given. activities throughout North America will be given. 1 �N Lake Superior Lake Superior 89° Wisconsin Wisconsin Lake Michigan Michigan Scale 13,508,800 0 50 100 150 200 kms 1:Diagram Diagram of ofthe the Upper Upper Peninsula Peninsula of of Michigan, showing relevant FFIGURE I G U E 1: counties towns. counties and small towns. 2 �ROAD ROAD LOG LOG This Crystal Falls. Falls. Crystal Crystal Exploration Exploration maintains maintains Thisroad roadlog logbegins beginsininthe theparking parkinglot lotof ofWilliams WilliamsMini Mini Mall in Crystal aa processing processinglaboratory laboratoryand andoffice officehere, here,ininconjunction conjunctionwith withDow DowChemical ChemicalCompany Companyand andAshton AshtonMining. Mining.These These facilities be toured toured as this field trip. Parking Parking should facilities will be as the the last last stop stop of of this should not not be be aa problem problematatany anyof of the the stops, stops,and and vehicleswith with 4WD 4WD or or high high clearance clearanceare arenot notrequired. required.The Thetotal totaldriving drivingdistance distanceisisapproximately approximately40 40miles. miles. vehicles Mileage Mileage 0.0 Begin Turn right and proceed east lotof of Williams Williams Mini Mall. Turn right onto onto highway highway US-2, and east through through Beginat atparking parkinglot town. town. 1.0 Turn Turnleft leftatatfour-way four-waystop, stop,and andproceed proceedeast eastononM-69. M-69. 10.2 Junction JunctionofofWay WayDam DamRoad Road and andM-69. M-69. Turn Turn left left on on Way Way Dam Road Road and and proceed proceed north. north. 10.7 A large outcrop should bebe barely visible above A large outcrop should barely visible abovetree treelevel leveltotothe thewest. west.This Thisexposure exposureofofHemlock Hemlock metavolcanics shows shows excellent excellent east-west east-west glacial striations, striations, and can serve serve as as an an additional additionalfield field trip metavolcanics stop, stop,time time and andinterest interestpermitting. permitting. 16.3 Turnleft leftonto onto Phelan Phelan Road, Road, also also known known as as the the access accessroad road to tothe theLake LakeEllen EllenBaptist Baptist Camp Camp and and Turn Public #14. Proceed Proceed north. north. Public Recreation Recreation Area Area #14. 17.1 Turn Turnleft leftonto ontoPhelan PhelanRoad, Road,and andproceed proceedwest. west. 17.3 Turn Phelan'slanding landing strip. strip. Parking Parking is is best best near near the the yellow yellow gate at the northern northern end endof of Turnright rightonto ontoPhelan's the thestrip, strip,atatmileage mileage17.4. 17.4.The Thewalk walktotothe theLake LakeEllen Ellenkimberlite kimberlitetakes takesapproximately approximatelyfive fiveminutes. minutes. Note Note the the granular granular kimberlite kimberlite that that has has been been used used as asroad roadgravel gravel throughout throughoutthis thisarea. area. Stop Stop 1: 1: The TheLake IakeEllen EllenKimberlite. Kimberlite. The TheLake LakeEllen Ellenkimberlite kimberlitewas wasdiscovered discoveredinin1971 1971by byKlaus KlausSchultz Schultzand andWilliam William Spence. Spence.The Thepipe pipeisislocated located in mileswest westand andnorth northofofChanning. Channing.Several Several in eastern easternIron Ironcounty, county,approximately approximately22miles milesnorth northofofKiernan Kiernanand and55miles exploration currently leased explorationcompanies companieshave haveevaluated evaluatedthe theeconomic economicpotential potentialofofLake Iake Ellen, Ellen, and the property property is is currently leased by byCrystal CrystalExploration. Exploration. The TheLake LakeEllen Ellenkimberlite kimberlitehas hasbeen beendescribed describedby byCannon Cannonand andMudrey Mudrey(1981) (1981)and andby byMcGee McGeeand andHearn Hem (1983). (1983). Readers Readers are are referred referredtotothese thesepublications publicationsfor fordetailed detailedmineralogical, mineralogical,petrographic petrographicand andhistorical historical descriptions. descriptions.Lake LakeEllen Ellenisisaadiatreme-facies diatreme-facieskimberlite kimberliteofofapproximately approximately20 20acres, acres,and andisisroughly roughlyellipsoidal ellipsoidalinin shape. in the thekimberlite, kimberlite,but buthave havenot notbeen been detected detectedinineconomic economicquantities. quantities.No No shape.Small Small diamonds diamonds are are present present in precise preciseage agedate datehas hasyet yetbeen beenobtained obtainedfor forLake LakeEllen, Ellen,but butthe thebody bodyisisknown knowntotobebepost-Ordovician post-Ordovicianby bycrosscrosscutting cuttingand andxenolithic xenolithicrelationships. relationships. 3 �Due logging road Lake Ellen Ellenisiscurrently currently one oneof ofthe thebest-exposed best-exposed kimberlites kimberlites in the the Due to to a logging road excavation excavationin 1992, Lake United 20 x 12 12 x 55 meter meter pit pit shows shows aa number numberof of subtle subtlestructural structuralfeatures, features,and andatypically atypicallylarge large United States. The The 20 kimberlite xenoliths and and rare eclogite nodules may kimberlite specimens specimensmay maybe be collected collectedfrom from the the pit floor. Crustal xenoliths mayalso also be be collected, collected, along alongwith with aavariety variety of of minerals minerals including including garnet, garnet, ilmenite, ilmenite, olivine, olivine, serpentine, dinopyroxene, clinopyroxene, calcite ilmenite megacxysts megacrysts from exceed 4 centimeters. centimeters. calciteand andphiogopite. phlogopite.Some Someof of the the pyrope pyrope and and ilmenite £ro this this locality localitymay exceed Processing Processingequipment equipmenthas hasbeen beenset setupupatatstop stop11totoallow allowparticipants participantsto to collect collect heavy mineral mineral concentrates. concentrates. The Theplastic plastictubs tubsand andsmall smalljig screens screens(saruca) (saruca)are aresimilar similarto toequipment equipmentused usedatatthe theCrater CraterofofDiamonds DiamondsState State Park Park in in Arkansas Arkansastotoprocess processsmall smalldiamonds diamondsfrom fromolivine olivinelamproite. lamproite.Granular GranularLake M eEllen Ellenkimberlite kimberlite can can be be placed placed into into these theseconical conicalscreens screensand andshaken shakenunderwaterunderwatecheavy heavyminerals mineralssettle settletotothe thebottom bottomininaadistinct distinct"eye", tleyett, which flattable. table.Good Goodconcentrates concentratescontaining containing whichcan can be beremoved removedafter afterthe thescreen screencontents contentsare areinverted invertedonto ontoa aflat ilmenite, ilmenite,garnet garnetand andchrome chromediopside diopsidecan caneasily easilybebeobtained obtainedininthis thismanner, manner,with witha aminimum minimumofofeffort. effort. 4 �FIGURE 2: Portion of FIGURE 2: of the the Kiernan Kiernan7½' 7%'USGS USGS topographic topographic map, map, showing showingthe thelocations locationsof offield field trip and1A 1A (Lake (Lake Ellen kimberlite) and the the Michigamme Michigamme kimberlite. trip stops stops11and 5 �Stop 1A LA:North North Side Side of of the the Lake Lake Ellen Ellen Kimberlite Kimberiite The brief IA will willallow allowparticipants participantsto toexamine examine several several rubbly rubbly outcrops outcrops and filled-in test test pits, pits, as as The brief walk to stop 1A well as gain gain aa sense sense of ofthe thegeneral general topography topography of of the the Lake Lake Ellen Ellen kimberlite. kimberlite. The The topography topography in this this area area is more more typical of ofother other Michigan Michigan kimberlites; kimberlites; most most do do not not have have distinct distinct surficial surficialexpressions, expressions, and and good good outcrops outcrops are typical rare. Stop 1A also provides an opportunity to discuss the the nearby nearby Michigamme Michigammepipe, pipe, aa kimberlite kimberlitelocated locatedin in the the Stop IA SE¼ of of the the N NW¾ theSW^ S/4 ofofsection W ofofthe section27. 27.This Thisbody bodywas wasdiscovered discoveredininthe themid-1980's, mid-19803, and and an an extensive extensive SE% collection ofdrill core has hasbeen beendonated donatedto tothe theDNRcore DNRcorelibrary libraryatMarquette Company, at Marquetteby by Kenecott Kenecott Exploration Company, collectionof drill core and is is available available for public use. The Lake Ellen kimberlite has a high relative relative eclogitic garnet garnet population population when compared to to other otherwellwellthe"reconstituted reconstituted mantle" mantle" known North American kimberlites, with eclogite comprising approximately 6%ofofthe (Schulze, 1993). While Whileno nodetailed detailedstudies studies are are yet yet available, available, ititisisinteresting interesting to to note note that the Michigamme Michigamme pipe apparently has a much greater greater eclogitic garnet population population than Lake Ellen. Core Coresamples samples from fromthe theMichigamme Michigamme apparently has eclogiticgarnet will be presented presented at at stop stop 1A; 1A all all cores cores must must be be returned to the ill be the core core library, library, but samples samples for both nonpipe w destructive offices at Marquette, and destructive and and destructive destructiveanalysis analysismay maybe be obtained obtainedby bycontacting contactingthe theDNR DNRoffices at Marquette, andfollowing following core library guidelines. guidelines. gate, and proceed proceed south to access access road. 17.4 17.4 Leave gate, 17.5 17.5 Turn left on Phelan Road, and proceed east. 17.7 Turn right right on on Phelan Phelan Road, Road, and proceed proceed south. south. 17.7 Turn 18.4 Turn right righton on Channing Channing(Way (WayDam) Dam) Road. Road. 18.4 Turn Junction of of Way Dam Road and M-69. M-69.Turn Turn left left on on M-69, M-69,and andproceed proceed east east. Extensive fields in in this this 24.6 24.6 Junction area are are based on on outwash outwash sediments sedimentsrelated related to tothe theGreen GreenBay Baylobe. lobe. 25.6 25.6 Turn right on Camp 5 road, and proceed south. 26.6 gravel pit. 26.6 Camp 5 gravel pit 6 �FIGURE 3: 3: Portion Portion of of the Lake Mary 7½' topographic map, 7W USGS topographic map, showing showingfield field trip trip stop 2 and select Iron county county kimberlites kimberlites (modified (modified from from Chartier, Chartier,1993). 1993) Approximate boundary of the Sagola moraine is also shown (re-drawn (re-drawn Peterson, 1985). from Peterson, 1985). 7 �I I Stop 2 2::Camp 5 Gravel Gravel Pit. Pit The The Camp Camp 55 gravel pit is a large exposure exposure of of coarse coarseglaciofiuvial glaciofluvial sediments at the western western margin margin of of the the Sagola moraine. moraine. Most Most rock rock types types present present as clasts can be be correlated correlated to to known known or or inferred inferred occurences occurences in in Sagola Dickinson county, and were deposited by by aa series seriesof of east-to-west east-to-westadvances advances of the Green Green Bay Bay lobe during during late late Wisconsinan time. The Crystal Sagola, and Sagola-I1 Sagola-Il moraines moraines were created by the Green Bay lobe, and and Wisconsinan time.The Crystal Falls, Falls, Sagola, were all created several outcrops in the Mansfield area show prominent striations or grooves oriented almost due east-west. striations or almost due east-west Kimberlite clasts clasts were were first first discovered discovered in gravel pit in in 1991. 1991.Several Severalhundred hundredclasts clastsranging ranging from from Kimberlite in the the Camp Camp 55gravel small pebbles pebbles to small boulders boulders in size have since since been been removed analysis. At least least eleven eleven different different small in size removedfrom fromthe thepit pit for for analysis. hand-samplevariations ofkimberlite catagories are hand-samplevariations of kimberlite have have been been recognized recognized atthe at thepit. pit These These somewhat somewhat subjective subjective catagories are acombination of ofmacroscopiccharacteristics, macroscopic characteristics, including includingcolor, abundance of ofcrustal xenoliths, color,type type and abundance crustalxenoliths, based on acombination the presence or absence of typical indicator minerals, and general textural relationships. presence or absence of general textural relationships. As seen in thin section, these inequigranular serpentine, calcite inequigranularrocks rocksare arecomposed composedprimarily primarily of of olivine, serpentine, with accessory accessory ilmenite, diopside, garnet, garnet, phlogopite and apatite. ranges from dominantly and spinel, with apatite. Olivine ranges euhedral in some samples to completely anhedral in others, others, and and most most olivine olivine is at least partly replaced by serpentine, calcite, well-definedautoliths autolithsare are notably notably absent, absent, and and finegrained opaques. Pelletal Pelletal lapilli and well-defined serpentine, calcite, and fine-grained of these these rocks are best most of best classified classified as as diatreme-facies diatreme-facies kimberlite breccias or or hypabyssal kimberlites. The The clasts seem to have been most susceptible hypabyssal clasts susceptible to to alteration, alteration, and and many many of the different different hand-sample "varieties" are are nearly identical in thin thin section, except for varying degrees degrees of oxidation and and calcite calcite "varietiesH of post-glacial oxidation leaching. Indicator mineral mineral populations populations are are extremely variable in the kimberlite from Camp 5. While While results are preliminary at this stage, it appears appears that that ilnienite ilmenite isisby by far far the themost mostcommon commonindicator, indicator,followed followedby by chromite, chromite, chrome diopside, garnet. While the hypabyssal hypabyssal clasts are quite rich in some some of ofthese theseminerals, minerals, most most chrome diopside, and and garnet. While many many of the of the diatreme-facies breccias do do not not contain contain indicator indicator minerals minerals in the 0.4 to 0.8 millimeter range. range. These of diatremefacies breccias 0.8 millimeter indicators that can be seen in thin section, and it is expected that digestion samples do have extremely small indicators of aa sufficiently sufficientlylarge large sample sample would would produce produce at least a few larger grains. of Ilmenite llmenite Chromite Chromite Chrome Diopside Diopside Garnet, Undifferentiated Undifferentiated Camp 55 Variation 11 Variation 24 0 0 0 Camp 55 Camp Variation Variation 22 57 1 1 1 Camp Camp 55 Variation Variation 33 0 0 0 0 Lake Ellen Ellen 42 0 0 30 FIGURE 4:4:Typical Typicalindicator indicatormineral mineralcounts countsper per gram gram of of various various disaggregated disaggregated kimberlite samples. Indicator FIGURE Indicator minerals reported variations 1 1 and and 22represent represent reported are arewithin within the the 0.4 0.4 to 0.8 millimeter range. Camp 5 variations hypabyssal clasts. Results for Lake lake Ellen Ellenmay may vary vary depending depending on on portion portion of pipe sampled. 8 �set of of ilmenites ilmenites from from Camp 5 variations variations 1 1 and and 22 and and from from Lake Lake Ellen Ellen was was sent sent to to aa commercial commercial laboratory laboratory A set microprobe analysis. An average averageMgO MgOvalue valueofof14.4% 14.4%was obtained for for ilmenite ilmenite from from variation variation1,1,and and14.1% 14.1% for microprobe analysis.An variation 2.2.These These values values indicate indicategood good diamond diamond preservation preservationpotential, potential,and andare are slightly slightlyhigher higher than than the for variation content of ilmenites and as as compared compared to average MgO content ilmenites from Lake Ellen, Ellen, both as as analyzed analyzed in this study study (13.7%) (13.7%) and the MgO/CrO diamond MgO/Cr203 plot of of McGee McGee and and Hearn Hearn (1983). Unfortunately, Unfortunately, minerals that are are useful in estimating estimating diamond grade approximations have clasts, and and no no statistically statisticallysignificant significantapproximations haveyet yet been been gradeare arenot not very very abundant abundantin in most mostCamp Camp55 clasts, obtained. One small anhedral chromite ilmenites for for chromite which which was was accidentally accidentally included included with the the variation variation 11ilmenites analysis did not plot within within accepted major-element diamond inclusion parameters. Although there are are several several kimberlites kimberlites and andkimberlite kirnberliteclusters clusterseast eastand andsoutheast southeastofofthe theCamp Camp55gravel gravelpit, pit, these bodies are are either either too too distant distant or ortoo toooblique obliqueto tothe theaccepted accepteddirection directionofofglacial glacial advance advance in in this this area area to to account abundance of kimberlite clasts the Camp kimberlite fragments account for the abundance ofkimberlite clastsin the Camp 5 sediments. Most Mostkimberlite fragmentsininthe theCamp Camp 5 pit pit are are probably probablyderived derivedfrom fromundiscovered undiscovered kimberlites kimberlites in eastern eastern Iron or western western Dickinson counties. These These bodies are probably small diatremes with associated dikes dikes or or sills. sills. twenty kimberlite kimberlite clasts clasts have have been been located throughout throughout the Approximately twenty thepit, pit, and and are are marked markedwith with wooden wooden stakes few samples samples of of greenstone greenstone and amygdaloidal Keweenawan Keweenawan basalt basalt have have also also been been stakes and flagging tape. A few flagged, as both both of ofthese theserock rocktypes typescan canresemble resemble kimberlite kimberlite at first firstglance. glance.Field Fieldtrip tripparticipants participantsare areencouraged encouraged flagged, all of ofthese these clasts clasts in in situ, situ, and ground searching searching can be as and evaluate evaluate for for themselves themselves how how effective ground as a to examine all supplemental exploration technique. Participants Participants may may collect collect and and keep keep any any of the kimberlite kimberlite clasts clasts they they wish; wish; willbe be provided provided ififattendance attendance is is larger larger than expected. additional samples will 26.6 Leave Camp 5 gravel pit, and and proceed north north to toM-69. M-69. 27.6 Junction Junction of of Camp Camp 5 road and and M-69. M-69. Turn left and proceed proceed west westtoward toward Crystal CrystalFalls. Falls. 38.0 38.0 Turn right right at at four-way four-way stop. 39.0 39.0 Return Return to parking parking lot lotatatWilliams Williams Mini Mini Mall. Mall. Stop 3: 3: Crystal Crystal Exploration established in The Sample Sample Preparation Facility Facility (SPF) of Crystal Crystal Exploration Exploration Inc. was established in 1984 1984 to process oneonebulk samples from various various Upper Upper Peninsula Peninsula projects projects in in preparation preparation for for diamond diamond analyses. analyses. The The ton kimberlite bulk facility was waslater later expanded expanded to to handle handle the processing processing of of field field samples. The SPF The kimberlite The SPF is partitioned into two sections. The kimberlite evaluation evaluationplant plant consists consistsof of two two ball mills, a small Wilfley Table,aatrommell, trommell,an anauger, auger,aaDenver DenverJig, and vibrating vibrating screens. screens. The sample processing processing plant Wilfley Table, Jig, and plant includes includes sample mixer, alarge a large Wilfley WilfleyTable, Table,aadrying dryingoven, oven,aamagnetic magneticseparator, separator, and and aasmall smallheavy heavyliquid liquidconcentrating concentrating a sample lab. The The SPF is isrun run by bytwo twotechnicians technicians operating operating the physical plant and one person conducting the conducting theheavy heavyliquid liquid concentrating procedures one-ton bulk sample can be be processed processed concentrating proceduresininthe thelab. lab. Under Under normal normal operating operatingconditions, conditions,aaone-ton fieldsamples samplescan canbe be reduced reduced to the in about two to three weeks. weeks. Approximately Approximately ten 50-kilogram 50-kilogram field the desired desired concentrate ready for heavy liquid separation in one one day. day. 9 �Figures55 and 6 contain flow Figures flowcharts chartswith withdescriptive descriptive notes notes outlining outlining the thevarious various stages stages for both both the bulk and field concentrates are field sample processing. The The final concentrates are either eithersent sentto to outside outsidefacilities facilitiesfor microscopic examination or Exploration's own experienced, experienced, in-house observation. Mineral or passed passed on on to Crystal Exploration's in-houseteam team for indicator mineral observation. Mineral grains grains requiring requiring further furtherprobe probeanalyses analysesare areshipped shippedtotovarious variouscommercial commercialfacilities. facilities. KIMBERL1TE KIMBERLTTE BULK BULK SAMPLES SAMPLES Stage Stage11---- 11 Ton Ton Bulk Bulk Sample Sample 11 ton bulk sample of of kimberlite kimberlite from from an an evaluation evaluationdrill drillhole/trench/pit. hole/trench/pit. Stage Stage 22---- Trommel Trommel (Cleans (Cleans & & Screens) Screens) Bulk trommel for cleaning cleaningand andscreening. screening.After Afterpassing passingthrough throughthe thetrommel, trommel,there there are are three three Bulk sample goes into trommel (3) size fractions. size fractions. (1) kilogram sample is shipped to a lab for diamond diamond and indicator indicator analysis. analysis. (1) ÷6mm +6mm 50 kilogram (2) (2) 2-6mm material is is placed placed in ball mill for reduction to to -2mm -2mm fraction. (3) -2mm material continues continues for for further furthersize sizedivisions divisions(Stage (Stage3). 3). Stage Stage 33---- Vibrating Vibrating Screen Screen Vibrating Vibrating screen screendivides dividesthe the-2mm -2mm material material into into three threesize sizefractions. fractions. (1) (1) 1-2mm l-2mm sample passes into a double hutched hutched Denver DenverJig. Jig. (2) (2) ¼-lmm Vi-lmmsample samplepasses passesonto ontothe theWiffley WilfleyTable. Table. (3) considered slimes and passes (3) -'/4mm -Vmm isisconsidered passes out outof of the theplant. plant Stage Stage44---- Denver DenverJig Jig The is then then concentrated by a Denver Jig. The concentrate The 1-2mm l-2mm fraction is concentrate is is magnetically magnetically separated separatedwith with the the non-magnetic laboratoryfor non-magneticfraction fractionbeing beingshipped shippedto to aa laboratory fordigestion digestionininhydrofluoric hydrofluoricacid acid and and diamond diamondanalysis. analysis.The The tails tailsfrom from the the DenverJig Denver Jigare arereduced reducedininthe theball ballmill millto toaa size size fraction fractionthat that is is less less than than 1mm 1mmand and then thenpassed passedover over the the vibrating vibrating screen. screen. Stage Stage55----Wilfley WiMeyTable Table The fraction is is concentrated concentrated by the the Wilfley WiffleyTable. Table.The Theconcentrate concentrateisistreated treated by by the the same methods methods as The'/4-1mm %-lmm fraction as the theDenverJig Denver Jigconcentrate. concentrate.The TheWilfley WilfleyTable Tabletails tailsare arereturned returnedtotothe theball ballmill millfor foraaspecified specifiedperiod periodof oftime timeand and then then passed passed over over the thevibrating vibrating screen. screen. *The remilling concentrating procedures. diarnond(s) isis not not missed missed in the concentrating procedures. **The remillingprocedure procedureof of the the tails tails insures insures that that aa diamond(s) When 2,000 pound sample sample is is reduced reduced to toaa weight weightof of around around 100 100pounds pounds (plus (plusthe the Whenthe theball ballmilling millingisiscomplete, complete,aa2,000 concentrates). concentrates). * 10 �FIELD FIELD SAMPLES SAMPLES Stage Field Sample Stage 11 --- Field Sample Samples consist Samples consist of of approximately approximately50 50kilograms kilogramsof ofglacial glacialtill till (soil (soil sample). sample). 2--- CleanIng Screening Stage 2 Cleaning & Screening Till is placed placed in in aa small smallcement cement mixer mixer to to disaggregate disaggregate the sand grains from the clay/silt matrix. The The resultant slurry is then passed through through aa screen screento toget gettwo two (2) (2) size size fractions. +1.2mm (oversized) (oversized) --stored stored for possible possible later kimberlite clasts. Once (1) +1.2mm later identification identification of ofkimberlite Once there thereisisno no use use for the sample, it is discarded. Table. (2) -1.2mm -1.2mm -- fraction (2) fraction is passed over over the theWilfley Wilfley Table. Stage Stage 33 --- Wllfley Wilfley Table Concentration Concentration The Wilfley WllfleyTable uses a shaking shaking motion motion combined combined with a water waterflowto separate the higher specificgravity The Table usesa flow to separate the higher specificgravity(S.G.) (S.G.) grains grains (lights). concentrate is grains (heavies) (heavies)from from the the lower lower S.G. S.G. grains (lights). This This heavy mineral concentrate is then then screened screenedinto intotwo two (2) size fractions. fractions. (1) +0.5mm +0.5mm is isthe the fraction fraction of ofmost mostinterest interest. In In this this size sizerange, range, kimberlite kimberlite mineral identification identification is much much easier than than in in the the-0.5mm -0.5mm fraction. This fraction is dried in an oven and over a magnetic magnetic easier This fraction and then then passed passed over separator (Stage (Stage 4). (2) -0.5mm -0.5mm fraction fraction is is stored stored as a back-up for indicator confirmation of aa sample sample or in determining determining the the number of indicator grains found in the entire sample. Stage Stage 44--- Magnetic Separator Separator As The magnetic separator uses a rare rare earth earth (steep (steepgradient) gradient) magnet magnetas asaahead head pulley pulley for for a short short conveyor. conveyor. As concentrate is conveyed over the magnet, the highly magnetic (left hand LH) and the partially magnetic (center magnetic (center concentrate is conveyed over the magnet, the highly magnetic (lefthand - LH) off the the end of -- C) C) grains adhere to to the the belt beltwhile while the thenon-magnetic non-magnetic (right (right hand hand -- RH) grains fall freely off of the conveyor. Since the the kimberlitic kimberlitic indicator indicator minerals minerals are are magnetic magnetic in in nature, nature, they will will fall fall in in the LH and C conveyor. Since compartments be in in the the RH RHcompartment compartment which which compartmentswhile whilethe themajority majorityof of the sample sample (including (includingany any diamonds) diamonds) will be inventoried or or discarded. is either inventoried Stage 5 5--- Heavy Heavy Liquid liquid Separation Separation & & Concentration Concentration separation process process using using The concentrate is further reduced by passing the grains grains through through aa heavy heavy liquid separation Polytungstate, Lithium lithium Metatungstate, Methylene Iodide, Sodium Polytungstate, Metatungstate,or orother otherheavy heavyliquid liquiddepending dependingon onthe theS.G. S.G. needed to recover the the specific specific indicator minerals desired. Observation Stage 66 -- Microscopic Observation After the heavy heavy liquid liquid separation, grams. This After the separation,the thetotal totalweight weightof ofthe thesample sampletotobe beobserved observedwill willbe bebetween between20-50 20-50grams.This for the the sample is then observed in detail by trained "pickers" "pickers" who examine the sample under magnification for desired indicator minerals. 11 �_____________ ________ ________ ____________ _________ ________ ____________________ _____ _____________________ _________ _______ ___________ ________________ _________ One—Ton Kiaberlite Processing Procedure Procedure One-Ton Kimberlite I • STAGE 1 1 Ton Bulk Sample I a I • .. , a I , 2 :a I . I •a I . I I I I I 1% • for g I • : : I I_................_ _•_••__•___I I I a : :__________ I 2—6mm —z : I I I a • a a • a • a • Ball Mill : I II I +6mm ——— Analysis II I . II Ia I I I • I : Trommel——Cleans Trommel--Cleans && Screens Screens a a STAGE 3 Vibrating Screen I - I • I I a I I • I I I I a 1—2mm • • • I a a I a —*mm I• I u I .:<-: . .: a •a • I <— I • • II II a a I 8 Ia Ball Ball —— :--: Tails Tails :--: —Mill Hill : : : :a II - I8 I1 ,I ' I I I I I8 - - • a a STAGE STAGE 44 Denver Denver Jig Jig . • •8I , I , • -a Ia II I a a I I l a a a • I Ia -1 • : Magnetic Magnetic : : Non—Magnetic Non-Magnetic : : Fraction Fraction : : Fraction Fraction : a a I .:-Storage I Storage 8 • I : a l I I I• a I I I a I8e I 8- a Magnetic a a I : Fraction • I I II g a • a : Non—Magnetic Non-Mwnetic : : Fraction Fraction : 8 a I a * - * a I a I I a I 8 a : Magnetic Magnetic : : Separator Separator : : •al • aI a Ia Ia I_ : Magnetic Magnetic Separator Separator • I * Concentrate Concentrate , , I a I a a • 8 I I $ * I Ial a : • I a - iI f • $I - 8I a a I I I I I •8I 4 II I 8 , I II I I 1 I I I • : Concentrate Concentrate : a I : I : STAGE5 STAGE 5 : I: I : : Wiltley Wilfley '—— :--: Tails Tails a__a :--: Ball Ball : Table Table : ': : : Mill Mill •I a I II I : : I _I • -* I a Slimes Slimes • I a II II 8 Ia • I- Ia I •8 II Is • I I I I I_.._.__._..___ -if-* a I a a a I 'a a a a $ I I Ia a l -8 a 8 : : HF HP : Digestion Digestion : I . a8 I a_ I • a • • .: Ia I • •a • Diamonds Diamonds : a a * a I8 a l a a II a8 I •1 I : HF HF : Digestion Digestion : Storage a • I I - a • a I a 8--r-8 I I •a : Ia • a8 Diamonds Diamonds : Ia I FIGURE 55 12 �____________ ________________ ___________ ___________ _________________________ ____________ ___________ _____ _____________________________ _____ Exploration Field Field Sample Sample Procedure Procedure in in the the S.P.F. S.P.F. Exploration , I 8 1 STAGE 11 STAGE Field Sample Sample Field t 91 : . . ----- : . , I * , .:-----; I 1 t STAGE 22 STAGE Cleaned && Screened Screened 1 6 I • I I1 8 I I a 1 I '* I I1 I I • a • • • : a +1.2fraction +1.2mg fraction I 1 • • . : : : I11 I :--—-—:: a Discarded Discarded I1 • I I I I1 9 Storage Storage 9 I1 I1 I II I I II I I I 9 I9 I I 9 1 1 : STAGE 33 STAGE I: : : Wilfley Wilfley Table Table Concentration Concentration : I 9 1 9 II I I 1 I I1 I 9 9 I. I I • • _____II I I : Lights Lights :---: ———i I I • : Retvies Heavies : I • : a Screened Screened 9 aI • • • : I I I :----: : I 9 I* I1 I II I +0.5m fraction fraction +0.5mm 8 * 9 I 9 1 9 9 Discarded Discarded : 9 I I I I I I 1 II I II • I I I • * II Il 9 II I I 9. I 9 I1 : -1.2fraction -1.2mm fraction I $ 1 • 1 •1 . I I I 9I I 1 I •1 I • I : I 9 II t I I I I I9 I I1 I 9 1 I1 : : I1 I . • I -0.5mm fraction fraction —0.5mm a I Storage Storage 9 : 9 II I a 1 -I I I , $ I1 : Dried Dried : I1 I I l a 1 I I • • • a STAGE 4 Magnetic Separator • 9 l I •* I I • I •I •9 9 9 I a : I •I *1 •99 • 9 I9 I • I I I I9 I : Center Center Portion Portion : : (part(part.magnetic) magnetic 1 : I 19 9 I I • • : : Left Left Portion Portion : (highly (highly magnetic) magnetic) : Portion (non-magnetic) • 9 9 I • 1 •: I — I I Right 9 1 I , •I • : •9 * Discarded Discarded • I I : a9 $ I I1 I9a I - STAQE 5 STAGES H e a v Liquid Reavy Liquid Separation && Concentration Concentration Separation I 9I I 9 a .: - I9 I 1 l I 1 •I • * I9 I : Concentrate Concentrate : FIGURE 66 FIGURE : : 9 STAGE 66 STAGE Microscope Microscope : ; ! 13 �Acknowledgments Acknowledgments Theodore J. Bomhorst Bornhorst of Michigan Technological Technological University for originally originallysuggesting suggesting this this Credit is due to Dr. Theodore field trip, and to Glen Adams Crystal Exploration Exploration for allowing allowing visits to the Lake Lake Ellen Ellen kimberlite kimberlite and and the the Adarns and Crystal Sample Processing Schinella-Mottes Construction ProcessingFacility. Facility. Gene Mottes and khinella-Mottes Construction also also deserve deserve credit creditfor for graciously graciously allowing brief visit visit to to the the Camp Camp 55 gravel gravel pit pit. Bob Bob Regis Regisisisthanked thanked for for permission permissionto to use use his his 5agola-II1! Sago1a-II allowing aa brief terminology the Michigan DNR is thanked thanked for general information terminology in this this study, study, and and Milt Gere of the information and support. 14 �REFERENCES Cannon, Cannon, W.F., and Mudrey, Mudrey, M.G. M.G. Jr., 1981. 1981. The The Potential Potential for for Diamond-Bearing Diamond-BearingKimberlite Kimberlite in in Northern Northern Michigan 15p. Michiganand and Wisconsin: Wisconsin: U.S. US. Geological Geological Survey Survey Circular Circular842, 842,15p. Charlier, Chartier, Torrie, Tome, 1993. 1993. Diamond Bearing Kimberlite(s) and and Related Related Geology Geology in in the the Upper UpperPeninsula Peninsulaof of Michigan: Michigan: Geological Geological Excursion Excursion Guide, Guide, Michigan Michigan Basin BasinGeological GeologicalSociety. Society. Dorr, Jr, and Michigan Press, I?., 1977. 1977. Geology Geologyof of Michigan: University of Michigan Press, Ann Ann Dorr, John John A. A Jr, and Eschman, Eschman,Donald DonaldF., Arbor, Arbor, 476p. 476p. Gibbins, Diamond Exploration Exploration in in the Northwest Territories: Gibbins, Walter A., A , and Atkinson, Dorothy, 1992. Diamond Temtories: Publication PublicationEGS EGS1992-1, 1992-1,Yellowknife, l8p. 18p. Jarvis, William, William, 1993. Michigan Prospectorsand andDevelopers DevelopersAssociaAssociaJarvis, Michigan Kimberlites: An An Update: Update: Abstract Abstract at Prospectors tion of Canada 61st Annual Meeting (Paper M-10). tion Canada 6lst Meeting (Paper M-10). McGee, McGee,E.S., E.S., and andHearn, H e m ,B.C. B.C.Jr., Jr.,1983. 1983.Lake LakeEllen EllenKimberlite, Kimberlite,Michigan, Michigan,U.S.A.: U S A :U.S. U.S. Geological GeologicalSurvey Survey Open-file 22p. 83-156,22p. Open-fileReport Report83-156, Mitchell, H., 1986. 1986. Kimberlites Kimberlites-- Mineralogy, Mineralogy, Geochemistry, Geochemism, and and Petrology: Petrology: Plenum Press, New New Mitchell, Roger Roger H., York, York,442p. 442p. Peterson, L.,1986. 1986.Surficial Sudcial Geologic Geologic Map Map of ofthe theIron IronRiver River10loxx2° 2O Quadrangle, Quadrangle,Michigan Michiganand and Peterson,Warren WarrenL., Wisconsin: Map 1-1360-C. Wisconsin:U.S. U.S. Geological GeologicalSurvey SurveyMiscellaneous MiscellaneousInvestigations InvestigationsSeries Series Map I-1360-C. Schuize, Garnet Xenocryst Xenocryst Populations Populations in North North American Kimberlites: short short course course paper Schulze,Daniel Daniel J., 1993. Garnet paper in in Diamonds: Diamonds: Exploration, Exploration, Sampling Sampling and Evaluation. Evaluation. Prospectors Prospectors and andDevelopers DevelopersAssociation Association of of Canada, Canada, Toronto, Toronto,Ontario. Ontario. 15 � https://digitalcollections.lakeheadu.ca/files/original/2458e2c7290330228ee152c9a122af26.pdf dd5f9d643297b8215da12959fb8228ce PDF Text Text Proceedings 40th Annual 40th Annual Meeting May 1111-14, 1 4 , 11994 994 May Michigan Technological University Michigan Houghton, Michigan Michigan Volume 40 Part 5—Lessons from mining case histories: West Menominee Range, Michigan By: A//an By: Allan M. M. Johnson Johnson L I 'U �I I 40TH ANNUAL MEETING INSTiTUTE ON LAnE SUPERIOR GEOLOGY I I Volume Volume 40 consists of I Part 1: 1: Program Programand and Abstracts Abstracts Part 2: Self-guided geological field trip to the 2: geological to the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan Part 3: Volcanic geology of eastern Isle Royale, Michigan Part 3: Volcanic geology of eastern Isle Royale, Michigan Part Part 4: 4:Michigan Michigankimberlites kimberlitesand anddiamond diamondexploration exploration techniques techniques Part Lessonsfrom frommining miningcase casehistories: histories:West WestMenominee MenomineeRange, Range,Michigan Michigan Part 5: 5:Lessons I Reference to material material in Volume 40, Part Part 11 should should follow follow the the example examplebelow: below: Woodruff, L.G., and Back, Back, J.M., J.M., 1994, 1994,Chalcocite Chalcocite mineralization mineralization in in the the L.G., Cannon, W.F. W.F. and Portage Lake Michigan (ábst.): (abst.): Institute on Lake Lake volcanics, volcanics, Keweenaw Keweenaw Peninsula, Peninsula, Michigan Superior Geology Proceedings, 40th Annual Meeting, Meeting, Houghton, Houghton,MI MI 49931, 49931,v. v. 40, 40, part pan 1. 1,P. p. 77. 77. Published and distributed by Institute Institute on on Lake Lake Superior Superior Geology Geology M.G. Mudrey, Jt, Secretary-Treasurer, M.G. Jr., Secretary-Treasurer, I.L.S.G. I.L.S.G. 106 N 3rd 3id Street Street Mt Mt.Horeb, Horeb, Wisconsin Wisconsin 53572 53572 LSSN ISSN 1042-9964 1042-9964 All from All volumes are available available for photocopying photocopying costs from Michigan Michigan Technological Technological University University Library Archives I I I I I 1 I I I I Michigan an equal equalopportunity opportunity educational educational institutiodequal institutiorVequalopportunity opportunity employer employer. MichiganTechnological Technological University Universityis an �Institute on Institute on Lake Superior SuperiorGeology Geology Proceedings Proceedings 40th Annual Meeting Meeting May 11—14, 1994 May 11-14,1994 Michigan Technological University Michigan Houghton, Michigan Volume 40 Volume Part 5-Lessons S—Lessonsfrom from mining mining case casehistories: histories:West WestMenorninee Menominee Range, Range, Michigan Michigan By: Allan Al/an M. M Johnson By: Johnson Department ooff Mining Mining Engineering Department Engineering -1 295 Michigan Technological Technological University, University,Houghton, Houghton,Michigan Michigan49931 49931-1295 �ITINERARY 7:30 am Leave MTU MTU from Union Circle Leave from Memorial Union 9:00 Arrive Iron Iron River River Area Area Arrive (NOTE: All (NOTE: All times timesare are EDT, EDT, but but Iron Iron County County is is Central Central Time Time Zone) Zone) 9:00-9:30 open pitlunderground pit/underground mine Isabella Mine - open footwall slate and Riverton iron formation formation part of Dober Dober Mine Was complex complex flooded pit pit (acid water) water) flooded 9:40-10:30 Dober Mine and Iron Iron River River Old Old Stambaugh Stambaugh sewage treatment treatment plant plant site site open pit/underground pitlunderground mine mine acid drainage drainage river diverted diverted diversion structure in river synergetic pond pond system for treating treating AMD holding ponds ponds - 10:30-11:30 . Cardiff Cardiff Mine Mine open shaft shaft 1992 death (drowning of teen in flooded flooded mine workings) 11:30-1:00 Iron County Historical Museum Museum U.S.) 1921 steel headframe (oldest in US.) Caspian Mine Site, 1921 boxed lunch on grounds boxed g m u d s -- inside inside if inclement inclement weather iron ore mining mining dioramas dioramas early life in Iron Iron County County life in logging logging museum museum also adjacent to Lee Le Le Blanc Art Center Center (memorial (memorial to to renowned renowned wildlife wildlife artist artist from Iron River) 1:00-1:30 Buck Mine Site Site acid drainage drainage surface and underground underground sources sources 1:30-2:00 Mine Smuggler Mine Old County Road 484 road cave-in, fatality road fatality 2:15-3:30 Homer-Wauseca Mine and Sherwood Mine Complex Homer-Wauseca Mine pumping pit for overburden dewatering dewatering site of USGS-MGS dewatering study study in in 1940's and USGS-MGS dewatering basis for Theis' groundwater groundwaterdrawdown drawdowncalculations calculations sand filling filling raises raises mine subsidence subsidence 3:30-4:00 Cardiff Cardiff Mine Mine Headframe Headframe shallow shallow underground underground mine mine 4:00-5:30 Return Return to to Houghton Houghton �. , * : > .,, -.,.$: , .,,,.3  Â, '.-' "*^Â¥; TABLE TABLE OP OFCONTENTS CONTENTS I I I I I I Page Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . Historical HistoricalSketch Sketch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lessons Lessonsfrom fromMining MiningCase CaseHistories Histories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Background Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mine MineRelated RelatedProblems Problems-- Introduction Introductionto toCase CaseHistories Histories . . . . . . . . . . . . . . . . . . Case Histories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaseHistories References References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,. : . . . . Introduction Introduction ' L., : .~ . 1 ?, 1 1 1 22 44 21 21 26 26 67 67 ~. LIST TABLES LISTOF OFTABLES I I   I Table Table 1.1. Rock RockUnits Unitsin inthe theIron IronRiver-Crystal River-CrystalFalls FallsDistrict District Page Page ................. 2.2. Iron IronOre OreShipments Shipmentsin inMichigan MichiganThrough Through1974, 1974,Menominee MenomineeIron IronRange Range-- Iron Iron River District RiverDistrict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 17 ,- 3.3. Iron IronOre OreShipments ShipmentsininMichigan MichiganThrough Through1974, 1974,Menominee MenomineeIron IronRange Range- Crystal Falls District 18 Crystal Palls District . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ^n% 18 4.4. Avenge AverageofofYearly YearlyAnalyses AnalysesofofDober DoberMine MineAcid AcidDrainage Drainage1975-1978 1975-1978 . . . . .., .6262 .%.,LC �I LIST LIST OF OF FIGURES FIGURES Figure Figure U Page Page \ J 1. 1. Location Location of of the theCities Citiesof ofCrystal CrystalFalls Fallsand andIron IronRiver Riveron onthe theMenorninee Menominee .......................... Drainage Drainage from fromthe theWest WestMenominee MenomineeRange Range . . . . . . . . . . . . . . . . . . . . . Range Range in in Iron IronCounty, County,Michigan Michigan 2. 2. 3. 3. Generalized Generalized Geologic Geologic Relationships Relationships of the Folded Paint River River Group Group Formations in the Iron River District Formations in the Iron River District . . . . . . . . . . . . . . . . . . . . . . . . . ......... ................ 4. StratigraphicGeologic Geologic Relationship in the Crystal Falls Falls District District 4. Stratigraphic 5. 5. Map Map of of Mined Mined Properties Propertiesin inthe theIron IronRiver RiverDistrict District 55 J 66 --. 8 99 11 11a, J 14 14 6. 6. Mine Mineand and Map MapPlate PlateLocations Locationsin inthe theCrystal CrystalFalls FallsDistrict, District,Menominee MenomineeIron Iron Range Range ............................................ 7. in the Iron River District of 7. Location Location of of the the Sherwood Sherwood Mine Mine Complex Complex in Northern Michigan Northern Michigan 15 15- .................................... 27 27 Isometric IsometricView View of ofthe theSherwood SherwoodMine MineShaft Shaftand and Levels Levels in in Relation Relation to to the the Main Ore Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MainOreBody 28 28 9.9. Generalized Generalized Profile Profileof of Glacial GlacialOverburden Overburden at at the theSherwood Sherwood Mine Mine in inthe theEast East Pit Pit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 29 8. 8. ................ Photograph Photographof of Initial InitialSubsidence Subsidence in in West West Pit Pit Area, Area,September September7, 7,1979 1979 . . . . Photograph Photographof of Enlarged Enlarged Subsidence Subsidence Pit Pit Which Which Caved Caved on October October 14, 14,1979 1979 . . Enlarged Enlarged West West Pit PitAfter AfterOctober October19, 19,1979 1979Subsidence SubsidenceEvent Event . . . . . . . . . . 10. 10. Location Location of ofSubsidence SubsidencePits Pitsatatthe theSherwood SherwoodMine Mine 11. 11. 12. 12. 13. 13. . . . . - 31 31 33 33 33 33 34 34 ' J 14. 14. Subsidence SubsidenceMonument MonumentLocations Locationsat atthe theSherwood SherwoodMine MineIncluding IncludingContours Contours of ofSubsidence SubsidenceBased Based Upon Upon the the Level Level Survey Survey of of December December 9, 9,1980 1980 . . . . . . . 36 36 15. 15. Location Locationof ofExtensometer Extensometer Installations Installations in in Shear Shear Zones Zones on on the the 1000 1000and and 1200 1200 Levels Levelsof of the theSherwood Sherwood Mine: Mine: Looking LookingEast East .................... 37 37 16. 16. Suggested SuggestedMechanism Mechanism to to Explain ExplainSurface SurfacePits Pits on onSouth SouthBlock Blockof ofSurface Surface Shear: Shear: Looking LookingWest West ............................... 38 38 J �- U [ LIST OF FIGURES continued unprovedConceptual ConceptualModel Modelof ofPiping PipingSubsidence SubsidenceOver Over an Underground 17. Improved an Underground 18. ........................................... SmugglerMine Mine Cave-in Cave-in on on County County Road Road 424: 424: Looking LookingEast East . . . . . . . . . . Smuggler 19. Close-upof ofSmuggler SmugglerMine Mine Cave-in: Cave-in: Looking LookingEast East Close-up Mine Mine ....... SmugglerMine Mine Cave-in Cave-in on on County County Road Road 424: 424: Looking LookingWest West 20. Smuggler 46 46 .... 47 .......... L Close-up of of Smuggler SmugglerMine Mine Cave-in: Cave-in: Looking LookingWest West 21. Close-up E PlanMap Mapofofthe theSmuggler SmugglerMine MineArea AreaShowing ShowingSubsidence SubsidencePits Pitsand andthe the 22. Plan Areas of Underground Workings . . . . . . . . . . . . . . . . . . . . . ...... Areas of Underground Workings 48 L 23 . Small SmallSubsidence SubsidencePit Pit (50 (50 ftftdiameter, diameter. 25 25ftftdeep) deep)South Southof ofCounty CountyRoad Road424 424 23. Above Smuggler Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Above Smuggler Mine 50 24. Cross-Section Cross-SectionMap Mapof ofthe theSmuggler SmugglerMine MineOre OreBody Body 24. 51 L L [ L L I! [ [ [ Ii [ 47 ............... 25 . Longitudinal LongitudinalSection Sectionof of the theSmuggler SmugglerMine MineOre OreBody Body 25. .. ........... 52 26 . Plan PlanMap MapofofIsabella, Isabella.Dober Doberand andHiawatha HiiwathaMines Mines 26. 55 SurfacePlan PlanMap Mapofofthe theDober-Hiawatha-Isabella Dober-Hiiwatha-IsabellaMine MineComplex Complex 27 . Surface 27. 57 28 . Isometric IsometricDiagram Diagramof ofPart Partof ofthe theHiawatha Hiawathaand andDober DoberMines Mines 28. 59 .... ....... 29. Schematic SchematicDiagram Diagram Showing Showing Flow Flow of of Water Waterin inthe theDober DoberMine MineComplex Complex 29. . . . 63 �.. * % %. ..~.*. *.* * c .WZ.. 1 - INTRODUCTION INTRODUCTION 4 . ." The Menominee Range of of northern northern Michigan Michigan was was aa major major producer producer of The Menominee Range of direct direct shipping shipping < '*a- 7, iron ore ore for iron for nearly nearly a a century. century. When Whenthe thelast lastunderground underground mine mine on on the the Range Range ceased ceased operation in in 1978, 1978, itit marked marked the the end endof of an an era. era. With operation With the the start start of of mining mining in in the the early early 1880's, 1880's, the the district district had had gone gone througlf througtf a full full cycle cycle from from the thestart-up start-up of ofmining miningthrough throughclose-down. close-down. During million long tons of iron ore ore were were produced produced and and shipped shipped from from During this this period period over over 200 200 million nearly 100 operations. This nearly 100 mining mining operations. Thisdevelopment developmentand and production production spanned spanned the the time time from from when the the United United States from an when States advanced advanced from an essentially essentially rural-agricultural rural-agricultural society society through through the the industrial revolution revolution and and into into the the beginnings beginningsof ofthe the computer computerand andspace spaceage. age. The industrial The location location of of the West West Menominee Menominee Range Range in in Iron Iron County County is is shown in Figure Figure 1. the shown in 1. . . < .' . , *,,,W" .. ~.. ,. %. ' . -..,&...:, *... . , . . '> -\7. - . HISTORICAL HISTORICAL SKETCH SKETCH '. , . .à , ,~~ . . Iron ore ore mining mining was the the impetus impetus for for the the development development of the the Crystal Crystal Falls Falls and and Iron Iron River centers of of mining. River centers mining. Mining Miningjobs jobs brought brought miners miners and and their their families families to to the the district, district, paid paid for the the roads roads and and railroads and supplies supplies in in and and the the ore ore out for railroads needed needed for for shipping shipping equipment equipment and out to to lower late lake markets. markets. Taxes lower Taxespaid paid by bymining miningdollars dollarsbuilt built the thecities cities and and towns, towns, including including the the schools, police and and fire fire departments, schools, hospitals, hospitals, police departments, and and attracted attracted all all the the businesses businesses that that comprise comprise ,:.:,4 $ .; thriving communities. thriving communities. . .. .. ....... . '. ' .. : , .., , .,*.~ Ore was vital vital to to the war effort effort of of two two Ore produced produced from from the the Menominee Menominee Range Range mines mines was the war World Wars and supported supported mining mining families families and and the the families families of of the the supportive supportiveservice service 6 Iron ore mining paid paid for the businesses businesses for a number of generations for one one century. century. Iron infrastructure of these just as infrastructure of these two two major major population population centers centers in in Iron Iron County County just as mining mining has has done done in other areas of of the the Upper Upper Peninsula. Peninsula. �2L During During this this century, century, great great advances advances were were made made in in mining m i n i and and processing processing iron ore ore into into steel. steel. Early mining mining was was done done largely largely by by human human manual manual labor labor and andhorse horsetransportation. transportation. Until dieseland andgasoline gasoline powered powered engines, engines, mining mining was was labor labor Until the the advent advent of of steam, steam, electrical, electrical, diesel intensive occupation. The intensive and and aa highly highly dangerous dangerous occupation. The County County Mine Mine Inspectors' Inspectors' records records are are < replete replete with with injuries injuries and and deaths deaths resulting resulting from fromdangerous dangerouswork work in intjie @eever-deepening ever-deepening underground rockfalls, falls,delayed delayedblasts, blasts, timber timber underground mines. mines. Deaths Deathsand andinjuries injuriesthat thatranged rangedfrom fromrock support support failures, failures, runaway runaway skips skips and and trams, trams, scalding scaldingsteam steam from from mine mine fires, fires, suffocation suffocationfrom from --. inadequate inadequate ventilation ventilation and noxious noxious gases gases and and other otherhazards hazardsincluding includingmine minecave-ins cave-insand and floodings. floodings. In 27men menwere werekilled killedone onenight nighton onthe the28th 28thofofSeptember September1893 1893when when Inone onetragedy, tragedy, 27 the the Mansfield Mansfield Mine Mine was was suddenly suddenly flooded flooded by an an inrush inrush of of water water through through aa failed failed shaft shaftlocated located adjacent River in in east adjacent to to the the Michigamme Michigamme River east Iron Iron County. County. However, However,technological technological improvements improvements in in mining mining evolved evolved during the the tenure tenure of ofthe theWest WestMenominee MenomineeRange Rangeresulting resulting ininhighly highlyproductive productiveand andmuch muchsafer safermining miningmethods methodsby bythe thetime timethe thelast lastmine--the mine-theSherwood Sherwood Mine--ceased operations Mine~ceased operationsin in1978. 1978. -.. ,ll,..> .!,- T .. - . s A:>,.. 4 * f . LESSONS LESSONS FROM FROMMINING MININGCASE CASEHISTORIES HISTORIES '2 There There are aremany many lessons lessons that that can can be be learned learned from from such such aa rich rich history. history. For Forexample, example, with inpast pastmining miningpractices practices and and mine mineclosure closure with the theuse useof ofcase casehistories, histories,deficiencies deficienciesin procedures proceduresthat thathave haveresulted resulted in incurrent currentenvironmental environmentalproblems, problems, can canbe beidentified identifiedand and studies. Theseenvironmental environmentalproblems problems can can be begrouped grouped into intothree threeareas: areas: 1) 1) mine mine studies. These '.a . subsidence; subsidence; 2) 2)mine minewater waterdrainage drainageproblems; problems; and and3) 3)problems problemsrelated related to toinadequate inadequatemine mine shaft shaftsealing sealingand andcapping cappingpractices. practices. 1 �L 3 I L L Mine has been a problem in Mine subsidence has in the the district. district. In In one one instance, instance, human human life life was was lost because of sudden stope of of an anold old sudden subsidence subsidence of a section section of county road into into aa shallow shallow stope mining Also, many many mines mines in in the the Iron Iron River River area area encountered encountered acid acid waters waters during during mining operation. operation. Also, L their and several continued to to drain drain acid acid water water when when they they became became flooded. flooded. The their operation operation and several continued The L acid acid waters waters flowed flowed from from the the mines mines into into the the Iron Iron River River and and eventually eventually the the Brule Brute River River system system causing pollution problems. problems. Because Becausethe theBrule BruleRiver River marks marksthe theborder borderbetween betweennortheastern northeastern Wisconsin Wisconsin and the Upper Peninsula Peninsula of Michigan, the the residents residents of of the the two two states statesare are [ concerned with the problem. There is one occurrence of human fatality resulting from falls into mine shafts in Iron L County. in 1992. The Thisoccurred occurredatatthe theChatham Chatham Mine Mine in Stambaugh Stambaugh in Thepresence presence of of County. This hundreds of of shafts, protection in in the the form form of of seals seals or or hundreds shafts, some some with with deteriorating deteriorating or or inadequate inadequate protection caps, remains remains aa cause cause for forconcern. concern. These These three three basic basic environmental environmental problems problems were were investigated investigated by by the the use use of ofcase case r L histories. histories. This This field trip guide guide is is structured structured to to present present information information on on these these problems problems and and to to [ show how these problems have been addressed addressed by the the mining mining companies, companies, local localgovernment government entities, and and the the Michigan Michigan Department of Natural Resources, to to lessen lessen their their impact impact on on this this mining district. The Theoverall overallobjectives objectives of of this this project project were: were: 1) 1) to document document deficiencies deficiencies in in L mine closure procedures procedures that that have have resulted resulted in in problems problems of of subsidence, mine closure subsidence, acid acid drainage drainage or or shaft shaft sealing/capping failures; 2) to examine sealingkapping examine these these problems and deficiencies deficiencies and attempt attempt to to develop ideas ideas on how how they they could have been prevented for their their effects effects lessened lessened by by action action L taken prior to 3)to torecommend recommend these these ideas ideas as asguidelines guidelinesin inmine mineclosing closing to mine mine closure; closure; and and 3) I procedures. �4 4 e+iJ Cy'li'SSi,!, . . ,^Hs.^i.ia . ^w". " ;.: .,%.'-:. ¥I ',; ?-'Â¥s' BACKGROUND BACKGROUND a,,, . . The I'l'sn&drystal Iron River—Crystal fte mining district district is Falls mining is located located on the the western : c?r$ Menominee in the the southern southern part of Iron Menominee Range Range in in the part of IronCounty County in the Upper Upper Peninsula Peninsula forms a a roughly The western The westernMenominee Menominee Range Range forms roughly shaped shaped ,.. . . .,. triangle, of which which extends extends between between Iron Iron River River on triangle, one one leg leg of on the the west west and and Michigan (Figure (Figure 1). 1). of of Michigan Falls on the east, Crystal Falls Crystal on the east, aadistance distanceof ofabout about 20 20 miles. miles. Fromthe the City City of of 3' From :*f:f : .9 ", .:. Iron River whichisis situated situated on on the the northwestern part of of the iron Iron River which northwestern part the range, range, the the i r a the Wisconsin is about formation formation trends trends southeasterly southeasterlytowards towardsthe Wisconsin border border which which is about five The third third leg leg five miles miles to to the the south. south. The of the of the triangle triangleextends extends south south of of Crystal Falls Falls paralleling paralleling and and then then crossing crossing the the Brule Brule River River into Wisconsin. into Wisconsin. Crystal The parallels the Menominee River The eastern eastern part part of of the the Range R a w e parallels the Menminee a v e r on on the the Michigan Michigan ,; .: %-, u i o : %.' ?~'--5?3'r->..l:.Â¥- : . p  .¥ ;a' , -,.,-. .!. .,,&'>.,.->jr' j::;?l~ .; &,,> & > ,:; ,..: . 7 ; . ~ , ~ side. side. The topDgraphy mostly rolling, rolling, varing varing from The topography is is mostly from about about 1300 1300 feet feet to to 1700 1700feet feet in in elevation. elevation. The higher elevations are and are near Iron Iron River, River, Michigan Michigan and southeast. as a result the drainage drainage is generally generally to the southeast. The The Iron Iron River River the western area southeasterly drains drains the western area southeasterly into intothe theBrule BruleRiver Riverwhich which forms forms the the The Crystal Falls Falls area The Crystal area is Brule andand Michigan-ane Rivers which which join, join, forming forming the the isdrained drainedby bythe thePaint, Paint, Brule Michiganne Rivers Michigan. border between border between northeastern northeasternWisconsin Wisconsin and and Michigan. MenomineeRiver, River,which whichultimately ultimately empties empties into into Lake Menominee Lake Michigan. Michigan. The drainage The drainage 2 is in Figure 2. is shown shown in Figure 2. The area has has been heavily glaciated glaciated and drift The area been heavily and the the soil soil is is thick thick glacial glacial drift mostly of glacial glacial till and consisting m consisting s t l y of till andoutwash outwashmorainal morainal sands sands and and gravels. gravels. The area is withnumerous nterous lakes lakes and and streams streams that that are The area is mostly mostly wooded wooded with are . . -.,; .,,,.,,: ...,. fran rain The glacial glacial ,,.,,., . ><'. ,. abundantly supplied supplied with abundantly with water £ra rainand and snow snow melt. melt. The ' *7 ~ , ~ < :':I , overburdenininthe thearea areaisis aa prolific prolific aquifer. overburden aquifer. is northern withrelatively relatively short The The climate climate is northern temperate temperate with short sinners sumers and and a a short growing season and andthe the winters winters are are cold short growing season cold and and long. long. �5 . . .~, . WISCONSIN IRON RIVER Figure 1. S T A L FALLS Location of the Cities of Crystal Falls and Iron River on the Mpnnminpe Ranae in Iron County, Michigan �LL Figure 2. L L Drainage from the West Menorninee Range L MENOMINEE RIVER LLL. C' �,, . . , - 7 . : ,...,*. Geology Geology . ~. ,. ?. .. .--of a series . T The h e west Menominee Range is is comprised of series of of complexly complexly folded ~ sedimentary rocks rocks of of Middle Precambrain Precambrain age. sedimentary age. The strata are the five The formations of of the Series. formations the Paint PaintRiver RiverGroup Group of of the theUpper Upper Animikie Animikie Series. L The The bottoanost unit unit is the Dunn Creek Slate Slate which is some 1000feet feet thick. thick. bottomnost is the Dunn Creek which is some 1000 The The upper 50 50 feet feet of of the the Dunn Formationcontains contains the the Wauseca member, member, aa Dunn Creek Formation upper L pyritic—graphitic slate. pyritic~qraphitic The Riverton Iron Iron Formation Formation overlies overlies the the Dunn Creek Formation and is in turn turn overlain overlain by by the Hiawatha Greywacke, Greywacke, which which is Creek [ L but is is absent absent in 500 feet but insome some areas. as thick as 500 The magnetic Stambaugh The Stambaugh Formation and the FortuneLakes LakesSlate Slateare arethe the next next higher higher units, units, Formation the Fortune *kspectively. respectively. More Moredetailed detaileddescriptions descriptionsof of the the rock rock units units are are presented presented in in Table 11 and and the the generalized generalizedgeologic geologicrelationships relationships of of the Table the folded folded Paint Paint River River [ [ Group strata strata as near Iron River, Michigan as ititexists exists near Iron River, Michigan isisshown shown in in Figure Figure 3. 3. Ore. Ore. - The Riverton Riverton Iron Iron Formation Formationis is not all ore. ore. The not all thin—bedded siderite and chert. thin-bedded siderite and chert. It consists It consists primarily primarily of of Oreoccurs occursonly onlyin in structurally structurally favorable Ore favorable areas where oxidation has has enriched enriched the the iron content of and oxidation iron content areas where deep deep weathering weathering and rock. the rock. the For the the most mostpart, part, the the ore ore bodies bodiesare are irregular irregular in in shape, size For shape, size and attitude, attitude, but to lie lie ininthe the flanks flanks of of steeply steeply but tend tend to thetroughs troughs or or along along the and plunging synclines. synclines. plunging surface. surface. Theore ore is is usually The usually continuous continuous from from depth depth to to the thebedrock bedrock Laterally the grade into into unoxidized Laterally the ore ore may may grade unoxidized iron iron formation. formation. Most Most of the ore has has been beenextracted extracted from fran tabular 100 of the mined mined ore tabular bodies bodies that thatare are 1 0 -or 0 o rmore more feet hundredstotothousands thousands feetininvertical verticalor or lateral lateral feet thick thick and and hundreds of of feet within deposits deposits from soft directions. even within The ore ore may vary between may vary between and and even from aa soft directions. The hydrated form to very hard hematite and hydrated hematite ore. ore. Generally the ore is the ore is described direct—shipping, old high phosphorous phosphorous ore. ore. as a direct-shipping, old range, range, norr-besseiner, non-bessemer, high is enriched ore from from some ore some mines is enriched in inmanganese. manganese. The The �8 TABLE 11 TABLE Rock Rock Units in the Iron Iron River-Crystal River-Crystal Falls Falls District District Rock units in the Pleistocene Till, anl, sand Ordovician Sandstone, dolomIte 0-425 Unconfonnity 0-100 Unconlonnity p. O- Silica rock Unconformity t ,Z Metadiabsce and metagabbro Fortune Lakes State Stainbaugh FormatIon hIawatha mtowuh. Oraywacke OmywÂ¥ck lilvorton Iron-Fonnation C Character known only for lower pert of section. exposed i0 eastern part of district, where strata eo,nt of gray slate, striped slate, aidesitic slat., wacke, and poesiMe Iron-formation. Most of unit not exposed or drilled with district. chlorite 100 lm -Cherty - ~laminated m " rock . and i massive - ~ w ~ slate, - - some 4 graywackt Many ports strongly magnetic, u"w-m.r..sMassIve 0-100 w .. graywecke commonly siderttlc, and gray slate. Lowermost part commonly contains abundant risen fragments. MIUnooaJiMTHll, — — Minor unoonionnity Thin-bedded rock, mainly chert end iron-rich cerbonste where unoxidized. Includes some graphitic slate, also stiipnomeiane beds and megnetite-rich 10-SO) w-m - - Dunn Duan Creek C q nSlate Stew 400—i. u@-L 100 5M Badwatar n a d w f r Greenstone 0 - 0-IS, * 4000 - Ñaf^SSES-S^-Mdwme.--Ñ beds in eastern part of district. Host rock for ore bodies. In eastern part or district, unit consists of siltatone underlain by black cherry slate, sideritlc aiate, end chert-arbons.te rock. In western pert of district, unit is chiefly siltstona and slate. Uppermost part throughout district is graphitlo pyritio slate (Waisseca Pyritic Member). Massive chioritized meac volcanic rock, In part flows with ellIpsoidal structure, =-sswa-- in part tuffs and agglomerates. Some pert. strongly magnetic. *ma Mostly interbedded slate and graywacke; In southeastern part of area 'ois highly metamorphosed equivalents. Probably contains some IernszlnOelS Amass Formation I, SW L- PrincIpally martite slate, with layers of eherty iron-lorhsiezion. Locally Hemlock Formation -M 6 000+ ** Saunders Formation I. 000(1) Mainly msesiva dolomite. Exposed in only a law places in southern part of dis. flot known Massive metabessit, in part with agglomeratic end ellipsoidal sfructnres. Mi&- . Meselve cherty rock that probably repreanti allidfisd erosion surface on dolo' mite. 4. + S I Mantle men thn Se percent of area. Flat-lying remnants of sandstone and dolomite in the southwestern part of the area. Granite, medlssm-grained, massive; In eastern part of district only. Trachyte as sparse thin dikes. Chlcritlxed. massive. Abundant dikes and sill., a law stocks. Granite and traebyte a, — Rare dikes. Unaltered; magnetIc and insanely polarized. Diabace 0 Remarks Estimated thIckness (feet) Rock unit g Iron River—Crystal Falls district 8 W - Greenstone In the Brule River ate. a., beds in uppesmoet pert, 1968 James, & etal., p.17, From James, p. 17, 1968 strongly magnetic. Mostly massive metabesalt. locally with ellipsoidal struchlree. Contains Bird Iron-Bearing Member ( ft thick) l,-l 400 feet below the top of the for- mation. Both the greenstone and the Bird Member are locally etzengly magnetic. trict. Some layers are sstsgnetic. �9 C GLACIAL a TILl. Ie a GLACIAL SAND& GRAVEL Relationships of the Figure s of t h e Folded Folded Paint P a i n t River R i v e r Group ~ i ~ u r d3.' ~ . kGeneralized , & n e r a l i z eGeologic d Relation i Formations Fpmations in i n the t h e Iron I r o n River R i v e r District rict ru ,7 ": , -5s-1*f.. ... , <Â¥:' , "Â¥j.' ;" ¥ i^, v;: II~ i �10 l1 On On the the western western end end of of the the Menominee Menominee Range, Range, near near Iron Iron River, River, the the ore ore bodies bodies occur occur in in the the basal basal part part of of the the Riverton Riverton Iron Iron Formation. Formation. They They are are in in .- direct direct contact contact with with the the underlying underlying pyritic—graphitic pyritic-graphitic slate slate of of the the Wauseca matter member of of the theDunn Dunn Creek Creak Slate. Slate. Complex Complex folding folding of the the strata strata has has resulted resulted w- z : -., .. L in in great great variations variations of of the the attitudes attitudes of of the the ore ore bodies, bodies, from from flat—lying flat-lying to to vertical vertical and and often often overturned. overturned. . Exposure Exposure of of the the pyritic pyritic slate slate to to air a.8~ ~ As As aa consequence, consequence, acid acid drainage drainage has has been been an an j . 1 ' > < ' known known to to ignite ignite spontaneously. spontaneously. accompanying accompanying serious seriousproblem. problem. :,. È , , -23' ' . f , : I I I i ' ! I ij I However, However, near Crystal Crystal Falls, the iron ore bodies occur some distance above above the the base base of of the theiron ironformation formationalong along aa perched perched footwall. footwall. ~. --. :. has has resulted resulted in in mine mine fires fires and and even even surface surface piles of the the slate slate have been 8 jr, j As As aa result result the the pyritic pyritic slate slate may may be be present present in in both both the the hanging hanging wall wall and and footwall. footwall. --.1 The The perched perched condition member, condition is isdue due to tothe thepresence presenceof ofa aslaty slaty member, the theRaindrop Raindrop Slate, Slate, lower one third a]. which which according according to to James, James,et. s. & (1968) is in the loner third of the the iron formation. formation. iron This This relationship relationship is is shown shown in in Figure Figure 4. 4. -- As As aa result, result, acid acid drainage been serious problem with the mine drainage from from mining operations operations has not k e n a serious Crystal Falls. near Crystal Falls. near Glacial Glacial drift. drift. ". ., , .,- , '" % . . -^'ÑÑ~.'s^ '9 , -.. .*~ , <~ J Bedrock Range Bedrock exposures exposures are are rare rare along along the the West West t4enominee Menominee Range due due to to the the presence presence of of aa thick thick glacial glacial drift drift cover. cover. The The drift drift is is locally locally as as much as as 300 300 feet feet thick, thick, but 100 100 to to 200 200 feet feet thicknesses thicknesses are are more more common. common. much is exposed onlyinin aa few fewplaces places in in the the valley Near Iron Iron River, River, bedrock bedrock is exposed only valley of of Near the surface subsidence pits. Exposures the Iron IronRiver River and and at atthe thebottom bottom of of some some surface subsidence pits. Exwsures are also also present of the the Riverton Riverton Iron Iron Fonuation Formation are present along a l o q aa thinly thinlycovered covered of bedrock ridge which extends south south from fromCrystal Crystal Falls. Falls. bedrock ridge which extends The surface material material in mainly outwash The surface in the the Crystal CrystalFalls Fallsarea areais is mainly outwashsand sand In the the Iron Iron River River area, area, with terminal and with sualler smallerareas areasofof terminal andground groundmoraines. moraines. In the part, the the glacial glacial cover cover varies varies but but in in the the northern northern part, theMineral Mineral Hills Hills area, area, j J U �L L [ L L L C [ L L C U Figure 4.4. Stratigraphic g e o l o g i c r e l a t i o n s h i p i n the Crystal F a l l s d i s t r i c t . Figure Stratigraphic geologic relationship in the Crystal Falls district. �12 the the drift may be characterized as as poorly consolidated consolidated sands sands with with minor minor gravels gravels overlain overlain by by aa fairly fairly continuous continuous sheet sheet of of very very competent competent boulder boulder till. till. The the glacial glacial drift drift is is aa copious copious aquifer, aa condition condition which which has has greatly great - activity and problns with influenced influenced mining mining activity and has has resulted resulted in problems with mine mine dewatering dewatering drainage, drilling, and and drainage, drilling, shaft shaft sinking sinking and surface surface subsidence. subsidence. -j Mining Minii-q by Harvey Mellen, aa Iron Iron ore ore was was discovered discovered in in Iron Iron County County in in 1851 1851 by Harvey Mellen, an outcrop outcrop in in the governnent government surveyor. surveyor. The The find find was was made made from from an the Iron Iron River River valley mile south southofof the the present present site site of valley about about one one mile of the theCity City of ofIron IronRiver. River.-. ore was However, However, it itwas was nearly nearly 30 30 years years before before the the first firstiron iron ore wasmined. mined. Mining Mining did did not not start start until until 1882 1882 when rail rail lines lines were were brought brought to to both both the the Crystal Crystal Falls Falls and and tron Iron River River districts. districts. fall fall of of 1882. 1882. The The first first ore ore shipuents shipments were were made made in in the the J All All of of the the early early production production on on the the West West Menominee Menominee Range Range came came pit operations the bedrock bedrockwas wasatat or or near near the from from small small open open pit operations where where the the surface. surface. With With time, time, however, however, these thesemines mines became became deeper deeper and and were were developed developed activity into underground operations. Concurrent into underground operations. Concurrent exploration exploration and and drilling drilling activity resulted underthick thick glacial glacial resulted in inthe thediscovery discoveryof ofnew new ore ore bodies, bodies, many many under sunk through throughthe thedrift drift adjacent overburden. overburden. Vertical Vertical shafts shaftswere were sunk adjacent to to the the ore ore bodies bodies and and they theywere were developed developed as asunderground underground mines. mines. -- .Underground Underqround mining mining methods. methods. , * The vertical to the vertical to near near vertical verticaland andtabular tabularshape shape of ononthethe Menominee dictated the of the theore orebodies bodies Menominee Range Range dictated theunderground undergroundmining mining most connon methods included in the the district. district. The methods methods that that were were used used in The most connmn methods included top top slicing, slicing,block blockcaving, caving,sublevel sublevelcaving caving and and sublevel sublevel and and other other stoping stoping caving methods methodswere wereused usedonly only where wherethe the ore ore was to aa methods. The caving was amenable amenable to methods. The were employed employedin in the the more caving operation. Stoping Stoping methods methods were more competent competent ore ore caving operation. a result, As a result,many many surface surfacepits pitswhich whichassume assume the the shape shape bodies. bodies. As *... .*, . -.. ., .,.*-,*--. .,.,.**- '". ,. .: . ;*-- ,- -:,. ." ..~., %r.. .: . . ..~ ÈÃ..,.....*?- J , .2.,. .> ,L za*., �13 13 of the underlying ore ore body are are present above above the the mines mines that that employed employed caving caving and top top slicing slicing techniques. techniques. Large open stopes s t o p s were produced in in the the more competent competent ore ore bodies bodies and surface surface subsidence subsidence may or or may not not have have occurred. occurred. Nearly all all of of the the shafts shafts that that served served the the mines mines in in the the district district are are vertical. The only only inclined inclined shafts shafts are are those those in in several several pre—1900 pre-1900 mines, and and these these shafts shafts were were at at steep steep angles angles (70 (70to to 80 80 degrees). degrees). Ore. - required little The little if The ore ore mined was was direct direct shipping shipping and and required if any any processing. processing. processing processing For most mines, mines, size size reduction For most reduction and and screening were the the only only techniques one mine mine and and drying drying techniques employed. Ore washing was used at one was required required at at another another where where the the ore ore was was wet. wet. characteristic of mines. characteristic of ore ore from from aa n*znber number of mines. High manganese manganese content content was was a a ores from The ores from this this Range Range exhibited increasing increasing concentrations concentrations of silica, silica, phosphorous phosphorous and and sulfur sulfur near near the footwall footwall contact contact and and sometimes sometimes also also at at depth. depth. These impurities impurities limited limited mines mined, although depth to which some the depth some ore ore bodies were were mined, although several several of of the the mines to depths feet. operated to 2000 feet. operated depths of of over over 2000 Miningoperations operations and Mininq and production. production. The mine properties properties were 40—acre The mine were all all &acre the individual parcels of than. Most of of the individual properties properties or or them. Most parcels or or combinations combinations of Records show "forties" had own was under under singular singularownership. ownership. Records show a a "forties" hadits its ownname name and and was total of operations were wereat at one one time time or or another another active active in total ofabout about100 100 mining mining operations in in the district, ororWest Of these, these, 55 the district. district. Of 55 were in the Iron Iron River River district, West Iron Iron the Falls district district or County, and and 45 45 in in the Crystal Falls County, or east east Iron Iron County, County, the. the locations locations of which are are shown shown in in Figures Figures 55 and 6, 6, respectively. time passed, of the into groups As As time passed, many many of themines mines were were combined combined into groups and and operated as operated asaaccxnplex. complex. In like ownership In like fashion fashionthe theoriginally originallydiverse diverse ownershipwas was gradually consolidated into into holdings of aa half companies. gradually consolidated holdings of halfdozen dozen large largesteel steel companies. active from The from 1882 1882 until until 1979, shipping shipping aa The Iron River district was active total of 147 total 147 million million long long tons tons of of ore. ore. Records for Records for the the Crystal Crystal Falls Falls area area �14 J J J C... Cty z I- It R 33 W II r N 34 W I— — I— _1_ • .V —l' r' M,nrnau. —26 • •' L I at' RIVER -ar. Hdr1TXMBAUGH Ia' -—"n-i —i - A SIC,.- :±9 I '/ — —20——— y:nnajj tI1I ..j.21 j • — Il-tON A HI- — NUT ;TN Ii 1J Acts' — 7 • —r— \\_ z ft I- :1: . :— E :cl — ii "ri , 0t Li U 'efl*cL.. —-' td.n —— Li Li I Ifl..d., J -a— Li I :-i — —— -j.. LI . ç1 ____ Source: Lake Superior Iron Ores Second Edition S((urce: 1952 1952 Li. U -j Li IJ j Figure 5. Map of Mined Properties in the Iron River District u �1 0 m CD 0 CD x ri- -S C, -4. Ct 0. In LA -' -Il —I Oi rt .5 IA Cl 'C CD IA 0 0j C.) rt 0 CD rt 03 0 0- 03 • CD 03— fl (D C '1 'a Mine and map p l a t e l o c a t i o n s i n t h e C r y s t a l F a l l s d i s t r i c t , Menominee Iron tang< to CD -I. rrrrnrrrnrrr FT r r r r r F i g u r e 5. 1, �16 show 1882 through show 59 million long tons of ore shipped from 1882 through 1969. 1969. -. The The production from each of the mining mining operations operations in the two sub-districts sub—districts are listed in in Tables Tables 22 and and 3. 3!\, . k. .. s . .. ... , , ~ ~~ '\ <.'. 9 .. 9 .A # ' Previous Work and Acknowledgements Acknowledgements Previous a . , Experience done previously on closed mines in Experience gained from work done in Iron Iron County, Michigan provided not only much of the background for for this this research, research, but was was also the the basis for developing the concept of this this project; project; i.e., i.e., . >.. . I -.. . ..+-. Y~. ,- 'Â¥.."<- studing the deficiencies resulting in problems problaus from the deficiencies from past mine closures closures with with.-/ .. *: %., "\ .*;J..,, ~, ? ;: the intent nDre effective mine closing the intent of developing better and more closing procedures. procedures.,.. The first first study whena aspecial special legislative legislative appropriation studybegan began in in 1974 1974 when appropriation by by The ...-. ' ... _.4 ~, the State the Stateof ofMichigan Michigan channeled channeled funds funds through through the theGeological GeologicalSurvey Survey Division Division of the of Natural for aa basic of theDepartment Department of Natural Resources Resources for basic study studyon onproblems problems 4. ,.,,* ..: '>Â¥ *a. -. '*& ".. water drainage in the the Iron associated with associated withmine mine subsidence subsidence and and acid acid water drainage problems problems in Ir+q,'z, . ,/>:, A second second appropriation appropriation was to complete River district district ofofMichigan. River Michigan. A was made made to complete tthe hifi?;?'.',' > work. work. I. These efforts reports by Johnson Johnson and Frantti These efforts resulted in two reports Frantti (1976, (1976, . ' $,* * /f 1978) which addressed these two problems and identified practical methods by 1978) which by impacts reduced reduced by corrected or their their impacts which the the problems problems could either be corrected planning. planning. -J An important part of this work was the the production production of of aa detailed map showing showing the the location location and extent of mine openings openings in in the the district district and and the the - of critical critical areas areas — those identification of those areas where in—use in-use surface surface structures were structures were underlain underlain by by mine mine workings. Additional funds available to perform similar funds were made available similar work work on on the the mines Crystal Falls mines in in east east Iron Iron County in the the Crystal Falls district district as as reported reported by by Macibnald and Macmnald and Johnson Johnson (1983). (1983). ' 1978 work work an an additionalappropriation additional appropriation was Following the the initial 1978 provided to do more more detailed detailed studies on on an acid mine mine drainage drainage problem at the Dober Mine in in the the Iron Iron River district. Pumping was recommended recommended as as aa means means to abate acid drainage in the 1979 report prepared by Johnson. I I I I �, . t*.~ . . . TABLL II TABLE I1 17 IRON ORE SHIPMENTS IN IN MICHIGAN MICHIGAN T THROUGH R ON O RE SHIPMENTS HROUGH 3974 1974 MENOMINEE IRON MENOMINEE IRON RANGE RANGE . II rron o n County I RON R RII V VE ERR 0 OISTRICT, I ST R I CT • k IRON ------------------------------------------------------------' I I I ~ Mine Mine Gross Tons Tons Gross - .. Baker Baker Bates Bates Beta Beta . , ^^"t^S ^ .. -*> '<.,;i .id. Group Buck Group *.:.z 'i ; Cannon Cannon <, n' ~ :10!- Chlcagon Chicagon . . . ,.,~ 4i Cottreil C ottrell ;*:;. 4,054,666 4.054.666 1915—1947 27,156 27,156 1886—1891 - . l fit.^. . , . ; 21.653,499 21,653,499 1901—1962 12,033,884 12,033,884 1910—1963 6,623,320 6,623,320 1903—1937 1,234,339 1,234,339 1911—1922 52.148 52,148 19121914 75,134 75.134 1915—1916 8,197,014 8,'197,014 1911—1953 128.599 128,599 1913—1921 95,759 95,759 1920—1925 2,283,822 2,283.822 1913—1939 22,162,905 22,162,905 1893—1967 17,493,590 17,493,590 1915—1971 8,326,342 8,326,342 1907—1954 373,765 373,765 18821908 5,881,550 5,881,550 1882—1937 2,907.375 2.907.375 1914—1942 116,299 116.299 1879'1909 lI2,536,O3 2.Ss6.W 1931—1974 4,195,111 4,195.111 igiz—1956 , > ' ~ , .:+;. .> ..%*, ,. Davidson Group Davldson Group ? . ; 4, ,: . 4 Davidson No. No. 4 Davldson .Â¥<-i . . . . . :,3* ii*!.-;t Delta D elta Forbes Forbes Hiawatha No. No. 2 Hlawatha No. 1 and No. 1 Homer—Cardi ff—Mlnckler Homer-Cardiff-Mlnckler "^'^~. .^Â¥ : \ . . James James ¥¥  ."X . Nanalnio Nana lm Riverton R i v e r t o n Group Group k.'. - ., .&'*' .. .. s:&? Sherwood Sherwood :;* z  '. , .i'V ; ,. ., ,~, .. :..$.?" CC , 6'; Wauseca—Aronson Wauseca-Aronson w . ,.--. . . -'Â¥<¥È!_ ^MM* ...:I? , ., ' , ? 5 ' ?, ;;2?: Sheridan Sples—VirgU S pies-Vlrgll <%:,t .P1  . f.fÈ Rogers Rogers 1936 :, . .> Cortland Cort land 1909-1935 , " ." ~! ' Â¥;<-.:! '$8" 267,107 267.107 4,200 4.200 R.. " . ' (.?. Casplan Caspian Years o of Years f ShIpments Shlpmmnts .&. .;<Èi'& : Brule - - .. . ~. '>¥ *" .. 15,364,448 lSe364,448 ., 1926—1929, 1940-1972 Wickwire 128,869 128.869 1911—1917 Youngs 802.751 802.751 1905—1928 TOTAL Snuirrn Rood (1Q7R' ~* ~s%:^^?ft~<^^%::::;::'.-iaw~fii'a)aa~i~ 147,019,683 147,019,683 ' �TABLE Tn 18 'I CRYSTAL FALLS DISTRICT, iron County Gross Tons Mine Years of Shipments h3i;3 113.395 iSBg—igI4 Balkarjudson 4,441,799 18821935 Book Book 2,317,523 1943—1958 ArmenIa 1! Bristol—Youngstown 14,804.805 1890—1934, 1950—1969 Carpenter "Carpenter .2.735.452 1914—1928 ls4,i92 Cayia Carla i,44,ois 1882—1913 33,770 1883—1896 Dunn Ounn 2,208,511 1887—1915 Fortune Fortune Lake Lake 1,316,905 1953—1958 Great Great Western Western 2.296.739 1882—1925 Hemlock Hemlock 2,125.756 1891-1919 Hilltop HI 1 1 top 98,202 1899—1919 143,117 1890—1914. Hops 28,530 1892—1903 KImball 35,757 1907—1915 558,524 18891910 Lawrence Lawrence 6,963 1920-1956 Lee Peck Lee Peck 2,844 1892 Falls Crystal Crystal Falls Delphic Delphic """' 1954 Holllster Kolllster Lanont 241,627 1891—1909 1,462,504 1890—1913 30,289 1909-1913 2,101,381 1916—1935 Paint paint River 382.078 1882—1913 Porter Porter 733,327 1916—1927 Rayenna—Prlckett Ravenna-Prlckett 635,227 191N1917, 19401943 RIchards Richards 5314,448 1913—1921 8,203 1887-1890 13,523,289 1882—1963 Lincoln Lincoln Mansfield Mansf leld McDonald Odgers Odgers j U LI South South Mastodon Hastodon Tobln—Columbia-Monongahela-Genesce Tobln-Columbia-Honongahela-Genesee 1) 3,417,030 Warner Warner cnnnrr. "Of. Li fl,-,,-'A A " .. (1O7IZ\ /,"7C! TOTAL TOTAL 58,727,872 1915—1934, 1951—1958 �<I' 19 From U.S. Vom 1978 through 1982 the U .S. Bureau of Mines funded funded aa study study of of the the closing of the Sherwood Mine Mine which which was was undertaken undertaken by by an an interdisciplinary team of investigators at Michigan Michigan Technological Technological University. Subsidence Subsidence monitoring performed performed during during this this project project showed showed that four different different monitoring subsidence mechanisms were active subsidence mechanisms active while while the the mine mine flooded. flooded. Hydraulically triggered subsidence subsidence and triggered and piping—induced piping-induced subsidence subsidencewere weretwo twonew newmechanisms mechanisms whichwere wereobserved observedtotohave havewider widerapplication. application. which This work has been Ttlis work has been prepared prepared as reports 1983) as reportsby by Johnson Johnson and and Frantti Frantti(1982, (1982, 1983)and andJohnson Johnsonand andHodek Hodek (1983). (1983). Although this report report deals deals largely largely with mine related problems on the although this the problemswith withmine minesubsidence, subsidence,drainage drainageand andshaft shaft seals seals Menominee Range; Flange; problems Investigations of have cropped croppedupupininother other mining miningdistricts districts ininMichigan. have Michigan. Investigations of miningdistricts districts have occurrences in both iron and copper mining these have provided provided these occurrences and the experience experience gained gained from them than have have materially materially additional insights and additional aided this this work. work. Some of of the the ideas developed developed from these efforts were Some incorporated in in aa paper paper entitled entitled "Hydrologic "Hydrologic Considerations Considerations in Mine Mine by Johnson Closings" by Closings" Johnson (1983) (1983) This wouldnot nothave havebeen beenpossible possiblewithout without the the help help and %is work work would and contributions of others associated and industry. industry. contributions ofmany many others associated with with both bothgovernment government and Reed, Robert Reed, Several of have made madeoutstanding outstandingcontributions contributions are: are: Robert Several of those those who who have Bal of Aistine of of the Geological Geological Survey Division, and Joseph Joseph Bal and Jack and Jack Van Van Alstine the Water Resources Division Division of of the of Natural Natural the Water Resources the Michigan Michigan Department Department of Rhoadesof of the the Resources;Alice AliceAllen Allen(ret) (ret),, Jacob (ret),,and Jacob Frank Frank (ret) and Charles Rhoades Resources; Hiltunen, Iron, of Mines; Mines; Peter Peter Korach, Korach, Reino Reino Laine Lame and U.S. U .S. Bureau of and Sub Sulo Hiltunen, Iron, Edwards County Mine Mine Inspectors, respectively; Robert Robert Edwards Gogebic and Houghton County Gogebic (ret) ofofInland Mining (ret) of of Cleveland Boyurn (ret) Cleveland (ret) InlandSteel Steel MiningCompany Company and and Burton Burton Boyum Cliffs Iron Mining Cliffs Iron MiningCompany. Company. Maclbnald of of the Larry MacDonald the Institute Instituteof ofMineral Mineral Larry �20 ! I UI mention Research at at Michigan Technological Universitydeserves deserves spial special mentionfor for Research TechnoliCal University his invaluable invaluable assistance assistance in in the the field field on on all all of of these these projects projects and and also also his his his professional professional contributions contributions to to this thisresearch. research. ,'>L;, i.., ,.~. ., .-Sp ,... '. m , .?. rtC,.Â¥' 1' I.' I -I J j �21 MINE ION TO ME RELATED RELATEDPROBLE2IS PROBLEMS— INTRODUCT 1TRODUCTION TO CASE CASE HISTORIES HISTORI -.., :iz. .:;z . :*,:,.$yc ., ~ p*,,,.;> --. Three basic types and abandoned typeoof problems w.v^blems associated associatedwith withclosed closed and abandoned 3 ; underground minesare areconsidered consideredininthis this report; iderground mines report;1) 1)mine minesubsidence subsidence2) 2)mine mine shafts but drainage -ainaqe and and 3) 3) the the safety safety of of surface surface openings, openings, mainly mainly shafts but also also .. topics isiscomprised including Each of of these these major major topics comprised of of several several icluding pits. pits. Each . t.subdivisions. ibdivisions. These These topics topics and and their their subdivisions subdivisions are are identified identified and and - . .. CK briefly .iefly discussed in in this this section which is is introductory introductory to to the the case case ,.. .,* .. - . . histories stories which which follow. follow. . . 2 . 7 ' : .,~ '. ;,A \, .,: 2...>+.. , .>. \..- *> ,. < f c*:,- . a':<; .,.Â¥-,' **" :..,-*-+.l-' i *.r.. , , Mine Mine Subsidence Subsidence . . u.i- .> ' * C -j < ' ,$ , - x , , *:&X"A*z.. ? :, -",-J: Three Biree categories categoriesof ofmine minesubsidence subsidencehave havebeen been recognized recognizedon onthe theWest West Menominee Menominee Iron Iron Range: Range: 1) 1) subsidence subsidence that that occurs occurs during during mining mining activity activity 2) 2) .aft!- subsidence ibsidence occurring occurring shortly shortly after the mine is is closed and while it is flooding flooding and and 3) 3) longer longer term term subsidence. subsidence. :-:, 7.1 For For the the most part, the the first first is related category of of subsidence subsidence is related to to the the use use of underground underground mining mining methods methods 5 category techniques include include top top slicing These techniques slicing&a 2.. that that resulted resulted in insurface surfacedisturbance. disturbance. These id caving caving mining mining methods. methods. and the ie extraction extraction of of ore. ore. With With these these techniques techniques the the surface surface subsides subsides with withe" 4:. In In top top slicing the the subsidence subsidence is is almost almost immediate imnediate because because mining is is started started near near the the surface. surface. With With the the caving caving methods, methods, ' *d :,.~..& surface tauporarily delayed delayed until the fracture fracture zone surface subsidence subsidence is often temporarily zone~.:~-.;.'.*,,~J.::. However, this type type of However, this of subsidence subsidence usually usually poses poses no no *.! problems as its its occurrence .:* %: problems as occurrence is isexpected expected and and the the surface surface opening opening conforms conforms Consequently, this this n .hi: quite closely closely to to the the shape shape of of the the ore ore extraction extraction area. area. Consequently, quite reaches reaches the the surface. surface. type subsidence iis notof ofprimary primaryconcern concerntoto this rk. This the type of subsidence s not this wrk. This leaves leaves .the.'&?-:"' remaining remaining tsn two categories categories of subsidence; 1) short short tern term subsidence subsidence which which occurs :curs while while the the mine mine floods floods and and 2) 2) longer longer term term subsidence. subsidence. categories itegories will will be be discussed discussed separately. separately. !>.!:ST..> . Each of these Bach of these, . ?e �22 Short Short term term subsidence. subsidence. Although it may seem initially illy that that the the only only distinction distinction between between subsidence subsidence occurring occurring during during the the period period of of mine mine flooding flooding j and at sane later date of timing, this is and subsidence subsidence that that occurs occurs at some later date is is one one of timing, this isnot not necessarily of aa mine cause profound profound changes changes in in the necessarily the the case. case. Flooding Flooding of mine may may cause the >,., mine mine environment environment that that may either trigger or result result in in subsidence subsidence activity. activity. In In fact, fact, the the period of of flooding flooding is is probably probably the the most critical critical period period in in which which subsidence subsidence may may occur. occur. friction friction between between rock rock masses. masses. .~ 3 . .. .~... ,.,. Water entering the mine as it floods floods can reduce - Frictional Frictional forces forces that that held held faulted faulted or or ,Â¥',., >'-' jointed jointed rock rock masses masses in in position position may becane become reduced reduced to to the the point point where where adjustments adjustments take take place. place. . "- '. '?'.I. -.' '... This often be enhanced This mechanism mechanism may may often enhanced by by processes processesA:~c*G3 --..-.-- that operating. Minerals in these that took took place place when when the the mine mine was was operating. Minerals in these planes planes of of weakness mayhave havebecome becanealtered alteredbybyexposure exposuretotoair air and in the and humidity humidity in the weakness may mine. are expandable expandableclay clayminerals minerals and and sulfides sulf ides and and other other minerals mine. Examples Examples are minerals J J .... .%.# ,,? ,, susceptible certain conditions conditions these susceptibleto tochemical chemicalchanges. changes. Under Under certain these reactions reactions may cause expansion expansionof of susceptible susceptible minerals and may cause minerals within withinplanes planesofofweakness weaknessand result mine resultin inspalling spallingand androck rockmass mass failure failureadjacent adjacenttotothe the mineopenings. openings Elevated Elevated hydraulic ran introduced introduced water water into into the planes of hydraulic pressures pressures ffrom of weakness weakness may may also also cause cause this this type type of of failure. failure. &:. -.... r:x ... 5 .. .n,,. : w : Secondly, Secondly, water has has mass mass and as as this this mass mass is is redistributed redistributed during during flooding, flooding, differential differential loading loading of of rock rock and and soil soil masses masses may may occur. occur. If If a2 delicate delicate equilibrium equilibrium exists exists between between these these masses masses and is is upset upset subsidence subsidence may mi : I :.' ' be be the the result. result. Steeply Steeply dipping dipping shear shear zones zones along along which which previous previous subsidence subsidence has susceptible to causedby bydifferenti; differential has occurred occurred are are most most susceptible tofurther furthermovement movement caused xs.: u8.3 loading theloss lossof of friction friction by loading during during flooding. flooding. Obviously Obviously the by the thei.ntrcx~ti< . . introduction - -< of be aa mitigating mitigating factor. of water water into into these these zones zones can can be factor. a~.j ::-.* . .' ?. .~~?K'ss"-; . . Thirdly, inflow into into the the mine mine through through previously previously subsided subsided areas, thirdly, water water inflow shafts and other other openings openings to to the the surface surfacemay may wash wash unconsolidated unconsolidated overburden overburden?, .:, shafts and I1 I ! ..,, .$& t. 1 i I I �23 L (sand, gravel, silt, silt, etc.) etc.) into into the the mine mine void. void. (sand, This can result This can result in in surface surface (overburden) adjustments that may be be quite (overburden) adjustments quite extensive. extensive. [ Fourthly, under flooding, piping special of mine special conditions conditions of mine flooding, piping activity activitymay may occur. occur. Piping Piping . . * .. involves of aa cavity unconsolidated involves the the developnent developnent of cavityor orvoid voidinin unconsolidatedoverburden overburden .,. . above the bedrock bedrockinterface interface as as aa result bybygroundwater above the resultofofsand sandtransport transport groundwater . flow flow into into the themine. mine. Laboratory Laboratory experiments experiments on on the thepiping pipingmechanism mechanism were were reported and Hodek Hodek(1983) (1983)and andpiping pipinginduced inducedsubsidence subsidenceactivity activity,, .-. reported by by Johnson Johnson and at documentedbybythem thanand andby byJohnson Johnsonand and Frantti Frantti atthe theShers.ood Sherwood Mine Mine was was documented (l983a, (1983a, l983b). 1983b) . mine A fifth fifthmechanism mechanism for for triggering triggering minesubsidence subsidencemay may occur occurwhen when aa mine mine. . becomes flooded. Great becomes flooded. Great hydraulic hydraulic forces forces can can be be generated generated within within aa flooded flo~ded~,>:~:,~> mine if sudden water displacement displacementoccurs occursfrom fromthe thefall fall of of surface material mine if sudden water surface material surging into into the the mine mine or or compression compression occurs occursby by rock rockmass massmovanent. movement. TThe h e surging water can or reactivate in areas areas of water can trigger triggernew new subsidence subsidence or reactivatemovement movement in of previous previ04$&,~~~ documentedcase caseofofthis this type type of of occurrence is described A documented occurrence is described by by subsidence. subsidence. A Johnson andFrantti Frantti (1983a, (1983a,1983b) 1983b)and andisisincluded includedininthis this report report as as aa case Johnson and case ,-... history. history. . .* category includes includes all all subsidence This category subsidence that that occurs occurs >. Long term subsidence. subsidence. This Long term It isisa avery verybroad broad category category in in ; following the flooding following the flooding of ofa amine minecomplex. complex. It ...a " ' ' , \ " ' L L L 6t.,% the the sense sense that that no no limit limitisisplaced placedon onthe theanount amount of of time time required required for for :.,? E.: .*:,*:. , subsidence to occur. subsidence to occur .. ::. .,.-w The mechanisms wDrk createthis thistype typeof of subsidence subsidence include include the the The mechanisms atatwork to to create ever of ever present present force force of of gravity, gravity,long longtern termchemical chemicaland and physical physicalweathering weathering of minerals ofof earth tremors of natural or man—made minerals and and the the triggering triggeringeffect effect earth tremors of natural or man-made , latter could The latter couldinclude includeshock shockwaves waves caused caused by by explosion explosion or or tremors t~f3Km-s origin. origin. The If subsidence occurs in in aa flooded subsidence occurs flooded -. caused by heavy heavymachinery machineryorortraffic. traffic. If caused by ,. . ,. ~.&..-F. ,~ , %<. ~ mine, the resulting resulting hydraulic disruptions could trigger additional mine, the . ..* hydraulic. disruptions -. . could . trigger additi~nal,~.;, . .. ..,,.,, , . . I ,. �24 subsidence subsidence. %. . ..,!. Gradual of rock the roofs roofs of of near Gradual sloughing sloughing of rock from from the near surface surface stopes stopes can can CJXU& s:..I , ; z., ,. ..% result of the the mined minedvoid voiduntil untilthe thesurface surfacefails. fails. resultin inthe theupward upward migration migration of .< .. .., , 7: This at work This is isprobably probablythe themost mostprevalent prevalentmechanism mechanism at work in in long long term term subsidence. delayed effect effect of and its its subsidence. The The delayed of long long term term subsidence subsidence and unpredictability unpredictability places places this thiscategory category of ofsubsidence subsidence into into one one of of great great .i.^Sy concern. concern. T .^ Mine Drainage Drainage Two typesor or sources sources of of acid drainage are Two types acid mine mine drainage are recognized recognized in in the theWest West Menominee Range;1)1)acid acidwater water from from underground undergroundsources' sources'and and2) 2) surface surface M e m i n e e Range; ^.*-?fia';.-:fc -*i- .> ,. sources sources of of acid acid drainage. drainage.', Acid drainage is is prevalent western part part or Acid drainage prevalent only only in in the theextreme extreme western or Iron Iron +f of the River West Menominee River area areaofofthe the West Menominee Range. Range. It It occurs occurs there there because because of the :". o s close the source ofof thethe acid —— close proximity proximity of of the theore oretoto the source acid - the the pyritic pyriticWauseca Wausecax ofthe the pyrite pyrite in menber of the Creekslate. slate. Oxidation Oxidation of in slate slateexposed exposed in in member of the Dunn Dunn Creek thesesoluble soluble sulfates sulfates - . , the solubleferrous ferrous sulfates. sulfates. When the mines mines produced produced soluble When these were dissolved in in water, were dissolved water, sulfuric sulfuricacid acidwas wasformed. formed. . When operating,many manyofofthe themines minesininthe the Iron Iron River River district pumped When operating, district pimped ~ ~ < s~ L acid highlyvisible visible pollution pollution as acid waters waters into into the the Iron Iron River River causing causing highly as the the acid acid became neutralized and and the the dissolved dissolved iron thenprecipitated precipitated toto became neutralized iron and and aluminum aluminum then form referred to as "yellow form insoluble insolublecompounds compounds referred tocoirinonly comnonly as "yellow boy". boy". < * y%, :.EL^' With the cessation cessation of of mining it was believed that that the was believed the acid acid drainage drainage With the mining it aciddrainage drainagereoccurred reoccurredat at several problem wouldcease ceaseto to exist. exist. However, problem would However, acid several . - - . of theyflooded, flooded,and andare areaa continual continual source source of of acid of the themines mines when when they acid drainage. drainage. Surface piles of of sulfur blackslate slate are are also Surface piles sulfur bearing bearing black also the the source source for for 3 groundwaters leach leach acid and near—surface near-surface groundwaters acid.'. Surface water water and some acid drainage. drainage. Surface some acid fran extensive black slate slate piles whichisissituated situated in in pilesatatone on mine complex lex which .. ,.. �25 the the Iron IronRiver River valley. valley. The The acid acid water water flows flows aa short short distance distance before before entering entering the the Iron Iron River River creating creating additional additional pollution. pollution. Case Case histories histories of of both both of of these these occurrences occurrences are are presented presented in in this thisreport. report. Safety Safetyof of Surface SurfaceOpenings Openinqs This This category category includes includes all all surface surface openings openingsresulting resulting either either directly directly mining activity (shafts, raises, open pits) or indirectly (subsidence pits, pits,caved Cavedground). ground). It Itdeserves deservesspecial specialattention attentionbecause because of of the thegreat great threat The threat threatisismagnified magnified threatthat thatthese theseopenings openings present present to to the thepublic. public. The because of the the attractiveness because of attractiveness of of these these areas areas to tothe thepublic publicand and their theirgeneral general lack for their lack of ofunderstanding understanding or or concern concern for theirdanger. danger. Injuries the fall fall of Injuriesor ordeaths deaths occurring occurring from from the of individuals, individuals,especially especially from from mining activity (shafts, raises, open pits) or indirectly (subsidence shaft or children, children, into into an an inadequately inadequately protected protected mine mine shaft or surface surfacepit pitprobably probably creates creates more more intense intense ill ill will will and and negative negativefeelings feelingstoward towardthe themining mining industry industry than than any any of of the the other other categories. categories. This srse This threat threat is is made worse because real attraction attraction for for the thegeneral generalpublic. public. because these these areas areas provide provide aa real Consequently, Consequently, it it is is not not out out of of place place to to give give serious seriousthought thoughtand and consideration of effective effective and consideration towards towards methods methods of and safe safe protection. protection. Case histories illustrate thethe various types ofof surface openings Case histories illustrate various types surface openingswhich which were originally inadequate, time have were originally inadequate, or orthroah through time havebecome become so. so. Included Included in in the the examples are shaft shaft openings that are exanples are openings that that are areuncapped, uncapped, some some that areinadequately inadequately capped, several that but have have deteriorated deteriorated either capped, and and several that were were well well capped capped but either because of aa poor selection of of material because of poor selection material or or engineering engineering that that did did not not take take into the eventual eventualdeterioration deteriorationthat thatwould uld take into account account the take place. place. , AA distinction made shaft seals distinctionisis made between between shaft sealsininbedrock bedrock and and surface surfacecaps. caps. Although the problems of providing and providing providing Although the problems of providing adequate adequate fencing fencing and maintenance are not not heavily theyare are obviously obviously important, important, as as is maintenance are heavily emphasized emphasized they is the theneed need of ofproviding providing surface surface markers markers for for identification identification and and aa means means to to -.&cate theshaft shaftopenings. openings ...,,'.~. , locate the .*~. %!. �26 CASE CASEHISTORIES HISTORIES * <..*. :-- . Short ShortTerm TermSubsidence SubsidenceEffects Effects .. ,~ .*.: 7.; >. In In the theprevious previoussection, section,short short term term subsidence subsidencewas wasdefined definedas asthose thosi subsidence subsidenceevents eventsthat thatoccurred occurred during duringthe thetime timerequired requiredfor fora amine mineto to well-docianented case casehistory historyinvolving involvingeach eachof ofthe thefive fivesubsidence subsidence flood. AA well—documented flood. mechanisms mechanismswhich whichwere wereproposed proposed to tobe be active activeduring duringmine mineflooding floodingwas was Sherwood developed developed atatthe the SherwoodMine. Mine. These included; 1)1)water These mechanisms mechanisms included; water lubrication blocks 3) 3) overburden waterloading loadingofoffault fault blocks overburden lubricationofofshear shearplanes planes2)2)water washing resulting in in shear shear failure failureof of sands sands4)4) piping piping produced produced cavities cavities in in washing resulting the theoverburden overburdenand and 5) 5)hydraulically hydraulicallytriggered triggeredsubsidence. subsidence. TheSherwood SherwoodMine Mineis islocated locatedabout aboutone onemile milenorth northofofthe theCity Cityof of Setting. Setting. The The mine mine opened opened in in 1943 1943 and and was was shut shut down down in in Iron 7). The Iron River River (see (seeFigure Figure7). 1978. 1978. Total Total shipments shipmentsthrough through 1978 1978 including including some someore oreextracted extractedfrom froman an adjoining adjoining property property during during the the1930's 1930's totaled totaled13.7 13.7 million million long long tons tons of of ore. ore. Sherwood Sub level level stoping stopingwas wasthe theonly onlymining miningmethod method used usedatatthe the Sherwood Sub The main main ore ore body body was was served served by by aa vertical vertical shaft shaftdepth depth of of 1625 1625feet. feet. Mine. The Mine. The The near near vertical, vertical, tabular tabular ore ore body body had had major major development developenton onthe the400, 400,800, 800, 1000, 1200, 1200, 1425 1425 and and 1625 1625 levels levels(Figure (Figure8). 8). 1000, present at at the theSherwood Sherwood Mine. Mine. present Thick Thick glacial glacial overburden overburdenis is The The thickness thickness varies varies because because of of 30-foot irregularities in inthe thebedrock bedrock surface, surface, but but averages averages 150 150feet. feet. AA 30—foot irregularities well consolidated glacial till overlies poorly consolidated sands These relationships relationshipsare areshown shown in in Figure Figure 9. 9. with with lesser lessergravels. gravels. These connected The Mineisispart part of of aa large connected Itisis The Sherwood Sherwood Mine largecomplex complex of ofmines. mines. It with on the the east with aa shallower shallower mine, mine, the theVirgil—Spies Virgil-Spies on east and and aadeeper deepermine, mine, the the thick, thick, well consolidated glacial till overlies poorly consolidated sands Although these these mines mines are are interconnected interconnectedand and Homer—Wauseca onthe the west. Homer-Wauseca on west. Although , . . would flood as would flood as one, one, they theywere were independently independently operated operated by by other othermining mining down —— hadbeen beenshut shut downearlier earlier -- the the Both of of these theseadjacent adjacentmines mineshad companies. Both companies. ;' , '.. E > z . ~ . ~ & ; ; ~ : : : ~ , . ~ ~ : : h : ~ . . ? :~' r~ * &,:, T*.." 2,. ..Z$ ~::+ :..,- ;..; ;,,. . . ,- .-r> *- �27 iron Iron - / - County County I I I I $ W o t Menooilnee Ran00 \ \ 'I' Shetwood Mine 4 Homer— Virgil- Spies Wauseca MacDonald Annex City of Li 114 mile MtneComplex Complex theI riron Rtver DDtstrtct Figure Figure 7. 7. Locatton Location of o f the theSherwood Sherwood Mime t n tn the o n Rtver tstrtct of ofNorthern NorthernMichigan Michtgan �'1 -a. XL,"-, in CD •1 C In Figure 8. C. C) (DID c-t a 0 0 X It — 0 -I. i4CD gJ - -aid, CD ZCD -a. fl LL L2 Lfl • c '<<0 -a 001) w o r am CD rtCD on -Sw-I .1.0J 0 -4)9 0& Isometric View o f t h e Sherwood Mine Shaft and Levels i n R e l a t i o n t o the Main Ore Body. LL L 0 -.4 01 -a LL L L L L -2 L 14 4 •1• L 'p LL L L U 'PS LL �29 L -ro:Th -. - - - L L - • C 'a — • d 20—30 -r Glacial flu C a 70-80 Sand and grays • a 0 0 S a — - - we I, "a '•- V N. V 05*00k •_ 'we Figure Figure 9. 9. - V V Cnd arsa Otbadroct Generalized att the Sherwood Generalized Profile P r o f i l e of of Glacial G l a c i a l Overburden a Sherwood Mine in i n the the East E a s t Pit Pit '3 �30 Virgil—Spies Virgil-Spies in in the the 1950's 1950's and and the the Homer—Wauseca Homer-Wauseca in in 1968. 1968. The The locations locations of of these these adjoining adjoining mines mines is is shown shown in in Figure Figure 7. 7. The has had The Sherwood Sherwood Mine Mine has had aa rather rather long long history history of of subsidence. subsidence. J Major Major thethe Sherwood stopes stopes in in the theupper upper levels levelsofof Sherwood Mine Mine on on both both the the east eastand andwest west margins property had had caved cavedto to the the surface. These cave—ins cave-ins margins of of the theSherwood Sherwood property surface. These resulted overburden. resulted in in large largedeep deep surface surface pits pits in inthe thethick thickglacial glacial overburden. The The West Pit caved in February 1956and andthe theEast EastPit Pit caved cavedto to the the surface surface in in West Pit caved In February 1956 pit locations August s aa w u s t 1964. 1964. The The pit locationsare areshown shown in in Figure Figure 10. 10. Also Also shown shown iis small Pits, known asthe the Central Central Pit. Pit. small pit pit located locatedbetween between the the East East and and West West Pits, known as This diameterpit pit appeared suddenly in in February This 100—foot 100-foot diameter appeared suddenly February of of 1967 1967 following following an an explosive explosive blast blastused used to tobreak breakup upconsolidated consolidatedoverburden overburden being being used used for for stope The blast blast apparently apparently triggered triggered the the collapse collapse of of aa stope filling filling operations. operations. The soil soil capping capping over over an an existing existing cavity cavity in in the the overburden. overburden. This this void had had probably probably been been formed Conned either either by by piping piping or or running running sands, sands, but buta aplug—type plug-type steeply failure A steeply failureof ofa ashallow shallowstope stopemay may also alsohave have been been responsible. responsible. A dipping Sherwood dipping (700 (70Âsouth) south)east—west east-west fracture fracturedeveloped developedininthe the SherwoodMine Mine during during November 1966the thefracture fracture was was evident evident on By November ofof1966 on the the the Spring Spring of of1966. 1966. By the The maximum maximum levelsplus plus on on the the surface. 400, 800, 800, 1000 1000 and and 1200—foot 1200-foot levels surface. The 400, displacement displacement was was three three feet feet on on the the 1000—foot 1000-foot level level as as observed observed in in aa major major drift. crosscut crosscut drift. systems installed installed at at the the Monitoring Monitoring of of post—mining post-mining subsidence. subsidence. Monitoring systems Sherwood Sherwood Mine Mine prior prior to to shut shut down down included included borehole borehole extensometers extensometers in in the the steeply dipping dipping fault fault zone zone within within the themine, mine, surface surface and and underground underground acoustic acoustic steeply emission emission sensors, aa grid of surface surface subsidence subsidence monuments monuments aa piezometer piezometer network network to to monitor monitor water water rise rise in in the the overburden overburden and and water water level level measuring measuring devices to to monitor monitor the the flooding flooding of of the themine minecomplex. complex. devices When the pumps pumpswere wereshut shut down downin in 1978, 1978, the the mine to When the mine complex complex began began to I �r ri West w e i t Pit Pit r r r East East PIt PI^ SHERWOOD SHERWOODMINE MINE PROPERTY PROPERTY PIt Central 4a Sherwood Sherwood Shaft Shaft r— Figure Figure10. 10. Location LocationofoSubsidence f SubsidencePits P i t at s athe t the Sherwood Sherwood Mine Mine Shaft Homer—Wauseca Pumpin9 Pond MINE PROPERTY HOMER—WAUSECA ri ri n n ri 0 I 0 meters 150 teat 500 SCALE Shaft 4 VIrgil VIRGIL VIRGILMINE MINEPROPERTY PROPERTY — �32 flood. flood. The The mine mine was was flooded flooded by by mid—1981, mid-1981, in in aa period period of of 2.75 2.75 years. years. About one one more more year year was was required required for for groundwater groundwater levels levels in in the the overburden overburden to to equilibrate. equilibrate. Subsidence. Subsidence. j During the the time time required required for for the the Shersaod Sherwood Mine Mine complex complex to to flood, three different major subsidence three different subsidence events events occurred occurred which which serve serve to to illustrate mechanians ascribed to to short short term term post—mining post-mining illustrate the the five five subsidence subsidence mechanisms subsidence. subsidence. Included Included were 1) 1) subsidence subsidence in the the West Pit Pit area area which which represents represents shear shear failure failure of of overburden overburden sands sands as as aa result result of of water water flow flow into into the the mine, 2) 2) broad broad surface surface subsidence subsidence as as aa result result of of rock rock mass mass movanent movement from from water water loading loading and and shear shear plane plane lubrication lubrication and and 3) 3) hydraulically hydraulically triggered triggered subsidence subsidence which which in in turn turn caused caused aa previously previously Conned formed soil soil cavity cavity to to suddenly suddenly develope develop into into aa subsidence subsidence pit pit with with the the collapse collapse of of the the protective protective capping. capping. This This cavity cavity is is believed believed to to have have been been caused caused by by piping piping of of overburden overburden sands sands into into aa mine mine stope. stope. Each of these events is described separately. these events is described separately. Shear Shear failure failure in in overburden overburden sands. sands. summer 1979, a in late sunnier Beginning in little little more than than one year following following shut shut down of the the mine, mine, aa snall small subsidence developed in sand sand fill fillin in the the West West Pit. Pit. subsidence pit developed 30 feet feet in in diameter diameter and and 10 10 feet feet deep. deep. circular, about 30 circular, The The pit was was one half A month and one the pit larger. later, later, additional additional subsidence subsidence caused caused the pittotobecome become much much larger. It now It now Several was about 100 feet inindiameter deep andand cone—shaped. was about 100 feet diameterand and40 40feet feet deep cone-shaped. Several days underwent was enlarged enlarged days later laterthe thepit pit underwentanother anothersubsidence subsidenceadjustment adjustmentand andwas Figures 11, to 200 60 feet feet deep. to 200 feet feet in indiameter diameter and and about about 60 deep. Figures 11, 12 12 and and 13 13 illustrate illustratethese thesethree threesubsidence subsidence events. events. It It is believed that following the rise of water in in the the overburden overburden above above thorugh the the pit the Sherwood Mine Mine that that water water flow flow into into the the mine mine thorugh pitarea areawashed washed the Sherwod into the filled stopes sand sand into the incompletely incompletely filled stopesbelow. below. "plug" "plug" consisting consisting of of j j from the the This loss loss of This of sand from previously washed washedinto intothe the opening openingin in the the top top of of sands sands previously UI �33 Figure i. Photograph of initial subsidence in West Pit area taken on September 7, 1979. The subsidence pit is about 30 feet in diameter and ten feet deep. The bent pipe in the foreground is an old well casing installed in the 1940's. Photograph taken with a 50 rim lens on a 35 m camera, looking southeast. Cave first observed August 31 1979. , Figure 12. Photograph of enlarged subsidence pit which caved on October 14, 1979. The resulting pit is about 100 feet in diameter and 60 feet deep. Note old well casing pipe in foreground; also cribbing and bent over 30—inch pipe in background at upper left, formerly used for sand filling stopes under this area. Looking southeast, photo taken with 35 rim camera eouiooed with a 50 rim lens. �U u 'I j j aa Greatly G r e a t l y enlarged enl-. -.ad subsidence subsiucSn.e pit p i t which which caved caved on on October October 19, 19, 1979. 1979. The The pit p i t is i s about about 200 200 feet feet in i n diameter diameter and and 100 100 feet f e e t deep. deep. Shear Shear rock r o c k walls w a l l s are a r e exposed exposed on on the t h e west west and and north n o r t h walls w a l l s of o f the t h e pit. pit. Note t h e far f a r right r i g h t and sand filling f i l l i n g pipe pipe Note the t h e old o l d well w e l l casing on the and This and cribbing c r i b b i n g on on the t h e left. left. This cave cave occurred o c c u r r e d on on October October 19, 19, 1979. 1979. View with 28 mm mm wide wide angle angle i t h a 28 View looking l o o k i n g north. n o r t h . Photograph taken w lens l e n s on on aa 35 35nun mm camera. camera. —a j Li U j U - — -Tyt tt:. S' - bb 4-'sc. t Close View is i g northwest. northwest. Close up ul of the October October 19, 19, 1979 1979 cave. cave. i s looking 1c Note p i p e in i n near foreground foreground and and old old Note 30-inch 30-inch diameter diameter sand sand fill fillpipe well 28 mm mm wide wide Photograph taken taken with w i t h aa 28 well casing castng in i n background. background. Photograph angle angle lens, lens, 35 35 mm mm camera. camera. Figure 13. Enlarged West Pit After October 19, 1979 Subsidence Event U U U j �35 the series of the caved caved stope, stope, caused caused the the observed observed series ofsubsidence subsidence events. events. The The circular circularshape shape of of the theopening, opening, the the tension tension fractures fracturesaround aroundthe theopening openingand and the the resulting resulting cone—shaped cone-shaped void all all suggest suggest that that shear shear failure failure from from gravity gravity loading loading of of the the unstable unstable sand sand mass mass best best explains explains this this subsidence subsidence occurrence. occurrence. Surface Surface subsidence subsidence resulting resulting from from rock rock mass mass movement. movement. Leveling Leveling surveys surveys of of aa 47—movement 47-movement grid grid were were performed performed periodically periodically at at the the Sherwood Slierwood Mine Mine following following its its shut shut down. down. Surface (25acres) acres) Surface subsidence subsidence over over aa broad broad area area (25 above above the the main main ore ore body body was was first first detected detected in in late late 1979. 1979. Surface Surface subsidence subsidence continued continued throughout throughout 1980 1980 until until the the maximum maximum downward downward displacement displacement was was 1.3 1.3 feet. feet. The The northern northern extent extent of of the the surface surface subsidence subsidence was was marked marked by by the the - - surface surface trace trace of of an an east—west east-west trending trending shear shear that that was was about about 100 100 feet feet south south 6 of of the the main main shaft. shaft. \> shown shown on on Figure Figure 14. 14. . ,- .. . ,. These These features features including inclding the the monument monument locations locations are are The contours of of subsidence upon aa level level survey The contours subsidence based based upon survey in in December 1980 are are also December 1980 alsoshown. shown. The surface subsidence developed in in response to rock The surface subsidence described described above above developed response to rock , initial phases this movement mass within the mass movement movement within the mine. mine. The The initial phasesofof this movement were were 70 south detected byextensometers extensometersinstalled installed across across the detected and and monitored monitored by the 700 south cross section of the shows the the themine mine in inFigure Figure15 15shows A cross section map map of dipping dipping shear shear plane. plane. A location mine location of of the the shear shear zone zone in in relation relationtotothe the mineworkings workings and and the the .%J.? extensometer extensometer installations. installations. The The relationship relationship between between the the movement movement on on the the .. shear shear plane plane and and the the broad broad surface surface subsidence subsidence is is shown shown in in Figure Figure 16. 16. It It is of the the meassive south block ishypothesized hypothesized that thatrenewed renewed movement movement of meassive south block of of It is islikely likely that that the occurredas as aa result result of the mine mine occurred ofmine mine flooding. flooding. It groundwater groundwater inflow inflow into into the the shear shear zone zone reduced reduced the the frictional frictional forces forces holding holding the block block in in position position and and perhaps perhaps loading loading of of the the sealed sealed stopes stopes within within the the the block with with water watermay may have have helped helped this this movement. block movement. It It is isalso alsopossible possible that that have been beenpartly partly responsible responsiblefor for initiating initiating movement movement on on the the shear shear plane may have �J 21. 36 SM j J 61 f -j .15 J 16 -J J 5 C LI 2' 3 J -j J a J 49. J 50 U Si TRAIL a._:TENSON CRACK :SURFACE :SURFACE PIT PIT : T E N Y O N CRACK t 2 MINESHAFT WINESHAFT a I 250' 0 'Si j - 11 -Si 51 MONUMENT MONUMENTSI BBSERIES. SERIES. WELLS WELLS . FENCE FENCE - +-+.. .+ . RAILROAD RAILROAD JL_ & ROAD ROA U -4——4- - --- - J BUILDING LTh: : aUPLOING -Figure F i g u r e 14. 14. Subsidence Subsidence Monument Monument Locations Locations at a t the the Sherwood Sherwood Mine Mine including including Contours Contours of of Subsidence Subsidence Based Based Upon Upon the the Leve' Level Survey Survey off December December 9, 9. 1980. 1980. I j I J �Sh.•s 37 t 1000 Arsi' +600 .-eoo + 400 t 200 •000 —'200 - 400 I  Figure Figure 15 15 Location Location of o f Extensometer Extensometer Installations I n s t a l l a t i o n s in i n Shear Shear Zones Zones on on the the Looking East East 1000 and and 1200 1200 Levels Levels of o f the the Sherwood Sherwood Mine: Mine: Looking 1000 �J 38 ç • J 1 -3i -..tC. 2 .±.'i'4 ... ,• '-. I...tj.-:t.-_: ;. overbufden: .. I •..• -• . • . ••,.. -. .. Hf.f-'C'... .. : • • - .. i _• . - U J Bedrock J J J j Ij U j 1 s.q Figure Figure 16. 16. xi. ..is * ." *..;a , Suggested to Explain Pits Suggested Mechanism t.lecBanf-wto E x p l a i n Surface Surface-Pi t s on on Looking West. South Block Block of o f Surface Surface Shear Shear - Looking West. - J J �39 the theWest WestPit Pitsand sandplug plug failure failuredescribed described in inthe theprevious previous section, section, although although sand sandmovement movementfrom fromgroundwater groundwaterinflow inflowwas wasundoubtely undoubtelyatatleast leasta acontributing contributing factor. Hydraulically triggered subsidence. In the late evening of April 1, 1981 1981when whenthe theSherwood SherwodMine Minecomplex complexwas waswithin within100 100feet feetofofbeing beingflooded floodeda a rrost bysurface surface most unusual unusual sequence sequence of of events events either either caused caused or or were were created createdby subsidence. Massive Massivesurface surfacesubsidence subsidencetook tookplace place in in the the East East and and West West subsidence. Pits,and andtwo t wother othernew newpits pitsof ofsignificant significantsize sizewere wereformed. formed. This This Pits, extensive extensivesubsidence subsidenceininturn turnproduced produced great greathydraulic hydraulicpressures pressuresininthe the '* ' Surgesof of water water were were forced forced up up mine mine shafts shaftsand and nearly nearlyflooded floodedmine minecomplex. complex. Surges sand The sandfilling fillingraises, raises,rupturing rupturing or or destroying destroying their their seals seals and and cappings. tappings. The sudden suddenuprush uprush of of water water forced forced water water from from the the mine mine openings openings to to the the surface surface causing In one one area, area, water water and andmud mud causing extensive extensiveerosion erosionnear near the theopenings. openings. In were carried carried into into aa diesel diesel engine engine repair repair facility facility located located in in mine mine buildings buildings were Evidence shows showsthat that water water in in the the Sherwood Sherwood near the theHomer—Wauseca Homer-Wausecashaft. shaft. Evidence near Mine Mine shaft shaftproduced produceda ageyser geysereffect effectas asaaresult resultof ofbeing being forced forced to toexit exit diameter pipe throughaa10—inch 10-inch diameter pipe in in the the securely securely sealed sealedand and capped capped shaft. shaft. through raises located beneath two pond The seals sealsinintwo t wvertical vertical raises located beneath t wsurface surface pondareas areas west west The Waters drained drained rapidly rapidlyfrom from these these of the Sherwood the Sherwod Mine Mine were were disrupted. disrupted. Waters showthat thatthe the water water level level in Measurements show in the the ponds into intothe the minecomplex. complex. Measurements ponds mine mine period which mine complex complex rose rose17—feet 17-feet over overaatwo—day two-day period which spanned spanned the the subsidence subsidence events, events, whereas, whereas, prior prior to tothe theevent eventthe theflooding floodingrate ratewas was about abouttwo twoand andone one half feet feetper perday. day. half None of these witnessed, as None of these occurrences occurrences were were witnessed, as the the short—lived short-lived event event apparently Mr.Robert RobertEdwards, Edwards, apparently occurred occurred during during the the night night of of April April1,1,1981. 1981. Mr. Mine (retired) , reported Mine Manager Manager (retired), reported that thataaresidence residenceof ofa ahome home just justnorth north of of the shaft heard theSherwood Sherwood Mine Mine shaft heard sounds sounds about about 11:30 11:30 p.m. p.m. on on April April 1st 1st that that .. . . . . - . . . ,. ' : * , .a,: ." ., . . . ,.,., * a : X~.?... . s , , 3.. 2 .. .. �40 , , .,.: .. -8 >: ,.- ..:, "sounded like theore the ore crusher "sounded like crusher starting startingup". up". Of Of course, course, the theore orecrusher crusherwas was no had no longer longer operating operatingand and in infact fact hadbeen beenremoved removed from from the theproperty propertyfor forsome some activity. time. is probable probable that that the the sounds sounds were were fromm froiom the the subsidence subsidence activity. time. It It is The The cause cause of of the the event w e n t is is not not known. known. However, However, it it is is likely likely that that the the subsidence by aa single single subsidence subsidence event. event. subsidence activity activity was was initiated initiated by AA large large mass mass of of sand sand and/or and/or rock rock falling falling into into the the nearly nearly flooded flooded mine mine would would have have . . displaced displaced and and pressurized pressurized the the mine mine water water causing causing it it to to surge surge throughout throughout the the mine mine complex complex and and to to initiate initiate the the other other disruptive disruptive events. events. Increased Increased activity activity from from an an acoustic acoustic emission emission sensor sensor was was recorded recorded prior prior to to the the April April 1st 1st event event which which suggests suggests that that the the triggering triggering subsidence subsidence event event may may have have initiated Sherwod property. initiated near near the the center center of the Sherwood property. If event was was triggered triggered by by aa single single surface surface If it it is is accepted accepted that that the the event a, subsidence, subsidence, it it follows follows that that the the hydraulic hydraulic force force generated generated by by the the first first subsidence subsidence event event caused caused additional additional subsidence. subsidence. This this occurrence occurrence could could have have been been repeated repeated several several times times similar similar to to aa chain chain reaction. reaction. It It is is likely likely that that a a series series of of subsidence subsidence events events did did occur, occur, each each one one triggering triggering additional additional 5 - S -i activity. activity. It It is is also also likely likely that that the the life life of of intense intense subsidence subsidence activity activity was perhaps on on the the order order of of one—half one-half hour hour or or less. less. was short, short, perhaps Unfortunately Unfortunately the the acoustic acoustic emission emission sensors sensors were were much much too too sensitive sensitive to to distinguish distinguish the the period period of of the the most most intense intense activity. activity. An interesting analogy to to this this subsidence subsidence event eventwould uld be interesting analogy be to tothink think of of 6 b openings of of the as the the the underground underground openings themine mine complex complex as the"pluming "pluming system" system" of of aa hydraulic unit with with the the nine mine water water representing representing hydraulic hydraulic fluid. fluid. However, However, hydraulic unlike aa hydraulic hydraulic systan system which which is is strongly strongly sealed sealed and and fluid—filled, fluid-filled, the the unlike mine seals on shafts shafts and other surface surface 'mine was was incompletely incompletely filled filled and the seals ' :, ' openings openings were were for for the the most most part part not not designed designed to to withstand withstand great great hydraulic hydraulic forces. forces. As As water water surged surged upward upward through through these these channels channels leading leading to to the the �41 surface, the of the the air between the the surface surface of the rising rising water water and and the the shaft shaft capping or or seal would have capping seal would have been been rapidly rapidly compressed. compressed. If the the surface If surface seal seal or or capping was was not capping not stong stong enough enough to to resist resist the the combined combined forces forces of of the the compressed compressed air and the rising water, water, it would would have been either either lifted lifted or or disrupted. disrupted. These These types types of of occurrences occurrences were were documented documented following following the the April April 1st 1st subsidence event Sherwood Mine. Mine. subsidence event at at the the Sherwood In similar fashion, the sand "seals" in the the bottom of of old old subsidence subsidence pits pits were were disrupted. These were formed These "seals" were formed by by the the gradual gradual inwash inwash of of sandy overburden into sandy overburden into the the pits pits following following subsidence. subsidence. sand plugs plugs would would be low. low. The strength strength of these these would be uncemented and and the the main main forces forces They would the sands sands in place would would be frictional frictional with gravity holding the gravity loading. loading. Compressed air air and Compressed and surging surgingwater water moving moving up up through through the the caved caved area area beneath beneath fail. these seals these sealscould could have have easily easilycaused caused them them to to fail. Piping—induced subsidence. Piping-induced One of the the most interesting interesting and and significant significant aspects of the hydraulic subsidence aspects the hydraulic subsidence event was was the the formation formation of of aa subsidence subsidence pit which was as aa concealed concealed cavity cavity in in was believed to to have have existed existed previously previously as the glacial glacial overburden activity. overburden formed by piping activity. Piping, as it relates surface subsidence, subsidence, occurs relates to surface occurs when when groundwater groundwater mineopenings openingsthrough throughopenings openings(fractures, (fractures,drill drill flows into into underground underground mine flows holes, arearelarge enough holes, etc.) etc.) that that large enoughtotoallow allowpassage passage of ofsand sand grains grainsfrom from the the This transport transport mechanian canresult result in in the of large overburden. This overburden. mechanism can the formation formation oflarge conditions that that cavities within cavities within the the soil soilabove above the thebedrock bedrock surface. surface, The the conditions above favor this process favor this process are are threefold: threefold: 1) 1) an an easily easilyerodible erodiblesoil soil abovebedrock, bedrock, water transported 2) channeiways that permit 2) channelways that permit water transported soil soiltotomove move from from the the Given overburden into the substantialgroundwater groundwater flow. flow. Given overburden into themine mine void void arid and 3) a substantial conditions plus overburden layer, these these conditions plus a thick thick overburden layer, large large volumes volumes of of groundwater groundwater mine void void reservoir (for (for water and and sand) sand) the the piping—induced piping-induced flow and a large mine �42 cavity cavity can can become become very very large. large. The surface layer The presence presence of of aa competent cornpeten-------- which which serves serves as as aa capping capping can can allow allow the the soil soil cavity cavity to to attain attain large large horizontal horizontal and and vertical vertical dimensions dimensions before before collapse collapse occurs. occurs. This of surface surface subsidence subsidence not not previously previously described in This mechanisti mechanism of in the the literature, and Frantti Frantti (1981). literature, was was presented presentedbybyJohnson, Johnson,1-lodek Hodek and (1981). AA ,* , conceptual conceptual model model of of the the piping piping subsidence subsidence phenomenen phenomenon is is illustrated illustrated in in Figure Figure 17. 17. It It can can be be seen seen in in Figure Figure 17 17 that that the the initial initial flow flow of of sand sand and and groundwater groundwater produces produces aa cavity cavity in in the the soil soil at at the the point point of of intersection intersection of of the the bedrock bedrock channel channel and and the the overburden. overburden. Growth Growth proceeds proceeds by by gravity gravity collapse collapse the undercut peripheryof of the the opening of of unstable unstable sands sands from from the undercut periphery opening — the the undercutting undercutting being being caused caused by by groundwater groundwater erosion erosion and and transport transport of of the the sand. sand. Cavity Cavity growth growth ceases ceaseswhen h e n any any of of the the following following conditions conditions are aremet: met: 1. 1. The The mine mine becomes becomes flooded flooded and and water water flow flow is is stopped. stopped. flow is is no 2. The volume volume and and velocity velocity of of groundwater groundwater flow no longer longer 2. The 3. 3. sufficient sufficientto toerode erodeand/or and/or transport transportsand sand into intothe themine mine void. void. *' The channelwayinto into the the mine minevoid void becomes becomesplugged pluggedorora afilter filter The channelway which"screens "screensout" out" clastic clastic pack pack of of sand sand and and gravel gravel develops develops which material. material. ? - -J If If the the diameter diameter of of the the hanispherical hemispherical piping cavity cavity exceeds exceeds the the length length that that the the surface surface capping capping will will withstand, withstand, surface surface collapse collapse will will occur. occur. resulting resulting The The pit will be be straight—walled straight-walled with a high high depth depth to to width width ratio. ratio. This This will will serve serve to to distinguish distinguish aa piping—generated piping-generated cavity cavity from from one one formed formed by by shear shear failure failure of of running running sands. sands. These These cavities cavities may may apparently apparently exist exist for for long periods periods without without any any surface surface expression expression to to indicate indicate their their presence. presence. Capping by outside outside forces; forces; i.e., i .e., explosions explosions or or Capping failures failures may may be be triggered triggered by " hydraulic hydraulic forces forces as as occurred occurred at at the the Sherwood Sherwood Mine. J �43 Mine Mine operating, operating. surface s u r f a c e and and underunderStope Stope underlies u n d e r l i e s erodible e r o d i b l e sands sandsand andcompetent competent till till capping. capping. A. A. ground ground pumping pumping in i n progress. progress. C. -., Soil S o i l cavity c a v i t y enlarges e n l a r g e s as as water water ininflow f:Low causes causes undercutting undercutting at at periphery periphery resulting r e s u l t i n g in i n sand sand collapses c o l l a p s e s from f r o mthe the roof. roof. S o i l i s c a r r i e d i n t o mine mine by by groundwater groundwater flow. flow. Competent Competent capping capping; layer still intact. Soil is carried into layer still intact. Figure 17. Improve'] con en ,I. tilt) 13. B. Mine closed, c l o s e d , pumping pumping stopped stopped Mine Groundwater rises rises in i n overburden overburden and and Groundwater mine mine begins begins to t o flood. flood. Cavity Cavity develops develops as sand/water sandhater I n sands sands above above bedrock bedrock as in mixture flows flows into i n t o the t h e stope s l o p e via v i a open open mixture fractures. fractures. D. D. Collapse of of cap, cap. subsidence subsidence is is Collapse complete complete the t h e mine mine is is flooded flooded ted n ~ the the d croundvater ttable a b l e is is at a t equilibrium. equilibri*. p.roundwater R e s u l t i n g pit p i t has has near near vertical v e r t i c a l walls walls Resulting and f l a t bottom. bottom. and aa flat U,OC)O1 or p tIpt 1 fIr :tiih:: I dc,irc' ii V., r tin tin. le rground mE ne. �-J 44 j Long Long Term Term Subsidence Subsidence Long Long term term subsidence subsidencewas was defined defined as as subsidence subsidence that that occurs occurs following following. mine mine closure closure and and the the time timerequired required for for aa mine mineto toflood. flood. It It was was mentioned mentioned previously previously that that the the major ma;or mechanism mechanism responsible responsible for for long long term term subsidence subsidence was was the the force force of of gravity gravity and and other other stresses stresses to to which which mine mine pillars pillars and and stope stope f , walls walls are are subjected. subjected. Loss Loss of of rock rock strength strength by by weathering, weathering, oxidation oxidation or or ) . J J j other other chemical/physical chemical/physical reactions reactions also also play play aa role role in in long long term term subsidence. subsidence.. Seismic shock— natural natural or or resulting resulting fran from man's man's activity activity may may also also be be aa Seismic shock causing causing factor factor in in long long term term subsidence. subsidence. Natural Natural shocks shocks would would occur occur from from earthquakes; earthquakes; man—made man-made shocks shocks would would include include explosions, explosions, operations operations of heavy rail, truck truck and ' machinery machinery arid and rail, and automobile automobile traffic. traffic. j Hydraulic Hydraulic shock shock which which was was described described in in the theprevious previous section sectioncould could also alsobe be aa factor factor in in aa flooded flooded mine, mine, natural or man—made being being generated generated by by either either natural or man-made shocks. shocks. by its its very implies aa process process that that is isslow slow Long term term subsidence, subsidence, by very name, name, implies Long and The factors factors which which control control the thetiming timing and unpredictable unpredictable in in terms terms of of timing. timing. The and ofofmine andposition position mineopenings openings and and the the Of these, these,the thesize size are many. many. of are ! thickness of the the bedrock above the the mine mine stopes stopes are are of thicknessand and competency competency of bedrock above of structural conditions inherent in in the particular The structural conditions inherent the rock, rock, the the particularimportance. importance. The of moisture effective and the the presence presence of moisture are are additional additionalimportant important effective stress stress field fieldand factors factors governing governing the the stability stability of of mine mine openings. openings. j j '.'. important factor factor in Generally Generally speaking, speaking, the the most m s t important in delayed delayed or or long long term term '1 mine subsidence relates to the proximity of the mine void to the surface. mine subsidence relates to the proximity of the mine void to the surface. l *-. j Other stopes have have the the greatest greatest Other variables variables being being equal, equal,near—surface near-surface stopes possibility possibility of of subsidence. subsidence. Although Although only only one one case case history history of of long long term term subsidence subsidence is is presented in in detail, detail, it it illustrates illustrates all all of of the the real real concerns concerns that that may arise arise from from this this delayed delay@ subsidence. subsidence. It It is is the the only only documented documented case case of of mine mine subsidence subsidence that that . . ~- *.- T* �45 I resulted resulted in in a a human human fataility fataility in in Iron Iron County. County. I I the the Iron Iron River River district. district. I I I I II 1 The Hie subsidence subsidence event event occurred occurred in in June June of 1960 1960 between between the the City City of of Caspian Caspian and and the the Village Village of of Gaastra Gaastra in in 2s &,A *,' The Hie following following description description of of the the circumstances circumstances of of the from a memorandum the subsidence subsidenceevent eventisis from a memorandum report reportprepared preparedbybyR.O. R.O. Pynnonen Pynnonen f ~ , 3'4 .. and R.L. Bernard of of the the U.S. U.S. Bureau Bureau of of Mines Mines in in 1968. 1968. çf and R.L. "A 40—foot section "A 40-foot section of of County County Highway Highway 424 424 approximately approximately 22 miles miles south south of of Iron Iron River River caved caved early early in in the the morning morning on on June June 11, 11, 1960. 1960. One One person person was was killed two others others injured killed and and two injured when when two two automobiles automobiles were were driven driven into into the the cave cave during during early early morning morning darkness darkness and and aa heavy heavy fog. foq. The The cave—in cave-in was was 40 40 feet 30 feet feet wide, and and about about 30 30 feet feet deep. deep. Records feet long, 30 Records show show that that the the cave—in on the the property cave-in occurred occurred on property line lineseparating separatingthe theoperating operatingBuck Buck Mine and the the abandoned Mine of ofPickands—Mather & Company Company and Pickands-Mather & abandoned Smuggler SnugglerMine, Mine, Gaastra Company. Mineproduced producedslightly slightly more GaastraIron Iron Company. The Hie Smuggler Smuggler Mine imre than than 8O0,0 800,000tons tonsof ofore orefrom from aa depth depth of of less lessthan than 520 520 feet. feet. A A stope stope 80 80 to to 120 feet wide 120 feet wide beneath beneath the the road road reportedly reportedlywas was mined mined to to within within 20 20 feet feet of of ledge." ledge." Following Following the the accident, accident, the the caved caved section section of of the the road road was was blockaded blockaded on on the the east east and and west. west. was was left left as as it it was. was. The The road has has not been repaired repaired and and the the subsidence subsidence pit pit Except Except for for the the growth growth of of vegetation vegetation and and trees trees the the area area little has has changed changed little from from 1960. 1960. pit. pit. Large Large slabs slabs of of broken broken pavement pavement lie lie in in the the Wooden posts connected by steel steel cables cables which which once once served served as as aa guard g Wooden posts connected by the north side of rail rail on on the north side of the the road road hang suspended suspended on on the the north north side side of of the pit. pit. Broken water pipes by the are exposed Broken water pipes which which were were exposed exposed by the cave—in cave-in are exposed in i the toaa local local resident resident the the two car bodies bodies in the pit the pit pit sides. sides. According According to twocar - were 1960 accident —— they they are are the theproper proper vintage. vintag were involved involvedininthe the 1960 accident Photographs of the the pit 21. 18through through.21. Photographs of pit taken takeninin1980 1980are areshown shown in inFigures Figures18 Except for the which grown in 20years yea in the the20 Except for the stall smallaspen aspenand andbirch birchtrees trees whichhad hadgrown following the accident, accident, little little has following the haschanged changed at at the thescene sceneand and ititremains remains as a a grim of one one of of the the most threatening aspects grim reminder reminder of most threatening aspects of of long long term term or or delayed delayed subsidence. Subsidence. The location of roan of UÂFigure Figure22 inthe theplan planmap =..~-n in The location of the thesubsided subsided area areaisisshown pit in which was traced traced from an aerial in the the Note the the subsidence subsidence pit which was from an aerialphotograph. photograph. Note LL I I ,A .. -. ,." ,. ; .. .,-:? , ..,... \ .. ., . ! ., ,:, �-J 46 j j Ii J j J 4 - Figure Figure 18. 18. J Smuggler Smuggler Mine Mine Cave—in Cave-in on on County County Road Road 424: 424: Looking Looking East Ease j I J j j J j Figure Figure 19. 19. Close-up Close-up of o f Smuggler Smuggler Mine Mine Cave—in: Cave-in: Looking Looking East East Li �Figure 20. 20. Cave—in un on County Smuggler Mine Cave-in i,ounty Road 424: 424: Looking West Looking Close-up of 2.1. &l.o.&-ub of Smuggler Smuggler Mine Mine Cave—in: caw.-in,: LLooking &'~. .,, . . iFigure - i ? . ~ 2L : . . . ~,A:. ~ West West �48 CITY OF CASPIAN CASPIAN -I j j U U BARRICADE j COUNTY ROAD 424 U j —— I SUBSIDENCE PIT -s-N .. 500 c UNDERGROUND WORKINGS 1 -j C. 'I- -I j j —. LI BARRICADE j j Figure Plan Map Mapof of the theSmuggler SmugglerMine Mine Figure22. 22. Plan Area Area Showing ShowingSubsidence SubsidencePits Pits and and the theAreas Areas of ofUnderground Underground Workings d TO TO GAASTRA QAAUTRA 1 �L L L 49 49 road of similar road and a second one of s i m i l a r size s i z e aa short s h o r t distance d i s t a n c e south south of of the t h e road. road. photograph photograph of this of t h i s second second subsidence subsidence pit p i t is is shown shown in i n Figure Figure 23. 23. these these pits p i t s are a r e underlain underlain by by the t h e Smuggler Smqgler Mine. Mine. L L A Both of m t h of Accurate Accurate mine mine maps maps of of the the Smuggler Mine are not available, however, two old maps maps were were found which show show Smuggler Mine a r e not available, however, t w a old found which ssection e c t i o n views views of of the t h e Smuggler Smuggler ore o r e body. body. Figure 24 cross view Figure 24 is is a a c r o s s ssection e c t i o n view looking north north and 25 is is aa longitudinal l o n g i t t d i n a l section s e c t i o n looking looking west. west. looking and Figure Figure 25 Although not shown, shown,i tit is is apparent any dwelopnent development Although tthe h e mine mine sstopes t o p s aare r e not apparent that t h a t any above would atmve tthe h e first f i r s tlevel lwel wouldhave have brought brought the t h e mine mine stopes stopes very very near near the t h e ledge ledge (thee bedrock surface). This This obviously b d r o c k surface). obviously occurred. occurred. L L was Perhaps no road road iin it was Perhaps at a t this t h i stime time there there was was no n tthis h i s area, area, or o r perhaps p e r h a p it onlyy a trail. trail. on tthe map sshown Figure 25, 25, i it is From ~rom iinformation n f o m a t i o n on h e map h m in i n Figure t is suggested that may have have been been used used to suggested t h a t rock rock may t o fill f i l l the t h e mine mine void. void. is not known. However, this However, this 424 over over a mined—out what is is clear, that County what c l e a r , isis t h awith t with CountyRoad b a d 424 a mined-out operation, tthat and and llargely a r g e l y forgotten forgotten early e a r l y mining mining operation, h a t the t h e stage s t a g e for f o r eventual eventual L [ subsidence ooff .the was set. set. subsidence t h eroadway roadway was The unfortuitous unfortuitous timing timing of of the The the subsidence event, on a foggy night, played a large role in causing the human fatality. Acid ~ c i Water d Drainage drainage is not aa problem tthat h a t is usually associated with Acid water drainege iron i r o n mines. mines. L I L 1 L i I However, district, direct i n the t h e [ron Iron River d i s t r i c t , the t h e iron i r o n ore o r e was in in d irect However, in contact with pyrite-rich Wauseca member of of the t h e Dunn Eunn Creek Creek contact w i t h the the underlying pyrite—rich lenses of of pyritic sslate l a t e and and lenses witicslate s l a t were e weresometimes sometimes found found iin n the t h e iiron r o n ore. ore. when the was When the pyritic p y r i t i cslate slate wasexpesed e x p s e d during during mining, mining, it itwould m u l d oxidize oxidize so so rapidly that rapidly t h a t sometimes sometims mine mine fires f i r e s were were the t h e result. result. Ass many of the A t h e mines mines were wet and required water was w e t and required pumping, pumpirq, the t h e pumped pumped water w a s acid. acid. Consequently, Consequently, water d drainage has been been aa problem problem iin the IIron River ddistrict acid a c i d water r a i n q e has n the r o n River i s t r i c t ssince i n c e tthe he were opened. mines were opened. were operating, When many many mines mines were pun@ from from acid waters waters pumped When operating, acid �oc :; ,", Figure 23. (50 U ft di,meter, 2 ft os) 95 ; aoqe 3di t flPUJ aDuepLsqn P &all .'Subs%dence Jo o* ,c3unoJ Cm*yt peo j7j7 Road 424 sbovt? at65nws Smgg%erMfne auLw .. deep) south (doap tnnos �51 1YR0A042.. C • —— lit LEVEL - -. S .0• —— - 2nd LEVEL 3rd LEVEL - 4thLEVEL.. 4th LEVEL - - - - SMUGGLER MINE CROSS SECTION 0 FEET SOUTH LOOKING NORTH SCALE 1" — 100 ft. ~. Figure Figure24. 24. Cross-Section Body Cross-Section Map Map of of the t h e Smuggler Smugg.ler Mine Mine Ore Ore Body .~ ".. �L. LL. 1 2 L...... Longitudinal Section Section ofofthe theSmuggi Smuggl L_ L L... Mine fine Ore Ore Body Body EL CL. L FOGARTY SMUGGLER MINE CROSS SECTION 200 !OOFEET FEET WEST W E 8 1LOOKING LOOKINO WEST WEST VOUNGS YOUNQS 2 L_ L_ L_ L CL.. 25. Figure 25. 4th LEVEL 3rd LEVEL 2nd LEVEL 1st LEVEL 3 C 4 S L. C L_ 4th LEVEL 2nd LEVEL in LEVEL LLL I I LEDGE LEDOE b 4 N Ui EL �53 than the. Iron River In more recent years them caused caused'the Iron a v e r to to run run red. red. In more recent years as asmines mines closed closed . and ceased, acid acid water water drainage mining companies and pumping punping ceased, drainage abated. abated. Some Some mining companies which which instituted institutedcorrective correctivemeasures measures to toimprove improve the the quality qualityof ofmine mine waters waters before before draining in the the acid draining than then into into the the river river also alsocaused caused aagreat greatimprovement improvement in acid water water In fact, for a hile, while, it seemed seemed reasonable reasonable that that acid acid water water situation. situation. drainage drainqe would cease cease to to be be aa problem problem in in the the district. Such however, for as as the the mines mines closed and punping pumping was was Such was not the the case, however, Workings Wrkings kept kept dry dry for for all all halted, underground underground water water levels levels began b q a n to to rise. rise. cases it took In some some cases took the the years years the the mines mines were were in in operation operation began began to to flood. flwd. The waters rose rose until they several several years years for for the the mines mines to to fill fill with water. water. -- reached the levels existing prior to to mining reached their their natural natural levels levels ——— the Mines collared at lower elevation in the Iron River valley activity. L G . flooded to the surface surface and flow from from some some of of them than carried carried acid acid into the Iron River. River. Sulfur—bearing black slate often often used used for for surface surface fill around mine mine Sulfur-tearing wrkings and acid acid workingscame caneinto intodirect direct contact contact with with the the elevated elevated groundwaters groundwaters and waters issued waters issued from from this this source source too. too. Discoloration present acid drainqe drainage is Discoloration of of the the Iron River by present is not as severe but it it is is still still aa concern. concern. severe as as it it once once was, was, but Tests by the Tests the Michigan Michigan other fish and aquatic Water Resources Resources Commission Commission show that trout and other organisns organisms can can and do do live live in in the the clouded cloded waters. waters. Nevertheless, Nevertheless, % . *, . : :> River visible and aesthetically discoloration discoloration of of the the Iron Iron a v e r is highly visible displeasing. objects objects with . , a fineness of the a yellow—brown yellow-brom slime and the extreme fineness where into the the Brule, Brule, Several miles south south of Caspian Caspian h e r e the the Iron Iron empties empties into their confluence is marked by by aa noticeable noticeable plume plume of of turbid turbid water water entering entering is marked * .. ~ ...... 9 all submerged coats all Precipitation of compounds Precipitation ofinsoluble insolubleiron iron compunds coats suhnerged precipitates downstream. carried far downstrean. precipitates allows allows than then to to be carried , .L. , 5' b .'~. r, ~ Z . . : ,. . . % . . .- �-J 54 the Brule River. the Brule River. Wisconsin. Wisconsin. National National J , The Brute Br-tileRiver River marks marks the the boundry The bundry between between Michigan Michigan and and J It isisalso 650,000 acre acre Nicolet Nicolet It alsothe thenorthern northernborder border of of the the 650,000 Forest. Forest. J A report report issued issued by Nicolet National National Forest Forest personnel personnel documents level, colored colored documents the pollution by by chariical chemical analysis the pollution analysis and and by by low level, aerial aerial photography photography (Runt, (Hunt, 1974). 1974). Since 1974 1974 the Institute Institute of Mineral Research has been studying studying acid j drainage drainage problans problems in in the the Iron Iron River River district. Two sources sources of acid acid drainage drainage properties were from closed mine properties were identified. identified. The most serious serious acid drainage drainaye J Dober Mine pit pit which which in the late 1970's was was that flowing from the k b e r Mine 1970's accounted for more than for than 75% 75% of the the acid drainage drainage into into the the Iron Iron River, on on the the basis basis of of The ranainder remainder of the acid drainage issues issues from from extensive extensive dissolved iron. iron. piles piles J J of pyrite—bearing pyrite-bearing black slate filling a low low marshy area area over over the the Buck Buck group group of of mines mines about about one one mile mile to to the the south. south. case histories histories for the the case for acid aciddrainage. drainage. J These two These two occurrences occurrences provide provide The information information has has been been extracted extracted The reports prepared from from reports prepared by by Johnson Johnson and and Frantti Frantti (1976, (1976, 1978) 1978) Cregger Cregger (1979) (1979) and and .- p -*. b t-7. Johnson Johnson (1979). (1979). underground source. source. mine drainage: drainage: underground Acid mine The most mostserious serious and and best best ..-The j documented source aciddrainage drainage theIron IronRiver Riverdistrict district occurs occurs at at the inin the the documented source of of acid The part of of aa larger consisting also The ~Dober o b e r~Mine i n eisispart largermine mine complex complex consisting also The mine minecomplex complexisissituated situated west of the of theIsabella Isabellaand andHiawatha HiawathaMines. Mines. The west of of It consists consists of of the City andsouth southofofthe the City City of of Iron the City of of Stambaugh Stambaugh and Iron River. River. It eight, forty—acre parcels identified identified as eight, forty-acre parcels asthe theDober, Ikiber, Isabella, Isabella, Stegmiller, Steqmiller, Dober k b e r Mine. Mine. I I Hiawatha #1 $1 West Hiawatha #2 Hiawatha #2 (formerly (formerly Duff), Duff), Hiawatha, Hiawatha, Hiawatha Hiawatha $1, #1, Hiawatha West and and Hiawatha #2 #2 West properties. The Iron River flows flows in in a southerly southerly direction direction over over the the Stegmiller, Stegmiller, Isabella Isabella and and Dober Ikiber properties. .. Locations of ~ocations of the the properties are shown in Figure properties are shown in Figure 26. 26. History. History. Mineswere weretwo tbKofofthe theearliest earliest iron The Dober Ibber and Isabella The Isabella Mines iron I J �55 W HIAWATHA i:ii [ L L .: j, &'' 2W DUFF L -Â¥ W DUFF -i L C L' Li CASPIAN U > [ U ... ISABELLA, ,c.?-5,., L..:.4- ,.,.it--:-F;. .. . ..:?..,., 4 . . . .~ -, .;. . - ' . ,* ...>.',,& ".. Scale I": 1 L DOBER & HIAWATHA MINES '.È*( . \ . . Plan Map Figure 26: L J M 5-7 �56 mines mines to to open open in in the the Iron Iron River River District; District; the the Isabella Isabella was was opened opened in in 1882 1882 and and the the Duber Dober in in 1888. 1888. Initially, Initially, both were started started as as open open pits pits and and later later were were developed developed into into underground underground mines. mines. from stopes. from open open stopes. The The direct direct shipping shipping ore ore was was mined mined The by one one shaft shaft The Isabella Isabella was was served served by to to aa depth depth of of 430 430 feet. feet. in in the the upper upper levels levels This is interconnected interconnected with with the the Dober Dober This shallow shallow mine mine is workings workings on on the the 4th 4th level. level. The by two two shafts; shafts; #1 #1 aa The Dober Dober Mine Mine was was served served by vertical vertical shaft, shaft, 950 950 feet feet deep, deep, north north of of the the open open pit pit and and #2 #2 an an inclined inclined shaft shaft which which descends descends to to the the 10th 10th level level (1000 (1000 feet feet deep) deep) and and is is located located just ji_- south south of of the the open open pit. pit. The The Dober and Isabella Isabella Mines Mines were were operated operated by by Oliver Oliver 'I Mining Mininq- Company Company until 1935 1935 at at which which time time they they were were combined combined with with the the Hiawatha Hiawatha - - until * Mine Mine under under single single ownership. ownership. *^ -4 ' , ..  ., ¥= ..A -- . "2 . i , ..-- I The The Hiawatha Hiawatha Mine Mine began began as as twa two separate separate operations operations from from two two vertical vertical: J shafts, shafts, No. No. 11 and and No. No. 2. 2. Hiawatha Hiawatha Iron Iron Company. Company. The The Hiawatha Hiawatha No. No. 11 was was opened opened in in 1893 1893 by by the the The The The No. 11 shaft shaft is is 2180 2180 feet feet deep. deep. The Hiawatha Hiawatha No. first it was was first named named was was put put in in to to mine mine ore ore Hiawatha or Duff Duff shaft shaft as as it Hiawatha No. No. 22 or from from the the western western extension extension of of the theDober Dober and and Isabella Isabella properties properties below below the the The Hiawatha No. 22 shaft shaft Hiawatha No. 10th 10th level level by by the the American American Boston Boston Mining Mining Company. Company. is is 2500 2500 feet feet deep. deep. tà ' i Dober Dober '1 Mine Mine maps maps show show aa bulkheaded bulkheaded 8th 8th level level drift drift and and an an open open 10th 10th level leve shafts. drift drift between between the the two two shafts. .j i depth. depth. at Daber The No. 22 shaft shaftinterconnects interconnectsthe the DoberMine Mine at The Hiawatha Hiawatha No. Open stopes stopes in in the the ore ore body body also also connected connected Open wrkings with with the the Hiawatha Hiawatha workings. workings. workings Levels Levels from from the the 10th 10th to to the the 21st 21st of No. 22 shaft shaft are are connected connected to to the the Hiawatha Hiawatha No. No. 11 shaft. shaft of the the Hiawatha Hiawatha No. ; Shaft Shaft locations locations are are shown shown in in Figure Figure 27. 27. & .. .I 1 When When the the Daber Dober and and Isabella operations were incorporated incorporated with with the the in 1935, the production andafter after Hiawatha No. No. 2 2 Mine Mine in 1935, the production records records were were combined combined and Hiawatha 2 mines 1943 the the shipping shipping records records of of the the Hiawatha No. No. 11 and and No. No. 2 mines were were 1943 closing in in 1967 1967 combined shipments shipments totaled totaled 22,162,905 22,162,905 long low combined. combined. Until closing : >.,, ." ~...X&?'J. . . -, .,. , . , . . . . .. . . . , , ,. �57 N To Stambaugh To Iron I River 1Scale: I I I ' \ Hiawatha H i awatha // I/ \V, un i' "- 1 8 Shaft Shaft 1 #1 ' -. >* t -I. Iron N. River 1" = 500' N /.- CLZ Isabella Pit L. and Shaft 1 it I '¼' D!'i .1 — Hiawatha Ii #2 Shaft Dober #2 Hwy. M-189 1 To To Caspian Caspian r It II Stambaugh —V N & Sewage Ii! Treatment Plant Figure__2?. Surfacei plan plan map map of of the t h e Dober-Hiawatha-Isabella Dober-Hiawatha-Isabella Mine Mine Complex Complex , I �58 tons. tons. Earlier Earlier production production from from the the Dober m b e r and and Isabella IsabellaMines Mines(prior (priorto to1935) 1935) f had had been been combined combined with with the the nearby nearby Riverton Riverton Mine Mine and and referred referredto toas asthe the Riverton total of of 5,881,550 5,881,550 tons tons were were reported reported for for the the period period RivertonGroup. Group. AA total s iff 1882—1937. 1882-1937. Structure Structure of of the the Dober—Hiawatha—Isabella Dober-Hiawatha-Isabella mine mine complex. complex. The The DDber— DoberHiawatha—Isabella Hiawatha-Isabella Mine Mine complex complex may may perhaps perhapsbe be more more readily readilydescribed described by by structural structural than than by by geographic geographic boundries; boundries; nanely namely as asthose thoseportions portionsof ofthe the iron iron formation formation bounded bounded on on the the north north by by the the North North Hiawatha Hiawatha fault, fault, on on the the south These south by by the the Duff Duff fault fault and and on on the the east east by by the theStegmiller Steqmillerfault. fault. These faults faults form form aa triangular triangular block block which which incorporates incorporates an an east—west east-west trending trending syncline The iron iron formation formationon on the thenorth northcomprising comprising synclineof ofthe theiron ironformation. formation. The the the Hiawatha Hiawatha No. No. 11 Mine Mine is is vertical vertical to to overturned overturned with with an aneast—west east-west trend. trend. On On the the east east the the iron iron formation formation trends trends north north south southand and dips dipswesterly westerly at atan an of about 60. angle angle of about 60¡ This This limb limb was was mined mined from from the the surface surfaceby by the the Isabella Isabella Mine. and DDber Dober Mines Mines and and at at depth depth by by the the Hiawatha Hiawatha No. No. 22 Mine. and These These relationships relationships are are shown shown in in Figure Figure 28. 28. 3 Acid Acid drainage drainage from from the the Dober—Hiawatha—Isabella Dober-Hiawatha-Isabella mine mine complex. complex. In In 1966 1966 after after nearly nearly 85 85 years years of of operation operation the the Dober Dober Mine Mine complex complex ceased ceased operations. operations. Pumping Pumping was was stopped stopped and and the the mine mine began began to to fill fill with with water. water. It It was was not not until until some some six six years years later later in in early early October October of of 1972 1972 that that water water first first appeared appeared in in the the open open pits pits of of the the Ebber Dober and and Isabella Isabella mines. mines. Over Over aa period period of of Local Local residents residents were as they they had had were quite quite surprised surprised to tosee seethe theDDber Dober and and Isabella IsabellaMines Mines flood flood as . , . been been dry dry for foras aslong longasas anyonecould couldremember remember since the themines mines were were open open anyone — since in in the the1880's. 1880's. ... ,.. The rising rising acid acid waters waters were were of of more more than than just just idle idle curiosity. curiosity. The The main main The ,. . . 'S, -. È!, sewage Sewage TreatmentPlant Plantpassed passed just just west line feeding sewage,lin% feeding the the stambaugh St-ugh Sewage Treatment west of of . !. .à pit rose 45 days days the the water water in in the theDober Dober pit rose about about 100 100 feet. feet. 45 -j I I �59 I..] I 5 —1 I• '——--F-.—— I I ii" L "(p L-I Jo St. 'tJ-tl "3 ~ Figure 28 Figure 28. Isometric Isometric diagram diagram of of part part of of the the Hiawatha Hiawatha and Dober Dober Mines. Mines. (from Dutton, 1969) 1969) .... . : ~ ,. ,. , .,, . ,, .. . . . # .( . .. ~ �60 the kober b e r Mine pit. The acid waters waters poured pured into into corroded corroded sections sections of of the the pipe and acid water entered the disrupting the the plant plant disrupting the bacteriological bacteriological sewage sewage The problemwas waseventually eventually solved The sewage sewage problem solved digestor. by the the DNR and the the City of Starobaugh Stambaugh insertinga aplastic plastic pipe pipe inside inside the line. of byby inserting the sewage sewage line. Water in Water in the Dsber ober Mine from the the pit pit to to lowered about about two two feet feet by by ditching ditching from the Mine pit pit was was lowered the river. the river. details of this The details this sequence sequence of events events have been documented documented by Van Van Alstine Alstine (1973). (1973). . . , ., '*Â¥ . Flooding of the mine complex took six years because neither the complex the :--'. ':* . .,,.:.*:. Records for 1948 No. for19484 No. 11 nor nor the the No. No. 22 were were exceptionally exceptionally wet wet mines. mines. Records .. minute (gçm) were pumped from the Hiawatha No. gallons per that 230 that 230 gallons per (gpn) from the Hiawatha No. ' 8 Hiawatha indicate 2 and 300 gpn from 300 gpn from the the Hiawatha Hiawatha No. No. 11 for for aa total totalof of530 530gpii. gpn. Using using these these >: ! conjunction with mine mine volumes data in in conjunction volumes calculated calculated from from ore ore shipping shipping records records stopes filling measurements measurements the time required to flood could have been and scopes estimated. made by Cregger (1977) Based on measurements made (1977) the the mine complex complex has a a volume of 281 281million million cubic cubic feet feet from ore removed, less aa stope has volume of from ore removed, less stope filling of 58 58million millioncubic cubicfeet feetresulting resulting in in aa total fillingsand sand volume volume of totalof of223 229 is: The calculation calculation of of the million feet. The million cubic cubic feet. the time time to to flood flood i e ; 2,;. : , . , ~ ! .- 1 ; X 106 106 FT3 rr3 xX 7.48 Time Flood = = 223 223 X 7.48 GAL/fl GAL/FT ,% = ,g 6.0- 4YEARS Time to to Flood 530 DAYS/YR 530 GAL/MIll -IN x 60 6 0MIN/HR MIN/HR x 24 24HR/13Y HR/DAY xx365 365 DMS/YR ' This simple calculation could been made madetotopredict predict the the time of This simple calculation could have have been time of flooding. flooding. one had hadanticipated anticipatedat at the the time that water, of course, Of course, no no one time that water, especially Mineinto into the the Iron especially acid acidwater, water,would would flow flow from from the the Dober Dober Mine Iron River. River. Flow rates rates of Dober Flow of acid aciddrainage drainagefrom fromthe the DoberMine Mine measured measured since since 1975 1975 have varied varied from a low of about to highs highs in in excess 30 gpxt gpn to excess of of 100 100 gpn. gpn. have from a low of about 30 During 1978the the flow flow rate rate ranged 39 to to 90 During 1978 ranged from from 39 9 0 gpn gpn with with an an average average of of 67 67 gpn. gpn- Chemicalcharacterization characterization of Chemical ofDober Dober Mine acid acid drainage. drainage. Acid Acid drainage drainage pit was during the the period to the Dober from the Dober Nine Mine pit was periodically periodicallysampled sampled during period 1975 1975 to j �61 1978. 1978. Chemical aluminun and sulfate Chemical analyses analyses for for iron, iron, manganese, aluminum sulfate were routinely routinely performed. performed. In In addition, addition, temperature, temperature, pH, pH, specific specific conductance conductance and and acidities acidities were were measured. measured. Results Results of of these these analyses analyses are are shown shown in in Table Table 4. 4. Average Average values values of of water water quality quality measurements measurements in in 1975 1975 were: were: pH pH == 4.1, 4.1, acidity acidity == 2900 specific conductance 2900 mgI! m g / l CaCO3, CaC03, specific conductance == 5000 5000 mhos/cm, mhos/cm, iron iron == 1125 1125 mg/i, itig/l, In In 1975 1975 drainage drainage from from the the accounted for nearly of the the total accounted for totalamount amount of of iron iron entering entering the the nearly 90% 90% of manganese manganese = = 121 121 mg/l mg/l and and sulfate sulfate = = 5130 5130 mg/i. mg/l. L [ Dober Dober Mine Mine fromall all mine drainagesininthe the District. District. For Iron River River from mine drainages For the the study study period, period, Iron 1975 1975 through through 1977, 1977,the theDDber Dober Mine Mine drained drained an an average average of of654 654pounds pounds of of iron iron of the per day day into into the the Iron IronRiver, River, of of71% 71% of the total totalanount amount per the river entering entering the river from all sources. from all sources. Dober Mine Model Mine complex. complex. Model for for acid acid drainage drainage from from the the Dober Simply stated, Simply stated, the oneof ofrecharging recharging the model model for for acid -aciddrainage drainage from from the the Dober Dober Mine Mine pit pit isisone surface complex surfacewaters waters entering enteringthe thenine mine complexabove abovethe theHiawatha Hiawatha workings workings on on the the west west side side of of the theIron IronRiver River to toforce forceacid acidwaters watersthrough throughthe theinterconnected interconnected via aa 10th 10th level level drift drift mine mine workings workings into intothe theDDber Dober "leg" "leg" of of the the mine mine via Hiawatha Sufficient head head exists existsininthe the Hiawathaworkings workings to to connecting connecting the theworkings. workings. Sufficient cause cause aa flow flow of ofacid acidwater waterfrom fromthe theDober Dober Mine Mine into into the the Iron IronRiver. River. Flow Flow occurs occurs because because of of recharge rechargeand and because because the theDober Dober Mine Mine pit pit lies liesatata alower lower relationships are elevation elevation in in the the Iron Iron River River Valley. Valley. These These relationships areshown shown schematically schematically in in Figure Figure 29. 29. Measurements of the the acid Measurements of acid flow flow from from the theDober Dober Mine Mine pit pit during during the theperiod period a low of about 1975 to to 1978 1978 ranged ranged from from a low of about 25 25 gpn qpn in in the the drought drought winter winter of of 1975 The response response of of 1976—77 highs of of about gpn during during spring spring runoff. runoff. The 1976-77 totohighs about 150 150 gpn flow to precipitation precipitation is flow to iswell well established. established. Prospects Prospects for for long longterm term acid aciddrainage drainagefrom fromthe theDober Dober complex. Dober—Hiawatha—Isabella Mine closedinin1967 1967the the workings Dober-Hiawatha-Isabella Mine closed workings were were When the the When �62 TABLE TV TABLE I V AVERAGE ANALYSES AVERAGE OF OF YEARLY YE YSES OF OF DOBER DOBER MINE MINE ACID ACID DRAINAGE DRAINAGE 197 5—1978 1975-1978 .? YEAR YEAR 1975 1975 Fe Fe Mnn M Al A1 mg/i mg/1 mg/i mg/1 mg/i mg/l mg/i mq/ 1 1125 1125 121 121 114 114 5130 51 30 504 pH PH Cond. Cond. pmhos/cm ~mhos/cm., .,.. ,<. 4.1 4.1 .Â¥= Acidity Acidity Spec. spec. ppm CaCO3/l ppm CaC03/1 2900 2900 4990 4990 .a. .. .,, 3500 3500 1290 1290 90 90 279 279 5450 5450 3.7 3.7 4910 4910 1977 1977* 707 707 59 59 157 157 3320 3320 2.4 2.4 2180 2180 1370 1370 1978 1978 1280 1280 80 80 123 123 5930 5930 --- -- 3680 3680 1976 1976 I J I J I J I j Li 1 * NOTE: Low 1977 values are due to dilution of surface waters in the Dober by runoff and flooding by the Iron River. pit J j j j 1 J 1 J J -j �63 LOOKING NORTH INES : LOOKING NORTH DOBER-HIAWATHA MINES , +- GROUNDWATER QROUNDWATER FLOW ^-FLOW OVERBURDEN IRON RIVER 19th St. DOBER #1 ERT S H A Ft I I BEDROCK ,._HIAWATHA #2 SHAFT I i I STOPE ___1ath_LLVLD3I3___ I Figure F i g u r e 29. 29. DIRECTION DIRECTION OF O F WATER WATER FLOW FLOW —, I Schematic Flow of of Water Water in i n the t h e Dober Dober Mine Mine Complex Complex Schematic Diagram Diagram Showing Flow �64 dry. Following Following closure closure the the mine mine complex complex was was allowed allowed to to flood. flood. Prior to to flooding, oxygen and water reacted with with pyrito-bearing pyrite—bearing slates wherever they were and footw'all were exposed in in the the hanging hanging and footwall and and in in caved caved stopes, stopes, forming forming soluble compounds. soluble ferrous ferroussulfate sulfate compounds. These dissolve readily These compounds compounds dissolve readily to to form form sulfuric result, nearly As aa result, nearlythe theentire entirevolume volume of of sulfuric acid acid and and soluble soluble iron. iron. As . : the wasflooded floodedwith withacid acidwater, water, except except perhaps perhaps for for the the mine mine complex complex was the very very uppermost portion of of the where most mostof of the the surface uppermost portion theHiawatha Hiawatha No. Nu. 1 1 workings workings where surface water apparently entered. the mine mine flooded, flooded, pyrite pyrite oxidation :ater,apparently entered. With With the oxidation no no longer longer occurred. .occurred. -'..\-.. ".. - ^f-Y y.r: , ,, th&Â¥Sj/tKawath Mines through the Water movesfrom fromtilthe levels dt of the Hiawatha Mines through the water moves e' upper 10~easts 10th connecting Hiawatha Dober 10th level level drift drift connectingthe the Hiawatha#2 #2shaft shaftwith withthe the Doberworkings. workings. Volumes themine minevoids voidsabove abovethe the10th 10thlevel level including including the the Daber, Isabella Volumes ofofthe Dober, Isabella I, ' and Mineworkings workings were weredetermined determined by by planimetering planimetering mine The and Hiawatha Hiawatha Mine mine maps. maps. The total 44,235,000ft3 ft3 without without subtraction subtraction for totalstope stopevolume volume calculated calculated was was 44,235,000 for stops fill or on an Based on an estimated estimated stope fill or addition addition for for shafts, shafts, drifts driftsand and raises. raises. Based average average flow flow rate rate of of 50 calculated that 50 gpn, g p , Johnson Johnson calculated that by by early early1979 1979 about about 25 25 million since it it flooded million ft3 ft3of ofacid acidwater waterhad haddrained drainedfrom from the themine mine complex complex since flooded in Subtraction of this this 25 25 million million ft3 ft3 of of acid acid water water from from the the in October October 1972. Subtraction total of 44 44 million million ft3 ft3 of of voids totalvolume volume of voids calcualted calcualted for for the theupper upper 10 10 levels levels left left19 19 million million ft3 ft3 of of simplified simplified acid water water remaining rnaining in in the the upper upper 10 10 levels. levels. This This calculation calculation indicated that 57 percent of the the acid water in in the the upper had been been replaced replaced with with surface surface water. water. upper 10 10 levels levels had If If drainage drainage continued continued at been required required to to (50gpm), gpm), about about 55 1/2 1/2years yearswould would have have been at this thisaverage average rate rate(50 flush this was flush the the acid acid from from the the upper upper ten ten levels levelsof ofthe themine. mine. However, However, this was not not possible would possible as asmixing mixing of of fresh ffeshwaters waterswith withthe thedenser denseracid acidwaters waters would occur occur and greatly lengthen toexpel expelthe theremaining remaining acid acidfrom from the the and greatly lengthen the the time time required required to mine complex. complex. �65 Field Field evidence evidence also also suggested suggested that that acid acid waters waters were were gradually gradually being being expelled expelled from from the the mine mine complex. complex. L It It was was logical logical to to assume assume that that as as the the recharging recharging groundwater groundwater mixed mixed with with acid acid water water that that the the head head differential differential between mines of between the the free free water surface surface in in the the various various mines of the the complex complex would would L equilibrate. equilibrate. Except Except for for slight slight differences differences due due to to recharge recharge and and frictional frictional losses, losses, the the fresh fresh water water surface surface would eventually eventually lie lie at at the the same same elevation elevation L L throughout throughout the the mine mine complex. complex. Comparison Comparison of of water water level level measurements measurements taken taken in in the the mine complex complex since since 1976 1976 indicates indicates that that this this equalization equalization process process is is well well underway. underway. L These These observations observations and and calculations calculations indicate, indicate, as as acid acid water water in in the the upper upper 10 10 levels levels is is replaced replaced with with fresh fresh water, that that acid acid water water drainage drainage from from the Dober-Hiawatha-Isabella Mine Mine complex complex will eventually eventually cease cease to to be be aa the tkter—Hiawatha—Isabella problem. problem. However, very large large amount amount of of acid water water remains remains in in the the mine mine However, aa very blockage blockage occurs occurs on on the the 10th 10th level level workings or interconnection interconnection between between the the Hiawatha Hiawatha and and Dober Dober workings or on on complex complex below below the the 10th 10th level. level. If If interconnections and the the Hiawatha *2 shaft shaft interconnectionsbetween between the theHiawatha Hiawatha *1 #l workings workings and Hiawatha #2 very These blockages blockages very serious seriousacid aciddrainage drainagecould could continue continuefor formany many years. years. These could in the could result result from from rock rock caving caving in the drifts driftsor orpossibly possiblyfrom fromthe theformation formation phenomena of damsin in drifts drifts connecting this latter latter phenomena of "yellow "yellow boy" boy" dams connecting the themines. mines. This was observed in in the Mineduring duringits its operation was observed the Sherwood Sherwood Mine operation 1, 1. Acid waters waters flowing in aa drift drift gradually flowing in gradually built built up up aaseries seriesofof"yellow "yellowboy" boy" deltas. deltas in in aa was terrace orstep—like step-like fashion fashion until until the thedrift drift wascompletely completelyblocked. blocked. terraceor Although this damming effect occurred occurred below below an an air-water air—waterinterface interface ititmay Although this damming effect may be be possible damming interface between oxygen— possible that thatthe the damming could could occur occur at atthe the interface between oxygenbearing acid waters waters on on the the 10th bearing "surface" "surface" waters waters and and lower lower acid 10th level level interconnections at the ofofthethe mine complex interconnections at thetime time that thatthe theupper upperlevels levels mine complex 11 Personal with Robert Robert Edwards, Edwards,former formerSuperintendent Superintendent of of the Personal communication communication with the Sherwood Mine,Iron Iron River, River, Michigan. Sherwaod Mine, Michigan. �66 are are flushed flushed of of acid acid water. water. This This #uld wouldcause causethe thewater water to to flow flow through through the the next next lower lower interconnection, interconnection, expelling expelling more more acid acid water. water. , lj The The process process could could conceivably conceivably continue continue until until the the entire entire mine mine was was purged purged of of acid. acid. .- Based Based on OB~ X'S mine calculations and and the the present present flow rate, severe mine volume volume calculations flow rate, severeacid acid drainage drainage ^*-- could could last last for for55 55 years; years; e.g., e.g., Total Total volume volume of of mine mine complex complex ,,* million ft3 25 25 million million ft3 ft3 . . == 223 223 million ft3 Volume years == Volume of of acid acid drained drained in in 77 years Volume of acid acid renaming 198 Volume of remaining 198 million million ft-5 ft-à the ....atatmillion the rate rate of of 25 25 million million ft3 ft3 drained drained in in 77 years, years, 198 ft3 198 million ft3 would would require require 55 55 years years to to drain. drain. : .., ! sr'? s-:~' *< -'fa fi*<-.-. :,:+.q:> ' ,'b ~, 3Â¥m1-I Actually, conditions were were met, met, acid aciddrainage"wou1d drainage u1d persist Actually, if if the the above conditions persist for for aa period period greater greater than than 55 55 years, years, as as the the acid acid waters waters cauld would continually continually mix mix fresher waters of acid flow. with resulting in some dilution and a greatly extended period U J J J J J 1 -I -I J J �67 REFERENCES REFERENCES Anonymous, Anonymous, (1938), Lake Lake Superior Superiar Iron Ores, Ores, Lake Superior Iron Ore Ore Association, Hanna Hanna Building, Building, Cleveland, Cleveland, Ohio, Ohio, 364 364 p. p. 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M. and and Frantti, Frantti, Gordon Gordon (1976), (1976), "Study of Mine Subsidence Subsidence and Acid Valley, Iron Acid Water Water Drainage Drainage in in the the Iron Iron River Valley, Iron County, Michigan — Status Status of of Initial Initial Work", Work", Institute Institute of Mineral Research, Michigan Technological nological University, University, Houghton, Houghton, Mich., Mich., 113 113 p. p. - Johnson, G.E., (1978), Subsidence and donnson, A.M., A.M., and and Frantti, Frantti, G .E., (1978), Study of Mine Subsidence Acid Acid Water Water Drainage Drainage in in the the Iron Iron River River Valley, Valley, Iron Iron River, River, Michigan, Michigan, Institute Institute of of Mineral Mineral Research, Michigan Michigan Technological Technological University, University, 220 220 p. p. Johnson, Hodek, and Johnson. A.M., A.M.. Hodek. R.J., R.J.. and Frantti, Frantti. G.E. G.E. (1982), (19821. Piping Pioim Induced Induced Subsidence Workshop subsidenceOver Over An Underground underground Mine Mine in Proceedings ~roceedi&ji ~orkshopon on Surface Surface Subsidence SubsidenceDue Due to to Underground Underaround Mining, Minim. Nov Nov 30 30 — Dec Dec 1981, 1981. W.V. W - V - Univ., Univ-. ~ ~ - Morgantown, W.V., Peng, S.S. and Harthill, M. eds., p. 268—273. Johnson, (19791, Study Study of Pumping As A Means To Control Acid M., (1979), uunnson, Allan Allan M., Water Water Drainage Drainage From From The The Dober—Hiawatha—Isabella Dober-Hiawatha-Isabella Mine Complex, West Iron County, of Mineral Research, Michigan Institute of Michigan Technological Technological County, Michigan. Michigan. Institute University, University, Houghton, Houghton, Mich., Mich., 74 74 p. p. Johnson, and A ACase thethe Sherwood Johnson, A.M., A.M., and Frantti, Frantti,G.E., G.E., (1982), (1982), CaseStudy Studyofof sherwoodMine Mine Closing, Contract Executive Sunnary, Summary, U.S.B.M. U.S.B.M. Contract J0285035, J0285035, 57 57 p. p. Closing, Volume Volume I, I, — Executive - Johnson, and A ACase thethe Sherwood Johnson, A.M., A.M., and Frantti, Frantti,G.E., G.E., (1983), (1983), CaseStudy Studyofof SherwoodMine Mine Closing, Contract Closing, Volume Volume II, 11, Field Field Investigation, Investigation, U.S.B.M. U.S.B.M. Contract J0285035, J0285035, 279 279 p. p. Johnson, and R.J. (1983), (19831, A Case Study Study of the the Sherwood Sherwood Mine Johnson, A.M., A.M., and Hodek, Hodek, R.J. Closing, Closing, Volume Volume III, 111, Piping Piping Experiments Experiments as as Evidence Evidence for for Piping Induced Induced Subsidence Contract Subsidence at at the the Sherwood Sherwood Mine, Mine, U.S.B.M. U.S.B.M. Contract J0285035, J0285035, 58 58 p. p. �68 Johnson, Hydrologic Considerations Considerations in Johnson, Allan Allan M., M., (1983), (1983), Hydrologic in Mine Mine Closings Closings 94E— EMEAIME AIME Preprint Preprint No. No. 83—365, 83-365, Salt Salt Lake City, Utah, Utah, S5 p. p. r Kleinman, Crerar, A., and Kleinman, Robert Robert L.P., L.P., Crerar, David A., and Mohring, Eric Eric H., H., (1978), (1978), Abatement Inhibition of Thiobacillus Thiobacillus Abatement of of Acid Acid Mine Drainage by Inhibition Ferrooxidans, Geologists, Hershey, Assoc. Eng. E q . Geologists, Hershey, PA. PA. Ferrooxidans, Abstract, Abstract, Assoc. MacDonald, Johnson, Allan Allan M., MacDonald, Lawrence Lawrence J.3., , and and Johnson, M., (1983), (1983),Assessment Assessment of of Inactive InactiveIron IronMines Mines in inEast EastIron IronCounty, County,Michigan, Michigan, Mich. Mich. Geol. Geol. Survey Survey:-,- Div. Lansing, Mich., Mich., EN% Lansing, Div. EtJR, 50 80 p. p. Reed, (1975), Reed, R.C., R.C., (1975),Michigan Michigan Iron IronOre OreShipments Shipmentsthrough through1974, 1974,One One Thousand Million Survey Division, Circular Million Tons, Tons, Michigan Geological Survey Circular 12, 12, 12 12 p. p. Van (1973), Acid Acid Mine Mine Water Water Problem Problem at at Stambaugh, Stambaugh, Michigan, Michigan, Van Alstine, Alstine, Jack Jack (1973), Mich. Mich. Geol. Geol. Survey, Survey, File File Report, 15 15 pages pages plus plus Appendix. -j  j I I I J I 1J U J Li J J J J j LI � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1994 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Houghton, Michigan. May 11-14, 1994. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1994 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/e93535ba9a7f7218964703f7fd8f6433.pdf 9907c8db5d636aa3e6933cfcb903ac20 PDF Text Text FORTY-FIRST ANNUAL MEETING ANNUAL MEETING INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY Marathon, MarathonyOntario Ontario May May 13-18, 13-1aY1995 1995 PROCEEDINGS PROCEEDINGS VOLUME VOLUME 41 41 PART 1: I : PROGRAMAND PROGRAM AND ABSTRACTS ABSTRACTS �Annual Meeting 41st Annual Meeting Institute lnstitute on on Lake Lake Superior Superior Geology Geology Ontario Marathon, Ontario May 13-18, 13-18, 1995 1995 Organizing Committee Organizing Committee Genera! General Chairman: Mark Smyk (Ontario Geological Geological Survey) Survey) Secretary-Treasurer: Mark Secretary-Treasurer: Mark O'Brien (Ontario (Ontario Geological Geological Survey) Survey) Program Chair/Abstracts lenbeck Chair /AbstractsEditor: Editor:Manfred ManfredKeh Kehlen beck (Lakehead (Lakehead University) Additional assistance provided by: Bernie Schnieders, Doug Mckay McKayand and Maurice Maurice Lavigne Lavigne (Ontario (Ontario Geological Geological Survey) Survey) with the cooperation cooperation of of the the Ontario Geological Geological Survey and the Ministry Ministry of Northern Development and Mines Proceedings Volume Volume 41: 41 : 1: Abstracts Part I: Part 2: Field Field Trip Trip Guidebooks Guidebooks 2a. Alkalic Rocks Rocks of the the Midcontinent MidcontinentRift Rift 2b. Geology and Base Metal Deposits of the Manitouwadge Greenstone Belt Metal 2c. Geology of the Schreiber Schreiber Greenstone GreenstoneAssemblage Assemblage and its its Gold Gold and Base Base Metal Metal Mineralization Mineralization 2d. Geology Geology and and Gold Gold Deposits Depositsof of the the Hemlo Hemlo Area Area 2e. Kimberlite, Kimberlite, Base Base Metal Metal and and Gold Gold Exploration Exploration Using Using Overburden, Wawa Area Published and Distributed Distributed by by the Institute lnstitute on Lake Lake Superior Geology Mark Jirsa, Secretary-Treasurer Secretary-Treasurer Minnesota Minnesota Geological Geological Survey Survey 2642 University University Ave. Ave. 551 14-1057 U.S.A. U.S.A. St. Paul, MN 55114-1057 ISSN 1042-9964 ISSN 1042-9964 �Institute Institute on on Lake Lake Superior SuperiorGeology Geology Marathon, Ontario Ontario 1995 May 13-18, 13-18, 1995 Proceedings Volume 41 41 Proceedings Volume Part 1: Program Programand andAbstracts Abstracts Mark Smyk Smyk General Chairman, 41st I.L.S.G. I.L.S.G. Ontario Ontario Geological Survey Survey Field Services Services Section Section -- Northwest Ministry of Northern Development Development and Mines James St. St. Suite B002, 435 S. James Thunder Bay, ON ON P7E 6E3 CANADA CANADA Manfred Kehlenbeck Kehlenbeck Abstracts Editor, Editor, 41st 41st I.L.S.G. Program Chair I/ Abstracts Department of Geology Geology Lakehead University Thunder Bay, ON ON P7B 5El 5E1 CANADA CANADA Reference to material material in in Volume Volume 41, 4 1,Part Part1,1,should shouldfollow followthe theexample examplebelow: below: Lightfoot, P.C. P.C .The Therelationship relationshipbetween between mantle mantle plumes, flood basalts and mineralization [abst];; Institute on Lake Superior Geology, Geology, 41st 41st Annual Annual Meeting, Meeting, Marathon, Marathon, ON, [abst] 1995, v.41, part 1, 1, p.42-43. �Contents Part 11 Part Program and Abstracts Institutes Institutes on Lake SuperiorGeology Superior Geologyto to 1995 1995 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . .. Constitutionof ofthe theInstitute Instituteonon Lake Superior Geology Constitution Lake Superior Geology . . . . . . . . . . . . . . . . . . . . . . . . . ii ... By-Laws By-Laws of of the the Institute Instituteon on Lake Lake Superior SuperiorGeology Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii iii Goldich Medal Guidelines Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv Goldich Medal Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Past Goldich Medalists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v 1995 Goldich Medal Recipient/Citation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Banquet Speaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Banquetspeaker Student Travel Award . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Student Student Travel Award Application Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii ... Board of Directors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii ... Local Committees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii LocalCommittees Report of the Chair Chair of of the the 40th 40th Aimual Annual Institute Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x Calendar Calendar of Events Events and and Program Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii Abstracts Abstracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 �INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY INSTITUTE NUMBER 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 DATE PLACE CHAIRMAN 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 Minneapolis, Minneapolis, Minnesota Minnesota Houghton, Houghton, Michigan Michigan East Lansing, Lansing, Michigan Michigan Duluth, Minnesota Minnesota Minneapolis, Minneapolis, Minnesota Minnesota Madison, Madison, Wisconsin Wisconsin Port Arthur, Ontario Ontario Houghton, Houghton, Michigan Michigan Duluth, Duluth?Minnesota Minnesota Ishpeming, Ishpeming?Michigan Michigan St. Paul, Minnesota Minnesota Sault Ste. Marie, Michigan Michigan East Lansing, Michigan Superior, Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Michigan Madison, Madison?Wisconsin Wisconsin Sault Sault Ste. Ste. Marie, Marie, Ontario Ontario Marquette, Marquette?Michigan Michigan St. Paul, Minnesota Thunder Thunder Bay, Ontario Ontario Milwaukee, Milwaukee, Wisconsin Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Wausau7 Kenora, Ontario Kenora? Wisconsin Rapids, Wisconsin Wawa, Ontario Ontario Marquette, Michigan Michigan Duluth, Minnesota Thunder Thunder Bay, Bay, Ontario Ontario Eau Claire, Claire?Wisconsin Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Ontario C.E. Dutton Dutton A.K. Sneigrove Snelgrove BL Sandehr B.T.Sandefur R.W. Marsden E.N. Cameron & R.A. Hoppin E.N. Cameron Cameron E.G. Pye A.K. Sneigrove Snelgrove H. Lepp Lepp A.T. Broderick P.K. Sims Sims & R.K. Hogberg R.W. R.W. White White W.J. W.J. Hinze Hinze A.B. Dickas Dickas G.L. LaBerge M.W. Bartley & E. Mercy D.M. Davidson J. Kalliokoski M.E. Ostrom P.E. Giblin J.D. Hughes M. Walton M.M. Kehlenbeck Kehlenbeck G. Mursky D.M. Davidson Davidson P.E. Meyers Meyers W.C. Cambray D.L. Southwick Southwick T.J. Bornhorst G.L. LaBerge C.E. Blackbum Blackburn J.K. Greenberg E.D. Frey & R.P. Sage Sage J. S. Klasner J.C. Green M.M. Kehlenbeck P.E. Meyers A.B. Dickas Dickas D.L. Southwick Southwick T.J. Bornhorst M.C. Smyk 1 �____________ CONSTITUTION CONSTITUTION OF OF THE THE INSTITUTE INSTITUTE ON ON LAKE SUPERIOR GEOLOGY Article Article I Name Geology'. The name of the organization organization shall be the "Institute Ynstitute on Lake Superior Geology". Article I1 Article II Objectives Obiectives The objectives objectives of this organization organizationare: are: region may exchange ideas and A. To provide a means whereby geologists A. geologists in the Great Lakes region scientific scientific data. data. promote better better understanding understanding of of the the geology of the Lake Superior region. B. To. To promote C. C. To plan and conduct conduct geological geologicalfield field trips. trips. III Article 111 Status Status No part of the income income of the organization shall insure to the benefit of any member or individual. individual. In the event event of of dissolution dissolution the the assets assetsof of the the organization organizationshall shallbe be distributed distributedto to (some tax free free organization). organization). be not not only "scientific" or (To avoid Federal and State income taxes, the organization should be "educational, "educational,but also also "non-profit".) "non-profit".) Mum. Stat. Anno. 290.01, subd. Minn. subd. 4 Minn. Stat. Stat. Anno. 290.05(9) 290.05(9) 1954 Internal Revenue Code s.501(c)(3) S S O 1(c)(3) Article Article IV Membership members hi^ shall consist consistof ofthe theboard boardof ofdirectors. directors. Any Any geologist The membership of the organization shall interested the annual meetings. interested shall be permitted to attend and participate in and vote at the Article V Meetings Meetings The organization year, preferably preferably during duringthe themonth monthof ofApril. April. The place and organization shall meet once a year, exact exact date date of of each each meeting meeting will will be be designated designated by by the the board board of ofdirectors. directors. Article VI Directors Secretary-Treasurer, and and the the last last three three past past The board of directors shall consist of the Chairman, Secretary-Treasurer, than five five persons, persons, by by reason reason of Chairman; but if the board should at any time consist of fewer than directors, the the vacancies vacancies on the unwillingness or inability of any of the above persons to serve as directors, board may be filled membership of the board up to five filled by the annual annual meeting meeting so so as as to bring the membership five members. Article Article VII VII Officers Officers The officers officers of of this this organization organizationshall shall be be aa Chairman Chairmanand and Secretary-Treasurer. Secretary-Treasurer. A. A. The Chairman Chairman shall be elected each year by the board of directors, who shall give due consideration consideration to the wishes of any group that may be promoting the next annual meeting. His His the annual meeting meeting over which he term of office office as Chairman Chairman will terminate at the close of the presides or when his successor shall have have been been appointed. appointed. He will then serve for a period period of three years years as as aa member member of of the the board board of of directors. directors. 11 �B. The Secretary-Treasurer Secretary-Treasurer shall shall be elected at at the annual annual meeting. meeting. His Histerm termof ofoffice officeshall shallbe be B. The two two years years or or until untilhis hissuccessor successorshall shallhave havebeen beenappointed. appointed. Article ArticleVIII VIII Amendments Amendments This This constitution constitutionmay may be be amended amended by by aa majority majority vote vote of of those persons persons who who are are personally personally present present at, at, participating participatingin, in,and andvoting votingatatany anyannual annualmeeting meetingofofthe theorganization. organization. BY-LAWS BY-LAWS I. Duties Dutiesof of the the Officers Officersand andDirectors Directors A. A. It shall shall be the the duty duty of of the the Annual AnnualChairman Chairmanto: to: 1. I. Preside Preside at at the the annual annual meeting. meeting. 2. 2. Appoint Appointallallcommittees committeesneeded neededfor forthe theorganization organizationof ofthe theannual annualmeeting. meeting. 3. Assume Assumecomplete completeresponsibility responsibilityfor forthe theorganization organizationand and fmancing financing of of the the annual annual meeting meeting over which he presides. over which he presides. B. B. shall be be the the duty duty of of the the Secretary-Treasurer Secretary-Treasurerto: to: It shall 1. I. Keep Keepaccurate accurateattendance attendancerecords recordsofofall allannual annualmeetings. meetings. 2. Keep accurate records of all meetings of, 2. Keep accurate records of all meetings of,and andcorrespondence correspondencebetween, between, the the board board of of directors. directors. 3. 3. Hold Holdallallfunds fbndsthat thatmay mayaccrue accrueasasprofits profitsfrom !?om annual annualmeetings meetingsor or field field trips trips and and to to make make these funds available for the organization and operation of future meetings as required. these fbnds available for the organization and operation fbture meetings as required. shall be be the the duty duty of of the the board board of of directors directors to plan locations locations of annual annual meetings meetings and and to to advise advise C. C. ItIt shall on on the the organization organizationand andfmancing fmancingof ofall allmeetings. meetings. 11. II. Duties and Ex~enses Exlenses There shall shall be be no no regular regular membership membership dues. dues. I. 1. There consultation Registration fees for the annual annual meetings shall be determined by the Chairman in consultation 2. 2. Registration with the board of of directors. directors. ItItisisstrongly stronglyrecommended recommendedthat thatthese thesebe be kept keptatataaminimum minimumto to encourage encourageattendance attendanceof of graduate graduatestudents. students. 111. III. Rules Rules of of Order Order The The rules rules contained contained in in Robert's Rules Rules of Order shall govern this organization organization in all cases to which they are are applicable. applicable. IV. IV. Amendments Amendments These These by-laws by-laws may may be be amended amended by by aa majority vote vote of of those persons who are personally personally present present at, at, participating participatingin, in, and and voting voting at at any any annual annual meeting meeting of of the organization; organization;provided provided that that such such modifications modificationsshall shallnot not conflict conflictwith with the the constitution constitutionas as presently presently adopted adopted or subsequently subsequently amended. amended. 111 �Award Guidelines Guidelines SAM GOLDICH GOLDICH MEDAL MEDAL Preamble Preamble The Institute on Lake Superior Superior Geology Geology was born on or around 1955, 1955?as as documented by the fact that the 27th annual annual meeting was held 1. The Institutes are exemplary in aspects of of held in in 198 1981. in their their continuing objectives of dealing with those aspects geographically to Lake Superior; Superior; of encouraging encouraging the discussion of subjects and sponsoring sponsoring field field geology that are related geographically academia7government government surveys, surveys, and industry; industry; and and of of maintaining maintaining an an trips which will will bring bring together together geologists geologistsfrom from academia, exceedingly informal but highly effective effective mode of operation. the course course of of its its existence existence the the membership membership of of the the Institute Institute (that (that is, is,those thosegeologists geologistswho whoindicate indicate an an interest interest in in During the the objectives objectives of of the the I.L.S.G. I.L.S.G. by by attending) attending) has has become become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to to the the improvement improvementof ofunderstanding understandingof of"Lake 'Lake Superior" geology geology mineral deposits. and its mineral deposits. The exemplary award award was was made made by by I.L.S.G. I.L.S.G. to to Sam Goldich Goldich in in 1979 for for his his many many contributions contributions to to the the geology geology of of the the region extending extending over over about about 50 50 years. years. Award Guidelines Guidelines 1) by the the I.L.S.G. I.L.S.G.Board Board of ofDirectors Directorstotoaageologist geologistwhose whosename name is is associated associated The medal shall be awarded annually by with a substantial substantial interest in, or a major contribution contribution to, the geology of the Lake Superior region. 2) shall appoint appointthe theNominating NominatingCommittee. Committee. The The initial initial appointment appointment will will be be of of The Board of Directors, 1.L.S.G. I.L.S.G. shall three members, one one to to serve serve for for three three years, years, one one for for two, two7and and one one for for one one year, year, the member member with the briefest briefest incumbency to be chairman. After the first the Board Board of ofDirectors Directorsshall shallappoint appointatateach each spring springmeeting meeting one one fxst year the three years. years. In the third year year this this member member shall shallbe bethe thechairman. chairman. The Committee new member who will serve for three membership should geographic distribution of I.L.S.G. membership. membership should reflect reflect the main fields fields of interest and geographic 3) By November 1, the Goldich Medal Medal Nominating NominatingCommittee Committeeshall shallmake makeits itsrecommendation recommendationto tothe the Chairman Chairman of of the Board of Directors Directors who who will then inform the Board of the nominee. 4) The Board Board of of Directors Directors normally normally will will accept accept the the nominee nominee of of the theCommittee, Committee, will will inform inform the the medalist medalist immediately, engravedappropriately appropriatelyfor forpresentation presentationatatthe thenext nextmeeting meetingofofthe theInstitute. Institute. immediately,and and will will have have one onemedal medalengraved 5) recommended that Institute set aside annually from whatever such funds will betorequired to fiom whatever sources,sources, such funds as will be as required It is recommended that thethe Institute set aside annually support the continuing continuing costs of this award. April 4, 1981 198I Kalliokoski, Chairman J. Kalliokoski, Bill Cannon Fred Kehlenbeck G.B. Morey Morey Greg Mursky iv �GOLDICH GOLDICH MEDAL COMMITTEE COMMITTEE1994-95 1994-95 Glen Adams (1995) Crystal Exploration, Exploration, Inc., Inc., Crystal Crystal Falls, Falls, MI MI 44420 44420 Crystal Penelope. Morton (1996) (1996) Department Department of of Geology, Geology, University UniversiQ of of Mimiesota Minnesota Duluth, Duluth, Duluth, Duluth, MN MN Card (1997) Ken Card (1997) Geological Survey Survey of of Canada, Canada,Ottawa, Ottawa,ON ON K1A KIA 0E8 OE8 Geological GOLDICH GOLDICH MEDALISTS MEDALISTS 1979 1980 1981 1982 1983 1984 1985 1986 Samuel Samuel S. Goldich Goldich 1987 Henry HenryH. H. Halls Halls 1988 Walter WalterS. S.White White 1989 Jorma JormaKalliokoski Kalliokoski 1990 Kenneth KennethC. C. Card Card 1991 William J. Hmze Hinze 1992 William F. Cannon Cannon WilliamF. 1993 Donald DonaldW. W. Davis Davis 1994 Cedric CedricIverson Iverson not awarded Carl E. Dutton, Dutton, Jr. Jr. Ralph W. Marsden Burton Burton Boyum Richard Richard W. W. Ojakangas Ojakangas Paul K. Sims Sims G.B. Morey 1995 Gene 1995 Gene LaBerge LaBerge /9525 &A 77%ch//e4inn/ ne ta/ir1o Citation Citation Gene L. LaBerge, 1995 Goldich Medal Recipient am pleased pleased and and honored honored to to introduce introduce you you to to For all of you associated associated with the Institute on Lake Superior Geology, II am Gene L. LaBerge as this year's recipient geologist whose whose name name recipient of of the the Sam Sam Goldich GoldichMedal. Medal. The medal is awarded "to a geologist is associated with with aa substantial substantialinterest interestin, in,or oraamajor majorcontribution contributionto, to,the thegeology geologyofofthe theLake LakeSuperior Superiorregion". region". Gene is certainly worthy on both counts. counts. Gene was born and raised in Ladysmith, Wisconsin, appropriately, appropriately,the thehome homeof ofthe therecently recentlydeveloped developedFlambeau Flambeau mine. mine. V �After a stint in the the U.S. U.S. Marine Marine Corps, Corps,he hebegan beganhis hisgeology geology education education at at UW-Superior, UW-Superior, eventually eventually obtaining his B.S., related to the the origin origin of of magnetite magnetite M.S. and Ph.D. degrees in geology from from UW-Madison. UW-Madison. The topic of his dissertation related iron-formation. in iron-formation. first two two summer summer jobs, jobs, while while he he was was aagraduate graduate student, student, introduced introduced him to aspects aspects of of geology geology that that were were to to Gene's first 1957, he was hired Ishpeming, Michigan Michigan become his primary research interests. In 1957, hired by Ralph Marsden of U.S. Steel in Ishpeming, Ralph and and Stan Stan Tyler of UW-Madison, Gene's fhture advisors, would include include the the to explore for iron-formation. Ralph future Ph.D. advisors, summer help on regional field field trips trips to look look at at iron-formation. iron-formation.Gene Geneclaims claimsthat thatititwas wasaadirect directresult resultof ofthe thequestions questions this area. It has led international posed by Ralph and Stan Stan that inspired inspired his research interest i n t e r e ~in in4his led40 to 6 publications in international journals, numerous of aa book book on on Precambrian Precambrian iron-formations. iron-formations. In numerous presentations presentations at at national meetings, and the editing of 1958, Gene Gene worked worked for U.S. Steel as a field assistant to to Ced Ced Iverson Iverson doing doing aa pebble pebble survey survey in in Wisconsin. Wisconsin. After 1958? identif'ing several identifying severalbillion pebbles that summer, summer, Gene was convinced convinced that the Precambrian geology of Wisconsin was more than aa "green "greenblob" blob" on on the the map. map. InIn1969, 1969,he heconceived conceivedand andinitiated initiated aa regional regional mapping mapping and Natural History Onthe theadvice adviceof ofCarl CarlDutton, Dutton, the the project project was was begun begun in incentral central Survey under the direction of George F. Hanson. On Wisconsin near Wausau. Since Wisconsin Since1982, 1982,support supportfor for this this on-going on-going research research has has been been provided provided by by the the U.S. U.S. Geological Geological Society. This national publications, numerous reports and maps for both the This program program has has resulted in several national the WGNHS WGNHS and the USGS, and over 30 papers at professional meetings. In In 1994, 1994,this work was collated to form the basis of his book, Geology Geolom of the Lake Superior Su~eriorRegion. Region. I know Gene best the best in in the the role role of of educator. educator. InIn1965, 1965,he hejoined joined the the faculty faculty at at UW-Oshkosh as the third member of the department with the charge of designing and building the geology program. Since he began teaching, he has led in the charge of designing program. Since I remember Gene saying that he "walked over more of Wisconsin that almost excess of 100 Wisconsin almost 100ovemight overnightstudent studenttrips. trips. anyone -- from Baraboo to Lake Superior". Superiorv'.We Wedidn't didn't doubt doubtit, it,but but wondered wondered ifif he he meant meant to to add add "on "on the the same sametrip". trip". He sure seemed seemed to have have the the stamina. stamina. Recently RecentlyGene Geneconfided confided in in me me that that aa major major stimulus stimulus for for his his work work in in central central Wisconsin was the students' students' questions, questions, "So "So simple, simple, yet so difficult difficult to answer". As Asaatestament testamentto tohis hissuccess successin inacademia, academia, Gene has received received all all of of the teaching teaching and and research research awards that UW-Oshkosh offers, the only faculty member to have done done so. so. Gene also has has aa long long history history with with the the ILSG. ILSG. Gene in Duluth in 1958 Gene attended attended his first f ~ smeeting t 1958 and presented presented his first paper at the 1960 meeting meeting in inMadison. Madison. Since that time, he has presented over 20 20 papers papers and led or co-led 5 field trips with accompanying accompanying guides. guides. Through the years, years?Gene Gene and and IIhave haveinteracted interacted on onmany manylevels, levels,teacher, teacher,mentor, mentor, fellow fellow guitar guitar player, player?researcher, researcher, colleague and and most most rewardingly, rewardingly,as as aa fiiend. friend. As he joins joins an elite and colleague As the the 16th 16threcipient recipient of the Goldich Goldich Medal, Medal, he distinguished group. II am am pleased pleased to to present present to you, Gene LaBerge. LaE3erge. Tim Flood Natural Sciences Sciences Division, St. Norbert College DePere, Wisconsin Wisconsin BANQUET SPEAKER SPEAKER Peter Lightfoot Peter Lightfoot(Ontario (OntarioGeological GeologicalSurvey, Survey,Sudbury) Sudbury) relationship between mantle plumes, plumes,jlood flood basalts basalts and and mineralization The relationship vi �__________________________________________________________________ _________________________________ ____________________ _______________ ______ ______ STUDENT TRAVEL STUDENT TRAVEL AWARD The 1986 1986 Board of Directors Directors established established the I.L.S.G. Student Student Travel Award to support student participation at the annual Institutes. The purpose. This Theawards awardswill will be be made made from from aa special special fund set up for this purpose. This award award is intended intended to help defray some some of the direct direct travel travel costs to the Institute Institute and includes a waiver of registration fees, but excludes expenses for meals, lodging, and field trip trip registration. The number of awards and value are determined by by the the annual Chairman Chairman in consultation consultation with the Secretary-Treasurer and will be announced at the annual banquet. The following following general general criteria criteria will be considered considered by the annual Chairman, Chairman, who is responsible for the selection: selection: 1) 1) The applicants applicants must have active resident (undergraduate or graduate) student status at the time of the Institute, certified Institute, certified by by the the department departmenthead. head. 2) 2) Students Students who are the senior senior author author on either an oral or poster paper will be given favored consideration. consideration. 3) It is desirable desirable for for two two or or more more students studentsto to jointly jointly request requesttravel travelassistance. assistance. 4) 4) In general, general, priority priority will be given to those in the Institute region who are farthest away. with an explanation of 5) Each Each travel award request shall be made in writing, to the annual Chairman, with need, possible author status or other significant details. possible author status or other significant details. Successful Successful applicants applicants will will receive receive their their awards awardsatatthe the time timeof ofregistration registrationfor forthe theMeeting. Meeting. INSTITUTE INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Student Travel Award Award Application Application Please Pleaseprint: print: Date: Date: Student Student Name: Name: Address: II certify that the the above named person is is an active resident student. 1I 1I1 Department Department Head Head -- Typed Typed Department Department Head Head -- Signature Signature Date Date Educational Educational Status: Are you the Senior Author of an oral or poster paper? Yes Yes Will any other students will be traveling with you? 1I - - No No - How many? many? Statement Statementof ofNeed: Need:(If(Ifyou youneed needmore moreroom, room,please pleaseuse usethe theback back of of the the page.) page.) Other Significant Significant Details: Details: return to: Please return vii �BOARD OF OF DIRECTORS DIRECTORS BOARD 1995 1995 MarkC. C.Smyk, Smyk,Chairman Chairman Mark Ontario OntarioGeological GeologicalSurvey, Survey,Thunder ThunderBay, Bay,Ontario OntarioP7E P7E6E3 6E3 1994 1994 TheodoreJ.J.Bornhorst Bornhorst Theodore MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton,Michigan Michigan49931 4993 1 Michigan 1993 1993 DavidL. L.Southwick Southwick David Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Minnesota 55114 55 114 1992 1992 AlbertB. B.Dickas Dickas Albert University University of of Wisconsin-Superior, Wisconsin-Superior, Superior, Superior, Wisconsin 54880 54880 Secretary-Treasurer Secretary-Treasurer Mark ursa Jirsa Mark MinnesotaGeolgical GeolgicalSurvey Survey Minnesota 2642 University UniversityAve. Ave. 2642 MN55 551 14-1057 St.Paul, Paul,MN St. 114-1057 LOCAL LOCAL COMMITTEES COMMITTEES GENERAL CHAIRMAN MarkC. C.Smyk Smyk Mark Ontario OntarioGeological GeologicalSurvey, Survey,Field FieldServices ServicesSection Section Thunder Bay, Bay, ON ON P7E P7E6E3 6E3 Thunder PROGRAM CHAIR AND EDITOR PROGRAM CHAIR AND ABSTRACTS ABSTRACTS EDITOR ManfredKehienbeck Kehlenbeck Manfred Department of of Geology, Geology,Lakehead Lakehead University University Department Thunder Bay, Bay, ON ON P7B P7B5E1 5E1 Thunder SECRETARY-TREASURER Mark O'Brien O'Brien Mark Ontario Ontario Geological GeologicalSurvey, Survey,Field Field Services ServicesSection Section Thunder Bay, ON P7E P7E6E3 6E3 Thunder COMMITTEE ASSISTANCE Bernie Schnieders, Schnieders, Doug McKay and and Maurice MauriceLavigne Lavigne Ontario Ontario Geological GeologicalSurvey, Survey,Field FieldServices ServicesSection Section P7E 6E3 6E3 Thunder Bay, ON P7E viii �STUDENT PAPER COMMITTEE Mark Jirsa Jirsa (Chair) (Chair) Mark Minnesota Minnesota Geological GeologicalSurvey Survey St.Paul,MN St. Paul, MN55114-1057 551 14-1057 Virginia Virginia Peterson Peterson Department Departmentof ofGeosciences Geosciencesand andAnthropology, Anthropology, Western Western Carolina CarolinaUniversity Cullowhee, Cullowhee, NC 28723-9047 28723-9047 David Laderoute Laderoute Ontario Ontario Geological Geological Survey, Survey,Field Field Services Services Section Section Thunder Bay, ON P7E 6E3 P7E 6E3 SESSION CHAIRS Ted Ted Bornhorst Bornhorst Michigan Technological TechnologicalUniversity University Michigan Houghton, Houghton, MI 49931 4993 1 Mark Jirsa Jirsa Mark Minnesota MinnesotaGeological GeologicalSurvey Survey MN 55114-1057 St. Paul, Paul, MN 551 14-1057 St. Maurice Maurice Lavigne Lavigne Ontario Ontario Geological Geological Survey, Survey,Field Field Services ServicesSection Section Thunder Thunder Bay, ON P7E P7E6E3 6E3 Jim Jim Miller Miller Minnesota Minnesota Geological GeologicalSurvey Survey Paul, MN 55114-1057 MN 551 14-1057 St. Paul, St. Bernie Schnieders Bernie Schnieders Ontario Ontario Geological GeologicalSurvey, Survey,Field FieldServices ServicesSection Section Thunder Bay, Bay, ON ON P7E P7E6E3 6E3 Thunder Cliff Shaw Shaw Cliff Department Department of of Geology, Geology,University Universityof of Western Western Ontario Ontario London, London, ON N6A N6A5B7 5B7 Laurel Woodruff United United States States Geological Geological Survey Survey MN 55112 St. Paul, Paul, MN 55 112 St. Eva Zaleski Zaleski Eva Canada Geological Survey Survey of of Canada Geological Calgary, AB T2L T2L 2A7 2A7 Calgary, AB ix �REPORT OF OF THE THE CHAIRMAN CHAIRMAN GEOLOGY 40TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY HOUGHTON, MICHIGAN MICHIGAN The 40th Annual Institute on Lake Superior Superior Geology Geology was held May 11-14, 11-14, 1994 1994 on on the the campus campus of of Michigan Michigan Technological University The meeting meeting was was hosted by the Department of Geological University in in Houghton, Michigan. Michigan. The Engineering, Geology, and Geophysics with assistance assistance from from the the Division Division of of Education Educationand andPublic PublicServices. Services. The The meeting Chairman was Theodore Theodore J. J. Bornhorst Bornhorst who who handled handled all all aspects aspects of of the the meeting meeting including including the the technical technical sessions and the field trips. published in in 55 parts parts as as Volume Volume 40, 40, Part 1: Program and The Proceedings of the 40th Annual ILSG was published and Abstracts Abstracts by Theodore J. J. Bornhorst and S. Douglas McDowell, McDowell, and and aa series series of of 44 field field trips, trips, including; including; Part Part 2: 2: Selfedited by guided geological field trip to the Keweenaw Peninsula, Peninsula, Michigan Michiganby by Theodore TheodoreJ.J. Bornhorst Bornhorst and and William William I.I. Rose; Part 3: Volcanic Royale, Michigan Michigan by by William WilliamI.I. Rose; Rose; Part Volcanic geology of eastern Isle Royale, Part 4: 4: Michigan Michigan kimberlites kimberlites and by Shawn Shawn M. M. Carlson and and Wayde Wayde Floodstrand; Floodstrand; and and Part Part 5: 5: Lessons Lessons from from mining mining diamond exploration techniques by case histories: West Menominee Range, Range, Michigan Michiganby byAllan AllanM. M.Johnson. Johnson. For the field trip to the White Pine and Caledonia Mines no ILSG ILSG guidebook guidebook was published and instead the trip used Society of Economic Geologists Guidebook Series Volume 13 13 titled "Keweenawan "Keweenawan Copper Deposits of Western Upper Michigan" Michigan" edited edited by Theodore J. Bomhorst. ofthe theILSG. ILSG. The field trip to Isle Bornhorst. Field Fieldtrips tripscontinue continueto to be be an an important important component component of Royale National Park was the first ever ever geological geological field trip to the island. A total of 154 meeting. Field 154 people registered for the meeting. Fieldtrips trips attracted attracted121 121paid participants, including: 24 for Keweenaw Peninsula, 13 13 for Isle Isle Royale, 41 41 for for Michigan Michigan kimberlites, kimberlites, 13 13 for Menominee Menominee Range and 30 for White Pine/Caledonia. PineICaledonia. banquet was was attended attended by by about about 105 people. people. Cedric The annual banquet Cedric Iverson Iverson was was awarded awarded the Institute's Institute's prestigious prestigious Goldich Medal. Medal. The given by by Geoffrey GeoffreyS. S. Plumlee, Plumlee,U. U. S. S. Geological GeologicalSurvey. Survey. His topic was was Goldich The banquet banquet address was given "The crucial (but underutilized) role of the economic economic geologist in predicting and remediating the environmental effect of mineral resource development." development." Optional lunch was offered on both days of the technical sessions and featured speakers, speakers, Larry Larry Lankton Lanktonon on Keweenaw Peninsula mining mining history history and and Stan Stan Dyl Dyl on on minerals mineralsin in Russia. Russia. The Keweenaw The lunch program was well received received as a total of 140 140attended attended the the two two lunches. lunches. The best student paper awards went to Nicholas Van Wyck, University of of Wisconsin, Madison Madison and and Elizabeth Elizabeth Kropf, Macalester College for best oral or poster presentation, respectively. respectively. Student Student travel awards, awards, for for aa total total of of $375, were awarded awarded to to Elizabeth Elizabeth Kropf, Kropf, Leslie Leslie Magnus, Magnus, Gwendolyn Gwendolyn Miner, Micheal Micheal Rogers, Rogers, and and Mark Mark Schmitz. Schmitz. lengthy discussion discussionon onthe thefuture futureofofthe theILSG. ILSG. At this time they they directed the the In 1993, the Board of Directors had a lengthy incoming Chairman, Chairman, T.J. Bomhorst, component of ofthe the40th 40thAnnual Annualmeeting. meeting. In incoming Bornhorst, to to increase increase the "environmental" "environmental" component resulted in in 20% 20% of the abstracts being response to this directive, "environmental" "environmental" papers were solicited which resulted "environmental" as compared to a median of 2% 2% in in this topic category for past meetings (by far the 40 year high). A mining-related environmental environmental field trip was solicited solicited (Menominee Range) and the banquet speaker addressed a topic. These mining-related environmental topic. These changes changes in in topics topics covered by the ILSG seemed to be well received by the meeting participants. The Board of Directors of the Institute Houghton, Michigan Michigan on on May May 12, 1994. Institute on Lake Superior Superior Geology met in Houghton, In attendance were were T. T.J. Bornhorst (Chairman), A.B. Dickas, G.L. LaBerge for Paul Meyers, Jim Miller for for Dave Dave J. (Chairman), A.B. Dickas, G.L. for Meyers, Jim Miller Southwick, and and M.G. M.G. Mudrey, Jr. (Secretary-Treasurer). Guests included Mark Smyk, Bill Cannon, and R. (Secretary-Treasurer). Guests included Sage. Actions Actions taken taken were: were: 1. Approved Approved an offer offer by by the the Ontario OntarioGeological GeologicalSurvey Survey to to host host the the 41st 41st Annual Annual Institute Institute (1995) (1995) in in Marathon, Marathon, Ontario. Mark MarkSmyk Smykwill willbe be Chairman. Chairman. x �2. Approved Approved an anoffer offerby bythe theU. U.S.S.Geological GeologicalSurvey Surveytotohost hostthe the42nd 42ndAnnual Annual Institute Institute (1996) (1996) near near Cable, Cable, 2. Wisconsin. Laurel Wisconsin. LaurelWoodruff Woodruffwill willbe bethe thefirst firstever everwoman womanChair Chairofofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology. Geology. 3. Endorsed Endorsedan anoffer offerby bythe theOntario OntarioGeological GeologicalSurvey Surveytotohost hostthe the43rd 43rdAnnual AnnualInstitute Institute(1997) (1997)ininSudbury, Sudbury, 3. Ontario. Approval Approvalwill willbe benecessary necessaryatataafuture futuremeeting meetingof ofthe theBoard Board of of Directors. Directors. Ontario. 4. 4. Appointed Appointed Theodore Theodore J. J. Bornhorst Bornhorst to to the the post of Associate Secretary-Treasurer. This This action action was was taken taken to facilitate guidebookunder underthe the auspices auspicesofofthe theInstitute. Institute. The facilitate selling selling the popular popular Keweenaw Peninsula field guidebook Associate Secretary-Treasurer Secretary-Treasurer will willbe be backup backup the the signature signatureon onthe theInstitute Institute accounts. accounts. Associate 5. Received Received and and accepted a Financial Report from Secretary-Treasurer Secretary-Treasurer Mudrey. Mudrey. The 5. The net net assets assets of the Institute Institute on Superior Geology as of May 10, 10,1994 1994are are $9,965 $9,965.26. Studenttravel traveland andpaper paper awards awardsand and39th 39thAnnual Annual Lake Superior .26. Student meeting overrun accounted for $3411.27 $3411.27 net decrease in assets. To Tohelp helpavoid avoidfuture futuredecrease decreaseininassets assetsthe theBoard Board of Directors Directors agreed agreedthat thatStudent StudentTravel TravelAwards Awardsbe belimited limitedtotointerest intereston oninvestments investments(the (theChairman Chairmanshould shouldcontact contact the the Secretary-Treasurer Secretary-Treasurerto todetermine determinethe theamount amount to to be be awarded) awarded) and and that that Student Student Paper Awards should should be funded by the local local meeting meeting budget. budget. 6. Approved Approved Cedric Cedric Iverson Iverson for forthe the 1994 1994Goldich Goldich Medal Medal Award. Award. K. Card Card(representing (representinggovermnent) government) to to aa 33 year year term termon onthe theGoldich Goldich Medal Medal Conmiittee. Committee. 7. Appointed Appointed K. 7. 8. 8. Discussed Discussedownership ownershipof of Institute Institutefield fieldtrip tripguidebooks guidebooksand and agreed agreedthat that the the Institute Instituteowned owned the the guidebooks guidebooks only only when it paid for printing. printing 9. 9. Discussed Discussed the the future future of of the theInstitute. Institute.Agreed Agreedthat thatenvironmental environmentaltopics topicsneed neednot notbe besolicited solicitedfor forthe theMarathon Marathon meeting (41st ILSG) next year, but for the Cable, Wisconsin (42nd ILSG) it may be desirable to once meeting year, but for the Cable, Wisconsin (42nd ILSG) it may be desirable to once again again solicit solicit environmental environmental material for for the the ILSG. ILSG. 10. of Secretary-Treasurer for for aa term term of of two two years. years. The 10. Approved Approved an election for the position of TheBoard Board discussed discussed be held, at least, every the the need need to to have have elections elections on on aa more more regular regular schedule. schedule. It was agreed agreed that elections should be every 4 years. years. The election for a new Secretary-Treasurer was held on May May 12, 1994 at at the the annual annualbanquet. banquet. Mark Jirsa, Jirsa, Minnesota Geological Geological Survey, Survey, was was elected elected to to the the post. post. I am am sure the institutes institute'sfinances finances are are in in good good hands. hands. Financially the 40th Annual ILSG was an overwhelming success. success. The The combination combination of excellent budget help of Marty Banks Banks and Mary Mary Rouleau, Rouleau,Michigan MichiganTech TechDivision Division of of Education Education and and Public Public Services Servicesand and advice advicefrom fromDave Dave Southwick Southwick helped me avoid the deficit deficit which which occurred occurred from from the the meeting meeting last last year. year. I am pleased to report a profit of about $4,000 $4,000 from from the the 40th 40th Annual Annual meeting. meeting. Exact Exactnumbers numbersare arenot notpossible possiblesince sincepublications publications continue continue to to be be sold. The TheKeweenaw KeweenawPeninsula Peninsulaguidebook guidebook(Volume (Volume40, 40, Part Part2), 2),published publishedand anddistributed distributedby by the the Institute Instituteon on Lake Lake Superior Superior Geology, Geology, is is now now in in its its second second printing printing as as the the first first printing printing of 250 250 copies is sold out. Profits from sale sale of the guidebook guidebook will go the Institute's treasury. treasury. On a personal note, I'm I'mglad gladtotobe befinished finishedwith with the thetask taskof of being being Chairman Chairmanof of the the 40th 40th Institute Institute on on Lake Lake Superior Superior Geology. It is is easier easier being being Chairman Chairman the the second second time, time, but but itit still still requires requires aa lot lot of of work. work. I thank all all those who who Geology. have have given given me me positive positive feedback, feedback, since since this helps make all of the work more worth doing. Despite Despitethe the disappointment disappointment for the White Pine/Caledonia PineICaledonia field field trip trip when when aa totally totally unexpected unexpected mine fire fire precluded precluded going going underground at White Pine, II consider consider the the 40th 40th ILSG ILSG to to have been a very successful successful meeting. Respectively Submitted, Submitted, Bornhorst Theodore J. Bomhorst Chairman 40th 40th ILSG ILSG Chairman September September 19, 19,1994 1994 Houghton, Michigan Michigan Houghton, xi �PROGRAM PROGRAM �C A L E N D A R OF O F EVENTS E V E N T S AND A N D PROGRAM PROGRAM CALENDAR PRE-MEETING FIELD FIELD TRIPS TRIPS PRE-MEETING Field trips depart from the Marathon Marathon Recreation Recreation Complex at 8:OO return each 8:00 a.m. and return evening by about 6:00 6100 p.m. p.m. 1995 SATURDAY MAY MAY 13, 13.1995 TRIP lIaa FIELD TRIP (DAY ONE OF TWO DAYS) DAYS) ALKALIC ROCKS OF THE MIDCONTINENT MIDCONTINENT RIFT FIELD TRIP 2A (DAY ONE ONE OF TWO DAYS) DAYS) MANITOUWADGE GREENSTONE MANITOUWADGE GREENSTONE BELT BELT SUNDAY MAY 1995 MAY 14. 14,1995 TRIP lIaa FIELD TRIP (DAY TWO OF TWO DAYS) IDAY DAYS) ALKALIC ROCKS OF THE MIDCONTINENT RIFT FIELD FIELD TRIP TRIP 2a (DAY TWO OF TWO DAYS) lDAY DAYS) MAN ITOUWADGE GREENSTONE GREENSTONE BELT MANITOUWADGE BELT FIELD TRIP 3a GREENSTONE ASSEMBLAGE SCHREIBER GREENSTONE ASSEMBLAGE FIELD TRIP 4 HEMLO HEMLO GREENSTONE GREENSTONE BELT BELT I:I: REGIONAL REGIONAL GEOLOGY GEOLOGY 1995 SUNDAY MAY 14. 14,1995 REGISTRATION REGISTRATION MARATHON RECREATION MARATHON RECREATION COMPLEX COMPLEX 4:00 pm. 1O:OO pm. pm. 4:OO pm. - 10:00 - POSTER (authors POSTERSESSION SESSION (authorsatatposters) posters) - - - CASH BAR BAR MIXER MIXER MONDAY 1995 MONDAY MAY MAY 15. 15.1995 REGISTRATION REGISTRATION CONTINUES CONTINUES 8:00 8:OO am - 4:30 pm pm - xii �TECHNICAL PROGRAM PROGRAM MONDAY MAY 15. 15,1995 1995 - MORNING - SESSION SESSION II MORNING CHAIRS: Ted Bornhorst Born horst and Eva Zaleski Zaleski 8:45 8145 WELCOME WELCOME 1. 8:50 8:50 BERENDSEN, BERENDSEN, P. P. HISTORY AND AND DEVELOPMENT OF OF THE THE SOUTHERN EXTENSION EXTENSION OF THE MID-CONTINENT MID-CONTINENT RIFT RIFT IN IN KANSAS KANSAS 2. ** HALLS, HALLS, H.C. H.C. MANSON, MANSON, M.L. M.L. ZHANG, ZHANG, B. B. ARE THE MAJOR THRUST FAULTS OF THE MID-CONTINENT MID-CONTINENT RIFT RIFT TECTONIC AND THE KAPUSKASING KAPUSKASING ZONE PART OF THE SAME TECTONIC ZONE? ZONE? 3. 9:10 9110 CORFU, F. CORFU, F. STOTT, G.M. STOTT, G.M. U-Pb GEOCHRONOLOGY OF THE SHEBANDOWAN SHEBANDOWAN GREENSTONE GREENSTONE BELT, SUPERIOR PROVINCE ONTARIO PROVINCE ONTARIO 4. 9:30 9130 * KING, KING, D. D. FRALICK, FRALICK, P.W. P.W. DEPOSITIONAL SYSTEMS SYSTEMS ASSOCIATED DEPOSITIONAL ASSOCIATED WITH THE 3.0 GA FINLAYSON AND LUMBY LAKE LUMBY LAKE GREENSTONE GREENSTONEBELTS, BELTS, NORTHWESTERN ONTARIO NORTHWESTERN ONTARIO 9:50 9:50 COFFEE BREAK BREAKAND AND POSTER POSTER SESSION SESSION 5. 10:20 LaBERGE, LaBERGE, G.L. G.L. CANNON, W.F. CANNON, W.F. KLASNER, KLASNER, J.S. J.S. 6. 10:40 10:40 * PUFAHL, PUFAHL,P.K. P.K. FRALICK, FRALICK,P.W. P.W. 7. 11:00 * PETERSON, 1l:OO PETERSON,D.M. D.M. 8. 11:20 11:20 9. 9. 11:40 I 1:40 JIRSA, M.A. CHANDLER, V.M. CHANDLER, BOERBOOM, T.J. BOERBOOM, T.J. NOON NOON LUNCH BREAK BREAK * SHORE, SHORE, C. G. NEW OBSERVATIONS ON THE THE GEOLOGY OF THE WESTERN WESTERN GOGEBIC IRON RANGE, NORTHERN WISCONSIN PALEOGEOGRAPHIC RECONSTRUCTION OF THE GUNFLINTGUNFLINTMESABI-CUYUNA MESABI-CUYUNA DEPOSITONAL DEPOSITONAL SYSTEM: SYSTEM: A BASIN BASINANALYSIS ANALYSIS APPROACH APPROACH SULFIDE DEPOSITS DEPOSITS EXPLORATION EXPLORATION IN THE TARGETING MASSIVE SULFIDE WESTERN VERMILLION DISTRICT: VOLCANOLOGICAL CONTROLS DISTRICT: VOLCANOLOGICAL CONTROLS ON THE ORIGIN OF ALKALINE GABBROIC ROCKS ROCKS IN THE COLDWELL PENINSULA PENINSULA AREA, COLDWELL COLDWELLALKALINE ALKALINECOMPLEX, COMPLEX, ONTARIO ONTARIO THE WISCONSIN WISCONSIN MAGMATIC MAGMATIC TERRANES TERRANES INTO EXTENSION OF THE THE MINNESOTA SEGMENT OF THE PENOKEAN OROGEN OROGEN ** Student Student paper paper ** cancelled ** cancelled paper ... xlii X lll �MONDAY MAY 15. 1995 - AFTERNOON - SESSION SESSION III1 AFTERNOON Jim Miller Miller and Maurice CHAIRS: Jim Maurice Lavigne Lavigne 10. 10. 2:00 2100 * SCHNEIDER, SCHNEIDER, D.A. D.A. HOLM, HOLM, M. M. HISTORIES OF OF COMPARISON OF POST-PENOKEAN THERMAL HISTORIES THE WATERSMEET AND REPUBLIC DISTRICTS, DISTRICTS, NORTHERN NORTHERN MICHIGAN: MICHIGAN:RESULTS RESULTSAND ANDIMPLICATIONS IMPLICATIONSOF OF40 40 Arl39 Ar/39 Ar DATING MINERAL AGE DATING 11. 11. 2:20 HOLM, HOLM, D.K. D.K. THERMOCHRONOLOGY OF CENTRAL CENTRAL MINNESOTA MINNESOTA REVISITED: REVISITED: IMPLICATIONS IMPLICATIONS FOR THE THE POST-COLLISIONAL POST-COLLISIONAL EVOLUTION OF THE OROGENIC BELT PENOKEAN OROGENIC 12. 12. 2:40 * DARRAH, DARRAH, KS. KS. HOLM, HOLM, D.K. D.K. APPLICATION BAROMETER APPLICATION OF THE ALUMINUM-IN-HORNBLENDE ALUMINUM-IN-HORNBLENDE BAROMETER ON EARLY PROTEROZOIC, POST-PENOKEAN PLUTONS, PLUTONS, CENTRAL CENTRAL MINNESOTA MINNESOTA 3:00 3100 COFFEE BREAK BREAK AND AND POSTER POSTER SESSION SESSION 13. 13. 3:30 3:30 * KOEBERNICK, KOEBERNICK, C.F. NEOARCHEAN COASTAL COASTAL SEDIMENTATION SEDIMENTATION IN THE THE C.F. NEOARCHEAN FRALICK, SHEBANDOWAN GROUP, NORTHWESTERN FRALICK,P.W. P.W. NORTHWESTERN ONTARIO ONTARIO 14. 14. 3:50 3:50 NORTH, NORTH, J. J. 15. 15. 4:10 4110 * FEHER, FEHER, L. L. FLOOD, T. AND SUPERGENE SUPERGENE OXIDATION OXIDATION OF PREKEWEENAWAN UPLIFT AND PENOKEAN, SUPERIOR TYPE IRON IRON FORMATION FORMATION VESICLES AND BRECCIA DUE TO INJECTION INJECTION OF MAFIC MAFIC MAGMA MAGMA INTO PARTIALLY LITHIFIED SEDIMENTS OF THE EARLY PROTEROZOIC IRONWOOD IRON FORMATION FORMATION WESTERN GOGEBIC RANGE, RANGE, NW NW WISCONSIN 4:30 SESSION SESSION END END 6:00 6:OO HALL - MIXER - CASH BAR MOOSE HALL 7:30 7130 HALL -- BANQUET MOOSE HALL BANQUET AND AWARDS AWARDS PRESENTATION PRESENTATION Speaker: Peter The relationship relationshipbetween between mantle Banquet Speaker: Peter Lightfoot Lightfoot-- The plumes, flood basalts basalts and mineralization. mineralization. ** Student Student paper xiv �TUESDAY MAY MAY 16. 16.1995 TUESDAY 1995 - MORNING MORNING- SESSION SESSIONIIIIll CHAIRS: Laurel Laurel Woodruff Woodruff and and Bernie Bernie Schnieders Schnieders CHAIRS: 16. 8:30 8:30 LIN, LIN,S.S. SKULSKI, SKULSKI,T. T. PERCIVAL, PERCIVAL,J.J. STRUCTURALGEOLOGY GEOLOGYAND AND TECTONIC TECTONICEVOLUTION EVOLUTIONOF OFTHE THE STRUCTURAL VIZIEN GREENSTONE GREENSTONEBELT BELTIN IN MINTO MINT0BLOCK,NORTHEASTERN BLOCK,NORTHEASTERN VIZIEN SUPERIORPROVINCE, PROVINCE,NORTHERN NORTHERNQUEBEC QUEBEC SUPERIOR 17. 8:50 8150 PETERSON, PETERSON,V.L. V.L. ZALESKI, ZALESKI,E. E. BREEMEN, BREEMEN, 0. 0. STRUCTURALEVOLUTION EVOLUTIONAND AND AGE AGE RELATIONSHIPS RELATIONSHIPSOF OFTHE THE STRUCTURAL MANITOUWADGEGREENSTONE GREENSTONEBELT BELTAND AND WAWA-QUETICO WAWA-QUETICO MANITOUWADGE SUBPROVINCE,SOUTHWESTERN SOUTHWESTERNSUPERIOR SUPERIORPROVINCE, PROVINCE, SUBPROVINCE, ONTARIO ONTARIO 18. 9:10 9:lO ZALESKI, ZALESKI,E.E. GEOLOGICALSETTING SETTINGAND AND GEOCHEMISTRY GEOCHEMISTRYOF OFMASSIVE MASSIVE GEOLOGICAL SULFIDE DEPOSITS AND ALTERATION ZONES IN THE SULFIDE DEPOSITS AND ALTERATION ZONES IN THE MANITOUWADGE GREENSTONE BELT, BELT, NORTHWESTERN NORTHWESTERN MAN ITOUWADGE GREENSTONE ONTARIO ONTARIO 19. 9:30 9:30 FRALICK, FRALICK,P.W. P.W. PURDON, PURDON,R.R. NEOARCHEANTRANSUBPROVINCE TRANSUBPROVINCEDEPOSITIONAL DEPOSITIONALSYSTEMS: SYSTEMS: NEOARCHEAN TEMPORAL VS. SPACIAL VARIABILITY IN WESTERN SUPERIOR TEMPORAL VS. SPACIAL VARIABILITY IN WESTERN SUPERIOR PROVINCE PROVINCE 9:50 9:50 COFFEE COFFEEBREAK BREAKAND ANDPOSTER POSTERSESSION SESSION 20. 10:20 10:20 BORNHORST, BORNHORST,T.J. T.J. WHITEMAN, WHITEMAN,R.C. R.C. NATIVECOPPER COPPERAND ANDASSOCIATED ASSOCIATEDMINERALS MINERALSININBASALTS BASALTS NATIVE ATTHE THECALEDONIA CALEDONIAMINE, MINE,WESTERN WESTERNUPPER UPPERMICHIGAN MICHIGAN AT 21. 10:40 10:40 SHAW, SHAW,C.S.J. C.S.J. GEOCHEMISTRYAND ANDFRACTIONATION FRACTIONATIONOF OFTHE THEEASTERN. EASTERN. GEOCHEMISTRY COLDWELLALKALINE ALKALINECOMPLEX COMPLEX GABBRO,COLDWELL GABBRO, 22. 11:00 I1:OO LIGHTFOOT, LIGHTFOOT,P.C. P.C. FARRELL, FARRELL,K.K. MOORE, MOORE,M. M. PEKESKI, PEKESKI,D.D. CRABTREE, CRABTREE,D.D. KEAYS, KEAYS,R.R. R.R. GEOCHEMICALVARIATIONS VARIATIONSWITHIN WITHINTHE THESUBLAYER SUBLAYERAND ANDTHE THE GEOCHEMICAL MAFIC-ULTRAMAFICINCLUSIONS, INCLUSIONS,WHISTLE WHISTLEMINE, MINE,SUDBURY SUDBURY MAFIC-ULTRAMAFIC IGNEOUS IGNEOUSCOMPLEX, COMPLEX,CANADA CANADA 23. 11:20 11:20 LEE, LEE,I.I. RIPLEY, RIPLEY,E.M. E.M. MINERALIZATIONAT ATTHE THE GENESIS CU-NiSULFIDE SULFIDE MINERALIZATION GENESIS OF OF Cu-Ni SPRUCE SPRUCEROAD ROADDEPOSIT, DEPOSIT,SOUTH SOUTHKAWISHIWI KAWISHIWIINTRUSION, INTRUSION, DULUTH DULUTHCOMPLEX COMPLEX 24. 11:40 11140 MILLER, MILLER,J.D., J.D.,Jr. Jr. PREDICTIONAND ANDDISCOVERY DISCOVERYOF OFPGE PGEOCCURRENCES OCCURRENCESIN INTHE THE PREDICTION DULUTH DULUTHCOMPLEX COMPLEXAT ATDULUTH DULUTH NOON NOON LUNCH LUNCHBREAK BREAK POSTERSMUST MUSTBE BEREMOVED REMOVEDBY BYNOON NOONTODAY TODAY POSTERS xv �1995 TUESDAY MAY 16. 16.1995 - AFTERNOON - SESSION SESSION IV IV AFTERNOON Jirsa and Cliff Cliff Shaw CHAIRS: Mark Jirsa 25. 25. ZBIKOWSKI, D.W. ZBIKOWSKI, D.W. 2:00 2:OO A CONTINENTAL CONTINENTAL CRUST FRACTURE FRACTURE INITIATION INITIATION PATTERN PATTERN AND HYPOTHETICAL MECHANISM - HYPOTHETICAL MECHANISM A CURVILINEAR DERIVATIVE CONTINENTAL INDICATIONS OF A MANTLE CONVECTION CARIBBEAN MANTLE CONVECTION PLUME PLUME 2:20 2:20 ZBIKOWSKI, D.W. ZBIKOWSKI, D.W. 2:40 2 40 PRESENTATION OF STUDENT PAPER AWARDS PRESENTATION 2:50 2 50 COFFEE COFFEE BREAK BREAK AND AND POSTER POSTER SESSION SESSION 27. 27. 3:20 3:20 MORRIS, T.F. MORRIS, T.F. MURRAY, C. MURRAY, C. CRABTREE, D. CRABTREE, D. HEAVY MINERAL MINERAL INDICATORS, INDICATORS, WAWA AREA 26. 28. 3:40 3:40 RUDASHEVSKY, RUDASHEVSKY,N.S. N.S. WEIBLEN, WEIBLEN, P.W. P.W. STOYNOV, H. H. STOYNOV, PRODUCTS OF ELECTRIC PULSE DISAGGREGATION DISAGGREGATION OF SOME KEWEENAWAN KEWEENAWAN ROCKS ROCKS 29. 29. 4:00 4:OO FREY, B. FREY, 6. U.S.A. CORE CENTRAL MINNESOTA, U.S.A. CORE LOGGING LOGGING AND ASSAY DATABASES DATABASES 26. 26. - 10:00 10:oo pm. pm. 7:00 7:OO - WINE AND CHEESE AND CHEESE HOSTED: BY Hemlo Branch of the Canadian Institute of Mining and Metallurgy at the Royal Royal Canadian Canadian Legion Legion 4:20 4:20 CLOSING REMARKS CLOSING REMARKS 4:30 SESSION SESSION END END xvi �POSTER PRESENTATIONS PRESENTATIONS Authors are are requested requested to to be be present present at at their their posters posters during during scheduled scheduled times. times. Authors Senior Author ** CARD, CARD, K. K. Title ]je LITHO-TECTONIC PROVINCE LITHO-TECTONIC AND MINERAL DEPOSIT MAPS OF THE SUPERIOR PROVINCE DESAUTELS, P. DESAUTELS, P. DAVID BELL DAVID BELL MINE MINE GERE, GERE, M. M. CURRENT INVENTORY INVENTORY OF MICHIGAN'S GEOLOGICAL CORE AND SAMPLE REPOSITORY MARQUETTE REPOSITORY AT MARQUETTE * EVEREST, EVEREST,J. J. IGNEOUS CHARACTERISTICS BRECCIA, CHARACTERISTICS OF THE MATRIX TO TO THE FOOTWALL FOOTWALL BRECCIA, NORTH RANGE, SUDBURY STRUCTURE, CANADA * DAVIS, DAVIS, D. D. 1.IGA NORTH AMERICAN MID-CONTINENT MID-CONTINENTRIFT RIFT GEOCHRONOLOGY GEOCHRONOLOGY OF THE 1.1 GREEN, GREEN, J. J. * KARKKAINEN, KARKKAINEN, N. N. GEOLOGY OF THE NORTH SHORE STATE PARKS TITANIUM WESTERN FINLAND TITANIUM ORE ORE POTENTIAL POTENTIAL OF GABBROS: GABBROS: EXAMPLES EXAMPLES FROM FROM WESTERN FINLAND LAWLER, T. LAWLER, EVALUATION, CENTRAL MINNESOTA MINERAL POTENTIAL POTENTIAL EVALUATION, LIGHTFOOT, P.C. LIGHTFOOT, P.C. THE SUBLAYER, MAIN MASS, AND GEOCHEMICAL RELATIONSHIPS RELATIONSHIPS BETWEEN THE OFFSETS, SUDBURY IGNEOUS IGNEOUS COMPLEX, CANADA MORRIS, T. MORRIS, T. KIMBERLITE KIMBERLITE HEAVY MINERAL INDICATORS IN OVERBURDEN, MICHIPICOTEN RIVER-WAWA AREA, NORTHEASTERN NORTHEASTERN ONTARIO ONTARIO MUIR, T. MUIR, T IMPORTANCE THE CURRENT SETTING OF THE HEMLO GOLD DEPOSIT, ONTARIO: IMPORTANCE OF FUNDAMENTAL FUNDAMENTALRELATIONSHIPS RELATIONSHIPS * PETERSON, PETERSON,D.M. D.M. GEOLOGICAL, GEOPHYSICAL AND GEOCHEMICAL COMPILATION OF THE GEOLOGICAL, WESTERN WESTERN VERMILLION VERMILLION DISTRICT: DISTRICT: TARGETING TARGETING FOR FOR GOLD GOLD AND AND MASSIVE MASSIVE SULFIDE SULFIDE DEPOSITS DEPOSITS SAGE, SAGE, R. R. KIMBERLITE IN KIMBERLITE IN ONTARIO ONTARIO SEVERSON, SEVERSON, M. M. SOUTHERN PORTION GEOLOGY OF THE SOUTHERN PORTION OF THE DULUTH DULUTH COMPLEX COMPLEX SKRECKY, G. SKRECKY, G. WILLIAMS WILLIAMS MINE MINE VIITALA, VIITALA, R. R. EFFECTS EFFECTS OF LARGE LARGE METEORITE METEORITE IMPACTS IMPACTS ON CRUSTAL ROCKS -- SUDBURY BASIN BASIN IN IN THIN THIN SECTION SECTION WOLFSON, WOLFSON, I.I. MANITOUWADGE, ONTARIO: ONTARIO:AAVOLCANOGENIC THE GECO MINE, MANITOUWADGE, VOLCANOGENIC MASSIVE SULPHIDE SULPHIDE DEPOSIT DEPOSIT (see Lockwood, Lockwood, H. for abstract) WOODRUFF, WOODRUFF, L. L. PROPOSED FIELD TRIPS FOR THE THE 42ND 42ND ANNUAL ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY * Student Paper Paper ** cancelled cancelled paper ** xvii �POST MEETING MEETING FIELD FIELD TRIPS TRIPS Field trips depart from the Marathon Recreation Complex Complex at at 8:00 8:00 a.m. a.m. All field trips, except trip number number 6, 6, return return to to Marathon Marathoneach each evening evening by by about about 6:00 6:00 p.m. p.m. 1995 WEDNESDAY. MAY 17. 17,1995 FIELD TRIP TRIP 1lb b (DAY ONE OF TWO DAYS) DAYS) ALKALIC ROCKS OF THE MIDCONTINENT RIFT FIELD TRIP 2b (DAY ONE OF TWO DAYS) DAYS) MANITOUWADGE MANITOUWADGE GREENSTONE GREENSTONE BELT BELT FIELD FIELD TRIP 3b 3b SCHREIBER GREENSTONE GREENSTONE ASSEMBLAGE FIELD TRIP FIELD TRIP 55 HEMLO HEMLO GREENSTONE BELT II: 11: DEPOSIT DEPOSIT GEOLOGY FIELD TRIP FIELD TRIP 66 (DAY ONE ONE OF OF TWO DAYS) DAYS) WAWA KIMBERLITE/GOLD EXPLORATION KIMBERLITEIGOLD EXPLORATION WAWA AT PARTICIPANT'S OVERNIGHT OVERNIGHT STAY STAY AT AT AT PARTICIPANT'S EXPENSE EXPENSE 1995 WEDNESDAY. MAY 17. 17.1995 TRIP 1lb FIELD TRIP b (DAY TWO OF TWO DAYS) IDAY DAYS) ALKALIC ROCKS OF THE MIDCONTINENT RIFT FIELD TRIP 2b FIELD (DAY TWO OF TWO DAYS) DAYS) MANITOUWADGE MANITOUWADGE GREENSTONE GREENSTONE BELT BELT FIELD TRIP FIELD TRIP 66 (DAY TWO OF TWO DAYS) IDAY DAYS) WAWA WAWA KIMBERLITE/GOLD KIMBERLITE/GOLDEXPLORATION EXPLORATION 6:00PM. PM. RETURN TO MARATHON MARATHON BY ABOUT 6:00 xviii �ORAL PRESENTATIONS ORAL PRESENTATIONS Senior Author Session Paper No. No. Session No. No. -.Paper BERENDSEN, BERENDSEN. PP. . . . . . . . . . . . . . . . . . . . . . . . . I—i BORNHORST, BORNHORST. T . . . . . . . . . . . . . . . . . . . . . . . . III- 20 CORFU, P CORFU. P. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 * DARRAH, DARRAH. K K. . . . . . . . . . . . . . . . . . . . . . . . . . . II - 12 * FEHER, FEHER. LL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . II - 15 FRALICK, P FRALICK. P. . . . . . . . . . . . . . . . . . . . . . . . . . III - 19 FREY, FREY. B B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lV-29 ** HALLS, H **HALLS. H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 HOLM, HOLM. D D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Il—Il JIRSA, JIRSA. M M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9 **KING,D KING, D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 * KOEBERNICK, KOEBERNICK, C C. . . . . . . . . . . . . . . . . . . . . . . . II - 13 LaBERGE, G 1-5 LEE, II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LEE. 111-23 LIGHTFOOT, P. LIGHTFOOT. P. (1) (1). . . . . . . . . . . . . . . . . . . . . . IIIIll - 22 22 LIGHTFOOT, P. LIGHTFOOT. P. (2) (2). . . . . . . . . . . . . . . . . . . . . . Banquet Banquet Presentation Presentation UN, S LIN. S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 - 1166 III MILLER, JJ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111-24 111 - 2 4 MILLER. MORRIS, T . . . . . . . . . . . . . . . . . . . . . . . . . . . . MORRIS. IV - 227 7 NORTH, JJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . NORTH. III - 114 4 * PETERSON, D.M . . . . . . . . . . . . . . . . . . . . . . . "PETERS0N.D.M 1 -7 1-7 PETERSON,V PETERSON. V. . . . . . . . . . . . . . . . . . . . . . . . . 111 - 1177 III * PUFAHL, PUFAHL. PP. . . . . . . . . . . . . . . . . . . . . . . . . . . -1-6 6 RUDASHEVSKY, RUDASHEVSKY. N.S N.S. . . . . . . . . . . . . . . . . . . . IV -28 IV-28 * SCHNEIDER, SCHNEIDER. D D. . . . . . . . . . . . . . . . . . . . . . . . 11II - 110 0 SHAW, C SHAW. C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 21 III-- 21 * SHORE, SHORE. G G. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 -8 1-8 ZALESKI, E ZALESKI. E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11III1-18 - 18 ZBIKOWSKI, D. ZBIKOWSKI. D. (1) (1). . . . . . . . . . . . . . . . . . . . . . IV -25 IV-25 ZBIKOWSKI, D. D. (2) (2). . . . . . . . . . . . . . . . . . . . . . ZBIKOWSKI. IV - 2266 *Student 'Student Paper Paper **cancelled paper "cancelled xix �RACTS ABSTRACTS �HISTORY AND DEVELOPMENT OF T HE SOUTHERN EXTENSION THE EXTENSION OF OF THE THE MIDCONTINENT RIFT IN KANSAS. IN KANSAS. BERENDSEN, Pieter, BERENDSEN, Pieter,Kansas KansasGeological GeologicalSurvey, Survey,University University of of Kansas, Kansas, Lawrence, Lawrence, KS 66047. 66047. KS Igneous and sedimentary sedimentaryrocks rocks associated with the southern southern extension extension of the the (MRS) in regionally significant significant MidcontinentRift Rift System System (MRS) Midcontinent in Kansas Kansasterminate terminate against a regionally northwest-trendingstructural structuralzone zone(Missouri (MissouriGravity GravityLow) Low) at at the the Kansas-Nebraska Kansas-Nebraska northwest-trending border. To the south, south,an anequally equallypronounced pronouncedstructural structuralzone zone(Fall (FallRiver RiverTectonic Tectonic south of of which no rift-related igneous or sedimentary Zone) defines defines a boundary south sedimentary the basement basement surface. surface.The The southern southern boundary boundaryalso alsoroughly roughlycoincides coincides rocks occur at the suture between between the the older older (1.63-1.80 (1.63-1.80 Ga) metamorphic with the suture metamorphic and and granitoid rocks of of the Central Plains orogen (Sims and Peterman, 1986) and younger (1.35( 1.35orogen to the north (Sims 1.48 Ga) rhyolitic rhyolitic and dacitic volcanic rocks rocks and and associated epizonal granitic plutons plutons to the south south (Denison, (Denison, and others, others, 1984). 1984).North-northeast-trending North-northeast-trending faults identified NW-SEthe subsurface subsurface are are not notas aspronounced pronouncednorth northand andsouth southofofthese thesesutures. sutures.NW-SEin the and NNE-WSW-trending NNE-WSW-trending faults geologic time. The and faultshave havebeen beenreactivated reactivated troughout geologic distribution pattern patternof ofPrecambrian Precambrianand andPaleozoic Paleozoic rocks rocks within the area area comprising comprising distribution the trend trend of of the the rift rift has has been been greatly greatly influenced influenced by by motion along these faults. Renewed resulted in in complex complex sets sets of closely spaced Renewed movement movement along basement faults resulted spaced younger rocks, and and are referred referred to Nemaha and and faults affecting younger to as tectonic zones. The Nemaha Peace Creek tectonic zones are SWare the themajor majorNNE-trending NNE-trending rift-related rift-related structures. structures.SWNE-trending tectonic tectonic zones zonesare are believed believedto tobe beolder older (Clendenin, (Clendenin,and andothers, others, 1989) 1989) and and NE-trending tectonic zones and cross the the rift rift zone. zone.The TheFall Fall River, River, Chesapeake, Chesapeake, Bolivar-Mansfield tectonic and Loware arethe the better better known known structures. structures. the Missouri Gravity Low activity associated associated with with the the active phase of rifting was essentially Magmatic activity synchronous along of 1097.5 ±3 Ma Ma obtained obtained from synchronous along its its length. length.A A concordant concordantU-Pb U-Pb age of 1097.5 ± of published baddeleyite in gabbro from a depth of about about 900 m. is within the range of 1992). In In the post-igneous stages of of rifting rifting initially coarse and ages (Van Schmus, 1992). by finer finer grained grained and more mature strata immature sedimentary sedimentaryrocks rocks followed by strata were were deposited in axial and flanking basins. There is no no geologic geologicrecord recordindicating indicatingthat that deposited sedimentary or igneous rocks accumulated in in the time span span between between the the end end of of the sedimentary Keweenawanand and the the onset of the Paleozoic, but instead instead the area was subjected to a Keweenawan Paleozoic, but long period of erosion and peneplanation. peneplanation. Faulting, Faulting, as evidenced by considerable vertical vertical displacement displacement of of Proterozoic Proterozoic igneous and and sedimentary sedimentary rocks rocks (Woelk (Woelk and Hinze, 1991; Berendsen, Berendsen,in inpress) press) played played an an important important role in preserving younger Hinze, graben structures rocks in graben structures and andexhuming exhuming older older rocks rocks on on hortsted hortstedblocks. blocks. Rocks of ofPermian Permianage ageare arethe theyoungest youngestsedimentary sedimentarystrata strata to to be be deposited deposited in Rocks the area. with the western edge of of the the rift province Cretaceous area. Closely Closely coinciding with rocks are present. They are believed to have extended farther farther to the east, but were eroded back to their their present presentposition, position,possibly possibly related to reactivation reactivation of rift structures. structures. The The occurrence occurrenceof of numerous numerousCretaceous Cretaceous(90 (90Ma) Ma) kimberlites occurring occurring at at or near the the surface surface as as well well as non-deposition non-depositionor or erosion erosion of of several several pre-Permian sedimentary sedimentary rock rock units units indicate indicate that thatsignificant significanttectonic tectonic activity activity took took place at at various times stresses responsible various times during duringthe thePaleozoic Paleozoicand andMesozoic Mesozoic eras. The stresses responsible for for all all craton during this activity originated at the the eastern easternmargins margins of of the the North North American American craton during continent continent to to continent continentcollisions collisions beginning beginning during during Grenville Grenville time and shifting to affecting the the midcontinent mldcontinent during during the the south with a major period of activity affecting Ouachita-Wicbita-Marathon Since Permian Permian sedimentary sedimentary rocks are the Ouachita-Wichita-Marathonorogeny. Since youngest strata strata in in the thearea areaunder underdiscussion discussionititisisdifficult, difficult,ifif not notimpossible, impossible, to to document document Cenozoic Cenozoic and recent tectonic activity (probably (probably of lesser intensity) that that 1 �undoubtedly must must occurred. occurred.The The stresses stresses are are believed to have been transmitted undoubtedly primarily via Precambrian Precambrian basement basement rocks rocks and and mostly mostly along along pre-existing pre-existing fractures. fractures. primarily direction from from which the stresses stresses were applied resulted in complex and The shift in direction often often reversal reversal of of movements movements on on faults. faults. influenced by the Depositional patterns of stratigraphic units quite often are influenced tectonic events eventsas as evidenced evidenced for for example example by by the the location location of of paleo-stream paleo-stream previous tectonic channels, and and the the location location of of carbonate carbonate build-ups. build-ups. Of Of more more practical practical consequences, consequences, it channels, important to to remember remember that that the the distribution distributionof of energy energy and and mineral mineral resources, resources, is important migration of fluids or gases is responsible for the concentration concentration especially where migration and accumulation accumulationof of aa commodity, commodity, is directly influenced by the tectonic framework and of the the rocks. rocks. REFERENCES REFERENCES Berendsen, Berendsen, P., (in (in Press), Press), Tectonic evolution of the the Midcontinent MidcontinentRift Rift System in Kansas: Geological Society of America Special Special Paper. Paper. Clendenin, W., and and Niewendorp, C. C. A., A.,1989, 1989,Reinterpretation Reinterpretation of of faulting faulting in C. W., Clendenin, C. southeast 2 17-220. southeastMissouri: Missouri:Geology, Geology, v. 17, 17, p. 217-220. Denison, G., Bickford, Bicklord, M. M. E., F., and and Kisvarsanyi, Kisvarsanyi, E. B., 1984, 1984, Geology and and Denison,R. R. F., E., Lidiak, Lidiak, E. E. G., E. B., geochronology of of Precambrian Precambrian rocks rocksin in the the central central interior interior region of of the United Professional Paper United States: States:U. U. S. S. Geological Survey Professional Paper 1241-C, 1241-C,20 20 p. p. Sims, P. P. K., K.,and and Peterman, Peterman, Z. E., 1986, 1986, Early Early Proterozoic Proterozoic Central Plains Orogen: A A major major Z. E., buried buried structure structureininthe thenorth-central north-centralUnited UnitedStates: States:Geology, Geology,v. v. 14, 14,p. p.488-491. 488-491. Van Schmus, R., 1992, Tectonic setting Schmus,W. R., setting of of the theMidcontinent MidcontinentRift RiftSystem: System: Tectonophysics, Tectonophysics, 213, 213, p. p. 1-15. 1-15. Woelk, T. S., S., and and Hinze, W. W. JJ., 1991, Model of of the the Midcontinent Midcontinent Rift ., 199 1,Model Rift System in northeastern 2 77-280. northeasternKansas: Kansas:Geology, Geology, v. 19, 19, p. p. 277-280. �NATIVE COPPER COPPER AND AND ASSOCIATED ASSOCIATED MINERALS IN IN BASALTS AT THE CALEDONIA NATIVE MINE, WESTERN WESTERN UPPER UPPER MICHIGAN MICHIGAN BORNHORST, Theodore Theodore J., J., Department Department of Geological Engineering BORNHORST, Engineering and and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, MI MI 49931 49931 and and WHITEMAN, WHITEMAN, Richard Richard C., C., Red Red Houghton, Metal Explorations, Explorations, Hubbell, Hubbell, MI MI 49934 49934 Metal The Caledonia Caledonia Mine Mine is is located located near near Mass Mass City City in in western western Upper Upper The Michigan. Michigan. It It lies lies within within an an area area of of native native copper copper deposits deposits some some 40 km krn southwest southwest of of the the major major deposits deposits of of the the Keweenaw Keweenaw Peninsula Peninsula 40 native native copper copper district. district. The The Caledonia Caledonia Mine Mine produced produced about about 33 million kg kg of of native native copper copper from from 1863-1881 1863-1881 and and 1951-1958. 1951-1958. Since Since million 1985 the the mine mine has has been been tested tested by by Red Red Metal Metal Explorations. Explorations. The The 1985 Caledonia Mine Mine provides provides access access to to continue continue studies studies of of native native Caledonia copper mineralization mineralization while while most most of of the the native native copper copper mines mines of of copper the the Keweenaw Keweenaw Peninsula Peninsula are are now now flooded flooded or or closed closed permanently. permanently. The Caledonia Caledonia Mine Mine intersects intersects the the Butler and Knowlton Knowlton flow flow The tops. tholeiitic tops. These These lava lava flows flows are are part part of of aa package package of of tholeiitic basalt basalt lava lava flows flows up up to to 210 210 mm in in total total thickness thickness within within the the Portage adit at at the the Portage Lake Lake Volcanics. Volcanics. For For most most of of its its length length the the adit Caledonia Mine Mine follows follows the the brecciated brecciated amygdaloidal amygdaloidal top top of of the the Caledonia Knowlton Knowlton flow flow which which dips dips at at about about 450 45' northwest. northwest. The The average average thickness of of the the stratabound stratabound Knowlton Knowlton lode lode (flow (flowtop) top) is is about about thickness 2.5 2.5 mm but but locally locally thickens thickens to to more more than than 66m. m. Native Native copper copper and and an an associated associated suite suite of of secondary secondary minerals minerals fill amygdules amygdules and and spaces spaces between between fragments fragments in in the the brecciated brecciated fill lava flow flowtop. top. Calcite Calcite is is the the most most abundant abundant secondary secondarymineral. mineral. lava Quartz, epidote epidote and and K-feldspar K-feldspar are are lesser lesser in in abundance abundance and and occur occur Quartz, in in subequal subequal amounts. amounts. Prehnite, Prehnite, pumpellyite, pumpellyite, and and chlorite chlorite are are present in in small small amounts. amounts. Native Native copper, copper, in in minor minor amounts, amounts, is is present associated associated with with even even less less abundant abundant native native silver. silver. Paragenetic Paragenetic sequence, sequence, based based on on filling filling of of amygdules amygdules and and open open spaces, spaces, is is KKfeldspar followed followed by by epidote epidote and and then then calcite+quartz. calcite+quartz. Native Native feldspar copper tends tends to to be be more more commonly commonly associated associated with with epidote, epidote, copper calcite, calcite, and and quartz. quartz. Rarely Rarely is is native native copper copper abundant abundant in in areas areas with with abundant abundant K-feldspar. K-feldspar. No No major major differences differences exist exist in in the the abundance abundance of of secondary secondary minerals averaged averaged over over the the scale scale of of 100's 100's of of meters. meters. In In minerals contrast, over the scale of a few meters the distribution contrast, over the scale of a few meters the distribution of of secondary secondary minerals minerals is is variable. variable. AA secondary secondary mineral mineral may may be be completely absent absent in in one one zone zone and and extremely extremely abundant abundant in in another. another. completely However, the the meter meter scale scale variation variation does does have have aa certain certain degree degreeof of However, regularity. regularity. In In some some areas areas the the occurrence occurrence of of secondary secondary minerals minerals is banded banded consistent consistent with with the the progressive progressive filling filling of of open open spaces spaces is indicated by by amygdule amygdule paragenesis. paragenesis. The The intensity intensity of of alteration alteration indicated footwall of of the the is highest highest near near both both the the hanging hanging wall wall and and footwall is brecciated brecciated flow flow top top lode. lode. Distribution Distribution of of secondary secondary minerals minerals also also correlates correlates with with the theoccurrence occurrenceof ofveins. veins. Veins Veins are are of of two two types. types. Some Some veins veins within within the the lode lode and and extending into into underlying underlying massive massive basalt basalt contain contain the the same same basic basic extending minerals minerals as as the the lode, lode, including including native native copper. copper. These These veins veins are are 3 �considered synchronous synchronous with with lode lode formation formation whereas whereas others others are are considered clearly clearly late-stage. late-stage. One One vein vein of of the the former former type type is is the the target target of of current current exploration. exploration. This This particular particular vein vein strikes strikes subparallel subparallel with with the the strike strike of of the the flow flow top top but but dips dips more more steeply steeply (about (about800 80' for the the vein) vein) and and has has been been traced traced for for over over 100 100m. m. The The vein vein is is for well well developed developed in in the the footwall footwall and and below, below, but but is is hard hard to to identify identify as as it it enters enters the the lode. lode. Within Within this this vein vein the the intensity intensity of of alteration alteration varies varies from from slight slight to to very very high. high. Original Original basalt basalt can can be be completely completely converted converted to to aa green green soft soft epidote+lesser epidote+lesser chlorite chlorite rock, rock, or or aa hard hard epidote+lesser epidote+lesserquartz quartz rock. rock. Overall Overall mineralogy mineralogy and and paragenesis paragenesis is is similar similarto to the thelode. lode. The The vein vein contains contains pockets pockets of of soft soft blue-green blue-green mineral mineral identified identified as as corrensite corrensite by by XRD XRD (mixed (mixed layered layered clay clay mineral mineral with with 50/50 50/50 chlorite chlorite and and smectite smectite unit unit cells cells stacked stacked in in perfect perfect alternation). alternation). This This vein vein has has recently recently yielded yielded outstanding outstanding world world class class quality quality specimens specimens of of crystalline crystalline native native silver silver which which was was originally originally encased encased in in white white calcite calcite (calcite (calcitewas was removed removed by by acid acid leaching), leaching),and and clusters clusters of of colorless calcite calcite crystals crystals internally internally laced laced with with native native copper copper in in colorless vugs. vugs. Several Several masses masses of of native native copper copper weighing weighing over over 100 100 kg kg and and small small groups groups of of copper copper crystals crystals originally originally encased encased in in white white calcite, calcite, some some coated coated with with very very small small cubic cubic native native silver silver crystals, crystals, have have also also been been recovered recovered during during exploration. exploration. Massive Massive datolite datolite is is associated associated with with native native copper, copper, occurring occurring on on and and within within native native copper. copper. This This vein vein is is quite quite similar similar to to veins veins described described by by Broderick Broderick (1931, (1931,Economic EconomicGeology, Geology,v. v.26, 26, p. p. 840840856) 856) in in the the Baltic Baltic and and Isle Isle Royale Royale Mines Mines about about 50 50 km km northeast northeast near near Houghton. Houghton. This This steeply steeply dipping dipping vein vein is is interpreted interpreted as as aa pathway pathway for for ascending ascending hydrothermal hydrothermalfluids. fluids. Other Other veins veins are are clearly clearly late-stage late-stageand and crosscut crosscut the the native native copper-mineralized copper-mineralized lode lode at at the the Caledonia CaledoniaMine. Mine. Late-stage Late-stage veins veins containing containing calcite calcite and and laumontite laumontite are are readily readily visible visible in in the the adit adit and and are are barren barren of of native native copper. copper. Adularia Adularia is is an an additional additional late-stage late-stage secondary secondary mineral mineral that that occurs occurs in in veins veins and and in in the the lode. lode. Veins Veins played played an an important important role role in in the the deposition deposition of of native native copper copper and and associated associated minerals minerals at at the the Caledonia CaledoniaMine. Mine. 4 �LITHO-TECTONIC THE SUPERIOR SUPERIOR LITHO-TECTONICAND AND MINERAL MINERALDEPOSIT DEPOSITMAPS MAPS OF OF THE PROVINCE PROVINCE K.D. Card, R.A. Frith, and K.H. Poulsen, Geological Survey Survey of of Canada, Canada, Ottawa Ottawa deposit maps Litho-tectonic and mineral deposit maps of Superior Province Province were were compiled compiled at 2.5 million million scale as part part of of aa contribution contributionto to Decade Decade of of North North American American Geology Geology (DNAG). (DNAG). Sources Sources induded includedpublished publishedand andunpublished unpublishedmaps mapscompiled compiledon onaaone onemillion millionscale scaleDigital Digital Chart Chart of the World base. base. Twenty maps were prepared, prepared, raster raster scanned and processed processed using usingArcArcInfo software over over aa two twomonth monthperiod. period. The TheMineral Mineral Deposit DepositMap Map was was prepared prepared from fromthe the Litho-tectonic Map and individual individualdeposits depositswere werekeyed keyed by by type, type, size sizeand andlocation locationfrom from dbase dbase files. files. Geological units were grouped grouped by by age age and and tectonic tectonic type, type, based based on on U-Pb U-Pb isochron isochron ages, inferred depositional sequence, in in order to depositional environments, environments, and and intrusive-orogenic intrusive-orogenic sequence, relate economic mineral mineral deposits deposits to toenvironments environmentsand andprocesses. processes. Supracrustal Supracrustal rocks rockswere were assigned to to late lateand andearly earlysuccessor successorbasins, basins,accretionary accretionarycomplexes, complexes, calc-alkaline calc-alkaline and and tholeiitic arc sequences, sequences,and and submarine submarine tholeiitic-komatiitic tholeiitic-komatiiticmafic maficplain plainsequences. sequences. Where Where regional metamorphism is high, high,bulk bulkcomposition, composition,metamorphic metamorphicand and "unknown" "unknown" affinity affinity designations designations were were used. used. 5 �GEOCHRONOLOGY OF OFTHE THESHEBANDO SHEBANDOWAN GREENSTONE BELT, BELT, U-Pb GEOCHRONOLOGY WAN GREENSTONE SUPERIOR PROVINCE, PROVINCE, ONTARIO ONTARIO SUPERIOR Corfu,F., F.,Jack Jack SatterlyGeochronology GeochronolosyLaborato,y, Laboratory,Royal Royal Ontario OntarioMuseum, Museum, 100 100 Queen's Park, Toronto Corfu, Satterly Pang Toronto M5S 2C6and and Stott, Stott, G.M., M5S 2C6 G.M., Precambrian Precambrian Geoscience Section, Ontario Ontario Geological GeologicalSurvey, Survey, 933 933 Ramsey Lake Road, Sudbuy, Sudbuy, Ontario OntarioP3E P3E 6B5 6B5 The Shebandowan Shebandowangreenstone greenstonebelt, belt,in inthe thewestern westernWawa Wawa Subprovince, Subprovince, is composed of Archean The Archean metavolcanic and composite batholith to to the the south southand andimpinging impinginginto intothe themetasedimentary metasedimentary metasedimentary rocks bound by a composite QueticoSubprovince Subprovinceto the the north. north. An An extensive extensive geochronological Quetico geochronological study studyhas hasbeen beenundertaken undertaken in in order order to constrain the stratigraphic stratigraphicrelationships relationshipsof of the the belt belt and anddate datethe theformation formationof of major majorplutonic plutonicsuites, suites,complementing complementingan an early early the U-Pb U-Pb study study carried carried out out in in the thebelt belt(Corfu (Corfuand andStott Stott1986). 1986). structural mapping mapping had had indicated indicated the the presence presence of of two two major major volcanic volcanic assemblages, assemblages, the Geological and structural north-facing Burchell assemblage in the northern northern part part of of the thebelt beltand andthe thesouth-facing south-facingGreenwater Greenwaterassemblage assemblage north-facing to the thesouth south(Williams (Williamsetetal. al.1991). 1991).Both Bothassemblages assemblages were were further furthersubdivided subdivided into into three threecycles cycles consisting consisting of to mafic and and minor minor komatiitic komatiitic volcanic volcanic successions successions capped intermediate to felsic felsic units. units. Our Ourpreliminary preliminary mafic capped by by intermediate geochronological data data show show that that most mostof of these thesevolcanic volcanic units units developed developed within within aa relatively relatively short short period period of of time time geochronological at around around2722 2722 to to 2718 2718 Ma. This time frame also includes the crystaffization crystallization of at frame also ofanorthosites anorthosites and and layered gabbroic gabbroic bodies such such the Haines Haines and and the the North NorthColdstream Coldstream gabbros. gabbros. A similar bodies similar age has also also been found found for for aa felsic felsic volcanic volcanic unit in the the Saganagon Saganagon belt belt to to the thesouthwest. southwest. An age ageof of 2733 2733 Ma, Ma, determined determinedin in the theprevious previoussurvey survey for aa porphyry porphyry sill sill intruding metabasalts metabasalts in the An northern part part ofofthe thebelt, belt,remains remainsunique uniqueand andcould couldindicate indicatethe thepresence presenceofofa atectonically tectonicallyinterleaved interleavedolder older northern verificationof ofthis thisage ageisisinin package or or ititcould couldbe beaaspurious spuriousage agebiased biasedby bya axenocrystic xenocrysticzircon zirconcomponent. component.AAverification package progress. The The only only older older unit unit found foundin inthis thisstudy studyisis2750 2750 Ma Ma tonalitic tonalitic gneiss gneiss of the the Northern NorthernLight LightComplex. Complex. progress. Zircons with with age agebetween between2750 2750 and and 2900 2900 Ma Ma occur, occur, however, however, as as detrital detritalcomponents componentsin inyounger youngersediments sedimentsor or Zircons as as xenocrystic xenocrystic grains grains in in granitic graniticrocks. rocks. A A young young volcanic episode at around around 2695 2695 Ma formed formed pyroclastic pyroclastic units located in northern northern segments segmentsof of the belt. belt. These Theseunits unitscorrelate correlatewith withthe thepreviously previously dated dated2696 26% Ma Ma synsyn- or or post post Dl D lShebandowan ShebandowanLake Lakepluton. pluton. the A previous previousage agedetermination determinationofof2689 2689Ma Mafor foran analkalic alkalicvolcanic volcanicrock rock isisnow nowsupported supportedby bynew newages agesofof 52692 A 2692 Ma for for aavolcanogenic volcanogenic unit of the Duckworth Duckworth group and for a breccia in the Strawberry Strawberry Hill area. An age of Ma about 2693 2693 was was also also obtained obtainedfor forthe thesyenitic syeniticTower Towerstock. stock.These TheseTimiskaming-type Timiskaming-type units units are arecoeval coevalwith with about emplacementof ofthe the2690 2690 Ma Ma Saganaga Saganagapluton pluton in in the the southwest, southwest, and and hence hence with with deposition deposition of of metasedirnentary metasedimentary emplacement units of of the the Knife KnifeLake Lakeassemblage assemblage in in Ontario Ontario and andMinnesota. Minnesota. The Theyoungest youngest ages ages of of 2683 2683 to 2680 2680 Ma were units obtainedfor forsyenitic syeniticto to granodioritic granodioriticphases phasesof of the the Kekekuab, Kekekuab, Icarus Icarusand andPerching PerchingGull GullLake Lakeplutons. plutons.These Theseages ages obtained 2684Ma Mapreviously previously obtained obtained for for the thepost-D2 post-D2Burchell Burchellpluton. pluton. overlap the the less lessprecise precisedate dateofof2684 overlap Amaximum maximum age ageof of deposition depositionof of about about2682 2682 Ma Ma isisprovided provided by by the the youngest youngest detrital detrital zircon zircon grains grains in in A conglomeraticunit unit in in the the northeastern northeasternpart partofofthe thebelt. belt.This Thisunit unitrepresents representsthe thelatest latestsedimentary sedimentarysuccession succession aa conglomeratic known in in the the region, region,postdating postdatingdeposition depositionand anddeformation deformationofofmuch muchofofthe theadjacent adjacentQuetico Queticosedimentary sedimentaryrocks rocks known and 1990). Deposition andof of the theSeine SeineGroup Group(Davis (Davisetetal.al.1989, 1989,1990). Depositionof ofthis thislate latesedimentary sedimentarysuccession successionprobably probablyreflects reflects some of of the thelatest latesttectonic tectonicadjustments adjustmentsoccurring occurringatatthe theboundary boundarybetween betweenWawa Wawaand andQuetico Queticosubprovinces. subprovinces. some References:Corfu Corfuand andStott Stott(1986). (1986).Can CanJ.J.Earth Earth Sci., 1075-1082. References: Sci., 23:23:1075-1082. Davis, and Kamo Kamo(1989). (1989).J.J.Geology, Geology,97: 97:279-398. 279-398. Davis,Poulsen Poulsen, ,and EarthPlant. Plant. Sci. Lett., 195-205. Davis,Pezzutto, Pezzutto,and andOjakangas Ojakangas(1990). (1990).Earth Davis, Sci. Lett., 99:99: 195-205. Williams, Stott, Stott,Heather, Heather,Muir, Muir,and andSage Sage(1991). (1991).Ont. Ont.Geol. Geol.Survey, Survey,Spec. Spec.Vol. Vol.4/1: 411:484-539. 484-539. Williams, 6 �APPLICATIONOF OF'THE THEALUMINUM-IN-HORNBLENDE ALUMINUM-m-HORNBLENDEBAROMETER BAROMETERON ONEARLY EARLY APPLICATION PROTEROZOIC,POST-PENOKEAN POST-PENOKEANPLUTONS, PLUTONS,CENTRAL CENTRALMINNESOTA. MINNESOTA. PROTEROZOIC, K.S.,and andHOLM, HOLM,D.K., D.K.,Department DepartmentofofGeology, Geology,Kent KentState StateUniversity, University,Kent, Kent, DARRAH,K.S., DARRAH, OH 2 16-672-4094; dholm@kentvm.kent.edu. dholm@kentvm.kent.edu. OH 44242; 44242; 216-672-4094; Archean and and Early Early Proterozoic Proterozoic metamorphic metamorphic rocks rocks in in central central Minnesota Minnesota record record relatively relatively Archean uniform uniform paleopressures paleopressures of of 5-6 5-6 kb kbassociated associated with with the thePenokean Penokean collisional collisional orogeny orogeny(1870-1830 (1870-1830 (18 12 Maand and—1770 -1770 Ma) Ma) tectonic tectonic Ma). These Theserocks rocksare areintruded intrudedby bysynsyn-(-1870 (-1870Ma) Ma)and andpostpost-(1812 Ma). Ma plutons, plutons, some some of of which which occupy occupy the the cores cores of of domal domalstructures structures in inthe thecountry countryrock rock(Southwick, (Southwick, and and others, others, 1988). 1988). InInorder ordertotoassess assessthe thepost-collisional post-collisional uplift uplifthistory history of of this this part part of of the the orogen orogen we we have have applied applied the theempirical empiricalAl-in-hornblende Al-in-hornblende igneous igneous barometer barometer of ofHammarstrom Hammarstrom and andZen Zen (1986) (1986) to to estimate estimateemplacement emplacementdepths depthsof ofthe themagmatic magmaticsuite. suite.This Thisbarometer barometercorrelates correlatesj,JtOt A P content content of of magmatic magmatic hornblende hornblende linearly linearly with with crystallization crystallization pressure of intrusion. Of Ofthe thesix six plutonic plutonic bodies bodies sampled sampled for for this this study, study, three three contain contain the theappropriate appropriatemineral mineral assemblage assemblage required for for the the barometer barometer and and yield yield relatively relativelyuniform uniform aluminum aluminumcontent contentfrom fromhornblende hornblenderim rim required microprobe microprobe analyses. analyses. The Theresults resultsofofmicroprobe microprobeanalyses analysesofofthe theundated, undated,moderately moderatelydeformed deformed Freedhem (iranodiorite Granodiorite(KA-F), (KA-F),and andthe the—1770 -1770 Ma Ma Isle Isle (K-4) (K-4) and and St. St. Cloud CloudGranites Granites(MN-35) (MN-35) Freedhem are are recorded recorded in in Table Table 1.1. The The barometer barometer has has been been verified verified experimentally experimentally by by Johnson Johnson and and Rutherford Rutherford (1989) (1989) and and more more recently recently by Schmidt (1992). The Theresults results of of our ourdata data using using both both of of these these calibrations calibrations isis given given below. below. Rock Rockunit unit St. St. Cloud Cloud Granite Granite Freedhem Freedhem Granodionte Granodiorite Isle IsleGranite Granite Johnson Johnson and andRutherford. Rutherford. 1989 1989 3.32 3.32 ±k0.5 0.5 kb kb 2.46 0.5 kb kb 2.46 ±k0.5 2.30 2.30±k0.5 0.5 kb kb Schmidt. 1992 1992 Schmidt. 4.62 4.62 ±k0.6 0.6kb kb 3.65 ± 0.6 kb 3.47 ± 0.6 kb TheJohnson Johnsonand andRutherford Rutherfordcalibration calibrationwas wasaccomplished accomplishedat at temperatures temperatures of of 740-780°C 740-780° The with with Pt0t Ptot == CO2 P c o 2 ++ F20, m 2 0 , whereas whereas the the Schmidt Schmidt calibration calibration was carried carried out out under under water water saturated saturated conditions conditions at at temperatures temperatures of of 700-655°C. 700-655OC. To Toour ourknowledge knowledgethere thereisisno noindication indicationfor for the thepresence presenceof ofaaCO2 C 0 2-bearing -bearing fluid fluid at at the the time time of of crystallization crystallization of of these these rocks, rocks, although although such such aa thing thing may may be, be, admittedly, admittedly, difficult difficult to to evaluate. evaluate. However, However,for forindependent independentreasons, reasons,we weconsider consider the the pressures pressures obtained obtained by by the theJohnson Johnsonand andRutherford Rutherford calibration calibration to to give givedepth depthofofintrusion intrusion estimates estimates that that are areunreasonably unreasonably low low (i.e., (i-e.,less lessthan than 10 10km kmfor forthe theFreedhem Freedhem Granodiorite Granodioriteand and Isle Isle Granite). Granite). Recent Recentthermochronologic thermochronologicdata data(see (seeHoim Holmand andLux, Lux,1995 1995ILSG ILSGabstract, abstract,this this volume) emplaced into into country country rock rock with withambient ambient volume) indicates indicates that that the the intrusions intrusions were were emplaced temperatures temperatures above above 300°C. 3OO0C. Considering Consideringan anupper-crustal upper-crustal geothermal geothermal gradient gradient in in the the range range of of 20-30°CIkm, 20-30°C/kmthis this indicates indicates aaminimum minimum depth depth estimate estimateof of 10-15 10-15km kmfor foremplacement emplacementof ofthese these plutons. plutons. Using (19921,the theSt. St.Cloud CloudGranite Graniteintruded intrudedatataapressure pressureofof Using the thecalibration calibration of of Schmidt Schmidt(1992), 4.62 0.6 kb. kb. Assuming Assumingananaverage averageoverburden overburdendensity densityofof2.7 2.7g/cc, gkc,this thiscorresponds correspondstotoaadepth depth 4.62 ±k0.6 of km. However, of —17 -17 km. However, the the comagmatic comagmatic (?) (?)Isle IsleGranite Graniteintruded intruded atataapressure pressureofof3.47 3.47±h0.6 0.6kb kb corresponding corresponding to to aa depth depthofof—13 -13 km. The Thefact factthat thatdifferent differentintrusions intrusionsofofthe the—1770 -1770 Ma Ma magmatic magmatic suite suite yield yield different differentemplacement emplacement pressures pressures suggests suggests that thatmagmatism magmatism occurred occurred simultaneously —1770 simultaneouslywith withpost-orogenic post-orogenicuplift. uplift.We Weinterpret interpretformation formationofofthethe -1770 Ma Mapost-tectonic post-tectonic plutons plutonsin ineast-central east-central Minnesota Minnesotato tohave haveresulted resulted from fromthermal thermal relaxation relaxation of of the theinternal internalzone zone of ofthe theorogen orogenwhich whichremained remainedoverthickened overthickenedfor for50-70 50-70Ma Ma after after collision. collision. We Weenvision envisionthermal thermal weakening weakening and andmelt meltproduction productionasasconcurrent concurrentwith withthe theonset onsetofofsignificant significantpost-orogenic post-orogenicuplift. uplift. Continued Continued unroofing unroofing is is suggested suggested by by the theabundant abundant 1760-1750 1760-1750 Ma Ma Rb-Sr Rb-Sr and andAr-Ar Ar-Arbiotite biotite cooling cooling ages ages throughout throughout central central Minnesota. Minnesota. Intrusion Intrusionand andcoeval coevaluplift upliftfollowed followedshortly shortlyby by orogen-wide orogen-widecooling coolingare areall allconsistent consistentwith withan anepisode episodeofoforogenic orogeniccollapse collapseproposed proposedby byHoim Holm and andothers others(1993). (1993). 7 �Although itit has has not notbeen beendated, dated?the thedeformed deformedFreedhem Freedhem Granodiorite Granodiorite has has been been Although commonly considered a syn-tectonic pluton associated with the Penokean collisional orogeny. commonly considered a syn-tectonic pluton associated with the Penokean collisional orogeny. However?its its shallower shallower depth depth of ofemplacement emplacement relative relative totothe thepost-tectonic post-tectonicSt. St.Cloud CloudGranite Granite However, suggests to us that it is also post-tectonic. We interpret deformation features in the Freedhem suggests to us that it is also post-tectonic. We interpret deformation features in the Freedhem Granodiorite (solid (solid state state foliation foliation and and cross-cutting cross-cutting shear shear zones), zones)?and and perhaps perhaps also also the the country country Granodiorite rock structural domes mentioned above? as features formed during uplift and collapse of the the rock structural domes mentioned above, as features formed during uplift and collapse of Penokeanorogen. orogen. Penokean Table1.1.Results ResultsofofMicroprobe Microprobeanalyses analysesononthe theFeedhem FeedhemGranodiorite Granodiorite(KA-F), (KA-F),the theIsle IsleGranite Granite Table (K-4)? and the St. Cloud Granite (MN-35). (K-4), and the St. Cloud Granite (MN-35). Sam~le Sample KA-F- 1 KA-F-1 KA-F-2 K-4-1 Si Ti A1 ME Si Ti Al Mg 6.891 0.147 0.147 1.335 1.335 2.724 2.724 6.891 1.329 2.708 2.708 6.915 0.143 0.143 1.329 6.915 6.761 0.142 1.511 2.510 6.843 0.148 1.424 2.597 6.850 0.128 1.356 2.790 6.822 0.147 1.439 2.641 6.845 0.158 1.340 2.721 6.832 0.160 1.401 2.709 6.819 0.142 1.455 2.659 6.853 0.109 1.381 2.552 6.808 0.117 1.470 2.488 6.857 0.117 1.407 2.522 6.927 0.083 1.360 2.642 6.891 0.104 1.391 2.539 K-4-2 6.942 0.101 1.319 2.574 7.008 0.086 1.290 2.587 6.991 0.091 1.275 2.633 K-4-3 MN-35-1 MN-35-2 6.955 0.093 1.314 2.567 6.974 0.073 1.320 2.640 6.833 0.112 1.453 2.529 6.590 0.224 1.640 0.242 6.552 0.217 1.643 0.248 6.580 0.212 1.627 0.221 6.712 0.159 1.542 0.214 6.735 0.143 1.530 0.234 6.642 0.161 1.630 0.219 MN-35-3 6.594 0.184 1.628 0.210 6.607 0.206 1.637 0.249 Ca Mn Ca Mn 1.897 0.077 1.897 0.077 1.876 0.071 0.071 1.876 Fe Na Fe Na KK 1.976 0.316 0.177 1.976 0.316 0.177 1.978 0.362 0.362 0.156 0.156 1.978 1.968 0.067 2.171 0.254 0.173 1.952 0.069 2.015 0.317 0.182 1.947 0.069 1.957 0.325 0.171 1.921 0.074 1.999 0.359 0.181 1.920 0.067 1.999 0.381 0.171 1.875 0.073 1.986 0.361 0.185 1.890 0.086 1.972 0.390 0.191 1.919 0.087 2.174 0.368 0.174 1.942 0.082 2.158 0.380 0.171 1.966 0.081 2.119 0.347 0.162 1.902 0.078 2.072 0.347 0.146 1.923 0.086 2.125 0.314 0.159 1.925 0.081 2.105 0.352 0.147 1.943 0.072 2.030 0.344 0.145 1.920 0.081 2.041 0.357 0.141 1.898 0.085 2.121 0.369 0.153 1.987 0.093 2.064 0.319 0.143 1.926 0.086 2.118 0.385 0.159 1.867 0.052 4.420 0.394 0.266 1.843 0.055 4.461 0.507 0.278 1.851 0.056 4.500 0.431 0.265 1.879 0.071 4.472 0.357 0.258 1.885 0.061 4.448 0.388 0.255 1.891 0.047 4.489 0.348 0.257 1.784 0.077 4.502 0.598 0.270 1.798 0.072 4.384 0.577 0.25 1 REFERENCES 1313. Hammarstrom J.M., and Zen, Zen7E-an, E-an71986, 1986?American American Mineralogist, Mineralogist?v. v. 71, 717p. p. 1297 1297-- 1313. Hamma.rstrom J.M., and Holm?D.K., D.K.? Holst, Holst, T.B., T.B., and and Lux, Lux7D.R., D.R., 1993, 1993?Canadian Canadian Journal Journal of of Earth EarthSciences, Sciences?v.v.30, 307p.p. Holm, 913-917. 9 13-917. 841. Johnson M.C., M.C.?and and Rutherford RutherfordM.J., M.J., 1989, 1989?Geology, Geology,v. v. 17, 17?p. p. 837 837-- 841. Johnson Schmidt? M.W.? 1992? Contributions to Mineralogy and Petrology7 v. 1lo7p. p. 304 304--310. 310. Schmidt, M.W., 1992, Contributions to Mineralogy and Petrology, v. 110, ., and McSwiggen? P.L., 198& Minnesota Geological Survey Southwick, D.L.? Morey, G.B Southwick, D.L., Morey, G.B., and McSwiggen, P.L., 1988, Minnesota Geological Survey Report of Investigations 37? scale 1:2507000. Report of Investigations 37, scale 1:250,000. 8 �Geochronology the 1.1 1.1 Ga North American Mid-Continent Geochronology of the Mid-Continent Rift D.W. Geology Dept., DepteIRoyal Royal Ontario Ontario Museum, Museum, Toronto, Torontol Ont., Onte1 D.W. Davisl Davis, Geology J. C. Greenl Geology Dept., Depts1Univ. Univ. of of Minn. Minn. Duluth, Duluthl Duluth, DuluthlMN, MNl Green, Geology M. Dept.# ROM, ROMl Toronto Toronto M. Manson# Manson, Geology Dept., Mid-Continent Rift Rift (MCR) The Mid-Continent (MCR) structure structure is is underlain underlain by by one one of the thickest crustal sections sections in in North North America America and and represents represents one one of of the the great great flood flood thickest crustal km3 of of basalt eruption of at at least least 1.5 1.5 million million km3 basalt provinces provinces of the world with eruption 1ava.The excellent much of of the igne0t.T~stratigraphy stratigraphy provides provides an an lava.The excellent preservation preservation 6f f much opportunity zircon geochronology and to opportunity to to test the resolving power of U-Pb zircon measure rates rates of of plume—driven plume-driven igneous igneous processes processes in the the Precambrian. Precambrian. Ages measure Ages discussed below are baddeleyite analyses discussed are based on on zircon zircon or baddeleyite analyses and are are given given with 95% confidence confidence errors. The The earliest earliest igneous igneous activity is is represented 95% represented by the the emplacement of +/- 11Ma)' ~a)'and and emplacement of alkaline alkaline plutons plutons such such as as the the Coldwell Coldwell complex complex(1108 (1108+/a syenodiorite within a syenodiorite within the the lower lower North North Shore Shore Volcanic Volcanic Group Group (NSVG, (NSVGI1107.0 1107.0 +/+/- 1.6 1.6 Ma); as well as as by the the emplacement emplacement of tholeiitic sills such such as the sills tholeiitic sills the Logan Logan sills +/- 0.6 0.6 Ma)3; ~ a ) ~and ; the the +4/-2 Ma)2 ~a)' and Nathan's Nathan's layered layered series series (1106.9 (1106.9 +1— (1109 +4/—2 eruption eruption of of felsic felsic lava lava in in the the Powder Powder Mill Mill group group (1107.5 (1107.5 +1— +/- 1.6 1.6 Ma), Ma) at at the the base base the Osler group group (1108 (1108 +41-2 +4/-2 Ma) Ma) and and in in the the lower lower part part of of the the NSVG NSVG (1108.0 (1108.0 of the +/-2.1 Ma). of these these units units are are paleomagnetically paleomagnetically reversed and appear to +/—2.1 Ma). All of represent an intense intense but short—lived short-lived episode episode of mantle mantle and and induced induced crustal crustal melting. AA significant significant time gap occurs occurs in in NSVG NSVG stratigraphy stratigraphy between between older older melting. paleomagnetically younger normal rocks. A sample sample from from the the Hovland paleomagnetically reversed and younger lavas collected collected near near the the top of of the the reversely reversely magnetized magnetized section section gives gives 1107.6 +/lavas 1107- 6 +/— 2.5 Ma, Ma, while while a sample sample from the Chicago Chicago Bay the 2.5 from the Bay lavas, l a v a ~near near ~ the base base of of the the normally normally magnetized section, gives gives 1100.5 1100.5 +/÷1- 1.9 1.9 Ma. Ma. This is followed followed by units aged aged magnetized 1097.9 +/1— 1.6 1.6 Ma, Mal 1098.1 +/-1.5 1.7 Ma Ma and and 1096.6 1096.6 ÷1— +/- 1.9 1.9 Ma Ma at at 1097.9 +/—l.5 Ma, Ma, 1098.5 +/1— 1.7 5 km. The The Duluth Duluth higher stratigraphic stratigraphic levels, comprising a thickness of about 5 layered gabbro complex was emplaced into the NSVG over a time span of at least 1099.3 +/1— 0.3 Lake 0.3 to to1098.6 1098.6 +1— +/- 0.5 0.5 Ma3.The ~ a ~ . T hPortage Portage e Lake Volcanics Volcanics (PLV) (PLV) comprise comprise 1099.3 structurally over 4 km of basalts and are faulted at the base but appear to be structurally above the the NSVG. Thick above Thick basalt basalt flows flows near near the the base base and and top top of of the the PLV PLV give give ages ages of of +1- 1.8 The PLV PLV is overlain by 1.8 Ma and and 1094.0 1094.0 +/+/- 1.5 1.5 Ma, MaI respectively4. respectively4. The 1096.2 +/sediments the Copper Copper Harbor Harbor Conglomerate sediments of the Conglomerate which which contain contain interlayered interlayered basaltic basaltic +/- 1.6 1.6 Ma4. Ma4. This This age age is is andesite flows, flowsI one of of which which gives gives an an age age of of 1087.2 1087.2 +1— coeval with emplacement of of a a felsic felsic porphyry on on Michipicoten Michipicoten Island Island at at 1086.5 1086.5 +1.3/—3.O and represents represents aa final the +I. 31-3.O Ma5 ~ a 'and final episode episode of of volcanism. volcanism. Thus, Thuslmagmatisxn magmatism in in the m.y. and appears to be MCR shows a total time span of slightly slightly more than 20 m.y. confined to three three main pulses, pulses, the the most most significant significant occupying occupying aa time time span span of of approximately approximately 77 m.y. m.y. Paleomagnetic studies of of MCR MCR rocks Paleomagnetic studies rocks have have furnished furnished the the most most reliable reliable apparent apparent polar polar wander wander curve curve for for the the Precambrian. Precambrian. Most Most sections sections show show aa single single R—N R-N polarity transition. polarity transition. The The age age of of this this reversal reversal is is constrained constrained between between the the 1100.5 1100.5 +1— +/- 1.9 Ma age age of of the the normally normally magnetized magnetized Chicago Chicago Bay Bay lavas lavas and and the the age age of of aa rhyo].ite sample from from Agate Agate Pointl Point, near near the the top top of the rhyolite sample the reversely reversely magnetized magnetized section of the the Osler Osler Group. Group. This section This age age was was formerly formerly reported reported as as 1098 1098 +1— +/- 44 Ma2 ~a'from from data data which had to to be be corrected corrected for for substantial substantial amounts amounts of of inheritance. inheritance. Recent Recent work small, apparently apparently inheritance-free inheritance—free zircon zircon fractions fractions gives a a preliminary preliminary work on smalll age age of of 1105 1105 +/— +/- 22 Ma. Ma. The within the The interpretation interpretation of of aa single single R-N transition transition within the MCR sequence sequence is is complicated the presence presence of of aa R-N-R—N R-N-R-N sequence sequence at at Mamainse Mamainse Point. Point. AA volcanic volcanic complicated by the from near near the the top unit top of the the lower reversed section section gives an age of 1096.2 1096.2 +/+1— unit from 1.9 Ma, implying a total 1.9 total of at at least least five five reversals reversals during during development development of of the the MCR. The Mamainse Point The Mamainse Point sequence sequence may may represent represent aa short short period period oscillation oscillation of of the the geomagnetic geomagnetic field field during during the the brief, briefl geochronologically geochronologically unresolved time time between between eruption +/- 33 Ma Ma from from eruption of of the the NSVG NSVG and and the the PLy. PLV. AA reversed reversed gabbro gabbro dated dated at at 1097.5 1097.5 +/— a drill in ~ a n s a smay ~ have The lower lower drill hole hole in Kansas6 may have also also been been emplaced emplaced during during this this period. The reversed section at Mamainse Mamainse Point Point shows shows aa coherent coherent geochemical geochemical and and isotopic isotopic that there there are are no significant age gaps gaps over over most most of this trend7,*implying implying that significant age this trend7'8 sequence. that the the reversed reversed paleomagnetic paleomagnetic poles poies determined determined from sequence. If If so, soI the fact that Mamainse Mamainse Point Point show show aa high high latitude latitude similar similar to to the the 1108 1108 Ma Ma poles poles implies implies that that at at least the early early part of of the the paleomagnetic paleomagnetic polar polar wander wander path path was was dominated dominated by by 9 �reversal reversal asymmetry asymmetry and there there may have been very little little continental continental drift. This This might explain explain why why plume—generated plume-generated volcanism9 volcanism9 in the the Lake Lake Superior Superior region region m.y. period when the degree of apparent persisted over a 20 20 m.y. apparent polar wander would suggest suggest a a continental continental drift drift of of several several thousand thousand kilometers. kilometers. '~eaman~ L.M. 'Heaman, L.M. and and Machador Machado, N. N. 1992. 1992. Timing Timing and origin origin of the Midcontinent Rift alkaline magmatismI North America: America: evidence evidence from from the the Coldwell Coldwell Complex. Complex. Contrib. Contrib. alkaline magmatism, North Mineral. Petrol. Petrol. 110: 110: 289—303. 289-303. '~avis~ SutcliffeI R.H. R.H. 1985. and 2Davis, D.W. D.W. and Sutcliffe, 1985. U-Pb U-Pb ages from the Nipigon plate and Am. Bull., Bull.I 96: 96: 1572—1579. 1572-1579. SOC. Am. northern Lake Lake Superior. Superior. Geol. Geol. Soc. northern 3Paces, J.B. -Mill-er, -'J.D. 3~acesI J.B.and and -MilkerI -3.D. -1993. 1993. - Precise .-U-Pbages -of of Duluth Precise-U—Pb Duluth Complex Complex and related mafic related maf ic intrusions, intrusionsI northeastern northeastern Minnesota: geochronological geochronological insights ins-ights to to physical, petrogenicI petrogenic, paleomagnetic tectonomagmatic processes with physicalI paleomagnetic and andtectonomagmatic processes associated associatedwith the 1,lGa the lIIGa Midcontinent Midcontinent Rift Rift system. system. J. J. Geophys. Geophys. Res. Res. 98: 98: 13997—14013. 13997-14013. 4Davis, D.W. D.W. and and Paces, Paces, J.B. J.B. 1990. 1990. Time Time resolution resolution of of geologic geologic events events on on the 4~avisI Keweenaw Peninsula and implications implications for for development development of of the the Midcontinent Midcontinent Rift Rift system. Earth Planet. Sci. Lett. Lett. 97: 97: 54—64. 54-64. Palmer, H.C. and U-Pb U-Pb geochronology geochronology of 'palmerI H.C. and and Davis, DavisI D.W. D.W. 1987. Paleomagrietism Paleomagnetism and of Island, Lake volcanic rocks from Michipicoten Superior, Canada: volcanic rocks Michipicoten IslandI Lake SuperiorI Canada: precise precise calibration of the Keweenawan Keweenawan polar calibration of the polar wander wander track. track. Precambrian Precambrian Res. Res. 37: 37: 157—171. 157-171. 6Van %an Schmus, SchmusI W.R. Tectonic setting of the 1992. 1992. Tectonic the Midcontinent Midcontinent Rift Rift System. System. Tectonophysics Tectonophysics 213: 213: 1—15. 1-15. 7K.W.Klewin and J.H.Berg J.H.Berg 1990. Geochemistry of the 7~.~.Klewinand the Mamainse Mamainse Point Point volcanics, volcanicsI Ontario, OntarioI and and their their implications implications for for the the Keweenawan Keweenawan paleomagnetic paleomagnetic record, recordI Can. Can. J.Earth Sci. 17: 17: 1194—1199. 1194-1199. 8Shirey, S.B., KlewinI Klewin, K.WSI K.W., Berg, Carison, R.W. 1994. *shireyI S.BeI BergI J.H. and and CarlsonI 1994. Temporal Temporal changes changes in the sources sources of flood flood basalts: Isotopic Isotopic and trace trace element element evidence evidence from from the the 1100 Ma old old Keweenawan Keweenawan Mamainse Mamainse Point Point Formation, FormationI Ontario, OntarioI Canada. Canada. Geochim. Geochim. Cosmochim. Acta Acta 58: 58: 4475—4490. 4475-4490. on the origin of the 9Cannon, W.F. and 9~annonIW.F. and Hinze, HinzeI W.J. W. J. 1992. 1992. Speculations on the North North American Midcontinent 213: 49—55. 49-55. American Midcontinent rift. rift. Tectonophysics Tectonophysics 213: 10 �DAVID BELL MINE MINE POSTER POSTER DISPLAY DISPLAY DESAUTELS, Pierre, Teck-Corona Operating Corporation, David David Bell Mine, P.O. Bag 11, 11, Marathon Marathon ON ON POT-2E0 POT-2E0 km east eastof ofMarathon, Marathon,Ontario Ontarioon onthe theTrans-Canada Trans-Canada Highway. Highway. The The mine mine lies lies The David Bell mine is is located located 35 35 km Belt and is jointly jointly own by Teck Corporation and Homestake Canada within the Schreiber-White River Greenstone Belt Ltd. f ~ sgold gold t pour took took place place Following the main ore zone discovery by consulting geologist David Bell in 1981, 1981, the first in May Since then, then, the mine has been May 1985 1985 after after two two years years of ofconstruction construction and and underground underground development. development. Since been in in continuous production production extracting extractingin inexcess excessof of2.0 2.0 million millionounces ouncesof ofgold. gold.Remaining Remainingreserves reservesasasofofDecember December31a, 3l', 1994 are estimated at 4.9 million million tonnes tonnes grading grading 10.85 10.85 grams grams per per tonne. tonne. The main ore group " A and and "D" "D" zone zone generally generally lies within within the the Moose Moose Lake Lake formation formation at the the group comprising comprising of the "A" contact between quartz feldspar porphyry rocks, often often in close porphyry and metasedimentary metasedimentary rocks, close relationship relationship with with a mafic mafic metavolcanjc unit. The lower "C" zone metavolcanic unit. zone lies lies within within the thelaminated laminated metasedimentary metasedimentary member member of the the Cache Cache Lake Lake formation. The ore horizons generally occur as tabular sheets striking at 102 102 degree and dipping between 50 and 61 degree north. Three workings and and in in the thedrill drillcore. core. Three distinct distinct ore ore characteristics characteristics were were observed observed in in the the underground underground workings The display plans, longitudinal projection of of the ore zones and aa typical display consists consists of of underground underground geology plans, longitudinal projection typical cross cross section. The sample collection includes a suite of representative representativemine samples samples and and drill drill core core specimens specimens covering covering the the ore horizons and and walirock wallrock lithologies. lithologies. 11 �IGNEOUS CHARACTERISTICS CHARACTERISTICSOF OF THE THE MATRIX TO THE FOOTWALL BRECCIA, NORTH IGNEOUS RANGE, RANGE, SUDBURY SUDBURYSTRUCTURE, STRUCTURE, CANADA CANADA 0.and andWatkinson, Watkinson,David DavidH., H., Department Department of of Earth Earth Sciences, Sciences,Ottawa-Carleton Ottawa-Carleton Everest, John 0. Everest, Geoscience Centre, Centre,Carleton Carleton University, University, Ottawa, Ottawa,Ontario, Ontario,Canada, Canada,Ki K1SS5B6; 5B6; Geoscience Farrow,Catherine., Catherine.,Ontario OntarioGeological GeologicalSurvey, Survey,Sudbury, Sudbury,Ontario, Ontario,Canada, Canada,P3E P3E6B6. 6B6. Farrow, Much Muchof ofthe theore orein inthe theNorth NorthRange Rangeof ofthe the1.85 1.85Ga GaSudbury SudburyStructure Structureisishosted hostedby by aa discontinuous discontinuous graniticunit unit knownas known asthe theFootwall FootwallBreccia. Breccia.Impact-generated Impact-generatedembayments embaymentshave haveprovided providedtopographical topographical granitic lows lowsfor forthe thecreation creationof ofaathickened thickenedheterolithologic heterolithologicbreccia brecciasequence sequenceoverlain overlainby by an an equally equally thickened thickened Sublayer unit. The Thexenoliths xenolithswithin withinthis thisbreccia brecciapile pileconsist consistof ofrandomly randomlyoriented, oriented,locally locallyderived derived Sublayer footwallgneisses gneissesas aswell wellas asexotic exoticclasts clastsof ofdiatexite, diatexite,diorite, diorite,gabbro, gabbro,pyroxenite, pyroxenite,anorthosite, anorthosite,diabase, diabase, footwall graniteand and Sudbury SudburyBreccia. Breccia. Depending Dependingon ontheir theirrefractory refractoryproperties, properties,these theseinclusions inclusionsmay mayhave havediffuse diffuse granite or sharp sharp contacts contactswith with the the matrix, matrix, and and may may be represented by a diverse range of sizes. Quite Quitefrequently frequently or these breccia breccia fragments fragmentsare areblanketed blanketedby byelongate elongatesulfide sulfideblebs, blebs,aatexture texturewhich whichmay mayhave haveformed formedduring during these the the initial initialmagma magmainjection. injection. The Thematrix matrixto tothese theseinclusions inclusionsisisaafine fine --to tomedium medium-- grained grainedgranitic graniticunit unit composed composeddominantly dominantly of ofgrains grainsof ofhornblende, hornblende,pyroxene pyroxeneand andlarge largeoptically opticallycontinuous continuousgrains grainsof ofpoikilitic poikiliticquartz quartzenclosing enclosing subhedral (Ano-.jo).Granophyric Granophyrictextures, textures, consisting consistingof of intergrowths intergrowthsof ofquartz quartzand and subhedralgrains grainsof ofplagioclase plagioclase(An050). fresh freshto to saussuritized saussuritizedalbite albiteare arevery verycommon, common,and andincrease increaseininabundance abundancetoward towardthe thecontact contactwith withthe the overlying overlyingnorite. norite. The Thematrix matrixisisalso alsoaamajor majorhost hosttotothe theNi-Cu-PGE Ni-Cu-PGEsulfides. sulfides.These Theseare arerepresented represented predominantly predominantlyby byblebs blebsofofpyrrhotite, pyrrhotite,chalcopyrite, chalcopyrite,pentlandite pentlanditeand andpyrite. pyrite.Characteristic Characteristicofofthe the mineralized breccia brecciaisisthe theincrease increaseininthe theoccurrence occurrenceof ofmafic maficminerals mineralswhich whichmay mayform formhalos halosaround aroundthe the mineralized sulfides. sulfides. Alteration Alterationof ofthe thematrix matrixby byinteraction interactionwith withformational formationalfluids fluidshas haslocally locallyproduced producedaamineral mineral assemblage quartz, calcic amphibole, biotite (XMgI(Mg+Fe) ==0.65), (XMg/(Mg+Fe) 0.65),chlorite chlorite (XMg/<Mg+Fe) 0.35-assemblageofofepidote, epidote, quartz, calcic amphibole, biotite (XMgI(Mg+Fe) ==0.35 0.5), 0.5),garnet, garnet, titanite, titanite,magnetite magnetite and and calcite calcite(Epidote (Epidote Zone, Zone, Fraser Mine). Fluid Fluidinclusion inclusionstudies studieshave have shown shownthat thatthese thesefluids, fluids,which whichwere weredriven drivenby bythe theheat heatof ofthe thecooling coolingSudbury SudburyIgneous IgneousComplex, Complex,formed formed this alteration assemblage and remobilized Cu, Ni, PGE, Au, Ag especially, at temperatures between this alteration assemblage and remobilized Cu, Ni, PGE, Au, Ag especially, at temperatures between210 210 and OC. and400 400°C. Petrographic albite(Ano) (Ano)patches patches and and veins veins with withcentrally centrally Petrographicstudy studyreveals revealsthe thepresence presenceof ofquartz quartz--albite located chloritefilled filledcavities. cavities.Quartz Quartzininthe thelatter lattercontains containsabundant abundant fluid fluid inclusions. inclusions. Locally, Locally, locatedquartz quartz--chlorite original originalalbite albitemineralization mineralizationwithin withinthe thegranophyric granophyricveinlets veinletshas hasbeen beenreplaced replacedby byaapink pinkpotassic potassic feldspar feldspar(orthoclase). (orthoclase). Themineralogy mineralogyand andtextures texturesthat thathave havebeen beenobserved observedindicate indicatethat thatthe theFootwall (1) FootwallBreccia Brecciawas was(1) The formed formedby by aamagmatic magmaticprocess processinvolving involvingassimilation assimilationof offootwall footwallrock, rock,and and(2) (2)subsequently subsequentlyaltered alteredby by hydrothermal hydrothermalfluids fluidsrelated relatedtotothe thecooling coolingSudbury SudburyIgneous IgneousComplex. Complex. 12 �VESICLES AND AND BRECCIA BRECCIA DUE DUE TO TO INJECTION INJECTION OF OF MAFIC MAFIC MAGMA INTO INTO VESICLES PARTIALLY LITHIFIED SEDIMENTS OF THE EARLY PROTEROZOIC IRONWOOD PARTIALLY LITHIFIED SEDIMENTS OF THE EARLY PROTEROZOIC IRONWOOD IRON-FORMATION, WESTERN WESTERN GOGEBIC GOGEBIC RANGE, RANGE, NW NW WISCONSIN WISCONSIN IRON-FORMATION, LEEANN FEHER, FEHER, Geology Geology Dept., Dept., St. St. Norbert Norbert College, College, DePere, DePere, LEEANN Wisconsin. Wisconsin. Tim Flood, Flood, Geology Geology Dept., Dept., St. St. Norbert Norbert College, College, DePere, DePere, Wisconsin. Wisconsin. Tim Detailed mapping mapping and and petrographic petrographic analysis analysis of of ironiron- and and Detailed silica-rich argillites argillites of of the the Ironwood Ironwood Iron-Formation Iron-Formationand and silica-rich associated mafic mafic and and felsic felsic intrusions intrusions was was undertaken undertaken in in the the associated Western Gogebic Gogebic Range Range near near Atkins Atkins Lake, Lake, Wisconsin. Wisconsin. The The purpose purpose Western of the the study study was was to to determine determine the the nature, nature, origin, origin, and and of relationships of of these these rocks. rocks. In In particular, particular, we we focused focused on on the the relationships The contact between between the the argillites argillites and and aa sill-like sill-likemafic mafic body. body. The contact contacts are are marked marked by by breccia breccia zones zones that that contain contain local local areas areas of of contacts argillite clasts clasts in in vesiculated vesiculatedbasalt basaltmatrix. matrix. argillite In places places the the In breccia resembles resembles aa peperite. peperite. breccia The study study area area is is approximately approximately 500 500 meters meters by by 500 500 meters meters and and The was mapped mapped at at aa scale scale of of 1:1000. 1:1000. The The rocks rocks trend trend approximately approximately was N70° and and have have an an average averagedip dipof of50°NW. 50°NW The The argillite argillite is is thinly thinly N70°E 45 meters. meters. bedded to to laminated laminated and and has has aa minimum minimum thickness thickness of of 45 bedded Concordant with with the the argillite argillite is is aa mafic mafic body body that that has has aa finefineConcordant grained diabasic diabasic to to medium-grained medium-grainedgabbroic gabbroic texture. texture. This Thismaf mafic grained Ic unit is is approximately approximately 50 50 meters meters thick. thick. The The contacts contacts between between the the unit argillite and and the the mafic mafic rocks rocks are are characterized characterized by by breccia breccia zones zones argillite up to to 20 20 meters meters thick. thick. The The breccia breccia consists consists of of angular angular to to up subangular, tabular tabular clasts clasts of of argillite argillite up up to to 11 meter meter In in subangular, diameter, some some of of which which are are bent. bent. Most Most of of the the clasts clasts are are silicasilicadiameter, rich, but but iron-rich iron-richclasts clasts have have been been observed. observed. Garnets Garnets up up to to 55 rich, 13 �mm in in diameter diameter are are common common and and unique unique to to the the breccia breccia zone. zone. mm Locally, lodestone lodestone occurs occurs in in the the iron-rich iron-richargillite argillite at at the the Locally, meter wide wide contact with with the thebreccia. breccia. Granitic Granitic dikes dikes up up to to 11 meter contact These granites granites are are intrude both both the the mafics mafics and andargillites. argillites. These intrude medium- to to fine-grained fine-grainedwith with chilled chilled margins. margins. medium22 thin thin sections sections Petrographic analysis analysis was was performed performed on on 22 Petrographic which included included textural texturaldescriptions descriptionsand and 500 500point point counts counts per per which The argillite argillite is is composed composed of of alternating alternating layers layersof of section. The section. fine-grainedmagnetite, magnetite, fine-grained fine-grainedbiotite biotite or or actinolite, actinolite,and and fine-grained The mafic mafic rock rock is is composed composed primarily primarily of of recrystallized quartz. quartz. The recrystallized medium-grainedamphiboles amphiboleswith with included included plagioclase plagioclaselathes, lathes, medium-grained probably aa relict relict ophitic ophitic texture. texture. Magnetite Magnetite is is common. common. probably Preliminary geochemical geochemical data data indicates indicatesaa tholeiitic tholeiitic composition. composition. Preliminary The breccia breccia consists consistsof of clasts claststhat that are are composed composedof of The recrystallized quartz quartz plus plus chlorite, chlorite, or or biotite biotite plus plus garnet garnet in in aa recrystallized basaltic matrix matrix that that is islocally locallyvesiculated. vesiculated. Vesicles Vesicles are are basaltic infilled with with chlorite, chlorite,with with or orwithout withoutquartz. quartz. Some Some vesicles vesicles infilled are composed composed of of quartz quartzwith withchlorite chloritecores. cores. The The granite granite is is are composed of of mediummedium- to to fine-grained fine-grainedpotassium potassium feldspar, feldspar,quartz, quartz, composed plagioclase,and and minor minor amounts amountsof of biotite. biotite. plagioclase, infer that that the the argillites argillites were were deposited deposited as as aa sequence sequenceof of We infer We thin, alternating alternating iron-rich iron-richand and silica-rich silica-richlayers. layers. The The sillsillthin, like mafic mafic body body intruded intruded into into these these water-rich water-richsediments sediments while while like Intrusion of the mafic magma lithified. they were wereonly onlypartially partiallylithif they led. Intrusion of the maf Ic magma into the the water-rich water-richsediments sediments resulted resulted in in the the formation formationof of the the into breccia, i.e. i.e.peperite. peperite. The The matrix matrix of of the the breccia breccia is is locally locally breccia, vesiculated due due to to interaction interaction of of the the mafic mafic magma magma with with water water vesiculated 14 �derived from from the the sediments. sediments. We We suggest suggest that that the the breccia breccia is is not not derived the result result of of aa mafic mafic lava lava flowing flowing onto onto or or into into unconsolidated unconsolidated the sediments because because of: of: 1) 1) development development of of aa medium-grained medium-grained gabbroic gabbroic sediments 2) capture capture of of angular, angular, texture in in the the interior interiorof ofthe themaf mafic body, 2) texture Ic body, 3) formation formation bent and and tabular tabular xenoliths xenoliths in in the the breccia breccia zone, zone, and and 3) bent of vesicles vesicles at at the the top top and and bottom bottomcontacts contactsof ofthe themaf mafic body with with of Ic body the breccia. breccia. Garnets Garnets only only occur occur in in the the breccia breccia zones zones and and most most the likely formed formed by by contact contact metamorphism metamorphism caused caused by by intrusion intrusion of of the the likely mafic sill. sill. mafic Significantly, emplacement emplacement of of the the mafic mafic magma magma into into partially partially Significantly, lithified igneous activity activity lithif led sediments sediments does does imply imply contemporaneous contemporaneous igneous and deposition deposition of of the the Ironwood Ironwood Iron-formation Iron-formation on on the the western western end end and of the the Gogebic Gogebic Range. Range. The The maf mafic now occurs occurs as as of Ic material material now metadiabase and and metagabbro, metagabbro, the the result result of of later later low-grade low-grade metadlabase metamorphism. Granitic Granitic dikes dikes that that intrude intrude concordantly concordantly to to metamorphism. discordantly into into the the mafic mafic and and argillitic argillitic rocks rocks have have chilled chilled discordantly margins and and lack lack metamorphic metamorphic features. features. In In addition, addition, the the margins surrounding country country rock rock does does not not appear appear to to have have been been contact contact surrounding metamorphosed by by the the granitic granitic intrusions. intrusions. We We infer infer that that these these metamorphosed emplaced after after cooling cooling of of the the mafic mafic sill sill and and the the dikes were were emplaced dikes argillites, and and are are likely likely related related to to nearby nearby Middle Middle Proterozoic Proterozoic argillites, granitic rocks. rocks. granitic 15 �Neoarchean Transubprovince Depositional Systems: Temporal vrs vrs Spacial Variability Systems: Temporal Variability in Province. Fralick, Western Superior Province. Fralick, P.W., P.W., and and Purdon, Purdon, R., R., Department Departmentof of Geology, Geology, University, Thunder Thunder Bay, Bay, Ontario, Ontario, P7B P7B 5E1. 5E1. Lakehead University, With the growing acceptance that plate tectonic tectonic processes similar to those operating operating the amalgamation amalgamation of of Superior Superior Province Province during the Late Late Archean Archean comes comes the the today led to the sequence stratigraphy stratigraphy techniques to analyze analyze tectonic control control of of basin basin opportunity to use sequence formation. formation. Application Applicationof ofthis thistechnique techniqueand andchemostratigraphy chemostratigraphyto tofour foursedimentary sedimentarybasins basins Wawa Subprovinces Subprovinces of of northwestern in the theWabigoon, Wabigoon, Quetico Quetico- and Wawa northwestern Ontario Ontario adds adds significantly to the the tectonic interpretation interpretation of significantly to of this this region. region. The Beardmore-Geraldton forearc basin, basin, located located in in the the southern southern Wabigoon Wabigoon Beardmore-Geraldton forearc Subprovince, and the Quetico Queticotrench trenchformed formedaayoked yokedsystem, system,with withvolcaniclastic volcaniclastic sediment sediment feed from the north north (see (seeEriksson Eriksson et etal, al,1994, 1994,and and references references therein). therein). Braided fluvial fluvial channels delivered delivered detritus detritus to to fan fan and and braid braid deltas, deltas, which in turn rerouted rerouted itit to to the theseafloor, seafloor, building sequence in forearc basin basin and and building aa submarine submarine fanlramp fan/ramp sequence in the distal portion of the forearc trench. Sediment Sedimentgeochemistry geochemistryof of the theforearc-trench forearc-trenchassemblage assemblageisisextremely extremely consistent, consistent, implying that a similar source terrain existed laterally for 300 kilometres, or a single area implying that provided most of the element ratios indicate that aacaic-alkaline provided most the sediment. sediment. Immobile Immobile element calc-alkaline extrusive-intrusive the extrusive-intrusivesuite suitepresent present in in the the Onaman-Tashota Terrane Terrane supplied sediment to the forearc and the portion portion of of the the trench trench to to its itssouth. south. Immobile Immobile element ratios and zircon zircon geochronology further further indicate that the volcanicthe western western trench trenchreceived received sediment sedimentfrom fromaavolcaniccratonic area to its its north. This Thisimplies impliesthat thatgeochemistry geochemistryof of the the arc arcsystem system was consistent from the continental arc in the west to the the eastern easternoceanic? oceanic? arc. arc. The sedimentary of an interarc interarc basin, present present in in the the Wawa Wawa Subprovince Subprovince sedimentary geochemistry of Terrace Bay, is very very similar similarto to the the Quetico Quetico trench. trench. This east of Terrace This basin basin is is dominated dominated by by distal distal submarine ramp turbidites, while the Quetico to the the north northisiscomposed composedof of proximal proximal ramp ramp turbidites. These turbidites. These data data imply imply that that the thedepositional depositionalsystem system overwhelmed overwhelmed the trench, trench, overflowed onto onto the the ocean floor and flooded into an interarc setting. setting. overflowed an interarc The fourth basin examined examined is in an intermontane intermontane setting setting within the Onaman-Tashota Onaman-Tashota Arc Terrane. It was filled by a mostly mostly subaqueous fan delta system system with local sources of variable composition supplying the detritus. Sediment supplying the Sedimentgeochemistry geochemistry confirms the variable nature of the source present in the area were source terrane terrane and and indicates indicates large granitic batholiths present intermontane basin the major contributors. The Thedifference difference in in sediment sediment source between the intermontane and other basins to to the south can only be be interpreted as as aa change change in in basin basin type type other synvolcanic synvolcanic basins through time reflecting cessation of volcanism volcanism in in the the area area and emplacement and unroofing emplacement and of later-stage later-stage batholiths. The Thebasin basin may may have been produced produced as a result of transpression but this conclusion awaits further structural structural studies. studies. FIGURE geologyofof portions portions of of the FIGURE 1: 1: Regional Regional geology the Wabigoon, Wabigoon, Quetico Quetico and and Wawa Wawa refer to areas Subprovinces, northwestern Ontario. Subprovinces, northwestern Ontario. Numbers Numbers refer areas samples samples for for sediment sediment geochemistry (Table). (Table). TABLE: Sediment geochemistry geochemistry of the areas areas indicated on Figure 1. 1. 16 �1 1 Wabigoon Forearc Forearc nn=7 = 7 Si02 Ti02 A1203 Fe203 MnO MgO CaO Na20 K20 P205 64.1 .54 15.4 530 .09 2.73 3.06 3.77 2.08 .14 22 Quetico Trench Trench 3 Quetico Quetico Trench Trench n=5 n =5 44 Quetico Quetico Trench n=1O n = 10 64.0 64.7 .56 15.4 6.60 .09 2.76 2.77 3.49 2.36 .17 64.4 .58 n=8 n = 8 36 152 5.77 .10 3.07 2.81 3.93 1.68 .15 152 6.06 .07 2.92 3.46 3.34 2.10 .14 55 Quetico Quetico Tench Tench n=14 n=14 64.1 .50 15.1 5.64 .12 231 3.80 3.32 2.16 .14 Ba Co Cr Cu Mo Nb Pb Rb 560 24 530 24 640 - - 21 106 35 1.1 170 48 1.1 5.9 94 73 175 142 119 - 38 50 Se Sr V Y 350 Zn Zr 5.2 85 68 274 89 10 61 103 350 390 97 540 - 6 15 83 66 620 7 6 Wawa Wabigoon Wabigoon Interarc Interarc Intermontane Intermontane n=6 nn=11 =ll n = 6 64.0 .58 153 5.23 .09 3.00 3.40 3.72 1.95 .19 6.0 26 57 - 369 - 300 94 13 13 78 127 lOi 14 78 138 3.56 2.44 .08 48 - 78 142 .05 .79 1.27 5.9 461 10 3.03 3.2 - 59 103 .32 14.8 550 340 108 16 71.8 1 and 2 - Fralick 1986; 4 -- Williams, 1 Fralick and Barrett, 1991; 1991; 3 -- Sawyer, Williams, 1978; 1978; Sawyer, 1986; 5 -- Stone Aniukun, 1980. Stone et aL, al., 1992; 1992; 6 -- Purdon, Purdon, in progress; 7 -- Amukun, 1980. 17 �CENTRAL CENTRAL MINNESOTA, U.S.A. U.S.A. CORE CORE LOGGING LOGGING AND AND ASSAY ASSAY DATABASES DATABASES Frey, Frey, Barry Barry A., A., Minnesota Dept. Dept. of of Natural Natural Resources, Resources, Minnesota Minerals Division, Division, P.O. P.O. Box Box 567, 567, Hibbing, Hibbing, Mn. Mn. 55746 55746 Minerals This work work includes includes the the relogging relogging and and assaying assaying of of existing existing DNR DNR Drill Drill Core Core Library Library This samples. planning and samples. The The purpose purpose is is to to provide provide data data for for land land use use planning and other other geologic geologic needs needs such such as as mineral mineral exploration. exploration. total of of 1241 1241 sample sample sets sets representing representing samples samples from from aa total total of of 850 850 drill drill AA total holes completion of of this thispoject, holes will will be logged at the completion project,and andapproximately approximately1500 1500 samples samples will will be be analyzed. analyzed. Many Many of of these these drill drill samples samples have have not not previously previously been been included on on the the DNR DNR Drill Drill Core Core Library Library Index Index (DCLI) (DCLI)(Ruhanen (Ruhanenand and Dzuck, Dzuck,1994). 1994). included Available historical historical information information has has filled filled many many previous previous data data voids voids for for drill drill Available samples samples previously previouslyon on the the DCLI. DCLI. The The DNR DNR Minerals InformationServices Services Minerals Management Management Information continues to to revise revise old old data data and and incorporate incorporate new new data data into into its its ever ever improving improving continues DCLI. DCLI Drill samples samples encountered encountered include include Proterozoic Proterozoic and and Archean Archean rocks, rocks, with with Drill scattered scattered Paleozoic, Paleozoic, Mesozoic, Mesozoic, lateritic lateritic weathering weathering products, products, and and glacial glacial materials, materials. Of Of the the lithologies lithologies encountered, encountered, the the iron iron formation formation(Proterozoic (Proterozoic Algoman Algoman type?) type?) related related rocks rocks (including (includingmetavolcanic metavolcanic schists) schists) are are typically typically deformed, deformed, metamorphosed metamorphosed (typically (typically low low grade), grade), altered, altered, and and recrystallized. recrystallized. Other Other rocks rocks include include gneiss, gneiss, Keweenawan Keweenawanrift rift material, material,and and some someschists schiststhat thatmay may represent the the continuation continuationof of the the Wisconsin Wisconsin Volcanic Volcanic Terrane Terrane that that hosts hosts Cu—Zn—Au Cu-Zn-Au represent deposits. deposits. Results for for the the 1300 1300 analyzed analyzed samples samples have have been been received received from from Bondar—Clegg Bondar-Clegg Results && Company Company Ltd. Ltd. of of Ottawa, Ottawa,Ontario. Ontario. Besides Besides being being (in (ingeneral) general) anomalously anomalously high high in in Mn Mn and and Fe, Fe, samples samples also also had had anomalous anomalous Ba, Ba, As, As, Hg, Hg, F, F, Li, Li, Nb, Nb, Zr, Zr, and and rare rare earths. earths. In In general general samples sampleswith withhigher higherTi02 Ti02also alsohad hadhigher higher1(20 K20 and and Al203. A1203. K-1 in in T47N T47N R2OW R20W Sec Sec Anomalous Zn Zn values values (with (withvisible visiblesphalerite) sphalerite)include includeDD}1 DDH K—i Anomalous 22 22 with with aa 5' 5' sample sample containing containing 2.25% 2.25% Zn. Zn. This This occurred occurred in in deformed deformed graphitic graphitic sulphide sulphide phyllite phyllite with with minor minor chloritic chloritic sericitic sericitic metatuff. metatuff. Drilling Drilling at at the the Arrowhead Arrowhead Mine Mine (graphite) (graphite) in in T48N T48N R18W R18W Sec Sec 32 32 produced produced brecciated brecciated graphitic graphitic sulfide sulfide schist schist samples sampleswith with several severalZn Zn values values over over 1300 1300ppm pprn (high 1916 ppm). pprn). (highof of 1916 Samples from from several several drill drill holes holes in in T43N T43N R32W R32W Sec Sec 12 12 had had anomalous anomalous base base and and Samples precious Perhaps the the most most interesting interesting values values came came from from drill drill hole hole 109. 109. precious metals. metals. Perhaps This 5' 5' sample sample contained contained 1383 1383 ppb ppb Au, Au, 1339 1339 ppb ppb Pd, Pd, 1156 1156 ppb ppb Pt, Pt, and and 1343 1343 ppm pprn Zn. Zn. This Another 2.3 ppm pprnAu. Au. Samples Samples (one (oneof of carbonate, carbonate, magnetite, magnetite, Another drill drillsample samplecontained contained2.3 silicate iron iron formation) formation) from from two two other other drill drill holes holes in in this this area area had had Cu Cu values values silicate of 1791 and and 1200 1200 ppm pprn respectively. respectively. In In T46N T46N R29W R29W Sec Sec 9, 9, DDH DDH 310 310 contained contained aa of 1791 sample with with chert(?), chert(?), hematite, hematite, quartzite(?) quartzite(?) iron iron formation formation with with aa Cu Cu value value of of sample 1622 1622 ppm, ppm, and and an an adjacent adjacent chert, chert, goethite, goethite, hematite, hematite, Mn Mn oxide(?) oxide(?) iron iron formation formation sample The highest highest As As value value was was 1362 1362 ppm pprn sample with with the the highest highest Li Li value value (1145 (1145ppm). pprn). The in tuffaceous tuffaceous carbonate, carbonate, chert, chert, goethite, goethite, magnetite, magnetite, red red hematite, hematite, silicate, silicate, in 280, located located in inT46N T46N R29W R29W Sec Sec sulfide iron iron formation formation (with (withtourmaline?) tourmaline?)in in DDH DDH 280, sulfide 2. The analyses analyses above above without without lithologies lithologiesindicate indicatethat thatthey theycame camefrom frompowdered powdered 2. The samples samples without without identifiable identifiablerock rockfragments. fragments. Pending Pending XRD XRD work work may may provide provide some some answers. =\Other locations locationsalso also contained contained anomalous anomaloussamples. samples. answers. =\Other The data data indicates indicates that that hydrothermal hydrothermal processes processes were were active active within within the the study study The area, area, and and that that there there may may be bea ahigh highprobability probabilityfor forundiscovered undiscovered economic economic mineralization. mineralization. Reconnaissancedrill drill core corelogging logginginformation informationhas has been been created createdand and stored stored Reconnaissance as This includes includesbasic basic information information about about rock rock types, types,alteration, as digital digitalfiles. files. This alteration, and Each database databaserecord record corresponds correspondsto to aa unique unique drill drill hole hole and and and mineralization. mineralization. Each footage footage interval. interval. A A separate separate"comments" "comments" database database contains contains aa brief brief synopsis synopsisof of each each drill drill hole hole and and notes notes on onunusual unusualfeatures. features. Other Other "related" "related" data data files files include include the theDCLI, DCLI, chemical chemical analyses, analyses,sample sample information, information,and andcore coregeophysical geophysical measurements. Combined, measurements. Combined, these these databases databases form form an an abundance abundance of of available available information information for forpossible possiblesynthesis synthesisby by users. users. The "constructed"using using aa data data manipulation manipulation system system The logging logging databases databases were were "constructed" called called WATFILE/Plus WATFILE/Plusand andSoftware SoftwareCarousel. Carousel. This This allowed allowed six six databases databasesto tobe be open open at at one one time, time, and and still still allow allow for for very very rapid rapid database database switching, switching, queries, queries, data data entry, entry, and and editing. editing. The The six six databases databases consist consist of of aa geographic geographic portion portion of of the the . 18 �DCLI, database, the lithologic code DCLI, the the logging logging database, database, the the logging logging comments comments database, code database, the alteration alteration code code database, database, and and the the database database containing containing sampling sampling information. While information. While not not being being truly truly "relational", "relational", the WATFILE the individual WATFILE databases databases were constructed constructed with the the common common fields fields necessary necessary for for linking linking after after importing importing into into aa relational relational database. database. The methodologies for utilization will will be dependent dependent upon upon The methodologies for data data synthesis synthesis and utilization hardware and hardware and software software limitations, limitations, and and the the ingenuity ingenuity of of the the user. user. One hope for for One hope a future future product product will be aa Paradox Paradox run—time run-time module that will make the the data data useable to to those those who-do who-do not not have have their .their own awn database database software. "software. Such Such "module" "module" users users should should be aware, aware, however, however, that that any packaged data queries will be limited to to those those of of the the developer's developer's preconceived preconceived notions. notions. Usage of this this data data can can make make geologic visits to to the the Drill Drill Core Core Library Library more more efficient. efficient. The The database database also also allows preliminary work allows preliminary work to to be be done done BEFORE BEFORE aa visit. visit. As database "development", this database database As in in any database "development", certain certain ideas ideas were were used used in in this formulation: formulation: 1) 1) TRY to convey to the the users users HOW HOW it was was put put together together and what what its its limitations limitations are; are; 2) TRY to be consistent consistent in in application application and and usage; usage; 3) 3) Create Create the data to support support anticipated anticipated queries; the queries; 4) 4) Convey uncertainty uncertainty as possible as best possible when it Lithology, alteration, and mineralization it exists; exists; 5) mineralization searches searches and and 5) Lithology, queries are are to make queries make use use of of text text string string matches; matches; 6) cognizant of the the 6) Be cognizant importance proper spelling as quantitative quantitative 7) Be Be as importance of of proper spelling and and spelling spelling variations; variations; and and 7) as possible possible within within the the context context of of the the data data structure. structure. THE THE MOST IMPORTANT IMPORTANT IDEA IDEA TO LET LET THE THE USER USER MAKE MAKE THE MOST MOST EFFICIENT EFFICIENT USE THE DATA. TO MAKE MAKE THE THE MOST MOST IS TO USE OF THE . TO OF THE DATA DATA WITHOUT WITHOUT BEING BEING LED LED ASTRAY! ASTRAY! certain concepts should be As in the the "utilization" "utilization" of of ANY ANY database, database, certain embraced; 1) Become familiar with the embraced; 1) the actual actual data, data, to to see see how how it it was was used, used, to to see possible, see how well it actually represents that see its its limitations, limitations, and if possible, which it queries that are supported supported by the the data; data; which it supposedly supposedly describes; describes; 2) Make queries 3) 3) In the case case of of descriptive descriptive data, be aware aware that that there there may may be be alternative alternative with similar meaning that should be included in making data queries; language with queries; 4) 4) Be cognizant cognizant of the specificity of your queries relative to the specificity of your data; data; and and 5) 5) Queries Queries done done on on the the "logging" "logging" database database should should also also be be done done on on the the "comments" "comments" database. database. samples exist from the study study area area of of An additional 2600 sets of drill samples Central Minnesota Minnesota and have These represent have not not been been logged. logged. represent samples samples from from approximately these samples 1600 drill drill holes. holes. Many of these samples are are drill drill core. core. Most of of approximately 1600 these samples these samples were were originally originally drilled drilled in in the the search search for for iron iron and and manganese manganese in in the the Cuyuna A lesser lesser number number Cuyuna Iron Iron Range Range area area during during the the first first half half of of this this century. century. of samples samples were drilled drilled for for base base metal, metal, uranium, uranium, precious metal, or diamond diamond drilled for or exploration. Additional samples samples were exploration. Additional were drilled for regional regional geologic geologic or engineering information. engineering information. with the data This work will 1995, with will be be published published in in July, July, 1995, data available available digitally in in a variety variety of of formats. formats. .. . The State State of of Minnesota Minnesota and and the the Department Department of Natural Natural Resources Resources neither endorse endorse products products or or services services listed listed nor nor accept accept any any liability liability arising arising from from the the use use products or of products or services services listed. listed. WATFILE WATFILE/Plus are are registered registered trademarks trademarks of of WATCOM WATCOM Systems Systems Inc. Inc. WATFILE and and WATFILE/Plus and WATCOM Publications Publications Ltd. Ltd. Software Carousel Software Carousel is is aa registered registered trademark trademark of of Softlogic Softlogic Solutions, Solutions,Inc. Inc. Paradox is Paradox is aa registered registered trademark trademark of of Borland Borland International, International, Inc. Inc. Index: Ruhanen, R. Dzuck, A., W., and and Dzuck, A., 1994, 1994, 1994 1994 Drill Drill Core Core Library Library Index: Ruhanen, R. Minnesota Minerals Division, Division,218 218 pages. pages. Minnesota Department Department of of Natural Natural Resources, Resources, Minerals 19 �CURRENT INVENTORY INVENTORY OF OFMICHIGAN'S MICHIGAN'S GEOLOGICAL GEOLOGICAL CORE AND SAMPLE REPOSITORY AT MARQUETTE MARQUETTE Milton Milton A. A. Gere, Gere, Jr., Jr., Regional RegionalGeologist Geologist William T. Swenor, William Swenor, Geological Geological Technician Technician Geological Survey Division, Division, Michigan DNR, Region I, Marquette, Marquette, Ml MI Survey Division Division (GSD) (GSD)of of the the Michigan Michigan Department Department of of Natural Resources Resources (DNR) (DNR) maintains maintains the The Geological Survey Geological This "Rock "Rock Library" Library" collection collectionof of core, core, cuttings cuttings Geological Core Core and and Sample Repository Repositoryat at Marquette, Marquette, Michigan. Michigan. This currently represents represents62 62of ofthe the83 83 counties countiesininthe the state. state. The materials are available for study to help and samples currently understand mineral resource resource potential potential of of the the state. state. understand the geology and mineral The collection continues to are submitted submitted to to grow grow in in an an effort to tobetter better represent representthe the geology geologyof ofthe thestate. state. Materials are the Repository Repository from a number number of sources: sources: 1) state metallic metallic and nonmetallic mineral leases; 2) various state sponsored projects; projects; 3) 3) company company donations; donations; 4) 4) other other state state and and federal federal government government agencies, agencies, such such as as the the U.S. U.S. Bureau Bureau of Mines. Since January January 1994, 1994, cuttings cuttings from from all all selected selected new new oil oil and and gas gas wells wells drilled drilled in Michigan have been sent to the the Repository. These Repository. These cuttings cuttings account for much of the material material currently currently being received. The most significant recent recent addition was was the early release release of of confidentiality of of the the deepest deepest all-cored all-cored Mineral Mineral Well in March, 1995. the confidentiality confidentiality on the core, well logs and file 1995. AJvIOCO AMOCO Production Company released the file data data for for their St. Amour #1-29 #1-29 and #1-29R #1-29R test test holes. holes. The #1-29R is a 7,238 foot hole hole that that was was drilled drilled in in late 1987 to learn more about the Midcontinent of Munising, Munising, near near Wetmore, Wetmore, in in Alger County in the MidcontinentRift. Rift. It was located southeast southeast of Upper Peninsula. Peninsula. The hole went through 110 110 feet of glacial glacial drift drift and and entered entered bedrock bedrock in in the thePaleozoic Paleozoicaged aged Autrain Autrain Formation Formation of Ordovician Ordovician time. time. The hole hole ended ended in inPrecambrian Precambrian aged aged Portage Portage Lake Lake Volcanics Volcanics of of Keweenawan time. time. This This core core should shouldbe be of of interest interestto to geologists geologistsfrom fromacademia, academia,the theoil oiland and gas gas industry, industry, and the Keweenawan mineral exploration exploration industiy. industry. On March 31, 1995, contained 766 complete complete drill drill hole cores totaling 246,679 feet; drill 1995, the Repository collection contained cuttings from 440 holes representing representing 491,735 feet of drilling, drilling, 424 424 holes holes represented represented by by abbreviated abbreviatedcore corefrom from 131,380 feet of of drilling, drilling, 2,229 feet of represented represented overburden overburden drilling, drilling, and many boxes of miscellaneous materials 13 1,380 feet This gives total of 1,685 (chip samples, samples, soils, outcrop outcrop samples, samples, assay assay pulps, pulps, etc.). etc.). This gives a collection collection total 1,685 drill drill holes holes representing representing872,023 872,023 feet (165 (165 miles) miles) of of drilling drilling plus plus numerous numerousboxes boxes of of miscellaneous miscellaneous materials. materials. The GSD's Metallic Mine Map and Data Collection is also also stored stored at at the the Repository. Repository. This collection also helps helps in Collection is the understanding being an aid to public understanding of the geology and mineral resource potential of the state, as well as being public safety safety and land use planning. ItItisisaarecord recordof ofpotential potentialmine minesubsidence subsidenceareas areas of of the the state statewhich whichshould shouldbe be avoided avoided when when construction is planned. planned. The Repository is open for for visitors visitors by byappointment appointmentto to study studythe thecontents. contents. Some sampling sampling and and loans loans of of material materialcan can be arranged for on a case-by-case case-by-casebasis. basis. Copies of of data derived derived from from the the use use of of the the collections are are to to be be submitted to be made part of the public record record for for future future use. use. For For information information or an an appointment, appointment, call Bill Swenor Swenor or Milt Gere at 906-228-6561. 906-228-6561. oil and and gas gas well well logs logs and and thousands thousands of of selected selected well well cuttings cuttings for oil oil and and gas gaswells wells The GSD also maintains all oil drilled prior to 1994 in in Lansing. Water Water well well records records for the entire state are kept in Lansing by the GSD, too. Call Call 517-334-6907 for for information. information. Copies of all Upper Peninsula, Region I, water well records and well cuttings from Office near Escanaba. Escanaba. Call Frank 610 selected water water wells wells are are maintained maintained by by the the GSD GSD at at the DNR's District 33 Office 906-786-2351 for more information. information. Chenier at 906-786-2351 20 �GEOLOGY OF THE THE NORTH NORTH SHORE SHORE STATE STATE PARKS PARKS GREEN, Geology GREEN, John C., C., Geology Department, Department, 211 211 Heller Heller Hall, Hall, University University of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, MN MN 55812 55812 The bedrock geology of of the the nine North The bedrock geology nine State State Parks Parks along along Minnesota's Minnesota's North Shore of Lake Lake Superior Superior has been mapped, with funding funding from the the MN Shore Department of of Natural Natural Resources. Resources. Recent mapping by by the the author author augments earlier earlier work work published published by by the Survey. augments the Minnesota Minnesota Geological Geological Survey. Notable features icial geology, features of of the thesurf surficial geology, such as as abandoned abandoned shorelines,deltas, deltas, and and stream stream channels, channels, are are also also mapped. mapped. For For some some shorelines, parks, B. A. A. M. M. Phillips Phillips (personal (personal parks, the the recent recent work work of of B. communication, communication, 1994 1994 and Phillips Phillips et et al., al., 1994) 1994) on on surf surficial icial features has has been been very very useful. useful. Along with with the the geologic geologic maps, maps, an an features account account of of the the geologic geologic history history of of the the region region was was prepared, prepared, as as well well as a description of the the relation relation of of geology geology to to the the scenery scenery in in each each as description of park. park. project is is aimed aimed at at publication publication of a book book for for the the The project general general public. public. The parks parks at at the the two two geographical geographical extremes, extremes, Jay Jay Cooke Cooke and and The Grand Portage, Grand Portage, are are underlain underlain principally principally by by Lower Lower Proterozoic Proterozoic ("2.0 (2.O billion years years old) old) metasedimentary metasedimentary rocks rocks (cut (cut by by 1.1 1.1 b.y. b.y. diabase diabase billion dikes) b.y. dikes) whereas whereas the remaining remaining seven seven are are underlain underlain by by 1.1 1.1 b.y. volcanic and and intrusive intrusive rocks rocks of of the the Midcontinent Midcontinent Rift Rift System. System. volcanic The The major scenic scenic features features of of the the North Shore Shore are are a a legacy legacy of of its geological geological history, history, coupled coupled with with the the effects effects of of differential differential its erosion erosion of of rock rock layers layers or or intrusions intrusions of of differing differing resistance. resistance. The The "Sawtooth the slow erosional etching "Sawtooth Range" Rangen is is the the result result of of the slow erosional etching out out of of thick, thick, resistant resistant lava lava flows flows and sills sills that that are are interlayered interlayered with more more easily easily eroded eroded sandstones sandstones and and thinner thinner lava lava flows, flows, all all tilted tilted gently toward toward the the lake. lake. The The highest highest eminences eminences near near the the lake, lake, the thick thick Palisade Palisade rhyolite rhyolite flow flow in in Tettegouche Tettegouche S.P., S.P., are are beside the made of of concentrations concentrations of of large large (10-100 (10-100 mm across) across) blocks of of resistant resistant anorthosite, anorthosite,carried carriedup up in in diabase diabasemagma magma from from the the base base of of the the earth's earth's crust, crust, now now enveloped enveloped in in the the solid solid diabase. diabase. Examples Examples are are in in Split Split Rock Rock Lighthouse Lighthouse State State Park Park and and Carlton Carlton Peak, Peak, Temperance Temperance River River S. S. P. P. Thick Thick sequences sequences of of volcanic volcanic rock rock underlie underlie many many of of the the parks. parks. For For instance, instance, Cascade River River S.P. S.P. includes includes a nearly nearly 2200—foot 2200-foot sequence of basalt basalt flows flows and and sandstone; sandstone; Judge Judge Magney Magney S.P. S.P. is is underlain by an underlain by an estimated estimated 4800 4800 feet feet of of interbedded interbedded basalt basalt and and rhyolite rhyolite flows. flows. Some of of the the large large rhyolite rhyolite flows, flows, such such as as in in Tettegouche Tettegouche and Judge Judge Magney, Magney, were were erupted erupted in in violent, violent, explosive explosive events much larger Helens (1980) (1980) or or Pinatubo Pinatubo larger than than the the Mt. Mt. St. Helens (1991) (1991) eruptions. eruptions. All of of these these volcanic rocks rocks were were erupted on on aa broad, broad, gradually gradually subsiding subsiding continental continental plateau. plateau. The river river gorges gorges and and many many other other interesting interesting North North Shore Shore features were produced during and since since the the melting melting of of the the last last Pleistocene Pleistocene ice ice sheet, sheet,when when the the west west end end of of the the Lake Lake Superior Superior basin basin was was occupied occupied by by aa deep, deep, ice—dammed ice-dammed lake lake whose whose level level fell fell in in stages stages between between 11,000 11,000 and and 8000 8000 years years ago. ago. Some Some of of these these features features include include abandoned abandoned shorelines, shorelines, deltas, deltas, and and river river meanders meanders (Jay (JayCooke Cooke S.P.) S.P.) and Waterfalls and channels channels (e.g. ( e . g . Judge Judge Magney). Magney). Waterfalls developed developed where where resistant resistant igneous igneous rocks rocks were were encountered encountered (Split (splitRock, Rock, Tettegouche, Tettegouche, Cascade, Cascade, Grand Grand Portage Portage S.P.), S.P.), or or columnar columnar jointing jointing in in basalt basalt flows flows localized localized erosion erosion (Gooseberry (GooseberryFal1s). Falls). 21 �ARE THE THE MAJOR MAJORTHRUST THRUSTFAULTS FAULTSOF OFTHE THEMID-CONTINENT MID-CONTINENTRIFT RIFTAND ANDTHE THE ARE KAPUSKASING ZONE PART OF THE SAME TECTONIC ZONE? KAPUSKASING ZONE PART OF THE SAME TECTONIC ZONE? HALLS,H.C., H.C., M.L. M.L. MANSON, MANSON,and andB. B.ZHANG ZHANG HALLS, Departmentof ofGeology, Geology,Erindale ErindaleCollege, College,University Universityof ofToronto, Toronto,Mississauga, Mississauga,Ontario OntarioL5L L5L1C6 1C6 Department Regional variations variations in in paleomagnetic paleomagnetic polarity polarity and and feldspar feldsparclouding cloudingin inthe the2.45 2.45 Ga GaMatachewan Matachewandyke dyke Regional swarm have been used to delineate major faults across which the southern Superior Province has been swarm have been used to delineate major faults across which the southern Superior Province has been krnorormore1. more1.These Theseobservations, observations,originally originallyused used to todefme defineNENEdifferentially uplifted uplifted by by about about10 10km differentially trending faults associated with the Kapuskasing zone ( a ) ' ' have been extended to a region lying trending faults associated with the Kapuskasing zone (KZ)1' have been extended to a region lying KZand andthe the1.1 1.1Ga GaLake LakeSuperior SuperiorBasin. Basin.Here Herechanges changesininregional regional between the the southern southernend endofofthe theKZ between magnetic polarity have defined two new faults and extended a third one. The new results suggest that magnetic polarity have defined two new faults and extended a third one. The new results suggest that KZisisprogressively progressivelydepressed depressedand anddisplaced displacedsinistrally sinistrallyby byaasystem systemof of N-S N-S trending trending towardsthe theSW, SW,the theKZ towards faults, the western one of which is the Agawa Canyon fault. Changes in feldspar clouding intensity faults, the western one of which is the Agawa Canyon fault. Changes in feldspar clouding intensity between dykes dykessuggest suggestthat thatthe theblocks blocksbetween betweenthe thefaults faultsalso alsohave havebeen beentilted tiltedto tothe theeast. east.The The new new data data between NW faulted faulted margin margin of of the the KZ KZ continues continues westwards westwards to to within within about about 60km 60kmof of the theLake Lake indicate that that the the NW indicate Superior eastern shoreline. Here, gravity, magnetic, and geological studies have identified several ENESuperior eastern shoreline. Here, gravity, magnetic, and geological studies have identified several ENEtrending reverse reverse faults faultswith withvertical verticaldisplacements displacementsup uptotoseveral severalkilometres2. kilometres2.Magnetic, Magnetic,reflection reflection trending seismic and bathymetric data from eastern Lake Superior suggest that two of these faults represent an seismic and bathymetric data from eastern Lake Superior suggest that two of these faults represent an easterlycontinuation continuationof of the the Isle Isle Royale Royale and and Keweenaw Keweenaw faults faults between between which which the the inversion inversionof of the theMidMideasterly Rift (MCR) has taken place to form a pop-up structure. Lithoprobe seismic data suggest that Continent Continent Rift (MCR) has taken place to form a pop-up structure. Lithoprobe seismic data suggest that NWmargin marginof ofthe theKZ KZdips dipstotothe theSE3, S E ~and and , hence hencethat thatthe theKZ KZalso alsorepresents representsaapop-up pop-upstructure. structure.The The the NW the foregoing evidence suggests that the reverse faults of the KZ and MCR are part of the same structure foregoing evidence suggests that the reverse faults of the KZ and MCR are part of the same structure (Fig.1) 1) and major ENE ENE to to NNE-trending NNE-trending compressional compressionaltectonic tectonic zone zonemore morethan than2000 2000 (Fig. and together together define defme aa major km long. Parts of this zone km long. Parts of this zone have experienced experienced periodic periodic have MAJOR CRUSTAL FAULTING IN THE MCR-KSZ TECTONIC ZONE reactivation since the reactivation since the Major reverse faults Cross-structure faults - -. (upthrown side iadicated) Archean,the the last last significant significant Archean, phase of of which which was was in in phase response to the the Grenvile Grenville response orogen at about 1050 Ma. orogen at about 1050 Ma. ,( - References: References: 1: Halls Halls et et al., al., 1994. 1994.Can. Can. J.J. 1: Earth Sci., 31, p. 1182; Earth Sci., 31, p. 1182; 2:2: Manson, M.L. M.L. and and Halls, Halls, Manson, Earth H.C., 1994. 1994. Can. Can. J.J. Earth H.C., Sci., 31, 3 1,p. p. 640; 640; 3: 3: Percival, Percival, Sci., J.A. and and West, West, G.F., G.F.,1994. 1994. J.A. Earth Sci., Sci., 31, 31, p.p. Can. J. Earth Can. 1256. 1256. 22 �THERMOCHRONOLOGY OF CENTRAL CENTRALMINNESOTA MINNESOTA REVISITED: REVISITED: THERMOCHRONOLOGY OF THE IMPLICATIONS FOR THE THE POSTCOLLISIONAL POSTCOLLISIONAL EVOLUTION OF THE OROGENIC BELT. PENOKEAN OROGENIC D.K., Department Departmentof of Geology, Geology, Kent KentState StateUniversity, University, Kent, Kent, OH OH44242 44242(2 (216HOLM, HOLM, D.K., 16672-4094; dholm@kentvm.kent.edu); and LUX, D.R., D.R., Department of Geological Sciences, University of of Maine, Orono, Orono, ME ME 04469. 04469. Rocks exposed in central Minnesota represent deep-seated metamorphic metamorphic and plutonic plutonic rocks of the internal zone of the Penokean their classic classic Penokean collisional orogen orogen (1870-1830 (1870-1830 Ma). Ma). In their study of the geochronology of Minnesota, Goldich and others (1961) obtained obtained Rb-Sr and K-Ar mica and whole whole rock ages ages from from central central Minnesota Minnesota in the the range range of of 1500-1800 1500-1800 Ma Ma (see (see mica and histogram below). below). The histogram The wide wide scatter scatter in in ages ageshas hashindered hindered their their interpretation, interpretation, although although the the relatively relatively older Rb-Sr dates have been attributed to to the onset of regional regional post-Penokean post-Penokean uplift uplift whereas younger K-Ar commonly considered considered to reflect an orogen-wide, orogen-wide, lowwhereas the younger K-Ar dates are commonly grade metamorphic resetting In this this study, study, we we have have dated dated mica mica separates separates from from Archean Archean resetting event. event. In and metamorphic and central Minnesota Minnesota using using the the and Early Proterozoic metamorphic and plutonic rocks from central modem ^Ar/^Ar incremental modern 40Ar/39Ar incrementalheating heatingtechnique. technique. Mica Mica separates separates collected collected across a >I30 >130 km northeast-southwest Minnesota yield age populations populations (see (see northeast-southwest transect transect in in central central Minnesota yield two distinct age histogram below). below). The histogram Theyounger younger population population (1680-1700 (1680-1700 Ma) Ma) represents represents data data obtained obtained solely solely McGrath gneiss dome. dome. The from samples collected within the McGrath The older older population population represents represents data data obtained from samples samples collected collected outside outside the the dome dome (both (bothto to the the north north and and southwest). southwest). They obtained from include the Archean/Early ArcheanIEarly Proterozoic Hiliman Hillman migmatite, the Early Proterozoic Proterozoic Little Little Falls Falls and Denham Denharn Formations (and unnamed equivalent rocks to the the north), north), and and Early Early Proterozoic Proterozoic plutons which are intrusive into the metamorphic rocks. These results provide important new information on the post-collisional thermal thermal history history ^Ar/^Ar ages and tectonic development of the Penokean orogen. orogen. InIncentral centralMinnesota Minnesotamica mica40Ar/39Ar obtained from late and post-tectonic plutons are obtained are concordant with mica ages ages obtained obtained from from the the Penokean-metamorphosed country rock. This suggests that post-Penokean Penokean-metamorphosed post-Penokean plutons (1812(1812—1770Ma?) Ma?)thermally thermallyequilibrated equilibratedwith with the the country country rock rock at temperatures -1770 temperatures above above 300°C. 300°C Emplacement of the post-tectonic magmatic suite was followed by an episode of regional uplift and cooling through —300°C justprior priorto to -1755 —1755Ma. Ma.We We propose propose that that the the dome and basin -300° just structural style, which appear from aeromagnetic data to be associated with the plutons, may have developed during uplift. uplift. We have developed during We further further speculate speculate that that dome dome formation formation may have been been triggered by the plutonic activity and that that the intrusions intrusions were were aa contributing contributing factor factor to to continued continued isostatic uplift. The isostatic uplift. Theremarkably remarkably uniform uniform ages ages obtained obtained from rocks outside of the McGrath McGrath gneiss dome suggest moderate moderate to to relatively relatively fast fast uplift uplift rates rates (see (see Holm Hoim and and others, others, 1993). 1993). We interpret the younger ages obtained from within the McGrath interpret McGrath gneiss dome as reflecting reflecting the the time of dome formation during yet another younger episode of uplift. Research in the previous decade decade has has shown shown that that Phanerozoic Phanerozoic orogenic orogenic belts belts developed developed during convergence are commonly structurally modified during their demise demise by by gravitational gravitational collapse. In like like manner, manner, we we propose propose that that crust crust thickened thickened at at 1870-1830 1870-1830 Ma Ma during during the the Penokean collisional orogeny underwent structural modification during its collapse from the InMinnesota, Minnesota, collapse collapseof of the theorogen orogen appears appearsto to mid to late 1700 1700 Ma (Hoim (Holm and others, 1993). 1993). In begun around around 1760 Ma shortly shortly following following an an episode episode of of magmatism. magmatism. We argue that the have begun magmas may have contributed of an overthickened which led to contributed to thermal weakening weakening of overthickened crust which collapse driven by gravitational instability. instability. Orogenic Orogenic collapse collapse was was apparently apparently episodic episodic with with significant significant pulses pulsesoccurring occurringatat—1755 -1755 Ma Maand andatat—1700 -1700 Ma. As noted by Hoim (1993), the the late late low-grade low-grade metamorphic metamorphic event widely Holm and and others others (1993), recognized in Wisconsin and Michigan apparently apparently affected affected these rocks to to aa much much lesser lesser extent extent than previously thought. 23 �U) 5g f1 E % 5 1 zo 3'61'4- 1850 .0 after 961)) after Goldich Goldich and others (1 (1 961 ~ 6U 1800 I 1750 I 1700 I.1 - U-. Z 01- 1850 1850 I- 1800 1800 I 1650 I 1600 I 1550 K-Ar mica - ~ data, r mica El K and whole rock and whole rock data, all pZ I8Rb-Sr Rb-Sr data, all biotite biotite 1500 after Hotm Holm and others others (1 (1 993) 993) after study and this this study LL I.'.'.' I•IsI•I 1750 1750 1700 1700 I data, mica mica Ar-Ar data, and one one hornblende hornblende and I 1650 1650 1600 1600 1550 1550 1500 1500 AGE AGE (Ma) (Ma) Comparison of age histograms of thermochronologic Comparison of thermochronologic data from from Archean Archean and Early Proterozoic rocks rocks of central Early Proterozoic central Minnesota Minnesota (both histograms histograms cover cover the the area area from from southwest southwest of of Little LittleFalls Fallsto tonear nearMoose Moose Lake). Lake). Goldich, Goldich, S.S., S.S., Nier, A.O., A.O., Baadsgaard, Baadsgaard, H., Hoffman, Hoffman, J.H., J.H., and and Krueger, Krueger, H.W., H.W., 1961, 1961, The The Precambrian geology and geochronoiogy of Minnesota: Minnesota Geological geochronology of Minnesota: Minnesota Geological Survey Survey Bulletin p. Bulletin 41, 41, 193 193p. Hoim, D.K., Hoist, Holm, Holst, T.B., and and Lux, D.R., 1993, 1993, Postcoiiisionai Postcollisional cooling of the Penokean orogen in east-cental Minnesota: Canadian Journal v. 30, 30, p. p. 913-917. 913-917. in Canadian Journalof of Earth EarthScience, Science,v. 24 �EXTENSION THE WISCONSIN WISCONSIN MAGMATIC MAGMATIC TERRANES TERRANES INTO THE EXTENSION OF THE INTO THE MINNESOTA PENOKEAN OROGEN MINNESOTA SEGMENT SEGMENT OF OF THE PENOKEAN Mark A. Jirsa, Val W. Chandler, and Terrence J. Boerboom Boerboom Geological Survey Survey 2642 University Avenue, St. Paul, MN 55114-1057 55114-1057 Minnesota Geological (6121-627-4780 FAX FAX (612)-627-4778 (6121-627-4778 phone (612)-627-4780 Previous work established that the Wisconsin Wisconsin and Minnesota segments of the Early Proterozoic Penokean generally equivalent, equivalent,and strata strata north north of the Niagara fault fault in Wisconsin have been correlated correlated with with orogen are generally supracmstal the Malmo Malmo structural structural discontinuity in Minnesota. The TheNiagara Niagarafault faultseparates separatessupracrustal those north of the rocks of the Marquette Marquette Range Supergroup Supergroup to the north, which have continental chemical affinities, from those of the Wisconsin Wisconsin Magmatic Terranes (WMT) to the south, which have volcanic arc compositions. Parts of the Marquette Range strata are analogous with the epicratonic rocks rocks of of the the Mille Mille Lacs Lacs Group north north of the little was was known known of of the the rocks rocks south south of the the Malmo Malmo discontinuity discontinuity in in Minnesota. Minnesota. However, However, little the discontinuity, Much of of that that bedrock bedrock was was interpreted interpreted as Penokean granitoid discontinuity, largely because outcrops are rare. Much intrusions, although geophysical signatures signatures imply imply that thatrock rocktypes typesand andstructures structuresare aremore morediverse. diverse. Recent Recent results of test drilling drilling and and geophysical geophysical studies provide new insight on the southern part of the the Penokean Penokean orogen. orogen. Our current work south of the Malmo structural discontinuity in Minnesota divides divides the the area into five geophysically distinct, arc-shaped terranes. The Thearcuate arcuatepattern patternisisinferred inferredto torepresent representnorthwest-verging northwest-verging tectonic imbrication imbrication during the Penokean orogeny; however, however, details details about individual individual terranes terranes and their Quaternary deposits and thick saprolite, by post- and synsynbounding structures are obscured by cover of Quaternary kinematic plutons plutons which which make make up up as much much as 50 percent of the subcrop, and and by by several generations of kinematic generations of faults. Nevertheless, Penokean orogen orogencan canbe bedeciphered. deciphered. The The McGrath McGrath terrane, terrane, on Nevertheless, some some elements of the Penokean the north, is aa dome dome of of Archean Archean McGrath McGrath Gneiss Gneiss mantled mantled by clastic clastic and and volcanic volcanic strata strata of of the the Denham Denham Formation. ItItisisseparated separatedfrom fromthe theHillman-Little Hillman-LittleFalls terrane to the south by a sharp geophysical break discontinuity. The itic here named the Mille Lacs discontinuity. TheHiliman-Little Hillman-Little Falls Falls terrane terraneisiscomposed composedofoffoliated foliatedtonal tonalitic to granodioritic rocks of the Hiliman Hillman Migmatite and the Sartel Sartel Gneiss, Gneiss, which which are metamorphosed metamorphosed to the amphibolite to granulite amphibolite to granulite facies, and the the Little Little Falls Falls Formation—a Formation-a pelitic schist schist containing containing biotite, biotite, staurolite, garnet, and and sillimanite. sillimanite. The rocks of the terrane are intruded staurolite, garnet, The metamorphic metamorphic rocks intruded by at least least two two generations generations of post-metamorphic post-metamorphic plutons including including granodiorite granodiorite dated at 1868-1869 1868-1869Ma, and several oval to irregularly shaped irregularly shaped granitic granitic bodies bodies in the range range of of 1770-1812 1770-1812 Ma, Ma, together together with with many many small small plug-like plug-like intrusions of unknown age which vary in composition from peridotitic to charnockitic. The The arcuate arcuatewestern western of Early Early Proterozoic edge of the Hiliman-Little Hillman-Little Falls terrane appears to represent the western termination of thrust sheets, and and isis marked marked by by sharp sharpgeophysical geophysicalcontrast contrast between between Proterozoic Proterozoic metaclastic metaclastic rocks rocks and and Archean granitoid gneiss. gneiss. The Milaca terrane isisthe themost mostlithologically lithologica1ly diverse, diverse, and from an exploration perspective, perhaps perhaps the the most most promising. promising. The perspective, The eastern eastern part of the the terrane terrane is is composed composed of aa variety variety of of plutons separating screens of older supracrustal rocks. These These older older rocks rocks include include exposures exposures of basalt and and anorthositic gabbro, and several drill holes intersected amygdaloidal and and porphyritic porphyritic basalt basalt and and dacitic to andesitic crystal-lapilli tuff. All Allare aremetamorphosed metamorphosedto to atatleast leastgreenschist greenschistfacies, facies, and and intense intense shearing shearing isis locally loca1ly evident in both plutonic and supracrustal supracrustal rocks. The Thewestern western part part of of the theterrane terraneisisalmost almostentirely entirely contains schistose schistose rocks rocks of The narrow Princeton terrane narrow Princeton terrane contains obscured by post-kinematic obscured post-kinematic plutons. plutons. The undetermined protolith and and granite. granite. The terrane terrane is is sharply sharply bounded bounded by by ENE-trending ENE-trending geophysical geophysical undetermined discontinuities that intersect linear anomalies trending trending eastward. The The geophysical geophysical pattern of of the the southernsouthernBecker terrane isismarked most Becker markedby bysemicircular semicircularanomalies anomaliesthat that suggest suggest the the presence of gneiss domes, and samples from several drill cores cores confirm confirm that that gneissic gneissic rocks rocks are are present, present, together together with with strongly strongly schistose schistose rocks of supracrustal supracrustal protolith. protolith. Correlation between between the the two segments Correlation segments of the the orogen orogen across across the the intervening intervening Middle Middle Proterozoic Proterozoic Midcontinent rift system, based on gross Midcontinent gross attributes attributes of of the the structural structural terranes, terranes, is is shown shown schematically schematically on on Figure 1. 1. These Theseattributes attributesare areinferred inferredfrom fromoutcrop outcropand anddrill-hole drill-holedata data in in Minnesota, Minnesota, published published geologic geologic geophysical maps maps of of both both states. states. We maps of Wisconsin, and derivative geophysical We depict depict the the bounding bounding structures structures between terranes on the Minnesota side of Figure 1 as relict thrusts. This Thisinference inference is is speculative speculativebecause because geophysical modeling indicates indicates that most contacts dip steeply, geophysical modeling steeply, and that that most most sources sources within within individual individual terranes extend to depths of 2-5 km. However, However, drill drill cores cores of some some supracrustal and gneissic sequences show much shallower dips, locally locally in in the the 305O0 30-50' range, range, and and we we infer infer that that many many of of the the anomalies anomaliesare are bounded bounded by by steep faults and plutons. The Themost mostcompelling compellingcorrelation correlation is is based based on on strong strong lithologic (and geophysical) contrasts across the Niagara fault and and its its Minnesota Minnesota analog—the analog-the Mille Mi11e Lacs and Malmo discontinuities. These faults separate strata of of continental continental affinity to the the north north that that typically typically lack lack plutons, plutons, from from volcanic volcanic 25 �rocks to to the the south south that that are arecut cutby byabundant abundant postpost- to to syn-tectonic syn-tectonic granitoid granitoid intrusions. Previous Previous work work by by rocks Southwick and and Morey Morey (1991) (1991)inferred inferredaasouth-dipping south-dippingsubduction subductionzone zonealong alongwhich whichPenokean Penokeanrocks rocks were were Southwick thrust northwestward northwestward over over continental continental crust crust of of the the Superior Superior craton. IfIfthis thisisiscorrect, correct,the theboundary boundarybetween between thrust pluton-bearing and and pluton-absent pluton-absentrocks—the rocks-the Niagara Niagara and and Mule MilleLacs-Malmo Lacs-Malmostructures—may structures-may represent representthe the pluton-bearing southernmost southernmostextent extentof ofcontinental continentalcrust crustbeneath beneathPenokean Penokeanstrata. strata. voIcaniclastic rocks in the the Milaca Milaca terrane terrane invites correlation correlation with the The presence presence of of volcanic volcanic and and volcaniclastic The Pembine-Wausau terrane terrane of of the the WMT. WMT. The ThePrinceton Princetonterrane terraneisisinferred inferredtotobe bean anearly, early,complex complexshear shearzone zone Pembine-Wausau separating the the supracrustal supracrustal rocks rocks of of the the Milaca Milaca terrane terrane from from gneisses gneisses of the Becker terrane. The ThePrinceton, Princeton, separating therefore, may maybe becorrelative correlativewith withthe theEau EauPlaine Plaineshear shearzone zonewhich whichseparates separatesthe thePembine-Wausau Pembine-Wausauterrane terrane therefore, from Proterozoic Proterozoic and and Archean Archean gneisses gneisses of of the the Marshfield terrane to the south. Correlation Correlation of of the the HillmanHillmanfrom Little Falls Falls terrane terrane isismore moreenigmatic, enigmatic, because because ititisisintruded intrudedby bysynsyn-and andpost-tectonic post-tectonic plutons plutons like likethe the Little WMT and and Milaca Milaca terrane, terrane, but butititalso alsocontains containsmigmatitic migmatiticgneiss gneiss(of (ofunknown unknownage) age)and andpelitic peliticschist schistlike like WMT the Falls isis aa hybrid hybrid the terranes terranes north north of of the theNiagara Niagara fault. fault. We Wetentatively tentativelysuggest suggestthat thatthe theHiliman-Little Hillman-Little Falls containing lithic Iithicand andstructural structuralelements elementsof ofthe theterranes terranesboth bothnorth northand andsouth southofofthe theNiagara Niagarafault. fault. ItIt may may containing not not have havean ananalog analogin inWisconsin, Wisconsin,or orititmay maybe berepresented representedby by aa poorly poorly exposed exposed tectonic tectonic sliver. sliver. Correlating segments segments of of the theorogen orogenacross acrossthe theMidcontinent Midcontinentrift rift isisnot notonly onlyofofscientific scientificinterest, interest,but but Correlating WMThost hostdeposits depositsof ofbase-metal base-metalsulfides sulfidesand andassociated associatedprecious precious also of of economic economic interest interestbecause becausethe theWMT also metals, metals, including including those those of of the the Ladysmith Ladysmith mine. mine. InInan anearlier earlierpaper paper(Minnesota (MinnesotaProsnector, Prospector,January January1995), 1995), we we asked askedthe thequestion question"can "canthe theEarly EarlyProterozoic ProterozoicWisconsin WisconsinMagmatic MagmaticTerranes Terranesbe be traced traced into into Minnesota?" Minnesota?" The Thesimple simpleanswer answerisisaaguarded guarded"yes." "yes." REFERENCE REiFXWNCECITED CITED Southwick, Southwick, D.L., D.L., and and Morey, Morey, G.B., G.B.,1991, 1991,Tectonic Tectonicimbrication imbrication and and foredeep foredeep development development in in the thePenokean Penokean orogen, interpretation based based on on regional regional geophysics geophysics and and the results of orogen, east-central east-central Minnesota—An Minnesota-An interpretation of testtestdrilling, Sims, P.K,, P.K., and and Carter, Carter,L.M.H,, L.M.H.,eds., eds.,1991, 1991,Contributions Contributions to to Precambrian Precambrian geology geology of of Lake Lake drilling, inin Sims, Superior Superiorregion: region:U.S. US.Geological GeologicalSurvey SurveyBulletin Bulletin1904-C, 1904-C,17 17p.p. ACKNOWLEDGMENTS ACKNOWLEDGMENTS Test Test drilling, drilling,outcrop outcropmapping, mapping, and and geophysical geophysical studies studies were were supported supported in in large large part part by bythe theMinnesota MinnesotaState State Legislature Legislatureon onthe theadvice adviceofofthe theMinnesota MinnesotaMinerals MineralsCoordinating CoordinatingCommittee. Committee. EAST-CENTRAL MINNESOTA AlTRIBUTES NORTH-CENTRAL WISCONSIN t Flambeau Flowage fault Figure Figure1.1. Schematic Schematiccomparison comparisonand andproposed proposedcorrelation correlationof of major majorstructural structuralterranes terranesofofthe thesouthern southern Penokean Wisconsin. Penokeanorogen orogeninineast-central east-centralMinnesota Minnesotawith withthose thoseofofnorth-central north-central Wisconsin. 26 �TITANIUN TITANITJM ORE ORE POTENTIAL P O T E N T I A L OF O F GABBROS: GABBROS: EXANPLES EXAMPLES FROM FROM WESTERN WESTERN FINLAND FINL,AND KARKKAINEN, Nub, Geological ~ R K ~ I N E N Niilo, , GeologicalSurvey Surveyof of Finland, Finland! 02150 02150 J., Department Department of of Espool Finland; Finland; BORNHORST, BORNHORST, Theodore, Theodorel J., Espoo, Geological Geological Engrg. Engrg. and and Science, Science, Michigan Michigan Technological Technological University, university, Houghton, Houghton, MI MI 49931 49931 Early Proterozoic Proterozoic Svecofennian Svecofennian gabbros gabbros are are being being explored explored for for Early ilmenite by the the Geological Geological Survey Survey of of Finland. Finland. Two Two different different ilmenite Pohjanmaa, western western Finland. Finland. types of of Ti—enriched Ti-enriched gabbros gabbros occur occur at at Pohjanmaa, types Subeconomic, low low grade grade titanium titanium deposits, deposits, with with ilmenite ilmenite and and Subeconomic, apatite as as major major ore ore minerals and minor magnetite, are hosted by apatite smallsmall- to to medium—size medium-size layered layered gabbros gabbros located located between between late late orogenic orogenic and and synorogenic synorogenic granite granite complexes complexes (Kauhajoki) (Kauhajoki). Potentially economic economic titanium titanium ore, ore, with with ilmenite ilmenite as as the the major major ore ore Potentially mineral and and vanadiniferous vanadiniferous magnetite magnetite as as aa minor minor ore ore mineral, mineral, is is mineral hosted km north north of of hosted by by aa small small layered layered mafic mafic intrusion intrusion located located 200 200 km Kauhajoki Mid-Finland Kauhajoki in in the the western western margin of the synorogenic Mid-Finland Granite Granite Complex Complex (Kälvià). (Kalvia). Kauhajoki Kauhajoki gabbros gabbros occur occur as as lenticular lenticular bodies bodies along along the the eastern eastern contact contact of of the the late late orogenic orogenic Lauhanvuori Lauhanvuori microcline microcline granite. granite. These These gabbros gabbros were were previously previously studied studied as as aa possible possible source source for for phosphorous. phosphorous. The The large large Perämaa Peramaa deposit, deposit, averaging averaging 5.8 apatite, belongs belongs to to the the same same gabbro gabbro province. province. The The best best 5.8 %% apatite, Ti-enriched Ti-enriched gabbro gabbro of of this this type type is is at at Kauhajàrvi. Kauhajarvi. Here Here apatite apatite and and oxides oxides occur occur together. together. Most of the the Ti at Kauhajàrvi ~auhajarviis is sited sited in in ilmenite. ilmenite. Disseminated ~isseminatedoxides oxides are are more more abundant abundant in in mela— melagabbro-norites at at the the bottom bottom of of the the steeply steeply dipping dipping intrusion. intrusion. gabbro-norites Coarse-grained coarse-grained plagioclase-rich plagioclase-rich gabbro gabbro with with thin thin anorthositic anorthositic layers layers composes composes the the roof roof of of the the intrusion. intrusion. Kauhajàrvi Kauhajarvi contains contains grades grades of of 44 to to 77 % apatite apatite and and 77 to to 12 12 %% ilmenite, ilmenite, but but is is subeconomic, partially partially because because of of thick thick overburden. overburden. The The total total subeconomic, amount 18-22 wt.% wt.% and amount of of apatite apatite and and oxides oxides is is normally between 18-22 the the ilmenite/magnetite ilmenitelmagnetite ratio ratio is is about about 2. 2. There There are are also also magnetite-rich layers layers with with slightly slightly increased increased ore ore grade, gradelhowever, however, magnetite-rich these these layers layers have have much much lower lower ilmenite/magnetite ilmenitelmagnetite ratios ratios (0.5-1.2). (0.5-1.2). Good quality concentrations concentrations of of ilmenite ilmenite and and magnetite, magnetite, as as well well as as Good quality the the beneficiation beneficiation of of phosphorous, phosphorous, are are indicated indicated by by metallurgical metallurgical tests. tests. The Koivusaarenneva Koivusaarenneva ilmenite ilmenite deposit deposit at at Kälvià Kalvia is is hosted hosted The by km long long and and 500 500 m m thick, thick, almost almost vertical vertical by an an unexposured unexposured 33 -- 55 km sill—like sill-like intrusion intrusion surrounded surrounded by by tonalites tonalites and and granodiorites, granodiorites, at at the the contact contact of of the the mid mid Finland Finland Granite Granite Complex Complex and and the the Sykãrainen Sykarainen Volcanic Volcanic Belt. Belt. The The intrusion intrusion is is clearly clearly identified identified from from aeroaeromagnetic magnetic maps. maps. Detailed Detailed magnetic magnetic and and gravimetric gravimetric surveys surveys have have been been used used for for locating locating drill drill holes. holes. The The gabbro gabbro body body is is cut cut by by fault zones zones and and is is divided divided into into two two main main units units along along strike strike fault with with significant significant displacement. displacement. The The intrusion intrusion consists consists of of 55 lithostratigraphic zones zones with with gradual gradual contacts. contacts. From From bottom bottom to to lithostratigraphic 27 �top these these zones zones are are 1) 1) heterogenous heterogenous lower lower barren barren uralite uralite gabbro gabbro top zone; 2) 2) main main ore ore zone zone consisting consisting of of disseminated disseminated ore ore in in gabbro, gabbro, zone; massive ore ore layers, layers, and and metapyroxenite metapyroxenite layers; layers; 3) 3) zone zone of of barren barren massive uralite gabbro; gabbro; 4) 4) layered layered zone zone consisting consisting mainly mainly of of uralite ilmenomagnetite disseminated ore in gabbro and barren uralite ilmenomagnetite disseminated ore in gabbro and barren uralite gabbro layers; and 5) mainly' coarse-grained uralite gabbro. The gabbro layers; and 5) mainly coarse-grained uralite gabbro. The most mafic rock in the intrusion is almost totally uralized most mafic rock in the intrusion is almost totally uralized metapyroxenite,which which exists exists as as thin thin layers layers in in several several zones, zones, but but metapyroxenite, mostly in the main ore zone. Coarse-grained plagioclase cumulates mostly in the main ore zone. Coarse-grained plagioclase cumulates of the the uppermost uppermost zone zone contain contain minor minor enrichment enrichment of of apatite. apatite. of Prominent enrichment of phosphorous, 2 to 5 % apatite, exists in in Prominent enrichment of phosphorous, 2 to 5 % apatite, exists some zones of ilmenite-barren medium-grained uralite gabbro. some zones of ilmenite—barren medium-grained uralite gabbro. lun along along The ore ore zone zone has has been been followed followed for for over over 22 km The strike. The ore is both massive and disseminatedThe massive strike. The ore is both massive and disseminated. The massive ore is up to 15 m thick and contains 23 to 52 wt. % ilmenite, ore is up to 15 m thick and contains 23 to 52 wt. % ilmenite, 44 magnetite and and 11 to to 22 wt. wt. %% iron iron sulphides. sulphides. It It is is to 18 18 wt. wt. %% magnetite to surrounded by a few tens of meters of ilmenite-rich disseminated surrounded by a few tens of meters of ilmenite—rich disseminated oxides, averaging averaging over over 10 10 %% ilmenite ilmenite with with minor minor vanadiniferous vanadiniferous oxides, magnetite. Massive ore is hosted by almost totally uralitized magnetite. Massive ore is hosted by almost totally uralitized metapyroxenite, whereas disseminated ore is mostly in uralite metapyroxenite, whereas disseminated ore is mostly in uralite gabbro . gabbro. Common features features of of Ti-enriched Ti-enriched gabbros gabbros of of western western Common Finland are small size, distinct layering, compositional range Finland are small size, distinct layering, compositional range from minor pyroxenite, through dominant gabbro-norite, to coarsefrom minor pyroxenite, through dominant gabbro—norite, to coarse— grained leuco-gabbro leuco-gabbrowith with only only thin thin anorthositic anorthositic layers. layers. grained ~conomically, the most most significant significant feature feature is is that that Ti Ti is is sited sited in in Economically, the ilmenite and and there there is is only only aa minor minor amount amount of of ilmenomagnetite. ilmenomagnetite. ilmenite ~eochemically, the Ti-gabbros Ti-gabbros are are characterized characterized by by enrichment enrichment of of Geochemically, the phosphorous. phosphorous. 28 �mi-POSITIONAL SYSTEMS ASSOCIATED AS SOCIATEII WITH WIT11 THE Till': 3.0 3.0 GA. GA.FINLAYSON FINLAY SONAND ANDLIJMBY LUMBY DEPOSITIONAL LAKE GREENSTONE BELTS, BELTS,NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO LAKE KING, David FRALICK Phillip, University KING, Davidand and FRALICK Phillip,Dept. Dept.ofof Geology, Geology, Lakehead Lakehead University Bay, Ontario OntarioP7B P7B 5E1, 5E1, Canada Canada Thunder Bay, The Late Lale Archean Archeiln Superior Province of the Canadian Canadian Shield Shield is known known to The Superior Province of the of alternating alternatinglinear linearbelts beltsofofgranite—greenstone granite-greenstone and andmetasedimentary iiietasedinientary consist of An accretionary accretionary model model has been been suggested, suggested, involving involving island island arcs a r c s and and terrains. An metasedimentar y complexes complexes colliding paired metasedimentary colliding with with older older cratonic cratonic masses masses (Langford and Morrin, Morrin, 1976). 1976). Support this model model has has come come from (Langford Support for this from recent of the t h e Quetico Quetico metasedimentary metasedimentary belt portions of of the the neighboring neighboring studies of belt and and portions Wabigoon Subprovince t o its i t snorth north (Williams,1986, 1986,1987; 1987;Devaney Devaneyand andWilliams, Williams, Wabigoon Subprovince to (Williams, 1989; Barret Fralick, 1989; 1989; Fralick Fralick et e t al., al., 1992). 1992). Quetico Quetico trench sediments sediments 1989; Barret and Fralick, a r e constrained constrained ininage a g ebetween betweenapproximately approximately 2710 2710 to to2690 2690 Ma Ma (Davis (Davis eett al., al., are 1990). 1990). The interior interior of ofthe t h eWabigoon Wabigoon Subprovince is is not notwell welldocumented. documented. Metasediments of tthe Metasediments of h e Finlayson Finlayson and and Lumby Lake within Lumby Lake greenstone greenstone belts, within t h e Wabigoon Wabigoon Subprovince, r e the the the Subprovince, aare focus of of this this study s t u d y (Fig. (Fig. 1). 1).Zircon Zircon ages from from the the volcanics volcanics and and + intr usiv es cutting cutting volcanics intrusives volcanics constrain constrain the the eruptive eruptiveepisode episodetoto2999 2999 Ma Ma and and greater than than2936 2936 Ma Ma for for the theLumby Lumby Lake Finlayson Belts Belts respectively respectively Lake and Finlayson (Stone et e t a!., al., 1992), 1992), and and overlying overlying sediments may be be related related to this sediments may this older volcanic volcanic episode episode (Fenwick, (Fen wick, 1976). The surrounding 1976). The surroundingMafic Mafic Tonalite Tonalite and Old Old Tonalite Tonalite of of the t h eMarmion Marmion Lake Lake Batholith and Tonalite of the Batholith and Tonali te Gneiss Gneiss of the Lumby Lumby Lake greenstone greenstone belts. belts. Lithofacies Lithofacies Dashwa Uashwa Gneiss complex complex are a r e3001, 3001,2953 2953 symbols symbols are the same same as as Figure Figure2. 2. and 2928 respectively (Davis, 2928 Ma, Ma, respectively (Davis, in in Stone et e t al., al., 1992) 1992) Sedimentary facies within Sedimentary facies within the the Finlayson Finlayson belt beltconsist consistofofmetaconglomerate, metaconglomerate, course—pebbly sandstone,medium-grained medium-grainedsandstone, sandstone,and andfine fine sand sand and and silt course-pebbly sandstone, silt turbidite deposits. deposits. Lesser Lesser chemical chemical sediments sediments include include cherty iron iron formation formation and and sulfide facies facies iron iron formation. formation. The lake clastic clastic sediments The Lumby Lumby lake sediments consist of of matrix matrix supported supported conglomerate, fine sand sand and and silt turbidites, conglomerate, fine turbidites, and andgraphitic graphiticslates. slates.Chemical Chemical sediments, including, including, ferrugineous ferrugineouschert, chert,chert—magnetite chert-magnelite IF, IF,chert—siderite chert-siderite IF, IF, sulfide sulfide facies facies IF, IF, and andmarble, marble,are a r edominant dominantininthe t h eLumby LumbyLake Lakemetasediments. metasediments. Well developedlateral lateraland and vertical vertical ttrends Well developed r e n d s are a r e recognized recognized within wilhin the the Finlayson Lake metasediments. metasediments.The TheLittle LittleFalls Fallslake lakearea, area, in in the extreme Finlayson Lake extreme southwest of of the t h ebelt, belt,isi dominated s dominatedbybycourse—pebbly course-pebbly sandstone, sandstone,medium medium sandstone sandstone and conglomeratic beds. Traveling north, along conglomeratic beds. Traveling north, along strike, strike, finer finer grained grainedsediments sediments become increasingly mimore prevalent, withonly onlyfine fine sand-sill sand—siltturbidity turbidity ccurrent become increasingly more prevalen t, with urrent deposits Verticalttrends deposits found found in the the north—east. north-east. Vertical r e n d s aare r e recognized recognized by by an an i t + + + increase; in average average grain grain size size as a s one one moves moves p upsection sectiontoward towardthe thedominant dominant increase synclinal axes running through the main running north—south north-south through main sedimentary sedimentary belt belt of of 29 �Finlayson Lake. Finlayson Lake. Trends within the t h e Lumby Lumby Lake Lake belt belt are a r esimilar. similar. Metasediments Metasedimenls grade grade Trends within along s t r i k e from dominantly fine sand-silt turbidites with minor chemical along strike from dominantly fine sand—silt turbidites with minor chemical sedi~ncm ts, in t11c west, west, to .topredominantly predomiriantly chemical chemical sediments h e east. east. A A sediments, in the sediments in in tthe clmnge from from chemical chemical dominated h e lower lower section, progressive change dominatedsediments sedimentsinin tthe section, to clastic dominance do~ninanceinin upper vertical trend trend recognized. recognized. elastic upper sections, sections, isis the vertical Similarities Similarities in lgneou% Roc<, sedimentary facies facies the sedimentary P1 MoStly F present, and in present, in lateral lateral voIccnw, and vertical vertical trends, trends, and Mostly Mot,c L_J volcanic, suggest that t h a t the the suggest roOcl;tC Finlayson and arid Lumby Lumby Finlayson Lake metasediments metasediments Lake Me to sed rn en a ry indicates sedimentation within a sedimentation within I3cando r gso m~e m~ t e, A '~' owon ,,,,inor ~ ~ ccr!,,.::. stngle single basin. The basin. The Sondsoon Corbonts ;~;;r;oter~~ corbon,:te% c,: tsnoltornwcteJ I r o n Formclion of felsic felsic predominance of Sandstone " " (deeper water) volcanic clasts within wit hi11 c:onglomeratic facies facies conglomeratic may represent I i1gure Figure 2 Paleogeographic sketch of of the Finlayson and subaerial volcar~isni to Lumby prograde north, from a Lumby Lake area. Clastic sediments prograde ttte soutli. the south. ~t is is vokanic source region, distal chemical sediments. volcanic over distal chemical sediments. suggested elastic suggested that elastic sediments were were derived from from a higher higher derived relief in the relief source source in the south, south, and and prograded prograded through through aashallow shallow water water environment in Little Falls Falls and and southern southernFinlayson Finlayson Lake Lake area. area. Deeper Deeper environment in the the Little water in the more water turbidity current c u r r e n t deposits deposits and and chemical chemical sediments sediments aare r e found found &the more distal northern Finlayson and Lumby Lake area. Figure 2 represents distal Finlayson and Lumby Lake area. Figure 2 r e p r e s e n t s a possible paleogeographic reconstruction. possible paleogeographic a fl F O ~ ~ C ~ ~ C - * saamsni to REFERENCES Barret, T.J. and Fralick, P.W., 1989. nehea. iedi.e.tatis. ii the learture—Gerattt,i Terral., hum: claitic aid chealcal &itp.aitiii ii a carrie iibaariae eralimie aargia. Zedi.e.t.l.pi, vii. U, p. 211—114. Davis, D.W., Pezzutto, F., and Ojakangas, R.W., 1990. The ale aid pr.,e.aece .1 .etiieLi.eutary cecil ii the Qeelico E.ipr.viuce, Oitarj., fri. ziule cite.. a.aiyaia: iaplieatieia fir Archeai ae&iie.tati,i aid teeticice ii the Eiperi.r Pr.eiice; Earth &i& Ucietary Eciecce Letteri, vii. 11, p. 111—225 b...dary aa aedi.eitiispieai if ac 1989. E,.I.tii. Devaney, J.R. J.R. and and Wiliams, ll.R., 1989. Wiliams, H.R., t v a l ~ t i a nat I . AAreheal ~ C ~ Smbpravimte C Xihpr.,iie ~ I bommiary: ~ c ~ i m c m t 0 1 a r i c aaid 4I 1 4 ii uertheri Jiurial if vet. IIt,G l etedy af if part aitractiral t r u c t ~ r a l almir par1 ifafthe Q ~ e t i c abh..dary o ~ i m r y im martberm hitari.. Omlaria. Caiadiau Canaiiam Jaarmal af Earth tarti Eciecee., S e i e m e c # ~ val. lbcVahig,.. Wabiraom— Queue. - 1111—lIlt. p, p. 1811-1116. Ii.ei, Ge.aeieece Dietriet af if laimy Fiii&piiu Lake the FimIayaam ate area, area, Dialriel h i m y li,er;Oitari. IivcriOmIaria Divicie. Biviaian .1 0 1 himcn1 Gcaaeicmcc 1976.Ge.l.gy ~ c a 1 a ~if aty the Fenwick, F.F. F.F. 1976. lcpart S l Up. 16p. Depict1 4ill, laui. dep.uila aid aispe Trcmck am& aIapc basin icpamita iiima.amArehea. Arekcam 1992. Truth Fralick, P.W., P-W-, Wu, WU, J., and a n d Williams, Williams, H., H., 1992. belt,Saptriar tuperi.r troiimce, trevilee, Ca.adia, Shield.C taia&ia. it Earth 9 , 2SSl—155. p . 2551-ISST. maetaaediaeitary e h a c i i m c ~ t a r ybeltl Camaiiam Siieli, a m t i a m J Jeirial a w m a 1 a1 tartb *cie.cea, Scicmceal vii. val. ii.1 p. hurt. bg if the Eiperi.r Pr,,iaee J.A., 1976. Langford, F-F. a n d Mori.11, J.A., 1976.The t i c devel.p.eit i e v e i a p m c m ~ at the Smpcrier Iravimce etif iirth.eater. martiwcalcrm omlaria b, .crgi.g Z. tei. vii. 111 mcrtimt lucid ialamtarea. area.1..Am. J. Sci. val. p. 2761112—1114 p. 1121-1834 Preeaahria. Ge.1. Stone, D., Kamine~ii,D.G. a n d Jackson, M.G., 1992. trecanbriam G C ~ I * WifafthetheAtik.ka. AlitatamArea. Area, lirt,eateru Ccii.Smrv. lit,. Ca.. I a r l w e ~ l c r mOetari.. Onlaria. Gcal. Can. liii. 1111. 421, 4 0 S l hIp 186p Ii the belt,muertheru laurie; Ii ~ t r m e l a r a l atadlee atttiea in the leatd.ue—Ceyildtei 1 ~ a r t m a r e - h a i i t a m beltl a r t k m m tataria; im taaaatj $amnary .1ofFIeld Fie14hoth, Workl Williams, ll.R., 1986. 1986.ttr.tturat W i i h I n ~ ,II.l<., 11*1, GeileglealS nlirvey, taper1 3Ill, r v c r ~~liaeellauciau i a c c l l a m e a a ataper 8 1 p. p. 1*$14I. 188-146. 191tl Octane Oataria Gcalaricai thi Q.etici aid i~ ii lbe Williams, ii tie ll.R., 1987. 1987.itnueterat Slraclurai autediec l d i e a in lkele&nda.re—Giraldt.e Ieardmare-Geralilan belt bell am4 Q ~ e l i c aid aa m 4Va.a Wawa aubpr.vieeea ambpravimtc#; ia w i u a m ~ ,II-R., 121, p.11—Il. li..any if Field S ~ r v t y ,IlaeelIaie... hiaccllamcau# taper taper l3Il p.18-92. sum mar^ ar riel& link, Workl ilti, 198IlOutari. Omlaria Ge.i.gical Gcalarical 1.rvey, Fralick, F.F. and Morin, Stone, D., Kamineni, D.G. and Jackson, M.G., 1992. 30 �NEOARCHEAN COASTAL SEDIMENTATION IN IN THE THE SHEBANDOWAN SHEBANDOWAN GROUP, GROUP, NORTHWESTERN ONTARIO NORTHWESTERN ONTARIO KOEBERNICK, Christa Christa F. and FRALICK, W., Dept. Geology, Lakehead FRALICK, Philip W., Lakehead 5E1, Canada. Canada. Bay, ON, ON, P7B P7B5E1, University, Thunder Bay, Many present day tidal environments, such as the Bay of Fundy and the Dutch Dutch Wadden Sea, Sea, have have been been the the objects objects of of broad broad and comprehensive comprehensive studies. studies. Such environments in the Phanerozoic have also been extensively studied, studied, and and as a result, Although there exists a wealth of information on tidally influenced environments. environments. Although represented in the rock record, record, very little little work has has been been done done on on tidal tidal settings settings in inthe the Precambrian. The The majority majority of of studies studies have have concentrated concentrated on on such such environments environments in in South Africa, Africa, with little emphasis on Precambrian rocks elsewhere in the world. Canadian Shield Shield of northwestern northwesternOntario, Ontario, there there exists existsan anexcellent excellentexample example In the Canadian of a Precambrian tidal environment. The section section containing containing this this example example is is located located environment. The approximately 50 50 kilometres west west of of Thunder Thunder Bay, Bay, near near Finmark. Finmark. The rocks, approximately rocks, which which are are Neoarchean in age, age, belong to the Shebandowan Group and occur within exposures exposures of the Shebandowan Shebandowan - Wawa greenstone A lack lack of of bioturbation bioturbationhas has allowed allowed for the the greenstone belt. belt. A superb preservation presetvation of sedimentary structures structures within these units. A variety of primary sedimentary structures such as herringbone cross-bedding, ladderback ripples and flaser to lenticular bedding are present. These These structures structuresare are environments. Many of the sedimentary considered characteristic of tidally-influenced environments. structures closely resemble those that are are present present in in Phanerozoic Phanerozoic and and present-day present-day tidal flat environments. Moving Movingoffshore offshorefrom fromthe thetidal tidalflat flat environment environment into intothe the dominates. Trough subtidal, coarse grained material dominates. Trough cross-stratification cross-stratificationand and parallel parallel lamination are present. present. There There isisno noevidence evidencein inthe the sequence sequence that that there there were were lengthy lengthy periods periods of emergence emergence above abovesea sealevel. level. trends are are present present throughout throughout the the section. section. The majority of Fining and coarsening trends layers fine fine upwards upwards into silts and muds from aa coarse individual layers coarse grained grained sandy sandy base. base. On a larger scale, scale, the the section section exhibits exhibits an an overall overall coarsening coarsening trend trend when when moving moving tidal towards the subtidal and and nearshore nearshore environment, or towards the centre of aa tidal channel. Occasionally, fining trend trendisissuperimposed superimposedupon uponthis thisoverall overallcoarsening coarsening Occasionally, aafining into the tidal flat trend, such as when moving out of aa tidal channel and back into environment. environment. There are also unique features features present present in in the the rocks rocks of of this this area. area. For For example, example, 10 I0 to 20 20 centimetre centimetre thick thick parallel parallel laminated laminated coarse coarse grained grained sand sand layers, layers, which which grade grade into into thin fine-grained tops tops are present. present. The The sand sand layers, layers, which are light in colour, stand stand in in marked contrast to the darker coloured rocks of the section. section. These These layers layers are to represent wave wave deposition deposition of of sand on a beach during believed to during a storm, and and appear appear with regularity throughout the section. The presence of storm layers in in the tidal flat environment differ storms usually usually move move sediment sediment differ from from the prevailing thought that storms offshore. The Thestorm stormlayers layersmay maybe beindicative indicative of of storms storms which which occurred occurred during during periods periods of high high spring spring tides. tides. - 31 �Tidal channels present throughout the section differ from those that are commonly described described in in the the literature. literature. Typically, tidal tidal channels are meandering, but in this case, the tidal channels show very few features that are diagnostic of either meandering or braided channels. Herring-bone Herring-bonecross-stratification cross-stratification and and parallel parallel lamination are present in the channels, with sediments sediments fining towards towards the the centre centre of of the thechannel. channel. (1988) outlined characteristics of supratidal supratidal deposits, such such as as the the Terwindt (1988) of plant remains, remains, gypsum gypsum or or salt salt pans. pans. None presence of Noneof of these these features features are present, present, in fact the supratidal environment environment appears appearsto to be be completely completelyabsent. absent. The absence of supratidal deposits is is often often noted notedin indescriptions descriptionsof ofPrecambrian Precambriantidal tidalsethngs, settings, and and may be a reflection reflection of environmental environmental conditions conditions that were prevalent prevalent during during this this time time period period The excellent preservation of sedimentary structures enables the determination determination of aa for this ancient tidal environment. environment. A paleotidal range for A minimal minimal tidal range range of 3.5 3.5 metres metres was calculated, using methods Terwindt (1988). (1988). This methods outlined by Klein Klein (1971), and Terwindt This comparable to to other other determined determined paleotidal paleotidalranges ranges of of Precambrian Precambriantidal tidal value is comparable environments, which range from 0.5 to to 12.5 12.5 metres. metres. References References Klein, G. deV., deV., 1971, 1971,Sedimentary Sedimentary Model Modelfor for Determining DeterminingPaleotidal Paleotidal Range. Range. Geological Geological Society Society of of America America Bulletin, Bulletin, v.82, v.82, p.2585-2592. p.2585-2592. J.H.J., Terwindt, J. H.J., 1988, Palaeo-tidal Palaeo-tidalReconstructions Reconstructions of of inshore inshoretidal tidal depositional environments, in P.L. P.L. de de Boer et. a/., a!., eds, eds, Tide-Influenced Tide-Influenced Publishing Company. Company. p.233-263. Environments and and Facies. Facies. D. Reidel Publishing p.233-263. 32 �NEW OBSERVATIONS OBSERVATIONSON ON THE THEGEOLOGY GEOLOGY OF OFTHE THEWESTERN WESTERN GOGEBIC GOGEBIC IRON IRON RANGE, NORTHERN WISCONSIN WISCONSIN Gene L. LaBergel LaBerge, Geology Geology Deptm1 Dept., University University of Wisconsin-Oshkosh, Wisconsin-Oshkoshl Oshkosh, Oshkoshl WI, Wll Gene L. and U.S. Geological Geological Survey W. F. F. Cannon, Cannonl U. S; Geological Geological Survey, Reston, Reston#VA Dept., Western Illinois University, John S. Klasner, Klasnerl Geology DepteI Universityl Macomb, Macomb#IL, lLl and and U.S. U.S. Geological Survey. Survey. From 1992 1992 to t o 1994 1994we wereexamined reexaminedthe theGogebic Gogebic Iron lron Range Range between Tyler From Forks River River and the western termination termination of ofthe therange rangenear nearLake LakeNamekagon. Namekagon. Several aspects of the stratigraphy Several aspects stratigraphy and and structure structure of ofthe therange rangehave havebeen beenrevised. revised. River Dolomitel Dolomite, at the base of the Early section, attains The Bad River Early Proterozoic sectionl a maximum thickness of about 300meters metersnear near the the Marengo Marengo River River south of of Grand Grand about 300 View, Wisconsin. It is typically aa dolomitic Viewl dolomitic marble marble with with abundant abundant lenses lenses and and beds beds Farther east, from near Penokee Gap to of chert, chertl partly partly replaced replaced by by tremolite. tremolite. Farther eastl near Penokee t o near near Ballou Creekl Creek, the the Bad Bad River River is is much much thinner thinner and and is is mostly a monolithic chert Ballou chert breccia and and conglomeratel conglomerate, locally locallywith with lenses lenses of of dolomite dolomite near nearthe the base. base. This breccia lithology is interpreted interpreted to t o be be aa residuum residuum of chert chert nodules nodules and and beds beds formed as the during the the weathering weathering interval interval prior prior tto deposition of the dolomite was dissolved dissolved during o deposition unconformably overlying Palms Formation. The residuum Palms Formation. residuum was variably reworked into conglomerate with with clastic clastic quartz quartz grains grains interspersed interspersed in otherwise cherty cherty matrix. Local Localconcentrations concentrationsof ofmagnetite magnetiteand and hematite, hematitel explored explored in in numerous numerous test pits, pitsl may may be be either either placers placers or or hydrothermal hydrothermal iron iron concentrations. concentrations. Near Atkins Lakel Lake, in the the far far western part of the Near Atkins the range, rangel the Ironwood Ironwood IronlronFormation grades grades laterally laterally from from typical typical cherty banded iron-formation into magnetic magnetic argillite and non-cherty silicate iron-formation. iron-formation, Large Largesills sills of ofmetadiabase metadiabase are are also also contrast tto common in the iron-formation in contrast o the situation in the central central part part of of the the range where igneous rocks rocks are are rare. rare. In the Atkins Atkins Lake Lake area the iron-formation iron-formation also contains two t w o interlayers, interlayersl up up I0meters meters thick, thickl of ofan anunusual unusualbreccia breccia consisting consisting of of angular angular slabs slabs of tto o about 10 banded siliceous siliceous sedimentary sedimentary rock rock that that are as as much much as as aa meter meter long. long. Some banded Some slabs slabs are bent and may not have been fully lithified lithified when when incorporated incorporated in in the the breccia. breccia. The slabs slabs superficially superficially resemble resemblenearby nearbyiron-formationl iron-formation,but butwith with only only aa ffew The ew exceptions, we have not observed fragments that that are are iron rich or or magnetic. magnetic. The exceptions, observed fragments The matrix is is a dark gray-green, gray-greenl mostly massive rock, at least least partly partly of of igneous igneous origin. origin. Although metamorphism obscured much much of of the original texturesl textures, in metamorphism has obscured in places places a basaltic texture texture and and small small euhedral euhedral plagioclase plagioclase phenocrysts are are well well preserved, preservedl as as It are amygdules. amygdules. The The origin of of this this rock rock isis controversial, controversiall even even among among the authors. authors. It are may be aa "pepperite" "pepperite" intruded at shallow level in the iron-formation prior tto o 33 �lithification. Alternatively, Alternativelyr itit may may be be an an extrusive extrusive that that has has incorporated incorporated sediments sediments over which itit flowed. features arguing for an extrusive origin are: over flowed. Salient Salient features arguing for an extrusive origin are: I1)) perfectly concordant contacts with with thinly thinly laminated laminated iron-formation iron-formation well exposed exposed at several outcropsl outcrops, and and the the lack lack of of any any observed observed cross-cutting cross-cutting contactsl contacts, 2) the several exotic nature of virtually virtually all all fragments fragments in in the the breccia breccia and and the absence absence of fragments 3)marked marked lithologic lithologic of iron-formation with with which whichthe thebreccia brecciaisisinterlayered, interlayered! and and 3) contrast between between the the breccia breccia and and undoubtedly undoubtedly intrusive intrusive sifls sills of coarse-grained, coarse-grained! massive! inclusion-free metadiabase metadiabase.within massive, within the same outcrops. Regardless of whether whether the breccias are extrusive or very shallow Regardless of shallow intrusions, intrusions, they indicate that abundant abundant igneous igneous activity was was occurring occurring contemporaneously contemporaneously with iron-formation iron-formation deposition deposition in the western part part of the the Gogebic Gogebic Iron lron Range. Range. The The situation is similar to that that of of the theeastern eastern part part of ofthe therange, range! where where the theEmperor Emperor Volcanic Complex Complex is is interlayered interlayered with with the Ironwood Iron-Formation. Iron-Formation. Apparently Apparently the platform-like conditions of the the central central part part of of the the range, range, where where volcanic volcanic rocks rocks are limited tto o a few f e w thin thin ash ash beds, beds! grade grade both both east east and and west into into more more volcanically volcanically active regions regions at both both ends ends of of the theGogebic Gogebic Iron lronRange. Range. Although volcanism contemporaneous with ironvolcanism appears appears tto o have have been been contemporaneous ironformation deposition deposition on on the the Gogebic Gogebic Iron lron Range, Range! we have have found no no Early Early Proterozoic mafic rocks rocks cutting the overlying Tyler Formation. Proterozoic mafic Formation. This This observation, observationl coupled with the the prominent prominent unconformity unconformity at at the the base base of of the the Copps Copps Formation, Formation! the Tyler equivalent on on the the eastern eastern Gogebic Gogebic Iron lron Range, Range! suggests a time gap gap between between iron-formation deposition and accumulation accumulation of the overlying graywacke-slate sequence during which which volcanic volcanic activity sequence during activity ended. ended. The Penokean structural history of the Penokean structural the area area has has also been clarified. Penokean deformation increases increasesin in intensity intensity from from the Tyler Forks area, area! where Penokean deformation deformational features features are are limited limited tto folds, to o a few outcrop-scale outcrop-scale folds! t o the the Mineral Mineral Lake Lake area, where where the the iron-formation is repeated repeated by by large, large, nearly nearlyisoclinal isoclinalfolds. folds. Those area! folds were originally originally upright, upright! but but because because of northward northward rotation rotation during during development of the Midcontinent rift, development of rift! they they are are now now recumbent, recumbent! and and the south south overturned, limbs of synclines are overturned. From the the east east end end of of Mount Whittlesey to the the west west end end of of the therange, range! Early Early Proterozoic strata are are structurally structurally detached detached from from underlying Archean Archean rocks. rocks. The The Proterozoic strata basal decollement decollement is is well well exposed exposed on on the the east east end end of of Mount Whittlesey! Whittlesey, where basal where Bad Bad River lies on on aa shear shear zone zonedeveloped developedininArchean Archeandacitic daciticbreccia. breccia. A A River Dolomite lies decollement within the sedimentary Marengo decollement sedimentary section is is also also well exposed exposed along the Marengo River where an intensely sheared zone several several tens tens of meters wide sheared zone wide separates separates Bad Bad River and Palms Palms Formation. Formation. Second-order faults splay splay upward from the River Dolomite and Second-order faults decollement, generally climbinghigher higherininthe thesection sectiont otothe theeast. east. On On Mount d e ~ o l l e m e n tgenerally ~ climbing Whittlesey, the Ironwood repeated by by one one of of those those faults faults which Whittlesey! Ironwood Iron-Formation Iron-Formation is repeated results in the unusually wide outcrop belt belt of of iron-formation. iron-formation. 34 �INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY 1995 1995 MINERAL POTENTIAL POTENTIAL EVALUATION, EVALUATION, CENTRAL CENTRALMINNESOTA MINNESOTA MINERAL Tom Lawler, Lawler, Minnesota Department Department of of Natural Resources, Division of Minerals, Hibbing, Minnesota Minnesota 55746, (218)262-6767 (218)262-6767 1525 3rd Ave. Ave. E., Hibbing, ABSTRACT: ABSTRACT: ~esources,Minerals Division, Division, has h& completed a low-cost The Minnesota Department of Natural Resources, tow-cost program program using computer computer enhanced contemporary methods to evaluate the mineral potential of a large enhanced contemporary methods to evaluate the mineral potential of a largepart part of of This project project isis oriented oriented toward toward identifying identifying nonferrous Central Minnesota Proterozoic greenstone belts. belts. This metallic mineralization, mineralization, associated lithologic units structures permissive permissive of such such metallic associated alteration alterationor or lithologic units and and structures partof ofthe theCentral CentralMinnesota Minnesotageographic geographicinformation information mineralization. This Thisinformation information will will become become aa part mineralization. system. The 2. To To encourage encourageprivate Theobjectives objectivesare: are: 1. To serve land land use planning planningwithin withinthe theD.N.R.; D.N.R.; 2. exploration through better data access, and; 3.3.To Toserve servegovernment governmentagency agencyplanning planning of future programs. programs. exploration Creating Listing mineral Creating an improved improved data data base base for for regional regional mineral mineral potential potential evaluation evaluation was done done by: 1. Listing occurrences, and and defining defining lithologic lithologic units and and structures structures permissive permissive of mineral mineral deposits. deposits. 2. Describing Describing and analyzing analyzing bedrock lithologies from existing drill core. 3. Creating Creating 1:62,500 1:62,500 scale scale inferred inferred geologic geologic maps, which which display display interpreted interpreted mineral mineral potential. potential. 4. Re-evaluating Re-evaluating existing existing geochemical surveys using contemporaneous statistical statistical analytical analytical methods. methods. 5. 5. Testing Testinggeophysical geophysical interpretations interpretations with drill holes. A contract was completed by Dr. Dr. Don L. Shettel Jr. and Dr. Patrick completed by Patrick O'Hara O'Hara to to interpret interpret three three existing existing ground water and and lake lake sediment sediment geochemical geochemical data sets using computer driven state of the art statistical statistical and geochemical modeling modeling methods. methods. From From these these models models Drs. Drs. Shettel Shettel and and O'Hara O'Hara constructed constructedanomaly anomaly maps for gold, base base metals, metals, iron iron and and uranium. uranium. Contracts were also completed by Dr. Allan Contracts were completed by Allan Spector Spector to to make make inferred inferred geologic geologic maps maps of of sixty-two sixty-two contiguous at aa scale scaleof of 1:62,500, 1:62,500, using usinggeophysical geophysical(primarily rimarily aeromagnetic contiguous townships at aeromagneticand and gravity gravity data), data), also geologic geologic data. data. Detailed magnetic ground traverses and and geophysical geophysical measurements measurements of density density and and magnetic magnetic susceptibility susceptibilitywere were made made on on selected selected logged logged samples samples for for computer computermodeling modeling of of geologic geologicfeatures features based based on on geophysical geophysical data. data. Dr. Spector's Spector's maps maps display display structurally structurally deformed, deformed, folded folded and and faulted, faulted, greenstones with associated associated metasedimentary metasedimentaryunits unitsand andintrusives. intrusives. An important of this contract important aspect of was construction constructionof of maps maps displaying displayingmineral mineral potential potential areas areas as as modeled modeled from fromgeophysical geophysicalcharacteristics characteristics of known known mines located in similar Precambrian terrains, based based on on the the contractor's contractor's experience experiencewith with such such features. Several areas of mineral features. Several mineral potential potential are are coincident coincident or or partially partiallycoincident coincident with with anomalous anomalous geochemical results defined defined by by Drs. Drs. Shettel Shettel and and O'Hara. O'Hara. InInthe geochemical results theShephard ShephardArea Area these these Mineral Mineral Potential Potential Areas include MPA2a, MPA5c MPA5c and and MPA6b; MPA6b; In In the the Shephard Shephard Area Area Extension Extension they include areas A3, A4 AlO. On Onthe theCamp CampRipley Ripleymap map there there are areMineral Mineral Potential Potential Areas, Areas, MPA3 MPA3 and MPA4, close to drill and A10. holes with anomalous anomalous gold and platinum group elements, Section 12, 12, T43N, T43N, R32W. R32W. In summary significant results include: Improved Improved definition definition of of geologic geologic features; features; Lithologic units and of areas features permissive of economic ore deposits; Detailed inferred geologic maps with definition of having mineral potential; potential; Multi element element geochemical geochemical anomalies anomalies with significant significant pathfinder pathfinder element element anomalies anomalies coincident coincident with with favorable favorable inferred inferred geologic geologic features. features. To test test the the inferred inferred geology, geology, in in cooperation with the Minnesota cooperation with Minnesota Geological Geological Survey, Survey, six vertical vertical holes holes were were drilled drilledthrough throughglacial glacial overburden to obtain bedrock samples. Examination Examinationof of the the core core confirms confirms inferred inferred geologic bedrock map lithologies P295lithologies in most of the drill holes. Native Nativecopper copperininaaKeweenawan Keweenawanlike likeconglomerate conglomeratefrom from hole hole P295Minnesota DNR DNR Report Report 284 284 records 960 ppb gold 6 suggests suggests mineral mineral potential. potential. Minnesota gold in in aa heavy heavy minerals minerals concentrate for for sample sample 23949. 23949. This T44N7 R31W, R31W, near concentrate This sample sample came from a gravel pit in Section 36, T44N, the trend of of aa mafic mafic volcanic-sediment volcanic-sediment contact contact where where Spector Spector maps maps several mineral mineral potential areas on the Shephard Area. 35 �GENESIS OF CU-NI CU-NI SULFIDE SULFIDE MINERALIZATION MINERALIZATION AT THE SPRUCE SPRUCE ROAD DEPOSIT, DEPOSIT, SOUTH KAWISHIWI INTRUSION, DULUTH COMPLEX Science Center, Center, Isotope Research Group, Yeoeun Dong 224-1, Yusung Ku, LEE, Insung, Korea Basic Science Yusung P.O. Box 41, Taejean 305-333, Korea. RIPLEY, RIPLEY, Edward Edward M., M., Department of Geological Sciences, Indiana University University Bloomington, Bloomington, Indiana Indiana 47405, 47405, U.S.A. U.S.A. Sciences, The South Kawishiwi Kawishiwi intrusion is one of several intrusions within the Duluth Complex, Minnesota - the principal exposed plutonic component of the Spruce Spruce Road Road of the 1.1 Ga Midcontinent Rift Rift system. system. In the area the South Kawishiwi Kawishiwi intrusion intrusion is divisible into seven distinct troctolitic troctolitic to to gabbroic gabbroic units, units, four four of of which contain 11 to 55 volume volume percent percent of of disseminated disseminated pyrrhotite, pyrrhotite, cubanite, cubanite, chalcopyrite, chalcopyrite, and pentlandite. 6S values S^S valuesofofthe themineralized mineralized units units range from 3.8 to 10.2%, 10.2%0,and and are are distinctly distinctly different from those of of non-mineralizedrocks rockswhich whichrange rangefrom from-3.4 -3.4toto2.8%0 2.8% (Figure (Figure 1). 1). The non-mineralized The proposed proposed model for the genesis of the sulfides involves the mixing mixing of sulfur sulfur derived derived from from two two sources, sources, accumulation accumulation of immiscible immisciblesulfi4e sulfide liquid, and emplacement of Twenty percent percent batch partial melting of a spinel spinel of sulfide-saturated sulfide-saturated magmas. magmas. Twenty Iherzolite mantle source source with with —20 -20 pprn pprn SS yields yieldsaaderivative derivativemelt meltwith with—76 -76 ppm pprn Cu Cu (65 (65 lherzolite mantle ppm Cu and 200 ppm ppm pprn from sulfide sulfide arid and 11 11 pprn total sulfur sulfur content content of of —1000 -1000 ppm. ppm from silicate) and a total ppm. In order to produce the relatively evolved, high-Al high-A1 olivine tholeiite tholeiite parental parental magmas magmas of of the theintrusive intrusive sequence, sequence, extensive extensive crystallization of of a primary melt in a lower crustal or mantle chamber is required. During fractional crystallization Duringthis this process sulfide saturation would have been achieved achieved and chalcophile elements removed from the magma liquid. Emplacement melt into into a higher level staging into a coexisting coexisting sulfide liquid. Emplacement of the the sulfide-saturated sulfide-saturated melt chamber permitted the assimilation assimilation of sulfur sulfur from from metasedimentary metasedimentary country country rocks. rocks. Reaction between externally-derived sulfur or neutral neutral species, species, would would externally-derived sulfur and metals metals initially present in the melt as silicate, oxide, or have produced a second liquid that that mixed mixed with with that that of mantle origin. second generation of immiscible immiscible sulfide liquid Sulfide-rich rocks of the South South Kawishiwi Kawishiwi intrusion represent melts derived from the high-level chamber chamber contamination with with sulfur of of crustal origin. origin. Because that had experienced contamination Because of of the the wide wide range range in in possible possible contaminant 34S values contaminant S^S values (e.g. (e.g. 00 to to 29% 29%0ininsulfides sulfidesfrom frommetasedimentary metasedimentary country country rocks), it is difficult to accurately assess the proportion of country rock sulfur sulfur present in the mineralized units, but a range of of to 70% 70% isisconsistent consistentwith with available availabledata. data. Sulfide assemblages are mineralogically zoned, such such from 30 to pyrrhotite-rich layers layers are are overlain overlainby bycubanite-chalcopyrite-rich cubanite-chalcopyrite-rich layers. layers. In situ situ crystallization, crystallization, that pyrrhotite-rich controlled by boundary layer layer fractionation fractionation and upward expulsion expulsion of of CuCu- and and Ni-enriched Ni-enriched residual residual liquid liquid proposed to explain explain the zonation. zonation. Upward Upward increases increases in in Cu Cu and andNi Nicontents, contents,as aswell wellas asincompatible incompatible is proposed elements such as Zr, Y, and P, may or possibly possibly as as a may be be controlled controlled either by aa filter-pressing filter-pressing mechanism, mechanism, or result of the decrease in density density of of an an interstitial interstitial liquid liquid related related to to enrichment enrichment of of volatiles. volatiles. 36 �34 -4 -2 0 2 S (°Ioo) 4 6 8 10 0 100 200 E -C 300 a) 400 500 600 Figure of sulfide minerals in the South Kawishiwi intrusion, Spruce Figure 1.1.S 5values s values of sulfide minerals in the South Kawishiwi intrusion, SpruceRoad Road area, MN. area,Duluth DuluthComplex, Complex,MN. 37 �Sublayer, Main Mass, and and Offsets, Sudbury Sudbury Geochemical relationships between the Sublayer, Igneous Complex, Canada Canada Lightfoot, P C . ' Farrell, Farrell, K.2, K., Moore, Moore, M.2, M.,, Pekeski, Pekeski, D.2, D., Crabtree, Crabtree, D.3, D . ~and ,andKeays, Keays,R.R.2 R.R.' Lightfoot, P.C.1. 1 Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario OntarioP3E P3E 6B5 6B5 Mineral Deposits Section, Ontario 2 2 Department of Earth Earth Sciences, Sciences, Laurentian Laurentian University, University, Sudbury, Sudbury, Ontario OntarioP3E P3E2C6 2C6 Department 3 Geoscience Survey, Sudbury, Sudbury, Ontario, Ontario, P3E P3E 6B5 Geoscience Laboratories, Laboratories, Ontario Geological Survey, major element element oxide and trace element concentrations in samples samples from the Analyses of the major Main Mass felsic norite, quartz quartz gabbro, gabbro, and and granophyre granophyre of of the the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) confirm t . % Si02, SiO,, (SIC) confirm that that there there is aa compositional compositional gap gap between between norites norites (e.g: (e.g: 55-60 55-60 w wt.% 3.5-5.5 wt.% (e.g: 65-74 65-74 w wt.% ppm Nb) Nb) and and granophyres granophyres (e.g: t.% 3.5-5.5 w t . % MgO, MgO, 5-8 5-8ppm ppmTh, Th, and and 5-10 5-1 0ppm SiO2; 0.5-1.6 0.5-1 .6wt.% wt.% MgO 13-17 SO2; 13-17ppm ppmTh, Th, and and112-1 2-1 8ppm Nb). Despite the differences differences in in elemental concentrations, rare earth concentrations, there is a remarkably remarkably narrow narrow range range of of ratios of the rare overlying elements (REE), (REE),Ba, Ba,Rb, Rb,Th, Th,U, U,Nb, Nb,Ta, Ta,Hf, Hf, Zr, Zr, and and YY in in the the felsic felsic norite and the overlying granophyre LaISm = dNb = -2.6, ThINb .I ). These similarities granophyre (e.g. (e.g. La/Sm = 5.4-7.0, 5.4-7.0, G Gd/Yb = 2.1 2.1-2.6, Th/Nb =0.9-1 =0.9-1 .1). simi'arities in ratios of elements are unlikely ttoo be be explained if the granophyre granophyre and felsic norite crystallised from magmas derived sources; rather, these data support models derived from from different sources; magma. We where the felsic norite norite and and granophyre granophyre are derived from a common magma. We explore explore the implications for this data for the the formation formation of of the the Main Main Mass Mass of of the theSIC, SIC, and and suggest suggest variations are are inconsistent inconsistent with with in-situ crystallisation of aa single intrusion that the observed observed variations or melt sheet. The reason for this is suggested to t o be be the compositional compositional gap between between the the which is not readily explained explained by by fractional fractional crystallisation crystallisation felsic norite and the granophyre granophyre which of one one pulse pulse of of magma. magma. The composition of quartz quartz diorite diorite from from the the Parkin Parkin and and Whistle Offsets Offsets and and leucocratic norites from the embayment structure at Whistle Mine, at the the north-eastern north-eastern margin of the SIC occupy occupy tight similar fields (quartz diorite: diorite: 55-64wt.% 55-64wt.% SIO2; SiO,; leucocratic norite: 59-62 for 59-62wt.% wt.%SiO2). SiO,). The The ratios ratios of of the theREE REE and other incompatible trace elements for these rocks are are very very similar similar tto those of of the the Main Main Mass Mass (e.g. (e.g.ThINb Th/Nb=0.8-1.2, these o those =0.8-1.2, La/Sm LaISm =5.36.6; Gd/Yb = 2.3-3.0), 2.3-3.0), although although in in detail, detail, when whenthese thesesamples samples are are normalised normalised to t o average average 6.6; GdNb = felsic norite, of the data for the norite, they they are are slightly slightly enriched enriched in inthe the light lightREE. REE. Comparison of the Parkin Offset Offset tto Parkin o other offsets offsets around around the the SIC SIC suggest that there is is aa broad broad compositional difference between those formed north of the SIC compared w with SIC compared i t h those formed tto o the south. With With the the exception exception of of the the Manchester Manchester Offset, Offset, those those formed formed to t o the thesouth southhave have TiO2 =0.65-0.80 wt.%, Sr = 150-350ppm, ppm, La/Sm LaISm==5-6 5-6and and La/Yb Lamb =10-15, = 10-15, whereas whereas those those TiO, =0.65-0.80 Sr =150-350 =0.8-1 .1, Sr = = 350-550 350-550 ppm, = 5.8-6.8, 5.8-6.8, and formed ttoo the north north have have TiO2 TiO, = 0.8-1.1, ppm, La/Sm LaISm = La/Yb = = 16-23. 1 6-23.The TheManchester Manchester Offset Offset has llow Lamb o w Ti02 TiO, and and Sr Sr with with elevated elevatedSiO2, SiO,, La/Sm, LaISm, and and La/Yb. Although the trace element ratios of most of the Offsets LaNb. Although Offsets overlap overlap with w i t h the the Main Main differences between those those tto Mass of the SIC, SIC, the small differences o the north and south of the SIC may be consistent w with i t h contamination contamination by by compositionally different country country rocks. rocks. Our new data for the the Sublayer Sublayer at Whistle Whistle Mine Mine suggest suggest that that there there is is aa compositional compositional spectrum between orthopyroxene-poor norites through norites containing up ttoo 40 4 0 modal modal percent cumulate orthopyroxene; orthopyroxene; the the more more orthopyroxene-rich orthopyroxene-rich samples samples sometimes sometimes contain contain olivine.The Theportion portionofofthe theembayment embaymentclosest closestt to the Whistle Whistle Offset Offset contains fresh Fo6567 Fo65.67olivine. o the leucocratic norite and quartz diorite. We believe that the classification of either the quartz quartz diorite. believe that quartz diorites of the Offsets Offsetsor orthe theleucocratic leucocraticnorite noriteof ofthe theembayment embayment as asSublayer-type Sublayer-typerocks rocks may be inappropriate, and w we inappropriate, and e suggest that they they are are more more closely related to t o the the magma magma Main Mass Mass of of the the SIC. SIC. giving rise ttoo the Main Compositional data data for the noritic noritic matrix matrix of of the theSublayer Sublayer in in the the embayment embayment structure structure at Whistle Mine indicate that the bulk composition of the Sublayer is more more mafic mafic (45-53 Sublayer is (45-53 1 38 �wt.% w t , % Si02; SiO,; 5-12 5-1 2 wt.% w t . %MgO) MgO)than thanthe thefelsic felsicnorite noriteand andheterogeneous heterogeneous with with respect respect to to major and trace element abundance. abundance. Much of the the heterogeneity heterogeneity may may be be due due to t othe thevariable variable amount of assimilation assimilation of of diabase diabase and and gabbro inclusions. The composition composition of of inclusion-free inclusion-free Sublayer markedly different when compared to Sublayer norite is markedly t o average felsic norite of of the the Main Main Mass. The Sublayer Sublayer from the Whistle Whistle embayment embayment has has Ti/Y T i N=1 175, =1 1.4, 75, DyIHf Dy/Hf = .4, LaISm La/Sm =3.9, = 3.9, and La/Ta La/Ta == 105, 105, which which contrasts contrasts with the felsic norite 0.9, norite which which has has Ti/Y T i N= = 220, Dy/Hf DyIHf = =0.9, La/Sm = = 6.2, 6.2, and and LLa/Ta =661. Compositionally, the the diabase and gabbro inclusions inc'usions have ana = 1. Compositionally, LaISm Ti/Y= T i N =192, 192, Dy/Hf DyIHf =2.8. La/Sm LaISm =3.2, and and La/Ta L a n a =44. ItItis is shown shown that that the the composition composition of of the Sublayer matrix reflects reflects aa component component of of assimilation assimilation of of hornfelsed hornfelsed diabase diabase inclusions, inclusions, and the composition of the the Sublayer Sublayer is inconsistent inconsistent with withthe theassimilation assimilationof oflarge largeamounts amounts of footwall footwall granitoid. granitoid. The The compositional compositional difference difference between betweenthe theSublayer Sublayer norite noriteand and the the suggests that they were emplaced different batches Main Mass norite suggests emplaced as different batches of of magma, magma, one one of of which was laden with partially assimilated inclusions of diabase. The presence of inclusions was laden with partially assimilated inclusions of diabase. The presence inclusions and footwall footwall breccias suggest suggest that that the breccias in the the massive massive suiphides sulphides and of Subayer Sublayer norite norite in In sulphides were formed after at and sulphides at least least some some of of the theSublayer Sublayer magma magma had had crystallised. crystallised. In detail, a more complete understanding of the geochemical variations variations in the Sublayer will detail, Sublayer will come from detailed microprobe studies of the the accessory accessory mineral mineral phases phases such such as as apatite, apatite, zircon, baddelyite, zircon, baddelyite, and biotite. 39 �Sublayer and the mafic-ultramafic mafic-ultramafic inclusions, Whistle Geochemical variations variations within within the Sublayer Mine, Sudbury Sudbury Igneous Igneous Complex, Complex, Canada Canada Lightfoot, P.C.1. P.c.', Farrell, Farrell, K.2, K . ~Moore, Moore, , M.', Pekeski, Pekeski, D.2, D . ~Crabtree, Crabtree, , D . ~and and , Keays, Keays,R.R.2 R.R.* Lightfoot, M.2, D.3, 1 Deposits Section, Section, Ontario Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario OntarioP3E P3E6B5 6B5 Mineral Deposits 22 Department of Earth Earth Sciences, Sciences, Laurentian Laurentian University, University, Sudbury, Sudbury, Ontario OntarioP3E P3E2C6 2C6 Department 3 Geoscience Laboratories, Laboratories, Ontario Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario, Ontario, P3E P3E 6B5 6B5 Geoscience i n the embayment embayment structure structure at at Whistle WhistleMine, Mine,Sudbury SudburyIgneous Igneous The Sublayer norites in orthopyroxene-poor to t o cumulate cumulate orthopyroxene-rich orthopyroxene-rich non-poikititic non-poikilitic Complex (SIC) consist consist of orthopyroxene-poor norites with w i t h up up to t o55modal modalpercent percent sulphide sulphide and and 10% 1 0 % inclusions. inclusions. The The Sublayer Sublayer textured norites often contains contains inclusions inclusions and and tends tends to t o be be heterogeneous; heterogeneous; multiple samples from the norite often t o analytical analytical same outcrop showing 1-10 1-10 times more variation than is attributed to The inclusion-free inclusion-free norites norites are less heterogeneous, heterogeneous, mostly i t h 1-5 1-5 times times more more uncertainty. The mostly w with t o analytical analytical uncertainty. uncertainty. A A small small number number of of samples samples of variation than can be attributed to norite contain contain fresh fresh olivine olivineofofcomposition compositionFo6567 Foc5-^ w i t h 970-1 970-13lOppm 3 1OppmNi. Ni. Sublayer norite with population at at Whistle Whistle isisequally equally split splitbetween betweenhornfelsed hornfelseddiabasediabaseThe inclusion population i t h anhedral anhedral porphyritic gabbro inclusions inclusions w with porphyritic clusters of feldspar, feldspar, and and poikilitic-textured poikilitic-textured melanorites It is is shown shown that that compositional compositional data data for for the thediabase-gabbro diabase-gabbro melanorites and pyroxenites. It o inclusions indicate broad broad similarities in major and trace element composition tto inclusions Matachewan diabase diabase dykes. The melanorite inclusions contain cumulate magnetite, Matachewan magnetite, apatite, apatite, zircon, baddelyite, baddelyite, orthopyroxene, orthopyroxene, ±Âolivine, olivine, and andintercumulus intercumulusaugite, augite, plagioclase, plagioclase, biotite, biotite, zircon, rocks and and are are unusual unusual in having having very high high apatite apatite(0.3 (0.3modal modal and sulphide. They are fresh rocks %), Fo7274 and 270-1490 %), and and biotite biotite(5-10 (5-10modal modal%) %)contents, contents,olivine olivinewith with and 11270-1 4 9 0 ppm ppm Ni, Ni, yet yet whole-rock MgO MgO contents contents of of 15-22 15-22wt.% w t . %MgO MgOand and50-80 50-80time timechondrite chondriteLREE LREE whole-rock 1 abundances. abundances. The melanorite and pyroxenite inclusions range range in composition corn positionfrom from88t to 28 wt.% wt.% o 28 MgO; the the least least mafic mafic poikilitic-textured poikilitic-texturedmelanorites melanoriteshave havetrace traceelement elementabundances abundancesand and ratios which, on on average, average, are are similar similar to t o the the Sublayer Sublayer norite norite matrix. matrix. The Theolivine-bearing olivine-bearing melanorite melanorite inclusions and pyroxenites have have elevated Ti/Y, Tim, Dy/Hf, DyIHf, La/Ta, Lana, and and low lowLa/Sm LaISm which which are are all features of the the Sublayer Sublayer matrix, but but the the most most ultramafic ultramafic samples samples show strong strong depletion in compared tto the Sublayer Sublayer matrix. matrix. Nd isotopic analysis of the in the the HREE HREE compared o the the melanorites .8SGa)isisbetween between -6 and -7 which which compares melanorites indicate that €Nd eNd (1 (1.85Ga) compares with with the the Sublayer matrix which which has has eNd eNd (1 (1.85Ga) -7.5 to t o-8. -8. Sublayer .85Ga)of of between between -7.5 There There is is aa significant significant range range in intrace traceelement elementabundance abundance and and ratios ratiosin i nthe themelanorites melanorites and and pyroxenites, pyroxenites, and and in detail, much much of of this this appears appears not not to t o be be linked linked to t oany anysingle single fractionating we fractionating mineral mineral phases phases such as olivine or hypersthene. hypersthene. Rather, Rather, w e suspect that the the compositional compositional variations are more a function function of of variations variations in in the the modal modal accessory accessory mineralogy of the rocks, rocks, and and we w e therefore therefore suggest suggest that that mineralogical mineralogical studies studies represent represent an an important next-step next-step in in unravelling unravelling the origin origin of of the the Sublayer. Sublayer. In the course of our our studies, studies, we w e have have acquired acquired compositional compositional data data from from aa number number of of embayment embayment structures structures around around the SIC, SIC, and we w e find find that that each each embayment embayment contains contains noritic noritic Sublayer Sublayer matrix with w i t h aa distinctive distinctivetrace traceelement elementsignature. signature. For For example, example, analysis analysis of of Sublayer matrix matrix from from the the Fraser Fraser and McCreedy McCreedy Mine areas on the northern northern margin margin of of the the SIC more closely resembles the composition of the the main main mass mass norite; norite; at at Crean Crean Hill Hill Mine Mineat at the Tim the southwestern southwesternmargin marginof of the theSIC, SIC, the thetrace traceelement elementsignature signaturehas has marked marked low low Ti/Y accompanied by low La/Ta La/Ta which is different different to t o both boththe the Whistle Whistle embayment embayment and and the Fraser-McCreedy em bayments.. These differences between embayments suggest Fraser-McCreedy embayments.. These between embayments suggest contributions contributions from from differing differingcrustal crustalreservoirs, reservoirs, and and suggest suggest that thatthe theSublayer Sublayer magmas magmas 40 �equilibrated andlor different different inclusion inclusion equilibrated at at depth depth and and in-situ in-situ with with either either different conduit walls and/or populations. populations. 41 �BANQUET TALK TALK - ABSTRACT ABSTRACT The relationship between between mantle mantle plumes, plumes, flood flood basalts basalts and and mineralization mineralization Peter C. C. Lightfoot Lightfoot 6B5. Mineral Deposits Deposits Section, Section, Ontario OntarioGeological Geological Survey, Survey, Sudbury, Sudbury, Ontario OntarioP3E P3E6B5. Mineral remarkable wealth of of information information on on the the chemostratigraphy chemostratigraphy of the basaltic basaltic rocks rocks found found in in A remarkable n o w available. available. Studies Studies of continental continentalflood floodbasalt basalt(CFB) (CFB) large igneous igneous provinces is now sequences sequences of the the Karoo, Karoo, Parana, Parana, Deccan, Deccan, Keweenawan, Keweenawan, West Westand andEast EastGreenland, Greenland, and and 1-15 k m thick thick successions successions of basaltic basaltic rocks rocks can can be be erupted erupted Siberian Traps Traps indicate indicate that that 1-15km close to t o continental continentalmargins marginsonto ontoyoung youngepicontinental epicontinentalsedimentary sedimentarysequences sequences and and ancient ancient close amphibolitic to t o granulitic granuliticterrains. terrains.These Thesegiant giantCFB CFBrecord record the the eruption eruptionof oflarge largevolumes volumes(up (up amphibolitic t o 2x106 2x1 O6 km3) km3) of magma over in some cases very short time time intervals intervals (e.g. (e.g. Deccan Deccan to Trap: < < 1 Ma.). Single Single lava flows flows may may extend extend for forseveral severalhundred hundred kilometers kilometerslaterally, laterally,and and chemical stratigraphy stratigraphy of of the the lavas lavas can can be be matched matched over over these these distances, distances, and and the the the chemical basalts can be be grouped grouped into into Formations. Formations. An A n important importantissue issue concerns concerns the the relationship relationship of of these these CFB CFB ttoo mantle plumes or hot spots. In In oceanic oceanic settings, mantle mantle plumes plumes are believed tto o control the distribution distribution of of ocean ocean Hawaiian chain. chain. Some Some of of these these island island chains chains converge converge with withCFB CFB island chains such as the Hawaiian continentalmargins, margins, and andthe theReunion-Chagos-Lacadive Reunion-Chagos-Lacadive system system is is one one example example where where the the at continental age of the the rocks rocks becomes becomes progressively progressively older older away away from fromthe thepresent-day present-day Reunion Reunion Island Island hot spot towards the 60 6 0 Ma. Ma. Deccan Deccan Trap. In detail, detail, recent work has shown that even the within the the Deccan Deccan appear appear tto o have migrated from o south as the eruptive centers within from north tto Indian Subcontinent Subcontinent migrated migrated northwards northwards over over the the Reunion Reunion hot hot spot. spot. In other settings, eruption more directly directly related tto rifting of eruption of of CFB CFB appears more o passive rifting of (c.30 3 0Ma.) Ma.)Parana Parana CFB. CFB. In In continental margins. margins. An A n example example of of this this is is the the more more protracted protracted(c. continental detail however, fall close close tto however, both both the the Parana Parana and Etendeka fall o the pre-rifting location location of of the the Tristan Tristan de Cunha Cunha hot spot, spot, and and so so even even in in these these cases cases plumes plumes appear appear to t o have have played played aa role. role. These features features are are all all very very satisfying satisfying confirmations of of the effects effects of of continental continental migration over mantle plumes, but the really exciting implications of these data comefrom from migration over mantle plumes, but the really exciting implications of these data come application in in mineral mineral exploration exploration strategies. strategies. One One of the the largest largest deposits deposits of of magmatic magmatic their application Ni, with the Ni, Cu, Cu, and and platinum platinum group group elements is associated with the Noril'sk Noril'sk Region Region of of the the Siberian Siberian Trap. Other major deposits are associated w with i t h the Keweenawan, Keweenawan, and and extensive extensive exploration programs programs have have been been pursued around the Insizwa Complex of the Karoo Karoo and and the Greenland Greenland CFBs. CFBs. At A t Noril'sk Norilfskininthe theSiberian Siberian Trap, Trap, the the lavas lavas are are split into into two t w osequences. sequences. The The Lower Lower Sequence has high high TiO, Ti02 (>1 .7) and ( > 1.7) and Gd/Yb (>2) ( >2)relative relativeto t othe theUpper UpperSequence, Sequence, but but both both Sequence has sequences contain picritic picritic basalts. basalts. The The Lower LowerSequence Sequence appears appears to t o have have been been derived derived from from deep asthenospheric mantle as the geochemical composition of the least contaminated deep asthenospheric composition of the least contaminated rocks rocks closely closely resembles resembles ocean ocean island island basalt basalt remobihsed remobilised from the mantle by by aa hot hot spot. spot. The The Upper Sequenceconsists consists of of aa ffew Upper Sequence e w picritic flows flows overlain overlain by by tholeiites, and and these rocks have geochemical signatures suggesting derivation from aa combination combination of of shallow shallow asthenospheric and the the continental mantle lithosphere. Basalts from from the the lower part asthenospheric mantle and lithosphere. Basalts of the the Upper Upper Sequence Sequence have havehigh highSi02, SiO,, LILE, LILE, LREE, LREE, and elevated elevated Th/Nb, ThINb, La/Sm, LaISm, and and radiogenic Sr-isotopic compositions. compositions. Basalts Basaltswwith 52-56wt.% Si Si02, La/Sm>3, > 3, and and SrSrradiogenic Sr-isotopic i t h 52-56wt.% O,, LaISm isotope signatures greater greater than than 0.707 0.707 have interacted w with i t h upper upper continental crust, and and become contaminated. Importantly, these lavas are also long bereft of their Ni, Cu, and become these lavas their Ni, Cu, and PGE, and have have CuIZrC0.2 Cu/Zr<0.2 and and Ni/MgO< NiIMgO <10; 10; these these are are features attributed to t o the the PGE, and equilibration of the magma with magma w i t h aa sulphide sulphide liquid. Upwards in the basalt stratigraphy, the degree of contamination contamination recorded in the rocks rocks is is progressively progressively less and this couples with with 42 �an increase in the tenor of of Ni, Ni, Cu, Cu, and and PGE. PGE. These features are found in the Nadezhdinsky Nadezhdinsky Formation lavas, lavas, and and these these lavas lavas were were erupted erupted in the Noril'sk Noril'sk Region close tto Region close o the Noril'skof Ni, Ni, Cu, Cu, and andPGE PGE missing from from the the Nadezhdinsky Nadezhdinsky Kharaelakh Fault. The amount of o account and Formation lavas lavas is is more more than than enough enough tto account for for the mineralisation at Noril'sk and and Talnakh intrusions consist of of at at most most several several hundred hundred meters meters of Talnakh. The Noril'sk and picritic to t o gabbroic gabbroic rocks, rocks, yet yethost hostthick thicklenses lensesofofmassive massiveNi-Cu-PGE Ni-Cu-PGEmineralisation. mineralisation. The The basalts in in this this context contextisisthat thattheir theirlow lowNi, Ni,Cu, Cu,and andPGE PGEcontents contentsare are importance of the basalts presumably due due tto o the extraction of of the the metals metals by by the the same same suiphide sulphide that that is is found found at at Noril'sk; Noril'sk; the the compositions compositions of of the the basalts basalts then become become important exploration tools. In In detail, the combination combination of of the the elemental elemental and and isotopic isotopic composition composition of of Sr Sr in inthe theintrusions intrusionsand andlavas, lavas, the together with w i t hthe theS-isotopic S-isotopic composition composition of of the the suiphides sulphides suggest suggest that that much much of of the the sulphur sulphur in the Talnakh ores was was derived derived from from Devonian Devonian evaporites. evaporites. This This suggests suggests that thatevaporite evaporite sulphur played a very important part in in the the genesis genesis of the Noril'sk Noril'sk deposits. deposits. In the Keweenawan, Keweenawan, aa thick thicksequence sequence of of lavas lavason onthe theBlack BlackBay BayPeninsula Peninsula and and St. St. In Ignace Island (the Osler Group) record many of the same same features as the Noril'sk Noril'sk basalts. basalts. lgnace Lower Formation Formation of of the the Osler Osler Group Group have have many many similarities similarities to t o the theLower LowerSequence Sequenceat at The Lower Noril'sk and and may be linked ttoo a mantle plume that initiated rifting. rifting. The The Central Central Formation of the Osler and ThINb, Th/Nb, and these these same same lavas lavas have have very very low SiO,, La/Sm, LaISm, and Osler Group has elevated Si02, Ni/MgO and moderate basalts of of Noril'sk. Noril'sk. Unfortunately moderate tto o low Cu like the Nadezhdinsky Nadezhdinsky basalts Cu was mobile during alteration, and therefore this this criterion criterion is is less less diagnostic diagnostic than than the the Ni/MgO ratio. The presence of abundant gabbroic rocks along the northern margin of NiIMgO ratio. The presence of abundant gabbroic rocks along the northern margin ofLake Lake Superior and and iin Plate, combined combined with with the presence n the Nipigon Plate, presence of giant Ni-Cu deposits at Duluth Duluth and and smaller deposits in in the the Crystal Crystal Lake Lake Gabbro Gabbro and Port Coldwell Coldwell Complex Complex encourage further exploration for Noril'sk-type Noril'sk-type targets targetsininthe theKeweenawan. Keweenawan. 43 �STRUCTURAL GEOLOGY GEOLOGYAND TECTONIC TECTONICEVOLUTION EVOLUTION OF OF THE THE VIZIEN VIZIEN GREENSTONE GREENSTONE STRUCTURAL BELT IN IN MINTO MINT0BLOCK, BLOCK,NORTHEASTERN NORTHEASTERNSUPERIOR SUPERIORPROVINCE, PROVINCE, NORTHERN NORTHERN BELT QUEBEC QUEBEC LIN, LIN, *Shoufa, *Shoufa,SKULSKI, SKULSKI,Tom, Tom,and andPERCIVAL, PERCIVAL,John JohnA., A.,Geological GeologicalSurvey Surveyof of Canada, Canada,601 601 Booth St., St., Ottawa, Ottawa,ON ONK1A KIA 0E8, OE8,Canada Canada Booth The Minto MintoBlock Blockin in the thenortheastern northeasternSuperior SuperiorProvince Provinceisis characterized characterizedby by north-northwesterly north-northwesterly structural structural The aeromagnetic trends trends that that contrast contrastwith with easterly easterly to to east-southeasterly east-southeasterlytrends trendsin in the the southern southern part part of of the the and aeromagnetic province. ItItconsists consistsmainly mainlyof ofplutonic plutonicrocks, rocks,but butalso alsocontain contain some some greenstone greenstone belts belts with with well-preserved well-preserved province. supracrustal sequences, sequences,including including the Vizien, Kogaluc, Payne our supracrustal Payne Lake Lake and and Qalluviartuuq Qalluviartuuq belts. belts. During our studyof of the the Minto MintoBlock, Block,we we paid paid special specialattention attention to to the the greenstone greenstone belts, belts, because because they they generally generally contain contain study more complete complete structural record than associated granitoid aa more granitoid rocks. rocks. Here we report results of a detailed structuralstudy studyof of one oneof of the thebelts, belts,the theVizien Vizienbelt, belt,and anddiscuss discusstheir their tectonic tectonicimplications. implications. structural C, D and X). PanelXXconsists consistsof of The Vizien belt consists of five structural panels (A, B, The Vizien belt consists of five structural Panel pillowed,nonvesicular, nonvesicular,low-K low-Ktholeiitic tholeiiticbasaltic basalticandesites andesitesintruded intrudedby byperidotite peridotiteand andgabbro gabbrosills sills(—2786 (-2786 pillowed, Ma), and and isisinterpreted interpretedto to be beaafragment fragmentof oftransitional transitionaloceanic oceaniccrust. crust.Panel PanelAAconsists consistsof ofupwardupwardMa), shoalingcalc-alkalic calc-alkalic(submarine (submarineto to shallow-marine shallow-marineor or subaerial) subaerial) mafic, mafic, intermediate intermediate and felsic felsic volcanic volcanic shoaling rocks(—2724 (-2724 Ma) formed in in aa continental continentalarc arc rocks Ma) and and minor minor sedimentary sedimentary rocks, and is interpreted to have formed environment.Panel PanelCCconsists consistsofofa abimodal bimodalsequence sequence subaerial high-Ktholeiitic tholeiitic lava flows -2722 environment. ofofsubaerial high-K lava flows ofof —2722 Ma, interpreted interpreted to to have have formed formed in in aa continental continental extensional environment Panel BB consists consistsof of aa basal basal Ma, environment. Panel conglomerate(<—2718 (<-27 18 Ma) tonalitic basement basement of of conglomerate Ma) and and greywacke greywacke that lie unconformably unconformably on saprolithic saprolithic tonalitic -2940 Ma. shear —2940 Ma. The The top of panel panel B consists of enigmatic enigmatic mafic tholeiitic tholeiitic lavas and a melange that is in shear Panel D D consists consists of of highly highly strained strained rocks of panels B, zone contact contact with, and contains clasts of, panel X. zone X. Panel CandX. C and X. Detailed Detailedstructural structuralanalysis analysisof of the theVizien Vizienbelt beltdemonstrates demonstratesfive fivegenerations generationsof of ductile ductile D5),asaswell wellas asbrittle brittlefaulting. faulting.Dl D lisisindicated indicatedby bythe thepresence presenceof ofaapre-D2 pre-D2foliation foliation deformation (Dl (Dl totoD5), deformation and D2isis and deformed deformed melange melange fragments. fragments. ItItisisinterpreted interpretedto to be be related related to to the the thrusting thrusting of panel X over B. D2 responsible for the main penetrative foliation (S2), axial-planar to tight to isoclinal F2 folds. The S2 responsible for the main penetrative foliation (S2), axial-planar foliation foliation generally generallystrikes strikessubparallel subparallelto to the thepanel panel boundaries boundariesand and lithological lithologicalcontacts, contacts,and anddips dipssteeply. steeply. On On the the S2 S2foliation, foliation,steeply steeplyplunging plunging mineral mineral and/or and/or stretching stretchinglineations lineations are are well well developed. developed. The TheD2 D2 deformation panels X X and and AIC. A/C. Kinematic deformationis is concentrated concentrated in a shear zone between panels Kinematic indicators indicate indicate that that panel panel X X was was thrust thrust over over both both panels panels A A and and C C during during D2. F3 F3and andF4 F4folds foldsare areopen opentototight, tight,with with NNW-SSEIncontrast contrastto tothe theF2 F2folds, folds, they they lack lack an an axial axial NNW-SSE-and and E-W-trending E-W-trendingaxial axial planes, planes, respectively. In planar F3and andF4 F4folds foldswarp warpthe theS2 S2foliation, foliation,panel panelboundaries boundariesand andlithological lithologicalunits. units. They They planar foliation. foliation. F3 dominate D5isisassociated associatedwith withdextral dextraltranscurrent transcurrentmovement movementalong alongaaNNW-SSE NNW-SSE dominatethe themap mappattern. pattern.D5 trending trending shear shear zone. zone. Analysis Analysisof ofthe thestructural structuraldata dataindicates indicatesthat thatthe theS2 S2foliation foliationwas wasplanar planarbefore beforebeing beingfolded foldedby by F3. F3.Therefore, Therefore,the thepre-F3 pre-F3geometry geometryofofthe thebelt beltcan canbeberestored restoredby byreorienting reorientingS2 S2into intoaaplanar planargeometry. geometry. The Therestored restoredgeometry geometryof ofthe theVizien Vizienbelt beltisismuch muchsimpler, simpler,with with panel panel BB on on one one side, side,and and panels panels A A and and CC on on the the other other side, side, of panel panel X. This Thisregular regulargeometry geometrysuggests suggeststhat that panels panels A A and and C C were were probably probably part part of of the same block when they were juxtaposed with panels B/X. Similar La/Nb ratios and Nd isotope the same block when they were juxtaposed with BJX. Similar LafNb ratios and Nd isotope compositions supportaamodel modelin inwhich whichpanel panelCCformed formedin inaarift riftwithin withinthe thepanel panelAA compositionsin inpanels panelsAAand andCCsupport continental continentalarc. arc. The Thearc arcwas wasseparated separatedfrom fromthe thebasement basementof ofpanel panelBBby by oceanic oceaniccrust, crust,anomalous anomalous fragments aspanel panelX. X. The Thecollision collisionrelated relatedtotothe theclosure closureofofthe theocean oceanwas was fragmentsof ofwhich whichmay maybe bepreserved preservedas responsible wasthrust thrustover overpanel panel B. B. Deposition Depositionofofpanel panel responsiblefor forthe theDl D ldeformation, deformation,during duringwhich whichpanel panelXXwas B sedimentary rocks is tentatively interpreted to have occurred in a foreland basin; geochronological data B sedimentary rocks is tentatively interpreted to have occurred in a foreland basin; geochronologicaldata on on panel panel BB volcanics volcanicswill will resolve resolvewhether whetherthey they are are autocbthonous autochthonousor or exotic. exotic. D2 D2deformation deformationwas wasrelated related to to back-thrusting, back-thrusting,during duringwhich whichpanels panelsX/B X/Bwere wereoverturned overturnedand andthrust thrustover overpanels panelsA/C. A/C. 44 �PREDICTION AND AND DISCOVERY DISCOVERYOF OFPGE PGEOCCURENCES OCCURENCESIN INTHE THEDULUTH DULUTH COMPLEX COMPLEX AT AT DULUTH DULUTH PREDICTION MILLER, James JamesD., D., Jr., Jr., Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAve., Ave., St. St. Paul, 55114 MILLER, Paul, MN MN 55114 Two intervals intervals of of anomalous anomalousPGE PGEconcentrations concentrationshave haverecently recentlybeen been discovered discovered in in the the medial medial part part of of the the Two series of of the the Duluth Duluth Complex Complex at at Duluth. Duluth. These Thesediscoveries, discoveries,though though far far from from economic, economic, validate validate layered series earlier speculation speculation (Miller, (Miller,1993) 1993)that thatCu-Ni Cu-Nisulfide sulfideand andPGE PGEmineralization mineralization might might be be associated associated with with earlier changes in cumulate cumulate mineralogy mineralogy and texture that are are thought thought to to represent represent interruptions interruptions to to the the abrupt changes steady-statecrystallization crystallization of of the the magma. magma. steady-state The layered layered series seriesat at Duluth Duluth (DLS) (DLS)isisaa4-km-thick 4-km-thickmafic maficlayered layeredintrusion intrusionthat that was was emplaced emplacedin in the the The lower part of of the the North Shore Shore Volcanic Volcanic Group Group (NSVG). Preceeding Proceedingthe theemplacement emplacementof of the the DLS DLS was was the the lower formation of an approximately 1-km-thick accumulation of gabbroic anorthositic rocks of the anorthositic formation of an approximately 1-km-thick accumulation of gabbroic anorthositic series. Despite Despiteaasharp sharpchilled chilledcontact contactbetween betweenthe theDLS DLSand andthe theoverlying overlyinganorthositic anorthositicseries, series,the thetwo two series have identical U-Pb U-Pb ages ages of 1099±0.5 1099kO.5 Ma (Paces and Miller, 1993). Overall, Overall,the the internal internalstructure structure series sheet-like DLS DLS dips dips 25400 25-40Âtotothe theeast, east,roughly roughlyconformable conformablewith with the the enclosing enclosingvolcanic volcanic rocks. rocks. of the sheet-like The cumulate cumulatestratigraphy stratigraphyand and cryptic cryptic layering layering of of the the DLS is consistent with bottom-up fractional fractional The crystallization crystallizationof of aashallow shallow(4-8 (4-8km) km)tholeiitic tholeiiticmagma magmabody bodythat thatwas wasintermittently intermittently open open to recharge recharge and and eruption. The TheDLS DLScan canbe bedivided dividedinto into55stratigraphic stratigraphiczones zones (Miller (Miller and others, 1993). 1993). Above Above aa 200200- to to eruption. 300-m-thick, heterogeneous basal contactzone zoneofofcoarse-grained coarse-grainedolivine olivine gabbro gabbro and and medium-grained medium-grained 300-rn-thick, basal contact troctolite, troctolite, the the DLS DLS passes passes into into to to aa 11-to to 1.5-km-thick 1.5-km-thick troctolite troctolitezone zoneofofmostly mostlyhomogeneous homogeneoustroctolitic troctolitic (Pl+01) cumulates. Marked Markedby by an an abrupt abrupttransition transition to to aa coarse coarse ophitic ophitic olivine olivine gabbro gabbro at its base, a 1-km1-km(P1+01) thick thick cyclic cycliczone zoneisischaracterized characterizedby by atatleast leastfive, five,5050-to to 200-rn-thick, 200-m-thick, macrolayered macrolayered couplets couplets of troctolitic and and gabbroic gabbroic(Pl+Aug+Ox±Ol) (Pl+Aug+Ox*Ol) cumulates. cumulates. Typically Typicallyabrupt abruptreversals reversalsto totroctolitic troctoliticcumulates cumulatesmark markthe the base base of of the the next next cycle. cycle.The Thegabbroic gabbroiccumulate cumulateintervals intervalslocally locallycontain containcmcm-to torn-scale m-scalelayers layersand andlenses lenses of of fine-grained fine-grainedilmenitic ilmeniticolivine olivinegabbro gabbro(microgabbro), (microgabbro),which whichare areclosely closelyassociated associatedwith withthe thePGE PGE mineralization. mineralization.The Thecyclic cycliczone zonegives givesway way to toaa11-to to 1.2-km-thick 1.2-km-thickgabbro gabbrozone zonethat thatisiscomposed composedmostly mostly of with locally locally abundant abundantanorthositic anorthositicseries seriesinclusions. inclusions.The Theupper upper contact contact of iron-rich iron-rich gabbroic cumulates with zone definedby by aaloss lossof of cumulate cumulatetexture textureand and isis very very uneven uneven in in thickness thickness owing owing to the irregular irregular nature nature zone isisdefined of of the the contact contactwith with overlying overlyinganorthositic anorthositic series. series. The Thezone zoneisiscomposed composedof ofaahybrid hybridrange rangeof of rock rocktypes types from from apatitic apatiticquartz quartzferromonzodiorite, ferromonzodiorite,which whichmakes makesup upmost mostof ofthe thezone zonewhere whereititisisthickest, thickest,totobiotitic biotitic ilmenite ilmeniteferrodiorite, ferrodiorite,which whicheverwhere everwhereforms formsthe the"chill" "chill"against againstthe theanorthositic anorthositicseries. series. Many Many models models of of sulfide-hosted sulfide-hostedPGE PGE mineralization mineralization in in mafic mafic layered intrusions (e.g., Campbell and others, 1983; Boudreau and McCallum, 1992) stress the importance others, 1983; Boudreau and McCallum, 1992) stress the importance of disruptions to the steady-state fractional fractionalcrystallization crystallizationby by such suchprocesses processes as as magma magma recharge, recharge, country country rock assimilation, volatile fluxing, and eruption. With recent mapping and petrologic studies fluxing, and eruption. With recent mapping and petrologic studies(Miller (Millerand andothers, others,1993) 1993)indicating indicating such an openness to the DLS system, the Minnesota Geological Survey, with funding from such an openness to the DLS system, the Minnesota Geological Survey, with funding fromthe theMinerals Minerals Coordinating CoordinatingCommittee Committeeof of the the Minnesota MinnesotaState StateLegislature, Legislature, has has set set out out to evaluate evaluate its potential for baseand and precious-metal precious-metal mineralization. mineralization.AAparticular particulartarget targetfor forstudy studywas wasthe themacrolayering macrolayeringof ofthe thecyclic cycliczone. zone. At At intermediate intermediatestages stagesof offractional fractionalcrystallization crystallizationand andunder underlow-pressure low-pressureconditions conditions(1-2 (1-2kb), kb),the theDLS DLS magma magmawas wassaturated saturatedininolivine olivineand andplagioclase plagioclaseand andwas wasevidently evidentlynearing nearingsaturation saturationiningabbroic gabbroicphases phases of of augite augiteand andilmenite. ilmenite.Although Althoughthe thetransitions transitionsfrom fromtroctolitic troctolitictotogabbroic gabbroiccumulates cumulateswithin withinthe thecyclic cyclic zone may have formed from normal crystallization differentiation causing saturation in these phases, the zone may have formed from normal crystallization differentiation abruptness of the transitions and the lack of noticeable cryptic variation across the units suggest that abruptness of the transitions and the lack of noticeable cryptic suggest abrupt abrupt changes changesin in physical physical conditions conditions of of crystallization crystallization also also may have played a role. Such Suchaachange changemay may have been an increase in pressure resulting from volatile (CO2 and perhaps 1120) saturation of have been an increase in pressure resulting from volatile (CO2 and perhaps H20) saturation of the themagma magma in in the the roof roof zone. zone. The Thebuild buildup upofofvolatiles volatilesininthe theroof roofzone zoneisisconsistent consistentwith withthe thepervasive pervasivehydrothermal hydrothermal alteration of the anorthositic series and could have caused failure of the cupola leading to volcanic alteration of the anorthositic series and could have caused failure cupola eruption eruption and and decompression decompressionof of the the chamber. chamber. Evidence Evidenceofofsuch suchdecompression decompressionisissuggested suggestedby bythe thesimilar similar ferrodioritic ferrodioriticcomposition compositionand andfine-grained fine-grainedtexture textureofofthe themicrogabbro rnicrogabbrolayers layerswithin withinthe thegabbroic gabbroic cumulates cumulatesof of the the cyclic cycliczone zoneand and of of the the "chill" "chill"against against the the anorthositic anorthositic cap. cap. Because Becauseof ofthe thestrong strongpositive positive effect effectof of pressure pressureon on water watersolubility solubilityin inmafic maficmagma magma at at low low total total pressures, pressures, decompression decompression may result in water-saturated water-saturatedconditions conditionswhich whichhas hasthe theeffect effect of of dramatically dramatically raising raising the the solidus solidus temperature temperature of the the magma magmaand andthereby therebyquenching quenchingit. it.Such Sucha aprocess processcould couldhave havecaused causedsimultaneous simultaneousrapid rapidcrystallization crystallizationofof 45 �the DLS "chill" "chill"zone zone and and microgabbro microgabbro layers. layers. Water-saturated Water-saturatedconditions conditionsare areindicated indicatedby by the the common common the occurrence of biotite biotite phenocryts phenocryts in in the the DLS DLS "chill". "chill".AAdecompression-quench decompression-quenchorigin originfor forthe theDLS DLS"chill", "chill", occurrence opposed to aa thermal thermal quench, quench, better explains explains the similar similar age of the DLS and anorthositic series and the as opposed the "chill", "chill",which which is is too evolved evolved to be parental to the entire DLS. The Thereturn returnto totroctolitic troctolitic composition of the cumulate crystallization crystallization may have have resulted resulted from from recharge and reinflation of the magma chamber by new new cumulate magma or or may may simply simplyindicate indicateaa return return to tolithostatic lithostaticpressures pressuresfollowing followingcessation cessationof ofvolcanic volcaniceruption. eruption. magma Decompression also also appears appears to have have a negative effect on sulfide sulfide solubility in silicate magmas, at least Decompression (Poulson and and Ohmoto, Ohmoto, 1990). 1990). Evidence Evidencethat thataasulfide sulfidesegregation segregationevent eventaccompanied accompanied at low pressures (Poulson decompression quenching quenching is is given by the discovery discovery of an anomalous concentration of sulfide (0.5 wt %) decompression at the base of aa microgabbro microgabbro layer. layer. Moreover, Moreover,the theconcentration concentrationof of sulfide sulfide(0.10-0.07 (0.10-0.07 wt wt %) %) in in the theupper upper at "chill" zone zone is is in in the the range range expected expectedfor forsulfide sulfidesaturation saturationof of an aniron-rich iron-rich(>10 (>lowt wt%) %)melt meltatatlow lowpressure pressure "chill" (Poulson and and Ohmoto, Ohmoto, 1990). 1990).Finally, Finally,the theobservation observationthat thatthe theaverage averagesulfide sulfideconcentration concentrationin in cumulates cumulates (Poulson below the the cyclic cycliczone zone isis about about 0.02 0.02wt wt %, %, compared compared to to about about 0.06% in the upper part of the intrusion, is below consistentwith with the the magma magmabecoming becoming sulfide sulfidesaturated saturated at at the the time time of cyclic zone formation. Sulfide Sulfide consistent decompression would cause cause segregation segregation of a dense sulfide melt thoughout much of the saturation by decompression magma system system that that could could then then scavenge scavengethe the magma magma of of PGE PGE as as it settled settled to the floor floor of the chamber. chamber. The The magma first occurrence occurrenceof of sulfide sulfidemelt melttotoform formininthis thisway wayshould shouldproduce producethe thehighest highestconcentration concentrationofofPGE. PGE. first Recognizing the the potential potential for for Cu-Ni Cu-Ni sulfide sulfideand and PGE PGE mineralization mineralization to be associated with horizons Recognizing representing perturbations perturbations to to the the steady-state steady-statecrystallization crystallization of the DLS, a suite suite of 50 handsamples were representing selected for for whole whole rock rock and and Pt-Pd-Au Pt-Pd-Au assay analysis. analysis. As Aspredicted predictedby by the themodel modeloutlined outlinedabove, above, selected anomalousPGE PGEconcentrations concentrationswere werefound foundassociated associatedwith withabrupt abruptchanges changesininrock rocktype typeininthe thecyclic cycliczone. zone. anomalous The two two most most PGE-nch PGE-richsamples samplesare aresituated situatedatatsimilar similarinterfaces interfacesbetween between gabbroic gabbroic cumulate cumulateand and The microgabbro and and at at approximately approximatelythe the same samestratigraphic stratigraphic level level within within the second second macrocyclic unit of the microgabbro cyclic zone. zone. The Themost mostanomolous anomoloussample samplehas has444 444ppb ppbPt, Pt,443 443ppb ppbPd, Pd,56 56ppb ppbAu, Au,whereas whereasthe theother otherhas has cyclic 44 ppb ppb Pt, Pt, 108 108ppb ppb Pd, Pd, and and 56 56ppb ppb Au. Au. The Thetwo twosamples samplesdiffer differgreatly greatlyinintheir theirCu-Ni Cu-Nisulfide sulfide 44 concentration with with the the high high PGE PGE sample samplecontaining containing 0.028% 0.028% S, S, 163 163ppm Cu, and 568 ppm Ni and the concentration lower PGE PGE sample samplecontaining containing0.50% 0.50% S, S, 5392 5392ppm ppm Cu, Cu, and and 852 852 ppm Ni. Average AveragePGE PGEconcentrations concentrationsfor for lower the the other other48 48 samples samplesare areapproximately approximately10 10ppb ppbPd, Pd,77ppb ppbPt, Pt,and and44ppb ppbAu. Au. Follow-up studies studiesare are in in progress progress to to confirm confirm and and more more fully fully chararacterize chararacterize the extent and nature of Follow-up this PGE PGE mineralization. mineralization.Nevertheless, Nevertheless,the theimportance importanceofofthis thisdiscovery discoveryisisthat thatititwas waspredicated predicatedon on this detailed characterization characterization of of the theigneous igneousstratigraphy stratigraphyof of the the DLS DLS and and petrologic petrologic interpretations of that detailed stratigraphy. Similar Similardetailed detailedstudies studiesalong alongthe thenorthwestern northwesternmargin marginofofthe theDuluth DuluthComplex Complex(Severson (Severson stratigraphy. and Hauck, Hauck, 1990; 1990;Severson, Severson,1994) 1994)reinforce reinforcethe the contention contention that that such such an an approach approach is the most effective effective and means meansof of evaluating evaluatingthe themineral mineralpotential potentialofoflayered layeredintrusions. intrusions. References References Cited Cited Boudreau, Boudreau,A.E., A.E., and and McCallum, McCallum,I.S., I.S.,1993, 1993,Concentration Concentration of of platinum-group platinum-group elements elements by magmatic fluids fluids in layered intrusions: intrusions:Economic EconomicGeology, Geology,v. v. 87, 87,p. p. 1830-1848. 1830-1848. Miller, Miller, J.D., J.D., Jr., Jr., 1993, 1993,Evidence Evidenceof of interruptions interruptionsduring during fractional fractional crystallization crystallizationof the Duluth Complex layered layered series Inst.on onLake LakeSuperior SuperiorGeology, Geology,v.v.39, 39,part part1,1,p.p.58-59. 58-59. seriesatatDuluth: Duluth:39th 39thInst. Miller, Miller, J.D., J.D., Jr., Jr.,Green, Green,J.C., J.C., and andChandler, Chandler,V.W., V.W., 1993, 1993,Field Field Trip Trip 4: 4: The The geology geology of of the the Duluth Complex Complex at at Duluth: Duluth: 39th 1-157. 39thInst. Inst.on onLake LakeSuperior SuperiorGeology, Geology,v.v.39, 39,part part2,2,p.p.13131-157. Campbell, Campbell,I.H., I.H., Naldrett, Naldrett,A.J., A.J.,and andBarnes, Barnes,S.J., S.J.,1983, 1983,A A model model for for the the origin origin of of platinum-rich platinum-richsulfide sulfide horizons horizons in the Bushveld Bushveldand andStillwater Stillwatercomplexes: complexes:Journal JournalofofPetrology, Petrology,v.v.24, 24,p.p.133-165. 133-165. Paces, Paces,J.B. J.B. and andMiller, Miller,J.D., J.D.,Jr., Jr.,1993, 1993,Precise PreciseU-Pb U-Pbages agesof of Duluth Duluth Complex Complex and and related mafic intrusions, intrusions, northeastern northeasternMinnesota: Minnesota:new newinsights insightsfor forphysical, physical, petrogenetic, petrogenetic, paleomagnetic paleomagnetic and and tectono-magmatic tectono-magmaticprocesses processes associated associatedwith with1.1 1.1Ga GaMidcontinent Midcontinentrifling: rifting:Journal JournalofofGeophysical GeophysicalResearch ResearchV.98, V.98,No NoB8, B8,13,997-14,013. 13,997-14,013. Poulson, H., 1990, 1990,An Anevaluation evaluationof of the the solubility solubility of of sulfide sulfidesulfur sulfur in in silicate silicate melts from from Poulson,S.R. S.R.and andOhmoto, Ohmoto,H., experimental experimentaldata dataand andnatural naturalsamples. samples.Chemical ChemicalGeology, Geology,v.v.85, 85,p.p.57-75. 57-75. Severson, Severson,M.J., M.J.,and andHauck, Hauck,S.A., S.A.,1990, 1990,Geology, Geology,geochemistry, geochemistry, and and stratigraphy stratigraphy of of aa portion of the Partridge Partridge River River Intrusion.University Universityof ofMinnesota-Duluth, Minnesota-Duluth,Natural Natural Resources Resources Research Research Inst. Inst. Technical Technical Report Report 89-11, 89- 1 1 ,236p. 236~. Intrusion. Severson, Severson,M.J., M.J.,1994, 1994,Igneous Igneousstratigraphy stratigraphyof ofthe theSouth SouthKawishiwi Kawishiwiintrusion, intrusion, Duluth Duluth Complex, Complex,northeastern northeastern Minnesota.University UniversityofofMinnesota-Duluth, Minnesota-Duluth,Natural NaturalResources ResourcesResearch ResearchInst. Inst.Technical TechnicalReport Report93/94, 93194,210~. Minnesota. 2 lOp. 46 �Kimberlite indicators in overburden, Michipicoten Xinberlite heavy mineral mineral indicators Michipicoten RiverArea, Northeastern River- Wawa Area, Northeastern Ontario. Ontario. Morris T.F., Morris T.F., Murray Murray C. C. Ontario Ontario G e o l o g i c a l Survey, Survey,933 9 3 3Ramsey R a m s e y Lake Lake Road, R o a d , Sudbury S u d b u r yON ON Geological P3E P 3 E 6B5, 6B5, Canada Canada AND D. Crabtree, D. Crabtree, Ontario Geosciences O ntario G e o s c i e n c e s Centre, C e n t r e , 933 9 3 3Ramsey R a m s e y Lake LakeRoad, R o a d , Sudbury S u d b u r yON ON P3E P 3 E 6B5, 6B5, Canada Canada Two diamonds, and Two diamonds, and possibly aa third, third, were were recovered recovered from from the the Wawa Wawa area area by by C. C. Clement Clement (local (local prospector) prospector) during during the the summer summer of of 1991. 1991. exact location location of of the the discovery discovery site site cannot cannot be be positively positively The exact identified. It is however, that identified. It is thought, thought, however, that the diamonds diamonds were were collected from collected from either either older older alluvium alluvium (sand (sand and and gravel) gravel) in in aa point point bar of of the the Dead Dead River, River, near near the the Michipicoten Michipicoten River Rivermand/or modern bar and/or modern alluvium alluvium (sand (sand and and gravel) gravel) associated associated with with Wawa Wawa Creek. Creek. The The diamond discovery discovery was reported reported to to the the Ontario Ontario Geological Geological Survey Survey (OGS) (OGS) in in the fall the fall of of 1993. 1993. Two diamonds were loaned then forwarded forwarded to Two of of the the 33 diamonds loaned to to the the OGS and then the Royal the Royal Ontario Museum, Department of Mineralogy, Mineralogy, for Ontario Museum, Department of for confirmation. confirmation. The stones stones were were identified identified as as industrial industrial grade grade diamonds diamonds with with carat carat weights weights of of 1.05 1.05 and and 1.13. 1.13. A sampling sampling program program was was initiated initiated by by the the OGS OGS in in September September of of 1993, 1993, in order to establish authenticity authenticity of diamond find. Ten, 25 kg in order to establish of the the diamond find. Ten, 25 kg samples were modern samples were collected collected from from the the reported reported discovery discovery sites: sites: 55 modern alluvium Wawa Creek samples from alluvium samples samples from from Wawa Creek and and 55 older alluvium samples a a point point bar bar associated associated with with the the Dead Dead River. River. Kimberlite indicator minerals (KIM'S) Kimberlite indicator minerals (KIM'S) isolated isolated from from these these samples samples include one "Gb" nG1Ongarnet garnet with with aa kelyphite kelyphite rim, rim, and 99 chrome chrome include one diopsides. Most of these indicators were recovered from the diopsides. these indicators were recovered from the Dead Dead River River point point bar bar and and verified verified that that the the 22 industrial industrial grade grade diamonds diamonds could could have have been been recovered recovered from from this this site. site. As preliminary discoveries, discoveries, the OGS OGS undertook undertook As aa follow-up follow-up to to these preliminary regional sampling program in the Michipicoten Michipicoten RiverRiver- Wawa Wawa area in a regional sampling program in the the the summer summer of of 1994. 1994. The The area area was was considered considered optimal optimalfor forkiinberlite kimberlite exploration as: a) a) it includes includes the the area area where the the 22 diamonds diamonds and and exploration as: associated heavy minerals were were recovered; recovered; b) bedrock bedrock and and overburden overburden associated heavy minerals geology is understood (Morris 1992a, 1992b; 1992b; Sage Sage geology is well understood (Morris 1990, 1990, 1991, 1991, 1992a, area is Kapuskasing structural 1994); the area 1994); and and C) c) the is close close to to the the Kapuskasing structural zone, zone, (Boland and an area area thought thought to to be be aa favourable favourable kimberlite kimberlite host host (Boland and 1989). Ellis Ellis 1989) 47 �Methodology, recommendations for kimberlite e~~loration exploration Methodology, results results and and recommendations for kimberlite from the 1994 1994 summer summer field field program program are are presented presented in in Morris Morris et et al. al. from (1994). (1994). indicators identified from from the the Michipicoten Michipicoten Kimberlite indicators RiverRiver- Wawa Wawa area area include: include: a) a) 44 "Gb" "GIOHchrome chromepyrope.garnets pyrope garnets and and 37 37 1G911 chrome garnets; b) 44 high chrome chromites chromites and and 104 104 low low "G9" chrome pyrope pyrope garnets; high chrome chrome magnesium rich chrome chrome chromites; chromites; c) c) 121 121 magnesium rich ilmenites; ilmenites; and and d) d) 39 39 chrome diopsides. diopsides. Several Several areas areas were were identified identified as as favourable favourable' for for kimberlite kimberlite exploration from: from: a) a) the the distribution of total total KIM'S; b) evaluating exploration distribution of evaluating site site results results e.g. e.g. the presence presence or or absence absence of of significant significant KIM'S KIM1s ( "GIO1 s and chrome chromites); chromites); and and C) c) the the variety variety of of KIM's. KIM'S. ("GlO's and high chrome All All of of the the favourable favourable areas areas exist exist on, on, or or southeast southeast of, of, the the northern northern margin margin of of the the Kapuskasing Kapuskasing structural structural zone. zone. References References Cited Cited Boland A.V. and and Ellis Ellis R.M. R.M. 1989. 1989. Velocity Velocity structure structure of of the the . Kapuskasing Kapuskasing uplift, uplift, northern northern Ontario, Ontario, from from seismic seismic refraction refraction studies; studies; Journal Journal of of Geophysical Geophysical Research, Research, v.94, v.94, n.B6, n.B6, p.7189p.71897204. 7204. Morris T.F. 1990. 1990. Quaternary Quaternary geology geology of of the the Wawa area, northern northern Morris Wawa area, Ontario; in in Summary Summary of of Field Field Work Work and and Other OtherActivities Activities1990,. 1990,. Ontario; Ontario Ontario Geological Geological Survey, Survey, Miscellaneous Miscellaneous Paper Paper 151, 151, p.149-151. p.149-151. Morris northern Morris T.F. T.F. 1991. 1991. Quaternary Quaternary geology geology of of the the Dog Dog Lake Lake area, area, northern Ontario; Ontario; in in Summary Summary of of Field Field Work Work and and Other Other Activities Activities 1991, 1991, Ontario Ontario Geological Geological Survey, Survey, Miscellaneous Miscellaneous Paper Paper 157, 157, p.149-151. p.149-151. Morris Morris T.F. T.F. 1992a. 1992a. Quaternary Quaternary geology geology of of the the Wawa Wawa area; area; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Map Map 192, 192, scale scale 1:50 1:50 000. 000. Morris 1992b. Quaternary Quaternary geology, geology, Dog Dog Lake Lake area, area, northern northern Morris T.F. 1992b. Ontario; Ontario; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Map Map 199, 199, scale scale 1:50 1:50 000. 000. Morris overburden Morris T.F., T.F., Murray Murray C. C. and and Crabtree Crabtree D. D. 1994. 1994. Results Results of of overburden sampling sampling for for Kimberlite Kimberlite heavy heavy mineral mineral indicators indicators and and gold gold grains, grains, Michipicoten Michipicoten RiverRiver- Wawa Wawa area, area, northeastern northeastern Ontario; Ontario; Ontario 69p. Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5908, 5908, 69p. Sage Sage R.P. 1994. 1994. Geology Geology of of the the Michipicoten Michipicoten Greenstone Greenstone Belt; Belt; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5888, 5888, 592 592 p. p. 48 �Heavy mineral mineral indicators, indicators, Wawa Wawa Area Area Heavy Morris T.F.', T.F.*~Murray Murray C. C. Morris Ontario G e o l o g i c a l S u r v e y f 933 Ramsey Lake Roadf Sudbury Sudbury ON ON Ontario Geological Survey, 933 Ramsey Lake Road, P3E 6B5, 6B5/ Canada Canada P3E AND Crabtree# D. D. Crabtree, O n t a r i o Geosciences Geosciences Centre, C e n t r e , 933 933 Ramsey Ramsey Lake Lake Road, Roadf Sudbury Sudbury ON ON Ontario P3E 6B5, 6B5, Canada Canada P3E Two diamonds, diamondsI and and possibly possibly aa third, thirdl were were recovered recovered from from the the Wawa Wawa Two area by by C. C. Clement Clement (local (local prospector) prospector) during during the the summer s m e r of of 1991. 1991. area The exact exact location location of of the the discovery discovery site site cannot cannot be be positively positively The identified. It is is thought, thoughtl however, howeverl that that the the diamonds diamonds were were identified. It collected from from either either older older alluvium alluvium (sand (sandand and gravel) gravel) in in aa point point collected bar of of the the Dead Dead River, Riverl near near the the Michipicoten Michipicoten River River and/or and/or modern modern bar alluvium (sand (sandand and gravel) gravel) associated associated with with Wawa Wawa Creek. Creek. The The diamond diamond alluvium discovery was was reported reported to to the the Ontario Ontario Geological Geological Survey Survey (OGS) (OGS)in in discovery the fall fall of of 1993. 1993. the diamonds were were loaned loaned to to the the OGS OGS and and then then forwarded forwardedto to Two of of the the 33 diamords Two the Royal Ontario Museuml Department of Mineralogyl for the Royal Ontario Museum, Department of Mineralogy, for confirmation. The The stones stones were were identified identified as as industrial industrial grade grade confirmation. diamonds with with carat carat weights weights of of 1.05 1.05 and and 1.13. 1.13. diamonds , sampling program program was was initiated initiated by by the the OGS OGS in in September September of of 1993, 1993# AA sampling in order to establish authenticity of the diamond find. Tenl 25 kg kg in order to establish authenticity of the diamond find. Ten, 25 samples were collected from the reported discovery sites: 5 modern samples were collected from the reported discovery sites: 5 modern alluvium samples samples from from Wawa Wawa Creek Creek and and 55 older older alluvium samples from from alluvium alluvium samples a point bar associated with the Dead River. a point bar associated with the Dead River. 6 Kimberlite indicator indicatorminerals minerals(KIM'S) (KIM'S)isolated isolatedfrom fromthese thesesaxiples samples Kimberlite include one ItGlOt1 garnet with a kelyphite riml and 9 chrome include "Gb" garnet with a kelyphite rim, and 9 chrome diopsides. Most of these indicators were recovered from the Dead diopsides. Most of these indicators were recovered from the Dead industrial grade diamonds River point bar and verified that the 2 River point bar and verified that the 2 industrial grade diamonds could have have been been recovered recovered from from this this site. site. could As aa follow-up follow-upto to these these preliminary preliminary discoveries, discoverieslthe the OGS OGS undertook undertook As a regional sampling program in the Michipicoten RiverWawa areain in a regional sampling program in the Michipicotn River- Wawa area the s m e r of 1994. The area was considered optimal for kimberlite the summer of 1994. The area was considered optimal for kimberlite exploration as: as: a) a) it it includes includes the the area area where where the the 22 diamonds diamonds and and exploration associated heavy minerals were recovered; b) bedrock and overburden associated heavy minerals were recovered; b) bedrock and overburden geology is is well well understood understood (Morris (Morris1990, 199011991, 199111992a, 1992a11992b; 1992b; Sage Sage geology 1994) ; and c) the area is close to the Kapuskasing structural zonel 1994); and c) the area is close to the Kapuskasing structural zone, an area area thought thought to to be be aa favourable favourable kimberlite kimberlite host host (Boland (Boland and and an Ellis 1989) 1989). Ellis 49 �Methodologylresults resultsand and recommendations recommendationsfor for kimberlite kimberlite exploration exploration Methodology, from the 1994 summer field program are presented in Morris et al. al. from the 1994 summer field program are presented in Morris et (1994). Kimberlite Kimberlite indicators indicators identified identified from from the the Michipicoten Michipicoten (1994). 4 nGIOn chrome pyrope garnets and 37 37 RiverWawa area include: a) River- Wawa area include: a) 4 "Gb" chrome pyrope gamete and 4 high chrome chromites and 104 low 11G911 chrome pyrope garnets; b) "G9" chrome pyrope gamnets; b) 4 high chrome chromites and 104 low chrome chromites; chromites;C) c) 121 121 magnesium magnesium rich rich ilmenites; ilmenites;and and d) d) 39 39 chrome chrome chrome diopsides. diops ides. Several areas areas were were' identified identified as as favourable favourable for for kimberlite kimberlite Several exploration from: a) the distribution of total KIM1s; b) evaluating exploration from: a) the distribution of total KIM'S; b) evaluating site results e.g. the presence or absence of significant KIM1s site results e.g. the presence or absence of significant KIM'S (llGIO1s and high chrome chromites) ; and c) the variety of KIM1s. ("GlO's and high chrome chromites); and c) the variety of KIM'S. All of of the the favourable favourable areas areas exist exist on, onl or or southeast southeast of, ofl the the northern northern All margin of the Kapuskasing structural zone. margin of the Kapuskasing structural zone. References Cited Cited References Boland A.V. A.V. and and Ellis Ellis R.M. R.M. 1989. 1989. Velocity Velocity structure structure of of the the Boland Kapuskasing upliftl northern Ontario, from seismic refraction Kapuskasing- uplift, northern Ontario, from seismic refraction n.B6 p.7189p. 7189studies; Journal Journal of of Geophysical Geophysical Research, ~ e s e a r c hv.94, v. ~ 94 n.B6, studies; 7204. 7204. Morris T.F. T.F. 1990. 1990. Quaternary Quaternary geology geology of of the the Wawa Wawa area, arealnorthern northern Morris Ontario; in in Summary Summary of of Field Field Work Work and and Other OtherActivities Activities1990, 19901 Ontario; Ontario Geological Geological Survey, Surveyl Miscellaneous Miscellaneous Paper Paper 151, 1511p.149-151. p.149-151. Ontario Morris T.F. T.F. 1991. 1991. Quaternary Quaternary geology geology of of the the Dog Dog Lake Lake area, areal northern Morris northern in Summary Summary of of Field Field Work Work and and Other OtherActivities Activities1991, 19911 Ontario; in Ontario; Ontario Geological Geological Survey, SurveylMiscellaneous MiscellaneousPaper Paper157, 1571p.149-151. p.149-151. Ontario Morris T.F. T.F. 1992a. 1992a. Quatemnary Quaternary geology geology of of the the Wawa Wawa area; area; Ontario Ontario Morris Geological Survey, Surveyl Open Open File File Map Map 192, 192# scale scale 1:50 1:50 000. 000. Geological Morris T.F. T.F. 1992b. 1992b. Quaternary Quaternary geology, geologyl Dog Dog Lake Lake area, area, northern northern Morris Ontario; Ontario Ontario Geological Geological Survey, Surveyl Open Open File File Map Map 199, 19g1 scale scale Ontario; 1:50 000. 000. 1:50 Morris T.F., T.F.! Murray Murray C. C. and and Crabtree Crabtree D. D. 1994. 1994. Results Results of of overburden overburden Morris sampling for for Kimberlite Kimberlite heavy heavy mineral mineral indicators indicators and and gold gold sampling grainsl Michipicoten Michipicoten RiverRiver- Wawa Wawa area, arealnortheastern northeasternOntario; Ontario; grains, Geological Survey, SurveylOpen Open File File Report Report 5908, 5908169p. 69p. Ontario Geological Ontario Sage R.P. R.P. 1994. 1994. Geology Geology of of the the Michipicoten MichipicotenGreenstone GreenstoneBelt; Belt; Sage Ontario Geological Geological Survey, Surveyl Open Open File File Report Report 5888, 58881 592 592 p. p. Ontario * Denotes Denotes speaker speaker * 50 �THE CURRENT CURR.ENT SETTING SETTING OF OF THE THE HEMLO HEMLOGOLD GOLDDEPOSIT, DEPOSIT, ONTARIO: ONTARIO: THE IMPORTANCE OF FUNDAMENTAL RELATIONSHIPS IMPORTANCE OF FUNDAMENTAL RELATIONSHIPS Muir, T.L., Ontario Ontario Geological Geological Survey, Sudbuiy, Sudbury, Ontario, P3E 6B5 The deformed Hemlo Gold Deposit (HGD) occurs occurswithin within moderately to strongly strongly strained, strained, folded, transposed, and metamorphosed metamorphosedvolcano-sedimentary volcano-sedimentary rocks rocks of of the the Hemlo-Schreiber greenstone greenstone transposed, and Lithologicinterpretation interpretationininthis thispart partofofthe thebelt beltisisimpeded impededby by polyphase polyphase strain, strain, possibly belt. Lithologic hydrothermal events. Many Many of of the the polyphase metamorphism, and bcally locally extensive, extensive, complex complexhydrothermal interrelationships among these these events events are are not not well well constrained. constrained. Strain superposed on the HGD is (medium grade) grade) or or Metamorphismhas hasaffected affected the the deposit depositin in11(medium of one, and likely 2, generations. Metamorphism events. The Thedeposit depositappears appearstotopredate predatefelsic felsicplutonism, plutonism,which whichpredates predatesaaD3 D3dextral dextralshear shear more events. event. event. nor strata bound. Much The HGD is neither stratiform nor Much of of the the deposit deposit currently: currently: -occurs on the hanging wall side of the south limb of a large-scale, large-scale, S-shaped fold, fold, delineated delineated,,in part, quartz-plagioclase-phyric rocks; part7by bymassive massiveand andfragmental, fragmental,felsic, felsic, quartz-plagioclase-phyric -lies largely within within 22 or or more, closely spaced, 290'-striking 290°-striking high-strain high-strain zones, zones, that that occur within most pervasive, pervasive, highly highly strained part part of of an an otherwise otherwisewesterly westerlystriking strikingbelt; belt; and and the most -transgresses transposed units units such suchthat thatititisishosted hostedlargely largelyby by highly highly altered altered sedimentary sedimentary rocks rocks in in -transgresses transposed quartz-plagioclase-phyricrocks in east and and central central parts, parts, and and by by altered altered sedimentary sedimentary rocks rocks and and quartz-plagioclase-phyric the east part. the west part. Ore-grade mineralization and at least some types of alteration are presently structurally controlled at various scales. Notable Notablechanges changesininalteration alterationand andmineralization mineralization occur occur from from one one part part deposit to to another, another,particularly particularlyspatially spatiallyassociated associatedwith with an aninflection inflection in in the the greenstone greenstonebelt, belt, of the deposit from W-striking There is is an an extensive envelope of altered rocks W-striking to to WNW-striking. WNW-striking. There rocks in in the the west west Strain,metamorphism, metamorphism, end of the deposit and a narrow alteration envelope towards the east end. Strain, superposed on on the the HGD HGD have have modified modified various aspects aspects of the primary alteration and alteration superposed country rocks, rocks, and and and mineralization characteristics, which has resulted in additional alteration of country remobilization of Au, Mo, Hg, As, and and Ba. Ba. Hg, As, Various depositional to the HGD. Establishing depositional models have been applied to Establishingfundamental findamental field relationships is of paramount importance importance for evaluating evaluating the appropriateness appropriatenessof of aa given given model. model. Particular attention attention must be given to: -- iidentifying d e n t i ~ n gprotoliths protoliths and establishing contact relationships, both both of which are are critical to to some depositional models; depositional models; -determining which are synchronous synchronous with which generations generations of of structural structural elements predate, predate, postdate, postdate, or are the deposit; deposit; -distinguishing features hydrothermal features resulting from regional metamorphic events as opposed to hydrothermal alteration events, and putting into context their relative timing with respect to structural context their structural elements; and current features -characterizing what current features of the deposit deposit reflect reflect modification by events subsequent to emplacement. emplacement. Other sites within the Hemlo--Schreiber greenstone greenstone belt, belt7which which contain contain barite barite and and display display to that of the HGD, may reflect large-scale, synchronous or diachronous alteration similar to hydrothermal events. events. 51 �KEWEENAWAN UPLIFT UPLIFT AND AND SUPERGENE SUPERGENE KEWEENAWAN SUPERIOR-TYPE IRON FORMATION SUPERIOR-TYPE IRON FORMATION OXIDATION OXIDATION OF OF PRE-PENOKEAN? PRE-PENOKEAN, Jon North North Jon 22 Gurdwara Gurdwara Road, Road, Nepean, Nepean? Ontario, Ontario? WMC International Limited, Limited? 22 WMC International Canada K2E 8A2 Canada K2E 8A2 The Riverton Riverton and and Negaunee Negaunee Iron Iron Formations Formations are are lower lower The Proterozoic Superior-Type Iron Formation respectively within the Proterozoic Superior-Type Iron Formation respectively within the Paint River and Menominee Groups, Marquette Range Supergroup, Paint River and Menominee Groups, Marquette Range Supergroup, Michigan (Figure (Figure 1). 1). The The primary primary iron iron formation formation is is carbonate carbonate or or Michigan oxide facies and contains 20 to 30% iron. The Marquette Range oxide facies and contains 20 to 30% iron. The Marquette Range Supergroup was was deformed deformed and and metamorphosed metamorphosed during during the the Ca. ca. 1.85 1.85 Ga Ga Supergroup Penokean orogeny and subsequently intruded and overlain by rocks of Penokean orogeny and subsequently intruded and overlain by rocks of the Keweenawan Rift at ca. 1.1 Ga. Stratabound bodies of secondary, the Keweenawan Rift at Ca. 1.1 Ga. Stratabound bodies of secondary, massive hematite-goethite hematite-goethite containing containing greater greater than than 50% 50% iron iron were were massive The orebodies orebodies mined as as high high grade grade direct direct shipping shipping soft" "soft"iron iron ores. ores. The mined occupy axes axes of of plunging plunging synclines synclines or or other other upward-opening upward-opening occupy structures in in contact contact with with footwall footwallaquicludes, aquicludes, they they are are not not structures deformed, and of lower metamorphic grade than their host rocks. deformed, and of lower metamorphic grade than their host rocks. Riverton Iron Iron Soft iron iron ore ore is is at at maximum maximum depths depths of of 800 800 mm in in the the Riverton Soft Formation and 1800 m in the Negaunee Iron Formation. Formation and 1800 m in the Negaunee Iron Formation. i) Formation of of soft soft iron iron ore ore is is aa two two stage stage process process of of i) Formation widespread pseudomorphism of siderite by hematite and goethite and widespread pseudomorphism of siderite by hematite and goethite and ii) dissolution dissolution of of chert by hematite hematite and and goethite. goethite. ii) chert and and replacement replacement by Mn is is fractionated fractionated from from iron iron and and depleted depleted in in iron iron ore ore relative relative to to Mn primary iron iron formation. formation. The The isotopes isotopes of of oxygen oxygen in in iron iron oxide oxide primary minerals imply imply that that the the iron iron oxides oxides interacted interacted with with waters waters with with minerals variable18°sNow 618~sMow of -6.85 -6.85 to to 16.69 16.69 per per mil. mil. Present Present meteoric meteoric waters waters of variable latitude of of the the Paint Paint River River Group Group are are ca. ca. -10 -10per per mil. mil. at the the latitude at Hence, the the soft soft iron iron ores ores probably probably formed formed by by the the interaction interaction Hence, of meteoric meteoric water water with with primary primary iron iron formation formation but but not not present present of meteoric water. water. Because Because Mn Mn and and Fe Fe can can be be dissolved dissolved in in waters waters of of low low meteoric pH but but ferric ferric oxides oxides or or hydroxides hydroxides precipitate precipitate at at high high Eh Eh whereas whereas pH manganous ions ions can can be be transported transported at at high high Eh, Eh, the the fractionation fractionationof of manganous Mn from Fe in the iron ores implies that they formed at low pH and Mn from Fe in the iron ores implies that they formed at low pH and high Eh Eh as as in in acidic acidic supergene supergene weathering weatheringprofiles. profiles. high The soft iron ores most likely formed when the water water table table was was The soft iron ores most likely formed when the lowered because of uplift of the Marquette Range Supergroup on the lowered because of uplift of the Marquette Range Supergroup on the south ridge and flank of the Keweenawan Rift at about 1.1 Ga and, south ridge and flank of the Keweenawan Rift at about 1.1 Ga and, meteoric water water descended descended through through the the iron ironformations, formations, along along aa meteoric footwall aquiclude to the static water table. Hence they represent footwall aquiclude to the static water table. Hence they represent supergene oxidation oxidation of of primary primary chert-siderite chert-siderite iron iron formation formation supergene analogous to karstification with an iron oxide residue. The analogous to karstification with an iron oxide residue. The differential maximum depths of the oxidation of the iron formations differential maximum depths of the oxidation of the iron formations to soft soft iron iron ores ores is is evidence evidence of of differential differential uplift uplift of of the the rift rift to 2). flanks across a profile resembling a fedora hat (Figure flanks across a profile resembling a fedora hat (Figure 2). 52 �______ EXPLANATION Main Iron Formations L0I 1.1 volcanic rocks Duluth Gabbro, Nipigon CoIdwell Complex Ga.— Sibley Group 1.5 Ga.— Anorogenic Granite 1.8 Go.— Ii ,1 2.7 Keweenawai, Rift sedimentary rocks Keweenawan Rift Wisconsin Magmatic Terrane Marquette Range Supergroup Archean FIGURE South outcrop of rift rocks 1 North Rift Axis 0 NEGAUNEE IRON —2 KILOMETRES FORMATION Soft Orebodies 1o o V.,tcaI £xogg.roton 25X FIGURE 2 FIGURE 2 53 �Targeting Massive Massive Sulfide Sulfide Deposit Deposit Exploration Exploration Targeting in in the the Western Western Vermilion Vermilion District: District: Volcanological Controls Controls Volcanological Peterson,DeanM., M. ,Department DepartmentofofGeology, Geology,University University of of Peterson,Dean Minnesota, Duluth Minnesota, Duluth The last last ten ten years years has has been been aa period period of of rapid rapid growth growth in in the the The understanding of of the the formation formation of of volcanogenic volcanogenic massive massive sulfide sulfide understanding deposits. deposits. Numerous Numerous detailed detailed studies studies in in established established mining mining camps camps ~ l i n Flon, Sturgeon Lake, etc.) provides data data that that (Noranda, (Noranda, Fun Flon, Sturgeon Lake, etc.) provides allows deposit deposit characteristics characteristics and and volcanic volcanic facies facies changes changes to to be be allows observed observed and and correlated. correlated. These These studies studies have have made made it it possible possible to: to: 1) 1) Describe Describe characteristics characteristicsand and facies faciesof ofvolcanic volcanicrocks, rocks, 2) 2) Discuss Discuss methods methods of of deposition depositionand and eruption, eruption, 3) 3) Describe ~escribemineralogy mineralogy and and zoning zoning patterns patterns of of alteration, alteration, 4) 4) Describe Describe the the significance significanceof of synvolcanic synvolcanicintrusions, intrusions, 5) 5) Discuss Discuss depositional depositional environments environments of of massive massive sulfide sulfide deposits. deposits. In In the the western western Vermilion Vermilion District District (Figure (Figure1), I), volcanic volcanic reconstruction reconstruction is is the the key key to to targeting targeting favorable favorable volcanic volcanic successions successions for for massive massive sulfide sulfide deposit deposit exploration. exploration. Detailed Detailed mapping mapping by by the the author author over over the the last last two two years years indicates indicates two two areas areas have favorable favorable volcanic volcanic characteristics characteristics for for hosting hosting such such have deposits. These These areas areas include: include: 1) 1) The The uppermost uppermost two-mile two-milesection section deposits. of the the Lower Lower Ely Ely Greenstone Greenstone (LEG), (LEG),and and 2) 2) The The informally informally named named of Gafvert Gafvert Lake Lake Felsic Felsic Complex. Complex. Previous Previous mapping mapping in in the the Lower Lower Ely Ely Greenstone Greenstone indicated indicated that that the the formation formation is is composed composed of of roughly roughly 99% 99% massive massive and and pillowed pillowed basalt. basalt. Recent Recent mapping mapping (1:1,250 (1:1,250to to 1:10,000) 1:10,000)in inthe the Fivemile FivemileLake Lake area area (Figure (Figure2) 2) of of the the LEG LEG documented documented many many classic classic features features associated associated with with massive massive sulfide sulfide deposits. deposits. These These features features include: include: 1) semi-conformable 1) Regional, ~egional, semi-conformablealteration, alteration, 2) 2) Cross-cutting, Cross-cutting,base-metal base-metal bearing bearing chlorite chlorite alteration alterationpipes, pipes, 3) 3) Four Four mafic-felsic mafic-felsic volcanic volcanic cycles cycles (the (thetwo two mile mile section sectionis is 30% 30% felsic felsic breccias, breccias,lavas, lavas,and andtuffs), tuffs), 4) 4) Synvolcanic ~ynvolcanicfaults faults with with associated associated debris debris flow flow deposits. deposits. The The informally informally named named Gafvert Gafvert Lake Lake Felsic Felsic Complex Complex(Figure (Figure3) 3) is is aa north north facing, facing, composite composite dacitic dacitic volcanic volcanic complex complex overlying overlying the orm mat ion. The The complex complex is is cored cored by by large largemasses masses the Soudan Soudan Iron Iron Formation. of of quartz-feldspar quartz-feldspar porphyry porphyry and and blocky blocky dacitic dacitic lava lava flows. flows.Course Course blocky blocky pyroclastic pyroclastic flow flowdeposits deposits grade grade outward outwardand and interdigitate interdigitate with epiclasticrocks. rocks.Thick Thicksillsillwith fine-grained fine-graineddacitic dacitic tuffs tuffs and and epiclastic like like masses masses of of quartz-feldspar quartz-feldsparporphyry porphyry occur occur throughout throughout the the complex. complex. The The complex complex is is capped capped by by aa large large mass mass of of carbonate carbonate fades faciesiron ironformation formationthat that grades grades outward outward into into oxide oxide fades faciesiron iron formation. formation. Lenses Lenses of of massive massive pyrite pyrite occur occur directly directly above abovethe the complex complex within within basalts basalts of of the theUpper Upper Ely Ely Greenstone. Greenstone.The TheGafvert Gafvert Lake Lake Felsic Felsic Complex Complex has has many many volcanic volcanic features featuresanalagous analagouswith with Kuroko Kuroko Type Type Massive Massive Sulfide Sulfidedeposits. deposits. 54 �N -A' — sir - Basalt + + + + + + + + + I!I + + + + +++ w.r9Yore.n.ton>6 + + + + + + + + + + + ÷ + + + + +__---/VVV' + I - Mdsalt. Fdelc + 2j-c'vvvVvVvvvvv' I ,IUP ? s+o1: + ++ + + +++ MeSa + + IVVVVVVVVVVVVVVVV + ;I2S? Miles Figure 1 - — - Quartz Quartz Feldspar FeldsparPorphyry Porphyy — Felsic Pyroclastic PyroclosticFlow flow Deposits Deposits - — luff and - Felsic Felsic Tuff ondEpiclastic EpiclaaticRocks Rock — Oxide Oxide Facies Focies Iron Iron Formation Formotion - — - Felsic Felsic Lava Lava flows flow [] — Basaltic Volcanic - Basoltic VolcanicRocks Rocks - Rhycilte — I MeSa — Manly. Basalt Gabbro/Dlodt. Pillow Basalt Felule - MeSs -Ba Folsic Xl Tuff — Fslslc Br.ccla - Bedded Scorla L Figure I - —Carbonate Focies lron Formation DiabaseSills Sills [11111 Carbonate Fades Iron Formation [] — Diabase - FiUlo 0 •A Gafvert Lake Lake Felsic Felsic Complex Complex — Massive Massive Pyrlte Pyrite — FelsIc Brsccla I SoudwJronFormdtioj++,/v v v v v v v v v v v v v v v' + — F.lsc Brsccla - RhyolBe lo Miles w LI 55 �Geological, Geophysical and Geochemical Compilation of the Western Vermilion District: Targeting for Gold and Massive Sulfide Deposits Peterson, Dean M., Department of Geology, University of Minnesota,- Duluth Mineral exploration for gold and massive sulfide deposits in the Western Vermilion District has occurred sporadically since the late 1960's. No minable deposits have been discovered, however, these efforts have greatly increased the understanding of the geological characteristics of the district. A digital compilation of all available geological and geochemical data has been integrated into a mineral potential interpretation of the District. The data includes 7573 assays from 2097 outcrop samples and 176 drill holes, integrated geology from the authors mapping, terminated lease files, thesis maps, and government maps. Contoured aeromagnetic data for the area is part of the statewide 1/4 mile spaced Aeromagnetic Program of the Minnesota Geological Survey. Over the last thirty years, 145 holes have been drilled for gold in the western Vermilion District. Gold mineralization discovered to date is concentrated within three structurally controlled domains. These domains include: 1) The wedge shaped block between the Vermilion Fault and the Mud Creek Shear Zone. Mineralization generally occurs at the brecciated contacts of iron formations and quartz-feldspar porphyry bodies. Gold is concentrated in the breccia zones with quartz-pyrite-arsenopyrite matrix. 2) The wedge shaped block between the Shagawa Lake Deformation Zone and Burntside Lake Fault. 3) within sheared and carbonatized basalt and porphyries along the Murray Shear zone Exploration for massive sulfide deposits has generally been targeted upon geophysical anomalies (EM conductors and magnetic highs) within the Upper Ely Greenstone and Soudan Iron Formations. The vast majority of this work occurred during the late 1960's and early 1970's. Recent mapping by the author indicates that large, well exposed areas of the western Vermilion District have yet to be explored for massive sulfide deposits. These areas include the Gafvert Lake Felsic Complex and the Lower Ely Greenstone Formation. 56 �STRUCTURAL EVOLUTION RELATIONSHIPS OF THE MANIMANISTRUCTURAL EVOLUTION AND AND AGE AGE RELATIONSHIPS OF THE TOUWADGE GREENSTONE GREENSTONE BELT BELT AND AND WAWA-QUETICO WAWA-QUETICO SUBPROVINCE, SUBPROVINCE, TOUWADGE SOUTHWESTERN SUPERIOR SUPERIOR PROVINCE, PROVINCE, ONTARIO ONTARIO Peterson, Department DepartmentofofGeosciences, Geosciences, Western Western Carolina Carolina University, University, Cullowhee, Cullowhee, North V.L. Peterson, Carolina, Carolina, 28723, 28723, U.S.A.; U.S.A.; E. Zaleski Zaleski and 0. 0.van vanBreemen, Breemen,Geological Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario, Ontario,K1A KIA 0E8 OE8 preferred structuraJ structural model model for for the theManitouwadge Manitouwadge greenstone greenstone belt belt (northern (northern Wawa Wawa subsubOur preferred ductile deformation deformation (Fig(Figthe adjacent adjacent Quetico Queticosubprovince subprovinceinvolves involves four four phases phases of ductile province), and the 2720Ma Mamafic-to-felsic mafic-to-felsic volcanic volcanic sequence, sequence, repeated Thegreenstone greenstonebelt beltcomprises comprisesaa2720 ure). The repeated across an easterly-trending syncline with with aa central centralcore coreof of metagreywacke. metagreywacke. Interlayered Interlayered metamormetamoreasterly-trending D2 syndine the volcanic volcanic sequence sequence north of of the the phosed felsic volcanic volcanic rocks, rocks, iron iron formation formation and and altered rocks in the syncline are are host host to t ovolcanogenic volcanogenic Cu-Zn ductile faults and folds, folds, interpreted from D2 syncine Cu-Zn deposits. deposits. D Dll ductile detailed mapping in the the area area of of known known base-metal base-metal deposits, deposits, repeat repeat mineralized mineralized horizons. horizons. D3/D4 D3/D4 detailed progressive dextral transpression produced produced the distinctive distinctive synformal synformal structure structure of of shortening and progressive D land andD2 D2structures, structures,and andinvolved involvedQuetico Queticometasedimentary metasedimentary the Manitouwadge Manitouwadge belt, reoriented reoriented Dl the rocks rocks in map-scale map-scale folds. folds. The Thetiming timingofofstructural structuralevents eventsand andaccompanying accompanyingamphibolite-facies amphibolite-facies metamorphism is is partly partly constrained constrainedby bythe theresults resultsofofan anongoing ongoingU-Pb U-Pbgeochronological geochronological study. study. metamorphism --- - Foliated K—feldspar porphyritic granitold Foliated trondjbemlte, tonalite. felsic meta— volcanic rocks, slllimanfte—mnscovit,e schist E: Metagreywacke Black Plc batholith Orthoainphibole—cordlerite—garnet gnelss Metamorphosed Iron formation Intermediat, to me! Ic metavolcanic rocks Fold anial trace Aeromainetic or foliation trend - Geology and location map of the Manitouwadge Manitouwadge greenstone G=Geco mine, mine, W=Willroy W=Willroy mine, mine, Geology greenstone belt. G=Geco NC=Nama NC=Nama Creek Creek mine, mine, E=Willecho E=Willecho mine. mine. D l faults faults(shear (shearzones) zones)are arerecognized recognized from from the thecoincidence coincidence of of truncated truncated lithological lithological units, units, Dl repeated mineralized mineralized sequences, sequences, and zones of gneiss interpreted annealed mylonite. mylonite. In In repeated of straight gneiss interpreted as annealed addition D lplanar planarfabrics fabricsare arepreserved preservedlocally locallyininthe thehinge hingeregions regions addition to t ozones zones of of straight straightgneiss, gneiss, Dl of D2 folds. folds. Although Althoughno nosense senseofofkinematics kinematicsororoffset offsethas hasbeen beenobserved, observed,sequence sequencerepetitions, repetitions, of D2 geometries consistent consistent with low angle early relative relative age age of of these these structures structures is is geometries with low angle truncation, truncation, and the early suggestive suggestive of of thrusting. thrusting. D2 structures structuresinclude include the thedominant dominantplanar planarand andlinear linearfabrics fabricsand andmany manyof ofthe theoutcrop-scale outcrop-scalefolds, folds, D2 D2fabrics fabricsare aretypically typicallydefined defined by by high high grade grade metamorphic metamorphic minerals, minerals, locally with with sheath sheathgeometry. geometry. D2 locally D2map-scale map-scalefolds, folds, suggesting deformation deformationbroadly broadly synchronous synchronouswith withpeak peakmetamorphism. metamorphism.Among AmongD2 suggesting sheath fold fold repeats repeats aamajor majorDl D lfault faultand andthe themineralized mineralizedsequence sequence in in the thehinge hinge region region of of the the aa sheath D3 Manitouwadge Manitouwadge synform. synform. D2 D2 shortening shortening resulted resulted in in repetition repetitionofofthe thevolcanic volcanicsequence sequence across across D3 theeasterly easterlytrending trendingsyncline synclineon onthe thesouthern southernlimb limbofofthe theManitouwadge Manitouwadgesynform. synform.Metagreywacke Metagreywacke the D2fabrics. fabrics. D2 D2shortening shorteningmight might also alsoaccount account in the thecore coreof of the thesyncine synclineisisfolded foldedand andcontains containsD2 in 57 �for for the the presence presence of of volcanic volcanic rocks in the the Dead Dead Lake Lake (central (central to t othe theManitouwadge Manitouwadge synform) synform) and and Banana-Otter areas areas (east (east of of Thompson Thompson Lake). Lake). Older Older phases phases of of the theBlack Black Plc Picbatholith batholithenclosing enclosing Banana-Otter the the Manitouwadge Manitouwadge belt, belt,and andK-feldspar K-feldsparporphyritic porphyriticintrusions, intrusions,have haveD2 D2fabrics fabrics and and were interpreted interpreted as as prepre- to t osyn-D2 syn-D2intrusions. intrusions. Blackman Lake Jim folds, including including the Manitouwadge Manitouwadge synform, synform, Blackman D3 map-scale folds, Lake antiform, antiform, and Jim Lake belt and the boundary. The Lake synform, fold fold the Manitouwadge Manitouwadge belt the Wawa-Quetico Wawa-Quetico subprovince subprovince boundary. The supracrustal supracrustalsequence sequence is is thickest thickest in in the thehinge hinge of of the theManitouwadge Manitouwadge synform, synform, which which plunges plunges northnortheasterly easterly at at 25°. 25'. D3 D3 fabrics fabrics include include map- and and outcrop-scale outcrop-scale folds folds and moderately to t o poorly poorly and aa moderately developed developed axial planar cleavage. cleavage. Relationships Relationships between between metamorphic metamorphic minerals, minerals, migmatitic migmatitic segresegregations, that D3 gations, and and deformation deformation fabrics fabrics indicate indicate'that D3was wasbroadly broadly coeval coeval with with peak metamorphism metamorphism in in the Quetico Quetico subprovince. subprovince. Map-scale Map-scale D4 D4 structures structures modify modify the the geometry geometry of of the the D3 D3 folds. Examples Examples the are the the Nama NamaCreek Creek shear shearzone zone along along the thenorthwest northwestlimb limbof of the theManitouwadge Manitouwadge synform synform and and open open are Blackman Lake Lake antiform antiform and and Jim Jim folds in the the Wawa-Quetico Wawa-Quetico boundary and the the axial axial traces traces of of the the Blackman folds Lake synform. synform. In In addition, addition, the theBanana BananaLake Lakeantiform antiformmay mayhave haveformed formed by byfolding folding and andshearing shearing Lake during during D3/D4 D3/D4 deformation. deformation. Outcrop-scale Outcrop-scale D4 D4structures structuresinclude includelocal localkink kinkfolds folds and andcrenulation crenulation cleavage, for example, outcrop-scale outcrop-scale asymmetric folds and associated associated crenulation crenulation cleavage cleavage in in the the cleavage, area area of of the the Geco Geco mine. The The dominantly dominantlyZ-asymmetry Z-asymmetryof of D3/D4 D3/D4 folds, folds, and and dextral dextralD3/D4 D3/D4kinematic kinematic indicators, indicators, are areinterpreted interpretedasasaaresponse responsetot oprogressive progressive dextral dextral transpression. transpression. Zircon provenance provenance ages constrain constrain the the maximum maximum depositional depositional age ageofofManitouwadge ManitouwadgemetametaZircon greywacke to t o 2693 2693 Ma (Zaleski (Zaleski et al., al., 1995), 1995),at atleast least25 25Ma Mayounger youngerthan than2720 2720Ma Mafelsic felsicvolcanism volcanism greywacke (Zaleski (Zaleski et al., al., 1994; 1994; Davis Davis et et al., al., 1994). 1994).Field Fieldobservations observations are areequivocal equivocal regarding regarding the therelationrelationship ship of of Dl D ldeformation deformation and andsedimentation; sedimentation; however, however, uplift uplift resulting resulting from from Dl D ldeformation deformation may may have contributed contributedsediment sediment sources. sources. Thus, Thus,Dl D is l istentatively tentativelyconstrained constrainedtotthe o the interval 2720-2693 have interval 2720—2693 2680A2 Ma Ma and and 2687±3 2687A3 Ma. U-Pb U-Pbzircon zircon ages, ages, determined determined for for three three prepre- to t osyn-D2 syn-D2 plutons plutons gave gave 2680±2 Ma. Ma Ma for for the the Nama NamaCreek Creekand andLoken LokenLake LakeK-feldspar K-feldspar porphyries porphyries respectively, respectively, and 2687+3/-2 2687+3/-2 Ma Ma for for the the oldest oldest diorite diorite of of the theBlack Black Pic Pic batholith. batholith.Hence, Hence,D2 D2deformation deformationand andpeak peakmetamorphism metamorphism in in the theManitouwadge Manitouwadge belt belt are areyounger younger than than2680 2680 Ma. Ma. AAfoliated foliated(D2?/D3?) (D2?/D3?)monzodiorite monzodioritephase phase of of the the Black Black Plc Pic batholith batholithhas hasan anage ageofof2677±3 2677±Ma, Ma,within withinerror errorofofthe themaximum maximumage agelimit limit on onD2 D2 deformation. deformation. Based Basedon onthe theinvolvement involvementofofthe theManitouwadge Manitouwadgemetagreywacke metagreywacke in inD2 D2folds, folds, the theage age of of sedimentation sedimentation is is bracketed bracketed by by 2693 2693 and and 2680 2680 Ma. Given Given the the similarity similarity in in lithology lithology and and age, age, we we interpret interpretthe theManitouwadge Manitouwadgemetagreywacke metagreywacke as as aa tectonic tectonicoutlier outlier of of the theQuetico Queticosubprovince. subprovince. Monazites Monazites from from intrusive intrusive and and altered alteredvolcanic volcanic rocks rocks in the the Manitouwadge Manitouwadge belt belt give give metamorphic metamorphic and and post-metamorphic post-metamorphicU-Pb U-Pbages agesofof2669-2676 2669-2676 Ma, and and 2661 2661 Ma Ma (Schandi (Schandl et al., al., 1991; 1991;Davis Davis et et a!., al., 1994; 1994; Zaleski Zaleski et a!., al., 1995). 1995). U-Pb U-Pbisotopic isotopicanalyses analysesofoftitanite titanitefrom fromfive fiveintrusive intrusiverocks rocksgive give two distinct distinct age agegroupings groupings of of circa circa 2673 2673 and 2655 Ma. 2680 Ma Nama Creek pluton and the the two Ma. The 2680 2672A2and and2674±2 2674k2Ma, Ma,respectively, respectively, which which 2677 Ma Ma Black Black Pic Pic monzodiorite monzodiorite have have titanite titaniteages agesof of 2672+2 2677 we 600°closure closure temperature temperature we tentatively tentatively interpret interpret as asthe thetime timeofofregional regionalcooling cooling through through the the600°C of of titanite titanite (Heaman (Heaman and and Parrish, Parrish,1991). 1991). Titanite Titanitefrom fromthe the2687 2687Ma MaLoken Loken Lake Lake pluton pluton has has an an age age of of about about 2652 2652 Ma, Ma, and andtitanite titanitefrom fromprepre-tot osyn-D3 syn-D3dykes dykesgives gives2658+4/-2 2658+4/-2 and and2655±3 2655k3Ma, Ma, suggesting suggesting aa widespread widespread retrograde hydrothermal hydrothermal event that that locally locally crystallized crystallized or reset reset titanite. titanite. Davis, Davis, D.W., D.W., Schandi, Schandl, E.S., E.S., and and Wasteneys, Wasteneys, H.A. H.A. 1994. 1994. U-Pb dating of of minerals minerals in alteration alteration halos halos of of Superior Superior Province Province massive massive sulphide sulphide deposits: deposits: syngenesis syngenesis vs. vs. metamorphism: metamorphism: Contributions Contributions to 115, 427—437. t oMineralogy Mineralogyand andPetrology Petrology 115, 427-437. Heaman, U-Pb geochronology Heaman, L., L., and andParrish, Parrish,R.R.1991. 1991. U-Pb geochronologyofofaccessory accessoryminerals. minerals.Mineralogical Mineralogical Association Association of of Canada, Canada,Short ShortCourse CourseHandbook Handbook19, 19,Applications Applications of ofRadiogenic Radiogenic Isotope Isotope Systems Systems to 59—102. t oProblems ProblemsininGeology, Geology, 59-102. Schandi, Schandl, E.S., E.S., Davis, Davis, D.W., D.W., Gorton, Gorton,M.P., M.P.,and andWasteneys, Wasteneys,H.A. H.A.1991. 1991.Geochronology Geochronology of ofhyhydrothermalalteration alterationaround aroundvolcanic-hosted volcanic-hosted massive massive suiphide sulphide deposits deposits in inthe theSuperior SuperiorProvince. Province. drothermal Ontario 156, 105—120. OntarioGeological GeologicalSurvey, Survey,Miscellaneous MiscellaneousPaper Paper 156, 105-120. Zaleski, 1994. 1994.Geological, Geological,geochemical, geochemical, and andage ageconconZaleski, E., E., Peterson, Peterson, V.L., V.L., and andvan vanBreemen, Breemen,0.0. straints straintson onbase basemetal metalmineralization mineralization ininthe theManitouwadge Manitouwadge greenstone greenstone belt, belt, northwestern northwestern Ontario. Ontario. Current 225—235. CurrentResearch Research1994-C, 1994-C,Geological GeologicalSurvey SurveyofofCanada, Canada, 225-235. Zaleski, 1995. Zaleski, E., E., Peterson, Peterson, V.L. V.L. and andvan vanBreemen, Breemen,0.0. 1995.Geological Geologicaland andage agerelationships relationships ofof the themargins marginsof ofthe theManitouwadge Manitouwadge greenstone greenstonebelt belt and andthe theWawa-Quetico Wawa-Queticosubprovince subprovince boundary, boundary, northwestern Geological 35—44. northwesternOntario. Ontario.Current CurrentResearch Research1995-C, 1995-C, GeologicalSurvey SurveyofofCanada, Canada, 35-44. 2 58 �PALEOGEOGRAPHIC RECONSTRUCTION OF THE GUNFLINT-MESABI-CUYUNA GUNFLINT-MESABI-CUYUNA DEPOSITIONAL BASIN ANALYSIS ANALYSIS APPROACH APPROACH DEPOSITIONAL SYSTEM: A BASIN and FRALICK, FRALICK, Philip W., Geology, Lakehead Lakehead PUFAHL, Peir K. and W., Dept. Geology, University, Thunder Bay, ON, P7B P7B 5E1, Canada Canada The depositional depositional system system responsible responsible for the the genesis genesis of of the the Proterozoic Proterozoicbanded banded iron formations in Minnesota Minnesota and Ontario has been hotly debated since the mid mid 1950's. Recent 1950's. Recent exploratory exploratory drilIing,the drilling,-the acquisition acquisition of of high high resolution resolution aeromagnetic aeromagnetic data and a better better understanding understanding of the the regional regional stratigraphy of the Biwabik Biwabik and and Trommald iron formations in Minnesota during the 1980's has provided provided insight insight into into the style of deformation deformation that that affected affected the the iron ironbearing bearingstrata strata during duringthe thePenokean Penokean Orogeny, 1860 m.y. ago. Researchers have since speculated, based m.y. Researchers have since speculated, based on on this this data, data, that that the deposition deposition of the chemical chemical and and clastic clastic sediments which comprise the Animikie Group in in Minnesota Minnesota occurred occurred in in aa migrating migrating peripheral peripheral foreland basin (Southwick and Morey, 1991). 1991). This problems that that have haveyet yetto to be be resolved. resolved. Most Morey, This model poses several several problems troubling, the model model is is incapable incapableof of explaining explaining the the observed observedlateral lateral distribution distributionof of facies facies in iron formation and associated strata. strata. There There is is an an apparent apparent lack lack of of coarse coarse turbiditic, turbiditic, deltaic and fluvial sediments adjacent adjacent to to the the fold-thrust fold-thrust belt. belt. Also, Also, ifif iron ironformation formation deposition occurred occurred in in aa migrating migrating foreland, foreland, sedimentation would have been restricted restricted deposition to the the outer outer platform platform(Hoffman, (Hoffman, 1987) 1987) and and consequently consequently the the chemical chemicalsediments sedimentswould would only be represented by facies characteristic of the distal shelf. shelf. The observed lateral The observed lateral fades within distribution of facies within correlatable units of iron iron formation are to the the contrary, contrary, aa complete shelf sequence, not just the distal portion portion is is present. present. These Theseinconsistencies inconsistencies to the need for the re-examination of iron formation in Ontario and have lead to re-examination of Minnesota. The The current current study study uses uses aa process process oriented oriented approach approach combined combined with with basin basin analysis to perform perform aa paleogeographic paleogeographicrecOnstruction reconstructionof of the the Gunflint-Mesabi-Cuyuna Gunflint-Mesabi-Cuyuna depositional system. depositional Twenty drill holes holes were logged logged from from the the Gunflint, Gunflint, Biwabik Biwabik and and Trommald Trommaldiron iron formations. Great Greatcare carewas wasexercised exercisedininrecording recordingchanges changesiningrainsize, grainsize, bed bed thickness, and sedimentary structures present present within within drill drillcore. core. This procedure procedure provides critical insight as to whether the organization of iron formation facies was process controlled allocyclic mechanism mechanism such such as as fluctuating fluctuating sea sea controlled or or governed governed by by an an allocyclic level, or both. Intrabasinal Intrabasinalcorrelations correlationsbetween betweenthe the Gunflint Gunflint and and Mesabi Mesabi iron iron ranges ranges were assisted by the presence presence of aa volcanic volcanic ash ash layer, layer, which served as aa stratigraphic stratigraphic marker, and by by comparison comparison of of sea sea level level curves generated from core core logs. logs. Stratigraphic correlations indicate that iron formation facies within the Gunflintdepositional system system exhibit exhibit aa marked fining fining and thickening of the Mesabi-Cuyuna depositional entire section to to the southwest. The The Gunflint Gunflint is is dominated dominated by medium medium to coarse coarse grained cross-stratified chert grainstone beds 5 to 50cm thick with abundant abundant rip rip ups. ups. Hummocky cross-stratified well sorted fine grained chert beds beds are are interbedded interbedded with with parallel and wavy bedded bedded magnetite-rich magnetite-rich slaty iron iron formation packages packages 33 to to 10cm 10cm Stratawithin within packages packages are are graded and 11 to 3mm thick. Chemical Chemicalsedimentary sedimentary thick. Strata comprising the Biwabik iron formation of the Mesabi iron facies comprising iron range are distinctly to medium grained grainstones 3 to finer grained than those those in in the the Gunflint. Gunflint. Fine to 30cm thick dominate, dominate, and and are are interbedded interbeddedwith withwavy wavy and andparallel parallellaminated laminated magnetite magnetite rich slaty iron iron formation packages, 10 10 to to 30cm 30cm thick. thick. Rip ups are present at the base base 59 �of of many many medium medium grained grained cross-stratified cross-stratified chert grainstones. The TheBiwabik Biwabikiron iron formation of of the the Emily Emily district district in in the the northern northern segment segment of of the the Cuyuna Cuyuna range rangeisis formation 10cmthick thickand andparallel parallel composed of of interbedded interbeddedfine fine grained grainedchert chert grainstones grainstones11to to 10cm composed and and wavy wavy laminated laminated slaty iron iron formation. Iron Ironformation formationfacies faciesininthe theTrommald Trommaldiron iron formation from from the the Cuyuna Cuyuna North Northrange rangeare are finer finer still, still, and and are are dominated dominated by by graded graded formation parallel laminated slaty iron formation. Slatybeds bedsrange rangeininthickness thicknessfrom from11to to4mm 4mm parallel formation. Slaty and and resemble resemble DE DE turbidites. This Thislateral lateraldistribution distributionof ofchemical chemicalsedimentary sedimentary facies facies parallels shelf ttoo slope parallels facies transitions observed observed in in modern modernshelf slopeenvironments. environments. Examination of vertical vertical fades facies trends trends ininiron ironbearing bearingstrata stratareveals revealsthe thepresence presence Examination of of both bothfirst first order order(sea (sealevel) level) and andsecond secondorder order(process (processcontrolled) controlled)depositional depositional cycles. Gunflintand and Biwabik Biwabik iron iron cycles. Three Threefirst firstorder ordercycles cyclesare arepresent presentininthe theGunflint formations; formations; aabasil basiltransgressive transgressive cycle, cycle, aa middle middle regressive regressive cycle, and and an an upper upper transgressive cycle. Each Eachextends extends 60 60 to to 80 80 meters meters upwards upwards through the sequence. sequence. AA transgressive pulse pulse of of volcanism volcanism is is preserved preserved in in the the lower lower portion portion of of the the upper uppertransgressive transgressivecycle cycle as as aa 3m 3mthick thickash ashlayer. layer. Its Its bottom bottomcontact contactisissharp sharpand andindicates indicatesaarapid rapidand andalmost almost instantaneous instantaneousinflux influx of of volcaniclastic volcaniclasticmaterial material into intothe thedepositional depositionalsystem. system. Its Itsupper upper contact contact isisgradational gradationalininplaces placesand andrepresents representswaning waningdelivery deliveryof ofvolcaniclastics volcaniclasticsto tothe the Animikie Animikie Basin. Basin. The Thepresence presenceofofsimilar similarallocyclic allocyclictrends trendshave havebeen beenrecorded recordedby by Morey Morey(1983). (1983). However, However,their theirrelative relativestratigraphic stratigraphicpositions positionsdiffer differsignificantly significantlyfrom from those those observed observedin inthis this study. study. Superimposed Superimposedwithin withinfirst firstorder ordercycles cyclesare aresmaller, smaller, coarsening coarsening upwards, upwards, second second order order cycles. cycles. These Thesepreviously previouslyunrecognized unrecognizedtrends trends in in the vertical distance of of 5 to to 10 meters. They They Gunflint and Mesabi Mesabi iron iron ranges span a vertical the Gunflint coarsen coarsengradationally gradationallyfrom fromparallel parallel laminated laminated slaty slaty iron iron formation formation to to medium mediumand and coarse-grained, coarse-grained, cross-stratified cross-stratified grainstone successions. Their Their top topcontact contactisis gradational gradational but but sharp sharp into into the the base base of of the the overlying overlying cycle. Similar Similarsequences sequences present present withinthe the iron ironbearing bearingstrata strataof ofthe theGogebic Gogebiciron ironrange rangeininWisconsin Wisconsinhave havebeen been within interpreted as as representing representing offshore offshore bar bar complexes. complexes. Their Theirpresence presenceisissignificant significantas as interpreted depositionalprocesses processesresponsible responsiblefor foroffshore offshorebar bardevelopment developmentprovide provideanother another depositional mechanism mechanismfor for the thegenesis genesisof ofinterbedded interbeddedcherty chertyand andslaty slatyiron ironformation. formation. References References Hoffman, Hoffman,P.F., P.F., 1987. 1987. Early EarlyProterozoic Proterozoicforedeeps, foredeeps,foredeeps foredeepsmagmatism magmatismand and Superior-type shield, in in Kroner, Kroner, A., A., ed. ed. Proterozoic Proterozoic Superior-type iron-formations iron-formations of the Canadian shield, lithospheric evolution. lithos~heric evolution. American AmericanGeophysical GeophysicalUnion UnionGeodynamics GeodynamicsSeries, Series,v.v.17. 17. p.85-98. p.85-98. Morey, Morey,G.B., G.B., 1983. 1983. Animikie AnimikieBasin, Basin,Lake LakeSuperior SuperiorRegion, Region,U.S.A.. U.S.A.. in in A.F. A.F.Trendall Trendall and Iron-Formation:Facts Factsand andProblems. Problems.Elsevier, Elsevier,New NewYork. York. andR.C. R.C. Morris, Morris,eds. eds. Iron-Formation: p.13-68. p. 13-68. Southwick, Southwick, D. D. LL.and andMorey, Morey,G.B., G.B., 1991. 1991. Tectonic Tectonicimbrication imbricationand andfordeep fordeep development developmentininthe thePenokean Penokeanorogen, orogen,east-central east-centralMinnesota-An Minnesota-Aninterpretation interpretation based basedon onregional regionalgeophysics geophysicsand andthe theresults resultsdrilling: drilling: U.S. U.S. Geological GeologicalSurvey Survey Bulletin Bulletin1904-C, 1904-C,17p. 17p. 60 �PRODUCTS PRODUCTS OF O F ELECTRIC ELECTRIC PULSE PULSE DISAGGREGATION DISAGGREGATION OF O FSOME SOMEKEWEENAWAN KEWEENAWAN ROCKS. ROCKS. RUDASHEVSKY, N. N.S., Saint Petersburg Petersburg Russia; Russia; RUDASHEVSKY, S., Mechanobr Mechanobr Technical Technical Corporation, Saint WEIBLEN WEIBLEN P.W. and and STOYNOV, STOYNOV, H., Department DepartmentofofGeology Geologyand andGeophysics, Geophysics, University of of Minnesota, Minnesota, Minneapolis, Minneapolis, MN MN 55455, 55455, and andSAINI-EIDUKAT, SAINI-EIDUKAT, B., B., University Department FargoND, ND,58105. 58105. Department of of Geosciences Geosciences North North Dakota Dakota State StateUniversity, University, Fargo A A new new facility facility atatthe theUniversity University of of Minnesota Minnesota for fordisaggregating disaggregating rocks rocks and and minerals minerals with with high high voltage voltage electrical electrical pulses pulses (Weiblen, (Weiblen, 1994) 1994) is is currently currently being being used used to to obtain obtain mineral mineral separates separates from Keweenawan Keweenawan rocks rocksofofthe theDuluth DuluthComplex, Complex,the theCopper CopperHarbor HarborConglomerate Conglomerate and andthe the from Nonesuch Previous research research at at the the Mechanobr Mechanobr Technical Technical Corporation Corporation in in Saint Saint Nonesuch Formation. Formation. Previous Petersburg, Petersburg, Russia Russia has hasdemonstrated demonstratedthe theefficacy efficacyofofelectric-pulse electric-pulsedisaggregation disaggregation to to separate separate minerals minerals of of contrasting contrastingdielectric dielectricproperties properties along alonggrain grainboundaries boundaries(Rudashevsky (Rudashevskyand andothers). others). The The electric-pulse electric-pulse method method of of comminution comminution preserves preserves the the original original grain-size grain-size distribution distribution of of liberated This phenomenon, phenomenon, which which contrasts contrasts with decrease in grain-size grain-size in in with the decrease liberated minerals. minerals. This mechanical mechanical comminution, comminution, facilitates facilitates recovery recovery of of fine-grained fine-grained minerals. minerals. Careful Careful materials materials handling handling of of the thedisaggregated disaggregatedproduct productremains remainsan animportant importantaspect aspectofofmineral mineralrecovery. recovery. Electric-pulse Electric-pulse disaggregation disaggregation of of Cu-Ni Cu-Ni bearing bearing samples samplesfrom from the the INCO, INCO, Spruce Spruce Road, Road, Test Test Pit Pit atat the the base base of of the theDuluth Duluth Complex Complex is is being being conducted conducted as as aa part part of of on-going on-going studies studies of of the the distribution and and petrogenesis petrogenesis of of platinum-group platinum-group minerals minerals (PGM's) (PGM1s)and their recovery. To-date, To-date, distribution several here-to-for here-to-for unreported unreported PGM's PGM's as as well as gold and silver alloys have have been been recovered. recovered. The The several PGM's PGM1sinclude: include: the the platinum-antimony-bismuth platinum-antimony-bismuth alloys sudburyite and froodite, and grains grains of of platinum-silver-selenide. The Theliberated liberatedgrains grainsretain retaindelicate delicatesurface surfacegrowth growthfeatures featuresand and have have aa platinum-silver-selenide. limited limitedgrain-size grain-size distribution distribution(0.01 (0.01 - - 0.1 0.1 mm). mm). Although Althoughsamples samplesfrom fromthe theINCO INCOSpruce SpruceRoad Road site site were were extensively extensively studied studied by by aanumber number of of investigators investigators in in the the past, past, discrete discrete grains grainsof of PGM's PGM's have The recovery recovery of of PGM PGM have not, not, to toour ourknowledge, knowledge, been been previously previously reported reported from fromthis thissite. site. The grains grains strengthens strengthensthe the view view that that aasignificant significantportion portion of ofthe theubiquitous ubiquitousabove abovebackground backgroundtoto 11 ppm assay assay values values for forplatinum platinum group group elements elements (PGEs) (PGE1s)ininthe theCu-Ni Cu-Niores oresofofthe theDuluth DuluthComplex Complex ppm are are due due to to discrete discretePGM PGM grains. grains. Further Furtherstudies studiesare arebeing beingdirected directedtoward towardproviding providingpreviously previously unobtainable unobtainable mineralogical mineralogical and and textural textural data on PGM's PGM's that that are are needed needed to to devise devise new new and and efficient efficientmethods methodsof ofmetal metalrecovery recoveryfrom fromDuluth DuluthComplex Complexores. ores. - The Themineralogy mineralogy and andtextures texturesof ofthe thefine-grained fine-grainedphases phasesininthe theCopper CopperHarbor HarborConglomerate Conglomerateand and the the Nonesuch Nonesuch Formation Formation of of the theWhite WhitePine Pinedistrict, district,Keweenaw KeweenawPeninsula, Peninsula,Michigan Michiganare arebeing being studied studied by by one one us us(Stoynov) (Stoynov) as aspart partofofa agraduate graduateresearch researchprogram. program. Electric-pulse Electric-pulse disaggregation of samples from these rocks has resulted in the recovery of fine-grained disaggregation of samples from these rocks has resulted in the recovery of fine-grained (<0.1 (< 0.1 mm) mm)barite baritecrusts, crusts,detrital detritalzircon, zircon,and andnative nativecopper coppergrains grainswith withdelicate delicatesurface surfacegrowth growthfeatures. features. Textural Textural and and compositional compositionaldata dataon on these thesematerials materials are arebeing being used used totoevaluate evaluatemodels modelsof ofcopper copper mineralization mineralizationprocesses processesininthese theserocks. rocks. The The electric-pulse electric-pulse facility facilityatatMinnesota Minnesota isisavailable available to to investigators investigators for for exploratoiy exploratory research. research. References References cited. cited. Rudashevsky, Rudashevsky, N.S., N.S., Burakov, Burakov, B.E., B.E., Lupal, Lupal,S.D, S.D,Thalhammer, Tlialhammer, O.A.R., O.A.R.,and andSaini-Eidukat, Saini-Eidukat,B, B,inin review, review, Liberation Liberation of of accessory accessory minerals minerals from from various various rock rock types typesby byelectric electricpulse pulse disintegration disintegration -- methods methods and and applications, applications, Transactions Transactions of of the the Institute Institute of of Mining Miningand and Metallurgy, Metallurgy,London. London. Weiblen, spearatesfor for Weiblen, P.W., P.W., 1994, 1994,AAnovel novelelectric electricpulse pulsemethod method for forobtaining obtainingclean cleanmineral mineralspearates geochemical 75,No. No.16, 16,p.p.70. 70. geochemicaland andgeophysical geophysicalresearch, research,EOS, EOS,Trans., Trans.,v.v.75, 61 �Kimberlite in in Ontario Ontario Xiinberlite Sage R. R. and and Morris MorrisT.F. T.F. Sage 933 Ramsey LakeRoad, Road,Sudbury SudburyOn On Ontario Geological Survey, Ontario Geological Survey, 933 Ramsey Lake P3E 6B5, Canada P3E 6B5, Canada To evaluate evaluate the the presence presence of of diamond diamond deposits deposits in inOntario, Ontario, the To the Ontario Geological Survey (OGS) initiated an investigation of known Ontario Geological Survey COGS) initiated an investigation of known kimberlitepipe pipeoccurrences occurrenceswithin withinthe theprovince. province. Each pipe will be kimberlite Each pipe will wilibe classified, it's exploration history defined and and models be classified, it's exploration history defined models will be developed to outline areas where other kimberlite pipes may exist developed to outline areas where other kixnberlite pipes may exist within the the province province (Sage (Sage1994). 1994). within Presently,there thereare are22areas areaswithin withinthe theprovince provincewhere wherekixnberlite kimberlite Presently, These are the Attawapiskat area and the area has been discovered. has been discovered. These are the Attawapiskat area and the area 1 ) . Kimberlite along the Lake Timiskaming Structural zone (Figure along the Lake Timiskaming Structural zone (Figure 1). Kimberlite core has has been been generously generously donated donatedto tothe the OGS OGS by by companies companiesworking workingin in core these areas. these areas. KWG Resources Resources and and Monopros Monopros Limited Limited have have provided provided core from the KWG core from the, Attawapiskat area. Dan Scholtz (University of Toronto) Attawapiskat area. Dan Scholtz (University of Toronto), Falconbridge Ltd., Ltd., Findore Findore Minerals Minerals Inc., Inc., Geological Geological Survey Survey of of Falconbridge Canada, KWG Resources Inc , Monopros Limited, Portland Firth, Canada, KWG Resources Inc., Monopros Limited, Portland Firth, Seymour Sears Sears (Consulting (Consulting Geologist), Geologist), Strike Strike Minerals Minerals Inc. Inc. and and Seymour Sudbury Contact Mines Ltd. provided core from the Lake Timiskaming Sudbury Contact Mines Ltd. provided core from the Lake Timiskaining StructuralZone. Zone. Examples Examples of of kimberlite kimberlite core corefrom from each each of of these these Structural areas are available for viewing. areas are available for viewing. . In addition addition to to the thecore, core, heavy heavy mineral mineral concentrates concentrates are are also also In KWG Resources donated chrome diopsides and available for viewing. available for viewing. KWG Resources donated chrome diopsides and it's C-14 pipe, Lake Timiskaming Structural pyrope garnets from pyrope garnets from it's C-14 pipe, Lake Timiskaming Structural Zone area. area. Monopros Monopros Limited Limited donated donated kiniberlite kimberlite core core from from the the Zone Guigues Pipe, Lake Timiskaming Structural Zone and KWG Resources Guigues Pipe, Lake Timiskanting Structural Zone and KWG Resources Inc. donated donated heavy heavy mineral mineral concentrates. concentrates. Inc. For each each area, area, kimberlite kimberliteand and heavy heavy mineral mineral concentrates concentrates available available For for display are listed in alphabetical order and in no way reflect for display are listed in alphabetical order and in no way reflect the level of importance of the contribution. the level of importance of the contribution. Two industrial industrialgrade gradealluvial alluvialdiamonds diamonds(1.05 (1.05and and 1.13 1.13 carat caratweight) weight) Two were recovered from the Michipicoten River-Wawa area in the summer were recovered from the Michipicoten River-Wawa area in the summer (C. Clement) who discovered the of 1991. The local prospector of 1991. The local prospector (C. Clement) who discovered the diamonds donated them to the Royal Ontario Museum who, in turn, has diamonds donated them to the Royal Ontario Museum who, in turn, has The story storybehind behind the the diamonds diamonds loaned them themto tothe theOGS OGSfor fordisplay. display. The loaned and follow-up work is summarized by Morris et al. (1994; this and follow-up work is summarized by Morris et al. (1994; this volume). volume) . 62 �References Cited References Cited Morris T.F., Murray C. and Crabtree D. 1994. Results of overburden Morris T.F., Murray C. and Crabtree D. 1994. Results of sampling for kimberlite heavy mineral indicators and gold overburden sampling kiniberlite heavy Wawa mineral grains, for Michipicoten Riverarea, northeastern Ontario; indicators and gold grains, River- Wawa northeastern Ontario; OntarioMichipicoten Geological Survey, Open area, File Report 5908, 69p. Ontario Geological Survey, Open File Report 5908, 69p. Sage R.P. 1994. Kimberlites of Ontario; in Summary of Field Work Sage and R.P.Other 1994.Activities Kirnberlites of Ontario; in SunnarySurvey, of Field Work 1994, Ontario geological and Other Activities Ontario geological Survey, Miscellaneous paper 1994, 163, p.113-115. Miscellaneous paper 163, p.113-115. 96 W + 76 N " ' 56 N Klznberljtes 0 L. 300 km Structuraj Zone 47 N__\ 96 W kche&n Supenor Provinc. Protrozo,c Soutbero ProTlig. (paxt of PeDokeaj OrogeA) Greovifle Protjic. (part of CrenvIIIe Oroge) Pbeoeroioic / \.. P.Ieozo1e Irid )IeIo2oIc baTiD sequecce. Figure 1. Index map showing the location of known kimberlite Figure 1. Index map showing the (from location known kimberlite clusters in Ontario Sageof1994). clusters in Ontario (from Sage 1994). 63 �COMPARISON POST-PENOKEAN THERMAL THERMAL HISTORIES HISTORIES OF OF THE THEWATERSMEET WATERSMEETAND AND COMPARISON OF POST-PENOKEAN REPUBLIC DISTRICTS, DISTRICTS, NORTHERN NORTHERN MICHIGAN: MICHIGAN: RESULTS RESULTSAND AND IMPLICATIONS IMPLICATIONSOF OF REPUBLIC 4 0 ~ r 1 3 9MINERAL ~r AGE 40ArI39Ar MINERAL AGE DATING D.A., HOLM, HOLM,D.K., D.K., (both (both at at Dept. Dept. of of Geology, Geology, Kent State University, Kent, OH SCHNEIDER, SCHNEIDER, D.A., 44242; 216-672-4094; 216-672-4094; dhoIm@kentvm.kent.edu) dholm@kentvm.kent.edu) and LUX, D.R. (Dept. of Geology, University Orono, ME 04469). of Maine, Orono, northern Michigan, Michigan, Archean Archean and and Paleoproterozoic Paleoproteroz~icrocks were were deformed deformed and and metamorphosed metamorphosed In northern during the 1870-1830 orogeny. Attoh 1870-1830 Ma Penokean orogeny. Attoh and andKiasner Klasner (1989) (1989) determined determined that that rocks rocks of of the the Watersmeet district reached pressures of 5-6 kbars and temperatures of 500-600OC, 500-600°C, whereas rocks of the Republic district attained similar temperatures but much lower pressures (2-3 (2-3 kbars). kbars). This pressure consistent with with the the contrasting contrasting ductility in the the rocks rocks of of these these two two regions. regions. variation across the orogen is consistent Paleoproterozoic ductile deformation fabrics fabrics are well-developed well-developed in in nearly nearly all all the rocks exposed in the Watersmeet area. In Incontrast, contrast,Paleoproterozoic Paleoproterozoicductile ductile fabrics fabrics are are only only well-developed in late mafic dike rocks of the Republic district. The Thecontrasting contrastingductility ductility and and pressure pressure determinations determinations from these regions suggests they would have experienced experienced different different cooling histories following the peak of metamorphism. In In assess this, this, we we have have applied appliedthe the40Ar/39Ar 40Ar139Arincremental order to assess incremental dating dating method method on on hornblende and biotite Thesedata dataallow allowcomparison comparisonof ofthe thethermal thermalhistories historiesbetween betweenthe thetwo tworegions regionsas aswell well from both regions. These as comparison of Ar/Ar RblSr biotite ages obtained obtained previously in other studies. ArlAr biotite ages ages with Rb/Sr Results from dated twotwo hornblende from the theWatersmeet Watersmeetdistrict. district.WeWe dated hornblendeseparates separatesfrom from the the Watersmeet district. An AnArchean Archeanamphibolite amphibolitecollected collected within within the the Watersmeet Watersmeet gneiss dome gave a welldefined plateau age of 1822±18 Weinterpret interpretthis this age ageas asrepresenting representing l822kl8 Ma (total gas age age == 1793A12 1793±12 Ma). We (the closure closure temperature temperature for hornblende). homblende). simple post-Penokean cooling of these these rocks rocks through through—500°C -5W° (the Hornblende obtained from a mylonitized mylonitized Archean Archean amphibolite amphibolite outside the dome dome gave gave no no plateau plateau age. age. Ma, similar similar to to aa UFb U/Pb zircon zircon However, a significant significant amount amount of of the the total total gas gas released released gave gavean anage ageof of —1750 -1750 Ma, age obtained on aa highly highly sheared sheared Paleoproterozoic Paleoproterozoic rock from within within the the Watersmeet Watersmeet gneiss gneiss dome dome Both ages probably represent the the time time of of shearing (Peterman and others, 1986). (Peterman 1986). Both probably represent shearing of these rocks at at temperatures temperaturesbelow below—500°C. -500OC. We obtained four biotite Ar/Ar ArlAr plateau ages from rocks within and adjacent to the dome which range Ma RblSr Rb/Sr biotite biotite ages obtained by Peterman range fronl from 1760 1760to to 1740 1740Ma, Ma,concordant concordantwith withthe thetwo two—1750 -1750 Ma and others (1980) and Sims and others (1984). One Onebiotite biotiteseparate separatefrom from aa rock collected collected 10 10km from from the dome yielded a somewhat somewhat disturbed disturbedspectrum spectrum with withaatotal totalgas gasage ageofof—1700 -1700 Ma (oldest increments increments were were Ma). Our 1720 Ma). Our biotite biotite ages agesare aresomewhat somewhatolder olderthan than Ar/Ar ArlAr biotite biotite ages ages obtained obtainedby by Winnett Winnett(1981) (1981) from from the same same rocks. The Thediscordance discordance between between the the two two studies studies reflects reflects the difference difference in the number number of increments analyzed per sample sample together with the fact fact that that low low temperature temperatureincrements increments are are considerably considerably younger than higher temperature temperatureincrements. increments. Interpretation. The ages obtained here Interpretation. The ages obtained here(see (seehistogram histogrambelow) below)support supportthe theinterpretation interpretationof of Sims Sims and others (1984) and Peterman and and others others (1980) (1980) that that the the Watersmeet Watersmeet district district experienced experienced significant significant cooling/uplift and concomitant deformation Ma, probably probably related related to to gneiss dome formation. coolinghplift deformation at at —1750 -1750 Ma, However, our 1822 1822 Ma homblende hornblende plateau age age indicates indicates that that metamorphism metamorphism in the the Watersmeet Watersmeet node node is is not related to heat transfer associated with rise of the dome rocks. We Weattribute attributegneiss gneissdome dome formation formation (and deformation of Penokean-aged isograds) to an episode of extensional collapse superimposed on an earlier history of crustal shortening (Schneider and Holm, 1994). Following Following uplift uplift and and stabilization stabilization at at —1750 Ma,this thisarea areahas hasnot not experienced experienced any significant thermal reheating. -1750 Ma, reheating. district. Three hornblende separates separates were dated from the Republic Republic Results from the Republic district. district, including two amphibolite amphibolite gneisses gneisses of probable probable Archean age and aa Paleoproterozoic Paleoproterozoic mafic mallc dike. One of the gneisses gneisses gave a plateau age of 1695±19 1695519 Ma and the dike rock gave a slightly older plateau age at 1720±13 Ma. AAsimilar ± 14 14 Ma) Ma) was was obtained on a dike dike rock rock by by 1720513 Ma. similar hornblende hornblende plateau age (1704 k on the the north north side side of of the the Winnett (1981). The Thethird third hornblende hornblende separate, separate, obtained from a rock collected on Marquette syncline north of Republic, did not give a plateau age; it yielded yielded aa disturbed disturbed spectrum specmm with a total gas Ma. Similar gas age age of of —1660 -1660 Ma. Similar disturbed disturbed ages ages were were obtained obtained by Winnett Winnett (1981) (1981)for for rocks rockscollected collected along the Marquette syncline. While Whileititisisdifficult difficulttotointerpret interpretthese thesedata, data,their theirlocation locationalong alongthe thefaultfaultbounded Marquette syncline syncline suggests suggests their disturbance disturbance might be related related to reactivation reactivation of of this this zone zonewell well Penokean orogeny. after the Penokean orogeny. 64 �____ were obtained obtained from from two two different different Paleoproterozoic Paleoproterozoicdikes. dikes. One gave an Two biotite separates were unreasonably old 27 old age attributed to to excess excess argon. argon. The other gave a well-defined well-defined plateau plateau age ageof of 1678 1678k±27 Ma. This Thisage ageisissimilar similartotothe theoldest oldestbiotite biotiteages agesobtained obtainedfrom fromthis thisarea areain inprevious previousthermochronologic thermochronologic studies using both the Ar/Ar ArIAr and Rb/Sr RblSr methods (see histogram below). Interpretation. The Interpretation. Thehornblende hornblendeplateau plateauages agesobtained obtained from from the the Republic Republic area area are are 100 100 Ma Ma younger than the hornblende age from the Watersmeet area. Given Giventhe therelatively relativelyshallow shallowdepth depthof of this this region, itit is is very very unlikely unlikely that that temperatures temperaturesin in the theRepublic Republicarea arearemained remained above above500°C 50O0Cuntil until 1720 1720Ma Maor or region, so following the. Penokean orogeny. We reflect. a significant fol1owing.the.Penokean -Wefeel feelthat thatthese theseages. ages.reflect significant thermal thermal resetting resettingevent, event, homblendes, well after the Penokean orogeny. orogeny. Schulz strong enough to reset hornblendes, Schulz and and others (1988) recently identified a —1733 -1733 Ma be responsible, responsible, Mapluton plutonlocated locatednortheast northeastof ofthe theRepublic Republicsyncline. syncline. This body may be in part, for the the existence existence of of aa near nearsurface surfacenegative negative gravity gravity anomaly anomaly in in the the Republic Republic area area (Attoh (Attoh and and Klasner, 1989). 1989). If so, so, we we speculate speculate that this this pluton pluton may also also be the the heat heat source source responsible responsible for the isotopic resetting. Maisis not not directly directly responsible responsible for for formation of the Republic resetting. If plutonism at at —1730 -1730 Ma node, it seems at least to be the cause metamorphic node, cause of aa major major thermal thermal perturbation superimposed on a pre-existing high regional temperature temperature distribution (cf. Peavy metamorphic metamorphic node; Attoh Attoh and and Vander Vander pre-existing Meulen, 1984) 1984) The 1680 1680 Ma Rb/Sr RblSr and Ar/Ar ArIAr biotite ages from the Republic area probably represent the time of 30O0C following the thermal reheating cooling through 300°C reheating event. event. The younger scatter in the biotite data is of partial partial resetting resetting associated associated with with the the long recognized recognized low-grade metamorphic event at about the result of 1630 Ma. 1630 gneiss dome formation gneiss post-Penokean cooling cooling I through through -500°C -5OO0C Lh g 51 5 .26 e% u/pb zir~ons U/Pb data, zircons • Peterman PetermanetetaL, al., 1986 1986 Rb/Sr data, biotite Rb/Sr data, biotite Peterman and and others, others. 1980 1980 9ms Slms and and others, others, 1984 1984 I I Ar/Ar data, Ar/Ar data, biotite biotite e 1j 0 nntt, 1981 Winnett, 1981 2 0 ' 1850 850 1800 lao0 II I I 1750 1750 1700 1700 AGE AGE (Ma) (Ma) This study This stMy 1650 Ar/Ar data, data, hornblende hornblende 1650 Ar/Ar l1 This Thisstudy study Age histogram of thermochronologic thermochronologic data from the the Watersmeet Watersmeet Area. Area. Rb/Sr data, biotite Rb/Sr data, and Sim, SIms, 1988 1988 Peterman and ' VanSchmusandWoolsey,1975 Van Schmus and W w b y , 1975 -1733 Ma plutonism 5 5 a rn i E ii I e-o0 1i ZE? z kQ . Ar/Ar Ar/Ar data, data, biotite biotite I Winnett, 1981 1981 0 Winnett, I c, I 1750 1750 is.. [] • 1 1700 1700 1650 1650 AGE (Ma) AGE (Ma) 1600 1600 1550 1550 This study study Ar/Ar data, data, hornblende hornblende Ar/Ar • l1 winnett, 1981 lg81 Winnett, This This study s t ~ y Age histogram of of thermochronologic thermochrono~ogicdata data from fromthe theRepublic RepublicArea. Area. Attoh, K., and Vander Meulen, Meulen, 1984, 1984,Journal Journal of of Geology, Geology,v. v. 91, 91, p. p. 417-432. 417-432. Attoh, K., and Kiasner, 911-933. Klasner, J.S., 1989, 1989, Tectonics, Tectonics, v. 8, 8,911-933. Peterman, Z.E., and others, others, 1980, 1980, Geological GeologicalSociety Societyof ofAmerica AmericaSpecial SpecialPaper Paper182, 182,p. p. 125-134. 125-134. Peterman, Z.E., and others, Peterman, others, 1986, 1986, U.S. U.S.Geological GeologicalSociety Societyof ofAmerica AmericaBulletin Bulletin1622-F, 1622-F,p. p. 51-64. 51-64. Peterman, Z.E., and Sims, Sims, P.K., 1988, 1988, Tectonics, v. 7, p. 1077-1090. 1077-1090. Schneider, D.A., D.A., and Holm, D.K., Schneider, D.K., 1994, 1994, Eos, v. 75, p. 691. Schulz, Schulz, K.J., K.J., and others 1988, 1988, ILSG, 34th 34th Annual Meeting, Marquette, Michigan, p. 95-96. 4.lp. Sims, P.K., and others, others, 1984, 1984, U.S. US. Geological Geological Survey Profesional Paper 1292-A, 1292-A, 41p. Van Schmus 1975, Canadian Canadian J. Earth Earth Sciences, Sciences,v. 12, 12,p. 1723-1733. 1723-1733. Schmus ,,W.R., and Woolsey, L.L., 1975, Winnett, T.L., 1981, 1981, [Master's [Master's thesis], thesis], Ohio State State University, lO6p. 106p. 65 �COMPLEX GEOLOGY OF THE SOUTHERN PORTION OF THE DULUTH DULUTh COMPLEX SEVERSON, MARK J.l J., Natural Resources Research Institute, SEVERSONl MARK Institutel University University of of Minnesota, Minnesotal Duluth, MN Duluthl MN 55811 5581I The Duluth plex (Middle (Middle Proterozoic Proterozoic -- 1099 1099 Ma) Ma) is isaalarge largeintrusive intrusivebody bodythat thatcontains contains Duluth Corn Complex numerous Recent work work has has shown shown that numerous smaller intrusions intrusions that collectively comprise comprise the Complex. Recent igneous stratigraphic sections can can be igneous stratigraphic sections be delineated delineated within these these intrusions intrusions through through detailed detailed relogging of drill corel core, e.g., Riverintrusion intrusionand andSouth SouthKawishiwi relogging e.g.l for the Partridge River Kawishiwi intrusion. More More I 4 0 drill holes are located located in in the the "South "South Complex" CompIeY study study area (Figure (Figure 1), I ) $which is an area than 140 between the Wyrnan Wyman Creek Cu-Ni Prospect (to the north) north) and and the the Boulder BoulderLake Lake area area (to (to situated between the south). south). Most of these holes holes (112 ( I 12 holes; holes; 88,000 881000feet of of core) core) have have been been relogged relogged and and correlated into several troctolitic troctolitic to to gabbroic gabbroic stratigraphic sections. While While each indMdual individual drilled drilled area exhibits good correlative units do do not extend into an area exhibits correlative units in drill hole, holel these correlative correlative units adjacent drilled area area that that is located adjacent drilled located aa few few miles miles distant. distant. This lack lack of of large-scale large-scale continuity continuity suggests suggests that either: either: 1) I )the the "South "SouthComplex" Complex"study studyarea area constitutes constitutesan an area area that actually actually includes includes several smaller smaller intrusive intrusive bodies; 2) several 2) drilling drilling is not not detailed detailed enough enough to to delineate delineatelarge-scale large-scale correlative units; 3) the effects of contamination contamination related to assimilation of footwall rocks rocks close close to to the contact hampers hampers large-scale correlations; or 4) combinations combinations of the above. above. In addition to exploration exploration for Cu-Ni Cu-Ni sulfide mineralization, mineralization1many of the holes holes drilled drilled in in the "South "South Complex" Complex" area intersected intersected smaller smaller plug-like plug-likebodies bodiesof of Oxide-bearing Oxide-bearingUltramafic UltramaficIntrusions Intrusions (OUl); the distribution distribution of large OUI OUl bodies are shown in Figure 1. (OUI); the I.The The OUI OUI are characterized by coarse-g rained to to pegmatitic pegmatitic clinopyr~xenite~ clinopyroxenite, picrite, coarse-grained picrite! peridotite, peridotitel and and dunite dunite that that are are intrusive intrusive into into troctolitic rocks. OUIvaries variesfrom from 15-20% 15-20Y0(disseminated) (disseminated)to thick thick massive massive the troctolitic rocks.Oxide Oxidecontent contentininthe theOUI oxide zones. Ilmenite llmeniteisis the the dominant dominant oxide oxidein insome some OUI; OUI; whereas, whereas1titanomagnetite titanomagnetiteis is dominant dominant in others. In Inalmost almostall allinstances, instancesl the the OUI OUI are are spatially spatially arranged arranged along along linear linear trends suggesting suggesting that structural control control was important important to their their genesis. At Atsome somelocalities, localitieslaagenetic geneticlink linkbetween between iron-formation assimilation assimilationat at the the basal contact and OUI OUI formation formation isisapparent apparent(Longnose, (Longnosel iron-formation Longear, and Section 17 This suggests that the OUI were initially formed at depth Longearl 17 bodies). bodies). This suggests that depth followed followed by by upward upwardinjection injectionof of OUI OUI material material along along fault zones. However, Howeverlother otherOUI OUI are are situated situated within, withinl or immediately immediately below, below1layered layered oxide-rich gabbroic rocks rocks (Boulder (Boulder Lake Lake area) suggesting that the OUI OUI formed by by aa differentiated differentiated iron-rich melt that drained down into into the the cumulate cumulate pile pile OUI do do not notshow showany anyimmediate immediaterelationships relationshipsto oxide-rich oxide-rich rocks rocks along fault zones. Still Stillother other OUI present within either the footwall or surrounding surrounding troctolitic rocks rocks and and possible possiblegenetic geneticlinks linksare are the 'South "South Complef Complex" area. area. The The Sulfide-mineralized zones are generally rare within the unknown. Sulfide-mineralized highest amount amount of sulfides associated associated with with troctolitic troctolitic rocks are are present present in holes drilled in the highest Water Hen and Whiteface Whiteface Resermir Reservir areas areas (Figure (Figure 1). I). of rock types on a geochemical basis is ongoing. The Comparison of TheOUI OUI are are the the most most interestingofof this this group group as each interesting each of of the the specific specific OUI OUI bodies bodies has has aadistinct distinctgeochemical geochemical 'Yingerprintl'relative relative to to each each other. other. Each of the OUI OUI also also has has significant significant variations variations in in overall owrall 'ingerprint" content of Ti02, TiO2! V2OS, V 2 m 1 Cr, Cu, Cul Ni, Nil and graphite graphite due to dominant dominant rock rock type, type1mineralogy, mineralogyl and and geographic location. location. For example the southernmost OUl OUI bodies generally have much much higher higher V2O5 contents contents than than the the northernmost OUls which which contain contain higher concentrations concentrations of of Crl Cr, Cu and and V205 Ni. While While graphite graphiteisiscommon commonto tomost mostOUI, OUI,the theWater Water Hen HenOUI OUI is is the the only only OUI OUI that contains contains thick thick massive graphite graphite (present (present in in the upper upper half half of of the the body). body). In some cases cases these these intersections of massive variations reflect the dominant mineralogy; mineralogy; however, howeverl in some some cases cases they they may mayreflect reflect different different modes of origin origin (or (or differences differences in in the the footwall footwall source source rock rock or or Complex Complexhost hostrock). rock). 66 �- Edge of D u l u t h Complex Cu-Ni DEPOSIT OXIDE-BEARING ULTRAMAFIC INTRUSION (OUI) 0EXPLORATION AREA 10 kilometers 0 OUTLINES ENLARGED AREA 1 Geology and ACAD by Mark J. Severson Februaw. 1994 67 �Geochemistry and and fractionation fractionation of of the the Eastern Eastern Gabbro, Gabbro,Coidwell Coldwell Geochemistry Alkaline Complex. Complex. Alkaline Shaw, Cliff Cliff S.J. S.J. Shaw, Department of of Earth Earth Science, science, University university of of Department Western Ontario, Ontario, London, London,Ontario, ~ntario, N6H 5B7. 5B7. Western N6H The Eastern Eastern Gabbro Gabbro is is the the oldest oldest major major intrusion intrusion in in the the 1108±1 1108± Ha Ma The Coldwell Alkaline Alkaline Complex Complex (CAC). (CAC). It It forms forms aa ring-dyke ring-dyke surrounding surrounding Coidwell variety of of lithologies lithologies ranging ranging from from quartz quartz syenite syeniteto to nepheline nepheline aa variety syenite. syenite. It is is part part of of the the first first intrusive intrusive center center in in the the CAC CAC and and It is associated associated with with iron—rich iron-rich augite augite syenite, syenite, monzodiorite monzodiorite and and is basaltic xenoliths. xenoliths. basaltic The Eastern Eastern Gabbro Gabbro consists consists of of four four subunits, subunits, in in order order of of The Gabbronorite (GN), (GN), Two Two Duck Duck Lake Lake Intrusion Intrusion emplacement these these are, are, Gabbronorite emplacement (TDLI), Layered Layered Gabbro Gabbro (LG) (LG)and and Malpas Malpas Lake LakeIntrusion ~ntrusion (MLI). (TDLI), (MLI). The The rocks are are plagioclase—rich plagioclase-rich cumulates cumulates that that contain contain variable variable amounts amounts rocks of of ilmenite, magnetite magnetite and and olivine, clinopyroxene, clinopyroxene, biotite, biotite, ilinenite, olivine, orthopyroxene. orthopyroxene. Rock and and mineral mineral Mg# Mg# and and compatible compatible elements elements decrease decrease in in Rock abundance in in the the sequence sequence GM GN - TDLI TDLI — LG LG — HLI. MLI. Incompatible Incompatible abundance - - - elements eg eg alkalis, alkalis,Ba, BatZr Zr and and REE REE increase increasein inthe thesame samesequence. sequence. elements There is is however however aa great great deal deal of of overlap overlap in in the the compositions compositions of of the the There GN, TDLI TDLI and and LG LG indicating indicatingthat thatthey theycrystallised crystallisedfrom fromiuagmas magmas with with GN, similar compositions. compositions. similar The composition composition of of the the magmas magmas which which crystallised crystallised to to form form the the The rocks of of each each subunit subunit was was estimated estimated by by analysis analysis of of fine—grained fine-grained rocks Theestimated estimatedmagma magmacomposition compositionof of samples and and weighted weighted averaging. averaging. The samples 68 �the TDLI TDLI and and LG LG are are similar similar to to typical typical Keweenawan Keweenawan olivine olivine the tholeiites. tholelites. The MLI MLI estimate estimate is is rich rich in in Si02 SiO, and and alkalis alkalis and and is is The akin to to aa Keweenawan Keweenawan basaltic basaltic andesite. andesite. The The estimate estimatefor forthe theGN GN is is akin not used used because because it it may may have have been been contaminated contaminated by by silica. silica. not Modelling of of fractionation fractionation in in the the Eastern Eastern Gabbro Gabbro suggests suggests that that Modelling there is is aa differentiation differentiation trend trend from from TDLI TDLI to to LG LG and and MLI. MLI. there The The similarities in in major major oxide oxide composition composition of of the the TDLI TDLI and and LG LG magmas magmas similarities and difference difference in in trace trace elements elements rules rules out out simple simplefractionation. fractionation. and more complex complex model model of of fractionation fractionation in in aa replenished replenished and and erupting erupting AA more In this this model model fractionation fractionation is is achieved achieved magma chamber chamberis is proposed. proposed. In magma by crystallisation crystallisationof of olivine, olivine,clinopyroxene clinopyroxeneand and plagioclase plagioclasein in the the by 1:4:6.7. ration 1:4:6.7. ration The magma magma removed removed is is evolved evolved and and the the replenishing replenishing The magma is is the the same same composition composition as as the the original originalstarting startingmaterial. material. magma This model model causes causes fractionation fractionation of of trace trace elements elements but but leaves leaves the the This major elements elements relatively relatively unaffected. unaffected. major 2-8 cycles cycles Using this this model model the the LG LG was was derived derived from from the the TDLI TDLI by by 2-8 Using of of fractionation, fractionation, eruption eruption and and replenishment. replenishment. Continued Continued fractionation of the LG LG leads leads to to the the MLI MLI and and eventually eventually to to the the fractionation of the iron-rich augite augite syenite syenite which which intrudes intrudes the the Eastern Eastern Gabbro. Gabbro. iron-rich 69 �ON THE THEO1UGIN ORIGIN OF OFALKALINE ALKALINE GABBROIC GABBROIC ROCKS ROCKS IN IN THE THE COLDWELL COLDWELL PENINSULA PENINSULA AREA, AREA, COLD WELL ALKALINE COMPLEX, COLDWELL COMPLEX,ONTARIO. ONTARIO. Shore, Geoff T., Department Department of of Earth Earth Science, Science, University of Western Ontario, Ontario, London, Ontario, Ontario, N6A N6A 5B7. 5B7. The Coidwell Coldwell Peninsula Peninsula Area Area (CPA) (CPA)represents representsthe thesouthernmost southernmostextension extensionof ofthe theKeeweenawan KeeweenawanCoidwell Coldwell Alkaline Complex Complex (CAC) (CAC) into intoLake LakeSuperior. Superior.Arcuate Arcuatebodies bodiesofofnepheline nephelinesyenite syeniteand andalkaline alkaline gabbro gabbro dominate dominate the CPA and together comprise the main lithologies within the second intrusive centre of the CAC. A of together comprise the within the second intrusive centre of the CAC. zone of heterogeneous-textured alkaline alkalinegabbroic gabbroicmegaxenoliths, megaxenoliths,varying varyinginincomposition compositionfrom fromgabbro gabbro to to olivine olivine gabbro, occupies occupies the thecentral centralportion portionof ofthe thepeninsula peninsulabounded bounded to to the the north north and and south southby by later laterintrusions intrusionsofofnepheline nepheline syenite. The xenolithsoccur occurasasblocks blocks(c (<1m Imtoto> lOOm)formed formedby by disruption, disruption, brecciation brecciation and > 100m) and The alkaline alkaline gabbroic xenoliths assimilation of an early assimilation early layered layered gabbroic gabbroicbody body by by later later syenitic syeniticphases. phases. Several large vicinity of of Port Coidwell. largelayered layered alkaline alkaline gabbro gabbro megaxenoliths megaxenoliths occur in the vicinity Coldwell. The Thelayered layered heterogeneous-textured gabbroic gabbroic rocks. rocks. gabbroic sequences sequences are are cut cut by by chemically chemically and mineralogically similar, heterogeneous-textured fractionated with with decreasing decreasing compatibles compatibles (Ni, Early, rhythmically layered alkaline gabbroic megaxenoliths are fractionated Cr, Co) and increasing increasing incompatibles incompatibles(Zr, (Zr, Y, Y, Th, Th, Nb, Ba) and alkali elements towards the south. south. Spectacular breccia breccia zones, zones, comprised comprised of of lobe lobe and and cuspate cuspate microgabbroic microgabbroic enclaves enclaves surrounded surrounded by a nepheline nepheline host, are are the the result result of of nepheline nepheline syenite syenite magmatism magmatismand andsynplutonic synplutonicmicrogabbroic microgabbroicdykes. dykes. Whole rock syenite host, and mineral geochemistry is is consistent consistentwith withderivation derivationofofthe thesynplutonic synpiutonicmicrogabbroic microgabbroic enclaves enclaves through througholivine olivine (Fo87), clinopyroxene (En43Wo48Fs8) andplagioclase plagioclase(Anw) (An67)fractionation fractionationofofa aprimitive primitivealkali alkali basaltic basaltic parent. parent. (Fog,), clinopyroxene (En43W040Fss) and Microgabbroic enclaves enclavesand andsyenites syenitesform formlinear lineartrends trends on on Mg# Mg# versus versus major major element (Na, K, Ca, Microgabbroic Ca, Al) Al) and andtrace trace element (Ni, Co, Zr, Nb, Ba, Ba, Rb) Rb) plots plots suggesting suggesting that that at at least least some some of the enclaves are related to the syenites assimilation. by assimilation. A four-stage four-stagemodel model isisproposed proposedtotoexplain explainthe theemplacement emplacement history of the main units within the CPA: 1) emplacement of centre I1 lithologies lithologiesand and initiation initiation of of alkaline alkaline gabbro gabbro fractionation; fractionation; 2) disruption disruption of the layered layered alkaline gabbro 3) nepheline nepheline syenite syeniteintrusion intrusionand and gabbro sequence sequenceand and intrusion intrusionby by cognate cognatealkaline alkalinegabbro gabbromagma; magma; 3) synpiutonic microgabbroic dyke intrusion. in situ differentiation; differentiation; 4) 4) amphibole amphibolenatrolite natrolite nepheline syenite and synplutonic 70 �WftUAMS MINE By: Gordon Gordon Skrecky, Gray, and Allan Skrecky, James JamesGray, Allan Guthrie Guthrie REGIONAL GEOLOGY The The Williams Williams Mine Mine lies lies on onthe thesouth southside sideofofthe theessentially essentiallyeast-west east-west trending trending Schreiber-White Schreiber-White River River Greenstone Belt Belt of of Archean volcanic Greenstone volcanic and and sedimentary sedimentary rocks. rocks. The belt has has been been subjected subjected to to regional regional s interpreted metamorphism, o amphibolite metamorphism, up up tto amphibolite grade. grade. It It iis interpreted as asbeing beingsynclinally synclinallyfolded. folded. Granitic Granitic intrusions and gneissic bodies bodiesbound boundthe thebelt belttto the north and south and intrude the synclinal axis gneissic o the axis of the the belt. belt. In the vicinity vicinity of of the theWilliams WilliamsMine Minethe thesupracrustal supracrustalrocks rocks are divided divided into into the the Playter Playter Harbour Harbour Group Group and and Heron Bay Group. The The former former is primarily primarily composed of maf Icvolcanic volcanic rocks rocksand andthe the latter latter primarily primarily of Bay Group. composed of mafic of felsic volcanic rocks and metasedimentary rocks with minor intrusive rocks. The Heron Bay Group dips to rocks rocks with minor intrusive rocks. The Heron Bay Group dips t o the north, structurally structurally overlies overlies the the Playter Playter Harbour Harbour Group, Group, and and contains contains all the the economic economic gold gold deposits deposits found to t o date date near Hemlo. Hemlo. PROPERTY GEOLOGY GEOLOGY PROPERTY The major rock rock units units on on the the property property strike strike 108° The major 108O and dip from 60° 60Âto to700 70Âto tothe thenortheast. northeast. The The general general property stratigraphy maficmetavolcanic metavolcanicrocks, rocks, lower lowermetasedimentary metasedimentaryrocks, rocks, an an stratigraphy from from south south to to north northisi smafic altered altered felsic felsic prophyry prophyryrock rockunit, unit,the thegold goldmineralized mineralizedrocks, rocks,and andthe theupper uppermetasedimentary metasedimentaryrock rocksequence. sequence. An intermediate to the upper upper metasedimentary metasedimentaryunit unitfrom fromthe thefelsic felsic porphyry porphyry to felsic fragmental fragmental unit unit separates separates the western portion portion of the the property. property. lower unit on the western Lowerand and upper upper denote the relative structural positions of the metasedimentaryrock rockunits units as asthe theyounging youngingdirections directionsare areunclear. unclear.An Anintermediate intermediateintrusive intrusive unit unit divides metasedimentary the felsic porphyry unit end of of the property. All of unit into intotwo twosegments segments at the east end of the the major majorrock rockunits unitsare are highly deformed. The major major intrusive rocks, order of age, are intermediate intermediate to to felsic dikes and felsic porphyry The rocks, in decreasing decreasing order age, are dikes, altered, altered, biotite-rich biotite-rich dikes, Iamprophyre. All All of these dikes, dikes, diabase, diabase, and lamprophyre. these intrude intrude the the orebody orebody and and the the basic basic stratigraphy. A mafic intrusive body cuts cuts the the felsic felsic porphyry porphyry rocks iin 'C' zone intrusive pipe-shaped pipe-shaped body n the 'C' zone pit pitand and is i s in in turn cut cut by by later later diabase diabase diking. diking. diabasedikes dikesand andyounger youngerlamprophyres lamprophyresare areProterozoic. Proterozoic.I In contrastto tothe theintermediate intermediate and and felsic felsic dikes dikes The diabase n contrast which are conformable to the stratigraphy, fill joints stratigraphy, they fill joints trending trendingnorth northand anddipping dippingvery verysteeply steeply east east and cut the earlier earlier dikes. dikes. MAIN THE M A I NOREI3ODY OREBODY The main main orebody orebody has hasaastrike strikelength lengthof ofabout about 1200 1200 m, m, dips dipsat at60 60° to to 70 70° to to The to the the northeast northeast and and plunges to the northwest at approximately approximately 45O. 450 ItItoutcrops to a vertical vertical depth of about 1300 outcropsat at surface surface and continues to m on the Williams property. property. Upon Uponcrossing crossing a claim claim line line to to the the east east ititbecomes becomes the Golden Giant deposit of Hemlo Gold. The maximum thickness thicknessof of ore ore iis 45 metres metresand andi sislocated locatedadjacent adjacentto tothe the Hemlo Hemlo Gold Gold boundary. boundary. Moving s 45 Moving The west declines iin width and grade. grade. The portion of west from that property boundary, boundary, the ore generally declines n width The western portion of 'B' zone reserves, reserves,from from about about the the provenlprobable proven/probable line category, incorporates 'B' line through through the the possible possible category, incorporates two two oreoregrade zones zoneswithin within the typical typical host lithology. waste pillar pillar of at lithology. These These are are separated separated by an internal waste at least least 10 10 metres horizontal horizontal thickness. thickness. This This mineralization mineralizationrepresents represents the fringe fringe of of the the'Hemlo 'HemloDeposit' Deposit'and andas assuch, such, continuity of erratic. continuity of ore oregrade grade and and thickness thickness become increasingly erratic. Williams Operating Corporation treated treated 2.3 2.3 million million tonnes of gold gold iin tonnes of ore to to produce produce 445,000 445,000 ounces ounces of n making itit one gold mines. Total Proven totalled at 30.9 1994, making one of Canada's Canada's largest largest gold Proven and Probable Probable Ore Ore Reserves Reserves totalled 30.9 million milliontonnes tonnes grading grading 5.7 5.7 grams grams of gold per per tonne tonne at at the the end end of of 1994. 1994. 71 �EFFECTS OF O NCRUSTAL. CRUSTAL ROCKS ROCKS EFFECTS OF LARGE LARGE METEORITE IMPACTS ON - N THIN THINSECTION SECTION - SUDBURY BASIN IIN Viitala, Reino Viitala, Reino L., Department of Geology, Geology, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, L., Department Ontario, P7B P7B5E1, 5E1, Canada Canada The origin of The of the theSudbury Sudbury Igneous Igneous Complex Complex (SIC), (SIC), in central Ontario, Ontario, has has been been aa subject of controversy for over subject over ninety ninety years. years. Since 1 1962 laboratory studies studies by Dietz, Dietz, Guy-Bray, Guy-Bray, Since 962 more more recent recent detailed detailed field and laboratory Peredery, the impact theory as Peredery, Dence, Dressier Dressler and many others have greatly strengthened the as the trigger mechanism mechanism for the the Sudbury Sudbury event. event. The Sudbury Sudbury impact occurred occurred during during an an active Penokean orogeny orogeny about about 1.85 1 .85b.y. b.y.ago ago[I]. [1]. One of of the the interesting interesting questions arising from the impact-theory impact-theory is is how how much much of of the the SIC SIC might be be impact impact melt melt rather rather than internally internally derived igneous igneous rock rock material? material? Presence of shock metamorphic features Presence of features have been observed by recent recent research research in in the footwall footwall of of the theSIC SIC (Dence (Dence 1972, 1972, Guy-Bray Guy-Bray and INCO INCO Geological Geological staff staff 1966, 1966, DressIer Dressier 1984) and in i n the the breccias breccias of the the Onaping Onaping Formation Formation (French (French 1968, 1970, 1970, 1972, 1972, Peredery Peredery 1 972, Muir Muir and Peredery 1984). 1 984). These These features featuresinclude: include: shatter cones, cones, microscopic microscopic planar 1972, feldspar, kink bands in biotite elements in quartz and feldspar, feldspar, plastic deformation of feldspar, biotite mica, mica, severe fracturing fracturing of garnet, recrystallized and incipient incipient melt bodies. severe recrystallized quartz and glasses, glasses, and bodies. Commonly found Commonly foundassociate associatefeature featurenear nearimpact impactsites sitesare areShatter-cones. Shatter-cones. Shatter-cones Shatter-cones are radial with striae 968, 11972). 972). The radial fracture fracture surfaces surfaces with striae that that fan fan from from an an apex apex (Dietz (Dietz11968, Thestriae striae are sharp grooves grooves between between intervening, rounded upon roundedridges ridges developed developedby bypressure pressure releases upon impact. Shatter-cones 7 km away. Shatter-conescan can be be found foundaround aroundthe theSIC SIC for fordistances distances as as much much as as 117 et al. al. 1969, Stoffer Stöffer 1967, 1967, Chao Chao 1968, DressIer Dressler 1970) Studies indicate (von Engelhardt et that weakerthan than 100 100 kilo-bars do not that shock shock pressures pressures weaker kilo-bars do not produce produce any any typical typicalshockshockmetamorphic features. features. Shock Shock experiments experiments using using plagioclase plagioclase feldspar [2] produced produced planar planar between 150 and 300 kilo-bars pressure. features between pressure. Between Between 300 300 and and 500 500kilo-bars kilo-barspressure, pressure, whole whole plagioiclase plagioiclasecrystals crystalsbecame became diaplectic diaplecticglass glass (maskelynite) (maskelynite) and above above 500 500 kilo-bars, kilo-bars, normal glass glass of plagioclase plagioclase composition composition was was formed. formed. The The corresponding corresponding working temperature reached reached during during the active stage stage of of the the SIC SICcan canbe be estimated estimatedfrom fromthe thework work of temperature 967)[3]. They at its norite intrusion They concluded concluded that that the the SIC at intrusion activity activity Naldrett and Kullerud Kullerud (1 (1967)[3]. level reached temperaturesofof 1000° 1000°C with with aa 20°C reached temperatures 20° per per 11km kmgeothermal geothermal gradient gradient at at an an emplaced emplaced depth of 55 km. km. From Fromthe theextent extentofofthe thepyroxene-hornfels pyroxene-hornfelsfacies facies of of 220 220metres metres from the estimated that that the SIC remained at temperatures of about the SIC, SIC, these these researchers researchers estimated SIC remained 600°C 600° for for more morethan than720,000 720,000 years years after after the the norite norite intrusion. intrusion. 72 �Some representative field with Some 23 23 representative field samples samplesfrom from the the SIC SIC [4] [4] were were collected along with several examination. several samples samples of of Shatter-cones Shatter-conesfor forthin-sectioning thin-sectioningfollowed followed by microscopic examination. Shatter-cones (Map #1,2), Sudbury SudburyBreccia Breccia North-range North-range (Loc (Loc #4), Field samples samples include: include: Shatter-cones (Map Loc bc #1,2), ry Breccia South-range (Loc #6), Footwal l Breccia (Loc #8,9,1 O), Nort h-range Onaping Sud bu Sudbury South-range (Loc #6), Footwall Breccia (Loc#8,9,10), North-range Onaping Basal Member (Loc (Loc #1 #111A), A), Gray Member Member (Loc (Loc#1 #11 B), Melt Melt Body Body(Loc (Loc#1 #11 C), Formations Basal 1B), 1C), Black (Loc #13), #13), South South Range-Basal Range-Basal Member (Loc #16), #16), Black Member (Loc Member (Loc (Loc #14), #14), Chelmford (Loc Onwatin Formation Formation(Loc (Loc#17), #17), SIC SICmember member Norite Norite(Loc (Loc#19), #19),SIC-member SIC-member Sublayer Sublayer (Loc (Loc Onwatin #20), and Nickel-copper sulphide sample from the discovery site at Murray Mine Open #20), suiphide sample from thediscovery site at Murray Mine Open pit pit (LOC (Loc #23). Shock metamorphic metamorphic features featurescan can be be viewed viewed in thin Shock thin sections sections ofofthese thesesamples. samples. Sections of Shatter-cones showthe theextent extentof of the the obliteration obliteration of quartz Sections of Shatter-cones show quartz grains grains along along the the pressure fractures fractures occurring occurring in arenite pressure arenite material. material. Similar features features as shatter-cones shatter-cones but not not formed formed in the the usual usual conical conical pattern pattern were were found found in in the the Basal Basal member member of of the the Onaping Onaping Formation on the south range sample site site #14 #14 south south of of Vermillion Vermillion Lake. range at sample Lake. This Thishands-on hands-on to some some of of the the Sudbury Sudbury Igenous Igenous Complex rock rock units units and and poster display provides a window window to their unique unique inherent inherent mineralogy. mineralogy. Cited References Cited [1] [I] Krogh T.E. et al. (1984) In T.E. et In The Geology Geology and and Ore Ore Deposits Deposits of of the theSudbury SudburyStructure Structure (E.G. Pye Pye et et al., at., eds.), eds.), Ministry Ministry of Natural (E.G. Natural Resources, Resources, Toronto. [2] Engelhardt. W.von, W.von, Arndt, J., Stöffler, D., D., Muller, W.F., J., Stoffler, W.F., Jeziorkowski, Jeziorkowski,H., H., and andGubser, Gubser, R.A. (1967) des Ries Riesvon von Nordlingen Nordlingen als R.A. (1 967) Diaplebtische Diaplebtische Gäser Gaser in den Breccien des als Anzeichen für Stosswellenmetamorphose; Contributions to Mineralogy and Mineralogy and fur Stosswellenmetamorphose; Contributions Petrology, 02. Petrology, Volume 15, 15, p.93-i p.93-102. [3] Naldrett, A.J., and and Kullerud, Kullerud, G. G. (1967) A study Mine and its Naldrett, A.J., (1967) A study of the the Strathcona Strathcona Mine its bearing on the Origin of the Nickel-Copper Ores of the Sudbury District, bearing on of the Nickel-Copper Ores of the Sudbury District, Ontario; Journal Journal of Petrology, Petrology, Volume 8, 8, Part Part 3, 3, p.453-531. p.453-531. [4] [4] DressIer B.D., B.D., Peredery Peredery W.V., W.V., Muir Muir T.L. 992)Geology Geology and andMineral Mineral Deposits of the Dressier T.L. (1992) Sudbury Structure, Structure, Ontario Ontario Geological Survey, Survey, Field Guidebook 8. 13 �The Geco Mine, Manitouwadge, Manitouwadge, Ontario: a volcanogenic volcanogenic massive massive suiphide sulphide deposit deposit H.Lockwood H. Lockwood by: I. I . Wolfson Wolfson presented by: Hemlo Gold Mines, Inc. Golden Golden Giant Giant Mine, Mine, Hemlo, Ontario Ontario The Geco Division of Noranda Mining and Exploration Inc. began production in 1957. To date, over 53 million tons of ore grading 1.85% 1.85% copper, 3.78% zinc, 0.30% lead, 1.64 1.64 ounces per ton silver silver and and 0.004 0.004 dollars at 1994 1994prices. prices. The The orebody orebody was was ounces per ton gold have been produced, worth over 5 billion dollars discovered by 3 prospectors prospectors in in 1953. 1953. now consists of of an underground mine with with 125 miles miles of of lateral drives serviced by by two shafts, a Geco now underground mine concentrator concentrator and and supporting supporting plant plant installations. installations.The Themine minecurrently currentlyproduces produces80,000 80,000tons tonsofof ore ore per per month. Most Most ore now comes month. comes from from remnants remnants and pillars using the the Geco Geco Running Running Tight Tight Fill Fill stoping stoping which uses uses immediate rock rock fill to stabilize weak stope walls as ore is removed. 260 people are method, which are employed. Copper and zinc concentrates averaging 29% copper and 55% zinc respectively are shipped by rail to Noranda's smelters smelters in Rouyn Rouyn and and Valleyfield, Valleyfield, Québec. Quebec. The The mine mine will will close closein in late late 1995. 1995. Geco's main ore zone pyrite-pyrrhotite-sphalerite-chalcopyritecore zone consists consists of of aamassive massive coarse-grained coarse-grained pyrite-pyrrhotite-sphalerite-chalcopyrite enveloped by stringer stringer pyrite-pyrrhotite-chalcopyrite pyrite-pyrrhotite-chalcopyrite ore in in aa silicified silicified sericite sericite schist schistunit. unit. The Thestringer stringerore ore margins are defined by assay, currently 2% copper. The main ore zone has a surface strike length of 2,400 feet, an average width of 65 feet, and plunges east at 40 degrees to 3450 feet below surface. The sulphiderich orebody grades laterally laterally into into aa siliceous siliceous magnetite-rich magnetite-rich iron iron formation. formation. Two Two narrow narrow copper copperand andzinczincrich stringer stringer zones(4/2 zones(412 copper and 8/2 812 zinc zone) total 3 million tons of marginal marginal ore ore and are are found found on on the the lower and upper contacts contacts of of the the sericite sericiteschist schist unit unit respectively. respectively. The main ore ore zone zone grades grades laterally laterally eastward eastward into into aasiliceous siliceousbanded bandedquartz-magnetite quartz-magnetite iron iron formation formation zones(Willroy, Willecho which has been followed for 15 15 miles miles with with diamond diamond drilling; drilling; several several other other ore ore zones(Willroy, and Nama Creek) have been located to the west on or near the Geco productive horizons in the 10 by 15 15 mile area of folded supracrustal supracmstalrocks that that comprise comprise the the Manitouwadge Manitouwadge Camp. Camp. The silicified orthoamphibole-biotite-gametorthoamphibole-biotite-gametsilicified sericite sericite schists schists that that host hostGeco's Geco'sore oreare areunderlain underlainbyby cordierite cordierite gneisses, which are interpreted as hydrothermally altered mafic to intermediate volcanics. This group extends several miles laterally, and there does not appear appear to to be be any anyparticular particular alteration alteration pattern pattern within it immediately immediately underlying the Geco ore zone. The deposit is overlain by varying textures of quartzfeldspar-biotite gneisses, gneisses, interpreted interpreted as as volcaniclastic volcaniclasticmetasediments, metasediments,with with intercalated intercalatedvolcanics, volcanics,quartzquartzmagnetite magnetite iron formation(locally formation(local1yzinc-rich) zinc-rich) and and tonalitic tonalitic intrusions. intrusions. 74 �PROPOSEDFIELD FIELD TRIPS TRIPS FOR FOR THE THE PROPOSED 42nd ANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKE SUPERIOR SUPERIOR GEOLOGY 42nd LaurelG. G.Woodruff woodruff1, William F. Cannon2 Cannon2 and andGene GeneL. L.LaBerge3 LaBerge3 Laurel 1, William U. S. S. Geological GeologicalSurvey; Survey;1St. 1st.Paul, Paul, MN, MN, 2Reston, *Reston, VA; 3UW WI U. 3UW Oshkosh, Oshkosh, Oshkosh, Oshkosh, WI The 42nd Annual Institute Institute on on Lake Lake Superior Geology Geology will The will be be held in Cable, Wisconsin from from 15 15 May to 19 May, tradition, two two Cable, May, 1996. 1996. In In keeping keeping with tradition, days of of technical technical session session on on May May 16 16 and 17 will days will be be bracketed bracketed by by pre-meeting pre-meeting and post-meetingfield fieldtrips. trips.The Thefield fieldtrips tripswill willcover coveraawide widerange rangeof of interests, interests,from from post-meeting Archean to to the the most mostrecent recentgeological geological the metamorphosed metamorphosed and and deformed deformed Archean the manifestations of the last last glaciation. glaciation. The The field field trips trips will will highlight highlight results results of of manifestations U.S. S.Geological Geological Survey, Survey, the the recentgeologic geologicefforts effortsin innorthern northernWisconsin Wisconsinby bythe theU. recent Wisconsin Geological Geological and staff at at the the active active Wisconsin and Natural History Survey, and the staff Flambeau massive massivesulfide sulfide mine. mine. Six Six possible field trips are currently planned but but Flambeau the final final selection selectionwill will depend depend on onthe the interest interestlevel level for for each each trip. trip. All Allof ofthe thefield field the trips are arewithin within easy easytravel traveldistance distance from from the the Institute Institute headquarters headquarters at atthe the trips TelemarkLodge, Lodge,Cable, Cable,Wisconsin, Wisconsin, allowing allowingmaximum maximumtime timein inthe thefield. field. Telemark Geologyof ofthe theSouth SouthLimb Limbof of the the Midcontinent MidcontinentRift, Rift, North-Central North-CentralWisconsin Wisconsin Geology U.S. S.Geological GeologicalSurvey Survey Bill Cannon, Cannon,Suzanne SuzanneNicholson, Nicholson,Laurel LaurelWoodruff, Woodruff,U. Bill Rocks of the the Midcontinent Midcontinent Rift Rift dated at at 1.1 1.1 Ga Ga cover cover much much of of northern northern Rocks Wisconsin. Geologists Geologistsatatthe theU. U.S. S.Geological Geological Survey have remapped the region region Wisconsin. remapped the as as part partofofthe theMetallogeny Metallogenyofofthe theMidcontinent MidcontinentRift RiftProject, Project, providing providing new new insight into intothe the structure, structure,geochemistry, geochemistry, and stratigraphy stratigraphy of the rift. The The area area of of insight this this field fieldtrip tripnear nearMellen, Mellen,Wisconsin, Wisconsin, provides providesaacomplete completestratigraphic stratigraphiccross cross section section of of the the rift, rift,from frompre-rift pre-riftBessemer Bessemer Quartzite Quartzite through through the thesyn-rift syn-riftFreda Freda Sandstoneand andincludes includesthe theintrusive intrusiveMellen MellenComplex, Complex,which which strongly stronglyinfluenced influenced Sandstone thedevelopment developmentofofthe therift riftininthis thisregion regionas asboth bothaavolcanic volcanicsource sourceand andaathermal thermal the and andstructural structuralhigh. high. From Archean:AA25 25km kmsection sectionof of the thecrust crust Fromthe theMiddle MiddleProterozoic Proterozoictotothe theArchean: Bill Cannon, Cannon,U.S. U.S. Geological Geological Survey Survey Bill AA25-km 25-km thick thick monoclinal monoclinalsuccession succession of vertical to steeply steeply dipping dippingstrata strataisis exposed between between the the shore shore of of Lake Lake Superior Superior and the the Gogebic Gogebic iron range range in in exposed northern northern Wisconsin. Wisconsin. The Themonocline monoclinewas wascreated createdby bycrustal-scale crustal-scale thrusting thrusting shortly shortly after after formation formation of of the theMidcontinent Midcontinent rift. rift. The The trip trip will willtraverse traverse 'downward' 'downward'through throughthe thecrust crustfrom fromthe theFreda FredaSandstone, Sandstone,through throughthe theMiddle Middle ProterozoicKeweenawan KeweenawanSupergroup, Supergroup,Early EarlyProterozoic Proterozoicstrata strataofofthe theGogebic Gogebic Proterozoic Archean volcanic volcanic rocks. rocks. This iron range, range, and andend endininLate LateArchean iron This is is one one of of the the most most complete completesections sectionsof of the the upper upperand andmiddle middlecrust crustexposed exposedon onearth. earth. Geologyand andEnvironmental EnvironmentalImpact Impactofofthe theFlambeau FlambeauMine, Mine,Ladysmith. Ladysmith,WI WI Geology Staff Staff Geologists Geologistsof of the the Flambeau FlambeauMine Mine The The open openpit pitFlambeau Flambeaumine, mine,operated operatedby byFlambeau FlambeauMining MiningCompany, Company,aa whollyowned ownedsubsidiary subsidiaryofofthe theKennecott KennecottCorporation, Corporation,isisdeveloped developedininaazone zoneofof wholly 75 �Late Proterozoic supergene enrichment on an an Early Early Proterozoic Proterozoic volcanogenic volcanogenic massive sulfide deposit. deposit. Copper chalcocite, bornite, Copper is extracted from chalcocite, bornite, and chalcopyrite in the supergene Gold is mined separately separately from an overlying, supergene zone. Gold gold-rich gossan. gold-rich gossan. The The development development of the project project employs employs the latest latest of the environmental controls of massive sulfide exploitation. environmental controls exploitation. The mine is scheduled scheduled to close in in 1997 1997and and the the area area restored restored to to its itspre-mining pre-mining condition. condition. This field trip will include detailed look include a visit to the working face of of the the open open pit pit and and a detailed look at the environmental aspects of of the the mine. mine. environmental aspects and WI WI Early Proterozoic Proterozoic Strata of the Marquette Range Supergroup, Supergroup. MI and Gene John Klasner, Gene LaBerge, University of Wisconsin, Oshkosh, John Western Illinois University, University,and andBill Bill Cannon, Cannon,U.S. U.S. Geological Survey Western Illinois Survey 2compriseaa 2Early Proterozoic Proterozoic strata strata of the Marquette Marquette Range Supergroup Supergroup comprise 3 km-thick sedimentary sequence recording sedimentation successively successively on on a stable craton, passive margin, margin, and and compressional compressional foreland. foreland. Recent detailed mapping has led to to new new insight insight about the depositional environments and postdeformation of Bad River River depositional deformation of the various units, which include the Bad Dolomite, the Palms Formation, the Ironwood Iron-Formation, Iron-Formation, and the Tyler Tyler Dolomite, Formation. As As many many as as three three possible possible trips may be developed from the recent work; examine the eastern part of of the the section section in in Michigan, Michigan, the work; these would examine near the Penokee western part part of of the the section section in in Wisconsin, Wisconsin, and aa cross-section cross-section near the structural structuraldeformation deformation and and stratigraphic stratigraphicrelations. relations. Gap, emphasizing emphasizing the Geology of of Northwestern Northwestern Wisconsin Glacial Geolo~v Adolphus College Mark Johnson, Gustavus Adolphus This field field trip will investigate the margin of This of the Superior Superior lobe lobe of of late late Wisconsinan age in northwestern looking at at landforms (tunnel Wisconsinan age northwestern Wisconsin, Wisconsin, looking (tunnel ice-walled-lakeplains) plains)and and typical typical sediment sediment types types channels, eskers, hummocks, ice-walled-lake Falls till, till, outwash, outwash, and and lake lake sediment). sediment). The trip will (Cooper Falls will also also look look at at the the Spooner eroded hills, built by catastrophic Spooner Hills, a band band of of high-relief, eroded catastrophic releases releases of one stop stop will will be be devoted to highlighting subglacial meltwater. Finally, Finally, one highlighting the the history history of of glacial glaciallakes lakes in inthe theClam-Yellow-River Clam-Yellow-River lowland. lowland. Sulfide Mineralization Mineralization in of the the Midcontinent Rift in Basalts of Cannon and Bill Cannon and Laurel Laurel Woodruff, Woodruff, U. U. S. Geological Survey Preliminary field field studies studies on on the north limb of Preliminary of the Ashland syncline syncline in isc cons in has revealed widespread copper sulfide mineralization in northern Wisconsin basalt basalt quarries quarries of of the theMiddle MiddleProterozoic ProterozoicChengwatana Chengwatana Volcanics. Volcanics. Mineralization has has been been found in numerous quarries Mineralization auarries and and natural natural exposures. exnosures. occurmostly mostlyin inamygdules amygdules and and open open space Chalcopyrite, bornite, and chalcocite occur filling in in altered fragmental basalt flow flow tops, tops, in in much much the the same same manner manner that filling fragmental basalt of the the Keweenaw Keweenaw Peninsula. Peninsula. This field native copper copper occurs occurs in correlative basalts of trip will visit several several exposures exposures displaying displaying various aspects of this little-known type type of mineralization. mineralization. 1 1 . 76 �GEOLOGICAL GEOCHEMISTRY OF OF MASSIVE MASSIVE SULPHIDE SULPHIDE DEDEGEOLOGICAL SETTING AND GEOCHEMISTRY AND ALTERATION ALTERATION ZONES ZONES IN THE THE MANITOUWADGE MANITOUWADGE GREENSTONE GREENSTONE POSITS AND ONTARIO BELT, NORTHWESTERN ONTARIO E. Zaleski, Zaleski, Geological KIA OE8 V.L. Peterson, GeologicalSurvey SurveyofofCanada, Canada, Ottawa, Ottawa, Ontario, K1A 0E8 and V.L. Department of of Geosciences, Geosciences, Western Carolina Carolina University, University, Cullowhee, Cullowhee, North Carolina, Carolina, 28723, 28723, U.S.A. The base-metal belt provide of the base-metal deposits deposits of the the Manitouwadge Manitouwadge greenstone greenstone belt provide a classic classic example example of difficulties encountered of mineralization mineralization in in complex complex metamorphosed metamorphosed and and difficulties encountered in in petrogenetic studies of polydeformed terranes. The Manitouwadge belt is a highly polydeformed Manitouwadge belt highly deformed deformed remnant of of supracrustal supracrustal rocks in in the volcano-plutonic Wawa subprovince, subprovince,immediately immediatelysouth southof ofthe the major major tectonic tectonic boundboundrocks volcano-plutonic Wawa the figure figure in in Peterson Peterson et et al., metasedimentary-migmatitic Quetico Quetico subprovince subprovince (see see the ary with the the metasedimentary-migmatitic this volume). volume). The The map map pattern patternisisdetermined determinedby byregional regionalD3 D3folds, fo ds, including including the the Manitouwadge Manitouwadge synform. Dl synform. D l and and D2 D2 structures structures repeat repeat mineraiized mineralized and and altered altered horizons. horizons. Our Our understanding understanding of of the depositional setting and genetic relationships relationships of of the base-metal deposits, alteration zones and host rocks, depends on unravelling the effects of of ductile ductile deformation deformation and metamorphic recrystallization. The belt belt comprises comprises aamafic-to-felsic mafic-to-felsic volcanic volcanic succession, succession, in which which felsic felsic rocks rocks are are interleaved interleaved with iron previously assumed assumed to iron formation formation and and massive massive sulphide sulphide deposits. deposits. Greywackes, Greywackes, previously t o reflect reflect 25 Ma Ma clastic sedimentation sedimentation (Friesen least 25 a transition from from volcanism volcanism tto o clastic (Friesenetet al., al., 1982), 1982), are are at least younger younger than the the2720 2720 Ma Ma felsic felsic volcanism volcanism and probably probably aa tectonic tectonic enclave enclave of of Quetico Quetico rocks rocks (Za(Zaleski al., 1995). 1995). AAsynvolcanic synvolcanic trondjhemite trondjhemite intrusion intrusion was was aareservoir reservoir for for felsic felsic volcanism volcanism and leski et al., heat source source for hydrothermal activity. All All rocks rocks have have been metamorphosed metamorphosed tto o upper amphibolite amphibolite facies, including including two zones zones of of synvolcanic synvolcanichydrothermal hydrothermal alteration, alteration, now now characterized by by metamorfades, phic phic minerals. minerals. Orthoamphibole+garnet±cordierite Orthoamphibole&garnet±cordieritgneiss gneiss forms a stratabound strataboundsheet sheet of ofregional regional extent, mantling trondjhemite in the stratigraphic mantling synvolcanic synvolcanic trondjhemite stratigraphic footwall footwall (structural (structuralhanging hangingwall) wall) to t o the the mineral mineral deposits. deposits. The Theunit unitisisprimarily primarilydefined definedon onthe thepresence presence of of orthoamphibole-bearing orthoamphibole-bearing assemblages, which are interleaved sillimanite-cordierite-biotite±garnelayers. layers. HornblendeHornblendeassemblages, which interleaved with sillimanite-cordierite-biotite+garnet plagioclase±orthamphibole±cummingtonite±garnet assemblages plagioclase&orthamphibole~cummingtonite~garnet assemblagesbecome becomemore morecommon commonaway away from known mineral deposits deposits and are interpreted as known mineral as less less intensely intensely altered altered mafic mafic rocks. rocks. The Theprecursers precursors to t o alteration, alteration,recognizable recognizable in inless lessaltered alteredenclaves, enclaves,were weremafic maficand andinterlayered interlayeredmafic-felsic mafic-felsicrocks rocks near the transitional sillimanite-muscovite-quartz transitional mafic-felsic mafic-felsic contact. The The second second alteration alteration unit, unit,sillimanite-muscovite-quartz schist, occurs in close proximity proximity to massive suiphide deposits, deposits, mostly mostly in in the stratigraphic massive sulphide stratigraphic hanging hanging wall orebodies including includingthe the largest largest in in the the belt, the wall (structural footwall). footwall). It It also also envelopes envelopes some orebodies Geco main orebody. orebody. The precurser found along-strike Geco main precursor to t o alteration alterationwas wasfelsic felsic volcanic volcanic rock found along-strike and in less altered enclaves. less enclaves. The Geco, massive sulphide suiphide deposits deposits lie lie in in the the northern part Geco, Willroy, Willroy, Nama Creek and Willecho massive part of the the southern limb and synform (see (see the the figure figure in in Peterson Peterson of and hinge hinge region region of the D3 D3 Manitouwadge Manitouwadge synform et al., this this volume). volume). A A Dl D l fault fault divides divides the the area area into into two two tectonic tectonic blocks blocks and repeats part of of the mineralized sequence. sequence. In the Willecho area, original original stratigraphic stratigraphic relationships relationships are further obscured mineralized Willecho area, by D2 folds folds of of the the Dl by D l fault fault and and mineralized mineralized sequence. sequence. The The structural structural complexity complexity can be be partly partly resolved by by examining examining the the characteristics of orebodies and mineralized horizons. Based resolved characteristics of orebodies and mineralized horizons. Based on on CuCuZn-Pb proportions, proportions, nature of and relationships Zn-Pb of mineralization, mineralization, and relationships tto o iron formation formation and alteration zones, orebodies of Manitouwadge camp divided into three main main types. types. Firstly, zones, the the orebodies of the Manitouwadge camp can can be be divided Cu-rich stringer/disseminated orebodies orebodies lie in the the orthoamphibole-garnet-cordierite Cu-rich stringer/disseminated orthoamphibole-garnet-cordieritefootwall footwall and, Secondly, the Geco Geco area, area,surround surroundthe themain mainorebody orebodyininsiffimanite-muscovite-quartz sillimanite-muscovite-quartz schist. schist. Secondly, in the massive and and semi-massive Zn-Cu-(Pb) orebodies orebodiesare are hosted hosted by by iron iron formation formation and enveloped by massive semi-massive Zn-Cu-(Pb) enveloped by siffimanite-muscovite-quartz schist, or or interleaved interleaved with with schist schist and quartz-phyric felsic rocks. rocks. This sillimanite-muscovite-quartz schist, group includes includes the largest orebodies; orebodies; the Geco Geco main main and Willroy Willroy #3 orebodies. orebodies. Thirdly, group the two largest massive and semi-massive Zn-Pb-(Cu)orebodies, orebodies,interpreted interpretedasashighest highestinin the the stratigraphy, are massive and semi-massive Zn-Pb-(Cu) hosted by iron formation sillimanite-muscovite-quartz schist. formation that thatoverlies overlies sillimanite-muscovite-quartz Despite Despite the unusual unusual extent extent and andcorcordance corcordance of ofalteration alterationzones zonesatatManitouwadge, Manitouwadge,geochemgeochemical trends from 'least-altered' ical 'least-altered7 to t o intensely intensely altered, altered, such such as as increase increase in FeO+MgO FeOf+MgOand andA1203, A1203, and depletion and CaO, CaO, are similar recorded in in alteration alteration pipes pipes in in the Abitibi depletion in alkalis alkalis and similar tto o those recorded Abitibi camp (Riverin and and Hodgson, Hodgson, 1980). 1980). All All felsic felsic extrusive extrusive rocks rocks show show evidence evidence of potassic alteration; alteration; whereas, synvolcanic trondjhemite preserved its primary primary sodic sodiccomposition. composition. Similar whereas, synvolcanic trondjhemite apparently preserved observations of of alkali alkali exchange exchangehave havebeen beenmade madeinin the the Abitibi Abitibi camp camp with with respect observations respect to t o the the synvolsynvolcanic canic Flavrian pluton and and its its extrusive extrusive equivalents equivalents (Goldie, (Goldie, 1979). 1979). 'Immobile' 'Immobile' elements in altered altered \ 77 �rocks at Manitouwadge tend to define bimodal populations that mimic element abundances in mafic and felsic precursers. The bimodal distribution shows that orthoamphibole-garnet-cordierite rocks and sillimanitic interlayers had both mafic and felsic protoliths; the metamorphic assemblage was determined by small variations in (FeOt+MgO)/A1203, apparently due to alteration and not inheritance from the protolith. The unusual extent of orthoamphibole-bearing gneiss at Manitouwadge may be partly due to the high metamorphic grade. With increasing grade, orthoamphibole-hornblende stability expands the range of orthoamphibole-bearing assemblages to more calcic bulk-rock compositions (Spear. 1993, pages 478—489). By inference, bulk-rock compositions that produced orthoamphibole-bearing rocks at Manitouwadge might, at lower metamorphic grade, be considered incipient alteration. The closest analogues for the stratabound regional orthoamphibole-bearing alteration are found in the Bergslagen area of the Svecofennian Baltic shield. At Bergslagen, exhalative base-metal deposits and iron formation are underlain by conformable stratabound Mg-rich alteration zones of regional extent (TrAgtrdh, 1988; Itipa, 1988; Baker et al., 1988). Amphibolite-facies metamorphism at Bergslagen may play a role, as at Manitouwadge, in facilitating identification of altered rocks. However, in both areas, it appears that alteration was partly focussed on aquifer horizons possibly consisting of permeable, poorly consolidated volcaniclastic deposits. Baker, J.H., Hellingwerf, R.H. and Oen, 1.5. 1988. Structure, stratigraphy and ore-forming processes in Bergslagen: implications for the development of the Svecofennian of the Baltic Shield. Geologie in Mjinbouw 67, 121—138. Friesen, R.G., Pierce, GA., and Weeks, R.M. 1982. Geology of the Geco base metal deposit. Geological Association of Canada, Special Paper 25, 343—363. Goldie, It. 1979. Consanguineous Archaean intrusive and extrusive rocks, Noranda, Quebec: chemical similarities and differences. Precambrian Research 9, 275—287. Ripa, M. 1988. Geochemistry of wail-rock alteration and of mixed volcanic-exhalative fades at the Proterozoic Stoilberg Fe-Pb-Zn-Mn(-Ag)-deposit, Bergslagen, Sweden. Geologie in Mjinbouw 67, 443—457. Riverin, G. and Hodgson, C.J. 1980. Wall-rock alteration at the Millenbach Cu-Zn mine, Noranda, Quebec. Economic Geology 75, 424—444. Spear, P.S. 1993. Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths. Mineralogical Society of America, Monograph, Washington, D.C., 799 pages. Trägá.rdh, 3. 1988. Cordierite-mica-quartz schists in a Proterozoic volcanic iron ore-bearing. terrain, Riddarhyttan area, Bergslagen, Sweden. Geologie in Mjinbouw 67, 397—409. Zaleski, E. and Peterson, V.L. 1995. Geology of the Manitouwadge greenstone belt overlain on shaded relief of total field magnetics. Geological Survey of Canada, Open File 3034, scale 1:25000. Zaleski, E., Peterson, V.L. and van Breemen, 0. 1995. Geological and age relationships of the margins of the Manitouwadge greenstone belt and the Wawa-Quetico subprovince boundary, northwestern Ontario. Current Research 1995-C, Geological Survey of Canada, 35—44. 2 78 �DERIVATIVECONTINENTAL CONTINENTALINDICATIONS INDICATIONSOF OFAACURVILINEAR CURVILINEARCARIBBEAN CARIBBEANMANTLE MANTLE DERIVATIVE CONVECTION CONVECTIONPLUME PLUME ZBIKOWSKI,Douglas DouglasW., W.,Geological GeologicalSociety Societyof ofMinnesota, Minnesota,7833 7833Able AbleSt StNE, NE,Spring SpringLake LakePark, Park, ZBIKOWSKI, MN MN 55432 55432 Inextricably Inextricablyinterrelated interrelatedto tothe therecurved-bow recurved-bowinterpretation interpretationof ofthe theMRS MRSdevelopment, development,isisintroduced introducedaa second secondhypothesis, hypothesis,proposing proposingthat thatwhen whenthe theIowa Iowabow bowinitially initiallyfractured, fractured,its itscontinental continentalterritory territorywas was positionedover overaadistinctively distinctivelycurvilinear curvilineararray arrayofofrelated relatedmantle mantleconvection convectionupwelling, upwelling,which whichoriginally originally positioned establishedand andcontinues continuesto todefine definethe the perimeter perimetermargins margins of of the the eastern eastern end end of the Caribbean Caribbean plate. The The established ancientformation formationof ofthis thiscurvilinear curvilinearplume's plume'scharacteristic characteristicarc arcshape shapeisisreasoned, reasoned,by byrationale rationaleand and ancient evidence, evidence,to toexhibit exhibitaacoriolis coriolisinfluence, influence, upon upon its its early early convection's convection's melt meltflow. flow. The Theemergent emergentscenario scenarioisisthat thatafter afterthe theIowa Iowabow bowfracturing fracturingofofthis thisfirst firstcontinental continentalsuperposition, superposition,the the plumeremained remainedstationary stationarywhile whilethe thecontinent continentwas wasmoved movedabout about160 160km, km,possibly possiblyby bythe thecollision collisionofofthe the plume GrenvilleProvince. Province.Subsequently, Subsequently,the themovement movementsubsided subsidedand andaasecond secondrift riftsystem systemdeveloped, developed,which whichisis Grenville indicated indicatedtoday todayby bythe theclear cleardelineation delineationofofthe thesame sameplume plumeprofile profileby byderivative derivativeaeromagnetic aeromagneticeffects effectsfrom from the theattendant attendantsurface surfacerifting; rifting;and andby byaasecond secondrecurved recurvedbow bowininsouthern southernMichigan, Michigan,which whichisissymmetrically symmetrically coincident 90 degree degree alignment alignment to to the Iowa Iowa coincidentto tothe therift riftpattern, pattern,and andexhibits exhibitsboth both aastressfully stressfullysignificant significant90 bow, bow,and andisisconcordant concordantwith withititinincurvature curvaturephase phasewith withrespect respecttotothe theinterior interiorside sideofofthe thesame samerift riftpattern. pattern. This Thisunique uniqueorientation orientationisisan anextremely extremelysignificant significantevidential evidentialcorrelation correlationbetween betweenthe therecurved-bow recurved-bow hypothesisand andthe theCaribbean Caribbeanconvection convectionplume plumehypothesis, hypothesis,asasititlends lendsvalidity validitytotoboth boththe theproposed proposed hypothesis mechanisms mechanismsby bygraphically graphicallyillustrating illustratingthe theinterrelationship interrelationshipbetween between the the two two developments. developments. Also, Also, supporting supportingconsistent consistentpattern patterncorrespondence, correspondence,the thepaleogeographic paleogeographicposition positionofofthe thelength lengthaxis axisofofthe theIowa Iowa bow, bow,paleomagnetically paleomagneticallymatches matchesthe theCaribbean Caribbeanplate's plate'snorthern northernmargin. margin. Could Couldaacurvilinear curvilinearmantle mantleconvection convectionplume, plume,positioned positionedunder underthe theCaribbean Caribbeanplate, plate,have havecreated createdthese these continental continentaland andoceanic oceaniccrustal crustalpattern patternreplications? replications?ItItisissuggested suggestedthat, that,asasaacomposition compositionimplies impliesaa history, history,the thecoincidence coincidenceof ofthree threephysical physicalmatchings matchings of of derivative derivativeeffects effects in in accessible accessible proximity, proximity, begs begs for for thoughtful consideration of a common causal source. thoughtful consideration of a common causal source. 79 �CONTINENTAL CRUST FRACTURE INITIATION PATTERN AND A CONTINENTAL AND HYPOTHETICAL HYPOTHETICAL MECHANISM MECHANISM Douglas W., Geological Geological Society Society of of Minnesota, Minnesota, 7833 7833 Able Able.St Spring Lake Lake Park, Park, ZBIKOWSKI, Douglas St NE, Spring MN MN 55432 55432 A A careful careful observation observation of of the the North North American American Midcontinent MidcontinentRift Rift System System (MRS) (MRS) as as detailed detailed on on aa Bouguer Bouguer gravity map map filtered filteredto to exclude excludefeatures featureswith withwavelengths wavelengthsgreater greaterthan than 250 250 km, km, reveals reveals aa distinctive distinctive gravity symmetry and and geometric geometric regularity regularity between southern Minnesota and southeastern Nebraska. The symmetry Nebraska. The SE,and andaa symmetry expressed expressedisis reflected reflectedrelative relativeto to both both aaprimary primaryaxis axisoriented orientedfrom fromthe the NW NW to tothe theSE, symmetry secondary axis axis oriented oriented orthogonally. orthogonally. The Theaxes axesof ofsymmetry symmetryon on the the map's map's surface, surface, are are interpreted interpreted to to secondary represent the the intersections intersectionsof of two two orthogonal orthogonalradial radialplanes planes of of reflection reflectionwith with the the spherical sphericalcrustal crustalsurface. surface. represent The observed observed symmetrical symmetricalpattern patternof of rift rift curvature curvaturesuggests suggestsaa causal causalrelational relationalinfluence influencesuperimposed superimposed The fracture formation formationprocess processby by some somecompelling compellingfeatures featuresor or events eventslocated locatednearby, nearby,and andwithin within upon the fracture these two two radial radial planes planes of of reflection. reflection.This Thisisisbecause, because,mechanistically, mechanistically,simple simplenatural naturalsymmetry symmetryisisthe the these physicalmanifestation manifestationof ofspatial spatialpattern patternthat thatreflects reflectsan aninvariance invarianceofofdistance distancedependent dependentcausal causal physical relationship. relationship. It is is hypothesized hypothesizedthat that the the crust crustfracture fracturecurvature curvatureisisthe the product product of ofaa curvilinear curvilineararray arrayof ofrelated relatedmantle mantle It convection upwelling upwelling aligned alignedunder under the the secondary secondaryaxis, axis, that that produces producestension tension and and other otherconvection convection convection related stresses stressesin in the the crust. crust.The Thesymmetrical symmetricalcurvature curvatureproduced producedby bythe theinitial initialpropagation propagationof ofcrustal crustal related This figure figure isis aa fracture under under these stresses, stresses, exhibits exhibits a profile very similar to an archer's recurved bow. This fracture surface surface expression expression of of an an extensional extensionalcrust crustfracture fractureregime, regime, and and delineates delineatesan an initial initialpenetrating penetratingnormal normal fault which which later later bounded bounded an an upwelling upwelling decompression melt. ItIt isisfurther furtherproposed proposed that that the the entire entire rift rift fault fracture started startedwith with this this figure, figure,that thatthe thecurvature curvatureresults resultsfrom froman anelastic elasticstrain strainrelease releaseof ofregional regionalcrustal crustal fracture material materialduring duringits itsfracture, fracture,and andthat thatsimilar similarsignature signatureprofiles profileshave havepast pastrecorded recordedoccurrences occurrencesworldwide. worldwide. A tensive, tensive,adjunctive adjunctiveemergence emergenceof ofaatriple triplejunction junctionof offracture fractureisisoffered offeredtotosupplant supplantits itspreviously previously A imagined imagined role role in in the the rift's rift's creation creation and and growth. growth. The Thesignature signaturebow bow fracture fracturehypothesis hypothesis isis further further supportedby by evidence evidenceof of the the regular regularappearance appearanceof of several severalcollateral collateralfeatures featureswhich whichare arelogically logicallyrelated related supported to the the bow's bow's development developmentand and have have been been noted noted at at other other suspected bow fracture locations. Thus, Thus,from fromthe the to creative application applicationof ofpattern patternrecognition recognitionwith with aamechanistic mechanisticunderstanding understandingof ofsimple simplenatural naturalsymmetry, symmetry, creative andgiving givingconsideration considerationtotogeometric geometricmaterial materialstress stressprojection, projection,aahypothetical hypotheticalfracture fracturedevelopment developmentisis and presented. presented. 80 � https://digitalcollections.lakeheadu.ca/files/original/81d7f8c9cd4ef4122e13d1b6328bd71c.pdf 0ffa2b160f299d59ab6be01138109912 PDF Text Text o f the Midcontinent Rift Rift Alkalic Rocks of Institute Instituteon onLake LakeSuperior SuperiorGeology Geology 41st 1995 41st Annual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon, Ontario Ontario Proceedings Part 2a 2a Proceedings Volume Volume 41: Part Field Field Trip TripGuidebook Guidebook 4JStJISC l_ Ii /—% — / 4I / I �Alkalic Rocks of the Midcontinent Rift by Ronald P. Sage' Sage1and andDavid. David.H. H. Watkinson2 Watkinson2 'Mineral 'MineralDeposits Deposits and and Field Field Services Services Section Section Ontario Geological Ontario Geological Survey Ministry of Northern Northern Development and Mines 8th Floor, Floor, 933 933 Ramsey Lake Road Sudhury, ON ON P3E 6B5 Sudbury, 6B5 2Department of of Earth Earth Sciences 'Department Carleton University Carleton University Ottawa, ON K1S 5B6 Frontispiece: Orbicular Orbicular jolite ijolitefrom the the Prairie PrairieLake Lake carbonatite, carbonatite, the the world's world's only only known occurrence of this texture occurrence texture in in aa rock rock of of this this composition composition (photograph (photograph courtesy of John Scott) Scott) �CHAIRMAN'S NOTE: Due to sudden illness, co-author co-author and and field trip trip co-leader co-leaderDr. Dr. David David Watkinson Watkinson could could not not take take part ininthese thesefield trips tripsthat thatfeature featurethe thealkalic alkalicrocks rocksassociated associatedwith withthe theMidcontinent Midcontinentr?ft rift in inthe the part vicinity Dr.Watkinson Watkinson's vicinity of of Marathon. Marathon. Dr. 's continuing research research into the petrology petrology and metallogeny of twenty-fiveyears. years. He He has expressed his his regrets regrets about not being able to these rocks dates back twenty-five G.. I.L.S.G.. attend but has has wished wished all all meeting meeting and and trip tripparticipants participants the thebest bestof ofluck luck during during the the 41st 41stIL.S. I'm that you will will join me in extending our best wishes for to I'm sure that join me for a speedy and complete recovery to Dr. Watkinson. Watkinson. In the absence of Dr. Watkinson, ClffShaw Watkinson, Dr. Cliff Shaw(Post-Doctorate (Post-DoctorateFellow, Fellow,University Universityof of Western Western field trips trips with with Dr. Dr. Ron RonSage. Sage. Dr. Shaw has just just Ontario) has graciously offered offered to co-lead thesefield completed his Ph.D. thesis on the gabbros of complex and and has has taken part part in the of the Coldwell complex recent 1:20 definitely be be an asset 1:20 000 000 scale scale mapping mapping project project of of the the complex. complex. This Thisknowledge knowledge will definitely during these trips. trips. On Onbehalf behalfofofthe theIL.SG. I.LSG.organizing organizingcommittee, committee,IIwould wouldlike like to toexpress express my my for stepping in on such such short short notice notice and and wish wishall allofyou ofyou aa great greatfield field trip! trip! gratitude to to Dr. Shaw Shaw for Mark Smyk Chairman, 41st Chairman, 41stI.L.S. I. L.S.G. G. April 23, 1995 �2 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The The authors authors were were helped helped in in preparation preparation of of trails trails and and sites sites by by Mr. Mr. Duncan Duncan Michano Michano of of Heron Heron Bay, Bay, Ontario. Ontario. Permission Permission to to examine examine outcrops outcrops of of the the Dead Dead Horse Horse Creek Creek Diatreme Diatreme was was granted granted by by Mr. Mr. John John Ternowesky, Ternowesky, Prospector, Prospector, Thunder Thunder Bay, Bay, Ontario. ~ntario.Mr. Mr. J. J. McGoran, McGoran, President, President, Fleck Fleck Resources Resources Ltd., Ltd., Vancouver, Vancouver, agreed agreed to to display display diamond diamond drill drill core core and and samples samples from Coldwell from the the Two Two Duck Duck Lake Lake intrusion intrusion within within the the Port Port Coidwell Complex. Complex. The The Ontario Ontario Geological Geological Survey Survey donated donated copies copies of of Geological ~eological Studies 27, 45 and 46 and Geological Report 264 to the the Studies 27, 45 and 46 and Geological Report 264 to Institute Institute of of Lake Lake Superior Superior Geology Geology in in support support of of the the alkalic alkalic rock These reports reports provide provide the the background background data data rock field field trip. trip. These and and more more detailed detailed maps maps for for the the Slate Slate Islands, Islands, Killala Killala Lake Lake Complex, Complex, Prairie Prairie Lake Lake Carbonatite Carbonatite and and Diatreme Diatreme structures structures found in the region. found in the region. �3 ALKALIC ROCKS OF THE MIDCONTINENT RIFT Introduction Introduction intrusions occur in an area that extends extends from Alkalic rock intrusions the north shore of Lake Superior in a north to east of north km. The The diatreme structures direction for approximately 140 km. Slate Islands(Sage, Islands(Sage, 1991) 1991) and and the the carbonatite carbonatite found on the Slate dikes with associated associated fenite fenite in in the the Geraldton Geraldton area(Sage, area(Sage, excluded from from the the present tour tour due due to to 1985) will be excluded access(Slate Islands) or distance(Chipman distance(Chipman difficulty of access(S1ate Lake)(Figure examine the the Lake) (Figure 1). 1). An An attempt attempt will will be be made made to examine types in in the the alkalic rock, carbonatite and major rocks types diatreme structures near Marathon, Marathon, ~ntario. Ontario. By necessity the visits to individual individual outcrops will be brief. Whenever Whenever possible, economic aspects aspects of the the alkalic alkalic rocks rocks will will be be emphasized. Some optional optional stops stops are included included in in the the guidebook for those who wish wish to to spend spend additional additional time on their own in the area examining exposures exposures which which time time does does not permit this this tour tour to to visit. visit. Regional Reuional setting settinq The Midcontinent Rift is is represented by aa horseshoe horseshoe shaped shaped gravity and aeromagnetic aeromagnetic anomaly open to to the the south south that that is is exposed in the region(Figure 2) the Lake Superior Superior region(Figure 2) and and lies lies east east of the Kapuskasing Structural Zone(KSZ) Zone(KSZ) and and northwest northwest of of the the (Figure 3). western Grenville Front Front Tectonic Tectonic Zone(GFTZ) Zone(GFTZ)(Figure 3). The western this gravity and aeromagnetic anomaly strikes limb of this strikes southwest southwest into Kansas and it it has been postulated postulated by by Adams Adams and Keller(1994) to to extend as far far south south as as west west Texas Texas and and eastern New Mexico. Mexico. The eastern arm of the the Midcontinent Midcontinent Rift Rift strikes strikes southeast southeast into into southern southern Michigan and and has has been been extended into Ohio and Kentucky by Dickas et al.(1992). al.(1992). The The Dickas et rift has been interpreted interpreted to to be a triple triple junction junction formed formed by by a rising and Dewey(1973); however, rising mantle mantle pluine(Burke plume(Burke and however, junction has has not not Green(1983) concluded concluded that a triple junction the usual sense sense due to the the U-shape of of the the rift developed in the and the abrupt abrupt termination termination of activity along along it. it. The The model model of decompression decompression melting over an upwelling upwelling mantle mantle plume plume in in an extensional extensional lithosphere lithosphere environment is is the the favored favored model model at present(Nicho1son present(Nicholson and and Shirley, Shirley, 1990; 1990; Hutchinson Hutchinson et et al. al. 1990). Nicholson Nicholson and Shirley(1990) indicated 1990). indicated that large large volumes of magma of dominantly tholeiitic tholeiitic composition composition extruded over a short short period is is consistent consistent with with the the mantle mantle model. Tre'hu plume model. Trethu et al.(1991) al.(1991) stated stated that that the the Midcontinent Rift resembles resembles a passive continental continental margin models of which is in marked contrast to to many models of active active and and extinct Phanerozoic rift zones. zones. Behrendt et al. (1988) (1988) have also noted that the Midcontinent Rift is different different from �4 :•::: 5O•OO. .. . . . . ...'. ..•. I komes al 4 a - B/ I I' LAKE SUPER/Cl? N Granitic rocks Supracrustil rocks Aikalic rock and carbonatite intrusions Major Major carbonatite—alkalic carbonatite-alkalic Intrusions Intrusions and and major major regional regionalfaufts fault8 48) 30) 30) Chlpman ChipmanLake Lakefenitea fenites 48) McKeflar McKeflarCreek Creekdiatreme diatrerne 49) 49) Gold GoldRange Rangediatreme diatreme dikes and carbonatite dikes diatreme 31) KIllala Klllala Lake Lake aliaflc a l k a kcomplex comdex 50) 50)Neys Neys diatrenr 31) 32) 32) Prairie PrairieLake Lakecarbonatite carbonattte 33) 33) Port PortCoidwelt ColdwellaNaNc alkaRccomplex complex A) 36) Slate SlateIslands Islandsdiatremes diatremes A) Michipicoten MichipicotenIsland Islandfault fault 30) B) and carbonattte carbonatit. dik. dike B) Big BigBay Bay- -Ashburton AshburtonBay Bay fault 47) Dead DeadHbrse HbraeCreek Creek dlatrem. diatreme fault and and Its its extrapolated extrapolated 47) northern northern extension extension Figure 1: 1: Index map showing showing the the location location of features features Figure associated associated with with Keweenawan Keweenawan alkaline alkalineinagmatism(from mag-matism(from Sage, Sage, 1986). 1986). �5 ID 92 56• / 88 / 84 so. 4UOSON a4Y / 52• i. ac ONTARIO 041(07.4 I MINNso - WISCONSIN 38 KIL.OMTERS a Figure2: 2: Index Indexmap mapshowing showinggeneral generallocation locationof ofthe the Figure includes Rift System (Shaded Area). Shaded area Midcontinent Rift System (Shaded Area). Shaded area includes Midcontinent high associated with the rift that that part of the gravity high associated with the rift that that part of the gravity the portion extending into is greater than -20 milligals; the portion extending into is greater than -20 milligals; Kansasisisdrawn drawnalong alongthe the-40 -40 milligal milligalcontour. contour. The Thegravity gravity Kansas defines location of dense high roughly, but not uniquely, defines location of dense high roughly, but not uniquely, Midcontinent Rift System. The rift crust associated with the Midcontinent Rift System. The rift crust associated with the although the gravity high is extends beneath Lake superior, although the gravity high is extends beneath Lake Superior, because of structural not continuous in this area because of structural not continuous in this area complexities.Modified Modifiedfrom fromKiasner Klasneretet al. al. (1982). complexities. (1982). �C' :: i.. II rP I• m H o i-i. •— • . mil WU)O 03 II Crap' H'< U. pa i-.. o tn '0 I-I. 0 40 Pa 03 rI —. r1 I-• l.a- I-m n ilH mm 0 Pa —. Jil pam Pa (DH II H U) P1 - ilL.3 Oil Oil t:-rtø Pfl) '11 Figure 3: Index map showing relationship of major regional structural features to the Midcontinent Rift System(Modified from Lumberst 1978; Brummert 1978; from Sage, 1986). �7 Phanerozoic rifts rifts in in that that it it has has aa crustal crustal thickness thickness equal equal Phanerozojc to or or greater greater than than the the surrounding surrounding unextended unextended terrane. terrane. to high-velocity lower lower crustal crustal layer layer is is thickest thickest beneath beneath the the AA high-velocity rift graben graben under under Lake Lake Superior Superior and and is is interpreted interpreted to to be be rift magmatic material material underplated underplated during during rifting(Behrendt rifting(Behrendt et et magmatic et al., al., 1991; 1991; Shay Shay and and Tre'hu, Trerhu,1993). 1993). al., 1990; 1990; Tre'hu Trefhu et al., Gravity modeling modeling requires requires large large buried buried masses masses of of mafic mafic Gravity igneous rocks rocks of of assumed assumed Keweenawan Keweenawan age age beneath beneath the the igneous Midcontinent Rift Rift whose whose distribution distribution is is asymmetric(Mariano asynunetric(Marian0 Midcontinent and Hinze, Hinzer 1994b; 1994b; Thomas Thomas and and Teskey(l994). Teskey(l994)- This This asymmetry asymmetry and implies that that the the northern northern margin margin of of the the rift rift is is dominated dominated by by implies plutonic rocks rocks and and the the southern southern margin margin by by volcanic volcanic plutonic rocks(Thomas Complex rocks (Thomas and and Teskey, Teskey, 1994)1994). The The Port Port Coldwell Coidwell Complex and Duluth Complex are manifestations of the dominant and Duluth Complex are manifestations of the dominant plutonic northern northern margin. margin. Allen Allen et et al. al. (1992) (1992) suggested suggested that that plutonic a topographic dome centered on Lake Superior represents the a topographic dome centered on Lake Superior represents the effect of the mantle plume active in the Keweenawan time of effect of the mantle plume active in the Keweenawan time of rifting which is now maintained isostatically by changes to rifting which is now maintained isostatically by changes to These changes changes consist consist of of magmatic magmatic the lithosphere. lithosphere. These the underplating and depletion of the upper mantle. Paces and and underplating and depletion of the upper mantle. Paces Miller(1993) compiled existing U-Pb geochronological and Miller(1993) compiled existing U-Pb geochronological and paleomagnetic data data for for volcanic volcanic and and intrusive intrusive rocks rocks within within paleomagnetic the Lake superior Basin. A simplified version of their data the Lake Superior Basin. A simplified version of their data is given in Table 1 which demonstrates that the Duluth is given in Table 1 which demonstrates that the Duluth U-Pb isotopic isotopic Complex and and Port Port Coldwell Coldwell Complex Complex have have similar similar U-Pb Complex ages and were emplaced just before and after a paleomagnetic ages and were emplaced just before and after a paleomagnetic reversal; from from reverse reverse polarity(Port polarity(P0rt Coidwell) Coldwell) to to normal normal reversal; polarity(Du1uth Complex). Samson and West(l994) reported polarity(Duluth Complex). Samson and West(1994) reported that this this reversal reversal occurred occurred at at approximately approximately 1097 1097 Ma. Ma. During During that this polar reversal the composition of the volcanic rocks this polar reversal the composition of the volcanic rocks changes from from those those displaying displaying crustal crustal contamination(Osler contamination(Os1er changes series) to those displaying typically uncontaminated series) to those displaying typically uncontaminated asthenospheric mantle—derived mantle-derivedmelts melts(Mamainse asthenospheric (Mamainse Point)(Lightfoot et al. 1994). series evolved evolved Point) (Lightfoot et al. 1994). Both Both volcanic volcanic series from high-Mg primitive basal members to those of tholeiitic from high-Mg primitive basal members to those of tholeiitic composition; the the earlier earlier flows(Osler flows(Os1er series) series) may may represent represent composition; series(Mamainse Point; deeper partial melts than the later deeper partial melts than the later series(Mamainse Point; Lightfoot et a1.(1994). Lightfoot et al.(1994). TABLE 11 TABLE (Simplified from Paces and and Miller, Miller, 1993) 1993) (Simplified from Paces Rock Unit Unit Rock Polarity Polarity Unnamed Unnamed Copper City City Flow Flow Copper Greenstone flow flow Greenstone Lake Shore Shore Trap Trap Lake Nathanfs Layered Layered Nathan's Series Series Complex Duluth Duluth Complex Bay Complex Complex Beaver Bay Beaver RR NN Age(Ma) (Ma) Age ++++++— ++— ++- Reference Reference NN NN RR 1097.5 1097.5 1096.2 1096.2 1094.0 l094.0 1087.2 1087.2 1106.9 1106.9 33 1.8 1.8 1.5 1.5 1.6 1.6 0.6 0.6 11 22 22 22 33 NN NN 1099.0 ++- 0.5 0.5 1099.0 +1096.0 1096.0 +- 11 33 33 �8 Logan Sills Sills Osler Porphyry Porphyry Agate point Rhyolite Rhyolite Port Coidwell Coldwell Complex Michipicoten Island Michipicoten Island Formation Formation R R R R +4 —2 -2 1108.8 +4 1107.5 1107.5 +4 +4 -2 -2 1097.6 1097-6 ++- 3.7 3-7 1108 ++- 11 1108 4 4 4 5 N 1086-5 +13 —3.0 -3.0 1086.5 6 S c h u s et al.(1990); ale(1990); 2) 2) Davis Davis and and Paces(1990); Paces (1990);3) 3) 1) Van Schmus Paces and Miller(1993); Miller(l993); 4) 4) Davis Davis and and Sutcliffe(1985); Sutcliffe(l985); 5) 5) Paces Heaman and Machado(1992); Machado(l992); 6) 6) Palmer Palmerand andDavis Davis(l986) Heaman and (1986) In the Lake Lake Superior Superior region separation separation along the the rift axis axis was on the the order of 50 to 60 60 kn(K1asner ale 1982; km(Klasner et al. the resulting resulting Chandler, 1983; Shay and Trerhu, Tre'hu, 1993) and the graben filled with 30 to 32 km of volcanic and sedimentary sedimentary graben rocks(Trerhu et al., al., 1991; Behrendt et al., al., 1988; Cannon Cannon et et rocks(Tre'hu 1989). Gravity Gravity modeling modeling is is consistent consistent with with the the Keweenaw, Keweenaw, al. 1989). Isle Royal, Thiel(Big Bay-Ashburton Bay), Bay), Douglas and Michipicoten l?aults being growth faults faults controlling controlling Michipicoten Island Faults rift development(Thoiuas development(Thomas and Teskey, 1994)(Figure rift Teskey, 1994) (Figure 4). 4). Cannon Cannon al.(l989) interpreted regional seismic seismic data to to suggest suggest et al.(1989) Superior changes changes that the central graben beneath Lake Superior attitude along strike strike and thus the the rift is segmented attitude segmented and requires requires accommodation zones zones between the segments. segments- Sexton Sexton Henson(l994), using using an an interpretation interpretation of of seismic seismic data, data, and Henson(1994), the modeling of accommodation zones and suggested suggested questioned the accommodation zones closer inspection inspection zones zones of accomodation that upon closer accommodation may not required to to account account for for changing changing attitudes attitudes along along strike. strike. be required data, the depth depth to the Moho Moho beneath western From seismic datat Lake Superior Superior is is 37-46 km, central Lake Superior Superior Superior 42-49 approximately 55 km and in eastern Lake Superior kin(Behrendt et al. al. (1988). Trerhu Tre'hu et km(Behrendt et et al. al. (1991) (1991) and Shay and Tre'hu(1993) Trefhu(1993) used seismic data to to interpret interpret the crustal thickness thickness beneath the Midcontinent Rift as diminishing diminishing rapidly to the the south from 55 to to 60 60 km at the centre of the the rift to 35 km and gradually gradually to to the the north north to to 40 40 km. km. Bisecting the the gravity anomaly of the horseshoe-shaped Midcontinent Rift is the Trans-Superior Tectonic Zone Zone that contains the Thiel or Big Bay-Ashburton Bay-Ashburton Bay Bay Fault(Sage, Fault(Sage, 1978, (Figures 3, 1978, Kiasner Klasner et et al., al., 1982) 1982)(Figures 3 t 5, 6, and 7). This This zone of deformation is represented by by changes in isomagnetic isomagnetic and isomilligal contouring of aeromagnetic and gravity data(Figures 6 6 and 7) 7) and is also represented as a topographic topographic high on lake lake bottom contours(Hough, 1958, Wold (Figure 8). 8). The The Slate Slate Island Island Diatremes Diatremes and and the the et al. 1982) 1982)(Figure Port Coldwell Complex occur where this zone impacts impacts on the the north shore shore of Lake Superior and is is proximal to the Proterozoic—Archean contact. contact. Extrapolating faults related to Proterozoic-Archean this zone to the region of Chipman Lake(Sage, Lake(Sage, 1985), 19851, a distance of approximately 140 km, reveals a change distance 140 reveals change in the �_____ ______ I. ca, II Go Kopka cone sheets 2. i o , 11 Go Beordmwe cone sheets 3 ca, II Ga Fox Mountain dike 4. co, I1 Go Pigeon River dike swarm 5. co, II Ga hkoskwo 6 1.54 Ga 7. co, 2.lGo Paleozoic Paleozoic Illinois and Illinois ond Michigan Michigan basins basins dike sworm Mesoproterozoic Midcontinent Rift Midcontinent Rift a English Bay Gronile Clastic Clostic sedimentary sedlmentory rocks rocks Kenoro-Fort Frances (Kubetogoma) dike sworm 0 j Volcanic Volcan~crocks rocks(1.11-109 (1.11-109Go) 601 [ Intrusive rocks ricks (1.11-109 (1.11- 1.09Ga) GO) Anorogenic/Post - orogenic suites Anorogenlc/Post-orogenic suites Sibley Group-sandstone, Sibley Group - sondslane, carbonate carbonate >1.54 > l , 5 4 Ga Ga FTTg Granilold rocks Granitold rocks (148-177 (140- I 7 7Ga) Gal 2 Paleoproterozolc I%leoproterozolc Ponokean Penokeon Orogen Orogen and Related Related Rocks Rocks 1111111G~anitold Gionitoldond and volcanic volcanic arc orc rocks racks LLIJILJ(189-184 (18 9 - 184 Gal GO) u.ull nimikie Group Animlk~e Groupand andMarquette MarquetteRange Ronge Siipergroup St~pergroup(Ca. (ca 2.1-1.85 2 I- 185 Ga) Go) Archean Archeon 0 '.' - ** International boundary bcundory tic complexes Selected alka olkol~c complexes (see Sage, Soge, this this volume volume for more more detail) deta~l) Dikes lll1~\1'[ D~kes I , ' Faults Faulfs 'P geological features found in the the 4: Proterozoic geological 4: Major Proterozoic Lake ~ a k esuperior superior region(from region (from Sutcliffe, ~utclif%e,1991). 1991) Figure . faults Thrust foults �10 0 0 Figure 5: 50 50 * 100 100 , 2P 200 3 W KILOMETERS 300 KILOMETERS Diagram indicating the amount of separation that Figure 5: occurred Diagram indicating the amount separation that may have during development ofof the Midcontinent may have occurred during development of the Midcontinent Tectonic Zone Rift System, location of the Trans-Superior Rift System, location of alkaline the Trans—Superior Tectonic Zone and the position of two features associated with and position of two alkaline featureset associated with the the tectonic zone(modified from Klasner al., 1982). the tectonic zone(modjfjed from Kiasner et al., 1982). Figure 6: Regional Bouguer gravity anomaly map over Lake Figure 6: with Regional Bouguer gravityTectonic anomaly Zone map over Lakesites Superior the Trans-Superior and two Superior with the Trans-Superior Tectonic Zone andHinze two sites of alkaline magmatism superimposed(modified from et of alkaline al., 1982). magmatism superimposed(modifjed from Hinze et al., 1982). �1966). al., et Hinze from superimposed(modified maginatism alkaline of sites two and Zone Tectonic Trans—Superior the with region Superior Lake of map intensity magnetic Total 7: Figure &— 5#_. — - — — ----. — - ,..l.,..k o ., .. t— ...,.., WNIS ,.n. so F00 no 500 - XA( COt-DWELL PORT MAP CONTOUR INTENSITY MAGNET/C TOTAL �12 SLATE ISLANDS \ I Figure Contour map map of of lake lake bottom bottom topography topography of of Lake Lake Figure 8: 8: Contour Superior(From Hough, 1958; Wold et al., 1982). Superior(From Hough, 1958; Wold et al., 1982). �13 scale activity. The scale of of alkalic alkalic inagmatic magmatic activity. The Port Port Coidwell Coldwell superimposed ring ring complexes complexes exposed exposed complex consists consists of of 33 superimposed complex along along the the shore shore of of Lake Lake Superior; Superior; the the smaller smaller Killala Killala Lake Lake Complex, Complex, 40 40 km km north north of of the the lake, lake, consists consists of of aa single single ring ring km complex. The The much much smaller smaller Prairie Prairie Lake Lake Carbonatite Carbonatite is is 30 30 km complex. north of of the the lake lake and and the the Chipman Chipman Lake Lake alkalic alkalic units, units, at north at aa distance km, consist consist of of carbonatite carbonatite dikes dikes and and fenite. fenite. distance of of 140 140 km, What structural structural or or tectonic tectonic significance significance this this change change from from What alkalic rock rock to to carbonatite carbonatite magmatism, magmatism, and alkalic and presumably presumably much much lower lower degrees degrees of of partial partial melting melting at at greater greater depths, depths, may aay have have is is unclear. unclear. Interpretation Interpretation of of the the aeromagnetic aeromagnetic data data in in eastern eastern Lake Lake Superior Superior by by Hinze Hinze et et al.(1966) al.(1966) indicates indicates that that the the Thiel Thiel or or Big Big Bay-Ashburton Bay-Ashburton Bay Bay fault fault offsets offsets the the Michipicoten Michipicoten Island Island fault fault left-laterally left-laterallyfor forapproximately approximately5.0 5.0miles(8.O miles(8.0kin). km). This This left-lateral left-lateral offset offset has has been been recognized recognized along along the the northern northern extension extension of of this this structure structure in in the the Chipman chipman Lake Lake area area where where offset offset of of approximately approximately 0.8 0.8 km km has has been been mapped(Sage, mapped(Sage, 1985). 1985). The The age age relationships relationships between between the the younger younger Thiel Thiel or or Big Big Bay-Ashburton Bay-Ashburton Bay Bay fault fault and and the the older older Michipicoten Michipicoten Island Island fault fault are are consistent consistent with with recent recent structural structural interpretations interpretations using using seismic seismic data(Mariano data(Mariano and and Hinze, Hinze, 1994). 1994) . Linear Linear trends trends in in the the topography topography approximately approximately 1.5 1.5 km km southeast southeast and and southwest southwest of of the the Slate Slate Islands Islands estimated estimated to to be be approaching approaching 240 240 metres metres in in depth, depth, are are consistent consistent with with the the fault fault trends trends established established by by Hinze Hinze et et al.(1966) al.(1966) and and Sage(1991). Sage(1991). These These trends trends likely likely represent represent subsidiary subsidiary faulting faulting related related to to the the two two regional regional fault fault trends. trends. The The Michipicoten Michipicoten Island Island fault fault follows follows the the margin margin of of the the Lake Lake Superior Superior Basin Basin and and is is likely likely to to have have been been active active during during basin basin formation. formation. The The water-filled-linear water-filled-linear southeast southeast of of the the Slate Coldwell Slate Islands Islands can can be be extrapolated extrapolated to to the the Port Port Coldwell Complex Complex where where it it joins joins with with the theLittle LittlePlc PicRiver Riverlineament, lineament, aa zone zone of of possible possible faulting. faulting. This This linear linear feature feature is is therefore therefore likely likely to to be be related related to to the the Thiel Thiel or or Big Big Bay— BayAshburton Ashburton Bay Bay fault faultsystem systemwhich whichcuts cutsthe thePort PortColdwe].l Coldwell Complex, Complex, dated dated by by U-Pb U-Pb techniques techniques as as 1108 1108 ++- 11 Ma(Heaman Ma(Heaman and and Machado, Machado, 1992). 1992). Some Some movement movement along along the the Thiel Thiel or or Big Big Bay— BayAshburton Ashburton Bay Bay fault fault thus thus postdates postdates the the emplacement emplacement of of the the Port Port Coidwell Coldwell Complex Complex and and likely likely represents represents reactivation reactivation of of earlier earlier regional regional structural structuralpatterns. patterns. Soon Soon after after extension extension and and rifting, rifting,between between1109 1109and and 1094, 1094, closing closing of of the the rift rift began(Cannon, began(Cannon, 1994). 1994). The The southwest— southwesttrending trending arm arm of of the the Midcontinent Midcontinent Rift Rift closed closed by by an an estimated estimated 30 the central central portion of the the graben graben was was inverted inverted along along 30 kin, km, the thrust thrust faults faults and and the the southeast—trending southeast-trending arm arm was was dominated dominated by by strike-slip strike-slip motion(Cannon, motion(Cannon, 1994). 1994). Rifting Rifting of of the the lithosphere lithosphere caused caused weakening weakening in in an an otherwise otherwise strong strong continental continental lithosphere lithosphere and and focused focused this this deformation deformation into into the in eastern eastern Lake Lake SuperiOr Superior the Midcontinent Midcontinent Rift. Rift. The The graben graben in �14 is 30 km wider than than in western Lake Superior, consistent thrusting in in the the west and strike-slip strike-slip faulting faulting in in the the with thrusting east(Cannon, 1994). 1994). Tectonic Tectonic transport transport was perpendicular to to east(Cannon, the Grenville ~renvilleFront Front with the transition transition between between thrusting thrusting the strike slip slip movement occurring where the the Midcontinent and strike changes trend(Cannon, trend(Cannon, 1994). 1994). The abundance abundance of eastRift changes faults and displacements in the the Midcontinent Rift north-east faults displacements in suggests accommodation accommodation perpendicular perpendicular to to the the axis axis of of the the suggests rift(Marian0 and and Hinze, 1994a). 1994a). The Thiel Fault or Big Bayrift(Mariano Ashburton Bay Bay Fault Fault is is the the most notable notable transform transform fault fault Ashburton separating separating distinct distinct segments of the the rift: rift: symmetrical symmetrical graben in haif—graben in in the the east, asymmetrical asymmetrical half-graben in the the west(Mariano west(Marian0 1994a). This accommodation zone is is the the Trans— Transand Hinze, 1994a). accommodation zone superior Tectonic Tectonic Zone Zone into which alkalic alkalic magma was emplaced Superior north of of Lake Lake Superior. Superior. Mariano and Hinze(1994a) Hinze(l994a) indicated that this this compression compression is demonstrated by drag faults faults along that the Keweenawan Keweenawan Fault, Fault, folds and anticlinal anticlinal structures in the the main basin, basin, and and reverse reverse faults faults to to the the north north and and south south of main Mariano and Hinze(1994a) report the central Lake Superior. central Lake Superior. Mariano and Hinze(1994a) report the presence of of an an anticlinal structure structure in in eastern eastern Lake Superior Superior bisecting and and paralleling the trend of the the rift which has as much of relief on the basalt layer. much as as 55 km km of relief the basalt layer. The The rapid rapid evolution of the Midcontinent Rift from an extensional to aa evolution of the Midcontinent Rift from an extensional to compressional feature feature occurred occurred at at approximately approximately 1080 1080 compressional Ma(Cannon, 1994). 1994). Ma(Cannon, Midcontinent Midcontinent Rift Rift and and the Grenville Grenville Front Front Tectonic Tectonic Zone (GFTZ1 Zone (GFTZ It It was was suggested suggested by by Gorden Gordon and and Hempton(1986) Hempton(1986) on on the the basis basis of of isotopic isotopic ages ages that that the the Midcontinent Midcontinent Rift Rift was was formed formed as as aa result result of of convergence convergence related related to to the the synchronous synchronous Grenville Grenville orogeny. orogeny. Cannon(1994) Cannon(1994) noted noted that that the the Midcontinent Midcontinent Rift Rift developed developed adjacent adjacent to to the Grenville Front Tectonic Zone and that that the the evolution evolution from from extension extension to to compression compression at at approximately approximately 1080 1080 Ma Ma was was coincident coincident with with renewal renewal of of northwest-directed northwest-directed thrusting thrusting in in the the Grenville Grenville Province, Province, probably continent—continent collision. probably in in response response to continent-continent collision. A reversal reversal of of movement movement occurred occurred along along the the major major graben graben faults faults of of western western Lake Lake Superior, Superior, and and in in eastern eastern Lake Lake Superior Superior the the compression compression was was taken taken up up in in reverse reverse faults faults oriented oriented normal normal to to the the Midcontinent Midcontinent Rift Rift axis axis and and parallel parallel to to the the Grenville Grenville Front (Manson and and Halls, Halls, 1994). 1994). In In most most cases cases Front Tectonic Tectonic Zone Zone (Manson these these faults faults reactivated reactivated pre-existing pre-existing faults faults within within the the Archean and Halls, 1994). Archean baseinent(Manson basement (Manson and 1994) Cannon(1994) Cannon (1994) has has interpreted interpreted geophysical geophysical data in in southern southern Michigan Michigan as as suggesting suggesting that that the the Grenville Grenville Front Front Tectonic Tectonic Zone Zone is is thrust thrust over over the the Midcontinent Midcontinent Rift(Figure Rift(Figure 9). 9). . Midcontinent Rift Rift and and the the Kapuskasinci Kawuskasincr Structural Structural Zone(KSZ) ZonefKSZ1 Midcontinent The The Kapuskasing Kapuskasing Structural Structural Zone(KSZ) Zone(KSZ) strikes strikes north north of of east east from from the the east east shore shore of of Lake Lake Superior, Superior, but but quickly quickly becomes becomes more more northerly northerly in in strike strike east east of of the the Lake. Lake. This This more more �15 Grenville Province Midcontinent Rift Midcontinent Rift s Magmotic Belt Seismic profile Seismic pofile Killarney / Provincial or State bou-biy - International boundary —. International undory Figure 9: Regional sketch map showing the positions of the Figure 9: Regional sketch map showing the positions of the Grenville Front, Grenville Front Tectonic Zone, Central Grenville Front, Grenville FrontZone. Tectonic Zone, Central Metasedimentary Belt Boundary The southeastern Metasedimentary Belt southeastern idcBoundary continentZone. Rift The in areas covered by extension of the extension of the Midcontinent Rift in areas covered by Paleozoic are geophysical interpretations.(From Easton, Paleozoic are geophysical interpretations. (From Easton, 1992). 1992). �16 northern strike strike is is closely closely parallel parallel to to the the trend trend of of the the northern 3, 10). The KSZ is aa Trans-Superior Tectonic Zone(Figures Trans-Superior Tectonic Zone(Figures 3, 10). The KSZ is broad zone of faulting at the east coast of Lake superior broad zone of faulting at the east coast of Lake Superior and aa very very narrow narrow zone zone near near Hudson Hudson Bay Bay to tothe thenorth. north. The The and zone is characterized by positive aeromagnetic and gravity zone is characterized by positive aeromagnetic and gravity anomalies and and west—dipping west-dipping zones zones of of high high refraction refraction anomalies velocities(Percival and West, 1994). The zone contains contains west— westvelocities(Percival and West, 1994). The zone Ion thick section dipping faults exposing an approximately 20 dipping faults exposing an approximately 20 km thick section of Archean Archean crust(Percjva]. crust(Perciva1 and 1983) related related to to of and Card, Card, 1983) transpressive tectonics(Perciva1 and West, 1994). Uplift transpressive tectonics(Perciva]. and West, 1994). Uplift took place place prior prior to to 2.45 2.45 Ga(Bursnall Ga(Bursnal1 et. et. al. al. 1994; 1994; Heaman, Heaman, took 1988), since relatively undeformed Matachewan dikes cut the the 1988), since relatively undeformed Matachewan dikes cut structure, and perhaps as early as 2630 Ma(Krogh and structure, and perhaps as early as 2630 Ma(Krogh and Moser(1994). and other other Moser (1994). ~ranulite-facies Granulite-facies metamorphism metamorphism and deformations took place prior to this KSZ event(Bursna11 et deformations took place prior to this KSZ event(Bursnall et al., 1994; Krogh and Moser, 1994). The ~apuskasing al., 1994; Krogh and Moser, 1994). The Kapuskasing Structural Zone Zone is is an an intracratonic intracratonic uplift uplift representing representing 27 27 Structural km of crustal shortening through brittle upper crustal km of crustal shortening through brittle upper crustal thrusting(Perciva1 and and West, West, 1994). 1994). Within Within the the KSZ KSZ the the Moho Moho thrusting(Percival compared to values near 45 occurs at a depth of about 53 km occurs at a depth of about 53 km compared to values near 45 km near Wawa and approximately 35 km near ~immins(~erciva1, km near Wawa and approximately 35 km near Timmins(Percival, 1990). 1990). Manson and and Halls(1994) Halls(1994) traced traced faults faults from from Mamainse Mamainse Point Point to to Manson the Keweenaw Peninsula and suggested that the Michipicoten the Keweenaw Peninsula and suggested that the Michipicoten Island Fault Fault may may be be traced traced into into Grindstone Grindstone Point Point Fault. Fault. Island mapped a large northeast-trending fault along Grunsky(1991) Grunsky(199l) mapped a large northeast-trending fault along the Montreal River which separated the Chapleau Gneiss the Montreal River which separated the Chapleau Gneiss Domain from from the the Batchawana Batchawana Volcanic Volcanic Domain—Ramsy Domain-Ramsy Gneiss Gneiss Domain ~omain. This fault contained gouge, breccia and quartz veins Domain. This fault contained gouge, breccia and quartz veins and was correlated with faulting associated with the KSZ. and was correlated with faulting associated with. the KSZ. Other northeast-trending northeast-trending faults faults with with aa brittle brittle style style of of , Other deformation occur along the Batchawana and Goulais rivers deformation occur along the Batchawana and Goulais rivers but their their relationship relationship to to the the KSZ KSZ is is not not as as clear clear but (Grunsky.1991). Sage(1994) correlated the Wawa-Hawk(Grunsky, 1991). Sage (1994) correlated the Wawa—Hawk— Manitowik Lake Lake Fault Fault with with the the Kapuskasing Kapuskasing Structural Structural Zone Zone Manitowik and suggested that it was rooted in Archean tectonics. The and suggested that it was rooted in Archean tectonics. The extension of this fault toward Lake Superior may account for extension of this fault toward Lake Superior may account for the straight coastline of Lake superior west of Wawa. the straight coastline of Lake Superior west of Wawa. km east east of of the the shoreline shoreline of of Lake Lake Superior superior ~pproximately15 15 km Approximately the Wawa-Hawk-Manitowik Lake Fault is cut by a smaller local the Wawa-Hawk-Manitowik Lake Fault is cut by a smaller local fault known as the Firesand River Fault(Sage, 1994). At this fault known as the Firesand River Fault(Sage, 1994). At this intersection, the mantle-derived Firesand River Carbonatite intersection, the mantle-derived Firesand .River Carbonatite was emplaced, emplaced, which which on on the the basis basis of of imprecise imprecise age age dating dating is is was prairie Lake ~arbonatite(~age and likely coeval with the likely coeval with the Prairie Lake Carbonatite(Sage and Watkinson, 1991). 1991). Numerous Numerous alkalic alkalic rock rock and and carbonatite carbonatite Watkinson, Zone which which complexes occur along the Kapuskasing Structural complexes occur along the Kapuskasing Structural Zone were emplaced at about 1.1 Ga(Sage and Watkinson, 1991; were emplaced at about 1.1 Ga(Sage and Watkinson, 1991; Bursnall et. et. al. al. 1994; 1994; Percival Percival and and West, West, 1994). 1994). Within within the the Bursnall alkalic constraints of existing isotopic age dating, constraints of existing isotopic age dating, alkalic magmatism along along the the Trans Trans Superior Superior Tectonic Tectonic Zone Zone and and magmatism ~apuskasing Structural Zone appear to be contemporaneous. Kapuskasing Structural Zone appear to be contemporaneous. The alkalic alkalic rock rock and and carbonatite carbonatite complexes complexes along along the the The Kapuskasing Structural Zone should also be considered Kapuskasing Structural Zone should also be considered �17 * Proterozoic, Phanerozoic cover Proterozoic Alkalic rock complex Archean Moose Quefico Metasedlmentary r: River Basin Belt Metavolcanic rx Granitoid rx Anorthositlc rx Granulites • 4• • ••••• CobaltT-- Figure 10: 10: Geologic Geologic sketch sketch map map of of the the Kapuskasing Kapuskasing Structural Structural Figure Zone Zone and and surrounding surrounding parts parts of of the the central central Superior Superior Province, Province, showing showing major major geological geological and and geographical geographical features. features. BLFZ, BLFZ, Budd Lake Lake fault fault zone; zone; BRF BRF Bad Bad River Riverfault; fault;FF, FF, Foxville Foxville Budd fault; ILFZ, ILFZ, Ivanhoe Ivanhoe Lake Lake fault fault zone; zone; KF, KF, Kineras Kineras fault; fault; fault; SLF, Saganash Saganash Lake Lake fault; fault; WRF, WRF, Wakusimi Wakusimi River River fault; fault; WHMF, WHMF, SLF, Wawa-Hawk-ManitoWik Wawa-Hawk-Manitowik Lake Lake fault; fault; rx, rxf rock rock types(modified typesfmodifiedfrom from Percival and and West, West, 1994). 1994). Percival �18 manifestations tectonic activity associated with the manifestations of tectonic development Rift. It It is also likely that development of of the the I4idcontinent Midcontinent Rift. late Archean faulting faulting associated with with the the KSZ KSZ was was reactivated at 1.1 Ga and played a major role in the development of the Midcontinent Rift in the the Lake Superior Superior region. region. Summarv of of Reczional Regional Settinq Summary Setting The locations locations of alkalic alkalic rock intrusions intrusions north and northeast northeast Superior are not haphazard or random. The intrusions intrusions of Lake Superior Trans—Superior Tectonic Zone occur within the Trans-Superior Zone and its northern extension extension with the largest intrusion occurring at the Proterozoic-Archean intersection of Proterozoic—Archean contact close to the intersection the Michipicoten Michipicoten Island and the Big Bay-Ashburton Bay—Ashburton Bay Faults. The Trans-Superior Trans—Superior Tectonic Zone bisects the Midcontinent Rift and has aeromagnetic, gravity and topographic topographic expression. The Trans-Superior Tectonic Zone is accommodation zone an accommodation zone separating the Lake Superior basin into two contrasting tectonic domains. domains. Development of the Midcontinent Rift is is intimately related to developments developments along the GFTZ and KSZ and likely strongly influenced by early structures structures in in the the Archean Archean basement. basement. The unique positions of the diatreme structures structures on the Slate Islands Islands is is more consistent with the tectonic development of the Midcontinent Rift impact(Sage, 1978; Rift than than meteorite meteorite impact(Sage, 1978; Halls and Grieve, Halls Grieve, 1976). 1976). �19 DAY11 DAY KILLALA LAKE COMPLEX The The Killala Killala Lake Lake Complex Complex is is an an alkalic alkalic complex complex consisting consisting of of an outer ring of troctolite troctolite followed followed inward inward by nepheline nepheline syenite(Figure syenite and then an inner core core of of amphibole amphibole syenite(Figure syenite 11). The interior syenites syenites are are coarse—grained, coarse-grained, equigranular, equigranular, 11). part of of the grey to buff on fresh surface in the southern part complex and red complex red to to reddish reddish brown, brown, coarse—grained, coarse-grained, inequigranular, seriate senate to to porphyritic, porphyritic, in in the northern part. Several part. Several minor lithologies lithologies are are also also locally locally present. In In the centre centre of the intrusion intrusion on on the the shores shores of Kentron Kentron and and Blank Lakes mafic banding is is very well well developed developed in in the the syenites(Sage, 1988). 1988). The size size and and number number of xenoliths xenoliths increase to the north as do the number of septa of enclosing enclosing wall wall rocks rocks projecting projecting into into the the syenite syenite mass. mass. The Killala Lake complex has been been dated by Rb-Sr techniques techniques as being 1050 1050 +— +- 35 Ma(Bel1 and Blenkinsop, Blenkinsop, 1980). 1980). This age 35 Ma(Bell with more more precise U-Pb isotopic is essentially coeval with isotopic age age dating at at the the Port Port Coidwell Coldwell Complex. Complex. Kila1a The Ki lalaLake Lake Complex Complex has has aa surface surface area area of of approximately approximately prevalence of 110 km The large number of xenoliths and prevalence wall rock septa suggest that the the northern northern part of the the ring ring complex is is exposed at a higher structural structural level level than than is is the the southern part and the intrusion intrusion which may plunge south southern south to to southwest toward the Lake Superior Basin. The isomagnetic isomagnetic contours contours on aeromagnetic aeromagnetic maps of of the the complex complex outline outline aa circular circular pattern in contrast contrast to to the the tear—drop tear-drop shape shape defined defined by mapping(ODM-GSC mapping(0DM-GSC 1963f, 1963f, g; g; Coates, Coates, 1970; 1970; Sage, Sage, 1988) (Figure 12). 12). The The northern northern projection projection of of the the ring 1988)(Figure complex complex has been interpreted interpreted as as aa sheet-like sheet-like or petal—like petal-like laccolithic laccolithic mass extending north of, and overlying the the outer outer gabbro ring which on the basis basis of of aeromagnetic aeromagnetic data data likely likely completely encloses encloses the the complex(Coates, complex(Coates, 1970; 1970; Sage Sage 1988). 1988). The arcuate, open-to-the-north horseshoe horseshoe shaped shaped lithologic lithologic distribution distribution suggests suggests the possibility of of a former former caldera caldera structure(Sage, 1988). 1988). Coates Coates (1967, (1967, 1970), 1970), Bathe Bathe (1977), (1977), Wanless (1976) Wanless (1976) and Sage, (1988) (1988) described described detailed detailed geology geology of the Killala Killala Lake Lake Complex. Complex. i The Killala Lake Complex Complex lies lies at at the the intersection intersection of of topographic topographic and aeromagnetic aeromagnetic linears. linears. A prominent aeromagnetic linear connects the Killala Lake Complex with the Prairie Lake Carbonatite, of similar age, to the southwest. Williams(1989) has identified a zone several several kilometres kilometres wide of deformed rocks rocks along along this this aeromagnetic aeromagnetic �20 o o kilomstr,. I 2 r • nwles Thur SItS- •.* * _j_,O,,,,.,., • •_o'-• .• • • I-. - •.&++**.+_ S.' KILLAL.A LAKE ALKAUC COMPLEX PROTEROZOIC r.::.:j Brn syenft. I°ó°°I NepheUns $yenits Buff syenite I] Syenodiont. Gobbro I .'lDiobose ARCHEAN Quartz monzonifs I. . • . , to gronodicdts Metosedirnents ~ i g u r e11: Geologic sketch map of the Killala Lake Alkalic Figure 11: GeologicSage8 sketch198G8 map of the Killala Lake Alkaljc Rock Complex(from 1988) Rock Complex(from Sage, 1986, 1988) �3 JEIoi. -4 I I-i DI I-' 1-d. CD I.,) 0 '— DI 0S(D DI C)0 GHD (DCD —.1-a I-P1 OIa. Figure 12: Aeromagnetic map of the Killala Lake Alkalic Rock CO~P~~X(ODM-GSC, 1963e, f). �22 trend which which he he referred referred to to as as the the Killala Killala Lake Lake Deformation Deformation trend ZoneA prominent topographic linear along the east side side of of Zone. A prominent topographic linear along the east Coates(l970) the complex has been interpreted by as aa the complex has been interpreted by Coates(1970) as fault(Bo0merang Lake Lake Fault) Fault) and and this this fault fault may may be be fault(Boomerang interpreted from from air air photographs photographs to to join join with with the the Little Little Pic Pic interpreted River lineament on the west side of the Port Coldwell River lineaiuent on the west side of the Port Coldwell Complex. The The Killala Killala Lake Lake Complex Complex lies lies within within the the northern northern Complex. part of the Lake Superior Tectonic Zone and along the part of the Lake Superior Tectonic Zone and along the interpreted extensions of the Big Bay-Ashburton Bay interpreted extensions of the Big Bay-Ashburton Bay Fault(Sage, 1978) 1978) or or Thiel Thiel Fault(Klasner Fault(K1asner et et al. al- 1982). 1982)- The The Fault(Sage, trend of this tectonic zone parallels approximately the trend of this tectonic zone parallels approximately the Kapuskasing Structural Structural Zone. Zone. The The topographic topographic linear linear Kapuskasing connecting the Port Coldwell and Killala Lake complexes may may connecting the Port Coldwell and Killala Lake complexes be extrapolated northward to the Chipman Lake area where be extrapolated northward to the Chipman Lake area where fenite and and carbonatite carbonatite dikes dikes are are widespread(sage, widespread(sage, fenite 1985)(Figure 13). Offset of lithologies across this this 1985) (Figure 13). Offset of lithologies across lineament at Chipman Lake is 0.8 -(Sage, 1985)lineament at Chipman Lake is 0.8 km(Sage, 1985). ~conomicGeology Geology Economic The Killala Killala Lake Lake complex complex has has been been prospected prospected for for its its copper copper The and nickel content in the early 195Os(Sage, 1988). and nickel content in the early 1950s(Sage, 1988). examined some some of of the the drill drill core coreremaining remainingfrom. from Bath(l977) examined Bath(1977) this effort and recognized pyrrhotite, chalcopyrite, this effort and recognized pyrrhotite, chalcopyrite, cubanite, pentlandite, pentlandite, and and valleriite. valleriite- The The complex complex remains remains cubanite, relatively untested for PGE. Within the area of Blank Lake, relatively untested for PGE. Within the area of Blank Lake, intrusion, zircon and pyrochlore are near the centre of the near the centre of the intrusion, zircon and pyrochiore are present within narrow pegmatite dikes(Sage, 1988). present within narrow pegniatite dikes(Sage, 1988). interest only. only. Pyrochlore and and zircon zircon are are of of mineralogical mineralogical interest Pyrochiore The complex is currently undergoing examination as a The complex is currently undergoing examination as a possible source source of of building building stone. stone. possible The road road log log is is from from the the intersection intersection of of Highway Highway 17 17 and and the the The Dead Horse Creek access road. Recent logging activities in Dead Horse Creek access road. Recent logging activities in the region now permit access to the margins of the Killala the region now permit access to the margins of the Killala Lake Complex. ComplexLake 18.4 Km Km @@ 18.4 Jackpine Road, Road, turn turn right right Jackpine 33.7 Km Km Prairie Lake Lake Carbonatite Carbonatite intersection intersection on on left. left. @@ 33.7 Prairie Continue north and cross the Little Pic River bridge and Continue north and cross the Little Pic River bridge and stay to to the the righthand right hand branch branch of of the the road. roadstay 55.2 Km Km @@ 55.2 Turn right right on on skid skid road. road. This This road road is is located located Turn just north north of of Sandspit Sandspit Lake. Lake. just 0-40 Km Km @@ 0.40 Park in in cleared cleared area. area. Park �23 CHIPMAN CHIPMAN LAKE LAKE AREA AREA PROTEROZOIC PROTEROZOIC I [ *Tj Fenite I Feniteandandcorbonotite c a r b m t i t edikes dikes ARCHEAN ARCHE AN p r d Diorite Diorite totoquartz quartzmonzonite mnzonite intrusive intrusiverocks rocks to syenodiorite intrusive rocks 1['J -1 DioriteDiorite to syenodbrite intrusive rocks I:1 iafic Mafic rnetavoicanics metavolcanics fault — —rood Figure 13: 13: Geologic ~eologicsketch sketch map map of of the the Chipman chipman Lake Lake area area Figure showing faulting faulting along alongthe thelong longaxis axisof ofChipiuan Chipman Lake. Lake. This This showing fault may may be be the the northern northern extension extension of of the the Boomerang Boomerang Lake Lake fault fault that that passes passes along along the the east east side fault side of of the the Killala Killala Lake Lake Alkalic Rock Rock Complex(from Complex(from Sage, Sage81985, 1985#1986). 1986). Alkalic �24 Stop Stop la la Walk approximately approximately 470 470 mm along along skid skid road road in in aa SE SE Walk direction and and up up hill(See hill(See Figure Figure 14; 14; Sage, Sage, 1988). 1988). direction Medium- to to coarse—grained coarse-grained equigranular equigranular olivine olivine gabbro gabbro to to Medium— troctolite occurs along the north side of road as rounded troctolite occurs along the north side of road as rounded grey outcrops. outcrops. Outcrop Outcrop is is cut cut by by dikes dikes of of pink pink to to red red grey Bathe(l977) described described samples samples syenite and and nepheline nepheline syenite. syenite. Bathe(1977) syenite from similar similar gabbro gabbro outcrops outcrops as as being being composed composed of of 45 45 to to 50 50 %3 from plagioclase(An56 plagioclase(An56 — An65), -651, augite augite clinopyroxene clinopyroxene 20 20 to to 25 25 %, %, olivine olivine 55 to to 30 30 %% and and accessory accessory apatite, apatite, biotite, biotite, green green amphibole, oxides oxides and and suiphides. sulphides. Noritic Noritic gabbro gabbro and and amphibole, larvikite are are described described by by Bathe(1977) Bathe(l977) as larvikite as being being associated associated with phase. In thin with the the olivine olivine gabbro gabbro to to trocto].ite troctolite phase. thin section section corona structure structure where where in the olivine—plagioclase olivine-plagioclase have have aa corona the in reaction with with water water under under middle middle to to contact, attributed attributed to to aa reaction contact, upper amphibolite-facies amphibolite-faciesconditions conditions(Laderoute, 1984). upper (Laderoute, 1984). - Stop Stop lb lb approximately approximately 130 130 mm east east of of la la Small outcrop outcrop of of coarse—grained coarse-grained nepheline nepheline syenite syenite with with up up to to Small 10 to 15 nepheline. The The nepheline nepheline syenite syenite has has been been I0 .to 15 %% nepheline. estimated to to contain contain approximately approximately 10 10 to to 15 15 %3 nepheline, nepheline, 00 estimated to dark green green to to green green brown brown amphibole, amphibole, 30 30 to to 70 70 %% to 25 25 %% dark perthite perthite and and 00 to to 65 65 %% sodic sodic plagioclase(Sage, plagioclase(Sage, 1988). 1988). Minor Minor amounts amounts of of clinopyroxene clinopyroxene and and biotite biotite are are present present with with accessory accessory sphene, sphene, magnetite, magnetite, apatite, apatite, sericite sericite and and carbonate. carbonate. Stop Stop lc lc approximately approximately 70 70 mm east east of of lb. lb. Nepheline Nepheline syenite syenite with with lower lower nepheline nepheline content. content. Stop Stop ld ld approximately approximately 145 145 mm east east of of lc lc Some Coarse—grained Coarse-grained equigranular equigranular buff buff to to pink pink syenite. syenite. Some pitting pitting of of the the surface surface may may be be due due to to weathering weathering of of nepheline nepheline but but most most is is due due to to the the mafic mafic mineral mineral content. content. The The buff buff syenite plagioclase(An2845 %% plagioclase(An28syenite contains contains approximately approximately 55 to to 45 An39), An39), 55 to to 25 25 %% amphibole, amphibole, and and 15 15 to to 95 95 %% perthite(Sage, perthite(Sage, 1988). 1988). Minor Minor amounts amounts of of olivine olivine 00 to to 11 %, %, biotite biotite 00 to to 10 10 %3 and and clinopyroxene clinopyroxene 00 to to 55 %% may may also also be be present present in in some some specimens. specimens. The The accessory accessory minerals minerals are are apatite, apatite, magnetite, magnetite, sericite, sericite, carbonate, carbonate, zircon, zircon, sphene, sphene, chlorite chlorite and and quartz(Sage, quartz (Sage,1988). 1988) . Stop Stop le le approximately approxinately 55 55 mm east east of of id ld Small Small outcrop outcrop as as previously previouslydescribed. described. �25 1 FROM: Ontario Qeologlcal Survey Study 4 5 FROM: Ontario 4 Chart Chart A SANDSPIT LAKE LAKE SANOSPIT 5 14 / LEOEI4D LEGEND 5 R.d Sy.nht. Red Synlte 4 SyenIt. &It Buff Buff $y.nIts Nepholin. Nephellne Syenlte Synlte Gabbro — — — 500 m•tr•s 500 metres / 2 GranIttc Rock Granitic Rock 1 M.tas.dlm.ntary Rock Metasedlment8ry Roek 3 J Figure 14: 1 4 : Geologic ~ e o l o g i csketch s k e t c h map map showing showing field f i e l d trip t r i p sites, sites, Killala K i l l a l a Lake Lake Alkalic A l k a l i c Rock Rock Complex. Complex. Base Base map map from from Sage(1988, Sage(1988, Chart Chart A). A). �26 Stop if If approximately approximately 125 125 m east of le; skid skid road road has has deteriorated. deteriorated. Coarse—grained Coarse-grained equigranular equigranular amphibole amphibole syenite. syenite. Feldspar Feldspar somewhat lath-like and mafic mineral content approximately approximately somewhat lath—like 15 to to 20 20 %. %. Outcrop similar similar to to id. Id. main road. road. Turn Turn Return to parking area and go back to the main 21.5 km to to intersection intersection of left back the way you came. Drive 21.5 a skid skid road road and and Jackpine Jackpine Lake Lake Road. Road. Turn right tan. right onto onto skid skid road road and continue continue to to 25.6 25.6 km. Turn right right onto onto partially overgrown overgrown skid skid road road and and continue continue this point the the road road splits. splits. until odometer odometer reads reads 26.6 26.6 km. At this Take the the right-hand fork fork and continue continue to to the the odometer odometer reading f to 26.7 km. km. An An overgrown overgrown skid skid road road leads leadsof off to the the reading of of 26.7 right up a a steep steep hill. Park Park at the the road road junction junction or or drive drive the the short short distance distance to to the the base base of of the the hill hill and and park. park. �27 PRAIRIE PRAIRIE LAKE LAKE CARBONATITE CARBONATITE The Prairie Prairie Lake Lake Carbonatite Carbonatite consists consists of of arcuate arcuate units units of of The sovite, sovite, silicocarbonatite, silicocarbonatite, ijolite ijolite and and wollastonite wollastonite ijolite(Figures ijolite(Figures 15, 15, 16a,b). 16a,b). Minor Minor amounts amounts of of biotitite(g1immerite) may The complex complex biotitite(glimxnerite) may locally be present. The forms forms aa prominent prominent hill, hill, which, which, in in spite spite of of its its topographic topographic relief, relief, has has only only rare rare outcrops. outcrops. Weathering weathering is is deep deep and and samples samples of of fresh fresh rock rock may may be be obtained obtained only only through through diamond diamond trenching or or in in logging logging skid skid roads roads where where lumps lumps drilling, drilling, trenching resistant resistant to to weathering weathering have have been been exposed exposed by by heavy heavy equipment. equipment. The carboatite carbo atite complex of complex has has aa surface surface area area of approximately approximately 8.8 8.8 km Ion 9. The The complex complex has has been been dated dated at at 1033 1033 ++- 59 59 Ma Ma by by the the Rb-Sr Rb-Sr technique(Bel1 and and Blenkinsop, ~lenkinsop,1980) 1980) and and is is considered considered to to be be technique(Bell essentially coeval coeval with with the the Killala Killala Lake Lake and and Port Port Coidwell Coldwell essentially Alkalic Alkalic rock rock complexes. complexes. The The Prairie Prairie Lake Lake Complex Complex has has aa prominent aeromagnetic aeromagnetic anomaly anomaly approximately approximately 2.5 2.5 km km in in prominent diameter(0DM-GSC, 1963a). 1963a). The The aeromagnetic aeromagnetic anomaly anomaly is is diameter(ODM-GSC, approximately approximately 1400 1400 gammas gammas absolute absolute total total field field above above the the surrounding background background area area which which is is underlain underlain by by granitoid granitoid surrounding rocks(Sage, rocks (Sage,1987) 1987)(Figure (Figure17). 17) . North-trending topographic topographic linears linears from from the the north north shore shore of of North-trending Lake Lake Superior Superior intersect intersect northeast—trending northeast-trending topographic topographic and and aeromagnetic linears at at the the site site of of the the Prairie Prairie Lake Lake aeromagnetic linears Carbonatite. Carbonatite. The The northeast northeast trending trending linear linear connects connects with with the the Killala Williams(1989) recognized recognized aa Killala Lake Lake Complex. Complex. Williams(1989) deformation deformation zone zone between between these these two two complexes complexes which which he he referred referred to to as as the the Killala Killala Lake Lake deformation deformation zone. zone. This This zone zone is is several several kilometres kilometres wide wide and and defines defines the the boundary boundary between between the the Wawa Wawa and and Quetico Quetico subprovinces(Williams, subprovinces(Williams, 1989). 1989). The The complex complex lies lies within within the the northern northern part part of of the the Trans-Superior Trans-Superior Tectonic Tectonic Zone(Klasner Zone(K1asner et et al, al, 1982) 1982) and and along along linear linear trends trends subparallel subparallel to to the the Big Big Bay—Ashburton Bay-Ashburton Bay Bay Fault Fault or or Theil Theil Fault trend(Sage, 1978; 1978; Kiasner Klasner et et al, al, 1982). 1982). The The geology geology Fault trend(Sage, and and mineralogy mineralogy of of the the Prairie Prairie lake lake Carbonatite Carbonatite have have been been described described by by Watkinson,(1971, Watkinson,(1971, 1973, 1973, 1976), 1976), Melnik(1984) Melnik(1984) and and Sage(1987). Sage(1987). Sage(1987) Sage(1987) ôites cites numerous numerous unpublished unpublished company company reports reports on on the the complex, complex, most most of of which which can can be be obtained obtained from from the Thunder the Assessment Assessment Files, Files, Resident ~esidentGeologist's ~ e o l o g i s t ~Office, office, s Thunder Bay. Bay. Economic Economic Geology Geology Uranium Uranium mineralization mineralization was was discovered discovered at at "Jim's "Jim's Showing" Showingwby by J. J. Gareau Gareau working working for for Newmont Newmont Mining Mining Corporation Corporation of of Canada Canada Ltd. Ltd. in in 1968 1968 and and the the company company completed completed radiometric, radiometric, magnetic magnetic and and geochemical geochemical surveys surveys over over the the intrusion. intrusion. At At "Jim's "Jim's �28 ••:•:•:•:•::. Stop metres 0 P00 4 q•• .tut. 200' • 890 Stop 4 PRAIRIE F'RAIRE LAKE LAKE CARBONATITE CARWATIE PROTEROZOIC PROTEROZOIC AlkalicDike DikeRocks Rocks. Alkalic E1: Sovite SovileSilicocarbonate Silicocarbonale IjoIite LiJ Ijolite E:.j Fenite Fenite a ---- .—-——fault fault LIJ Archecn 0 Archem - stream stream Figure Figure 15: 15: Geological Geological sketch sketch map map of of the the Prairie Prairie Lake Lake Carbonatite Carbonatite showing showing field field trip trip sites sites and and potential potential sites. sites. (Modified (Modified from from Sage, Sage, 1986, 1986, 1987). 1987). �1986). Figure 16a: Idealized plan view of a carbonatite intrusion showing the idealized distribution of rock types(from Sage, Figure 16b: Idealized cross section through a carbonatite intrusion illustrating an idealized distribution of rock typ.s(froa Sag., 1986). %0 t..J �30 1.6 km Figure 17: Prominent aeromagnetic anomaly that outlines the Figure 17:Lake Prominent Carbonatite(0DM-GSC, 1963e).that outlines the prairie aeromagnetic anomaly Prairie Lake Carbonatjte(oDM-Gsc, 1963e). �31 Showingw the the company company outlined outlined 109,024 109,024 tons tons grading grading 0.12 0.12 %% Showing" U3O8 in in aa deeply deeply weathered weathered ferruginous ferruginous dolomite. dolomite. This This was U308 expanded by by Nuinsco Nuinsco Resources Resources Limited Limited in in 1975 1975 to to 200,000 200,000 expanded tons grading grading 18 1.8 pounds pounds U308 U3O8 and and 5.0 5.0 pounds pounds Nb205 Nb205 per per ton ton in in tons aa zone Watkinson(l976), zone 300 300 feet feet long long and and 275 275 feet feet deep. deep. Watkinson(1976), using the the microprobe, microprobe, identified identified the the uranium-bearing uranium-bearing mineral mineral using as pyrochiore pyrochlore which which displayed displayed increasing increasing uranium uranium contents contents as from from core core to to rim. rim. Uranium Uranium may may comprise comprise up up to to 30 30 %% of of pyrochlore (Watkinson, (Watkinson, 1976). 1976). In In 1975 1975 the the complex complex was was pyrochiore examined for for possible possible residual residual apatite apatite deposits deposits by by the the examined ~nternationalMinerals Minerals and and Chemical Chemical Corporation(Canada) Corporation(Canada) Ltd. International Ltd. and and in in 1983 1983 New New Insco Xnsco Mines Mines Ltd. Ltd. tested tested the the carbonatite carbonatite complex for for its its wollastonite wollastonite potential. Sage(1987) Sage(l987) provided complex additional information information regarding regarding these these exploration exploration efforts. efforts. additional Walk Walk approximately approximately400 400in m up up the the skid skid road. road. Stop 2. MediumMedium- to to coarse-grained coarse-grained inequigranular inequigranular ijolite ijolite is is Stop 2. present as as weathered weathered lumps lumps and and outcrop. outcrop. This This exposure exposure is is present typical of of the the coarser-grained coarser-grained phases phases of of the the Prairie Prairie Lake Lake typical Carbonatite. Carbonatite. In In addition addition to to the the pyroxene pyroxene and and nepheline, nepheline, calcite, calcite, magnetite magnetite and and garnet garnet are are present present in in this this outcrop outcrop and and titanite titanite has has been been observed observed in in similar similar rocks rocks within within the the complex. complex. The The outcrop outcrop is is deeply deeply weathered weathered with with secondary secondary carbonate carbonate along along joint joint surfaces. surfaces. This This exposure exposure is is much much larger larger than than most most exposures exposures within within the the intrusion. intrusion. Return You may may note note the the presence presence of of Return to to the the vehicles. vehicles. You phiogopite in the skid road as you return to the vehicles. phlogopite in the skid road as you return to the vehicles. Drive Drive back back approximately approximately 0.1 0.1 km km where where the the road road splits splits and and take the right hand fork. Drive along this partially Drive along this partially take the right hand fork. overgrown for approximately approximately 0.8 0.8 km km overgrown skid skid trail trail up up the the hill hill for and and park. park. Stop Stop 33 Wollastonite Wollastonite ijolite. ijolite. This This site site displays displays deeply deeply weathered weathered wollastonite wollastonite ijolite ijolite which which has has been been torn torn up up during during logging logging operations. operations. The The material materialisispegniatitic pegmatitic and and prismatic prismatic crystals crystals of of wollastonite wollastonite up up to to 15 15 cm cm or or more more have have been been found found here. here. The The wollastonite wollastonite will will sometimes sometimes appear appear as as veins veins cutting cutting the the ijolite. ijolite. The The wollastonite wollastonite crystals crystals are are perpendicular perpendicular to to the the vein vein trend. trend. Return f to Return or or drive driveback back0.35 0.35 km. km. AAflagged flaggedtrail trailleads leadsofoff to the in. m. the left left into intothe thebush bushfor forapproximately approximately100 100 Stop Stop 44 Orbicular Orbicular ijolite(optional). ijolite(optiona1). The The orbicular orbicular ijolite ijolite never in solid solid outcrop outcrop projecting projecting above above ground ground never occurred occurred in level level but but consisted consisted of of large large frost—heaved frost-heaved blocks. blocks. Collectors Collectors �32 have dug dug aa pit pit at at the the discovery discovery site site and and over over the the years years have large large quantities qyantities have have been been removed. removed. The The site site was was overgrown overgrown and the the pit pit filled filled in in the the fall fall of of 1994 1994 and and it it will will have have to to and be exposed additional sampling. AA equipment for for additional exposed with heavy equipment visit to to the the site site will will be be depend depend on on whether whether arrangements arrangements can can visit be be made made to to expose expose deeper deeper material. material. This material material is is one one of of the the finest finest examples examples of of orbicular orbicular This texture this is the only known known occurrence texture known known arid and this occurrence of of this this texture 1987). The The texture in in rocks rocks of of this this composition(Sage, composition(Sage, 1987). orbicules orbicules consist consist of of aa multitude multitude of of concentric concentric bands bands consisting consisting of of varying varying proportions proportions of of aegirine—augite, aegirine-augite, nepheline melanite garnet. garnet. Apatite Apatite and and biotite biotite are are also also nepheline and and melanite present present as as well well as as aa white white alteration alteration mineral, possibly melilite(Sage, 1987). 1987). The The orbicules orbicules are are up up to to 33 cm former melilite(Sage, em in in former diameter diameter and and the the largest largest have have aa medium—grained medium-grained equigranular equigranular ijolite core. core. It It is is assumed assumed that that all all orbicules orbicules will will have have ijolite this equigranular equigranular core core if if they they have have been been cut cut through through the the this centre. Several Several large large blocks blocks of of the the material material recovered recovered in in centre. initial initial sampling sampling suggest suggest that that the the orbicules orbicules may may occur occur along along distinct distinct bands bands within within equigranular equigranular ijolite. ijolite. Return Return to to vehicles vehicles and and return return to to the the main main road road (Jackpine (Jackpine Road). Turn Turn right right on on the the main main road road and and go go 15.2 15.2 km km to to the the junction junction with with the the Dead Dead Horse Horse Creek Creek access access road. road. Turn 10.1 km km and and park park at at the the side side of of the the Turn right right and and go go north north 10.1 road. small lake lake will will lie lie to to the the west west and and aa steep steep hill hill road. AA small occurs occurs to to the the east east across across aa flat flat area area used used as as aa storage storage area area for for logs. logs. Walk to the the east east and and along along the the skid skid Walk approximately approximately 100 100 metres metres to road This hill hill is is the the west west side side of of the the road up up the the steep steep hill. hill. This Prairie Prairie Lake Lake Carbonatite. Carbonatite. Various Various cobbles cobbles and and boulders boulders of of sovite sovite and and silicocarbonatite silicocarbonatite have have been been turn turn up up by by logging logging equipment into the the deeply deeply equipment in in the the skid skid road. road. In In deep deep cuts cuts into weathered weathered carbonatite-rich carbonatite-rich soil soil relict relict primary primary banding banding may may sometimes sometimes be be observed. observed. At At the the top top of of the the hill hill aa partly partly overgrown overgrown skid skid road road leads leads into into the the interior interior of of the the carbonatite carbonatite and and aa former former campsite campsite near near Centre Centre Lake. Lake. This This trail trail is is not not aa difficult difficult walk walk and and is is approximately the length approximately 1.2 1.2 kin km in length. Due to the length of of the the walk walk and and time time involved involved these these sites sites will will not not be be visited visited unless gained-toall allsites sitesdescribed described for for Stops Stops unless access access can can be gainedto 5 5 thru thru 7. 7. �33 Optional Optional stops stops 5, 5, 6, 6, and and 77 Stop Stop 55 Sovite Sovite and and banded banded sovite. sovite. This This is is the the largest largest natural natural outcrop on on the the Prairie Prairie Lake Lake Carbonatite Carbonatite and and occurs occurs in in the the outcrop stream stream bed bed of of the the small small stream stream connecting connecting Centre Centre and and Anomaly Anomaly Lakes. Lakes. The The outcrop outcrop is is weathered weathered and and thickly thickly mantled mantled with with moss. moss. The The stream stream bed bed contains contains abundant abundant rhombs rhombs of of carbonate carbonate as as well well as as grains grains of of phiogopite phlogopite and and magnetite. magnetite. This This mineral mineral assemblage assemblage is is typical typical of of sediment sediment found found in in streams streams flowing flowing through carbonatite. through aa deeply deeply weathered weathered carbonatite. Stop Stop 66 Frost—heaved Frost-heaved sovite. sovite. Some Some specimens specimens may may contain contain some some ijolitic ijolitic material material as as elongated elongated clots clots or or irregular irregular masses. masses. This frost—heaved frost-heaved material material occurs occurs on on the the south south shore shore of of This Centre Lake Lake but but the the exposure exposure was was flooded flooded out out in in the the fall fall of of Centre 1994. 1994. Stop Stop 77 Trench Trench in in deeply deeply weathered, weathered, radioactive, radioactive, ferruginous ferruginous dolomite This dolomite of of "Jim's *@Jim's Showing". Showingt8. This trench trench was was caved caved and and poorly poorly exposed exposed during during mapping mapping in in the the 1970's 1970's and and could could not not be be relocated relocated in in the the fall fall of of 1994. 1994. This This trench trench contains contains material material typical typical of of weathered weathered ferruginous ferruginous dolomite dolomite that that hosts hosts U-Nb U-Nb minerals. minerals. Return Return to to the the vehicles vehicles and and drive drive back back down down the the Dead Dead Horse Horse Creek Access Road toward Highway 17. At approximately 24.9 At approximately 24.9 Creek Access Road toward Highway 17. km park in the open area on the east side of road on the km park in the open area on the east side of road on the north At the the far far north side side of of the the bridge bridge over over Dead Dead Horse Horse creek. creek. At end of this partially overgrown parking area is a trail end of this partially overgrown parking area is a trail leading leading to to the the U-Y U-Y showing showing at at Dead Dead Horse HorseWest. West. �34 DEAD HORSE HORSE CREEK CREEK DIATREME DIATREME DEAD The Dead Dead Horse Horse Creek Creek Diatreme Diatreme is is the the largest(1600 largest(1600 xx 400 400 m) m) The of several several diatreme diatreme structures structures occurring occurring east east of of the the Port Port of Coldwell complex(Sage, 1982, 1991)(Figure 18). The complex Coidwell complex(Sage, 1982, 1991) (Figure 18). The complex consists of of aa broad broad spectrum spectrum of of heterolithic heterolithic breccias breccias that that consists have undergone varying degrees of alteration and are have undergone varying degrees of alteration and are variably radioactive(Sage, radioactive(Sage, 1982). 1982). The The diatreme diatreme was was variably discovered by Mr. Gordon Yule while completing field discovered by Mr. Gordon Yule while completing aa field assignment at Lakehead University in 1976(Mitchell and assignment at Lakehead University in 1976(Mitchell and Platt, 1977; Gordon Yule, personal communication, 1995). Platt, 1977; Gordon Yule, personal communication, 1995). Since the the diatreme diatreme was was radioactive radioactive prospectors prospectors working working for for Since Gulf Minerals Canada Ltd. investigated the diatreme Gulf Minerals Canada Ltd. investigated the diatreme structure for for its its uranium uranium content. content. The The complex complex occurs occurs within within structure the thermal thermal aureole aureole of of contact contact metamorphism metamorphism of of the the Port Port the Coldwell Complex(Walker, Complex(Walker, 1967) 1967) and and rare rare granitoid granitoid fragments fragments Coldwell found in the eastern part of the breccia may be from the found in the eastern part of the breccia may be from the Port Coldwell Complex(Sage, 1982). Preliminary unpublished Port Coldwell Complex(Sage, 1982). Preliminary unpublished U-Pb isotopic isotopic ages ages on on zircons zircons from from the the Dead Dead Horse Horse Creek Creek West West U—Pb +6 Ma(1.82% subcomplex have given values of 1128.7 subcomplex have given values of 1128.7 +— 6 Ma(l.82% +- 44 Ma(—2.49% Ma(-2.49% discordant) discordant)(Krogh and discordant) and and 1112.7 1112.7 +discordant) (Krogh and Wilkinson, 1995, personal communication). These preliminary Wilkinson, 1995, personal communication). These preliminary ages suggests suggests the the possibility possibility that that the the Dead Dead Horse Horse Creek Creek ages diatreme is slightly older than the Port Coldwell Complex diatreme is slightly older than the Port Coldwell Complex dated at at 1108 1108 ++- 11 Ma Ma by by Heaman Heaman and and Machado Machado(1992). Until the the dated (1992). Until isotopic investigations are completed the age relationship isotopic investigations are completed the age relationship between the the diatreme diatreme and and the the alkalic alkalic rock rock complex complex remain remain between somewhat speculative since critical outcroppings needed to somewhat speculative since critical outcroppings needed to establish a relationship are lacking. The age dating does establish a relationship are lacking. The age dating does indicate that that the the mineralization mineralization within within the the Dead Dead Horse Horse Creek Creek indicate diatreme is Keweenawan in age and related to alkalic rock diatreme is Keweenawan in age and related to alkalic rock magmatic events events of of the the Midcontinent idc continent Rift. ~ i f t .Failure ~ a i l u r eto to magmatic correlate lithologies across Dead Horse Creek have prompted correlate lithologies across Dead Horse Creek have prompted Walker(1967) and Sage(1982) to propose that a fault may Walker(1967) and Sage(1982) to propose that a fault may occur along the trend of the creek. The minor subcomplexes occur along the trend of the creek. The minor subcomplexes generally have have aa northwest—trending northwest-trending long long axis axis suggesting suggesting generally structures(Sage, 1982). that they may occupy crosscutting that they may occupy crosscutting structures (Sage, 1982). The diatreme diatreme lies lies at at the the northern northern end end of of the the Big Big BayBayThe Ashburton Bay Fault(Sage, 1978) or Thiel Fault(K1asner et Ashburton Bay Fault(Sage, 1978) or Thiel Fault(Klasner et al. 1982) within the Trans Superior Tectonic Zone. The al. 1982) within the Trans Superior Tectonic Zone. The diatreme lies lies within within north, north, to to east east of of north, north, trending trending diatreme regional linears, some of which are likely to be faults. faults. regional linears, some of which are likely to be On the the basis basis of of the the anomalous anomalous concentrations concentrations of of K, K, Nb, Zr, Nb, Zr, On and LREE elements, Sage(1982) interpreted the Dead Horse and LREE elements, Sage(1982) interpreted the Dead Horse Creek Diatreme Diatreme to to be be the the high high level level expression expression of of aa Creek possibly coeval with the emplacement of the the carbonatite, carbonatite, possibly coeval with the emplacement of prairie Lake carbonatite. Smyk et al. (1993) came to Prairie Lake Carbonatite. Smyk et al. (1993) came to aa similar conclusion conclusion and and proposed proposed that that the the carbonatite— carbonatitesimilar emplacement event was followed by a later mineralizing event event emplacement event was followed by a later mineralizing �_______ _____IMETASEDIMENTS 35 DEAD HORSE ::: +++ + •+ + + + + + + ± + + + + + + + +.+ + + + +_+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +++ + + + + -1- +4+4+ + + + + 4 + + + + + + + + + + + + + + . + + + . + + + + + •. . ...... . . . . AD HORSE CENTRAL ++1+. + . + DEAD HORSI . + 4 + HORSE NORTH + + + + + .I .. + + II EAST.::::::::::::::::::: + + + + + + + + + + + + + I*l'I—Iu + 200m + + + + 4 + —. --' ++++++4 'DEAD HORSE SOUTH + + + + + + ,II 4$t4)+ +4+4++'.iPROTEROZOIC ++Ij+++BREccIA fault' + :::: :::::::. INTRUSIVE CWTACT ::••..•. :: : :::::::::::::::::::::::::::::::::::::. ' MONZONITE, .1V///// QUARTZ MONZONITE —. ,. ' /''7c'1/$/I"E. t'1,V7AC7 1 DIABASE ARCHEAN INTR(.IS/VE CONTACT -''.i' MAFIC TO : INTERMEDIA1E METAVOL.CANICS Figure Figure 18: Geological sketch map of the Dead Horse Creek Diatreme Diatreme with with field field trip trip sites sites indicated(modified indicated(m0dified from from Sage, Sage, 1982). 1982). �36 an agpaitic agpaitic nature. nature. This of an This suggestion suggestion is is based based on on the the observation that that HREE(Gd-Lu) HREE(Gd-Lu) are are concentrated concentrated in in the the observation shear cutting the Dead Horse Creek West diatreme mineralized shear breccia(Smyk et al., al., 1993). 1993). This This HREE-enrichment is more more characteristic of agpaitic agpaitic syenites syenites and and peralkaline peralkaline granites granites characteristic carbonatites that are typically typically LREE-enriched. LREE-enriched. Smyk than carbonatites than Smyk et et al. (1993) (1993) correlated this late-stage HREE mineralization al. mineralization with the the possible possible emplacement emplacement of of the the Port Port Coidwell Coldwell complex. complex. Economic Economic Geology Geology The The complex complex was prospected for its uranium content by Gulf Minerals Canada Ltd. Ltd. who found the best mineralized area at the the Dead Horse Creek West subcomplex. The company completed mapping, sampling, diamond drilling and radiometric surveys over over the the complex complex in in 1977-1978. 1977-1978. Unocal Unocal Canada Canada Ltd. Ltd. examined examined the Diatreme in in the the late late 1980's 1980's principally principally the Dead Dead Horse Horse Creek Creek Diatreme for its its I Y content. content. The diatreme has has very high high concentrations concentrations of Zr Zr and and Be Be which have not been been examined examined for for their their economic economic potential. potential. Take Take the the trail trail SW SW for for approximately approximately 750 750 mm from from the the parking parking area. This trail trail is is up and down down and and numerous numerous wet wet and and rocky rocky area. This areas areas exist. exist. - Stop The U-YU-YStop 88 Unocal Unocal YY prospect prospect - Dead Horse Horse Creek Creek West. The Be-Zr mineralization mineralization found found within within the the Dead Dead Horse Horse Creek Creek Diatreme Diatreme is is most highly concentrated concentrated in in the the Dead Dead Horse Horse West West subcomplex subcomplex breccia breccia and is is associated associated with with shearing shearing trending trending 290 290 with with vertical vertical dip. dip. The The mineralization mineralization is is best best exposed exposed at at the in aa narrow narrow zone zone the west west end end of of the the stripped stripped area area in approximately The richest richest mineralization mineralization occurs occurs approximately 15 15 cm wide. The as as very very fine— fine- grained, grained, chocolate-brown, chocolate-brown, vitreous vitreous material. material. Silicification Silicification accompanied accompanied the the mineralization. mineralization. Highest Highest assays assays occur occur over a width of 1.5 1.5 m and and length length of of 82 82 m(Smyk et et al., al., 1993). 1993). The The main minerals minerals are are calcium calcium zirconosilicate zirconosilicate with subordinate subordinate zircon, zircon, uraninite, uraninite, thorite, thorite, monaZite—(Ce) monazite-(Ce) and xenotime-(Y)(Smyk xenotime-(Y)(Smyk et al., al., 1993). 1993). Phenakite(Be2SiO4) Phenakite(Be2Si04) is is the et al., al., 1993). 1993). Smyk Smyk the Be-bearing mineral (Sage, (Sage, 1982, 1982, Smyk Smyk et et et al.(1993) al.(1993) reported reported that that xenotime xenotime occurs occurs as as inclusions inclusions in in niobjan niobian rutile rutile and and that that the the monazite monazite is is associated associated with with calcite, calcite, K-feldspar K-feldspar and riebeckite. riebeckite. Assays Assays range range up up to to 11.6 11.6 %% Zr, Zr, 0.6 0.6 %% Be, 2.5 2.5 % Th, 250 250 ppm Sc, Sc, 1850 1850 ppm 1, Y, 300 300 ppm ppm Nb, 903 903 to to 1004 1004 ppm HREE(sum of of Gd Gd to to Lu) Lu) and and 4600 4600 ppm ppm U(Smyk U(Smyk et et al. al. 1993). 1993). In In the the central central stripped stripped area area of of Dead Dead Horse Horse Creek Creek West West aa heterolithic heterolithic breccia breccia is is well exposed. exposed. This This breccia breccia contains contains subrounded ite subrounded to to subangular subangular clasts clasts of of white whiteto topink pinkquartz quartzite �37 rocks of of the the Sibley sibley Group, Group, the the nearest nearest outcrops outcrops of of which which now now rocks exist 60 km to the west on islands in Lake superior near exist 60 km to the west on islands in Lake Superior near Rossport. The The clasts clasts are areup upto to0.3 0.3 in m in in diameter diameter and and have have Rossport. been exposed by stripping(~age, 1982). At the south end of been exposed by stripping(Sage, 1982). At the south end of the stripped area a 10 to 15 cm wide quartz vein trending the stripped area a 10 to 15 cm wide quartz vein trending phenacite(~e~sio~)(not 115 and and dipping dipping south south contains containsphenacite(Be2SiO4) 115 (not visible to the naked eye). visible to the naked eye). At the the eastern eastern end end of of the the stripped stripped area area exposures exposures of of At heterolithic breccia and a lamprophyre(carbonatite) dike are are heterolithic breccia and a lamprophyre(carbonatite) dike present. present. Follow aa flagged flagged trail trail from from the the partially partially stripped stripped area area Follow below the main stripping for a distance of approximately 550 below the main stripping for a distance of approximately 550 m to south. in to the the south. 9: Cliff Cliff face face of of heterolithic heterolithic breccia. breccia. This This is is one one of of Stop 9: Stop the larger exposures of breccia close to the western contact the larger exposures of breccia. close to the western contact of the the Dead Dead Horse Horse Creek Creek South South subcomplex. subcomplex. The The cliff cliff is is of approximately1010inm high high and and 100 100inm long long and and gives gives aa strong strong approximately channel. response on on aa scintillometer, scintillometer, particularly particularly on on the the KK channel. response The clast-supported, angular to subangular breccia is red to to The clast—supported, angular to subangular breccia is red brick red red with with clasts clasts commonly commonly displaying displaying concave concave centres centres brick and raised raised rims rims suggesting suggesting silicification silicification of of the the margins. margins. and Clasts up up to to 11 mm occur occur but but most most are are less less than than 0.3 0.3 m. m. The The Clasts matrix consists consists of of carbonate, carbonate, biotite, biotite, amphibole amphibole and and quartz quartz matrix and because because of of the the high high carbonate carbonate content content weathers weathers and recessively, leaving leaving the the clasts clasts in in relief. relief. Exposed Exposed within within recessively, is aa carbonate-rich carbonate-rich lamprophyre lamprophyre dike dike the face face of of the the cliff cliff is the his dike dike 28 cm cm wide, wide, trending trending 250 250 and and dipping dipping 75 75 south. south. This 28 sharply cross cross cuts cuts the the breccia breccia and and is is visually visually estimated estimated to to sharply opaque minerals, minerals, 50 50 to to 70 70 percent percent contain 10 10 to to 15 15 %% opaque contain carbonate and and 30 30 to to 40 40 %% biotite(Sage, biotite(~age,1982). 1982). carbonate km and and Return to to the the vehicles vehicles and and continue continue south south to to 25.7 25.7 km Return park on on the the east east side side of of the the road. road. This This is is on on aa curve curve so so be be park careful careful. . Walk aa few few metres metres east east of of the the road road to to the the outcrop outcrop of of Walk side of of the the hill. hill. heterolithic breccia breccia exposed exposed on on the the side heterolithic - Scapolite-replaced heterolithic heterolithic breccia breccia - Discovery Discovery Stop 10: 10: Scapolite—replaced Stop is the the first first outcrop outcrop on on the the Dead Dead Horse Horse outcrop. This This outcrop outcrop is outcrop. Creek Diatreme Diatreme examined examined by by prospectors prospectors working working for for Gulf Gulf Creek Minerals Canada Canada Ltd Ltd searching searching for for the the cause cause of of radioactivity radioactivity Minerals in the the area. area. The The breccia breccia weathers weathers grey, grey, is is clast—supported, clast-supported, in and has has aa "ragged "ragged jagged" jaggedw surface(Sage, surface(Sage, 1982). 1982). The The fragments fragments and are angular angular to to rounded rounded and and generally generallyless lessthan than0.3 0.3inm in in are �38 maximum dimension. The clasts clasts are extensively altered along the margins margins and scapolite scapolite in in fibrous fibrous crystals crystals up to 5 cm may the replace parts of some some clasts. clasts. On weathered surface surface the replace scapolite is easily recognizable recognizable by by its its white white fibrous fibrous habit; habit; scapolite is however, on fresh fresh surface surface it is extremely difficult to recognize in in hand sample. sample. In thin section section the the matrix recognize consists of quartz, carbonate, amphibole, opaques opaques and consists scapolite and and the the clasts clasts show scapolite show replacement replacement by by carbonate, carbonate, amphibole amphibole and and scapolite(Sage, scapolite(Sage, 1982). 1982). to the the vehicles and continue continue south south to Highway 17 at Return to 28.6 km. km. 28.6 Time Time permitting we will go to the optional stop, the McKel].ar Creek Creek diatreme. diatreme. From From the the Junction Junction of of the the Dead Dead Horse McKellar Creek km to to McKellar McKellar Creek. Creek. Creek access access road road turn turn right(west) right(west) 2.2 2.2 km The trail is on on the the west west side trail to to the the McKellar McKellar Creek Creek Diatreine Diatreme is of McKellar Creek Creek and and one one must must park park on on the the shoulder shoulder of of Highway 17 17 so so be careful. There is a skid road going south the east east side side of of McKellar McKellar Creek Creek which which may may also also be be used used as as on the a parking parking site. site. Walk approximately approximately 430 metres north along the skid road and the the two two outcrops outcrops of of breccia breccia representing representing this this diatreme diatreme occur occur the east on the east side side of of the the trail. trail. Stop 11: McKellar Creek diatreme. This This diatreme diatreme was was located located interpreted it it to to be be aa possible possible Animikie Animikie by Walker(1967) who interpreted conglomerate. The fact fact that that it it was was radioactive radioactive and and most most likely intrusive intrusive into into the the enclosing enclosing rocks rocks was was recognized recognized much later(Sage, later(Sage, 1982). 1982). The The McKellar McKellar Creek Creek Diatreme Diatreme is is aa clast supported supported heterolithic heterolithic breccia breccia similar similar to to that that exposed exposed at stop stop 99 on the the Dead Horse Horse Creek Creek South South subcomplex. subcomplex. The The clasts clasts are are red from alteration, alteration, angular angular to to subrounded, subrounded, and and generally 0.3 0.3 m or less less in in maximum dimension. dimension. Sibley Sibley Group Group clasts clasts are are abundant and in in thin thin section section the the quartz quartz displays displays Sibley Group Group curved deformation deformation lamellae. lamellae. In In addition addition to to Sibley clasts and clasts clasts from the the surrounding surrounding Archean Archean rocks, rocks, Rove Rove Formation Formation clasts clasts have also also been identified identified by by thin thin section section examination(Sage, examination(Sage, 1982). 1982). The The space space between between the the clasts clasts is is carbonate—rich carbonate-rich and generally generally weathers weathers low low leaving leaving the the clasts clasts outcrops exposed in relief. Behind the outcrops exposed by the the road, a 22 x 33 m clast clast of rounded Sibley Sibley Group Group rock rock may may be be examined. examined. On On the the basis of outcrop outcrop and soil soil composition composition the the McKellar McKellar Creek Creek Diatreme in size size and and on on the the Diatreme is is estimated to to be 240 240 xx 60 60 mm in basis basis of similar similar alteration alteration styles, styles, interpreted interpreted to to be be coeval coeval 1982). At with the the Dead Horse Horse Creek Creek Diatreme(Sage, Diatreme(Sage,1982). At present, present, the the closest closest outcroppings outcroppings of of Sibley Sibley Group Group rocks rocks are are 60 60 km west, on on islands islands in in Lake Lake Superior Superior near near Rossport. Rossport. �39 DAY DAY 22 The second day is is devoted devoted to to the the Port Coldwell Coldwell Alkalic Alkalic Rock Rock Complex and will consist consist of aa west to east traverse traverse through through the complex along Highway Highway 17. 17. The tour starts starts at at the the Dead Creek access access road road and and distances distances are are given given from from that that Horse Creek The Port Port Coidwell Coldwell Alkalic Alkalic Rock Rock Complex Complex has has been been the the point. The subject of many field trips trips in in the the past and the the reader reader may wish to to refer refer to to these these guidebooks guidebooks for for additional additional information(Puskas, 1970; 1970; Mitchell Mitchell and and Platt, Platt, 1977, 1977, 1982, 1982, information(Puskas, Several stops stops described described by by Mitchell Mitchell and and Platt, Platt, (1994) (1994) 1994). Several are revisited and the the reader should refer to to their their guidebook guidebook for supplementary supplementary detailed detailed mineral mineral chemistry. chemistry. General Geology Geology Coldwell Complex Complex occurs occurs within within the the Trans Trans Superior Superior The Port Coldwell Tectonic Zone(Klasner Zone(K1asner et et al. al. 1982) 1982) where where the the Big Big BayBayTectonic Ashburton Bay(Sage, 1978) 1978) or or Thiel Thiel Fault(Klasner Fault(K1asner et et al. (1982) intersect intersect Archean Archean rocks rocks of of the the Superior province al.(1982) on the the north north shore shore of Lake Lake Superior. Superior. This This fault fault may may be be 140 km north, as as far far as as Chipman Chipman Lake Lake using using extrapolated 140 airphotographs, LANDSAT and and local local geologic geologic mapping(Coates, mapping(Coates, airphotographs, LANDSAT 1970; Sage, 1985). 1985). The Port Coidwell Coldwell Complex occurs occurs on the the northern flank flank of the the Lake Lake Superior Superior Basin Basin at at or or close close to to the the northern Proterozoic—Archean Proterozoic-Archean contact(Sage, contact(Sage, 1991). 1991). The The Slate Slate Islands, Islands, located approximately 10 km southwest of the the Port Port Coldwell Coldwell Complex, have Keweenawan Keweenawan volcanic rocks of the the Osler Osier Group exposed on the shoreline shoreline and as isolated isolated blocks blocks in in diatreme diatreme structures(Sage, 1991). 1991). These islands islands occur very close close to the the intersection intersection of the the Michipicoten Island Island Fault Fault and and the the Fault or or Thiel Thiel Fault. Fault. The The Michipicoten Michipicoten Big Bay-Ashburton Bay Fault Island Fault appears to closely follow follow the the Proterozoic— ProterozoicArchean contact. The Port Port Coidwell Coldwell Complex Complex has has been been mapped (1967), Currie(1980) Currie (1980) and and more more recently recently by by Walker by Tuominen Tuominen(1967), al.(1993a,b). The Port Coidwell Coldwell Complex is is one one of the the et al.(1993a,b). largest alkalic rock complexes complexes in in the world having a surface area of diameter of approximately approxim tely 25 km and a surface 2 (Figure19). km(Figure approximately 490 km 19). Milne(1967) Milne(1967) and and Muir(1982) Muir(1982) completed a limited amount of mapping along the the eastern eastern margin of the the intrusion intrusion and and Walker(1967) completed completed aa similar similar area of mapping along along the the western western margin. margin. Walker(1967) Walker(1967) defined a thermal aureole of contact metamorphism of approximately 1.6 approximately 1.6 km width along the western margin which would envelope envelope the the Dead Dead Horse Horse Creek Creek Diatreme Diatreme structure. structure. Aubut(1977) determined determined that that this this thermal thermal aureole aureole attained attained pyroxene hornfels facies facies where in direct contact contact with the intruding intruding gabbro. gabbro. The Port Coidwell Coldwell Complex consists consists of 3 ring coinplexes(Mitchell and and Platt, Platt, 1978; Currie, 1980) complexes(Mitchell 1980) superimposed superimposed on each other and younging systematically to �Figure 19: Geology nodi4ed Fr-on Volker et at., Colwel1 Alkalic Rock Complex. 1993a,b. Geological_sketch map_oC the Port Mafc Metavotcanic Rocks Rocks Inter-mediate to Fetsic Metavoconc Metasedimentary Rocks Massive to Foloted Grantod Rocks A RC HE AN rELSIC TO INTERMEDIATE P1JTliNIC ROCKS Macc Vo1canc, Subvotcarc and Hypabyssal Intrusive Rocks c3abro Aka1ne Gabbro 0 Recr'ysta1tzed Arphiboe Quartz Syenite Iron-Rich Aug;te Syente Amphbote Syente NepheUne Syenite Amphbo(e Natro1te-NepheLne Syerte AmphiboLe Quartz Syente CDLDWELL LKALIC COMPLEX PRECAMBRIAN LEGEND �41 the southwest southwest along along the the trend trend of the the Trans Trans Superior Superior Tectonic Tectonic the Zone(Figure 19). 19). The oldest ring complex is centered centered north north Craddock Cove, Cove, the the next north north of the the town town of of Port Port of Craddock Coldwell and the the youngest is is centered on on Pic Pic Island(Currie, Island(Currie, Coidwell 1980). 1980). Mitchell and Platt(1994) classified these centres as Centre 11 - Saturated Saturated alkaline rocks with follows: Centre rocks oversaturated residue; Centre Centre 2 — Miascitic oversaturated residue; Miascitic alkaline rocks undersaturated residue residue and and Centre Centre 33 — Alkaline Alkaline rocks with undersaturated with with oversaturated oversaturated residue. residue. - - - The oldest consist dominantly dominantly of an an oldest rocks rocks of Centre 11 consist olivine gabbro gabbro outer outer ring and a ferroaugite ferroaugite centre. The The gabbros have been studied studied as a consequence consequence of their their sulfide sulfide content and are are described below under economic economic geology. Shaw(1994) subdivided subdivided the eastern eastern gabbro into into four four intrusions; Gabbronorite, Two Duck Lake Intrusion, Layered Gabbro Gabbro and and Malpas Malpas Lake Lake Intrusion. Intrusion. The The most primitive primitive gabbro gabbro is the Two Duck Lake Lake Intrusion Intrusion which is equivalent equivalent to to a high-Al in composition(Shaw, composition(Shaw, 1994). 1994). The The ferroaugite ferroaugite high-A1 basalt basalt in syenites syenites have have been been classified classified as as laurvikite laurvikite by by Puskas(1967) Puskas(1967) and have undergone undergone detailed detailed study study by by Jago(1980), Jago(1980), McGill (1980), Mitchell Mitchell and and Platt(1978) Platt(l978) and Whittaker(1976). McGill(1980), The detailed composition composition of the amphiboles amphiboles in centres centres 11 and 3 have been 146—149). The been summarized summarized by by Mitchell, Mitchell, (1990 (1990p. p.146-149). augite syenite augite syenite contains contains minor amounts amounts of fayalite fayalite olivine(Fa83—98)(Whittaker, 1976; olivine(Fa83-98)(Whittaker, 1976; Mitchell Mitchell and and Platt, Platt, 1978). 1978). The ferroaugite ferroaugite syenite syenite was highly evolved at the the time time of by fayalitic olivine, olivine, diopsidicintrusion as revealed by hedenbergite and (Mitchell and hedenbergite and ferro-hastingsitic ferro-hastingsitic hornblende hornblende(Mitchel1 Platt, 1978). The The REE mineralogy of the syenites syenites and associated associated pegmatites pegmatites was was studied studied by by Nicol(1990). Nicol(1990). The centre centre 22 rocks rocks consist dominantly of an outer outer ring ring of alkalic biotite gabbro and a inner core of nepheline nepheline syenite. The syenite syenite has been studied studied by by Whittaker(1976), Whittaker(1976), McGill(1980), Clark(1983) McGill(1980), Clark(1983) and Mitchell and Platt(1982). Platt(1982). Mitchell and Platt(1982) interpret the nepheline nepheline syenite syenite to to be the the product of fractional fractional crystallization crystallization of a basaltic magma. Centre Centre 33 syenites syenites have have been been studied studied in in detail detail by by Jago(1980), Jago(1980), Lukosius—Sanders(1988) Lukosius-Sanders(1988) and Mitchell et al.(1993). al.(1993). The The REE rare—metal minerals associated with centre 3 were and rare-metal concentration of examined by Nicol(1990) who documented the concentration REE REE and rare rare metals metals in in the residual residual liquids liquids of these these syenitic inagmas. Mitchell et et al. al. have have interpreted interpreted the centre syenitic magmas. Mitchell 3 syenites to be the differentiation products of more than mantle—derived basalt magma. magma. These syenites one batch of mantle-derived syenites now represent represent the the product product of multiple intrusion, intrusion, contamination contamination and brecciation giving rise to complex field and petrologic relationships(Mitchell et al. 1993). relationships(Mitchel1 1993). �42 Lainprophvres Lamprophyres are are abundant abundant'within the centre centre 11 rocks, rocks, Lamprophyres within the in the the western western part part of of the the complex. complex. They They have have particularly in been studied studied by by Aubut(1977), Aubut(1977), Evans Evans(1984), Laderoute(1987), been (1984), Laderoute(1987), Mitchell et et al. al. (1991) (1991) and and those those external external to to the the complex complex at at Mitchell McKellar Harbour Harbour by by Platt Platt and and Mitchell(1979, Mitchell(1979, 1982a,) 1982a,) Platt Platt McKellar 1983). The The lamprophyres lamprophyres have have aa variety variety of of strikes strikes but but et al. 1983). the dominant trend trend is is approximately approximately east-west east-west with with greatly greatly the subordinate NW and and NE trends. The subordinate The lamprophyres lamprophyres are are generally generally less than than 1.0 1.0 m in in width width and and are are interpreted interpreted to to be be less dominantly related to centre22 magmatism(Mitchell magmatisin(~itchel1et et al., al., dominantly tocentre Mitchell and Platt(1994) summarized summarized classification classification of of 1991). Mitchell the lamprophyres lamprophyres and and one one alkalic alkalic basalt basalt dike dike in in their their order order the of emplacement emplacement as as follows: follows: of MAFIC OCELLAR OCELLAR LAMPROPHYRES o foftthe h e camptonitic c a m p t o n i t i c variety, variety, MAFIC LAMPROPHYRES These These rocks rocks contain c o n t a i n phenocrysts phenocrys t s of o f olivine, 01ivine, aluminous a 1uminous pyroxene, pyroxene, 1. 1. with w i t h or or without w i t h o u t carbonate-rich c a r b o n a t e - r i c h ocelli, o c e l l i , are a r e widespread. widespread. k a e r s u t i t e and and titanian t i t a n i a n ferroparg'asite f e r r o p a r g a s i t e set n aa matrix kaersutite set iin matrix o off magnesian hastinsgite, h a s t i n s g i t e , augite, a u g i t e , plagioclase, p l a g i o c l a s e , biotite, biotite, magnesian m a g n e t i t e , sphene sphene and and minor minor nepheline. n e p h e l i n e . The The ocelli ocelli are are magnetite, commonly commonly concentrated c o n c e n t r a t e d bby y f flow l o w ddifferentiation i f f e r e n t i a t i o n in i n the the centers centers of o f the the dikes. d i k e s . In a d d i t i o n t o c a l c i t e , the ocelli ocelli contain contain scapolite, and f l u o r i t e . s c a p o l i t e , epidote e p i d o t e and In addition to calcite, the fluorite. 2. 2 . QUARTZ-BEARING QUARTZ-BEARING MAFIC MAFIC LAMPROPHYRES LAMPROPHYRES which w h i c h are are camptonites, camptonites, o f quartz q u a r t z with w i t h aa hexagonal hexagonal c h a r a c t e r i z e d by b y phenocrysts p h e n o c r y s t s of characterized habit. The phenocrysts p h e n o c r y s t s are a r e typically t y p i c a l l y resorbed resorbed and and mantled m a n t l e d by by h a b i t . The c l i n o p y r o x e n e . Carbonate Carbonate ocelli o c e l l i are a r e commonly commonly present. p r e s e n t . The The clinopyroxene. p r i n c i p a l exposures e x p o s u r e s of o f these these dikes dikes are a r e to t o be be found found within within principal the the gabbros gabbros and and ferroaugite f e r r o a u q i t e syenites syenites located l o c a t e d on on the the lakeshore (see Aubut, l a k e s h o r e to t o the the west w e s t of o f the t h eLittle L i t t l ePic p i cRiver River(see Aubut, 1977). 1977). 3. 3 . SANNAITE-TYPE SANNAITE-TYPE LAMPROPHYRES LAMPROPHYRES characterized c h a r a c t e r i z e d by b y the the presence presence of o f euhedral e u h e d r a l phenocrysts p h e n o c r y s t s of o f aluminian a l u m i n i a n and and chromian chromian diopside. diopside. These These pyroxenes p y r o x e n e s exhibit exhibit complex complex zonation z o n a t i o n and and mantling m a n t l i n g due d u e to to the The groundmass groundmass is i s composed composed of of the effects e f f e c t s of o f magma magma mixing. m i x i n g . The ferroan f e r r o a n paragasite, p a r a g a s i t e , aluminian a l u m i n i a n diopside, d i o p s i d e , biotite, b i o t i t e , albitized albitized plagioclase p l a g i o c l a s e and and epidotized e p i d o t i z e d alkali a l k a l i feldspar. feldspar. 4. 4 . MONCHIOUITIC-TYPE MONCHIOUITIC-TYPE LAMPROPHYRES LAMPROPHYRES with w i t h silicate s i l i c a t e and and carbonate c a r b o n a t e ocelli. o c e l l i . These These rocks rocks are a r e characterized c h a r a c t e r i z e d by b y the the presence p r e s e n c e of o f brown brown titaniferous t i t a n i f e r o u s ferro—paragasite f e r r o - p a r a q a s i t e phenocrysts phenocrysts The silicate s i l i c a t e ocelli ocelli set set in i n aa matrix m a t r i x of o f devitrified d e v i t r i f i e d glass. g l a s s . The consist c o n s i s t of o f paragasitic p a r a g a s i t i c amphibole, amphibole, alkali a l k a l i feldspar f e l d s p a r and and analcime. a n a l c i m e . The The monchiquites m o n c h i q u i t e s are a r e considered c o n s i d e r e d to t o be be heteromorphs heteromorphs of o f the the camptonites(Mitchell c a m p t o n i t e s (Mitchell et e t al. a1 1991). 1991) . . �43 5 . FELDSPAR FELDSPAR GLOMEROPORPHYRY GTJOMEROPORPHYRY MID AND ALKALI ALKALI BASALT BASALT DIKES DIKES. These These 5. n o t been been studied s t u d i e d extensively e x t e n s i v e l y but b u t may may be be not r e p r e s e n t a t i v e of o f contemporaneous contemporaneous basic b a s i c magmas. magmas. representative r o c k s have have rocks . 6 . ANALCIME ANALCIME TINGUAITE(heronites). TINGUAITE ( h e r o n i t e s ) Porphyritic P o r p h y r i t i c salic s a l i c dikes dikes 6. commonly of o f an an orange orange or o r reddish—brown reddish-brown colour. c o l o u r . Phenocrysts commonly Phenocrysts be found, found, set set o f analcime, analcine, alkali a l k a l i feldspar f e l d s p a r and and nepheline nepheline can can be of iinn aa fine f i n e grained grained m a t r i x o f a l t e r e d a l k a l i f e l d s p a r s and matrix of altered alkali feldsparè and a c n i t i c pyroxene. pyroxene. The The least l e a s t altered a l t e r e d occurrences occurrences of o f this this acmitic s u i t e are are found found in i n the t h e country country rocks r o c k s close c l o s e to t o the t h e eastern eastern suite margin of o f the t h e complex complex and and along along railroad r a i l r o a d tracks t r a c k s in i n the t h e Heron Heron margin Bay region. r e g i o n . Modern Modern mineralogical mineralogical studies s t u d i e s of o f these t h e s e rocks r o c k s have have Bay n o t been been undertaken. undertaken. not The lamprophyres lamprophyres are are common common in in centre centre 11 rocks rocks less less common common in in The centre 22 and and rare rare in in centre centre 3( 3( Mitchell Mitchell et et al., al., 1991; 1991; centre Mitchell and and Platt, Platt, 1994). 1994). Mitchell Mitchell et et al.(1991) al.(1991) interpreted interpreted Mitchell the lamprophyres to be the product of centre 2 magmatism and the lamprophyres to be the product of centre 2 inagmatism and their absence within a given lithologic unit may be used as their absence within a given lithologic unit may be used as rocks from from centres centres 11 one criterion criterion for for separating separating centre centre 33 rocks one and 2 . The Marathon lamprophyre dikes dated as 1.65 +- 0.12 0.12 and 2. The Marathon lainprophyre dikes dated as 1.65 +Ga by the Rb-Sr technique(P1att and Mitchell, 1983) and the Ga by the Rb-Sr technique(Platt and Mitchell, 1983) and the Slate Island lamprophyre dated as 282 +11 Ma to 310 +18 Slate Island lamprophyre dated as 282 +- 11 Ma to 310 +— 18 Ma by the K-Ar technique(Sage, 1991) have been redated by Ma by the K-Ar technique(Sage, 1991) have been redated by Heaman(persona1 communication, communication, 1994) 1994) as as 1145 1145 +15/—b +15/-10 Ma Ma and and Heaman(personal 1141 +9 Ma respectively using the U-Pb technique on 1141 +- 9 Ma respectively using the U-Pb technique on perovskite. The The Marathon Marathon dikes dikes and and the the Slate Slate Island Island dike dike perovskite. intrude the Archean supracrustal assemblage west of the Port Port intrude the Archean supracrustal assemblage west of the Coldwell Complex and may represent a pro-Port Coldwell Coidwell Complex and may represent a pre-Port Coidwell Complex alkalic alkalic event event since since the the Complex Complex has has been been dated dated by by Complex +1 MafHeaman and Machado, 1992). the same method at 1108 the same method at 1108 +- 1 Ma (Heaman and Machado, 1992). Diatremes Diatremes On the the west west coast coast of of the the Coldwell Coldwell peninsula, peninsula, 4.0 4.0 km km south south of of On the Neys Provincial Park headquarters, is a diatreme the Neys Provincial Park headquarters, is a diatreme structure described described in in detail detail by by Balint(1977). Balint(1977). This This diatreme diatreme structure is approximately 75 x 240 m and contains rounded to angular is approximately 75 x 240 and contains rounded to angular clasts of of Port Port Coidwell Coldwell Complex Complex rocks. rocks. The The long long axis axis of of the the clasts intrusion strikes north of east and it appears to have a intrusion strikes north of east and it appears to have a vertical dip(Sage, dip(Sage, 1982). 1982). The The rounding rounding of of the the clasts clasts vertical suggests turbulent flow in a high velocity gas-solid suggests turbulent flow in a high velocity gas-solid system(Balint, 1977, considered the the systein(Balint, 1977, Sage, Sage, 1982). 1982). Sage(1982) Sage(1982) considered diatreme to be a high-level feature similar to those found diatreme to be a high-level feature similar to those found in porphyry porphyry copper copper systems systems exposed exposed at at high high structural structural in The origin of the this diatreme is not comparable to to levels. levels. The origin of the this diatreme is not comparable the Dead Horse Creek and McKellar Creek diatremes on the the Dead Horse Creek and McKellar Creek diatremes on the east flank flank of of the the Port Port Coidwell Coldwell Complex Complex which which are are likely likely the the east high level expression of mantle-derived carbonatite high level expression of mantle-derived carbonatite magmatism(Sage, 1982). 1982) magmatism(sage, . Hornfelsed CaD Cap Rocks Rocks Hornfelsed �44 In In the the Wolf Wolf Camp Camp Lake Lake area area and and at at aa number number of of sites sites on on the the north flank flank of of the the Port Port Coidwell Coldwell Complex Complex subhorizontal subhorizontal north massive to to amygdaloidal amygdaloidal flow massive exposed(Wa1ker flow rocks rocks are are exposed(Walker 1993a,b). 1993a,b). These These volcanic volcanic remnants remnants have have been been preserved preserved by by fracturing and down—dropping down-dropping of the the former former volcanic ring fracturing edifice above the the intrusion(Sage, intrusion(Sage, 1986). 1986). The The basaltic rocks edifice vary from from fresh fresh andesine—oligoclase andesine-oligoclase basalt, basalt, hornfelsed hornfelsed vary to metasomatized metasomatized basalt in in flows flows up to to 55 m basalt to thick(Mitchel1 and Platt, 1994). 1994). Nicol(1990) Nicol(1990) has studied studied the the thick(Mitchell flows and considers considers them to be of tholeiltic tholeiitic lineage. lineage. The flows hornfelsed flows flows contain contain some some orthopyroxene orthopyroxene and and the the amygdule amygdule hornfelsed fillings greenish caic—silicate calc-silicate fillings were were metamorphosed metamorphosed to to aa greenish mineral mineral assemblage. assemblage. Xenoliths Xenol iths In Nicol(1990), In addition addition to to the the study study of of xenoliths xenoliths by by Nicol(1990), Mitchell Mitchell and and Platt(1979) Platt(1979) examined examined feldspar feldspar porphyry xenoliths xenoliths in in nepheline nepheline syenite syenite displaying displaying nephelinenephelineplagioclase plagioclase intergrowths intergrowths and determined that the the nepheline has has likely likely resulted resulted from a Na—K Na-K cation exchange. This metasomatism metasomatism caused caused desilication desilication of of the the andesine andesine phenocrysts phenocrysts but did did not not form form nepheline nepheline in in the the groundmass(Mitchell groundmass(Mitche1l and and Platt, developed alkali alkali feldspars of Platt, 1979). 1979). The The nietasomatism metasomatism developed aa wide wide range range of of compositions(Mitchell compositions(Mitche11 and and Platt, Platt, 1979). 1979). Isotone Studies Studies Isotope Excluding isotopic isotopic studies studies directed directed toward toward age age determinations, determinations, Heaman and Machado(1992) examined Sr, Nd and Pb Pb isotopes isotopes and and determined determined that that Midcontinent MidcontinentRift Riftmagnias magmas have aa uniform uniform Nd isotopic isotopic composition. composition. Heaman and have Machado(1992) compared 1.1 1.1 Ga carbonatites carbonatites with Port Coldwell Coldwell Complex Complex data data and and found found that that carbonatites carbonatites have have lower lower Rb/Sr Rb/Sr and and higher higher U/Pb U/Pb and and Sm/Nd Sm/Nd ratios. ratios. This This means means that that there there were were two two isotopic isotopic reservoirs reservoirs present present at at 1.1 1.1 Ga; Ga; an an enriched plume—component plume-component represented represented by by most most Midcontinent Midcontinent Rift Rift magmatisiu magmatism and a carbonatitic carbonatitic coniponent(Heaman component(Heaman and and Machado, (1992) interpreted Machado, 1992). 1992). Heaman Heaman and and Machado Machado(1992) interpreted the the presence presence of of nonradiogenic nonradiogenic Pb Pb compositions compositions and negative negative Nd values Coldwell magmas magmas as as values in in silica—saturated silica-saturated Port Port Coldwell documenting documenting the the interaction interaction of of plume—derived plume-derived mantle mantle melts melts lower crust. crust. with with low low U/Pb U/Pb granulite-facies granulite-facies lower Geochronolocrv Geochronolociy Currie(1980) provided some some K-Ar isotopic isotopic ages ages and and Rb/Sr Rb/Sr isotopic isotopic ages ages have have been been provided provided by by Platt Platt and and Mitchell(1982b) Mitchell(1982b) and and Bell Bell and Blenkinsop(1980). Blenkinsop(1980). The means of determining determining the the Rb/Sr Rb/Sr isochron isochron of of Platt Platt and and Mitchell(l982b) Mitchell(1982b) �45 was discussed discussed by Blenkinsop was (1983) and Platt Platt and and Blenkinsop and Bell (1983) Mitchell(1984). isotopic ages ages were were first first Mitchell(1984). Uranium-lead isotopic et al. al. (1985) (1985) and and the the results results discussed discussed undertaken by Turek Turek et undertaken by Thorpe(1986) Thorpe(l986) and Turek Turek et et al(1986). al(1986). Heaman Heaman and and Machado(1992) reported reported aa U-Pb isotopic isotopic age age of of 1108 1108 +— +- 11 Ma which is age. Heaman and is now accepted accepted as the the most accurate accurate age. could not not distinguish distinguish the the three three intrusive intrusive Machado(1992) could isotopic ages. ages. The The distinction distinction centres on the basis of isotopic between these intrusive intrusive centres centres rests rests on on field field observations. observations. Local Structure Structure The Port Coidwell Coldwell Complex Complex occurs occurs at at the the Proterozoic—Archean Proterozoic-Archean contact just north of the the intersection intersection of the the Michipicoten Michipicoten 1978) Island Fault and the the Big Bay-Ashburton Bay Fault(Sage, 1978) Fault(Klasner et al., or Thiel Fault(K1asner al., 1982). 1982). The The Michipicoten Michipicoten Island Fault parallels and may mark the the limits limits of the the Proterozoic basin. The The Port Port Coldwell Coldwell Complex Complex lies lies within within the the Proterozoic Trans Superior ZonefKlasner et et al., al., 1982). 1982). Within Within Superior Tectonic Tectonic Zone(Klasner the Port Coidwell Coldwell Complex Complex mafic mafic banding, banding, trachytoidal trachytoidal textures textures and xenolith xenolith preferred preferred elongation elongation may may locally locally be be used to outline outline the the configuration configuration of of parts parts of of the the various various centres centres of intrusion. These These planar planar features features have have been been used used by Currie(1980) to to speculate speculate on on the the centres centres of of emplacement emplacement Coldwell for the three ring complexes complexes that make up the the Port Coldwell Complex. The three three intrusive intrusive centres centres young young in in aa southwest southwest Complex. direction toward the the Slate Slate Islands(Sage, Islands(Sage, 1991) 1991) and and along along the the Big Bay-Ashburton Bay Fault Fault trend. trend. The The successive successive emplacement of superimposed superimposed ring ring complexes complexes accompanied accompanied by by repeated faulting faulting and and stoping, sloping, multiple multiple intrusion, intrusion, metamorphism and metasomatic metasomatic activity activity has has created created very very complex petrographic, petrologic complex petrographic, petrologic and and field field relationships. relationships. The presence of abundant abundant xenoliths xenoliths in in some some lithologies lithologies and and large roof pendants indicate indicate that the the complex complex is is barely unroof ed and and is is thus thus exposed exposed at at a a very very high high structural structural unroofed level. Lilley(1964) proposed that that the the Port Port Coldwell Coldwell Complex Complex is is aa funnel-shaped intrusion funnel-shaped intrusion and Puskas(1967) has proposed that it is a lopolith. Currie(1980) considers the complex complex to to consist of an interlocking interlocking group group of of cone cone sheets sheets and and ring ring dikes. The arcuate outer outer gabbro gabbro unit unit of centre centre 11 may be be interpreted as a ring dike as may the alkaline biotite 2. Arcuate Arcuate faults faults and and large large down—dropped down-dropped gabbro of centre centre 2. roof pendants are are consistent consistent with with ring ring fracturing fracturing and subsidence, subsidence, characteristic characteristic of of caldera caldera emplacement(Sage, emplacement(Sage, Mitchell and (Figures 1986, Mitchell and Platt, Platt, 1982b, 1982b, 1994, 1994, Walker, Walker, 1993) 1993)(Figures 20, 21). 21). Each intrusive intrusive centre centre has has likely likely undergone undergone aa similar Platt(1994) similar series series of of intrusive intrusive events. events. Mitchell Mitchell and and Platt(1994) consider intrusive intrusive centres centres 22 and and 33 to to be exposed exposed at at aa higher higher level than centre one one due due to to the the abundance abundance of of xenoliths; xenoliths; however, the large large xenoliths xenoliths or or roof roof pendants pendants near near Wolf Camp Camp �-4 c 4 c u 3 a 0 -4 -4 JJ h Q 6 >I10 JJ m a- dr-1 A Figure 20: Idealized ap of rock type distribution in a ciaple ring coaplex(froa sage, 1986). a 0 & a 0> u a H N -4-4 hi - on 2!3 N à -44 4 ^ a a a o a Â¥ 0 04 .. B> c 6  h 2tna% a 1986). Figure 21: Idealized vertical section displaying rock type in a siaple alkalic ring complex(from Sage, distribution * NAN?%.I MAPIC ANO %L,mAMA,,c øocs �47 Lake and and in in the the northern northern parts of of the the complex are largely Lake centered on on centre centre 1. 1. The The difference difference in in the level of centered structural exposure between the three centres is not likely to be very very great. great. Sage(1986) Sage(1986) suggested suggested that the southern to of the the Port Port Coldwell Coldwell Complex Complex may be exposed at a part of slightly deeper deeper level slightly level than than that that of of the the north due to the the abundance abundance of of xenoliths xenoliths and and rook rook pendants in the northern part part of of the the intrusion. intrusion. Geophysics Geophysics and and LANDSAT LANDSAT Imagery Imauerv The The Port Port Coldwell Coldwell Complex Complex is is covered covered by by LANDSAT LANDSAT imagery(Canada Centre Centre for for Remote Remote sensing, Sensing, 1987) 1987) and and the the imagery(Canada large large Port Port Coldwell Coldwell Complex Complex is is easily easily recognized. recognized. Local Local faults be faults and and linears linears are are easy easy to to trace trace and and often often can can be extended beyond beyond the the limits extended limits of of the the complex. complex. Meru(1965) studied studied the the angle angle of of emergent emergent seismic seismic P waves at Meru(1965) Marathon, Marathon, Ontario Ontario and and interpreted interpreted his his data to indicate that the the Moho Moho below below Marathon Marathon dips dips southwest southwest under under the the Lake Lake Superior Superior Basin Basin at at 44 degrees. degrees. He He also also concluded concluded that that the the crust crust was was much much thicker thicker to to the the southwest southwest of of Marathon Marathon than than to to the the northeast(Meru, northeast (Meru, 1965). 1965) . Lilley(1964) Lilley(1964) examined examined the the aeromagnetic aeromagnetic expression expression of of the the Port Port Coldwell Coldwell Complex Complex and and observed observed intense intense negative negative anomalies anomalies over over the the eastern eastern gabbros gabbros of of centre centre (Figure (Figure 22). 22). The atat 1108 -F-+- 11 The emplacement emplacement of ofthe thePort PortCoidwell ColdwellComplex Complex 1108 ina(Heaman and Machado, Machado, 1992), therefore, took ma(Heaman and took place place just just prior prior to to aa magnetic magnetic reversal reversal that that occurred occurred between between 1096.2 1096.2 +— +1.8 1.8 Ma and and 1097.6 1097.6 Ma(Davis Ma(Davis and and Paces, Paces, 1990). 1990). The The age age of of reversal reversal may may closely closely approximate approximate the the age age of of reversal reversal for for the the Osler Osier Group(Davis Group(Davis and and Paces, Paces, 1990, 1990, Paces Paces and and Miller, Miller, 1993). 1993). Isomagnetic Isomagnetic contouring contouring of of the the aeromagnetic aeromagnetic data data clearly clearly distinguishes distinguishes the the Port Port Coldwell Coldwell Complex Complex from from the the surrounding surrounding Archean Archean rocks rocks and and reveals reveals aa prominent prominent circular circular pattern(Figure pattern (Figure 22). 22) . Currie(1980) Currie(1980) cites cites gravity gravity data data as as indicating indicating that that the the Port Port Coidwell Coldwell Complex Complex has has aa mafic mafic component component at at depth(Figure depth(Figure 23). 23). Since Since mostly mostly light light syenitic syenitic rocks rocks are are exposed exposed at at surface surface postulation Ic rocks rocks beneath the postulation of of maf mafic the syenites syenites is is required required to to explain explain the the positive positive gravity gravity anomaly. anomaly. Mitchell Mitchell et et al. al. (1983) modeled the gravity data and suggested that the (1983) modeled felsic to 55 km—thick km-thick layer layer over over aa felsic rocks rocks represent represent aa 33 to differentiated differentiated basic basic intrusion intrusionconsisting consistingof of3 3toto5 5kin km of of gabbro The presence presence gabbro underlain underlain by by peridotite peridotite or or pyroxenite. pyroxenite. The of of large large volumes volumes of of mafic mafic rocks rocks at at depth depth supports supports the the concept concept that that some some of of the the Port Port Coidwell Coldwell Complex Complex felsic felsic rocks rocks are are differentiates differentiates (Figure (Figure 23). 23). During During Keweenawan Keweenawan rifting rifting upper Ic magmas magmas migrated from the upper mantle-derived mantle-derived maf mafic the southwest southwest to to the the northeast northeast and and came came to to rest rest at at Port Port Coldwell(Mitchell Coldwell(Mitchel1 et et al., al., 1983). 1983). �48 Figure 22: 22: Aeromagnetic Aeromagnetic map of of the the Port Coldwell Alkalic Figure Alkalic Rock Complex(ODM—GSC, Complex(0DM-GSC, l963a,b,c,d). 1963a,b,c,d). Rock Figure Coidwell Alkalic Figure 23: 23: Bouguer Bouguer anomaly anomaly map map of of the the Port Coldwell Rock Rock Complex. Complex. The The solid solid straight straight line line is is the location of a gravity profile(fr0m Mitchell Mitchell et et al., al., 1983). gravity profile(from 1983). �49 The The Port Port Coidwell Coldwell Complex Complex and and surrounding surrounding Archean Archean terrane terrane has has been been covered covered by a reconnaissance reconnaissance airborne airborne gamma—ray gamma-ray spectrometer survey(Graham and Bonham-Carter, Bonham-Carter, 1993). 1993). The The spectrometer in the the Port Port Coidwell Coldwell Complex Complex concentration concentration of of radioelements radioelements in is high in in contrast to the enclosing Archean supracrustal supracrustal rocks. rocks. Graham Graham and and Bonham-Carter (1993) (1993) indicated indicated that that in in general each each lithologic lithologic unit may be distinguished on on the the general basis basis of of its its gross gross radiometric radiometric signature signature and and that that the the three three intrusive intrusive centres centres display display minor minor correlatable correlatable differences. differences. The Port Port Coldwell Coldwell Complex Complex is is also also covered covered by side-scanning side-scanning The radar radar imagery imagery completed completed by the the Canada Canada Centre Centre for for Remote Remote Sensing Bonham— Sensing and these these data were merged by Graham and BonhamCarter(1993) Carter(l993) in in their their study study of the the radiometric radiometric data. The The radar imagery imagery reflects reflects the the rugged rugged topography topography of the the Port Port radar Coidwel]. Complex area. Coldwell Complex area. Economic Geolow Economic Geoloqy The The Port Port Coidwell Coldwell Complex had several several small small quarries quarries developed developed for for building building stone stone in in the the ferroaugite ferroaugite syenite syenite close close to to the the CPR CPR tracks tracks and the the town town of Marathon in in the the early early l930's(Puskas, 1930fs(Puskasf 1967). These efforts efforts failed failed to to be commercial and and the the efforts were soon soon abandoned. The Port Port commercial Coldwell Complex Complex has has repeatedly repeatedly been been evaluated evaluated as as aa Coidwell potential source source for for building stone stone due due to to the the pronounced pronounced potential blue to gold schiller texture of the feldspars in the blue to gold schiller texture of the feldspars in the ferroaugite syenite. syenite. In the late late 1930's 1930fs efforts were made to to ferroaugite evaluate evaluate the the titaniferous titaniferous magnetite magnetite showings showings in in the the gabbros(Puskasf 1967). 1967). Other Other than than surface surface peripheral gabbros(Puskas, peripheral trenching and and pitting pitting little little work work was was completed completed and and no no trenching tonnage tonnage was was outlined. outlined. The The titaniferous titaniferous magnetite magnetite at at Stop Stop 15 15 occurs in in the the area area where where most efforts efforts were were expended expended in in occurs search search of of titaniferous titaniferous magnetite magnetite deposits. deposits. 1950fs porphyritic syenite syenite dikes were prospected for for In the the 1950's In their Nb Nb and and Zr Zr content. content. The their The principal principal areas areas of of investigation were Port Port Munro Munro near near the the former former siding siding of of investigation Angler on on the the CPR CPR and and north north of of west west from from the the west end end of of Angler Craddock Lake Lake within within the the interior. interior. None None of of these these efforts efforts Craddock proved sufficient sufficient grade grade or or tonnage tonnage to to be be of of economic economic proved interest. One of these dikes was tested for for U and Th without interest. success. success. In In the the 1960's l96Ofs the the nepheline nepheline syenites syenites on on the the Neys Neys Peninsula Peninsula and Pic Pic Island Island were were evaluated evaluated as as aa possible possible source source of of and ceramic grade grade nepheline. nepheline. This This work work proved proved unsuccessful unsuccessful ceramic because the the impurities impurities could could not not be be removed removed from from the the because nepheline. nepheline. The The poikilitic poikilitic nepheline nepheline commonly commonly contains contains tiny tiny inclusions of of ferromagnesian ferromagnesian minerals minerals which which cannot cannot be be inclusions removed removed in in milling, millingf thus thus the the desired desired ceramic ceramic grade purity purity could could not not be be obtained. obtained. �50 The Port Port Coldwell Coldwell Complex Complex offers offers the the best potential potential as as aa The source source for for Cu-Ni-PGE. Cu-Ni-PGE. Exploration Exploration of of the the suiphide sulphide mineral mineral assemblages assemblages in in the the peripheral peripheral gabbros gabbros of of centre centre 11 on on both both the western western and and eastern eastern flanks flanks of of the the intrusion intrusion started started in in the the the 1950's 1950fs and and peaked peaked in in the the 1960's. 1960fs. Most Host of of this this work work was was done in in the the eastern eastern gabbro gabbro north north of of Marathon Marathon by by Anaconda Anaconda done American TWODuck Duck American Brass Brass Ltd. Ltd. on on aa deposit deposit now known known as as the the Two Lake Occurrence. Occurrence. Watkinson Watkinson and and Ohnenstetter(1992) Ohnenstetter(l992) indicated indicated Lake that Two Duck Duck Lake Lake Occurrence Occurrence occurs occurs in in aa separate separate that the the Two gabbroic intrusion intrusion within within the the outer outer ring ring of of centre centre 11 gabbro. gabbro. gabbroic The mineralization mineralization occurs occurs in in coarse coarse gabbro gabbro and and pegmatite pegmatite and and The is is interpreted interpreted to to be be the the product product of of interaction interaction of of aa magmatic mineral mineral assemblage assemblage with with fluids fluids of of mixed mixed magmatic magmatic magmatic origin and and fluid fluid generated generated by by the the breakdown breakdown of of abundant abundant origin xenoliths8 principally principally felsic felsic metavolcanic metavolcanic rocks(Watkinson rocks(Watkinson xenoliths, and Ohnenstetter, Ohnenstetter, 1992). 1992). Good Good and and Crocket(1994b) Crocket(1994b) have have and proposed that that the the Two Two Duck Duck Lake Lake Occurrence Occurrence was was intruded intruded as as aa proposed plagioclase-rich crystal crystal mush mush which which had had fractionated fractionated at at plagioclase-rich depth depth and and contained contained suiphide sulphide droplets. droplets. The The suiphide sulphide mineral mineral assemblage precipitated precipitated after after rapid rapid solidification solidification of of the the assemblage crystal crystal mush mush with with little little Cu Cu or or PGE PGE migration(Good migration(Good and and Crocket, Crocket8 1994b). 1994b). Good Good and and Crocket(1994b) Crocket(1994b) suggested suggested that that the the origin origin of of the the mineralization mineralization is is analogous analogous to to that that of of the the Duluth Duluth Complex. Complex. Shaw(1994) Shaw(l994) has has interpreted interpreted the the Two Two Duck Duck Lake Lake Intrusion Intrusion to to be be the the most most primitive primitive unit unit of of 44 subunits subunits within within the the eastern eastern gabbro gabbro and and similar similar to to high—Al high-A1 basalt. basalt. This This magma magma underwent underwent fractionation fractionation in in an an open open system system with with removal removal and and recharge 10 cycles cycles in in an an expanding expanding magma magma recharge in in 33 — 10 chainber(Shaw, chamber(Shaw8 1994). 1994). The The reader reader should should refer refer to to Shaw(1994) Shaw(l994) for for details. details. In In the the 1980's l98Ofs interest interest in in the the Two Two Duck Duck Lake Lake deposit deposit was was revived revived by by Fleck Fleck Resources Resources Ltd. Ltd. who who have have outlined Cut0.04 0.04 %%Ni, ~i~ outlined 37,000,000 3780008000tons tons grading grading 0.31 0.31 %% Cu, 251,000 2518000 oz oz Pt, Pt8 1,001,000 l8OOl8O0Ooz oz Pd, Pd8 84,000 848000 oz oz Au Au and and 43,000 43#000oz oz Rh(Canadian ( See %(Canadian Nines MinesHandbook, Handbook81993—1994, 1993-1994#p.p.145) 145)( See Stops Stops 25, 25# 27). 27). Platinum—group—element Platinum-group-element mineralization mineralization is is also also present present in in association association with with aa large large block block of of gabbro gabbro within within the the north north central central part part of of the the Port Port Coidwell Coldwell Complex. Complex. This his is is known as as the the Geordie Geordie Lake Lake Occurrence Occurrence and and grade grade and and tonnage tonnage known have have not not been been determined. determined. The The Geordie ~ e o r d i eLake Lake Occurrence Occurrence has has been interpreted as a late-stage hydrothermal been interpreted as a late-stage hydrothermal product product of of the the final crystallization of a plagioclase-rich intrusion of final crystallization of a plagioclase-rich intrusion of gabbroic gabbroic magma(Good magma(Good and and Crocket, Crocket8 1994a). 1994a). The The dominant dominant sulphides are chalcopyrite, pyrrhotite, pyrite, sulphides are chalcopyrite8 pyrrhotite8 pyrite8 cubanite cubanite and and rare pentlandite. Table 2 lists other minerals found rare pentlandite. Table 2 lists other minerals found in in studies completed completed over over the the years years in in these thesemineralized mineralized rocks. rocks. studies The reader should refer to the references for details and The reader should refer to the references for details and to to Walker(1993c) Walker(l993c) for for another another brief brief discussion discussion of of the the economic economic geology. geology. - Table 2: Mineralogy Mineralogy of of the the mineralized mineralized gabbros gabbros of of the the Port Port Table 2: Coldwell Coldwell Complex Complex �51 Mineral Reference Altaite(PbTe) Atokite(Pd3Sn) Bornite(Cu5Fes4) Electrum(Au,Ag) Guanglinite(pd3As) Galena(Pbs) Ressite(Ag2Te) Hollingworthite (RhAsS) Irasite(IrAsS) 2 12 5 2 112 2 4 Kotuiskite (PdTe) Si and Pb-bearing Kotuiskite Mackinawite((Fe,Ni)958 Majaicite(NiPdAs) 1,2 1,2 1,2 5 2 Merenskyite, solid solutions, (PbTe2) Mertieite—II(Pd35b3) Palladoarsenide(Pd2As) Ag—Pentlandite(p'e,wi)958 with Ag Platarsite (PtAsS) 1,2 1,2 1,2 2 1,2 Rhenium sulphide Sopcheite, solid solutions, (Pd2Ag4Te4) Sperrylite(PtAs2) Telargpalite((Pd,Ag)3Teçp) Troilite(Fes) Unnamed (PdsAs?), Pd—bearing nickeline Unnamed Pd16N].As15 4 1,2 1,2 2 5 1,2 3 Zvyaginskite(pd3pb) 1,2 1) Ohnenstetter et al., 1991; 2) Watkinson and Ohnenstetter, 1992; 3) Mulja and Mitchell(199o); Mitchell et al., 1989; 5) Lum, 1973 Field Trip Log At 2.0 km from the Dead Horse Creek access road Stop 12: Molybdenite along fractures in hornfelsed wacke. Molybdenite occurs throughout the Port Coldwell Complex as tiny isolated grains and rosettes along joint planes. Ho concentration of molybdenite has been found which warrants further testing. The outcrop is locally cut by gabbro and syenite. At this site the molybdenite occurs as tiny grains and rosettes up to 2 mm along joint planes which may display some alteration to yellow ferrimolybdite. The syenite dikes contains abundant xenoliths of both wall rock and phases of the complex. East of the exposure, the road cut reveals various phases of syenite with abundant xenoliths. The general trend of the bedding in the wacke is 050 with a �52 steep but extreme extreme variation variation in in bedding bedding steep southerly southerly dip, dip, but attitudes attitudes occur. occur. At 2.9 Jan Stop Stop 13: 13: Optional: Optional: Rheomorphic Rheomorphic breccia. breccia. This his stop stop requires requires at 20 minute minute walk walk over over aa skid skid trail trail that that is is at least least aa 20 overgrown overgrown and and often often wet. wet. Park Park the the vehicles vehicles on on the the north north side side of Be careful careful and and be be sure sure that that you you of the the curve curve in in the the highway. highway. Be can the highway highway safely and that can get get on on and and of offf the that the the shoulder shoulder of of the the road road is is not not soft. soft. The The skid skid trail trail was was made made for for power power line line construction construction and and leads leads off off into into the the bush bush from from the the top top of of the the outcrop outcrop on on the the south south side side of of the the highway. highway. At 795 mm the the power power line line tower tower to to the the east east of of At approximately approximately 795 the the trail trail is is on on aa syenite syenite outcrop outcrop containing containingvery very fine— finegrained grained gabbro gabbro xenoliths xenoliths with with concentric concentricrings ringsof of alteration. alteration. The The reaction reaction rings rings are are 0.5 0.5 to to 1.0 1.0 cm cm wide wide and and weather weather high high compared compared to to the the core core of of the the xenolith. xenolith. The The xenoliths xenoliths are are in in coarse—grained coarse-grained syenite syenitecut cutby by aa fine— finegrained aplite up up to to 20 grained syenitic syenitic aplite 20 cm cm wide wide that that trends trends165. 165. Between Between this this tower tower and and Highway Highway 17 17 to to the the east, east, the the outcrops outcrops are are dominantly dominantly layered layered gabbro. gabbro. The The very very fine-grained fine-grained gabbro gabbro is is the the oldest oldest gabbroic gabbroic phase phase and and often often has has aa knobby knobby weathered weathered surface surface which which may may be be observed observed in in outcrops outcrops on on the the trail trail beneath beneath the thepower powerline. line. . Continue Continue walking walking to to approximately approximately 1270 1270 mm The skid skid trail trail The takes wide loop loop to to the the south south and and comes comesout out at at the the base base of of takes aa wide aa tower tower on on the the power power line line east east of of the the earlier earlier stop. stop. The The exposure exposure beneath beneath the the tower tower and and aa few few metres metres to to the the east east is is one of rheomorphic rheomorphic breccia breccia observable observable one of of the the best best examples examples of on Coldwell Complex. Complex. Angular Angular to torounded roundedclasts clastsof of on the the Port Port Coidwell metasediiuentary metasedimentary rock occur occur in in aa fine fine grained grained remobilized remobilized anatectic 0.3 mm and and some someare are anatectic matrix. matrix. Some Some clasts clastsare are up up to to0.3 rusty. rusty. The The clasts clasts have have contorted contortedbanding banding in inaamatrix matrix displaying displaying aa fluxion fluxion structure structuresuggesting suggestingthe thefragments fragmentswere were ductile The xenoliths xenoliths are are randomly randomly ductile in in aa flowing flowing medium. medium. The oriented oriented and and angular angular to to rounded rounded fragments fragmentsof of vein vein quartz quartzare are locally locally present. present. From From the the exposure exposure beneath beneath and and just just east east of of the the tower tower walk walk west west along along the the skid skid road road beneath beneath the thepower power line line and and note note the the rapid rapid change changefrom from rheomorphic rheomorphicbreccia brecciainto into less less and and less lessdeformed deformedmetasedimentary metasedimentaryrocks. rocks. • At At 60 60 to to 70 70 mm convoluted convolutedbedding beddingas aswell wellas assegmented segmentedquartz quartz veins are easily recognized. There are good examples veins are easily recognized. There are good examplesof of boudinaged boudinaged quartz quartzveins veinsat atthis thissite sitedirectly directlybelow belowthe the power line. At approximately 100 m good compositional power line. At approximately 100 m good compositional convolutionbut but the the layering(bedding) layering(bedding) displays displaysmuch much less less convolution quartz veins are still boudinaged. The bedding is trending quartz veins are still boudinaged. The bedding is trending approximately 295with with aa 75 75 south southdip dipand andthere thereis isopen open approximately295 kinking of the bedding. The kink bands 345and and dip dip kinking of the bedding. The kink bands trend trend 345 �53 vertically. The The plunge plunge of of the the fold fold axis axis in in the the kink kink band band is is vertically. approximately 35 35 NW. NW. approximately At approximately approximately165 165inm the the bedded bedded metasedinientary metasedimentary rocks rocks are are At much less less contorted contorted and and bedding bedding trending trending 300 300 and and dipping dipping 70 70 much north north is is easy easy to to recognize. recognize. Some Some open open folding folding in in the the metasedimentary rocks rocks and and some some minor minor faulting faulting trending trending 345 345 inetasedimentary dipping 75 75 north north offset offset the the bedding bedding by by as as much much as as 20 20 - 25 25 dipping cm. The fault trend is parallel to the trend of the kink cm. The fault trend is parallel to the trend of the kink bands. bands. - To To observe observe even even less less deformed deformed rocks rocks continue continue west. west. After After of your your observations observations return return to to the the vehicles. vehicles. completion of completion At 3.2 km Stop 14: 14: Mineralized Mineralized western western gabbro. gabbro. Park Park at at the the entrance entrance to to Stop the trail trail to to Middleton Middleton siding siding on on the the south south side side of of the the road. road. the The trail trail is is aa good good walking walking trail trail which which leads leads to to the the CPR CPR The tracks. tracks. At At approximately approximately925 925in m an old trench trench in in rusty, rusty, mediummediumgrained grained gabbro gabbro occurs occurs on on the the west west side side of of the the trail. trail. The The gabbro 0.5 to to 1.0 1.0 %% gabbro is is massive massive and and locally locally contains contains 0.5 chalcopyrite chalcopyrite and and pyrrhotite. pyrrhotite. This This exposure exposure is is typical typical of of mineralized mineralized western western gabbro gabbro and and differs differs from from the the mineralized mineralized eastern eastern gabbro gabbro in in the the lack lack of of well well developed developed pegmatitic pegmatitic textures. textures. This This trench trench was was probably probably made made in in the the late late 1950's. 1950fs. Wilkinson(1983) Wilkinson(1983) reported reported that that the the olivine olivine from from this this site site is is Fo Fo 49 49 to to 51 51 and and that that plagioclase plagioclase is is An An 47 47 to to 52. 52. The The western western gabbros gabbros are are less less evolved evolved than than the the eastern eastern gabbros gabbros which which have have olivine olivine compositions compositions of of Fo Fo 43 43 to to 46 46 and and plagioclase An 51 51 to to 57 57 (Wilkinson, (Wilkinson,1983). 1983). plagioclase compositions compositions of of An At 3.3 km to Remain Remain parked parked at at stop stop 14 14 and and walk walk east east along along Highway Highway 17 17 to the the large large outcrop outcrop on on the the north north side side of of the the road. road. This This is is stop Platt(1994) stop 10 10 of of Mitchell Mitchell and and Platt(l994) Stop Stop 15: 15: This This site site is is noted noted for for its its spectacular spectacular 'hydronephelinite" (natrolite) syenite llhydronephelinite"(natrolite) syenite pegmatite pegmatite enclosing enclosing medium medium grained grained gabbro gabbro xenoliths. xenoliths. The The outcrop outcrop is is cut cut by by aa late late lamprophyre lamprophyredike. dike. The Theniedium-grained medium-grained angular angular gabbro gabbro xenoliths xenolithsupuptoto1.0 1.0inm in in size size have have aa wide wide 11 to to 22 cm cm dark dark reaction reaction rim rim with with the the enclosing enclosing syenite syenitepegmatite. pegmatite. The The natrolite natrolitesyenite syenitepeginatites pegmatites contain contain patches patches of of red red to to orange-red 15 cm, cm, perthitic perthitic feldspars feldspars orange-red natrolite natrolite up up to to 10 10 - 15 up up to to 30 30 cm cm and and dark dark green green to toblack black amphibole amphibole up up to to20 20 to to25 25 cm. cm. Mitchell Mitchell and and Platt(l994) Platt(1994) reported reported the the presence presence of of pleochroic titaniteand and biotite. biotite. pleochroic clinopyroxene, clinopyroxene,zircon, zircon,titanite - �54 The fine-grained fine-grained lamprophyre lamprophyrethat thatcuts cutsthe thenatro].ite natrolite The pegmatite pegmatite trends trends 040, 040, dips dips 55 55 north north and and is is approximately approximately 40 40 cm cm wide. wide. Mitchell Mitchell and and Platt(1994) Platt(1994) indicated indicated that that most most lamprophyres lamprophyres in in this this area area may may be be classified classified as ascamptonites. camptonites. Continue continue east east along along the the face face of of the the outcrop outcrop from from the the natrolite pegmatites. pegmatites. The The rock rock is is aa finefine- to to medium-grained medium-grained natrolite nepheline syenite syenite with with nepheline nepheline indicated indicated by by the the chalky chalky nepheline weathering. Occasionally Occasionally aa grain grain of of reddish reddish orange orange weathering. "hydronephelinite" (natrolite) is **hydronepheliniteg~(natrolite) is recognizable. recognizable. continue east east along along the the face face of of the the outcrop outcrop to to almost almost the the Continue end end of of the the exposure exposure to to examine examine various various syenite syenite and and syenite syenite pegmatite pegmatite units. units. Near Near the the end end of of the the outcrop outcrop medium-grained medium-grained titaniferous titaniferous magnetite magnetite with with minor minor clinopyroxene, clinopyroxene,plagioclase plagioclase and and apatite apatite is is exposed exposed in in the the road road cut. cut. This This material material has has been been prospected prospected in in the the past past as as aa source source for for titaniferous titaniferous luagnetite. The best best outcropping outcropping is is approximately approximately 150 150 mm east east magnetite. The of of the the lamprophyre lamprophyre dike dike that thatcuts cutsthe thenatrolite natrolitepegmatite. pegmatite. The The various various rock rock types types exposed exposed in in this this road road cut cut have have been been assigned assigned to to various various intrusive intrusive centres centres by by Mitchell Mitchell and and Platt(1994). Platt(1994). The The gabbro, gabbro, and and ferroaugite ferroaugitesyenites syenites are are related activity, amphibole amphibole syenites syenites to to centre centre 33 related to to centre centre 11 activity, and the the natrolite natrolitepeginatites pegmatites to to centre centre 2(Mitchell 2(Mitchell and andPlatt, Platt, and 1994). 1994). McGill(1980) McGill(1980) has has examined examined the the natrolite natrolite pegmatites pegmatites and titaniferous titaniferousmagnetite magnetite accumulations accumulationsin inthe thegabbro. gabbro. and Return Return to to vehicles vehicles At 5.5 km Stop Stop 16: 16: Intrusive Intrusive breccia breccia on on the the east east side side of of the the Little Little Pic Park at at the the large largeturn turnout out at at the the east east end end of of the the Pic River. River. Park bridge bridge and and walk walk along along the the highway highway to to the the first first outcrop outcrop on on the the south southside sideof ofthe theroad. road. Angular Angular blocks blocks of of fine— fine- to to medium—grained medium-grained equigranular equigranular oligoclase oligoclase gabbro gabbro occur occur in in aa matrix matrix of of medium—grained medium-grained pink pink quartz quartz syenite. syenite. The The gabbro gabbro appears appearsto to be be shattered shattered and and veined veined by by the the syenite syeniteand and some someof of the the fragments fragmentsmay may visually visually be The quartz quartz be refitted refittedas as one one would would aa jig jig saw sawpuzzle. puzzle. The syenite syenite filling filling in in around around the the fragments fragmentslocally locally contains contains miarolitic miarolitic cavities cavities up up to to several severalcentimetres centimetresin in width width which which may may contain contain euhedral euhedral quartz quartz and and feldspar feldsparcrystals. crystals. White White calcite calcite may may partially partially fill fill some someof of these these cavities. cavities. This This oligoclase oligoclase gabbro gabbro occurs occurs only only in inthis this area area of of the the Little Little Pic Pic River lookout(Stop 17) 17) where where River and and up up to to the the Little Little Plc Pic River River lookout(Stop Mitchell referto toit itas as an an oligoclase oligoclase Mitchell and and Platt(1994) Platt(1994) refer basalt. basalt. Volcanic Volcanic textures textureshave have not not been been observed observed in in this this unit. The Little Little Plc Pic River River occupies occupiesaa strong strong lineament lineament which which unit. The may may be be traced traced on on airphotos airphotosto to the thewest west flank flank of of the the Killala Killala Lake Thelineainent lineament is is likely likely aa fault fault zone zone LakeComplex Complexand andnorth. north.The �55 but offset offset cannot cannot be be determined determined at at this this location. location. The The Little Little but Pic River River lineament lineament can can be be interpreted interpreted to to be be the the onshore onshore Pic extension of of aa deep deep water—filled water-filled linear linear located located southwest southwest of of extension the Slate Slate Islands(Sage Islands(Sage 1991) 1991) which the which probably probably represents represents the the onshore expression expression of of faulting faulting related related to to the the Thiel(Klasner Thiel(K1asner onshore et et al. al. 1982) 1982) or or Big Big Bay-Ashburton Bay-Ashburton Bay Bay Fault(Sage, Fault(Sage, 1978). 1978). Laws(1983). Parts of of the the breccia breccia zone zone have have been been studied studied by by Laws(1983). Parts of the the intrusive intrusive breccia, breccia, weakly weakly At the the extreme extreme western western end end of At trachytoidal ferroaugite ferroaugite syenite syenite occurs occurs in in outcrop. outcrop. The The trachytoidal spectacular cliff cliff faces faces observed observed on on the the west west side side of of the the spectacular Little Pic Pic River River consist consist of of ferroaugite ferroaugite syenite. syenite. Little At 6.3 km Stop 17: 17: Little Little Pic Pic River River turn turn out. out. This This is is aa frequent frequent stop stop Stop for visitors visitors to to the the Port Port Coidwell Coldwell Complex Complex as as it it provides provides for safe safe parking parking of of the the vehicles. vehicles. Be Be careful careful and and watch watch for for vehicles vehicles while while you you examine examine exposures exposures along along Highway Highway 17. 17. This This is is stop stop 17 17 of of Mitchell Mitchell and and Platt(1994). Platt(1994). Walk Walk from from the the parking parking area area to to Highway Highway 17 17 and and examine examine the the intrusive intrusive breccias breccias and and xenolith—rich xenolith-rich syenite. syenite. Oligoclase Oligoclase gabbro gabbro veined veined with with quartz quartz syenite syenite occurs occurs along along the the south south side of the road and various syenitic rocks with side of the road and various syenitic rocks with xenoliths xenoliths occur syenites are are pyroxene-amphibole pyroxene-amphibole occur on on the the north north side. side. The The syenites syenites syenites containing containing xenoliths xenoliths of of alkali alkali gabbro, gabbro, alkali alkali diorite diorite and and various various syenites. syenites. The The syenitic syenitic xenoliths xenoliths vary vary from from coarse-grained coarse-grained equigranular equigranular blocks blocks to to porphyritic porphyritic phases. ratio of of alkali alkali gabbro gabbro to to diorite diorite increases increases to to phases. The The ratio the the east east toward toward the the entrance entrance to to the the lookout. lookout. The The alkali alkali gabbro is cut cut by by grey grey nepheline nepheline syenite syenite with with some some gabbro to to diorite diorite is reddish reddish orange orange "hydronephelinite" "hydronephelinite" toward toward the the entrance entrance to to the the lookout. lookout. The The amphibole amphibole tends tends to to be be somewhat somewhat acicular acicular in in the the nepheline-rich nepheline-rich phases phases and and locally locally they they have have somewhat somewhat gradational gradational contacts contacts with with the the alkali alkaligabbro gabbroto todiorite. diorite. Pegmatitic Pegmatitic dikes dikes of of quartz quartz syenite syenite outcrop outcrop opposite opposite the the entrance entrance to to the the lookout. lookout. East East of of the the turn turn off off to to the the lookout lookout the the mediummedium- to to coarse— coarsegrained amphibole-pyroxene syenite is inequigranular senate grained amphibole-pyroxene seriate and the number of xenoliths has greatly diminished. and the number of xenoliths has greatly diminished. The The syenites syenites at at this this location location have have been been related related to to centre centre 33 and Mitchell Mitchell intrusive intrusive activity activity and and Lukosius-Sanders(1988) Lukosius-Sanders(1988) and et et al.(1993) al.(1993) described described these these syenites syenites in in detail. detail. In In the the order Platt(1994) list list the the order of of emplacement emplacement Mitchell Mitchell and and Platt(1994) syenites syenites as as follows: follows: magnesio—hornblende magnesio-hornblendesyenite, syenite, contaminated contaminated ferro-edenite ferro-edenite syenite, syenite, ferro—edenite ferro-edenite syenite syenite and and quartz quartz syenite. syenite. Sannaite Sannaite lamprophyre lamprophyre and and ocellar ocellar camptoniticlamprophyre arereported reportedto tooccur occur in in the the camptonitic lamprophyreare area(Mitchell 1994). Lukosius—Sanders(1988) area(Mitchel1and andPlatt, Platt.1994). Lukosius-Sanders(1988) �56 classified classified the the syenites syenites as as miaskitic, metaluminous metaluminous enriched enriched in in U, Th, Th, REE REE and and Zr Zr due due to to the the presence presence of of zircon, zircon, chevkinite((Ca,Ce,Th)4(Fe,Mg)2(Ti,Fe)3si4022}, REEchevkinite{(Ca,Ce,~h)~(Fe,~g)~(Ti,~e)~~ REEi~O~~), carbonates, carbonates, Nb—rutile Nb-rutile and and aeschylite aeschylite {(Y,Ca,Fe,Th)(Ti,Nb)2(O,OH)6}. { (Y ,Ca,Fe,Th) (Ti,Nb) 2 (0,OH) G>. The centre centre 33 syenites syenites have have affinities affinities to to A-type A-type granites granites and and have have been been interpreted interpreted to to be be the the result result of of fractional fractional crystallization crystallization of of mantle— mantlederived itche ell et et magma(Lukosius-Sanders, 1988; 1988; Mitchell derived basaltic basaltic magma(Lukosius-Sanders, al. al. 1993). 1993). At 9.8 km Stop to Neys Neys Provincial Provincial Park. This Stop 18(Optional): 18(Optional): Turn Turn of offf to This will to this this area area will be be the the site site of of an an optional optional stop. stop. Access Access to may may not not be be possible possible in in the the early early spring spring since since the the park park is is This stop stop has has been been described described as as stop stop 15 15 closed closed to to visitors. visitors. This by by Mitchell Mitchell and and Platt(1994). Platt(1994). Drive along park park access road km along road and and park park Drive approximately approximately 2.8 2.8 kin at at Neys Neys Park Park headquarters. headquarters. Walk east east and and south south along along the the beach beach for for approximately approximately400 400in m to to the the first first large large outcrop outcrop on on the the shore shore of of Lake Lake Superior. Superior. SAMPLE AT THIS SAMPLE COLLECTING COLLECTINGAT THIS SITE SITE IS IS PROHIBITED PROHIBITED MediumMedium- to to coarse—grained coarse-grained biotite biotite gabbro gabbro of of centre centre 22 outcrops outcrops on on the the eastern eastern part part of of the the exposure exposure and and nepheline nepheline syenites syenites of of centre centre 22 are are exposed exposed on on the the western western part part of of the the outcrop. outcrop. The The texture texture and and composition composition of of the the nepheline nepheline syenites syenites are are heterogeneous heterogeneous and and possibly possibly represent represent magma magma mixing process not not yet yet studied studied in in detail detail mixing and and hybridization, hybridization, process within within the the Port Port Coidwell Coldwell Complex. Complex. One One may may continue continue walking walking south south along along the thecoast coastfor forseveral several100 100inm and and observe observe nepheline nepheline syenites syenites with with well well developed developed layering layering and and structures structures reminiscent reminiscent of of "soft—sediment" wsoft-sediment**deformation. deformation. The The layered layered syenites syenites are are divided divided into into large large blocks blocks by by aa later later intrusion The earlier earlier syenites syenites were were intrusion of of nepheline nepheline syenite. syenite. The subjected wsedimentationm and and then then subjected to to current current action action and and "sedimentation" subsequently subsequently forcibly forcibly intruded intruded by by younger younger syenites syenites of of similar similar composition. composition. The Theinafic mafic mineral is is hastingsite(Mitchell hastingsite(Mitchel1 and and Platt, Platt, 1994). 1994). The The general general trend trend of of the the banding banding is is NNW NNW with with aa highly highly variable variable dip. dip. Return Return to to Highway Highway 17 17 and and continue continue east east Stop Stop 19 19(Optional): (Optional): At f to former At 14.6 14.6 km km turn turnof off former townsite townsite of of Port Port Coidwell. Coldwell. Distance Distance remains remains from from the the Dead Dead Horse Horse Creek Creek access accessroad. road. Drive Drive approximately approximately 0.2 0.2 km km and and park park near near the the CPR CPR tracks. tracks. �57 THISISIS A VERYDANGEROUS DANGEROUS LOCATION. LOCATION. THE THE SHAPE SHAPE OF OF THE THE HILLS HILLS THIS A VERY AND ONE MAY NOT HEAR MODIFY THE SOUND OF APPROACHING TRAINS MODIFY THE SOUND OF APPROACHING TRAINS AND ONE MAY NOT HEAR BE ALERT AT ALL TIMES. A TRAIN UNTIL IT IS EXTREMELY CLOSE. A TRAIN UNTIL IT IS EXTREMELY CLOSE. BE ALERT AT ALL TIMES. Amphibole-nepheline syenites syenites of of centre centre 2. 2. Walk Walk east east for for Amphibole-nepheline approximately 700 700 mm along along the the CPR CPR tracks tracks to to the the high high cliff cliff approximately faces along the west side of the railroad opposite Echo faces along the west side of the railroad opposite Echo Lake. These These cliffs cliffs are are composed composed of of nepheline nepheline syenite syenite and and Lake. there is abundant loose rock above so be careful. The there is abundant loose rock above so be careful. The nepheline syenite syenite is is generally generally aa massive massive equigranular equigranular rock rock nepheline The with local reddish orange spots of whydronephelinite". with local reddish orange spots of "hydronephelinite". The rock surface is highly stained and fresh surfaces may only rock surface is highly stained and fresh surfaces may only be obtained obtained from from breaking breaking open open pieces pieces that that have have fallen fallen from from be the cliff. the cliff. continuing beyond beyond this this cliff cliff face face one one may nay examine examine Stop Stop 88 of of Continuing Mitchell and Platt(1994). This stop is on the shore of Mitchell and Platt(1994). This stop is on the shore of Redsucker Cove Cove 1.6 1.6 km km from from Port Port Coldwell Coldwell village. village. At At aa Redsucker concrete embankment leave the tracks and go down to the lake lake concrete embankment leave the tracks and go down to the nepheline syenite veins and a shore to examine diorite, shore to examine diorite, nepheline syenite veins and a analcite trachyte trachyte dike(Mitchell dike(Mitchel1 and and Platt, Platt, 1994). 1994). To To the the analcite east various varieties of nepheline syenite may be observed, east various varieties of nepheline syenite may be observed, and to to the the west, west, breccias breccias of of gabbro, gabbro, diorite diorite and and nepheline nepheline and syenite may be examined. A number of camptonitic syenite may be examined. A number of camptonitic lamprophyres and and one one sannaite sannaite lamprophyre lamprophyre occur occur at at this this lamprophyres site(Mitchel1 and Platt, 1994). For details of this stop site(Mitchell and Platt, 1994). For details of this stop refer to to Mitchell Mitchell and and Platt, Platt, (1994). (1994). refer Return to to the the vehicles vehicles and and continue continue east east along along Highway Highway 17 17 Return At 16.1 16.1 km km highway highway 17 17 crosses crosses Mink Mink Creek. Creek. There There is is aa At waterfall in in syenite syenite approximately approximately 100 100 mm south south of of the the waterfall You may may park park on on the the small small logging logging access access road road highway. You highway. 17 west west of of Mink ink Creek Creek and and take take aa leading north north from from Highway ~ighway17 leading short trail trail south south of of the the highway highway to to the the falls. falls. short At 19.2 km Biotite gabbro gabbro intruded intruded by by various various types types of of Stop 20: 20: Biotite Stop nepheline syenite. syenite. nepheline This stop stop is is at at aa broad broad curve curve in in highway highway 17 17 and and one one should should This be very CAREFUL OF VEHICLES. be very CAREFUL OF VEHICLES. 18.8 km km outcrops outcrops on on the the east east side side starting at at approximately approximately 18.8 Starting of the highway of grey to buff pyroxene amphibole syenite of the highway of grey to buff pyroxene amphibole syenite contain orange orange fluorescing fluorescing hackmanite, hackmanite, aa variety variety of of contain W This mineral can only readily be seen with sodalite. This mineral can only readily be seen with aa UV sodalite. lamp. The The syenite syenite contains contains numerous numerous mafic mafic xenoliths xenoliths up up to to lamp. 25-30 cm cm in in maximum maximum length. length. The The xenoliths xenoliths are are subangular subangular to to 25—30 subrounded and the mafic minerals within the syenite tend to subrounded and the mafic minerals within the syenite tend to �occur occur in in clots. clots. The The larger larger xenoliths xenoliths may nay have have feldspar feldspar phenocrysts or or porphyroblasts porphyroblasts up to to 1.0 1.0 cm. The phenocrysts The phenocrysts phenocrysts or porphyroblasts porphyroblasts display or display aa seriate senate size size distribution distribution and and comprise comprise up up to to 55 %% of of the the rock. rock. km an an alkalic alkalic biotite biotite At the the centre centre of of the the curve curve at at 19.2 19.2 kin At gabbro is is exposed exposed on on the the north north side side of of the the highway. highway. The The gabbro mediummedium- to to coarse—grained coarse-grained gabbro cut by by gabbroisis extensively extensively cut medium— medium- to to coarse—grained coarse-grained syenite syenite and and some some of of the the nepheline nepheline has has been been altered altered to to reddish reddish orange orange "hydronephelinite". Hhydronepheliniten. There There may be be two two ages ages of of alkalic alkalic gabbro gabbro with the the older older coarser coarser may grained gabbro gabbro displaying displaying dark dark selvages selvages up up to to 77 or or 88 cm cm wide wide grained more and an an irregular irregular shape shape suggesting suggesting that that it it behaved behaved in in aa more and or less less ductile ductile manner. or manner. The The alkalic alkalic gabbros gabbros have have aa clotty dotty mafic mineral mineral assemblage. assemblage. The The surface surface of of the the coarser coarser grained grained mafic biotite gabbro gabbro is is pitted pitted from from the the weathering weathering of of mafic mafic clots. clots. biotite Dikes of of nepheline nepheline syenite syenite pegmatite pegmatite occur occur on on the the north north side side Dikes of the the highway highway at at the the inflection inflection in in the the curve. curve. At At this this site site of two two ages ages of of nepheline nepheline syenite syenitepeginatite pegmatite of of essentially essentially identical identical composition composition cut cut each each other. other. The The trends trends of of these these dikes dikes are are approximately approximately 340 340 dipping dipping 60 60 south south and and 090 090 dipping dipping 50 50 north. north. The The dike dike trending trending 090 090 cuts cuts the the dike dike trending trending 340 340 and both both are are on on the the order order of of 20 20 to to 30 30 cm cm in in width. width. The The dikes dikes and have Puskas (1970). Both dikes have been been sketched sketched by byPuskas(1970). dikes are are zoned zoned from from an an amphibole-rich amphibole-rich margin margin to to aa feldspar— feldsparnatrolite(hydronephe1inite)-rich core. core. The The central central parts parts of of natrolite(hydronephelinite)—nich these these dikes dikes are are commonly commonly relatively relatively rich rich in in reddish reddish orange orange "hydronephelinite". 18hydronepheUniten.West West from from the the two two dikes dikes toward toward the the hackinanite-beaning outcrop, coarse-grained coarse—grained alkalic hackmanite-bearing outcrop, alkalic biotite biotite gabbro gabbro is is intruded intruded by by medium medium to to coarse coarse grained grained pyroxene, pyroxene, amphibole amphibole syenite syenite with with traces traces of of nepheline. nepheline. Both Both of of these these rock rock types types are are in in turn turn cut cut by by coarse—grained coarse-grained nepheline nepheline syenite syenite dikes. dikes. Brecciation Brecciation is is so so intensive intensive that that the the outcrop outcrop is an an igneous igneous breccia. breccia. West West toward toward the the hackmanite—bearing hackmanite-bearing is outcrop outcrop the the syenite syenite is is pink pink to to grey, grey, fine— fine- to to medium— aedium- grained, senate with grained, inequigranular inequigranular seriate with dotty clottyassemblages assemblagesof of mafic mafic minerals. minerals. On On the the south south side side of of the the highway highway coarse-grained coarse-grained alkalic alkalic gabbro gabbro appears appears to to be be cut cut by by medium-grained medium-grained alkalic alkalic gabbro gabbro which which is is in in turn turn intruded intruded by by mottled mottled pink pink to to grey, grey, inequigranular inequigranular senate seriateamphibole amphibolesyenite. syenite. There There is is aa slight slight coarsening coarsening in in texture texture next next to to the the medium—grained medium-grained gabbro gabbro and and aa dike material projects projects from from the the contact contact with with dike of of similar similar material the the medium-grained medium-grained gabbro gabbro through through both both phases phases of of alkalic alkalic gabbro. gabbro. At 24.4 km Stop Stop 21: 21: Hornfelsed Hornfelsed roof roof pendants, pendants, Wolf Wolf Camp Camp Lake Lake �59 This is Tot is stop 7 of Mitchell Mitchell and and Platt(1994). Platt(1994). Hornfelsed Hornfelsed rocks rocks overlying the the Port Port Coidwell Coldwell Complex were recognized recognized early in in overlying the mapping mapping of of the the intrusion intrusionby by Tuoininen(1967) Tuominen(1967) and and the Puskas(1970) and and are are likely likely representative representative of a former former Puskas(1970) volcanic edit edifice(Sage, volcanic ice(Sage, 1986). 1986). Mitchell Mitchell and and Platt(1994) and studied these rocks in in detail and consider Nicol(1990) have studied these basalts to to be contemporaneous contemporaneous with the Port Coldwell these to represent represent a tholeiitic lineage. The basalts Complex and to are fresh, fresh, inetasomatized are and hornfelsed hornfelsed andesine-oligioclase andesine—oligioclase metasomatized and basalt flows flows estimated estimated to to have a thickness thickness of of up up to to 55 m basalt (Nicol, Mitchell and (Nicol, 1990, Mitchell and Platt, Platt, 1994). 1994). At this this stop stop amygdaIoidal amygdaloidal basalt basalt with calc-silicate calc-silicate amygdule amygdule fillings is is well well exposed. exposed. The fillings The ameboid ameboidaniygdules amygdules are are unlike unlike amygdules found found in in Archean Archean metavolcanic metavolcanic rocks rocks of of the the region region amygdules and more more typical typical of of those those found found in in Keweenawan Keweenawan flows. flows. The The and greenish caic-silicate calc-silicate amygdule amygdule fillings fillings are are interpreted interpreted to to greenish represent the the metamorphic metamorphic product product of of former former calcite, calcite, quartz quartz represent etc. fillings fillings of of the the amygdules. amygdules. Exposures Exposures of both massive etc. and amygdular amygdular flows flows may may be be found found on on the the hills hills and and cliffs cliffs and southwest of of Wolf Wolf Camp Camp Lake Lake and for for aa short short distance distance along along southwest Highway 17 17 east east of of this this stop. stop. Hornfelsed Hornfelsed mafic flows flows are are Highway also present present in in the the northern northern part of of the the complex complex also (Tuominen,1967) where they have been observed observed to to overlie overlie (Tuominen,1967) syenitic rocks rocks of of the the Port Port Coldwell Coldwell Complex. Complex. These These flows flows are are syenitic thought to to be be the the remnants remnants of a once once former former volcanic edifice edifice thought that have have been been preserved preserved due due to to ring fracturing fracturing and caldera caldera that subsidence. subsidence. At At 33.9 33.9 km km Turn of offf to Turn to the the town town of Marathon Marathon At 35.6 km Stop 22: 22: Layered Layered gabbro. gabbro. This This is is stop stop 44 of of Mitchell Mitchell and and Stop Platt(1994). Platt(1994). The The gabbros gabbros of of the the eastern eastern contact contact area area are are well well exposed exposed at at this this site site and and considered considered to to represent represent centre centre is part part of of an an outer outer ring ring 11 intrusive intrusive activity. activity. This This gábbro gabbro is that that encompasses encompasses the the eastern eastern and and most most of of the the northern northern parts parts of Coldwell Complex Complex separating separating the the external external Archean Archean of the the Port Port Coldwell rocks rocks from from the the internal internal syenitic syenitic rocks rocks of of the the intrusion. intrusion. These These gabbros gabbros are are reversely reversely magnetized magnetized and and form form prominent prominent lows lows on on aeromagnetic aeromagnetic maps(Lilley, maps(Lilley, 1964). 1964). This This stop stop is is close close to to the the ferrosyenite—gabbro ferrosyenite-gabbro contact contact and and there there is is aa lack lack of of intermediate compositions compositions between between these these two two rock rock types types intermediate implying implying two two distinctly distinctly different different magmas. magmas. Relationships Relationships between between these these two two magma magma types types are are unknown. The ferroaugite ferroaugite syenite syenite is is best best observed observed at at the the western western end end of of the the outcrop outcrop miarolitic cavities cavities up large miarolitic where where pegmatitic pegmatitic phases phases contain contain large to to 22 mm lined lined with with euhedral euhedral feldspar, feldspar, quartz quartz and and amphibole. amphibole. McLaughlin, McLaughlin, (1990) (1990) reports reports the the presence presence of of fluorocarbonates (bastnaesite, parisite, parisite, synchysite) fluorocarbonates(bastnaesite, synchysite) Nb— Nb- �60 futile, Nb—bearing Nb-bearing ilmenite, ilmenite, columbite, columbite, pyrochlore pyrochlore and and rutile, zircon zircon in in these these pegmatites. pegmatites. The best best exposure exposure for for viewing viewing the the layered layered gabbró gabbro is is in in the the The east central central part part of of the the road road cut cut at at the the top top of of the the outcrop. outcrop. east Small Small pegmatitic pegmatitic dikes dikes of of quartz quartz syenite syenite cut cut the the outcrop. outcrop. The The rhythmic rhythmic layering layering is is due due to to variation variation in in the the plagioclase-mafic mineral mineral content content and and individual individual layers layers of of plagioclase—mafic plagioclase-rich plagioclase-rich rock rock are are 0.5 0.5 to to15 15cm cmthick thickand andniafic mafic The banding banding mineral-rich mineral-rich layers layers are are 0.2 0.2 to to 2.0 2.0 cm cm thick. thick. The strikes roughly roughly parallel parallel to to the the road road and and dips dips approximately approximately strikes 45 45 west. Mitchell Mitchell and and Platt(1994) Platt(1994) believe believe this this rhythmicrhythmiclayered layered gabbro gabbro is is aa rafted rafted block. block. The The trend trend of of banding banding in in this this area area is is somewhat somewhat erratic, erratic, dips dips are are consistently consistently west west Outcrops west west of of this this stop stop on on the the north north side side but but variable. variable. Outcrops of of the the highway highway display display aa less less distinct, distinct, wispy, wispy, streaky streaky banding banding due due to to slight slight variations variations in in mafic—felsic mafic-felsic mineral mineral contents. contents. The The reader reader may may wish wish to to refer refer to to Shaw(1994) Shaw(1994) for for aa detailed petrological petrological study study of of the the eastern eastern gabbro. gabbro. detailed At 37.3 km Stop Stop 23: 23: Eastern Eastern gabbro gabbro in in contact contact with with rheomorphic rheomorphic breccia breccia at at the the eastern eastern contact. contact. This This is is aa deeply deeply weathered weathered outcrop outcrop of of suiphide-bearing sulphide-bearing gabbro gabbro at at the the contact contact with with Archean Archean wall wall rocks. rocks. The The gabbro gabbro contains contains abundant abundant xenoliths xenoliths of of the the wall wall rock rock and and very very fine fine grained The gabbro gabbro is is cut cut by by irregular irregular dikes dikes of of grained gabbro. gabbro. The quartz quartz syenite syenite pegmatite. pegmatite. The The rheomorphic rheomorphic breccia breccia is is identical contact(Stop 13) 13) identical to to that that observed observed at at the the western western contact(Stop where where the the exposure exposureis is better. better. The Therheoiuorphic rheomorphic breccia breccia is is characterized characterized by by convoluted convoluted flow flow lines lines and and xenoliths xenoliths in in random random orientation, orientation, some some of of which which appear appear to to have have been been ductile ductile and and partially partially assimilated. assimilated. Some Some xenoliths xenoliths retain retain aa somewhat somewhat angular angular outline outline and and some some display display aa boudinage boudinage structure structure as as they they underwent underwent further further fragmentation. fragmentation. The The contact rocks may may be be observed observed contact between between the the gabbro gabbro and and wall wall rocks but but due due to to its its irregular irregular trend trend its its attitude attitude is is uncertain. uncertain. The The sulphide-bearing sulphide-bearing gabbro gabbro has has been been prospected prospected north north and and south south of of highway highway 17 17 at at this this point. point. The The suiphides sulphides are are principally principally chalcopyrite chalcopyrite and and pyrrhotite. pyrrhotite. Return Return to to the the vehicle vehicle and and return return to to the the intersection intersection of of the the road road to to Marathon Marathon and and Highway Highway 17. 17. From From the the intersection intersection of of the the Marathon Marathon road road with with Highway Highway 17 17 take take the the following followingroute: route: Go f, cross the CPR tracks tracks and and turn turn Go 5.3 5.3 km km from from the theturn turnof off, right right toward toward Lake Lake Superior. Superior. Go km and and pass pass the the hotel hotel on on the the right, right, Moose Moose Lodge Lodge on on Go to to 5.7 5.7 km the the left left and and turn turnright right on on Winston Winston St. St. �61 Go Go to to 6.0 6.0 km km crossing crossing the the CPR CPR tracks tracks and continuing continuing to to the the right. right. Go to to 6.7 6.7 km km where where the the road road splits. splits. Take Take the the left left hand fork fork Go along along the the shore shore of of Lake Lake Superior. Superior. At 7.2 Km small quarry quarry in in Stop 24: 24: Ferroaugite Ferroaugite syenite. syenite. This This is is aa small Stop ferroaugite syenite syenite on on the the shore shore of of Lake Lake Superior Superior where where ferroaugite coarse grained grained equigranular equigranular specimens specimens of of the the syenite syenite may may be be coarse This quarry quarry was was probably probably made made in in the the 1930's 1930's and and collected. collected. This is typical typical of of centre centre 11 ferroaugite ferroaugite syenite syenite referred referred to to as as is laurvikite (1967). Puskas(1967). laurvikiteby byPuskas At 7.8 km Stop Stop 25: 25: Layered Layered ferroaugite ferroaugitesyenite. syenite. Park Park at at the the end end of of the the road road which which is is aa boat boat landing landing and and walk walk north 680 in. north along along the theshore shoreline linefor forapproximately approximately 680 m. There There is is aa partial partial trail trail for for most most of of the the distance. distance. The The broad broad expanses expanses of of ferroaugite ferroaugite syenite syenite exposed exposed along along the the shoreline shoreline display display excellent excellent glacial glacial grooving grooving and and polishing. polishing. Be Be careful careful where where seepage seepage from from the the surrounding surrounding bush bush onto onto the the rocks rocks has has permitted his green green algae algae is is very very permitted green green algae algae to to grow. grow. This slippery. slippery. Also Also be be careful carefulafter afterwalking walkingthrough througha'a sandy sandy area area and then then stepping stepping onto onto outcrop. outcrop. Sand Sand on on the the sole sole of of the the boot boot and may may act act like like ball ball bearings bearings on on the the glacially glacially polished polished outcrop outcrop surface surface and and you you may may slip. slip. At 340 mm along along this this traverse traverse near near the the bushbushAt approximately approximately 340 outcrop outcrop line line of of demarcation demarcation aa fine-grained fine-grained inequigranular inequigranular porphyritic porphyritic senate seriatesyenite syenitedike dike1.5 1.5inm wide, wide cuts cuts the the ferroaugite ferroaugite syenite. syenite. The The dike dike trends trends 150 150 and and has has aa vertical vertical dip. dip. The The dike dike locally locallycontains contains10, 10 to to 15 15 %% feldspar feldspar phenocrysts phenocrysts up up to to 1.0 1.0 cm cm in in long long dimension. dimension. Similar Similardikes dikesin in the the region region have have been been prospected prospected for for their their niobium(pyrochlore) content. zirconium(zircon)content. niobium(pyroch1ore)and andzirconium(zircon) Continue Continue north north to to the the banded banded ferroaugite ferroaugite syenite. syenite. The The banding banding is is wispy, wispy, discontinuous discontinuous and and may may bifurcate. bifurcate. The The general general trend trend is is 070 070 with with aa 60 60 north north dip. dip. The The banding banding is isdue due to Ic mineral content. The to varying varying maf mafic The glacial glacial grooving grooving has has aa general 240 degrees. degrees. This This is is the the second second best best general trend trend of of 240 location location to to study study mafic mafic banding banding in in the the pyroxene pyroxenesyenites. syenites. The The best best site site is is east east of of Marathon Marathon on on the the shore shore of of Lake Lake Superior walk(Stop27). 27). longwalk(Stop Superior and and involves involvesaa long �62 Return to to the the core core shack shack of of Fleck Fleck Resources Resources Ltd. Ltd. Marathon. Marathon. Return building on the the west side side of the the road This is is a blue-grey building This into into Marathon. Marathon. Stop Stop 26: 26: Mr. Mr. J. McGoran, President, President, Fleck Fleck Resources Resources Ltd. Ltd. will place place on on display display drill drill core core from from the the Two Two Duck Duck Lake Lake will Gabbro. The The PGE-rich PGE-rich sulphides sulphides are are cubanite, cubanite, pyrrhotite pyrrhotite and and Gabbro. chalcopyrite interstitial interstitial to to the the rock rock forming forming minerals minerals of of chalcopyrite the gabbro. gabbro. The The pegmatitic pegmatitic phases phases of of the the gabbro gabbro are are the the most the suiphide-rich. sulphide-rich. End End of of formal formal tour. tour. Optional 27: For For the the connoisseur connoisseur of igneous igneous petrology Optional Stop Stop 27: or the better or of of the the geology geology of of the the Port Coldwell Coldwell Complex, the part part of of aa day day should should be be spent spent walking walking along along the the shore shore of of Lake Superior east of Marathon to observe analcite Lake Superior east of Marathon to observe analcite tinguaite tinguaite dikes dikes cutting cutting the the Archean Archean wall wall rocks, rocks, excellent excellent exposures exposures of of banded banded ferroaugite ferroaugite syênite syenite and and fine-grained fine-grained hybrid hybrid gabbro. gabbro. These wave-washed outcrops outcrops are are excellent excellent These glacially glacially polished, polished, wave—washed to reasonably calm calm Lake Lake Superior Superior to study. study. Good Good weather weather and and aa reasonably are are highly highly desirable. desirable. The The trail trail along along this this shore shore line line starts starts at at the the end end of of Howe Howe St. St. in in Marathon Marathon and and these these outcrops outcrops have have itche ell and and Platt(1994) Platt(1994) as as been described described in in some some detail detail by by Mitchell been stop stop 6. 6. Optional Optional Stop Stop 28: 28: For For the the economic economic geologist geologist aa visit visit to to the the Cu-Ni-PGE Cu-Ni-PGE deposits deposits at at Two Two Duck Duck Lake Lake is is advisable. advisable. This This is is private private property property and and requires requires the the permission permission of of Fleck Fleck Resources Resources Ltd. Ltd. to to visit. visit. The The road road to to these these deposits deposits begins begins and the the road road to to opposite opposite the the junction junction of of highway highway 17 17 and Marathon. Marathon. The The distance distance to to the the Cu-Ni-PGE Cu-Ni-PGE deposits deposits is is in in excess 12 km km and and the the road road is is often often impassable impassable even even with with aa excess of of 12 4-wheel 4-wheel drive drive vehicle. vehicle. At At this this site site aa sill-like sill-like gabbro gabbro body body referred referred to to as as the the Two Two Duck Duck Lake Lake Gabbro Gabbro intrudes intrudes earlier earlier eastern eastern gabbros gabbros of of the the centre centre 11 intrusive intrusive centre. centre. This This gabbro gabbro is is medium— medium- to to coarse— coarsegrained grained and and contains contains pegmatitic pegmatitic phases. phases. The The Cu Cu and and PGE PGE enrichment enrichment is is considered considered to to be be of of hydrothermal hydrothermal origin(Watkinson origin(Watkinson and and Ohnenstetter(1992) Ohnenstetter(1992) and and is is represented represented by by platinum—group platinum-group minerals, minerals, chalcopyrite, chalcopyrite, and and cubanite. cubanite. The The Canadian Canadian Mines Mines Handbook(1993-1994, Handbook(1993-1994, p. p. 145) 145) lists lists the the reserves Cut 0.04 0.04 %% Ni, Nit reserves as as 37,000,000 37,000,000 tons tons grading grading 0.31 0.31 %% Cu, 251,000 251,000 oz oz Pt, Pt, 1,001,000 1,001,000 oz oz Pd, Pd, 84,000 84,000 oz oz Au Au and and 43,000 43,000 oz 02 Rh. Rh. One One should should refer refer to to Ohnenstetter Ohnenstetter et et al. al. (1991), (1991), Watkinson Watkinson and and Ohnenstetter(1992), Ohnenstetter(1992), Good Good and and Crocket(1994b) Crocket(1994b) and and Shaw(1994) Shaw(1994) for for details details on on the the mineralization mineralization and and petrology petrology of of eastern eastern gabbro. gabbro. �63 SELECTED SELECTED BIBLIOGRAPHY BIBLIOGRAPHY Adams, D.C. D.C. and and Keller, Keller, G.R., G.R., 1994. 1994. Possible possible extension extension of of Adams, the Midcontinent Midcontinent Rift Rift in in west west Texas Texas and and eastern eastern New New Mexico; ~exico; the Canadian Canadian Journal Journal of of Earth Earth Sciences, sciences, v. v. 31, 31, P. p. 709-720. 709-720. Allen, Allen, D.J.; D.J.; Hinze, Hinze, W.J. W.J. and and Cannon, Cannon, W.F., W.F., 1992. 1992. Drainage, Drainage, Topographic and and Gravity Gravity anomalies anomalies in in the the Lake Lake Superior Superior Topographic Region: 1100 Ma Ma Mantle Mantle Plume; Plume; Geophysical Geophysical Region: Evidence Evidence for for aa 1100 Research Research Letters, Letters, v. v. 19, 19, n. n. 21, 21, p. p. 2119—2122 2119-2122 Aubut, A., 1977. 1977. The The geology geology of of the the southwest southwest margin margin of of the the Aubut, A., Coldwell Coldwell complex; complex; unpublished unpublished B.Sc. B.Sc. Thesis, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, Ontario Ontario Balint, F., 1977. 1977. The The Neys Neys diatreme, diatreme, Coidwell Coldwell alkaline alkaline Balint, F., complex, complex, northwestern northwestern Ontario; Ontario; unpublished unpublished B.Sc. B.Sc. Thesis, Thesis, Lakehead Lakehead University, University, Thunder Bay, Ontario, hip. lllp. Bathe, Killala Bathe, D., D., 1977. 1977. The The Geology Geology and and Petrogenesis Petrogenesis of of the the Killala Lake Lake Alkalic Alkalic complex; complex; unpublished unpublished B. B. Sc. Sc. thesis, thesis, Carleton Carleton University, University, 74p. 74p. Behrendt, Behrendt, J.C.; J.C.; Hutchinson, Hutchinson, D.R.; D.R.; Lee, Lee, N.; M.; Thoruber, Thoruber, C.R.; C.R.; Tre'hu, W. and and Green, Green, A., A., 1990. 1990. GLIMPCE GLIMPCE seismic seismic Tre8hu, A.; A.; Cannon, Cannon, W. reflection reflection evidence evidence of of deep—crustal deep-crustal and and upper upper mantle mantle intrusives intrusives and and magmatic magmatic underplating underplating associated associated with with the the Midcontinent Tectonophysics, Midcontinent Rift Rift System System of of North North America; America; Tectonophysics, v. v. 173, 173, p.595—615. p.595-615. Behrendt, Behrendt, J.C.; J.C.; Green, Green, A.G.; A.G.; Cannon, Cannon, W.F.; W.F.; Hutchinson, Hutchinson, D.R.; D.R.; Lee, Lee, M.W.; M.W.; Milkereit, Milkereit, B.; B.; Agena, Agena, W.F. W.F. and and Spencer, Spencer, C., C., 1988. 1988. Crustal Crustal Structure Structure of of the the Midcontinent Midcontinent Rift Rift System: System: Results Results from from GLIMPCE GLIMPCE deep deep seismic seismic reflection reflection profiles; profiles; Geology, Geology, v. v. 16, 16, P. p. 81—85. 81-85. all, . and e l l , K. and Blenkinsop, Blenkinsop, J. J. 1980. 1980. Grant Grant 42, 42, Ages Ages and and Initial Initial oIsr_805r Ratios p. 16—23 16-23 ~r-^~r Ratios from from Alkalic Alkalic Complexes Complexes of of Ontario; Ontario; p. in Geoscience Geoscience Branch Branch Grant Grant Program, Program, Summary Summary of of Research, Research, in 1974—1980, 1974-1980, Ontario Ontario Geological Geological Survey Survey Miscellaneous Miscellaneous Paper Paper 93, 93, 262p. 262p. Blenkinsop, Blenkinsop, J. J. and and Bell, Bell, K. K. 1983. 1983. Rb-Sr Rb-Sr geochronology geochronology of of the the Coldwell Coldwell complex, complex, northwestern northwestern Ontario, Ontario, Canada: Canada: Discussion; Discussion; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 20, 20, p. p. 1499—1500. 1499-1500. Bruminer, J., 1978. 1978. Diamonds Diamonds in Canada, Brununer, J., Canada, Canadian Canadian Institute Institute of of Mining Mining and and Metallurgy Metallurgy Bulletin, Bulletin, v. v. 71, 71, p. p. 64—79 64-79 Burke, K. and and Dewey, Dewey, J.F., J.F., 1973. 1973. Plume-generated Plume-generated triple triple Burke, K. junctions: junctions: Key Key indicators indicators in in applying applying plate plate tectonics tectonics to to old old rocks; rocks; Journal Journal of of Geology, Geology, v. v. 81, 81, p. p. 406—433. 406-433. �64 Bursnall, J.T.; J.T.; Leclair, eclair, A.D.; A.D.; Moser, Moser, D.E. 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The North American Midcontinent Rift Beneath Lake superior from from GLIMPCE GLIMPCE seismic seismic Reflection Reflection Profiling; Profiling; Superior ~ectonics, v. 8,8,n.n.2, p. 305—332. 305-332. Tectonics, v. .2, p. - Cannon, W.F., W.F., 1994. 1994. Closing Closing of of the the Midcontinent idc continent Rift Rift — AA Cannon, far-field effect effect of of the the Grenville Grenville compression. compression. Geology, Geology, v. v. far—field 22, p. p. 155—158. 155-158. 22, Chandler, V.C., V.C., 1983. 1983. Correlation Correlation of of magnetic magnetic anomalies anomalies in in Chandler, east-central Minnesota and northwestern Wisconsin: east—central Minnesota and northwestern Wisconsin: Constraints on on magnitude magnitude and and direction direction of of Keweenawan Keweenawan Constraints rifting; Geology, V. 11, p. 174-176. rifting; Geology, V. 11, p. 174—176. Clark, J.G., J.G., 1983.Geology 1983. 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Field Field Guide Guide to to aspects aspects Mitchell, R.H. of of the the geology geology of the the Coidwell Coldwell alkaline alkaline complex; complex; Field Field guide guide prepared for for the the 23rd. 23rd. Annual Annual meeting meeting of of the the Institute Institute on on prepared Lake 34p. Lake Superior Superior Geology, Geology8 34p. R.H. and Platt, Platt8 R.G., R.G., 1978. 1978. Mafic mineralogy mineralogy of of Mitchell, R.H. ferroaugite syenite syenite from from the the Coidwell Coldwell alkaline alkaline complex, complex8 ferroaugite 0ntario8 Canada; Canada; Journal Journal of of Petrology, Petrology, v. v. 19., 19*, p. p. 627-651. 627-651. Ontario, Mitchell, Mitchell, R.H. R.H. and Platt, Platt, G.R., G * R O 81979. 1979. 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Franklin F'ranklin editor; editor; Geological ~eologicalAssociation of CanadaCanadaMineralogical Mineralogical Association Association of of Canada. Canada* Mitchell, Mitchell, R.H.; R.H.; Platt, Platt, G.R G.R and and Cheadle, Cheadle, S.P., S.PO8 1983. 1983. AA gravity Coldwell complex, complex8 northwestern northwestern Ontario Ontario gravity study study of the the Coidwell and and its its petrological petrological significance; significance; Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 20, 20, p. p. 1631—1638. 1631-1638. Mitchell, R.H.; Laflamme, Laflame, J.H. J.H. and and Cabri, Cabri, L.J., L.Je8 1989. 1989. Mitchell8 R.H.; Rhenium Rhenium suiphide sulphide from from the the Coidwell Coldwell alkaline alkaline complex, complex, northwestern northwestern Ontario, Ontario8 Canada; Canada; Mineralogical Mineralogical Magazine, Magazine, v. v. 53, 53, p. 635—637. 635-637. p. 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Vein Vein Lake; Lake; Ontario Ontario Department Department of of Mines Mines Geological Geological Survey Survey of of Canada, Canadaf Aeromagnetic Aeromagnetic Map Xap 2158G, 2158Gt Scale Scale 11 inch inch to to 11 mile(l:63,360). mile(l:63f360). Ohnenstetterf D.; D.; Watkinson, Watkinsonf D.H. D.H. and and Dahi, Dahlf R., R o t1991. 1991. Zoned Zoned Ohnenstetter, from the the Two Two Duck Duck Lake Lake intrusion, intrusionf Coidwell Coldwell hollingsworthite from hollingsworthite complex, complexf Ontario; Ontario; American American Mineralogist, Mineralogistf v. v o 76, 76# p. p. 169416941700. 1700. �70 Paces, Pacesl J.B. J.B. and and Miller, Millerl Jr., J r e 1J.D., J.Def 1993. 1993. Precise Precise U—Pb U-Pb Ages Ages of Ic Intrusionsf Intrusions, Northern of Duluth Duluth Complex Complex and and Related Related Maf Mafic Northern Minnesota: Geochronological Geochronological Insights Insights to to Physical, Physicall Minnesota: Petrogeneticl Paleomagnetic Paleomagnetic and and Tectonomagmatic Tectonomagmatic Processes Processes Petrogenetic, Associated Midcontinent Rift Rift System; System; Journal Journal Associated with with the the 1.1 1.1 Ga Ga Midcontinent of of Geophysical Geophysical Research Research Letters, Lettersl v. v. 98, n.B8, n.Bgf p. p. 13,997— 13199714,013. 141013. Paces, Pacesl J.B. J.B. and and Davis, Davisl D.W., D e w a l1988. 1988. Implications Implications of of high high precession precession U-Pb U-Pb age age dates dates on on zircons zircons from from Portage Portage Lake Lake volcanic volcanic basalts basalts on on Midcontinent Midcontinent Rift Rift subsidence subsidence rates; rates; lava lava flow flow repose repose periods periods and and magma magma production production rates; rates; p. p. 85—86, 85-861 .jfl Program with with Abstracts Abstracts 34th 34th Annual Annual Meeting Meeting of of the the Institute Institute Program on on Lake Lake Superior Superior Geology. Geology. Palmerf H.C. H.C. and and Davis, Davisf D.W., D.W.# 1987. 1987. Paleomagnetism ~aleomagnetismand and U-Pb U-Pb Palmer, Geochronology of of volcanic volcanic rocks rocks from from Michipicoten Michipicoten Island, Islandf Geochronology Lake Superior, Superiorf Canada: Canada: Precise Precise calibration calibration of of the the Keweenawan Keweenawan Lake Polar Wander Wander Track; Track; Precambrian ~recambrianResearch, Researchl v. v. 37., 37.1 p. p. 151— 151Polar 171. 171. Percival, Percivalf J.A. J.A. and and West, Westf G.F., G.Fef 1994. 1994. The The Kapuskasing Kapuskasing Uplift: Uplift: aa geological geological and and geophysical geophysical synthesis; synthesis; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciencesl v. v. 31, 311p. p. 1256—1286. 1256-1286. Percival, Percivall J.A., J.A.! 1990. 1990. AA field field guide guide to to the the Kapuskasing Kapuskasing Uplift, cross section section through through the the Archean Archean Superior Superior Upliftl aa cross Province; Province; P. P. 227-283, 227-2831.jn Exposed Cross-sections Cross-sections of of the the Continental Continental Crust; Crust; M.H. M.H. Salisbury Salisbury and and D.M. D.M. Fountain Fountain editors; editors; Kiuwer Kluwer Academic Academic Publishers, PublisherslNetherlands. Netherlands. Percival, Percivall J.A. J.A. and and Card, Cardl K.D., K.DeI 1983. 1983. Archean Archean Crust Crust as as revealed revealed in in the the Kapuskasing Kapuskasing Uplift, Upliftl Superior Superior Province, Provincef Canada; Canada; Geology, Geologyl v. v. 11, llfp. p. 323—326. 323-326. Platt, Plattl G.R. G.R. and and Mitchell, Mitchellf R.H., R.H.# 1979. 1979. The The Marathon Marathon Dikes. Dikes. I: I: Zirconium-rich Zirconium-rich titanium titanium garnets garnets and and manganoan manganoan magnesium magnesium ulvospinel—inagnetite ulvospinel-magnetite spinels; spinels; American American Mineralogist, Mineralogistl v. v. 64, 64# p. p. 546—550. 546-550. Platt, Plattl G.R. G.R. and and Mitchell, Mitchelll R.H., R.H.# 1982a. 1982a. The The Marathon Marathon Dikes: Dikes: ultrabasic ultrabasic lamprophyres lamprophyres from from the the vicinity vicinity of of McKellar McKellar Harbour, Harbourl NW. N.W. Ontario; Ontario;American AmericanMineralogist, Mineralogistfv. v. 67., 67.# p. p. 907—916. 907-916. PLatt, PLattl G.R. G.R. and and Mitchell, Mitchell! R.H., R.Hef1982b. 1982b. Rb-Sr Rb-Sr geochronology geochronology of of the the Coidwell Coldwell complex, complexl northwestern northwestern Ontario, Ontariof Canada; Canada; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciencesf v. v. 19, 1glp. p. 1796—1801. 1796-1801. Platt, PlattlG.R.; G.R.; Mitchell, MitchellfR.H. R.H. and andHolin, Holml P.M., P.Me1 1983. 1983. Marathon Marathon dikes: Rb-Sr and and K-Ar K-Ar geochemistry geochemistry of of ultrabasic ultrabasic dikes: Rb-Sr lamprophyres lamprophyresfrom from the the vicinity vicinity of of McKellar McKellarHarbour, Harbourl northwest Journal of of Earth Earth Sciences, Scienceslv. v. northwest Ontario; Ontario; Canadian Canadian Journal 20, 201p. p. 961—967. 961-967. �71 Platt, G.R. and Mitchell, R.H., 1984. Rb-Sr geochronology of the coldwell complex, northwestern Ontario, Canada: Reply: Canadian Journal of Earth Sciences, v. 21, p. 126. j Puskas, F.W., 1970. The Port Coidwell Alkali Complex; p. 87100, Proceedings for the 16th Annual Meeting of the Institute on Lake Superior Geology. Puskas, F.P., 1967. Geology of the Port Coldwell Area, Ontario Department of Mines Open File Report 5014, 94p. Sage, R.P., 1978. Diatremes and Shock Features in Precambrian Rocks of the Slate Islands, Northeastern Lake Superior; Geological Society of America Bulletin, v. 89., p. 1529—1540. Sage, R.P. 1982. Mineralization in Diatreme Structures North of Lake Superior; Ontario Geological Survey study 27, 79p. Sage, R.P. 1985. Geology of Carbonatite — Alkalic Rock Complexes in Ontario: Chipman Lake Area, Ontario Geological Survey Study 44 40p. Sage, R.P. 1987. Geology of Carbonatite - Alkalic Rock Complexes in Ontario: Prairie Lake Carbonatite Complex, district of Thunder Bay; Ontario Geological Survey Study 46, 91p. Sage, R.P., 1986. Alkalic Rock Complexes—Carbonatites of Northern Ontario and their Economic Potential; unpublished Phd. Thesis, Carleton University, Ottawa, Ontario, 335p. Sage, R.P. 1988. Geology of Carbonatite - Alkalic rock Complexes in Ontario: Killala Lake Alkalic Rock Complex, Ontario Geological Survey Study 45 l2Op. Sage, R.P., 1991. Precambrian Geology, Slate Islands; Ontario Geological Survey Report 264, hip. Sage, R.P., 1994. Geology of the Michipicoten Greenstone Belt; Ontario Geological Survey Open File Report 5888, 592p. Sage, R.P. and Watkinson, D.H., 1991. Alkalic rock— carbonatite complexes of the Superior Structural Province northern Ontario, Canada; Chronique de la Recherche Miniere N. 504, p. 5—19. Samson, C. and West, G.F., 1994. Detailed basin structure and tectonic evolution of the Midcontinent Rift System in eastern Lake Superior from reprocessing of GLIMPCE deep reflection seismic data; Canadian Journal of Earth Sciences, v. 31, p. 629—639 �72 Sexton, J.L. J.L. and and Henson, Jr., Jr., H., 1994. 1994. Interpretation Interpretation of Sexton, seismic reflection reflection and and gravity gravity profile profile data data in in western western Lake Lake seismic superior; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 31, 31, p. p. 652— 652Superior; 660. 660. Shaw, Shaw, C.S.J., C.S.J., 1994. 1994. Petrogenesis Petrogenesis of of the the Eastern Eastern Gabbro, Gabbro, Coldwell Alkaline Alkaline Complex, Complex, Ontario; Ontario; unpublished unpublished Phd. Phd. Thesis, Thesis, Coldwell University university of of Western Western Ontario, Ontario, London, London, Ontario, Ontario, 292p. 292p. Shay, Shay, 3. J. and and Tre'hu, Trefhu, A., A., 1993. 1993. Crustal Crustal Structure Structure of of the the central central graben graben of of the the Midcontinent Midcontinent Rift Rift beneath beneath Lake Lake Superior; Superior; Tectonophysics, Tectonophysics, v. v. 225, 225, p. p. 301-335. 301-335. Smyk, Smyk, M.C.; M.C.; Taylor, Taylor, R.P.; R.P.; Jones, Jones, P.C. P.C. and and Kingston Kingston D.M. D.M. Geology and and Geochemistry Geochemistry of of the the West West Dead Dead Horse Horse creek creek 1993. 1993. Geology Rare—Metal Occurrence, Northwestern Ontario; Exploration Rare-Metal Occurrence, Northwestern Ontario; Exploration Mining Mining Geology, Geology,•v. v. 2, 2, n. n. 3, 3, p. p. 245—251. 245-251. - Sutcliffe, Sutcliffe, R.H., R.H., 1991. 1991. Proterozoic Proterozoic Geology Geology of of the the Lake Lake superior Area; p. 627-658, in Geology of ~ntario, Ontario Superior Area; p. 627-658, jn Geology of Ontario, Ontario Geological Geological Survey Survey Special special Volume Volume 4, 4, pt. pt. 1, 1, 709p. 709p. Thorpe, Thorpe, R.I., R.I., 1986. 1986. U-Pb U-Pb geochronology geochronology of of the the Coldwell Coldwell complex, complex, northwestern northwestern Ontario, Ontario, Canada: Canada: Discussion; Discussion; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 23, 23, p. p. 125-127. 125-127. Thomas, Thomas, M.D. M.D. and and Teskey, Teskey, D.J., D.J., 1994. 1994. An An interpretation interpretationof of gravity gravity anomalies anomalies over over the the Midcontinent Midcontinent Rift, Rift, Lake Lake superior, superior, constrained constrained by by GLIMPCE GLIMPCE seismic seismic and and aeromagnetic aeromagnetic data; data; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 31., 31., p. p. 682—697. 682-697. Tre'hu, Z.; Trethu,A., A., Morel—a—Huissier, or el-a-Huissier, P.; P.; Meyer,R.; Meyer,R.; Hajnal, ~ajnal, 2.; Karl, Karl, J.; J.; Mereu, Mereu, R.; R.; Sexton, Sexton, 3.; J.; Shay, Shay, J; J.; Chan, Chan,X.-R.; X.-R.; Wendling, wendling, S.; S.; Milkereit, ilke ere it, B.; B.; Green, Green, A. A. and and Hutchinson, Hutchinson, D. D. 1991. Imaging the the Midcontinent Midcontinent Rift Rift beneath beneath Lake Lake Superior Superior 1991. Imaging using using large large aperture aperture seismic seismic data; data; Geophysical Geophysical Research Research Letters, Letters, v. v. 18, 18, n.4, n.4, p. p. 625—628. 625-628. Tuominen, Coldwell Area, Area, Ontario Ontario Department Department Tuominen, H.V., H.V., 1967. 1967. Port Port Coldwell of of Mines Mines map map P114, P114, Scale Scale 11 inch inch to to1/4 114 mile(1:15,840). mile(l:15,840). Turek, Turek, A.; A. ;Smith, Smith,P.E. P. E. and andSynions, Symons, D.T.A., D.T.A., 1985. 1985. U-Pb U-Pb geochronology geochronology of of the the Coidwell Coldwell complex, complex, northwestern northwestern Ontario, Ontario, Canada; Canada; Canadian ~anadianJournal Journal of of Earth Earth Sciences, Sciences, v. v. 22, 22, n. n. 4, 4, p. p. 621—626. 621-626. Turek, D.T.A, 1986. Smith, P.E. P.E. and Symons, D.T.A., 1986. U-Pb U-Pb Turek, A.; A. ; Smith, geochronology northwestern Ontario, Ontario, geochronology of of the the Coldwell Coldwell complex, complex, northwestern Canada: Canada: Reply; Reply; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 23, 23, p. p. 127—128. 127-128. Van Martin, M.W.; M.W.; Sprowl, Sprowl,D.R.; D.R.; Geissman, Geissman,J. J. Van Schumus, Schumus,W.R.; W.R.; Martin, and and Pb Pbisotopic isotopic composition composition and Berendsen, Berendsen, P., P., 1990. 1990. Age, Age, Nd Nd and �73 and magnetic Midcontinent Midcontinent Program Program with with polarity polarity for for subsurface subsurface samples samples of of the the 1100 1100 Ma Ma Rift; p.Al74, Geological Society Society of of America Rift; p.A174, Geological Abstracts, Abstracts, v. v. 22. 22. Walkert E.C.; E.C.; Sutcliffe, Sutcliffe, R.H.; R.H.; Shaw, Shaw, C.S.J.; C.S.J.; Shore; Shore; G.T. G.T. and and Walker, P e n m a k t R.S., R.S.t 1993a. 1993a. Precambrian Precambrian geology, geology, Port Port Coidwell Coldwell Penczak, Complex, east east half; half; Ontario Ontario Geological Geological Survey Survey Preliminary Preliminary Complex, Map P3233, P3233# scale scale 1:20,000. 1:2Ot0O0. Walker, E.C.; E.C.; Sutcliffe, Sutcliffet R.H.; R.H.; Shaw, Shawl C.S.J.; C.S.J.; Shore, Shoret G.T. G.T. and and Walker, Penczakt R.S., R.S.t 1993b. 1993b. Precambrian Precambrian geology, geology, Port Port Coldwell Coldwell Penczak, Complext west west half; half; Ontario Ontario Geological Geological survey, surveyt Preliminary Preliminary Complex, Map Map P3232, P3232, scale scale 1:20,000. 1:20,000. Walkert E.C.; E.C.; Sutcliffe, ~ u t c l i f f eR.H.; R.H.; ~ Shawl C.S.J.; C.S.J.; Shore, Shoret G.T.; G.T.; Walker, Shaw, Penczak, R.S., R e S o l1993c. 1993c. Precambrian Precambrian geology geology of of the the and Penczak, Coldwell Alkalic ~ l k a l i ccomplex; complex; Ontario Ontario Geological Geological Survey, Survey, Open Open Coidwell File 30p. File Report Report 5868, 5868, 30p. Walker, J.W.R. J.W.R. 1967. 1967. Geology Geology of of the the Jackfish Jackfish Middleton Middleton Area; Area; Walker, Ontario Ontario Department Department of of Mines, Minest Geological Geological Report Report 50, 50, 41p. 41p. Wanless, Wanlesst P. P. 1976. 1976. Petrology Petrology and and Geochemistry Geochemistry of of the the Killala Killala Lake Alkali Alkali Complex; Complex; unpublished unpublished B. B. Sc. Sc. thesis, thesist Queen's Queents University, University, Kingston, Kingston, 66p. 66p. Watkinsont D. D. H. H. 1971. 1971. Petrology Petrology and and U-Nb U-Nb mineralization mineralization of of Watkinson, the the Alkalic Alkalic Rock-Carbonatite Rock-Carbonatite Complex Complex at at Prairie Prairie Lake, Laket Ontario; Ontario; (abstract) (abstract) Canadian Canadian Mineralogist, Mineralogist, v. v. 10, lotpt. pt. 5, 5, p.921. p.921. Watkinson, Watkinsont D.H. D.H. 1973. 1973. Pseudoleucite Pseudoleucite from from Plutonic Plutonic Alkalic Alkalic Rock-Carbonatite Rock-Carbonatite Complexes; Complexes; Canadian Canadian Mineralogist, Mineralogisttv. v. 12, 12,p. p. 129—134. 129-134. Watkinson, Watkinsont D.H. D.H. 1976. 1976. Geology Geology of of the the Uranium—Niobium Uranium-Niobium Mineralization Rock-Carbonatite Complex, Complext Mineralization of of the the Alkalic Alkalic Rock-Carbonatite Prairie Prairie Lake, Laket Ontario; Ontario; unpublished unpublished report. report. Watkinson, Watkinson, D.H. D.H. and and Ohnenstetter, Ohnenstettert D., D.! 1992. 1992. Hydrothermal Hydrothermal origin origin of of platinum group group mineralization mineralization in in the the Two Two Duck Duck Lake Lake intrusion, intrusiont Coldwell Coldwell complex, complex, northwestern northwestern Ontario; Ontario; Canadian Canadian Mineralogist, Mineralogistt v. v. 30, 30t P. p. 121—136. 121-136. Whittaker, Whittaker, P.J., P.J., 1976. 1976. Geology Geology of of the the East East Central Central Port Port Coidwell Coldwell Complex Complex from from the the Pic Pic River River to to Red Red Sucker Sucker Cove; Cove; unpublished unpublished M.Sc. M.Sc. Thesis, Thesist MacMaster MacMaster University, University, Hamilton, Hamilton, Ontario. Ontario. Wilkinson, Wilkinson, S.J., S.Jet 1983. 1983. Geology Geology and and sulphide sulphide mineralization mineralization of the the marginal marginal phases phases of of the the Coidwell Coldwell complex, complext northwestern northwestern Ontario; Ontario; unpublished unpublished M.Sc. M.Sc. Thesis, ThesistCarleton, Carleton, University, Universityt Ottawa, Ottawat 129p. 129p. with with appendix appendix �74 Williams, WilliamsI H.R. H.R* 1989. 1989. Geological Geological studies studies in in the the Wabigoon, WabigoonI Quetico Quetico and and Abitibi—Wawa Abitibi-Wawa subprovinces, subprovincesI Superior Superior Province Province of of Ontario, Ontario, with with emphases emphases on on the the structural structural development development of of the the Bearbore-Geraldton Belt; Belt; Ontario Ontario Geological Geological Survey, SurveyI Open Open Beardmore-Geraldton File File Report Report 5724, 5724, 189p. 189p. Wold, WoldI R.J.; R o s e ;Hutchinson, HutchinsonI D.R. D - R . and and Johnson, Johnson, T.C., T . C * , 1982. 1982. Topography icial structure structure of Lake Superior Topography and and surf surficial Superior bedrock bedrock as as based on on seismic seismic reflection reflection profiles; profiles; p. p. 257-272, 257-272, ft Geological Geological Society Society of of America America Memoir Memoir 156 156 �75 �NOTES NOTES �NOTES NOTES � https://digitalcollections.lakeheadu.ca/files/original/157c2078900a8fba2519d21214d63003.pdf d696c36d2d38bf5d60590b38819e07da PDF Text Text Geology, Structure Sfructure and Age Relationships of Manitou wadge Greenstone Greenstone Belt and the the Manitouwadge Wawa-Quetico Subprovince Boundary, Boundary, Wawa-Quetico North western Ontario Ontario North Institute Instituteon onLake LakeSuperior SuperiorGeOlogy Geology 41st 1995 41st Annual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon, Ontario Ontario Proceedings ProceedingsVolume Volume 41: Part Part2b 2b Field Field Trip TripGuidebook Guidebook 41$t JJSG —7' I 'P �Geology, structure structure and age relationships Geology, relationships of the Manitouwadge greenstone belt and the the Wawa-Quetico Wawa-Quetico subprovince boundary, northwestern northwestern Ontariol Ontario1 Field guidebook guidebook by by Peterson3, H. Lockwood4 E. Zaleski2, Zaleski2, V.L. Peterson3, Lockwood^ and 0. 0.van vanBreernen2 Breemen2 1Geological Survey of of Canada Canada Contribution Geological Survey Contribution 13995 13995 Project funded funded by by the the Canada-Ontario Canada-OntarioSubsidiary Subsidiary Agreement Agreement on Northern Ontario OntarioDevelopment Development (1991-1995), (1991-1995), Canada-Ontario Canada-OntarioEconomic Economic and and Regional Region al Development Development Agreement 2Continental Survey ooff Canada, Canada, Continental Geoscience Geoscience Division, Geological Survey 601 Booth Booth Street, Ottawa, K I A 0E8 OE8 Ottawa, Ontario, Ontario,K1A 3Department Departmen t of o fGeosciences Geosciences and Anthropology, Western Carolina Carolina University, University, Cullowhee, North Carolina, Carolina,28723, 28723, U.S.A. U.S.A. 4Hemlo ^Hemlo Gold Mines, P.O. Box Box 40, 40, Marathon, Ontario, Ontario,POT POT 2E0 2E0 Marathon, (formerly of o f Geco Mining Division, Noranda Minerals Inc.) (formerly Sillimanite knots in in metamorphosed metamorphosed altered altered felsic felsic rocks near Willroy mine (left). Folded and and Frontispiece: Sillimanite near the Willroy (left). Folded brecciated right). Mafic Mafic to tointermediate in termediatemetavolcanic metavolcanic inclusions in tonalite tonalite along along the the brecciated iron formation formation (upper right). folded at ten tuated extensions extensions of o f the theManitouwadge Manitouwadge greenstone belt (lower (lower right). folded attentuated �TABLE OF OF CONTENTS CONTENTS INTRODUCTION INTRODUCTION 11 Methodology ........................................................................................ Methodology REGIONAL REGIONAL SETTING SETTING -22 Relationships in in the theWawa Wawasubprovince subprovince Relationships 33 Structural and and tectonic tectonic setting setting ....................................................................... Structural Metamorphism .....................................................................................-44 Geochronological constraints constraints ........................................................................ -44 Geochronological HISTORICAL BACKGROUND BACKGROUND OF OF THE THEMANITOUWADGE MANITOUWADGEBELT BELT HISTORICAL - 55 History of deposits ................................................................................. 66 interpretations ............................................................... Previous mapping and interpretations 66 Historical nomenclature, the the 'Mine 'Mine Series' Series' ........................................................... DESCRIPTION OF OFUNITS UNITS DESCRIPTION rock units units .............................................................................-77 Supracrustal rock 77 3) ............................................................... Mafic metavolcanic rocks (Unit 3) 99 Mixed mafic-felsic mafic-felsic metavolcanic rocks (Unit 4) 4) ................................................... 99 Intermediate to tomafic maficmetavolcanic metavolcanic rocks (Unit 5) 5) ............................................... Intermediate 10 Felsic to intermediate intermediate metavolcanic metavolcanic rocks rocks (Unit (Unit 6) 6) ..............................................10 11 7) ......................................................11 Aphyric felsic metavolcanic rocks (Unit 7) 11 11 felsic metavolcanic rocks (Unit 8) 8) ................................................ Quartz-phyric felsic 12 12 (Unit 9) 9) ........................................................ Metamorphosed iron formation (Unit rocks (Unit (Unit 10) 10) ..............................................................13 13 Metasedimentary rocks 13 Tectonic rock units ................................................................................. 13 13 Straight gneiss gneiss (Unit (Unit 11) 11) ....................................................................... 13 Straight 13 rock units units ................................................................. 13 Metasomatically altered rock 13 Orthoamphibole-garnetkordierite gneiss gneiss (Unit (Unit 2) 2) .............................................. 13 Orthoamphibole-garnet±cordierite Sillimanite-muscovite-quartz Sillimanite-muscovite-quartzand sillimanite-knot sillimanite-knot felsic felsic schist (Unit (Unit 1) 1) ..........................14 14 15 Synvolcanic Synvolcanic intrusions intrusions .............................................................................. 15 (Unit 12) 12) ........................................15 15 Foliated trondhjemite-hornblende granodiorite (Unit 15 Syn- to post-tectonic intrusions intrusions ..................................................................... 15 15 granitoid (Unit (Unit13) 13) ............................................. 15 Foliated K-feldspar porphyritic granitoid Undivided foliated intrusive rocks rocks (Unit (Unit 14) 14) .................................................... 16 16 Pegmatite, aplite aplite and and foliated foliated granite granite (Unit (Unit 15) 15) ................................................16 16 17 Alkalic Alkalic rocks (Unit (Unit 16) 16) ......................................................................... 17 17 Quetico Quetico subprovince subprovince ................................................................................ 17 17 Metasedimentary rocks rocks (Unit (Unit lOq) lOq) 17 Proterozoic Proterozoic intrusions intrusions ..............................................................................18 18 dykes .................................................................................18 18 Diabase dykes STRUCTURAL GEOLOGY D1 Dl deformation deformation ....................................................................................18 18 D2 deformation ....................................................................................19 19 Da deformation deformation ....................................................................................24 24 D3 D4 D4 deformation deformation ....................................................................................25 25 Late faults faults .........................................................................................26 26 Late GEOCHRONOLOGY Zircon—Metavolcanic and metasedimentary metasedimentary rocks Zircon-Metavolcanic and rocks ....................................................26 26 Zircon and rocks and and brackets on deformation and monazite—Intrusive monazite-Intrusive rocks deformation ...................................28 28 31 Titanite ............................................................................................ 31 Titanite SETTING OF OFMINERALIZATION MINERALIZATION SETTING Relationships Relationships of orebodies and host host rocks rocks ...........................................................32 32 Structural Structural complications—DuD2 complications-Di/D2 folds folds and faults faults ...................................................33 33 GEOCHEMISTRY GEOCHEMISTRY 34 Metavolcanic and and subvolcanic subvolcanic rocks rocks ................................................................. 34 rocks ....................................................................................... 38 Altered rocks 38 DISCUSSION DISCUSSION setting and and deformation deformation of of massive massive sulphide sulphide deposits deposits and and alteration alterationzones zones ..............41 41 Depositional setting ............................................................. ............................................................. 11 �Structuraland andtectonic tectonicsynthesis synthesis ................................................................... 4242 Structural REFERENCES ......................................................................................... 4444 REFERENCES FIELD-TRIPSTOPS STOPS FIELD-TRIP ............................................................................................ Introduction 49 Introduction Knowneconomic economicdeposits, deposits.inner innervolcanic volcanicbelt belt .......................................................49 -49 A .Known A. A1-A8 . Willroy-Geco Willroy-Gecoarea area .........................................................................4949 A1—A8. SlimLake Lakesection section ......................................................................... 5555 A9-A20 . Slim A9—A20. A21.Nama NamaCreek Creekdeposit deposit ..........................................................................5656 A21. metavolcaniccontact contact ....................................57 57 A22-A23 . Da A22—A23. D2 folds folds of of iron formation/felsic formation/felsic metavolcanic and inner inner hinge hingeof ofthe theManitouwadge Manitouwadgesynform synform .............................59 59 A24-A26 . Willecho A24—A26. Willecho 33 pit pit and B.Outer Outervolcanic volcanicbelt belt ................................................................................. -606 0 B. B l Northern . Northerncontact contactzone zone .........................................................................6060 Bi. B2-B10 . Gaug area, comparison comparisonto toinner innervolcanic volcanicbelt belt .........................................61 61 B2—B10. Gang Lake area, B11-B21 . Hinge Manitouwadgesynform synformnear nearSwill SwillLake Lake ...............................64 64 Bi 1—B2 1. Hingeregion region of of the the Manitouwadge C .Inner InnerManitouwadge Manitouwadgesynform, synform,Dead DeadLake Lakesuite suite .......................................................67 67 C. D .Eastern Easternextension extensionofofthe the'Geco 'Gecohorizon' horizon' .............................................................. 70 70 D. Dl-D2 . Eastern inner inner volcanic volcanic belt, belt. 'Geco 'Gecohorizon' horizon' .................................................70 70 D1—D2. 70 D3-D4 . Orthoamphibole-cordierite-garnet rocks, rocks, Banana Banana area area ....................................... D3—D4. 70 E .Quetico Queticosubprovince, subprovince.Jim JimLake Lakesynform synform .............................................................. 72 72 E. El-E3 . Quetico subprovince, subprovince. eastern eastern Manitouwadge Manitouwadgearea area ........................................... 73 73 E1—E3. E4-E6 . Jim Lake Lake synform, synform. Jim/Davis JimIDavisLakes Lakesarea area ................................................... 7373 E4—E6. BlackPic Picbatholith, batholith.supracrustal supracrustalscreens screensand andmajor majorfolds folds .............................................74 74 F.F .Black Pic batholith batholith ......................................................................... 74 74 F1-F5 . Black Pic F1—F5. F6-F12 . Western Blackman Blackmail Lake antiform antiform (D3), (D3). Janet JanetLake Lakeroad road ...................................75 75 F6—F12. G .Quetico Queticosubprovince, subprovince.western western and andcentral centralManitouwadge Manitouwadgearea area ........................................ 76 76 G. 77 ACKNOWLEDGEMENTS ............................................................................. 77 ACKNOWLEDGEMENTS iii 111 �Manitouwadge greenstone belt belt Introduction INTRODUCTION Despite its its relatively relatively small small size, size, the the Manitouwadge Manitouwadge greenstone belt is is host host to tosignificant significant economic economic Cu-Zn deposits, the most most productive productive being being Noranda's Noranda's Geco Geco mine. mine. ItIt isisamong amongthe thelargest largestof ofCanadian Canadianvolcanogenic volcanogenic massive suiphide deposits, deposits, with with total lifetime production production projected projected at 55.9 tonnes. The massive sulphide 55.9 million tonnes. Thedeposits deposits of of the belt belt have have been been known known since since the the 1950's, 1950's, and and early early theories theories of of their their origin origin and and geological geological history history are aa microcosm microcosm of the major major debates debateson onmassive massivesulphide sulphide petrogenesis. petrogenesis. In Inmore morerecent recentyears, years,aavolcanogenic volcanogenicorigin origin has has been been generally generally accepted accepted for for the the Manitouwadge Manitouwadge deposits deposits (Friesen (Friesen et et al., al.,1982; 1982;Bakker Bakker et et al., al.,1985; 1985;Williams Williams et et al., al., 1990), 1990), although although their their stratigraphic, stratigraphic, structural structural and andtectonic tectonic setting, setting,their theirrelationships relationships and and detailed detailed petrogenesis petrogenesis were were largely largely unknown unknown or or controversial. controversial. In interest of of the area In recognition recognition of the economic economic interest area and and the theimpending impendingclosure closure of of the the Geco Geco mine, mine, the the Manitouwadge project was conceived to further further understanding of mineralization, alteration, metamorphism Manitouwadge project conceived to metamorphism and camp. Within this mandate, and deformation deformation and their their relationships relationships in the Manitouwadge Manitouwadge camp. mandate, the the project project has has focussed on 1) 2) the theinfluences influences of of primary primary depositional depositional setting, setting, focussed on 1) the the evolution evolution of of the theManitouwadge Manitouwadge belt; belt; 2) deformation, on the the belt belt and its mineral deposits; deposits; and and 3) 3) the relationship of the the belt belt to deformation, and metamorphism metamorphism on relationship of the the enclosing enclosing plutonic rocks rocks and the the adjacent adjacentWawa-Quetico Wawa-Quetico boundary. boundary. The The Manitouwadge Manitouwadge project is is still still ongoing; ongoing; although most of of the the field field component component has has been been completed, completed, laboratory laboratory and andfollow-up follow-up investigations continue. The The first first part partof ofthis thisvolume volumeisis intended intended as asaacomprehensive comprehensive interim report of of our our results results to to date. date. Some Someofofthe thematerial materialisisofofa apreliminary preliminarynature naturealthough, although,we wehope, hope, presented backgroundand andinterpretation interpretationto to stimulate stimulate discussion. discussion. The second presented with sufficient sufficient background second part of of this this volume is a field field guide guide to to the Manitouwadge area, consisting of of stops, stops, outcrop descriptions and and maps maps arranged arranged as as aa series series of day or part-day part-day field field trips. The Theorganization organization of of the field field trips is is mostly mostly thematic, with stops stops selected selected to to demonstrate demonstratecritical criticalororrepresentative representativeobservations. observations. Methodology Methodology Our Our approach approach in inthe theManitouwadge Manitouwadgeproject project has hasbeen beenprimarily primarilyfield-based, field-based,entailing entailing mapping mapping varying varying in in scale scale from from 1:5000 1:5000 in in the thearea areaofofknown knowneconomic economicCu-Zn Cu-Zndeposits, deposits, toto1:10000 1:10000and and1:20000 1:20000mostly mostlyalong along the the extensions extensions of the belt belt and and ininperipheral peripheral areas. areas. In In detailed detailed mapping, mapping, we we made madeuse useofofexisting existinggrids, grids, cut for for mineral mineral exploration exploration purposes purposes and and varying varying greatly greatly in in age, age, condition condition and and utility. utility. The Theco-operation co-operationof of cut private-sector companies, prospectors, prospectors, and Ontario Ontario government government geologists geologists contributed success of of the the private-sector contributed to the success project. Unpublished Unpublished data, data,mostly mostlyininthe theform formofofgeological, geological,geophysical geophysical and and grid grid maps, maps,drill drilllogs, logs,reports reports project. A. Turner Turner and geochemical geochemical analyses, analyses, were Noranda Inc., Granges Granges Inc., Minnova Minnova Inc., and and A. and were contributed contributed by by Noranda (prospector). (prospector). F. F. Breaks Breaks and andH. H.Williams Williams(Ontario (OntarioGeological GeologicalSurvey) Survey) allowed allowed access access to their field field notes, notes, station location locationmaps mapsand andthin thinsections, sections,providing providinguseful usefulsupplemental supplementalobservations observationsininareas areasofofplutonic plutonicrock rock station and (1957),Milne Milne and near near the theQuetico Queticoboundary. boundary.InIncombination combinationwith withthe thepublished publishedgeological geologicalmaps mapsofofPye Pye(1957), (1974) and Williams Williams and Breaks Breaks (1990b), (1990b), we used this information to direct direct mapping mapping and, and,ininsome somecases, cases, to to (1974) interpolate or orextrapolate extrapolategeological geological contacts. contacts. Our Ourfield fieldobservations observations were were compiled compiled in digital maps maps and and data data interpolate bases. bases. Aeromagnetic information, in in combination combination with with field field observations, observations, proved to be be aapowerful powerful tool tool ininrereAeromagnetic solving the complex complex structure of of the the Manitouwadge Manitouwadge belt. The Theaeromagnetic aeromagnetic data datawere were collected collected during during high high solving resolution surveys, surveys, flown flown by Dighem Surveys and Processing Inc. for Noranda Exploration Exploration Ltd., Ltd.,and andreleased released resolution by Noranda Noranda to tothe theGeological GeologicalSurvey Survey of of Canada Canada for for compilation compilation by the Geophysical Geophysical Data Centre. Centre. Published Published by (Geological Survey of Canada, 1993a, 1993b; Zaleski (Geological Canada, 1993a, Zaleski and and Peterson, Peterson, 1995) and and unpublished unpublished aeromagnetic maps based on on these these surveys surveys were were invaluable invaluable for for focussing focussing our contacts in in areas areas of of poor poor based our mapping, extrapolating contacts 1:25000map, map,showshowexposure, and and interpreting interpretingthe thelocations locationsofoffaults faultsand anddiabase diabasedykes. dykes.The Theaccompanying accompanying1:25000 exposure, ing ing geology geology draped draped over over shaded shaded relief relief of of total totalfield field magnetics, magnetics,demonstrates demonstratesthe theclose closecorrespondence correspondencebetween between map-scale map-scale structure structure and andaeromagnetic aeromagneticexpression. expression. Field observations observations and and interpretations interpretationswere were followed followed up by by laboratory laboratorystudies, studies,including includingpetrographic petrographic Field observations, in in particular particularpetrofabric petrofabricstudies studiesofoforiented orientedsamples samplesand anddocumentation documentationofofmetamorphic metamorphicminminobservations, eral assemblages. assemblages. In Inconjunction conjunctionwith withmetamorphic metamorphicstudies, studies,electron-microprobe electron-microprobe determination determinationof of mineral mineral eral compositions has been initiated. initiated. Whole-rock Whole-rockgeochemical geochemical analyses, analyses, including including major, trace and and rare-earth rare-earth compositions elements, were were done on a sample sample suite suite representing representing apparently apparently unaltered unaltered or or'least-altered' 'least-altered' metavolcanic metavolcanicrocks rocks elements, and their theiraltered alteredequivalents, equivalents,-metasedimentary metasedirnentary rocks rocks from from the theManitouwadge Manitouwadge belt beltand andQuetico Queticosubprovince, subprovince, and iron formation, formation, and and intrusive intrusiverocks. rocks. Geochronology Geochronology samples samples were were collected primary iron collected with with the the aim of dating primary volcanism, bracketing bracketing deformational deformational events and and metamorphism, metamorphism, bracketing bracketing sedimentation sedimentation and anddetermining determining volcanism, provenance, provenance, and dating dating intrusive intrusiveactivity. activity. 1 �Manitouwadge Manitouwadge greenstone greenstone belt belt Regional Regional setting setting FIG. FIG.1.1.Tectonic Tectonicmap mapofofthe thesouth southcentral centralSuperior SuperiorProvince Provinceshowing showingthe theWawa, Wawa,Quetico Queticoand andWabigoon Wabigoon subprovinces subprovinceswith with the thearea areaof of Figure Figure 22 outlined. outlined. 11==Rainy RainyLake Lake area; area; 22 ==Vermilion Vermiliondistrict, district,Minnesota; Minnesota; 33 ==Shebandowan Shebandowangreenstone greenstone belt; belt; 44 ==Max MaxCreek Creek conglomerate; conglomerate;55==Beardmore-Geraldton BeardmoreGeraldton belt; belt; 66 == Schreiber-Hemlo Schreiber-Hemlogreenstone greenstone belt; 77 == Michipicoten Michipicoten greenstone greenstone belt; 88 == Dayohessarah-Kabinagami Dayohessarah-Kabinagami greenstone greenstone belt; belt; 99 ==Kapuskasing Kapuskasingstructural structuralzone; zone;QQ ==Quetico Queticofault; fault;AA ==Atikokan; Atikokan;TB TB ==Thunder Thunder Bay; Bay;SS==Schreiber; Schreiber;GG==Geraldton; Geraldton;M M==Manitouwadge; Manitouwadge;W W==Wawa; Wawa;LL==Lepage Lepagefault faultzone. zone. Adapted Adapted from fromWilliams Williams et etal. al. (1991) (1991) and and Percival Percival (1989). (1989). The heinset insetshows showsthe thesubprovinces subprovincesof of the thesouthern southern Superior Superior Province Provinceafter afterCard Cardand andCiesielski Ciesielski(1986), (1986),and and the thearea areadetailed detailedininthe thetectonic tectonicmap. map. REGIONAL REGIONALSETTING SETTING Relationships Relationshipsin inthe theWawa Wawasubprovince subprovince TheManitouwadge Manitouwadge greenstone greenstone belt belt lies liesininthe thevolcano-plutonic volcano-plutonicWawa Wawasubprovince subprovince ofofthe theSuperior Superior The Province, near near the theboundary boundarywith withthe themetasedimentary-migmatitic metasedimentary-migmatiticQuetico Queticosubprovince subprovince(Fig. (Fig.1). 1).The Thebelt beltisis Province, aaremnant remnantofofvolcanic volcanicand andsedimentary sedimentaryrocks, rocks,highly highlydeformed deformed and and metamorphosed metamorphosed to to upper upper amphibolite amphibolitefafar cies. cies.Williams Williamsetetal.al.(1991) (1991)proposed proposedcorrelations correlationswith withthe theDayohessarah-Kabinakagami Dayohessarah-Kabinakagamiand andSchreiber-Hemlo Schreiber-Hemlo greenstonebelts, belts,and andsuggested suggestedthat thatthese theseare aredismembered dismemberedparts partsofofananoriginally originallycontinuous continuousgreenstone greenstonetertergreenstone rane.Regional Regionalmapping mappingestablished establishedthat thatsupracrustal supracrustalrocks rocks(mostly (mostlymafic maficmetavolcanic metavolcanicrocks) rocks)extend extendeast east rane. of ofManitouwadge Manitouwadge to to the the Moskinabi Moskinabi belt, and and southeast southeast to tothe theFaries FariesLake Lake belt belt (Fig. (Fig.2), 2),asasaasemicontinuous semicontinuous unitand andasasinclusions inclusionsininfoliated foliatedplutonic plutonicrocks rocks(Williams (Williamsand andBreaks, Breaks,1989; 1989;1990a, 1990a,b; b;Williams Williamset etal., al.,1992). 1992). unit The a layered complex comprising TheMoshkinabi Moshkinabiand andFaries FariesLake Lakebelts beltsare areintruded intrudedbyby a layered complex comprisinggabbro, gabbro,leucogabbro, leucogabbro, anorthosite Breaks, 1989; 1990b). anorthositeand andperidotite peridotite(Williams (Williamsand and Breaks, 1989; 1990b). The TheManitouwadge Manitouwadgebelt beltisisbounded boundedtotothe thewest westand andsouth southbybyfoliated foliatedmultiphase multiphaseplutonic plutonicrocks, rocks,colleccollectivelyknown known as as the theBlack Black Pic Picbatholith batholith(Fig. (Fig.2). 2).To Tothe thesouth, south,foliations foliationsininthe theBlack BlackPic Picbatholith batholithdefine defineaa tively structuraldome dome(Williams (Williamsand andBreaks, Breaks,1990a, 1990a,b), b),and andplutonic plutonicrocks rocksextend extendtotothe theSchreiber-Hemlo Schreiber-Hemlogreengreenstructural stone thethe west of of thethe Manitouwadge greenstone inclusions stonebelt belt(Williams (Williamsetetal., al.,1991). 1991).ToTo west Manitouwadge greenstonebelt, belt,abundant abundant inclusions ofofmafic mafictotointermediate intermediatesupracrustal supracrustalrocks rockswere werelikely likely derived derived from from the the belt. belt. On Onaeromagnetic aeromagneticmaps, maps,the the corresponding area areashows shows aapronounced pronouncedstriping stripingparallel paralleltotofoliation foliationtrends trends(accompanying (accompanying1:25000 1:25000map), map), corresponding interpretedtotoreflect reflectthe thepresence presenceofofdiscontinuous discontinuoussupracrustal supracrustal septa. septa.Areomagnetic Areomagneticlineaments lineaments that thattrend trend interpreted southwesttoward towardthe theSchreiber-Hemlo Schreiber-Hemlogreenstone greenstonebelt beltsupport supportlinkage linkageofofthe thegreenstone greenstoneterranes terranes(Williams (Williams southwest al.,1991). 1991).InIncontrast, contrast,the the BlackPic Pic batholith south Manitouwadge containsfew fewsupracrustal supracrustalinclusions inclusions etetal., Black batholith south of of Manitouwadge contains and andthe theaeromagnetic aeromagneticsignature signatureisislow lowand andfiat. flat. 2 �_____ Regional setting greenstone belt Manitouwadge greenstone — Proterozoic/Paleozoic Rocks Quetico subprovrnce Metasedimentary/ — intrusive rocks Quetco — Wawa & Wabigoon subprovinces •. Metavolcanic & Granitoid rocks related rocks . Isograd ——-Faults . •. .. Opz _vz C — I. FIG. 2. greenstone belt belt and 2. The TheWawa, Wawa,Quetico Quetico and andWabigoon Wabigoon subprovinces subprovinces with the Manitouwadge Manitouwadge greenstone the area greenstonebelt; belt;FF = = Faries belt; Mo = Schreiber-Hemlo greenstone Faries Lake Lake belt; MO = area of of Figure Figure 33 outlined. outlined. SH SH ==Schreiber-Hemlo Moshkinabi greenstonebelt; belt; DK DK = greenstonebelt; belt;BPb BPb = = Black Moshkinabi greenstone = Dayohessarah-Kabinakagami Dayohessarah-Kabinakagami greenstone Black Pic Pic batholith; isograd; SS = = Schreiber; M= = batholith; Pb ==Pukaskwa Pukaskwa batholith; batholith; Opx Opx ==orthopyroxene orthopyroxene granulite granulite isograd; Schreiber; M Manitouwadge; WL WL = = Winston Winston Lake Lake Zn-Cu mine; H = = Hemlo Hemlo Au camp. Adapted Adapted from fromWilliams Williams et et al. al. (1991). (1991). Structural Structural and tectonic setting Stockwell (1964)originally originallyused usedstructural structuraltrends trends and and style style to subdivide Stockwell (1964) subdivide the Superior Superior Province Province (Fig. 1), contrasting with the curvilinear trends of the I), contrasting the linear linear east-west east-west trends trends of the the Quetico Quetico subprovince subprovince with curvilinear trends Wawa and and Wabigoon subprovinces, subprovinces, the the latter latter defined by by remnants of greenstone belts lying between between domical Wawa Subsequently, lithological lithologicalfeatures featureswere werealso also used used to to define subprovinces, by by contrasting the batholiths. Subsequently, define subprovinces, dominantly supracrustal rocks in the volcano-plutonic dominantly volcanic volcanic origin of supracrustal volcano-plutonic terranes with with the thesedimentary sedimentaryorigin originof of the Quetico Quetico subprovince subprovince (Stockwell, (Stockwell, 1970; 1970; Card and and Ciesielski, Ciesielski, 1986). 1986). In some some cases, cases, boundaries boundaries were were defined defined rocks from from the the Quetico subprovince subprovince (Williams, (Williams, 1991). Supracrustal Supracrustal sequences to exclude mafic metavolcanic rocks sequences in subprovinces resemble resemblearc-type arc-type deposits deposits in in modern modern orogenic orogenicbelts belts (Card, (Card, 1990). Among the volcano-plutonic subprovinces the recent recent tectonic tectonic models models for for the theWabigoon, Wabigoon,Quetico Quetico and andWawa Wawa subprovinces, subprovinces, an an arc-accretionary arc-accretionary model model (1990). In has been favoured by Percival Percival (1989), (1989), Percival Percival and Williams (1989) (1989) and Williams (1990). In this thisscenario, scenario, the Quetico Quetico subprovince subprovince represents accretionary complex complex that accumulated southward from the margin margin represents an accretionary that accumulated of the Wabigoon Wabigoon arc, above a northerly dipping dipping subduction subduction zone. zone. Collision Collision of the Wawa arc from the south amalgamated the the three three subprovinces. subprovinces. The Therelatively relativelyhigh high temperature-low temperature-low pressure pressure metamorphic metamorphicassemblages assemblages preserved preserved within the the Quetico Quetico and and northern northernWawa Wawasubprovinces subprovinces could could be explained by ridge subduction subduction or or by by post-subduction post-subduction thermal thermal relaxation relaxation (Percival, (Percival, 1989). 1989). identification of structures produced by dextral dextral transcurrent transcurrent motion motion isisaafeature featurecommon commonto tovarious various The identification structural studies of the Quetico and its its boundaries. boundaries. Both Quetico subprovince subprovince and Both ductile ductile and brittle structures structures have have been typically in shear zones or deformation zones near subprovince subprovince boundaries boundaries (Fig. (Fig. 1). Exambeen identified, typically zones near Examinclude the Quetico fault (Borradaile (Borradaile et al., al., 1988), 1988), the Vermilion Vermilion district (Hudleston et 1988), the ples include district (Hudleston et al., 1988), l986), Beardmore-Geraldton belt (Devaney and Williams, Williams, 1989), l989), the Shebandowan Shebandowan belt and Stott, Stott ,1986), Beardmore-Geraldton belt (Devaney belt (Corfu and Shebandowan-Quetico boundary (Borradaile and Spark, Spark, 1991), 1991), and the the Hemlo-Schreiber Hemlo-Schreiber belt (Williams, (Williams, the Shebandowan-Quetico 1989). Zones Zones of of distributed distributed dextral motion have have been been noted noted in the western 1989). western Quetico (Bauer et al., al., 1992), 1992), as as have dextral shear shear zones zones well well within the the Wawa Wawa subprovince, for example in the Dayohessarah-Kabinakagami Dayohessarah-Kabinakagami greenstone belt (Leclair, 1990). In the the Shebandowan Shebandowan belt, the the timing timing of of dextral dextral transcurrent transcurrentmotion motion(local (localD2) Da) is constrained 2689+3/-2 and and 2684+6/-3 2684+6/-3 Ma Ma (Corfu (Corfu and andStott, Stott,1986); 1986);however, however, temporal temporal correlacorrelaconstrained to between 2689+3/-2 tion with dextral dextral motion motionelsewhere elsewhere in in the theWawa-Quetico-Wabigoon Wawa-Quetico-Wabigoon region the timing timing region isisuncertain. uncertain. Although the of dextral dextral motion motion varies varies widely, widely, in several several areas it isis associated associated with with later laterphases phasesofofdeformation deformation and style of 3 �Regional setting setting Manitouwadge greenstone belt Bauer et et al., 1992). In the western Quetico (Hudleston et al., 1988; 1988; Devaney and Williams, 1989; Bauer Quetico subprovince, subprovince, dextral motion has been been attributed attributedtotodextral dextraltranspression transpressionfollowing followingoblique oblique arc arccollision collision (Hudleston (Hudleston et al., al., 1988; Borradaile Borradaile and and Spark, 1991; 1991; Bauer et al., al., 1992). 1992). Evidence of thrusting thrusting prior prior to dextral Evidence of dextral transcurrent transcurrent motion motion has has been been observed observed in several several areas of the Wawa-Quetico-Wabigoon region.In In the the BeardmoreGeraldton Beardmore-Geraldton belt, belt, stratigraphic stratigraphic packages are separated by Wawa-Quetico-Wabigoon region. by dip-slip faults faults attributed attributed to dip-slip to thrust thruststacking stackingininan anaccretionary accretionarywedge wedge (Devaney (Devaney and Williams, Williams, 1989). 1989). Early Early (local Dl) Di) thrusting (local thrusting and andnappe nappeformation formationininthe theVermilion Vermiliondistrict districtof ofthe thewestern westernWawa Wawasubprovince subprovince may may have been been associated with accretion (ursa associated with (Jirsa et etal., al.,1992). 1992).Along Alongthe theWawa-Quetico Wawa-Quetico boundary boundary near near Schreiber, Schreiber, Williams (1989) (1989) identified identifiedstructures structures possibly possiblyrelated relatedto toearly earlydip-slip dip-slipthrusting. thrusting. Early Early (D2 (D2 and and earlier) earlier) thrust thrust structures in by Arias and Helmstaedt in the theMichipicoten Michipicoten greenstone greenstone belt were were described described by Helmstaedt (1990) (1990) and McGill McGill (1992). Detailed mapping in the Manitouwadge greenstone belt belt has also led led to to the recognition of of ductile ductile shear shear (1992). zones, interpreted as the the loci loci of of early thrusting thrusting (Zaleski (Zaleski and Peterson, Peterson, 1993a). 1993a). Williams et a!. al. (1992) interpreted interpreted the theManitouwadge, Manitouwadge,Moshkinabi Moshkinabi and and Faries Faries Lake Lake greenstone belts belts (Fig. (Fig. 2) as a semicontinuous easterly trending supracrustal supracrustalsuite suite(Manitouwadge-Hornpayne (Manitouwadge-Hornpayneassemblage), assemblage),belonging belonging to a discontinuous layer along along the the northern northern margin of the Wawa subprovince, traceable to discontinuous mafic metavolcanic layer the east to to the the Lepage Lepage fault fault zone zone (Williamset (Williamset al., al., 1991) 1991) (Fig. 1). 1). In In the thearea areaof of the the Manitouwadge, Manitouwadge, Moshkinabi belts and the Quetico and Faries Lake belts Quetico subprovince to the north, north, Williams Williams and and Breaks Breaks (1989; (1989; 1990a) 1990a) described a 5-phase sequence of of deformation deformation in in which which D2 D2was wasthe themain mainfabric-forming fabric-formingevent. event.The The easterly easterly regional regional trend trend of the greenstone belts is modified by by D3 northeasterly northeasterly trending Z-shaped from west west to to east; east; Blackman Z-shaped folds, from Lake antiform, Manitouwadge Manitouwadge synform, Banana Lake Lake antiform antiform and andMoshkinabi MoshkinabiLake Lake synform synform(Williams (Williamsand and Breaks, 1990b). The axial parallel with with the east-west regional trends of axial traces traces of of the the Z-folds Z-folds curve, becoming parallel the Quetico Quetico subprovince to the north north (Williams (Williams et et a!., al., 1992). 1992). Metamorphism There is a regional regional metamorphic metamorphic gradient gradient from from amphibolite amphibolitefacies facies in in the theSchreiber-Hemlo Schreiber-Hemlogreenstone greenstone belt belt (Corfu and Muir, 198gb), at Manitouwadge, Manitouwadge, to upper amphibolite amphibolite and and granulite granulite 1989b), through upper amphibolite amphibolite at facies in in the Quetico subprovince immediately north of Manitouwadge (Williams (Williams and and Breaks, 1989) (Fig. 2). facies facies kb) in in the ManiThermobarometric results are areconsistent consistentwith withupper upperamphibolite amphibolite facies(600—700°C, (600-700°C3—6 3-6 kb) Maniand facies (680—770°C, kb)in in the the Quetico touwadge belt (Petersen, (Petersen,1984; 1984;Pan Panand andFleet, Fleet,1992), 1992), andgranulite granulite facies (680-77O0C14—6 4-6 kb) subprovince to to the the north (Pan subprovince (Pan et et al., al.,1994). 1994). In Inthe theManitouwadge Manitouwadgebelt, belt, metamorphic metamorphic grade grade increases increases to the north, with with muscovite-sillimanite-quartz muscovite-sillimanite-quartzschists schists near the the Geco Geco mine on the southern southern limb limb of the Manitouwadge synform, giving giving way way to to sillimanite-microcline-quartz sillimanite-microcline-quartzschists schists(Fig. (Fig.3). 3).Migmatites Migmatitesare are ubiquitous ubiquitous north north of of the Blackman Lake antiform. Metagreywackes along the southern limb of Blackman Lake Metagreywackes along of the the Manitouwadge Manitouwadge synform contain garnet-sillimanite-biotite in pelitic pelitic layers, layers, but but are are not migmatitic. garnet-sillimanite-biotite in migmatitic. Similar Similar rocks near the Quetico Quetico boundary boundary contain tonalitic segregations, in some cases caseswith withcordierite cordieriteand andgarnet. garnet. In the Manitouwadge belt, dominant Manitouwadge belt, D2 fabrics are defined D2 fabrics defined by high high grade grade minerals minerals and and deformed deformed by by D3 Da folds; folds; hence, hence, peak peak metamorphism metamorphism was was broadly synchronous synchronous with D2. D2. Petrographic Petrographicevidence evidenceof ofdecompression decompression reactions reactions (e.g. (e.g. cordierite cordierite mantling mantling cooling was high temperatures temperatures persisted persisted sillimanite and orthoamphibole) orthoamphibole) suggests suggests that that cooling was protracted protracted and that high during D3 D3 deformation. Along most of its its length, length, the theQuetico Queticosubprovince subprovinceisissymmetrically symmetrically zoned zoned from from low low grade margins margins adjaadjacent to the the Wawa Wawa and and Wabigoon Wabigoon subprovinces, to central high grade migmatites (Percival, 1989). 1989). The ManManitouwadge area area is unusual unusual in two respects. respects. Firstly, the Manitouwadge boundary itouwadge Manitouwadge belt and the the Wawa-Quetico Wawa-Quetico boundary preserve amphibolite-facies assemblages, assemblages, and secondly, secondly, amphibolite-facies assemblages preserve upper amphibolite-facies assemblages are are transitional to orthopyroxene-bearing orthopyroxene-bearing granulites, found in aa lensoid lensoid area area (about (about 80 80x10 granulites, the the latter found x 10 km) km) near near the southern 1994) (Fig. 2). Moreover, Moreover, sammargin of the Quetico subprovince (Williams and Breaks, 1990a, b; b; Pan et al., 1994) pling study shows shows that that orthopyroxene-bearing orthopyroxene-bearing rocks rocks in the the Quetico Quetico subprovince subprovince extend somewhat pling during this study south of the Williams Williams and Breaks Breaks (1990b) (1990b) isograd, to within 1.5 1.5 km of the subprovince boundary. boundary. Geochronological constraints Geochronological constraints In the Manitouwadge Manitouwadgebelt, belt,felsic felsicmetavolcanic metavolcanicrocks rockshave have primary primaryvolcanic volcanicages agesof ofcirca circa2720 2720 Ma Ma(Zaleski (Zaleski al., 1994; 1994; Davis Davis et et al., al.,1994), 1994),as asdoes doesaasubvolcanic subvolcanic trondhjemite trondhjemite north of of the the Willroy Willroy and and Geco Geco mines mines et al., (Zaleski 1994). In In the theSchreiber-Hemlo Schreiber-Hemlobelt, belt, felsic felsic volcanism volcanism ranges in age from 2772±2 2772&2 Ma Ma (Hemlo(Hemlo(Zaleski et et al., 1994). Black Hemlo gold 26952~2Ma for the the Heron Heron Black River River assemblage, assemblage,Williams Williamsetetal., al., 1991) 1991) near near the the Hemlo gold camp camp to to 2695±2 Muir, 1989a). 1989a). Felsic Felsic metavolcanic metavolcanic rocks rocks (Schreiber (Schreiber assemblage, assemblage, Williams Bay volcanic complex (Corfu and Muir, al., 1991) 1991) associated associated with with the the Winston Winston Lake Lake Zn-Cu Zn-Cu mine mine are are 2723±2 2723&2 Ma Ma (Schandl (Schandl et et al., al.,1991), 1991),within within et al., at Manitouwadge. Manitouwadge. The Theages ages suggest suggest that that'Manitouwadge-Hornpayne' 'Manitouwadge-Hornpayne' assemblage assemblage is related error of those at related to Schreiber assemblage, assemblage, rather than thanthe theHemlo-Black Hemlo-BlackRiver River assemblage assemblage as as originally originally proposed by Williams the Schreiber et al. al. (1991). (1991). InInthe thewestern westernAbitibi Abitibisubprovince, subprovince, east east of of the theKapuskasing Kapuskasing structural structural zone zone (Fig. (Fig. 1), I),felsic felsic rocks base-metal mineralization mineralization at Timmins, Timmins, Abitibi Abitibi greenstone greenstone belt, belt, have have been been bracketed bracketed rocks associated associated with with base-metal at 2710—2717 2710-2717 Ma Felsic tuff underlying the Shunsby Shunsby base-metal base-metal Ma(Bleeker (Bleekerand andParrish, Parrish,pers. pers. comm., 1994). Felsic occurrence in the Swayze Swayze greenstone belt is is 2724±2 2724&2 Ma Ma (Heather (Heather etetal., al.,1995). 1995).Evidently, Evidently,circa circa2710—22 2710-22 Ma Ma 4 �Historical background Manitouwadge greenstone belt felsic volcanism volcanisminin the the Wawa Wawa and and western western Abitibi Abitibi subprovinces tended to be associated felsic subprovinces tended associated with with hydrothermal hydrothermal activity and mineralization. mineralization. The U-Pb systematics systematicsof of metavolcanic metavolcanic rocks from the Manitouwadge belt do not suggest suggest any any inheritance inheritance of older crustal components. AA model modelage age of of 3000 3000 Ma Ma based based on on Pb Pbisotopic isotopicanalyses analysesof of galena galena from fromthe theGeco Geco mine (Tilton (Tilton and and Steiger, Steiger,1969) 1969)reflects reflects the the inadequacies inadequaciesof of early models of Pb isotopic evolution; recalculation recalculation gives model ages ages near near or slightly younger (i.e. by circa Ma)than than the the 2720 2720 Ma Ma age age of of the volcanic host host gives model circa 5—15 5-15 Ma) rocks (R. Thorpe, Thorpe, written written comm., comm., 1994). 1994). The Theslight slight discrepancy discrepancy could be the result of limited isotopic resetting during regional regional metamorphism metamorphism (ibid.), (ibid.), an an interpretation interpretation supported by the presence Pb-bearing amazonite presence of of Pb-bearing in pegmatites in in contact contact with withmassive massivesulphide sulphide (Stevenson, (Stevenson, 1985). 1985). U-Pb zircon geochronology of various variousphases phasesofofthe the Black Black Pic Pic batholith continues geochronology of continues under the theauspices auspices of the Manitouwadge project. Two Manitouwadge project. Two dioritic dioritic phases phases of the Black Black Pic batholith batholith have have ages ages of of 2687+3/—2 2687+3/-2 and 2677±2 2677&2 Ma (see (see Geochronology). Geochronology). Two prepre- to to syn-D2 syn-Da bodies bodies of of K-feldspar K-feldspar porphyry, porphyry, the the Loken Loken Lake Lake and and Nama Creek Creek plutons, near the the margins margins of of the theManitouwadge Manitouwadge belt belt (Zaleski (Zaleski et a!., al., 1995), 1995), have have zircons zircons that that yield intrusive ages of of 2687+2/-3 2687+2/—3Ma Maand and 2680zk3 2680±3 Ma, Ma, respectively. respectively.Titanites Titanites from from the the Nama Creek Creek pluton yield intrusive and from the 2677 2677 Ma Black Black Pic diorite have U-Pb ages of 2672±3 2672&3 and 2674±2 2674&2 Ma, respectively, tentatively interpreted as of as metamorphic metamorphiccooling cooling ages. In In comparison, comparison, south of of the Schreiber-Hemlo Schreiber-Hemlo belt, marginal rocks of the Pukaskwa Pukaskwa batbolith batholithwere were intruded intrudedatat2719+6/—4 2719+6/-4 Ma Ma(Corfu (Corfuand andMuir, Muir,1989a), 1989a),broadly broadlycoeval coevalwith withfelsic felsic volcanism at Winston Lake Hemlo,several severalgranodiorite granodiorite plutons plutonscluster cluster volcanism at Lake and Manitouwadge Manitouwadge (Fig. 2). Near NearHemlo, closely Ma,whereas whereasamphibolite-facies amphibolite—facies metamorphism datedbybytitanite titanite peaked around closely around 2687—2688 2687-2688 Ma, metamorphism dated around 2676—2678 Ma,coeval coeval withthe thelate latetectonic tectonicGowan GowanLake Lakepluton plutonatat 2678dz2 2678±2 Ma Ma (Corfu (Corfu and Muir, 2676-2678 Ma, with Muir, 1989b). 1989b). Synmetamorphic monazites have ages of of 2675k1 2675± 1Ma MaatatGeco Gecoand and2677&1 2677±1Ma MaatatWinston Winston Lake Lake (Schandl (Schandlet et al., al., Synmetamorphic youngermonazite monazite(2661&1 (2661±1Ma) Ma)in inbiotite biotite schist schist at at Geco Geco was wasinterpreted interpreted to to date local K-metasomatism 1991); younger (Davis et aL, (Davis et al., 1994). In In general, general, metamorphic metamorphic titanite and and monazite monazite ages ages suggest suggest that metamorphism metamorphism was was nearly synchronous, synchronous, or or diachronous diachronousover overabout about55Ma, Ma,throughout throughout this this part part of the Wawa subprovince. In the nearly Wawa subprovince. subprovince, Percival Percival (1989) (1989) suggested suggested that that metamorphism was approximately approximately coeval with with granitic Quetico subprovince, plutonism from2670—2650 2670-2650 Ma. plutonism from Metagreywackes of of the the Quetico Quetico subprovince subprovince have havebeen beeninterpreted interpreted as an accretionary complex Metagreywackes complex continuous with the Ma (Percival (Percival and Williams, 1989). the Wawa Wawasubprovince subprovince atatleast leastsince since2689—2684 2689-2684 Ma 1989). Geochronological Geochronological studies of Quetico metasedimentary rocks have have been been mainly mainly confined confinedto towest westand and north north of of Thunder Thunder Bay (Fig. sedimentation to to 27023Z4 2702±4 Ma Ma for for the the southern southern Quetico near near 1). Detrital Detrital zircons zircons constrain the the maximum maximum age age of sedimentation Thunder Bay Bay (Percival (Percival and and Sullivan, Sullivan, 1988), 1988), and to to 2698±3 2698&3 Ma Ma for the the northern northern Quetico Queticonear nearAtikokan Atikokan(Davis (Davis et al., al., 1990). 1990). Minimum Minimumdepositional depositional ages ages were were constrained constrained by by intrusions intrusions of of 2687+19/-13 2687+19/-13 Ma and and 2688±4 2688&4 Ma, respectively for each each area. area. in respectively for In both bothcases, cases,zircons zircons older older than than 3000 3000 Ma Ma indicated indicated input input from fromold oldsources sources (ibid.). In sources to to the north, In the theAtikokan Atikokanarea, area,the thezircons zirconscould couldhave have relatively relatively proximal proximal sources north, including including the the 3003±5 Ma Marmion Marmion Lake Lakebatholith batholith (Davis (Davisetet al., al., 1990). 1990). In the case greater than 2800 Ma in 3003k5 Ma case of of zircons zircons greater 2800 Ma the southern Quetico, Quetico, no no local localpotential potentialsources sources are areknown known (Percival (Percival and and Sullivan, Sullivan, 1988). 1988). The TheCoutchiching Coutchiching metagreywackesinin the the Rainy metagreywackes Rainy Lake area of of the the Wabigoon Wabigoon subprovince subprovince contain detrital detrital zircon zircon populations populations similar to those of similar of Quetico Quetico rocks (Davis et al., al., 1989). 1989). The Themaximum maximumdepositional depositional age age was was established established at 2704±3 2704k3 Ma and the the minimum minimum age age at at 2692±2 2692zk2Ma, Ma, the theage ageof of aa cross-cutting cross-cutting intrusion. intrusion.The Thepresence presenceofofzircons zircons as old as 3059 3059 Ma indicated indicated aaMesoarchean Mesoarchean source. source. sequences are are comparable comparable to Timiskaming In both the the Wabigoon Wabigoonand andWawa Wawa subprovinces, subprovinces, conglomeratic conglomeratic sequences rocks facies associations These sequences sequences include (Fig. 1); 1); the the Max Max Creek Creek conglomerate conglomerate with with rocks in in facies associations and and age. age. These a maximum depositional age of 2687±3 2687&3 Ma (Percival (Percival and Sullivan, Sullivan, 1988), 1988), the Seine Seine group near near Rainy Rainy Lake Lake and 2686+2/-i 2686+2/-1Ma Ma(Davis (Daviseteta!., al.,1989), 1989),and and the theShebandowan Shebandowan group (Borradaile (Borradaile bracketed between 2696+5/-3 and and Brown, 1987) with depositional age depositional contact with a maximum depositional age of of 27043~2 2704±2 Ma Ma and and in depositional contact with alkalic 1986). volcanic rocks rocks of of 2689+3/-2 2689+3/-2 Ma Ma (Corfu (Corfu and Stott, Stott, 1986). THE MANITOUWADGE MANITOUWADGE BELT BELT HISTORICAL BACKGROUND OF THE History of deposits Department of Mines, Mines, while of 1931, JJ.E. In 1931, .E. Thomson, Thomson, Ontario Department while engaged engagedinin mapping mappingthe the north north shore of Lake Superior, was local Ojibway Ojibway Indians of rusty rocks near Manitouwadge Manitouwadge Lake Lake was told told by the local Lake to to the north (Brown, 1963). Thomson and and his his guide, guide, M. M. Fisher, completed completed a canoe traverse to t o the the area areaand andfound foundsuiphide sulphide mineralization and 'considerable 'considerable magnetic disturbance' (Thomson, (Thomson, 1932) 1932) on the future future sites sites of of the the Geco Geco and and mineralization Willroy returned in in 1943 1943and and staked staked the the showing, showing, but but he he was was unable unable to tofind findfinancial financial Willroy mines mines (Fig. (Fig. 3). 3). Fisher returned backing during the war years and allowed allowed his his claim claimto tolapse lapse(Pye, (Pye, 1957). 1957).Ten Tenyears yearslater, later,interest interest in in base base metal metal potential was heightened and the the showings showings on Thomson's map were staked by 'weekend 'weekend prospectors', prospectors', Dawd, Barker Forster (ibid.). (ibid.). Within Withinthe theyear, year,drilling drillingintersected intersected an anorebody orebodyand andGeco GecoMines Mines Limited Limited was was Barker and Forster incorporated. In In the theensuing ensuingstaking stakingrush, rush,the theWillroy, Willroy,Nama NamaCreek Creekand andWillecho Willechodeposits depositswere werediscovered, discovered, all of Willroy and Geco Geco mines went in 1957. 1957. of which which were were eventually eventually mined. mined. The Wiliroy went into production in 5 �Historical background background Manitouwadge greenstone belt The is the the only mine mine currently currently active in the area. Geco The Geco Geco mine, scheduled to close in late 1995, is Geco was was by tonnes with an overall far the largest deposit; total total production production for for its its lifetime lifetime is projected to to be be 55.9 55.9 million tonnes of 1.85% Cu, Cu, 3.76% 3.76%Zn Znand and 46.9 46.9 gramltonne gram/tonne Ag. Ag. Minor grade of Minor amounts of Au, Cd and and Bi Bi are arerecovered recovered and, and, until 1988, of 0.30% 0.30%Pb Pb was wasextracted extracted (Williams et et al., 1990) as as aa by-product of purification of CU Cu 1988, an average of concentrate. Combined concentrate. Combined production production from from the the Willroy, Willroy, Nama Nama Creek Creek and and Willecho Willecho deposits, deposits, until until the theclosure closure of the Wiliroy mine in 1977, was was 8.0 8.0 million milliontonnes tonneswith withaa grade grade of of 0.9% 0.9%Cu, Cu, 4.9% 4.9%Zn Znand and 50 50 gram/tonne gram/tonne of Willroy mine Ag. Exploration continues in the area, on identifying identifyingtargets targets at at depth and Ag. area, mainly mainly focussed focussed on and along along the the folded folded extensions of of the the belt. extensions Previous m mapping and interpretations interpretations Previous a p p i n g and The The first systematic systematic mapping mappingof of the the Manitouwadge Manitouwadge greenstone belt was undertaken by by Pye Pye (1957) (1957) for the Ontario Department Departmentof of Mines, Mines, from from1954 1954 to 1957. 1957. He outlined the the general general shape shapeof of the the Manitouwadge Manitouwadgesynform synform rocks along along the the inner inner and outer margins supracrustal sequence. and recognized mafic metavolcanic rocks margins of the the folded folded supracrustal sequence. At the time time of Pye's mapping, mapping, most most of of the the presently presently known known economic deposits had already been discovered and, in many cases, his detailed maps maps of of mine mine properties properties are are the theonly onlypublished publishedrecord recordofofgeological geological relationships relationships replacement that postthat were were obliterated by by mining. mining. Pye Pye regarded regarded all all the themineralization mineralization as as Algoman-age Algoman-age replacement postof diabase diabase dykes. dykes. He He interpreted most supracrustal dated intrusive activity, activity, with the the possible possible exception of supracrustal rocks rocks Mime (1974) (1974)remapped remappedthe the area area of of major economic economic interest interest for for the the as metasediments. metasediments. From From 1968 1968 to 1970, 1970, Milne Ontario Division of Mines, reinterpreting most of of the the felsic felsic rocks as as volcanic or volcanogenic. The base-metal base-metal deposits deposits of of the the Manitouwadge Manitouwadge greenstone greenstone belt are are aaclassic classicexample example of of the theproblems problemsenencountered in petrogenetic studies of mineralization in complex polydeformed polydeformed terranes. terranes. Early studies countered studies tended tended to focus on evidence of local replacement, replacement, remobilization and and structural structural control control (Pye, (Pye,1957; 1957;Timms Timmsand andMarMarshall, 1959; 1959; Brown Brown et al., al., 1960; 1960; Watson, Watson, 1970). 1970). Associated Associated orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnetgneiss gneisshas hasbeen been interpreted as metasediment et al., 1960; Watson, 1970), restite from from the extraction of metasediment (Pye, 1957; 1957; Brown Brown et 1960; Watson, 1970), restite partial melt melt (Robinson, (Robinson,1979), 1979),and andmetamorphosed metamorphosedaltered alteredvolcanic volcanicor orvolcaniclastic volcaniclasticdeposits deposits with withpossible possible pelitic interbeds (James Sillimanite-muscovite-quartz schist in proximity to (James et et al., al.,1978; 1978;Friesen Friesen et al., al., 1982). 1982). Sillimanite-muscovite-quartz orebodies has also been been variously interpreted as metasediment, metasediment, with the the most mostmuscovitic muscovitic zone zone corresponding corresponding to aa concordant altered metasediment Brown et a!., concordant fault fault (Milne, (Milne,1974); 1974);epigenetically epigenetically altered metasediment (Pye, 1957; 1957; Brown al., 1960); 1960); metamorphosed altered volcanic and volcaniclastic rock rock (Friesen (Friesen et et al., a!., 1982; Bakker Bakker et et al., 1985); metamorphosed 1985); and synsynalteration (Schandl et al., 1991; metamorphically altered rock, possibly with a prehistory of synvolcanic alteration 1991; Davis et a!., al., 1994). 1994). Suffel Suffel et et al. al.(1971) (1971)were were the the first first totopropose proposeaavolcanogenic volcanogenic origin, interpreting textures and and microstructures the result result of of superimposed superimposed metamorphism metamorphism and and remobilization. remobilization. More More recently, recently, aa syngenetic syngenetic for the the base-metal deposits and origin for and altered altered rocks rocks has has been been increasingly increasingly accepted (James (Jameset eta!., al.,1978; 1978;Friesen Friesen et al., al., 1982; 1982;Bakker Bakker et al., al., 1985). 1985). Historical h e 'Mine Series' Series' Historical nomenclature, nomenclature, tthe Most previous detailed mapping has been who have have adopted the Most previous detailed been done done by by private-sector private-sector geologists geologists who the hishistorical 'Mine Series' lithological units (Table 1). 1). This Thisconfusing confusing nomenclature nomenclature is is of of wide wide use locafly locally and has found its way way into the the literature. literature. The The'Mine 'MineSeries' Series'consists consistsofofaafour-fold four-fold subdivision subdivision of supracrustal rocks rocks (Friesen et et al., 1982; (Friesen 1982; Williams et al., al., 1990) 1990) into; into; Granite Granite Gneiss Gneiss group, group, Sericite Sericite Schist Schist group, group, Grey Grey Gneiss Gneiss group and Hornblende Schist group. group. The group The 'Granite 'GraniteGneiss Gneissgroup' group'refers referstotoorthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss, interpreted as as metamorphosed metamorphosed synvolcanically synvolcanically altered rocks lying in the stratigraphic stratigraphicfootwall footwall (struc(structural hanging hanging wall) to the the mineral mineral deposits deposits (ibid.). (ibid.). The Themisleading misleading name name dates dates back back to to the thediscovery discovery drill holes of the Geco mine; mine; by by a quirk of nature and holes of and karma, karma, the the holes holes penetrated penetrated foliated foliated granite granitebefore before emergemerging into massive sulphide, sulphide, and and hence, hence, all the rocks of of the structural hanging grouped as as 'granite hanging wall wall were were grouped 'granite gneiss'. 'Sericite muscovite-quartzksillimanite schist, and (although (although gneiss'. 'Sericite schist' schist' was was originally originally Pye's field field term for muscovite-quartz±sillimanite corrected by Pye (1957) on on the basis of of petrography) petrography) the misnomer persists persists in the 'Mine Series'. The The 'Sericite 'Sericite Schist group' has been been viewed viewed as the the lateral lateralequivalent equivalentof of the the'lower 'lower Grey Grey Gneiss Gneiss group', group', representing representing either either a sedimentary facies (Milne, (Milne, 1974) 1974)or or an an alteration alteration product product (Friesen (Friesen et al., 1982; 1982; Bakker Bakker et al., 1985). 1985). The The 'Grey Gneiss group' corresponds to Pye's metasedimentary metasedimentary unit, later later subdivided subdivided into into lower lower (northerly) (northerly) and and upper (southerly) (southerly) members. members. The The'lower 'lowerGrey GreyGneiss Gneissgroup' group'isisapproximately approximatelyequivalent equivalenttotofelsic felsicto tointermediintermediate metavolcanic interlayered with with iron formation, extending extending from from Geco Geco to to north north of the Willecho metavolcanic rocks, interlayered Willecho area (Fig. 3). The The'upper 'upperGrey GreyGneiss Gneissgroup' group'mainly mainlyincludes includesmetagreywackes metagreywackes and and foliated foliated tonalite tonaliteoccupying occupying (Fig. synform. The The contact contact between between the the 'lower' 'lower' and and 'upper 'upper the centre of the southern southern limb limb of the Manitouwadge Manitouwadge synform. Grey Gneiss' has been been considered considered as transitional, reflecting reflecting a change change from a depositional depositional regime dominated dominated sedimentation (iron formation and suiphide by volcanism and chemical sedimentation sulphide mineralization), to one dominated dominated by by clastic 1982; Bakker al., 1985). Our Our U-Pb U-Pb dating datingof of detrital detritalzircons zirconsshows shows clastic sedimentation sedimentation (Friesen (Friesen et et al., 1982; Bakker et et a!., that the the 'upper 'upper Grey GreyGneiss Gneiss group' group' is is at at least least 25 25 Ma Ma younger younger than 'lower Grey than the 'lower Grey Gneiss Gneissgroup', group',and andthat that the former is likely metagreywackes of likely correlative with migmatized metagreywackes of the the Quetico subprovince (Zaleski (Zaleski et et al., 1995; see Geochronology). The 'Hornblende 'Hornblende Schist Schistgroup' group'corresponds correspondstotomafic maficmetavolcanic metavolcanicrocks, rocks,now nowrecognized recognized to lie at the the stratigraphic stratigraphicbase baseof ofthe theentire entiresequence. sequence. 6 �Description of units Manitouwadge greenstone belt TABLE 1 1.. Comparison of of M Map TABLE a p Units and Historical 'Mine Series' -- - Mine series series Upper Grey Grey Gneiss Gneiss -- Map units, this this work work Metasedimentary rocks (and tonalite) tonalite) (Unit (Unit 10) 10) depositional age depositional <2693 Ma'a ' <2693 ~ unconformity or fault . . . . . . . . . . . .. .. .. ... .. unconformity Lower Grey Gneiss Gneiss Felsic metavolcanic metavolcanicrocks rocks (and (and iron formation), Felsic formation), quartzitic variant quartzitic variant of of sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist (Units 1, 6, 7, 8, 9) 2720 ~Ma'a ' Sericite Sericite Schist Schist Sillimanite-muscovite-quartz schist, schist, altered altered felsic Sillimanite-muscovite-quartz felsic rocks (Unit 1) volcanic rocks 2720 Ma2 ~a~ Granite GraniteGneiss Gneiss Ortboamphibole-cordierite-garnet gneiss, gneiss, altered Orthoamphibole-cordierite-garnet altered mixed rocks (Unit (Unit 2) mixed mafic-felsic mafic-felsic volcanic rocks 2) 2720 Ma Hornblende Schist Hornblende Mafic metavolcanic metavolcanic rocks rocks (Unit (Unit 3) Mafic 1ZnIeski et al. (1995) l ~ a l e a k iet (1995) 2720 22720Ma Ma 22Davia ~ a v i aet at. al. (1994) (1994) Contradictions exist in the literature literature with with respect respect to tothe thestratigraphic stratigraphicsuccession successionand andyounging younging direction direction of the 'Mine 'Mine Series'. Series'. The Theconfusion confusionisisrelated related totothe thepresence presenceofofan anearly earlyfold, fold,originally originallyproposed proposedby bySuffel Suffel et al. al. (1971) (1971) and and Touborg Touborg (1973), (1973), that that repeats repeatsthe theaupracrustal supracrustalsuccession succession across across the southern southern limb limb of of the the Manitouwadge synform. Pye Pye (1957) (1957) assumed assumednortherly northerlyyounging youngingfor forthe theentire entirebelt. belt. Reinterpretation of the Manitouwadge synform. massive sulphide deposits as as volcanogenic volcanogenic implied a southerly southerly younging younging sequence sequence for the the Wiliroy-Geco Willroy-Geco area (Suffel et et al., al., 1971) and, and, in some cases, cases, southerly southerly younging youngingwas wasextrapolated extrapolatedto to the the entire entire belt (Friesen et al., (Suffel 1982). 1982). DESCRIPTION D E S C R I P T I O N OF O F UNITS UNITS The Manitouwadge Manitouwadge greenstone greenstone belt beltcomprises comprisesaamafic-to-felsic mafic-to-felsicsuccession, succession, the thefelsic felsiccomponent componentof ofwhich which is circa 2720 pattern isisdominated dominatedby byD3 D3folds, folds, and and the the greatest greatest thickness thicknessof of supracrustal supracrustalrocks rocks 2720 Ma. Ma. The map pattern D3Manitouwadge Manitouwadge synform (Fig. 3). Away Away from from lies hinge region region and along along the the southern southern limb limb of of the theD3 lies in the hinge the hinge region, and invaded invaded by plutonic rocks. rocks. On On the the southern southern limb, limb, region, supracrustal supracrustal units units are attentuated and the volcanic succession north and andsouth southby byaaD2 D;syncline synclinewith withaacentral centralzone zoneofofmetagreywacke metagreywacke succession is is repeated repeated to north The northern northernsequence sequence is is here referred referred to as the 'inner' volcanic volcanic belt, and the the southern southern as as the the (see Structure). The 'outer' volcanic belt, with with respect respect to tothe theinner innerand andouter outerregions regionsofofthe theManitouwadge Manitouwadgesynform. synform. All Allknown known 'outer' volcanic Cu-Zn deposits, including the the Geco, Geco, Willroy, Willroy, Nama Creek and and Willecho Willecho deposits, lie lie in the the inner inner volcanic volcanicbelt belt along the southern limb limb and andinner innerhinge hingeregion region of of the theManitouwadge Manitouwadgesynform. synform. Our definition of map units units partly partlyreflects reflectsdifferences differences in scale of mapping, exposure and accessibility; accessibility; for example, mafic, example, mafic, mixed mixed mafic-felsic, mafic-felsic,and andfelsic felsictotointermediate intermediatemetavolcanic metavolcanicrocks rocks(Units (Units3,3,44and and 6) 6) in in the inner volcanic belt belt give way way to to undifferentiated undifferentiated intermediate intermediate to to mafic mafic metavolcanic metavolcanicrocks rockstotothe thenorth north (Unit All supracrustal supracrustal rocks rocksare aremetamorphosed, metamorphosed, although although the the prefix prefix 'meta' 'meta' isissometimes sometimes omitted omitteddepending depending 5). All on the context. context. 'Alteration' 'Alteration'isisused usedtotomean meanmetasomatic metasomatic changesininwhole-rock whole-rockcomposition, composition,inferred inferredfrom from changes metamorphic and metamorphic mineral mineral assemblages assemblagesand and abundances. abundances. Unless Unlessstated, stated, timing timing isis not not implied implied by by 'alteration' 'alteration' and it could could be be synvolcanic synvolcanic (premetamorphic), (premetamorphic), synmetamorphic numbers, synmetamorphicor or post-peak post-peak metamorphic. metamorphic. The unit numbers, locations, geographic geographic names references to aeromagnetic aeromagnetic trends in the the following following discussion discussion refer locations, names and references refer to to the refer to field stops accompanying 1:25000 1:25000map, map, generalized generalizedin infigure figure3.3. Stops Stops and and figures figures prefixed prefixedby by aa letter letter refer and maps found in in the the field-trip field-trip section section of of this this volume. volume. Supracrustal rock units units Mafic rnetavolcanic is Mafic metavolcanicrocks rocks(Unit (Unit3)3)occur occurininboth boththe the inner inner and and outer outer volcanic volcanicbelts. belts. The outer belt is mafic rocks, comprising a steeply dipping section of up to to 33 km km of of interleaved interleaved hornblende-rich hornblende-rich dominated by mafic mafic mafic schists, schists, laminated laminated rocks rocks and and foliated foliated gabbros. gabbros. These are folded folded around around the hinge of of the Manitouwadge synform near in aa zone zone of high strain along the northwestern margin margin near Mills Mills Lake, Lake, and and continue continue to to the northeast in of the Manitouwadge Manitouwadge belt Nama Creek Creek pluton of beltuntil untiltruncated(?) truncated(?) by by the Nama pluton (Unit (Unit 13a). 13a). To the east east on on the the limb of the the Manitouwadge Manitouwadge synform, synform, the unit thins thins and andisisincreasingly increasingly engulfed engulfed by by plutonic plutonic rocks. rocks. southern limb 7 �Manitouwadge greenstone belt 8 --\\ LEGEND Foliated K-feldspar porphyritic granitoid Foliated tonalite felsic to intermediate meta volcanic rocks,sillimanite-muscovite schist Metasedimentary rocks Ij [ [ IOrthoamphibole-cordierite-garnet gneiss Metamorphosed iron. formation - Intermediate to mafic melavolcanic rocks - Fold axial trace Fault # - Aeromagnetic or foliation trend (t a) C' a)U) l) d o U) o a).— .4-i ' Cl) Q) 0 a) 0 0 'a)Oa) d U) -4-, a) 1.OO U) C) 0I- C) .4-' C) a) cj.c .— (j._ 0 C) _U)U)C) •U) U) — a) ' a)4_' N a)r-.,C )0r .4-, a) -' o C) C) . a) - a) -E'4-. OI.a) — I C) ., a) c' Cl) C) Q --'.0 Cl) '4_l) O o C C)O a) • —000 ) 0 C) Description of units o O-'0 — FIG. 3. Generalized geology of t h e Manitouwadge greenstone belt, omitting diabase dykes (see the accompanying 1:25000 map for details). The regional structure is dominated by major Dn folds; the Manitouwadge synform, Blackman Lake antiform and Jim Lake synform. The inner and outer volcanic belts a r e correlative, repeated by a Dg syncline, the axial trace of which lies in metasedimentary rocks on the southern limb of t h e Manitouwadge synform (Fig. 5). Asterisks mark economic and subeconomic base-metal deposits. The area detailed in Figure 4 is outlined. A-A' is t h e trace of the projection in Figure 7. �Description of units Manitouwadge greenstone belt of the the Banana Lake antiform is poorly exposed, but foliation trends in in the the enclosing enclosing tonalite tonalite The hinge region of suggest a possible connection to to the Faries Lake Lake belt belt (Fig. (Fig. 2). 2). Aeromagnetic trends are more consistent with an easterly continuation continuationof of the the mafk maficunit, unit,although althoughweak weak trends trendsobscured obscuredby by diabase diabase dykes dykes may be consistent with by the the Banana Lake antiform. In trondjemite folding by In the theinner innervolcanic volcanic belt, belt,mafic mafic inclusions inclusions in synvolcanic trondjemite (Unit 12), near-continuous screens screens traceable traceable in in outcrop outcrop for for distances distances of of 3.5 3.5 km km (from (from the the 12), in some some cases, form near-continuous Mose Lake Lakefault fault to to the the road road east of Wowun Lake). Mafic Maficrocks rocksofofUnit Unit33are are transitional transitionalto to the the south south to Mose Wowun Lake). interleaved mafic-felsic mafic-felsic metavolcanic rocks (Unit 4). 4). Mafic metavolcanic rocks rocks are are strongly strongly foliated, fine grained, grained, homogeneous homogeneousto to thinly thinly layered Mafic metavolcanic layered schists, and medium to coarse grained grained metagabbro, typically interlayered. interlayered. In the area of medium of detailed detailed mapping mapping between between Mills and Swill Swill Lakes, Lakes, layers layers of schist schist and and metagabbro metagabbroare are50—100 50-100 metres (Fig. B3). B3). Near Near Gaug Gaug Lake, Lake, metres thick thick (Fig. metagabbro forms forms aa larger metagabbro larger body in fine fine grained schist. The Themetagabbro metagabbroisiscommonly commonly aa hornblende-augen hornblende-augen cmininsize), size),locally locallywith with well welldeveloped developedasymmetric asymmetrictails, tails, lie lie in in a fine schist in which lenticular augen augen (0.5—1 (0.5-1 cm matrix. In some high strain zones, metagabbro or augen schist schist is is transitional transitional to fine grained grained schistose matrix. homogeneous schist, schist, suggesting suggesting that that some schist could could have have originated originated as gabbro, homogeneous some homogeneous schist gabbro, commmuted comminuted by deformation (Stop B15). B15). In both the theinner innerand andouter outervolcanic volcanicbelts, belts,mafic maficschists schistsare arelocally locallypillowed pillowed but, but, with with few few exceptions, exceptions, deformation makes makes younging younging or or structural structural facing determinations suspect. In deformation In an anexposure exposurebetween between Swill Swill and and Mills Lakes, Lakes, pillow pillowshapes shapessuggest suggestsoutherly southerly younging younging(Stop (Stop B14), B14), and and northerly northerly younging has been reported west of of Gaug Gaug Lake Lake (W. (W. Bates, Bates, Granges Inc., pers. pers. comm., 1992). In view in the west Granges Inc., comm., 1992). view of the polyphase polyphase folding folding in Manitouwadge belt, belt, these these few few younging youngingdeterminations determinationscontribute contributelittle little to to regional regional interpretation. interpretation. Manitouwadge schists consists consists of ofhornblende-plagioclasekgarnet&biotite&clinohornblende-plagioclase±garnet±biotite±clinoThe typical mineral assemblage assemblage in mafic schists pyroxene with with quartz, magnetite, titanite, titanite,sulphide sulphideminerals minerals and and apatite apatiteininaccessory accessory or or trace trace amounts. amounts. LamiLaminations Iamellae. Epidote occurs in calc-silicate calc-silicate lenses lensesor orboudins. boudins. Garnetiferous Garnetiferous nations are are defined defined by plagioclase-rich lamellae. zones (up to 40% garnet), in some cases cases with with quartz, quartz, magnetite and cummingtonite, cummingtonite, are particularly particularly common common in mafic schists schists in the outer outer volcanic volcanic belt. Near Near the thenorthern northerncontact contacttotometagreywacke, metagreywacke,mafic mafic rocks rocks of the outer belt interleaved felsic felsicschist, schist,foliated foliatedtonalite, tonalite, garnetiferous garnetiferous hornblendebelt are areinvolved involved in in aa complex complex zone of interleaved biotite±magnetite biotitehmagnetite gneiss, gneiss, iron iron formation formationand andorthoamphibole-plagioclase±garnet±magnetite±hornblende orthoamphibole-plagioclase&garnet&magnetite&hornblende gneiss (Stops (Stops B Bil and gneiss and B20). B20). The intensity intensity of of deformation deformation generally generally makes it difficult difficult to unambiguously identify the physical protolith to mafic interlayered with with schists may be mafic rocks. rocks. Metagabbros Metagabbros interlayered be massive massive flows, flows, massive massive bases bases of flows, flows, or sills. Some origin, but highly sills. Some laminated laminated mafic mafic schists may have have had aa tuffaceous tuffaceous or or volcaniclastic volcaniclastic origin, highly strained strained pillowedflows flowscould couldalso alsobebepresent. present. Orthoamphibole-bearing Orthoamphibole-bearingrocks rocksnear nearthe thenorthern northern contact contact of of the the outer pillowed orthoamphibole-cordierite-garnet gneiss gneiss of the belt are are interpreted interpreted as asequivalent equivalentto tothe themuch muchmore moreextensive extensiveorthoamphibole-cordierite-garnet inner belt, and alteration (see (see Unit Unit 2). 2). However, inner and hence hence as as metamorphosed metamorphosed synvolcanic synvolcanic alteration However, at least some some of the garnet±cummingtonite zones zones of ofthe the outer outer belt belt are apparently discordant of garnetkcummingtonite discordant to tectonic tectonic fabrics, fabrics, and hence, hence, of later origin (Stop B20). B20). Mixed mafic-felsic mafic-felsicmetavolcanic metavolcanicrocks rocks(Unit (Unit4)4)ofofthe theinner inner volcanic volcanicbelt beltlie liemostly mostlyalong alongthe the transitional transitional contact between mafic rocks north, and and felsic felsic (Units 6 and 8) and orthoamphibole-bearing rocks rocks rocks (Unit 3) to the north, trondhjemite (Unit 2) 2) to to the thesouth. south.Mixed Mixedmafic-felsic mafic-felsic rocks rocks also also form form inclusions inclusions and screens in synvolcanic trondhjemite (Unit 12) 12) north north and andeast eastofoforthoamphibole-bearing orthoamphibole-bearingrocks. rocks.Layering Layeringofofmafic maficand andfelsic felsiccomponents components(cm—i (cm-1 m width) might might suggest suggest contemporaneous contemporaneous mafic mafic and and felsic felsic volcanism, volcanism, or tectonic tectonic interleaving. interleaving. Mafic Maficlayers layers are more abundant than thanfelsic, felsic,and andconsist consistofofdark, dark,fine finegrained, grained,strongly stronglyfoliated, foliated,hornblende-plagioclase hornblende-plagioclase without magnetite, magnetite, quartz, quartz,cummingtonite, cummingtonite, biotite biotite and and garnet garnetand andgenerally generallysimilar similar to tomafic mafic schist, with or without schist Layers rich rich in in biotite, and garnet garnet are more schist of Unit 3. 3. Layers biotite, cummingtonite cummingtonite and more common common near the the southern southern contact. Intercalations Intercalationsofofquartz-rich quartz-richfelsic felsicand andleucofelsic leucofelsicschist contain plagioclase, plagioclase, biotite and, and, locally, locally, quartz quartz phenocrysts, phenocrysts, magnetite and and garnet. garnet. West WestofofFox FoxCreek, Creek,outcrops outcropsofoffelsic felsicschist schist with withelongate elongatehornblendehornblendericher patches or 'clasts' are inclusions in in aa trondhjemite trondhjemite areinterpreted interpretedasasan anintrusion intrusionbreccia brecciaof ofmafic mafic volcanic volcanic inclusions matrix. of Garnet Garnet Lake Lake and and west west of of orthoamphibole-bearing orthoamphibole-bearing Unit 2 were were also also Two areas of mafic rocks north of grouped with mixed mafic-felsic mafic-felsic rocks. the rocks rocks are are charchargrouped rocks.These Theseare are somewhat somewhatatypical atypicalofofthe theunit unit in in that the acterized by abundant abundant calc-silicate calc-silicate minerals minerals including including Ca-amphibole, Ca-amphibole, epidote, epidote, clinopyroxene, clinopyroxene, titanite and acterized titanite and plagioclase, as Microcline, garnet and calcite are present in in minor minor amounts. amounts. Diffuse Diffuse semiconsemiconplagioclase, as well well as as quartz. quartz. Microcline, lenses (typically (typically 0.5—30 0.5-30 cm and grain grain tinuous layers or lenses cmininwidth) width)are are defined definedby byvariations variations in in the the abundance and size of of calc-silicate calc-silicate and and felsic felsicminerals. minerals. In In some some cases, cases,quartz quartz eyes eyes resemble resemblerelict relictphenocrysts. phenocrysts. The The origin origin of of these they are are the the result result of of these rocks rocks and and their relationship relationship to to more more typical typical Unit Unit 44 isis uncertain; uncertain;but but itit may may that they alteration of of felsic felsic volcanic volcanic rocks, rocks, possibly possibly with with interleaved interleaved mafic mafic rocks. rocks. calc-silicate alteration Intermediate mafic metavolcanic metavolcanic rocks rocks (Unit (Unit 5) 5) comprise comprise aaheterogeneous heterogeneous group group of of undifferentiundifferentiIntermediate to mafic ated rocks, rocks, dominantly dominantlyhornblende-plagioclase, hornblende-plagioclase,hornblende-plagioclase-biotite hornblende-plagioclase-biotite and andhornblende-plagioclasehornblende-plagioclasegarnet±clinopyroxene±magnetjte garnet&clinopyroxene&magnetite schists, and and foliated foliated diorites. diorites. The unit defines defines the attenuated attenuated northern northern 9 �Manitouwadge greenstone belt Description of units limb folds to to the north (Blackman limb of the the Manitouwadge Manitouwadge synform and related map-scale folds (Blackman Lake Lake antiform, Jim Lake synform). Between Between Rabbitskin RabbitskinLake Lakeand andthe therailway railwaywest westofofFox FoxLake, Lake,exposure exposureisispoor poorand andinaccessible; inaccessible; however, aeromagnetic trends trends suggest that that the however, aeromagnetic the unit unit isis continuous continuous east to to One One Otter OtterLake. Lake.West WestofofRabbitskin Rabbitskin Lake, fine fine to medium medium grained, grained, mafic mafic to to intermediate intermediateschist schistand andminor minorfelsic felsicschist schistare arehomogeneous, homogeneous,lamilaminated nated or or layered, layered, and and host host many manyintrusions intrusions of of foliated foliated pegmatite, pegmatite, granite granite and and tonalite. tonalite.Garnetiferous Garnetiferouszones zones and patches, garnet porphyroblasts porphyroblasts and and lesser lesser amounts amounts (<lo%) (<10%) of magnetite, patches, in in some somecases cases with with30—40% 30-4076 garnet are are common. common. South SouthofofFox FoxLake, Lake,laminated laminatedtotolayered layered(1(1mm—10 mm-10 cm), cm), fine fine grained, grained, mafic mafic to to intermediate intermediate metavolcanic rocks rocks are are present present both north and asinclusions. inclusions. The Theminminand south south of of the the Nama Nama Creek Creek pluton, pluton, and andas eral hornblende-plagioclase±clinopyroxene±quartz±biotite, with eral assemblage assemblage includes hornblende-plagioclasekclinopyroxenekquartz&biotite, withepidote epidotelocally locallyininknots, knots, and and accessory accessory titanite, titanite, magnetite magnetiteand andapatite. apatite.Southeast SoutheastofofFox FoxLake, Lake,exposures exposuresofofheterogeneous heterogeneousinterleaved interleaved (1 cm—i m) foliated foliated pegmatitic pegmatitic granite, biotite cm-1 m) biotite and andhornblende-biotite hornblende-biotitefelsic felsic schist schist locally locally grade grade to togarnetifgarnetiferous strongly magnetic magnetic gneiss. gneiss. Garnet Garnetporphyroblasts porphyroblastscomprise compriseup uptoto50% 50%ofofthe thegneiss, gneiss,occurring occurringininlenses lenses (2—3 cmwide) wide)between between anastomosing anastomosing mafic layers of of fine grained hornblende, (2-3 cm hornblende, clinopyroxene clinopyroxene and and magnetite. magnetite. In some some cases, cases, quartz eyes eyes and aggregates aggregates are abundant. The Themagnetic magneticgneisses gneisses undoubtably contribute contribute to to the the high high aeromagnetic aeromagnetic signature signature of of the the area. area. In the thevicinity vicinityof of the theBlackman BlackmanLake Lake and andJim JimLake Lakefolds, folds,the theManitouwadge Manitouwadgebelt beltcomprises comprisesthinly thinlylayered, layered, fine to medium grained, mafic to intermediate well as as foliated foliated diorite and gabbro that intermediate metavolcanic metavolcanic rocks, as well that may rocks. The rocks are commonly strongly magnetic may be be recrystallized recrystallized homogeneous homogeneous volcanic or subvolcanic rocks. and, in in addition, addition, are areinterleaved interleaved with with minor minor iron iron formation formation (Stop E6). E6). The TheJim JimLake Lakesynform synformisisdefined defined by mappable mappable zones zones of mafic to intermediate intermediate screens screens and inclusion inclusion swarms in foliated tonalite and and pegmatite. pegmatite. mafic to intermediate intermediateblocks blocks (with (with discordant discordant foliation foliation trends) trends) in inan anintrusive intrusivematrix matrixresemble resemble Locally, rotated rotated mafic agmatite agmatite or or intrusion intrusion breccia. breccia. At At least leasttwo twonearly nearlycontinuous continuouszones zonesof ofmafic maficrocks rocks can can be bemapped mappedinside insidethe theManitouwadge Manitouwadgesynform, synform, zones of high variable variable aeromagnetic aeromagnetic relief. relief. These These rocks, rocks, here here called called the theDead DeadLake Lakesuite, suite, corresponding to zones comprise aa complex complex association association of of interleaved foliated gabbro, diorite, diorite, and and layered layered mafic mafic to to intermediate intermediaterocks rocks comprise of probable supracrustal origin. origin. The TheDead DeadLake Lake suite suiteincludes includes aa distinctive distinctive group group of of strongly strongly magnetic magnetic rocks rocks of characterized by by hornblende-magnetite±plagioclase±garnet±clinopyroxene±sulphicie hornblende-magnetitekplagioclasekgarnetkclinopyroxeneksulphide minerals, with with variable variable characterized amounts irregular lenticules (Stops C3—C5). amounts of of quartz quartz (minor (minortoto50%) 50%)ininquartz quartzeyes eyesand and irregular lenticules (Stops C3-C5). Titanite Titanite and and apatite are arepresent presentininminor minoramounts amounts(1—3%), (1-3%), and monazite in trace trace amounts. amounts. apatite and allanite/epidote, zircon and monazite hornblende-magnetite&garnet rocks rocks are usually fine fine to medium grained grained and homogeneous, homogeneous, at The hornblende-magnetite±garnet at least at hand-sample scale. Themore moreleucocratic leucocratic varieties varieties resemble resemble synvolcanic synvolcanic trondhjemite with hand-sample scale. The trondhjemite (Unit (Unit 12), but with disseminated hornblende, and/or magnetite. magnetite.However, However,ininmany manycases, cases,thin thinlayering layering(1—5 (1-5 cm) cm) and and disseminated hornblende, garnet garnet and/or grading, interpreted interpretedasasmodified modifiedbedding, bedding, isis defined defined by by variations variations in in grain grain size size and mineral mineral abundances abundances (Stop (Stop grading, C4). C4). Layered Layered rocks rocks are associated with magnetite-bearing quartzites (metachert?) (metachert?) or or with withmafic maficmetavolcanic metavolcanic rocks with with garnet-cummingtonite(?) garnet-cummingtonite(?)concentrated concentratedinininterconnected interconnectedganglions. ganglions.Field Fieldobservations observationssuggested suggested rocks an origin origin as asmetamorphosed metamorphosed and and digested digested (by (by intrusion) intrusion) ferruginuous ferruginuous chert (G. (G. Stott, Stott,Ontario OntarioGeological Geological an Survey, Survey, pers. comm., comm., 1994) 1994) and iron formation. formation. These These proposals proposals are are supported supportedby by an an exposure exposure on on the thewestern western shore of of Wowun Wowun Lake, in which foliated granite contains contains inclusions inclusions of mafic rock shore rock and and weakly weakly magnetic magnetic quartzrich layered layered iron formation, the latter latter dispersed dispersed over over a width of of 2 to 33 metres. metres. However, However, the high TiO2 TiOs and rich Zr Zr geochemistry geochemistry of magnetite quartzite, quartzite, hornblende-magnetite±garnet hornblende-magnetitekgarnet rocks rocks and and garnet-horublende-bearing garnet-hornblende-bearing trondhjemiteare aremore moreconsistent consistentwith withsedimentary sedimentaryconcentration concentrationof of heavy heavy minerals, minerals, rather rather than thaniron ironformation formation trondhjemite (see (see Geochemistry). Geochemistry). The The relationship relationship of of the the Dead Dead Lake Lake suite suitetotothe themain mainsupracrustal supracrustalassemblage assemblageisisproblematic. problematic. The The two two zones zones of of the the suite suiteare areindistinguishable indistinguishable and and may mayrepresent represent aastructural structuralrepetition. repetition. They They are aresimilar similar to mafic maficrocks rockselsewhere elsewhere in in the theManitouwadge Manitouwadgebelt, belt,especially especiallygarnetiferous garnetiferousmafic maficrocks, rocks,but buthornblendehornblendeto magnetitekgarnet rocks rocks and andassociated associated layered layered magnetite magnetite quartzite quartzite are are unusual. unusual. Aeromagnetic Aeromagnetic trends trends corcormagnetite±garnet responding to to the theDead DeadLake Lakesuite suitecontinue continue easterly easterly both both north northand andsouth southofofthe thecentral centralLoken LokenLake Lakepluton pluton responding 13b). On On the thesouthern southern side, side, the theaeromagnetic aeromagnetic trend tends to to converge converge with the main main southern southern limb limb of of (Unit 13b). (Unit the Manitouwadge Manitouwadge synform. synform. Rocks Rocks similar to the garnet-hornblende garnet-hornblende 'trondhjemite' 'trondhjemite' occur occur east east of of Banana BananaLake Lake the orthoamphibole-garnet-cordierite screens in plutonic plutonic rocks rocks (Stop (Stop D4). D4). North Northof of in association association with with mafic mafic and and orthoamphibole-garnet-cordierite in screens the Loken Loken Lake Lake pluton, pluton, aa pronounced pronounced aeromagnetic aeromagnetic anomaly extends north of of Straight, Straight, Loken Loken and Thompson Thompson the Lakes, Lakes, and apparently apparently continues continues around around the the hinge hinge of of the the Blackman Blackman Lake antiform. The The same same distinctive distinctiverock rock exposedeast eastofofLarry LarryLake, Lake,enclosed enclosedby bytrondhjemite trondhjemite type (grouped (grouped with with the theDead DeadLake Lakesuite suiteofofUnit Unit5)5)isisexposed type to the thenorth northof ofthe themain mainsupracrustal supracrustalbelt. belt.Along Alongthe thenorthern northerncontact contactofofthe theLoken LokenLake Lakepluton, pluton, aazone zone of of to mafic rocks rocks associated associated with with subeconomic subeconomicZn Zn mineralization mineralization (Noranda's (Noranda's Straight StraightLake Lakezone) zone) may may also alsobelong belong mafic to tothe theDead DeadLake Lakesuite. suite. 6) are are among among the the most most unsatisfying unsatisfying and and frustrating frustratingof of Felsic to to intermediate intermediatemetavolcanic metavolcanic rocks rocks (Unit (Unit 6) Felsic units totomap, map,consisting consistingofofsubtly subtlyheterogeneous heterogeneousand andtransitional transitionallithologies lithologiesincluding: including: fragmental fragmentalrocks; rocks; units calc-silicate, sillimanite-muscovite, sillimanite-muscovite, and and felsic-intermediate felsic-intermediate schists; straight gneiss gneiss (see (see Unit Unit 11); 11); and and foliated foliated calc-sihcate, 10 �Description of units Manitouwadge greenstone greenstone belt tonalite, but but generally generally without without marker marker units units to toallow allow useful useful subdivision. The unit unit contains contains lithologies lithologies typical of Units 1, as minor minor exposures exposures typical typicalofofUnits Units22and and 3, 3, but but not on a mappable scale. 1, 7, 8, 11 11 and 14, 14, as well well as of some of of the complexity is probably probably due due to In the the inner inner hinge hinge region region of of the theManitouwadge Manitouwadge synform, synform, some complexity is cryptic early faults faults and and folds folds (see (see Structural StructuralGeology). Geology). Homogeneous Homogeneous to to weakly weakly layered, layered, quartz-phyric quartz-phyric and Microcline is heterogeneously aphyric schists with with minor biotite±muscovite aphyric felsic felsic schists biotiteztmuscovite are predominant. predominant. Microcline heterogeneously disdislayers. In tributed, in in some some cases cases absent absent entirely, entirely, or or in inothers, others,confined confined to tomillimetre-wide millimetre-wide microcline-rich microcline-rich layers. the vicinity vicinity of of the thetwo twoiron ironformation formationlayers layerssouth southofofthe theWillecho Willechodeposit, deposit,felsic felsicrocks rockssporadically sporadicallyconconbetain large large zoned sillimanite sillimanite knots identical to those those of of Unit Unit lbl b(aillimanite-knot (sillimanite-knotfelsic felsic schist) schist) described described be" zoned low. Fragmental-looking enclaves in in an intermediate matrix low. Fragmental-looking rocks have lenticular aphyric felsic enclaves matrix containing containing biotite±hornblendegarnet±magnetite. The biotite&hornblende&garnet&magnetite. Thefragmental fragmentalappearance appearance may may be be partly partly an an artifact artifact of of tectonism tectonism or alteration. alteration. Where Wherethe thematrix matrixisismore morefelsic felsicinincomposition composition(less (lessaltered?), altered?),felsic felsicenclaves enclavesare aremore moredefined defined and resemble clasts in an volcaniclastic or epiclastic breccia. breccia. The outer outer hinge hinge region from Nama Creek to Swill Lake, is underlain by felsjc felsic to intermediate intermediate metavolcanic metavolcanic rocks and biotite biotite schist schist (mostly (mostly metasedimentary?) metasedimentary?) invaded by by foliated tonalite. Aphyric felsic felsic metavolcanic metavolcanicrocks rocks(Unit (Unit7)7)are are present present in in the the outer volcanic Aphyric volcanic belt in three three main mainareas; areas; interlayeredwith with mafic maficrocks rocks(Unit (Unit3) 3) in in the Swill-Mills Lakesarea, area,north northofofGaug Gaug Lake, Lake,and and north north of of interlayered Swill-Mills Lakes Lake near near the Fox Manitouwadge Lake Fox Creek fault. In Inthe theSwill-Mills Swill-MillsLakes Lakes area, area, two two semicontinuous semicontinuous felsic felsic units markers outlining map-scale map-scale symmetrical symmetrical and and asymmetrical asymmetrical folds folds near near the hinge region of the form useful useful markers synform (Fig. (Fig. B3). B3). The southernmost Manitouwadge synform southernmost unit, unit,up uptoto50 50metres metresthick, thick,can canbe berecognized recognizedlocally locallyas as of fine grained to aphanitic a highly deformed deformed monolithologic monolithologic felsic breccia, consisting of aphaniticlapilli-size lapilli-size felsic felsic clasts clasts B12 and and1313). B13). The The breccia brecciaisisassociated associated in a matrix matrixof of biotite-muscovite biotite-muscovite or or garnet-hornblende garnet-hornblende schist schist (Stops (StopsB12 disseminated pyrite pyrite and and pyrrhotite (Stop B14). with minor iron formation and, locally, disseminated B14). North of Gaug Lake, aphyric felsic rocks and and interleaved interleavediron ironformation formation (Unit (Unit 9) 9) lie lie along along or or near the North felsic rocks metavolcanic rocks rocks (Unit (Unit 3) and metagreywacke (Unit 10). The contact between mafic metavolcanic metagreywacke (Unit Thefelsic felsicrocks rocks include include homogeneous schist, and monolithologic monolithologic and heterolithic volcaniclastic volcaniclastic breccias. Monolithologic Monolithologicclasts clasts mostly mostly vary from 2 to to10 10centimetres centimetres ininsize, size,but butsome somebreccias brecciashave havelarge large(cm—m (cm-m scale) angular clasts clasts (Stop (Stop B4). B4). Some large clasts have reentrant reentrant angles, angles,and andsome somenearest nearestneighbours neighbourshave havecomplementary complementaryshapes shapessuggestive suggestive of in situ fragmentation fragmentation of larger blocks. blocks. The The matrix matrix isisfelsic felsic to to intermediate, intermediate, normally normally containing containing biotite, but in and garnet garnet porphyroblasts. interpreted as in some some cases, cases, dominated dominated by hornblende hornblende and porphyroblasts. The breccias breccias were were interpreted Granges Inc., pers. pers. comm., comm., 1992) 1992) or or proximal volcanic volcanic deposits, deposits, possibly possibly derived derived from from phreatic phreatic (W. Bates, Granges hydrothermal limited transportation. transportation. Heterolithic hydrothermal explosions involving limited Heterolithic breccias breccias contain contain felsic felsic and hornblendegarnet-rich garnet-rich clasts clasts (generally (generally 2 to to 10 10centimetres centimetres in in size), size),typically typically inina abiotite-hornblende-garnet-bearing biotite-hornblende-garnet-bearing that matrix. The Thehornblende-garnet hornblende-garnet clasts clastsresemble resemble matrix matrix material materialofofmonolithologic monolithologic breccias, suggesting suggesting that reworked proximal deposits were a source for heterolithic breccias (Stop B5). reworked B5). North of Manitouwadge Lake and south of the Agam Lake fault, fault, exposures of of white white laminated laminated quartz-rich felsic schists schists are are interpreted interpreted as volcanic volcanicor orintrusive intrusiverocks. rocks.To Tothe thenorth, north, they they are bounded bounded by by a topographic felsic depression markingthe thetrace traceofofthe the Agam AgamLake Lakefault. fault. On On the the north north side side of of the the fault, fault, the biotite schist depression marking schist is typical of metasedimentary metasedimentary rocks rocks of of Unit Unit 10. The have aa strong fabric, possibly related to the typical of The felsic felsic rocks rocks have possibly related the fault, defined by partially annealed quartz quartz ribbons, ribbons, minor minor biotite biotite and andmuscovite. muscovite. Quartz-phyric feisic met avol canicrocks rocks(Unit (Unit8), 8),ininthree threebodies bodiesininthe theinner inner volcanic volcanicbelt, belt, are are spatially felsic metavolcanic associated with with the known with iron formation (Unit associated known mineral deposits. Quartz-phyric Quartz-phyric rocks are interlayered interlayered with sulphide deposits deposits hosted hosted by iron formation, and sillimanite-muscovite-quartz schist (Unit (Unit 1); at 9), massive massive sulphide sillimanite-muscovite-quartz schist least some of of the the interlayering interlayering isis interpreted interpreted to to be due to structural least structural repetition repetition by by early early faults faults and and folds folds (see (see 20%,typically typically1—3 1-3 Structural Geology). Geology). The The unit unit isischaracterized characterized by byabundant abundantquartz quartzphenocrysts phenocrysts(up (uptoto20%, forming lenticular lenticular augen, augen, in in a fine grained grained biotite felsic matrix. The mm in size), commonly forming felsic to leucofelsic leucofelsic matrix. matrix consists consists of quartz, quartz, plagioclase, plagioclase, microcline and biotite, with with accessory accessory or trace trace amounts amountsof of muscovite, muscovite, epidote and garnet. garnet. Magnetite Magnetiteporphyroblasts porphyroblasts(1—3 (1-3 mm in size) are prominent. As As in in felsic felsic rocks rocks of of Unit Unit 6, 6, microcline and and muscovite muscovite are are heterogeneously heterogeneouslydistributed, distributed, even evenon on aa thin-section thin-section scale, scale,suggesting suggestingthat that their their microcline presence is is related related to potassic alteration rather presence rather than thanprimary primarymagmatic magmaticcomposition composition(see (see Geochemistry). Geochemistry). In In some cases, quartz-phyric rocks grade to to aphyric aphyric rocks, rocks, especially especially toward contacts. The three schists and and fragmental fragmental rocks, rocks, the the latter both monothree quartz-phyric quartz-phyric bodies bodies include include homogeneous homogeneous schists monolithologic and heterolithic. heterolithic. In Inone onelocation, location,angular angularmonolithologic monolithologic quartz-phyric quartz-phyric felsic felsic clasts, ranging from large large (>0.5 (>0.5 m) m) to to small small (<1 (<1cm), cm),are areunsorted unsortedand andapparently apparentlymatrix-supported, matrix-supported, ininaamicrocline-biotitemicrocline-biotiteepidote-horublende matrix (Stop A18). epidote-hornblende matrix A18). The The breccia breccia could could be be aa proximal proximal volcaniclastic volcaniclastic deposit, or aa flow-top flow-top (<I-30 cm cm or flow-foot flow-foot breccia. More Moretypically, typically,volcaniclastic volcaniclasticrocks rockscontain containlenticular lenticularlapilli-size lapilli-sizefragments fragments(<1—30 long), and both fragments and matrix long), matrix contain contain quartz quartz phenocrysts phenocrysts (Stop A3). The The clasts clasts show show subtle variavariation in colour and grain size that could could be be attributed attributed totovariable variableresponse response to to alteration alteration (e.g. (e.g. devitrification, devitrification, Willroy-Geco diagenesis, alkali-exchange) of oforiginally originallycomagmatic comagmaticcrystalline crystallineand and glassy glassycomponents. components. In In the Wiliroy-Geco area, the the matrix matrixcontains contains muscovite, muscovite, biotite, biotite, garnet garnet and andmagnetite. magnetite.North NorthofofWillecho, Willecho,fragmental fragmentalrocks rocks are are \ 11 �Description of units Manitouwadge greenstone belt more difficult to identify unambiguously. calcunambiguously. Diffuse Diffuse lenticular quartz-phyric quartz-phyric felsic felsic enclaves are present present in in aacalcmatrix including plagioclase, Ca-amphibole, Ca-amphibole, epidote epidote and and garnet, garnet, as well as magnetite, muscovite silicate-rich matrix and microcline. microcline. In all three quartz-phyric bodies, bodies, the the abundance abundanceof of caic-silicate calc-silicate minerals tends to to increase increase toward contacts contacts with formation. In the the Willroy Willroy area, area, outcrops outcrops dominated dominated by bythe thecaic-silicate calc-silicateminerals; minerals; plagioclase, plagioclase, with iron formation. clinopyroxene,Ca-amphibole, Ca-amphibole,garnet, garnet,epidote epidoteand and titanite, titanite, can be clinopyroxene, be traced traced laterally laterallyinto intoquartz-phyric quartz-phyricfelsic felsic rocks (Stop A4). The rocks The calc-silicate calc-silicate rocks rocks were interpreted as as metasomatically metasomatically altered. altered. Metamorphosed iron iron formation (Unit (Unit 9) three subunits; a) quartz-magnetite 9) includes three quartz-magnetite iron iron formation, formation, b) b) Metamorphosed silicate iron iron formation, formation, and and c) c) sulphidic suiphidic iron iron formation. formation. These These occur occur in in both both the inner silicate inner and and outer outer volcanic volcanic rocks (Units (Units 6, 7 and and 8) and sillimanite-bearing schist (Unit belts, interlayered mostly with felsic felsic metavolcanic rocks 1). Most associated with with quartz-magnetite iron iron formation that that grades laterally to Most of the Cu-Zn Cu-Zn orebodies are associated to sulphidic iron formation and and to to massive massive sulphide sulphide (Pye, (Pye, 1957; 1957; Timms Timms and and Marshall, Marshall,1959; 1959;Friesen F'riesen et et al., al., 1982). 1982). Quartz-magnetite iron formation, formation, by by far the most abundant type, Quartz-magnetite type, isis characterized characterized by by alternating alternating white white coarse grained (recrystallized) (recrystallized)quartz quartzlayers layersand anddark darkmagnetite~grunerite~actinolite~garnet&clinopyroxene magnetite±grunerite±actinolite±garnet±clinopyroxene coarse grained layers. The relative minerals is is variable variable and and even even magnetite magnetite is is present present only only in in trace layers. relative proportions proportions of of iron-rich minerals amounts, or absent, in in some some cases. cases. Suiphide Sulphide minerals minerals (pyrrhotite, pyrite, pyrite, sphalerite, sphalerite, chalcopyrite) chalcopyrite) and carcarbonate may be present present in minor minor or or trace trace amounts, amounts, as aswell well as as stilpnomelane, stilpnomelane, apparently of retrograde origin. Layering, interpreted interpreted as aa modification precipitated bedding, bedding, varies varies from from dark lamellae Layering, modification of chemically chemically precipitated lamellae in aa quartz-dominated rock to to dark dark and andlight lightlayers layersof of 10 10 centimetres centimetres or or more more in in width. width. Iron Ironsilicate silicateminerals, minerals,esescmlength), length), typically with weakly developed pecially grunerite, vary vary from from medium medium to tovery verycoarse coarsegrained grained(1—5 (1-5 cm at least in D2 folds. tectonic fabrics. However, However, at in some some localities, grunerite defines a foliation axial planar to to D2 is commonly commonly disrupted disrupted by by breccia breccia zones zones and and outcrop-scale outcrop-scale folding. folding. A A tectonic tectonic origin is indicated indicated Layering is for minor folds by by the observation that systematic systematic changes changes in asymmetry asymmetry are related related to tomap-scale map-scale D2 D2 folds. folds. Breccia zones zones of ofangular angular and and rotated rotated quartzose fragments in a dark Breccia dark magnetite-silicate magnetite-silicate matrix matrixare aresandwiched sandwiched between coherent layers layers (Stop A22), features features typical of intraformational breccias. between coherent breccias. However, However, the apparently apparently competent behaviour behaviour of of quartzose fragments fragments suggests that that brecciation brecciation occurred occurred after afterdiagenesis diagenesisor or low low grade grade metamorphism. Tectonic Tectonic fragmentation fragmentation isis also also suggested suggested by by local local breccia breccia zones zones in the the hinges hinges of of minor minor folds, folds, and by quartzose quartzose fragments that that preserve preserve fold fold hinges. hinges. In In the the case case of of breccias breccias related to to folds, folds, dark dark iron-rich iron-rich material encloses encloses quartzose fragments, fragments, evidently evidently having having migrated migrated into intothickened thickened hinge hingeregions. regions. Silicate iron iron formation is dark the dark layers Silicate dark and and homogeneous, homogeneous, resembling resembling the layers in in quartz-magnetite quartz-magnetite iron iron formation, except except that that garnet garnet tends to be formation, be coarser coarser and and more more abundant. abundant. Minor Minor amounts amounts of of quartz quartz may may be be present, dispersed Silicate iron iron formation formation occurs occurs mainly mainly near near the contacts present, dispersed among the iron-rich iron-rich minerals. minerals. Silicate contacts of quartz-magnetite quartz-magnetite iron iron formation. formation. It may unit or stratiform alteration of may represent represent an an original original depositional depositional unit related to iron formation contacts. Alternatively, related Alternatively, its similarity to iron-rich material in quartz-magnetite iron evidence of of outcrop-scale outcrop-scale remobilization, remobilization, suggest silicate iron formation formation may may represent represent formation, and evidence suggest that that silicate large-scale large-scale remobilization remobilization and and segregation segregation of of material material derived derived from from quartz-magnetite quartz-magnetite iron formation. Suiphidic iron iron formation is generally generally similar similar to to quartz-magnetite iron formation, but with Sulphidic with disseminated disseminated or stringer rarely forms forms a mappable unit, occurring mainly stringer pyrite, pyrrhotite or sphalerite. ItIt rarely mainly in in the the transition iron formation formation to to massive massive suiphide sulphide (Stop A3). from quartz-magnetite iron the inner inner volcanic volcanicbelt belt along alongthe thesouthern southernlimb limbofofthe theManitouwadge Manitouwadgesynform, synform,iron ironformation formationdefines defines In the Southwest of of the theNama NamaCreek Creek deposit, deposit, the themost mostsoutherly southerlyiron ironformation formationisisthickened thickened by by four main belts. Southwest D2 folding (see (see Structural Structural Geology). formation is is present present along along its its northern contact D2 folding Geology). Silicate iron formation contact and and forms forms west side of a sliver of Lake. The The sliver sliver is is a thicker zone on the west of iron iron formation formation that that extends toward Garnet Lake. separated from formation by Some of iron formations in separated from the the main main belt belt of iron formation by an an early early fault. fault. Some of the thin iron in the Willroy area west Willroy area similarly similarly represent representstructural structural repetitions repetitions (see (see Structural Structural Geology). Geology). In In the Geco area and west of Fox Fox Creek, southernmost iron iron formation formation isis heavily heavily invaded invaded by concordant concordant sheets sheets of of foliated foliated tonalite, tonalite, Creek, the southernmost mostly at the thescale scaleof of mapping; mapping; hence, hence, the the true truevolume volumeof of iron iron formation formation is is exaggerated. exaggerated. The The mostly not separable at southern contact contact between between iron iron formation formationand andmetagreywacke metagreywackeis is mostly mostly obscured obscured by by tonalite tonalite sheets. sheets. North of Garnet Lake, Lake, iron formations formations are tectonically tectonically thinned, in in some some cases occurring occurring as boudin trails or pinching out entirely. In the the Willecho Willecho area and and to to the thenorth, north,iron ironformation formationdefines definesmap-scale map-scale folds folds and is thickened by folding. Iron formation the hinge hinge of the Blackman Lake antiform. North North of of formation was also mapped on the limbs and near the Straight Lake, Lake, zincian suiphidic sulphidic quartz-rich rocks (Noranda's Jim Jim Lake Lake zone), associated with orthoamphibolebearing rocks, were interpreted formation. West West of of One One Otter Otter Lake Lake and andbetween between Jim Jimand andDavis DavisLakes, Lakes, interpreted as iron formation. magnetic rocks rocks grouped grouped with withiron ironformation formationare arehornblende-plagioclase-rich hornblende-plagioclase-rich with withthin thinlayers layers(mm—cm (mm-cm width) width) magnetic defined by defined by varying varying proportions proportions of of fine fine grained grained mafic maficand andfelsic felsicminerals mineralsand andmagnetite magnetite(Stop (Stop E6). E6). They are mainly associated with with mafic mafic to to intermediate intermediatemetavolcanic metavolcanicrocks rocks and and may may represent represent chemical chemical precipitates precipitates with with considerable detrital or or tuffaceous tuffaceous component, component, or altered altered volcanic volcanic rocks. Minor Minor exposures exposures of more typical a considerable quartz-magnetite iron iron formation formationare arelocally locallypresent present in in the the area, area,and andalso alsoin in the theDead DeadLake Lakesuite suite in in an an exposure exposure quartz-magnetite 12 �Description of units Manitouwadge greenstone belt on Wowun Lake. West of the Manitouwadge belt and Wowun Lake. and Kern Kern (Blackman) (Blackman) Lake, Lake,two two lenses lenses of of quartz-magnetite quartz-magnetite batholith in iron formation are present as as inclusions inclusions in tonalite of the Black Pic batholith in an an area areaof of strong strong aeromagnetic aeromagnetic striping. Metasedimentary rocks (Unit (Unit 10) lie between Metasedimentary rocks between the inner and and outer outer metavolcanic metavolcanic belts belts along along the thesouthsouthcentral to the ern limb of the the Manitouwadge Manitouwadge synform, synform, central the D2 D2'Manitouwadge 'Manitouwadge syncline' syncline' (see Structural GeolGeology). Mostly Mostly comprising comprising monotonous monotonous metagreywacke, metagreywacke, they are are dominated dominatedby byhomogeneous, homogeneous,grey, grey,foliated, foliated, fine grained, grained, poorly to strongly layered, schist. biotite-quartz-feldspar~hornblende~muscovite schist. Locally, Locally, more more fine layered, biotite-quartz-feldspar±hornblende±muscovite pelitic layers contain garnet and/or and/orsillimanite. sillimanite.Layering Layeringorormodified modifiedbedding bedding(0.5—30 (0.5-30 cm in width) width) isisdedefined by by variation variation in mafic and locally locally graded. graded. Concordant fined mafic mineral abundance,abundance,. and Concordant and and semiconcordant semiconcordant intruintrusions of of plagioclase-phyric plagioclase-phyrictonalite tonalite are are common. common. East of contains quartz- and sions of Agam Agam Lake, Lake, metagreywacke metagreywacke contains and plagioclase-crystal clasts, plagioclase-crystal clasts, interpreted interpretedasasevidence evidencefor foraa tuffaceous tuffaceousvolcanogenic volcanogenic component. component. Chaotic Chaoticfolds, folds,some some cm) and and sandwiched between undisturbed eye-shaped, spanning aa thickness thickness of of several several layers layers (totalling (totalling5—20 5-20 cm) layers, are are interpreted interpreted as the result of transposed soft-sediment deformation (Stop (StopAl). Al). layers, soft-sediment deformation age of of the Manitouwadge metagreywackesisisatat least least 25 25 Ma Ma younger younger than than The maximum maximum depositional depositional age Manitouwadge metagreywackes associated with with Cu-Zn mineralization mineralization (Zaleski et a!., the age of of felsic volcanism associated (Zaleski et al., 1995). 1995). The The metagreywackes metagreywackes in map-scale map-scale D; D2folds foldssouth southof ofthe the Nama Nama Creek Creek deposit deposit and and the dominant foliation are involved involved in foliation is ascribed ascribed metavolcanic rocks rocksto to north north and south, The contact contact between between metagreywackes metagreywackes and metavolcanic south, largely to D2 deformation. The obscured by by intrusions intrusions and and deformation, deformation,isisinterpreted interpretedtoto be be either either an an unconformity unconformityoror an an early early (pre(pre- to obscured syn-D2) fault. fault. Tectonic nits Tectonic rock rock uunits Straight gneiss (Unit Straight (Unit 11), l l ) ,or or laminated laminatedfelsic felsicgneiss, gneiss, was was identified identified in isolated exposures exposures and and in insemiconsemicontinuous map-scale between quartz-phyric quartz-phyric felsic felsic bodies bodies (Unit (Unit 8) in in the Wiliroy map-scale layers or lenses between Willroy area, associated with iron formation (Unit 9) and sillimanite-knot felsicschist schist(Unit (Unit lb) ib) in the Willecho Willecho area, and associated with sillimanite-knot felsic with iron formation and sillimanite-muscovite-quartz schist (Unit (Unit la) south of Lake. In the sillimanite-muscovite-quartz schist of Wowun Wowun Lake. the Wiliroy Willroy area, zones map-scale truncations truncations of of iron formation and repetition zones of straight gneiss gneiss coincide coincide with map-scale repetition of of aa disdis(see Structural Geology). tinctive lithological sequence sequence (see Geology). Locally, Locally, straight gneiss is associated with high high strain strain in iron formation, manifested either straight alternating manifested as either alternating quartz-rich quartz-rich and and dark dark magnetite-rich magnetite-rich laminations laminations (Stop Dl) Dl) or orconcordant concordant zones zones of of iron iron formation formation slivers slivers and boudins. On Onthe thebasis basisofofthese theseobservations, observations, straight gneiss straight gneiss was interpreted interpreted as asannealed annealed mylonite mylonite (see (see Hanmer, Hanmer, 1988 1988 for a definition) lying on early ductile faults. Straight gneiss gneiss is fine fine grained to to aphanitic, aphanitic,and andcharacterized characterizedby bycontinuous continuoustotostreaky streakylamellae lamellae(<1—1 (<I-1 mm width) of quartz and and feldspar, feldspar, and andat atsome somelocalities, localities,micaceous micaceous or hornblende-rich lamellae. Petrographic Petrographic shows that that straight gneiss examination shows gneiss has an annealed annealed granular texture but, but, in insome somecases, cases, strained strained quartz quartz ribbons were interpreted as as remnants remnantsof of an anoriginal originalmylonitic mylonitic fabric. fabric. felsicrocks rocksand andpegmatite. pegmatite.On On the the north north The protolith to to straight straight gneiss gneiss apparently apparently mostly comprised comprised felsic of the Willecho Willecho 33 pit, pit, a transition side of transition from from pegmatite pegmatite to tostraight straightgneiss gneissisisexposed exposedover over several several metres metres (Stop (Stop A26). With increasing A26). increasing intensity of strain, strain, near-massive near-massive pegmatite grades to sheared pegmatite with with strongly strongly lineated sillimanite on on shear shear surfaces, pegmatite, to streaky fine lineated surfaces, to porphyroclastic porphyroclastic pegmatite, fine grained grained straight straight gneiss. gneiss. In porphyroclastic porphyroclastic pegmatite, pegmatite, enclaves enclaves of coarse grained grained quartz and and feldspar feldspar are areenclosed enclosed by by fine fine grained grained gneiss containing lineated sillimanite. sillimanite. laminated gneiss Metasomatically Metasomatically altered rock units units Extensive orthoamphibole-bearing gneiss sillimanite-bearing schist themafic-felsic mafic-felsic Extensive zones zones of orthoamphibole-bearing gneiss and sillimanite-bearing schist near the transition belt and, to transition in the the inner inner volcanic volcanic belt to aa limited limited extent, extent, in in the theouter outervolcanic volcanic belt, belt, are are interpreted interpreted as as zones of of synvolcanic synvolcanichydrothermal hydrothermal alteration, alteration, modified by high grade regional metamorphism metamorphism and deformation. deformation. Orthoamphibole-garnetdicordieritegneiss the basis basis of of surface surface observations observations and and subsurface subsurface Orthoamphibole-garnet±cordierite gneiss (Unit (Unit 2), on the data, data, forms forms aa sheet sheet of of regional regional extent, extent, mantling mantling synvolcanic synvolcanic trondhjemite (Unit 12) 12) and folded folded by the ManMangneiss extends continuously for 30 km km from from Rabbitskin Rabbitskin itouwadge synform. synform. Orthoamphibole-garnet gneiss for at at least 30 northern limb limb of of the theManitouwadge Manitouwadge synform, synform, around the the hinge hinge of of the thefold fold to tothe theWillroy-Geco Willroy-Geco Lake on the northern and east east to tothe theHucamp Hucampand andFalconbridge Falconbridgezones zones of of subeconomic subeconomic mineralization of the the area, and mineralization(Fig. (Fig. 3). 3). East of however, aa prominent and Hucamp zone, exposure is poor; however, prominent aeromagnetic aeromagnetic anomaly anomaly continues continues the the same trend and the unit was was intersected intersected in in drill drill holes. holes. North North of of Straight StraightLake, Lake,orthoamphibole-garnet orthoamphibole-garnet rocks and sphaleritebearing attentuated northern northernlimb limbofofthe theManitouwadge Manitouwadgesynform, synform, are are correlated correlated with with bearing iron formation, on the attentuated the same horizon. East East of of Thompson Thompson and andBanana BananaLakes, Lakes,orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss, gneiss, defining a series of same of map-scale map-scale folds foldswith with aanortherly northerly trending enveloping enveloping surface, surface,isisinterpreted interpreted as a repetition of the same horizon, possibly in the 'keel' 'keel' of of aa D2 D2 fold involved in (Peterson and andZaleski, Zaleski, in aa Dz/Da D2/D3 fold fold interference interference pattern pattern (Peterson Orthoamphibole-garnet rocks by deep deep drill drill 1994b; Zaleski Zaleskietet al., al., 1995). 1995). Orthoamphibole-garnet rocks have have also also been been intersected intersected at at depth by holes penetrating plutonic rocks rocks inside the the Manitouwadge Manitouwadge synform. For For example, the the 'Geco 'Geco deep deep hole', hole', drilled drilled penetrating plutonic 13 �Manitouwadge greenstone belt of units Description of test the thedown-plunge down-plungeprojection projection of of the the Willroy Willroy deposits, deposits, intersected intersected about about 300 300 metres metres of of orthoamphiboleorthoamphiboleto test or sillimanite-bearing rocks. rocks. the area areaof of known known economic economic mineralization, orthoamphibole-garnet rocks lie north of of mineral deposits deposits In the Nama Creek, Creek, Willroy Willroy and and Geco, Geco, along along the the contact contact between between synvolcanic synvolcanic trondhjemite trondhjemite and andextrusive extrusivevolcanic volcanic at Nama rocks. The The precursers precursors to toalteration, alteration,still stillrecognizable recognizable in in less less altered altered enclaves enclaves mostly mostly on on the the margins margins of of the the rocks. unit and and to tothe thenorthwest northwestfurther furtherfrom fromknown knowndeposits, deposits,were were mafic mafic (Unit (Unit 3)3)and andinterlayered interlayeredmafic-felsic mafic-felsic rocks the transitional transitional mafic-felsic mafic-felsic contact. the outer outer volcanic volcanic belt, belt, orthoamphibole-garnet orthoamphibole-garnet rocks (Unit (Unit 4) near the contact. In the assemblages are are found found locally locally in in mafic mafic metavolcanic metavolcanicrocks rocksininaa discontinuous discontinuouszone zonenear near the the northern contact to felsic felsic metavolcanic rocks and metagreywacke metagreywacke (Stop B1). Bl). Orthoamphibole-bearing Orthoamphibole-bearing zones zones are much much less less extensive in the outer belt belt than thanininthe theinner; inner:however, however,,garnetiferous earnetiferous zones are common in mafic rocks. zones are common in mafic rocks. " The unit isis defined defined primarily primarily by by the thepresence presence of of orthoamphibole. orthoamphibole. Orthoamphibole-bearing Orthoamphibole-bearing rocks are astypically with first-order first-order metre-scale metre-scale layering metamorphic mineral astypically layered, layered, with layering defined defined by by variations variations in metamorphic semblages, size (Stops (Stops A6, A13, A14, D4). Second-order Second-order layering layering semblages, proportions, proportions, textures textures and and grain size A6, A13, A14, D3 and D4). consists of semi-continuous auartz-rich which locally locallv define define rootless intrafolial intrafolial quartz-rich lamellae or fine felsic bands. bands, which isoclinal the Wiliroy willroy area, area, garnet-orthoamphibole garnet-orthoamphibole layers layers that that anastomose anastornosearound aroundhornblende-rich hornblende-rich isoclinal folds. folds. In the resemble deformed deformed altered altered pillow pillow selvedges selvedgesor orfracture-controlled fracture-controlled alteration. alteration. Local enclaves resemble Local exposures exposures of of semisemiconcordant hornblende-cummingtonite-plagioclase hornblende-cummingtonite-plagioclase layers, and linear linear swarms swarms of of lenticular lenticular felsic felsic enclaves enclaves in an an orthoamphibole-garnet matrix, have been interpreted as orthoamphibole-garnet as remnants remnants of of dykes. dykes. In Insome someareas, areas,orthoamphiboleorthoamphibolesnake-like garnetiferous garnetiferous enclaves enclavesin inaastructure structure suggesting segmented layering garnet rocks enclose lenticular or snakelike and reminiscent of of aa coarse coarse breccia breccia (Stop (Stop D4). D4). In In general, general, the the layering layeringisisinterpreted interpreted as as the the result result of of transpotranspoor early fractures, dykes or sills, sition of syngenetic structures including including tuffaceous tuffaceous bedding, possible pillows or and domains domains of more and less less altered rocks. rocks. The orthoamphibole orthoamphibole commonly commonly displays blue iridescence, iridescence, characteristic of of cryptocrystalline cryptocrystalline exsolution exsolution from a composition above the the gedrite-anthophyllite gedrite-anthophyllitesolvus solvus(Robinson (Robinsonetetal., al.,1982). 1982).ItIt occurs occurs in in a variety variety of of composition above whichinclude includegarnet&cordierite&sillimanite&plagioclase garnet±cordierite±sillimanite±plagioclase and and cummingtonite&hornblende&plagcummingtonite±hornblende±plagassemblages, which ioclase±garnet. ioclasekgarnet. Hornblende-plagioclase±cummingtonite±garnet Hornblende-plagioclase&cummingtonite~garnetassemblages assemblages interlayered with orthoamphiborthoamphibole-bearing assemblages are are interpreted as indicative indicative of of lower intensity hydrothermal alteration alteration of ofmafic maficvolvolrocks. Orthamphibole-garnet-cordierite area, interleaved (on Orthamphibole-garnet-cordierite assemblages assemblages dominate in the Willroy-Geco area, canic rocks. a 10 scale)with withsillimanite-cordierite-biotite&garnet sillimanite-cordierite-biotite±garnetlayers layers(Stop (StopA5). A5).Quartz Quartz and and magnetite are 10 cm—10 cm-10 mmscale) ubiquitous, and and small small amounts amountsof of sulphide minerals, staurolite, staurolite, and and gahnite gahniteare arecommon. common.More Moreexotic exoticminerals minerals are found in the [(Ti,Sn)(Fe,Mg,Zn,Mn)e(Al,Fe)ie032] the Geco Geco mine, mine, including including corundum, corundum,cassiterite, cassiterite,högbomite hogbomite[(Ti,Sn)(Fe,Mg,Zn,Mn)6(Al,Fe)16032] (Spry, 1982; 1982;Petersen, Petersen, 1986). 1986). In orthoamphibole-bearing and nigerite [(Sn,Ti)2(Zn,Mg,Fe,Mn)4(Al,Fe)16032J [(Sn,Ti)2(Zn,Mg,Fe,Mn)4(Al,Fe)i6032] (Spry, rocks, biotite habits suggest both metamorphic and retrograde generations, the latter of latter forming forming pseudomorphs of coarse orthoamphibole sprays (Stop AS). A5). Plagioclase small amounts amounts in in orthoamphiboleorthoamphibolePlagioclase is absent or present in small bearing assemblages, assemblages, particularly particularly in in the theWillroy-Geco Willroy-Gecoarea. area. Sillimanite-muscovite-quartz schist (Unit 1) Sillimanite-muscovite-quartzand and sillimariite-knot sillimanite-knot felsic schist 1) are subdivisions representing 'endmembers' of Unit 1, orebodies in in the the Willroy-Geco Willroy-Gecoarea, area,and and the the latter latter 1, the former found mainly to the south of orebodies area and north. The in the Willecho area Theunit unitalso alsoincludes includestransitional transitionalquartzites quartzitesinterleaved interleavedwith withmicaceous micaceousschist. schist. Sillimanite-muscovite-quartz schist occurs occurs in in close proximity to to massive suiphide deposits deposits and envelopes the Sillimanite-muscovite-quartz schist close proximity massive sulphide Geca Geco main orebody. Abundant muscovite and/or sillimanite sillimanite and quartz quartz are are typical of the unit, and and plagioclase, plagioclase, biotite, K-feldspar, K-feldspar, garnet and and magnetite magnetite may may also alsobe be present. present. Felsic Felsic volcanic volcanic rocks lying along strike and in less altered altered enclaves enclaves are are interpreted interpreted as the protolith to to alteration. alteration. Along the southern southern limb limbof of the theManitouwadge Manitouwadgesynform synformin inthe theWiliroy-Geco Willroy-Gecoarea, area,two twozones zonesof ofsillimanitesillimaniteschist converge convergetotothe the east east near near the Geco mine, mine, where where they they are are separated by an early fault (see bearing felsic schist (see Structural Geology). schist (Stop (Stop A19) A19) to quartzGeology). The The northern northern zone zone grades grades easterly easterly from from sillimanite-knot sillimanite-knot schist muscovite-sillimanite schist schist consisting consisting of of finely finely interlayered interlayered quartz quartz and muscovite with sillimanite muscovite-sillimanite sillimanite sprays sprays on on the foliation surface (Stop A6). Near schist that that Near Wiliroy, Willroy, the southern belt consists consists of a thinly thinly layered layered felsic schist becomes more muscovitic muscoviticand andsilicic silicictotothe theeast, east, merging mergingwith withthe the northern northern belt belt and grading to aa suiphidic becomes more sulphidic muscovite-biotite quartzite in the Geco muscovite-biotite quartzite Geco area. area. Near the the hinge hinge region region of of the the Manitouwadge Manitouwadge synform synform in in the theWillecho Willecho area, area, sillimanite-knot sillimanite-knot felsic felsic schist schist is is interleaved (on a metre scale) felsic schist, schist, straight straight gneiss gneiss and and sheared sheared pegmatite pegrnatite (Stop interleaved scale) with with non-sillimanitic non-sillimanitic felsic A24). Similar rocks occur sporadically sporadically to to the south of associated with with iron iron formation formation that can A24). of Willecho, Willecho, associated can be be traced continuously to the the Willroy Willroy area. area. The Thesillimanite-bearing sillimanite-bearingrocks rocks contain contain quartz, quartz,plagioclase, plagioclase,microcline microcline and biotite and and are aregenerally generally more more feldspathic feldspathic than those those in in the theWiliroy-Geco Willroy-Geco area. Sillimanite occurs in cminindiameter), diameter), typically typically zoned zoned with with greenish greenish cores cores mantled mantled by by white fibrous sillimanite. sillimanite. coarse knots (1—8 (1-8 cm and vary from sparse sparse to to about about 20 percent. In general, general, the knots are are disseminated disseminated and vary in abundance abundance from percent. At At aafew few tuff or ortuffaceous tuffaceousmetasediment metasedimentcontains containsabundant abundant sillimanite that that localities, thinly layered quartz-phyric felsic tuff coalescesinto intosillimanitic sillimaniticlayers. layers. In In these these cases, cases, the the distribution distribution of of sillimanite sillimanite isis stratabound, stratabound, concentrated coalesces concentrated from near the tops(?) tops(?) of of modified modified beds. A A northward northward increase increase in metamorphic metamorphic grade is indicated by a change from 14 �Description of units units Manitouwadge greenstone belt sillimanite-muscovite sillimanite-muscovite to to sillimanite-microcline sillimanite-microclineassemblages. assemblages. Synvolcanic intrusions Synvolcanic intrusions Foliated trondhjemite-hornblende 12)underlies underlies aa large large area area inside inside the theManitouwadge Manitouwadge trondhjemite-hornblende granodiorite granodiorite (Unit (Unit 12) synform, forming forming an elliptical ring cored by the younger Lake pluton pluton (Unit 13b). cored by younger Loken Loken Lake 13b). Granodiorites Granodiorites and and tonalites of of similar appearance extend around around the the Blackman Blackman Lake Lake anticline, to the the hinge hinge region region of of the the Jim Jim Lake synform. The Lake synform. The area area of of the theunit unitdisplays displaysaahigh highvariable variableaeromagnetic aeromagnetic signature, signature, probably probably related to to the abundance abundance of of magnetite magnetite and andtotothe thepresence presenceofofsupracrustal supracrustalscreens, screens,for forexample examplethe theDead DeadLake Lakesuite. suite. A deep deep drill hole, hole, collared about one one kilometer north of the Geco Geco mine, penetrated mostly mostly trondhjemite trondhjemite to to granodiorite granodiorite for for the the uppermost uppermost1470 1470metres, metres,before beforeencountering encounteringfine finegrained grainedmafic maficmetavolcanic metavolcanicschist. schist. Along Along its its outer outer perimeter, perimeter,trondhjemite trondhjemiteintrudes intrudesmafic mafic(Unit (Unit3)3)and andmixed mixedmafic-felsic mafic-felsicmetavolcanic metavolcanic rocks rocks (Unit gneiss (Unit (Unit 2). 2). The outermost trondhjemite is a quartz-rich (Unit 4), 4), and and orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss quartz-rich (30—50%) leucocratictonalite tonalitewith withminor minorbiotite, biotite, magnetite magnetite and, locally, garnet. ItItvaries (30-50%) leucocratic variesfrom fromfine fine to tocoarse coarse grained, grained, but but typically typically contains contains coarse coarse quartz grains up to to 55 millimetres millimetres in diameter. Minor Minor or trace amounts amounts of titanite, apatite, allanitelepidotemay mayalso alsobe bepresent. present.InInthe theWillroy-Geco Willroy-Gecoarea, area,the the of microcline, titanite, apatite,zircon zircon and andallanite/epidote abundance of biotite and garnet garnet tends tends to toincrease increase toward toward the the southern southern contact contact with with orthoamphibole-bearing orthoamphibole-bearing rocks, rocks, and and locally, locally, the trondhjemite trondhjemite isishost host to tonarrow narrowseams seamsof of biotite, biotite,orthoamphibole, orthoamphibole,cordierite cordieriteand andgarnet garnet (Stop A7). A7). The Theseams seamswere were interpreted interpreted as aspre-metamorphic pre-metamorphic fracture-controlled fracture-controlled alteration related related to tosynvolsynvolcanic hydrothermal activity, implying that that trondhjemite is a synvolcanic intrusion. Our field activity, implying synvolcanic intrusion. field interpretation of of synvolcanic synvolcanic intrusion intrusion was wasconfirmed confirmedby bygeochronology geochronology(2720±3 (2720h3Ma, Ma,see seeGeochronology). Geochronology). Despite some variations in modal abundances, Unit 12 is is characterized characterized by by abundant abundant coarse grained quartz, quartz, disseminated biotite, and disseminatedmagnetite magnetiteporphyroblasts porphyroblasts(1—3 (1-3 mm), minor biotite, and aa weakly weakly to to moderately moderately developed developed fabric. fabric. Away Away from its outer perimeter perimeter in in the thehinge hingeregion region of of the the Manitouwadge Manitouwadge synform, foliated trondhjemite grades to to more more granodioritic granodioritic and and granitic graniticcompositions, compositions, although although not not in inany anyregular regularor orsystematic systematicfashion. fashion.Younger Younger foliated foliated granites, granites, pegmatites pegmatites and and aplites aplites(and (andprobably probablyyounger younger foliated foliated tonalites) tonalites) are are also also present, present, and and these these are intrusion. In are not not always always easy easy to to distinguish distinguish from from the the synvolcanic synvolcanic intrusion. In the the inner inner synform, synform, the the Dead Dead Lake Lake suite suite isis intruded intruded by by foliated foliated multiphase multiphase tonalite, tonalite, granite granite and and pegmatite-aplite, pegmatite-aplite, and and at atleast leastsome someof of the thetonalite tonalite isis similar most tonalites tonalites in proximity similar to tothe thesynvolcanic synvolcanictrondhjemite trondhjemite (Stop (Stop C6). C6). However, However, most proximity to the the Dead Dead Lake resemblingthose thoseofofthe the outer outer margin margin in in textures, textures, and and in magnetite Lake suite, while while resembling magnetite and quartz quartz content, content, have have aa higher higher proportion proportionofofmafic maficminerals, minerals, including including hornblende. hornblende. Some Someof of the the hornblende, hornblende, present present as ascoarse coarse grained cm),randomly randomly to to moderately moderately oriented poikiloblasts, looks secondary. In the grained (0.5—1 (0.5-1 cm), the Dead Dead Lake Lakesuite, suite, leucocratic to to melanocratic melanocratichornblende-magnetite-plagioclase±garnet hornblende-magnetite-plagioclasehgarnetrocks, rocks,with withconspicuous conspicuousquartz quartzeyes eyesor or leucocratic lenticules, resemble altered or contaminated contaminated tonalite tonalite (Stops (StopsC3 C3and andC5). C5).InInsome somecases, cases,blocky blockyinclusions inclusionsof of lenticules, hornblende-magnetite-plagioclasehgarnetrock rockinintonalite tonalitehave havenarrow narrow(1—10 (1-10 cm) cm) transitional transitionalcontact contactzones, zones, hornblende-magnetite-plagioclase±garnet apparently apparently due dueto toreaction reactionorormixing mixingofofthe thetwo tworock rocktypes. types. In In general, general, although although the themore morepotassic potassic and andhornblende-bearing hornblende-bearing intrusive intrusive rocks toward the central central ManManitouwadge synform, west of of the the Loken Loken Lake Lake pluton, are are texturally texturally and and modally modally similar similar to to itouwadge synform, and and north north and west synvolcanic trondhjemite, it is not clear synvolcanic trondhjemite, clear in in outcrop outcrop whether whether they they are are comagmatic, comagmatic, or or belong belong to to different different and possibly younger intrusions. However, However, geochemical geochemical analyses least some some are are comagmatic comagmatic(see (see possibly analysessuggest suggestthat that at least Geochemistry). Foliated Foliated trondhjemite trondhjemite has hasnot notbeen beenobserved observedininthe theouter outervolcanic volcanicbelt; belt;however, however,amongst amongst Geochemistry). undivided foliated foliated intrusive intrusive rocks rocks (Unit (Unit14), 14),aalayer layerofofstrongly stronglymagnetic magneticfelsic felsic rocks, rocks, lying lying within within the the mafic mafic undivided sequence sequence striking through through Gaug GaugLake, Lake, has hassome sometextural texturaland andgeochemical geochemical(see (seeGeochemistry) Geochemistry) similarities similarities to to hornblende-magnetite-plagioclasehgarnet~clinopyroxene rocks and magnetite magnetite quartzite quartziteofofthe the the quartz-eye quartz-eyehornblende-magnetite-plagioclase±garnet±clinopyroxene the rocks Dead Dead Lake Lake suite. suite. Synpost-tectonic intrusions intrusions Syn- to post-tectonic 13)could could be be grouped grouped with the the Black Black Pic Pic batholith; batholith;howhowFoliated K-feldspar K-feldspar porphyritic granitoid granitoid (Unit (Unit 13) Foliated ever, two two mappable mappable bodies bodies can be be distinguished distinguished from the multiphase plutonic 3). These Theselie lienear near ever, plutonic suit (Fig. 3). the margins marginsof of the thegreenstone greenstonebelt belt(including (includingsubvolcanic subvolcanicintrusions), intrusions), and andhave havebeen beeninvolved involvedininD3 Dafolds. folds. the The northwestern northwestern contact contactbetween between supracrustal supracrustal rocks rocks and and foliated foliated tonalites tonalites of of the the Black Black Pic Pic batholith, batholith,inside inside The the Blackman Blackman Lake Lake antiform, antiform, isismantled mantledby byaalong longsinuous sinuousbody bodyofoffoliated foliatedhornblende-biotite hornblende-biotite (up (uptoto35%) 35%) the granitoid, granitoid, here here called called the the Nama Nama Creek Creek pluton pluton (Unit (Unit13a). 13a). Microcline Microcline phenocrysts, cm in in phenocrysts, typically typically 11 to 2 cm length, vary vary in in abundance abundance from sparse to about about 25%. 25%. The The matrix matrixvaries varies from from tonalitic to granitic granitic in in modal modal length, 10-20%, titanite composition, in some some cases, cases, containing containing little little K-feldspar. K-feldspar. Quartz Quartzcontent contentvaries variesfrom fromabout about10—20%, composition, is commonly commonly present (I%), and apatite, apatite, zircon, zircon, opaque minerals and allanite are are trace traceconconis present in minor amounts (1%), stituents.AAmoderate moderatetotostrong strongtectonic tectonicfabric, fabric,defined definedbybymafic maficminerals mineralsand andaugen-shaped augen-shapedphenocrysts, phenocrysts, isis stituents. D3 Blackman Blackman Lake Lake antiform antiform and and outcrop-scale outcrop-scale Z-folds Z-folds (D3). The folded fabric, and the the presence presence folded by by the the D3 folded of folded folded pegmatite-aplite pegmatite-aplite dykes, dykes, suggest suggest that that the theintrusion intrusionisisprepre-totosyn-D2. syn-Dg. of Anothermicrocline microclinephenocrystic phenocrysticgranitoid granitoidintrudes intrudesthe theinnermost innermostcore coreof of the theManitouwadge Manitouwadgesynform synform (Fig. (Fig. Another 3) the Wowun-Luckyshoe 3) and andisishere herecalled calledthe theLoken LokenLake Lakepluton pluton(encompassing (encompassing the Wowun-LuckyshoeLakes Lakes mass mass of of Williams Williams 15 �Manitouwadge greenstone belt of units Description of et al., 1992). 1992). With With the the exception exception of of the the western western part part of of this this body, body, exposure exposure is poor, poor, and and the thecontacts contacts were were tocoincide coincide with with an anelliptical ellipticalarea areaof oflow low flat flat aeromagnetic aeromagnetic expression. expression. The Thebody bodyisischaracterized characterized interpreted to to 15 15cm cm long, long, varying varying in in abundance abundance from from sparse to 25%. 25%. Large Large areas areas by microcline megacrysts, typically 5 to of the intrusion intrusion consist consist of of non-porphyritic non-porphyritic rock rock resembling resembling the matrix matrix of of porphyritic porphyritic varieties; varieties; however, however, Kfeldspar phenocrysts phenocrysts or augen have been been observed observed close closeto to contacts contacts to to the west west and northeast of of Dead Dead Lake, Lake, Thompson Lake. Lake. In comparison and south of Thompson comparison to the Nama Nama Creek Creek pluton, the the Loken Loken Lake Lake pluton has larger larger 5% biotite. Quartz Quartz isisabundant abundant(25—40%) (25-40%) and phenocrysts and is more leucocratic, containing about 5% and apatite, apatite, titanite, opaque opaque minerals, minerals, zircon zircon and, and, in in some some cases, hornblende titanite, hornblende are are typically typicallypresent present in intrace trace amounts. amounts. Where present, the therock rock looks looksdisconcertingly disconcertingly similar to to synvolcanic synvolcanic trondhjemite of K-feldspar phenocrysts phenocrysts are not present, 12, but but geochronology geochronology confirms a post-volcanic age of Unit 12, of 2687+2/-3 2687+2/—3 Ma Ma (see (see Geochronology). Geochronology). A A strong tectonic tectonic fabric, fabric, commonly commonlyL>S, L>S, isis delineated delineatedby by quartz, quartz, feldspars, feldspars,biotite, biotite, and and microcline microclineaugen augen(Stop (StopCl). Cl). Variations in fabric orientation suggest folding by by the the D3 D3 Manitouwadge Manitouwadgesynform synformimplying implyingthat, that, like likethe the Nama Nama Creek intrusion is is prepre- to to syn-D2. syn-Da. Creek pluton, the intrusion Undivided rocks of of the the Black Black Pic Pic Undivided foliated foliated intrusive rocks rocks (Unit 14) include foliated multiphase plutonic rocks batholith, as well well as foliated foliated tonalitic tonalitic intrusions intrusions within supracrustal suite of of the the Manitouwadge Manitouwadge belt. within the supracrustal Near the southern margin belt, at least Near margin of of the the Manitouwadge Manitouwadge belt, least 33intrusive intrusive phases phases can can be berecognised recognised in in the the Black rocks, diorite diorite and and Black Pic batholith. The Thecontact contactisisaatransitional transitionalzone zoneofofinterleaved interleaved mafic mafic metavolcanic metavolcanic rocks, younger tonalite, tonalite, all involved younger involved in tight tight intrafolial intrafolial folds. folds. The oldest oldest intrusive intrusive phase phase (2687+3/—2 (2687+3/-2 Ma, Ma, see see Geochronology), medium medium to to coarse grained, grained, foliated foliated hornblende-biotite hornblende-biotite diorite diorite to to monzodiorite with plagioclase augen, dominates dominatessome someoutcrops outcropsand andforms formsblocky blockyinclusions inclusionsininyounger youngerphases. phases.Quartz Quartzis is present from 5-20%, present from 5—20%, from <2-15%, <2—15%,and andhornblende hornblendeplus plusbiotite biotite comprise comprise 15-35%. 15—35%.The Therock rockcontains containsminor minorto to trace trace microcline from of titanite titanite and opaque amounts of opaque minerals, and trace amounts of apatite, allanite/epidote allanite/epidote and andzircon. zircon. AAstrong strong schistosity is defined by mafic minerals and plagioclase plagioclase augen. Younger Younger foliated foliated monzodiorite monzodiorite (2677±2 (2677zk2Ma) Ma) is predominant of the area north of predominant in much of of the the Banana Banana Lake Lake antiform antiform (distribution (distribution based based on on petrographic petrographic observations Ontario Geological Survey), that is is the the area area between between observations on thin thin sections sections made made available available by F. Breaks, Ontario the easterly easterly extensions extensions of the inner and and outer outer volcanic volcanic belts. Inclusions of the the oldest oldest diorite are engulfed by foliated foliated biotite biotite tonalite to granite, Inclusions of engulfed by granite, possibly possibly representing representing more than one one intrusive intrusive phase. The The youngest youngest phase phase on on the the southern southern margin margin of of the the Manitouwadge Manitouwadge belt cuts cuts across diorite, tonalite and granite, foliated granite, granite, aplite and pegmatite granite, as asdykes dykes of of weakly weakly foliated pegmatite and, and,locally locally as as more bodies. These rockshave haveminor minortototrace trace amounts amounts of of biotite, biotite, and and trace more discrete discrete bodies. These youngest youngest leucocratic leucocratic rocks amounts of opaque minerals and apatite. apatite. Diffuse Diffuse transitions between between granite granite and and pegmatitic pegmatitic enclaves enclaves can can be be observed locally. locally. Tonalitic rocks of of the the Black Pic batholith extend extend west west of of the the Manitouwadge Manitouwadge belt, belt, inside inside the the hinge hinge region region of the Blackman Blackman Lake Lake synform synform (D3). Near the the Blackman Blackman Lake Lake of Lake antiform antiform (D3) (D3) and and north north of of the Jim Lake (D3). Near antiform, weakly foliated to to massive, medium to to coarse grained grained tonalite tonalite is commonly present present on the short weakly foliated massive, medium short of minor folds and outcrop-scale shear zones. zones. Diffuse contacts to the limbs of Diffuse contacts the foliated foliated host host rocks rocks are aresuggestive suggestive of localized localized coarsening coarseningand and recrystallization, recrystallization,or or of of anatectic anatectic mobilizates mobilizatesthat that migrated into dilational of dilational zones. zones. Evidence of of migmatization migmatization increases increases northward northward toward toward the the Quetico boundary. boundary. Northwest of the Manitouwadge belt, septa septa of of mafic mafic to to intermediate intermediatesupracrustal supracrustalrocks, rocks,likely likely derived derived from from the the main mainsupracrustal supracrustalsequence, sequence, correspond to pronounced aeromagnetic quartz-magnetite aeromagnetic striping striping parallel parallel to to foliation trends. trends. AAfew few screens screens of quartz-magnetite iron formation are present; also are commonly commonlystrongly stronglymagnetic. magnetic. The The striping and the also mafic inclusions are the linear linear straighter and trending more nearly map pattern are are transitional transitional across across the theQuetico Quetico boundary, boundary, becoming becoming straighter east-west toward toward the north. east-west fine to to medium medium grained, granodiorite and tonalite Irregular bodies and and dykes dykes of of homogeneous, homogeneous, foliated, fine tonalite intrude the the main main supracrustal supracrustalbelt. belt.Tonalites Tonalitesare aremost mostcommon, common,typically typicallycontaining containingplagioclase plagioclasephenocrysts, phenocrysts, and accessory biotite and/or and/or hornblende. hornblende. The Thehinge hingeof ofthe theManitouwadge Manitouwadgesynform synform in the the vicinity vicinity of of Cadawaja Cadawaja Lake is dominated by granodiorite-tonalite granodiorite-tonalitecontaining containing inclusions inclusions of biotite schist (Unit (Unit 10) 10)and andfelsic felsic to to interintermetavolcanic rocks rocks(Unit (Unit 6). 6). In In general, general, the the contacts contacts of of this this body body are are gradational gradational and their position mediate metavolcanic is poorly near the contact poorly constrained. constrained. Tonalite Tonalite is is pervasive pervasive near contact between between iron formation and metasedimentary metasedimentary rocks in in the inner volcanic belt, and in mafic rocks of ofthe the outer outer belt belt near near their contact to metasedimentary rocks volcanic belt, mafic rocks metasedimentary rocks. Concordant to m)intrude intrude all all supracrustal supracrustal rock rock units, in rocks. to slightly slightly discordant discordant tonalite tonalitedykes dykes(<10 (<I0cm—i cm-1.5.5m) some cases, cases, cutting across straight straight gneiss tonalite foliations gneiss (annealed mylonite) or early folds. In most cases, tonalite are parallel parallel to the dominant dominant fabric fabric of of the host host rocks rocks and and at at least leastsome some tonalite tonalite dykes dykes can can be be interpreted interpreted as as syn-D2 syn-Dz (Stop A23). A23). Pegmatite, sheets and and Pegmatite, aplite and and foliated foliated granite (Unit (Unit 15) 15) are are present present as as foliated foliated and and massive massive dykes, sheets which can can be be shown shown at at the scale of of mapping. mapping. The irregular subconcordant bodies, bodies, aa few few of which The largest is is aa foliated foliated granite intruding north of of the Geco intruding supracrustal supracrustal rocks rocks and and synvolcanic synvolcanic trondhjemite immediately immediately north Geco mine. In In general, the unit comprises of quartz, K-feldspar general, comprises undivided undivided leucocratic leucocratic intrusions intrusions of of various various ages, composed composed of K-feldspar with accessory accessory muscovite muscoviteororbiotite. biotite. Garnet is and plagioclase, plagioclase, with is present present locally locally in pegmatite, pegmatite, mainly mainly near near 16 �Description of of units units Description Manitouwadge Manitouwadge greenstone greenstone belt belt contacts contacts to to iron iron formation. formation. North Northand andwest westofofthe theNama NamaCreek Creekdeposit, deposit,pegmatites pegmatiteshave havesheared sheared contacts contacts and surfaces for example example as as described describedin in the the transition transition to straight surfaces coated by aligned sillimanite, for straight gneiss gneiss north of of the the Willecho Willecho 3 pit pit (Stop (Stop A26). A26). InInmany manycases, cases,pegmatites pegmatitesshow show tectonic tectonic fabrics fabrics only only near near contacts contacts or or in Locally, discordant discordant pegmatite pegmatite dykes dykes and and dyke dyke swarms swarms show show little little evidence evidence of in fine fine grained grained aplitic aplitic zones. zones. Locally, deformation, gashesat at aa high high angle to contacts. deformation, excepting exceptingquartz—filled quartz-filled gashes contacts. Alkalic 16) including including hornblende hornblende syenite, syenite, hornblendite and and lamprophyre, lamprophyre, both bothmassive massiveand and Alkalic rocks (Unit (Unit 16) foliated, sporadically throughout throughout the the map area. These foliated, were were encountered encountered sporadically Thesegenerally generally form form dykes dykes or irregular irregular bodies, bodies, too too small small to to show show at atthe thescale scaleofofmapping, mapping,and andininsome somecases, cases,with withcomplex complex contacts contacts or or internal internal relationships massivehornblendite hornblenditebody bodyof ofabout about250 250metres metresinindiameter, diameter, relationships that thatwere were not notmapped mappedinindetail. detail.AAmassive lying lying northeast northeast of ofCadawaja CadawajaLake, Lake,isisthe theonly onlyone oneshown shownon on our our 1:25000 1:25000 map, map, but but other otherexposures exposuresof of the theunit unit were were observed observed southwest of of Swill Swill Lake, northwest of Willecho, near the the town town of of Manitouwadge, Manitouwadge, and and1.5 1.5km km south south of of Manitouwadge ManitouwadgeLake Lake just west west of of the the extension extension of of the the Fox Fox Creek fault. fault. The Theunit unitgenerally generallycorresponds corresponds to to the the'Appinite 'Appinitesuite' suite'ofofWilliams Williamsetetal. al.(1992) (1992)and andthe theFox FoxCreek Creeklocality localitywas was described described by by them. them. On On outcrop, outcrop,syenite-hornblendites syenite-hornblenditesare areusually usuallyheterogeneous, heterogeneous,pink pinkand andgreen greenvarying varyingfrom fromleucocratic leucocratictoto melanocratic, hornblende. Tectonic fabrics, where recognizable, are typically weaker than melanocratic, with withup uptoto80—90% 80-90% hornblende. than in D3 in adjacent adjacent host hostrocks. rocks.An Anexception exceptionisisaafine finegrained grainedsyenite syenitewith withaastrong strongfoliation foliationfolded foldedby byasymmetric asymmetricD3 folds, folds, exposed near the the Geco Geco gatehouse gatehouse (Stop (Stop Bi). Bl).The Therocks rocksare arecharacterized characterizedbybyhornblende hornblendephenocrysts, phenocrysts, up up to to15 15mm mmininlength, length,riddled riddledwith withinclusions inclusionsof oforiented orientedbiotite biotiteblades. blades.The Theorientation orientationofofinclusions inclusionsvaries varies between apparently being being related related to hornblende crystallographicstructure structure rather rather than to between phenocrysts, phenocrysts, apparently hornblende crystallographic to any any penetrative penetrative fabric. fabric. Minor Minorclinopyroxene clinopyroxene is is also also commonly commonly present, as skeletal or corroded corroded phenocrysts phenocrysts or or as as ragged hornblende. Titanite and apatite ragged relicts coring hornblende. apatiteare areeither either abundant abundantor orpresent presentinintrace traceamounts amountsalong along with with allanite, allanite, opaque opaque minerals, minerals, epidote and quartz. quartz. InInmany manycases, cases,the therocks rockslook looklike like hybrid hybrid mixtures mixtures of of leucocratic leucocratic and and melanocratic melanocratic material. material. Northwest of about 50 metre width Northwest of of Willecho, Willecho, a syenite-hornblendite syenite-hornblendite dyke of width was was traced traced for for 500 500 metres. metres. The Thedyke dykeconsists consistsof of dark, dark,medium mediumto tocoarse coarsegrained, grained,hornblende hornblendeporphyry, porphyry,with withhornblende hornblendephenocrysts phenocrystsininaa matrix matrixof of plagioclase plagioclase and/or and/or microcline microcline(up (up to to35%). 35%).Diffuse, Diffuse, medium medium grained grained to to pegmatitic, pegmatitic, feldspathic feldspathic net net veins veins cut cut the the porphyry. porphyry. The Theveins veinsare areflattened flattened and andhave haveaatectonic tectonic lineation. lineation. Inthe thetown townof of Manitouwadge, Manitouwadge, aafoliated lamprophyre dyke dyke (about (about 11m wide) cuts across diorite and aplitic aplitic In foliated lamprophyre dykes dykes of of the the Black Black Pic Pic batholith. batholith.The Thelamprophyre lamprophyredyke dykeconsists consistsofofbiotite biotiteand andclinopyroxene clinopyroxenephenocrysts phenocrysts (up (up to to55mm mmininsize) size) in in aaquartz+plagioclase quartz+plagioclase matrix matrixwith with minor minor horublende hornblende and apatite apatite (about (about 2%). 2%). The The Fox Fox Creek Creek occurrence occurrence (1.5 (1.5km kmsouth southofofManitouwadge ManitouwadgeLake) Lake)ofofsyertite-hornblendite syenite-hornblendite is is notable, notable, although althoughititwas wasnot notmapped mappedininany anydetail. detail.ItItintrudes intrudesBlack BlackPic Pictonalites tonalitesofoflow lowaeromagnetic aeromagneticresponse responseand andisis itself associated associated with with an anisolated isolatedhigh high aeromagnetic aeromagneticanomaly anomaly (partly (partlymasked maskedby bydiabase diabasedykes). dykes).The Theexposure exposure itself isis relatively relatively extensive (at (at least least 300 300 metres). Internal Internalstructures structuresinclude includeorbicular orbiculargabbro gabbro(Williams (Williamsetetal., al.,1992), 1992), rhythmiclayering layering(cm-scale) (cm-scale) defined defined by mafic and felsic mineral truncations of of layering layering that that rhythmic mineral abundance, and truncations resemblecross-bedding cross-bedding(Stop (StopF5). F5).Locally, Locally,the therock rockisisananintrusion intrusionbreccia brecciacomprising comprisinglithic lithicclasts clasts(1—10 (1-10 cm cm in in resemble size) in in aa hornblende-porphyritic hornblende-porphyritic matrix matrixtypical typicalofofthe theunit unit(Stop (StopF4). F4).The Theclasts clastsare aremostly mostlymafic mafic(hornblende(hornblendesize) biotite-plagioclase-titanitekepidotekopaque minerals), minerals),apparently apparentlywith withcoarse coarsegrained grainedhybridized hybridizedmargins, margins,inin biotite-plagioclase-titanite±epidote±opaque somecases, cases, with with aa fine fine grained grained core. core. Particularly Particularlynotable notableisisthe thepresence presenceofofaasingle single(observed) (observed)massive massivesulphide sulphide some clast, clast,22centimetres centimetres in inlength, length,consisting consistingof of pyrite, pyrite, magnetite, magnetite, ilmenite ilmenite and and chalcopyrite. chalcopyrite. Presumably Presumablythe theclast clast population of of the the breccia breccia represents represents rocks rocks sampled sampled by the the intrusion intrusion during during its itsascent ascentand andemplacement; emplacement; population however, the closest closest known known massive sulphide occurrence is Rock units unitsinin however, is the the Geco Geco mine mine 3.5 3.5 km km to to the north. Rock thisarea areaare aresteeply steeplydipping dippingand, and,according accordingtotoour ourcurrent currentunderstanding understandingofofthe thesubsurface subsurfacestructure, structure,unlikely unlikely this toextend extend below below the the intrusion intrusion breccia. breccia. The Thesubsurface subsurfacedips dips and and extent extent of of the the syenite-hornblende syenite-hornblende body are not to known, known, but but ititseems seemslikely likely that thatthe thebody bodysampled sampledsome someunknown unknownsulphide sulphidemineralization mineralization during duringits itsascent. ascent. Quetico Queticosubprovince subprovince Metasedimentary rocks rocks (Unit (Unit lOq) lOq) of of the theQuetico Queticosubprovince subprovince are aredominated dominatedby bymonotonous monotonousmetametaMetasedimentary greywacke and and biotite biotiteschist, schist,lithologically lithologicallysimilar similarto tometagreywacke metagreywackein in the theManitouwadge Manitouwadgegreenstone greenstone belt belt greywacke (Unit 10), lo),except exceptfor forthe theubiquitous ubiquitouspresence presenceofofmigmatitic migmatiticsegregations. segregations. Quetico Queticomigmatitic migmatiticmetasedimenmetasedimen(Unit taryrocks rocksextend extendacross acrossthe thenorthern northernpart partofofour ourmap, map, defininga broadly a broadlycurved curvedsubprovince subprovinceboundary, boundary, tary defining concave to to the thesouth. south.Similar Similarmetasedimentary metasedimentaryrocks rockscan canbe betraced tracedinindiscontinuous discontinuousoutcrops outcropsfrom fromJim JimLake Lake concave toeast eastofofAppelle AppelleLake, Lake,totoDavis Davisand andLarry LarryLakes, Lakes,folded foldedby bythe theJim JimLake Lakesynform synform(D3) (Da)and and aarelated related to map-scale Z-fold Z-fold in the the Davis Davis Lake Lake area. area. The Theposition positionofofthe thefolded foldedsubprovince subprovinceboundary boundaryisisbased based on onexexmap-scale posuresof of migmatitic migmatiticbiotite biotiteschist schist(Quetico (Queticosubprovince) subprovince)and andfoliated foliatedtonalite tonalitewith withmafic maficinclusions inclusions(Wawa (Wawa posures subprovince), especially especially between between Appelle Appelle Lake Lake and and the therailway railwaywest west of ofJim JimLake. Lake.The Themafic maficinclusions inclusionswere were subprovince), interpreted as asthe thecontinuation continuationofofmetavolcanic metavolcanic rocks rocks (Unit (Unit 5) 5) of of the the Manitouwadge Manitouwadge belt. Immediately Immediatelyeast east interpreted of Jim JimLake, Lake,exposures exposuresof of foliated foliated granitoid granitoidwith withinclusions inclusionsof of biotite biotiteschist schistwere weregrouped grouped with withQuetico Queticorocks. rocks. of Queticometagreywackes metagreywackesare arecompositionally compositionallylayered layered(typically (typically2—50 2-50 cm), locally with politic to psammitic psammitic Quetico pelitic to grading defined defined by by variations variations in in biotite, biotite, quartz quartzand andfeldspar feldsparproportions proportions(Stop (StopE3). E3).Pelitic Peliticlayers layerscommonly commonly grading 17 �Manitouwadge Manitouwadge greenstone greenstone belt belt Structural Structuralgeology geology contain contain garnet garnet and, and,less lesscommonly, commonly,sillimanite. sillimanite. In Insome somecases, cases, hornblende hornblende isis associated associated with with biotite biotiteininmafic mafic layers, layers, especially especially near near contacts contacts tototonalitic tonaliticrocks rockswith withmafic maficinclusions. inclusions.Ubiquitous Ubiquitousmigmatitic migmatiticsegregations, segregations, mainly mainly pegmatitic pegmatiticand andtonalitic tonaliticleucosome, leucosome,locally locally with with garnet garnet and andcordierite, cordierite,are arepreferentially preferentiallyconcentrated concentrated in (1—2 inpelitic peliticlayers. layers.North NorthofofDavis DavisLake, Lake,garnetiferous garnetiferousmetagreywacke metagreywackeisislocally locallyinterlayered interlayeredwith withthin thin (1-2 cm), cm), contorted contorted and andsegmented, segmented,quartz-rich quartz-richrusty rustyiron ironformation, formation,and andassociated associatedmigmatitic migmatiticsegregations segregationscontain contain coarse cm)grunerite gruneriteporphyroblasts porphyroblasts (Stop (StopE5). E5).AAsingle singlesample, sample,collected collectednorth northofofAppelle AppelleLake Lakeand and coarse (to (to11cm) about about200 200metres metresbeyond beyondthe thenorthern northernedge edgeofofour our1:25000 1:25000 map, map, contained contained orthopyroxene-biotite-garnet, orthopyroxene-biotite-garnet, while while another anothersample sampleabout about140 140metres metrestotothe thesouth southcontained containedbiotite-garnet-sillimanite-spinel. biotite-garnet-sillimanite-spinel.These Theseassemblages assemblages suggest suggest aa metamorphic metamorphic transition transition to togranulite granulitefacies facies just north north of of the the map maparea. area. The Thewestern western exposures exposures of of Quetico Quetico metasedimentary metasedimentary rocks, rocks, approximately approximately as as far far east east as asAppelle AppelleLake, Lake, are are interlayered interlayered with with medium medium to tocoarse coarsegrained grainedgabbroic gabbroic and anddioritic dioriticrocks. rocks.Foliated Foliatedgabbro-diorite gabbro-dioriteisisfound foundon on both both sides sidesof of the thesubprovince subprovinceboundary, boundary, but butisislocally locallydifficult difficulttotodistinguish distinguishunambiguously unambiguouslyfrom fromtonalitic tonalitic and mafic mafic (recrystallized (recrystallized metavolcanic) metavolcanic) rocks Wawa subprovince The and rocks typical typical of of the the northern northern Wawa subprovince in in the the area. The gabbro-diorite EverestLake Lake pluton, pluton, aalenticular lenticular gabbro-diorite (not aa separate separate unit unit on onour ourmap) map)isispartly partlyequivalent equivalent to to the theEverest intrusion km in width) lying intrusion (about (about1—1.5 1-1.5 km lying along along the the Wawa-Quetico Wawa-Quetico subprovince boundary grouped with the the Black Pic Pic batholith batholith (Williams (Williams and and Breaks, Breaks, 1990a; 1990a; Williams Williams et al., al., 1992). 1992). Our Ourobservations observations suggest suggest that that Black the the intrusion intrusioncomprises comprisessheets, sheets, varying varying considerably considerably in thickness, thickness, that that transgress transgress the thesubprovince subprovinceboundary. boundary. Interlayering (10 m m plus) to thin Interlayering with with Quetico Quetico metasedimentary metasedimentary rocks rocks apparently apparently varies varies from outcrop-scale outcrop-scale (10 thin (20 (20 cm) cm) concordant concordant sheets sheets (Stop (Stop G2). G2). Aeromagnetic Aeromagnetic striping in the the area, area, parallel parallel to toand andtransgressing transgressing the the Thegabbro-diorite gabbro-diorite isis subprovince subprovince boundary, boundary, isis inferred inferred totoreflect reflectthe thepresence presenceofofgabbro-diorite gabbro-dioritesheets. sheets. The foliated, foliated,but butsome somelow lowstrain strainenclaves enclavesare arenearly nearlymassive, massive,for forexample exampleininboudinaged boudinagedremnants remnantsofofextended extended layers layers(Stop (StopG2). G2).Locally, Locally,blocky blocky gabbroic gabbroicinclusions inclusions in aa matrix matrixof of contorted contorted migmatite migmatitemay mayhave haveoriginated originated as aspre-metamorphic pre-metamorphicdykes. dykes. Proterozoic Proterozoicintrusions intrusions Diabase Diabasedykes dykes (Unit (Unit17) 17)likely likely include include representatives representatives of of at at least least three threeProterozoic Proterozoicswarms; swarms;Matachewan, Matachewan, Biscotasing Biscotasing and and Marathon Marathon dykes dykes (K. (K. Buchan, Buchan, pers. pers. comm., comm.,1992). 1992).They Theyproduce producepronounced pronouncedaeromagnetic aeromagnetic lineaments. lineaments.The Themost mostvoluminuous voluminuousdykes dykesin inthe theManitouwadge Manitouwadgearea areaare arenorthwest-trending northwest-trending dykes dykesinferred inferredto to belongto tothe theMatachewan Matachewanswarm, swarm,dated datedatat2454±2 2454zt2Ma Ma(Heaman, (Heaman,1988). 1988).AAsecond secondset setof of northeasterly northeasterly trend, trend, belong probably probablybelonging belongingto tothe the2166.7±1.4 2166.7zt1.4Ma MaBiscotasing Biscotasingswarm swarm(Buchan (Buchanetetal., al.,1993), 1993),isismainly mainlyrepresented representedby by aawide widedyke dyke (up (upto to80 80m) m)striking strikingthrough throughSwill SwillLake. Lake. Northerly Northerly trending trending dykes dykes are are inferred inferred to to belong belong to to the the 2170 2170 Ma Ma Marathon Marathonswarm swarm(Fahrig (Fahrigand andWest, West,1986). 1986). STRUCTURAL STRUCTURALGEOLOGY GEOLOGY Ourpreferred preferred model model accounts accounts for for structural structuralobservations observations in in the theManitouwadge Manitouwadge belt belt inin aa4-stage 4stagehishisOur toryof ofductile ductile deformation. deformation. The Themap mappattern patternofofthe thebelt beltis is largelycontrolled controlledbybynortheasterly northeasterlyplunging plungingD3 D3 tory largely folds,including including the theManitouwadge Manitouwadge synform. synform. D1 Dl and and D2 D2folding folding and and faulting faulting produced produced much much of of the the internal internal folds, complexity of of the thebelt, belt,particularly particularlyapparent apparentininthethe hinge regionofofthe the Manitouwadgesynform. synform.HeterogeHeterogecomplexity hinge region Manitouwadge neously distributed distributedD4 D4deformation deformationlocally locallymodified modified the the map mappattern patternand andcaused causedsporadic sporadicdevelopment developmentofof neously outcrop-scale outcrop-scalestructures. structures. D1 deformation D 1 deformation D1 Dl encompasses encompasses all all structural structural features features that that pre-date D2 Dadeformation deformation and and ititmay mayrepresent representmore morethan than onephase phaseof ofdeformation. deformation. Most MostD1 Dlstructures structuresare areinterpreted interpretedfrom frommap-scale map-scaleobservations observationsand andare arecryptic cryptic one atatoutcrop-scale, outcrop-scale, due duetotooverprinting overprintingby bysubsequent subsequentmetamorphism metamorphismand andcomplex complexdeformation. deformation. The Themost most Dl map-scale map-scale structures structures isisin in the thearea areaof of known known mineralization mineralization (Fig. (Fig.4). 4).InInthe theWillroyWillroycompellingevidence evidencefor for D1 compelling Gecoand andWillecho Willecho areas, areas, aaprominent prominent discontinuity discontinuityisisassociated associated with with truncation truncationofofiron ironformation formationand andother other Geco units,and andwith withrepetition repetitionofofthethe lithological sequence;quartz-phyric quartz-phyricfelsic felsicrocks, rocks,iron ironformation formationand andmassive massive units, lithological sequence; sulphidemineralization, mineralization,sillimanite-muscovite-quartz sillimanite-muscovite-quartzschist. schist.The Thediscontinuity discontinuityisismarked markedby byseveral severalmappable mappable sulphide zones of of laminated laminated straight straightgneiss gneiss(Unit (Unit11), l l ) ,interpreted interpretedasasannealed annealedmylonite. mylonite.An Anadditional additionaldiscontinuity discontinuity zones expressed as asaa'finger' 'finger' dominated dominatedby bysilicate silicateiron iron formation formation that thatextends extendsfrom fromthe thethick thicksouthernmost southernmostiron iron isisexpressed formationnortherly northerlytoward towardGarnet GarnetLake Lake(accompanying (accompanying1:25000 1:25000map). map). formation Thestraight straightgneiss gneissisistypically typicallya ahard hardlaminated laminatedfelsic felsicrock, rock,characterized characterizedininthin thinsection sectionbybymillimetremillimetreThe scale scalequartz quartzand andfeldspar feldsparlamellae, lamellae,mostly mostlyannealed annealedtoto aagranular granulartexture. texture. Despite Despite annealing, annealing, the thegrain grain size asquartz quartzribbons. ribbons. North Northofof sizeremains remainsvery veryfine fineand, and,ininsome somecases, cases,vestiges vestigesofofmylonite mylonitefabric fabricsurvive surviveas the theWillecho Willecho 33pit pit(Fig. (Fig.4), 4),pegmatite pegmatiteisistransitional transitionaltotostraight straightgneiss, gneiss,asasalready alreadydescribed described(see (seeTectonic Tectonic rock rock units). units). InInthe theWillecho Willechoarea areainingeneral, general,straight straightgneiss gneissoccurs occurs adjacent adjacent to totruncated truncatedand andboudinaged boudinaged iron gneiss Willroy-Geco ironformation. formation.Straight Straight gneissininthethe Willroy-Gecoarea areaextends extendseasterly easterlyand andisisexposed exposednear nearthe thesouthern southern endofofWowun Wowun Lake, Lake, in in contact contactwith withhighly highlystrained, strained,straight-laminated straight-laminated iron iron formation formation (Stop (Stop Dl). Dl).These These end observations observationsled ledus ustotointerpret interpretstraight straightgneiss gneissasasannealed annealedmylonite mylonitelying lyingon ondiscontinuities discontinuitiesrelated relatedtotoearly early ductile ductilefaults. faults. 18 �______ Structural Structuralgeology geology Manitouwadge Manitouwadge greenstone belt belt Metaaediment.ry rock. — Iron Straight joel.. . granite to tonalite Orthoamphlbole—cordlerlte— : Quartz—phyric feteic Slflhnanlte—mu.covite—quartz EI garnet joel.. .1 ( ... ..• f. .. .. N. -' . . Foliated trondhjexnite Inner . . * metavolcanic rocks Mafic, mixed maflc—fel.ic metavolcanic rocks Massive .ulphide deposit Fold azial trace (02. 03) Fault — Interpreted • formaUon Felaic to intermediate met..— volcanic rock., foliated Dl thruat fault Schematic D2 - volcanic sheath fold belt / FIG. 4. Geology Geology of of the the area area from from the the Geco Geco mine mine (G) in in the the east, east, to tothe theWiliroy Willroyorebodies orebodies (1 (1 to to 6), 6), the Nama Nama Creek Creek mine mine (N) (N) and and the theWillecho Willecho orebodies (El (El to toE3) E3)ininthe thewest. west.All Allthe theknown knowneconomic economic Cu-Zn deposits lie in the the inner inner volcanic volcanic belt. The Theinset insetshows showsaaschematic schematicview view of of the theD2 D2sheath sheath fold fold interpreted interpreted to torepeat repeatthe theD1 Dlfault faultand andmineralized mineralizedsequence sequencebetween between the theNama NamaCreek Creek (N) (N)and andWillecho Willecho deposits deposits (El, (El,E2, E2,E3). E3). Straight gneiss gneiss mostly mostly lacks lacks any any well well defined defined lineation, lineation, and and where where aa lineation lineation isisobvious, obvious,for forexample example Straight sillimanite in sheared pegmatite, itit may may have have developed developed in lineated sillimanite in response response to to later later deformation. deformation. Due to the paucity of of lineations lineations and and kinematic kinematicindicators, indicators,and andthe thedifficulty difficulty in in interpreting interpretingoffsets offsets based based on on stratigraphy, stratigraphy, paucity transport direction directionofofearly earlyductile ductilefaults faultsisisnot notknown; known;however, however,the thelow lowangle angleofofthe thediscontinuities discontinuities the transport suggests thrust faults. faults. Straight gneiss gneiss layering layering is mostly parallel parallel to to dominant dominant D2 D2foliation, foliation, except except in in the thehinge hingeregions regions of of some some Straight D2 D2 folds. folds. Relationships Relationships suggesting pre-D2 age gneiss fabrics fabrics and associated associated faults are are best best suggesting aa pre-D2 age for for straight gneiss preserved in the hinge hinge region of the D2 map-scale preserved map-scale fold foldsouthwest southwestofofthe theNama NamaCreek Creekdeposit deposit(Fig. (Fig.4). 4). In In this Dz folds in felsic area, minor D2 felsicrocks rocksare aredefined definedby byan anearlier earlier(Dl) (Di)gneissosity gneissositythat thatwe weinterpret interpret to to be be related related to straightgneiss gneisslayering layering(see (seeStops StopsA22—A23). A22-A23). The fault that thatfollows followsthe thefinger fingerof of iron ironformation formation(see (seeabove) above) straight GarnetLake Lakeisisdeformed deformedby bymap-scale map-scaleD2 Dzfolds. folds. toward Garnet Willechodeposits, deposits,aamap-scale map-scaleisoclinal isoclinalfold fold is is defined defined by quartz-phyric quartz-phyric felsic felsic rocks, iron of the theWillecho Northeast of formation and and sillimanite-knot sillimanite-knot felsic The southern southern limb limb of of the the fold fold is is apparently apparently truncated truncated formation felsic schist schist (Fig. (Fig. 4). 4). The by aa D1 Dl fault, fault,suggesting suggesting that thatthe thefold foldwas wasproduced produced by by progressive progressive D1 Dl deformation. of by deformation. Irregular truncation of units along along D1 Dl fault fault traces traces in in general general could could be the the result result of of prepre- or or early early D1 Dl folding. The map map pattern pattern of of D1 Dl units structures isisalso alsocomplicated complicated by by later laterdeformation, deformation, particularly particularly during duringD2. D2. structures D2 D 2 deformation deformation The dominant dominant planar planar and andlinear linearfabrics, fabrics, and andoutcrop-scale outcrop-scale folds, ubiquitous The ubiquitous in in most most rocks, rocks, are are attributed attributed to D2 D2 deformation. deformation. The Thedominant dominantD2 D2foliation foliationisistypically typically aa pervasive pervasive moderate moderate to tostrong strongschistosity, schistosity,defined defined to by micas, amphiboles, amphiboles, and and deformed deformed quartz quartz and and feldspar. feldspar. Except Exceptininthe thehinge hingeregions regionsof of D2 Dz folds, the foliation by is aa composite composite D2-D1 Dg-Dl fabric, generally parallel lithological contacts. Early elements elements of the the fabric fabric include include is parallel to lithological contacts. Early 19 �Structural Structural geology geology Manitouwadge greenstone belt =:'!;;!*- I AXIAL SURFACE TRACES OF FOLDS FIG. 5. syncline' repeats repeats the 5. Axial Axial traces traces of ofD2 D2synclines, synclines, D3 D3 and D4 D4 folds. folds. The The D2 Dz 'Manitouwadge 'Manitouwadge syncline' belt) about aa central sequence (OVB = = outer volcanic volcanic belt, belt, IVB = = inner volcanic belt) central zone zone of of metametavolcanic sequence on the the southern limb greywackes on limb of the D3 Manitouwadge synform. The The Manitouwadge Manitouwadgemetagreywackes metagreywackes are interpreted to to be be correlative correlative with with Quetico Quetico rocks. rocks. Another Another D2 D2syncline syncline could could account account for the the two two of the the Dead Dead Lake Lake suite suite (DL) (DL) or, or, alternatively, alternatively, the the Dead Dead Lake Lake suite suite could couldbe beequivalent equivalentto toouter-belt outer-belt zones of mafic rocks rocks repeated repeated by the Orthoamphibole-cordieriteD2 syncline syncline centred centred on on the themetagreywackes. metagreywackes. Orthoamphibole-cordieritemafic the D2 garnet gneiss and mafic mafic rocks rocksinin the the One One Otter-Banana Otter-Banana Lakes Lakesarea areato to the the east (0-B) are garnet gneiss and areinterpreted interpreted as repetitions of of the thesupracrustal supracrustalsequence sequenceby byaaD2 D2synclinal synclinal'keel' 'keel'involved involvedininD2-D3 D2-D3fold foldinterference interference patterns. modified bedding, bedding, metamorphic layering, transposed intrusive modified intrusive sheets, sheets, and andshortened shortenedpillows, pillows,volcanogenic volcanogenic fragments, fragments, mafic clots in intrusive rocks and sillimanite knots. D2 D2 fabrics fabrics are are well well developed in most intrusive rocks, including including synvolcanic synvolcanictrondhjemite trondhjemite(Unit (Unit 12), 12),early earlyphases phasesofofthe the Black Black Pic Pic batholith batholith (Unit 14), rocks, 14), the the Lake and and Nama Nama Creek Creek plutons plutons (Unit 13), and undivided intrusive rocks (Unit 14) Loken Lake 14) within the supracrustal supracrustal sequence. sequence. In the Quetico Quetico subprovince to the north, the the dominant dominant planar planar fabric fabric is is correlated correlated with with D2 D2 fabrics in the the Manitouwadge and Jim Lake the Manitouwadge Manitouwadge belt. belt. D2 D2foliations foliations are aredeformed deformed by by D3 Da folds, including the synforms and the Blackman Blackman Lake antiform (Figs. 5 and 6). 6). Metamorphic minerals minerals characteristic characteristic of of upper amphibolite-facies, such as sillimanite, amphiboles Metamorphic amphibolite-facies, such amphiboles and micas, define the the orientation of the east-northeastly plunging plunging D2 D2 mineral lineation. In In some some places, unoriented sprays of of orthoamphibole orthoamphibole and and sillimanite are are present present in in the the same sameoutcrop outcropas aslineated lineatedgrains. grains. The Thejuxtaposition juxtaposition of lineated lineated and randomly oriented may reflect reflect patterns patterns of of strain strain partitioning, or it may oriented grains may may suggest suggest postkinematic recrystallization. Locally, Locally,strong strongelongation elongationof of sillimanite sillimanite knots, knots,feldspar feldsparaugen, augen,orormafic maficenclaves enclaves produced produced L>S tectonites. tectonites. InIngeneral generalacross acrossthe theregion, region,the therelationships relationships between between orientations orientations of of lineations lineations and later later folds folds are are variable. variable. In Inmany manyareas, areas,the theD2 D2lineation lineationisisnearly nearlycoaxial coaxialwith withD3 D3fold foldaxes; axes;however, however, in the inner of the inner volcanic volcanic belt, belt, the the orientation orientationof of the thelineation lineationvaries varies systematically, systematically, from the hinge hinge region of Manitouwadge synform, synform,to to the the southern limb (Figs. 5 and 6). Manitouwadge D2 foliations and east-northeasterly east-northeasterly plunging Dz foliations plunging mineral/stretching lineations lineations are are parallel parallel to toaxial axialsurfaces surfaces and axes folds. In the inner hinge synform, mapmap- and and outcrop-scale axes of local D2 folds. hinge region of the D3 Manitouwadge synform, D2 are defined by iron formation formation and D2 folds are and felsic felsic rocks. Locally, Locally, minor minor folds folds have circular circular eye eye shapes shapes produced produced by curving hinge lines. Southwest Southwest of the the Nama Nama Creek Creek deposit, deposit, aaprominent prominent map-scale map-scalefold fold of of iron iron formation formation inconsistent with with a parasitic relationship synform. In has S-asymmetry S-asymmetry inconsistent relationship to the the D3 D3 Manitouwadge Manitouwadge synform. In the the hinge hinge region of the axial surfaces surfaces of map-scale minor folds of the S-fold, outcrop-scale folds change change asymmetry across the axial of 20 �Manitouwadge Manitouwadge greenstone greenstone belt belt Structuralgeology geology Structural FIG. FIG.6.6. Structural Structural subareas subareas AAtotoKKofofthe theManitouwadge Manitouwadgearea, area,corresponding correspondingtotothe theaccompanying accompanying stereonets (this (thisand andfollowing followingpage). page). Equal Equalarea areanets nets(A—K) (A-K) show the distribution distribution of of the the dominant dominantD2 D2planar planar stereonets (filled linear (cross) (cross) fabric fabricelements. elements. The The structural structural data data was (filled circle) and linear wasparsed parsed into intoapproximately approximately30 30subareas subareas on on the thebasis basisofofsimilar similarorientation. orientation.The Thesubareas subareasononthe themap mapare arecomposites compositesshowing showingthe themajor majorchanges changesinin (S) and and linear linear (L) (L) data data points points isis structural trends trendsrelated related totomap-scale map-scale folding. folding. The The number number of data planar (S) structural shown best fit for planar data. shown for each net, and and the the great greatcircle circle and and pole pole (filled (filled square) is the cylindrical best data. 21 �Manitouwadge greenstone greenstone belt Structural Structuralgeology geology 22 �Structural Structuralgeology geology Manitouwadge greenstone belt ..... • . k :. .... : .. .. • . . .•• Foliated tondhjemlte Tonalite, metagreyweoke, felaic roake, a,llimanlte— muocov,t,e schiat ——————— 1- 1km . Orthoamphibole—garnet— cordierite gnei.a — — Interpreted Interpreted fault fault Quarto—phyrlc blab metavobcan,c rocka e.ni intermediate to maf Ic metavolcanic rocica ---,'- Da fold fold trace trace D2 FIG. 7. 7. Down-plunge Down-plunge projection projection of of the the inner inner hinge hinge region region of of the the Manitouwadge Manitouwadge synform. synform. The The line line of projection projection is the plunge plunge of the synform synform at 065°/25°. 065O/25'. A-A' A-A?isis the theline lineof of intersection intersection between between the projection plane plane and and the the horizontal horizontal at at350 350metres metres elevation. elevation. Topographic Topographic relief (about 140 140 metres) is not shown. trace of of the the projection. projection. G = shown. See See Figure 3 for the surface surface trace = Geco Geco mine, mine? 11 to 66 ==Wiliroy Willroy orebodies, =Nama Nama Creek Creek mine, mine?EE ==Willecho Willecho33 orebody. orebody. orebodiesl NC = the iron iron formation-felsic formation-felsiccontact contact (Stops (StopsA22—A23). A22-A23). The plungingD2 D2mineral mineral lineation lineation the The dominant northeasterly plunging gneissosityl interpreted axes of of minor folds. Felsic Felsic rocks have a folded folded gneissosity, is parallel to axes rocks near near the contact have interpreted to to be be a Dl fabric? Dl foliation D1 fabric, and local micaceous enclaves enclaveshave haveaaschistosity schistositythat that is is oblique obliqueto to the the D1 foliation and parallel parallel to the the theaxial axialplanes planesofoflocal localD2 D2folds. folds.To Tothe thesouth, southlmetagreywackes metagreywackesare areinvolved involved in in map-scale map-scale D2 D2 folds and the the the dominant dominantfoliation foliation isis ascribed ascribed to toaaD2 D2axial-planar axial-planar fabric. fabric. Between the Nama Nama Creek Creek and and Willecho Willecho deposits, deposits, lithological lithological units and and D1 Dl faults faultsdefine define aacomplex complexgegeBetween interpreted as the the result result of of folding folding by aa map-scale map-scale D2 sheath ometry interpreted sheath fold fold (Fig. (Fig. 4). 4). The Thegeometry geometry of of the the structures in in the theinner innerhinge hingeregion regionofofthe theManitouwadge Manitouwadgesynform synformcan canbe beviewed viewedinina adown-plunge down-plunge pre-D3 structures The mapped mapped D1 Dl faults are interpreted interpreted to be be part part of of aa single single ductile ductile thrust fault, fault?folded folded projection (Fig. 7). The projection map-scale D2 D2 sheath produced a continuous continuous fault northeast and and an an eye eye fold fold to to by aa map-scale sheath fold fold that produced fault trace trace to the northeast southwest. The Thesheath sheathfold foldrepeats repeatsmineralized mineralizediron iron formation formation (Willecho (Willecho deposits) the southwest. deposits) lying lying on on or near the Dl fault. Alternatively, Alternatively? the the map mappattern patternofofthe thearea areacould couldbebeexplained explainedby bymushroom-shaped mushroom-shaped D2/D3 D2/D3 fold fold D1 however? the nearly coaxial coaxial relationship relationship of of D2 D2 and and D3 D3 linear fabric fabric elements elements (see (see below) below) is more interference; however, plunging sheath fold. Also, the intrafolial repetitive consistent with a northeasterly plunging intrafolial character? character, rather than aa repetitive fold fold pattern, pattern?suggests suggests sheaths sheaths rather ratherthan thaninterference. interference. the southern southernlimb limbof of the theManitouwadge Manitouwadgesynform, synform?the the progression progression from from volcanic to sedimentary rocks On the syncline (Suffel (Suffel et al., al., was previously previously interpreted as as aa stratigraphic stratigraphicsuccession succession repeated repeated by by an an early earlysyncline (Fig. 3) was of the theGeco Gecoorebodies orebodiesfrom from north north 1971; Touborg? 1971; Touborg, 1973)? 1973), the the 'Manitouwadge syncline'. syncline'. An increase in Zn/Cu of to south, southland andthe thepresence presenceofoforthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss gneiss(metamorphosed (metamorphosed equivalent equivalent of of footwall footwall to synvolcanic alteration) the north, north?support supportsoutherly southerlyyounging youngingfor forthe theWillroy-Geco Willroy-Geco area area(Suffel (Suffel et et al., al.? synvolcanic alteration) to the 1971; Friesen al. 1982). 1982). Our Ourmapping mappingconfirms confirmsrepetition repetitionofofthe thelithological lithologicalsequence; sequence;mafic maficmetavolcanic metavolcanic 1971; Friesen et al., rocks?felsic metavolcanic rocks interlayered metasedimentary rocks rocks (Figs. (Figs. 33 and and 5). 5). The The rocks, interlayered with iron formationl formation, metasedimentary correlation of of volcanic volcanic sequences sequences is belts, the the correlation is strengthened strengthened by the ages of felsic felsic rocks rocksin in both both inner inner and outer belts, orthoamphibole-cordierite-garnet same within within error error atat2720 2720Ma Ma(see (seeGeochronology). Geochronology).The Theextensive extensiveunit unitofoforthoamphibole-cordierite-garnet same rocks in the the inner inner volcanic volcanic belt belt has has aacounterpart counterpartininthe theouter outerbelt beltininsporadic sporadicorthamphibole-bearing orthamphibole-bearingzones zones rocks in mafic mafic rocks rocks near their their northern northern contact. contact. InInour ourinterpretation, interpretation? volcanicand andsedimentary sedimentarysequences sequencesare are in volcanic repeated across across the the southern southern limb limbof of the theD3 D3Manitouwadge Manitouwadge synform by a D2 syncline with in repeated with an axial trace in the central central metagreywacke metagreywacke (Fig. (Fig. 5). 5). the our preferred preferred structural structural interpretation, interpretation?map-scale map-scale D2 D2 folding folding is is responsible responsible for repetitions repetitions of of In our supracrustal rocks along along the axial trace of of the the Manitouwadge Manitouwadge synform The two two zones zones of of supracrustal synform (Figs. (Figs.55 and and 8). 8). The 23 �Structural Structuralgeology geology Manitouwadge Manitouwadge greenstone greenstone belt belt nMafic meiavoicanic rocks Mafic metavolcmic rocks Iron formation El FIG. 8. 8. Block Block diagram diagram showing showing schematic schematic prepreD3 D3 relationships relationships of supracrustal supracrustal rocks, rocks, repeated repeated by D2 D2folds. folds. The The fold fold trace traceininmetagreywacke metagreywacke between between the inner (IVB) (IVB) and and outer outer (OVB) (OVB) volvolcanic belts belts represents represents the the'Manitouwadge 'Manitouwadge synsyndine' cline' (Fig. (Fig. 5). 5). The Thesheath sheathfold folddefined defined by by iron iron formation formation represents represents the Nama Nama Creek Creek to toWilleWillecho area in Figure 4. DL DL = = Dead Dead Lake Lake suite, 0-B 0-B ==One One Otter-Banana Otter-Banana area. area. Metagreywacke the Dead and orthoamphibolebearing orthoamphibole-bearing rocks rockseast eastof ofOne OneOtter Otter and and Banana Dead Lake Lake suite and and exposures exposures of mafic and Lakes Lakes may represent D2 D2 synclinal synclinal 'keels', 'keels', involved involved in in D2/D3 D2/D3 fold fold interference interference patterns. patterns. Alternatively, Alternatively, the the Dead Lake suite might might simply simply be be septa septaof ofmafic mafic volcanic volcanic and and associated associated rocks rocks that thatwere wereincluded includedinindeeper deeper levels of the synvolcanic synvolcanic trondhjemite intrusion. intrusion. levels D3 deformation deformation The regional D3 folds, folds,from fromnorth northto to south; south; the Jim regional map pattern is is dominated dominated by by easterly easterly plunging plunging D3 Lake synform, synform, the Blackman Blackman Lake Lake antiform and the the Manitouwadge Manitouwadge synform. The Banana BananaLake Lakeantiform antiform Lake synform. The could be either a D3 D3 or or aa D4 D4 fold fold or or shear shear zone. zone. There There isis aagradational gradational change change to the the south, south, from from tight tight could fold hinges and dominantly dominantly east-west eat-west structural structural trends, trends, totomap-scale map-scalefolds foldswith withbroader broaderhinge hingeregions regions and and northeasterly northeasterly traces. traces. The Thecrude crudeZ-asymmetry Z-asymmetryof ofmap-scale map-scale D3 D3 folds and the the curvature curvature of of their their axial axialtraces traces suggests formation during during oblique oblique dextral dextral transpression. transpression. The changes from from aa broad broad rounded rounded inner inner hinge hinge to to a tighter The shape shape of of the theManitouwadge Manitouwadge synform changes tighter outer outer hinge Lakes area area (Figs. (Figs. 33 and and B3). In the the inner inner hinge hinge region, region, the the synform synform has has aa shallow shallow to hinge in the the Swill-Mills Swill-Mills Lakes moderate northeasterly northeasterly plunge. plunge. The Theaxial axialsurface surface dips dips to tothe thesouth, south,based basedon onshallow shallowsoutherly southerly dips dipsof ofthe the northern limb, limb, and and near-vertical near-vertical to to moderate moderate southerly southerly dips of the southern southern limb. limb. D2 D2planar planar fabrics fabrics in in the the Willecho-Geco area define a girdle with a moderate to 6, area area A), A), generally generally to shallow shallow easterly plunging plunging axis axis (Fig. (Fig. 6, parallel to the from the hinge region region to to the southern the axis axis of of the the synform. synform. D2 D2lineations lineations vary vary systematically systematically from limb of the synform, small circle circle rotation rotation (Fig. (Fig. 6, areas synform, defining defining aa small areas A and B). B). This This suggests suggests aa component component of fiexural flexural slip during folding, possibly possibly due to mechanical mechanical anisotropy produced by iron formation formation or or altered altered rocks. rocks. In In the the outer outerhinge hingeregion, region,D2 D2foliations foliations in supracrustal rocks and in the Black Black Pic Pic batholith batholith define define aa girdle with aa moderately moderately to the D2 lineations lineations consistently consistently plunge moderately the moderately northeast-plunging northeast-plunging pole, pole, and and D2 northeast. northeast. InInagreement agreementwith withfield fieldobservations, observations,orientations orientationssuggest suggest that thatearly earlyfabrics fabrics are are strongly strongly transposed transposed by D3 folding. Local enclaves of of westerly westerly plunging plunging D2 D2lineations lineationsare are likely likelythe theresult result of of reorientation reorientation by minor to the theManitouwadge Manitouwadgesynform. synform. folds related to D3 map-scale minor folds folds are are identified identifiedacross acrossthe themap map area. area. In map-scale minor In the the outer outerhinge hingeregion region of of the theManiManitouwadge synform, D3 folds are defined defined by contacts contacts between between felsic felsic or intermediate intermediate and andmafic maficmetavolcanic metavolcanic rocks. rocks. In In the theinner innervolcanic volcanicbelt, belt,iron ironformation formation contacts contacts define define D3 D3 folds in the northern northern hinge hinge region region and southern limb of the Manitouwadge synform. In In the the One One Otter-Banana Otter-Banana area along along the the eastern eastern axial trace of of Manitouwadge synform. the the synform, synform, aa thin thinbelt beltofofsupracrustal supracrustalrocks rocksdefines definesseveral severalfolds folds which which also also deform deform the foliation foliation (Fig. (Fig. 5). 5). Underground Underground at at the the Geco Geco mine, mine, the the'Geco 'Gecodrag dragfold' fold'(Brown (Brownetetal., al.,1960; 1960;Friesen Friesen etetal., al.,1982) 1982)may mayalso alsobe be a D3 D3 structure. structure.The TheZ-shaped, Z-shaped,easterly easterlyplunging plungingfold foldpair pairisisdefined definedbybyquartz-muscovite-sillimanite quartz-muscovite-sillimaniteschist, schist, which hosts the main orebody which hosts orebody at at Geco Geco (see (see Setting of Mineralization). Mineralization). (Note (Note that Brown Brown et al. al. mistakenly mistakenly refer to S-asymmetry in their their figures.) S-asymmetry in their their discussion, discussion, but show show Z-asymmetry Z-asymmetry in figures.) The main main orebody orebody has has aa teardrop shape of the 'Geco shape and and lies lies within within the the synformal synformal axial axial region region of 'Geco drag fold' (ibid.). The Thegeometry geometry isis consistent with that synform and and similar similarto to that that of of that expected expected for for aa parasitic parasitic fold fold related to the the Manitouwadge Manitouwadge synform outcrop-scale folds folds (see (see below). below). D3 outcrop-scale Locally outcrop-scale D3 D3folds foldsvary varyin in character character depending depending on on rock rock type and position Locally developed developed outcrop-scale position with with respect to to larger larger structures. structures. InInthe theSwill SwillLake Lakearea areaininthe theouter outerhinge hingeregion regionofofthe theManitouwadge Manitouwadgesynform synform (Fig. B3), B3), two two felsic felsic layers layers in in the themafic maficvolcanic volcanic sequence sequence define define map-scale symmetrical and asymmetrical asymmetrical D3 folds (Stops B11—B21). The moderately moderately open D3 folds deform D2 foliation foliation and, locally, Bll-B21). The locally, layering. Fold Fold asymmetry changes changes from dominantly dominantly Z-asymmetry Z-asymmetry on the the southern southern limb limb of of the thesynform, synform,to toM-asymmetry M-asymmetryinin the the hinge hinge region, region, to to S-asymmetry S-asymmetry on on the the northwestern northwestern limb. limb. In Inthe thevicinity vicinityof ofthe theGeco Gecoand andWillroy Willroydeposits, deposits, both on on surface surfaceand andunderground, underground,micaceous micaceousrocks rockslocally locallypreserve preserveD3 D3folds, folds,typically typically with withshallow shalloweasterly easterly or westerly plunges and gently gently curving curving hinge hinge lines. Sulphide Sulphide mineral mineral are are commonly commonly concentrated in in the thehinge hinge 24 �Structural geology Structural geology Manitouwadge greenstone belt regions of of the the D3 folds folds in in the Geco regions Geco mine. In In aafew fewsurface surface exposures, exposuresl the the D2 D2mineral mineral lineation lineation isis evidently evidently folded at aa low low angle angle to to the thefold foldaxes. axes. In general, general) D3 axial planar planar fabrics fabrics are areweakly weakly developed. developed. Locally, Locally, a crenulation crenulation cleavage cleavage lies in the axial axial regions of of D3 D3 outcrop-scale outcrop-scalefolds, folds,and andan an associated associatedcrinkle crinklelineation lineationisisparallel paralleltotofold foldaxes. axes. On the limbs regions limbs of map-scale D3 folds, folds, schistosity schistosity in in micaceous micaceous layers layersisis locally locallyoblique obliqueatat aa low low angle angle to the dominant dominant D2 D2 foliation. The The absence absence of of aa pervasive pervasive D3 D3 axial axial planar planar fabric fabric may may reflect reflect post-peak post-peak metamorphic metamorphic conditions, conditions, the presence of a strong D2 D2 anisotropy and the the paucity paucityof ofmicaceous micaceous rocks. rocks. The Blackman Blackman Lake Lake antiform antiform is is defined defined by folded folded D2 foliation and mafic to intermediate intermediate rocks, rocks, which which mostly occur as screens in foliated plutonic rocks (Fig. 3). Along Along the the western western trace trace of of Blackman Blackman Lake Lake antiform in the foliated tonalite tonalite change orientation around the Janet JanetLake Lakearea area(accompanying (accompanying1:25000 1:25000 map), D2 fabrics in foliated define aa girdle girdlewith withan aneast-northeasterly east-northeasterly plunging plungingaxis axis(Fig. (Fig.6) 6,area areaF). F). On On the the northerly northerly trending trending the fold and define short limb limb of of the thefold, fold)D2 D2foliations foliationsin inmigmatitic migmatiticrocks rocksare arereoriented reorientedininoutcrop-scale outcrop-scaleshear shearzones zones(1—3 (1-3 m long) and in convolute folds. The shear zones have northerly northerly strikes) strikes, steep steep dips, dips, and and either either sinistral or convolute minor folds. zones have in plan plan view. view. The folds vary vary in in style styleand and orientation) orientation, but but most most have have S-asymmetry S-asymmetry and and moderate moderate dextral offset offset in they deform an an earlier earlier (D2?) (D2?) mineral mineral lineation. lineation. Along the the easterly trending northeasterly plunges, plunges) and locally, they long limb limb of of the Blackman long Blackman Lake Lake antiform, antiform) south of Blackman Blackman Lake Lake (or Kern Lake) Lake) (Fig. (Fig. 3), 3)$moderately moderately east-northeasterly plunging, plunging, Z-shaped Z-shaped folds folds are commonly commonly parallel to aa distinct distinctstretching stretchinglineation. lineation.Locally, Locally, pegmatites of folds. North pegmatites and and granitic graniticveins veins are are concentrated concentrated in in the the short shortlimbs limbsof North of of Blackman Lake, migmatitic segregations and veins increase toward toward the Quetico boundary. Abundant Abundant screens screens of of mafic mafic gneiss, gneiss, and locally, locally, iron formation could could be be an extension of the outer volcanic belt of of the Manitouwadge synform. In In the One extension of volcanic belt Manitouwadge synform. Otter area, area, the theBlackman BlackmanLake Lake antiform antiform is is defined defined by the attentuated attentuatedextension extension of of the theinner innervolcanic volcanic belt belt (Fig. 5). D2 girdle with with an east-southeasterly east-southeasterly plunging plunging pole pole (Fig. (Fig. 6) 6, area G). D2 fabrics define define aa girdle The The most most northerly northerly D3 D3fold, fold,the theJim JimLake Lakesynform, synform)isisdefined defined by by zones zones of of mafic mafic inclusions in tonalite tonalite and and by migmatitic metasedimentary rocks of of the Quetico (Fig. 3). Migmatitic Quetico subprovince subprovince (Fig. Migmatitic biotite biotite schist schist can can be be traced to traced to the the south southasasfar farasasLarry LarryLake Lakeand andisisinvolved involvedin inaaparasitic parasiticZ-fold Z-fold between between Jim Jim and andDavis DavisLakes Lakes (accompanying 1:25000 map). Away from fold fold hinges, hinges, dominant dominant D2 foliations foliations are are mostly mostly east-west east-west trending 1:25000 map). Away from and steeply steeply dipping, dipping, parallel parallel to to the theaxial axialsurfaces surfacesof of tight-isoclinal tight-isoclinal D3 D3 folds. folds, The Thefoliations foliationsdefine define aacrude crude girdle with a near-horizontal near-horizontal easterly easterly plunging plunging axis, axis, subparallel subparallel both both to tolineations lineationsand andD3 D3fold foldaxes. axes. Outcrop-scale structures in in migmatitic migmatitic rocks rocks in the Quetico subprovince and near the subprovince boundubiquitous Z-folds with easterly easterly to to northeasterly northeasterly plunging plunging axes axes that that fold the dominant ary include, include) ubiquitous Z-folds with dominant planar planar fabric (D2?), shear bands, bandsl foliation foliation fish, fish, and and rotated rotated boudinage, boudinage)mostly mostlyshowing showing dextral dextral kinematics kinematics and and ininterpreted to reflect dextral shear. shear. Their that they are terpreted reflect oblique oblique dextral Their relationship relationship to the dominant dominant fabric suggests suggests that are correlative with with D3 D3 deformation deformation in in the Manitouwadge belt. All correlative Manitouwadge belt. All of of the the minor minor structures structures deform deformmigmatitic migmatitic layering, but are are transected transected by by discordant discordant migmatitic migmatiticveins veins which, which, in some cases, casesl are subparallel to the axial axial surfaces of folds. folds. These observations suggest that that peak peak metamorphism metamorphismand andmigmatization migmatizationwere weresynchronous synchronous progressive deformation and the the D3 D3 map-scale map-scale folds near the subprovince subprovince boundary. with progressive D4 deformation deformation D4 deformation has limited limited map-scale map-scale expression, expression, in part part consisting consistingof of gentle gentle deflections deflections of the Blackman Blackman Lake antiform, Jim Lake synform and the Wawa-Quetico subprovinceboundary boundaryininthe the northeastern northeastern map area Wawa-Quetico subprovince (Fig. 5). 5). The Thegeometry geometryofofthe thedeflections deflectionsisisconsistent consistentwith withdextral dextraltranspression transpression focussed focussed on on the theWawaWawaQuetico boundary. Another D4 structure structure is a northeast-trending Quetico boundary. Another possible possible map-scale map-scale D4 northeast-trending shear shear zone zone along along the northwestern margin of supracrustal rocks northwestern rocks folded folded by the the Manitouwadge Manitouwadge synform. The Theshear shearzone zonefollows follows aa pronounced northeasterly northeasterly trending trendinglineament, lineament)defined defined by by truncated truncated aeromagnetic aeromagnetictrends, trends)and andgenerally generallycovered covered by recent deposits deposits in the Nama Nama Creek Creek valley. valley. Mafic Mafic rocks metavolcanic belt dramatically by recent rocks of of the the outer outer metavolcanic belt thin thin dramatically and show increasing increasing transposition transposition with with proximity proximity to to the the shear shear zone) zone, and and may may be be truncated truncated by the zone. High High plunging stretching lineation, lineation) strain is manifested by by spectacular spectacular L>S tectonites with a moderate northeasterly plunging defined by (especially in folded quartz veins), and streaky streaky mafic mafic lenses in intermediate defined by hornblende) hornblende, quartz rods (especially metavolcanic rocks. rocks. Earlier Earlier structures, folds, are are strongly strongly transposed, transposed, so that metavolcanic structuresl including including D3 and possible possible D2 folds) D4lineations. lineations. all linear features are are essentially essentially parallel to to the thelocal localD4 D4 kink folds and crenulation locally, particularly particularly in micaceous rocks associated D4 crenulation cleavage cleavage are developed developed locallyl with mineralization on on the the southern southernlimb limbof ofthe theManitouwadge Manitouwadgesynform. synform.Intersections Intersectionsof ofcrenulation crenulationcleavage cleavage and foliation produce intersection lineation cleavage has produce an intersection lineation with with a moderate easterly plunge. plunge. The cleavage has a variable variable northeasterly strike, strike, and and both bothkinks kinksand andcleavage cleavagetypically typically have have aa Z-asymmetry. Z-asymmetry. In In some someexposures exposures of of quartzmuscovite schist schist (Unit (Unit la), la), D4(?) A6). Crenulations muscovite D4(?) kinking kinking produced dextral asymmetric quartz lenses (Stop A6). are also present in retrograde retrograde biotite-rich biotite-rich zones zones in in orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss gneiss (Unit (Unit 2). 2). the vicinity vicinity of of the the Jim JimLake Lakefold fold and and in in the theQuetico Queticosubprovince, subprovince, tight tight kink kink folds folds of of small small amplitude amplitude In the (<lo common1plunging plunging moderately and west. west. In Insome somecases, cases, small small northeast-striking northeast-striking (<10 cm) are common, moderately to to both east and shears shears of foliation foliation are transitional transitional to to kink kinkfolds. folds. West West of of Jim Lake Lake on on both both sides sidesofofthe theWawa-Quetico Wawa-Quetico an oblique oblique foliation, foliation, usually defined defined by biotite, strikes northwesterly across across the the dominant dominanteast-west east-west boundary, an 25 �Manitouwadge greenstone belt Geochronology Geochronology migmatitic migmatitic layering. layering. The The oblique oblique foliation foliation increases in intensity to to the the west west and and isisnearly nearly ubiquitous ubiquitous between between Appelle and Hourglass Hourglass Lakes. The The foliation foliation transects transects tight-isoclinal tight-isoclinal folds folds in migmatitic migmatitic rocks rocks and and is is deformed deformed by D4 D4 kinks; hence, it post-dates post-dates D3, D3, and and pre-dates predates D4, D4,deformation. deformation. Late Late Faults Faults A number of brittle-ductile to toductile ductilefaults faultsininthe theManitouwadge Manitouwadgearea areawere werepreviously previously identified identified by by Pye Pye (1957) and Milne (1974). The The Agam Agam Lake Lake fault fault (Pye, (Pye,1957) 1957)forms forms aapronounced pronounced strike-parallel strike-parallel topographic topographic lineament mostly in metasedimentary metasedimentaryrocks rocks on on the the southern southern limb limb of the Manitouwadge synform. It It is is primarily primarily a brittle brittle fault, fault,but butlocal localoccurrences occurrencesof of L-tectonites L-tectonites suggest suggest an an earlier earlier ductile ductile history. ItItappears appearstotocorrespond correspond to aa change change in in aeromagnetic aeromagnetic signature, signature, from from high high in the south south to tolow low ininthe thenorth, north,possibly possiblysuggesting suggesting involvement involvement of of subsurface subsurface volcanic volcanicrocks. rocks. High-angle faults associated associated with with brittle structures are High-angle faults are marked marked by by aeromagnetic aeromagnetic and and topographic topographic linealineaments. The TheMose Mose Lake Lake fault fault (Pye, (Pye, 1957) 1957)has has aanorthwesterly northwesterly strike, strike, parallel parallel to tothat thatofofMatachewan Matachewandykes, dykes, the oldest area. More oldest Proterozoic Proterozoic dyke swarm in the Manitouwadge Manitouwadge area. More nearly nearly north-south north-south faults faults include include the the Cadawaja fault (ibid.), (ibid.), interpreted interpreted totoextend extendacross acrossthe theWawa-Quetico WawsQuetico boundary boundary on onthe thebasis basisofofleft-lateral left-lateral displacement aeromagnetic aeromagnetic trends. trends. The Slim Lake Lakefault fault (ibid.) (ibid.) to to the east produced little apparent horizontal displacement. mineralization at at the Geco displacement. The The Fox Fox Creek Creek fault fault displaces displaces massive massive sulphide mineralization Geco mine, mine, apparently apparently with east-side east-side up and and 60 60metres metres of of left-lateral left-lateral movement movement(ibid.; (ibid.; Brown Brown et et aL, al., 1960). 1960). GEOCHRONOLOGY GEOCHRONOLOGY Our ongoing studies are focussed ongoing geochronology geochronology studies focussed on determining ages ages of of volcanism, volcanism, sedimentation, sedimentation, sedsedimentary and plutonism, and on events and and metamorphism in the imentary provenance, provenance, and on bracketing bracketing deformational deformational events metamorphism in Manitouwadge Manitouwadge greenstone belt and and the the adjacent adjacentQuetico Queticosubprovince subprovince(Fig. (Fig.9,9,Table Table2). 2). Black Pic batholith Orthoamphibole—bearing gneiss MaIlc—intermediate metavolcar,Ic rocks KM 5.0 0 Fold axial trace Fault 9. Locations Locationsof of 12 12geochronology geochronology samples. Table FIG. 9. samples. The numbered sample locations match those in Table IVB ==Inner Innervolcanic volcanic belt, belt, OVB OVB ==Outer Outervolcanic volcanic belt. belt. 2. IVB Zircon-Metavolcanic and metasedimentaryrocks rocks Zircon—Metavolcanic and metasedimentary The oldest oldest ages ages thus thusfar faremerging emergingfrom from the theManitouwadge Manitouwadge belt belt are areU-Pb U-Pb zircon zircon ages ages of of circa circa 2720 2720 Ma, Ma, The dating felsic felsic volcanism in the inner inner and and outer outervolcanic volcanic belts. belts. An Anaphyric aphyricfelsic felsic breccia breccia from the the barren barren dating in both the (unmineralized) sequence gave an age of 2722±2 2722k2 Ma 10, Stop Stop B5), B5), within within error of of (unmineralized) sequenceofofthe the outer outer belt belt gave Ma (Fig. 10, 2720h2 Ma muscovite muscovite schist the Geco Geco mine, mine, interpreted interpreted as as an analtered alteredfelsic felsicvolcanic volcanic rock rock (Davis (Davis et al., al., 2720±2 schist at the 26 �Manitouwadge greenstone belt Geochronology Geochronology 1994). Our age of 2720±3 foliated trondhjemite sampled north of 2720&3 Ma, for foliated of the Willroy Willroy and and Geco Geco mines mines (Fig. (Fig. 9, Stop A7), interpretation of subvolcanic intrusion (Fig. (Fig. 11). The A7), confirmed confirmed our field interpretation subvolcanic intrusion The 2720 2720 Ma Ma barren barren and and mineralized felsic rocks rocks stratigraphically stratigraphically overlie overlie mafic mafic metavolcanic metavolcanicrocks rocksinin the the inner inner and mineralized felsic and outer outer volcanic volcanic belts and, andlbarring barring unknown unknown structural structuralcomplications, complicationslmafic maficvolcanism volcanism was was either either contemporaneous contemporaneous (within (within analytical uncertainty), uncertainty), or orsignificantly significantly older. We We are in the process of testing these alternatives with aa sample sample of of felsic volcanic breccia interlayered with the themafic maficsequence sequencebetween between Swill Swill and and Mills MillsLakes Lakes (Stop (StopB13). B13). TABLE 2. Summary Summaryof ofGeochronology Geochronology Rock type type Mineral Mineral Relationships Relationships Age Age VOLCANISM VOLCANISM Felsic breccia, outer outer volcanic volcanic belt belt (1)1 (1)' zircon zircon Geco mica schist, inner volcanic volcanic belt zircon zircon 2722±2 2722&2Ma2 Ma2 2720±2 2720&2Ma3 Ma3 2720±3 2720&3Ma2 ~a~ Foliated trondhjemite, trondhjemite, inner volcanic volcanic zircon zircon belt (2) (2) felsic volcanic protolith protolith synvolcanic synvolcanic SEDIMENTATION SEDIMENTATION Manitouwadge Manitouwadgemetagreywacke metagreywacke (3) (3) zircon zircon 1eq2693 leg2693 Ma4 Ma4 depositional age, pre-D2 postD1 Dl Loken pluton (4) Loken Lake pluton (4) Black Pic diorite (5) Black diorite (5) Nama Nama Creek Creek pluton pluton (6) (6) Black Pic Pic monzodiorite(7) monzodiorite(7) FL PL UTONISM UTONISM 2687+2/—3 Ma prepre-to tosyn-D2 syn-D2 2687+2/-3 Ma 2687+3/—2 Ma preto syn-D syn-D2 2687+3/-2 Ma zircon zircon zircon zircon 2680±3 2680&3Ma4 Ma4 2677±2 2677&2 Ma Ma zircon zircon zircon zircon pre- to tosyn-D2 syn-D2 preprepre- to to syn-D3 syn-D3 METAMORPHISM METAMORPHISM and RETROGRESSION Geco Geco mica mica schist schist Black Pic monzodiorite Pic monzodiorite (7) (7) monazite monazite 2675±1 2675&1Ma3 Ma3 titanite 2674±2 titanite 2674&2 Ma Ma Nama Creek Creek pluton pluton (6) (6) titanite titanite Syn-D2 tonalite tonalite dyke dyke (8) (8) monazite 2671±3 2671&3Ma2 Ma2 monazite monazite monazite 2669±3 2669&3Ma2 Ma2 monazite 2661±1 2 6 6 l h l Ma5 ~a~ monazite PrePre- to to syn-D syn-Dlpegmatite pegmatite(9) (9) Geco Geco biotite biotite schist schist Syn-D3 Syn-D3 tonalite tonalitedyke dyke(10) (10) Syn-D3 Syn-D3 granite granitedyke dyke(11) (11) Loken Lake pluton pluton (4) (4) 2672&3Ma Ma 2672±3 titanite titanite titanite titanite titanite titanite Synkinematic granite dyke, Synkinematic granite dyke, Quetico Queticomonazite monazite metamorphic metamorphic regional regional cooling cooling through through cloclosure sure temperature temperature regional cooling cooling through through clocloregional sure sure temperature temperature retrograde? retrograde? retrograde 2658+4/-2 Ma retrograde 2658+4/—2 Ma retrograde 2655&3Ma Ma retrograde retrograde 2655±3 2652&4Ma Ma 2652±4 2642&2 Ma Ma 2642±2 retrograde retrograde? subprovince subprovince (12) (12) umbers in in paratheses parathesesrefer refer to to locations locations in in Figure Figure 9. 'Numbers 2Zaleski et al.(1994) (1994) 2~aleski et al. 3Davis al. (1994) (1994) 4~aleski al. (1995) (1995) 3 ~ a v i et s al. 4Zaleski et al. Schandi Schandl et et al. al.(1991) (1991) limb of of the the Manitouwadge Manitouwadge synform synform (Fig. 9), 91, contained contained aasuite suiteof ofconcorconcorMetagreywacke on the southern limb dant or or slightly slightly discordant discordant detrital detritalzircons, zircons,ranging ranging in in age age from from 2719±2 2719&2 Ma to 2679±11 2679kll Ma (Fig. 12, 12?Stop Al). dant The youngest youngest zircon, zircon, together together with with another anothergrain grainofofmore moreprecise preciseage ageof of2692±1 2692ztl Ma, Ma,provide provideaaconservative conservative The maximum limit on deposition deposition of 2693 Mal lea& 25 25 Ma Ma younger younger than than the theage ageofoffelsic felsicvolcanic volcanic rocks rocks to maximum Ma, at least north and and south. south.Zircon Zirconanalyses analysestend tendtotocluster clusteraround around2700 2700Ma, Ma,an anage agenot notknown knownelsewhere elsewhere in in the the the north belt. The Theoldest oldestzircon zirconofof2719±2 2719h2Ma Macould couldbebederived derivedfrom fromlocal localvolcanic volcanicrocks, rockslwhich whichwould would Manitouwadge belt. imply their exposure exposure at at or or before before the the time time of of sedimentation. sedimentation. In In general, general, the zircon zircon population and maximum imply depositional age age are are similar similar to tothose thosedetermined determinedfor forthe theQuetico Queticosubprovince subprovincewest west of of Thunder ThunderBay Bay(Percival (Percival depositional and Sullivan, Sullivan,1988; 1988; Davis Davis et et al., a].,1990). 1990).The TheManitouwadge Manitouwadgemetagreywacke metagreywacke is is lithologically lithologically indistinguishable indistinguishable and that of ofthe theQuetico Queticosubprovince, subprovincelthe themain maindifference difference being being in in the the higher higher metamorphic metamorphic grade grade and andprespresfrom that ence of migmatitic segregations We are attempting attempting to to bracket bracket the the minimum minimum depositional depositional age of ence segregations in in the the latter. latter. We Manitouwadge metagreywacke Manitouwadge metagreywacke by by dating dating a cross-cutting cross-cutting tonalite tonalite dyke (Stop Al). Al). 27 �Geochronology Geochronology Manitouwadge greenstone belt belt 0.64 0.64 0.53 o.53- v, Foliated Foliated trondhjemite trondhjemite A A Z992—P191Z ZB92—W24Z ZB92-W24Z 3 .0 0 Felsic Felsic breccia breccia C 2720 - 2720 .0 .0 a. Q- C 2722 ±2 Ma 2700 0.62 0.52 0.52 2720±3 Ma 0.50 13.2 13.6 207Pb/235U 207Pb/235U FIG. 11. Concordia Concordia diagram diagram with with zircon zircon analyses analyses FIG. from foliated subvolcanic trondhjemite in the the inner inner volcanic belt (Location (Location 2, 2, Fig. Fig. 9). 9). FIG. FIG. 10. Concordia Concordia diagram diagram showing showing zircon zircon analanalyses yses from felsic breccia breccia in the the outer outervolcanic volcanic belt belt (Location 1, 1,Fig. Fig. 9). 9). Manitouwadge metagreywacke 27 detrital zircon Concordia diagram diagram of detrital detrital zircons zircons FIG. 12. 12. Concordia from Manitouwadge metagreywacke between the the ininner and outer volcanic volcanic belts (Location 3, Fig. 9). All All analyses are from single single abraded abraded crystals, crystals, except 'A' which represents aa fraction fraction of of about 20 which represents 20 grains. The The maximum maximum age of deposition is constrained constrained to to 2693 2693 Ma by the the two two youngest youngest grains. grains. 207Pb/235U and monazite—Intrusive monazite-Intrusive rocks n d brackets on deformation deformation Zircon and rocks aand We have attempted to tobracket bracketdeformation deformation by by sampling sampling dykes dykes that that show show relative relative timing timing relationships relationships We with respect respect to to various various generations generations of tectonic fabrics and structures. In Ingeneral, general, we we had had limited limited success success at at with dating these these intrusions intrusions because, because, either either they they did did not notcontain containzircon, zircon, or orthe thezircon zirconwas washighly highlyfractured fractured and and dating vulnerable to secondary secondary Pb Pb loss. loss. In Inthose thosecases casesininwhich whichzircon zircon of of doubtful doubtful quality quality was was analysed, analysed, the the result result scatter of of discordant discordant points. points.Some Somedykes dykescontain containmonazite, monazite,apparently apparentlyofofigneous igneousmorphology, morphology,analysed analysed was a scatter the expectation expectation that thatititwould wouldgive giveprimary primarycrystallization crystallizationages. ages. Monazite, Monazite,including including some some prismatic grains in the pyramidal terminations, terminations, and and fractured fractured zircon zircon (not (not analysed), analysed), were were separated separated from from aa prepre- totosyn-Di syn-Dl with pyramidal transitional to tostraight straightgneiss gneissalong along an an interpreted interpreted D1 Dl ductile ductile fault (see (see Stop A26). Two Two monazite pegmatite transitional analyseslie lie above aboveconcordia concordia(Fig. (Fig.132, 13 ,suggesting suggestingthe thepresence presenceofofexcess excess206Pb ^Pb derived derivedfrom from230Th, "OTh, aa short-lived short-lived analyses intermediate daughter daughter product product of of2 8U W decay. The The preferential preferential incorporation incorporation of of230Th ^OTh into into monazite monaziteduring during lie above above concordia (Parrish, 1990). 1990). The The spread spread of of crystallization commonly results results in isotopic analyses that that lie concordia suggests subsequent minor Pb Pb loss; loss; hence, hence, the the concordance concordance of of aa single single grain grain (Fig. (Fig. analyses down to concordia 13, 'Z') isislikely likely due due to tocombined combinedexcess excess 206Pb ^Pb and Pb loss. loss. The Thebest bestage ageestimate estimateisisthe the207Pb/235U 2 0 7 ~ b / 2 model 3model 5~ 13, 2669k3 Ma Ma defined defined by by the theslightly slightlydiscordant discordantgrains grainsabove aboveconcordia. concordia. age of 2669±3 Nama Creek Creek deposit deposit (Fig. (Fig. 9), 9), aa syn-D2 syn-Dz tonalite dyke, dyke, subparallel to the the axial axialsurfaces surfaces Southwest of the Nama of D2 D2 folds of between iron iron formation formation and and felsic felsic rocks planar foliation. foliation. of of the contact between rocks (Stop (Stop A23), has an axial planar The dyke dyke contained contained only only monazite, monazite,giving giving slightly slightly discordant isotopic analyses that define define an an age age of of 2671±3 2671± The Ma (Fig. (Fig. 14). 14).This Thisage ageisiswithin withinerror errorofofmonazite monazitefrom fromthe thesyn-D1 syn-Dl pegmatite pegmatiteand andofof2675± 2675± Ma 1 Ma age reported for metamorphic metamorphic monazite monazite from from the theGeco Gecomine mine (Davis (Daviset etal., al.,1994). 1994). for Two intrusions, intrusions, interpreted interpreted to tobe besyn-D3, syn-D3,were were sampled sampled in in the theSwill-Mills Swill-Mills Lakes the hinge hinge of of Two Lakes area near the the Manitouwadge Manitouwadge synform synform (Fig. 9). These These intrusions intrusions have have only yielded yielded useful ages (see below). below). A the useful titanite titanite ages third sample, sample, from from aa foliated foliated granitic granitic sheet sheet both both deformed deformed by, by, and and cutting, cutting,D3 D3 folds folds (Stop (Stop B18), B18), is is still being being third processed. processed. i 28 �- - Geochronology Geochronology Manitouwadge greenstone belt '.''- 0.515 FIG. FIG. 13. 13. Concordia Concordiadiagram diagramshowing showing monazite monazite analanalyses from pegmatite pegmatite involved in a D1 strain zone Dl high strain north of Willecho 3 deposit (Location (Location 9, 9, Fig. Fig. 9). 9). of the the Willecho Grains lying lyin above above concordia concordia suggest suggest the thepresence presence of 'excess' derived from from 2°Th 'excess' 206Pb '06Pb derived Th incorporated incorporated into the monazite during crystallization. crystallization. The The spread spread of analyses down down to grain 'Z' 'Z' on onconcordia concordiasuggests suggests subsequent minor Pb Pb loss and, hence, subsequent minor hence, that the the conconcordance of of grain grain 'Z' is is aa fortuitous fortuitous combination combination of of excess and Pb Pb loss. loss. In excess 206Pband In view view of of these these features features of U-Pb systematics in monazite, the best estimate estimate of of age age isis the the207Pb/235U 207Pb/235Umodel age of 2669±3 2669k3 Ma Ma defined by grains grains ''X' defined by X'and 'Y'. 'Y7. pegmafite pegmatite Pre— Pre- to to syri—D1 syn-Dl ZB91 ZB9 1—55Z -55Z 2670 C N Z -a 00 2669±3Ma C 0 N 12.7 2O7p b/235U 12.9 Syn-D tonalite dyke ZB9 1 - P I 3Z 3 FIG. 14. 14. Concordia Concordia diagram diagramshowing showing monazite analdyke (Location (Location8, 8,Fig. Fig.9). 9). yses from a syn-D2 tonalite tonalite dyke 2671 & 3 M8 27 2% CC 288O, Loken Loken Lake Lake pluton pluton Nama Creek pluton ZB93-87AZ 2660— Z893—417AZ ZB93-417AZ fl 5 0 2687 +2(3 M 0.50 'C 0.49 Ga n Ai 12.0 207Pb/235U FIG. 15. 15. Concordia Concordiadiagram diagramshowing showing zircon zircon and and titiFIG. tanite (TA, (TA, TB) TB) analyses analyses from from the the prepre- totosyn-D2 syn-D2 tanite ThezirzirNama Creek pluton (Location 6, Fig. 9). The con age of of 2680k3 2680±3 Ma Ma is is interpreted interpreted as the age of the intrusion intrusionand andthe themaximum maximumage ageofofD2 D2deformadeformathe tion. The Thetitanite titaniteage ageofof2672±3 2672&3Ma Maisisinterpreted interpreted tion. as the thetime timeofofregional regionalcooling cooling through through the theclosure closure as temperature of of titanite. titanite. temperature - 12.4 207Pb/235U 12.8 FIG. 16. 16. Concordia Concordia diagram diagramshowing showing zircon and tiFIG. tanite tanite(Ctit) (Ctit)analyses analysesfrom fromthe theprepre-totosyn-D2 syn-D2Loken Loken Thezircon zircon age age of of Lake pluton (Location 4, Fig. 9). The 2687+2/-3 Ma is the the age age of of intrusion, intrusion,whereas whereasthe the 2687+2/—3 2652~t4Ma is interpreted interpreted as a late late titanite age age of of 2652±4 titanite retrograde retrograde event that crystallized crystallized or reset titanite. titanite. In the theQuetico Quetico subprovince subprovince (Fig. (Fig. 9), 91,aamuscovite-biotite muscovite-biotite granitic granitic dyke dyke was was interpreted interpreted to to be becontemcontemIn with progressive progressive deformation (late D3 D3 or D4) D4) and, and, judging judging by by the thepresence presenceofofmuscovite, muscovite,late lateinin poraneous with 29 29 �Manitouwadge Manitouwadge greenstone greenstone belt belt Geochronology Geochronology Black Pic batholith Foliated diorite Black Pic batholith Foliated monzodiorite--.... 2~ 2680 J m ZB94-86BZ 207Pb/235U 207Pb/235U FIG. FIG.17. 17. Zircon Zircon concordia concordia diagram diagram of of the the oldest oldest phase phase of of the theBlack BlackPic Picbatholith, batholith,foliated foliatedplagioplagioclase clase porphyritic porphyritic diorite diorite (Location (Location 5, S1Fig. Fig. 9). 9). The The age ageof of 2687+3/—2 2687+3/-2 Ma is within error error of of that thatof ofthe the prep r e totosyn-D2 syn-D2Loken LokenLake Lake pluton. pluton. FIG. FIG. 18. 18. Concordia Concordia diagram diagram showing showing zircon zircon and and titanite(Atit, (Atit,Btit) Btit)analyses analysesfrom fromfoliated foliatedmonzomonzotitanite diorite of of the the Black Black Pic Pic batholith batholith(Location (Location7,7,Fig. Fig. diorite 9). The Thezircon zirconage ageof of2677±2 2677&2Ma Ma dates dates the theintruintru9). sionand andisiswithin withinerror errorof ofthe theNama NamaCreek Creekpluton. pluton. sion 2674&2Ma Maindicates indicatescooling cooling Thetitanite titaniteage ageofof2674±2 The through the theclosure closuretemperature temperature of oftitanite titanitesoon soon through after afterintrusion. intrusion. themetamorphic metamorphicand andanatectic anatectichistory. history.The Thedyke dykeisissubparallel subparalleltotothe theaxial axialplanes planesofofZ-folds Z-foldsininmigmatitic migmatitic the rocks and and has hasan anaxial axialplanar planarfoliation foliation (Stop (Stop E2). E2). Shear Shearbands bandsininthe thehost hostrock rockand andthe thedyke dykecut cut across across the the rocks contact.Zircons Zirconsfrom from the thedyke dyke gave gave scattered discordant discordant analyses, apparently in part due due to toinheritance. inheritance. Of Of contact. two monazite monazite grains grainsanalysed, analysed,one onewas washighly highlydiscordant, discordant,and andthe theother otherslightly slightlydiscordant discordantabove aboveconcordia concordia two (see 206Pbabove), giving an age age of of 2642±2 2642&2 Ma Ma (Table (Table2). 2). (seediscussion discussionof of excess excess 206Pb We had had better bettersuccess success inindating datinglarger largerplutonic plutonicbodies. bodies. InInsome somecases, cases,the therelative relativeage ageofofthese thesewith with We respect TwoK-feldspar K-feldspar porphyritic porphyritic granitoids, granitoidsl the the respect to todeformation deformation can can be beinferred inferredwith withsome someconfidence. confidence. Two Nama Creek Creek and and Loken Loken Lake Lake plutons plutons (Fig. (Fig. 9), 9))are are both both interpreted interpreted asasprepre-totosyn-D2 syn-D2intrusions intrusionsbased based on on Nama tectonic tectonicfabrics fabricsdeformed deformedby byD3 D3folds. folds.Analyses Analysesof ofzircon zircon from from Nama NamaCreek Creekpluton plutondefine definean anage ageofof2680±3 2680k3 Ma Ma(Stops (StopsF11—F12, F11-F121 Fig. 15), 15)! whereas those from the Loken Lake pluton are are slightly slightly older older at a t2687+2/—3 2687+2/-3 Ma Ma (Fig. (Fig. 16). 16).The Theoldest oldestdioritic dioriticand andthe theyoungest youngestaplitic aplitic(not (notprocessed) processed)phases, phasesl both bothfoliated, foliatedlof of the the Black Black Pic Pic batholithwere weresampled sampledsouth southofofthe theManitouwadge Manitouwadgebelt belt(Stop (StopF3). F3).Zircon Zirconanalyses analysesfrom fromthe thediorite dioriteyield yieldan an batholith age —2 Ma Ma (Fig. 17), ageof of2687+3/ 2687+3/-2 171, within error of of the the Loken Loken Lake Lake pluton. Foliated Foliatedmonzodiorite monzodiorite of of the theBlack Black Picbatholith, batholith,between betweenthe theeastern easternextensions extensions of of the theinner inner and andouter outervolcanic volcanicbelts belts (Fig. (Fig.9), 91,has hasananage ageofof Pic 2677±2 2677&2Ma Ma(Fig. (Fig.18). 18).The Theage ageisiswithin withinerror errorofofthe theNama NamaCreek Creekpluton, pluton,but butthe themonzodiorite monzodioritefoliation foliationcould could be beaaD2 D2ororD3 D3fabric. fabric. 1 0.532 Syn—D3 fonaIie dyke Syn-D3 tonalite dyke Z893—P1 ZB93-PIO2AZ 02AZ 0.508 2 ÷41-2 Ma -o ci- 0.504 FIG.19. 19.Concordia Concordiadiagram diagramshowing showingtitanite titaniteanalyanalyFIG. sesfrom fromaasyn-D3 syn-D3tonalite tonalitedyke dykenear nearthe thehinge hingeregion region ses theManitouwadge Manitouwadgesynform synform(Location (Location10, 10,Fig. Fig.9), 911 ofofthe defining definingan anage ageofof2658+4/—2 2658+4/-2 Ma. Ma. () ,,>v27%77, /€.2 Ga — 12.2 207Pb/235U 12.6 30 �Setting of mineralization Manitouwadge greenstone belt belt Titanite Titanite were done done on on titanite titanite from U-Pb isotopic analyses analyses were from intrusive intrusive rocks rocks in in order order to toplace placeminimum minimumage ageconconstraints on magmatism magmatism and and metamorphism. metamorphism. The The analyses analyses group group around around two two distinct distinct ages ages of of 2673 2673 and 2655 Ma. The titanite ages 2672k3 The 2680 2680 Ma Nama Creek pluton and and the the 2677 2677 Ma Ma Black Black Pic monzodiorite have titanite ages of 2672±3 Ma (Fig. 15) 15) and 2674±2 26744Z2 Ma Ma (Fig. (Fig. 18), 181, respectively. respectively. We tentatively interpret these these as as the the time timeof ofregional regional cooling through the 600°C closure temperature temperature of titanite titanite (Heaman cooling through 6OO0C closure (Heaman and and Parrish, Parrish,1991) 1991)and, and,for for the thecase case of of the the Nama Creek pluton, about about 88 Ma Ma after afterintrusion. intrusion.Titanite Titanitefrom fromthe the2687 2687Ma MaLoken LokenLake Lakepluton plutondefines definesan anage age of 26524Z4 2652±4 Ma (Fig. 16), of 161,whereas whereas syn-D3 syn-D3 intrusions intrusions in in the theSwill-Mills Swill-Mills Lakes area gave gave ages of 2658+4/—2 2658+4/-2 Ma from a tonalite dyke (Fig. 19), and 2655±3 from 26554~3Ma from a granitic sheet (Table 2). The The circa circa 2655 2655 Ma titanites titanites suggest aa widespread widespread late late hydrothermal hydrothermal event event that that locally locally crystallized crystallizedor orreset resettitanite. titanite. suggest SETTING S E T T I N G OF O F MINERALIZATION MINERALIZATION sulphide deposits deposits lie lie in the inner The Geco, Gecol Wiliroy, Willroyl Nama Creek and Willecho Willecho massive massive sulphide inner volcanic volcanic belt belt along the the southern limb and hinge region of the the D3 Manitouwadge Manitouwadgesynform synform(Fig. (Fig.3). 3). Our Our understanding understanding of of along region of deformation of of the the area and the complex complex pre-D3 pre-D3 deformation and of of the theprobable probable original original relationships relationships of of sulphide sulphide deposits deposits depends on detailed detailed lithological lithological and and structural structural mapping, as well as any any additional additional clues clues that that could be gleaned gleaned depends well as from features characteristic of of individual deposits. Except Except for for Nama Nama Creek, Creek, each each of of these these deposits deposits comprised comprised several massive, massive, semi-massive semi-massiveorordisseminated disseminatedsulPhid&orebodies sulphide orebodiesofofwidely widelyvarying varyingCu, Cu,Zn Znand and Pb Pb grades several and ratios (Table 3). On On the the basis basis of of Cu-Zn-Pb Cu-Zn-Pb proportions, nature of mineralization and relationship relationship to iron formation, the sulphide orebodies of the the Manitouwadge camp can can be be divided dividedinto into three three main main types. types. Firstly, orebodies of Manitouwadge camp Firstly, Cu-rich stringer and disseminated Cu-rich disseminated orebodies orebodies are are hosted hosted by by orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss gneiss (footwall (footwall alteration) sillimanite-muscovite-quartzschist. Secondly, Secondly, massive massive and alteration) or or envelop envelop the the Geco Geco main main orebody orebody in insillimanite-muscovite-quartz semi-massive Zn-Cu-(Pb) orebodies orebodies are associated associated with iron formation horizons interleaved with sillimanitesemi-massive Zn-Cu-(Pb) schist or 6r quartz-phyric quartz-phyric felsic felsic rocks. Thirdly, Thirdlylmassive massive and and semi-massive semi-massive Zn-Pb-(Cu) orebodies orebodies muscovite-quartz schist sillimanite-muscovite-quartz schist. schist.With Withsome someexceptions exceptions(see (seebelow), below), by iron iron formation formation south southofofsillimanite-muscovite-quartz are hosted by the spatial spatial distribution distribution of of orebodies orebodies defines defines a tendency tendency to more Zn-rich Zn-rich and and Pb-rich Pb-rich deposits deposits toward toward the the south. In terms of of classification based Manitouwadge belt collectively collectively fits based on Cu-Zn-Pb, the Manitouwadge fits Franklin's Franklin's (1986) Cu-Zn Cu-Zn Group la, l a ,which which includes includes the the deposits deposits of of the the Abitibi Abitibigreenstone greenstone belt, belt,the theNorwegian Norwegian Caledonides Caledonides and and other other areas dominated by by basaltic basaltic volcanism volcanism (Fig. (Fig. 20). 20). TABLE 3. 3. Types aand TABLE n d Grades G r a d e s of Mineralization Orebody Orebody TYPe Type %Cu %Cu %Zn %Zn %Pb %Pb g/tAg Geco 412 4/2 Cu Cu disseminated disseminated 1 .8 1.8 0.3 0 .3 — 16 16 Geco Main massive massive 2.3 2 .3 8.2 8 .2 0.4 0.4 74 74 Geco Main stringer, disseminated stringer, disseminated 1 .5 1.5 0.1 0.1 — 0.2 0.2 4.9 4.9 — 36 36 Geco ZnIF massive, disseminated massive, disseminated semi-massive semi-massive - 22 22 8/2 Zn Geco 812 0.1 0.1 8.6 8.6 0.8 0.8 41 41 Willroy Willroy 11 disseminated, disseminated,stringer stringer 1.3 1 .3 - — 99 Willroy Willroy 22 semi-massive semi-massive <O.l <0.1 6.0 6.0 0.2 0 .2 64 64 Willroy Willroy 33 1.3 1 .3 4.5 4.5 0.2 0 .2 56 56 — - 8.0 8.0 1.2 1.2 168 168 — 6.0 6.0 0 .2 0.2 28 28 — — Willroy Willroy 44 massive massive massive* semi-massive massive, semi-massive Willroy 55 Willroy semi-massive semi-massive Willroy 66 stringer stringer 2.0 2.0 1.0 1.0 Willroy 77 massive 0.4 0.4 5.0 5.0 Nama Creek semi-massive semi-massive 0.8 0.8 3 .9 3.9 Willecho 11 Willecho semi-massive semi-massive 1.O 1.0 3.0 3 .0 Willecho 22 Willecho semi-massive semi-massive 0.2 0.2 5.8 5.8 Willecho 33 Willecho semi-massive semi-massive 0.6 0 .6 3 .8 3.8 - — 14 14 39 39 — 28 28 — 42 42 — 42 42 — 53 53 Datacompiled compiledby by -H. .H. Lockwood, Lockwoodl Noranda Inc. from from unpublished unpublishedcompany companyrecords. records. Data from an an unpublished unpublished report report by by Derry, Derry, Michener Michener and Booth Booth (1971) (1971)for Willroy data data from Willroy Mines Inc. Inc. Willroy Tiand Marshall Marshall (1959), (1959),or estimated estimated Willroy %Pb %Pb from Timms depositwas wasnever nevermined. mined. constant Zn/Pb. Zn/Pb.The TheWillroy Willroy77deposit assuming near constant The suiphide sulphide mineralogy is generally generally simple, simple, consisting consistingofofpyrite, pyrite,pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite,sphalerite sphalerite and and galena Marshall, 1959; 1959; Friesen Friesen et al., 1982). 1982). Many Many details detailsof ofindividual individual orebodies orebodies have have been been galena (Timms and Marshall, 31 �Manitouwadge greenstone belt Narna Nama Cree Creek Willecho Type 3 Type 2 Type Setting of of mineralization mineralization Setting Cu Wiflroy Geco Urn #4 A #2. J/5, #7 .0 #3 * #1 2 3 + orebody #6 #1 I ZnIF ZnIF 8/2 Zn zone main orebody *I main stringer, £ main orebody 4/2 Cu zone T FIG. FIG. 20. 20. Cu-Zn-Pb Cu-Zn-Pb ternary ternarydiagram diagram(weight (weight %) showing showing the metal metal composition composition of of the the %) In orebodies of of the theManitouwadge Manitouwadge camp. camp. In orebodies the key key and and the thedotted dottedfields, fieldsl orebodies orebodies the are grouped grouped into into Types Types 1,l l 22 and and 33(see (see are text). The The average averagebase-metal base-metal proportions proportions text). in the theAbitibi Abitibibelt, beltlNorwegian NorwegianCaledonides, Caledonidesl in Japanese Green Green Tuff Tuffbelt, belt, and and the the BathurstBathurstJapanese Newcastle area area of of New New Brunswick Brunswick are arefrom from Newcastle Lydon (1984). (1984). Lydon Coladonides Ablflbi Jopon Type2. V Pb V V V Bothursi. Type 3 V '.1 V V Zn described described by by Pye Pye (1957), (1957)>Timms Timms and and Marshall Marshall (1959), (1959)1Brown Brown et al. al. (1980) (1960) and and Friesen Friesen et et al. al. (1982) (1982) and and only only observations observations pertinent pertinent to toour ourreinterpretation reinterpretationare arereviewed reviewedhere. here. Relationships m d host host rocks rocks Relationships of of orebodies orebodies and The Geco 4/2 Cu zone, and Willroy 1 and depositslconsist consistof of Cu-rich, Cu-richldisseminated disseminatedor orstringer stringersulphides sulphides The Geco 412 Cu zonel and Willroy 1and66deposits, on on or or near near the the contact contactbetween between orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss gneiss and and sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist (Fig. (Fig. 4, 21). 21). On Onthe thesouth southside sideofofthe the4/2 412Cu Cuzone, zone,a aweakly weaklymineralized mineralized'breccia' 'breccia' of offlattened flattenedquartz quartzlenses lenses in in an anorthoamphibole orthoamphibolematrix matrixhas hasbeen beenvariably variablyinterpreted interpretedasasaltered alteredpyroclastic pyroclasticrock rock(Friesen (Frieseneteta!., al.l1982) 1982) or or disrupted disruptedaltered alterediron ironformation formation(Bakker (Bakkeretetal., al.?1985). 1985). The TheGeco Gecomain mainorebody orebodylies liessouth southofofthe the4/2 412Cu Cuzone, zonelenveloped envelopedby bysillimanite-muscovite-quartz sillimanite-muscovite-quartz schist schist and andquartzite. quartzite. ItItisisby byfar farthe thelargest largestand andhighest highestgrade gradeofofthe theorebodies, orebodieslalthough althoughthe theproportions proportionsof ofCuCuZn-Pb sillimanite-muscovite-quartz Zn-Pbare aresimilar similartotoWillroy Willroy33(Fig. (Fig.20). 20).AAhalo haloofofchalcopyrite chalcopyritedisseminated disseminatedininsillimanite-muscovite-quartz schist surrounds surroundsthe themassive massivezone zone (Table (Table3, Geco Geco main main stringer), stringer)>especially especially on on the the lower lower eastern eastern margin margin and and schist south 1982). south side side (Friesen (Friesen et al., ale$ 1982). The Themain mainorebody orebody has hasbeen been traced traced totothe theeast eastininunderground undergroundworkings, workings, where where itit grades grades and andthins thinstotoZn-rich Zn-richmassive massivesulphide sulphide interleaved interleaved with iron iron formation, formation, the the latter lattercorrelated correlated with iron ironformation formationformerly formerlyexposed exposedininthe theGeco Gecoquarry quarryatatsurface surface(Geco (Gecomine, minelunpublished unpublishedcross-sections). cross-sections). with We We are are not notable abletotoconfirm confirmthis thisrelationship relationshipand, andlfurthermore, furthermorelsurface surfacemapping mappingofofthe thesurviving survivingexposures exposures shows shows that the theGeco Geco main main orebody orebody lies lies to the the north north of of the thesouthernmost southernmost iron iron formation, formationl and and that that the theiron iron formation is is continuous continuous to the the quarry. quarry. The Thesubsurface subsurfacerelationships relationships imply imply that that the theeastern easternextension extensionofofthe the formation main orebody orebody crosses crosses stratigraphy stratigraphyatataalow lowangle angle(ibid.); (ibid.);but butwe weare areunable unabletotodiscriminate discriminatebetween betweenpossible possible main syngenetic syngenetic or or epigenetic epigeneticrelationships relationships(see (seebelow). below). Low grade economic and subeconomic Geco main orebody orebody to to Low grade economic subeconomic Cu mineralization is continuous from from the Geco the 1982), near transition from sillimanite-muscovite-quartz the8/2 812Zn Znzone zone(Friesen (Friesenetetal., al.> 1982)> nearthe the transition from sillimanite-muscovite-quartzschist schisttotomore more quartzitic varieties varieties of the same same unit. The The8/2 812Zn Znzone zoneand andiron ironformation formationon onthe thesame samehorizon horizon project project to to quartzitic surface south south of of the themain mainorebody. orebody.The Thesouthernmost southernmostorebody orebodyatatthe theGeco Gecomine mineisisa azincian zincianiron ironformation formation surface (Table (Table 3, 31ZnIF) ZnIF) in in micaceous micaceous quartzite, interpreted interpreted as asan analtered alteredvolcanic volcanic rock. rock. Zincian Zincian iron iron formation formation attains attains aL11985; 1985;Williams Williams economicgrades grades in in deeper deeper levels levels of of the the mine mine-near theMose Mose Lake Lake Fault Fault (Fig. (Fig. 4) 4) (Bakker (Bakkeretetal., economic near the etetal., aL11990). 1990). G&O main mainorebody orebodywas wasdisplaced displacedby by the thesteeply steeplydipping, dippinglhigh-angle high-angleFox Fox Creek Creek fault fault (Pye, (Pyel1957; 1957; TheGeco The Brown et et al., aL11960). 1960).Well Wellaway awayfrom fromthe theFox FoxCreek Creekfault, faultlevidence evidenceofoftectonic tectonicremobilization remobilizationofofsulphide sulphide Brown minerals is is ubiquitous, ubiquitous, in in part partrelated relatedtotolayer-parallel layer-parallelmovement movement(Friesen (Friesen et et a!., alm1 1982). For Forexample, example1wallwallminerals 1982). rock rock breccias breccias have have aa sulphide sulphide matrix, matrix, and anddisrupted disrupted segmented segmented pegmatite pegmatite and andtonalite tonalitedykes dykes can can be betraced traced across massive massive sulphide. All All orebodies orebodies are are conformable conformable to to the the nearly nearlyvertical vertical host hostrocks, rocks,and andelongate elongatewith with across shallow to to moderate moderate easterly easterly plunges, plungeslsubparallel subparallel to tothe thedominant dominantmineral minerallineation. lineation.The Themassive massivesulphide sulphide shallow zone of of the the Geco Geco main main orebody orebody isisthickest thickest ininthe thehinge hingeofofthe theeasterly-plunging easterly-plunging Z-shaped Z-shaped 'Geco 'Geco drag drag fold' fold' zone (ibid.), inferred inferred to tobe beaaD3 D3ororlater laterfold foldbased basedononthe theinvolvement involvementofoffolded foldedfoliation. foliation. The TheZ-asymmetry Z-asymmetryisis (ibid.), consistent with with the thegeometry geometryexpected expected for foraaparasitic parasiticfold foldon onthe thesouthern southernlimb limbofofthe theD3D3 Manitouwadge consistent Manitouwadge synform.Locally, LocallylCu Cugrades gradesare arehighest highestininfold foldnoses noses(Friesen (Friesenetetal., al.,1982) 1982)and andminor minor(less (lessthan thanmetre-scale) metre-scale) synform. folds foldshave havepods podsofofmassive massivechalcopyrite chalcopyriteinindilational dilationalzones. zones. TheZn-rich Zn-richWillroy Willroy2, 3,3,4, 55and The and7 7deposits depositslielieon oniron ironformation formationhorizons horizonssouth southofofthe theWiliroy Willroy1 1and and Cu-stringerdeposits, depositslintercalated intercalatedwith withquartz-phyric quartz-phyricfelsic felsicmetavolcanic metavolcanicrocks rocksand andsillimanite-muscovitesillimanite-muscovite66Cu-stringer 32 �Setting of of mineralization mineralization Manitouwadge greenstone belt Unconformity Unconformity or fault fault 1 Quartzite,felsic rocks -....- .,------I Reconstructed trace of of DDil fault. Reconstructed trnce fault Type Type 33 Zn—Pb—(Cu); Willroy 4, 4, Ceco Zn-Pb-(Cu); Willroy Ceco ZnIF ZnlF Quartzite *. '\, K-A1 alteration '\.(Sillimanite-muscovile)' / lkall-depleted Pe-Mg altera (Orthoarnphibole-cordierite- Type Type 22 Zn—Cu--(Pb); Zn-Cu-(Pb); Willroy Willroy 2,2 , 3, 3, 5, 5, Ceco Geco main main orebody, orebody, 8/2 812 Zn Zn Nama Nama Creek Creek WIllecho 3, Willecho 1, 22 , 3, Type Type I1 Cu Cu stringers; Willroy Willroy 1, 66 Geco 4/2 Cu Geco 412 Cu Trondhjemite FIG. FIG. 21. Schematic Schematic reconstructed reconstructed section section of of the the probable probable relationships relationships between between orebodies, orebodies, showing the trace trace of of the D1 showing the Dl fault that divides divides the area. area. Stringer/disseminated Stringer/disseminated zones zones are are shown and iron formations cross-hatching, and formations are stippled. stippled. Some ambiguity remains in in shown as cross-hatching, detailed correlations correlations of of mineralized mineralized horizons horizons between between the the Geco Geco main main and andWiliroy Willroyorebodies. orebodies. schist. The TheWiliroy Willroy33orebody, orebody, the thesouthernmost southernmost and and largest largest of of the theWiflroy Willroy deposits, deposits, is is zoned zoned from quartz schist. relatively Cu-rich Cu-rich core (Cu=Zn) to to aa Zn-rich Zn-rich margin, margin, to to barren barren pyrite-pyrrhotite pyrite-pyrrhotite sulphidic sulphidic iron iron formation formation a relatively 1957; Timms and Marshall, Marshall, 1959). 1959). The TheWiliroy Willroy 44 orebody orebody and andGeco Gecozincian zincian iron ironformation formationhave have the the (Pye, 1957; highest Pb Pb grades grades of of the the Manitouwadge Manitouwadge deposits deposits (Table 3, Fig. 20). The Nama Nama Creek Creek deposit, deposit, located located near near the thecontact contactbetween between orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnetgneiss gneiss and The sillimanite-muscovite-quartz schist, schist,consisted consistedof of marginally marginally economic economic Zn-rich mineralization (Table (Table 3), 31, hosted hosted sillimanite-muscovite-quartz by iron iron formation formation and and much much intruded intruded by by pegmatite. pegmatite.North Northofofthe thehinge hingeregion regionof ofthe theManitouwadge Manitouwadgesynform synform by 41, three three Willecho Willecho deposits deposits are arehighly highlydeformed deformed Zn-rich Zn-rich semi-massive semi-massive sulphide (Fig. 4), suiphide sheets interleaved with iron formation formation and and altered alteredrocks. rocks. S t r u c t u r a lcomplications—D1/D2 complications-Dl/D2 folds and a n d faults faults Structural The interpreted sillimanite-muscovite-quartz interpreted D1 Dl fault faultofofthe theWillroy-Geco Willroy-Gecoarea areacontinues continueseastward eastwardininsillimanite-muscovite-quartz schist schist to highly highly strained strained iron iron formation formation and and straight straight gneiss gneiss exposed exposed east of of Wowun Wowun Lake Lake (Fig. 3). Our Our allow some fault with with respect respect to tothe theGeco Gecomain mainorebody; orebody;ititcould could observations allow some latitude latitude in the position of the fault orebody. The TheWillecho Willecho deposits deposits lie lie near or on on the the D2 D2 fold repetition of of the D1 Dl fault, fault, or south south of of the theorebody. lie north or their original originalstratigraphic stratigraphicrelationship relationshiptotothe theWiliroy-Geco Willroy-Gecoorebodies orebodiesisisobscure. obscure. and their interpretation,the theD1 Dlfault faultdivides dividesthe theNama NamaCreek-Wiliroy-Geco Creek-Willroy-Gecoarea areainto into22tectonic tectonicblocks blocks (Fig. (Fig. In our interpretation, The Wiliroy Willroy 33 orebody orebody and and Geco Geco zincian iron formation lie Willroy 1, 1, 2, 21). The lie in in the southern block, and the Willroy orebodies, Nama Nama Creek Creek and and Geco Geco 4/2 412 Cu Cu zone zone lie lie in in the the northern northern block. block. The TheGeco Gecomain mainorebody orebody 4, 55 and and 66 orebodies, 4, 812Zn Zn zone zone could could lie either on on the the northern northern margin marginof of the the southern southernblock, block,or or the thesouthern southernmargin marginof of the the and 8/2 northern block. block. The TheCu-rich Cu-richdisseminated disseminatedand andstringer stringerzones, zones,the theGeco Geco 4/2 412Cu Cuzone, zone,Willroy Willroy 11and and 66 deposits deposits northern to lie lie on on the thesame samehorizon, horizon, and andare areprobably probably related related totothe thedisseminated disseminatedCu Cumineralization mineralization are interpreted to around the theGeco Gecomain mainorebody. orebody.Zn-rich Zn-richmassive massiveand andsemi-massive semi-massivesulphide bodies north north of of the theD1 Dl fault, fault,the the around Willroy 2, 5 and and Nama Nama Creek Creek deposits, deposits, could could lie lie on on the thesame sameiron iron formation formationhorizon horizon as asthe theWillroy Willroy33deposit deposit Willroy on the the south south side side of of the the fault. fault.The TheGeco Gecozincian zincianiron iron formation formation in in the the southern southern block block is is interpreted interpreted to to be be on correlative with iron iron formation formation hosting hosting the the Wiliroy Willroy 44 deposit deposit in in the the northern northernblock. block. correlative The Wiliroy Willroy 33 and and Geco Geco main main orebody orebody are are similar similar in in Zn-Cu-Pb Zn-Cu-Pb (Fig. (Fig. 20). 20). Cu-to-Zn Cu-to-Zn zoning zoning toward toward iron iron The formation, such such as as that thatexhibited exhibitedby bythe theWillroy Willroy33deposit, deposit,isischaracteristic characteristicofofvent-proximal vent-proximalmassive massivesulphide sulphide formation, bodies (Lydon, (Lydon, 1984). 1984). Similarly, Similarly, stringer stringer sulphide sulphide zones, zones, like like those associated associated with with the theGeco Gecomain mainorebody, orebody, bodies are typical typical of of subsurface subsurface feeder feeder zones zones of proximal deposits. These features features suggest suggest the the Wiliroy Willroy 33and andGeco Geco are deposits. These 33 �Manitouwadge greenstone belt belt Geochemistry Geochemistry main orebody precipitated close close to to a hydrothermal vent, and and that the orebody precipitated hydrothermal vent, the Geco Geco main main orebody orebody could could also also lie lie on or or near near the theWiliroy Willroy3,3,2,2,55and andNama NamaCreek Creekhorizon. horizon.However, However,we wecannot cannotdiscriminate discriminatebetween betweenseveral several possible interpretations of iron-formation-hosted eastern eastern of the the relationships relationships between between the the Geco Geco main orebody, its iron-formation-hosted extension in the Geco quarry (i.e. the southernmost iron formation), and early faults. Structural Structuralcomplications complications are possible juxtaposing the main possible including, early faulting juxtaposing main orebody orebody with with an an unrelated unrelatediron-formation-hosted iron-formation-hosted deposit and, and, remobilization remobilization of of sulphides sulphides along along early faults faults and and iron iron formation formation layers. layers. The TheCu-to-Zn Cu-to-Znzoning, zoning, reported in in the the sulphide-iron sulphide-iron formation formation transition transition in in the thequarry, quarry,argues arguesagainst againstremobilization, remobilization,as as does does the the observation observation that, that,atatGeco Gecoand andininother otherdeformed deformedmassive massivesulphide sulphidebodies bodies(e.g. (e.g.Valenta, Valenta,1994), 1994),remobilization remobilization generally generally involves involves redistribution redistribution of of chalcopyrite. chalcopyrite. The increase increase in Zn/Cu Zn/Cu of of the theGeco Gecoorebodies orebodies from from north north to to south, south.characteristically characteristicallv aa stratigraphicstratiffraohic". upwards sulphide deposits, deposits, and the upwards zonation zonation in in volcanogenic volcanogenic massive sulphide the presence presence of of orthoamphibole-cordieriteorthoamihibole-cordieritegarnet footwallalteration, alteration, to to the the north have garnet gneiss, gneiss, the the metamorphosed metamorphosed equivalent equivalent of synvolcanic synvolcanic footwall have both been been used area (Suffel et al., al., 1971; et al., 1982). used to to infer infer southerly southerly younging younging in the the Willroy-Geco Willroy-Geco area (Suffel et 1971; Friesen Friesen et 1982). The The northerly northerlyposition positionof ofthe thesynvolcanic synvolcanictrondhjemite trondhjemiteintrusion intrusionisisconsistent consistentwith withexposure exposureofofprogressively progressivelydeeper deeper levels of a volcanic edifice edificein in that that direction. Southerly levels of Southerly younging younging in the the Willroy-Geco Willroy-Geco area implies implies that the the northern northern tectonic tectonic block block is, is, in in general, general, stratigraphically stratigraphically lower lower than the the southern southern tectonic tectonicblock block (Fig. (Fig.21). 21). A A consequence consequence of D2-fold repetition of sequences on the southern southern limb limbof ofthe theManitouwadge Manitouwadgesynform synformisis that that the themineralized mineralizedand andaltered alteredintervals intervalsof ofthe theWillroy-Geco Willroy-Geco area area are are repeated repeated in inthe theouter outervolcanic volcanicbelt, belt, assuming younger greywackes. assuming that that they theywere werenot notremoved removedby byerosion erosionororfaulting faultingalong alongthe thecontact contactwith with younger greywackes. Sporadic orthoamphibole, garnet garnet and minor cordierite rocks of of the outer volcanic belt are Sporadic zones of orthoamphibole, cordierite in mafic rocks volcanic belt interpreted as asincipient incipient synvolcanic synvolcanic alteration alteration correlative correlative with with altered alteredrocks rocksin inthe theWillroy-Geco Willroy-Gecoarea. area. GEO CHEMISTRY GEOCHEMISTRY A A suite suiteof of 127 127samples samples was was collected collected to to represent represent supracrustal supracrustal and andplutonic plutonicrocks rocksofofthe theManitouwadge Manitouwadge greenstone belt, the the Black Black Pic Picbatholith, batholith,and andthe theQuetico Queticosubprovince. subprovince. These were greenstone were analysed analysed for for major major H20, C 0 2 and S, St,and andmost mostwere werealso alsoanalysed analysed for for trace traceelements, elements,including including rare-earth rare-earth elements, ferrous ferrous iron, iron, H2 elements, 0, CO2 elements from the area elements (REE). Our Our data dataare aresupplemented supplemented by bysome somemajor-element major-element analyses analyses of samples from area of of known mineral deposits, made made available available by Noranda Inc. Evaluation Evaluation of of results results of of our our geochemistry geochemistry program program known is is ongoing ongoing and many of the interpretations interpretations presented presented here here are areincomplete incomplete or or preliminary. preliminary. Metavolcanic Metavolcanic and a n dsubvolcanic subvolcanicrocks rocks A sample sample suite suite of of 54 54metavolcanic metavolcanic and and associated associated rocks rocks was was chosen chosen to to represent represent primary primarygeochemistry, geochemistry, A avoiding evidence evidence of retrogression as much much as as possible possible (with (withsome someexcepexcepavoiding of synvolcanic synvolcanic alteration alteration and and later retrogression tions discussed discussed below). below). The Thesuite suiterepresents represents55main mainrock rocktypes; types;aphyric aphyricfelsic felsicmetavolcanic metavolcanicrocks, rocks,quartzquartztions phyric metavolcanic metavolcanic felsic rocks, foliated mafic metavolcanic rocks, and hornblendephyric foliated trondhjemite-granodiorite, trondhjemite-granodiorite, mafic magnetite-garnet rocks/magnetite rocks/magnetite quartzites. quartzites. The Thelatter latterinclude includemagnetite-rich magnetite-rich layered layered rocks rocks (see (see Unit Unit 5), 5), magnetite-garnet resembling sedimentary concentrations of heavy minerals, and quartz-richer quartz-richer transitional rocks rocks interpreted as as resembling contaminated trondhjemite. trondhjemite. To Tofacilitate facilitatediscussion, discussion, the the suite suitecan canbe besubdivided subdividedinto into66geographic geographicgroups; groups; contaminated the inner inner and andouter outervolcanic volcanic belts, belts, and andthe theDead DeadLake, Lake,eastern eastern extension, extension, One One Otter-Banana Otter-Banana Lakes Lakes and and JimJimthe Davis Lakes Lakes areas (Fig. 22). The The foliated foliated trondhjemite-granodiorite trondhjemite-granodiorite in in the the inner inner volcanic volcanic belt belt isisinterpreted interpreted Davis as synvolcanic; synvolcanic; similar to test test their theircompositional compositional similarity similarity and and as similar rocks rocks were weresampled sampledtoto the the east east and north to the the extent extentofofpossibly possiblycomagmatic comagmaticintrusive intrusiverocks. rocks. Mafic metavolcanic rocks 23). The ThecompocompoMafic rocks throughout throughout the Manitouwadge belt belt are tholeiitic basalts (Fig. 23). sitions of of mafic rocks from attentuatedand andfolded foldedextensions extensions sitions from the the inner and outer volcanic belts, and from the attentuated of the the belt, belt,for forthe themost mostpart, part,are arepermissive permissiveofofcorrelation correlationand andsuggest suggestthat thatallallmafic maficrocks rockscould couldhave havebeen been of produced by the same same magma magma system. The The tendency tendency of of the outer outer belt belt to tohigh highMg, Mg,low low Ti02 Ti02 (Fig. (Fig. 24), 24),and and produced low light REE REE (Fig. (Fig.26) 26)contents, contents,isisdefined definedby bygabbros gabbrosand andsamples samplesfrom fromthe theSwill-Mills Swill-MillsLake Lake area area (near (near the the low hinge of the Manitouwadge Manitouwadge synform southwestern part Mafic compositions compositions in the inner inner hinge synform in in the southwestern part of Fig. 22). Mafic and outer outer belts beltsshow showconsiderable considerable overlap, overlap, and andthe theslight slightdifferences differences could could reflect reflect aa bias biasininwhich whichgabbros gabbros and and rocks rocks deeper deeper in the the stratigraphic stratigraphicsection section were were not sampled sampled in the inner inner belt. belt. The Thesingle singlesample sample from from the and inner belt belt that thatplots plotsininJensen's Jensen's(1976) (1976)field fieldofofbasaltic basaltickomatiite komatiite(Fig. (Fig.23) 23)isisassociated associated with with altered alteredrocks rocks inner (see below) and may may have have undergone incipient magnesian magnesian alteration. A sample sample (from (from the One One Otter-Banana Otter-Banana (see alteration. A area) area) that thatlies liesininthe thefield fieldofofcalc-alkaline calc-alkalineandesites, andesites,persistently persistentlyshows showsanomalous anomalousgeochemistry geochemistrywith withrespect respect toother othermafic maficrocks rocks in in the theManitouwadge Manitouwadge belt. belt. Hornblende-magnetite-garnet Hornblende-magnetite-garnet rocks rocks and magnetite magnetite quartzites quartzites to in the the Dead Dead Lake Lake suite, suite, and and aasingle single sample sample from the outer volcanic belt, Ti02, in belt, have have distinctive distinctive high high FeOt FeO and Ti02, and andlow lowMgO MgO contents contents(Figs. (Figs.23, 23,24). 24). Felsic volcanic volcanic rocks and synvolcanic trondhjemite are are transitional transitionalcaic-alkaline calc-alkalineto totholeiitic tholeiiticrhyolites rhyolitesand and Felsic dacites (Fig. (Fig.23), 23),mostly mostlycontaining containing65—80 65-80 percent quartz-phyric dacites percentSiO2 Si02(Fig. (Fig.24). 24). In In terms terms of of Al-(Fet+Ti)-Mg, Al-(Fe+Ti)-Mg, quartz-phyric felsic rocks show a somewhat wider compositional range that could be be due dueto to aa mafic mafic component component in in heterolithic heterolithic felsic that could breccias, breccias, and/or and/or incipient incipient alteration. alteration.The Thenarrow narrowcompositional compositionalrange rangeofofsynvolcanic synvolcanic trondhjemite trondhjemite in in the the 34 �Inner volcanic volcanic Felsic Felsic rnetavolcanic metavolcanic rocks rocks Quartz—phyric felsic rocks Quartz-phyric felsic Trondhjemite—granodiorite Trondhjemite-granodionte Mafic metavolcanjc rocks Mafic metavolcanic rocks Hornblende—magnetite—garnet Hornblende-magnetite-garnet rocks/magnetite rockslmagnetite quartzite quartzite belt belt (JVB) (IVB) 9 (2) (2) (6) (6) (8) (6) • •+ rn (6) •(6) Outer volcanic volcanic belt belt (OVB) (OVB) l @ Dead Lake Dead Lake (DL) (DL) One Otter— OtterBanana (OB) Banana (OB) Eastern extension (E) (E) extension Jim-Davis Jim—Davis (JD) (JD) Noranda suite suite (3) (3) (7) 0(7) .(1) e (1) 0 o (7) (7) •t) (5) (5) 13 (2) (2) (4) 4v 4 • (1) (1) • (3) (3) 0 6 (1) 0(3) 0 (3) rn (3) • (3) Gq CD jq '1 CD CD a4. 0 CD CCD 01 e e LEGEND Metasedimentary rocks Orthoamphibole-cordierite-garnet gneiss 0Intermediate to mafic metavolcanic rocks --- ----- Fold axial trace Fault FIG. 22. associated geochemical geochemical samples in in the t h eManitouwadge Manitouwadge greenstone greenstone FIG. 22. Locations Locations ofof metavolcanic metavolcanic and and associated The key key shows shows tthe h e symbols symbols used rock types types and and geographic geographic areas, and the the number number belt. The belt. used to to represent represent rock areas, and of samples samples is is in in parentheses. parentheses. Locations Locations of of samples samples analysed analysed by by Noranda Noranda Inc., Inc., all all from from the t h e inner inner volcavolcaof belt, are a r enot notshown. shown.'2'2pts' pts' indicates 2 samples f r othe m t same h e same location. Swill-Mills Lakes Lakes area area nic belt, indicates 2 samples from location. TheThe Swill—Mills most westerly westerly samples samples in in the the outer outervolcanic volcanic belt. belt. encompasses the t h e 33 most (see text) encompasses CD 0 CD E a '1 �__ Geochemistry Geochemistry Manitouwadge greenstone belt Fet+Ti Fe+Ti Fet+Ti A49 \ \ \ rhyolule Al \ \ docite V \ high—Mg \ \ thoisili. \ ' andesite V c&c—alkaline calc-alkaline bosailic komotlite \ ' \ \bOZOif \J • Mg Al A1 Mg rhyolite docite V \ \ high—Mg \ tholeilie \ \ ondesite V catc—olkalirie calc-alkaline basaltic komotlite ' \basait \/ V Mg FIG. 23. and associated associated rock rock compositions compositions in in terms of Jensen's (1976) 23. Metavolcanic Metavolcanic and (1976) definition definition of tholeiitic rhyolite to to basalt, basalt, and basaltic komatiite, based based on on Al-(Fet+Ti)-Mg Al-(Fe+Ti)-Mg (cation tholeiitic and and calc-alkaline calc-alkaline rhyolite (cation to be mobile during sea-floor sea-floor alteration alteration and regional metamorphism. Symbols %), elements elements less likely to Symbols %), as as in in Figure Figure 22. 22. The Thefields fieldsofofquartz-phyric quartz-phyric felsic felsic rocks rocks (dotted), (dotted)>and and innerinner- (dash-dot) (dash-dot) and andouterouterbelt (dashed) (dashed) mafic mafic rocks rocks are outlined outlined as as in in Figure Figure 24. 24. The Thesamples samplesare aredivided dividedbetween between 22 plots plots to to minimize minimize overlap. overlap. volcanic belt tends tends totoencompass, encompass,or ornearly nearlyso, so,analyses analysesofofsimilar-looking similar-lookingrocks rocks from from the theDead DeadLake, Lake, inner volcanic areasl suggesting suggesting aa comagmatic comagmatic relationship. relationship. Some Sometrondhjemite trondhjemite Otter-Banana, and andJim-Davis Jim-Davis Lakes Lakes areas, One Otter-Banana, samples in in the the vicinity vicinity of of the Dead Dead Lake Lake suite tend to to have have high FeOt and Ti02 Ti02 contents, contents,intermediate intermediatebetween between samples that of of hornblende-magnetite-garnet hornblende-magnetite-garnet rockslmagnetite that rocks/magnetite quartzites and inner-belt trondhjemite, consistent with with contamination. contamination. Mafic rocks distinguished from Mafic rocks in in the inner volcanic belt belt can be distinguished from felsic felsicrocks rockson onthe the basis basis of of Ti02 Ti02 and FeOt content, content, with with mafic mafic rocks rocks having TiO2>l% and FeO>10%, F'eOt>lO%, and and felsic felsic rocks rocks having having Ti02<0.4% FeO Ti02>1% and Ti02<0.4% and FeO<8% FeOt<8%(Fig. (Fig.24). 24).AAsingle singlefelsic felsicsample samplewith with Ti02=1.36% Tio2=1.36%isisaamicaceous micaceousquartz-phyric quartz-phyric heterolithic heterolithic breccia. breccia. The The majority majorityof ofquartz-phyric quartz-phyricfelsic felsicrocks rocks have have Ti02 Ti02between between0.27 0.27 and and0.39%. 0.39%. 'Unaltered1felsic felsic extrusive extrusive rocks rocks in in the theManitouwadge Manitouwadgebelt belthave haveundergone undergoneextensive extensivealkali alkaliexchange, exchange, 'Unaltered' Na20 and andCaO CaOcontent content(Fig. (Fig.25). 25).Quartz-phyric Quartz-phyricfelsic felsicrocks rocks are areprepreresulting in wide wide variations in K20, Na20 resulting potassic. In In contrast, contrast, synvolcanic synvolcanic trondhjemite is sodic and has a relatively relatively restricted restricted range of dominantly potassic. CaO, consistent consistent with with limited limitedsecondary secondary redistribution. redistribution. Trondhjemite Trondhjemitesamples samplesnear nearthe theDead DeadLake Lake alkalis and CaO, suite extend hornblende-magnetite-garnet extend to tomore morecalcic calciccompositions, compositions,again againsuggesting suggesting contamination contamination by by hornblende-magnetite-garnet rockslmagnetite quartzites quartziteswhich whichgroup groupwith withmafic maficmetavolcanic metavolcanicrocks. rocks. rocks/magnetite Chondrite-normalized REE in mafic rocks volcanic belts that are are Chondrite-normalized rocks in in the the inner inner and outer volcanic belts define define patterns patterns that have slightly elevated light REE, REE, with with weak weak negative or positive Eu anomalies anomalies (Fig. 26). 26). The The relatively flat or have haahigher higherlight lightREE REE levels (11-40 x chondrite) than than the theouter outerbelt belt(6—2 (6-255xxchondrite). belt has inner belt levels (11—40 chondrite). The lowest light REE REE contents contentsin inthe theouter outerbelt beltare areiningabbroic gabbroicrocks rocksand andsamples samplesfrom fromthe theSwill-Mills Swill-MillsLakes Lakes area, area, again again light possibly reflecting reflecting a sampling bias. Heavy REE levels levels in are nearly nearly identical. identical. possibly in both belts are In In contrast contrasttotomafic maficrocks rocksfrom fromthe theinner innerand andouter outervolcanic volcanicbelts, belts,which whichshow showconsiderable considerablecompositional compositional overlap, REE patterns patterns define define two two distinct distinct suites suites of of felsic felsic volcanic volcanic rocks. REE abundance abundance in in two two overlap, rocks. The total REE samples of of northernmost northernmost outer-belt outer-belt aphyric aphyricfelsic felsicrocks rocks isis relatively relatively low, low, and normalized REE REE define define a steeply samples sloped La/Yb == 8) sloped pattern from from light light to to heavy heavy (normalized (normalized LaIYb 8) and aa moderately moderately negative negative Eu anomaly anomaly (Eu/Eu* (EuIEu* == 0.65—0.83) 0.65-0.83) (Fig. (Fig. 27). 27). Zr/Y, ZrIY,which whichgenerally generallymimics mimics the the light light to toheavy heavyREE REEslope slope(Lesher (Lesheretetal., al.,1986), 19861,isis high at at 32—44. 32-44. REE outer-belt felsic felsic rocks are typical of barren (not (not mineralized) mineralized) high REE and and Zr/Y Zr/Y in northernmost outer-belt felsic volcanic volcanic suites Wabigoon and Abitibi Abitibi subprovinces subprovinces (ibid.). AAsingle singlesample sampleofoffelsic felsic breccia, breccial felsic suites in in the Wabigoon interleaved with with mafic mafic rocks rocks in in the theSwill-Mills Swill-Mills Lakes area, has REE REE contents contents between between those those of of felsic felsic rocks rocks in interleaved the inner inner and andouter outerbelts. belts.Inner-belt Inner-beltfelsic felsicrocks, rockslincluding includingboth bothvolcanic volcanicrocks rocks and and subvolcanic subvolcanic trondhjemite, trondhjemite, the 2.34.9)1 more more are characterized characterized by higher higher total REE, REE, moderately moderately sloping sloping patterns (normalized (normalized LaIYb are La/Yb == 2.3—4.9), 36 �Geochemistry Geochemistry Manitouwadge greenstone belt belt hO, 0.1 0.5 1.0 80 0 0 •0 70 0 0 m a. C,) 60 60 - Inner Inner volcanic volcanic belt belt(IVB) (IVB) Quartz—phyric Quartz-phyric felsic felsic metavolcanic rnetavolcanic rocks rocks (9) (9) - - Mafic Maf~cmetavolcanic rnetavolcan~crocks rocks (9) (9) Outer Outer volcanic volcanicbelt bell(OVB) (OVB) _— Mafic Mafic metavolcanic rnetavolcanic rocks rocks (7) (7) , ---- .- (• I I , I , , I I I ,-\ ' / — 50 50 - & -- - l l l l 31 '; l 20 00 0 - FIG. 24. Si02and andFeOg FeOt (weight (weight %) 24. Si02 %) as as functions functions of of Ti02 T i 0 2(weight (weight%, %, logarithmic logarithmic scale). scale), Mafic Maficand andfelsic felsicrocks, rocks,especially especially in in the the inner inner volcanic volcanicbelt, belt, can canbe bediscrimdiscriminated inated on on the the basis basis of of Ti02 T i 0 2abundance, abundance, aa valuable valuable observation as as Ti02 T i 0 2isisrelatively relatively immobile immobile during alteration alteration and and metamormetamorphism. phism. Symbols Symbolsas as in Figure 22. The The outoutlined lined sample sample fields in this and and other other plots plots are are intended intended as as aa visual visual aid, aid, without without stastatistical tisticalsignificance. significance. a 0a, ---- U- ,, @c 10 0 U 0 S • a S 0•00 • S 0 0.1 hO2 0.5 1.0 K20 FIG. FIG. 25. 25. CaO-K20-Na20 CaO-K20-Na20 (weight (weight %) %) proportions. proportions. The The compositional compositional variation variation of ofquartz-phyric quartz-phyric felfelsic sic rocks rocks (dotted (dotted field) field) suggests suggests alkali alkali exchange exchange dominated dominated by by potassic potassic alteration. alteration. TrondhjemiteTrondhjemitegranodiorite (symbols (symbols as in Fig. Fig. 22) 22) has has aarelatively relatively granodiorite restricted restricted range range of ofsodic sodiccompositions. compositions. HornblendeHornblendemagnetite-garnet magnetite-garnet rocks rocks and and magnetite magnetite quartzites quartzites lie lie with with calcic calcicmafic maficrocks. rocks. Ca 37 Na20 �Geochemistry Geochemistry Manitouwadge greenstone belt FIG. 26. 26. Chondrite-normalized Chondrite-normalized rare earth earth element element (REE) (REE) abundances abundances in in mafic mafic metavolcanic metavolcanic rocks. The The positive Eu anomaly in the the inner inner volcanic volcanic belt belt isisdedefined by a single fined by single sample; all others have have nearly nearly fiat flat or weakly negative Eu/Eu*. Eu/Eu*. Gd weakly negative Gd was was interpolated interpolated asassuming a linear distribution distribution between between normalized normalizedSm Sm and Yb. (Tb (Tbwas wasnot notused usedbecause because of ofits itsrelatively relatively high detection limit). limit). Normalization Normalizationvalues valuesare arethose those of Taylor and McLennan McLennan (1985). (1985). ID v d.t.clion dd.clian datactlan limit limit ilmil limit - 0Inner Inner volcanic volcanic belt—mafic belt-mafic rocks (6) (6) Outer (7) Outer volcanIc volcmic belt—maflc belt-mark rocks (7) • U 5 Z 0E a 0 U .0 — 0>. I a E — .0 >- ..j too FIG. 27. 27, Chondrite-normalized Chondrite-normalized REE abundances abundances in felsic rocks. Normalfelsic metavolcanjc metavolcanic and subvolcanic subvolcanic rocks. Normalization values and interpolated Gd Gd as as in in Figure Figure 26. 26. 10 Inner volcanic volcanic belt. belt Foliated trondhjemite Quartz—phyrlc felsic rocks (8) Quartz-phyric felslc (6) Aphyrlc felsic (2) Aphyric telsic rocks (2) Outer volcanic volcanic belt belt Aphyrlc felsic rocks (2) Aphyric felsic (2) - - doteelian ----- limIt - Swill-Mills Lakes Lakes felsic (1) — felsic breccia breeds (I) Swill—Mills d O "- LL zV i , ? , z f & 2 G : e 3 pronouncednegative negativeEu Euanomalies anomalies(Eu/Eu* (Eu/Eu8= = 0.20-0.58), and andZr/Y Zr/Yfrom from1.7—11. 1.7-11. Quartz-phyric Quartz-phyricfelsic felsicsamples, samples, pronounced 0.20—0.58), three lenses lenses in in close close proximity to to massive massive sulphide deposits deposits (Fig. (F'ig. 4), 41,form formaacoherent coherent collected from each of the three compositionally similar to synvolcanic trondhjemite (Fig. 27). On On the thebasis basisof of similarity similarity in in composition composition group compositionally and age, age, the the trondhjemite trondhjemiteisisinterpreted interpretedtotohave havebeen beenaareservoir reservoirfor forquartz-phyric quartz-phyric felsic felsic volcanism. volcanism. In In general, general, and inner-belt felsic felsicrocks rocks are aregeochemically geochemically comparable comparableto tofelsic felsic volcanic volcanic suites suites associated associatedwith withmassive massivesuiphide sulphide inner-belt mineralization in in the theWabigoon Wabigoon (Sturgeon (Sturgeon Lake Lake area), area), Abitibi Abitibi and andUchi Uchi subprovinces subprovinces (Lesher (Lesher et al., al., 1986), 1986), in in mineralization particular particular in in the themagnitude magnitudeofofnegative negative Eu Euanomaly. anomaly. Altered Altered rocks rocks In concordance Manitouwadge, In view view of of the theunusual unusualextent extentand and concordanceofofaltered alteredrocks rocksat at Manitouwadge,especially especially orthoamphibole-bearing rocks, rocks, geochemistry geochemistry was applied in order order to todefine define compositional compositional trends trendsassociated associated orthoamphibole-bearing with alteration, alteration, to totest testthe theconsistency consistencyofofour ourfield fieldidentification identification of of probable probable protoliths, protoliths, and and to tocompare compare with compositions of altered and and unaltered unaltered rocks rockswith withthose thosereported reportedfrom fromsimilar similarand anddissimilar dissimilargeological geologicalsetsetcompositions tings. In Inthis thisdiscussion, discussion,'alteration' 'alteration'and and'protolith' 'protolith'imply implytheir theirpremetamorphic premetamorphicequivalents equivalents and, and,although although tings. some element element mobility is likely likely during metamorphism, this is is presumed presumed to to have have occurred occurred on onaalocal localscale, scale, some not significant significant to to the the discussion discussion here. here. Altered Altered rocks rocks are are compared compared with with unaltered unaltered or or 'least' 'least'altered alteredvolcanic volcanic not rocks sampled in the the inner inner volcanic volcanic belt belt on on the thesouthern southernlimb limband andininthe thehinge hingeregion regionofofthe theManitouwadge Manitouwadge rocks synform. Samples Samples representing representing synvolcanic synvolcanic alteration, including including orthoamphibole-cordierite-garnet gneiss gneiss and synform. sillimanite-biotite-cordierite interlayers, interlayers,as aswell well as sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist and associated quartzite, sillimanite-bjotite-cordjerite quartzite, were collected collected in the Wiliroy-Geco Willroy-Geco area. The Thesample samplesuite suitewas wassupplemented supplemented by bywhole-rock whole-rock major-element major-element were analyses made available by km north north of of the the analyses by Noranda Noranda Inc., extending extending from from the the Willroy Wiliroy 215 2/5 deposit deposit to about 11km axial trace trace of of the theManitouwadge Manitouwadgesynform synform (Fig. (F'ig. 4). 4).Orthoamphibole-bearing Orthoamphibole-bearingrocks rocksand andsillimanitic sillimaniticinterlayers interlayers axial 38 �Geochemistry Geochemistry Manitouwadge Manitouwadge greenstone belt belt Ti0, 0.1 80 * * * * A * + A + +A . 70 A ** N 0 (I) 1.0 0.5 o. Unaltered arid least altered and 'least' altered rocks rocks Quartz—phyrio felsic znetavolcanic Quartz-phyric felsic metavolcanic rocks (9) (9) o0 Felsic F e h c metavolcanic metavolcanic rocks rocks (2) (2) 60 — - .. Mafic metavolcanic -----Mafic metavolcanic rocks rocks (9) (9) a0 Slightly Slightly altered altered pillowed pillowed rocks rocks (1) (1) • t - + A A AA ,-, A A S. / iA Metamorphosed Metamorphosed altered altered rocks rocks * Sillimanite—muscovite—quartz Sillimanite-muscovite-quartz schist (8) (6) * ,' a, Orthoamphibole—cordierite—garriet Orthoamphibole-cordierite-garnet gneiss gnelss A A Orthoarnphibole—bearing. Orthoamphibole-bearing, Geco—Willroy Geco-Willroy (a) (8) A A Orthoamphibole—bearing. Orthoamphibole-bearing. Nama Nama Creek—west Creek-west (4) (4) 50 50 - , ++ Sillimanitic Sillimanitic interlayers interlayem (7) (7) I , , I I , , ( , , , , ,, \ .,', AA /,/ + ! '\, i i \', .', \'\ +A \ A ----<.------7-A - 20 20 - - A + + AA ) FIG. FIG. 28. 28. Si02 Si02and andFeOg FeOt(weight (weight %) %) as as functions of Ti02 Ti02 (weight (weight % % logarithmic logarithmic scale) scale) for samples samples from from the the inner inner volvolcanic canic belt. Ti02 Ti02abundance abundancein inunaltered unaltered or 'least' 'least' altered alteredrocks rocksdefines defines aa bimodal bimodal population population corresponding corresponding to felsic felsic and and mafic rocks. rocks. The The bimodal bimodal distribution distribution isis mimicked by altered rocks. rocks. The Thefields fields for for quartz-phyric quartz-phyric felsic felsicrocks rocks and andmafic maficrocks rocks are are from from Figure Figure 24. 24. A A..A I 0a) A A 10 + * A + -IA A +1 + 0 0 0.1 I 0* *-• Ti02 0.5 1.0 in the area represented by the Noranda in the theWillroy-Geco Willroy-Geco area are are mostly mostly intensely intensely altered, whereas whereas the represented by Noranda suite suite includes includes transitional transitional or or incipient incipient alteration. alteration. Both Both orthoamphibole-bearing orthoamphibole-bearingrocks rocksand andsillimanitic sillimaniticinterlayers interlayers have bimodal distributions distributions of of Ti02 Ti02 content content similar similar to to that thatofofmafic maficand andfelsic felsic rocks, rocks, suggesting suggesting that Ti02 Ti02was wasrelatively relatively immobile immobile during alteration and and that, that,ininmost mostcases, cases,the theprotolith protolithof ofaltered altered rocks rocks can can be be inferred inferred from Ti02 abundance (Fig. 28). In In low low Ti02 rocks (<0.5%), Ti02 Ti02 shows shows aa negative negative correlation correlation with Si02 Si02 that that could could be beinterpreted interpretedasasa adifferentiation differentiation rocks trend. of samples sampleswith with TiO2<O.1% Ti02<0. 1% suggests suggests either either Ti02 Ti02 loss and/or, and/or, trend.However, However,the thehigh highSi02 Si02content content(75—81%) (75-81%) of silicic alteration alteration accompanied accompaniedby by volume volume increase increase and and dilution dilution of of Ti02. Ti02.FeOt FeOtininmafic, mafic,felsic felsicand andaltered alteredrocks rocks silicic shows the same bimodal distribution as Ti02, and the the Fe0 FeOtcontent contentofofaltered alteredrocks rocksisisgenerally generallysimilar similar to, to, or or shows Ti02, and slightly slightly higher, higher, than than that thatofof'least' 'least'altered alteredrocks. rocks.These Theseobservations observationsare areconsistent consistentwith withfield fieldidentication identicationofof protolith, schist, protolith,that thatis,is,felsic felsicvolcanic volcanicrock rockfor forsillimanite-muscovite-quartz sillimanite-muscovite-quartz schist,and andinterlayered interlayeredfelsic felsicand andmafic mafic rocks for for orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss. gneiss. Interestingly, Interestingly, the distribution distribution of of orthoamphibole-bearing orthoamphibole-bearing rocks layers orthoamphibole-cordierite-garnet gneiss gneiss is apparently apparently not not determined determinedby by layers and and sillimanitic sillimaniticinterlayers interlayers in in orthoamphibole-cordierite-garnet protolith. protolith. The alteration alterationtrends trendscan canbebesummarized summarizedbybyviewing viewingcompositions compositions of of 'least' 'least' altered alteredand andaltered alteredrocks rocks The (FeOt+MgO)-(A1203/2)-(K20)-(Na20+CaO) tetrahedron (Fig. (Riverinand andHodgson, Hodgson, in an an 'unfolded' 'unfolded' (Fe0+Mg0)-(Al203/2).(K20)-(Na20+Ca0) in tetrahedron (Fig. 29)29) (Riverin 1980; Luff Luff et al., 1992). 1992). The Themobility mobilityof of alkalis alkalisin in felsic felsic rocks is apparent apparent from from their their wide widecompositional compositionalrange range 1980; Sillimanite-muscovite-quartzschist schistshows showsconsiderable considerableoverlap overlap in projections projections showing showingK20-(Na20+CaO). K20-(Na20+CaO).Sillimanite-muscovite-quartz in with felsic felsic rocks, rocks, but but also alsoextends extendsto toproportionately proportionatelymore more(Fe0 (FeOt+MgO)-rich andAl203-rich A1203-richcompositions. compositions. with +MgO)-rich and 'Least' altered alteredmafic maficrocks rocksdefine defineaarestricted restrictedcompositional compositionalrange. range.Orthoamphibole-cordierite-garnet Orthoamphibole-cordierite-garnetgneiss gneiss 'Least' has proportionately proportionately higher higher (FeOt+MgO) (F'eOt+MgO) and Al203, A1203, and and lower lower (Na20+CaO), (Na20+CaO), than than 'least' 'least'altered alteredrocks. rocks. has (I?eOt+MgO)/A1203, the Orthoamphibole-bearing rocks and sillimanitic sillimanitic interlayers interlayers are mainly different different in Orthoamphibole-bearing in (Fe0 +MgO)/Al2 03, the latter latter being beingslightly slightlymore morealuminous. aluminous. Transitional Transitional altered altered rocks, rocks, mainly mainly from the the area area northwest northwest of of the the 39 �Geochemistry Geochemistry Manitouwadge Manitouwadge greenstone greenstone belt belt Na20+CaO Unaltered and and 'least' 'least" altered altered rocks rocks Unaltered A Average alteration trends, Average alteration trends, Noranda Noranda camp camp / \ / \ Millenbach quartz—feldspar quartz-feldspar porpi porphyry Millenbach - ---------Millenbach andesite andesite - Millenbach -.-.-.-.-.-.- \ / / \ Quartz—phyric telsic rnetavolcanic Quartz-phyric felsic metavolcanic rocks rocks (9) (9) oo Felsic Felsic u,etavolcanic metavolcanic rocks rocks (2) (2) r Mafic metavolcanic metavolcanic rocks rocks(8) (81 -_-Mafic Slightly altered alteredpillows pillows (1) (1) Slightly Metamorphosed Metamorphosed altered altered rocks rocks * * Sillimanite—muscovite—quartz Sillimanite-muscovite-quartz schist schist (6) (6) . Orthoamphibole—cordierite—garnet Orthoamphibole-cordierite-garnet gneiss gneiss - FeO+ Na20+CaO -willrOY(8) Orthoamphibole—bearing. Geco—Willroy @) Creek-west (4) Orthoainphibole—bearing, Name Creek—west Sillimanitic interlayers (7) Al K20 20 3/2 Na20+CaO FIG. FIG.29. 29.Unfolded Unfoldedtetrahedron tetrahedronshowing showingcompositional compositional trends trends (molar (molar proportions) proportions) associated associated with withununaltered, altered,'least' 'least'altered, altered,and andaltered alteredrocks. rocks.Orthoamphibole-bearing Orthoamphibole-bearingrocks rocksfrom fromthe theWillroy-Geco Willroy-Geco area area (filled (filled triangles) triangles) are are generally generally more more intensely intensely altered than than those those west west of of the the Nama NamaCreek Creek deposit deposit (open (open triangles). triangles).The Thefields fieldsofoforthoamphibole-bearing orthoamphibole-bearingrocks, rocks,quartz-phyric quartz-phyricfelsic felsicrocks rocksand andmafic maficrocks rocksare are outlined. outlined.Average Averagealteration alterationtrends trendsfor forthe theMillenbach Millenbachandesite andesite(dashed) (dashed)and andquartz-feldspar quartz-feldsparporphyry porphyry (dash-dot) (dash-dot)are areshown shownfor forcomparison comparison(analyses (analysesfrom from Table Table 3, 3, Riverin Riverin and and Hodgson, Hodgson, 1980). 1980). The Theform form of of the theplot plotisisbased basedononRiverin Riverinand andHodgson Hodgson(1980) (1980)and andLuff Luffetetal. al.(1992). (1992). Nama NamaCreek Creekdeposit, deposit,tend tendtotohave havecompositions compositionsbetween betweenmore morealtered alteredWillroy-Geco Willroy-Geco rocks and 'least' 'least' altered altered rocks, rocks,in insome somecases, cases, overlapping overlapping with 'least' 'least' altered alteredrocks. rocks.Alteration Alterationtrends trendsfor forthe theMillenbach Millenbachandesite andesiteand and quartz-feldspar porphyritic porphyritic rhyolite rhyolite associated associated with with alteration alterationpipes pipesininthe theMillenbach Millenbachmine mine(analyses (analysesfrom from quartz-feldspar Table Riverinand andHodgson, Hodgson,1980) 1980)are areshown shown for for comparison. comparison. Although Although alteration alterationzones zonesatatMillenbach Millenbach Table33ofofRiverin are aremuch muchsmaller smallerininextent extent(100's (100'sofofmetres), metres),compositional compositionaltrends trendsgenerally generallycorrespond correspond to to those thoseof ofaltered altered and'least' 'least'altered alteredrocks rocksatatManitouwadge. Manitouwadge.The Themost mostintensely intenselyaltered alteredfelsic felsicrocks rocksatatboth bothManitouwadge Manitouwadge and andMillenbach Millenbachare areconsiderably considerablyhigher higherin in(FeOt+MgO) (FeOt+MgO)and andA1203 AlaOathan thanchloritic chloriticand andsericitic sericiticaltered alteredquartzquartzand feldspar feldsparpyroclastic pyroclasticrocks rocksfrom fromthe theBrunswick BrunswickNo. No. 12 12deposit deposit of of the the Bathurst Bathurst camp camp(compare (compareFig. Fig.1515ofofLuff Luff etetal., al.,1992). 1992). termsofofAFM AFM(Fig. (Fig. 30), compositions of orthoamphibole-bearingrocks rocksfrom fromManitouwadge Manitouwadge InInterms 30), thethe compositions of orthoamphibole-bearing mostly cordierite-anthophylliterocks rocksderived derivedfrom fromaltered alteredvolcanic volcanicprecursers, precursors,asas mostlylie lieininthe thefield fielddefined definedbybycordierite-anthophyllite compiled by by Reinhardt Reinhardt(1987). (1987).Reinhardt's Reinhardt'sfield fieldofofevaporatic evaporaticclays claysand andmagnesian magnesianpelites, pelites,which whichencomencomcompiled passescordierite-anthophyflite cordierite-anthophyllite metasedimentary metasedimentary rocks rocks from from the the Rosebud Rosebud syncline, syncline, Australia Australia isis restricted restricted toto passes Cordierite-anthophylliterocks rocksfrom fromthe theHemlo Hemlogreenstone greenstone belt, belt, interpreted interpreted to tobe bethe the MgO/(MgO+FeO)>0.7. Cordierite-anthophyllite MgO/(MgO+FeO)>0.7. metamorphic metamorphicequivalent equivalentofofimmature immatureclastic clasticsedimentary sedimentaryrocks rocksderived derivedfrom fromaamafic-ultramafic mafic-ultramaficsource source(Pan (Pan etetal., al.,1991), 1991),are arepredictably predictablyindistinguishable indistinguishablefrom fromaltered alteredvolcanic volcanicrocks. rocks. 40 �Discussion Discussion Manitouwadge greenstone belt A plot of oforthoamphibole-bearing orthoamphibole-bearing alalFIG. 30. 30. AFM plot tered rocks at Manitouwadge. Manitouwadge. An An additional additional sample sample tered shown) lies at at negative negative FM FM proportions. proportions. The The (not shown) AFM values (molar proportions) proportions) are are calculated calculated after after the the method methodof of Reinhardt Reinhardt(1987) (1987)ininwhich; which; A=Al203—(Na20+K20+CaO), A=A1203-(Na20+K20+CaO), FFeO —6(1—m)K20, F=FeOt -6(l-rn)K20, F M £A ManiLouwadge orthoamphibole—bearing rocks (11) Manitouwadge orthoamphibole-bearing ( 1 1) + Hemlo Hemlo belt, belt, cordierlte—anthophyllite cordierlte-anthophyliite rocks rocks (5) (5) M=MgO—6mK2O, M=MgO-6rnK20, and and m=MgO/(MgO+FeOt )wholerock. m=MgO/(MgO+FeOt)who~erock. The calculation attempts to 'correct' calculation scheme scheme attempts 'correct' for for oxoxides present present in biotite biotite and and feldspars, feldspars, assuming assuming that MgO/(MgO+FeOg) MgO/(MgO+FeOt) of biotite can be approximated approximated by by the value value of of the whole whole rock. rock. Reinhardt's Reinhardt'sfields fieldsof of alaltered volcanics, volcanics, and evaporitic evaporitic clays clays and and magnesian magnesian pelites are are shown shown for for comparison, comparison, as as are are five five analyanalyses ses of cordierite-anthophyllite cordierite-anthophyllite metasedimentary metasedimentary rocks rocks from the the Schreiber-Hemlo Schreiber-Hemlo greenstone belt belt (from (fromTable Table 2, Pan Pan et et al., al.,1991). 1991). DISCUSSION DISCUSSION Depositional setting and suiphide deposits and alteration and deformation deformation of of massive sulphide alteration zones zones When the presence area is is taken taken into account (Figs. 4 presence of the D1 Dl fault that that dissects dissects the theWillecho-Geco Willecho-Geco area and 21), relationships to to stratigraphic 21), alteration alteration zones zones and and orebody orebody types types at at Manitouwadge Manitouwadge have systematic relationships level, despite remaining ambiguities about detailed correlations of of some some mineralized mineralizedhorizons. horizons. Cu Cu stringer stringer and disseminated orebodies orthoamphibole-cordierite-garnet orebodies (Wiliroy (Willroy 11and 6, 6, and and Geco Geco 4/2 412 zones, zones, Table 3) lie in orthoamphibole-cordierite-garnet gneiss of of the footwall alteration zone. zone. The Theenveloping enveloping Geco Geco main stringer zone zone lies higher in the the stratigraphy, stratigraphy, linking the largest main orebody, and possibly possibly the 8/2 812 Zn Zn zone, zone, with with footwall footwall alteration. These These zones zones have have features features characteristic characteristic of ofsubsurface subsurfaceconduits conduitsfor formineralizing mineralizingfluids fluids and and may maymark markthe thelocations locationsofoffocussed focussed cross-stratal that supplied cross-stratal flow flow that supplied deposits deposits higher in the the stratigraphy. stratigraphy. Zn-Cu-(Pb) Zn-Cu-(Pb)orebodies orebodiesassociated associated with with iron Willecho Gecomain mainorebody orebodyand and8/2 812ZnZnzone, zone,Nama NamaCreek Creekand and Willecho1—3) 1-3) are are iron formation formation(Willroy (Willroy2,2,33and and5,5,Geco sea-floor sea-floor precipitates precipitates or or near-sea-floor near-sea-floor replacement deposits. This Thisgroup, group,representing representingvoluminous voluminousbase-metal base-metal precipitation precipitation and and the thepeak peakofofhydrothermal hydrothermalactivity, activity, includes includes the the largest largest deposits, deposits, the theWillroy Willroy33and andGeco Geco main orebodies. orebodies. The The Cu-to-Zn Cu-to-Zn zoning zoning of the Willroy Willroy 3 orebody orebody toward main toward the hosting iron formation, and the stringer stringer zones zones associated associated with with the theGeco Gecomain mainorebody, orebody,are aresuggestive suggestiveof of proximal deposits centred centred on on areas areas of of hydrothermal upflow. upflow. In In other otherZn-Cu-(Pb) Zn-Cu-(Pb)orebodies, orebodies,possible possibleprimary primaryfeatures, features,such suchasaslayering layeringororzoning, zoning, have not been been reported. reported. However, However, comparison comparison with metal metal ratios ratios in in the theMillenbach Millenbach and and Amulet Amulet orebodies orebodies in in the the Noranda Noranda camp camp (Knuckey (Knuckey et et al., al., 1982), 1982), suggests suggests that their their higher higher Zn/Cu Zn/Cu isisaafeature featureofofdeposition depositionfurther further from the main main area area of of hydrothermal hydrothermalventing. venting. The Theiron-formation-hosted iron-formation-hostedZn-Pb-(Cu) Zn-Pb-(Cu)orebodies orebodies(Willroy (Willroy44and and Geco Geco zincian iron formation) are highest in the stratigraphy stratigraphy and and formed formed during during the thewaning waning of of hydrothermal hydrothermal activity. activity. A sedimentary sedimentary association association for for the thedeposits depositsof of Manitouwadge Manitouwadgebelt belt has hasbeen been previously previouslyemphasized, emphasized,largely largely the assumption assumption that thatthe theManitouwadge Manitouwadgegreywackes greywackes represent a transition transition from from volcanism volcanism to to clastic clastic based on the presence of iron formation and contact (Franklin (Franklin et et al., al., 1981; 1981; sedimentation, and on the presence and quartzites near the contact Friesen et al. et al., al. 1982; 1982;Williams Williamset al., 1990). 1990). Detrital Detritalzircon zirconages agesshow show that thatthe thegreywacke greywackeis is considerably considerably younger the underlying underlying volcanic rocks, unconformity or than the rocks, and and that that the contact is either an unconformity or aa fault. fault. The quartzite silicified felsic volcanic sillimanite-muscovite-quartz schist which it is is is aa silicified volcanic rock, rock, locally locally gradational gradational to sillimanite-muscovite-quartz schist (with which grouped as a map map unit) unit) and andiron ironformation. formation.We Weregard regardall allofofthese theserocks rocksasasthe theproducts productsofofsynvolcanic synvolcanic grouped alteration or or through through precipitation precipitation from from hydrothermal hydrothermal fluids. fluids. hydrothermal activity, either through alteration 'Least' 'Least' altered alteredfelsic felsicvolcanic volcanic rocks rocks atatManitouwadge Manitouwadgehave have all allundergone undergone alkali alkaliexchange, exchange, dominated dominated enrichment in K K and and with withlittle littleeffect effect on onother otherelements, elements,typical typicalofoflow low temperature temperaturesea-floor sea-floor alteration alteration by enrichment (Lagerblad and andGorbatschev, Gorbatschev,1985). 1985).Synvolcanic Synvolcanictrondhjemite trondhjemitewas wasnot notaffected affectedby bywidespread widespreadalkali alkaliexchange, exchange, (Lagerblad despite despite the the local localFe-Mg Fe-Mg alteration alteration near nearcontacts, contacts,asasinferred inferredfrom fromorthoamphibole-garnet orthoamphibole-garnet seams. seams. Similar Similar observations of of alkali exchange in the Abitibi camp, camp, involving involving the sodic Flavrian Flavrian pluton pluton and andits itsmore morepotassic potassic observations comagmatic volcanic volcanic rocks, were were interpreted as as the theresult resultofofsea-floor sea-floorpotassic potassic alteration alterationofofextrusive extrusiverocks, rocks, comagmatic and preservation preservation of of primary primarycompositions compositionsin inthe thesubvolcanic subvolcanicbody body (Goldie, (Goldie,1979). 1979). and The lateral lateraldistribution distributionand andgeochemistry geochemistryof ofsillimanite-muscovite-quartz sillimanite-muscovite-quartz schist suggest these rocks rocks The suggest that these 41 �Discussion Discussion Manitouwadge greenstone belt interacted interacted with with hydrothermal hydrothermalfluids fluidsand andare arenot notsimply simplyaamore moreextreme extremeexample exampleof ofsea-floor sea-floor alkali alkali exchange. In In the Manitouwadge Manitouwadge camp, camp, they they have have been regarded as as a favourable exploration tool indicating indicating proximity to to ore. ore. This reconcile with with the the stratigraphic stratigraphic position This is difficult to reconcile position of of sillimanite-muscovite-quartz schist in in the the hanging hanging wall to orebodies, and of iron iron formation. formation. Locally, the distribution and sandwiched sandwiched between between semi-continuous layers of distribution of thin sillimanitic rocks was was apparently apparently governed governed by by bedding bedding and and is most consistent with sillimanitic layers in tuffaceous rocks sea-floor alteration. The and 66 areas, areas,interpreted interpretedasaszones zonesof ofprobable probablehydrothermal hydrothermalupflow, upflow, sea-floor alteration. The Geco, Geco, Willroy Willroy 11and are an exception exception in that thatsillimanite-muscovite-quartz sillimanite-muscovite-quartz schist schist directly directly overlies overlies orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet footwall alteration. The of hydrothermal hydrothermal fluids fluids from from this this area, area, either either footwall alteration. The observations observations suggest lateral percolation percolation of Geochemicallyand andmineralogically, mineralogically,the theschist schistresembles resembles the the in the the subsurface subsurface or or on on the thesea seafloor floorororboth. both.Geochemically muscovite-aluminosilicate suiphide camp (Walford and Franklin, muscovite-aluminosilicate rocks rocks in the the Snow Snow Lake massive sulphide Franklin, 1982; 1982; Zaleski, 1989) and and sericitic sericitic alteration alteration capping capping and peripheral peripheral to chioritic pipes of of Noranda-type Noranda-type deposits deposits (Franklin (Franklin et et 1989) chloritic pipes a!., interpreted as representing al., 1981), interpreted representing the outer cooler cooler parts of of aa hydrothermal hydrothermal system. system. It is is generally generally accepted that thatsubvolcanic subvolcanic intrusions intrusions provide provide the necessary necessary heat for for driving driving hydrothermal hydrothermal systems, and that deposits (Campbell (Campbell et et al., 1981). In the Snow that these these commonly commonly intrude their their own own volcanic volcanic deposits Snow Lake camp, camp, synvolcanic synvolcanicplutons plutonsboth both intrude intrude altered altered rocks rocks produced produced by by their their hydrothermal hydrothermal system, system, and show show Lake evidence of of alteration; alteration; however, the distribution distribution of intrusive contacts contacts (Fig. of alteration alteration zones zones oniy only crudely follows intrusive 11 in in Galley, Galley, 1993). 1993). The very close relationship between between the the trondhjemite trondhjemite contact contact and stratabound close spatial relationship stratabound alteration alteration at at Manitouwadge Manitouwadge is is unusual, unusual, and and the the stratigraphic stratigraphiccontrol controlisisperhaps perhapseven evenmore more pronounced pronounced when when the unaltered unaltered or or weakly weakly altered altered character character of of supracrustal supracrustal inclusions inclusions in trondhjemite trondhjemite is taken taken into into account. account. The semi-concordant contact and supracrustal semi-concordant contact supracrustal septa septa suggest suggest aa sill sillor orlaccolith, laccolith,or ormultiple multiplesemi-concordant semi-concordant intrusions, with alteration along the the upper upper contact. It that the alteration focussed focussed along It is is also also possible possible that the trondhjemite trondhjemiteinvaded invaded deeper parts of of the the hydrothermal hydrothermal system system and and that thatsurviving survivinginclusions inclusions of of altered altered rocks rocks are are not not exposed exposed at at the the surface. Regional semi-conformable alteration alteration zones associated with volcanogenic volcanogenic massive sulphide deposits typically involve involve alkali-exchange, alkali-exchange,silicification silicificationand andepidotization epidotization (Galley, (Galley, 1993), 1993),rather rather than than alkali-depleted Fe-Mg alteration. alteration. Despite Despitethe theunusual unusualextent extentand andconcordance concordanceofofalteration alterationzones zonesatatManitouwadge, Manitouwadge,the thegeochemical geochemical FeOt+MgO and andA1203 A1203and and depletion depletion in in alkalis alkalis trends from 'least-altered' 'least-altered' to to intensely intensely altered, altered, of of increase increase in FeO+MgO and CaO, CaO, are are similar similar to to those those recorded recorded in in alteration alteration pipes pipes in inthe theAbitibi Abitibicamp camp(Riverin (Riverinand andHodgson, Hodgson,1980). 1980). The bimodal bimodal grouping grouping of of altered altered rocks, rocks, defined defined by by 'immobile' 'immobile' element element abundances, abundances,mimics mimicsmafic mafic and andfelsic felsic volcanic precursers. precursers. Orthoamphibole-garnet-cordierite rocks and and sillimanitic interlayers interlayers had had both mafic Orthoamphibole-garnet-cordierite rocks mafic and and volcanic felsic protoliths and the the metamorphic metamorphicassemblage assemblagewas was determined determined by by small smallvariations variationsin in (FeOt (FeOt+MgO)/A1203, +MgO)/Al203, apparently due to alteration alteration and and not not inheritance inheritancefrom from the the protolith. protolith. There Thereisisno noevidence evidence to tosuggest suggest the the prespresence of politic pelitic rocks, although some and local redeposition redeposition of of some layering in altered rocks could reflect reworking and unconsolidated volcaniclastic material. unconsolidated The unusual gneiss at at Manitouwadge may be be partly partly due to the unusual extent extent of of orthoamphibole-bearing orthoamphibole-bearing gneiss Manitouwadge may the high high metamorphic grade. stabilityexpands expands the the range grade. With increasing increasing grade, orthoamphibole-hornblende orthoamphibole-hornblende stability range of of orthoamphibole-bearing assemblages pages 478—489). assemblages to to more morecalcic calcicbulk-rock bulk-rockcompositions compositions(Spear, (Spear,1993, 1993, pages 478-489). By inference, inference, bulk-rock bulk-rock compositions compositionsthat that produced orthoamphibole-bearing rocks rocks at Manitouwadge By Manitouwadge might, at aa lower lower metamorphic grade, be be considered considered incipient alteration. In Inthe thegreenschistgreenschist-and andamphibolite-facies amphibolite-facies metavolcanic rocks of of the Snow zonesofof chloritic chloriticalteration alteration have have aa lateral exmetavolcanic rocks Snow Lake area, semi-continuous semi-continuous zones extent of of up up to totwo twototothree threekilometres kilometres(Galley, (Galley, 1993). 1993). The Theclosest closest analogues analogues for the the stratabound stratabound regional regional orthoamphibole-bearing alteration at orthoamphibole-bearing alteration a t Manitouwadge Manitouwadge are found in in the the Bergslagen Bergslagen area area of ofthe theSvecofennian Svecofennian Baltic shield. At At Bergslagen, Bergslagen, exhalative exhalative base-metal base-metal deposits deposits and and iron ironformation formationare areunderlain underlainby byconformable conformable stratabound Mg-rich of several, several,to toseveral severaltens tensofofkilometres kilometres(Traghrdh, (Trägrdh, stratabound Mg-rich alteration alteration zones zones with a regional extent of Ripa, 1988; 1988; Baker Baker et et al., a!., 1988). Amphibolite-facies Amphibolite-facies metamorphism metamorphism at at Bergslagen Bergslagen may may play play a role, as at 1988; Ripa, Manitouwadge, in facilitating identification identification of of altered altered rocks. rocks. However, However,ininboth bothareas, areas,itit appears appears that alteration alteration was partly focussed focussed on on aquifer aquifer horizons horizonspossibly possibly consisting consisting of of permeable, permeable, poorly poorly consolidated consolidatedvolcaniclastic volcaniclastic deposits. Structural S t r u c t u r a l and a n d tectonic tectonic synthesis synthesis preferred structural structural model model for for the the Manitouwadge Manitouwadge greenstone greenstone belt, and the the adjacent adjacent Quetico Quetico subsubOur preferred province, involves Dl faults (shear (shear zones) zones) are are recognized recognized from the the coincicoinciinvolves four four phases phases of of ductile ductile deformation. deformation. D1 dence of lithological units, repeated mineralized mineralized sequences, sequences, and zones of truncated truncated lithological zones of of straight straight gneiss gneiss interpreted interpreted Although no no sense sense of of kinematics kinematics or or offset offset has been been observed, observed, sequence repetitions, geas annealed mylonite. Although ometries consistent the early early relative relative age age of of D1 Dl structures, structures, suggest suggest thrusting. thrusting. consistent with with low angle angle truncation, truncation, and the Dg planar and linear linear fabrics, fabrics, typically typically defined defined by high grade metamorphic minerals, suggest D2 deDominant D2 formation broadly synchronous synchronous with peak metamorphism. metamorphism. D2 D; shortening shortening resulted resulted in inrepetition repetitionofofthe thevolcanic volcanic formation 'Manitouwadge syncline' on the southern limb limb of of the D3 D3 Manitouwadge Manitouwadge sequence across across the the easterly trending 'Manitouwadge possibly accounts for the presence presence of volcanic volcanic rocks One Otter-Banana Otter-Banana synform, and possibly rocks in in the the Dead Lake and One Lakes 'Manitouwadge syncline' is folded and contains D2 Ds fabrics. Lakes areas. areas. Metagreywacke in in the core of the 'Manitouwadge 42 �Manitouwadge greenstone belt belt Discussion Discussion Temperature (°C) (OC) —,. + Geological Geological Event Event 600 600 > 2720 Volcanism Volcanism and and mineralization mineralization Dl Ductile faults (thrusts) 2700 Erosion? Erosion? *0Q'4y --' . 2680 st. I 2660- / 1 Sedimentation, Sedimentation, distal distal volcanism volcanism Loken Loken Lake Lake pluton, pluton, Black Black Pic Pic diorite diorite D2 D2 D3 D3 D4 Nama N a m e Creek Creek pluton pluton Peak metamorphism metomorphisrn (Manitouwadge (Manitouwadge belt) belt) Peak Black Black Plc Pic monzodiorite monzodiorite Titanite Titanite closure closure Peak Peak metamorphism metamorphism (Quetico (Quetico subprovince) subprovince) Local Local retrograde retrogradeK—metasomatism K-metasomatism Local Local retrograde retrograde hydrothermal hydrothermal activity activity FIG. FIG. 31. 31. Temperature-time Temperature-timeplot plotshowing showingrelationships relationships between between the thedeformation deformationsesequence, quence, metamorphism metamorphism and plutonism plutonism in in the the Manitouwadge Manitouwadge belt belt and andQuetico Queticosubsubprovince. province. Alternative Alternative paths pathsare areshown shownfor forthe theManitouwadge Manitouwadgebelt belt assuming assumingeither, either, unconformable unconformable deposition deposition of sedimentary sedimentary rocks (dashed) or, or, emplacement emplacement by by early early faulting faulting (dash-dot). (dash-dot). Da Manitouwadge Manitouwadge synform, Blackman Lake antiform, and Jim Jim Lake Lake synform, synform, fold the Manitouwadge Manitouwadge The D3 The belt and andthe theWawa-Quetico Wawa-Queticosubprovince subprovince boundary. Relationships Relationships between metamorphic minerals, migmatitic segregations, and deformation fabrics D3 was was broadly broadly coeval coeval with peak metamorphism metamorphism in the the segregations, fabrics suggest suggest that D3 Quetico subprovince. subprovince. Map-scale Map-scale D4 D4 structures structures modify modify the the geometry geometry of D3 Da folds. Quetico folds. The The dominantly dominantly Z-asymmetry D3/D4 folds, folds, and and dextral dextral kinematic kinematic indicators, indicators, are are interpreted interpreted as asaaresponse responsetotoprogressive progressive dextral dextral of the the D3/D4 of transpression. transpression. In In aapreliminary preliminary structural structuralmodel model(Peterson (Petersonand andZaleski, Zaleski,1994a), 1994a),we weproposed proposeda a5-phase 5-phase deformation sequence sequence for Manitouwadge area. The preliminary preliminary model model interpreted the the Blackman Blackman Lake Lake deformation for the the Manitouwadge area. The antiform and and Jim JimLake Lakesynform synform as as D4 D4 structures structures that thatfolded foldedthe theaxial axialtrace traceofofthe theD3 D3Manitouwadge Manitouwadgesynform. synform. antiform Although our our observations observationsstill stillpermit permitthe the5-phase 5-phasemodel, model,ititrequired requiredaamore morecomplicated complicateddeformation deformationscheme scheme Although than thanour ourpreferred preferredsimpler simpler4-phase 4phasemodel. model. The Wawa-Quetico Wawa-Quetico boundary the Manitouwadge Manitouwadge area transitional on on structural structural and andlithological lithological The boundary in the area is transitional criteria. criteria. Firstly, Firstly, there there is is aagradational gradational change change to to the thesouth, south,from fromdominantly dominantlyeast-west east-west structural structural trends, trends, to to map-scale map-scale folds folds with with broader broaderhinge hingeregions; regions;secondly, secondly, Manitouwadge Manitouwadge and and Quetico Quetico metasedimentary metasedimentaryrocks rocks are are indistinguishable. indistinguishable. Zircon Zircon provenance provenance ages ages constrain constrain the themaximum maximumdepositional depositionalage ageofofManitouwadge Manitouwadge metagreywacke to 2693 2693 Ma, at at least least 25 25Ma Mayounger younger than thanthe the2720 2720Ma Mafelsic felsicvolcanism volcanism (Zaleski (Zaleski et al., al., 1994; 1994; metagreywacke D2tectonic tectonic Davis et et al., al.,1994). 1994).The Themetagreywacke metagreywackecontains containsupper upperamphibolite-facies amphibolite-faciesassemblages assemblages and and aaD2 Davis fabric, hence hence the the minimum minimumage age of of deposition deposition can can be be inferred inferred to tobe becirca circa2680 2680Ma Ma(see (seebelow). below). Provenance Provenance fabric, studies on on Quetico Quetico metasedimentary metasedimentaryrocks rockshave have established established age agebrackets brackets of of circa circa2700 2700 to to2688 2688 Ma Ma (Percival (Percival studies and Sullivan, Sullivan, 1988; 1988; Davis et al., al., 1990), 1990), overlapping overlapping the Manitouwadge. In contrast contrast to tothe the and the age brackets brackets at Manitouwadge. detritalzircons zirconsof of Mesoarchean Mesoarchean age recovered recovered from detrital from Quetico Queticorocks rocks(ibid.), (ibid.), at at Manitouwadge, Manitouwadge, the the oldest oldest detrital zircon of of 2719±2 2719zt2 Ma Ma could could be be derived derived from from local local volcanic volcanic rocks. rocks. The The Quetico Quetico studies studies were were done done at atleast least200 200 zircon km west west of of Manitouwadge, Manitouwadge, and both both source source areas areas and and timing timingof of sedimentation sedimentation could could be be expected expected to tovary. vary. km In In the theManitouwadge Manitouwadgebelt, belt,uplift upliftresulting resultingfrom fromD1 Dldeformation deformationcould couldhave havecontributed contributedsediment sedimentsources, sources, although our our field fieldobservations observations are are equivocal equivocal regarding the relationship relationship between D1 Dl and sedimentation. The The although presence of of straight straight gneiss gneiss (annealed (annealed mylonite) mylonite) on D1 Dl thrust faults faults indicates indicates ductile ductile deformation deformation and andsomewhat somewhat presence elevated temperatures. temperatures. Two Twopost-D1 post-Dl pre-D2 pre-Dz time-temperature time-temperature paths pathsare arepossible possiblefor for the theManitouwadge Manitouwadge belt, belt, elevated one assuming assuming erosion erosion and and unconformable unconformable deposition deposition of of sedimentary sedimentary rocks, rocks, the the other otherconsistent consistentwith withtectonic tectonic one emplacement of of an anallochthonous allochthonoussequence sequence by by prepre- or orsyn-D2 syn-Da faulting faulting(Fig. (Fig.31). 31). emplacement A major majorepisode episode of of magmatic magmatic activity activityfrom from 2687 2687 to to 2677 2677 Ma Ma isis indicated indicated by by the theage ageofoffour fourplutonic plutonic A 43 �Manitouwadge greenstone belt References References rocks; Black Black Pic diorite (2687+3/—2 (2687+3/-2 Ma), the Loken Loken Lake pluton (2687+2/—3 (2687+2/-3 Ma), the Nama Nama Creek Creek pluton pluton (2680±3 (2680k3 Ma) and Black Pic monzodiorite (2677±2 (2677k2 Ma). The The first first three threeof of these these are areprepre- to tosyn-D2 syn-D; intrusions, intrusions, and hence, D2 deformation and contemporaneous peak metamorphism is constrained to hence, the the maximum maximum age age of of D2 2680 Ma. Ma. Magmatic activity could could have contributed to metamorphic metamorphic heating. heating. Peak metamorphic thebelt belt (Petersen, (Petersen, 1984; Pan Pan and Fleet, metamorphictemperatures temperaturesofof600—700°C 600-700° ininthe Fleet, 1992) 1992) are are close close to temperature of 600°C closure closuretemperature temperature to the the 700°C 700° closure temperature of the the U-Pb U-Pb system system in monazite, and exceeded the 600° of titanite titanite (Heaman (Heaman and andParrish, Parrish,1991). 1991).Metamorphic Metamorphicmonazites monazitesfrom frommetavolcanic metavolcanic and and altered altered rocks rocks range range in in age Ma(Schandl (Schandietetal., al.,1991; 1991;Davis Davisetetal., al., 1994; 1994;Zaleski Zaleskietetal., a!., 1995), 1995),and and encompass encompass the circa age from from 2675—2669 2675-2669 Ma 2673 Ma Ma titanite ages 2). We ages from the Nama Nama Creek Creek pluton and and Black Black Pic Pic monzodiorite monzodiorite (Table (Table 2). We tentatively tentatively interpret the the titanite titaniteages agesasasthe thetime timeofofregional regionalcooling cooling through 00°C 600°(Fig. (Fig.31); 31);however, however, itit isispossible possible that that the crystallization or the metamorphic metamorphicfluids fluids that thatallowed allowed the the crystallization crystallizationof of monazite monazite were were also also responsible for crystallization resetting of titanite. titanite. Field Fieldobservations observations indicate indicate that thatpeak peakmetamorphism metamorphismand andmigmatization migmatizationin inthe theQuetico Quetico subprovince was synchronous with progressive deformation and and the map-scale folds (D3) (Da) near the the boundary boundary progressive deformation (Peterson and and Zaleski, Zaleski, 1994a). 1994a). Peak Peakmetamorphism metamorphismininthe theQuetico Queticosubprovince subprovincecould couldhave havebeen beencoeval coevalwith with granitic magmatism Ma(Percival, (Percival,1989). 1989).The The regional regional distribution distribution of of metamorphic ages and magmatism at at2670—2650 2670-2650 Ma assemblages is consistent with progressively progressively later development development of peak conditions, conditions, and andincreasing increasinggrade, grade,from from south Maamphibolite-facies amphibolite-faciesmetamorphism metamorphism in in the the Schreiber-Hemlo south to tonorth; north;from from2676—2678 2676-2678 Ma Schreiber-Hemlo greenstone belt (Corfu and Muir, 1989b), 1989b),to to 2680 2680 Ma Ma upper upper amphibolite-facies amphibolite-facies metamorphism metamorphism in in the the Manitouwadge Manitouwadge belt, belt, to to and Muir, 2670—2650 Magranulite-facies granulite-faciesmetamorphism metamorphismininthe the Quetico subprovince (Fig. 2). 2670-2650 Ma 2). A transitional of the Superior transitional boundary boundary between between volcano-plutonic volcano-plutonic and metasedimentary metasedimentary subprovinces subprovinces of Superior Province have been described Province is not unique unique to to the theManitouwadge Manitouwadge area. area. Similar relationships relationships have described between between the Coutchiching metasedimentary rocks in the the Rainy Rainy Lake Lake area areaof of the theWabigoon WabigoonsubsubQuetico subprovince and Coutchiching province et al., 1989), and Kehienbeck (1985)considered consideredthe theBeardmore-Geraldton Beardmore-Geraldtonbelt belt to to be be a strucprovince (Davis et Kehlenbeck (1985) tural tural and and lithological lithologicaltransition transitionzone zonebetween between the theQuetico Queticoand andWabigoon Wabigoonsubprovinces subprovinces(Fig. (Fig.1). 1).Kehienbeck's Kehlenbeck's Beardmore-Geraldton belt beltdeveloped developedthrough throughdeformation deformationinvolving involving the themargins marginsof ofboth both theBeardmore-Geraldton conclusion that the Wawa-Quetico boundary the Manitouwadge Manitouwadge area. area. subprovinces is equally applicable to the Wawa-Quetico boundary in the Wawa-Quetico subprovince west Studies along the Wawa-Quetico subprovinceboundary boundaryindicate indicatethat that itit varies varies in in character. character. To the west Manitouwadge, rocks although in in some some of Manitouwadge, rocks of of volcanic volcanic and and sedimentary sedimentary origin origin are are mostly mostly in in fault contact, although earlier structures can can be be correlated correlated across across the the boundary boundary (Percival, (Percival, 1989). 1989). To To the the east, east,between between the the areas, earlier I),sedimentary sedimentary and andvolcanic volcanicrocks rocks are are apparently apparently (Fig. 2) 2) and and the theLepage Lepage fault faultzone zone (Fig. (Fig.1), Moshkinabi belt belt (Fig. interbedded along the subprovince subprovince boundary variation along-strike along-strike suggests interbedded boundary (Berger, (Berger, 1985). 1985). The variation suggests that that the subprovince boundary Manitouwadge area preserves preserves features subprovince boundary in the Manitouwadge features of of early early ductile ductile deformation deformation that that may lateral transition transition between between the the conformable conformable contact to the east and and fault fault juxtaposition juxtaposition to tothe thewest. west. represent a lateral REFERENCES REFERENCES Arias, Z.G., and and Helmstaedt, Helmstaedt, H., H.,1990: 1990:Structural Structuralevolution evolutionof ofthe theMichipicoten Michipicoten(Wawa) (Wawa) greenstone greenstone belt, belt, an Archean Archean fold fold and andthrust thrustbelt. belt.Ontario Ontario GeologicalSurvey, Survey,Miscellaneous Miscellaneous Superior Province: evidence for an Geological Paper Paper150, 150,p.p.107—114. 107-114. Baker, J.H., J.H., Hellingwerf, Hellingwerf, R.H. 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Suffel, G.G., and Ridler, Ridler,R.H., R.H.,1971: 1971:Metamorphism Metamorphismof ofmassive massivesulfides sulfides at at Manitouwadge, Manitouwadge, G.G., Hutchinson, R.W., and Ontario, Canada. Canada.Society Society of of Mining Mining Geologists Geologists of Special Issue No. 3, p. p. 235—240. 235-240. of Japan, Special McLennan, S.M., S.M., 1985: 1985: The Continental Crust: Its Its Composition Composition and and Evolution. Evolution. Blackwell, Blackwell, Taylor, S.R., and McLennan, Oxford, 312 p. 1932: Geology Geology of Heron Bay-White Bay-White Lake Lake area. Ontario Department Department of of Mines, Mines, Annual Annual Thomson, J.E., 1932: of the Heron Report XLI(6), Report XLI(6),p.p.34—47. 34-47. Tilton,G.R., G.R.,and andSteiger, Steiger,R.H., R.H.,1969: 1969:Mineral Mineralages agesand andisotopic isotopic composition composition of of primary primary lead lead at atManitouwadge, Manitouwadge, Tilton, Ontario. 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Sweden.Geologie Geologie in in Mjinbouw, Mjinbouw, v. v. 67, 67, p. p. 397—409. 397-409. darhyttan Vallenta, Mount Isa. Economic Economic Vallenta, R., 1994: Syntectonic Syntectonic discordant discordant copper copper mineralization mineralizationinin the the Hilton Hilton mine, Mount Geology, v. v. 89, 89,p.p.1031—1052. 1031-1052. Geology, 47 �Manitouwadge greenstone belt References References and Franklin, Franklin, J.M., J.M.,1982: 1982:The TheAnderson AndersonLake Lakemine, mine,Snow SnowLake, Lake,Manitoba. Manitoba.Geological GeologicalAssociAssociWalford,P.C., and ation of of Canada, Canada,Special SpecialPaper Paper25, 25,p.p.481—523. 481-523. 1970: The geology geology and evolution of the Geco Geco massive massive sulphide deposit deposit at at ManiManiWatson, D.W., 1970: and structural evolution Ontario, Canada. Canada. Ph.D. Ph.D.thesis, thesis,University Universityof ofMichigan, Michigan,272 272 p. p. touwadge, northwestern Ontario, 1989: Geological studies in the the Wabigoon, Wabigoon, Quetico Quetico and and Abitibi-Wawa Abitibi-Wawasubprovinces, subprovinces,Superior Superior Williams, H.R., 1989: structural development development of Beardmore-Geraldton belt. Ontario Province of Ontario, with emphasis on the structural of the Beardmore-Geraldton Geological Survey, Open File Report Report 5724, 5724,188 188 p. p. 1990: Subprovince Williams, H.R., 1990: Subprovince accretion accretion tectonics tectonics in in the the south-central south-central Superior Province. Canadian Journal of of Earth EarthSciences, Sciences,v.v.27, 27,p.p.570—581. 570-581. Williams, H.R., H.R., 1991: 1991: Quetico Quetico subprovince. subprovince. in in Geology Geology of Ontario, OntarioGeological Geological Survey, Survey, Special Special Volume Williams, Ontario, Ontario 4(1), 4(1), p.p.383—403. 383-403. and Breaks, Breaks, F.W., F.W.,1989: 1989:Geological Geological studies in in the theManitouwadge-Hornpayne Manitouwadge-Hornpayne area. area. Ontario Ontario Williams, H.R., and Geological Geological Survey, Survey,Miscellaneous MiscellaneousPaper Paper146, 146,p.p.79—91. 79-91. and Breaks, Breaks, F.W., F.W., 1990a: 1990a:Geological Geological studies in the the Manitouwadge-Hornpayne Manitouwadge-Hornpayne area. Ontario Ontario Williams, H.R., and Geological Geological Survey, Survey, Miscellaneous MiscellaneousPaper Paper151, 151,p.p.41—47. 41-47. and Breaks, Breaks,F.W., F.W.,1990b: 1990b:Geology Geology of of the the Manitouwadge-Hornpayne Manitouwadge-Hornpaynearea. area. Ontario OntarioGeological Geological Williams, H.R., and Survey, Open File File Map Map142, 142,scale scale1:50000. 1:50000. Breaks, F.W., F.W., Schnieders, Schnieders,B.R., B.R., Smyk, Smyk, M.C., M.C., Charlton, Charlton,S.G., S.G.,and andLockwood, Lockwood,H.C., H.C.,1990: 1990:Field Field Williams, H.R., Breaks, the Manitouwadge Manitouwadge area. in in Franklin, Franklin, J.M., J.M., Schnieders, Schnieders, B.R., and Koopman, Koopman, E.R., E.R., eds., eds., Mineral Mineral DeDeguide to the in the the Western WesternSuperior SuperiorProvince, Province,Ontario: Ontario:8th 8thIAGOD IAGODSymposium, Symposium,Field FieldTrip TripGuidebook, Guidebook,Geological Geological posits in Survey of Canada, Canada, Open Open File File2164, 2164, p. p.7—25. 7-25. Stott,G.M., G.M.,Heather, Heather,K.B., K.B.,Muir, Muir,T.L., T.L.,and andSage, Sage,R.P., R.P.,1991: 1991:Wawa WawaSubprovince. Subprovince.Geology Geology Williams, H.R., Stott, of Ontario, Special Special Volume 4, Part 1, 1, p. p.485—539. 485-539. Breaks, F.W., F.W., and andMilne, Milne,V.G., V.G.,1992: 1992:Geology Geology of of the theManitouwadge-Hornpayne Manitouwadge-Hornpayneregion, region, DisDisWilliams, H.R., Breaks, tricts of of Thunder ThunderBay, Bay,Algoma Algoma and and Cochrane. Cochrane.Ontario OntarioGeological Geological Survey, Survey, unpublished report, report, 149 149 p. p. tricts Zaleski, E., 1989: 1989: Metamorphism, Metamorphism, structure and andpetrogenesis petrogenesisof ofthe theLinda Lindavolcanogenic volcanogenicmassive massivesuiphide sulphide Zaleski, Ph.D. thesis, thesis, Winnipeg, Winnipeg, Manitoba, Manitoba, Canada, Canada,University Universityof of Manitoba, Manitoba, deposit, Snow Lake, Manitoba, Canada. Ph.D. 344 p. p. 344 Zaleski, E., and and Peterson, Peterson, V.L., V.L., 1993a: 1993a: Lithotectonic Lithotectonic setting setting of of mineralization in the the Manitouwadge Manitouwadge greenstone greenstone Zaleski, belt, Ontario: Ontario: preliminary preliminary results. results. Current Current Research, Research, Part C, C,Geological Geological Survey 93-lC, p. p. belt, Survey of of Canada, Canada, Paper Paper 93-iC, 307—317. 307-317. and Peterson, Peterson, V.L., V.L.,1993b: 1993b:Geology Geology of of the the Manitouwadge Manitouwadge greenstone greenstone belt, belt, Ontario. Ontario.Geological Geological Zaleski, E., and Zaleski, Canada,Open OpenFile File2753, 2753,scale scale1:25000. 1:25000. Survey of Canada, and Peterson, Peterson, V.L., V.L., 1995: 1995:Geology Geology of of the the Manitouwadge Manitouwadgegreenstone greenstone belt belt overlain overlain on on shaded shaded relief relief Zaleski, E. and 1:25000. of total totalfield fieldmagnetics. magnetics.Geological GeologicalSurvey Surveyof ofCanada, Canada,Open OpenFile File3034, 3034,scale scale1:25000. of Peterson, V.L., V.L., and andvan vanBreemen, Breemen,0., O.,1994: 1994:Geological, Geological,geochemical, geochemical,and and age age constraints constraints on on base base Zaleski, E., Peterson, metal mineralization mineralization in in the theManitouwadge Manitouwadge greenstone greenstone belt, northwestern northwestern Ontario. Ontario. Current Current Research Research 1994-C, 1994C, metal Geological Geological Survey of Canada, Canada, p. p.225—235. 225-235. and Peterson, Peterson,V.L., V.L.,1995: 1995:Geology Geologyof of the theManitouwadge Manitouwadgegreenstone greenstonebelt beltoverlain overlain on shaded shaded relief relief Zaleski, E. and Zaleski, totalfield field magnetics. magnetics.Geological GeologicalSurvey Surveyof ofCanada, Canada,Open OpenFile File3034, 3034,scale scale1:25000. 1:25000. of total Zaleski, E., Peterson, V.L., V.L., and and van van Breemen, Breemen, 0., O.,1995: 1995:Geological Geological and age age relationships of the margins margins of the Zaleski, and the the Wawa-Quetico Wawa-Quetico subprovince boundary, Current Manitouwadge greenstone belt and boundary, northwestern northwestern Ontario. Current 1995-C, Geological Survey of Canada, p. 35—44. 35-44. Research 1995-C, Canada, p. 48 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide FIELD-TRIP STOPS STOPS Introduction The field trips in this this guidebook guidebook are are organized organized thematically thematicallyand and geographically, geographically,to to represent represent the thegeology geology of of the the outcrop outcrop observations observations critical critical to to our our structural, structural, stratigraphic the Manitouwadge area, and give examples of stratigraphic interpretations. The and petrological petrological interpretations. The guidebook guidebook is partly intended intended for the field field trip to to the theManitouwadge Manitouwadge greenstone belt belt sponsored by the Forty-first of the the Institute on greenstone Forty-first Annual Meeting Meeting of on Lake Lake Superior Superior Geology Geology and, tours that can by anyone anyone interested. interested. A A short in the longer term, term, as as aa series series of of self-guided self-guided tours can be be easily easily followed followed by For more detail and introductory section summarizes of each each area. For introductory summarizes the geology geology and significance significance of and regional regional synthesis, the the reader reader is referred referred to the interim report that synthesis, that comprises comprises the the first first part part of of this thisvolume. volume. A. Known economic deposits, iinner n n e r volcanic belt All of the known economic massive sulphide deposits of the Manitouwadge greenstone belt, comprising known massive sulphide deposits of comprising Nama Creek Creek and and Willecho Willechodeposits, deposits,lie lieininthe the inner inner volcanic volcanicbelt belt of ofthe the southern southern limb limb of of the Geco, Geco, Willroy, Nama synform (1:25000 (1:25000map). map). The The Geco Geco mine, mine, scheduled scheduledto to close close in in late late 1995, is is the only the D3 Da Manitouwadge Manitouwadge synform currently currently producing deposit. In In the thecase caseofofmined-out mined-outorebodies, orebodies, some some spatial spatialrelationships relationships can can be beinferred inferred from the positions of open open stopes stopes and pits with formation from positions of with respect respect to to the thehosting hosting metavolcanic metavolcanic rocks, rocks, iron formation and metamorphosed inthe the area area metamorphosed alteration alterationzones zonesalongalong-and andacross-strike. across-strike.Detailed Detailed1:5000 1:5000mapping mapping(1991—92) (1991-92) in of known deposits was was critical critical to our of known deposits our definition definition of lithological lithological units, and interpretation interpretation of ofpre-D3 pre-Da deformadeformarelationships. To the north, supracrustal tion and probable probable depositional relationships. supracrustal rocks rocks are are bounded bounded by by aa synvolcanic synvolcanic trondhjemite which metavolcanic rocks. rocks. The trondtrondhjemite which also also engulfs engulfs screens screens of mafic and interlayered interlayered mafic-felsic mafic-felsic metavolcanic trondinterpreted as hjemite is mantled by by orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss, interpreted as the the metamorphosed metamorphosed equivalent equivalent of a synvolcanic hydrothermal hydrothermal alteration zone, of zone, developed developed in a protolith protolith of of intercalated intercalatedmafic-felsic mafic-felsic rocks. To TO rocks and and mineralized mineralized iron iron formation formation the south of of orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss, gneiss, felsic felsic metavolcanic rocks sillimanite-muscovite-quartz schist representing metamorphosed synvolcanically synvolcanically altered are interlayered with sillimanite-muscovite-quartz felsic rocks. rocks. The volcanic sequence sequence isis repeated repeated in in the outer volcanic volcanic belt by the the D2 Da 'Manitouwadge 'Manitouwadge syncline', D3Manitouwadge Manitouwadge the axial axial trace trace of of which lies in the metasedimentary rocks rocks central central to to the thesouthern southernlimb limbof ofthe theD3 synform (Fig. 5). Stratigraphic Stratigraphicyounging youngingininthe theWillroy-Geco Willroy-Gecoarea areaisissoutherly, southerly, based based on ongenerally generallysouthward southward increase increase in Pb/Zn and andZn/Cu Zn/Cuofoforebodies, orebodies,and andononthe theposition positionofoforthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gniess gniess (footwall-type alteration) alteration) and synvolcanic trondhjemite trondhjemite to to the north. (footwall-type the The area area of of the the inner inner hinge hingeregion region and and southern southernlimb limbof of the theManitouwadge Manitouwadge synform synform (D3) preserves preserves the best map.. of the the pre-D3 pre-D3 structural structural history (see (see Structural Structuralcomplications—Dl/D2 complications-Dl/D2 map- and outcrop-scale outcrop-scale evidence of folds and faults). The Thenear-continuous near-continuous layers layers of of iron iron formation formation are are excellent excellent marker marker units, units, useful useful in in linking linking correlative our structural structural interpretation, interpretation, aa D1 Dl correlative stratigraphic horizons and outlining outlining structural structural features. features. In our ductile fault divides the area area into into upper (southern) (southern)and andlower lower (northern) (northern) tectonic tectonic blocks blocks and and isis responsible responsible for the repetition repetition of of mineralized mineralized horizons. horizons. Between Between the the Nama NamaCreek Creek and andWillecho Willecho deposits, deposits, the theD1 Dl fault faultsurface surface by a map-scale D2 sheath fold (Fig. 4). is deformed deformed by area has has many many hazards associated with previous mining operations. operations. Permission The Geco-Willecho Geco-Willecho area associated with previous mining Permission for access, via aa locked locked gate gate across across the the Willroy Willroymine mineroad, road,must must be be arranged arranged in in advance advance with with Noranda Noranda Inc. Inc. Many access, via stops in this this area area were were previously previously described in the the guidebook guidebook for the International International Association Associationon on the theGenesis Genesis of Ore Deposits (Williamsetet al., al., 1990), and IAGOD stop numbers numbers are are given given here here to facilitate of Deposits (IAGOD) (IAGOD) (Williams 1990), and IAGOD stop comparison with with our our descriptions descriptions and and reinterpretations. reinterpretations. Our station numbers comparison numbers with prefix prefix 'ZB' are are also also given for each stop as aa cross-reference to sample and analytical data cross-reference to data in in preparation preparation for for open open file file release. release. A1-A8. Al—A8. Willroy-Geco Wiliroy-Geco area The following field-trip stops stops (1:25000 map) generally generallyproceed proceedfrom fromyounger youngertoto older older (and (and deeper following field-trip (1:25000 map) deeper in the section) section) rocks, rocks, from from the the metagreywackes metagreywackes central to the the D2 D2'Manitouwadge 'Manitouwadge syncline', syncline', to to iron iron formation formation interlayered with felsic felsic volcanic rocks, to to sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist and and orthoamphibole-cordieriteorthoamphibole-cordieritegarnet gneiss, gneiss, to to subvolcanic trondhjemite. The Thegeneral generalsequence sequence was interpreted as a stratigraphic stratigraphicsuccession succession by Snifel a!. (1971), based on comparison Suffel et al. comparison with with successions successions typical of other greenstonc greenstone belts. belts. Suffel Suffeletetal. al.were were also the first first to to interpret interpretthe theManitouwadge Manitouwadgedeposits depositsasasvolcanogenic volcanogenicmassive massive sulphides, sulphides, and and orthoamphiboleorthoamphibolebearing rocks as metamorphosed footwall footwall alteration. Stop metagreywacke, Z1391-10, ZB93-410, A l Manitouwadge , Manitouwadge metagreywacke, ZB91-10, ZB93-410,ZB94-87. ZB94-87. Starting Startingatatthe thelocked locked gate gateon on S t o p Al, the Wiliroy mine road, road, drive drive north north about 300 metres metres up up the short hill, turning west track Willroy mine west (left) on the gravel track near the hill hill top. About About200 200metres metresmore morebrings brings you you to to aaparking parking area areaon onthe theeast eastside sideof ofaasmall smalldam damacross across valley. Cross Cross the the foot foot bridge bridge and and rock rock dam dam to an outcrop on the west the Slim Lake valley. west side. The The dam dam contains contains tailings from the Willroy Willroy deposits that that were were dumped dumped into intoSlim SlimLake Lake (now (now mostly mostly aa meadow) meadow) from from 1950's 1950's to to 1970's. is periodically periodicallypumped pumped into into the the ponded ponded water water to to neutralize neutralize acidity acidity and and precipitate precipitate metals. metals. The 1970's. Lime is north-south lineament of the the Slim Lake Lake fault, fault, a high-angle north-south lineament is the topographic topographic expression expression of high-angle brittle fault with with minor dextral offset. offset. 49 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide Manitouwadge guide The Manitouwadge rocks comprise comprise biotitekgarnetksillimanite biotite±garnet±sillimanite schist schist and and biotiteManitouwadge metasedimentary metasedimentary rocks biotitehornblende schist, mostly mostly homogeneous, homogeneous,but but also also with with layering layeringand and grading grading defined definedby by the the abundance of hornblende schist, abundance of mafic minerals. Metagreywackes rnm—2 Metagreywackes in in this thisexposure exposureare arethinly thinly(2(2 mm-2 cm) cm)totothickly thickly(10 (10cm—2 cm-2 m) m)layered layered (transposed bedding) and and contain contain plagioclaseplagioclase- and quartz-crystal quartz-crystal clasts, clasts, evidence evidence of of aa tuffaceous tuffaceous component. Some layers have possible lithic fragments (1—10 cmlong) long)with withdiffuse diffusemargins. margins.The The layering, layering, and and the sub(1-10 cm parallel parallel foliation foliation(1)2), (D2), are near-vertical and straight, straight, and and aastrong strongmineral minerallineation lineationplunges plungeseasterly. easterly. Locally Locally developed intrafolial folds, some eye-shaped, eye-shaped, probably probably originated as soft-sediment folds that were were subsequently subsequently transposed during further tectonic tectonic deformation. deformation. detrital zircon Based on U-Pb provenance study of detrital zircon from this site site (Fig. (Fig. 12), 12),the the maximum maximumage ageof of deposition deposition is 2693 Ma, Ma, at at least 25 Ma younger than felsic volcanism volcanism (circa (circa 2720 2720Ma) Ma)ininboth both the the inner inner and outer volcanic belts. The in D2 D3 folds folds indicates indicatesthat that sedimentation sedimentation predated pre-dated D2 D2 and and that Theinvolvement involvement of of metagreywacke metagreywacke in the contact contact isis either either an anunconformity unconformity or or aaprepre-totosyn-D2 syn-D2fault. fault.Field Fieldobservations observationsare areequivocal equivocalregarding regarding the relationship relationship of of D1 Dl deformation deformation and and sedimentation; sedimentation; however, however, uplift uplift resulting resulting from from D1 Dl deformation deformation may may have contributed sediment sources. We We interpret interpret the theManitouwadge Manitouwadgemetagreywackes metagreywackes as a tectonic tectonic outlier outlier of of Quetico Quetico rocks. rocks. Foliated tonalite width) intrude intrude metagreywacke at a low tonalite dykes dykes (25 (25cm—2 cm-2 mmininwidth) low oblique angles to layering, layering, and some show stretching and boudinage related to to layer-parallel layer-parallel shear. One One of of these these dykes dykes was was collected collected for geochronologytoto constrain constrain to to the minimum age of of sedimentation sedimentation (analysis (analysis in in progress). progress). A geochronology A nearly nearly massive massive but has concordant aplitic apophyses; the pegmatite muscovite-pegmatite cross-cuts foliation but pegmatite shows shows thickening in the hinge hinge region region of a minor minor fold. fold. Stop A2, Iron formation, ZB91-l1, ZB92-P18, IAGOD S t o p A2, I r o n formation, ZB91-11,ZB92-P18, IAGOD#2. #2.Return Returntotothe theWillroy Willroymine mineroad roadand andcontinue continue 200 metres metres north, north, turning west track. Continue tower and and a 200 west at another another gravel gravel track. Continue about 1.5 1.5 km km to to aa microwave microwave tower large outcrop outcrop area on on the hill top. The large The space space for parking and turning around is small, soft and sandy. From the rocky crest, looking to the east, east, the the Geco Geco headframe headframe and the the open open cuts cuts of of Willroy Willroy deposits deposits are visible, visible, situated in sillimanite-muscovite-quartz in aanarrow narrowinterval intervalofofiron ironformation, formation,quartz-phyric quartz-phyricfelsic felsicrocks rocksand andsillimanite-muscovite-quartz schist. The The outcrop outcrop on on which which you stand is is part part of of the the thick thick southernmost southernmost quartz-magnetite quartz-magnetite iron iron formation, with zincian zincian iron iron formation formation at at the Geco apparently unmineralized in the Willroy area, and possibly correlative with mine. mine. The iron cm)with withalternating alternating white white to to smoky smoky quartzose quartzose layers layers and and dark iron formation formation isis layered layered (1 (1 mm—10 mm-10 cm) layers rich in magnetite and and Fe-silicates. Fe-silicates. The Thelayering layeringis is tightly tightly folded folded (D2 (D2or or combined combined D2/transposed Da/transposed D1?) Dl?) about easterly-plunging axes, and and fold fold asymmetry asymmetry varies varies across acrossthe theoutcrop outcrop area. area. The mineral easterly-plunging axes, mineral lineation lineation is parallel to fold axes and, locally, grunerite defines defines an an axial axial planar planar foliation. foliation. The southernmost iron formation has been thickened thickened by by folding, folding, and and we we interpret interpret these theseoutcrop-scale outcrop-scalefolds foldsas asrelated relatedtotomap-scale map-scale1)2 D2folds foldsof of formation/felsic contact to the the west west (Stop (Stop A23, A23, Fig. A3). the iron formation/felsic The metamorphic metamorphic assemblage assemblage in dark layers layers consists of magnetite, grunerite with with epitaxial epitaxial overgrowtbs overgrowths of green amphibole clinopyroxene(ferrosalite), (ferrosalite),and and minor minor pyrrhotite and (ferroactinolite-ferrohornblende), clinopyroxene and amphibole (ferroactinolite—ferrohornblende), garnet (Alm/Sps/Grs/Pyp (Alm/Sps/Grs/Pyp = = 58/22/17/2). geochemical analyses 3 samples containing variable garnet 58/22/1712). Whole-rock Whole-rock geochemical analyses of 3of samples containing variable proportions of material, have Si02 from 68.2—90.7%, from 5.6—26.0%, proportions ofquartzose quartzoseand anddark dark material, have Si02 from 68.2-90.7%,FeO FeO from 5.6-26.0%,MnO MnOfrom from0.3— 0.3andTiOz<0.02%, Ti02<0.02%, Al2O3<0.53%, Al203<0.53%, Na20<0.08% Na2O<0.08%and and K20<0.08%, suggesting 1.3%, CaO from 0.70—2.25%, 0.70-2.25%, and suggesting negligibledetrital detrital or or volcanic volcanic component. component. The The base base metal metal content very low; low; CCu<8 ppm, Pb<9 ppm negligible content is also very u e 8 pprn, ppm and Zn<28 ppm. m in in width) including granodiorite with mafic The iron iron formation formation isis cut cutby byfoliated foliateddykes dykes(30 (30cm—i cm-1.5.5m mafic tonalite-granodiorite. The dykes subparallel to to the axial traces clots and plagioclase-porphyritic tonalite-granodiorite. dykes are generally subparallel of D2 folds with with very very long long limbs limbs (+lo (+10 m). In Da folds but, locally locally show asymmetric folds Infold foldhinges, hinges, the thefoliation foliation margins and and axial axial planar planar to folds. belongto to aa suite suite of of in the dykes dykes is discordant discordant to dyke margins folds. The The dykes dykes likely likely belong tonalite tonalite dykes, dykes, some some of of which which show show structural structural relationships relationships suggesting suggesting syn-D2 syn-Dz emplacement. emplacement. AAdiscordant discordant pegmatite cuts both iron iron formation formation and and dykes. dykes. Stop rocks and and iron formation nnear S t o p A3, Quartz-phyric Quartz-phyric felsic rocks e a r the t h e Wiliroy Willroy 2, 3, 4 aand n d 5 orebodies, ZB91-12—14,ZB92-P139, ZB92-P139,ZB92-P152-P153. ZBO2-P152—P153. Return Willroy mineroad roadand andproceed proceedabout about 800 metres ZB91-12-14, Return to to thetheWillroy mine north to decrepit core core racks, racks,all allthat that remains remains of ofWillroy WillroyMines Mines#1 #1and and#2 #2 to aa large large gravelled gravelled area with some decrepit shafts and millsite millsite (Fig. (Fig. Al). Al).On Onthe thesouth southside sideofofthe thegravelled gravelledclearing, clearing,aachain-link chain-linkfence fencerestricts restrictsaccess access to the map, Fig. Fig.Al). Al). The the open open stope stope of of the the Willroy Willroy 33 orebody orebody (1:25000 (1:25000 map, The road road continues continues to the the northwest northwest side of the clearing, clearing, and down down aa hill hill toward toward an an abandoned abandoned railway railway linking linking the Willroy Willroy and and Geco Geco properties. properties. On the hill-top plateau to to the theeast eastofofthe theroad, road,another anotherchain-link chain-linkfence fence restricts restricts access access to dangerous dangerous ground immediately above above the the Willroy Willroy 4, 4, 22 and and 5 orebodies. orebodies. Within 50 metres metres on both sides sides of the road, road, there there are are several pavement outcrops of of quartz-phyric quartz-phyric felsic felsicbreccias brecciasand andthin thin interleaved interleavediron ironformation formation(mostly (mostlytoo too thin thin to show on the 1:25000 1:25000 map). The more rocks in in which which both both matrix and fragments more southerly outcrops outcrops consist consist of of felsic fragmental rocks fragments (<1 (<1 cm—10 cm)have havequartz quartzphenocrysts. phenocrysts.The Thevariation variationininclast clastlithology lithologyisisnot notdramatic dramatic and and might might be be attributed cm-10 cm) 50 �A. Known Known deposits, inner inner volcanic volcanic belt Manitouwadge field guide ..,,... I 0 I 400 metres FIG. Al. FIG. Geology and field-trip Geology field-trip stops stopsof of the theSlim SlimLake Lakesection section(A9— (A9- A20), and andWiliroy WillroyStops StopsA3—A5. A3-A5. Structure Structure symbols symbols show show dominant dominant D2 Dz foliations foliations and lineations, lineations, and and asterisks are the locations asterisks are locations of the the Willroy 2 to 55 orebodies. orebodies. In this this Wiliroy and and the thefollowing following figures, the the figure figure locations are shown on the the accomaccompanying map and lithopanying 1:25000 1:25000 map lithological units are shown logical units shown by bold bold numbers numbers that match match the the map mapleglegend. Circled Circledalpha-numerics alpha-numerics refer refer to field-trip stops. Dotted Dotted lines lines are are topographic contours at at 10 topographic contours 10 metre metre intervals. variable alteration alteration of of crystalline crystalline and and glassy glassy materials materials in in aavolcaniclastic volcaniclastic deposit; deposit; but but some somebiotite-rich biotite-rich to variable streaks could represent represent more mafic clasts. Microcline Microcline and muscovite muscovite are both heterogeneously heterogeneously distributed, even thin section, section, suggesting suggesting that that the theK20 K 2 0abundance abundancewas wasdetermined determinedby byalkali alkaliexchange exchange even on on the scale of a thin rather than than primary primary magmatic magmaticcomposition. composition. Magnetite Magnetite porphyroblasts porphyroblasts are are ubiquitous ubiquitous and and garnet garnet isis present present locally. These breccias are part of locally. of the thesouthernmost southernmostlens lensofofquartz-phyric quartz-phyric metavolcanic metavolcanic rocks rocks in in the theWiliroy Willroy area. In scattered outcrops outcrops on the the north northside sideofofthe theplateau, plateau,semi-continuous semi-continuous and and discontinuous discontinuous thin iron iron the felsic felsic breccia are difficult difficult to Dl ductile fault is interpreted formations intercalated with the to trace laterally. A D1 rocks (not (not exposed). exposed). The to pass through through this this area, area,following following the northern northern contact contact of of quartz-phyric quartz-phyric felsic felsic rocks south are aremoderately moderatelymuscovitic muscoviticand andcontain containquartz quartzeyes eyesand andquartz quartzpods podsupuptoto 5-10 cm cm felsic rocks rocks to the south 5—10 long. In the ditch west outcrop of of iron iron formation formationininthe thefirst firstbushes bushesatat the the top top of of long. west of the road, a small small (2 m2) outcrop shows two two types types of of iron iron formation; formation; firstly, firstly, aa breccia breccia of of quartzose quartzosefragments fragmentsinin aa dark dark the north-facing slope shows matrix and, and, secondly, secondly, homogeneous homogeneoussilicate silicateiron ironformation. formation. The The iron iron formation formation lies lieson on the the north side of the on or or near near the thesame samehorizon horizonas asthe theZn-Pb-rich Zn-Pb-richWillroy Willroy44orebody orebody (Fig. (Fig.21, 21,Table Table3). 3).Two Twogeochemical geochemical fault, on samples from from the the outcrop showed showed elevated elevatedZn Zn(32 (32and and68 68ppm), ppm),and andlow lowCu Cu(4(4and and13 13ppm) ppm)and and Pb Pb (7 (7 and 11 11 ppm) abundances. Between the the road road and the Between the chain-link chain-link fence to the east, east, sulphidic sulphidic iron iron formation formation crops crops out out along-strike along-strike 215 orebodies. orebodies. This Thisisisone oneof of the thefew few exposures exposures of a transition from from quartz-magnetite quartz-magnetite iron iron from the Willroy 2/5 to sulphidic sulphidic iron iron formation formation associated associated with withan anorebody. orebody.Two Twogeochemical geochemical samples, samples, separated separated by by55 formation to 51 �Manitouwadge Manitouwadgefield field guide guide A. A. Known Known deposits, deposits, inner innervolcanic volcanicbelt belt metres levels of ofbase basemetals. metals. The more distant (western) metres of of strike-length, strike-length, show show elevated levels (western) sample sample has Cu=18 Cu=18 ppm, ppm, Pb=14 Pb=14 ppm pprnand andZn=431 Zn=431ppm; ppm;whereas whereasthe thenearer nearer(eastern), (eastern),more moresulphidic sulphidic sample sample has has Cu=132 Cu=132 ppm, ppm, Pb=88 Pb=88 ppm pprnand andZn=474 Zn=474 ppm. ppm. Along the the hilltop hill topback backtoward towardthe theWillroy Willroyroad, road,aasmall smallbranch branch road road leads leadsdown down hill to to the the northwest northwest (Fig. (Fig. Along Al). metres down down the the road road along along the the ditch on the north side, Al).About About20—30 20-30 metres side, aa biotitic biotitic variety variety of of silhmanitesillimanitemuscovite-quartz schist between the projected projected horizons horizons of the Willroy Willroy 44 and and 2/5 215orebodies. orebodies. In In muscovite-quartz schist crops out between the the schist, schist, numerous numerous sillimanite sillimaniteknots knotsare areassociated associatedwith withplagioclase, plagioclase,garnet, garnet,and andminor minorsulphide sulphideminerals. minerals. Monocrystalline and and polycrystalline polycrystalline quartz quartz eyes, eyes, observed observed in thin thin section, section, resemble resemble relict relict quartz quartz phenocrysts phenocrysts Monocrystalline and and suggest suggest that thatquartz-phyric quartz-phyric rocks rocks were were the protolith protolith to topremetamorphic premetamorphic alteration. alteration. S t o pA4, A4,Wiliroy Willroy millsite calc-silicate rocks, ZB91-171-175,ZB92-P318, ZB92-P318,P123, P123, IAGOD IAGOD #3. AAgroup group Stop milisite caic-silicate rocks, ZB91-17l—l75, of of stripped stripped glacially-polished glacially-polished outcrops, on the the north-facing north-facing slope slope leading leading down down from from the the plateau plateauofofStop StopA3, A3, can be be accessed accessed either either by by walking walking down down the brow brow of of the the hill hillor ordriving drivingdown down and andwalking walkingback back up up(Fig. (Fig. can Al). Al).These Theseenigmatic enigmaticexposures exposuresofofcalc-silicate calc-silicaterocks rocksalways alwaysgenerate generate much much discussion, discussion, although although they they are are not 1:25000map. map. InIngeneral generalininthe theManitouwadge Manitouwadgebelt, belt,caic-silicate calc-silicateminerals minerals are are not aaseparable separable unit uniton onour our1:25000 sporadically sporadically distributed distributedthroughout throughoutfelsic felsicto tointermediate intermediaterocks, rocks,and andparticularly particularlyconcentrated concentratedinincalc-silicatecalc-silicaterich rich zones zones adjacent to contacts contacts with with iron iron formation. formation. The TheWillroy Willroy millsite millsite outcrops are atpyical atpyical in structure structure (for (for example, example, fracture-control on caic-silicate calc-silicate distribution) and and in in their their evidently evidentlycomplex complex multistage multistage history, history, unusual unusual features features that thatmake makethem themdifficult difficultto toplace place in inaaregional regionalcontext. context. TheWillroy Willroymilisite millsite calc-silicate calc-silicate rocks lie in the stratigraphic stratigraphic footwall footwall of the Willroy Willroy 2/5 215orebodies, orebodies, and and The grade grade laterally laterallytotoquartz-phyric quartz-phyricfelsic felsicrocks rocks(the (thenorthernmost northernmostlens lenson onthe theWillroy Willroyproperty) property)which whichwe weconsider consider to tobe bethe theprotolith protolithtotometamorphism metamorphismand andcalc-silicate calc-silicatealteration. alteration.The Theabundance abundanceofofclinopyroxene, clinopyroxene,garnet, garnet,CaCaamphibole,plagioclase, plagioclase, epidote, epidote, calcite calcite and and titanite, titanite,asaswell wellasasquartz quartzand andmicrocline, microcline,isisvariable. variable.Locally, Locally,for for amphibole, example example in in exposures exposures high high on onthe theslope, slope,dark darkcalc-silicate calc-silicateminerals mineralsoccupy occupyaadeformed deformedconjugate-fracture conjugate-fracture8et set in which which flattened flatteneddiamond-shapes diamond-shapes(looking (lookingdown-plunge) down-plunge)outline outlinemore moreleucocratic leucocraticfelsic felsicdomains domainscomprising comprising in quartz, quartz, microcline, microcline, plagioclase plagioclase and minor minor hornblende, hornblende, biotite, garnet garnet and and epidote. epidote. Fractures Fractures oriented oriented at at high high angle angle to to foliation foliation are arefolded folded (shortened), (shortened), whereas whereas those those atatlow lowangle angletotofoliation foliation are are straight straightand andlook look extended. Pervasive Pervasivecalc-silicate calc-silicatezones zones (coarse (coarsegrained, grained, green green with with epidote, epidote,clinopyroxene clinopyroxene and and Ca-amphibole), Ca-amphibole), extended. of metrewidth, width,are aresubparallel subparallel to to local local foliation foliationtrends trends and cross the the fracture-controlled alteration. of 0.25—1 0.25-1 metre alteration.The The pervasive pervasive zones zones have have the the appearance appearanceofofbreccia brecciaand, and,locally, locally,some some'fragments' 'fragments'preserve preservelayering layering or orfracturefracturecontrolled calc-silicate alteration. cases, early at the thecontact contacttoto controlled alteration. In some cases, early structures structures look look rotated rotated or truncated at the thepervasive pervasivecalc-silicate calc-silicatematrix. matrix. Thisgroup groupofofoutcrops, outcrops,and anda asuite suiteofofcalc-silicate calc-silicaterocks rocksfrom fromthe theGeco Gecomine mine(Sufi'el (SuffelCollection), Collection), were were This (1992),who whoconcluded concluded that thatdispersed dispersedCa Cawas wasremobilized remobilized and and concentrated concentrated during during studied by by Pan Panand andFleet Fleet(1992), studied metamorphism. High High Cl Clinincalcic calcicamphibole amphibole from from the theGeco Gecomine minecould could indicate indicate aa memory memoryofofprevious previous metamorphism. synvolcanic enrichment during sea-floor sea-floor alteration (ibid.). In Inour ourview, view,the thelocalization localizationofofcalc-silicate calc-silicatezones zones synvolcanic near iron iron formation formation contacts contacts could could be be attributed attributedtotoeither eitherprimary primaryororsecondary secondaryprocesses. processes. One Onepossibility possibility near thatcaic-silicate calc-silicatezones zones formed formed during during metamorphic metamorphic redistribution redistribution of of Ca Ca during during decarbonation decarbonation reactions reactions of of isis that carbonate-facies iron formation. However, However, arguing arguing against against this this isisthe thelack lackofofevidence evidencefor forcarbonate-facies carbonate-facies carbonate-facies precursors for for metamorphosed metamorphosed iron iron formation formationatatManitouwadge, Manitouwadge,and and the thepaucity paucityof ofcarbonate carbonateminerals mineralsininthe the precursers calc-silicaterocks. rocks. Alternatively, Alternatively,ininaamodel-driven model-drivensyngenetic syngeneticscenario, scenario,the thedistribution distributionofofcaic-silicate calc-silicaterocks rocks caic-silicate could reflect reflect synvolcanic synvolcanic hydrothermal hydrothermal alteration alteration in inwhich which iron iron formation formationacted acted as asaacap caprock. rock. could From the theeastern easternbase baseof of the themain mainoutcrop, outcrop,walk walk east east along along the the road road to toanother anotheroutcrop outcropabout about1010metres metres From into intothe thewoods woods on on the thesouth southside. side.Here, Here,the therock rockisisdominated dominatedby by coarse coarse grained grained garnet garnet and andhornblende, hornblende, and and moretypical typicalof ofcaic-silicate calc-silicatezones zones in general. There There isislittle littleevidence evidence of of a felsic precursor short distance distance more precurser until, a short tothe theeast east(just (justbefore beforea agravel gravelroad roadbranching branchingtotothe the south), a pavement (ZB92-P123) quartz-phyricfelsic felsic to south), a pavement (ZB92-P 123) ofofquartz-phyric rocks,typical typical of ofthose thosealong-strike along-strikeofofthe theWiliroy Willroymilisite millsitecaic-silicate calc-silicaterocks. rocks. rocks, S t o pA5, A5,Wiliroy Willroy railway u t , ZB91-15, IAGOD (continued).Looking Lookingnorth northfrom fromthe theWillroy WillroymillmillStop railway cut,c ZB91-15, IAGOD #3#3 (continued). site,the therock rockwall wallofofthe theWiliroy-Geco Willroy-Gecorailway railway cut cut 150 150metres metres away away isissubparallel subparallel to tothe thedominant dominantfoliafoliasite, orthoamphibole-cordierite-garnet gneiss, gneiss,and andthe theeasterly-plunging easterly-plunginglineation lineationisisobvious obvious tionofofthe theexposed exposedorthoamphibole-cordierite-garnet tion andspectacular spectacular(Fig. (Fig.Al). Al).Orthoamphibole-cordierite-garnet Orthoamphibole-cordierite-garnet gneiss gneiss (Unit (Unit 2) 2) isisinterpreted interpreted totobe bemetamormetamorand phosed alteration in the deposits. The phosed synvolcanic synvolcanic alteration the stratigraphic stratigraphicfootwall footwall to to known known economic economic deposits. The unit unitisis concontinuous around around the theinner innerManitouwadge Manitouwadge synform synform from from ltabbitskin Rabbitskin Lake Lake in in the the north, north,totothe theFalconbridge Falconbridge tinuous zone of of subeconomic subeconomic mineralization distance of of about about 30 30 km km (1:25000 (1:25000 map). (Don't spend spend too too zone mineralization to to the east, aa distance map). (Don't long at at this thisoutcrop; outcrop;it's it'snice, nice,but butthere thereare aremuch muchbetter betterexposures exposuresofofaltered alteredrocks rocksatatStops StopsA6 A6and andA7.) A7.) long Theinterlayered interlayered (metre-scale) (metre-scale) orthoamphibole-garnet-cordierite±biotite±plagioclase±staurolite orthoamphibole-garnet-cordierite&biotite~plagioclase&stauroliteand and garnetgarnetThe biotite-sillimanitedxordieriteassemblages assemblages are typical of Orthoamphibole is is present present both both as asaligned aligned biotite-sjllimanite±cordierite of the unit. Orthoamphibole prismsand andlarge large(4—5 (4-5 cm) radiating radiating sprays, sprays,variation variationpossibly possiblyresulting resultingfrom fromheterogeneous heterogeneousdeformation deformationoror prisms post-kinematic post-kinematic recrystallization. recrystallization. Biotite, Biotite, atatleast leastininpart, part,is isfound foundininpseudomorphs pseudomorphsafter afterorthoamphibole, orthoamphibole, suggestingretrograde retrogradepotassic potassicmetasomatism. metasomatism.Quartz Quartzpods podslocally locallycontain contain very verycoarse coarse(10 (10cm cmplus) plus)crystals crystals suggesting 52 �Manitouwadge Manitouwadgefield field guide guide A. A. Known Known deposits, deposits, inner innervolcanic volcanic belt belt I 1 50 metres 0 -- streaky felsic layers Grt-Qtz knots, Bt-St \ e \ I ' - - ---- ,. ,' - - - , 2-X ' f pagmolltc ' Isoclinal rootless folds ; t / I ' \ 1 I I I ' I ' Cpy-Py-Mog ,stringers In I -----' Sll knots FIG. A2. A2. Detailed Detailedgeology geology of of the the Wiliroy Willroy 11 Cu stringer orebody (Table 3) and host host rocks. rocks. Structure Structure FIG. symbols show show dominant dominant D2 D2 foliations foliations and and lineations, lineations, except except for for post-D2 post-D2 kinks kinks (labelled). (labelled). Mineral Mineral symbols abbreviations are areafter afterKretz Kretz(1983). (1983).Dotted Dottedlines linesshow showoutcrop outcropareas. areas. abbreviations of of blue blue cordierite. cordierite. S t o pA6, A6,Wiliroy Willroy 1 alteration section, ZB91-146-147, 164-170, ZB92-P1--P7, ZB92-PI-P7, IAGOD From the the Stop 1 alteration section, ZB91-146--147, 164—170, IAGOD#4. #4. From Willroy milisite, millsite, take take an anovergrown overgrown gravel gravel road east east for for about about1.25 1.25km kmtotothe thechain-link chain-linkfence fenceon on the thenorth north Wiliroy side of of the theroad. road. From Fromthe thewestern westernend endofofthe thefence, fence,the theopen openstope stopeofofthe theWiliroy Willroy11stringer stringerCu Cuorebody orebodyisis side visible (Fig. (Fig. A2). A2). The Therocky rocky knolls knolls to to the the north northand andininthe thefenced fencedarea areaare aremostly mostlypegmatite. pegmatite.The Thefollowing following visible outcrop descriptions descriptions are are from from south south to tonorth, north,from fromstratigraphic stratigraphichanging hangingwall walltotofootwall footwallofofthe theWillroy Willroy11 outcrop orebody. orebody. Walk about about 50 50 metres metres southeast southeast along along aa gravel gravel track rock knoll knoll south The white white Walk track to to a rock south of of the the track. track. The asweathering felsic felsic schist, with with muscovite-rich muscovite-rich partings and shears, shears, is is aa highly highly strained strainedmetavolcanic metavolcanic rock rock asweathering sociated sociated with withthe theinterpreted interpretedD1 Dlfault faultthat thatpasses passesthrough throughthe theWillroy-Geco Willroy-Gecoarea. area. Relict Relictquartz quartzphenocrysts phenocrysts are are visible visible in in thin thin section, section, as aswell well as asabundant abundantmicrocline microcline and and minor minor biotite, biotite, garnet garnet and and epidote. epidote. Foliated Foliated tonalite dykes dykes that thatcut cutthe thefelsic felsicschist schistcould couldbelong belongtotothe thesyn-D2 syn-D2suite. suite.AAmassive massiveaplite-pegmatite aplite-pegmatitedyke dyke tonalite intrudes intrudesalong alongthe theaxial axialsurface surfaceofofa ahigh-angle high-anglekink kinkofofschistosity schistosityand andhas hasan anasymmetrical asymmetricaltail tailthat thatextends extends along alongaafoliation-parallel foliation-parallel shear. shear.The Thetiming timingrelationships relationshipsare areambiguous; ambiguous;either eitheraapre-existing preexistingshear shearinfluenced influenced the theintrusion intrusiongeometry, geometry,ororthe thedyke dykewas wasdeformed deformedduring duringlocal localreactivation reactivationofofshears. shears. Return toward toward the thefence fence to toaarusty rustypavement pavementon onthe thetrack. track.This Thisoutcrop outcropand andseveral severalalong-strike along-strikeare are Return examplesof of sillimanite-muscovite-quartz schist (Unit la), la),in inthis thisexposure, exposure, consisting consisting of of thin alternating alternatinglayers layers examples (1-5 mm) and coarse coarse grained grained muscovite. muscovite.Locally, Locally,the thelayers layersdefine defineisoclinal isoclinalfolds folds(mm(mm-totocm-scale). cm-scale). (1—5 mm) of of quartz quartz and Sillimaniteknots knots are arepresent presentinindiscontinuous discontinuouszones. zones.Several Severalfeatures featuresshow showdextral dextral sense sense of of motion motion in inplan plan Sillimanite view including, including,an anoblique obliquemuscovite muscovitefoliation foliationresembling resemblingaa C-S G S fabric fabric with with mainly mainlydextral dextralasymmetry, asymmetry,quartz quartz view 53 �A. Known deposits, inner volcanic volcanic belt Manitouwadge Manitouwadge field field guide guide lenses with asymmetric tails, and and Z-shaped Z-shaped folds folds and crenulations of the dominant dominant schistosity schistosity (D2). (D2). Muscovite Muscovite lineation (D2?) plunges to the the east, east,whereas whereas the the axes axesof of Z-folds Z-folds and crenulations (D3 or later?) plunge plunge to to the the west. Continue alongthe the south south side side of ofthe the fence fencefor forabout about50 50metres metrestotoaa pavement pavementjust justinin the the trees. trees. The Continue along sillimanite-muscovite-quartz schist has large elongate (easterly-plunging) (easterly-plunging) sillimanite knots, knots, locally locally coalescing coalescing layers. Dyke relationships interesting; a concordant foliated foliated tonalite dyke (50 cm into sillimanitic layers. relationships are again interesting; wide) is cut by several wide) several thin aplitic aplitic dykes. dykes. The Theaplitic apliticdykes dykeshave havesigmoidal sigmoidal traces traces in in the thetonalite tonalite(syn-D2?) (syn-Do?) and tail apophysesininthe the host host schist. schist. The tonalite tail off off into asymmetrical asymmetrical foliation-parallel foliation-parallel apophyses tonalite dyke dyke shows shows small amounts of offset offset along along the the cross-cutting cross-cutting aplites. aplites. In plan view, the asymmetry asymmetry and and offsets offsets are consistent with dextral motion. motion. Interestingly, Interestingly,- 8illimanite sillimanite knots are absent in the host host schist schist for for about about 30 30 cm cm on on each each side side of the tonalite sillimanite-muscovite-quartz schist schist of tonalite dyke. dyke. About About5050metres metresfurther furthereast, east,another anotheroutcrop outcropofofsillimanite-muscovite-quartz contains a foliated tonalite dyke and aplite-pegmatite aplite-pegmatite boudins. boudins. Continue around southeast corner corner of the fence fence and immediately immediately to the east, east, several several Continue around the the southeast of the the fence. fence. At the excellent of muscovite muscovite schist schist are are in in abrupt contact excellent outcrops of contact (covered) (covered) with with orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss (Unit 2). The gneiss Themuscovite muscoviteschist schist isis silky silky white white and and has hasrosettes rosettesofoffine fineaillimanite sillimaniteon on foliation foliation surfaces. surfaces. Close to the contact, contact, the theschist schist isis quartz-rich quartz-rich with with aysmmetric aysmmetricquartz quartzlenticules lenticulesand andpods podsconsistent consistentwith withdcxdextral kinematics, kinematics, and and kinks, kinks,crenulations crenulationsand andfolds foldsof of the thedominant dominantfoliation foliationare arewell welldeveloped developedand andpervasive. pervasive. open stope is along-strike along-strike west westof ofthe the contact. contact. Orthoamphibole-bearing Orthoamphibole-bearing rocks rocks to to the the north are The Willroy 1 open overgrownby byporphyroblastic porphyroblasticminerals. minerals. Orthoamphibole Orthoamphibole displays streaky with semicontinuous quartz lamellae overgrown a blue iridescence, orthoamiridescence, characteristic of of the the presence presence of of exsolution exsolution lamellae lamellae in in an an originally originallysupersolvus supersolvus orthoamphibole. Magnetite and staurolite phibole. staurolite are are also also present, present, the the latter lattermantled mantledby bycordierite cordieriteor orby byaacordierite-gahnite cordierite-gahnite intergrowth, petrographic petrographic evidence evidence of of metamorphic metamorphic decompression decompression reactions. Metre-scale compositional compositionallayering layeringisisdefined definedby byvariation variation in in proportions, proportions, textures and Metre-scale and assemblages assemblages of metamorphic minerals; minerals;for forexample, example,on onthe the northern northern part part of of the outcrop, garnet-poor metamorphic garnet-poor rocks are transitional to to garnetiferous garnetiferous rocks. rocks. First-order First-order compositional compositionallayers layers and and second-order second-order lamellae probably represent aa comcombination of primary and tectonic tectonic structures. the trail to Continue to the north north side side of of the the fence, fence, and and follow follow the to the the outcrops outcrops between between the thefence fence and and Strike Strike Lake, comprising an excellent section typical of rocks in in the footwall of alkali-depleted alkali-depleted Fe-Mg Fe-Mg rocks footwall to to the theWillroyWillroyGeco deposits. There There isisaagradual gradualnorthward northwardincrease increaseininleucocratic leucocraticfelsic-looking felsic-lookinglenses lenses and and semicontinuous semicontinuous layers, in some cases, resembling attentuated hinge hinge zones zones of of isoclinal isoclinal folds. Quartz-rich Quartz-rich layers layers and andlamellae lamellae are overgrown by garnet garnet porphyroblasts showing differential differentialdextral dextralrotation. rotation. Some layers layers are are spotted by overgrown by porphyroblasts showing by staurolite with aa white plagioclasewhite mantle mantle of of partially partially pinitized pinitized cordierite. cordierite. The Thepresence presence of of the theassemblage, assemblage, plagioclasewide) suggests suggestseither, either, that that the dyke biotite-gedrite-cummingtonite, in a concordant intermediate dyke (20 cm wide) dyke was hydrothermally hydrothermally altered altered or, or, that itit exchanged was exchanged with altered host rocks rocks during metamorphism. and obliterates layering and and foliation. foliation. The biotite A local irregular discordant patch of of biotite biotite overgrows overgrows and biotite weakly or or randomly randomly oriented oriented but but shows shows aa poorly poorly developed developedcrenulation crenulationsuggesting, suggesting,asasatatStop StopA5, A5,that that at is weakly least some biotite is of retrograde origin. in biotite, biotite, extracted extracted from from mica mica schist schist at the least origin. Monazite Monazite inclusions inclusions in the Geco mine, define define aa U-Pb U-Pb isotopic age of of 2661&1 2661±1 Ma, Ma, possibly possiblydating dating aa retrograde retrograde event event (Schandl (Schandi et et al., Geco mine, isotopic age 1991). 1991). Stop trondhjemite, ZB91-20, ZB92-P191--P193. S t o p A7, A7,Synvolcanic Synvolcanic trondhjemite, ZB91-20, ZB92-P191-P193. Return Return totothe theWillroy Willroymilisite millsite and and railway cut, cut, and find the easiest map). Continue easterly railway easiest access access to the railway railway bed (1:25000 (1:25000 map). easterly along the old railway keeping keeping track track of of distances distances from fromthe the first first outcrop outcrop on on the the south south side side (just east of a fluorescent? bright green pond). Initially orthoamphibole-cordierite-garnet gneiss (Unit 2), foliated Initiallythe theroute routepasses passesexposures exposuresof of orthoamphibole-cordierite-garnet trondhjemite mafic and and felsic felsic rocks rocks(Unit (Unit 4), 4), the the latter interpreted trondhjemite (Unit 12), 12), and and enclaves enclaves of mixed mixed mafic interpreted to to be be protolith to tosynvolcanic synvolcanicalteration. alteration. After After400 400metres, metres,foliated foliatedtrondhjemite trondhjemitetypical typicalofofUnit Unit1212isisexposed exposed the protolith in several contains magnetite magnetite and and biotite biotite and, and, near the several outcrops. outcrops. In general, general, trondhjemite trondhjemite contains the contact contact with with orthoamphibole-garnet-cordierite gneiss, orthoamphibole-garnet-cordierite gneiss,garnet garnetisislocally locallyabundant. abundant. Our Our field field interpretation interpretation of of the the unit as a synvolcanic intrusion corroborated by by U-Pb U-Pb zircon zircon geochronology geochronology giving of 2720±3 2720&3 Ma, Ma, within within synvolcanic intrusion was corroborated giving an age of of the the age age of of felsic felsic volcanism volcanism (Figs. 10 10 and 11, 11,Table Table 2). 2). 'Immobile' 'Immobile'elements elementsiningeochemical geochemicalanalyses analyses error of of of trondhjemite from from this this and andother otherlocations locationsare areindistinguishable indistinguishablefrom fromthose thoseofofquartz-phyric quartz-phyricfelsic felsicrocks rocks 24 and 27), suggesting intrusive and extrusive equivalents of of the same magma. (Figs. 24 Continue to rock knolls knollson onthe the north north side side of ofthe the rail rail bed; bed; you you are are about about 100 metres metres north north to 750 750 metres to to low rock of Strike Lake (not visible) and Stop Stop A6. A6. Trondhjemite Trondhjemite isis host host to todiffuse diffuse 'seams' 'seams' of of garnet-orthoamphibolegarnet-orthoamphibolecordierite-biotite, some cordierite-biotite, someofofwhich whichare arefolded foldedand andhave havean anaxial axialplanar planar foliation. foliation. We We interpret interpret the seams as the result result of of synvolcanic synvolcanic alteration similar similar to to that thatofofadjacent adjacentorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss gneiss and, and, by trondhjemite as as aa high-level high-level synvolcanic to by implication, we we interpret interpret the trondhjemite synvolcanicintrusion intrusionthat that contributed contributed heat to the hydrothermal system. Trondhjemite Trondhjemite intruded intruded its itsown own aureole aureole of hydrotbermally hydrothermally altered rocks and, upon subsequent cooling, was was subject subject to incursion by hydrothermal subsequent hydrothermal fluids. fluids. Stop rocks, ZB91-21, A8,Pillowed Pillowedmafic mafic rocks, ZB91-21,ZB92-P202. ZB92-P202. This Thisisisa aspecial specialstop stopfor forkeeners keenersand andsceptics sceptics S t o p A8, 54 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide who need proof proof of of mafic mafic volcanic volcanicrocks rocksnorth north of of the the Willroy-Geco Willroy-Gecoarea. area. Continue Continue for for about about 1.5 km along who need the railway railway cut to to dark dark rocks rocks exposed exposed on both both sides. sides. On Onthe thenorth northside, side,some somehighly highlydeformed deformed pillows pillows are discernible. Geochemically, these rocks rocks are are tholeiitic tholeiitic basalts basalts similar to mafic rocks in the outer Geochemically, these outer volcanic volcanic belt belt of the the Manitouwadge Manitouwadgesynform synform(Figs. (Figs.23—26). 23-26). A9—A20. Slim Lake Lake section section A9-A20. Slim field trip trip visits visits many many rock rock units units already described, but but it is The Slim Lake Lake field already described, is useful useful as aa near-continuous near-continuous 'stratigraphic' section 'stratigraphic' section across across the Willroy Willroy area (Fig. (Fig. Al) Al)including including exposures exposures of of straight straight gneiss gneiss (annealed (annealed mylonite) associated with with the interpreted mylonite) associated interpreted D1 Dl fault. The Theoutcrops outcrops are aremainly mainly along along the themargins margins of of aatailings tailings meadow, formerlySlim SlimLake. Lake. The The trip trip is divided meadow, formerly divided into two parts; firstly, firstly, north of of the the Willroy Willroy road road along along the eastern exposuresare are described describedfrom fromnorth north to south; eastern side side of of the themeadow meadow(A9—A14), (A9-Al4), exposures south; secondly, secondly, south of of the road descriptionscontinue continuetotothe thesouth. south. The base road along along the thewestern western side sideof of the themeadow meadow(A15—A20), (Al5-A20), descriptions base of of the supracrustal supracrustal section section(to (tothe thenorth) north)comprises comprisesinterlayered interlayeredmafic maficand andfelsic felsicmetavolcanic metavolcanicrocks, rocks, invaded invaded by by trondhjemite to granodiorite. To synvolcanic trondhjemite To the the south, south, about about150 150metres metres of of orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss (Unit 2) and rocks (Unit 4) are and enclaves enclaves of less altered mixed mafic/felsic mafic/felsic rocks are overlain overlain by aa discontinuous discontinuous belt or quartz-phyric felsic or lens lens of quartz-phyric felsic metavolcanic rnetavolcanic rocks (Unit 8). This Thisnortherly northerlylens lensofofquartz-phyric quartz-phyricfelsic felsicrocks, rocks, about 150 150 metres thick at at Slim Slim Lake, Lake, is is interpreted interpreted to tobe beequivalent equivalent to tothe thesoutherly southerlylens lensofofsimilar similarrocks rocks (e.g. Stop A3), repeated across across a D1 Dl fault (Zaleski (Zaleski and Peterson, 1993a). 1993a). Quartz-phyric Quartz-phyric rocks rocks are are overlain overlain by the iron formation (not exposed) that that hosts hoststhe theWiliroy Willroy22and and55deposits depositstotothe theeast, east,and andbyby50—100 50-100 metres (not exposed) of sillimanite-muscovite sjllimanite-muscovitefelsic felsjcrocks rocks(Unit (Unitla). la). The The southernmost southernmost unit unit on on the traverse is a laminated of laminated felsic felsic interpreted to lie on on the D1 fault that truncates some Dl fault some map units (notably (notably iron iron formation) and straight gneiss interpreted repeats part part of of the thesection section(quartz-phyric (quartz-phyricfelsic felsicrocks, rocks, iron iron formation, formation,sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist). west on on the the Willroy Wiliroy mine mineroad roadfrom fromthe the millsite millsiteand andrailway railwaycut, cut,turning turning north north on on the dirt road Continue west that follows meadow. Stay on the high road over a containment dam (Stop that follows the east side of the tailings meadow. (Stop A12 A12 is short eastern eastern fork fork of of the the road road somewhat somewhatbelow belowthe thedam). dam).Although Althoughthe theroad roadpeters petersout out after after the the dam, along aa short you should should be be able to drive (at your own risk) to the north end own risk) end of of the meadow meadow to another dam. Be Be sure sure to to look down down over over the the steep steep northern northern side of the dam for a view of the remnants of Slim Lake and a perspective look on the thickness thickness of the tailings tailings pile. pile. Stop trondhjemite, ZB92-P99. S t o p A9, A9, Potassic Potassicvariant variantofofsynvolcanic synvolcanic trondhjemite, ZB92-P99.The TheStop Stopisiseast eastofofthe thetailings tailings dam along the edge edge of the woods woods (Fig. (Fig. Al); Al);more moreoutcrops outcrops of of the the same samerock rock lie lie along along the the west west side side of of the the dam. dam. The Thefoliated foliatedgranodiorite granodioriteisistexturally, texturally,modally modallyand andgeochemically geochemicallysimilar similarto to trondhjemite trondhjemite(e.g. (e.g.Stops StopsA7 A7 and Al2), A12), especially especially in the the abundance abundance of of coarse coarse grained quartz and and magnetite magnetite porphyroblasts. porphyroblasts. We We interpret interpret potassic variety variety of of the thesynvolcanic synvolcanic intrusion. foliated granodiorite as aa potassic Stop S t o p AlO, A10, Quartz-phyric Quartz-phyricfelsic felsicrocks rocksini nmixed mixedmafic-felsic mafic-felsicrocks, rocks,ZB92-Pl01. ZB92-PlOl. Retrace Retrace the the route to the south approximately approximately 300 300 metres to an old old drill road. Walk Walk 50 50 metres east along drill road to to some some small outcrops on on the north side with a few quartz quartz eyes is part of outcrops side of of the the road. road. The Thefelsic felsicmetavolcanic metavolcanic rock rock with eyes is of the the package of of interlayered mafic and felsic affected by by synvolcanic alteration. alteration. felsic metavolcanic rocks, elsewhere affected Stop mafic-felsic rocks, (optional), ZB92-Pl02. S t o p All, A l lMixed , Mixed mafic-felsic rocks, (optional), ZB92-PlO2.Retrace Retracethe theroute routefor foranother another100 100metres metres south of south of the drill road and and look look for an outcrop just in in the the woods woods to the the east. east. The Theexposure exposurebelongs belongs to to the the same map unit unit as asStop StopAlO, AlO,here herecharacterized characterizedby byintimitely intimitelyinterlayered, interlayered,fine finegrained grainedmafic maficand andfelsic felsicrocks. rocks. that mafic volcanism was waspartly partly coeval. coeval. The The numerous numerous thin thin cross-cutting The interlayering suggests that mafic and felsic felsic volcanism quartz-rich and granitic granitic veinlets veinlets have have been been folded. folded. Stop ZB92-P104, ZB91-4. A12,Foliated Foliatedtrondhjemite, trondhjemite, ZB92-PlO4, ZB91-4.Continue Continuesouth southover overtailings tailings dam damtotoaalower lower S t o p A12, eastern fork fork of of the the road; road; turn north and short distance outcrop on on the the east. eastern and continue continue down down aa short distance to a pavement pavement outcrop The exposure exposure is is typical typical of of synvolcanic trondhjemite, quartz-rich leucocratic and foliated, with magnetite magnetite and and local biotite-rich tonalite dyke dyke (20 (20 cm) probably biotite-rich patches. patches. A A foliated foliated plagioclase-porphyritic plagioclase-porphyritic tonalite probably belongs belongs to the syn-D2 syn-D2 suite. suite. Stop S t o p A13, Orthoainphibole-garnet-cordierite Ortho-phibole-gwnet-cor&eSte gneiss gneiss and andmixed mixedmafic-felsic mafic-felsic nietavolcanic metavolcanic rocks, ZB92-P106,P109, P109,P441. P441. Continue Continuesouth south to to a broad broad area of pavement pavement outcrops outcrops that that form the top ZB92-PlO6, top of of the the low low knoll east of Slim Lake and north of knoll east Lake and of the the Willroy Willroy road. These These extensive extensive outcrops are part of of the thefootwall footwall alteration zone zone characterized characterized by byorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss; gneiss; however, however, hydrothermal hydrothermal alteration alteration was apparently apparently heterogeneous, protolith. Compositional heterogeneous, leaving leavinghints hints of of the the interlayered interlayered mafic-felsic protolith. Compositionallayering layeringis is defined by by metamorphic metamorphic assemblages that that include; quartz, quartz, orthoamphibole, garnet, cordierite, cummingtonite, cummingtonite, hornblende, sillimanite,staurolite, staurolite, gahnite gahuite and and plagioclase. plagioclase.IfIftime timepermits, permits,aa visit visit to to the the eastern eastern end of of the hornblende, sillimanite, interesting. The fold limb limb isistruncated truncated outcrops is interesting. The metamorphosed metamorphosed altered altered rocks rocks are are folded and in one place, a fold by a broad, of the the same minerals, suggesting local metamorphic metamorphic redistribution redistribution of broad, diffuse diffuse zone of of orthoamphiboleorthoamphibolebearing assemblages. assemblages. Stop gneiss, ZB92-P108 (optional). S t o pA14, A14, Orthoaxnphibole-garnet-cordierite Orthoamphibole-garnet-cordierite gneiss, ZB92-PI08 (optional).Return Returntotothe theWillroy Willroyroad road about 50 50 metres to to an an outcrop outcrop on on the the east east side. side. In Inthis thisexample exampleof of metamorphosed metamorphosed altered altered and continue south about 55 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide rocks, layering is defined defined by sillimanite-cordierite sillimanite-cordierite and orthoamphibole-cordierite-staurolite orthoamphibole-cordierite-staurolite assemblages. assemblages. AA biotite-rich zone is interpreted to to be be the the result result of of local local potassic retrogression. Note Note the the somewhat somewhat disorganized, disorganized, D3 or D4crenulations crenulations and and kink folds, preferentially preferentially developed developedin in the the micaceous micaceouszone. zone. Note Note also also the the spectacular sprays of orthoamphibole nearest nearest to the the road. road. Stop ZB92-P37. S t o p A15, A15,Felsic Felsic metavolcanic metavolcanicrock rockwith withorthoamphibole-garnet, orthoamphibole-garnet, ZB92-P37.Take Takethe theWillroy Willroyroad road to the second leg leg of of section. section. The first brief stop is the west west side side of of the the Slim SlimLake Lake tailings tailings meadow meadow to to commence commence second is a pavement outcrop thethe following stops (A15—A20) outcrop along alongthe thesouth southside sideofofroad. road.This Thisand and following stops (Al5-A20) are areeasily easilyaccessed accessed by walking along the western margin margin of of the the meadow. meadow. We have back-tracked back-tracked to to the north and We have and are areonce onceagain againininUnit Unit4,4,interlayered interlayeredmafic-felsic mafic-felsic rocks, rocks, here amounts of biotite, hornblende, by heterogeneous heterogeneous felsic felsic metavolcanic metavolcanic rock. rock. Minor Minor amounts hornblende, magnetite, magnetite, represented by garnet, zones of of garnet, and and local local quartz quartz and andplagioclase plagioclasephenocrysts(?) phenocrysts(?) define define aa weak weak compositional compositional layering. A few zones orthoamphibole-garnet alteration, although much of the orthoamphibole orthoamphibole-garnet are typical of synvolcanic alteration, orthoamphibole has been been replaced replaced by biotite. The Themetavolcanic metavolcanic rocks rocks are are intruded intruded by by foliated foliated tonalite. tonalite.Some Someminor minorfolds foldsare arepresent, present, and there there isis an anindication indication of of dextral, dextral,north-side-down north-side-down kinematics kinematics from porphyroblasts porphyroblasts with asymmetric asymmetric tails of matrix material. S t o p A16, A16, Contact Contactofoftrondhjemite t r o n d G e m i tand e a naltered d altered rocks, ZB92-P77. Walk southalong alongwest west side side of of Stop rocks, ZB92-P77. Walk south meadow, keeping keepingtrack track of of the the distance distance from from the the first first outcrop beyond beyond Stop A15. A15. At 60 metres, just before before an outcrop of fine grained hornblende schist, schist, head west west up into the the woods. woods. After After climbing climbing up up aa steep steepslope slopeover over deadfall (50—60 m),go gototothe the north north end of a low (50-60 m), low ridge of outcrop. The north end end of of the the outcrop outcrop isis medium medium to to coarse coarse grained trondhjemite; trondhjemite; the contact between between this and altered rocks is exposed exposedin inthe the central central part part of of the the outcrop outcrop under under aa tree limb. limb. At the contact, the the trondhjemite trondhjemite finer grained, grained, more more strongly stronglyfoliated foliatedand andcontains containsmore moregarnet garnetand andbiotite biotitethan than usual. usual. The altered is finer altered rocks rocks grading from from very very coarse coarse grained grained garnet-biotite garnet-biotite schist schist near near the contact to are heterogeneous, heterogeneous, grading tofiner finer grained grained felsic rocks, rocks,to to intermediate intermediate rocks rocks with with hornblende hornblende and and cummingtonite layers. layers. The garnetiferous felsic The relationships relationships suggest that incipient incipient alteration alteration affected affected trondhjemite along the contact. Carefully scramble scramble back back down downtoto the the meadow meadowand and continue continuesouth. south. Take Take aa quick quick look look at at the hornblende Carefully schist previously noted, a less of the rocks just visited. less altered altered equivalent equivalent of some of visited. Stop synvolcanic alteration, ZB92-P56, P79. Continue S t o p A17, A17,Metamorphosed Metamorphosed synvolcanic alteration, ZB92-P56, P79. Continuetotoa alarge largeoutcrop, outcrop,about about 150 metres metres south, south, dominated by pegmatite but with with aa sheet sheet of of garnet-orthoamphibole-biotite garnet-orthoamphibolebiotite schist schist with very coarse garnet. garnet. About coarse About 40 40 metres metres further further on on (190 (190 m), m),ininaasmall smallpavement pavement outcrop outcrop fresh fresh blue blue cordierite cordierite is is present, with sprays sprays of of orthoamphibole, and tiny staurolite staurolite grains. grains. Stop felsic rocks, ZB92-P81—P83, S t o pA18, A18,Quartz-phyric Quartz-phyric felsic rocks, ZB92-P81-P83,P54. P54.Continue Continuetotoseveral severallow lowoutcrops outcropsbetween between about 300 300 to to 400 metres south. south. These Theserocks rocks are arepart partofofthe thenorthern northernbody bodyofofquartz-phyric quartz-phyricfelsic felsicmetavolcanic metavolcanic rocks, characterized characterized by by abundant abundant (to 20%) porphyroblasts. 20%) quartz phenocrysts and ubiquitous magnetite porphyroblasts. Optional for keeners head up up into woods near near the northernmost keeners and breccia breccia lovers; lovers; head northernmost exposures exposures of the quartz-phyric felsic felsic rocks rocks looking looking for the the cut cutlines lines(somewhat (somewhatovergrown) overgrown)of of the theWillroy Willroygrid. grid.Find FindL130+OOE L130+00E at approximately and a small stripped stripped outcrop approximately25+OON 25+00N and outcrop of of monolithologic monolithologic quartz-phyric felsic breccia. Angular Angular fragments, ranging ranging in in size size from from very very small small to to metre-scale, metre-scale, are are supported supported in in a pale green fragments, green matrix enriched enriched in biotite, hornblende and epidote. Stop felsic schist, ZB92-P86, P87. Several small outcrops S t o p A19, A19,Sillimanite-knot Sillimanite-knot felsic schist, ZB92-P86, P87. Several small outcropsbetween between500 500and and600 600 1. metres document the presence presence of Unit 1. Stop (annealed mylonite), ZB92-P88. At At approximately S t o p A20, A20,Straight Straightgneiss gneiss (annealed mylonite), ZB92-P88. approximately600 600metres, metres,go go10 10metres metres with some some thin thin biotitebiotite- and into the woods to a large outcrop. The The pink pink to to white, white, quartzose quartzose laminated gneiss, with hornblende-rich layers, example of straight gneiss, gneiss, forming part of of a zone zone hornblende-rich layers, isis very very hard hard and flinty. flinty. This is an example of laminated rocks, lying on on the interpreted D1 Dlfault that that passes passes through the the Willroy-Geco Willroy-Geco area. In In this this case, case, the straight granoblastic texture. texture. Some Somegarnet garnetisispresent presentlocally, locally,and andvery very straightgneiss gneiss is is completely completely annealed to to aa granoblastic fine magnetite porphyroblasts are surrounded surrounded by by leucocratic leucocratic halos. A21. Naina N a m a Creek Creek deposit deposit S t o p A21, A21,Naina N a m aCreek Creek Mines deposit, ZB91-110, IAGOD#5. #5.From F'romthe thewestern westernmargin margin of of the tailings tailings Stop Mines deposit, ZB91-110, IAGOD meadow, drive continuation of Willroy road Nama Creek Creek and and Willecho Willecho meadow, drive northwest northwest on on the continuation of the Willroy road leading leading to to the Nama (1:25000 map). 600 metres from the meadow, turn off off on a gravel road to the the southwest southwest and and deposits (1:25000 map). About 600 flooded open cut of of the the Nama Nama Creek Creek deposit deposit (Fig. (Fig. A3). A3). continue 500 metres metres to the flooded Nama Creek Creek Mines Mines deposit deposit (also (also known known as the the Big Big Nama Nama deposit) deposit) was was aa marginally marginally economic economic ZnThe Nama (Table 3) hosted hosted by by iron iron formation formationimmediately immediately south south of of orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss gneiss rich orebody (Table The iron iron formation formation can can be be traced traced east east to to that thathosting hosting the theWiliroy Willroy 2/5 215 orebodies. orebodies. As As traced traced by by (Unit 2). The subeconomic extension of the Nama Nama Creek Creek mineralization mineralization apparently apparentlyplunges plungeseasterly easterlytotoconverge converge drilling, the subeconomic in the subsurface subsurface with the Willroy Willroy 3 horizon horizon (1:25000 Dl fault, (1:25000map). map). The The two two zones zones are are separated separated by by the D1 56 �A. A. Known Known deposits, depositsl inner inner volcanic volcanic belt belt Manitouwadge Manitouwadgefield field guide guide I L 22 r 22 Dl DI gneissosity gneiss0sit.y D2 D2 foliation foliation -21 D2 D2 lrneation lineation . \\\40 40 D2 D2 fold f o l d axial a x i a l plane plane x22 D2 fold f o l d axis axis 22 D2 FIG. A3.Geology Geologyand andfield-trip field-tripstops stopsininthe thearea areaofofananS-shaped S-shapedD2 D2fold foldofofiron ironformation formation(Unit (Unit9)9) FIG.A3. andfelsic felsicmetavolcanic metavolcanic rocks rocks (Unit (Unit 6). 6). Dashed Dashedlines linesare arecut cutlines linesofofNoranda's Noranda'sWiliroy Willroygrid. grid. and interpreted deposit extensively interpreted totolie liesouth southofofthe theNama NamaCreek Creekdeposit. deposit.The The depositis is extensivelyinvaded invadedby bypegmatite-aplite pegmatiteaplite sheets sheets which which tend tendtotoobscure obscurefield fieldrelationships. relationships. On flooded orthoamphibole-garnet-cordierite On the thenorth northside sideofofthethe floodedcut, cutl orthoamphibolegarnet-cordieritegneiss gneisshas has minor minor amounts amountsof of magnetite?ilmenite, ilmenite, chalcopyrite, chalcopyritel pyrrhotite pyrrhotite and and biotite, biotite?asaswell wellasasstaurolite stauroliteinclusions inclusionsinincordierite cordieriteand and magnetite, garnet.Orthoamphibole-bearing Orthoamphibolebearinggneiss gneissisisintercalated intercalatedwith withsillimanitic sillimaniticlayers layersand, and,ininsome somecases, cases?sillimanite sillimanite garnet. occurs in in orthoamphibole-bearing orthoamphibolebearing assemblages. assemblages. However, However? sillimanite or occurs sillimanite isis mantled mantled by by cordierite cordierite or or quartz, or engulfed engulfed by by skeletal skeletal garnet, garnet?textures texturessuggestive suggestiveofofmetamorphic metamorphicdecompression decompressionreactions. reactions. At pegmatite is is interleaved Atthe theeastern easternend endofofthe thecut, cut, pegmatite interleavedwith withchlorite-mica chloritemicaschist, schist?foliated foliated tonalite tonaliteand and semi-massive pyrite and and magnetite. magnetite. In Inthe theconcordant concordantpegmatite pegmatitedyke, dyke,coarse coarsegrained grainedquartz, quartz?plagioclase plagioclaseand and semi-massive sprays sprays of of sillimanite sillimanite (to (to 55cm) cm)tend tendtotobebeoriented orientedperpendicular perpendicular totodyke dykemargins, margins?looking looking as as though though they they nucleated nucleated on on the thewall wall rock rock and and grew grew into into the the pegmatite, pegmatite, apparently apparentlywithout withoutsubsequent subsequent deformation. deformation. A22—A23. D2 foldsof ofiiron formation/felsic metavolcanic A22-A23. D 2 folds r o n formation/felsic metavolcanic contact contact Southwest of of the the Nama NamaCreek Creek deposit, deposit?the thethick thicksouthernmost southernmost iron ironformation formation(the (thesame sameas asthat thatofofStop Stop Southwest A2) A2) of of the theinner innervolcanic volcanicbelt beltdefines definesaamap-scale map-scaleS-fold S-fold (1:25000 As). Interdigitations Interdigitationsofoffelsic felsic (1:25000 map, mapl Fig. Fig. A3). rock and andiron ironformation formationrelated relatedtotoparasitic parasiticfolds foldsininthe thehinge hingeregion regionare arewell wellexposed. exposed.Locally, Locally,aagneissic gneissic rock fabric (Dl)ininthe thefelsic felsicrocks rocksisisinvolved involvedin in folding. folding.The Thedominant dominantD2 D2foliations foliationsand andlineations lineations are areparallel paralleltoto fabric(D1) theaxial axialplanes planesand andfold foldaxes, axes?respectively, respectivelylofofoutcrop-scale outcrop-scale folds. folds. The Theaxial axialtrace traceofofthe themap-scale map-scaleS-fold S-foldisis the 57 �A. Known Known deposits, deposits, inner innervolcanic volcanicbelt belt A. Manitouwadgefield field guide guide Manitouwadge D2 folds of D l fabric tonalite dyke with D 2 schistosit~ FIG. A4. A4. Sketch Sketchof ofoutcrop outcroprelationships relationships(Stop (StopA23) A23)between betweenD2 D2folds foldsof ofDi Dlgneissosity gneissosityininfelsic felsic FIG. metavolcanic rock, rock, and and D2 D2 schistosity schistosity in in aa syn-D2 syn-D2 tonalite tonalitedyke. dyke. metavolcanic D3Manitouwadge Manitouwadgesynform synform and and the theS-asymmetry S-asymmetryisisinconsistent inconsistentwith withwhat whatwould wouldbe beexpected expected deformed by by the theD3 deformed for aa D3 D3 parasitic parasitic fold fold related related to tothe thesynform. synform.On Onthe thebasis basisofofthese the= observations, observations,the theS-fold S-fold isis interpreted interpreted to to for be a D2 fold that reorients vestiges of Dl fabric preserved in felsic rocks in the strain shadow near the hinge be a D2 fold that reorients vestiges of D1 fabric preserved in felsic rocks in the strain shadow near the hinge region. A A major majorD2 D2sheath sheath fold fold isis interpreted interpreted to torepeat repeatthe theD1 Dl fault faultand andmineralized mineralizediron iron formation formation of of the the region. Willroy-Geco area between the the Nama Nama Creek Creek and and Willecho Willecho deposits deposits (Fig. (Fig. 4). 4). Wiliroy-Geco area between Access to to the the exposed exposed contact contactinvolves involves about about 700 700 metres metres (one (one way) way) of of bushwacking bushwacking on on the the somewhat somewhat Access overgrown cut lines of the Willroy grid. The exposures are worth viewing for those interested in the pre-D3 overgrown cut lines of the Willroy grid. The exposures are worth viewing for those interested in the pre-D3 structuralhistory historyof ofthe thearea. area.On Onthe thesouth southside sideofofthe theflooded floodedcut cutofofthe theNama NamaCreek Creekdeposit, deposit,look lookfor forL95E L95E structural (17+00N, English Although the the picket picket may may be be fallen fallenand andillegible, illegiblelitit should should be be possible possible to tospot spotthe theold old (17+OON, English units). units). Although (218') about 530 metres to the Willroy baseline. Remember that your compass cut and follow it southwest cut and follow it southwest (2 18°) about 530 metres to the Willroy baseline. Remember that your compass may not notbe bereliable. reliable. may S t o p A22, Foldsinin iron formation, ZB91-46. Continue northwest(308°) (308O)170 170metres metres on on the the Willroy Willroy Stop A22, Folds iron formation, ZB91-46. Continue northwest baseline to about 20 metres beyond L90E and some excellent stripped outcrop. In the quartz-magnetite baseline to about 20 metres beyond L9OE and some excellent stripped outcrop. In the quartz-magnetite iron formation formation some some groups groups of of layers layers define define S-folds S-folds (D2) are disrupted disrupted by by stratabound strataboundbreccia breccia iron (D2) and and others others are zones. The Thebreccias, breccias,consisting consisting of of segmented segmented quartzose quartzose layers layers in dark matrix, matrix,tend tendtotobebelocalized localizedwhere where zones. in aa dark quartzose layers layers are are thin thin and/or and/orproportionately proportionatelyless lessabundant abundantthan thandark darklayers layersofofmagnetite magnetiteand andFe-silicates. Fe-silicates. quartzose Quartzose fragments fragments are are preferentially preferentially oriented oriented subparallel subparallel to to the the axial axial traces traces of of folded folded layers. layers. The The apparently apparently Quartzose competent behaviour of quartzose fragments suggests that brecciation occurred after diagenesis or lowgrade grade competent behaviour of quartzose fragments suggests that brecciation occurred after diagenesis or low metamorphism, conditions conditions under A pegmatite pegmatite cuts cuts across across the the iron iron metamorphism, under which which quartz quartz is is relatively relatively competent. competent. A formation and and contains contains aa discontinuous discontinuous (<5 (<5 mm) mm) garnetiferous garnetiferous zone zone at the contact. contact. formation at the S t o pA23, A23,D2 D folded 2 folded contact, ZB91-50, ZB92-Pl3.Continue Continuenorthwest northwest on on the thebaseline baselineanother another 50-60 Stop contact, ZB91-50, ZB92-P13. 50—60 metres to to the the crest crest of of aa hill hill with with aaview view down down to to Garnet Garnet Lake Lake and and along along the the hill hill top top and and metres the baseline. baseline. On On the northwest-facing slope, there are are good good exposures exposures of of interfingering interfingering iron felsic rock. Scattered northwest-facing slope, there iron formation formation and and felsic rock. Scattered outcrops of of folded folded iron iron formation formation in in the the thick thick bush bushshow show changes changes between between ZS-asymmetry related to the the outcrops Z- and and S-asymmetry related to axial traces traces of ofD2 D2 minor minorfolds folds(Fig. (Fig.A3). A3). axial Continue just over the the hill hill crest crest north north of of the thebaseline baseline and and along along L87+50E L87+50E to to exposures exposures of of the thefolded folded Continue just over contact between between iron iron formation formation and andfelsic felsicrock rock (with (withsparse sparsequartz quartzeyes). eyes). Locally, Locally, the the felsic felsic rock rock has has aa contact crenulated gneissic gneissic layering layering (D1) (Dl) defined defined by by quartz quartz lamellae lamellae and and biotite-garnet-rich biotite-garnet-rich zones. zones. The Thebiotite biotitehas has crenulated a crystallographic-preferred orientation parallel to crenulation traces. Near the folded contactl felsic gneiss a crystallographic-preferred orientation parallel to crenulation traces. Near the folded contact, felsic gneiss contains odd odd irregular irregularmuscovite-schist muscovite-schistenclaves enclaves (some (some look look angular, angular, some some like like rootless rootless isoclinal isoclinal folds). folds). The The contains gneissosity in in the the host host rock rock isisfolded, folded,whereas, whereas, muscovite muscovite in in the the enclaves enclaves has has an an axial axial planar planar orientation orientation(Fig. (Fig. gneissosity A4). We We interpret interpretthe thegneissosity gneissositytotobe bea aD1 Dlfoliation foliationpreserved preservedin inthe thehinge hingeregion regionof ofthe themap-scale map-scaleD2 D2fold. fold. A4). A tonalite dyke subparallel to the axial traces of D2 folds (of somewhat variable orientation) near the A tonalite dyke subparallel to the axial traces of D2 folds (of somewhat variable orientation) near the iron formation/felsic contact has an axial planar foliation, parallel to that in the irregular muscovite-schist iron formation/felsic contact has an axial planar foliation, parallel to that in the irregular muscovite-schist enclaves in adjacent felsic felsic rocks Ad). The Therelationships relationships suggest suggest that that the thedyke dyke was was intruded intruded during during enclaves in adjacent rocks (Fig. (Fig. A4). D2 deformation, deformation, interpreted interpreted to to be bebroadly broadlycoeval coeval with with peak peak metamorphism. metamorphism. On Onthe thebasis basisofoflithology, lithologylfield field D2 relations and geochemistry, the dyke is one of a suite of tonalite dykes, other probable examples of which relations and geochemistry, the dyke is one of a suite of tonalite dykes, other probable examples of which were seen seen at at Stops StopsAl, Al,A2 A2and andA5. A5.AAsample sampleofofthe thedyke, dyke,collected collectedfor forgeochronology, geochron~logy~ contained no noseparable separable were contained 58 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide zircon. Monazite, definesaa U-Pb U-Pb age age of of 2671k3 2671±3 Ma Ma (Fig. 14, Table zircon. Monazite, including including grains of of igneous igneous morphology, defines 2), from the the Geco mine (Davis (Davis et et al., 1994), 21, within error of of both both 2675±1 2675kl Ma Ma metamorphic metamorphic monazite monazite from Geco mine 19941, and 2669±3 Ma monazite monazitefrom fromaa prepre- to to syn-Di pegmatite (Stop (Stop A26). A26). The 2669h3 Ma syn-Dl pegmatite The estimated estimated temperature temperature of of peak peak metamorphism (650°C (650°C) in in the Manitouwadge belt is is less lessthan than the the closure closure temperature temperature of of the the U-Pb system in Manitouwadge belt monazite Heaman and and Parrish, 1991). (7OO0C, Heaman 1991). Nevertheless, Nevertheless, it would would appear that monazite monazite ages ages are are dating dating monazite (700°C, metamorphic or late metamorphic metamorphic events, eventsl or that that monazite monazitecontinued continued to toexchange exchange isotopes isotopes during during protracted protracted regional cooling and and decompression. decompression. A24—A26. Willecho3 3pit pitaand inner hinge hinge of of tthe A24-A26. Willecho n d inner h e Manitouwadge synform D1/D2 folding folding and and faulting faulting near the hinge region of of The three three Willecho Willecho orebodies orebodies lie in an area of complex D1/D2 synform (1:25000 (1:25000mapl map,Fig. Fig.4)> 4),and andititisisdifficult difficulttotoreconstruct reconstructtheir theirexact exactstratigraphic stratigraphic the D3 Ds Manitouwadge synform relationship relationship to orebodies orebodies in the the Wiliroy-Geco Willroy-Geco area. North NorthofofWillecho Willecho3, 3,the thesequence; sequence;quartz-phyric quartz-phyric felsic felsic rocks, iron formation, schist, is repeated in formationl sillimanite-knot sillimanite-knot felsic felsic schist, in aamap-scale map-scale isoclinal isoclinal fold, fold, possibly possibly aa Dl fold. In the the Wiliroy-Geco Willroy-Geco area, we interpret a similar sequence as a stratigraphic succession. succession. Sillimanite-knot felsic schist schist in in the Willecho area (Unit ib) Willecho area lb)is, is,iningeneral, generallmore morefelsic felsicthan thansillimauite-muscovite-quartz felsic sillimanite-muscovite-quartzschist schist in the Wiliroy Willroy area (Unit la, la,Stop StopA6), A6),although although the thelatter latteralso alsohas hasfelsic felsic variants. variants. Typically, Typically, layers layers with layers, and sillimanite-biotite-garnet large disseminated sillimanite knots are interleaved with non-sillimanitic layersl schists are of of local local occurrence. occurrence. In general, from muscovite-sillimanitegenerall toward toward the north north ininthe theWillecho Willechoarea, area,there thereisisa transition a transition from muscovite-sillimaniteassemblages, consistent consistent with with northerly northerly increase in metamorphic microcline to sillimanite-microcline assemblages, metamorphic grade. grade. Stop felsic schist, ZB91-2, ZB92-228. A24,Sillimanite-knot Sillimanite-knot felsic schist, ZB91-2, ZB92-228.From F'romthe theNama NamaCreek Creekjunction, junction, continue continue S t o p A24, west about about 2.25 km on on the gravel road toward toward the the Willecho deposit. Where Where the the road road starts uphill on the west 2.25 km gravel road Willecho deposit. northwest side of of Garnet Lake, stop at some outcrops in in the ditch on the north northwest some low outcrops north side side(1:25000 (1:25000 map). The The outcrops are typical of of Unit Unit ib; lb;diffuse diffuselayering layering in in the thedominantly dominantlyfelsic felsic rocks rocks is is defined defined by concentrations of disseminated large large (to 2 cm) zoned white-green sillimanite knots knots and and local local garnet. garnet. The disseminated white-green sillirnanite The sillimanite sillimanite knots knots are are strongly elongate, plunging northeasterly. northeasterly. Zoning Zoning in the the knots knotscommonly commonlyconsists consists of of aa muscovite-sillimanite muscovite-sillimanite oriented by by sprays of of fine finesillimanite, sillimanite, in in turn turn mantled by strongly oriented sillimanite core mantled by weakly oriented sillimanite fibres engulfed engulfed or or overgrown overgrownby bycoarse, coarse,either eitheroriented orientedor or random random muscovite. muscovite. In one sample, the cores fibres cores of of sillimanite knots knots contain contain relict relict andalusite. andalusite. The sillirnanite The matrix matrix has has aafew few quartz quartzeyes eyesand andisiscomposed composed of of quartz, quartz, plagioclasel Muscovite mostly looks like late unoriented overgrowths, overgrowths, but plagioclase, microcline, microcline, biotite biotite and muscovite. Muscovite commonly some blades, interleaved with foliated biotite, biotitel are are concordant concordanttotoschistosity. schistosity. Boudins of pegmatite wrapped strain, possibly wrapped by by gneissic gneissic layering indicate high strain, possibly related to tostraight straightgneiss gneiss exposed at the exposed south of the road, exposed the Willecho Willecho pit (Stop (StopA26). A26). Sillimanite-knot Sillimanite-knotfelsic felsic schist is also also well exposed along an overgrown overgrown track Garnet Lake. Lake. track angling southeast toward Garnet Stop Driveononabout about500 500 metres of Stop to a gravelled ZB92-87. Drive metres westwest of Stop A24 A24 to a gravelled S t o p A25, A25,Limb Limbof ofD1 D l (?) ( ? ) fold, ZB92-87. clearing shaft, which clearing and the remains remains of of building building foundations marking marking the location of the the former former Willecho Willecho shaftl which intersected the down-plunge extension of of the the Willecho orebody. Continue Continue on on the road west of the Willecho 33 orebody. the clearing clearing intersected down-plunge extension about 100 100 metres to to an overgrown track branching to the north, north, and andwalk walk about about 50 50 metres metres to to excellent excellent stripped stripped outcrops near L5N L5N (may or may not be be visible) visible) of the Willecho grid. The The stripping stripping exposes exposes the the folded folded contact contact between quartz-magnetite (?) map-scale quartz-magnetite iron ironformation formationand andsillimanite-knot sillimanite-knotschist schiston onthe thelimb limbofofthe theD1 Dl(?) map-scale fold. fold. The enveloping surface of of the contact enveloping surface contact trends trends about about260°; 260°whereas, whereas,metre-scale metre-scale isoclinal isoclinal S-shaped S-shaped folds folds of the contact contact and andlayered layered iron ironformation formationhave haveoblique obliquewesterly-trending westerly-trending axial axial traces. traces. Schistosity (composite D1/D2?) defined asymmetry Dl/Dz?) defined by biotite biotite and and flattened flattened sillimanite sillimanite knots is axial axial planar planar to to the thefolds. folds. The asymmetry of minor folds and and of fabrics with a parasitic relationship to the map-scale D1 fold, fold, but but the minor folds fabrics is consistent consistent with relationship to map-scale Dl schistosity defined by high grade minerals may be a D2 transposition of D2 fabric developed during transposition of the the early early fold. fold. S t o p A26, A26,Willecho Willecho33pit pitand and straight gneiss, ZB92-551 IAGOD#6. #6.The The Willecho33pit pitisison on the the south south Stop straight gneiss, ZB92-55, IAGOD Willecho of the gravel grave1 road about 3.5 3.5 km km west west of of the the Nama Nama Creek Creek (Stop (Stop A21) A21) junction. AAgravel graveltrack trackslopes slopes side of pit. Watch Watchfor forhazardous hazardousloose looserocks rocks on on the the steep steep pit pitwalls. walls. The Thepit pitwalls wallscomprise compriselenticular lenticular gently into the pit. layered sillimanite-garnet-biotite sillimanite-garnet-biotite schist, iron formation, minor minor orthoamphibole-garnet orthoamphibole-garnet gneiss to layered gneiss and semimassive to disseminated sulphide mineralization (pyrite-pyrrhotite-sphalerite-chalcopyrite). (pyritepyrrhotite-sphalerite-chalcopyrite). Locally, rotated garnet porphyroblasts wrapped wrapped by by biotite-sillimanite biotite-sillimanite suggest suggest north-over-south north-over-south sinistral kinematics. Along the top of the northern northern side side of of the the pit, pitlfrom from about aboutmidway midwayalong along its its length length and andcontinuing continuingeasterly, easterly, it is possible to walk gneiss over walk out out a transition from sheared pegmatite to straight gneiss over about about 100 metres metres (at low low angle to strike, true width may < l o m). m). The Thewesternmost westernmost outcrops outcrops of of pegmatite are are cut cut by by anastomosing anastomosing may be <10 discrete shears with abundant abundant coarse coarse strongly strongly lineated lineated sillimanite sillimanite on shear surfaces. Sheared Sheared pegmatite pegmatitegrades grades to porphyroclastic porphyroclastic pegmatite pegmatitewith withcoarse coarsequartz-K-feldspar-plagioclase quartz-K-feldspar-plagioclase enclaves enclaves (2—5 (2-5 cm) cm)in in aa fine grained matrix; lineated sillimanite sillimanite coats shear surfaces. Closer to the eastern end end of the pit, pit, very very fine fine grained layered rocks of gneiss (annealed mylonite), mylonite), possibly possibly of of aa mixed mixed felsic felsic of felsic felsic composition composition were were grouped grouped with with straight gneiss metavolcanic Thepresence presenceof of concordant concordant and andlow low angle angle pegmatite pegmatitedykes dykessuggests suggests metavolcanic and pegmatitic parentage. The 59 �_________ Manitouwadge field guide B. Outer Outer volcanic volcanic belt multiple of pegmatite pegmatite intrusion. multiple generations generations of intrusion. Immediately Immediately below below in the the wall wall of of the thepit, pit,mineralized mineralizedsheets sheets lenses of Willecho 33 deposit north and and plunge plunge northeasterly, northeasterly, underneath underneath the the and lenses of the Willecho deposit dip moderately moderately to the north straight gneiss. with the D1 gneiss. We We interpret the the straight straightgneiss gneiss as as lying lying on a D1 Dlfault, correlative correlative with Dl fault of the Willroy-Geco area, repeated repeated by by a map-scale D2 sheath fold fold (Fig. 4). By Willroy-Geco area, By implication, implication, the the pegmatite pegmatite involved involved straight gneiss gneiss transition transition was was intruded before before or during Dl sample of pegmatite pegmatite in the straight or during D1 deformation. deformation. In In a sample geochronology, only 2669k3 Ma collected for U-Pb geochronology, only monazite monazite was was suitable suitable for for isotopic isotopic analysis. aflaly8is. The The age of 2669±3 (Fig. 13) 13) is apparently apparently aa metamorphic metamorphic age subject to the the same same ambiguities ambiguities as the monazite monazite age from the syn-D2 tonalite tonalite dyke dyke (Stop (Stop A23). A23). B. Outer O u t e r volcanic volcanic belt Bi. Bl. Northern N o r t h e r ncontact contact zone zone Although the volcanic volcanic sequences correlative, the outer belt belt lacks lacks vovoAlthough sequencesofofthe theinner inner and and outer outer belts belts are correlative, luminous luminous synvolcanic synvolcanic intrusions, intrusions, extensive extensive units unitsof oforthoamphibole-bearing orthoamphibole-bearingororsillimanite-muscovite-bearing sillimanite-muscovite-bearing rocks and (known) (known) massive sulphide belt, the the northern northerncontact contactbetween betweenmafic mafic rocks sulphide deposits. deposits. Throughout Throughout the outer belt, metavolcanic rocks and felsic and metasedimentary metavolcanic rocks metasedimentary rocks rocks is aa complex complex zone zone that thatincludes includessemicontinuous semicontinuous garnetiferous domains (locally (locally with orthoamphibole-cordierite), orthoamphibole-cordierite), tonalite and minor minor iron ironformation. formation. garnetiferous tonalite sheets and orthoamphibole-garnet-cordierite zones the distal distal equivalent equivalent of of the theextensive extensivezones zones of of The orthoamphibole.-garnet-cordierite The zones are are interpreted interpreted as the metamorphosed synvolcanic alteration in the the inner inner belt. belt. 100 metres metres 61 90 Unit Unit 10. 1C Cm Cm quartzite quartzite m eta sedimentary? metasedimentary? JiotedHblsyen,e -72 Hbl syenite ,-foliated \ \c_____ 72 89 89 \ / Unit 22 k_______ — (.: —— Cr1 caic—silicate gate j \ N . gabbro high strain disrupted pillows? pillows 69 FIG. FIG. Bi. Bl. Outcrop geology geology of the the Geco Geco gatehouse section, section, showing showing exposures exposures of of mafic and and orthoamphibole-bearing orthoamphibole-bearing rocks rocks of the the outer outer volcanic volcanic belt and and the theconcontact tact with with metagreywacke. metagreywacke. Structure Structure symsymbols bols show show dominant dominant D2 D2 foliations and unlineations, and and the the axial axialsurface surfaceof of aa post-D2 post-D2 eations, Minfold in foliated hornblende syenite. Minabbreviations from from Kretz Kretz (1983). (1983). eral abbreviations 74 Grt /I \ Unit 3 380 Foliated Foliated tonalite tonalite Metagreywacke .:1 Metagreywacke r l Mafic Mafic rnetavolcanic rnetavolcanic rocks rocks Iron Iron formation formation and/or and/or orthoamphibole odhoamphibole gneiss gneiss B lGeco , Geco gatehouse section, ZB92-P249-P251,ZB93-P306, ZB93-P306, IAGOD IAGOD #I. Thisstop stop encompasses encompasses S t o pBi, Stop gatehouse section, ZB92-P249--P251, #1. This extend along along the the east eastside sideof of the theroad roadtotothe theGeco Gecomine, mine,starting startingacross acrossfrom fromthe thegatehouse gatehouse outcrops that extend at the the Geco Geco main main entrance entrance (Fig. (Fig. B1). Bl). Many Many units units typical typical of of the the outer outer volcanic volcanic belt, and the the intruded intruded and and at to younger younger metagreywacke, are tectonized contact to are exposed exposedover overaashort shortdistance. distance. Begin Beginat at the the southern southern end of of 60 �B. Outer Outer volcanic volcanic belt belt B. Manitouwadge Manitouwadgefield field guide guide the the outcrops outcrops (south (south of of the the gate) gate) and andwork work north to to the the eastward eastward curve curve in the the road sign-posted to the Geco Geco #4 shaft. shaft. The Thesection sectionbegins beginsininthe thenorthern northernpart partofofmafic maficmetavolcanic metavolcanicrocks rocksof ofthe theouter outerbelt belt(1:25000 (1:25000map). map). The Thehighly highlydeformed deformedpillows pillows and and pillow pillow breccias in the the first first outcrop outcropwere werethe themain mainfocus focusofofprevious previousfield fieldtrips trips (Williams (Williams et al., al., 1990). 1990).The Thepillows pillows are arebest bestexamined examinedon onthe theglacially glaciallypolished polished top topsurface surfaceof of the theoutcrop. outcrop. The The pillows pillows appear significantly significantly shortened on both top top and andfront frontsurfaces surfacesof of the theoutcrop. outcrop.Pillow Pillowselvedges selvedgesare are dark of garnet. garnet. Interpretation dark in in colour colour and and have have local local concentrations concentrations of Interpretation of of structural structural facing facing is is tempting, tempting, but but ambiguous ambiguous (go (go ahead, everybody everybody does does it). it). Moving Moving north along along the theoutcrop, outcrop,mafic Aaficmetavolcanic metavolcanicrocks, rocks,mostly mostlywithout withoutrecognizable recognizablepillows, pillows,are are interleaved interleaved with with foliated foliated tonalite tonalite sills sills (Fig. (Fig. Bi). Bl).InInthe thevicinity vicinityofofthe thefence, fence,foliated foliatedcoarse coarsegrained grained hornblendehornblendeplagioclase with mafic mafic schist. schist. The gabbro thickens to the west plagioclase gabbro is interleaved interleaved with west in the the Gaug Gaug Lake Lake area. area. North North of of the thefoliated foliatedgabbro, gabbro,mafic maficmetavolcanic metavolcanicrock, rock, with with garnetiferous garnetiferouslayers layersand andcalc-silicate calc-silicateboudins, boudins,and and foliated foliated tonalite continue continue to the end end of of the the first first outcrop. outcrop. Note Note the the steep steep easterly easterly plunging plunging lineation. lineation. A A thin thin layer layer of of rusty, rusty, locally locally magnetic rock, interpreted as as iron iron formation, formation, is exposed exposed at the thecontact contactbetween between mafic mafic rocks rocks and and tonalite tonalite near near the the northern northern end endof of the theoutcrop. outcrop. Along outcrop includes Along the road road about about 25 25metres, metres, the the southern southern part part ofofthe thenext next outcrop includesinterlayered interlayered orthoamphibole-plagioclase-biotite orthoamphibole-plagioclase-biotite gneiss and iron formation. formation. Along Along strike strike just just west westof ofManitouwadge ManitouwadgeLake, Lake, orthoamphibole contain cordierite, cordierite, garnet, garnet, staurolite, and gahnite, orthoamphibole gneisses gneisses contain gahnite, similar similar assemblages assemblages to those in in altered altered rocks rocks near near the theWillroy Willroydeposit deposit (Stops (Stops A5, A5, A6). A6). The Thecentral central outcrop outcroparea areaisisdominated dominatedby byfine finegrained, grained, foliated syenite, possibly belonging foliated hornblende-microcline hornblende-microcline syenite, belonging to aahornblendite-syenite hornblendite-syenite suite suitesporadically sporadicallyexexD3Z-fold Z-fold ofofthe thedominant dominantsyenite syenite posed posed throughout throughout the the Manitouwadge Manitouwadge area (compare (compare Stops F4, F5). F5). AAD3 foliation foliation is exposed on the top surface surface of the outcrop. The The northern northern end endof of this, this,and andall allofofthe thenext nextoutcrop, outcrop, The are possibly due due to silicification. are cummingtonite-bearing cummingtonite-bearing rocks rocks of intermediate to felsic felsic composition, composition, possibly silicification. The cummingtonite-bearing cummingtonite-bearing rocks rocks were were grouped with metasedimentary metasedimentary rocks; rocks; however, however, their origin origin is is uncertain. uncertain. The The remaining remaining outcrops outcrops to to the thenorth northalong alongthe theinside insidecurve curveofofthe theroad roadare aremore moretypical typicalbiotite-quartzbiotite-quartzplagioclase plagioclaseschist schist interpreted interpretedasasmetagreywacke. metagreywacke. B2—B1O. Lakearea, area, comparison comparison to inner inner volcanic volcanic belt belt B2-B10. GGaug a u g Lake TheGaug GaugLake Lakearea arealies liesininthe theouter outervolcanic volcanicbelt belton onthe thesouthern southernlimb limbofofthe theManitouwadge Manitouwadgesynform synform The (1:25000 map) and, and, like like the the inner inner belt, belt,comprises comprisesmafic mafic and and felsic felsic rocks and iron formation (Fig. (Fig. B2). B2). Much Much (1:25000 of the the area areabelongs belongs to to the the'Central' 'Central'Granges GrangesInc. Inc.claim claimgroup group and andgrid. grid.Felsic Felsicrocks rocks and andiron iron formation formation are are of less abundant abundantthan thanininthe theinner innervolcanic volcanicbelt, belt,although althoughthis thismay mayreflect reflectpreservation preservationrather ratheroriginal originalvolumes. volumes. less Felsic Felsic rocks are are of of the the same sameage agein inboth bothbelts belts(circa (circa2720 2720Ma), Ma),but butdiffer differinincomposition, composition,comprising comprisingaphyric aphyric rhyodacites and and dacites dacites in inthe theouter outerbelt. belt.Garnet-hornblende Garnet-hornblendeassemblages assemblagesininmafic maficand andfelsic felsicrocks rocks could could be be rhyodacites the theresult resultofofsynvolcanic synvolcaniccaic-silicate calc-silicate alteration alteration and andsubsequent subsequentregional regionalmetamorphism. metamorphism. Inthe theGaug GaugLake Lakearea, area,foliations foliations are are generally generally steep and lineations lineations plunge The area area In plunge east east to to northeast. northeast. The encompasses enclaves enclaves of relatively low strain strain where where volcaniclastic volcaniclastic deposits deposits are are remarkably remarkably well well preserved. preserved. encompasses Thepresence presence of of outcrop-scale outcrop-scale D2, D2, and and D3 D3 or or later laterfolds, folds, suggests suggests that that atatleast leastsome someintercalation intercalationofoffelsic felsic The rocks and and iron iron formation formationisisdue duetotofolding. folding.The TheAgam AgamLake Lakefault faultforms formsaapronounced pronouncedeast-west east-westtopographic topographic rocks lineament,mainly mainlywithin withinmetasedimentary metasedimentaryrocks, rocks,but butlocally locallyjuxtaposing juxtaposingmetavolcanic metavolcanicand andmetasedimentary metasedimentary lineament, rocks. Evidence Evidenceof of an anearly earlyductile ductilehistory historyisisrecorded recordedininisoclinal isoclinalfolds folds and and aastrong strongstretching stretchinglineation lineation near near rocks. thefault faultzone. zone.Locally, Locally,rocks rocks preserve preserve mylonitic mylonitic textures, unusual unusual in that that straight straightgneiss gneissassociated associatedwith withlow low the angle angle faults faults(Di) (Dl)ininthe theinner innerbelt beltisismostly mostlyannealed. annealed.There Thereisisalso alsoevidence evidenceof oflater laterbrittle brittlemovement movementon onthe the Agam Agam Lake Lake fault fault(W. (W.Bates, Bates,Granges GrangesInc., Inc.,pers. pers.comm., comm.,1992). 1992). Theaccess access isis along along ATV ATV trails trails and andcat cattracks tracksleaving leavingfrom from the thebase baseof ofthe theManitouwadge Manitouwadgeski ski hill. hill. For For The those intending intending to use use an an ATV, ATV, the the ATV ATV trail trail starts starts from from the the road road about about500 500 metres metres east east of of the theski skihill hill those parking parking lot. lot. Note, Note,however, however, that that the thecat cattrack trackthat thatbranches brancheswest westtotothe theGranges Granges area areamay may not notbe besuitable suitable for forATVs. ATVs. The TheGaug GaugLake Lakearea areaitself itselfisisabout about1.5 1.5km kmbeyond beyondthe theski skihill, hill,and andthe thestops stops are arelocated located using usingthe the cut lines linesof of the the Granges Granges grid grid (metric (metric units). The Thecondition condition of of the the grid grid and and pickets pickets is variable and it is best to cut measure distance distancealong alongthe thecat cattrack trackinincase casesome somegrid gridlines linesare aredifficult difficultto tospot, spot,ororpickets picketsillegible. illegible. measure S t o pB2, B2,Deformed Deformed pillow basalt, ZB93-408.Beyond Beyondthe therope ropetow, tow,head headup upthe themost mosteasterly easterly ski skirun run Stop pillow basalt, ZB93-408. forabout about500 500metres metrestotowhere wherethe therun runcrosses crossesa apowerline powerlineclearing clearingnear nearsome somesmooth smoothsloping slopingoutcrops outcrops(Fig. (Fig. for B2). The Thepillow pillowbasalts basaltsbelong belongtotothe theouter outermafic maficmetavolcanic metavolcanic belt. belt. The Thepillows pillows are are small small (<0.5 ( ~ 0 .m) 5m)and and B2). flattenedwith withselvedges selvedgesand andinterstices intersticesdefined definedby bycoarse coarsegrained grainedhornblende hornblendeporphyroblasts porphyroblastsoriented orientedparallel parallel flattened totoschistosity. schistosity. S t o pB3, B3,Mafic Mafic schist, ZB93-382. Continue runabout about200 200metres metrestotothe thenext nextgood goodoutcrop, outcrop,more more Stop schist, ZB93-382. Continue upup thethe skiskirun typicalof ofmafic maficmetavolcanic metavolcanic rocks rocks in in the theManitouwadge Manitouwadgebelt. belt.Here, Here,medium mediumgrained grainedgabbroic gabbroicaugen augenschist, schist, typical possibly originally originally aa massive massiveflow flow or or base base of of aaflow, flow,grades gradestotolaminated laminated(1(1mm—i mm-1 cm) cm)fine finegrained grainedhighly highly possibly strainedmafic maficschist. schist.InInthe thehigh-strain high-strainzone, zone,layer layertruncations truncationsresulting resultingfrom fromboudinage boudinagehave have aasuperficial superficial strained 61 �B. Outer Outer volcanic volcanic belt Manitouwadge field guide Geology and and field-trip field-trip stops stops(B2—B10) (B2-BlO) ofofthe Dashed FIG. B2. Geology the Gaug Gaug Lake Lake area, area, outer outer volcanic belt. belt. Dashed lines are cut lines lines of the Granges Granges grid. grid. Structure Structuresymbols symbolsshow show dominant dominant D2 D2 foliations and lineations. resemblance to cross-bedding. Layering Layering also also shows subtle rootless isoclinal folds. The The layering layering looks somewhat tuffaceous, but but could be entirely of tuffaceous, of tectonic origin. origin. Return down the ski run to to the thepowerline powerline and and follow follow the rough Return down rough trail leading northwest northwest under under the line 200 metres Follow the crossing the stream at the the east east end end for 200 metres to to join join the ATV trail. Follow the ATV ATV trail trail to to the north, crossing continuing up Leave the of Gaug Lake Lake after after 1 km, and continuing up the hill on on the north side for 100 metres. metres. Leave the ATV ATV trail trail and take the cat track track (drill (drill road) road) heading heading west. The The cat cat track track crosses crosses cut lines (azimuth=OO) (azimuth=0°) of the 'central at 100 100 metre metre intervals, intervals, the the ATV ATV trail trail being being at at approximately approximately L5W. L5W. Granges grid' at Stop rocks and iron formation, S t o p B4, B4, Felsic Felsic metavolcanic rocks ZB93-366. Find L13W L13W on formation, ZB93-366. on the the cat cat track track at edge of a drill-site drill-site clearing clearing and continue on the northern edge and continue on the the line line to to 5+40N 5+40N (about 40 metres north of the clearing). The The stripped stripped patch patchofoffelsic felsicmetavolcanic metavolcanic rocks, rocks, and another another of of quartz-magnetite quartz-magnetite iron iron formation formation clearing). 25 metres to the the north-northeast north-northeast (15 (15metres metres east east of of L13W Ll3W at 5+65N), are typical of intercalated about 25 intercalated units in Continueeast east about about40 40metres metresin inrelatively relatively open open bush bush to to aa long long (20 (20 m) northeasterly trending ledge the area. Continue exposures of with excellent exposures of felsic felsic breccia. breccia. Angular Angular monolithologic monolithologicfelsic felsicclasts clasts(up (upto to 30 30 cm) cm) are supported darker matrix matrix rich rich in in garnet, garnet, horublende hornblende and biotite. The The large large size size and and angularity angularity of of the the clasts clasts is is in a darker and biotite. characteristic of proximal volcaniclastic deposits, Bates, Granges Granges Inc., Inc., characteristic deposits, possibly possibly fragmented fragmented by by phreatic (W. Bates, pers. comm., 1992) or hydrothermal explosions. The The abundance abundance of of calc-silicate calc-silicate minerals in the matrix matrix suggests suggests preferential synvolcanic alteration alteration of permeable unconsolidated matrix material. S t o p B5, B5,Felsic Felsicbreccia, breccia,mafic-felsic ma&-felsiccontact, contact, ZB93-367.OnOn track near L15W, monolithologic Stop ZB93-367. thethe catcat track near L15W, monolithologic felsic clasts are are similar, similar, except felsic breccia brecciaisisexposed exposedon onledges ledgesand andflat fiatoutcrops. outcrops. In In this this case, case, the the matrix and clasts that the thematrix matrixisismore morebiotitic. biotitic.U-Pb U-Pbzircon zircongeochronology geochronologyon onaasample samplefrom fromthis thisoutcrop outcropconstrains constrainsfelsic felsic 2722~t2Ma Ma (Fig. (Fig. 10), lo), within within error error of of the the mineralized mineralized sequence sequence in the volcanism volcanism in in the the outer volcanic belt to 2722±2 inner belt. 62 �Outer volcanic volcanic belt belt B. Outer Manitouwadge Manitouwadge field field guide guide On On L15W L15W immediately immediately south of of the the cat cattrack track(6+OON), (6+00N), there there are aremore moreexcellent excellent exposures exposures of of both both monolithologic cm) felsic felsic clasts clasts are are supported by aa monolithologic and heterolithic breccias. In Inthe thefirst firstcase, case,coarse coarse(2—10 (2-10 cm) matrix B4,suggesting suggesting preferential preferential alteration alteration matrixwith with variable variableamounts amountsof of hornblende hornblende and and garnet, garnet,again again as as at atStop StopB4, of of the the matrix. matrix. The Theheterolithic heterolithicbreccias brecciascontain containboth bothfelsic felsicand and garnet-hornblende-rich garnet-hornblende-rich clasts, clasts, the the latter lattersimilar similar The clast clast types types suggest suggest that thatthe theheterolithic heterolithicbreccias breccias represent represent to to the thematrix matrixofofmonolithologic monolithologic breccias. breccias. The erosion breccias, and and by implication, that erosion and redeposition redeposition of clasts and matrix matrix material materialof ofmonolithologic monolithologic breccias, alteration alteration of of matrix matrixmaterial materialpredated predatedits itsincorporation incorporationinto intoheterolithic heterolithic deposits. deposits. Continue ledge that that trends southerly Continue west west of of the grid grid line line about about 15 15metres metres to toaalow low west-facing west-facing ledge southerly for for about about 100 100 metres to to Leach Leach Lake Lake and and crosses crosses the the contact contact between between felsic felsic and and mafic mafic rocks. rocks. Initially, Initially,there thereisisaasequence sequence (north-to-south) (north-to-south) from from felsic felsic rocks, rocks, to to about about55metres metresofofweakly weaklyrusty rustyvery verymagnetic magneticsilicate silicateiron ironformation, formation, to clasts. The iron formation has about to heterolithic heterolithic breccias breccias again again with with felsic felsic and hornblende-garnet-bearing hornblende-garnet-bearing clasts. 25—35% garnetup upto to 1 cm, hornblende, 25-35% garnet hornblende, magnetite, minor grunerite grunerite and and disseminated disseminated quartz. quartz. Follow Follow the the ledge ledge to the the south south to toaasharp sharpcontact contactofoffelsic felsicrock rock and andmafic mafic schist, schist, the the latter lattertypical typicalof ofmost most of of the themafic mafic metavolcanic metavolcanic unit. Tightly Tightlyfolded folded tonalite tonalitedykes dykeshave have an an axial axialplanar planar foliation foliation parallel parallel to tothe theschistosity schistosity(D2) (D2) of of the the mafic mafic host rock. rock. The The folds folds and tonalite tonalite fabric fabric are are interpreted interpreted to to be be D2 D2structures. structures. Stop iron formation andand felsic rock, ZB93-409. thethecatcattrack foldofof iron formation felsic rock, ZB93-409.OnOn track3030metres metreswest west S t o pB6, B6,D3(?) D3(?)fold of 9W, a flat rock (volcanic or or subvolcanic) subvolcanic) and and a thin of Li LlgW, flat outcrop outcropconsists consistsof of homogeneous homogeneous white felsic rock thin (<1 (<I m) m) iron iron formation. formation. The Theiron ironformation formation and and aastrong strongfoliation foliation in in the the felsic felsic rock rock are both both deformed deformed by an isoclinal interpreted to be D3 of the the dominant (D2) fabric. fabric. The axial trace of isoclinal fold, interpreted D3 or later, based based on folding of of the limb, a 20-cm the fold fold is is subparallel subparallel to to the thedominant dominantfabric fabricin inthe thearea. area.On Onthe thesouthern southern limb, a 20-cmzone zoneofoffelsic felsicrock rock penetrates penetrates through through the theiron ironformation, formation, apparently apparently in in an an intrusive intrusive relationship. relationship. AAthin thin(10 (10cm) cm)concordant concordant strongly stronglyfoliated foliated tonalite tonalitedyke dykealso alsolies lieson onthe thefold foldlimb. limb. Stop dyke, garrietiferous mafic rocks, ZB93-336. Outcrops lielienear S t o pB7, B7,Folded Foldedzoned zonedgabbroic gabbroic dyke, garnetiferous mafic rocks, ZB93-336. Outcrops nearL21W L21W and the thecat cattrack, track,and andnorth northononL21W L21Wnear near6+90N 6+90N(15 (15mmfrom fromtrack), track),the thelatter latterananexcellent excellentpavement. pavement.The The and immediate area area isisdominated dominatedby byfelsic felsicrock, rock,locally locallybreccia breccia with with recessive recessive weathering weathering clasts clasts (up (up toto1010cm). cm). immediate The The felsic felsic rock rock is is cut cut by byaafolded folded(D2?) (D2?)composite-zoned composite-zoned gabbroic gabbroic dyke dyke (1.25 (1.25 m m in in width). width).The Thedyke dykedefines defines an an asymmetric asymmetricfold fold in in which which the the northern northern limb limbcuts cutsacross acrossthe thelocal localdominant dominantfoliation, foliation,and andthe thesouthern southernlimb limb generally concordant. concordant. Foliation Foliation in the the dyke dyke is is parallel to that that ininthe thehost. host.The Thesouthern southernlimb limbshows showssome some isis generally odd features; features;the thedyke dykeisisapparently apparentlyrepeated repeated against againstthe thesouthern southernlimb limbininwhat whatlooks lookslike likeaasinistral sinistraloffset. offset. odd The Thecomposite composite and and zoned zoned nature natureofofthe thedyke dykeare arealso alsounusual, unusual,asasisisthe thepresence presenceofofananintermediate-mafic intermediate-mafic dyke dykein inthe thefelsic felsicrocks. rocks. Continueon onthe thecat cattrack trackabout about5050 metreswest westofofL21W, L21W,crossing crossingthe thecovered coveredcontact contactinto intomafic maficrocks. rocks. Continue metres The first first exposure exposure isisof of rusty rustygarnetiferous garnetiferous (25% (25% to to 22cm), cm),locally locally strongly strongly magnetic, magnetic, mafic mafic rock. To Tothe the The west and andsouthwest, southwest, the themafic maficrock rock isisstreaked streaked with with quartz quartzveinlets veinletsand andmottled mottledwith withirregular irregularepidosite epidositeand and west bleached patches. patches.Buff Buffleucotonalite leucotonalitedykes dykescontaining containingsome somemafic maficinclusions inclusionsare are tightly tightlyfolded folded(D2) (Dz)and andhave have bleached thickened thickened hinges. hinges. S t o pB8, B8, Deformed pillow basalt, ZB93-337. Continue metreswest westofofL24W L24Watat3+50N 3+50N(160 (160 mm Stop Deformed pillow basalt, ZB93-337. Continue to to 1010 metres southof ofthe thetrack) track)totoa alarge largestripped strippedoutcrop, outcrop,unfortunately unfortunatelymossing mossingover. over.The Thefine finetotomedium mediumgrained grainedmafic mafic south rock has haspillows, pillows,0.4—1 0.4-1 metres quartz-rich, selvedges. selvedges. A A few few pillow pillow shapes shapes give give hints hints of of rock metres in in length, length, with rusty, quartz-rich, northerly northerlyyounging, younging,but butthe thepillows pillowsare arestrongly stronglydeformed deformedand andsome someselvedges selvedgesdefine definelocal localS-folds. S-folds. Tenmetres metreswest westof ofL24W L24Watat3+1ON, 3+10N, on on aastripped strippedoutcrop, outcrop,mafic maficrocks rocksand andtonalite tonalitedykes dykesdefine definetight tight Ten folds (D2) (D2) with with straight straightlimbs limbsparallel paralleltotoschistosity. schistosity.About About15 15metres metresfurther furtherwest, west,the themafic maficrock rockcontains contains folds minor (<10%)garnet. garnet. minor (<10%) S t o pB9, B9,Unusual Unusual magnetic rocks, ZB93-338. Continue southononL24W L24Wtoto2+75N 2+75N to to aastripped strippedoutcrop outcrop Stop magnetic rocks, ZB93-338. Continue south about30 30metres metres west west of of the the line. line. These Theseare areunusual unusual and andenigmatic enigmatic rocks. rocks. To To the the north, north,about about33metres metresofof about fine grained grained rusty rusty intermediate intermediate rock rock has has thin thin (<15 (<I5cm) cm)dykes dykesof of 22types; types; irregular irregular boudinaged(?) boudinaged(?) gabbroic gabbroic fine dykes and, and,hybrid hybrid dykes dykescontaining containing 30% 30% tonalitic tonalitic streaks streaks and andpatches patcheswith withhornblende hornblendeporphyroblasts, porphyroblasts, inin dykes gabbroic matrix. matrix. The Thetextures texturesofofhybrid hybriddykes dykesresemble resemble those those of of magma magma mixing. mixing. To To the the south, south,about about66 aagabbroic metres rock containing 20—80% metresisisexposed exposedofofvery veryheterogeneous heterogeneousmagnetic magnetic rock(hornblende-clinopyroxene-bearing) (hornblende-clinopyroxene-bearing) containing 20-80% ovoid ovoid or or annular annular dark dark1-cm 1-cmspots spotsininaaleucocratic leucocraticmatrix. matrix.The Thespots spotsconsist consistofofhornblende-magnetite hornblende-magnetite cores cores orrings ringsininaafelsic felsicmatrix. matrix.Could Couldthese thesebe bemetaspherulites metaspherulitesorormetavarioles? metavarioles?Locally, Locally, the the spotted spottedrock rock grades grades or (northerly) to tosomething somethingthat thatlooks lookslike likeaafracture fracturebreccia breccia cut cutand andveined veinedby bydark darkmagnetite-rich magnetite-rich material. material. (northerly) Thedark darkmaterial materialisissimilar similartotosilicate silicateiron ironformation, formation,containing containingmagnetite, magnetite,grunerite(?) grunerite(?)and andminor minorpyrite pyrite The and andpyrrhotite. pyrrhotite. S t o pBlO, BlO,Again AgamLake Lake fault, ZB93-420.North Northofofthe thecat cattrack track(100 (100m) m) on onL27W L27W at at6+60N 6+60N isisaalarge large Stop fault, ZB93-420. outcroparea areanear neara astream streamononthe theAgam AgamLake Lakefault faultlineament. lineament.Laminated Laminatedtoto lensy felsicrocks rocksimmediately immediately outcrop lensy felsic southofofthe thestream streamhave haveintrafolial intrafolialisoclinal isoclinalfolds, folds,apparently apparentlysteeply steeplyplunging plungingto toboth bothwest westand andeast, east,possibly possibly south relatedtotoductile ductilemovement movementon onthe theAgam AgamLake Lake fault. fault. About About15 15metres metres to tothe thesouth, south,there thereisisaacontact contacttotomore more related 63 �B. Outer volcanic volcanic belt Manitouwadge Manitouwadge field guide intermediate to to mafic mafic rocks which are cut by by tonalite tonalite dykes dykes that thatdefine defineS-shaped S-shapedfolds folds (D2). (D2).Schistosities Schistositiesin in the host rock rock and and tonalite tonalite have have an an axial axial planar planar orientation. orientation. B11—B21. Hingeregion regionof oftthe Bll-B21. Hinge h e Manitouwadge synform near n e a r Swill SwillLake Lake In the folded in in the hinge region the Swill Swill Lake area, the the outer outer belt beltofofmafic maficand andfelsic felsic metavolcanic rnetavolcanic rocks is folded of the D3 map). The D3 Manitouwadge synform (Fig. B3, 1:25000 1:25000 map). The southernmost southernmostunit unitisisaathick thicksequence sequenceofofmafic mafic metavolcanic rocks that include include homogeneous schist, laminated and layered schist (tuffaceous?), and deformed pillowed flows. As As in in the Gaug pillowed flows. Gaug Lake Lake area, area, foliated foliated gabbroic gabbroic rocks, rocks, interlayered interlayered with the the fine fine grained grained mafic mafic schists, may be massive or bases bases of offlows, flows,ororsills. sills.High Highstrain strainzones zonesininmetagabbro metagabbro are are characterized characterized by by massive flows or grained homogeneous homogeneousschist schistand and cloud cloudthe the distinction distinction between between tectonic tectonic and and stratigraphic stratigraphic units. Highly fine grained Highly strained strained pillows pillows are are recognized locally and, and, in one location, location, deformed deformed pillow shapes suggest southerly younging. In view of the folding in the area, area, this thisisolated isolatedyounging younging determination determinationdoes doesnot nothave haveregional regionalsignificance. significance. Garnetiferous zones (less (less that that 15 rocks, particularly particularly near the northern 15 metres in width) occur in the mafic rocks, contact to units(compare (compareStop Stop Bl). Bi). Locally, to felsic—intermediate felsic-intermediate units Locally, garnet is is concentrated concentrated in inpillow pillow selvedges, selvedges, and just west and west of of Swill Swill Lake Lake (Fig. (Fig. B3), B3), aathick thickgarnetiferous garnetiferous zone zone is is associated associated with with minor minor exposures exposures of orthoamphibole-bearing rocks. In some zones are are discordant discordant to tectonic fabrics or are orthoamphibole-bearing rocks. some cases, cases, garnetiferous garnetiferous zones are concentrated along along the the traces traces of of fold fold hinges, hinges, suggesting suggesting synkinematic metasomatism. Within Withinthe thethick thicksequence sequenceofofmafic maficrocks, rocks,two two semi-continuous semi-continuousfelsic felsic units units are areuseful useful markers markersdefining definingmapmapscale symmetrical symmetrical and and asymmetrical asymmetricalfolds. folds. The The southern southern unit, up to to 50 50metres metres wide, wide, isis aahighly highlydeformed deformed monolithologic felsiclapilli lapillituff(?), tuff(?),with withfine finegrained grainedto to aphanitic aphanitic felsic felsic clasts clasts in a matrix monolithologic felsic matrixof ofmica micaschist. schist. The unit unit isisassociated associated with with thin, thin,discontinuous discontinuousexposures exposures of of iron iron formation formation and and locally locally hosts hosts disseminated disseminated pyrite and pyrrhotite. pyrrhotite. North Northofofthe themafic maficmetavolcanic metavolcanicrocks, rocks, fine fine grained grained felsic felsic to intermediate intermediate rocks are strongly deformed and commonly commonlylaminated. laminated. The dominance of hornblende hornblendeover overbiotite biotitesuggests suggeststhat that they they strongly deformed and dominance of had aa metavolcanic metavolcanic protolith. protolith. Felsic Felsic to tointermediate intermediaterocks rocksare areextensively extensivelyinvaded invaded by by foliated foliated tonalite, tonalite, which which dominates in the northeast. The dominant dominant D2 D2planar planarfabric, fabric,well well developed developed in in the the Swill Swill Lake Lake area, area, isis folded folded by the the D3 D3 Manitouwadge Manitouwadge synform. D2 folds folds with with axial axial planar planar fabrics fabrics are are preserved preserved locally locallyininthe the east. east. There is aa dramatic synform. dramatic westward westward in post-D2 post-D2 strain (Fig. B3), which transposes transposes all earlier fabrics. fabrics. High increase in High strain fabrics, best exposed exposed in synform, include include spectacular spectacular L>S L>S tectonites and the hinge region of the Manitouwadge synform, and folds folds with aa moderate moderate northeasterly plunge, plunge, parallel paralleltoto lineations. lineations. The The tectonites tectonites may, may,inin part, part, be the result northeasterly result of of transposition transposition of of D3 structures during on the western contact of supracrustal rocks D3 during deformation deformation focussed focussed on rocks with with the the Black Black Pic Pic batholith. The Two coarse diabasedykes dykescut cutthrough throughthe the area area (Fig. Two coarse grained, grained, plagioclase-megacrystic plagioclase-megacrystic diabase (Fig. B3). B3). The exposed and probably belongs to the Biscotasing swarm of of about 2167 Ma Ma northeasterly-trending dyke dyke is is well well exposed (Buchan et al., al., 1993). 1993). The Thelocation location of of the thenorthwesterly-trending northwesterly-trending dyke dyke isis inferred inferred from from one one outcrop outcrop exposure exposure Ma It probably probably belongs belongs to the the Matachewan Matachewan swarm of about 2454 Ma and aeromagnetic aeromagnetic and topographic trends. It (Heaman, 1988). (Heaman, 1988). in the the area are held by by Noranda Noranda Inc. Inc. in in the the northwest, northwest, A1 Al Turner Turner in in the the central central area, area, and Granges Granges Claims in Inc. in the east. east. Access Accessisis by by old old logging roads north of the Caramat Caramatroad roadleading leadingto toextensive extensiveareas areasof of variably variably overgrown clear cut. cut. Deep overgrown clear Deep streams streams and and washouts washouts on on most most of of the themain mainlogging logging roads roads severely severely limit limit vehicular vehicular access. Some outcrops f i r n e r claim claim group. To To reach reach the the access. outcrops are are located located using using aa cut cut grid (metric units) on the Turner Swill Lake Lake area, area, follow followthe the Caramat Caramat Road west west from Highway Highway614 614approximately approximately7.5 7.5km kmand andturn turn north north on on a logging road just just beyond beyond the landfill-site entrance entrance on on the the south side of of the the Caramat Caramat Road. Road. The Thefirst firstwashout washout logging road at at 0.8 0.8 km may or or may may not not be be passable; passable;ifif the theroad roadisiswet, wet,the theslope slopeon onthe thefar farside sideof of the thewashout washoutwill willprobably probably Continue north along along the the road. road. be greasy mud. Continue Stop flu, mafic metavolcanic At 750 750 metres metres north north of of the the first first Stop B l l , Folded m&c metavolcanicrocks, rocks,ZB93-2, ZB93-2, ZB93-P50. ZB93-P50. At washout, several several outcrops outcrops lie lie on on a small knoll washout, knoll to the the east, east,beginning beginning approximately approximately 80 metres metres from the mafic schist schist and foliated gabbro, road. The Themafic m d cmetavolcanic metavolcanic rocks rocks comprising comprising laminated laminated mafic mafic gneiss, gneiss, mafic S-foldswith withassociated associatedcrenulation crenulationcleavage cleavage are typical of of the the southern southern Swill SwillLake Lake area. area. Structures Structuresinclude includeS-folds (D3), a possible D2/D3 fold fold interference interferencepattern, pattern, ductile shear zones in in the the foliated gabbro with indeterminate (possibly dextral) shear sense, sense, and and brittle brittlefractures, fractures,typically typicallyfilled filled with with epidote epidote and andhaving havingdextral dextraloffset offsetin in plan view. view. B12,Felsic Felsicbreccia, breccia, ZB93-Pl75.Continue Continueanother another400 400metres metres northward northward along along the road road and then S t o p B12, Stop ZB93-P175. northeast across across a clear clear cut cut for for 200 200 metres metres to to the thelarge largelight-coloured light-coloured outcrop at at the thebase baseof ofthe thecliff cliff clearly clearly visible from from the the road. This visible Thisisisan anexcellent excellent exposure exposure of of the the southern southernfelsic felsic unit, unit,aahighly highlydeformed deformed but butwell well preserved mono1ithologic monolithologicfelsic felsicbreccia. breccia. AA geochemistry geochemistrysample samplefrom fromthis this outcrop, outcrop, prepared prepared by extracting preserved clasts and carefully avoiding be aa caic-alkaline calc-alkaline rhyolite, avoiding the the high high angle angle brittle brittle fractures, shows shows the the unit unit to be rhyolite, in in contrast to the the tholeiitic tholeiitic basalts basalts to to north north and andsouth. south.There Thereisisa afine, fine,streaky streakylineation lineationon onfoliation foliationsurfaces, surfaces, and small Z-folds Z-folds are common across the outcrop, although at at least leastone oneS-fold S-fold was was also also observed. observed. 64 �30 '- 1)2 —p" 1)2 23 Fold axial plane Fold axis. Z—asymmetry Fold axis, S—asymmetry foliation lineation axis, symmetrical Fold axis, unknown symmetry Cabbrolc interlayers Fold 14 S '-9. '• , L 3 0' 2YJ 23 '4 S "a •3i• 3, ".r •2 / 0.5 32 9 1.0 kn FIG. B3. Geology and field—trip stops (B11—B21) of the Swill—Mills Lakes area near the hinge region of the D3 Manitouwadge synform. Dashed lines are the cut lines of A. Turner's Swill Lake grid. 0 2+ '1 2+ �B. B. Outer Outervolcanic volcanicbelt belt Manitouwadge Manitouwadgefield field guide guide Stop lineation, ZB93-P71, P72. Return to to thethe road and S t o pB13, B13,Felsic Felsicbreccia, breccia,stretching stretching lineation, ZB93-P71, P72. Return road andcontinue continueanother another 200 200 metres, then follow follow a drill road branching branching to the southwest. southwest. After After about about 100 100metres, metres, take take the thenorthern northern fork fork of of the the drill drillroad road and andcontinue continuewesterly westerly 350 350 metres metres to to aalow low open open area areawhere where several several tracks tracks branch branch off off and northerly L7W. and the thedrill drillroad roadintersects intersectsL7W L7Wofofthe theTurner Turnergrid. grid.Continue Continue northerly(0100) (010')along along L7W.AtAt6+OOS 6+OOSand and about about 50 50metres metres to tothe theeast, east,the thesouthern southernunit unitofofmonolithologic monolithologicfelsic felsicbreccia breccia crops crops out. out. Note Notethe thepronounced pronounced stretching stretching lineation. lineation. The Thenorthern northernend endofofthe theoutcrop outcroparea areaisismafic maficschist. schist. Just Justwest westofofthe theline lineatat6+OOS, 6+OOS, the felsic felsic unit, unit, here here containing containing some some garnet garnet (rimmed (rimmed by by plagioclase) plagioclase) and and with with clasts clasts less less distinct, distinct,isisinterlayered interlayered with with rocks rocks of of more more intermediate intermediate composition. composition. The Thenorthern northerncontact contactwith withmafic maficschist schistisisexposed. exposed. Stop pillows, suiphidic felsic rocks, ZB93-P77—P78, Continue westerly S t o pB14, B14,Deformed Deformed pillows, sulphidic felsic rocks, ZB93-P77-P78,P82. P82. Continue westerly200 200metres, metres, following the crude drill road to outcrops along along north north side of of an open area following the to east-west-trending east-west-trending outcrops area just west west of of LOW. These are are the best LOW. These best preserved preserved pillows pillows that we we have have seen seen in in the the Manitouwadge Manitouwadge area, area, some some with with cusps cusps suggesting suggesting southerly southerly younging, younging, although although of of questionable questionable regional regional significance. significance. The The pillows pillows are are zoned zoned from from dark dark hornblende-rich hornblende-richselvedges selvedges to to lighter lightercores. cores. Walk Walk 50 50 metres metres north north to toaatrenched trenchedarea areaof ofrusty rustysulphidic sulphidic(mostly (mostlypyrite) pyrite)rocks rocksgrouped groupedwith withthe thesouthern southern felsic with plagioclase, biotite biotite and hornblende. In felsic unit. unit. The Thevery veryfine finegrained grainedsiliceous siliceous rocks rocks have have some layers with In aa second second trench, trench, visible visible to to the thenorthwest, northwest,felsic felsicrock rock isis intruded intrudedby byfoliated foliatedleucocratic leucocratictonalite. tonalite. Continue and an outcrop Continue northeast northeast from from the the trench, trench, finding finding LOW L9W and outcrop that that crosses crosses the theline linenear near6+50S. 6+50S. The The exposure exposure shows shows aa contact contact between between very very highly highly deformed deformed (mylonitic), (mylonitic), garnet-bearing garnet-bearing felsic felsic breccia and garnet-rich mafic maficschist. schist. garnet-rich Continue LlOW, 6+50S and another another exposure exposure of of the the felsic felsic breccia of the southern southern felsic felsic unit, unit, in in Continue west west to to L1OW, this this case, case, represented represented by by aaribbon ribbonmylonite. mylonite.Strongly Stronglyelongate elongateclasts clastsare arestill stillrecognizable recognizabledefining definingaalineation lineation that that plunges plungesmoderately moderately to tothe thenortheast. northeast.As Aspreviously, previously,garnet garnet tends tendstotobe berimmed rimmedby byplagioclase. plagioclase. Stop in metagabbro, ZB93-P81. Follow L1OW ZB93-P81. Follow L10Wnorthward northwardtotoananoutcrop outcropwest west of of S t o pB15, B15,High Highstrain s t r a izones n zones i n metagabbro, the of metagabbroic metagabbroic layers layersin inthe the thick thick mafic maficsequence. sequence.In In the the transition transition to theline lineatat6+OOS, 6+OOS, a beautiful example of high high strain strainzones, zones,the thegabbro gabbroisismedium mediumtotocoarse coarsegrained, grained,foliated foliatedand andcontains containshornblende hornblendeporphyroclasts. porphyroclasts. In In zones zones of of high high strain, strain,the thetextures texturesand andfabrics fabricsare aresimilar similartotothose thoseofofthe thefine finegrained grainedhomogeneous homogeneous mafic mafic schist schist common common throughout the thearea, area,suggesting suggestingthat thatsome someofofthe thehomogeneous homogeneousmafic mafic schist schist may maybe behighly highly strained metagabbro. metagabbro. strained Stop hinge of of thethe Manitouwadge synform, ZB93-P151, S t o p BiG, B16, Symmetrical SymmetricalM-folds M-foldsininthe the hinge Manitouwadge synform, ZB93-P151,P135. P135. Continue Continue north north on on L1OW L10W about 200 200 metres metres until until ititintersects intersectsaalogging loggingroad. road. Note Note in in passing passing the themafic mafic metavolcanic metavolcanic rocks and metagabbro along along the way. way. Follow Follow the road road west west for for 700 700 metres to to where where the the main main road road makes makes aa broad broad turn turntotothe thenorth northand anda aside sideroad roadcontinues continueswestward. westward.Follow Follow the the side side road road for for about about 60 60 metres metres and and then thentake takethe theright-hand right-handnorthwesterly northwesterly(less (lesstravelled) travelled)fork forkfor for300 300 metres metres to toaasmall smallpavement pavement on on the the south southside sideof of the thetrail. trail.The Thefirst firstoutcrop, outcrop,intended intendedasasvery verybrief briefstop, stop,isisdominantly dominantlyhomogeneous homogeneousfine fine grained, grained, mafic mafic schist (highly (highly strained strained gabbro?) gabbro?) with withan aninclusion inclusionof oflayered layered quartz-magnetite quartz-magnetiteiron ironformation, formation, both cut cutby byfoliated foliated granite. granite. both Continue metresto toan anoutcrop outcrop area area extending extending south of the road. Continuewest west along alongthe thetrack trackfor for100—120 100-120 metres road. The Thearea area lies lies in the the hinge hinge region region of the Manitouwadge Manitouwadge synform. Garnetiferous Garnetiferous mafic mafic metavolcanic rocks are interlayered with with rocks rocks of more intermediate intermediate composition. composition. The Thelayering layeringand anddominant dominantfoliation foliation(D2) (D2)are areextensively extensivelyfolded, folded, mostly although some some S-folds S-foldsoccur occuratatthe the northern northern end of the outcrop mostly into into symmetrical symmetrical M-shaped M-shaped D3 D3 folds, although area. area. Some Somelayers layers have have abundant abundantcoarse coarse(cm-scale) (cm-scale)magnetite magnetiteporphyroblasts. porphyroblasts. Stop folds and lineation, ZB93-P134 (optional). Continue 150—170 S t o pB17, BIT,Felsic Felsicrocks, rocks,D3D3 folds a nstrong d strong lineation, ZB93-PI34 (optional). Continue 150-170 metres metres west metressouth south of of the the track, climbing over over logs logs and and brambles brambles to find the west of of Stop Stop B16 B16 and and30—40 30-40 metres the outcrop. outcrop. Felsic intercalated with Felsic metavolcanic rocks belonging to the northern northern felsic felsic unit of of the the Swill Swill Lake area are intercalated with more more intermediate intermediate hornblende-bearing hornblende-bearing rocks. rocks. Tight Tightfolds folds (D3) (D3) of of the the dominant dominant foliation foliation (D2) (D2) plunge moderately to the the northeast, northeast,parallel parallel to toaavery very strong strongstretching stretching lineation. lineation. Stop rocks and ZB93-P154, P155, ZB94-84. Return S t o pB18, B18,D3 Dafolds foldsofofmetavolcanic metavolcanic rocks a ngranite, d granite, ZB93-P154, P155,ZB94-84. Returneast east(about (about 550 m) to where the main road turns turns north. north. Continue Continuenorthward northwardfor for220 220 metres metres to to aa westerly westerly branching track. Follow the track for 150 Follow the 150 metres to to the thetop topofofaahill hilland andextensive extensiveoutcrops outcropsofofstrongly stronglylineated lineatedand andfolded, folded, plagioclase-hornblende-bearing intermediate metavolcanic metavolcanic rocks. rocks. From From the the hill top, continue northerly to plagioclase-hornblende-bearing intermediate to the the base of the steep steep north north slope, slope, then then head headwesterly westerly (about (about 300 300 m) m)in inthe thelow lowcleared cleared area, area,keeping keeping the the slope slope and and log log piles to your your left. You You are are heading heading for for the the top top of of aa low low hill, hill, on the the southeast southeast side sideof of which which lies a small clean clean pavement visible in the distance. distance. The Thehill hillisisabout about200 200metres metres north northofofaalong longwood wood pile. pile. Intermediate rocks. Many Intermediate metavolcanic metavolcanic rocks rocks are dominant, dominant, thinly thinly interlayered interlayered with magnetite-rich mafic mafic rocks. tight folds folds (D3) (Da) reorient reorient the the foliation foliation (D2) (D2) and and plunge plunge northeasterly, northeasterly, parallel parallel to to aavery verystrong strongstretching stretching lineation. At and 30—40 Atthe thesouthern southernend endofofthe thehill hilltop, top, and 30-40 metres metreswest, west,mafic mafic metavolcanic metavolcanic rocks rocks and sheets sheets of foliated granite granite are are both bothinvolved involvedin inoutcrop-scale outcrop-scaleM-folds. M-folds. The Themafic maficrock rock has hasaastrong strongfolded foldedschistosity schistosity 66 �C. Dead Dead Lake Lake suite suite Manitouwadge field guide (D2), and a moderately developed axial axial planar fabric. fabric. The granite forms sheets parallel to the D2 D2 schistosity of the host rock and its of its most most obvious obvious fabric is axial planar to to the the D3 D3folds. folds. in an an attempt to The granite, interpreted as aa pre-D3 pre-Ds intrusion, was collected collected in to bracket bracket the theage ageof of D3 D3 Analyses of ofzircon zircongave gaveaascatter scatter of of discordant discordant points, points, whereas whereas titanite deformation by U-Pb geochronology. geochronology. Analyses defines an an age age of of 2655h3 2655±3 Ma Ma (Table 2), within error of of the the age age of of titanite titanitefrom fromaasyn-D3 syn-Datonalite tonalitedyke dykeless less defines and also within error error of of titanite from Lake pluton. pluton. The circa Ma than aa kilometre kilometre away, away, and also within from the Loken Loken Lake circa 2655 2655 Ma titanite. titanite ages ages are interpreted as as dating dating aa late late hydrothermal hydrothermal event that that crystallized crystallized or recrystallized recrystallized titanite. Stop metavolcanic rock, ZB93-P157 intermediate metavolcanic rock, ZB93-P157(optional). (optional).Retrace Retracethe theroute route B19, Lineation Lineationininintermediate S t o p B19, eastward to the main large wood wood pile pile and eastward main road. road. Continue Continue northward northward along along the the main main road road for for 200 200 metres metres to to aalarge metres to to a small clean clean outcrop on the south side an easterly branching side road. Follow Follow the side road for 70 metres of the the road. Thin of Thinstreaky streakyhornblende-rich hornblende-richand andfelsic felsiclayers, layers,and andthe thedominant dominantfoliation foliation(D2), (D2),define definesmall smallfolds folds (D3) with a weak weak Z-asymmetry. Z-asymmetry. A A beautiful beautiful lineation, lineation,strongly strongly developed, developed, plunges plunges northeasterly northeasterly parallel parallel to to fold axes. axes. Stop ZB93-4, S t o p B20, B20, Garnetiferous Garnetiferousmafic maficrocks, rocks,diabase, diabase, ZB93-4,P54. P54.Return Return(south (southand andthen then east) east) along along the main road for about 1.5 1.5 km, km, crossing crossing a narrow narrow deep washout washout and stream just before before intersecting intersecting a major major northwest-trending logging logging road. road. This is the road northwest-trending road on on which which the the vehicle(s) vehicle(s) are are parked parked somewhere somewhere (depending how many many washouts washouts were werenegotiated) negotiated)to to the the south. Cross follow how Cross the the intersection intersection with with the themain mainroad, road,and andfollow by the deep long gully gully that that has the road road leading leading uphill and northward, northward, also also identifiable identifiable by has been been eroded eroded into into it. it. After 150 metres, metres, the the road road curves curves to to the the east. Continue to the end of the road where it branches to the east east of Swill SwillLake. Lake. The The southeast southeast branch branch leads leadsto to aa trench trench 50 50 metres metres distant. The and south, 150 150 metres metres west west of The stripped outcrop outcrop area areaand andtrench trenchare aredominated dominatedbybydark darkmafic maficmetavolcanic metavolcanicrocks rockswith withgarnetiferous garnetiferouszones. zones. cmwidth, width,that that anastornose anastomose through through the the dominant foliation while while Garnet is is most most abundant abundantininseams seamsof of10—30 10-30 cm maintaining a generally cm in in diameter, and generally concordant concordant orientation. orientation. Grain Grainsize sizeranges ranges from from pinhead pinhead to to1—2 1-2 cm shape from equant to &type tails tails indicate indicate aanorth-side-up to lensoid, lensoid, parallel to foliation. In thin thin section, section, 6-type north-side-up shear shear sense with a slight of motion motion (also (also discernible discernibleon onoutcrop). outcrop). The abundance of of garnet garnet sense with slight sinistral sinistral component component of implies metasomatic alteration of of the the mafic mafic protolith; protolith; however, however, relationships between between tectonic fabrics, garnet porphyroblasts and anastomosing seams are are most most consistent consistent with with synkinematic synkinematic alteration alteration and anastomosing garnetiferous garnetiferous seams garnet crystallization. crystallization. Walk southeast to the outcrops in in the vicinity of the beaver Walk southeast the shore shore of of Swill Swill Lake. Lake. Water-washed Water-washed outcrops vicinity of beaver dam are dominated dominated by by coarse coarsegrained grained diabase diabasewith withmegacrysts megacrystsofofplagioclase, plagioclase,one one of of many manyexposures exposuresof of the thewide wide northeast-trending dyke dyke that thatcuts cutsacross acrossthe theSwill SwillLake Lake area. area. Return to to the the branch branch in in the theroad road and, and,just justwest west of of the thebranch, branch, head head south south on on L1W L1W to to aa small small outcrop outcrop 25 25 metres west schist with with minor minor garnet garnet is interinterwest of the line at at 0+75S. 0+75S. Dark Dark fine fine grained grained hornblende-plagioclase hornblende-plagioclase schist calated with schist. This is is one one of of with lighter-coloured lighter-coloured orthoamphibole-cummingtonite-plagioclase-garnet-biotite schist. the few orthoamphibole-bearing orthoamphibole-bearing rocks in the Swill Lake Lake area area and and suggests aa link link with with similar similar orthoamphiboleorthoamphibolenear Manitouwadge Manitouwadge Lake bearing rocks rocks to the east near Lake (e.g. (e.g. Stop Stop Bl). Bi). Stop metavolcanic rocks, ZB93-P179. metavolcanic rocks, ZB93-P179.Return Return5050metres metrestotothe theroad roadand andhead headwest, west, S t o p B21, B21, Intermediate Intermediate then follow follow L5W several outcrops then L5Wnorth north to to 2+25N 2+25N and and several outcropsscattered scatteredabout about35 35metres metreswest westofofthe the line. line. The rocks vary vary from from thinly thinly layered layered to to laminated and, are Uintermediate metavolcanic metavolcanic rocks are locally locally quite quite felsic. felsic. The TheUshaped northwestern part of the outcrop area may may be aa D2 D2 fold, based observation that shaped fold fold in in the northwestern based on on the observation that it folds layering, layering,whereas whereasthe the dominant dominantfoliation foliationappears appearsto to be be axial axial planar. planar. An interesting with straight folds interesting dyke, with sharp margins, cuts across across foliation in the southern southern part part of of the theoutcrop outcroparea. area.ItItcontains containspillow-like, pillow-like,medium medium mafic blobs blobs in in aa leucocratic leucocratic matrix matrix dominated grained, hornblende-rich hornblende-rich mafic dominated by microcline microcline and plagioclase. plagioclase. The dyke can can be be traced for about 200 200 metres to the the east-northeast east-northeast and andthere thereare aresimilar similarexposures exposures south south of of Swill Swill Lake. C. Inner Inner Manitouwadge Manitouwadge synform, Dead Lake suite The Dead foliated gabbro, diorite, and Dead Lake Lake suite suite comprises comprises aa complex complex association association of interleaved foliated and laylayered mafic grouped with with mafic ered mafic to intermediate intermediate rocks rocks of of probable probable supracrustal supracrustal origin origin collectively collectively grouped mafic to interintermediate metavolcanic metavolcanicrocks rocksofofUnit Unit5.5. The suite mediate suite can can be be mapped mapped in in atatleast leasttwo twonearly nearlycontinuous continuouszones zones within the within the Manitouwadge Manitouwadge synform synform corresponding corresponding to to high high variable variableaeromagnetic aeromagnetic relief relief (1:25000 (1:25000 map). map). It hornblendeincludes a group of distinctive homogeneous homogeneous or layered, strongly magnetic rocks rocks characterized characterized by by hornblendemagnetite±plagioclase±garnet±clinopyroxene±sulphide minerals mineralswith with variable variableamounts amountsofofquartz quartz (minor (minor to to magnetite&plagioclase&garnet&clinopyroxene&sulphide in eyes eyesor orlenticules. lenticules. Layered Layered varieties, varieties, in in particular, particular, resemble metamorphosed iron formation 50%), commonly in or ferruginous ferruginous chert; however, however, their their geochemical geochemicalcomposition composition(high (highFeOt, FeOt,TiOz Ti02 and and Zr) Zr) suggests sedimentary sedimentary concentration of heavy minerals. The The extent extent of of synvolcanic synvolcanic trondhjemite trondhjemite and andcomagmatic comagmaticrocks rocks in in the the inner innerManitouwadge Manitouwadgesynform synform is is not not easily answered answered on on the the basis of of outcrop outcrop and and petrographic petrographic observations. observations. At least some tonalite tonalite and granodiorite 67 �C. Dead Dead Lake Lake suite suite Manitouwadge field guide intruding the the Dead Dead Lake Lake suite suite isis texturally texturallyand andcompositionally compositionallysimilar similarto tosynvolcanic synvolcanic trondhjemite trondhjemite (Figs. (Figs. 23 23 and 24). However, However, most quartz-rich quartz-rich tonalites in the the area areahave have aahigher higher content contentof ofmafic mafic minerals, minerals, including including hornblende, than coarse grained (0.5—1 than those thosenear nearthe theWiliroy-Geco Willroy-Gecoarea. area.Some Someofofthe thehornblende, hornblende,present presentasas coarse grained (0.5-1 cm), randomly to moderately moderately oriented oriented poikiloblasts, poikiloblasts, appears appears secondary. secondary. The mafic rocks of of the Dead Dead Lake Lake suite suite are are tholeiitic tholeiitic basalts, basalts,geochemically geochemically very like like mafic rocks in the regard them to be inner and outer volcanic volcanic belts, with which which we we regard be correlative. correlative. The The two two zones zones of of the the suite suite are are indistinguishable and could couldrepresent representaastructural structural repetition. repetition. The structural relationship of the suite to the indistinguishable and relationship of the main main supracrustal supracrustalsequence sequencein inthe theManitouwadge Manitouwadgebelt beltisisbest bestexplained explainedby bysome somevariation variationon onaamodel modelinvolving involving major D2 D2 folds. folds. One One possibility possibility is that that the theentire entiresequence sequence between between the the Loken Loken Lake Lake pluton pluton and and the theBlack Black Pic batholith is is folded folded by the the D2 Dz 'Manitouwadge 'Manitouwadge syncline', syncline', the axial trace of of which which lies in metasedimentary metasedimentary rocks on the southern that the D3 Manitouwadge Manitouwadge synform (Fig. 5). This This model implies that theDead DeadLake Lake southern limb limb of of the the D3 suite is equivalent of the outer volcanic belt, and that equivalent to the the lower lower stratigraphic levels levels of volcanic belt, that trondhjemite trondhjemitepinches pinches out in of the the fold. Trondhjemite might might be be represented represented in in the outer belt in the the subsurface subsurface between between the two two limbs of of the the thin concordant units of map). A by some of of tonalite, for for example, striking through Gaug Lake (1:25000 (1:25000 map). second possibility is that that the thetwo twozones zones of of the the Dead Dead Lake Lake suite suite represent represent aa D2 Dz synclinal synclinal 'keel', 'keel', analogous analogous to to the the 'keel' of the D2 syncline' (Figs. (Figs. 55 and and 8). 8). This implies that the D; 'Manitouwadge 'Manitouwadge syncline' the Dead Dead Lake Lake suite suite isis equivalent equivalent screens included included in in trondhjemite trondhjemite in the Willroy-Geco area (and north to metavolcanic screens Willroy-Geco area north to toR.abbitskin Rabbitskin Lake) Lake) and the presence presence of a D2 anticlinal trace within the the trondhjemite. trondhjemite. The The Loken Loken Lake pluton, occupying the innermost area of the Manitouwadge Manitouwadge synform, is a biotite tonalite tonalite to long. It has aa strong to granite granite characterized characterized by by microcline microcline megacrysts, 5 to 15 cm long. strong tectonic tectonic fabric, fabric,commonly commonly represented represented by L>S tectonites. tectonites. The Theabundance abundanceofofmegacrysts megacrysts varies varies from from sparse sparse or or none none to to25%, 25%,although although near the to find find at least one the contacts contacts (based (based on on aeromagnetic aeromagnetic signature and mapping), it is usually usually possible to one megacryst depending depending on the the size size of the area exposed. Large Large areas of non-porphyritic rock, mainly more central to the the pluton, pluton,would would otherwise otherwise be be difficult difficult to to distinguish distinguish on outcrop outcrop from synvolcanic trondhjemite. However, However, the rocks Loken Lake Lake pluton plutonisissignificantly significantlyyounger younger atat2687+2/—3 2687+2/-3 Ma Ma rocks are are geochemically geochemically distinct, and and the theLoken (Fig. 16). Layering and the dominant dominant foliation foliation (D2) (D2) in the the Dead Dead Lake Lake area, including including foliations in the Loken Loken Lake axis (110°/250) (110°/25°), interpreted interpreted to to be the axis Lake pluton, are folded folded about an an east-southeasterly east-southeasterly plunging plunging axis axis of of the D3 synform. On this basis, the Loken Lake pluton pluton was was interpreted interpreted to be aa preD3 Manitouwadge synform. Loken Lake pre- to tosyn-D2 syn-Da intrusion. The Dead road north north from the Camp Dead Lake Lake area is reached reached by taking a logging logging road Camp 70 70 road road east east of of ManiManitouwadge. touwadge. The Camp Camp 70 70 road road intersects intersects the the Geco Geco mine road 22 km km east of of town, town, and and 11km km further, further,crosses crosses aa lumber lumber yard and railway railway line. Follow Follow the Camp 70 70 road for about about 99 km km from from the the railway railway line, line, crossing crossing the bridge across across the the Black Black River, River,passing passingaasign-posted sign-postedturn turnfor forTwist Twistroad roadand andaasand sandpit pit on on the the north, the bridge garbage dump dump and and you you will will latter about about 1.7 1.7km km before before the the logging logging road. The Thelogging logging road road also also leads leads to to aa garbage know you you made madethe the right right turn turn by by the garbage on the road road and to the west. know garbage on west. About About 300 300 metres metres north north of of the the turn and and on on the the north north side side of of the the dump, dump,aadirt dirtroad roadthat thatbranches brancheswest west totoWowun Wowun Lake Lake leads to Stop Stop Dl. Dl. Drive on past past the branch Drive on branch road road and and keep keep track track of of your your distance distance from it. Watch Watch out outfor forprobable probable washouts, washouts, hopefully negotiable with care. Stop ZB94-27. Continue Continue on on the logging road for for 6 km, winding around east C l , Loken Loken Lake Lake pluton, pluton, ZB94-27. logging road winding around S t o p Cl, Lake (not visible), making no no turns turns off off the the main main road road (1:25000 map). The stop is aa and north of of Wowun Wowun Lake visible), making (1:25000 map). low rocky rocky knoll knoll on on the the north side of the road, ditch. The low road, immediately immediately north of of the the water-filled water-filled ditch. The location location isis 400 metres metres east east of a railway (which you you will willnot not see see unless unlessyou youovershoot). overshoot). In In this exposure, 400 railway crossing crossing (which exposure, the Loken Lake Lake pluton pluton contains contains about 5% megacrystic megacrystic microcline microclineaugen, augen,ofofabout about 10 10cm cmin inlength, length, in in aa tonalitic Loken Thestrong strongsoutheasterly southeasterlyplunging plunging lineation lineation matrix with minor biotite and and trace trace amounts amounts of of hornblende. hornblende. The D2/D3?) is (L>S, composite composite Dz/D3?) is partly partly defined defined by asymmetrical asymmetrical (both oa- and 6-type, &type, Hanmer Hanmer and and Passchier, Passchier, 1991) tails tails on microcline augen. augen. Most of these are consistent with dextral, dextral, north-side-down, north-side-down, sense sense of rotation, rotation, show sinistral sinistral kinematics. kinematics. The conflicting rotations could could be due to variations although some show conflicting rotations variations in in the the original original orientation orientation of of long long axes axes of of phenocrysts. phenocrysts. C2, High Highstrain strain zone, contact t o Dead Lake suite, ZB93-360, ZB94-30.Cross Crossthe therailway railway at at 6.4 6.4 S t o p C2, Stop zone, contact to Dead Lake suite, ZB93-360, ZB94-30. continue on pavement outcrop of the road. km and continue on to 8 km stopping at aa pavement outcrop that extends from from the north side of This is the the first first exposure exposure of of the theDead DeadLake Lake suite, suite,here hererepresented represented by by interleaved interleaved white white quartzofeldspathic, quartzofeldspathic, intermediate (30—40% hornblende+biotite), and mafic (60—70% hornblende)layers, layers,0.5 0.5to to 30 30 cm cm in width. (3040% hornblende+biotite), (60-70% hornblende) width. Abundant to 3 mm, is concentrated in some some layers. layers. The Abundant magnetite, either fine grained grained or porphyroblastic porphyroblastic to concentrated in general appearance is that thatofofhighly highlyrecrystallized recrystallized and andcoarsened coarsened mafic mafic to tointermediate intermediatevolcanic volcanicrocks rocks with with tonalite sheets. sheets. rocky ledge ledge (3—4 (3-4 mmhigh) The Cross to aa rocky high)visible visibleabout about50 50metres metresaway awayon onthe the south south side side of of the the road. The very strong strong foliation foliation and and some some streaky quartz quartz ribbons, ribbons, could could be be aahighly highlystrained strained leucocratic tonalite, with aa very equivalent of either either synvolcanic synvolcanictrondhjemite trondhjemiteor or aa non-porphyritic non-porphyritic variety variety of of the the Loken Lake pluton. pluton. The equivalent of Loken Lake The presence of and magnetite magnetiteininsome somelayers layerssuggests suggests the the former. former. presence of pinhead pinhead garnet and 68 �C. Dead Lake suite Manitouwadge Manitouwadge field guide Stop rocks, ZB93-361, ZB94-108. qumtz-gmnet-magnetitehomblmde rocks, ZB93-361, ZB94-108. ConConS t o p C3, C3, Dead DeadLake Lakesuite, suite,quartz-garnet-magnetite-hornblende tinue to where the road bends to the just past the the southwest southwest (8.3 km) just the top top of of aa small small hill, hill, and and down down hill to aa gravelly area west westoff offthe theroad roadat at 99 km. km. The stop further along the road road on the first gravelly area stop is is 150 150 metres further first knoll knoll on the west west side, just beyond beyond aa swampy swampy area. area. Several Several rock rock types types are are exposed exposed including; including; 1) 1) strongly strongly magnetic, medium to coarse rock,locally locallywith withup upto to 50% 50% quartz quartz and coarse grained, grained, garnet-magnetite-hornblende-plagiocla.se garnet-magnetite-hornblende-plagioclase rock, minor sulphides suiphides and titanite, minor titanite, 2) 2) fine fine grained grained hornblende hornblende schist with with local local biotite biotite porphyroblasts, porphyroblasts, 3) 3) fine fine to to disseminated magnetite, magnetite, and 4) aa discordant medium grained, weakly weakly foliated, foliated, white white tonalite tonalitewith with2—5% 2-5% disseminated discordant pegpegmatite dyke. dyke. In Insome someplaces, places,quartz-garnet-magnetite-hornblende quartz-garnet-magnetite-hornblende rock forms a transitional transitional zone zone along along the the contact between hornblende hornblende schist schist and more leucocratic leucocratic rocks. rocks. The orientation of the dominant dominant fabric fabric (D2) (D2) and biotiteporphyroblasts porphyroblastsininhornblende horublendeschist schistlook look to to be defining is somewhat variable variable (038—075°/18—34°), (038-075°/18-340) and biotite a weak oblique foliation. From the south end of the outcrop, outcrop, climb climb up the hill hill to to several several outcrops along its crest about 80 80 metres west of of the road. quartz-garnet-magnetitewest road. The Therock rocktypes typesare aresimilar similartotothose thoselisted listedabove, above,with withmore morequartz-garnet-magnetitehornblende rock, rock, locally cut by weakly hornblende weakly foliated tonalite and forming forming angular angular inclusions inclusions in strongly strongly foliated foliated tonalite (trondhjemite?). (trondhjernite?). Biotite porphyroblasts porphyroblasts and selvedges selvedges in hornblende schist are developed developed mostly mostly might include include both both D2 and D3 folds, folds, the the near contacts with tonalite. tonalite. Tight Tightoutcrop-scale outcrop-scale folds folds of layering might with axial planes planes parallel parallel to to the the dominant foliation foliation (D2), (D2), and and the the latter latter with a weak weak axial planar fabric former with developed only in biotite selvedges developed selvedges at tonalite-hornblende tonalite-hornblende schist schist contacts. contacts. Stop rocks, ZB94-101. S t o p C4, Dead Dead Lake Lake suite, suite,layered layeredquartz-garnet-magnetite-hornblende qumtz-gmnet-magnetite-hornblende rocks, ZB94-101.Continue Continue south on the road, passing aajunction junction at at9.6 9.6 km km with with aa road road heading heading uphill to the west and, and, at at 9.9 9.9 km, km, reaching vehicles and and drivers. drivers. The next a muddy flooded stretch which may not be drivable drivable depending on water levels, vehicles stop, aa long of the road, is 450 long (150 (150 m) pavement pavement outcrop along the west side of 450 metres further on on and and worth worth a short hike. hike. The Theoutcrop outcropisisdominated dominatedbybyfine finegrained grainedhomogeneous homogeneous foliated foliated biotite tonalite tonalite with with some some thin (5 at the southern (5 cm) cm)concordant concordant aplitic aplitic layers. layers. On scattered scattered exposures exposures at southern end of of the the outcrop outcrop area, area, it isis possible possible to totrace tracea avery verymagnetic magnetic1—2 1-2 metre layer layer through aa series series of of complex complex folds. The Themagnetic magnetic layer of quartz, quartz, plagioclase, plagioclase,magnetite, magnetite,hornblende, hornblende,epidote, epidote,garnet garnetand andtitanite. titanite. The proportions layer consists consists of proportions of these minerals layering and and grading that minerals define define second-order second-order (cm-scale) (cm-scale) layering that looks lookslike likemodified modified bedding bedding and and suggests protolith. Locally, layer is is cut cut by diorite and pegmatite. Geochemical suggests a sedimentary protolith. Locally, the magnetic magnetic layer Geochemical analysis of addition to to high high FeOt FeOt (18.0%) (18.0%) and and CaO CaO (8.31%), (8.31%), analysis of a sample of of the magnetic layer shows shows that, that, in addition it is is relatively relatively high in Ti02 T i 0 2(1.36%) (1.36%) and and Zr Zr (2900 (2900 ppm). Ti02 T i 0 2and andZrZrare aretypically typicallyvery verylow lowininchemical chemical precipitates, their presence normally attributed to presence being normally to aa detrital detritalor orvolcanic volcaniccomponent. component. However, However, the high values here to the the enigma, enigma, values here may be more suggestive of of sedimentary sedimentary concentration concentration of of heavy heavy minerals. minerals. To add to preliminary of geochemical geochemical analyses preliminary interpretation of analyses of of quartz-garnet-magnetitehornblende quartz-garnet-magnetite-hornblenderock, rock,such suchas asthat that seen at Stop C3, and and hornblende-bearing hornblende-bearing trondhjemite, trondhjemite, suggest suggest that that these these represent represent synvolcanic synvolcanic trondhjemite trondhjemite by aa component component similar similar to to the the magnetic magnetic layer layer here. contaminated or altered(?) by diorite relationships, ZB943, ZB94-229. C5, Dead D e a dLake Lakesuite, suite,metagabbro, metagabbro,trondhjemite, trondhjemite, S t o p C5, Stop diorite relationships, ZB94-3, ZB94-229. Continue along the road 800 metres beyond the mud bath bath (10.7 (10.7 km km cumulative cumulative distance if you are still in your vehicle), to to another another extensive extensive outcrop outcrop in in the the ditch ditch on on the west. and tonalitic rocks rocks similar similar to to vehicle), west. Among dioritic and those seen at previous previous stops, stops, aavery very dark darkmafic maficvariety varietyof of magnetic magnetic hornblende-magnetite-plagioclase-garnet hornblende-magnetite-plagioclase-garnet rock Locally, the magnetic rock is veined veined by rock contains contains only minor minor amounts of of quartz. Locally, by fine and coarse grained grained felsic rocks, latter resembling resembling synvolcanic synvolcanic trondhjemite. felsic rocks, the the latter Continue south for another another 300 300 metres (11 km cumulative) to 100 metres Continue to another extensive outcrop outcrop about 100 west from the road road for for 50 50 metres. metres. The Therock rocktypes typesinclude; include;1)1)medium mediumtotocoarse coarsegrained grained long and stretching west metagabbro varying varying from from 80—90% 80-90% hornblende metagabbro hornblendetotoplagioclase-spotted plagioclase-spotted(30% (30%toto55mm, mm,phenocrysts? phenocrysts? or blasts?), fine to to medium medium grained grainedmagnetic magnetichornblende-magnetite-garnet hornblende-magnetite-garnet rock rock also alsolocally locallyplagioclase-spotted plagioclasespotted (up (up 2) fine 50%), 3) 3) fine fine to tocoarse coarsegrained grained trondhjemite, trondhjemite, 4) 4)fine finegrained grainedfoliated foliated diorite dioritewith with50% 50%hornblende hornblende and and to 50%), minor biotite porphyroblasts, and aplitelpegmatite. The Themetagabbro metagabbro isisinterpreted interpreted as asthe theoldest oldestrock; rock; minor biotite porphyroblasts, and 5) aplite/pegmatite. is cut cut by by trondhjemite trondhjemite and andboth bothmetagabbro metagabbroand andtrondhjemite trondhjemite are areengulfed engulfed by by foliated foliated diorite. diorite. Diorite Diorite it is contain local local inclusions inclusions of magnetic that the themetagabbro metagabbrolocally locallyhas hasnearly nearly5% 5% and trondhjemite contain magnetic rock. rock. Note that brown spots (1—3 (1-3 mm) section, looks looks like wormy aggregates. Although Although brown mm)ofoftitanite, titanite, which which in in thin section, wormy pods pods and aggregates. geochemically basalt, itit has hasrelatively relativelyhigh highTi02 Ti02(2.80%) (2.80%)and andanomolously anomolouslylow low geochemicallythe the metagabbro metagabbro is a tholeiitic basalt, Zr/Ti02. S t o pC6, C6,Foliated Foliatedgranodiorite, granodiorite, synvolcanic?, ZB94233. Continue southalong alongthe theroad roadfor for1150 1150 Stop synvolcanic?, ZB94-233. Continue toto thethe south metres metres (12.15 (12.15 km km cumulative), cumulative),just just 300 300metres metresnorth northofofthe thehairpin hairpinbend bendatatthe the southern southern end end of ofthe the road. road. An An outcrop area area stretches stretcheswest west of ofthe theroad roadfor for50—60 50-60 metres, coarse grained homogeneous homogeneous foliated metres, dominated by coarse granodiorite with disseminated disseminated magnetite porphyroblasts The strong strong porphyroblasts (up to 4 mm in size) and minor biotite. The foliation (D2) (Dz) undulates Therock rock isisrepresentative representative of of exposures exposures south from from here here foliation undulates in small folds and shears. The and, in texture, texture, and andgeochemical geochemical and andmodal modalcomposition, composition,resembles resembles synvolcanic trondhjemite, except for the the microcline. presence of of 10—15% 10-15% microcline. 69 �Eastern extension extension D. Eastern Manitouwadge Manitouwadge field guide D. Eastern extension extension of the t h e 'Geco 'Geco horizon' horizon' The The easternmost easternmost exposure, exDosure. of of what whatisislocally locallvcalled called the the'Geco 'Gecohorizon', horizon'.,crops crom outeast eastofofWowun WowunLake Lake . out near (1:25000map). map). Straight gneiss near the the Hucamp Hucamp zone zone of Lf subeconomic subkonomic mineralization mineralfzation (1:25000 gneiss in this this exposure exposure is is interpreted interpreted to tolie lie on on the thecontinuation continuation of ofthe theD1 Dl fault faultthat thatdissects dissectsthe theWillroy-Geco Willroy-Geco area area (Stops (StopsA3, A3, A6 A6 and and A20). A20). East East of ofthe theHucamp Hucampzone, zone,exposure exposure is is poor, poor, but but aaprominent prominentaeromagnetic aeromagneticanomaly anomaly continues continues on on the the same same trend, trend, and andthe the'Geco 'Gecohorizon' horizon'was wasintersected intersectedinindrill drillholes holes extending extending east east totothe theFalconbridge Falconbridgezone zone of of subeconomic mineralization. Orthoamphibole-garnet-cordierite mafic rocks rocks and and minor iron formation subeconomic mineralization. Orthoamphibolegarnet-cordierite gneiss, mafic east east of of Banana Banana Lake Lake (Noranda's (Noranda's East EastOne OneOtter Otterand andBanana Bananaclaim claimgroups, groups,Stops StopsD3—D4) D3-D4) are interpreted to to be be correlative correlative with the 'Geco horizon', horizon', but their structural structural relationship relationship is subject to to interpretation. interpretation. They Theyare are involved of map-scale map-scale folds, folds, that that also deform the the dominant foliation (D2), (D2), with aa northerly northerly trending trending involved in a series of enveloping surface. In In aa preliminary preliminary interpretation, interpretation, we we correlated correlated the the East East oOne Otter and enveloping surface. n e otter and Banana Banana zones zones with the the Falconbridge Falconbridge zone, zone, across across aa fault faultwith withsinistral sinistraloffset offset(Zaleski (Zaleskiand andPeterson, Peterson,1993b; 1993b;Peterson Petersonand andZaleski, Zaleski, 1994a). This model interpretation, as it implies that the model has ramifications ramifications to regional regional interpretation, the northern northern limb, limb,axial axial trace trace and and the theinner innervolcanic volcanicbelt beltofofthe thesouthern southernlimb limb(including (includingthe the'Geco 'Gecohorizon') horizon')ofofthe theManitouwadge Manitouwadge synform by the Blackman antiform and and the Jim synform (D3) are refolded refolded by Blackman Lake antiform Jim Lake Lake synform, synform, making making these latter latter D4 elements of of the preliminary D4 folds folds (see (see Structural StructuralGeology). Geology). Several Several elements preliminary model proved proved to be be problematic, problematic, among among them the thepostulated postulatedsinistral sinistralfault, fault,requiring requiring2.5 2.5km kmofofmap-view map-viewdisplacement, displacement,for forwhich whichwe wecould could find neither field nor aeromagnetic aeromagnetic evidence. evidence.In In our our preferred preferredrevised revisedmodel, model,the theEast EastOne OneOtter Otter and and Banana zones represent a D2 'keel', involved in in aa D2/D3 D2/D3 fold fold interference interferencepattern pattern along the the axial trace of the D2 synclinal 'keel', D3 map). This model allows for for aa simpler simpler more more elegant elegant interpretation interpretation D3 Manitouwadge synform (Fig. 5, 1:25000 1:25000 map). of the regional structure in that determine in which which the major folds that determine the the map map pattern patternofofthe thebelt belt(Manitouwadge (Manitouwadge synform, synform, Blackman Lake Lake antiform, antiform, Jim Jim Lake Lake synform) synform) are areall allD3 D3folds. folds. The Thefirst firsttwo twostops stops(D1—D2) (Dl-D2) are accessed from the logging road on the the east east side sideof of Wowun Wowun Lake, Lake, the thesame same road that C1—C6). thatwas wasused usedtotoaccess accessthe theDead DeadLake Lakesuite suite(Stops (Stops Cl-C6). The Thelast lasttwo twostops stops(D3—D4) (D3-D4) are areaccessed accessed by by continuing continuing east east on onthe theCamp Camp70 70road roadfor for1717km kmbeyond beyondthe theDead DeadLake Lakelogging loggingroad. road. D1—D2. Eastern inner inner volcanic volcanic belt, belt, 'Geco horizon' horizon' Dl-D2. Eastern Stop exposure of of thet h'Geco horizon', ZB93-P16. S t o p Dl, D l ,Easternmost Easternmostsurface surface exposure e 'Geco horizon', ZB93-Pl6.Take Takethe theCamp Camp70 70 road road and turn turnnorth northon ontotothe theDead DeadLake Lakelogging loggingroad road(see (seeC. C.Dead DeadLake Lakesuite, suite,for for more more detail), detail), after after300 300metres, metres, and turn turn west west off off the Dead Dead Lake Lake road on to aa dirt dirt road road around around the thenorth northside sideof of aagarbage garbage dump. dump. Drive Driveon on700 700 metres until until aapavement pavementoutcrop outcropisisjust just visible visiblethrough throughaastrip stripofofbushes busheson onthe thesouth southside sideof ofthe theroad road(1:25000 (1:25000 metres map). map). On Wowun Lake, Lake,an anattentuated attentuated sequence comprising comprising (north (north to to south); south); trondhjemite trondhjemite (synOn the the west west side of Wowun (synvolcanic), orthoamphibole-garnet orthoamphibolegarnet (or (orcummingtonite-garnet) cummingtonite-garnet)and andsillimanite-cordierite-biotite-garnet sillimanitecordieritebiotitegarnetgneisses, gneisses, volcanic), iron formation formation and metagreywacke, metagreywacke, crops the east east side side iron crops out out over over an an interval interval of of about about 200 200 metres. metres. Here, on the of Wowun Wowun Lake, 'Geco horizon' is marked by (north (north to tosouth); south);1)1)felsic felsicstraight straight of Lake, near near the Hucamp zone, the 'Geco thin (2 (2m) m)straight straightstreaky-layered streaky-layeredhighly highlystrained strainediron ironformaformagneiss containing containing some elongate elongate garnet, 2) aa thin gneiss tion, tion, 3) 3) <5 <5metres metresofofaahighly highlystrained strainedquartz-eye quartz-eyerock rock(possibly (possiblyquartz-phyric quartz-phyricfelsic felsicmetavolcanic metavolcanic rock) rock) with with fine grained grained garnet-magnetite in the the matrix, matrix, and and4) 4)rusty rustyfelsic felsic rock. rock. We We correlate correlate this high high strain strain zone zone with with fine interpreted D1 Dl fault fault in inthe theWillroy-Geco Willroy-Geco area. Throughout Throughout the theoutcrop, outcrop,there thereare areconcordant concordantfoliated foliated the interpreted Thedykes, dykes,although although plagioclase-porphyritic tonalite dykes, probably plagioclase-porphyritic tonalite dykes, probably belonging belonging to to a syn-D2 tonalite tonalite suite. The highly strained, strained, look look less less so than the the host host rocks. rocks. Note Notethe thesoutherly southerlydip dipofofthe thedominant dominantfoliation foliation(D2); (Dz);here, here, highly the the southern southernlimb limbofofthe theManitouwadge Manitouwadgesynform synformisisoverturned. overturned. S t o pD2, D2, Eastern Easterncontinuation continuation maficrocks rocksofof inner volcanic belt, ZB94-60.Return Returntotothe the Stop ofofmafic thethe inner volcanic belt, ZB94-60. Dead Lake Lake logging logging road, road, turn turnnorth northand andcontinue continuefor for650—700 650-700 metres east side side Dead metres to to an extensive outcrop on the east of coarse of the the road. road. The Thesouthern southernpart partofofthe theoutcrop, outcrop, coarsegrained grainedhomogeneous homogeneousfoliated foliatedtrondhjemite trondhjemitewith withlocal local magnetite and and biotite, biotite,isistypical typicalofofsynvolcanic synvolcanic trondhjemite. To To the the north, north,trondhjemite trondhjemiteisisinterleaved interleavedwith with magnetite mafic rocks rocks in a transitional transitional contact contact zone zone to to fine fine grained grained mafic mafic and laminated schist, the latter latter correlated correlated mafic with mafic mafic metavolcanic metavolcanic screens screens in the west. west. The Themafic maficschist schistlocally locallycontains containsplagioclase plagioclase with in trondhjemite to the porphyroclasts(?),possibly possibly derived derived from from dismembered dismembered veins, veins, and biotite biotite porphyroblasts, porphyroblasts, apparently apparentlydefining defining porphyroclasts(?), weak near-horizontal near-horizontal foliation. Stop Dl, Dl,layering layeringand and the thedominant dominantfoliation foliation (D2) (D2)dip dip moderately moderately to to aa weak foliation. As at Stop the the south. south. D3-D4. Orthornphibole-garnet-cordierite Banana area area D3—D4. Orthoamphibole-garnet-cordierite rocks, Banana The Banana Banana and and East EastOne OneOtter Ottergrid gridareas areasare aredominated dominatedby bymultiphase multiphase granitic granitic tototonalitic tonaliticrocks rocks The with variably variablydeveloped developed(mainly (mainlyweak) weak)fabrics. fabrics.AtAtleast leastsome someintrusive intrusiverocks rockscontain containabundant abundant ( 1 ~ 5 %disdis) with (1—5%) seminatedmagnetite magnetiteporphyroblasts porphyroblastsand, and,texturally texturally and compositionally (Figs. 23-25), resemble resemblesynvolcanic synvolcanic seminated and compositionally (Figs. 23—25), trondhjemitenorth northofofthe theWillroy-Geco Willroy-Gecoarea. area.Supracrustal Supracrustalrocks, rocks,including includingorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite trondhjemite rocks, mafic mafic metavolcanic metavolcanic rocks and iron iron formation, formation, are arepresent presentasasscreens screensand andinclusions inclusionsdefining defining aa narrow narrow rocks, (about 50 50m) m)zone zoneof ofmap-scale map-scale folds folds related related to to the theD3 D3Manitouwadge Manitouwadge synform (Fig. Dl). Dl). InIn our ourpreferred preferred (about 70 �D. Eastern Easternextension extension D. Manitouwadge Manitouwadgefield field guide guide FIG.Dl. Dl.Geology Geologyand andfield-trip field-tripstops stopseast eastofofBanana BananaLake Lakealong dongthe theeastern easterntrace traceofofthe theD3 D3 FIG. Manitouwadgesynform. synform. Dashed Dashed lines linesare are cut cutlines linesof of Noranda's Noranda's Banana Bananagrid. grid.Structure Structuresymbols symbols Manitouwadge show show dominant dominantD2 D2foliations foliationsand andlineations. lineations. D28ynform synform(Fig. (Fig.5). 5).Folded Foldedfabrics, fabrics,interpreted interpretedasas D2, structuralmodel, model,the the zonefollows followsthe thefolded foldedtrace traceofofa aD2 structural zone D2, are areeasiest easiestto tosee seeand andmeasure measurewithin withinthe thesupracrustal supracrustalscreens. screens.The Thearea areawas wasthe thefocus focusofofmineral mineralexploration; exploration; however, however, aa drill drillhole hole in in the theEast EastOne OneOtter Otterzone zoneintersected intersectedonly onlyminor minordisseminated disseminatedsuiphide sulphidemineralization, mineralization, and andgeophysical geophysicalsurveys surveysofofthe theBanana Bananazone zonefailed failedtotoshow showany anyconductive conductiveanomalies. anomalies. Fkomthe thejunction junctionwith withthe theDead DeadLake Lakelogging loggingroad, road,follow followthe theCamp Camp70 70road roadfor forabout about1717km kmeast eastand and From north, ofofThompson north,turning turningtotothe theeast eastatata junction a junctioneast east ThompsonLake Lakeonon aagravel gravelroad roadsign-posted sign-postedfor forHillsport. Hillsport. Continue easterly easterly for for about about 33 km, km, taking taking aa dirt dirtroad roadto tothe thesouth southwhere wherethe themain mainroad road bends bends sharply sharply to tothe the Continue north.Continue Continuesoutherly southerlyfor for33km, km,ininpart partalong alongthe theeastern easternshore shoreofofa alake lake(which (whichmight mightbebeflooding floodingthe the north. road),until untilaacut cutline line(running (runningdown downthe thehill hilltotothe theeast) east)intersects intersectsthe theroad. road.The Theline lineisisthe the7S7stie tieline lineofofthe the road), Bananagrid. grid.The Thefollowing followinglocations locationsare arereferenced referenced to tothe thegrid grid(metric (metricunits). units). Banana S t o pD3, D3,Mafic, Mafic,orthoainphiboleorthoamphibolecummingtonite-bearing ZB93-313-315. Follow TL7S Stop andand cummingtonite-bearing rocks,rocks, ZB93-313--315. Follow TL7S theeast eastuphill uphillforfor 160 metres LO, and north to some rocky knolls ledges from 6+00S totothe 160 metres to to LO, and LOLOtotothethe north to some rocky knolls andand ledges from 6+OOS toto3+75S this distance from south to to north, thethe sequence; 3+75Son onboth bothsides sidesofofthe thegrid gridline line(Fig. (Fig.Dl). Dl).Over Over this distance from south north, sequence; trondhjemite,orthoamphibole-bearing orthoamphibole-bearingrocks, rocks,hornblende-biotite±cummingtonite hornblende-biotite&cummingtonite mafic maficrocks, rocks,trondhjemite, trondhjemite, trondhjemite, isisexposed. exposed.The Thetrondhjemite trondhjemiteisismedium mediumtotocoarse coarsegrained, grained,contains containsmagnetite magnetiteporphyroblasts porphyroblastsand andisisgeochemgeochemically contains inclusions ofofdioritic-looking icallyindistinguishable indistinguishablefrom fromthe thesame sameunit unitininthe theWillroy-Geco Willroy-Gecoarea. area.It It contains inclusions dioritic-looking fine finetotomedium mediumgrained grainedmetabasite metabasite(about (about50% 50%hornblende-biotite) hornblend+biotite) that thatmay maybe becoarsened coarsenedmetavolcanic metavolcanicrock. rock. Granitic Graniticrocks rockswith withassociated associatedpegmatite pegmatiteare arealso alsocommon, common,apparently apparentlyrepresenting representingyounger(?) younger(?)intrusions. intrusions. At relatively At5+65S, 5+65S,there thereisisa acontact contacttoto relativelyleucocratic leucocraticrocks rockswith withcoarse coarsesprays sprays(to (to5 5cm) cm)ofoforthoamphibole orthoamphibole (or (orcummingtonite?), cummingtonite?),and andlocally locallybiotite, biotite,inina aquartz-plagioclase quartz-plagioclasematrix. matrix.Locally, Locally,orthoamphibole orthoamphiboleand andbiotite biotite defineaastrong strongeasterly easterlyplunging plunginglineation. lineation.The Theorthoamphibole orthoamphibolerocks rocksstrike strikesubparallel subparalleltotothe thegrid gridline line(00) (0') define definingthe thehinge hingeofofan anopen openeasterly easterlyplunging plungingfold foldwhich whichwe weinterpret interpretasasthe thehinge hingeregion regionofofthe theManitouwadge Manitouwadge defining synform.Orthoamphibole-bearing Orthoamphibole-bearing rocks rocks can can be betraced tracedtotothe theeast easttotoorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordieriterocks rocks synform. onthe thelimbs limbsofofthe thefold. fold.AtAt5+OOS 5+00S about about20 20metres metreseast eastofofthe theline, line,trondhjemite trondhjemiteand andgranite-pegmatite granite-pegmatite on 71 �Manitouwadge field guide E. Quetico, Jim Lake synform with abundant mafic (hornblende±cummingtonite) screens become dominant in the core of the fold until 3+80S. At 4+15S, a sample of fine to medium grained mafic schist (about 60% hornblende-curnmingtonite) has the major-element composition of a tholeiitic ferrobasalt, in contrast to mafic metavolcanic rocks from the supracrustal sequence to the west, which are high and low Mg tholeiites. The high Fe01 and presence of metamorphic cummingtonite may be due to alteration. At the base of the rocky hill at 3+80S, cummingtonite(+orthoamphibole?)-hornblende schists on the northern limb of the open fold strike at 070° and dip southerly underneath plutonic rocks, defining the northern limb of a synform. Stop D4, ZB93-287, Z894-93. Follow the trend (070°) of rocky ledges and knolls for about 130 metres to L1+25E, looking at the extensive exposures of orthoarnphibole-garnet-cordierite rocks. Plutonic rocks form the highest knolls to the south. The orthoarnphibole-garnet-cordierite rocks are coarse grained (locally with garnet to 10 cm and coarse orthoamphibole sprays) and heterogeneous with garnet-rich and orthoamphibolerich layering or enclaves (e.g. just west of L1+25E, 3+005). Garnet textures and distribution are fascinating, ranging to very coarse (to 10 cm) garnet porphyroblasts to fine grained garnetite, and local garnetiferous 'snakes' in an orthoaznphibole-riclj matrix. Locally, orthoamphibole-garnet-cordierite rocks are cut by irregular white veinlets (1—4 cm wide) characterized by quartz-sillimanite-garnet-cordierite. The margins to the host rock are diffuse and, although the veinlets have no systematic orientation and are discordant to the dominant foliation, the dominant foliation is found in both host rock and veinlet. The relationships suggest that the veinlets are the result of local channelling of metamorphic fluids. Orthoamphibole-garnet-cordierite rocks do not continue east of L1+25E beyond 40 metres; foliation trends indicate the presence of an antiformal hinge (Fig. Dl). At 2+755, on L1+25E and 20 metres to the west, plutonic rocks contain 2 layers (1 about S m thick) of an unusual strongly magnetic rock consisting of abundant (50%) quartz eyes in a matrixof fine grained magnetite, hornblende, clinopyroxene, garnet and minor plagioclase. The quartz eyes are monocrystalline, flattened and strained; locally, they are sufficiently abundant to coalesce into layers. The rock closely resembles quartz-garnet-magnetite-liornblende rocks of the Dead Lake suite, and possibly originated as a contaminated or altered quartz-phyric metavolcanic rock or trondhjemite. The quartz-eye magnetite-garnet rock tends to crop out to the east of orthoamphibole-garnet-cordierite rocks in the Banana area, including immediately to the east of the last exposure of orthoamphibole-garnet-cordierite rocks in the antiformal hinge. Orthoamphibole-garnet-cordierite rocks also crop out near L2+50E, 5+40S and L3-I-75E, 5+505 along the southern limb of the open fold. The road can be regained either by returning along tie line 75 or by continuing to base line 0 which also extends westerly to the road. Either of these routes crosses extensive outcrops of multiphase plutonic rocks, mainly magnetite-bearing trondhjemite and granite-pegmatite. E. Quetico subprovince, Jim Lake synform The Quetico subprovince in the Manitouwadge area is characterized by migmatitic biotite schists and metagreywackes, similar in texture, composition and depositional age, to those in the Manitouwadge belt (1:25000 map). The main difference is in metamorphic grade; rocks of the Quetico subprovince have been metamorphosed to granulite facies just north of the subprovince boundary and are extensively migmatized. Typically homogeneous or layered, they comprise biotite-plagioclase-quartz±garnet±cordieritethsilhimanite schist with extensive concordant, folded and cross-cutting tonalitic segregations. The dominant planar fabrics are interpreted to be correlative with D3 or D3 structures in the Manitouwadge belt. Northeasterly plunging Z-shaped folds of foliation, with a moderately developed, northeasterly striking axial-planar cleavage (in some cases, crenulation cleavage) are interpreted to be due to D3 deformation. Locally, the folds are associated with outcrop-scale structures (e.g. foliation fish) indicating dextral oblique shear. The D3 structures deform, and are cut by, migmatitic layers and veins, suggesting that D3 was approximately synchronous with peak metamorphism in the Quetico subprovince. The D3 Jim Lake synform is defined by mappable zones of mafic to intermediate metavolcanic screens and inclusions, with minor iron formation, enclosed in foliated to weakly foliated tonalite. Quetico metagreywackes can also be traced around the synform and along its southern limb as far as Larry Lake (1:25000 map). The Jim/Davis Lakes area lies near the hinge region, although most of the exposure lies along the southern limb and, in particular, near a map-scale 2-fold apparently parasitic to the Jim Lake synform. Quetico metasedimentary rocks in the Jim/Davis Lakes area are represented by migmatitic biotite schist with local thin iron formation. On the inside of the fold, northeast of Davis Lake, coarse grained trondhjemite to granodiorite resembles synvolcanic trondhjemite (Unit 12) in texture and composition (Figs. 23—25). South of the southern limb, foliated microcline porphyritic granitoid belongs to the Nama Creek pluton, which forms a sinuous body between supracrustal rocks and the Black Pic batholith folded by the Blackman Lake antiform. The Jim Lake synform is a tight fold and early fabrics are largely transposed and subparallel to the axial surface; however locally, dominant fabrics (D3) are folded around the hinge region and L-tectonites have a strong stretching lineation parallel to the axes of D3 minor folds. 72 �E. Quetico, Jim Lake Lake synform Manitouwadge field guide The The eastern eastern part partofofthe theQuetico Queticosubprovince subprovincein inthe theManitouwadge Manitouwadgearea areacan canbe beaccessed accessedfrom from the theHilisport Hillsport road (continuing from Stops Stops D3-D4). D3—D4).The Thesouthern southernlimb limbofofJim Jim Lake Lakesynform synformininthe the vicinity vicinity of of Jim Jim and road (continuing from Davis Lakes Lakes isis reached reachedby by continuing continuingto tothe the north north on the Camp 70 road beyond the Hillsport Hillsport junction east east of of Thompson Lake. El—E3.Quetico Quetico subprovince, subprovince, eastern eastern Manitouwadge Manitouwadge area area El-E3. S t o p El, E l ,Z-folds Z-foldsand a n kinks, d kinks, ZB93-P293.From Fromthe theBanana Bananaarea, area,return return 33km kmnorth north to tothe theHillsport Hillsport Stop ZB93-P293. road where where it curved sharply north north (1:25000 map). Continue Continue north north and and then northeast for road curved sharply (1:25000 map). for 4.5 4.5 km, turning turning right on to aa gravel right (southeast) (southeast) on gravel road. road. On On the thenorth northside sideofofgravel gravel road, road, 1.1 1.1 km km from from the the intersection, intersection, a pavement asediment ary rocks rocks shows showswell welldeveloped developedmigmatitic migmatiticlayering layeringparallel parallelto to aa fine finebiotite biotite foliation foliation pavement of of met metasedimentary (D2/D3). The The dominant dominant planar planar fabrics fabrics are areparallel parallel to tothe theaxial axialsurfaces surfacesof offolds foldswith with Z-asymmetry Z-asymmetry and, and, in in folded by by a kink (D4), also with Z-asymmetry. A coarse grained cordierite-bearing segregation one place, folded segregation cuts cuts discordantly across the outcrop. discordantly Stop indicators, ZB93-P294. Continue southeast ZB93-P294. Continue southeasttotoa alarge largepavement pavement outcrop outcrop S t o p E2, E2, Dextral Dextralkinematic kinematic indicators, north of the road road 1.7 1.7 km km from from the the intersection. intersection. The Themetagreywackes metagreywackes contain contain extensive extensive concordant and crosscrossD3, include include asymmetric asymmetric folds (most with cutting migmatitic segregations. Outcrop structures, interpreted interpreted as asD3, Z-asymmetry), foliation foliationfish, fish,rotated rotated boudins, boudins, and and incipient incipient shear shear bands, bands, all all indicating indicating a dextral sense Z-asymmetry), sense of of granitedyke dykeintrudes intrudessubparallel subparallelto to the the axial surfaces of D3 folds folds shear. A A coarse coarse grained grained muscovite—biotite muscovite-biotite granite of biotite schist, apparently rotated and has an axial axial planar planar foliation. foliation. ItItcontains containswall-rock wall-rock inclusions inclusions of rotated during during incorporation intruded during during incorporation into the dyke, dyke, and and folded folded migmatitic migmatitic schist. schist. The dyke dyke was interpreted interpreted as intruded progressive deformation late late in the metamorphic and anatectic progressive deformation anatectic history, history, hence, hence, contemporaneous with late late D3 D3 to D4. Zircon Zircon from from aa sample sample of of the the dyke dyke gave gave aa scatter scatter of ofdiscordant discordant analyses. analyses. AAsingle singleslightly slightlydiscordant discordant monazite grain with with an age of 2642±2 Ma (Table (Table 2), 2), is is difficult difficultto to interpret interpret in in isolation; isolation; itit could could date date the monazite grain 2642A2 Ma intrusion, or retrograde crystallization crystallization or resetting resetting of of monazite. Stop Z-folds, ZB93-P287. easy, but longish, S t o p E3, E3, Graded G r a d e layering, d layering, Z-folds, ZB93-P287.This This easy, but longish,walk walktotosee seea asingle singleoutcrop outcrop of of bedding) and spectacular graded layering (modified (modified bedding) spectacular folds folds in in Quetico Quetico metagreywacke metagreywacke is worth while, while, ifif time time permits. Return Return to tothe theHilisport Hillsportroad, road,turning turningsouthwest southwest to to retrace retrace the theroute routefor for 250 250 metres to an intersection road on on the north side with an overgrown overgrown road side of an an open open area. area. Walk Walk along along the theovergrown overgrown road north and and west west metres, crossing crossing aa small stream, stream, beyond which, continue south south 50 metres metres to an open area for 725 metres, area of of pavement pavement outcrop. The Theoutcrop outcropisisdominated dominatedby bylayered, layered,fine fine to to coarse coarse grained, grained, quartzofeldspathic quartzofeldspathic biotite biotiteschist, schist,locally locally with sillimanite and abundant abundantgarnet. garnet.Layers Layersofofmore morepelitic peliticcomposition compositionhave havemore moremigmatitic migmatiticsegregations. segregations. between the the coarse garnet-biotite-richtop(?) top(?) of A sharp folded contact (Z-asymmetry) (Z-asymmetry) between coarse garnet-biotite-rich of one layer, layer, and and the the quartz-plagioclase-rich of another, another, suggests suggests relict graded bedding with southward younging. younging. Folds Folds quartz-plagioclase-rich bottom(?) bottom(?) of various scales mostly mostly have Z-asymmetry Z-asymmetry and, locally, locally, are associated associated with an an axial axialplanar planarcrenulation crenulation on various cleavage. Folds Folds with with S-asymmetry S-asymmetry dominate dominateone onearea, area, indicating indicatingthat that the axial trace of cleavage. of aa larger larger scale scale fold fold crosses no closures closures are exposed. crosses the the outcrop, although no E4—E6.JJim Lakes area E4-E6. i m Lake synform, Jim/Davis Lakes S t o p E4, E4, Foliated Foliatedtrondhjemite, trondhjemite, ZB93-P270. From Hillsportjunction, junction,take takethe theCamp Camp70 70 road road northnorthStop ZB93-P270. From thetheHilisport westerly around the northern northern ends ends of of Thompson, Thompson, Loken Loken and Straight Straight Lakes Lakes (1:25000 (1:25000 map). At 77 km km beyond beyond westerly turn north northon onthe theJim JimLake Lakeroad; road;the thesingle-lane single-laneFox FoxLake Lake siding siding road road continues continues to the the west. west. the junction, turn Continue north Jim Lake Lake road, road, turning turning west west on on to to aagood gooddirt dirtroad roadwhich whichleads, leads, in in300 300 Continue north for 3.6 3.6 km on the Jim metres, area of of flooded flooded sand The road road isis visible visible beyond beyond the and metres, to an area sand pits. pits. The the flooded flooded area; area; it's it's best best to park and will be necessary (allowing for wade across as, 200 200 metres metres further further down the road, it will forthe the vagaries vagariesof ofnature) nature) to to 10 m m long). long). The Theroad roadcontinues continuesin in good good shape shape beyond beyond these these obstacles. obstacles. cross a beaver dam (less than 10 On the south south side side of of the the road, road,200 200metres metres west west of of the the beaver beaver dam, dam,aalarge largearea area(100 (100mmlong) long)of offiat-lying flat-lying outcrops consists of indistinoutcrops consists of homogeneous homogeneouscoarse coarsegrained grainedtrondhjemite trondhjemitewith with minor minor biotite biotite and magnetite, indistinguishable fabric is is foliated foliated to to gneissic gneissic and, and, guishable from from synvolcanic synvolcanictrondhjemite trondhjemiteinin the the Willroy-Geco Willroy-Gecoarea. area. The fabric deflected by by both both sinistral and dextral locally, deflected dextral minor minor shear shear zones. zones. S t o p E5, E5, Migmatitic Migmatiticbiotite biotite schist d iron formation, ZB94207. Continue alongthe theroad roadfor for540 540 Stop schist anda niron formation, ZB94-207. Continue along metres look for overgrown track 100 metres metres east low metres and and look for a very overgrown trackthat that heads heads off off to to the the south, south, about 100 east of a low Bushwack south for for 300 300 metres and and then thensouthwesterly southwesterlyfor for 100 100 metres metres following following the track, track, at at swampy area. Bushwack which point new growth is is very very thick. thick. Continue Continue westerly westerly about about 50 50 metres metres to toaalarge largeoutcrop outcrop(visible (visibleon on which point the new 37-15, Ministry road and and west west of of airphoto 90/2-4909 37-15, Ministry of of Natural Natural Resources, Resources, Ontario) Ontario) on on the the north side of the road small swamp. The Thebiotite biotiteschist, schist,containing containingpinhead pinhead garnet, garnet,was wasgrouped groupedwith withQuetico Queticometasedimentary metasedimentary a small rocks. Tonalitic Tonaliticleucosome leucosome is is more more abundant abundantininpelitic peliticlayers layersand andhas hasbiotite-garnet-rich biotite-garnet-richselvedges, selvedges,1—5 1-5 cm rocks. Leucosome apparently apparently shows shows 2 generations generations of of folding, folding, the of which which are east-southeasterly east-southeasterly in width. Leucosome the latest of plunging (121°/180 deform early plunging (121°/18°) folds foldsthat that deform early folds foldsand and have havean an axial axial planar planar biotite biotite schistosity schistosity (D3?). (D3?). Thin Thin (1-5 of iron formation, are (1—5cm) cm)rusty rustyquartzose quartzoselayers layerswith withminor minormagnetite magnetiteand andgrunerite, grunerite, the the remnants remnants of 73 �F. Black Black Pic batholith Manitouwadge field guide segmented and contorted in the the migmatitic migmatitic matrix. matrix. Leucosome Leucosome adjacent to to the the iron iron formation formationcontains contains some some coarse (to 11cm) cm) porphyroblasts porphyroblasts of of grunerite. grunerite. Stop formation, Nama Creek pluton, ZB94-197, ZB93-P281— S t o p E6, E6, Mafic Maficmetavolcanic metavolcanicrocks, rocks,iron iron formation, Nam a Creek pluton, ZB94-197, ZB93-P281282, ZB94210. ZB94-210. Make Make your your way wayback backto to the the road and continue passing the the remains of of an old cabin continue westerly, westerly, passing 1070 metres metres west west of of the the beaver beaver dam. dam. At 1070 At 1345 1345metres metres west west of of the thedam, dam,excellent excellent exposures exposures south south of of the the road comprise about 25% rocks included includedin in coarse coarse grained grained to to pegmatitic pegmatitic 25% mafic to intermediate metavolcanic rocks tonalite. Fine Finetotomedium mediumgrained grainedscreens screensofofmafic maficrock, rock,locally locallywith withepidote epidoteknots, knots,show showlayering layeringdefined defined by grain size The screens screenstend tend to to be boudinaged or segmented size and and hornblende hornblende abundance abundance (20—80%). (20-80%). The segmented and, in some cases, biotite-rich biotite-rich rims are related to to intrusive intrusive contacts. contacts. Intermediate Intermediatetotofelsic felsiclayered layered screens screens with with disseminated magnetite and possible quartz eyes are present present in lesser lesser amounts. Continue west 30 metres on the same outcrop area area to to aa weakly weakly magnetic quartzose iron iron formation formation (about (about 30 metres of strike-length strike-length is exposed) exposed) with minor minor sulphide sulphide minerals minerals associated associated with mafic mafic to to intermediate intermediate rocks. layer, up up to 55 metres rocks. The The iron iron formation formation is is aa semi-continuous semi-continuous layer, metres thick, thick, tracable tracable along-strike along-strike for about 150 metres metreson onboth both sides sidesofofthe theroad, road,and andcropping croppingout outagain again11km kmtotothe thewest. west.To Tothe thesouth, south,the the unit unit trends trends 150 south-southwesterly south-southwesterly around the the map-scale map-scale Z-fold Z-fold in the Davis Davis Lake area. Continue along the the road road for 1650 metreswest westofofthe the beaver beaverdam damto to an an outcrop outcrop on on the road itself Continue along 1650 metres itself and extending to the the north. north. The Theexposure exposureisistypical typicalof ofthe the2680 2680 Ma Ma Nama Creek pluton, pluton, medium medium to to coarse coarse grained granodiorite, strongly inicroclinephenocrysts phenocrystsabout about 11 cm cm long. long. The matrix strongly foliated foliated with with about about10—25% 10-25% microcline matrixhas has white chalky plagioclase and and about about 20% biotite biotite and and hornblende. hornblende. Fine grained biotite and hornblende inclusions outline growth zoning present, and an zoning in the phenocrysts. phenocrysts. Some Some minor minor mafic mafic screens screens are present, an extensive extensive network network of folded aplite-pegmatite aplite-pegmatite dykes. dykes. F. Black Black Pic P i c batholith, supracrustal supracrustal screens screens and a n d major m a j o r folds folds F1—F5. BlackPPlc batholith F1-F5. Black i c batholith Supracrustal rocks Supracrustal rocks of of the the Manitouwadge Manitouwadge belt belt are areenclosed enclosed by multiphase foliated foliated to to massive massive plutonic plutonic rocks rocks collectively knownas asthe the Black Black Pic Plc batholith batholith (1:25000 map). Foliations Foliations in in the the Black Black Pic batholith mimic collectively known (1:25000 map). mimic the the of the dominant D2 foliations foliations in in the supracrustal suite and are orientations of are folded folded by the the D3 Da Manitouwadge Manitouwadge synform. To the rocks are mainly mainly tonalitic tonalitic to granodioritic, synform. the south south of of the theManitouwadge Manitouwadge synform, synform, plutonic plutonic rocks granodioritic, but also also include dioritic and granitic phases, phases, commonly commonly on On the the basis basis of of cross-cutting cross-cutting on aa single single outcrop. outcrop. On relationships, mafic phases are generally generally older than than felsic felsic phases. phases. Stop contact zone,zone, ZB93-61—62. Fl,Black BlackPic/supracrustal Pic/supracrustal contact ZB93-61-62. Take Takethe theCaramat CaramatIndustrial Industrial road road west west S t o p Fl, from Highway Highway 614 614for for1.2 1.2km, km,turning turningsoutheast southeaston onaagravel gravelroad roadjust justwest westofofan anindustrial industrial area. area. In about 300 metres, a long pavement crops out north of the road under aa powerline (1:25000 (1:25000map). map). The The northern northern outcrops are dominated by by layered layered fine fine grained mafic mafic to intermediate intermediate hornblende-biotite hornblende-biotite amphibolite amphibolite (metavolcanic), (metavolcanic), locally with epidote hornblende-biotite 10—20% epidote knots knots and andgarnet. garnet.Foliated Foliated hornblende-biotitediorite, diorite,with with 10-20% plagioclase plagioclase augen augen (mostly 0.5 0.5 cm), cm), increases increasesinin abundance abundancetoward towardthe thesouth. south. The The diorite, diorite, typical typical of of the the oldest oldest phase phase of of the the (mostly Black Pic batholith, is cut Black Pic cut by by multiphase, multiphase, concordant concordant and discordant discordant granite, pegmatite and and aplite aplite dykes, dykes, Both diorite diorite and and granite graniteare areinvolved involved in in tight tight folds folds with metavolcanic metavolcanic varying from strongly foliated to massive. Both rocks. The The schistosity schistosity in the amphibolite amphibolite is is parallel parallel to axial axial plane plane traces and and also also undulates undulates in in broad broad open open rocks. S-folds (plan view). view). Continue 100 metres powerline clearing Here in aa high high strain strain metres south on the powerline clearingon onthe the east east side side of of the the road. Here mm) mafic mafic rocks rocks are are unusual in having zone, streaky laminated laminated (submm—10 (submm-10 mm) having aa westerly-plunging westerly-plunging lineation. lineation. diorite. Intercalated mafic The zone is cut by by plagioclase-porphyritic plagioclase-porphyritic diorite. mafic and dioritic rocks and pegmatite-aplite pegmatite-aplite dykes continue continue to to the south. south. Stop inclusions, ZB93-63. Retrace thethe route about S t o p F2, F2, Aplitic Apliticgranite g r a n i twith e w i tdiorite h diorite inclusions, ZB93-63. Retrace route about100 100metres metresfrom from the the first outcrop outcrop of of Stop Stop Fl Fl and first and turn turnon ontotoa aroad roadbranching branchingsoutheast southeastskirting skirtingthe theindustrial industrialarea; area;100 100metres metres further, there are are patchy patchy pavement pavement outcrops outcrops in in the the cleared cleared area area west west of of the the road. road. The Thewhite whiteweathering weatheringfine fine pegmatitic patches and more discrete veins. The to medium grained weakly foliated aplitic granite has diffuse pegmatitic The granite resembles the youngest phase of Stop Stop Fl F land andcontains containssome someminor minorinclusions inclusionsof offoliated foliatedplagioclaseplagioclaseporphyritic diorite. Stop PicPbatholith, ZB93-67, ZB94-86. S t o p F3, F3, Three Threephases phasesofofthe t hBlack e Black i c batholith, ZB93-67, ZB9486. Stops StopsF3, F3,F4 F4and and F5, F5, are are accessed at the the railway railway crossing crossing east of of Little Little Manitouwadge Manitouwadge Lake; 100 metres accessed from from the the Camp 70 road at metres east east (1:25000 of crossing, turn off the Camp Camp 70 road to to the the southwest southwest on on to to aaroad roadparalleling paralleling the thetracks tracks(1:25000 of the crossing, turn off map). After After 500 500 metres, large large rocky knolls slope slope down downon onthe the southeast southeast side sideof ofthe theroad. road. Three main plutonic youngest; 1) 1) strongly foliated (D2) coarse grained hornblende-biotite diorite rocks are exposed, from oldest to youngest; correlated with oldest phase phase of of Stops Stops Fl F land andF2, F2,2)2)fine finetotomedium mediumgrained, grained,buff buffweathering, weathering, foliated foliated correlated with the oldest granodiorite with <5% biotite and, and, 3) 3) weakly weakly foliated foliated pegmatitic-aplitic pegmatitic-aplitic granite, and granodiorite with <5% granite, similar similar to to Stops Stops FFll and plagioclase F2 but more more pegmatitic. pegmatitic. The Thediorite dioritecontains containssubtle subtle plagioclaseaugen augen(3—5 (3-5 mm) mm) and and locally locally approaches approaches 74 �F. Black Black Pic batholith batholith Manitouwadge Manitouwadge field guide monzodiorite with about about 10% 10%microcline. microcline. ItItcontains containssome somedark dark fine fine grained grained elongate elongate mafic mafic enclaves. Diorite, sampled on this outcrop, Ma (Fig. (Fig. 17, Table Table 2), 2), within sampled on outcrop, has has aa U-Pb U-Pb zircon zircon age age of of 2687+3/—2 2687+3/-2 Ma within error error of the Loken Lake microcline-megacrystic microcline-megacrysticpluton, pluton, and and both both are interpreted as as aaprepre- totosyn-D2 syn-D2intrusions. intrusions. The granodiorite granodiorite has has aastrong strongfoliation, foliation,locally locallygneissic, gneissic, and itit contains contains angular angularand andelongate elongateinclusions inclusions of diorite and minor exposures, and and it may be minor mafic mafic schist. This This phase phase is is difficult difficult to correlate correlate between between exposures, be that that there similar appearance appearance that that post-date diorite there are are several several granodioritic-tonalitic phases of similar diorite and and pre-date predate aplitic aplitic granite. Aplitic Aplitic granite granitedykes dykes cut cut the theolder olderphases phasesatatlow lowtotomoderate moderateangles anglestotofoliation, foliation,and andhave haveaaweak weak fabric apparently with the same same orientation as that that in inhost host rocks. rocks. AAsample sampleof of aplitic apliticgranite, granite, collected collected for for geochronology on this this outcrop, had only poor quality geochronology on quality zircon. zircon. Stop intrusion breccia, ZB93-69. Continue southwest S t o pF4, F4,Syenite-hornblendite Syenite-homblendite intrusion breccia, ZB93-69. Continue southwestalong alongthe theroad roadtoto1.8 1.8 km, on the the north side of the the road. Multiphase km, 100 100 metres east of of a powerline, to good outcrop ledges and knolls on Multiphase plutonic are olutonic rocks here are similar to those of Stop F3, F3. but the the relationships relationshi~s aremore more difficult difficult to see. see. Of Of note note are are the originating as as aa diatreme, diatreme, although the rubbly rubbly outcrops outcropsand and blocks blocks of an interesting intrusion breccia, possibly originating we have not mapped here here in in any any detail detail(see (see Alkalic Alkalic rocks (Unit 16), 16), Fox Creek occurrence). An assortment assortmentof of lithic fragments cm),mostly mostlyangular angular mafic mafic to to intermediate hornblende-biotite-rich, are embedded fragments (1—25 (1-25 cm), embedded in in aa coarse grained matrix hornblende and and biotite with hornblende matrix comprising comprising plagioclase, hornblende hornblende phenocrysts (euhedral (euhedral prisms to 1.5 apatite and titanite. 1.5 cm) and minor to trace amounts of quartz, microcline, apatite titanite. Locally, Locally, hornblende looks to be be of of metasomatic metasomatic igneous igneous origin, origin, forming radiating sprays or oriented oriented perpendicular perpendicular to to inclusion inclusion contacts, as though surfaces. Biotite is mainly mainly present present as laths within hornblende and though nucleated nucleated on on inclusion inclusion surfaces. tends to to be beuniformly uniformlyoriented orientedinineach eachphenocryst, phenocryst,locally locallylooking lookinglike likepartial partialreplacement replacementofofhorublende. hornblende. Although the breccia massive, itit is is cut by aplitic dykes. dykes. The breccia contains at least one breccia looks massive, one fragment fragment (2 (2 cm size) of massive sulphide suiphide (pyrite-chalcopyrite-magnetite) transported from depth? during (pyrite-chalcopyrite-magnetite) transported duringemplacement; emplacement; interesting concept, concept, as contact to supracrustal supracrustal rocks and the theclosest closest an interesting as the the contact rocks lies lies about about 1 km km to the north, and known massive the Geco Geco mine. The The area area of of the thebreccia breccia crudely crudely known massivesulphides sulphidesare aremore morethan than 33 km km to to the the north at the corresponds to several highs (1:25000 (1:25000map). map). The breccia was grouped by several isolated anomalous aeromagnetic aeromagnetic highs Williams Williams et al. (1992) (1992) in in an an 'appinite 'appinite suite', suite', with withother otherexamples examples intruding intruding the theRawluk Rawluk Lake Lake pluton to to the the east in in the the Faries Faries Lake Lake area area (Fig. (Fig. 2). 2). S t o p F5, F5, Syenite.hornblendite Syenite-hornblenditeinternal internal structures, Black batholith, ZB93-70. Continuedirectly directly Stop structures, Black PlcPic batholith, ZB93-70. Continue under the powerline, south of of the road, to an outcrop. The powerline, south an area area of of extensive extensive outcrop. The first first exposures exposures are apparently F4, here here represented represented by by aaheterogeneous heterogeneous suite suiteincluding including continuation of of the the syenite-hornblendite syenite-hornblendite of Stop Stop F4, a continuation of layering analogous rhythmically layered rocks, with truncations of analogous to to cross-bedding. cross-bedding. About About 200 200 metres metres further further powerline, two main plutonic rocks The uphill along the powerline, rocks more more typical typical of of the the Black Black Pic Pic batholith batholith are exposed. The oldest, medium medium grained grained well well foliated granodiorite with with about about15% 15%biotite biotiteand andhornblende, hornblende,isiscut cutby byaayounger younger oldest, network of pink massive aplite-pegmatite aplite-pegmatite dykes. dykes. F6—F12. Western Blackman Blackman Lake Lake antiform antiform (D3), (D3), Janet Janet Lake F6-F12. Western Lake road road In Manitouwadge In contrast contrast totothe theBlack BlackPic Picbatholith batholithsouth southofofthethe Manitouwadgebelt belt(Stops (StopsF1—F5), F1-F5), plutonic plutonic rocks rocks to to the thenorthwest northwestcontain containmany manysupracrustal supracrustalscreens, screens,including includingmafic maficmetavolcanic metavolcanic rocks rocks and and iron iron formation. formation. Outcrop-scale structures, foliation foliation and aeromagnetic aeromagnetic trends suggest the presence presence of major fold, fold, the theD3 Dg Outcrop-scale trends suggest of a major Blackman Lake antiform, Janet Lake Lake area area (1:25000 (1:25000 map). In Blackman antiform, with with a northeasterly trending axial trace in the Janet the accompany changes changesin in foliation foliation orientation. orientation. The the hinge hinge region, region, changes changes in in vergence vergence of outcrop-scale folds accompany limb of of the the Blackman Blackman Lake Lake fold forms the main main supracrustal supracrustal belt beltand andmay mayhave havebeen been eastern limb forms the contact to the the the locus locus of of post-D2 post-D2 shearing. shearing. The Theprepre-totosyn-D2 syn-D2microcline-porphyritic microcline-porphyritic Nama Nama Creek Creek pluton pluton was was intruded intruded contact. The Thesupracrustal supracrustalscreens screenson onthe thewestern westernlimb limbofofthe theBlackman BlackmanLake Lakeantiform antiformmay mayhave have along the contact. been derived derived from a highly attentuated attentuated hinge hinge region region of of the the Jim JimLake Lake synform synform or, alternatively, alternatively, they may may be be a continuation continuation of of the the outer outer volcanic volcanic belt to to the thesouth, south,displaced displaced by by apparent apparent dextral dextralshear. shear. The The Janet JanetLake Lakeroad roadisisreached reachedby byfollowing followingthe the Caramat Caramatroad roadwest westfrom fromHighway Highway614 614passing passing the thebridge bridge across Nama Creek Creek (14 the north, north, and andcontinuing continuing northerly northerly about about 7.5 7.5 across (14 km), km), where where the the Caramat Caramat road turns to the km. The TheJanet JanetLake Lakeroad roadisismostly mostlya agood goodsingle-lane single-lanegravel gravel track, track, but butrough roughand andslow. slow. S t o pF6, F6,Supracrustal Supracrustal screens in tonalite, ZB93-273. Drive eastfor for1.6 1.6km kmon onthe theJanet JanetLake Lake road road to Stop screens in tonalite, ZB93-273. Drive east extensive pavement outcrop outcrop on on the the south southside side(1:25000 (1:25000 map). map). The Thefoliated foliatedtonalite tonalitecontains containsmany manyscreens screens an extensive of cm),fine finegrained, grained, mafic maficto to intermediate intermediate metavolcanic rocks. rocks. Screens of homogeneous homogeneous to to layered layered (1—10 (1-10 cm), Screens up to to 1.5 metres in in width width comprise comprise about about25% 25%of of the theoutcrop. outcrop.Some Someofofthe thelayering layeringlooks lookslike liketransposed transposed veins veinsor or 1.5 dykes, and some screens have have intrafolial intrafolial (nearly) (nearly) folds foldsapparently apparentlytruncated truncated by by the the tonalite host rock. rock. ItItisis difficult to unequivocally unequivocally correlate sequence; but difficult correlate the the fabrics fabrics in in screens screens with with those those in in the main supracrustal sequence; the whereas the the foliation in in the tonalite may the screens screens may contain contain D1 Dl and D2 D2 fabrics and folds, whereas may be be aa D2 D2 or or D3 D3 fabric. fabric. S t o p F7, F7,Iron Ironformation formation tonalite, ZB93-K126.AtAt 4 km eastononthe theJanet JanetLake Lakeroad roadtake takethe theroad road Stop in in tonalite, ZB93-K126. 4 km east goodpavement pavementon onthe thewest west to the the north northfor for2.1 2.1km, km,then thenkeep keeptotothe theleft leftfork forkfor foraafurther further300 300metres. metres. AAgood to 75 �G. Quetico Quetico subprovince subprovince Manitouwadge field guide of the road exposes screens of of iron iron formation formationand and mafic mafictotointermediate intermediaterocks rocksininfoliated foliatedtonalite. tonalite. The The side of exposes screens layered quartz-magnetite quartz-magnetite iron formation, about 1.5 by layered 1.5 metres metres thick, thick, isisfolded folded and andsegmented, segmented, and andenclosed enclosed by which is also strongly strongly magnetic. magnetic. The amphibolite consists of streaky layered, medium medium to coarse amphibolite which grained, intermediate intermediate metavolcanic metavolcanic rock with local smeared-out pegmatite. pegmatite. Some Somemore more homogeneous homogeneous foliated hornblende-biotite The silicate silicate mineralogy mineralogy of iron hornblende-biotitediorite dioriteisis subconcordant subconcordanttoto the the supracrustal supracrustal rocks. rocks. The of the iron typical of of iron iron formation in in the Manitouwadge belt; belt; garnet, garnet, grunerite and clinopyroxene (bright formation is typical clinopyroxene (bright green mineral?). mineral?). Pegmatite green Pegmatite invading invading the the iron iron formation formationisis loaded loaded with with coarse coarsegrained grained magnetite, magnetite,suggesting suggesting crops out out about 11 km to the northeast. contamination. Iron formation also crops northeast. Stop F8,Z-fold, 2-fold,ZB93-137. ZB93-137. Return Return to tothe theJanet JanetLake Lakeroad, road, and andcontinue continue east east for for aa further further 2.8 2.8 km km to aa S t o p F8, pavement west of a small small stream. stream. Layering Layering in in the the fine fine grained grained foliated foliated pavement on on the the south south side side of of the road just west tonalite-diorite is is defined defined by the thehornblende hornblendeabundance, abundance,which whichvaries variesfrom fromabout about10—60%. 10-60%. A strong rodding rodding lineation is parallel to to the theaxis axisof ofaaZ-fold Z-fold (D3) (Ds) with with very very long long limbs. limbs. Locally, Locally, layers layers are are boudinaged boudinaged along alongthe the long limbs of folds. Pegmatite Pegmatite dykes dykes follow follow the the axial axialtraces tracesofofsome somefolds. folds. Stop rock tonalite, ZB93-133. Continue S t o p F9, F9, Mafic Maficmetavolcanic metavolcanic rockinifoliated n foliated tonalite, ZB93-133. Continuefor for3.8 3.8km km past past the the junction junction (Stop F7) to to good outcrop on both sides sides of the road. The The stop stop isis near near the thehinge hingeregion region of of the Blackman Blackman Lake antiform, and fabric fabric trends trends are aregenerally generally variable, variable, due due to to minor minor folds. folds. Medium Medium to to coarse coarse grained grained (coarsened?) (coarsened?) metavolcanic rocks (hornblende-plagioclase-quartz-biotite-clinopyroxene) (hornblende-plagioclase-quartz-biotite-clinopyroxene) are layered mafic metavolcanic areinvaded invadedby by foliated foliated either transected by tonalite to to diorite. diorite. The Themafic maficinclusions inclusionsshow show some some early folding either by foliation foliation or or with with axial axial planar foliation. inclusions in in foliated foliated coarse coarsegrained grainedtonalite tonalite show show some somerotation rotation of of planar foliation. Locally, Locally, blocky blocky mafic inclusions schistosity. schistosity. Stop Lake antiform, ZB93-129. 4.4 S t o p FlO, F10, Hinge Hingeregion regionofofthe t h Blackman e Blackman Lake antiform, ZB93-129. On Onthe theJanet JanetLake Lake road, road, 4.4 km past the the junction, junction, the the road road bends bends 90° 90' to tothe thesouth southand, and,after afteranother another300 300metres, metres,aapavement pavement lies lies east east of the road. road. The Thestop stopisisininthe thehinge hingeregion regionofofthe theBlackman BlackmanLake Lakefold. fold.Multiphase Multiphasefoliated foliatedplutonic plutonicrocks rocks with diffuse layering (5 (5 mm—10 are dominated dominated by bymedium mediumtotocoarse coarsegrained grainedtonalite tonalite with diffuse layering mm-10cm) cm)defined definedbyby5—40% 540% mafic minerals. The granite-pegmatite-aplite which whichvaries variesfrom from The tonalite tonaliteisisintruded intrudedbybyabout about10—20% 10-20% pinkish granite-pegmatite-aplite concordant and and folded folded dykes to net veins. veins. Pegmatite Pegmatitetends tendstotobe bepresent presenton onsmall smallshears shearsororshort shortlimbs limbsofoffolds folds on fold fold limbs. limbs. Locally Locally white white in tonalite, tonalite, and andlocally locallytonalite tonalitelooks lookscoarsened coarsened and andhomogeneous homogeneous in diffuse diffuse zones on tonalite is is either either massive massive or or has hasaaweak weakfoliation foliation(possibly (possiblyaxial axialplanar) planar)defined definedby byabout about30% 30%coarse coarse(3—8 (3-8 mm) hornblende porphyroblasts. Fabric Fabric trends trends are arevariable variableand andcommonly commonlyswirly, swirly, averaging about 300°/45°. 300°/45<' dominantly S-shaped S-shaped folds foldsin in the the southeast southeast to dominantly There is a general change across the outcrop from dominantly Z-shaped folds in in the northwest, accompanied Z-shaped accompanied by a change change in foliation trends from from northerly northerly to towesterly. westerly. Stop pluton, ZB93-91. Continue 2.52.5 kmkmbeyond S t o p Fil, F l lNama , N a mCreek a Creek pluton, ZB93-91. Continue beyondthe thesharp sharpbend bendtotothe thesouth southto toaahigh high knoll See Stop Stop F12 F12 for for aa description. description. knoll east east of of the road. See S t o p F12, F12,Nama N a m aCreek Creek pluton, ZB93-87. The stop kmsouth southononthe theroad roadbeyond beyondthe thesharp sharpbend; bend; Stop pluton, ZB93-87. The stop is is 4.64.6km however, itit will will probably probably be necessary the road is. however, necessary to to walk walk the thelast last1—2 1-2 km, depending on how overgrown overgrown the is. rocky knoll l l and F12 are both in The outcrop is a rocky knoll in in the the bush bush about about 50 50 metres metreswest westofofthe theroad. road.Stops StopsFFli the microcline-porphyritic Nama Creek pluton; Stop Stop F11 F l l is is more more easily easily accessed, accessed, but Stop StopP12 F12was wassampled sampled for geochronology. geochronology. Both outcrops outcrops are aretypical typicalofofthe therelatively relativelyhomogeneous homogeneousintrusion, intrusion,consisting consistingof ofcoarse coarse foliated hornblende-biotite hornblende-biotitegranodiorite granodioritetototonalite tonalite with 0-20% microcline microclinephenocrysts phenocrystsororaugen, augen,1—3 1-3 grained foliated with 0—20% Thepluton plutonisisinterpreted interpretedasasprepre-totosyn-D2, syn-Dg,on onthe thebasis basisofoffoliations foliationsfolded folded around around the thehinge hinge cm in length. The west of of One Otter Lake map). The strong linear and of the Blackman Lake antiform west Lake (1:25000 (1:25000 map). and planar planar fabrics fabrics south Lake may may be be related related to totransposition transposition during during post-D2 post-D2 deformation deformation near the south of Janet Lake near the the contact contact to the The geochronology geochronology sample Manitouwadge belt. belt. The sample of ofthe the Nama NamaCreek Creekpluton pluton contained containedboth both zircon zirconand and titanite, titanite, 2687 Ma the former giving an age of intrusion of 2680k3 2680±3 Ma (Fig. 15, Table 2), somewhat somewhat younger younger than than the 2687 presyn-Da Loken titanite age age of of 2672±3 2672k3 pre- to syn-D2 Loken Lake Lakepluton pluton and and oldest oldest diorite diorite of ofthe the Black BlackPic Picbatholith. batholith. The titanite regional cooling through the closure closure temperature of titanite titanite (600°C, (600°CHeaman Hearnan and and Parrish, Parrish, Ma suggests that regional 1991) 1991) occurred occurred about about 8 Ma after intrusion. G. Quetico subprovince, western n d central Manitouwadge aarea rea western aand In general, the the description description for for the theQuetico Queticosubprovince subprovincein in the theeastern easternManitouwadge Manitouwadgearea area(Stops (StopsE1—E3) El-E3) western and central central area. area. However, However, in in the the latter latterarea areanear nearthe theWawa-Quetico Wawa-Queticoboundary, boundary, also applies applies to the western is commonly interleaved with with gabbroic gabbroic and dioritic migmatitic metagreywacke metagreywacke is commonly interleaved dioritic rocks. rocks. Diorite Diorite apparently intrudes rocks along and field field observations observations suggest prealong the the subprovince subprovince boundary boundary and and to the north, and suggest that that itit predates migmatization migmatization (Stop G2). G2). Williams Breaks (1990a) (1990a) mapped lenticular unit unit of of melanocratic melanocratic Williams and and Breaks mapped a lenticular diorite (not (not differentiated differentiated on on our our 1:25000 1:25000 map) called called the the Everest Everest Lake Lake pluton pluton (Williams (Williamsand andBreaks, Breaks,1990b; 1990b; Williams 1992), extending along the western western subprovince Williams et et al., 1992), subprovince boundary boundary as as far east as Appelle Lake. They considered multiphase Black Much of the generally considered the the Everest Everest Lake Lakepluton pluton to to be be part of the multiphase Black Pic Pic batholith. batholith. Much aeromagnetic striping striping on on both both sides sidesof of the the western western subprovince subprovince boundary boundary could could be be related related east-west trending aeromagnetic to concordant diorite sheets. 76 �Manitouwadge Manitouwadge field field guide guide Quetico subprovince subprovince G. Quetico The western-central is most most easily easily accessed accessedfrom fromthe the Caramat Caramat Industrial road west western-central Quetico Quetico subprovince is west of the Manitouwadge belt. However for Stop Stop G2, G2, this this assumes assumesthat that a major washout, about 33 km However for km east east on on the the Husak road, has been repaired; the latest suggests that that the road latest information information (Feb. (Feb. 1995) 1995) suggests road is is passable. passable. S t o pGi, G l Migmatitic , Migmatitic metagreywacke, folds n d new fabrics, ZB9450. stop is reached following Stop metagreywacke, folds andanew fabrics, ZB94-50. TheThe stop is reached bybyfollowing CaramatIndustrial Industrial road road about about32 32km kmfrom fromHighway Highway 614 614 to to an an intersection intersection with with the the Michal Michal Lake Lake road road the Caramat (to the the west) west) and and the the Husak Husak road (to (to the the east). east). The Theintersection intersection isis about about 9.75 9.75 km km north north on on the the Caramat Caramat road from from the junction with with the theJanet JanetLake Lakeroad road(Stops (StopsF6—F12). F6-F12). Turn west west on on the the Michal Michal Lake Lake road road and and drive on for about 1.3 1.3 km to to an an extensive extensive area area of of pavement pavement outcrops outcrops in in an an old old clearing clearing or or road road leading leading south, south, between Hourglass and Slingshot Slingshot Lakes Lakes (1:25000 (1:25000 map). The Theexposure exposureof ofmigmatitic migmatiticmetagreywacke, metagreywacke,locally locally with with cordierite cordierite or or garnet garnetininleucosomes, leucosomes,shows shows multiple multiple folds folds and and complex complex structural structural relationships. relationships. Near Near the road, road, stretched stretched and andboudinaged boudinagedmigmatitic migmatiticsegregations segregationsdefine define isoclinal isoclinal folds, and some rotated boudins boudins show dextral kinematics kinematics (in (in plan plan view). view). Elsewhere Elsewhere on on the the outcrop, outcrop,layering layeringand andfoliation foliation show show both both ZZ- and and show S-shaped folds, folds, some some of of which which refold refold earlier folds folds of migmatitic segregations. segregations. In Inmicaceous micaceouslayers, layers,an anaxial axial S-shaped planar planar spaced spacedcleavage cleavageisiscommonly commonlydeveloped, developed, with with less less micaceous micaceous microlithons preserving preserving earlier earlier fabrics; fabrics; in in psammitic layers, layers, spaced spaced cleavage cleavage is less Locally, in psammitic less developed developed and and folded folded fabrics fabrics dominate. dominate. Locally, in the hinge of an S-fold, S-fold, asymmetric kink bands that that deform deformthe thespaced spacedcleavage cleavage were were interpreted interpreted as asthe theresult resultofofprogressive progressive deformation. deformation. S t o p G2, G2,Migmatitic Migmatiticmetagreywacke metagreywacke interleaved w i diorite, t h diorite, ZB94C45.Return Returntotothe theintersection intersection Stop interleaved with ZB94-C45. with with Caramat Caramat road road and and continue continue through to the the east east on on the theHusak Husak road road for for about about 13.5 13.5km km (about (about 1.5 1.5km km west of the junction with with the the Olson Olson Lake Lake road). road). Turn Turn left left on on to toaasmall smalltrack track leading leading northeasterly northeasterly and and up up west hill, as itit turns turns to the metres. About 70 metres further, the track hill, following following itit as the northwest northwest (left) after 360 metres. track is is crossed clear area area of ofoutcrops outcrops trending trending north-northeasterly. north-northeasterly. Three crossed by a large (200 m long) clear Three main main rock rock types types are are exposed; exposed; 1) 1) medium mediumto tocoarse coarsegrained grainedfoliated foliateddiorite, diorite,commonly commonlywith withup uptoto40% 40%plagioclase plagioclasephenocrysts phenocrysts(2—5 (2-5 mm) hornblendeand and biotite, biotite, 2) fine to medium grained layered mm) and and10—50% 10-50% hornblende layered heterogeneous foliated tonalite tonalite to hornblende-biotite hornblende-biotite diorite, diorite, and and 3) 3) migmatitic migmatiticbiotite biotiteschist schistwith withboudinaged boudinaged and andfolded folded layers layers of of tonalitictonaliticto pegmatitic leucosome. leucosome. These rock types are interleaved interleaved on The diorite diorite pegmatitic on a scale of of 10 cm cm to several metres. metres. The isis foliated, foliated,but butlow lowstrain strainenclaves enclavespreserve preserveigneous igneoustextures. textures.Diffuse Diffusecoarse coarseleucocratic leucocraticenclaves, enclaves,suggesting suggesting incipient migmatization, migmatization, are areheterogeneously heterogeneously distributed, distributed, in inpart, part,localized localizedinindilational dilationalzones zonessuch suchas asboudin boudin incipient necks. In Inmany manycases, cases,coarse coarseleucocratic leucocraticzones zonesform formananinterconnecting interconnectingnetwork networkofofganglions ganglionsenclosing enclosingenclaves enclaves necks. of dioritic dioritic protolith. The Theoverall overallimpression impression is is that thatthe thediorite dioritesheets sheetsshow showless lessstrain strainthan thanmetagreywacke, metagreywacke, of possibly a function function of of competency competency contrast. The Theheterogeneous heterogeneous and and patchy patchy distribution distributionof ofcoarse coarseleucocratic leucocratic possibly domains in diorite diorite suggests suggests that that migmatization migmatization may may have have partly partly been been driven driven by by the the introduction introductionof offluids fluids or or domains fluxing components. components. Note Note also also that thattight tighttotoisoclinal isoclinalfolds foldsof oflayering layering are are transected transected locally locallyby by an anoblique oblique fluxing southeasterly trending trending foliation foliation defined defined by hornblende hornblende and biotite. biotite. southeasterly ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS Noranda Minerals Minerals Inc. (Geco (Geco Division), Division), Granges Granges Inc., contributed to this this Noranda Inc., Minnova Minnova Inc. Inc. and and A1 Al Turner Turner contributed project by by providing providing access access to unpublished maps and reports. Noranda NorandaMinerals Mineralsreleased released data dataacquired acquiredduring during project to Joan Joan Tod, Tod, GSC. GSC. The The data datawere were compiled compiled aa high resolution aeromagnetic survey (contracted to Dighem Inc.) to by Warner Warner Miles, Miles, and and the theresulting resultingaeromagnetic aeromagneticmaps maps(Open (OpenFiles Files2754, 2754,2755) 2755)were were valuable valuable aids aidsto tomapping mapping by and interpretation. interpretation.Our Ourspecial specialthanks thanksgogo Hugh Lockwood,Noranda NorandaMinerals MineralsInc., Inc.,for fordiscussions, discussions,ideas, ideas, and toto Hugh Lockwood, A1Turner Turnerand and and support supportofofour ourefforts effortsduring duringthe thefield fieldseason. season.Thanks Thanksalso alsogo goto toRob RobReukl, Reukl,Jody JodyHache, Hache,Al and Neil Poster. Poster. Rob RobReukl Reukland andJody JodyHache Hachecollected collectedthe thegeochronology geochronology sample sample of of the the Nama Nama Creek Creek pluton, pluton, and and Neil Doug McKay, McKay, Mark Smyk and Greg Greg Chariton Charlton helped helped in incollecting collecting various various other other problematic problematic samples. samples. We We Doug benefited from from field field trips trips and/or and/ordiscussions discussionswith withDoug DougMcKay, McKay,Mark MarkSmyk, Smyk,Bernie Bernie Schnieders, Schnieders, Fred Fred Breaks Breaks benefited and Howard Howard Williams, Williams, Ontario OntarioGeological GeologicalSurvey; Survey; Greg Greg Charlton, Charlton, Isobel Isobel Wolfson Wolfson and Paul Paul Degagne, Degagne,Noranda Noranda and Inc.; and and Warren Warren Bates, Bates, Granges Granges Inc. Inc. Our Ourfield fieldwork work was was greatly greatly aided aided by by the themapping mappingof of David David Copeland Copeland Inc.; and Katherine KatherineBoggs, Boggs, and andthe theassistance assistanceofofJoanne JoanneTreidlinger, Treidlinger,Andrea AndreaDorval, Dorval,Shannon ShannonWalsh Walshand andMike Mike and Thomas. The Themanuscript manuscriptwas wasimproved improvedby bythe thecomments commentsof of Jack Jack Henderson, Henderson, John John Lydon Lydonand andKen KenCard. Card. Thomas. 77 �NOTES �NOTES NOTES � https://digitalcollections.lakeheadu.ca/files/original/68bc76c7e587f90855b020ecc763137c.pdf 0139123474755ae9c5e522bc255dfb24 PDF Text Text Greenstone Geology of the Schreiber Greenstone Assemblage and and its its Assemblage Gold and Base Metal Mineralization r Institute Instituteon onLake LakeSuperior SuperiorGeology Geology 41st 1995 41stAnnual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon,Ontario Ontario Proceedings 41: Part Part2c 2c ProceedingsVolume Volume 41: Field Field Trip TripGuidebook Guidebook I 1 �Geology of of the the Schreiber Schreiber Greenstone Greenstone Assemblage and and its its Gold and Base Metal Mineralization Mineralization by Mark Mark C. C. Smyk Smyk and Bernie Bernie R. Schnieders Schnieders Ontario OntarioGeological GeologicalSurvey, Survey, Field Field Services ServicesSection Section Ministry of of Northern Northern Development Development and Mines Suite 435 S. James Suite B002, BOO2,435 JamesSt. St. Thunder Thunder Bay, ON P7E 6E3 6E3 with contributions contributionsby: by: Steven A. A. Osterberg (BHP Minerals Minerals International International Inc.) Inc.) Rob Sim, Gerard Gerard Doiron, Doiron, Masood Masood Siddiqui Siddiqui and and Matthew Bliss (Winston Lake Division, Metal1 Metall Mining Corporation) Corporation) Frontispiece: 19166 Frontispiece:Trip Triptotothe theEmpress EmpressGold GoldMine, Mine,Syine Syine Township, Township,July July 29, 29,191 (photograph Bourguignon) (photographcourtesy courtesy of Msgr. G. Bo urguignon) �ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS authors would would like like to to acknowledge acknowledgethe the support support of of the the Ontario Ontario Geological Geological Survey Surveyand and the the The authors st Institute on Lake Ministry of Northern Development and Mines in both the 41 41st Lake Superior Geology and its associated associated field field trips. trips. the staff staff of of the the Field Field Services Services Section Section -- Northwest for their administrative and We are indebted to the logistical support. Doug DougMcKay McKayprovided providedinvaluable invaluable assistance assistance in the drafting and generation generation of drawings in this report. Discussions Discussionswith withother othermembers membersof of the the Ontario Ontario the AutoCAD drawings Geological Survey, Survey, especially especially Dr. Andy Fyon, are gratefully gratefully appreciated. appreciated. Finally, Finally, we would like like to thank Rob Sim, Sim, Gerard Doiron, Masood Siddiqui and Matthew Bliss of Metall Mining Corporation's Winston Lake Division Mine for their their contributions contributions to to this this field field Metal1 guide as well as their support support in previous endeavours. Dr. Dr. Steven Steven Osterberg Osterberg has contributed contributed greatly to the understanding understanding of of Winston Winston Lake's Lake's geology geology and and this this has has been been so so noted. noted. The authors authors have tremendously tremendously benefitted benefitted from from the the work work and and ideas ideas of countless countless government governmentand and industry geologists North Shore. We geologists and prospectors that have worked on the North We wish wish the the best best of of luck to those those who who follow. follow. �. TABLEOF OFCONTENTS CONTENTS TABLE RoadLog Road Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Introduction GENERALGEOLOGY GENERAL GEOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Definitionof ofTerms Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Definition RegionalGeology Regional Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 SupracrustalRocks Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Supracrustal GranitoidRocks Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Granitoid StructuralGeology Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Structural EconomicGeology 11 Economic Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 STOPDESCRIPTIONS: DESCRIPTIONS: STOP SteelRiver RiverTurbidites Turbidites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 15 STOP 1: 1:Steel STOP . . . 17 STOP 2A: 2A: Steel SteelRiver RiverKomatiites Komatiites ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 STOP STOP 2B: 2B: Jackfish JackfishPillowed PillowedBasalts Basalts . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 28 STOP 35 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 STOP 3: Terrace TerraceBay Bay Batholith Batholith .... STOP Gold Mineralization Mineralizationin inthe the Schreiber SchreiberArea Area Gold . 38 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 41 STOP 4: 4: Gold GoldRange RangeProspect Prospect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 STOP LocalGeology 42 Local Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Geologyof ofthe theNo. No .77Vein VeinShaft ShaftArea Area . . . . . . . . . . . . . . . . . . . . . . . . . 46 46 Geology �. STOP 5: 5: Winston Winston Lake Lake Cu-Zn Cu-Zn Mine Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . Exploration Exploration and Mining History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mine Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MineGeology Hydrothermal Alteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Massive Massive Suiphide Sulphide Ore Ore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Individual Individual Stop Stop Descriptions Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 48 48 48 51 51 57 62 62 64 64 REFERENCES 73 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 �LIST LIST OF OFFIGURES FIGURES Figure Figure1:1:Tectonic Tectonicassemblages assemblagesmap mapof ofthe theWawa Wawasubprovince subprovince . . . . . . . . . . . . 33 Figure Figure 2: 2: Regional Regionalgeology geologyofofthe theSchreiber SchreiberAssemblage Assemblage . . . . . . . . . . . . . . . . 55 Figure 3 :Geology Geologyand andStop Stoplocations, locations.Jackfish Jackfisharea area Figure 3: . . . . . . . . . . . . . . . . . . . . 13 13 Figure Stops 2Aand and2B 2B . . . . . . . . . . . . . . . . 22 22 Figure 4: 4: Detailed Detailedflow flowcross-sections, cross~sections. Stops2A Figure Figure 5:5: Jensen JensenCation CationPlot Plotof ofSteel SteelRiver Rivermafic maficvolcanic volcanic rocks rocks . . . . . . . . . 25 25 Figure Figure 6: 6: Map MapofofGold GoldRange RangeProspect, Prospect.showing showingvein vein locations locations . . . . . . . . . . 43 43 Figure 7:Geology Geologyofofthe theWinston WinstonLake LakeMine Minearea area . . . . . . . . . . . . . . . . . . . . . 56 56 Figure7: Figure 8A:Geochemical Geochemicalchanges changeswith withalteration, alteration.Ladder LadderFlow Flow Figure 8A: . . . . . . . . . . . 60 60 Figure 61 Figure8B: 8B:Geochemical Geochemicalchanges changeswith withalteration, alteration.QFP QFPRhyolite RhyoliteFlow Flow . . . . . 61 Figure Figure9A: 9A:Detailed Detailedsurface surfacegeology, geology.Winston WinstonLake Lakefootwall footwallsection section . . . . . . 65 65 Figure Figure9B: 9B:Composite Compositecross crosssection, section.Winston WinstonLake Lakefootwall footwallsection section . . . . . . . 66 66 �LIST OF OF TABLES TABLES Table 1: 1: Geochemistry, Geochemistry,tholeiitic tholeiiticand andkomatiitic komatiitic basalts, basalts, Stops Stops2A 2A and and 2B 2B . . 26 . . Table 2: Stratigraphic Stratigraphicsubdivision subdivisionof of part part of of the Winston Footwall Block .... 55 55 Table 3: Partial Partialwhole wholerock rockand andtrace traceelement elementgeochemistry, geochemistry,Winston Winston Lake Lake .. 59 59 LIST OF PLATES PLATES Plate 1: 1: Photomicrograph Photomicrographof of spinifex-textured, spinifex-textured, basaltic komatiite, komatiite. Stop 2A . 2211 . Plate 2: Photomicrograph Photomicrographof of spinifex-textured, spinifex-textured, basaltic komatiite, Stop 2A .. 21 21 Plate 33:: Photographofvariolitic, Photograph of variolitic,pillowed pillowedhigh-Mg high-Mgtholeiite, tholeiite. Stop Stop2B 2B . . . . . 31 31 Plate 4: Photomicrograph Photomicrographof of variolitic, variolitic,pillowed pillowed high-Mg tholeiite, Stop 2B 31 31 Plate 5: 5: Photograph of vein-related alteration, Gold Range property, Stop Stop 4 .. 45 45 Plate �Guide to to the the Schreiber SchreiberGreenstone GreenstoneAssemblage Assemblage Field Guide includes includes stop stop descriptions descriptions for: for: -- STOP STOP 1: 1: Steel Steel River River Turbidites Turbidites - STOP STOP2:2:Steel SteelRiver RiverKomatiites/Pillowed KomatiitedPillowedTholeiites Tholeiites -- STOP STOP3: 3:Terrace TerraceBay Bay Batholith Batholith - STOP STOP4: 4:Gold Gold Range Range Prospect Prospect - STOP STOP5: 5: Winston WinstonLake LakeMine Mine - Road Road Log Logfor forStops Stops11-- 55 (Marathon (Marathon Starting StartingPoint) Point) Total TotalKilometres Kilometra LandmarWieId Trip TripStop Ston Landmark/Field 0.0 Junction of of Highways Highways17 17and and626 626 Junction (Marathon (MarathonTurn-off) Turn-off) 33.9 Dead Horse Horse Creek Creek road road turn-off turn-off Dead 50.6 STOP STOP 1: 1: Steel Steel River River Turbidites Turbidites 52.6 STOP STOP2A: 2A: Steel Steel River RiverKomatiites Komatiites 53.2 STOP STOP2B: 2B:Steel Steel River Ever Pillowed PillowedTholeiites Tholeiites 58.7 Coach CoachHouse HouseMotel Motel 65.0 STOP STOP3: 3: Terrace TerraceBay BayBatholith Batholith 79.0 TouristInformation InformationCentre, Centre,Terrace TerraceBay Bay Tourist 88.5 Turn-off to to STOP STOP 4: 4: Gold Gold Range Range Prospect Prospect Turn-off 92.6 VoyageurRestaurant/Service Restaurant/ServiceStation, Station, Voyageur Schreiber Schreiber 101.7 Turn-off to to STOP STOP 5: 5: Winston WinstonLake LakeMine Mine Turn-off �INTRODUCTION INTRODUCTION This field trip highlights geology and mineral deposits deposits of the western portion of the highlights the geology Neoarchean Schreiber-Hemlo Schreiber-Hem10greenstone belt. This Thissegment, segment,termed termed the the Schreiber Schreiberlithotectonic lithotectonic assemblage, extends from assemblage7 from the western contact contact of of the the Mesoproterozoic MesoproterozoicCoidwell Coldwellalkalic alkaliccomplex, complex, west to Schreiber and north to the Big Duck Lake area (Figures 1 and 2). ItIt comprises comprises aa large large of Lake Superior and and the the Slate Slate Islands. Islands. The Trans-Canada Highway portion of the shoreline of (Highway 17) 17) provides access to the southern southern part of the area and a number of excellent roadside numberof of field field guides, guides?including includingthose those of of Pye Pye (1969), (1969)? exposures of greenstone belt rocks. AAnumber Schnieders et al. (1991) and Sabina (1991) describe describe various various aspects aspects of of the thegeneral generalgeology. geology. Other guides, guides?reports and papers papers will be referenced in describing individual individual stops stops and/or andfor areas. areas. Please note that many of the field trip stops stops located on the side of Highway 17 17 do not provide adequate parkinglpull-off parking/pull-offareas. areas.Extreme Extremecaution cautionmust mustbe beexercised exercisedwhen when stopping, stopping, parking parking and and visiting visitingthese thesesites. sites.Permission Permissionisisrequired requiredfrom fromproperty propertyowners ownerswhen when visiting visiting the the Gold Range and Winston Lake Mine properties. Please Pleasecontact contactthe theResident ResidentGeologist's Geologist'sOffice, Office? Schreiber-Hemio District? District, Thunder Bay7 Bay, for current information regarding regarding property property ownership at at Schreiber-Hem10 475-1331. 1331. (807) 475- Schreiber Assemblage 22 Sclzreiber Assemblage �W W 9w SP 8. 89' 9W 87.w B7'W 68' west Port Perf West Long Lok, Long Lok Quet ice Subprovince 49N -. ...ntOfl Slot lxi — fi- S .S - Lk —SSSS AnoL0-1- s) , Lake Superior .SSSS_J_S___2_ 87W Legend Legend Metavolcanic Metmlconic and ondmetasedimentOry metosedtmentoryassemblages ossembloges (2.73 Go) Heron Bay, Gamitogama, Greenwoter 12.73tot o2.70 2.70 Go): Hercm Boy, Gomitogorno,Cattish, Cotftsh, Greenwoter Pmteromlccover m r - Animikie AnimikieBasin, Bosin,Nipigon NipigonEinbayrnent Emboyrnent Proterozoic b r tColdweil Coldwellalkalic olkoliccomplex complex Proterozoic intrusions intrusions~Port Proterozoic ' 0 Groniticrocks rocks(large (lorgeareas oreosbetween, between,and ondsmall smollplutons plutonswithin, wtthin, Gronitic greenstone belts) belts) greenstone Shebondowon ossembloge, Loke assemblage ossembloge (-2.69 Shebondowon assemblage, Knife Knife Lake (-2.69 Go) Metosedimentory assemblages ossembloges (probably tprobobly -2.70 -2.70 Ga) Go): Mishi, Mishi, Metosedimentory Gorgontuo,Quetico Ouet~cu Gargantua, Memvolconicassemblage ossembloges Soganagoris Sogonogonsassemblage ossemblo~e Metavolcanic Metovolcanie Metovolconicand and metasedimentary mttOsedimentoq assemblages ossembloges (2.77 (2.77 toto2.70 2.70GO, GO, probably2.77 2.77tot2.75 o 2.75 Schreiber, Monttouwoage-Mrnepoyne, prababiy Ga)'Go) Schreiber, Monhtouwadge-HornePOYfle, Chapleou, Doyohessuroh-Kobinokogomi Chopleou, Doyohessaroh-Kabinakagorni Metovoicanic Metovolconic assemblage ossembloge (2.77 12.77toto2.75 2.75Ga) Go]: Hernia, nernlo, Wawa, WOWO, Burchell ~ ~ ~ ~ h ~ l l Metavolconic Metmlconic assemblage oisembloge (-2.89 Ga) GobHawk Howk / Geological Geologicalboundary bmdory v Fault and/Or shear zone; arrow Faun om/or sheor zone; orrowindico indtm sense .a sense of of direction directton 7 Top TOPdirection direction Synform, Synform, ontitorfin antiform ,r, International boundary / / htem~on o boundary l LS*fZ LSWZLake LokeSuperior-Hernia Superior-Hemlofault fOlIltzone ZOfK NLpG Northern Northern Light-Perching Light-Perchtng Gull GullLakes WeS NLPG botholithic batholithic-complex CUfnplW Tectonic T d cassemblage assemblagemap mapofofthe theWawa WawaSubprovmce, Subp~&ce, showing showingthe thegreenstone grcmsmnebelts Mtsand andtheir thatconstituent mstitumtassemblages, assmblages. selectedsuaiigraphic-facing smtigraphic-facingdata, data,major majorgranitoid gmnitmd faults. masses and faults. masses Figure 1. 1. (Williams et al. al. 1991) 1991) Figure Schreiber Assemblage Asse~nblage 33 Schreiber �Sclzreiber Assemblage 4 �_______ _________________________________________________________ _____________ 87°O0' + + + ++ + 4 49°O0 4s000' 4 49°OO 8 L ++ + + rlgUre F • + 4 •? + + + + + + + + + + + ' ++ ++ + + + + ÷ + roaman + +.4 4 + + + + + + + + + + + • 0 + + + + a + + + + + 01 + + + + +, + + +,+ + + + +1+ + + I'.. + + + + %+ + + % + + + + ++' +\.fV j..—tVV,4+ + 4jVVVVVVv + + + + + +'. + + vLak. vv v + + 4'... + ++ ++ + ++ + + + + + + + + + + + + + + + + + + +++/f''VV VV + . V + ++ + + + + + + + + +__/+ + + + vVvV Vv +++++++ + + + 4. + + + V + + vv4 ++ + + + + + VVV V + VVVVV..V + + + + + + + v+ + + + + .•.vV + + ++ + + + .+ +,-#_\ VLOk. + + + + vV1+++ ++S.( + + +(ff + + + VV74 + + + + + VV ++ + + + + + —. + VV/ + + + + + + + + Vf+ + + + + + + + + + + + + +Vv+ + + + + + + + + + vr+++++++++÷++. ++ Vl + + + + + ÷/V + VVVVVVVVV>V'+ + +/VVVVVVV + +++++++++VVVVVVVVVV,, vvc\ v'.,+ ++ ++ +/vVvVVv ++ + + + ÷\'..1vvvvvv 1'+ + ++,'..yv + + + + ++v' vs_VvV %4VVVvv V VSv' V v —————-..—'vVV' Whlteeond batholuth v v v v v v 'Ji'.k v v V V . + + + + + 4. V + + + 44 ++ çvVv V + + + vv : +vVvvvVvVvc:;cVv ++ 3 +-+ 4 + + + + + IV' VVVVVVVVV V + + + + \VVV VV VVVVVVVVVVVV + + +1+ Jvvvvvvvvvv + + + + + +fr VVv VVVVVVVVVvV 17 Lk. -vv vv v + + ÷ ++++++++ v Vvvvvvvvvvvv C re er v a + + + + 4 v Bay + + vvvvvvvv VVVV5 + +++\.v ++++ + botholith vvV V + + vvv\ v + VVVtf+t.v 4 /f// I jc .10011ffh I V + & 4S0W +++++ V' + + 4 +J1 + + + + 0 + 7v vv , .+T:rroce.&::f" VVV' V V V £' VV, V VVV Vv V 2 Coldweli. Aikalic complex V Boy 1 Coppar blond Jack fish Channel Figure 3 vvv V VSlatev Islands vvvvv Scale 10 VV V 2?km Lake Superior 87°00 LEGEND LEGEND PROTEROZOIC PROTEROZOIC SYMBOLS SYMBOLS @ Carbonatitlc-Alkalic lntrualve Rock Carbonatitic—Alkalic Intrusive Rocks Sop LI] FieldField hipTrip Stop vv vv vv vv Osier Group Group Maflc Maflc and and Felsic Felslc Volcanic Volcanic Rocks Racks Osler and associated associated conglomerate canglamerote ond and orkose arkase ARCHEAN ARCHEAN Felsic Intrusive Intrusive Rocks Rocks Felsic 5 Tonalitic Tonalitic to t oGranodloritic GranodiaritlcCnelsses Cnelases G ~ ~ I O Contact ~h n I t~a Ic t Geological EEII @ Fault Fault Highway Highway Producing Mine L!I1 Producing Mine I.1.Winston WinstonLake Lake(Zn.cu.Ag) (Zn,Cu,Ag) Maflc Maflc to to Ultramaflo Ultrarnaflc Intrusive Intrusive Rock, Rocks Pad Praduclng Mlne [II] Poet Producing Mine Migrnatlzed Supracrustai Supracrustol Rocks Rock Migmatized Metosedimentary Metasedimentary Rocks Racks of of the theQuetico QueticaSubprovlnce Subpravlnce , vvv Figure Figure 2. 2. MaRc Maflc to FelsIc Felalc Metovolcanic Metavolcanlc Rocks Rocks and andassocloted associated Metasedirnentary Rock, Rocks Metosadlmentary Regional Regional geology geology of the the Schreiber Schreiber assemblage. assemblage. Schreiber Schreiber Assemblage Assemblage 55 2. ZenIth/Zenmac Zenlth/Zenmac (Zn.Cu) (Zn,Cu) 2. 3. 3. North NorthShore, Shares(Au) (Au) 4. 4. Davis Davis Sulphur Sulphur Ore Ore (5) (S) 5. 5. Harkneas—Hoys Harkness-Hays (Au) (Au) 6. 6. Empress Empress(Au) (Au) �GENERAL GEOLOGY Definition of Terms The term tectonic assemblage assemblageas asinformally informally applied applied by by the the Ontario Ontario Geological Survey in the Ontario part of the Superior Province has been defined by Thurston (1991) as consisting of: "stratified volcanic and/or sedimentary rock units built during during aa discrete discrete interval of time in a common depositional or volcanic setting. The The rock rock share aa common common or or dominant dominant lithofacies; lithofacies; they they may may also also share share units typically share some additional attributres, such as structural, metamorphic, geochemical geochemical and geophysical features features... ... An An assemblage assemblage is is typically typically bounded bounded by by faults, faults, unconformities or or intrusions." intrusions." term greenstone greenstone belt refers to: The term "elongate or belt-like, kilometre-scale areas of supracrustal rocks within granite-greenstone granite-greenstone subprovinces, subprovinces, with tectonic or intrusive boundaries. Greenstone belts may consist of one or more assemblages. assemblages. AAsubprovince subprovince generally consists consists of of several several greenstone greenstone belts." belts. " (Thurston (Thurston 1991) 1991) Regional Geology The Schreiber lithotectonic assemblage comprises Neoarchean con~prisesthe western segment of the Neoarchean (Williams et et al. al. 1991). ItIt consists Schreiber-Hemlo greenstone belt of the Wawa Subprovince (Williams consists of of Schreiber Assemblage 66 Schreiber Assem.blage �narrow, arcuate arcuate segments segments of of supracrustal supracrustal rocks rocks that that are are bounded bounded and and enclosed enclosed by by a number of narrow, Regionalmetamorphic metamorphicgrade graderanges rangesfrom fromupper uppergreenschist greenschistfacies faciesto tomidmid- to to granitoid bodies. Regional Themajority majority of of lithologic lithologic and and structural structural upper amphibolite facies near granitoid contacts. The (1922),Harcourt Harcourt(1939), (1939), has been been gleaned gleaned from from regional regional scale scale mapping mapping by by Hopkins Hopkins(1922), information has (1939; 1942), 1942),Pye Pye (1964), (1964),Walker Walker (1967) (1967)and andCarter Carter(1988). (1988). Bartley (1939; Supracrustal SupracrustalRocks Rocks supracrustal rocks have been recognized by Carter (1988): (1988): (1) (1) tholeiitic, Three major types of supracrustal (2) calc-alkalic, mafic to felsic volcanics, and (3) (3) clastic and chemical sedimentary mafic volcanics, (2) rocks. Tholeiitic volcanic rocks comprise mainly massive to pillowed basalt, tuffs and related autoclastic breccias (STOP (STOP 2B). 2B). Basaltic Basaltickomatiites komatiiteshave haverecently recently been been recognized recognized within tholeiite-dominated (STOPS 2A, 2B). Calc-alkalic, Calc-alkalic, felsic felsic rocks are dominated by tholeiite-dominated successions (STOPS fine to coarse pyroclastic units that attain significant thicknesses in the Prairie River to Rhumly Lake (STOP5). 5).Sedimentary Sedimentaryrocks rocksconsist consistmainly mainly of of wacke wacke Lake area and in the Winston Lake area (STOP and slate of turbiditic origin and lesser, but significant oxide- and sulphide-facies banded iron formation (STOP1). 1). formation (STOP Few Few geochronologic geochronologic data data are are available available from from this this part part of of the the Wawa Wawa subprovince. subprovince. AAU-Pb U-Pbzircon zircon Schreiber Assemblage Assemblage 77 �+ dateof of2723 2723± 22Ma Mawas wasdetermined determinedby bySchandl Schandletetal. al.(1991) (1991)for forhost hostrhyolite rhyoliteat atthe theWinston Winston date + Lake Mine. Mine. AAvirtually virtuallyidentical identicalage ageof of2720 2720± 22 Ma Ma(Davis (Daviset et a!. al. 1994) 1994)was was derived derived from from Lake altered felsic felsicvolcanic volcanicrocks rocksatatthe theGeco GecoMine Mine in inthe theManitouwadge Manitouwadgegreenstone greenstone belt. belt. Monazites, Monazites, altered interpreted as as synmetamorphic, synmetamorphic,gave gaveages agesof of2677±1 267721Ma Ma and and 2675±1 267551Ma Ma at atWinston WinstonLake Lakeand and interpreted Geco, respectively respectively (ibid). (ibid). Geco, GranitoidRocks Rocks Granitoid The supracrustal supracrustalrocks rocksare areintruded intrudedby byand andbounded boundedby bytwo twomain mainsuites suitesof ofNeoarchean Neoarchean The granitoids: aa gneissic gneissictonalite tonalitesuite, suite,and and aa massive massive granite granite to to granodiorite granodiorite suite. suite. Rocks Rocksof ofthe the granitoids: gneissictonalite tonalitesuite, suite,comprising comprisingfoliated foliated to to gneissic gneissic tonalite tonalite to to granodiorite granodiorite with with minor minor gneissic supracrustalinclusions, inclusions,bound bound the the greenstone greenstonebelt belt to to the the northeast, northeast, south south of of Killala Killala Lake. Lake. Similar Similar supracrustal rocks occur occur within within Quetico Queticometasedimentary metasedimentaryrocks rocks to to the the north. north. Williams Williamseteta!. al.(1991) (199 1)have have rocks consideredthat that the the tonalitic tonaliticrocks rocks may, may, in in part, part, be be synvolcanic synvolcanic with with regard regard to to the the 2.77 2.77 to to 2.70 2.70 Ga Ga considered greenstone assemblages. assemblages. greenstone Massivegranite granitetotogranodiorite granodioriteintrusions intrusionscomprise compriseaamore morevoluminous voluminousand andperhaps perhapsmore more Massive influentialsuite suiteof of rocks rocks within within and and adjacent adjacent to to the the Schreiber Schreiber assemblage. assemblage. These Theseso-called, so-called, influential km. "internalgranitoids", granitoids",are aretypically typicallycomposite, composite,ovoid ovoidintrusions intrusionsthat thatvary varyininsize sizeup uptoto25 25km. "internal They have haverelatively relativelysharp sharpcontacts contactswith withthe thesupracrustal supracrustalrocks, rocks,characterized characterizedby byassimilated assimilated They Schreiber Assemblage Schreiber Assemblage 88 �septa,xenoliths xenolithsand and hybridization, hybridization, suggesting suggestinghigh-level high-level emplacement. emplacement. Walker Walker(1967) (1967)mapped mapped aa septa, narrow, amphibolite-facies amphibolite-facies contact contact aureole aureole around around the the Terrace Terrace Bay Bay batholith (STOP 3) 3) and and noted noted narrow, batholith (STOP that some someremnant remnant supracrustal supracrustalslivers slivershad had been been metamorphosed metamorphosed to to granulite-facies. granulite-facies. AAfoliation foliation that or gneissosity gneissosityisis commonly commonlydeveloped developedin in the the intrusion intrusion parallel parallel and and adjacent adjacent to to its its contact contact with with the the or countryrocks. rocks. country Intrusionsare arecomposite, composite,with withlithologies lithologiesranging rangingfrom fromdominantly dominantlygranite graniteand andgranodiorite, granodiorite,toto Intrusions quartzdiorite, diorite,syenite, syenite,and andquartz quartzmonzonite, monzonite,accompanied accompaniedby bytheir theirgneissic gneissicequivalents equivalentsand and quartz apliteand andpegmatite pegmatite dykes. dykes.These Theseintrusions intrusionsare areconsidered consideredtotobe besynsyn-totopost-tectonic post-tectonicand and are are aplite Hemloassemblage assemblagetotothe theeast. east. probablycorrelative correlativeininage ageand andemplacement emplacementstyle styletotothose thoseininthe theHemlo probably Plutonsin inthe theHemlo Hemloassemblage assemblagereturned returnedages agesbetween between 2678 2678 and and 2688 2688 Ma Ma (Corfu (Corfu and and Muir Muir Plutons 1989).Examples Exampleswithin withinthe theSchreiber Schreiberassemblage assemblageinclude includethe theTerrace TerraceBay, Bay, Crosman CrosmanLake Lake and and 1989). Whitesandbatholiths. batholiths. Whitesand StructuralGeology Geology Structural Despite aa marked markedlack lackof ofstratigraphic stratigraphicfacing facing determinations, determinations, recent structural structural studies studies suggest suggest Despite that there thereisislikely likelyaagreat greatdeal dealof oftectonic tectonic juxtaposition juxtaposition between between supracrustal supracrustal units in in addition addition to that ubiquitous, upright upright folding folding(Schnieders (Schnieders1987; 1987;Carter Carter 1988; 1988;Williams Williams 1989). 1989). Facing Facingreversals, reversals, ubiquitous, conflictingyounging younging directions, directions, unit unit repetition, repetition, inhomogeneous inhomogeneous deformation deformation and thickening of conflicting Schreiber Assemblage Schreiber Assemblage 99 �successions indicate that kilometre-scale folding and duplication duplication by by thrusting thrusting were were significant significant successions (Williams 1989). 1989). Schnieders Schnieders(1987) (1987)noted noted complex complexfolding folding events, events, accompanied accompanied by large-scale large-scale faulting in the Steel River area. Deformation Deformationof of original original stratigraphy stratigraphy has has resulted resulted in in aa fragmentationof of volcano-sedimentary volcano-sedimentarysuccessions successionsand and produced produced aa pseudostratigraphy. pseudostratigraphy. fragmentation Williams (1989) and and others others have have noted that, that, for for the the most most part, part, the the supracrustal supracrustal rocks rocks in in the the Schreiber assemblage assemblage display display non-penetrative non-penetrative strain strain fabrics fabrics produced by rotation, rotation, without without significant significant internal internal distortion. distortion. In Inmarked markedcontrast, contrast,discrete discretezones zones of of strong strong deformation, deformation, such such as as by dip-slip dip-slip style, style, steeply steeply plunging, plunging, mineral mineral the Jackfish-Middleton shear zone, are characterized by and stretching Phyllites and stretching lineations lineationsthat that are are superimposed superimposedon on tectonic tectonic layering layering or or schistosity. schistosity. Phyllites slates, derived from volcano-sedimentary volcano-sedimentary protolith, are locally locally carbonatized, carbonatized, sericitized sericitized and and hematitized. hematitized. clastic sedimentary sedimentary rocks rocks are are juxtaposed with with the the supracrustal supracrustal and and granitoid granitoid Quetico subprovince subprovince clastic rocks of the Wawa subprovince along its northern boundary. The The Quetico Quetico accretionary accretionary complex complex was likely contiguous 2689-2684 Ma, Ma, and and possibly possibly contiguous with the Wawa subprovince at least since 2689-2684 since 2696-2689 2696-2689 Ma (Percival 1989). 1989). AAU-Pb U-Pb zircon zirconprovenance provenance study study of of Manitouwadge Manitouwadge belt belt I wackes by Zaleski Zaleski et et al. al. (1995) (1995) placed placed aa maximum maximum age age limit limit on on deposition deposition of of 2693 2693 Ma. Ma. I A variety of diabase rocks. These diabase dyke swarms swarms intrude the granite-greenstone country rocks. These include include the Paleoproterozoic Paleoproterozoic Hearst Hearst (northwest-trending, (northwest-trending,2454 2454 Ma) Ma) and and Marathon Marathon(north-trending, (north-trending, Schreiber Assemblage Assemblage 10 Schreiber 10 �2170 Ma) Ma)swarms, swarms,and andMesoproterozoic MesoproterozoicPigeon PigeonRiver Riverand andPukaskwa Pukaskwa(north-northeast (north-northeastand and 2170 northwest-trending,respectively; respectively;1100 1100Ma) Ma)swarms swarms(Osmani (Osmani1991). 1991). northwest-trending, Economic EconomicGeology Geology Metallic mineral mineraldeposits depositswithin withinthe theSuperior SuperiorProvince Provinceof ofOntario Ontarioconsist consistof: of:(1) (1)those thoserelated relatedtoto Metallic the the tectonic tectonicsetting settingof ofrock rockassemblages, assemblages,and and(2) (2)those thoserelated relatedto toorogenic orogenicprocesses, processes, superimposedupon upon rock rock assemblages assemblages(Fyon (Fyon et et al. al. 1991). 1991).Rocks Rocksof ofthe theSchreiber Schreiberassemblage, assemblage, superimposed like those thosein inall allgranite-greenstone granite-greenstonesubprovinces, subprovinces,host hostexamples examplesof ofboth bothtypes typesof ofmineralization. mineralization. like The Thefirst firstcategory categorycomprises comprisesthose thosedeposits depositsthat thatwere wereformed formedduring duringearly earlytectonic tectonicand andmagmatic magmatic events, events,including includingsyn-volcanic, syn-volcanic,base base metal metal sulphide sulphide deposits. deposits. Volcanogenic, Volcanogenic,massive massivesuiphide sulphide (VMS),zinc-copper-silver zinc-copper-silvermineralization mineralizationoccurred occurredininthe thebimodal, bimodal,subaqueous subaqueousvolcanic volcanic (VMS), succession (STOP5). 5).The Thehost hostrocks rocksconsist consistof ofmafic maficflows flowsand and successionat at the the Winston Winston Lake Lake Mine Mine (STOP felsicpyroclastic pyroclasticrocks. rocks.Similar Similarrocks, rocks,characterized characterizedby bythe thesame samedistinctive distinctivemajor majorand andtrace trace felsic element elementchemistry chemistryand andhydrothermal hydrothermalalteration alterationmineral mineralassemblages assemblagesoccur occurininthe thePrairie PrairieRiver River area, km to to the thesoutheast southeast(Schnieders (Schniedersand and Smyk Smyk1994). 1994).Lithologic, Lithologic,metallogenetic metallogeneticand and area,45 45 km temporalsimilarities similaritiesthat thatexist existbetween betweenthe theWinston WinstonLake Lakeand andManitouwadge ManitouwadgeVMS VMS camps campsmay may temporal suggest suggestan anoriginal originalstratigraphic stratigraphicconnection. connection. Schreiber SchreiberAssemblage Assemblage 1111 �VMS deposits, deposits, oxideoxide- and and sulphide-facies sulphide-faciesbanded banded iron iron formations formationslocally locally Closely related to VMS within both both volcanic volcanic and and sedimentary sedimentarysuccessions, successions,but but have have limited limited lateral lateral and and vertical vertical occur within Magnetite,pyrrhotite pyrrhotiteand/or and/or pyrite pyrite are are intercalated with chert, wacke Study of extent. Magnetite, wacke or or pelite. pelite. Study km south southof of Schreiber, Schreiber,by by Schnieders Schnieders(1987) (1987) and and Fralick Fralick et etal. al. the Morley pyrite pyrite deposit, deposit,33 km (1989) suggested that massive sulphide precipitation resulted both from the (1989) the venting of hydrothermal hydrothermal fluids fluids and and activity activity of of deep-water, deep-water,organic organic mats. mats. Archean lode lode gold gold deposits, deposits, which which exemplify exemplifythe the second, second,epigenetic epigenetictype type of of mineralization, mineralization,are are Archean typically associated associated with late late tectonic elements elements such as regional deformation zones (Colvine et al. 1988). 1988). However, However,gold goldoccurrences occurrencesininthe theSchreiber Schreiberassemblage, assemblage,while while commonly commonly hosted hosted by by with major major deformation deformation zones. zones. They discrete, local structures, structures, have no discernable association with They to felsic intrusive intrusive rocks rocks on on aa variety variety of of scales. scales. The The are spatially, and perhaps genetically, related to majority of gold gold occurrences occurrences in in the the Schreiber Schreiberarea area lie lie at at or or near the the contact contact of of the the Terrace Terrace Bay Bay porphyry serves as as aa locus locus for for gold gold batholith (Marmont 1983), 1983), while the Big Duck Lake quartz porphyry mineralization in that area (Pye 1964; mineralization 1964; Patterson et al. 1985). The The majority majority of of occurrences occurrences are are quartz quartz vein-hosted, vein-hosted, narrow, narrow, high-grade high-grade deposits deposits which which have have collectively collectively produced produced several several STOP 4). thousand ounces ounces of gold (e.g. Gold Range prospect, STOP 4). Schreiber Assemblage Assemblage 12 Schreiber 12 -- �________ __________ LEGEND CENOZOIC RECENT AND PLEISTOCENE Sand gravel clay and boulders + + — +1..) J + + + + + + + + - + — + + + + + + + + + 1- .4- + s... +(I, + 4. + .4- + GREAT UNCONFORMITY • .4- .4- — + + + 4. + + 4- 4. + + + • + + 4. + + + 4. - PRECAMBRIAN + LATE PRECAMBRIAN + Oiabase UNCONFORMITY I + + + + + + + + + + + 4. + + 1• + — + + + + EARLY PRECAMBRIAN Grani(ic rocks: aplite, pegmatite, LJ0t + + 4. phyries; pink and grey horn blende and + biotite granite and gneiss; hybrid 4- granites. 1 4• + 4.- iNTRUSIVE CONTACT + 7///,2 Greywacke and slate; minor quartzite %7J and conglomerate; guartz-seriCile .4- ,- V/////h7////A biotite-garnet schisis and gnefsses from + sediments. .4- + + + + + + + + + 1- + + Acidic volcanics: agglomerate and tuft; porphyritic lava; guanz.seric,te.gatnet schist and gneiss; minor layers of sediments and basic volcanics. ' + + + 4_ I I Basic to intermediate olcanics: pillow lava and tuft; diabasic to dioritic lava: uinniw !IflhIIthIIIIII I ii chloritebiOtitehOrnblende garnet schists: black hcrnblende-plagioclaS garnet gneiss; chert and minor acidic and sedimentary layers. ao (IL. Field Trip Stop 'I. 0 /c 2km Il'/ ''7-'f717A Lake Superkw Bottle Point Geologyand andStop StopLocations, Locations,Jackfish Jackfisharea; area;Geology Geologyfrom fromWalker Walker (1956). (1956). Figure 3. Geology Schreiber Assemblage 13 Assemblage 13 �DESCRIPTIONS: Stops 11-5 FIELD STOP DESCRIPTIONS: -5 STOP 1: 1: Steel SteelRiver River Turbidites Turbidites STOP 2A: Steel SteelRiver River Komatiites Kornatiites STOP STOP 2B: Jackfish JackfishPillowed Pillowed Basalts Basalts STOP STOP 3: 3: Terrace TerraceBay Bay Batholith Batholith STOP 4: Gold GoldRange Range Prospect Prospect STOP 5: STOP 5: Winston WinstonLake LakeCu-Zn Cu-Zn Mine Mine Schreiber Assemblage Assemblage 14 Schreiber �STOP 1: STEEL STEELRIVER RIVER TURBIDITES TURBIDITES This roadcut exposes exposes clastic clastic sedimentary rocks within aa structured, structured, submarine submarine fan fan sequence sequence with submarine submarine volcanic volcanic rocks and metalliferous metalliferous sedimentary sedimentary rocks, rocks, including including rocks and associated locally with (1 987) and and sulphide-facies As described described by by Schnieders Schnieders (1987) suiphide-facies iron formation formation (Schnieders 1987). As Fralick and Barrett Barrett (1991), (1991), the sedimentary sedimentary succession succession here is dominated dominated by A- and and organized into into upward (southward) (southward) coarsening and thickening, AB-turbidites, organized thickening, and fining and thinning sequences. sequences. These Theseassemblages assemblageswere were thought thought to to represent represent deposition deposition on suprafan suprafan lobes and submarine channels, channels, respectively respectively (Schnieders (Schnieders 1987; 1987; Fralick Fralick and and Barrett Barrett 1991) 1991) Purdon (in progress) has has recognized recognized features features ascribable ascribable to a submarine submarine ramp environment environment in in McKellar Harbour Sequence. These These elastic clastic sedimentary sedimentary rocks, what he has termed the MeKellar dominated by sandy krn east east to to Middleton Middleton where where they they are are truncated truncatedby by the the sandy turbidites, turbidites, extend extend 16 16km Coidwell Coldwell alkalic alkalic complex. complex. Constituent Constituentturbidites turbiditestypically typicallyshow showonly only obscure obscureordering, ordering, transitional boundaries between subsequences and no evidence of channelized channelized deposition. deposition. Local transitional Local turbidites km along strike. There turbidites are are laterally continuous; continuous; some some units have been traced for over 1 km There is also a general thinning- and fining-upward trend within within this this sequence. sequence. In In this this context, context, the the Steel River turbidites may represent channelized channelized deposition on a small lobe on the larger, larger, submarine ramp (R. Purdon, personal communication, 1995). Geochemical Geochemical similarities similaritiesbetween between the Steel common Steel River rocks and and the main part of the McKellar Harbour Sequence support a common provenance and similar similar tectonic tectonic setting. setting. Schreiber Assemblage Assemblage 15 15 �Primary sedimentary sedimentary features, features, such such as as graded southerly Primary graded bedding, bedding, scours scours and and load load casts, casts, indicate indicate aa southerly younging direction. These Thesefeatures featureshave havebeen beenobscured obscuredand and somewhat somewhat transposed transposed along younging along aa 20Âto to bedding. bedding. Schnieders Schnieders(1987) (1987)has has noted noted other other features, features,such such as as foliation, oriented oriented at at about about 200 foliation, parallel and and convolute convolutelamination, lamination,cross-bedding, cross-bedding,flame flamestructures, structures,ripples, ripples, loaded loaded ripples ripples and and parallel rip-up clasts. rip-up clasts. This locality localityisis close closeto to the thewestern westernend endof ofwhat whatWilliams Williams(1989) (1989)described described as the the This Jackfish-Middleton/ McKellar McKellar Harbour Harbour shear zone. This Thisnortheast-trending northeast-trending zone lies between Jackfish-Middletonl mafic volcanic volcanicrocks rocksto to the thesouth southand andsedimentary sedimentaryrocks rocksto to the the north, north, varying varyingin inwidth widthbetween between22 mafic and 3 km. krn. The Thebiotite-in biotite-inisograd isogradand andmore morenortherly northerlygarnet-in garnet-inisograd isograd (Walker (Walker 1967) 1967)obliquely obliquely transect transect the the shear shear zone. zone. Phyllites Phyllitesderived derivedfrom frommafic maficvolcanic volcanicand andsedimentary sedimentaryrocks rocksexhibit exhibit vertical vertical stretching stretchingand and mineral mineral lineations, lineations,horizontal horizontalcrinkle crinklelineations lineationsand and flat-lying, flat-lying, calcite-filled calcite-filledextension extension fractures. fractures. Steeply Steeplyplunging, plunging,tight tightto toisoclinal isoclinalfolds foldsoccur occurwithin withinthe the wackes, metapelites. Tectonic wackes, but but fold fold limbs limbs parallel parallel aa strongly strongly developed developed slaty cleavage in the metapelites. Tectonic disruption, disruption, bed attenuation attenuationand conflicting conflicting kinematic and younging indicators characterize much of of this zone (Schnieders 1987). 1987). Williams Williams(1989) (1989) has suggested suggested that an early dip-slip style of deformation deformation was was followed followedby by dextral dextralshear shearas asevidenced evidenced by by overprinting, overprinting,Z-asymmetric Z-asymmetricfolds foldsand and sub-horizontally sub-horizontally plunging plunging slickensides. slickensides. Schnieders Schnieders(1987) (1987)has has suggested suggestedtwo two separate separate folding folding events events or or aa polyphase polyphase folding folding event eventin inthe the Steel SteelRiver River area. area. Schreiber Assemblage Assemblage 16 16 �STOP 2A: STEEL STEELRIVER RIVER KOMATIITES KOMATIITES This section sectionof of the the local localvolcanic volcanicsuccession successionhas hasbeen beeninvestigated investigatedbecause becauseof ofthe therecent recent This discovery of of aa spinifex-textured spinifex-textured flow flow unit unit within within pillowed, pillowed, tholeiitic tholeiitic basalt, basalt, similar similarto to pillowed pillowed discovery units exposed exposed 600 600 m northwest (STOP (STOP 2B). 2B). These Thesetwo twosections, sections,while whilepart part of of the the same same volcanic volcanic units package, are are remarkably remarkably different differentin interms termsof oftheir their lithologic lithologicand and eruptive eruptivecharacteristics. characteristics. package, This 70 70 m m detailed detailedsection section(Figure (Figure4) 4)along alongthe thesouth southside sideof ofthe thehighway highwaycomprises comprises aa number of This different flows/flow flows/flowunits units which which dip dip steeply steeply (60°SE) (60°SEand and young to the southeast. Subsequent Subsequent different tectonic deformation, deformation,alteration alterationand andquartz-carbonate quartz-carbonateveining veininghave haveobscured obscuredsome someof ofthe theprimary primary tectonic features featuresand and relationships. relationships. Individual Individualflow flowunits, units,separated separatedby bysharp, sharp,locally locallysheared, sheared,contacts, contacts, range range in in thickness thickness from from approximately im 1mto to perhaps perhaps 20.m. 20 m. These Theseunits unitscomprise comprisemassive, massive, locally locally pillowed, pillowed, basalt, basalt, iso1ate""isolate"-toto"crowded"-pillow "crowdedu-pillowbreccia brecciaand and massive massive to to spinifex-textured, spinifex-textured, basaltic basaltic komatiite. komatiite.Individual Individualflow flowunits unitsdisplay displaymarked markedgeochemical geochemicalvariation. variation. Perhaps komatiite. ItItisis Perhaps the the most most noteworthy noteworthy lithologic lithologic unit unit is is the the spinifex-textured, spinifex-textured, basaltic komatiite. apparently metapyroxenite(?)base, base, an anoriented, oriented,plate plate apparently aa composite compositeflow flowconsisting consistingof ofaamassive, massive,metapyroxenite(?) spinifex-textured spinifex-texturedcentral centralunit unitand andaafiner-grained, finer-grained,randomly randomlyoriented, oriented,upper upperspinifex-textured spinifex-textured portion. portion. Serpentine-rich Serpentine-richveins veinsoccur occurwithin withinthe themassive massive flow. flow. Whole-rock Whole-rockgeochemistry geochemistryshows shows aa progression progressionfrom frombasaltic basaltickornatiite komatiiteatatthe thebase baseto tohigh-magnesium, high-magnesium,tholeiitic tholeiiticbasalt basaltatatthe thetop top of of the the flow flow(Table (Table1). 1).Immediately Immediatelyabove abovethe thecontact contactwith withthe themassive massivekomatiite, komatiite,spinifex spinifex crystals crystals Schreiber Schreiber Assemblage Assemblage 17 17 �are oriented cm)crystals crystals oriented parallel parallel to to the the contact. contact. Less than a metre up from the contact, large large (58 (8 cm) and sheaf-like aggregates are oriented at right angles to the contact and and locally locally branch branch upwards upwards in Coarse-grainedspinifex spinifexgradually graduallygives givesway way to toaafiner-grained, finer-grained, more more a plumose fashion. Coarse-grained randomly oriented texture in which individual crystals are ~O.8 0 .cm 8cmlong. long. to44mm, mm, massive, non-magnetic, non-magnetic, basalt basalt flows flows are are characterized characterized by by 22to Incipiently pillowed, largely massive, light green varioles which coalesce into lobate, amoeboid patches patches or may may concentrate concentrate along irregular (synvolcanic?) stockwork fractures. Pillow Pillow forms forms are are indistinct indistinct but but are are suggested suggested by by lobate variole pods and selvage-like patterns. Selvages Selvages are are characterized characterized by by bands bands of of coalescing coalescing varioles, and/or andlor quartz quartz ±Âhyaloclastite hyaloclastite layer(s). layer(s). This unit may be related or transitional with an isolate pillow breccia, a massive flow unit with discrete, isolated isolated or detached detached pillows pillows and and pillow pillow fragments. fragments. "Crowded' "Crowded" pillow pillow breccia contains a higher proportion of discernable pillows and pillow fragments ranging in size from 10 10 to 100 100 cm. Smaller pillows are spherical to bun-shaped, while larger counterparts are are ovoid ovoid to to mattress-shaped. Many mattress-shaped. Many of of the the larger larger pillows pillows contain contain stacked, stacked, quartz-filled, "drain-away" cavities which represent successive stands of falling lava (cf. Wells Wells et et al. al. (1978). (1978). Hyaloclastite occurs in the interpillow spaces and within lenticular pods in seemingly more massive flow units. Autoclastic breccias occupy most flow contacts. textural variation variation The spinifex-textured flow shows remarkable similarities with the serial textural SchreiberAssemblage Asse,nblage 18 Schreiber �described by Pyke et al. a!. (1973) (1973) in in the the Abitibi Abitibigreenstone greenstonebelt. belt. Common subunits, in descending descending order, include: chilled, fractured and brecciated upper contact; contact; upper, upper, randomly randomly oriented oriented spinifex spinifex zone (KOM-3); lower, plate spinifex zone (KOM-1); foliated phenocryst zone (KOM-7) and a massive, ultramafic base (KOM-2,-5,-6). (KOM-2,-5,-6). Thin section and X-ray diffraction diffraction analyses analyses reveal that the constituent constituent crystals in the spinifex spinifex are optically continuous, skeletal, skeletal, branching grains of magnesio-hornblende magnesio-hornblende and chlorite (clinochiore) (clinochlore) likely the the alteration products products of of primary, primary, magensium-rich magensium-richclinopyroxene. clinopyroxene. The (Plate 1). They are likely matrix is a fine-grained fine-grained matte matte of of talc, talc, serpentine, serpentine, carbonate, carbonate, chlorite chlorite and amphibole amphibole resulting resulting from greenschist-facies metamorphism. alteration and greenschist-facies metamorphism. The massive, basal portion of the flow (samples (samples KOM-2,-5,-6), KOM-2,-5,-6), interpreted as a metapyroxenite, consists of a very fine-grained, decussate to weakly foliated (parallel to flow contact), talcose, Fe-oxides and andcalcite. calcite. Relict, equant serpentinized matrix with minor amphibole, Fe-oxides clinopyroxene(?) clinopyroxene(?) phenocrysts phenocrysts average average0.15 0.15 mm mm in in size. size. Foliated spinifex (KOM-7) occurs at the lower contact of the spinifex-bearing portion of the flow. ± calcite aggregates that have replaced It is characterized by subparallel, talc  subparallel, serpentine serpentine ++ talc mm phenocrysts. phenocrysts. Equant, blocky clinopyroxene phenocrysts phenocrysts (50.6 (0.6 xx1.0 acicular, 0.3 xx 1.0 mm 1.0mm, mm, 0.15 to 2 mm mm square) are also evident. evident. Phenocrysts and pseudomorphs are set in a averaging 0.15 finer-grained finer-grained matrix matrix of of subparallel, subparallel,0.05 0.05to to 0.07 0.0755 mm, acicular crystals and Fe-oxides. Fe-oxides. Schreiber Assemblage Assemblage 19 19 �Plate 1. Photomicrograph Photomicrograph(PPL) (PPL)of of optically opticallycontinuous, continuous,branching branching and and plumose plumose rnagnesio-hornblende and chlorite textured, magnesia-hornblende chlorite (clinochiore) (clinochlore)in in coarse, coarse, plate plate spinifexspinifex-textured, (KOM-1), STOP 2A. Field Field of of view view is is 4.0 mm. mm. basaltic komatiite (KOM-I), Plate 2. Photomicrograph Photomicrograph(PPL) (PPL)ofofupper, upper,randomly randomlyoriented orientedspinifex—textured spinifex-textured portion of flow (KOM-3), STOP 2A. Field Field of of view view isis 4.0 4.0 mm. mm. Schreiber Assemblage Assemblage 20 Schreiber �Schreiber Schreiber Assemblage Assemblage 21 21 �1 STOP 2A 2A STOP STOP 2B 2B STOP LEG: Lithologic units units Lithologic Al: A1: A2: Az: Bl: B1: B,,: B: Cl: Cj: Chilled Zone Zone (upper (upper contact) contact) Chilled S p W a zone zone (Au: (Aa: upper. upper, rendomly randomly oriented orientedzone) zone) spinhlex lower, plate plate spinllex spinifex zone) zone) (As: (Aa : Ie'wer. Foliated spinitex spinifexzone zone Foliated Massive, ultramafie ultraxnafic basal basalzone zone(unsubdivided) (unsubdiyided) Massive, bfa=si~e brisdt/basdtic komatlite Massive basalt/basaltic kornatlite , Crowded' pifiow basalt/basaltic komatilte Cze : mCrowded*. pfflow basalt/basaltic komatiite C2: Ca : hci*iently pillowed b a s a l t f i n d t i c komatilte komatUte Inciient1y pillowed basalt/basaltic Ca: bx : : Autoclastic Autocladic breccia breccia(broken (brokenpillow/flow pUow/flow breccia) breccia) bx I Figure 44 : Geological Geological sketch maps, maps, detailed detailed flow flow cross—sections cross-sections (looking (looking southwest), southwest), stops stops2A, ZA,2B. 2B. Figure : Sc1zreibe1-Assemblage 22 Schreiber Assemblage 22 �LEGEND Symbob 1-1 Flow Flow contact/Internal contact/internd subdiviaion subdivision IH m Pillow outline ixI OUwe Hyaloclastite Hyaloclasti~ 1 x 1 Drain—away Drain-away ca'vities cadties Schreiber Assemblage Assemblage 23 23 Schreiber 1 7 1Spinifex orientation orientation Spinifex • . qv T Sample Sample location location and and number KOM—l) number(e.g. (e.g. KOM-1) quartz quartz1-/— +/- calcite calcite vein/pod v8in/pod �Plate spinifex spinifex(KOM-1) (KOM-1)isischaracterized characterizedby by amphibole amphibolepseudomorphs pseudomorphsof of 0.15 0.15toto0.2 0.2 mm, mm, acicular acicular Plate crystals that that occur occur in in optically optically continuous continuous aggregates aggregates up up to to 1.0 1.0 mm nlm wide and in excess of 20 mm mm crystals long. Amphibole-replaced Amphibole-replacedcrystals crystalsare areseparated separatedby by serpentinized serpentinizedcrystals. crystals. Relict, Relict,subhedral subhedral long. pyroxene phenocrysts, phenocrysts, equant equant to to lathlike, lathlike, reach reach lengths lengths of up to 1.0 1.0 mm. The Thefine-grained fine-grainedmatrix matrix pyroxene consists consists mainly mainly of of plumose plumoseto to sheaf-like sheaf-likeserpentine, serpentine7with with subordinate subordinateepidote epidote (sausserite?). (sausserite?). The serpentinized, con~pletely serpentinized,0.05 0.05 xx 1.0 1.0mm, mm, The upper, upper, spinifex-texured spinifex-texuredflow flow(KOM-3) (KOM-3)consists consistsof ofcompletely mm) randomlyoriented orientedbooks booksof of crystals crystalsin in aa devitrified devitrifiedglass glass matrix matrix (Plate (Plate 2). 2). Larger Larger(0.3 (0.3xx44mm) randomly phenocrystscomprise compriseapproximately approximately5% 5%of ofthe therock rockand andhave havebeen beenaltered alteredtotoserpentine serpentine++epidote epidote phenocrysts ++calcite. calcite. The flow Theoverlying overlyingbasaltic basaltickornatiite kon~atiite ilow(KOM-4) (KOM-4)consists consistsof of aavery veryfine-grained, fine-grained,decussate decussate intergrowth (after intergrowthof of turbid turbid amphibole amphiboleand and epidote. epidote. Pseudomorphs Pseudon~orphs (afterpyroxene) pyroxene)are areequant equantand and blocky mm in in size. size. Fe-oxides Fe-oxidesare arenotably notablyrare. rare.Pyroxene Pyroxenephenocrysts, phenocrysts, blocky and and average average 0.1 0.1 to to 0.2 0.2 mm comprising comprisingapproximately approximately3% 3%ofofthe therock, rock7fange rangeuo uototo0.6 0.6mm mmininsize sizeand andare areinvariably invariablyaltered alteredtoto magnesian magnesianchlorite chlorite(penninite) (penninite)±&epidote epidote± serpentine. serpentine. Schreiber Assemblage 24 �FeC ÷ Fe203 +Ti02 High-Fe Tholeätic Basalt KOM-3 KOM-4 • KOM-2, KOM- 1 Basaltic Komatite A1203 AE03 Figure Figure5: 5:Jensen Jensen(1976) (1976)Cation CationPlot PlotofofSteel Stee!IRiver Rivermafic maficvolcanic volcanicrocks. rocks. Schreiber SclzreiberAssemblage Assemblage 25 25 ''Uttramafic MgO �Table Table 1.1.Geochemical GeochemicalResults, Results,Tholeiitic Tholeiiticand andKomatiitic KomatiiticBasalts, Basalts,STOPS STOPS2A 2A and and 2B 2B Sample Sample SiO2 Si02 A1203 A1203 Fe203 Fe203 MgO MgO CaO CaO Na20 Na20 K2O K20 P2O5 P205 Ti02 Ti02 MnO MnO BaO BaO Cr203 Cr2O3 SrO SrO LO1 LOl Total(%) (%) Total KOM-i 48.00 11.29 11.82 1000 9.10 1.89 0.12 0.146 0.701 0.182 0.013 0.174 0.10 2.7 96.1 KOM-2 41.08 9.42 13.25 19.53 7.03 0.10 0.01 0.106 0.545 0.215 0.006 0.350 0.001 6.7 98.3 KOM-3 48.35 11.60 12.14 8.07 11.70 1.49 0.05 0.099 0.660 0.191 0.007 0.250 0.013 3.6 98.2 KOM-4 47.40 11.07 12.66 10.84 9.28 1.72 0.06 0.084 0.656 0.206 0.007 0.219 0.008 3.8 98.0 JACK-i JACK- 1 48.71 13.95 12.34 7.17 12.35 1.13 0.24 0.065 0.932 0.203 0.011 0.085 0.009 2,6 99.8 BRS-48 BRS-48 44.77 10.43 13.37 12.04 8.67 1.96 0.01 0.16 0.65 0.26 7.40 99•741 SRG-22 SRG-22 51.70 14.40 12.00 7.04 7.81 2.86 <.10 0.90 0.21 SRG-14 SRG-14 45.70 13.00 11.10 11.80 7.74 2.18 0.24 1.12 0.18 5.00 98.062 SRG-15 SRG-15 37.50 4.40 9.15 32.00 2.05 0.07 0.05 0.03 0.29 0.15 13.0 98.582 Pyrox F'yroxb 46.27 7.16 11.45 16.04 14.08 0.92 0.64 0.38 1.47 0.16 1.26 99.83 PerjcJt Perid'' 42.26 4.23 10.19 31.24 5.05 0.49 0.34 0.10 0.63 0.41 5.27 99.46 Dunite Dunite 38.29 1.82 12.97 37.94 1.01 0.20 0.08 0.20 0.09 0.71 5.27 98.53 Schreiber Schreiber Assemblage Assemblage 26 26 97.522 �Sample Sample Descriptions: Descriptions: STOP 2A: KOM-l: KOM1:Coarse, Coarse, plate plate spinifex-textured, spinifex-textured, basaltic komatiite KOM-2: Massive, basal metapyroxenite metapyroxenite unit (basaltic (basaltic komatiite) KOM-3: Randomly oriented,fine-grained, KOM-3: oriented,fine-grained, spinifex-textured upper flow (high-Mg tholeiitic basalt) KOM-4: Overlying, Overlying, pyroxene-phyric, pyroxene-phyric, pillowed pillowed basaltic basaltic kornatiite komatiite STOP 2B: JACK-1: Variolitic Varioliticpillow, pillow,section sectionrim rimtotocore core(high-Mg (high-Mgtholeiitic tholeiiticbasalt) basalt) JACK-i: BRS-48: Ultramafic [3 km east of STOP2A]' STOP~A]~ Ultramaficintrusion, intrusion,Little LittleSteel Steel Lake Lake [3 Massive,high-Mg high-Mgtholeiitic tholeiiticbasalt, basalt,Stoughton-Roquemaure Stoughton-RoquemaureGroup, Group,Abitibi AbitibiBelt2 Belt2 SRG-22: Massive, SRG-14: Massive, Massive,basaltic basaltickornatiite, komatiite,Stoughton-Roquemaure Stoughton-RoquemaureGroup, Group,Abitibi AbitibiBelt2 Belt2 SRG-15: Pillowed, Pillowed,ultramafic ultramafickomatiite, komatiite,Stoughton-Roquemaure Stoughton-RoquemaureGroup, Group,Abitibi AbitibiBelt2 Belt2 'from Schnieders from Schnieders (1987) 2from 'from Jensen (1976) (1976) 3Average Major Element Compositions of Igneous Rocks 'Average Major Rocks (LeMaitre (LeMaitre 1976) 1976) Schreiber Assemblage 27 Schreiber Assemblage �STOP 2B: JACKFISH JACKFISHPILLO PILLOWED BASALTS WED BASALTS complete without a pillow lava stop! However, However, not not only only does doesthis this stop stop No trip would be complete exemplify well-preserved volcanic volcanic features features it also also represents represents one end of the deformationdeformationmetamorphism spectrum in the Schreiber assemblage. ItIt represents represents the most unmetamorphosed unmetamorphosed (greenschist comparison, the rocks we see see (greenschist fades), facies), undeformed supracmstal supracrustal rocks rocks in in the the area. area. By comparison, east along along the the highway highway are are progressively progressively more more deformed, deformed,metamorphosed metamorphosedand and altered. altered. to the east This exposure, first mentioned by Walker (1 967), affords an (1967), an excellent, excellent, three-dimensional three-dimensional view view of of basalt flows flows which which dip dip steeply steeply relatively undeformed, pillowed, high-magnesium tholeiitic basalt (70°SE) and young to the southeast. About (70°SE Aboutone-half one-half of ofthe the flow flowsuccession successionwithin within the the 60m 60m is pillowed; pillowed; the the remainder remainder is is relatively relatively massive massive or or shows shows some some detailed section section (Figure (Figure 4) is incipient pillow development. Where Wheretraceable, traceable,flow flowcontacts contacts are are sharp sharp and and conformable conformable with other, horizontal features such as drain-away cavities and lava lava tube tube surfaces. surfaces. Flow Flow morphology morphology thickness are and thickness are not readily readily apparent apparent because because of of the the lack lack of of reliable reliable marker units units and and the the limited limited exposure along strike. strike. Internal Internalfeatures featuresof ofthe theflows, flows,however, however, are are remarkably remarkably well-preserved well-preserved and provide insight insight into into the the nature nature of of the the lava lava and and its its eruptive eruptive environment. environment. The pillow-forms pillow-forms vary vary from from small, small,ellipsoidal, ellipsoidal,bun-shaped bun-shaped masses masses (50-100 (50-100cm) cm) to to large, large,flat, flat, in) which are interepreted as lava tubes (nomenclature mattress megapillows(2 ( 33 m) mattress megapillows (nomenclature of Dimroth et al. 1978). 1978). Pillows Pillowsare aretightly tightlypacked packedand andmolded molded to to one one another, another, with with little little massive, massive, interpillow interpillow Schreiber Assemblage Assemblage 28 28 �Thereisisconsiderable considerablesize sizevariation variationamongst amongstpillows pillows within within the the same same part part of of the the flow. flow. space. There 979). There There is is Areas with rounded, bulbous pillow forms may represent flow tops tops (Wells et et al. al. (1 (1979). some evidence evidenceof of lateral lateralbudding buddingof ofpillows pillowsininthe theform formofof"neck-and-knob'1 "neck-and-knob"development developmentand and some re-entrants of of chilled chilled pillow pillowcrust, crust,perhaps perhapsindicating indicatingtoo too rapid rapid chilling. chilling. Pillow re-entrants Pillow imbrication imbricationis. is minimal. minimal. Hyaloclastiteis is locally locally developed developed in in the the interpillow interpillow spaces. Autoclastic Autoclasticbreccias brecciasare arenotably notably Hyaloclastite absent southeast absent in in this this part part of of the the succession succession but become volumetrically significant to the southeast (STOP (STOP 2A). 2A). Interfiow Interflowsedimentary sedimentaryrocks, rocks,absent absentin inthis this section, section, occur occur within stratigraphically lower flows to the northwest. Quartz-filled Quartz-filleddrain-away drain-awaycavities cavities or or lava lava shelves shelves provide provide excellent excellent geopetal indicators. indicators. Individual Individualpillows pillowsmay maycontain containup up to to44 or or55stacked stackedcavities, cavities, which which represent represent successive successive stands stands of of falling falling lava lava (cf. (cf. Wells Wells et et al. al. 1979). 1979). Although Although small, small,2-4 2-4 mm, mm, spherical sphericalvesicles vesiclesand and amygdules amygdulesof of quartz quartzand and calcite calciteare areevident, evident,the the local flow succession is characterized characterizedby bythe thedevelopment developmentofoflime-green lime-greenvarioles. varioles.Smaller Smaller(52 (2 mm) (1 00mm) mm) varioles varioles tend tend to to develop develop near pillow selvages selvages while larger (51 mm)counterparts counterpartsoccur occur closer closer to the core core of of the the pillow. pillow. They Theytypically typicallycoalesce coalesceto toform formarcuate, arcuate,somewhat somewhatconcentric concentric bands Insome someexamples, examples, bands and and pods pods along along flow flow contacts, contacts, selvages selvages and in pillow cores (Plate 3). In they they comprise compriseover over one-half one-half of of the the pillow. pillow. Some Somevarioles variolesdisplay displayaaconcentric, concentric,macroscopic macroscopic zonation zonation between originally originally plagioclase-rich plagioclase-rich cores and more mafic, outer envelopes. Plagioclase Plagioclase crystals crystals may may project project radially radially outwards outwardsfrom fromthe the otherwise otherwisefairly fairlysmooth, smooth,spherical sphericalvariole variole margin. margin. Schreiber Assemblage Assemblage 29 29 �Plate 3. Photograph Photographof of coalescing coalescing varioles varioles in pillows, STOP 2B. Note Note hyaloclastite hyaloclastitein in interpillow interpillow spaces. Lens cm in in diameter. diameter. Lenscap capisis55 cm Plate 4. Photomicrograph Photomicrograph(PPL) (PPL)of of reticulate reticulateplagioclase plagioclase microlites microlites and and devitrified devitrified glass glass in variole (JACK-I),high-Mg high-Mg basalt, basalt, STOP STOP 2B. 2B .Note Noteeuhedral euhedralphenocryst phenocrystofofplagioclase(?), plagioclase(?), (JACK-i), pseudomorphed by fine-grained quartz and and epidote epidote (dark (dark patches patches near near core). core). Field of view is 4.0 mm. Schreiber Assemblage Assemblage 30 Schreiber �Schreiber Assemblage 31 Schreiber Assemblage 31 �Local pillows are morphologically similar similar to spherulitic spherulitic pillows pillows described described by by Dimroth Dimroth and and They described described aa rim rim to to core core succession: succession: Lichtblau (1979). They devitrified glass @asscrust-4 crust* zone zone of of albite albitespherulites spherulites—, -4 isolated isolated spherulites spherulites -4 -4 hyaloclastite -4 devitrified spherulites -4 coarse, coarse,fibrous fibrous spherulites spherulites or or dendrites dendrites -4 -4 microlitic microlitic zone zone (core). (core). coalescent spherulites section, the the varioles varioles consist consist of of aa glassy, glassy, altered altered groundmass groundmass which which hosts hosts aa polygonal polygonal In thin section, network of discrete, 0.02 to 0.04 mm wide, dendritic and plumose plagioclase microlites (Plate 4). Subparallel, branching branching microlite microlite arrays/intergrowths an-ays/intergrowths Fe-oxides occur adjacent to the microlites. Subparallel, These linear linear arrays arrays are are somewhat somewhat similar similar to to quenchmay occupy sections between larger crystals. These (1974) in Archean, hightexture, skeletal olivine chains described by Gelinas and Brooks (1974) magnesium tholeiites. The The fine, fine, fibroradial textures described by Fowler et al. (1987) (1987) are notably notably absent. absent. Conspicuous, Conspicuous, subhedral subhedral to to euhedral euhedral phenocrysts phenocrysts have have been been replaced replaced by by fine-grained fine-grained quartz. quartz.They They are typically <:1 1 mm mminindiameter diameterand andoccur occurboth bothwithin withinvarioles variolesand andininthe themore moremafic mafic groundmass. groundmass. Quartz comprises coarser, polygonal mosaic-textured cores and finer-grained margins. Hollow Hollow crystal crystal cores commonly host "islands" "islands" of epidote. Crystal Crystalhabit habitand andshape shapesuggest suggestthat that the the original and/orolivine, olivine,both both of of which whichhave havesimilar similarcross-sections cross-sectionsinin original phenocrysts phenocrysts were were plagioclase plagioclaseand/or orientations parallel to the c-axis. Quench Quench olivine olivine described described by by Gelinas Gelinas and and Brooks Brooks (1974) (1974) bears some striking similarity to the phenocrysts in question. They They described described hollow, hollow, quartz-replaced quartz-replaced olivine olivine euhedra euhedra in in aa matrix matrix of of plumose plumose and and branching branching clinopyroxene, clinopyroxene, with with intervening intervening calcic calcic Schreiber Assemblage 32 Schreiber Assemblage 32 �plagioclase and and devitrified devitrified glass. glass. These Thesequench quenchtextures textureswere wereascribed ascribedtotorapid rapidcooling cooling(not (not plagioclase necessarily supercooling) supercooling) and and are are identical identical to to those those found found in modern submarine submarine lavas. lavas. necessarily The greener greener (in (in hand hand specimen) specimen)areas areasbetween between the thevarioles variolesConsist consist of coarse, polygonal chlorite The aggregates with with accessory, accessory, blocky blocky epidote, epidote, quartz quartz and and Fe-oxides. Fe-oxides. aggregates This section section of of subaqueous subaqueousbasalt basalt flows flowswas was probably probably extruded extrudedin in fairly fairlydeep deepwater wateras assuggested suggested This low vesicularity and and small small vesicle vesicle size size and and sphericity, sphericity, by the absence of significant significant volumes volumes of by low al. 1978). 1978). The Theconformity conformityof of primary primary horizontal horizontal features features suggests suggests (cf. Dimroth et a!. pillow breccia (cf. relatively flat flat depositional depositional surfaces. surfaces. Stacked Stackedmegapillows megapillowsare areinterpreted interpreted as as successively successively relatively emplaced flow flow lobes lobes or or lava lava tubes, tubes, each each behaving behaving as as aa single cooling unit. These Thesetubes tubeswere were emplaced perhaps feeders for overlying, overlying, pillowed sections. The The lack lack of of isolated, isolated, detached detached pillows pillows may perhaps relate relate to to relatively relatively slow slow rates rates of of spreading spreading and and lava lava production. production. However, However,laboratory laboratoryexperiments experiments conducted by by Gregg Gregg and and Fink Fink (1995) (1995)showed showed that that pillows pillows become become larger larger and and flatter flatter as as effusion effusion conducted rate rate and and slope slopeincrease increaseand/or and/orcooling coolingrate ratedecreases. decreases. The origin originof of varioles varioleshas hasbeen beenrelated relatedtotoundercooling undercoolingof ofthe theliquid liquidduring duringcooling cooling(Fowler (Fowlereteta!. al. The 1987). havebeen beensuggested suggestedfor for 1987).Lava Lavaeruption eruptiontemperatures temperaturesofofbetween between13000 1300'and and1400° 1400' CChave basaltic (R.Keays, Keays,personal personal communication, communication,1994). 1994).In In basaltickomatiites komatiitesand and siliceous, siliceous,high-Mg high-Mgbasalts basalts(R. Archean Archean tholeiites, tholeiites,varioles variolesare arespherulites spherulitesproduced produced by by crystallization crystallizationwhen when nucleation nucleation is is suppressed suppresseduntil until the thephase phaseisiswell wellbelow belowits itsliquidus liquidustemperature; temperature;this thistextural textural development developmentisisdue due Schreiber Assemblage 33 Schreiber Assemblage 33 �to immiscibility. ItItisisinteresting interesting to to note note that that Fowler Fowler et et a!. al. (1987) (1987) stated that the textural development of varioles and komatiites are analogous in that both result from supersaturation brought about by supercooling. supercooling. about by Schreiber Assemblage Assemblage 34 34 �STOP 3: TERRACE TERRACEBAY BAY BATHOLITH stop is is located located near near the the northeastern northeastern contact contact of of the the Terrace Terrace Bay is in in This field stop Bay batholith, batholith, where where it it is predominantly mafic mafic metavolcanic metavolcanic rocks, rocks, similar similar to to those those at at Stops Stops2A 2A and and 2B. 2B. The The contact with predominantly along the the base base of of aa prominent, prominent, east-trending east-trending ridge ridge of of mafic mafic metavolcanic metavolcanic rocks rocks that that contact lies along 800 m m north north of of this this highway highway stop. stop. approximately 800 lies approximately 30 km km from from south south of of Schreiber Schreiber is ovoid ovoid in in plan plan view view and and extends extends for for approximately approximately 30 The batholith is to this vicinity. As Asdescribed describedby byMarmont Marmont(1984), (1984),the the bulk bulk of of the the batholith batholith consists consistsof of massive, massive, homogeneous, equigranular, medium-grained granodiorite. However, However, variations variations in in texture, texture, grain grain size, colour and composition are common, especially at and near near intrusive intrusive contacts. contacts. Largely Largely pristine and and undeformed, undeformed, the the batholith batholith may may exhibit exhibit local, local, weakly weakly developed developedmineral mineral foliations foliations and lineations near its margins. Marmont Marrnont(1984) (1984)suggested suggestedthat that the the lack lack of of a chill margin, the presence presence of of perthitic perthitic feldspar feldspar and and the the largely largely homogeneous, homogeneous,medium-grained medium-grained texture texture suggest suggestaa level. The relatively slow cooling history and a mesozonal emplacement level. The abundance abundance of assimilated country stoping was was important. important. country rock rock xenoliths xenolithsindicates indicates that that passive passive stoping A number of of polymetallic, polymetallic, auriferous auriferous quartz quartz veins, veins, including including the the Mogotherium, Mogotherium,Beaver BeaverCreek, Creek, Ferguson Ferguson (Crystal (CrystalCreek), Creek), Elgin/Siville-Ferrier ElgidSiville-Ferrier and and Mocan Mocan occurrences, occurrences,occur occur in in the the vicinity. vicinity. The largest largest of these, the Empress Empress Mine Mine (see (see Frontispiece), Frontispiece), is is located located approximately approximately 11 km km north north of this field stop, ridge. Operated stop, midway up the aforementioned aforementioned metavolcanic ridge. Operated around around the the turn turn Schreiber Assemblage Assemblage 35 35 �Base metal metal suiphides sulphides of the century, this mine reportedly produced just just over 100 ounces of of gold. gold. Base galena, chalcopyrite and sphalerite tend to characterize auriferous The Ferguson Ferguson such as galena, auriferous veins. veins. The (Ag2Te),acanthite acanthite(Ag2S), (Ag2S),native native occurrence is is somewhat somewhatunique uniquein inthat thatthe theminerals mineralshessite hessite(Ag2Te), occurrence bismuth, nuffieldite nuffieldite(CuPb2(Pb,Bi)Bi2S7) (CuPb2(Pb,Bi)Bi2S7)and andan anunidentified unidentifiedCu-Bi-Pb-sulphide Cu-Bi-Pb-sulphide have have been been discovered there (Patterson (Patterson et al. 1987; 1987; Kissin and McQuaig 1988). The The possible possible role role of of the the Terrace Bay batholith batholith in in epigenetic, epigenetic, Au-Cu-Mo Au-Cu-Mo mineralization mineralization is is discussed discussed prior prior to to the the description Stop 4. 4. description of Stop The granite granite exposed exposed at at this this location location isis grey-weathering, grey-weathering,equigranular, equigranular,medium-grained medium-grainedand and contains contains approximately approximately 25% quartz, quartz, 40% potash feldspar, 25 to 30% oligoclase-andesine and 5% hornblende or biotite biotite (Walker (Walker 1967). 1967). Minor Minorconstituents, constituents,in inorder orderof of decreasing decreasing abundance, abundance, are are and magnetite. magnetite. Molybdenite sphene, apatite, fluorite, tourmaline, muscovite, epidote and Molybdenite has has been been noted locally. locally. These glacially polished outcrops outcrops are are characterized characterized by numerous, numerous, partially digested, digested, rounded rounded to to sub-rounded, mafic xenoliths. The Thexenoliths xenolithsrange range in in size sizefrom from <1 4 to to 15 15cm, cm, averaging averaging 22 to to 55 cm. Average Averageabundance abundanceisis in in the the order order often of tenxenoliths/m2. xenoliths/m2.Xenoliths Xenolithsrange range in in composition compositionfrom from small, small, amphibole amphiboleclots clots that that presumably presumably represent represent the the refractive refractive residuum residuum left left over over from from partial partial digestion, amphibole-phyric, diorite and mafic metavolcanic fragments. Xenoliths Xenolithsare are digestion, to larger, amphibole-phyric, recessively weathered, perhaps due to the presence of biotite. These These xenoliths xenolithsrepresent represent assimilated mafic metavolcanic metavolcanic country country rocks rocks and and earlier, earlier, more more mafic mafic intrusive intrusive rocks rocks Schreiber Assemblage Assemblage 36 Schreiber �that pre-dated pre-dated granitic granitic intrusion. intrusion. Marmont Marrnont(1984) (1 984)stated statedthat thatthe theabundance abundanceof ofmafic maficenclaves enclavesisis that directly proportional proportional with with their their proximity proximity to to the the present present batholith batholith contacts contacts and its upper/roof upperlroof directly zone. zone. Hematitic Hematitic alteration alterationselvages selvageshave havedeveloped developedalong alongcross-cutting cross-cuttingfractures fracturesin inthe thegranodiorite. granodiorite. Minor, chlorite occur occur on joint surfaces. The Therock rock Minor, glassy glassy quartz quartz veins veins are are also present. Epidote Epidote±Âchlorite cut cut immediately immediatelyeast eastof of the the polished polished outcrops outcrops has has followed followed aa prominent, steeply dipping joint plane. plane. A A composite, composite,east-southeast-trending, east-southeast-trending,Proterozoic Proterozoicdiabase diabasedyke dykeintrudes intrudesthe thegranite graniteaashort short distance distanceto tothe theeast eastand andisisexposed exposedon onboth both sides sidesof of the the highway. highway. This Thisdyke dykeisis1.2 1.2rn mwide wideand and dips dipssteeply steeplynorth northto tovertically. vertically.ItItisislocally locallycharacterized characterizedby byquartz-carbonate quartz-carbonateveinlets veinletsand andclay clay alteration. alteration. Schreiber Schreiber Assemblage Assemblage 37 37 �Mineralizationin the the Schreiber Schreiber Area Area Gold Mineralization The Schreiber Schreiber area area first first gained gained notoreity notoreity in in 1851 1851when when Terrace Terrace Bay Bay became became the the site site of of the the first first The molybdenite discovery discovery in in Canada Canada(Geological (GeologicalSurvey Survey of of Canada, Canada, Report Report of of Progress, Progress, 1853-1856, 1853-1856, molybdenite Someofofthe theearliest earliestclaim claimstaking stakingon onthe thenorth northshore shoretook took place place on on aa gold gold property property south south p.40). Some Schreiber in 1872, 1872, prior to the construction of the Canadian Pacific Railway. Early gold gold of Schreiber Railway. Early discoveries bewteen bewteenthe themidmid-1 890's and 1920 1920 around around Schreiber Schreiberand and north north at at Big Big Duck DuckLake Lakewere were discoveries 1890's described by Hopkins Hopkins (1922). (1922). This Thisexploration explorationultimately ultimatelyled ledto to surface surfaceand and underground underground described development development on on a number number of small small properties, resulting in a modest, collective gold production of approximately approximately 3000 3000 ounces. ounces. The Thelargest largestproducer, producer,the theNorth North Shores ShoresMine, Mine, yielded yielded 2441 2441 ounces ounces at at an an average average grade grade of of 0.64 0.64 ounce Au per ton. Exploration Explorationand and test test milling milling have have continued continued since since mining mining activity activity lapsed lapsed in in the the 1930's. 1930's. Much Much of the the following followinginformation informationhas has been been gleaned gleaned from from aa variety variety of of unpublished unpublished reports reportsand and articles articles archived archived in in the the Resident Resident Geologist's Geologist'sFiles, Files, Schreiber-Hemlo Schreiber-HemloDistrict, District,Thunder ThunderBay. Bay. The The vast vast majority majority of of the the more more than than 25 25 gold gold occurrences occurrencesin in the the Schreiber Schreiberarea area are are hosted hosted by by discrete ± carbonate veins. Vein discrete structures, structures, usually composite, composite, quartz quartz 2 Vein orientations orientations are are generally generally subparallel subparallelto to one one another anotherand and to to fault/joint faultljointsets setsin inhost hostrocks; rocks;en enechelon echelonand andconjugate conjugatearrays arrays are common. common. Auriferous Auriferousstructures structuresare arehosted hostedby by aavariety varietyof of rock rock types, types, including including supracrustal supracrustal and and felsic felsic intrusive intrusive rocks. rocks. Veins Veinsare arecommonly commonlylocalized localizedalong along contacts contactsand and discontinuities. discontinuities. Schreiber Assemblage 38 Schreiber Assemblage 38 �Host rocks show little evidence of ductile deformation although some primary be primary features features may maybe somewhat somewhat flattened. flattened. There is a strong strong spatial spatial association association between between gold gold occurrences occurrencesand and felsic felsic intrusive intrusiverocks rocks (quartz(quartz- quartz-feldsparporphyries, porphyries, syenite syenite and and trondhjemite) trondhjemite) as as well well as as lamprophyre lamprophyre dykes. dykes. and quartz-feldspar (1984) investigated investigated the the occurrence occurrenceof of polymetallic, polymetallic, auriferous auriferous veins veins and and Cu-MoCu-MoMarmont (1984) bearing veins in and around the contact zone of the Terrace Bay batholith. batholith. Locally Locally auriferous, auriferous, sericite-chlorite-quartz-pyrite ± carbonate sericite-chlorite-quartz-pyrite carbonate ± Âtourmaline alteration is commonly commonly developed developed around around veins, but is is usually usually of of limited limited lateral lateralextent. extent. The vein-hosted nature of of the the gold gold suggests suggests that that mineralization mineralization took took place place in in aa brittle brittle shear shear setting. Dilatancy Dilatancyin insuch suchan anenvironment environmentmay may have have resulted resulted chiefly chiefly from from bulk, bulk, inhomogeneous inhomogeneous flattening, perhaps related flattening, related to compressive compressive stress stress imaprted imaprted by the the enclosing enclosing Terrace Terrace Bay Bay and and Whitesand batholiths. Zones (e.g. contacts, contacts, Zonesof ofcompetency competencycontrast contrastand and pre-existing pre-existing weakness weakness (e.g. interfiow interflow sedimentary sedimentary units, units, etc.) etc.) were were important important in in the the localization localization of of shear shear zones zones and and fractures. fractures. The close close spatial spatial association associationbetween between felsic felsic intrusive intrusive rocks, rocks, gold gold occurrences occurrencesand and hydrothermal hydrothermal loci for for fracturing. fracturing. It suggests that the alteration may reflect the fact that these rocks are loci hydrothermal activity which which accompanied accompanied gold gold deposition deposition may be related related in in part to to late-stage late-stage events within these intrusions. intrusions. Schreiber Assemblage Assemblage 39 Schreiber 39 �The two two most most important important exploration explorationcriteria criteriaappear appear to to be: be: The (1) evidence evidenceof ofhydrothermal hydrothermalfracturing fracturingand andalteration, alteration,and and (2) rocks rocksthat thatare areattributable attributabletotofelsic felsicmagmatism, magmatism,the thelate latestages stagesof of which which may may often often lead lead to to the the (Burnhamand and Ohmoto Ohmoto1980). 1980). formationof of hydrothermal hydrothermal ore ore deposits deposits(Burnham formation A number number of of volcanic volcanic and and intrusive intrusive igneous igneous rocks rocks sampled sampled by Carter Carter (1988) (1988) near Schreiber Schreiber have have alkalic, shoshonitic shoshoniticaffinities. affinities. They Theycan canbe begeochemically geochemicallyclassified classified(LeMaitre (LeMaitre1989) 1989)as as latites, latites, alkalic, mugearites -like mugearites and and biotite biotitelamprophyre lamprophyre(kersantite), (kersantite),similar similarto to those those of ofthe the Timiskaming Timiskaming-like successions successionsof of the the Shebandowan Shebandowangreenstone greenstone belt (summarized by Fyon et al. 1991). Pye Pye(1969) (1969) referred referred to to aa package packageof ofconglomerate, conglomerate,quartzite quartziteand andlimestone limestonemapped mapped by by Harcourt Harcourtand andBartley Bartley (1939) south southof ofSchreiber Schreiberas asTimiskaming. Timiskaming. Hornblende-phyric, Hornblende-phyric,syenitic syeniticrocks rocks are are spatially spatially associated associated with withmany many gold goldoccurrences occurrencesin inboth bothareas, areas,bearing bearingsimilarity similaritywith withsyenite-hosted syenite-hostedgold gold deposits deposits in in the the Matatchewan Matatchewanand and Kirkland KirklandLake Lake areas areas of of eastern eastern Ontario. Ontario. Schreiber Schreiber Assemblage Assemblage 40 40 �STOP 4: 4: GOLD GOLDRANGE RANGEPROSPECT PROSPECT STOP Goldwas wasdiscovered discoveredjust justbefore beforethe theturn turnof ofthe thecentury centuryon onaa northeast-trending northeast-trending ridge ridge of of Gold km east eastof of Schreiber. Schreiber. metavolcanicrock rocknear nearthe thecontact contactwith withthe theTerrace TerraceBay Baybatholith, batholith,44km metavolcanic Severalsubsequent subsequentdiscoveries discoveriesof ofauriferous auriferousquartz quartzveins veinsled ledtotothe thedevelopment developmentof ofthe theadjoining adjoining Several Otisse,Harkness-Hays Harkness-Haysand andGold GoldRange Rangeproperties. properties. Otisse, TheGold GoldRange Rangeprospect prospectwas wasfirst firststaked stakedinin1917 1917and andexplored exploredfor forseveral severalyears. years. In In 1922, 1922,two two The aditswere weredriven driveninto intothe thehillside hillsideby bythe theJackson JacksonDevelopment Development Co. Co. Ltd. Ltd. Newly Newlyincorporated incorporated adits Gold Range RangeMines MinesLtd. Ltd.acquired acquiredthe theproperty propertyin in1934, 1934,continued continuedunderground undergrounddevelopment developmentand and Gold investigatedthe the placer placer potential potential of of the the sand sand and and gravel gravel at at the the base base of of the Overburden investigated the hill. hill. Overburden oneextractedfrom from test test shafts shaftswas was treated treated with with aa Denver Denver concentrator. concentrator. Sampling Samplingof oftwo twoshafts shaftsatat oneextracted footintervals intervalsin in1936 1936returned returnedaverages averagesof of0.04 0.04ounce ounceAu Auper perton tonto to17 17feet feetand and0.10 0.10ounce ounceAu Au foot tramwayand andaasmall smallmill millwere wereerected erectedon onsite siteto tohandle handlehighhighper ton ton to to 22 22 feet, feet,respectively. respectively.AAtramway per grade vein vein ore. ore. Ore Orewas wascrushed, crushed,pulverized pulverizedand androasted. roasted. Gold Goldwas wasrecovered recoveredwith with grade amalgamation;tables tableswere werereportedly reportedly installed installed to to produce produce aa suiphide sulphide concentrate concentrate as as well. well. The The amalgamation; first gold gold brick brick(22 (22ounces), ounces),representing representing40% 40%of ofthe thetotal totalgold goldconcentrates concentratesprocessed processedto tothat that first time,was waspoured pouredin inmid-1936. mid-1936.Gold GoldRange RangeMines Mineswas wassubsequently subsequentlysucceeded succeededby byRolac RolacMines. Mines. time, Theproperty propertybecame becameinactive inactivearound around1941. 1941.ItIthas hasbeen beenexplored exploredby byvarious variousindividuals individualsand and The companiessince sincethen. then. companies Schreiber Assemblage Assemblage 41 41 Schreiber �Local Local Geology Geology The property property straddles straddlesthe the northern northerncontact contact(trending (trending0300) 030¡of the the Terrace Terrace Bay Bay batholith batholith with with mafic metavolcanic rocks. This This contact contact is is locally locally obscured by deep glacial drift. The mafic mafic drift. The metavolcanic rocks are are locally locally pillowed pillowed and and have have been been upgraded upgraded to amphibolite-facies amphibolite-facieswithin within the the contact metamorphic aureole of the batholith. Coarser-grained, Coarser-grained, mafic mafic units units have have been been interpreted interpreted Sulphide-and andoxide-facies oxide-faciesbanded banded iron ironformation, formation,wacke wacke and and conglomerate conglomerate are are as gabbros. Suiphideintercalated with the mafic flows. Tracing Tracingof ofone one iron iron formation formation across across the the Harkness-Hays, Harkness-Hays, Gold intercalated 1939;Resident Resident Otisse properties properties reveals reveals tight tight to to isoclinal isoclinal folds folds (Hoibrooke (Holbrooke1939; Range and Otisse Geologist's Files, Files, Schreiber-Hemlo Schreiber-HemloDistrict, District, Thunder Thunder Bay). Bay). Geologist's In the vicinity of the main workings, workings, aa series series of quartz-feldspar quartz-feldspar porphyry dykes dykes intrudes intrudes the the 20° to to 40 40°northwest. northwest. Biotite-bearing, 030" and dips 20 Biotite-bearing, brown brown mafic metavolcanic metavolcanic rocks and and strikes strikes 030° to black lamprophyre lamprophyre (kersantite?) (kersantite?) dykes dykes intrude intrude all all of of the the aforementioned aforementionedrocks rocks and and are are intimately associated with some some of of the the veins. veins. Gold mineralization mineralizationon on the the property property is is associated associated with with aa series series of of at at least least seven seven numbered, numbered, subparallel veins that strike subparallel strike north-northeast north-northeast and dip steeply steeply to the northwest northwest (Figure (Figure 6). 6). surface, only only veins veins No.'s No.'s 1I and 2 were investigated investigated Although all these veins were discovered on surface, and mined underground underground using using three three adits adits and and short short drifts. drifts. Schreiber Assemblage 42 Schreiber Assemblage 42 �/ S / S —4,- . ^-S^ 0 Sw No.3 No. 3 ad/f adit S Overbt.rden Test Holes S • No.1 adit •e- No;2 adit S Overb'sden 1 OverburdenTest TestPtts Pits / S  S aD 0 DD° 0 30m Sketchmap mapofofthe theGold GoldRange Rangeprospect prospect(from (fromHoibrooke Holbrooke1939) 1939) Figure 6. Sketch Sclzreiber Assemblage 43 Schreiber Assemblage 43 • • • • S �The veins are typically narrow (5 to 25 cm) but are remarkably persistent along strike. They may split and develop horse-tail" structures that increase the vein width. Sub-parallel microveinlets are also common. The veins are rarely composite or crack-seal textured, but do contain septa and xenoliths of wall rock. Cockscomb textures are developed in drusy quartz and calcite. Vein breccias contain fragments of other vein gangue as well as altered wall rock. Slickensides are visible along vein margins. Despite the narrow widths of the veins, hydrothermal alteration extends from the vein margins several centimetres into the wall rock. This alteration is manifested as a pale, grey to lime green zone that has a rusty weathered appearance (Plates). Marmont (1984) has identified mineralogic zonation within the alteration envelope (from host towards vein): [host] I sericite-biotite sericite-carbonate-Mg(?)-chlorite carbonate-Fe(?)-chlorite-quartz [vein] I I potassic alteration I carbonatization I silicification I Sulphides, predominantly pyrite, are ubiquitous, but are locally developed immediately adjacent to the vein itself. Altered zones are themselves commonly auriferous. Coarse, visible gold occurs within quartz, but it also occurs as discrete grains within large (s2,5 cm), euhedral pyrite crystals. The No.2 vein displays abundant pyrite euhedra where the vein is crosscut by a lamprophyre dyke. Gold-bearing tellurides, calaverite (AuTe,) and sylvanite Schreiber Assemblage 44 �((Au,Ag)Te2),have have also also been been noted. noted. Accessory Accessorysulphides sulphidesinclude includepyrite, pyrite,with withlesser lesserchalcopyrite, chalcopyrite, ((Au,Ag)Te2), pyrrhotite,sphalerite, sphalerite,molybdenite molybdeniteand andgalena. galena. Calcite, Calcite,graphite, graphite,epidote epidoteand andmagnetite magnetite are are also also pyrrhotite, present. In Inaddition, addition,Sabina Sabina(1991) (1991)noted notedgarnet, garnet,goethite goethite and basaluminite (A14S04(OH),,,~4H20) present. and basaluminite (A14SO4(OH)104H20) on the the adjacent adjacentHarkness-Hays Harkness-Haysproperty. property. on Plate 5. 5.Alteration Alterationenvelope envelopearound aroundquartz quartzvein veininingabbro, gabbro,Gold GoldRange Rangeprospect prospect(STOP (STOP4). 4). Plate 1.5cm cminindiameter. diameter. Coinisis1.5 Coin Schreiber Assemblage Assemblage 45 45 Schreiber �Sampling by Holbrooke Holbrooke (1939) (1939) of of the the No. 22 vein vein returned returned an an average average of of 0.49 0.49 ounce ounce Au Au per per ton ton Sampling Theseresults resultswere were probably probably typical typical of of the best-mineralized over 0.28 m for a length of 7.6 m. These sections of the veins. Typical Typicalgrab grabsamples samplesof ofhigh-grade high-grade material material have have commonly commonly returned returned sections between and 20 20 ounces ounces Au Au per per ton. ton. Silver Silvervalues valuesare areabout aboutone-half one-halfthat that of of the the corresponding corresponding between 55 and samples. Approximately Approximately42 42ounces ouncesof of gold gold were were eventually eventually recovered recovered during during gold assays in these samples. early mining mining operations. operations. Geology of the No. 7 Vein Shaft Area The shaft shaft exposed exposed near near the the access accessroad road was was sunk sunk to to aa depth depth of of 7.7 7.7 m m to to investigate investigatethe the No. No. 77vein. vein. This This vein, vein, striking striking040° 040Âand and dipping dipping 75° 75O northwest, returned up to 0.98 ounce Au per ton over 0.36 0.36 m; most most samples samples returned returned only only trace trace amounts amounts of gold (Hoibrooke (Holbrooke 1939). 1939). Harcourt Harcowt (1939) (1939) reported that the the vein vein was was wider and and carried gold at the shaft bottom. Visible Visiblegold goldwas was noted notednear near the the shaft shaft bottom bottom by by the the authors authors during during aa 1987 1987 property visit. Diamond Diamonddrilling drillingand andthe thestripping stripping in in the the vicinity vicinity of of the the No.7 No.7 vein vein were were carried out in 1987 1987 by Forerunner Resources Limited (now Beardmore Beardmore Resources Resources Limited). Limited). The host host rocks rocks consist consistdominantly dominantly of ofequigranular equigranulargabbro gabbrothat that has has been been intruded intrudedand and brecciated brecciated by dykes dykes of pink pink granodiorite granodiorite that extend off the main mass of ofthe the Terrace Terrace Bay Bay batholith batholithto to the the Schreiber Assemblage 46 Schreiber Assemblage 46 �east, across across the the road. road. InInthin thinsection, section,the theunaltered unalteredgabbro gabbrocontains containsplagioclase plagioclaseand and pyroxene, pyroxene, east, includinginverted inverted pigeonite. pigeonite. Where Wherealtered alteredadjacent adjacentto toquartz quartzveins, veins,the the original originalgabbroic gabbroictexture texture including has has been been replaced replaced by by aafine-grained fine-grainedmatte matteof of carbonate, carbonate,sericite, sericite,quartz, quartz,epidote epidoteand andpyrite. pyrite. Coarse grains grains of of visible visible gold gold have have been been noted noted in in this this altered alteredzone. zone. Coarse Subparallel Subparallelstringers stringersof of quartz, quartz, enveloped envelopedby by conspicuous, conspicuous,rusty, rusty, carbonate-rich carbonate-richalteration alterationhaloes, haloes, are exposed at the shaft collar. Well-developed, prominent. Dump Well-developed, orthogonal joint sets are also prominent. Dump material, material, extracted extracted during during shaft shaftexcavation excavationand and subsequent subsequentreclamation, reclamation,has has been been piled piled nearby. nearby. Vein Vein material material with with ubiquitous ubiquitousalteration alterationisisabundant abundantin inthe thedump. dump. Schreiber Assemblage Schreiber Assemblage 47 �STOP5: 5: WINSTON WINSTON LAKE LAKE Cu-Zn Cu-ZnMINE MINE STOP Explorationand andMining MiningHistory Historyof ofthe theWinston Winston Lake Lake Mine Mine Exploration Theexploration explorationhistory historyof ofthe theWinston WinstonLake LakeMine Minehas hasbeen beendescribed describedby byBalint Balintetetal. al.(1990) (1990)and and The Severinet et a!. al. (1990). (1990). The Theearliest earliestexploration explorationactivity activityisislargely largelygleaned gleanedfrom fromgovernment governmentreports reports Severin andother otherdocuments documents(Resident (ResidentGeologist's Geologist'sFiles, Files,Schreiber-Hemlo Schreiber-HemloDistrict, District,Thunder ThunderBay). Bay). and Activityin inthe thearea areadates datesback backto tothe thediscovery discoveryand and initial initial development development of of the the Zenith Zenith Mine Mine in in Activity 1879. High-grade High-grade (45% (-45%Zn), Zn),sphalerite-rich, sphalerite-rich,massive massivesuiphide sulphidewas was mined mined on onsurface, surface, 1879. hand-cobbedand andshipped shippedoverland overlandto toaarailway railway spur spurnear near Schreiber. Schreiber. Around Aroundthe theturn turnofofthe the hand-cobbed century,the theGrand GrandCalumet CalumetMining MiningCompany CompanyLtd. Ltd.mined minedand andconcentrated concentratedapproximately approximately2700 2700 century, ZenmacMetal MetalMines Mines tonsof ofore. ore.The Theproperty propertyremained remainedlargely largelydormant dormantuntil untilthe the1960's 1960'swhen whenZenmac tons Limitedbegan beganshaft shaftsinking, sinking,underground undergrounddevelopment developmentand anderected erectedsurface surfaceplant plantfacilities. facilities. Limited Productionfrom from1966 1966toto1970 1970totalled totalled164 164000 000tons tonsofofore oreatataagrade gradeofof16.5% 16.5%Zn. Zn. Production InOctober, October,1978, 1978,Corporation CorporationFalconbridge FalconbridgeCopper Copper(CFC) (CFC)carried carriedout outreconnaissance reconnaissancegeological geological In andlithogeochemical lithogeochemicalsurveys surveysaround aroundthe theZenith ZenithMine Mineininorder ordertotoassess assessthe theexploration explorationpotential potential and of this this portion portionof ofthe theBig BigDuck DuckLake Lakevolcanic volcanicassemblage, assemblage,previously previouslymapped mappedby byPye Pye(1964). (1964). of Rockspreviously previouslyinterpreted interpretedas asmetasedimentary metasedimentarywere wererecognized recognizedas ashydrothermally hydrothermallyaltered, altered, Rocks felsicmetavolcanic metavolcanicrocks. rocks.The Thelithogeochemistry lithogeochemistryofofthese thesealtered alteredrocks rockswas wasnoted notedto tobe besimilar similarto to felsic Schreiber Assemblage Assemblage 48 48 Schreiber �that of rocks at CFCs CFC'sSturgeon SturgeonLake LakeMine, Mine, primarily primarily on on the the basis of sodium sodium depletion depletion and and zinc zinc Thedelineation delineationof ofan analteration alterationzone zone 1200 1200m m west west of of the the Zenith Zenith Mine Mine prompted prompted CFC CFC enrichment. The to acquire acquire on on option option on on the the Zenith Zenith property property and and stake stake the the ground ground around around it. it. , In 1979 1979 and 1980, 1980, detailed detailed geological, geological, lithogeochemical lithogeochemicaland and geophysical geophysical (magnetometer, (magnetometer, VLF-EM, and Max-Mm 11) surveys were conducted. Although Although geophysical geophysical results results were were Max-Min II) disappointing, disappointing,geological geological and and lithogeochemical lithogeochemicalsurveys surveyssucceeded succeededin in discovering discovering zones zonesof ofcherty, cherty, bedded ash ash within within the the calc-alkaline, calc-alkaline, felsic felsic volcanic volcanic rocks rocks and and they they further further delineated delineated the the hydrothermal alteration alteration zone. AAgeological geologicalmodel modeldepicted depictedthe the Zenith Zenith deposit depositas as aa raft raft of of massive massive suiphide that had been stoped stoped off off of of aa larger, larger, as as yet undiscovered, undiscovered, felsic felsic volcanic-hosted, volcanic-hosted, sulphide sulphide sulphide deposit by a composite, composite, gabbroic gabbroic intrusion. intrusion. In 1981, 1981, eight eight diamond diamond drill drill holes holes were were completed, completed, four four of of which which tested tested the the geological geological model. model. They intersected intersected aa cherty cherty ash ash horizon horizon that that occurs occurs at at the the top top of of the the felsic felsic volcanic volcanic pile, pile, overlying overlying the alteration alteration zone, at the contact with the gabbro. Encouraging Encouragingresults results included included up up to to 0.5% 0.5% Zn Zn over 4.3 m. Subsequent Subsequentborehole boreholepulse pulse EM EM surveys surveysdetected detected aa strong, strong, edge-type edge-type anomaly anomaly down-dip of the mineralized mineralized exhalite exhalite intersection. intersection. 1.10% Cu, 19.11% In June, 1982, 1982, a follow-up follow-up drill drill hole hole intersected intersected 2.1 2.1 m m of of massive massive sulphide sulphide (@ (@ 1.10% 19.11% Zn, 22.2 g/t glt Ag Ag and and 0.73g1t 0.73glt Au) Au) at the base of the gabbro gabbro sill, sill, 300 300 m m below below surface. surface. Assemblage 49 Schreiber Assemblage 49 �Subsequent definition definition drilling and exploratory shaft sinking produced produced aa reserve reserve figure figure of of 2 675 000 t grading grading 0.94% 0.94% Cu, Cu, 17.8 17.81% 1% Zn, Zn, 25.3 25.3 glt g/t Ag Ag and and 0.85glt 0.85g/t Au Au (Severin (Severin and and Balint Balint 1984). A production decision decision was was delayed delayed as as the the price price of of zinc zinc fluctuated fluctuated and development development was was suspended suspended 1985. Activity Activitywas wasrenewed renewed by by Minnova Minnova Inc. and development ore was to surface in 1985. was hoisted hoistedto throughout 1987. 1987. Original Originalmineable mineablereserves reserves(all (allcategories, categories, including including 20% 20% dilution dilution at at zero zero on November November 1, 1, 1987 1987were 33 076 076 339 339 tonnes tonnes at at aa grade grade of of 1.00% 1.00% Cu, Cu, 15.60% 15.60% Zn, Zn, grade) reported on g/t Ag and 1.02 glt g/t Au (Severin et al. a!. 1990). The 30.87 glt The first concentrate was produced in January, In May, 1993, 1993, Minnova Minnova Inc. 1988 and the mine's official opening took place place in in July, July, 1988. In merged with aa wholly-owned wholly-owned subsidiary subsidiaryof of Metal! Metal1 Mining Corporation. Corporation. Mine reserves as of January 1, 1, 1995 1995 stood stood at 733 733 306 306 tonnes at at a grade grade of 12.05% 12.05% Zn, 0.89% 0.89% Cu, Cu, glt Ag and 1.647 1.647g/t glt Au Au (G. Doiron, 26.82 g/t Doiron, Metal! Metal1 Mining Corporation, Corporation, personal communication, communication, 1995). These Theseestimates estimatesinclude include proven, proven, possible possible and and potential ore with a 20% dilution at 0% grade. grade. Metall m level level of of the the Winston Winston Lake Lake Mine Mine in in August, August, 1993 1993in in order orderto to Metal1 began drifting drifting from from the the 615 615 m assess the Pick Lake upper zone deposit. This Thisdeposit depositwas was initially initially defined defined by by surface surface drilling drilling from the mid-1980's to 1992. 1992. The Thedeposit depositconsists consists of of two two thin, thin, but but continuous, continuous, massive massive sulphide sulphide sheets with a down-plunge length of 1400 m. The TheUpper Upper Zone Zone and and Lower Lower Zone average average approximately 2.2 and 4.0 m in thickness, respectively. Potential Potential reserves reserves stand stand (as (as of of January, January, 1995) at 1147 1 147442 442 tt (20% (20%dilution dilutionat at 0% 0% grade grade included) included) at at 1.24% 1.24% Cu, 20.05% Zn, 56.11 g/t glt Ag Assemblage 50 Schreiber Assemblage �and 0.33 glt Au. Au. Underground drilling drilling in early 1995 1995 will be used to determine determine the economic economic feasibilty of mining mining the the Pick Pick Lake Lake deposit. deposit. feasibilty Geology of of the the Winston Winston Lake Mine Geology The local local geology, geology, particularly particularlythose those aspects aspects which which are are associated associated with with volcanogenic volcanogenicmassive massive sulphide, Cu-Zn Cu-Zn mineralization, mineralization, has has been been studied studied by the aforementioned aforementioned authors, authors, as as well well as as Osterberg Osterberg (1993), (1993), Osterberg Osterberg and and Morrison Morrison (1991), (1991), Severin Severin and and Balint (1984) (1984) and and Thomas Thomas (1991). (1991). The Winston Winston Lake Lake area area lies lies within within the the northernmost northernmost portion portion of of the the Schreiber Schreiber greenstone greenstone the boundary boundary with with the the Quetico Quetico subprovince. subprovince. Local assemblage and the Wawa subprovince, near the metavolcanic, km by by 15 15km kmpackage package metavolcanic, metasedimentary metasedimentaryand and associated associated intrusive intrusive rocks rocks comprise comprise aa 44 km of rocks informally informally referred to as as the Big Duck Duck Lake Lake greenstone greenstone belt (Balint (Balint and and Severin Severin 1984). 1984). These rocks are are separated separated from from the bulk of of the Schreiber Schreiber greenstone greenstone assemblage assemblage to the south south by by granitoid rocks of the Crosman Lake batholith. Several Severalmapping mapping projects projects covered covered the Big Big Duck Duck (1909), (1915; 1921) Bartley (1 (1942). 1) and Bartley 942). Gold Gold was was Lake area, including those of Collins (1 909), Hopkins (1 9 15; 192 discovered discovered at Big Duck Duck Lake Lake in in 1906, 1906,leading leading to to the the subsequent subsequent discovery discovery and and exploration explorationof of over over twenty gold and polymetallic polymetallic occurrences for the next two decades. Activity Activity in in the the "Duck "DuckLake Lake gold field", field", as as itit was was then then termed, termed,peaked peaked in in the the 1920's 1920'sbut but has has continued continued to to the the present. present. Schreiber Assemblage Assemblage 51 51 �flanks of of this this part part of of the the Schreiber Schreiberassemblage assemblagehave have undergone undergone upper upper greenschist greenschistto to The outer flanks arnphibolite grade grade regional metamorphism, typified by garnet and hornblende, while amphibolite while rocks rocks in the quartz-chlorite-actinolite-albiteassemblages assemblagestypical typical of of greenschist greenschistfacies facies(Pye (Pye1964). 1964). core display display quartz-chlorite-actinolite-albite Pye (1964) (1964) also did a comprehensive comprehensive investigation investigation of the mineral deposits deposits of of the the area area in in the the course of his mapping. Balint and Severin Severin (1984) (1984) outlined outlined the the basic basic architecture architecture of of the the supracrustal supracrustal and and associated associated rocks rocks 7): in the vicinity the Winston Winston Lake Lake Mine Mine (Figure (Figure 7): vicinity of the (1) (1) Winston Winston Lake Lake Sequence: Sequence: metasedimentary rocks - calc-alkaline, felsic and mafic metavolcanic metavolcanic and lesser metasedimentary - predominantly lava flows flows with subordinate subordinate pyroclastic pyroclastic rocks (2) (2) Big Duck Duck Lake Big Lake Sequence: Sequence: - overlies overlies Winston Winston Lake Lake Sequence Sequence - predominantly predominantly tholeiitic tholeiitic basalt basalt flows flows - flows intruded by Big Duck Lake quartz- and quartz-feldspar quartz-feldspar porphyry sills sills series of of differentiated, - separated from Winston Lake Sequence byby aa series differentiated, tholeiitic, tholeiitic, mafic mafic to to ultrarnafic ultrarnafic sills sills As a result 1%O's, subsequent subsequentbase base metal metal result of of mapping mapping and and lithogeochemical lithogeochemicalsampling samplingin in the the 1980's, Schreiber Assemblage Assemblage 52 52 �exploration and and associated associated research research have have been been confined confined to the the Winston Winston Lake Lake Sequence, Sequence, which which exploration Winston Lake, Lake, Zenith Zenith and and Pick Pick Lake Lake deposits, deposits, as as well well as as aa number number of of surface, surface, hosts the the Winston occurrences. Metall Metal1Mining MiningCorporation Corporationconducted conducted surface surface exploration explorationand and copper and zinc occurrences. diamond drilling on their Cleaver Cleaver Lake, Lake, Ciglen, Ciglen, Gesic, Gesic, Pick Lake, Lake, Winston Lake Lake and and Zenith Zenith properties in in 1994 1994(G. (G. Doiron, Doiron,Metall Metal1Mining Mining Corporation, Corporation,personal personal communication, communication,1995). 1995). properties volcanological studies Physical volcanological studies by Osterberg Osterberg (1993) (1993) and and Osterberg Osterberg and and Morrison Morrison (1991) (1991) indicated indicated by interlayered interlayered successions successions of of that the footwall rocks to the Winston Lake Mine are dominated by deep-water volcaniclastic, sedimentary and flow units. Footwall Footwall volcanic volcanic stratigraphy stratigraphy apparently apparently developed developed as the result result of of cyclic cyclic accumulation accumulation of of volcaniclastic volcaniclastic and and volcanic volcanic rocks rocks in in aa subsiding, subsiding, subaqueous, stratigraphiccolumn columndepicting depicting the the lithologic lithologic subdivisions subdivisionsof of the the subaqueous, rift environment. environment. AAstratigraphic Winston Footwall Block (Osterberg 1993) 1993) is shown in Table 2. Volcanic Volcanic rocks rocks have have been been extensively extensively intruded intruded and and block block faulted. faulted. Tectonic Severin(1984), (1984), Tectonic deformation deformation features features in in local local rocks rocks have have been been described described by Balint Balint and and Severin (1993) Osterberg (1 993) and Williams (1989). Ductile Ductiledeformation deformation is is typically typically manifested in flattening flattening and foliation, as well as minor folds. The Thedegree degreeto to which which original originalstratigraphic stratigraphicand and contact contact relationships have been relationships been modified modified by tectonism tectonism is is still still aa matter matter of of much much debate. debate. Williams 1989)has has described described extremely extremely deformed deformed rocks rocks of of what what he he termed termed the the Big Big Duck Duck Williams (1988, (1988, 1989) Lake shear zone. In Inhis hisopinion, opinion,the theubiquity ubiquityof oftectonic tectoniclayering layering precludes precludes recognition recognitionof of the the Schreiber Assemblage Assemblage 53 53 �deformation and original lithologic relationships. Moreover, Moreover,Williams Williams (1988) (1988) interpreted interpreted state of deformation and altered altered footwall footwallrocks rocks the schistose schistose contact contact between between the the hanging hanging wall wall gabbro, gabbro, the the ore ore zone zone and 5A) asashighly highlysheared, sheared,with withslip slipdirections directionsgenerally generally down-dip down-dip of the schistosity, schistosity, (Stop5A) (Stop suggestive suggestive of of thrusting thrustingand and dip-slip dip-sliptectonics. tectonics. Schreiber Assemblage 54 Schreiber Assemblage 54 �Table 2. Stratigraphie Stratigraphicsubdivision subdivision of of part partofofthe theWinston WinstonFootwall FootwallBlock Block (from (from Osterberg Osterberg 1993) 1993) Table Winston Lake Lake Horizon Horizon (WLH) (WLH) Winston Winston Lake Lake VMS VMSDeposit Deposit(WLH-MS) (WLH-MS) Winston Mafic volcanic volcanic and and intrusive intrusivefeeder feederrocks rocks (WLH-FR) (WLH-FR) Mafic (WLH-CRT)" Mixedlaminated laminatedash ashand andexhalative exhalativesedimentary sedimentaryrocks rocks(WLHCRT)5A Mixed Maficlava lavaflows flows(WLH-MA), (WLH-MA),including includingFootwall FootwallFlow Flow(WLHFWF)sB (WLH-FWF)'" Mafic ................................................................................................... Upper Upper Clastic ClasticSuccession Succession(UCS) (UCS) Clotted ClottedRhyolite Rhyolite(CLR)5B (CLR)5B Volcaniclastic Volcaniclasticand andassociated associatedrocks rocks(SIV) (SIV) Felsic Felsictuffs tuffs(SIV-FT), (SIV-FT),Intermediate Intermediatevolcaniclastic volcaniclasticrocks rocks(SIV-VC) (SIV-VC) ................................................................................................... Middle MiddleFlows FlowsSuccession Succession(MFS) (MFS) Synvolcanic (CT)SD Synvolcanicfelsic-derived felsic-derivedvolcaniclastic volcaniclasticsedimentary sedimentaryand andtuffaceous tuffaceousrocks rocks (CT)'" Undivided Undividedmafic maficrocks rocks(MA) (MA) Middle andassociated associatedrocks rocks(MMF) (MMF) Middlemafic maficflow flowand Camp dikes (QFF)SC CampFlow Flowrhyolite rhyoliteand andassociated associatedfeeder feeder dikes (QFF)5c Ladder Ladderbasalt basaltflow flow(LF)5E (LF)^ (QFP)5F "Main Main"quartz-feldspar quartz-feldsparporphyry porphyry (QFP)" Trip Stopwhich displays this unit.) (n.b. (n.b.Superscripted Superscriptednumbers numbersdenote denotethe theField Field Trip Stop which displays this unit.) Schreiber Schreiber Assemblage Assemblage 55 55 �VVVVVVVV VVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVV VVVVVV VVVVVVVVVVVVVVVVV VVVVVVVVV V VVVVVV VV VVVVVVVVVVVVV VVVVVVVVVVVVVVVVVV VVVVVVVV V VVVVVVVVVV VV V VVVVVVVVVVVVVVVVVVVV V VVVVVVVVVV VVVVVV VVVVVVV LV V V V V V V V V V V V V V V V V V V V V VVV V V V VVVVVVV V V V VVVV VVV V V VVVVVVV VVVVVVV VVVVV VV VVV V V VVVVVVVVVVVV V VVVVVV V V V V V V V V V VVVVVVVV (VVVVVVVVVVVVVVVV VVVVV VV V VV V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V VVVVVVV 'VVVVVVVVVVVVVVVVVVV V VVVVVVVV V VVVVVVVV VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV (VVVVVVVVVVVVV VVVVVVV VVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVV VVVVV VV VVVVVVvv VVVVVVVVVVVVVVVVV VVVVVVVVVVVVV VVVVVVV VVVV VVVVVVV VVVVVVVVV VV VV V VVVVVV VVVV V V V V VVVVVVVVVVVVVVVVVVVVVV IVVVVVVVVVVVVVVVVVV •VV VV V V VV V VV V V VV V V V VVVV VVV VV V VVVVV V V VVVV VVVV VVV V VVV VV V V V V 4VVVVVV VVVVVV VVVV VVVVVV VVVVVVVVV VVVVVV VVVVVVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVV VVVVVVV VVVVVVVVV VV VVVVVVVVVVVVVVVVVVVVVVV VVV VVVVVVVVVVVVVVVV • VVV VVVV V VV V V VVVV V VV V V VVVVVVVV VVVVVVVVVV VVVVVVVVVVVVVV VV V V V V V V VV VV VVV VVVVVV VVVVVVVVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVV+ VVVVVVVVVVVVV VVVVV VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV VVVVVV VVVVVVVVVVVVVVVVVVVVV VVVVVVV VVVVVVVVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVVVVVVVVVV VVVVV V VVV VVVVVVVVVVV VVVV VVV VVVVVVVVVVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVVVV 1VVVVVVVVVVVVVVVVVVVVVVV 4VVVVVVVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVVVVVVVVVVVVV 'V VV V VV V V V VVVVV V V V V V V VV 'VVVVVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVV VVVVVVVVVVVVV VVVVV VVVVV V VVVVVVVVVVVVVVVV VVV VVVVVVVVVV V VVVVVVVVVV VVVVVVVVVVVVVVVVVVVVVVVVVV 'VV VVVVVVVVVVVVVVVVVVVVV(,VV - 'VVVVVVVVVVVVVVVVVVVVVVVV 'VVV V VVV V VVVVV VVVV V V V V V VVV VVVV V V VVV V V V VVV VVV V VV V V V VVVV4 VVV V VVVVVV V 'VVVVVVVVVVVVVVVV V VVV VVVVVVVVVVVVVVV - /VVVVVVVVVVVVVVYVVVVVVVVVVVVVVVV 'V VV V V V V V VVV V V VV VVVVV VVV VVV #VVVVVVVVVVVVFVVVVVVVV 'V V V V V V V V V V Vj V V V V V V V V V V V V V V V V V V V VVVVVVVVVV4VVVVVVVVVVVVVVVVVVV V V V V V V V V 4\V V V V V V V V V V V V V V V V V V V VVVVV VVV4.IVVV VVVVVVV VVVVVVVV + - IVVV VV V VI? V V VV V VV V V V V VV VVVVV ?VV VV V V V V V V V V V VVVV V VVV V V + 4 4. + 4' ± + 4' + + + 4 4 + 'VVVVV"' 4' + 4 + + + 4 4 + + + + + 4' VVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVV + + 4. 4- 4' VVV VV VV VVV VV V V V VV + + + + 4' VVVVVV VVV V V VVVVVV V VVVVVVVVVVVVVVVVV + + 4. 4 + 4 + 4 + + + 4' + + PICK ÷ LAKE i + + 4 + + PICK LAKE f + 4' + 4 + 4 + 4 + '4.4.44. + + + + # + + + + + - + ALTER ATIC+ t,,_Z,,t.1 + + +4 + + + 4' + + + + 4• + + + + + + + , CASt + + + + C t' 4' SALM ALTERAn0N ZONE +4'++++++++++ + 4+ t + 4+4.4 .++ + + + + ,4 4+4 +4+4+4+ +44+444 + ++ + + 4 I - 4 4 4 ÷ + + ÷ + -' ÷ + 4 4'+ + + + + + + + # 4 Km 0 FELSIC TO INTERMEDIATE VOLCANICLSTIC GRANITE DIFFERENTIATED GABBRO SLLS Iiv- + LAKE AREA WINSTON MAP GEOLOGY Fl ure 7 APHYRIC "'i' MAFIC - SchreiberAssemblage Assemblage 5656 QUARTZ FELDSPAR PHRIC FLOW - QFP FLDW/SUBVOLCAIIC FLOWS FELDSPAR PHYRIC MAFIC FLOWS ALTER ATION -':': ':c—:- INTRUSION METASEDIMENTS WACKES S ARENITES MINERALIZEQ HORIZON �Hydrothermal Alteration Hydrothermal Alteration The recognition hydrothermally altered altered rocks at Winston Winston Lake by CFC CFC geologists geologistsin in the the late late recognition of hydrothermally 1970's led to the acquisition hrther exploration ultimately acquisition of the property, prompted further exploration work and led ultimately to the discovery of the Winston Lake and other deposits. The The occurrence occurrence of cordierite cordierite and orthoamphibole (anthophyllitelgedrite)or or sillimanite sillimanitewas was ascribed ascribed to syn-volcanic, syn-volcanic, hydrothermal hydrothermal orthoamphibole (anthophyllite/gedrite) metamorphism. Osterberg metasomatism and subsequent, subsequent, isochemical amphibolite-facies metamorphism. Osterberg (1993) (1993) has noted that approximately approximately50% 50Y0of of the the footwall footwall stratigraphy stratigraphy has has been altered altered in in sub-concordant sub-concordant to cross-stratal cross-strata! zones, presumably related related to to original, lithologic lithologic permeability. permeability. Other minerals that comprise the various various alteration alterationassemblages assemblagesinclude include tremolite-actinolite, tremolite-actinolite,biotite, biotite, muscovite! muscovite/ sericite, staurolite, staurolite, chlorite, chlorite, K-feldspar K-feldspar and and quartz. quartz. Hydrothermal alteration has greatly changed the primary lithogeochemistry. Mineralogic Hydrothermal Mineralogic variation variation in in altered alteredrocks rocks isisreflected reflectedby byvariable variableenrichment enrichmentof ofMgO, MgO,Fe2O3T, Fe203T,and 1(20, K20, as well as depletion CaO and and Na20 Na20(Osterberg (Osterberg 1993; 1993;Severin Severin and and Balint B a h t 1984 1984(Figures (Figures8A,B; depletion of of CaO 8A,B;Table Table3); 3); a!. 1990). Osterberg Severin et al. Osterberg(1993) (1993) noted noted that that all all major oxides, with the exception exception of Ti02 Ti02and A12O3, showsignificant significantmobility. mobility. Component changes, while similar A1203,show similar in each each alteration alterationtype, type, sillimanite 5 generally increase biotite << sillimanite staurolite 5 generally increase in the order: order: tremolite/actinolite tremolitelactinolite5 biotite ± staurolite anthophyllite/gedrite anthophyllitelgedrite(Osterberg (Osterberg 1993). 1993). Osterberg Osterberg (1993) (1993) has has envisaged envisaged aa multi-stage, multi-stage, syn-volcanic syn-volcanic hydrothermal hydrothermal model model at at Winston Winston Schreiber Assemblage Assemblage 57 Schreiber �Lake that involves involves at least least three three distinct distinct hydrothermal hydrothermal fluids, fluids, including: including: (1) seawater-based seawater-based fluids fluids that were primarily responsible responsible for Mg-enrichment, Mg-enrichment, (2) chemically chemically evolved evolved fluids fluids that reacted with the rocks rocks to produce produce stratiform stratiform zones zones of variable Fe-aluminous assemblages, and (3) metalliferous metalliferousfluids fluids that that were were base base metal-rich metal-rich and and probably otherwise otherwise similar similarto to chemically evolved evolved fluids. fluids. Schandi and Gorton Schandl Gorton (1991) (1991) identified identified REE-rich REE-rich monazite monazite and xenotime xenotime within within chiorite-sericitechlorite-sericitebiotite biotite alteration alterationaround around the the Winston Winston Lake Lake and and other other Precambrian Precambrianmassive massive sulphide sulphidedeposits. deposits. Intimate textural the alteration textural associations associations suggested suggested that these REE-enriched phosphates and the fluid at 2677 2677 2± 1Ma iMa (U-Pb assemblage minerals co-precipitated from a common fluid (U-Pb age age of monazite, monazite, Schandl Schandl et al. al. 1991). 1991). This interpretation interpretation conflicts conflicts with the widely accepted accepted model of synvolcanic synvolcanic alteration alteration by stating stating that that alteration alteration represents represents aa late, late, post-mineralization, post-mineralization, metasomatic metasomatic overprint. overprint. A U-Pb zircon age of 2723 ±2 2 2Ma Mafor forthe thehost hostrhyolite rhyoliteat at Winston Winston Lake Lake was was published published by by Schandl et al. (1991). (1991). Schreiber Assemblage Assemblage 58 Schreiber �PartialWhole WholeRock Rockand andTrace TraceElement ElementGeochemistry, Geochemistry,Winston WinstonLake Lake Volcanic Volcanic Rocks Rocks Table 3. Partial Lithology Lithology Si02 Si02 A1203 Al203 FeOT FeOT MgO MgO CaO CaO Na20 Na20 K20 1(20 Ti02 Ti02 Cu Cu Zn Zn WLH-FWF WLH-FWF 48.7 15.25 8.49 6.94 7.89 7.89 4.06 0.75 1.01 94 35 WLFlFWF* WLH-FWF* 34.3 19.72 11.83 19.85 0.80 0.80 1.12 1.88 1.26 104 50 MMF MMF 52.1 15.49 8.49 5.01 7.96 7.96 3.71 0.48 1.34 45 10 MMF* rnF* 51.2 14.69 10.00 11.57 0.11 0.11 0.54 1.39 0.89 109 43 F-IV F-IV 72.2 10.96 3.25 1.19 2.53 2.53 5.04 0.26 0.41 36 12 FIV* F-IV* 68.1 11.35 6.04 5.92 0.53 0.53 1.13 1.79 0.36 441 125 QFPRF QFPRF 77.3 12.18 1.63 0.32 1.23 1.23 6.06 0.09 0.23 3 7 QFPRF* QFPRF* 74.9 10.32 3.63 6.19 0.62 0.62 0.47 1.13 0.27 83 17 LF LF 46.7 18.00 10.51 5.06 7.25 7.25 3.59 1.67 0.94 233 21 LF* LF* 49.6 14.35 19.29 7.65 0.34 0.34 0.52 0.19 0.82 42 76 QFP QFP 74.6 11.43 2.22 0.91 1.88 1.88 4.16 0.65 0.30 5 23 QFP* QFP* 79.9 7.86 5.60 2.64 0.06 0.06 0.06 2.03 0.27 20 58 Gabbro Gabbro 50.9 14.30 11.60 7.94 11.10 11.10 1.85 0.30 0.76 Pyroxenite Pyroxenite 41.5 6.03 15.50 24.20 5.05 5.05 0.07 0.02 0.50 Key Key to to Abbreviations: Abbreviations: WLII-FWF FootwallMafic MaficFlow Flow WLH-FWF Footwall MMF Middle MiddleMafic MaficFlow Flow F-IV F-IV Felsic-Intermediate Felsic-IntermediateVolcaniclastics Volcaniclastics QFPRF QFPRF Quartz-Felsdspar-Phyric Quartz-Felsdspar-PhyricRhyolite fiyolite Flow LF LF 'Ladder" Mafic "Ladder" Mafic Flow Flow QFP QFP Quartz-Feldspar Quartz-Feldspar Porphyry Porphyry Hydrothermally (*). Hydrothermallyaltered alteredequivalents equivalentsare aremarked marked with with an an asterisk asterisk (*). Data Data from from Severin Severinand andBalint B a h t (1984). (1984).Some Someabbreviations abbreviationsfrom fromOsterberg Osterberg(1993). (1993). Schreiber Assemblage 59 Schreiber Assemblage 59 �Geochemical Geochemical Changes Changes with Alteration "Ladder" "Ladder" Mafic Mafic Flow Flow - Legend }LF LP Figure 8A. Geochemical Geochemicalchanges changesbetween between unaltered unaltered (LF) (LF) and and altered altered (LF*) (LF*) rocks, rocks, "Ladder't "Ladder" mafic flow. Data (1984). Datafrom from Severin Severin and and Balint B a h t (1984). Schreiber Assemblage Assemblage 60 60 - �Geochemical Changes Changes with with Alteration Alteration Geochemical Quartz-Feldspar-PhyricRhyolite RhyoliteFlow Flow Quartz-Feldspar-Phyric Legend 1QffPRF QFPRF — ,—.—.—.—.—;'. t Na20 K20 Figure 8B. 8B.Geochemical Geochemicalchanges changesbetween betweenunaltered unaltered(QFPRF) (QFPRF)and andaltered altered(QFPRF*) (QFPRF*)rocks, rocks, Figure quartz-feldspar-phyric rhyolite rhyolite flow. flow. Data Datafrom fromSeverin Severinand andBalint Balint(1984). (1984). quartz-feldspar-phyric SchreiberAssemblage Assemblage 61 61 Schreiber �Suiphide Ore Massive Sulphide The ore zone at Winston Winston Lake, Lake, as as described described by Severin Severin et al. (1990) and Balint B a h t et et a!. al. (1990), varies varies in in thickness from 2m to >20 m (horizontal), averaging 7m. Two Two main, main, apparently apparently unzoned, unzoned, ore ore types exist: exist: (1) "low-grade" "low-grade" (7-14% (7-14% Zn): - massive to locally banded, fine- to medium-grained - homogeneous mix of sphalerite, sphalerite, pyrrhotite, pyrrhotite, pyrite, chalcopyrite chalcopyrite - 10-20% included fragments fragments (<1-5 (<I-5 cm) (2) "high-grade" "high-grade"(5 ( 54% Zn): (2) 54% Zn): - massive, mediummedium- to coarse-grained coarse-grained sphalerite sphalerite - locally banded with chalcopyrite chalcopyrite andlor pyrrhotite Less conmion common metallic metallic minerals minerals include include magnetite, magnetite, marcasite, marcasite, arsenopyrite, arsenopyrite,mackinawite mackinawite and and galena galena (Barr 1991). galenobismutite(PbBi2S4)and and anhydrite anhydrite (Ban199 1). Bismuthinite Bismuthinite(Bi2S3), (Bi2S3),gladite gladite(CuPbBi5S9), (CuPbBi&), galenobismutite(PbBi&,) have also been identified identified by X-Ray diffraction diffraction analysis analysis (Resident (Resident Geologist's Geologist's Files, Files, Schreiber-Hemlo Schreiber-Hemlo andtellurobismuthite tellurobismuthite(Bi2Te3) (Bi2Te3)have have also also been been District, Thunder Thunder Bay). Bay). Hessite Hessite(Ag2Te), (Ag2Te),native nativesilver silverand noted, as have the spinels spinels franklinite, franklinite, chromite chromite and and gahnite. gahnite. Schreiber Assemblage Assemblage 62 Schreiber 62 �of the the ore ore zone zone corresponds corresponds to to the the thickest thickest portion portion of of the the footwall footwall alteration alterationzone. zone. The thickest thickest part of There is no apparent zinc and copper zonation within the deposit, although although there there is is evidence evidence of of remobilization concentricallyzoned, zoned,sulphide-filled sulphide-filledcavity cavity was was discovered discovered remobilization on a small scale. scale. AAconcentrically during mining operations in 1992 chimney, akin akin to to "black 1992 and has been interpreted as a sulphide chimney, smokers" of modem consists of aa chalcopyrite-rich chalcopyrite-rich core, core, a modern oceanic hydrothermal systems. ItIt consists crystals. Sulphur sphalerite zone and an outer zone of large selenite crystals. Sulphur isotope analyses of the massive suiphide and selenite-rich values of -0.6 %o % and and ++13.1 (G. sulphide selenite-rich portions portions returned returnedo34S 634Svalues 13.1 %o, %, respectively (G. Doiron, Metal! Metal1 Mining Corporation, personal communication, 1995). Samples Samples of of massive massive suiphide sulphide anhydrite from the Geco valuesof of+0.5 +0.5 and and +10.0 +10.0,, and anhydrite Geco Mine, Mine, Manitouwadge, Manitouwadge, returned similar similar o34S 6^S values respectively (Franklin (Franklinetetal. al.1981). 1981).Most MostPrecambrian Precambrianmassive massivesuiphide sulphidedeposits depositsyield yield ore ore suiphide sulphide 0% (close values close to 0%0 (close to the "mantle" "mantle" composition). Metamorphism Metamorphism precludes reasonable interpretation of data data and isotopic isotopic disequilibria. disequilibria. metalliferous fluids fluids migrated migrated through through Osterberg (1993) proposed a metallogenetic model in which metalliferous altered rocks and were trapped under impermeable CLR cap rock. rock. Synvolcanic Synvolcanic faulting faulting allowed allowed environment, resulting resulting in the the these fluids fluids to migrate from the pressurized reservoir to the sea floor environment, repeated repeated precipitation precipitationof of massive massive ZnZn- and and Cu-sulphides. Cu-sulphides. Schreiber Assemblage Assemblage 63 Schreiber 63 �Individual Individual Stop Descriptions: Footwall Footwall Stratigraphy Stratigraphy The following that structurally and following stops stops exemplify both altered and unaltered footwall lithologies that massive sulphide suiphide deposit. deposit. These stops stratigraphically underlie the Winston Lake massive stops have been prepared and used on on numerous numerous field field trips trips and and therefore therefore their their descriptions descriptions have have been been largely largely gleaned gleaned Balint from previous workers, including including Balint B a h t et et a!. al. (1990), Severin Severin and B a h t (1984) and Severin Severin et et a!. al. (1990). (1 990). The Thestratigraphic stratigraphicand andvolcanological volcanologicalsetting setting of of the the individual individual field field stops stops has has been been described most recently and completely completely by Osterberg Osterberg (1993), (1993), whose lithologic lithologic nomenclature nomenclature (Table (Table 2) 2) will will be be descriptions. Refer Refer to toFigures Figures9A 9A and and 9B 9B for for stop stop locations. locations. adopted for these descriptions. STOP STOP 5A: 5A:Winston WinstonLake LakeHorizon Horizon/ /Hanging HangingWall WallGabbro GabbroContact Contact STOP 5B: Creek CreekCopper Copper Showing Showing STOP 5C: 5C: Altered Camp Flow Rhyolite STOP 5D: STOP 5D: Incipiently IncipientlyAltered AlteredLadder LadderFlow Flow /1Trail Trail Showing STOP STOP 5E: 5E: Altered AlteredPillowed PillowedLadder LadderFlow Flow STOP STOP 5F: 5F: "Main" "Main"Quartz-Feldspar Quartz-FeldsparPorphyry Porphyry Schreiber Assemblage 64 Schreiber Assemblage 64 �- _____ _____ _____ Figure 9A Figure 9A Winston Lake Lake Winston Detailed Surface Surface Geology Geology Detailed - 0 0 100 100 200 - 3 0 0 rn. 200 300 m. Winston Lake Deposit / / Projection 00—O 0 0 0 0 0 0 0 0 0000000000000 O000 000000000 000000000000000 0000000000000000 00000000000000000 000000000000 0000000000000°Trail°0 00 O oShowjn 0000000 0000000000 0000000 GAB B RO 0000000 00000000 META - PYROXENITE 00000000 000000000 V V VV MAFIC 000000000 FLOWS VVV 0000000000 000000 CHERTY ASH 000000 000000 FELSIC/ INTERMEDIATE 000000 VOLCANICLASTICS• 000000 000000 FELSIC TUFFS/SEDIMENTS 000000 000000 QUARTZ - FELDSPAR P1-lYRIC 000000 000000 RHYOLITE FLOW 0 00 0 0 0 000 QUARTZ - FELDSPAR 00000000 000 PORPHYRY 0000000 0000000 ALTERATION 000000 000000 '0000 5 D TOUR STOPS '000 Schreiber Assemblage 65 DO DO llII Creek Copper Showing • ,—• ,' \ / �Schreiber Assemblage 66 a 0 a 0 a 0 0 0 0 a 0 0 0 0 0 0 0 0 0 0 0 000000000 no 0000 00000 000000 00 0 0 a 0 000000 0000000 0000000 00000000 0000 000 0 0 d' 00 0 0 00 00000 00000 no 0 00 000 on 000.. 00 0000 no 0 Figure 9B Zn 30.0 gm/T 16.O0 100 %Cu Ag Au 0 500m. Winston Lake Deposit COMPOSITE SECTION LOOKING noon 0000000000 0000 0000 0000 0000 anon 0000 anon 000 000 000 000000000 000000 000000 000000 000000 0 0 0 0 0 0 0 0 ..,' 000000000 0000000.. 0000 00000 0000 0000 0 o CI 4' a 0 0 MASSIVE SULPHIDES ALTERATION PORPHYRY QUARTZ- FELDSPAR NNW 0 Io-1 a] QUARTZ- FELDSPAR PHYRIC RHYOLITE FLOW FELSIC TUFFS/SEDIMENTS FELSIC/ INTERMEDIATE VOLCAN ICLASTICS CHERTy ASH MAFIC FLOWS META- PYROXENITE GAB B RO �STOP STOP 5A: WINSTON LAKE HORIZON! HORIZON1 HANGING WALL GABBRO CONTACT This stop lies at the top of the Winston Footwall Block (WFB) where it is in contact with with gabbro of the Big Duck Sequence. Sequence. The Theuppermost uppermostpackage packageof of footwall footwall rocks, rocks, the the Winston Winston Lake Lake Horizon Horizon Succession (WLH), consists of volcanic volcanicand and volcaniclastic volcaniclastic rocks situated situated between the underlying underlying Clotted Rhyolite (WLH-CLR) (WLH-CLR) and and overlying overlying mafic flows flows and gabbro of the Big Duck Duck Sequence. Sequence. The Winston Lake massive suiphide m sulphide deposit is hosted by the WLH rocks, approximately 450 m down-dip along this contact. contact. The WLH WLHrocks rocksatatthis thissite siteare areinterepreted interepretedas asmixed mixedlaminated laminatedash ashand and exhalative exhalativesediments sedimentswhich which are thinly laminated and locally folded (WLH-CRT). They as fine-grained, fine-grained, recrystallized recrystallized They appear appear as and dark dark green. green. Their rocks which range in colour from white to creamy yellow, light and Their mineralogy is is variety of of accessory accessory minerals. minerals. Felsic dominated by quartz, plagioclase and lesser hornblende and a variety Felsic volcaniclastic/tuffaceous units predominate; minor cherty exhalites exhalites are are also also present. present. Pyrite to mafic volcaniclastic/tuffaceous Pyrite and pyrrhotite dominate, dominate, comprising comprising up to 20% of the rock locally. Near Near the the Winston Winston Lake Lake deposit, deposit, sphalerite-rich beds and massive magnetite have been noted. sphalerite-rich It has been noted noted by many many observers observersthat that this this exposure exposuredisplays displaysaa great great deal deal of of hitherto hitherto undescribed undescribed deformation, deformation, manifested manifested in in aa pervasive pervasive schistosity schistosity(locally (locally crenulated), crenulated),steeply steeplyplunging plungingmineral mineral lineations, chioritic chloritic shear planes and minor folds. ItIthas haseven evenbeen been suggested suggestedby by Williams Williams(personal (personal lineations, cornmuncation, 1988) that these these laminated laminated rocks represent a mylonitized mylonitized anorthosite anorthosite that that contains contains communcation, 1988) Schreiber Assemblage 67 Schreiber Assemblage 67 �very calcic plagioclase. There Therehave havealso alsobeen beensuggestions suggestionsof of dip-slip dip-slip movement movement and and thrusted thrusted contacts in this vicinity. vicinity. contacts STOP STOP 5B: 5B: CREEK COPPER COPPERSHOWING SHOWING CREEK This stop comprises comprises aa variety variety of of lithologic lithologic units, units, suiphide sulphide mineralization mineralization and and alteration-related alteration-related straddlesthe thecontact contactbetween between rocks rocks of of the the WLH WLH and volcaniclastic rocks of the features. ItItstraddles underlying Clotted Rhyolite (CLR). (CLR). Outcrops Outcropson onthe theeast eastside sideof of Selim SelimCreek Creek consist consist of of alternating alternating flows and thin, ashy sedimentary units. Gabbro Gabbro outcrops outcrops approximately approximately 10 10to to 15 15m m bands of mafic flows east of the creek. Volcaniclastic Volcaniclastic(CLR) (CLR)rocks rocksextend extendfrom from this this location location south south and and west west and and host host the the pyrite- and and chalcopyrite-bearing, chalcopyrite-bearing, Creek Creek suiphide sulphideshowing showing(gossan) (gossan) on on the the access access trail. trail. The mafic flows flows (WLH-MA) range in thickness thickness from from 2 to 33 m; most are between between 4 and and 10 10m m thick thick and uniform in thickness. They Theyare aretypically typically finefine- to to medium-grained, medium-grained, aphyric, aphyric, dark dark green-gray green-gray to black where fresh. Although Althoughprimary primary features features@illows, (pillows, sheet structures, hyaloclastite, autoclastic autoclastic breccias) are rare, long, long, pillow-like pillow-like structures structures have been been noted noted at at this this locality. locality. In the vicinity vicinity of the Winston Lake deposit, deposit, these these mafic mafic rocks rocks have been altered to a cordierite-anthophyllite-biotite cordierite-anthophyllite-biotite assemblage. assemblage. The CLR volcaniclastics volcaniclastics exposed exposed along along the the trail trail are are heterolithic, heterolithic, containing containing both both mafic mafic and and felsic felsic Schreiber Assemblage Assemblage 68 68 �(quartz-phyric) elongate, flattened fragments ranging in Finely laminated laminated in size from from 44 to to 100 cm. cm. Finely sections are also present. The Themajority majorityof of the the CLR CLR has has been been interpreted interpreted as as aa felsic felsic pyroclastic pyroclastic flow. flow. Incipient hydrothermal alteration alteration has has affected affected the mafic mafic component, component, smaller smaller felsic felsic fragments fragmentsand and ash ash component Relatively unaltered, unaltered, felsic felsic component to produce a biotite-cordierite-anthophyllite biotite-cordierite-anthophyllite assemblage. Relatively lenses may therefore therefore be preserved preserved in in aa dark, dark, altered altered matrix, matrix, producing producing what has has been been locally locally termed termed aa clastic protolith. protolith. "pseudo-fragmental" texture texture that that is is not not necessarily necessarily predicated upon upon aa primary primary clastic "pseudo-fragmental" STOP STOP SC: 5C: ALTERED CAMP FLOW RHYOLITE RHYOLITE Felsic rocks of the Camp Flow Flow rhyolite (QFF), thought to represent massive lava flows, outcrop on the access trail immediately immediately west of the mine road. This Thisunit unit isis laterally laterally extensive extensive (>5 (>5 km) km) but but relatively thin (50 (50 to 200 200 m). Phenocrysts Phenocrystsof ofquartz quartzand andplagioclase plagioclaserange range in in size size from from 11to to 33 mm mm quartzo-feldspathic matrix. matrix. The and are set in a fine- to medium-grained, recrystallized, quartzo-feldspathic The recognition of individual flow flow units units is is precluded precluded by by shearing, shearing, recrystallization recrystallization and and hydrothermal hydrothermal alteration. alteration. Compositional banding developed in mafic minerals (biotite, hornblende, hornblende, magnetite) magnetite) may may represent represent flow banding. Such Suchbanding bandingisisexposed exposedin inaaroadside roadsideexposure exposureacross across from from the the Cleaver Cleaver Lake Lake campsite. Unaltered QFF rocks vary vary from from tan tan to pale pale gray, gray, while while their altered altered counterparts counterparts may may be be bright bright white white (sericite-rich) or brownish (biotite-rich). With Withincreasing increasinghydrothermal hydrothermal alteration alterationthese these rocks rocks may may Schreiber Assemblage Assemblage 69 69 �contain: contain: (1) Quartz Quartz -- Muscovite Muscovite -- Biotite Biotite ++ Feldspar Feldspar (2) Quartz Cordierite -- Sillimanite Sillimanite -- Biotite Biotite ++ Staurolite Staurolite ++ Garnet Garnet Quartz -- Cordierite (3) (3) Quartz Quartz -- Cordierite Cordierite -- Anthophyllite Anthophyllite ++ Sillimanite Sillimanite ++ Staurolite Staurolite ++ Garnet Garnet Where exposed exposedalong alongthe thetrail, trail,QFF QFFrocks rocksare arevariably variablyaltered. altered.Large Large(_<2.5 (52.5 cm) cm) dark darkred red Where porphyroblasts of of garnet garnet and and smaller, smaller,honey-brown honey-brownstaurolite stauroliteporphyroblasts porphyroblasts occur occur in in the the more more porphyroblasts outcrop. Fine-grained, Fine-grained,whitish-pink whitish-pinkandalusite andalusiteporphyroblasts porphyroblastsoccur occur in in aa pervasively pervasively easterly outcrop. sericitized matrix matrix at the outcrop outcrop west along the trail. Intense Intensebiotitization biotitization characterizes characterizes altered altered core core sericitized samples samples at at the the site. site. It is notable that altered altered rocks containing containing in excess excess of 30% 30% biotite biotite (perhaps (perhaps regarded 75% Si02. SiO,. regarded as as "mafic") "mafic")still still contain containapproximately approximately75% STOP STOP5D: 5D: INCIPIENTLY INCIPIENTLYALTERED ALTERED LADDER LADDER FLOW FLOW / TRAIL TRAIL SHOWING SHOWING The Ladder Ladder Flow Flow (LF) (LF) is is aa 20 20 to to 200 200 m m thick thick series series of of mafic mafic rocks rocks consisting consisting of of thin thin sheet sheetflows, flows, thicker massive hyaloclastite. No massive flows flows and flow flow lobes, pillow lava, pillow breccia and hyaloclastite. No obvious obvious discernable discernable facies facies relationships exist. exist. Sharp Sharpcontacts contactsbetween between different different flow flow morphologies morphologies suggest suggest compound coarsecompound lava lava flows. flows. These Theselavas lavasvary varyfrom fromfine-grained, fine-grained,dark darkgrayish-green grayish-greento to mediummedium- to to coarsegrained, grained, greenish-brown, greenish-brown,altered alteredequivalents. equivalents. Schreibçr Assemblage 70 Schreiber Assemblage 70 �location, dark dark green green flows flowshost host 11 to Elongatepillows pillows At this location, to 55 mrn, mm, lathlike lathlike plagioclase plagioclase phenocrysts. phenocrysts. Elongate (feeders to lava lava lobes?) lobes?) display display local local budding budding and and re-entrant, re-entrant, hornblende-rich selvages. hornblende-rich selvages. zones usually very very rare, rare, occurs occurs as 10 to Hyaloclastite, usually as 10 to 20 20 cm cm wide, wide, 11 to to 55 m m long, long, discontinuous discontinuous zones 40 cm cm subsubbetween lobate, pillowed and massive flows. A A flow flow breccia, breccia, consisting consisting of of 20%. 10 to to 40 20%, 10 rounded to sub-angular sub-angular pillow fragments fragments occur occur at the base of the LF. Trailcopper coppershowing showingconsists consistsof ofaapyrite-, pyrite-, pyrrhotitepyrrhotite- and and chalcopyrite-bearing, chalcopyrite-bearing, felsic felsic interfiow interflow The Trail sedimentary unit (CT). ItItisisexposed exposedas as patches patches of of aa rusty-weathering, rusty-weathering, laminated, siliceous siliceous rock. 6230 ppm Cu Cu have have been been returned returned from from this this 0.15 0.15 rn m thick thick unit unit (Severin (Severinand and Balint Baht Values of up to 6230 1984). This This unit unit occurs occurs within within mafic mafic flows and between the quartz-feldsparporphyry porphyry (QFP) (QFP) the "Main" Main" quartz-feldspar Garnet occurs occurs within within the the altered altered base base of of this this unit unit and and is is and mafic flows farther south along the trail. Garnet displayed along along aa steeply steeply dipping dipping outcrop outcrop surface surface which which follows follows the the undulating undulating top top of of the the underlying underlying displayed lava flow. The Themafic maficlava lavaflows flowson on either either side side of of the the sedimentary sedimentary unit are partially altered to anthophyllite-biotite-cordierite+garnet assemblages. Hyaloclastic anthophyllite-biotite-cordierite+gamet Hyaloclastic units may be preferentially altered. ALTERED PILLOWED PILLOWED LADDER LADDER FLOW FLOW STOP SE! STOP 5E: ALTERED opportunity to view pervasively altered and This series of large large outcrops outcrops provides provides an an exceptional exceptional opportunity to view pervasively altered and 71 Schreiber Assemblage 71 �metamorphosed, undeformed, undeformed, pillowed basalt flows. East-younging, East-younging,metre-scale metre-scalepillows pillows have have metamorphosed, bladed to to sheaf-like sheaf-like recessive-weathering, biotite-altered biotite-altered selvages. selvages. Pillow cores coreshost hostcoarse coarse(55cm) (5cm) bladed anthophyllite and and blue-gray blue-gray cordierite cordierite porphyroblasts (Figure 13). Anthophyllite Anthophylliteand and cordieriite cordieriite anthophyllite have undergone undergone some some retrograde retrograde alteration alterationto to chlorite chlorite++ talc talc and pinite, respectively. Siliceous Siliceous occupy interpillow interpillow spaces. spaces. Further Furtherwest, west,garnet garnethas has pervasively pervasively(up (up to to 100% 100%garnet garnet++ material may occupy quartz) quartz) replaced primary, ovoid ovoid patches (selvages? lava tubes?) to cm) to produce coarse coarse (53.5 (3 .5 cm) porphyroblasts, porphyroblasts, armored armoredwith with biotite. biotite. STOP STOP 5F: 5F: "MAIN" "MAIN"QUARTZ-FELDSPAR QUARTZ-FELDSPARPORPHYRY PORPHYRY The "Main" "Main" QFP, QFP, confonnably conformablyoverlain overlainby by mafic mafic (LF) (LF) rocks, rocks, extends extends along strike for over 4.6 km and reaches an apparent map thickness of 11 km. ItItvaries variesin inappaearance appaearancefrom from tan tan to to pinkish-gray pinkish-gray to to gray-brown. gray-brown. Unaltered UnalteredQFP QFPisisremarkably remarkablyhomogeneous, homogeneous,massive massiveto to foliated, foliated,and and contains contains20 20 to to 50% 50% quartz quartz phenocrysts phenocrysts and and I1to to25% 25%lath-shaped, lath-shaped,feldspar feldsparcrystals. crystals. ItIthas hasbeen beeninterpreted, interpreted,ininpart, part, as as aa subaqueous, subaqueous, felsic felsic lava lava flow flow deposit. deposit. Alteration Alterationassemblages assemblagesin inthe the QFP QFPinclude: include: Quartz-Muscovite Quartz-Muscovite Quartz-Biotite-Sillimanite Quartz-Biotite-Sillimanite Cordierite-Quartz-Biotite-Sillimanite Cordierite-Quartz-Biotite-Sillimanite Cordierite-Quartz-Anthophyllite Cordierite-Quartz-Anthophyllite plus plus accessory accessorystaurolite, staurolite,garnet, garnet,spinel, spinel,magnetite, magnetite,zircon zirconand andrutile. rutile. Schreiber SchreiberAssemblage Assemblage 72 72 �REFERENCES REFERENCES Balint, F., Sim, R.C. and Morrison, Morrison, I.R. 1990. The Winston Lake massive sulphide deposit; deposit; in Mineral Deposits of Central Canada, Canadian Institute of of Mining Mining and and Metallurgy, Metallurgy, Field Field 1/6, p.63-78. Trip Guidebook Guidebook # 1/6, Barr, C. 1991. 1991. 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J.A. 1989. 1989.A A regional regionalperspective perspectiveof ofthe the Quetico Queticometasedimentary metasedimentarybelt, belt, Superior Superior Province, Canada; Canadian Journal of Earth Sciences, v.26, p.677-693. Province, Canada; Canadian Journal of Earth Sciences, v.26, p.677-693. Schreiber Assemblage Assemblage 75 75 �1964. Mineral Mineral deposits deposits of of the the Big Big Duck Duck Lake Lake area; area; Ontario Ontario Department Departmentof of Mines, Mines, Pye, E.G. 1964. 47p. Geological Report 27, 27,47p. -----. 1969. 1969. Geology Geology and and scenery, scenery, north north shore shore of of Lake Lake Superior; Superior; Ontario Ontario Department Department of of Mines, Mines, . Geological Guide Book Book 2, 2, 144p. l44p. (in progress). progress). Lithostratigraphy Lithostratigraphyand and geochemistry geochemistryof of the the McKellar McKellar Harbour Harbour area; area; Purdon, R. (in unpublished M.Sc. M.Sc. thesis, thesis, Lakehead Lakehead University, University, Thunder Thunder Bay. Bay. unpublished Naldrett, A.J. A.J. and and Eckstrand, Eckstrand,O.R. O.R. 1973. 1973.Archean Archean ultramfic ultramfic flows flows in in Munro Munro Township, Township, Pyke, D.R., Naldrett, Ontario; Geologiëal Geological Society Society of America Bulletin, v.84, p.955-978. 1991. Rocks and minerals minerals for for the collector: collector: Sudbury Sudbury to Winnipeg; Winnipeg; Geological Geological Survey Survey Sabina, A.P. 1991. of Canada,Miscellaneous Canada,MiscellaneousReport Report 44 Schandl, Schandi, E.S. and Gorton, M.P. 1991. Postore mobilization of rare rare earth earth elements elements at at Kidd Kidd Creek Creek and other Archean massive sulfide sulfide deposits; deposits; Economic Economic Geology, Geology, v.86, p.1546-1553. p. 1546-1553. Schandi, H.A. 1991. 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R. 1990. 1990.Geological Geologicalsetting setting of of the the Winston Winston Lake Lake massive massive suiphide in Mineral Mineral deposits deposits of of the the western western Superior Superior Province, Province, Ontario, Ontario, 8th 8th sulphide deposit; deposit; in IAGOD Symposium, Symposium, Field Field Trip Trip Guidebook Guidebook #9, #9, p.58-73. p.58-73. Schreiber Assemblage Assemblage 76 Schreiber 76 �Thomas, D.A. D.A. 1991. 1991.The The application applicationof of mineralogy, mineralogy, whole whole rock rock chemistry chemistry and and mineral mineralchemistry chemistryto to Thomas, volcanogenic massive sulphide sulphide exploration exploration at the Winston Lake Zn-Cu deposit, deposit, volcanogenic massive northwestern Ontario; unpublished M.Sc. thesis, Queen's University, Kingston, Ontario, northwestern Ontario; unpublished M.Sc. thesis, Queen's University, Kingston, Ontario, 329p. Thurston, P.C. 1991. 1991. 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Subprovince accretion in the southern Superior Province (or cross-section cross-section through through the the Wawa-Quetico-Wabigoon Wawa-Quetico-Wabigoon subprovincial subprovincialboundaries boundaries and and the the Beardmore-Geraldton Beardmore-Geraldtonbelt); belt); Geological Geological Association Association of of Canada-Mineralogical Canada-MineralogicalAssociation Association of Canada-Society Canada-Society of Economic Geologists, Joint Annual Meeting, Toronto '91, Field Trip B6 Guidebook, 26p. Williams, H.R., Stott, Stott, G.M., G.M., Heather, Heather, K.B., K.B ., Muir, Muir, T.L. T.L. and and Sage, Sage, R.P. R.P. 1991. 1991.Wawa Wawa subprovince; subprovince; in Geology of Ontario, Ontario, Ontario Ontario Geological Geological Survey, Survey, Special Special Volume 4, Part Part 1, 1, p.485-539. p.485-539. 0. 1994. 1994.Geological, Geological, geochemical geochemical and age age Zaleski, E. Peterson, V.L. and Van Breemen, 0. constraints constraints on base metal mineralization mineralization in in the Manitouwadge Manitouwadge greenstone greenstonebelt, belt, northwestern Ontario; in Current Current Research Research 1994-C, 1994-C, Geological Geological Survey Survey of of Canada, Canada, p.225p.225northwestern Ontario; in 235. 235. ----- . 1995. 1995. Geological Geological and and age age relationships relationshipsof of the margins margins of of the Manitouwadge Manitouwadge greenstone greenstonebelt belt . and the Wawa-Quetico in Current CurrentResearch Research Wawa-Quetico subprovince subprovince boundary, boundary, northwestern northwestern Ontario; Ontario; in 1995-C, Geological Geological Survey of Canada, p.35-44. Survey of Canada, p.35-44. Schreiber Assemblage 77 Schreiber Assemblage 77 �NOTES NOTES �NOTES NOTES � https://digitalcollections.lakeheadu.ca/files/original/ed5aa49809fd3764d2fca6d149c243fc.pdf 89cf4530938bfeb7fc00e2b97b962941 PDF Text Text GEOLOGY AND GOLD GOLD DEPOSITS DEPOSITS OF THE HEMLO AREA REVISED EDITION EDITION REVISED Compiled and Edited by T.L. B.R. Schnieders Schnieders and M.C. Smyk T.L. Muir, B.R. �Archean Archean Mafic Metavolcanics Granitoids Intermediate to toFeisic FelsicMetavolcanics Metavolcanics Intermediate and Related RelatedMetasediments Metasediments and Mafic Intrusions Intrusions Mafic Metasediments Metasediments Ultramafic Ultramafic Intrusions Intrusions Proterozoic Coidwell Complex (alkalic) Field to 29 29 not not Field Trip Trip Stop Stop (numbers (numbers 88 to shown 5) shown for for clarity: clarity: see see Figure Figure 5) Headframe: Headframe: Hemio Hemlo Deposit Deposit LL Lake Lake Figure14. 14. Location Locationmap map(inset) (inset) and and regional regionalgeology geology of of the the Hemlo-Heron Hemlo-HeronBay Bayarea. area. Figure STOPS 11to to 7, 7. and 30, 30,31 indicated. Other Otherstops stopsare areshown shownon onFigures Figures18 18and and19. 19. STOPS 31 are indicated. P.2701, P2702, P2738, P.2739). (Modified after OGS maps 2220, 2439, 2452, (Modified after OGS maps 2220,2439,2452, P.2701, P.2702, P.2738, P.2739). �Originally published published for the the Originally Geological Geological Association Association of of Canada Canada Mineralogical Association Canada Mineralogical Association of Canada Society of Economic Economic Geologists Geologists Joint Annual Annual Meeting, Meeting,1991 1991 Toronto, Ontario, Canada Canada Toronto, GEOLOGY AND GOLD GOLD DEPOSITS DEPOSITS OF THE HEMLO AREA REVISED REVISED EDITION EDITION Compiled and Edited Edited by by T.L. Muir 1, B.R. Schnieders Schnieders 22 and and M.C. Smyk T.L. 1, B.R. Smyk22 with contributions contributions from from A. Chong Chong 3,, P. Johnston3,, R. , D. I? Johnston R. Kusins Kusins 3, D. Mcllveen 3,, K. K. McNena McNena3and andG. G.Patterson Patterson 22 1 Ontario 1 Ontario Geological Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario Ontario P3E 6B5 2 Northern Development Developmentand and Mines, Mines, Resident ResidentGeologist's Geologist's Office, Office, 2 Ministry of Northern Schreiber-Hemlo District, 435 435 James James Street Street South, South, Thunder Thunder Bay, Bay, Ontario Ontario P7E P7E 6E3 6E3 Schreiber-Hemlo District, 3 Hemlo Gold Mines Mines Inc., Inc., Golden Golden Giant Giant Mine, Mine, P.O. P.O. Box 40, Marathon, Marathon,Ontario OntarioPOT POT 2E0 2E0 3 TORONTO 19jj GAC/AGC •M A C / A M C • SF6 SEG GACIAGC MA(/AMC Original published published with the permission permissionof V.G. VG. Milne, Original Milne, Director, Director, Ontario Ontario Geological Geological Survey Survey permission of J. Wood, Director, Revision published with the permission Director, Ontario Ontario Geological Geological Survey @ Copyright Copyright Geological GeologicalAssociation Associationof ofCanada, Canada,Toronto Toronto '91 '91 Committee Committee © �Cover Photograph: Photograph: Hemlo camp gold mines, summer summer 1989. 1989. Photograph courtesy of Ray Ray Ettinger. Ettinger. TORONTO '91 '91 FIELD TRIP COMMITTEE: COMMITTEE: TORONTO Chairman: R.M. R.M. Easton Easton Vice-Chairman: Vice-chairman: G.W. G.W. Johns Johns Guide Book Production: M.G. M.G. Easton Easton Other Assistance Provided Provided by: P. P. Hinz Hinz RECOMMENDED RECOMMENDEDCITATION: CITATION: Muir, T.L., Schnieders, Schnieders, B.R. B.R. and and Smyk, Smyk, M.C., M.C., (Compilers and and Editors), 1995, Geology and Gold Muir, T.L., Deposits of the Hemlo Area; Geological Association of Canada—Toronto'91, Hemlo Area; Geological Association of Canada-Toronto991, Hemlo Field Field Trip Trip Guidebook, 120p. 120p. Guidebook, PUBLISHED BY: PUBLISHED AND AND DISTRIBUTED DISTRIBUTED BY: Geological Association of of Canada Canada TORONTO '91 '91 Organizing Committee, do c/o Ontario Ontario Geological Geological Survey Survey Room 8056, 933 Ramsey 8056,933 Ramsey Lake Road Road Sudbury, Ontario Ontario Canada Canada P3E P3E 6B5 6B5 First edition, edition, printed printedApril April1991. 1991. Revised edition, edition, printed printedMarch March1995. 1995. Printed in Canada by Love Printing Service Ltd., Stittsville, Ontario Ontario �GEOLOGY AND GOLD GOLD DEPOSITS DEPOSITS OF THE HEMLO AREA TABLE TABLE OF OF CONTENTS CONTENTS Part 1: 1 1: Introduction Introduction ....................................................................................................................................................1 Schnieders and M.C. Smyk by TL. T.L.Muir, Muir, B.R. Schnieders Smyk Part 2: Exploration Exploration History History ....................................................................................................................................... 3 3 by B. R.. Schnieders Schnieders and C.. Smyk B.R and M. M.C Regional Geology Geology .......................................................................................................................................... 8 Part 3: Regional by TL. TL.Muir, Muir, B.R. B.R. Schnieders Schnieders and M.C. Smyk Property ...................................................................................................................................10 10 Part 4: Peekongay Property R.. Schnieders Schnieders and and M. C. Smyk Smyk by B. B.R M.C. Mineralization Types 10 Mineralization Types ................................................................................................................... 10 11 11 Main Zone Mineralization Mineralization .......................................................................................................... BayMine 11 Heron Bay Mine ............................................................................................................ 11 Bowhill Mines Bowhill Mines Trench ...................................................................................................12 12 Porphyry Porphyry Zone Zone .............................................................................................................................12 12 CZone 13 C Zone ........................................................................................................................................... 13 13 South South Zone Zone ................................................................................................................................... 13 14 14 Part 5: Hemlo Deposit Overview Overview ........................................................................................................................... by B.R. and T.L. TL. Muir B.R. Schnieders, Schnieders. M.C. Smyk and Part 6: Geology of the Golden 16 Golden Giant Mine and Golden Sceptre Orebody .................................................... 16 by R. R. Kusins, Kusins. A. A . Chong, Chong. P I? Johnston, Johnston. D. D.Mcllveen Mcllveen and and K. K.McNena McNena Introduction Introduction ..................................................................................................................................16 16 Mine Geology 16 Geology ............................................................................................................................... 16 Formation ................................................................................................19 Moose Lake Formation 19 Lower Mineralized MineralizedZone Zone (Unit (Unit 5) 5) .................................................................19 19 Footwall Footwall Schists Schists (Unit (Unit 3) 3) ...............................................................................19 19 Mafic Mafic Fragmental Fragmental (Unit (Unit 4) 4) .............................................;...............................20 Main Ore Zone (Unit (Unit 5) 5) .................................................................................20 20 Cedar Creek Formation 21 Formation ............................................................................................... 21 Intrusive Rocks Rocks ............................................................................................................. 21 21 Level Level Plan Plan Descriptions Descriptions ...............................................................................................22 22 4750 Main Main Drift ...............................................................................................22 22 4700 2W Crosscuts Crosscuts ...................................................27 4700 Sublevel SublevelPlan Plan— - OW, OW, 2W 27 Observations Observations ................................................................................................................. 29 29 Golden Sceptre Property Property ...........................................................................................................31 31 Discussion Discussion .................................................................................................................................... 32 32 Summary ...................................................................................................................................... 33 33 Part 7: Road Log for the Hemlo-Heron HemIo-Heron Bay Bay Area ............................................................................................... 34 by TL. TL. Muir Introduction 34 Introduction .................................................................................................................................. 34 Heron Heron Bay Bay Area Area Segment Segment (STOPS (STOPS 1-4) 1-4) ..................................................................................36 36 Hemlo Hemlo Area Segment Segment (STOPS (STOPS 5-31) 5-31) ....................................................................................... 43 43 Hemlo 91 Hemlo Deposit Deposit Segment: Segment: Williams Williams Property PropertyVisit Visit (STOPS (STOPS 32-35) 32-35) ....................................91 103 8: References References ................................................................................................................................................. 103 Part 8: 107 Photographs .............................................................................................................................................. 107 Part 9: Photographs �Introduction Introduction 1 THE HEMLO AREA AREA GEOLOGY AND GOLD DEPOSITS OF THE PART 1: INTRODUCTION INTRODUCTION by by TL. Muir, B.R. Schnieders Schnieders and T.L. Muir, B.R. and M.C. Smyk 35 km Marathon, Ontario, The Hemlo Hemlo gold gold deposit depositisislocated locatedroughly roughly35 kmeast eastof of the the Town Town of Marathon, Ontario,and andlies, lies, in in part, part, beneath beneaththe theTrans-Canada Trans-CanadaHighway Highway(Highway (Highway17) 17)(see (seeFigures Figures14 14and and19 19on on inside insidefront front and and back covers, respectively, and and Figure 21). 21). Estimates, Estimates, in in 1989, 1989, indicated indicated there were at at least least 80 million tonnes g/tAu Au(Harris (Harris 1989). 1989). The The deposit deposit is currently currently being million tonnes of of ore ore at at an average average grade grade of of 7.7 7.7 glt being mined by three companies: Teck-Corona Teck-CoronaOperating OperatingCorporation Corporation(David (DavidBell BellMine), Mine),Hemlo HemloGold Gold Mines (Golden Giant Mine), and Williams Williams Operating Operating Corporation Corporation (Williams mines Mines Inc. (Golden (Williams Mine). All All33 mines were 50 gold producers producers in the world world in 1992. 1992. Their Their standings were: Williams were ranked rankedin in the the top top50 standingswere: WilliamsMine, Mine, Golden Giant Mine, 19th; and David David Bell Bell Mine, Mine,49th. 49th. Collectively, Collectively, they 8th, 17th: Golden 19th; and they would would have haveplaced placed8th, accounting accounting for almost 4% of the total production production of of the the top top 50 50 gold gold producers. producers. Annual production from the 33 mines mines has has totaled totaled over over 11 million million ounces ounces for for the the last last66years years (Figure I), 1), for for aatotal total production, production, since commencing commencing operations (1989-1994) (Figure operationsin in1985, 1985, until untilthe the end end of 1994, of almost almost 9.5 9.5 million million ounces ounces (see Table Table1). 1). Production Production for the last 5 years years has has accounted accounted roughly for over one-half of Ontario's gold production production and and roughly roughly one-quarter one-quarter of of Canada's Canada's gold gold production. The total contained ore-grade gold of the deposit (mined and remaining) is about The total contained ore-grade gold of the deposit (mined and remaining) is about 20.69 million January 1, 1994. Ore reserve reserve and million ounces ouncesbased basedon on data data as as of January 1,1994. and grade grade estimates estimates(as (asof of January January 1, 1, 1995) 1995) are presented presentedininTable Table 2. 2. Table 1: 1: Hemlo Hemlo Deposit Deposit Gold Gold Production: Production:1985-1994 1985-1994 YEAR 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1993 1994 1994 TOTALS DAVID BELL MINE MINE 20,989 20,989 52,888 52,888 130,122 130.122 218,333 218,333 312,190 312.190 318,098 318,098 295,284 295,284 210,121 210,121 215,188 215,188 192,217 192,217 1,965,430 1,965,430 GOLDEN GIANT GIANT MINE MINE WILLIAMS WILLIAMS MINE MINE 10,369 10,369 98,155 98,155 254,545 254,545 369,300 369,300 336,700 336,700 378,400 378,400 435,300 435,300 443,438 443,438 451403 451,403 422,528 422,528 446,850 446,850 3,636,581 3,636,581 198,515 198,515 256,809 256,809 378,827 378,827 494,127 494,127 594,128 594,128 518,703 5 18,703 496,920 496,920 492,251 492,251 445,320 445,320 3,885,969 3,885,969 TOTAL TOTAL OUNCES 129,513 129,513 505,948 505,948 756,231 756,231 933,860 933,860 1,184,717 1,184,717 1,347,526 1,347526 1,257,425 1,257425 1,158,444 1,158,444 1,129,967 1,129,967 1,084,387 1,084,387 9,488,018 9,488,018 Table 2: Ore OreReserve Reserveand and Grade Grade Estimates Estimates Ore Reserves Reserves (tonnes) David David Bell BellMine Mine11 Golden Giant Golden Giant Mine Mine 22 Williams Mine Mine 3 I 4,956,219 4,956,219 10,582,000 10,582,000 30,890,000 30,890,000 Grade Grade (g/t Au) (g/t Au) 10.86 10.86 11.10 11.10 5.72 5.72 Mineable and diluted ore ore reserves, reserves, Dec. Dec.31, 31,1994; 1994;P. F?Desautels, Desautels, Chief Chief Geologist, Geologist, David David Bell BellMine, Mine,Teck-Corona Teck-Corona Operating Operatin! Corporation, ;orporation, personal personalcommunication, communication,1995. 1995. Total ore reserves reserves as as of of Dec. Dec.31, 31,1994; 1994;R. R.Kusins, Kusins,Chief ChiefGeologist, Geologist, Golden Golden Giant GiantMine, Mine,Hemlo HemloGold GoldMines MinesInc., Inc.,personal person! 2 Total ommunication,1995; 1995;includes includestonnages tonnagesofof99504 504463 463t t@@11.38 11.38g/t g/tAu Au(Golden (GoldenGiant GiantDeposit DepositNo. No.1),I)and ,and1 1077 077176 176t @ t @8.74 8.74glt communication, g/t AI Au (Quarter QuarterClaim). Claim). Total proven and reserves as as of of Dec. Dec. 31, 31,1994; 1994;J. Gray, Senior Geologist, williams WilliamsMine, Mine,Williams William and probable diluted ore reserves Senior Production Production Geologist, Operating )prating Corporation, Corporation,personal personal communication, communication,1995. 1995. �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 2 The delineation of the Hemlo Hemlo deposit deposit in in the the early early 1980s 1980s spurred spurred an exploration exploration blitz blitz of of the the Schreiber-Hemlo greenstone belt. belt. Several Several years years later, although much more is known about the area, no other economic gold deposit has been found. However, However, the presence presence of of aa major major gold gold deposit within any belt carries with it the substantial possibility that additional deposits remain to deposit with the substantial possibility that be discovered. discovered. This deals mainly with the geology of the Hemlo deposit deposit vicinity, touches on vicinity, but but touches This field field trip trip guide guide deals mainlywith the geology some guide includes includes updated updated some other other interesting interestingoccurrences occurrencesas asfarwest farwestas asHeron HeronBay. The field trip guide and detailed descriptions of the Exploration Exploration History History of the Hemlo Hemlo area, area, brief brief overviews overviews of the Regional Regional Geology of the Hemlo area and the Hemlo deposit, a description of the the geology geology of of the the Golden orebody (both (both of of Hemlo Hemlo Gold Gold Mines Mines Inc.), Inc.), and a detailed Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre orebody Road Log for the Hemlo-Heron Bay area. area Although Hemlo-Heron Bay Althoughoriginally originallywritten writtenfor forthe theGAC-MAC-SEG GAC-MAC-SEG Toronto '91 meeting, the the guide guide has has been been updated, updated, and and serves servesas asaa 3-day 3-dayplanned plannedoverview overviewofofthe the Hemlo Hemlo deposit, deposit, or or reference referencefor for aa more more detailed, detailed, self-guided self-guidedtour. tour. We had had initially initially hoped hopedthat that contributions contributionsby bystaff stafffrom fromall all33mines minesininthe theHemlo Hemlocamp, camp,using usingaa common basis for documenting observations, would permit a preliminary 3-dimensional configuration deposit to be envisaged, particularly particularly in distributions as uration of of the deposit in terms terms of element and mineral distributions as well well as as lithologic, lithologic, structural, structural, metamorphic, metamorphic, and and alteration alteration features. This Thiswould wouldhave haveinvolved involvedaa significant significant additional additional work-load work-load for for geological geological mine mine staff, and, as such, it is is unfortunate unfortunate that that the the deposit represented here. However, a description of the However, adescription deposit component componentfrom from 22 of the mines cannot be represented central central and and westernmost westernmost part partof of the the deposit deposit is is presented, presented, in in this this field field guide, guide, by by staff at the Golden Golden Giant Mine a!. (1986), Mine (see (see Part Part 6). 6). Papers Papersby byWalford, Walford,Stephens Stephensetetal. (1986),and andWalford, Walford,Weicker, Weicker,and and Guthrie (1986) provide the most recent, detailed descriptions of the Williams Mine, as does the Guthrie (1986) Williams Mine, as paper by Burk eta!. etal. (1986) (1986) for the David David Bell Mine. Readers Readerswill will find find additional additional information information on on surface and subsurface geological features features of of the the Hemlo deposit deposit area in other subsurface geological other field field guides guides prepared prepared by by Patterson Patterson(1984), (1984), McMillan McMillanand andRobinson Robinson(1985), (1985), Harris Harris(1986a, (1986a, 1986c), 1986c), Harris Harris and and Muir (1987), and and Smyk Smyk eta!. etal.(1990). (1990). HEMLO HEMLO MINES, 1985-1994 1985-1994 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1993 1994 1994 Figure Figure1. 1. Hemlo Hemlo camp camp gold gold production productionfrom from 1985 1985 (initiation) (initiation)to to1994. 1994. �ExplorationHistory History Exploration 3 PART 2: 2: EXPLORATION EXPLORATIONHISTORY HISTORY PART by by B.R. B.R. Schnleders Schniedersand andM.C. M.C.Smyk Smyk Exploration dates back Explorationininthe theHemlo Hemloarea areadates backtoto1869 1869when whengold goldwas wasdiscovered discoveredby byMoses MosesPee-KongPee-KongGay reported activity there: Gaynear nearthe the present presenttown town of of Heron Heron Bay. Bell Bell (1873) reported there: pits pitsand andshafts shaftswere were reportedly reportedlysunk sunkon onauriferous auriferousquartz quartzveins veinsand andaasmall smallamount amountofofore orewas wasshipped shipped(The (TheWeekly Weekly Sentinel,Port PortArthur, Arthur,Ontario, Ontario,March March1,1,1889; 1889;McKellar McKellar1874). 1874). Sentinel, In Canadian Pacific Inthe the 1920s, 1920s, J. LeCours, a station agent agent with the Canadian Pacific Railway Railwayat at Hemlo Hemlo station, station, sank sanktest test pits pitson onaamineralized mineralizedshear shear zone zone "a "a few few hundred hundred feet north north of of the the station" station" (Bartley (Bartleyand and Page Page 1957), 1957), 6 km km southwest southwest of the the Hemlo Hemlo deposit. deposit. Reported Reportedassays assaysranged rangedfrom from0.22 0.22toto4.16 4.16 ounces gold per 1927; July ouncesgold perton ton(The (TheFort FortWilliam WilliamDaily DailyTimes TimesJournal, Journal,Fort FortWilliam, William,Ontario, Ontario,July July12, 12,1927; July 25, 1927). As on aamineralized 25,1927). Asreported reportedby byThomson Thomson(1933), (1933), atestpitwas a test pit wassunk sunkon mineralizedshear shearzone, zone,but butno no gold values were obtained. Additional work and assays for occurrences north and south of the gold values were obtained. Additional work and assays for occurrences north and south of the railway described (Canadian August12, 1927). At Ataboutthe railwaywere were also also described (Canadian Mining Mining Journal, August 12,1927). about thesame sametime, time, aagroup small quartz groupof of claims claimswas wasstaked stakedon onaasmall quartzvein veinjust justnorth northofofmile milepost post38 38(measured (measuredfrom fromWhite White River) was done (Bartley River)on on the the railway. railway. Some Somelow lowgold gold assays assays were were obtained, obtained, but but no no further further work workwas (Bartley andPage Page1957). 1957). and J.E. J.E. Thomson Thomson mapped mapped the the area areainin1930 1930and and1931 1931for for the theOntario OntarioDepartment DepartmentofofMines Mines (Thomson 1933). He recommended several Hemlo (Thomson1931, 1931,1933). He recommended severalareas, areas, including includingthe the area areanortheast northeastof of the the Hemlo station stationand andanother anotheraround aroundManitouwadge ManitouwadgeLake, Lake, for for further further exploration. exploration. In Bowhill Mines explored explored in vicinity of in the vicinity of Heron HeronBay Bay and and shipped shippedaa 500 500 lb. Ib. (227 (227 kg) kg) test test In1937, 1937, Bowhill sample sample which returned returned 0.30 0.30 ounce ounce gold gold per per ton ton and and1.53 1.53 ounces ounces silver silver per perton ton(Resident (Resident Geologist's Geologist'sFiles, Files,Ministry MinistryofofNorthern NorthernDevelopment Developmentand andMines, Mines,Thunder ThunderBay). Bay). In Inthe the early early1940s, 1940s,Zeb Zeb and and Simon Simon Moses Mosesof of Heron Heron Bay Bay noticed noticed"shiny "shinyminerals" minerals"ininthe therocks rocks on on the the north northside sideofofMoose MooseLake Lakewhile while checking checkingZeb's Zeb's father's father's (Peter (Peter Moses) Moses) trapline. They Theytold told Peter Peter Moses Moses who prospected prospected and and collected collected samples samples from from the area area in in 1944 1944(Peter (PeterMoses, Moses, prospector, prospector, Marathon, personal communication, 1990). Moses Moses discovered discovered aasiliceous, siliceous,minermineralized (Bartley alizedshear shearzone zone approximately approximatelyone-half one-halfmile mile(0.8 (0.8 km) km) north northof of mile milepost post 37 37 on the railway (Bartley and and Page Page 1957). 1957). Samples Samplesreturned returnedassays assaysupto up to0.415 0.415 ounce ounce gold gold perton per ton(Bartley (Bartleyand andPage Page1957; 1957; 1958). 1958). Peter PeterMoses Mosesapparently apparentlybrought brought the the showing showing to to the the attention attention of of Harry HarryOllmann Ollmannof of Heron Heron Bay, Bay, who in turn interested interestedDr. Dr. Jack Jack K. K. Williams Williams of Maryland. Maryland. Eleven Elevenclaims claimswere werestaked stakedinin1945: 1945: five Ollmann'sname namein inAugust, August, 1945, 1945, and and six were recorded recorded in in Williams' Williams' name name in in fivewere wererecorded recordedininOllmann's September, September, 1945 1945 (Mining (Mining Recorder's Recorder's Files, Ministry Ministry of Northern Northern Development Developmentand and Mines, Mines, Thunder Thunder Bay). Bay). The Theeleven elevenclaims claimsthey theystaked stakedand andstarted startedexploring, exploring,inin1945, 1945,became becameknown knownas asthe the Ollmann-Williams Ollmann-Williams property. Gold Goldvalues valueswere were encountered encounteredin inaa large largeshear shear zone zone and and during during the the next trenching, and and diamond diamond drilling drilling were were conducted. conducted. The next year, year, stripping, trenching, The program program of of X-Ray X-Ray diamond diamond drilling drilling was unsuccessful unsuccessful mainly mainly due to the the inefficient inefficient operation operationof of the themachine machine(Page (Page 1948), and and thus, thus, likely, likely, poor poor core corerecovery. recovery. 1948), In In the the spring spring of of 1946, 1946, consulting consultinggeologist geologistTrevor TrevorPage Pagestaked stakedaa group groupof of claims claimsadjoining adjoiningthe the Ollmann-Williams Ollmann-Williams property property on the east. These These claims, together with others others staked by associates including includingMoses MosesFisher Fisher(J.E. (J.E. Thomson's Thomson'sguide), guide),became becamepart partof of the the property propertyheld heldby byLake LakeSuperior Superior Mining (Bartleyand andPage Page1957, 1957, 1958). Samples Samples collected collectedby byPage Pageon onthe the Mining Corporation Corporation Limited Limited(Bartley newly newly staked staked ground ground assayed assayed from from trace trace to to 0.13 0.13 ounce gold per ton whereas whereas samples samples from the the Ollmann-Williams property reportedly returned up to 0.49 ounce gold per ton (Prospectus, Lake Ollmann-Williams property reportedly returned up to 0.49 ounce gold per ton (Prospectus, Lake �4 Geology Geologyand and Gold Gold Deposits Depositsof of the the Hemlo HemloArea Area Superior Superior Mining Mining Corporation Corporation Limited, Limited,1947). 1947). InIn1947, 1947, Lake Superior Superior Mining Mining Corporation Corporation Limited Limited was was formed formedand andcarried carriedout outmapping, mapping,trenching, trenching,chip chipand andchannel channelsampling, sampling,and andX-Ray X-Raydiamond diamond drilling drilling on on both both properties properties under under the direction direction of of Page. Page. Fifteen Fifteenand andthirteen thirteenX-Ray X-Raydiamond diamonddrill drill holes were drilled on the Ollmann-Williams and Lake Superior properties, respectively, on what holes drilled on the Ollmann-Williams and Lake Superior properties, respectively, on what was 947a, 1948). 1948). This drilling tested tested the the shear shear zone zone was termed termedthe theLake LakeSuperior SuperiorShear ShearZone Zone(Page (Page11947a, over over approximate approximate strike strike lengths lengthsof of600 600m m and and 500 500 m m on on the the Ollmann-Williams Ollmann-Williams and and Lake Lake Superior Superior properties, properties,respectively, respectively,and andestablished establishedthe the lateral lateralcontinuity continuityof of the the mineralized mineralizedshear shear zone zone over at at least least three three kilometres kilometreson onboth bothproperties properties(Resident (Resident Geologist's Geologist's Files, Files, Ministry Ministry of of Northern Northern Development Developmentand and Mines, Mines, Thunder ThunderBay). Bay). Page recognizedthat: that: Page (1947b) initially recognized "The "The main main mineral-bearing mineral-bearing structure structure consists consists of a quartz porphyry porphyry that that has has undergone undergone intense intense alteration alteration through through shearing, shearing, silicification silicification and and sericitization." sericitization." Page Page (1948) (1948) later later stated: stated: "The HemloFault Faultis is considered consideredto to be be the the most most important importantstructural structuralfeature featureas asititappears appears T h eHemlo to to bear bearaaclose closerelationship relationshiptotothe theLake LakeSuperior SuperiorShear ShearZone Zoneininwhich whichall allpresent presentgold gold discoveries discoveriesof ofeconomic economicinterest interesthave havebeen been found. With Withititalso alsoare are associated associatedporphyporphyries riessimilar similarto to those thoseof of the the shear shear zone. Probably Probablythe thegreatest greatestfeature featuretotodate datehas hasbeen beenthe the use use of of the the fault fault in in locating locatingthe theprojection projectionofofthe theore-bearing ore-bearingzone:' zone." Page HemloFault Faultwas was continuously continuouslytraceable traceableover overaadistance distanceofof Page(1949) (1949) suggested suggestedthat that the theHemlo 13 km. 13 km and and the the Lake Lake Superior SuperiorShear ShearZone Zone for for over over11 11 km. W.L.Greer, Resident Resident Geologist, Geologist, Department WL.Greer, Departmentofof Mines, Mines, Port Port Arthur, Arthur, Ontario Ontario noted in aa memorandum, 1949 (Resident Geologist's Files, Ministry of Northern Northern Development memorandum,dated datedJune June24, 24,1949 (Resident Geologist's Development and andMines, Mines,Thunder ThunderBay): Bay): 'Further drilling drillingand and trenching trenching should should be be done, done, particularly to to the the east east of of the the present present "Further drilling. 400feet feettotothe theeast, east,aa north-south north-southtrending trendingdiabase diabasedike dikecuts cutsacross across drilling.Here, Here,about about400 the theshearing shearingatatright rightangles. angles.ItItisispossible possiblethe thegold goldvalues valuesmay maybe bebetter betterconcentrated concentratedinin the theshear shearzone zonefor foraafew fewhundreds hundredsofoffeet feeton oneither eitherside sideofofthe thediabase." diabase." Ollmannand andWilliams' Williams'initial initialgrubstake grubstakemoney moneywas wasexhausted exhaustedduring duringthe thedrilling drillingprogram, program,and and Ollmann the thepair pairdecided decidedto topool pooltheir theireleven elevenclaims claims for for the the purpose purpose of patenting. patenting. Harry HarryOllmann Ollmanndied diedinin December 1947 1947 and the eleven eleven claims claims were were put put in in Williams' Williams' name name in intrust trustby bymutual mutualconsent consent December (Financial 1987). Other (FinancialPost, Post,August August3, 3,1987). Othergroups, groups,including includingNorthern NorthernCanada CanadaMines MinesLtd., Ltd.,had hadstaked staked presumed presumedstrike strikeextensions extensionsofofthe themineralized mineralizedzones zonesto tothe theeast eastof of the the properties properties(Page (Page1948). 1948). InIn 1948, Lake Lake Superior Superior Mining MiningCorporation CorporationLimited Limiteddrilled drilledfour fourholes holesto to the the southeast, southeast, south southof of Cedar Cedar 1948, Lake(see (seeFigure, Figure,inside insidefront frontcover) cover)on onclaims claimsstaked stakedby byZeb ZebRenshaw; Renshaw;no noassays assayswere werereported reported Lake (Resident (ResidentGeologist's Geologist'sFiles, Files,Ministry MinistryofofNorthern NorthernDevelopment Developmentand andMines, Mines,Thunder ThunderBay). Bay). Explorationon onthe theLake LakeSuperior SuperiorMining MiningCorporation Corporationproperty propertycontinued continuedinto intothe thespring springofof Exploration 1949, at at which which time time diamond diamond drilling drilling had had indicated indicated aamineralized mineralizedzone zone with with aastrike strikelength lengthofof 1949, 900 (2m) m)and andan an average averagegrade gradeof of 0.256 0.256 ounce ouncegold goldper per 900feet feet(275 (275m), m),an anaverage averagewidth widthofof6.5 6.5 feet feet(2 ton(Northern (NorthernMiner, Miner,April April21, 21,1949). Thiszone zonewas waslater laterreported reportedtotohave haveaastrike strikelength lengthof ofonly only ton 1949). This 200 m)(Northern (NorthernMiner, Miner,June June9,9,1949). 1949). 200feet feet(61 (61m) Bartleyand andPage Page(1957) (1957)noted noteddiscrepancies discrepanciesbetween betweendrill drillcore coreand anddrill drillsludge sludgeassays assaysinintwo two Bartley drill drillholes holesand andstated statedthat thatititwas wasaasignificant significantfeature: feature: 'Inone onecase, case,core coreassays assaysreturned returned0.327 0.327ounce ouncegold goldacross across8.3 8.3feet feet[2.5 [2.5m] m]while while30 30feet feet "In [9.1 m] m] of sludge returned 0.243 ounce ounce [gold [gold per per ton]. Inthe thesecond secondcase, case,core corereturned returned [9.1 sludge returned toni. In �Exploration Exploration History 5 ounce gold gold [per m], and and sludge sludge returned returned 0.594 0.315 ounce [per ton] across across 5.0 feet feet [1.5 [1.5 m], 0.594 [ounce [ouncegold gold per ton] ton] across across25 25feet feet[7.6 [7.6 m]." m]." Page (1949) related the mineralization mineralization to the observed observed structure: structure: "The 'Hemlo Break' is probably part of the Heron Bay Break which is recognized recognized as one 'Hemlo Break' is probably part Heron Breakwhich structural features associated associated with the Precambrian section of the large structural Precambriangeology geology in this section bodies with with which mineralization of the the Canadian Canadian Shield. Shield. Porphyry Porphyry bodies mineralization of of economic economic importance importance is associated associated have have been been guided guided in in their their emplacement emplacement by by this this regional regional structural pattern." Lake Superior Mining Corporation Limited had had diversified diversified their their exploration exploration program program and and discovered radioactive discovered radioactive zones zones (including (including the Herrick Herrick occurrence) occurrence) adjacent adjacent to to its its original originalproperty property (Northern Miner, June 9,1949). 9, 1949). Deeper and south of mile post 36 (Northern Deeper diamond diamond drilling drillingwas was initiated initiatedinin m), were were drilled drilled (Resident the fall of of 1949 1949 and and eventually eventually 10 10 holes, holes, totalling totalling 3761.5 3761.5 feet (1146.5 (1146.5 m), Geologist's Ministry of Northern Northern Development mineralized zone Geologist's Files, Ministry Developmentand and Mines, Thunder Bay). A mineralizedzone containing depth of with a calculated calculated width containing31 31 543 543 tons tons to to aadepth of 300 300 feet feet (91 m) with widthof of 8.8 8.8 feet feet(2.7 (2.7 m) m) and and a cut grade of 0.22 ounce ounce gold outlined (Northern 1950). Trenching cut grade gold per per ton ton was outlined (NorthernMiner, Miner,May May18, 18,1950). Trenchingof ofthe the strike extension of the mineralized zone to to the east extension of mineralized zone east near near the the Struthers Struthers railway railway station was was undertaken in position was secured secured by Lake Superior Superior Mining Corporation Corporation Limited undertaken in 1950 1950 when land position Limited (Resident Geologist's Files, Ministry Ministry of Northern Northern Development Developmentand and Mines, Mines,Thunder ThunderBay). Bay). Teck-HughesGold GoldMining MiningLimited Limitedoptioned optionedthe the Lake Lake Superior Superior property property and comIn 1951, 1951, Teck-Hughes Files, Ministry Ministry of of pleted 6 diamond drill holes totalling 2733 feet (833 m) (Mining Recorder's Recorder's Files, Northern Development and Mines, Mines, Thunder Thunder Bay) Bay) in in addition addition to the over Development and over 6000 6000 feet feet of of drilling drilling completed to that time by by Lake Lake Superior Superior Mining Corporation Limited. The Thesize sizeofofzone zoneNo. No.11 (formerly increased to 76 76653 grade of 0.27 ounce gold per ton (Northern (Northern 'A zone) was increased 653 tons tons at at aagrade (formerlythe the 'A 25, 1951). One Miner, January 25,1951). One of the holes holes missed missed what what is is now now the the main main Hemlo Hemlo ore ore zone zone by by less less than 30 m (Patterson (Patterson 1985). 1985). The The prevailing prevailingUS$35 US$35 per per ounce ounce gold price price and and the the relatively relativelylow low grade precluded further work for Teck Exploration Exploration Company for the the next next few few years. years. In 1957, 1957, Teck Company Ltd. Ltd. carried packsack diamond diamond drilling. Seven Sevenholes holestotalling totalling289 289feet feet(88 (88m) m) were were drilled drilledin in carried out out some packsack the footwall footwall mineralized mineralized zone zone ('B ('B zone') which which returned returned values values ranging ranging from from trace trace to to 0.04 0.04 ounce ounce gold per per ton ton (Resident (Resident Geologist's Geologist's Files, Files, Ministry Ministry of of Northern NorthernDevelopment Developmentand andMines, Mines,Thunder Thunder Bay). Bay). M.W. T.W. Page Pagewrote wrote aageological geological report report on the Hemlo area (Bartley M.W. Bartley and T.W. (Bartley and and Page Page for the the Canadian Canadian Pacific Railway 1957) for Railway and stated: "The section from Hemlo attention Hemlo to Struthers has received considerable prospecting attention to date, and its potential depends mainly on further exploration ...'I. Cusco Mines Mines Ltd. optioned the the ground ground from Lake Lake Superior Mining Corporation Limited Limited in in 1958 and and carried carried out out diamond drilling drilling to test the main 1958 main mineralized mineralized zone zone which which contained contained an an estimated estimated 71 000 tons averaging averaging 0.22 0.22 ounce ounce gold gold per per ton ton within withinaazone zone550 550feet feet(168 (168m) m)long, long,10 10feet feet (3 (3m) m) thick, and and 300 300 feet feet (91 (91 m) deep (Northern (Northern Miner, Miner, October October 23, 1958). 1958). The Theprogram's program'sresults resultswere were "inconclusive" "inconclusive" but but sufficient sufficient mineralization mineralizationwas encountered encountered to maintain maintain interest interest (Northern (Northern Miner, November 5, 1959). November 5, 1959). As no exploration had had recently recently been been undertaken undertaken on on the the Williams Williams property, property, aa caution caution (lien (lien by Harry Ollmann's Ollmann's brother brother to to protect protect his against title) was filed on the eleven claims, in 1955, by interest. interest. Williams Williams died died that that year year and and his his lawyers lawyers attempted in vain to clear up the partnership partnership agreement. The 1987, agreement. Thecaution cautionwas wasstricken strickenfrom fromthe theclaim claimblock blockinin1970 1970(Financial (FinancialPost, Post,August August3,3,1987, p.1-2). �6 Geology Geologyand andGold GoldDeposits Depositsofofthe theHemlo HemloArea Area The TheLake LakeSuperior Superiorproperty propertyhad hadbeen beenstaked stakedintermittently intermittentlyby byprospectors prospectorsduring duringthe the1960s. 1960s. Walter west ground in in 1961, WalterBaker, Baker,accompanied accompaniedbybyhis hisson, son,Nelson, Nelson,prospected prospected westofofthe theWilliams Williams ground 1961,on on what whatbecame becamethe the Golden GoldenSceptre Sceptreproperty. property.Several Severalgold golddiscoveries discoverieswere weremade madeon onsurface surfaceand and goldwas waspanned pannedininthe thesandy sandyloam loamoverburden overburden(Nelson (NelsonBaker, Baker, prospector, prospector,personal personalcommunicacommunicagold tion, tion,1990). 1990).These Theseoccurrences occurrenceswere wereinvestigated investigatedininthe thenext nextfew fewyears yearswith withtrenching trenchingand andX-ray X-ray drilling, drilling,ininpart partfunded fundedby byFred FredJowsey. Jowsey. Visible Visiblegold goldwas wasreported reportedininthe thedrill drillcores cores(Lefolii (Lefolii1987). 1987). Stairs StairsExploration Explorationand andMining MiningCompany CompanyLtd. Ltd.funded fundedaaprogram programof ofsoil soilsampling samplingand andprospecting prospectinginin H.Hansen Hansenand andD. D.Michano Michano(Harris (HarrisHansen, Hansen,prospector, prospector,personal personal 1964and and 1965 1965 conducted conducted by byH. 1964 communication,1990). 1990). communication, The The Lake LakeSuperior Superiorproperty propertywas wasstaked stakedby byJ.E. J.E. Halonen Halonenin in1973 1973 for for Ardel Ardel Explorations ExplorationsLtd. Ltd. who whodrilled drilledthree threeholes holestotalling totalling789.9 789.9feet feet(241 (241m) m)(Resident (ResidentGeologist's Geologist'sFiles, Files,Ministry MinistryofofNorthern Northern Development Development and and Mines, Mines, Thunder Thunder Bay). Bay). The Thedeposit deposittonnage tonnagewas wasincreased increasedtoto150 150000 000tons tons grading 1973). grading0.21 0.21ounce ouncegold goldper perton tonabove above60 60feet feet(18 (18m) m)depth depth(Northern (NorthernMiner, Miner,November November8,8,1973). Ardel Ardeldropped droppedthe theclaims claimsand andwas waslater laterfollowed followedby byCypress CypressResources ResourcesLtd. Ltd. Claims property and Claimswere werestaked stakedby byR.G. R.G. Newman Newmanin in1976 1976 west of the Williams property and investigated investigated byCopper CopperLake LakeExplorations ExplorationsLtd. Ltd.inin1977. 1977. Soil Soil and and rock rockgeochemical geochemicalsampling samplingsucceeded succeededinin by identifying zone of identifyingaazone of anomalous anomalousgold goldvalues values(up (up to to 10000 10 000ppb) ppb)roughly roughlycoincident coincidentwith withthe thecontact contact between between metasedimentary metasedimentaryand andquartz-feldspar-porphyritic quartz-feldspar-porphyriticrocks rocks(Resident (ResidentGeologist's Geologist'sFiles, Files, Ministryof ofNorthern NorthernDevelopment Developmentand andMines, Mines,Thunder ThunderBay). Bay). Ministry T.L. T.L. Muir Muir of the the Ontario OntarioGeological GeologicalSurvey Surveymapped mappedthe theHeron HeronBay Bayand andHemlo Hemloareas areasinin1977 1977 In addition to summarizing the area's exploration and1978, 1978,respectively respectively(Muir (Muir1982a, 1982a,1982b). 1982b). In addition to summarizing the area's exploration and activity activity and and economic economic potential, potential, Muir Muir reported reported an an occurrence, occurrence, presently presently referred referred to to as asthe the "Highway Hemlo "HighwayZone", Zone", in in altered altered felsic felsic metavolcanic metavolcanicrocks rocksseveral several kilometres kilometreswest west of of the themain mainHemlo deposit. deposit.This Thisoccurrence occurrenceisisprobably probablyininthe the vicinity vicinityof of the the mile mile post post 38 discovery of the 1920s. A A grab grabsample samplereturned returned0.32 0.32 ounce ouncegold goldper perton tonand and0.48 0.48 ounce ounce silver silver per per ton ton (Muir (Muir 1982b). 1982b). Claim Claim stakers stakersand andexplorationists explorationistswould wouldlater laterbase basemuch muchof of their their land land acquisition acquisitionduring duringthe the staking stakingrush rush on Muir's Muir's maps. maps. on Various Hemlo camp camp have havebeen beenoffered offered by by Various accounts accounts of of the the recent recent developments developments in in the the Hemlo Patterson Patterson(1983, (1983,1984), 1984),Knoll Knoll(1984), (1984),Hart Hart(1985a, (1985a,1985b), 1985b),Lefolii Lefolii(1987) (1987)and andBittler Bittler(1988), (1988),among among others. others. The Thefollowing followingsynopsis synopsisdraws drawsupon uponthese theseand andother othersources, sources,published publishedand andunpublished, unpublished, including includingthe the Resident ResidentGeologists Geologist'sFiles Files(Ministry (Ministryof of Northern NorthernDevelopment Developmentand andMines, Mines,Thunder Thunder Bay). Bay). Beginning Beginning in in December, December, 1979, 1979, prospectors prospectors Donald McKinnon and John Larche staked staked the the claims claims surrounding surroundingthe the 11 11 patented patented Williams Williams claims. claims. The Thetwo twomen menagreed agreedto topool pooltheir theirclaims claimsin inaa partnership partnershipand and unsuccessfully unsuccessfullytried tried to find a potential optioner. In InSeptember September 1980, 1980, an optioner finally found found in in the the form formof ofCorona CoronaResources ResourcesLtd., Ltd., aaVancouver-based Vancouver-based junior exploration exploration was finally company which later later became became International InternationalCorona CoronaResources ResourcesLimited. Limited. Following Following preliminary preliminary company linecutting linecuttingand and geophysical geophysicalsurveys surveysin inlate late1980, 1980, Corona Coronabegan began aa $600 $600 000 000 drilling drilling program, program, in in January supervision of consulting consulting geologist, David January1981, 1981, under the supervision David Bell. In InMarch, March,R. R. Hughes Hughesand and F. optioned 156 partnership's claims F. Lang optioned 156 of the partnership's claims which which lie lie to the the east east and and west of the Williams Williams and and Corona Corona properties. properties. These Theseclaims claimswere wereput putinto intothe theholding holdingofoftheir theircompanies, companies,Golden GoldenSceptre Sceptre ResourcesLtd. Ltd. and and Goliath Goliath Gold Gold Mines Mines Ltd., who subsequently relinquishedcontrolling controllinginterest interestto to Resources subsequently relinquished Noranda Exploration ExplorationCompany CompanyLtd. Ltd. Noranda In representatives of LAC Minerals Ltd. visited Corona's In May, May, 1981, 1981, representatives Corona's drill drill site site and and exchanged exchanged information pursuant to a possible joint-venture agreement. While negotiations with Williams' possible joint-venture agreement. While negotiations Williams' �Exploration History 7 7 widow in in Maryland Maryland for for the the Williams Williams property propertywere were ongoing, ongoing, diamond diamonddrilling drilling was was stepped steppedback backto to the outlined deposit. deposit. Drill section grading the east east of the outlined Drillhole hole76 76 intersected intersectedaa10.5-foot 10.5-foot (3.2 m) section grading 0.209 ounce depth ofof336.5 Hemlo ounce gold gold perton per tonata at adepth 336.5feet(102.5 feet (102.5m). m).This Thisnew, new,separate separatezone zonewas was the the main main Hemlo orebody. orebody. By ByAugust, August,120 120drill drillholes holestotalling totalling43 43000 000feet feet(13 (13106 106m) m) had had delineated delineated750 750000 000tons tonsof of rock ounce gold gold per per ton ton in in the the 'West' 'West' zone zone and and had had begun begunto to indicate indicate the much much larger rock grading grading 0.10 0.10 ounce reserves 1981). Corona reserves of of the the 'East' 'East' or or main mainzone zone (Northern (NorthernMiner, Miner, August August 13, 13,1981). Coronashares, shares,buoyed buoyedup up by the new discovery, soared from less than $2 to $34 by year-end. The Hemlo gold rush, new discovery, soared from less than $2 year-end. The Hemlo gold rush, ultimately 7000new newclaims claimswere were staked stakedin in the the area area by by the ultimatelyinvolving involving180 180 companies, companies, ensued. ensued. Over Over7000 end end of of 1982. 1982. Both Corona and LAG had been been actively actively negotiating negotiating for the the Williams property. In LAC had In July, July, Mrs. Williams accepted LAC's offer. Corona, citing a breach LAC'S offer. breach of a fiduciary agreement, agreement, sued LAC LAC for ownership of the Williams claims. Teck Teck Corporation Corporation subsequently subsequently entered entered into into aa joint joint venture venture agreement with Corona to develop what what would would become the David Corona in in December, December, 1981 to David Bell Mine, presently presently controlled controlled by by the the Teck-Corona Teck-Corona Operating Operating Corporation. Corporation. In August 1982, LAC LAG announced announced the the discovery of of the deposit deposit on on their their property, property,which whichwould would become known known as as the thePage-Williams Page-WilliamsMine. Mine. Drilling Drilling by Goliath Gold Gold Mines Mines intersected intersected the the northward-dipping northward-dippingextension extensionof of the the ore ore zone. The The Goliath Goliathpart partof of the the deposit depositbecame, became,after afteraajoint joint venture with with Noranda Noranda Exploration ExplorationCompany Company Limited, Limited, the the Golden GoldenGiant GiantMine. Mine. In January, January,1987, 1987, ownership of the Golden Golden Giant Giant Mine Mine was gained gained by Hemlo Hemlo Gold Mines Mines Inc. Inc. by by acquiring acquiring Golden Golden Sceptre Resources Resources Limited, and Goliath Goliath Gold Gold Mines Mines Limited Limited (Canadian (Canadian Mines Mines Handbook, Handbook, 1987-88, p.185). p.185).The Themajor majorshareholder Gold Mines Mines Limited Limited is shareholderof Hemlo Hemlo Gold is Noranda Noranda Inc. Inc. By Bythe the end end of 1985, all all three three mines had commenced commenced gold production. production. In March March 1986, after after several several months of testimony, testimony, the the Supreme Supreme Court Court of Ontario Ontario awarded awarded the Page-Williams Mine to to International Corona Resources Ltd. Ltd. LAC LAC appealed appealed the the decision decision to to the the Ontario conditions imposed OntarioCourt Court of of Appeal Appeal but but continued continuedto to operate operate the the mine mine under under conditions imposedby bythe thecourt. court. The Ontario Ontario Court Court of of Appeal Appeal upheld upheld the the earlier earlier decision decision in in October, October, 1987. 1987. The Supreme Supreme Court Court of Canada later granted LAG LAC the right to appeal appeal the provincial provincial court ruling. ruling. In August, 1989, 1989, the the Supreme Supreme Court Court of of Canada Canadaawarded awardedthe thePage-Williams Page-WilliamsMine, Mine,Canada's Canada's largest largestgold goldproducer, producer,to to Corona which shortened the name name to to the theWilliams Williams Mine. Mine. In July, 1982, 1982, Homestake Homestake Mining Mining Company Corona Corporation Corporation and Willams and David Company took took over Corona and thus thus acquired acquired 50% 50% interest interest in in the Willams Bell Bell Mines. The Theremaining remaining50% 50%interest interestisisstill stillheld heldby byTeck Teck Corporation. Corporation. �8 Geology and Gold Deposits of the Hemlo Hemlo Area PART 3: REGIONAL REGIONAL GEOLOGY by by TL. Schnieders and T.L. Muir, Muir, B.R. Schnieders and M.C. M.C. Smyk Smyk The geology geology of of the the Hemlo Hemloarea areahas hasbeen beenmapped mappedby byThomson Thomson(1931, (1931, 1933), 1933), Bartley Bartleyand andPage Page Mime (1967, (1967, 1968), 1968),Muir Muir(1982a, (1982a, 1982b), 1982b),and andSiragusa Siragusa (1984a, (1984a, 1984b, 1984b, 1985a, 1985b). This (1957), Milne This regional mapping inside of of front front cover) cover) shows shows that that the the Hemlo Hemlo deposit deposit occurs regional mapping (refer (refer to Figure Figure 14 14 on inside generally east-trending, east-trending,mixed mixedassemblage assemblage of Archean Archean metavolcanic metavolcanic and and metasedimenmetasedimenwithin aa generally tary granitoid bodies. bodies. These tary rocks rocks sandwiched sandwichedbetween betweenmajor major granitoid These supracrustal supracrustalrocks rocksare are part part of of what is termed the Schreiber-Hemlo Schreiber-Hemlo greenstone greenstone belt belt of of the the Wawa Wawa subprovince. subprovince. (1 982a,1982b, 1 982b,1983) 1983) tentativelysubdivided subdividedthe theHeron HeronBay-Hemlo Bay-Hemlo part part of the the greenstone greenstone Muir (1982a, tentatively belt into two groups: (1) (1) the the southern southern Playter PlayterHarbour Harbour Group, Group, comprising comprising mainly tholeiitic mafic mafic subordinate, intercalated, flows with subordinate, intercalated,intermediate intermediatetotofelsic felsictuffs tuffsand andsiltstones; siltstones;and and(2) (2) the the northern northern Heron Bay Bay Group comprising mainly dacitic dacitic and Heron comprising mainly and rhyolitic rhyolitic calc-alkalic calc-alkalic pyroclastic pyroclastic rocks rocks and and reworked equivalents, equivalents, and and tholeiitic tholeiitic basalts. basalts. AAperceived progressive decrease in grain and perceived progressive decrease in grain and fragment size, together with a general increase in the the proportion proportion of of volcaniclastic volcaniclastic and epiclastic sedimentary sedimentary units units toward toward the the east, east, was interpreted interpreted in in terms terms of a volcanic complex, centred in the Heron Bay area, that shed material material into into aa distal distal basin basin to to the the east east (Muir (Muir1982b, 1982b, 1983). 1983). Subsequent to this interpretation interpretation and and the the discovery discovery of of the the main main part part of of the the Hemlo Hemlo deposit deposit in in 1981, moredetailed detailedmapping mappingindicated indicatedthe thepresence presenceofofafelsicvolcanicpile afelsicvolcanicpileininthe thevicinity vicinityof ofHemlo Hemlo 1981, more a!. 1985). 1985). U-Pb (Brown et at. U-Pb geochronology geochronology has has since since shown shown that that the the volcanic volcanic piles pilesat atHemlo Hemloand and different in respectively, 2772 Ma and 2695 2695 Ma (Corfu (Corfu and and Muir Heron Bay are notably different in age, being, respectively, 1989a). facies model model may may not not be be appropriate. appropriate. Conse1989a). This This suggests suggests a simple proximal/distal proximalldistal facies quently, Corfu proposed that Corfu and and Muir Muir (1989b) (1989b) proposed that an an extensive extensive structural structuralbreak break(i.e., (i.e., the theHemlo Hemlofault) fault) may separate separate 2 different different assemblages assemblages of supracrustal supracrustal rocks, although they pointed out this model rocks, although they pointed out this model poses its own problems. In keeping keeping with the the above above alternative alternative model, model, Williams Williams et et aL al. (1991) (1991) have have proposed proposed aa redefinition of redefinition of the the general general construction construction of of the the supracrustal supracrustalrocks rockseast east of the Coldwell Coldwell Complex. In In their their scenario, scenario, the the Hemlo Hemlofault fault as as seen seen on on Highway Highway17 17 near the Hemlo Hemlo deposit, deposit, is is extended extendedwest, west, the Coldwell CoIdwell Complex, Complex, and southeast southeast to eastbetween the Gowan Lake and Heron Bay plutons to the southeast southeast from the the Highway Highway 17 17 location location to to the the east east end end of of the the Schreiber-Hemlo Schreiber-Hemlogreenstone greenstonebelt. belt. The extent extent and and position positionof of the the fault fault is is speculative speculativeat atthis thisstage stageand andisisnot notshown shownon onthe the map map(inside (inside front cover). The The supracrustal supracrustalrocks rocksare aresubdivided subdividedinto intothe the Heron HeronBay Bay assemblage, assemblage, south south of of the the assemblage, north north of of the the fault. fault. Muir Hemlo Fault, and the Hemlo-Black Hemlo-Black River assemblage, Muir(1988) (1988) presented presented supracrustal rocks differences and similarities between lithological and structural features of the supracrustal a!. (1991) to the north north and and south of the Hemlo Hemlo fault in the vicinity vicinity of of the the Hemlo Hemlo deposit. deposit. Pan Panetetal. (1991) maintain a geochemical uniformity uniformity throughout throughout the supracrustal supracrustal rocks, maintainthat there is ageochemical rocks, to to the the north north and and lo deposit, which, which, they south of the Hemlo Hemlo fault fault several several kilometres kilometresto to the the east eastof of the the Hem Hemlo they suggest, suggest, single tectonic tectonic environment, not notaajuxtaposition juxtaposition of ofsuspect suspectterrains. terrains. More detailed detailed field field favours a single work and additional geochronologic geochronologic results results are are required required to to resolve resolvethis this issue. issue. any case, case, recent recent detailed detailed mapping mapping in the the vicinity vicinity of the the Hemlo Hemlo deposit, deposit, and elsewhere elsewhere in the the In any Hemlo-Heron HemIo-Heron Bay part of the Schreiber-Hemlo greenstone belt, indicates that that the the interpretation interpretation and delineation delineation of incompatible with of "groups" "groups" and and simple simple facies changes changes in this belt is incompatible with the the degree degree and style of deformation deformation now now recognized recognized (e.g., (e.g., see Part Part 7). geochronology from from zircon zircon crystals crystals indicates indicates that that there there are are 3 main generations of U-Pb geochronology �Regional RegionalGeology Geology 99 granitoidplutonism plutonismin in the Hemlo-Heron Hemlo-Heron Bay area: -2719Ma, Ma,-P2688 -2688 Ma, Ma(Corfu (Corfuand and granitoid area: 2719 Ma, and and-2678 2678 Ma Muir 1989a). 1989a). The Thefollowing followingages agesare arefrom fromCorfu Corfuand andMuir Muir(1989a). (1989a).To Tothe thesouth southofofthe thebelt beltlies liesthe the Muir Pukaskwa Gneissic Complex Complex which to gneissic gneissic phases phases of of Pukaskwa which consists mostly of weakly foliated to tonalite tonalite and and granodiorite granodiorite(2688 (2688Ma) Ma) with with pegmatite pegmatiteand andaplite aplitedikes. dikes. AAmarginal marginalzone zone(2719 (2719Ma) Ma) possibly thick, exhibits possiblyup upto to 11 km km thick, exhibitsaa weak weak mylonitic mylonitic fabric fabric generally generallyoriented orientedparallel parallelto tothe thecontact contact with with the the supracrustal supracrustal rocks. rocks. Within Withinthis thispart partofofthe thegreenstone greenstone belt beltlie lie two two major major granodioritic granodioritic plutons: plutons: the theHeron HeronBay BayPluton Pluton(2688 (2688Ma) Ma)to tothe thewest, west, and andthe theCedar CedarLake LakePluton Pluton(2688 (2688Ma), Ma),with with the smaller, smaller, satellite Cedar Creek Stock To the north of the belt belt lies lies a the Stock (2684 (2684 Ma), Ma), to to the the east. east. To granitoid separated from granitoidgneiss gneisscomplex, complex,the theBlack-Pic Black-PicBatholith Batholith(Mime (Milne1968), 1968),which whichisisseparated fromthe thebelt beltby by the the crescent-shaped crescent-shapedgranodioritic granodioritictotoquartz quartzmonzonitic monzoniticGowan GowanLake LakePluton Pluton(2678 (2678Ma). Ma). The variations variations Themetamorphic metamorphicgrade rangeslocally locallyfrom fromggreenschist The grade ranges reenschist to to amphibolite amphibolite facies. The reflect reflect the the proximity proximityto to granitoid granitoidbatholiths batholithsand/or and/orthe thesuperposition superpositionofofup uptotoseveral severalepisodes episodesofof metamorphismand andhydrothermal hydrothermalalteration alteration(Kuhns (Kuhns1988; 1988;Kuhns Kuhnseta!. etal.1994; 1994;Corfu Corfuand andMuir Muir1989b; 1989b; metamorphism Pan Pan and and Fleet Fleet 1992). 1992). The The rocks rocksof of the the Hemlo Hemlodeposit deposit area area have have undergone undergone amphibolite amphibolite facies facies regional regionalmetamorphism. metamorphism. In In the the vicinity vicinity of of the the Hemlo Hemlodeposit, deposit,Muir Muirand andElliott Elliott(1987) (1987) and and Muir Muir eta!. etal. (1988) (1988)identified identifiedatat least least four four generations generations of of structures structures produced produced by at least least two deformation events: events: (1) (1)an anearly early phase F, folds folds and and possible possiblelow-angle low-anglenormal normalor or thrust thrustfaults; faults;(2) (2)aamajor, major, phaseresulting resultingininsmall-scale small-scaleF1 regional, second secondphase phase producing producingsmallsmall- to large-scale, large-scale, tight tight to to isoclinal, isoclinal, generally generally northwestnorthwest- to to regional, north-northwest-plungingF2 F2folds, folds, along along with with a penetrative penetrative axial axial planar schistosity and differentinorth-northwest-plunging differentiatedlayering layering(S2), (So),possibly with sinistral sinistral shearing shearing and mylonitization; (3) dextral dextral shear shear ated possibly associated associated with mylonitization; (3) which whichlocally locallyresulted resultedinins-c-c' s-c-c'mylonitic myloniticrocks rocksand andsmallsmall-to to medium-scale, medium-scale,generally generallynortheastnortheast-to to F3folds folds with with axial axialplanar planarschistosity schistosityand andcrenulation crenulationcleavage cleavage(S3); (S3);and and(4) (4)smallsmalleast-plunging,F3 east-plunging, scale scale F4 F4kink kink folds folds and and brittle brittle faults. faults. AAsomewhat somewhatdifferent differentstructural structuralhistory historyhas hasbeen beengiven giveninin Kuhns a!. (1994) Kuhns (1986, (1986, 1988), 1988), Kuhns Kuhns et etal. (1994) (see (seePart Part6), 6),and andMichibayashi Michibayashi(1991). (1991). The interrelationship interrelationshipofofstructural structuralelements elementsand andintrusive intrusivebodies bodiesin in the the vicinity vicinity of, of, and and within, within, The the theore orezone zoneat atHemlo Hemlosuggests suggeststhat thatintrusions intrusionssuch suchas asthe theCedar CedarLake LakePluton Plutonand andassociated(?) associated(?) dikes dikeswere werelikely likelyemplaced emplacedafter afterF1, F,, during duringthe thelate latestages stagesof, of,ororafter, after,F2, F2,but butbefore beforeF3 F3(see (seeMuir Muir 1993). The Therelationships relationshipsbetween betweenstructural structuraland andmetamorphic metamorphicelements elementswithin withinthe thedeposit depositremain remain 1993). somewhat somewhatcontroversial controversialbecause becauseof of the the complex, complex, polymetamorphic/metasomatic polymetamorphic/metasomaticcharacter characterof ofthe the ore orezone zone(e.g., (e.g., see see Parts Parts55and and6). 6). U-Pbgeochronology of titanite, rutile, and monazite (Corfu andMuir Muir1989b) 1989b)reveals revealsaanumber number U-Pbgeochronologyoftitanite, rutile, and monazite (Corfu and of interesting features. Outside of of an anill-defined ill-definedbroad broadzone zone of ofalteration alterationand andmineralization mineralization of interesting features. Outside associated associatedwith withthe theHemlo Hemlodeposit, deposit,titanite titaniteages agesrange rangefrom from00toto10 10Ma Mayounger youngerthan thanzircon zirconages, ages, averagingabout about66Ma Mayounger. younger.However, However,within withinthis thisbroad broadzone, zone,titanite titaniteages agesrange rangefrom from1313toto15 15 averaging Mayoungerthan younger thanzircon zirconages. ages.Rocks Rocksoutside outsidethe thezone zonecontain containessentially essentiallyno norutile, rutile,whereas whereasmany many Ma of ofthe therocks rockswithin withinthis thiszone zonedo docontain containrutile rutilecrystals crystals(and (andininone onecase, case,monazite) monazite)which whichare areabout about 25 crystals. This 25to to40 40 Ma Ma younger than the titanite crystals. Thissuggests suggeststhat that an an episodic episodicor or protracted protractedthermal thermal historyhas hasoccurred occurredwithin withinthis thiszone, zone,which whichlies lieswithin withinone oneofofseveral severalhigh-strain high-strainzones zones(Corfu (Corfuand and history Muir1989b; 1989b;Hugon Hugon1986). 1986).However, However,ititcan canbe beargued arguedthat that this thispossibility possibilitycan canonly onlybe betested testedififrutile rutile Muir isisalso alsopresent, present,and anddated, dated,ininrocks rocksoutside outsideofofthe thezone. zone. Allof of the the aforementioned aforementionedArchean Archeanrocks rocksare areintruded intrudedby bymuch muchyounger youngerProterozoic Proterozoicintrusive intrusive All rocksincluding includingup upto toseveral severalages agesofofdiabase diabasedikes, dikes,and andyounger youngerlamprophyre lamprophyreand andalkalic alkalicdikes dikes rocks that thatare aremost mostlikely likelytemporally temporallyassociated associatedwith withthe thealkalic alkalicCoIdwell ColdwellComplex, Complex,centred centredwest westofof Marathon.The TheColdwell ColdwellComplex Complexhas hasbeen beendated datedatat1108±1 1108±Ma Mafor for early early gabbroic gabbroic and and syenitic syenitic Marathon. phases, (Heamanand andMachado Machado1987). 1987). phases,and and-'1099 -1099 Ma Mafor forlate lategranitoid granitoidphases phases(Heaman �10 Geology and Gold Deposits Deposits of the Hemlo Area 4: PEEKONGAY PART 4: PEEKONGAY PROPERTY PROPERTY by by B.R. Schnieders and B.R. Schnieders and M.C. M. C. Smyk The Peekongay property is located located in in Plc Pic Township, Township, centred near near the the town town of of Heron HeronBay, Bay, and and extends from Lake Superior to the Pic former Heron extends Lake Superior Pic River. ItIt includes includes the the sites sites of the former Heron Bay Bay Mine Mine and and V. Stenlund. Stenlund. The property property has has the mineralized mineralized Bowhill Bowhill Mines test trench, and is currently held held by V. also been referred referred to as the Bowhill Bowhill Mines Mines property, the Stenlund Stenlund property, property, and the Lytton Lytton Minerals Minerals property. The The carbonate-quartz carbonate-quartzvein veinofofthe theHeron HeronBay BayMine Mineoutcrop outcrop(described (describedbelow; below;see see Stop Stop 11 of road log as well) represents one type of of gold mineralization that that was discovered early in the in the the late late 1860s. 1860s. Recently, Recently, additional history of sporadic exploration of the area, which began in exploration, to the the Heron Bay Bay Mine, Mine, has hasidentified identified other other gold gold occurrences occurrences exploration, the west, within 3 km of the and mineralized mineralized zones. Lytton Minerals oned the property property from Stenlund Stenlund in 1982 and and conducted conducted 3 phases phases Lytton MineralsLimited Limitedopti optioned of diamond drilling, to May May 1985, 1985, totalling approximately 40 000 feet (12 (12 192 192 m) from 53 holes holes Geologist's Files, Files, Schreiber-Hemlo Schreiber-HemloDistrict, District,Thunder ThunderBay). Bay). The The drilling drilling resulted resulted in the the (Resident Geologist's outlining of some additional gold-bearing zones, termed the "Porphyry Zone" and the "C Zone", outlining additional gold-bearingzones, termed the "Porphyry Zone" and the "C Zone", as as well as further delineating delineating the the "Main "Main Zone" Zone" and and a mineralized mineralizedzone termed the "South "South Zone". The The Main Zone Zone includes mineralization in the Heron Bay Mine and the the Bowhill Mines trench. trench. MINERALIZATION TYPES TYPES MINERALIZATION Hartwick et a!. a/, (1985) (1985) described 4 major major types of of gold gold mineralization mineralization on on the the Peekongay Peekongay property, which are summarized summarized below, from Patterson Patterson (1986): "(1) possibly stratiform stratiform unit in Ic to '(1) A A pyritic pyritic quartz-rich quartz-richmolybdenite-bearing, molybdenite-bearing, possibly in mat mafic intermediate intermediate tufts tuffs ("C" ("C" Zone). Zone). Vuggy, pyritic pyritic quartz-carbonate quartz-carbonate veins and stringers cutting a possible subvolcanic (2) Vuggy, quartz-feldspar quartz-feldspar porphyry porphyry sill sill ("Porphyry" Zone). quartz-sericite-altered, dacitic pyroclastics and, to aa lesser lesser (3) Pyritic, silicified and and quartz-sericite-altered, extent, mafic mafic to intermediate intermediatetufts tuffs (Main (MainZone, Zone, eastern eastern part part of of North NorthZone). Zone). (4) Quartz-carbonate veins and vein breccias with variable amounts of pyrite, chalcopyrite, galena, galena, sphalerite sphalerite and and tourmaline tourmaline (Bowhill (Bowhill trench, trench, 1872 1872 shaft shaft area area trench, trench, western part part of North North Zone)." Zone)." The gold mineralization mineralization and and mineralized mineralized zones zones are are further further described describedby byPatterson Patterson(1986) (1986) based on the report of Hartwick eta!. (1985). eta/, (1985). intersections over "Ore grade intersections over significant significantwidths widths(Le., (i.e., 66feet feet (2 (2 m) m) or or greater) greater) have havebeen been obtained from the "C" and and "Porphyry" "Porphyry" Zones. Zones. In contrast, contrast, the silicified and and quartzquartzsericite-altered sericite-alteredpyroclastics pyroclasticsofofwhich whichthe theMain MainZone Zoneisisthe the most mostprominent, prominent, are are characcharacterized by geochemically anomalous gold values values in the order of 100 to 200 ppb with oz/ton Au Au over 3.1 31 feet (0.91 locally high values as great great as as 0.11 0.11 ozlton (0.91 m), but no ore grade intersections have intersections have been been obtained. obtained. "Quartz-carbonate veins veins and and vein vein breccia breccia occur occur in essentially "Quartz-carbonate essentially all all lithologies lithologies and, and, although these veins at at some places places contain contain gold gold values greater greater than than 0.40 0.40 oz/ton ozlton Au, Au, they are very erratic and discontinuous. The The continuity continuity both both laterally laterallyand and vertically, vertically, of of high grade intersections intersections is is very very limited." limited." �Peekongay Property 11 11 Discontinuous and erratically distributed quartz-carbonate quartz-carbonate veins veins and and stringers stringershave havebeen been observed observed by the authors authors over over a strike strike length length of of 2 km km in the Heron Heron Bay area. The individual individual zones zones are are described described in in more more detail detail below. below. MAIN MAIN ZONE ZONE MINERALIZATION MINERALIZATION mineralization includes ill Mines The Main Main Zone mineralization includesthe theold oldHeron HeronBay BayMine Minesite, site,and andthe theold oldBowh Bowhill Mines Trench site. As summarized by Patterson (1986): Trench site. As summarized by Patterson (1986): "The zone consists of a series of sericitic units 'The units within felsic felsic metavolcanic metavolcanic rocks and trends across the the property. property. The moderately moderately foliated foliated sericite sericite schist trends at at 0600 060' across schist contains contains55 to to 10% blue blue quartz quartz eyes that that are up to to 22 mm mmin insize. size. The The quartz quartz eyes are deformed deformed parallel parallel the most strongly foliated sections, the quartz to foliation. foliation. In the quartz eyes eyes are are absent absent and and the the molybdenite. Drilling narrow quartz-rich layers (less than 2 mm) contain molybdenite. Drillingand andsurface surface exploration has defined five occurrences are exploration hasdefined five parallel parallelunits. units. AA number number of occurrences are known knownalong alongthe the zone. The The best bestintersection intersectionreported reportedwas was4.83 4.83 ounces ouncesper perton tongold goldacross across1.0 1.0 feet." feet." East of the the Peekongay Peekongay property, property, Esso Minerals Canada Limited reported results results from from aa mineralized mineralized zone on strike from the Main Main Zone, with with assays assays up up to 1300 1300 ppb ppb Au and and 280 ppm ppm Mo 0.6 m (Resident Geologist's Files, Ministry Ministry of Northern across 0.6 Northern Development Development and and Mines, Mines, Thunder Thunder Bay). Bay). Heron Heron Bay Bay Mine Mine The abandoned abandoned Heron Heron Bay Bay Mine Mine is located locatedadjacent adjacent to to the thecommunity communityofofHeron HeronBay, Bay,and andisis approximately and30 30 m m south south of of the the CP CP Railway. Railway. The exploration approximately 200 m west of Highway Highway 627, 627, and history of the old mine mine dates back to 1869 1869 with the discovery of of veins by by Moses Moses Pee-Kong-Gay Pee-Kong-Gay western one is is 16 16 m deep), and (Roland 1887). Two Two shafts (the (the eastern eastern one one is is 8 m deep and the western some open cuts were developed developed in in 1873 1873 and 1874. 1874. Ore was apparently shipped and processed processed (McKellar 1874; Strickland 1979; (McKellar 1874; Strickland 1979; Patterson Patterson1984). 1984). carbonate-quartz vein, approximately 70 m long stripped stripped A carbonate-quartz vein, up upto to 11 m m thick, is exposed exposed on an approximately outcrop, in which 2 shafts shafts are separated separated by m (see (see Road Road Log, Log, Figure Figure 16). 16). The The vein vein strikes strikes outcrop, by about 40 rn at 270° 270' to 300°, 300° dips 70°N 70° to vertical, and is hosted within a shear zone which cross-cuts the obliquely. The volcanic stratigraphy obliquely. The foliation foliation within the the metavolcanic metavolcanic rocks rocks strikes from 245° 245O to 262° and dips from 50° ions trend 262O 50' to 64°N. 64ON. Mineral Minerallineat lineations trend 250° 250' and andplunge plungefrom from 32° 32' to to38°W. 38OW. The carbonate-quartz carbonate-quartz vein contains contains abundant abundant ankerite ankerite (up (up to to 70%) 70%) and andblack blacktourmaline, tourmaline, chalcopyrite, pyrite, sphalerite, and molybdenite. molybdenite. Barite galena, chalcopyrite, Barite has has also been identified (Patterson 1986). Patterson Patterson (1984) (1984) described the vein material thus: "Samples of vein material, when slabbed, show several generations of vein development: (a) (a) barren barren white white quartz; quartz; (b) (b) carbonate-rich; carbonate-rich;(c) (c) tourmalinetourmaline- and and sulphide-bearing; sulphide-bearing; (d) banded quartz-carbonate quartz-carbonate and and barite:' barite." Gold values within within the vein vein are are erratic erratic and and sporadic. sporadic. Patterson reported aachip chip sample Gold Patterson(1984) (1984) reported returned 0.22 ounce 3.00 ounces per per ton ton Ag Ag across across 0.82 0.82 m. m. Grab samples, by the returned ounce per ton Au and 3.00 authors, of dump material assayed assayed up up to to 0.04 0.04 ounce ounce per per ton ton Au. Au. Samples authors, Samplesfrom from nearby nearby pyritic pyritic quartz-se ricite units (Resident Geologist's quartz-sericite unitsassayed assayedup upto to0.314 0.314 ounces ouncesper per ton ton Au Au over over 0.9 m (Resident Geologist'sFiles, Files, Ministry of Northern Development and Mines, Thunder Bay). Earlier workers reported that, at Ministry Northern Development and Earlier reported that, at the the �12 12 Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Number 1 shaft, predominantly predominantlycopper-, copper-, zinc-, zinc-, and and lead-bearing lead-bearing minerals minerals were were found, along along with with "deposit" of gold and silver. However, However, at at aa depth depth of of 35 feet (10.87 m), a rich "deposit" of gold gold and and less less copper copper was discovered District, Thunder Bay). discovered (Resident (Resident Geologist's Geologist's Files, Files, Schreiber-Hemlo District, The host volcanic rocks consist of interbedded, fine- to coarse-grained, pyroclastic rocks of intermediate intermediate to felsic felsic composition. composition. The metavolcanic metavolcanic rocks display display intense intense shearing shearing and and alteration (bleaching) on the north side of the the vein. vein. The pyroclastic breccia is commonly matrixsupported except except for for the very section. Two supported very coarse coarse fragmental fragmental section. Two predominant predominant clast clast types types are are present: a whitish quartz-porphyritic present: quartz-porphyritic variety and a mafic, mafic, chloritic chloritic type type containing containing feldspar feldspar phenocrysts. AA sample sample of of aaquartz-porphyritic quartz-porphyritic fragment fragment within within the the altered altered zone, zone, taken taken by by the the authors, assayed assayed 102 ppb gold Ministry of Northern Northern Development Developmentand and gold (Geoscience (Geoscience Laboratories, Ministry Mines, Mines, Toronto). Toronto). Bowhill BowhillMines MinesTrench Trench The Bowhill located about town of Bowhill Mines Mines trench trenchis is within within the the Main MainZone Zone and and is is located about11km km west west of the town Heron Bay. Bay. The Heron The following following description of the trench trench is is taken taken from from an an assessment assessment file report report submitted by Hartwick Hartwick eta!. etal.(1985), (1985), for for Lytton Lytton Minerals Minerals Limited: Limited: "This trench, excavated excavated by by Bowhill Bowhill Mines Mines in in the middle middle 1930s, 1930s, is about 200 feet (60 m) long by 30 feet (9 m) m) deep deep and and 10feet feet (3 (3m) m)wide. wide. The trench trench is largely largely caved caved in in but but the pyritic quartz-sericite schist unit unit is is exposed exposed at the end end of of the the carbonate-quartz carbonate-quartz vein vein which sample of taken presumably presumably which contains containssphalerite, sphalerite,galena galenaand andpyrite; pyrite;aabulk bulksample of 500 500 Ibs, taken from this this vein vein material materialby byBowhill BowhillMines, Mines, assayed assayed0.3 0.3 oz oz Au/ton Aulton and and1.5 1.5 oz Ag/ton." Aglton." The following section section is is from from Patterson Patterson(1986): (1986): Lytton Minerals Limited Limited (Resident Geologist's Geologist's Files, "Drilling and geochemical geochemical work by Lytton Ontario Ministry Ministry of of Northern Northern Development Development and and Mines, Mines, Thunder Bay) shows the Main Main Zn, Cu. The Zone to be depleted in Na Na and enriched enriched in K, Mo, Au, Zn, The Main Main Zone Zone and and the the carbonate dyke. The carbonate carbonate vein vein are are cut cut by a lamprophyre dyke. carbonate vein vein also also contains contains black black tourmaline and molybdenite. tourmaline molybdenite. "Stripping on the main Occurrence (1100 (1100 m east of "Stripping main zone just west of the Bowhill Mines Occurrence Highway No. 627 and 200 200 m m south south of ofthe the Canadian Canadian Pacific Pacific Railway) Railway) has exposed exposed ashear a shear Highway zone evidence of progressive deformation. deformation. The zone which shows evidence Theearliest earliestphase phase was was largely largely ductile, with the the volcanic volcanic fragments fragments within a felsic felsic pyroclastic pyroclastic rock rock being being folded folded and and stretched cite schist stretched out out parallel parallel to foliation. foliation. Next Nextaaseries seriesof of discrete discretesen sericite schist zones, zones, 20-200 20-200 wide and heavily heavily carbonatized carbonatized cut cut across across the theductile ductileshear. shear. Carbonate Carbonate pods pods within within cm wide the cite schist have been deformed. deformed. Subsequently, the sen sericite Subsequently,aa mafic mafic dyke dyke 30-60 30-60 cm wide was intruded into intruded into the sericite schist. schist. The Thedyke dykecontains containsfragments fragmentsof of sericite sericite schist schistand andhas has where it crosses the the sericite sericite schist zone. zone. The final phase appears to have been folded where deformation, with been brittle deformation, with the the formation formation of of quartz-tourmaline quartz-tourmalineveins veins along along the the margin margin of the mafic mafic dyke dyke and and in in the the carbonate carbonatepods." pods." PORPHYRY ZONE following section The following section is is from from Patterson Patterson(1986): (1986): "Further "Further detailed detailed work work by by Derry, Derry, Michener, Michener, Booth Booth and and Wahl identified identified aa mylonite mylonitezone zone Bay. This unit was along the north contact contact of a porphyry porphyry intrusion intrusion 11 km west of Heron Bay. previously ~ u s l ycalled a thinly bedded bedded hematitic hematitic ash ash tuff tuff marker marker(W.N. (W.N. Pearson, Pearson, personal person;a1 previ( communication, nunication, Geological Geological Consultant, Consultant, Derry, Derry, Michener, Michener, Booth Booth and andWahi, Wahl,Toronto, Toronti3, comn 1985).I~ 1985). �Peekongay Peekongay Property Property 13 "The unit is is highly highly foliated foliated and and locally locally folded. folded. It is comprised comprised of of fine-grained, fine-grained, red red drill core the mylonite grades (hematitic) thinly (hematitic) thinly laminated laminatedchlorite chloriteand andfelsic felsiclayers. layers. In drill grades into sheared and deformed feldspar porphyry to the south." south." white quartz veins from 1 to 5 cm thick with with minor minor The porphyry apparently contains 10% white tourmaline. Diamond foot section section within within the pyrite and 3 to 5% black tourmaline. Diamond drilling intersected a 23.5 foot porphyry near porphyry near the the hanging hangingwall walland andhad hadaagrade gradeofof0.19 0.19 ounces ounces per per ton ton Au Au (Patterson (Patterson1986). 1986). C C ZONE ZONE following section The following section is is from from Patterson Patterson(1986): (1986): "The C-Zone C-Zone mineralization mineralization occurs at or or near near the the footwall footwallof ofthe thefeldspar feldsparporphyry. porphyry. Mineralization consists quartz up to 1 cm cm thick thick in in aa chlorite chlorite schist schist Mineralization consistsof of layers layersand and lenses lenses of quartz (possibly a sheared mafic metavolcanic). The quartz-rich layers contain molybdenite. The quartz-rich layers contain molybdenite. occurs as as 1 to 3 mm cubes cubes which have have been deformed and and possibly possibly Pyrite (5-10%) (5-10%) occurs rotated rotatedin in foliation. foliation. The Thezone zoneappears appearsto to cross-cut cross-cutthe the mafic maficmetavolcanic metavolcanicrocks rocksand andthe the feldspar porphyry. porphyry. Late Latequartz-carbonate quartz-carbonateveins veinscut cutthe the foliation foliationin inthe the zone. zone. Most Mostof of the the rocks north north of of the railway railway tracks consist consist of heavily carbonatized mafic mafic volcanics volcanics which have a felsic appearance. The Thebest bestdiamond diamonddrill drillintersection intersectionobtained obtainedwas was17.0 17.0feet feet of of 0.19 ounces per ton ton gold." gold:' 0.19 ounces SOUTH SOUTH ZONE ZONE The following section section isis from from Patterson Patterson(1986): (1986): sericitic zone occurs approximately approximately 100 south of the Heron "A sericitic zone similar to the main zone occurs 100 m rn south Heron Stripping and and trenching trenching has has exposed quartz-carbonate veins veins within within a Bay Mine. Mine. Stripping exposed quartz-carbonate sheared volcanic volcanic breccia. breccia. tourmaline." The veins The veins contain contain chalcopyrite, chalcopyrite, galena, galena, pyrite and and �14 Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area Geology PART 5: HEMLO PART 5: HEMLODEPOSIT DEPOSITOVERVIEW OVERVIEW by by B.R. Schnieders, C. Smyk L. Muir B.R. SchnIeders, M. M.C. Smyk and and T 1L. The The Hemlo Hemlo deposit deposit isis situated situatedwithin withinsupracrustal supracrustalrocks rocksininaasouthern southernbifurcated bifurcatedsegment segmentofofthe the eastern eastern part partof of the theSchreiber-Hemlo Schreiber-Hemlogreenstone greenstonebelt. belt.Page Page(1947a, (1947a,1947b, 1947b,1948, 1948,1949) 1949)was wasthe the first important structural structural feature firstgeologist geologistwho who recognized recognizedthe theHemlo HemloFault Faultas as an important feature and and identified identifiedthe the close close co-planar co-planarrelationship relationshipthe thefault faulthad hadwith with the the Lake Lake Superior Superior Shear Shear Zone. He Healso also recognized recognized that thatall allthe the gold golddiscoveries discoveriesat atthat thattime timewere werehosted hostedby bythe theLake LakeSuperior SuperiorShear ShearZone, Zone, and andstated stated that that the thezone zone had hadbeen beentraced tracedon on surface surface for for over over 12 12 kilometres. Page Pagealso alsonoted notedthat thatthe thegold gold mineralization mineralizationwas was associated associated with with felsic felsic porphyritic porphyriticbodies bodiesand andthat thatthe theemplacement emplacementof of these these porphyries Break". porphyrieswas was related related to to aa major majorstructure structurewhich which he hetermed termedthe the"Heron "HeronBay-Hemlo Bay-HemloBreak". The The Hemlo Hemlo deposit deposit largely largely lies lies at at or near the contact contact between between felsic to intermediate intermediate quartzquartzfeldspar-phyri imentary rocks. feldspar-phyricc rocks (pyroclasti (pyroclasticc and subvolcanic(?) subvolcanic(?) varieties) varieties) and andmetased metasedimentary rocks. Here, the rocks generally strike at 290° to 295° and dip between 60° and 700 to the northeast. Here, the rocks generally strike at 290' to 295' and dip between 60' and 70' to the northeast. Hugon Hugon (1984) (1984) presented evidence that the Hemlo Hemlo deposit is is contained contained within within aamajor majorductile, ductile, dextral, dextral,shear shearzone. zone. He Heinterpreted interpretedthat thatthe thedeposit depositoccupies occupiesthe themost mostintensely intenselydeformed, deformed,central central portion portionof of aalarge-scale, large-scale,wide widezone zone of of ductile, ductile, oblique obliquethrusting thrusting(Hugon (Hugon1986). 1986). The Hemlo Hemlo deposit deposit isispresently presentlyinterpreted interpretedby bythe theauthors authorsas asbeing beinglargely largelyhosted hostedwithin within The 290°-striking, 290°-strikinghighly highly strained, strained, transposed, transposed, and and juxtaposed, lithotectonic lithotectonic supracrustal supracrustalsegments, segments, which generally east-striking whichlie lieininaagenerally east-strikinggreenstone greenstonebelt. belt.The Thedeposit deposithas hasnot notbeen beendemonstrated demonstratedtotobe be stratiform or stratabound. stratiform or stratabound. Sporadically Sporadically distributed, distributed, anomalous anomalous gold goldmineralization mineralizationhas hasbeen been noted, noted,several severalkilometres kilometressoutheast southeastand andeast-southeast east-southeastof ofthe theHemlo Hemlodeposit depositon onthe theLac LacMinerals Minerals Limited, spatially associated associated with with sericitic and Limited, White White River River property, as being spatially and pyritic pyritic rocks rocks within within what whatisisinterpreted interpretedas asaabrittle-ductile brittle-ductileshear shearzone zone(Pan (Panand andFleet Fleet1988, 1988,1989, 1989,1990; 1990;Pan Pan1990). 1990). Undergroundmapping mapping and and drilling drilling have demonstrated existence of of parallel parallel mineralized mineralized Underground demonstrated the existence zones zones within within both boththe themetavolcanic metavolcanicand andmetasedimentary metasedimentaryrocks, rocks,as aswell wellas asmineralized mineralizedzones zones which which transect transectthe themetavolcanic-metasedimentary metavolcanic-metasedimentarycontact. contact. The The Hemlo Hemlodeposit depositorebodies, orebodies, collectively, collectively, extend extendfor for aastrike strikelength lengthofofabout about3.7 3.7 km, km,aadepth depthofof1.35 1.35 km, km,and andan anapproximate approximate down-plunge down-plungedistance distanceofof2.5 2.5km km(see (seeFigures Figures21 21and and22). 22). The Themain mainmineralized mineralizedzone zoneextends extendsfor foraa strike down-dip distance of strikelength lengthofofabout about2.9 2.9 km, km,and andaadown-dipdistance of2.5 2.5 km km (Harris (Harris1989). 1989).The Thethickness thicknessofofthe the main theDavid DavidBell BellMine Mine(Burk (Burketa!. etal.1986) 1986)toto50 50mrnininthe the mainmineralized mineralizedzone zoneranges rangesfrom fromabout about22mmininthe Williams WilliamsMine Mine(Walford, (Walford,Stephens Stephenseta!. etal.1986). 1986). Several mines,based basedlargely largelyon onthe thepredominant predominant Severaltypes typesof ofore oreare aredelineated delineatedinineach eachof ofthe the33mines, mineral(s) and/or textures present. Commonly, because of extensive metasomatism and mineral(s) and/or textures present. Commonly, because of extensive metasomatism anddeformadeformation, protolith(s).Alteration, Alteration,collectively, collectively,isisinin tion,the themineralized mineralizedzones zonescomprise compriserocks rocksof of equivocal equivocalprotolith(s). the theform formof ofwidely widelyvarious various degrees degrees of of microclinization, microclinization, sericitization, sericitization, biotitization, biotitization,silicification, silicification, carbonatization, albitization, albitization, pyritization, pyritization, and andtourmalinization. tourmalinization. Significant Significantamounts amountsof of barite barite of of carbonatization, equivocal equivocalorigin originare arelocally locallypresent. present.Bright Brightgreen greenvanadian vanadianmuscovite muscovite(Harris (Harris1989) 1989)isiscommonly commonly present presentin inthe thealtered alteredrocks, rocks,as asisismolybdenite. molybdenite.AtAtleast leasttwo twoages agesofofquartz quartzveins veinscan canbe befound found within within the theore orezones: zones:some someveins veinsdisplay displayconsiderable considerablefolding, folding,attenuation, attenuation,boudinage, boudinage,and and dismemberment, dismemberment,whereas whereasothers othersdisplay displayminimal minimaldeformation. deformation. In In some some cases, cases, outside outsidethe theore ore zone, zone, there thereare arenumerous numerousquartz quartzveins veinswhich whichtend tendto todisplay displayaalower lowerdegree degreeofofdeformation. deformation. Collectively,the theores oresare areenriched enrichedininAu, Au, Mo, Mo,Sb, Sb, Hg, Hg, As, As, TI, TI, V, V, and Ba. Gold Goldisiscommonly commonly Collectively, disseminated disseminatedalong alongwith withmolybdenite. molybdenite. Native Native gold gold grains grains are are mercury mercuryrich richand andoccur occuralong along �a r 9,' Hemlo Deposit Overview 15 ! quartz-feldspar and pyrite grain boundaries and fractures, as well as inclusions in, or rimmed with, several varieties of sulphide minerals including, rarely, pyrite and molybdenite (Harris 1989). Visible gold is not common overall, but does occur within quartz veins in feldspathized, molybdenite-bearing rocks, along molybdenite-green-mica-bearing fractures, in stibnite- and cinnabarbearing quartz pods, and rarely in fractures in some of the plagioclase-porphyritic dikes. Molyb- a C P rp c' r C 0 fl a a a a p p r r U' a a P U U a a p a a denite is the second most abundant sulphide, after pyrite, and occurs as fine- to very fine-grained, foliation-parallel blades, euhedral crystals, and platy masses mostly in association with silicate minerals, chiefly feldspar and quartz (Harris 1989). During the pastdecade, since the discovery of the Hemlo gold deposit as it is nowdelineated, various metallogenic models have been proposed. As summarized by Patterson (1984), Harris (1986b, 1989), Corfu and Muir (1989b), and Muir (1993), earlier workers favoured syngenetic, exhalative models in which mineralization was penecontemporaneous with volcanism (e.g., Cameron and Hattori 1985; Goldie 1985; Quartermain 1985; Valliant and Bradbrook 1986). Later workers suggested a porphyry deposit model (e.g., Kuhns 1986, 1988; Kuhns eta!. 1994; Johnston and Smyk 1992; Johnston et a!. in press), structural/hydrothermal models (e.g., Burk et al. 1986; Hugon 1986; Walford et a!. 1986), and a skarn model (e.g., Pan and Fleet 1991, 1992). It is interesting to note that the earliest observations in the Hemlo camp, made by Page (1947a, 1947b, 1948, 1949), invoked a close relationship between regional structure, local faults and shear zones, porphyries, alteration, and gold mineralization. Geochronologic evidence, coupled with field and underground observations, attest to the difficulty in clearly defining the timing of the gold mineralization relative to deformation events, the regional metamorphic event(s), and hydrothermal alteration events (Corfu and Muir 1989b). This is also evident by the variety of differing observations, some apparently in conflict, reported by Burk et at (1986), Kuhns (1986), Hugon (1986), Walford, Stephens et at (1986), Muir and Elliott (1987) and Muir (1993). Muir and Elliott (1987) suggested that apparent conflicts in observations may be a result, in part, of comparing features related to different deformation and/or alteration and/or metamorphic events. They also noted that dextral shear zones did not everywhere control the site of mineralization and that the deposit has been affected possibly by two generations of structures, including at least some of the dextral-shear-related deformation. In reviewing the various Hemlo genetic models, Harris (1989) stated that more recent research and evidence led to the recognition of features which tend not to favour the earlier syngenetic models but more stronglysupport ore deposition by hydrothermal fluids within or near a ductile shear zone. The Hemlo deposit has been ductiley deformed. Neither a temporal association between a porphyry intrusion(s) and the mineralizing event(s) nor a temporal association between the mineralizing event(s) and early ductile shearing has yet to be clearly established. In addition, disagreement exists as to whether the deposit formed prior to regional metamorphism (Kuhns 1986; Kuhns eta!. 1994), pre- orsyn-metamorphism (Burk etat 1986). or post-metamorphism (Walford, Stephens etat 1986; Pan and Fleet 1991, 1992). Muir (1993) has summarized some of the points that are consistent or inconsistent with the various depositional models proposed forthe Hemlo deposit. The complex geological history of the Hemlo area has led to some incongruous observations or interpretations which only much-needed, careful, and detailed additional studies may help to resolve. The past 15 years have resulted in a spectrum of geological observations, interpretations, and proposed models. Currently, no single genetic model adequately explains all of the complexities of the Hemlo deposit. It is possible that a combination of more than one model or the development of a new model may be required to account for the formation of the Hemlo deposit Genetic models can be useful exploration tools but must be used with caution. The Hemlo deposit was "overlooked" for over 30 years, possibly in part, because it did not fit classic genetic gold deposit models. �Geology Geologyand and Gold GoldDeposits Depositsof of the theHemlo HemloArea Area 16 I PART PART 6: GEOLOGY GEOLOGYOF OFTHE THE GOLDEN GOLDENGIANT GIANTMINE MINE AND ANDGOLDEN GOLDENSCEPTRE SCEPTREOREBODY OREBODY by by I I I I Robert Doug MCII veen and RobertKusins, Kusins,Albert AlbertChong, Chong,Paul PaulJohnston, Johnston, Doug Mcllveen andKen KenMcNena McNena 4 INTRODUCTION INTRODUCTION The The Golden GoldenGiant GiantMine Mineis is located located35 35km kmeast east of of Marathon, Marathon, Ontario Ontario(Figure (Figure2) 2)and andlies lieswithin within the the central centralpart partof of the the much muchlarger larger Hemlo Hemlo deposit. deposit. Three Threeseparate separatemining miningoperations operationshave havebeen been established established on the deposit deposit since since its its discovery discovery in in 1981. 1981. The TheGolden GoldenGiant GiantMine Minehas hasbeen beeninin production productionsince sinceApril, April,1985 1985and andhas hasproduced produced11436 436163 163ounces ouncesofofgold goldfrom from33892 892218 218tonnes tonnes mined 31, 1989. Current 1990, stand stand at at 16 16227290 minedas as of of December December31,1989. Currentreserves, reserves, as as of of December December31, 31,1990, 227 290 tonnes millioncontained containedounces ounces(178 (178662 662kg). kg). tonnesat at11.01 11.01 g/t, or 5.269 million The Hemlodeposit deposit is is situated situated within within aa "sequence" "sequence"of of moderate moderate to to locally locally high-grade high-gradeclastic clastic The Hemlo and and volcanic rocks rocks of of the the Schreiber-Hemlo Schreiber-Hemlo greenstone greenstone belt. This Thisbelt beltranges rangesfrom from88toto20 20km kminin width widthand andisispart partofofthe theeast-trending, east-trending,Schreiber-White Schreiber-WhiteRiver Riversection sectionofofthe theWawa WawaSubprovince Subprovince within 1982a,1982b). 1982b). withinthe theSuperior SuperiorProvince Provinceofofthe theCanadian CanadianShield Shield(Muir, (Muir,1982a, The are taken, taken, in part, from a field The following following descriptions and summary are field trip trip guide guide book book prepared et a!. a/, 1990). 1990). AAprevious previousfield fieldguide guidecovered covered prepared for the the 8th 8th IAGOD IAGODSymposium Symposium (Brown (Brown et additional additional features features (Brown (Brown et eta!. a/.1986). 1986). Stratigraphic Stratigraphicterminology terminologyin in Part Part66 of of this this field fieldguide guideisis used informally by Hemlo Gold Mines Inc. and Noranda Exploration Limited. used informally by Hemlo Gold Mines Inc. and Noranda Exploration Limited. MINE MINE GEOLOGY GEOLOGY The The "stratigraphy" "stratigraphy" in in the the mine mine area area as as shown shown on on the the surface surface plan plan (Figure (Figure 3), 3), has hasbeen been subdivided subdivided into into four four major major formations. From Fromsouth southto tonorth norththey theyare arethe theCache CacheLake, Lake,Rule RuleLake, Lake, Moose Lake, formations. The Lake, and Cedar Creek formations. The Moose Moose Lake Lake formation formation is is the the most mostimportant important economically mineralized zones. number of other mineralized zones. These These economicallyas asitithosts hoststhe the main main Hemlo Hemlodeposit depositand and aa number formations formations represent represent aa package package of rocks rocks approximately approximately 3 km thick within the tower lower part part of of the the Heron Heron Bay Bay group. Rocks Rocksininthe themine minearea areastrike strikeat at115° 115O and and dip 65° 65' northeast. northeast. <. Figure2. 2. Location Locationmap mapof of Hemlo. Hemlo. Figure �Geology Geology of the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody Orebody 17 17 The Cache Lake formation, formation, which forms the structurally lowermost unit of the the "stratigraphy", comprises comprises mafic metavolcanic metavolcanicschists and granofels. In In the deposit deposit area, this formation is is about thick. It was was used used as as aadistinct distinct marker marker during during initial initial deep deep exploration exploration drilling drilling of the deposit. deposit. 150 m thick. Drill holes holes were normally normally stopped once they reached reached this formation, formation, being being deemed deemed through through the the potentially favourable ore zones. The The formation formationtends tendsto tobe bemore morehighly highlysheared shearedand andcontains contains hematite-filled hematite-filled fractures fractures adjacent adjacent to its its contact contact with with the the overlying overlying Rule Rule Lake formation. The Rule consists of laminated laminated metasedimentary metasedimentary schists Rule Lake formation consists schists and and gneisses. The The total portion of total thickness thicknessof of this thisformation formationisisabout about150 150m m in in the mine area. The The basal basal portion of the the formation formation is dominated by gneiss, whereas whereas the the upper portion is comprised of by amphibole-feldspar-biotite amphibole-feldspar-biotite gneiss, caic-silicate-rich calc-silicate-richmetasedimentary metasedimentaryrocks rockswhich which commonly commonly contain contain kyanite, kyanite, staurolite, staurolite, and and garnet adjacent adjacent to the structurally structurally overlying overlying contact. contact. This Thisformation formationisiscomprised comprisedof ofrock rocktypes typessimilar similar to to the Cedar Cedar Creek Creek formation formation and and there there is is no no observable observable difference difference between between the the two. two. 12 Diabase 1 Gronodlorlte CEDAR CREEK FORMATION 7 6 Clastic Sedinentory Rock Upper Fraonentnl MOOSE L A K E F O R M A T I O N 5 Minei-nllzed Zone 4 Mafic F r o p e n t a l 3 Moose Lake Porphyry - RULE L A K E FORMATION 2 S u r f a c e Plan C t c Sedimentar-y Rock CACHE L A K E F O R M A T I O N FIgure Figure3. 3. Geological Geologicalcompilation compilationof of the theHemlo Hemlocamp camp(modified (modifiedafter afterKuhns Kuhns1988). 1988). �Geology and Gold Deposits of the Hemlo Hernlo Area ' 1 1 - Golden Giant Mine Section 10075 E 1 1 LEGEND P O ~ P ~ Y ~ Y hw n e t a s e d 1 men t s o r e zone footwa L L sch i s t 5 b i o t i t l c schists n a f i c fragnen t a L fw n e t a s e d i men t s FIgure Figure4. 4. Generalized Generalized cross-section cross-sectionthrough throughthe theGolden GoldenGiant Giantorebody. orebody. �Geology Geology of the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody Orebody 19 19 The Moose Moose Lake formation formation within within the the Golden Golden Giant Giant Mine, Mine, shown shown on on aa typical typical cross-section cross-section (Figure (Figure 4), can can be be subdivided subdivided into into four units units which, from south south to north, northl are: are: (1) Lower Mineralized MineralizedZone; Zone; (1) Lower (2) (2) Footwall Footwall Schists; Schists; (3) Mafic Mafic Fragmental; Fragmental; (4) Main Main Ore Ore Zone. Footwall Schists are interpreted interpreted to to have have been been derived derived largely largely from from the the Moose MooseLake Lake The Footwall Porphyry, which is avariably much Porphyry, a variably altered altered and anddeformed deformedquartz-feldspar quartz-feldspar porphyry porphyry that constitutes constitutes much Moose Lake formation. Thisformation formationattains attainsthicknesses thicknessesupto up to100 100mmininthe themine minearea, area, and and of the Moose formation. This up to the the west west of ofthe thedeposit deposit area. area. The formation formation pinches pinchesto to the the east east until until the the Cedar Cedar Creek Creek up to 400 m to formation structurally structurally overlies the Rule Lake formation. In Inthis this area, area, the the transition transition between between the the Cedar Creek and Rule thick silicate silicate and and oxide oxide facies facies iron iron Rule Lake Lake formations is is marked marked by an 8 m thick formation. formation. Moose Lake Formation Formation Lower Mineralized Mineralized Zone (Unit (Unlt 5) 5) The Lower Lower Mineralized Zone, Zone, normally located along the contact between betweenthe theMoose MooseLake Lakeand andRule Rule Lake Lake formations, formsaa mineralized mineralizedzone zonefrom from11to to 20 20 contact formations, forms m this zone, located located in the the lowerwestern lowerwestern partof orebody, is is commonly commonly m thick. The The thicker thicker part part of of thiszone, part ofthe theorebody, uneconomic uneconomicdue due to low low gold grades. Locally Locallythough, though, the the zone zone may may contain contain economic economicgold gold grades grades over thicknesses thicknesses of of 33 m. m. Economic Economicmineralization mineralizationwithin withinthe theLower LowerMineralized MineralizedZone Zonetends tendstotobe bemore morerestricted restrictedtotothe the lower levels levels in the the mine, mine, generally generally in in areas areas where where the the Main MainOre OreZone Zonehas hasbegun begunto topinch pinchout. out. Typical Typical ore ore thicknesses thicknessesare areininthe the22to to 55 m m range, range, with with this this zone zone representing representing2.2 2.2million milliontonnes tonnesofof the stated statedreserves. reserves.The Thepredominant predominantrock rocktypes typesare arevery verysimilar similartotothose thoseininthe theMain MainOre OreZone Zone the and include feldspathic feldspathic and and sericitic sericitic varieties varieties which which locally locally may may be bebaritic baritic andlor and/orpyritic. pyritic. Gold mineralization mineralization tends tends to to be be less less dependant dependant on rock rock type type in comparison comparison to the Main Main Ore Ore Zone. Plagioclaseporphyry porphyrysills, sills,which whichessentially essentiallybisect bisectthe theorebody orebodyalong alongits itslength, length,are arecommon common Plagiociase within the the zone zone and and locally locallymake makeeither eitherthe thehanging hangingwall wall and/or andlor footwall footwall lenses lenses uneconomic uneconomic to to Overall,sills sillsrange rangein inthickness thicknessfrom fromless lessthan than 11m mto to in in excess excessof of 10 10 m. m. mine. Overall, Footwall FootwallSchlsts Schists(UnIt (Unit3) 3) The The Footwall Footwall Schists Schists generally generally structurally structurallyoverlie overliethe theLower LowerMinerMineralized Zone, Zone, but but itit is is common common to to get get aa thin thin zone zone developed developedon on the the underlying underlyingfootwall footwallside sideof ofthe the alized Lower Mineralized Zone. Zone. This 3a)# This unit unittypically typically isiscomprised comprisedof ofQuartz QuartzEye EyeSchist Schist(Subunit (Subunit3a), FeldspathicSchist Schist (Subunit (Subunit3b), 3b), and and Biotitic BiotiticSchist Schist(Subunit (Subunit3c). 3c). ItItforms formsthe thestructural structuralfootwall footwallto to Feldspathic the the Main Main Ore Ore Zone. Zone. Footwall Schist in the mine mine area area and and is is comprised comprised of of quartzquartzSubunit 3a dominates the Footwall muscovite~feldsparschists schists with with distinctive distinctive 11to to33mm mmquartz quartzlenses lensesor or"eyes" "eyes" and, and, locally, locally, fewer fewer muscovite±feldspar plagioclaseeyes. eyes. This ThisQuartz QuartzEye EyeSchist Schistsubunit, subunit,which whichisispart partofofthe theMoose MooseLake LakePorphyry, Porphyry,may may plagioclase also contain minor tourmaline, tourmaline, anhydrite, anhydrite, green green mica mica and andpyrite. pyrite. Adjacent zones of of Adjacent to Unit Unit 55 zones 5% pyrite, pyrite, minor minor mineralization, the subunit may be weakly weakly mineralized, mineralized, containing mineralization, the subunit containing up up to 5% gltrange. range. molybdenite,and and gold goldvalues values in inthe the 11to to55g/t molybdenite, termed Feldspathic FeldspathicSchist, Schist, is is massive massive to to weakly weakly schistose schistoseand andisiscomprised comprised Subunit 3b, termed predominantly amounts of of muscovite. muscovite. Lenticular predominantly of feldspar, quartz, and lesser amounts Lenticular plagioclase plagioclase eyes are common. common. Locally, Locally,generally generallyininproximity proximityto todiabase diabaseintrusions, intrusions,this thissubunit subunitmay maybe behematized hematized are andlor potassium-rich resulting in a pink to Contacts between between this this subunit subunit and and/or to red colouration. colouration. Contacts �20 20 Geology and Gold Deposits Deposits of the Hemlo Hemlo Area either plagioclase porphyry porphyry sills may be quite quite gradational. gradational. InInthe either the Quartz Quartz Eye Eye Schist Schist and plagioclase thelower lower levels of the mine, the unit becomes more porphyritic porphyritic in appearance appearance and and itit is is often often difficult to establish discrete contacts Schist and and plagioclase plagioclase porphyry porphyry sills. sills. The contacts between the Feldspathic Schist is weakly weakly mineralized mineralized with pyrite pyrite and and molybdenite molybdenite occurring occurring within within hairline hairline subunit locally is fractures. Subunit 3c, termed Biotitic Biotitic Schist, Schist, consists consists of of aaquartz-biotite-muscovite quartz-biotite-muscovite schist schist which which generally generallylacks lacks quartz quartzor or plagioclase plagioclaseeyes. eyes. This Thissubunit, subunit,which whichisisnot notpresent presentin in the the upper upper levels levels of the levels, locally locally marking the strike extension of, or the mine, becomes becomes more more abundant in the lower levels, being proximal to, weakly FootwallSchists. Schists. This subunit subunit may may weakly mineralized mineralized zones within the the Footwall represent represent less less altered altered metasedimentary metasedimentaryrocks rocksor or aa fine-grained fine-grainedMafic Mafic Fragmental Fragmentalrock. rock. Mat Ic Fragmental Fragmental Unit Mafic Unit(Unit (Unit4) 4) The Schists The Mafic MaficFragmental FragmentalUnit Unit occurs occurs between betweenthe Footwall FootwallSchists and the structurally overlying metasedimentary rocks rocks of of the the Cedar Cedar Creek Creekformation. formation. The unit overlying metasedimentary unit comprises quartz granofels granofels and and biotite biotite schist within a comprises lenticular lenticular fragments of feldspar porphyry, quartz strongly foliated biotitic biotitic matrix. matrix. The distribution of this this unit unit shows shows an anoverall overall antipathetic antipathetic relationshipwith withthe theMain MainOre OreZone, Zone,pinching pinchingout outat atdepth depthand andto tothe theeast eastand andwest westof of the the Golden Golden relationship Giant orebody (Walford, Weicker eta!. 1986; Burk eta!. 1986). The predominant subunit is a Biotitic predominantsubunit is Biotitic Giant orebody (Walford, Weicker eta/. 1986; Burk eta/,1986). Fragmental composition of 40% biotite, 8% Fragmental (4a) having having an average composition 4O0loquartz, 24% 24Y0 biotite, 8Ol0plagioclase, plagioclase,7% 7Y0 actinolitic 7% pyrite (Kuhns, 1988). 1988). The unit actinolitic hornblende, hornblende, 3% 3OlOtremolitic tremolitic hornblende, hornblende, and 7Y0 unit locally locally contains contains economic economic grades grades of of gold gold mineralization mineralizationbut, but, in in general, general, only only contains containsanomalous anomalousgold gold values. values. Other subunits subunits within withinthe theMafic MaficFragmental FragmentalUnit Unitconsist consistof of Sericitized SericitizedFragmental Fragmental(4b) (4b)and and Other Fine-grained Sericitized Fragmental Fine-grained Fragmental (4c). The Sericitized Fragmental commonly commonly occurs occurs as as an an altered alteredzone zone between replacement of biotite with between Biotitic BiotiticFragmental Fragmentaland and ore ore units. units. It is characterized characterized by the replacement biotite with muscovite, pyrite, molybdenite molybdenite and muscovite,and and an an increase increase in in the amount of green mica, pyrite, and gold. The TheFineFinegrained Fragmental Fragmentalis generally difficult metasedimentaryrocks rocks of the grained difficult to distinguish distinguish from clastic clastic metasedimentary Cedar Cedar Creek Creek and and Rule RuleLake Lake formations. formations. Main Ore Zone (Unit (Unit 5) 5) The Main Main Ore Ore Zone comprises comprises several distinctive distinctive subunits subunits that that are are characterized Zone subunits subunits contain contain molybdenite molybdenite characterizedon onthe thebasis basisof of mineralogy. In In general, Main Main Ore Zone and tend to be be either either feldspathic or sericitic. Accordingly, Accordingly, the the two two most most common common subunits subunits are Feldspathic Feldspathic Ore Ore (5a) and Sericitic Sericitic Ore Ore (5b). (5b). 5a consists consists ofofquartz-microcline quartz-microcline granofels granofels with with10% 10Y0pyrite, pyrite,0.1% 0.lY0 fine-grained fine-grained Subunit 5a molybdenite, 3% green mica. The characteristic blue-grey The molybdenite molybdenitegives gives the rock rock its its characteristic blue-grey rnolybdenite,and and11 to 3Y0 colour. colour. Subunit 5a 5a isis commonly commonly further furthersub-divided subdivided into intohighhigh-and andlow-pyrite-barite-bearing low-pyrite-barite-bearing varieties corresponding correspondingchemically chemicallyto to lowlow-and and high-aluminum high-aluminum contents, pyrite-baritecontent content varieties contents, with with pyrite-barite increasing at the the expense expense of of microcline. microcline. Baritic-Feldspathic Ore (5d) contains contains fragments fragments of of Siliceous FeldspathicOre Oresurrounded surroundedby by aa Au-Mo-poor matrix of barite Feldspathic Au-Mo-poor granoblastic granoblastic matrix barite andlor and/or pyrite. Siliceous (5q) consists consists of of aamixture mixtureofoffine-grained fine-grainedfeldspar, feldspar, molybdenite, molybdenite, and quartz occurring occurring in in Ore (5q) massive massive layers layers 0.5 to to 55 m m thick. Pyrite occurs occurs as as very very fine-grained, fine-grained, euhedral to anhedral crystals within the ore, ore, and and as as Pyrite coarser grains grains in in the the matrix matrix of feldspathic ore that that has has undergone deformation.There Thereisisno no coarser feldspathic ore undergone brittle brittle deformation. direct correlation correlationbetween betweengold goldgrades gradesand and pyrite pyritecontent, content, although, although,iningeneral, general, as as the the pyrite pyriteand and direct barite barite contents contentsof of the the ore oreincrease, increase, the the gold goldgrades grades decrease. decrease. (vanadian muscovite) are the best best visual visual indicators indicators for for the the Molybdenite and green mica (vanadian presenceof of gold gold mineralization. mineralization.Gold Goldoccurs occursininnative nativeform formalong alongsilicate silicategrain grainboundaries boundaries(Brown (Brown presence �Geology of the Golden Giant Mine and Golden Sceptre Orebody 21 et a!. 1985) and along pyrite-gangue grain boundaries (Harris 1986b). Visible gold has been observed in most subunits but is most commonly noted in feldspar-quartz pods or biotitic shears within the ore. The feldspar-quartz pods that occur in the green-mica-molybdenite-rich subunit may contain titanite, titanite, cinnabar, cinnabar; realgar, stibnite, sphalerite, sphaleritel pyrite, pyrite, and and molybdenite. molybdenite. Cedar Creek Formation Formation (UnIt (Unit7) 7) The Cedar Creek formation consists of a diverse group of clastic metasedimentary metasedimentary rocks rocks which subunits (Kuhns 1988). The two most common subunits intersected which can can be be divided divided into into 14 14 subunits intersected L., &I.-:-A ..,a..l.:--. - . ..A. I & C-lA,.:..-b kn:-.. P-1-:I:--&C..L..-:A /-A\ --A A IA---A P--:-:L:by workings the Golden eU Giant Mine CaIc-silicate Subunit (7d)~ and Sericitic uy the LI IG mine IIIIIIG WUI KII lya at LI IG UUIUGII IIL ~ IVIII IG ~are I u G m - W I I GDUUUIIIL ~ L G \/u) I ~Altered U~ i e r aerluuG e u Subunit Subunit (7e). (7e). The CaIc-silicate Calc-silicate Subunit Subunit is is predominant predominant and and consists consists of of brown brown to to black, black, laminated laminated and banded, banded, fine-grained, fine-grained, granoblastic-textured, granoblastic-textured, foliated, quartz-biotite-feldspar schist. schist. This This schist is interbanded with medium to dark green, amphibole-feldspar-biotite granofels. The schist is interbanded medium amphibole-feldspar-biotite The unit unit may also contain contain minor minor kyanite, kyanite, garnet, garnet, and and staurolite. staurolite. There appears to be an an increase increase in in abundance abundance of of alumino-silicate alumino-silicateminerals minerals proximal proximal to the Moose Moose Lake formation. The Thecalc-silicatecalc-silicaterich predominant in the lower levels of of the the mine. mine. Some sections sections within rich bands become predominant within the the subunit subunit . . a consist of massive calc-silicate crystals, and commonly contain pyrite and pyrrhotite mineralization. The Altered Sericitic Subunit is a pyritic, quartz-muscovite-feldspar schist spatially associated isISfine clatea with w m the meMain wlam Ore ure Zone. Lone. It11 m e grained, grariea, granoblastic grarioulasuctextured, textures,light llgnlbrownish Drownlsngrey greyto 10grey, grey, laminated laminatedand and foliated, foliated, and and exhibits exhibits gradational gradationalcontacts contactswith withother otherunits unitsand andsubunits, subunits,of ofwhich whichitit may be an an altered altered or or bleached bleached equivalent. equivalent. The average composition composition of the subunit is 4G0lO 46% quartz, quartz, 26% microcline, and 4Y0 4% plagioclase piagioclase (Kuhns (Kuhns 1988). 1988). Kyanite, is locally 26Y0muscovite, muscovite,13% 13OlOpyrite, pyrite, 10% 10Y0microcline, common. contains rare grains of molybdenitel molybdenite, green common. This Thissubunit subunitisisslightly slightlyanomalous anomalousin in gold gold and and contains mica, arsenopyrite. Pods mica, and and arsenopyrite. Podsconsisting consistingofofquartz quartzor orfeldspar feldsparare arelocally locallypresent, present,and andmay maycontain contain minor minor realgar and and stibnite. stibnite. Intrusive Intrusive Rocks Rocks Intrusive Intrusive rocks found in the Hemlo Hemlo stratigraphy stratigraphy are divided divided into into four four units. units. Feldspar-porphyritic, Feldspar-porphyritic,quartz quar monzonite and monzodiorite sills, referred to:oas asUnit Unit9, 9,occur occuras as thin thin to to thick thick (0.5 (0.5 to to 30 30 m), m), nearly nearly concordant concoraamintrusions lnuuslonswithin w m nand ana structurally suucwrallybelow belowthe theMain MainOre Ore Zone, commonly in the hanging wall wall metasedimentary metasedimentary rocks. The Zone, and and less less commonly The sills sills occur occur individually individually or in swarms swarms containing containing up upto sills, and andare arecommonly commonlyfoliated. to 20 sills, foliated. Thicker Thicker sills sills (5to (5 to 30 30 m) m) generally exhibit of feldspar and in places exhibit minor minor to moderate moderate sericitization sericitization of feldspar crystals, crvstals, and places are are cut cut by by quartz+orthoclase+fluorite quartz+orthoclase+fluoriteveins. veins. A particularly Darticularlvinteresting interestinaintrusion intrusionoccurs occurs in in the the central central part Dartof of the the deposit, depositl as as observed observedon on 4600 the flexure in &elliptical ellipticalporphyry porphyryplug plugoccupies occupi~s theaxis axis;of)faaflexure ( ~ i ~ u5). r i 5Here, Here, ) . an 4600 level Ii v e l (Figure inthe the geologic geologic units. The cmthe Theplug plugplunges plungesto tothe thenorthwest northwestatatabout about60° 60' as asoutlined outlinedon thegram-metre-value gram-metre-value , ,.4:....1 tr:-, G6). @\ Thn n:.b,.:..I.....,.. . .-.-I longitudinal section transection I ~ ~G I U I U I I(Figure trlyul w). The I IIGintrusion 11 ILI U ~ I U I shows I31I U W a ~ C I general YGI I G I ~ IA-..----b:..m L I ~ I ~ G G L Ifrom from U ~ ~ footwall footwall to hanging hanging longitbu11 wall with with depth depth in in relationship relationshipto to the the Main Main Ore Ore Zone The TIi e ore wall adjacent to this pporphyry ore zone adjacent lorphyrybody body is relatively thin. ..A,.*:.... ,-A Basaltic to dacitic sills, known as Unit 10, occur throughout the mine area. They eyare arethin thin(5 (5to to 50 cm) and cut all mineralization and alteration associated with the deposit. These "mafic "maficsills", sills",as as they to .. .-> are -. - commonly --......-. ..> referred .-.-. . --to .-in...the .. .- mine ......- terminology, .-. ......-.-aJl are, -. -, on -. .average, -.-aw, composed - w m m n yof ofw35 35 ~~ tod40% 40Yo biotite, biotite, 35 35to to40% 4070hornblende, hornblende,10% 1O0hplagioclase, plagioclase,00 to to 10% 1O0l0microcline, microcline, and and00to to10% 10Y0quartz, quartz,with with minor zoisite, pyrite, pyritel magnetite, magnetite.calcite, calcite.and andtitanite titanite(Kuhns (Kuhns1988). 1988). -- �22 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area is a asmall, The third main intrusive intrusive unit is the the Cedar Cedar Creekstockwhich Creek Stockwhich is small, oval, granitoid granitoid intrusion intrusion located about 800 800 to to 850 850 m m north north of of the the Main Main Ore Ore Zone. This Thisintrusion intrusionisis2.5 2.5by by1.5 1.5 km km in in surface surface located about extent, and its southern margin is subconcordant The subconcordant with with the the upper metasedimentary metasedimentary schists. schists. The stock consists mainly mainly of a medium-grained, hypidiomorphic-granular hypidiomorphic-granular rock which has an average composition 35Y0 quartz, quartzl 15 15 to to 35% 35Y0plagioclase, plagioclase, 10 10 to to 25% 25Y0microcline, microcline, 10 10 to to 20% 20Y0 composition of of 25 to 35% O / O biotite, hornblende, and 1 to to ~5% biotite, with minor magnetite, titanite, and apatite. high angles. angles. Diabase dikes dikes represent Proterozoic mafic mafic intrusions intrusions which which cut cut the the strata at high These dikes, referred to as Unit 121 12, are are composed composed mostly mostly of of pyroxene pyroxene and and plagioclase. plagioclase. Typically they they exhibit exhibit gabbroic gabbroic textures textures internally internallyand andgrade grade outward outwardto to chilled chilled margins. margins. Four Fourmain maindiabase diabase dikes cut the Main Main Ore Ore Zone Zone and and range range in in thickness thickness from from 11 to to 30 30 m. m. DescrIptions Level Plan Descriptions MaIn Drift DrIft The 4750 Level drift 4750 Main drift plan (Figure 7) covers covers the the main main access access to to the the Golden Golden Giant Giant orebody adjacent adjacent the shaft area, including both the hanging wall and footwall rocks. The hanging shaft area, including both the hanging and footwall The hanging wall metasedimentary rocks in this area are composed mostly of Unit Unit 7d 7d "calc-silicates" llcalc-silicates" with with either garnetiferous garnetiferous (subunit (subunit 7a), 7a), or or characterized characterized by by garnetgarnetinterbanded metapelites that are either staurolite±kyanite/sillimanite (subunit staurolite~kyanite1sillimanite (subunit7b). 7b). 7 / Golden G i a n t Mine .. Plan 4600 Level 4a __,+_+ + + + + + + ++ ++ ++ ++ ++ + + ++ ++ ++ ++ ++ ++ ++ + + +÷ ++ ++ ++ ++ ++ + + + + • + + /+ + + + + + + + + + + + ' ++ ++ ++ i095+ + + + + + + + ++ ++ ++ ++ ++ + + ++ ++ ++ ++ + + + + + ÷ + - + + - .* + + + + + + + - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 3 -- + + + + + + + + ÷ ÷ + + + + + + + + + + + + ÷ + + + + + + +_ LEGEND LEGEND +_ + + + INTRUSIONS INTRUSIONS z77L/71777 27___, 275 + + + + 4+ + + + + .•+ + + + ÷ + + + + + + + - + + 9 9 Feldspar Feldspar Porphyry Porphyry CEDAR CEDAR CREEK CREEK FORMATION FORMATION 3 - 0 5 5 10 10 metres FIgure 5. Figure intrusion. intrusion. 15 15 3 Hongingwoll Clastic 7 Hangingwoll Clastic Metasediments Metasediments I ERID MINE RID MI N MOOSE LAKE MOOSE LAKE FORMATION FORMATION 5 5 4 4 3 3 Mineralized Mineralized Zone Zone Fragmentol Fragmental Unit Unit Footwall Footwoll Schist Schist Level plan plan of of part of Level of the the 4600 4600 level levelshowing showing the the elongate elongateplagioclase plagioclase porphyry porphyry �Geology of the Golden Giant Mine and Golden Sceptre Orebody 9800 5200 23 23 10220 M_© ©U Golden Giant Giant Mine Mine Longitudinal Longitudinal Projection Projection Gram—Metre Gram-Metre Values II 1 4800 4800 4400 4400 20 0 20 40 9800 10200 FIgure 6. Longitudinal Figure Longitudinal projection projection of of the the Golden GoldenGiant Giant orebody orebody showing showinggram-metre gram-metrecontours contours (Au grade by by ore ore thickness thickness in in gram-metre/tonne gram-metreltonnevalues). values). �24 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Moving south, or structurally through the strata, subunit Moving south, structurally downward downward through subunit 7e 7e isisencountered encountered structurally Zone. The structurally above, and adjacent adjacent to, the Main Mineralized Mineralized Zone. The quartz-muscovite-feldspar quartz-muscovite-feldspar schist (subunit 7e) is almost everywhere found found in in this this stratigraphic stratigraphic position, position, and is thought to alteration envelope envelope surrounding surrounding the the Main Main represent the upper part of an asymmetrical, sericitic alteration 4750 MAIN DRIFT MAIN DRIFT ACCESS LEGEND LEGEN INTRUSIONS INTRUSIONS 10 10 9 9 Mafic Sill Mafic Sill Feldspar Porphyry Sill Feldspar Sill CEDAR CREEK CEDAR CREEK FORMATION FORMATION 7 Hongingwall Hangingwall Clastic Clastic Metasediments Metosediments MOOSE LAKE LAKE FORMATION FORMATION Mineralized Zone 5 Mineralized Zone 4 Fragmental 4 Fragmental Unit Unit 3 Footwoll Footwall Schist Schist 3 Figure Figure7. 7. 4750 SCALE: / I 1:250 LEVEL DATE: APRIL 1990 II Geology Geology plan plan of the 4750 main access access drift. drift. �Geology Geology of the the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody Orebody 25 25 Mineralized Mineralized Zone. ItItis is weakly weakly mineralized, mineralized, most most obviously obviously with pyrite, but but studies studies show that itit is is also enriched enriched in ore-related minor in most most of the ore-related minorelements elements(Ba, (Ba, Ag, Hg, Hg, As, Sb). This This unit unitalso also shows shows aa very strong, pervasive pervasive planar planar foliation, the same as seen in the very the ore ore zone, zone, indicating indicating the the sericitic alteration was developed prior to, to, or at the same same time time as, as, metamorphism and andtectonism. tectonism. Chip 4750 MAIN MAIN DRIFT DRIFT ACCESS ACCESS SYMBOLS SYMBOLS CHIP SAMPLE SAMPLE LOCATION LOCATION 17.5 ASSAY (g/t Au) ASSAY (g/t Au) [te[nn)0@<3f~^S CHIP 4750 / SCALE: 1:250 GOLDEN GIANT MINE PLAN LEVEL DATE: APRIL 1990 Figure Assay plan plan of of the the 4750 4750 main main access access drift. drift. Figure8. 8. Assay �26 26 Geology and Gold Deposits Deposits of the Hemlo Area which are are typical typical of Unit 4. These sample grades (Figure 8) show anomalous gold values which These values values are insufficient insufficient to meet minimum mining requirements requirements currently set at 2.8 2.8 glt g/t Au over 3.0 m. Moving southward southward again, again,into intothe thefootwall footwallschist, schist,subunit subunit3a 3aisisencountered. encountered. This quartzMoving muscovite-feldspar characterized by muscovite-feldsparschist schistis is the the most most common common variety variety of of Unit Unit 3, and and is characterized by lenticular lenticular plagioclase eyes, eyes, and andcommonly commonlycontains containstourmaline tourmalinecrystals. crystals. This unit is is quartz eyes and lesser plagioclase rhyolitic in chemical a/. 1986) 1986) and is is interpreted interpreted as as being being an an altered altered chemical composition (Kuhns (Kuhns et a!. porphyry intrusion interbanded with subunit intrusion which is is part part of of the the Moose Moose Lake Lake Porphyry. Porphyry. It is interbanded subunit 3b, 3b, which is microcline-rich microcline-rich and and contains contains lenticular lenticular plagioclase plagioclaseeyes. This Thisbuff buff to to pink pink rock rock is is marked marked by potassium enrichment, a decrease in muscovite, and a more massive texture. PlagioclasePlagioclaseintrusions (Unit "mafic sills" sills" (Unit (Unit 10) 10) extensively extensively cut the the footwall footwall schist schist porphyritic intrusions (Unit 9) 9) and "mafic throughout the extent of the Hemlo Hemlo deposit. Here, Here,feldspar-porphyritic, feldspar-porphyritic,quartz-monzonite quartz-monzonitesills sills 9a), and fine-grained fine-grained dacitic dacitic sills sills (subunit (subunit 10a) ba) can (subunit 9a), can be be examined. examined. - 4700 Sublevel Sublevel Plan 2WCrosscuts Crosscuts The Plan - OW, OW, 2W The4700 4700Sublevel Sublevelplan plan(Figure (Figure9) 9)covers coversthe the00West West West crosscuts crosscuts located approximately half-way down down dip dip on on the the Golden Giant part of the and 2 West deposit, just west of the the upper part part of ofthe theorebody orebodywithin within the the Quarter Quarter Claim. Claim. The ore at this this location location deposit, occurs as 2 lenses, termed hanging hanging wall ore lens and footwall ore lens, separated by a body body of subeconomic, Unit 4, quartz-mica-feldspar-amphibole quartz-mica-feldspar-amphibole schist. The hanging wall metasedimentary The hanging metasedimentary rocks are poorly exposed, as cutting into them with drift walls causes excessive dilution. The ore exposed exposed in the crosscuts crosscuts and and sill drifts drifts is is typical typical of ofthe the Golden GoldenGiant Giantorebody, orebody, with with occurrencesof of Feldspathic FeldspathicOre Ore (5a), (5a), Sericitic Ore (5b), and Baritic Ore (5d). The footwall occurrences Sericitic Ore footwall ore lens predominantly Baritic Baritic Ore, Ore, which which is is typical typical for for most mostof of the the Golden GoldenGiant Giantorebody. orebody. It contains is predominantly contains some quartz-rich material(subunits (subunits5d, 5d,5q) 5q)and andisiscut cutby by numerous numerous"mafic "maficsills" sills"(subunit (subunitbOa). 1Oa). The The quartz-rich material Unit 4 quartz-mica-feldspar-amphibole quartz-mica-feldspar-amphiboleschist schist separating separating the the 22 ore ore lenses lensesconsists consistsof, of, inin body of Unit part, avery a very representative representative example of the the Biotitic Fragmental Fragmental subunit 4a. 4a. At the contact between this body of Unit 4 and the footwall ore lens, is an occurrence occurrence of footwall footwall schist schist that that contains an unusual unusual amount amount of green green mica. mica. distinct lack of barite and is typically composed The hanging wall ore lens shows a distinct composed of more Sericitic Ore (5b) (5b) as as opposed opposed to to Feldspathic FeldspathicOre Ore (5a). (5a). The Thehanging hangingwall wall contact contactof of this this ore ore lens lens is is Sericitic Ore marked by the presence of of the Calc-silicate Caic-silicate Subunit (7d), (7d), with with the the more typical typical Altered Altered Sericitic Subunit (7e) found further within the hanging hanging wall. wall. Small-scale folding folding is observable within the footwall ore lens. lens. Tight, eastward eastward plunging plunging Small-scale observable within Z-shaped folds with axial axial planes planes parallel parallel to foliation foliation are are most most common. common. Brittle units such as as boudinaged. However, plagioclase porphyry sills and mafic dikes are boudinaged. However, there is is no no predominant predominant direction. Overall, elongation direction. Overall, the the ore ore zone zone at at this this location location shows shows moderate moderate to strong strong tectonic disruption as indicated indicated by by the the folding folding visible visible in in the the footwall footwall ore ore lens, lens, boudinage boudinage of of mafic mafic sills sills (subunit bOa),and andoffsets offsetsalong alongcross-cutting cross-cuttingfractures. fractures. The The degree degree of of tectonic tectonic disruption disruption is (subunit IOa), orebody, due, due, in in part, part, to to the the lenticular lenticular greater here as compared to the rest of the Golden Giant orebody, nature of the ore. Parts Partsofofthe theorebody orebodythat thatare arecomposed composedsolely solelyof of Unit Unit55generally generallyshow show less less tectonic disruption. disrupt ion. (Figure 10) 10) is typical of the Grade distribution within the footwall ore lens at this location (Figure deposit. The Thefootwall footwalllens lensshows showslower-than-average lower-than-average grades grades as as compared compared to to the the hanging hangingwall wall lens, due to increased increased amounts of barite and pyrite which tend to dilute the the gold gold content. content. �Geology Geology of of the the Golden Golden Giant Mine and Golden Sceptre Orebody Orebody 27 27 Observations Observations To date, date, the following observations observations have have been been made made concerning concerningthe the principal principalfeatures featuresof of the the Golden Giant orebody: Golden Giant orebody: 1. the Main Ore Ore Zone Zoneis isneither neitherdemonstrably demonstrablystratiform stratiform nor norstrata-bound. strata-bound. Non-economic 1. Overall, the Non-economic mineralization subzoneswithin withinthe the mineralizationgenerally generallyhas hasthe thesame sameform formas as the the Main Main Ore Zone. High-grade High-gradesubzones Main Main Ore Ore Zone Zone tend tend to toshow showtransecting transectingrelationships, relationships, from from footwall footwall to to hanging hangingwall, walll with with increasing increasing depth depth in in section section and and from from east east to west in plan. These These same sametransecting transectingrelationships relationships are are exhibited exhibited by by the the plagioclase plagioclaseporphyry porphyrysills, sillsl whereas whereas the the relative relativeorientation orientationof ofthe themafic maficsills sillsis is too irregular to permit a valid generalization. too irregular to permit a valid generalization. 2. icult to 2. Ore Oreisishosted hostedwithin withinaavariety varietyof oflithological lithologicalunits. units.Protoliths Protolithsare arevery veryduff difficult to determine determineas as aa result degree of metamorphism metamorphism and deformation, deformation, but thought to be represented represented by result of the high degree but are thought mudstones, as well as felsic felsic and and mafic mafic volcanic volcanic and andvolcaniclastic volcanictasticrocks. rocks. The distribution of the Mafic Mafic Fragmental Fragmental Unit shows an antipathetic relationship relationship to the distribution distribution of of the the ore. ore. 3. 3. The Thepredominant predominantstyle styleof ofmineralization mineralizationininthe theGolden GoldenGiant Giant orebody orebodyis is disseminated disseminatedgold gold and and molybdenite molybdenite within within rocks rocks containing containing the the assemblages assemblages microcline-quartz, microcline-quartz, muscovite-quartz, muscovite-quartz, biobiotite-microcline-quartz, and andrarely, rarely, calc-silicate calc-silicate minerals. minerals. AAsecondary, secondary, minor minor style style of of mineralizamineralizatite-microcline-quartz, tion tion consists consists of of gold, gold, stibnite, stibnite,and andcinnabar cinnabarwithin within deformed deformedquartz quartzpods podsand andveinlets. veinlets. 4. 4. High High gold grades grades within the the Main Main Ore Ore Zone Zone are are related related to tohigh highrelative relativeabundance abundance of of molybdenumand andvanadian vanadianmuscovite muscovite(green (greenmica). mica).Low Lowgold goldgrades gradesare arenoted notedininMain MainZone ZoneOre Ore molybdenum subunits subunits containing containingabundant abundant coarse coarse pyrite pyriteand/or andlor greater greater barite baritecontents. contents. 5. Ore-related Ore-relatedelements elementsfound spatialassociation associationwith withthe theAu Auand andMo Mo mineralization mineralizationinclude includeHg, Hg, 5. found ininspatial Ag, Zn, and and locally locally minor W, W,Tel Te,and andTI. TI.Studies Studies indicate indicate strong strong spatial correlation correlation V, Znl Agl Ba, Ba, As, Sb, V, between between Au, Aul Ag, Ag, and and Mo Mo as as the the principal principaldisseminated disseminatedore oretype, type,and andAu, Au,Hg, Hg,and andSb Sbas asaaminor, minor, quartz quartz pod pod(remobilized) (remobilized)ore oretype type(Kuhns (Kuhns1988). 1988). 6. 6. Ore Oreisishosted hostedwithin withinamphibolite amphibolitefacies faciesmetamorphic metamorphicrocks, rocksland andmineralization mineralizationpreceded precededpeak peak Thisisisindicated indicatedby bythe thepresence presenceof ofkyanite kyaniteand and sillimanite sillimanite in in the the hanging hanging wall wall metamorphism. This metasedimentary prograde metasedimentary rocks adjacent to the ore ore zone zone and and by by gold gold grains grains in in contact contact with withprograde kyanite kyanite(Kuhns (Kuhns1988). 1988). 7. 1 Alteration Alteration consists consistsof of an an interior interior potassic potassic (microcline/biotite) (microclinelbiotite) zone zone with with localized localized silicification silicification and pyritization, pyritizationl aasurrounding surroundingsericitic/phyllitic sericiticlphyllitic (muscovite±pyrite) (muscovite~yrite) zone,and andan anouter, outer, discondisconand zone, tinuousaluminosilicate aluminosilicate(kyanite) (kyanite)"halo" "halo"(Figure (Figure11). 11). Secondary Secondaryalteration alterationconsists consistsofofcalc-silicate calc-silicate tinuous (actinolite/tremolite) (actinoliteltremolite) zones in and and around around the the mineralized mineralized rocks; rocks; aa weak, weak, widely widelydistributed, distributed, fracture-controlledl sericitic sericitic alteration alteration (bleaching); (bleaching); aa secondary secondaryaluminosilicate aluminosilicate(fibrolite) (fibrolite)zone zone fracture-controlled, coincident coincident with the the kyanite kyanite zone; zone; and and local local carbonate carbonate alteration alteration associated associated with with parts partsofofthe the barren barren hanging hanging wall rocks rocks or locally locally within within biotitic biotiticsubunits subunitswithin withinthe theMain MainOre OreZone. Zone. 8. Mineralized Mineralizedzones zonesare arespatially spatiallyassociated associatedwith withaahighly highlydeformed deformedand andmineralized mineralizedquartz quartzeye eye 8. porphyry (footwall (footwall schist), schist), and and numerous numerous post-mineralization post-mineralization feldspar porphyry sills and and dikes dikes porphyry related Pluton. related to to the theCedar CedarCreek CreekStock Stockand andCedar CedarLake LakePluton. 9. At Atleast least33deformational deformationalevents eventshave havebeen beenrecognized recognizedininthe theHemlo Hemloarea area(Kuhns (Kuhns1988): 1988): 9. (i) (i) Pre-peak Pre-peak metamorphic metamorphicisoclinal isoclinal folding foldingand andfaulting. faulting. This This first first event event is is recognized recognized by by the the presence of isoclinal folds through which a penetrative metamorphic fabric has developed. presence of isoclinal folds through which a penetrative metamorphic fabric has developed. (ii) Syn-peak Syn-peak metamorphic metamorphic isoclinal isoclinal folding folding and and post-peak post-peak metamorphic metamorphic ductile-brittle ductile-brittle shearing shearing (ii) and associated associated drag drag folding. folding. The Thesecond secondfolding foldingevent eventisisindicated indicatedby bythe thepresence presenceofofisoclinal isoclinal and foldingof of the themetamorphic metamorphicfabric fabricand andrefolding refoldingof of F1 F, generation generation structures. structures. The Theore orezones zonesand and folding non-mineralized non-mineralizedcountry country rocks rocks are are strongly strongly foliated foliated and and exhibit exhibit dextral dextral mylonitic mylonitic and and cataclastic cataclastic textures texturesattributed attributedtotopost-peak post-peakmetamorphic, metamorphic,ductile-brittle ductile-brittleshearing. shearing. (iii) Late Late brittle brittle faulting. faulting. Brittle Brittledeformation deformationisisindicated indicatedby bymultiple, multiplelwell-developed, well-developed,angular angularfault fault (iii) brecciasand andclayey clayeyto to rock rock flour-rich flour-richgouge gouge zones zones which which are developed subparallel to to the the regional regional breccias developed subparallel metamorphic metamorphicfabric. fabric. �Geology and Gold Deposits of the Hemlo Hem10 Area 28 0 X-CUT q 2W X—CUT X-CUT - - -- ---- - - -- --- — 277 -ov.. 274'__L, 1W X—CUT LEGEND INTRUSIONS 10 10 99 Mafic Mafic Sill Sill Feldspar Feldspar Porphyry Porphyry Sill Sill CEDAR CEDAR CREEK CREEK FORMATION FORMATION 7 Hangingwall Hangingwall Clastic Clastic Metasediments Metasediments MOOSE MOOSE LAKE IAKEFORMATION FORMATION Mineralized Mineralized Zone Zone 44 Fragmental Fragmental Unit Unit 3 Footwall Schist 55 4700 SUBLEVEL FIgure Geology plan plan of of the the 4700 4700level. level. Figure9. 9. Geology �Geology of the Golden Golden Giant Mine and Golden Sceptre Orebody Orebody 29 0 X- U T 2W X—CUT X-CUT — 2.1 Ore Waste -- /5.7 -- Ore 18.2 17.8 12.7 12.4 0.7 14.8 6.2 1W X—CUT 8.2 1s :-33 5.8 77 I / SYMBOLS 1 LocA CHIP SAMPLE SAMPLE LOCATION GOLDEN ;OLDEN GIANT GIANMINE MINE 17.5 ASSAY (g/t Au) ASSAY (g/t Au) 1 I11 CHfP SAMPLE CHIP SAMPLE PLAN PLAN 4700 SUBLEVEL 4700 SUBLEVEL SCALE: DATE: APRIL APRIL 1990 1:250 1 ~ 2 5 0 DATE Figure 10. Figure 10. Assay plan of the 4700 level. level. �30 30 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area GEILDEN GOLDEN GIANT G I A N T DEPUSIT DEPOSIT A±eraion A t t e r a t i o nand andMineroiization Mineratization 10 10 AU CEDAR CEDAR CREEK FORMATION FaRMA J l U N 7c UNALTERED UNALTERED ALUMINU—SILICATES ALUMIND-SILICATES 7b 7e --- 45cxb MOOSE MaUSE LAKE LAKE FORMA TION :::::: 3 3b 3b --RULE LAKE LAKE FORMATION SERICITIC SERICITIC PDTASSIC PUTASSIC UNALTERED UNALTERED POTASSIC PUTASSIC 5a SERICITIC SERICITIC 3a POTASSIC PUTASSIC UNALTERED UNALTERED PDTASSIC PDTASSIC 3cx SERICITIC SERICITIC 5ob PDTASSIC PUTASSIC SERICITIC SERICITIC 2b,e 3a ALUMINU—SILICATES ALUMIND-SILICATES UN AL TE RE D UNALTERED Mocified Modified after a f t e rKuhns Kuhns1988, 1988, FIgure Figure11. 11. Generalized Generalizedspatial spatial relationships relationshipsof of alteration alteration and and mineralization mineralization characteristics characteristics of of the the Golden Golden Giant Giant orebody. orebody. Modified Modifiedafter afterKuhns Kuhns(1988). (1988). Qz QZ MOOSE LAKE LAKE PORPHYRY PORPHYRY MOOSE Louden Giant Ghnt Golden A Goden GoLden Sceptre Sceptre 0 granite 0 0 0 1) q u a r t z syenlte UR q u a r t z nonzonite q u a r t z monzodlorlte PG Figure Figure12. 12. Normative Normative orthoclase orthoclase (OR), (OR), piagioclase plagioclase (PG), and quartz (QZ) (QZ) plot plot for for the the Moose Moose Porphyry from the Golden Golden Giant and Golden Sceptre areas. Modified Modifiedafter afterKuhns Kuhns(1988). (1988). Lake Porphyry �S Geology of the Golden Giant Mine and Golden Sceptre Orebody 31 GOLDEN SCEPTRE PROPERTY In the summer of 1990, 1-lemlo Gold Mines Inc. began open pit mining of the North Zone of the Golden Sceptre property. Mining was carried out in conjunction with a quarrying operation that was to provide rockfill for a tailings dam expansion project. The Golden Sceptre pit/quarry is situated about 1.5 km west of the Golden Giant minesite. Numerous, weakly mineralized zones have been identified on the Golden Sceptre property. The most promising of these zones, referred to as the North Zone, is currently being mined. Approximately 180 000 tonnes at a grade of 2.6 g/t Au will be extracted from the North Zone and milled at the Golden Giant Mill. The North Zone occurs within a package of probable clastic metasedimentary and felsic metavolcaniclastic rocks. Host rock protolith determination is difficult due to deformation and alteration. North of the mineralized zone, rock types are more obviously sedimentary, consisting of metamorphosed equivalents of sandstone, pelite, and minor conglomerate. The Moose Lake Porphyry body (Golden Sceptre porphyry of Kuhns, 1988), lies about 100 m south of the Golden Sceptre pit. Kuhns (1988) recognized three textural varieties of the Moose Lake porphyry on this property, which comprise: a predominantly unaltered, minimally strained, feldspar porphyry; a weakly foliated, mica-bearing, feldspar porphyry; and a minimally altered and strained quartz porphyry. Normative quartz÷orthoclase-*.plagioclase abundances indicate a granite to granodiorite composition (Figure 12). Variation in composition is likely due to alteration (Kuhns 1988). Comparable rocks found within the Moose Lake Porphyry may be found in the Footwall Schist of the Golden Giant orebody and have been referred to as the Golden Giant porphyry (Kuhns 1988). North Zone mineralization is characterized by stockwork molybdenite-filled fractures accom- panied by feldspar and biotite alteration. The most obvious alteration occurs as fine-gralned, feldspathic selvages about molybdenite-(±green mica)bearing fractures. Biotite is commonly developed beyond the feldspathic alteration. Carbonate is pervasive throughout the entire mineralized zone. The stockwork zone has been slightly flattened parallel to the regional foliation. Feldspathic margins of fractures oriented perpendicular to foliation are wider and folded relative to contiguous linear fractures oriented parallel to foliation (Figure 13). Complex cross-cutting relationships between mineralized and unmineralized fractures and overprinting of alteration suggests multiple fracturing and mineralizing events. Visible gold is observed along the molybdenite- and green mica-bearing fractures and within the feldspathic alteration rind. There is a direct relationship between gold mineralization and the amount of molybdenite and green mica, Where molybdenite stockwork fracturing is intense, gold grades In excess of 15 g/t Au have been measured. Euhedral, black tourmaline crystals occur along fractures bearing molybdenite + green mlca±pyrlte. The tourmaline grains are randomly oriented within the fracture planes and in some cases are boudinaged. Randomly oriented tremolite and carbonate crystals within vein-like structures or discrete lenses cross-cut the feldspar rinds and molybdenite-green-mica-bearing fractures. �32 Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Area Geology DISCUSSION DISCUSSION Geological relationships evident evident on on the the Golden Geological relationships Golden Sceptre Sceptre property property have been useful useful in in understanding understandingthe the Hemlo Hemlo deposit. The The similarities similaritiesand anddifferences differencesbetween betweenthe the Golden GoldenGiant Giant and and Golden Golden Sceptre Sceptre orebodies orebodiesare arediscussed discussedbelow. below. The gold grade of the Golden Sceptre orebody is much lower than than that that of the the Golden Giant orebody. orebody. In the Golden Golden Sceptre Sceptre orebody, orebody, gold mineralization is confined confined to to narrow narrow fractures fractures dispersed throughout large large volumes volumes of of barren dispersed throughout barren rock, rock, whereas whereas in the the Golden Golden Giant Giant orebody, orebody, mineralization mineralization is is contained contained in in aa zone zone of of pervasively pervasivelyand and intensely intenselyfractured, fractured,feldspathized, feldspathized,and and subsequently subsequently strained strained rocks. rocks. Intense sericitic alteration typical of of the the Golden Golden Giant Giant orebody orebody is is not not developed developed on on the the Golden Golden Sceptre property. Since Since the the competency competency of of the the host hostrocks rockshas hasnot notbeen beenreduced reducedby by sericitization, sericitization,strain strainisismuch muchlower loweron onthe theSceptre Sceptreproperty propertythan thanon onthe theGolden GoldenGiant Giantproperty. property. LEEEND rnolybdenvte green mica bo±i1e £e1dspr 10cm 0 scoe scale FIgure showing the the style style of of alteration alteration and mineralization Figure13. 13. Tracing from a photograph showing mineralization of of the the Golden Sceptre orebody. Golden Sceptre orebody. �Geology Geology of the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody 33 The 22 orebodies orebodies display display similar similarmineralogy. mineralogy. Both deposits show the same same relationship relationship grade and and the the abundance abundanceof ofgreen greenmica micaand andmolybdenite. molybdenite. Feldspathic Feldspathic alteration alteration is between gold grade associated with associated with gold gold mineralization mineralizationon on both bothproperties, properties,however, however, ititisisnot not as as intense intenseor or pervasive pervasive on the Golden Golden Sceptre Sceptre property. property. The Hemlo deposit is is commonly commonly described described as as aadisseminated disseminatedgold-molybdenum gold-molybdenum deposit, deposit, implying implying that gold and and molybdenite molybdenite are evenly evenly distributed distributed throughout the ore ore zone. zone. Close Close examination examinationof of ore ore at at aa hand hand sample sample scale reveals reveals that molybdenite molybdenite(and (andgold gold where whereobserved) observed)isis concentrated along along anastomosing anastomosing seams and and vein structures structures within within pervasively pervasivelyfeldspathized feldspathized that the style of mineralization mineralization of the Golden Sceptre and rock. It is becoming apparent that and Golden Giant orebodies is similar. The Golden Giant orebody represents a much more altered, and similar. The Golden Giant orebody represents a much more altered, and mineralized, equivalent of the Golden Golden Sceptre Sceptre orebody. orebody. Golden Sceptre Sceptre mineralization mineralization exhibits exhibits the same spatial relationship relationship to felsic rocks as does the Golden Giant mineralization. The occurrence of the Golden The occurrence of the GoldenGiant Giant orebody orebody at at the the interface interface between quartz-eye quartz-eye schist pelitic metasedimentary between schist (Moose (Moose Lake Lake Porphyry) Porphyry) and and politic metasedimentaryrocks rocksisisnow nowwell well established. Although Althoughthe the Golden GoldenSceptre Sceptre North NorthZone Zone orebody orebody is is not not in in direct direct contact contact with with the the isproximal proximalto toit.it. Other Other mineralized mineralized zones zones on onthe theGolden Golden Sceptre Sceptre property property Moose Lake Porphyry, itit is occur within the the Moose Moose Lake Lake Porphyry. Except Except for for differences differences in in strain, the parts parts of of the the Moose Moose Lake Porphyry at the Golden Sceptre property and in the Golden Giant Mine are very similar in appearance. appearance. There has much dispute dispute over formation and There has been been much over the origin origin of the Moose Moose Lake formation and many many different different protoliths protoliths have have been been suggested suggested to explain favoured genetic models. ItItisistempting temptingjust just to todeclare declare Whatever the the origin of the Hemlo aa rock-hosted deposit and and be be done done with with it. Whatever the Moose Moose Lake Lake Hemlo rock-hosted deposit formation, itit empirically empirically is is the locus locus of hydrothermal hydrothermal alteration and mineralization. mineralization. SUMMARY SUMMARY The Hemlo Hemlo deposit deposit has has undergone undergone a complex complex geological geological history which makes makes genetic genetic modelling of the the orebody orebody rather difficult. difficult. One points that has recognized is that the modelling Oneof of the the key key points has been recognized distribution distribution of of the the ore ore zones zones is is strongly strongly controlled controlled by by the the presence presence of of the the Mafic MaficFragmental Fragmentalunit unit and host host rocks. rocks. The which has resulted resulted in well-defined contacts between ore and The distribution distribution of of the the Mafic Fragmental unit shows an antipathetic relationship with the gold gold mineralization mineralization and and may may In suitable site site for for focussing focussing mineralization. mineralization. In have provided, or represented, an extension of aa suitable addition, addition, the the plagioclase plagioclaseporphyry porphyryintrusions intrusionscommonly commonlyfollow followthe thesame sametrends trendsas asthe the higher highergold gold grades, indicating indicating aa strong strong spatial spatial association associationand andsource sourcefor for the the mineralizing mineralizingevent. event. Hemlo Hemlo Gold Mines Mines Inc. Inc. is committed to an an ongoing, ongoing, detailed examination of the Hemlo Hemlo deposit surrounding area. This deposit and and surrounding Thiscommitment, commitment,in in the the form form of exploration exploration drilling, drilling, structural structural and and geochemical geochemical studies studies (both (both in-house in-houseand and academic), academic), three-dimensional three-dimensionalcomputer-aided computer-aidedmodelmodelof information with neighbouring operations, will help towards a better underling, and sharing of standing standing of this world-class world-class gold gold deposit. �Geology and Gold Deposits of the Hemlo Hemlo Area Geology Gold Deposits 34 PART PART 7: 7: ROAD ROAD LOG LOG FOR THE HEMLO-HERON HEMLO-HERON BAY AREA by 1L. Muir INTRODUCTION INTRODUCTION road guide in this volume incorporates incorporatesover over 30 30 stops, many many of which are are not not part part of of the the The road actual actual field field trip. trip. ItIt is is hoped hoped that that the the guide guide will will provide provide an an opportunity opportunityfor forsubsequent subsequentself-guided self-guided tours 3-day overview (*) tours by by other other geologists. geologists. Stops Stopsintended intendedfor foraa3-day overviewtrip tripare areflagged flaggedwith withan anasterisk asterisk(*) and and cover cover many many of the features features in in the the Hemlo Hemloarea, area, and andsome someof of the the features featuresininthe theHeron HeronBay Bayarea. area. The additional additional stops are intended intended to toprovide provideaamore morecomplete completepicture. picture.ItIti sismandatory mandatory to obtain obtain permissIon permission from the the appropriate mining mining and and exploration explorationcompanies companies to to examine examine outcrops outcrops that that are are not noton onthe thehighway highwayrIght-of-way. right-of-way.Such Suchstops stopsare areindicated. indicated. Over the Hemlo area area have have undergone undergone partial partialto to the last last ten ten years, many many of the exposures exposures in in the Hemlo radical radicalface-lifts, face-lifts,including includingobliteration. obliteration.Those Thoseoutcrops outcropsininthe theimmediate immediatevicinity vicinityofofthe themines mineshave have been susceptible, but been the most most susceptible, buteven even the the highway highway exposures exposures have have undergone undergoneat at least least three threephases phases of modification due to road construction. 1970s, largely due construction. The Thelatest latestand andmost most modification since the late late 1970s, extensive phase phase involved involvedthe the removal, removal,during duringthe the 1989 1989 field field season, season, of up up to 2 m of the exposures extensive back either side side of the highway for safety, safety,drainage, drainage, and andesthetic(?) esthetic(?) reasons. This back from either This resulted resultedin in the loss (e.g.,Patterson Patterson1984; 1984; loss of many many features features that that have have hitherto hithertobeen beenshown shownon onprevious previoustrips trips(e.g., Quartermain Quartermain1985). 1985). The Theoutcrop outcropdescriptions descriptionsprovided providedininthis thisguide guidehave havebeen beenupdated, updated,as asmuch much as possible, to reflect information,based basedon previous as reflect what is observable. observable. Additional Additional information, previous exposures, exposures, is provided few further configuration have providedand and so so noted. noted. AAfew further changes changesin in outcrop outcrop or road configuration haveoccurred occurredsince since the with embossed the original originalpublication publicationofofthis thisguide guideinin1991. 1991. All All Stops Stops have have had had metal metal (claim) (claim) tags tags with embossed Stop Stop numbers numbers attached attached to to the the outcrops outcrops(somewhere) (somewhere) for for cross-referencing cross-referencingwith with the thefield fieldguide. guide. The 3-day 3-day field field trip trip version version begins begins in in Heron Heron Bay Bay (Figure (Figure 14, 14, inside inside front front cover) cover) with with an an The examination of pyroclastic rocks, typical of this section of the greenstone belt, at the Peekongay examination of pyroclastic rocks, typical of this section of the greenstone belt, at the Peekongay Hemloarea. area. property, which is one one of of the the more moreinteresting interestinggold goldoccurrences occurrencesoutside outside of of the theHemlo property, be Followingthis, this, the the Northern NorthernEagle Eagleproperty, property,located locatedabout about21 21km kmwest westof ofthe theHemlo Hemlodeposit, deposit,can canbe Following examined. Here Herealteration alterationand andmineralogy mineralogyare aresimilar similarto tothat thatof ofthe the Hemlo Hemlodeposit, deposit,with withthe thenotable notable examined. exception exception that that gold gold (and (and possibly possibly molybdenite) molybdenite) is is present present only only in in low low and and erratically erraticallydistributed distributed amounts. amounts. Next, Hemlo deposit depositarea area(see (see Figure Figure 18), 18), the Homestake Homestakeproperty propertycan can Next, at at the outskirts outskirtsof of the the Hemlo be visited, in order order to to view view aa variety variety of of features features and and to to provide provide an an opportunity opportunity to to discuss discuss the the relevance to the Hemlo Hemlo deposit. Finally, Finally, aa visit visit to to the the erratically erraticallyauriferous, auriferous, low-grade low-grade Highway Highway Hemlofault fault zone, zone, which which isisnear nearand andsubparallel subparallel to to Highway Highway 17 17 for for several several Zone and and to to the the Hemlo Zone kilometres, kilometres, should shouldcomplete completeDay Day1.1. The second day of the planned field trip includes: includes: aa detailed detailed examination examination of the tectonotectonostratigraphic section section through through the the Hemlo Hemlo deposit deposit along along Highway Highway 17; 17; a visit with the the staff staff of of the the stratigraphic Williams property to see see some some exposures exposures that are are illustrative illustrative of of the the structural structuraland andalteration alteration complexitiesininthe theimmediate immediatevicinity vicinityofofthe theHemlo Hemlodeposit; andaavisit with the the Hemlo HemloGold Gold staff staff to complexities deposit; and visit with examine core and specimens from the Golden Giant Mine. The Thesection sectionalong alongHighway Highway17 17isis presentedin in an an east-to-west east-to-west direction because this allows the field trip participants start with with presented direction because participants to start the and/or altered alteredrocks rocksand andwork work towards towards an anincreasing increasingnumber number of of geological geological the least least strained strained and/or conundrums. conundrums. Two figures are repeatedly referencedin inthe the text. text. Figure Figure14 14shows shows the the regional regionalgeology geologyof of the the Two figures are repeatedly referenced Hemlo-Heron Bay area, along with some of the accompanying field stops, and is located locatedon on the the Hemlo-Heron �Road — Introduction Road Log Introduction 35 35 inside front cover. Figure Figure19 19 shows shows the the local local geology geology of of the the Hemlo Hemlo deposit, deposit, along alongwith withmost mostfield field stops, and is located on the inside back cover. and is located on the inside back cover. It will become become evident evident over the course of the tour that many particularly those many of the rocks, particularly thoseinin the Hemlo Hemlo area, area, have have undergone undergone considerable considerable deformation deformation and, and, locally, locally, alteration, alteration, which whichhave have developed developed heterogeneously. heterogeneously. ItIt is acknowledged, therefore, that these factors, coupled with the the metamorphism, render types, quite quite effects of metamorphism, render lithologic lithologic terms, terms, used used to to denote primary rock types, interpretive interpretive in in many many cases. The Theterms termsused usedin inthis thisfield field guide guide are are based based on on the the examination examination of of many many rocks rocks in in the area area and and their their applicability applicabilitymay may not not be be readily readily apparent apparent in in any any one one outcrop. outcrop. InIn many the interpretation interpretation of many cases, there is is no consensus, among geologists, of the of protolith, protolith, structural structural features, metamorphic metamorphicand/or and/oralteration alterationfeatures, features,and andrelative relativetiming timingof of the the various variousrelated relatedevents, events, features, including including in in some some cases, cases, intrusive intrusiverelationships relationships(see (seeMuir Muir1993 1993for for aa more moredetailed detaileddiscussion). discussion). Another point to note note is is that that the the present present configuration configurationof of the theunits, units,for forinstance instanceas asviewed viewed along the highway highway for this trip, represents represents a highly modified crustal section. The Therocks rockshave have undergone transposition, attenuation, undergone various various stages stages of folding, transposition, attenuation,shearing shearing(i.e., (Le., largely largelyductile), ductile),and and faulting (i.e., largely brittle). The units shown in Figure 19, for example, actually represent (Le., The units shown in Figure 19, for example, actually represent an an assemblage of lithotectonic assemblage of lithotectonic components, components, only some of of which which preserve preserve reasonably reasonably original original stratigraphic stratigraphic segments. segments. In the more more highly highly strained strained parts parts of of this this greenstone greenstonebelt, belt, the theoriginal original stratigraphy stratigraphy is is aa matter matter of of notable notable conjecture, conjecture, and and hence, hence, no no formal formal stratigraphic stratigraphic nomenclature nomenclature has has been been applied. applied. A simplified simplified interpretation interpretation of of the the structural structural history historyused usedfor for this this field field guide guide is is based based on on Muir Muir and given below. Structural and Elliott Elliott(1987) (1987) and and given Structuralmeasurements measurementsare arepresented presentedininthis thisguide guideusing usingthe the right-hand (i.e., strike given such that dip direction direction is is to to the the right). right). right-hand rule rule (i.e., S sedimentaryfeatures. features. S, S refers Sorefers referstotobedding, bedding, generally generally with primary sedimentary refersto to aa composicomposi- Sowith tional layering layering similar similar to bedding which lacks lacks sufficient sufficientcriteria criteriato to be be termed tional bedding but butwhich termed S0 with confidence. confidence. S, small scale. (F,), apparently apparentlyon onaasmall scale. These Thesefeatures featuresare areoverprinted overprintedby by Soand/or and/or S S,are arelocally locallyfolded folded(F1), an S2 So fabric which forms the axial axial planar planar cleavage cleavage to F2 F2 folds, which appear to reflect reflect aa regional regional folding folding event. event. The fabric occurs as a penetrative penetrative foliation, foliation, or a spaced spaced cleavage, and/or a differentiated differentiated Sofabric The S2 layering layering which which locally locally shows showsevidence evidenceof ofmore morethan thanone one stage stageof of development. development.The TheF2 Fgfolds foldsare are open commonly display display S-shaped open to tight (locally (locally presently presentlyisoclinal), isoclinal), and and commonly S-shaped asymmetry asymmetryin in the Hemlo deposit vicinity. The Thefolds foldsplunge plungemoderately moderatelytowards towards the northwest northwest in in the the western western part part of of the the A number number of Hemlo area, and moderately toward toward the the northeast northeast in in the the eastern eastern part part of of the the area. area. A equivocal equivocal explanations explanationsfor for this this configuration configurationcould couldbe beinvoked. invoked. S3fabric fabric above structures structures are are overprinted overprintedby by aa widely widely developed, developed, generally generallymicaceous, micaceous,S3 The above which which is is axial axial planar planar to to F3 F3 folds. The TheF3 F3folds folds have have Z-shaped Z-shaped asymmetry asymmetry and, although although locally locally S3fabric fabricranges rangesfrom from weakly weakly steeplyplunging, plunging,generally generallyplunge plungemoderately moderatelyto to the the northeast. northeast.The TheS3 steeply developed(common),to (common), topossibly possiblypredominant predominantininhigh-strain high-strainzones. zones.The Thefabric fabriclocally locallyisispresent presentas as developed be a crenulation crenulation cleavage, cleavage, particularly particularlywithin withinand andnear nearF3 Fafolds folds and and boudin boudin necks. necks. ItIt appears appears to to be associated associatedwith withaaperiod periodof ofdextral dextralshear, shear, in in which which case, case, where where the the high highstrain strainzones zonesoccur, occur, the the S3 S3 fabric system of components components corresponding fabrics ininshear fabricisisinterpreted interpretedto toconsist consistof of aasystem correspondingwith withs-c-c' s-c-c'fabrics shear S30,and andS3c. S3^. Some Someofofthe thecrenulation crenulationfabrics, fabrics,and andaccompanying accompanyingF3 F3 zones, here here denoted denoted as S33, zones, S3, S3, folds, superposed on shear fabrics, fabrics, possibly possibly as aa result result of ofprogressive progressivedeformation. deformation. IfIf folds, appear appear to to be superposed not specified, specified, the the term termS3 Sofabric fabric refers refers to to the the flattening flatteningfabric fabricof of the the developing developingshear shearsystem system(i.e., (i.e., not S38). S3s). �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 36 36 Locally F4folds. folds. In In some some Locally there there are are kink kinkfolds, folds, some some in in conjugate conjugatepairs, pairs, which whichare aretermed termedF4 cases, the sense movement on the the conjugate conjugate kinks suggests an east-west directed directed shortening. sense of movement kinks suggests shortening. Only vague hint hint of ofnorth-south north-south oriented oriented pressure pressure shadows; shadows; no no north-striking north-striking Only rarely rarely is there even a vague foliation has cases, conjugate brittle fractures indicate a north-south has been been observed. observed. In other cases, directed shortening. shortening. Relatively late, layer-parallel, layer-parallel, brittle breccias, breccias, ultracataclasites, ultracataclasites, and/or andlor pseudotachylite occur in most units in the vicinity of the Hemlo deposit. deposit. These These features features rarely rarely provide dextral. However, provideany any sense sense of movement, but where determinable, the sense sense is dextral. However,because because these these features featuresappear appearrelatively relativelyfresh, fresh,and andrarely rarelydisplay displayany anyfabric, fabric, they they may maybe be considerably considerablylater later (Proterozoic?) than would be features formed by a progressive transition from ductile to brittle (Proterozoic?) to brittle dextral deformation. dextral deformation. Designations Designations for planar planar fabrics of undetermined undetermined chronology are alphabetically alphabetically subscripted subscripted (e.g., northerly direction direction except (e.g.,5a' Sa,Sb). SJ. Dips Dips are, almost everywhere, in a northerly except for for isolated isolatedcases cases of the 83 S3 crenulation crenulationfabric. fabric. HERON HERON BAY AREA SEGMENT SEGMENT Figure (inside front cover) depicts depicts the generalized generalized geology Figure 14 14 (inside geologyof of the the Hemlo-Heron Hemlo-HeronBay Baypart partof of the indicates the approximate approximate location location of the field stops. Note, indicates the greenstone greenstone belt belt and indicates Note, a "h" "*" indicates field field stops stops intended intended for for the the 3-day 3-day overview overview field field trip. Hotel iy 627 , I I I I I I I- CPR tracks CPR tracks *' £ N -/- store I 00 I 165m 40 4I 0 20 20 I 60 60 I m m scale scale approximate approximate 0 0 A @-Outcrop designation ®..___0utcroP designation :® a—atop A - s t o p number number lamprophyre quartz—carbonate Quartz-carbonate vein aystem, system, crenulated fabrics fabrics Figure Figure15. 15. Stops Stops1,2: 1,2: Simplified Simplifiedsketch sketchmap mapof of the the Heron HeronBay Bay area area stops. Outcrop Outcropat atStop Stop11is is arelapilli-tuff lapilli-tuffand and lapilli-tuff, and and pyroclastic pyroclasticbreccia breccia(see (seeFigure Figure16). 16). Outcrops Outcrops"a" "antoto"d" "d"ofofStop Stop22are lapilli-tuff, lapilli-stone. lapilli-stone. �Road Log Log — -Heron Heron Bay Bay Area Area Road 37 37 * Stop 15 &&16) Stop1: 1: PEEKONGAY PEEKONGAYPROPERTY PROPERTY(Figures (Figures14, 14,15 16) Permission property is formation on Permissionfor for access access to to the the property is required. required. InInformation on whom whom to to contact contact should should be obtained obtained from from the the Resident Resident Geologist's Geologistk Office, Office, Thunder Thunder Bay (see address address on title title page). Location: just south of the Lecours Location: 165 165 m west of Highway 627 on the gravel road just Lecours sporting goods goodsstore, store,about about80 80m msouth southof ofthe theCP CPrailway railwaytracks tracksat atthe thetown townof of Heron HeronBay. Bay. Climb Climbover overthe thehill hill at cleared off outcrop outcrop area. area. A description description of at the the north northside sideof of the the road road to a cleared of the the Peekongay Peekongayproperty property in the section section "Part 4: Peekongay Peekongayproperty" property" in in this this field field guide. guide. The Theoutcrop outcropfor for in general general is given in the Stop shafts of of the the Heron Heron Bay Bay Mine Mine (see (see "Main "Main Zone Zone Mineralization", Mineralization", Stop11(Figure (Figure16) 16)is is the the site site of of the the 22 shafts Part Part4). 4). This This outcrop outcroparea areaconsists consistsofofheterolithic, heterolithic,intermediate intermediate(to (tofelsic), felsic),quartz-feldspar-phyric, quartz-feldspar-phyric, lapilli-tuff size). Variations lapilli-tuff and pyroclastic breccia (by fragment size). Variations in in the the size size and andabundance abundance of of fragments fragments in in the the outcrop outcrop can can be be seen, particularly particularly from from north north to to south, south, but but no no bedding bedding is is clearly clearly defined. defined.Some Somefragments fragmentsare areblocks blocksup uptoto50 50cm cmlong. long.The Themajority majorityofoffragments fragmentsare aremore morefelsic felsic than than the the matrix. matrix. Some Somefragments fragmentsconsist consistmainly mainly of of chlorite chlorite and and feldspar feldspar phenocrysts. phenocrysts. The The Metavoicanic Rocks SYMBOLS — lithologic iithoiogiccontact contact —-.,_......—.—— fault/shear faultlshearzone zone small small cliff cliff shaft shaft 3 pit/open p w o p ecut n cut dump dumpmaterial material —• • . . la heterolithic breccia with some mafic clasts lb iapilli-tuff and/or massive porphyritic rocks 22 mafic(biotite—rjch) (biotite-rich) dike dike mafic 33 sericite-carbonate achiet schist serlcite—carbonate quartz-carbonate vein vein quartz—carbonate trail trail outcrop outcrop access access \ 10 m Figure Figure16. 16. Stop Stop1:1: Detailed Detailedsketch sketchmap mapof ofan anoutcrop outcropon onthe thePeekongay Peekongayproperty propertyatatthe theold old Heron Heron Bay Bay Mine. Mine.Outcrop Outcropconsists consistsofofcalc-alkalic, calc-alkalic,intermediate intermediatecomposition, composition,quartz-feldsparquartz-feldsparporphyritic, porphyritic,pyroclastic pyroclasticdeposits depositswith withlocal localcarbonatization carbonatizationand andaamineralized mineralizedquartz-carbonate quartz-carbonate vein veinsystem. system.(Geology (GeologybybyB.R. B.R.Schnieders, Schnieders,MNDM, MNDM,1990). 1990). �Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 38 fragments are elongated and plunge moderately to the west. west. Sericite±chlorite Sericitekchloriteare arepresent presentinin various variousamounts amountsin inthe the matrix matrixand andfragments. fragments. Two Twoto to three threeplanar planarfabrics fabricsare arepresent presentand andalthough although the the rock rock has has aa "sheared" "sheared" appearance, appearance, kinematic kinematic indicators indicators are are insufficiently insufficientlydeveloped developedto to allow allow deduction deduction of of sense sense of of movement, movementl if any. any. AAsample sampletaken takenfrom fromthis thisoutcrop outcropfor forU-Pb U-Pbzircon zircon geochronology 2 6 9 5 e Ma Ma(Corfu (Corfuand andMuir Muir1989a). 1989a). geochronologygave gavean anage ageof of 2695±2 The rocks carbonatization as quartz-carbonate veins rocks show pervasive, disseminated carbonatization as well as quartz-carbonate which planarfabrics, fabricsl Sa Saand and Sb. AAconspicuous conspicuous0.3 0.3to to22mmthick, thick'sinuous sinuous which are are deformed deformedabout about22planar carbonate quartz vein carbonate++quartz veinsystem systemcuts cutsacross acrossthe the outcrop, outcrop,striking strikingfrom from 275° 275O to to 300°, 300°oblique obliqueto to the the predominant planar fabrics in in the theoutcrop. outcrop. The vein system system locally consists consists of up up to to 70% 70% carbonate. Sulphide minerals minerals present present include include pyrite, pyrite, chalcopyrite, chalcopyrite, galena, galena, sphalerite, sphaleritel and and carbonate. molybdenite. tourmaline veinlets veinlets molybdenite. The The wall wall rocks rocks to to the the vein vein system system appear appear bleached. Quartz Quartz++tourmaline which quartz + carbonate±chlorite±tourmaline(?) which are are slightly slightly deformed deformedare are locally locallypresent, present' as as are quartz + carbonat~chloritektourmaline(?) veinlets. veinlets. Structural StructuralSummary: Summary: Overall flattening flattening of of fragments; fragments; Sa Sa 250/44 250144 Overall Subordinate Subordinate fabrics fabrics (not (not everywhere everywherefound): found): 256166 (forms (forms diamonds/lozenges diamondsllozengeswith withabove) above) Sb 256/66 5b Sc 225/45 225145 S 280187 (crenulates (crenulatesthe the above above 22 to to33 fabrics) fabrics) Sd S,, 280/87 275/23 elongation Lineations: elongation 1. 275123 Lineations: 290/35 L ,, 290135 (tourmaline) (tourmaline) mineral mineral L, crenulation L 252/30, 252130, 266/0 266107275/23 275123 crenulation Stop Stop 2: 2: HERON HERON BAY BAY PYROCLASTIC PYROCLASTICROCKS ROCKS(Figures (Figures14 14 && 15) 15) 110 m msouth south of of the the CP CP railway railway tracks tracks at the town of Location: Set Set of outcrops outcropson on Highway Highway627, 627,110 Location: Heron Bay. Bay. Heron These These outcrops outcropsare are typical typicalof of Heron HeronBay Bay pyroclastic pyroclasticrocks rocksand andconsist consistof oflapilli-tuff lapilli-tuffand andlapillilapillistone. The The rocks rocksare are caic-alkalic calc-alkalic dacite (intermediate) (intermediate) in composition, compositionl although although rhyolite rhyolite breccias breccias are heterolithic in texture and are locally locally found. Overall, Overall,the thefragments fragmentsare are subrounded subrounded to to subangular, subangularl heterolithic composition, commonly more felsic than the matrix, and quartz-feldspar phyric. Some Someof ofthe the compositionl matrixl fragments fragments are more mafic than the the matrix matrix and and include include intermediate, intermediate, feldsparfeldspar- ±quartz-phyric Quartz-phyric Thematrix matrix and mafic, mafic, aphyric aphyric rocks. rocks. Bluish quartz phenocrysts are locally common. The rocks, and consists quartz, sericite, *chlorite. The Theupper upperparts partsof ofoutcrops outcrops"b" "bl' and and"c" "c"reveal revealthat that consists of of feldspar, feldspar' quartzl sericite, ±chlorite. the degree of fragment elongation elongation is greater greater than than the the degree degreeof offlattening. flattening. Elongation lineations plunge plunge moderately moderately to to shallowly shallowly to to the the west. west. The outcrops, outcrops, particularly "b" llbll and and "c", llclll display display evidence evidence of of irregularly irregularly developed, developedl dissemidisseminated carbonatization, light-brown-weatheringl quartz-carbonate quartz-carbonate veins. veins. carbonatization, as as well well as asdeformed, deformedl light-brown-weathering, Pyrite 3 mm) are are present present in inthe thecountry country rock. rock. Within Within this zone Pyrite cubes cubes upto up to55 mm rnm across across (commonly (commonly3 of carbonatized carbonatized rocks, fragments, which which contain contain chloritekbiotite, chlorite±biotite, may have quartz quartz rocks' the more more mafic fragments, are intruded by aa foliated pyrite cubes. cubes. These outcrops outcrops are foliated (Archean?), (Archean?), carcarphenocrysts and pyrite bonatized, bonatized, biotite biotitelamprophyre lamprophyre dike. dike. The south face of of outcrop outcrop "b" "b" shows shows folded, foldedl quartz-carbonate quartz-carbonate veins veins and and schistose schistose planes planes with lineations. The with 2 and possibly possibly 3 sets of crenulation lineations. The south south end end of of outcrop outcrop "c" shows shows a planar fabric compared to the fabrics in the the fragments. fragments. There fabric in the matrix matrix that is oriented differently compared There are also a few, few, west-plunging' west-plunging, minor folds folds with with "S" asymmetry. �Road Log — Heron Bay Area 39 Structural Structural Summary: Summary: Outcrop "b": 'b": Predominant (undulating) Predominantfabric fabric —270/87 -270187 (undulating) Crenulation Crenulation lineations: lineations: 090/00±07 09010M7 L1 LLC* —088/67 L). -088167(overprints (overprints L,). consists of short, consists short, small-amplitude, small-amplitude, small-scale, small-scale, anastomosing anastomosingcrenulations. crenulations. L1 Ll L, is predominant. predominant. Outcrop "c": "cn: General flattening 240/50 flatteningof of fragments fragments 240150 Fabrics in fragments (anastomosing): predominant 258/? predominant 245/? 24519 and subordinate 25817 matrix: 268/? Fabric in matrix: 2681? Elongation lineation lineation (fragments): Elongation (fragments): Le 280/30 280130 275/75; 290/44 Minor "S" " Sfold: fold: axial plane 275175; axis 290144 Quartz-tourmaline Quartz-tourmaline veinlet veinlet 240/60 240160 THOLEIITIC PILLOWED Stop 3: Stop 3: THOLEIITIC PILLOWED FLOWS FLOWS (Figure (Figure 14) 14) Location: north on Highway Highway 627, from the the railway railway crossing crossing at Heron Heron Bay, to to an an outcrop outcrop Location: Go 4.2 km north 627 from on the west side where a power line crosses the the highway. highway. This is a minor stop and is intended to illustrate belt are are relatively relatively undeformed undeformed compared compared to illustratethat that some some segments segmentsof of this this part part of the belt to rocks rocks in in the Hemlo deposit vicinity. Discrete Discretezones zones of of significant significant strain, up up to several metres thick within pillowed flows exposed on the shoreline mafic pillowed flows for example, example, are are well exposed shoreline of Lake Lake Superior Superiorat at Pulpwood Pulpwood National Park to to the the south. south. However, Hemlo deposit, Harbour in Pukaskwa National However, in the vicinity of the Hemlo significant significant strain strain is is essentially essentiallypervasive. pervasive. Several The more more northerly northerlyones onesconsist consistof of aa "massive", "massive", Several small outcrops constitute constitute this stop. The mediummafic,tholeiitic tholeiiticflow. Oneoutcrop outcropdisplays displayswhat appearstotobe beaadike with medium- to fine-grained, fine-grained, mafic, flow. One what appears dike with highly irregular Themain mainoutcrop outcropconsists consistsof of mafic, mafic, tholeiitic tholeiiticpillows pillowsand andaa "massive" "massive" irregular orientation. orientation. The section, possibly part part of the same flow. Although the pillows pillows are somewhat flattened, they have flow. Although well-defined shapes preserved and indicate well-defined indicate that that the the top top direction direction is toward toward the the south. south. The most southerly outcrop exposes exposes aa section section that thatdisplays displayspossible possibleflow flowbanding bandingand andwhat whatappears appearsto tobe beaa southerly outcrop breccia or pillow breccia. Minor Minorquartz±carbonate quart*carbonate veins veins are arepresent, present, particularly particularlyininthe the flow top breccia main outcrop. Structural Structural Summary: Summary: S —100/75 "flattening" Sp 400175 "flattening"of of pillows pillows V 190/25 quartz-carbonate V 190125 quartz-carbonate vein vein * Stop Stop 4: 4: NORTHERN EAGLE NORTHERN EAGLE PROPERTY PROPERTY(Figures (Figures14 14&& 17) 17) Permission for access to the property is required, required. In formation on whom to contact Permission Information contact should should be Resident Geologist's page). obtained from the Resident Geologistk Office, Thunder Bay (see address on title page), Location: Return north to Highway Location: Highway 17 17 and head head 6.3 km east on Highway Highway 17 17 to the the Black Black River River bridge, the east end end of of the the bridge. bridge. (This point can be more more accurately accurately bridge, then continue continue 900 900 m m beyond the located gravel road, locatedby bynoting notingaagravel road, that thatheads headssouth southfrom fromthe the highway highwayabout about650 650m mfrom from the the bridge, bridge,then then continuing320 320 m m beyond beyond it, it, to to aa point point 30 m past the Beaver Beaver Tourist Centre Take the the diamond diamond continuing Centre sign.) Take drill road, which is on the north side of Highway 17 at at this this point, point, and follow it, essentially essentially north, north, for about 230 230 m to a power [Note: As of 1993, aanew about power line. line. [Note: newsubsidiary subsidiary powerline powerline now now crosses crosses the the highway here rendered delineation delineation of difficult. However, here and and has rendered of the the drill drill road road difficult. However,the thedrill drill road roadintersects intersectsthe theeast east side of the powerline powerline right-of-way near the the west the highway.] highway.] Cross the power line (slight jog to the across continue on essentially north, across a small creek) and and continue on the same drill road, again essentially north, to to aa small hill. Go Go �4ab end of clearing / 4ab 5bc 5ac 2a3d 411a 6 —3d,2? 4b 4ab - 4dba 4b- 0 3a 2 - 54acj 4a 5ab_t 4c - 4c(a,b)'2a 4b 2d,3c garnet 3ab 4b,3ab 3a 3a 4b,3ab 2dbc C 4 3a 6 -4b 4a,3a 14e 4aI' 2b a3a 2b 8 4b'4b 1 4e,5b \p Trench 4 m °4a 4ab 5d 2b 4a.(2b) 4d e5c 5d 4ab 5c - 4cac 4c /4ba Trench 1 x=rocks with distinctive spaced cleavage 4ba ,_2d 5a- 4b 4c 2d3c -2d A CD 3 0 -' CD CD 0 -I' Cl) 0 Cl) -C CD a a 0 G) a p) 0 0 CD CD G) 0 Geology and Gold Deposits of the Hemlo Area �Road — Heron Road Log Heron Bay Area Figure legend below) Figure17. 17. (Opposite (Oppositepage, page, legend below) Northern Eagle property. Detailed Stop 3: 3: Eagle property. Detailed sketch map of the main barite showing. showing. Upper Upper part of figure figure represents represents the west half of the the stripped area. area. Lower Lower part part represents representsthe the east east half. Point Point"A" "A" in each part of figure figure represents represents the same geographic geographic location. location. Identification Identification of alteration is minerals and alteration is based basedon on field field obserobservations and and interpretation. interpretation. (Geology by by T.L. T.L. Muir, OGS, 1990). 1990). LEGEND: STOP STOP 4 LEGEND: Mafic Metavolanics(?) ~etavolanicd?) 1 1 biotite+amphibole biotite+amphibole schist (mafic), (mafic), subgneissic subgneissic Metamudstone 2a 2a black black 2b 2b 2c 2c dark gray dark 2d 2d medium—light gray gray medium-light mediumgray, gray, sandstone medium sandstone Altered Rocks Mudstone Rocks Derived Derived from from Mudstone 3a 3a sericitekbiotite (laminated, cleaved) cleaved) sericite±biotite (laminated, 3Sb b sericite+biotite+pyrite (laminated, cleaved) cleaved) sericite±biotite+pyrite (laminated, 33c c 3d 3d feldspar+sericite+green feldspar+sericite+green mica+pyrite mica+pyrite schist feldspar+sericite schist feldspar+sericite schist Altered Rocks Rocks of of Undetermined Undetermined Protolith Protolith Schistose Schistose 4aa 4 4b 4b 4c 4c 4d 4d 4e 4e feldspathized sericitized, feldspathized sericitized, pyrite sericitized, sericitized, green green mica, mica, pyrite pyrite sericitized, silicifled sericitized, silicified sericitized, sericitized, silicified, silicified, barite barite Granular 5a 5a feldspathized+silicified+ barite feldspathized.i-silicified±barite 5b 5b 5cc 5 5 5dd feldspathized+pyrite (commonly feldspathized+pyrite (commonly in in seams)+barite seams)tbarite silicified±feldspathized+pyrite silicified* feldspathized+pyrite barite—richsilicifiedfeIdspathized±pyrite barite-richtsilicified~feldspathizedkpyrite Dikes Dikes 6 / / feldspar porphyry porphyry quartz vein quartz 41 41 over the the hill on an old grid line to a up and over m from from the the power powerline. line. clearing, about 360 m The road road and grid line are flagged flagged and and recut recut for this this trip. the Northern Northern Eagle Eagle For the most part, the property structurally overlies overlies south-dipping south-dipping mafic metavolcanic metavolcanic and and metasedimentary metasedimentary rocks. In Inthe the stripped strippedarea, area, exposures exposureshave have been overastrike been created over astrikelength lengthof ofabout about100 100 m and a width width of up to to 12 m m (Figure (Figure 17). 17). The showing showing is is now now considerably co-nsiderablyovergrown overgrown and and oxidized in parts. parts. In 1995, significant additional stripping stripping was undertaken undertaken to the north, north, adjacent to the original stripping. This adjacent stripping. This new new exposure has not been mapped by the auauthor. As presently presently exposed, exposed, the the outcrops outcrops consist of argillite, argillite, which which locally locally has has been been moderately to intensely altered and demoderately to intensely altered deformed, massive massive to laminated laminated barite barite and and sulphide minerals, minerals, sericite sericite schists, minor mafic schists, and feldspar In feldspar porphyritic porphyritic dikes. dikes. In earlier reports, these rocks collectively collectively have have interpreted to been interpreted to be be barite±sulphide-bearbariteksulphide-bearing cherts and quartzites, quartzites, as graphitic as well well as graphitic argillite, siltstone, quartz ÷+ seriargillite, siltstone, arkose, arkose, quartz sericite±carbonate±limoni schists, "massive" "massive" cite±carbonate±Iimonite barite, and barite, and quartz-feldspar quartz-feldspar porphyries porphyries (MNDM assessment assessmentfiles, files, Thunder ThunderBay; Bay;GlidGlid(MNDM don 1985). don 1985). The western western part of the the stripped stripped area area consists of black to dark dark grey grey argillite, argillite, and and white-weathering rocks, rocks, consisting consisting of feldwhite-weathering spar, quartz, quartz, sericite, sericite, and and green green mica, mica, which which interpreted to be altered altered argillite because are interpreted of the similar of similar cleavage cleavage developed developed in both both rocks and the intimate intimate spatial spatial association association between light light and dark coloured between coloured rocks. rocks. Xenoliths of the green-mica-bearing green-mica-bearing schists are present in the feldspar feldspar porphyry porphyry dikes. dikes. suggests that that the alteration This suggests alteration preceded preceded intrusion, because black black argillite is intrusion, because is locally locally present present as the host rock rock to the dikes, and and itit is considered unlikely that alteration considered unlikely alteration could could have pervasively pervasively altered altered the the dike dike (and (and xenolith) and not the immediately immediately adjacent adjacent councountry rock. The The porphyritic porphyriticdikes dikesare are similar similar to inferred to have have inindikes at Hemlo that are inferred truded at truded at 2687±3 2687± Ma Ma (Corfu (Corfu and and Muir Muir 1989a). 1989a). �42 42 Geology and Gold Deposits Deposits of the Hemlo Area If the the alteration alteration exposed property was contemporaneous contemporaneous with exposed at the Northern Northern Eagle Eagle property withthe themineralizmineralization of the Hemlo Hemlo deposit, and if the porphyry dikes at this stop are coeval with those at at the the deposit, then then aa minimum minimum age age of of mineralization mineralizationisis2687±3Ma. 2687±3Ma The majority of the remainder remainder of the exposures in the east part of of the the stripped stripped area area are are interpreted to be be highly highly altered altered rocks rocks derived derived from from an anequivocal equivocalprotolith. protolith. However, several several outcrops along the north north side and east east end endreveal revealgrey greyand anddarkgrey darkgreyargillitic argillitic metasiltstones metasiltstones which which outcrops along locally schists. An locally can can be seen to grade relatively abruptly into white to buff schists. An isoclinal isoclinalfold fold can can be be seen near the east end of the stripped stripped area. The The main mainfabric fabrichere hereis isaxial axial planar planarto to the the fold fold and and is is parallel weakly defined layering in inthe thesiltstone. siltstone. Transposition and differentiation differentiation of the layering parallel to weakly layering appears appears to have have locally locally taken taken place. place. As Assuch, such,the thelayering layeringpresent presentin inthese theseoutcrops outcropsshould shouldnot notbe be assumed to be bedding. In Inthis thisarea, area, several several discordancies discordanciesof of fabrics fabrics and and layering layering can can be be seen suggesting suggesting faulting faulting has has taken taken place. place. There trenches across exposed area. These variety of There are are 4 trenches across the width of the exposed These trenches trenchesreveal revealaavariety schists and "massive" rocks which are heavily weathered. weathered. The rocks are considerably considerably deformed and appear to have resulted, based on field identification (i.e., (i.e., no laboratory laboratory confirmation) confirmation) from from feldspathization, silicification, sericitization, and and pyritization, pyritization, which which in in places places is is reminiscent reminiscent of of alteration at alteration at the the Hemlo Hemlo deposit deposit(e.g., (e.g., Stop Stop33A) 33A) and/or and/or the the Barren BarrenSulphide SulphideZone Zone (Sucker (SuckerZone) Zone) (Stop 14). The The schists schists range range considerably considerably in in their their content content of of green green mica, mica, barite, barite, feldspar, quartz, quartz, sericite, and and pyrite. pyrite. The Thegreen greenmica micahere hereisissomewhat somewhat different different in in colour colour than than that that of of the the Hemlo Hemlo deposit and thus may contain different types or relative abundances of trace elements. The green deposit and relative abundances of trace elements. along cleavage cleavage planes. planes. Pyrite is mica at this stop is largely present in flattened lenses and along is the The barite occurs in common sulphide. The in zones zones of of various various concentrations concentrations and and isiscommonly commonly equigranular and and fine fine grained. grained. Gliddon recrystallized. Barium equigranular Gliddon (1985) interprets it to have been recrystallized. Barium occurs in trenches trenches ito barite-rich zones occurs 1 to33ininamounts amountsininexcess excessof of 20% 20% (Cavey (Cavey 1984). Some Some of the barite-rich zones variably laminated laminated parallel parallel to tothe thepredominant predominantfabric. fabric. The The origin originof ofthe thebarite bariteisiscontentious. contentious. It are variably appears here to be spatially associated associated with with shear shear zones zones (Gliddon (Gliddon 1985) 1985) and and alteration, alteration, and andlies lies within isoclinally isoclinally folded folded and tectonically tectonically disrupted disrupted argillite. results from these trenches returned returned values of of 50.005 0.005 oz Assay results ozof ofAu/short Aulshortton, ton,up upto to 32.76% 32.76% Ba in zones containing containing barite, barite, and and up up to 1000 1000 ppm As (MNDM (MNDM assessment files office, office, Thunder Thunder Bay). Gold ton have been reported reported (Northern 1983, Goldvalues valuesup upto to0.12 0.12 oz. per ton (NorthernMiner, Miner,November November23, 23,1983, p.23), but were not noted noted in the assessment assessment files. Structural Summary: Structural West end: end: Fabrics Fabrics at at 090/80, 090180,and and 077/83 077183 in argillite argillite Foliated Foliated dike oriented oriented at 265/56 265156 with internally internally deformed deformed quartz quartz veins veins Central: Central: Fabrics at 082/77 and 072/77 in in green mica mica schist schist 084171 plane of west-closing isoclinat isoclinalfold fold at at084/71 East East end: end: Layering and axial plane Fabric Fabric overprinting overprinting fold at at 095/77 095177 cleavage at Faint cleavage at 077/79 077179 �Road Road Log Log — -Introduction Introduction 43 HEMLO AREA AREA SEGMENT: SEGMENT: HIGHWAY HIGHWAY17 17 HEMLO Figure 18 18 displays the location location of of field field stops stops numbered numbered 5 to 31 inclusive. Figure Figure19 19(inside (inside Figure back back cover) cover) and and Figure Figure 20 illustrate illustrate the lithologic lithologic units units and and major major structural structural components components in in more more detail. detail.Figure Figure21 21shows showsthe the"cultural" "cultural"features featuresand andprojected projectedore orefor forthe theHemlo Hemlodeposit depositand andvicinity, vicinity, and and includes includes locations locationsfor for Stops Stops 77 through through 26. Figure Figure22 22 depicts depictsaa projected projectedlongitudinal longitudinalview viewof of the (*) Hemlodeposit deposit at at the the same same scale scale as as in in Figure Figure 21. 21. Note, Note,an an asterisk asterisk(*) the main mainore ore zone zone of of the the Hemlo indicates indicatesfield fieldstops stopsintended intendedfor forthe the3-day 3-dayoverview overviewfield fieldtrip. trip. Stop INTERIOR OF OF CEDAR CEDAR LAKE LAKEPLUTON PLUTON(Figures (Figures14 14and and18) 18) Stop5: 5: INTERIOR Location: km east east of of the the Highway Highway 614 turnoff turnoff (to Location: Highway Highway17, 17, about about 1.1 1.1 km (to Manitouwadge), Manitouwadge),ororififone one is Creek which enters iscoming comingfrom fromthe theeast, east,ititisisabout about3.7 3.7 km km west west of Wabikoba Creek enters Cedar Cedar Lake. Lake. The The stop stopisisat at the the west west end endof of aa long long roadcut roadcut on both both sides sides of the highway. The The following followingdescription descriptionisis based basedon on the the westernmost westernmost 75 75 m m of of the the roadcut roadcut on on the the north-northwest north-northwestside. side. The The majority majority of of the theCedar CedarLake LakePluton Plutonconsists consists of of very veryweakly weakly totomoderately moderatelyfoliated, foliated, medium-grained, microcline-megacrystic, microcline-megacrystic, hornblende-biotite hornblende-biotite granod granodiorite contains ubiqubiqmedium-grained, iorite that contains uitous mafic/ultramafic(?) xenoliths. This main main phase phase has has been been intruded intruded by by aanumber number of of uitous mafic/ultramafic(?) xenoliths. This subordinate,fine-grained, fine-grained,more moremafic maficphases. Themegacrystic megacrysticphase phaseatatStop Stop5 hasbeen beendated dated at at subordinate, phases. The 5 has 2688±3 2688± Ma Ma (Corfu (Corfu and and Muir Muir 1989a). 1989a). The The effects effects of of hematization hematization and and epidotization epidotization are are locally locally present, present, and and may may be be extensive. extensive. There There isissome some evidence evidence that that this this type type of of alteration alteration may maybe be associated with fault zones. associated with fault zones. Other Other exposures exposures of of this this phase, phase, such such as ason onHighway Highway614 614toto Manitouwadge, Manitouwadge,display displayaa wider wider variety varietyof of xenoliths xenolithsand anddikes, dikes, including includingaplite apliteand andpegmatite. pegmatite. Themicrocline microclinemegacrysts megacrystsrange rangefrom frommedium mediumto tocoarse coarsegrained, grained,up uptoto2.5 2.5cm cmlong, long,and and The contain contain fine-grained fine-grained crystals crystals of of hornblende, hornblende, quartz, quartz, plagioclase, plagioclase, and and possibly possibly biotite. biotite. Crude Crude zoningisisapparent apparentininsome somemegacrysts. megacrysts.The Thexenoliths xenolithsrange rangefrom fromabout about55mm mmtoto30 30cm cmlong, long,and and zoning are are most most commonly commonly about about 2 to to 44 cm cm long. long. Most Mostofofthem themappear appeartotobe befine-to fine-tomedium-grained medium-grained amphibolite, amphibolite, although although some some appear appear to to have have little littleor or no nosalic salicminerals mineralsand andare are hence hencepresently presently ultramafic. ultramafic. The The xenoliths xenoliths are are generally generally aligned aligned parallel parallel or subparallel subparallel to the the foliation foliation in in the the granodiorite,where wherethe thelatter lattercan canbe bediscerned. discerned.The Theorientation orientationofofthe thefoliation foliationisissimilar similartotothat thatof of granodiorite, S3 Soin in the the country countryrocks rocksand andisisinterpreted interpretedtotobe bemost mostlikely likelyrelated relatedtotoD3. Do. Themegacrystic megacrysticgranodiorite granodioriteatatthis thisstop stophas hasbeen beenintruded intrudedby byaafew fewintermediate intermediatedikes, dikes, The likely Archeanage, age, and and aa Proterozoic Proterozoicbiotite biotite lamprophyre lamprophyredike. dike. The TheArchean Archeandikes dikesare aresheared, sheared, likelyof ofArchean with withan anapparent apparentdextral dextralsense. sense. This Thisrelationship relationshipand andthe thepresence presenceofofan an"S3-oriented" "So-oriented"fabric fabric within postdated intrusion withinthe thepluton plutonsuggests suggeststhat thatatatleast leastsome someof ofthe the D3 Dostrain postdated intrusionand andcrystallization crystallization (i.e., (i-e,,2688 2688Ma). Ma). Structural StructuralSummary: Summary: S9 Sgranges rangesfrom from260/70 260170toto275/60; 275160; alignment alignmentofofmafic maficminerals mineralsiningranodiorite granodiorite shearedintermediate intermediatedike; dike;fabric fabricsubparallel subparalleltotodike dikemargins margins Sd Sd 302° 302' sheared dike;biotite/hornblende; biotitehornblende;back backrotated rotated Sa Sa 281° 281 inindike; Sb Sb 327° 327' inindike; dike;deflects deflectsSa Sa DD 145/70 14-5/70 lamprophyre lamprophyredike dike * Stop Stop6:6: WEST WESTCONTACT CONTACTOF OFCEDAR CEDARLAKE LAKEPLUTON PLUTON(Figures (Figures14, 14,18 23) 18 &&23) LocatIon: Location: Go Goabout about1.1 1.1km kmwest-southwest west-southwestof ofthe theHighway Highway614 614turnoff turnoff(to (toManitouwadge) Manitouwadge)on on Highway Highway17, 17,to to the the contact contactof ofthe theCedar CedarLake LakePluton Plutonnear nearthe theeast eastend endofofaalong longroadcut roadcutbeginning beginning on onthe thenorthwest northwestside sideofofthe thehighway. highway.The Thelast lasthighway highwayexposure exposure(in (inthis thisdirection) direction)ofofmicroclinemicroclinemegacrystic megacrysticgranodiorite granodioritelies liesabout about300 300mmeast-northeast east-northeastofofhere. here. �5 A A0 BAA ^</ otham A Williams Mine A e Hwy 17 Manitouwadge If / White River 0 CD 0 0 CO a. Yellow Brick Road 0 0 a a CD 0 Cl) 0-1 I CD CD 3 0 -' CD �— Hemlo Area Road Log - 45 45 The contact contact phase phase of of the the Cedar Cedar Lake LakePluton Plutonisisfinefine-totomedium-grained, medium-grained,biotite-hornblende biotite-hornblende granodiorite weak foliation within several several metres metres of the the contact. contact. This granodioritewhich whichisismassive massiveexcept exceptfor for aaweakfoliation This phase is not exposed exposed elsewhere the bush phase elsewhereon on roads roadsor or railways railwaysand and its its extent extentin in the bush is is unknown, unknown, as as is is its its relationship phase(s) (see 5). The relationshipwith with the the main main megacrystic megacrysticphase(s) (seeStop Stop5). The granodiorite granodioriteatStop at Stop66has hasbeen been 2687± Ma Ma (Corfu (Corfu and and Muir Muir 1989a). 1989a). dated at 2687±3 to 40 cm thick, thick, and some pegmatitic pegmatitic The granodiorite is intruded by many aplite dikes, up to cmthick. thick. Some of of the the dikes dikes are arecomposite composite aplitelpegmatite. aplite/pegmatite. Although dikes, up to 10 cm Althougheither eithertype type may crosscut the other, other, more often often than not, pegmatitic dikes crosscut aplite dikes. The Thedikes dikes terminate against against the the schist, ductile deformation within the contact terminate schist, although some some display display ductile deformation within contact granodiorite (Photo granodiorite (Photo 1). 1). This This may may indicate indicate that that extensions extensions of the dikes into the country rocks have been sheared off. The The dikes dikes display display aa range range in in strike strike but tend to have preferred preferred orientations orientations as as approximated approximatedbelow. below. DIke orientations: orIentations: Dike 305/52 5 m from contact 290/64, 290164,305152 260±5°, 290±5O 290±5°, 330S0 330±5° 10 m from contact contact 260±5O 65 m from contact 250±5°, 250±5O270±5° 270±5 The country within about The country rocks within about 9 m m of of the the contact contact consist consist of of crenulated crenulated mafic mafic schist schist containing containing several several aplitic aplitic and and granodioritic granodioriticdikelets dikeletsand andstringers stringerswhich which display displayrefolded refoldedfolds foldsand and are locally dismembered. dismembered. Refolded dikeletsadjacent adjacentto to granitoid granitoidbodies bodiesin in the the area area Refoldedfolds foldsin inaplitic aplitic dikelets have been noted elsewhere elsewhere (e.g., (e.g., Cedar CedarCreek CreekStock, Stock,Pukaskwa PukaskwaBatholithic BatholithicComplex). Complex). Although Although it may be inferred inferred that these refolded by F3 (which is is associated associated with the crenulation these are are F2 F, folds refolded Fy (which crenulation fabric), this poses poses problems based on the inferred timing of intrusion relative to regional regional folding folding be more more likely likely that, that, during during intrusion, intrusion, differential differential ductile movement (see Stop 11). It may be movement between Stop 11). relatively softened, contact-metamorphosed relativelysoftened, contact-metamorphosedcountry countryrocks rocksand and the the intruding intruding granitoid granitoid magma, led to marginal-restricted marginal-restricted zones zonesof of progressive progressivedeformation deformationthat thatdid didnot not produce produceanalogous analogousstructures structures farther farther away away from the plutons. plutons. To the the west west of of the the crenulated crenulated mafic schists, schists, for for about about 15 15 m, m, the the country country rocks rocks consist of of a To mixture of mafic, biotite-hornblende schist (either of sedimentary or igneous origin), pyritiferous argillitic rocks, dikeletsand and argillitic rocks, and and some some metawacke, metawacke,all all of of which which have have been been intruded intrudedby by aa few few aplitic aplitic dikelets quartz veins. veins. Within this schist, a granodioritic granodioritic dike intruded intruded by quartz quartz veins veins contains contains minor minor molybdenite, molybdenite, although although most most of this this has has been "excavated" "excavated" by by moly-thirsty moly-thirsty "geotourists". "geotourists". For approximately approximately the the next next 150 150 m, m, the the country rocks consist For consist mostly of various various sets sets of of metawackes and metasiltstones which which have been been intruded intruded by by swarms swarms of of dikes. dikes. These These sets are crudely differences in layering layering thickness, thickness, composition, composition, and and grain grain size. size. Several crudely defined defined based on differences sets consist of feldspathic metasandstones and, and, in in at at least least one onecase, case,possibly possiblyquartzite. quartzite. A few gossans occur in some of the feldspathic metawackes. There There are are several several isoclinal isoclinal folds folds which which have developed locally. have developed locally.AAfew fewof of these theseappear appearto to be be intrafolial. intrafolial. InInthe thefirst firstoutcrop outcropto tothe thewest westof of the the "Yellow Brick Road" highway sign, the S2 S2 fabric is clockwise clockwise with with respect respect to to layering, layering, as as ititisisat at Stops Stops 66 (west (west end) end) and and 77 (west (westend). end). Figure 18. strip map map of of the Highway 17 section of (opposIte page) Three-component strip Figure 18. (opposite field stops numbered area. The numbered 5 to 31 inclusive, for the Hemlo area. The uppermost uppermost strip strip represents representsthe the west third; the lowermost lowermost strip represents represents the east east third. East and west boundaries boundaries defining defining connected strips are are mutually mutually adjoining adjoining (i.e., (i.e.,no no overlap). overlap). Only the outcrops outcrops for field field stops stops described in this road log are shown. described in this road log are �LSSZ Lake Superior Shear Zone 82, Sg in granitoids Figure 20. Form-surface map of the Hemlo deposit area showing generalized traces of different generations of fabrics. (Modified after Muir and Elliott, 1987). HFZ Hemlo Fault Zone •.. High Strain Zone '— Supracrustal/Granitoid contact So, Si, and/or Sm (mylonitic) Form Surface Lines 0 0) 3 0 -' CD CD CD I 0 C') 0 C/) CD a 0. 0 0 0. (0 0 0 CD Geology and Gold Deposits of the Hernlo Area �Road Log — Hemlo Area 47 The dikes within the above-mentioned above-mentionedsets sets comprise compriseaa wide wide variety variety of foliated granitoiddikes dikes foliated granitoid mostly of weakly as well as some some mafic mafic dikes dikes that that display display boudinage. boudinage. The granitoid dikes consist mostly foliated granodiorite, granodiorite, which is is similar in grain size and composition to the marginal marginal phase of the Cedar Lake Pluton, and some some plagioclase-porphyritic plagioclase-porphyriticdikes. dikes. The The granitoid granitoid dikes dikes have have been been intruded by fine-grained, dikes. The Therelationship relationshipbetween betweenthe the granitoid granitoid fine-grained, intermediate-composition intermediate-composition dikes. dikes and the mafic dikes (Archean) is not established. established. A A small small diabase diabase dike (Proterozoic) (Proterozoic) has intruded the country rocks. Structural StructuralSummary: Summary: S1 330/66 84 m S, 330166 m from the contact contact S 318/52 mafic S predominant predominant 318152 mafic schist schist 296/57 S3 crenulation crenulation S3 296157 crenulation Ilneation LC 104126 crenulation lineation L 104/26 METASEDIMENTARY ROCKS 14,18,19 & 23) ROCKS AND GRANODIORITE GRANODIORITE SHEET (Figures (Figures 14,18,19 Stop 7: Stop 7: METASEDIMENTARY essentially a continuation continuation (for Stop 6. 6. For Location: Stop Location: Stop 7 is essentially (for another another 200 m) of the roadcut for Stop the most part, the features features described described here here are are on on the southeast southeast side of the the highway. highway. The Thestop stop begins about west of of the the "Yellow Brick Brick Road" Road" highway highway sign. sign. The about 65 m west The more more important importantfeatures featuresof of this roadcut roadcut are are at at the the east-northeast east-northeastend, end,say, say, for for the the first first 80 80 m m (see (see Figure Figure23). 23). In the northeast northeast end end of this outcrop is a thick, composite composite sheet sheet of of foliated, foliated, medium-grained, medium-grained, plagioclase-porphyritic, biotite-amphiplagioclase-porphyritic,amphibole-biotite amphibole-biotitegranodiorite, granodiorite,and and foliated, foliated, finer-grained, biotite-amphibole granodiorite, granodiorite, both bothof of which which were were intruded intrudedby by aplitic aplitic dikes dikes and and subsequently subsequentlyby by quartz quartz veins. veins. bole The granodiorite occurs occurs as as "layers" or sheets, The finer-grained finer-grained granodiorite "layers" or sheets, parallel to the the foliation. foliation. The relationship between established but circumstantial circumstantial evidence relationship between the the two two phases phases is is not not well established evidence suggests suggests that the finer-grained younger. Aplitic dikelets finer-grained phase is younger. dikelets in the country country rocks rocks are are folded folded about about the foliation. Thedikelets dikeletshave havealso alsobeen beensinistrally sinistrallyoffset offsetin in a number of places. phase foliation. The places. The porphyritic porphyritic phase has been 2687±Ma Ma(Corfu (Corfuand andMuir Muir1989a). 1989a). been dated dated at at 2687±3 Across Across the highway highway at the the structurally structurally lower lower contact contact of of this this sheet, sheet, apophyses apophyses of of the the porphyritic granodiorite porphyritic granodiorite are are folded foldedabout aboutaa less lesssteeply steeplydipping, dipping, S2-like So-likefoliation, foliation, with with attendant attendant attenuation and boudinage which has taken place in two two dimensions dimensions (features (features on on horizontal horizontal section are no longer longer visible). visible). This relationship relationship could could suggest suggestthat thatthe theintrusions intrusionspredated, predated, orwere orwere section the overall overall deformation deformation of of the S2 synchronous with, the D2 Doevent. event. However, However, the So fabric near near the the granitoid bodies Hemlo area area suggests that the intrusions intrusions post-dated post-dated most, most, ifif not not all, all, the the D2 Do granitoid bodies in in the Hemlo deformation (see deformation (see Figure Figure 20). The units of metasedimentary metasedimentary rock west of the granodioritic sheet sheet consist consist of of aa variety variety of of metawacke with minor amounts of of metasiltstone. metasiltstone. Different Differentunits units collectively collectively display displayaarange rangeof of biotite/amphibole biotitefamphibole ratios ratios from biotite biotite predominant predominant to amphibole predominant. As As exposed exposedin in the the roadcut, be crudely crudely subdivided subdivided into into several several sets, sets, based based on on roadcut, the metasedimentary metasedimentary rocks can be composition, composition, grain-size, grain-size, and and layering layering thickness thickness and and definition. definition. Metasedimentary units west of the sheet sheet (for (for about about 120 120 m), m), display display layering layering that that tends tends to to become S2 cleavage cleavageis isnot notdistinct distinctfrom fromlayering, layering,which suggests: transposition transposition of become wispy. Here, Here, the So which suggests: the intersection intersection of S, S1 and and So S2isisessentially essentiallyhorizontal. horizontal. Vertical layering has taken place; or the Vertical faces faces cleavage that that strikes strikes parallel parallel to to the the layering layering and and dips dips less less steeply steeply to to the the locally show an S2-like So-like cleavage fold axes axes are are essentially essentially horizontal horizontal here. here. Subhorizonnortheast. This Thiswould would suggest suggest that that the the F2 F2fold tally plunging visible in the the roadcut roadcut face. face. Insufficient plunging folds in some mafic dikes are visible Insufficientinformation informationis is define the character 7, to available to define characterof of the the range rangein in orientation orientationof ofF2 Fnaxes axes from from horizontal horizontalat atStop Stop7, northeast plunging northeast plunging at at Stop Stop 8, 8, to to northwest northwestplunging plungingat at Stop Stop33B. 33B. �03 Hemlo Gold Mines (Goliath Gold Property) Yellow Brick Road South Z w - Teck-Corona Hemlo Gold Mines (Golden Sceptre Property) 0 CD 2. 0 CD - a. G) 0 0.5 0 a km CD XX, - Ore /Subore /Subore Zone Zone at at Surface Surface Ore Up-dip Projection Zone to to Surface Surface Up—dip Prolection of of Ore Zone I2 00 A Shaft Shaft/Headframe /Headframe . • Main Mine Mine Buildings/Structures Buildings/Structures Main Field Field Trip TripStop Stop Mine-Related Mine-Related Road Road 0 C,) o i CD Figure21. 21. Main Main cultural cultural features features of of the theHemlo Hemlocamp, camp, and and up-dip up-dip ore ore projection projection of of the the Hemlo Hemlo FIgure Same scale 26, and 32 to 35 are shown for reference. deposit. Locations of field stop numbers 7 to deposit. Locations of field stop numbers 7 to 26, and 32 to 35 are shown for reference. Same scale (Modified after after Smyk Smyk eta!. eta/.1990). 1990). as Figure Figure 22. (Modified as -' CD �Road Log — Hemlo Area 49 49 of the the roadcut indicate that the S2 cleavage is clockwise with respect The last 50 m or so of respect to layering, relationshipas as with with the the "Jake" "Jake" unit unit(see (seeStop Stop8) 8) which whichisison on the the southwest southwestlimb limb layering, the same relationship of a southeast-closing northwest fold closure closure may may be present within southeast-closing F2 fold. fold. This suggests that a northwest the vicinity of Cedar Cedar Creek Creek where there is is essentially essentially no no exposure. exposure. Ill w w Co) 0 Iii z -l -J 'LI a > a w z I- z a z 'Li a -J 0 C, 'Li z a, -J -J z orebody projected projected onto onto aavertical vertical plane. plane. Property Longitudinal section of the Hemlo orebody Longitudinal Property boundaries projected onto the orebody plane plane before final projection. projection. Same Samescale scaleas asFigure Figure21. 21. (Modified (Modified after after Canadian CanadianMining MiningJournal, Journal, February February1990, 1990,p.28, p.28, 29). 29). Figure Figure22. �Geology and Gold Deposits of the Hemlo Area 50 Co0 • Structural Summary: Structural S0/S1 323/62 away from contact with granitoids Sn/S, 323162 granitoids 336/? S, 3361? toward west end of roadcut S2 S1/S2 granitoids 3 10/49 S,/S, 310149 near granitoids S3? 297/? alignment of amphibole S3? 297/? alignment amphibole Sg 305/? granitoid sheet Sg 305/7 in granitoid sinistral faults in aplitic aplitic dikelets dikelets in Range of sinistral in sheet: sheet: 285° 285O to to 320° 320 I ..2 '0 •00 00,_• fa 00 * Stop 8: CEDAR CREEK FOLD FOLD in in metawacke/ metawackel metasiltstone turbidites (Figures metasiltstone turbidites (Figures18, 18,19 19 & & 24) 24) 0 U — 0 Location: 650 west-southwest Location:GoGo 650mm west-southweston onHighway Highway 17 from from the the Yellow Brick Road Road (Golden (GoldenGiant Giant Mine) Mine) turnoff point at the first turnoff at at the the west west end end of Stop Stop 77 to aa point first large roadcut large roadcut east east of Cedar Cedar Creek. Creek. The set set of of exposures on the south south side side of the the highway, highway, at this roadcut, extends for about 400 m. The The starting starting point for this stop is on the south south side, side, at at aa northeastnortheastfacing rock with the facing rock face with the word word "Jake" "Jake" plastered plasteredon on itit (loathsome (loathsome as as itit is is to acknowledge acknowledgerock rock defacing defacingof of any kind, let alone outcrop painting), painting), assuming that highway maintenance personnel have not painted painted over it in an an attempt attempt to to deface deface the the defacement. defacement. This starting point is about 120 120 m east of a "0 m" m" referreference point at the west end end of this this set set of outcrops. outcrops. 50 0 .2 00 .0 o. 00 z>. C 0 00 The main features of interest lie on both sides this point and further of the highway, between this and 75 m m further along along the highway highway to the the east-northeast east-northeast (i.e., (i.e., at at about 195 m). m). In In this this part part of of the the roadcut, roadcut, aa section section through a mediummedium-to through to large-scale, large-scale, southeast-closing southeast-closing F2 fold fold is unusually well exposed exposed as as a result F, unusually well result of of original construction, despite original highway construction, despite recent recent highhighway "improvements". "improvementsn. 00 0>, •0— 0 :20 0 o * •0 E o 04 U o U 0 5 C 0 V 0 C C 0 C 0 V The outcrops along along this this part of the the highway highway show a variety show variety of of turbiditic turbiditic deposits depositscomposed composed mostly of medium mostly medium grey grey metawacke metawacke and and metametasiltstone. Light and dark grey varieties are locally siltstone. locally Ic metawackes present. Some Somecrenulated crenulatedmaf mafic metawackes are are exposed at 2 exposed 2 places, places, at at about about 55 55 m m and and 300 300 m m(see (see Figure 24) 24) and are inferred to be folded about the which is Cedar Creek fold axis axis which is located locatedat atabout about163 163 m. These Thesemafic maficmetawackes metawackes also also contain contain minor minor conglomeratic components conglomeratic componentsconsisting consistingof of wacke wacke and and sub-porphyritic granitic clasts subporphyritic clasts in a mafic matrix. LoLocally there there are are unidentified unidentifiedretrograded retrogradedporphyroporphyroparticularly just just to the west of blasts (andalusite?), particularly the eastern, mafic schist unit. A fewmicaceous micaceous eastern, schist unit. Afew gossans occur on both sides of the axial gossans occur on both sides of the axialplane. plane. It is is not clear any of the gossans not clear whether whether any gossans can be be matched across the axial matched axial plane plane as as folded foldedunits. units. FIgure 23. Stops 6,7: Simplified contact of the Cedar Figure Stops 6,7: Simplifiedsketch sketchmap map of the west contact Cedar Lake Lake Pluton Pluton (Stop (Stop 6) and adjacent metasedimentary rnetasedimentaryrocks rocks(largely (largelymetawacke) metawacke)and andgranitoid granitoidsheet sheet (Stop (Stop7). 7). �____ __ _ ______________ Road Log — Hemlo Area 51 51 The "Jake" 24) is a reference turbidite for this stop in "Jake" unit (see Figure 24) reference turbidite in terms terms of of primary primary features, m). The The "Jake" "Jake" unit unit(Photo (Photo2) 2)is features, and and isto is to be be compared comparedto to the "anti-Jake" "anti-Jake"unit unit (at (at about 193 m). is interpreted turbiditeunit unitin in the the following following context. context. The The structurally structurallylower lowerhalf half of the unit unit is fine interpreted to be aaturbidite fine grained, light weathering, and quartzo-feldspathic. quartzo-feldspathic. The Thestructurally structurallyupper upperhalf halfisiscoarser coarsergrained, grained, darker weathering, weathering, biotite- ±amphibole-bearing, and has has aa set set of of laminations defined defined by mafic ±amphibole-bearingand minerals in its uppermost uppermost part. The minerals Thedarker darkerhalf half is is considered consideredto to be bethe the upper, upper, more more silty silty part part of of the the turbidite turbidite deposit deposit which, which, through throughmetamorphic metamorphic recrystallization, recrystallization,has hasbecome becomecoarser coarsergrained grainedthan than the lower quartzofeldspathic part. lower quartzofeldspathic part. AAtraverse traversealong alongthis this section section of of the the exposure exposure to the "anti-Jake" unit (this unit is is not not likely likely the same bed bed as the "Jake" unit, but is an unmarked unmarked reference reference unit unit for comparison) reveals reveals bedding bedding deformed deformed about about the the fold fold axis, axis, with preservation of the comparison) the turbidite turbidite features northeast limb. structurally lower features in in reverse reverse on the northeast limb. That Thatis, is, the laminations laminationsare are on on the structurally lower part part which is interpreted to indicate overturned of the unit, which overturned bedding. Within the lame F2fold, fold, the thelayering layeringthickness thicknessisisgreatly greatlyexaggerated, exaggerated,pseudof pseudoflame the nose nose of of the theF2 have developed developed from incipient incipient transposition of layering, and recrystallization recrystallization is is more more structures have pronounced. AAfoliated, foliated,boudinaged, boudinaged,plagioclase-porphyritic plagioclase-porphyriticdike dike(at (atabout about170 170m) m)isisnear nearand and paraltel parallel to the axial plane. The The strike strikeof of the the foliation foliationappears appearsto to be be parallel parallelto to S2. So. An Anuncommon, uncommon, relatively medium-grained,mafic maficdike relatively fresh, medium-grained, dike which which is chemically chemically equivalent to calc-alkalicandesite calc-alkalic andesite has intruded the mafic mafic metawacke metawacke of the northeast northeast limb limb (at (at about about 296 296 m). m). Possible graded graded bedding at 405 m (end of exposure exposure on the the southeast side) suggests suggests tops are to the southwest, as bedding with with the the "anti-Jake" "anti-Jake" unit. unit. Stereonet construction of the fold indicates indicates itit is is reclined reclined with with aa northeast-trending, northeast-trending,modermodernorthwest-striking axial ately plunging plunging axis axis and a northwest-striking axial plane. plane. Structural Structural facing facing is is toward toward the the northwest. northwest. Exposures Exposures along along the highway highway to the the southwest southwest and and northeast northeast of of Cedar Cedar Creek Creek (about (about 335 335 m m from highway) suggest that anorthwest-closing a northwest-closing fold present, which would would the fold axis along the highway) fold may may be present, produce an overall S-shaped pair of folds. folds. The The axial axialplanar planar cleavage, cleavage, S2, S2, strikes at about about 310°, 310° roughly parallel parallel to the contact contact with the the Cedar Cedar Lake Lake Pluton Pluton to the northeast northeast (Stop (Stop 6), and and oriented oriented 40° clockwise relative 40' clockwise relative to to Stop Stop 13. 13. Another fabric be 53. S3. fabric is is weakly developed developed throughout throughout the folded folded strata strata and and is is interpreted interpreted to to be of strike strike span span over over 50 50°which whichsuggests suggeststhat: that: more than one deformation deformation feature Measurements of was measured; measured; or products was measured measured (e.g., S38'S3=, S3, etc.); or more more than than one one component componentof of the the D3 D3productswas (e.g., S3=, etc.); or deformation subsequent to the so-called so-called D3 D3 event (separate or progressive) progressive) has occurred. occurred. Crenulation schistosities measured measured in in the the mafic mafic schist schist (i.e., (i.e., mafic maficmetawacke) metawacke) show show aa range rangein in 26, and orientations which is is consistent consistent with with that that of of other otheroutcrops outcrops (e.g., (e.g., Stops Stops 25, 25,26, and 29). 29). Cedar Creek Cedar Creek fold axial plane axial plane // N /// 0 9 2 0 2P 400 4 60 60 m scale approximate aproximate scale / \60 \/ \r\ ,, L gossan gossan gossan I I "Jake', Jake gossan gossan / zone zone of disarray disarray / (shallow (shallow plunge plunge of of folds. folds, transposed layering) transposed \\' \ ri p—u p clasts dark wacke dark thick bedded dark wacke wacke " \ \ crenulated crenulated mafic schist; minor granule conglomerate conglomerate fl8$C 5' — —4- gossan g,ossan ,9ossan ,flossan Anti Jake /Anti Jake" ° Y I j\ poi - 0 0 2 A " 1" medium—to to coarse-grained coarse—grained medium54 wacke wacke conglomerate F conglomerate \ \\ \ ^, -- Hwy 17 Hwy 17 J.- I\ — - pgabbrol \ ° e I dark wacke feldspar Lhick feldspar porphyry porphyry I" "1w thick bedded bedded —' crenulated wacke crenulated Nmafic porphyry ' fold axis Nsmafic schist schist feldspar retrograded porphyroblasts porphyroblasts retrograded (andalusite?) (andalusite?) Figure 24. Figure 24. Stop 8: Simplified sketch map of turbiditic metawacke metawacke and siltstone units units of of the the (Fo). Cedar Creek Creek fold fold (F2). �Geology Geology and Gold Gold Deposits Deposits of the the Hemlo Hemlo Area 52 52 After completing the section section from from "Jake" "Jake" to to "anti-Jake", "anti-Jake", cross the highway highway and and walk back through this different section of the fold. The through The"beds", "beds", not not all all of of which which show show sufficient sufficient primary primary features for top indications, indications, overall overturned, as expected from features overallreveal revealthe the layering layeringto be overturned, as would be expected an uncomplicated uncomplicated fold, (see next nextparagraph). paragraph). Semi-aligned Semi-aligned rip-up clasts can fold, which which this this may may not be (see to the northeast northeast of the fold axis (see Figure 24). 24). Here, S2 fabric strikes strikes at be seen at a point to Here, the the S2 296°, (S0/S1 at 344°). A sampling of clasts indicates alignment ranges from 291° 296O, (S&, at 344O). A sampling of clasts indicates alignment ranges from 291' to to309°, 30g0, suggesting the clasts did did not not completely completely rotate rotate into into the the S2 S2 plane. Opposite a point point about about 25 25 m m east east of of aa hydro hydro pole pole (see (see Figure Figure 24), 24), is is aa zone zone of of structural structural complexity, about 5 m northeast northeast of the fold fold axis, that that has no no unequivocal unequivocal explanation, explanation, particularly particularly after of the devilish devilish structural structural inconsistencies inconsistenciesin inthe thefold. fold. Here, after recent recent blasting blasting removed some of Here, some of the the layering layering ranges ranges from from pseudoflame pseudoflame features to notable notable transposition transposition and andwispy wispy development of-differentiated oLdifferentiated layering parallel to to So. S2. What is no longer evident is is that that there there is a section folds, best defined by the section of the the units unitshere herethat thatdisplayed displayedshallow, shallow, northwest-plunging northwest-plunging folds, laminations at exposed laminations at the the overturned(?) overturned(?)top topof of one one of the beds. The The actual actual nose nose of of the main main fold, exposed on this this side side of of the the highway, highway, appears appears to be relatively relatively uncomplicated. uncomplicated. Structural side of of highway (see Figure distance StructuralSummary: Summary:southeast southeast side highway (see Figure24; 24; distancereference referencefrom fromwest west end end of of exposures) Distance Distance (m) (m) Measurement Feature S o6 so/si 306/63 50 50 306163 315/63 50 s2 315163 50 S2 308/60 163 s2 S, axial axial plane plane 308/60 163 crudely crudely fans fans from from 296° 296O to to 320° 320Âand and crudely crudelydips dipsmore moresteeply steeply(5° (5Oto to10°) lo0)on on southwest southwest limb limb 045/55 163 axis F2 axis 045155 163 332/55 210 so/Si so& 332l55 210 312/53 210 % 312l53 210 53 to 265 265 S3 overail; overall; biotite, biotite, faint faint(crudely (crudelyfanned?) fanned?)264° 264Oto to316° 316O 120 to (crudely fanned?) (crudely fanned?) 260/85 to 280/72 S3 crenulation, biotite biotite 53 and 298 S, crenulation, 260185 280172 53 298 (range is present present in in each outcrop outcrop of mafic mafic metasedimentary metasedimentaryrocks) rocks) —070/67 L crenulation 53 L, crenulation(various) (various) -070167 53 —073/63 298 -073163 298 —0871—70 porphyritic dike dike L, boudin -0871-70 ininporphyritic Lb boudin N ------.-. E2 F 2 fold fold axis axis Bell Mine Mine David Bell --\ Teck—Corona Roa \ j 82 cwS1 8 2 ccw S 1 .1... / Hwy 17 S2 ccw S1(?)—c w u^- intermediate dike dike'/ pole mafic dike (boudins) (boudins) Mixed metasediments metasediments retrograded porphyroblasts porphyroblasts (andalusite?) Metawacke Metawacke FIgure Stops 9,10 Simplified Figure 25. Stops sketch map mapof of F2-folded Fg-foldedmetawacke metawacke(Stop (Stop9) 9) and andF2-folded, F2-folded, Simplified sketch mixed metasedimentaryrocks rocks(Stop (Stop10) 10) at at the the Teck-Corona Teck-Corona Road Road turnoff. turnoff. mixed metasedimentary �Road — Hemlo Road Log Hemlo Area Area 53 53 Stop 19 & Stop 9: 9: FOLDED FOLDEDMETAWACKE METAWACKE(Figures (Figures18, 18,19 & 25) 25) Location: Corona Road Location: Northeast Northeastcorner cornerofofthe theTeck TeckCorona Roadturnoff turnoff (to (tothe the David DavidBell BellMine) Mine)on on Highway Highway 17, about370 370m mwest-southwest west-southwestof ofthe the "Jake" "Jake"unit. unit. Note: 17, about Note: this this outcrop outcrop is is now now "landscaped" "landscaped"(i.e., (i.e., largely largely covered coveredover). over). With the the exception exception of of the theeast eastend endofofthe theeasternmost easternmostoutcrop outcropat atStop Stop10, 10,this thisoutcrop outcrop represents a relatively thickset thick set of grey grey representsthe thelast lastexposure, exposure,as asone oneheads headswestward westwardon onHighway Highway17, 17,of arelatively wacke/siltstoneunits, units, which which are are interpreted interpretedto to be be turbidites. turbidites. This Thisset setofofunits unitsextends, extends,ininterms termsof of wacke/siltstone highway highway exposure, exposure, from from here herealmost almostto tothe theCedar CedarLake LakePluton, Pluton,about about1.3 1.3km kmalong alongthe thehighway. highway. The biotite±amphibole metawacke and metasiltstone. metasiltstone. Some The outcrop outcrop at Stop Stop 9 consists of biotitekamphibole Some of the the metawacke metawackeis is relatively relativelyfeldspathic. feldspathic.An AnF2 F2fold foldisispartly partlyexposed exposedand anddisplays displaysgood goodexamples examples of Socharacteristics. characteristics. of aa variety variety of of S2 The Therange rangeininthe thestrike strikeof ofS2 S2cleavage cleavageisisapproximately approximatelythe thesame sameas asthe therange rangeininstrike strikeofoflayering layeringon on the the limbs limbsof of the the fold. fold. This Thisrelationship relationshiphas hasbeen beenshown shownfor forother otherF2 F2folds foldsas aswell, well, for for example, example, the the fold fold at Stop 10° to to 12Owithin 12° within the the same same structure. structure. Locally, Stop13, 13, and and commonly commonlyresults resultsininaa local localrange rangeof of S2 S2of 10' Locally,the the S2 S2 fabric at this this stop stop has has been been deformed deformed near near the the fold fold nose, nose, possibly possiblyby byD3. D3. The developed in 9. The Thefirst, first,S2a, Sga, The S2 S2 fabric appears appears to have have developed in two stages stages in in the the locality localityof of Stop Stop9. appears appears to be be aa vein-like vein-like cleavage cleavage with with development development of of quartz quartz ++feldspar feldspar±Âamphibole amphibolewhich which isis presently presently at aa relatively relatively high high angle angle to the the axis axis of of the the fold. fold. The Thesecond, second,S2b, Sob,isis represented representedby by aa spaced, biotite and wispy compositional spaced, hairline hairlinethick thickcleavage, cleavage, and and by by biotite and wispy compositionallayering layering which which is is essentially essentially the the typical typicalaxial axialplanar planarcleavage cleavage(see (seeMuir Muirand andElliott Elliott1987 1987for for more moredetails). details). Pseudoclasts have locally locally developed developed in in some some layers layers in in the the nose nose of of the fold as Pseudoclasts have as aa result result of of compositional of the rock compositional changes changes of rock along along the the S2 S2cleavage cleavage and and transposition transposition of of the thelayering. layering. Retrograded Retrogradedporphyroblasts, porphyroblasts,possibly possiblyinitially initiallymediummedium-to tocoarse-grained coarse-grainedandalusite, andalusite,are arepresent presentat at the this stop. stop. A set of of narrow narrowquartz quartz veins veinswith withassociated associated saussuritization(?) saussuritization(?) the west west and and east ends of this of of feldspar feldspar isis locally locallypresent. present. Structural StructuralSummary: Summary: Note: Note:complexities complexitiesininthe thesouthwest southwestcorner cornerofofthe theoutcrop outcropsuggest suggestthat thatthe thefold foldmay maybe bedeformed deformedand/or andlornot notcompletely completelyintact. intact. S0/S1 S2a S2b S3 QV Southwest Northeast Southwest limb limb Northeast limb limb 297/56 286/56 297156 286156 280/61 298/61 280161 298161 286/52 292/61 286152 29 216 1 272/? 273/63 27217 273163 262/74 set of of quartz quartz veins veins associated associatedwith with"bleaching" "bleaching" 262174 set ** Stop Stop10: 10: FOLDED, FOLDED,MIXED MIXEDMETASEDIMENTARY METASEDIMENTARYROCKS ROCKS(Figures (Figures18, 18,19 19&& 25) 25) Location: Location: Southwest Southwestcorner cornerofofthe theTeck TeckCorona CoronaRoad Roadturnoff turnoffon onHighway Highway17. 17. There There are are 33 outcrops outcrops to to this thisstop. stop. Most Most of of the the exposure exposure here hereconsists consists of ofvariably variablyrusty rusty weathering, weathering, feldspathic and and biotitic, biotitic, locally locally garnet-bearing garnet-bearing metawackes with a variety variety of of many many amphibole-rich <5 cm amphibole-richinterlayers. interlayers.The Thepresent presentlayering layeringisisgenerally generallyc5 cm thick, thick, but but tectonic tectonicmodification modificationisis evident. evident. The The eastern eastern end end of of these theseexposures exposures consists consists of of light lightgrey greymetawacke metawacke with withsome some amphibole-rich amphibole-richlayers. layers. Retrograded Retrograded porphyroblasts, porphyroblasts, possibly initially initially medium-to medium-tocoarse-grained coarse-grained andalusite, andalusite,are arepresent presentwithin withinsome somelayers. layers.The Theporphyroblasts porphyroblastsare arealigned alignedwithin withinthe theS3 S3and andL3 Lw(fold (fold axis) axis) structures; structures; aarelationship relationshipwhich whichhas hasbeen beenestablished establishedelsewhere elsewhere(Muir (Muirand andElliott Elliott1987, 1987, �S Geology and Gold Deposits of the Hemlo Area 54 S Muir 1988), more than 1 km from the Hemlo deposit. This suggests that a relatively large-scale (regional?) metamorphic event was contemporaneous with the dextral shear event. Vestiges of the S2 cleavage can be seen locally. Both counterclockwise and clockwise orientations relative to layering can be seen (see Figure 25), but no fold closures are discernible. However, the presence of at least 3 folds was corroborative from previous exposures across the highway (presently "pleasingly" landscaped with grass). Some of the 2 fabric has taken the form of a spaced cleavage commonly filled with thin quartz seams. Examples of this style of cleavage are better displayed at Stop 9. A mat ic dike with backrotated boudins can be seen adjacent to an intermediate dike exhibiting no boudinage. An example of layer-parallel brecciation is present in the middle exposure and locally is discordant (at 265°) to the layering. As a matter of not-insignificant note for the "ditch-pigs" among you, a few, small outcrops in the highway ditch, within 50 m west of the westernmost outcrop of this stop, successively reveal the presence of: dark grey, amphibole-bearing metawacke; garnet + staurolite + aluminosilicate(?) porphyroblastic, schistose metasedimentary rocks; and a felsic quartz-feldspar-porphyritic sericite schist. These units structurally overlie the metaconglomerate/metawacke unit of Stop 11, but because of lack of exposure, are not well delineated within the tectono-stratigraphic section beyond this locality. Structural Summary: S S S 290/50 $dS1 S 305/53 alignment of amphibole; spaced, quartz-tilled cleavage 53 272/65 alignment of micas, locally amphibole * Stop 11: METACONGLOMERATE, METAWACKE (Figures 18 & 19) Location: About 130 m west-southwest on Highway 17 from Stop 10 to a set of outcrops on the northwest side (the main outcrop is easily visible). 5 S S The set of 3 outcrops at this stop reveal several units of metaconglomerate and metawacke that form a relatively distinctive unit up to about 70 m thick (on surface). The main, western-most outcrop consists of 2 metaconglomerate units, one with predominantly cobble- and boulder-sized clasts, the other with predominantly pebble-sized clasts, separated by a medium- to coarse- grained metawacke with an entrained zone of pebble- to cobble-sized clasts (Photo 3). Any possible grading is equivocal because, at least in part, the units are too deformed. The clasts comprise various proportions of feldspar-porphyritic rocks, biotite±amphibole schist, teldspathic rocks, and wacke. The porphyritic clasts, with plagioclase phenocrysts up to 8 mm long, are not identical to the many feldspar-porphyritic dikes in the Hemlo area which tend to have smaller and more uniformly sized phenocrysts. A small proportion of some of the coarsergrained crystals are presently K-feldspar. This feature has not been noted elsewhere in plagioclase-porphyritic dikes of this area, and some microscopic evidence suggests that this may be a product of metasomatism. These crystals appear to occur as phenocrysts in some clasts, and/or phenoclasts in the matrix. The matrix consists of biotite, quartz, and feldspars. Rare, small, quartz crystals can be found as phenoclasts in the matrix and as phenocrysts in some fragments; virtually none are seen in the feldspar-porphyritic clasts. The adjacent outcrop to the east consists of athick subunit of coarse-grained metawacke, and metaconglomerate. The third outcrop consists of several thinner subunits of granule to pebble, S 5 S S S S S S S �Road Log Road — Hemlo Area 55 55 polymictic metaconglomerateand andmedium-to medium- tocoarse-grained coarse-grainedmetawacke, metawacke,all allof of which which are are notably notably polymictic metaconglomerate the other other 22 outcrops. outcrops. In these these thinner thinner subunits subunits of of metaconglomerate, metaconglomerate, more amphibole rich than in the some of the clasts are mafic in composition; composition; felsic felsic clasts clasts are are generally either fine-grained fine-grained and homogeneous, feldspar-phyric. InInall homogeneous, or feldspar-phyric. alloutcrops outcropsat at this this stop, stop, magnetite magnetiteis islocally locallynoticeable noticeableininthe the matrix matrix and in some clasts. clasts. Some of the subunits subunits here here are are reminiscent reminiscentof of amphibole-rich amphibole-richconglomerate/wacke conglomerate/wacke units units north north of the North North Zone Zone on on the Golden Golden Sceptre Sceptre property, property, and and near near Botham Botham Lake Lake (see (see Figure Figure 18 18 for location of the there is is insufficient insufficient information information to to relate the two units, stratithe lake). lake). However, However, there units, stratigraphically or structurally. graphically structurally. The metaconglomerates metaconglomeratesand and metawackes metawackes of the the unit unit at at Stop Stop 11 11 are are moderately moderatelyto to strongly strongly deformed. On Onthe the relatively relativelyhorizontal horizontaloutcrop outcropsurface, surface, the the clasts clasts appear appear "flattened" "flattened" with with aspect aspect ratios of about about 2:1 to to 5:1 5:1 (locally (locally greater). greater). There slightly sinuous ratios There is is aaslightly sinuous shape shape to many many of the clasts as a result result of the development development of of an an anastomosing anastomosing pattern pattern in in the the matrix matrixand andthe themicaceous micaceousclasts. clasts. This D3on onD2. Do.The Theclasts clasts This pattern patternisisinterpreted interpretedtotobe bethe theresult, result,atatleast leastininpart, part,of ofthe theoverprinting overprintingofofD3 aligned slightly slightly clockwise are aligned clockwiseto to the the crude crude layering; layering; the the alignment alignmentis is interpreted interpretedto to be beparallel parallelto to S2 S2 consistent with this this unit northeast limb the large fold fold on on the the Williams Williams property property and is consistentwith unit being being on the northeast limb of the (see Figure 19). The The unit unit can can be be traced, traced, for for the the most most part, part, into into the the fold foldnose. nose. 2 fabric clockwise relative to that that at at Stop Stop 13. 13. This This represents represents part part fabricatatStop Stop11 11isis about about 200 20Âclockwise The So "swing" in in orientation orientation of of S2 So from about 305160 270165 at Stop 13 13 (see of the "swing" 305/60 at Stop 8, to about 270/65 Figure 20), and is possibly possibly a result result of of deformation deformation from the the intrusion, intrusion, or presence, presence, of the Pukaskwa Pukaskwa Figure Gneissic Complex (2719 +61-4Ma Maand and 2688± 2688±3Ma) Ma) to to the the southwest, southwest, the Cedar Lake Lake Pluton Pluton (2719 +61-4 (2687±3 east-northeast, the Stock (2684 (2687± Ma) to the east-northeast, the Cedar Cedar Creek Creekstock (2684+4/-3 +4/-3 Ma) Ma) to to the the north north(ages (agesfrom from Corfu D3 event. Corfu and and Muir Muir 1989a), 1989a), and/or andlor the the D3 A fine-grained, felsic dike dike has has intruded the boulder fine-grained, foliated, foliated, amphibole-bearing, amphibole-bearing, felsic boulder metametaconglomerate conglomerate (westernmost (westernmost outcrop), outcrop), and and is is locally locally deformed, deformed, along along with with the the clasts, clasts, into intoaa small, small, open, F3 fold. fold. The The presence presence of of amphibole amphibole in in the the matrix matrix of of the the metasedimentary metasedimentaryrocks, rocks,ininsome some clasts, the dike dike may may be beinferred inferredto toindicate indicate that thatsome sometype typeof ofalteration alteration has hasbeen beensuperposed superposed clasts, and and in the on the rocks, or, alternatively, alternatively, it reflects metamorphism of of compositionally compositionally distinct distinct metasedimenmetasedimentary rocks rocks with local local effects effects on on the dike. Structural Summary: Structural Summary: 287/53 287153 clast alignment biotite fabric S2 291/74 Sy 291174 alignment and biotite fabric flattened 282/50 flattened side of aligned clast, parallel to to fabric in that that clast 282150 Sa Sa Sac,? 3001? weak; part part of of "anastomosing" "anastomosing"system system 300/? weak; S3? axial plane S3*? 250/? axial plane of of small small F3 F3fold S38? 250/? L 065/45 Lpa 065145 axis axis of above above fold fold elongation of IL0 à 005/47 005147 elongation of clasts clasts (from (from south south side side of of highway) highway) S0/S1 SdS, * Stop 12: FELDSPATHICVOLCANICLASTIC VOLCANICLASTIC METASEDIMENTARY METASEDIMENTARY ROCKS ROCKS ("ARKOSE") 12: FELDSPATHIC (Figures 18 (Figures 18 & & 19) 19) LocatIon: 50 50 mm west-southwest onon Highway 1717 from Location:GoGo west-southwest Highway fromStop Stop11 11totoan anoutcrop outcropon on the the south south side. There are 3 3 relatively relatively small small outcrops outcrops at at this this stop. stop. somewhat similar that the This unit unit is somewhat similar to to that that of of Stop Stop 15 15 except that the layering layering is is thinner, thinner, ranging rangingfrom from cm, and and the the quartz quartz crystals (phenoclasts?) 3 to 15 cm, (phenoclasts?) are are generally generally fewer and and finer grained grained (<1 ( 4 mm). weathers rusty brown brown from oxidation oxidation of fine-grained fine-grained pyrite. The The outcrop weathers The matrix matrixis is fine-grained, fine-grained, white, and feldspathized and sericitized to and appears appears to have have been feldspathized and sericitized to some some degree. degree.Very Veryminor minorgreen green �Geology Geology and and Gold Gold Deposits Depositsof of the the Hemlo HemloArea Area 56 56 mica grab sample (Schnieders micais is present. present. AAgrab samplefrom fromthis thisoutcrop outcropreturned returnedan anassay assayvalue value of of 77 ppb ppb Au (Schnieders eta!. etal.1988). 1988). AApebble pebbleconglomeratic conglomeraticunit unitisisvisible visibleatatthe theeast eastend endof of the the easternmost easternmostoutcrop outcropand and possibly possibly is is part part of of the the unit unitseen seenat at Stop Stop11. 11. AA felsic felsic dike dike isislocally locallydiscordant discordanttotothe thelayering. layering. The The feldspathic feldspathic volcaniclastic volcaniclastic metasedimentary metasedimentaryrocks rocks of of this this stop stop have have been interpreted interpreted to be be the the equivalent equivalentof of the the unit unitat atStop Stop15, 15, folded folded about about the the large largefold foldaxis axiscentred centredon onthe theWilliams Williams property property(Kuhns (Kuhns1988). 1988). InInany anycase, case,the therocks rocksat atStop Stop12 12do do not not have have the the same same adjacent adjacentunits unitsat at both fold, the the S2 2 fabric, both locations. locations.IfIfthis thisunit unitisison onthe the northeast northeastlimb limb of of the large fold, fabric,ififpresent, present,should should be be clockwise clockwiseto to layering. layering.Fabric FabricSb Soisisininsuch suchan an orientation orientationbut butisisnot notclearly clearlyan anS2 S2fabric. fabric. ItIt is is still still possible D3. possiblethat thatthe theSb Sbfabric fabricmay maybe be related relatedto toD3. Structural StructuralSummary: Summary: 290/56 S&, 290156 S0/S1 Sa 275/63 275163 sericite sericite Sa Sb 299/? 2991? sericite sericite Sb (Figures 18,19,26 ROCKS (Figures 18,19,26 Stop13: 13: FOLDED, FOLDED, PORPHYROBLASTIC, PORPHYROBLASTIC,METASEDIMENTARY METASEDIMENTARY ROCKS * Stop & & 27) 27) west-southwest on Location: Go Go 100 100 m m west-southwest on Highway Highway17 17 to a roadcut, roadcut, on on the the north northside, side, that thatbegins begins LocatIon: The roadcut consists of almost The roadcut consists of almost with an outcrop on which there is a survey tripod and pin. with an outcrop on which there is a survey tripod and pin. continuous continuous exposure exposure for for the the next next 200 200 m, m, but but is is divided divided into into 33 stops stops for for lithological lithological(if(ifnot notlogical) logical) reasons. to aahydraulically hydraulically cleaned cleaned area. The reasons. Stop Stop13 13extends extendsfor forabout aboutthe the first first 150 150 m to The rocks rocks range range from open-folded metapelites from straight-layered straight-layeredmetapelites metapelitesand andmetawackes, metawackes,at at the the eastern eastern end, to open-folded metapelites and and metawackes, metawackes,to to sheared shearedand and tightly tightly folded folded metapelites metapelitesat atthe the western westernend. end. Figure Figure27 27shows showsaa detailed detailed sketch sketchmap mapof of the the west westhalf halfof of this thisstop. stop. The west end of Stop 13 is is "on "on strike" strike" from from the the axial axial plane plane of of the the relatively relatively large, tight, northnorthnorthwest-plunging, west-closing fold best exposed on the Williams property (see Figure 19) northwest-plunging,west-closing fold best exposed property (see Figure 19) and thus expected to display display an overall overall "M" "M" oorr U "W" configuration. Complicated thus might might be expected Wconfiguration. Complicatedfeatures featuresininthe the outcrop suggest that a simple folding event is inadequate to explain all of the features. Hugon Hugon (1986) described a progressive, ductile, dextral shear event for the Hemlo area. Muir Muirand andElliott Elliott survey tripod tripod and and marker marker / mafic dike dike (boudins) (boudins) discontinuous outcrop; outcrop; S2 S 2 ccw c c w Si S1 Outcrop Outcrop shown shown in in detail detailininFigure Figure 27 27 dike mafic dike 9 bouctins 20 10 3 m scale approximate approximate . Barren Sulphide Sulphide Zone Zone . F2 fold axis axis p Stops13, 13,14, 14, 15: 15: Simplified Simplified sketch map of folded and sheared metapelitic metapelitic rocks rocks Figure Figure26. 26. Stops (Stop 13), 13), sheared and altered rocks rocks of of the the Barren Barren Sulphide Sulphide Zone Zone (Stop (Stop 14), 14), and and feldspathic feldspathic metavolcaniclastic metavolcaniclasticrocks rocks (Stop (Stop15). 15). �Road Log — Hemlo Area 57 57 (1987) (1987) proposed that F2 F2 generation folds may may have have been been produced produced during during aa sinistral sinistralevent, event, followed F3 folds. followed by by aa dextral dextral event event which which produced producedF3 The layering is generally well defined in much of this this section section of of exposures, exposures, and andappears, appears, differencesbetween betweenbeds bedsof of siltstone, siltstone,wacke, wacke, and andthe the preprelargely, to reflect original original compositional compositional differences cursors to the amphibole-rich layers. The Theamphibole-rich amphibole-richlayers layersin in the the east east end end of the stop display cursors amphibole-rich layers. display reaction rims involving some type type of of bleaching bleaching process. process. The involving some The outcrop outcrop depicted in Figure Figure 27 27 displays displays aa zone zone in in which the the amphibole-rich amphibole-richlayers layersappear appearto to be be unaltered, unaltered,followed followedto to the thewest westby by increasingly altered altered amphibole-rich amphibole-richlayers layers which which are are completely completely bleached bleached at at the the west west end. end. increasingly The layering is presently presently enhanced enhanced by by the development of porphyroblasts asts which which occur occurin inaa variety of composition. of combinations combinations and and are arecontrolled controlledto some extent by bedding/layering lyering composition. Porphyroblasts staurolite, aninopnymie~gearite, anthophyllite/gedrite, cummingtonite, cummingtonite, sillimanite, sillimanite, Porphyroblasts identified identified are garnet, stauroli~e, I'etrograded cordierite, retrograded cordierite, retrograded kyanite(?), and and possibly possibly chloritoid, chloritoid, in aa variable retn^graded kyanite(?), variable matrix matrix (sonsisting of consisting of biotite, biotite, muscovite, muscolvite, quartz, quartz,and andfeldspar feldspar(Muir (Muir1982b; 1982b;Patterson Patterson1984; 1984;Burke BurkeetetaL at. .. . , ... orcummingtonite 1986). iyub). Anthophyllite/gedrite Antnopnyiiite/aearlteor cumminatoniteare arepresent presentininindividual individuallayers lavers(based (basedon onaalimited limited thin section sextion study) study) and and are are locally locally variably variably lineated. lineated. Staurolite tends to to be be'non-preferentially non-preferentially oriented. oriente?d.Cross-twinned Cross-twinnedcrystals crystalsare arelocally locallypresent. present.Some Somegarnet garnetporphyroblasts, porphyroblasts,in inoriented orientedthin thin sections, display open Z-shaped patterns in inclusion trails (Hugon 1986). However, S-shaped "~ - , patterns in (oriented thin section) in inclusion inclusion trails trails in in some some garnet garnet porphyroblasts porphyroblasts (oriented section have been recently recently noted, noted,from fromthe theauthor's author'sstudy, study, iningarnet-staurolite garnet-staurolitemetapelitic metapeliticrocks rocksalong aloneHighway 17, about 11 km trails, km west west of ofStop Stop27. 27. The regional regional significance of the the asymmetry asymmetry of of inclusion in( therefore, therefore, is is not notreadily readilyassessable. assessable. >--a. rn ..a. . a . - The F2 generation I I I G open U ~ G Ifolds I U I Uin 111 ~ the me west W G part ~ LL of UI ~ Stop Q ~ LI U13 1 ~ 0 are cue interpreted ~ ~ ~ ~ e r p rto LU ebe iue eu r2 ymieraiiurifolds d d sbased basedon on their style. style. The Theretrograded retrogradedcordierite cordieriteoccurs occursas their ssurfaces, aslenses, lenses,most mostvisible visibleon onweathered weatheredsurfaces, which which are are constrained constrainedto tospecific specificlayers layersand andlie lieparallel parallelto to what whatis is interpreted interpretedto tobe bethe theaxial axialplanar planar -..- a- few cleavage (i.e., there are are lenses (i.e., S2) of these these folds. folds. Locally, Locally,, mere ~ew ~urisusof uifresh, Tresn, unrecrystallized urirecrystallized cord lerite that appear boud ins and andare arenot notapparently apparently related related to to the the retrograded retrograded lenses. cordierite appear to be boudins lenses. The The metapeliticrocks rocksininthe thewestern westernpart partofofthe theoutcrop, outcrop,shown shownininFigure Figure27, 27, are are similar similar to to those those in in Stop Stop metapelitic 17 in terms of types types of of porphyroblasts porphyroblasts (garnet, (garnet, staurolite, sillimanite), folds, and the S3 S3 fabric overprint. overprint. &I,.-..- 1-.-. I----- -1 ^..--I,. easternmost 30 m m or or so so of ofStop Stop13 13display displayequivocal equivocalevidence evidencefor forthe thelimb/layering limbllayering The easternmost relationshipin interms termsof of the the large large fold fold centred centred on on the Williams This stems stemslargely largelyfrom from the the relationship Williams property. property. This significantly well-developed well-developed S3 S3 cleavage here and the lack lack of retrograded retrograded cordierite cordierite porphyroporphyrosignificantly blasts.Within Withinthe thenext next50 50mmororso, so,up upto tothe theeast eastend endof of the the outcrop outcropdepicted depictedininFigure Figure27, 27,there thereare are blasts. retrograded retrograded cordierite cordierite lenses lenses which which are are aligned aligned counter-clockwise counter-clockwise to the layering. The The relationrelationship of the retrograded in the the east part part of the outcrop indicates that retrograded porphyroblasts to layering in many of the the rocks rocks in in the the east east part part of this this pelitic peliticunit unitare, are, in in aa relative relative sense, sense, on on the the north northlimb limbof of an an many east-closingfold. fold. This Thisappears appearsto tobe becontrary contrarytotowhat whatwould wouldbe beexpected expectedififthe theaxial axialplane planeofofthe the east-closing large fold on the Williams property extended extended through the centre of a thickened, repeated repeated unit unit of large pelitic pelitic metasedimentary metasedimentaryrocks rocksin inthe the nose noseof of the thefold. fold. Further Further study is is required required to to resolve resolvethis this problem. problem. partly preserved, preserved,west-northwest-closing, west-northwest-closing, northeast-plunging northeast-plunging fold is well exposed at the A partly west westend endof of Stop Stop 13 13 (Figure (Figure 27). 27). Based Basedon onthe thestyle styleof ofthe thefold foldand andthe thedevelopment developmentofofaxial axialplanar planar is interpreted interpreted to be an F2 fold. The axial axial plane plane is slightly convex convex to the cleavage, this structure is fold. The northeast, northeast,ranging rangingfrom from 270° 270' to 275°. 275'. The Theplunge plungeof of the the fold, fold, is is similar to that that of the Cedar Cedar Creek Creek fold 8), but butis is contrary contraryto tothe theplunge plungeofofF2 F2folds folds to to the the west-northwest west-northwestof ofthis thisstop, stop,including including fold (Stop (Stop8), the the large large fold fold on on the the Williams Williams property, property, which which are are generally generally north-northwest north-northwestplunging. plunging.Generally, Generally, �D3-sheared metapelitic rocks with Figure 27. Stop 13: Geology of F2-folded, 'ocally altered, detail. (After Muir 1990). amphibole-rich layers. Inset shows central area of outcrop in more 0 (J1 p3 CD -' 0 Cl) I-. 0 Cl) CD 0 0. 0 G) 0. CO 0 0 CD Geology and Gold Deposits of the Hemlo Area �Road Log Log — -Hemlo Hemlo Area Area Road 59 59 F, fold axes plunge to Interestingly,aa minor minor fold fold in in a rootless rootless section section of of an an altered altered F3 to the northeast. Interestingly, amphibole-rich layer plunges to the northwest, northwest, next to a northeast-plunging northeast-plunging fold in in contiguous contiguous amphibole-rich layering. layering. Note Notealso alsothat thatthe theaxial axialplane planeorientation orientationofofS2, S2,at at 2700 270Âto 275°, 275O, is uncharacteristically uncharacteristically (i.e., counterclockwise) counterclockwise)than than is isthe the case case for for much much of of the the Hemlo Hemloarea, area, north north of of more west-striking west-striking (i.e., more Highway from Stop 6 to Stop Highway 17, 17, from Stop 24 24 (Figure (Figure20). 20). The disrupted, in part along The southern southernlimb limb of of the the fold fold in this outcrop is partly disrupted, along ill-defined ill-defined faults which display display apparent apparent dextral and sinistral displacements. displacements. Some which Some layers layers within within the the folded folded metasedimentary rocks rocks display display aligned aligned lenses lenses which have have been been interpreted to to be be retrograded retrograded metasedimentary cordieriteporphyroblasts. porphyroblasts.The Thelenses, lenses,which whichare arenot notreadily readilyvisible visibleon onfresh freshsurfaces, surfaces,lie lieparallel parallelto to cordierite what is interpreted to be the axial planar cleavage (i.e., S2) of the fold. Proceeding eastward, there what is interpreted to be the axial planar cleavage (i.e., of the fold. Proceeding eastward, is aa poorly poorlyexposed exposedeast-closing east-closing fold fold that that can can be bedetected detectedfrom fromchanges changesininthe theorientation orientationofof is layering and and from minor, minor, or parasitic, fold asymmetry. Recent Recentblasting blastinghas has removed removedmuch much of of the the layering previously previouslyexposed exposedparts partsof ofthis thisfold. fold. The The western westernend endof ofthe theoutcrop outcropat atStop Stop13 13is is variably variably schistose, schistose,and andaltered altered(feldspathized, (feldspathized, sericitized). Some Someofofthat thatalteration alterationincludes includespyritization, pyritization,leading leadingtotoaarusty rustyweathering weatheringsurface surface sericitized). that tends tends to to obscure obscuresome somefeatures. features. The Theschistose, schistose,altered alteredrocks rocksofofthe theBarren BarrenSulphide SulphideZone, Zone, that immediately pelitic rocks. immediatelyto tothe thewest, west, may mayhave have been been derived, derived, at at least least partly, from these politic rocks. Locally, Locally, boudins or or "rafts" "rafts" of of what what are are interpreted interpretedto to be be altered altered amphibole-rich amphibole-rich layers layers are "adrift" in in the the boudins schistose schistose matrix, matrix, attesting attesting to to the theanisotropic anisotropictectonic tectonicdisruption disruptionof oflayering. layering. The The metasedimentary metasedimentaryrocks rocks have have been been intruded intruded by by aa plagioclase-porphyritic plagioclase-porphyriticgranodioritic granodioritic dike,aaboudinaged maficdike withinternally internallydeformed deformedlayering, layering,and andaathin thindiabase diabasedike dikeininthe thewest west dike, boudinaged mafic dike with end of of Stop Stop 13. 13. The The feldspar feldspar porphyritic porphyritic dike dike uncharacteristically uncharacteristicallycontains containsgarnet garnetcrystals. crystals. This This end type typeof of porphyritic porphyriticdike dikeininthe theHemlo Hemloarea area typically typically did did not not incorporate incorporate xenoliths xenoliths of of country country rock rock duringintrusion, intrusion,so so intrusive intrusivecontamination contamination is is not not considered considered important. important. The Thequestion questionremains remains during whetherthe the dike dikeunderwent underwentalteration alterationinvolving involvingrelative relativealuminum aluminumenrichment, enrichment,in in which which case case aa whether relativetiming timing for for the the alteration alterationmay maybe beinferred inferred(i.e., (i.e., postdating postdating about about 2687 2687 Ma: Ma: see seeCorfu Corfuand and relative Muir 1989a), or or whether whether the the dike dike intruded intrudedaluminous, aluminous, altered alteredmetasedimentary metasedimentaryrocks rocksand andwas was Muir 1989a), subsequentlymetamorphosed, metamorphosed,which whichwould wouldput putaaminimum minimumage agefor foralteration alterationatatabout about2687 2687Ma. Ma.ItIt subsequently shouldnot notbe be automatically automaticallyassumed assumedthat that this this alteration alterationisis related related to to the the gold gold mineralization. mineralization.The The should aboveproblem problemisissimilar similarto tothat thatoutlined outlinedfor forthe thedikes dikesatatthe theWilliams WilliamsAAZone Zonepitpit(Stop (Stop2121B), B),and andatat above the theNorthern NorthernEagle Eagleproperty property(Stop (Stop4). 4). The superposition superpositionof ofalteration alterationand andcomplex complexdeformation deformationon onthe therocks, rocks,particularly particularlythose thoseinin The thewest westhalf halfof ofthe theoutcrop, outcrop,has hasresulted resultedininthe therecording recordingof ofaa"microcosm" "microcosm"ofofevents eventswhich whichhave have the affectedthe therocks rocksininthe theHemlo Hemloarea areaaswell. Forinstance, instance,there thereisisevidence evidencefor foraanumber of fabrics fabrics affected as well. For number of within withinthe therocks rocksofofthe thewest-northwest-closing west-northwest-closingfold fold(Figure (Figure27). 27). Deflection, Deflection,backrotation, backrotation,and and sinuous sinuous and and anastomosing anastomosing sericitic and and biotitic biotitic schistosities schistosities present present aa confusing confusing picture. picture. ItIt requisitedegree degreeof ofsimplification simplificationand andinterpretation!), interpretation!),that thatthe theF2 Fofolds, folds,with withthe the appears,(with (withaarequisite appears, axialplanar planarS2 S2cleavage, cleavage, have have been been overprinted overprinted by by aa dextral dextral shear shear event event which which has has led led to to the the axial developmentofofs-c-c' s-c-c'fabrics. fabrics.The Theorientation orientationofofthese theseshear shearfabrics fabricsrelative relativetotolayering layeringisisvariable, variable, development dependingmostly mostlyon onthe theorientation orientationof oflayering layeringwithin within the the F2 F2structures. structures. The Thegeneralized generalizedfabric fabric depending orientations orientationsand andrelationships relationshipsare arepresented presentedbelow. below. Structural StructuralSummary: Summary: S0/S1 SdS, variable variablewithin withinfolds; folds; —290° -290 away away from from detectable detectablefolds folds S2 S2variable variablewithin withinfolds; folds; generally -270167 fans fansfrom from265° 265Ototo275°; 275O; generally—270/6Z biotite, biotite,alignment alignmentofofretrograded retrogradedcordiente cordieritelenses lenses S3, S3c 292/54 292154 locally locallysinuous, sinuous,deflects deflectsS2; S2;biotite biotite S3. S3c- 318/46 318146 locally locallysinuous sinuousand andspaced, spaced,deflects deflectsS2 S2and andS3; S3.; biotite biotite �Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 60 60 locally S(?), locally locally backrotated by S&(?), locallyanastomosing anastomosingwith withS2; Sg; biotite biotite general generalF2 F, fold foldaxes axes Leg —320/49 -320149 isolated isolatedF2(?) F,(?) fold fold axis axis LF2 stretch and/or crenulation (?) -312100 stretch andlor crenulation (?)lineation, lineation,variable, variable,depends dependson onreference referenceschistosity, schistosity,may maybe beshallowly shallowlyeasteast-or orwestwest—312/00 L,, plunging plunging S38 S3* 2601? 260/? Lm LF2 -043149 —043/49 L * Stop Stop14: 14: BARREN BARRENSULPHIDE SULPHIDEZONE ZONE (Figures (Figures 18, 18, 19 19 & & 26) 26) Location: Location: Immediately Immediately adjacent adjacent to the the west west end end of of Stop Stop 13 13 (Figure (Figure 26) and and comprises comprises aa few few noticeably noticeably rusty rustyweathering weatheringsection sectionof ofoutcrops outcropstotalling totallingabout about30 30m malong alongthe thehighway. highway. This This rusty rusty weathering weathering Barren Barren Sulphide Sulphide Zone Zone (BSZ), (BSZ), also also known known "affectionately" "affectionately" as as the the "Sucker Zone", does not have clearly defined contacts because it appears to "grade" into the Zone", appears "grade" into the adjacent development and composition. composition. The adjacent "units" "units" in in terms terms of fabric development TheBSZ BSZappears, appears, though, though, to to be be about about 15 15 m thick here here based based on on the the most most intensely intenselyaltered alteredand andsheared shearedrocks. rocks. The BSZ BSZ consists of sericitized, feldspathized, feldspathized, and pyritized pyritized schist schist which has has an equivocal equivocal protolith(s). It is is in in ill-defined ill-defined (because (because of of exposure) exposure) contact contact with with the thealuminous, alurninous,well-layered well-layered protolith(s). metasedimentary metasedimentaryrocks rocksto to the theeast east (Stop (Stop13), 13), and and the quartz-crystal-bearing quartz-crystal-bearingfeldspathic feldspathicvolcanvolcaniclastic iclastic metasedimentary metasedimentary rocks rocks to the west (Stop (Stop 15). The The oxidation oxidationon on weathered weathered surfaces surfaces is is severe, and it is not possible to positively recognize features of the adjacent units within the BSZ, severe, and it is possible positively recognize features of the adjacent units within the BSZ, assuming these units. Towards assuming the BSZ BSZ was derived from either or both of these Towards the structurally lower "contact" "contact" there there isis what what appears appears to to be be quartz-crystal-bearing quartz-crystal-bearing rock bounded by sericitic sericitic schists. schists. Elsewhere Elsewhere in the exposures, exposures, rare rare quartz quartz crystals crystalscan can be be seen seen which which suggests suggests the the protolith protolithisisthe the feldspathic described, from diamond diamond feldspathicvolcaniclastic volcaniclasticmetasedimentary metasedimentaryrock rockof of Stop Stop15. 15. The The BSZ BSZ is is described, drill core pyrrhotitelpyrite, and and 10% 10% core specimens, specimens, as consisting consisting of of 10 10 to to 20 20 cm cmofofmassive massivepyrrhotite/pyrite, disseminated suiphides footwall units units (Quartermain (Quartermain sulphides extending 10 10 m into into the the hanging hanging wall wall and and footwall 1985). Grab Grabsamples samplesfrom fromthe thehighway highwayexposure exposurereturned returnedAu Auvalues valuesofof<0.01, ~0.01,0.02, 0.02, and and0.51 0.51 ounces ounces per per ton ton (Patterson (Patterson1986), 1986), and and 11 11 ppb ppb (Schnieders (Schnieders eta!. et a/.1988). 1988). The schist some up up to to 1 m by schist displays lozenges, lozenges, some by 0.3 0.3 m m ininplan planview, view, with with apparently apparently backrotated deflected, and anastomosing fabrics. These backrotatedfabrics fabricsas as well well as sinuous, deflected, These fabrics fabrics could, could, given their relative relationships, be representative of s-c and possibly c' fabrics of a dextral given their relative relationships, be representative of s-c and possibly c' fabrics of a dextral shear system, system, although althoughthis thisisisnot notcompletely completelyclear. clear. A relatively relatively fresh-appearing, dike occurs fresh-appearing,competent, competent,multiplely multiplelyboudinaged, boudinaged,mafic maficdike occursininthe thewest west part of the BSZ outcrop. The dike is comparable in composition to tholeiitic basalt but has elevated part outcrop. comparable in composition tholeiitic basalt elevated Ni and and Cr Cr contents contents relative relative to to most mostmafic maficdikes dikesininthe thearea areahaving havingsimilar, similar,major majorelement element compositions. compositions. Structural Structural Summary: Summary: 284/59 284159 sericite, sericite,deflects deflectsSb; Sb;also also crude crude compositional compositionallayering layering S predominant predominant(S*?) (S?) 272/66 S, (S2?) (S,?) 272166 sericite sericite S8 254158 sericite, sericite, backrotated backrotated within within lozenge lozenge Sb Sb(S38?) (Saç? 254/58 246166 folds foliation, foliation, almost almost chevron chevron style style F3 246/66 Axial plane planeof ofF3 Axial VOLCANICLASTIC METASEDIMENTARY METASEDIMENTARY ROCKS ROCKS ("ARKOSE") ("ARKOSE") * Stop Stop 15: 15: FELDSPATHIC VOLCANICLASTIC (Figures 19 & (Figures18, 18,19 & 26) 26) Location: Location: This stop, stop, immediately immediately adjacent adjacent to Stop Stop 14, 14, accounts accounts for for the the westernmost westernmost 25 25 m, m, approximately, approximately, of the section section of of exposures exposuresfor for Stops Stops 13 13 to to 15. 15. �Hemlo Area Road Log — Hemlo 61 61 The rusty weathering, layered, feldspathic, feldspathic, quartz-crystal-bearing quartz-crystal-bearing The outcrops outcrops consist consist of slightly rustyweathering, (phenoclast?, (phenoclast?, phenocryst?) phenocryst?)rocks. rocks. The Thelayering layeringis is poorly poorly to to moderately moderatelydefined definedby by grain grain size size and and mineral thick, and displays displays no other primary primary sedimensedimenmineral abundance, ranges from about 4 to 20 cm thick, tary tary features. features.The Thequartz quartzcrystals crystalsappear appearmoderately moderatelystrained strainedand andrange rangefrom from0.5 0.5toto44mm mmacross; across; most crystals are about 1 mm across. The matrix consists largely of feldspar and sericite. The matrix consists largely The rock rock has has an almost chalky white to grey appearance towards the Barren Barren Sulphide Zone (i.e., coupled with the presence presence of irregularly irregularly disseminated disseminated pyrite, (i.e,, to the east). This, coupled pyrite,small smalllenses lensesof of green mica less less than than 33 mm mm long, long, and and moderate moderate amounts amounts of of microcline microcline along along some some bedding! bedding1 cleavage cleavage planes, planes, indicates indicatesthis thisunit unithas hasundergone undergonealteration alterationsimilar similarto to that thatof of the theHemlo Hemlodeposit. deposit. rocks appear appear to "grade" "grade"into into the the Barren BarrenSulphide Sulphide Zone Zone unit unit at at the the structurally structurallyupper uppercontact. contact. The rocks The feldspathic feldspathic volcaniclastic volcaniclasticrocks rocks are are structurally structurallyunderlain, underlain, based based on on highway highway exposure, exposure, by by quartz-feldspar-porphyritic,felsic felsicmetavolcanic, metavolcanic,fragmental fragmentalrocks rockstotowhich whichthey theymay maybe berelated relatedas as quartz-feldspar-porphyritic, reworked reworked equivalents. equivalents. As mentioned for Stop interpreted the mentionedfor Stop12, 12, Kuhns Kuhns (1988) (1988) has has interpreted the unit unitexposed exposedat atStop Stop15 15to to be be the the folded equivalent equivalent of the unit unit exposed exposed at at Stop Stop 12. 12. Figure 19 19 suggests this may may be be the the case. case. However, should be noted noted that the unit unit at these locations locations is is bounded boundedby by different differentrock rocktypes typesat atits its However, it should structurally upper and lower contacts, facing directions are not not determinable, determinable, and and structural structural complexities that may require an alternative interpretation. pr complexities are present Structural Structural Summary: Summary: S0/S1 SdS, 294/58 294158 generally, generally, locally deflected to 302° 277° (possibly forms small Sgand and Sb: Oh: sericite 277 and 286° c.uu ipuoofwiy S2 uo and S3, u3aÃrespectively, iwot^3uttvwiy, but uuiindeterminable); 1 1 l U d d lllllICIUIuJ, oinati lozenges lu~utlMuO Sa sericite Sd: possiblyS3, S 302°; note similarity to to deflected SO/SI So: possibly 302O; note similarity deflected So/Sl * Stop 19 && 28) Stop16: 16: FELSIC FELSICPYROCLASTIC PYROCLASTICROCKS ROCKS(Figures (Figures18, 18,19 28) LocatIon: 50 50 m further west onon Highway 17,17,south Location:GoGo m further west Highway southside, side,totoaatailings/haulage tailingsfhaulageroad roadturnoff turnoffto to the parts:Stop Stop16A 16Alies liesto to the the southeast southeastof of the the turnoff, turnoff, and and Stop Stop16B 16B the south. south. This Thisstop stopconsists consistsofof22parts: lies lies just to the the west west of of the the turnoff. turnoff. * Stop Stop 16A: TECK-CORONA TECK-CORONATRIANGLE TRIANGLE(Figure (Figure 28) 28) Permission Permissionto to visit visitthis thisstop stopisisrequired requiredfrom fromthe theTeck-Corona Teck-CoronaOperating OperatingCorporation. Corporation. These hydraulically uartz-feldspar-porphyritic fragmental hydraulically cleaned cleanedexposures exposuresshow showfelsic, felsic, qquartz-feldspar-porphyritic fragmental rocks structurally overlying "dl,and and "b", "c", rocks (outcrop (outcrop "a") structurally overlyingfeldspathic feldspathicmetasedimentary metasedimentaryrocks rocks(outcrops (outcrops"b", "d"). The Thefragments fragmentsininthe thepyroclastic(?) pyroclastic(?)rocks rocksare arefairly fairlymonolithic monolithicand andrange rangefrom fromlapillilapilli-to tosmall small block-size, 5:1. This unit is better better represented represented block-size,and andhave have aspect aspect ratios ratiosranging rangingfrom from about about 3:1 up to 5:1. in Stop 16B. in Stop 166. The southern southern 33 exposures exposures comprise comprise well-layered, feldspathic, metavolcaniclastic(?) metavolcaniclastic(?) rocks. (%i+nrn* "k'l nnn~~itÈ+t n 4 + h i n l / l n ~I - x n r n A ~InnunA Outcrop "b" schistose rocks. The >^'UL^IUIJ u consists ^UIIOIOLO of UI thickly Llll^i\ly layered, l a y c l c u , cleaved, ^>icavcu,and ai1u locally 11%ally Thelayering layeringisis disrupted <jisrupted by by irregularly irregularly shaped, shaped, locally locally truncated truncated bodies bodlies ofof"layer-parallel" "layer-parallel" breccia, breccia, and and by by numerous highand low-angle faults accompanied by some block rotation. The metasedimentary Iiumerous highmetasedimentary low-angle accompanied soni e block rotation. .--I.- display A:--I,... -..A&.. .....AL.-~:..n..~-~-rocks zones. ILJLR~ U I ~ ~ irregular 11 I I~ GY YU I ~ Irusty I UWY weathering W G ~ LIGI I IIIY LUI I B ~ Outcrop .UULGIUIJ "c" "c" consists consists of of similar rocks rocks except that here, layers relatively relatively rich rich in in amphibole amphibole are present. Locally Locallythere thereisisaaconsistent consistentasymmetrical asymmetrical distribution distribution of of amphibole amphibole across across the the thickness thickness of of the thelayers, layers, with withmore moreabundant abundant amphibole amphibole present on the structurally structurally upper upper (i.e., (i.e., north) side. The Thehighhigh-and andlow-angle low-anglefaults faults(relative (relativeto to layering) collectively display dextral offsets. offsets. Some laye?ring)found found here here collectively display apparent apparent sinistral sinistraland and dextral Some light-coloured light-coloured pseudotachylite/u Itracataclasite, ppossibly associated with the ossibly associated the layer-parallel layer-parallel faulting, faulting, based based on on PSeudotachylitelultracataclasite, :W-..-..~m- �Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 62 62 of the the outcrop. outcrop. Outcrop other exposures, is present near the southwest end of Outcrop "d" "d" shows showsaa highly highly deformed mafic dike within feldspathic metasedimentary metasedimentary rocks. of these rocks suggests that they may The white-, and locally rusty, rusty, weathering character of have undergone some degree of alteration. This bestudied studiedininmore moredetail. detail. Thisaspect aspectneeds needsto to be Structural Structural Summary: Summary: Felsic Felsic porphyritic porphyriticrocks rocks predominant, flattening(?) flattening(?) fabric fabric 286/55 S, Sp 286155 predominant, rocks Feldspathic metasedimentary rocks SO/SI 290/62 SdS, 290162 alignment of amphibole amphibole 267/? S,w minor alignment S2? 2677 Displacements along generalized subvertical sets: Displacements along displacement with the orientation displacement orientation of of aa fault) fault) * Stop Stop 16B: 16B: 305O, 340°, 340°020°, 020°050° 070°(there is no no apparent apparent consistent consistent sense sense of of 305°, 050°, 070°, FELSIC PYROCLASTIC PYROCLASTIC UNITS(Figure UNITS(Figure 28) This the best best for fordisplaying displayingthe thefragmental fragmental character character of of this this unit. unit. Here, This exposure exposureis is one of the Here, one felsic, quartz-feldspar-phyric, quartz-feldspar-phyric, fragmental fragmental rocks rocks interpreted interpreted to represent can see crudely layered, felsic, pyroclastic deposits. pyroclastic deposits. The south part of of the the outcrop outcrop consists consists of of lapilli-tuff lapilli-tuff which contains contains heterolithic heterolithic fragments. fragments. Some fragments are more mafic than the matrix, and many are not porphyritic. porphyritic. Several Severallayers layersof of lithified tuff, or volcaniclastic volcaniclastic sedimentary material, separate the lapilli-tuff lapilli-tuff from the structurally structurally The tuff tuff is similar overlying pyroclastic breccia. overlying breccia. The similar to to what what isisinterpreted interpreted to to be bevolcaniclastic volcaniclastic metasedimentary rocks north and northwest of of the the Hemlo Hemlo deposit. deposit. The pyroclastic pyroclastic breccia metasedimentary rocks to the north breccia (block and ash flow?) is almost monolithic: one one ill-defined ill-definedlayer layer is is defined defined by by an an abundance abundance of of block-size fragments. block-size fragments. Hwy 17 - o 20 20 10 30 30 m m pyroclastics scale approximate scale approximate Teck—Corona Property 11 Stop 16: Figure ure 28. 28. Stop 16: Simplified sketch map of quartz-feldspar-porphyritic fragmental rocks structurally overlying feidspathic, metasedimentary metasedimentary rocks breccias and structurally overlying layered, feldspathic, rocks with with layer-parallel layer-parallel breccias and pseudotachylite/ultracataclasite. pseudotachylite/ultracataclasite. �Road Log Log — -Hemlo Hemlo Area Area Road 63 63 Both the the fragments fragments and and matrix matrix of of the the fragmental fragmental rocks rockscontain containquartz quartzand andfeldspar feldsparphenophenoBoth crysts. are more felsic than the matrix crysts. Most Most fragments fragments are more felsic matrix which which contains contains more more biotite. biotite. The The phenocrysts phenocrystsrange rangefrom fromabout about11to to55mm mmacross. across. The The predominant predominant fabric fabric in in this thisoutcrop outcropisisthe the one one in inwhich which the thefragments fragmentsare areflattened. flattened. ItIt isis interpretedtotobe bethe theS2 S, axial axial planar planar cleavage cleavage and and is here counter-clockwise tothe thelayering. layering.This Thisisis interpreted counter-clockwise to S& relationship atStop Stop24, 24, so there may may be an contrarytotothe theS1/S2 contrary relationship at an east-closing east-closing fold nose somewhere somewhere betweenthese these stops. stops. The Thedistribution distributionofofquartz-feldspar-phyric quartz-feldspar-phyricrocks rocks(see (seeFigure Figure28) 28)supports supportsthe the between bethe the "mate" "mate" possibilityof of aa tectonically tectonicallydisrupted disruptedfold foldclosure closuresoutheast southeastofofStop Stop13, 13,which whichcould couldbe possibility to property. If the the structural structural and and lithological lithological interpretation is to the the large large fold on the Williams property. is correct, the unit unitat at Stop Stop16 16 represents representsthe the repeated repeatedunit unitwhich whichhosts hoststhe theore, ore, although althoughcomplexities complexitiesmake make the thisinterpretation interpretationequivocal. equivocal.The Theunit unitisisconsiderably considerablythicker thickerininthe thevicinity vicinityofofthis thisstop stopand andexhibits exhibits this lithological characteristics characteristicsas aswell well as as heterogeneous heterogeneous strain strain and and alteration from outcrop outcrop aavariety variety of lithological alteration from to to outcrop outcrop(e.g., (e.g., compare compareStop Stop17 17with withStop Stop16B). 16B). As reported reportedby byQuartermain Quartermain(1985) (1985)from fromthe theexamination examinationofofdiamond diamonddrill drillcore, core,part partof of this this unit unit As contains "molybdenite-bearing fragments". fragments". The ramifications containsan an "ore "ore clast", clast", with visible gold, and "molybdenite-bearing ramifications implicit in in these these interpretations interpretations highlight highlight the the necessity necessity for for explicit explicit documentation documentation of of details details implicit regarding primary features, the timing of of mineralization mineralization relative to deformation, deformation, and and the the stratistratiregarding graphic graphicand andstructural structuralfeatures featuresthus thusproduced. produced. Structural StructuralSummary: Summary: S0/S1 SdS, 295/46 295146 273/56 S2 S, 273156 alignment alignmentofofflattened flattenedfragments fragments S38(?) S3J?) 252° 252O sericite sericite S3J?) 285° 28S0 deflects deflectsS3 S3s 53C(?) 1.2 L-> (L0?) (L?)352/42 352142 also alsopossible possibleelongation elongationlineation lineation ** Stop Stop17: 17: BILITHOLOGIC BILITHOLOGICOUTCROP OUTCROP(Figures (Figures18 18&&19) 19) Location: north side, from the tailingslhaulage tailings/haulage turnoff Location: Go Go115 115m m west west on on Highway Highway17, 17, north turnoffatatStop Stop16. 16. The a structurally overlying Theoutcrop outcropconsists consistsof ofaa felsic felsic metavolcanic(?) metavolcanic(?)unit, unit, and and astructurally overlying metasedimentary metasedimentary felsicrock rockin in contact contactwith withan an approximately approximately30 30m mthick, thick, unit.The Thewest westend endof ofthe the outcrop outcropshows showsthe thefelsic unit. subalkalic subalkalic(i.e., (i.e., common) common)diabase diabasedike. dike. Felslc FelsicMetavolcanic MetavolcanicRock Rock The Thestructurally structurallylower lowerpart partof ofthis thisoutcrop outcropconsists consistsof of altered, altered, felsic, felsic, lenticular, lenticular, quartz-"eye"quartz-"eye3'bearing due totothe bearingrock. rock.On Onfresh freshsurfaces, surfaces,the thematrix matrixisispale palegreenish greenishyellow, yellow,possibly possiblydue thepresence presenceofof saussurite. saussurite.The Therock rockappears appearstotobe berecrystallized recrystallizedand andaltered. altered. 10:l (Photo (Photo4) 4) are are The lenses, lenses, which which generally generally have have aspect aspect ratios in in the the order order of of 4:1 4:1 to to10:1 The commonlypinkish pinkishand/or and/ormedium mediumto todark darkgrey greyininappearance. appearance.Some Somelenses lensesare arelighter-coloured lighter-coloured commonly thanthe thematrix. matrix.The Thepink pinkcolouration colourationextends extendsalong alongsome somecleavage cleavageplanes, planes,forms formsill-defined ill-definedand and than irregularlyshaped shapedbut butcommonly commonlylenticular lenticularzones, zones, and andforms formsrims rimsaround aroundsome someofofthe thedarkish darkish irregularly lenses(Photo (Photo4). 4). Staining Stainingindicates indicatesthe thepink pinkcolour colourisisdue, due,atatleast leastininpart, part,to topotassium potassiumfeldspar. feldspar. lenses Some colouration may may be be the the result resultofofcontact contact Some geologists geologists have have suggested suggested that the pink pink colouration metamorphismfrom fromthe thenearby nearbydiabase diabasedike. dike.The Thedark darkcolour colourininsome somelenses lensesisispossibly possiblydue duetoto metamorphism chlorite chloriteand/or and/orbiotite. biotite.The Thedarker darkercolour colourisisnot notevident evidenton on weathered weathered surfaces. surfaces. AAdeeper deeperpinkish pinkish orangealteration alterationalso alsoextends extendsalong alongrelatively relativelylate latefracture fractureplanes planesatathigh highangles anglestotothe thefabric, fabric. ItIt orange has potassicor orhematitic hematiticalteration. alteration. hasnot notbeen beendetermined determinedwhether whetherthis thisisispotassic �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 64 64 The quartz 4:1 in faces 1.5:1 to 4:1 quartz "eyes" "eyes" are are variably variably flattened flattened and and range range in in aspect aspect ratios ratios from from 1.5:1 perpendicular to to dip and dip direction. The "eyes" are heterogeneously distributed and The "eyes" are heterogeneously distributed and are not surfaces. Finereadily apparent on fresh surfaces. Fine-to to medium-grained medium-grainedfeldspar phenocrysts phenocrysts are present present be throughout the matrix although although they they are are best seen in cut surfaces. There Thereare arewhat what appear appearto to be feldspar fe~ ldspar crystals (phenocrysts?, (phenocrysk?, porphyroblasts?) within the lenses. lenses. Discontinuous the predominant Discontinuous Iaminae laminae of quartz are locally present as stringers 1parallel to the . . .. . . , .. . * Several quartz-muscovite clots Quartz veins are buckled and/or dismembered. clots are are fabric. uuartz veins are DucKlea analor aismemDerea. beverai A . present. present. Although the rock is is altered and and deformed (possibly mylonitized), it is interpreted to have have been, originally, originally, aaquartz-feldspar quartz-feldspar porphyritic porphyritic fragmental (pyroclastic?) (pyroclastic?) rock particularly particularly given given that that the outcrop outcrop is on strike strike with with the the one one at at Stop Stop16B. 16B. Porphyroblastlc PorphyroblasticMetasedimentary Metasedimentary Rock Rock The structurally upper part of this outcrop presently consists of finely laminated, laminated, aluminous which are in sharp contact with with the felsic metavolcanic rock described metasedimentary rocks which above. The above. The layering, layering, defined defined by by variations variations in in mineral mineral content content and and grain grain size, size, shows shows no no primary primary sedimentarv features. amohibole-rich lavers which underdone attenuation and Relict amphibole-rich layers which have undergone attenuation and sedimentary features. - -- - r - - ..- . .- -,* -boudinage locally present. The inage are locally The layering layering presently presentlydefines defines an an east-closing, east-closing, almost almosit isoclinal, boud isoclinal, F2 F2 been overprinted overprinted and and modified modified by bythe the S3 S3foliation foliation(D, (03). fold, which subsequently has been ,). The south - I J J :A -..-I.. ÑÑ&&AK..M&AJ * . L., . I & ~L..:AI...AAA L A IA.,Af iiL;niI ~ W UI it; iciye~ ing. There There is limb OT of ims this 1IUIU fold is IIIUGI muchI Imore attenuated as :..J~J:A..&AJJ indicated by thickness of &LIthe layering. is I I U I ~ciiiei iuci~eu cis 11 I U I L . ~u ~ y~ LIthe U LI some eqi equivocal evidence for for aa west-closi~ west-closing fold to the south of this fold. A few late fractures / south of this fold. iivocal evidence 4 few late fractures ng fold to the associated with pink-orange pink-orangealteration alteration are are present. present. associateid with J -1 1.L:- -Adn ;4 . . . A I The porphyroblasts comprise staurolite, sillimanite, sillimanite,and and possibly possibly aa fourth type ~ U IIYIUUIWS ~ I G W I I ~ 13e I ygarnet, a I let, staurolite, type represented white-weathering which may be be retrograded retrograded crystals. ring mineral(s) which ssented by roughly equant, white-weathe repre Garnet fine- to to medii medium-grained, crystals which are distributed, distributed, ~m-grained,euhedral crystals let occurs as reddish brown, fineGarn &LAt.accoruiny to KJ the me composition G U I I I ~ U S I L I Uof UI I ~ the me layering. layering. Staurolite crystals are fine- to coarsecoarsein part, pan, according grained, euhedral euhedral to subhedral, dark to medium medium brown, and and locally locally have have overgrown overgrown and and preserved preserved layering. The the modified metasedimentary layering. The entrained entrained layering is straight within the crystals, crystals, suggesting static suggesting static conditions conditionsduring duringgrowth. growth. Many Manyof of these these crystals crystalshave havesubsequently subsequentlyundergone undergone a cl clockwise fold as as indicated indicated by the the re-orientation re-orientation of the layering. Fgfold layerir1Q. lockwise rotation, rotation, on on both bothlimbs limbs of of the F2 Thiss suggests the effects effects of the dextral dextral shear shear event event post-dated post-dated porphyroblast porphyroblastgrowth, growth, at at least least: in Thi in Pnrnhvrnhlactc whioh appear annoar in in long Innn section cortinn on nn the tho outcrop niitornn chnw weak tonrlonov to tn part. which tendency par-t,. Porphyroblasts ,. uk^k^Vui VÇÇ.N^Iw show Iv..aa weak ..VuI. .w be be aligned parallel aligned parallel to to the the S3 S3 fabric. -I:-- .__A 1.- ÑÑ .., I VltaflUU.u *JVw.lw.. llVII I 1V4uI Sillimanite occurs occurs as as fibrolite fibrolite and appears, on the glaciated Sillimanite appears, on glaciated surface of this outcrop, outcrop, as as The tibrolite relatively dark, wispy, splaying, aligned, aligned, sigmoidal sigmoidal ("S") ("S") clusters of crystals. wispy, splaying, crystals. The fibrolite is is commonly adjacent to, to, and locally is commonly is deformed deformed around, around, staurolite porphyroblasts, porphyroblasts, particularly where angle to to the the layering. layering. The The sigmoidal sigmoidal deflection deflection of the clusters clusters appears appears where the the latter latter are are at at a high angle represent an an s-c s-c fabric fabric relationship relationship in in aa dextral dextral shear shear zone. zone. These to be a D3 feature and may represent metasedimentary strike from metasedimentaryrocks rocksare arevery verysimilar similarto tothose thoseat atStop Stop13, 13, although althoughthey they are are not not along along strike this this outcrop. outcrop. Structural Structural Summary: Summary: Metasedimentary Rocks Metasedimentary Rocks S1 282/58 S, 282158 S3 S3 273/? 273/7 alteration) Late fracture (pink-orange (pink-orangealteration) Metavolcanic Rocks Met, S predominant (mylonitic?) 292/51 356/90± 356/90 �— Hemlo Area Road Log - 65 65 * Stop Stop 18: 18: FELDSPATHIC FELDSPATHIC METASEDIMENTARY METASEDIMENTARYROCKS ROCKS(Figures (Figures18, 18,19 29) 19 && 29) LocatIon: weston south side, to apoint a point just just before before a turnoff Location: Go Go 160 160 m west onHighway Highway17, 17, south side, from from Stop Stop17, 17, to to the north. north. This Thisunit unitisisapproximately approximatelyon onstrike strikewith withthe themetasedimentary metasedirnentaryunit unitatatStop Stop16A. 16A. This outcrop outcropis is not not nearly nearly as as illustrative illustrativeas as itit was before before the recent recent blasting. blasting. ItIt shows grey to to This shows grey light grey grey weathering, feldspathic feldspathic metasedimentary metasedimentaryrocks rocks with with some someamphibole-rich amphibole-richlayers laversand and light garnet-bearing layers. layering is likely a result of a combination comll in at ion of some minor garnet-bearing layers. The present layering of primary compositional compositional layering layering and and subsequent, subsequent, locally locally developed, tectono-metamorphic tectono-metamorphic layerprimary layerA --. ...l~&'. GUU~I~LS Atthe theeast eastend endof of the the outcrop outcroo some layers lavers disolav reoetitive. liahtldarkgrey-grade" ing. At display repetitive, light/dark -,- .~, -,-- . . a -. . - grey-graded couplets (dark part on on the north north side) side) (ci. (cf.Stop stop 16A). 16A). Some Someflattened, flattened,S-shaped S-shapedfolds folds in inquartz quartzveins veinswith with (dcirk part dismembered present. The The flattening flattening fabric fabric ranges ranges from parallel parall1el to slightly counterdismembered limbs are present. clockwise to the the layering. laverina. d o ckwise to --, - - - - - - - - - 4 - - -z - W~ Several low-angle, low-angle, counter-clockwise counter-clockwise (to (to layering), layering), dextral dextral faults faults are are present presentand andmay maybe be Several genetically breccias and and pseudotachylitelultracataclasite pseudotachylite/ultracataclasite geneticallyrelated relatedto to several severalzones zones of layer-parallel breccias that are are visible visible at at this this stop. stop. The faults are are locally locally parallel parallel to to layering layering along along strike. strike. The The pseudotachylite, which locally contains spherical to elongate elongate vesicular features (naturally (naturally at aa precarious spot at the top edge edge of of the the roadcut), roadcut), has has possibly possibly undergone ductile deformation in places. places. At At the theeast eastend endof ofthe theoutcrop outcropat atroad roadlevel, level, is is aazone zone of of breccia brecciain inwhich which blocks blocks of of metasedimentaryrocks rocksappear appearto to have have undergone undergone clockwise clockwise rotation rotationwith withinfilling infillingby bymore morefinely finely metasedimentary brecciated variety of breccias brecciatedhost hostrock. rock.This Thismay may~.represent representaavariety of the the layer-parallel layer-parallel brecciasthat thathave haveresulted resulted . from displacement. There from dextral sense displacement. There are are also also sets sets of of numerous, numerous, relatively late, brittle brittle faults faults which whichare areat ataahigh highangle angleto tolayering. layering. On bepurplish purplishgrey greyand andpale pale On the the fresh fresh roadcut roadcutface, face, the the metasedimentary metasedirnentaryrocks rocksappear appearto tobe ----:.... ~. greenisrl grey. However, nowever, the ine greenish greenisn grey grey colour coiour is spanany associatea with wiin the inesets seis of OTfractures Traciures greenish spatially associated mentioned above, above, and appears appears to be be some some type of of alteration alteration involving involving bleaching bleaching of of the the rock. rock. mentioned Locally, similarly bleached. This Locally, up up to 80% 80% of the rock rock is similarly Thisraises raisesquestions questionsabout abouthow howmuch muchofofthe the rocks, what form form of alteration alteration has taken place. Some rocks, here here and and elsewhere, elsewhere, are altered, and what Some hematiticalteration alterationisispresent, present,along alongwith with quartz quartzand andchlorite, chlorite,on on some some fractures. Other Otherfractures fractures hematitic contain epidote epidote ++ calcite±amphibole. calcite±amphiboleThe The metasedimentary metasedirnentaryrocks rocks are are intruded intruded by by aa schistose schistose contain dike, not not readily readily apparent apparent on on horizontal horizontal surfaces, surfaces, that that has has undergone undergone significant significant pinching pinching and and boud in age. boudinage. ---!-I- I I !-L LL- ---L?-t* -!-.--I ~ .LL a*-- - r r ~ - - The metasedimentary metasedirnentaryrocks rocksat atthis thisstop stopshould shouldbe be compared comparedto to those those at at Stop Stop 24, structurally The structurally underlying underlyingthe the deposit, deposit, which which some somegeologists geologiststhink think are are part partof of the thesame sameunit. unit. 1" 00 N 30 30 20 20 10 10 m m scale scale approximate approximate A Hwy 17 Hwy 17 itewac % m b i o . \ ~ wacke e k 1 layer-Darallel breccia breccia layer—parallel // / O\POI~ amyg7I eudotac hylite with ~seudotachylite with amygdules 1 deformed deformed mafic mafic dike dike zone zone of rotated rotated blocks blocks (related (related to tolayer—parallel layer-parallel breccia) breccia) Figure feldspathic metasedirnentary metasedimentary rocks Figure29. 29. Stop Stop18: 18: Simplified Simplifiedsketch sketch map map of feldspathic rocks with with breccibrecciated ated zones zones and and pseudotachylite/ultracataclasite. pseudotachylite/ultracataclasite. �66 66 Geology Geology and and Gold GoldDeposits Depositsof of the the Hemlo HemloArea Area StructuralSummary: Summary: Structural SOIS, 297/55±5 297/55± overall overall S/S1 layeringadjacent adjacenttotozone zoneofofaligned alignedblocks blocks(see (seedescription descriptionabove) above) S0/S1 SOIS, 285/? 2851? layering 303Oto to320° 32O0 (long (longaxis) axis) Alignmentof ofblocks blocks 303° Alignment Low-angle,faults faults 265/80 265180 dextral, dextral,brittle-ductile; brittle-ductile;03 D3 Low-angle, High-anglefaults faults 358/85 358185 dextral dextral High-angle sinistral;offsets offsetsaalow-angle, low-angle,03-related D3-relatedfault fault 328/90 sinistral; 328/90± 010190± 010/90 sense sensenot notdetermined determined L, (slickenside) (slickenside) -297/05± -297/05 L5 Stop19: 19: "HANGING "HANGINGWALL" WALL"METASEDIMENTARY METASEDIMENTARYROCKS ROCKS(Figures (Figures18 18&&19) 19) * Stop Location: 50 m west on on Highway 17,17, south side, Location:Go Go 50further m further west Highway south side,from fromthe thewest westend endofofStop Stop18 18(which (whichisis opposite oppositeaaturnoff turnoffto tothe thenorth). north). This Thisisisthe thefirst firstrelatively relativelylarge largeoutcrop outcropto tothe theeast eastofofthe theMain MainMineralized MineralizedZone Zone(Stop (Stop20A), 20A), and the highway. highway. The metasedimentary metasedimentary and best best represents representsthe the "hanging "hanging wall" unit unit as exposed along the rocks rocks display display indistinct, indistinct, possibly possiblytransposed transposed layers, layers, defined defined mostly mostly by by various various proportions proportionsofof feldspar, feldspar, quartz, and biotite, biotite, as as well well as assome someamphibole-rich amphibole-rich layers. layers. There There are are also also zones zones consisting associated with few veinlets associated with tourmaline tourmaline consistingof of numerous numerousamphibole-rich amphibole-richknots knotsor or lenses. AA few and and bleaching bleaching of the the country country rock rockare arepresent. present.There Thereare areseveral severallayer-parallel, layer-parallel,fine-grained fine-grained gossans gossans which which are are locally locallyill-defined. ill-defined. In In this this outcrop, outcrop, there thereare areseveral, several,weakly weakly defined, defined,angular angulardiscordancies discordanciesbetween betweensets setsofof layered rocks and between angular of cleavage cleavagewith with respect respect to to layering. layering. These angular relationships of These features may be examples of juxtaposed faulted blocks, or, possibly 3 or so ill-defined, tight, F2 features may be examples of juxtaposed faulted blocks, or, possibly 3 or so ill-defined, tight,F2 folds, folds, or or aa combination combinationof of both bothfeatures. features.F2 F2folds foldshave havebeen been observed observedin in the the hanging hanging wall rocks rocks at the the Williams Williams A A Zone Zone pit, pit, and and north northof of the the highway highway along along the the effluent/haulage effluentlhaulageroad roadbetween betweenStops Stops 19 and and 20. 20. 19 The The metasedimentary metasedimentaryrocks rocksexposed exposedat at this this stop stopshould should be be compared comparedto to those thoseat atStop Stop22 22 which footwall rocks rocksto to the the main mainpart partof of the theQuartzQuartzwhich form, form, with with respect respectto to highway highwayexposure, exposure, the the footwall Feldspar-PorphyriticComplex Complex(Stop (Stop20). 20). Feldspar-Porphyritic StructuralSummary: Summary: Structural Northpart partof of outcrop: outcrop: North (predominant) 295/60 295160 $S(predominant) South part partof of outcrop: outcrop: South Rangeof ofSO/SI SdS, layering layering 282° 282O to to 297° 297O Range Rangeof of possible possibleS2 Q,cleavage cleavage 292° 292O to to 282° 282 Range QUARTZ-FELDSPAR-PORPHYRITICCOMPLEX COMPLEXAND AND MAIN MAINMINERALIZED MINERALIZEDZONE ZONE Stop 20: 20: QUARTZ-FELDSPAR-PORPHYRIT1C * Stop (Figures 30 && 31) (Figures18, 18,19, 19,30 31) further weston low-lying outcrop Go 235 235 m m furtherwest onHighway Highway17 17from from Stop Stop19, 19, to a low-lying outcrop (Stop (Stop20A), 20A), Location: Go north northside, side, about about55 55m mwest westof of an aneffluent/haulage effluentlhaulageroad. road. * Stop Stop20A: 20A: MAIN MAINMINERALIZED MINERALIZEDZONE ZONE(Figure (Figure30) 30) This completely buried, This outcrop, outcrop, which whichused usedto to be be larger larger before before being completely buried, then then partly partlyrecovered, recovered, is property (see Figure 22). The is part part of of the the rootless, rootless, mineralized, mineralized,West West Zone of the Teck-Corona property The West 17. West Zone Zone presently presentlyisisnot noteconomical economicaltotomine, mine,ininpart partbecause becauseofofits itslocation locationbeneath beneathHighway Highway 17. �Road Log — Hemlo Area 67 67 The outcrop outcrop consists consists of of rusty rustyweathering, weathering, schistose, schistose, locatly locallylenticular, lenticular,heterogeneously heterogeneously sericitized sericitized and and pyritized pyritizedquartz-feldspar quartz-feldsparporphyritic porphyritic rock rockwhich whichdisplays displaystourmaline, tourmaline, some some relarelatively of very very fine-grained fine-grained molybdenite. molybdenite. The tively large large green green mica mica lenses, and wisps of The green green mica micain in the the Hemlo camp has been determined to be vanadian muscovite (Harris 1986b, 1989). Grab samples Hemlo camp determined muscovite (Harris 1986b, 1989). Grab samples from this outcrop outcrop returned returned values values of of 016 016 ounce ounce Au Au per per ton ton (0.05% (0.05% MoS2) M0S.J (Patterson (Patterson1984), 19841, 6.35 6.35 24.35 ppm ppm Au, Au, and and 550 550 ppm ppm Mo Mo(Schnieders (Schnieders eta/. eta!. 1988). 1988). Channel samples from this outcrop and 24.35 (J. Londry, Londry, geologist, geologist, Hemlo Hemlo Gold Gold Mines Mines Inc., lnc., assayed assayed up up to to 9.0 9.0 ppm ppmAu Au across across1.14m 1.l4m (J. by Hemlo Gold Mines Mines Inc., lnc., personal personal communication communication1994). 1994). Despite considerable considerable recent recent oxidation, oxidation, one one can can still still see see a variety Despite variety of of lenses lenses defined defined by by and porphyriticlnon-porphyritic, schistose/"massive"), schistose~lmassive~'), and differences in grain grain size, size, texture texture (e.g., (e.g., porphyritic/non-porphyritic, composition (e.g., sericite/biotite) (Photo 5). Some (e.g., sericitelbiotite) Someof of the the lenses lensesconsist consist of of quartz quartz which which may may indicate indicate that that some some quartz quartz veins veins have have been been completely completely dismembered. Considerable Considerable variation variation in in texture and between fabric-parallel, fabric-parallel, non-lens-bearing texture and grain grain size size also also can can be be seen between non-lens-bearing"zones", '2ones", some someof of which are not pyritized. There consensus as to the the protolith protolith of the the unit. unit. Some geologists interpret to be There is is no consensus Some geologists interpretthe the rock rockto be a mylonite, and others a deformed, deformed, possibly possibly mylonitized mylonitized pyroclasticlvolcaniclastic pyroclastic/volcaniclastic fragmental. fragmental. The unit appears texturally unit appears texturallysimilar similar to to sericitized sericitized"fragmental" "fragmental"rocks rocksininthe themines minesand andininthe theTeck-Corona Teck-Corona trench (Stop A). Felsic, monolithic and heterolithic, quartz-feldspar-phyric quartz-feldspar-phyric pyroclastic/volcan(Stop 21A). pyroclastic/volcaniclastic rocks rocks can can be be seen seen elsewhere in the area, (e.g., (e.g., Stop 16B, 16B, and outcrops on the Williams Because of of the internal property and Golden Sceptre property property property (Hemlo (Hemlo Gold Mines Mines Inc.)). lnc.)). Because internal complexities in this unit (particularly (particularly to to the the west-northwest), west-northwest), such as "massive" and and fragmental porphyritic rocks, Muir Muir (1985) (1985) coined the term "Quartz-Feldspar "Quartz-Feldspar Porphyritic Complex" Complex'' for the essentially contiguous essentially contiguous quartz-feldspar-phyric quartz-feldspar-phyricrocks, rocks, of of which which this this unit unit appears appears to to be be part. part. m east east of the east east end end of the the main main outcrop outcropat at Stop Stop20A, 20A,shows showsaa22m m A small outcrop, about about 77 m ium-grained, subporphyritic subporphyritic (plagioclase) granodiorite dike thick, apparently apparently unaltered, unaltered, med medium-grained, dike which has intruded has muscovite muscovite intruded the sericitized, sericitized, pyritized, pyritized, porphyritic porphyritic rocks. rocks. The dike has poikitoblasts. poikiloblasts. c- ----- -— - I lensy (fragmental?), porphyritic, (fragmental?), quartz—(feldspar)q u a r t z - ~ f e I d sporphyritic, par~-~o~~~~ ~ i tI~ quartz-(feldspar) ~ quartz—(feklspar) porphyritic, sericite sericite schist t— sericiteschist schist IJ sericite 0 plagioclase-subporphyritic granodiorite granodbrite J plagioclase—subporphyritic Figure 30. 30. Stop 20A: 20A: Detailed sketch sketch map & 22) 22) map of the West Zone Zone (See (See Figures Figures21 21 & (Teck-Corona property) as originally originally exposed exposed (Teck-Coronaproperty) along Highway 1Z Present outcrop outcrop outline outline Highway 17 differs. (Modified (Modifiedafter afterPatterson Patterson1984). 1984). 0plagioclase—subporphyriUc plagioclase-subporphyritic granodiorite granodiorite FIgure Figure31. 31. Stop Stop 20B: 20B: Detailed Detailed sketch sketch map map of part of of the the Quartz-Feldspar-Porphyritic Quartz-Feldspar-Porphyritic ComComplex, structurally structurally underlying underlying the West West Zone Zone 221, as as originally originally exposed exposed (See Figures 21 & 22), along Highway Highway 17. 1Z Present Present outcrop outcrop outline outline difdiffers. (Modified after Patterson 1984). fers. (Modified after Patterson 1984). �Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 68 68 Structural StructuralSummary: Summary: S (predominant) (predominant) (S*?) 2881-70 S (S?) 2881-70 (subordinate)(S35?) (S3*?) 263/? 26W? deflected deflectedby byabove aboveSS(predominant) (predominant) SS(subordinate) (subordinate) (Sw?) 29777 backrotates backrotatesSS(predominant) (predominant) 297/? SS (subordinate) (S.?) S3?(late (lateoverprint?) overprint?) 250174 250174 crenulation crenulationininF3 F3fold fold S3? Axial Axial plane planeboundary boundary 011/? O l l l ? sinistral sinistralsense sensekink kink "MASSIVE" "MASSIVE"QUARTZ-FELDSPAR QUARlZFELDSPARPORPHYRY PORPHYRY(Figure (Figure31) 31) Stop 20B: 20B: * Stop LocatIon: Go 55 m to the west of Stop 20a, north side. This Th low-lying outcrop structurally underlies the main mineralized zone, seen IininStop Stop20A, 20A, and and consists porphyry which consist! of white-weathering, felsic, foliated, green-mica-bearing, quartz-feldsparr porphyry intrllnen by nv several n r n r i..,....v r t T l r : rllKI+S. 1 lie quartz-feldspar-porphyritic q u ~ ~ ~ ~ - ~ ~ i u ~rock rock p ~ may ~ -have have p ~ ~ p i ~ y is intruded several feldspar nr-.r porphyritic dikes. The may - -. -. Telnsnar .-.--r-. -...--. been subvoicanic intrusion low. Some Some of of the the dikes dikes display display boudinage boudinagewith with intrusion or or part part of a massive massive fflow. be(?n a subvolcanic cs. The dikes are foliated with sericite&chlorite, D3-related features (Le., 83, F3) evident in the necks. The dikes are foliated with sericite±chlorite, D3, and contain non-preferentially-oriented muscovite ana conlam non-pre~erenua~~y-orlen~ea rnuscovne poikiloblasts. poikiloblasts.Small-scale, Small-scale,conjugate(?), conjugate(?),sinissinistral and dextral kinks (F4?) are present. m d dextral kinks (F4?) are present. tral i 8 8.. --"- .,w, Structural summary: Predominant fabric 286/70 Subordinate fabric anastomosing with above 275/74 304° weakly developed fabric deflects(?) above 037° Trace of sinistral kink band boundary 002° Trace of dextral kink band boundary Teck—Corona Teck-Corona trench trench 3>5 \a •.(fewer (fewer lenses) lenses) A quartz-feldspar—porphyrltiC sericite schist quartz-feldspar-porphyritic sericite schist (± (*feldspathized. feldspathized, sheared) sheared) 1a lb quartz—feldspar-porPhYritic sericite schist quartz-feldspar-porphyritic sericite schist with (k feldspathized. feldspathized, sheared) sheared) with green green mica mica (± 2a sericitized. sericitized, pyritized, pyritized, feldspathized feldspathized lensy lensy schist schist with quartz—feldspar fragmental(?) quartz-feldspar phenocrysts: fragmental(?) 2b biotitized biotitized feldspathized feldspathized lensy lensy schists schists with with quartz—feldspar quartz-feldspar phenocrysts; phenocrysts: fragmental(?) fragmental(?) 3 feldspathlzed feldspathized metasedimentary metasedimentary schist schist with with biotite biotite 5 foliated quartz dioritic dike 6 plagioclase—porphyritic granodioritic ~nodioriticdike dike abruptly transitional contact — sharp contact la 0 5 10 m lb k-Corona trench trench showing showing Figure 32. Stop 21A: Detailed sketch map of the westernmost Teck-Corona the AALone. Zone. (Geology T.L.Muir, Muir,OGS OGS1987). 1987). the non-economic, non-economic.on-strike on-strikeequivalent eaulvalentofotthe tneWilliams Witt~ams (tieotogybybyT.L. �Road Log — Hemlo Area * Stop Stop 21: 21: 32 & 33) 33) 32 & 69 69 TECK-CORONA TRENCH and and WILLIAMS WILLIAMS A 18, 19,21,22, TECK-CORONA A ZONE ZONE PIT PIT SITE (Figures 18,19,21,22, Location: m west west from from Stop Stop20B 20Bto toaashort shortturnoff turnoff to to the the north north used for access to the A Location: Go 165 m Zone exhaust turbines. * Stop 21A: TECK-CORONA TECK-CORONATRENCH TRENCH(Figure (Figure32) 32) Permission Permission to to visit visit this this site site is is required requiredfrom from Teck-Corona Teck-CoronaOperating OperatingCorporation. Corporation. Location: Enter thebush the'bush (to Location: (to the north), north), from from the the highway highway right-of-way, right-of-way, on a cut line about 25 m east of the the short short turnoff road. Follow the line/trail for about 40 m to to aa 35 35 m m long long stripped stripped "trench1' "trench" Follow Iineltrail which is is roughly roughly on strike strike with with the the Williams Williams Mine Mine A A Zone. foliated, sericitic, felsic, quartz-feldspar The southern end of the stripped zone consists of foliated, quartz-feldspar porphyry which locally contains contains green mica lenses. Structurally Structurallyoverlying overlyingthis this isisaamineralized, mineralized, rusty, highly schistose (sheared?), lensy, lensy, sericitic sericitic rock with with quartz eyes, pyrite, and sparse, very fine-grained molybdenite. fine-grained molybdenite.AAgrab grabsample samplefrom from the the mineralized mineralizedpart partof of this thistrench trenchreturned returnedaavalue value of 2.27 ppm ppm Au and and 105 105 ppm ppm Mo Mo (Schnieders (Schnieders et eta!. a/.1988). 1988). There There is is no no agreement agreement as as to to whether whether the the lenses lensesare are in in whole whole or or in in part partprimary, primary,but but this this rock rock appears to to be the the sericitized equivalent of of the structurally overlying, overlying, schistose, schistose, biotitized biotitized rock appears which contains contains heterolithic heterolithic lenses. lenses. Both Bothrocks rockshave havebeen been altered altered and and are referred referred to generally in terminology as "fragmentals", although although the term term is used used non-genetically non-genetically by some some geologists. geologists. mine terminology To the north, the rocks in the trench consist of schistose, quartz-eye-bearing, biotite biotite + sericite To the somewhat feldspathized feldspathized and and sericitized sericitized metasedischists, structurally overlain by what may be somewhat metasediplagioclase-porphyritic granodioritic granodioritic dikes and mentary rocks. The The rocks rocks have have been intruded by plagioclase-porphyritic fine-grained, "quartz dioritic" dioritic" dikes. dikes. Structural StructuralSummary: Summary: North end of stripping stripping S S, (mylonitic?) (mylonitic?) 295/57 BY57 S3? 284/70 S3?(forms lozenges with above above fabric) fabric) 28470 South defined by sericite) sericite) South end end of stripping stripping (all fabrics defined S S (predominant) (predominant) 291/64 291164 S S (subordinate) (subordinate) 281/64 281164 forms lozenges with above fabric fabric 304/57 seems to deflect deflect either (subordinate) S (subordinate) 304157 either or or both both of of the the above abovetwo two fabrics fabrics Stop 21 WILLIAMS A * Stop 21 B: WILLIAMS AZONE ZONE PIT PIT (Figures (Figures22 22 & & 33) 33) Operating Corporation. Permission to visit this site is required from Williams Williams Operating Corporation. Location: stripping where a flagged flagged shortcut Location: Return Return to just south of the south end of the stripping shortcut takes takes one westerly westerly to the A Zone pit area, or, or, return return to tothe the highway highway right-of-way right-of-way and approach approach the fencedfencedto the AZone off open pit area from from the the short short turnoff road. This stop" which which is achieved by walking This is is a "view stop1' is best best achieved by walking north along along the the outside outsideof of the the east east end end of the fenced-off area area for about 50 m to Hidden just north to aa knoll. knoll. Hidden in the bush original small bush on the way in in is what appears appears to be one of the original small pits pits created createdininthe the1940s. 1940s. The west end of the open pit shows a rusty zone which which crudely marks the uneconomic, onstrike extent extentof of the the A AZone Footwallrocks rocksto to the the ore ore zone zone are are variably variably altered altered strike Zone of the the Williams Mine. Footwall schistose, felsic, felsic, quartz-feldspar quartz-feldspar porphyry. tight to to isoclinally isoclinally and schistose, porphyry. The The hanging hangingwall rocks consist of tight folded and transposed metawacke and metasiltstone with with amphibole-rich amphibole-rich layers. layers. Staurolite Staurolite and �0 N 10 m 30 40 S 50 . 2 S Approximate outline of present day pit—' Figure 33. Stop 21 B: Generalized sketch map of detailed surface geology of the Williams A to excavation for the open pit. (Modified after mapping by T.L. Muir 1985; Muir et a!. 20 S Interpreted ill—defined Iithologic contact: observed generalized outcrop area with patch of remaining overburden . CD CD I -P 0 C,) - C,) V 0 CD 0 0. 0 0 0. CO 0 0 CD 0 0 Geology and Gold Deposits of the Hemlo Area �Road Log — -Hem Hemlo Road Log lo Area 71 71 kyanite are present present in these hanging zone up to to about about 50 m m thick thick (Walford, Stephens Stephens kyanite in these hangingwall wall rocks rocks in in aazone eta!. 1986). The biotitized/sericitized "fragmental" unit appeared, on surface, to pinch out to the eta/. 1986). The biotitizedlsericitized "fragmental" unit appeared, on surface, to pinch about midway the open open pit pit area area (Figure (Figure 33). 33). The ore, as exposed exposed on surface surface west, about midway into into what is now the (Photo 6), 6), was was interpreted interpreted to to be derived, (Photo derived, for the most most part, from from feldspathized feldspathized and pyritized 4, Figure 33). 33). At metasedimentary rocks (Unit 4, At surface, itit was up to 35 m thick and and "H" shaped shaped Weicker eta/. eta!. 1986) 1986) with tails tails to to the the east east and andwest. west. (Walford, Weicker Open pit operations, which began in August, 1985 1985 and ended July 1986, 1986, resulted in the the extraction of 3.8 million million tons tons of of rock, rock, including including0.8 0.8 million milliontons tons of of ore oregrading grading5.13 513 ppm ppm Au Au (A. (A. Guthrie, Williams Operating Corp., written communciation communciation1992). 1992). Pit dimensions are are approxapproximately 275 imately 275 m m by by 170 170 Int T? (top), 150 m by 25 m (bottom), and 70 m deep (Resident (ResidentGeologist GeologistFiles, Files, MNDM, Thunder Bay). Bay). Plagioclase-porphyritic and and quartz quartz dioritic dikes dikes appear appear to have have intruded intruded the the AAZone Zoneore ore (Photo (Corfu and Muir 1989a). Kuhns (1988) also also interpreted interpreted feldspar porphyry porphyry and and intermediintermedi(Photo 7) (Corfu ate composition composition "sills" "sills" to to have have intruded intruded the the Golden Golden Giant orebody. orebody. The The dikes dikes within within the the AA Zone Zone (and elsewhere in the Hemlo area) typically contain contain muscovite muscovitepoikiloblasts poikiloblastsand andare areanomalous anomalousinin (and elsewhere ore, then a minimum Au, Ba, Hg, and Au, and Sb. Sb. IfIf they actually intruded intruded an existing ore, minimum age age for for the the mineralization mineralization can can be be inferred inferred to to be be about about 2680 2680 Ma, Ma, based based on on U-Pb U-Pb dates dates from from Corfu Corfu and and Muir Muir likely have undergone subsequent metamorphism metamorphism which would would account (1989a). The dikes likely account for the poikiloblasts. poikiloblasts. Whether Whetheror ornot notthe the dikes dikes assimilated assimilatedmineralized mineralizedmaterial material or "absorbed" the metals during unclear. Native fractures within an essentially essentially during metamorphism metamorphismis is unclear. Native gold gold is locally locally found along fractures unaltered, plagioclase plagioclase porphyritic porphyritic dike dike that has unaltered, has intruded intruded the the David David Bell Bell Mine Mineorebody orebody(Paul (Paul Bankes, Teck Exploration Exploration Limited, Limited, personal communication, communication, 1987), suggesting that 19871, suggesting that some some remobilremobilization has occurred. LEGEND:STOP STOP 21B LEGEND: Metavolcanic? /1 Metasubvolcanlc? Metavolcanic? Metasubvolcanic? Rocks 1 a la lbb 1 felsic. variably microcline felsic, variably schistose: schistose: quartz—feldspar quartz-feldspar porphyritic. porphyritic, sericite± sericiteLmicrocline intermediate, variably variably schistose: schistose: quartz-feldspar quartz—feldsparporphyritic, porphyritic. biotite ± sericite ±microcline biotite?sericite~microcline intermediate, Fragmental? Rocks volcanic? volcaniclastic? volcaniclastic? - volcanic? Rocks — 2a 2a 2b 2b biotitized, feldspathized, biotitized, feldspathized, lensy rock sericltized, sericitized, feldspathized. feldspathized, lensy lensy rock rock (with (withgreen Qreenmica mica lenses) lenses) Metasedimentary Rocks Rocks 3a 3a wacke, feldspathic siltstone?amphibole-rich layers feldspathicarenite arenite±ksiltstone±amphibole—rich schistose wacke, feldspathic feldspathic arenite±siltstone areniteksiltstone feldspathized feldspathized to to schistose schistosemetasediments metasediments feldspathized metasediments 3d feldspathized 3d metasediments 3b 3b 3c Schists Origin (possibly metasedimentary) Schists and and Granofels Granofels of Undetermined Undetermined Origin metasedimentary) 4a sericite±biotite schist±mlnerallzation sericitekbiotite schisthnineralization 4b intensely mineralization intensely feldspathized feldspathized rocks± rocks~mineralization 4c 4c feldspathized to schistose rocks feldspathized to Dikes Dikes 5 foliated, quartz dioritic dioritic intermediate, foliated, 66 plagioclase—porphyritic Qranodiorite granodlorite plagioclase-porphyritic intrusive contact contact 7 7 diabase diabase intrusive contact contact 8 magnetlte—biotite lamprophyre lamprophyre (Proterozoic) (Proterozoic) magnetite-biotite Most ore 4a Most ore comprises comprises subunits subunits 4 a and and 4b 4b �__ ________ ________ ______ 72 72 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area operation, and From this open pit operation, and given given the character characterof the the rocks rocks in in the nearby nearby Teck-Corona Teck-Corona trench, one can appreciate the potentially potentially narrow narrow "windows" (Figure 22) of exploration for ore ore of this type, type, even even though though this this is a large large deposit. deposit. One bodies of One can can also also appreciate the relative quietness of the highway highway after after leaving leaving this this stop. Structural ural Summary: Summary: 292±5/64±4 292±5164 hanging hangingwall w,all S0/S1 iIlR/Ci h-nilinn ut 305/62 hanging wwe, wG ,, ,, , wall ..all S2 schistose schistose ore; ore; felsic felsic metavolcanic metavolcanicrock rock S3? 270/65±5 2701695 schistose schistose ore, ore, felsic felsic metavolcanic metavolcanicrock rock 295/60±5 295160± S3? 060/60, schistose ore F3 060160,100/43 100143 schistose ore tourmaline 307/33 307133 tourmaline mineral mineral lineation lineation Lm slickenside 107/07 107107 slickenside L3 19 & 34) * Stop 22: MAGNETITE-LAYER-BEARING MAGNETITE-LAYER-BEARINGMETAWACKE METAWACKE (Figures (Figures18, 18,19 34) Location: Location: This stop is is beside besic and opposite the A Zone pit turnoff referred to for rthe theStop Stop21 21 location. location. * Stop Stop 22A: MAGNETITE-BEARING METAWACKE AND AND PORPHYRY DIKES (Figure 34) 34) MAGNETITE-BEARING beleaguered outcrop, on the the north side, immediately immediately to the west of of the the turnoff, turnoff, is all all that that The beleaguered remains of of a larger larger predecessor. predecessor. The The rocks rocksare are mostly mostlytransposed, transposed, foliated foliated metawacke metawacke with ± amphibole-rich layers magnetite  layers (Photo 8). 8). The metawacke metawacke appears to contain contain muscovite muscovite poikiloblasts. It has been intruded by two types of plagioclase-porphyritic dikes, both of which poikiloblasts. magnetite crystals have magnetite crystals within within many manyof of the the phenocrysts phenocrystssuggesting suggestingthis thisisisaa secondary secondary(metamor(metamorphic?) phenomenon. The The structurally structurallyupper upperdike dike is is more more typical typical of of feldspar feldspar porphyry porphyrydikes dikesin inthe the Hemlo (although a wide variety of textures and grain sizes sizes exists exists among among dikes) dikes) and and contains contains Hemlo area (although numerous, medium-grained, medium-grained, plagioclase plagioclasephenocrysts. phenocrysts. The structurally lower dike, now now visible only in the the blasted blasted face, contains contains fewer, fewer, and and mediummedium- to to coarse-grained, coarse-grained, plagioclase plagioclase phenocrysts. phenocrysts. It is colloquially known as "popcorn" "popcorn" porphyry. porphyry. Structural Summary: Structural Summary: 290/62 S,, 290162 S1, S2(?) S2(?) A—Zone Pit A-Zone t magnetite layers layers no magnetite layers \ gossan go; popcorn porphyry 0 I A 10 20 30 , , I plagioclase porphyry Hwy 17 cjD lQ^ amphibole—magnetite layers layers amphibole-magnetite m scale scale approximate approximate magnetite layers layers-" feldspathizedfsericitized rocks feldspathized ± sericitized rocks :0 ..,diamond drill drill corepile pile :..iam01 core exploration shack shack foundation foundation exploration etite-amphiSimplified sketch map of transposed metawacke with magnetite-amphibole layers and localized alteration. Figure 34. Stop 22: Figure �Road Log — Hemlo Area Stop 22B: 73 METAWACKE WITH WITH MAGNETITE-AMPHIBOLE-RICH MAGNETITE-AMPHIBOLE-RICH LAYERS (Figure 34) Almost immediately south of the turnoff is is an an outcrop outcrop of of foliated foliated but but "massive"-appearing "massive"-appearing metawacke which has magnetite + + amphibole-rich amphibole-rich layers and and is is locally locally garnet garnet rich. rich. The The layering layering appears to to be transposed to some some degree. degree. Some appears Some of of the the amphibole-magnetite-rich amphibole-magnetite-rich layers layers are disrupted. There disrupted. Thereare arediscordancies discordanciesbetween between blocks blocks or or wedges wedges with with respect respect to tolayering layering and and fabrics. Some Some of of the the layering layering may may be tightly folded with "S" asymmetry. The The rock rock isis intruded intruded by by foliated, boudinaged, plagioclase-porphyritic dikes containing muscovite poikiloblasts. plagioclase-porphyritic poikiloblasts. Structural summary: Structural summary: 289/68 S1, S2(?) S2(?) St, 289168 Stop Stop 22C: 22C: \ ALTERED MAGNETITE-BEARING MAGNETITE-BEARINGMETAWACKE METAWACKE (Figure (Figure 34) 34) The northernmost northernmostoutcrop outcropof of this thispart partof ofthe thestop stoplies lies27 27m msouth southof of the thewest westend endof of Stop Stop22B 22B and consists of metawacke with poorly defined magnetite magnetite layers. A the and consists A second second outcrop outcroplies lies 8 m to the southeast and consists of variably schistose, schistose, sericitized and locally pyritized pyritized rocks rocks intruded intruded by by Several years years ago ago one one could see felsic dikes. dikes. Several see magnetite magnetite layers layers within feldspathic feldspathic whitewhiteweathering rock, magnetite-bearing metawacke which weathering rock, suggesting suggestingthe the rock rock is altered magnetite-bearing metawacke (see (see Stop 23 which the outcrops is approximately on strike from this this outcrop). outcrop). Presently the outcrops in this area area are are being being reclaimed by lichen. A two more sericitic sericitic outcrops reclaimed A trail trail to to the the southeast southeast of of here here leads to two outcrops as as well as pile of ofdrill drill core. core. This was the campsite of the the foundation to a drill core shack and an unruly pile Lake Superior Mining Mining Corporation Corporation from from the the late late1940s. 1940s. Structural Summary: Structural Summary: St 284174; S,? S1 284/74; S2? * Stop Stop 23: 23: 29417; 294/?; S3 S, 066/88 066188 crenulatiort) (weak crenulation) LOWER MINERALIZED 35 & MINERALIZEDZONE ZONE (Figures (Figures18, 18, 19, 19,35 & 36) 36) Location: GoGo 110 mm further west Location: 110 further westononHighway Highway17, 17,north northside, side, from from the the A A Zone pit pit turnoff, past a small, previously previously unexposed, unexposed, rusty rusty weathering, weathering, schistose, schistose, alteration alterationzone, zone, to to aarusty rustyweathering, weathering, hydraulically cleaned outcrop (Figure 35). The small alteration zone returned a value from a grab grab hydraulically cleaned 35). alteration returned communication, 1990). sample of 43 ppb Au (M. Smyk, MNDM, personal communication, 1990). outcrop at Stop 23 is is the the surface surface expression expression of of aazone zoneof ofmineralization mineralization that that structurally structurally The outcrop underlies the main ore body, and is ore grade at about a depth of 900 m. Surface grab underlies body, and ore grade at about a depth of 900 m. Surface grab samples samples returned values of 0.02 0.31 ounces Au Au per ton (Patterson 1986). 1986). The 0.02 and 0.31 The outcrop outcrop consists consists of of transposed wacke transposed wacke \ feldspathized and sericitized,Z. feldspathized and sericitized. silicified(?) metasediments slllcified(?) . . metasediments . feldspathized. feldspathized, sericitized \\ 1 transposed wacke transposed w a c k e (magnetite) (magnetite) wacke magnetite-bearing w a c k e \ magnetite—bearing n 9 intermediate—mafic dike dike intermediate-mafic 10 10 .- , 20 2,0 I m m scale approximate approximate granodiorite dike granodiorite V / Hwy 17 Hwy 17 / rmediate— mafic dikes intermediate-mafic uartz-feldspar rtz—feIdspar porphyry / / Approximate location location of of Figure Figure 36 36 Stop 23: Mineralized Figure 35. Figure 35. Stop 23: Simplified Simplified sketch sketch map map of the surface equivalent of the Lower Mineralized Zone quartz-feldspar porphyry, metasedimentary rocks Zone quartz-feldspar porphyry, and and the adjacent, locally altered, metasedimentary rocksstructurstructurally underlying underlying magnetite-bearing magnetite-bearingmetawacke. metawacke. �______ _____ 74 74 Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area altered, schistose, schistose, quartz-feldspar quartz-feldspar porphyry, (structurally lower part of the outcrop), outcrop), which is is in in sharp contact contact with with intensely intenselyaltered alteredrocks rocksthat thatpossibly possiblyare arederived derivedfrom fromthe the structurally structurallyoverlying overlying sharp metawacke. metawacke. recognizable features indicative indicative of of aa volcanic volcanic origin, is is white The porphyry, which shows no recognizable consistsof of feldspar feldspar (some (some of which weathering, except exceptfor for local, local, bright bright orange, surface weathering, surface staining. ItIt consists which pyrite, tourmaline, and sparse green mica. Locally, Locally, the is microcline), quartz, and sericite, with pyrite, Baritehas hasrecently recentlybeen beennoted notedinincrosscrosstourmaline is is euhedral euhedraland and up up to several millimetres tourmaline millimetres long. Barite cutting cutting veinlets veinlets and and layer-parallel layer-parallel seams seams (B.R. (B.R. Schnieders, Schnieders, personal personalcommunication communication1994). 1994). feldspathized/sericitizedrocks rocksadjacent adjacent to to the the porphyry porphyryare areabout about40 40 cm cm thick thickand andare are The feldspathized/sericitized distinguishable largely largely because of the lack lack of quartz eyes, eyes, finer finer grain size, and and more more abundant abundant distinguishable sericite. Layering Layeringisisdefined definedby bygrain grainsize sizedifferences differencesand andvariations variationsin inthe the abundance abundanceof of sericite. sericite. sericite. Locallythere there are are fragment-like fragment-likefeldspathic feldspathiclenses lenseswhich whichmay mayhave haveresulted resultedfrom fromdisrupted disruptedlayering layering Locally "veins". There Thereare arealso alsonumerous, numerous,small, small, white white porphyroblasts porphyroblastswhich which appear appear to to be be or alteration "veins". retrograded. retrograded. The Theorigin originof of the the rock rockisisequivocal. equivocal. Tracing the contact between the the 2 rock types on on the the outcrop outcrop indicates indicates that that it is only locally straight: straight: ititappears appearstotochange changeabruptly abruptlybecause becausethe theporphyry porphyryisisnot notpresent presentatatthe thewest westend endofofthe the outcrop. Where Where the thecontact contactisisstraight straightand andparallel parallel to to the thepredominant predominant fabric, fabric, the the layering layering is is conformable. conformable.However, However,atatthe thewest westend, end,the thelayering layeringand andsome some of the the numerous numerous quartz quartz veins veinsfound found here are folded folded and and disrupted disrupted (Figure (Figure36) 36) and and possibly possibly transposed, transposed, suggesting suggesting the the contact contact has has here been left stepping. stepping. Several fine-grained, fine-grained, foliated, foliated, boudinaged, boudinaged, intermediate, intermediate, biotitebiotitebeen folded and is left bearingdikes dikes appear appearto to be be unaffected unaffectedby by this this folding, folding,suggesting suggestingthe thefolding foldingisisof ofthe theF2 F2generation. bearing generation. outcrop shows a fine-grained, fine-grained, biotite granodiorite dike with with finefine- to to The southwest end of the outcrop coarse-grained coarse-grainedmuscovite muscovitepoikiloblasts. poikiloblasts. -- - - - -- - -1 N quartz quartz veins veins sericite sericite schist schist 1 \ m scale scale approximate appioximate feldspathized and/or andlor silicified silicified rock rock Figure outcrop shown shown in Figure 35, as originally originally Figure36. 36. Stop Stop23: 23: Detailed Detailedsketch sketchmap mapof of part part of of the outcrop in Figure exposedalong alongHighway Highway17. 1Z Location Locationof of the the sketch sketch map map site, indicated in Figure Figure35, 35, is is approximate. exposed indicated in approximate. (Modified (Modifiedafter afterPatterson Patterson1984). 1984). �Road Log — Hemlo Hemlo Area 75 75 The adjacent to porphyry display display a fairly fairly abrupt abrupt "contact" "contact" with with the the The altered rocks adjacent to the porphyry structurally overlying overlying metawacke. metawacke. The The metawacke metawacke displays displays wispy wispy to ill-defined ill-defined layering which is structurally possibly transposition. Within possibly the the result result of transposition. Withinthe themetawacke metawackeare are transposed transposedlayers layers rich rich in in magnetite magnetite and amphibole. amphibole. Two Two outcrops outcrops to the the north north of of the theroadcut roadcutare arepart partofofthis thismagnetite-bearing magnetite-bearing metawacke unit, seen at at Stop Stop 22. 22. The magnetite-bearing unitl which has already been seen magnetite-bearingmetawacke metawacke is is intruded by feldspar porphyry dikes. intruded by porphyry dikes. Structural Summary: Summary:' Predominant Predominantcleavage cleavage (sericite) (sericite) Subordinate Subordinate fabric fabric (sericite) (sericite)(S3?) (S3?) S3? S3?fabric (sericite) in in boudin boudin neck neck * Stop Stop 24: 24: 280/68 280168 269/65 269165 242/78 242178 (late (lateoverprint?; overprint?;see see Stop Stop20A) 2OA) FELDSPATHIC METASEDIMENTARY ROCKS FELDSPATHIC METASEDIMENTARY ROCKS (Figures (Figures 18 18 and and 37) 37) Location: south side, roadcut with with outcrop Location: Continue Continuewest weston onHighway Highway17, 17 south sidel for for about about410 410 m to a roadcut outcropon on both both sides sides of of the the highway, highway, south of Moose Lake. The The features features of of the the unit unitat atStop Stop24 24should shouldbe be compared comparedto to those thoseat atStop Stop18, 1BI which which some some geologists geologistsinterpret interpretas asthe the same sameunit. unit. ItItshould shouldbe bekept kept in in mind mind that that the the highway highway exposures exposures do not not provide provide a continuous continuous section through the deposit "stratigraphy", and that that changes in rock types are evident %tratigraphy", and changes in evident along strike and and down down dip. dip. The The immediate hanging wall and and footwall footwall rocks rocks to to the Hemlo hanging wall Hemlo deposit are not not exposed exposed along along the the highway. highway. South SouthSide Side of of Highway Highway17 17 The The east east end end of of the the roadcut roadcutshows shows aa finefine- to to medium-grained medium-grainedplagioclase-pyroxene-phyric plagioclase-pyroxene-phyric diabase diabase dike. dike. This Thisisisthe thesame samedike dikethat thatlies liesnear near the the boundary boundarybetween betweenthe the Williams Williamsproperty propertyand and the Figure 22). 22). Country the Golden Golden Giant property (see Figure Country rocks adjacent adjacentto to the thedike dikeshow shownotable notable epidote epidote and and pink pink (hematized?) (hematized?)feldspar. feldspar. The outcrop consists consists mostly mostly of ofrelatively relativelyfeldspathic feldspathic metasedimentary metasedimentary rocks The remainder remainder of the outcrop which at the the next nextstop. stop. Compared Compared which show show some cleavage-parallel alteration that is better displayed at to which, although notably to Stop Stop 25, 2sl the the rocks rocks here here display display more more pronounced pronounced layering whichl notably tectonic tectonic in in origin, partly reflect reflect modified modified primary primary compositional originl is is interpreted interpretedto to at at least least partly compositionallayering, layeringlas as itit is is similar to tectonized rocks variations and partl by by grain size variations and the to less less tectonized rockselsewhere. elsewhere. The Thelayering layeringisisdefined, defined, in in part, abundance examples (modified?) abundanceof of amphibole amphiboleand/or andlorfeldspar. feldspar. Some Someof ofthe thelayers layersappear appearto to be be examples (modified?)of of amphibole-rich amphibole-rich layers common common in in other other metasedimentary metasedimentaryunits. units. For the most most part, part, the the S2 S2 Moose Moose Lake Lake mpostf8ParP0rPhYrYSwarm claim post gossan layer—parallel layer-parallel breccia breccia \ lamprophyre m -A " scale approximate :caI::Pr:ima: 1gossan Hwy 17 / N feldspar porphyry swarm 1 1gossan breccia diabase ,/ tite lamprophyre biotite lamprophyre tourmaline tourmaline alteration alterationand andbleaching bleaching I variety variety of oflayer—parallel layer-parallel breccias breccias 1 Figure feldspathic, Figure37. 3Z Stop Stop 24: 24: Simplified Simplified sketch sketch map map of of "footwall", "footwall", mylonitic(?), myl~nitic(?)~ feldspathicl metasedimetasedimentary mentary rocks rocksand andlayer-parallel layer-parallelbreccias. breccias. �Geology and Gold Deposits of the Hemlo Area 76 cleavage, where identifiable, is oriented counterclockwise to layering. Intrafolial folds are present near the east end of the outcrop and near the eastern gossan and may reflect an F1 folding event. There are two gossans in this outcrop which are sufficiently oxidized on surface to hinder determination of the "protolith' The western gossan, about 1 m thick, appears to be composed of metasedimentary rocks similar to the bounding layers. The eastern gossan, about 3 m thick, appears to consist of rocks with more biotite and feldspar (alteration?) than the bounding metasedimentary rocks, and has along its northern boundary a narrow (c20 cm), somewhat heterolithic, lensy unitwhich may have been a volcaniclastic/conglomeratic rock initially. Some of the lenses/fragments are feldspar phyric. This zone may be the eastern extension of the Highway Zone (Patterson 1986) (see Stop 27). A grab sample from this gossan returned a value of 0.01 ounces Au per ton (Patterson 1986). The roadcut face reveals clots of calcite + pyrite + tourmaline, quartz + pyrite, and pink/ orange feldspar + fluorite. Subhorlzontal to shallowly west-plunging slickensides are also present. The outcrop at Stop 24 displays layer-parallel breccias. Collectively, in the Hemlo deposit area, layer-parallel breccias are relatively late, given that there is rare evidence of ductile deformation in most cases and generally no overprinting fabric. The brecciation has affected all Archean rock types (except possibly diabase). Overall, in this part of the greenstone belt, the breccias occur from the mafic metavolcanic rocks near the Pukaskwa Gneissic Complex, about 2 km to the south, to the metawacke units about 3 km to the north (Golden Giant Mine tailings site). The breccias are most common and volumetrically important in relatively competent feldspathic rocks such as this outcrop. Layer- and fabric-parallel fault gouges within sericitic rocks, spatially associated with the Hemlo deposit, are likely equivalent examples of this brecciation. Light grey to black pseudotachylite, with or without internal layering, is spatially and apparently genetically associated with the breccias in the more feldspathic rocks. The sense of movement on the fault planes is generally not determinable, but locally shows a dextral component of displacement. Some of the breccias terminate abruptly along strike and become thin seams which may or may not contain pseudotachylite/ultracataclasite. The brecciation could be associated with a continuation of the dextral shearing noted in other stops, resulting from a change from predominantly ductile to predominantly brittle processes, or it could be a manifestation of Proterozoic crustal movement, or both. Examples of these breccias that show at least 3 stages of brecciation have been noted locally. There are about 4 "types" of layer-parallel breccias exposed in one part of the outcrop at Stop 24: (A) an uncommon semi-ductile type, with aligned layering in fragments and blocks at about 075° — the boundaries of the breccia are ill-defined; (B) the most common type, with angular, unoriented fragments in a matrix similar in colour to the host rock — generally has sharp boundaries to the breccia zone with one side commonly straight and the other slightly to very irregular in form — possibly affects (Le., postdates), type A; (C) tabularzone with angular, unoriented, various-sized fragments of country rock in a light-brownweathering, relatively high proportion of matrix. A thin section of this breccia shows that prehnite constitutes a significant portion of the matrix; (D) an in-situ shattering of the country rocks with a recessively weathering matrix — predominant fracturing at 342°. North Side of Highway 17 S S S S S S S S 5 5 S S 5 S The units are much the same as for outcrops on the south side. Several previously interesting features did not survive recent blasting. S S S �a a r ______ Road Log — Hemlo Area 77 Some features to note: • some amphibole-bearing layers contain small quantities of garnet; • collectively, both the slightly discordant faults and the layer-parallel breccias cut across layering structurally up and down; • a very-fine-grained, white matrix of a layer-parallel breccia body (type C?) south of the claim post (Figure 37). Locally forms up to 50% of the breccia; • a swarm of feldspar porphyry dikes occurs at the east end of the outcrop as did some epidotebearing pseudotachylitefultracataclasite (before recent blasting); • there are some sinistral and dextral kinks (F4) in the layering; • northerly striking, Proterozoic, biotite + pyroxene(?) lamprophyre dikes occur in the western third of the outcrop; one has a central "core" consisting of a 3 cm thick calcite vein. Structural Summary: SI 82? cleavage (local) 285 to 293/62±2 298/56 5? fabric (sericite) L? (intersection) 2 72/63 (muscovite elongation?) L1? (intersection) 345/53 078/49 L (slickenside) 103/08 to 283i8 * Stop 25: HEMLO FAULT ZONE (Figures 18, 19 & 38) LocatIon: Go 600 m furtherwest on Highway 17, north side, from the claim post shown in Figure 37, to a set of small outcrops on both sides of the highway, about 60 m west of the Williams Mine tailings/effluent overpass. These outcrops also show many of the same features as at Stop 26 but have suffered less from the ravages of recent blasting. This is one of several sets of outcrops that depict the Hemlo fault zone, which the highway roughly parallels for a few kilometres. The Hemlo fault zone is characterized, in this area, by strongly deformed rocks which comprise mafic, magnesian schists at or near the contact between gneissic amphibolite and gneissic feldspathic rocks. The layering in these rocks is Interpreted to be, in part, mylonitic (Photo 9). The amphibolite is part of the mafic unit of Stops 26 and 28 and has a whole rock composition comparable to high-iron tholeiltic basalt. No primary volcanic features have been observed. Multiplely deformed veinlets of quartz, feldspar, epidote, and calcite are common in the amphibolite. The gneissic feldspathic rocks are felsic in composition and locally contain phenoclasts(?) of quartz, similar to volcaniclastic metasedimentary rocks in the area. a a a a a a 0 a N gnelssic feldapathic rocks chlorite schist. © 'hand fold 1 chlorite sohist amphibolite S breeds br•ccla with epidole and hematite Hwy 17 0 'P . m scale approximate 20 5 °"e7 Williams Mine telling; overpass gnelsslc amphibolite FIgure 38. Stop 25: Simplified sketch map of lithologic units and structures of the Hemlo fault zone, including the "hand" fold. �78 78 * Stop Stop 25A: 25A: Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area NORTH NORTHSIDE SIDEOF OFHIGHWAY HIGHWAY 17 17 (Figure (Figure38) 38) Outcrop "a" Feldspathic Feldspathiclaminated laminated rock rock showing: showing: (1) tectono-metamorphic features such such as as symmetrical, symmetrical, pale pale pink (hematite?, potassic feldspar?) (1) tectono-metamorphic features (hematite?, potassic and sericitic sericiticalteration alterationalong alongcleavage cleavageplanes planesas as well well as as bleached bleached rims rims along along planes planes defined defined by by and chlorite chlorite(similar (similarto to that thatseen seenlocally locallyat atStop Stop24); 24); (2) (2) west-closing west-closing fold fold in inlayering; layering; (3) (3) quartz quartz necks necksin in boudins boudins(traces (tracesof ofnecks neckson on surface surfaceare are080±5), 080&5),and androlls rolls(075/50) (075150) in in undulating, undulating, locally garnet-bearing layers; locally garnet-bearing layers; (4) (4) fine-grained, intermediate intermediate dike; dike; (5) of recent blasting). The (5) zone of layer-parallel, cataclastic breccia breccia (not well exposed because of The exposure exposure used used to to show show that that the the country country rocks rocks and and the the intermediate intermediate dike dike were were brecciated. brecciated. (See (See Stop Stop24 24 for for discussion discussionof oflayer-parallel layer-parallelbreccias.) breccias.) Outcrop Outcrop "b" This This outcrop outcrop displays displays the the contact contactbetween betweengneissic gneissic feldspathic feldspathic rocks rocks and andgneissic gneissicamphibolite amphibolite containing chlorite + amphibole schist. The feldspathic rocks form part of a unit that containing chlorite + amphibole The feldspathic rocks form part of a unit that structurally structurally overlies overliesthe theamphibolite amphiboliteunit unitfor foratatleast leastseveral severalkilometres. kilometres.To Tothe theeast east(e.g., (e.g., Stop Stop24), 241,the therocks rocksofof this this package package display display layering layering that that isisbetter betterdefined definedand andsomewhat somewhat resembles resembles less less tectonized tectonized feldspathic metasedimentary metasedimentary rocks. rocks. To To the thewest, west, opposite opposite"Fault" "Fault" Lake Lake (Figure (Figure 18), 18), the the correcorrefeldspathic sponding quartz-feldspar phyric spondingfeldspathic feldspathicrocks rocks(i.e., (i.e., structurally structurallyabove above the the amphibolite amphibolite unit) unit) are quartz-feldspar phyric and and contain contain lapilli-size lapilli-size lenses lenses suggesting suggesting a fragmental protolith. The Thefeldspathic feldspathicrock rockpackage package may volcaniclastic deposits maycomprise comprisemore more than than one one primary primary unit unit derived derived from pyroclastic pyroclastic and/or andlor volcaniclastic deposits that thathave havebeen beenheterogeneously heterogeneouslytransposed. transposed. In outcrop outcrop 25b, 25b, the the thinly thinlylayered layeredfeldspathic feldspathicrocks rockshave haveaatectono-metamorphic tectono-metamorphiclayering/ layering1 In cleavage cleavage which is is interpreted interpreted to be, be, in in part, part, mylonitic. mylonitic. Many Manyofofthe thecleavage cleavageplanes planeshave have an an associated associated symmetrical symmetrical alteration alteration which which itself itselfproduces producesaasmall-scale small-scaletectono-metamorphic tectono-metamorphic layering, considered consideredhere hereto to be be superposed superposedon on flattened flattenedand andtransposed transposedprimary primarylayering. layering.The The layering, layersare arelocally locallydisplay displaypinching pinchingand andboudinage, boudinage,which whichhas hasresulted resultedininapparent apparentintrafolial intrafolialfolds foldsinin layers some places. places. The Thelayers layersare arealso alsolocally locallydiscordant discordantas asaaresult resultofofslightly slightlyoblique obliquedextral dextralfaults. faults. some Isolated, Isolated, small, small, flattened flattened quartz quartzcrystals crystals(phenoclasts?) (phenoclasts?)are aresparsely sparselydistributed. distributed. Elsewhere, Elsewhere, quartz quartzoccurs occursas asflattened(?) flattened(?)thin thinseams, seams, particularly particularlywithin withinill-defined ill-definedzones. zones. The mafic maficschists schistsare arephyllonites phyllonitesand andmay mayhave havebeen been derived derived from from the theamphibolite amphiboliteunit unit The exposed andlor from from relatively relatively magnesian-rich magnesian-richdikes dikes in in the the fault fault exposedon onthe thesouth southside sideof ofthe thehighway highwayand/or zone zone(see (see Stop Stop 26). 26). As Aswith withStop Stop26, 26,deflection, deflection,backrotation, backrotation,and andcrenulation crenulationofofmore morethan thanone one fabricappears appearsto to have havedeveloped developedin in response response to ductile shearing. Irregular Irregularzones zones and and clusters clustersor or fabric podsconsisting consistingof ofcoarse-grained coarse-grainedtourmaline tourmalineand andaafine-grained fine-grainedunidentified unidentifiedwhite whitemineral mineralcan can pods locally befound. found. locallybe At Atleast leasttwo twotypes typesofofdikes dikesare arepresently presentlycontained contained within within the the schists: schists: both bothtypes typesshow show boudinage. boudinage. The Thetypes typesare: are: (1) (1) an analtered, altered,chloritized chloritizedgranitoid granitoiddike dikewhich whichhas hasundergone undergoneboudinage boudinageand andhas hasirregularly irregularly distributed distributedpink/hematitic pinklhemat iticalteration; alteration; (2) (2)aafoliated foliatedmafic maficdike dikecontaining containingnumerous numerousmafic maficxenoliths xenoliths(possibly (possiblyakin akintotothe thelamprophyre lamprophyre dike dikeof ofStop Stop29), 29),and andhaving havingaafolded foldedand andcrenulated, crenulated,internal internalfabric. fabric. Towards the the east east end end of of this this outcrop outcrop within within the the feldspathic feldspathicrock, rock, isisaa 10 10 cm thick, thick, brittle brittlefault fault Towards breccia(oriented (orientedatat345/74), 345174),which whichdisplays displaysat atleast leasttwo two stages stages of of brecciation brecciation (i.e., (i.e., breccia brecciawithin within breccia �— Hemlo Area Road Log - 79 79 breccia). breccia). The Thecountry countryrocks rockshave haveundergone undergone hematization hematization and and epidotization epidotization within within and and adjacent adjacent to this zone. The does not to exposure exposure limitations) limitations) to have affected the The breccia brecciadoes not appear appear (in part due to have affected phyllonite.However, However,with withthe theexception exceptionofofrelatively relativelylate latestrike strikeslip slipmovement movementon onearlier earlierfaults, asis is phyllonite. faults, as suggested in the Hemlo Hemlo area area by by offset offset diabase diabase dikes and subhorizontal slickensides, slickensides, the fault breccia is is considered considered to to post-date post-date ductile ductile deformation deformationbecause because of of the theundeformed, undeformedlangular, angularl fragments it contains. Outcrop Outcrop "C" "c" This is aa small small outcrop, outcrop, about about 25 25 m m west west of of outcrop outcrop 25b, 25b, which which shows shows schistose schistose and and gneissic gneissic amphibolite notably folded. folded. The amphibolite intruded intruded by by granitoid granitoid dikes, dikes, all all of which have been notably The main main fold, the "hand fold", fold", is atypical in in that that the the "fingers", "fingers", defined defined by by several several folds in in aa granitoid granitoid dike, dike, display display multiple orientations of a crenulation cleavage defined defined by by the the schists schists (Photo (Photo 10). 10). Crenulation Crenulation cleavage various orientations D3, and although it displays various orientationsin inany any cleavage in the Hemlo Hemlo area area is is ascribed ascribed to D3, one outcrop outcrop (±200 for example), example), ititgenerally generallystrikes strikes east-northeast east-northeast to to east-southeast. east-southeast. However, (X?OOfor However, in this case, the about 125O 125°from fromnorth north to to southeast. southeast. Although this the strike strike of of the the cleavage cleavage spans spans a range of about Although not fully understood, this fold fold could could be be an aberration aberration within the the fault fault zone zone because becauseof of the the overall overall orientation large-scalecrumpling crumpling of orientation of of the the layering layering and and dikes. It is possibly a result of a relatively large-scale layers adjacent to a detachment. detachment. Chevron-like Chevron-likefolding folding of of the theschistose schistoselayering, layeringl and andisolated isolated boudins of dikes attest to considerable shortening and extension in different Isolated boudins different directions. directions. Isolated "knots" of mediummedium- to coarse-grained coarse-grained tourmaline are locally present. \ Structural Summary: 280/60 (tectono-metamorphic in feldspathic 280160 (tectono-metamorphic feldspathic rock) rock) Layering Layering S 265/83 S* 265183 chlorite; chlorite;various various orientations orientations chlorite; various orientations orientations 300/85 chlorite; S*, 300185 205/78, 225/77, 240/8 247/53, S3 205178, 225177 240187 247153,297/51 297151 crenulation crenulation fabric fabric with with corresponding: corresponding: S3 242/52, 282/70, 022/43, 015/40, 043/39 crenulation lineations 282/70,022/43, 015140,043139 lineations L 242152, 281/06 slickenside 281106 slickenside lineation lineation L8 S. Stop 25B: SIDE OF HIGHWAY Stop 25B:SOUTH SOUTH SIDE OF HIGHWAY17 17(Figure (Figure38) 38) Outcrops "d" "d" and "e" "e" The gneissic amphibolite amphibolite is is considered considered to to be be derived derived from from highly highly deformed deformedmafic maficmetavolcanic metavolcanic rocks because it can be traced as part of a "wedge" of mafic mafic rocks rocks into into the the pillowed pillowed mafic mafic rocks rocks described at Stop 28. However, there are no unequivocal (let alone equivocal?) volcanic features described at Stop However, there are no unequivocal (let alone equivocal?) volcanic features at this outcrop. outcrop. The Theamphibolite amphiboliteconsists consistsofofplagioclase, plagioclaselhornblende, hornblende,and andlesser lesseramounts amounts of of biotite. biotite. The Thelayers layersare arepoorly poorlyto tomoderately moderatelydefined definedby byvariations variationsininthe the abundance abundanceof of these thesethree three constituents. Well-defined main mineral constituents. Well-definedmicaceous micaceouslayers, layers, comparable comparableto to those thosedisplayed displayedat at the the "hand fold" outcrop (25c), were present near outcrop 25e before recent blasting. outcrop (25~1, 25e before recent It is not not known known whether these layers layers are largely primary primary (e.g., (e.g., interflow interflow sediments) sediments) and/or tectonic in in origin. origin. The outcrop contains numerous veins veins consisting consistingofofeither either quartz quartz or or quartz quartz + epidote k± contains numerous feldspar. feldspar. The The veins veinshave havebeen beenbuckled, buckled,dismembered, dismemberedl and/or and/or transposed transposed depending depending on on their their orientation and time of emplacement relative to the complex tectonic history. Various Various veins veins are are folded with "S" "S'' or "Z" asymmetry: asymmetry: locally locallyrefolded refoldedfolds folds are are present. present. Two fabrics in the amphibolite, one one parallel parallel to to the the layering layering and and one one axial axial planar planar to to the the folds, folds, Closeinspection inspectionofofthe thefabrics fabricsreveals revealsaathird thirdfabric fabricwhich whichappears appearsto to can be locally discerned. Close crenulate crenulate the other other two. two. Structural Summary: Structural Layering —290±5/81 (with Layering -29M5181 (with internal internal foliated foliated biotite) biotite) Fabric —276/85 biotite Fabric -276185 biotite biotite, -260±5/85(±) S3 fabric -26W5185(*) biotite, crenulating crenulating fabric fabric �_I 03 0 5 012345 Legend:Stop 26 Legend: Stop 26 1 1 22 gneissic(mylonitic?) (mylonitic?) amphibolitic amphiboliticmafic maficmetavolcanic metavolcanic gneissic m gneissic (mylonitic?) (mylonitic?) feldspathic feldspathicvolcaniclastic volcaniclasticmetasediments metasediments gnelssic 1 3a 3a chlorite±actinolite±talc schist chlorite~actinolite~talc schistdikes? dikes? 3b 3b biotite schist schistdikes dikes biotite -outline of ofoutcrop outcrop outline 4 n - -- - - - - ! lithologiccontact contact ——-lithologic 3c 3c tourmaline ± feldspar dike/vein tourmaline±quartz ?quartztfeldspar dikelvein + —. 44 plagioclase-porphyritic dike dike plagioclase—porphyrltic 55 diabase dike dike dlabase ..ae. fault fault top edge edge of of roadcut roadcut 4 2 :zz=-:-3b 2 3b —___, 2 0 CD 2 0 0 31 cc 0. 2 C) 0 a 0 CD D 0 C,, Hwyl7 Hwy 17 C,) 0 -I, -I. i CD Detailed sketch sketch map map of of the the Hemlo Hemlofault fault zone zone and andthe thecontact contactbetween between Figure39. 39. Stop Stop 26: 26: Detailed Figure and mylonitic(?), gneissic amphibolite feldspathic, mylonitic(?), gneissic, metasedimentary rocks, feldspathic, mylonitic(?), gneissic, metasedimentary rocks, and mylonitic(?), gneissic amphibolite with withschists schistsderived derivedfrom fromsheared shearedmagnesian-rich magnesian-richdikes. dikes. (Modified (Modifiedafter afterSmart Smart1988). 1988). 5 CD �Road Log — Hemlo Area 81 81 Stop 19 &&39) Stop 26: 26: HEMLO HEMLOFAULT FAULT(Smart's (Smart'soutcrop) outcrop)(Figures (Figures18, 18,19 39) Location: Go Go about about370 370 m m to to the thewest weston onHighway Highway17, 17 north north side, side, to to aa steep, steep,77m mhigh highroadcut. roadcut. The outcrop outcrop has has been been studied studied in in detail detail(Smart (Smart1988) 1988) although although the theexposed exposedface facehas hasbeen been The considerably modified modifiedby by subsequent blasting. The The outcrop outcrop shows the contact between between gneissic considerably feldspathic' rocks rocks and and structurally structurally underlying, underlying, gneissic, amphibolitic rocks, rocks, both both of of which which are are feldspathic similar to corresponding units described for Stop 25. similar corresponding units described for Stop 25. Refer to Stop Stop 25 25 for for aa more moredetailed detailed descriptionof ofthese these22rock rocktypes. types. At AtStop Stop26, 26, a pyritiferous gossan lies lies within the feldspathic rocks description pyritiferous gossan feldspathic rocks at or near the contact with the amphibolite. amphibolite. Mafic Mafic schists schists of of distinct composition composition lie lie within the gneissic gneissic amphibolite. amphibolite. The mafic and mafic schists schists comprisechlorite±tremolite/actinolite comprise~chlorite~tremolite/actinolite andchlorite chlorite++talc±tremolite/actalettremolitelacphyllonites, all of of which which contain contain sufficient sufficient magnetite magnetite to attract attract aa hand hand magnet magnet to to some some tinolite phyllonites, degree. These Theseschists schistscommonly commonlycontain containundeformed, undeformed,med medium-grained, pyritecubes cubes(common (commonin in degree. ium-grained, pyrite similar shoreline near Heron Bay). The similar schistose schistose rocks rocks as as far far away away as the Lake Superior shoreline The schists schists are interpreted interpreted to to have havebeen beenderived derivedlargely largelyfrom fromlineated/foliated, lineatedlfoliated, finefine- to tomedium-grained medium-grained actinolite-rich actinolite-rich dikes, dikes, as as can can be be seen seen 1.0 1.0 km to the west on the north side of of the highway highway at the contact between between amphibolite amphibolite and feldspathic rocks. These These dikes dikes are highly highly deformed within the contact picriticbasalt basalt(based (basedon on Irvine lrvine and and Baragar Baragar fault aacomposition fault zone. They Theyhave compositioncomparable comparableto to picritic .komatiitic .....have .Dasait .. ,. . . .. .. - ... . 1971) basalt (based contain considerably I Y A 1 or Komatlmc pzsea on on Jensen Jensen 1976) i.---. w q and contain considerablymore moreMgO, M ~ ONi, Ni, , and andCr cr than chioritic schists than the the tholelitic tholeiiticbasalts basaltsand andamphibolite amphibolite(see (see Muir Muir 1982b). 1982b). Locally, Locally, some of the chloritic schists which which have have aa somewhat somewhat different different colour, colour, appear appear to have have been been derived derived from from the thegneissic aneissic amphibolite. amp >--A. The by: mafic I ne gneissic gnelsslc feldspathic tetaspatnlc rocks rows have nave been intruded by: maficdikes dikes which which may may have have been been isoclinally folded and are now biotite schists; and numerous plagioclase-porphyritic dikes that isoclinally folded and are biotite schists; and numerous plagioclase-porphyritic dikes thatare are slightly boudinage. Some porphyritic dikes display slightlydiscordant discordantto tothe the gneissosity gneissosityand and display display boudinage. Some of of the porphyriticdikes poikilofracture and and cleavage cleavage controlled controlled hematization, hematization, and and some some show show subhedral subhedral muscovite muscovite poikilofracture blasts. AAfine-grained, fine-grained,feldspathic, feldspathic,dike-like dike-likebody, body, containing containing crystals crystals and and clumps clumps of of crystals crystals of of blasts. mediumto very coarse-grained tourmaline, occurs within chlorite + actinolite schist. Coarse+ Coarsemedium- very coarse-grained grained grained tourmaline tourmaline also also occurs occurs as as clusters clusters or or pods pods in in the schists. schists. The phyllonites phylloniteshave haveaavariety varietyof of fabrics, fabrics, within within and andbetween betweenlozenges, lozenges,that thatdisplay displaydeflected deflecteld The 1; n,,w,,eA\ L.-+nLwn+-4..A A ..., A-nn..l-+..A C-t..-:-... k:-L. --.. -----A - A tu - result ---.. n (IS., WI VGUJ, backrotated, uawuuiawu, and a11ucrenulated WGIIUI~LGU Ifabrics ~ J I I G S WIIIGII are tr~~erpreteu ue aa resuil of OTD3 u3 (i.e., curved), which are interpreted to be deformation deformation (see (see also Muir Muir and Elliott 1987). 1987). Many Many of of the the fabrics fabrics appear appear to to be be consistent consistent with with ductile that thev they disdavs-c-c'-like display s-c-c'-like confiaurations. configurations. However, ductiledextral dextralshear shear(see b e eHugon Huaon1986) 19861in that However,the the :-A fi A- L- IA -f following points should be made: (1) The temporal and geometric relationships of fabrics are locally complex and equivocal, with with some overprinting by another set of crenulation fabrics, possibly due to progressive flattening/ ling1 shearing. (2)Extension kxtension by ~yboudinage, Douainage,shortening snortenmgby Dyfolding, tolamg,and andundulations undulationsininthe thelayers layersand anddikes, dikes,has has (2) occurredinin33 dimensions, dimensions,resulting resultingininhighly highlyvariable variableorientations orientationsof oflozenges, lozenges,fabrics, fabrics,and andminor minor occurred fold fold axes. axes. D2event event produced produced regional regionalfolds, folds, with with "S" "S" (3) The The structural structuralhistory historyof ofthis thisarea areasuggests suggeststhat thatthe theD2 (3) asymmetry, asymmetry, that thatmay mayhave haveresulted resultedfrom fromaacomponent componentofofsinistral sinistralshear. shear. alnnfl this t r--.-.-. t ~ c t ~ discontinuity disrmntin~~itv ~ r A .... .-..J should c Therefore. a s- i m,-. ~-lhistory e.historvof movement Therefore, simple structural not - - - - ,a -. ,of- .movement . .-along .= this -...- zone --. .- of -. s-.. -.---. whould not be assumed. assumed. AAdiabase diabasedike dikehas hasintruded intrudedall allrock rocktypes typesatatthe theeast eastend endofofthis thisoutcrop. outcrop. be ~~ �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 82 82 Structural Structural Summary: Summary: structures, overall, are are quite quite variable within within the the outcrop; "typical" "typical" orientations (most measured structures, orientations are are listed listedbelow) below) Layering -'263/63 Lm —312/42 D S, —265/60 —259/60 S3 —283/59 —243/64 L3 '-053/37 S —290/17 * Stop Stop 27: 22 gneissic gneissic mineral lineation of hornblende and locally tourmaline orientation of porphyritic porphyritic dikes orientation dikes chlorite chlorite chlorite (deflects Ssc) chlorite (deflects53c) crenulates above crenulates above planar planar fabrics fabrics (later (later overprint?) overprint?) crenulation crenulation lineation lineation possible possible stretch stretch lineation lineation HIGHWAY ZONE ZONE (Figures (Figures 18 18 & 40) Proceed 1.3 17,north northside, side, to to aa point point 175 m m to to the west of the Location: Proceed 1.3 km west on Highway 17 Highway sign indicating indicating "Cigar "Cigar Lake". Lake". The highway sign is incorrect, but there is no Highway sign highway sign no widely the lake lying immediately immediately to to the the south south of of the the highway highwayat atthis this location. location. This accepted name for the This term "Fault" reference in the assessment guide uses uses the term "Fault" Lake Lake because becauseof of a similar earlier reference in the assessment records records because it is geologically geologically appropriate. appropriate. (Officially and because (Officiallyrecognized recognizednames namesfor forother otherlakes lakesininthe thearea area named Lake (also (alsooccasionally occasionally applied applied to to "Fault" "Fault" Lake) Lake) already already exist.) exist.) At Stop named Cigar Cigar Lake Lake and Rule Lake 27, aa hydraulically hydraulically cleaned cleaned outcrop outcrop extends extends up up the the hill, hill, to to the north, north, within the 27 the cleared clearedhighway highway right-of-way. right-of-way. This This exposure exposure is is particularly particularlyuseful usefulfor for at at least leasttwo two reasons. reasons. ItItisisone oneof of the the best bestexposures exposuresof of what is locally locally known as the Highway Zone, and it demonstrates some of the structural complexknown Highway demonstrates the structural complex- that complicate complicate stratigraphic stratigraphic reconstruction reconstruction and and interpretation. interpretation. The Highway Highway Zone is is ities that essentially a deformed, and possibly possibly altered, erratically quartz-feldsparerratically auriferous auriferous unit unit of felsic, quartz-feldsparphyric, phyric, fragmental fragmentalrocks rockswhich whichare areinterpreted interpretedtotobe bevolcanic volcanicininorigin. origin.ItItisistraceable traceablefor forabout about22km km but its character along strike does change from from place place to to place. The The style style of of deformation deformationin inthe the outcrop, including discordancies in andlor fabrics, illustrates illustrates that that folding, folding, including numerous discordancies in the layering layering and/or ductile and brittle faulting have ductile shearing, shearing, and have produced, produced, on this mesoscopic mesoscopic scale, scale, aa tectonotectonostratigraphic primary, stratigraphic stratigraphic section. section. Detailed stratigraphic section section rather rather than a preserved, primary, Detailedmapping, mapping, overall, suggests this style of deformation deformation is is represented represented on a much larger scale as well. The southern half of the outcrop consists of: of: aa zone of slightly rusty weathering, schistose, garnetiferous, metasedimentary rocks rocks which which display display thinly garnetiferous, biotite-quartz-feldspar-bearing biotite-quartz-feldspar-baring metasedimentary laminated, tectono-metamorphically modified modified primary primary layering; and a zone of feldspathic metasedimentary rocks which which display display highly highly cleaved, cleaved, more more widely widely spaced, spaced,tectono-metamorphic tectono-metamorphic layering. The Thelayering, layering, which which may may be be mylonitic, mylonitic, at at least least in part, reveals reveals sharp, tight, and and in some cases cases rootless, S-shaped S-shaped folds with later, locally locally developed, Z-shaped folds. The central part of of this this outcrop outcrop consists consists of what what appear appear to be be wedges wedges or or lozenges lozenges of fragmental units units which are juxtaposed juxtaposed and apparently interleaved interleaved with medium fragmental medium to to coarse-grained coarse-grained wacke. The Thefragmental fragmentalrocks rockscan canbe besubdivided, subdivided,at atleast leastlocally, locally, on on the the basis basis of of type, type, size, size, and and abundance of the fragments. The structurally lowest fragmental unit is pyritiferous, rusty abundance the fragments. lowest fragmental unit pyritiferous, rusty weathering, quartz-feldspar phyric, and relatively monolithic, although a variety of fragments is weathering, present overall (Photo 11). Some Some of the the fragments fragments have been converted converted into into 22 or or more more smaller smaller lenses by the development of of aa sericitic sericitic cleavage through through them. them. Some lenses consist entirely of completely dismembered. dismembered. The quartz which may indicate that some quartz veins have been completely structurally distinctive for its chloritickbiotiticfragments, chloritic±biotitic fragments, many display 2 many of which display2 structurallyuppermost uppermostunit unit is distinctive or more "tails". "tails' Grab ounces per ton Grabsamples samplesfrom fromthe thepyritiferous pyritiferousunit unitreturned returnedAu Auvalues valuesof of <0.01 <0.01 ounces ppb (M. (M. Smyk, Smyk, MNDM, MNDM, personal personal communication, communication, 1990). 19861, and 164 ppb (Patterson 1986), �Road Log Log — -Hemlo Hemlo Area Area Road 83 83 At the the north northend endofofthe theoutcrop, outcrop,the thefragmental fragmentalunits unitspresently presentlylielieadjacent adjacenttotolayered, layered, At feldspathic, volcaniclastic volcaniclasticmetasedimentary metasedimentaryrocks rockswhich whichdisplay displayvestiges vestigesofofF2, Fg,S-shaped S-shapedfolds folds feldspathic, F3, Z-shaped folds. Relatively small lenses of a tectonically overprinted by narrow, planar zones of overprinted by narrow, planar zones of F3, Z-shaped folds. Relatively small lenses of atectonically disrupted unit unit of of schistose, schistose, garnetiferous garnetiferousmetawacke, metawacke, illustrate illustrate the the disruption disruption of of layering layering in in the the disrupted northern third of the outcrop (e.g.. Unit 1 e in Figure 40). northern third of the outcrop (e.g., Unit 1 e in Figure 40). Although aa few few straight straight quartz quartz veins veins are arepresent presentininthe theoutcrop, outcrop,most mostsecondary secondaryquartz quartz Although occurs as knots or deformed veins. The deformed veins range from continuous and buckled, to occurs as knots or deformed veins. The deformed veins range from continuous and buckled, to highly dismembered. Brittle faults, which overprint the ductile deformation fabrics, are mostly highly dismembered. Brittle faults, which overprint the ductile deformation fabrics, are mostly byapparent apparentsense senseof ofdisplacement. displacement. dextralby dextral The country countryrocks rocksare areintruded intrudedby byfoliated, foliated,medium mediumgrey, grey,fine-grained fine-graineddikes, dikes, one one of of which which The Archean diabase dike which has locally shows tightly folded internal layering, and by a late shows tightly folded internal layering, and by a late Archean diabase dike which has locally intrudedparallel parallelto to the thelayering. layering. intruded Pyritiferous, schistose, schistose, high-strain high-strainzones zones are are exposed exposed in in 22 other other places places to to the the west west of of this this Pyritiferous, They may be the equivalent of the Highway Zone but each has somewhat different outcrop. outcrop. They may be the equivalent of the Highway Zone but each has somewhat different lithologiccharacteristics. One gossan,inin rockcut about350 350mmtotothe thewest westof ofStop Stop27 an lithologic characteristics. One gossan, a arock cut about 27, returned returned an assay value of 337 ppb Au, and the other gossan, near a turnoff to the north (shown on Fiaure 18), assay value of 337 ppb Au, and the other gossan, near a turnoff to the north (shown on Figure * - -18), allout700 DM, 700mmwest westof Stop stop27, 27 returned returnedan anassay assayvalue valueofof22ppm ppmAu Auand and66ppm ppmAg Ag(M. (M.Smyk, smyk,MN MNDM, about communication,1990). 1990).Previous Previousassay assayresults, results,from fromthe thelatter lattergossan, 0.32 ounces ounce;sAu Pisrsonalcommunication, Au personal gossan, ofof0.32 ar tnn 2nd ft AQ nl mr^nc*A n n n r tnn ivvGI xfnrn rannr+a/Â¥ hi, k h i i r /ift00l^\ .-+-Aif-li .A- È -A n 4 n n 4 PL. .", ,and w.-ru ounces uunwuQ cuul i cby UY ~ Muir IVIU~I (1982b), IIWLU,, a1 IUvalues V ~ I U C Sof UI<0.01, <-U.UI,0.01, U.U I, and and per ton 0.43 Ag per ton were reported and 0.04 ounces ouncesAu Au per per ton ton were were reported reportedby byPatterson Patterson(1986). (1986). This Thisgossan gossanisisinincontact, contact,on onthe the north north 0.04 side, with a locally highly strained and hematized, plagioclase-porphyritic felsic body that has side, with a locally highly strained and hematized, plagioclase-porphyritic felsic body that has been intruded by less deformed, essentially foliation-parallel, plagioclase-porphyritic felsic dikes. been intruded by less deformed, essentially foliation-parallel, plagioclase-porphyritic felsic dikes. of ui lu>ci StructuralSummary: Summary: Structural Feldspathicmetasedimentary metasedimentaryrocks rocks(south (southpart partofofstop): stop): Feldspathic Myloniticlayering layering 270/64 270164 Mylonitic PossibleS2 Syfabric fabric 279/74 279174 Possible PossibleS3 S3fabric fabric 253/74 253174 Possible Metasedimentaryschists: schists: Metasedimentary Mylonitic layering 275-290160 Mylonitic layering 275-290/60 Sericitic,quartz-feldspar-phyric quartz-feldspar-phyricfragmental fragmentalrock: rock: Sericitic, Crudelayering layering(S0/S1?) (SdS,?) 2700 270 Crude S2fabric fabric (alignment (alignmentof of fragments) fragments) 283° 283O S2 Sericitic fabric 252i5O Sericitic fabric 252±5° Volcaniclasticmetasedimentary metasedimentaryrocks rocks(north (northpart): part): Volcaniclastic SdS, layering layering 270/61 270161 SO/SI S2cleavage cleavage(axial (axialplanar planarto toS-folds) S-folds) S2 280167 in feldspathic schist 280/67 in feldspathic schist 295167 in inadjacent adjacentfeldspathic feldspathicwacke wacke 295/67 S3fabric fabric 255/61 255161 in in feldspathic feldspathicschist schist S3 245Oto to255° 255O Axialplanar planar(to (toF3 F3Z-folds) 2-folds)S3 S3 245° Axial 230° 310° 340 Dextral brittle-ductile faults Dextral brittle-ductile faults 230°, 310°, 340° �Geology Geologyand andGold GoldDeposits Depositsofofthe theHemlo HemloArea Area 84 84 amphibole + garnet ± quartz layer opposite page) Stop Flgure40. 40. (legend (legend on oppositepge) Stop27: 2 2 Detailed Detailedsketch sketchmap mapof of the the Highway HighwayZone: Zone: Figure folded folded and and faulted, faulted,auriferous, auriferous, felsic, felsic,quartz-feldspar-phyric quartz-feldspar-phyric pyrociastic pyroclastic rocks rockssandwiched sandwichedbebetween T.L.Muir, Muir,OGS, OGS, 1990). 1990). tween variably variably strained strainedmetasedimentary metasedimentaryrocks. rocks. (Geology (Geologyby byT.L. �Hemlo Area Road RoadLog Log — - Hemlo Stop 28: * Stop 85 TURNOFF MAFIC HEMLO TURNOFF MAFIC PILLOWS PILLOWS(Figures (Figures18 18&& 41) 41) west on Highway 17, north side, side, for for 2.6 2.6 km to an unmarked Location: Continue west 17 north unmarked gravel road road turnoff, to the westbound passing passing lane (this the south, south, at at the the west west end end of a awestbound (this road road leads leads to the old old site of Hemlo). Hemlo). The outcrops outcrops at at this this stop stop display display pillowed pillowedand and non-pillowed, non-pillowed, high-iron high-irontholeiitic tholeiiticbasalt basaltflows. flows. They are part of a large, tectonic(?) "wedge" of mafic rocks that are 250 m thick here and thin to the They are part alarge, tectonic(?) "wedge" of mafic rocks that are 250 m thick here and thin tothe than 50 50 m. m. The stratigraphic stratigraphic relationship east to less than relationshipof of this this "wedge" "wedge"to toaathick thickpillowed pillowedunit, unit,lying lying LEGEND: STOP STOP 27 27 Volcaniclastic Volcaniclastic Metasediments Metasediments la feldspathic wacke: wacke: highly strained, strained, mylonitic(?), mylonitlc(?), transposed, cleaved lb garnet-biotite-feldspar garnet—biotite—feldsparwackelsiltstone: wacke/siltstone: mylonitic(?), transposed, transposed, laminated laminated highly strained, mylonitic(?), ic garnetiferous garnetiferous wacke, transposed transposed 1d feldspathic siltstone: siltstone: with preserved preservedS0S, S& layering generally with 1e metawacke: garnet—feldspar—biotjte garnet-feldspar-biotite schist schist if feldspathic, feldspathic, feldspathized(?) feldspathized(?) arenite Quartz-Feldspar-Porphyritic, Felsic Units Ouartz—Feldspar—Porphyritic, Felsic Pyroclastic Pyroclastic Units 2a 2a tuff(?) crystal tuff(?) 2b 2b relatively monolithic relatively monolithiclapilli—tuff, lapilli-tuff, lapilli—stone, lapilli-stone, tuft: tuft pyritiferous, altered(?) pyritiferous, sericitic, sericitic, altered(?) 2c 2c heterolithic lapilli-tuff, lapilli—stone: !a.pilliistone: heterolithic lapilli—tuff, with chloritic and and sericitic lenses lenses Dikes Dikes 3 fine—gralned, intermediate intermediate fine-grained, Intrusive Contact Contact 4 diabase outline of of outcrop with outline with internal internal patch patch of of overburden overburden lithologic contact: contactmay mayalso alsobe betectonic tectonicdiscontinuity discontinuii layering layering - —- — apparent tectonic discontinuity discontinuity — predominant cleavage predominant cleavage bounded zone zone of F3 bounded F3 'Zn—shaped 'Ze-shaped folds quartz veins, veinlets veinlets �86 86 Geologyand and Gold Gold Deposits Depositsof of the the Hemlo HemloArea Area Geology to the thenorth northand andwest-northwest west-northwestat atBotham BothamLake Lake(and (andextending extendingintact intactto tothe theColdwell Coldwellalkalic alkalic to complexl 27 km to the west)] is unclear. The exposures at this stop allow one to view the vestiges of complex, 27 km to the west), is unclear. The exposures at this stop allow one to view the vestiges of some primary features which, beyond about 1750 m to the east, are no longer preserved] even some primary features which, beyond about 1750 m to the east, are no longer preserved, even though the the mafic mafic unit unit can canbe betraced tracedfor forwell wellover over10 10km kmfurther. further. The The unit unit appears appears to to be be though geometricallyand andgeographically geographicallycontrolled, controlled,for forthe themost mostpart, part,by bythe theHemlo Hemlofault fault zone. zone. geometrically i Opposite the the turnoff, turnoff, on onthe thenorth northside sideofofthe thehighway, highway]are aregarnetiferous garnetiferousand andnon-garnetifnon-garnetifOpposite erous, moderatelystrained basalt pillows with aspect ratios of at least 511. The strike of ill-defined ill-defined erous, moderately strained basalt pillows with aspect ratios of at least 5:1. The strike of unitsis is about about 2700, 270°slightly Fine- to garnet, present presentin in both both units slightly oblique oblique to to the the highway. highway. Fineto coarse-grained coarse-grained garnet, the selvages and pillow cores] is most abundant here. Overall, garnet is heterogeneously the selvages and pillow cores, is most abundant here. Overall, garnet is heterogeneously distributedthroughout throughoutthe theremainder remainderofofthe theoutcrop outcropto tothe thewest westwhere wherethere thereare arenon-pillowed non-pillowed(Le., (i.e., distributed massive) units units as as well. well. Prior Priorto torecent recentblasting, blasting,features featuresreminiscent reminiscentof of highly highlystrained strainedflow flow top top massive) breccias, and and possibly possibly interfiow interflowsediments, sediments]were were present. present. breccias, Varioliticpillows pillowsare arepresent presenton onthe thesouth southside sideof ofthe thehighway highwayto tothe thewest westof of the the turnoff. turnoff.To Tothe the Variolitic east of of the the turnoff turnoff (not (notshown shown on on Figure Figure40), 401, on on the the south south side side of of the the highway, highway, there are variolitic variolitic east there are and non-variolitic non-varioliticpillowed units. At Atleast least2,25 2,25 cm cmthick, thick]interflow interflowunits unitsof of rusty-weathering, rusty-weathering]pyritic, pyritic] and pillowed units. mediumto very dark grey metasiltstone are present at about 95 m and 155 m from the turnoff. medium- to very dark grey metasiltstone are present at about 95 m and 155 m from the turnoff. The flows flowshave havebeen been intruded intrudedby by at at least least three types of of foliated, fabric-paralleldikes: dikes: The three different different types foliated, fabric-parallel plagioclase-porphyritic; schistose mafic; and fine-grained intermediate. A recently intermediate] intermediate, plagioclase-porphyritic; schistose mafic; and fine-grained intermediate. A recently revealedcarbonatitic/alkalic carbonatiticlalkalicdike, dike,oriented orientedatat355/77, 355177 occurs occurs at at the the first first(heading (headingeast) east)oxidized, oxidized, revealed interflow, metasiltstone unit. The dike appears to be associated with fracturinglfaulting and some interflow, metasiltstone unit. The dike appears to be associated with fracturing/faulting and some form of alkalic(?) alteration. form of alkalic(?) alteration. StructuralSummary: Summary: Structural Predominant andflattening flatteningfabric fabric 266/70 266170 Predominant and Subordinate,locally locallypresent presentfabric fabric 276/72 276172 Subordinate, Stop29: 29: HOMESTAKE HOMESTAKEPROPERTY PROPERTYF3 F3Z-SHAPED 2-SHAPED FOLD FOLD(Figures (Figures18 18&&42) 42) ** Stop Permissionfor foraccess accessto tothe theproperty propertyisisrequired. required. InInformation onwhom whomto tocontact contactshould shouldbe be Permission formation on obtained from the Resident Geologistb Office, Thunder Bay (see address on title page). obtained from the Resident Geologist's Office, Thunder Bay (see address on title page). Lecours Tp Tp Lecours 1 Bomby Bomby Tp Tp gossan pillowed flow flow pillowed variety of dikes garnetiferous garnetiferous pillowed flow flow pillowed P0 le N A / .massiven flow massive flow - 00 20 20 40 40 - - garnetiferous gmassivemflow variolitic variolitic pillowed pillowed flow flow Microwave Tower Tower 60 60 m m Hemlo s c a l e approximate approximate scale Figure41. 41. Stop Stop28: 28: Simplified Simplifiedsketch sketchmap mapof of varieties varietiesof of pillowed pillowedand and"massive" "massive"mafic maficflows flows FIgure which are locally garnetiferous or variolitic. which are locally garnetiferous or variolitic. �Road Road Log Log — - Hemlo Hemlo Area 87 lb lb la brittle ¶ 2b LEGEND: STOP STOP 29 LEGEND. 024 0 Intermediate Intermediate Metavolcanics Metavolcanics(CaIc—alkalic) (Calc-alkalic) llaa massive flow llb b pillowed flow flow Ic lapilli—tuff or or volcaniclastic volcaniclastic l c lapilli-tuff conglomerate 2 6 6 8 81 4 10 0 m m 2c lc Volcaniclastic/Epiclastic VolcaniclasticlEpiclastic Metasediments Metasediments feldspathic arenite (altered wacke?) wacke?) 2a 2a feldspathic 2b 2 b thinly layered, light gray and buff wacke layered, sparse sparse 2c thickly layered, 2dd 2 granule—pebble clasts granule-pebble clasts fine—grained, gray wacke, siltstone: brittle breccia very thinly layered to thickly laminated 2e gray wacke: wacke: thinly layered layered 2c 2d 2d Dikes Dikes 3a fine—grained,gray, gray, intermediate, fine-grained, 3b 3b with sparse sparse biotite biotite phenocrysts phenocrysts fine—grained,gray grayt o to pink pink (hematitic). (hematitic), fine-grained, m fine—grained, mafic: mafic: fine-grained, moderately foliated foliated tto moderately o very very schistose schistose 2dd 2 intermediate (alkalic?) (alkalic?) rn version" of versio;' m "net-veined above two dike above two d ~ k etypes 2dd 2 2d mafic, mafic to mafic, biotite biotite lamprophyre± lamprophyretmafic to ultramaf Ic xenoliths: xenoliths: very very schistose ultramafic I 1? I? types feldspathized rock with with disseminated disseminated pyrite pyrite ...... ... ... feldspathized —maybe bemore moreintensely intenselyaltered altered equivalent equivalent of 2a -may 2a 2d 2d - ------ lithological contact: contack observed observed lithologicsl contact: Interpreted lithological interpreted trace of layering -.Z trace of layering T S -- —- — -. --- / -..- approximate boundary of highly strained pillows 2e fault (horizontal (horizontal component component of of movement movement shown ifIf observed) shown outline of of outcrop with outline with internal internal patch patch overburden remaining remaining of overburden {( J1 3 2e boundary of highly strained pillows -- approximate zones of weakly defined zones dismembered quartz quartz veins dismembered 2d 2e t. J 2d 2d 2d unusually large, Z-shaped, fold with with high-alumina high-alumina basalt Figure Stop29: 29: Geology Geologyof an unusually Z-shaped, F3 F3fold basalt FIgure 42. Stop F2-folded metasedimentary metasedimentary rocks, gabbro dikes, and pillows, F2-folded rocks, numerous numerousArchean Archean lamprophyre lamprophyre and and gabbro local, minor "Hemlo style1'(?) style"(?) alteration 1990). local, minor "Hemlo alteration(Homestake (Homestakeproperty). property).(Geology (GeologybybyT.L. T.L.Muir, Muir,OGS, OGS, 1990). �88 88 Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area Location: south side, Location: Continue Continuefor for525 525mmwest weston onHighway Highway17, 17 south side, from from the the Hemlo Hemloturnoff, turnoff,to to aa 44 m m high roadcut. roadcut. Climb Climbthe theoutcrop outcroptotothe thehydraulically hydraulicallycleared clearedarea areawhich whichextends extendsfor forabout about70 70 m m high south from from the the roadcut. roadcut. This This stripping stripping was was undertaken undertaken by by Esso Esso Minerals Minerals Limited Limited prior prior to to acquisitionof of the the proerty propertybybyHomestake HomestakeExplorations ExplorationsLimited. Limited.Exposed Exposedhere hereisisone oneof of the the largest largest acquisition F3 generation, Z-shaped folds presently presently observed observed in in the Hemlo Hemlo area. The TheF3 F3fold fold has has resulted resulted in in F3 generation, Z-shaped rotation rotationof of the thelayering layeringfrom fromabout about285° 285' to to330°. 330'. The The north northend endof of the the outcrop outcrop consists consists of of pillowed pillowed flows. The The pillows pillowsare are feldspar feldspar phyric phyricand and are presently presently alkalic alkalic in in composition. composition. Locally, Locallylamygdaloidal/vesicular amygdaloidal1vesiculartextures textures can can be be seen. seen. The The are pillows pillows contain contain finefine- to to medium-grained medium-grained hornblende crystals. The Theselvages selvages are are relatively relativelythick, thick, biotiterich, richland andlocally locallypyritiferous. pyritiferous.The Thepillows pillowsare arefound foundnowhere nowhereelse elseininthe thearea area(except (exceptfor for the the biotite adjacent suggestions that adjacent roadcut roadcutabout about 70 70 m m to the west). This This has has led led to suggestions that these these rocks rocks represent represent altered altered tholeiitic tholeiiticpillows pillows(MNDM (MNDMassessment assessment files, files,Thunder ThunderBay). Bay). However, However! the the significant significant (cf.Stop Stop28), andthe the differencesbetween betweenthe thetwo two"types" "types"ofofpillows, pillows,ininterms termsofofselvages selvagesand andcores cores(cf. differences 28), and presenceof of small, smalll feldspar feldspar phenocrysts, phenocrysts, suggests suggests the the pillowed pillowedunit unitat at Stop Stop29 29was was not nottholeiitic tholeiitic presence originally. originally. Chemically, Chemically, the the pillows pillowsare are relatively relativelysodic sodic(from (fromspilitization?) spilitization?)and andmore moreakin akinto tohigh high alumina basalt. alumina basalt. The pillowed pillowed unit unit displays displays an an abrupt abrupt change, change, towards towards the the south, south, from fromslightly slightlydeformed deformed The pillows to moderately and highly strained equivalents, within the northern part of the fold. pillows to moderately and highly strained equivalents, within the northern part of the fold. ItItisis not not clear D3folding foldingor orwhether whetheraazone zoneofofheteroheteroclear whether whether the the considerable considerable strain strain isisaaresult resultof of the theD3 geneous, strained pillows pillows pass into (relationship (relationship geneous$high highstrain strainformed formedprior prior to to the the F3 F3 fold. The highly highlystrained unclear) unclear)aa volcanic volcanic breccia brecciaor or volcaniclastic volcaniclasticunit. unit.The Thefragments fragmentsininthis thisunit unitare arevariably variablystrained, strainedl feldspar phyric, and appear to be similar in composition to the pillows (pillow breccia?). feldspar phyricl and appear to be similar in composition to the pillows (pillow breccia?). metasedimenAdjacent to to this thisfragmental fragmentalunit unitare are"units" "units"of oflight lightgreygrey-to towhite-weathering white-weatheringmetasedimenAdjacent tary taryrocks rocksand andmedium mediumgrey grey metasedimentary metasedimentaryrocks. rocks. Although Althoughthe thetwo two"units" "units"overall overallare aredistinct distinct from from one one another, another, detailed examination shows that some of the colour colour differences differences are are locally locally independentof oflayering. layering.This Thissuggests suggeststhat thatat atleast leastsome some of of the feldspathic characterof ofthe the lighter lighter independent feldspathic character weatheringunit unitmay maybe bedue dueto tofeldspathization, feldspathizati~n~ typeofofalteration alterationcommon commonininthe theHemlo Hemlodeposit. deposit. weathering aatype Locally tol the thecontact contactbetween betweenthe thefragmental fragmentalunit unitand andthe the feldspathic feldspathic Locallyat, at, and andslightly slightlydiscordant discordantto, metasedimentaryrocks rocksisisaableached, bleachedlrusty rustyweathering, weatheringltabular tabularzone zonethat thatappears appearstotohave havebeen been metasedimentary (F3)and and is is very very similar similar in in appearance appearance to to some some of the alteration in the the Hemlo Hemlodeposit depositarea. area. AA folded(F3) folded alteration in grabsample sample from fromthis thiszone zonereturned returnedan anassay assayvalue valueofof103 103ppb ppbAu Auand and100 100ppm ppmMo Mo(M. (M.Smyk, Smykl grab MNDM, MNDM,personal personalcommunication, communication,1990). 1990). The remainder remainder of of the theoutcrop outcropconsists consistspredominantly predominantly of of varieties varieties of of variably variablydeformed deformed The metawacke garnetkmagnetite octaoctametawacke and metasiltstone metasiltstone locally locally containing containing sparse sparse garnet±magnetite hedrakretrograded,yellowish yellowish porphyroblasts porphyroblastswhich which were were possibly possibly staurolite. staurolite.InInthe thesouth southhalf halfofof hedra±retrograded, theoutcrop, outcrop,preserved preservedF2 F2folds foldswith withS-asymmetry S-asymmetrycan canbe beseen seenamongst amongstF3, F3,locally locallychevron-like, chevron-likel the Z-shaped In one one case, casel an anindividual individuallayer layerdisplays displaysaaF2, F2,S-shaped S-shapedfold foldadjacent adjacenttotoaaF3, F3, Z-shapedfolds. folds. In Z-shaped Z-shapedfold. fold. Strainwas washeterogeneous heterogeneousas asindicated indicatedby bythe thelayering layeringwhich whichranges rangesfrom fromwell welldefined definedand and Strain continuous, continuousl to to wispy wispyand anddiscontinuous, discontinuous,suggestive suggestiveofoftransposition. transposition. Transposition Transposition isisalso also suggested suggestedby bythe theconsiderable considerable disruption disruptionand anddismemberment dismemberment of of quartz quartz veins veins and anddikes dikesconconstrained strainedto tocrudely crudelydefined definedzones zoneswhich whichare aresubparallel subparallelto tolayering layering(see (seeFigure Figure42). 42). Severalfoliated foliateddikes dikeshave haveintruded intrudedthe themetavolcanic metavolcanicand andmetasedimentary metasedimentaryrocks rocksand andall allof of Several them dike, and themhave havebeen beenaffected affectedby bythe theF3 F3folding. AA relatively relativelythick thickdikes andseveral severalnarrower narrowersubsidiary subsidiary dikes*of of Archean, Archeanl mafic, maficl biotite biotitelamprophyre lamprophyre show show diverse diverse textures textures and, andl to to aalesser lesserextent, extent, dikes, �Road Log Log — -Hem Hemlo Road lo Area mineralogy. mineralogy. They They locally locally contain contain mafic mafic to to ultramafic ultramaficxenoliths xenoliths which which are are locally locallyconcentrated concentratedinin zones. The The matrix matrix of of these these dikes dikes is is similar similar to that that of of intrusion intrusion breccia breccia (diatreme) (diatreme) bodies bodies on on the Golden Sceptre and Williams properties. properties. Conflicting Golden Sceptre Conflictingrelationships relationshipsare are present, present, but but itit appears that these dikes have been been followed by numerous, numerous, thin, gabbroic dikes which have have behaved more competently during subsequent deformation. deformation. competently gabbroic dikes locally locally display display considerable The gabbroic considerable variation variation in in response responseto to strain strain (e.g., (e.g.,buckling buckling boudins), depending depending on on orientation orientation relative to shortening or and regularly spaced, backrotated boudins), dike extension. AA locally locally developed developedbrecciation brecciation involving involving fragmentation fragmentation of of the main main lamprophyre dike and adjacent metawacke, chloritic matrix, and adjacent metawacke,and andhaving havingaachloritic matrix,can canbe beseen seenin in the the north northpart partof of the the outcrop. outcrop. The matrix is foliated. Relatively late, sinistral and dextral, brittle brittle faults faults have have produced producedminor minoroffsets offsetsof of layering. layering. Some earlier(?) ductile sinistral indicated by hooked disrupted dikes. sinistral sense movement is indicated hooked tails on disrupted Structural Structural Summary: Summary: S0/S1 from 285' 285° (local (local strike) strike) to SdS, from to 340° 340Â(on (on short shortlimb limbof of large largeF3 F3fold) fold) —305° S2 fabric fabric S, -305' fabric S3 fabric ranges from strike of 230° 230' to 280°, 280°and dip of 85°N 85ON to 85°S 85's (rarely (rarely 65°S) 65's) depending depending on on position positionwithin withinF3 F3fold fold 068/72, 105/47 various 068172, 105147 F3 axis: axis: various L crenulation: 096/62, 110/34, 265/60 & crenulation: various various 096162, 110134, 265160 080/20 L, boudinage 080120 Lb boudinage Zones of transposition 285° to 290 290° 285O Backrotated Backrotated boudins boudins of mafic mafic dike: dike: 285° 285' (within (within layering layering that that strikes strikes at at 295°) 295') General trend of late breccias 225° and breccias 225' and 3550 355' Late 3 15°,330° 330°, 345' 345° Late dextral dextral faults faults 315O, Late 180°, 210° 210°, 225' 225° Late sinistral sinistral faults faults 180° Stop 30: Stop CONTACT OF HERON (Figures 18 HERON BAY PLUTON (Figures 18 and 43) furtherwest on north side, roadcut opposite Location: Proceed Proceed1.5 1.5 km furtherwest onHighway Highway17, 17, north side, to to aa 7 m high roadcut opposite an area cleared cleared of of trees trees on on the the south south side. side. This outcrop outcrop shows: whichappears appearstotorepresent representthe themarginal marginalrock rockof ofthe theHeron Heron (A) plagioclase-porphyriticgranodiorite plagioclase-porphyritic granodiorite which similar in in many many ways waysto to some someof ofthe theplagioclase-porphyritic plagioclase-porphyritic dikes dikes found in the the Bay Pluton and is similar supracrustal rocks in the area. area. The aplitelpegmatite dikes and The granodiorite granodiorite is is intruded intruded by pink aplite/pegmatite white quartz veins; N A I Metasediments Metasedirnents Metasedirnents - 1 Granodiorite 0 o 10 io 20 20 30 30 m rn H w y 17 I scale s c a l e approximate approximate lamprophyre larnprophyre I I 89 89 FIgure 43. Figure Pluton. Pluton. Stop Stop 30: Simplified sketch geology at Simplified sketch map map of the geology at the the east east contact contactof of the the Heron HeronBay Bay �90 90 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area (B) deformed deformed (e.g., biotite-hornblende-bearing metawacke (e.g.,folds, boudins), boudins), medium medium to to dark dark grey, biotite-hornblende-bearing metawacke which which locally locally contains containsgarnet garnet(east (eastside side of of diabase diabase dike); dike); veins, in in the the metawacke, metawacke, which display display boudinage boudinage (sub-horizontal (sub-horizontal (C) quartz-feldspar-muscovite quartz-feldspar-muscovite veins, necks). The The top top surface surfaceof of the the outcrop outcrop used used to show that necks). that boudinage boudinage had occurred occurred in the the horizontal horizontal and vertical vertical planes; planes; (D) a mediummedium- to fine-grained, piagioclase-porphyritic plagioclase-porphyriticdiabase diabase dike; dike; Proterozoic, massive, massive, pyroxene(?)-magnetite pyroxene(?)-magnetitelamprophyre lamprophyre dike dike likely likely associated associatedwith withLake Lake (E) a Proterozoic, Superior rift ing. Superior rifting. Stop Stop31: 31: HERON HERON BAY BAY PLUTON PLUTON(Figure (Figure18) 18) Location: km from from Stop30, Stop 30, to to aa roadcut roadcut (both sides) about Location: Continue Continueeast easton on Highway Highway17 17for for 1.3 1.3 krn about 180 m west west of of the the "Rouse "Rouse Lake" highway sign. sign. The correct correct name name of of the the lake lake is is Rous Rous Lake. Lake. The The outcrop outcrop is is opposite opposite aa large largeclump clumpof of trees treesbetween betweenthe thehighway highwayand andthe thelake. lake. These These outcrops outcrops are are typical typical of of the the inner inner part part of of the the Heron Heron Bay Bay Pluton, Pluton, as as exposed exposed along along the the highway, although although different different phases, microcline-megacrystic, are within the phases, such as microcline-megacrystic, are present presentfurther furtherwithin the pluton. granodiorite is is intruded pluton. At this this roadcut, roadcut, massive massive biotite-hornbiende biotite-hornblende granodiorite intruded by aplite aplite and and pegmatitic dikes. The xenoliths. An Thegranodiorite granodiorite locally locally contains contains sparse mafic xenoliths. An extremely extremely faint faint fabric 300' to to330°. 330'. fabric appears appears to to strike strikefrom from300° The dikes 050°, and 070 070°and anddip dipsteeply steeplyto tothe thesoutheast. southeast. The The latter latter dikes commonly commonlystrike strike at at 030°, 030°050° two orientations few quartz-rich quartz-rich veins veins which which cut cut the dikes are oriented oriented orientations tend tend to to be predominant. AA few at 260-280/40 260-280140 and display a fabric which is possibly mylonitic. mylonitic. Samples within the Samples for for U-Pb U-Pb geochronology, geochronology, taken here here and farther within the pluton, pluton, gave gave a combined combined age age of 2688±5 2688± Ma Ma for the the granodiorite granodiorite(Corfu (Corfuand andMuir Muir1989a). 1989a). END END OF OFHIGHWAY HIGHWAY 17 17 ROAD ROADTRIP TRIP Note: Note: Those Thosechoosing choosingto todo dothe theentire entirefield fieldtrip tripfrom fromeast east to to west west should should proceed proceed to to Stop Stop 4, about 31) on to apoint a point on on the the north north side, about about13.2 13.2 km km to to the the west west (of (of Stop Stop31) on Highway Highway17, 17,to about 900 900m m east east of the Black Black River River bridge. bridge. �Stop Stop Descriptions Descriptions— -Hemlo HemloDeposit: Deposit:Williams Williams Property Property 91 91 HEMLO DEPOSIT SEGMENT: WILLIAMS PROPERTY PROPERTY VISIT HEMLO SEGMENT: WILLIAMS This part of the trip will be be supervised supervised by by Williams Williams Operating Operating Corporation Corporation staff. Hard Thispart Hardhats hats and and safety be worn wornby by everybody everybodywhile whileon onthe theproperty. property. safety glasses glasses must mustbe This This is is an an instrumental instrumental part part of of the the Hemlo Hemlotrip tripbecause because of of the theexposures exposuresavailable available on on the the property. property. However, However, at at the the time time of of writing writing and andup up to to the the time time of of the the field field trip, no no guarantees guarantees can can be made made as to which exposures exposureswill will be be "available". "availableJ'.In Incase case some some of the the exposures exposuresare are "unavailable", "unavailableJ', brief descriptions of detailed sketch sketch maps brief descriptions of the the potential potentialstops stops are are presented presentedhere, here, with examples examples of detailed showingthesalient thesalientfeatures. features.Because Becausethe thegeological geologicalhistory historyisiscomplex, complex,aasummary whatwill willbe be showing summary ofofwhat presented detailed presentation presentation of the development development of the interpretapresentedis is given given for each stop, not a detailed interpretation. tion. Matters Mattersofofcontention contentioncan canbest bestbe bedebated debatedon on the spot. Previous Previousfield field guides guides covering covering similar and eta!. al. (1985) (1985) and and and additional additional aspects aspects of of the the mine mine and andproperty property were were presented presented in in Valliant Valliant et Walford, Walford, Weicker, Weicker, and and Guthrie Guthrie(1986). (1986). [Note: Stop 33A outcrop has all all but but vanished; vanished; Stop Stop 35 35 outcrop outcrophas has been been destroyed.] destroyed.] Stop Stop 32: 32: "BACK "BACK40s" 40s"OUTCROPS OUTCROPS(Figures (Figures18 18&& 44) 44) LocatIon: Location: The The Back Back40s 40s outcrops outcrops lie lie about about 450 450 m m northeast northeastof of the the Heritage Heritageoutcrops outcrops(Stop (Stop33). 33). They They have have miraculously miraculouslyavoided avoidedburial burialfor forsome some time time now. now. The Theoutcrops outcropshave havebeen beenchosen chosen(aside (aside from from the the fact fact that that they they are arethe the only onlyones onesleft leftin in this this area), area), because becausethey they show showaa number numberof of features features that that epitomize epitomizethe thestructural structuralhistory historyofofthe thearea, area,and andthey they are are relatively relativelyfar faraway away from from the the ore ore zone with with its itsattendant attendanthigh highstrain strainand and substantial substantial alteration. alteration. The The southernmost southernmostand andlargest largestof ofthis thisset setof of exposures exposuresconsists consistsof ofaavariety varietyof ofmetasedimenmetasedimentary tary rocks rocks derived derivedfrom fromvolcaniclastic(?) volcaniclastic(?) feldspathic feldspathic arenite, arenite, wacke, wacke, siltstone, siltstone, and andpossibly possibly conglomerate. conglomerate. There There are are also alsonumerous numerousamphibole-rich amphibole-richlayers. layers. The The northernmost northernmostoutcrop outcrop consists consistsof of turbiditic turbiditicwackes, wackes,some somecontaining containingrip-up rip-upclasts. clasts. These These exposures exposures lie lie on on the the northeast northeastlimb limbof ofaatight, tight,large-amplitude, large-amplitude,northwest-closing, northwest-closing, north-northwest-plunging north-northwest-plunging fold, centred centred on on the the Williams Williams property property (Figure (Figure 19). 19). The TheS2 S2cleavage, cleavage, which whichisisprominent prominentin in this this outcrop, outcrop, is is thus thus oriented oriented clockwise clockwisewith with respect respectto to the the layering. layering.Several Several layers, suggest that the units layers, including one comparable comparable to volcaniclastic volcaniclastic conglomerate, conglomerate, suggest units are are overturned overturned at at this this location, location,assuming assumingnormal normalgrading. grading. Structural Structural features featuresthat thatare areimportant importantare areas asfollows: follows: F1 Fl sheath fold fold or interference interferencefold fold F1 conglomeratic(?) rocks Fl isoclines isoclines in an unusual, unusual, layer-parallel layer-parallel zone of conglomeratic(?) rocks F2 F2 S-shaped, parasitic parasitic folds folds with with north-northwest north-northwestplunges plunges S2 within some layers, layers, and andSo 2 fabric S2 stripey cleavage developed within fabricand andclast clast alignment alignment in in others others F3 F3 related related folds folds in in boudin boudinnecks necks S3 fabric occurs: boudin necks crenulation cleavage; S3 fabric occurs: in in F3 F3folds and and boudin necks as as a crenulation cleavage;ininsericitic sericiticlayers; layers;and andas as pressure pressureshadows shadows around aroundgarnet garnet porphyroblasts. porphyroblasts. Two structural discontinuity Two zones of structural discontinuityoccur occurininthe theBack Back40s 40s outcrops, outcrops,one one at at the the south southend endof of the 12),the theother othernear nearthe the north northend endof of the northernmost northernmostexposure. exposure. thesouthernmost southernmostexposure exposure(Photo (Photo12), The The southern southernzone zonehas hasbeen beeninterpreted interpretedto tobe befolded foldedabout aboutthe theF2 F2axis axis and and thus thus predates predatesthat thatfold fold generation. generation. Its Itsorigin originisisnot notwell wellunderstood understoodbecause becauseititdisplays displaysfeatures, features,some someof of which which can canbe be interpreted (e.g., soft soft sediment sediment slump slump structures), and others in in aa tectonic tectonic interpreted in in aa primary primary sense sense (e.g., sense sense(e.g., (e.g.,low-angle-to-layering low-angle-to-layeringfaulting faulting or or thrust thrust faulting). faulting). Both Bothprocesses processesmay mayhave haveoccurred. occurred. The The northern northern zone zone isisassociated associatedwith withvarieties varietiesofofmetasiltstone metasiltstoneand andamphibole-rich amphibole-richlayers layers displaying discordant layering, disrupted folds, layer-parallel breccias and sinistral faults. The displaying discordant layering, disrupted folds, layer-parallel The �______ Geology and Gold Deposits of the Hemlo Area 92 92 2D 2D 2B— 2C 0 0 10 5 5 15 metres metres Detailed sketch sketch map map of of the Back Figure Figure 44. 44. (legend on opposite opposite page) page) Stop 32: 32: Detailed Back 40s property), showing showing aa variety variety of of lithologic lithologic units units and and structures structures that that reflect the outcrop (Williams property), to D-,. D3. Legend and scale same as as for for Figures 45 45 and and 46. 46. (After Dl to (AfterMuir Muir1986). 1986). events of D1 �Descriptions — -Hemlo Hemlo Deposit: Deposit: Williams Property Property Stop Descriptions 93 93 strike, across across what appears appears to be a folded contact, contact, into into thick-layered, thick-layered,rip-uprip-upzone passes, along strike, clast-bearing metawackes metawackeswhich which do do not not seem to (SeeMuir Muir and and clast-bearing to show show similar similar deformation deformation features. features. (See more details.) Elliott (1987) for more lithologic Fine-to medium-grained garnet garnet porphyroblasts are are common common within within many of the lithologic the southern southern 30 m m of ofexposures, exposures,including includingthe theamphibole-rich amphibole-rich layers. layers. The occurrence occurrence here units of the here of garnet in amphibole-rich amphibole-rich layers, which elsewhere is uncommon, may may be be aa result result of of alteration alteration prior to metamorphism. metamorphism. Outcrops Outcrops in in the the central central part part of ofthe theoutcrop outcroparea areacontain containgarnet garnet and and staurolite porphyroblasts. two generations. generations. The earlier(?) generation generation is staurolite porphyroblasts. The Thelatter latterappear appear to to be of two aligned parallel to the S2 S2 fabric, and and is is partly partly retrograded retrograded to to staurolite, staurolite, quartz, quartz, feldspar, feldspar, and and muscovite. The Thelater latergeneration generationtends tendsto tobe besubhedral subhedral and and non-retrograded. non-retrograded. alteration, at at least least on on aa more more local localscale, scale, involves involvesan an incipient incipientto to wellwellAnother example of alteration, developed, stripey, development of "lenses", "lenses", along the S2 S2 stripey, differentiated layering, and locally aa development cleavage in silty and arenaceous layers. layers. Here, mineralogical composition of the Here, the textural and mineralogical non-primary layers and lenses so produced, presently resembles resembles the range of compositions compositions among silty and arenaceous arenaceous layers. Hence, interpreted feldspathic Hence,some some or or all all of the interpreted feldspathicarenite arenitemay may actually alteration of wacke and possibly possibly siltstone. siltstone. This actually be be a result of alteration This underscores underscoresthe thedifficulty difficultyinin distinguishing between originally feldspathic feldspathic rocks and feldspathized feldspathized rocks, rocks, particularly if the the latter were initially feldspathic. Two gabbro dikes dikes intrude the the central part of these these exposures. One Two gabbro One dike dike isislayer-parallel layer-parallel and and displays boudinage with with quartz fillings in the the necks. necks. The The other other dike dike is is slightly slightly discordant discordant and, and, although otherwise otherwise similar similar in in appearance appearance and and composition, composition, displays displays back-rotated back-rotatedboudins boudinswith with quartz + + tourmaline neck fillings and locally associated bleaching of the country rocks. rocks. In the southern slightly discordant gabbro southern part part of of the the main main outcrop, there there is is a slightlydiscordant gabbro dikelet dikelet which which isis somewhat somewhat similar to the adjacent amphibole-rich layers. adjacent amphibole-rich layers. LEGEND LEGEND STOPS 32,33 32, 33 Symbols Symbols PROTEROZOIC PROTEROZOIC Lamprophyre: Lamprophyre: biotite, pyroxene pyroxene 6 ARCHEAN ARCHEAN Quartz, Quartz, veins veins and and pods: pods: kyanitetpyrite c7 Outcrop outline: 4 Outcrop outline: 1986 mapping 1986 mapping •2 Outcrop outline: L.Outcrop outline: 1985 1985 mapping mapping .A'> ±tourmalinetmuscoviteichloritet itourmalinetmuscoviteichlorite~ Alteration Alteration Feldspathized: Feldspathized: locally identifiable !dentifiable as epiclastic epiclastic and and volcaniclastic metasediments metasedlments Pyritized: locally identifiable Feldspathized and Pyritized: identifiable as as and volcaniclastic volcan,clastic metasediments metasedimnts epiclastic and Feldspathized Feldspathizedand and Biotitized: Biotitized: locally locally identifiable identifiableas as epiclastic epiclastic and and volcaniclastic volcaniclasticmetasediments metasediments Intrusions Intrusions Felsic dike: feldspar, quartz, sericite sericite biotite, feldspar Intermediate dike: biotite, Mat icdike, dike,gabbro: gabbro: xenoliths shown Mafic shown where significant significant :I'.-:.-.. -— .' ? Outline of of specific features in altered zone ::--I zone see pa em (see pattern) locally . bedding destroyed, very fine bedding destroyed, very finegrained: grained: locally with molybdenite wlth molybdenite oo highly highlyschistose, schistose,fissile fissileon onoutcrop outcropsurface surface 0 Metasediments1 ~etasediments' Caic—silicate Calc-silicate IEIJJI 2C a 2* lB is Siltatone Siltstone Wacke Wacke Arenite: Arenite: largely volcaniclastic volcaniclastic largely volcaniclastuc Conglomerate, granule and pebble: largely volcaniclastic Metaporphyries Metaporphyries Felsic, sericitic, porphyry: flow?, sericitic, quartz—feldspar quartz-feldspar porphyry: flow?, hypabyssal hypabyssalintrusion? intrusion? Felsic, aericitic, porphyritic pyroclastic sericitic, quartz—feldspar quartz-feldspar porphyritic pyroclastic rock rock Outline of pervasively altered delineable Outline of delineable units units of conglomerate limonite covered _— Limits of pervasive alteration / alteration u 's Fault: sense senseshown shown where where determined determined ,-' -" FoldFold axis: trace of unexposed axial axis: trace of unexposed axialplane plane -'- - Bedding Beddingtop topdirections: directions: upright facing, facing, overturned overturned fabric trends @ Local Local bedding or fabric trends 555 nferred extension Inferred extension of of units unitswith withdistinctive distinctivesimilar similar features IT Till: cemented cemented D D Dirt: overburden overburden B B Boulder: erratic erratic c Clast: composite Clast: composite �94 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Structural StructuralSummary: Summary: South South part part of of stripped strippedoutcrops outcrops S0/S1 290/75 general orientation in SOBl 290175 general orientation in outcrop outcrop S0/S1 292/63 north north limb limbof of aa F1 S& 292l63 Fl isocline isocline S0/S1 288/60 south SdSl 288160 Fl isocline isocline south limb limb of of same same F1 312-316/82 range overprinting above range of of S2 S2 overprinting above F1 Fl isocline isocline s2 312-316182 S3 275/73 commonly sericitic sencitic s3 27973 252/63 pressure porphyroblasts: (possibly 252163 pressure shadows about garnet porphyroblasts: (possibly aa later later development development of S3(?)) S3(?)) 32 1/67 isocline isoclinefold fold axis axis LF1 LFI 321167 290/47 one foldlinterferencefold fold one hinge hinge of sheath sheath foldfinterference Lm 290147 311/77 parasitic parasiticF2 F2fold fold axis axis LF2 LF~ 311177 L \ North North part part of stripped stripped outcrops outcrops 289/72 tops to to south(?): south(?): grading gradingand and distribution distributionof of amphibole amphibole SO/SI SdS1 289172 s2 s3 S3 * Stop Stop 33: 33: 301/83 301183 260/73 260173 HERITAGE HERITAGE OUTCROPS (Figures 18,45 18,45 && 46) 46) These These exposures exposuresare areconsiderably considerablyworse worsefor forwear wearthan thanaafew few years years ago. ago. The Theurge urgefor forparking parking lots "clearly" illustrated lots to reproduce reproduceand and grow grow is is "clearly" illustratedhere. here.Many Manyofofthe thefeatures featuresininthe theeast eastoutcrop outcropare are no longer visible, relative to Figure 45. no longer relative to Figure 45. Stop Stop 33A: 33A: HERITAGE HERITAGE EAST EAST OUTCROP OUTCROP (Figure (Figure45) 45) Location: Location: About 40 m to the west of the security building. The considered the the mineralized, mineralized, The Heritage HeritageEast Eastexposure exposureused usedto to show show part part of of what might might be considered 6 Zone Zone (Figure (Figure 22; Photo Photo 13), 131, although although itit may may not notbe be equivalent of Williams Mine B updip equivalent of the Williams connected connectedto to it. it. In some aspects, this mineralized mineralizedsection is similar similar to the the A A Zone section, section, based based section is on (F2?),footwall, sericitized sericitizedand and microclinized, microclinized,quartzquartzon surface surface exposures. exposures. The Theinternally internallyfolded folded(F2?), feldspar m thickzone thick zone of of considerably considerably folded, folded, transposed, feldspar porphyry porphyryisisstructurally structurallyoverlain overlainby byan an 18 18 rn and and altered, altered, metavolcaniclastic metavolcaniclasticdeposits depositsof ofwacke wacke and and granule granule and and pebble pebble conglomerate. conglomerate. The alteration alteration is is interpreted interpreted to to include includefeldspathization feldspathization (microclinization), (microclinization), sericitization, sericitization, pyritization, and and possibly possibly local local silicification, silicification, with withanomalous anomalousgold gold and and locally locallyvisible, visible, very very finefinepyritization, grained molybdenite. molybdenite.Numerous, Numerous,deformed deformedquartz quartzveins veinslie lieininaacentral centralzone zoneof of feldspathized feldspathizedand and grained biotitizedvolcaniclastic volcaniclasticmetasedimentary metasedimentaryrocks, rocks, which which are are structurally structurally overlain overlain by by feldspathized, biotitized feldspathized, sericitized, and and pyritized pyritized metasedimentary metasedimentary rocks. The The zone zone of of altered altered rocks rocks is is in in sharp, faulted sericitized, contact with the the hanging hanging wall wall volcaniclastic volcaniclastic metasedimentary metasedimentary rocks which are are locally locally partly partly alteredand and isoclinally isoclinallyfolded. folded.Initially, Initially,the theexposure exposureshowed showed44folds, folds,with with alternating alternatingeast eastand andwest west altered closures closures (the (the folds folds must mustnow nowbe be examined examinedat at Stop Stop 33B). 33B). The hanging hanging wall rocks to the the zone zone of of alteration alteration and andmineralization mineralization were were intruded intruded by by aa xenolith-rich (net-veined?) (net-veined?) gabbroic gabbroic dike, and and subsequently subsequently by a swarm of granitoid dikes. The The xenolith-rich quartz-feldspar porphyritic porphyriticfootwall footwall unit unit was was intruded intruded by by dikes of intermediate intermediate composition. composition. quartz-feldspar Structural StructuralSummary: Summary: S 293/74 Sl 29374 % s3~' S38? S? sac? Sac,? S3.? Lm Lm L0 La 287/75 287175 265/70 26W70 275/63 27963 320/76 320176 323/55 32355 348/51 348151 volcaniclastic volcaniclastic metasediments metasediments stripey stripeycleavage cleavage altered alteredrock rockininmineralized mineralizedzone zone altered alteredrock rockininmineralized mineralizedzone zone altered alteredrock rockininmineralized mineralizedzone zone tourmaline tourmalinelineation lineation elongation elongationof of clasts clasts in in volcaniclastic volcaniclastic conglomerate conglomerate �a e r ___ - Stop Descriptions — Hemlo Deposit: Williams Property I-c 047776 Im 0 081/34 077-128/50 291)80 Vq 090±5° F3 95 crenulation (sericite) lineation retrograded feldspar('?) porphyroblasts told axes feldspar porphyry dike (from swarm) generalized quartz vein orientation (steep dipping) Fo)ded, Transposed Section consists of about 31% dikes a a p a a a a a a U a a a a a a a 0 a a a a fr a '4 2C Dextraly sheared, Folded, Transposed, Altered / I 0 5 10 15 metres 'U FIgure 45. Stop 33A: Detailed sketch map of the Heritage East outcrop (Williams property), showing highly transposed and altered/mineralized, metavolcaniclastic/meta-epiclastic rocks (possibly equivalent to the Williams Mine B Zone) between footwall quartz-feldspar porphyry, and hanging wall metavolcaniclastic/meta-epiclastic rocks. Legend and scale same as for Figures 44 and 46. (After Muir 1986). �Bedding Bedding Folded (possibly 2 folds), Transposed, Disrupted Section consists of about 37% dikes 0 2C Bedding Transposed 2D 2D20Q 2C 2C 20 , ', 25 Incipiently Altered Altered 5 10 10 15 15 -\ ' 4 0 0 (0 a C) 0 a. ci CD 00 1 CD metres metres V 0 0) 0-I, :7 CD the Heritage Heritage West outcrop (Williams property), Figure Figure46. 46. Stop 33B: 33B: Detailed sketch map of the disrupted and metavolcaniclastic/meta-epiclastic showing disrupted and tightly tightly F2-folded, F,-folded, mixed, mixed, hanging wall metavolcaniclastic/meta-epiclastic rocks, as well as a swarm of granitoid dikes. Legend Legendand and scale scale same same as as for for Figures Figures 44 44 and and 45. 45. (After (After Muir Muir 1986). 1986). �Stop Stop Descriptions Descriptions— -Hemlo Hemlo Deposit: Deposit: Williams Williams Property Property 97 97 Stop Stop 33B: 33B: HERITAGE HERITAGE WEST OUTCROP OUTCROP (Figure (Figure 46) 46) Location: Location: About 50 m to the west-northwest of the Heritage Heritage East East outcrop. This outcrop outcrop shows shows the the hanging hanging wall metasedimentary metasedimentaryrocks rocks which which are are composed composedof of folded folded This metavolcaniclastic wacke, pebble conglomerate, and siltstone, with numerous numerous amphibole-rich amphibole-rich layers. staurolite bearing. The layers. Some Somelayers layers within within the the northernmost northernmostfold fold are garnet and/or staurolite The rocks rocks aswarmof of granitoid granitoiddikes dikes(the (thesame same swarm swarmno no longer longervisible in the Heritage Heritage have been been intruded intrudedby by aswarm have visible in East outcrop). The The granitoid granitoiddikes dikespostdate postdateF2 F2folding folding and and display display muscovite muscovitepoikiloblasts. poikiloblasts. ~hree,'ti~ht, F2-generationfolds folds are are well exposed These folds folds are are associated associated Three, tight, F2-generation exposed in this outcrop. These with cleavagewith with local local attendant attendant transposition transposition and disruption So cleavage and disruption with aa well-developed, well-developed, axial axialplanar, planar, S2 of layering, particularly in in the noses noses of the folds where horsetail structures are locally locally developed developed (Photo in response to the strain, (Photo 14). 14). The The variations variations of layers layers of different different composition, composition, in response to strain, is is particularly particularly interesting. interesting. Locally, in the the nose of the the northernmost northernmost fold, staurolite occurs within within grey grey weathering weathering rock. rock. This rock represents represents the remnant remnant part of the metasedimentary metasedimentary unit unit that that has has been been unaffected unaffected by alteration planes. Interpretation Interpretationisis alteration (bleaching) (bleaching) along along multiple, multiple, fairly fairly closely closely spaced spaced S2 cleavage planes. equivocal equivocal regarding regarding the timing timing of the formation formation of of the the staurolite staurolite crystals crystals relative relativeto to the thedevelopdevelopment ment of cleavage/alteration. cleavagelalteration. Dextral displacement subparallel subparallel to the the limbs limbs isisdemonstrable. demonstrable. Smaller-scale, sinistral sinistral displacement of the layering is also present. Some of the conglomeratic units show asymmetric displacement present. conglomeratic distribution of about the fold axes of lenses lenses within layers layers which reverses reverses about axes and and is is interpreted interpreted to to represent representgrading grading of of clasts. clasts. IfIfthe the grading gradingwas was normal, normal, the the northeast northeastlimbs limbsare are overturned overturnedwhich whichisis consistent with evidence, albeit equivocal, for the large, F2 fold (see Stop 32), 32),and implies implies a equivocal, for structural structural facing facing to to the the east-southeast. east-southeast. However, However,this this isisnot not consistent consistentwith withthe theF2 F2fold fold at at Stop Stop 8. A zone of incipient incipient alteration alteration is present present in the the south south end endof ofthis thisexposure. exposure. Quartz Quartz +tourmaline + tourmaline Azone alteration, alteration,and andquartz quartz++muscovite muscovite++kyanite kyaniteknots knotsare arepresent presenthere herebut butalso also occur occurlocally locallyininother other parts parts of of the the Heritage Heritageoutcrops. outcrops. A north-northeast-striking, north-northeast-striking, Proterozoic, Proterozoic, bifurcating, bifurcating, biotite biotite ++pyroxene pyroxene lamprophyre lamprophyre dike is is present present in in parts parts of of recessively recessivelyweathering weathering fractures fractures in in the the east east part part of of the the outcrop. outcrop. Structural StructuralSummary: Summary: S 293/66 SI 293166 to to 303/73 303173 279/73 279173 to to282/81 282181 287/78 % 287178 257/66 S3 s3 257166 F2 316/62 FZ 316162 vq 090±5° vq 090±S north northlimb, limb,E-closing E-closingF2 Fafold fold south south limb, limb,E-closing E-closingF2 F, fold fold generalized generalizeddue due to to variations variationsthroughout throughoutoutcrop outcrop generalized generalized quartz quartz vein vein orientation orientation (steeply (steeply dipping) dipping) * Stop EASTCCZONE ZONEOUTCROP OUTCROP(Figures (Figures18 18&&47) 47) Stop 34: 34: EAST Location: Location: About About 400 400 m m west west of of the the Heritage Heritageoutcrops. outcrops. This feldspathized (microclinized (microclinized and albitized?), albitized?), sericitized, This outcrop outcrop consists consists of variably feldspathized sericitized, and and silicified silicified quartz-feldspar-porphyritic quartz-feldspar-porphyriticrocks rockswhich whichhave havebeen been localty locally pyritized pyritized and and mineralized mineralized with gold gold and locally locally visible, visible, very very fine-grained fine-grained molybdenite. molybdenite. Figure Figure47 47depicts depictsthe thevisually visuallyapproxiapproximated distribution of the various types of alteration and mineralization. The quartz-feldspardistribution of the various types of alteration and mineralization. The quartz-feldsparporphyritic porphyriticrocks rockshave haveno nounequivocal unequivocalmajor majorprimary primaryfeatures featurespreserved, preserved,such suchas asunit unitlayering. layering. �______ Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 98 — 0 ' -'- ', e —— - '\\ \\ \\ Iy 'I__ alt t - --- - 4 4, '4 \\ 4 £ OV bo \. \__---_--• D Mo .. e sea - D — \ 0 0 -- - 0 bo 10 0 15 metres Detailed sketch sketch map map of of part part of of the the C C Zone, Zone, (legend on on opposite oppositepage) page) Stop Stop 34: 34: Detailed Figure Figure47. 47. (legend east property), showing showing variably variably altered altered and andmineralized mineralizedquartz-feldspar-porphyritic quartz-feldspar-porphyritic east end (Williams property), rocks (lapilli-tuff?) (iapilii-tuff?) intruded by several several dikes dikes of of various various compositions. compositions. (After (After Muir Muir 1988). 1988). �______ _____ Stop Descriptions Descriptions — -Hemlo Hemlo Deposit: Deposit: Williams Property Property LEGEND: STOP STOP 34 LEGEND: / Quartz veins INTRUSIVE C CONTACT INTRUSIVE ONTACT Dikes I Biotite—plagioclase—porphyritiC, biotite biotite diorite Biotite-plagioclase-porphyritic, diorite (sheared) e INTRUSIVE CONTACT aa Biotite gabbro (sheared) (sheared) b b Biotite quartz diorite Biotite diorite c Feldspar porphyry porphyry d d Quartz-feldspar porphyry Quartz-feldspar porphyry INTRUSIVE CONTACT Country Rock Country r\ Sericitic, porphyry S e r ~ c ~ tquartz—feldspar quartz-feldspar ~c, porphyry r— ] Feldspathized, biotitized, quartz—feldspar Feldspathlzed, blotltized, quartz-feldspar porphyry porphyry [J Feldspathized quartz—feldspar Feldspathlzed quartz-feldsparporphyry porphyry 1-1 Quartz—feldspar porphyry with with irregularly Quartz-feldspar porphyry ~rregularlyshaped shaped chlorite—sericite lenses, layers chlor~te-seric~telenses, Pyritized quartz—feldspar porphyry with m j Pyritized quartz-feldspar porphyry with irregularly shaped ~rregularly shaped chlorite—sericite chlorite-sericite lenses, lenses, layers layers [ ] Intensely feldspathized rockrock withwith py—Mo—Au(?) Intensely feldspathized py-Mo-Ad?) mineralization m~neralization m j Zone Zone of notable pyritization, pyritization, Au(?) Ad?) rock (dike—like) (dike-like) Intensely silicified rock - -- — - Intensely - - # - - - Quartz stringers, veinlets veinlets *' Quartz veins Quartz veins r\ [ -- ] pink (tiematitic) pink (hematitic)alteration alteration conspicuous fracturelshear, fracture/shear, conspicuous with wlth or or without without alteration alteration -.-- alteration vein" along alteration %einW alongfracture fracture '2 \ \\ i\ --* D D area of of fragment—bearing fragment-bearing rocks closely spaced fracture sets closely spaced fracture sets ,highly schistose zones highly schistose zones dirt d ~rt 99 9 9 However, many many parts parts of of the outcrop However, outcrop display display numerous lapilli-sized lenses considered considered to be be possible pyroclasts pyroclasts (Figure possible (Figure 47; Photo 15). Many of the small of small lapilli-size lapilli-size fragments fragments are are barely barely discernible because of the the alteration. There There is is also a section of the outcrop outcrop reminiscent reminiscent of a coarse fragmental unit. unit. This exposure is on on from, and about about 400 400 m to the east of, a strike from, porphyritic rock quartz-feldspar porphyritic rock dated dated at at 2772 2772 (Corfu and Ma (Corfu and Muir Muir 1989a). 1989a). There There are several several dikes in this this outcrop outcrop which collectively have a variety variety of of composicompositions and textures. The The dikes dikes strike strike parallel parallel to the main 275' to to 280°, 280° main fabric, which which is is at at about about 275° and are also also foliated. foliated. Some of the dikes display Some dikes display muscovite poikiloblasts. poikiloblasts. AA few muscovite few of of the the dikes dikesare are with a hematitic hematitic alteration spatially associated with which, which, in at at least least one one case, case, appears appears to to have have affected the dike and thus postdates it. Two Two of the dikes consist consist of of quartz-feldspar quartz-feldspar porphyry porphyry roughly on and are roughly on strike strike from, from, and and about about400 400m m of, aaquartz-feldspar quartz-feldspar porphyritic porphyritic dike to the east of, dike that was dated at either 2684 Ma Ma or 2695 Ma (geochronological (geochronological problems not not resolvable; resolvable; Corfu and Muir Muir 1989a). 1989a). Note that the more more felsic dikes, dikes, in particular, to have infelsic particular, appear appear to intruded the the altered, truded altered, pyritized, pyritized, and and minermineralized(?) country rocks. rocks. It is not clear whether the dikes could could have have undergone undergone the same same alalteration history teration history as the country rocks, rocks, but reacted to itit differently differently because because of of chemical chemical and and rheological properties. The The same same problem problem has been 13and and21. 21. been addressed addressedfor for Stops Stops13 A few few of of the thedikes dikeshave haveundergone undergone boudinage. F3 boudinage. F3folds folds with with axial axial planar planarS3 S3 crecrenulation cleavage occupy many of the the necks. necks. The The more mafic dikes display display the effects effects of of ductile, dextral ductile, dextral shear. shear. quartz is abundant in the exNon-primary quartz posure whole. It occurs occurs as: dike-like dike-like zones posure as aa whole. of silicification; irregularly shaped silicification; irregularly shapedzones zones assoassociated with intense intense feldspathization feldspathization and very fine-grained fine-grained molybdenite; molybdenite; zones zones of of numerous, numerous, thin stringers stringers parallel to the main main fabric (Photo 16); local local areas areas of of brecciated brecciated country country rock rock with with a quartz quartz matrix matrix (Photo (Photo 16); 16); and and two two or or more more generations of quartz veins, generations of veins, some some of of which which show considerable shortening shortening due due to to buckling. buckling. �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 100 100 northwest-striking set set of ofnorthwest-striking northwest-striking veinA northwest-striking setof of dextral dextralsense sense faults faults is is present presentas as is is a set veinlike alteration alteration zones. involved intense, intense, fracture-controlled fracture-controlled feldspathizzones. These Theseveins veins appear appear to have involved feldspathization, possibly albitization (i.e., which overprinted overprintedthe thesericitization. sericitization. In irregularly (Le., not microcline)which defined, specific zones, north-striking set defined, but but specific zones, there there is is an almost north-striking set of closely spaced fractures. There There are also relatively relatively late late northeast-striking, northeast-striking,sinistral sinistraland anddextral dextralfaults. faults. Structural Structural Summary: Summary: various fabrics - sericite sericite sericite sericite sericite (locally sericite (locally within withinAV AV 320°) 320') sericite; crenulation sericite; crenulation fabric fabric sericite sericite crenulation fold axis —074/51 074151 alteration 320' vein-like alteration 262°, 27g0, 279°, 292°, 262O, 292O,320° relatively early fracture sets (with without displacement) early fracture (with or without displacement) 260°, 311/70 260°311/70 relatively late late fracture fracture set (with (with or without without displacement) displacement) 004/77 210/61 004177 210161 relatively S8 2700 S3? S3? 282° 282' 290/70 290170 264/82 264182 258/80 258180 sa sSbb Sd % sS33 F3 F3 AV CE CE CL CL 270 , within mafic Fabrics within mafic dike: dike: s3~ 3c s3~ s3e Sac- S3S LS 1.8 Vq vq b L9 chlorite chlorite chlorite chlorite chlorite chlorite slickenside 102/10 1OZlO slickenside orientation (steeply dipping) dipping) 000°, 000°020°, 020°060°, 060°090° O W 0 generalized quartz vein orientation glacial striation 236° 236O glacial striation 273/70 27W70 284/69 284169 308/75 308175 Stop 35: Stop 35: WEST WESTCCZONE ZONEOUTCROP OUTCROP(Figures (Figures18 18 and 48) Location: About 200 m Location: m west-northwest of the the East East C C Zone Zone outcrop. outcrop. quartz-feldspar-phyric, This outcrop outcrop consists consists of of metamorphosed metamorphosed and notably notably altered: altered: quartz-feldspar-phyric, heterolithic fragmental rocks, many of which have the characteristics of lapilli-tuff, lapilli-stone, and heterolithicfragmental rocks, many which the characteristics tuff (Photo 17); volcaniclastic(?) granule granule and and pebble pebbleconglomerate; conglomerate;and andwacke. wacke. A few of the 17); volcaniclastic(?) the contacts are well welldefined, defined,sharp, sharp, and andfolded. folded. Some contacts between between subunits subunits of lapilli-stone lapilli-stoneand lapilli-tuff are of the quartz-feldspar-phyric quartz-feldspar-phyric rocks rocks may may be be intrusive intrusive (subvolcanic?) (subvolcanic?) porphyry. Remnant layering layering in in the the country rocks Remnant rocks (Photo (Photo 18), 181, where identifiable, identifiable, commonly commonly strikes northeast displays S-shaped northeast and and displays S-shaped asymmetric folds. The The predominant predominantfabric, fabric, which which is is considered considered to be S2, is is clockwise clockwise to to the the layering. layering. This indicates indicates that there there is is either either another another fold fold axis axis south south of the major northwest-closing fold centred on the Williams property (Figure 19), or that tectonic Williams (Figure 19), that tectonic crust have have resulted resulted in in this this configuration. configuration. There are also juxtaposition of segments of the upper crust displacements of layering, numerous displacements layering, up to a few metres apparent magnitude, along the predomipredomifabric, which which has resulted resulted in aa very very blocky blocky configuration configuration of rock rock types types in places. places. There are a nant fabric, few north-northwest north-northwestand and west-northwest-striking, west-northwest-striking,dextral dextral faults faults and and east-northeast-striking, east-northeast-striking,sinissinistral faults. faults. Stop 35: Figure (opposite page) Stop Figure 48. 48. (opposite 35: Detailed Detailed sketch map of part part of the the C C Zone, Zone, west west end end (Williams property), property), showing showing variably variably altered, altered, folded, folded, faulted, faulted, and discordant blocks of (Williams of metametapyroclastic rocks and rocks intruded intruded by several dikes of and metavolcaniclastic/metasedimentary metavolcaniclastic/metasedimentary rocks various compositions. compositions. Vein-like shear-controlled alteration/mineralization alteration/mineralization overprints Vein-like and and fault- or shear-controlled earlier pervasive alteration/mineralization. alteration/mineralization. (After (AfterMuir Muir1989). 1989). �Stop Stop Descriptions Descriptions — -Hemlo Hemlo Deposit: Deposit:Williams Williams Property Property Overburden Overburden DIKES, DIKES,VEINS VEINS Diabase Diabase INTRUSIVE INTRUSIVECONTACT CONTACT Quartz Quartzveins, veins, stringers, sthgers, knots knots 11111111 llIlllll Biotite Biotitegabbro gabbro PIaocIase Ptadoclaseporphyry m y r y b\\F Granodiorite Granodiorite INTRUSIVE INTRUSIVECONTACT CONTACT Fragmental Fragmentalrocks rocks (pyrocIastic (pyroclastic,volcaniclastic) vdcaniclastic) aa coarse coarse bb medium mediumtotofine fine Granule Granule to to pebble pebbleconglomerate conglomerate Wacke Wacke 101 SYMBOLS SYMBOLS ALTERATION ALTERATION (vein-like) (vein-like) ...... Feldspathization Feldspathization(and/or (andlorsilicification?) silicification?) -* Sicification, Siliiification,molybdenite molybdenite Feldspathization, Feldspathization,pyrite pyrite(±(tAu?) Au?) — Iron carbonate Iron carbonate FAULTS FAULTS (ductile (ductile and/or andlwbrittle) brittle) .-& . - Senseof ofdisplacement &splacementknown known Sense Planarschistose schistosezones zones—sense -sense unknown unknown Planar BEDDING BEDDING - Internal Internalbedding bedding Unit contact contact Unit �102 102 Geology and Gold Deposits Deposits of the Hemlo Area Pervasive alteration is in the the form form of offeldspathization feldspathization and andbiotitization. biotitization. Some Some of the layering to be selectively feldspathized. Vein-like alteration alteration is is in the form of appears to feldspathized. Vein-like of feldspathization feldspathization (albitization?), carbonatization, pyritization, and silicification. Molybdenite Molybdeniteisislocally locallyassociated associated feldspathization±silicification. The with the vein-like feldspathization~silicification. The "veins" "veins" are are collectively collectively oriented oriented with with prepreferred strikes of about 250°, 290°. which which have been been locally locally dextrally dextrally offset. offset. Sizeable 250°270°, 270°and 290° Sizeable quartz veins are uncommon but but there there are are numerous numerousquartz quartz knots. knots. A few of these knots show of the the country country rock with with associated development of coarse-grained coarse-grained adjacent, incipient bleaching of muscovite in dilational zones. Gold distribution but muscovite Goldmineralization mineralizationisissporadic sporadicin in grade grade and and distribution but is is most associated with molybdenite this outcrop. outcrop. About 100 m east-northeast east-northeast commonly associated molybdeniteand/or andlor pyrite in this was aa small small exposure exposure containing containing sugary sugary textured barite, pyrite, and of the West C Zone outcrop was and possibly molybdenite. molybdenite. Three types of dikes, which are presently presently foliated, foliated, have have intruded intruded the the country countryrocks rocksand andare are parallel or subparallel to the predominant fabric. An unfoliated Archean diabase dike crosscuts parallel subparallel to the predominant fabric. unfoliated Archean diabase crosscuts all the rock types on the west side of the exposure. Structural Summary: Structural Summary: 250/72 S0/S1 sds~ 250172 parallel to to long dimension of 260/77 S2 s2 260177 parallel long dimension of fragments fragments (horizontal (horizontal surface) surface) 050°, axial planar folds S3 s3 050°080° 080' axial planar to to F3 F3 folds 270/55, 290/73 vein-like alteration; alteration; most AV Avf 270155, 290173 vein-like most are are feldspar feldspar rich rich 260/75, 280/75, 300/74 vein-like alteration; alteration; some some are are carbonate carbonate rich rich AV AVC 260175, 280175,300174 vein-like 265°-290° planar o C 265'-290 planar schistose schistose zones (with (with or or without withoutapparent apparentdisplacement); displacement); some are associated associated with pyrite molybdenite ± silicification? silicification? pyrite ± Au?, some with molybdenite elongation lineation 328/58 b 3281% elongation lineation of fragments I.e rare, relatively 070° '4 070 relatively long long quartz quartz vein vein orientation orientation Vq * * �103 I03 References References 8: REFERENCES PART 8: REFERENCES Bartley, 1957AAgeological geological report report on on the the Hemlo Hemlo area, area,Thunder Thunder Bay Bay District; District; unpublished unpublished Bartley, M.W M.W. and andPage, Pagel T.W. 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Muir, T.L. 1985. Hemlo tectono-stratigraphic tectono-stratigraphic study; inSummary Summary of of Field FieldWork Work and andOther OtherActivities Activities1985, 1985, Muir, T.L. study; in Ontario Paper 126, p.71-74. OntarioGeological GeologicalSurvey, Survey,Miscellaneous Miscellaneous Paper 126, p.71-74. Muir, tectono-stratigraphic study; Muir, T.L. T.L. 1986. Hemlo tectono-stratigraphic study; in inSummary Summary of of Field FieldWork Work and andOther OtherActivities Activities1986, 1986, Ontario OntarioGeological GeologicalSurvey, Survey,Miscellaneous MiscellaneousPaper Paper132, 132,p.95-106. p.95-106. Muir, tectono-stratigraphic study; Muir, T.L. 1988. Hemlo tectono-stratigraphic study; in inSummary Summaryof of Field FieldWork Workand andOther OtherActivities Activities1988, 1988, Ontario OntarioGeological GeologicalSurvey, Survey,Miscellaneous MiscellaneousPaper Paper141, 141, p.226-229. p.226-229. Muir, T.L. T.L. 1989. 1989.Geology Geologyofofthe theHemlo Hemlodeposit depositarea: area:AAtectono-stratigraphic Summary of Field tectono-stratigraphicstudy; study; in insummary Field Work and and Other Other Activities Activities1989, 1989,Ontario OntarioGeological GeologicalSurvey, Survey,Miscellaneous MiscellaneousPaper Paper146, 146,p.92-96. p.92-96. Muir, T.L. T.L. 1990. 1990.Geology Geology of ofthe theHemlo Hemlodeposit deposit area: area: A tectono-stratigraphic tectono-stratigraphic study; Summary of study;ininsummary ofField FieldWork Work and Survey, Miscellaneous Paper 151, p117-119. and Other OtherActivities Activities1990, 1990,Ontario OntarioGeological Geological Survey, Miscellaneous Paper 151, p.117-119. Muir, T.L. 1993. The The geology geology of of the the Hemlo gold deposit; deposit; Ontario Muir, T.L. OntarioGeological GeologicalSurvey, Survey,Open OpenFile FileReport Report5877, 5877, 264p. 264p. Muir, T.L. and Elliott, C.G. C.G. 1987 Hemlo tectono-stratigraphic tectono-stratigraphic study; in in Summary of Field Field Work and Other Muir, T.L. Activities Paper Activities1987, 1987, Ontario OntarioGeological GeologicalSurvey, Survey,Miscellaneous Miscellaneous Paper13Z 137p.117-129. p.117-129. Muir, T.L., T.L., Elliott, Elliott, C.G. C.G. and Corfu, F. F. 1988. 1988.The Thetectono-stratigraphic tectono-stratigraphic setting of the Hemlo Hemlo Au-Mo Au-Mo deposit, deposit, Ontario, Ontario, Canada; Canada; in in Bicentennial Bicentennial Gold Gold '88, '88, Melbourne, Melbourne, Victoria, Victoria, May May1988, 1988,extended extendedabstracts, abstracts, poster poster program program voll, vol.1, p.95-97 p.95-97 Page, 1947a. AA report report on the Ollmann-Williams group of claims, Hemlo, Ontario; Ontario; assessment assessment files, Page, T.W. T.W. 1947a. Resident Geologist's office, Schreiber-Hemlo District, Thunder Bay, 8p. Resident Geologist's off ice, Schreiber-Hemlo District, Thunder Bay, 8p. Page, T.W. T.W. 1947b. 1947b.Report Reporton onthe theproperty property of ofthe the Lake Lake Superior Superior Mining Mining Corporation Corporation Ltd.; assessment files, Resident office, Bay, 1lp. Resident Geologist's off ice, Schreiber-Hemlo District, District, Thunder Bay, p. Page, T.W. 1948. 1948.AA report report on on the the property of Lake Superior Mining HemloArea, Area,Ontario; Ontario; Page, T.W. Mining Corporation CorporationLtd., Ltd.,Hemlo assessment files, Resident Geologist's office, Schreiber-Hemlo District, Thunder Bay, 23p. assessment files, Resident Geologist's office, Schreiber-Hemlo District, Thunder Bay, 23p. Page, T.W. 1949. 1949. Report Report on on the the properties properties of Lake Superior Mining Page, T.W. Mining Corporation CorporationLimited; Limited;assessment assessmentfiles, files, Resident Resident Geologist's Geologist's office, office, Schreiber-Hemlo Schreiber-HemloDistrict, District,Thunder ThunderBay, Bay, 4p. 4p. Pan, 1990. Metamorphic Metamorphic petrology petrology and gold mineralization mineralization of the White Pan, Y. Y 1990. White River River gold gold prospect, prospect, Hemlo Hemloarea, area, Ontario; unpublished PhD thesis, University of Western Ontario, London, Ontario, 256p. Ontario; unpublished PhD thesis, University of Western Ontario, London, Ontario, 256p. Pan, Y. and and Fleet, Fleet, M.E. M.E. 1988. 1988.Metamorphic Metamorphic petrology petrology of the the White River gold prospect, prospect, Hemlo Pan, Y River gold Hemloarea, area, Ontario; Ontario; in in Geoscience GeoscienceResearch ResearchGrant GrantProgram, Program,Summary SummaryofofResearch Research1987-1988, 1987-1988, Ontario Ontario Geological Geological Survey, Survey, Miscellaneous MiscellaneousPaper, Paper,p164-176. p.164-176. Pan, Y. Metamorphic petrology petrology and and gold gold mineralization mineralization of of the White River Y and Fleet, M.E. M.E. 1989. Metamorphic River gold gold prospect, prospect,Hemlo Hemloarea; area;ininGeoscience GeoscienceResearch ResearchGrant GrantProgram, Program,Summary SummaryofofResearch Research1988-1989, 1988-1989, Ontario Ontario Geological GeologicalSurvey, Survey,Miscellaneous MiscellaneousPaper Paper143, 143,p.42-52. p.42-52. Pan, Y. and Fleet, M.E. 1990. Metamorphic petrology and gold mineralization of of the White River Y Metamorphic petrology and gold mineralization River gold gold prospect, prospect, Hemlo Hemloarea; area;ininGeoscience GeoscienceResearch ResearchGrant GrantProgram, Program,Summary SummaryofofResearch Research1989-1990, 1989-1990, Ontario Ontario Geological GeologicalSurvey, Survey,Miscellaneous MiscellaneousPaper Paper150, 150, p13-26. p.13-26. Pan, and Fleet, Fleet, M.E. M.E. 1991. 1991.Metamorphic Metamorphicpetrology petrologyand andalteration alteration assemblages assemblages of of the the Hemlo gold district; district; Y and Pan, Y. in in Geoscience Geoscience Research Research Grant Grant Program, Program, Summary SummaryofofResearch Research1990-1991, 1990-1991, Ontario Ontario Geological Geological Survey, Survey, Miscellaneous MiscellaneousPaper Paper156, 156,p.p.147-169. 147-169. Pan, Y. and Fleet, M.E. 1992. Calc-silicate alteration in in the the Hemlo Hemlogold golddeposit, deposit,Ontario: Ontario:mineral mineralassemassemPan, Y. blages, constraints and significance; blages, P-T-X P-T-X constraints significance;Economic EconomicGeology, Geology,v.52, v.52, p.53-69. p.53-69. Pan, Y, Y., Fleet, Fleet, M.E., M.E., and and Stone, Stone, W.E. WE. 1991. Geochemistry of of metasedimentary metasedimentary rocks in 1991. Geochemistry in the the Late Late Archean Archean Hemlo-Heron Bay greenstone belt, Superior Province, Ontario: implications for provenance Hemlo-Heron Superior Province, Ontario: implications for provenanceand and tectonic tectonic setting; setting;Precambrian PrecambrianResearch, Research,v.52, v.52, p.53-69. p.53-69. Patterson, G.C. G.C. 1983. 1983. Exploration history in the Hemlo area; in in The geology of gold gold in in Ontario; Ontario;Ontario Ontario Geological GeologicalSurvey, Survey, Miscellaneous MiscellaneousPaper Paper110, 110, p.227-229. p.227-229. Patterson, G.C. 1984. 1984. Field trip guidebook to the the Hemlo Hemlo area; area; Ontario Ontario Geological GeologicalSurvey, Survey, Miscellaneous Miscellaneous Paper 118, 118,31p. Paper 31p. �106 106 Geology and Gold Gold Deposits Deposits of of the Hemlo Hemlo Area Area Patterson, Patterson, G.C. G.C. 1985. 1985. Hemlo-a Hemlo-a golden golden difference; difference; Thunder Thunder Bay Bay Field FieldNaturalists' Naturalists'Newsletter, Newsletter,v.39, v.39, no.4, no.4, November, November,1985, 1985,p.2-6. p.2-6. Patterson, files, SchreiberPatterson,G.C. G.C. 1986. 1986. Report Report on on the the Lytton LyttonMinerals MineralsLimited Limitedproperty, property,Resident ResidentGeologist's Geologist'sfiles, SchreiberHemlo Hemlo District, District,Thunder ThunderBay, Bay,6p. 6p. Quartermain, Quartermain,R. R.1985. 1985.Road Roadguide guideto tothe thegeology geologyofofthe theTeck-Corona Teck-CoronaMine MineatatHemlo, Hemlo,Ontario; Ontario;ininGold Goldand and copper-zinc copper-zinc metallogeny rnetallogeny within withinmetamorphosed metamorphosedgreenstone greenstoneterrain, terrain,Hemlo-ManitouwadgeHemlo-ManitouwadgeWinston WinstonLake, Lake, Ontario, Ontario, Canada, Canada, joint publication publication of of Geological Geological Association Association of of Canada Canadaand andCanaCanadian dian Institute InstituteofofMining Miningand andMetallurgy, Metallurgy,p.39-46. p.39-46. Roland, Roland, W. W. 1887 Algoma west: Its Itsscenery sceneryand andindustrial industrialresources; resources;Warwick Warwickand andSons, Sons,Toronto, Toronto, Ontario. Ontario. Siragusa, geology, White White Lake Lake area, area, western western part, part, District of Thunder Siragusa, G.M. 1984a. 1984a. Precambrian geology, Thunder Bay; Bay; Ontario OntarioGeological GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP2701, P.2701,scale scale1:15 1:15840. 840. Siragusa, Siragusa,G.M. G.M. 1984b. 1984b.Precambrian Precambriangeology, geology,White WhiteLake Lakearea, area, eastern easternpart, part,District Districtof of Thunder ThunderBay; Bay;Ontario Ontario Geological 1:15840. 840. GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP.2702, P.2702,scale scale1:15 Siragusa, Siragusa, G.M. G.M. 1985a. 1985a. Precambrian Precambriangeology, geology, White White Lake Lake area, Animons Lake Lake section, section, District Districtof of Thunder Thunder Bay; 1:15 840. 840. Bay; Ontario Ontario Geological GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP2739, P.2739,scale scale1:15 Siragusa, 1985b. Precambrian Precambrian geology, White Lake area, Theresa Lake section, District of Thunder Thunder Siragusa, G.M. G.M. 1985b. Bay; Bay; Ontario Ontario Geological GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP2738, P.2738,scale scale1:15 1:15 840. 840. Schnieders, Schnieders, B.R., B.R., Smyk, Smyk, M.C. M.C. and andWhite, White,G.D. G.D.1988; 1988;ininReport ReportofofActivities Activities1987 1987Resident ResidentGeologists, Geologists, Ontario Paper 138, p.135-159. OntarioGeological GeologicalSurvey, Survey,Miscellaneous Miscellaneous Paper 138, p.135-159. Smart, lithologicalstudy studyalong alongthe theHemlo Hemlofault; fault;unpublished unpublishedBSc BScthesis, thesis,Queen's Queen'sUniversity, University, Smart, PP.1988. 1988.AAlithological Kingston, Kingston,Ontario, Ontario,43p. 43p. Smyk, Smyk,M.C., M.C., Schnieders, Schnieders,B.R. B.R.and andMuir, Muir,T.L. T.L. 1990. 1990. Field Fieldtrip trip guide guideto to the the Hemlo Hemloarea; area;ininMineral Mineraldeposits depositsinin thewestern westernSuperior SuperiorProvince, Province,Field Fieldtrip trip99guidebook, guidebook,8th 8thIAGOD IAGODSymposium, Symposium,Ottawa, Ottawa,August, August, the 1990; 1990;p.26-38. p.26-38. Strickland, Strickland,H.M. H.M. 1979. 1979. Silver Silver under under the sea: sea: The Thestory storyofofthe theSilver SilverIslet IsletMine Minenear nearThunder ThunderBay, Bay,Ontario, Ontario, Canada; Canada;Highway HighwayBook BookShop, Shop,Cobalt, Cobalt,Ontario. Ontario. Thomson, Thomson,J.E. J.E.1931. 1931. Geology Geologyof of the the Heron HeronBay Bay area, area, District Districtof of Thunder ThunderBay; Bay; Ontario OntarioDepartment Departmentof ofMines, Mines, Annual AnnualReport, Report,v.40, v.40,pt.2, pt.2,p.21-39. p.21-39. Thomson, Thomson, J.E. J.E. 1933. 1933. Geology Geology of of the the Heron HeronBay-White Bay-White Lake Lake Area, Area, District District of ofThunder ThunderBay; Bay;Ontario Ontario Department DepartmentofofMines, Mines,Annual AnnualReport, Report,v.41, v.41, pt.6, pt.6,p.34-52. p.34-52. Valliant, Valliant, R.I., R.I., Guthrie, Guthrie, A., A., Bradbrook, Bradbrook, C., C., Motzok, Motzok, A., A., Mcllveen, Mcllveen,D., D., Kent, Kent,J., J., MacMillan, MacMillan,G., G.,Skrecky, Skrecky, G., G., Wingfield,T. T. and andSheehan, Sheehan,D.G. D.G. 1985. 1985.Field Fieldguide guide to to geological geologicalsetting settingofofLac LacMinerals MineralsLtd. Ltd.pyritic pyritic Wingfield, gold gold orebodies, orebodies, Hemlo HemloOntario; Ontario;ininGold Goldand andcopper-zinc copper-zincmetallogeny metallogenywithin withinmetamorphosed metamorphosed greenstone terrain, terrain, Hemlo-Manitouwadge-Winston Hemlo-Manitouwadge-Winston Lake, Lake, Ontario, Ontario, Canada, Canada, joint joint publication publicationofof greenstone Geological GeologicalAssociation AssociationofofCanada Canadaand andCanadian CanadianInstitute InstituteofofMining Miningand andMetallurgy, Metallurgy,p.47-57 p.47-57 Valliant, Valliant,R.I. R.I. and andBradbrook, Bradbrook,C.J. C.J.1986. 1986.Relationship Relationshipbetween betweenstratigraphy, stratigraphy,faults faultsand andgold golddeposits, deposits,PagePageWilliams Mine, Mine, Hemlo, Hemlo, Ontario, Ontario, Canada; Canada; ininProceedings ProceedingsofofGold Gold'86, '86,Toronto, Toronto,Ontario, Ontario,1986, 1986, Williams p.355-361. p.355-361. Walford, of the Zone, Page-Williams P., Stephens, Stephens,J., J.,Skrecky, Skrecky,G. G.and andBarnett, Barnett,R. R.1986. 1986.The Thegeology geologyof the"A' %'Zone, Page-WilliamsMine, Mine, Walford,P., Hemlo,Ontario, Ontario,Canada; Canada;ininProceedings ProceedingsofofGold Gold'86, '86,Toronto, Toronto,Ontario, Ontario,1986, 1986,p.362-378. p.362-378. Hemlo, Walford, Walford, P.C., PC., Weicker, R. R. and Guthrie, Guthrie, R. R. 1986. 1986. The Page-Williams Page-Williams property; property; in inThe The Hemlo Hemlogold golddeposits, deposits, Ontario; Ontario;Field FieldTrip Trip4: 4: Guidebook, Guidebook,Geological GeologicalAssociation AssociationofofCanada-Mineralogical Canada-MineralogicalAssociation Associationofof Canada-CanadianGeophysical GeophysicalUnion, Union,joint jointannual annualmeeting, meeting,May May1986, 1986,Ottawa, Ottawa,Ontario, Ontario,p.53-62. p.53-62. Canada-Canadian Williams, Subprovince; inThe geology Williams,H.R., H.R.,Heather, Heather,K.B., K.B.,Muir, Muir,T.L., T.L., Sage, Sage,RP. R.P.and andStott, Stott,G.S. G.S.1991. 1991. Wawa Subprovince; inThegeology of ofOntario, Ontario,Ontario OntarioGeological GeologicalSurvey, Survey,Special SpecialVolume Volume4,4,Part Part1,1,p.485-539. p.485-539. �107 PART PART 9: PHOTOGRAPHS PHOTOGRAPHS Photo 19,23). 23). Highly strained (mylonitized) aplite dike within virtually Photo1:1: STOP 6 (Figures 18, 19, unstrained biotite biotite granodiorite. Aplite Aplitelocally locallydisplays displaysribbon ribbonquartz. quartz. Fabric Fabricisislikely likelyS3. S3. unstrained Photo 19,21,24). Turbidite Photo2: 2: STOP STOP88 (Figures (Figures18, 18,19,21,24). Turbidite(top (topand andbottom bottomoutlined outlinedininpart partby bywhite whitelines lines at at left) left) consisting consisting of of aafeldspathic feldspathic arenite arenitebottom bottompart part(lower (lowerpart partofofphoto), photo),aafeldspathic feldspathicwacke wacke middle middle part, part, and and aa laminated laminated (not (not clearly clearly visible visible ininthis thisphoto) photo)uppermost uppermostpart. part. View View toward toward northeast. northeast. �108 Geology and Gold Deposits of the Hemlo Area (Figures 18, 18, 19, 19,21). 21). Moderately strained conglomerate in Photo 3: STOP 11 (Figures in two two well-defined well-defined Photo 3: units units (left and and right right sides sides of of photo) photo) and and one one ill-defined ill-defined unit unit (near (near centre) centre) entrained entrained within within feldspathic wacke (centre). Main structuralfeatures are indicated. Scale card outlined at centre is Main structural features are indicated. Scale card outlined at 9 cm long. View View toward toward northwest. northwest. �, Photographs 109 109 Photo 4: STOP 17 (Figures 18, 19, 21). Variably altered, highly strained, quartz-(feldspar)Ph )ar)phyric fragmental from stained OT potassium poiassium feldspar, relaspar, as evident eviaent Trom stainea slab sIaD face, race, ~ragmeniairock. rocK. Distribution uisiriDuiion of appears to have been partly controlled by the presence of fragments fragments and and cleavage cleavage planes. planes. C = deformed clast. QE deformed clast. QE == quartz quartz eye. eye. MM= =microcline-rich microcline-richzone. zone. P = = pyrite-rich pyrite-rich zone. zone. Some Some concentrations concentrations of of potassium potassium feldspar feldspar are are oval oval and enigmatic enigmatic (E). (E). �110 Geology and Gold Deposits of the Hemlo Hemlo Area STOP 20A (Figures (Figures 18, 18, 19, 19, 21, 21, 30). 30). Highly strained, feldspathized and and Photo 5: 5: (above) (above) STOP sericitized are indicated. sericitized fragmental fragmentalrockfrom rock fromthe theMain Mainmineralized mineralizedzone. Main Main structural structural features featuresare indicated. This rock may be the feldspathized equivalent of of a biotite-predominant conglomerate or biotite fragmental unit, spatially Hemlodeposit deposit(see (seeMuir Muir1993). 1993). spatially associated associatedwith with the theHemlo (Figures 18,19,21,33). 18, 19, 21, 33).General General view view of of the the western western Photo 6: (opposite page, top) STOP 21BB(Figures Photo (opposIte page, half of the A Zone as seen seen before before open open pit pit mining. mining. View toward west. west. Generalized Generalized Zone orebody, orebody, as from left to to right: A — footwall, footwall, partly partly microclinized, descriptions of major units in the photo are, from quartz-plagioclase porphyry; — feldspathized metasedimentary metasedimentary quartz-plagioclase porphyry; B B— -plagioclase-phyric plagioclase-phyric dike; C — structurally lower, sericitized, and pyritized lower, rusty-weathering, rusty-weathering, microclinized, sericitized, pyritized rocks rocks rocks; D (ore), likely derived from metasedimentary E— -variably variably feldspathized feldspathized and andschistose schistose (ore), metasedimentary rocks; E wackes; F feldspathized, sericitized, sericitized, pyritized schists F— -structurally structurally upper, upper, rusty-weathering, rusty-weathering, feldspathized, schists (ore), derived derived from metasedimentary rocks; G — hanging wall, mixed wacke, siltstone, metasedimentary rocks; G - hanging wacke, siltstone, and amphibole-rich layers amphibole-rich layers (Figures 18, 18, 19, 19,21, 21,33). 33). View of main part part of of Photo 7: (opposite (opposite page, page, bottom) bottom) STOP 21 BB(Figures orebody showing showing aa dioritic dioritic dike swarm that that intruded a mineralized pseudobreccia pseudobreccia(ore). (ore). The orebody (PBX) is enhanced enhanced by differential weathering of of highly altered and pseudobreccia (PBX) and tectonized tectonized rocks. The lenses consist mostly of feldspathized rockand the matrix is largely granularpyrite largely granular pyrite with rocks. The lenses consist mostly of feldspathized rockand atbottom some biotite. Dikes Dikesare are partly partly indicated indicated by by dashed lines at bottom of photo. Scale Scale card card outlined at centre left left is is 9 cm long. View View toward toward east. east. à �Photographs Photographs 111 �112 112 Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area (Figures 18,19,21,34). 18, 19,21,34). Subtle folding and transposition transposition (enhanced Photo8: STOP STOP 22A (Figures Subtle folding (enhancedby by acidacidPhoto etched, sawn hand specimen surface) in layered, layered, magnetite-rich, magnetite-rich, feldspathic feldspathic wacke, wacke, located located between the Main Main mineralized mineralizedzone, and and the the Lower Lower mineralized mineralizedzone. zone. �Photographs 113 113 I I I I Photo 9: STOP 25A (Figures 18, 19, 21, 38). Gneissic feldspathic metasedimentary/ rocks Pht rocks displaying spaced cleavage. Quartz disp1cty11 lY tectonometamorphic LGUUI IUI I I G L ~I IUI I [JI IILlayering IC~YGI11 19and ctl IU layer-parallel 1ctp1-pct1 ~~IIG apct~eu I LIGC~VC~YG. UUC~I LL gash ydbl I infilling indicated (Qz). North Northtoward toward top top of of photo. photo. �Geology and Gold Deposits of the Hemlo Area folded mafic schist, STOP 25A (Figures (Figures 18, 18, 19, 19, 21, 21, 38). 38). Polyclinally Polyclinally folded schist, gneissic gneissic Photo 10: 10: STOP amphibolite, and and subporphyritic subporphyritic granitic granitic dikes dikes within within the Hemlo amphibolite, Hemlo fault fault zone. zone. S3 crenulation cleavage collectively as indicated indicated by by dashed dashed lines. lines. Folding Folding may may collectively fans fans over over a range of about 125°, 125O, as with attendant attendant crumpling crumpling or folding of units and have resulted from a detachment along a plane with fabrics. Hammer North toward toward top of photo. existing fabrics. Hammer is 40 cm long. North �Photographs 115 115 Photo 11: STOP 27 (Figures 18, 40). Moderateiy to strongly deformed possibly altered, felsic, Pho slsic, quartz-plagioclase-phyric lapillistone. Most fragments are similar in composition and texture. A , e . A quat.- r.-a .--.--- -I - - - - -r - - - few lenses are composed composed of quartz quartz (Qz) (Qz) and and may may represent represent accidental, accidental, fragmented fragmented quartz quartz or or tectonically dismembered quartz quartz veins. North Northtoward towardtop topof ofphoto. photo. J -9 �Geology and Gold Deposits of the Hemlo Area 116 116 Photo 12: (above) STOP 32 (Figures 18, 19, 21, 44). Back 40s outcrop, south half. Zone of PI tectonic disruption, by lines LCII canI be teuiui iiti UULIII ICU v long-dashed lui uc traced 11aucu around aiuui IU large-scale la1UG-ouaic fold IUIU on un - uiai - - uuiiui -,-- - I. outlined - - -- u -, - iu-uaai - - - icu - - mica Williams and is is aa Dl D1or or Do D0feature. feature. Main Main structural structural features features 2are W i l kims property (Figure 19), and ire indicated. Gabbroic View toward toward west. west. Gabkxoic dikelet outlined by short-dashed lines. View d 3 4 ---- - n - I-----:A.R c ~ n onn n ~ r ' : - . . ~ -4 -n 4 n n 4 A C \ I I--:L--STOP 33A irlyuies (Figures 18, 19,, L21,45). Heritage easi east uutcrop, outcrop, south south i ur oort 10, w I , 43). neiiiciye Photo (opposite page, A&-\ top) Photo 13: 10: \uppusiie iup; o half. Outcrop Outcrop almost almost entirely covered covered over now. now. View to east-southeast. Squiggly Squiggly lines lines represent faults. Width Widthof of visible visible outcrop outcropisis about about 15 15 m. Generalized Generalized descriptions descriptionsofofnotable notablesegments segmentsininthe the photo are, from right to to left: left: A A -footwall, — footwall, partly partly microclinized microclinized and andsericitized, sericitized, quartz-plagioclase quartz-plagioclase porphyritic displaying fraaments: fragments;BB—variably metasedimentary rocks; porohvritic rock, rock. locally locallv -variably feldspathized metasedimentarv .disolavina C -— transposed, microclinized and possibly silicified metasedimen1structurally lower gossan of transposed, metasedime!ntary contents; D — zone similar similarto exceptwith rocks, locally locally with with molybdenite molybdeniteand and ore-grade ore-grade gold gold contents; D -zone to C except wiith tan/ rocks, b - : -. E E A $ f n l A / t f t ' - i + h I - ~ n / "//-*-AIr\r)\ i n n r 4 l-\!n+!+!-~nArn-l^(t more- uudi quartz veins; central zone of teldspathized and rocks LL v e i n s L-— LEI I L I ~ LUI I ic ui icluauaii IILGU I(sodic?) Q U U I ~i :ai iu Ubiotitized I~LILILGU iuuno with vviii I numerous I iuiiiciuUS mOie -- deformed quartz veins; F-zone F— zone of of variably variablyand andrelatively relativelyweaklyfeldspathized weaklyfeldspathized metasedimentary metasedimentary def ormed quartzveins; rocks; —structurally upper weathering, feldspathized, feldspathized, metasedimentary rocks; upper gossan of rusty weathering, ks; G -structurally roc I1 ..-..:-I-!.. --A --A k:-&:&:--A--b--~A:-~-b-w., B.--I.— hanging...wall, variablyanu and--l-b:.,-l.. relativelyI--lessC-lA---bk:--A feldspathized and metasedimentary rocks H -iianging wail, vanauiy ~eiaiivt!iy lea^ ie iuq~aini~a e1 uIU ubiotitized ~ u i m ~ ie i~ u e i a ~ e u ~iiai i i i ye IUL>I\S> ~ m B a - - ~a,!+hr^ia^^r-tnrn n m + v < - t l "rnnn . -I--- - ? - I----:-- - , . ....au west ...,".outcrop. ~~tcrop. STOP w33B (Figures 18, 19, 21, ,46). Heritage w,a-a page, Photo 14: m-r. t(opposite wppwen puy-, bottom) w of tiaht tight FF2 fold fold disolavina displaying"horsetail" "horsetail"structure structure and andtransoosed transposed laverina. layering. Darker Darker layers lavers are Nose of 6- wubbummm, m - v \n v w 0 - 9 8 u, 4, amphibole rich. Main structural features are indicated. Dismembered quartz vein outlined by ar dashed lines. d< �I -I. -L Cl, V 0 0 (0 -' Photographs �118 Geology and Gold Deposits of the Hemlo Hemlo Area 19, 21, 21,47). 47). C C Zone Zone east east outcrop. outcrop. Pervasively Photo 15: Pervasively feldspathized Photo 15: STOP 34 (Figures 18, 18, 19, quartz-plagioclase-phyric Arrows indicate some of the quartz-plagioclase-phyric rock rock (tuff/lapitli-tuff?). (tuffllapilli-tuff?). Arrows the many, many, variably variably discernible fragments. Lens green muscovite muscovite indicated indicated (Gm). (Gm). Scale Scale in centimetres. centimetres. North discernible fragments. Lens of green North toward top of photo. photo. �I I I I Photographs Photographs 119 ENTIMETRES Photo16: 16: STOP STOP 34 34 (Figures (Figures 18, 18, 19, 19,21,47). Feldspathizedand and possibly possibly Photo 21, 47). C Zone Zone east east outcrop. outcrop. Feldspathized partlysilicified silicifiedquartz-plagioclase-phyric quartz-plagioclase-phyricrock rockwith with numerous numerous quartz quartz stringers stringers (OS) (QS) and and breccia breccia partly (QBX) consisting of angular country rock fragments within Northtoward toward top top of of (QBX) within aa quartz quartz matrix. matrix. North photo. photo. �120 120 Geology and Gold Deposits of the Hemlo Area 35 (Figures 18, 19, 19,21, 21,48). 48). C C Zone Zone west west outcrop. outcrop. Variably feldspathized Photo 17: Photo 17: STOP 35 feldspathized and and biotitized, quartz-plagioclase-phyrictuff-breccia. tuff-breccia. Strain Strainisismoderate moderatebut butlower lower half half of biotitized, heterolithic, heterolithic,quartz-plagioclase-phyric near-dip-face plane plane thereby thereby masking the the degree degree of offlattening. flattening. View toward south. Scale photo is a near-dip-face Scale card is 9 cm long. 35 (Figures (Figures 18, 18, 19, 19,21, 21,48). 48). C C Zone Zonewest westoutcrop. outcrop. Folded feldspathic wacke Photo Photo 18: 18: STOP 35 (outlined quartz-plagioclase-phyric lapilli-tuff lapilli-tuff(top (topand andbottom). bottom). (outlined by dashed lines) separates units of quartz-plagioclase-phyric Clasts are aligned parallel to to So. S2. All All units units are arefeldspathized feldspathized to tosome somedegree. degree. North towards right of of photo. Hammer 40 cm cm long. long. Hammer(beside (besidescale scale card) card) isis40 �Mafic Metavolcanics 1 1 Metavolcanics 7 Metaconglomerate 7 Metaconglomerate 2 Mixed MixedMafic—Felsic Mafic-Felsic Gneissic Gneissic Rocks Rocks 8 8 Metawacke Metawacke with with Magnetite Magnetite Layers Layers 3 3 Felslc FelsicQuartz—Feldspar Quartz-Feldspar Metaporphyry Metaporphyry and Metapyroclastics Metapyroclastics and 4 Intermediate Intermediate to to Mafic, Mafic, coarse Metavolcaniclastics Metavolcaniclastics 5 Intermediate, medium to coarse coarse Intermediate, medium to MetavolcafliClastics ~etavolcaniclasti~~ 9 9 Metawacke/turbidite Metawackelturbidite 10 10 Metasiltstone/Pelite MetasiltstonelPelite 11 Meta-arkose 1 1 Meta—arkose -"n. • A a - Lithotectonic Contact Lithotectonic Contact Fold Axis Fault/shear Faultlshear Field Stop Field Stop (Numbered) (Numbered) Headframe Headframe 12 Granodiorite 12 Granodiorite / Diabase Diabase 6 Feldspathic Feldsoathic Metavolcaniclastics Metavolcaniclastics Figure 19. Simplified geological Figure 19. Simplified geologicalmap mapof ofthe the Hemlo Hemlodeposit depositarea, area,covering coveringSTOPS STOPS77to to26, 26, and and32 32 to 35. Units Unitsshown shownrepresent representlitho-tectonic litho-tectonicunits: units:that thatis,is,each eachunit unitdepicts depictsaavariety varietyofofsimilar similarrock rock be simple to complex complex internal internal structures which, which, in some some cases, cases, appear appear to be types displaying simple independentof of the the adjacent adjacentunits. units.(Geology (GeologybybyT.L. T.L.Muir, Muir,1985-1990). 1985-1990). independent � https://digitalcollections.lakeheadu.ca/files/original/ea1eccc25b4d3d1f273041ef65d84b32.pdf d2761042fa5199cca6962ebf6395a06d PDF Text Text Kim berlite, Base Metal and and Gold Gold Exploration Kimberlite, Exploration Using Overburden, Overburden, Wawa WawaArea Using Institute Instituteon onLake LakeSuperior SuperiorGeology Geology 41st 1995 41st Annual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon, Ontario Ontario Proceedings ProceedingsVolume Volume 41: 41: Part Part2e 2e Field Field Trip TripGuidebook Guidebook �Kimberlite, Base Metal and Gold Exploration Using Overburden, Overburden, Wawa Wawa Area by Tom F. Morris Morris Sedimentary Sedimentary Geoscience Geoscience and and Geochemistry GeochemistrySection Section Ontario OntarioGeological GeologicalSurvey Survey Ministry Ministry of of Northern Northern Development Development and and Mines Mines 7th Floor, 933 7th Floor, 933 Ramsey Lake Road Sudbuiy, Sudbury, ON ON P3E P3E 6B5 6B5 Frontispiece: 1500(after (afterAgricola Agricola1556, 1556,p.323, p.323, Frontispiece:Sluicing Sluicingoperation operationcirca circa1500 reproduced Mining Journal, Journal, February, reproduced from the the cover of Canadian Mining February,1975) 1975) �I TABLE OF CONTENTS BACKGROUND INFORMATION Introduction History of Quaternary Geology Mapping, Wawa Area Wawa Quaternary Geology Project Michipicoten River- Wawa Quaternary Geology Project Physiography Topography Drainage Basin Characteristics Climate and Vegetation Regional Geology Bedrock Geology Quaternary Geology Time Frame Ice Advance Ice Flow Indicators Material Subglacial Till Ice Retreat Bedrock Features Materials and Related Landform Flow Till and Related Landform Glaciofluvial Materials and Landform Glaciolacustrine Materials and Landform Flow Till, Glaciofluvial and Glaciolacustrine Materials as Media for Drift Prospecting Recent Deposits Eolian Deposits Colluviurn Older Alluvium Modern Alluvium Eolian Deposits, Colluvium, Older Alluvium and Modern Alluvium as Media for Drift Prospecting. Overburden Sampling Methodologies Sampling Design Material Sampling 1 1 1 4 5 5 5 5 6 6 9 9 10 10 10 10 11 11 11 11 12 12 .14 .14 14 14 14 14 15 15 15 16 Field Trip Introduction Site * 1: Introductory Overview Site DrivetoSite*2 2: Pothole, Mafic Volcanic Rock, Lamprophyre Dyke Drive to Site * 3 Site * 3: Lodgement Till Section Site 4$ Soil Weathering Subglacial Till as a Media for Drift Prospecting. DrivetoSitejt4 Site 4$ 4: Proglacial Outwash Section... DrivetoSitelt5 17 18 18 19 19 20 20 23 28 28 28 �Table of Contents (Continued) Field Trip (Continued) Site ft 5: Moraine and Ice-Contact Stratified Drift Drive to Site ft 6 Site * 6: Minong Delta Drive to Site U 7 Site ft 7:kame and Kettle (Dead Ice) Topography Drive to Site ft 7A Site ft 7A: Modern Alluvium, Ice Margin Deposit Sampling Modern Alluvium Restrictions of Stream Sediment Sampling. Drive to Site U S Site U 8: Mink Lake Glaciofluvial Fan, Striae and "P" Forms Drive to Site U 9 Site * 9: Older Alluvium Section.. Drive to Site ft 10 Site ft 10: Glaciolacustrine Section. 30 32 32 33 33 33 34 34 36 36 38 39 40 41 41 Drive to Site ft 11 Site U 11: Steephills Falls Moraine. Drive to Site ft 12 Site ft 12: Summary Site 43 43 44 44 ACflOWLEDGENTS 45 REFERENCES 45 List of Figures Figure 1: Location Figure 2: Wawa and Michipicoten River- Wawa Quaternary Geology Project Locations Figure 3: Regional Bedrock Geology Map Figure 4: Wawa Area Geology Map Figure 5: Distribution of Glaciofluvial Meitwater Channels Figure 6: Lodgement Till Section Figure 7: Location of Till Sampling Transects Figure 8: Mall Lake Dispersal: small local target Figure 9: Wawa Lake Dispersal: larger, regional target Figure 10: Black Trout Lake Dispersal: topography shadow Figure 11: Proglacial Outwash Section Figure 12: Ice Contact Stratified Drift Section Figure 13: Scott Lake Moraine Section Figure 14: Sampling Modern Alluvium Within Drainage Basins Figure 15: Glaciolacustrine Section 2 3 7 8 13 21 24 25 26 27 29 31 35 37 42 APPENDICES Appendix A: Route Maps Appendix B; Site and Material Observation Sheets MAPS; QUATERNARY GEOLOGY MAPS (Back Pocket) .49 .54 �KIMBERLITE, KIMBERLITE , BASE BASE METAL AND GOLD GOLD EXPLORATION EXPLORATION USING USING OVERBURDEN, OVERBURDEN, WAWA WAWA AREA Background Backcrround Information Information Introduction Introduction Wawa Wawa is is located located 220 220 km km north north of of Sault Sault Ste. Ste. Marie, Marie, Ontario, Ontario, east east of of Lake Lake Superior Superior (Figure (Figure1). 1). Wawa, Wawa, accessed accessed by Highway Highway 17, 17, Highway Highway 101 Michipicoten greenstone greenstone 101 or scheduled scheduled air service, service, sits sits on the Michipicoten belt which (Gledhill which has been been mined for for iron iron and and gold gold since since 1866 1866 (Gledhill 1927). 1927) History of Quaternary Geology Mapping, Wawa Area Surf icial materials materials of of the the Wawa Wawa area area were were first delineated at a Surficial a regional A more more detailed detailed regional scale by by Boissoneau Boissoneau (1966, (1966, 1968). 1968) . engineering and terrain geology geology map map was compiled by Gartner and engineering and McQuay provide a McQuay (1979). (1979). The The purpose purpose of of this this map map was was to to provide a guide guide for for engineering engineering and and resource resource planning planning functions. functions. Frey Frey (1987) (1987) defined defined and outwash systems systems and and glacial glacial and described described several several glacial glacial outwash landforms. landforms. Recently, Recently, the the On.tario Ontario Geological Geological Survey Survey (OGS) (OGS) initiated initiated 22 Quaternary Quaternary geology geology projects. projects. The The first first project project involved involved 22 summer summer field seasons seasons in in 1990 1990 and and 1991. 1991. The second second project project involved involved aa field field visit visit in in the the fall fall of of 1993 1993 and and aa summer summer field field season seasonin in 1994. 1994. WAWA WAWA QUATERNARY QUATERNARY GEOLOGY GEOLOGY PROJECT PROJECT The The area area mapped mapped and and sampled sampled during the the summers summers of 1990 1990 and and 1991 1991 includes includes the the 1:50 1:50 000, 000, NTS NTS 42 42 C/2 ~ / Hawk 2 Hawk Junction Junction map map sheet sheet (84°30'W (840301W and and 48O15'N), 48°15'N), the the northern northern half and 85°00'W; 850001W;48°00'N 480001Nand half of of the the 1:50 1:50000, 000, NTS C/l Manitowik Manitowik Lake Lake map map sheet sheet and and the the southern southern half half of of the the NTS 42 42 c/i 1:50 1:50 000, 000, NTS NTS 42 42 C/8 C/8 Franz Franz map map sheet sheet (84°00'W (840001Wand and 84°30'W; 840301W;48°07'30"N 48O07'30I1N and and 48°22'30"N; 48O22'30I1N;Figure Figure 2). 2). This This area area was was chosen chosen in in order order to to cover cover as much of the Michipicoten greenstone belt as possible in 2 field as much of the Michipicoten greenstone belt as possible in 2 field seasons. seasons. The The purpose purpose of of the the first first OGS OGS Quaternary Quaternary geology geology project project was was to: to:a) a) compliment OGS bedrock mapping and related projects focused over over the Michipicoten greenstone the Michipicoten greenstone belt belt (Sage (Sage1994); 1994); b) b) define define the the types, types, distribution, distribution, physical and geochemical geochemical properties of of overburden overburden materials; c) define define the the Quaternary Quaternary history history of of the the region; region;and and d) d) materials; c) apply apply this this knowledge knowledge towards towards exploration, exploration, environmental environmental and and land land use use applications. applications. Quaternary geology mapping and and an an overburden overburden materials program were were initiated materials sampling sampling program initiated to meet these these goals goals (Morris (Morris 1990, 1990, 1991, 1991, 1992a, 1992a, 1992b) 1992b). 1 �ONTARIO ONTARIO Thunder Thunder Study Bay Area LAKE SUPERIOR 11mm ins Timmins . 'mLcwawa /Sault ',Ste •Marie Sudbury Sudbury  U.S.A. 'LZ '1 200 0 U.S.A. km Figure 1: 1: Study Study area area location location Figure 2 �PI;J 85JO i 7?2200 C. 5:: '1 CD . tJ HO igJ ¼DCD CD '10 (D(D CD mci Itj'< H H- 0 LQrt I-. I P1 '1 H• U. (DQ 00 C)(D rtO POSSIBLE SITES, ALLUVIAL DIAMOND ALLUVIAL DIAMOND c) mo H TOWNS CD '1(l) 1 O 1h(D WATER BODIES WATER BODIES H '0 RAILROADS P. HP) ::i PP @ § ci 64OO .. C. /-o ,.,.,... ;. .:; '.' .,....,,,. : ;,; C. �MICHIPICOTEN RIVERRIVER- WAWA QUATERNARY QUATERNARY GEOLOGY PROJECT PROJECT MICHIPICOTEN Two Two diamonds, diamonds, and possibly possibly aa third, recovered from the the third, were were recovered Michipicoten River-Wawa area area (Figure 2) by C. C. Clement Clement (local Michipicoten River-Wawa (Figure 2). (local prospector) during prospector) during the the summer summer of of 1991. 1991. The exact exact location location of of the the discovery discovery site site could could not not be be positively positively identified. identified. It is thought, thought, It is however, the diamonds however, that that the collected from either either older older diamonds were were collected alluvium (sand (sand and gravel) in a point bar of the Dead River, near alluvium gravel) in the Michipicoten River and/or modern alluvium alluvium (sand (sand and and gravel) gravel) associated This discovery discovery was OGS associated with with Wawa Wawa Creek. Creek. This was reported reported to to the the OGS the fall in the fall of of 1993. 1993. Two of the the 3 diamonds loaned to to the OGS and then forwarded to Two diamonds were loaned forwarded to the Royal the Royal Ontario Ontario Museum, Museum, Department of Mineralogy, Mineralogy, for for Department of confirmation. stones were were identified identified as as industrial industrial grade grade confirmation. The stones diamonds diamonds with with carat carat weights weights of of 1.05 1.05 and and 1.13. 1.13. focused sampling program was A focused sampling program was subsequently subsequently initiated initiated by by the the OGS OGS in in September of of 1993, 1993, in order order to to establish establish authenticity authenticity of the the diamond Ten, 25 kg samples samples were collected collected from reported from the reported diamond find. find. Ten, 5 modern modern alluvium alluvium samples samples from from Wawa Wawa Creek Creek and and 55 discovery sites: 5 older alluvium samples from a a point point bar bar associated associated with with the Dead Dead River. Kimberlite indicator sampling indicator minerals recovered recovered from from this this sampling River. Kimberlite program verified that the 2 2 industrial industrial grade diamonds could have been been recovered recovered from from the the Dead Dead River River site site (Morris (Morriset et al. al. 1994). 1994). follow-up to these preliminary preliminary discoveries, discoveries, the undertook As a follow-up the OGS undertook a program in Michipicoten River-Wawa River-Wawa area a regional regional sampling sampling program in the the Michipicoten area in in The area 2). area from from the the first first OGS OGS the summer of of 1994 1994 (Figure (Figure 2). Quaternary Quaternary mapping mapping project project was was included. included. In In addition, the mapping mapping addition, the and sampling sampling of of Quaternary Quaternary materials materials was was extended extended to to include include the the northern scale N/15 Michipicoten Michipicoten Harbour Harbour NTS northern third third of of the the 1:50 000 000 scale map sheet (84°O0'W (840001Wand and 85°00'W; 850001W;47°07'30"N 47'07' 30"Nand and 48°00'N) 480001N) map sheet . The area area was was considered considered optimal optimal for for kimberlite kimberlite exploration exploration as: as: a) a) The it includes the the area where where 22 industrial grade diamonds and it includes industrial grade diamonds and associated bedrock and overburden overburden b) bedrock associated heavy heavy minerals minerals were were recovered; recovered; b) geology is is well understood (Morris (Morris 1990, 1990, 1991, 1991, 1992a, 1992a, 1992b; 1992b; Sage geology 1994); and C) c) the the area includes includes the the northern northern contact contact of of the the 1994); and Kapuskasing structural structural zone, zone, a bedrock bedrock zone zone thought thought to be aa favourable host favourable host for for kimberlite. kimberlite. This provide regional regional information 1) provide information on on the the This study's purpose purpose was was to: to: 1) types and distribution of kimberlite heavy mineral indicators types distribution of kimberlite heavy mineral indicators(KIM) (KIM) found within overburden overburden in in the the Michipicoten Michipicoten River-Wawa River-Wawaarea. area. In In addition visible gold grains were also also identified addition to to the the KIM's, KIM'S, visible gold grains identified in in characterize the way the heavy 2) heavy mineral mineral assemblage; assemblage; 2) characterize the way heavy heavy fluvial systems minerals are are transported transported through through modern fluvial systems by minerals evaluating variations variations in gold grains grains with with evaluating in concentration concentration and and wear wear on on gold distance from from a known source; 3) distance known point point source; determine the the types, types, 3) physical and geochemical distribution, physical geochemical properties properties of of overburden overburden 4 �materials within the the Michipicoten Michipicoten River River valley valley area; area; and and 4) materials 4) determine the Quaternary history of the Michipicoten River valley determine area. area. Phys iography Physiography TOPOGRAPHY TOPOGRAPHY Topography of the area is described as moderate to undulating by by Boissoneau (1966, Boissoneau (1966, 1968) 1968) and moderately moderately to severely severely rugged rugged by by landscape can can be be flat, flat, Gartner and and McQuay McQuay (1979). (1979) Locally this landscape although relief in in some some areas areas achieves achieves 198 198 m. m. although relief . DRAINAGE BASIN DRAINAGE BASIN CHARACTERISTICS CHARACTERISTICS The study study area is is located located south south of of the the Great Great Lakes-Hudson Lakes-Hudson Bay regional regional drainage drainage divide divide and and all all water water within within the the study study area area flows flows south south to to the the Lake Lake Superior Superior basin. basin. Three major drainage drainage basins basins cross the cross the study study area. area. These These include, include, from from west west to to east: east : the the Dore', Dore1, and Michipicoten Michipicoten rivers rivers Magpie and (the Michipicoten Michipicoten being being the (the the The largest). The orientation orientation of many of of the the major major rivers rivers and and lakes lakes largest) within drainage drainage basins basins is controlled by bedrock bedrock structural structural features features within is controlled Emily Bay, Bay, Dog Lake and such as deformation deformation zones zones (e.g. Emily and McKewen McKewen Lake (Heather and Buck Buck 1988). Lake deformation deformation zones) zones) (Heather 1988). . Water flow in the Water the upper upper reaches reaches of each of of the the major major drainage drainage basins is relatively basins relatively slow slow due due to to low low stream stream gradients. gradients. As aa result, alluvium is is poorly poorly sorted sorted in in their their northern northern (upstream) (upstream) reaches. In addition, drainage drainage within within the Magpie and Michipicoten Michipicoten reaches. In addition, rivers is rivers is now largely largely controlled controlled by hydro hydro electric electric dams. dams. CLIMATE CLIMATE AND VEGETATION VEGETATION In the Wawa area, area, Lake Lake Superior Superior has aa moderating moderating effect effect on on the the climate in climate in a belt 60 60 to to 91 91 km inland inland from from the the Lake Lake Superior Superior shore. shore. Cooler, summer Cooler, more moist shoreline shoreline conditions conditions prevail during the summer months which result in in more more frequent frequent cloud cloud or or fog fog cover. cover. This This reduces local local evaporation reduces evaporation rates rates and and slightly slightly modifies modifies temperature temperature and precipitation. precipitation. July July has the the warmest warmest monthly monthly mean mean temperature temperature and (15.6' C) while January has the the coldest coldest (-14. lo C). C) The yearly yearly (15.6° C) (-14.1° C. The The temperature average based on on the the monthly mean is is 2.0° 2.0' C. wettest month is is September September (113.8 (113.8 mm) while the the driest driest month month is is monthly precipitation February (55.9 mm). mm) . The The monthly precipitation average average is is 78.8 78.8 mm. mm. February (55.9 . The area east east of of Wawa Wawa (towards (towards Chapleau) Chapleau) is is classified classified as aa subarctic continental subarctic continental climate. climate. July has the the warmest monthly mean temperature (17.0° The temperature (17.0' C) while January January has has the the coldest coldest (-16° (-16' C). C) The yearly temperatureaverage averagebased basedon onthe themonthly monthlymean meanis is1.3° 1.3' C. C. The yearly temperature The month is wettest month is September September (116.9 (116.9 mm) mm) while the the driest driest month month is is mrn). The monthly precipitation average based on on the the March (48.9 (48.9 mm). yearly precipitation total yearly precipitation is is 75.1 75.1 mm. mm. . 5 �In In the the Wawa area area the the St. St. Lawrence Lawrence vegetation vegetation assemblage assemblage is is present present largely largely due due to to the the moderating moderating effect effect of of the the local local climate climate by by Lake Lake Superior This vegetation assemblage is at Superior (Rupert (Rupert 1979). 1979) at it's it's . northern northern limit in in the the Wawa Wawa area area and and includes includes maples, maples, white white and and yellow birch, red red and and white white pine, pine, jackpine, jackpine, hemlock, hemlock, cedar cedar and and spruce. spruce. AA low low crown crown density density and and thick thick development development of of underbrush underbrush are characteristic characteristic of the the assemblage assemblage in in the the Wawa Wawa area. area. East East towards Chapleau, Chapleau, the vegetation is is dominated dominated by by conifers, conifers, more more typical typical of of Boreal Boreal forest. forest. Regional Geology Bedrock Bedrock Geology Geology The The Michipicoten Michipicoten River-Wawa River-Wawaarea area lies lies within within the the Wawa Wawa subprovince subprovince of the the Superior Superior Province Province of of the the Canadian Canadian Shield. Shield. The The study study area area straddles much of of the the Michipicoten Michipicoten greenstone greenstone belt. belt. This This belt belt extends inland 150 km, km, to to the the northeast, northeast, from from the the Lake Lake Superior Superior shore with 38 km. km. This greenstone greenstone belt belt with an average average width of of 38 This consists consists largely largely of of supracrustal supracrustal rocks rocks of of Archean Archean age. age. Younger Younger Archean Archean granitic granitic rocks rocks surround surround the the greenstone greenstone belt belt (Figure (Figure3). 3). The The Kapuskasing Kapuskasing structural structuralzone zone extends extends east east from from the the shore shore of of Lake Lake Superior northeast through Superior and and then then northeast through Kapuskasing Kapuskasing into into the the Hudson Hudson Bay Bay Lowland Lowland (Figure (Figure 3). 3). The The northern northern margin of of this this zone zone is is traced traced through through Wawa, Wawa, Hawk, Hawk, Manitowik Manitowik and and Dog Dog lakes. lakes. This This structure structure is is significant significant as as it it consists consists of of fractured fractured crustal crustal material material that that may may host Structures kimberlite rock rock (Boland (Boland and and Ellis Ellis 1989). host kimberlite 1989). Structures associated associated with with this this zone zone include include northeast northeast striking striking Proterozoic Proterozoic lamprophyre 1994). lamprophyre dykes dykes formed formed by by alkalic alkalic magma magma emplacement emplacement (Sage (Sage1994). The The Precambrian Precambrian geology geology of of the the area, area, and and related related studies, studies, are are summarized There are (1994) are 44 major major sedimentary sedimentary and and summarized by Sage Sage (1994). metavolcanic metavolcanic rock rock types types recognized recognized within within the the Michipicoten Michipicoten greenstone 1) intermediate intermediate to to mafic mafic metavolcanic metavolcanic greenstone belt. belt. These These are: are: 1) rocks; 2) intermediate intermediate to to felsic felsic volcanic volcanic rocks; rocks; 3) 3) clastic clastic rocks; 2) metasedimentary 4) chemical chemical metasedimentary metasedimentary rocks rocks metasedimentary rocks; rocks; and and 4) (Figure 4) . (Figure4). . Intermediate Intermediate to to mafic mafic metavolcanic metavolcanic rock rock is is exposed exposed throughout throughout most most of of the the greenstone greenstone belt. belt. The The intermediate intermediate to to felsic felsic metavolcanic metavolcanic rocks rocks are are less less widespread widespread and and are are restricted restricted to to belts belts and and blocks blocks scattered scattered across across the the greenstone greenstone belt. belt. The The intermediate intermediate to to mafic mafic and major, and and aa and felsic felsic metavolcanic metavolcanic rocks rocks were were deposited deposited during during 22 major, third third minor, minor, volcanic volcanic cycles. cycles. The The materials materials derived derived from from the the 22 major major volcanic volcanic cycles cycles range range in in composition composition from from tholeiitic tholeiitic basalt basalt to Materials 1986) Materials to calc-alkalic calc-alkalic felsic felsic volcanics volcanics (Thurston (Thurston 1986). derived derived from from the the third third minor minor volcanic volcanic cycle cycle represent represent basaltic basaltic to to . peridotitic peridotitic komatiite komatiite volcanism volcanism followed followed by by calc-alkalic calc-alkalicfelsic felsic volcanism 1991). volcanism (Sage (Sageand and Heather Heather 1991). 6 �H'1 CD Li.' t. ¼01Q • a-; : •' : . ' . . •.. . • ,Qu;coSu8povi.jc'. 4...4 •: '• : S • + + 4- • .. .- '. : . p.' I-i CD '1 0 C) (Q CD 0 0 H- Hi CD '-1 0 C') p.' (Q CD p.' pi Metavolcanic and Metasedirnentary Rocks Metovolcanic and Metasedimentary Rocks Massive to Foliated Felsic Plutonic Rocks Massive to Foliated Felsic Plutonic Rocks Tonolitc-Granodiorite Gneisses Tonolite—Granodjorjte Gneisses Towns CD p.' Ct CD Towns Paragneiss and Migmotic Rocks Poragneiss and Migmotic Rocks Huronian Group Rocks Huronian Group Rocks Coldwell Complex Coidwell Complex Ice Flow Direction Ice Direction (1 Flow Oldest Flow, 2 Youngest Flow) - (1 Oldest Flów 2 Youngest Flow) �U H- H- CD CD 0 Ci) Ii rt CD CD '1 CD rt 0 C) H H- 'ti a H- CD rt 0 0 (.Q 'QCD CDPJ cl)'l Cl) 0C) 'lCD CD 'I (Q Figure 4: Precambrian geology of the Michipicoten greenstone belt (from Sage 1994) �Metasedimentary rocks are more common in the western part of the the study study area area than than they they are are in in the the east. east. They They were were deposited deposited within within aa marine marine alluvial alluvial fan fan depositional depositional environment environment and and were were subsequently shallow braided stream stream environment environment (Neale subsequently buried buried by a shallow (Neale 1981; The metasedimentary rocks rocks Consist consist of of either either 1981; Thomas Thomas 1984). 1984) The conglomerate, conglomerateI wacke, wacke, and and siltstone siltstone or or argillite aFgillite (Sage (Sage and and Heather Heather . 1991) 1991). Iron chemical metasedimentary metasedimentary rock found Iron formation formation is is the dominant chemical rock found within belt and and is most most Commonly commonly found found in the the within the greenstone greenstone belt southwestern, central and northeastern parts of the the study study area. area. southwestern, The The iron iron formation formation consists consists of of 55 facies facies which which include, includelfrom from base base to to surface: b) pyrite pyrite (sulphide (sulphide surface: a) a) siderite siderite (carbonate (carbonate facies); facies); b) c) chert-magnetite chert-magnetitewacke wacke (oxide (oxidefacies); facies);and and d) d) argilliteargillitefacies); c) facies); pyrite-graphite. pyrite-graphite. Occasionally, Occasionallyl calcite calcite substitutes substitutes for for siderite siderite and 1991). The and represents represents the the fifth fifth facies facies (Sage (Sageand and Heather Heather 1991). The origin origin of of the the iron iron formation formation is is summarized summarized by by Sage Sage and and Heather Heather (1991). (1991). Intermediate mafic intrusions peridotite to quartz Intermediate to to mafic intrusions consisting consisting of of peridotite to quartz diorite diorite occur predominantly predominantly within within the the central central part part of of the the greenstone They belt. They vary vary in in age age and and are are finefine- to to coarsecoarsegreenstone belt. grained. grained. Several Several stocks stocks are are scattered scattered across across the the greenstone greenstone belt. belt. These These stocks trondhjemite to to granodiorite granodiorite to to stocks range range in in composition composition from from trondhjemite granite. granite. All All are are younger younger than than the the surrounding surrounding supracrustal supracrustal rocks rocks and and may may have have been been emplaced emplaced at at the the same same time time as as the the granitoid granitoid rocks rocks external external to to the the greenstone greenstone belt. belt. Surrounding Surrounding the the supracrustal supracrustal rocks rocks are are felsic felsic intrusive intrusive rocks rocks that that range tonalite and and trondhjemite trondhjemite to to granite granite (Sage (Sageand and Heather Heather range from from tonalite External 1991). 1991). External granitoid granitoid rocks rocks on on the the south south side side of of the the greenstone greenstone belt belt are are older older than than the the external external granitoid granitoid rocks rocks on on the the north north side. side. Quaternary Quaternary Geology Geology TIME FRNE Overburden Overburden materials materials throughout throughout the the Michipicoten Michipicoten River-Wawa River-Wawa area area were were deposited deposited during during the the last lastglaciation. glaciation. The The Wawa Wawa area area has has likely Wisconsin which which likely been been covered covered by by glacial glacial ice ice since since the the Early Wisconsin occurred 000 years yearsago. ago. Bedrock Bedrock features, featuresI materials materials and and occurred about about 115 115 000 landforms landforms associated associated with with this this advance advance include: include: a) a) ice ice flow flow indicators whalebacks, indicators (straie, (straiel grooves, grooves whalebacks chattermarks); b) b) chattermarks); enhancement enhancement of of bedrock bedrock structure structure (structure (structureparallel parallel to to ice ice flow flow is is enhanced, flowis enhancedl structure structure perpendicular perpendicular to ice flow is not); not); and and c) c) thin thin till till over over bedrock bedrock (subglacial (subglacialtill). till) . 9 �100 years A radiocarbon radiocarbon date date of of 9210 9210 ±k 100 (GSC 1851) 1851) from from aa basal basal years BP (GSC organic sediment in Alfies sediment in Alfies Lake (south Wawa) provides provides a a minimum minimum (south of Wawa) date of deglaciation of ofthe the Wawa Wawa area area (Saarnisto (Saarnisto1974). 1974). Howeverl However, Mothersill (1988) (1988) argued that radiocarbon radiocarbon dating of material from with old old within the Lake within the Lake Superior Superior basin is potentially potentially contaminated contaminated with carbon. Using Using palaeomagnetic palaeomagnetic dating, datinglMothersill Mothersill concluded concluded that that the the Lake Lake Superior Superior basin basin had had been been deglaciated deglaciated by by 8200 8200 years years BP. BP. This This is is compiled by Mahanic and Teller Teller (1985). (1985). in agreement with data compiled Mahanic and The types and distribution distribution of Quaternary Quaternary materials materials and and features features are are The types summarized in Quaternary Geology Geology maps, mapsl back back pocket. pocket. summarized in the Quaternary ICE ADVANCE ADVANCE ICE Ice Flow Flow Indicators Ice Indicators Striations, Striationsl glacial glacial grooves grooves , chattermarks chattermarks and ice moulded bedrock and ice bedrock knobs knobs are preserved preserved on on smooth, smoothl unweathered bedrock bedrock surfaces. surfaces. , Striations Striations are the most common common glacial glacial erosion erosion feature feature and and are are found found throughout throughout the the study study area. area. The orientation of these these glacial erosion features varies between 165° to 263O 263° with with a 1 65' to a mean mean of of 214°. 214O. Most of the the striae striae variation variation is is due due to to deflection deflection of of regional regional flow flow by by bedrock bedrock highlands. highlands. Cross-cutting straie Cross-cutting straie have have been been observed observed in in only only 44 places. places. In In all all cases, the location casesI location of these these sites sites are are within within major major west west trending trending bedrock controlled bedrock controlled valleys. valleys. At the the 44 sites sites straie straie formed formed by the the regional ice flow flow (mean (mean of of 214°) 214O) are cross-cut by aa younger younger set set of of regional ice cross-cut by striae (mean The younger 266'). younger set set of of striae striae are are orientated orientated striae (meanof of 266°). parallel to the parallel the orientation orientation of of the the bedrock bedrock controlled controlled valleys valleys within which within which they they were were observed. observed. The older set striae represents represents flow flow that was was largely largely unaffected unaffected The older set of striae younger set of straie straie represents by bedrock bedrock topography. topography. The younger represents flow flow controlled by bedrock bedrock topographyI topography, commonly in westerly controlled commonly in the the westerly orientated valleys. This occurred occurred due thinning during orientated valleys. This due to ice sheet thinning latter stages stages of of glaciation. glaciation. the latter Material Material Till Subglacial S ubglacial T i l l discontinuous till till was was deposited deposited over over the the area area by ice A thin, thinl discontinuous ice associated associated with with the the last last glaciation. glaciation. This till was derived from the debris base of it advanced. the debris rich rich base of the the ice ice as as it advanced. This This interpretation of the subglacial origin origin of of the the till till is is based based upon upon interpretation the subglacial morphology, structural characteristics morphologyl characteristics and and pebble pebble composition. composition. tillls thickness thickness varies varies from from non-existent non-existentover over bedrock bedrock highs highs This till's This to 1.0 to 1.5 m thick in bedrock lows. outcrops are are 1.0 to 1.5 m thick in bedrock lows. Bedrock outcrops commonly associated this unit unit and and the material commonly associated with with this material can be be 10 �described as aa thin, thinl discontinuous discontinuous veneer. veneer. described as The unweathered exposures exposures of this this till till are are usually usually structureless structureless and massive. and massive. Occasionally faint shear shear were observed observed in in sections sections located up-ice up-ice of of bedrock bedrock ridges. ridges. When When dry, dryl the the material is is very located detailed discussion discussion regarding regarding subglacial subglacial till till as as aa hard. A more more detailed hard. A media for for drift drift prospecting prospecting is is contained contained in in the the notes notes for for Site Site media "Field Tript1 Trip" section. # 3, 3, l1Fie1d section. # RETREAT ICE RETREAT Bedrock Features Features The with ice ice retreat retreat in in the the Wawa The 2 bedrock bedrock features features associated associated with Wawa area area forms. are the the potholes potholes and and 1lP1l forms. Both features features are formed formed by sediment Potholes are glacial meitwater meltwater under under high high pressure. pressure. Potholes are sediment rich rich glacial not widely widely recognized not recognized throughout throughout the the Wawa Wawa area. area. They They are are circular circular features that can extend 1 to 3 m below the the rock rock surface surface and and are are formed by the circular circular rotation rotation of boulders boulders within within swirling swirling water water under high pressure pressure at the the base base of of the the ice. ice. The boulders are are dentistls drill, drill, whereby whereby the the boulders boulders literally literally analogous to aa dentist's drill drill into into the the rock. rock. Grinders, Grindersl as as these these boulders are are called, called, can can sometimes be found sometimes found in in the the bottom bottom of of the the hole. hole. llPtl the Magpie and the the Wawa Wawa "P" forms forms were were observed only within the Magpie valley valley and Lake Lake basin. basin. Characteristic Characteristic "P" llPtl forms include include furrows, furrowsI comma comma form form forms and 1989, Kor Kor et et al. al. 1991). 1991) Although and sicheiwannen sichelwannen (Sharp (Sharp and and Shaw Shaw 1989, Although . "P" forms are commonly l1Pl1 commonly restricted restricted to to valley valley floors, floorsI they were were observed on sides 65 65 mm above above the the Magpie Magpie River. River. They are are on valley sides aligned oblique to to valley valley orientation orientation suggesting suggesting that that glacial glacial aligned meitwater flow did meltwater did not not necessarily necessarily follow follow bedrock bedrock controlled controlled depressions. Straie exist exist within "P" forms suggesting suggesting that that glacial depressions. Straie l1Ptt forms ice was let let back back down down onto onto the the bedrock bedrock surface surface after after glacial glacial meltwater was meltwater was expelled. expelled. Materials and and Related Related Landforms Landforms The landform indicate The distribution distribution of materials and related landform that indicate that the ice margin retreated to the the north in in the the western western part part of of the the of region and to to the the northeast northeast in in the the eastern eastern part. part. The bulk of overburden materials were deposited deposited within within bedrock bedrock controlled controlled overburden materials valleys where valleys where glacial glacial meitwater meltwater was was concentrated. concentrated. Flow Till T i l l and Related R e l a t e d Landforms Landforms A second second type type of of till till was was deposited deposited during during ice ice recession. recession. This This (>I m) m) than than the the subglacial subglacial till. till. It is is commonly comonly till is is thicker thicker (>1 associated moraines, or or is found in isolated associated with west trending morainesl isolated patches commonly located at the headwaters of outwash systems or around Bedrock around the the periphery periphery of of former former glacial glacial lake lake basins. basins. Bedrock outcrops are rarely rarely associated associated with with this this till till type. type. 11 �The material material comprising comprising this this till till type was derived derived from from the the subglacial subglacial (base), (base), englacial englacial (middle) (middle) or or supraglacial supraglacial (surface) (surface) positions wflowsw. Because Because of of the the positions of of the the glacier glacier and and deposited deposited as as "flows". flow-like flow-likestructure structure associated associated with with these these tills tills , they they are are commonly commonly referred referred to to as as flow flow tills. tills. , Glaciofluvial Materials Glaciofluvial M a t e r i a l s and Landform subdivided into into 22 units: units: ice-contact ice-contact Glaciofluvial deposits are subdivided stratified drift and and glaciofluvial glaciofluvial outwash. outwash. The The sides sides of of iceicecontact contact stratified drift drift deposits are are commonly commonly steep due due to to deposition deposition of of the the sediments sediments against against ice ice walls. walls. Deposits Deposits consist consist of of a a wide wide variety variety of of materials materials ranging ranging from from sandy sandy silt silt to to boulders. boulders. Related Related landform landform consist consist of of eskers eskers and and moraines. moraines. Glaciofluvial outwash deposits deposits commonly commonly have gentle gentle slopes slopes as as Glaciofluvial outwash outwash outwash was was deposited deposited in in front front of of but but proximal proximal to to the the ice ice margin. margin. Kettles associated with glacial ice Kettles are are associated with several several outwash outwash deposits deposits as as glacial ice blocks blocks buried buried by by outwash outwash melted. melted. Materials Materials comprising comprising the the outwash outwash range range from from sand sand to to coarse coarse boulders. boulders. Within area glacial glacial meltwater meltwater flowed Within the the western western part part of of the the area flowed freely freely downslope from from the the ice ice margin margin toward toward the the Lake Lake Superior Superior basin. basin. Associated with this this free-flow free-flow of of water water there there are are several several well well defined within the bedrock controlled defined meltwater meltwater channels channels situated situated within controlled valleys 5) valleys (Figure (Figure5). . In In the the eastern eastern part part of of the the area, area, glacial glacial meitwater meltwater was was commonly commonly trapped in in glacial glacial lakes lakes which which formed formed between between bedrock bedrock controlled controlled topographic topographic highs highs and and the the ice ice margin. margin. Meltwater Meltwater flow flow from from these these lakes occurred occurred either either through through channels channels which which opened opened between between the the lake margin or lake and and ice ice margin or topographic topographic lows lows situated situated around around the the rim rim of of the the ice-controlled ice-controlledlake lake basin. basin. Smaller Smaller glaciofluvial glaciofluvial deposits deposits are are associated associated with with bedrock bedrock depressions glacier, melted melted depressions where where blocks blocks of of ice, ice, detached detached from from the the glacier, in-situ. Where meltwater in-situ. meltwater was dispersed dispersed onto open open space space from from concentrated channel flow flow leading leading from from this this wasting wasting ice, ice,small, small, fan-shaped fan-shaped bodies bodies of of aggregate aggregate were were deposited. deposited. Glaciolacustrine Materials and Landform Glaciolacustrine M a t e r i a l s and. Landform Glaciolacustrine materials consist consist of of fineGlaciolacustrine materials fine- and and coarse-grained coarse-grained sediments. sediments. The The fine-grained fine-grained sediments sediments consist consist of of horizontally horizontally bedded bedded couplets couplets of varved silt silt and and clay clay deposited deposited within within deep deep (quiet) (quiet) water. water. They They are are exposed exposed at at surface surface along along the the shores shores of of Dinginan Bay on on Manitowik Manitowik Lake Lake and and Localsh Bay on Dingman Bay on Dog Dog Lake. Lake. They They were deltaic section section associated associated with were also also observed observed at at the the base base of of a deltaic with the the Magpie Magpie River. River. Coarse-grained material occurs Coarse-grained material occurs where where the the western, western, free-flowing free-flowing glaciofluvial glaciofluvial systems systems empty empty into into the the Lake Lake Superior Superior basin basin and and 12 �N UI 000IacS F E In Ia F In N C C F g I) 0 " OcLc,cS C NW Figure Figure 5: 5: Distribution Distribution of of glaciofluvial glaciofluvial meitwater meltwater channels channels 13 �in shallow glacial lakes formed between the ice ice margin and and the the eastern these lakes lakes coarse-grained coarse-grained sediments eastern bedrock bedrock highlands. highlands. In In these sediments formed deltas and and sheet sheet sand sand deposits. deposits. Where rivers rivers have have cut cut through deltaic deposits, in response to to lake lake level level lowering lowering in in the the through deltaic deposits, in response Lake Superior Superior basin, basin, magnificent terraces terraces have have developed developed in in the the Dore', Dore1, Magpie and and Michipicoten Michipicoten river river valleys. valleys. More detailed detailed discussion of of the the lake lake level level history history in in the the Lake Lake Superior Superior basin basin is is discussion contained contained in in the the description description at at Site Site ## 8. 8. Flow Till, Materials a ass Media T i l l , Glaciofluvial G l a c i o f l u v i a l and Glaciolacustrine G l a c i o l a c u s t r i n e Materials for D r i f t Prospecting f o r Drift These media for drift These materials materials are are not not desirable desirable overburden overburden media for local local drift prospecting prospecting since since they: 1) 1) are are not widespread throughout the the Wawa area; 2) commonly commonly do do not not give give aa local local signature signature of of the the bedrock bedrock as as area; 2) material is is aa blend blend of of both both regional regional and and local local materials materials derived derived from the the basal, basal, englacial englacial and supraglacial supraglacial positions positions of of the the icesheet; icesheet; and 3) 3) undergo undergo several several depositional depositional processes processes that that may may either either concentrate concentrate or or dilute dilute the the indicator indicator signatures. signatures. Glaciofluvial materials materials found found in in eskers eskers and glaciolacustrine glaciolacustrine deposits to gain aa quick, deposits are used used successfully successfully to quick, inexpensive inexpensive regional Craigie 1993). 1993). regional indicator indicator signature signature (Baker (Baker 1985; 1985; Craigie RECENT RECENT DEPOSITS DEPOSITS Eolian Eolian Deposits Deposits Eolian deposits deposits consist consist of of yellow, yellow, fine fine to to medium-grained medium-grained sand. sand. These These deposits deposits are are not not widespread widespread and and are are commonly commonly located located on on the the down-wind down-wind side side of of glacial glacial lake lake and and glaciofluvial glaciofluvial deposits deposits such such as as the the broad outwash outwash plain plain east east of of Goudreau. Goudreau. A A very very thin thin cover cover of of eolian eolian material material exists exists on on the the Steephills Steephills Falls Falls Dam, Dam, Magpie Magpie River. River. Colluvium Colluvium Colluvium Colluvium consists consists of of light light brown brown to to brown, brown, coarse sand sand and and boulders. Well boulders. Well developed developed colluvium colluvium aprons aprons are are most most commonly commonly associated associated with with terrace terrace scarps scarps within within the the Magpie Magpie River River valley. valley. Older Older Alluvium Alluvium Older Older alluvium alluvium consists consists of of pale pale brown, brown, fine fine to to coarse coarse sand. sand. Older Older alluvium alluvium is is restricted restricted to to the the lower lower reaches reaches of of the the Dore', Dore', Magpie Magpie and Wawa region, and Michipicoten Michipicoten rivers. rivers. In In the the Wawa region, alluvium alluvium consists consists of of material material derived derived from from the the erosion erosion of of higher higher elevation elevation glaciolacustrine glaciolacustrine deltas deltas within within these these valleys valleys as as lake lake level level dropped dropped within the Lake Superior basin. within the Lake Superior basin. Modern Modern Alluvium Alluvium Modern minor quantities Modern alluvium alluvium consists consists primarily primarily of of sand sand and and minor quantities of of organic rich sand and gravel. Thick deposits of alluvium organic rich sand and gravel. Thick deposits of alluvium (>1 (>1m) m) 14 �commonly associated associated with rivers or or streams streams flowing flowing are commonly with those rivers through glaciofluvial glaciofluvial or or glaciolacustrine glaciolacustrine deposits deposits where where there there is is through a ready ready supply supply of erodable erodable material. material. Where a Where stream stream or or river river flow flow is is over bedrock bedrock dominated dominated terrain terrain alluvial alluvial sand sand is is scarce, scarce, found found usually as small pockets within sediment traps (behind (behind or under boulders, steps in in the the stream stream bed, bed, or or inside inside curves curves of of streams). streams). boulders, steps Colluvium, Older Older Alluvium Alluvium and and Modern Modern Alluvium Alluvium as as Eolian Deposits, Eolian Deposits, Colluvium, Media for for Drift Drift Exploration Exploration Media Eolian deposits, colluvium and older alluvium are not recommended Eolian deposits, colluvium recommended as for local for the the same same reasons given for for as media for local drift exploration exploration for reasons given flow tills, tills, glaciofluvial glaciofluvial and glaciolacustrine glaciolacustrine deposits. deposits. In In addition, addition, they have all undergone undergone at least least one one more more cycle cycle of of transportation and deposition deposition which which will will likely likely further further erosion, transportation complicate tracing tracing of of any any indicator indicator signature signature back back to to the the source source or or complicate target. target. modern alluvium alluvium is is regionally regionally prevasive prevasive and thought to to As modern and is thought represent aa signature signature of of a a whole it is is commonly represent whole drainage drainage basin basin it commonly used used as a means for for gaining fast, regional signature as gaining a fast, signature for either gold or kimberlite kimberlite exploration exploration (Gonzaga (Gonzaga et et al. al. 1994; 1994; Marshall Marshall 1986; 1986; Maurice 1988, 1988, 1991; Morris et et al. al. 1994; Seely and and Senden Senden 1994; 1994; Sutherland Sutherland 1982, 1982, 1993; 1993; Wolf Wolf et et al. al. 1975). 1975) Commonly, samples samples are are taken at the mouths mouths of drainage drainage basins basins to provide provide a a regional regional heavy heavy taken mineral signature signature for for that that drainage drainage basin. basin. The The merits of such such aa sampling program are 7a. sampling are discussed discussed in in the the write-up write-up for for Site Site *# 7a. . Overburden Samolincr Methodolocries Overburden Samlin Methodologies Sampling Sampling Design Commonly overburden overburden materials are are sampled sampled at at 22 different different scales; scales; regional and and local. local. Regional scale scale sampling sampling in in Ontario Ontario involves involves the collection collection of samples samples from from glaciofluvial glaciofluvial deposits deposits such such as as eskers and outwash, outwash, glaciolacustrine glaciolacustrine deposits, deposits, modern modern alluvium alluvium and eskers lacustrine deposits. This type of sampling lacustrine deposits. This type of sampling program program allows allows evaluation evaluation of aa large large area area relatively relatively quickly quickly and and inexpensively. inexpensively. The density at scale varies depending depending on the commodity commodity The sample sample density at this this scale of material material being collected being sought, distribution distribution of collected and being sought, exploration exploration cost. cost. Local scale sampling usually done done once an anomaly has been sampling is usually identified from the identified the regional regional scale scale sampling. sampling. Individuals have have sampled from from a variety soil sampled variety of of materials materials and and from from different different soil horizons. The exploration horizons. exploration limitations limitations of these these materials materials are are discussed In Samplingwand and at at all all "Field "Field Trip" Tripw stops. stops. In discussed in in "Material "MaterialSampling" the Wawa area subglacial subglacial till is is probably probably the the best best material material to to sample due to it's relatively relatively simple simple depositional depositional history and and aa to it's local heavy mineral and geochemical signature. Sample collection local heavy mineral and geochemical signature. Sample collection sites are based on on an an artificial artificial grid grid placed placed over over the the anomaly. anomaly. Grid Grid spacings spacings are are commonly commonly 30 30 to to 300 300 mm apart apart (Craigie (Craigie1991). 1991). 15 �Material Sampling Consistently overburden material material in overburden Consistently sampling samplincr the same same overburden in an overburden - the sampling program is critical critical when it it comes comes to to interpreting interpreting the the geochemical geochemical and/or and/or heavy heavy mineral mineral data. data. Often, Often, individuals individuals collect collect material exists at aa prescribed prescribed sample sample point point without without whatever material taking the time time to to evaluate evaluate the the site site or or material material being being sampled. sampled. different depositional depositional histories histories of the the materials materials and and the the The different different ways ways and and rates rates at at which which certain certain materials materials weather weather give give different different different geochemical, geochemical, and possibly, possibly, different different heavy mineral mineral signatures. signatures. For For example, example, sulphide minerals near surface surface minerals in a near oxidizing oxidizing environment environment weather weather quickly. quickly. Because of of this, this, it is is essential essential to take take the the time time to to make make some some basic sample sample site site and and material material observations. observations. This can can be be done done quickly and and accurately by providing the sampler sampler with with a a checklist of quickly accurately by providing the checklist of observations. These observations. These observations, observations, if if done done correctly, correctly, may be be invaluable invaluable during during data data interpretation. interpretation. Appendix B consists site observation observation sheets sheets and aa list list of of consists of of 22 site related term Although there term definitions. definitions. there is always always room room for for improvement, prove useful useful in improvement, these these observation observation sheets sheets prove in providing an outline for for some some of of the the fundamental fundamental observations observations that that should should be be made made at at either either aa till till or or sand sand and and gravel gravel sample sample site site (Appendix (AppendixB, B, p. p. 55) 55) or or aa modern modern alluvium alluvium sample sample site site (Appendix (AppendixB, B, p. p. 57). 57). humus geochemical geochemical sampling gm of of organic organic rich rich For humus sampling at at least 20 gm material material is is required. required. Ensure Ensure that that the the sample sample consists consists primarily primarily of of organics, removing removing as as much much of of the the mineral mineral material material as as possible. possible. organics, For "B" I1BI1and and "C" I1CI1horizon horizon geochemical geochemical sampling sampling (-63 ( - 6 3 micron micron or or finer) finer) For of 200 gm of of material material is is required. required. of aa subglacial subglacial till, till, only only 200 Preferably, horizon Preferably, the the unoxidized unoxidized "C" llC1l horizon should should be be collected, collected, however, however, this this horizon horizon may may not not always always be available available or or practical to to get deep is is required. required. A get at at as as soil soil pit pit or or section section at at least least 11 mm deep subsample 50 or or more more pebbles pebbles is is worth worth collecting collecting as as the the pebbles pebbles subsample of of 50 willgive will giveyou youan anexcellent excellentsignature signatureof of the the local local bedrock. bedrock. For For the the "B" I1BI1or or "C" I1CI1horizon heavy heavy mineral mineral sampling, sampling, material should should be be passed cm2 steel steel mesh mesh sieve. sieve. AA sample sample of of at at least least 10 10 passed through through aa 11 cm2 kg kg of of the the -10 -10 mesh mesh (-2 (-2mm) mm) fraction fraction should should be be collected. collected. The materials collected The types types and and quantities quantities of of materials collected can can be streamlined streamlined for for specific specific indicators. indicators. However, However, when when possible possible and and feasible, feasible, collect kg sample collect samples samples of of humus, humus, "B" 10 kg sample I1Bl1and and "C" I1CI1horizons, horizons, aa bulk bulk 10 of "C" llCI1horizon horizon material material and and pebbles pebbles at at each each sample sample site. site. Since Since much much in in the the way way of of financial financial resources resources is is invested invested in in placing a crew in in aa field field area, area, as as wide wide aa variety variety of of material material should should be be sampled sampled as as possible possible while while the the crew crew is is at at the the sampling sampling site. site. Sampling of modern modern alluvium alluvium or or other other sand sand and and gravel gravel deposits deposits is is commonly commonly done to to obtain obtain aa heavy heavy mineral mineral concentrate concentrate (specific (specific 16 �. gravity gravity >3.3). >3.3) Material Material should shouldbe be passed passed through throughaa11cm2 cm2 steel steel mesh mesh sieve sieve so so that that 10 10 kg kg of the the "finer" "finerwmaterial material is is collected. collected. Pebbles Pebbles from the the coarser coarser fraction fraction should should also also be be sampled. sampled. If resources resources permit, "finern material can can be further further processed in in permit, the the 10 10 kg kg of "finer" field through through the use use of of finer finer meshed meshed sieves sieves and and shaking shaking the field tables. tables. This This will will reduce reduce the the cost cost of of shipping shipping materials materials from from the the field, field, but will will potentially potentially increase increase the the field field time time and and hence hence expense expense of of field field programs. programs. Field Field Trip Trio Introduction Introduction The The Wawa Wawa region region was was initially initially settled settled in in 1725, 1725, with with the the establishment establishment of of aa fur fur trading trading post post at at the the mouth mouth of of the the Michipicoten gold rush accompanied Michipicoten River. River. In In the the late late 1890's 1890's aa gold rush was accompanied by the the establishment establishment of of the the Wawa Wawa townsite. townsite. Attention, Attention, however, however, quickly ore discovery, discovery, the development of quickly focused focused on on an an iron iron ore the future future development of which which became became the the town's town's main main industry. industry. Between Between 1900 1900 and and 1922, 1922, iron iron was was mined mined from from an an open open pit pit at at the the Helen Helen Iron Iron Range Range and and gold gold from from deposits deposits around around Wawa. Wawa. Mining Mining ceased ceased until until the when in mining of siderite siderite for began from the 1930's when in 1938, 1938, mining for iron iron began from the the Helen Iron Iron Range. Range. Operations continue continue to to the present. present. Gold Gold prospecting prospecting flourished flourished during during the the 1930's 1930's but but decreased decreased during during World World War Recently 11. Recently aa renewed renewed interest interest has developed developed for for the the War II. exploration exploration and and mining mining of of gold gold (Sage (Sage and and Heather Heather 1991). 1991). In In 1978, 1978, the the OGS OGS initiated initiated aa systematic systematic bedrock bedrock geology geology mapping mapping program program of of the the Wawa Wawa area area which which was was completed completed in in 1988. 1988. During During the the summers 1991, a regional regional Quaternary Quaternary mapping mapping program program was was summers of of 1990 1990 and 1991, completed mapping and provide provide Quaternary completed to to compliment compliment the the bedrock mapping geology mineral exploration, geology information information for for mineral exploration, environmental environmental and and land land use use applications. applications. With With the the announcement announcement of of he he alluvial alluvial diamond diamond discovery discovery in in the the Michipicoten Michipicoten River River area area in in the the fall fall of of 1993, 1993, the the OGS OGS extended extended it's it's mapping mapping and and overburden overburden sampling sampling program program to to the the Michipicoten Michipicoten River River valley. valley. From From these these Quaternary Quaternary mapping mapping projects projects an an understanding understanding of of overburden overburden types, types, their their distribution, distribution,and and physical physical and and geochemical geochemical properties guidebook and properties has has been been established. established. The The purpose purpose of of this this guidebook and related related field field trip trip is is to review review what what these local local overburden overburden materials effectively for mineral materials are are and and how how they they can can be used most effectively for mineral exploration. exploration. 17 �#I: Introductory Introductory Overview Overview Site Site Site *1; Appendix Appendix A: Algoma Algoma Ore Ore Division, Division, Helen Helen Mine Mine This first first stop stop overlooks overlooks abandoned abandoned open open pit pit workings workings on on the the Helen This Helen Iron Range from which a hematite-goethite hematite-goethite gossan gossan above siderite Iron Range from which above the the siderite and suiphide sulphide facies facies iron formation formation was was removed. removed. Extractive Extractive operations operations between 1900 1900 and and 1918 1918 produced produced an an estimated estimated 2,780,236 2,780,236 tons tons of of ore. ore. Operations Operations did did not not resume resume until until 1939 1939 when when open open pit pit mining mining of of the the unweathered unweathered siderite siderite began. began. Underground Underground mining mining of of siderite siderite began began in in 1949 1949 and and continues continues to to the the present. present. An estimated estimated 83,711,391 tons of siderite 83,711,391 tons siderite have been been produced produced up up until until 1986; 1986; reserves as of of 1984 1984 were were estimated estimated at at 58,246,000 58,246,000 tons tons (Sage (Sage and and Heather Heather 1991). 1991). On On aa clear clear day, day, this this site site provides provides aa spectacular spectacular overview overview of of the the Wawa area. The Wawa townsite, Citadel Gold Mines and the Wawa area. The townsite, the Lake Lake Superior basin can can be be seen seen to to the the southwest. southwest. Directly Directly south south is is Wawa Lake Lake which which occupies occupies a a linear linear bedrock controlled controlled valley 1 1 km km wide by by 88 km km long, long, and and 20-35 20-35mm deep. deep. During During deglaciation, deglaciation, this this valley was connected to higher lake levels within the Lake Superior valley was connected to higher lake levels within the Lake Superior basin. basin. The west end end of of this this basin basin closed closed as as aa barrier barrier bar, bar, on on which which Wawa Wawa is is built, built, formed formed during during regression regression of of lake lake levels. levels. At the the east east end end of of the the lake, lake, one one can can see see where where water water was forced forced through narrow bedrock bedrock controlled through aa narrow controlled constriction constriction to to form form aa delta delta in in Glacial Glacial Lake Lake Minong. Minong. To To the the north north is is aa spectacular spectacular view view of of the the defoliated defoliated zone zone where the the impressive impressive terraces terraces of the the Magpie River can be seen. can be seen. At summary of the the area's area's cultural cultural and and economic economic history, history, At this this site site aa summary vegetation, vegetation, climate, climate, bedrock bedrock and and Quaternary Quaternary geology geology in in addition addition to to the the physiography physiography will will be be reviewed. reviewed. Much Much of of this this information information is is provided guidebook. "Background Information" information^ section section of of this this guidebook. provided in in the the "Background Drive Drive to to Site Site #2. #2. As As we we pass pass through through Wawa the the road road rises rises onto onto aa pronounced, pronounced, raised raised The eastern part of Wawa is built entirely on sand surface. surface. The eastern part of Wawa is built entirely on sand and and minor minor gravels gravels of of aa barrier barrier beach beach bar bar that that sealed sealed the the southwest southwest end end of the the Wawa Wawa Lake Lake basin basin during during the the middle-Minong middle-Minong Lake Lake stage. stage. The The barrier beach was was modified modified by by aa combination combination of of shoreline shoreline wave wave cutting and fluvial terrace development of the Magpie River. cutting and fluvial terrace development of the Magpie River. The The western half terrace/beach half of of the the town occupies occupies aa prominent prominent terrace/beach surface. surface. There There is is an an arcuate arcuate escarpment escarpment edge edge that that limits limits urban urban development. Three steep escarpments are traceable across development. Three steep escarpments are traceable across town. town. 18 �Site *2: #2: Pothole. Pothole, Mat Mafic Lamwrowhvre Dike. Dike. Site ic and and Volcanic Volcanic Rock and Lamprophyre Appendix A: South South side side of of Highway Highway 101, 101, about about 10 10 km km east east of of Wawa. Wawa. Appendix This pothole, maf mafic volcanic rock lamprophyre This site site features features aa pothole, ic volcanic rock and and a a lamprophyre dyke. dyke. At At this this location location the the ice ice margin margin retreated retreated north-northeast north-northeast and and east east from from around around this this bedrock bedrock high. high. Debris-charged Debris-charged meltwater meltwater from this this wasting ice ice created created aa delta delta at at the the Glacial Glacial Lake Lake Minong Minong from level level within within the the Lake Lake Superior Superior basin. basin. Remnants Remnants of of this this delta delta are are visible visible below; below; aa site site we we will will visit visit later. later. At this this site, site, meltwater meltwater was was forced forced through through this this narrow narrow opening opening in in the bedrock under great hydrostatic pressure. demonstrated the bedrock under great hydrostatic pressure. This This is is demonstrated by by the the formation formation of of aa scour scour pool pool and and pothole. pothole. As As water water was was forced forced up and through this narrow bedrock up and through this narrow bedrock constriction, constriction, it it scoured scoured the the ground low side side of of the the constriction, constriction, leaving leaving what ground on on the the upf upflow what is is now now Ghost Ghost Lake. Lake. Within this this constriction, constriction, the the circular circular rotation rotation of of water rotated rotated "grinders" "grindersn that that literally literally drilled aa hole hole into into the the bedrock bedrock surface. surface. As ice ice continued continued to to waste waste eastward eastward from from this this site, site, this this meltwater meltwater channel channel was was abandoned abandoned and and flow flow was was directed directed south through the Firesand Creek Creek meltwater meltwater channel, channel, to to the the east east the Firesand . (Figure (Figure5). 5) There There are are excellent excellent exposures exposures of pillowed mafic volcanic bedrock and and aa lamprophyre lamprophyre dyke. dyke. The The dyke dyke has has an an elevated elevated radiation radiation level. level. There which likely There are are several several of of these these dykes dykes which likely radiate radiate outwards outwards from from aa carbonatite mineralogy carbonatite to to the the south. south. Little Little is is known known about about the the mineralogy of these these dykes dykes and and their their possible possible association association to to kimberlite. kimberlite. Drive Drive to to Site Site #3 #3 As As we we proceed proceed east, east, the the landscape landscape opens opens up up and and becomes becomes flat. flat. This This feature feature is is aa glaciofluvial glaciofluvial outwash outwash plain, plain, with with glacial glacial drainage drainage south Firesand Creek Creek meltwater meltwater channel channel to to the the south through through the the Firesand Michipicoten Michipicoten River River valley valley (Figure (Figure5). 5). Highway Highway 101 101 crosses crosses several several terraces downcutting of the outwash outwash surface surface terraces which which are are the the result result of downcutting of the by rivers rivers as as the the base base (lake) (lake) level level in in the the Lake Lake Superior Superior basin basin dropped. dropped. During it's it's eastward eastward retreat retreat across across this this valley, valley, the the glacier glacier likely likely stopped stopped several several times. times. Thebest The best evidence evidence for for this this is aa moraine moraine composed composed of of ice-contact ice-contact stratified stratified drift drift which which is is orientated perpendicular to the the valley valley axis. axis. The The highway highway cuts cuts through examine the materials of this moraine moraine through this this feature: feature: we we will examine the materials of this at 5. at Site ##5. At the the turnoff turnoff to to Hawk Hawk Junction, Junction, note note the the depression depression on on the the west side side of of Highway Highway 547. 547. This This circular circular depression depression is is aa kettle kettle which which formed when an ice block, after being detached from the main formed when an ice block, after being detached from the main ice ice body, These outwash and andsubsequently subsequentlymelted. melted. These body, was was buried buried by by outwash circular depressions, depressions, when filled filled with with water, water, look similar similar to to circular circular lakes lakes associated associated with with kimberlite. kimberlite. The The ice ice sitting sitting in in this this valley Firesand valley continued continued to to force force water water west west and and south south through through the the Firesand Creek meltwater channel water south Creek meltwater channel but but now now also also forced forced water south through through the the 19 �Grant Lake Lake meltwater channel (Figure (Figure 5). 5). meltwater channel In In route route to the town town of of Hawk Hawk Junction Junction Highway Highway 547 547 has been built on fine sand associated the distal distal edges edges of of aa glaciofluvial glaciofluvial fan. fan. associated with with the To the north north the the road road crosses crosses several several cycles cycles of of finefine- and and coarsecoarseTo the grained grained sand. sand. Each of these these cycles cycles represents represents proximal (coarse (coarse sand, boulders) and distal (fine sand) fans sand, boulders) and distal (fine sand) facies facies of glaciofluvial glaciofluvial fans associated stillstands of the the ice ice margin margin during during northward northward associated with stillstands retreat McVeigh Creek Creek valley. valley. retreat up up the the McVeigh Site #3: #3: Lodgement Till Section Section Appendix Appendix A: West of of Hawk Hawk Junction Junction this site site aa section section through through lodgement lodgement till is is examined examined and At this discussed discussed (Figure (Figure6). 6). The site is located located on on the the up-ice up-ice side side of of aa site is prominent bedrock Here, a prominent bedrock high. high. Here, relatively thick thick lodgement lodgement a relatively (subglacial) till has (subglacial) has been been deposited. deposited. The section consists consists of of aa black black (10 (10YR YR2/1 2/1rn), m), 10 cm cm thick thick humus humus The section layer containing abundant abundant decomposed decomposed roots roots and and leaf leaf matter. matter. The The I1Ael1horizon horizon lower contact is is wavy wavy and and clear. clear. The underlying "Ae" consists of consists of 13 13 cm cm of of light light grey grey silt silt (10 (10YR YR 7/2 7/2 m) m). This This material material appears The lower appears massive when when wet wet but but platy platy and and loose loose when when dry. dry. The lower contact is contact is wavy wavy and and diffuse. diffuse. The I1Bl1horizon horizon consists consists of of 25 25 cm cm of of The "B" reddish brown (10 (10 YR 4/4 4/4 m), m) , thick thick sandy sandy silt. silt. This is This material is massive and and slightly slightly compact. compact. Subangular clasts, up cm in in up to 9 cm diameter, diameter, are are common. common. The The lower lower contact contact is is wavy wavy and and diffuse. diffuse. The The I1Cl1 brown (10 (10 YR YR 4/4m), 4/4m), >> 50 "C" horizon horizon consists consists of dark dark yellowish yellowish brown 50 cm thick, sand. material is very very fissile, fissile, platy and and thick, silty sand. This material compact. to subangular subangular clasts clasts are are abundant. abundant. compact. Angular Angular to . In general, general, clast abundance abundance within within subglacial subglacial till till ranges ranges from from rare rare In with clasts to common, common, with clasts usually usually concentrated concentrated near the the bedrock bedrock contact. Till Till pebble lithology lithology determinations determinations indicate contact. indicate that that clasts clasts collected from collected from this this till till facies facies tend tend to to have have local local origin. origin. Pebbles Pebbles subglacial till collected from subglacial collected over over the the greenstone greenstone belt belt consisted consisted of granitic clasts clasts and 69.2% 69.21 clasts of 29.81 29.8% granitic the clasts derived derived from the supracrustal supracrustal rocks. rocks. Pebbles Pebbles from from till till collected collected over over the the granitic granitic terrane consisted consisted of granite clasts clasts and 30% clasts clasts derived derived from from terrane of 701 70% granite greenstone belt. the greenstone belt. SOIL SOIL WEATHERING Soil horizons are produced produced due due to to the the weathering weathering of of overburden overburden translocation of of weathered materials subsequent translocation weathered products products materials and subsequent through the through the soil soil profile. profile. This commonly commonly leads leads to to the the development development "B" and "C" of humus, "Aw, l1BI1 l1Cl1horizons. horizons. humus, "A", Soil profile profile studies studies have have demonstrated demonstrated geochemical geochemical differences differences between the oxidized "B" horizon (Coker between the oxidized I1Bl1horizon and unoxidized "C" l1CI1horizon (Coker and DiLabio DiLabio 1989; 1989; Shilts Shuts and and Kettles Kettles 1990; 1990; Law Law et et al. al. 1991). 1991). 20 �___ 1.0- Humus - Humus - "A" Horizon Horizon "B" W" Horizon Honzon iii ii. :. x z • 0 ... . . "C" C" Horizon Horizon 217/ç 148' 0— CL '••••• Si .. Ss Civ I GRftJN GRAIN SIZE SIZE CL Clay Clay Si SI Ss Cry Grv Sdt Silt Sand Sand Gravel Gravel 0- a Vvç bedding Mvy, bedding Humus Humus EIJ Fabric Fab(iC Figure 6: Lodgement till till section. See See text text for for description. description. 21 �Commonly, Commonly, the chalcophile chalcophile elements elements such such as as copper, copper, lead, lead, zinc, zinc, cobalt and nickel are leached out of the horizon the "B" I1Bv1 horizon due due to to the the breakdown of of the host host suiphide sulphide mineral. mineral. Chromium is as Chromium is not as susceptible to leaching-out I1BI1horizon horizon as as it it is is commonly commonly leaching-out of the "B" hosted hosted in in more more resistant resistant chromite. chromite. A horizon A relationship relationship exists exists between between the the clay clay percentage percentage of of aa soil soil horizon and and the the metallic metallic element element abundance abundance within within that that horizon. horizon. Clay Clay has has a high high element element adsorption adsorption capacity capacity due due to to the the large large clay clay mineral mineral a surface surface area and and related related charge. charge. and Kettles Kettles Shilts and (1990) (1990) demonstrated ( ~ 2 micron) micron) yields yields demonstrated that that the the clay clay fraction fraction (<2 significantly higher higher metallic metallic element element values values than than the the silt silt and and clay significantly clay size micron) fraction (~63 micron) fraction of of the the same same sample. sample. This This is is due due to to the the size (<63 dilution dilution of the the metal metal rich rich clay clay fraction fraction by by the the metal metal poor poor silt silt fraction. fraction. The clay clay mineral mineral distribution distribution with depth in in soil soil profiles profiles is is largely largely dependant dependant upon upon the the local local leaching leaching conditions conditions and and depth depth of of the soil soil profile. profile. Leaching conditions can be broken broken down down into into extensive, extensive, moderate and negligible negligible categories categories with with the the extensive extensive and negligible leaching and negligible leaching conditions conditions producing producing uniform uniform grain grain size size and and geochemistry geochemistry throughout throughout the the profile. profile. Intermediate leaching leaching Intermediate conditions provide variable variable grain grain size size and and geochemistry geochemistry through through conditions can can provide the (Birkland1974). 1974). the soil soil profile profile (Birkland Most of of the the till till deposits deposits in in the the Wawa Wawa area area are are thin thin and and consist consist largely horizon. largely of of aa "B" IIBI1 horizon. The The degree degree of of leaching leaching is is assumed assumed to to be be intermediate intermediate to to extensive extensive given given the the climatic climatic conditions conditions and and vegetation vegetation type. type. The The geochemistry geochemistry of of some some composite composite soil soil profiles profiles from from the the Wawa Wawa area area indicate arsenic and antimony are concentrated concentrated in indicate that that lead, lead, zinc, zinc, arsenic in the the humus humus layer layer relative relative to to the the other other soil soil horizons. horizons. This This may may be be due to to anthropogenic anthropogenic reasons reasons and and may may not not be be due due to to a a local local bedrock due bedrock source horizon llB1l horizon geochemistry geochemistry does does not not indicate indicate source as the the related related "B" any any anomalous anomalous geochemical geochemical values. values. The platy structure horizon has has the the typical typical platy structure and and light light colour colour of of The "A" "ANhorizon an horizon llAell horizon (Agriculture (AgricultureCanada Canada 1977). 1977) The an "Ae" The "Ae" I1Ael1 horizon of of the the horizon Wawa area area is is characteristically characteristically depleted depleted of of metallic metallic elements elements as as Wawa . clay from horizon. I1BI1 horizon. from this this horizon horizon has has been been eluviated eluviated into into the the "B" he "B" I1BI1horizon horizon commonly commonly has has aa sharp sharp upper upper contact contact with with the the "Ae" I1Ael1 The horizon. The horizon. The "B" IIBI1horizon is is typically typically enriched enriched with with element element illuviated horizon. illuviated from from the the "Ae" I1AeI1 horizon. The The occurrence occurrence of of aa "C" I1CI1horizon horizon in in the the subglacial subglacial till till is is rare. rare. Where horizon Where observed, observed, the the "B-C" llB-C1l horizon contact contact is diffuse diffuse with with no no accumulation The geochemistry accumulation of of clay clay at at the the contact. contact. geochemistry data data indicates indicates that an an enrichment enrichment of of metallic metallic elements elements within within the the "C" I1CI1 horizon horizon does does not not occur. occur. 22 �SUBGLACIAL TILL TILL AS AS A A MEDIA MEDIA FOR FOR DRIFT DRIFT PROSPECTING PROSPECTING SUBGLLCIAL from aa mineral mineral deposit deposit has has properties properties that that make make it it Till derived from unique from from surrounding surrounding tills. tills. unique properties properties could could These unique include specific specific clast clast types types or geochemical geochemical or heavy heavy mineral mineral signatures. signatures. The The unique unique property property is is referred referred to to as as the the indicator. indicator. bedrock from from which which these these unique unique properties properties were were derived derived is is The bedrock called called the the target. target. The indicator indicator is is usually concentrated concentrated at or or the target target (the (the head) head) and and decreases decreases exponentially exponentially down down ice ice near the (the tail; 1989, Peltoniemi Peltoniemi 1985, 1985,Szabo Szabo et et al. al. (the tail; Kazycki Kazycki and and Shilts Shuts 1989, . 1975, 1975, Shilts Shilts 1976) 1976) Recognition of variables variables which which control control material material dispersal dispersal were were defined defined during during the the first first OGS OGS Quaternary Quaternary project project in in the the Wawa Wawa area. area. This done through through examining examining the regional and local distribution distribution This was was done the regional of of clasts clasts within within till. till. On regional scale, control the relative On a a regional scale, the the rate rate of of ice ice flow flow will control the relative distance pass over distance of of material material transport. transport. Faster Faster flowing flowing ice ice will pass over a surface surface many many more more times times relative relative to to slower slower moving moving ice ice and and therefore therefore incorporate incorporate and and disperse disperse more more target target material. material. Studies Studies have demonstrated demonstrated that that ice ice streams streams within within ice ice sheets sheets transport transport materials materials farther farther than than the the surrounding surrounding ice ice (Dyke (Dykeand and Morris Morris 1989). 1989). One the more more important important observations observations made One of of the made from from the the regional regional clast clast data data was was that that ice ice flow flow over over the the Wawa Wawa area area was was relatively relatively uniform. uniform. This This is is reflected reflected in in the the relative relative uniform uniform concentration concentration and and dispersal dispersal distance distance of of clasts clasts from from related related bedrock bedrock types. types. This This is is not f of not to to imply imply that that the the broad broad dispersal dispersal of of material material on onto toor orofoff of different different bedrock bedrock terranes terranes is is everywhere everywhere equal. equal. There There are are local local factors which can can control control local local distance distance of of transport; transport; bedrock bedrock topography topography being being one one of of prime prime importance. importance. Some Some of of the the more more important important controls controls of of mineral mineral dispersal dispersal were were determined from from several several semi-regional semi-regional studies studies in in the the Wawa Wawa area. area. These These semi-regional semi-regionalstudies studies involved involved collection collection of of till till samples samples in in a a down down ice ice direction direction from from aa chosen chosen target. target. Indicators Indicators within within the the till were clasts till were clasts which which had had been been eroded eroded from from the the target. target. Although Although several studies are presented presented here here (Figure (Figure studies were completed completed only only 33 are 7). 7) Some Some of of the the more important important controls controls recognized recognized are: are: a) a) target target size size (Figures 8, 9); 9); b) b) topography topography (Figure (Figure 10); 10); c) c) relative relative hardness hardness of of (Figures 8, materials materials (Figure (Figure9); 9); and and d) d) relative relative rate rate of of ice ice flow. flow. The The semisemiregional regional studies studies indicate indicate that that distance distance of of transport transport was was consistently less less than than 88 km km and and commonly commonly less less than than 55 km. km. Source Source areas, perpendicular to areas, or or targets, targets, for for these these studies studies had had width width perpendicular to ice ice flow km or or greater. greater. flow of of 44 km 23 �H Cu H 0< rt (DLQ 0 rr (Drt (/)1—' (D• tiw (Drt CD '1w 1I1 CDrt rI) d CD I-i '<HH CD -o 0 irt H woo :j:i H Q F- (t PJ(DPJ rtNQ CD(D0 ci t CD II I-I. Ph Figure 7: Location of till sampling tranSeCtS. Although several were done, only 3 are presented here. See text for details. C in O 4 6 8 10 kilometers flow Pilot project Transect line. Orientation of line in direction of ice Felsic instrusive terrane Supercrustol terrane 2 �(rse u) NOUYA3 I 8 I .2 1 0 wc >t 0CLL ø 0 0 0 co 0 O 0 0 sseio % Figure Figure 8: 8: Mall Mall Lake Lake dispersal dispersal (small, (smallIlocal local target). target). Ice flow flow has has Ice dispersed dispersed granitic granitic clasts clasts southwest southwest of of granitic granitic terrane terrane over over the the greenstone greenstone belt. belt. The The percentage percentage of of granitic granitic clasts clasts decreases decreases exponentially, exponentiallyIas as expected, expected, until until the the ice ice crossed crossed aa small small granitic granitic stock. stock. The The percentage percentage of of granitic granitic clasts clasts increases increases at at this this point point then thendisappears disappears to within4 4km kmdownice downiceof of the the stock. stock. to O0%within 25 �(Ts i) NOLLVA31 . 1-e '- 8 I' r C-) C) C 0 >±f ocu-0 I DM1 I sseio % Figure Figure9:9: Wawa Wawa Lake Lake dispersal dispersal (larger, (larger! regional regional target). target). Granitic Granitic clasts clasts were were dispersed dispersed southwest southwestonto ontothe the greenstone greenstonebelt belt through f of through the the Wawa Wawa Lake Lakebasin basinofoff of aa granitic granitic terrane. terrane. This This granitic granitic terrane terraneis isaa large large target target with with flow flow into into aa basin. addition! the theindicator, indicator,granitic graniticclasts, clasts! is is basin. In In addition, relatively relativelyharder harder than thanmaterial material making-up making-upthe the greenstone greenstone belt. of belt. These These factors factorsallow allowfor foraalonger longerdistance distanceof transport, transport,10 10km. kmlthan thanmost mostother othersites. sites. 26 �(rse ii) NOUYA313 88 ,- - 'Eli 8 I .2 — 0 c E oE DII 0 0 0 (0 s1sIo % Figure Figure 10: 10: Black Black Trout Trout Lake Lake dispersal dispersal (topographic (topographicshadow). shadow). The The ice dispersed granitic clasts southwest off ice dispersed granitic clasts southwest off the the granite granite terrane topographically terrane onto onto the the greenstone greenstone belt in a topographically One sample rough area. collected on on the the down down ice ice rough area. One sample was collected side of a bedrock high, a site protected from site from the the side of a bedrock high, deposition deposition of of material material from from the the granitic granitic terrane. terrane. 27 �Drive Drive to to Site Site #4. #4. Air DaleI Dale, a sea We head back along Highway 547 to the turnoff to Air plane plane base that that caters caters largely largely to to sport sport fishermen fishermen during during the the summer. summer. Proglacial Outwash Site #4: Proqlacial Outwash Section Section Appendix A: Southeast Junction Appendix Southeast of Hawk Junction This This site site is is typical typical of of aa proglacial proglacial outwash outwash deposit deposit (Figure (Figure11). 11). The section section exists exists as as material material from from this this site site was was used used for for local local road construction. glacier was close proximity proximity to site road construction. The The glacier was in in close to this this site during deposition deposition of of the the material. material. This is indicated indicated by the the coarseness of of the the sediments sediments in in the the lower lower part part of the coarseness the section section indicating a high high energy, energyl ice ice proximal proximal depositional depositional environment. environment. The associated associated glacial meitwater meltwater spilled through the the Hawk Hawk Lake Lake basin meltwater channel Firesand Creek Creek meltwater channel and and south south into into the the basin into into the the Firesand Grant Grant Lake Lake meitwater meltwater channel channel (Figure (Figure5). 5). The The upper upper part part of of the the section, sectionl Unit Unit 11 (Figure (Figure11), 11)1consists consists of of 1.9 1.9 m pale brown brown (10 m of pale (10 YR YR 6/3 6/3 m) m) cobbly, cobblyl coarse coarse sand. sand. The The material is material is massive and and slightly slightly cemented cemented with with calcium calcium carbonate. carbonate. The lower lower contact is marked marked by a a 15 15 cm cm layer layer of of finely finely planar, planarl laminated laminated underlying unit, coarse coarse sand sand (Unit (Unit2). 2). The The underlying unitl Unit Unit 3, consists consists of of 3.5 3.5 m Faint, planar bedding 6 1 3 m) m) cobbly cobbly sand. sand. FaintI m of of pale pale brown brown (10 (10 YR YR 6/3 is best observed observed after after aa rain rain storm storm event. event. The beds dip dip gently gently west, westl parallel parallel to to Hawk Hawk Lake. Lake. Clasts Clasts are are subangular subangular to to subrounded subrounded and the the lower lower contact The lower lower unitl unit, Unit Unit 4, 4, consists consists and contact is is diffuse. diffuse. The pale brown of >13.7 >13.7 m of pale brown (10 (10 YR YR 6/3 613 m) m) boulder-rich boulder-rich gravel gravel with with aa The material coarse sand sand matrix. matrix. material is massive massive and loose loose with with subangular subangular to to subrounded subrounded boulders. boulders. material at this site The material site would be useful useful for for aa regional regional heavy heavy mineral is not not an ideal ideal media media for mineral or or pebble pebble sample. sample. It It is for local local drift drift sampling depositlsrestricted restricted distribution distribution and and more more sampling due to to the the deposit's regional regional material material composition. composition. This site, sitel and the the finefine- grained grained material we crossed crossed upon upon entering Hawk Junction, Junctionl demonstrate the variability materials associated associated with glaciofluvial glaciofluvial variability in in textures textures of materials outwash. With distance outwash. distance from from the the ice ice margin, marginl material material generally generally sorted becomes better and heavy mineral becomes better sorted and heavy mineral signatures more signatures more concentrated. concentrated. Drive to to Site Site #5 #5 Road conditions gravel track west that that Road conditions permitting, permittingl we we will will follow follow aa gravel track west skirts skirts the the outwash outwash plain plain to to the the south south and and the the south south shore shore of of Hawk Hawk Lake. Lake. 28 �____ . 19.25 S •s S. 5 S Unit II . • • . S • • . 17.35 17.20 . . ... ...- .•: . • . • Unit Unit 22 ...- ....-..- •\ •\\ .\\ •:•: I= w I Unit 3 Unit 3 •;::•;•::•; 2940 2624. ::.: 2460 13.7- . .. Unit 4 i * . . . CL Si Ss Grv GRAIN SIZE SIZE GRAIN CL CL Si Si ss Ss Grv Grv Clay Clay Sift Silt Sand Sand ?c m!/ Gravel Gravel bed bed Course dirty Course dirty outwash outwash Planarsand Planar sand beds beds I Paleocurrent Gravel Gravel Figure Figure 11: Proglacial outwash outwash section. section. See text for detailed description description and and discussion. discussion. 29 �#5: Moraine and Ice-Contact Ice-Contact Stratified Stratified Drift Drift Site #5: Appendix Appendix A: Southwest Southwest end end of of Hawk Hawk Lake Lake At At this we will this site will examine ice-contact stratified site we examine ice-contact stratified drift drift This is is the the associated with a a recessional recessional moraine (Figure (Figure 12). 12) same moraine moraine that that we we crossed Sites #2 and #3 while crossed between Sites #2 #3 while travelling travelling east east on on Highway Highway 101. 101. The ice ice sheet sheet existed existed in in aa state state of equilibrium equilibrium long enough enough to to deposit deposit the the morainic morainic material. material. Occasional flows of of diamicton diamicton (flow (flowtill) till) extended extended out out from from the the ice ice Occasional flows margin. The meitwater meltwater associated associated with this ice margin flowed margin. with ice margin flowed Firesand Creek Creek meltwater meltwater channel channel westward south into into the the Firesand westward then south (Figure 5) (Figure 5). . . section consists upper unitI unit, Unit lI 1, of reddish reddish The section consists of of 10 10 cm cm of an upper 413 m) m) cobbly cobbly sand. sand. The unit is is massive massive and and the the brown (5 YR 4/3 cobbles cobbles are are well well rounded, roundedIsome some flat. flat. The The lower lower contact contact is and is wavy and sharp. 514rn), m) I sharp. Unit Unit 22 consists consists of of 21 21 cm cm of of yellowish yellowishbrown brown(10 (10 YRYR5/4 very very fine fine sandy sandy silt. silt. The The material is masSive, massive, compact compact and and shows shows material is no reaction reaction with with HC1. HCl. Common Common clast types are of of rounded rounded granite granite and mafic mafic volcanic volcanic rock. rock. The lower lower contact contact is is smooth smooth and and wavy. wavy. is composed composed of 1.6 1.6 m m of of dark dark greyish greyish brown brown (10 (10 YR YR 4/3 413 m), m)I Unit 3 is coarse coarse sand. sand. The upper few few centimetres centimetres are massive with a few few large, largeI subangular subangular granite granite clasts. clasts. The The massive structure structure grades grades to to planar bedded sand, sandI with the layers accentuated by darker heavy mineral mineral bands. bands. The lower contact contact is is sharp. sharp. The lower Unit 4 4 consists consists of 3.61 3.61 m m of of light light yellowish yellowish brown brown (10 (10 YR YR 6/4 6 1 4 m) m) sand. sand. The upper 83 cm cm is is coarse coarse sand sand with with planar planar beds beds and and some some fine downwards to to sand sand which which comprises comprises most most of of the the ripples which fine The lower lower part of the the unit consists consists of of 1.44 1.44 m m of of m) unit (2.17 (2.I7 m). cycles cycles of of finer finer and and coarser coarser sand sand with with low low and and high high angled angled ripples, ripplesI some some with with foreset foreset bedding. bedding. The lower lower contact contact is is clear clear and and wavy. wavy. Unit 5 consists consists of greyish brown brown (10 4/2 m) coarse coarse Unit of 12 12 cm cm of dark greyish (10 YR 412 pebbly sand. pebbly sand. The The material material is is massive massive and and loose. loose. The are The pebbles pebbles are subangular subangular to to subrounded subrounded and and consist consist mainly mainly of of granitic granitic rock. rock. The The lower lower contact contact is is clear clear and and wavy. wavy. . consists of 38 38cm Unit 6 6 consists cmof of greyish greyish brown brown (10 (10YR YR 5/2 5/2 m) m) silty silty sand. sand. The material material is massive, compact The is massiveI compact and and reacts reacts strongly strongly with with HC1. HCl. The The lower contact is is wavy wavy and and clear. clear. Unit 7 7 consists consists of of of >5 m of brown (10 greyish brown (10 YR YR 5/2 512 m) coarse, coarseI pebbly pebbly sand. sand. The is The material is and loose. loose. There are abundant abundant subangular subangular to to subrounded subrounded massive and clasts. clasts. This lengthy lengthy section section description description emphasises emphasises the the stratification stratification of of materials associated with this type of deposit. The lower part of materials associated with this type of deposit. The lower part of the section (Units demonstrate the the very very close close proximity proximity of the section (Units 66 and 7) demonstrate of the site to the ice margin. Unit 66 represents f the site to the ice margin. Unit represents aa debris debrisflow flowofoff the margin, whereas the ice ice marginI whereas the the very very coarse coarse Unit Unit 77 represents represents aa highhighenvironment typical energy glaciofluvial typical of of an glaciofluvial environment an ice ice proximal proximal The upper units location. location. upper units represent represent either either an an ice ice marginal, marginalI 30 �31 for text See description. section. drift stratified contact Ice 12: Figure bedding Way, Paleocurrent bedding Planar 2W liii Colluvium outwash dirty Coarse, bed Gravel Gravel Sand Grv Silt Clay Si CL SIZE GRAIN 0 7 Unit 1 2 6 Unit 5 Unit 3 (I, 2350 Ui 0 z 271° 4 Ui 295° 4 Unit 5 6 229° 3 Unit 7 2 Unit 8 1 Unit Ss �perhaps fluctuating fluctuating setting, setting! or or aa braided braided stream stream environment. environment. The material associated associated with with this this site site is is not not regarded regarded as as aa prime prime sampling media f or local drift prospecting studies. sampling media for local drift prospecting studies. The The materials materials are derived derived from from both both local local and and distal distal sources. sources. In In addition, addition, the the distribution of material is distribution not widespreadI making it of this this material is not widespread, it difficult to to maintain maintain sample sample continuity. continuity. In In terms terms of of aggregate aggregate potentialI the materials are not not ideal ideal for for roadbed roadbed use use due due to to their potential, the materials are their example of how poor this this material is is for for fine-grained nature. An example fine-grained nature. roadbed construction construction is is demonstrated demonstrated by by the the poor poor road road which which we roadbed we just just travelled travelled over. over. Drive D r i v e to to Site S i t e #6 #6 Just east Site #5 the road takes takes a sharp sharp bend bend across across the the channel channel Just east of of Site where meltwater flowed from the Hawk Lake basin into the Brummer Lake into the Lake basin basin before before exiting exiting into the Firesand Firesand Creek Creek meitwater meltwater channel. As we we continue continue east, east! the enters onto a a broad broad channel. the road enters glaciofluvial outwash associated with the the Firesand Firesand Creek Creek glaciofluvial outwash plain associated meltwater meltwater channel. channel. Site Minon Delta S i t e ##6: 6 : Minonu Delta Appendix Appendix A: North North side side of Highway Highway 101, loll 10 10 km IUII east of Wawa The road which we have turned onto (Loonskin (Loonskin Lake Road) follows a series series of of sites sites which which demonstrate demonstrate features features associated associated with meltwater channels. channels. This site site is is at the the terminus terminus of a meltwater meitwater channel. HereI flowing from from ice ice situated situated in in the the Scott Scott channel. Here, meltwater flowing basinI empties into into Glacial Lake Lake Minong Minong (308 (308 mm asi). asl) The Lake basin, The materials you you see see here here are are associated associated with with aa delta delta which formed in in materials which formed this this lake lake about about 9200 9200 years years ago. ago. . There are There are several several excellent excellent sections sectionsthrough throughthe thelower lowerpart. part of of this this delta. delta. Material associated with the the upper upper part of of this this delta delta is is obscured by colluvium. It does does not not appear, appearI however, however! that the the by colluvium. topset beds of aa classic classic Gilbert-style Gilbert-styledelta delta exists exists at at this this site. site. topset beds of The lower lower part of of the the delta delta consists consists of of steeply steeply dipping dipping foreset foreset beds composed composed of poorly poorly sorted, sorted! subrounded subrounded to to subangular subangular cobbly cobbly gravel and and coarse coarse sand. sand. The bedding has has aa strong strong paleocurrent paleocurrent weakly to moderately cemented direction directionofof222266°. '. The The clasts clasts are are weakly to moderately cemented by by and, to a lesser lesser extent, extentI iron iron oxides, oxidesI primarily primarily limonite. limonite. calcite and! The origin The origin for for the the carbonate carbonate cement cement is is not not well well understood. understood. There There are 2 potential sources: are 2 sources: 1) 1) from abundant abundant syngeneic syngeneic carbonate carbonate alteration alteration (primarily (primarily ankerite) ankerite) of the the local local early early Precambrian Precambrian or; 2) from clasts originating from bedrock! or; clasts originating from the the metavolcanic bedrock, 2) Paleozoic carbonates of the Hudson Bay Lowland, Lowland! found found within within the the material. material. 32 �This This deposit deposit is is of of limited limited value value for for local local drift drift prospecting. prospecting. The The clast signature is a a blend blend of of both both local local and and heavy mineral and clast distal distal sources. sources. In addition, additionl the regional regional distribution of this this material material is is restricted restricted to to bedrock bedrock controlled valleys. valleys. The The aggregate aggregate from from this this pit pit has has been been used used for for road road bed bed construction. construction. Drive Drive to to Site Site #7 #7 We proceed proceed along Loonskin Lake Road as it it skirts skirts the the meltwater meltwater channel associated with the Minong Delta. the Minong Delta. Loonskin Lake Lake Road Road provides mined from was mined from the the provides access access to to the the Eleanor Eleanor Iron Iron Range Range which which was Sir Sir James James Dunn Dunn open open pit pit from from 1958 1958 to to 1967 1967 and and produced produced 1,646,000 116461000 tons tons of of siderite. siderite. Reserves Reserves below below the the pit pit floor floor are are estimated estimated at at 1,250,000 112501000tons tons of of siderite siderite (Sage (Sage and and Heather Heather 1991). 1991). The The Eleanor Eleanor Iron Range is at the eastern extension Iron Range is extension of the Helen Iron Iron Range and occurs in in aa wedge-shaped block bounded bounded on on the the west west and and the the east east by occurs wedge-shaped block Wawaof the the Mildred Mildred Lake Lake Fault Fault and and on on the the south south by by the the Wawabranches of Hawk-Manitowik Hawk-Manitowik lakes lakes fault. fault. Once pit, the passes over Once we we pass pass the the Sir Sir James James Dunn Dunn open open pitl the road road passes over the the surface flat! open open surface of of the meltwater meltwater channel channel represented represented by by flat, stretches stretches of of ground ground covered covered by by sand sand and and gravel. gravel. Site #7: and Kettle Xett].e(Dead (DeadIce) Ice)ToQoqraQhy ToPoraDhv # 7 : Xa.me Kame and A an excellent excellent example A brief brief stop stop is is made here here to to view an example of of kame kame and and kettle kettle topography. topography. Here, Herel aa block block of of glacial glacial ice ice became became detached detached from from the the active active ice ice margin and and was was subsequently subsequently buried by buried by glaciofluvial glaciofluvial deposits. deposits. Upon Upon melting, melting! depressions depressions and and conical conical hills hills composed composed of of sand sand and and gravel gravel formed. formed. Material associated associated with with this this deposit deposit is is derived derived from from both both local local and distal The distal sources. sources. The associated associated heavy heavy mineral mineral and and clast clast signature signature would be useful useful for for obtaining obtaining aa regional regional heavy heavy mineral mineral signature. signature. The The aggregate aggregate is is excellent excellent for for roadbed roadbed use. use. Drive Drive to to Site Site #7A Loonskin The Loonskin Lake Lake Road Road eventually eventually splits. splits. The west west branch, branch! now now blocked, blockedl leads to the the Lucy Lucy Pit Pit developed developed within the the Lucy Lucy Iron Iron Range. eastern extension Range. The The Lucy Lucy Iron Iron Range Range is is the the eastern extension of of the the Eleanor Eleanor Iron separated from the Eleanor Eleanor Iron Range by roughly roughly Iron Range. Range. It It is separated from the Iron Range 3500 m m of of left-lateral left-lateralfaulting. faulting. Mining operations operations were were short short lived lived and and ceased ceased in in 1970 1970 after after 33 years years of of operation. operation. The The operation operation produced 110731000tons tons of of siderite siderite and and reserves reserves are are estimated estimated at at produced 1,073,000 1,300,000 tons of siderite (Sage and Heather 1991). 113001000tons of siderite (Sage and Heather 1991). We We proceed proceed north north along along the the north north branch branch of of Loonskin Loonskin Lake Lake Road Road as as it it begins to drop in elevation. begins to drop in elevation. The The road road splits splits again again just just south south of of Scott lakel this this is is Site Site #7a. #7a. Scott lake, 33 �Site #7A: #7A: Modern Alluvium. Alluvium, Ice Ice Margin Maruin Deposit Deoosit site provides provides an an excellent excellent opportunity opportunity to to emphasize emphasize the the This site complexity complexity of of glaciofluvial glaciofluvial systems systems and associated associated meltwater meltwater channels. channels. As As noted, noted, the the road road falls falls in in elevation elevation from from the the Lucy Lucy Pit Pit turnoff to to this this site. site. For glacial meltwater to feed feed into into the the Loonskin Lake meltwater channel and the Minong Delta, Delta, Site Site ## 6, 6, drainage through Loonskin Lake have been been drainage through the the Loonskin Lake channel channel had had to have blocked. blocked. This This required required the the presence presence of of an an ice ice margin margin at at this thissite. site. However, margin receded, opening occurred However, as as the the ice ice margin receded, an an opening occurred between between the the ice ice margin margin and and the the bedrock bedrock controlled controlled high high ground. ground. This caused This caused abandonment of the the Loonskin Loonskin Lake Lake meitwater meltwater channel channel and and the the the abandonment establishment of glacial meltwater the Magpie Magpie River River establishment of glacial meltwater flow into the meltwater meltwater channel channel (Figure (Figure5). 5) . The Loonskin Lake Lake Road exposes exposes material material The section section on on the the east east side side of Loonskin associated associated with with this this moraine moraine (Figure (Figure13). 13). Although Although in in contact contact with with the margin, the the ice ice margin, the sand sand and and gravel gravel deposited deposited is is remarkably remarkably clean. clean. Unit yellowish brown consists of of 2.7 2.7 m m of of dark dark yellowish brown (10 (10 YR YR 4/3 4/3 m) m) sand sand Unit 11 consists (Figure material is massive and (Figure13). 13). The The material is massive and loose loose and and the the clasts clasts are are rounded. Unit 2 consists of 1.2 m layer of boulders that angle rounded. 2 consists of 1.2 m layer of boulders that angle upward through consists of of >5 m of of dark dark through the the section. section. Unit 33 consists yellowish brown brown (10 YR 4/3 4/3 m) m) cobbly sand sand containing containing abundant abundant angular angular clasts clasts and and boulders. boulders. As at at Site Site #7, #7, materials materials associated associated with with this this deposit deposit are are derived derived As from from local local and and distal distal sources. sources. Limestone Limestone clasts clasts from from the the Hudson Hudson Bay Bay Lowland, Lowland, for for example, example, have have been been found found here. here. Therefore Therefore the the heavy mineral mineral and and clast clast component component of of this this deposit deposit would would be be useful useful heavy for obtaining obtaining aa regional regional signature. signature. The The sand sand and and gravel gravel would would be be for an an excellent excellent source source for for road road bed. bed. SAMPLING SAMPLING MODERN ALLUVIUM A A small, small, unnamed unnamed stream stream flows flows north north into into Scott Scott Lake Lake at at this this site. site. As is heavily As this this stream stream flows flows through through glaciofluvial outwash it is charged with sediment sediment allowing allowing for for aa modern modern alluvium alluvium sampling sampling demonstration. The sample demonstration. sample site site consists consists of of aa well well developed developed diagonal modern alluvium diagonal bar. bar. Site Site observations observations are are made made using using the the modern alluvium site site sampling sampling observation observation sheet sheet (Appendix (AppendixB, B, p.57). p.57). Material Material is collected collected from beneath beneath the bar surface surface and and passed passed through a 1 cm2 steel mesh sieve. When enough material (10 kg) has has through a 1 cm2 steel mesh sieve. When enough material (10kg) passed passed through through the the sieve, sieve, excess excess water water is is drained drained from from the the sample sample and and poured poured into into aa sturdy, sturdy, well well labelled labelled plastic plastic bag. bag. The The bag bag is is placed placed in in aa haversack haversack and and the the weight weight is is roughly roughly checked checked by by scale. scale. A "baggywand and A piece piece of of paper paper with with the the sample sample number number is is placed placed in in aa "baggy" inserted inserted in in with with the the sample sample before before the the bag bag is is sealed. sealed. 34 �13. 12 • Unit II • 11 307' • 273-4. Unit2 Unit 2 243' 10 10 9 8 7 /L 6 Unit3 Unit 3 /L 5 4 3 30' /i 0 165' /L 2 /L 0 Si Ss Grv GRJN StZE CL CL CL Si ss Ss Grv Gw Figure Figure Clay Clay Silt Sand Sand Gravel Gravel [] Sand and gravel Sandandgravel BOUfS BOUHWS 13: Scott Lake Lake moraine moraine section. section. description description and and discussion. discussion. [] Cobbly C o wSand sand J% l pa~men Paleocurrent t See See text text for for detailed detailed 35 �Approximately 50 to 100 clasts Approximately 50 clasts are subsampled subsampled from the the coarse coarse material material retained retained on on the the screen. screen. In In additionl a subsample subsample of of the the addition, a finer finer grained grained material material (<1 (elcm2) cm2) is is panned and observations observations of of the the heavy mineral mineral fraction fraction are are made. made. material is also also The panned material stored in in a labelled labelled "baggy" vvbaggyll and put put in in with with the the clast clast sample sample bag bag stored and for future reference. reference. Any associated with for future samples associated Any interesting interesting rock rock samples the the site site are are also also collected collected and and labelled. labelled. The minerals and are derived derived The heavy heavy minerals and clasts clasts collected collected from from this this site site are from both the bedrock and from both the bedrock and overburden overburden through through which which this this stream stream has has passed. When interpreting passed. interpreting the data data from from this this sample, sampleI it it is is essential essential to to catalogue catalogue what what bedrock bedrock types types and and overburden overburden materials materials exist exist within within the the catchment catchment area area of of the the stream. stream. This This information information will provide a guide as to whether the stream sediment sediment signature will provide a guide as to whether the stream signature is is local. local. Any indicators indicators from from this this stream stream may may very very well well have have come come from from a great distance distance away away given given that that they they may may have have been been derived derived from large glaciofluvial glaciofluvial deposit deposit present present in in the the immediate immediate area. area. from a large RESTRICTIONS SEDIJ!4ENT SAMPLING SAMPLING RESTRICTIONS OF OF STREAM STREAM SEDIMENT Stream Stream sediment sediment sampling sampling in in the the Wawa Wawa area area has has demonstrated demonstrated that that aa sample collected at the mouth of aa drainage drainage basin basin gives gives aa heavy heavy mineral signature of the overburden (and to a lesser extent signature the overburden (and to a lesser extent the the bedrock) over which the over the stream stream flows between the sample sample site and the significant sediment standing body of water the first first significant sediment trap trap (i.e. (i.e. a standing such Therefore, as a to maximize such as a lake). lake). Thereforel to maximize the the area area being being "fingerprinted", it is advisable I1fingerprintedvv, it advisable to choose choose aa sample sample site site that that maximizes maximizes the the length length of of stream stream between between a a lake lake and and the the sample sample site site . (Figure (Figure 14). 14) It It is is also also critical critical to to recognize recognize the the orientation orientation of of the the drainage drainage basin being being sampled sampled relative relative to to ice ice flow. flow. The The heavy heavy mineral mineral signature modern alluvium alluvium sample reflect a deposit deposit farther farther signature of of a a modern sample may reflect up up the the drainage drainage basin basin or or beyond. beyond. Glacial Glacial erosion erosion of of such such aa target target may may result result in in related related heavy heavy minerals minerals being being transported transported and and deposited within the the area area of of the the stream stream segment segment that that the the sample sample site site represents. represents. If the the drainage drainage basin basin being being sampled sampled is is not not aligned aligned in in the the direction direction of of ice ice flow, flow, aa danger danger exists exists in in that that the the heavy mineral signature signature of that that drainage drainage basin basin may may represent represent aa target target located located up-ice up-ice but but in in the the neighbouring neighbouring (or (orfarther farther removed) removed) drainage drainage basin basin (Figure (Figure14). 14). Such Such a a problem problem was was recognized recognized in in aa sampling sampling program program in in Brazil Brazil (Gonzaga (Gonzaga et et al. al. 1994). 1994). Drive Drive to to Site S i t e #8 #8 We We will will backtrack backtrack south south down down Loonskin Loonskin Lake Lake Road Road to to the the Sir Sir James James Dunn Dunn Pit. Pit. Here Here we we will will follow follow an an abandoned abandoned rail rail bed bed north north to to the the defoliated defoliated zone zone of of the the Magpie Magpie River River drainage drainage basin. basin. The The railbed railbed initially cuts through bedrock terrane as as it it skirts skirts around around Lena Lena Lake Lake before before veering veering sharply sharply west west towards towards the the Magpie Magpie River River valley. valley. Just Just after after the the sharp sharp turn turn west, westl the the ground ground opens opens up up into into a a 36 �lndicator Dispersal Dispersal Examples of of Kimberlite Kimberlite Indicator within within Fluvial FluvialDrainage Drainage Basins Basins A t'o14 ¼ —KimberIite Pipe Kimberlite Indicator Mm erals Drainage Basin B Kimberlite Kirnberlite Indicator Indicator Minera Minerals \ Kirnberlite Drainage Basin I I I& 4?? A Kimberlite Indicator Minerals Drainage Basin 2 Lake Figure associated with modern alluvium Figure 14: 14: Problems Problems associated with sampling sampling modern alluvium within within drainage demonstrates llA1l demonstrates the the ideal ideal drainage basins. basins. Part Part "A" orientation I1Bf1 orientation of of drainage drainage basin basin to to ice ice flow. flow. Part Part "B" demonstrates problems associated associated with drainage drainage basin basin demonstrates problems orientation orientation perpendicular perpendicularto toice ice flow flow and and the the effects effects of of a a lake lake on on heavy heavy mineral mineral dispersal. dispersal. See See text text for for details. details. 37 �remarkable landscape, landscapeI reminiscent of the midwest midwest prairies prairies or or reminiscent of central arctic central arctic desert. desert. The glaciofluvial deposit which has been The road road passes over over a broad glaciofluvial fed number of meltwater meltwater channels fed by a number channels issuing issuing from from the the more more rugged, rugged! bedrock controlled controlled landscape landscape to to the the north north (Figure (Figure5). 5). As As the the road road bedrock swings south, pass onto swings southl we pass onto the the surface surface of of aa delta delta which which formed formed in in glacial Lake Lake Minong. Minong. surface elevation elevation of delta is is The surface of this delta equivalent to eqyivalent to the the surface surface elevation elevation of of the the delta delta at at Site Site #6. #6. As we we continue south south on on this this road, roadl we we will will descend descend over over several several terrace terrace surfaces which which formed surfaces formed as as the river river cut cut through through the the delta delta in in response to to lower lower lake lake levels levels in in the the Lake Lake Superior Superior basin. basin. *8: Mink Lake Glaciofluvia]. Fan, Straie Straie and and NU Forms Site #8: Glaciofluvial Fan, Forms This This site site overlooks overlooks the the basin basin that that contains contains Mink Mink Lake. Lake. Around Around the the shores of Mink Mink Lake Lake are These are shores are several several conical conical hills. hills. These are kames deposited in in association association with dead dead ice. ice. interpreted to be kames North, basin, is a smaller basin North! and immediately immediately in front of the basinI rimmed with rimmed with sand. sand. These These features features demonstrate demonstrate aa process process which which has has occurred throughout throughout the the topographically topographically higher higher areas. areas. Blocks Blocks of of ice ice became detached detached as as the the ice ice sheet sheet wasted wasted back. back. Over Over time time these these sediment-rich blocks of ice sediment-rich blocks ice melted melted in in place place leaving leaving kame kame deposits deposits such as In as those those which rim rim Mink Mink Lake. Lake. In addition, addition! meltwater meltwater associated with the blocks drained from from the basin basin associated the wasting of these blocks often leaving often leaving small small fans fans composed composed of of coarse coarse sand. sand. The heavy minerals and and clasts clasts associated associated with with these these deposits deposits are are derived from and distal distal sources sources and therefore therefore give give a regional regional derived from local local and signature. signature. They are not useful useful for for local local studies studies because because of of the the distal component of the material and their erratic and restricted distribution. distribution. Beyond the the small small fan fan there there is is aa spectacular spectacular view view to to the the northwest northwest of the the Magpie Magpie River River terraces terraces and and glaciofluvial glaciofluvial sandur sandur surface surface to to the northeast. The delta surfaces the northeast. The terrace terrace surfaces surfaces grade grade to to former former delta surfaces composed composed of material material transported transported to the Lake Lake Superior Superior basin basin by by meltwater meltwater channels. channels. Lake levels post date the last last retreat retreat of glacial glacial ice ice from from the the water plain in the Lake area. area. The highest continuous continuous water Lake Superior Superior basin associated with Minong which which existed within the basin basin is is associated with Lake Lake Minong existed within the basin PointI Sault Sault Ste. Ste. at about 9500 years years EP. BP. A drift drift sill sill at at Nadoway Nadoway Point, about 9500 Marie area, area! was cut through in in 5 5 or or 66 steps steps reflecting reflecting temporary lake lakes are referred lake levels levels in in the the Lake Lake Superior Superior basin. basin. These lakes to post-Minong (Dorion-I-IV) levels and terminated terminated with the to as the post-Minong (Dorion-I-IV)levels lowest, lowest! Houghton Houghton level level prior prior to to the the isostatic isostatic rebound rebound of of an an outlet outlet North Bay. at North Bay. The The terrace terrace surfaces surfaces viewed viewed from from this this site site are are all all related related to to the the above above chronology. chronology. 38 �Below the the Houghton Houghton level level there there were were aa series series of of additional additional lakes lakes Below which formed formed at at subsequently subsequently lower lower levels levels within the Lake Superior which within the Superior basin. Evidence basin. Evidence of of these these lower lower levels, levelsI which which include include the the Nipissing! Algoma! Sault and sub-Sault, sub-Sault! are all preserved within Nipissing, Algoma, lower reaches reaches of of the the Magpie Magpie and and Michipicoten Michipicoten river river valleys. valleys. the lower The The coarse coarse material material on on the the terrace terrace surfaces surfaces northeast northeast of of this this site site does does not not extend extend much much farther farther southwest. southwest. This This coarse coarse material material was was deposited by a progradation deposited by progradation of sandur sandur south south onto onto the the terrace terrace surfaces surfaces as as water water levels levels dropped dropped in in the the Lake Lake Superior Superior basin. basin. This This coarse material is overlies up to 33 m of finer finer thick and overlies coarse material is only only 11 m thick grained glaciolacustrine glaciolacustrine material material associated associated with with the the bulk bulk of of the the grained delta delta deposit. deposit. Once ice ice receded receded from from the the area area this this supply supply of of coarse material was coarse material was no no longer longer available. available. Site Site #10 #10 will will demonstrate demonstrate this this relationship relationship of of coarsecoarse- and and fine-grained fine-grainedmaterials. materials. North North of of the Mink Lake Lake basin basin is is an an exposed exposed surface surface of of highly highly polished polished and and striated rock which has also also been been incised incised by by glacial glacial meltwater meltwater forming forming ttfl I1Pl1forms. forms. Measuring when using overburden Measuring striae striae orientation orientation is is essential essential when overburden as as an an exploration exploration medium. medium. Obviously Obviously it is is necessary necessary to to know know the the direction direction from from which which materials materials were were derived. derived. At this this site site striae striae are are aligned aligned southwest southwestat at235°. 235'. The actual actual direction direction of of ice ice flow flow is is The determined determined by looking looking at at the the morphology of small small scratch scratch marks on on the bedrock surface. wall, the the the bedrock surface. On On the the up-ice up-ice side side of of the the fracture fracture wall! wall been plucked plucked by ice wall is is steep steep as as it it had had been ice freezing freezing onto onto the the rock rock surface, surface! thereby thereby pulling pulling the the rock rock away. away. As As ice ice continued continued to to flow flow over over the the fracture, fracture! the the down down ice ice wall wall was was smoothed smoothed by by abrasion. abrasion. Much Much controversy controversy exists exists regarding regarding the the formation formationof of "P" l1Pwforms. forms. Some Some argue argue that that they they are are the the result result of of strictly strictly glacial glacial erosion erosion while while others others argue argue they they are are caused caused by by glacial glacial meltwater meltwater flow flow under under high high pressure forms pressure between between the the rock rock surface surface and and ice ice base. base. These P" llP1l forms were were likely likely caused caused by by aa combination combination of of both both glacial glacial ice ice and and glacial glacial meltwater. forms llP1l forms indicates indicates meltwater. The The presence presence of of straie straie within within the the "P" that down onto the rock rock surface surface once once meltwater meltwater had that ice ice was let back down had been evacuated evacuated from from the the base base of of the the ice. ice. The The orientation orientation and and location of the I1Pl1 forms indicates that meitwater meltwater under high high the "P" hydrostatic pressure pressure did not not have have to to follow follow bedrock bedrock controlled controlled channels. The channels. The water water formed formed channels channels within within the base base of of the the glacier, glacier! ignoring ignoring the the configuration configuration of of the the bedrock bedrock topography. topography. Drive Drive to to Site S i t e #9 #9 • We backtrack backtrack northeast northeast along the Magpie River River road road to to Site Site #9, #9! crossing over the coarse surface of at least 2 terraces. crossing over the coarse surface of at least 2 terraces. 39 �#9: Older Alluvium Section Section Site *9: Appendix Appendix A: Magpie Magpie River River Road This site site is is optional optional given given the the time timeand andnunther number of of participants participants willing to willing clamber down down 33 coarse terrace terrace colluvium. to claniber 33 m of of coarse colluvium. Remember, in in this this case, case, that that what goes goes down down must must come come back back up up to to the the trucks. trucks. This site site is is situated situated on on the the south south bank bank of of the the Magpie Magpie River River just just upstream from where the sharp northwest jog upstream from where the river river takes takes a sharp jog around a bedrock outcrop. bedrock outcrop. The The section section is is through through a small small terrace composed of older older alluvium alluvium which which exists exists north north of of and and away away from from the the base base of of the 33 m of coarse terrace colluvium. coarse terrace colluvium. The The origin origin of of the the material material within this derived directly directly from sheet but within this terrace terrace is is not derived from the the ice ice sheet consists of reworked material derived from from the the higher higher elevation elevation deltas. This terrace terrace surface is graded to aa lower lower lake lake level level deltas. within the Superior basin basin after after glaciers glaciers had receded receded from within the Lake Lake Superior from the immediate area. immediate area. The bulk of of the the section section consists consists of of light light brown brown fine fine sand, sand, about about 1.5 m thick. thick. The material consists of couplets about 10 to 20 cm thick comprised comprised of thick of light light brown brown sand sand with with foreset foreset beds, beds, capped capped by by 55 cm of darker darker brown brown silt. silt. Paleocurrent measured from from the the fine— finegrained grained sand sand indicates indicates that that the the direction direction of of flow flow was was upstream! upstream! The couplets couplets of sand sand and and silt silt suggest suggest that that the the river river flow flow was was cyclic. cyclic. Cyclicity is is likely likely related related to to seasonal seasonal changes changes in in flow. flow. During the reduced During the summer summer months sand sand was deposited and during the reduced flow winter months the flow of the winter the deposition deposition of of the the finer finer grained grained silt silt took place. took place. Obviously, the silt would have to to settle settle through through aa standing body upstream flow direction is standing body of of water. water. The The upstream flow direction is confusing confusing until the site site is is put into into context context with the the bedrock bedrock obstruction obstruction downstream. downstream. This This site site was likely likely a whirlpool at one point in in time as as river river flow flow was was deflected deflected upstream upstream off off of of the the bedrock bedrock obstacle. obstacle. modern analogue analogue to occurs just downstream downstream from A modern to this this process occurs from this this site. site. The heavy minerals minerals and and clasts clasts associated associated with with this this alluvium alluvium deposit deposit The heavy would provide a regional regional signature as the materials are derived from both local local and and regional regional sources. sources. As aa local local indicator indicator this this material is is aa very very poor poor media media to to use. use. Not only only is is the the material material blended distally derived blended with with both both locally locally and and distally derived material, material, but but it it has has several cycles cycles of transportation and gone through through several of erosion, erosion, transportation gone deposition, deposition, making making it it impossible impossible to to trace trace an an indicator indicator back back to to it's In material is restricted source. In addition, addition, the material restricted to the lower lower source. reaches of the area's major rivers, rivers, making it it impossible impossible to to use use this material as as aa regional regional sampling sampling media. media. 40 �Drive Drive to to Site Site #10. #lo. We backtrack along Magpie River We continue continue to to backtrack along the the Magpie River Road Road until until the the road road branches just below a glaciofluvial escarpment. branches just below a glaciofluvial escarpment. Fine Fine sand sand winnowed winnowed from the coarse coarse aggregate aggregate by by prevailing prevailing northeast northeast winds winds blowing blowing off fromthe off Lake Superior is trapped trapped on on the the southwest southwest side side of of this this bedrock bedrock the road road bed bed is is made made of of eolian eolian sand, sand, it may not not be be As the possible to to get get to to Site Site #10 #10 if if the the road road is is wet. wet. possible high. high. Site #10: #lo: Glaciolacustrine Glaciolacustrine Section Section Appendix A: Magpie Magpie River River Road Appendix The The section section at at this this site site shows shows the the complete complete suite suite of of materials materials associated his is is one one of the the few few associated with with the the terraces terraces (Figure (Figure15). 15). This sites sites where where the the terrace terrace escarpment escarpment is is not not obscured obscured by by boulders. boulders. In In simple simple terms, terms, the the section section consists consists of of 33 main main units. units. The The upper upper unit, unit, Unit Unit 1, 1, consists consists of of 11 mm of of brown brown to to dark dark brown brown (10 (10YR YR 4/3 4/3 m) m) coarse coarse sand sand and and boulders. boulders. The The material material is is massive massive and and loose. loose. The The boulders and clasts clasts consist consist of of aa wide wide variety variety of of lithologies lithologies of of varying sizes sizes and and degrees degrees of of roundness. roundness. The lower lower contact contact is is abrupt abrupt and and smooth. smooth. Unit Unit 22 makes makes up up the the bulk bulk of of the the terrace. terrace. The The description description here here is is an an extremely extremely simplified simplified description description of of the the associated associated material material structures Essentially, structures and and textures. textures. Essentially, Unit Unit 22 consists consists of of alternating m) coarse coarse sand, sand, brown brown (10 (10 alternating beds beds of of pale pale brown brown (10 (10YR YR 4/3 4/3 m) YR YR 4/3 4/3 m) m) sand sand and and light light grey grey (2.5 (2.5 YR YR m) m) fine fine sand. sand. Thicknesses Thicknesses of of each each sandy sandy bed varies varies between between 22 mm and and 30 30 cm. cm. Related Related structures structures include include massive massive to to planar planar beds beds in in the the course course sand, sand, planar planar beds beds to to trough trough cross-bedding cross-bedding in in the the sand sand and and trough trough cross-bedded, cross-bedded,planar planar and and massive massive beds beds in in the the fine fine sand. sand. The The vertical vertical distribution distribution of of sand sand textures textures represent represent fining fining upward upward cycles. cycles. The The lower lower contact contact associated associated with with the the coarse coarse sand sand is is often often smooth smooth and and clear. clear. The The lower lower contacts contacts associated with the other other sand sand textures textures are are more more gradual gradual or or diffuse. diffuse. Unit 3, the the lowermost lowermost unit, unit, consists consists of of horizontally bedded bedded Unit 3, couplets couplets of of varved varved silt silt and and clay. clay. There There are are at at least least 25 25 couplets couplets each about about 25 25 cm cm thick. thick. The lowest lowest couplet couplet drapes drapes the the bedrock bedrock The surface. surface. This This section section represents represents the the progradation progradation of material (Units (Units 11 and over material deposited in deeper water (Unit 3) Clearly, 2) Clearly, 2) over material deposited in deeper water (Unit 3) this section indicates that the bulk of material that makes this section indicates that the bulk of material that makes up up the the is fine-grained and has limited use as an aggregate terraces terraces is fine-grained and limited as an aggregate resource. resource. Samples Samples of of the the heavy heavy minerals minerals and and clasts clasts of of this this deposit deposit would be useful These would be useful to define define aa regional regional signature. signature. These same' same * materials for local local prospecting prospecting due due to: to: the the materials would would not not be be as as useful useful for local and distal distal sources sources for for the the materials; materials; and and the the restricted restricted distribution distributionof of these these deposits deposits to to the the mouths mouths of of major major rivers rivers around around . . 41 �Unit II Unit Gravel Gravelbed bed Wavy, planar planarbed bed 278° Trough Trough cross cross bed bed /203° Planar Planarbed bed Foreset Foresetbed bed \1500 Massive Massive bed bed Diffuse Diffusebed bed 1195° Rounded Roundedclasts clasts '\145° 260° Unit 2 Unit2 220° 277 CL Si Ss Grv Paleocurrent Paleocurrent Clay Clay Silt Silt Sand Sand Gravel Gravel Ui (I) 228° 230° . /'220° 25 Couplets Unit 33 Unit 0 CL CL Si Si Ss Grv Gw GRAIN GRAIN SIZE SIZE Figure Figure 15: Glaciolacustrine Glaciolacustrine section. section. discussion. discussion. See See text for description and 42 �the the Lake Lake Superior Superior basin. basin. Drive to Site Site *11 #11 again backtrack backtrack to the the Magpie Magpie River Road and and continue continue north We again toward across glaciofluvial glaciofluvial outwash #ll. The The road road continues continues across toward Site Site #11. associated with aa remarkable remarkable glaciofluvial glaciofluvial fan, fanl east east of of the the road. road. associated with Parallel to to the the railroad railroad is is an an elongated elongated lake. lake. This is is aa scour scour #2. Note the lag lag of of pool similar to the the one one discussed discussed at Site Site #2. boulders on the the downf downflow low side side of of the the lake lake which which where where literally outwash surface surface by by water water under under blasted out of the the glaciofluvial glaciofluvial outwash tremendous hydrostatic hydrostatic pressure. pressure. tremendous Site *11: #11: Steephills Stee~hillsFalls Falls Moraine Moraine Appendix Appendix A: Magpie Magpie River River Road This site site provides an example of a recessional recessional moraine moraine composed of This materials materials more more typically typically described described in in the the literature. literature. The The moraine represents state of equilibrium equilibrium between between ablation ablation and and accumulation accumulation represents aa state of ice within the ice within the ice ice sheet's sheetlsglacial glacial budget. budget. However! this state state However, this was short-lived short-lived since since the the moraines moraines are are relatively relatively of equilibrium was small sections through small and and not not laterally laterally extensive. extensive. There are no sections this moraine moraine although although the this the moraine moraine is is likely likely composed composed of of flow flow tills. tills. This assumption assumption is made from from observations observations of sections sections through through recessional moraine moraine elsewhere recessional elsewhere in in the the area. area. Clast abundance abundance ranges ranges from from rare rare to to common common with with clasts clasts sometimes sometimes concentrated within flow concentrated flow structure. structure. Pebble type assemblages assemblages Pebble determined moraine deposited deposited over over greenstone greenstone and and determined from from flow flow tills tills in in moraine granitic granitic terranes terranes were were compared. compared. Pebble Pebble assemblages assemblages within flow flow till associated with moraine till associated with moraine deposited deposited on the the greenstone greenstone belt belt consisted of granitic clasts clasts and and 67.8% 67.8% clasts clasts of 31.6% granitic of greenstone greenstone consisted of 31.6's Pebble assemblages within flow till of belt origin. origin. Pebble assemblages within of moraine moraine deposited granitic terrane 34.91 clasts clasts of greenstone greenstone deposited on on granitic terrane consist consist of of 34.9% belt origin origin and and 61.5% granitic granitic clasts clasts. These belt These pebble pebble type type assemblages differ little from from the the pebble assemblages differ little pebble type assemblages type assemblages associated with subglacial subglacial till till collected collected from from over over granitic granitic and and greenstone greenstone belt belt terrane. terrane. . The average average concentration concentration of Paleozoic Paleozoic clasts clasts within lodgement lodgement and The However, flow tills tills differs differs little. little. However, Paleozoic within Paleozoic clasts within subglacial till till have aa more regional! homogeneous homogeneous distribution distribution subglacial more regional, throughout the region whereas Paleozoic Paleozoic clasts clasts tend to have a more more throughout the region distribution within moraines; moraines; more more concentrated concentrated within within erratic distribution certain moraines moraines over certain over others. others. The geochemical, heavy mineral The geochemicall mineral and and clast clast composition composition of of the the morainal material morainal material at at this this site may be be useful useful as a regional as a regional as the moraine is signature as is composed composed of of materials materials derived derived from from local and reason! the the moraine moraine would would not not local and distal distal sources. sources. For For this this reason, be be useful useful as as aa local local sampling sampling media. media. 43 �Drive D r i v e to t o Site S i t e #12 #12 The The trip trip continues continues towards towards the the Steephills Steephills Falls Falls Dam. Dam. West West of of the the dam, daml the the road road crosses crosses several several valleys valleys filled filled with with glaciofluvial glaciofluvial materials. materials. These These are are former former meitwater meltwater channels channels that that fed fed into into the the Magpie southlHighway Highway 17 Magpie River River valley valley (Figure (Figure5). 5). Proceeding Proceeding south, 17 drops drops below below the the Lake Lake Minong Minong level level north north of of Wawa Wawa and and again, againl the the road road crosses over several terrace surfaces. crosses over several terrace surfaces. Site S i t e #12: Summary Summarv Site Site Appendix Appendix A: A: Visitors Visitors centre, centreIWawa Wawa This This last last stop stop provides provides an an excellent excellent view view over over the the lower lower reaches reaches of of the the Magpie Magpie River River valley. valley. Several of the the terraces terraces thatrim thatrim the the valley valley walls walls provide provide aa perspective perspective of of how how high high former former lake lake levels levels were were within within the the Lake Lake Superior Superior basin. basin. visitors centre centre is is The visitors situated m) situated on on the the lowest lowest Glacial Glacial Lake Lake Minong Minong terrace terrace surface surface(294 (294m). . It It is is sincerely sincerely hoped hoped that that this this guidebook guidebook and and related related field field trip trip provided provided an an appreciation appreciation regarding regarding the the use use and and limitations limitations of of overburden overburden in in mineral mineral exploration. exploration. When When done done correctly, correctly, drift drift prospecting prospecting can can be be an an effective effectivetool tool to to aid aid mineral mineral exploration. exploration. Sunixnary of Sites: Sites: Summary of 1) 1) Bedrock Bedrock surface surface features features associated associated with with glacial glacial advance advance and and ice ice margin #I and and 8). 8). Discussion Discussion margin retreat retreat were were reviewed reviewed (Sites (Sites#1 included included the the importance importance of of ice ice flow flow indicators indicators in in establishing establishing ice ice flow flow direction, directionl essential essential for for determining determining material material source. source. 2) 2) The The need need to to understand understand local local Quaternary Quaternary history history was discussed discussed (all sites) local ice ice flow flow patterns patterns across across an an area area (all sites) to determine determine local and and to to determine determine ice ice margin margin retreat retreat patterns patterns and and associated associated meltwater meltwater flow. flow. This This aids aids in in interpreting interpreting the the results results of of any any glaciofluvial glaciofluvial (Sites (Sites#2, #21 4, 4, 8), 81, glaciolacustrine glaciolacustrine(Sites (Sites#6, #GI 8, o1 10) or or modern modern alluvium alluvium (Site (Site #7, #71 7a) 7a) samples samples taken. taken. 10) 3) The The use use of of subglacial subglacial till till (Site (Site *3) #3) as as the the important important medium 3) for for local local drift drift prospecting prospecting was was highlighted. highlighted. The The physical physical characteristics characteristicsand and pedogenic pedogenic processes processes that that affect affect geochemical geochemical signatures signatures and and style style of of material material sampling sampling were were reviewed. reviewed. 4) 4) Glacially Glacially derived derived materials materials and and related related landforms landforms that that provide provide aa more more regional regional signature signature for for drift drift prospecting prospecting were were discussed. discussed. These These included included proglacial proglacial outwash outwash (Site (Site#4), #4) ice ice contact contact stratified stratified drift drift (Site (Site *5), #5), glaciofluvial glaciofluvial outwash outwash (Sites (Sites#7, #7# 7a, 7a1 8), 8)1 recessional recessional moraine moraine (Site (Site #11) #ll) and and glaciolacustrine glaciolacustrine 10). The The discussion discussion considered considered the the value value deposits (Sites (Sites#6, #GI10). deposits and and limitations limitations of of these these materials materials as as drift drift prospecting prospecting media. media. 44 �5) The materials materials and arms that that have have undergone undergone several several 5) The and related related landf landforms cycles cycles of of erosion, erosionl transportation transportation and and deposition deposition were were investigated. investigated. These These include include modern modern alluvium alluvium (Site (Site #7, #7, 7a), 7a)! older alluvium (Site #9) #9) and and glaciolacustrine deposits (Site (Site#6, #GI older alluvium (Site glaciolacustrine deposits 10). The The value value and and limitations limitations of of using using these these materials materials as as 10). sampling media media for for drift drift prospecting prospecting were were also also reviewed. reviewed. sampling ACKNOWLEDGEMENTS The or allowing allowing The author author thanks thanks Rudy Rudy Hoffman Hoffmanand and Algoma AlgomaOre OreDivision Divisionffor property property access. access. This This trip trip would not not have have been been possible possible without without their cooperation. Ed Freyls Frey's comments comments regarding regarding Quaternary Quaternary studies studies their cooperation. within the the Wawa Wawa area area was was appreciated. appreciated. Ron Ron Sage Sage (OGS) (OGS) provided provided direction regarding regarding the bedrock component component of this this field field trip. trip. Catherine Catherine Farrow and Cam Cam Baker Baker (OGS) (OGS) reviewed the the manuscript. manuscript. 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Geology of the Michipicoten greenstone belt; Ontario Geological Survey, Open File Report 5888, 592p. Sage R.P. mineral Canada, Toronto and Heather K.?. 1991. The structure, stratigraphy and deposits of the Wawa area; Geological Association of Society of Economic Geologists, Joint Annual Meeting, '91, Field Trip AG, Guidebook, 118p. Seely J.B. and Senden T.J. 1994. Alluvial gold in Kalimantan, Indonesia: a colloidal origin?; Journal of Geochemical Exploration, v.50, p.457-478. Sharp D.R. and Shaw J. 1989. Erosion of bedrock by subglacial meltwater, Cantley, Quebec; Geological Society of America Bulletin, v.101, p.1010-1020. Shuts W.W. 1976. Glacial till and mineral exploration; in Glacial Till, Royal Society of Canada, Special Publication 12, p.205-224. Shilts W.W. and Kettles I.M. 1990. Geochemical/mineralogical profiles through fresh and weathered till; in Handbook of Indicator Tracing, A.A. Balkema, Rotterdam, p.187-216. Sutherland D.G. 1982. The transport and sorting of diamonds by fluvial and marine processes; Economic Geology and the Bulletin of the Society of Economic Geologists, v.77, no.7, p.1613-1620. Sutherland D.G. 1993. The diamond deposits of the Mandala basin, SE Guinea, West Africa; Transactions of the Royal Society of Edinburgh; Earth Sciences, v.84, p.137-149. Szabo N.L., Govett G.J.S. and Latjai E.Z. 1975. Dispersion trends of elements and indicator pebbles in glacial till around Mt. Pleasant, New Brunswick, Canada; Canadian Journal of Earth Sciences, v.12, p.1534-1556. Thomas D.A. 1984. Stratigraphy, Lithology, Petrography and Depositional Environments of the Dore' Sediments Proximal to the Lucy Iron Range, Wawa, Ontario; Unpublished BSc. Thesis, Carleton University, Ottawa, Ontario, 37p. Thurston P.c. 1986. Volcanic cyclicity in mineral exploration: the caldera cycle and zoned magma chambers; in Volcanology and Mineral Deposits, Ontario Geological Survey Miscellaneous Paper 129, p.104-123. Wolfe W.J., Lee H.A. and Hicks W.D. 1975. Heavy mineral indicators in alluvial and esker gravels of the Moose River Basin, James Bay Lowland, District of Cochrane; Ministry of Natural Resources Geoscience Report 126, 60p. 48 �APPENDIX APPENDIX A A ROUTE ROUTE MAPS Appendix Appendix Appendix A A consists consists of: of: Regional Regional plan plan of site site locations, locations, Appendix A-i A-1 : Portion Portion of NTS Sheet Sheet 42 42 C/2 C/2 (Hawk (Hawk Junction), illustrating illustrating location location of of site site Junction), numbers 6, 7, 7, 7A, 7A, 8, 8, 9, 9, 10, 10, ii 11and numbers 1, 1, 2, 2, 6, and route; route; Appendix Appendix A-2. A-2. : Portion Portion of of NTS NTS sheet sheet 42 42 C/2 C/2 (Hawk (HawkJunction) Junction) illustrating illustratinglocation locationof of site sitenumbers numbers3, 3,4, 4, 5 5 and and route, route, Appendix Appendix A-3. A-3. : Portions Portions of of NTS NTS sheets sheets 42 42 C/2 C/2 (Hawk (Hawk Junction) (Michipicoten Junction) and and 41 41 N/15 ~/15 (Michipicoten Harbour) illustrating illustrating location location of of site site Harbour) nuniber 12 and and route; route; Appendix Appendix A-4. number 12 A-4. 49 �0 I-i. (D Appendix A - 1 N. C. •7S N. C. C. RAILROADS ROADS VATER BODIES TDWNS SIt• Numb•r 723325 N. C. 7?tOO . C. I § �'___i V - V\ —H - L \Site#l - I Appendix Appendix A-2 A-2 51 �Appendix Appendix A-3 A-3 52 52 �Appendix A-4 53 �APPENDIX APPENDIX B B SITE SITE AND AND MATERIAL MATERIAL OBSERVATION OBSERVATION SHEETS SHEETS Appendix Appendix consists consists of: of: Till Till observation observation forms, forms, p.55 p.55 : Modern Modern alluvium alluvium observation observation forms, forms, p.57 p.57 : Field Field note note definitions, definitions, p.58 p.58 (modified (modified from from Agriculture Agriculture Canada Canada (1977) (1977) 54 �Air Photo: Photo: Air U.T.M. U.T.M. Ref.: Ref.: Stop Stop Number: Number: Sample Sample Number(s): Number(s): -- Comment: Comment: Site Site Description Description A) A ) Genetic Genetic Material: Material: B) B) Surface Surface Expression: Expression: apron/ apron/ blanket! blanket/ fan/ fan/ hummocky/ hummock$/ inclined/ inclined/ • level/ level! rolling/ rolling! ridged/ ridged! steep/ steep! terraced/ terraced! undulating/ undulating/ veneer! veneer/ location: location: C) C) Slope: Slope: InclinationInclination- AspectAspect- D) D) Drainage: Drainage: Well Well drained! drained/ Moderately Moderately well well drained/ drained/ Poorly Poorly drained drained E) E) Vegetation: Vegetation: TypeType- Coniferous! Coniferous/ Deciduous/ Deciduous/ Mixed/ Mixed/ Scrub! Scrub/ Grass! Grass/ Bog! Bog/ Other: Other: State: State- Virgin! Virgin/ Logged! Logged/ Fired! Fired/ Stress: Stress: F) F) Material Material Thickness: Thickness: Class Class 1/ I/lÀ! 1A/2/ 2/ 3/ 3 / Other: Other: Material Material Description Description Horizon: Horizon: AA BB C A) A ) Colour: Colour: Munsell Munsell Code: Code: B) B) Texture Texture Sand: Sand: Coarse! Coarse/ Medium! Medium/ Fine Fine Silt: Silt: Sandy! Sandy/ Silt! Silt/ Clayey Clayey Clay: Clay: Silty! Silty/ ClayClay- Organic Organic C) C ) Structure Structure Type: Type: Structureless! Structureless/Block! Block/ Plate! Plate/ Prism! Prism/ Flow Flow Other: Other: Kind: Kind: Massive! Massive/ Blocky, Blocky, << blocky! blocky/ Platy/ Platy/ Prismatic, Prismatic,Columnar Columnar Flow: Flow: Size: Size: D) D) Consistency Consistency WetWet- Nonsticky/ Nonsticky/ Slightly Slightly ' Sticky! Sticky/ Sticky Sticky MoistMoist- Loose! Loose/ Friable! Friable/ Firm Firm DryLoose! Soft! Dry- Loose/ Soft/Kard Hard E) E) Plasticity Plasticity —Nonplastic/ -Nonplastic/Slightly Slightly Plastic! Plastic/Plastic Plastic 55 �Material Material Description Description (Cont) (Cont) Horizon: Horizon: A B C F) Cementation Cementation (Yes/ (Yes/ No) No) - Weak! Weak/ Strong! Strong/ Indurated Indurated C) G) Clasts Clasts Rare/ Few! Few/ -Abundance; Rare! Common! Common/ Abundant -- Size; Size; -- Shape; Shape; Rounded! Rounded/ Subrounded Subrounded Angular/ Angular/ Subangular Subangular -Striated (Yes/ No); No); -Striated (Yes! -Type; -Type; Plutonic/ Plutonic/ SupraSupracrustal/ Marine Marine H) Lower Lower Horizon Horizon Boundary Boundary Diffuse/ -Distinctiveness; Diffuse! Gradual! Gradual/ Clear Clear - Form; Form; Smooth! Smooth/ Wavy! Wavy/ Irreg. Irreg. I) I) Unit Unit Thickness: Thickness: COMMENTS/ COMMENTS/ DIAGRAM(S) DIAGRAM(S) 56 �__ _________ MODERN ALLUVIUM ALLUVIUM OBSERVATION OBSERVATION FORM FORM General General Aerial Aerial Photo: Photo: U.T.H. U.T.M. Reference: Reference: #: Stop #: Stop Sample SampleNuiriber(s): Nurnber(s) : Site Site Description Description A) Material: Material: A) B) B) Surface Surface Expression: Expression: apron! apron/ blanket! blanket/ fan! fan/ hunimocky! hummocky/ inclined! inclined/ level! level/ rolling! rolling/ ridged! ridged/ steep! steep/ terraced! terraced/ undulating! undulating/ veneer veneer AspectAspect - C) Slope: Slope: InclinationInclinationC) D) D) Drainage: Drainage: Strong! Strong/ Moderate! Moderate/ Weak! Weak/ Ephemeral Ephemeral E) E) Vegetation: Vegetation: TypeType- Coniferous! Coniferous/ Deciduous! ~eciduous/Mixed! Mixed/ Grass! Grass/ Bog! Bog/ Other; Other; StateVirgin! Logged! State- Virgin/ Logged/ Fired! Fired/ Stress: Stress: Material Material Description Description Munsell Mimsell Code: Code: A) Colour: Colour: A) B) Fine/ Other: Other: B) Texture: Texture: SandSand- Coarse! Coarse/ Medium! Medium/ Fine! C) C) Structure: Structure: Structureless! ~tructureless/Current Current and and Wave Wave Ripples! Ripples/ Cross Cross Bedding! Flaser and and ~edding/Climbing Ripple Lamination! Lamination/ Flaser Lenticular Bedding! Graded Bedding! Rhythmites/ Flow! LenticularBeddinq/ Graded~edding/ Rhythmites/ Flow/ Undetermined Undetermined D) D) Form: Bar Form: Bar ROW Foan Pattern Longitudinal: Transverse: [) i\_"'' Pton 1) " Growth Pattern Transverse Longitudin( J ..—. ' /'' -' Pot Diagonot: E) Clasts: Clasts: E) \ — Abundance; Abundance; Rare! Rare/Few! Few/Common/ Common/ Abundant Abundant Size Size Range; Range; Shape; Subrounded/ Angular Shape; Rounded! Rounded/ Subrounded/ Angular Striated; Striated; Yes! Yes/ No No Types; Types; 57 �FIELD DEFINITIONS FIELD NOTE NOTE DEFINITIONS Stop Number: HJxx/91 Stop Number: HJxx/91 HJRefers : HJRefers to sheet. to project project NTS NTS map sheet. xxRefers : xxRefers to Sample numbers numbers run to sample sample number. number. Sample run consecutively from consecutively from 1-n. 1-n. /91- Refers Refers to : /91to the the project project year. year. U.T.M. Reference: Reference: This This fixes fixes the the ground ground sample sample point point to to a a location location U.T.M. on on the the NTS NTS topographic topographic map map (identified (identified in in the the stop number). stop number). Aerial Photograph: Photograph: This This number number is is the the aerial aerial photograph Aerial photograph number which which relates relates to to the the sample sample collection collection site. site. Sample Sample Number: 91FxxLBA 91FxxLBA : 9191- Refers Refers to to the the project project year. year. : F F -- Refers Refers to the the NTS NTS map map sheet. sheet. xx- Refers Refers to : xxto the the sample sample number. number. Sample Sample numbers run numbers run consecutively from from 1-n. 1-n. Each sample sample has has it's consecutively own number. own number. L -- Refers Refers to material : L type; i.e. i.e. till, till, material type; glaciolacustrine, outwash, lacuatrine lacuatrine etc. etc. glaciolacustrine, outwash, B -- Refers Refers to fraction : B fraction sampled. sampled. B B refers refers to to bulk, bulk, C refers refers to to clasts clasts only. only. : AA- Refers to to soil soil horizon horizon sampled; sampled; H, HI A, A, B, B, C. C. Genetic Material: This mapping unit and landform landform type Genetic Material: This describes describes the the mapping unit and type from from which the the sample sample is is being being taken. taken. Surface Surface Expression: Expression: Refers Refers to to the the lay lay of of the the land. land. - Apron: Apron: - A relatively relatively gentle gentle slope slope at the the foot foot of a steeper steeper slope, slope, and formed formed from from the the materials materials of of the the steeper steeper slope. slope. Blanket: A mantle of unconsolidated materials thick enough enough to - Blanket: - mask minor irregularities irregularities in in the the underlying underlying unit unit but but which still still conforms conforms to the general underlying topography. topography. -- Fan: Fan: A A fan-shaped fan-shapedform form that that can can be be likened likened to to the the segment segment of of aa cone, and possessing possessing a perceptable perceptable gradient cone, gradient from from the the apex apex to the the toe. toe. Huinmocky: A very complex -- Hummocky: complex sequence sequence of slopes slopes extending from from somewhat rounded rounded depressions depressions or or kettles kettles of of various various size to size to irregular irregular to to conical conical knolls knolls or or knobs. knobs. There There is a general lack of concordance between knolls is general lack concordance between knolls or or depressions. Slopes and350• 35'. depressions. Slopes are are generally generallybetween between55and 58 �- - - - - - Inclined: Inclined: A A sloping, sloping, unidirectional unidirectional surface surface with a a generally generally constant broken by marked marked irregularities. constant slope slope not broken irregularities. Slopes Slopes are are between between 11 and and 35°. 35'. The form form of inclined inclined slopes slopes is is not related related to to the the mode mode of of origin origin of of the the underlying material. underlying material. Level: unidirectional surface surface with flat, or or gently sloping, sloping, unidirectional Level: A flat, a generally generally constrant slope slope not broken by marked elevations elevations and and depressions. depressions. Slopes Slopes are are generally generally<10. <lo. Rolling: Rolling: A very regular regular sequence sequence of moderate slopes slopes extending from rounded, from rounded, sometimes sometimes confined, confined, concave concave depressions depressions broad, rounded wave-like to broad, rounded convexities convexities producing producing aa wave-like pattern Slope length pattern of of moderate moderate relief. relief. Slope length is is often often or greater greater and and gradients gradients are are <5 c5 %. %. 0.5 km 0.5 km or Ridged: Ridged: A A long, long, narrow narrow elevation elevation of of the the surface, surface, usually sharp usually sharp crested, with crested, with steep steep sides. sides. The ridges may The ridges may be be parallel, parallel, sub-parallel or sub-parallel or intersecting. intersecting. Steep: Erosional unconsolidated and Steep: Erosional slopes, slopes, >35°, >35O, on both unconsolidated and consolidated materials. The form consolidated materials. The form of of a a steep steep erosional erosional slope is not not related related to to the the slope on unconsolidated unconsolidated materials materials is origin of the underlying material. initial mode of origin the underlying material. Terraced: Scarp Scarp face face and and the the horizontal horizontal or or gently gently inclined inclined Terraced: surface surface (tread) (tread) above above it. it. Undulating: Undulating: A very very regular regular sequence sequence of of gentle gentle slopes slopes that that extend from from rounded, rounded, sometimes sometimes confined confined concavities concavities extend to broad rounded rounded convexities convexities producing producing wave-like wave-like pattern of low local relief. Slope length pattern of low local relief. Slope length is is km and dominant c1 km dominant gradient gradient of of slopes slopes generally <1 from 2-5 2-5 %.. - Veneer: Veneer: Unconsolidated unconsolidated materials too too thin thin to mask the minor irregularities irregularities of of veneer will range veneer will range and and will will pocesses pocesses genesis. genesis. the the underlying underlying unit unit surface. surface. A between 10 cm and 1 m between 10 cm and 1 m in in thickness thickness no no form form typical typical of of the the material's material's Slope: Describes Describes the the slope slope inclination inclination and and aspect. aspect. Drainage: Drainage: Describes Describes the the slopes slopes ability ability to to drain. drain. Well drained: - Well drained: Water is removed from the soil readily downward - - - into or laterally as into underlying underlying previous previous material material or laterally as subsurface subsurface flow. flow. Soils Soils have have aa low low to to intermediate water water moisture intermediate moisture storage storage capacity. capacity. somewhat slowly Moderatley well drained: Water is is removed somewhat slowly in in relation relation to to supply. supply. Excess water is is Excess water removed removed somewhat somewhat slowly slowly due due to to low low perviousness, perviousness, shallow shallow water water table, table, lack lack of gradient or or some some combination combination of these. Soils have intermediate intermediate to of these. Soils to water storage high water storage capacities. capacities. 59 �- Poorly Poorly drained: drained: Water Water is is removed removed so so slowly slowly in in relation relation to to supply that the supply the soil soil remains remains wet for for aa comparitively large comparitively large part of of the the time time the the soil soil •is not frozen. frozen. Excess is not Excess water water is is evident evident in in the the soil for a a large large part part of of the the time. time. soil for Refers to to the the type type of of vegetation cover, cover, coverage coverage and Vegetation: Refers vegetation vegetation state. state. - Type: Type: ConiferousConiferous- More More than than 80 80 1% coniferous coniferous cover. cover. - Deciduous- More 80 1 % deciduous deciduous cover. cover. DeciduousMore than than 80 MixedMixed- Mix of coniferous coniferous and deciduous deciduous cover cover with one or the c80 1% of of the the cover. cover. the other other <80 c50 1 % canopy, canopy, mixture of open grass or bushland Scrub- <50 Scruband tree. and tree. Grass- >50 >50 1% grass grass cover. cover. GrassBog>50 1% wetland. wetland. Bog- >50 - State: No evidence evidence of of recent recent cutting cutting or or forest forest fire. fire. Virgin- No State: VirginForest is Forest is mature. mature. Loggedrecent logging logging activity. activity. Forest Logged- Evidence of recent Forest area area mature mature cover cover largely largely logged. logged. Fired- Evidence Forest area area mature FiredEvidence of of recent recent fire. fire. Forest cover largely cover largely burned. burned. StressStress- Evidence that vegetation vegetation is stressed by by envirtonment; i.e. envirtonment; i.e. drought, drought, insects insects etc. etc. Material unconsolidated Material Thickness: Thickness: Refers Refers to to the the thickness thickness of unconsolidated material material over over the the bedrock bedrock surface. surface. Virtually bare - Class bare bedrock. bedrock. Maybe Maybe thin thin drift drift within within Class 1: Virtually - undulations of undulations of the the bedrock bedrock surface. surface. Thin drift drift (<1 over bedrock. bedrock. Does - Class (el m) over Does not not obscure obscure the the Class 1A: Thin - bedrock bedrock topography. topography. 2: Pockets of drift within within bedrock bedrock depressions >1 >1 m m -- Class Class 2: thick. c1 m m of of drift. drift. thick. Bedrock crests crests are are covered covered by by <1 -- Class Class 3: Bedrock surface surface expression expression obscured by by unconsolidated unconsolidated material >1 mm thick. thick. material >1 Colour: Refers Refers to to the the colour colour of of aa sp[ecific sp[ecific unit unit based based on on the the Munsell Munsell Soil Soil Colour Colour Chart. Chart. representative grain size of a particular Texture: Refers to the representative unit. unit. - Coarse Coarse Sand: 25 1 % or more very corase corase or or coarse coarse sand, sand, and and <501 ~50% - any any other other one one grade grade of of sand. sand. very coarse Sand: 25 1 - Sand: % or or more very coarse or or coarse coarse sand sand and and medium medium sand, sand, - and c50 1% fine fine or or very very fine fine sand. sand. and <50 - Fine Fine Sand: Sand: 50 1% or or more more of of fine fine sand, sand, or or <25 c25 1% very very coarse, coarse, - - Sandy Sandy - Silt: Silt: - coarse coarse or or medium medium sand. sand. silt, and and <50 c50 1% sand. sand. Silt: Contains Contains >50 >50 1% silt, Contains at Contains at least least 80 80 1% silt silt and and <2 c2 1% clay. clay. 60 �- Clayey Clayey Silt: Silt: Contains Contains >50 >50 % silt, silt, and and <50 c50 1% clay. clay. - Silty Silty Clay: Clay: >501 >SO% clay clay and and <501 ~50% silt. silt. - Clay: Clay: Contains Contains at at least least 40 1% clay, clay, <45 c45 1% sand sand and and <40 c40 1% silt. silt. - Organic: Organic: Contains Contains at at least least 30 30 6% organic organic material. material. - Structure: Structure: Refers Refers to to the the physical physical characteristics characteristics of of the the unit. unit. - Type: Type: StructurelessStructureless- Simply Simply no no structure. structure. - BlocklikeBlocklike- Have Have distinct distinct blocklike blocklike shape shape consisting consisting of of 44 or or more more sides. sides. PlatelikePlatelike- Ped(s) Ped(s) are are arranged arranged horizontally horizontally to to give give aa platelike platelike structure. structure. PrismlikePrismlike-Peds Peds are are longer longer than than wide wide giving giving aa columnar columnar or or peaked peaked shape, shape, the the peak peak towards towards the the top top of of the the ped. ped. FlowFlow- There There is is the the presence presence of of flow flow structure; structure; flow flow cones, cones, stringers, stringers, injections, injections, rip-ups, rip-ups,flames, flames, balls, pillows, dish, planar, crossbedding, balls, pillows, dish, planar, crossbedding, trough trough crossbeds, laser, graded. crossbeds, ripples, ripples,fflaser, graded. - Kind: Kind: MassiveMassive- Refers Refers to to structureless structureless type, type, and indicates indicates homogeneous homogeneous arrangement arrangement of of materials. materials. Angulartype, where where there Angular- Refers Refers to to the the bloc]clike blocklike type, there are are just sides to to the the ped. ped. just 44 sides SubangularSubangular-Refers Refers to to the the blocklike blocklike type, type, where where there there are are 5 or or more more sides. sides. •PlatyRefers to to the the platelike platelike type, type, where the Platy- Refers the peds peds are are arranged arranged horizontally. horizontally. PrismaticPrismatic- Refers Refers to to the the prismlike prismlike type, type, where where the the peds peds are are rounded rounded or or angled angled at at the the surface. surface. ColumnarColumnar- Refers Refers to to the the prismlike prismlike type, type, where where the the peds peds are are longer longer than than wide wide and and do do not not have have a a rounded rounded or or angled angled surface. surface. FlowFlow- Indicate Indicate the the flow flow regime regime based based on on the the flow flow structure structure type. type. Consistency: cohesion and and adhesion adhesion Consistency: Refers Refers to to the the degree degree and and kind kind of of cohesion or or to to the the resistance resistance of of the the soil soil to to deformation deformation or or rupture. rupture. -- Wet: Wet: NonstickyNonsticky- After After release release of of pressure, pressure, practically practically no no soil soil material material adheres adheres to to thumb thumb and and finger. finger. Slightly Slightly stickysticky- After After pressure pressure is is applied, applied, the the soil soil material material adheres adheres strongly strongly to to both both the the thumb f one thumb and and forefinger, forefinger,but but comes comesofoff one or other rather rather cleanly. cleanly. The or the the other The soil soil is is not appreciably stretched when the digits not appreciably stretchedwhenthe digits are are separated. separated. StickySticky- After After pressure pressure is is applied, applied, the the soil soil material material adheres thumb and forefinger forefinger adheres strongly strongly to to both both the the thumb and and tends tends to to stretch stretch somewhat somewhat and and pulls pulls apart apart rather than pulling free from either digit. rather than pulling free from either digit. -- Moist: Moist: LooseLoose- Noncoherent Noncoherent soil soil material material 61 �- Friable- The soil soil material crushes crushes easily easily under under gentle gentle Friableto moderate pressure between betweenthe thethumb thumbarid and to moderate pressure forefinger forefinger and and coheres coheres when when pressed pressed together. together. FirmThe soil soil material material crushes crushes under under moderate moderate pressure pressure Firm- The or greater, greater, but resistance resistance is is distinctly distinctly or noticeable. noticeable. Dry: LooseLoose- Noncoherent soil material material Dry: Noncoherent soil Soft- The The soil soil material is is weakly weakly resistant resistant to to pressure pressure Softand easily easily broken broken between between the the thumb thumb and and forefinger. forefinger. and Hardis moderately resistant or or greater Hard- The The soil soil material material is moderately resistant greater to pressure, it can can be broken in in the the hands hands with with pressure, it moderate to moderate to some some degree degree of of difficulty. difficulty. Plasticity: Plasticity: Is Is the the property property of of changing changing shape shape continuously continuously under under the influence influence of an applied applied stress and of retaining retaining the the of an stress and the new shape new shape after after removal removal of of the the stress. stress. - Nonplastic: Nonplastic: A A roll roll 44 cm cm long long and and 44 mm mm thick thick cannot cannot be be formed. formed. Slightly plastic: - Slightly A roll roll 44 cm cm long plastic: A long and 2 mm mm thick thick can be be formed formed - but will will not not support support its its own own weight. weight. - Plastic: Plastic: A roll roll 4 4 cm long and 2 mm mm thick thick can be be formed formed and will will - support support it's it's own own weight. weight. Cementation: soil is cemented cemented and the Cementation: Refers Refers to to whether whether or or not the the soil degree degree to to which which the the unit unit is is cemented. cemented. Clasts: Describes the relative abundance abundance of each type, type, shape Clasts: Describes the type, type, relative and size and size of of clasts. clasts. Rare- <5 - Abundance: Abundance: Raree5 1% Common- 15Common15- 20 1% FewFew- 10 10 1% Abundant- >20 >20 '% Abundant-- Size: Size: State common and and largest largest size. size. State common Shape: Rounded, Rounded, subrounded, -- Shape: subrounded, subangular, subangular, angular. angular. Striated: Yes -- Striated: Yes or or no no Type: As detailed sample -- Type: detailed pebble counts counts are usually done per sample site, it is site, is only necessary necessary to to describe describe the the clasts clasts generally generally as as granitic, granitic, volcanic, volcanic, metamorphosed metamorphosed or or sedimentary. sedimentary. - Lower Lower Horizon Horizon Boundary: Boundary: Describes Describes the characteristics characteristics of the units units lower lower contact. contact. - Distinctiveness: Distinctiveness: DiffuseDiffuse- Vertical change >15 cm - - Gradual- Vertical Vertical change Gradualchange within within 55 to to 15 15 cm. cm. to 55 cm. cm. Clear- Vertical Vertical change change within within 22 to Cleare2 cm. cm. AbruptVertical change change <2 Abrupt- Vertical Form: Smooth- Nearly Form: SmoothNearly aa plane. plane. Wavy- Pockets WavyPockets wider wider than than deep. deep. IrregularIrregular- Pockets Pockets wider wider than than deep. deep. Unit Thickness: Thickness: State State thickness thickness of of each each horizon. horizon. 62 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1995 Description An account of the resource Institute on Lake Superior Geology. Marathon, Ontario. May 13-18, 1995. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1995 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/454203bdafbcf2bc7c5abe3f8b5cf5b5.pdf 2f835a3f7d8f969acd904f670359f1da PDF Text Text 42' Annual INSTITUTE ON LAKE LAKE SUPERIOR GEOLOGY CABLE, WISCONSIN WISCONSIN CABLE, 19,1996 MAY 15 --19, 1996 '''''I ,,I1I/ 1II / I 1%/ 'I ' I..I I ,' ,' '. '''''I,,,,,, - ..-' % .' % % % I/I/I/I 1I/II 'I I I I I / I / / I PROCEEDINGS VOLUME VOLUME 42 1--PROGRAM PART 1 PROGRAMAND ANDABSTRACTS ABSTRACTS �42ND ANNUAL ANNUAL MEETING MEETING 42ND INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY Volume 42 consists consists of: Program and and Abstracts Abstracts Part 1: Program Part Suffide Deposits Deposits of of Northern Northern Part 2: Volcanogemc Volcanogenic Massive Sulfide Wisconsin: Wisconsin: A Commemorative Volume Field Trip Guidebook Part 3: Field 1. Glacial geology of western Wisconsin 1. Glacial 2. Geology Monodine: Geology of of the Montreal River Monocline: through 25 km of the crust A traverse through 4. Early Early to to Middle Middle Proterozoic Proterozoic geology of the Lake Namekagon region 5. Lake Lake Namekagon and Penokee Gap areas, west Gogebic Range, Wisconsin Reference to material in this volume should should follow follow the example below. Darrah, K. S., 5., Holm, Darrah, K. Hoim, D. K., Dahl, Dahi, P. P. 5., S.,and and Lux, Lux, D. D. R., R.,1996, 1996,Petrographic Petrographicand and thermobarometric thermobarometric metamorphosed Little Formation, central central Minnesota, Minnesota, with with implications implications for for Little Falls Formation, analysis of the metamorphosed Early Proterozoic tectonism [abstract]; Institute on Lake Superior Geology Proceedings, 42nd Annual Meeting, v. 42, part part 1, I, p. 1010 -11. 11. Annual Meeting,Cable, Cable,WI, WI,1996; 1996; v. Published Published and and distributed distributedby bythe theInstitute Instituteon onLake Lake Superior Superior Geology Mark Jirsa, Secretary-Treasurer Minnesota Geological Survey 2642 University University Avenue 2642 St. MN 55114-1057 55114-1057 USA St. Paul, MN ISSN 1042-9964 1042-9964 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 42ND ANNUAL MEETING MAY 15 - 19, 1996 CABLE, WISCONSIN CABLE, SPONSORED BY: SPONSORED BY: U. S. S. GEOLOGICAL GEOLOGICAL SURVEY SURVEY AND UNIVERSITY OF WISCONSIN WISCONSIN - OSHKOSH UNIVERSITY OF PROCEEDINGS PROCEEDING S VOLUME 42 1----PROGRAM PART 1 PROGRAMAND AND ABSTRACTS ABSTRACTS EDITORS: LAURELG. G. WOODRUFF, WOODRUFF, U. U. S. GEOLOGICAL SURvEY,ST. ST.PAUL, PAUL,MN MN GEOLOCICAL SURVEY, LAUREL SUZANNE W. NICHOLSON, NICHOLSON, U. U. S.S.GEOLOGICAL GEOLOGICAL SURVEY, SURVEY,RESTON, RESTON,VA VA �CONTENTS Part 1 Program and Abstracts Institutes onLake Lake Superior SuperiorGeology Geology to to 1996 1996 Institutes on onLake Lake Superior Superior Geology Geology Constitution of the the Institute Instituteon Constitution of i ii Institute on on Lake Lake Superior Superior Geology Geology By-Laws of the Institute iii .iii and Field Field Trip Trip Guidebooks Guidebooks Index of Proceedings Proceedings Volumes Volumes and .iv iv Award Guidelines Guidelinesfor for Sam Sam Goldich Goldich Medal Medal Award ix Board of Directors x Local Local Committees xX Student Paper Committee xi Session Chairs xi Goldich Medal Committee xi 1996 1996 Goldich Goldich Medal Recipient xii Past Goldich Goldich Medalists xii Banquet Speaker xii 1996 1996 Goldich Goldich Medal Recipient Citation xiii Student Travel Award xv Chair of of the 41st Annual Institute Report of the Chair xvi Calendar of Events and Program xxi Abstracts 11 �ON LAKE LAKE SUPERIOR GEOLOGY INSTITUTES ON GEOLOGY INSTITUTE DATE INSTITUTENUMBER NUMBER DATE 11 1955 1956 1956 1957 1958 1959 1959 1960 1960 1961 1961 1962 1963 1963 1964 1965 1966 1966 1967 1968 1969 1969 1970 1971 1972 2 3 4 55 6 77 8 99 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 1973 '---1973 1974 L-1975 L--l975 L—1976 1...---1976 1977 L— L-- ~ c_ — 1978 1978 1979 1980 1980 L-1981 t.<1981 1982 1983 — 1983 <.--1.984 -1984 1985 1985 L __ t—1986 v--1986 t 1987 1987 \.--1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1994 1994 1995 1995 1996 PLACE Minneapolis, Minnesota Houghton, Michigan East Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Arthur, Ontario Houghton, Michigan Michigan Duluth, Minnesota Ishpeming, Michigan St. St. Paul, Paul, Minnesota Ste. Marie, Marie, Michigan Sault Ste. East Lansing, Michigan Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Ste. Marie, Marie, Ontario Ontario Sault Ste. Marquette, Michigan St. Paul, Minnesota St. Thunder Bay, Thunder Bay, Ontario Milwaukee, Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Michigan Wausau, Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wawa, Ontario Marquette, Michigan Duluth, Minnesota Thunder Thunder Bay, Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Cable, Wisconsin CHAIRMAN CE. Dutton C.E. Dutton A.K. Sneigrove AK. Snelgrove B.T. Sandefur B.T. Sandefur RW. Marsden G.M. G.M. Schwartz Schwartz & & C. C. Craddock Craddock E.N. Cameron E.N. Cameron E.G. Pye A.K. Sneigrove AK. Snelgrove H. Lepp A.T. Broderick AT. P.K. P.K. Sims Sims & & R.K. R.K.Hogberg Hogberg R.W. White RW. White W.J. Hinze Hinze W.J. A.B. A.B. Dickas LaBerge G.L. laBerge & E. Mercy M.W. Bartley & D.M. D.M. Davidson J. J. Kalliokoski M.E. Ostrom M.E.Ostrom P.E. Giblin J.D. Hughes Hughes J.D. M. Walton M.M. Kehlenbeck Kehienbeck G. Mursky D.M. Davidson D.M. Davidson P.E. Meyers W.C. Cambray W.C Cambray D.L. D.L. Southwick Southwick T.}. Bornhorst T.J. G.L G.L. LaBerge laBerge C.E. Blackburn CE. J.K. Greenberg J.K. Greenberg E.D. Frey Frey & & R.P. R.P. Sage E.D. }.S.Klasner 1. S. Kiasner J.C. J.C Green M.M. Kehienbeck M.M. Keh1enbeck P.E. Meyers P.E. A.B. Dickas AB. D.L. Southwick D.L. Southwick T.J. Bornhorst Bornhorst T.J. M.C. M.e. Smyk L.G. Woodruff L.G. Woodruff �__________ CONSTITUTION OFTHE THE INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR GEOLOGY GEOLOGY CONSTITUTION OF Article I Name ~ on Lake Lake Superior Geology'. Geology". The name of the organization shall be the "Institute 'Institute on Article II Objecti yes Objectives The objectives of this organization organization are: A. To A. Toprovide provideaameans meanswhereby wherebygeologists geologists in in the the Great Great Lakes Lakes region may exchange exchange ideas and and scientific scientific data. B. To promote better understanding Lake Superior Superior region. region. understanding of of the the geology of the Lake C. To plan and conduct conduct geological geological field trips. Article III Status ~ No part of shall insure insure to to the the benefit of any member or of the the income income of the organization organization shall individual. In In the theevent eventof of dissolution dissolution the assets of of the the organization organization shall shall be be distributed distributed organization). to (some tax free organization). (To avoid avoid Federal taxes, the the organization organization should should be not (To Federal and and State State income income taxes, not only only "scientific" butalso also "non-profit".) "non-profit".) "scientific" or or "educational, 'educational, but 290.Q1, subd. subd. 44 Minn. Stat. Anno. Anno. 290.01, Minn. Stat. Stat. Anno. Anno.290.05(9) 290.05(9) 1954 RevenueCode Codes.501(c)(3) s.501(c)(3) 1954 Internal Internal Revenue IV Article [V Membership of the the organization shall consist of the The membership of the board. board.of ofdirectors; directors. Any geologist interested shall be permitted to attend and participate in and vote at the the annual annual meetings. meetings. Article V Meetings The organization shall year, preferably preferably during during the the month of April. April. The shall meet once aa year, The place place and exact exact date date of of each meeting will be designated by the board of directors. Article VI VI Directors The board of of directors directors shall shall consist consist of the Chairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and the last last three past Chairmen; but ifif the board should should at any time of fewer than five three Chairmen; but the board time consist consist of fewer than five or inability inability of of any any of of the the above above persons persons to to serve as as persons, by reason of unwillingness unwillingness or directors, the the vacancies vacancies on the board may be filled filled by the annual meeting meeting so so as as to to bring bring the membership of of the the board up up to to five five members. Artide VII Article VII Officers The officers of this this organization shall be a Chairman Chairman and Secretary-Treasurer. A. The A. TheChairman Chairmanshall shallbe beelected elected each each year year by by the board of directors, who shall give due consideration to to the the wishes wishes of of any any group group that that may may be be promoting promoting the the next next annual annual consideration meeting. His will terminate terminate at at the close close of of the the ann.ual annual meeting. His term term of of office office as Chairman Chairman will meeting over which he presides or when his his successor successor shall have been been appointed. appointed. He will then serve for a period of three years as a member of the board board of of directors. directors. B. The The Secretary-Treasurer Secretary-Treasurershall shallbe beelected electedatatthe theannual annual meeting. meeting. His His term term of of office office be two years or until his his successor successor shall shall have have been beenappointed. appointed. shall be 11 ii �Article VIII VIII Amendments of those those persons persons who who are are personally This constitution may may be be amended amended by by a majority vote of present the organization. organization. present at, at, participating participating in, in, and and voting voting at at any annual meeting of the BY-LAWS I. Duties of the Officers Qfficers and Directors Directors duty of of the the Annual Annual Chairman Chairman to: to: A. It shall be the duty 1. Preside 1. Presideat atthe the annual annual meeting. meeting. 2. Appoint 2. Appointall allcommittees committees needed needed for for the the organization of the annual meeting. 3. Assume Assumecomplete completeresponsibility responsibility for for the the organization and financing financing of the annual meeting over over which which he he presides. presides. meeting B. It shall be the duty duty of of the the Secretary-Treasurer Secretary-Treasurer to: to: 1. Keep 1. Keep accurate accurateattendance attendancerecords recordsof ofall all annual annual meetings. meetings. 2. Keep and correspondence between, the board 2. Keep accurate accurate records records of of all all meetings meetings of, and of directors. 3. Hold Holdall allfunds fundsthat thatmay mayaccrue accrueas as profits profits from from annual meetings meetings or or field field trips trips and and to and operation operation of of future to make make these these funds funds available available for for the organization organization and meetings as required. to plan locations locations of of annual annual meetings meetings and C. It shall be the duty of the board of directors to to advise on the organization and financing of all meetings. the organization and financing of all II. and Expenses Expenses Duties and 1. 2. III. There shall be no regular membership dues. Registration for the the annual annual meetings shall be be determined determined by by the the Chainnan Chairman in Registration fees fees for meetings shall consultation with the board of directors. directors. ItIt is is strongly strongly recommended recommended that these be kept at a minimum to encourage attendance of of graduate graduate students. students. Rules of Order The rules contained in in Robert's Robert's Rules Rules of Order shall govern this this organization organization in in all all cases cases to which they are applicable. IV. Amendments These by-laws may be amended by those persons persons who are personally by a majority majority vote of those present at, participating present participating in, and voting voting at at any any annual annual meeting meeting of of the the organization; organization; with the the constitution constitution as as presently provided that that such such modifications modifications shall shall not conflict conflict with presently adopted adopted or or subsequently subsequently amended. 111 iii �AND FIELD FIELDTRIP TRIP GUIDEBOOKS GUIDEBOOKS INDEX OF PROCEEDINGS VOLUMES VOLUMES AND OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY 1955-1996 Compiled by Mark MarkJirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer,LLSG ILSG Compiled by ** Denotes abstracts volumes and and guidebooks guidebooks which which can can be ordered ordered from from the the Secretary-Treasurer. Secretary-Treasurer. 2642 University UniversityAvenue, Avenue,St. St.Paul, Pau"MN, MN,55114-1057, 55114-1057,Phone: Phone:(612)-627-4539, (612)-627-4539,fax: fax:612-627-4778, 612-627-4778, jirsaOO1@maroon.tc.umn.edu e-mail: jirsa001@maroon.tc.umn.edu as author, author, editor, editor, chairperson, chairperson, and and sponsoring sponsoring organization A complete list containing such information as maintained by erson Spence, archivist at byMs. Ms.Theresa TheresaSand Sanderson at the the J. Robert Van Pelt Library, Michigan is maintained Photocopiesof ofback backvolumes volumes can can be be Technological University, University, Houghton, Houghton,MI MI49931 49931 (906-487-2505). (906-487-2505). Photocopies ordered from copy rate. rate. Some guidebooks guidebooks were published ordered from Ms. Ms. Sanderson Sanderson Spence at the prevailing copy separately by and Wisconsin Wisconsin Geological Geologicaland and Natural History separately by the theMinnesota MinnesotaGeological Geological Survey Survey (MGS), (MGS), and History Survey (WGNHS), as indicated indicated below; below; however, most are no longer available. (Each italicized item is aa separate bound document) LOCATION 1 1955 MINNEAPOLIS, MINNESOTA Program Abstracts(contains (contains no no record record of of field field trips) Program and Abstracts HOUGHTON, MICHIGAN 2 1956 Program and Abstracts Geological GeologicalExploration Exploration(inferred (inferred to tobe beaa field field guide) guide) 3 1957 EAST EAST LANSING, MICHIGAN Program and Abstracts 4 1958 DULUTH, MINNESOTA Program and Abstracts Abstracts 55 1959 MINNEAPOLIS, MINNESOTA Program and Abstracts 6 1960 MADISON, WISCONSIN Program and Abstracts 7 PORT ARTHUR, ONTARIO 1961 Program ted label reads reads 6th annual meeting) Program and and Abstracts Abstracts(misprin (misprinted 8 1962 HOUGHTON, MICHIGAN Program and Abstracts 9 1963 DULUTH, MINNESOTA Program and Abstracts Itinerary: Stratigraphy Stratigraphyofofthe theBiwabik Biwabik Iron Iron Formation Formation Field Itinerary: 10 1964 ISHPEMING, MICHIGAN Program and Abstracts Abstracts Field Trip: Marquette iron-mining iron-mining district district and and Republic Republic trough 11 1965 ST. PAUL, PAUL, MINNESOTA Program and Abstracts Gaud granite district, central Minnesota Field Trip Guide to the St. Cloud VOL. YEAR YOL, YEAR 12 1966 SAULT STE. MARIE, ONTARIO Program and and Abstracts Abstractsincludes includesfield field guides to: Regional geology geologyof ofthe theSault SaultSte. Ste. Marie Marie area area 1. Regional 2. 2. Geology Geology and and mineral mineral deposits deposits of of the the Manitouwadge Manitouwadge Lake Lake area, Ontario 3. The River area, area, Ontario Ontario 3. The relationship relationship of of mineralization mineralization to to the Precambrian stratigraphy, Blind River 4. Sudbury Sudbury nickel nickel irruptive irruptive tour, tour, Ontario Ontario 4. iv �13 14 15 16 17 17 18 19 1967 EAST LANSING, MICHIGAN Program and Abstracts . Field Trip: Grenville Province of of southeastern Ontario, Bancroft-Madoc Bancroft-Madoc area area 1968 SUPERIOR, WISCONSIN Technical Sessions and Abstracts Guide for Field Field Trip Trip in the Duluth Minnesota Guidefor Duluth Complex Complex near Ely, Ely, Minnesota 1969 OSHKOSH, WISCONSIN Technical Sessions Sessions and and Abstracts Technical Guidebook: Central Wisconsin Wisconsin volcanic volcanic belt belt Guidebook: 1970 THUNDER BAY, ONTARIO THUNDER BAY, Technical Sessions, Abstracts and and Field Field Guides Field trips: A. Proterozoic formations formations in in the the Thunder ThunderBay Bay area A. Proterozoic B. Sturgeon River metavolcanic-metasedimentary formations in the Beardmore-Geraldton area B. Sturgeon C. The The Port PortCoidwell Coldwell alkalic alkalic complex complex D. Geology D. Geology of of the the Atikokan Atikokan area area (title (title not not exact) exact) 1971 DULUTH, MINNESOTA Technical Sessions, Sessions, Abstracts and Field Field Guides Field trips: A. A. North NorthShore ShoreVolcanic Volcanic Group Group B. Precambrian Precambrian rocks rocks of of northwestern northwestern Cook Cook County County as as exposed along the Gunflint Trail B. C. Mesabi C. Mesabi Range Range magnetite magnetite taconite taconite D. D. Geology Geology of of the the Vermilion Vennilion metavolcanic-metasedimentary metavolcanic-metasedimentary belt, northeastern Minnesota 1972 HOUGHTON, MICHIGAN Part Part I.1. Technical Technical Sessions-Agenda Sessions-Agenda and Abstracts (describes (describes trips A-D) Field Trips: A. Penokean A. PenokeanOrogeny Orogenyin inthe thecentral centraland andwestern westernGogebic Gogebic region, region, Wisconsin Wisconsin and Michigan Michigan B. B. Guide to to Penokean deformation style and regional metamorphism at the western Marquette Marquette Range, Michigan 1973 WISCONSIN MADISON, WISCONSIN Technical Program and and Abstracts* Abstracts" Field Trip: Field Trip: Guidebook Guidebook to the geology and and mineral deposits of the the central central part of Jackson Jackson County County and and part of Clark County, Wisconsin (WGNHS) part of Clark County, Wisconsin (WGNHS) Field Trip:Guidebook Guidebook to to the the Precambrian Precambrian geology geology of ofnortheastern northeastern and north-central Field Trip: north-eentral Wisconsin Field Trip:Guidebook Guidebook to the upper upper Mississippi Field Trip: Mississippi Valley Valley base-metal district district (WGNHS (WGNHS Information Information circular No. 16) circular No. 16) of Current Research inin the theLake Lake Superior Superior Region Region Bibliography of Current Research 20 SAULT STE. MARIE, MARIE, ONTARIO 1974 Field Trip 1: 1: Middle Keweenawan Keweenawan rocks rocks of of the the Batchawaria-Mamainse Batchawana-Mamainse Point area FieldTrip Trip2:2: unknown Field Field Trip 3: 3: Precambrian igneous rocks rocks of the north shore of Lake Lake Huron Huron region Field Trip 4: Stratigraphy and and sedimentation sedimentation of of the Huronian Huronian Supergroup Supergroup Field Trip5:5: The Michipicoten greenstone belt Field Trip Bibliography of Current Current Research Region (First (First Supplement) Supplement) Research in the the Lake Lake Superior Region 21 1975 MARQUETFE, MARQUETTE, MICHIGAN Proceedings Includes the following field trip guides and and aa supplement supplementby by Burton Burton Boyum Boyum containing containing aa color color map of the Marquette Marquette Mineral Mineral District: District 1. Glacial 1. Glacial geology (trip canceled, no guidebook) 2. Greenstone 2. 3. The The Jacobsville Jacobsville Sandstone: Sandstone: Evidence Evidence for a Lower-Middle Keweenawan age 4. Marquette Marquette Iron Iron Range Range 5. and 6. 6. The TheEmpire EmpireMine Mineand andMill, Mill,Palmer, Palmer, Michigan Michigan vV �22 23 24 25 26 27 28 29 1976 ST. PAUL, PAUL, MINNESOTA Proceedings Includes abstracts abstracts and and guide guidetotoField Field Trip Trip BB (no formal formal guidebook guidebook printed) Field Trip A: Minnesota Minnesota River River Valley Valley field conference (no printed) Field Trip B: B: Engineering Engineering and and Pleistocene Pleistocene geology in the Twin Cities area 1977 THUNDER BAY, BAY, ONTARIO THUNDER Proceedings Field Field Trip Trip AA Geology of the Coldwell alkaline Complex Field Trip Proterozoic rocks rocks of of the the Thunder Thunder Bay Bay area, northwestern northwestern Ontario Ontario("Proterozoic ("ProterozoicTrip") Trip") Field Trip BB Proterozoic Field TripCC Archean metallogeny and stratigraphy Field Trip stratigraphyof ofthe theSouth South Sturgeon SturgeonLake Lake area area ("Mattabi ("Mattabi Trip") Trip") MILWAUKEE, WISCONSIN 1978 MILWAUKEE, Abstracts and and Proceedings Proceedings Abstracts Field Trip II Southwestern Field Trip Trip Guide Guide Book Book Number Number 1) Field Trip Southwestern Wisconsin Wisconsin zinc-lead zinc-lead district district(WGNI-IS (WGNHS Field FieldTrip TripIIII Mineral Mineral extraction extractionand and processing processingequipment equipment manufacturers manufacturers in the Greater Milwaukee Field area (no guidebook) FieldTrip TripIII III Precambrian rhyolite and Field and granite graniteinliers inliersin insouth-central south-eentralWisconsin Wisconsin(WGNI-IS (WGNHS Field Field Trip Guide Book Book Number 2) 1979 DULUTH, MINNESOTA TechnicalSessions Sessionsand andAbstracts AbstractsJoint Joint meeting meeting with with North-Central Technifal North-eentral Section SectionGSA. GSA. Field Trip Guidebooks: some some were were published publishedseparately separatelyas as MGS MGS Guidebook Guidebook Series referenced below, the remainder are apparently apparently unavailable. unavailable. AAtotal total of of eight eight trips trips were were listed listed in in GSA GSA proceedings: 1. Middle 1. Middle Precambrian Precambrian volcanic volcanic and plutonic plutonic rocks rocks of northern northern Wisconsin 2. Stratigraphy, Stratigraphy,structure structureand andmineral mineralresources resourcesofofeast-central east-eentralMinnesota Minnesota(MGS (MGS Field Field Trip no.9) 9) Guidebook Series Series no. 3. Quaternary 3. Quaternarygeology geology of of the Duluth area 4. Geology 4. Geology of of the the Mesabi Mesabi Iron Range 5. Geologic Geologic history history and and engineering engineeringgeology geology of of the the western Lake-Superior Lake-Superior region 6. Cambrian 6. Cambrian and and Ordovician Ordovician stratigraphy stratigraphy and and paleontology paleontology of southeastern Minnesota 7. Keweenawan Keweenawan(Upper (UpperPrecambrian) Precambrian)North NorthShore ShoreVolcanic VolcanicGroup, Group,Minnesota Minnesota(MGS (MGS Field Field Trip Trip Guidebook no. 11) Guidebook no. 11) 8. Archean District, northeastern northeastern 8. Archean volcanism volcanism and and sedimentation sedimentation of of the the western western Vermilion District, Minnesota Guidebook Series (MGS Guidebook Series no. 10) 10) Minnesota (MGS 1980 EAU EAU CLAIRE, CLAIRE, WISCONSIN WISCONSIN Proceedings and Abstracts Trip 1 I Precambrian Field Trip Precambrian geology geology of of the Chippewa Chippewa Valley, Valley, Wisconsin Field Trip 22 Precambrian Precambriantectonic tectonichistory historyofofthe theBlack BlackRiver River Valley Valley the Wausau Wausau and Stettin syenite plutons, Field Trip 3 Petrology, geochemistry, and contact relations of the Central Wisconsin Field Trip44 Precambrian geology and tectonics of Marathon County, Wisconsin Field Trip EAST LANSING, LANSING, MICHIGAN 1981 EAST Abstracts and Proceedings Proceedings Field Field Excursion ExcursionGuide GuideThe TheHuronian Huronian rocks rocks between between Sault Sault Ste. Ste. Marie Marieand and Thessalon, Thessalon, District of Algoma, Ontario 1982 INTERNATIONAL INTERNATIONAL FALLS, FALLS, MINNESOTA Proceedings: Abstracts Abstracts and and Field FieldTrips Trips(in (inone one volume) volume) Proceedings: Field Trip I Mineral Mineral deposits depositsof ofthe the Fort Fort Frances-Mine Frances-Mine Centre area, Ontario Field Trip II Archean Archean geology geology of of the the International International Falls-Kabetogama Falls-Kabetogama area, Minnesota 1983 HOUGHTON, MICHIGAN VolumeI:I: Abstracts Abstracts and Field Trip -- Ropes gold mine and its Volume its geological setting Volume VolumeII:II: Field Field guide guide to the geology of the Keweenaw Peninsula Vl vi �30 1984 WAUSAU, WISCONSIN Abstracts Field Trip I1 Guide to Proterozoic rocks rocks in in northeastern northeastern Wisconsin to the the geology geology of the Early Proterozoic Field Trip 22 Early Proterozoic tectonostratigraphic terranes terranes of of the the southern southern Lake Lake Superior Superior region region Field Trip33 The Field Trip The Wausau Wausau Syenite Syenite Complex 31 1985 KENORA, KEN ORA, ONTARIO Abstracts Field Trip Guidebook Guidebook 1. The Cameron 1. Cameron Lake Lake Deposit 2. Geologic Geologic setting settingand andstyle styleof ofgold gold mineralization mineralizationininthe theLake Lake of of the the Woods Woods area area 3. Geological River subprovincial subprovincial Geological relationships relationships in in the the vicinity vicinity of the Wabigoon-Winnipeg Wabigoon-Winnipeg River interface in the Kenora area 4. A A volcanic volcanic facies facies interpretation interpretationof ofthe the Berry Berry River River Formation 5. Granitoid Granitoid related related mineralization mineralization in in the the Dryden area 32 1986 WISCONSIN RAPIDS, RAPIDS, WISCONSIN Abstracts* Abstracts· Field Field Trip Trip[I The Wolf and Baraboo Baraboo interval interval (published (published as Field Field Trip Trip Guide Book Wolf River Batholith and Number Number 12, 12, Wisconsin Geological and Natural History History Survey) Survey) Field TripIIII Penokean Field Trip Penokean deformation deformationand andmetamorphism metamorphisminincentral central Wisconsin: Wisconsin: volcanic volcanic rocks and gneisses (published as un-numbered un-numberedField Field Trip Trip Guide Guide Book Book of the Wisconsin Geological and and Natural History Geological History Survey) Survey) ia ~ (compiler note: new newreference referencedesignations designationswere wereadopted adoptedtotoconform conformto to ISSN ISSN standards standardsin in1987) 1987) WAWA, ONTARIO ONTARIO 33 1987 WAWA, Part Part 1: 1: *• Abstracts Part 2: and gold mineralization Part 2: *• Geology of the Wawa area and Part Part 3: 3: *"" Geology and stratigraphy stratigraphyof of the the Michipicoten Michipicoten Iron-Formation Iron-Formation Part Part 4: 4: *"" Geology of the Hemlo Deposit Part Part 5: 5: *"" The Kapuskasing Uplift: Uplift: Archean Archean greenstones and granulites 34 MARQUEITE, MICHIGAN 1988 MARQUETTE, Part 1: Part 1: *"" Abstracts 2: Field Part 2: Field Trip Guidebook 1. An the Marquette 1. An introduction introductionto to Archean Archean geology geology and precious precious metal mineralization of the Greenstone Belt, Greenstone Belt, Michigan 2. Marquette Marquettemineral mineraldistrict districtofofMichigan, Michigan, mining mining history history and and geology geology partof of the the Penokean Penokean orogen illustrating Early Proterozoic 3. A A structural structuraltraverse traverseacross acrossaa part overthrusting in overthrusting in northern northern Michigan Michigan 35 DULUTH, MINNESOTA 1989 1: Abstracts Part 1: 2: Field Trip Guidebook Part 2: 1. North Shore Shore rhyolites, rhyolites, Minnesota Minnesota 1. North 2. Penokean PenokeanStructural StructuralTerranes Terranesin ineast-central east-eentralMinnesota Minnesota 3. Mellen Mellen Complex, Complex, Wisconsin Wisconsin Archean gold gold occurrences occurrences and and their their structural structural settings settings (Virginia (Virginia Hom) 4. Archean Horn) 36 1990 THUNDER BAY, ONTARIO THUNDER BAY, Part 1: Abstracts Part 2: Field Trip Guidebook 1. Mafic intrusions, 1. intrusions, PGE PGE mineralization, mineralization, and and granitoid granitoidrocks rocks of of Lac Lac des Illes Illes area Geology of of the the Shebandowan Shebandowan and andQuetico Quetico Archean Archean subprovinces subprovinces 2. Geology 3. Granitoid-related Granitoid-relatedmineral mineraldeposits depositsin inthe the western westernLake Lake Superior region 4. Base 4. Base metal mineralization mineralization in in the the Shebandowan Shebandowan Greenstone Greenstone Belt Belt vii VB �CLAIRE, WISCONSIN WISCONSIN 1991 EAU CLAIRE, Part Part 1: 1: *"" Abstracts Part 2: 2: *"" Field Trip Guidebook 1. 1. Mountain Mountain Shear Shear Zone Zone --- a post Penokean discrete ductile ductile deformation deformation zone Features and andsignificance significance of of the the Precambrian-Cambrian Precambrian-<:ambrian contact in western 2. Features western Wisconsin 3. Proterozoic Proterozoicvolcanogenic volcanogenic massive massivesulfide sulfidedeposits depositsof ofNW NW Wisconsin Wisconsin 38 1992 HURLEY, HURLEY, WISCONSIN WISCONSIN Part 1: 1: *"" Program and Abstracts Abstracts Part Part 2: 2: *"" Field Trip Guidebook 1. Archean Archean and andEarly EarlyProterozoic Proterozoicgeology geologyof ofthe the Gogebic Gogebic District District 2. Evolution 2. Evolution of of the Keweenawan sedimentary sequence 3. Geology Geology of of the the Keweenawan Supergroup Supergroup at at Porcupine Mountains 4. Geology late Archean Archean paleosuture paleosuture Geologyof of the theGreat GreatLakes Lakes Tectonic Tectonic Zone-Marquette area -- a late 39 1993 EVELETH, EVELETH, MINNESOTA MINNESOTA Part Part 1: 1: *"" Program and Abstracts Abstracts Part Part 2: 2: *"" Field Trip Guidebook: 1. Geology Geology and and taconite taconite mines mines of of the the Mesabi Mesabi range 2. DNR Core Library Library (Biwabik Iron 2. DNR Iron Formation, Formation, Partridge Partridge River Riverand and South South Kawishiwi Kawishiwi intrusions, intrusions, Regolith in Rotasonic cores-northern Minnesota) 3. Geology Geologyof of Archean Archean greenstone-granite greenstone-graniteterrane: terrane:Cook-Side Cook-Side Lake Lake area area Duluth Complex Complex at Duluth Duluth 4. Duluth 40 1994 HOUGHTON, MICHIGAN Part 1: 1: *"" Program and Abstracts Part Part 2: 2: *"" Self-guided geological field field trip to the Keweenaw Peninsula, Michigan (available from Dr. T.]. Bornhorst, 402 Emerald EmeraldStreet, Street,Houghton, Houghton,MI MI49931-1413 49931-1413(906-482-5507)) (906-482-5507» T.J. Bomhorst, 402 Part 3: Volcanic Volcanic geology geology of of eastern easternIsle IsleRoyale, Royale, Michigan Michigan Part Part 4: 4: *"" Michigan kimberlites and diamond diamond exploration exploration techniques techniques Part Part 5: 5: *"" Lessons from mining mining case case histories: West West Menominee Range, Michigan Michigan 41 1995 MARATHON, ONTARIO 1995 Part 1.* 1. "" Program Program and Abstracts Abstracts Part 2: Field Field Trip Trip Guidebooks Guidebooks (some (some may may also also be acquired from Ontario Geological Survey, Ministry 002,435 of Northern Northern Development Developmentand andMines, Mines,Field FieldServices Services Section, Section, Suite Suite B B 002, 435 South James Street, Thunder ThunderBay, Bay, Ontario OntarioCanada, Canada,P7E P7E6E3, 6E3,Phone: Phone:807-475-1331) 807-475-1331) 2a.* 2a. "" Alkalic Alkalic rocks rocks of the Midcontinent Midcontinent Rift Rift 2b.* 2b."" Geology and base metal deposits of the Manitouwadge Greenstone Greenstone Belt Belt 2c. Schreiber Greenstone Greenstone assemblage assemblage and and itit gold gold and and base metal mineralization 2e. *"" Geology of the Schreiber 2d. 2d. Geology Geologyand andgold golddeposits depositsof of the the Hemlo HernIo area 2e.* overburden, Wawa 2e. "" Kimberlite, base metal, and gold exploration using overburden, Wawa area area CABLE, WISCONSIN 1996 42 1996 CABLE, WISCONSIN Part 1: 1: Program Program and and Abstracts Abstracts 2: Volcanogenic Volcanogenic Massive Massive Sulfide Deposits Part 2: Deposits of of Northern Northern Wisconsin: Wisconsin: A Commemorative Volume (published (published in in conjunction conjunction with with Field Field Trip Trip 3 to the Flambeau Flambeau Mine) Mine) Part 3: 3: Field Field Trip Guidebook 1. Glacial 1. Glacial geology geology of western western Wisconsin Wisconsin 2. Geology Geology of of the the Montreal Montreal River River Monocline: Monocline: A A traverse traverse through through25 25 km km of of crust crust 4. Early Early to to Middle Middle Proterozoic Proterozoic geology geology of of the the Lake Lake Namekagon region Lake Namekagon Namekagonand andPenokee PenokeeGap Gaparea, area,west westGogebic Gogebic Range, Range, Wisconsin 5. Lake Future Meeting Meeting Locations: Locations: 1997 SUDBURY, ONTARIO ONTARIO 43 1997 1998 KENORA, 44 1998 KEN ORA, ONTARIO 37 37 vu' viii �AWARD GUIDELINES SAM GOLDICH G0LDIcH MEDAL SAM MEDAL Preamble Lake Superior Geology was born bom on or around 1955, 1955, as The Institute on Lake as documented documented by by the fact fact that the meeting was was held held in in 1981. 1981. The The Institutes Institutes are are exemplary exemplary in in their their continuing continuingobjectives objectives of of 27th 27th annual meeting encouraging the with those those aspects aspects of of geology geology that that are are related related geographically to Lake Superior; of encouraging dealing with subjects and sponsoring sponsoring field field trips which will will bring together geologists geologists from discussion of subjects from academia, academia, government government surveys, surveys,and andindustry; industry;and andof ofmaintaining maintainingan an exceedingly exceedingly informal but highly effective mode of operation. During the the course course of of its its existence existence the membership membership of of the the Institute Institute (that (that is, is, those those geologists geologists who who indicate indicate by attending) attending) has has become become aware aware of the fact fact that certain of their an interest interest in In the the objectives objectives of of the the I.L.S.G. I.L.S.G. by colleagues contributions to to the improvement of colleagues have made particularly particularly noteworthy and meritorious meritorious contributions understanding of"Lake "Lake Superior" Superior" geology and its mineral deposits. understanding of The exemplary award award was wasmade madeby byI.L.S.G. I.L.S.G. to to Sam Sam Goldich Goldich in 1979 1979 for to the the for his his many contributions to geology of the region extending extending over over about about 50 50 years. Award Guidelines 1) 1) Directors to to aa geologist whose name The medal shall shall be be awarded awardedannually annuallyby bythe theI.L.S.G. I.L.S.G. Board of Directors with aa substantial substantial interest interest in, in, or or aa major major contribution contribution to, to, the the geology geology of of the the Lake Lake is associated with Superior region. region. 2) Directors, LL.S.G. appointment The Board of Directors, LL.S.G.shall shallappoint appointthe theNominating NominatingCon::unittee. Conmittee. The initial appointment will be of three one for three members, members, one to to serve serve for for three three years, years, one for two, and one one for for one one year, year, the the member with with the the briefest briefest incumbency incumbency to to be be chairman. After After the the first first year yearthe theBoard Boardof ofDirectors Directors shall appoint who will will serve serve for forthree three years. years. In the third appoint at at each each spring spring meeting meeting one new member member who year this this member member shall shall be be the the chairman. chairman. The The Committee Committee membership membership should should reflect reflect the the main main fields fields of interest and geographic geographicdistribuhon distributionofofI.L.S.G. LL.S.G. membership. membership. interest and 3) By Committee shall shall make make its its recommendation to the By November 1, I, the Goldich Medal Nominating Committee the Chairman of Chairman of the the Board Board of of Directors Directors who who will will then then inform inform the the Board Board of of the nominee. nominee. 4) the Committee, will inform the medalist The Board of Directors normally will accept the nominee of the medalist immediately, and and will will have have one one medal medal engraved engraved appropriately for for presentation presentation at at the the next next meeting meeting of the Institute. 5) It is recommended that that the the Institute Institute set set aside annually from whatever sources, such funds as will be required to support supportthe thecontinuing continuingcosts costs of of this this award. required to April 4, 1981 1981 April 4, J. Kalliokoski, Kalliokoski, Chairman Bill Cannon Bill Cannon Fred Kehlenbeck G.B. Morey Greg Mursky ix IX �BOARD OF DIRECTORS 1996 Laurel G. Woodruff, Chair U. S. Geological Survey, St. Paul, Minnesota Minnesota 1995 Mark C. Smyk Ontario Ontario Geological Geological Survey, Thunder Thunder Bay, Bay, Ontario 1994 Theodore J. Bornhorst Michigan Technological University, University, Houghton, Houghton, Michigan 1993 David L. Southwick Minnesota Geological Survey, St. St. Paul, Minnesota Permanent Secretary-Treasurer Permanent Secretary-Treasurer Mark Mark Jirsa Minnesota Geological Survey 2642 University Ave. 2642 University MN55114-1 55114-1057 St. Paul, Paul, MN 057 LOCAL COMMITTEES GENERAL CHAIR Laurel G. Woodruff U. S. Geological Survey, St. Paul, Minnesota PROGRAM COMMITTEE Laurel G. Woodruff, U. S. S. Geological Geological Survey, Survey, St. St. Paul, Paul, Minnesota Suzanne W. W. Nicholson S. Geological Geological Survey, Reston, Virginia U. S. FIELD TRIP COMMITTEE Gene Gene L. L. LaBerge LaBerge University of University of Wisconsin-Oshkosh, Wisconsin-oshkosh, Oshkosh, Wisconsin William William F. F. Cannon U. S. S. Geological Survey, Survey, Reston, Virginia SECRETARY-TREAS URER SECRETARY-TREASURER Sally LaBerge LaBerge University of University of Wisconsin-Oshkosh, Wisconsin-Gshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin x �STUDENT PAPER PAPER COMMITTEE COMMITrEE Jirsa Mark Jitsa Minnesota Geological Minnesota Geological Survey, Survey, St. St. Paul, Paul, Minnesota Minnesota Suzanne Nicholson U. S. S. Geological Geological Survey, Reston, Virginia SESSION CHAIRS Glen Adams Consulting Consulting Geologist, Geologist, Rhinelander, Rhinelander, Wisconsin Wisconsin Terry Boerboom Minnesota Geological Survey, St. Paul, Minnesota Sidney Hemming Lamont-Doherty Earth Earth Observatory, Observatory, Palisades, Palisades, New York York Mark Jirsa Minnesota Geological Geological Survey, Survey, St. Paul, Minnesota Minnesota Suzanne Nicholson U. S. S. Geological Geological Survey, Reston, Virginia Edward Ripley Indiana University, University, Bloomington, Bloomington, Indiana Ron Sage Ontario Geological Survey, Sudbury, Ontario Ontario Ontario Klaus Schulz S. Geological Geological Survey, Reston, Virginia U. S. Mark Smyk Ontario Geological Ontario Geological Survey, Survey, Field Field Services Services Section, Thunder Bay, Bay, Ontario Ontario 1995-96 GOLDICH 1995-96 GOLDIeH MEDAL MEDAL COMMITrEE COMMITTEE Penelope Morton (1996) (1996) University of Minnesota-Duluth, Duluth, Minnesota Ken Card Ca.rd (1997) (1997) Ontario Geological Ontario Geological Survey Survey (retired), (retired), Kanata, Ontario Ontario Dan England England (1998) (1998) Eveleth Fee Office, Incorporated, Eveleth, Minnesota xi �1996 GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT David L. 1. Southwick Minnesota Geological Survey University of Minnesota St. Paul, Paul, Minnesota St. MEDALISTS PAST GOLDICH MEDALISTS 1979 1979 1980 1980 1981 1982 1982 1983 1983 1984 1985 1986 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 Samuel S. Goldich not awarded awarded Carl E. Dutton, Dutton, Jr. Jr. Ralph W. Marsden Burton Boyum W. Ojakangas Ojakangas Richard W. Paul K. K. Sims C. G. B. Morey Henry H. Halls Walter S. Whit Walter Jorma Kalliokoski Kenneth C. Card William J. Hinze William F. F. Cannon Donald W. Davis Cedric Iverson Gene LaBerge LaBerge 1996 BANQUET SPEAKER SPEAKER 1996 BANQUET Steven Kesler Department of Department of Geological Geological Sciences University of Michigan Ann Arbor, Michigan Sustainable Mineral Development Development -- Fact or Fiction? xii Xl! �CITATION David S.S. Goldich Goldich Medal Medal Recipient David L. L. Southwick, Southwick, 1996 19965.5. It is my pleasure pleasure to to introduce introduce to to you you this this evening, evening, David David L. L. Southwick, Southwick, 17th 17th recipient for for 1996 1996 of the Institute's Institute's S.S. 5.s. Goldich medal. recipient When Laurel asked me me to to make make these she prefaced When Laurel Woodruff Woodruff asked these remarks remarks she prefaced her request by noting noting that that II had had worked worked with with Dave Dave on on several several projects and that II had had been been the Institute Institute for for many many years. years. Dave Dave and and II have have worked worked together together for many years around the been fortunate fortunate to to have have him him as as a professional colleague However, and I have been colleague and and friend. friend. However, having been around aroundthe theInstitute Institutefor for aa long long time time is is nothing nothing more more than than aa matter matterof ofluck, luck, and II now find myself writing memorials for friends who were not so lucky. Believe now find myself writing memorials friends l~cky. Believe me, this occasion occasion is is much much more more enjoyable. enjoyable. So who is Dave Dave Southwick? He He was was born bornin inRochester, Rochester, Minnesota Minnesota in in 1936 1936 and graduated from School in in 1954. 1954. He He wanted wanted to be a draftsman, graduated from Rochester Rochester Senior Senior High School but his his parents parents prevailed prevailed and and he hegraduated graduatedfrom fromCarleton Carleton College College in in Northfield, Northfield, there he he went on to graduate Minnesota with aa degree degree in in geology geology in 1958. 1958. From there graduate school school where he he studied studied under under Aaron Aaron Waters. Waters. His at the Johns Hopkins University University where His Ph.D. Ph.D. dissertation to do do with with ultramafic ultramafic rocks rocks in the Cascades Cascades of He dissertation had had to of Washington. Washington. He wondered about about ophiolites ophiolites long long before before it was was fashionable fashionable to do so. so. After graduate school, his professional professional career career with with the the U.S. U.s. Geological Geological Survey, school, Dave Dave started his Survey, Eastern States States Branch, Branch, in 1962. 1962. He He returned returned to to Minnesota Minnesota in in January, January, 1968 1968 having a joint joint appointment in the appointment the Department Department of of Geology Geology and and Geophysics Geophysics at the the University University of of Minnesota Minnesota and andthe theDepartment DepartmentofofGeology GeologyatatMacalester MacalesterCollege College in inSt. St. Paul, Paul, Minnesota. Minnesota. He moved as aa Professor Professor of of Geology. Geology. During that moved to to Macalester Macalester full-time full-time in in 1971 1971 as that time, time, Survey. He summers for for the the Minnesota Minnesota Geological Geological Survey. He began began full-time full-time work work Dave worked summers with with the the Survey Survey as asaaSenior SeniorScientist Scientist in in 1977, 1977, and has been Director of the Survey since 1993 and and Professor of Geology in the Department Department of of Geology Geology and and Geophysics Geophysics since since 1993 1994. So much for vital 1994. vital statistics. statistics. It goes without without saying saying that that receiving receiving the the S.S. S5. Goldich Goldich medal considerable medal is a considerable honor. Unfortunately, Unfortunately, II do not not know know what what criteria criteria were were used used by bythe theSelection Selection Committee when they chose to honor Dave. In fact I do not even know who sits on the they chose Dave. In I Selection Committee. Therefore, will look look toto the the medal medal itself itselffor forguidance. guidance. On the Selection Committee. Therefore, II will reverse side itit reads reads "presented "presentedfor for outstanding outstandingcontributions contributionsto tothe thegeology geologyof of the the Lake Lake What does does that that tell tell us? Superior region." What "geology" refers The word "geology" refers to to aa science science and and profession profession dedicated dedicated to to the the study of of the the Earth. Earth. Obviously Obviouslythe thescience science and andprofession profession is is practiced practiced by by geologists. geologists. the history of who study study the the history history of of the the earth earth like like to to call themselves earth These days some people who scientists rather than than geologists. geologists. II distinguish distinguish the the two two groups by by the the fact that geologists geologic maps. Looking over over the the list list of of previous previous medal medal recipients, recipients, many were make geologic maps. Looking first mappers. Dave first and foremost foremost geologic geologic mappers. Dave has has produced produced aa variety variety of of very very good good xiii �geologic Surveys. By geologic maps while with both both the the U.S. U.s. and Minnesota Minnesota Geological Geological Surveys. By that that criterion Dave Dave is is aa worthy worthy recipient recipientof of the the medal. medal. The word word "contributions" "contributions" on the medal medal refers—again refers-again in my view—to view-to any "body work" which has advanced geologic knowledge in in the the region. region. Again it seems seems to me me of work" geologic knowledge that any number for their their "bodies "bodies of ofwork" work" that number of of the the previous previous recipients recipients were honored for have included included research, research, teaching, teaching, and and above above all all professionalism. professionalism. Dave Dave has made made professional contributions in in the the areas areas of of both both research research and and teaching. teaching. His professional contributions His extensive extensive topics and and is is frequently frequently cited. cited. More importantly, bibliography covers a wide variety of topics however, there are any however, any number number of of younger younger geologists geologists in the the profession profession who who have have received basic basic training under Dave's tutelage. tutelage. Many received Many of you are in this room! room! The The fact fact that.you are here here makes makes him himaaworthy worthyrecipient recipientof of the the medal. medal. that you are significance of "outstanding" is The significance of the the word "outstanding" is somewhat subjective subjective and a little on. A is warranted. warranted. The more difficult to get aa handle on. A little little history is The medal medal is is named named in in honor of S.S. S.s. Goldich. Goldich. Many of you are are probably probably too too young young to to remember remember Sam. Sam. I have the pleasure of knowing him 40 years. years. Most him for nearly 40 Most of you have heard war stories stories about him and and many many probably probably are are true. true. After Aftermy my first first year year in in graduate graduate school school II decided that my family family had forgotten forgotten to to tell tellme methat thatmy myreal realname namewas was"Morey 'Moreyyou youstupid stupid_." _." In truth truth Sam was a wonderful man, but he could be be tough tough at at times. times. He was very much like the Drill Instructor we see on TV ads for for the the U.s. U.S.Marine MarineCorps. Corps. Sam Sam was was tough like TV ads because he he wanted wanted you you "to "to be be the the best best that that you you can can be." be." He He wanted wanted his his people to because people to excel—topush push the the envelope-at envelope—atwhatever whateverthey theydid. did. He wanted his people to excel-to to make make aa to be outstanding—to outstanding-to make a difference. difference--he wanted them to difference. Dave has excelled and has His structural and has pushed pushed the the envelope. envelope. His structural studies studies on the the Penokean Penokean orogen orogen represented aa scientific scientific revolution of sorts. sorts. His ideas have changed the way many of us for me me about about iron-formation. iron-formation. Thus think about the the rocks--and rocks--and especially especially for Thus by by Sam's Sam's geologists whose whose body body of of work work has has made made aa difference. difference. All of creed, Dave is one of those geologists him. II know us are better geologists because of him. know Sam is pleased and that makes makes Dave Dave a worthy recipient recipient of of the the medal. to present present to you the 17th worthy medal. Therefore, Therefore, I am pleased pleased to 17th s.s. Goldich metal, David David L. L. Southwick. recipient of the the S.S. G.B. Morey G.B. Minnesota Geological Survey University of Minnesota St. Paul.. Minnesota Minnesota 55114 55114 xiv �TRAVEL AWARD AWARD STUDENT TRAVEL I.L.S.G.Student StudentTravel Travel Award Award to support support The 1986 1986 Board of Directors established the I.L.S.G. student student participation participationatatthe theannual annualmeeting meeting of of the the Institute. The The awards awards will will be be made made from a special fund set up up for this purpose. This This award award is intended intended to to help help defray defray some of the direct travel travel costs costs to to the the Institute Institute and and includes includes a waiver waiver of of registration registration fees, fees, but but excludes expenses for meals, lodging, and field field trip trip registration. registration. The number number of of awards awards and value value are are determined determinedby bythe theannual annualChairman Chairmanin inconsultation consultationwith withthe theSecretarySecretaryTreasurer and and will will be be announced announced at at the the annual banquet. The following general general criteria criteria will be considered by the annual Chairman, who who is is responsible for for the the selection: selection: 1) 1) The The applicants applicants must musthave have active active resident (undergraduate or graduate) student status student statusatatthe thetime time of of the the annual meeting meeting of the Institute, certified by the department department head. head. 2) Studentswho whoare arethe thesenior seniorauthor authoron oneither either an an oral oral or or poster poster paper paper will will be be 2) Students given favored consideration. consideration. 3) It is desirable for two or more students students to to jointly request travel travel assistance. assistance. 4) In 4) Ingeneral, general,priority prioritywill willbe be given given to to those in the Institute region who are farthest away. away. 5) Each 5) Eachtravel travelaward awardrequest requestshall shallbe be made made in in writing, writing, to to the annual annual Chairman, Chairman, with with an an explanation explanation of of need, possible author status or other significant details. Successful applicants will receive their awards at the time of registration for the Meeting. xv �41ST ANNUAL INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY MARATHON, ONTARIO The 41st Annual Institute The Institute on onLake Lake Superior SuperiorGeology Geology was was held heldMay May13-18, 13-18, 1995, 1995, in in Marathon, Ontario. The Marathon, The meeting meeting was was organized organized by by staff staff of of the the Ontario OntarioGeological Geological Survey, Services Section, Chairman, Mark Mark Smyk, Smyk, was was Survey, Field Services Section,based based in in Thunder Thunder Bay. Bay. Chairman, assisted in the the organization organization of of the the Technical Technical Sessions Sessions by former chairman, Manfred Kehienbeck of Lakehead University. Kehlenbeck The Proceedings of the the 41st 41st ILSG ILSG was Proceedings of was published published in six parts: Part 1: Program Programand andAbstracts Abstracts (edited (editedby by Mark Mark Smyk Smyk and and Manfred Manfred Kehienbeck) Kehlenbeck) Part 2: 2: Field Field Trip Guidebooks 2a: Alkalic Alkalic rocks rocks of the Midcontinent Midcontinent rift (Ron Sage and David Part 2a: Watkinson) Part 2b: of the the Manitouwadge Manitouwadge 2b: Geology, Geology, structure and age relationships of greenstone belt and the Wawa-Quetico Wawa-Quetico subprovince subprovince boundary boundary (Eva Zaleski, Virginia VirginiaPeterson, Peterson,Hugh Hugh Lockwood Lockwood and and Otto van (Eva Zaleski, Breeman) Part 2c: Schreiber greenstone greenstone assemblage assemblage and its gold and 2c: Geology Geology of the Schreiber base metal mineralization mineralization (Mark (Mark Smyk and Bernie Bernie Schnieders) Part 2d: Geology Geology and and gold gold deposits deposits of of the the Hemlo Hernlo area area (Tom (Torn Muir, Muir, Bernie Bernie Schnieders and Mark Smyk) and Mark Smyk) Part 2e: metal and gold exploration exploration using overburden, 2e: Kimberlite, Kimberlite, base metal Wawa area (Tom Morris) (Torn were run both as pre- and post-meeting All trips, with the the exception exception of Wawa, were post-meeting events in in order to to accommodate accommodate large large subscription subscription levels levels and and travel travel schedules. schedules. The The Hemlo Hemlo trips trips order spurred spurred the the revision revisionand andre-publication re-publication of of aa guidebook guidebook first first published published jointly jointly by by the the Geological Association of of Canada, Canada, the Mineralogical Associationof of Canada Canada and and the Mineralogical Association Geological Association the Society of Economic Geologists Geologists in in 1991. 1991. The The successful successful running running of of the the meeting and the associated field field trips trips gave valuable insight insight in in the the planning associated gave some some valuable planning of a field field trip trip associated with with the the International International Geological Geological Correlation Program in August. Logistical Logistical in May May were were put put to to use use when when Ron Ron Sage Sage and II led led the the IGCP IGCP delegates delegates lessons learned in through alkalic rocks rocks of larger trip looking looking at through the alkalic of the the Marathon Marathon area area as as part part of of aa larger the Midcontinent rift. intrusive rocks associated with the intrusive rocks There 145 paid registrants at the the 41st 41st ILSG. ILSG. The The nine nine field field trips trips attracted attracted163 163 There were 145 participants, some of whom were not able to attend the technical sessions. participants, some of whom were not able the technical banquet was was attended attendedby by approximately approximately 135 135 delegates. The The Goldich Goldich Medal, Medal, The annual banquet contributions to to the the understanding understandingof of Lake Lake Superior Superior geology, geology, exemplifying outstanding outstanding contributions The award was awarded awarded to toGene GeneLaBerge LaBerge of of the the University University of of Wisconsin, Wisconsin, Oshkosh. The was presented by by Tim Tim Flood Flood of St. St. Norbert College. College. The banquet speaker was was Peter Lightfoot Geological Survey, the relationship relationship Lightfoot (Ontario Geological Survey, Sudbury) Sudbury) who who addressed the between mantle plumes, plumes, flood flood basalts and mineralization. xvi XVI �PaperAward Awardrecipients recipientswere wereGeoff Geoff Shore (University of Western Ontario) The Student Student Paper spoke about aboutalkaline alkaline gabbroic gabbroic rocks rocks of of the the Coidwell Coldwell alkalic alkalic complex, complex, and and Kim Kim who spoke Darrah (Kent State University) University) who of the the who presented presented information information on on the application of aluminum-in-hornblende barometer. Five students were given travel awards totaling barometer. Five $500. The Board of Directors of the Institute on Lake Superior Superior Geology Geology met in Marathon on on attendance were wereMark MarkSmyk Smyk (1995 (1995 meeting chair), Ted Bornhorst Bornhorst (1994 (1994 May 15, 1995. 1995. In attendance and associate associate secretary-treasurer), secretary-treasurer), Jim Jim Miller Miller (proxy for David David Southwick, Southwick, 1993 1993 chair and (secretary-treasurer). Guests Guests included included Laurel Laurel Woodruff Woodruff (chair (chair for for chair) chair) and Mark Jirsa (secretary-treasurer). 1996 Cable, Wisconsin), Wisconsin), Gene Gene LaBerge LaBerge (alternate 1996 meeting), 1996 meeting meeting in Cable, (alternate chair for 1996 Sally LaBerge, Wilf Sally LaBerge, Wilf Meyer Meyer and and Ron Sage Sage (co-chairs (co-chairs for for 1997 1997 meeting meeting in Sudbury, Ontario). The Board of Directors: 1. Accepted 1. AcceptedReport Reportof ofChairman, Chairman,40th 40thILSG ILSG meeting 2. ApprovedCable, Cable,Wisconsin, Wisconsin,as ashost hostfor for 42nd 42nd ILSG ILSG (1996) (1996) with 2. Approved with Laurel Woodruff as Chair; Gene LaBerge LaBerge agreed agreed to to assist assist Laurel Laurel and and take take over Chair duties, if need be. 3. Approved ApprovedSudbury, Sudbury,Ontario, Ontario,asashost hostfor for43rd 43rdILSG ILSG (1997). (1997). Wilf Wilf Meyer Meyer suggested suggested 3. topical sessions field trips trips that highlight highlight correlations correlations and and contrasts contrasts between sessions and field the Huronian Huronian and and the theequivalent equivalentstrata stratain inWisconsin, Wisconsin, Michigan, Michigan, and Minnesota. Minnesota. He further suggested that a session session devoted devoted to to environmental environmental remediation remediation would would appropriate, and be appropriate, and the the Board Board agreed. 4. Accepted ILSG ILSG Financial Financial Report (Mark Jirsa Jirsa and and Ted Bornhorst) 5. Approved 5. ApprovedGene GeneLaBerge LaBergeas asrecipient recipientof of1995 1995 Goldich Medal 6. 6. Approved ApprovedDan DanEngland Englandasasnew newGoldich GoldichMedal Medal Committee Committee member member (replacing (replacing Glen Glen Adams) 7. Approved 7. Approvedmotion motiontotoallow allowsecretary-treasurers secretary-treasurers to to set setreduced reducedprices priceson onback backILSG ILSG volumes to to reduce reduce inventory inventory and and make make volumes volumes affordable affordable before their shelf shelf life is exceeded. The The motion motion also also allows the secretary-treasurers some lee-way to set those prices to accommodate regional considerations and costs. 8. Approvedaamotion motiontotodonate donate$1.00 $1.00 from from each each meeting registrant to the the Michigan Michigan 8. Approved efforts. Technological Technological Institute Institute Library Library to to assist assist in in their their research research and archiving efforts. They only known known full full set set of of ILSG ILSG volumes the They maintain the only volumes dating dating back to the in 1955. 1955. Donations Donations ($100-$150) ($100-$150) will inception in Institute's inception will be be made made following following the 1996 1996 meeting meeting and every year thereafter. 9. Approvedaamotion motiontotoallow allowdonation donationofofselected selectedback backvolumes volumesof ofILSG ILSG Proceedings 9. Approved their collection collection the Minnesota Minnesota Geological Geological Survey Survey (MGS) (MGS) Library to the Library to to rebuild their after theft. xvii �10. Approved 10. Approvedloan loanof ofVan VanHise Riseand andLeith Leithmonograph monograph(1911) (1911) to a secure section section of MGS MGS Library for safe-keeping. The monograph was was donated donatedto tothe theILSG. Il.SG. The monograph and Suggestions Suggestions to to Chairpersons." Chairpersons." Ted 11. Discussed "Requirements "Requirements and Ted Bornhorst Bornhorst is is constructing with time and passed constructing a manuscript manuscript that can be modified modified with passed from from chairperson to chairperson. chairperson. It It would would detail detail what must be done by the chair and meeting that that runs runs in in the the black. black. The suggest tips for how to operate a smooth smooth meeting board agreed agreed that that would would be be very very helpful. helpful. It will eventually eventually reside with the the secretary-treasurer who will have responsibility to see see that that itit isis passed passed onto the responsibility to incoming Chair. 12. OTHER 12. OTHER BUSINESS BUSINESS a. Motion a. Motion approved approvedtotoprohibit prohibitthe theuse useof ofcameras cameras in in both both oral oral and and poster postersessions, sessions, unless the photographer has of individual individual authors. tmless has the permission of b. Motion b. Motion approved approvedto torequire requirepeer peerreview review of of abstracts. abstracts. The The local local chairpersons chairpersons must establish review committee committee (size (size and composition composition at at their their discretion). discretion). establish aa review Implicit in the the review review process process is is the the right right of of the the committee committee to to refuse refuse acceptance. acceptance. Authors of of rejected rejected abstracts can make changes changes and re-submit, if they can do so within the within the time time limit limit established establishedfor for receipt receipt of of abstracts. abstracts. c. Ted Bornhorst suggested that that the Board into desktop Ted Bornhorst suggested Board look look into desktop publishing of peerpeerreviewed, expanded abstracts and short papers. This This would allow allow authors who might not normally publish in established journals to semi-formally publish their not normally publish in established journals research. The The idea idea was was tabled tabled for for future future discussion. discussion. d. AAsuggestion newsletter that that would be suggestionwas wasmade madeby byTed TedBornhorst Bornhorstto to create create an ILSG ILSG newsletter published early published early in in the the calendar calendar year. year. ItItwould wouldserve serve to to publicize publicize upcoming upcomingILSG ILSG meetings and and other meetings other events, events, as as well well as as highlight highlight exploration exploration and research research activities. The approved. Ted activities. The concept concept was generally generally approved. Ted will prepare aa mock-up mock-up in the following months with a student assistant. assistant. Board Board members will continue to and track track the the progress progress of of the venture. discuss and e. Board 1995. Boardagreed agreedtotohave havea aformal formalmeeting meetingatatthe theIGCP IGCPConference, Conference,August August25-27, 25-27,1995. Budgeting for the 41st was designed designed to to keep keep registration registration costs costs at at aa minimum in 41st ILSG ILSG was order to to help help attract attractpotential potential delegates delegates to to Marathon Marathon despite despite prohibitively prohibitively long long travel travel distances. Fees were largely largely set set on on a cost-recovery basis. Many Many of of the the duties cost-recovery basis. duties and Fees were services which could normally services normally be contracted contracted out to to other other agencies agencies (e.g., (e.g., university university OGS staff staffininorder order to to reduce reduce costs. costs. Field trip extension services) were taken care of by OGS guidebooks guidebooks were also sold at at just just above above cost cost to to attendees. attendees. Since Since the the meeting, the guidebooks guidebooks have have been beenreprinted reprintedseveral severaltime; time;sales sales in in Thunder ThunderBay Bay continue continue to to be be brisk, brisk, especially during during field field season. The financial analysis The final final financial analysis appears appears to indicate that the 41st ILSG ILSG managed managed to to turn turn a Thisis, is,ininitself, itself, especially especially rewarding, rewarding, considering our 'user-friendly' 'user-friendly' modest profit. This pricing practices, unforeseen unforeseen print-run print-run problems problems and and losses losses in inCanada-US Canada-US exchange exchange xviii XVlll �is to to be be commended for his role in rates. Mark MarkO'Brien, O'Brien, local local Secretary-Treasurer, Secretary-Treasurer, is commended for in keeping us keeping us on onan aneven evenfinancial financial keel. keel. I have received many favourable favourable comments and kudos on the the organization organization of of the the 41st 41st flSG. Despite typical) north north many'arms-length' 'arms-length'logistical logistical problems, uncooperative (but typical) ILSG. Despitemany shore weather and and minor minor glitches, glitches, itit proved proved to to be be aa very very successful successful meeting. meeting. I must again thank all all the the people people in in Thunder Thunder Bay Bay and Marathon who helped helped to pull itit off. off. Special thanks must also go out to all the field field trip trip leaders for for their their perseverance. perseverance. Cliff Cliff Special Shaw graciously filled in on the Shaw graciously filled the alkalic alkalic rocks rocks trip for for Dave Dave Watkinson, Watkinson, who was was unfortunately ill. Former chairmen, Ron Sage, Ted Bornhorst, Manfred Kehienbeck unfortunately ill. Former chairmen, Ron Sage, Ted Bornhorst, Kehlenbeck and Ed Frey Ed Frey provided provided invaluable invaluable organizational organizational advice. advice. Lastly, II would would like like to to to Marathon and who continue to acknowledge all those who made made the the effort to come come to to support the support theInstitute Instituteon onLake LakeSuperior Superior Geology. Geology. Mark Smyk MarkSmyk Chairman,41st 41stILSG ILSG Chairman, Thunder Thunder Bay, Bay, Ontario xix �PROGRAM �OF EVENTS EVENTSAND AND PROGRAM PROGRAM CALENDAR OF WEDNESDAY, MAY WEDNESDA Y, MA Y 15 8:00 AM AM - 6:00 PM FIELD FIELDTRIPS TRIPS 11 AN]) AND 22 1. GLACIAL GLACIALGEOLOGY GEOLOGY OF WESTERN WISCONSIN Leader: Mark Mark D. D. Johnson (Gustavus Adoiphus Adolphus College) College) 2. GEOLOGY GEOLOGYOF OFTHE THE MONTREAL MONTREAL RIVER RIVER MONOCLINE: TRAVERSE THROUGH 25 KM OF THE A TRAVERSE 25 KM THE CRUST Leader: William WilliamF. F. Cannon Cannon(U. (U. S. S. Geological Survey) 5:00 PM PM - 8:00 PM REGISlRATION REGISTRATION 7:00 PM PM ICEBREAKER AND POSTER POSTERSESSION SESSION(Cash (Cash Bar) Bar) PM - 10:00 PM ICEBREAKER AND 9:00 PM) (Authors present at posters 7:30 PM (Authors present at posters 7:30 PM - THURSDAY, THURSDA Y, MAY 16 NOTE: ThCHNKAL SESSIONS ARE IlW NOTE: TECHNICAL SESSIONS AREIN INTHE THENAMEKAGON NAMEKAGONROOM, ROOM,TELEMARK TELEMARK LODGE ...* STUDENT STUDENT PRESENTAnON PRESENTATION 8:00 8:00 AM AM REGISTRATION REGISlRATION CONTINUES CONTINUES TECHNICAL TECHNICAL SESSION I SESSION CHAIRS: CHAIRS: KLAUS AND GLEN GLEN ADAMS ADAMS SESSION KLAUS SCHULZ AND — 8:55 8:55 AM AM OPENING - 42ND ANNUAL ANNUAL INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY L. G. G. Woodruff, Woodruff, General Chair L. 9:00 AM KEYNOTE ADDRESS Miller, J. D., Jr., and Vervoort, Vervoort, J.J. D. D. The Latent Magmatic Maginatic Stage Stage of ofthe theMidcontinent MidcontinentRift: Rft: A Period of Magmatic Magmatic The Crust Underplating and and Melting Melting of of the the Lower Crust — 9:30 AM Bornhorst, T. Bornhorst, T. J., and Dolan, Dolan, M. M. T. T. An Electronic Electronic Component Component of of the Institute Institute on on Lake Lake Superior Geology L 9:50 AM AM 10:00 10:00 AM AM PRESENTATION OF PROPOSED PROPOSEDCHANGES CHANGESTO TOTHE THE1.I.L.S.G. L.S.G. CONSTITUTION COFFEE BREAK AND POSTER SESSION xxi XXi �10:20 AM 10:20 AM Ames, D. E., Jonasson, Jonasson, 1.I. R, R.,Parrish, Parrish, RR R., R., Watkinson, Watkinson, D. H., and and Gibson, Gibson, H. H. L. L. Regional HydrotherrnJ1l'Massive Hydrothermal Massive Sulphide Suiphide Producing System and U/Pb U/Pb Hydrothermal Titanite Age ping FOrrnJ1tion, Formation, Sudbury Age Constraints, Ona Onaping Structure, Ontario 10:40 AM 10:40 AM Ripley, E. Ripley, E. M. Pet rogenetic Relationships between A pat ite-B earingand andApatite-Deficient Apatite-Deflcient Iron Petrogenetic Apatite-Bearing Oxide-Rich Intrusions Intrusions and and Massive Massive Sulfide SulfideMineralization Mineralizationinin the the Duluth Duluth Oxide-Rich Complex, Complex, MN 11:00 AM 11:00 AM "'Peterson, D. D. M. M. *peterson, Targeting Targeting Footwall Footwall Copper-PGE Copper-PGE Deposits Deposits in the the Duluth DuluthComplex ComplexBased Based on on Sudbury Mining Mining Camp Camp Analogs Analogs 11:20 AM 11:20 AM Saini-Eidukat, B., Rudashevsky, N. N. S., 5., and Polozov, Polozov, A. A. G. G. Saini-Eidukat, B., Occurrence of Hibbingite Hibbingite in in the the Duluth Complex, Complex, Minnesota, Minnesota, and in the Noril'sk Complex Iron Ore Deposit, Russia Complex and Korshunovskoe Korshunovskoe Iron ,-11:40 AM 12:00 PM 12:00 PM Mudrey, M. G., G., Jr., Jr., Brown, Brown, B. B. A., Freiberg, P. G., and and Simo, Simo, J. J. A. A. Mudrey, M. Mineralization in the Fox River Valley, Mississippi Valley-Type Valley-Type Mineralization Valley, Eastern Wisconsin LUNCH BREAK BREAK TECHNICAL SESSION SESSION II II TECHNICAL SESSION ED RIPLEY RIPLEY AND SMYK SESSION CHAIRS: CHAIRS: ED AND MARK SMYK \-/ 2:00 PM Boerboom, Boerboom, T. T. J. J. Southward Extension the Penokean PenokeanTerrane Terrane through through Steams Stearns County, Central Extension of the Minnesota 2:20 2:20 PM PM "'Darrah, *Darrah, K. 5., S., Holm, Hoim, D. D. K., K., Dahl, Dahi, P. P. 5., S.,and and Lux, Lux, D. D. R. it Petrographic Pet rographic and Thermobarometric Analysis of the Metamorphosed Little Falls Formation, Central Minnesota, Minnesota, with with Implications Implications for Early Early Proterozoic Proterozoic Tectonism ."j/ 2:40PM 2:40 PM Hoim, D. Holm, D. K., K., Dahi., Dahl., P. S., 5., and Lux, Lux, D. D. R. R Was Lithospheric Lithospheric Delamination Delamination an an Important Process in the Evolution Was Evolution of of Early Proterozoic Collisional Orogens? '( / 3:00 PM PM BREAK AND AND POSTER POSTER SESSION SESSION COFFEE BREAK 3:20 3:20 PM PM Schmidt, S. Th., and Stern, Stern, W. W. Clay Minerals of of the North Shore Shore Volcanic Volcanic Group and and Possible Possible Relationship Relationship to to Copper Precipitation during Alteration xxii XXll �'I 3:40 PM PM *BeMcer A., A., and and Karhu, *Bekker, Karhu, J. J. A. Study of ofCarbon Isotope Ratios Carbon Isotope Ratios in in Carbonates Carbonates of of the the Early Early Proterozoic Proterozoic Snowy Snowy Pass Supergroup, WY WY and and Its Its Application Application for Correlation with with the the Chocolay Chocolay ian Supergroup, Supergroup, ON ON Group, MI and the Huron Huronian 4:00 PM 4:00PM Larsen, C. Late Holocene Lake Lake Superior -- Isostatic and Climactic Climactic Lake-Level Lake-Level Change 4:20 PM Uchytil, S. S. J., Steffensen, C. K., Jarvie, D. M., Dickas, A. A. B., B., Uchytil, Mudrey, M. and Mudrey, M. G., G., Jr. Jr. Outcrop and and Subsurface Subsurface Core Core Analysis and Relationship Relationship to to Regional Regional Hydrocarbon Pros pectivenessof ofthe theMiddle MiddleProterozoic ProterozoicNonesuch Nonesuch Formation in Prospectiveness in Northern Wisconsin and Michigan Wisconsin I. — — PM MIXER 6:30 PM - 7:30 PM MIXER - CASH BAR v PM ANNUAL 7:30 PM - 9:30 PM ANNUALBANQUET BANQUET&&AWARDS AWARDSPRESENTATION PRESENTATION Announcement Announcement of of the the 43rd Annual Annual Meeting Meeting location. location. 1996Goldich GoldichAward Award presentation presentation to Dr. Dr. David Southwick, 1996 by Dr. Dr. G. G. B. B. Morey. Minnesota Geological Survey, by Banquet speaker: Dr. Dr. Stephen Stephen E. E. Kesler, University of Michigan, Michigan: Ann Arbor, Michigan: — SUSTAiNABLE MINERALDEVELOPMENT DEVELOPMENT-OR FICTION? FICTION? SUSTAINABLE MINERAL -- FACT OR FRIDAY, FRIDAY, MAY 17 8:30 8:30 AM AM REGISTRATION CONTINUES TECHNICAL SESSION SESSION III III TECHNICAL SESSION CHAIRS: SIDNEY HEMMING AND SIDNEY HEMMING ANDTERRY TERRY BOERBOOM BOERBOOM V 9:00 AM 9:00AM Chandler, V. W. Chandler, V. The West-Central West-Central Minnesota Minnesota Earthquake EarthquakeofJune of June5,5,1993: 1993:An AnOpportunity Opportunity to The Re-examine Seismicity Seismicity near near the the Morris Fault 9:20 9:20 AM AM S. M., M., and Kiasner, *Wilson, S. Klasner, J.J. S. A Structural Structuraland andKinematic Kinematic Analysis Analysis of of the McCaslin Formation near near McCaslin McCaslin Mountain, Wisconsin Wisconsin 9:40 AM AM 9:40 Westjohn, D. Westjohn, D. B. B. Regional Finite Strain Strain Patterns in Proterozoic Slates and and Quartzites: Regional Finite Proterozoic Slates Implications for for Heterogeneous Heterogeneous Strain Strain Related Related to to Flexural Flexural Slip Slip Folding in the Marquette Synclinorium 10:00 AM 10:00 AM COFFEE BREAK BREAK AND AND POSTER POSTER SESSION xxiii �10:30 AM AM *Adamson, K. F. Petrology, Stratigraphy, Stratigraphy, and andSedimentation Sedimentationof ofthe the Middle Middle Proterozoic Proterozoic Bayfield Bayfield Group of Northwestern Wisconsin Wisconsin 10:50 AM 10:50 AM Ojakangas, R W. Ojakangas, R. Tidalites of Early Proterozoic Age in the Western Lake Lake Superior Region: Region: Minnesota, Wisconsin Wisconsin and and Michigan Michigan 11:10 AM AM Ojakangas, G. W. Ojakangas, Cyclic Tidal Tidal Laminations Laminations in in the the Early Early Proterozoic ProterozoicPokegama PokegamaFormation: Formation: Digital Digital Cyclic Image Analysis and Computer Modeling Modeling 11:30 AM AM LUNCH BREAK clIE NOTE: ALL POSTERS MUSTBE BEREMOVED REMOVED LUNCH BREAK NOTE: ALL POSTERS MUST TECHNICAL TECHNICAL SESSION SESSION IV JIRSA AND AND RON SAGE SESSION CHAIRS: MARK JIRSA 1 \ 1:30 PM Hemming, S. S. R., R, McLennan, S. S. M., Hemming, M., and and Hanson, G. N. Geochemical GeochemicalSource SourceCharacteristics Characteristicsand and Diagenetic Diagenetic Trends Trends of the the Virginia Formation, Mesabi Iron Range, Range, Minnesota 1:50 PM Medaris, Jr., Fournelle, J. Medaris, L. L. G., G., Jr., Dott, R. R H., Jr., J. H., Johnson, C. C M., M., Schott, R. C, C., and Baumgartner, Baumgartner,L. L. P. P. Age and and Geological the Baraboo Baraboo Quartzite Quartzite Geological Significance of the 2:10 PM PM Jirsa, M. A. of a Timiskaming-Like Timiskaming-Like Sequence Sequenceininthe theSouthern Southern Wawa Wawa Subprovince, Genesis ofa Northeastern Minnesota 2:30 PM PM Smyk, M. M. C Kingston, D. D. M. C. and Kingston, Basaltic Komatiites Associated Rocks: Rocks: Implications Implications on on the the Nature Nature of Komatiites and Associated Volcanism Part of of the Schreiber-Hemlo Schreiber-Hemlo Greenstone Volcanism in Part Greenstone Belt, Belt, Northwestern Northwestern Ontario 2:50 PM PM PRESENTATION OF STUDENT PAPER AWARDS PRESENTAnON 3:00 PM PM CLOSING C LOSING REMARKS REMARKS 3:10 PM PM COFFEE BREAK 3:30 PM Gene LaBerge Discussion of for the Flambeau Flambeau Mine Mine Field Field Trip of Logistical Details for Minerals of of the Flambeau (no abstract) abstract) Flambeau Mine Mine (no 4:00 PM PM SESSION ENDS xxiv XXIV �SATURDAY, MAY 18 7:00 AM AM - 6:00 PM PM FIELDTRIP3 FIELD TRIP 3 3. TOUR TOUROp OFFLAMBEALI FLAMBEAUCOPPER-GOLD COPPER-GOLD MINE Leaders: Gene GeneL. L. LaBerge LaBerge (University of Wisconsin-oshkosh) Wisconsin-Oshkosh) and Staff Geologists, Flambeau Mine SUNDAY, MAY 19 8:00 AM AM - 5:00 PM FIELD TRIPS TRIPS 4 AND 5 PM FIELD 4. EARLY EARLYTO TOMIDDLE MIDDLEPROTEROZOIC PROTEROZOICGEOLOGY GEOLOGY OF OF THE THE LAKE LAKE NAMEKAGON REGION Leaders: William William F. F. Cannon, Laurel G. Woodruff, and Suzanne W. Nicholson Nicholson (U. (D. S. Geological Survey) LAKENAMEKAGON NAMEKAGONAND ANDPENOKEE PENOKEE GAP GAP AREAS, AREAS, 5. LAKE WEST GOGEBIC RANGE, RANGE, WISCONSiN WISCONSIN Leaders: John John S. S. Kiasner Klasner (Western Illinois University) and LaBerge (University (University of Wisconsin-oshkosh) Wisconsin-Oshkosh) Gene L. L. LaBerge POSTER SESSION SUZANNE NICHOLSON SESSION CHAIR: PM WEDNESDAY, WEDNESDAY, MAY MAY 15, 15, TO TO NOON NOON FRIDAY, FRIDAY, MAY 17 17 7:30 PM Cannon, W. W. F., F., and andKress, Kress, T. T. H. H. Cannon, New Minnesota, Wisconsin, Nw Digital Digital Geologic Geologic Map of ofMinnesota, Wisconsin, and Upper Michigan (no abstract) (no Cannon, W. F., F., Nicholson, Nicholson,S. S. W., W., Woodruff, Woodruff, L. L. G., Hedgman, C. A., A., and and Schulz, Schulz,K. K. J. J. Cannon, W. Hedgman, C. Geologic Map Map of the the Ontonagon Ontonagon and part of the Wakefield Wakefield30' 30' xx 60' 60' Quadrangles, Michigan Geologic (no (no abstract) Gere, M. M. A., A., Jr. Michigan Mineral Mineral Lease Lease Exploration Exploration Data Inventory Johnson, Johnson, A. A. M., M., and andGere, Gere,M. M. A., A., Jr. Jr. IdentifyingGeologic Geologic and and Other OtherPotential Potential Resources Resources from Abandoned Underground Identfying from Michigan's Michigan's Abandoned Mine inventory Inventory Kalliokoski, J.J. Kalliokoski, Bay, Michigan ", Keweenaw An Ancient AncientLandslide Landslideatat"Red "RedRocks Rocks", Kweenaw Bay, ./' Kucks, R P., P., and andHorton, Horton,R. R J.J. Aeromagnetic Aeromagnetic Map Map of ofLake Lake Superior xxv �Morey, G. G. B., B., and and Cleland, Cleland,J.J. M. M. Morey, Preliminary Sedimentologic and Petrologic Analysis of the Early Proterozoic Mahnomen Preliminary Sedim.entologic (North Range Range Group) Group) East-Central East-Central Minnesota Minnesota Formation (North *Naiman, Z., *Naiman, Z., Wirth, Wirth,K. K. R., R, Morey, Morey,G. G. B., B., and and Miller, Miller, J.J. D. D. Metamorphism Chengwatana Volcanic from Osseo Metamorphism of ofChengwatana Volcanic Group Group near near Taylors Taylors Falls Falls and and-from Osseo Core *Neilson, K. Stendahl, R, Kropf, E., and J. P. Stendahi, R., and Craddock, Craddock, J. A Continuum ContinuumofofStress-Strain Stress-StrainFields Fields(2.0-1.0 (2.0-1.0 Ga) Ga) along along the the Northern Northern Margin Marginofofthe theKeweenaw Keweenaw Province, Ontario, Canada Province, R P., Morris, T. F., Crabtree, D., Murray, C. C. A., Bennett, G., Hailstone, M., Sage, R. Hailstone, M., Nicholson, T., T., Painosi, Painosi,S., S., and andJosey, Josey, S. S. Nicholson, Exploration in in Wawa Ultramafic Dike Dike with Mantle Xenoliths: Xenoliths: Implications Implications to Diamond Exploration Wawa Spector, A., and and Lawler, Lawler, T. T. L. Northeastern Minnesota Minnesota Duluth DuluthComplex Complex Mineral Potential Swenor, Swenor, W. W. T. T. Update on on the the Geological Geological Core Core and and Sample Sample Repository Repository Wattrus, Wattrus, N. N. J., J., Anderson, Anderson,K., K., Sharkey, Sharkey,J., J., and and Holcombe, Holcombe, T. T. Bathymetric Map Map of ofLake Lake Superior A New Bathymetric Wirth, Wirth, K. K. R., R., Naiman, Naiman,Z., Z.,Vervoort, Vervoort,J.J. D., D.,Miller, Miller, J.J. D., D., and and Morey, Morey,G. G. B. B. Chengwatana Volcanic Geochemistry of ofChengwatana Volcanic Group near.Taylors near Taylors Falls Falls and and from from Osseo Osseo Core Core xxvi �ABSTRACTS �PETROLOGY, STRATIGRAPHY, PETROLOGY. STRATIGRAPHY, AND AND SEDIMENTATION SEDIMENTATiON OF OF THE MIDDLE PROTEROZOIC BAYFIELD GROUP GROUP OF OF NORTHWESTERN NORTHWESTERN WISCONSIN. WISCONSIN. PROTEROZOIC BAYFIELD Minnesota, Duluth, ADAMSON, Kent Kent F., F., Department of Geology, University of Minnesota, 10 University Drive, Drive, Duluth, Duluth, MN MN 55812, 55812,kadamson@d.umn.edu kadamson@d.umn.edu Petrographic and Petrographic and field field evidence evidence suggest suggest that that the the Bayfield Bayfield Group Group units, units, the the lithofeldspathic Orienta Formation Formation and and the the lithofeldspathic Iithofeldspathic Chequamegon Chequamegon Formation, Formation, Iithofeldspathic Orienta are the same unit Formation. Previous unit beneath beneath the quartzose quartzose Devils Island Island Formation. Previous stratigraphic thefollowing following order, order, from from the the bottom bottom up: up: stratigraphic studies studies place place the the three threeunits unitsininthe Orienta, Devils Myers, 1971). 1971). The Devils Island Island and and Chequamegon Chequamegon (Thwaites, (Thwaites, 1912; 1912; Myers, The contact contact between the Devils Devils Island Island Formation Formation and and Chequamegon Chequamegon Formation Formation is not not present present on on Devils Island Island as as previous previous studies studies suggest. suggest. This Thisstratigraphy stratigraphywould would better better match match the the correlative units units some some tens tens of ofmiles miles to to the the west west in in east-central east-central Minnesota, Minnesota, the the probable correlative lithofeldspathic Fond du Lac Formation and the overlying quartzose Hinckley lithofeldspathic Fond du Lac Formation and the Sandstone. The Orienta Orienta and and Chequamegon Chequamegon Formations Formations both both appear to have been been formed formed by by fluvial processes processes while while the the Devils Devils Island Island Formation Formation is is more more indicative of a shallow standing body body of of water water (Ojakangas (Ojakangas & & Morey, Morey, 1982; 1982; Morey Morey & Ojakangas, Ojakangas, 1982). Supporting evidence includes includes aa northeasterly northeasterly paleocurrent paleocurrent direction trend for both the Orienta and Chequamegon Formations. The The Devils Devils Island Island Formation Formation has has aa less less prominent northeasterly paleocurrent paleocurrent trend along with many many divergent divergent paleocurrent paleocurrent directions. Preliminary petrographic data data from the Devils Devils Island Island Formation show that nearly 100% of the primary primary framework framework grains are are quartz. quartz. The primary framework grains of the Orienta Formation Formation are are 45 45 to to 65% 65% quartz, quartz, 35 35 to to 50% 50% feldspar, feldspar, and and 00 to to 10% 10% rock rock fragments (volcanic and granitic). The to the the TheChequamegon Chequamegon Formation is very similar to quartz, 30 30 to to 50% 50% feldspar, feldspar, and and 55 Orienta Formation, generally generally consisting consisting of of 45 to 65% quartz, to 10% rock rock fragments. fragments. References Morey, G. Morey, G. B., B., and R. W. Ojakangas, Ojakangas, 1982 1982, Keweenawan Keweenawan sedimentary sedimentary rocks of eastern Minnesota and northwestern Wisconsin, in Wold R. W. J. Hinze, eds., R. J. J. and W. basin: GSA GSA Memoir Memoir 156, 156, p. p. 135-146. 135-146. Geology and tectonics of the Lake Superior basin: Myers, W. D., 1971, The sedimentology and tectonic significance of the Bayfield Myers, 1971, sedimentology significance the Bayfield Group (upper Keweenawan?) Wisconsin and Minnesota: Minnesota: Unpublished Unpublished Ph.D. Ph.D. of Wisconsin, Madison, Madison, Wisconsin, 269 p. University of dissertation, University Ojakangas, R. R. W., W., and and G. G. B. B. Morey, Morey, 1982, 1982, Keweenawan Keweenawan sedimentary sedimentary rocks rocks of of the the Lake Lake R. J. and W. J. Hinze, eds., Geology and summary, ininWold WoldR. J. and W. J. Hinze, eds., Geology and Superior region: aasummary, tectonics of the Lake Lake Superior basin: GSA GSAMemoir Memoir 156, 156, p. p. 157-164. 157-164. T., 1912, 1912, Sandstones Sandstones of the Wisconsin Thwaites, F. 1., Wisconsin coast coast of of Lake Lake Superior: Superior: Wisconsin and Natural Natural History History Bulletin Bulletin 25, 25, 117p. 117p. Geological and 1 1 �REGIONAL HYDROTHERMAL MASSIVE REGIONAL HYDROTHERMAL MASSIVE SULPHIDE SULPHIDE PRODUCING SYSTEM AND PRODUCING SYSTEM AND U/PB U/PB HYDROTHERMAL TITANITE TITANITE AGE AGE CONSTRAINTS, CONSTRAINTS, ONAPING HYDROTHERMAL ONAPING FORMATION, FORMATION, SUDBURY SUDBURY STRUCTURE, ONTARIO. D.E.*, Ames , D.E. Jonasson, I.R., I.R., Parrish, Ames, *, Jonasson, Parrish, R.R. R.R. Geological Geological Survey Survey of of Canada, Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8; Centre, Department of Earth KIA OE8; Watkinson, Watkinson, D.H. D.H. Ottawa-Carleton Ottawa-Carleton Geoscience Geoscience Centre, Department of Earth Sciences, Sciences, Carleton Carleton University, H.L.. Geology Geology Department, Department, Laurentian Laurentian University, University, Sudbury, Sudbury, University, Ottawa, Ottawa, Ontario, Ontario, K1S KIS 5B6; 5B6; Gibson, H.L, Ontario, P3E 2C6. The objectives objectives of Fonnation, Sudbury Structure of the the present study study in the Onaping Formation, Structure are are to to detennine: determine: 1) the stratigraphic and and structural stratigraphic structural controls controls on on alteration, alteration, 2)2)the thespatial spatialdistribution, distribution,mineralogy, mineralogy,mineral-chemical mineral-chemical characteristics, timing, and and origin originof ofalteration alterationtypes typesand, and,3)3)the therelationship relationshipbetween betweenregional regional scale scalehydrothermal hydrothennal alteration alteration with with intra-Onaping intra-Onaping base base metal metal occurrences occurrences and to to the the overlying overlying Zn-Cu-Pb Zn-Cu-Pb Errington Errington and and Vermilion Vennilion massive sulphide deposits. deposits. Research Research isis based based on on 1:2000 1:2000scale scale mapping mapping carried carried Out out during three field field seasons, of of ten transects up up to to 66 km of the the structural structural transects k:m width width across across the theOnaping Onaping Formation, Fonnation, distributed distributed around around the the circumference circumference of basin. The Paleoproterozoic Onaping Formation Fonnation forms fonns the the base base of of the the Whitewater Whitewater Group, Group, Sudbury Sudbury Structure Structure and and is footwall sequence sequence to the the 8.7 8.7 Mt MtErrington Erringtonand andVermilion VennilionVMS VMSdeposits. deposits. Comprehensive Comprehensive field field evidence evidence is the footwall indicates that that this fall and flow, indicates this 1400m 1400m thick thick fragmental fragmental succession succession isis hydrothermally hydrothermally altered altered pyroclastic-like pyroclastic-like fall flow, debris-flow deposits hydroclastic breccia (Ames and and Gibson, Gibson, 1995). 1995). Syndepositional Syndepositional radial and minor minor debris-flow deposits and and hydroclastic breccia (Ames radial and faults partially control emplacement emplacement of the lower part of the the Onaping Onaping Formation Fonnation and are conduits conduits for for concentric faults metasomatic fluids. fluids. Evidence Evidence for for aa regional regionalsubseafloor subseafloorhydrothermal hydrothennal system system includes includes vertically vertically stacked, stacked, alkali metasomatic "basin-wide" semiconfonnable alteration from base base to to top, silicification, albitization, basin-wide' semiconformable alteration zones zones consisting consisting of, of, from chioritization, and celsian. chloritization, carbonatization carbonatization and feldspathization. feldspathization. The latter latter includes includes microcline, rnicrocline, hyalophane hyalophane and celsian. The syndepositional basal zone zone of of silicification silicification consists consists of of an an earlier phase of K-feldspar by albite albite and and syndepositional basal K-feldspar overprinted overprinted by quartz quartz with with minor minor epidote. epidote. These These events events are are also also mimicked mimicked ininthe theoverlying, overlying, locally locally discordant, discordant, zones zones of of syndepositional albitization. Chlorite syndepositional albitization. Chlorite although although dominant dominant in in the the Contact Contact units units isis present present throughout throughout the the Onaping Onaping Formation and deposits deposits and and the the basal silicification Fonnation as pycnochlorite-ripidolite except near base base -metal occurrences occurrences and silicification zone where more Mg-rich associated with withpyrrhotitepyrrhotiteMg-rich varieties varieties are present. present. A A late late stage stageofofhigh highFe-ripidolite Fe-ripidolite isisassociated chalcopyrite-siderite the base-metal chalcopyrite-siderite inin the base-metal deposits deposits and occurrences. occurrences. Proximal Proximal alteration alteration to to base base metal metal deposits deposits includes, muscovite, hyalophane, carbon, ankerite, ankerite, dolomite dolomite and late siderite. siderite. Regional Regional includes, barian barian muscovite, hyalophane, celsian, celsian, quartz, quartz, carbon, and late carbonatization, consists of of calcite, calcite, and and is pervasive in the carbonatization, consists the upper upper 1I km k:m except except around around base base metal metal showings showings and and local zones of lower temperature temperature siicification. silicification. The Theupper upperzone zoneofoffeldspathizaiion feldspathization contains contains low-temperature local zones low-temperature kfeldspar with minor minor albite albite which which isisoverprinted overprintedby bycelsian, celsian,reflecting reflectinglow-temperature low-temperature seawater-rock seawater-rock reactions in the shallow subseafloor. Amphibole veins with with albitized haloes represent one of the youngest hydrothermal events events in in the the Onaping Onaping Amphibole veins youngest hydrothennal Formation: Fonnation; they they crosscut igneous -textured intrusions intrusions cogenetic cogenetic with with the the fragmental fragmental andesitic andesitic Onaping Onaping Formation. Fonnation. Conventional of hydrothermal Conventional U/Pb U/Pb geochronology geochronology of hydrothennal titanite titanite within within the themetasomatized metasomatized haloes haloes of the amphibole amphibole veins yields yields an an age circa 1850 veins 1850 Ma. Ma. One One of ofthe theworld's world'smost mostextensive extensivehydrothermal hydrothermalcirculation circulationsystems systemsdeveloped developed in the the Onaping Onaping breccias breccias due due to to heat heatloss lossfrom from the the1850 1850Ma MaSudbury SudburyIntrusive IntrusiveComplex Complex and and coeval coeval sublayer sublayerrocks. rocks. was new U/Pb U/Pb titanite titanite age age on onlate-stage late-stagehydrothermal hydrothennal alteration proves the complex complex Sudbury Sudbury event event was This new proves that the complete within within error error of of geochronological geochronological dating. dating. volcanic The mechanisms of brecciation and emplacement of the Onaping Formation are similar to some volcanic deposits deposits however, however, itit is not not aatypical, typical,volcanic volcaniccauldron cauldronsequence sequence ororfallback fallbackbreccia. breccia. The TheOnaping OnapingFormation Fonnation represents a dominantly deposited impact impact melt melt based based on on the the epsilon epsilon Nd Nd crustal crustal signature dominantly subaqueously subaqueously deposited signature between between -lack of of phenocrysts phenocrysts in in explosive explosive ash ash flow-like flow-like deposits suggesting suggesting little crustal residence time, the the 7.6 to -10.3, the lack presence presence of abundant abundant shock shock metamorphic metamorphie features features including including shocked shocked zircons zircons and and cuspare, cuspate, plaley platey and and blocky blocky microvesicular microvesicular shard morphologies. morphologies. Emplacement of the the SIC SIC and and sublayer sublayer provided provided the the heat heatrequired requiredto. to initiate initiate 1.4 km k:m thick fragmental sequence and led to the development of a short-lived hydrothermal hydrothennal fluid circulation in the 1.4 system the overlying replacement deposits depositshosted hosted inin carbonate carbonate sinter sinter mounds. mounds. The The system that produced produced the overlying Zn-Cu-Pb Zn-Cu-Pb replacement 22 �exceptional preservation preservationof of the the fragmental strata and one exceptional fragmental strata one of ofthe theworld's world'smost mostextensive extensivesemi-conformable semi-conformable involved in generating Paleoproterozoic alteration systems, permits detailed investigation of processes processes involved Paleoproterozoic massive suiphide deposits, deposits, the the role in large and the sulphide role of of hydrothermal hydrothermal processes processes in large scale scale meteorite meteorite impact impact structures structures and the emplacement mechanisms for large large impact impact crater-ifil crater-fill deposits. deposits. HL. 1995: Controls geological setting regional hydrothermal hydrothermal alteration within within Ames, D.E. and Gibson, H.L. Controls on and geological setting of of regional Errington and and Vermilion Vermilion base base metal metal deposits, deposits, Sudbury Sudbury Structure, Ontario; footwall to the Errington the Onaping Formation, footwall in Current Research 1995-E; 1995-E; Geological Survey of of Canada, Canada, 161-173. 161-173. 3 �STUDY OF CARBON ISOTOPE RATIOS RATIOS IN CARBONATES OF THE EARLY PROTEROZOIC PROTEROZOIC· SNOWY PASS SUPERGROUP, WY WY AND AND ITS ITS APPLICATION APPLICATIONFOR FORCORRELATION CORRELATIONWITH WITh THE CHOCOLAY GROUP, MI MI AND AND THE THE HURONIAN HURONIAN SUPERGROUP, SUPERGROUP, ON. ON. BEKKER, Andrey, Andrey, Department Department of ofGeology, Geology, University of Minnesota, Duluth, Duluth, MN, MN, Bekkergeo1.uchicago.edu and A., Geological Geological Survey Survey of of Finland, Finland, 55812, Bekker@geol.uchicago.edu andKARHU, KARHU,Juha JuhaA., FIN-02 150 Espoo, Finland, Juha.Karhugsf.fi. FIN-02I50 Juha.Karhu@gsf.fi. Carbon has a relatively to the the mixing mixing time time of of sea sea water, water, thus thus making making marine marine waters waters relatively long long residence time in the oceans relative to nearly homogenous in respect As such, such, carbon carbon isotope isotope ratio ratio changes changes can can be be used used for for respect to to carbon carbon isotope isotope composition. composition. As stratigraphic correlations between basins. In In addition, addition, carbonates are are usually usually considered considered to to between carbonate carbonate units deposited in open basins. retain their diagenetic and and even even in in metamorphic metamorphicalterations. alterations. In this their original original carbon carbon isotope isotope signatures signatures nearly unchanged in diagenetic study, analyses of Schist, and the Nash Fork Formation were of carbon carbon isotope isotope ratios ratios from from the Vagner Vagner Formation, the Lookout Schist, carried carried out. We Wecompare compareour ourresults resultswith withavailable availabledata datafrom from the the Huronian Huronian and and Marquette Marquette Range Range Supergroups, Supergroups, and other other sequences worldwide ofdeposition, deposition, and and to to draw draw aa correlation correlation between between these thesesequences. sequences. worldwide to to put put some some constraints constraints on on the the time time of Our results results also also have haveimplication implicationfor for understanding understanding of ofthe the carbon carbon cycle cycle in Early Proterozoic time. consists of of the the Deep Deep Lake Lake(DLG) (DLG)and andthe the Libby LibbyCreek Creek (LCG) (LCG) Groups. Groups. The The The Snowy Pass Supergroup, Wyoming, Wyoming, consists DLG and the lower lower LCG LCG were were deposited deposited between between 2.45 2.45 and and 2.1 2.1 Ga Ga (Premo (Premo and and Van Van Schmus, Schmus, 1989) 1989) and and are areoverlain overlainby bythe the cycles with tillites at the base and allochthonous upper LCG. The Theupper upperDLG DLG and and the the lower lower LCG LCG exhibit three-large scale cycles sandstones Fm., Vagner Vagner Fm.~Rock Fm.-3Rock Knoll Knoll Fm., Fm., Headquarters Fm.—*Heart Fm.and and Fm.~Cascade Fm., Fm.~Heart Fm. sandstones above above (Campbell (CampbellLake LakeFm.—+Cascade Medicine Peak Quartzite). Limestones glacial retreat; they exhibit fme Limestonesof ofthe theVagner Vagner Formation Formation were were deposited deposited following following glacial of the the lower lower LCG locally locally includes interlayering with with siltstone. The TheLookout Lookout Schist Schist of laminations and interlayering includes thin thin layers of brown brown impure impure TheNash NashFork ForkFormation Formation isisaathick thick(>2 (>2 km) km) sequence sequence of of siliceous siliceous cross-bedded dolomites dolomite. dolomite. The dolomites with flat-pebble conglomerates, pseudomorphs after gypsum, gypsum, and and stromatolite stromatolite bioherms, biohenns, enclosed enclosedby byblack blackphyllites phylliteswith withgraphite graphiteand andpyrite, pynte, indicating a reducing environment. To of deposition deposition were were suggested suggested for for this this unit unit To that thatend, end, intertidal intertidal and andsubtidal subtidal environments environments of the grade grade increases increases to to the the lower lower (Houston and Karlstrom, 1992). 1992). Greenschist Greenschistmetamorphic metamorphic facies facies dominate dominate in all units, units, but the amphibolite facies to the NE, NE. the Vagner Fm. were were analyzed analyzed for forcarbon carbonand andoxygen oxygenisotope isotoperatios. ratios.Each Eachsample sample exhibits exhibits aa Fourteen samples from from the Vagner Fm. negative carbon isotope -2. l96. Data of 6'3C= 8 1l C= -2.1960. Data comparison comparison with with the the correlative correlative Bruce Bruce Member Memberof ofthe the isotope values values with with an an average average of Espanola Formation, (Huronian by Veizer Veizer et a!. a!. (1992) reveals reveals a strong strong resemblance resemblance (Fig. (Fig. 1), 1),which which (Huronian Supergroup) Supergroup) reported reported by -l8.7%o, PDB) we follow the supports their correlation. 8180values values(average (averagefor forthe theVagner Vagner Fm.: Fm.: 8 180 == -18.7960, correlation. Regarding Regarding the the low low 8O of Veizer et a!. a!. (1992) (1992) that that the the lower lower values values may may be be due due to to meteoric meteoric water water flux. flux. suggestion of IJ 6O == -19.05960, -19.05%o, PDB. The8"C Only one one sample sample was was analyzed analyzed from from the the Lookout LookoutSchist; Schist;ititshowed showed8"C 5'C == 2.7960, 2.7%o, 8'"0 PDB. The C is is Only intermediate between 8"Cvalues valuesmeasured measuredfrom fromthe theunderlying underlying Vagner Vagner Formation Formation and the the high high values values of of the the overlying overlying between the the low low '3C Nash Fork Fm. These indicateaasignificant significantpositive positive shift shift in in the the isotopic isotopic composition of the marine carbonates. Thesedata dataseem seemtotoindicate Four samples were the Nash Nash Fork Fork Formation. Formation. All except one one exhibit high positive carbon isotope isotope were analyzed analyzed from from the 8 1J C= 5%o, 5960, highest: ratios (average: (average: S'3C highest:8"C= 3"C= 8.23960). 8.23%o).These Thesecarbon carbonisotope isotoperatios ratiosresemble resemblevalues valuesof ofthe theKona KonaDolomite Dolomite(Fig. (Fig. I), Fennoscandian carbonates, and other carbonates of about about the the same same age age worldwide worldwide(see (seeKarhu, Karhu, 1993). 1993). Based on Sm-Nd and UPb dating of sequences in which this excursion occurs occurs in in Fennoscandia, Fennoscandia, itit isis bracketed bracketed between between 2.21 2.21 and and 2.06 2.06 Ga. Ga. Correlation Correlation Formation with wIth these these better better geochemically geochemicallystudied studiedand anddated datedunits unitson onthe thebasis basisof of of the Kona Dolomite and the Nash Fork Formation carbon isotope ratios suggests a similar time of deposition. should be be noted, however, that one sample from from the Nash Fork deposition. ItIt should "low" carbon carbon isotope isotope ratio in comparison comparison with both the Kona Kona Dolomite Dolomite and the Formation has a "loW' with the the general general trend. trend. In addition, both values than than the the 2.2 2.2 -- 2.1 Ga Fennoscandian carbonates (6"C (O"C= 10 ± 3%o; 3960; Karhu, Nash Fork Formation have somewhat lower values 1993). (1993) correlated correlated the the DLG DLG and the the lower lower LCG LCG with the the Huroman Huronian Supergroup, Supergroup, and and the the upper upperLCG LCG Roscoe and Card (1993) stratigraphic, sedimentological, sedimento logical,and andage agesimilarities. similarities. Our data support with the Marquette Marquette Range Range Supergroup Supergroup on the bases of stratigraphic, ofchemostratigraphy chemostratigraphy as aa tool tool in in the the correlation correlation of ofEarly Early Proterozoic Proterozoic their correlation and and demonstrate demonstrate the the applicability applicabilityof carbonates from different basins. Our data confirm the aforementioned aforementionedcarbon carbonisotope isotopeexcursion. excursion. This This carbon isotope isotope confmn the worldwide character of the matter, leading leading to to increased increased atmospheric atmosphericoxygen oxygenlevel. level. This increase in of burial of of organic organic matter, excursion indicates a high rate of oxygen level level was was suggested between 2.2-1.9 2.2-1.9 Ga Ga based based on on independent independent geological geologicaldata data(Holland (Hollandand andBeukes, Beukes, 1990). 1990). Iron oxygen formations formations were were deposited deposited after after the the deposition depositionof ofthe the"C-enriched 'C-enriched carbonates carbonates in in MI, MI, WY, WY,and andFennoscandia. Fennoscandia. This This indicates excursion, while while dissolved dissolved iron iron was was transported transported and and precipitated precipitated in in the shallow that deep oceans remained anoxic even after the excursion, shelf areas. The Thehigh highpositive positiveexcursion excursioninincarbon carbonisotope isotope ratio ratio might might be be correlated correlated with rifting, formation formation of of anoxic basins and sedimentation rate rate and and many manyother otherfactors. factors. More detailed work is necessary carbonate platforms, high biomass fertility, fertility, high sedimentation before a working model can be developed. developed. 4 �Fig.1. Fig.1. Scatter Scatter diagram diagram of of d180 d180 vs. vs. d13C dl3C for studied Early Proterozoic carbonates. Data for the Kona Dolomite Dolom ite from from Feng Feng (1986) (1986) and and for the Member from from Veizer Veizer et et al. al. (1992). (1992). Bruce Member IIil •Vagnec .VagrerFm. Fm. Nash Fork l1li Nash ForkFm. Fm. Loo1ScFst A LookotJ Sellst Kor Dolomite X Kora DolomiteFm. Fm. Brte Member. • Bru::e Member. . 8.2 x X 7.2 X X I i*'\ :l.~ X x X • X x xX III X X 6.2 ::.xX 5.2 X 4.2 iii o x Q. U ..,(.) 3.2 ... 2.2 'C 1.2 1.2 l1li I -21 •• -20 •• • ••• -19 I I -18 -17 , -. I I •.- -16 .15 -15 I -14 -13 • •• •• •.sS •• I.. ":.# • I • • •• •• • ••• I I -12 -11 .2 I -10 -9 -8 -7 -0.8 -1.8 -28 -2.8 d180 References Precambrian marine marine sulfate and chert: chert: Unpub. Unpub. M.S. thesis, Feng, J., 1986, 1986, Sulfur Sulfurand andoxygen oxygen isotope isotope geochemistry geochemistry of Precambrian Illinois University. University. Northern illinois H. D. D. and andBeukes, Beukes,N. N.J., J.,1990, 1990.AApaleoweatheting paleoweatheringprofile profilefrom fromGriqualand GriqualandWest, West,South SouthAfrica: Africa: evidence evidencefor foraa Holland, H. rise in inatmospheric atmosphericoxygen oxygen between between 2.2 and 1.9 1.9 b.y.b.p.: b.y.b.p.: Am. J. Sci., 290A, p. 1-34. 1-34. dramatic rise R. S. S. and andKarlstrom, Karlstrom,K. K.E., E.,1992, 1992,Geological Geologicalmap mapof ofPrecambrian Precambrian metasedimentaty metasedimentary rocks rocks of ofthe the Medicine MedicineBow Bow Houston, R. Mountains, Albany Albany and andCarbon CarbonCounties, Counties,Wyoming: Wyoming: U. U. S. S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsMap MapI-1Mountains, 2280, scale 1:50,000. 1:50,000. Karhu, J. A., 1993, 1993, Paleoproterozoic Paleoproterozoic evolution evolution of of the carbon isotope ratios of sedimentary carbonates in the Fennoscandian Shield: Geological ofFinland Finland Bulletin Bulletin371, 371, 8'7p. 87p. Geological Survey Survey of W. R. R. and and Van VanSchinus, Schnms,W. W.R., R.,1989, 1989,Zircon Zircongeochronology geochronology of Precambrian·rocks in southeastern southeasternWyoming Wyoming and and Premo, W. Precambrianrocks in northern Geology of of the theSouthern SouthernRocky RockyMountains, Mountains,(Eds.) (Eds.)Grambling, Grambling,J.J.A., A., and and northern Colorado: Colorado: In Proterozoic Geology Tewksbury, Geological Society of America Special Paper 235, pp. 13-48. 13-48. Tewksbuxy, M. and and Card, Card,K. K.D., D.,1993, 1993,The Thereappearance reapPearanceofofthe theHuronian HuronianininWyoming: Wyoming: rifting rifting and and drifting drifting of ofancient ancient Roscoe, S. M. continents: Canadian J. Earth EarthSci. Sci. 30, 30, pp. pp. 2475-2480. 2475-2480. Canadian J. Veizer, J., Clayton, Clayton, R. R. N., N., and andHinton, Hinton,R. R. W., W.,1992, 1992,Geochemistiy Geochemistry of ofPrecambrian Precambrian carbonates: carbonates: IV. IV. Early Early Paleoproterozoic Paleoproterozoic vol. 56, 56, pp. pp. 875-885. 875-885. (2.25± 0.25 0.25 Ga) Ga) seawater seawater:Geochimica GeochimicaetetCosmochimica CosmochimicaActa, Acta, vol. (2.25± 5 �SOUTHWARD EXTENSION SOUTHWARD EXTENSION OF OF THE THE PENOKEAN PENOKEAN TERRANE TERRANE THROUGH THROUGH STEARNS STEARNS COUNTY, CENTRAL CENTRAL MINNESOTA MINNESOTA BOERBOOM, Terrence J., I., Minnesota MinnesotaGeological Geological Survey, Survey, St. St. Paul, Paul, Minn., Minn., 55114-1057. 55114-1057. E-mail Boerb00l@maroon.tc.umn.edu BoerbOOI@maroon.tc.umn.edu ofthe thePrecambrian Precambrian bedrock bedrockgeology geology of ofStearns StearnsCounty County Recent remapping remapping by by the the Minnesota MinnesotaGeological Geological Survey1 Surveyl of has identified identified aa previously previously unrecognized unrecognized southwestern southwestern extension extension of of the the Penokean Orogen (Fig. 1). 1). Prior Priorto tothis this study, most of of Stearns Stearns County County was was considered.to considered.to be be underlain underlain by by Archean Archean high-grade granitoid gneisses, with the exception of county. Although of some some Penokean Penokean intrusions intrusions in in the the southeastern southeastern part of the county. Although the the northwestern northwestern part part of of the county isis still still interpreted interpreted to to be beArchean Archean gneiss, gneiss, itit is is now now recognized recognized that that Early Proterozoic Proterozoic rocks, which Formation, as as well well as as many many intrusions intrusions of of include supracrustal rocks of the Mule Mille Lacs Group and Little Falls Formation, varied size and and composition, composition, are are predominant. predominant In Inaddition, addition, thrust thrust and and strikestrike- or dip-slip faults are an important aspect of glacial drift drift and and patches patchesof of of the geology in this region. Because Becausemost most of of Stearns Stearns County County is covered by glacial Cretaceous rocks, structural and and lithologic lithologic rocks, drill-hole drill-hole and and geophysical geophysical data data were utilized utilized extensively to infer the structural attributes of of the the bedrock. bedrock. The revised revised geology geology can can be be subdivided subdivided into into the the following following six six broad lithologic units, listed from oldest to youngest: (1) (I)Archean Archeangranitoid granitoidgneisses; gneisses; (2) (2)the theArchean Archeanor orEarly EarlyProterozoic, Proterozoic, grarnilite-grade granulite-grade Sartell Gneiss (broadly grouped with with the Hiiman HillmanMigmatite Migmatiteoutside outside of ofStearns Stearns County); County); (3) (3) the theEarly Early Proterozoic Proterozoic Mille Mille Lacs Lacs Group; (4) Formation; (5) (4) the the Early Early Proterozoic Proterozoic Little Little Falls Formation; (5) Animikie strata of the Long Prairie and (6) (6) Group; Prairie basin; basin; and Early Proterozoic Proterozoic intrusions intrusions that thatintrude intrude most most of ofthe the above. above. Archean granitoid granitoid gneiss gneiss at at the the northwest northwest corner corner of of the the county is is foliated and variably lineated along a epidote. The minerals northeast trend and locally pervasively altered to epidote. The Sartell Sartell Gneiss Gneiss contains the metamorphic minerals orthopyroxene, garnet, gamet, sillimanite, sillimanite, and and local local hercynite hercynite and and corundum, corundum, and and includes includes some some granitoid gneiss. between older Archean Archean The Mule Mille Lacs Lacs Group Group underlies underlies the the southwest southwest corner corner of of the county in a block wedged between basement rocks. rocks. This Thisgroup groupofofrocks rocksisisconjectured conjecturedto toconsist consistof ofmetamorphosed metamorphosed volcanic volcanic and and sedimentary rocks of iron-formation. Thrust Thrustfaults faults are are indicated indicated by by geophysical geophysical data to occur both within and marginal and thin beds of marginal to the Mille Lacs Group. to Group. The Little Falls Falls Formation Formation contains contains aa sillimanite-garnet-staurolite sillimanite-gamet-staurolite assemblage that typifies this unit to the north. The north. Thewestern westernedge edgeof ofthe theLittle LittleFalls FallsFormation Formationhas hasbeen beenthrust thrustover over the the Mille Mille Lacs Lacs Group. Group. The Long Prairie Prairie basin basin forms forms an an outlier outlier of of Animikie Animikie strata strata that that correlates correlates with, but but is is physically physically separated from, the Virginia Formation from, Formation to to the the northwest. northwest. The Thestrata strataare areonly onlyweakly weakly deformed deformed relative relative to to other other Early Early Proterozoic is strongest strongest along along its its southeastern southeastern edge, where it is has been Proterozoic supracrustal supracrustal rocks, rocks, but but deformation deformation is overthrust by older older rocks rocks of of the the Penokean Penokean Orogen. Orogen. The intrusive intrusive rocks rocks range range widely widely in in size size and and composition composition from from small small ultramafic ultramafic plugs, plugs, irregularly irregularly shaped shaped mafic charnockitic chamockitic bodies, bodies, large large plutons plutons of ofgabbroic gabbroic to to granitoid granitoid rocks, rocks, to to thin thin cross-cutting cross-cutting dikes dikes of of diabase diabase and and orall allof ofthese these intrusions intrusions are are inferred inferred to to be be latelate- to post-kinematic with porphyritic granite. Most Mostor with regard regard to to the the the southeast southeast part part of of Penokean orogeny. They Theyoccur occurnot notonly only as as discrete discrete bodies bodies in in the the supracrustal supracrustal rocks but, in the the county, as as aa continuous continuous plutonic plutonic terrane terrane of ofdominantly dominantly granitoid granitoid bodies bodies that include the Richmond Granite, Reformatory granodiorite. granodiorite. Earlier workers workers established established Early Early Rockville Granite, St. Cloud (Red) Granite, and the Reformatory Proterozoic ages for these granitoid rocks and diabase dikes, dikes, but but modern modern geochronologic geochronologic data dataare arelacking. lacking. These These plutonic rocks at a scale of 1:2400 rocks are are so so well well exposed exposed in in this this part part of of the the county county that that local local remapping on airphotos airphotos at was possible. been recognized recognized from fromgeophysical geophysicaldata. data. The The wedge wedgeof ofMille Mile Lacs Several gross structural attributes have been is bounded bounded on on its its northwest northwest side side by by aa steep steep northwest northwest dipping dipping fault fault interpreted interpreted to to be be an Archean Archean Group strata is orogeny. On bounded by by aa brittle brittle tear tear structure reactivated during the Penokean orogeny. On its its southwest southwest side the wedge is bounded fault that has juxtaposed the the Penokean Penokean strata against older Archean rocks over some 50 km length and produced a terminate against against this this major offset of the Penokean margin. Although Although supracrustal supracrustal rocks rocks of of the Penokean Orogen terminate fault, evidence suggests that the across but but may may be be affected affected by by it. it. The fault, the Penokean Penokean Rockville Granite extends across The fault north-striking, southeasthas has also acted as a locus of emplacement for other smaller Penokean Penokean plutons. plutons. Other north-striking, southeastdipping thrust faults have have imbricated imbricated the the Mille Mille Lacs Group strata; they they also also occur occurbeneath beneath the the overriding overriding Little Little Falls Formation. These Thesesoutheast-dipping southeast-dippingthrust thrustfaults faultsare areconsistent consistentwith with previously previouslymapped mapped faults faults in in Penokean Penokean Archean ofthe the thrusts thrusts within within the the Penokean Orogen near the Archean strata to the north. The Theeast-curving east-curvingmorphology morphology of block to the northwest northwest imply imply that thatthe the latter lattermay may have have acted acted as as an an buttress buttress that that deflected deflected deformation. deformation. County are are the the recognition recognition The most important important findings fmdings of of the the newly newly interpreted interpreted bedrock geology of Stearns County terrane extend extend considerably considerably farther farther that the Mille Lacs Group Group and Little Little Falls Formation within the Penokean Penokean terrane south than previously recognized, recognized, that that aa tear tear faulthas fault hassubstantially substantiallyoffset offset the the Penokean Penokean margin margin and and juxtaposed juxtaposed the the Penokean terrane terrane against against older older Archean Archean rocks, rocks, and and that that thrust thrust faults faults have have played played a significant significant role in the structural evolution of recognized of this area. The Thesize, size,distribution, distribution, and and abundance abundance of ofPenokean Penokean intrusive intrusive rocks are also better recognized and understood. 'This 1This interpretation interpretation was was completed completedasaspart partofofthe theStearns Steamscounty countygeologic geologicatlas atlas(Minnesota (MinnesotaGeological Geological Survey, Survey, County County Atlas Series Atlas Atlas C-b, C-10,Part PartA), A),which whichincludes includesdata database, base,bedrock bedrockgeology, geology,surficial surficialgeology, geology,Quaternary Quaternarystratigraphy, stratigraphy, depth to bedrock, bedrock, bedrock bedrock topography, topography, and and mineral mineral resources resources plates. plates. depth �.. ._ ..95O .. ... .' ... ... .-. -, .,.--.. -.. -.. "",J,~""'~"'" ... ..' .— .. —. ... — ... ... —, —. —, —. -.. -.. - .— — "~~"""""",, 4 -.. -.' -. - - -. -.' -' - " A- " -" -'"-'" -' -"-' . -' -"--fl - #-c•-" -. -, -.fl — -.. - ... .-. — — -k-• — -' . — -.' ..' -'fi — -'fi — -. ..' -.fl -. .— -. -. -'fi -fi -. .0.0.0 .0..' fl .0 -. -. -. .— —. .0.0 .0.0 .0 .0 .0 .0 .0.0.0.0.0. .0 .0 .0.0.0.0' .0.0 .0 .0.0 .0 0.0.0.0.0.0• .0.0.0.0.0 _0 -' .0.0'.0 .0.0.0.0.0..0 .0 .0 .0.0.. .0 — .0 .0.0.0.0' .0 .0 .0 .0 .0.0 .0 .0..' .0 .0 .0.0 .0 .0 .0.0.0 .0 .0 .0 .0 .0 f fi , A / Location of Stearns County Partial funding funding for the Steams Steams Partial for the ' '-// ij7 /// ',,, ,';' -1 ii S's..' '1'.(" //(1''-l'••' " ,5,s -l—I-l-l-I—I County At/as Atlas was was approved approved by by the the Minnesota Legislature Legislature (M.L. (M.L. 91, Minnesota 91. Ch. Ch. 254, 254, Art. Art. 1, I, Sec. Sec. 14, 14, Subd. Subd. 4[F], 93, Ch. Ch. 172, 172. Sec. Sec. 4[FJ, and and M.L. M.L. 93, 14, II[gJ) as recommended 14, Subd. Subd. 1119]) by the Legislative Legislative Commission Commission on Minnesota Resources Resources from from the Minnesota the Minnesota Environment and Natural Resources Trust Trust Fund. Fund. 5/., - I - I1.<i:k5., .,, ,,. ., , : III'LJ III,. _ 5 5 miles miles EXPLANATION EARLY PROTEROZOIC ROCKS to ultramafic plutons; includes ~ Mafic to peridotite, gabbronorite. gabbrononte, & gabbro. peridotite. Falls Formation 1-) Little (staurolite schist). Gabbro, norite, nonte, chamockite;includes [.. :. . . :. .j Gabbro, Mule Lacs Lacs Group. Group, undivided. ~ Mille '. '. charnockitic affinities. affinities. granites with charnockitic c:=J Granitoid plutons, undivided Granitoid plutons. undivided -, . Richmond Granite ~ Rockville Granite Rockville D Reformatory Granodiorite Granodiorite çcq Long Prairie ~ Long Prairiebasin basin(Animikie (Animikie LJ Basin, argillite and graywacke). ~ Basin. argillite and graywacke). Strike-slip or dip-slip fault. ~ Miscellaneous metamorphosed ~ volcanic and sedimentary rocks. rocks. t+:+:+j St. Cloud (Red) (Red) Granite Granite ~~j~j Little Falls F0f!"ation (staurolite schist). Thrust fault. ARCHEAN ROCKS ~ Sartell Gneiss Gneiss and and Hillrnan Hillman ~ Migmatite (may be Early Proterozoic). f ......1 Granite-greenstone terrane. terrane. o Lithologic contact. contact. High-grade gneiss terrane. Figure 1. Simplified Figure Simplified pre-Cretaceous pre-Cretaceous geologic geologic map map of of central Minnesota. Stearns Minnesota. Stearns County is is outlined. outlined. 7 �AN ELECTRONIC COMPONENT OF THE INSTITUTE ON LAKE SUPERIOR AN COMPONENT OF INSTITUTE ON GEOLOGY BORNHORST, Theodore Theodore J., and DOLAN, Michael, T. Department Department of of Geological Geological Engineering and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, tjbornho@mtu.edu, mtdolan@mtu.edu. Houghton, MI 49931; tjbornho@mtu.edu, is becoming an increasingly increasingly important important part part of daily The information superhighway superhighway is becoming.an Electronic communication communication can, can h~lp help the the Institute on Lake Superior Superior professional activities. Electronic Geology better serve itit constituents, Geology constituents, perhaps perhaps attract attract new professionals professionals to participate in the organization, make the the JILSG n...SG better Lakes region. region. organization, and make better known known beyond beyond the the bounds bounds of the Great Lakes The Board of Directors of the Institute on Lake Superior Geology has authorized the creation Institute Geology has authorized the creation of an ILSG home page. page. 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For more information on the Lake Superior Geology Geology discussion list, email the list list server server at at Michigan Michigan Tech: Tech: For information on the the list: list: Send Send mail mail to: to: majordomo@mtu.edu Subject: Subject: (enter no subject) Body of message: message: info Isg-l lsg-l To subscribe: subscribe: Send mail mail to: Send to: majordomo@mtu.edu Subject: (enter no subject) Subject: Body of message: message: subscribe subscribelsg-1 lsg-l 8 �THE WEST-CENTRAL OF JUNE JUNE 5, 1993: WEST-CENTRAL MINNESOTA MINNESOTA EARTHQUAKE EARTHQUAKE OF 1993: AN AN OPPORTUNITY OPPORTUNITY TO RE-EXAMINE RE-EXAMINE SEISMICITY NEAR NEAR THE MORRIS MORRIS FAULT CHANDLER, VAL VAL W., W.,Minnesota Minnesota Geological Geological Survey, Survey, 2642 University University Ave., Ave., St. St. Paul, Minn., 55114-1057 1) provides provides an an opportunity opportunity 1993, west-central west-central Minnesota Minnesota earthquake earthquake (mbLg=4. (mbLg=4.1) The June 5, 1993, Minnesota seismicity seismicity and and its its possible possible relationship relationship to to reactivated basement basement to re-investigate Minnesota structures. The The earthquake earthquakeoccurred occurred within within 25 25 kilometers kilometers of of the the much larger July 7, 1975, 1975, which has has been been attributed attributed to to the the Morris west-central Minnesota earthquake (mbLg=4.6), (mbLg=4.6), which fault, a northeast-striking crustal fault, crustal discontinuity discontinuity separating separating two two distinct distinct Archean Archean terranes. terranes. Intensity data data from Intensity from the the 1993 1993 earthquake earthquake confirm confirm the the position position of the the instrumentally instrumentally determined epicenter epicenter and and reveal reveal a felt area of of about about 69,500 69,500 square square kilometers, kilometers, with a determined of V. V. Some Somelocal localperturbations perturbations in in the the isoseisms isoseisms correlate correlate with with features features maximum intensity of in the Precambrian bedrock, bedrock, implying implying that that seismic seismic energy may be focused significantly by crustal structure. Focal Focal depth depthestimates estimates based based on on intensity intensity data data imply imply that that the 1993 1993 focal depth is similar to that that of of the the 1975 1975 earthquake, earthquake, which which has has been been independently estimated estimated to to be 7.5 kilometers. The Morris fault has been generally thought to be the major seismogenic feature in the region, but neither the 1993 1993 hypocenter inferred by by this this study study nor nor the the 1975 1975 hypocenter hypocenter agree the fault fault as as revealed revealed by seismic-reflection seismic-reflection data agree with the subsurface trace of the data and and magnetic modeling. Alternative Alternativesources sourcesfor forthe the1975 1975and and1993 1993earthquakes earthquakesinclude includewest— westare interpreted to consist consist chiefly chiefly of of mafic mafic northwest-striking sub-vertical structures that are Someof ofthese thesefractures fractures are are associated associated with with minor minor faulting—as faulting-as dikes and related fractures. Some small offsets offsets in in the the Morris Morris fault—and fault-and possible possible disruption disruption of Cretaceous Cretaceous evidenced by small strata. Neither the Morris Morris fault fault nor nor the the west-northwest west-northwest structures structures agree with with aa loosely loosely constrained focal mechanism for the 1975 1975 earthquake, but the west-northwest west-northwest structures structures are are to be be reactivated reactivated by by the the east-northeast east-northeast regional regional compression compression that that has has favorably oriented to been averaged for for the the eastern eastern United United States. States. This indicates that that minor minor basement basement structures, structures, such such as mafic mafic dikes dikes and and This study indicates associated fractures, may a largely may play playa largely unappreciated unappreciatod role role in in seismicity seismicity of of mid-continental mid-continental regions. Such regions. Suchstructures structuresmay maynot notbe beevident evidentin inmany many existing existing geological geological and and geophysical geophysical data sets. This study study was Minnesota through through the the State Special Special This was supported by the the University University of Minnesota ofthe the Minnesota Legislature. Appropriation Appropriation of 9 �Petrographic and Petrographic and thermobarometric thermobarometricanalysis analysisof ofthe the metamorphosed metamorphosed Little Little Falls Falls Formation, central Minnesota, Minnesota, with with implications for Early Proterozoic Proterozoic tectonism tectonism DARRAH, KS., K.S., HOLM, HOLM, D.K., D.K., DAHL, DAHL, P.S., P.S., Dept. Dept of of Geology, Kent State University, Kent OH 44242; and LUX, D.R., Dept. of of Geological Sciences, University of of Maine, Orono, ME 04469. Recent advances in in thermobarometry thermobarometry have have significantly significantly increased increased our our Understanding Understanding of regional metamorphism metamorphism in in ancient ancient orogenic orogenic belts, belts, allowing allowing important important constraints constraints to to be be made made on on their tectono-thermal evolution. However, their tectono-thermal evolution. However, there have been been few few quantitative quantitative studies studies of the the pressure and temperature of rocks rocks metamorphosed metamorphosed during the Early Proterozoic (1870 temperature evolution evolution of -1820 Ma) Penokean Penokean orogeny orogeny in Minnesota. Minnesota. One One previous previous study study in in east-central east-central Minnesota Minnesota suggests that that Early Early Proterozoic Proterozoic sedimentary sedimentary rocks rocks metamorphosed metamorphosed during during the the Penokean Penokean orogeny orogeny reached temperatures of 450-600°C and minimum pressures of 5-6 kbar (Hoim and Selverstone, Selverstone, temperatures of 450-600°C and minimum pressures of 5-6 kbar (Holm and 1990). Formation (LFF), (LFF), located located within within the the internal internal zone zone of of The Early Proterozoic Little Falls Formation orogenic belt, belt, isis aa biotite-quartz-plagioclase-muscovite biotite-quartz-plagioclase-muscovite schist schist whose whose protolith protolith was was the Penokean orogenic graywacke sequence sequence with with carbonate carbonate concretions. Metamorphic Metamorphic'grade gradeincreases increasesfrom from a shale and graywacke garnet grade in the north to staurolite grade in the south. south. One One drill drill core core sample sample and and one outcrop outcrop sample both from from within within the the staurolite staurolite zone zone contain contain synkinematic synkinematic garnets and post-kinematic post-kinematic Thegarnets garnetsare areabout about1-2 1-2mm mm in in diameter diameterand and are are characterized characterized by by quartz-inclusionquartz-inclusionstaurolite. The rich cores and of crystal crystal and inclusion-free inclusion-free rims, rims, indicating indicating that that there there may may have have been been two two episodes episodes of Thesegarnets garnetsoccur occurboth both within within the the matrix matrix and and as as inclusions inclusions within the staurolite. staurolite. The The growth. These the main main fabric fabric of of the the unit. unit. Petrographic staurolite occurs as 1-2 1-2 cm em porphyroblasts that cross cut the the foliation foliation preserved preserved within within the the staurolite staurolite (as (as quartz quartz and and garnet garnet inclusions) inclusions) is is work shows that the Overall, the the petrographic petrographic features of the LFF are similar to parallel to the foliation in the matrix. matrix. Overall, to that described for Early Early Proterozoic Proterozoic metasedimentary metasedimentary rocks located over 150 150 km to the the northeast northeast (Hoim and Selverstone, 1990). (Holm Detailed microprobe microprobe analyses analyseswere wereperformed performedon onboth bothsamples samplesofofthe theLFF. LFF. Garnet Garnet Detailed interiors exhibit uniform with an overall almandine. interiors uniform compositional compositional patterns patterns with overall composition composition of almandine. and spessartine spessartine Closer to the rims, the the almandine almandine and pyrope content increases and the grossular and prograde garnet garnet growth. growth. These content decreases, decreases, a trend that suggests prograde These compositional compositional changes changes appear to correspond correspond with the the transition transition from from inclusion-rich inclusion-rich core an inclusion-free inclusion-free rim. appear core to an However, the textural change within the garnets is abrupt whereas the compositional change is gradational. The LFF contains contains appropriate appropriate mineral mineral assemblages assemblages on on which which geothermobarometry geothermobarometry can can be be performed. Weapplied appliedthe thegarnet-biotite garnet-biotite thermometer thermometer (Ferry (Ferry and and Spear, Spear, 1978; 1978; Hodges Hodges and and performed. We Spear, 1982) 1982) and and the the garnet-plagioclase-biotite-muscovite garnet-plagioclase-biotite-muscovite barometer (Ghent and Stout Stout 1981; 1981; Hodges and and Crowley, to the LFF Hodges Crowley, 1985) 1985) to LFF samples samples in order order to to determine determine the the pressure pressure and and temperature conditions during during garnet garnet growth. growth. Core of 450-500°C 450-500°C temperature conditions Core analyses analyses gave gave temperatures temperatures of Sinceonly onlyquartz quartzoccurs occurs as asinclusions inclusions within within the the garnets garnets we we used used and pressures of 5-6 kbar. Since in order to estimate the pressures of matrix plagioclase, biotite, and muscovite muscovite compositions compositions in pressures of garnet core growth. Rim Rimanalyses analysesyield yieldhigher highertemperatures temperaturesofofapproximately approximately500-550°C 500-5500C and and The isobaric similar pressures of 5-6 5-6 kbar. kbar. The isobaric garnet growth we infer infer presumes presumes that that matrix matrix similar pressures plagioclase did not change in composition during garnet garnet growth. growth. These composition during These results results concur concur with with plagioclase did previous work done of the the orogenic orogenic belt belt (Hohn (Holm and and Selverstone, Selverstone, 1990). 1990). done in in other other areas areas of We interpret interpret the the inclusion-rich inclusion-rich core of of the the garnets garnets to to represent represent syntectonic syntectonic mineral mineral growth oflate late garnet garnet rim rim and andstaurolite staurolite growth during during the Penokean Penokean orogeny. orogeny. However However the the timing timing of growth is uncertain. ItItisispossible just after after the the possiblethat thatboth boththe thegarnet garnetrims rimsand and the thestaurolite staurolite grew grew just formation of the foliation within the rock. rock. In Inthis thisscenario, scenario, the the 'peak' 'peak' metamorphic metamorphic conditions conditions formation would associated with with conductive conductive relaxation relaxation after after crustal crustal thickening thickening during during the the orogeny orogeny would be associated Alternatively the the garnet garnet rim rim and late staurolite (Holm 1988). Alternatively staurolite growth growth could could have have (Holm and and others, 1988). 10 �occurred much later, perhaps perhaps as as aathermal thermalresponse responsetotothe the—1770-1760 -1770-1760 Ma Ma post-tectonic post-tectonic occurred much magmatism in in the region. then the the 'peak' 'peak' metamorphism metamorphism would yield yield pressure pressure and and magmatism region. If so, then temperature conditions well after the Penokean Penokean orogeny. orogeny. In In this this second scenario, the the discordance discordance between 'peak' metamorphic pressures pressures (5-6 (5-6 kb) and the emplacement pressures determined determined for the post-tectonic plutons (3.0-4.5 kbar, Holm, 1995) 1995) would the post-tectonic piutons (3.0-4.5 kbar, Darrah' Darrah and and Hoim, would require rapid uplift concomitant with plutonism. 9Ar hornblende 40Arf3 two 40Arf39Ar hornblendecooling coolingdates datesmay mayallow allowusustoto distinguish distinguish between between the two scenarios presented above. above. Country Countryrock rockhornblende hornblendedates datesolder olderthan than—1770 -1770 Ma would indicate temperatures Three temperatures below below 500°C 500°C prior to to pluton pluton intrusion, intrusion, thus thus ruling ruling out out the the second second scenario. scenario. Three from widely scattered scattered samples samples of of both both Archean Archean rocks rocks and and metamorphosed metamorphosed hornblende separates from Early to the east of the LFF all yield yield dates dates approximately coeval or slightly Early Proterozoic Proterozoic rocks rocks to concordant with with the the uniform uniform 1750-1760 younger than the age of the plutons, and approximately concordant 1750-1760 Ma 40Ar(39Ar Thus, although although somewhat somewhat preliminary preliminary 40Ar/39Arbiotite biotitedates datesof ofHolm Hoimand andLux Lux (1996). (1996). Thus, (more (more hornblende hornbiende dates dates are currently currently being being processed), processed), the the data data at at present present may may suggest suggest a major major period of rapid rapid unroofing unroofmg of of this this portion portion of of the the Penokean Penokean orogenic orogenic belt during aa pulse pulse of ofpostpostThe new new results results presented presented here are consistent consistent with occurrence of tectonic tectonic plutonism. plutonism. The with the the occurrence of a of orogenic collapse of the Penokean orogeny proposed episode of orogeny (Holm (Hoim and and Lux, Lux, 1996; Schneider 1996). and others, 1996). References Darrah, K.S., and Holm, D.K., O.K., 1995, 1995, Application of the Aluminum-in-hornblende barometer on Early Proterozoic, post-Penokean post-Penokean plutons, Lake Superior Superior plutons, central central Minnesota: Minnesota: Institute on Lake Geology Abstracts, v. 41, p. 7-8. Ferry J.M., J.M., and Spear, F.S., 1978, calibration of of the the partitioning partitioning of Fe and Mg Ferry 1978, Experimental Experimental calibration between biotite Contributions to Mineralogy Mineralogy and Petrology, Petrology, v. 66, p. 113113between biotite and and garnet: garnet: Contributions 117. Ghent, E.D., E.D., and Stout, M.Z., 1981, of plagioclase-biotiteGhent, 1981, Geobarometry Geobarometry and and geothermoetry of assemblages: Contributions garnet-muscovite assemblages: Contributions to Mineralogy and Petrology, v. 76, p. 9297. Hodges, 1985, Error estimations estimations and empirical geothermobarometry geothennobarometry Hodges, K.V., and Crowley, P.D., 1985, for pelitic systems: American American Mineralogist, Mineralogist, v. 70, p. 702-709. Hodges, K.V., and Spear, F. F. 1982, 1982, Geothermometry, Geothermometry, geobarometry geobarometry and and the the A12SiO5 Al2SiOs triple point at Mt Mt. Moosilauke, New Hammpshire, American Mineralogist, Mineralogist, V. V. 67, 67, p. p. 1118-1134. Holm, DX., D.K., Hoist, Holst, TB., T.B.,and andEffis, Ellis,M.A., M.A,1988, 1988,Oblique Oblique subduction, subduction, footwall footwall deformation, deformation, and Hoim, imbrication: A model for the Penokean orogeny in east-central east-central Minnesota: Geological imbrication: Minnesota: Geological v. 100, p. 1811-1818. Society of America Bulletin, v. Holm, D.K., and Selverstone, J., 1990, 1990, Rapid groth and strain rates inferred inferred from from synkinematic synkinematic Hoim, Geology, v. 18, 18, p. 166-169. garnets, Penokean orogeny, Minnesota: Minnesota: Geology, Hoim, Holm, D.K., and Lux, D.R., D.R., 1996, 1996, Core Core complex model proposed for gneiss gneiss dome dome development development during collapse of the Paleoproterozoic Penokean orogen, Minnesota: during collapse the Paleoproterozoic Penokean orogen, Minnesota: Geology Geology (in (in press). Schneider, D., Holm, D.K., and Lux, D., 1996, 1996, On the origin of of Early Proterozoic Proterozoic gneiss gneiss domes domes and metamorphic nodes, northern northern Michigan: Michigan: Canadian and metamorphic nodes, Canadian Journal Journal of of Earth Earth Sciences Sciences (in (in press). 11 �MICHIGAN MINERAL MINERAL LEASE EXPLORATION DATA INVENTORY MICHIGAN INVENTORY Milton A. Gere, Jr. Real Estate DMsion, Division, Michigan Department Department of of Natural Natural Resources Resources Marquette, MI MI49855 49855 Upon Upon termination of a metallic or or nonmetallic nonmetallic mineral mineral lease lease on on State State of of Michigan Michigan owned owned minerals minerals land, land, exploration data, data, geological records and and samples, samples, including including drill drill cores cores and and cuttings, cuttings, from the work exploration performed are performed are submitted submitted to to the the State State to to become become part part of ofthe the public public record. record. Periodically, exploration on private land leases is also donated to the State. information collected by companies during dUring work on Records are on on file file for exploration exploration and and mining mining activity activity for for numerous numerous mineral mineral commodities. commodities. Past Records are Past leases leases involved efforts to locate locate and/or and/or mine mine copper, copper, diamonds, diamonds, gold, iron, iron, limestone limestone and and dolomite, dolomite, uranium uraniumand and and base base metals. metals. associated precious and The exploration information is is now inventoried on a computer database which allows access by county name, town and and range, range, company company name name or orState State lease leasenumber, number,etc. etc. The The inquiry indicates if geological or name, town geophysical geophysical work work was was performed, performed, ifif any any drilling was was done, done, what what type type and and any any drill drill log log confidential status. It also lists if any drill core, were submitted submitted and additional core, cuttings cuttings or other samples or assays were information. inventory is is kept kept in in hard hard copy copy files files which may may be be reviewed reviewed on on an an appointment appointment Information listed in the inventory basis. Geologic Geologic and and geophysical geophysical data on file may prove to be an important lead to the future basis. understanding of Michigan's Michigan's geologic geologic and and mineral mineral resources. resources. Commodities Commodities located located in in the past may now understanding of be economic to produce. Also, Also, the the lack lackof ofknown known specific specificresources resources in in an an area area may maysuggest suggest that that expenditure expenditure of new exploration exploration dollars dollars would would be be better betterused usedininanother anotherMichigan Michiganlocation. location. Additionally, Additionally, determined for a parcel other companies are interested in leasing so terminated lease status may be determined their exploration activities activities can can take place. place. The quantity quantity and and quality quality of of the the information informationon onfile filevaries variesdrastically drasticallyfrom fromlease leasetotolease. lease. The The type typeof of lease, or or contract, contract, the the years years that that the the lease lease was was in in effect, effect, the the amount amount of of work work done done on on the the property property and and lease, the lessee lessee all all playa play a part part in in determining determining what what eventually is submitted to be the public consciousness consciousness of the be placed into open-file status. placed The leasing of State owned minerals is a function long managed by the Minerals Lease Management Section, Real Estate Division of of the Michigan Michigan Department Department of of Natural Natural Resources Resources (MDNR). (MDNR). For For many many years the the collection of exploration data and samples at the termination of of the leases leases was handled by the However, during during the the split split of of functions functions of of the the MDNR, MDNR, Michigan Geological Geological Survey Division (GSD). (GSD). However, Quality October 1, 1995, the GSD was placed placed into the new Michigan Michigan Department of Environmental Quality (DEQ). During geologic, metallic and (DEQ). During this this process process the limited general geologic, and nonmetallic mineral resources and groundwater resource resource related related functions, functions, and and staff, staff, of the GSD were were transferred transferred to the Real Estate Division Division (RED) (RED) of the DNR. RED geologic staff and functions are located in Lansing, Escanaba, and Marquette. Through the above changes, records from terminated State mineral leases changes, the geologic records leases now now reside reside in files of the RED/MDNR. samples submitted submitted at at lease leasetermination terminationare. are. RED/MDNR. Any Any geological geological drill core or other samples in the the GSD/DEQ's GSD/DEQ's Geological Geological Core Core and and Sample Sample Repository Repositoryfor for public public use. use. Both the Mineral then placed placed in Lease Lease Data Data Inventory Inventory and and the the Repository Repository are are located located in in the the Marquette, Marquette, MI Ml locations of the DNR and the DEQ. information about about the the Mineral Mineral Lease Lease Data Data Inventory, Inventory, call call Milt Milt Gere, Gere, RED/DNR, RED/DNR, or or for for information information For information about the Repository, Repository, call Bill Swenor, Swenor, GSD/DEQ. Both Both can can be reached via phone phone at at 906/228-6561. 906/228-6561. 12 �GEOCHEMICAL SOURCE TRENDS OF THE SOURCE CHARACTERISTICS CHARACTERlSTICS AND DIAGENETIC TRENDS FORMATION, MESABI MESABI IRON IRON RANGE, RANGE, MINNESOTA MINNESOTA VIRGINIA FORMATION, Hemrriing, Lamont-Doherty Earth S. R. Hemming, Earth Observatory, Observatory, Rt. Rt. 9W, Palisades, NY 10964, ng@lamont.ldeo.columbia.edu; S. M. McLennan,and and G. 0. N. Hanson, hemming@lamont.ldeo.columbia.edu; S. M. Mclennan, hem Department of Earth and Space Sciences, SUNY, Stony Brook, NY 11974 Understanding of the Animikie Animikie Basin is integral to understanding the regional tectonic Understanding the the evolution evolution of (heat Lakes Proterozoic. The Animikie Basin Basin contains contains aa framework in the Great Lakes area area during during the Early Proterozoic. number of of approximately approximately correlated correlated shale to turbidite sequences that fonn form the youngest wlit unit within the Animikie Aniniikie Group. Group. In Inthe the Mesabi Mesabi Iron Iron Range Range of of northern Minnesota, Minnesota, the Virginia Virginia Fonnation Formation is is of shales and is is relatively relatively undeformed. undefonned. The geochemistry of of sedimentary composed dominantly of powerful information rocks provides powerfiul informationconcerning concerningbasin basinevolution. evolution. However, However, there there are are aa number number of of complexly interactive parameters that control the composition of The ideal ideal of sedimentary sedimentary rocks. rocks. The ofelements elements that could could be used to quantify the original composition of the characteristics characteristics of the ultimate ultimate igneous inunobility in igneous source are relative immobility in most most natural natural fluids fluids and and different different enough enough behavior behavior during during igneous differentiation as to be sensitive to source source composition. composition. Although Although no element is completely igneous immune well known immune from chemical attack, it is well known that that the the rare earth elements elements and and Th Th and and Sc are well isotopes provide valuable constraints on on the characterizing source source compositions compositions and and Nd isotopes suited for characterizing of the sources. Compared Compared to to post-Archean post-Archean Australian average antiquity of average shale shale (PAAS), (PAAS), shales shales of of the Early Proterozoic Proterozoic Virginia Virginia Formation Formation have have light light rare earth earth element element enriched patterns and high of rare earth elements, elements, low low m/Sc thlScratios ratiosthat thatare arecorrelated correlatedto toTh Thabundances abundancesand andhigh high abundances of LaiTh ratios. The La!Th TheSm-Nd Sm-Ndisotope isotopecomposition composition of ofVirginia Virginia samples indicates a source that was earth element element depleted depleted reservoir, and and the the trace trace element element long-tenn light light rare rare earth recently derived from aa long-term character best fit fit aa young young character indicates indicates itit was was aa continental continental source. These Thesegeochemical geochemical data best as the the dominant dominant source source for for the Virginia Formation. differentiated arc as Elements are variably susceptible attack by by surface suthce waters waters and and thus thus well well susceptible to chemical chemical attack understood trends in chemical composition are arecreated createdduring duringweathering. weathering. Published Published reports reports have have chemical composition showed that major major element variations predicted by thennodynamic thermodynamic calculations calculations are are generally generally consistent with trends in weathering weathering profiles. proffles.In Incontrast, contrast, many diagenetic diagenetic reactions reactions may may create create an an approximately reverse trend trend from from weathering. weathering. Accordingly, approximately reverse Accordingly, estimates of weathering intensity rocks will will tend tend to to be be minimum minimum estimates. estimates. Major of sedimentary sedimentary rocks Major based on chemical compositions of elements elements in elements and alkali and alkaline earth trace elements in the the Virginia Virginia Fonnation Formation are are strongly are substantially substantially divergent divergent from igneous contents are correlated and are igneous differentiation differentiationtrends. trends. Ca contents extremely low, mostly less than 11 wt. %. %. Thus the sediments' compositions are almost almost totally totally controlled by aqueous alteration alteration during during sedimentary sedimentary processes. Two Twomain mainlines linesof ofevidence evidence suggest the measured measured compositional compositional trends are largely products of of diagenetic/metamorpbic diagenetic/metamorphic reactions. First Firstof ofall, all,aaSHRJMP SHRIMPU-Pb U-Pbzircon zircon age age from from an an ash ash layer layer near the base base of of the Virginia Formation constrains the time time of of deposition depositiontotobe beabout about1.85 1.85Ga. Ga. However, However, aa Rb-Sr isochron isochron from from (Petennan, 1966, 1966, the Virginia Formation is is very very well well correlated and yields a 1.6 Ga age estimate (Peterman, GSA Bulletin), consistent consistent with with a time time of of pervasive resetting of of the Rb-Sr system in in the region. ternary (CIA, (CIA, chemical chemical index index of of alteration) alteration) the the samples samples lie lie Secondly, on a A1203-Na20+CaO-K20 Al20 3-Na20+CaO-K20 ternary along a mixing mole % albite. Illite and mixing line line between between illite and albite, ranging from about 50 to 80 mole albite are commonly commonly formed fonned during burial diagenesis. diagenesis. The strong strong correlation between K K20 Na20 2 0 / Na20 Rb/Sr isis likely likely aa product productof ofvarious variousmixtures mixturesof ofthese thesediageneticlmetamorphic diagenetic/metamorphic minerals, minerals, and and· and Rb/Sr thus the 1.6 1.6 Ga Ga Rb-Sr Rb-Srage ageapproximately approximately dates dates the the time time of of their formation. fonnation. 13 �WAS LITHOSPHERIC LITHOSPHERIC DELAMINATION AN IMPORTANT IMPORTANT PROCESS PROCESS IN IN THE THE WAS DELAMINATION AN EARLY PROTEROZOIC PROTEROZOIC COLLISIONAL OROGENS? EVOLUTION OF EARLY HOLM, D.K., DAHL, P.S., Dept Dept. of Geology. Geology, Kent State University. University, Kent, 44242 HOLM, DAHL. P.S., Kent, OH 44242 (216-672-4094; (216-672-4094; dholm@kentvm.kent.edu) dholm@kentvm.kent.edu)and and LUX, LUX, D.R., D.R., Dept. Dept. of Geological Geological Sciences, Sciences, University of Maine, Orono, ME 04469. Mantle lithospheric lithospheric delamination delaminationhas has been been proposed proposed as as a ubiquitous Mantle ubiquitous process process in collision zones to the point that it may require a paradigm shift in our understanding Phanerozoic coffision of how collisional evolve. The collisional orogens orogens evolve. The process process of ofrapid rapid mechanical mechanical thinning thinning of of the the mantle mantle orogenic belt ("delamination") has fundamental implications for both the lithosphere beneath an orogenic chemical and structural evolution of of continents (Nelson, 1991, 1992). Although Althoughgeophysical geophysical data data from relatively young orogens orogens seem to to support support the the delamination hypothesis, hypothesis. these these data data (i.e., (Le.• deep deep seismic profiling) profiling) seem limited (at best) for assessing very ancient ancient orogens. orogens. seismic assessing delamination delamination in very importance in in Precambrian Precambrian orogenic belts must rely, rely. unfortunately, unfortunately. on on less less Evaluation of its importance Evaluation direct evidence. Two Twoconsequences consequences of ofmantle mantle lithospheric lithospheric delamination delamination are rapid isostatic uplift of the overlying overthickened crust (orogenic collapse) and heating of the lower crust resulting magmas (Turner (Turner and and others. others, 1992). 1992). Investigations in generation generation of post-tectonic post-tectonic magmas Investigations of of the the postpostplutonism may therefore be a means to collisional uplift history and its relation to post-tectonic plutonism assessing the delamination hypothesis in the Precambrian. Precambrian. We We summarize summarize below below evidence evidence from from two which may may be at least two Early Proterozoic orogens orogens in the the North North American American midcontinent midcontinent which least consistent with (though not exclusively indicative of) the delamination hypothesis. Southern Trans-Hudson Trans-Hudson orogen. orogen. In In the thesouthern southern Black Black Hills Hills of ofSouth SouthDakota, Dakota,medium medium pressure rocks metamorphosed during an Early Proterozoic collisional orogeny where uplifted at least 8-10 km km before before being being intruded intruded by by the thepost-tectonic post-tectonic Harney Harney Peak PeakGranite Graniteatat—1700 -1700 Ma. Abundant thennobarometric thermobarometric data indicate that the granite was emplaced at midcrustal depths depths (12(12km) and thermochronologic Ma period period of 14 km) thennochronologic data data suggest suggest emplacement emplacement was was followed followed by byaa—200 -200 Ma stability tectonic quiescence quiescence with with little little uplift. uplift. Isotopic Isotopic and trace-element data from the the stability and tectonic granite (Nabelek (Nabelek and and others, b) indicate indicate that that at least the interior portions of the pluton granite others. 1992a, 1992a, b) were derived melting of biotite in were derived from high-extent high-extent vapor-absent vapor-absent melting in deep-seated deep-seated Archean/Early ArcheanlEarly rocks. The Proterozoic metasedimentary rocks. The generation generation of of the the granite granite has has commonly commonly been been attributed attributed to thennal relaxation relaxation of to thermal of the the overthickened overthickened crust crust following following collision. collision. However, However. heat-flow heat-flow modeling results results suggest suggest that that thermal was probably modeling thennal relaxation relaxation was probably not a viable viable mechanism mechanism for achieving the the >850°C temperatures achieving temperatures (Vielzeuf and Holloway, Holloway. 1988) 1988) necessary necessary to to produce produce We speculate speculate that that generation generation of of the the Harney Harney Peak voluminous voluminous crustal crustal melts melts in in the the Black Black Hills. Hills. We Granite magma and the crustal uplift which preceded preceded it may have been the result of thinning of the mantle lithosphere the mantle lithosphere (delamination) (delamination) beneath beneaththe the southern southernBlack BlackHills. Hills. This scenario seems supported the whole whole of of the the Black Black Hills, Hills. the the Harney Harney Peak Peak Granite Granite is is spatially spatially supported by the fact that, in the associated with with the deepest exposed exposed Early Early Proterozoic Proterozoic country country rock. rock. Because associated Because uplift uplift preceded preceded midcrustal granite emplacement, we emphasize emphasize that that this this spatial spatial association association is not related to in emplacement, we situ melting of the deepest-exposed portions of the orogen. orogen. Rather, Rather, preferential preferential intrusion intrusion into the the is exactly exactly what what would be expected if if both uplift uplift and and melt melt generation generation were deepest exposed rocks is the result of of the the delamination delamination process. process. Recent Recentage ageconstraints constraintssuggest suggestsyncollisional syncollisional regional regional -1740-1750 Ma the at —1740-1750 metamorphism at Masuggesting suggesting aa time-lag time-lag of of 30-50 30-50 Ma between collision and the proposed delamination. Penokean orogen. orogen. In Lake Superior Superior region region Early Early Proterozoic Proterozoic post-Penokean post-Penokean granites granites In the Lake Holm and and Lux Lux (1996) (1996) suggested intruded into rapidly uplifting crust beginning around around 1770 Ma. Ma. Holin represent deep deep crustal crustal melts melts related related to to an an episode episode of of orogenic orogenic collapse collapse perhaps perhaps that the granites represent triggered lithospheric delamination. delamination. Abundant Abundant post-Penokean post-Penokean NE-striking NE-striking basaltic triggered by by mantle lithospheric dikes intruded synchronously with with dikes (in both central Minnesota and Wisconsin) which were likely intruded 14 �or just after the the granites granites are are evidence evidence for for aa significant significant mantle mantle thermal thermal input input into into the the base base of of the the (Van Wyck, Wyck, 1995). 1995). The Thespatial spatialand andtemporal temporalrelation relationcif of rapid uplift, melting of the lower crust (Van and basaltic basaltic dike dike intrusion intrusion isisconsistent consistentwith withan anepisode episodeofofmantle mantlelithospheric lithospheric·'thinning. thinning. crust and Alternatively, somewhat younger younger (-.1730 (-1730 Ma) Ma) deformational deformational and and Alternatively, recent recent evidence evidence for for aa somewhat metamorphic event suggests metamorphic event suggests the the post-Penokean post-Penokean reheating reheating event event responsible responsible for for magma magma generation might be related to distant subduction to the south (Van Wyck, 1995). Conduding remarks. The summaries presented above suggest that for the southern Black Concluding Hills crustal thinning thinning preceded preceded granite granite emplacement emplacement whereas whereas for the Penokean orogeny igneous intrusion occurred occurred during during tectonic We suggest suggest that that this this difference difference in in the the relation relation intrusion tectonic thinning. thinning. We between plutonism and uplift between the two orogenic belts may be more apparent than real by simply being being an an artifact artifact of the the level level of exposure available for for us us to to investigate. investigate. That is, the simply exposure available Penokean orogenic during the theproposed proposedcollapse collapse episode episodewhereas whereas orogenic belt belt exposes exposes midcrustal midcrustal depths depths during midcrustal depths after after the the period period of of post-collisional post-eollisional uplift. uplift. the Black Hills exposes midcrustal Nelson (1991) has suggested that the delamination process may actually involve both the mantle portion of of the the lithosphere lithosphere and and portions portions of of the the lower lower crust, crust, making making itit perhaps perhaps aa critical critical step step in both the chemical and structural evolution of continental continental lithosphere. lithosphere. Nelson's proposed view of craton evolution relies heavily on uniformitarian principles by invoking processes observed in active or young orogenic belts to have occurred throughout throughout the the Earth's Earth's history. history. Detailed studies of the the exposed exposed mid-and mid-and lower lower crustal crustal roots roots of of Precambrian Precambrian orogenic orogenic belts belts will will provide provide one one important test of of Nelson's unified view of of craton evolution. References ReCerences Holm, D.K., O.K., and Lux, D.R., 1996, 1996, Core complex complex model model proposed proposed for gneiss gneiss dome development development of the the Paleoproterozoic Penokean orogen, Minnesota: Geology (in press). during collapse of Nabelek, P.1, C., and and Haeussler, G.T., 1992a, isotope evidence evidence for for the p.r, Russ-Nabelek, Russ-Nabelek, C., Haeussler, G.T., 1992a, Stable isotope petrogenesis and fluid evolution evolution in the the Proterozoic Proterozoic Harney Hamey Peak Peak leucogranite, leucogranite, Black Black petrogenesis Geochimica et et Cosmochimica Cosmochimica Acta, v. 56, p. 403-417. Hills, South Dakota: Geochimica Nabelek, p.r., Russ-Nabelek, Denison, J., 1992b, 1992b, The The generation generation and and crystallization crystallization Nabelek, P.1., Russ-Nabelek, C., C., and and Denison, conditions of of the Proterozoic Harney Hamey Peak leucogranite, Black Hills, South Dakota, USA: Petrologic and geochemical constraints: Contributions geochemical constraints: Contributions to to Mineralogy Mineralogy and Petrology, v. llO,p.p.173-191. 110, 173-191. Nelson, Nelson, K.D., K.D., 1991, 1991, A unified unified view view of of craton craton evolution evolution motivated motivated by by recent recent deep deep seismic seismic results: Geophysical reflection and refraction results: Geophysical Journal Journal International, v. 105, p. 25-35. Nelson, K.D., K.D., 1992, 1992, Are Are crustal crustal thickness thickness variations variations in in old old mountain mountain belts belts like like the theAppalachians Appalachians delamination? Geology, Geology, v. 20, p. 498-502. a consequence of lithospheric delamination? S., Sandiford, Sandiford, M., M., and and Foden, Foden, J., 1., 1992, 1992, Some Some geodynamic geodynamic and and compositional compositional constraints constraints Turner, S., on "postorogenic" magmatism: magmatism: Geology, v. 20, 20, p. p. 931-934. 931-934. Geology, v. ofeclogites, eclogites, N., 1995, 1995, Oxygen Oxygen and and carbon carbon isotopic isotopic constraints constraints on on the the development development of Van Wyck, N., Holsnoy, Norway Norway and and Major Holsnoy, Major and and trace trace element, element, common common Pb, Sm-Nd, Sm-Nd, and and zircon zircon geochronology constraints constraintson on petrogenesis petrogenesis and and tectonic tectonic setting setting of pre-and geochronology pre-and early early Proterozoic rocks in Wisconsin: Ph.D. dissertation, dissertation, University University of of Wisconsin-Madison. Wisconsin: Ph.D. Vielzeuf, D., and Holloway, deterniination of the fluid-absent melting melting Holloway, J.R., 1.R., 1988, 1988, Experimental determination relations Contributions to to Mineralogy Mineralogy and and Petrology, v. 98, p. 257relations in the pelitic system: system: Contributions 276. 15 �______ GENESIS OF OF A A TIMISKAMING-LIKE SEQUENCE SEQUENCE IN THE SOUTHERN WAWA SUBPROVINCE, SUBPROVINCE, NORTHEASTERN MINNESOTA J1RSA,Mark Mark A., A., Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642University University Avenue, Avenue, St. Paul, Minn., JIRSA, Minn., 55114-1057;e-mail: e-mail: jirsa001@maroon.tc.urrin.edu 55114-1057; jirsa001@maroon.tc.umn.edu unusual conglomeratic conglomeratic sequence sandwiched between two An unusual two units of Archean Archean graywacke graywacke in in the the Virginia (Fig. 1) 1) has has been been recognized recognized since the the 1960s 1960s as attributes of of the theclassic classic Virginia Hom Horn (Fig. as having attributes Timiskaming in the Kirkland Kirkland Lake area, area, Ontario. Ontario. Since Since that time, considerable attention has been been given to such sequences sequences throughout the the Superior Superior Province, Province, and many are now now well well documented. documented. focus on the Timiskaming was fueled in part by the association of these these sequences sequences with major The focus gold camps. strata were were deposited deposited in structurally camps. Most Most Timiskaming-like Timiskaming-like strata structurally controlled controlled basins basins inferred be the product during early of the inferred to. to be product of of localized localized extension extension during early regional regional transpression transpression of the greenstone sequences pull-apart basins) basins) prior prior to metamorphism greenstone sequences (i.e., (i.e., pull-apart metamorphism which accompanied accompanied D2 Because they they are are the the youngest youngestof of Archean Archean supracrustal supracrustalrocks, rocks, the the Timiskaming-like Timiskaming-like deformation. Because sequences are unique temporal sequences temporal pins in the structural and stratigraphic stratigraphic evolution of the Superior Province. 92°37'30' 92°30'00· 92"22'30' 92°15'00. 17°3T30 , .. '" ..' ," .. ' .. '" .. ' .. " .. " .. ' .. ' ..' ..' ..' ..' ..' ...' ...' ..' ..' .. ' ..' ..' ..' .. ' . . ' .... ' ..' .. ' .. ' ..' ..' .. ' .. ' .. ' ..' ..' ..' 47°37'30" .. "'"" " " " " " " , , , , , , , , , , , , .. , , , , , , , , .. .. .. .. .. " " '" . .. .. ................................................... . PROTEROZOIC EARLY PROTEROZOIC . Virginia Formation Formation 1,*;Jii~.1 Virginia """""""""""""" " """"", '" " ' "..".." " . " " ' . ' " ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' " ' " " " " " " " " " " " '" 1'''''''''''''''''' .. .. ", , , , , , , '" ".. , , , , ,.., ,. . .. " " " , , ,", , , , '" .. , , , , , , , , , , , , .. .. . . . . . " '" " . .." .. .." . " .. " " " " , .. " " " " .. , .. " " " " , "" .. " """ "" "" " "" .. .......... , .. " , .. " " " .. " "...... , ...... " " ...... "" " ,.. ." "," .. " , .. " "" .. ," .. " " " ...." " " , .. .. " , ," , ." , "" " ...." , , " ", " , W~~,,>< +)-,I;l£t'jti(~ .~~ Biwabik Iron Iron Formation Formation D Pokegaina Formation Pokegama LATE ARCHEAN ARCHEAN ' 1:-, :-, :-, I Giants Range batholith • Timiskaming-like (TLS) sequence (TLS) ~~~~~~ Graywacke and slate [IllIll] fflffl Metavolcanic rocks The term "Virginia "Virginia Hom" Horn' refers to Figure 1-- Simplified geologic geologic map of the Virginia Horn Hom area. area. The the hook or or horn-shaped hom-shaped distribution distribution of of Early Early Proterozoic Proterozoic Biwabik Biwabik Iron vicinity Iron Formation Formation in in the vicinity The iron-formation onlaps of Virginia, Minnesota, surrounding it. The onlaps of Virginia, Minnesota,and and isis applied applied to to the area surrounding Archean bedrock, which is is likely the southernmost exposures of the Wawa subprovince. The Timiskaming-like Timiskaming-like sequence sequence (TLS) (US) in the Virginia Virginia Hom Horn lies lieswithin within an an east-trending, east-trending, broadly broadly synclinal succession rocks. It succession of graywacke graywacke and and slate underlain by mafic to intermediate volcanic rocks. forms a northeast-trending northeast-trending structural structuralwedge wedgeat atleast least 55 km km long long and and aa maximum maximum of of 11 km thick. thick. The The TLS TLS isis homoclinal, homoclinal, steeply steeply dipping, dipping, and and consistently consistently south south facing. facing. Early Proterozoic strata conceal "'Ml"westem part of the TLS, TLS, and and the the sequence sequenceisisterminated terminatedon onthe theeast eastby byaafault. fault. Although Although the the boundaries boundaries of of the the US TLSare arerarely rarelyexposed, exposed,aacomposite compositesection sectioncan can be be inferred inferred in in aa few few areas areas from from aa combination The sequence sequence is combination of of drill drill core core and and outcrops. outcrops. The is divided divided into into several several units units that vary in character along strike. The The basal basal unit unit isis sandstone sands.tone and andpebbly pebblyconglomerate, conglomerate, which which thickness and character absent to to 30 30 m thick, and coarsens up-section. composed of of detritus detritus derived, derived from varies from absent up-section. ItIt isis composed greenstone, and distinctive distinctive quartz phenocrysts phenocrysts eroded from the quartz-feldspar quartz-feldspar porphyry porphyry older greenstone, is a fault intruded the thegreenstone. greenstone. The The basal basal contact contact is fault in in most most places; places; but butlocally locally is that intruded atop aa variety variety of of older rocks. rocks. A A thin thin and and discontinuous discontinuous volcanic volcanic unit unit containing containing unconformable atop 16 �flows and and hypabyssal hypabyssal sills sillsofofa adistinctive, distinctive,caic-aLkalic, calc-alkalic, hornblende hornblende trachyandesite trachyandesite porphyry flows (HAP) isis present present locally above the the basal the volcanic unit is (HAP) locally above basal unit. Where Where the volcanic unit is absent, absent, laterally laterally equivalent strata are anit can be seen in in outcrop, outcrop, it are dominated dominated by by HAP HAP clasts. clasts. Where Where the the volcanic volcanic unit grades into flowtop flowtop breccia, breccia, agglomerate, agglomerate, and conglomerate conglomerate made up almost almost entirely entirely of of clasts clasts of of HAP. This This conglomeratic conglomeratic unit unitmakes makesup upthe thebulk bulkofofthe theTLS TLS sequence sequence and and is is composed composed of of poorly poorly sorted, clast-supported, clast-supported, and vaguely graded beds. Clasts more sorted, Clasts within within the the conglomerate conglomerate become become more diverse and bedding, grading, and and sorting diverse in texture texture and and composition composition up-section, up-section, and bedding, grading, sorting are better better developed. This stratigraphic sequence records a progression from gentle subsidence of aa sediment-starved Clasts in the basin, followed followed by volcanism, volcanism, basin collapse, collapse, and in-filling in-filling with coarse detritus. Clasts the conglomeratic unit were conglomeratic unit were initially initially derived derived largely largely from from intrabasinal intrabasinal volcanic volcanic rocks, rocks, but progressively more extrabasinal extrabasinal material material was was supplied supplied as as the the basin's basin's watershed watershed expanded. expanded. The progressively more The absence implies that that much much of the deposition was absence of demonstrably lacustrine or fan-delta fan-delta deposits deposits implies subaerial. The Thegreat greatthickness thicknessof ofcoarse, coarse, poorly poorly sorted sorted conglomerate conglomerate indicates indicates deposition within within subaerial. alluvial local bedded and and cross-bedded cross-bedded sandier units probably have a fluvial fluvial origin. origin. alluvial fans, fans, and local Lateral continuity of of individual in part because individual units units is difficult difficult to establish, establish, in because of abrupt facies facies Lateral continuity changes along along strike, strike, which which are are inferred inferred to to be the changes the result result of of deposition deposition in the the many many sub-basins sub-basins pull-apart settings. common in pull-apart settings. Earlier Earlier workers in the the Archean Archean of of the the Virginia Virginia Horn Horn attempted attempted to to link link deposition deposition of of the the TLS TLS with that by inferring with that of of the theenclosing enclosing graywacke-slate graywacke-slate sequence sequence by inferring that the the TLS TLS represented represented proximal turbidite channel deposits, while the graywacke and slate slate units units were deposited as distal proximal graywacke and which utilized utilized outcrop and aa series Remapping, which series of of cores cores drilled drilled by by exploration exploration turbiditic fans. fans. Remapping, companies along the basal contact contact of of the the sequence sequence (which (which were not available available earlier), demonstrates that they do not not represent represent aa depositional depositional continuum continuumfor for the the following following reasons: reasons: Structural data indicate sequence isis twice twice folded, folded, and and in fact 1. Structural indicate that that the the graywacke-slate graywacke-slate sequence fact much of the graywacke strata was was overturned overturned during during DI, Di, prior to deposition of the the TLS. US. much graywacke strata deposition of Locally Locally recumbent, recumbent, east-trending east-trending F1 FI folds folds are are cut cut at at an an acute acute angle angle by by the the basal basal unconformity and and faults faults which which bound bound the theTimiskaming-like Timiskaming-like sequence. 2. Quartz-feldspar porphyry intruded the greenstones, but not not the the TLS, US, and greenstones, but and in in fact fact provided provided detritus to to the the TLS. TLS. 3. Flows, and detrital detrital hornblende hornblende Flows, intrusions, intrusions,and andclasts clastsofofHAP HAP are are unique uniquetoto the theTLS US,, and derived from from HAP HAP is is common common in in conglomerate conglomerate matrices matrices and associated associated sandstone units. homblende does Detrital hornblende does not notoccur occurin in the thegraywacke-slate graywacke-slate sequence. sequence. 4. Hornblende-phyric Hornblende-phyric dikes, dikes, texturally texturally similar similar to to and inferred to be be feeders feeders of of HAP HAP flows, flows, cut all all rock rock types. types. 5. A sharp contrast contrast in in depositional depositional style style occurs occurs between between the the resedimented resedimented facies facies graywackegraywackeand the thevolcanic volcanicand andalluvial alluvialfan-fluvial fan-fluvialfacies faciesdeposits depositsofofthe theTLS. TLS. slate sequence, and The TLS TLS contains contains all all the the characteristics of pull-apart pull-apart basin basin deposition, deposition, including including structural structural and and The characteristics of unconformable boundaries, lateral facies facies changes, changes, thick thick and and variable variable alluvial alluvial sediments, sediments, unconformable boundaries, abrupt lateral and the the association association of unique volcanism. volcanism. Although Althoughother otherconglomeratic conglomeratic units units in in Minnesota Minnesota may be candidates candidates for aa similar similar designation designation (Seine (Seine Group in in the the Rainy Rainy Lake Lake area area and and Okishkemucie Okishkemucie conglomerate in the the Knife Knife Lake Lake Group), Group), none none has the unique combination of Timiskaming Timiskaming attributes attributes present in this present this sequence. sequence. Support for mapping in the Support for mapping in the Virginia Virginia Horn Horn isis being being provided provided by by the the State State Legislature Legislature and and is is administered by administered by the the Minerals Minerals Coordinating Coordinating Committee. Committee. 17 �Identifying Geologic Geologic and and Other Other Potential Resources From Michigan's Abandoned Underground Mine Inventory Allan M. M. Johnson(1) Johnson(1) and and Milton Milton A. A. Gere, Gere, Jr.(2) Allan Introduction.AAtwo-year two-yearcontract contractto toinventory, inventory, document document and and map map abandoned abandoned underground mines mines Introduction. in the the State StateofofMichigan Michigan was wasawarded awardedtotoMichigan Michigan,Technological rechnological University University (MTU) in (MTU) by by the Geological Survey Division (GSD) of ofthe the Michigan Michigan Department Department of ofNatural Resources (M1)NR) (MDNR) in in Natural Resources late summer summer of of1995. 1995. The project is is now now being being overseen overseen by the Real Real Estate Estate Division Division (RED) (RED) following structure of ofthe the MDNR. following recent changes in the structure is needed preserve aa data data base base on on the location of The inventory inventory is needed to permanently permanently preserve location and condition condition of underground mine openings openings and identifYand andrank rankany anyunsafe unsafeconditions conditionsfound found during during the the field field and to identii investigation phase phase ofthe of theproject. project. These data will willhelp helpplanners plannerstoto avoid avoid undermined undermined areas for future investigation future development will call call attention to the the conditions conditions needing corrective action to protect protect public public development and will safety. Similar 1970's for the Similar work work on on abandoned abandoned iron iron ore ore mines minesinin Iron Iron County Countywas was done done in in the the 1970's for the GSD-MDNR problems ofmine of minesubsidence subsidenceand andacid aciddrainage drainagewere were addressed addressed (Johnson and GSD-MDNR in which problems An inventory inventory of of mines mines was This research research Frantti, 1978). An was also alsodone done(MacDonald (MacDonaldand andJohnson, Johnson, 1984). 1984). This been useful useful for for planning planningpurposes purposesand andininpreserving preservingaarecord record of of the the mines which otherwise might has been might lost with with the the passage passageof have been lost oftime, time, and andalso also in in documenting documenting first-hand first-hand knowledge knowledge from from aging aging miners, 15'0 years becomes a relic of the past. miners, as underground mining activity of the last last 150 Goals.. The project project requires requires a computerized mine mine map Goals. The map data base compatible with MIRIS (Michigan System), the the State's State's Geographical GeographicalInformation Information System. System. This This will will preserve mine Resource Information System), map data data and andwill willultimately ultimately make make ititavailable available electronically electronically to the the public. public. The three three major major map of the project project are: are: requirements of 1. To provide provide accurate accurate information on the location and and extent of of underground openings for each of 1. To of the more more than than 500 500 abandoned abandoned and andclosed closedunderground underground mines mines in in Michigan. Michigan. Selected mine mine map map software. information will be digitized digitized and stored in a computerized data base using AutoCAD software. 2. To provide information and county-by-countybasis. basis. and maps maps for for each eachofthe of the underground underground mines on a county-by-county This will willinclude includemine minename, name,location, location,years yearsofofoperation, operation,production productionrecords, records, mine mine ownership, ownership, mine mine operator, number number of of shafts shafts and and other other openings openings to the the surface, surface, subsidence subsidence pits pits if if present, and other data obtainable obtainable from from records records and and mine mine maps. maps. Also Also included included will will be be assessments assessments of the relevant data condition of of shafts and other other surface surface features features at at each eachmine mine based based upon upon field field observations. observations. 3. identify and and rank rank: potential potential problems problems atat abandoned abandoned mines mines in in terms terms of ofpublic public safety safety from from open open 3. To identify shafts, caving around shafts, deterioration of shafts, of shaft seals or caps, subsided areas, and other unsafe 18 �conditions. Assistance mmmg company company personnel, other Assistance of of mining personnel, county county mine mine inspectors inspectors and and other knowledgeable individuals will be important in the field field inspection inspection phase phase of of this this project. Opportunities and and Attributes. Attributes. It is is recognized recognized that abandoned abandoned mines mines do possess possess esoteric esoteric many old mines have historical significance which, remnants attributes. For Forexample, example, many attributes. which, if enhanced by remnants ofold of old mine minebuildings buildingsand andartifacts, artifacts,may maybe beof ofvalue valuefor fortourism. tourism. A A good good example example is is the the Keweenaw Keweenaw National Historic Park. On-going research research has has identified identified aa number number of of Michigan Michigan underground underground mines mines as as sites sites of active active bat hibernation during during winter winter months months (Millie (Millie Hill Hill Mine in in Iron Iron Mountain). Mountain). The International Bat Conservancy, seeking to preserve preserve these these mines, mines, reports that large large numbers numbers of of bats bats migrate migrate from from surrounding states and and Canadian Canadian provinces to hibernate there. there.. Flooded mines mines represent representaapotential potentialresource resourceof ofhuge hugevolumes volumesofwater of water suitable suitable for for industry (Norrie Mine, Mine, Ironwood) Ironwood) and, and, inin some somecases, cases,high highquality qualitypotable potablewater water(Champion (ChampionMine, Mine,Painesdale). Painesdale). Flooded mine pools are also geothermal energy suitable suitable for extraction ofreadily readily available geothermal also aa source source of using heat pump technology technology (Osceola (Osceola Mine, Mine, Calumet). Calumet). Formerly discarded mine mine wastes, waste rock and mill tailings, are becoming recognized as mill tailings, as valuable valuable Formerly raw materials materials for for industry. inJustry. Examples Examples include include using using these these wastes wastes as as aggregate aggregate (iron and copper districts) ice and in districts) and snow snow traction traction (Keweenaw (Keweenaw Peninsula) Peninsula) and and potentially potentially as as raw raw materials materials in manufacturing such such products productsas asfloor floorand andceiling ceiling tiles, tiles, thermal thermal insulation, insulation, building and construction manthcturing materials products. Tailings of speciality speciality products. Tailings from from the the Republic Republic Mine are being being used for for materials and a variety of Corporation in in Alpena. Alpena. portland cement manufacture at Lafarge Corporation References Johnson, AM and and Frantti, Frantti, GE, GE, 1978, 1978, Study Study ofMine of MineSubsidence Subsidenceand andAcid AcidWater Water Drainage Drainage in the Iron Iron Johnson, River Valley, Valley, Iron Iron County, County, Michigan, Michigan,prepared preparedfor forGSD-MDNR, GSD-MDNR,Lansing, Lansing,MI MI by by Institute Institute ofMineral of Mineral Research, Michigan Michigan Technological Technological University, University, 220 p. p. MacDonald, U and MacDonald, U and Johnson, Johnson, AM AM,1984, 1984,AADirectory Directoryof ofIron IronMines Mines ininIron IronCounty, County, Michigan, Michigan, Report prepared Report prepared for for GSD-MDNR, GSD-MDNR, Lansing, Lansing, MI by by Institute Institute of ofMineral Mineral Research, Research, Michigan Michigan p. Technological University, University, Houghton, MI, 294 p. (1) Director, Director, Mineral Mineral Technology Technology Research Research Group, Group, Department Departmentof ofMining Mining Engineering, Engineering, Michigan Michigan Technological University, 49931 and and Project Project Principal Principal Investigator. Investigator. University, Houghton, MI, Ml, 49931 (2) Geologist, Geologist, Real Real Estate Estate Division, Division, Michigan Michigan Department Department of Natural Natural Resources, Resources, Marquette, Marquette, MI, MI, 49855 and Project Officer. Officer. 19 �AN ANCIENT LANDSLIDE AT AT "RED "RED ROCKS", ROCKS", KEWEENAW KEWEENAW BAY, BAY, MICHIGAN MICHIGAN Jorma Kalliokoski, Kalliokoski, Professor Professor Emeritus, Emeritus, Michigan Technological University, University, Houghton, Houghton, MI MI 49931 49931 At the south end of of Keweenaw Keweenaw Bay Bay is is an an outlier outlier of Jacobsville Jacobsville At Sandstone, red along the highway and purplish Sandstone, purplish grey along along the the lake lake shore where the batton botton 1—3 1-3 m m of the the section section is is exposed, exposed, and and rests rests Michigaimiie on Michigamme Michigamme slate slate (Fig.l). (Fig. 1). There Therethe thesub—horizontal sub-horizontal Michigamme surface exhibits parallel parallel striations, striations, leading leading Murry Nurry (1955) (195) to surface exhibits to period of of glaciation. glaciation. Conversely, Conversely, on propose a a pre--Jacobsville pre-Jacobsville period on the the basis of bedding slips in in the the sandstone, sandstone, and evidence evidence for for aa non-glacial paleoclimate, paleoclimate, I I suggested that the striations striations were were produced by basal pebbles as the the entire entire sandstone mass mass slid slid northerly (Kalliokoski, (Kalliokoski,1982). northerly 1982). Additional detailed mapping mapping last last summer summer revealed revealed aa clayey clayey fault, fault, traceable for about 15 15 m m along the the slate/sandstone slate/sandstone contact contact traceable (Fig.1) At Sta.43 Sta.43 aa strand strand of of this this shear shear rises rises obliquely obliquely (dip (dip 1~ 1° (Fig.l) At SW) through a SW) a 40 cm cm sandstone bed, bed, and and merges merges into into the the base base of of the overlying conglomerate. the conglomerate. The The orientation orientation of of the fault fault indicates that that the indicates the upper block mcved moved northeast. northeast. About 20 20 mm southwest is a a larger larger one one along which which sedimentary sedimentary southwest of this fault is beds have moved up up along along aa low—angle low-angle ramp ramp fault fault (strike (strike N35 N35 W, W, 30°SW: Fig.1, dip 3ifSW: Fig.1, Sta.23; Sta.23j Fig.2). Fig.2). The The orientation orientation of of this this fault fault also denotes northeast movement. movement. Moreover, Moreover, features features in in Fig.2 Fig.2 indicate indicate that that the footwall footwall conglomerate first moved along a a bedding fault, fault, and at this this locality, locality, up up an an inclined inclined fault fault (a (a stage beyond that illustrated illustrated at Sta.43). Sta.43). When When movement movement of of this this conglomerate had slowed or ceased, ceased, the the poximal poximal part part of of the the conglomerate bed bed over—rode over-rode the the previously previously ramped ramped one. one. Below the (Fig.2j Sta.43) are parallel striations striations on on the fault fault (Fig.2; Sta.43) there are 2 faint ones at Michigamme slate slate surface: surface: 12 at at 54°-234° 5~-234°, the Michigamme , and 2 90~270c. The prevalent direction is is the same as for the fault fault 90-2'7O° movement vectors, vectors, and suggests suggests strongly strongly that that the the striations striations and and movement faults formed within the faults the same same dynamic dynamic system. system. . The south of of the the Bishop The elevation of Michigamme Michigamme slate outcrops outcrops south Earaga statue statue and along the lake Baraga lake shore shore suggest suggest that that the the 'sub-Jacobsville surface surface slopes slopes about about 6° ~ northerly. 'sub—Jacobsville The indicates that that the the sandstone sandstone outlier outlier slid slid The above above evidence indicates northeast along along bedding bedding faults, faults, one one along along the the smooth smoothMichigamine Michigamme slate surface and others along higher slate higher bedding bedding surfaces. surfaces. Where Where aa the mass stopped moving, more distal distal portion of the moving, stresses within the portions of of beds beds to to override override the system caused the more proximal portions the in landslides the distal distal ones, ones, as as is characteristic in landslides and and along along zones of imbricate imbricate thusting. thusting. 20 20 �Mass Mass movement movement of the sandstone in post—Glacial post-Glacial of the sandstone probably occurred in time. This may the sub-vertical, time. may be the cause cause for for the sub-vertical, north dipping exposure, not fractures in in the highway exposure, not seen anywhere else in in Jacobsville Sandstone outcrops, outcrops, and for for the more irregular irregular jointing in in the the lowermost lowermost beds. beds. The purplish color in in the the basal basal sandstone may be aa product product of of groundwater flow above the the Impermeable impermeable Michigamme Michigamme basement. basement. References Kalliokoski, J., J., 1982, Jacobsvllle Jacobsville Sandstone, Sandstone, in in Wold, Wold, J. J. R., R., and Hinze, Hinze, W W. E., E., eds., eds., Geology Geology and and tectonics tectonics of of the the Lake Lake Superior Basin: Basin: Geological G~ological Society Society of of America America Memoir Memoir 156, 156, 147—155. p. 147-155. p. Murry, 1955, Late Murry, R. R. C. C. ,,1955, Late Keweenawan Keweenawan or or Early Cambrian glaciation in Upper Michigan: in Michigan: Geological Society of of America America Bulletin, Bulletin, v. 66, p. p. 341-344. 341—344. .- .••.. ~""""""""""~""""""'" 15 . D ... . . . 35 a Michlgamme Michigamme slate • F--H Jss Jssconglomerate conglomerate JacobsvilleSs overburden . Ii 2 meters meter~ 3, Figure 1. Vertical shore outcrop; Figure 1. Vertical outcrop; azimuth of of profile profile 55°. 55°. Jacobsville Sandstone is is in in fault contact <Wavy (Wavy line) line) with with Michigamme slate, and and rests on striated slate at Sta.43. Sta.43. At At Sta. Sta. 43 43 and 23 are inclined inclined thrust faults, faults, indicating indicating that that higher higher strata have have moved moved NE. HE. slate, overburden V JV 'I V -. • b C . • meters 21 Figure 2. 2. Detail Detail at at Sta.23; Sta.23; b, sandst, , c, sandst., sandst. Lower sandst. inclined congl. slid on its inclined congl. its inclined base and up an inclined fault surface. fault surface. Later Later the the sandst. and and congl. congl. of the sandst. upper plate plate were thrust into upper into place. a, a, corigl. congl.,, indurated indurated �Aeromagnetic Map of Lake Superior by P. Kucks· and Robert Robert J. J. Horton Horton· Robert P. Kucks and ** U.S. Geological Survey, Survey, Box Box 25046, 25046, MS MS 964, 964, Denver Denver Federal Federal Center, Center, Denver, Denver, CO., 80225. CO., 80225. Introduction An aeromagnetic map of the Lake Superior Superior" region (figure (figure 1) 1) was compiled as part of the Great Lakes International Multidisciplinary Program on Crustal Crustal as set was was compiled from digitized Evolution (GLIMPCE). (GLIMPCE). The magnetic anomaly data set and digital data data acquired acquired from from aa diverse diverse group group of of magnetic magnetic surveys. surveys. This abstract describes the procedures used to reduce and and merge the individual aeroinagnetic surveys surveys to to make make the the Lake Lake Superior Superior aeromagnetic map. aeromagnetic map. Surveys Aeromagnetic Surveys The aeromagnetic aeromagnetic surveys surveys were were flown flown with with flight-line flight—line spacings spacings ranging ranging The surveys surveys were were flown mode from 0.25 0.25 mi mi (0.4 (0.4 3cm) kID) to to 33 mi mi (4.8 (4.8kin). kID). The flown in draped mode (constant (constant elevation above terrain or water) water) at at elevations elevations ranging ranging from from 300 300 ft ft (91.44 to 1000 1000 ft Figure 22 shows shows the the location location of of the the surveys (91.44 in) m) to ft (304.8 (304.8 in). m). Figure compiled to make the Lake Lake Superior Superior aeromagnetic aeromagnetic map. map. Reduction Data Reduction Data set J, 3, for the UP (Upper Data (Upper Peninsula Peninsula Michigan), was was only only available available as as hand—contoured Digital data data were were created created by by digitizing digitizing hand-contoured magnetic magnetic maps. maps. Digital 1:24,000 and 1:62,500 1:62,500 magnetic magnetic maps. maps. For For maps maps with with 0.5 0.5 mi mi (0.8 (0.8kin) km) flight line line spacings, spacings, data were generated by digitizing the intersections of contour lines lines In with flight flight lines. lines. In the case where individual individual surveys surveys were were flown flown at at 0.25 0.25 mi mi (0.4 km), 3cm),every every other other line line was was digitized digitized due due to to the the time time allotted for the (0.4 Part of project and the expected anomaly resolution of the final final product. product. Part survey 3 J was flown flown with flight line line spacings of 1.0 and 3.0 mile (1.6 (1.6 and 4.8 kin). For greater control, kID). control, these more widely spaced data were digitized both at contour intersections along the flight at inflection points of at flight lines and at contours between flight flight lines. lines. Gridding For magnetic the seven sets that up J, 3, the magnetic surveys surveys B, E, F, F, G, G, B, H, and and the seven sets that make make up the total—intensity total-intensity data data were were projected projected to tothe theLambert Lambert conic conic conformal conformal projection projection (standard 42.5°N (standard parallels parallelsofof 42.5ONand and48.5°N 48.5ON and and central central meridian meridian of of88.5°W) 88.5OW) then then gridded gridded at 0.4 km km using using aa computer program program (Webring, (Webring, 1981) 1981) at an interval of 0.4 Surveys A, A, B, B, C, based on on minimum minimum curvature curvature (Briggs, (Briggs, 1974). 1974). Surveys C, D, D, and II were were and were reprojected and and regridded regridded to to the the above above acquired in grid form and projection and and grid grid interval interval specifications. specifications. The digital surveys surveys (A, (A, B, B, C, C, H) H) at aa 0.25 flown at 0.25 mile mile (0.4 (0.4kin) kID) spacing spacing were gridded at at aa finer finer interval interval of of 0.2 0.2 km (0.125 0.4 km and then regridded to 0.4 (0.125 mile) mile) to to honor honor the the data data more more closely closely and km (0.25 mile) and BB were were used used to (0.25 mile) for for the the final final merge. merge. Surveys A A and to minimize minimize edge edge effects along 83GW longitude, and and therefore therefore were were not not used used in their entirety. effects 830W longitude, entirety. Reference Field Field Removal Removal The geomagnetic reference fields calculated for the date and location location of the individual individual surveys surveys were subtracted subtracted from from the the total—intensity total-intensity grids grids to to produce the the residual residual total—intensity total-intensity grids. grids. The particular geomagnetic geomagnetic reference field field removed removed depended depended on on the the year year in in which aa given given survey survey was was flown flown International Geomagnetic Geomagnetic Reference Reference Field Field and consisted of the definitive International (sweeney, (Sweeney, 1990) 1990) or or in in the the case case of of the the Minnesota Minnesota Survey Survey C, C, the the American American World World Chart (AWC) (AWC) Regional Regional reference reference field field (Peddie, (peddie, 1976). 1976·). consisted of the definitive Merging Merqjii data sets, magnetic field values of of each survey grid were were Before merging data sets, magnetic field values adjusted by aa constant amount amount using survey D D as an absolute datum, datum, to to minimize Theoriginal original observation surfaces of discontinuities at merge boundaries. boundaries. The observation surfaces of the at merge been maintained maintainedwhich whichmay may alsoaccount accountforforslight slight discrepancies discrepancies at data have have been also at merge boundaries. 22 22 �two grid grid Data set J J was created created from from seven seven separate grids by removing two the gap using using the the cells from the edges of each and assigning assigning values across across the one—dimensional splining and others others one-dimensional splining techniques described by Bhattacharyya and merged by by (1979). The major surveys surveys denoted on the index map were then merged one and and two two grid grid cells cells respectively, respectively, from from the borders of survey E and removing one the remaining remaining sets. sets. The resultant grids grids were were combined combined leaving leaving data data gaps gaps gaps were then assigned data values within the final final composite composite grid. grid. These gaps using the computer computer program program MEGAPLUG MEGAPLUG (Phillips (Phillips and and others, others, 1993), 1993), by the same minimum curvature curvature technique technique used used by by Briggs Briggs (1974) (1974) and Webring (1981) (1981) when gridding. Data were then then removed removed from from areas areas where where no no reasonably reasonably compatible compatible Some margin surveys exists (white (white areas areas in in the the southwest southwest part part of of figure figure 1). 1). Some areas along along latitude latitude 46°N 46~ contain data created by the process, process, but due due to to their minimal impact, impact, they they have have been been retained. retained. of 0.4 0.4 km km (0.25 mi) and and The final final compiled data set has a a grid spacing of (0.25 mi) is projected using aa Lambert conformal parallels of of conformal conic conic projection (standard (standard parallels 42.5°N and 48.5°N, central meridian of 42.5~ and 48.5~, central of 88.5°W, S8.5OW, and base latitude latitude of of 46°). 46°). The of Interior, EROS gridded magnetic data are are available available from from the U.S. u.S. Department of Interior, EROS Data 1990), or or from NOAA (Hittelman Data Center Center (I(ucks, (Kucks, 1990), (Hittelman and and others, others, 1992). 1992). The above grid using the the color aeromagnetic map (figure (figure 1) 1) was produced from the above program GDRELIEF (unpublished (unpublished USGS USGS program, program, information information available from from the author). References Ehattacharyya, Bhattacharyya, B.K., B.K., Sweeney, Sweeney, R.E., R.E., and and Godson, Godson, R.H., R.H., 1979, 1979, Integration of times with with varying varying elevation elevation and and aeromagnetic data acquired at different different times line spacing: spacing: Geophysics, v.44, v.44, no. no. 4, 4, pp. pp. 742—757. 742-757. Briggs, I.C., 1974, 1974, Machine Machine contouring contouring using using minimum minimum curvature: curvature: Geophysics, Geophysics, Briggs, I.C., V.39, no. no. 1, 1, p.39-48. p.39—48. Hittelman, Buhmann, R.W., R.W., Racey, Racey, S.D., S.D., and and Chandler, Chandler, V.W., V.W., 1992, 1992, Hittelman, A.M., Buhmann, Minnesota Region Region CD-ROM, CD-ROM, Aeromagnetics Aeromagnetics Earth Earth System System Data, Data, DOS DOS Release, Release, September 1992: 1992: U.S. U.S. Department Department of of Commerce, Commerce, National National Oceanic Oceanic and and Atmospheric Administration, Administration, National National Geophysical Geophysical Data Data Center, Center, Boulder, Boulder, CO. 80303 CO. 80303 Kucks, Kucks, R.P., R.P., 1990, 1990, Description Description of of magnetic magnetic tape tape containing containing Lake Lake Superior Superior region magnetic anomaly data, data, United States and Canada: Canada: U.S. U.S. Department Department of Interior, EROS EROS Data Data Center, Center, Mundt Mundt Federal Federal Building, Building, Sioux Sioux Falls, Falls, South Dakota, 57198. 57198. [phone: [phone: 605-594—6976] 605-594-6976] Peddie, N.W., N.W., and and Fabiano, Fabiano, E.B., E.B., 1976, 1976, Model Model of the the Geomagnetic Field for for Peddie, 1975: Journal of 1975: of Geophysical Research, Research, V. V. 81, 81, pp. pp. 2539—2542. 2539-2542. Phillips, J.D. Duval, Duval, J.S., J.S., and and Ambroziak, Ambroziak, R.A., R.A., 1993, 1993, National geophysical Phillips, J.D. data grids-—gamma—ray, grids--gamma-ray, gravity, gravity, magnetic, magnetic, and topographic data for the States: U.S. U.S. Geological Survey Digital Data Series conterminous United States: DDS-9, DDS—9, 11 CD—ROM CD-ROM disk. disk. [includes [includes potential-field potential-field software software version version 2.1] 2.1] Sweeney, R.E., R.E., 1990, 1990, IGRFGRID, IGRFGRID, AA program program for for creation creation of of aa total total magnetic Sweeney, field (International (International Geomagnetic Reference Field) Field) grid representing the Earth's main magnetic field: field: U.S. U.S. Geological Survey Open-File Report Report 9045a, 37 45a, 37 p. p. Webring, M.W., M.W., 1981, 1981, MINC: MINC: AA griddirig gridding program based based on on minimum minimum curvature: curvature: U.S. U.S. Geological Survey Survey Open—file Open-file Report Report 81—1224, 81-1224, 41 41 p. p. 23 23 �AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY REFERENCES REFERENCES Survey A A Bracken, Bracken, R.E., R.E., and Godson, Godson, R.H., R.H., 1987, 1987, Aeromagnetic Aeromagnetic map map of 0 x 2° International. Falls Falls 110 Quadrangle, Minnesota and International x 20 Quadrangle, and U.S. U.S. Geological Geological Survey Survey Open—File Open-File Report Report 87—620, 87-620, scale scale the Ontario: Ontario: 1:250,000. 1:250,000. B B Bracken, R.E., and and Godson, Godson, R.H., LH., 1988, Bracken, R.E., 1988, Aeromagnetic Aeromagnetic map map of of the the northwestern part part of of the the Ribbing Hibbing 10 10 xx 20 20 Quadrangle, Quadrangle, Minnesota: Minnesota: U.S. U.S. Geological Geological Survey Survey Open—File Open-File Report Report 88—0008, 88-0008, scale scale 1:62,500. 1:62,500. C. C Chandler, V.W., V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic magnetic Chandler, intensity anomaly, anomaly, Cook and Lake Lake Counties: Counties: Minnesota Geological Geological Survey Map A—I, A-I, 22 sheets, sheets, scale scale 1:250,000. 1:250,000. C C Chandler, V.W., V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic magnetic Chandler, intensity anomaly, St. County: Minnesota Geological Survey Survey St. Louis County: Map A—2, A-2, 22 sheets, sheets, scale scale 1:250,000. 1:250,000. C C Chandler, V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic magnetic Chandler, V.W., intensity and Pine Pine Counties: Counties: Minnesota intensity anomaly, anomaly, Carlton Canton and Survey Map Map A—3, A-3, 22 sheets, sheets, scale scale 1:250,000. 1:250,000. Geological Survey C C Chandler, V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic Chandler, V.W., intensity anomaly, anomaly, east—central east-central region: region: Minnesota Geological Geological Survey Map A—4, A-4, 2 sheets, sheets, scale scale 1,250,000. 1,250,000. D D Geological Survey of Canada, Geological Canada, 1977, 1977, Magnetic Magnetic anomaly anomaly map map of of Canada: Canada: Geological Geological Survey of of Canada Map 1255A, 1255A, scale scale 1:5,000,000. 1:5,000,000. E E Geological Canada, 1988, 1988, Aeromagnetic Aeromagnetic survey survey of of Lake Lake Geological Survey of Canada, Superior, data. Superior, unpublished data. F F U.S. Geological Survey, Survey, 1979, 1979, Aeromagnetic Aeromagnetic map map of of Sault Sault Sainte Sainte Marie Marie U.S. and vicinity, Michigan: Michigan: U.S. Survey Open—File Open-File Report Report U.S. Geological Survey 79—833, scale 1:250,000. 79-833, 1:250,000. C G U.S. Survey, 1980, 1980, Aeromagnetic Aeromagnetic map map of of the the Manistique Manistique Lakes Lakes U.S. Geological Survey, area, U.S. Geological Survey area, Michigan: U.S. Survey Open—File Open-File Report Report 80—830, 80-830, 44 sheets, scale scale 1:62,500. 1:62,500. H H u.S. Geological Survey, Survey, 1988, 1988, Aeromagnetic Aeromagnetic survey of of Northwestern Northwestern U.S. Wisconsin, data. Wisconsin, unpublished data. I I Wisconsin Geological Geological and Natural Natural History Survey, Survey, 1983, 1983, Aeromagnetic Aeromagnetic map map of northern Wisconsin: of Wisconsin: Wisconsin Geological Geological and and Natural Natural History History 83-4,scale 1:250,000. Survey Map 83—4, scale 1:250,000. JJ Zietz, and Kirby, Aeromagnetic map map of of the northern Zietz, I., I., and Kirby, J.R., J.R., 1971, 1971, Aeromagnetic the northern peninsula, Michigan and and part part of of northern northern Wisconsin: Wisconsin: Geophysical peninsula, Investigations GP-750, scale 1:250,000. 1:250,000. Investigations Map Map GP—750, 24 �490 490 •5•sS..•••.• .5. f...•s... , w. . . . . . . S • • • S • • *.f*.SS.S.S.S.S..S. A S•.lr• . . . . 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VV5-5 46° __ -_,_, S •___ 930 93° 840 LINE SPACING 1I1E SPACING fW4~ ,?::~:~~, .5 PIlLEOR OR LESS LESS • 5MILE E3 f:::~1-1.2 1-1.2lilIES ftlLES m 2 MILES 'ULES ~ :33 MILES 'ULES ~ MILES OR 6 'ULES OR GREATER GREATER Lake Superior Aeromagnetic Survey Index Figure 2. Index map map showing showing the the location Figure 2. Index location of of individual individual surveys, surveys, flight line spacing, spacing, year(s) year(s) flown, flown, flight flight altitude in thousands thousands of altitude in of feet feet above above ground ground (.SAG (.sAG = 500 feet above ground), and data feet above ground), and data format (D format (0 = = digital). digital). �This page intentionally left blank �Glimp c e/Lake Sl.-lperior Superior Magnetics Glimpce-/Lake -92° —p2° -90° —90° -88° —88° 5fJ0 50° -86° —86° -84° —84° 500 50° 1000.0 900.0 800.0 490 49° I l ' ,. 48° I '., .i:.¥.• ,~.~~~ ;r.,,-",·,~.iii-:.t:~ 470 47° 14. , "_ .~~. :. ' . -.' ",,_ j -- - .' ;~. ~ ~. ~~ ~<~=~. . --- ;.'- ~ ...... JJ11"f3.."• ~: ~~,5;·;·>,.~ "/~___ ,. ~ .'.'1:. ,~~~~~~".:~~ '~',,",:,:~-:~.~.- I 490 49° . -4 I 48° '" '"~ .~~.'--a I . . . ~.T_ _ _ _ "" 46° 47° 47° 46° -92° -88 0 -90° o 0 -86 0 ca1e scale 100 II 200 kilometers I _ L L _ Li . L J I I I I I I I I I I I I I I I I - . J U i F4gure F~gufe 1. 10 I Kucks and and Horton KllCks Honon -84 0 I 700.0 600;0 1600;0 500.0 400.0 300.0 200.0 i10o.0 100.0 i :o.o i 0.0 —100.0 100 . 0 ! -200.0 !200.0 i -300.0 —300.0 -400.0 —400.0 -500.0 —500.0 —600M ~I ~ -600.0 -70.0.0 —700.0 ~800.0 —800.0 -900.0 —900.0 1- �This page intentionally left blank �LATE LATE HOLOCENE LAKE LAKE SUPERIOR SUPERIOR -- ISOSTATIC AND CLIMATIC CLIMATIC LAKELAKEE., U. S. S. Geological Geological Survey, Reston, Reston, VA VA LEVEL LARSEN, Curtis E., LEVEL CHANGE. CHANGE. LARSEN, 22092 Beach-ridge complexes complexes along along the the south shore of Lake Superior record Beach-ridge record a composite from 5,000 5,000 B.P. B.P.toto the the present that composite history history of lake-level lake-level change change from that includes includes the effects effects of past past climatic climatic episodes episodes superimposed superimposed on on differential differential pattern of of isostatic isostatic uplift plays plays aa dominant dominant role role basin. The The pattern isostatic uplift of the basin. reconstructing past past lake-level lake-level changes changes from from coastal landforms. in reconstructing For Lake Superior, uplift uplift increases with distance distance northeastward from from For Lake Superior, increases with Duluth, Minnesota, Ontario. Isobases Minnesota, to to Michipicoten, Michipicoten, Ontario. Isobases of equal movement trend trend northwest to to southeast southeast across across the basin. The The outlet outlet to to the the basin basin at at Sault Sault Ste. Ste. from northwest Marie is rising at an apparent apparent constant constant rate rate of of 0.27 0.27 meter per century relative relative to to Duluth. Michipicoten, rising at at about about 0.5 0.5 meter per century relative relative to to Michipicoten, Ontario, Ontario, isis rising Duluth. The throughthe theoutlet outletchannel, channel, however, however, controls controls the the mean mean The flow flow rate rate through level of of the the lake. level lake. For For modern modern Lake Lake Superior, Superior, the outlet is rising more rapidly U. S. shore of the lake. mean level level than the U. lake. Such differential movement raises the mean at Duluth meter per per century. century. Along Duluth and and submerges submerges that that area area at at aa rate rate of of 0.27 0.27 meter Along the the Canadian shore, shore, uplift exceeds that at at the Canadian exceeds that the outlet so that the the mean mean level level falls falls relative to the outlet. This pattern of of submergence submergence of the southern shore shore and and relative This pattern emergence of the northern shore is is a relatively recent event linked to the uplift of the St. Mary's Rivers rapids rapids above above the the surface surface of of Lake Lake Huron Huronatatabout about2,100 2,100 B.P. B.P. Between 5,000 5,000and and 2,100 2,100years yearsago, ago, Lake LakeSuperior Superiorwas was part part of the Between the Algoma phases of the upper Great Lakes. Nipissing and Algoma Lakes. A confluent lake linked linked the three basins at Sault Sault Ste. Ste. Marie. Marie. The The mean mean level level of of the the lake lake was was controlled controlled basins at mainly by the outlet to Lake Huron at Port Huron, Michigan. Michigan. Coastal landforms from Nipissing and and Algoma Algoma phases phases are are common common to to all all three three lake lake basins. basins. from the Nipissing These landforms landforms have have been been uplifted to the controlling outlet at Port These uplifted relative relative to controlling outlet Port Huron and Huron and correlate correlate directly directly between between Lake Lake Huron Huron and and Lake Lake Superior Superior near near Sault Sault Ste. Following the the separation separation of of Lake Lake Superior lakes at Ste. Marie. Marie. Following Superior from from the the lower lower lakes of lake-level lake-level change change developed. developed. Beach-ridge 2,100 B.P., 2,100 B.P., aa different different record of complexes near Sault Ste. Marie Marie and along the Canadian Canadian shore shore of of Lake Lake Superior Superior Lake Huron Huron have have been been raised raised above above the the control control of of their their controlling controlling outlets; outlets; and Lake preserve aa subaerial subaeriallake-level lake-level record recordfrom from5,000 5,000 B.P. B.P. to present. these complexes preserve 2,100 B.P. After 2,100 B.P.Lake LakeSuperior Superiorhas hasits itsown ownunique unique lake-level lake-levelrecord. record. Uplift of the St. Mary's River relative to Duluth has caused aa progressive progressive submergence submergence of of the the St. coast as the outlet outlet has has risen. risen. 29 �Near Duluth and and the the Apostle Apostle Islands, Islands, much much of of the the coastal Near Duluth geomorphological record At least least 5.8 5.8 m m of of submergence submergence has has geomorphological record isis submerged. submerged. At occurred at Duluth Duluth and andabout about4.4 4.4 m m at atthe theApostle Apostle Islands Islands since since uplift upliftof of the the St. St. Mary's rapids B.P. The Nipissing rapids became became the the sole sole control control of of Lake Lake Superior Superior 2,100 2/100 B.P. level of the confluent Great Lakes is indicated by by a raised coastal beach and Lakes that is dune dune complex complex at at an an elevation elevation about about13 13 m m above above the the surface surface of Lake Superior near near Sault Ste. Ste. Marie Marie isis preserved as an apparent Sault preserved as apparent inner inner barrier barrier island island system system preserved in in marshes marshes atatBark Bark Bay Bay and and Big Big Bay Bay State preserved State Park, Park, Wisconsin, Wisconsin, and and most noticeably as an inner noticeably as inner bar bar system system bordering bordering Duluth Duluth harbor harbor at at Superior, Superior, Wisconsin, these bays bays and and the outer Wisconsin. Prominent Prominent beaches beaches at the lakeward edges of these barrier island island at at Duluth Duluthrepresent representthe theprobable probableposition positionofofthe theAlgoma Algomabeach beach(Ca. (ca. 3,500 B.P.). B.P.). This This landform landform has has continued to build vertically as the mean level of 3/500 Lake Superior has risen. studies of of beachbeachLake Superior risen. The The record record is is complex, complex, but detailed studies ridge complexes complexes and and marshes marshes (such (such as as Bark Bark Bay) Bay) indicate steadily rising rising water water levels in this part part of of Lake Lake Superior controlled controlled by uplift uplift of of the the outlet outlet at at Sault Sault Ste. Ste. Marie. by drowned drowned in Marie. Recent Recent submergence submergence is also evidenced evidenced by in situ situ trees near Ashland, Wisconsin, and in in Duluth Duluth harbor. harbor. Our studies suggest Wisconsin, and suggest that that the the rate rate of of uplift at Sault Ste. Ste. Marie has remained constant constant for for at at least least the the past past4,000 4,000 years. years. The long-term prognosis for western Lake Superior Superior is is aa continued rise in mean mean lake level, level, upon upon which which may may be be superimposed superimposed both both higher higher and and lower lower lake lake level level lake episodes episodes related related to to climate climate changes. changes. The range of past in Lake Superior is past climate-related climate-related fluctuations fluctuations in Lake Superior is also The significant. From significant. From an an historical historical perspective, perspective, the range range of of Lake Lake Superior levels levels from 1860 1860 to 1.2 m to present present is 1.2 m or or ca. ca. ±±0.6 0.6mmabout aboutthe themean. mean. The earliest historical accounts from from the 1830's suggest a range of 2.4 accounts 1830's and 40's 40's suggest 2.4 m (± (± 1.2 1.2 m) m) prior to to Our most most recent recent research results from from submerged submerged construction of the Soo locks. locks. Our spit at at Ashland, Ashland, deposits at atBay Bay Mills, Mills, Michigan, and the active Long Island spit spit deposits Wisconsin, indicate 1.5 m lower than than present presentabout aboutAD AD1400 1400 indicate that that lake lake levels levels were were 1.5 m higher higher during the early during the the 'Medieval 'Medieval Warm Phase' and about 11 - 1.2 m 1700's. The range of premodern lake level appears to to have 1700's. level appears have been on order of of double the range of of modern modern levels. levels. 30 �AGE AND GEOLOGICAL SIGNIFICANCE OF OF THE BARABOO BARABOO QUARTZITE QUARTZITE MEDARIS, L.G., Jr., DOTT, RH., R.H.,Jr.; JI.;FOHRNTELLE, FOURNELLE, JH., J.H., JOHNSON, JOHNSON, C.M., SCHOTT, RC., R.C.,and andBAUMGARTNER., BAUMGARTNER, L.P., L.P., Department Department of ofGeology Geology & &Geophysics, Geophysics, University ofWisconsin-Madison, of Wisconsin-Madison, Madison, Madison, WI, WI, 53706 University Post-Penokean mature red quartzites in the southern Lake Superior region (Baraboo, Barron, and Sioux Sioux Quartzites) Quartzites) provide provide important important evidence evidence on on Proterozoic Proterozoic cratonic cratonic evolution. evolution. The Baraboo Quartzite has been re-examined to resolve resolve the the question question of ofits its age, age, identify identify its its mineralogy, mineralogy, determine conditions determine conditions of weathering weathering in in the the source rocks and subsequent metamorphism, metamorphism, and and regime in which the mature red quartzites were formed. formed. evaluate the mid-Proterozoic tectonic regime Age ofthe of the Baraboo Baraboo Quartzite: Quartzite: the the Baraboo BarabooQuartzite Quartziteisisunconformable unconformable on on rhyolite rhyolite (Daiziel (Dalziel & Dott, 1970; 1970; Dott, 1983), 1983), but but was was previously previously thought to be be intruded intruded by the Baxter Hollow & granite (Gates, 1942). Both Bothrhyolite rhyoliteand and granite granite were were interpreted interpreted to to be be correlative correlative with with 1760 1760 Ma Ma (Gates, 1942). rhyolite and granite elsewhere in Wisconsin, Wisconsin, and this this interpretation has been confirmed by U-Pb U-Pb of 1754±44 l754±44 Ma Ma for for rhyolite rhyolite from from the the north north limb limb of ofthe the Baraboo Baraboo syncline syncline and and 1752±15 l752±15 zircon ages of Thus, aa geological geological paradox paradox arises: arises: how Ma for the Baxter Hollow granite (Van (Van Wyck, Wyck, 1995). 1995). Thus, could a mature quartz feldspar, be closely associated in space quartz arenite, arenite, which which is is virtually virtually devoid of offeldspar, and time with granite-rhyolite magmatism? magmatism? The quartzite-granite contact has been re-examined in Baxter Hollow, and in cores from eight drill drill holes holes that that penetrated the quartzite-granite contact, which were obtained obtained by the U.S. Army Corps of of Engineers in in 1959. 1959. There There isis no no evidence evidence in in the the field, field, or in any of of the drill cores, that quartzite was intruded by granite. Shearing Shearinghas hasdeveloped developednear nearthe thecontact, contact,especially especiallyin in granite, which has been transformed locally to illite-quartz illite-quartz semi-schist. semi-schist. Among the drill drill holes holes that that penetrated the quartzite-granite contact, material Among material from the contact interval was was recovered recovered only only in in Hole Hole No. No. 613, 613, where where there there is is aa two-foot two-foot thick, reddish-purple zone interval fine-grained hematite, hematite, quartz, illite, and kaolinite, kaolinite, which which appears appears to to be a regolith, between of fine-grained illite, and overlying Pebbles in in the quartzite quartzite consist consist mostly mostly overlying pebbly pebbly quartzite quartzite and and underlying, underlying, ahered altered granite. granite. Pebbles of quartz, quartz, although although a few few pebbles pebbles of of red, red, altered altered rhyolite rhyoliteoccur. occur. We conclude that the Baraboo Quartzite is unconformable on the Baxter Hollow granite, and and that that shearing shearing was was localized localized along along the contact between these two two competent competent rock rocktypes typesduring during later later folding. folding. The two-foot interval interval between quartzite and and granite granite may represent a paleosol, which was derived from weathering of ofthe underlying granite and and modified modified by subsequent subsequent shearing shearing and and the underlying metamorphism, In addition, addition, metamorphism,,and·a anda chemical chemical investigation investigation isis in inprogress progress to to test test this hypothesis. hypothesis. In detrital zircons, some of of which are euhedral, have been separated from the quartzite quartzite and and are are being being analyzed any were derived derived from 1760 1760 granite-rhyolite granite-rhyolite sources. sources. analyzed to to test whether any Mineralogy: Minera1o: sheet sheetsilicates silicatesininthe theBaraboo BarabooQuartzite Quartziteare aredominated dominatedby bypyrophyffite, pyrophyllite, A14Si5O20(OH)4,and andkaolinite, kaolinite, Al A14Si4O10(OH)8, whichoccUr occurinterstitially interstitially in in quartzite quartzite and in Al4Sig0ZO(OH)4' in 4Si40lQ(OH)g, which K15A14[Si65A115O20](OH)4, and and occurs interstitially pyrophyllite-rich layers. K-mica K-micaisisilhite, illite, - K1.5Al4[Si6.5Al1.50zoJ(OH)4' in alteration product product of offeldspar feldspar in in granite. granite. in quartzite, in the regolith(?) in Hole 613, and as the alteration Diaspore, a-AlO(OH), a-A1O(OH), was discovered in in quartzite quartzite in in Holes Holes 613 613 and and 6l4A, 6l4A, where where itit is is associated associated Diaspore, with pyrophyllite, Thepresence presenceof ofsuch suchaluminous aluminous minerals minerals in the Baraboo pyrophyllite, kaolinite, kaolinite, and and illite. jute, The Quartzite indicates derivation from from maturely maturely weathered weathered soil, soil, such such as aslaterite, laterite,and andsignifies signifies aa mid-Proterozoic episode ofintense intense chemical chemical weathering weathering and and leaching leaching of ofalkalies. alkalies. episode of 31 �common assemblage, assemblage, Metamorphism: the common quartz+pyrophyllite+kaolinrte±illite,linritsthe quartz±pyrophyffite+kaolinite+illite, limits the H20 temperature of metamorphism to less than 280°C at an of less ~ 280~ tillite v assumed P(~O) P(H20) of of 500 bars. bars. However, assumed However, kaolinite kaolinite occurs as micron-scale interlayers in pyrophyllite, pyrophyllite, and and if kaolinite isis aa retrograde retrograde mineral, ifkaolinite mineral, rather than temperatures could could have have been been as as high high as as prograde, temperatures 3 50°C,which which isis the the stability linrit limit ofpyrophyllite. of pyrophyllite. 350°C, in the the Baraboo Quartzite is always separated Diaspore in from quartz by pyrophyffite, pyrophyllite, and may represent relict grains, which were derived from a lateritic detrital grains, source, and which were protected by by surrounding Qtz ern And Cm pyrophyffite from complete complete reaction reaction with quartz pyrophyllite from during metamorphism. metamorphism Geological Significance of ofthe the Baraboo Baraboo Interval: Interval: the the Baraboo Baraboo interval interval was was defined defined by Dott (1983) as as aa sequence sequence of ofsedimentation, sedimentation, deformation, deformation, and andmetamorphism metamorphismin in the the time time span span of of1450 1450 to 1750 region. Deposition 1750 Ma in the southern Lake Superior region. Deposition of of the Baraboo, Barron, and Sioux quartzites was was thought to have occurred after 1750 quartzites 1750 Ma, but prior to 1650 1650 Ma, Ma, which which was a time of Rb-Sr isotopic re-setting in Wisconsin Wisconsin and and perhaps perhaps folding folding of of the the Baraboo Baraboo Quartzite Quartzite (Van (Van Schmus, 1980). 1980). Now that the post-1760 post-1760 Ma Ma age age of ofthe theBaraboo BarabooQuartzite Quartzitehas hasbeen beenfirmly firmly established, established, based based on the new evidence from drill core 613, the deposition deposition of ofred, red, mature, mature, fluvial fluvial quartz quartz arenites, arenites, which are regionally regionally extensive extensive and and up up to to 2,000 2,000 meters thick, thick, can be viewed viewed as as the result result of cratonic cooling and subsidence, following following the cessation of of 1760 Ma granite-rhyolite magniatism. magmatism The time of the Baraboo Quartzite of folding and metamorphism of ofthe Quartzite is is still still unclear; it could could have have been at 1650 1650 Ma, Ma, but but recently recently obtained obtained isotopic isotopic evidence evidence indicates indicates the the existence existence of ofaametamorphic metamorphic event at at -1720 —1720Ma Maininthe thesouthern southernLake LakeSuperior Superiorregion region(Van (VanWyck, Wyck,1995). 1995). Thus, Thus, the event Baraboo-Barron-Sioux triad triad could could have have been deposited in either of ofthe 1760-1720 Ma, Baraboo-Barron-Sioux the intervals, 1760-1720 or 1720-1650 Ma. Ma. In either case, ample time, on the order of 40 or 70 Ma, would In either case, ample time, on the order of 40 or 70 Ma, would have have been been available available for for development development of mature mature quartz sandstones, especially in in response to lateritic aluminous minerals weathering, as indicated by aluniinous minerals in in the the Baraboo Quartzite. The Baraboo interval is a valid and useflul useful concept conceptfor for interpreting interpreting the the mid-Proterozoic mid-Proterozoic evolution of of the the Lake Lake Superior Superior region, region, but but itit applies applies only onlytotopost-1760 post-1760 Ma Ma quartzites. quartzites. Treating all evolution Proterozoic quartzites quartzites in in Wisconsin Wisconsin as correlative leads to serious misinterpretations of of the Baraboo Quartzite, in in particular, and and of ofthe Proterozoic Proterozoic evolution evolution of ofthe the Lake Lake Superior Superiorregion, region, in in generaL general. REFERENCES CiTED REFERENCES CITED Dalziel, I.W.D. and Dott,R.R, RJ{, Jr. (1970) Wis. Wis. Geol Nat. Hist. DalzieL LW.D. and Dott, Rist. Sun'. Surv. Inf Inf Circ. Circ. 14, 14, 164 164 p. p. Dott, RH., 1. R.H.,Jr. Jr.(1983) (1983)GeoL Geol.Soc. Soc.Amer. Amer.Memoir Memoir160, 160,129-14 129-141. Amer. Mineral., Mineral., v. 27, Gates, R.M. (1942) Amer. 27, 699-711. 699-711. Schmus, W.R. Soc. Amer. Amer. Special Special Paper 18, Van Sckmus, W.R. (1980) Geol. Soc. 18, 159-168. 159-168. Van Wyck, Wyck, N. N. (1995) Ph.D. thesis, UW-Madison, OW-Madison, 280 p. p. <28O 32 �THE LATENT MAGMATIC STAGE OF THE MIDCONTINENT MIDCONTINENT RIFT: A PERIOD OF MELTING OF THE LOWER CRUST MAGMATIC UNDERPLATING AND AND MELTING MILLER: J.D., Jr., Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642 University University Ave., Ave., St. St. Paul, Paul, MN MN 55112 55112 MILLER, (mi1le066@maroon.tc.umn.edu) andVERVOORT, VERVOORT,J.D., J.D.,Dept. Dept.ofofGeosciences, Geosciences,University University of of (mille066@maroon.tc.umn.edu) and Arizona, Tuscon, Tuscon, AZ AZ85721 85721(vervoort@geo.arizona.edu) (vervoort@ geo.arizona.edu) Field studies, seismic and and gravity gravity data, data, U-Pb U-Pb zircon zircon dating, dating, and and geochemical geochemical studies studies of of intrusive rock rock suites suites around around the the Lake Lake Superior Superior basin basin show show that that the the Midcontinent Midcontinent rift rift volcanic and intrusive Most (MCR) evolved in several distinct magmatic stages stages between between 1109 1109 and and 1086 1086 Ma Ma (1-4). (1-4). Most recently, a period of of substantially reduced reduced volcanism volcanism and and aa shift to to more more intermediate intermediate to to felsic felsic has been been identified identified between between 1107 1107 and and 1100 1100 Ma—an Ma-an interval interval we we refer refer to to as as magma compositions has 1). Overall, Overall, MCR MCRmagmatism magmatism resulted resulted from from an an anomalously anomalously hot the latent magmatic stage stage (Fig. (Fig. 1). mantle plume emplaced at at the the base base of of the the lithosphere lithosphere at at about about 1109 1109 Ma Ma (5). (5). The most obvious magmatism is is the the large large volume volume (over (over 22 million million km3) km 3) of mostly basaltic volcanic aspect of this magmatism rock that accumulated in of up up to 20 20 km km (1). (1). Less Lessobvious,. obvious, in the the central central rift rift graben graben to to thicknesses thicknesses of but equally significant is is aa comparable comparable volume volume of of mafic mafic magma magma that that intruded intruded and and underplated underplated the the (6,7). We crust beneath the Lake Superior region (6,7). We present present evidence evidence here here that that suggests suggests a not aa causal causal relationship relationship between between the the latent latent magmatic magmatic stage, stage, magmatic magmatic contemporaneous ifif not underplating, and lower lower crustal melting. melting. The first hint of of aa latent latent magmatic magmatic stage stage was was recognition recognition of of aa hiatus hiatus in in mafic mafic intrusive intrusive activity activity 1107 Ma and 1099 Ma (8). More recent recent U-Pb U-Pb dating dating of of the the in the Duluth Complex between 1107 (8). More Group (9) (9) and and the the Powder Powder Mill Mill Group Group (10) (10) has has revealed revealed aa decrease decrease in in North Shore Volcanic Group Volcanic rocks rocks occuring occuring within within and and adjacent adjacent to both both volcanic activity over this same period. Volcanic these low production intervals intervals are are mixed mixed rhyolite, rhyolite, andesite, andesite, and and evolved basalt (4, (4, 11). 11). Insufficient dating has has been been conducted conducted to to determine determine if if aa similar similar decrease decrease in in basaltic basaltic volcanism volcanism is is However, itit is is noteworthy noteworthy that that the the present in the Osler and Mamainse Point volcanics volcanics suites. suites. However, and. central 12), yields an Agate Point rhyolite, which separates the upper and, centralsuite suiteof of Osler OslerGroup.( Group.(l2), l105±2 Ma (9). At Mamainse Mamainse Point, Point, abundant abundant felsic flows and intrusions have been age age of 1105±2 (9). At mapped below the 420-rn-thick, 420-m-thick, polymict Great Conglomerate (13), which presumably signifies volcanic activity. activity. Further Further evidence evidence that that felsic volcanism predominated a prolonged hiatus of volcanic during an overall diminution of volcanic activity comes from the preponderance of rhyolite clasts in the Copper Harbor Conglomerate and their age of 1104±2 1104±2 Ma (14). We propose that the latent magmatic stage represents a period of reduced extension coupled underplating and and melting melting of of the the lower lower crust. crust. If the rate and intensity of with extensive magmatic underplating extension in the MCR was largely controlled by external stresses imparted by contemporaneous Grenvillian tectonism (15), then then ponding of magmas at the crust-mantle interface was likely a passive response to decreased tensile (or perhaps compressive) stresses in the lithosphere. However, to the extent that lithospheric thinning and extension was driven by the bouyancy and thermal energy of the mantle mantle plume (16), then perhaps magma underplating actually caused diminished extension of of the the crust crust by by delam.inating delaminating and structurally decoupling it from the lithospheric mantle. In In either eithercase, case, underplating underplating was was probably probably instigated instigated by the heating and of the earliest mantle-derived magmas coupled anatexis of the lower crust caused by the passage of The creation creation of of felsic felsic melts melts and and an increasingly ductile with heating from the rising plume. The lower crust would have created density density and and rheologic barriers to impede the passage of mafic melts and promote their ponding (17). Once magma chambers would have Once initiated, initiated, mafic mafic magma continued to expand as as additional additional rising mantle mantle melts melts became trapped and triggered more more At the the peak peak of of the the latent latent stage, stage, the lower crust may have widespread melting of the lower crust. crust. At magmas. Although Although the the resumption resumption of volcanic activity at been largely impermeable to mafic magmas. about 1102-1100 Ma (earlier near the axis of the rift) may have been externally triggered by of the the crust, crust, itit seems seems also also possible possible that that density cleansing of the lower crust increased extension of caused by the upward migration of low density felsic melts and perhaps thinning of the ductile lower crust concomitant with magma underplating may have played important roles in allowing basaltic magmas to emerge from deep crustal magma chambers. 33 �The formation fonnation of of large large magma magma chambers chambers in in the the lower lower crust crust helps helps explain explain many of of the the lithologic, and geochemical characteristics characteristics that that are are generally generally common to all volcanic suites formed during the latent fonned latent magmatic magmatic stage stage as as well well as as magmatism magmatism leading leading up to and following itit (Fig. 1). Some Some of ofthe the more more cogent cogent features features are: are: (Fig. • Felsic magmatism—The magmatism-The bulk bulk and and isotopic isotopic composition composition of of rhyolite rhyolite flows flows and and their their greater greater abundance relative to to flows flows of of intermediate intennediate composition composition indicates indicates that that many many if if not not most most were were generated from partial melting melting of of crustal crustal sources sources rather rather than than as as differentiates differentiates of of mafic mafic magmas magmas (18, 19). The The greater greaterconcentration concentration of offelsic felsic lavas lavas in in stratigraphic stratigraphic intervals intervals straddling straddling the the latent latent stage (Fig. 1) 1) is consistent with with itit being being aa period period of of lower lower crustal melting melting coupled coupled with with diminished diminished basaltic volcanism. volcanism. However, basaltic However, the the moderately moderately negative ENd(1100) Nd(1100) (--4) (—-4)ofoffelsic felsiclavas lavas in in the the lower part of the NSVG (Fig. 1) 1) is is difficult difficult to to explain explain by by melting melting of of Archean Archean lower lower crust, crust, which which should should have £Nd(1 100) = -12 to -17 (18,19). (18,19). Although have cNd(lIOO) Although this this may may indicate indicate mixing mixing of of Keweenawan Keweenawan felsic differentiates with Archean crustal melts melts (19), (19), an an intriguing intriguing alternative alternative explanation is is that that the the lower crust (ENd(1100) -12). The crust isis composed composedofofEarly EarlyProterozoic Proterozoicrocks rocks (cNd(lloo) ==-4 to -12). The persistence persistence of well into into the middle of felsic volcanism volcanismwith withvaried variedENd(1100) ENd( 11 00) well of main main stage stagemagmatism magmatism(—1096 (-1096 Ma) Ma) ofof thethe high cNd(1 may reflect reflect melting meltingof ofthe thebase baseofofthe thevolcanic volcanicpile pileproducing producingsome some high CNd( 100) 1100) (18) or levels with low £Nd(1 100). melting of of progressively progressivelyhigher higher(Archean) (Archean)crustal crustal levels with low ENd(1100). • Evolved basalt and and intermediate intennediate lavas—Basalt lavas-Basalt in in all all stratigraphic stratigraphic intervals intervals straddling straddling the the latent latent general indicator of the differentiated stage displays a broad, but overall low low range range of of mg# mg# - aa general composition of mafic magmas (Fig. 1). Moreover, Moreover, intermediate intennediate lava lava compositions compositions that that were probably generated by differentiation of of mafic mafic magmas magmas (e.g., (e.g., basaltic andesite, andesite, andesite andesite and and icelandite) are highly concentrated within within these these same same intervals intervals in in the the Powder Mill Mill Group Group (4) (4) and and Thisconcentration concentration of ofevolved evolved lava lava compositions compositions is is consistent consistent North Shore Volcanic Group (11). This with prolonged crustal staging of mantle-derived mantle-derived magmas magmas leading leading to to greater greater degrees degrees of of differentiation during this period. period. The The broad broad and and commonly commonly erratic erratic range range of of compositions erupted prior prior to to and and following following the the latent latent stage stage (e.g., (e.g., 21) 21) suggests suggests that that multiple, multiple, open-system open-system staging chambers existed throughout the lower lower crust. • Contaminated basalt—Trace basalt-Trace element (e.g. (e.g. ThIYb) and Nd isotope geochemistry of basalts (Fig. 1) suggest that crustal contamination was most prevalent in the period leading up to the latent 1) magmatic stage. The The greatest greatestpotential potential for for interaction interaction between between mantle mantle melts melts and continental crust would be expected to occur during the inital inital development of of lower crustal magma chambers. Once chambers. Once established, established, crystallization crystallizationand andcontinued continued inflation inflation of of such chambers would have insulated them from further contamination and and diluted the initial contamination. • Plagioclase crystal mush—Leucocratic mush-Leucocratic intrusions of of the Mellen Complex formed fonned at 1102 1102 Ma Ma (10), the anorthositic series of of the Duluth Duluth Complex at at 1099 1099 Ma (9), and the widespread lava flows flows (p. (p, Fig. Fig. 1) I) indicate indicate that that plagioclase-enriched plagioclase-enriched basaltic basaltic occurrence of plagioclase-phyric lava the upper upper crust crust between between 1108 1108 and and 1096 1096 Ma. Ma. Such magmas were commonly emplaced into the plagioclase crystal mushes were were likely likely generated in lower crustal magma chambers where high high flotation of plagioclase plagioclase (20). (20). An pressures would have promoted the flotation An implied consequence of this flotation is the fonnation formation of of anorthositic anorthositic roof roof zones zonesininthese thesedeep deepchambers. chambers. Such roof-zone flotation material was the likely source of of anorthosite anorthosite inclusions inclusions found found in in the Beaver Bay Complex. The interpretation of of the latent latent magmatic magmatic stage stage as as a period period of of extensive magmatic magmatic underplating and crustal melting melting carries significant significant implications implications for the geodynamic and magmatic evolution of the MCR which need need to to be be more more fully fully explored. explored. Whether Whether underplating was the cause or effect of of reduced crustal extension and and the development of of the latent latent magmatic magmatic drives continental continental rifting. rifting. Future stage hinges on the larger question of what drives Future petrologic studies at evaluating the the extent to to which which open-system open-system crystallization differentiation of of should be directed at mantle-derived magmas under high high pressures pressures (7-10 (7-10 Kb) Kb) can account for the compositional range range of MCR lavas and at more precisely determining determining the the sources sources of of felsic felsic magmas. magmas. In addition, more high precision U-Pb ages ages are are necessary necessary to to verify verify the the existence and duration of of the the latent latent all sequences and and to to better establish correlation between Mamainse Mamainse Point Point magmatic stage in all lavas and volcanic sequences sequences in in the the western western Lake Lake Superior Superior region. 34 �References (1) Cannon, 1992, (1).Cannon, 1992, Tectonophys T~ctonophys 213, p.41; p. 41; (2) (2) Shirey Shirey et et a!., aI., 1994, 1994, GCA GCA 58, 58, p. aI., 1995, 1995, MGS MGS p. 4475; (3) Miller et al., Guidebook et al., aI., in in review, review, CJES; CJES; (5) (5) Hutchinson Hutchinson et et al., a!., 1990, 1990, JGR JGR 95, 95, p. 10869; 10869; (6) Behrendt et GUidebook 20; 20; (4) (4) Nicholson Nicholson et al., aI., 1990, 1990, Tectonophys Tectonophys 173, 173, p. 1991, GRL 18, p. p. 625; & Miller, 1993, 1993, JGR 98, p. p. 617; (7) Trehu Trëhu et aI., at., 1991, ORL 18, 625; (8) Paces & 13997; 9; (10) (10) Zartman Zartman et et al., aI., in in review, review, CJES; CJES; (11) (11) Green, Green, 1972, 1972,Geol Geol of ofMN: 13997; (9) (9) DaVIS Davis et aI., al., 1995, 41st ILSG, p. p.9; MN: Cent. Vol., Vol., p. p. 294; 294; (12) (12) Lightfoot Lightfoot et et al., aI., 1991, 1991, JGeol JGeol 99, 99, p. 739; (13) Annels, 1973, 1973, GSC Paper 72-10; (14) Davis Davis & Paces, 1990, 1990, EPSL EPSL 97, 97, p. p. 54; 54; (15) (15) Cannon Cannon & &Hinze, Hinze, 1992, 1992, Tectonphys Tectonphys 213, 213, p. Campbell & Griffiths, 1990, 1990, p. 49; (16) CampbeLl EPSL 99, p. 66; 66; (17) (17) Huppert Huppert & & Sparks, Sparks, 1988, 1988, JPet JPet 29, 29, p. p. 599; 599; (18) (18) Nicholson Nicholson & & Shirey, Shirey, 1990, JGR JGR 95, 95, p. p. 10851; (19) Vervoort Ver~oort & & Green, Green, in in review, review, CJES; CJES; (20) (20) Miller Miller & & Weiblen, Weibien, 1990, 1990, JPet JPet 31, 31, p. 295; (21) Brannon, 1984, 1984, WashU WashU PhD 1988, MTU PhD thesis; (23) (23) Nicholson, Nicholson, 1992, 1992,.USGS Bull 1970-B. 1970·B. PhD theSIS; thesis; (22) Paces, 1988, USGS Bull TECTONOMAGMATIC GEOLOGIC, GEOCHRONOLOGIC AND AND INTERPRET INTERPRETATION GEOCHEMICAL DATABASE DATAB Magmatic Chrono- lLithostrati a h Basalt Chemostrati a h Eruption Crust~l Magma Magma EXlenslOn Stage P Inlr. NSVG PLlPM OGflR MPF ENd (1100) m8# Rate Rate Sources Staging 'J!1IYb 1092 ~-+t:r"""'---:--+-~--I-;;"="T--+---+-";;-~ Late \ .\ Gp7 /~ lrhyolite\ \ 1094 V 1096 r sv ~ --- 1098 : / :I :/ / ~1102 / / / I: Ii /~ ~'-'!~bvl \/ Volcanism (LC) , \ \ Volcanism I I I I r \ Early EP+LM (Laue) / Ii I If I V basalt I I \ \ 1104 . Latent EP UCIKL / ), a) a.> 1108 / ~ "' I I I I I 1 I : 1100 1106 \ . :. ~ !PL EP EP+LM j M H L M H FIGURE1.I.Correlation Correlationofofunits, units,summary summaryofoflithologic lithologicand andchemical chemicalcharacteristics, characteristics, and and interpretations interpretations of of the FlGu1 tectonomagmatic evolution during during magmatic magmatic stages stages of ofthe theMidcontinent Midcontinentrift. rift. Intervals Intervals of of Normal and Reversed magnetic magnetic tectonomagmatic evolution polarity indicated (P). Relative Relativeabundances abundances of ofbasaltic basaltic and and felsic felsic volcanics volcanics schematically schematically portrayed portrayed and and genera! general locations locations of plagioclase porphyritic flows flows (p) (p) noted noted for for the the major major volcanic volcanic suites—NSVG-North suites-NSVG-North Shore Shore Volcanic Volcanic Group( Group( 11); 11); PLIPMPLlPM- Portage Lake Volcanics Volcanics and and Powder Powder Mill Mill Group Group (4); (4); OG/IROGIIR- Osler Osler Volcanic Volcanic Group Group and and PL PL on on Isle Isle Royale Royale(12); (12); MPF- Mamainse Point Formation(2,13). Subdivisions Subdivisions of ofvolcanic volcanic suites suites are are NSVG: NSVG: IGP/uGP, IGP/uGP, HL, HL, NSV-n, NSV-n, SLBlower/upper Grand Portage lavas, Hoviand Hovland !avas, lavas, NSVG-normal NSVG-normal polarity, polarity, and and Schroeder-Lutsen Schroeder-Lutsen basalts basalts of (11); PM: ISCluSC, 1KC/uKClKC/uKC· lower/upper ISC/uSC, lower/upper Seimens Seimens Creek Creek lavas lavas and and lower /upper Kallander Creek volcanics volcarncs of (4); (4); OG: OG: lower, central and upper suites of (12); MPF: Groups 1-7 1-7 of(2).; of (2).; CHC-Copper CHC-Copper Harbor Harbor Conglomerate; Conglomerate; CCGC- Great Great Conglomerate. Conglomerate. Intrusive rock units are LS- Logan Sills, CC- Coldwell Complex, Complex, NLSNLS- Nathan's Layered Series, MC- Mellen Complex, Average U-Pb V-Pb ages ages for for various various volcanic volcanic and and intrusive intrusive rocks rocks indicated indicated DC- Duluth Complex, BBC- Beaver Bay Complex. Average ENd(I'OOl data from MPF (2), filled (felsic) by filled (felsic) and and open open (mafic) (mafic)circles; circles;data datafrom from (8), (8), (9), (9), (10), (10), and and sources sources listed listedtherein. therein. EN1OI PLIPM (4), NSVG rhyolite (19), NSVG basalt (21). mg# PL/PM mg#(=(=MgO/(MgO+FeO)* MgO/(MgO+FeO)*100) 100) of of common range displayed by 22,23). ThIYb data data from from MPF MPF (2), (2), PM (4), OG (12), NSV-n (21), PL (22, 23). basalt in all volcanic suites (2,4,11,12,21, 22, 23). ThJYb 23). Relative from thicknesses thicknesses of volcanic Relative eruption eruption and and extension extension rates rates (Low, Medium, High) interpreted from volcanic suite suite relative relative to to Magmasources sourcesfor forbasaltic basalticcomposition: composition: EPEP- enriched enriched plume, plume, LMLM- lithospheric lithospheric mantle, mantle, DMDMperiod of eruption. Magma in parentheses: parentheses: LCLC(3)). Magma Magma sources sources for for felsic felsic compositions compositions in depleted asthenospheric mantle (modified from (2) and (3)). lower crust, UC UC -- upper crust, KL - Keweenawan lavas. Interpretations of relative volumes of magma staging in the lower crust (LC) and upper crust (UC) (VC) denoted by by relative relative widths widths of of curves. curves. �PRELIMINARY PETROLOGIC ANALYSIS ANALYSIS OF OF THE THE EARLY EARLY PRELIMINARY SEDIMENTOLOGIC SEDIMENTOLOGIC AND PETROLOGIC PROTEROZOIC MAHNOMEN MAHNOMEN .FORMATION RANGE GROUP) GROUP) EASTEASTPROTEROZOIC FORMATION (NORTH (NORTH RANGE CENTRAL MINNESOTA CENTRAL MOREY, G.B., G.B., and CLELAND, MOREY, CLELAND, J.M., Minnesota Geological Survey, 2642 2642 University Ave., Ave., St. Paul, Paul, Minn. Minn.55114-1057 55114-1057 The term North Range Range Group Group was was proposed proposedby bySouthwick Southwick et etal, al. (1988) (1988) for Early Proterozoic Proterozoic The strata sandwiched sandwiched between between the the underlying underlying Mule Mille Lacs Lacs Group and overlying Animikie Group on Cuyuna range. range. As Asdescribed describedby bySchmidt Schmidt (1963), (1963), the group consists consists of a lower lower the North Cuyuna siltstone-shale sequence-the sequence—the Mahnomen Mahnomen Formation; Formation; an an intermediate intermediate and dominantly Fe Fe + Mnunit-the Trommald Formation, Formation, and aa upper uppergraywacke-shale graywacke-shale sequence—the sequence-the Rabbit Rabbit Lake Lake rich unit—the Formation. Much Much of of the the Trornmald Trommald Formation Formation contains contains evidence evidence of hydrothermal or or fumarolic fumarolic processes; little is known To clarify processes; little known however, however, about about the the enclosing enclosing epiclastic epiclastic strata. strata. To clarify the sedimentary history history of of the the Mahnomen Mahnomen Formation, Formation, we we have have re-examined re-examined more more than than 320 320 m m of of continuous core first described described by by Grout Grout and and Wolff Wolff (1955) (1955) from from four four sites sites across across the range. However, our work must has estimated However, our must be be considered considered preliminary, preliminary, for for Schmidt Schmidt has estimated that the the Mahnomen isis at Mahnomen at least least 600 600 m m thick. thick. as 90 90 percent of of the the Mahnomen Mahnomen core core consists of laminated to very thin-bedded thin-bedded As much as claystone, shale, and and siltstone. siltstone. Claystone-now clay-size sericite sericite ±. ± claystone, mudstone mudstone or shale, Claystone—now mainly clay-size chlorite—contains <5 <5 modal modal percent, percent, silt-size silt-sizequartz. quartz. Mudstone contains contains from from ~25 25 percent chlorite-contains percentsiltsiltsize size quartz scattered more or less less randomly randomly through the the matrix, matrix, whereas whereas in shale shale similar amounts of quartz quartz define define aa fissile fissile layering. layering. Siltstone Siltstonecontains contains 25-80 25-80 modal modal percent percent silt, silt, plus plus some fine some fine sand-size sand-size quartz quartz ± trace trace amounts amounts of of chert chert or or iron-formation. iron-formation. Some Some beds beds are are calcareous 20 modal modal percent percent calcite, calcite, whereas whereas others others contain contain >50 >50 modal modal percent, percent, calcareous with with 20 The fine-grained rocks define constituting limestone of of several several varieties. varieties. The fine-grained rocks define upward-fining constituting limestone sequences 5-20 5-20 mm thick, thick, where where siltstone siltstone predominates predominatesinin the the lower lower parts parts and and claystone and sequences claystone and is straight straight and and regular mudstone or shale predominate predominate in upper parts. parts. Bedding Bedding is regular but mudstone in the upper interrupted in and other evidence in places places by by synsedimentary synsedimentary faults, faults, overturned overturned folds, folds, and evidence of slumping. are graded, graded, and are topped by slumping. Many Many siltstone siltstone beds beds have have scoured scoured lower lower surfaces, surfaces, are by climbing-ripple laminae. Compaction climbing-ripple laminae. Compaction features features such as flame flame structures and load load casts(?) casts(?) are common. Contrary to to earlier earlier published published descriptions, descriptions, sandstone sandstone is is aa rare rare component component comprising comprising no no more than the described cores. cores. It occurs in generally structureless to vaguely graded than 55 percent of the and layered they are are interspersed interspersed throughout throughout the the cores. cores. Most layered beds beds 2-3 2-3 cm to 1 meter thick; thick; they Most fine- to medium-grained, medium-grained, quartzose quartzose or or lithic lithic wackes wackes having having>15 beds are fine>15 modal percent matrix (mainly (mainly chlorite ± sericite). sericite). Other constituents (Fig. (Fig. A) include 2-29 2-29 modal percent percent cement cement (possibly (possibly ankerite ankerite ± hematite) hematite) and and 52-94 52-94 modal modal percent percent framework framework grains. grains. Quartz (50-92 (50-92 percent), dominates dominates the theframework frameworkgrains grains(Fig. (Fig. B), B), especially in coarser modal percent), coarser grained samples, followed fragments of of metasedimentary metasedimentary origin origin (9-43 (9-43 modal percent) and feldspar, feldspar, followed by by rock fragments modal percent) (5-15 modal mainly plagioclase (5-15 modal percent). percent). These modal abundances are misleading, however, for there is considerable textural evidence evidence that that much much of of the the matrix matrix has has been been formed by the there considerable textural formed by breakdown breakdown of of unstable metasedimentary metasedimentary rock rock fragments. Nonetheless, Nonetheless, the the Mahnomen is is clearly a second-cycle second-cycle sequence sequencederived derivedfrom froman anolder oldermetasedimentary metasedimentaryprovenance-most provenance-most likely the the underlying Mule Lacs Group, a possible provenance also suggested by quartz types that point Mille possible provenance also suggested by to a "low rank metamorphic metamorphicsource" source" (Fig. (Fig. C). C). 'low rank Major, minor, minor, and trace-element (Fig. D) D) are are similar similar to to those those of of an average Major, trace-element compositions compositions (Fig. shale, where plagioclase and, consequently, sodium are generally lacking and where potassium potassium is associated associated with sericite. sericite. REE REE compositions compositions (Fig. (Fig. E) cratonic is E) are are broadly broadly consistent consistent with with a cratonic source, HREE and are· marked marked by by flat flat Ce Ce anomalies anomalies and and mostly mostly source, show show slight depletion in HREE and are positive Eu anomalies. anomalies. However, However, aa few few samples samples have have low low REE REE totals totals and negative negative Eu Eu positive Eu Beds of of volcanogenic material as thick anomalies; they may contain a volcanogenic component. Beds 36 �cm, are are mainly ash-fall ash-fall tuff. tuff. They have been recognized and as 10 em, and described described from from elsewhere elsewhere on on the range range by byMeicher Melcheretetal. al.(1996). (1996). The The North Range Range Group Group has has been been folded folded at at least least twice twice and and metamorphosed metamorphosed to to the the greenschist facies. As such it is is part part of of the the Penokean Penokean fold-and-thrust fold-and-thrust belt. Hemming et et al. al. greenschist facies. As belt. Hemming in the the Mahnomen Mahnomen were were derived derived from from an an (1993) used (1993) used Sm-Nd Sm-Nd techniques techniques to to show show that detritus in provenance. Morey Morey and and Southwick Southwick (1995) (1995) used information to Archean provenance. used that information to suggest suggest that the Mahnomen was was deposited deposited on on an an evolving evolving continental continental margin margin early early in in thetectonic the tectonic history history of of the the Penokean orogen. orogen. However, second-cyde sand, sand, such such aa suggestion suggestion Penokean However, because because the Mahnomen is a second-cycle orogen. may no longer be applicable to the tectonic evolution of the Penokean orogen. 100 100 Fiamework Framewor1( greene grains ! A D. •0. 10 10 If J 10.1 10.1 en • • 0.u ntHlEui1 ThY Ybt.u 0.01 Rb BaTh U U NbTal( M,Th LaC.SrNdI"SmZrHfEun ThY Vb Lu • • PolycrystalNne PoIyerystaJ!ne quartz Cement -/ / Matrix Matrtx ra,* rn.twIOrpC Low Lowl1lnk~ au.,tz Quartz 6.1' I ••• • . .e • / / ••• :\ •.'' / / I.Idde and UIlC* • rank~ / / •• / / / / / Plutonic • • . • quartz 10g. E. S 10 S N-3 IC WCSI ~ Uthc wucice 1 Week.(manix (matrix> 15%) Wed. > 15%) Si Fe4dspar Feldspar 5/ I 51 5.1 00 N13. N-13· S.f 5/ — SI RocX'IWgi".tta tVu4ut. Rod< (1nctudInQ thart) chert) 37 1 0.1 0. N<l Sm Eu Th LICI4dSrnEUTh L. C. Yb Lu Vb �IN THE FOX FOX RWER RIVERVALLEY, VALLEY, MISSISSIPPI VALLEY-TYPE MINERALIZATION [N EASTERN WISCONSIN M1JDREY, MUDREY, M.G. ,, Jr. Ir. and BROWN, B.A., Wisconsin Geological and Natural History 100, Survey, WI 53705-5 53705-5100, Survey, 3817 Mineral Point Road, Madison, WI mgmudrey@facstaff.wisc.edu, babrown l@facstaff.wisc.edu; FREIBERG, FREIBERG, mgmudreyfacstaff. wisc. edu, and babrownl@facstaff.wisc.edu; PG., and P.G., and SIMO, SIMa, J.A., lA., Department Department of ofGeology Geology and and Geophysics, Geophysics, 1215 1215 W. Dayton St., Madison, Madison, WI WI53706-1692, 53706-1692,simo@geology.wisc.edu simogeology.wisc.edu St., Regional NURE (National Uranium Resource Evaluation Program) Program) geochemical geochemical data data suggest suggest that anomalous concentrations concentrations of ofarsenic arsenic and and other other mineral mineral exploration exploration path-finder path-finder elements elements are are of Green Green Bay, Wisconsin Wisconsin where the Sinnipee, Sinnipee, Ancell present in the area southwest of Ancell and Prairie du Chien Groups are the uppermost bedrock units. units. InInaddition, addition,fluorine fluorine levels levels in in groundwater groundwater have long been known to be be high high in the Fox River valley between Green Bay and Appleton, where fluorite and other other Mississippi Mississippi Valley-type minerals in well minerals are are reported to be present in cuttings from the Sinnipee Sinnipee Group. Areas of elevated values values occupy occupy northwestern Outagamie county and of significantly significantly elevated adjacent areas. areas. AAclearly clearly defined defined nickel nickel province that spatially corresponds to the arsenic polymetallic (As, Co, Mo, Mo, Ni, Ni, Th, Th, V) V) hydrogeocheniical hydrogeochemical province province exists exists province suggest that aa polymetallic in eastern Wisconsin Wisconsin and and may may relate relate to to documented documented faults faults (Mudrey (Mudrey and and Bradbury, Bradbury, 1992). 1992). The The geology differs from the better documented documented five-element five-element (Ni-Co-As-Ag-Bi) veins (Kissin, (Kissin, 1993) being carbonate hosted rather by being rather than than shale shale or or volcanic volcanic hosted, hosted, but bUf are are similar similar in in essential essential mineralogy and elements. elements. Economic concentrations of ofMississippi Mississippi Valley-type mineralization have not been found in Wisconsin Wisconsin outside of Grant, Iowa, and and Lafayette Lafayette Counties, Counties, but but geologic geologic logs logs of of16 16 mineral mineral in eastern eastern Wisconsin Wisconsin contain reports of ofminor minor 600 water water wells wells in exploration holes and more than 600 mineralization. In addition, more than 100 occurrences of sulfide mineral have been reported mineralization. In addition, more than 100 occurrences of sulfide mineral have been reported from outcrops and and quarries quarries throughout throughout southern southern and and eastern eastern Wisconsin Wisconsin (Brown and and Maass, 1992). AAfairly fairlycontinuous continuoushorizon horizonofofsulfide sulfidemineralization mineralizationhas hasbeen beenobserved observedininquarries quarries and and drill cores from Kenosha to Green Bay. Bay. Mineralization Mineralizationwithin within this this horizon horizon infills infills intergranular drill m below below the the base base of ofthe the middle-Ordovician middle-Ordovician Platteville and moldic porosity from 2 m above to 66 m Formation, cross-cutting the cross-cutting bedding bedding and and strata strata of ofvarying varying lithologies lithologies that immediately immediately underlie underlie the and Freiberg, Freiberg, in in press).] press).] Platteville Formation (Simo, Freiberg, and References: Brown, B.A., and Maass, R.S., 1992, 1992, AAreconnaissance reconnaissancesurvey surveyof ofwells wells in in eastern eastern Wisconsin Wisconsin for indications of of Mississippi Valley type mineralization: Wisconsin Geological and and Natural Natural History History p. Survey Open-file Report WOFR WOFR 1992-3, 1992-3,31 3 1 p. Brown, B.A., and possible source source and Maass, Maass, R.S., R.S., 1994, 1994, Mississippi Mississippi Valley-type Valley-type mineralization: mineralization: A possible 38 �of heavy metal anomalies in the Paleozoic carbonate carbonate aquifers aquifers of ofWisconsin Wisconsin (abs.): (abs.): American American Water Resources Association Wisconsin Wisconsin Section Section Meeting, Meeting, 18th (Wisconsin (Wisconsin DeUs), Dells), paper 37. Kissin, S.A., 1993, Five-element Five-element (Ni-Co-As-Ag-Bi) (Ni-Co-As-Ag-Bi) Veins:· Veins: in in P.A. P.A. Sheahan Sheahan and andM.E. ME. Cherry, Kissin, S.A., v. 6, 6, p. Ore Deposit Models, Volume II, Geoscience Canada Reprint Series, Series, v. p. 87-98. Mudrey, M.G., Jr., and Bradbury, K.R., 1992, NIJRE hydrogeochemical Mudrey, 1992, Evaluation Evaluation of ofNURE hydrogeochemical data for use in Wisconsin Wisconsin groundwater studies: Wisconsin Geological and and Natural History Survey Openfile Report WOFR 93-2, 61 file 61 p., p., 1 computer computer diskette. Mudrey, M.G., Jr., Bradbury, Mudrey, M.G., Bradbury, K.R., K.R., and and Kammerer, Kammerer, P., P., 1992, 1992, Progress Progress towards towards rapid rapid retrieval retrieval of of Wisconsin's NURE dataset (abs.): American Water Resources hydrogeochemical data from Wisconsin's Association Wisconsin Wisconsin Section Section Meeting, Meeting, 16th 16th (La (La Crosse), Crosse), paper paper 26. 26. Simo, in press, press, Geologic Geologic constraints constraints on on arsenic arsenic in in Simo, lA., J.A., Freiberg, P.G., and Feiberg, K.S., in groundwater with with applications applications to to groundwater groundwatermodeling: modeling: University University of ofWisconsin Wisconsin Water groundwater Resources Center. 39 �______________________________________ Group Near Taylors Taylors Falls Falls and and From Metamorphism of of Chengwatana Volcanic Volcanic Group Osseo Core NAIMAN, Zachary and WIRTH, WIRTH,Karl Karl R., R., Geology Geology Department, Department, Macalester Macalester College, St. Paul, Minnesota 55105, 55105, znaiman@maca1str.edu znaiman@macalstr.edu and G.B. and wirth@macalstr.edu; wirth@macalstr.edu; and and MOREY, G.B. and MILLER, James, D., D., Minnesota Minnesota Geological Geological Survey, Survey, 2642 University University Ave., Ave., St. MILLER, James, St. Paul, Paul, Minnesota 55114, 55114, moreyO0 morey001@maroon.tc.umn.edu 1 @ maroon.tc.umn.eduand andmille066@maroon.tc.umn.edu mille066@maroon.tc.umn.edu The southernmost exposed flows flows from from the the 1100 1100 Ma Ma Midcontinent Midcontinent rift rift of of North North America America comprise comprise the Chengwatana Volcanic Group, aa sequence sequence of more Volcanic Group, more than seventy mafic flows exposed in in the the Taylors Falls-Interstate State Park region (>2800 meters Taylors meters thick) thick) on on the the Minnesota-Wisconsin Minnesota-Wisconsin borborder. A A core at at Osseo Osseo (63 (63 km SW of the exposures) sampled 980 meters of more than fifty der. fifty flows flows of Chengwatana Chengwatana basalt basalt 230 230 meters below the surface. Flows Flows in both sequences are typically interlayered with sedimentary of the the North North sedimentary breccia. breccia. Stratigraphic Stratigraphic correlation correlation with other volcanic volcanic sequences sequences of Shore region of of the the rift rift are are complicated complicated by by faulting. faulting. Volcanic (plagioVolcanic flows flows from from both both regions regions have have similar similar primary primary igneous mineral assemblages (p!agioFe-Ti oxides) and and display aa variety of igneous textures (ophitic, (ophitic, sub-ophitic, sub-ophitic, clase + clinopyroxene clinopyroxene ++ Fe-Ti ophimottled, intergranular, textures indicate indicate a ophimottled, intergranular,intersertal, intersertal,plagioclase plagioclasephyric, phyric,and andseriate). senate). The The textures sequence of plag -> cpx -> oxides typical crystallization sequence Single flows flows comtypical of of tholeiitic tholeiitic basalt. basalt. Single ophitic texture texture isis more monly exhibit more than one texture; ophitic more common common in in flow flow interiors interiors where where the the cpx presumably presumably had sufficient sufficient time time to to crystallize crystallize during during slow slow cooling cooling whereas whereas intersertal intersertal and and textures are more common at at flow flow tops tops where where more more rapid rapid cooling cooling prevented prevented the the forforophimottled textures Osseoflows flows have have aa higher higher proportion proportion of ofophitic ophitic texture texture and and on on averavermation of large cpx crystals. Osseo age are coarser coarser grained grained than than Taylors Taylors Falls Falls flows. flows. The metamorphic environment of the Chengwatana volcanics volcanics is is best modelled by the CaOMgO-A1203-Fe203-Si02-H20-C02 (CMAFSH-CO (CMAFSH-C02) basaltic system determined by by Liou Liou et et al. al. ) basaltic system detennined MgO-AI203-FeZ03-SiOTHZO-COZ z (1985) and Cho and Liou (1987). The (1985) and Cho and Liou (1987). equilibrium metamorphic mineral assemFigure 11 pumpellyite - actinolite blage of the top top 670 670 meters meters of of the the Osseo Osseo facies core consists of of calcite ++ epidote ++ chlocWoOsseo -- upper flows • rite + quartz + albite rite albite + + oxides oxides ± ± white white .~ Osseo Osseo - lower flows ,L:.....J Taylors Falls Towardthe the bottom bottomof ofthe the drill drill core, core, mica. Toward the occurrence occurrence of calcite is is limited limited to to the prehnite - pumpellyite veins and amygdules amygdules whereas whereas actinolite actinolite facies becomes prominent in the the groundmass. groundmass. t These assemblages, defined by the reac- ~ greenschist tioncal+chl+qtz=ep+act+H20+ tion cal + chI + qtz = ep + act + H20 + Q: facies C02, COz, are are consistent consistent with with the the transition transition from calcite-chloritefacies calcite-chlorite facies to greenschist greenschist calcite- I ÷ facies (Fig. (Fig. 1). 1). The entire section section at The entire chlorite /ShiftoffieldbounShift of field boun;f daries as a function Taylors Falls displays the mineral assemJ>of Xco2 Xc02 blage: blage: actinolite actinolite + epidote + chlorite chlorite + Shift of invariant quartz ++ albite ++ oxides oxides ± ± white white mica. mica. ShftofI.nanant points with The stability region of the calciteincreasing Fe+ increasing Fe33 chlorite facies in PIT is constrained constrained chloritefacies prr space is Temperature by amounts of CO2 CO 2 and by the amounts and Fe+ Fet33 in the E 40 �________________________________________ 0.8 , . . - - - - - - - - - - - - - - - - . , Chengwatana Volcanic Volcanic Group Figure 2 Actinolite Analyses system (Fig. (Fig. 1). Currently Currently there there are are no no geothermometers which which can can be applied to geothermometers this system. system. However, this However, the the Na-content Na-content of o0 Osseo Core the M4-site (NaM4) of actinolite in the pres06 CJ 0.6 Tailors Falls •I Taylors Falls ence of chlorite, chlorite, epidote, epidote, and and quartz quartz is aa ence 'til ~ useful geobarometer (Brown, 1977). 1977). SEMSEMusefulgeobarometer(Brown, ~ 5 kb analyses of actinolite in the Osseo core analyses of actinolite in the Osseo core EDS ....Q contain less NaM4 than actinolite from the C 0.4 CJ Taylors Falls region Taylors Falls region suggesting suggesting that the the = Q 4kb Osseo flows Osseo flows were were metamorphosed metamorphosed at at <.I eo: slightly lower pressure (Fig. 2). Z 0.2 The temperature temperature conditions during during kb metamorphism of the Chengwatana flows 2 kb o Taylors Falls Falls are are constrained constrained by the presat Taylors ence of actinolite ence actinolite and epidote (Fig. (Fig. 1), 1), by 00.0 0 the absence of co-existing prehnite and absence co-existing prehnite and the 0.0 0.2 0.4 0.6 0.8 pumpellyite, and by the lack of hornblende Al content of tetrahedral site coexisting with epidote, chlorite, actinolite, Epidote,rather ratherthan thanclinozoisite, clinozoisite, isis present present in in the the Chengwatana Chengwatana flows flows due due to to the the highhighand quartz. Epidote, iron protolith. At Ata apressure pressureof of2.5 ::::::2.S kbar,thetheequilibrium equilibriummineral mineralassemblages assemblages iron content content of of the th protolith. kbar, of 325 325 -- 37SoC. indicate metamorphic temperatures temperatures of 375°C. Assuming a peak metamorphic temperature of 350°C and burial depth of 7.5 3S0°C 7.S km, km, the the metamorphic metamorphic data data from from the the Chengwatana Chengwatana flows flows imply imply aa geothermal gradient of approximately this portion geothermal approximately 45-50°C/km 4S-S0°C/km within this pbrtion of the the midcontinent midcontinent rift. rift. results have have have determined elsewhere elsewhere in in the the midcontinent midcontinent rift rift and and in in the the Kenya Kenya Rift Rift of Similar results have determined east Africa. facies in in the the Osseo core, the ubiquitous presThe change from calcite-chlorite to greenschist greenschistfacies greenschistfacies ininthe ence of greenschistfacies the Taylors Taylors Falls Falls exposures, exposures, and and the the lower NaM4 content of of actinolite sampled by by the the Osseo Osseo drill drill core core were in the Osseo core imply imply that the the Chengwatana Chengwatana flows flows sampled were not Taylors Falls. Falls. IfIf the buried as deeply as the flows exposed at Taylors the flow flow sequences sequences in in these these two two regions regions are part of the same volcanic plateau-segment plateau-segment of of the the midcontinent midcontinent rift, rift, and and ifif the the these these regions regions are are not separated with large offsets, the the flows flows sampled sampled in in the the Osseo Osseo core core might might be not separated by structures structures with large offsets, of the the Taylors Taylors Falls Falls region. region, stratigraphically younger than than those those of - - References Cited Brown, E.H., 1977, to pressure of metamorphism: metamorphism: Journal of Petrol1977, The crossite content of Ca-amphibole as a guide to ogy, v. 18, 18, P. p. 53-72. Cho, M. and Liou, J. G., 1897, to greenschist greenschist facies facies transition transition in in the the Karmutsen Karmutsen metabasites, metabasites, 1897, Prehnite-pumpellyite Prehnite-pumpellyite to Cho, Vancouver Island, B.C.: B.C.: Journal Journal of ofPetrology, Petrology, v.v. 28 28 p. 417-443 Green, lC., 1983, 1983, Geologic Geologic and and geochemical geochemical evidence for for the the nawre nature and and development development of of the the Middle Middle Proterozoic Proterozoic Green, J.C., 94, p.p.413-437. 413-437. (Keweenawan) Midcontinent Rift Rift of North North America: America:Tectonophysics, Tectonophysics,v.v.94, of volcanic volcanic and and volcaniclastic volcaniclastic rocksrocksLiou, J.G., Maruyama, S., S., and and Cho, Cho, M., M., 1987, 1987. Very Very low-grade low-grade metamorphism metamorphism of and mineral mineral facies: facies: in in Frey, M., ed., Low Temperature mineral assemblages and Temperature Metamorphism, Metamorphism, Glasgow, Blackie, p.59-113. p. 59-113. G. R., R., Brew, D.A., and Ford, A.B., 1995, Low-grade, M1 M 1 metamorphism of of the Douglas Douglas Island Island Volcanics, Volcanics, Himmelberg, G. western metamorphic H.W., editors, Low-Grade Low-Grade MetamorP. and Day, H. W., editors, metamorphic belt belt near near Juneau, Juneau. Alaska: Alaska: in in Schiffman, Schiffman, P. of Mafic Rocks, Rocks, Geological Geological Society Society of ofAmerica America Special Special Paper Paper296, 296, p. 51-66. phism of 41 �A CONTINUUM OF STRESS-STRAIN STRESS-STRAIN FIELDS FIELDS (2.0-1.0 (2.0-1.0 Ga) CONTINUUM OF Ga) ALONG THE MARGIN OF OF THE THE KEWEENAW KEWEENAW PROVINCE, NORTHERN MARGIN PROVINCE, ONTARIO, CANADA NEILSON, NEILSON, Kim, STENDAHL, STENDAHL, Rebekah, KROPF, KROPF, Elizabeth and and CRADDOCK, CRADDOCK, John P., Geology Dept., Macalester College, St. Paul, MN 55105, 55105, Craddock@Macalstr.edu evolution of of the the Keweenaw Keweenaw rift rift (1.1 (1.1 Ga) Ga) is well constrained for for much much The The structural evolution of the exposed southern arm, arm, and and involved involved early early extensional extensional faulting faulting and and magmatic magmatic activity, followed by by closure closure of of the the rift rift along along the the same same boundary boundary faults faults by thrust activity, followed (e.g., Douglas Douglas and andKeweenaw-Lake Keweenaw-LakeOwen Owenthrusts) thrusts)at at -1.06 Ga (Bornhorst et et motion (e.g., -—1.06 al., 1987; Cannon, 1994). 1994).This Thisstructural structural scenario scenario isis complimented complimented by studies of 1987; Cannon, of the the mechanical preserved in in calcites calcites (amygdules, (amygdules, veins, veins, cements, cements, mechanical twinning strains preserved clastic dikes, dikes, and overlying overlying Paleozoic Paleozoic limestones) region cements in clastic cements limestones) throughout the region rift, followed followed by which record syn-rifting subhorizontal subhorizontal shortening parallel to the rift, rift-normal subhorizontal closure of the rift rift (Craddock (Craddock rift-normal subhorizontal shortening shortening related related to to thrust closure et al., in press). The other portions of the Keweenaw rift-triple junction are press). The other portions of the Keweenaw rift-triple unexposed (gravity, (gravity, magnetic anomaly) beneath the Michigan Michigan basin or poorly poorly constrained north of Lake Superior. of Lake Superior. In this study study we we have have characterized characterized the the structural structural relations relations of of calcite calcite twinning twinning patterns to to the the "failed "failed third arm" arm" portion of the rift system between the Kapuskasing suture, the the Coidwell Coldwell alkali alkali complex complex and the the Nipigon Nipigon Embayment Embayment over the the interval interval -2.0-1.0 Ga. regional —2.0-1.0 Ga.Our Ourresults results(Table, (Table,Figs. Figs.1-3) 1-3)suggest suggestthat thatthe the orientation orientation of the regional compressive stress (or shortening strain) strain) field was subhorizontal and N-S field was N-S prior to to compressive stress rifting, subhorizontal and rift-parallel rifting, rift-parallel during rifting, and subhorizontal subhorizontal and and riftriftnormal as the rift rift closed closed by thrusting. Sample 11 2 3 4 55 6 7 8 9 10 11 12 13 13 14 15 16 16 17 18 18 19 20 21 22 23 24 25 26 e1(%) el(%) pI) e1(tr el(tr && p1) -7.7 -3.5 -5.5 -2.1 -4.5 -5.9 -9.8 -3.4 -3.3 -0.2 -0.8 -0.7 -2.4 -1.6 -1.2 -6.7 -1.9 -0,4 -0.4 -0.2 -0.2 -0.2 -0.6 -2.9 -4.9 -0.4 -0.4 -4.9 340°,0° 0° 340°, 170°, 8° 8° 170°, 5° 5° 16°, 5° 5° 164°, 0° 0° 50°, 0° 41 0, 0° 41°, 52°, 0° 55°, 0° 20,0 20, 0 3550, 20° 355°, 76°, 76°, 8° 56°, 56°, 17° 150°, 0° 150°, 171°, 0° 171°,0° 162°, 0° 0° 165°, 0° 0° 165°, 170°, 00 0° 170°, 0° 0° 0° 168°, 0° 270°, 5° 270°, 160°,7° 253°, 00 0° 170°, 5° 5° 355°, 12° 12° 300°, 7° 7° NEVs (%) (%) 16 a 0a 0 21 12 30 28 37 0 47 28 5 0 26 30 14 13 33 0 8 7 100 100 0 20 30 16 42 -Age (Ga) Calcite e —Age (Ga) Calcite type Dikemarginvein Dike margin vein Dike Margin vein Dike Sibley Limestone Sibley Limestone Limestone Basalt amygdule amygdule Basalt Basalt amygdule amygdule Basalt Basalt amygdule Basalt amygdule Basalt amygdule amygdule Basalt Vein Vein Vein Carbonatite Vein Vein Vein Vein-amygdu.le Vein-amygdwe Veth-amygdule Vein-amygdwe Vein Vein Vein Carbonatite Vein Vein Vein Lamprophyre 2.0 2.0 1.54 1.54 1.54 —2.0 -2.0 1.1 1.1 1.1 1.1 -1.1 —1.1 —1.1 -1.1 -1.1 —1.1 -1.1 —1.1 <1.06 <1.06 <1.06 <1.06 <1.06 <1.06 <1.06 <1.06 -1.1 —1.1 <1.06 <1.06 <1.06 <1.06 �Kenora-Kabetogama and Sibley Group (2.0-1.5 Ga) Gal Group (2.0-1.5 Figures 1-3: 1-3: Regional Regional summary summary calcite twinning data plots of calcite (see (see Table) Table) for for time time increments between—2.0-1.0 -2.0-1.0 Ga. between Ga. Solid, Solid, bold lines are are calcite calcite shortening shortening lines strain axes, with sample number number (see Table). Table). RegionaF compressive (see Regional compressive strain (E) (E) stress(cr) stress(o) or shortening shortening strain fields are inferred from these data fields are for each each time period. Lake for Lake Superior is used as a reference, is reference, with no attempt being made to include plate or fault fault boundaries boundaries that that plate or active during during the were active billion years years of of Earth Earth history billion involved. \ Wiscon5in Portage Lake Volcanics-Osler Group (1.1 Gal Ontario Late Keweenawan Keweenawan (<1.06 «1.06 Ga) Gal o "o_ColdweU~ .), .. Ontario Complex ~24 References Bornhorst, P.J., P.J., Paces, N.K., 1987, Paces, J.B., J.B.,Grant, Grant, N.K., N.K.,Obradovich, Obradovich, J.D., J.D.,and and Huber, Huber, N.K., 1987,Age Ageof ofnative native copper copper mineralization, mineralization, Peninsula,Michigan: Michigan:Economic EconomicGeology, Geology, v. Keweenaw Peninsula, v. 83, 83, p. 619-625. Cannon, W.F., W.F., 1994, 1994, Closing of the Midcontinent Midcontinent rift: rift: aa far-field far-field effect effect of Grenvillian Grenvilliancompression: compression:Geology Geology22, 22,p.p.153153Cannon, 38. A., McGovern, McGovern, M., M., Kropf, Kropf, E.P., E.P., Moshoian, Donnelly, K., K., in press, Post-extension Craddock, J.P., J.P., Pearson, A., Craddock, Moshoian, A., A., and and Donnelly, shortening strainspreserved preservedinincalcites calcitesofofthe theKeweeriawan Keweenawanrift: rift:Geological GeologicalSociety Society of of America America shortening strains Special Paper Paper 312. 312. 43 �CYCLIC TIDAL LAMINATIONS IN THE EARLY PROTEROZOIC POKEGAMA EARLY PROTEROZOIC FORMATION: DIGITAL IMAGE ANALYSIS AND COMPUTER MODELING OJAKANGAS, W., Department of of Geology, Geology, University University of of OJAKANGAS, Gregory W., Minnesota, 10 University University Dr., Dr., Duluth, Duluth, MN MN 55812, 55812, Minnesota, 10 gojakang@d.umn.edu Evidence of the diurnal inequality inequality operating operating in in Early Early Proterozoic Proterozoic time is apparently recorded in in aa sequence sequence of of alternating alternating thicker thicker time is and thinner clastic silt laminae laminae identified identified in in the the lower lower member member of Formation of of northern northern Minnesota. Minnesota. The sequence sequence of of of the Pokegama Formation apparently semidiurnal semidiurnal laxninae laminae is lens-shaped is present present in aa silty lens-shaped the argillaceous member, member, interpreted interpreted to to be be aa small small arm arm of of bed of the aa tidal the shore shore of of the the transgressive transgressive sea sea that that tidal channel system on the occupied the ancient Animikie Animikie basin. basin. The sequence consists of of approximately 60 60 thin (0.1 (0.1 -- 1mm) silty laminae which tend to to in thickness, thickness, separated separated by by thin thin mica-rich mica-rich layers layers that that alternate in exhibit a similar tendency. a tendency. Such thick-thin thick-thin patterns are are expected to be generated by sediment transport transport in in semidiurnal semidiurnal tidal environments, environments, due to the alternating magnitudes of tidal of successive tidal velocity peaks in in such such environments environments (i.e., (i.e., due to the tidal inequality). to inequality). Thus, they may be used to to support Thus, they tidal environments of of deposition deposition (cf. (cf. de de Boer Boer et et al., al., proposed tidal 1989), here strongly strongly supports supports the the 1989), and the sequence described here conclusion of Ojakangas (1983) (1983) that that the the Pokegama Pokegama Formation is is of tidal origin. that the the depositional depositional site site was tidal origin. It also suggests that probably non-equatorial in in the the Early Early Proterozoic. Proterozoic. Hand specimens specimens of the rhythmic sequence described above and other specimens sequence described above and other specimens from the the lower lower member member of of the the formation formation displaying periodicities from slabbed, coated with oil oil to to enhance enhance detail, detail, and and have been slabbed, photographed. The resulting images were then then digitized and are currently under analysis using using image-processing image-processing techniques. techniques. In order to better understand the the potential for for extraction the ancient lunar lunar orbit orbit from from rhythmic rhythmic tidal tidal of information on the sedimentary sequences such as the one described here, here, a computer model has been created (Ojakangas model (Ojakangas et et al.,1995) al.,1995) which which generates generates synthetic tidal tidal rhythinites rhythmites from from first first principles, principles, given arbitrary the earth and and moon, moon, and and the latitude and orbital elements of the longitude of a a hypothetical location location on on the the earth. earth. Assuming in the the open open ocean, ocean, tidal tidal currents currents are are equilibrium tide heights in generated in a hypothetical tidal tidal channel channel linking linking the the ocean ocean to to aa tidal basin. The current in in the the channel, channel, driven driven by the the difference in water surface elevation elevation between between the the basin basin and and the the open ocean, uniform turbulent turbulent flow flow according ocean, is computed assuming uniform (cf. Dingman,1984), Dingman, 1984) , and and this this flow flow is is assumed to Chezy's equation (cf. transport capacity capacity as described by Yang to carry sediment at peak transport and Stall (1976). (1976). Both mud and and silt, silt, transported transported in in suspension, suspension, are deposited when the current speed speed drops drops below below respective respective 44 44 �critical values. values. The vertical vertical eddy diffusion diffusion time time is is assumed assumed critical short relative to the the tidal tidal cycle, cycle, so so deposition is is w "instantaneous". ninstantaneous synthetic • The program successfully produces synthetic that closely closely resemble resemble those those of of known known rhythmite sequences that rhythmites, such as those of the Late Proterozoic Elatina rhythmites, Formation described by Williams (1991), (1991) ~ Because the the tides tides are are analytically generated, generated, the the significance significance of peaks in in the the power power spectrum of the synthetic rhythmites rhythmites can be understood. understood. The The conditions under which predetermined lunar lunar orbital parameters can can be retrieved from from the the corresponding corresponding synthetic synthetic rhythmites rhythmites are are under investigation with this this model, model, as is is the probable appearance and spectral content of very ancient rhythmites, rhyt~ites, as as yet undiscovered. undiscovered. With this this model as a tool, tool, lamina sequences sequences Formation including including the the one one described described above are from the Pokegazna Pokegama Formation under analysis for for possible clues to to the the ancient lunar lunar orbit. orbit. References; Reerencep: de Boer, Boer, P.L., P.L., Oost, Oost, A.P., A.P., and Visser, M.J., M.J., 1989, 1989, The diurnal inequality of a parameter for for recognizing tidal of the tide as as a influences. J. J. Sed. Sed. Petrology, Petrology, V. V. 59, 59, p. p. 912-921. 912-921. Dingman, Dingman, SS.L., 1984, Fluvial Hydrology, L., 1984, Hydrology, W. W. H. H. Freeman and Company, p. 112-113. Company, 112-113. Ojakangas, Ojakangas, G.W., G.W., Tan, Tan, H., H., and and Sickler, Sickler, B., B., 1995, 1995, TidaL TidaL rhytbmites rhythmites and the ancient lunar lunar orbit: orbit: Improved Improved understanding through through aa synthetic model (abs): (abs): Bull. Bull. Am. Am. Astron. Astron. Soc., Soc., Proceedings proceedings of the 27th Annual meeting of the the Division for for Planetary Planetary Sciences, p. p. 57. 57. Ojakangas, R.W., Ojakangas, R.W., 1983, 1983, Tidal deposits in the early Proterozoic Proterozoic basin of the Lake Superior region region -- The Palms and the the Pokegarna Formations: Evidence Evidence for for subtidal-shelf subtidal-sheif deposition Pokegama Formations: of Superior-type Superior-type banded banded iron-formation: iron-formation: in in Medaris, Medaris, L.G. L.G. Jr., ed., Jr., ed., Early Proterozoic Proterozoic Geology of the Lake Superior Region: Geological Society Society of of America America Memoir Memoir 160, 160, p. p. 49-66. 49-66. Williams, G.E., 1991, 1991, Upper Upper Proterozoic Proterozoic tidal tidal rhytbmites, rhythmites, South South Williams, G.E., Australia: Australia: Sedimentary Sedimentary features, features, deposition, deposition, and and implications for the the earth's earth's paleorotation: paleorotation: in in Smith, Smith, D.G., D.G., Reison, Zaitlin, B.A., B.A., and R.A. R.A. Rabmani, Rahmani, eds., eds., Clastic Reison, G.E., G.E., Zaitlin, Tidal Sedimentology: Sedimentology: Canadian Society of Petroleum Geologists Memoir Memoir 16, 16, p. p. 161-178. 161-178. Yang, C.T. C.T. and Stall, Stall, J.B., J.B., 1976, 1976, Applicability Applicability of of unit unit stream stream Yang, equation, American American Society Society of of Civil Engineers Engineers power equation, Proceedings, Proceedings, Journal of the the Hydraulics Division, Division, V. V. 102 102 (HY(HY. 5), 5), 559—568. p. 559-568. 45 45 �TIDALITES OF EARLY PROTEROZOIC AGE AGE IN IN THE THE WESTERN WESTERN LAKE LAKE SUPERIOR SUPERIOR REGION: REGION: MINNESOTA, WISCONSIN AND MICHIGAN OJAKANGAS, RICHARD Geology, University of OJAKANGAS, RICHARD W., W., Department Department of of Geology, Minnesota, Duluth, MN 55812, 55812, rojakang@d.umn.edu rojakang@d.umn.edu Minnesota, Duluth, The Palms of the Gogebic The Palms Formation Formation of Gogebic Range Range of Michigan Michigan and and the the lithologically correlative correlative Pokegama PokegamaFormation Formationofof the the Mesabi lithologically Mesabi Range Range of Minnesota, deposited upon upon Archean Archean basement basement and and both both underlying underlying Minnesota, both both deposited major iron-formations, major iron-formations, are terrigenous clastic clastic units interpreted to be are terrigenous tidal deposits of aa tidal deposits formed formed on on the the east-west-trending east-west-trending shoreline shoreline of northward-transgressing Early Early Proterozoic Proterozoic sea (Ojakangas, northward-transgressing (Ojakangas, 1983). 1983). The above four four formations formations were were either either deposited depositedon on aa stable stable shelf shelf prior above prior to the the the peripheral peripheral bulge bulge development of foreland basin, basin, or were were deposited deposited on the development of aa foreland of aa foreland foreland basin basin developing developing to north of aa major major fold fold and and thrust thrust belt belt of to the the north caused by by the caused the collision collision of of the the Wisconsin Wisconsin Magmatic Magmatic Terrane Terrane with with the the In either either model, model, itit can can be be assumed assumed that that the the terrigenous terrigenous continent. In clastics and the the iron-formations iron-formations form form continuous, continuous, but but diachronous, diachronous, clastics and sheetlike deposits deposits across across the sheetlike the basin. basin. The well-exposed 150 m m thick has a minor The well-exposed 150 thick Palms Palms Formation Formation has minor basal basal largely comprised comprised of of three conglomerate, but is largely conglomerate, three major major gradational gradational facies facies which are which are as as follows: follows: 1. A thin-bedded thin-bedded argillaceous argillaceous facies facies (lower (lower member), 2. 2. AA dominant dominantargillite-siltstone-sandstone argillite-siltstone-sandstone facies facies (middle (middle member) thin-bedded intercalated intercalated lithologies sandstone facies facies member) of of thin-bedded lithologies and and 3. 3. aa sandstone (upper member) of thick (upper member) of thick beds beds of of parallel parallel and andplanar planarcross-stratified cross-stratified The sandstones. The middle middle member member includes includes lenticular, lenticular, wavy, wavy, flaser flaser and and parallel bedding A total parallel bedding and and minor minor mudcracks. mudcracks. A total of of 250 250 paleocurrent paleocurrent measurements, mostly including sole sole marks, marks, measurements, mostly cross-bedding cross-bedding but but including asymmetrical ripples, trough axes, axes, yields yields an an overall overall bimodal-bipolar bimodal-bipolar asymmetrical ripples, and and trough distribution. The modes are are roughly roughly parallel parallel to The modes to the the inferred inferred shoreline. shoreline. The poorly Formation,as as thick thick as as 50 The poorly exposed exposed Pokegama Pokegama Formation, 50 m, m, contains contains the same the same sequence sequence of sedimentary sedimentary facies facies as as does does the the Palms. Palms. A few few dozen dozen scattered paleocurrent indicators polymodal paleocurrent paleocurrent plot, plot, but scattered paleocurrent indicators form form aa polymodal detailed work work on on one one long long roadcut roadcut yielded yielded 57 57paleocurrent paleocurrent indicators, indicators, detailed mostly paralleling paralleling the presumed shoreline an embayment, embayment, but but with with oneonemostly the presumed shoreline of of an fifth of of them them normal normal to to the the shoreline. shoreline. By the By the application application of Walther's Walther's Law, Law, the the lateral lateral relationships relationships can can be be 46 �interpreted. The conglomerate facies locally present present on on the the lowlowThe conglomerate facies was was locally lying peneplaned surface transgression of the sea. sea. The The argillite argillite lying peneplaned surface prior prior to to transgression of the facies facies was was the the most most proximal proximal marine marine facies facies (i.e., upper tidal flat)' upper tidal flat) resting upon conglomerate or basement upon conglomerate or basement Archean Archean rocks. rocks. Seaward the upper upper tidal tidal Seaward of of the flat was was the the middle middle tidal flat (argillite-siltstone-sandstone and (argillite-siltstone-sandstone facies) fades) and still further further seaward seaward was the lower lower tidal tidal flat or subtidal environment environment was the or subtidal (sandstone facies). (sandstone facies). As As the sandstone sandstone fades facies is is gradational gradational with with the the overlying iron-formation, overlying iron-formation, this places the the site site of the formation formation of of iron this places of the minerals on the shelf, shelf, seaward seaward of of the theterrigenous terrigenous clastics. clastics. minerals on the Ignoring basal conglomerates, conglomerates, which which likely likely have have aanOn-tidal non-tidal Ignoring the the basal origin, the Palms and the Pokegama are coarsening-upward sequences origin, the Palms and the Pokegama are coarsening-upward sequences which are which are interpreted products of aamarine marine transgression. transgression. Such interpreted as as products Such aa model has been described by Reineck (1972) and Yeo and Risk (1981). model has been described Reineck (1972) and Yeo and Risk (1981). Dutch tidal Dutch tidal flats flats provide provide aamodern modern analogy analogy (De (DeJong,1977). Jong,1977). Consistent with with aa tidal Consistent tidal environment environment is the the textural textural and and mineralogic mineralogic maturity the sands sands (Swett (Swett et al., a!., 1971; 1971; Balazs Balazs and and Klein, Klein, 1972). 1972). maturity of of the Rounding best in in the the sandstone sandstone facies facies where where the the energy energy was was Rounding and and sorting sorting is is best first-cycle quartz quartz sand sand eroded highest. However, However, first-cycle eroded off off of of the the vegetationvegetationfree, weathered and and wind-swept wind-swept adjacent adjacent peneplain peneplain may may have have already already been been free, weathered we 11- rou nded. well-rounded. REFERENCES Balazs, Klein, G. G. deV., deV., 1972, 1972,Roundness-mineralogical Roundness-mineralogical relations relations Balazs, R. R. J., and and Klein, v. 42, 42, p. p. 425-433. 425-433. of some some intertidal intertidal sands: sands: Jour. Jour. of Sed. Sed. Pet., Pet., v. DeJong, Sedimentary Geo!., Geol., v. 18, p. Dejong, J.D., 1977, Dutch Dutch tidal flats: flats: Sedimentary v. 18, p. 13-23. 13-23. J.D., 1977, Ojakangas, the early early Proterozoic Proterozoic basin basin of the the Ojakangas, R.W., R.W., 1983, 1983, Tidal Tidal deposits deposits in in the Lake Superior region--The region--The Palms Palms and and the the Pokegama Pokegama Formations: Formations: Lake Superior Evidence subtidal-shelf deposition deposition of of Superior-type Superior-type banded banded ironironEvidence for for subtidal-sheif Medaris, L.G. L.G. Jr., Jr., ed., formation: in Medaris, formation: ed., Early Early Proterozoic Proterozoic Geology Geology of of the the Geol. Soc. Lake Region: Geol. Soc. of America America Memoir Memoir 160, 160, p. p. 49-66. 49-66. Lake Superior Region: and Hamblin, Hamblin, W.K., eds., eds., Reineck, Rigby, J.K., J.K., and Reineck, H.E., H.E., 1972, 1972, Tidal Tidal flats: flats: in Rigby, Recognition of of Ancient Ancient Sedimentary Sedimentary Environments, Environments, Soc. Soc. of of Econ. Econ. Recognition 146-159. Paleont. and Mineralogists Mineralogists Special Special Publication Publication 16, 16, p. Paleont. and p. 146-159. Swett, Keene, Keene, Klein, deV., and and Smit, Smit, D.E., D.E., 1971, 1971, AA Cambrian Cambrian tidal tidal sand sand Swett, Klein, G. G. deV., An ancientancientbody--the Eriboll Sandstone Sandstone of of Northwest Northwest Scotland: Scotland: An body--the Eriboll recent analog: Journal Journal of Geology, Geology, v. 79, 79, p. p. 400-415. 400-415. recent analog: R.K. and and Risk, Risk, M.J., M.J., 1981, 1981, The Thesedimentology, sedimentology, stratigraphy stratigraphy abd abd Yeo, R.K. Yeo, intertidal deposits deposits in in the preservation the Minas Minas Basin Basin System, System, Bay Bay preservation of intertidal v. 51, 51, p. p. 245-260. 245-260. of Fundy: Fundy: Jour. Sed. Pet., Pet., v. Jour. of Sed. 47 �Targeting Footwall Copper-PGE Deposits in the Duluth Duluth Complex Complex Based Based on Sudbury Sudbury Mining Mining Camp Camp Analogs Analogs Dean M. M. Peterson, Peterson, University University of of Minnesota -- Duluth Dean workers have have studied studiedthe thegenesis genesisof ofthe the footwall footwall Cu-PGE Cu-PGE mineralization in Numerous workers the Sudbury Mining Camp. Camp. The TheCu-PGE Cu-PGE deposits deposits are are characterized characterized by by massive massive chalcopyrite veins, pods, and stringers halos. The stringers with with little little (if (if any) alteration halos. The deposits deposits are are spatially spatially hundredsof of meters meters into into the the footwall footwall associated with contact Ni-Cu ore deposits and extend hundreds Veingrades gradesofof30% 30% Cu, Cu, 3% 3% Ni, and 0.30 0.30 oz/st precious metals metals rocks beneath these deposits. Vein oz/st precious (Au, Ag, Ag, Pt, Pt, Pd) Pd) are are typical. typical. The most fundamental geologic process process associated associated with the Sudbury Mining Mining Camp Camp is is the the migration migration of of the the ore ore metals metals from from the the footwall deposits of the Sudbury Naldrettetetal. al.(1982) (1982) suggested that that Sudbury Igneous Complex into the footwall environment. Naldrett the fractional fractional crystallization crystallization of the sulfide liquid responsible for for the the the ores are attributable to the formation of the contact Ni-Cu Ni-Cu deposits. deposits. The The footwall footwall ores are believed to have formed by migration of the the fractionated, fractionated, copper-rich copper-rich residual liquid away from from the early crystallizing crystallizing monosuiphide into and along along footwall footwall structural structural zones. zones. Subsequent monosulphide solid solution (mss), into geological studies have refined this this early ore ore deposit deposit model. model. The targeting of mineralization beneath the Duluth Complex must first be based on the fundamental geologic geologic process process (migration (migration of of fractionated metals metals into into the the footwall) footwall) associated associated fundamental The diagnostic diagnostic criterion criterion that that indicates indicates copper migration is the spatial with deposit formation. The variation of Cu-Ni Cu-Ni grades and the lowering of the the Cu/Ni Cu/Ni ratio ratio in the the source rock. rock. An approach is being being developed developed to generate Cu-PGE exploration target areas in is in the the footwall footwall rocks rocks beneath Determination of of copper copper depletion depletion in in mineralized mineralized basal basal troctolites troctolites of of the the Duluth Complex. Determination Duluth Complex is the first step in the generation generation of of footwall exploration targets. The likelihood footwall Cu-PGE Cu-PGEmineralization mineralization beneath beneath the the Duluth Complex is is being being modeled modeled from from of footwall visualizing visualizing the the three-dimensional three-dimensional distribution of of Cu-Ni Cu-Ni in inthe the Duluth Diluth Complex. Complex. The The distribution of Cu-Ni in the Duluth Complex has been determined from a comprehensive compilation of hole chemistry database (Cu, of all all available availabledrill drillhole holechemistry. chemistry. To To date, date, the the drill drillhole S. Au, Au, Ag, Ag, Pt, Pt, Pd, Rh, Ir, as, Os, V, V, Cr, Cr, and and Co) Co) includes 61,560 assays (249,629 (249,629individual individual 61,560 assays Ni, 5, analyses) analyses) from from 1435 1435drill drill holes holes (Table (Table2). 2).Individual Individual analyses analyses are are located located in in three-dimensions three-dimensions (UTM east, east, UlM UTMnorth, north, elevation/ elevation/feet (UlM feet above above basal basal contact) contact) from collar information information and and basal basal 95% of of all drill hole assays are currently in the database. contact piercing points. Approximately Approximately95% Total assays assays for for the the areas in the Duluth Complex included in this study Total study are are given given in in Table Table 1. 1. The drill hole chemistry has been used to create weighted average (over 50 to 100ff used to create weighted average (over 50 to 100ft zones) gridded gridded image image maps of of Cu-Ni grades, Cu-equivalent, Cu-equivalent, and Cu/Ni zones) Cu/Niratios ratiosfor for individual individual deposit areas. The The maps maps reflect reflect the the distribution distribution of of the the ore-metals ore-metals in relation to the basal contact the Duluth Complex. Complex. Eight Eight zones have been used to to define define the distribution distribution of of ore-metals in of the the basal 500ff of the the ten ten main main Cu-Ni Cu-Ni deposits of the Duluth Complex. 500ft of Complex. The Thezones zonesinclude include0-50', a-50', 50-100', 50-100', 100-150',150-200',200-250',250-300',300-400' 100-150', 150-200', 200-250', 250-300', 300-400'and and400-500' 400-500'above abovethe thebasal basalcontact. contact. The of high high Cu-Ni Cu-Ni grades grades and and low low Cu/Ni Cu/Ni ratios for individual zones has been correlation of determined by merging the Cu-Ni grade and Cu/Ni Cu/Niratio ratiodata datasets. sets. An An example example of of a composite composite copper migration migrationin in the the basal basal 500' 500' of the Spruce Road Deposit is image depicting modeled copper Posted within withinthe theimage image are are dots dots representing representinglocations locations of of drill drill hole hole presented in Figure 1. Posted the Duluth Duluth Complex, Complex, in in the the underlying underlyingGiants Giants Range Range Granite. Granite. A A strong strong assay samples, beneath the >1% hole assays assays with with>1 % Cu (suffide (sulfide veins ranging to to correlation exists between footwall drill hole 7.9%Cu) Cu)and and the the modeled modeled copper copper migration migration in in the the overlying overlying Duluth Duluth Complex. Complex. Based on 7.9% preliminary data, this new method appears to to be be a good mineral exploration targeting method that could be used to to predict predict favorable favorable areas areas for for hosting hosting footwall footwall deposits. deposits. 48 �sSpruce pru ceRa adD epas it Road Deposit ,+ 4_,____J ,- + + + + +__+~ + + +"t + + + + ,(25 + , ; Granite 1- + 4- 4- + + ÷ 1- + + Modeled Copper Copper Migration' Migration Modeled in the Basal Basal 500 500' ofofthe the in Duluth Complex Complex + + :::÷:÷:÷:÷ + + + T High .- HiKh 19 + 1- + + I.• -1- • •- Low Coer Assays Copper Assay'sBeneath Beneath the the buluth Duluth Complex Complex in In the the I Footwall Giants Range Range Granite . I: 26 30 Granite Granite - Duluth Compiel Complex Basal Basal ContactDips Contact Dips to to theSE at25 IheSEat2S' Duluth Complex — •->l%Cu • - > 1% Cu C!! = 694) I - <1%Cu < 1% Cu I • Figure 1. Correlation of of modeled modeled copper coppermigration migrationin in the the basal basal 500 500' of of the the Duluth DuluthComplex Complex and and 1. Correlation known mineralization mineralization in in the the footwall footwall Giants Giants Range Range Granite, Spruce Road Deposit. Table 1. Total Total deposit deposit assays/ assays' Deposit analyses for for individual individual element Table 2. 2. # of analyses Element # Element Spruce Road Sprnce Road 9282 9281 Copper 61,159 Palladium 5,897 Maturi 3246 Nickel 60,300 Rhodium 1,881 Birch lake 958 Sulfur 37,120 Iridium 203 Dunka Pit 4223 Cu/Ni 60,266 Osmium 202 102 Serpentine 2000 Gold 5,109 Vanadium 1,770 1,770 30069 Silver 4,223 Chromium 2,799 Dunka Road Road 2607 Platinum 5,598 Cobalt 3,202 Wetlegs 1248 Babbitt Wyman Creek Waterhen # # 922 1813 Bibliography Naldrett, A.J., A.J./ Innes, D.G., Sowa, hines, D.G., Sowa, J.J. And And Gorton, Gorton, M., M., 1982/ 1982,Compositional Compositionalvariation variation within within and between 5 Sudbury ore deposits; Economic Geology, v. 77/ p. 1519-1534. between 5 Sudbury ore deposits; Economic Geology, v. 77, p. 1519-1534. 49 �PETROGENETIC RELATIONSHIPS BETWEEN BETWEEN APATITE-BEARING APATITE-BEARING AND AND APATITE-DEFICIENT APATITE-DEFICIENT IRON IRON PETROGENETIC RELATIONSHIPS OXIDE-RiCH OXIDE-RICH INTRUSIONS INTRUSIONS AND AND MASSIVE SULFIDE MINERALIZATION IN THE DULUTH DULUTH COMPLEX, COMPLEX, MN. RIPLEY, RlPLEY, Edward M., Department of Geological IN Geological Sciences, Sciences, Indiana University, University, Bloomington, [N 47405 Within the Duluth Complex oxide-rich, mafic to ultramafic ultramafic·intrusions by Severson intrusions (referred to as OUI by and and Hauck, Hauck, 1990), occur as as cross-cutting cross-cutting bodies bodies and and semi-conformable semi-conformable lenses. lenses. These bodies are rich in both ilmenite and titanomagnetite, and and have have been been the subject of of recent investigations investigations by Jill Pasteris Pasteris and and students at Washington University, University, and and Penny Penny Morton Morton at at the the University University of ofMinnesota, Minnesota,Duluth. Duluth. Although Although these oxide-rich bodies occur throughout the Complex there are some differences between those located located of the Complex and those in in the central and northern sections that have only in the southern portion of recently been recognized. The The best best studied studied OUl OUI in in the the central central and and northern northern portion of of the Complex are characterized by by low apatite content. In Incontrast, contrast,many manyof ofthe theOUT OUI in the southern portion of of the Complex, in particular the Boulder Lake Lake area area (Severson, (Severson, 1995), 1995), are are marked markedby byabundant abundantapatite. apatite. In at least a few areas true nelsonites (ilmenite-apatite rocks) rocks) have have been been found. found. These types of apatite-oxide occurrences are similar to cross-cutting bodies bodies that are frequently found found associated with massif-type massif-type anorthosites (e.g. Marcy, Grenville Province, Province, Rogaland Rogaland Complex). Complex). Accessory minerals in the nelsonites spinel, and sulfides. include biotite, zircon, Zn-rich spine!, Massive sulfide mineralization at at the the Babbitt Babbitt deposit is is also cross-cutting in in form, form, and and is is composed of essentially the same mineralogy as the apatite-oxide rocks, but obviously in different of mineralogy but in different proportions. Euhedral Euhedral apatite apatite (locally (locally up up to to 5%) 5%) occurs occurs disseminated disseminated in in the massive sulfides, along with spinel, baddeleyite, biotite, Zn-rich hercynitic spine!, baddeleyite, ilmenite, ilmenite, and and other other oxides. oxides. We have previously proposed of a volatile-rich, immiscible imm iscible that the massive mineralization mineralization at at Babbitt Babbitt resulted resulted from from the the emplacement emplacement of sulfide liquid. The Thesame same elements elements may may be be partitioned partitioned into into an an immiscible immiscible Fe-Ti-P-rich oxide liquid, liquid, and an origin similar to that of the massive sulfides is proposed. Sulfur is proposed. Sulfur isotopic isotopic values of of the netsonites nelsonites (34%o) 4%o), and suggest that 4%0) are distinctly different different from from those thoseof ofthe themassive massivesulfides sulfidesatatBabbitt Babbitt(10-1 (10-14%0), sulfur contamination of of the the nelsonites nelsonites has has not not occurred. The distinctly lower lower Cl Cl and and REE REE contents of of the apatite from nelsonite and related rocks (Fig. 1) I) suggests that they either either crystallized crystallized from from aa magma magma that that had had previously previously separated a ClCI- and and REE-rich REE-rich fluid, or that had experienced prior crystallization crystallization of aa CICl- and and REE-compatible REE-compatible mineral. mineral. Both mechanisms are are consistent consistentwith with the the premise premisethat thatthe theapatite-rich apatite-richOUT OUI are genetically genetically associated associated with with highly evolved, residual melts. For Forexample, example, Severson Severson (1995) (1995) has has described layered oxide-rich gabbros in in the the Boulder Lake Lake area area where where apatite apatite isis aa cumulus cumulus mineral. mineral. Just to the south in in the the Duluth Duluth Layered Layered Series, Miller (1995) has also also described described five-phase five-phase cumulates cumulates where whereapatite apatiteisisaaprimocryst primocrystmineral. mineral. In In Series, contrast, apatite apatite is is never never aa cumulus cumulus phase phase in in the the Partridge Partridge River River (PRI) (PRl) and South South Kawishiwi Kawishiwi (SKI) Apatite in in the massive sulfide mineralization at Babbitt Intrusions in the central portion portion of the the Complex. Complex. Apatite in troctolites of of the PRI PRl (Fig. 1) 1) are characterized by by and that which occurs as an interstitial mineral in higher Cl CI and REE values relative relative to to apatite apatite in in the the apatite-rich apatite-richOUT. OUI. The The 01_fl OUI in in the the central portion of of the > 45 vs. Fo Fa < 45 in in apatite-rich apatite-rich OUI), OUI), and and the Complex are not as as chemically evolved evolved (e.g. (e.g. olivine olivine Fo Fo> <45 appear to be related to interstitial melts melts of of the the FRI PRl and SKI. In Inboth bothtypes typesof ofOUT OUI the paucity of of feldspar liquid component suggests that fractionation either through buoyant mineral accumulation or liquid immiscibility is an important genetic factor. 50 �References Jr., 1995, 1995,Emplacement Emplacementand and open-system open-system crystallization crystallization of ofthe the Duluth Duluth Complex Complex at at Duluth, Duluth, Miller, J. D., Jr, Minnesota (Abs.): Proceedings of IGCP Conference, Duluth, MN, 1995, P. 127-128. ofIGCP 1995, p. 127-128. Severson, M. J., and Hauck, Hauck, S. S. A., A., 1990, 1990, Geology, Geology, geochemistry, and stratigraphy stratigraphy of ofaa portion portion of ofthe the NRRITechnical TechnicalReport ReportNRRIJGMIN-TR-89NRRIlGMIN-TR-89-11, Partridge River Intrusion: NRRI 11, 236 p. Severson, M. J., 1995, 1995, Geology Geology of of the the southern southern portion portion of of the the Duluth Duluth Complex: Complex: NRRI NRRI Technical Technical Report Report NRRI/GMIN-TR-95-26, N RRIJG MIN-TR-95-26, in in press. press. F F + + Duluth Complex Complex Apatite OH Cl CI 1.2 1 Duluth Duluth Complex Apatite 0~ l UJ w w UJ a:: •*U.. • • 0.8 0.6 •* 0.4 , 0.2 0 0 0 ...--, . •* 1 • •* *• • * •. • U 0.5 U U. •• • • • • • • U Troctolite • . • Sulfide Suffide U U Nelsonite U 1I *• 1.5 2 CI wt.% Cwt% Figure 1. 1. Compositional Compositional variations variations between between apatite apatite from from apatite-rich OUI (here nelsonite), massive sulfide mineralization at Babbitt, and and Fe-Ti-P-rich gabbroic to troctolitic tfoctolitic rocks of of the Partridge Partridge River River Intrusion. 51 �ULTRAMAFIC DIKE WITH MANTLE TO MANTLE XENOLITHS: XENOLITHS: IMPLICATIONS TO DIAMOND EXPLORATION DIAMOND EXPLORATION IN IN WAWA WAWA Sage. R P.1, P.l, Morris, Morris, T. T. F.1, F.1, Crabtree, D.2, 0. 2, Murray, C. A.1, A.l, Bennett, G.1, G.l, Hailstone, Hailstone, M.l, Pianosi,S.f, 5.1,and andJosey, Josey,S1. 51. M.1,Nicholson, Nicholson, T.3, i., Pianosi, 1 Ontario Geological Survey, 1 Ontario 933 P3E 6B5 6B5 933 Ramsey Ramsey Lake Lake Road, Road, Sudbury, Sudbury, ON P3E 2 Ontario Geosciences Centre, 933 2 933 Ramsey ON P3E P3E6B5 6B5 Ramsey Lake Lake Road, Road, Sudbury, Sudbury, ON 33Prospector, Prospector, Wawa, ON The Ontario Geological Survey completed completed 10 10 years years of of bedrock bedrock mapping mapping in the Geological Survey Wawa of R. R. Sage. Sage. When Wawa area area in 1988 1988 under under the supervision supervision of When the the Survey Survey undertook O±tario for for ~amond diamond in undertook aa project project to to examine examine kimberlite occurrences in ontario 1993, R. R.Sage Sagerevisited revisitedthe theWawa Wawaarea area to toexamine examineultramafic ultramaficdikes dikes that that displayed displayed 1993, kimberlitic At the the time time of of this this visit visit Mr. Mr. Seymour Seymour Sears, Sears, Consulting Consulting kimberlitic features. features. At the attention attention of of the the OGS OGS that that Mr. Mr. "Mickey" "Mickey" Clement had Geologist, Geologist, brought to the found what appeared appeared to to be be diamonds diamonds in the area. The The stones stones were confirmed confirmed to be diamond which promptly promptly launched the diamond by by the the Royal Royal Ontario Museum in in 1993 1993 which OGS under the OGS into a sampling program for for kimberlite indicator minerals (K[Ms) (KIMs) under T. Morris. Morris. The alluvium sampling found abundant abundant KIMs KIMs just south south direction of T. prompting prospecting of Wawa prompting prospecting activity activity in the region. In InAugust August1995 1995 Mr. Mr. Terry Nicholson, Prospector, Prospector, Wawa, Wawa, encountered encountered subcrop subcrop of of what what appeared appeared to be aa Nicholson, lamprophyre dike with 1.0 m m wide wide lamprophyre with mantle-derived mantle-derived xenoliths xenoliths approximately approximately 1.0 trending 245 245 degrees, dipping 74 74 south in August 1995. 1995. Preliminary analysis of and some some of of the the xenoliths xenoliths has identified identified minerals the mineralogy of the dike and comparable to those found found in in kimberlite. kimberlite. Thin section, analysis and and geochemical geochemicalstudy study of of this this dike dike are in section, microprobe microprobe analysis progress within within the the OGS. OGS. 52 �OCCURRENCE OF HIBBINGITE HIBBINGITE IN IN THE THE DULUTH DULUTH COMPLEX, COMPLEX, MINNESOTA, MINNESOTA, AND AND IN NORn..'SK COMPLEX COMPLEX AND AND KORSHUNOVSKOE KORSHUNOVSKOE IRON ORE DEPOSIT, DEPOSIT, IN THE NORIL'SK RUSSIA Department of of Geosciences, Geosciences, North North Dakota Dakota State State University, University, SAINI-EIDUKAT, Bernhardt, Department Fargo, ND, 58 105-5517 USA (sainieid@badlands.nodak.edu). RUDASHEVSKY, NO, 58105-5517 USA RUDASHEVSKY, 21 Line Line 8A, 8A, St. St. Petersburg, Petersburg, 199026 199026 Nikolai S., Mechanobr Technical Corporation, 21 Russia. G., Institute Institute of of Geochemistry, Geochemistry, SB SB RAS, RAS, P.O. P.O. Box Box 4019, 4019, Russia. POLOZOV, Alexander G., 664033 Irkutsk, Russia (poloz@igc.irkutsk.su) Hibbingite, y-Fe2(OHhCl, ?-Fe2(OH)3C1,first firstidentified identifiedas as an an unnamed unnamed iron iron hydroxy hydroxy chloride chloride in the the Deep Copper Zone of the Sudbury Complex (Springer, (Springer, 1989), 1989), was was characterized characterized and and named named based based on on drill core samples from the Duluth Complex (Dahlberg, (Dahlberg, 1987, 1987, Dahlberg Dahlberg and and Saini-Eidukat, Saini-Eidukat, 1991; 1991; Saini-Eidukat and others, 1994). is also also found found associated associated 1994). Our Our investigations investigations show show that that hibbingite hibbingite is with platinum-group minerals in in the the Noril'sk Noril'sk Complex Complex and and with with the the Korshunovskoe Korshunovskoe iron iron ores ores of of the southern Siberian platform. as aa platfonn. Hibbingite Hibbingite has has also also been been documented documented by by Buchwald Buchwald (1995) (1995) as terrestrial weathering product of Antarctic Antarctic meteorites meteorites and and of of ancient ancient iron iron archeological archeological artifacts. artifacts. product of Hibbingite found in ofthe the Duluth Duluth in samples from from the the Noril'sk Noril'sk Complex Complex differs differs from from that that of Complex in containing significant significant kempite kempite (Mn2(OH)3C1) (Mn2(OHhCl) component; in some cases it contains mol. % % Mn. The grains, which are up to 0.6 mm in diameter, are associated over 50 mol. associa.ted with with the the platinum-group minerals froodite, froodite, cabriite, cabriite, urvantsevite urvantsevite and and with with native native silver silver in in massive massive pentlandite—cubanite—chalcopyrite pentlandite-cubanite-chalcopyrite ore. ore deposit, Hibbingite was also recognized in drill core from the Korshunovskoe iron ore km to to the the NNE NNE of of Irkut.sk Irkutsk city in the southern Siberian platform platform located approximately 500 km (Polozov and others, 1995). fine-grained 1995). The sample in which it was found is composed of fine-grained magnetite ore associated with halite. Late pyrrhotite, calcite and chlorite crystals occur occur in in numerous cavities; pyrrhotite may contain inclusions of of halite. Hibbingite, hematite hematite and and silver grains are are found in cavities in halite; the reddish-brown hibbingite grains usually grains usually occur occur as as encrustations in the cavities. The The size size of ofhibbingite hibbingite and and hematite hematitegrains grainsisisup uptoto100 100I.tm. ~m. The grains from the the Korshunovskoe Korshunovskoe deposit deposit were were analyzed analyzed in in spring spring 1992, 1992, immediately immediately after after polished section preparation, and again in winter 1995-1996. 1995-1996. The re-analysis established that that chlorine content of the grains decreased to approximately 6 wt.% with time the cWorine wt. % concomitant with with a small increase in iron. This agrees with re-analyses of Duluth Complex hibbingite and with the Fe8(O,OH) 16CL<2, hibbingiteis isakagendite, akageneite, Feg(O,OH) 16Ck2, for for which which Cl Cl hypothesis that that aa breakdown breakdownproduct productofofhibbingite 1991). is probably an essential component (Post and Buchwald, 1991). 53 �References Cited: c.B., 1995, 1995, Hibbingite Hibbingite (-Fe2C1(OH)3C1), (~Fe2Cl(OHhCl), aa chlorine-rich chlorine-rich corrosion corrosion Buchwald, V.F,, V.F., and Koch, C.B., product in meteorites and ancient iron objects [abstr.j: [abstr.]: Meteoritics, Meteoritics, v.v. 30, 30, p.p. 493. 493. Dahlberg, E.H., E.H., 1987, Drill core evaluation for platinum group mineral mineral potential of the basal basal Dahlberg, platinum group 39 p. 255,39 p. zone zone of the the Duluth Duluth Complex: Complex: Minnesota Minnesota Department Department of Natural Natural Resources, Resources, 255, Dahlberg, Dahlberg, E.H., E.H., and and Saini-Eidukat, Saini-Eidukat, B., B., 1991, 1991, A chlorine-bearing chlorine-bearing phase phase in in drill drill core core of serpentinized troctolitic rocks rocks of of the the Duluth Duluth Complex, Complex, Minnesota: Minnesota: Canadian CanadianMineralogist, Mineralogist,v.v. 29, p. 29, p. 239-244. AG., Vorontsov, A.E., AE., and Amirzhanov, A.A., A.A, 1995, The latest process Polozov, A.G., process of mineragenesis in iron ore deposits of of the Angara-Ilim Angara- Him type, type, Siberian Siberian Platform Platform [abstr.]: [abstr.]: ill Petrology and Metallogeny of Volcanic and and Intrusive Intrusive Rocks Rocks of of the the Midcontinent Midcontinent Rift Rift System, System, Proceedings, IGCP IOCP Project 336 International Field Field Conference and and Symposium, Symposium, Duluth, Duluth, MN, MN, p.151. p. 151. Post, I.E., J.E., and Buchwald, V.F., 1991, Post, 1991, Crystal structure refinement refinement of of akagenéite: akageneite: American American Mineralogist, v. 76, p. 272-277. H., 1994, 1994, Hibbingite, Hibbingite, 'y-Fe2(OH)3C1, y-Fe2(OH)3Cl, a new mineral Saini-Eidukat, B., Kucha, Kucha, H., H., and and Keppler, Keppler, H., of Fe-bearing Fe-bearing from the Duluth Complex, Minnesota, with implications for the the oxidation oxidation of from American Mineralogist, Mineralogist, v. v. 79, 79, p. p. 555-561. 555-561. compounds compounds and and the transport of metals: metals: American Springer, uncommon minerals minerals in the the Strathcona Strathcona Deep Deep Springer, G., G., 1989, Chlorine-bearing and other uncommon zone, Sudbury Sudbury District, Disthct, Ontario: Ontario: Canadian p. 311-313. 311-313. copper zone, Canadian Mineralogist, Mineralogist, v. 27, p. 54 �Clay minerals Clay minerals of the the North North Shore Shore Volcanic Volcanic Group Group and and possible possible relationship to copper copper precipitation precipitation during alteration alteration relationship SCHMIDT, Susanne Th & STERN, Willem, Mineralogisch-Petrographisches Institut, Bemoullistr. 30, CH 4056 Basel, Switzerland; email: SchmidtS@ubaclu.unibas.ch Bernoullistr. chalcopyrite, covellite, Several occurrences of native copper with chalcopyrite, Several small occurrences covellite, and and galena are known Precambrian North North Shore Whole rock values for known in the Precambrian Shore Volcanic Volcanic Group, Group,Minnesota. Minnesota. Whole rock values for flow units units (massive (massive flow flow interiors) range range copper in altered (flow (flow tops tops and bottoms) bottoms) and less altered flow between Due to the between 11 11 and 241 241 ppm, ppm, and and Zn Zn values values between between 49 49 and and 167 167 ppm. ppm. Due the general general of the the series from a continental to an aborted rifting geochemical evolution of rifling environment there is a general increase in in the the lava lava flow flow interiors interiors from stratigraphically stratigraphically lower lower to to in the the primary primary Cu Cu content content in higher flows (Basaltic Volcanism Project, 1982; Schmidt, Schmidt, 1990). 1990). Superimposed Superimposed on on this this trend trend are are secondary trends. In Inlower lowermetamorphic metamorphic grade grade flows, flows, the the massive massive flow interiors (dark square square in in Fig. la) la) show show in in general general higher higher copper copper values values than the flow flow tops tops and and bottoms. bottoms. This This trend trend isis Fig. of the the series series where where the the flows flows show show alteration alteration assemblages assemblages typical typical of of reversed at the the bottom bottom of reversed beginning greensehist greenschist facies (prehnite-pumpellyite-chlorite (prehnite-pumpellyite-ehlorite or epidote-chlorite epidote-chiorite assemblages). assemblages). Here, Here, the altered flow flow tops tops and and bottoms bottoms and and the the transitions transitions zones show higher Cu values values than than the the massive flow interiors. At Atall allstratigraphic stratigraphiclevels, levels, the the highest highest copper copper values values are are observed observed in in the the transition transition zone zone to the the massive massive flow flow interior, interior, i. e. the the near near top top or or near near bottom bottom areas areas with with clay clay minerals ± ± quartz quartz -- prehnite ± pumpellyite ± albite assemblages. is only in the highest grade flow A similar trend is observed for zinc. zinc. ItIt is flow where the massive flow interior shows lower values values than than the the other other flow flowunits units(Fig. (Fig.Ib). ib). Again flow Again the transition zones to the massive flow interior interior (near (near bottom bottom and and near near top) top) display display the the highest highest values. values. minerals show a great variety in chemical composition as well as In these metabasites clay minerals in structural type. Various Varioustypes types have have been been identified identified based based on on electron electron microprobe microprobe analysis, analysis. Xray diffraction and deconvolution analysis. Smectites Smectites and and mixed mixed layer layer phyllosilicates phyllosilicates are are common in the flow tops higher levels levels of of lower lower metamorphic metamorphicgrade. grade. Chiorites in tops of of strat.igraphically stratigraphically higher Chlorites and more common common in in flow flow tops tops of of the the stratigraphically stratigraphically lower lower part part or or higher higher grade grade corrensite are more Smectites as as well well as as metamorphic (Schmidt, 1993 1993 and metamorphic units units (Schmidt, and Schmidt Schmidt & & Robinson, Robinson, submitted). submitted). Smectites mixed-layer minerals identified in massive flow stratigraphically minerals have also been identified in the massive flow interior of stratigraphically lower or higher grade flows. 55 �Clay minerals have been been isolated isolated from from the the different different morphological morphological units and have have been been by XRF.. XRF. They They show show varying varying contents contents of of copper copper and and'zinc. zInc. In addition, selenium has analyzed by In addition, been detected in in smectite. Smectitic relationship of clay This suggests a close relationship clay minerals minerals to to copper copper mineralization. mineralization. Smectitic phases dominant in low grade grade metamorphic metamorphic rock will not be stable under beginning beginning greenschist greenschist conditions. They They will willbreak breakdown down and and the the copper copper will will be bereleased. released. Chlorite Chlorite ± prehnite prehnite ± ± conditions. stable and and copper will will be be locally enriched in these these pumpellyite ± ± albite ±± quartz assemblages wifi will be stable assemblages. Basaltic Volcanism Study Project Project (1981) (1981) Basaltic Basaltic Volcanism Volcanism on the !.he Terrestrial Planets, Planets. Pergamon Pergamon Press, Press. New York, p. York. 1289 1289 p. metamorphism in in the the North North Shore Shore Volcanic Volcanic Group. Group, Schmidt, S. Th. (1990) Alteration under conditions of burial metamorphism Minnesota -- Mineralogical and geochemical zonation. Heidelberger Geowissenschaftlicbe Abhandlungen. Geowissenschaftliche Abbandlungen, Band 41, 41. 3O9p. 309p. Group. Schmidt, S. Th. (1993) Regional and local patterns of low-grade metamorphism in the North Shore Volcanic Group, Minnesota, USA. 401-414. of Metamorphic Metamorphic Geology, Geology. 11, 11.401-414. USA. Journal Journal of Schmidt, S. Th. & Robinson, Schmidt. Robinson. D. D. (submitted) Metamorphic grade and porosity/permeability controls on mafic in aa regional regional metamorphic metamorphic zeolite to greenschist facies transition of ofthe the North North distributions in phyllosilicate disthbutions fades transilion Shore Volcanic Group, Group. Minnesota. GROUP, WHOLEWHOLE ROCK VOLCANIC GROUP, NORTH SHORE SHORE VOLCANIC ::. top of sequence zeolitezones zeolite zones <:l!.. D: • o~ ~ III 0 0 ~ Ll. beginning beginnin,g green8chl8t greenechist zones bottom of sequence 8o AVO '" <> ~ 0 • o0 25 26 50 <:> "'-0 00 00 • • • • 00 00 ~ <D aDa tV0 o Ll. 0o 6 0 o • • ~ 0 A ~ 0 0 cl>o 0 • <> near bottom •• massive massive flow flow o near top 6 flow top 0'" Av:v; :• :. <> 10 ooo~ '11 6 'V 0 6 00 ~ 0 'V flow Fwrn bottom ROCK 'V ~o 0 to.o oU0 o~. 0 0 o ~ • 0 75 100 175 200 100 125 125 150 150 175 200 2252500 Cu (ppm) (ppm) 20 40 0 60 {:;,. <> 'V 140 160 80 100 120 140 160 180 Zn (ppm) (ppm) Cu content content (Fig. (Fig. 1a la ) and and Zn Zn content content(Fig. (Fig.1b) ib) in in basaltic basaltic lava lava flows Cu 56 0 <> �BASALTIC KOMATIITES AND ASSOCIATED ROCKS: ROCKS: IMPLICATIONS IMPLICATIONS ON ON THE THE NATURE OF VOLCANISM IN PART OF THE SCHREIBER-HEMLO GREENSTONE BELT, NORTHWESTERN ONTARIO BELT, SMYK, Survey, Ministry of NQrthern SMYK, M.C., M.C., Ontario Geological Survey, Development and Mines, Mines1 Suite B002, Development B002, 435 S. S. James St, Thunder Bay, St, Bay, Ontario, Ontario, P7E P7E 6E3, 6E3, and and KINGSTON, KINGSTON, D.M., Surface Science Western, Western, University of D.M., Western Ontario, Ontario, London, London, Ontario, Ontario, N6A N6A 5B7 5B7 Well-preserved, basaltic basaltic komatiltes komatiites have have recently recently been been discovered discovered Well-preserved, succession of of subaqeuous subaqeuous basalts basalts and andinterf interflow within aa succession low sedimentary rocks of the the Neoarchean Schreiber-Hemlo Schreiber-Hemlo greenstone greenstone belt. Two, sections consist consist of of pillowed pillowed to to massive, massive, Two, detailed sections high-Mg tholeiitic basalt and basaltic komatiite. komatiite. Individual flow sub-units, sub-units, varying in thickness m, are flow thickness from 1 to 20 20 m, "Crowded' and and/or conformably conformably stacked. stacked. "Crowded" intercalated and/or (- 10% 10% pillows) pillows) flows flows and and autoclastic autoclastic incipiently pillowed (— breccias comprise the the bulk bulk of of the the succession. succession. Pillows pillows range from from small small ((~ 30 30 cm), cm), bun-shaped bun-shaped forms forms to to large, large, mattress-shaped mattress-shaped (>3 m). m). Broken pillow breccia and hyaloclastite megapillows (>3 occur between flow flow units and in in interpillow interpillow spaces. spaces. These These extrusive rocks are characteristically variolitic; variolitic; varioles varioles tend tend to coalesce in pillow cores, to cores, along selvages selvages and and along along flow flow contacts. A A 99 m m thick, thick, composite, composite, basaltic basaltic komatiite komatiite flow flow has has been been identified in in the the upper upper section. section. It It consists of of aa massive, massive, ultrarnaf Ic base base (MgO ~ 20%) ultramafic 20%) followed upwards by three, three, spinifexspinifextextured flow flow units: units: (i) foliated; (ii) (ii) coarse (~8 cm), cm), lower, foliated; coarse (8 (I) lower, plate; plate; and (iii) (iii) upper, upper, randomly randomly oriented. oriented. The The MgO MgO contents contents of of flow units range range from from 8% 8% to to 11%. 11%. Primary minerals have have these flow been replaced and pseudomorphed by metamorphic mineral assemblages consisting consisting of of tremolite-actinolite, tremolite-actinolite, serpentine, serpentine, calcite, quartz and Magneslan hornblende has replaced calcite, and chlorite. chlorite. Magnesian primary clinopyroxene clinopyroxene that that originally originally comprised comprised the the spinifex spinifex megacrysts and In addition addition to to these characteristic and phenocrysts. phenocrYsts. In petrographic features, features, the major element chemistry is is consistent consistent with known known basaltic basaltic komatiites. komatiites. Thin section petrography has revealed revealed polygonal dendrite networks, skeletal / hollow-cored phenocrysts led networks, skeletal/hollow-cored phenocrysts and and devitrif devitrified glass. textures, together together with with the the various various spirilfex spinifex glass. These textures, textures and tremendous variole development, development, suggest suggest rapid rapid textures The chilling/quenching and chilling/quenching and undercooling undercooling of of these these basaltic basaltic lavas. lavas. the pillowed and brecciated brecciated low vesicularity and disposition of the flow units units suggest suggest deep deep water extrusion, flow extrusion, on relatively flat flat Successive flow lobe depositional surfaces. surfaces. lobe or lava tube emplacement, with fluctuating fluctuating lava lava levels, levels, is is supported supported by by emplacement, stacking and and the the presence presence of of stacked stacked lava lava shelves shelves megapillow stacking pillows. The progression from from (mega)pillow-dominated (mega)pillow-dominated within pillows. flows section, to incipiently pillowed and flows in in the the lower section, brecciated units in in the the upper, upper, komatiitic section section may indicate indicate waning from from high high to to lower lower effusion effusion rates. rates. 57 �NORTHEASTERN MINNESOTA MOR!rDASTElUf MIMHESarA DULUTH COMPLEX MINERAL IlIHERAL POTENTIAL Allan Allan Spector, Allan Allan Spector Spector, Spector and and Associates Associates Ltd., Ltd., Toronto, Canada, M5N 1S7 157 Toronto, Canada, 24 Strathallan Boulevard, Boulevard, 24 Strathallan T.L. Lawler, of Natural T.L. Lawler, Minnesota Department Department .of Natural Resources, Resources, Division Division of of Minerals, Minerals, 1525 Third Ave. E., Hibbing, Hibbing, Z1 MN 55746 55746 Ave. B., of northeastern northeastern Minnesota Minnesota show show older older assemblages assemblages of of late late Archean Archean Geologic maps of and early early Proterozoic Proterozoic rocks truncated by crescent shaped shaped intrusive intrusive unit unit rocks truncated by aa crescent approx~ately 1.1 billion billion years years old. old. The igneous rocks welled in a rift of the approximately 1.1 welled up in earths crust which runs northeasterly from Nebraska, through Iowa earths and up the the Iowa and eastern side side of of Minnesota. Minnesota. It then curves curves out out into intoLake Lake Superior Superior and and runs It then southerly into Michigan. The is aa major major continental continental feature feature which which is well into Michigan. Therift rift is is well defined by gravity and defined by gravity and aeromagnetic surveys. surveys. Extrusive Extrusive volcanic rocks to rocks related related to these intrusivee these intrusives are are found found in the the north north shore shore volcanics, volcanica, widespread widespread volcanic volcanic assemblages in the western western part assemblages part of of the Opper Upper Peninsula Peninsula of Michigan Michigan and some some flows flows in Wisconsin. In in northern Wisconsin. In Minnesota the the intrusive intrusive rocks rocks are are known as the Duluth Complex. form a belt extending north from Complex. These rocks form from Duluth Duluth to to Hoyt Hoyt Lakes Lakes then running northeasterly, northeasterly, then running then east east to to Lake Lake Superior, Superior, not not far far south south of the Canadian They underlie underlie an area with considerable border. They of about aDout 20,000 considerable area of 20,000 square miles with outcrop, or or covered bya athin thin layer layer of of glacial outcrop, covered by glacial deposits. deposits. The rocks rocks of The of the theDuluth DuluthComplex complex form a a patchwork patchwork of intrusions.Some Some of of layered layered intrusions. the minerals contain contain iron iron and and are are quite quite dense, dense, therefore therefore they they display display distinct distinct responses on gravity and magnetic surveys. surveys. Similar intrusive rocks in; in; Montana (the Stillwater Stillwater Complex), complex), Africa (the (the Buahveld Bushveld Complex), Complex), Ontario (the (the Sudbury Sudbury Igneous Igneous Complex), complex), and and Russia Russia (the (the Noril'ak—Talnakh Noril' sk-Talnakh Intrusion) Intrusion) host host economic economic deposits of copper—nickel, and some deposits copper-nickel, platinum platinum group group minerals, minerals, and some gold. gold. Massive Massive copper—nickel sulfide p.g.m. are are commonly cozon1y found copper-nickel sulfide deposits deposits with with minor p.g.m. found near near the the base base with intruded intruded rocks rocks or or as as dike dike like of the intrusive at or or near the contact contact with like intrusive body, at bodies intruded intruded into into the footwall footwall rock. rock. In In addition addition platinum platinum group group minerals, and and chromium horizons chromium horizons are are found found in in reefs, conmonly commonly well above aDove the intrusive intrusive contact. contact. bearing sulfide In the mid 1960a of dark 1960s outcrops outcrops and and boulders boulders of dark igneou. igneous rocks rocks bearing sulfide copper—nickel minerals were recognized along the the footwall footwall contact contact of of the the Duluth Duluth copper-nickel Complex in the northeast complex northeast trending trending section section of the the contact contact zone. zone. Exploration Exploration of of this area located mineral deposits deposit. which contained marginal economic mineralization estimated est~ted to be 4.4 billion tons with a a copper copper content content of of 0.66% 0.66\ copper to nickel ratio and a copper ratio of of 3.3:1 3.3:1 (Liaterud (Listerud and and Meineke). Meineke). of the of the Inferred the footwall footwall of the Duluth Duluth Complex Complex based based on Inf erred geological geological maps naps of geophysical interpretations, interpretations, were prepared by Dr. Dr. Allan spector Spector and Associates Associates under contract display lithology, under DNR. The The maps maps display lithology, structure, depth to contract to to the the DNR. magnetic basement basement and and mineral potential modeled from geophysical magnetic geophysical characteristics. characteristics. data (shown mineral potential areas are are character:ized characterized by The mineral by gravity gravity and and magnetic data on profiles) which indicates the intrusive. extend to to the the west west of of the the mapped mapped on profiles) which indicates the intrusives extend contact as sills, contact sills, or features not not explained explained by by outcrop outcrop or or drilling. Some of of the MPAS correlate with geochemical Alminas (Alminas and northern KPAs geochemical anomalies anomaliesmapped mapped by Alminas Dahlberg). Dahlberg) • structure, depth drilling. Alminas, Henry V. and Dahlberg, B. B. Henk, Henk, 1994, 1994, Platinum, Platinum, palladium, palladium, and and gold gold and Dahlberg, of the the Duluth distribution distribution in B—Horizon B-Horizon soils soils on on the the northwestern northwestern part part of Complex, Complex, Minnesota: Minnesota: Mimi. Minn. Dept. Dept. of Natural Natural Resources, Resources, Div. Div. of of Minerals, Minerals, Report 308, 308, Hibbing, Bibbing, Minn., Minn., p. p. 15. 15. Listerud, Listerud, W.B. portion of the the W.H.and andMeineke, Meineke,D.G., D.G.,1980, 1980,Mineral Mineralresources resourcesofof aa portion Duluth Complex and adjacent rocks in Louis and and Lake Lake Counties, Counties, in St. St. Louis northeastern Minnesota: Mimi. Minn. Dept. of Natural Resources, Div. of Minerals, Minerals, Report 93, 93, Hibbing, Hibbing, Mimi., Minn., p. p. 49, 49, illustrations illustrations 47, 47, tables tables 3. 3. Spector, Allan, 1995, 1995, Report Report on on aeromagnetic aeromagnetic data data interpretation interpretation western western Duluth Duluth Complex: Prepared Prepared for for the the Minn. Minn. Dept. of of Natural Natural Resources, Resources, Div. of Complex: Minerals, Proj. Minerals, Proj. 308, 308, p. 15, figs. 24. p. 15, figs. 24. 58 �UPDATE ON ON THE THE GEOLOGICAL CORE AND SAMPLE REPOSITORY REPOSITORY William T. T. Swenor Geological Survey Division, Department Of Environmental Quality Marquette, Michigan Marquette, The The Geological Geological Survey Survey Division Division (GSD) (GSD) of the the Michigan Michigan Department Department of Environmental Environmental Quality Quality (DEQ) (DEQ) drill maintains maintains the the Geological Geological Core Coreand andSample SampleRepository RepositoryatatMarquette, Marquette,Michigan. Michigan. The The collection collection of of dnll core, core, cuttings, cuttings, and and other other samples samples are are from from 63 63 counties counties in in Michigan, Michigan, including including 14 14 of the 15 counties from the the Upper Upper Peninsula. Peninsula. The The purpose purpose of of this this collection collectionisisto to act act as as aa "rock" rock" library library and and make make the the stored stored researchers and industry for geological study study and and to to promote promote mineral mineral and and samples available to individual researchers fuel exploration and fuel and development in Michigan. As January 1, 1996, there holes containing As of January 1, 1996, there are are 771 771 drill drill holes containing 251,000 251,000 feet feet of of actual actual core, core, mostly mostly from from the the Upper Peninsula. Peninsula. Another holes have have abbreviated abbreviated core core representing representing 124,000 124,000 feet. feet. Also, an Another 365 365 holes Also, an additional 202 holes have cuttings cuttings that that represent represent 54,000 54,000 feet. feet. In addition to the exploration exploration drill holes, holes, additional In addition the repository repository is storing oil and and gas cores cores and cuttings from throughout throughout the the State. State. Since January, January, 1994, 1994, selected selected cuttings cuttings from from all all new new oil oil and and gas gaswells wellsdrilled drilled inin Michigan Michigan have have been beensent sentto tothe the repository. repository. The 317 317 wells wells have have cuttings cuttings that that represent representover over538,000 538,000feet. feet. An An additional additional 9,100 9,100 feet of oil and and gas core is is also in storage. The most was the the early The most significant significant recent recent addition addition was early release release of confidentiality confidentiality of of the the deepest deepest all-cored all-cored mineral March, 1995. 1995. AMOCO AMOCO Production Production Company Company released released the confidentiality on core, mineral well well in in March, the confidentiality on the the core, wells logs logs and and file file data data for their St. Amour #1-29 and wells and #1-29R test wells. The 1-29R 1-29R is is aa 7,238 7,238 foot foot hole hole drilled in in late late 1987 1987 to to learn leam more more about about the the Mid-continent Mid-continent Rift. Rift. It was was located located southeast southeast of that was drilled Munising, near near Wetmore, Wetmore, inin Alger Alger County County in in the the Upper The hole hole went went through through 110 110 feet feet of Munising, Upper Peninsula. Peninsula. The glacial drift and entered bedrock bedrock ininthe the Paleozoic Paleozoicaged agedAutrain AutrainFormation FormationofofOrdovician Ordoviciantime. time. The The hole hole glacial and entered ended in Precambrian Precambrian aged aged Portage Portage Lake Lake Volcanics Volcanics of of Keweenawan Keweenawan time. This This core core should should be be of of ended interest to to geologists geologists from from academia, the oil and gas and the mineral exploration interest exploration industry. industry. The GSD's metallic mine includes thousands mine and and data data collection collection isis also also stored storedatatthe the repository. repository. This includes thousands of of surface and maps from from early to more recent mines from the and underground underground maps the western westem one-half one-half of of the the Upper Upper Peninsula. Reports Reports and and other other miscellaneous miscellaneous information information isis also also available available from from this same area. area. This collection helps helps in in the the understanding understandingof ofthe the geology geology and and mineral mineral resource resourcepotential potential of of the the State, State, as as well well collection as being being an an aid aid to to public safety and land use planning. as planning. ItIt is a record record of potential potential mine mine subsidence subsidence areas areas of the State State which should be avoided when when construction is planned. planned. The repository occupies occupies two two separate separate buildings. buildings. The first building building is is 4,000 square feet with electricity and and examination room. room. The a heated heated examination The second second building building contains contains 3,200 3,200 square square feet of of storage storage space space and and is is adjacent to to the main building. Retrieval, replacement, replacement, splitting, splitting, and and slabbing slabbing of material material is provided by adjacent building. Retrieval, Limited sampling sampling of material is allowed cores and and other other samples samples is is possible possible on on aa staff. Limited allowed and and borrowing borrowing cores case-by-case basis. case-by-case basis. Currently, no user user fees. fees. The is open open by by appointment, appointment, Monday Monday The facility is Currently, there there are no through Friday, Friday, 8:00 8:00 a.m. a.m. to 4:30 p.m. Also, a complete complete inventory inventory of of the the Core Core and and Sample Sample Repository Repository isis appointment or at at thethe Upper available. For an aøpointment available. For or more moreinformation, information,call callBill BillSwenor, Swenor.Geological GeologicalTechnician, Technician, Uer Peninsula Peninsula Field Headquarters in in Marquette at 906- 228-6561. 228-6561. The GSD GSD also also maintains maintains oil oil and and gas gas well well cuttings cuttings from from over over 10,000 10,000 wells wells drilled drilled prior prior to to 1994 1994 and and over over The 45,000 drillers logs logs and thousands of geophysical geophysical logs. logs. Contact Contact the the Petroleum Petroleum Geology Geology and andProduction Production water well well logs Unit in Lansing Lansing for more more information information at at 517-334-6930. 517-334-693.0. For Statewide Statewide water logs and and microfilm microfilm records, contact contact Lisa Lisa Farhat Farhatinin the the Administrative AdministrativeSupport SupportUnit Unitatat517-334-6936. 517-334-6936. Copies Copies of of all all Upper Upper records, Peninsula water well well records records and and well well cuttings cuttings from from over over 600 Peninsula water 600 selected selected wells wells are are stored stored at at the the DNR DNR Escanaba Office. Call Escanaba Office. Call Frank Frank Chenier Chenier at at 906-786-2351 906-786-2351 for for more more information. information. 59 �OUTCROP AND SUBSURFACE CORE ANALYSIS AND RELATIONSHIP OUTCROP AND RELATIONSHIP TO REGIONAL HYDROCARBON INNORTHERN NORTHERNWISCONSIN WISCONSIN PROSPECTIVENESS OF THE MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC NONESUCH NONESUCH FORMATION FORMATION IN AND MICHIGAN MICHIGAN S. J. J. Uchytil Uchytil and and C. C. K. K. Steffensen. Steffensen,Vastar Vstar Resources, S. Resources. Inc. Inc. Houston, Houston. TX 0. M. D. M. Jarvie, Jarvie. Humble Geochemical Services, Services. Humble, Humble, TX TX A. B. B. Dickas, A. Dickas. University Wisconsin-Superior, Wisconsin-Superior. Superior, Superior. WI WI M. G. 0. Mudrey, WI M. Mudrey. Jr., Jr.. Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Madison, Madison, WI The Middle Proterozoic Nonesuch Formation, Formation. often often described described as as aa hydrocarbon hydrocarbon generating generating source source rock, rock. partially partially infill sequence sequence of composes the sedimentary rock infill of the the Midcontinent Midcontinent Rift Rift System System in in northern northern Wisconsin Wisconsin and and Michigan. Michigan. Nonesuch Formation, Formation. acting acting as as both both aa hydrocarbon hydrocarbon source source and and reservoir reservoir unit, unit. is is The exploration potential of the Nonesuch supported the VVhite White Pine Pine. Ml, MI. and numerous geochemical geochemical studies studies that that demonstrate demonstrate supported by oil seeps in the Pine Mine. Mine, White White Pine, derived from from the the Nonesuch Nonesuch Formation. Formation. that the oil inri the White Pine Mine is derived Outcrop, subsurface core samples. samples, and an oil sample from the White Pine an Outcrop, Pine Mine were collected, collected. along an approximate 150 150mile miletransect transectfrom fromnorthwest northwestWI WInortheast northeastto tothe the Keweenaw KeweenawPeninsula Peninsulaof ofMI, Ml, and and analyzed analyzed for fortheir their approximate organic organic geochemical characteristics charactenstics (Figure I). In addition. addition, the rate rate of kerogen kerogen decomposition was measured on on a Nonesuch Formation Formation shale shale core core sample. sample. The exposure is is required required to to convert convert Nonesuch The kinetic kinetic results results suggests suggests a high thermal thermal exposure Nonesuch Formation Formation kerogen kerogen into hydrocarbons, in the the Nonesuch hydrocarbons. and and the the Nonesuch Nonesuch Formation Formation is a poor to fair source source rock rock in areas quality hydrocarbon hydrocarbon source source rock. rock. areas examined examined and and presumably never was a high quality While we do not discount the possibility ofMidcontinent Midcontinent Rift Rift hydrocarbon hydrocarbon accumulations accumulations in in the the study study area, area. possibility of successful hydrocarbon exploration, in the the northern northern Midcontinent Midcontinent Rift Rift for for major major successful exploration. targeting targeting the the Nonesuch Nonesuch Formation Formation in million barrels barrels of of oil oil equivalent) is unlikely. 10 million unlikely. reserves (over 10 Outside the Nonesuch Formation outcrop area, area. the the hydrocarbon hydrocarbon prospectiveness prospeetiveness is is less less well known. known. However, However.with with St. Amour #I-29R release release of of the the former former proprietary proprietary Amoco St. #l-29R core (Alger County, County, MI), Ml), the known deposition of Nonesuch-type stratigraphy is extended Nonesuch-type extended eastward eastward to tothe thelongitude longitudeofofMunising. Munising.Here Here182 182 ftft of of brown, brown. gray, gray, and and black black fine-grained typical Copper Harbor Conglomerate Conglomerate rocks. rocks. fine-grarned clastics, clastics. enveloped enveloped in in 46 and and 50 50 ftft basalt basalt flows, flows. underBe underlie typical This diversion from the Oronto Group type-section type-section sequence sequence suggests suggests an an eariier earlier initiation rnitiation of of Nonesuch-style Nonesuch-style deposition in in the the eastern eastern Lake Superior Basin. Basin. Consideration deposition Consideration of of multiple multiple time penods periods of Nonesuch-type NoneSUch-type deposition during the extension phase of Midcontinent Midcontinent Rift Rift development development would would indicate indicate the the hydrocarbon hydrocarbon potential potential of of the the Middle Middle U. S. is yet to be fully evaluated. Proterozoic Proterozoic of the the midcontinent U. Bibliography Bibliography AlIen, 0. J., the J.. Hinze, Hinze. W. J., J.. Dickas, Dickas. A. B., B.. and and Mudrey, M. 0. G. Jr., Jr.. in in press, press. Integrated Integrated geophysical modeling of the Allen. D. North American American Midcontinent Rift System: new interpretation for western Lake Superior, North Superior. northwestern Wisconsin, Wisconsin, w.. Dickas, Dickas. A. B. B. and Green J. C. (eds), (eds). Middle Proterozoic to Cambrian and and eastern eastern Minnesota: Minnesota: in Ojakangas. Ojakangas, R. W.. rifting, central North America, ofAmerica, America.Special SpecialPaper Paper312. 312. rifting, America. Geological Geological Society Societyof Elmore. R. R. 0., Elmore. D.. Milavec. Milavec. S. S. W., W .. Imbus, Imbus.S. S.W. W.and andEngel, Engel.M. M.H.. H..1989, 1989. The The Precambrian Precambrian Nonesuch Nonesuch Formation Formationof ofthe the North American Midcontinent rift, lacustrine deposition: North American rift. sedimentology and organic geochemical aspects of lacustnne Precambrian 43.p.p.191-213. 191-213. Precambrian Research, Research,v.v.43, Hieshima, G. G. B.. 8., Zaback, potential of Precambrian Precambrian Nonesuch Nonesuch Formation, Formation, Hieshima. Zaback. 0. D. A., A.. and and Pratt, Pratt. L. L. M., M.. 1989, 1989. Petroleum potential Mid-Continent Rift Rift System (abstract). (abstract), Bulletin American Association of Petroleum Geologists, Geologists. v. 73, 73. p. 363. Hieshima, 0. Sulfur/carbon ratios ratios and and extractable organic matter of the Middle Proterozoic G. B. B. and and Pratt, Pratt. L.L. M., M.,1991, 1991. Sulfur/carbon Proterozoic Nonesuch Formation. Formation, North American Midcontinent v. 54, 54, p. p. 65-79. 65-79. Nonesuch Midcontinent Rift: Rift: Precambrian Precambrian Research, Research. V. 60 �Imbus. S. S. W. W., Engel. The origin. ongin. distribution distnbution and hydrocarbon Imbus. Engel. M. M. H. H.. Elmore, Elmore. R. R. D., D.. and and Zumberge. Zumberge. J.J. E., E.. 1988, 1988. The generation potential of organic-rich facies generation facies in in the the Nonesuch Nonesuch Formation, Formation. central central North North Amencan Amencan Rift Rift System: System: aa regional study: Geochemistry v. 3, p. regional study: Organic. Organic Geochemistry, v. 13, p. 207-219. 207-219. Imbus. S. S. W., W. Engel, Imbus. Engel, M. M. H.. H.. and and Elmore, Elmore, R. R. 0., D.,1990, 1990, Organic Organic geochemistry geochemistry and and sedimentology sedimentology of of Middle Middle Proterozoic ProterozoIc Nonesuch Formation-hydrocarbon Formation—hydrocarbon source source rock rock assessment assessmentof ofaa lacustrine acustnne sift sift deposit deposit: in in Katz. Katz. B. B. J. J. (ed), (ed), Lacustnne Lacustrine Nonesuch basin exploration case studies and basin and modem modem analogs: analogs: American American Association Association of of Petroleum Petroleum Geologists Geologists Memoir Memoir 50, 50, p. p. 197-208. Kelly, W.C. W.C. and and G.K. GK. Nishioka, and the the role role of hydrocarbons hydrocarbons on on copper copper Kelly, Nishioka. 1985, 1985, Precambrian Precambrian oil inclusions in late veins and mineralization at at White White Pine, Pine, Michigan: Michigan: Geology, G.e!agy, v. 13, 13. p. 334-337, 334-337, 1985. 1985. mineralization Pratt. Pratt, L. L. M.. M., Summons, Summons, R. R. E., E.. and Hieshima, Hieshima. G. G. B., B., 991, 1991, Sterane Sterane and and trrterpane trtterpane biomarkers biomarkers in in the the Precambrian Precambrian Acta. v. v. 55,55. p. p. 911-916. 911-916. Nonesuch Formation, Formation, North North American AmericanMidcontinent MidcontinentRift: Rift:Geochemica GeochemicaetetCosmochemica Cosmochemica Acta. Price, K. K. L.: L Huntoon. the Price. Huntoon.J.J.E.. E..and andMcDowell, McDowell,S.S.D., D.,996, 1996,Thermal Thermalhistory historyofof the1.1 1.1 Ga Ga Nonesuch Nonesuch Formation, Formation. North North American Mid-Continent Rift, Rift, White White Pine, Pine. Michigan: Michigan: American American Association of of Petroleum Petroleum Geologists Bulletin, Bulletin, v. v. 80, 80. p. p. 1-15. 1-15. Price. S. D., 993, 1993, Illite/smectite Illite/smectite geotherinometry geothermometry of ofthe the Proterozoic Proterozoic Oronto Oronto Group, Group, Midcontinent Midcontinent Price, K. K. L. L, and and McDowell, McDowell, S. 41, 41.p.p.134.147. 134-147. Rift System: Clays Claysand andClay ClayMinerals, Minerals,v. v. Uchytil, S. S. J., J., Jarvie. 0. Uchytil, D. M., M., and and Steffensen, Steffensen, C. C. K., K.. in in press, press. Hydrocarbon Hydrocarbon prospectiveness prospectiveness of of the the Middle Middle Proterozoic ProterozoIc Nonesuch Formation Formation in northern Wisconsin and Michigan: Wisconsin Geological and Natural History Survey. Nonesuch Survey. ..a_........, WISCONSIN i-"'=".- _ ..-.. 'ACQIa1OI.U - 1--'- _1Dl ~ "",,"1UClI ~~:=... _itA IT.~ ~ "'lIlA . . . .AIDl N i ~ _u.- - vou:.uc ee.~ - 15 MI o FRda Fonft8l1on • NonnuctI Form8l1on m:m ~ Fm. HwDor ~ PortaGe LaIaI Vol. GrOUIl Figure I.I. GeologiC Geologic and and location map of the southern region. Circles of the the southem Lake Superior region. Circles identify identify cored cored sites sites (1-6) (1-6) of Nonesuch Formation Formation by by the Bear Creek Mining Company. Company. Squares Nonesuch Squares identify identify outcrop outcrop sections sections (7-20) (7-20) where where Nonesuch Map redrawn redrawn from from Elmore Elmore and others, 989, 1989, and and Allen Allen and andothers, others, inin Nonesuch Formation Formation samples were collected. collected. Map press. 61 �New Bathymetric Map of Lake Superior A New Nigel 1. Wattrus, Large Large Lakes Lakes Observatory-University Observatory-University of of Minnesota; Minnesota; Ken Keri Anderson, Anderson, University University of i. Wattrus, John Sharkey, Sharkey, Large LargeLakes LakesObservatory-University Observatory-Universityof ofMinnesota; Minnesota; and andTroy TroyHolcombe, Holcombe, Minnesota; John National Geophysical Data Center Center -- NOAA, Boulder, Boulder, Colorado. INTRODUCTION The Large Lakes Observatory is producing The producing a new new bathymetric bathymetric map map of Lake Superior using data collected by the the National Ocean Survey (formerly the U.S. Coast and Geodetic Survey) and archived by archived at at the the National National Geophysical Boulder. Colorado. This data is is supplemented with with data digitized from from earlier earlier Geophysical Data Center in Boulder, bathymetric charts to to create create maps maps that that show show detail detail never never before before attained. attained. this project project is focused focused on western western third Lake Superior, Superior. from The initial phase phase of this The initial third of Lake from Duluth Duluth up up to to the international border near Isle Royale. Subsequent phases of this project will address the central and and eastern eastern portions of the lake. lake. DATA ANALYSIS After the the data are received and remove bad data points. After received they they are carefully carefully checked checked to to identify identify and remove bad points. Maps are created using using the the GMT GMT software software system system (Wessel (Wessel and Smith, Smith. 1991) 1991) for for gridding gridding and and contouring. contouring. The The data data are to aa 3-minute 3-minute grid. grid. Figure Figure 1I shows shows an an example example of ofthe themaps maps produced. produced. This This example example shows shows the the are fit to bathymetry of of the the lake lake at its extent near near Duluth. Duluth, Minnesota. Minnesota.The The map map isis contoured contoured at at 5 m bathymetry its westernmost westernmost extent intervals. The new new map map reveals reveals details details not not previously previously seen seen in in earlier bathymetric bathymetric maps of the lake. The steep slope of of the North Shore of Minnesota exhibits irregular ridges ridges and and channels channels that that probably probably correlate correlate with with dikes dikes and and fracturing of of the contour maps. maps, the the GMT can also fracturing the basalt basalt exposed exposed on the the shoreline. shoreline. Besides Besides contour GMT package package can produce produce a variety variety of other other displays displays of of the the data. data. Figure Figure 22 illustrates illustrates an an example example of of the the shaded shaded relief relief maps maps that that GMT GMT can produce. produce. This type type of of display display can can enhance enhance low low relief relief structures structures which which are not not readily readily observed in the contour displays. In In this this particular particular example, the lake lake floor near near the the Wisconsin Wisconsin south south shore shore is shown by a tight is shown illuminated illuminated by light source source located located at 120 120 degrees degrees to the the lake. lake. The lake lake floor floor exhibits exhibits aa well well developed network of of low low amplitude amplitude ridges ridges and and furrows furrows that that trend trend approximately approximately NE-SW. NE-SW. These These features features are probably related to the glacial history of the Lake Superior region. region. CONCLUSION The GMT software system is being used to create a new new bathymetric map for Lake Superior. The new new map reveals details not not previously seen in in earlier earlier maps maps of of the the lake. lake. Subtle Subtle features features on on the the lake lake floor floor can can be be reveals details previously seen enhanced using the tools available in GMT. REFERENCES Wessel, P. and Smith, W.H.F., W.H.F.• 1991, 1991. Free software helps map and display data, EOS Trans. AGU, 72, pM!. p441. 62 �0 0 268° 30' 268 268 268° 00' J I I I rwo Harbo Harbor iTwo 47" 47° 00' 0 ~---+------+--- 47° 00' 47 -4 r ',' 0 268° 30' 268° 268 00' I, Bathymethc Bathymetric map map of ofwestern western Lake LakeSuperior Superiorbetween between Duluth Duluth and and Two Two Harbors. Harbors. (5m (5m contours) Figure 1. 0 268° 10' 268 0 268° 20 268 20' 0 268° 268 20' 268° 10' 268 0 Figure 2. 2, Shaded Shaded relief map the Wisconsin Wisconsin south shore. shore. Source of illumination illumination located 120 120 map of the lake floor near the degrees from the map. map. 63 �REGIONAL FINITE STRAIN PATTERNS IN PROTEROZOIC SLATES AND QUARTZITES: IMPLICATIONS FOR HETEROGENEOUS STRAIN RELATED QUARTZITES: TO FLEXURAL SLIP FOLDING IN THE MARQUETTE SYNCLINORIUN SYNCLINORIUM WESTJOHN, D.B., U.S. U.S. Geological Survey, Survey, 6520 6520 WESTJOHN, D.B., MI 48911 Mercantile Way Suite suite 5, 5, Lansing, Lansing, MI are part of Proterozoic rocks in the Marquette synclinorium are metasediments that extends extends from aa sequence of deformed metasediments northern Michigan (Marquette (Marquette Range Supergroup; Supergroup; MRSG) MRSG) to (Animikie Group). Group). Slates in the MRSG near Minnesota (Animikie Marquette, Michigan, Marquette, Michigan, contain reduction reduction spots, spots, sandstone dikes, and deformed dikes, deformed veins. veins. Quartzites contain conglomerates, ellipsoidal ellipsoidal spots, spots, deformed deformed veins, veins, deformed conglomerates, and grain grain aggregates. aggregates. These strain rutile needles, and experienced weak to indicators are present present in in rocks rocks that. that experienced to' substantial substantial distortions, distortions, and they were used to to characterize regional finite finite strain strain patterns. patterns. Quartzites in open folds folds show no indication of being Strains in quartzites can be strained. strains be discerned discerned where where fold 60 degrees, degrees, and the the largest fold limbs dip greater than 60 strain ratios were observed observed in in steep steep and and overturned overturned limbs. limbs. heterogeneous, and the the deformation Strains in quartzite are heterogeneous, style ranges from from slight slight constriction constriction to to slight slight flattening; flattening; strain ratios are are less less than than 1.3. 1.3. Argillites experienced experienced early early compactional strain and slight distortions related to the development of open flexures. strains in early early stages stages of of Strains must have developed in folding, because veins are buckled or stretched folding, stretched even even in in weakly deformed deformed argillites. argillites. Strains are heterogeneous, particularly along contacts between units that have large Angular shear strain estimates ductility contrasts. contrasts. AngUlar These indicate extensions locally locally exceed exceed 200 200 percent. percent. strains are localized in slate beds, and are not in beds, and are not representative for the MRSG at the regional regional scale. scale. strain Strain ratios for slates are approximately twice twice those those observed for quartzites in closed and overturned folds. in and overturned folds. The orientation of the principal strain axes in fold fold limbs to fold geometry (except near show aa consistent relation to fold geometry (except near major shear zones); zones); the XY plane is is approximately parallel to (maximum to the axiai axial trend of the Marquette Marquette trough, trough, and and X (maximum stretch) stretch) is is subvertical. subvertical. Major structural features features in in the MRSG appear to have inherited from from the the Archean Archean basement. basement. Fold geometry is is been inherited tectonics involving consistent with basement-controlled tectonics translations along faults faults and shear zones zones in in the the Archean Archean blocks. Regional strain patterns and and orientations orientations of of penetrative fabric fabric support aa heterogeneous heterogeneous strain model model that includes folding folding related related to to flexural flexural slip. slip. 64 �A STRUCTURAL AND KINEMATIC ANALYSIS OF THE McCASLIN FORMATION NEAR McCASLIN MOUNTAIN, WISCONSIN WISCONSIN FORMAnON of Geology, WILSON, Susan Susan M., M., and John S., WILSON, and KLASNER, KLASNER, John S., Department Department of Geology, Western Western Illinois Illinois University, University, Macomb Macomb Illinois Illinois 61455. ABSTRACT Located along the north edge of the Wolf Wolf River River batholith in northeastern Wisconsin is the McCaslin McCaslin Formation. Formation. The The formation formation is one of several Precambrian quartzite bodies that lie within the Penokean orogen orogen and and may may be be Penokean Penokean in age the Penokean (LaBerge, Klasner Klasner and and Myers, Myers, 1991). As the dominant foci of Mancuso Mancuso (1960) (1960) and and Olson (1982) were the the lithology and provenance of the McCaslin, our field study Olson (1982) were the lithology and provenance of the McCaslin, Qur field study addressed its structure and kinematics. Detailed structural mapping mapping was was carried on within a four-section area of the McCaslin near McCaslin Mountain. Kinematic analysis involved the identification of sense-of-movement indicators indicators in the field and of sense-of-movement the laboratory, as well as as Fry Fry (1979) (1979) analysis. analysis. the laboratory, as well Our studies Our studies showed showed the the following: following: The McCaslin 1) The McCaslin is mostly aa thick-bedded thick-bedded orthoquartzite orthoquartzite with with a conglomeratic conglomeratic unit unit at its base. generally weak absent except except along along two two newly newly discovered discovered zones zones of of 2) Foliation is generally weak or or absent intense shearing. 3) Great-circle pi plots to bedding indicate the area is folded gently toward the northeast. which diverge diverge toward toward 4) Within exposed as as two 4) Within the the study study area area the the quartzite quartzite is exposed two limbs limbs which toward' the south. overturned toward the northeast; the southern limb is stratigraphically overturned shear zone indicate 5) Fry analyses of the quartzite and c-s fabrics within the thrusting toward thrusting toward the the south in the main shear shear zone. zone. the main area of Based on on these in the area Based these findings findings we we conclude conclude that, that, iIi of study, study, the the McCaslin McCaslin We also Formation is part of a south-verging fold-thrust belt. We also suggest that the Baraboo and of the McCaslin is a part of the family of quartzite quartzite bodies that include the Baraboo and which were Waterloo, which were thrust southward southward during during convergent convergent Penokean Penokean tectonism. tectonism. This suggests that the McCaslin is pre-Penokean and significantly older than previous interpretations. interpretations. REFERENCES Fry, N., 1979, Random point distributions Fry, N., 1979, Random point distributions and and strain strain measurements measurements Tectonophysics, v. 60, p. 89-105. 89-105. 60, P. in In rocks: LaBerge, G. G. L., New observations on the J. S., and Meyers, Meyers, P. P. E., 1991, 1991, New observations on the age age and and LaBerge, L., Kiasner, Klasner, J. S., and structure of Proterozoic in Contributions structure Proterozoic quartzites quartzites in Wisconsin: Wisconsin: in Contributions to the Precambrian M. H. H. Precambriangeology geologyofofthe theLake LakeSuperior Superiorregion, region,P.P.K.K. Sims Sims and and L. L. M. Carter Geological Survey 1904-B, pp. Carter (eds.): (eds.): U. U. S. Geological Survey Bull. Bull. 1904-B, pp. B1-B18. Bl-Bl8. Mancuso, 3. structure of the the McCaslin McCaslin district, district, Wisconsin: Wisconsin: Mancuso, J. J., 1960, 1960, Stratigraphy Stratigraphy and and structure Unpublished Ph. thesis, Michigan Michigan State State University, University, 101 p. Unpublished Ph. D thesis, p. M., 1982, 1982, The The sedimentation sedimentation and and petrology petrology of of the theLower LowerProterozoic Proterozoic McCaslin McCaslin Olson, J. M., Formation, Formation, northeastern northeastern Wisconsin: Wisconsin: Unpublished Unpublished M. M. S. thesis, University of Minnesota, 106 Minnesota, 106 p. p. 65 �______________________________ _________ Volcanic Group Geochemistry of Chengwatana Volcanic Group Near Taylors Taylors Falls Falls and From Osseo Core WIRTH, Karl WIRTH, Karl R., R., and and NAIMAN, NAIMAN, Zachary, Zachary, Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN 55105,wirth@macalstr.edu 55105,wirth@macalstr.edu and and znaiman@macalstr.edu; znaiman@macalstr.edu;VERVOORT, VERVOORT, Jeff D., D., Department of Geosciences, Geosciences, University of Arizona, Arizona, Tucson, Tucson, AZ AZ 85721, 85721, vervoort@geo.aiizona.edu; andMILLER, MILLER, James, James, D., D., and and MOREY, G.B., vervoort@geo.arizona.edu; and G.B., Minnesota Minnesota Geological Survey, Geological Survey, 2642 2642 University University Ave., Ave., St. Paul, Paul, Minnesota Minnesota 55114, 55114, rnille066@maroon.tc.umn.edu and andmorey00 moreyOOI@maroon.tc.umn.edu. mil1e066@maroon.tc.umn.edu 1 @ maroon.tc.umn.edu, the composition composition and character of volcanism volcanism in the Keweenawan Keweenawan (1100 (11 00 Ma) Previous studies of the Midcontinent Rift have primarily focused on the well-exposed flow Midcontinerit flow sequences in the the Lake Superior Superior region. This This study study presents presents geochemical data of flows flows from from the the more more poorly poorly exposed exposed Chengwatana Chengwatana Volcanic Group Group of the Taylors Taylors Falls Falls region region and sampled by drill core (Osseo, Minnesota). Minnesota). Volcanic A 3000 meter thick Section of the Chengwatana Fe+2 ++Fe3 Fe+3 ++Ti Ti section the Chengwatana F' Fe2 Fi19ure gure 11 . " volcanic Group is volcamc IS exposed in ill the the Taylors Falls - St. region. This This section section isis composed composed pripriCroix Falls region. ro Taytors Falls marily of of mafic volcanic flows flows with with minor interfiow interflow Osseo Core sedimentary rock. The basalt basalt flows flows are are high-Fe high-Fe sedimentary rock. The tholelites tholeiites (Figure (Figure 1) 1) with plagioclase plagioclase phenocrysts phenocrysts and and clinopyroxene. Much Much of of the the ophitic to sub-ophitic clinopyroxene. basalt is olivine-nonnative olivine-normative or weakly quartz-nonnaquartz-normative, but olivine is not present in thin section. AbunAbunchlorite, epidote, epidote, and and actinolite actinolite inindant secondary chlorite, dicate that the group was metamorphosed that the group was metamorphosed to to Komatiite greenschist facies. facies. These These basalts basalts are are characterized characterized Mg#'s (0.58-0.37) (0.58-0.37) and and Ni Ni contents contents (185-36 (185-36 by low Mg#'s ppm) which indicate indicate that that the the flows flows have have undergone undergone Mg AI fractionation. Flows Flows near near the top of the Al significant fractionation. exposed section have lower Mg#, Ni, Cr, Cr, and and higher higher Ti0 Ti022 and and PP205 indicate that the the younger 20 S and indicate flows fractionated. Incompatible Incompatible element element abundances abundances are inversely correlated with flows are are the most fractionated. on most most variation variation plots plots can can be be grouped grouped into into highhigh- and and low trace element element groups groups (e.g. (e.g. Mg#; samples on Ti, P, Zr). The P, Zr). The basalts basalts are are enriched enriched in in the the light light rare rare o30 r=:---:-------;::===~ 00 Taylors Taylors Falls Falls Figure earth elements and Th (Figures 22 & 3), 3), but are variFigure 22 Osseo Core Core \ • Osseo relative to Ce Ce and and Th Th ably depleted in Ta and Nb relative (Figure 4). Initial Initial143NdJ1"4Nd 143Nd/ l44 Nd compositions (1100 (Figure Ma) of 1099 20 fof the the group group range range from from0.51122 0.51122 toto0.5 0.51099 (initial ENd =+0.1 0.1 to ENd = to 4.5), -4.5),but butten tenof oftwelve twelve samples samples s: have that fall have Nd isotopic isotopic compositions compositions that fall within within a . • narrow range 0 range (initial (initial ENd ENd==-1.6 1.6 to to -2.5); 2.5); flows with • •.. • 10 f-• (+0.1) and lowest lowest (4.5) (-4.5)initial initialENd ENd valval10 the highest (0. 1) and ues ues have isotopic isotopic compositions compositions that are are inversely inversely correlated with trace element abundances and ratios (e.g. (e.g. La/Yb, LaIYb, Th/La, ThlLa, ThJTa). Thffa). The The combined combined major major and trace element and Nd isotopic data suggest that °0.3 0.4 0.7 0.5 0.6 0.7 0.8 Mg# the flows at Taylors Falls originated originated by variable variable fracfrac- I a o1 -. . -. 66 �________ 4..------------------, o tional crystallization crystallization and crustal crustal contamination contamination of asthenospheric interacted with with enriched enriched asthenospheric melts melts that interacted Figure Fi gure33 o o o r~O-T-aYI-OI;-F-all-S 0 Taylors Falls -~I lithospheric mantle. U • Osseo Osseo Core Core I o 33 o More than 900 meters of of mafic volcanic flows flows q,O o were were sampled by a drill sampled by drill core core near near Osseo. Osseo. Petroo graphic features features and and major majorelement elementcompositions compositionsofof . 2 graphic o o these flows are similar to the flows from from the the Taylors .c 6'0 EoFalls are generally generally more more primiprimiFalls region except they are • ~ tive (Si02 (Si0 2 == 44-50 44-50 wt. wt. %; %; Mg# Mg# == 0.72-0.42; 0.72-0.42; Ni Ni = tive • = — 0-. 200-70 Most of ofthe the Osseo Osseo flows flows would would be be 200-70 ppm). ppm). Most • low-Ti0 2 flows flows near near Taylors Falls, grouped with the low-Ti02 OL----.....JL....---.....J ---' however some Osseo flows flows have have very very high P205 P 20 5 however some Osseo 0 200 200 300 o 100 300 (>0.39 wt. wt. %). Several Several fractionation fractionation cycles cycles can can be be Zr (ppm) Zr(ppm) recognized in the sequence and there is an an overall overall recognized trend toward more evolved of the the Osseo core similar similar to to the the trend seen in in the the evolved flows flows in in the the upper upper part part of ofOsseo Osseo and and Taylors Taylors Falls Falls flows flows plot plot Chengwatana section exposed near near Taylors Falls. Analyses Analyses of NbIY versus versus Zr/Ti02 ZrfTi02 and and Ti-Zr-Y Ti-Zr-Y and are are most most similar similar to to regions on diagrams diagrams of Nb/Y in identical regions Osseo flows flows exhibit exhibit lower lower trace trace element element abundances abundances transitional basalts and continental tholeiites. Osseo (e.g. REE, Zr, Y) and ratios (e.g. CelYb, major element element Ce/Yb, Th/La) ThJLa) consistent consistent with their more primitive major compositions On diagrams diagrams involving involving elements that are sensitive compositions (Figures (Figures 2,3 2,3 && 4). 4). On sensitive indicators indicators of crustal and mantle mantle components components (e.g. (e.g. Mg# Mg# versus versus NbINb*, NblNb*, Th-Nb/16-Hf/3; Th-Nb/16-Hf/3; Ce/Th CefTh versus versus ThfNb) ThlNb) Osseo flows are displaced displaced toward toward more more mantle mantle compositions compositions relative relative to to the the Taylors Taylors Falls Falls flows flows & 4). These features features indicate indicate that that the the melts melts sampled sampled in the Osseo core underwent less (Figures 3 & 4). These interaction with continental crust or subcontinental lithosphere than those those near near Taylors Taylors Falls. Falls. If the the Osseo flows are stratigraphically higher, higher, as suggested by their generally lower pressure metamormetamorvolphic mineral compositions (Naiman et al., this vol0.5 0.5 t 00 TJylors TaylorsFafls Falls I Figure 4 ume), then the Chengwatana Chengwatana flows might might record record aa C,Lr rust C Osseo Core Core 1• Osseo decrease in aa 'crustal' componentas asmagmatism magmatism proprocrustal component 04 0.4 ofthe the Furthermore,the theChengwatana Chengwatanaflows flows of gressed. Furthermore, Osseo core appear to contain Osseo core contain a greater greater 'depleted 'depleted 0.3 component (Figure 4). Similar Similar trends trends have have ~ 0.3 mantle' component oO~ been recognized in other Keweenawan basaltic flow ~ 02 in the the Lake Superior Superior region region (Shirey (Shirey et et al., al., Eo- 0.2 sequences in 05' • ••• 1994; Nicholson Nicholson et al., al., 1995). 1995). This may suggest that 1994; O~.'. 0.1 magmas in the later stages of of rifling rifting were were produced _N41 ORB _N-MORB Primit~ ~ : ... Primitive • •UI'• •U.• • Mantle Mantle • by melting a greater proportion of of depleted asthenosphere and that these melts underwent less contami00 80 20 40 80 60 nation during their passage through the lithosphere. Ce/Th Ce / Th - I ..—- .. ._.... ...'"• _• .,..'1 . o• • References Cited S.w., Shirey, S.B., Schulz, K.J., K.J., Berg, Berg, J.H., Kiewin, Klewin, K.W., K.W., and Green, J.C., J.e., 1995: 1995: Proceedings, Proceedings, InternaInternaNicholson, S.W., tional Project 336, 336, Meeting Meeting on on the the Petrology Petrology and and Metallogeny Metallogeny of ofVolcanic Volcanic and and IntruIntrutional Geological Correlation Project sive Rocks of of the Midcontinent Midcontinent Rift Rift System, Duluth, Duluth, Minnesota, Minnesota, 141-142. 141-142. Shirey, Klewin, K.W., K.w., Berg, Berg, J.H., J.H., Carlson, Carlson, R.W., R.W., 1994: 1994: Geochimica et Cosmochim. Acta, Shirey, S.B., SB., Kiewin, Acta, 58, 4,475-4,490. 67 � https://digitalcollections.lakeheadu.ca/files/original/de64836c611ae9690c258daa7805c96f.pdf a6f2b99ac876d5c8d466f886d58f029c PDF Text Text Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume Edited by Gene L. LaBerge Institute on Lake Superior Geology Proceedings Volume 42, Part 2 �Front Cover Aerial photo of the Flambeau mine and vicinity looking north. Flambeau Mining Company photo. © T-BO Stiios Back Cover Photo of a 4.0 cm tall twinned orthorhombic chalcocite crystal recovered from a cavity in the supergene ore. The purple patina is produced by a thin coating of bornite on the chalcocite. From the collection of F. John Barlow. Photo by Malcolm Hjerstedd, Munroc Studios, Neenah, WI. �Proceedings Volume 42, Part 2 FIRST PRINTING—MAY 1996 Publisher Institute on Lake Superior Geology Distributor Theodore J. Bornhorst do Department of Geological Engineering, Geology, and Geophysics Michigan Technological University 1400 Townsend Drive Houghton, Michigan 49931-1 295 ISSN 1042-9964 Reference to Volume 42, Part 2 should follow the example below: LaBerge, G. L., Ed., 1996, Volcanogenic massive sulfide deposits of northern Wisconsin: A commemorative volume: Institute on Lake Superior Geology Proceedings, 42nd Annual Meeting, Cable, WI, v. 42, part 2, 179 p. �Proceedings Volume 42, Part 2 Institute on Lake Superior Geology Volcanogenic massive sulfide deposits of northern Wisconsin: A commemorative volume Edited by: Gene L. LaBerge Department of Geology University of Wisconsin Oshkosh, Oshkosh, WI 54901 Published for 42nd Annual Meeting Institute on Lake Superior Geology Cable, Wisconsin May 15-19, 1996 ISSN 1042-9964 �PREFACE The mineral industry has played an important role in deciphering the local and regional geology of the Lake Superior region by gathering basic geologic information to assist in the exploration for and development of mineral resources. More than a century ago the discovery of the great iron ore resources in the Lake Superior region led to numerous studies by mining companies, government surveys, and academic institutions, providing a wealth of information on the geology of the iron-bearing districts, as well as the sedimentary sequences and the contained ore deposits. The copper deposits of northern Michigan provided the impetus for similar detailed and regional studies yielding a basis for understanding these important resources. Although research on the genesis of the mineral deposits and the regional geology is on-going, we continue to utilize much of the basic data provided by mining companies. However, relatively little information was compiled on the area of northern Wisconsin now known as the Wisconsin magmatic terranes. In the 1960s, a new concept of sulfide ore deposition related to volcanic activity — volcanogenic massive sulfide deposits — led to widespread exploration activity by numerous companies for this type of deposit in the Lake Superior region. Along with new concepts of ore deposition came new technology to aid in the search for mineral deposits. Aeromagnetic and airborne electromagnetic (EM) surveys became standard procedures, and, along with ground magnetics, EM and gravity surveys, these geophysical techniques have greatly modified both detailed and regional exploration. Drill core data provided by exploration companies has provided the "ground truth" to permit broad-scale correlation of rock units within the region. Much of these data have been made available to government surveys to permit at least a "first pass" at deciphering the bedrock geology of the "Wisconsin magmatic terranes," which are very poorly exposed because of the thick cover of glacial deposits. Although our present understanding of the geology of northern Wisconsin is an outgrowth of the efforts of many scientists, I believe it is important that we recognize the central role that the mineral industry has played. Therefore, I feel it is appropriate that all of the chapters in this volume except one were written by geologists in the mineral industry, for some of these authors represent some of the corporations and individuals who have been at the forefront of generating some of the basic data. I am confident that the data and interpretations contained in these papers will be helpful in promoting an understanding of massive sulfide deposits as well as further refining the regional geology of the Wisconsin magmatic terranes. �11 ACKNOWLEDGEMENTS This volume was conceived by Edwarde May, who thought a volume on volcanogenic massive sulfide deposits in Wisconsin would be appropriate in conjunction with the field trip to the Flambeau Mine. We all owe Ed a vote of thanks for initiating the project. Each of the authors took time from their schedule to prepare descriptions of the various deposits. I would like to acknowledge, with thanks, their efforts. I extend my thanks to Suzanne Nicholson of the U.S.G.S. who reviewed all of the manuscripts. A very special thanks to Mary Fahley, in the Geology Department at UW-Oshkosh, who undertook the task of getting all the manuscripts on one computer and formatting the volume. I really couldn't have done it without her. Proceeds from the sale of this volume will be used by the Institute on Lake Superior Geology to help fund student travel to future Institute meetings. The following organizations and individuals have made financial contributions to help defray the cost of publication of the volume, and in so doing, have contributed to future generations of student participants at Institute meetings. Thanks to each contributor. List of Contributors Flambeau Mining Company Kennecott Exploration Company Ames Construction, Inc. BHP Minerals International, Inc. Crandon Mining Company Boart-Longyear Cooper Engineering DeWitt, Ross & Stevens, S.C. Foth and Van Dyke David Hoffman Peter J. Hoffman Midwest Drilling Minnesota Exploration Association North Central Mineral Ventures, Inc. (in memory of F. H. Eisenbrey) T. D. Drilling, Inc. Wood Communications Group Ayres Associates F. John Barlow Edwarde R. May Casey Jones, Burminco Glen W. Adams Russell C. Babcock Jack V. Everett Gene L. LaBerge Paul G. Schmidt �111 DEDICATION Edward H. Eisenbrey 1926 - 1985 "Ned" Eisenbrey, to whom, along with his co-worker Jack Phillips, this volume and meeting are dedicated, can truly be said to be one of the "fathers" of the study and exploration for volcanogenic massive sulfide mineral deposits in Wisconsin. Those of us who had the good fortune to work with Ned in the Precambrian shield of the Upper Midwest and elsewhere, recognize that he had a unique talent as an ore finder, a geologist, and a teacher. In the last ten years of his life, during my close association with him as a co-worker and friend, I marveled at his uncanny, often apparently intuitive knack for sizing up a mass of geophysical data, mix it with an apparent minimum of hard geologic ground truth and to come up with targets that, in a remarkable number of cases, were not graphite, not "formational," not just pyrite, but were mineralized prospects and potential base and precious metal deposits. During his tenure in Wisconsin and Bear Creek (Kennecott) he was responsible for the initiation of drilling at the site of the current Flambeau Mine. He also recognized and proposed �iv drilling at the Thornapple site (now fittingly named the Eisenbrey prospect). Subsequently, in his year with the North Central Mineral Venture and in his capacity as a senior geologist with Earnest K. Lehmann & Associates, he recognized the mineralization of the Reef deposit and was instrumental in, among others, the discovery of the Ritchie Creek prospect and the Horseshoe deposit which was discovered on the day of his untimely death. His insight was also important in our later discovery of the Bend deposit in Taylor County. Ned was born in 1926 and grew up in Cleveland, Ohio. He attended the Staunton Military Academy in Virginia. During World War II, he enlisted in the U.S. Navy at age 17 and served in the South Pacific. He graduated in geology from Case Western in 1950 and obtained a MS from the University of Toronto in 1952. During his college summers, he worked as a surveyor on the Quebec, Nova Scotia and Labrador Railroad then being built to develop the Labrador iron mines. On graduation, he joined the American Metal Company and worked on massive sulfide deposits in New Brunswick. Later, he transferred to various other locals including Virginia, Colorado, Wyoming, and Arizona. Following the merger of American Metals and Climax to form AMAX in 1958, he was a consultant and mine operator in Arizona. In 1959, he joined Bear Creek, working first on the exploration of the porphyry copper deposit at Safford, Arizona, and later as an assistant to Paul Bailey, the President of Bear Creek. In 1963 he joined the Rocky Mountain regional office of Bear Creek and in 1967 moved to the upper midwest. Leaving Bear Creek in 1971, he first managed the North Central Mineral Venture for Superior Oil, and then joined Ernest K. Lehmann & Associates in 1975. He worked with ELA until his death in 1985. He and Elizabeth (Liz) Eisenbrey were married in 1955. They have two children, Mary and Fred. With Liz's help and the support of his family, he was able to maintain an active and full life in spite of a severe diabetic condition, which hampered him during almost all of his adult life. His interests outside of geology were strongly focused on his desire to share his knowledge and his abilities as a teacher. In this capacity, he was active in the Boy Scouts and in his church. In the later years of his life, he had a keen interest in introducing earth science teachers to geology and ore deposits. He participated in a program for this purpose at the University of Wisconsin-Platteville. Teaching came naturally to him. This skill, coupled with his acute knowledge of economic geology generally and volcanogenic massive sulfides in particular, was a gift from which all his associates benefitted. We are still indebted to him for his knowledge, his skill in applying that knowledge and his sharing it with us. Ernest K. Lehmann August, 1995 Memorial to John S. Phillips 1928 - 1987 On March 20, 1987, Jack Phillips was killed in a plane crash as he was returning from work at Andacollo, Chile, to his home in Santiago, ending an outstanding career in minerals exploration. Jack grew up on a ranch 30 miles south of Cripple Creek, Colorado, and his interest in geology may have been stirred by visits to this old mining camp. He graduated from the Colorado School of Mines in 1949, and began his professional career at the New Jersey Zinc Company mine in �V Gilman, Colorado. This was interrupted by a two-year hitch with the U.S. Army in Germany, where he met his caring and supportive wife, Danielle, a French interpreter with the Army. On returning to the U.S., he earned his M.S. degree at Syracuse, and his Ph.D. at Harvard, studying under Hugh McKinstry. Jack joined Cominco in 1960, exploring the Jerome District in Arizona, applying the volcançgenic model recently developed at Bathurst, New Brunswick. In 1965, he was hired by Kennecott to manage a drilling project near Marquette, Michigan, testing the Kona Dolomite for rhodesian-type copper deposits. At the same time, Jack was characteristically looking for other exploration possibilities, and, influenced by his Jerome experience, recognized the area west of Ladysmith, Wisconsin, as having potential for hosting volcanogenic massive sulfide deposits. Before his transfer to another assignment, Jack's enthusiasm and persistence led to Kennecott's approval of an INPUT survey, which resulted in the discovery of the Flambeau deposit in 1968. Jack continued to work for Kennecott for a number of years, mostly in the Western U.S., but including foreign assignments as well. He joined Chevron in 1978, was instrumental in bringing it into the Stillwater platinum operation, and later headed its copper exploration in Chile. Jack is remembered by those of us privileged to have known him, for his keen interest in all types of ore deposits, his enthusiastic approach to exploration, and his enjoyment in exchanging thoughts with fellow geologists. Ray E. Gilbert Englewood, Colorado �vi TABLE OF CONTENTS PREFACE ACKNOWLEDGEMENTS DEDICATION INTRODUCTION HISTORY OF EXPLORATION FOR VOLCANOGENIC MASSIVE SULFIDES by Russell C. Babcock IN WISCONSIN 1 GENERAL CHARACTERISTICS AND GEOLOGIC SETFING OF THE WISCONSIN by Gene L. LaBerge MAGMATIC TERRANES 17 A GEOLOGIC FRAMEWORK FOR EARLY PROTEROZOIC VOLCANOGENIC MASSIVE SULFIDE DEPOSITS IN WISCONSIN: AN EXPLORATION MODEL by Theodore A. DeMatties 31 AN OVERVIEW OF THE FLAMBEAU SUPERGENE ENRICHED MASSIVE SULFIDE DEPOSIT GEOLOGY AND MINERALOGY, RUSK COUNTY, WISCONSIN by Edwarde R. May and Stephen R. Dinkowitz 67 CASE STUDY OF ENVIRONMENTAL REQUIREMENTS FOR THE PERMITFING, OPERATION, AND RECLAMATION OF A METALLIC MINERAL MINE IN by Jana E. Murphy and Richard T. Dachel WISCONSIN-FLAMBEAU MINE EISENBREY: A STRUCTURALLY COMPLEX PROTEROZOIC COPPER-ZINC MASSIVE SULFIDE DEPOSIT, RUSK COUNTY, WISCONSIN by Edwarde R. May GEOLOGICAL SUMMARY - CRANDON DEPOSIT by A. J. Erickson and R. COt .... 95 107 129 THE BEND DEPOSIT: AN EARLY PROTEROZOIC COPPER-GOLD by Theodore A. DeMatties and William F. Rowell VMS DEPOSIT. 143 GEOLOGY OF THE LYNNE BASE-METAL DEPOSIT, NORTH-CENTRAL by Glen W. Adams WISCONSIN, U.S.A. 161 �1 HISTORY OF EXPLORATION FOR VOLCANOGENIC MASSIVE SULFIDES IN WISCONSIN Russell C. Babcock Chief Geologist (Retired) Kennecott Exploration Company Salt Lake City, Utah INTRODUCTION Exploration for massive sulfide deposits in Wisconsin was driven by the observation that whereas numerous base metal deposits and mines were present in the Superior Craton north of Lake Superior, none were known in rocks suspected to be of the same age south of the lake. It was assumed that the reason for this was not a lack of deposits but rather the presence of extensive glacial cover south of the lake. Therefore, exploration in Wisconsin focused on techniques that would lead to the discovery of blind deposits beneath this glacial cover. Such was the reasoning of Kennecott geologists who began the first phase of the modern era of base metal exploration and mining in Wisconsin in the early 1950's. Kennecott pursued its exploration program in Wisconsin without competition intermittently for almost two decades before announcing the discovery of the Flambeau Deposit in 1970. With this announcement dozens of competitors joined Kennecott in Wisconsin, opening a second phase of this exploration history, one of competitive and relatively unencumbered activity. This phase ended and the third phase began when Exxon announced the discovery of the huge Crandon Deposit in 1976. Within a year after this announcement the political climate changed dramatically in Wisconsin. The third phase of exploration in Wisconsin became one of difficult regulation, permitting, and taxation, made even less palatable by a sustained period of very low base metal prices. In 1993 Kennecott finally brought the Flambeau Deposit into production, and in 1995 Exxon and Rio Algom joined in an attempt to bring the Crandon Deposit on stream. Perhaps a fourth, productive phase will soon be added to this history. PHASE ONE: THE KENNECOTF YEARS Early Kennecott Exploration Kennecott established an exploration program on the Duluth Gabbro in 1951 following the discovery of copper-nickel mineralization along the Kawishiwi River in Minnesota. A few years later an office was set up in Mellen, Wisconsin, to test some copper-nickel occurrences in the Mellen Gabbro. The geologist in charge of this office, George Moerlein, began looking for massive sulfide deposits in Wisconsin in 1954, and although he found a number of iron sulfide occurrences, none contained more than trace amounts of base metal sulfides. Moerlein compiled the references to sulfides in the literature and visited the offices of the government geologists who were involved in mapping in Wisconsin and Upper Michigan. Carl Dutton, a U.S.G.S. geologist working with the Wisconsin Geological and Natural History Survey, showed Moerlein a copper-stained rock reported to have come from a hand-dug well at a schoolhouse south of Ladysmith. Moerlein could find little at the schoolhouse site other than a �2 small amount of felsic schist with some weak copper staining but with little evidence of having contained much sulfides. Kennecott flew extensive airborne electromagnetic surveys over their copper-nickel properties in Minnesota and the Mellen, Wisconsin, area in 1954. Several surveys of several lines each were also flown over sulfide occurrences in Wisconsin that were felt to have some potential for base metals. One of these surveys was flown over the schoolhouse south of Ladysmith. None gave Kennecott much encouragement and no anomalous response was seen at the schoolhouse. On the basis of this survey Kennecott assumed that the glacial overburden in western Wisconsin was probably too thick for effective use of airborne electromagnetics. In spite of this lack of encouragement, Kennecott continued to feel strongly that base metal massive sulfide deposits could be hidden under the glacial overburden in Wisconsin. Through the last half of the 1950's Dr. W. F. Read, Professor of Geology at Lawrence College in Appleton, spent a good part of his summers prospecting in northern Wisconsin for Kennecott. Using glacial till sampling (pebble counts), abundant stone fences in some areas, and mapping every outcrop he could find, Bill Read added significantly to Kennecott's understanding of the bedrock geology of Wisconsin. He found almost no base metals but mapped several areas of pyritic felsic schist. The author worked with Read for two of these summers, visiting the schoolhouse site for the first time in 1956, but like most young geologists of the time, had no understanding of what was to become the volcanogenic massive sulfide model. Moerlein recognized the potential for Rhodesian-type copper deposits in the Kona Dolomite near Marquette, Michigan, just prior to the closure of Kennecott's Wisconsin office in 1962. In 1965 Jack Phillips was hired by Kennecott to pursue this target and establish an office in the Upper Peninsula. In 1966 Phillips visited the Wisconsin Geological and Natural History Survey and U. S. Geological Survey in Madison to see if other prospects could be generated in Michigan and Wisconsin. There he "rediscovered" the copper-stained sample of felsic schist from the well at the schoolhouse south of Ladysmith, reportedly still on Carl Dutton's desk. Dutton told Phillips of showing the rock to Moerlein and some of the work Kennecott had done in Wisconsin. Fortunately for Kennecott, Phillips had spent his previous several years working on volcanogenic massive sulfide deposit exploration and was fully aware of the new model for these types of deposits developed in Canada in the early 1960's. He knew that the discovery of the major base metal deposits at Bathurst, New Brunswick, and Kidd Creek, Ontario, were the direct result of applying this new model to exploration in Canada. He recognised in the schoolhouse rock the slightly pyritic, felsic volcanic material common to the new volcanogenic massive sulfide model. When he visited the schoolhouse site a few weeks later he recognized and became very excited about the potential for finding another Kidd Creek deposit in Wisconsin. Schoolhouse became a pivotal prospect for Kennecott in Wisconsin. A review of the Kennecott files led to Read's and Moerlein's work, which in turn led Phillips to quickly recognize the presence of several pyritic felsic volcanic piles elsewhere in north-central Wisconsin. The records in Madison and some mapping indicated sulfides to the west of Ladysmith near Weyerhaeuser and at Blue Hill. Magnetic surveys run with dip needles along widespaced lines in the early 1900's by the Wisconsin Geologic and Natural History Survey indicated areas of possible "greenstone" bedrock. It was clear that a major exploration effort was justified. Phillips' experience in volcanogenic massive sulfide exploration exposed him to the newly developed INPUT system, the time-domain airborne electromagnetic system of Barringer Research. �3 This system had significantly greater resolution and depth of penetration than the system used by Kennecott in the 1950's. The success of the volcanogenic model and the INPUT system in Canada, and the confidence and enthusiasm of Phillips in and for the potential of the felsic volcanic terrain he saw in Rusk County, was sufficient for Kennecott to plan a significant program in 1967. With this new model and new technology they would try one more time to find a massive sulfide deposit under glacial cover south of Lake Superior. Flambeau Discovery Flying began in May, 1967, on a survey located just west of Ladysmith (Figure 1). The first line indicated a strong, six-channel conductor that was to become the Flambeau Deposit; the second line to the west picked up only a weak conductor. On the strength of the first line conductor, and the strong recommendation of the Geoterrex geophysicist, Don Wagg, two additional lines were flown to the east of line one, and confinned the presence of a very strong but short responsive body at shallow depth. Other anomalies were found, many of which were long and although strong, probably represented formational conductors. Wagg was convinced that the first line anomaly, called F-22, was the best and should be drilled first. It was not the first anomaly drilled, however, for reasons of land availability rather than priority. The apparent success of Kennecott's first airborne survey encouraged them to plan a second survey east of their initial one. At the same time crews were mobilized to conduct ground follow-up surveys on the better anomalies as land agreements were signed. Electromagnetic, magnetic and gravity surveys were completed at anomaly F-22 and all were strongly indicative of a sizeable massive sulfide deposit. There were no nearby outcrops which would give any clue as to the geology of the anomaly, but one outcrop of andesitic volcanics one mile to the south suggested that the right environment was present. Based on the geophysical signature Kennecott geophysicist Carl Schwenk was absolutely certain he was seeing a classic volcanogenic massive sulfide deposit. On November 6, 1968, Kennecott's first hole, drilled under the direction of Helmut Sichermann, intersected tens of feet of chalcocite mineralization hosted by pyritic metavolcanic rocks. The next few holes established F-22 as the first volcanogenic massive sulfide copper-zinc deposit to be found in the Superior Craton south of Lake Superior. The presence of thick chalcocite mineralization was a complete surprise to Kennecott, and the fact that it clearly represented Precambrian enrichment prior to the deposition of the basal Cambrian sandstone was even more intriguing. Thornapple Discovery Detailed geologic mapping and prospecting began in the Ladysmith area in 1966 and was accelerated as soon as it was apparent that the airborne survey had turned up a sizeable number of anomalies. This work identified several occurrences of felsic volcanic rocks in and around Rusk County, the pattern of which determined the lay-out of Kennecott's first airborne survey. One outcrop in particular, found by geologist Bill Spence under a railroad bridge over the Thornapple River, contained weakly mineralized iron formation. When Kennecott's third airborne survey was flown in 1969 it covered this Thornapple area, and a modest anomaly was found, but it was coincident with a local power line, railroad, and bridge, and was attributed to "culture". Responsibility for the Wisconsin project was handed over to E. H. "Ned" Eisenbrey, one of Kennecott's senior geologists, in early 1967. He was as enthusiastic about the Ladysmith area as �4 RUSK COUNTY DEPOSIT c \ BLUE HILLS \ * \WEYE RHAE U S ER RUSK COUNTY I .1 1967 INPUT SURVEY 0 Ladysmith * Proterozoic Outcrop with Sulfides Madison 0 0 2 4 6 8 10 Miles Figure 1. WITH KENNECOTT'S FIRST AIRBORNE ELECTROMAGNETIC SURVEY THE LOCATION OF MASSIVE SULFIDE DEDPOSITS AND CHIEF OUTCROPS, RUSK COUNTY, WISCONSIN �5 Phillips had been before him. He supervised the initial flying and encouraged Wagg to fly the extra lines on the F-22 anomaly. He also managed the detailed geological and geophysical work and drilling that followed. He had made a large commitment to the success of the project. As a sign of this commitment he was not about to let the Thornapple anomaly, coincident with mineralized iron formation, go untested. He and geologist Bob Stuart completed three holes in the Thornapple area before overcoming the objections of the geophysicists and securing some ground surveys. They completed a ground magnetic survey which produced a good anomaly west of the wealdy mineralized outcrop and ran one gravity line which also was anomalous. In 1970 the fourth hole at Thornapple intersected thick sulfides with intervals of copper and zinc mineralization. Kennecott had made their second volcanogenic massive sulfide discovery in Wisconsin. Momentum built in the Kennecott program and new airborne surveys continued to produce new anomalies. Broad areas were flown with aeromagnetics to locate favorable volcanics, and smaller areas were flown with INPUT (Figure 2). Land was acquired and ground surveys completed farther to the north and east. Like the anomalies near Ladysmith, most were related to formational sulfides or graphite, while others consisted of only sulfides. Some anomalies were on land that could not be acquired at the time, and were deferred for later follow-up. Surveys in the Schoolhouse area produced only weak airborne anomalies, indicating that little conductive material was present. Perhaps the 1955 survey was testing bedrock after all, but no conductors were present. Had Kennecott covered the area to the north of Schoolhouse, Flambeau might have been found thirteen years earlier. Newcomers Join the Search Kennecott announced the discovery of the Flambeau Deposit in 1970. Several companies already knew or learned then that Kennecott had discovered something new and exciting in Wisconsin, and recognized an enviromnent favorable for volcanogenic massive sulfides. Duval, Exxon, Noranda, U.S. Steel and several other companies joined the search and were flying or planning surveys by 1972. But while others were moving in, Kennecott was moving out. Late in 1971 Kennecott's exploration program suffered heavy and universal budget cuts which essentially ended the Wisconsin program. Drilling continued on the F-22 anomaly, now called the Flambeau Deposit, and at Thornapple, but all exploration in Wisconsin had ceased by the end of 1972. At this time Kennecott had flown less than half of the favorable terrane, as it was then known. In 1966 the author pointed out to an enthusiastic Jack Phillips on his first visit to the Schoolhouse prospect that the most difficult job was not to convince Kennecott that they should fly an airborne geophysical survey over part of Rusk County, but that they should continue to fly airborne surveys in Wisconsin until they found "the big one." In spite of their success, in 1972 Kennecott was leaving with the job undone. PHASE TWO: EXPANDED EXPLORATION Kennecott continued to drill both the Flambeau and Thornapple deposits over the next few years, defining reserves at Flambeau that would be developed for production in 1993, but outlining only a small, structurally complex resource at Thornapple. Detailed descriptions of these deposits will be the subject of separate articles in this volume by May and Dinkowitz (Flambeau) and May (Thornapple, now the Eisenbrey Deposit). In 1969 the job of drilling out the Flambeau Deposit was assigned to Ed May, who became and remains Kennecott's key geologist and project champion. Drilling under May's direction defined the precious metal gossan, chalcocite enrichment zone, and the underlying, classic copper-zinc �6 Kennecott Aeromagnetic Surveys DEPOSITS F Eisenbrey Flombeau B Bend E Ritchie Creek T Tomahawk P Pelican River R I Lynne C Cranclon Figure 2. KENNECOTT PRE—CRANDON AIRBORNE ELETROMAGNETIC AND MAGNETIC SURVEYS (in order flown, 1967—1971) �7 volcanogenic massive sulfide deposit. He persisted in producing excellent geologic records at a time when the outlook for the project was uncertain, a contribution which would pay off for Kennecott in the 1990's. Exxon Program Exxon was the second major company to begin a volcanogenic massive sulfide program in Wisconsin. Jim Mancuso of Exxon's Houston office became aware of Kennecott's intense drilling activity at Ladysmith in 1969 and recognized the marks of a new discovery. In 1970 he assigned Mel Erskine the task of organizing and implementing an exploration program. Erskine completed a wide-spaced airborne magnetic survey over a large area east and northeast from Ladysmith and identified several potentially favorable terrains for airborne electromagnetic surveys. Exxon also began to map and prospect the geology of northern Wisconsin in great detail, and by this means added several other target areas to their list. Paul Schmidt became Exxon's District Manager in early 1971 and took over responsibility for the Wisconsin program, and Jerry Dolence was transferred in as Project Geologist. Eleven airborne electromagnetic surveys were flown in 1971 and 1972, including one in the Tomahawk area (Figure 3). Results were equivocal and there was talk of pulling Out of Wisconsin. After all, Flambeau had already been found and was small. However, follow-up of the Tomahawk survey in 1973 led to the discovery of the small Hawk deposit which, although not commercially viable, gave Exxon sufficient encouragement to undertake additional airborne surveys, including a huge airborne magnetic survey of most of northern Wisconsin. This was used successfully to identify volcanic bedrock areas favorable for testing with electromagnetic surveys. Field geology and prospecting was expanded. This second surge of activity included a survey eastward from the Tomahawk area where a completely covered greenstone belt was inferred based on the interpretation of magnetic survey results. Airborne Magnetic Survey 1970 Airborne Magnetic Survey Miles 0 DEPOSITS F Eisenbrey Flambeau B Bend E Rjchje Creek I Tomahawk R P I Pelican River Lynne C Crandon Figure 3. Exxon Pre-Crandon airborne electromagnetic and magnetic surveys (1 = 1970, 2=1972, 3=1973, 4=post-Crandon) 50 �8 After four years and little more than a technical success to show for their efforts, Exxon decided to terminate exploration in Wisconsin in 1975. Schmidt was given sufficient funds to drill four more anomalies before wrapping up the program. One of these was a mile-long, six-channel anomaly at Skunk Lake detected in the 1974 survey east of Tomahawk. Although the anomaly was rated only as "fair" because it lacked a magnetic response, Schmidt decided it deserved a test (Schmidt, 1991). The first drill hole in this anomaly in July, 1975, discovered clearly ore-grade base metal sulfides. By July, 1976, when the details of the new Crandon Deposit were released to the public, it was apparent to the industry and the public that Exxon had found "the big one." Noranda Program Noranda was the third major player in Wisconsin. Geologic reconnaissance work began in 1968 and in 1970 Bob Miller heard Gene LaBerge talk about the rhyolites at Wausau while attending a meeting of the Institute on Lake Superior Geology, visited the area, and liked what he saw. Miller started a program right away under the direction of District Geologist Lawrence Machesky (Mudrey, et a!., 1991). Frank Condon also came down from Canada as project geologist. Several airborne electromagnetic surveys were completed in the early 1970's, including a large survey in Forest and Oneida Counties flown in 1973 (Figure 4). A large number of good-looking anomalies turned up on this survey, many of which were on County land. An agreement was reached with Consolidated Paper Company to explore their large holdings in northern Wisconsin, which gave the Noranda program a good start. A strong anomaly on the Pelican River was acquired and drilled, and Noranda had its first discovery. The Pelican River Deposit turned out to be small and of only modest grade, but it stimulated one of the longest, most continuous exploration efforts by any company in Wisconsin. Don Cross was brought in from Canadian operations in 1975 because of his volcanogenic massive sulfide experience. Figure 4. Noranda pre-Crandon airborne electromagnetic surveys (1= 1971, 2= 1973, 3-post 1974) �9 Like Exxon, Noranda completed considerable geological mapping and prospecting to supplement their airborne work, and compiled the available data. Noranda had the perceived advantage of their experience in the Noranda District in Quebec, a classic volcanogenic massive sulfide district. Miller recognized that the outcrops around Monico were what they were looking for in Wisconsin, and their work in the Pelican River area started from there and expanded outward. Every company had their own idea of what constituted favorable terrane for prospecting in Wisconsin, based on their interpretation of poorly exposed bedrock and differing views of the detailed volcanogenic massive sulfide model. Noranda was attracted to the large area of pyritic felsic volcanics around Monico. Their airborne surveys were located on the basis of geology, magnetic patterns, assumptions regarding land availability, previous exploration by competitors, and the limits of budgets. There was no sure way of knowing what areas had been flown by the competition, and there was often an overlap of competing surveys. After the announcement by Exxon of the Crandon discovery, Noranda realized that one of their surveys stopped just short of Skunk Lake. In looking over the tapes of the survey it became clear that the survey plane had made its turn over Crandon and had actually picked up a strong, six channel anomaly. Such data picked up outside the survey area is often discounted or not reported, and in this case escaped Noranda's consideration. In addition, so many responses turn up in the course of an ordinary electromagnetic survey that is unlikely that all will be checked. Coming back to these old surveys with new ideas and new models is standard procedure, and eventually paid off for Noranda at Lynne. U. S. Steel Program By 1974 both Noranda and Exxon realized that their chief competitor in the greater Monico area was U. S. Steel. U. S. Steel had been exploring in Wisconsin since the early 1950's, admittedly for iron. The U. S. Steel program was conceived by Ralph Marsden, who felt that perhaps they could find an iron deposit of higher than taconite grade in the older, more highly metamorphosed rocks south of the Gogebic Range. The field work was being directed by Cedric Iverson and consisted of relatively crude magnetic surveys, but also detailed geologic mapping and pebble counts on three-mile centers all across northern Wisconsin. Iverson used large numbers of student geologists, including at least one current authority on the geology of northern Wisconsin, Gene LaBerge. When U. S. Steel learned of the discovery of the Flambeau Deposit, Iverson was asked why he had not found it, a question many exploration managers would be asked as subsequent discoveries were announced. This was enough to stimulate the conversion of Iverson's program from iron to base metals, and by 1970 U. S. Steel was flying airborne surveys in Chippewa County. They based their priorities on their knowledge of Precambrian bedrock, pebble count results, and some semiquantitative geochemical results from soil samples taken at pebble count stations. Their program moved to Taylor, Wood, and Portage Counties, and there was no shortage of anomalies (Figure 5). U. S. Steel flew some large aeromagnetic surveys, but mostly in the search for iron formation north of the Niagara Fault. Drilling results were not encouraging, however, and the U. S. Steel crew referred to themselves as the "Pyrrhotite Kings" of Wisconsin. Of course they would drill only those anomalies with a magnetic response, a consequence of their understanding of the volcanogenic model. The U. S. Steel airborne program had moved into the area south of Monico and Crandon by 1974, again with a number of airborne anomalies but no base metals. They were gravitating to the Monico area for the same reasons that Noranda and Exxon favored the area, the abundance of sulfide-bearing felsic schist. There must have been considerable overlap of surveys, if not out and out competition for land. �10 DEPOSITS E F Eisenbrey Flambeau B Bend R Rjchje Creek T Tomahawk P Pelican River L Lynne C Crandon Figure 5. U.S. Steel pre-Crandon airborne electromagnetic surveys (in order flown, 1970-1975) When it became apparent to U. S. Steel that Exxon had a discovery at Crandon they took a look at their data for the area. Like Noranda, U. S. Steel had flown two lines over the Crandon Deposit which picked up the anomaly. One they attributed to culture and the other to topography. Part of the problem was that the airborne system that U. S. Steel was using was not as sensitive as that used by Exxon. U. S. Steel looked at their pebble count and geochemical data, too, and found that a gravel pit near Crandon had more sulfide-bearing felsic volcanic pebbles than anywhere else in the state. Hindsight is wonderful; the more difficult task is converting hindsight into foresight and carrying on. Not many succeed. Kennecott, Noranda, and U. S. Steel had all missed their chance to find "the big one." Iverson kept at it for a couple years after Crandon, but eventually U. S. Steel retired from the Wisconsin scene empty-handed. He observed that all the base metal deposits and occurrences were located along a fairly narrow east-west line from Crandon to Flambeau, with only iron sulfides on either side. It remains to be seen whether or not this "Highway Eight Lineament" has any geological merit, or whether it is merely an artifact of the exploration model of the day. Other Companies The Duval Corporation learned of Kennecott's activity at Flambeau and quickly initiated a field program in 1970, flying an area in Marinette County in 1971. This program under the direction of A. L. Barker was designed to explore an area with some favorable volcanics but little outcrop well east of Ladysmith, in an area where large blocks of County and some State land might be available �11 for leasing (Mudrey, et a!., 1991). A small, low-grade sulfide iron fonnation-type deposit was found in early 1972 after ground testing and drilling eight anomalies. Although no further discoveries were made by Duval, their technical success tended to expand the efforts of other companies into eastern Wisconsin. As many as a dozen other companies came into Wisconsin in the early 1970's; some of these are listed on Table 1. More surveys were flown, offices opened and closed, and anomalies drilled, but only small deposits or shows were found. In later years much of the data generated by these companies became available to others through joint ventures and farm-out agreements, and provided a foundation for intermittent exploration and the discovery of a few additional small deposits in the 1980's. But no more large deposits were found. TABLE 1 Companies Exploring in Wisconsin 1969 to 1976 Exxon Kennecott AMAX Superior Oil Cominco Universal Oil Products New Jersey Zinc Texasguif ACNC (INCO) Cleveland Cliffs Noranda U. S. Steel Anaconda Homestake ASARCO Phelps Dodge Cerro de Pasco Calumet & Hecla National Lead Kimberly Clark Midwest Oil General Crude Oil The political climate in Wisconsin prior to 1976 was beginning to show signs of the problems which would erupt within a year. The State recognized at the time of the Flambeau announcement that it did not have sufficient regulatory and statutory control to handle a developing base metal industry. Kennecott worked with the State to develop a set of permitting rules and reclamation regulations which, although modified, form the basis for the current legal framework. Kennecott also began to work with the legislature to develop a reasonable tax regime. Unfortunately by 1976 many of the issues surrounding mine development and taxation were moving toward discord, rather than agreement. PHASE THREE: THE PROBLEM YEARS The discovery of the Crandon Deposit was the beginning of the third phase of base metal massive sulfide exploration in Wisconsin. Exxon accelerated its program and others came into the state, or rebuilt their earlier programs. Unfortunately, the excitement of the exploration community was soon severely dampened by political events in Madison. Efforts to regulate and tax, or even stop, base metal mining were accelerated. What was perhaps a local issue involving Kennecott and the residents of Rusk County suddenly took on a new perspective. Acrimonious debate began on a new level over both economic and environmental issues. In 1976 Kennecott was denied a local zoning permit to develop its Flambeau deposit. The following year the Wisconsin Legislature enacted an untenably high tax on base metal mining. The years between 1976 and 1991, when Kennecott finally received approval for the Flambeau mine, became a roller coaster ride of off-again, on-again exploration involving intermittent political negotiations at local and state levels, compounded by historically low metal prices. �12 Kennecott Returns Kennecott attempted to resurrect the Flambeau project several times, but concern for the political climate in Wisconsin, severe financial problems brought on by depressed copper prices, opportunities in gold elsewhere, and new ownership, all impacted the project and kept it on the shelf. In 1986, Larry Mercando was assigned to the project and moved to Ladysmith, and by the late 1980's had developed a strong commitment from Kennecott management to obtain permits for an open pit, direct shipping operation. This coincided with an upturn in copper prices, the purchase of Kennecott by RTZ, and a new government attitude in Madison which was more supportive of mining. Although some of the negative concerns of the earlier years remained to be overcome, Mercando's five-year effort brought reason to the front and in January, 1991, Kennecott received the necessary state and local permits and started construction. ln May, 1993, after a brief delay for a final environmental review, based on the discovery of an unusual, wayward clam in the nearby Flambeau River, the mine was in production. Exxon Leaves Geological and engineering work progressed smoothly at Crandon following the initial drilling. Ed May was hired to manage the development drilling and produce resource and reserve estimates, and his experience at Flambeau was put to good use. By 1980 most of the technical work was in hand and it remained for the engineers and managers to develop a mine plan and get it permitted. Exxon began to encounter the same kind of political problems at Crandon that Kennecott ran into at Flambeau. Development of a reasonable mine plan was frustrated by the passage of the punitive tax law in 1977 and a series of unresolved revenue and environmental issues. These uncertainties complicated the permitting process. Although a revised tax law took effect in 1981, other issues such as local zoning were still obstacles to obtaining a permit. The political climate in Wisconsin was decidedly unfriendly. On top of this, metal prices were as low as they had been in decades. It was not a good time to try to promote a base metal mine in Wisconsin to management. Before permitting efforts could be carried forward, a decision was made by Exxon in 1986 to get out of the minerals exploration business and to divest itself of its mineral properties. Over the next several years several companies entertained the possibility of developing Crandon in joint venture with Exxon, but again a combination of poor metal prices and concern over the political risks in Wisconsin prevailed. In 1994 Exxon and Rio Algom announced a joint effort to permit and operate a scaled-down underground zinc mine at Crandon, subject to a positive feasibility report and acquisition of the necessary permits. This effort is currently in full swing and appears to be headed toward success. Governor Thompson has repeatedly supported responsible mining, and it appears that the overall political climate has changed for the better. Noranda Persists The years following the Crandon announcement were difficult ones for Noranda, as well. Carl Schwenk took over management of the program and continued to explore the greater Monico area with encouragement but no real success. Glen Adams joined the program from Exxon. In 1978 Wisconsin passed into law the Geologic Information Act which required all subsurface exploration data, whether from government or private land, to be made a part of the public record. You can imagine the concern this caused in the exploration community, given the number of companies involved and the intensity of competition. Noranda took up the cause of the industry and filed suit �13 against the state in 1979 to overturn this law. To demonstrate the seriousness of their concern for this law and the punitive tax burden, Noranda closed their Wisconsin office in 1978, although they maintained their land holdings and continued on a reduced basis to test their better targets. In anticipation of success in overturning the Geologic Information Act, Noranda reopened their Rhinelander office in 1981, and renewed their exploration efforts. They still liked, but could not acquire, the Oneida County land. Several more good grade but small size discoveries would come along, but nothing approaching economic scale. Although Noranda was frustrated by the fact that good anomalies on Oneida County land could not be acquired, they maintained their interest in them and worked with the County to develop a leasing policy. When it was announced in 1989 that there would be a lease sale, Noranda had a good idea of what land was favorable. They won the bid for land in Lynne Township and drilled their second significant discovery in January of 1990. The Lynne Deposit is a tribute to the persistence of Noranda, their faith in the volcanogenic massive sulfide model, and the importance of appreciating and using old data. New Companies Join The Search Competition continued at a high level after 1976, in spite of the adverse political environment and low metal prices. In addition to the standard base metal companies with their "go-it-alone" approach, a proliferation of joint ventures were formed. Leading the way was Ernie Lehmann who established several ventures with oil companies such as Chevron, Getty, Superior and General Crude. Ernie had been a consultant for several of these companies prior to Crandon, but became an equity partner in these new ventures. Ned Eisenbrey joined Ernie after Kennecott pulled out in the early 1970's, and Ernie attributes much of the success of these joint ventures to Ned's ability to sort out which anomalies were sulfides and which were graphite. From 1980 to 1984 these ventures added Ritchie Creek, Bend, Horseshoe, and Jump River to the list of discoveries in Wisconsin. These are small deposits, at this point, but continue to be of interest and may some day, like any of the other numerous small deposits, lead to bigger things. Opportunities still exist for those who persist. A list of some of the companies who entered the fray following the Crandon announcement are shown in Table 2. This list is probably not complete, but will illustrate the scale of interest and competition that existed, and essentially continues today. TABLE 2 Companies entering Wisconsin After Crandon AMOCO Chevron Kerr McGee Falconbridge Inspiration Newmont St. Joe Rayrock Getty Dennison B.I.A. (Mole Lake) BHP Cyprus Sharp Resources �14 PHASE FOUR: THE PRODUCTIVE YEARS Entry into the next phase of the history of massive sulfide exploration in Wisconsin is almost upon us, or may have already started. Two operating base metal mines in northern Wisconsin confirm Kennecott's original thesis of the 1950's: there is no reason why major deposits should not occur under glacial cover on the Superior Craton south of Lake Superior. Exploration now has been conducted for forty years based on this premise, by a large number of companies. North of Lake Superior new discoveries are still being made after a much longer period of exploration, using more sophisticated technology and models. There is no reason why the same persistence and approach will not be brought into Wisconsin. Many of the anomalies found in earlier electromagnetic surveys remain untested, for reasons of land inaccessibility, weaker response, or unavailability of the proprietary data. Some areas with potential may have been missed, deep targets under small, nearsurface occurrences may be developed, and clearer understanding of the bedrock geology may generate a more favorable interpretation of potential for parts of northern Wisconsin. Whatever the case, the fact that two major deposits have been found and were brought into, or are headed for, production will certainly stimulate a resurgence in exploration. Let us all hope that this fourth phase of massive sulfide exploration in Wisconsin is the smoothest, longest, and most successful. Acknowledgements A history is never complete because all the people who form it are generally not always represented in the telling of it, nor are the memories of those polled always reliable. In the case of the early volcanogenic massive sulfide exploration in Wisconsin a few of the players are still around and have given advice on this presentation of some of the history involved. Much of the Kennecott story was compiled as part of a paper authored by Michael Mudrey of the Wisconsin Geological and Natural History Survey in 1991 in which this author participated. Other comments on Kennecott's experience were solicited from Larry Mercando and Ed May. Events in Exxon's history were discussed with Paul Schmidt and Ed May. Noranda's experiences were reviewed with Bob Miller, Michael Donnelly, Carl Schwenk, and Glenn Adams. The activities of U. S. Steel were recounted by Cedric Iverson and Thon Ginn. Ted DeMatties and Ernie Lehman offered comments on the more recent exploration history in Wisconsin. All contributed to the list of players on Tables 1 and 2. Ed May and Jay Hammitt reviewed this paper and provided very constructive comment and encouragement. Exploration history is complicated by the fact that programs and discoveries are team efforts. Geologists, geophysicists, and managers at several levels all become intricately involved in the planning and implementation of any one program. All deserve a share of the credit, and the blame, as things go right and wrong. Explorationists understand that it is often external factors that force decisions that make or break a program. It is a tribute to explorationists that they persist in their optimism and enthusiasm, often for decades, in spite of the variety of obstacles they encounter. The successful but unfinished search for volcanogenic massive sulfide deposits in Wisconsin is a prime example of how talent and persistence combine to win the day, to the benefit of us all. �15 References Cited DeMatties, T. M., 1994, "Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview," Economic Geology, vol. 89, P. 1122. Mudrey, M. G., Jr., Evans, T. J., Babcock, R. C., Jr., Cummings, M. L., Jr., Eisenbrey, E. H., LaBerge, G. L., 1991, Hollister, V. F., ed., "Case Histories of Mineral Discoveries, Volume 3, Porphyry Copper, Molybdenum, and Gold Deposits, Volcanogenic Deposits (Massive Sulfides), and Deposits in Layered Rock": Society for Mining, Metallurgy, and Exploration, Inc., p. 117. Schmidt, P. G., "Discovery Case History of the Crandon Massive Sulfide Deposit, Forest County, Wisconsin, j Hollister, V. F., ed., "Case Histories of Mineral Discoveries; Volume 3, Porphyry Copper, Molybdenum, and Gold Deposits, Volcanogenic Deposits (Massive Sulfides), and Deposits in Layered Rock": Society for Mining, Metallurgy, and Exploration, Inc., P. 99. �16 �17 GENERAL CHARACTERISTICS AND GEOLOGIC SETTING OF THE WISCONSIN MAGMATIC TERRANES by Gene L. LaBerge Geology Department UW-Oshkosh Oshkosh, WI ABSTRACT The Wisconsin magmatic terranes (referred to by workers in the mineral industry as the "Ladysmith-Rhinelander volcanic belt") constitute a major addition to the Lake Superior region that formed during Early Proterozoic convergent tectoucs. Radiometric dating indicates that the volcanic and plutonic rocks were generated between 1,890 and 1,830 million years ago. Continuing geological, geochemical, and geophysical studies have allowed refinements on earlier interpretations of the general character and tectonic setting of the terranes. Available information indicates that a variety of different geological environments, including an oceanic island arc, back arc basins, and a continental volcanic arc, and perhaps other environments are represented within the area commonly referred to as the Wisconsin Magmatic terranes. Recognition of the existence of the magmatic terranes in the 1960's led to extensive exploration for volcanogenic massive sulfide deposits in Wisconsin. Geophysical surveys identified dozens of exploration targets that were subsequently drilled. These data have added greatly to the database on the volcanic belt, an area that is generally very poorly exposed because of the thick cover of glacial deposits. Three areas within the magmatic terranes contain sufficient outcrop to permit traditional geologic mapping: the Pembine area in northeastern Wisconsin, the Monico area in the central part of the belt, and the Marathon County area on the southern margin of the belt. Studies in these areas suggest that each area represents a different environment. The Pembine area contains remnants of a dismembered ophiolite and an oceanic island arc. The Monico area contains an older sequence of gneissic rock overlain by a bimodal suite of basalts and rhyolites that may represent a back-arc, or perhaps an intra-arc rift environment. This postulated rift may represent the "Highway-8" lineament, along which most of the major sulfide deposits formed. The Marathon County area contains several sequences of volcanic and plutonic rocks that appear to have a more complex origin. Some volcanic rocks belong to a basalt-andesite-rhyolite sequence that appears to be arc-related. A sequence of caldera-related rocks in the Wausau area unconformably overlies an older volcanic sequence, and appears to be a post-tectonic feature. These various environments may host rather different types of mineral deposits. INTRODUCTION In the past several decades great strides have been made in understanding the geologic evolution of the Lake Superior region. One of the major developments has been the recognition of a major belt of Early Proterozoic volcanic and plutonic rocks, named the Wisconsin Magmatic Terranes, that extends across northern Wisconsin from near Pembine, Wisconsin, westward approximately 200 miles to near Weyerhaeuser, Wisconsin (Figure 1). However, rocks correlated with the magmatic terranes are present in eastern Minnesota and northern Iowa, and the terranes extend eastward under Lake Michigan (probably to the Grenville Front). The belt is overlain by �18 930 890 880 DULUTH HINGE LINE FOR KEWEENA WAN TILTING CONTINENTAL MARGIN ASSEMBLAGE 450 44 100 MILES 150 KILOMETERS Figure 1. Generalized tectonic map of the southern part of the Lake Superior region (modified from Sims, 1992). �19 Paleozoic rocks to the east and west, and most of the belt is covered with a thick mantle of glacial deposits, with the result that much of the belt is not exposed. The northern boundary of the belt is the Niagara Fault zone (Greenberg and Brown, 1983), which separates the volcanic and plutonic rocks from the dominantly Early Proterozoic sedimentary rocks of the Marquette Range Supergroup that were deposited on the margin of the Archean Superior Craton. The southern margin of the volcanic and plutonic belt is near Stevens Point, in central Wisconsin, where Archean rocks are again present (Morey and others, 1982). Thus, the belt is about 100 miles wide. The Middle Proterozoic Wolf River Batholith cuts out a major portion of the volcanic and plutonic belt in northeastern Wisconsin. Because of the cover of glacial deposits, elucidation of the major features of the volcanic and plutonic belt has been a long-term process with major input from the mineral industry. The early compilation of geologic data by Dutton and Bradley (1970) demonstrated that outcrop density necessary for mapping was present in only a few areas: the Pembine area in the east, the Monico area about 80 miles to the west, and the Wausau area in the south. The Wausau area was mapped in 1969-1975 (LaBerge and Myers, 1983); the Pembine area was the subject of several graduate theses, and was mapped by Sims and Schulz (1993); the Monico area was also the subject of several graduate theses (Schriver, 1973; Venditti, 1973; Bowden, 1978), and was mapped by LaBerge, John Franidin, and John Klasner in 1990-199 1 (LaBerge and Kiasner, in review). However, it remained for the regional aeromagnetic survey by Karl (Zietz, Karl, and Ostrom, 1978) to provide a basis for extrapolation of data from one area to another. Detailed aeromagnetic and EM surveys and drill core data from various mining companies have provided much of the lithologic information currently available for unexposed portions of the Wisconsin magmatic terranes. The general distribution of major units within the volcanic belt was shown on the regional geologic map of Morey and others (1982). Recent lithologic, geochemical, geochronologic, and structural data permitted Sims (1992) to refine the bedrock geology of the belt. General Features of the Wisconsin Magmatic Terranes The Wisconsin magmatic terranes consist of an extensive suite of volcanic, plutonic, and associated sedimentary rocks that formed in the Early Proterozoic Penokean Orogen of the Lake Superior region. The rocks were produced during a complex convergent tectonic regime that existed from about 1,890 m.y. to 1,830 m.y. ago along the southern margin of the Archean Superior craton. A number of massive sulfides and other mineral deposits were produced during the Penokean igneous activity and tectonism. Convergent tectonics culminated with accretion of an island arc (or arcs) to the Superior Craton as well as collision of an Archean "microcontinent" of unknown dimensions with the accreted island arc. Outcrops and drill core data indicate that the most widespread rocks are massive and pillowed basalts, with localized areas of andesitic to rhyolitic volcanic rocks and associated sedimentary rocks, mainly graywackes (Figure 2). Areas of metasedimentary rocks may represent a variety of environments. Graphite is abundant in some sedimentary sequences, but is largely lacking in others. In the Pembine area the older rocks in the volcanic succession are tholeiitic basalt and basaltic andesite with associated gabbro sills (Sims and others, 1989) that comprise the Quinnesec Formation. The discovery of sheeted dikes, serpentinites, and plagio-rhyolite within the Quinnesec Formation suggests that these rocks are a dismembered ophiolite (Schulz, 1987). The tholeiites are overlain by a sequence of caic-alkaline rocks (the McAllister and Pemene volcanics, Jenkins, 1973) ranging in �20 VOLCANIC ISLAND Figure 2. Idealized east-west cross-section of the Wisconsin magmatic terranes, showing felsic volcanic centers alternating with sedimentary basins. composition from andesite to rhyolite, whose composition falls within the fields of subduction-related magmatic suites and are geochemically similar to volcanic suites from oceanic island arcs (Sims and others, 1989). Both subaerial rhyolites (volcaniclastic rocks) and subaqueous (hyaloclastite) rhyolites are present in the Pemene Formation, indicating at least periodic emergence in the area. Volcanic rocks in the Monico area comprise a bi-modal sequence of high-Al basalts and lowSi02 andesites interbedded with felsic volcanic rocks of dacite to rhyolite composition (Sims and others, 1989). The mafic rocks are massive to pillowed with pillow breccia (Figure 3) relatively common. Pillows tend to be highly vesicular. Felsic volcanic rocks are massive porphyritic flows and lithic tuffs (subaqueous?) along with some probable subaerial welded tuffs (Figure 4) (LaBerge and Klasner, in review). The bimodal volcanic sequence has generally undergone only greenschist grade metamorphism, and presumably overlies amphibolite grade rocks exposed north of Highway 8 (Figure 5). A large quartz porphyry (the Neptune Lake porphyry) is intrusive into the amphibolitegrade rocks, and may have resulted in widespread chloritization, epidotization, and quartz-feldspar veining of the overlying volcanic succession near the Pelican River deposit (Figure 6). Several massive sulfide deposits, the Pelican River, Duckblind, and Wolf, occur within the volcanic sequence, and may have formed from the fluids that gave rise to the hydrothermal alteration. The volcanic rocks are compositionally similar to the bimodal calc-alkaline rocks that host Kuroko-type massive deposits elsewhere (Sims and others, 1989) and may represent a back-arc basin. However, according to K. J. Schulz (personal communication, 1995) the composition of the Monico volcanic suite appears to be unique within the Wisconsin magmatic terranes. He suggests that the volcanic rocks in the Monico area may be a remnant of an intra-arc rift that split the Pembine-Wausau Terrane, and may be the setting of the massive sulfide deposits. This postulated intra-arc rift may account for the so-called "Highway 8 lineament" formed by the known distribution of massive sulfide deposits within the terrane. In central Wisconsin, the basaltic rocks in Marathon County are tholeiitic with compositions that are very similar to basalts of the Quinnesec Formation (Sims and others, 1989). Several large gabbroic bodies and several serpentinites are also associated with the basaltic rocks in Marathon County (LaBerge and Myers, 1983) (Figure 7). The tholeiitic sequence in Marathon County is overlain by calc-alkaline andesite to rhyolite rocks (LaBerge and Myers, 1984) that contains abundant, vaguely bedded, waterlaid tuffs and breccias and some welded (subaerial) tuffs and flows. Thus, �21 Figure 3. Photo of basaltic debris flow southwest of Monico. Wisk broom in upper right-hand portion of photo provides a scale. Figure 4. Photomicrograph of somewhat deformed felsic tuff southwest of Monico. Note the deformed quartz phenocryst near the center of the photo. Horizontal dimension of photo is 6 mm. �Xfv / — — -- Xmv——— / / / x mY // / — -,- - - - Xfv MILES - — ,. PELICAN 2 LAKE Xg — / Xmv — MON1CO / - -- Xmv XAgn Xqp —— — —P xA<j Xfv — N. — N XA9n - N N IN OS Xfv; -, XAmg " XAgn Figure 5. Geologic map of the Monico area. (From LaBerge and Kiasner, in review.) Xg Xqp .—-. - -- -.- Xfv , Xmv XAgn Xfv -- xfv X rn V —._ Facing direction of pillows XAgn—t.neissic rocks XPng-Metagabbro Early Proterozoic or Archean Xmv—Mafic metavolcanics Xfv-Felsic mtavolcanics Xmd—Metadi abase Xqp-Quartz porphyry Early Proterozoic Xg— Pink to red granite Yd— Diabase — Xfv -- - -- -- 8 —— — - -—--'- Xqp — 6 Yd Xmv'Xrn/'xrnv Middle Proterozoic LEGEND —— Xmv PELICAN DEPOSIT /Xfv —.- / ,)(Agn // , , , -— -. XAgn / / , /, / / / �23 Figure 6. Photo of highly altered basalt from west of the Pelican River deposit. Knife is four inches long. there are similarities between the rocks in central Wisconsin and the Pembine area. However, the calc-alkaline rocks in the Wausau area are chemically distinct from those in the Pembine area (Schulz, 1984; Sims and others, 1989). It is possible that the Marathon County area may have developed at least in part on an older basement, perhaps similar to the Archean rocks in central Wisconsin. This interpretation is supported by the presence of numerous Early Proterozoic intrusions into Archean basement rocks, and sillimanite-bearing quartzite xenolith in the 1,500 m.y. Wausau Pluton. The quartzite is interpreted to have been buried beneath the 1,850 m.y. volcanic rocks and subsequently carried up to its present level in the syenite pluton (LaBerge and Myers, 1984). Sims and others (1989) also suggest that volcanics in the Marshfield terrane were deposited on Archean basement. The Wausau area in central Wisconsin contains at least two distinctly different types of rhyolitic rocks. An older group of rhyolitic rocks is composed mainly of somewhat recrystallized and deformed subaqueous lithic tuffs and breccias, such as those exposed along County Hwy. J about five miles east of Wausau, and along County Hwy. A about five miles west of Wausau. They typically have a steeply dipping northeast trending foliation, with prominently flattened clasts. They are commonly interbedded with pillowed basalts, andesites, and graywackes, as shown in eastern and west-central Marathon County (fv and vs on Figure 7) (LaBerge and Myers, 1983). Locally the felsic volcanics show bleaching from hydrothermal alteration associated with significant pyritization. The younger rhyolites are subaerial welded pyroclastic flows, flow breccias, and possible rheoignimbrites along with associated volcanic sandstones and conglomerates. These rocks are �1 2 a Ninemile Granite Wolf River Batholith Diorite-Quartz Diorite Gneiss. Migmatite and Amphibolite Anorthosite Mafic Volcanics Quartz Monzonite Quartz Syeoite ARCHEAN Intermediate Volcanica Felsic Volcanics Volcanogenic Sediments IJltramatic Rocks Granite Metagabbro Mylonitic Rocks Quartzite LOWER PROTEROZOIC Syenite Nepheline Syenite MIDDLE PROTEROZOIC deposits Paleozoic and Quaternary (From LaBerge and Myers, 1983) Figure 7. Geologic map of Marathon County. The "Reef deposit" is located north of Ringle in the eastern part of the map. a WISCONSIN GEOlOGICAL AND NATURAL HISTORY SURVEY MARATHON COUNTY, WIS. OF GEOLOGY EXPLANATION �25 gently-dipping, essentially non-foliated with excellently preserved primary volcanic textures and structures. In short, they appear to be unconformable on the "older" volcanic units. Weidman (1907) named the conglomeratic units the "Marshall Hill Conglomerate", and suggested that it is unconformable on surrounding volcanic rocks. These lithologies are well exposed within the city of Wausau and in the Brokaw area south of the red granite pluton. A number of presumably normal faults offset various rhyolite lithologies within the 3M quarry at Brokaw. These offsets juxtapose lithologies unfavorable for quarrying against favorable horizons and present problems in the quarry operations. The various rhyolites consist of welded tuffs, rheoignimbrites, laharic deposits, massive flows, volcanic sandstones, and massive porphyritic rhyolite. The rhyolite flows, tuffs, and lahars may be part of a caldera complex and the massive rhyolite may represent part of a resurgent dome. In Sections 12 and 13, T.29N., R.7E and Section 8, T.29N., R.8E, just north of Wausau, a northeast-trending block of pillow basalts is in fault contact with gently-dipping rhyolite lithologies on both its north and south margins. The fault-bounded block of pillow basalts may represent an uplifted block of the older volcanic rocks on which the caldera-related rocks were deposited. The rocks interpreted as pre-caldera phases consist of basalts, andesites, and rhyolites, and typically have a well-developed steeply dipping northeast-trending foliation. In contrast, the calderarelated rhyolites are gently dipping, and are mainly non-foliated. This suggests that the proposed caMera rhyolites are unconformable on the foliated rocks and may be post-tectonic. The red granite north of Wausau truncates the several rhyolite lithologies, and may post-date the postulated caldera. In summary, the three areas with relatively good exposure appear to represent rather different environments within the volcanic belt: the Pembine area may be a remnant of an oceanic island arc; rocks in the Monico area may represent an intra-arc rift or back-arc basin; and the Marathon County area is a complex area formed during the general convergent tectonics that produced the Wisconsin volcanic belt. Areas of Economic Interest The Wisconsin magmatic terranes are the host for a number of mineralized areas, mostly volcanogenic massive sulfide deposits. Although numerous areas containing some mineralization have been identified, only a handful are large enough to be of economic interest. The richer deposits include the Flambeau deposit (in production) (May, 1977, 1996), the Crandon deposit (actively working on permitting) (Schmidt and May), the Bend deposit (continued exploration) (DeMatties, 1996), the Eisenbrey (Thornapple) deposit (continued exploration) (May, 1996), and the Lynne deposit (presently inactive) (Adams, 1996). These deposits are the subject of separate chapters in this guidebook. Some smaller deposits (the Pelican River, Duckblind, and Wolf) also occur as was noted earlier in this chapter. Because these major deposits are covered in separate chapters within this volume, they will not be described here. Deposits other than massive sulfides may also be present in the Wisconsin magmatic terranes. Examples of two other types of deposits, an epigenetic gold deposit and mineralization associated with a postulated caldera setting are discussed here. The Reef gold deposit, in eastern Marathon County, has been examined by a number of mining companies since the mid-1970s. Mineralization in the area was first recognized during regional geologic mapping in 1970 (LaBerge and Myers, 1972). At least 80 core holes have been drilled in the area in an effort to characterize the mineralization. �26 The main rock types in the area of the Reef deposit are steeply dipping mafic volcanic rocks, gabbros, and serpentines with a chemistry suggesting that they have ophiolitic affinities (K. J. Schulz, personal communication, 1995). A swarm of granophyric to porphyritic felsic dikes or sills cut the mafic rocks in the mineralized area (Kennedy and Harding, 1990). The mineralized area is one of intense deformation near the Eau Claire River shear zone and lies just west of the western margin of the Wolf River Batholith. A thick sequence of metasediments and felsic volcanics, in which massive sulfides consisting mainly of pyrrhotite have been drilled, occur just west of the gold mineralized area. Mineralization at the Reef consists of pyrrhotite, chalcopyrite and gold in silicified shear zones and quartz veins that cut the mafic volcanic rocks and gabbros. According to Kennedy and Harding (1990), the northeast-trending, northwest-dipping quartz-sulfide veins and zones of sulfideveinlets host gold, copper, silver, and tellurium mineralization in the area of interest. They state that the mineralization is closely associated with the felsic dikes and sills and that the intrusions and vein system are hosted by a granofels unit (a distinctive, biotite-rich, foliated to mylonitic rock derived chiefly from gabbro). Visible gold in quartz-goethite blocks, widely distributed at the surface, is probably the result of weathering of gold-bearing veins (Kennedy and Harding, 1990). Seven distinct zones of mineralization containing 454,600 tons grading 0.262 opt gold and approximately 0.28% copper have been identified, and the deposit is open at depth. The transgressive nature of the mineralization (in sheared gabbroic rocks) and the apparent relationship to felsic intrusions, indicates that the Reef deposit is epigenetic, and thus is distinctly different from the volcanogenic massive sulfide deposits elsewhere in the magmatic terrane. Deformation resulted in the development of numerous shear zones and mylonitic rocks similar to those illustrated in Figures 8 and 9 from the Monico area. Epigenetic gold mineralization in sheared rocks of the Reef deposit suggests that other mylonitic zones may also have potential for gold mineralization. Possible mineralization associated with the caldera-type rhyolites include the following features in the Wausau area. (1) Waste rock at an abandoned small shaft along the fault contact between pillow basalts and rhyolite along Troy Avenue in northeastern Wausau contained abundant sphalerite, some galena in a breccia zone cemented by quartz, and carbonate. (2) Numerous jasper veins and patches occur within the rhyolitic rocks in the Brokaw area. These veins appear to be jasperoid alterations of the volcanics and associated sediments and locally contain pyrite. In 1978 roadcuts for a new subdivision north of County Hwy. W on -the east side of the Wisconsin River at Brokaw exposed tuffs with rounded and angular clasts to 5 cm in a finer volcanic matrix interbedded with conglomerate to the north. The conglomerate contains clasts up to 12" in diameter. Most clasts are rhyolite, but quartzite and granite boulders are also present. The matrix of the conglomerate is mainly volcanic sandstone, with local jasperoid cement in the coarser conglomerate. Extensive epidotization of units is also common. (3) Disseminated sulfide (pyrite and chalcopyrite) in the rhyolites exposed in the railroad cuts in Gilbert Park and at the former hospital in northeastern Wausau. Tectonic Setting The general tectonic setting in which the Wisconsin magmatic terranes formed has been discussed in the literature since the mid-1970s. There is now a general consensus that the Penokean orogen formed in a complex convergent tectonic environment. Lack of subduction-related volcanic �27 U Figure 8. Photo of sheared basaltic rocks with abundant quartz veins. This lithology is transitional between massive basalt and the banded mylonite shown in Figure 9. From west of the Pelican River southwest of Monico. Figure 9. Photo of outcrop of banded mylonite that cuts basaltic rocks southwest of Monico. Hammer provides a scale. �28 rocks north of the Niagara Fault zone (the exposed margin of the Superior craton) clearly indicates that subduction was away from the craton margin. Ophiolitic rocks with associated calc-alkaline rocks in the Pembine area suggest the development of an oceanic island arc between 1,890 and 1,860 m.y. ago that docked against the Superior craton about 1,860 m.y. ago along the Niagara Fault zone (Sims and others, 1989). Schulz (1984) suggests that the arc was "evolved," or "mature," based on its chemistry. The tectonic history of the southern margin of the volcanic belt is much more equivocal. Some models suggest northward subduction, away from the Archean "microcontinent" that borders the Marshfield terrane on the south (Cannon and others, 1991) whereas others suggest a southward subduction beneath the Archean microcontinent (LaBerge, 1986). The author favors a model with south-directed subduction, but recognizes that northward subduction beneath the just-accreted island arc probably also occurred. Subduction may have been Jth north-dipping and south-dipping before final closure of the "Penokean Sea" about 1,840 m.y. ago. References Cited Adams, G. W., 1996, Geology of the Lynne Base-Metal deposit, north-central Wisconsin, U.S.A. iii Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume, G. L. LaBerge (ed.), Institute on Lake Superior Geology, v. 42, part 2. Bowden, D. R., 1978, Volcanic rocks of the Pelican River massive sulfide deposit, Rhinelander, Wisconsin: A study of walirock alteration: Unpublished M.S. Thesis, Michigan Technological University, 62 p. Cannon, W. F., Lee, M. W., Hinze, W. J., Schulz, K. J., and Green, A. G., 1991, Deep crustal structure of the Precambrian basement beneath northern Lake Michigan, mid continent, North America: Geology, v. 19, p. 207-210. DeMatties, T. A., 1994, Early Proterozoic volcanogenic massive sulfide deposits in Wisconsin: An overview: Economic Geology, v. 89, p. 1122-1151. DeMatties, T. A., 1996, A geologic framework for Early Proterozoic volcanogenic massive sulfide deposits in Wisconsin: An exploration model: iii Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume: G. L. LaBerge (ed.), Institute on Lake Superior Geology, v. 42, part 2. Duuon, C. E., and Bradley, R. E., 1970, Lithologic, geophysical, and mineral commodity maps of Precambrian rocks in Wisconsin: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-631, scale 1:500,000, with accompanying report, 15 p. Greenberg, J. K., and Brown, B. E., 1983, Lower Proterozoic volcanic rocks and their setting in the southern Lake Superior district: In Early Proterozoic geology of the Great Lakes region. Edited by L. G. Medaris, Jr., Geological Society of America, Memoir 160, p. 67-84. Jenkins, R. A., 1973, The Geology of Beecher and Pemene Townships, Marinette County, Wisconsin (Abstract), Institute on Lake Superior Geology, 19th, Madison, Wis., p. 15-16. Kennedy, L., Harding, T., 1990 �29 LaBerge, G. L., 1986, The Proterozoic geology of the Lake Superior region: j LaBerge, G. L., Attig, J. W., and Mode, W. N., Guidebook 50th Annual Tn-State Geological Field Conference, Wausau, Wisconsin, p. 1-29. LaBerge, G. L., and Kiasner, J. S., (in review), Geology and tectonic significance of Early Proterozoic rocks in the Monico area, Wisconsin: U.S. Geological Survey Bulletin. LaBerge, G. L., and Myers, P. E., 1972, 1971 progress report on mapping of Precambrian geology of Marathon County: Open file report, Wisconsin Geological and Natural History Survey. LaBerge, G. L., and Myers, P. E., 1983, Precambrian Geology of Marathon County Wisconsin: Wisconsin Geological and Natural History Survey, Info. Circular 45. LaBerge, G. L., and Myers, P. E., 1984, Two Early Proterozoic successions and their tectonic significance: Geological Society of America Bulletin, v. 95, p. 246-253. May, E. R., 1977, Flambeau: A Precambrian Supergene Enriched Massive Sulfide Deposit: Geoscience Wisconsin, v. 1, p. 1-26. May, E. R., and Dinkowitz, S. R., 1996, An Overview of the Flambeau Supergene Enriched Massive Sulfide Deposit: Geology and Mineralogy, Rusk County, Wisconsin: jj Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume: G. L. LaBerge (ed.), Institute on Lake Superior Geology, v. 42, part 2. Morey, G. B., Sims, P. K., Mudrey, M. G., and Southwick, D. L., 1982, Geologic Map of the Lake Superior region, Minnesota, Wisconsin, and northern Michigan: Minnesota Geological Survey State Map Series S-13. Schniver, G. H., 1973, Petrochemistry of Precambrian greenstones and granodiorites in southeastern Oneida County, Wisconsin: Unpublished M.S. Thesis, University of Wisconsin-Milwaukee, 83 p. Schulz, K. J., 1984, Early Proterozoic Penokean igneous rocks of the Lake Superior region: Geochemistry and tectonic implications: Abstract, 30th Annual Institute on Lake Superior Geology,Wausau, Wisconsin, p. 55-56. Sims, P. K., 1992, Geological Map of Precambrian rocks, Southern Lake Superior region, Wisconsin and northern Michigan: U.S. Geological Survey Miscellaneous Investigations Series Map I2 185. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean orogen: Canadian Journal of Earth Sciences, v. 25, p. 2145-2158. Venditti, A. R., 1973, Petrochemistry of Precambrian rocks in southeastern Oneida County, Wisconsin: unpublished M. S. Thesis, University of Wisconsin-Milwaukee, 93 p. Weidman, S., 1907, The Geology of North Central Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 16, 697 p. �30 Zietz, I., Karl, I. H., and Ostrom, M. E., 1978, Preliminary aeromagnetic map covering most of the exposed Precambrian terrane in Wisconsin: U.S. Geological Survey Miscellaneous Field Study MF-888, scale 1:250,000. �31 A GEOLOGIC FRAMEWORK FOR EARLY PROTEROZOIC VOLCANOGENIC MASSIVE SULFIDE DEPOSITS IN WISCONSIN: AN EXPLORATION MODEL by Theodore A. DeMatties Geological Consultant 10-353rd Ave. NW Cambridge, Minnesota 55008 ABSTRACT The Early Proterozoic greenstone belt of northern Wisconsin possesses some of the best volcanogenic (volcanic-hosted) massive sulfide (VMS) potential in North America. A 100-million-ton resource of base- and precious-metal-bearing mineralization, distributed in 13 or more deposits and occurrences and clustered in three districts, has been identified in the belt. Host rocks for the VMS mineralization are part of the 144 mile long, east-west trending Ladysmith-Rhinelander metavolcanic complex, which consists of various greenschists, amphibolites, cherty iron-formations, and sericite to quartz-sericite schists. These 1880-1860 Ma old metamorphic rocks are concealed beneath Pleistocene glacial cover. Development of the Flambeau mine, initiation of mine permitting for the Lynne deposit, and reactivation of the Crandon Project indicate the belt will receive a higher level of activity than in the past. Geologic and geophysical data compiled since the late 1960s define three depositional environments, each containing volcanogenic massive sulfide (VMS) mineralization in the 1880 to 1860 Ma Ladysmith-Rhinelander metavolcanic complex: (1) a main volcanic-arc sequence, the structural core of the complex; (2) laterally equivalent and/or younger(?) back-arc-basin volcanicvolcaniclastic succession that includes a series of mafic volcanic piles; and (3) major felsic volcanic centers in the back-arc basin and along the flanks of the main volcanic arc. VMS mineralization in all three depositional environments includes: (1) syngenetic and epigenetic strata-bound to stratiform massive sulfide mineralization and epigenetic strata-bound stringer sulfide mineralization within, along the flanks of, or near the top of the felsic volcanic centers; (2) syngenetic strata-bound to stratiform massive-sulfide mineralization associated with cherty magnetic iron-formation within the main volcanic-arc sequence; and (3) epigenetic stringer sulfide mineralization and syngenetic stratiform massive sulfide mineralization associated with mafic volcanic piles developed within the back-arc basin. Identified VMS deposits and occurrences are classified by metal content into three groups (Cu, Zn-Cu, Zn-Pb-Cu). Each group exhibits various styles of mineralization which include sheets, mounds, stacked lenses, and replacements. Potentially economic deposits are associated with felsic volcanic centers and sulfide-bearing meta-argillite formations that are favorable stratigraphic units deposited before, during, or after the ore-forming event(s). Stratigraphic correlations supported by lead isotope data suggest most VMS deposits in the greenschist succession formed in a narrow time interval. �32 INTRODUCTION Four potentially economic volcanogenic (volcanic-hosted) massive sulfide (VMS) deposits have been discovered in northern Wisconsin since the 1960s. Only one, Kennecott's Flambeau, is currently being developed; the Crandon deposit, with an identified resource in excess of 70 million tons, is being permitted for development by the Rio Algom-Exxon joint venture. The Lynne deposit, discovered in 1990 by Noranda, is temporarily on hold because of environmental concerns, but the Bend deposit, discovered in 1986, continues to be evaluated by Canadian junior companies Sharpe Energy and Resources and Freewest. The Precambrian of northern Wisconsin has some of the best VMS potential in North America. About 400 prospects drill-tested since the mid-1960s has resulted in discovery of four potentially viable deposits, approximately one for each 100 prospects tested. This very high success ratio has been offset by a strict state permitting process that is believed to be responsible for the slow pace of mine development in northern Wisconsin. A general geologic framework for volcanogenic massive sulfide mineralization was proposed for the western end of the belt (DeMatties, 1989). This paper is an expansion of that communication and summarizes important geologic features which characterize volcanogenic massive sulfide mineralization identified in the belt thus far. The proposed geologic framework can be utilized as both a genetic and empirical model for future exploration in the belt. However, as with all models, change is inevitable. Regional Geologic Framework of VMS Deposits in Wisconsin Regional metamorphism that developed during intense isoclinal folding has overprinted the original volcanic and sedimentary rock units in the Precambrian terranes of northern Wisconsin. This metamorphic overprinting varied in intensity, ranging from upper amphibolite facies (relict textures are totally or partially obscured and foliation, in this case schistosity, is intense) to lower greenschist facies (relict textures are well preserved and foliation development is weak). Knowledge of these metamorphic rock units and their distribution is derived mainly from geophysical patterns, drillhole data, and few bedrock outcrops. The present paper emphasizes the character of the rocks, their structural and stratigraphic setting, and interpretations of the original lithology and depositional environment before metamorphism and structural dislocation modified the original patterns. Major Geologic Terranes The VMS deposits in northern Wisconsin lie within the Early Proterozoic Penokean fold belt of the Southern Structural Province of the Precambrian Shield (Fig. 1). In Wisconsin the fold belt is divided (Greenberg and Brown, 1983; Sims et al., 1989) into two major terranes (Fig. 2). The first is the northern Penokean terrane (NP'!'), distinguished in part by a thick platformal turbidite sequence of clastic and chemical sedimentary rocks (Sims's continental margin assemblage) interbedded with subordinate tholeiitic metavolcanic rocks (bimodal suite of basalt-rhyolite). The NPT contains major oxide-facies iron-formations and some rare granitic intrusions. This supracrustal assemblage was deposited on an Archean basement and correlates stratigraphically with the Marquette Range Supergroup in Michigan. �33 La Roni Belt 200 MI Uchi 200 KM Huronian — Supergroup North Range & MUle Lacs Group . • .\ Wisconsin Magmatic Terranes (Penokean Volcanic Belt) Marquette Range S u perg roup Figure 1. Geologic provinces of the Canadian Shield, including Early Proterozoic supracrustal sequences of the Penokean Fold Belt and major greenstone belts of the Canadian Shield, including the Penokean Volcanic Belt of Wisconsin (modified from Franklin and Thorpe, 1982). �Marquette Range Supergroup Northern Penokean Terrane (NPT) CONTINENTAL-MARGIN ASSEMBLAGE Gneiss (2 800 Ma) Metavolcanic and granitoid rocks (1,835-1,890 Ma) MARSHFIELD SUBTERRANE Metavolcanic and granitoid rocks (Ladysmith—Rhinelander & Wausau Volcanic Complexes; 1,760-1,880 Ma) PEMBINE- WA USA U SUBTERRANE Penokean Volcanic Belt (PVB) WISCONSIN MAGMATIC TERRANES Anorogenic igneous rocks (1,470-1,510 Ma) A Athens shear EP Eau Pleine shear (suture) JR Jump River shear M Mountain shear D Dunbar dome Shear zone Thrust fault Figure 2. Geologic map of northern Wisconsin showing major terranes (modified from Sims, 1989). A High-angle fault and greenstone (2,600-3,550 Ma) >\' (1,820-2,100 Ma) and gneiss, granite, + Middle Proterozoic (Keweenawan) maf Ic igneous and sedimentary rocks of Midcontinent rift system (1,000-1,200 Ma) Sedimentary rocks (Paleozoic) Explanation _______ �35 The second major terrane, south of the NV!', the Penokean volcanic belt (PVB) or Wisconsin magmatic terrane, is characterized by a volcanic island-arc-basin assemblage containing abundant calcalkaline metavolcanic units (basalt, andesite, and rhyolite) and lesser amounts of deep- and shallowwater metasedimentary rocks. It lacks major oxide-facies iron-formation but contains abundant tonalite-granite intrusions. Radiometric dating by Sims et al. (1989) has established an Early Proterozoic age ranging from 1889 to 1835 Ma. They further divide this southern terrane into two volcanic-arc subterranes, the Pembine-Wausau (P-W) and the Marshfield, on the basis of lithology and structure (LaBerge and Myers, 1984). The more northern of the two, the Pembine-Wausau subterrane, was deposited during the interval 1860 to 1889 Ma and is dominated by calc-alkaline metabasalt-andesite-rhyolite with oceanic affinities and localized bimodal high-A1203 metabasalt-rhyolite suites. In the vicinity of Wausau, a younger, more restricted calc-alkaline metavolcanic succession with abundant rhyolite (LaBerge and Myers's greenschist succession) was deposited at approximately 1835 to 1845 Ma on the older succession, which is considered to be 1860 to 1889 Ma in age and is part of LaBerge and Myers's amphibolite succession. Granitoid plutons dated at 1870 to 1760 Ma, ranging from gabbro and diorite through quartz monzonite and granite, intruded the volcanic succession (Sims et a!., 1989; LaBerge and Myers, 1983). The southern subterrane, the Marshfield, is believed to represent remnants of an 1860 Ma volcanic succession that stratigraphically overlies Archean basement (Sims et al., 1989). The NPT, P-W, and Marshfield terranes and subterranes are separated from one another by two major paleosuture zones -- the Niagara Fault Zone and the Eau Plaine Shear Zone (Fig. 2) -- that are believed to represent Proterozoic subduction zones (Sims et a!., 1989). The more prominent Niagara Fault Zone is as much as six miles wide and is defined by a broadly arcuate system of ductile shears. At the exposed east end, Schulz (Sims et a!., 1989) has recognized dismembered subductionzone-type ophiolites along the fault structure, which was active from 1900 to 1830 Ma, during the Penokean orogeny. This major orogenic event also resulted in intense regional-scale folding, regional metamorphism, and emplacement of major granitic plutons. Most past and present base-and precious-metals exploration activity has been in the PembineWausau arc sequence. Wausau volcanic complex From regional gravity and magnetic data, and limited lithologic, geochemical, and structural data, at least two volcanic complexes can be defined in the Pembine-Wausau subterrane (Fig. 3). One in the Wausau area has been intruded by the Middle Proterozoic (1469±28 Ma) Wolf River Batholith and the Wausau syenite-granite plutonic series. The unintruded portion of the Wausau volcanic complex has been intensely explored since the 1960s because of its thin glacial cover and relatively abundant outcrop. The Wausau volcanic complex as mapped by LaBerge and Myers (1983), consists of an older (Archean? and lower Proterozoic- 1880-1860 Ma?) amphibolite facies sequence (quartz-feldspar gneisses and amphibolites-metabasalts) unconformably overlain stratigraphically by younger (18451835 Ma) greenschist facies, cal-alkaline mafic to felsic volcanic rock suite. The volcanic rocks were syntectonically intruded by numerous calc-alkaline epizonal plutons. The complex is characterized by a number of large, nearly vertical, cataclastic fault-shear zones which form the boundaries between greenschist and amphibolite facies sequences. �37 Several well-developed, sulfide-bearing, felsic volcanic host sequences or centers (greenschist facies succession) mapped in the complex are interpreted by LaBerge and Myers (1983) as representing in part a subaerial depositional environment. Such an environment would not be conducive for development of VMS systems and may be one reason why no significant VMS occurrences have been discovered in this complex. Rather the complex appears to be a more favorable host to gold mineralization; a number of lode gold (quartz veins) occurrences and a small (454,600 tons @ 0.262 opt Au), structurally controlled gold deposit (Reef) are known. Ladysmith-Rhinelander volcanic complex The northern portion of the P-W subterrane is occupied by the Ladysmith-Rhinelander complex, referred to informally as the Ladysmith-Rhinelander Greenstone Belt (Fig. 3). Its areal extent is at least 144 miles long and 30 to 50 miles wide, striking easterly across northern Wisconsin and into the Upper Peninsula of Michigan. Sequences of metavolcanic-volcanoclastic and associated metasedimentary rocks that have been metamorphosed to varying degrees dominate the complex. Three basic rock packages have been defined and will be discussed later in detail. The complex is covered by glacial deposits up to 200 feet thick, and bedrock outcrops are relatively rare. Unlike the Wausau Complex, the Ladysmith-Rhinelander Complex contains a number of VMS occurrences and deposits, including the potentially economic Crandon, Flambeau, Lynne, and Bend deposits. The original contact relationship between the Wausau and the Ladysmith-Rhinelander complexes is not known, but they are now in juxtaposition, their contact marked by major faults, shear zones, and granitic intrusives (Fig. 3). GEOLOGIC SETIING OF VMS MINERALIZATION IN ThE LADYSMITH-RIIINELANDER VOLCANIC COMPLEX An extensive geophysical database and abundant drillhole information compiled since the late 1960s by exploration companies and the state geologic survey has allowed mapping of broad, regional rock units that represent basic volcanic fades changes within the complex (Table 1, Fig. 3, 4a, anl 4b). Interpretations of rock units, contact relationships, and fault structures are based on magnetic and gravity patterns. Because of the thick, widespread glacial overburden, information from outcrops is limited. Three basic rock packages are defined. Each has distinctive rock types and structural setting. Further, each package contains VMS mineralization that is thought to be correlative based on stratigraphic and radiometric evidence. Main Volcanic Arc Sequence (Pinv) This sequence is characterized by the presence of magnetic and nonmagnetic amphibolite or amphibolitic schist and, to a lesser degree, quartzo-feldspathic schists. Regional metamorphic grade is high, generally reaching amphibolite rank, and as a result few relict primary textures are present. Thin, interbedded oxide-facies iron-formations (Algoma type) are quite common in the sequence and can be traced in some cases for thousands of feet. Several serpentinized ultramafic intrusions are present. �(Pfv) Felsic Center (Pvs) Basin Arc Back - (Pmv) facies iron-formation (Algoma type) ; serpentinized metasediments) - Altered felsic volcanic sequence (daciterhyodacite to rhvolitic flows, metatuffs, lapilli tuffs, cherty metatuffs, and associated chemicalvolcaniclastic (Pmvf) - Tuffaceous metasediments (metagraywackes, reworked metatuffs, chemical metasedlments) and lesser graphiteand/or sulfide-bearing meta-argillite (Pms), porphyritic and/or amygdaloidal metahasalt to meta-andesite flows (calc-alkaline and tholeiitic affinity) and subvolcanic intrusi'Jes (Ply) - Intermediate to mafic metavolcanic flows, interbedded metatuffs, tuff breccias, tuffaceous metasediments oxide - Same Same Steeply dipping, isoclinally folded to to locally gently dipping volcanic sections; northeasterly fold axes that plunge easterly are common (F-l) , more open coaxal folding locally (F-2( almandine - almandine - (amphibolite fades) - muscovite assemblages cordier ite - (lower greenschist facies( to andalusite- muscovite -albite-quartz Chlorite -epidote - fades) assemblages. muscovite -albite- quartz (middle greenschist (lower greenschist facies) to biotite- -quartz centers developed in the Ladysmith, Bend, Ritchie Creek, Lynne, Pelican Lake areas; larger felsic sequence in Ladysmith area repeated; repetition result of volcanic cycles or folding (amphibolite) succession. Major Mainly greenschist orogeny - LaBerge et al (1986) suggested that these rnetasediments may have been deposited in a number of basins formed by fault grabens during the late Penokean epidote muscovite -albite Chlorite - assemblages (lower greenschist fades) Greenschist succession, possibly a younger volcanic sequence or shallower part of Partially volcanic arc, envelops core (Pmv) Chlorite -epidotemuscovite -albite -quartz facies) assemblages (amphibolite hornblende - Aniphibolite succession, forms structural core of complex; possibly an older volcanic sequence or deeper part of volcanic arc. Dominantly kyanitesillimanite -staurolite- Steeply dipping, isoclinally folded volcanic section; WMW-NE fold axes common (F-l), and tight coaxial folding (F-2) common. Aniphibolite or Main Volcanic Arc amphibolitic schist and lesser quartzo-micaceous to quartzo-feldspathic schists; little or no relict textures preserved; interpreted as mafic metavolcanic flows, interflow tuffs and sediments, Comments Metamorphic Grade Structure Dominant Lithology Mineralization - mineralization at or near stratigraphic top of or deeper within Pfv, or along the flanks of the center; e.g., Flambeau, Bend, Crandon, and Lynne deposits. Zn- Pb-Cu-Ag) - Depositional environment Syngenetic number 1 strata-bound and stratiform massive sulfide (Cu-Au or mineralization at or near stratigraphic top of Pmvf. E.g., Kivela Zone (Ritchie Creek), Horse Shoe, Spirit prospects. (Zn-Pb-Cu-Au) Depositional environment Epigenetic number 3 stringer sulfides (Cu-Au) and syngenetic strata-bound, stratiform massive sulfide deposit. (Zn-Cu) associated with cherty magnetic iron-formation; e.g., Eisenbrey (Thornapple) (pyrrhotite -pynite) Depositional environment Syngenetic, number 2 stratiform, dominantly massive sultides VMS General Description of Regional Volcanic Facies in the Ladysmith-Rhinelander Volcanic Complex. Sequence Table 1. �a metadiorite and rnletasyenite Pmv — mafic to ultramafic volcanicintrusive complex; includes metavolcsnic flows, interflow tufts and sediments, and cherfy iron formation (if) Main Volcanic Arc Sequence CLEAR CREEK Ply — dominantly intermediate to mafic mefavolcanic flows and interbedded metetufts and tuffaceous metasediments Pmv Pmvf — dominantly intermediate to mafic metavolcanic flows and subvolcanic intlusives Pvs — dominantly tuffaceous metesediments; includes metagraywacke, bedded or reworked metatuffs, and associafed chemical metasediments Back-Arc Basin Sequence Pmv\ Pmv Pms — graphific, sulfide-bearing melaargillite formations Pm intrusives, syenodiorite -.. Metagabbro, altered ultramafic Lower Proterozoic Metavoicanic and Related Rocks -' [, Metagranite, quartz metadiorite, Pfv — dominantly intermediate to felsic mdtavOlcanic tuffa/lapilli metatuffs (lithic/ crystal) and flows, cherty metatuffs, and associated chemical mefasediments (metachert) Felsic Center(s) 0 A 0 \\ 5km DEPOSIT (Zn, P4Ag) 5 miles Reverse and normal magnetized mafic dikes (Keweenawan age) Deposit with defined reserves Prospect Shear zone —— Projected or inferred fault Contact, based on airborne magnetic data Figure 4a. General geologic map of the western portion of the Ladysmith-Rhinelander Volcanic Complex (after DeMatties, 1990). a- Lower Proterozoic Barron Quartzite Units locally covering basement metavolcanic units not shown :'': Undifferentiated Cambrian sandstone formations; thin (<50 It) sandstone Lower Proterozoic (?) Intrusive Rock Units £ Sedimentary Rock Units —— o 0, 0 0 U a C A �B 5km I I 5miles Pms__ Figure 4b. General geologic map of the east-central portion of the Ladysmith-Rhinelander Volcanic Complex. 0 I I LANG LADE — Crandon Unit Pfv (Zn, Pb, Cu, Ag, Au) CRANDON DEPOSIT (Zn, Pb, Cu, Ag, Au) MOLE LAKE PROSPECT (Zn, Cu) -RABBIT & DUCK BLIND WOLF RIVER PROSPECT �41 The sequence, which was deposited between 1880 and 1860 Ma (Sims et cii., 1989), is assigned to the amphibolite succession. Its magnetite-rich mafic composition produces a geophysical expression of strong magnetic anomalies with steep gradients and distinct gravity highs. This mappable unit forms the core of the complex and is interpreted as representing dominantly mafic flows and interfiow tuffs and sediments generated in a central to proximal submarine volcanic facies and referred to in this paper as depositional environment #2. Structurally the sequence has been complicated by steeply dipping isoclinal folding (F-i) and a pronounced second(?) refolding (F-2). This deformation has produced a fold pattern of tight, steeply plunging antiform and synform structures within the unit. VMS mineralization is known to occur in this environment. Eisenbrey (Thornapple), the only significant deposit discovered thus far, probably represents the style of mineralization that can be expected in this sequence, i.e., tightly folded, steeply plunging, syngenetic stratiform massive sulfide mineralization (stacked lenses) associated with thin cherty magnetic iron-formation. Partially enveloping the core sequence is a steeply dipping, isoclinally folded unit (Piv) dominated by intermediate to mafic, porphyritic and nonporphyritic metavolcanic flows and lesser chloritic schists, phyllites, and semi-schists. The unit is interpreted to be a sequence of volcanic flows with interbedded metatuffs, tuff-breccias, and tuffaceous sediments. Because regional metamorphism is lower grade and relict textures are discernible, this unit is assigned to the greenschist succession. A proximal subaqueous volcanic environment is indicated by the rock protoliths, insofar as it is known. Back-Arc Basin Sequence (Pvs) The back-arc basin is characterized by a steeply dipping, isoclinally folded, sequence of dominantly feldspathic, quartzo-micaceous, and chlorite schists-semischists and metachert believed to be originally tuffaceous metasediments. Rock protoliths include interbedded metagraywackes and argillites, reworked pyroclastic rocks, and chemical sediments including locally oxide-sulfide facies iron formation. Lesser intermediate to mafic metavolcanic flows are also present in the sequence. The sequence is geophysically expressed as weak to neutral magnetic anomalies and weak, broad gradient gravity anomalies. Structurally, this unit flanks the main volcanic arc and is interpreted as representing a distal subaqueous marginal volcanic basin facies. Regional metamorphism is generally lower rank than in the main volcanic-arc sequence (Pmv) and therefore the sequence can be assigned to the greenschist succession. Locally, amphibolite grade contact metamorphism resulting from thermal effects is achieved near intrusions. The metavolcanic flow units (Pmvf) within the basin facies tend to concentrate in distinct piles that can be mapped as moderately high magnetic anomalies. Drilling indicates that these units are usually porphyritic and/or amygdaloidal metabasalts to meta-andesites and associated tuffaceous and chemical metasediments. These volcanic piles are referred to below as depositional environment #3 and are associated with epigenetic stringer sulfide mineralization and syngenetic stratiform massive sulfide mineralization. Examples include the Kivela zone at the Ritchie Creek prospect, the Spirit occurrence and the Horse Shoe deposit. An important series of units within the basin facies and also the Piv unit of the main volcanic arc facies are the meta-argillite formations (Pms) which are described later in detail. These units are �42 characterized by their distinct linear electromagnetic anomaly patterns, which allows them to be used as mappable marker horizons. These key formations are intimately associated with all the potentially economic VMS deposits. Felsic Centers (Pfv) The felsic centers have been defined by drilling and identified in some outcrops, particularly toward the east end of the complex; but their magnetic expression is neutral and cannot be readily distinguished from metasediments or granitic intrusives in covered areas. Thus the exact areal extent of most of the centers is poorly known. Extensive drilling indicates that the centers are steeply to moderately dipping sequences dominated by strongly to weakly metamorphosed and sheared quartz±feldspar-sericite-chlorite schistssemischists (commonly crystal and/or fragment-bearing) and metacherts. Protolithologies include altered dacitic to rhyolitic metavolcanic flows, pyroclastic rocks, and associated chemicalvolcaniclastic metasediments. Mafic to felsic subvolcanic intrusions, feeders for the volcanic units, may be quite abundant. In several centers such as those hosting the Flambeau and Lynne deposits, large intrusions which may or may not be related to the volcanic activity have either disrupted or cut out significant portions of the felsic sequences. At Lynne, post-intrusive activity is so extensive that the host volcanic section occupies an embayment of a large tonalite pluton. Lesser interbedded mafic metavolcanic suites are almost always present in the felsic centers, resulting in a bimodal sequence. The sequences are interpreted as proximal subaqueous felsic volcanic pile facies and designated depositional environment #1. This environment hosts massive syngenetic stratiform and epigenetic strata-bound massive to stringer sulfide mineralization which occurs within (e.g. Flambeau, Bend, and Crandon), along the flanks of (e.g. Lynne), or near the stratigraphic top (e.g. Ritchie Creek main zone) of felsic volcanic centers. Host rock units are generally hundreds of feet thick, range in composition from quartzsericite schist (felsic tuffs, e.g. Flambeau and Bend) to chioritic schist (argillite, e.g. Crandon), and may contain abundant chemical sediments (chert and carbonate-rich exhalites) which can overlie the syngenetic stratiform mineralization (e.g. Flambeau and Bend), or are interbedded with it (e.g. Crandon). Although the locus of VMS mineralization within a center commonly occurs at breaks or changes in volcanic activity, there is not yet enough information to link mineralization to specific volcanic cycles within the centers. Hydrothermal alteration associated with VMS mineralization in the centers includes sericitization, silicification, and to a lesser extent, chloritization. Limited immobile trace element studies (Lavery, 1985, and DeMatties and Rowell, 1991), indicate that widespread intense silicification (silica enrichment) may be responsible for many of the dacitic to rhyolitic compositions found in some of the centers. At least seven major centers are known in the complex, four of which host the four potentially economic deposits. Other deposits or occurrences hosted by this environment include Pelican River, Catwillow, Wolf River, Spirit, Hawk(?), School House, and Clear Creek. The known centers are assigned to the greenschist succession and are located within the back-arc basin or along the flanks of the main volcanic arc. �43 DISTRIBUTION AND CLASSIFICATION OF MASSIVE SULFIDE MINERALIZATION To date about 100-million-short-ton resource (80 million short tons of potentially economic reserves) of base- and precious-metal massive sulfide mineralization, in 13 or more deposits or occurrences, has been discovered in the Ladysmith-Rhinelander Volcanic Complex (DeMatties, 1989; DeMatties and Mudrey, 1991) (Fig. 5 and Table 2). (All tonnages herein are in short tons.) The world-class Crandon deposit accounts for approximately 72 percent of this total. The remaining tonnage is distributed among 12 or more occurrences and deposits whose average size is approximately 2.5 million short tons. Only four deposits are believed to be potentially viable economically; the largest is Crandon, containing an identified resource of 72.5 million tons. Next are Lynne, with a resource of 7.5 to 8 million tons (a mining reserve of 6.7 million tons), and Flambeau, with a resource of 6 to 7 million tons (a mining reserve of 1.9 million tons). The fourth is the Bend deposit, which contains a reserve base of 3.7 million tons. Further exploration on other deposits could expand their size and define potential mineable reserves. The obvious gap in size between these deposits is dramatized in Figure 5. This lopsided distribution may be a function of exploration having been focused on a particular deposit or area. Table 3 compares the known Wisconsin tonnage distribution with other VMS provinces and belts. Assuming the tonnage distribution for Wisconsin VMS deposits will define a natural geometric progression similar to those in other greenstone belts, and given the large size of the complex (approximately 5700 square miles) as well as the Penokean Volcanic Belt (approximately 19,000 square miles), additional deposits with mineable reserves in the 10- to 60-million-ton range are likely to exist. Current knowledge suggests that the known VMS deposits and occurrences are concentrated into three clusters or districts within the Ladysmith-Rhinelander Volcanic Complex (Fig. 6). The spatial distribution of the three districts appears to be linear, trending in an east-west direction (the socalled Highway 8 trend), with deposits separated by 20 to 30 miles. However, a more complicated arrangement of individual deposits and occurrences is evident within each district. Massive sulfide deposits and occurrences may be classified by ratios of principal metals into groups of copper deposits, zinc-copper deposits, and zinc-lead-copper deposits. Because of its simplicity, Solomon's classification scheme, as modified by Huston and Large (Large, 1992), has been used in classifying Australian VMS deposits and has been adopted in this paper (Large, 1992). This classification is based upon principal metal ratios (Cu/Pb/Zn), and by use of a copper ratio (100 Cu/Cu+Zn) and a zinc ratio (100 Zn/Zn+Pb). Under this scheme, the Wisconsin deposits can be categorized (Fig. 6) into the following groups: 1. Cu deposits: Cu ratio > 60, Zn ratio > 60; e.g., Flambeau, Bend, Ritchie Creek (Main Zone). 2. Zn-Cu deposits: Cu ratio < 60, Zn ratio > 90; e.g., Crandon, Thornapple, Pelican River, Catwillow, and Hawk. (1) The terms "resource", "reserve", "reserve base", "indicated", and "inferred" are used herein as defined in USGS Circular 831, 1980. �0.1 II I 10 I I I 100 II III Medium to iarge (10-60 million st) deposit(s) World-class remaining to be VMS deposit d iscovered* which might be discovered 'C 11111111 1o ':3 0 l- iI Millions of short tons (st) 1 11111 Tonnage classification: ++ Geologic Reserve Base (drill indicated & inferred) + Identified Resource (drill indicated and/or inferred) (* The Duval deposit (10 million st) in Marinette County is considered a sulfide facies iron formation and not a typical VMS deposit in the belt.) deposit with mineable reserves ® Potentially economic VMS ICb 40' 0 0 1< CD5 CCD o (D E. C C) Figure 5. Current (1992) tonnage distribution of known VMS deposits and occurrences in the Wisconsin Penokean Volcanic Belt. 1 5 10 50 100-:: )c �- Prospect 2.9 1.5 Prospect Prospect Catwillow Hawk Prospect N + - 1% Cu 2.76% Zn 5.31% Pb 100 Cu/Cu+Zn 100 Zn/Zn+Pb 1991 prices @ § Calculated from average grade of deposit Geologic reserve base Average grade of deposit 0.9 ? ** * (Main Zone) BLM preference right lease Ritchie Creek in 1993 Application made for Bend Flambeau Under development6 to 7 operating mine 0.74 Prospect Horse Shoe Cu Type 7.5 to Mine permitting on hold Lynne Zn-Pb-Cu Type 2.2 Prospect 3 Pelican (Thornapple) Eisenbrey 72.5 Total Resource Identified (million st) - 3.7 (1990) 0.045 opt Au (1989) - 5.33 opt Ag 2.11 (1.49 (4.1 (1972) 10.5 1.9 2.45 (1990)! -- 6.7 (1992) 0.64 -- trace trace 0.9 1.65 - - approx 0,5k 8 -- 1.5 0.8 present -- 0.48 -- - Pb (%) 1.0 1.5 (1.04 (%) Cu -- -- (1979) 67.4 Drill' indicated Reserved (million st) 0.37 0.010 present 0.3) 0.88)* 0.10 2.1 0085 1.05 0.10 006 245 2.45 3.77 13.78 6.54 6.07 5.06 1.77 0.023 2.96 0.45 2.7 2.8 4.13 Grade' present L00 trace Copper- equivalent 0.02 0.51 trace l,25)* )opt) Ag present trace trace 0.035 (opt) Au 1.60 535 870 2.7 2.60 4.50 34 556 (%) Zn Tonnages and Grades Reported for Wisconsin VMS Deposits 0.5 million Tons or More in Size. Mine permitting in progress Status Total-resource Crandon Zn-Cu Type Deposit Table 2 85 100" SO.5 31.4 6.9 22.9 36.6 18.2 29.4 15.8" Cu Ratio 100 100" 100** 85.5 ,, 84.1 100 100 100 100 92.05** Zn Ratio �38.5% Southern Province Penokean Volcanic Belt (Proterozoic) Kuroko Provence (Miocene) (Paleozoic) Tasman Geosycline (Proterozoic) Central Volcanic Belt 80.0% 33.0% 92.9% 59.0% Churchill Province Fun Flon, Lynn Lake, LaRonge Belts (Proterozoic) *Includes reserves and/or identified resources •*Includas total number of deposits Australia Arizona 33.0% Slave Province Hackett River, Elu Inlet, Black River, Cameron River, Besulleu River Belts (Archean) 42.0% Su,erior Province Abitjbi, Wawa, Wabigoon Belts (Archean) (0.1-1.1) 0.1-1.0 1.8% 57.1% 5.7% 54.0% 34.0% 58.7% 43.0% 1-10 (1.1-10.1) 7.7% Ruttan (40.7 ml) Flon (57.5 mt) 1.6% (30 mt) Motoyama (15 ml) Matsutnine (16.0 ml) Hellyer (19.4 tnt) 7.1% Rosebery United Verde (72.7 mt) 1.4% Crandon (65.8 ml) Elm Fox Lake (13.2 mt) 7% Izok Lake (13.4 mt) 8.3% Mattaganni Lake (19.6 mt) Louvicour t (24 mt) 13.8% 10-100 (10.1-101.1) st) 1.0 tnt (1.1 st) less than (3.0 st) 2.7 mt (1.1 st) less than 1.0 St (2.5 2.3 tnt 1.60 tnt st) (1.80 )3.1 at) 2.8 ml 1.65 mt (1.83 st) Median Size 126 42 70 13 44 12 72 Number of Deposits Data from Franklin and Thorpe, 1982, Large, 1990, and Lindberg, 1989. 0% 2.4% Mt. Lyell (119.9 mt)** 0% 0% 0% 0% (140.95 mt) Kidd Creek 1.4% 100* (101.1.) Arizona, Australia, and Japan Militons of Metric Tonnes Short Tons)* ComparisOn of Tonnage Distribution of VMS Deposits in Canadian Shield (including Wisconsin) (as percentage of deposits in each size range) - Canadian Shield Table 3. �0 I' N type ZnPb-Cu Shoe A Horse / Zn Thornapple Hawk Pelican River Catwi Plow Zn-Cu type Ritchie Creek (Main Zone) IFlambeau I type Cu Figure 6. Weight proportions of base metals in Wisconsin VMS deposits (after LaBerge, 1992). Pb CR = 100 Cu Cu + Zn ZR = 100 Zn Zn + Pb 0 Cu type • Zn-Cu type A Zn-Pb-Cu type Explanation IBend I Cu �48 3. Zn-Pb-Cu deposits: Cu ratio < 60, Zn ratio = 60 to 90; e.g., Lynne, Horse Shoe. The general mineralogy of each deposit type is given in Table 4. An analysis of these data shows that, in general, the largest Cu deposits (Flambeau and Bend) occur in the Ladysmith district, at the west end of the complex. Zn-Cu and Zn-Pb-Cu deposits become much more prevalent in the Somo and Crandon districts. Along with this change in basemetal ratios, both gold and silver content change from the Ladysmith district (high gold, low silver) to the eastern Somo and Crandon districts (high silver, low gold) (Fig. 7). These changes in metal ratios and content between districts give rise to a broad regional zoning pattern with generally copper- and gold-rich deposits (Cu type) toward the west, in the Ladysmith district, and zinc-rich (Zn-Cu type) deposits toward the east, in the Crandon district. Telescoping or overlapping of deposit types (Cu, Zn-Cu, and Zn-Pb-Cu) occurs in the centrally located Somo district. These zoning patterns may be more apparent than real, and may be a function of exploration and discovery. However, if they are real, the variable metal ratios may indicate a progressive or systematic change in hydrothermal fluid chemistry (i.e., temperature, f02, pH, salinity), and discharge site conditions (i.e., original composition and permeability of stratigraphic footwall unit(s), and seawater depth). The average tonnages and grades of the three deposit types are listed in Table 5 and compared with other VMS districts in the world. Although the number of Wisconsin deposits is limited, the table does suggest that the Cu deposits are above average in copper grade and gold content when compared to other Cu deposits in the table. The Wisconsin Zn-Cu and Zn-Pb-Cu deposits as a whole contain relatively average base- and precious-metal grades, but generally lowerthan-average tonnages if Crandon is excluded. Styles of Wisconsin VMS Mineralization At least seven styles of VMS mineralization have been recognized in the P-W subterrane. These include the following: Layered Sheet Thus far only the Flambeau deposit (Cu type) is known to exhibit this style within depositional environment #1. It is characterized by an extensive copper rich sheet of stratiform, syngenetic, layered massive sulfide with minor zinc-pyrite lenses and gold-bearing chert in the stratigraphic hanging wall. No well-developed epigenetic alteration pipe or stringer sulfide zone is present. However, a widespread laterally extensive sericite-disseminated pyrite alteration halo is developed mainly in the stratigraphic footwall rock units but also extending into the hanging wall as well (Figs. 8a and 8b). Sulfide deposition for this style may be related to poorly focused, lower temperature (<300 degrees C) hydrothermal fluid flow (Large, 1990). �Sphalerite, pyrrhotite, galena, pyrite, chalcopyrite Zn—Pb—Cu (± tetrahedrite, polybasite, native silver, pyrargyrite electrum, native gold) arsenopyrite, tetrahedrite— tennantite (± marcasite, electrum, covellite, chalcocite) Pyrite, pyrrhotite, sphalerite, chalcopyrite (± galena, magnetite) Zn—Cu chalcocite, bornite tennantite, gold tellurides, lead telluride, electrum, native gold, arsenopyrite, sphalerite (± galena, magnetite, pyrrhotite) Pyrite, chalcopyrite, tetrahedrite — Cu Type Minor Minerals Lynne Crandon Ritchie Creek Kennedy et al., 1991 Lambe & Rowe, 1987 May, 1977 DeMatties & Rowell, 1991 DeMatties, l99O Fl ambe au B end References Examples Summary of the typical ore-related opaque minerals in Cu, Zn—Cu, and Zn—Pb-Cu VMS deposits in Wisconsin. Major Minerals Table 4. VMS in Wisconsin �0 2 I 6 I 8 I I 10 I Lynne A 12 0 0 Cu type S Zn-Cu type Explanation (Cu + Pb + Zn) % 4 I .s. A 0 0 2 0Bend I 6 I Catwillow 8 I Flambeau , , o /// Shoe ,1 A I 10 I ' A Horse S Crandon (Cu + Pb + Zn) % 4 / A Zn-Pb-Cu type 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Lynne Figure 7. Variation in Au and Ag content with base-metal content for the Cu, Zn-Cu, and Zn-Pb-Cu VMS deposits in Wisconsin. I o Ritchie Creek Catwillow 0.02 .s. Horse Shoe Flambeau Crandon5 0 Bend 0.04 0 0.06 0 c 0.08 0.10 0.12 2.4 2.6 12 �Number of Deposits (%) Cu tonnage 5 2 Zn-Cu Zn-Pb-Cu 1 Zn-Pb-Cu 20 0.6 17 1 Zn—Cu Zn-Pb-Cu 17 0 0.0 0.2 2.0 1.2 1.6 1.0 10 Zn-Pb-Cu 10 0.5 4.7 6.9 11.8 1.6 1.1 4.7 1.7 11 Zn-Pb-Cu [Cu! (Cu+Zn) 1100 3. average Ag Au 0.01 0.02 0.02 0.01 0.04 0.09 0.04 0.01 0.06 0.02 0.05 0.0 0.0 3.5 Million Short Tons Zn 100 Ratio 13.6 3.6 3.7 8.4 9.1 13.9 20.9 5.7 3.5 15.7 2.2 17.3 5.9 3.7 82 100 87 72 93 85 86 98 100 71 88 98 100 84.8 2.4 100 (Crandon not included) 0.03 0.09 (opt) Au ani g grades. 2.81 1.71 0.15 3.39 1.77 0.23 0.06 0.06 1.8 6.2 1.1 0.26 1.75 0.48 0.43 (opt) 4. Close clusters or unit orebodies of Kuroka deposits are grouped as single deposits. Data for all deposits other than Wisconsin are from Large, 1992. [Zn/(Zn+Pb)JlOO 2. 1. Number of deposits for wtiicfl data are available to calculate 1 0.0 3.8 1.3 2 Zn-Cu 3 2 0.0 0.2 1.1 4 (Tertiary) 1.0 3 0.0 0.2 1.3 Cu Tuff Belt4 4 Zn-Cu Jananese Green 16 Cu 14 7 0.0 19 0.5 2.2 1.9 Australian Deposits (Archean-Paleozoic) 7 Cu 5.5 1 1.4 10.0 2.7 Norwegian Caledonides (Paleozoic) Zn-Pb-Cu 34 0.1 3.7 1.5 6 2 0.0 1.3 7.0 1.6 2 0.8 0.5 3.8 1.2 2 Note1 1.8 trace (%) Pb 0.5 (%) Zn and grade data of Wisconsin and other VMS deposits. 2.6 Bathurst Camp (Paleozoic) 36 Zn-Cu Canadian 7 Cu Canadian Archean Deposits 3 Cu Wisconsin Deposits (Proterozoic) Deposit Type Table 5 — Comparison of mean VMS in Wisconsin 2 27 26 84 8 19 85 45 43 79 9 21 28 69 19.2 26.8 88.5 Cu Ratio �NW 250 Cholcopyrite CJ)5 na ted cosson U- VAt. u ES SE I Enrichment Supergene Base of Au Figure 8b. Schematic cross-section showing zonation patterns - Flambeau (after May, 1977). C,) EE 00 >, U) > U) :0 CU) U) 0) (Cove lute) Bornite 00 O C .C U) Chalcocite Oxide (I'- .10-20 Leached Sandston GociaI Overburden J30 600 j B ________Saprolite _________ �53 Bedded sheet plus strata-bound stringer zone This style of mineralization is similar to the layered sheet, except a well defined copper-rich strata-bound epigenetic stringer zone is present and extends the full length stratigraphically below a main massive zinc-lead horizon. This style of VMS mineralization commonly forms between volcanic cycles in sedimentary host units such as argillites and is characteristically developed by giant (>55 million st) VMS deposits such as Crandon (Zn-Cu type), which is hosted in depositional environment #1. Sulfide deposition may be related to hot (>300 degrees) poorly focused hydrothermal fluids moving through a permeable footwall rock package (Large, 1990). At Crandon the stratigraphic footwall consists of a series of breccia (debris flow) lobes (Fig. 9). This style is also represented in depositional environment #3 by the high-grade Horse Shoe (Zn-Pb-Cu type) deposit which exhibits a semiconformable stringer zone. Stacked lenses Most identified Wisconsin VMS deposits assume this style, in which massive sulfide lenses develop at several stratigraphic levels and are connected by zones of fragment-bearing semimassive sulfides, stringer mineralization, or intense alteration with disseminated sulfides. Metal zonation and/or upward base-precious metal refining from the lowermost lens to the upper lens is common. Depositional environment #1 (greenschist succession) frequently hosts this style of mineralization as exemplified by Bend (Cu type) (Fig. 10), Pelican River (Fig. 11), Hawk, Wolf River(?) and Catwillow (all Zn-Cu types). Only the Eisenbrey (Thornapple) deposit and possibly one other occurrence (the Fence prospect) are known to exhibit this style of mineralization in depositional environment #2 (amphibolite succession). Massive sulfide mound This style is not common in the P-W subterrane; only the Kivela zone (Zn-Cu type in depositional environment #3) at the Ritchie Creek prospect has been reported to exhibit this classic style. It is characterized by a mound-shape, syngenetic massive-semimassive sulfide accumulation which is stratigraphically underlain by a crosscutting epigenetic stringer sulfide-chiorite-sericite alteration zone. Vertical metal zonation from a copper±zinc±lead rich stringer zone to a zinc±lead±copper rich massive-semimassive zone is evident (Fig. 12). The footwall sericite-pyrite (pyrrhotite) alteration halo is generally limited in aerial extent. This style develops when hydrothermal fluids are well focussed along a syn-volcanic structure and through a relatively impermeable footwall sequence such as the mafic flows present at the Kivela zone (Large, 1990). Sulfide mound replacement Generally a thick mound-shaped, epigenetic sulfide accumulation which forms as a result of successive, subsurface replacements of previously deposited exhalite (commonly carbonate and/or chert rich). Vertical metal zonation pattern from a copper-rich base to a zinc-lead-silver top is strong. The Lynne deposit (Zn-Pb-Cu type) in depositional environment #1 is reported to exhibit this style of mineralization (Fig. 13). The replacement mound style may develop from hot (>350 degrees C) well focussed hydrothermal fluids (Large, 1990). �Footwall •1 0 0 S — -200rn o 400 I 200 meter, 800 tee, lopilli luff coarse tuft - S 0 0 C GaciaI Overburden orgillite Breccia lobes Il & Ill Stringer sulfide mineralization Massive sulfide mineralization Carbonaceous-pyrilic argitite and tuft Crandon Unit: Explanation Crondon Unit Hangingwall fluffs cherl and debris flows) Slraligraphic Top I0 S S Figure 9a. Geologic cross-section 94360E - Crandon (after Lambe and Rowe, 1987). uoo I — 0 See L,,et 0 4, 0 0 S (tufts and volcanic breccios) — 200m — 400' A I •1 0 S 0 n. 4, 0 0 S 0 o — -ZOOm 400 200 meter, coo feci argillite .t C S S GIocaI Overburden Breccta lobes I, II & Ill Stringer sulfide mineralization Massive sulfide mineralizalion Carbonaceous-pyrilic argillite and tuft Crandon Unit: Explanation Crandon Unit Hangingwall (tutts,chert and debris flows) Strotigraphic Top 4, C S S Figure 9b. Geologic cross-section 94400E - Crandon (after Lanibe and Rowe, 1987). tOO — 0 Sec Level (tufts and volcanic breccios) Footwoll — 200,, — 400m B ______ �— 05cc — 200' — 400' — 600' — 800' in feet ElenOliOn Level Southwest Looking West — Regional fuL n -4 9 I 8$ F H 1 N Mineralized sequence: Hanging-wa)) andesite: mat ic metavolcanic flows with associated melatuff a and tu)faceous metasediments Quartz diorite Breccialed rock Explanation 9 I 6S (XI unit) OuOrtZ Crystal lelsic luff Gold mineral izoliOn (tuck—unde, gold zone) stringer sulfide ove, print sulfide ,nineroli lotion with (bedded ond massive) Figure 11. Geologic cross-section 110 +OOE - Pelican River (after Bowden, 1978). Footwall andesile: mafic melavolcanic flows, flow breccia, inlerflow metatuffs and tuffsceous metasediments Hydrothermal alteration Multiple massive to semimassive sulfide lenses 0 Top .1. Fragment - beorinA semimossive II' f','tO 9' en,,- J-s A°, Fit4d n j'°bO Ott Slrotigrophic S Andesilic to felsic cherty metatuffs and tullaceous melasediments -1000 —500' .e4 DFPTH IFT) Moss,ne sulfide ninerOljzolion Es plan of ion Footwall sequence bedded tuffs Precambrian regolith Glacial Overburden NW Figure 10. Geologic cross-section 49235E - Bend (after DeMatties and Rowell, 1991). Looking Slroligrophic Top complex felsic flow/ fragmental Hanging-wall sequence' — l000• — 1200' SE — 400 �56 Line 12E, looking northwest DEPTH, IN FT 0 Granitic intrusive Intermediate to mafic amygdaloidal metavotcanic flows i. ft mineralization Laminated cherty metatuff Felsic metatuff Intense chlorite + sericite alteration (altered mvf) Semimassive (30%-50%) fragment-bearing pyrrhotite (± pyrite + chalcopyrite + sphalerite) lens + Cu 300 Stockwork-stringer mineralization mvf Q) a) \\ 900 Stratigraphic top mvf Ct 1200 0 100 FT Figure 12. Geologic cross-sectionLine 12E - Kivela Zone of the Ritchie Creek Prospect. �M OH + Marble Tonalite + + + Tonal te + ± + + + Looking west + + VOS + Talc Figure 13. Geologic cross-section Line I000E - Lynne (after Kennedy et al.. 1991) Volcaniclastic unit Skarn Massive P0, Mt H. ] Talc + + Semi-massive to massive sulfide 2 'j Rhyolite ] vcs__ IIIIIJIIII + BPM Talc. ??':0; ___jChert 100FT ELE\'. IN FT 1000 1200 1400 1600 �58 Replacement This style is similar to the mound replacement but represents only a partial replacement of previously deposited exhalite. The Ritchie Creek main zone (Cu type) in depositional environment #1 isa good example (Fig. 14). Stockwork/disseminated Broad zones of stockwork pyrite±chalcopyrite with associated sericite alteration characterize this style. These horizons could represent failed VMS systems or possibly contain central zones of massive pyrite-chalcopyrite mineralization. Minor copper±zinc lenses may be present at the stratigraphic top of the system. Good examples of this style in depositional environment #1 are found at the School House and Clear Creek (Cu type) prospects. This style may develop from hot and dense hydrothermal fluids which move laterally through permeable volcanic units below the sea floor (Large, 1990). MASSIVE SULFIDE MINERALIZATION ASSOCIATED WITh META-ARGILLITE FORMATIONS (PMS) The meta-argillite formations (Fig. 4a and 4b) are important stratigraphic sub-units within the greenschist succession of the P-W subterrane and may be related in both time and space to the economic VMS deposits. These important lithologic units are expressed geophysically as long formational airborne electromagnetic (AEM) conductors, both with and without direct magnetic response. As previously mentioned, the source of the AEM conductors is usually graphite, and/or pyrrhotite-pyrite, hosted by black to greenish-gray, weakly to strongly schistose, chlorite-rich metaargillites and associated tuffaceous metasediments (metagraywackes). Individual units are generally less than 100 feet thick and may exhibit well-developed internal lamination or bedding. These units contain only geochemically anomalous base-metal-bearing pyrrhotite and/or pyrite mineralization with varying amounts of associated graphite or, in some cases, carbon. The sulfide-tographite ratio varies widely from conductor to conductor; the argillites are thought by some workers to be sulfide-facies iron-formations. Textural evidence (Finlow-Bates, 1980) suggests that significant amounts of sulfide mineralization in these units is hydrothermal in origin rather than diagenetic. Drillhole data from many of these strataform AEM conductors indicate that the sulfide mineralization can mimic, at least in part, typical VMS systems that have both syngenetic and epigenetic components. In some systems, graphite is not present and the massive pyrrhotite beds (with and without fine sphalerite intergrowths) may be tens of feet thick. These massive pyrrhotite beds contain fragments (usually altered meta-argillite clasts) and have a stratigraphic footwall underlying alteration zone consisting mostly of sericite, chlorite, and/or quartz (silicification), some with crosscutting pyrrhotite stringers containing fine chalcopyrite and sphalerite intergrowths. There may be more extensive stringer zones of network-textured pyrrhotite and sometimes chalcopyrite. The texture is formed by anastomosing veinlets hosted by altered meta-argillite. Cyclic repetition of one or both components of the sulfide mineralization within a given section is common in the more well-developed systems, possibly reflecting multiple hydrothermal �59 A A' 100 ft Scale: lOOm Explanation Mineralized horizon: Massive (>50%) to semi-massive (3050%) sulfide mineralization :::: Sulfide-bearing hydrothermal alteration (altered exhalite?) • Limit of stockwork sulfide halo (<30% sulf ides) Intermediate to mafic subvolcanic intrusive Gold assay zone Figure 14. Geologic cross-section A-A' - Ritchie Creek Main Zone (after DeMatties, 1990). ft - felsic to mafic tuff-lapilli tuff (quartz-biotite-feldspar to biotite-feldspar-amphibole-quartz schist). mf - altered and mineralized felsic tuff yritic quartz-sericite schist). mt - mafic to intermediate tuffs and tuffaceous sediments (feldspar-biotite-amphibole-quartz schistsemischist). �60 pulses. Metamorphic overprinting and/or shearing may have locally remobilized the sulfides, but relict primary features are still recognizable in many formations. Interbedded cryptocrystalline laminated chert, displaying the typical interlocking-quartz-grain texture (serrated grain boundaries) in thin section, or cherty tuffaceous sediments are almost always associated with the sulfide mineralization. Because the meta-argillite units are structurally incompetent, shear zones are easily developed within them, resulting in the brittle deformation (brecciation and fragmentation) of the chert units. Meta-argillite is believed to be deposited as fine-grained epiclastic sediments, possibly in smaller isolated sedimentary basins, generally within the back-arc-basin sequence, under reducing conditions and during periods of volcanic quiescence. Although clusters or groups of these metaargillite formations are found in the P-W subterrane, they are concentrated in the back-arc-basin sequence and commonly along the flanks of the main volcanic arc (Piv) of the Ladysmith-Rhinelander Volcanic Complex. No formations have been recognized in the central portion of the main volcanicarc sequence (amphibolite succession). Argillite formations have also been mapped in the Marshfield subterrane, but their spatial distribution is not clearly understood. All of the VMS districts defined to date are generally within a mile or less of major argillite formations. This spatial relationship was recognized early by explorationists in Wisconsin. Although to date this sulfide mineralization has been generally found to be only geochemically anomalous or to contain low grades of copper and zinc, its presence in meta-argillite formations has metallogenic significance in terms of a possible indicator of potentially economic VMS mineralization. Discussion Aside from a close spatial relationship to VMS mineralization, certain mineralized metaargillites may be genetically related to VMS ore-forming events. In other words, the barren or wealdy metal-bearing sulfide mineralization might have formed before, during, or after major ore deposition, reflecting either the beginning of the event, or deposition itself, or the last stages of the hydrothermal event in the VMS system. In terms of a modern analog, it might be considered "black smoker debris." Current geologic data indicate that all four potentially economic and many of the subeconomic or under-explored deposits contain these units in their "local" stratigraphic section (Fig. 4a and 4b). As has been described, the Massive Sulfide Zone of the Crandon deposit is within one of these units (Crandon Unit). Finlow-Bates (1980) discussed the possibility that the formation of graphitic argillite (carbonaceous sediments) was the result of ore deposition which set up anoxygenic conditions, a type of ground preparation in which reducing conditions allow the preservation of carbon (whose source is uncertain). The model assumes that the ore-fluid chemistry was in a reduced state, which it likely was during the Precambrian. This might explain the close spatial (genetic?) relationship of the Pms formations with the major deposits discovered thus far. If this empirical-genetic model is valid, the stratigraphic implications are obvious: Pms formations associated with VMS deposits would represent gross time-marker horizons which mark ore-forming events and could be used in regional correlations. This concept of "favorable horizon" is a characteristic of other VMS districts, in the Canadian shield and elsewhere in the world. �61 Figures 3, 4a, and 4b show formations in the P-W subterrane and the western and east-central parts of the Ladysmith-Rhinelander Volcanic Complex. A number of major formational groups can be seen. However, the geology is complicated and has been made even more so by isoclinal folding and faulting. Detailed correlations of individual formations are impossible at our current level of knowledge. Using the general geologic framework which has been established for the cOmplex, it is possible to grossly correlate the formational clusters on the basis of structural and stratigraphic position relative to the central core of the main volcanic-arc complex. At least two "sets" or groups can be defined in the western portion of the Complex: Pms I, structurally along the flanks of (probably stratigraphically above) the core, and Pms II, in the back-arc basin. A tentative interpretation of the composite stratigraphy in this area is presented in Figure 15. Under this stratigraphic arrangement, the Eisenbrey (Thornapple) deposit would occupy the lowest position within the amphibolite succession. The first major ore-related argillite formational group (Pms I) in the greenschist succession occurs stratigraphically above the Flambeau deposit, but possibly below the Lynne deposit. However, because stratigraphic interpretation has been further complicated in the Lynne area by more complex faulting, folding, and igneous intrusion, the Lynne deposit may actually be closer stratigraphically to the meta-argillite formational group than the composite section indicates, or possibly laterally equivalent to Flambeau. The Bend deposit occupies the highest stratigraphic position and appears to be associated with the second major ore-related argillite formational group (Pms II) in the back-arc basin. This concept can be extended to the eastern part of the belt where one prominent formational group (Pms I) can be seen linking together the Pelican River, Wolf River, and Catwillow deposits (Fig. 3 and 4b). The Crandon Unit is associated with the formational group south of the deposit, which may be the lateral equivalent of the ore horizon(?) and, using this scheme, would be considered to be associated with the Pms II formational group. Because of complex regional isoclinal folding, the true spatial and stratigraphic separation between the two productive formational groups may be much less; they may even be the same unit in different volcanic facies. Nonetheless, gross correlations suggest that most of the ore deposits in the greenschist succession were formed in a fairly narrow stratigraphic interval and are nearly coeval in their time of deposition. The narrow stratigraphic interval and the correlation of Pms formational groups to link the VMS deposits in time are partially supported by lead isotope data. Afifi et al. (1984) established a lead model age of approximately 1.8 to 1.9 Ga for Flambeau, Pelican River, Hawk, and Crandon. A strong linear trend is defined by the lead isotope data, suggesting that the deposits are nearly coeval in their formation (Fig. 16). More recent lead isotope work by Thorpe (written communication, 1992) on the Ritchie Creek, Spirit, Horse Shoe, and Lynne deposits indicates that they also plot along this trend, further supporting this contention. Thorpe's lead model age for the VMS mineralization is approximately 1.86 Ga. As previously mentioned no meta-argillite formational groups have yet been identified in the amphibole succession of the main volcanic-arc facies. However, thin but laterally extensive oxidefacies iron-formations are known and, as described for Eisenbrey (Thornapple), may represent a similar type of favorable horizon for VMS mineralization. There are no lead isotope data for the Eisenbrey deposit; therefore, it is not known whether it plots on the linear trend defined by Thorpe. If it does plot on the trend line and is coeval with the �62 Cambrian Mt. Simon Fm. (sandstone) Barron Quartzite a pre-Cambrian regolith Pvs 0 Pms Pmvf a Pfv Greenschist Succession - - (j)) / Bend Deposit (Cu, Au) PmsIl o Nm o oa o 0° o 1 - Pvs Ci) Pvs (chemical sediments) Pfv Lynne Deposit Ag (Zn, Pb, Ag) > Pvs W Ci C> PmsI Zn Cu-Au (Cu, Au) Pfv Unconformity, fault, and/or gradational contact?? (0 If 0 > E-' E ('3 0 . • Flambeau Deposit <.Pjv G) — Ci) I Pmvf I— Li .E Q > -' Thornapple Arnphibolite Succession xxxxxxxxxxxxxxxxx — Deposit (Cu,Zn) Cu /xxxxIf Unconformity Archean (>2500 MA) Basement: granitic gneiss, migmatite, amphibolite Figure 15. Schematic composite stratigraphic section, west-central portion of the Ladysmith-Rhinelander Volcanic Complex. �63 15.5 15.4 207/ 204 15.3 15.2 15.1 15.2 15.4 15.6 15.8 16.0 206/204 Figure 16. Lead isotope data for VMS deposits in the Wisconsin Penokean Volcanic Belt (after Thorpe, et a!.). greenschist succession deposits, then the oxide-facies iron-formations could possibly represent lateral equivalents of the ore-related Pms units. Conclusions 1. Two volcanic complexes can be recognized in the Early Proterozoic Penokean volcanic belt (Wisconsin magmatic terrane) on the basis of lithology, structure, and age relationships. These include the Wausau Complex, host to at least one structurally controlled gold deposit, and the larger Ladysmith-Rhinelander metavolcanic complex, which contains at least 13 volcanogenic massive sulfide deposits and occurrences, clustered in three districts. 2. Volcanogenic massive sulfide mineralization occurs in at least three distinct geologic depositional environments. The four potentially economic deposits occur in environment #1, which is the felsic volcanic center facies. 3. The identified volcanogenic massive sulfide deposits and occurrences can be classified on the basis of metal content and divided into three groups (Cu, Zn-Cu, Zn-Pb-Cu). Each group exhibits various styles of mineralization. �64 4. The meta-argillite association in the Ladysmith-Rhinelander metavolcanic complex may have significant exploration importance, i.e., certain formations or formational groups at the right stratigraphic level could theoretically lead to potentially economic VMS mineralization particularly in areas where they are associated with felsic centers (depositional environment #1). Two key formations are known and others may be present in the Ladysmith-Rhinelander metavolcanic complex and Marshfield subterrane. 5. The Wausau volcanic complex is known to contain only a few meta-argillite formations. That lack, indicating no major breaks in volcanism, and felsic centers which may be mostly subaerial and younger (1835-1845 Ma) than the main ore-forming event (1860 Ma) might explain the poor rate of discovery of significant massive sulfide deposits in this area. Acknowledgments The author is grateful to Ernest K. Lehmann and Associates Inc. for permission to release data for this paper. Also to Economic Geology for allowing publication of portions the original manuscript for this memorial volume. A final thanks to the late Ned Eisenbrey for his major contribution to the ideas expressed here. His exploration effort on behalf of Kennecott in the 1960s coupled with earlier work compiled by the late Jack Phillips, led to the discovery of the Flambeau and Thornapple deposits (now appropriately named the Eisenbrey deposit) and paved the way for later explorers to enter the Wisconsin greenstone belt. On a personal note, Ned was my mentor at E. K. Lehmann and Associates for many years. He helped shape my exploration philosophy, and it is with gratitude and friendship I contribute to this commemorative volume. References Cited Afifi, A., Doe, B. R., Sims, P. K., and Delevaux, M. H., 1984, U-Th-Pb isotope chronology of sulfide ores and rocks in the Early Proterozoic metavolcanic belt of northern Wisconsin: Economic Geology, v. 79, p. 338-353. Bowden, D. R., 1978, Volcanic rocks of the Pelican River massive sulfide deposit, Rhinelander, Wisconsin: a study in wallrock alteration: Unpublished MS Thesis, Houghton, Michigan Technological University, 62 p. DeMatties, T. A., 1989, A proposed geologic framework for massive sulfide deposits in the Wisconsin Penokean volcanic belt: Economic Geology, v. 84, p. 946-952. 1990, The Ritchie Creek Main Zone: a Lower Proterozoic copper-gold volcanogenic massive sulfide deposit in northern Wisconsin: Economic Geology, v. 85, p. 1908-1916. DeMatties, T. A., and Mudrey, M. G., Jr., 1991, Geologic setting of the Early Proterozoic base- and precious-metal-rich metavolcanic belt of Wisconsin: 37th Annual Institute on Lake Superior Geology, Eau Claire, Wisconsin, 1991, Proceedings, p. 29-33. �65 DeMatties, T. A., and Rowell, W. F., 1991, Bend, a Lower Proterozoic, copper- and gold-enriched volcanogenic massive-sulfide deposit in Taylor County, Wisconsin: 37th Annual Institute on Lake Superior Geology, Eau Claire, Wisconsin, 1991, Proceedings, p. 34-40. Finlow-Bates, T., 1980, The chemical and physical controls on the genesis of submarine exhalative orebodies and their implications for formulating exploration concepts, a review: Geologisches Jahrbuch, Ser. D, no. 40, p. 131-168. Franidin, J. M., and Thorpe, R. I., 1982, Comparative metallogeny of the Superior, Slave and Churchill provinces in Hutchinson, R. W., Spence, C. D., and Franklin, J. M., Precambrian sulfide deposits (H. S. Robinson Memorial Volume): Geological Association of Canada Special Paper 25, p. 3-90. Greenberg, J. K., and Brown, B. A., 1983, Lower Proterozoic volcanic rocks and their setting in the Southern Lake Superior district: Wisconsin Geological and Natural History Survey Miscellaneous Paper 83-4, 18 p. Kennedy, L. P., Harding, T. A., Schaff, J. H., and Zielinski, A. M., 1991, The Lynne massive sulfide deposit, Oneida County, Wisconsin: 37th Annual Institute on Lake Superior Geology, Eau Claire, Wisconsin, 1991, Proceedings, p. 63. LaBerge, G. L. and Myers, P. E., 1983, Precambrian geology of Marathon County, Wisconsin: Geological and Natural History Survey Information Circular, No. 45, 88 p. LaBerge, G. L. and Myers, P. E., 1984, Two Early Proterozoic successions in central Wisconsin and their tectonic significance: Geologic Society of America Bulletin, v. 95, p. 246-253. Lambe, R. N., and Rowe, R. G., 1987, Volcanic history, mineralization, and alteration of the Crandon massive sulfide deposit, Wisconsin: Economic Geology, v. 82, p. 1204-1238. Large, R. R., 1990, Tonnage-grade data for VMS deposits in Ore deposit studies and exploration models: Center for Ore Deposit and Exploration Studies, University of Tasmania, Master of Economic Geology Work Manual, v. 1, section 4, parts 1, 2, and 3. 1992, Australian volcanic-hosted massive sulfide deposits: Economic Geology, v. 87, p. 471-510. Lavery, N. G., 1985, Quantifying chemical changes in hydrothermally altered volcanic sequences silica enrichment as a guide to the Crandon massive sulfide deposit: Journal of Geochemical Exploration, v. 24, p. 1-27. May, E. R., 1977, Flambeau - a Precambrian supergene enriched massive sulfide deposit: Geoscience Wisconsin, v. 1, p. 1-26. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen: Canadian Journal of Earth Sciences, v. 26, p. 2145, 2158. �66 �67 AN OVERVIEW OF THE FLAMBEAU SUPERGENE ENRICHED MASSIVE SULFIDE DEPOSIT: GEOLOGY AND MINERALOGY, RUSK COUNTY, WISCONSIN Edwarde R. May Consulting Mining Geologist and Stephen R. Dinkowitz, Geologist Flambeau Mining Company INTRODUCTION The discovery of the Flambeau orebody coincided with the signing of the National Environmental Policy Act (NEPA) in 1968. As a consequence, both the development of this supergene enriched massive sulfide deposit and implementation of NEPA went through intense public debate. At the same time basic industrial segments of the economy such as mining, steel, and auto manufacturing were restructuring to compete in an emerging global economy. Neither Kennecott Copper Corporation (Kennecott), the mining industry, nor governmental regulatory agencies fully appreciated the consequences of NEPA when development drilling of the Flambeau orebody was completed in 1971. Kennecott was aware, however, of the deteriorating copper market. Therefore Kennecott's Flambeau development policy was to secure the mining permits, then make a decision whether or not to develop the project. The project was discontinued in 1977 after receipt of an approved Environmental Impact Statement (EIS) but before issuance of the mining permits, due to depressed metal prices and unfavorable economics. A lean, restructured base metal mining industry reemerged by the mid-1980's, one ready to meet mine development challenges within the context of a strong national and state environmental awareness. Kennecott reopened the Flambeau project and, shortly thereafter, entered into discussions with local city, township, and county officials and citizens. Once their concerns had been identified, a Local Agreement was drafted and signed that alleviated their concerns and allowed permit hearings to proceed under a more cooperative and constructive spirit. This bold and innovative approach has since been incorporated in Wisconsin's metallic mineral regulations. The Flambeau Mine has been in successful production for the past three years. It has been successful economically, environmentally, socially and politically. Considerable up-front planning, public dialogue, and company commitment resulted in dire environmental predictions not coming true, for example, the water treatment plant out performs even its most enthusiastic design predictions. Geologically, this mine has presented the industry with unusual mineral assemblages as well as an example of high grade ores which have not been mined in North America since the turn of the century. Enriched Canadian Shield massive sulfide orebodies are rare; moreover, the size and grade of the Flambeau orebody is unusual. Sampling and mining of the overlying gold-rich gossan was a technical challenge rarely experienced by North American mining geologists. The opening of the Flambeau orebody thus became a dual challenge of extracting gossan while simultaneously mining 10% Cu ore. Each of these ores required a different sampling and mining approach. This was accomplished without environmental incident during start-up of the mine through one of Wisconsin's �68 wettest summers. There was no offsite discharge of waters from the 182 acre site except through the approved water treatment discharge line. The following paper is intended to give an overview of the geology and gossan/sulfide mineralogy. It is limited to observed megascopic-macroscopic data, supported only by minor microscopic and geochemical work conducted in the early 1970's. HISTORY Kennecott discovered the Flambeau deposit in November 1968, following a long history of exploration in the upper Midwest, when their first diamond drill hole, drilled to test a geophysical conductor, intersected 47.7 feet averaging 9.25% Cu and 0.049 opt Au. During the 1950's George Moerlein noted that Precambrian volcanic rocks, similar to those known to host massive sulfide deposits in the Canadian Shield of Quebec, Ontario, and Manitoba occurred in Wisconsin (Babcock, 1996). Of particular note was the recording of a well dug about 9 miles south of Ladysmith in 1915 that yielded a specimen of volcaniclastic rock with copper oxide mineralization. Amazingly, this specimen is still on file in Madison eighty years later. A small airborne electromagnetic (EM) geophysical survey was flown over the nearby Schoolhouse Prospect in 1955 with negative results (Figure 1). In 1966 Jack Philips continued the pioneering work of Moerlein with the discovery of additional "favorable looking" volcaniclastic rocks west and northwest of Ladysmith. A large airborne geophysical survey flight block including the Schoolhouse Prospect in the southeast corner, some weakly pyritized outcrops between Weyerhaeuser and Bruce, and outcrops of similar rock northwest of Bruce, was flown in May 1967. The east boundary of the aerial survey was coincident with the Flambeau River as it flows south past the future Flambeau mine site. A favorable response was noted and brought to Ned Eisenbrey's attention. He approved the addition of two short flight lines between the river and State Highway 27. These three lines delineated what was later to be the Flambeau deposit, thus initiating the rebirth of Wisconsin's base metal mining industry after an absence of nearly 25 years when the lead-zinc mines in the southwest corner of the state were closed (Schweuk 1977). Delineation drilling at the Flambeau deposit was accomplished from 1969 to 1971. An Environmental Impact Report was compiled during 1974 and infill drilling on the west end of the deposit was completed. The EIS was approved by the Wisconsin Department of Natural Resources in early 1976; however, the mining permit application hearing was canceled after Rusk County turned down the Company's zoning request. In 1986, the Flambeau project was reopened and another round of infill and confirmation drilling completed on the east end of the deposit. The scope of the project was changed to mine only the supergene enriched mineralization as direct shipping ore, thus eliminating on-site milling and disposal of tailings as originally proposed in the 1970's. In addition, the smaller open pit was to be backfilled and not flooded as proposed for the larger pit designed in 1976. Economic considerations precluded underground mining; consequently, the planned open pit development was restricted to a depth of 225 feet, which is the base of the deepest secondary enrichment zone. A second EIS was submitted in 1990 to mine 1.8 million tons averaging 10.92% Cu and 0.088 opt Au. Hearings were held in 1990 and permits and approvals to commence construction were issued in January of 1991. Flambeau Mining Company, a wholly owned subsidiary of Kennecott Minerals, commenced construction in July 1991, only to be stopped by an injunction filed �PROTEROZOIC OUTCROP HAND DUG WELL #" 0 LEGEND Figure 1 Location of Massive Sulfide Deposits and Chief Outcrops. Rusk County, Wisconsin EISENBREY DEPOSIT SCALE 1"6.5 MILES �70 shortly thereafter. The injunction was based on the Endangered Species Act and the suspected presence of purple warty-backed clams and unusual dragon flies. Subsequent studies showed that the proposed operation would not endanger the species in question. Construction recommenced early in 1992 and ore production began in May 1993. All told, 24.5 years had elapsed from discovery to production, although active time spent on the project was 16 years (1968 to 1977 and 1986 to 1993). LOCATION AND CULTURAL SETFING The Flambeau orebody is located in northwestern Wisconsin approximately 150 miles northeast of Minneapolis-St. Paul and 220 miles northwest of the state capital at Madison (Figure 1). The town of Ladysmith, immediately north of the 2700 acre project site, is a picturesque rural-retail community of 3,900 and the Rusk County seat. Ladysmith lies at the junction of north-south and east-west highway and railroad systems. The orebody may be conveniently reached by traveling south 1.5 miles on State Highway 27 from its junction with U.S. Highway 8, then west 0.2 mile on a paved private road. Rusk County and the project site are characterized by low, gently rolling sub-parallel ridges striking generally in an east-to-northeast direction. Greatest relief is normally found along the outside bends of the major rivers, although banks greater than 45 feet are uncommon. The Flambeau River cuts diagonally across the county from the northeast corner, meandering through Ladysmith, across the project site and over the west end of the deposit before turning south to its confluence with the Chippewa River. Weather conditions are typically continental with temperature extremes ranging from a recorded high of 108°F to a low of -40°F. Precipitation averages 32 inches per year. Annual snowfall averages 43 inches, typically covering the ground from late November to the beginning of April. GENERAL GEOLOGY OF NORTHERN WISCONSIN At least 13 volcanogenic massive sulfide deposits have been discovered within Early Proterozoic greenstone rocks of northern Wisconsin (DeMatties, 1994). The Ladysmith-Rhinelander metavolcanic belt, which strikes across the state for a distance of 150 miles, is the host rock for this mineralization. These 1.86 to 1.88 billion year old rocks consist of mafic metavolcanics, gabbroic sills, lesser amounts of felsic metavolcanics, and some cherty iron formations. The LadysmithRhinelander metavolcanic belt clearly shows on regional airborne gravity and magnetic reconnaissance maps of northern Wisconsin as an anomalous linear feature. North of the Ladysmith-Rhinelander belt are rocks that form a thick platformal turbidite sequence of clastic and chemical metasedimentary rocks including major iron formations. The Niagara Fault separates the Northern Penokean Terrane of continental margin assemblages from the Pembine-Wausau Subterrane that contains the Ladysmith Rhinelander belt of rocks (Figure 2). The paper written by G. LaBerge in this volume shows the location of these subterranes. South of the Ladysmith-Rhinelander belt are rocks of the Wausau and Marshfield Complexes. The Eau Pleine shear separates the Marshfield Subterrane from the Pembine-Wausau Subterrane (LaBerge, 1996). The Marshfield Subterrane is characterized by Archean gneisses and 1.86 billion year old metavolcanic rocks and granitoids. The Wausau Volcanic Complex consists of 1.88 billion year old amphibolite facies rocks unconformably overlain by 1.84 billion year old intermediate to felsic metavolcanics. Intruding the Wausau volcanic complex are anorogenic igneous rocks, 1.47 to �I FLAMBEAU MINE CRANDON DEVELOPMENT EISENBREY DEPOSIT 0 10 20 SCALE 40 MILES 1"40 Figure 2 Generalized Geology of Northern Wisconsin (Modified after Morey, Sims, Cannon, Mudrey, Southwich, 1982) �72 1.51 billion year old, the largest of which is the Wolf River Batholith. DeMatties and LaBerge more fully discuss these subterranes and the Wausau Volcanic Complex in this volume. Paleozoic sediments onlap the southern portions of the Southern Superior Province of the Precambrian Canadian Shield. MINE SITE GEOLOGY Geological data for the Flambeau orebody initially came from airborne geophysical data, 63,220 feet of diamond drill core, one outcrop and a subcrop. Interpretation of the airborne EM and magnetic data provided exploration geologists with the regional rock fabric as well as possible areas of "greenstone" rock and plutons. Most of the geology and mineralogical descriptions for the remainder of the paper are from observations made during mining of the open pit. Data from core holes in the deeper and less altered rock have been extrapolated to supplement descriptions of the upper and more altered rocks. Subcrop is approximately 1,100 feet in elevation with planned pit bottom elevations of 880 to 94.0 feet. Identification of rock units while core logging was difficult due to intense alteration, The dominant regional metamorphic alteration suites particularly in the supergene enriched zone. of minerals were first identified in drill core, and subsequent petrographic work provided clues to rock genesis and identification of rock units. An angular unconformity between steeply dipping, saprolitic altered intermediate volcaniclastic rocks and Upper Cambrian Mount Simon Sandstone crops out approximately one mile south of the mine on the banks of Meadowbrook Creek. A subcrop of Precambrian rock was discovered in 1988 during very low waters in the Flambeau River west along strike of the orebody. This rock consisted of small and large fragments of quartz-sericite schist and rusty metachert containing small amounts of malachite. The Flambeau orebody is interpreted to be overturned to the southeast; however, stratigraphic nomenclature will be used throughout this paper. Structural hangingwall rocks in the mine on the north side of the orebody are actually the stratigraphic footwall. Since 1993 detailed open pit mapping has occurred to the scale of 1 inch to 20 feet. This mapping has confirmed the earlier derived geological model and added some structural complications not recognized during core examination. The rock classifications (Table 1) were developed by Jeff Hulen for Kennecott in 1970, and in general hold true today. A water-lain tuff in the footwall of the ore horizon and felsic tuff altered to sericite-clay beds in the hangingwall sequence have been added to this classification since mining began. PLEISTOCENE Several ages of Pleistocene glaciation covered the area and deposited unconsolidated, poorly sorted materials that range in thickness from 12 feet to 30 feet. Most deposits are typical outwash with materials ranging from silt to boulders up to four feet in diameter. These poorly sorted outwash deposits are more interbedded with silty bess away from the Flambeau River. A two to three foot thick bess deposit covered the interbedded outwash deposits over the eastern half of the deposit. Iron and manganese staining is prevalent in the lowermost parts of the outwash and is interpreted to be of �TABLE 1 CLASSIFICATION OF FLAMBEAU MINE ROCK TYPES RUSK COUNTY, WISCONSIN Rock Name Genetic Name Quartz-eye schist andalusite-biotite schists, Sericite-clay schist Dacite quartz crystal tuff and Rhyolitic quartz crystal lapilli tuff Dacitic flows and tuff Dacitic and andesite tuffs and lapilli tuffs Felsic tuff Quartz-sericite schist Metachert Massive sulfides Feldspar-clay schist Rhyolitic tuffs and lapilli tuff Chert Massive Sulfides Felsic tuff Actonolite Schist Hangingwall Chlorite, spessartite and Ore horizon Footwall Actinolite and chlorite phyllite Actinolite and andalusite-biotite schist Quartz-eye schist Andesitic tuff Dacitic-andesitic lapilli tuff Rhyolitic-dacitic quartz crystal tuff recent origin, unrelated to the underlying sulfide orebody. A relatively well sorted, heavily ironstained, rounded, pebble to cobble outwash overlies the sandstone and is clearly older than the overlying purplish silt-rich outwash, indicating at least two ages of Pleistocene glacial deposition at the mine site. The last glacial period almost completely eroded the underlying Cambrian sandstone outlier. Glaciation has removed the sandstone, approximately 450 feet along strike, on the west and east ends of the orebody. In addition, several large blocks of sandstone were removed down to bedrock north of the pit perimeter (Figure 3). A Pleistocene to Recent stream meandered across the west end of the orebody in a southwesterly direction and a waterfall was created where the stream flowed over the footwall metachert. Water-worn chert boulders were clearly evident as well as near total removal of gossan over a 200 foot strike length. The stream gravels are still visible on the south wall of the open pit. Pleistocene glaciation has played a small structural role in the host rock geology. A small thrust fault is visible in the west pit wall. It has been interpreted that glacial forces from the north squeezed Out a highly incompetent, 10 foot thick clay-sericite bed. The glacier then moved more competent footwall volcanic rock south to cover the truncated and incompetent tuffaceous unit. CAMBRIAN SANDSTONE A thin, narrow, near flat-lying outlier of Upper Cambrian sandstone overlies most of the Flambeau deposit. The presence of this outlier was of enormous economic significance in that areas of poorly cemented gossan and supergene enriched sulfides were protected from erosion. The sandstone has been identified as the Mount Simon Formation. It is a light yellow to tan, very poorly cemented, medium to coarse grained sandstone with numerous light green-gray shale partings. The sandstone is characterized by rounded to subrounded, frosted, medium sized quartz grains. A thin �HIi �75 basal conglomerate is present and consists of rounded to subrounded white quartz particles up to 2.5 inches in diameter. Sandstone has been deposited in depressions and collapsed structures at the top of the gossan and in depressions between the more resistant and enclosing metachert units. No evidence was seen to suggest that these structures were post-Cambrian. The base of the sandstone has been examined for evidence of gossan mineralization incorporated within the basal conglomerate and appears to contain no fragments of Precambrian bedrock other than quartz pebbles. PRECAMBRIAN GEOLOGY STRATIGRAPHIC FOOTWALL The footwall rocks (stratigraphic footwall) on the north side of the deposit consist of three main units: metadacite, quartz-eye tuff, and andalusite-biotite schist (Figure 4). A more detailed description of the composition of these units has been reported previously by this author (May, 1977a). A comparison of Flambeau dacite and rhyolite tuffs with average whole-rock chemistry for such lithologies is shown on Table 2. Certain oxides such as Si02, A1203, and Fe203 are generally close to average. Metasomatic alteration, associated with mineralization, probably explains the large increase in FeO, and MgO and general decreases in CaO, Na20 and K20. TABLE 2 A COMPARISON OF FLAMBEAU WHOLE-ROCK ANALYSES WITH WORLD AVERAGE DACITE AND RHYOLITE COMPOSITIONS Nt. % Si02 Al203 Fe203 FeO MgO CaO Na20 K20 Flambeau Worldm Flambeau Deviation Norld (1) Flambeau Deviation Rhyolitic Deviation Avg. Dacitic from Avg. Rhyolitic from Qtz. Crystal From Dacite Lapilli Tuff World Av. Rhyolite Lapilli Tuff World Av. Lapilli Tuff (2) World Avg 63.58 63.12 -0.46 73.66 73.28 -0.38 73.07 -0.59 16.67 2.24 3.00 2.12 5.53 3.98 1.40 16.78 2.25 6.45 8.13 0.73 0.54 2.00 0.11 0.01 3.45 6.01 -4.80 -3.44 0.6 13.45 1.25 0.75 0.32 1.13 2.99 5.35 14.47 1.86 2.23 3.42 0.91 0.64 3.19 1.02 0.61 1.48 3.10 -0.22 -2.35 -2.16 13.46 0.01 1.01 -0.24 2.05 5.29 -0.63 2.80 5.61 0.50 1.88 1.67 -1.11 -3.68 (1) Average dacite and calc-alkali rhyolite from Nockolds (1954) (2) Analyses by Kennecott Exploration Services, Salt Lake City, Utah Ouartz Eve Schist. The northern-most unit of the footwall stratigraphy generally consists of a very well foliated quartz eye schist that has been interpreted as a quartz crystal ignimbrite of intermediate composition. This unit is distinctive due to the presence of "bluish quartz eyes" that vary in size from 1 mm to 10 mm. Under the microscope these eyes are actually aggregates of quartz grains. Some show relict euhedral outlines, but most commonly they are polygonal-shaped grains. A triple-point junction was a commonly observed feature suggesting metamorphic recrystallization. The �PIT PERIMETER- Figure 4 Geological Plan Map 1050 Level, Flambeau Mine Rusk County, Wisconsin 0 1" =200' SCALE100 i FEET 200 SURFACE ELEVATION 1120' BIOTITE—FELDSPAR (lUFF) QUARTZ—SERICITE (RHYOLITE TUI MASSIVE SULFIDES "A" LENS "B" & "C" SULFIDE HORIZONS METADACITE (FLOWS, TUrFS) ANDALUSITE—BIOTITE (SEDIMENTS) QUARTZ—EYE (TUrF) PRECAMBRIAN PROTEROZOIC MOUNT SIMON SANDSTONE CAMBRIAN [II] GLACIAL TILL PLEISTOCENE LEGEND �77 quartz eye schist also contains numerous but difficult to recognize lithic fragments of similar composition. These fragments have been greatly elongated parallel to schistocity, as have all fragments associated with the Flambeau orebody. Chief alteration minerals are chlorite, sericite, and clay, with chlorite being the dominant mineral. Whole rock chemistry taken from samples below the supergene alteration zone indicates the quartz eye schist to be dacite tuff to rhyolite lapilli tuff in composition. Metadacite. A major lithologic change occurs at the hangingwall or south of the quartz eye schist. A complex suite of greenish-purple metadacitic rock was deposited that probably reflects intermediate flows and associated tuftheds. Pillow structures have been sought but not found, but there is evidence of volcanic bombs. The metadacite flows produced a more massive, poorly foliated rock that has been altered from an actinolite schist below the supergene alteration zone to chloriteclay-sericite. Surrounding and on the flanks of the metadacite are chlorite schists that are well foliated consisting of chiorite-clay-sericite. These chlorite schists are either fine-grained, chilled borders of flows, or dacite tuffs. Contacts between rock units in the pit are generally sharp in contrast to that reported previously from examination of core samples (May, 1977b). The metadacite unit forms a major rock unit in the north wall from sections 401 to 420 in contrast to minor flows found in the south wall. Andalusite-Biotite Schist. Partially enclosing the metadacite is another distinctive unit known as the andalusite-biotite schist. This unit extends along the entire north side of the orebody, as does the quartz eye schist. The andalusite-biotite schist contains up to 10 to 15% laths of andalusite, some of which exceed 2 inches in length. Andalusite is scattered irregularly throughout the rock and is best displayed on foliation planes. Coarse biotite occurs as distinctively cross-cutting porphyroblasts; however, it also occurs within foliation-bounded "beds" and is more common than andalusite. The andalusite-biotite porphyroblasts range in length from 0.2 mm to 3 mm and from 5 to 25% in volume. Whereas the quartz eye schist and metadacite contain 1 to 2% pyrite, the andalusite-biotite schist contains 2 to 15% pyrite. Andalusite and biotite porphyroblasts decrease in volume eastward in the open pit, with a corresponding increase in chlorite and sericite. The andalusite-biotite schist is in contact with the northern boundary of the ore horizon and occupies the stratigraphic footwall position. In many other volcanogenic massive sulfide deposits, the stratigraphic footwall contains the stringer or feeder zone. However, no strong evidence for the presence of a discrete feeder zone or alteration pipe in these rocks has yet been identified at Flambeau. What is observed in the andalusite-biotite schist is a gradual southward increase up the footwall stratigraphic column of sericite, sulfide and chert mineralization over a stratigraphic thickness of 100 feet towards the orebody. Fragments, less than 1 inch thick, of both chert and quartz-sericite with pyrite and/or chalcopyrite increase toward the ore horizon. The quartz-sericite and chert fragments are better mineralized than the matrix, containing 5 to 7% pyrite with less that 2% chalcopyrite. The contact between the quartz-sericite and other rocks of the ore horizon is, therefore, gradational over 5 to 15 feet and difficult to identify in the pit. Geochemically, the ore horizon is readily identifiable due to the sharp increase in gold values (Table 3). Two beds of sericite-clay and spessartite garnet occur in the footwall north of the orebody, identified as a 5 to 15- foot wide fissile sericite-clay bed that was probably a felsic tuff. One of these sericite-clay beds has been used recently as a marker horizon. Alteration has totally destroyed original mineralogy leaving a greasy mixture of highly foliated sericite-clay. This bed can be traced from the west wall to the east end of the pit where it is covered by the main haulage ramp. �78 TABLE 3 BUILD-UP IN GOLD VALUES iN HOLE 13, TOWARDS ORE HORIZON FLAMBEAU MINE, RUSK COUNTY, WISCONSIN Geology Hangingwall Ore Horizon Footage (it) Ondalusite -- 21 5-220 Biotite Schist Quartz-Sencite Schist Massive Sulfides 220-225 225-230 230-232 232-237 237-242 242-247 247-252 Copper (%Cu) 0.189 0.226 0.531 1.544 11.154 6.286 11.762 11.559 Gold (opt Au) Trace 0.005 0.050 0.080 0.030 0.090 0.210 0.120 A second marker bed consisting of spessartite-chiorite has been recognized in the footwall on the east end of the orebody in core samples taken beneath the pit. Metadacite flows have interrupted this bed to the west. The unit is recognized at depth by the presence of 20 to 25% chlorite and 2% lightorange to pink dodecahedral spessartite porphyroblasts. This unit has not yet been recognized in the pit. ORE HORIZON Ouartz-Sericite Schist. The quartz-sericite schist of the ore horizon is interpreted to have originally been a rhyolite tuff based upon thin section studies. Interbedded within the tuff and in close association are metacherts and massive sulfide mineralization. Metacherts are interbedded with, and flank much of the enriched ore, with the thicker silica-rich beds in the stratigraphic footwall on the north side of the deposit. The quartz-sericite schist has been explored and traced a strike length that exceeds 12,000 feet. True thickness varies from approximately 20 feet to as much as 180 feet. The average thickness is 105 feet, where it hosts the orebody. Along strike away from the orebody, the well foliated unit is recognized by an increase in sericite and pyrite but less quartz and chalcopyrite. The unit was traceable geophysically by using induced polarization (IP) which responded positively to the ho?izon's 5 to 15% pyrite content. Along strike, away from the massive sulfides, are also narrow zones containing cherty fragments with up to 1 or 2% chalcopyrite and/or sphalerite. In the pit, the quartz-sericite schist is a light gray, very well foliated rock containing up to 60% quartz, up to 50% sericite, and averages 15% pyrite. There are minor amounts of chlorite, andalusite, and biotite present, particularly towards the outer edges of the unit or along strike, where a greater proportion of mafic tuff and volcanic debris appears to have been deposited. Lapilli Tuffs. Lapilli tuffs on the stratigraphic hangingwall side of the orebody are intercalated with tuffs and exhalitive deposits of the ore horizon. In general, the lensoidal-shaped felsic fragments make up from 5 to 10% of the unit although certain beds consist predominately of fragments. The ore horizon is, nevertheless, dominated by sediments and sulfides deposited under quiescent conditions with occasional outbursts of high energy as evidenced by internal lapilli units. The size of the siliceous fragments are generally less than one inch with an occasional fragment to 2 or 3 inches. Most fragments consist of sugary-textured quartz with varying amounts of sericite, �79 pyrite, and chalcopyrite that have been enriched to chalcocite and/or bornite. Metachert fragments up to 3 to 4 inches long and one-half inch thick have been observed in the ore horizon. Fine Grained Tuff. A well-bedded, light milky tan colored siltstone or very fine grained water-lain tuff occurs at the stratigraphic top of the ore horizon. Sulfide mineralization which averages 15% in the quartz-sericite schist decreases to 2 to 4% in this horizon. An occasional fine-grained, highly elongated sulfide fragment has been noted. Near the hangingwall of the quartz-sericite schist, and the argillized sericite schists on the east end, are erratic gold-mineralized zones. These gold-rich zones occur within fine grained massive to semimassive pyrite zones and are associated with porcelaneous-type clays. Arsenopyrite and minor galena is preferentially found in this area of the ore horizon and in the footwall or north side of the fine grained tuff. The fine grained tuff has been included within the ore horizon since this unit generally represents a water-lain sequence of materials in a quiescent depositional environment, and contains greater compositional and genetic affinities to the other units of the ore horizon than with the hangingwall rocks south of the ore horizon. A pronounced change occurs in rock deposition stratigraphically above the fine grained tuff with the return of volcaniclastic materials similar to those in the footwall rock. STRATIGRAPIIIC HANGINGWALL The geology of the hangingwall is less well known since core holes and the Flambeau pit extend for only a short distance into these poorly mineralized rocks; still, a pronounced lithologic change is evident. In general, the rock units are thinner and consist of interbedded chlorite-phyllites, quartz eye schist, metadacite and biotite-feldspar schist. These lithologies represent deposition of intermediate to mafic volcaniclastic and flow rock. Further to the south, away from the deposit, the hangingwall becomes mostly quartz eye schist. One of the deep exploration drill holes intersected a foliated mafic rock with repetitive narrow one to 2 inch zones of chlorite-epidote. These were inferred to be pillow lava structures in a mafic "dacitic" rock. Excellent pillows have, subsequently, been mapped in the hangingwall at the east end of the open pit. STRUCTURE The Flambeau orebody has been interpreted to occur on the limb of a large isoclinal fold which is indicated by the fact that cleavage is parallel to the bedding. Slickensides have been noted on foliation planes indicating dynamic metamorphism during the Penokean Orogeny. The chief rock fabric is the N45 °E striking foliation that dips 690 to 760 to the northwest, parallel to lithologic units. Cross-cutting faults have been noted in the massive sulfides but cannot be traced with any degree of certainty into the host volcaniclastic rocks. Numerous, small cross-cutting displacements, with 2 to 5 foot offsets, in the footwall chert and massive sulfides on the north contact of the orebody have been disclosed by pit mapping. These displacements could represent minor graben and horst development in the original ocean floor. The presence of these fault blocks indicates to the authors that the Flambeau orebody has not been highly folded and sheared as suggested by some geologists. These structures are shown on Figure 5. r �FOLIATiON BIOTITE—FELDSPAR (lUFF) QUftTZ—SERlC[TE (RI-IYOLITE lUFF) MASSWE SULFIDES ANDALUSITE—BIOTITE (SEDIMENTS) METACHERT — FAULT r:i PRECAMBRIAN PROTEROZOIC GLACIAL TILL PLEISTOCENE LEGEND Rusk County, Wisconsin Figure 5 Geology of 1070 Bench, Flainbeau Mine A LENS 0 SCALE1 1"20 10 20 _ // FEET (.n 0 1 D I z D I- I- N (Il D �81 The largest recognized cross-cutting fault occurs near mine Section 408 where the east side of the stratigraphic footwall of the orebody has been offset 30 feet to the south. The fault strikes N85°W, and dips 65° to 85° NE. This right lateral offset relationship holds true along the strike length of the orebody where other smaller offsets have been mapped. Although these cross-cutting structures appear to be a part of the northwest fabric identified by Sims and others (1989) for the Precambrian in northern Wisconsin, none of the northwest faults at Flambeau can be traced southward into the hangingwall. Cross-cutting faults can be traced for short distances of less than 50 feet north into the footwall where they rapidly deteriorate into weak joint surfaces. It is therefore suggested that these faults are penecontemporaneous with the mineralizing events and not more deep-seated structures associated with the later Penokean Orogeny. The east end of the orebody may have been subjected to post-ore faulting, with the end of the orebody rotated clockwise to the south. There is evidence of a fault offset at the very east end of the orebody with the east side dropped down an unknown distance. Deep drilling into the down-dropped block gave negative results. The rock in the Flambeau open pit is intensely fractured by several series of joint sets. There are two predominant flat joint sets, one striking approximately N65°W and dipping 15° to 25°N, the second striking N75°W and dipping 30° to 40°N. There are also three principal groups of high angle joints striking: 1) N40°E dipping 65° to 85°S; 2) N85°W, dipping 65° to 85°N; and 3) N70°E dipping 65° to 85°N. ALTERATION The Flambeau orebody has been subjected to intense alteration associated with primary sulfide mineralization, regional metamorphism during the Penokean Orogeny, and by significant near-surface supergene alteration of the silicate rocks leading to enrichment of the massive sulfides. The combined effect of these three processes is that original mineralogy is obscured and in some cases totally changed. No systematic study of the alteration zones has been undertaken; therefore, the account given here is preliminary. Mineralogy of the rocks stratigraphically below the ore zone suggest a complex history of hydrothermal alteration. Abundant andalusite in the footwall rocks indicates that the primary volcanic rocks have been significantly enriched in alumina. This may have been accomplished by hydrothermal leaching by acidic fluids which removed K, Na, and Ca from the felsic and intermediate volcanic rocks (Table 2). FeO and Mg were added with iron-rich chlorite probably accounting for most of these increases. The altered rocks were presumably rich in kaolinite, which was prograded to andalusite during regional metamorphism to upper greenschist facies. The decrease in andalusite at the east end of the orebody suggests less hydrothermal alteration of the primary volcanic rocks. This hydrothermal alteration was presumably associated with massive sulfide deposition. It must be emphasized, however, that no well-defined alteration "pipe" or stringer ore found in other massive sulfide deposits has been identified in rocks associated with the Flambeau orebody. The two beds of spessartite-chlorite in the stratigraphic footwall indicate significant manganese enrichment in those horizons. Origin of the manganese-rich horizons is problematical. They may be the result of seawater-sediment interaction, and may not be related to hydrothermal alteration associated with the massive sulfide deposition. �82 Regional metamorphism produced an upper greenschist or lower amphibolite facies suite of minerals with predominately biotite, andalusite and some cordierite. Supergene alteration, while low temperature and low pressure, profoundly altered the first two mineralogical events. The alteration effects on the sulfide mineralogy will be discussed further in the subsection entitled Supergene Enrichment. Supergene alteration produced acidic conditions that totally bleached the host rocks for a horizontal distance of 100 feet into the footwall and 50 feet horizontally south into the hangingwall volcaniclastics. The ferromagnesian minerals have been almost completely altered to clay (montmorillonite) and sericite or chlorite-sericite further away from the orebody. As described further under the subsection entitled "Gossan," large volumes of supergene activated silica were mobilized and recemented to form-s hard, dense silica breccia. On the margins of the highly bleached zone is the leached and oxidized zone where the chloritized ferromagnesium minerals plus small amount of sulfides (1 to 2%) have been oxidized. Overlying the bleached and weathered leached zones is a thick saprolite layer. This layer varies from about 5 feet to over 30 feet of intensely clay-altered volcaniclastic rock. X-ray diffraction has identified the chief minerals to be montmorillonite, micron-sized silica and in some areas pyrite. OREBODY SHAPE In general, the Flambeau orebody is a steeply dipping, near tabular massive sulfide lens. It averages 45 to 50 feet in thickness reaching a maximum thickness of about 70 feet on section 407. The strike length is 2,400 feet and is parallel to foliation. The orebody subcrops at the 1 100-foot elevation and bifurcates below the 1070-foot elevation, suggesting it is actually the roots of a much larger and eroded mineral system. The main part of the orebody is referred to as the "A" lens. The "B" lens, located south of the "A" lens, averages 10 feet in thickness. It is joined to the "A" lens at section 4.06 and diverges south/westward into the hangingwall, so that on section 400 it is about 100 feet south of the "A" lens. The "C" mineralized horizon occurs 50 feet north of the "A" lens in the footwall and probably represents an early mineralizing event in an emerging mineral-rich system. The "C" horizon is less than 10 feet thick discontinuous, deficient in gold values, and poorly mineralized with chalcopyrite. Contrary to previous reports (May, 1977) the hangingwall and footwall contacts are sharp and clearly defined where seen in the open pit. MINERALOGY The supergene mineralogy, paragenesis, and crystallography probably ranks Flambeau as unique among massive sulfide deposits in the Canadian Shield. Although other enriched massive sulfides have been found in the Shield, none have been as well preserved, with an extensively supergene enriched copper zone capped by a gold-enriched gossan. PRIMARY MINERALIZATION Primary mineralization occurs 130 to 185 feet below the subcrop and supergene enriched mineralization. Pyrite (60%) is the chief mineral with lesser amounts of chalcopyrite (12%) and sphalerite (2.5%). Gold, silver, galena, and pyrrhotite occur in minor quantities. The above minerals occur in various proportions and combinations as massive, semimassive, and disseminated �83 sulfide mineralization. Based on drill-core observations, the author has defined massive sulfide to contain greater than 50 weight percent sulfides, semimassive to contain between 20 and 50 weight percent sulfides, and disseminated to contain less than 20 weight percent sulfides. Although the above definitions may conflict with previous work on other deposits, they best suit conditions found in the Flambeau deposit. Massive sulfide dominates the upper part of the steeply dipping and overturned deposit to 600 feet beneath the subcrop. However, the east central portion of the sulfide deposit contains semimassive mineralization. Semimassive mineralization increases with depth from a strike length of 500 feet in subcrop to 2,400 feet at 600 feet beneath the surface. A disseminated sulfide halo which averages 215 feet in width and contains 7% pyrite encloses the massive-semimassive mineralization. The halo extends along strike for at least 5000 feet in either direction and downdip for an unknown distance. Therefore, massive-semimassive sulfide mineralization gradually decreases with depth and rapidly decreases horizontally away from the deposit. The massive sulfide mineralization displays well developed mineral zoning across the deposit. The stratigraphic footwall or northern part of the ore zone tends to be chalcopyrite-rich with sphalerite noticeably more abundant toward the hangingwall. Most of the hangingwall satellitic lenses are sphalerite-rich. Based on stratigraphic-mineral zoning work conducted in the Noranda District (Gilmour, 1965), where copper favors the stratigraphic footwall, it is believed that the Flambeau deposit is overturned. The semimassive sulfide mineralization is weakly zoned with pyrite the dominant sulfide. It forms narrow, sub-concordant, massive to semimassive layers interbedded with wealdy mineralized and chloritized quartz-sericite schist and metachert. Chalcopyrite is coarser grained than that found in the massive sulfide mineralization, occurring as large irregular masses up to 50mm in diameter. It also occurs as interstitial fillings around the 1mm to 3mm pyrite grains. Small amounts of sphalerite (less than 1%) are scattered throughout the zone as grains, as narrow bands up to 6mm in width, and as occasional irregular clots less than 7mm in diameter. Gangue minerals in both the massive and semimassive zones are quartz (metachert), sericite, and lesser amounts of chlorite and andalusite. The grain size and distribution of the gangue minerals is highly variable: they may occur as small, irregular particles 2mm to 5mm; across, as patchy inclusions 40mm to 50mm; across, or as narrow, concordant, ellipsoidal lenses or fragments. COSSAN A total of 115,000 tons of gossan with an average grade of 0.6 opt Au have been mined from the top of the massive sulfide orebody. Three types of gossan have been recognized during core examination and mining, which, in general, grade from chert gossan in the west end of the pit, to argillic gossan, then to ankeritic gossan in the far east end. Chert Gossan. Chert gossan was dominant in the west half of the open pit and has been further sub-divided into the cherty breccia, the purple-red, and the sandy gossan (Figure 6). A cherty breccia zone overlaid a purple-red gossan from Section 401 to 413. A sandy gossan occurred on the hangingwall between Sections 404 and 408. All three zones consisted of subrounded to angular cherty and possibly secondary quartz fragments. Iron oxide coated the silica-rich particles and fragments in varying amounts. Fine-grained gold was present in all three zones. Hematite was the chief iron oxide followed by goethite with lesser amounts of jarosite. �NW SE 03 BR IAN SANOSTO NE CHERIY BRECCIA ±0.1—0.6 opt Au SAPROLITE 20PURPLE— RED ±1.0 opt Au 3—5' —FOOTWALL CHERT UPPER ZONE CI-IALCOCITE 15—80' II MIDDLE ZONE CHALCOCITE—BORNITE —FOOTWALL MIDDLE ZONE 35—125' GOLD HORIZON BORNITE—CHALCOPYRITE ORE HORIZON - - - LOWER ZONE CHALCOPYRITE—BORNITE CHALCOCITE 10—80' / 10 SCALE 0 20 FEET 1" =20' LOOKING NORTHEAST Figure 6 // // Supergene Vertical Zoning — Generalized Section West End, Flambeau Mine Rusk County, Wisconsin �85 i) Cherty Breccia. The cherty breccia or silica-rich gossan was not a true breccia, although it did contain abundant fragments of partially decomposed chert. The stratigraphic footwall chert on the north side in many places collapsed on top of this zone during volume reduction as the massive sulfides were being oxidized. These collapsed chert fragments (<2 inches) and blocks (<2 feet) capped much of the gossan. A gradual disintegration occurred from the footwall massive, hard chert towards the hangingwall where the chert became sandy in texture. A large amount of secondary silica has remained high up in the gossan, which could have been derived by solution of small amounts of cherty inclusions found around sulfide grains in the protore. Botryoidal and stalagmitic silica has been observed in the west wall gossan. The cherty breccia must have been in constant flux as the underlying massive sulfides were being leached, enriched, and then oxidized with the gossan collapsing on top. Eventually a stage of semi-equilibrium was reached where the cherty breccia was recemented into a hard, dense, light gray, poorly to nonfoliated silica-rich rock. This rock consisted of 2 mm to silt-size subrounded to angular quartz particles. Very small amounts of iron oxide, and traces of native copper, and gold make up the remainder of the rock. Quartz content ranges from 88 to 96 volume % of the rock. The cherty breccia thickness ranges from 6 to 12 feet and has a sharp contact with the underlying purple-red gossan. ii) Purple-Red. The purple-red gossan was named because of its distinct coloration resulting from a high hematite content. This zone was unconsolidated, subrounded to angular quartz grains in a matrix of hematite, goethite, and jarosite. Hematite occurs as botryoidal coatings up to 1 cm in diameter or as earthy masses. Small amounts of kaolinite have been noted. The purple-red zone ranges in thickness from 6 to 12 feet. iii) Sandy-Gossan. A sandy gossan zone formed in the stratigraphic hangingwall adjacent to the cherty breccia and purple-red zones over a thickness of 20 feet and a strike length of about 500 feet. Contacts with the adjacent two zones was gradational over a foot or two, and less gradational with the hanging wall volcaniclastics to the south. This zone had a distinct salmon pink to purple-red color, was unconsolidated and consisted of fine-grained, subrounded quartz grains with varying amounts of iron oxide and less clay particles. It was a well-sorted, iron stained quartz sand with high gold content. Fragments and blocks of sandstone several inches to a foot in size were noted as deep as 13 feet into the sandy gossan. These blocks have been tentatively identified as Late Precambrian sandstone incorporated within a water reworked section of the gossan. Gold content was in places at least two to four times higher than that in the purple-red zone. Gold in all three zones of the chert gossan occurred as less than 20 micron-sized grains with only small amounts of silver. Silver in the gossan does not occur as electrum. In the cherty breccia zone, gold contained 2 to 4% silver, whereas gold in the purple-red contained less than 0.5% silver. The purple-red zone however, generally hosted about three to four times more gold than the overlying cherty breccia. Argillic Gossan. The argillic zone formed over the orebody from Section 413 to 418. Petrographic examination of this zone has shown it to be dominated by quartz with smaller amounts of hematite, goethite, jarosite, chlorite, montmorillonite, illite, rutile, chalcopyrite, and the alunitejarosite family of minerals. This gossan was yellow-brown in color, highly foliated, broken, and contained a moderately developed zone of purple-red gossan along the base. The purple-red gossan corresponded well to underlying internal massive sulfide zones within a predominantly semimassive portion of the orebody. Free-silica values were significantly lower in both the argillic �86 and ankeritic gossans than in the chert gossan. The argillic gossan was about 40 feet wide and 15-20 feet thick. Ankeritic Gossan. Gossan in the east end was characterized by a high ankerite and very low silica content. At least 35 vertical feet of ankerite gossan have been mined with small zones going to greater depths along contacts or strong joints. This zone was a dark purple-brown poorly to well cemented, massive textured gossan. Ankerite was well developed with cleavage planes and crystal faces. up to 0.5 inch developed. It also contained quartz grains with hematite, iron oxides, native gold and lesser amounts of chalcopyrite. Silver values, in the inunediate underlying enriched copper zone, are up to ten times higher than in the rest of the orebody. The reason for this phenomenon is still uncertain, but is suspected to be linked to the ankerite mineralization. OXIDE ZONE An oxide zone was present beneath much of the gossan and had a thickness of two to five feet. This zone consisted of cuprite, goethite, and malachite, with lesser amounts of azurite, chalcopyrite, and native silver. The oxide zone contained up to 20% copper oxides. Malachite occurs as earthy coatings or occasionally as botryoidal fillings. Azurite occurred as earthy fillings and occasional small crystals. Copper oxides have been found on faults and fractures 60 feet or deeper below the subcrop. At the top of the oxide zone, horizontal manganese "pipes" up to two to three inches in diameter were observed. These tubes, now filled with sand, appear to have once transported large volumes of groundwater along the top of the enriched massive sulfide orebody. The gossan and oxide zones wrap around the sides of the sulfide orebody. The oxide zone descended about five to ten feet, whereas the gossan zone with minor azurite and malachite draped 20 to 30 feet down the flanks of the orebody in more porous areas. The top of the black supergene enriched sulfides below the gossan and oxide zones was remarkably smooth, and sloped gently at the edges towards the enclosing volcanic host rocks. Vertical relief rarely exceeded two to four feet with slope angles of one to two degrees. SUPERGENE ENRICHMENT Supergene enrichment affected the primary massive, semimassive, and disseminated sulfide halo zones. The extent and degree of enrichment depended upon original base metal mineralogy, rock permeability, foliation planes, structure, and a fluctuating groundwater table. The well developed schistosity planes in the wealdy mineralized volcaniclastic host rock directed mineral-rich, acidic waters to depth. Medium grained, subhedral to granular, and weakly foliated massive sulfides had a higher permeability than the clay-rich host rock permitting the supergene enrichment processes to extend to greater depths. The west end of the orebody has been enriched locally to 185 feet below the subcrop, and the east end to 140 feet, as shown on Figure 7. Enrichment has been restricted to 80 to 100 feet below the subcrop in the central part of the deposit. Enrichment in the volcaniclastic host rock was generally several tens of feet shallower and of much lower grade due to its lower permeability. The more felsic and extensively pyritized stratigraphic footwall volcaniclastic rock have been preferentially enriched relative to the more basic, less pyritic, and chlorite-rich hangingwall rocks south of the orebody. Individual grains of primary sulfides in the disseminated sulfide halo have been partially or completely replaced with chalcocite and/or bornite. These secondary minerals form solid replacement minerals, microrimmings on the protore surfaces, or as sooty coatings. Sphalerite and galena were preferentially replaced relative to chalcopyrite and even less reactive pyrite. Consequentially, zinc �QUARTZ—SERICITE SCHIST BIOTITE—FELDSPAR SCHIST CHERTY GOSSAN PURPLE—RED GOSSAN ANDALUSITE—BIOTITE SCHIST, SERICITE—CLAY MASSIVE SULFIDES PRECAMBRIAN PROTEROZOIC MOUNT SIMON SANDSTONE CAMBRIAN MEGACHERT [] GLACIAL TILL PLEISTOCENE LEGEND Section 406 1=50 i 50 FEET Rusk County, Wisconsin LOOKING NORTHWEST 0 SCALE25 Figure 7 Geological Cross Section 406 & 418, Flambeau Mine Section 418 11 B LENS �88 values are generally less than 0.05% and lead is rarely detectable in the enriched ore. It is suspected that some of the high grade sooty chalcocite zones were formed in areas of high primary sphalerite. The supergene enriched mineralization is zoned vertically. The Upper zone is chalcocite dominant, the Middle zone is bornite-chalcocite dominated, and the Lower zone is a mixture of chalcopyrite-bornite-chalcocite. The formation of these zones is determined by original base metal content, fracturing, and faulting that directed supergene enriched fluids to depth within the orebody. Some of the structural features that helped determine this pattern of enrichment are shown on Figure 8. Supergene sulfides in the Upper and Middle zones were developed at the expense of all of the primary base metal minerals and much of the pyrite. The contact between the two zones is gradational. Chalcocite occurs as irregular steely masses, microrimmings, sooty films, sandy zones and fracture fillings. Some of the best copper grades were found in sandy-chalcocite areas located close to and parallel with the orebody contacts. The Upper and Middle zones of the west end of the deposit are of approximate equal vertical thickness of about 75 feet. In the Middle zone, bornite occurs as massive replacements or as numerous reticulating veinlets replacing chalcopyrite. As this replacement became more complete the veinlets coalesced to form irregular bornite masses and "veins". The replacement process continued with bornite being replaced by chalcocite. At each successive enrichment stage, additional pyrite was consumed so that at the end of the replacement process significant amounts of pyrite had been replaced. The supergene paragenesis, described in the next subsection, is based on relationships observed in the supergene enriched zone. Botryoidal secondary chalcopyrite is common in the Lower zone as well as in the Middle zone. Chalcopyrite botryoids have been observed ranging from less than a millimeter in thickness to over five millimeters. Most of the thicker botryoids show fluctuating deposition with bornite. Micron-size tetragonal chalcopynte crystals have been frequently noted, particularly on bornite. Bornite has not shown any crystal habits. On the other hand, chalcocite occurs in a variety of spectacular crystals both twinned and untwinned. These crystals are generally coated by blue to purple iridescent or gold colored chalcopyrite and more rarely bornite. To form an enriched orebody the size of Flambeau would require weathering, taking mineralization into solution, and reprecipitation of a deposit on the order of 6 to 10 million tons. Therefore, the enrichment must predate deposition of the overlying Cambrian sandstone, because the volume of rock between the sandstone and the enriched zone could not have produced the enriched ore present. PARAGENESIS The paragenesis of the Flambeau orebody has been subdivided into three stages as shown on Figure 9. These stages are: 1) primary deposition of the host rocks and mineralization, 2) regional metamorphism, and 3) secondary enrichment and weathering. Stage 1 consists of three main stages of base metal and silica deposition commencing with the early "C" horizon. The second stage resulted in the formation of the "A" horizon with at three exhalative silica pulses. Pulse one formed the thicker footwall chert, pulse two was ongoing weak intermittent deposition of silica within the orebody, and pulse three formed the hangingwall chert south of the orebody. Base metal mineralization during stage two is dominated by copper with a few areas of zinc. The third stage is dominated by zinc, gold, �L 400 LEGEND INTERPRETED FAULTS PRIMARY SULFIDES 410 MINE SECTION LOOKING NORTHWEST Figure 8 Longitudinal Section of Supergene Mineralogical Zoning, Flambeau Mine Rusk County, Wisconsin BORNITE—CHALCOCITE CHALCOCITE, LOWER ZONE BORNITE—CHALCOCITE, MIDDLE ZONE CHALCOCITE—BORNITE, MIDDLE ZONE CHALCOCITE—DOMINANT, UPPER ZONE GOSSAN PRECAMBRIAN PROTEROZOIC MOUNT SIMON SANDSTONE CAMBRIAN GLACIAL TILL PLEISTOCENE SW 420 0 75' 150' 5 300' 424 300' 600' • 150 75. 37.5' 0 NE �90 and decreasing amounts of copper extending out into the hangingwall (i.e., the "B" lens), giving a zoning profile of copper changing to zinc upward in the original stratigraphy. Regional metamorphism is characterized by the formation of upper green schist to lower amphibolite facies minerals. Diagnostic minerals are andalusite, spessertite garnet and biotite. Quartz "sweats" are common with many showing boudinage structures. Schistose textures and foliation developed during this stage. Chalcopyrite, and other sulfides, were remobilized to form coalescing irregular blebs, while pyrite recrystallized to form medium grained subhedral grains. These sulfides along with minor gold are associated with localized quartz "sweats" on the flanks of the orebody. The enrichment stage resulted in the formation of a suite of secondary minerals, probably during late Precambrian time. Simplistically this stage produced significantly enriched copper values in the upper part on the deposit through the removal of iron and reprecipitation of copper from higher levels in the weathering zone. The enrichment shows the classic mineral zonation, with the conversion of primary pyrite to secondary chalcopyrite in deeper levels of the deposit, overlain by a bornite-nch zone, developed by enrichment of the chalcopyrite. Chalcopyrite is commonly found in three forms: botryoidal, rosettes of platy chalcopyrite; and shiny brassy platy open-fracture fillings. Finally, chalcocite developed by removal of iron from the bornite, probably at the paleo-water table. Native copper, cuprite, azurite and malachite developed in the oxidized zone above the paleo-water table. However, this simple pattern was complicated by local variations in porosity, permeability and mineralogy in the ore. For example, irregular masses of primary pyrite and chalcopyrite are found within the secondary chalcocite. Possible fault zones allowed oxidation and enrichment to extend much deeper in the orebody. The result is a very irregular mixture of minerals within the ore. The mineralogy is also complicated by major changes in the level of the water table that occurred subsequent to the main enrichment. The present water table is much closer to the surface than the paleo-water table during supergene enrichment, as shown by the presence of secondary oxide minerals below the present water table. In addition to massive material, much chalcocite occurs as "sooty" and granular, or sandy-textured material that may have formed by replacement of the granular pynte produced by metamorphism or by replacement of massive beds of sphalerite. Enrichment also produced numerous cavities within the ore, in which late-stage minerals developed. Some cavities contain well-formed chalcocite crystals in a variety of crystal forms to nearly three inches long. These chalcocite crystals typically have a blue, purple, or brassy yellow patina produced by a thin surface coating of bornite and/or chalcopynte. The surface coating probably formed when the rising water table placed the chalcocite crystals in the stability field of bornite and chalcopyrite. Chalcocite crystals occur as psuedohexagonal plates up to two inches in diameter, stacked psuedohexagonal columns or barrels up to 0.75 inch long by 0.25 inch wide, twinned orthorhombic crystals, up to 2.5 inches in length by 0.75 inch in width, and curvilinear "scimitar-like" forms up to 0.5 inch long. A picture of a twinned orthorhombic chalcocite crystal appears in this memorial volume. �EARLY LATE PRIMARY METAMORPHISM SECONDARY 1.76 BY upper greenechist to lower amphibolito late Pro-Cambrian -? early Cambrian Cu-Au-Ag-Zn VMS DEPOSITED IN BACK-ARC BASINAL SETTING PYRITE CHALCOPYR lIE SPHALERITE GALENA EXHALATIVE SILICA QUARTZ ARSENOPYRITE DURING OROGENY, SULPHIDES RECRYSTALLIZED, LOCAL PRECIOUS METAL MOBILIZATION, QUARTZ INJECTION, LOCALIZED FOLDING. POSSIBLE EXTENSIONAL SMEARING FROM REGIONAL FOLDING SUPERGENE ENRICHMENT OF COPPER SULPHIDES, ASSOCIATED WITH GOSSAN GENESIS ON OVER-TURNED, SUB-VERTICAL DEPOSIT DIT FLUCTUATING WATER TABLE OXIDING AND VERY ACIDIC Zn mobized out of system —— '7 Pb mobtzed out of system —— AN DALU SITE CHLORITE (ALTERED DACITIC) BIOTITE SERICITE (ALTERED RHYOLITIC) GARNET GOLD SILVER CHALCOCITE BORN ITE CHALCOPYR lIE ANKERITE-SIDERITE HEMATITE ? CALCITE ?IN PRIMARY EXOTICS AZURITE MALACHITE CU PR lIE DIGENITE CHALCOCITE PSEUDOMORPH AFTER GALENA BORNITE PSEUDOMORPH AFTER BOTRYOIDAL CHALCOPYRITE CHALCOCITE CRYSTALS NATIVE COPPER BORNITE 'BULLETS & BOTRYOIDS AFTER CHALCOPYRITE (WITH INTERNAL CHALCOPYRITE LAYERS) HORIZON PYRITE CHALCOPYRITE SPHALERITE GALE NA GOLD SILVER CHERT QUARTZ Figure 9 "C', . PRIMARY "A" - -I — --— —1- _- -_ — "B" pt— --— A w GENERALIZED PARAGENESIS OF THE FLAMBEAU OREBODY �92 Occasionally some bizarre relationships or textures occur, for example, the exquisite "scimitar-like" chalcocite crystals that occurred high up in the orebody (1070 level). In contrast, twinned orthorhombic chalcocite crystals were collected from a 3x3x 10-foot vug on the 1010 level. Other cavities contain botryoidal growths of bornite, chalcopyrite or chalcocite, or may contain encrustations of carbonate minerals (mainly ankerite, dolomite and siderite). Some carbonate crystals have tiny rosettes of chalcopynte on which are specks of lead oxide scattered on crystal faces. Agaul, the chalcopyrite may have formed after the water table rose. The gold-rich gossan evidently formed by residual concentration of gold as erosion slowly lowered the paleosurface as supergene sulfide enrichment was in progress. Coarse crystalline pyrite with scalehedrons of arsenopyrite have been collected near the stratigraphic hangingwall. Quartz pods are associated with this mineralization, as are native gold, bornite, and chalcocite. This gold is very fine grained and is possibly a supergene product. Similar gold has been observed within, but close to, the orebody's contacts. This gold is intimately associated with quartz that contains bornite, minor chalcocite, and lesser chalcocite psuedomorphs after galena and is interpreted to be related to remobilization processes during regional metamorphism, later acted upon by supergene processes. CONCLUSIONS The Flambeau orebody is a well preserved supergene enriched massive sulfide deposit capped by a gold-enriched silica-iron oxide gossan. A small, thin, poorly indurated Cambrian sandstone outlier capped the gossan and supergene enriched mineralization and helped protect them from significant glacial erosion. The dominant chalcocite-bornite enriched mineralization was formed to depths up to 185 feet below the subcrop. Copper values in excess of 20% have been mined, particularly in areas of massive steely-gray chalcocite, and zones of sooty chalcocite that probably replaced massive sphalerite. A total of 1.71 million tons grading 10.3% Cu, 0.116 opt Au, and 1.837 opt Ag will be mined from 1993 to 1997. Three products are shipped via rail from the open pit. Gossan ore and direct smelting shipping ore greater than 14% Cu are railed to Noranda's Home Smelter at Rouyn-Noranda, Quebec, Canada. Mill ore grading 6 to 10% Cu is railed to the Kidd Creek Mill located at Timmins, Ontario, Canada where it is concentrated then redirected to the smelter. While modest in size, the Flambeau orebody will be remembered for its classical supergene mineral zoning, high copper and gold grades, and exquisite twinned chalcocite crystals. The importance of the pioneering environmental safeguards implemented at Flambeau match the economic contributions made by both private and public institutions (May, 1977) Successful mining of the orebody beside the Flambeau River and City of Ladysmith, while enhancing and maintaining surface and groundwater quality respectively, is in itself a milestone for the American base metal mining industry (Murphy, 1996). �93 Acknowledgments The authors wish to thank Tom Myatt, General Manager of Flambeau Mining Company, for allowing this paper to be written and for supporting and hosting the 1996 Institute on Lake Superior Geology field trip. A considerable amount of assistance was provided by Jay Hammitt, Russ Babcock, Gene LaBerge, and Ray Yost, all of whom polished the manuscripts with almost too much enthusiasm but whose insights and efforts were greatly appreciated by the authors. A special thanks to Tammy Fredrickson who repeatedly deciphered our geological scribblings and prepared the manuscript for this volume. References Cited Babcock, R, 1996, History of Exploration for Volcanogenic Massive Sulfides in Wisconsin: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip Volume. DeMatties, Theodore A., 1994, Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview: Economic Geology, v. 89, p. 1122-115 1. Gilmour, P., 1965, The Origin of the Massive Sulfide Mineralization in the Noranda District, Northwestern Quebec: Geologic Association of Canada, v. 16, p. 63-82. LaBerge, G. L., 1996, General Characteristics and Geologic Setting of the Wisconsin Magmatic Terranes: Institute on take Superior Geology, 42nd Institute, 1996 Field trip volume. May, E. R., 1977a, Flambeau - A Precambrian Supergene Enriched Massive Sulfide Deposit: Geoscience Wisconsin, v. 1, p. 1-26. May, E. R., 197Th, Case study of Environmental impact - Flambeau Project: Mining Congress Journal, v. 63, p. 39-46. Morey, G. B., Sims, P. K., Mudrey, M. G., and Southwick, D. L., 1982, Geologic Map of the Lake Superior region, Minnesota, Wisconsin, and northern Michigan: Minnesota Geological Survey State May Series S-13. Murphy, J., Dachel, R., 1996, Case Study of Environmental Requirements for the Permitting Operation, and Reclamation of a Metallic Mineral Mine in Wisconsin - Flambeau Mine: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip volume. Schwenk, C. G., 1977, Discovery of the Flambeau Deposit, Rusk County Wisconsin Geophysical Case History: Geoscience Wisconsin, v. 1, p. 27-42. - A �94 �95 CASE STUDY OF ENVIRONMENTAL REQUIREMENTS FOR THE PERMITFING, OPERATION, AND RECLAMATION OF A METALLIC MINERAL MINE IN WISCONSIN FLAMBEAU MINE by JANA E. MURPHY Supervisor of Environmental Affairs, Flambeau Mining Company and RICHARD T. DACHEL Environmental Chemist, Flambeau Mining Company INTRODUCTION The Flambeau Mining Company (Flambeau), a subsidiary of Kennecott Minerals Company, owns and operates an open pit copper mine located just south of Ladysmith, Wisconsin. The 181 acre mine site is bounded on the west by the Flambeau River, on the east by State Highway 27, and to the north by the City of Ladysmith. While Flambeau owns the majority of the surrounding properties as a buffer, there are private properties and homes within 100 feet of the perimeter of the mine site. The surrounding natural and anthropogenic features made the permitting of the Flambeau Mine especially unique. A representation of the unique features within and surrounding the project area are listed below: • • • • • • • Flambeau River located 140 feet from west edge of pit; Intermittent streams requiring relocation and re-establishment; Wetlands requiring mitigation; State highway within 1000 feet of facilities; Private landowners within 100 feet of the perimeter of the mine site; The center of the City of Ladysmith is located 1.6 miles north of mine site; Relatively shallow groundwater table within 20 feet of surface. FLAMBEAU PERMITS Another unique aspect of Flambeau is that it is currently the only operating metallic mineral mine in the State of Wisconsin. The Flambeau Mine is also the only metallic mineral mine to receive permits under Wisconsin's current mining laws. Flambeau received its eleven permits following: 1) extensive baseline monitoring; 2) data compilation and review; 3) identification of potential environmental impacts; 4) facility design to minimize impacts; 5) submittal of permit applications and management plans; 6) Wisconsin Department of Natural Resources (WDNR) review; 7) public comment; and 8) a contested case hearing. Typically, four to five years (or longer) is required to complete the aforementioned process prior to the granting of permits allowing the operation of a mining facility. The WDNR granted eleven permits to Flambeau during January 1991. Flambeau's permits are listed below: • • • • Mine Permit Wisconsin Pollutant Discharge Elimination System (WPDES) Permit Air Pollution Control Permit Groundwater Withdrawal Permit �96 • • • Permit for a One-Time Disposal Facility Water Regulatory Permits (five individual permits) Approval for the Wastewater Treatment Facility In addition, numerous management plans, studies and models were submitted to the WDNR which detailed the measures to be taken to protect the environment. These management pians were incorporated by reference into Flambeau's permits. STUDIES AND MODELS Waste Rock Characterization Several studies were performed and models developed prior to the final design of the Flambeau site facilities. One of the primary considerations was characterization of the various waste rock products. Characterization of waste rock determines: 1) the best practices for temporary stockpiling; 2) methods of water treatment prior to discharge to the Flambeau River; 3) preferred methods of backfilling the open pit; and 4) prediction of groundwater quality down gradient from the backfilled pit. Waste rock characterization studies included both static and kinetic geochemical tests performed in a laboratory on samples which had been collected during core drilling of the orebody and surrounding waste rock. The static tests included bulk chemical analyses for all potential mine waste and acid production and neutralization tests on the waste rock composites. The kinetic tests included wet-dry leaching tests which simulated the conditions under which the waste rock would be temporarily stored. The wet-dry leaching tests were followed by saturated leaching tests which simulated conditions within the backfilled pit. The results of the wet-dry leaching tests determined that waste rock containing less than two percent sulfur had a very low acid-producing potential. The low sulfur waste rock can be temporarily stockpiled without an underlying liner system since there is minimal potential impact to groundwater quality. Likewise, the waste rock containing high sulfur (>2%) is required to be temporarily stored on a high density polyethylene liner (HDPE) and leachate collection system since these materials have the potential to produce acidic leachate. Flambeau chose to add an additional factor of protection by restricting the waste rock placed in the unlined stockpile to that containing less than one percent sulfur. Waste rock containing less than one percent sulfur is referred to as Type I material. Type II material is that waste rock containing one percent or greater sulfur content. Water Treatment Methods The waste characterization also determined the appropriate treatment methods for water contacting each waste rock type. Water which contacts the Type II waste rock must be treated through Flambeau's onsite Wastewater Treatment Plant (WWTP). The types of water treated are groundwater, storm water and snow melt runoff that discharge into the open pit and leachate from the Type II stockpile. The WWTP operation is discussed in detail in a following section. The Type II stockpile was anticipated to generate acidic leachate shortly after stockpiling was initiated. Following two years of stockpiling, the Type II stockpile has recently begun to generate a lower pH leachate of approximately 6 standard units (s.u.). This pH is still significantly higher than the leachate studies predicted. These studies resulted in a model predicting the leachate to have a pH of 2.95 - 4.10 s.u. Water contacting Type I wasterock requires minimal treatment. This treatment includes two settling �97 ponds designed to contain in excess of a 25-year storm event. Intermittent discharges from the settling ponds were anticipated during spring, summer, and fall; however, the storm water runoff has infiltrated into the open pit rather than requiring discharge. Pit Backfill The laboratory testing of the two types of waste rock helped determine the most appropriate methods of backfihling the pit. The waste rock will be returned to the pit in the following order, bottom to top: 1) Type II waste rock; 2) Type I waste rock; 3) saprolite; 4) sandstone; 5) till; and finally 6) topsoil. Each material type is segregated as mined from the pit to allow for a sequential backfill. The saturated leaching tests indicated the potential for leachate to contain substances from the Type II waste rock. Four parameters (copper, iron, manganese and sulfate) were predicted to be found in measurable concentrations in the groundwater emanating from the Type II waste rock in the reclaimed pit. Further testing showed that the addition of lime significantly reduced the concentration of some substances within the leachate. As a result, lime will be backfilled with the Type II waste rock at the rate of 2.5 pounds lime for each ton waste rock. The impact of these four parameters is minimal to the Flambeau River. Based upon a mean river flow of 1, 855 cubic feet per second and predicted groundwater flow into the river from the waste rock zone of 0.0045 cubic feet per second, the incremental increase in river concentrations would be: • • • • Copper - 0.000000034 mg/l Manganese - 0.0000013 mg/i Iron - 0.00000078 mg/l Sulfate - 0.0033 mg/i. The predicted increase in river concentrations will be below analytical detection limits. It is evident that there will be minimal, actually undetectable, impact upon the Flambeau River associated with materials backfilled within the pit. Groundwater Drawdown Model Another study performed is the model of the predicted groundwater drawdown contour and potential impacts upon private wells. Five private wells are known to be located within the maximum extent of drawdown which has been modelled to extend 2750 feet from the edge of the mine pit. Four of the wells will not be significantly impacted, while the fifth well could be impacted by a predicted eight foot drop in water elevation. The potential effects upon the five wells are considered within the Local Agreement that Flambeau signed with the local government entities. If wells are impacted by mining activities, Flambeau will provide water or replace the wells. To date, water supply to local wells has not been significantly impacted and property owners are convinced that the palatability of their water supply has improved. OPERATION PHASE The studies and models previously mentioned provided Flambeau the knowledge to use modern technology and a pro-active environmental commitment in the construction of an environmentally safe facility. Flambeau has constructed and is operating a facility that is a model of modern mining technology, engineering and science, providing superior environmental protection. Environmental safeguards include the treatment of all contact water, suppression of dust, erosion �98 control, on-site spill prevention programs and an extensive monitoring program that ensures that the environmental safeguards work as they were designed and approved by the WDNR. Wastewater Treatment Plant The WWTP is a key component of Flambeau's protection of groundwater and surface water in its commitment to conducting environmentally responsible mining. Sources of contact water include mine seepage, precipitation into the open pit and storm water run-off from the lined Type II stockpile and the lined crusher/loader areas. The WWTP design allows for pH neutralization and metal removal in a three-stage process consisting of lime treatment, sulfide precipitation and multi-media filtration (Figure 1). The WWTP design capacity of 800 gpm is more than adequate to handle normal conditions. The open pit acts as an ultimate sump during extreme storm events. Mine seepage and precipitation require an average pumping rate of approximately 225 gpm throughout the year. The WWTP incorporates scientific treatment processes with advanced computer technology through its control system, a General Electric LM 90-70 Series Programmable Logic Controller. Flambeau's WWTP operators, certified by the state use knowledge, experience and the control system to ensure optimum treatment and compliance with stringent effluent limitations. Flambeau began operation of the WWTP on March 15, 1993 and to date over 340 millions gallons of high quality effluent has been discharged into the Flambeau River. FLAMBEAU MINING COMPANY WASTEWATER TREATMENT PROCESS PaYUER PRECJPT*TI rL1RA1Y TRELT() AT(R Figure 1. Flambeau's Wastewater Treatment Plant Schematic �99 Flambeau's WPDES permit was issued during January 1991 and defines the limitations under which the WWTP must operate. The WPDES permit contains categorical and water quality-based chemical specific limitations. The Wisconsin Administrative Code in NR809.541 places a copper action limit of 1300 ugh as compared to Flambeau's WPDES permit limit of 50 ugh for copper. A representation of the stringent limitations and Flambeau's effluent long-term average concentrations are listed in Table 1. WWTP effluent has fully complied with all WPDES permit categorical and water quality-based chemical specific limitations during some extreme operational periods that included a 100-year flood event on September 15, 1994. Table 1. SUMMARY OF FLAMBEAU'S WPDES PERMIT LIMITATIONS AND EFFLUENT LONG-TERM AVERAGE CONCENTRATIONS. Cadmium Chromium Copper Lead Silver Zinc Daily Maximum Limit (ugh) 79.8 5400 50 590 6.6 300 Weekly Average Limit (ugh!) 7.1 980 — — 140 Effluent Long-Term Average (ug/l) 0.02 <10 8.9 0.35 0.09 11 Flambeau has an on-site laboratory with a 4100 atomic absorption graphite furnace that provides the resources to monitor the WWTP and make minor treatment adjustments to optimize its efficiency. Flambeau's on-site laboratory also allows WWTP effluent to be tested prior to discharge to the Flambeau River ensuring full compliance with chemical specific limitations. An internal limit of 25 ug/l for copper, equal to one-half the permit limitation, has been established by Flambeau to be used as a guideline for discharge criteria. If the on-site laboratory results are not less than one-half the permit limit, the WWTP effluent is discharged to the runoff pond and retreated through the WWTP until it meets this criteria. Flambeau monitors the WWTP process a minimum of every two hours to ensure that the proper adjustments are made for optimum treatment. Whole effluent toxicity (WET) testing is also required by the WPDES permit. Flambeau's effluent is subject to chronic WET testing using Ceriodaphnia dubia (C. dubia), a water flea, and Pimepliales promelas (P. promelas), fathead minnow, as test species. Flambeau's chronic WET is based upon reproduction (C. dubia) and weight gain (P. promelas). Acute WET testing is also required using C. dubia and P. promelas as test species and is based upon mortality within 100 percent effluent. Acute toxicity tests have shown only one of the two test species, C. dubia, to be sensitive in undiluted effluent. Two acute toxicity tests using C. dubia as the test species resulted in a mortality rate greater than 50 percent which represents a positive acute toxicity. These two positive acute toxicity tests occurred within a twelve month period requiring Flambeau to complete a toxicity reduction evaluation (TRE) as prescribed by Flambeau's WPDES permit. �100 Flambeau conducted a TRE during the period December 1993 through January 1995. Trace-metal copper within Flambeau's WWTP effluent was determined to acutely effect the test species C. dubia at concentrations that were substantially below Flambeau's permit limitation of 50 ug/L copper. Research toxicity testing was performed to evaluate the relationship that hardness and organic compounds have upon acute toxicity in Flambeau's effluent. The addition of an organic chelating agent into Flambeau's effluent was found to provide effective and consistent reduction of acute toxicity. Citric acid was selected to provide the citrate ion which greatly reduced copper bioavailability within the effluent. Following approval from the WDNR, Flambeau implemented the use of citric acid within its treatment process reducing trace-metal copper toxicity to C. dubia. In October 1995 Flambeau presented its TRE as a case study at the 68th annual Water Environment Federation Conference held in Miami Beach, Florida. Stockpile Monitoring The Type I stockpile is equipped with a collection lysimeter used to determine the characteristics of the exfiltrate. The lysimeter is sampled on a quarterly basis for a variety of parameters. Type I exfiltrate analyses to date have shown pH values in the range of 5.9-6.8 s.u. which are comparable to shallow well samples as was predicted in the waste rock characterization studies. The Type II stockpile is lined with an HDPE liner and a collection system made up of polyvinyl chloride leachate lines. All runoff and exfiltrate is contained within the system and gravity flows into the surge pond. This contact water is then treated through the WWTP as previously discussed. The integrity of the Type II system is confirmed through annual inspections. The series of pipes between the Type II stockpile and the surge pond are camera inspected. The leachate line system below the stockpile responsible for the collection of the leachate is also assessed. Flambeau River Monitoring The Flambeau River is monitored through an extensive program that further ensures the discharged effluent does not impact the quality of the river. Figure 2 shows the locations of all the Flambeau River sample points. The monitoring program began as part of the environmental studies supporting the initial permitting process. River samples were collected from sample points located upstream from the mine area as well as downstream. The collection of background water quality data was conducted once a month from October 1987 through September 1988. As required by Flambeau's mining permit, Flambeau again commenced conducting similar surface water quality monitoring on a quarterly basis. This surface water quality monitoring consists of samples being collected at SW-i (upstream from the mine area) and samples being collected at SW-2 (downstream from the mine site within the mixing zone of the WWTP effluent). Over 20 water quality analyses are conducted on each collected sample. The Flambeau River monitoring program to date, has shown no significant difference in the upstream samples as compared to the downstream samples. Flambeau's environmental monitoring of the Flambeau River includes sampling river sediment. Flambeau River sediment analysis began in 1988 with the collection of sediment samples to establish a point of reference for background concentrations of selected chemical parameters. This list of chemical parameters include arsenic, beryllium, cadmium, chromium, mercury and nickel. Sediment sampling has been conducted throughout the operation phase of the mine on an annual basis. �F—i 'ZD M—l S—i c SW—i AIR MONITOR SITE SAMPLING LOCATIONS FOR MACRO— INVERTEBRATES SAMPLING LOCATIONS FOR SEDIMENTS SAMPLING LOCATIONS FOR SAMPLING LOCATIONS FOR SURFACE WATER SAMPLES Figure 2 Flambeau River Monitor Locations and Air Monitor Locations. PORT ARTHUR 0 .5 ScaIe 1.0 Miles �102 Collection of walleye on the Flambeau River is an annual monitoring event conducted by Flambeau. During the low flow period of the year various sizes of fish are collected at an upstream site (Ladysmith Flowage) and at a downstream site (rhornapple Flowage). Fillets with skin left on are tested for total mercury. The livers of fish collected at each sample site are composited and analyzed for an extensive list of parameters. Fish surveys were initiated during the Fall 1987. Flambeau has started conducting fish surveys annually again in 1991 with no significant differences in metal content of fish tissue sampled downstream of mine compared to upstream of the mine. Crayfish are collected annually from the Flambeau River at three sampling locations for metal analyses. Whole bodies are used for analysis and the results represent a composite for all crayfish collected per site. Flambeau has conducted crayfish surveys annually starting in 1991 with no significant differences in metal content of fish tissues sampled downstream of mine compared to upstream of the mine. Groundwater Monitoring Flambeau regularly monitors groundwater quality to ensure that the environmental protection measures work as they were designed. Collection of groundwater data began in the 1970s as baseline groundwater quality and groundwater flows were evaluated. The collection of groundwater data has continued through the construction phase and into the operational phase. Groundwater elevations are determined weekly at numerous wells strategically located around the perimeter of the open pit. The collection of this data allows for the interpretation of the groundwater drawdown in the area surrounding the open pit. Figure 3 shows the locations of the groundwater monitoring wells. The data collected indicates the groundwater drawdown is similar to that predicted in the groundwater drawdown model previously discussed. Groundwater quality data is collected quarterly at eleven different monitoring wells strategically placed up gradient and down gradient from the open pit. Groundwater samples are evaluated based on twelve different parameters, which are copper, manganese, pH, conductivity, hardness, sulfate iron, alkalinity, total dissolved solids, color, odor and turbidity. Quarterly groundwater monitoring has indicated no adverse impact upon the area groundwater supply during mining. An extensive, long-term groundwater monitoring program will continue after the completion of the operational and reclamation phase of mining. The monitoring program will include a dynamic monitoring schedule for monitoring wells up gradient and down gradient of the reclaimed open pit. Two monitoring well nests will be established inside the backfilled pit following the completion of the reclamation construction activities. Each well nest will consist of two wells which will be sampled similarly to the previously established monitoring wells. Wetland Monitoring Water level gauges were placed in five separate wetlands outside the parameter of the mine site, but within one mile of the perimeter fence. Figure 3 shows the locations of the wetland staff gauges which are recorded monthly. If staff gauge readings as well as visual inspections of wetlands indicate a need for wetland mitigation, Flambeau will mitigate the wetlands by the addition of water. The monthly staff gauge readings will continue until the pit is backfilled. The data will then be compared to preconstruction levels and recent precipitation history for the region resulting in an established long-term and maintenance monitoring schedule. �0 MW—100SP MONITORING WELL LOCATION WETLAND STAFF GAUGE MW— 1002 MW—i 002G o ——— 0 SCALE500 DWT-2 Jansen Rod = = = = = = = = MW—100SP MW—1005 MW—1005S Figure 3 Groundwater Monitoring Well Locations and Wetland Staff Gauges Ancillary Facilites Low Sulfur Waste Rock Stockplie FEET 1000 I �104 Ambient Air Monitoring Particulate matter in the ambient air generated by mine operations is suppressed by the use of WWTP effluent and monitored by four high-volume air samplers. Figure 2 shows the four sampling site locations. The four sampling site locations were based on USEPA siting criteria and are calibrated on a quarterly basis. The instruments are audited at least on an annual basis by the WDNR. Each monitor operates for 24 consecutive hours starting at midnight. During the preproduction phase each monitor operated once every three days. During the mining phase, each monitor was operated once every other day. Since Flambeau had not exceeded its Total Suspended Particulates (FSP) secondary standard of 150 ug/m3 following one year of mining, the sampling schedule was reduced to once every six days. Each filter from the TSP monitors is retained with a portion of each filter being composited for a three month period. These composites are analyzed for arsenic, chromium, nickel, beryllium, cadmium and mercury. Analyses of the filter composites have resulted in very low to non-detectable cOncentrations of these metals. Asbestiform monitoring is another component of Flambeau's air quality monitoring program. Asbestiform monitoring was conducted monthly from May through September during the years 1993 through 1995. Asbestiform monitoring during the first three years of active mining indicated that no asbestiform fibers were generated from the mining operations. As a result, Flambeau is no longer required to monitor for asbestiform fibers. Meteorological data is obtained from Flambeau's Meteorological Station located south of the mine site. The meteorological station continuously collects information on the precipitation, temperature and wind speeds and wind direction. This information is submitted with the air monitoring data to the WDNR. RECLAMATION AND LONG-TERM CARE The reclamation of the mine site includes backfilling the open pit and returning the site to a topography which approximates the original contours. Following establishment of final contours, reclamation includes wetland construction, topsoil, vegetative stabilization, tree planting, and longterm care and maintenance. Wetlands Construction Prior to site construction, wetland delineation had identified 8.3 acres of low to medium quality wetlands which would be disturbed. The disturbed wetlands are required to be replaced. The hydric soils from the disturbed wetlands were stockpiled to be used during wetland construction. During Fall 1991, Flambeau constructed a one-acre wetland referred to as the aquascape in the northeast corner of the property. The aquascape varies from a sedge meadow to open water which allows for a range of wetland species as does the hydric soil stockpile. The aquascape not only serves to replace one acre of disturbed wetland area, but also provides information to be used for the construction of the remaining wetland area. The aquascape has been assessed on an annual basis since 1992. The aquascape has become a stable wetland area which supports a diversity of wetland species. The aquascape was originally established with both plants and seeds. Over the past four years species diversification has dramatically increased. Several species which had been seeded remained dormant and have become �105 evident in only the last year. The 1995 assessment has shown an increase in diversification by seven species compared to the previous year. Topsoil Stabilization Approximately 220,000 cubic yards of stockpiled topsoil were placed between the east end of the mine and Highway 27 and will be replaced on the mine site following backfihling and contouring. The topsoil will be stabilized with a vegetative cover consisting of native prairie grasses and wild flowers with a nurse crop of oats. Additional erosion control features including straw bales, silt fence, and mulch will be utilized. The species of wild flowers and grasses to be used during final reclamation has not been definitively determined at this time. The species of wild flowers and grasses will be selected based upon studies performed on the prairie seed test plots. Prairie seed test plots were established on the mine site during 1993. The test plots are located on the mine site north of the Type I stockpile and south of the open pit. A total of 196 test quadrants were defined which consider the following test variables: 1) type of fertilizer; 2) type of mulch; 3) mowing; and 4) type of seed mix. The annual assessments show the progression from exotic species to desirable native species. The information gathered from the prairie seed test plot annual assessments will be utilized to select the best methods for establishment of native species for stabilization. Tree Planting During 1991 the WDNR and Flambeau selected trees from the mine site to be transplanted to a temporary nursery located north of the Type I stockpile. The tree selection was primarily based upon the WDNR approved tree species and appropriate tree size. Trees which would grow too large before transplanting would have a low survival rate when replaced to the mine site, and were therefore not selected for placement in the temporary nursery. Additionally, Flambeau has planted nursery stock tree seedlings into the temporary nursery during 1993 and 1995. The tree seedlings have provided information on survival rates of specific species. Also, the management of the seedlings has established procedures which will be implemented during the planting of approximately 14,000 seedlings at the time of final reclamation. Long-Term Care and Maintenance Flambeau will be responsible for the reclaimed mine site in perpetuity with a minimum long-term care and maintenance period of 40 years. Long-term care will initiate when final site grading and revegetation have been completed. Long-term care and maintenance will include inspections of the site, maintenance of land forms, vegetation and monitoring devices, and monitoring groundwater, surface water, vegetation and terrestrial ecology. The long-term care period monitoring plan is shown in Table 2. �106 Table 2. SUMMARY OF FLAMBEAU' LONG-TERM CARE PERIOD MONITORING PLAN. Event Site Inspections Year 1-4 5-40 Groundwater Monitoring Perimeter Wells Backfilled Pit Wells 1-40 2-4 5-7 8-40 Frequency Semi-annual Annual Quarterly Quarterly Annually Every 5 years Sediment, Crayfish & Fish 1-2 Annually River Water Quality 1-2 Annually Wetland Surface Flows 1-10 Spring, Summer, Fall Vegetation Assessment 1-6 Annually Terrestrial Ecology 1-4 Annually Every 5 years 5-40 CONCLUSION Flambeau's commitment to environmental protection goes beyond permit compliance. Respect for the environment is a personal commitment for every employee at the Flambeau Mine. This continued commitment is evident with the successful operation of this environmentally responsible mine. Flambeau's use of modern technology and personal creativity provides the environmental protection criteria which may serve as a benchmark for the mining industry. �107 EISENBREY: A STRUCTURALLY COMPLEX PROTEROZOIC COPPER-ZINC MASSIVE SULFIDE DEPOSIT, RUSK COUNTY, WISCONSIN by Edwarde R. May Consulting Mining Geologist Littleton, Colorado INTRODUCTION The discovery of the Flambeau copper-gold massive sulfide deposit in late 1968 (May and Dinkowitz, 1996) rapidly expanded Kennecott's search for satellite deposits. The search was immediately conducted along strike of the Flambeau discovery and soon expanded to cover all airborne electromagnetic (EM) anomalies within the Glen Flora airborne survey selected for review and ground follow up (Babcock, 1996). Ned Eisenbrey recalled a rusty, wealdy mineralized iron formation outcrop located by Bill Spence in 1967 along the bank of the Thornapple River about 7 miles northwest of Flambeau. A weak airborne EM conductor detected in the area of the outcrop was not encouraging since a farm and railroad bridge were located on either side of the strike extension of the outcrop to which the anomaly was attributed. Eisenbrey, nevertheless decided to drill the weakly copper-zinc-silver anomalous exposure in 1970 over the doubts and objections of most of his colleagues. The first drill hole encountered a 14.6-foot interval within an iron formation that averaged 477 ppm Cu, 2400 ppm Zn, and 422 ppm Pb. The second hole was collared 350 feet to the west and resulted in the discovery of the Thornapple deposit. This hole intersected 5.9 feet true width of massive sulfides that averaged 0.44% Cu, 1.36% Zn, 0.02 opt Au, and 0.29 opt Ag. The Thornapple deposit was, therefore, a geological discovery; ground geophysics were conducted over the deposit after its discovery. Ground magnetics were run in 1970 and 1971 to trace pyrrhotite and iron formation mineralization, and one line of gravity was conducted at the same time over the thickest portion of the deposit. A development team took over the project in 1971 after Ned and Bob Stuart had completed ten holes, six of which intersected mineralization. Unlike Flambeau, no significant supergene mineralization was encountered. The project was shelved in 1974 due to falling copper prices; however, land was purchased by Kennecott to cover the deposit and any potential strike extension. A total of 40 holes had been drilled by 1974 to an average depth of about 500 feet below surface. A complex, isoclinally folded, eastward plunging, thin multi-lensed deposit was partially defined consisting of zoned bodies of pyrrhotite-chalcopyrite and pyrite-sphalerite mineralization. The resource was estimated to be 1.6 million tons of 1.3% Cu, 0.06% Zn, 0.007 opt Au, and 0.20 opt Ag, and 700,000 tons averaging 0.35% Cu, 4.10% Zn, 0.02 opt Au, and 0.4 opt Ag. While initial results were disappointing, the deposit was not thoroughly drilled and was open to depth. The Thornapple deposit was renamed Eisenbrey in 1994 to honor the significant contributions made by Ned Eisenbrey to Wisconsin economic geology. In the same year, Flambeau Mining Company, a wholly owned subsidiary of Kennecott Minerals, decided to test the deposit to depth. A gravity survey was conducted to verify that the deposit was indeed plunging steeply to the east. To everyone's astonishment, a large anomaly was recognized that could not be explained by the shallow, thin sulfide intercepts cored by previous drilling campaigns. Eight holes drilled in 1994-1995 confirmed the presence of a large, near vertically dipping and plunging, complexly folded deposit. Resource estimates to depths in excess of 3000 feet indicate the presence of 50,000,000 to possibly �108 100,000,000 tons of low-grade copper-zinc mineralization in which copper and gold values are erratic and zinc values consistently low. LOCATION The Eisenbrey deposit is easily reached via paved roads commencing at the intersection of Highways 8 and 27 in Ladysmith. Drive north on Highway 27 four miles to the junction with County Road A. Proceed west on County A for a distance of two miles then north 'on Bass Lake Road for 1.75 miles to the 514.5-acre project site which is east of the Flambeau township road (Figure 1). The Thornapple River bisects the west one third of the site and is entrenched 50 feet within glacial outwash. The Wisconsin Central Railroad also cuts across the site and river in a southeasterly direction. The project site is essentially flat, has an elevation of about 1160 feet, and is covered east of the river by highland mixed deciduous forest. West of the river the site is covered by old meadows and woods. GENERAL GEOLOGY OF NORTHERN WISCONSIN At least 13 volcanogenic massive sulfide deposits have been discovered within Early Proterozoic greenstone rocks of northern Wisconsin (DeMatties, 1994). The Ladysmith-Rhinelander metavolcanic belt within the Pembine-Wausau Subterrane, which strikes across the state for a distance of 150 miles, is the host rock for this mineralization. These 1.86 to 1.88 billion year old rocks consist of mafic metavolcanics, gabbroic sills, lesser amounts of felsic metavolcanics, and some cherty iron formations. The Ladysmith-Rhinelander metavolcanic belt clearly shows on regional airborne gravity and magnetic reconnaissance maps of northern Wisconsin as an anomalous linear feature. North of the Ladysmith-Rhinelander belt are rocks that form a thick platformal turbidite sequence of clastic and chemical metasedimentary rocks including major iron formations. The Niagara Fault separates the Northern Penokean Terrane of continental margin assemblages from the Pembine-Wausau Subterrane (Figure 2). The paper by G. LaBerge in this volume shows the location of these subterranes. South of the Ladysmith-Rhinelander belt are rocks of the Wausau and Marshfield Complexes. The Eau Pleine Shear separates the Marshfield Subterrane from the Pembine-Wausau Subterrane (LaBerge, 1996). The Marshfield Subterrane is characterized by Archean gneisses and 1.86 billion year old metavolcanic rocks and granitoids. The Wausau Volcanic Complex consists of 1.88 billion year old amphibolite facies rocks unconformably overlain by 1.84 billion year old intermediate to felsic metavolcanics. Intruding the Wausau volcanic complex are anorogenic igneous rocks, 1.47 to 1.51 billion year old, the largest of which is the Wolf River Batholith. DeMatties and LaBerge more fully discuss these subterranes and the Wausau Volcanic Complex in this volume. Paleozoic sediments onlap the southern portions of the Southern Superior Province of the Precambrian Canadian Shield. SITE GEOLOGY Glacial outwash covers the entire site to a vertical depth of about 50 to 60 feet into which the Thornapple River has entrenched itself to expose Precambrian bedrock. Outcroppings of Precambrian metasedimentary, metavolcaniclastic, and igneous rocks occur on either side of the Wisconsin Central Railroad bridge (Figure 3). �0 S. HAND DUG WELL PROTEROZOIC OUTCROP LEGEND "V Figure 1 Location of Massive Sulfide Deposits and Chief Outcrops. Rusk County, Wisconsin EISENBREY DEPOSIT SCALE I 1 6.5 MILES HA WK IN S �0 MINNESOTA LEGEND PALEOZOIC [-€J CAMBRIAN SANDSTONE FLAMBEAU MINE CRANDON DEVELOPMENT SCALE20 0 10 1"4O EISENBREY DEPOSIT Figure 2 Generalized Geology of Northern Wisconsin (Modified after Morey, Sims, Cannon, Mudrey, Southwich, 1982) 40 MILES �IRON FORMATION EAST LENS MAFIC TUFFS SILICIFIED INTERMEDIATE TUFFS INTERMEDIATE TUFFS LIII MASSIVE SULFIDES LI1 PRECAMBRIAN PROTEROZOIC DIABASE KEWEENAWAN LEGEND .1 Rusk County, Wisconsin Figure 3 Thornapple River Outcrops, Eisenbrey Prospect. GEOCHEMLCAL SAMPLE AND SAMPLE NUMSER — FAULT -> OUTCROP INFERRED GEOLOGIC CONTACT — GEOLOGIC CONTACT 0 1" =50' SCALE25 50 FEET �112 Upstream of the bridge a distance of about 0.25 mile is an outcrop of a Keweenawan diabase dike. Downstream and immediately east of the bridge are outcroppings of another dike that cuts across intermediate tuffs and graywackes. These highly regionally-metamorphosed and silicified rocks contain thin units of mafic tuffs that show very tight isoclinal folding with a near vertical plunge. West of the bridge is a mafic tuff (amphibolite schist) that contains a rusty and broken iron formation. The upstream iron formation is in a fold nose and the formation does not strike beneath the river. Instead it is interpreted to be folded back upon itself to reemerge further downstream (field observations by P. Lindberg, Aug. 1995). The second outcropping of iron formation strikes west across the river and is interpreted to be the ore horizon for the Eisenbrey deposit. Volcaniclastic and graywacke rocks of intermediate composition occur between the mafic tuff and pyroxenite downstream. The pyroxenite is interpreted to be part of a gabbro sill with a chilled margin in sharp contact with the host sediments. The sill occupies the center of syncline that hosts the Eisenbrey deposit. Four zones within the outcrop were sampled and geochemically analyzed. It was these geochemical results and rock exposures upon which the Eisenbrey drilling was founded. The geochemical results are shown in Table 1. TABLE 1 GEOCHEMICAL RESULTS FROM THE EISENBREY OUTCROPS EISENBREY DEPOSIT, RUSK COUNTY, WISCONSIN Sample Number 1 2 3 4 Copper % Cu 0.03 0.03 0.04 0.06 Zinc % Zn 0.03 0.05 0.17 0.20 Gold opt Au trace 0.003 0.010 0.002 Silver opt Ag trace 0.1 0.3 0.1 GEOPHYSICAL SURVEYS The Eisenbrey project site was flown for Kennecott in 1969 as part of the Glen Flora airborne survey, and a weak EM anomaly was recorded west of the Wisconsin Central railroad bridge. A ground check, however, found a power line and railroad bridge coincidental with the EM conductor; therefore, it was discounted as culture. A large magnetic response was also recorded with the EM conductor, but this anomaly was attributed to the bridge. Ned Eisenbrey was not convinced the response was entirely the result of culture and was determined to drill the outcrop even though the iron formation did not fit the "Noranda" model being used by the company while exploring Wisconsin. No ground geophysical work was done until after base-metal anomalous massive pyrite and pyrrhotite mineralization had been drilled. Ground geophysics conducted after the discovery consisted of magnetic and gravity surveys. The gravity survey, however, consisted only of one north-south line run over the nose of the fold that contained most of the Eisenbrey mineralization. Ground magnetics were also run on north-south lines spaced from 50 to 200 feet apart with the closer spaced lines over mineralization. Readings were taken on 50 or 100 foot intervals over an area that eventually covered approximately five square �113 miles and surrounded the deposit. This survey was useful in helping decipher bedrock structure and in locating suspected iron formations and one thin pyrrhotite lens. A complex magnetic anomaly shown in (Figure 4) was observed over an east-west strike length of 1750 feet by 700 feet north-south. Drilling confirms that the large east-west elliptical response of up to 8000 gammas on the west end is coincident with the pyrrhotite-chalcopyrite fold nose of the Eisenbrey deposit. An iron formation occurs to the southeast and accounts for a northeast striking response that peaks at 12000 gammas. Near the center of the anomaly is an unexplained northwest striking response peaking at 4800 gammas. A ground gravity survey recommended by Paul Schmidt was conducted in 1994 before commencement of deep drilling (Figure 5). The purpose of the survey was to confirm that the interpreted steeply east plunging deposit was true. This survey did indeed suggest a very steeply dipping and plunging deposit, but the size and magnitude of the anomaly was much larger than expected and could not be explained by sulfides encountered in the previous shallow drilling. GENERAL GEOLOGY The Eisenbrey deposit is hosted within a thick pile of interbedded intermediated tuffs, lapilli tuffs and graywackes which have been regionally metamorphosed and folded. These Proterozoic volcaniclastic and sedimentary rocks form the platform into which younger mineralized and altered rocks were deposited. On the flanks of the massive sulfide mineralization are magnetite iron formations with weak base metal mineralization. Closer to the suspected center of "ore"/sulfide deposition the host rock is interpreted to be a dirty chert and volcanic rock altered to anthophyllite, cordierite, and magnetite with associated mafic tuffs. Minor rhyolite flows have been recognized, but do not appear to play a significant role in the formation or hosting of sulfide mineralization. A gabbro sill was emplaced after the mineralizing events and before folding. A series of Keweenawan diabase dikes were intruded after the Penokean Orogeny to cut across the property in a northeasterly direction. Approximately 60 feet of Pleistocene glacial outwash covers the project site except where the Thornapple River has exposed Proterozoic and Keweenawan aged rocks east of the deposit. GEOLOGY OF THE EISENBREY DEPOSIT Introduction. A brief geological description is presented below and is based upon core examinations, outcrop and some petrographic work conducted by Mary Jø Sweany in the 1970s. In general the rock descriptions commence with what are believed to be the oldest rock units through to Pleistocene Till. Intermediate Dacitic Tuff and Graywacke. The most abundant rock types within the footwall, upon which massive sulfide mineralization was later deposited, consist of dacite tuffs, lapilli tuffs, and graywackes (Figure 6). Petrographic analyses of core samples repeatedly suggested the presence of graywacke. Graywacke, if present, is intercalated with thick sequences of dacitic lapilli tuffs all of which have been highly recrystallized by regional metamorphism. In general, these tuffaceous and sedimentary rocks have been metamorphosed to a finegrained, sugary to granular mixture of plagioclase, biotite, amphibole, and minor amounts of garnet and quartz. Relict bedding is observed under the microscope and in the Thornapple outcrop where �Figure 4 1" = 300' i FEET 300 Eisenbrey Prospect. Rusk County, Wisconsin Magnetic Anomalies, 0 SCALE150 -—--1000--- GAMMAS LEGEND �Eisenbrey Prospect, Rusk County, Wisconsin Gravity Anomaly, Figure 5 LEGEND I �STRATIGRAPHIC TOP ANTICLINE SYNC LINE LAPILLI TUFFS, MAFIC TUFFS. INTERMEDIATE TUFFS, MASSIVE—SEMIMASSIVE SULFIDES IRON FORMATION PYROX EN lIE PRECAMBRIAN PROTEROZOIC LII1 KEWEENAWAN LEGEND Figure 6 Geology Plan Map 900—foot Elevation, Eisenbrey Prospect. Rusk County, Wisconsin WEST LENS 0 1=200' SCALE100 i FEET 200 �117 thin (1 to 2 inches) mafic ash beds have been isoclinally folded. Table 2 shows a strong similarity between Eisenbrey dacite tuffs and world wide average rhyolites (Nockolds, 1954). TABLE 2 A WHOLE ROCK ANALYTICAL COMPARISON BETWEEN EISENBREY DACITE TUFF AND RHYOLITE WITH WORLDWIDE AVERAGE RUSK COUNTY, WISCONSIN Oxide Mineralization Si02 A12O3 Fe203 and FeO MgO CaO Na20 1(20 Partial Totals Eisenbrey World'Mde Dacite luff Dacite Average 67.2 14.0 6.63 2.84 2.60 3.76 63.58 16.67 5.24 2.12 5.53 3.98 1.67 1.40 98.52 98.70 Eisenbrey Rhyolite 70.4 14.5 4.54 1.62. 2.34 2.38 2.84 98.60 Wotidwide Rhyolite Average 73.66 13.45 2.00 0.32 1.13 2.99 5.35 98.90 Dacite Lanilli tuffs. Lapilli tuffs are interbedded with intermediate composition tuffs and graywackes stratigraphically beneath the Eisenbrey deposit. Stratigraphic thicknesses range from a few feet up to 75 feet. Felsic to intermediate lapilli fragments are generally well preserved although collapsed and elongated due to regional deformation. The lapilli tuff fragments consist of biotite, plagioclase, quartz, and amphibole within a matrix of biotite and amphibole. Lapilli fragments range in size from less than 0.5 inch to over 4 inches in length by 0.2 to 0.5 inches in width. Intense deformation has elongated the fragments so that they now plunge nearly vertically. Occasional fragments contain 1 to 6% disseminated pyrrhotite, pyrite, chalcopyrite, and magnetite grains. The average mineral composition for the Eisenbrey dacite tuffs was obtained from 13 petrographic thin sections of core as shown on Table 3. These minerals consist of fine to coarse grains which have been metamorphosed into growths of subrounded to subangular grains. Minerals such as epidote and sericite are present in some examined rock thin sections. Opaque minerals consist of varying proportions of hornblende, garnet, sphene, and interstial clay generally kaolinite. Intrusion of the gabbro sill and strong regional metamorphism have severely baked the host rock and "sweated" quartz into the matrix of the dacite tuffs. The tuffs were misinterpreted by this author and previous geologists during the 1970's as a rhyolite dome. Major oxide geochemistry needs to be conducted to quantitatively determine original rock composition. Anthophyllite-Magnetite Ore Horizon. An anthophyllite-rich horizon is intimately associated with sulfide mineralization and is on strike of the iron formation outcrop (Figure 7). It is a distinctive rock consisting of sheaf-like bundles of radiating needles of anthophyllite within a fine grained, sugary, granular matrix of quartz, magnetite, antigorite, and cordierite. The anthophyllite rock could possibly represent the altered footwall rock containing the stockwork zone. The Eisenbrey deposit has undergone penetrative deformation so that the mineralization has been stretched into a vertically plunging pencil-shaped deposit. The underlying stockwork and footwall alteration zone appears to have been transposed to a position that is now in lateral conformity with the stretched sulfide body similar to that seen at Flin Flon and Snow Lake, �118 TABLE 3 MINERAL COMPOSITION PERCENTAGES OF VARIOUS EISENBREY ROCKS RUSK COUNTY, WISCONSIN Mineral Name Quartz Cordierite Plagioclase Anthophyllite Chlorite Antigorite Epidote Sericite Muscovite Carbonate Homblende Garnet Sphene Andalusite Clay Magnetite Opagues Totals Dacite Tuff 46 Anthophyllite Altered Rock Mafic 30 24 12 Tuff 10 16 19 7 10 6 12 1.5 10 1 3 1.5 8 3 2.5 48 7 2 2.5 5.5 6 2.5 99.5 2.5 100 3 99 Manitoba (Lydon, 1984). Lydon also reported major additions of magnesium and iron to the alteration pipe and surrounding rock at Fun Flon and Snow Lake as suggested by the presence of a cordierite-anthophyllite assemblage. The anthophyllite-magnetite rock at Eisenbrey is found on either side of the northwest fold nose, partially shown in Figure 6 (Section 5500E) and Figure 7 (Section 5850E) and is similar to observations reported by Lydon (1984). This strongly suggests the Eisenbrey deposit has been isoclinally folded with stratigraphic footwall occurring on either side on the northwest fold nose. Table 4 shows the mineralogy on either side of the fold nose based upon rock thin section studies. TABLE 4 ANTHOPHYLLITE-MAGNETITE ROCK MINERALOGY ON EITHER OF THE NORTHWEST FOLD NOSE, EISENBREY DEPOSIT, RUSK COUNTY, WISCONSIN Mineralogy Quartz Chlorite Sericite Anthophyllite Cordiente Andalusite Antigonte Magnetite Pyrrhotite Pynte Total North of Fold Nose South of Fold Nose % 35 7 3 15 30 2 0 6 % 25 6 0 25 20 0 20 2 I 100 100 �IJIIII • L 1000 ,j,:'/,,i ',/' IIii I I / / ,T—22 II1/ I ,1 ii / I / I II I 500 1 I 1—18 4c6 8/3 ' I / hj /1' /1/ / / / '14' /' I'/ I 1 / - I,, __L___ Ii/,"—/4c II / II! II ,/ 11/ I I ,'/ I III I 3/8k r I I I Ij' III I /jI''I 4 III II II I ti, 'Ix 4c!! I / j / 'II —500 / ' I/S / / / / I I I ii (// II I 1 I I I I I j / I I I ! I I INTERMEDIATE TUFFS LAPILLI TUFF L1 RHYOLITE—RI-IYOIJTE I, I QUARTZ—SERICITE SCI-IIST l I' ' I /4 II / I SYNCLINE P I 'I I 'I \T II 1318/f / 'III Ii 6a ii I I I I I ALTERED ROCK — l/i II I ANTHOPHYLLITE—MAGNETITE 8 II I I I MASSIVE SULFIDES 4 !j I II I I I I PRECAMBRAIN PROTEROZOIC I '8/"'III I I TILL jI I, I I / I I I PLEISTOCENE 3/I / I II I I I I KEWEENAWAN [] DIABASE DIKE & SILL I I 1 LEGEND //II I I iii", ii II I I III, I/Il I/Il I,,! III jI I I I HII II I! I IJ /1 I I j I ,i, I, I, II I II 8/4,I I /1/Il —1000 I I I '4c HI'6',' II 4 I / /// III Ill /111, / // // / / I I I '5; 6a1_JLIf 1/ i, I I JT—4 / I, I H, (6//I I /j3 / 1//3d' 54, —.4—— 51T, 4 11 i7',, I 40 I I , '18 —1500 I / z QI 0 0! I 0 'I h/ ii' 'ii z 3,',! I II ' 4 6a E—45 0 0 Figure 7 Geological Cross Section 5850E, Eisenbrey Prospect. Rusk County, Wisconsin 300 FEET 1" =300' Iz 1/ 150 SCALE i z 0 0 0 U, �120 Another distinguishing mineral is magnetite that occurs as euhedral grains up to 0.2 inch octahedrons. Magnetite content ranges from one to 15% and generally occurs within a granular mixture of quartz, cordierite, plagioclase, minor garnet, and an unknown clove-brown silicate mineral, possibly grunerite. Immediately west of the south syncline the mineral content and texture of the ore horizon changes dramatically. The matrix is massive chlorite containing 8 to 15% magnetite as octahedral crystals up to 0.25 inch in diameter. Light gray patches or poikiloblasts of quartz, cordierite, plagioclase, and smaller magnetite crystals also occur within the chlorite matrix. These irregular intergrowths make up approximately 35% of the rock volume. Sulfide mineralization is generally low and makes up less than 2 to 5% of the rock volume. It is possible that this chlorite-magnetite horizon could represent the center of a feeder pipe that supplied mineralization to the Eisenbrey depositional basin. Metachert. A few thin impure metachert horizons have been recognized in the core. Generally the metachert is closely associated with or incorporated within the above anthophyllitemagnetite horizon. The metachert has a distinctive sugary texture made up of recrystallized quartz and impurities consisting of minor amounts of plagioclase and ferromagnesian minerals. Occasionally, very fine bedding, characteristic of chert horizons reported at other deposits, has been observed in the Eisenbrey core. Magnetite and sulfide minerals are uncommon and generally average less than 5% of the rock volume. Rhyolite. A rhyolite dome had been interpreted by previous geologists to have been intruded in the footwall beneath the east end of the 4eposit and outcrops east of the railroad bridge. Petrographic studies have indicated, however, that the rhyolite is a hard, dense almost baked dacite tuff or greywacke. Quartz content usually ranges from about 45 to 55% and averages 46%, as shown on Table 3. A few thin rhyolite flows have been recognized and are distinguished by being extremely hard, and composed of a fine-grained to aphanitic groundmass with occasional (5%) phenocrysts of feldspar. A partial whole rock chemical analyses of a couple of rhyolite flows are averaged and included in Table 2. Mafic Tuffs. Mafic tuffs are intimately associated with massive sulfide mineralization as thin beds flanking or within the sulfides. Table 3 shows that the mafic tuffs are rich in amphibole and chlorite. The rock is usually fine-grained, and well-foliated with indistinct lapilli fragments, and occurs as thin beds less than 20-feet thick. Thin beds of predominantly ferromagnesian minerals are intercalated with much thicker beds of massive sulfides. One sample taken within the northwest fold nose was petrographically examined and found to contain chlorite (5%), anhydrite (15%), gypsum (20%), serpentine (possibly antigorite after olivine) (10%), dolomite (10 to 15%), calcite (3 to 5%), magnetite (15 to 20%), and pyrite (15%). The amount of gypsum and anhydrite varies considerably throughout the rock. Likewise serpentine is irregularly distributed. Talc has also been detected by X-ray defraction. Iron Formation. The term iron formation is used at Eisenbrey to describe a rock rich in magnetite with accessory epidote, garnet and amphibole (actinolite). Thin sections were prepared on a core sample collected east on strike of the iron formation outcrop in drill hole 9. The rock consisted of quartz (25%), chlorite (10%), actinolite (20%), garnet (5-10%), epidote (10%), carbonate (5%), magnetite (20%), and pyrite (2%). �121 Magnetite is concentrated into thin one to two-inch thick black bands consisting of 30 to 70% magnetite. Actinolite with epidote and garnet enclose the magnetite-rich beds, whereas chlorite occurs as veinlets and disseminated grains throughout the host rock. Light gray to white beds of nearly pure quartz could represent recrystallized chert. Iron formations have been interpreted to strike for over two miles into a series of isoclinal folds, with associated minor amounts of sulfide mineralization, along the eastern-most strike extension. Much of the Eisenbrey magnetic anomaly, particularly on the south side, is due to iron formation. It is unclear whether the iron formation in the area is one horizon that has been folded and faulted, or whether more than one unit of iron formation is present. Ouartz-Sericite Schist. A number of thin, less than 20-foot thick, quartz-sericite schist beds or alteration zones have been intersected during the 1994-1995 deep drilling program. The schists are light gray, highly foliated and in close association with sulfide mineralization located in the south syncline. Sulfide content is low within the schists, averaging about 10 to 15%. Quartz-sericite schist is the dominant lithology of the ore horizon at the Flambeau orebody, but this rock type or alteration zone is uncommon at Eisenbrey. Gabbro. A sill or multiple sills of gabbro occur within the hangingwall of the axial portion of the steeply plunging Eisenbrey syncline axis. It consists of a medium-to coarse-grained recrystallized mixture of feldspar (35%), hornblende (35 to 40%), epidote (10%), and chlorite (5 to 10%). A chilled margin is present having a true thickness of 3 to 5 feet. Closer to the surface, the gabbro has been largely altered to chlorite (up to 60 to 65% of the rock volume). Intrusion of the gabbro greatly elevated the temperature of the enclosing volcaniclastic and sedimentary rocks. This could account for the wide variety of amphibolite facies minerals seen in the deposit and its host rocks. Diabase Dikes. Keweenawan diabase dikes and sills are fresh, medium-grained, holocrystalline, intergranular, non-porphyritic rock having a typical diabasic texture. The rock consists of plagioclase (35%), interstitial chlorite (25%), biotite (3-5%), muscovite (5%), hornblende (1-2%), augite (10%), olivine (10%), serpentine (2-3%), carbonate (5%), and ilmenite (3%). An 80-foot thick dike striking N 60°E and dipping 650 NW intersects the Eisenbrey deposit as shown on Figure 6. The dike splits on the east end of the West lens and also forms a sill in the footwall of the West lens (Figure 7). Pleistocene Till. Approximately 60 feet of unconsolidated glacial outwash materials blanket the Eisenbrey deposit and surrounding area, except where removed by the downward and westward migrating Thornapple River. STRUCTURE The structure of the Eisenbrey deposit is complex based upon outcrop observations, and interpretation of geophysical and drill core data. The current geometry of the deposit is interpreted to be the result of isoclinal folding with possible fault offsets. This interpretation is supported by the following observations: �122 i) a one-to two-inch thick mafic tuff bed found in the outcrop east of the railroad bridge has been tightly isoclinally folded and has a near-vertical axial plunge; and, ii) in the same outcrop elliptically shaped rod structures that also have a vertical plunge, and S planes that show a very steep plunge to the east. The iron formation also shows evidence of isoclinal folding as described above in subsection on Site Geology. In addition, mineral zoning briefly described in the Mineralogy subsection suggests the presence of folding due to repetition of zones within drill holes. Therefore, the deposit is interpreted to strike west from the outcrop through the East massive sulfide lens (Figure 6). A north to northwest striking fault is believed to have offset the gabbro and mineralized horizon. Further evidence for significant faulting comes from hole 4 which contains a large gouge zone where rock foliation is rotated on either side of the structure. This fault is coincident with the northwest striking magnetic response; however, offsetting relationships, if present, are unclear. ALTERATION The Eisenbrey deposit has been subjected to multi-phased hydrothermal and metamorphic processes. To date, no stringer zone or alteration pipe has been definitively recognized. It is interpreted that there is a thermal metamorphic aureole caused by intrusion of a gabbro sill superimposed upon Penokean regional upper greenschist metamorphism. As a result, some unusual mineral assemblages are present, such as chiorite-tremolite-forsterite and pyroxene-garnet-quartz. Regional metamorphism has produced a suite of silicate minerals that include actinolite, albite, garnet, andalusite, anthophyllite, chlorite, cordierite, quartz and sericite-muscovite. The relative abundance of pyrrhotite is interpreted to be a product of localized thermal metamorphism. The host rocks have not been altered by supergene processes although small patches of supergene enrichment have been cored at the top of the deposit. FORM OF THE DEPOSIT The geometry of the Eisenbrey deposit is shown in plan in Figure 6; the deposit occurs as pinched and remobilized massive sulfide enlargements at fold noses within impure chert, anthophyllite, and iron formation host rocks. The isolated East lens has probable structural complications at depth whereas the west lens is a complex arrangement of two synclines open to the east with an intervening very tightly folded anticline. The south syncline is a convoluted, accordion type fold over a north-south direction of almost 200 feet. The ore horizon continues west of the east lens, through a pyrite-sphalerite lens and into a tight syncline referred to as the northwest fold. The south limb of this syncline strikes east into a very tight anticline whose south limb returns west one half the distance of the north limb to enter into a complex and convoluted syncline known as the south fold. The fold nose within massive sulfide mineralization is approximately 170 feet north-south. The south limb may either continue south into an iron formation (Lindberg) or continue east to be intruded by the gabbro (May). In cross section 5850 East, the massive sulfide lenses extend for at least 2500 feet below surface as near-vertical plunging rods, as shown on Figure 7. The length of the deposit, including the east and west lenses, is 3300 feet prior to folding. Isoclinal folding has compressed the once tabular deposit into an area 400 north-south by 1000 east-west. �123 MINERALOGY Base metal mineralization occurs within both pyrrhotite and pyrite matrices. Pyrrhotite is found within and on the south side of the anticline and on the west end of the south syncline nose, and minor pyrrhotite occurs on the south side of the northwest syncline. Chalcopyrite is generally associated with pyrrhotite, whereas pyrite hosts most of the sphalerite and gold mineralization. The Northwest syncline is predominantly pyrite, as well as the north side of the anticline and south side of the South syncline. In shallow drilling the pyrrhotite occurs as massive, amorphous lenses containing irregular grains and layers of chalcopyrite. Chalcopyrite also occurs as finely disseminated grains within the matrix. Most of the copper values, however, are within the larger chalcopyrite patches, many of which halo single or clusters of pyrite cubes. Chalcopyrite can also occur as conformable blebs, some of which are irregular in shape and cross cut pyrrhotite laminations. The pyrrhotitechalcopyrite zone is restricted to the nose of the south fold and has been intersected at depth. Figures 8 and 9 show the general distribution of copper and zinc, respectively, on the 900-foot level. Pyrite occurs as subeuhedral to anhedral grains with interstitial sphalerite and minor chalcopyrite. Chalcopyrite is found as microscopic grains within sphalerite or as small irregular lenses interbedded with pyrite. Typical sphalerite-pyrite layering, common to many massive sulfide deposits, is present, but not well developed. At depth and along strike of the south fold nose the pyrrhotite-chalcopyrite and pyritesphalerite mineral zoning becomes less distinct. Instead, pyrrhotite and pyrite are intermixed within a ragged almost shredded texture of wispy pyrrhotite patches within medium- to fine-grained subhederal pyrite. Wisps of pyrrhotite vary in size from a fraction of an inch to one to two inches. Some areas consist of large masses of amorphous pyrite with essentially no base metal mineralization, whereas some other zones contain thick sequences of cherty chalcopyrite. A distinctive mineral zone contains abundant chalcopyrite-pyrite fragments within a pyrrhotite matrix. The relatively small grain size at Eisenbrey is surprising, as one would have expected coarser grained sulfides due to amphibolite grade regional and contact metamorphism. Near the surface there are thin interbeds of metadolomite present within the massive sulfide in the nose of the sulfide-rich anticline. The beds are about one to two feet thick consisting of 80% dolomite, 10% veined chlorite, 5% magnetite, 3 to 4 % pyrite, and 1% epidote. The relationships between the above mineral zones and structure of the deposit are not clear. Identification of a copper-rich "hot spot" within this very large structurally and mineralogically complex system is proving to be difficult. CONCLUSIONS AND COMPARISONS The Eisenbrey deposit is a typical massive sulfide deposit in that it is hosted within a thick sequence of volcaniclastic lapilli tuff, tuff and graywackes, and capped by a gabbro sill or intrusive. It is an unusual Wisconsin massive sulfide deposit because it is very large, structurally complicated, contains unusual silicate minerals and sulfide textures, and is associated with an iron formation. Bedded magnetite occurs on the flanks of the sulfide system and as disseminated grains or blebs adjacent to or within the deposit. �ANTIC LINE SYNCLINE DRILL HOLE <—0.25 0.25—0.49 0.50—0.99 1.00—1.49 1.50—1.99 >2.00 % Cu LECEND Rusk County, Wisconsin Figure 8 Distribution of Copper Grades, 900ft. Elevation, Eisenbrey Prospect. 0 1" =100' SCALE50 FEET 100 �ANTICLINE SYNCLINE DRILL HOLE <0.50 0.50—0.99 1.00—1.99 2.00—2.99 3.00—3.99 >4.00 % Zn LEGEND Rusk County, Wisconsin Figure 9 Distribution of Zinc Grades, 900ft. Elevation, Eisenbrey Prospect. 0 i FEET 100 —'I 1" = 100' SCALE50 �126 In detail the structure, mineralogy, texture, and metal grades of the Flambeau and Eisenbrey deposits are very dissimilar. A comparison between the similarities and differences are listed on Table 5. ACKNOWLEDGMENTS The author wishes to thank Tom Myatt, general manager, Flambeau Mining Company for allowing this paper to be written. Considerable advise and suggestions were provided by Russ Babcock, Stephen Dinkowitz, Jay Hammitt, Paul Schmidt, Paul Lindberg and Gene LaBerge and to Tammy Fredrickson who somehow managed to put all the comments together. Finally this paper is dedicated in memory of Ned Eisenbrey whose foresight and persistence resulted in the discovery of an interesting and significant metal resource. References Cited Babcock, R., 1996, History of Exploration for Volcanogenic Massive Sulfides in Wisconsin: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip Volume. DeMatties, Theodore A., 1994, Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview: Economic Geology, v. 89, p1122-1151. LaBerge, G. L., 1996, General Characteristics and Geologic Setting of the Wisconsin Magmatic Terranes: Institute on Lake Superior Geology, 42nd Institute, 1996, Field trip volume. Lydon, J. W., 1984, Ore Deposit Models-8. Volcanogenic Massive Sulfide Deposit Part 1: A Descriptive Model: Geoscience Canada, V.11, N.4. May, E. R., and Dinkowitz, S. R., 1996, An Overview of the Flambeau Supergene Enriched Massive Sulfide Deposit - Geology and Mineralogy, Rusk County, Wisconsin: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip Volume. Nockolds, S. R., 1954, Average Chemical Compositions of Some Igneous Rocks: Bulletin Geol. Soc. Am. 65, pp. 1007-1032. �Preservation of Depositional Features Dikes Foliation Strike and Dip Faulting Folding 8. Structural Sefting Outcroppings Overburden Weakly mineralized iron formation, volcaniclastics, and pyroxenites on Thomapple River bank. None recognized but presence suspected Slightly eroded; looking at the top of a very large system. 60 feet of Pleistocene Till. Iron formation with bedded magnetite or disseminated magnetite with anthophyllite. Impure cherts Intermediate dacite tuffs and lapilli tuffs capped by gabbro sill. IEisenbrey Deposit Structurally complex - tight isoclinal folding. Strong evidence of significant faulting with foliation dip changes on either side of gouge. Moderately Foliated E-W, dipping very steeply north or vertical with near vertical plunge. None Thick diabase dikes and sills occuping probable NE regional tension cracks. Pillows, volcanic bombs, lapillis,graben Lapillis well preserved and highly rodded. and horst features, and facies changes well preserved. Structurally simple-on limb of large isoclinal fold. Strong evidence of prenecontemp oraneous localized stuctures; little evidence of post depositional faults Strongly Foliated N45° E, 75U NW; probably overturned. Intermediate dacite tuffs altered to andalusite-biotite Schist with pillow lavas in stratigraphic hangingwall. None recognized; could be eroded Probably deeply eroded; looking at roots of a much lager system. 0 to 20 feet of Cambrian sandstone and 12 to 30 feet Pleistocene Till. Subcrop of weakly mineralized metachert and quartz-sericite schist under east side of Flambeau River. Host Rocks Atteration Pipe Precambnan Erosion Quartz-Sericite Schist or rhyolite tuff. Metacherts common Flambeau Orebody Ore Horizon A._Depositional Environment TABLE 5 COMPARISON BETWEEN THE FLAMBEAU AND EISENBREY DEPOSITS RUSK COUNTY, WISCONSIN �Supergene Protore Size E. Economic Geology Sphalerite Chalcopyrite Chief Sulfide texture D. Massive Sulfide Textures Gold Cap Precious Metals Gossan Supergene Enrichment Magnetite Sulfide Halo Protore Metamorphic Grade C. Mineralogy I Eisenbrey Deposit 2400 feet long, 45 feet thick 900 feet below subcrop. Approximately 6 million tons total resource. Insufficient size to support a mill. 3% Cu, 2% Zn. Economical. 1 .8 million tons at 10% Cu, 0.1 optAu. Insufficient tonnage. Approximately 1500 feet long, upto 200 feet thick and open below 3000 feet. Plus 50 million ton resource. Sufficient size but low grade. 1% Cu, 2.5% Zn. Poorly bedded. Massive pyrite and pyrrhotite with Well bedded with remobilized large pyrite cubes in pyrrhotite rimmed with chalcopyrite In semi massive protore. Occasslonal sulfide or cherty fragment. chalcopyrite. Whispy pyrrhotite and magnetite. Numerous magnetite and cherty/volcanic fragments. Remobilized and recrystallized around pyrite In massive beds to ragged patches in cubes, disseminated in pyrrhotite, or finely semimassive protore disseminated in sphalerite. lnterstial grains with pyrite, weakly bedded. Well bedded - massive beds Amphibolite grade. Upper greenschist to lower amphibolite. Pyrite with sphalerite and pyrrhotite Pyrite with chalcopyrite, minor with chalcopyrite. sphalerite and trace pyrrhotite. Halo restricted to anthophyllite magnetite Disseminated pyrite with chert rock package. Thickness complicated by folding up to 300 feet wide. Several percent magnetite in some massive Trace to few percent of magnetite in sulfides, host rock, and along strike in ironmafic rocks. None associated formation. with ore. Minor enrichment within 25 feet of subcrop. Extensive enrichment 80 to 185 feet beneath subcrop. Well preserved gold, silica, iron oxide, Minor gossan with iron oxides and minor precious metals. and ankerite gossan. Low precious metal content with gold associated High gold content associated with with sphalerite. chalcopyrite. Precious metal cap on top of massive None recognized. sulfides. Flambeau Orebody �129 GEOLOGICAL SUMMARY - CRANDON DEPOSIT By A. J. Erickson, Jr. Exxon Coal & Minerals Co., Houston, TX and R. COté Rio Algom Exploration Inc., Val d'or, Quebec, Canada INTRODUCTION Crandon Mining Company, a Wisconsin general partnership of subsidiaries of Exxon Coal and Minerals Company (Houston, Texas) and Rio Algom Limited (Toronto, Ontario, Canada) is in the process of seeking the required local, state, and federal agreements, approvals, and permits to mine the Crandon volcanogenic zinc-copper sulfide deposit. The deposit, located in Forest County, Wisconsin, is approximately 5 miles south of the town of Crandon, and 2 road miles east of State Highway 55, on Little Sand Lake Road. The deposit was discovered in 1975 by an Exxon Coal and Minerals predecessor company, Exxon Minerals Company (Schmidt et a!., 1978; May and Schmidt, 1982; Lambe and Rowe, 1987; and Schmidt, 1991). As described by Schmidt (1991), Exxon had been active in the Lake Superior region since the late 1960's and initiated work in northern Wisconsin in 1970 with reconnaissance mapping and airborne electromagnetic surveying (INPUT). A number of targets were identified and drilled. Additional (INPUT and other) airborne surveys were flown in 1974 over areas interpreted to contain favorable felsic volcanics. This work lead to the identification of other anomalies and further land acquisition, including the Skunk Lake target. Follow-up ground geophysical work was carried out in the spring of 1975 which confirmed the presence of a bedrock conductor. Drilling of the target was initiated in June 1975 and discovery was made with the first hole. The deposit was subsequently renamed the Crandon Deposit after the nearby town of Crandon. The target was the 25th prospect drilled by Exxon over a 5 year period of exploration (1970-1975) in Wisconsin after an expenditure of approximately $2.5 million. Since discovery, a total 340,000 feet of drilling of various types and diameters has been completed in 272 holes in and about the deposit. All interpretive work is based on this drilling as the nearest outcrops are several miles from the deposit. REGIONAL GEOLOGY The deposit is hosted by early Proterozoic rock of the Precambrian Southern Province of the Canadian Shield in the east-west trending Rhinelander-Ladysmith Greenstone Belt (Schmidt et al. 1978; May and Schmidt 1982). The belt is between 30 and 50 miles wide (N-S) and approximately 200 miles long (E-W) extending from the towns of Ladysmith in the west to Pembine in the east. (Sims, 1984, refers to the area as the Ladysmith-Pembine volcanic belt). The northern portion of the belt consists of mafic metavolcanic rocks, basalts, locally pillowed, basaltic andesites, flows, tuffs, some gabbroic rocks, and associated granites, tonalites, and granite gneiss. More felsic to mafic pillowed flows, dacitic to rhyolitic tuffs, porphyries and dikes are present in the southern portion of the belt (Sims, 1992). �130 The Rhinelander-Ladysmith greenstone belt forms the most northern portion of the Wisconsin Magmatic Terranes in the Penokean fold belt, south of the Niagara Fault as shown on Figure 1 (Hoffman, 1989; Sims et a!., 1989; Sims, 1992; and DeMatties, 1994). The magmatic terranes are complex, poorly exposed, and have been divided into three "subterranes" identified from north to south as, the Ladysmith-Pembine Belt, the Chippewa-Wausau Belt, and the Marshfield-Stevens Point Belt (Sims, 1984). More recently, Sims et a!. (1989), and Sims (1992), combined the two northern "subterranes" into the Pembine-Wausau Terrane. The southern belt has been renamed the Marshfield Terrane. The juxtaposed terranes and contained sulfide deposits, as shown in Figure 1, are interpreted to be the result of plate tectonic processes during the early Proterozoic. These terranes are believed to be the renmants of volcanic arc - continent and volcanic arc - volcanic arc subduction and plate collision zones. This accretion of the plates was initially at a juncture now referred to as the Niagara Fault Zone with subsequent accretion of a second plate along the Eau Pleine Shear Zone. This deformation and accretion occurred during the Penokean Orogeny, dated at approximately 1860 to 1840 Ma (Van Schmus, 1975; Schulz, 1984; Hoffman, 1989; Sims et a!., 1989; Sims, 1990; Kiasner et al., 1991). The recent summary by LaBerge (1994), provides a simplified discussion of these complex Proterozoic plate tectonic relationships, and the Lake Superior regional geology. GENERAL DEPOSIT GEOLOGY The following details are largely summarized from the descriptions of Schmidt et al. (1978), May and Schmidt (1982), Rowe and Hite (1984), and Lambe and Row (1987). Their work is supplemented by more recent work by the authors. Specific citations from all individual items are commonly not included in this summary and the reader is encouraged to consult the references for further details. The Crandon deposit is a "typical" volcanic hosted sulfide deposit as described in reviews by Solomon (1976), Franldin et a!. (1981), or Lydon (1988), of the "primitive" zinc-copper rich type using Hutchinson's (1980) classification. The deposit consists of two major styles of mineralization 1) a syngenetic, commonly laminated, zinc-bearing, pyrite-rich, sulfide zone which is partially underkuin by 2) an epigenetic, cross cutting zone of copper-bearing, quartz-pyrite-chalcopyrite stringer mineralization in altered volcanic rocks stratigraphically beneath the zinc mineralization. Early published reserve estimates (Schmidt et al., 1978; May and Schmidt, 1982; Rowe and Hite, 1984; and Lambe and Rowe, 1987) have generally included both the zinc and copper mineralization of the primary sulfide facies. The referenced tonnage is in the 55 to 65 million ton range with corresponding grades reported for this material as slightly over 1% copper, 5% zinc, and only minor amounts of lead, silver, and gold. The reserve estimate for the conformable syngenetic zinc mineralization alone is estimated as 30 million tons containing 9.4% zinc and 0.4% copper (Anon, 1994). At the property scale, the deposit is conformably contained in a sequence of mafic, intermediate, and felsic volcanic rocks. Pyroclastic units are dominant but numerous intercalated flows have been noted within the volcanic sequence. Chert, argillites, bedded sulfides, and volcaniclastic sandstone intercalations probably indicate periods of quiescence during formation of �______ / I 47. 46 45. EAU PLEINE ZONE — .) 0 Possible limit rhyolite-granite 0 44• terrana S. 0 I MINNESO1>1 IOWA Baraboo Synciine o -..----—- Waterloo 0 43 4 MA 1)ISOIV WISCONSIN 9T PROTEROZOIC Middle Proterozoic (Keweenawan) mafic igneous & sedimentary rocks of Midcontinent rift system (- 1,100 Ma) island-arc metavoicanic & granitoid rocks in EIBllHff Pembine-Wausau terrane (1834-1,880 Ma includes post-tectonic granttic rocks (1.760 Ma) island-arc metavoicanic & granitold rocks (1,835-1,890 Ma) Anorogenic granites. syenite, & anorthosite (1470 -1525 Ma) L._.... 2128148 Baraboo, Barron, Waterloo quartzites (age uncertain) (<1750 Ma?) Central Wisconsin myoiites & granite rocks (—1760 Ma) —.. High-angie fault WISCONSIN MAGMATIC TERRANES Sedimentary rocks of Paieozolc age CONTINENTAL MARGIN ASSEMBLAGE . Marquette Range Supergroup (1 .820-2,100 Ma) ARCH EAN Basement gneiss, granite, & greenstone IttF (2600 - 3550 Ma) I Thrust fault - Possible suture Sulfide Deposits 75 MILES 0 I I I TECTONIC MAP SOUTHERN LAKE SUPERIOR REGION Modified after Sims, 1992 Figure 1 �132 the volcanic pile. Syn-and post-volcanic, commonly mafic but occasionally felsic, intrusive dikes and sills constitute a small portion of the sequence. The host volcaniclastic assemblage along with the contained sulfide deposit strike generally east-west (N85°W) and dip steeply (7O09O0) north. Relict depositional features, internal mineral zonation within the sulfide mineralization, and gross sulfide zone relationships consistently indicate a normal, north facing volcanic sequence. A small portion of the deposit on the extreme west end is steeply overturned to the south. Rowe and Lambe (1986), have informally divided the volcanic package into a lower Hemlock Creek Group, which contains the Crandon deposit, and an upper Swamp Creek Group. Figure 2 is their reconstructed stratigraphic column and is included to provide a general summary of the lithologies and stratigraphic relationships. Detailed description of the units, discussions of the stratigraphic relationships, and interpretations of the genesis of the units are included in the above reference. Discussions here will be limited to the deposit features in the Crandon Unit with its conformable zinc mineralization, and to the stringer copper mineralization within the underlying Sand Lake Formation. SULFIDE DEPOSITS As indicated, the two major mineralization types of the Crandon deposit include 1) conformable, locally laminated, syngenetic, zinc-rich pyritic sulfide lenses and 2) cross cutting, epigenetic copper-bearing stringer sulfides commonly beneath the zinc deposit. Fine grained felsic and intermediate pyritic ash and lapilli tuffs, cherts, laminated pyritic cherts, and black thinly laminated pyritic argillite are locally interbedded with the conformable sulfide mineralization. Overprinting of stringer copper zone mineralization on the zinc mineralization is occasionally seen near the base of the zinc-rich sulfide zones. Crandon zinc mineralization consists of three or locally four sub-parallel stacked lenses of sulfide (COté et al., 1994), which are locally interbedded with tuffs and argillites. The lenses, occur either as unique horizons separated by epiclastic or pyroclastic lithologies containing lesser amounts of total sulfides, as shown on section A - A', Figure 4, or as stacked sulfide horizons with common boundaries, as shown in portk)ns of section B - B'. The sulfide bands contain sphalerite as continuous or discontinuous laminae and patches in laminated to more massive pyrite. Laminae or seams of chalcopyrite or galena are present but less common and are often cross-cutting due at least in part to late remobilization. The mineralization was cyclically deposited by pulses of sulfide-rich emanations in a restricted basin characterized by a shallow western half and a deeper central portion. At the eastern extremity of the deposit the sulfides thin and pinch out in the shallow end of the basin. Relationships are well illustrated on the mine level plan, Figure 3, at a depth of approximately 665 feet below surface and on cross sections A - A', B - B', and C - C' (Figure 4). Figure 5 provides an east-west longitudinal projection, showing the distribution of the zinc mineralization at a >3% zinc cutoff. The cyclicity of mineralization is shown in simplified form in the three sections as interpreted from internal stratigraphy and assay data analysis. This cyclicity has been clearly documented in recent logging and analysis of core from the latest drilling program and re-analysis of earlier drilled core. Thesethree main stratigraphically stacked sulfide lenses are laterally very continuous and can be traced in the majority of holes. The correlation diagram D - D' on Figure 6 highlights the internal sulfide stratigraphy and relative zinc and copper values as they relate to the specific sulfide facies �____ ___ __________ L dg DuCK LAKE GABBRO (dg) GENERALLY 25 M IN WIDTH t'4 TRUSIVES U L: UNALTEREOANDUNFRACTURED U: UNDIFFERENTIATED. GENERALLY ALTERED DIKES OF WHICH SOME COULD BE SMALL FLOWS LLJLLJ (3 U - FOREST UNIT (fi) A SEQUENCE OF EPICLASTIC ARGILL5CEOUS CONGLOMERATE AND SANDSTONE CONSISTING OF GRANITE CLASTS AND VOLCANIC CLASTS LOCAL FLOWS AND TUFF, ft I I I :<Lf) ' J 7 PINE UNIT (pn) A BASINAL SEQUENCE CF CHERTY TUFF. CHEAT AND SILICIFIED lUFF BECOMES MORE SERICITIC. PYRITIC, AND ARGILLITIC TO THE WEST. u-J (.f) 7 LINCOLN UNIT (In) PORPHYRITIC RHYOLITIC FLOWS WITH NTERBEDDED TUFF. CHEAT AND ARGILLITE. $ SKUNK LAKE UNIT (sk) A BASINAL SEQUENCE OF SLUMPED AND L CONTORTED CHEAT AND ARGILLACEOUS TUFF LAMINAE. SOFT SEDI MENT FEATURES ABUNDANT. LOCAL INTERBEDOED CHEAT OR TUFF, AND LOCALLY UP TO 10% SULFIDES. RICE LAKE UNIT (rc) A SERIES OF VOLACANIC DEBRIS FLOWS AND rc EUTAXITIC ASH FLOWS. rcm BLUEBIRD SUBUNIT (rcb1) BLOCKY TO TABULAR CHLORITIC FRAGMENTS. (LOCALLY EXHIBITING ATTENUATION). MATRIX PREDOMI- NANTLY FELSIC: (rcb2) CHLORITIC FRAOMENTS MODERATLEY ATTENUATED. POSSIBLY WEAKLY WELDED. cb2 CARRIDGE SUBUNIT (rcc) DOMINANTLY WELDED ASH FLOWS ALTHOUGH DEGREE OF WELDING VARIABLE. INTERBEDDED TUFF U COMMON. -J CHEPTY TUFF. LOCAL REWORKED TUFF. No SULFIDES. MILLSTREAM SUBUNIT (rcm) : i< OAK LAKE UNIT (Ok) A BASINAL SEQUENCE CONSISTING DOMI- ok F I NANTLY OF CHERTY TUFF AND SERICITIC TUFF CONTAINING I TO 5% STRATABOUND PYRITE. LOCAL INTERBEDOED CHEAT OR CHLORITE SERICITETUFF MOLE LAKE UNIT (ml) A FINE TUFF CONTAINING ONLY MINOR ml p I BASINAL ENVIRONMENT. USUALLY COARSE PYROCLASTICS. THE EAST HALF OF THE FORMATION IS A FINE CHLORITIC TUFF. THE WEST HALF ISA SILTY. HOMOGENEOUS, SERICITE ml CHLORITE REWORKOED TUFF. CONTAINING 0 TO 4% PYRITE. INTER- I LU BEDDED CHEAT IS COMMON IN THE WEST HALF. PROSPECT SUBUNIT (mip) FELSIC DEBRIS FLOWS. GENERALLY 4 TO U 15MM FELSIC DEBRIS IN A FINE CHLORSTIC MATRIX. EAGLE SUBUNIT (mle) A VOLCANIC SANDSTONE CONTAINING 80% ROUNDED QUARTZ SAND IN A SERICITE-CHLORITE MATRIX U 0 cr J I CRANDON UNIT (Cr) A BASINAL SEQUENCE CONSISTING OF STRATABOUND MASSIVE SULFIDE (GREATER THAN 50% TOTAL SULFIDE), PYRITIC ARGILLITE AND PYRITIC TUFF LOCAL THIN CHERT BEDS. LU SAND LAKE UNIT (Sd) FINE DRAINED TUFF WITH MINOR DEBRIS FLOWS, CHERTY TUFF AND FLOWS. GRADES WITH DEPTH INTO COARSER REWORKED TUFF AND FINE LAPILLI TUFF. TOWNSHIP SUBUNIT (sdt) A SERIES OF VOLCANIC BRECCIAS CONSISTING OF ANGULAR. POORLY SORTED HETEROLITHIC OR MONOLITHIC FRAGMENTS. MATRICS STRONGLY SILITIC sdt1 A TRANSITIONAL BRECCIA AT THE TOP OF THE SAND LAKE UNIT. CONSISTING OF FRAGMENTS OF TUFF,AAGILLITE. CHERT AND MASSIVE SULFIDE. sdt2 VOLCANIC BRECCIA CONSISTING OF HETEROLITHIC FRAGMENTS EXHIBITING MANY STAGES OF SILICIFICATION. sdt3 VOLCANIC BRECCIA CONSISTING OP MONOLITHIC FRAG- MENTS. FRAGMENTS GENERALLY WEAKLY SILICIFIED. NASHVILLE UNIT (nh) PORPHYRITIC BASALTIC FLOWS. LOCAL THIN TUFF BEDS CRANDON DEPOSIT - RECONSTRUCTED STRATIGRAPHIC COLUMN LAMBE & ROWE (1987) Figure 2 �I I 7 0 I 9 I I 12 -- 11 13 14 I 1 I 16 274000 £ 274400 C MODEL_LEVEL 13 270000 MINE PLAN ELEV. 1025 GEOZONE OUTLINES Crandon Mining Company 0 274400 — 6 C RA2RI 201 ==-I 5 274000 IA -— 13 20 I I 0 21 22 23 24 25 I 275200 I I N 0 I 276000 I I I I £ I 276400 275600 £ — C I I I £ I 'I I I £ 277620 C I I III Z77 E/// Zo C I C 276404 B --# B' 71 --- 64 65 66 67 CA 69 70 - I 270400 0 59 60 61 62 6 I 274000 MINE RA LI ZATI ON ZINC 4849 50 51 52 57 54 55 56 57 277200 2 43 44 45 46 4 I 276400 C RI C A' 72 73 II C I Figure 3 I I I 81 82 83 84 C RAN DON 80 FORMATION I I _ I 279600 4 75 76 7? 70 7 I 279200 CRANDON DEPOSIT — CRANDON DEPOSIT MINERALIZATION ON THE PROPOSED 665 LEVEL 275204 MIDDLE MINEROLIZED GEOZONE 2021 OJ LO/ER M1NRALIZED GEOZONE 2023 Z UPPER MINERALIZED GEOZONE 0011 0 I —_- MINE LEVEL 665 LECENI?: I £ 6 27 28 29 30 3 32 33 34 35 36 37 38 39 40 275600 COPPER MINERALIZATIO ZONE 19 £ 240000 �2f28215 C N - S SECTION C-C' 2,276,793 E LOOKING WEST CH 0 400 800 1200 FT. N - S SECTION B-B' 2,278,565 E LOOKING WEST (0 0 0 c'J z Figure 4 N - S SECTION A-A' 2,279,008 E LOOKING WEST CRANDON DEPOSIT - SIMPLIFIED GEOLOGIC CROSS SECTIONS �Limit Copper Stringer Zone 200 et [Z) 400 9)0 IAJEJRCI9 IF II RC/r IA I E Jr .RC 1119 1119196 12/2195 11115195 Area of prolonged hydrothermal activity & thick sulfide accumulation MINERALIZATION ZINC & COPPER Longitudinal Projection Looking North 1200 -800 — N 0 8 0 C- Ui I 0 ((9 9)0) 9— (20 W0 9- z 00z IN U) ———--—-9— C CO Limit Copper Stringer Zone I' B — 0 A >3% Zn 'Crandon Zinc Zone - 0 0 0 2F28213 k/ .1-- Figure 5 CRANDON DEPOSIT - EAST-WEST LONGITUDINAL PROJECTION SHOWING LIMITS OF MINERALIZATION U - -k 0-z 0 CRANDON MINING COMPANY -400 — West — - a Level OO 20 o— A' �137 depicted by drill holes 137, 159, and 265. Individual lenses generally consist of an upper, zinc-rich, bedded to laminated pyrite-sphalerite (±galena) facies which grades stratigraphically downward into a commonly zinc-lean, poorly bedded pyritic fades. These primary textural variations and associated metal zoning are essentially repeated from one sulfide lens to the next, analogous to that described at the Mobrun deposit in the Noranda camp (La Rocque et a!., 1993). Typically, the lower facies consists of fme-grained colloform or spheroidal pyrite with lesser granular (in part, recrystallized) medium grained pyrite with fine interstitial sphalerite and/or fine "lacy" interstitial chalcopyrite. This lower facies may also locally include an appreciable amount (20-40%) of fine botryoidal silica gangue thought to represent a primary exhalative gel or sinter. Individual lenses generally average from 40 to 55 feet in true thickness and taper to thin horizons at the margin of the basin. Where sulfide lenses are in direct contact, the true thickness of the sulfide package may exceed 100 feet. Stringer copper zone mineralization occurs stratigraphically beneath the zinc mineralization. It consists of multiple stages of quartz, quartz-pyrite, quart.z-pyrite-chalcopyrite, locally quartz-pyritechalcopyrite-sphalerite, and thin pyrite veinlets. Age relationships are complex. Barren milky white quartz veinlets clearly predate the mixed quartz sulfide veinlets, whereas most thin barren pyrite veinlets post-date the quartz sulfide veinlets. This network of veinlets is localized as a semiconformable envelope in the Sand Lake Formation "breccias" immediately below the Crandon Unit with its contained zinc mineralization as described by Lambe and Rowe (1987). Although described as mono and heterolithologic volcanic breccias, it should be noted that some of the breccia-like textures are clearly alteration features. SULFIDE MINERALOGY Sulfide mineralogy is simple in both the conformable sulfide zinc zone and the footwall copper stringer zone. Pyrite is clearly the dominant sulfide in the zinc zone and may range up to nearly 100% at the base of individual sulfide lenses and in the less prevalent sub-seafloor replacement pyrite immediately beneath some of the zones of zinc mineralization. Sphalerite is the zinc sulfide. There are lesser amounts of chalcopyrite, galena, tetrahedrite, and rare pyrrhotite and arsenopyrite are present in both the zinc and copper zones. Marcasite and enargite have been reported. Near surface, a typical iron oxide, silica-rich gossan is present due to pre-Cambrian weathering of the sulfide mineralization. The gossan generally extends less than 100 feet below the subcrop, and is commonly only a few tens of feet thick. Very locally it extends in excess of 400 feet below the subcrop along particular lithologic horizons, or contacts within and along the margin of the Crandon Unit. A limited amount of supergene sulfide mineralization, chalcocite, covellite and rare bornite, is present beneath the gossan as well. Minor amounts of copper oxides have been noted. The supergene enriched zone is small, in part due to the proportionally low amount of copper in the primary mineralization and in part due to its removal through weathering and erosion since perhaps the middle Paleozoic. In this respect the Crandon deposit contrasts with the Flambeau deposit in western Wisconsin (May 1977). At Flambeau, the primary mineralization is generally more copper rich and the secondarily enriched ore zone was largely preserved from weathering, erosion, and Pleistocene glaciation by the presence of the Cambrian cover rock. ALTERATION Synvolcanic hydrothermal alteration at Crandon is most strongly and extensively developed within the Crandon Unit and the immediate stratigraphic footwall (Sand Lake Formation) unit south of the zinc mineralization. However, alteration features are complex and commonly overlap. Footwall �Pv ItIcf a-a a R. C., A.J.E. Jr., J.T.S Il b I- k'Y1 I'" "'1 /11/ / / \\\\ \ \\\\ /\I/Il \\\\/ I//I \ \\\\\ \ \ \ \ \ \ \ \ \ \\ \ 159 __— a N IA —R D Sand Lake Breccias Lower poorly bedded granular, colliform, pyrite. Sphalerite lean Upper laminated sphalerite rich sulfide Pyritic argillite 'a a ET i; UL çT' aa,O Diorite — I I_— mafic lapilli tuffs. Mole Lake: Intermediate to HANGING WALL - a -a - - a - I' II Ill EARLY LATE C - - a - - a Q - - I 0 I 25 a FEET I 50 - o0 a 0— O - I 100 2F28526 I 75 / / / II \\\ / / / / / / / / / / / I // / I I / /\\ I//I pyritized footwall polymitc felsic/ intermediate "breccias". COPPER r ZINC - // / / / \ \ \\\ \ \ /\\\I//I \ \\\\ \ \\\/ \ \\\\ I/I/I / ,,, FOOTWALL Sand Lake: Strongly silicified & - SULFIDE CYCLES C -o 265 \ \\ / / I 7/ \\ \ \ \ / / 7/I III / / I \ \\ \ \ \ \\ \/ \\\\ \ \\\ / / / // / / / \ \\ \ \ \\ \ \ \ \\ \ \\\ \\\ \ \ \\\\\\ Relative histograms at different scales Figure 6 a a. fl 17 — —= - D' 137 SECTION D ________ _____________ _______ __________ SELECTED ORE ZONE SULFIDE CORRELATION DIAGRAM �139 alteration is dominated by partial to pervasive silicification, whereas lesser chioritization, sericitization, and carbonatization (mostly dolomite) are also present. Intense pyritization in zones varying in thickness from 25 to 200 feet immediately below the conformable zinc zone accompany this alteration. Limited information on the footwall stringer mineralization and the fact that erosion has left only a portion of the original deposit make it difficult to fully define a classic feeder pipe beneath the tabular zinc mineralization, as described by Lydon (1988). A zone of prolonged hydrothermal activity is inferred due to thick alteration and mineralization located approximately middistance between cross sections B-B' and C-C' (See Figure 5). Here an important thickness of massive and semi-massive sulfides exhibits an abundance of textural features that are interpreted to be the result of sub-seafloor replacement. Intense black chlorite alteration within the footwall Sand Lake Formation is well developed at this locality. The "tabular appearing" footwall silicate alteration assemblage illustrated on the level plans by Lambe and Rowe (1987) suggest more intense chloritic alteration beneath the western half of the deposit, whereas to the east sericitic alteration is more abundant. Within the Crandon Unit, some of the "pyritic argillite" in fact represents strongly metasomatized zones of magnesium-chlorite alteration within the laminated, pyrite bearing, fine epiclastic sediment. In other areas, however, the "pyritic argillite" represents pyrite-rich zones of intense black, magnesium-iron-chlorite alteration as is typically found in footwall stringer zones in volcanic-hosted sulfide deposits. This later hydrothermal alteration is both cross-cutting and locally conformable to bedding. Most commonly, it is associated with epigenetic, stringer copper mineralization and localized as multistage quartz-sulfide, or sulfide veinlets in a complex semiconformable zone of quartz-sulfide brecciation in the footwall beneath the zinc mineralization. STRUCTURE AND METAMORPHIC ATFRIBUTES The Penokean Orogeny produced a generally steep dipping attitude in the volcano-sedimentary assemblage hosting and surrounding the Crandon deposit. Bedrock units in the area of the deposit have been metamorphosed to the lower greenschist facies. The structural deformation is generally weak to moderate such that delicate primary volcanic and sedimentary textures are preserved at various localities. The resulting overprint of principal structural fabric includes a regional east-west trending subvertical dipping schistosity and the local development of longitudinal east-west shears. The pervasive planar structure or S1 schistosity, as noted in core, is presumed axial planar to the regional fold features and is generally sub-parallel to the bedding attitudes except where small scale parasitic folding is developed. Local zones of more pronounced to strong shearing are less frequent and preferentially developed as bedding parallel features and along major lithological contacts. Major faults have not been recognized at Crandon as shown on level plans (Figure 3) and cross-sections (Figure 4). These figures illustrate the undisturbed lateral continuity of the hanging wall contact of the deposit indicating minimal structural complications as might otherwise be indicated by marked thickening, thinning or offset due to significant folding and/or faulting. This lack of significant structural offset has been substantiated in five separate drilling programs since 1980. All holes intersected stratigraphy as anticipated, thus indicating no important structural effects. �140 CONCLUSIONS The lithological and mineralogical features of the Crandon Deposit described above are typical of many submarine volcanogenic sulfide deposits emplaced at and directly below the sea floor. Internal sulfide stratigraphy, as indicated by mappable sulfide facies, document the presence of at least three major stacked lenses, i.e., pulses of pyrite-sphalerite mineralization. Long lived, both focused and diffuse discharge of metal-bearing hydrothermal fluids are indicated. These solutions percolated upward through the Sand Lake submarine volcanics to precipitate their contents at and below the Proterozoic sea floor. The resulting concentration of the conformable pyritic, zinc-rich sulfides, uninterrupted by major structural dislocation, and the underlying discordant, copper-rich stringer mineralization is the largest known volcanic-hosted zinc copper deposit in the Rhinelander-Ladysmith Greenstone Belt. Acknowledgment We would like to take this opportunity to thank T. E. Warren, Rio Algom Exploration Inc., and G. Westra, Exxon Coal and Minerals Company, for constructive comments and Crandon Mining Company, Exxon Coal and Minerals Company and Rio Algom Exploration Inc.,for permission to publish this paper. Secretarial support by L. Gonzales and drafting by J. L. Shaw, Exxon Coal and Minerals Company, is greatly appreciated. References Cited Anon, 1994, Annual Report, Rio Algom Limited. Cot, R., Erickson, A. J., Jr., Donahue, S. V., Thresher, J. E. Jr., and Anderson, P. F., October 1994, Bedrock Hydrogeology of the Crandon Project Site: Foth & Van Dyke Memorandum, 19 p. DeMatties, T. A., 1994, Early Proterozoic Volcanographic Massive Sulfide Deposits in Wisconsin: An overview: Economic Geology, v. 89, p. 1123-1 151. Franidin, J. M., Lydon, J. W., and Sangster, D. F., 1981, Volcanic-associated massive sulfide deposits: Economic Geology, 75th Anniversary Volume, p. 485-627. Hoffman, P. F., 1989, Precambrian geology and tectonic, history of North America: in Bally, A. W., and Palmer, A. R., eds., The Geology of North America-An Overview; G.S.A., The Geology of North America, v. A, p. 447-512. Kiasner, J. S., Ojakangas, R. W., Schulz, K. J., and LaBerge, G. L., 1991, Nature and Style of deformation in the foreland of early Proterozoic Penokean Orogen, Northern Michigan: USGS Bull 1904-K, p. K1-K22. Lambe, R. N., and Rowe, R. G., 1987, Volcanic history, mineralization, and alteration of the Crandon Massive Sulfide Deposit, Wisconsin: Econ. Geol. v. 82, p. 1204-1238. LaBerge, G. L., 1994, Geology of the Lake Superior Region: Geoscience Press, Phoenix, AZ, 309p. �141 LaRocque, A. C. L., Hodgson, C. J., and La Fleur, P. J., 1993, Gold distribution in the Mobrun volcanic-associated massive sulfide deposit, Noranda, Quebec: A Preliminary Evaluation of the Role of Metamorphic Remobilization: Economic Geology, v. 88, p. 1443-1459. Lydon, J. W., 1988, Volcanogenic massive sulfide deposits Part 1: A descriptive model: Part 2: Genetic models: in Roberts, R. G., and Sheahan, P. A., eds., Ore Deposit Models, Geoscience Canada Reprint Series 3, Geol. Assn. Canada, Memorial University, St. Johns. Nfld. p. 145-181. May, E. R., 1976, Flambeau - A Precambrian Supergene Enriched Massive Sulfide Deposit: SME preprint 76-1-55, 35p. May, E. R., and Schmidt, P. G., 1982, The discovery, geology, and mineralogy of the Crandon Precambrian massive sulfide deposit, Wisconsin: in Hutchinson, R. W., Spence, C. D., and Franklin, J. M., eds., Precambrian Sulfide Deposits, H.S. Robinson Memorial Volume, Special Paper 25, Geol. Assn. of Canada, p. 448-480. Rowe, R. G., and Hite, R. G., 1984, Applied geology: The foundation for mine design at Exxon Minerals Company's Crandon Deposit: in Erickson, A. J., Jr., ed., Applied Mining Geology, SME, Denver, p. 9-26. Schmidt, P. G., 1991, Discovery case history of the Crandon Massive Sulfide Deposit, Forest County, Wisconsin: in V. F. Hollister, ed., Porphyry Copper, Molybdenum, and Gold Deposits, Volcanogenic Deposits (Massive Sulfides) and Deposits in Layered Rock, SME Case Histories of Mineral Discoveries, v. 3, p. 99-102. Schmidt, P. G., Dolence, J. D., Lluria, M. R., and Parsons III, (3., 1978, Geologists block out Exxon's big find of Zn-Cu at Crandon: Engineering and Mining Journal, v. 179, p. 61-66. Sims, P. K., 1984, Metallogeny of Archean and Proterozoic Terrains in the Great Lakes Region - A Brief Overview: in Bush, A. L., ed., Contributions to Mineral Resources Research, 1984, USGS Bull. 1694, p. 57-71. Sims, P. K., (compiler), 1990, Geologic map of Precambrian rocks of Iron Mountain and Escanaba 10 x 2° Quadrangles, Northeastern Wisconsin and Northwestern Michigan: USGS Miscellaneous Investigation Series, Map 1-2056. Sims, P. K., (compiler) 1992, Geologic map of Precambrian rocks, southern Lake Superior Region, Wisconsin and Northern Michigan: USGS Miscellaneous Investigation Series, MAP 1-2 185, 2 sheets. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terrains of the Penokean Orogen: Can. J. Earth Sci. v. 26, p. 2145-2158. Solomon, M., 1976, "Volcanic" massive sulfide deposits and their host rocks - a review and explanation: in Wolf, K. H., ed., Handbook of Stratabound and Stratiform Ore Deposits, Elsevier, Amsterdam, v. 2, p. 21-50. Van Schmus, W. R., 1976, Early and Middle Proterozoic history of the Great Lakes area, North America: Phil. Tran. R. Soc. Lond. A. 280, p. 605-628. �142 �143 THE BEND DEPOSIT: AN EARLY PROTEROZOIC COPPER-GOLD VMS DEPOSIT by Theodore A. DeMatties and William F. Rowell Geological Consultants INTRODUCTION Exploration conducted between 1985 and 1994 by the former Jump River Joint Venture, and more recently Sharpe Energy and Resources, has identified a potentially economic copper-gold volcanogenic massive sulfide deposit in the Chequamegon National Forest of north-central Wisconsin. The deposit, known as Bend, is located in Taylor County, approximately 19 miles north-northwest of Medford, the county seat (Fig. 1). Mineral rights controlling the known deposit and its extensions are currently held under a BLM Preference Right Lease Application, BLM prospecting permits, and private leases by a joint venture consisting of Sharpe Energy and Resources, Freewest Resources and Cyprus-Amax. Originally discovered as a single high-priority, six-channel electromagnetic (INPUT) anomaly in 1978, the property was not available to the former Jump River Joint Venture for acquisition until 1985. Drilling began in 1986 on the blind (100-120' of glacial overburden) electromagnetic target and since that time a total of 38 diamond driliholes (approximately 47,000 feet of drilling) have indicated a resource of 3.9 million short tons grading 1.87% copper, 0.09 opt gold, and 0.39 opt silver. LOCAL AND REGIONAL GEOLOGY The Bend deposit is one in a cluster of at least three volcanogenic massive sulfide (VMS) deposits which occur within the Ladysmith district (Fig. 2). Other significant deposits in this district include Flambeau (Cu-Au), which is currently being mined, and Eisenbrey (Thornapple) (Zn-Cu) where exploration has recently (1995) been conducted; previously explored VMS showings also occur at the Schoolhouse (Cu), and Clear Creek (Cu) prospects. This district, as well as two others which have been identified, is located in the LadysmithRhinelander volcanic complex. The complex lies in the Early Proterozoic Penokean volcanic belt (or Wisconsin magmatic terrane), which is a major component of the Southern Structural Province of the Canadian Shield. The Bend deposit is hosted by a felsic center located structurally along the southern margin of a major volcanic arc and within a back-arc basin facies. Locally, the center is associated with, and occurs along the flanks of, a mafic pile succession (Fig.3). The host rock section is up to 2000 feet thick and consists of steeply dipping (upright), interbedded, schistose, rhyolitic to rhyodacitic, bedded metatuffs (sericite schist) and quartz-crystal metatuffs (quartz-sericite schist-semischist, Fig.7A) that are overlain (stratigraphic hangingwall) by an andesitic to rhyolitic (dominantly dacitic-rhyodacititc) metavolcanic flow-fragmental sequence and associated fine tuffs or metasediments (Fig. 4 and Table 1). �130N T31 132 N T33 N P3W Substation 01 2345 miles P1W Figure 1. Bend project location map, Taylor County, Wisconsin. j P2W Power transmission line uss..wgbs,. P4W z, a-. North PIE U R2E Fig.1 R3E �Anorogenic igneous rocks (1,4701,510 Ma) Alkali-feldspar granite (=1835 Ma) Xv Gneiss and schist (2,800- 3,000 Ma); includes tonalite (1,890 Ma) Volcanic rocks in the Marshfield subterrane Wausau Volcanic Complex Ladysmith-Rhinelander Volcanic Complex Back arc basin sequence (greenschist succession) Main volcanic arc sequence (amphibolite succession) Volcanic and lesser sedimentary rocks (1,840-1,880 Ma): Gneiss and granitoid rocks (1 835-1,865 Ma) •j—. 1 - Tonatite-granodiorite-granite (1,760-1870 Ma) -,- + + + .- + + + + ÷ + + + + + + + Wolf River + Batholith + + + Xs Shear VMS Shear-zoneoccurrence hosted gold deposit A Thrust x — High-angle --- Potential economic VMS deposit Foliation — Gneiss (2,700-3,550 Ma) Marquette Range Supergroup (=1,850-2,100 Ma) CONTINENTAL-MARGIN ASSEMBLAGE + + , + + VMS deposit + + ÷ + + ________ II AEM formational group and type Figure 2. Geological map of northern Wisconsin showing major volcanic complexes, and distribution of VMS deposits and occurrences (modified Sims, 1989). + IH Middle Proterozoic (Keweenawan) mafic igneous and sedimentary rocks of the Midcontinent rift system (1,0001,200 Ma) rocks Paleozoic sedimentary WISCONSIN MAGMATIC TERRANES (PENOKEAN VOLCANIC BELT) _______ �if I Main Volcanic Arc Sequence Piv — dominantly intermediate to malic metavolcanic flows and interbedded metatufts and tuffaceous metasediments intnisive complex; includes melavolcanic flows, interfiow tuffs and sediments, and cherty iron formation (if) F' ' \N Pmv — mafic to ultramafic volcanicI I I Back-Arc Basin Sequence intwsives, syenodiorite Pms — graphilic, sulfide-bearing metaargillite formations \ Pmvf — dominantly intermediate to mafic metavolcanic flows and subvolcanic infrusives Pvs — dominantly tuffaceous mela--1 sediments; includes metagraywacke, bedded or reworked melatuffs, and associated chemical metasediments I Pvs • I.. .1 Metagabbro, altered ultramafic Lower Proterozoic Metavolcanic and Related Rocks Lower Proterozolc (?) Intrusive Rock Units . j Metagrariite, quartz metadiorite, -' ' metadiorite and metasyenite I ::I Lower Proterozoic Barron Quartzite Sedimentary Rock Units Undifferentiated Cambrian sandstone formations; thin (<50 ft) sandstone units locally covering basement metavolcanic units not shown — PPE PROSPECT ,,y BEND DEPOSIT (Cu,Au) DeMatties, 1994). 0 0 Deposit with defined reserves A 4 /92 Z z LYNNE DEPOSIT (Zn, Pb,Ag) 5km Smiles Reverse and normal magnetized mafic dikes (Keweenawan age) Prospect Shear zone a Figure 3. General geologic map of the western portion of the Ladysmith-Rhinelander metavolcanic complex (after CH - - _ -< magnetic data Contact, based on airborne —— Projected or inferred fault — — __ ___ Pfv — dominantly intermediate to felsic mdtavolcanic tuffs/lapilli metatuffs (lifhicl cryslal) and flows, cherty metatuffs, and associated chemical mefasediments (metachert) Felsic Center(s) v4I1 C) 0 N 0 (0 0 3 C) _____ �I 500 FEET Figure 4. �Tab'e 1 DESCRIPTION OF LITHOLOGIC UNITS VOLCANIC UNITS HANGING-WALL SEQUENCE (FEISIC FLOW-FRAGMENTAL COMPLEX) fl/ I D L I V7 INTERMEDIATE TO MAFIC FLCMSLVR ] INTERMEDIATE TO FELSIC FLOWS (dacite to rhyo(andesite to basaltic andesite) Dark greenish dacite) Greenish gray, gray, fine— to medium— fine— to medium—grained, thin—to thick bedded, grained, massive, commonly porphyritic (feldspar and fractured and healed ferrornagnesian mineral (quartz and carbonate), porphyritic (feldspar phenocrysts) and nonporphyritic inetavolcanic flows and flow breccias. Interflow tuffs and sediments and interbedded siliceous and metavolcanic flows occur locally. IV11T i- phenocrysts) metavolcanic flows and/or subvolcanic intrusives. FELSIC FLOWS (rhyolite) Light gray to pinkish— white, fine— to medium— grained, massive, fractured and healed, very hard, commonly porphyritic (blue quartz eyes and feldspar phenocrysts), siliceous rnetavolcanic flows, sub— volcanic intrusives, and flow breccias; localized well-developed banding?. flow Locally, weakly mineralized and altered. INTERBEDDED FLCYS AND INTERFLOW PYROCLASTIC BEES Dominantly thin, intermediate to felsic metavolcanic flows (Vp) , flow breccias, and carbonath-rich lnterflow metatuffs and lapilli metatuffs. LT INTERMEDIATE TO FELSIC LAPILLI TUFFS Greenish gray, medium- to coarse— grained, thin- to thick-bedded, carbonate-rich coarse metatuffs, lapilli metatuffs, and tuff breccias. Normal graded bedding is common. LLI INTERMEDIATE TO FELSIC FINE AND COARSE TUFFS Light to dark greenish gray, fine- to medium—grained, thinly bedded to laminated metatuffs and associated tuffaceous meta— Black meta—argillite laminations sediments. locally. Intercalated thin inter- mediate to felsic metavolcanic flows (VD) locally. I Cs TUFFACEOUS SEDIMENTS Dark gray to CT black, fine—grained, laminated, commonly graphitic, chlorite—rich meta—argillite. Commonly sulfide— bearing. Chert laminations common. CHERTY TUFF Fine-grained, finely laminated cherty and hematitic inetatuff. Chert component greater Thin massive-sulfide than 50%. beds may be present. MINERALIZED SEQUENCE ALTERED AND MINERALIZED QUARTZ-CRYSTAL FELSIC TUFF Medium to light gray, fine- to inedium-grained, poorly bedded, well-foliated (schistose) , crystal-bearing (blue quartz eyes) quartz-sericite schist. Well—developed tuffaceous texture is preserved. Widespread stockwork sulfide mineralization is characteristic, consisting of up to 30% (commonly l%-lO%) pyrite ± chalcopyrite as disseminations, cross-cutting veinlets, and conformable bands. This unit hosts copper- and gold— bearing massive to semimassive and stringer mineralization. 1xT1_31 ALTERED AND MINERALIZED CRYSTAL FELSIC TUFFS Medium to light gray, fine- to poorly to well—bedded, weakly to well—foliated (schistose), crystal—bearing (quartz and feldspar crystals), locally fragmental qnartz—sericite (ifeldapar) schists and semi—schists. Widesprad disseminated sulfides (pyrite ± chalcopyrite) and conformable massive to semitnassive sulfide bands. Crystal tuff units are separated by thin argillite (CS) and felsic tuff (GT) beds. Unit XT medium-grained, hosts copper-bearing fragmental massive sulfide and stringer sulfide mineraliztion FOOTWALL SEQUENCE GT7 BEDDED FELSIC TUFF Gray to greenish gray, fine—grained, thinly to thickly laminated, well—foliated (schistose) sericite schist. disseminated pyrite, up to 5%. [F 9203001 CE11O3 GEO Commonly contains INTERMEDIATE TO MAFIC FLOWS AND INTERFLOW SEDIMENTS (andesite) Dark greenish gray, fine- to medium-grained, locally laminated, foliated (schistose) chlorite Carbonate alteration common. schist. �— MPFIC FLOW(S) (basalt) Dark greenish gray, aphanitic to fine—grained, nonfoliated, fractured and healed, nonporphyritic (massive) metavolcanic flows and/or subvolcanic intrusives VM INTRUSIVE UNITS 1 +] SUBVOLCANIC INTRUSIVE Dark gray, medium—grained, equigranular, massive, fractured [± intermediate to mafic dike or sill. +1 and healed, SULFIDE MINERALIZATION MASSIVE SULFIDE MINERALIZATION Fine- to very fine—grained, poorly to well-bedded, locally fragment—bearing (less than 20% XT fragments) , massive (greater than 50%, up to 90%) granular pyrite with varying amounts of fine chalcopyrite and tetrahedrite-tennantite intergrowths. Gangue minerals include quartz + sericite ± chlorite. SEMIMASSIVE SULFIDE MINERALIZATION 30% to 50% pyrite. SULFIDE MINERALIZATION Medium- to coarse-sized, sithrounded to subangular, coimnonly silicified XT fragments (greater than or equal to 20%) FRAGMENT-BEARING supported in a fine-grained matrix of semimassive pyrite (30%-5O%) ± chalco— pyrite. --- FRAGMENTAL SULFIDE MINERALIZATION Medium- to coarse-sized, subrounded to (py) fragments (greater than or equal to 30%) supported in a fine matrix of quartz and sericite. subangular sulfide /JJ STRINGER SULFIDE MINERALIZATION Fine—grained cross—cutting pyrite (1O%-3O%) ± / chalcopyrite or wispy chalcopyrite veinlets and blebs; commonly overprints massive sulfide and fragment-bearing sulfide mineralization. HYDROTHERMAL ALTERATION alteration and weak to Includes weak to strong fine—grained black wispy chlorite intense silicification. DL — upper lens LL — lower lens Level GEOLOGIC SYMBOLS contact N observed projected in drillhole or infeed contact strike + dip of relict bedding strike of vertically dipping bedding strike of foliation (sistosity) strike fault, dashed where projected Plans of vertically dipping foliation (sjstosjty) relict bedding attitude foliation attitude (schistosity) flow breccia unless otherwise designated shear zone TOP direction of stratigraphic top Abbreviations py-pyrite, po-pyrrhotite, cp-cbalcopyrite, sp—sphalerite, tet—tetrahedrite DDH significant sulfide mineralization base- and precious-metal—bearing Ore grade Cu Ore grade Au sulfide mineralization �150 The felsic sequence remains open along strike to the west of the deposit, but is cut off to the east by an extensive rhyolitic dome-flow complex of unknown dimensions. In general, the felsic complex is relatively unaltered, although localized hydrothermal alteration has produced zones of moderate to intense silicification, sericitization and chioritization. Disseminated pyrite often occurs within sericitized zones, whereas stringer-like chalcopyrite is associated with black chlorite alteration. Geophysically mappable meta-argillite formational units closely parallel or are interbedded with the felsic tuffs and the deposit. These units locally contain anomalous copper mineralization and are an important ore equivalent marker horizon that extends several miles along strike in both directions. Regionally the felsic center may be isoclinally folded, though there is no evidence of folding in the immediate deposit area. Metamorphic grade of the succession is lower greenschist; a weak to moderately strong foliation (schistosity) has developed parallel to relict bedding in the tuffaceous units; however, many relict volcanic and sedimentary features have been preserved. GEOCHEMISTRY To classify the geochemical affinity of the volcanic succession, major and trace element compositions were determined for 58 core samples taken from 12 driliholes that intersect the deposit. Twenty-two samples were from the host quartz-sericite schist (mineralized quartz-crystal felsic metatuff, designated the XT unit), 26 samples were of relatively unaltered volcanic rocks from the hangingwall sequence and 4 samples were from the felsic dome-flow complex. FeO* Alk MgO Figure 5. AFM diagram for hangingwall and felsic dome. Squares = hangingwall volcanics; Crosses = felsic dome samples. �151 Because the hangingwall and felsic dome rocks are generally not hydrothermally altered and have undergone only lower greenschist facies regional metamorphism, they can be classified based on major element composition. On an AFM diagram (Fig. 5) most samples plot within or near the calc-alkali field. Limited data on Si02 and alkali content suggests that the hangingwall sequence includes a fully differentiated rock suite ranging from basaltic-andesite to rhyolite (Fig. 6). Samples from the felsic dome complex plot primarily in the rhyolite field. To ascertain the primary geochemical affinity of the hydrothermally altered quartz-sericite schist it is necessary to use immobile element ratios. TiC)2 and Zr are generally considered to remain immobile in rocks that have been subjected to low-grade metamorphism and/or hydrothermal alteration (Pearce and Cann, 1973). If these elements have remained immobile during alteration, they should define a regression line that trends toward the origin in binary plot. The precursor composition of the altered rock can be determined by the intersection of the trend of the plot with the fractionation trend developed by less altered rocks of the sequence. On a TiC)2 vs. Zr plot (Fig. 7), rocks from the hangingwall and felsic dome define a normal differentiation trend of decreasing Ti02 with increasing Zr. In contrast, quartz-sericite schist samples plot along a linear trend toward the origin which is consistent with relative immobility during hydrothermal alteration. The regression line for the quartz-sericite schist intersects the felsic end of the fractionation trend indicating rhyolite/rhyodacite as the precursor rock type. Immobile element plots also provide an indication of the nature and extent of mass changes due to hydrothermal alteration. Mass loss due to solution increases the relative concentration of immobile elements, whereas mass addition, such as during silicification, has the opposite effect. Samples that have undergone mass addition will plot between the fractionation trend and the origin, whereas those with mass loss will plot above the fractionation trend. On the Ti02 vs. Zr plot, most quartz-sericite schist samples are located between the fractionation trend and the origin indicating mass dilution. Visually, it is apparent that dilution is probably related to silicification and, to a lesser extent, the addition of sulfides. Evidence of a net silica increase can be demonstrated graphically on a plot of Zr vs. Si02 (Fig. 8). For the hangingwall and felsic dome rocks a positive linear trend consistent with normal fractionation is apparent. In contrast, the trend of decreasing Zr with increasing Si02 evident for the quartz-sericite schist samples indicates dilution due to silicification. In Figure 9 it is apparent that, in addition to silicification, the quartz-sericite schist has undergone K-enrichment and Na-depletion during hydrothermal alteration. Changes in the alkali composition would have been produced during sericitization of the quartz crystal tuff precursor. Silicification must have occurred after changes in the alkali composition because sericitization produces a net quartz loss. MINERALIZATION Massive-Semimassive Sulfide Mineralization Drilling completed thus far indicates that the bulk of the deposit consists of two steeply dipping, stacked, proximal massive (50%-90%) and semimassive (30%) sulfide lenses developed at �152 16 14 12 0 10 + 8 0 z Cl, 6 4 2 0 35 40 50 45 60 55 65 70 75 SiO 2 Figure 6. Volcanics from the hangingwall and felsic dome complex classified on the basis of alkali and silica content (after Lebas et al., 1986). Symbols same as Figure 5. 1.0 0.8 Basaltic Andesite LiLI L1 0.6 0 Li I— Li 0.4 LII Li Li Li LI >EILIX Li 0.2 Li fl Li Li Rhyolite 0.0 0 50 100 150 200 Zr Figure 7. Ti02 vs. Zr plot for quartz-sericite schist, hangingwall volcanics and felsic dome complex. Hangingwall and felsic dome samples (squares) define a normal differentiation trend of decreasing Zr with increasing Ti02. In contrast, quartz-sericite schist samples (X) plot along a trend toward the origin. �153 90 I x 'XXrXD 80 70 El El El ElEl x El El 60 50 — 0 40 50 0 I I 100 150 200 Zr Figure 8. Plot of Zr vs. Si02 vs. Zr for quartz-sericite schist, hangingwall volcanics and felsic dome. Hangingwall and felsic dome samples (squares) plot along a normal differentiation trend, while for quartzsericite schist samples (X) Zr is diluted due to silicification. X 0 El / El x Hydrothermal 0 Alteration 4 X x x >:< x x X El 2 x x 1 I o 0.0 I 0.2 I 0.6 0.4 0.8 K 0/Na Q+K 0 2 2 2 Figure 9. Plot of Na2+K20 vs. K20/Na20+K20 for quartz-sericite schist, hangingwall volcanics and felsic dome. Quartz-sericite schist samples (X) and Na depleted and K enriched relative to the sodic hangingwall and felsic dome samples (squares). �154 or near the stratigraphic top of an altered quartz-crystal felsic tuff (XT) unit. True thicknesses of the lenses range from 5 to 40 feet. The lower lens is thickest near the center of the deposit but interfingers with quartz-crystal tuff (Xl') downdip and along strike; the upper lens is more continuous along dip and strike (Fig. 10 and 11). Both lenses extend to subcrop and are overlain by 100-120 feet of Chippewa end moraine. Other stratigraphically lower massive sulfide lenses are known, particularly along the eastern flank of the deposit, but have not been well defined by drilling. Each lens contains medium to very fine grained, granular (locally recrystallized), pyrite with varying amounts of interstitial chalcopyrite ± tetrahedrite-tennanite ± arsenopyrite ± bornite ± chalcocite and ± gold tellurides. Gangue minerals include quartz, carbonate (calcite), and sericite. Petrographic analysis indicates that chalcopyrite and bornite also occur as exsolutions within pyrite grains. The presence of tetrahedrite-tennanite, arsenopyrite, and gold tellurides explains the unusual geochemistry of the mineralization, which includes anomalous concentrations of arsenic, antimony, bismuth, and tellurium. Individual beds within the lenses may be fragment-bearing (altered and unaltered quartzcrystal tuft); the stratigraphically lower lens is massive or exhibits vague bedding, whereas the upper lens is generally well bedded and laminated (Fig. 12B). Sedimentary features, such as graded bedding, have been observed in drill core. The pyritic lenses are connected by a fragment-bearing semimassive sulfide zone (a debris apron) that has been overprinted by poorly developed epigenetic copper and gold stockwork-stringer mineralization (Fig. 10 and 11). The semimassive sulfide zone is characterized by a fine pyrite matrix which supports subrounded to angular, silicified quartz-sericite schist clasts that, in general, range from 2 to 10 cm in diameter. The zone thickens where the two lenses converge up dip toward the center of the relict sulfide mound. Isopach data suggests that the original mound developed within and along the flanks of a paleotopographic high formed by a thickening of the quartz-crystal tuff unit. The double plunge (east and west) of the upper massive sulfide lens may be a primary feature produced by paleotopographic control of sulfide deposition. Near the subcrop both lenses exhibit evidence of shallow oxidation and supergene enrichment. A thin ( 5') replacement zone containing secondary chalcocite and bornite after primary sulfides is known from drilling. Stockwork-stringer sulfide mineralization Stockwork-stringer mineralization consists of fine cross-cutting chalcopyrite and/or pyrite ± chalcopyrite ± gold tellurides (calaverite, petzite, and krennerite) anastomosing veinlets-veins (Fig. 12C). In addition to overprinting the semimassive sulfide zone, wispy chalcopyrite stringers locally cross-cut bedded massive sulfide (Fig. 12D). The stockwork-stringer mineralization may be accompanied by weak to strong silicification and generally weak, wispy chlorite alteration. Both lenses are enveloped by a pyritic stockwork sulfide halo ( 30% sulfides) which extends an undetermined distance along strike. The halo, which is associated with widespread pervasive sericitization, consists of pyrite disseminations, discontinuous bands or laminations and veinlets that are cross-cutting and parallel to foliation and bedding. Stockwork-stringer mineralization developed stratigraphically below the major lenses grades both vertically and laterally into the halo. �a C • 0 / . a* 0 • 200 C 0 I 1 • • 0 • FEET C C 0• • 3 200 o * 0 . C C C CL A C . L • o C — C. V0 - . a C . 0 Figure 10. Geologic cross-section 49505E. 0 . . 0 0 a. .__, C C 0 ° C: ,..::. . •. —'.--- a • GT GT SAPR0LTE XT LOOKING WEST �________ . °•c •0 LOOKING WEST C .0 0. o .Q .0 o '. •.•• .,.,,• . •o .•0. .00 •0 '. . .c' •.'• Q0 • •C pD0 ,o Q• . Q. , .0 GLACIAL -. I VD L GT 4 20 GT JO Fig. H �157 Copper-Gold Distribution The deposit, classified as copper-type VMS mineralization (DeMatties 1994), contains only minor amounts of zinc and, therefore, has not developed any zonation of base metals. However, the deposit does exhibit distinct copper-gold zoning patterns, i.e. development of copper-rich massive sulfide lenses accompanied by several prominent parallel gold zones. In the massive sulfide mineralization hypogene copper grades exhibit a significant increase stratigraphically upward from the lower to upper lens. The well-bedded stratigraphically upper lens contains the highest copper grades in the deposit. This copper distribution may have resulted from hypogene enrichment by stratigraphically upward migration or "refining" during multiple copper-gold hydrothermal pulses within the developing sulfide mound. The highest gold values in the system occur stratigraphically below each lens as semiconformable ore-grade ( 0.1 opt) gold assay zones (designated as the "tuckunder" and lower gold zones). These zones, which developed in the enveloping stockwork-sulfide halo, appear to be stratigraphically controlled and have continuity along strike and down dip. Locally, structures cross-cutting the halo host auriferous quartz-carbonate veins containing gold-silver tellurides that assay in the multiple ounce-per-ton range. The frequency of cross-cutting gold-silver mineralized structures is unknown at this time. Widespread gold values 0.01 opt have been found throughout the stockwork sulfide halo. Higher values can form poorly developed stratiform assay zones of limited down dip or lateral extent. POTENTIAL ORE RESERVES A potential copper ore reserve (copper zone) is contained in the two stacked lenses, semimassve sulfide zone, and associated stringer mineralization. The zone contains accessory amounts of gold and silver reported as gold and silver telluride minerals. Where the lenses coalesce, the copper zone may total 70 feet in thickness. Overall dimensions of the zone include a strike length ranging from 1100 feet at the subcrop to 1800 feet at depth and a thickness which varies from 10 to 70 feet; it has been tested to a depth of 2000 feet. A 1994 estimate calculated a drill indicated resource of 3.3 million tons grading 2.05% copper, 0.07 opt gold and 0.41 opt silver (estimate includes "tuckunder" gold zone). A high-grade core in the center of the copper zone contains 1.42 million tons grading 3.11% copper, 0.07 opt gold and 0.41 opt silver. The copper zone remains open down dip and down plunge to the west; it appears to terminate against the domal complex along its eastern margin. In addition to the copper zone, ore potential exists in the adjoining lower gold assay zone, which is characterized by pyritic gold mineralization with minor copper and silver values. Though poorly defined, it is estimated (1994) to contain a resource of 602,850 tons grading 0.885% copper, 0.21 opt gold, and 0.26 opt silver. The zone remains open in all directions. EXPLORATION POTENTIAL In addition to expanding the identified resource down dip and down plunge, there is good potential for discovery of additional VMS deposits along strike to the east where the ore-equivalent horizon has been located. The horizon is represented by a section of laminated to thin bedded hematitic cherty tuffs (tetsusekiei), meta-argillites (commonly graphitic or sulfide-bearing) and �Figure 12 Polished drill core samples from the Bend deposit. 158 A B Altered felsic quartz-crystal metatuff (quartzsericite schist) host rock, productive XT unit. Note flattened and elongated blue (dark gray in photo quartz eyes which characterize this unit. A. Bedded and laminated massive sulfide from the upper lens of the copper zone. Relict bedding features are well preserved. Large host host rock fragment (quartz-sericite schist) is draped by bedding. Darker laminae are B. tetrahedrite-tennantite. C C. Pyritic stringer mineralization cross cutting quartz-crystal tuff. D D. Fine chalcopyrite stringer mineralization (light gray) overprinting massive pyritic sulfide, copper zone. F E E. Laminated cherty hematitic metatuff (tetsusekiei) that stratigraphically overlies the deposit along its eastern flank. The light laminae are the tuffaceous (sericite-rich) component whereas the darker laminae represent the exhalative (quartz-hematite) component. F. Mineralized argillite. Note fine discontinuous pyrite-chalcopyrite laminations (light gray). 0 1 2 3inches �159 copper-bearing massive sulfide beds (Figs. 12E and 12F). Although the horizon is interrupted by the felsic dome, geophysical surveys suggest it reappears again on the northeastern margin of the complex and extends along strike for nearly 5000 feet. Several isolated electromagnetic anomalies have been identified along the trend of the horizon. These targets remain untested. Acknowledgments The author would like to acknowledge Sharpe Energy and Resources for permission to release these data. Also thanks are extended to Mark Burdick who prepared the illustrations. References Cited DeMatties, T. A., 1994, Early Proterozoic massive sulfide deposits in Wisconsin: an overview: Economic Geology, v.89, p. 1122-1151. LeBas, M. J., LeMaitre, R. W., Streckeisen, A., and Zanettin, B., 1986, A Chemical Classification of Volcanic Rocks Based on Total Alkali Silica Diagram: Journal of Petrology, v. 27, p. 745750. Pearce, J. A. and Cann, J. R., 1973, Tectonic Setting of Basic Volcanic Rocks Determined Using Trace Element Analyses: Earth and Planetary Science Letters, v. 1, p. 290-300. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectonic-stratigraphic evolution of the early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen: Canadian Journal of Earth Sciences, v.26. p 2145-2158. �160 �161 GEOLOGY OF THE LYNNE BASE-METAL DEPOSIT, NORTH-CENTRAL WISCONSIN, U.S.A. by Glen W. Adams Geological Consultant Rhinelander, Wisconsin ABSTRACT The Lynne polymetallic deposit was discovered in early 1990 by Noranda Exploration Inc., in north-central Wisconsin, U.S.A. The deposit is the most recent base-metal discovery in the Early Proterozoic, Rhinelander-Ladysmith greenstone belt and has a reported open-pit reserve of 5.61 million tons grading 9.27% Zn, 0.47% Cu, 1.71% Pb, 2.38 opt Ag, and 0.021 opt Au. Mine permitting procedures have been suspended and the future of the deposit is uncertain. The Lynne deposit consists of four stacked, strataform massive to semi-massive sphalerite-rich bodies hosted within a predominantly felsic sequence of subaqueous volcanic and volcaniclastic rocks, volcanic—derived wackes and tuffs, and chemical sediments. Unusually abundant amounts of carbonate rocks are directly associated with the sulfide ore. The Lynne stratigraphy is underlain by an intrusive tonalite body that locally disrupts and intrudes the lowest sulfide unit. No definitive stringer zone or alteration pipe has been identified; however, a broad alteration assemblage, similar to other volcanogenic massive sulfide deposits, envelopes the immediate host rocks. Skarn-style mineralization is associated with carbonate rocks along the flanks of the sulfide bodies. Metal zoning compatible with volcanogenic massive sulfide deposits is present. Although the Lynne deposit has characteristics of both volcanogenic massive sulfide and skarn-type deposits, a volcanogenic model is preferred. INTRODUCTION The Lynne polymetallic deposit is located in Lynne Township approximately 25 miles west-northwest of Rhinelander in north-central Wisconsin (Figure 1). The deposit site is approximately nine miles north of State Highway 8 and the small town of Tripoli. All-weather paved and gravel roads access the project area and the Wisconsin Central Railway has a siding at Tripoli. The Lynne deposit occurs on Oneida County surface and mineral lands that are under lease to Noranda Minerals Wisconsin Corp. (Figure 2). Subsequent to the discovery of the deposit in January, 1990, 138 drill holes were drilled to delineate the Lynne massive sulfide body and conduct stratigraphic tests in the immediate deposit area. In January, 1992, a Notice of Intent To Collect Data and Proposed Scope of Study was filed with the Wisconsin DNR as Noranda's initial step in the involved Wisconsin mine permitting process. The deposit is intimately associated with an area of wetlands that would be disturbed by mining. On October 23, 1993, Noranda suspended all permitting activity, citing uncertainties surrounding DNR wetlands and lake-bed designation issues and metal prices. All surface disturbances related to the exploration and initial permitting procedures were reclaimed as of January, 1996 and the future of the deposit is uncertain. All Noranda's county mineral leases on the Lynne deposit remain in good standing. �1Lake, \) 5TL 0 7VQ ,c ';( c__in \O , Lke-' UPineL I S I( Fk!( L 1u e 3 ? N2 - !ueL } I Tomahè4k 4H A( 3%/cs Jkainao \C!ear ( Flo ' Sa tI -. _- -J t- kó z.L1I 2("— 1r\ I c o pA fn -i -Wi3jw - .iThree-*zaes Sugar Camp ethurst \'J Bear LateU ch / stL I F!owa -McNau t n —f —--Ste//a L -.' \, s8\.\ Jf,' (1 9( __c NE cagen RhineIander'7 L Scale \\ \r onico •I5fl, ci 10 miles 10 3Ci -- 'r-2 Jennhigs0 15 kilometers /A /T WISCONSIN Piaure 1 Location Map Lynne Base—Metal Deposit Oneida County, Wisconsin �_____ i: ,/ ti 0 2000 0 60 4000 feet Private land Private land purchased by Noranda Figure 2 Noranda Mineral Lands Lynne Base-Metal Deposit Oneida County, Wisconsin 1200 meters �164 REGIONAL GEOLOGY The Lynne deposit is located in the central part of the Rhinelander-Ladysmith greenstone belt, a belt of Proterozoic, volcanic and sedimentary rocks within the Southern Province of the Canadian Shield. The Rhinelander-Ladysmith greenstone belt (Figure 3), is the informal designation for the northern part of the Pembine-Wausau terrane of Sims et a!. (1989). It is approximately 50 miles wide and extends roughly 150 miles in an east-west direction across northern Wisconsin and the central Upper Peninsula of Michigan. Rocks within the greenstone belt range in age from 1,860 Ma to 1,889 Ma (Sims eta!., 1989), and have been affected by the Penokeon Orogeny, resulting in locally intense folding, major faulting, thermal metamorphism, and granitic plutonism. Widespread Pleistocene glacial deposits mantle much of the greenstone terrane resulting in minimal outcrop exposure. On the west the greenstone belt is overlain by Late Proterozoic quartzite and Paleozoic sandstones, while on the east there is an onlap of Early Paleozoic sandstone and carbonate rocks. Indepth reviews .f the Rhinelander-Ladysmith Greenstone belt are presented in this volume by DeMatties and by LaBerge. Mineral exploration over the past 30 years, dominated by airborne geophysical surveys, has identified over two dozen significant base-metal massive sulfide occurrences scattered throughout the Rhinelander-Ladysmith greenstone belt (Figure 4). The Flambeau mine, currently in production, and three other potentially economic occurrences, the Crandon, Bend, and Lynne deposits, all occur within the Rhinelander-Ladysmith greenstone belt. Geologic knowledge of the Lynne deposit area is very limited due to poor outcrop exposure. Regional airborne E.M. and magnetic data and scattered drill hole information suggest that the general geology of the Lynne area consists predominantly of mafic to intermediate volcanic rocks with at least one felsic eruptive and intrusive event, represented by the lithologies in the immediate Lynne deposit area. The felsic volcanic-related rocks associated with the Lynne deposit predominate over mafic to intermediate rocks by a significant amount. The increase of felsic volcanic rocks in the Lynne deposit area is common to other significant base-metal occurrences in northern Wisconsin and elsewhere (DeMatties, 1994). LYNNE DEPOSIT DISCOVERY HISTORY The Lynne deposit is the most recent major base-metal discovery in Wisconsin. However, at least two exploration companies were aware of the Lynne airborne E.M. anomalies up to 14 years before its discovery. Exxon Minerals identified isolated anomalies over what is now the Lynne deposit from an airborne E.M. survey flown in the mid 1970's. Because the mineral rights covering the anomalies were owned by Oneida County, and unattainable at that time, no serious interest was given to the target. Kerr McGee conducted an airborne E.M. survey over the area in the early to mid-1980's following up on anomalous lake sediment samples taken about two miles southeast of the deposit. They too had detected the Lynne E.M. response; however, Oneida County lands were still not available for mineral leasing. Not until Oneida County made their mineral lands available for lease through competitive sealed bid in 1989, did the lands hosting the Lynne deposit become attainable. Unfortunately, by this time neither Exxon Minerals nor Kerr McGee were still actively exploring in Wisconsin. Noranda Exploration remained active in the state on the belief that Wisconsin's greenstone belts hosted additional base-metal deposits. Noranda's staff was experienced in Wisconsin exploration and knew of the Lynne airborne E.M. anomalies. Noranda's perseverance paid off when, in May �Figure r 3 Schematic Geology Rhinelander-Ladysmith Greenstone Be North—Central Wisco Paleozojc sediments Flamb — a foIith :__I::!-: - A • Massive sulfide occurrence __:: 50 miles Scale �4 I 0 20 Scale p 40 60 miles Massive Sulfide Occurrences North-Central Wisconsin Figure N A �167 1989, they were the successful bidder on four sections of Oneida County mineral lands in Lynne Township. Initial ground geophysical surveys conducted by contractor Rodney Ikola and Associates, and later by Noranda staff, revealed a moderate to strong E.M. anomaly with an associated strong out-ofphase E.M. component (Figure 5), which was initially attributed to an overburden response. Gravity data indicated a relatively low, but anomalous, gravity response of about 0.8 milligals. On January 6, 1990, after two failed attempts to penetrate 56 feet of glacial overburden, the Lynne massive sulfide deposit was intersected in the first of two initial drill holes (Adams, 1990). Discovery hole W90-1 intersected 128 feet of zinc-rich massive sulfides followed by a second hole, drilled 150 feet to the north of the first hole, which stayed in relatively massive sulfides for over 375 feet (Fable 1). It was now understood that the large out-of-phase E.M. response was caused by widespread, relatively poorly conductive, massive sphalerite mineralization. The massive orebody corresponds with the main strong in-phase E.M. anomaly of Figure 5. The narrow in-phase E.M. anomaly southeast of the orebody is not related to sulfide mineralization. On June 19, 1990, Noranda publicly announced the discovery of the Lynne deposit. After 18 years of exploration, the drilling of several promising massive sulfide occurrences, and the expenditure of several millions of dollars in Wisconsin, Noranda appeared to have a massive sulfide deposit with commercial potential. Reported reserves of 5.61 million tons grading 9.27% Zn, 0.47% Cu, 1.71% Pb, 2.38 opt Ag, and 0.021 opt Au (American Mines Handbook, 1995), are considered recoverable by open pit methods. In 1990, Noranda flew a detailed airborne E.M. survey over the Lynne deposit and surrounding region defining additional attractive targets. To date no other discoveries have been made, although the exploration potential is favorable. In early 1993, Noranda Exploration Inc. closed its Wisconsin exploration office sighting a general unfavorable mineral exploration and development climate in the state. GEOLOGY AND MORPHOLOGY OF THE LYNNE DEPOSIT The area hosting the Lynne deposit is covered by 40 to 75 feet of unconsolidated glacial till. Lithologies, alteration and structure of the orebody and its host rocks are derived from drill hole information and detailed ground and airborne geophysical data. The only known outcrop within several miles of the deposit is an area of moderately foliated granitic rock occurring in, and adjacent to, the Willow River about 4000 feet northeast of the orebody. There is evidence of an oxidized cap on the ore deposit. The Lynne ore body consists of four strataform, massive to semi-massive, stacked, polymetalhic, sulfide bodies with an aggregate thickness of approximately 325 feet in the central part of the ore zone. The sulfide bodies exhibit abrupt thickening and coalescing in the core of the ore zone with ore dissipating relatively quickly on the flanks. Sphalerite is the predominant sulfide mineral followed in abundance by pyrrhotite, pyrite, galena, and chalcopyrite. Gold occurs in the lower sulfide body and in association with skarn mineralization on the flanks of the deposit along with magnetite. Silver mineralization occurs in the central to upper part of the ore body. Metal zoning occurs as a relative enrichment of copper toward the base of individual sulfide units. Metal zoning also occurs as a progression of relative copper and iron enrichment toward the base of the composite sulfide deposit, grading upward into strong zinc mineralization followed by concentrations of lead and silver in the upper parts of the ore zone. The sulfide-bearing zone has a strike length of approximately 1300 feet and both the ore deposit and its host rocks strike in a general east-southeast �168 Table 1 Assay Results From Drill Holes W90-l & W90-2 Lynne Base-Metal Deposit Oneida County, Wisconsin Composite Zones from Drill Hole W90-1 From (Ft) To (Ft) Width (Ft) Zn Cu % Pb Ag Au % % opt opt 135.50 150.70 15.20 34.78 0.38 3.64 0.608 0.010 150.70 168.20 17.50 5.02 0.83 0.36 0.293 0.012 168.20 197.20 29.00 34.44 0.88 3.13 1.104 0.006 205.40 263.50 58.10 22.17 0.58 3.83 1.435 0.014 135.50 263.50 128.00 22.71 0.64 2.95 1.039 0.011 Ag opt Au opt Composite Zones from Drill Hole W90-2 To (Ft) Width (Ft) Zn Cu % % Pb % 55.00 66.60 11.60 18.59 0.05 8.47 8.558 0.016 102.60 242.30 139.70 6.41 0.17 2.82 10.746 0.014 250.90 320.60 69.70 21.64 0.54 2.82 1.257 0.012 320.60 350.20 29.60 2.79 0.12 0.77 0.901 0.012 372.20 405.50 33.30 4.71 0.16 0.29 0.498 0.009 405.50 439.00 33.50 11.20 0.74 0.76 0.844 0.018 55.00 439.00 384.00 8.45 0.26 2.09 4.736 0.012 From (Ft) �Max-Mm 0 S 5 0 0 EXPLANATION 100 1.00 Sc 01. 800 eel I 200 meters Out a) Phase In Phase {HLEM response widths) HLEM Ground Geophysical Data Lynne Base-Metal Deposit Oneida County, Wisconsin Figure t5 N ( �170 direction dipping northeasterly at about 40 degrees. Graded beds within the host rocks indicate that the stratigraphy is upright with tops to the northeast. The zinc-rich sulfide bodies lie within a subaqueous, volcaniclastic, sedimentary and carbonate-rich sequence of rocks. Drill hole data from host rocks indicate a general coarsening of pyroclastic material to the north, or down-dip, suggesting a more proximal location to a possible volcanic eruptive source in that direction. The lowest sulfide-rich horizon of the deposit is underlain, and locally disrupted and cut off, by an intrusive tonalite body. The deposit and its host rocks show no major structural complexities. East to southeast striking, vertical to sub-vertical, fracture zones exhibit minor movement in stratigraphy within and down-dip from the ore zones, and according to Kennedy (1992), postdate the tonalite. The fracture zones are commonly filled with rhyodacite dikes and less often with basaltic dikes. A shallow depression or trough occurs in the upper surface of the tonal ite beneath the thickest, central part of the ore deposit. There has been some speculation that the fracture zones may have some relationship to this trough-like feature, and that the fracture zones, and possibly the depression in the tonalite, are genetically related to the deposition of sulfide mineralization (Adams, 1991). Both structural features may represent remnants of a down-dropped, or graben-like, feature that helped to localize ore deposition. The entire lithologic package, although variably altered and locally affected by contact metamorphism and skarnification, is metamorphosed to greensehist metamorphic rank. Evidence of retrograde alteration of higher temperature minerals to lower temperature minerals is widespread. Chlorite and talc-bearing alteration assemblages occur in the lower parts of the Lynne stratigraphy; however, no distinct stringer zone or alteration pipe is evident. A pervasive alteration assemblage does occur in the enveloping host rocks. Because of the unusual combination of base-metal and alteration assemblages, and the host rock lithologies, the Lynne deposit exhibits characteristics common to both volcanogenic massive sulfide and carbonate-related skarn, deposits. Sulfide Mineralization The massive and semi-massive strataform lenses of the Lynne ore deposit are divided into four separate zones or units based on physical, or discrete compositional, differences (Adams, 1990; Adams, 1991). The sulfide lenses are designated as units A through D with A being the lower-most, and progressing stratigraphically upward to units B, C, and D (Figures 6 and 7). Unit A Sulfide Unit A exhibits the greatest lateral extent of all the zones and reaches up to 60 feet in thickness, although it is locally disrupted and intruded by the foot-wall tonalite. The zone is a pyritic, massive sphalerite body enriched in chalcopyrite and pyrrhotite relative to the other zones. Over 50 percent of the copper and over 30 percent of the gold content of the ore deposit occurs in cherty, chloritic, pyrrhotitic massive to semi-massive sulfide portions of this unit (Kennedy, 1992). Partially enveloping the unit is a talc-rich assemblage containing disseminated to massive sulfides with Mgchlorite, phiogopite and lesser tourmaline, serpentine, cummingtonite, and galena (Kennedy et a!., 1991). Also present locally within the alteration envelope is stringer-like and disseminated sphalerite and pyrrhotite. An extensive barren zone of this alteration assemblage, with laminated cherts containing disseminated pyrrhotite, pyrite and minor magnetite lanünae, continues up to 300 feet along strike and down-dip from Unit A. �6 Sulfide Units (Section 10,000 E.) Lynne Base-Metal Deposit Oneida County, Wisconsin Figure Looking West �7 Composite Assay Results from Sulfide Unit (Section 10,000 E.) Lynne Base—Metal Deposit Oneida County, Wisconsin Ficrure Looking West )16 088 �— 173 Unit B Narrow intervals of carbonate rock, with local skarn-type mineralization, separate units B and A. Sulfide mineralization in Unit B differs strongly from Unit A in that it occurs in association with lenticular masses of chemical sedimentary rocks including calcareous and siliceous fades. Disseminated sphalerite and pyrite is ubiquitous to the carbonate host rocks, and massive to semimassive sphalerite, with lesser galena and subordinate chalcopyrite, forms lenses up to 50 feet thick. The composite thickness of Unit B reaches approximately 150 feet in the central part of the ore body. Unit B contains over 50 percent of the total deposit tonnage and almost 60 percent of the total zinc content of the deposit (Kennedy, 1992). Thin beds of carbonate-rich volcaniclastic and sedimentary rocks within the unit are pervasively replaced by caic-silicate minerals. Sphalerite, and to a lesser extent pyrrhotite and pyrite, are disseminated throughout the carbonate host rocks. The carbonate rocks are relatively planar bedded near the base of the unit becoming increasingly disrupted toward the top. Carbonate beds tend to be finer grained and well bedded off the flanks of Unit B. Unit C Narrow beds of barren volcaniclastic wackes or tuffs and a rhyolitic sill separate units B and C. Unit C is approximately 160 feet thick and consists predominantly of contorted, folded, or disrupted calcareous chemical sediments that can be divided into two zones. The lower calcareous zone is about 50 feet thick and consists of marble with massive to semi-massive sphalerite and galena. The upper 110 feet of the unit is calcareous, but within the upper 50 feet it becomes extremely siliceous containing cherty layers and diopside-rich cherts. Sulfide mineralization in the upper part of Unit C consists of disseminated to semi-massive sphalerite, pyrite and galena. A large proportion of the deposit's silver content occurs in the upper siliceous part of Unit C in the form of native silver, tetrahedrite, and argentiferous galena. Here, silver content averages over 100 ounces per ton for several tens of feet. As with Unit B, this unit shows a relative abundance of chalcopyrite toward the base of the sulfide assemblages. An envelope of diopside-garnet-pyrrhotite-magnetite skarn mineralization occurs on the south side of the lower part of Unit C and on the upper part of Unit C in association with rhyolite sills (Kennedy, 1992). Unit D Unit D, the uppermost sulfide unit, is a massive to semi-massive zone of sphalerite with accessory galena and appreciable chalcopyrite in siliceous, cherty, chemical sediments. This unit is truncated by the bedrock surface and grades rapidly down-dip into barren volcaniclastic sediments. The unit is separated from the underlying unit C by a 50-foot thick, rhyolitic sill. Host Rocks The rocks hosting the Lynne deposit (Figure 8), have had little in-depth investigation with the exception of work done by Kennedy (1992), who, in conjunction with Noranda's predevelopment staff, studied the immediate host-rocks and their alteration assemblages as part of the deposit delineation drilling program. Much of the following information on the host rocks is drawn heavily from Kennedy (1992), and the findings of the predevelopment staff. Kennedy (1992) has divided the Lynne deposit host rocks into five units consisting of, in ascending order, the Lower Rhyolite, the ore-bearing Lynne Horizon, the Upper Rhyolite, the Upper YCS and the Hanging Wall Unit. Subsequent to the deposition of this felsic volcanic-rich sequence, the rocks were intruded by a probable subvolcanic tonalite body that partially ingested and disrupted the lower surface of sulfide Unit A. �174 Lower Rhyolite The Lower Rhyolite consists of massive to poorly sorted, rhyolitic lapilli to ash tuff containing abundant pumice fragments and locally poorly graded beds of fine ash tuff. Dark green to black chioritic material is common as veinlets and irregular masses. Kennedy (1992) interprets this lithologic package as a sequence of subaqueous debris flows. Angular and shattered coarser felsic lapihi fragments suggest possible local autobrecciation of rhyolitic flow rocks. The Lower Rhyolite interfingers with the stratigraphicahly higher Lynne Horizon north of the orebody but is absent from the immediate vicinity of the orebody either due to non-deposition or incorporation into the intruding tonalite. Rhyolitic tuffs with distinctive angular lapilli clasts occur north of the orebody and approximately one mile south of the orebody, suggesting that this unit may be relatively widespread. Lvnne Horizon The Lynne Horizon hosts the Lynne ore deposit and consists of a sequence of predominantly volcaniclastic, detrital, and chemical sedimentary rocks with lesser interlayered intermediate to felsic volcanic flow rocks and minor rhyohitic crystal tuffs. The horizon is up to 320 feet thick and extends over one-half mile east of the ore deposit. The volcaniclastic rocks consist of greywackes and laminated siltstones of volcaniclastic or reworked volcanic material interbedded with and grading into crystal to crystal-hithic tuffs. Carbonate-rich sediments, characteristic to this horizon, and lesser laminated cherts occur over 1300 feet away from the orebody and increase in abundance and thickness toward the orebody where they exceed 200 feet thick in the center of the ore deposit (Kennedy, 1992). The bulk of the carbonate rocks are directly associated with the massive to disseminated parts of the sulfide ore zones where they are partially or mostly replaced by sulfide minerals. Some partial replacement continues for a considerable distance away from the main orebody to the north and east where it is often associated with an envelope of potassic and magnesium alteration. On the flanks of the Lynne Horizon the carbonates are often well bedded, while less sulfide-rich carbonate zones within and between the main ore zones are commonly laminated though often disrupted and contorted. The carbonate rocks form sharp contacts with overlying volcaniclastic horizons. Descriptions by Kennedy et al. (1991), Kennedy (1992), and Kennedy and Donnelly (1992), suggest that the carbonate assemblages at Lynne show considerable compositional variations. Dolomitic rocks are the most abundant, and directly associated with base-metal mineralization, while limestones are associated with barren or poorly developed sulfide mineralization on the eastern and western flanks of the deposit. The tendency of more Mg-carbonate toward the central part of the orebody, combined with Mg-silicate alteration assemblages in the immediate host rocks, could denote Mg-metasomatism related to carbonate build-up and ore formation. Since the initial drill holes into the ore body, it has been speculated that the buildup of carbonate material is directly associated with ore deposition (Adams, 1990). The carbonate rocks are relatively restricted to a north-northeasttrending basinal feature (Kennedy, 1992), which coincides with the thickest part of the sulfide ore body, suggesting a direct relationship between the ore body and a carbonate build-up. Upper Rhyolite The Upper Rhyolite unit consists of rhyolite crystal and crystal lithic, lapilhi tuffs and massive rhyohite with minor interlayers of dacite and andesite, and thin basal horizons of greywacke and chert. The unit is over 300 feet thick north of the orebody and thins southward where it becomes interlayered with the ore stratigraphy. Rhyohitic sills that intrude the ore body are similar to massive rhyolites in the Upper Rhyolite. Epidote-rich skarn is associated with some of the rhyolitic sills on �175 the west edge of the ore body, suggesting a possible correlation between the intrusion of narrow rhyolite sills of the Upper Rhyolite and the formation of skarn mineralization. The Upper VCS Unit The Upper VCS Unit consists of volcanic-derived greywacke and laminated siltstone with increasing amounts of andesite as the horizon is traced northward. The updip southerly projection of the horizon is represented by the narrow, upper-most, silicious sulfide Unit D. In the immediate vicinity of the orebody, the Upper VCS Unit is less than 100 feet thick but thickens to over 200 feet to the north and west. Iron sulfides commonly occur in this unit as fracture fillings within 100 feet of the orebody, and form sulfide-rich laminae associated with magnetite in siltstones. Chlorite, epidote and minor actinolite alteration minerals are common. Hanging Wall Unit The Hanging Wall Unit is a mixture of felsic to mafic tuffs, heterolithic wackes and agglomerates, or conglomerates. Characteristic to this unit are clast-supported agglomerates containing beige to pink lapilli-sized rhyolitic clasts. The wackes contain lapilli-sized rhyolitic to andesitic clasts and plagioclase and quartz crystals in a mafic groundmass. Interpretations by the Noranda pre-development team suggest that the unit may be a series of debris flows that appear to dissipate to the north and are therefore derived from a southerly source area. Tonalite The tonalite underlies the Lynne ore and host-rock stratigraphy. It has an irregular upper contact that dips at a shallow angle to the northeast. The tonalite intrudes and disrupts the lower part of sulfide Unit A, displacing and enclosing parts of the unit. Flexures in the overlying stratigraphy appear to be associated with a northeast-striking trough in the tonalite surface. The intrusive is often porphyritic with quartz ovoids and euhedral, zoned plagioclase crystals in a fine-grained, commonly graphic, matrix (Kennedy and Donnelly, 1992). Within 50 feet of the contact, the tonalite is characterized by a granophyric texture. Low temperature alteration is common in the tonalite, but is strongest in association with local fracturing or faulting. Within 35 feet of the tonalite, local recrystallization of adjacent volcanic and volcaniclastic rocks occurs and a hornfels texture is sometimes present (Kennedy and Donnelly, 1992). The magnetic response associated with the known area of tonal ite grades into a relatively constant regional magnetic low south of the deposit that is interpreted as a large granitic body. Alteration There does not appear to be a distinct alteration pipe, or stringer zone, beneath or adjacent to the Lynne deposit as is common to other volcanogenic massive sulfide deposits (Franklin et a!., 1975; Franklin et a!. 1981). It is possible that the subvolcanic tonalite body has engulfed and destroyed any pre-existing alteration stringer zone. There is, however, an alteration mineral assemblage associated with the lower Lynne ore stratigraphy and the stratigraphically higher encompassing host rocks. Talc-rich zones up to 25 feet thick occur beneath and grade into the lower massive sulfide Unit A, and talc-rich zones up to 15 feet thick separate zinc-rich ore from skarn and marble units along the northern flank of the orebody (Kennedy, 1992). Local stringer-like veins and disseminations of sphalerite and pyrrhotite occur within Mg-chlorite and muscovite-rich talcose rocks associated with the lower parts of sulfide Unit A (Adams, 1990; Kennedy, 1992). Observations by the Noranda predevelopment team (personal communication), reveal a Mg- and K-rich secondary mineral assemblage extending laterally up to 1300 feet down-dip, and over 2000 feet east, in the footwall rocks of the orebody, and within several hundred feet of the orebody, feldspar in tuffs of the �176 Upper Rhyolite and the Upper VCS Unit are altered to muscovite and chlorite. These criteria support a broad alteration assemblage similar to semiconformable alteration zones found in conjunction with several world-wide volcanogenic massive sulfide occurrences described by Franldin et al. (1981). Tonalite in contact with the orebody, on the other hand, appears to be little altered, suggesting a postalteration intrusive event. Skarn Mineralization The abundant caic-silicate mineral assemblage associated with the Lynne deposit is uncommon to volcanic-related massive sulfide deposits. It is apparent that the skarn-style of mineralization is directly related to the anomalous amount of carbonate rock associated with the orebody. The most intensive skarn mineralization is associated with the extensive replacement of carbonate along the updip flanks or projected edges of the orebody (Figure 8). Here pyrrhotite and magnetite are also locally abundant, especially along the southern edges of the orebody. Quartz-diopside skarn assemblages are characteristic of the upper parts of the deposit and epidote skarn occurs in conjunction with intrusive rhyolitic sills within the orebody (Kennedy, 1992). Skarn mineralization is seldom associated with base-metal ore, but the highest ore-grade gold concentrations have a direct skarn relationship (Adams, 1991; Kennedy, 1992). No other known massive sulfide occurrence in the Rhinelander-Ladysmith greenstone belt is associated with such abundant carbonate material. DeMatties (1990) describes possible carbonate-rich exhalites at the Ritchie Creek occurrence, and significant dolomitic units make up part of the Crandon deposit stratigraphy (Lambe and Rowe, 1987). Franklin et a!. (1975) refer to a dolomitic host rock package for the Mattabi deposit in the Sturgeon Lake camp of northwestern Ontario. The significant skarn assemblage associated with the Lynne deposit makes this one of the most unique base-metal deposits of the Rhinelander-Ladysmith greenstone belt. Proposed Genetic Model for the Lynne Deposit Although the Lynne deposit has characteristics of both volcanogenic massive sulfide and skarn-related deposits, it is believed that the supporting evidence is sufficient to suggest a volcanogenic origin for deposit. A sulfide depositional scenario is proposed whereby a graben-like depression, perhaps developed in conjunction with a caldera collapse feature, forms on the flank of a felsic volcanic complex centered to the northeast of the present-day Lynne deposit. The association of the near-vertical fracture zones in the Lynne stratigraphy, and the trough-like depression in the tonalite surface, with the rapid thickening of the core of the ore deposit, may represent remnant features of the postulated graben. Within the confines of the down-dropped block of felsic volcanic rocks, and using bounding growth faults as conduits, volcanic vents may have began an effusive build-up of carbonate-rich chemical sediments. Either syndepositionally, or closely following the carbonate build-up, solutions rich in zinc, with subordinate lead, silver, copper and gold, replaced much of the central portion of the carbonate mound. At least four episodes of metal infusion prevailed over the deposition of volcaniclastic and chemical sedimentary material within the graben complex. As the sulfide deposition evolved, the relatively abundant copper and iron dropped out of solution, both at the onset of each sulfide event, and throughout the entire sulfide depositional period, and was supplanted by zinc with progressively increasing amounts of lead and then silver. Coincident with the evolution of metal-bearing solutions was the progression from carbonate-rich toward silicarich chemical sedimentary facies. The confines of the proposed graben feature may account for the stacked layering of chemical sedimentation and sulfide deposition. �j • 0 • t + co — carbonate oh — chert. (Qz) Gt Massive Po, Mt + T 0. 509 0' + Tonal t e Semi—massive to Massive Sulfide Disseminated sulfide + + 0 — talcose sk — Tr, Di, + + 10 304 0 Talc BPM 0 9''0BpMo •O•O•O•O•Q/.O 0 O0Q 1.0. IR1 (After Kennedy, 1992) Rhyolite 794 0 1.0. Tonal ite Marble Ml 666.0' + 553.0' 1.0. + Chert Volcaniclastic unit Gt+Di ± Tr Skarn + Looking West CH ___ Figure 8 ft. Host Rock Geology (Section 10,000 E.) Lynne Base—Metal Deposit Oneida County, Wisconsin MS 100 Scale _1lp 0 .i!O _L0° �178 Associated with a resurgence of volcanic activity, the sulfide-bearing stratigraphy was covered with a sequence of felsic to intermediate, volcanic flow, pyroclastic, and epiclastic rocks, and intruded by rhyolitic sills. At the same relative time, or subsequent to this point in the volcanic history of the area, a subvolcanic, tonalitic mass intruded the base of the graben feature and its metalrich sequence of volcanics and chemical sediments. During its intrusion, the tonalite could have engulfed an alteration pipe associated with the graben-bounding fracture system leaving only the more widespread wallrock alteration assemblage. Associated either with the intrusion of the tonalite, the intrusion of higher level rhyolitic sills, or a combination of both, a skarn-style alteration assemblage developed in the flanks of the carbonate mound in which sulfide mineralization was less pronounced. Pyrrhotite, magnetite and gold mineralization was produced or remobilized in association with this event. Later movement reactivated the bounding faults and subsequent bimodal intrusive activity filled some of the fault zones with dikes. It is of course unknown if additional massive sulfide bodies were deposited in this graben feature prior to, or following, the formation of the current Lynne sulfide units, their possible existence being either destroyed by the intruding tonalite or erosion. Since the geological environment favored the deposition of the Lynne deposit, it is likely, as substantiated by base-metal camps throughout the world, that additional massive sulfide deposits formed in conjunction with the Lynne felsic build-up of the prolific Rhinelander-Ladysmith greenstone belt. Summary The Lynne base-metal deposit consists of a series of four strataform, massive to semi-massive, sphalerite-rich sulfide bodies containing accessory galena, silver, copper, and gold. The deposit is hosted by a dominantly felsic volcaniclastic and sedimentary sequence of rocks with a significant amount of carbonate-rich chemical sediments. The immediate ore-bearing stratigraphy is overlain by felsic to intermediate volcanic flow, pyroclastic, and epiclastic rocks. An intrusive tonalite underlies the Lynne stratigraphy disrupting and intruding the lower-most sulfide unit. No definitive alteration or feeder pipe is evident; however, an alteration assemblage common to volcanogenic massive sulfide deposits world-wide, is present in the deposit's immediate host rocks. Metal zoning is suggested by relative copper enrichment toward the base of individual sulfide units. Deposit-wide metal zoning occurs as a relative enrichment in copper and iron in the lower sulfide units, an upward increase in zinc, and the development of galena concentrations and strong silver enrichment in the upper parts of the deposit. There is a corresponding evolution from carbonate-rich rocks lower in the sequence to more siliceous chemical sediments higher in the host rock stratigraphy. Skarn-type mineralization is characteristic to the carbonate-rich host rocks, especially along the up-dip flanks of the deposit and locally associated with intrusive rhyolitic sills. The highest concentrations of gold, and an increase in pyrrhotite and magnetite mineralization, are associated with the skarn-type assemblage. Characteristics common to volcanogenic massive sulfide and skarn-related deposits occur within the Lynne deposit lithologic sequence. Data suggest that the main sulfide mineralizing events were related to a volcanogenic-related, carbonate-generating, hydrothermal system. Skarn development in carbonate rocks within the main sulfide orebody and its lateral equivalents may be related to the intrusion of the subvolcanic tonalite, the rhyolite sills, or a combination of both events. �179 Acknowledgements The author strongly acknowledges the contributions of the Lynne predevelopment team of L. Kennedy, T. (Harding) Kennedy, J. Schaff, A. Zielinski and T. Suszek for their contributions to the author's knowledge through reviews, reports and conversations during the delineation of the Lynne deposit. Special recognition is due Larry Kennedy, author of the Noranda summary report, from which much of the descriptive text regarding alteration assemblages and host rock lithologies was taken. The management of Noranda Exploration Inc. is also acknowledged for their philosophy of exploration persistence and their confidence in the Superior District staff. I also thank Noranda Exploration Inc. for permission to publish this paper. References Cited Adams, Glen W., 1990, Lynne Base-Metal Discovery, North-Central Wisconsin: New Discoveries in North America Session, Northwest Mining Association 96th Annual Meeting, Spokane, Washington, transcript, 18 p. Adams, Glen W., 1991, Lynne Base-Metal Discovery: The Minnesota Prospector, Vol.!, No. 5, p. 2-7. AMERICAN MINES HANDBOOK, 1995, Noranda Exploration Inc., Company Profiles, Southam Magazine and Information Group publishers, p.167. DeMatties, T. A., 1990, The Ritchie Creek Main Zone: A Lower Proterozoic Copper-Gold Volcanogenic Massive Sulfide Deposit in Northern Wisconsin: Economic Geology, Vol. 85, p. 1908-1916. DeMatties, T. A., 1994, Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview: Economic Geology, Vol. 89, p. 1122-1151. Franklin, J. M., Lydon, J. W. and Sangster, D. F., 1981, Volcanic-Associated Massive Sulfide Deposits: ECONOMIC GEOLOGY 75th ANNIVERSARY VOLUME, p. 485-627. Franldin, J. M., Kasarda, J., and Paulsen, K. H., 1975, Petrology and Chemistry of the Alteration Zone of the Mattabi Massive Sulfide Deposit: Economic Geology, Vol. 79, p. 63-79. Kennedy, L. P., Harding, T. A., Schaff, J. H., and Zielinski, A. M., 1991, The Lynne Massive Sulfide Deposit, Oneida County, Wisconsin: Annual Institute on Lake Superior Geology, 37th, Eau Claire, Wisconsin, 1991, p. 63 Kennedy, L. P., 1992, Lynne Project Summary Geologic and Geotechnical Report: unpublished report, Noranda Exploration, Inc., Rhinelander, Wisconsin, 29 p. Kennedy, L. P., and Donnelly, M. E., 1992, Geology of the Lynne Zn-Pb-Cu-Ag Deposit, a Proterozoic Massive Sulfide, Oneida County, Wisconsin: unpublished report, Noranda Exploration Inc., Rhinelander, Wisconsin, 3 p. Lambe, R. N., and Rowe, R. G., 1987, Volcanic History, Mineralization, and Alteration of the Crandon Massive Sulfide Deposit, Wisconsin: Economic Geology, Vol. 82, p. 1204-1238. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-Stratigraphic Evolution of the Early Proterozoic Wisconsin Magmatic Terranes of the Penokean Orogen: Canadian Journal of Earth Sciences, Vol. 26, p 2145-2 158. �� https://digitalcollections.lakeheadu.ca/files/original/71b0c827f509c536d2918ec571adc342.pdf 68c03aa4e70493a5c919ae04e3a00d7c PDF Text Text I P ANNUAL P r INSTITUTE ON LAKE SUPERIOR GEOLOGY P CABLE, WISCONSIN WISCONSIN CABLE, P - MAY 19, 1996 M A Y 15 15- 19,1996 H - [1 ' ''-F,,, '- - '- \_ '- '- ' ',-,-''' '''-Fe,,',,, '-F',',', •' # / ''''-F-F/-F-F H P 'I, -F,,, ''''' '' -F ) 1 1. Glacial geology of western Wisconsin 2. Archean --Middle Middle Proterozoic Proterozoic transact transect Nainekagon region 4. Geology Geology of the Lake h7amekagon 5. Structure Structureof of the the western western Gogebic Gogebk Range I) PT P PROCEEDINGS VOLUME 42 PART 3- FIELD TRIP GUIDEBOOK P �I I I I I INSTITUTE ON LAKE SUPERIOR GEOLOGY 42NDANNUAL A N N U A L MEETING 42ND MEETING - M A Y 15 19,1996 MAY 15-19, 1996 CABLE, WISCONSIN CABLE, WISCONSIN SPONSORED BY: SPONSORED BY: U. S. GEOLOGICALSURVEY U. S. GEOLOGICAL SURVEY AND AND UNIVERSITY OF WISCONSIN OSHKOSH UNIVERSITY OF WISCONSIN - OSHICOSH - 1 I I I I I I I I I I PROCEEDINGS VOLUME 42 PART 3-- FIELD TRIP GUIDEBOOK EDITORS: SUZANNE W. NICHOLSON, U. S. GEOLOGICAL SURVEY, RESTON, VA SUzANNE W. NICHOLSON, U. S. GEOLOGICAL SURVEY, RESTON, VA LAUREL G . WOODRUFF, U.S. GEOLOGICAL SURVEY, ST. PAUL, MN LAUREL G. WOODRUFF, U. S. GEOLOGICAL SURVEY, ST. PAUL, MN �GLACIAL GEOLOGY OF OFWESTERN WESTERNWISCONSIN WISCONSIN FIELD TRIP #1: GLACIAL LEADER: MARK MARK D. JOHNSON LEADER: Department of Geology Gustavus Adolphus Adolphus College 56082 St. Peter, Minnesota 56082 FIELD TRIP #2: #2: GEOLOGY RIVER MONOCLINE: MONOCLINE: FIELD GEOLOGY OF OF THE MONTREAL RIVER TRAVERSETHROUGH THROUGH 25 25 KM OF THE CRUST A TRAVERSE LEADER: WILLIAM F. F. CANNON LEADER: U. S. Geological Geological Survey Survey National Center MS-954 National CenterMS-954 Reston, Virginia 22092 22092 FIELD FIELD TRIP TRIP #4: #4: EARLY EARLYTO TOMIDDLE MIDDLEPROTEROZOIC PROTEROZOICGEOLOGY GEOLOGY OF OF THE LAKE NAMEKAGON NAMEKAGON REGION LEADERS: F. CANNON!, CANNON1, LAIJRELG. LEADERS: WILLIAM WILLIAM F. LAURELG.WOODRUFF2, WOOD RUFF^, SUZANNE W. NICHOLSON1 AND SUZANNE NICHOLS ON^ 1U. 1 U. S. Geological Survey National Center MS-954 National Center MS-954 Reston, Virginia 22092 22092 2U. S. Geological Survey 2 U. Survey Woodale Drive 2280 Woodale Paul, Minnesota 55112 55112 St. Paul, FIELD TRIP TRIP #5: #5: LAKE LAKENAMEKAGON NAMEKAGONAND ANDPENOKEE PENOKEEGAP GAPAREAS, AREAS, WEST WEST GOGEBIC RANGE, WISCONSIN LEADERS: GENE L. LABERGE2 LEADERS: JOHNS. JOHN S.KLASNER1 KLASNER~AND AND GENE LABERGE~ 1 1 Department of Geology Western Western Illinois University minois 61455 Macomb, Illinois 61455 2 Geology 2 Department of Geology University of University of Wisconsin Wisconsin - Oshkosh Oshkosh, Wisconsin Oshkosh, Wisconsin 54901 54901 - L �I I 11 U TABLE OF CONTENTS I I FIELD TRIP #1: GLACIAL GEOLOGY OF WESTERN WISCONSIN M. D. Johnson I OVERVIEW OF THE BEDROCK GEOLOGY OF THE CABLE-BURLEY AREA, WISCONSIN W. F. Cannon and S. W. Nicholson I I I I I I I I I I 3 FIELD TRIP #2: GEOLOGY OF THE MONTREAL RIVER MONOCUNIE: A TRAVERSE THROUGH 25 KM OF THE CRUST W. F. Cannon 35 49 FIELD TRIP #4: EARLY TO MIDDLE PROTEROZOIC GEOLOGY OF THE LAKE NAMEKAGON REGION W. F. Cannon, L. G. Woodruff, and S. W. Nicholson 67 FIELD TRIP #5: LAKE NAMEKAGON AND PENOKEE GAP AREAS, WEST GOGEBIC RANGE, WISCONSIN J. S. Kiasner and G. L. LaBerge 83 �fl I I I I I I I 1 I I I 1 I I I GUIDE FIELDTRIP TRIP##11 GUIDEFOR FIELD GLACIAL GEOLOGY OF WESTERN WISCONSIN �I I I I I I I I HELD TRIP TRIP #I #1 HELD GLACIAL GEOLOGY OF OF WESTERN WESTERNWISCONSIN WISCONSIN by Mark D. Johnson of Geology, Geology, Gustavus Gustavus Adolphus Adolphus College Department of St. Peter, Peter, Minnesota Minnesota 56082 56082 I. Introduction I. The purpose purpose of of this this ILSG fieldtrip trip isis to to get of the the The ILSG field get aa general general overview overview of history of the Pleistocene features of of northwest landforms, sediments, and geologic geologic history Pleistocene features Wisconsin. To that end, the field trip has been designed to show exposures exposures and and Wisconsin. outcrops that reveal the different types of of deposits deposits and and landforms landforms throughout throughout the outcrops different types region. Though will hand hand out and refer to a publication region. Though not not bound bound in in this this booklet, booklet, I will of Wisconsin" Wisconsin"by byClayton Claytonand and others others (1991). (1991). Figures Figures 1 1 through through 5 called "Glaciation of are the figures figures from from the the"Glaciation "Glaciation of of Wisconsin" Wisconsin" brochure; the figures figures included included within this report start start with with Figure Figure 6. Certainly, one of of the goals goals of of aa regional regionalunderstanding understanding of of glacial glacialdeposits deposits isis to to able to to predict, variationsthat that in in part part be able predict, or at at least least expect, expect, surface-material surface-material variations be determine the character with the landscape determine the character of of human interaction interaction with landscape (groundwater (groundwater resources, geologic engineering character Additionally, glacial resources, character of of sediment, etc.). etc.). Additionally, the primary primary record record for forthe the study study of of the the nature nature and and sediments and landforms provide the of former ice ice sheets. sheets. Studies of of these these features, features, along alongwith with the the use use of of modern modern history of environments as as analogs, analogs, provide provide aa foundation upon which glacial environments foundation upon which one can can glacial reconstruct glacial history. II. Ice Ice lobes, lobes, phases, stratigraphy, and brief glacial history of western Wisconsin Wisconsin 11. Wisconsin was was glaciated glaciated several several times times during during the Pleistocene, Northwestern Wisconsin Pleistocene, but theNorthwestern topography associated primarily primarily with with advances advances of of topography and and surficial surficial sediment are associated the Superior Lobe Lobe and Grantsburg Grantsburg Sublobe Sublobe (an offshoot of the Des Des Moines Moines Lobe) Lobe) during during the the last lastpart partofofthe theWisconsinan WisconsinanGlaciation Glaciation(Fig. (Fig.1-4). 1-4). The earliest earliest known known glacial glacial advance advancewas wasduring during the the Reeve Reeve Phase Phase ofof the the Des Des The Lobe, which which occurred probably probably over over 730,000 730,000years yearsago agoand and deposited deposited gray, Moines Lobe, Moines loam till This material material is is deeply buried till of of the thePierce PierceFormation Formation(Fig. (Fig.1-3, 1-3, 1-5). 1-5). This occur in in throughout the region region and and occurs occurs only in patches; patches; some surface exposures occur southern St. St. Croix Croix County County and and Pierce PierceCounty. County. The The till till is deeply weathered, weathered, even southern I 1 �AOKA JSANT) .— KANABEC _\ - _____ N I / &; WASHBURN ri* — 0' I BURNETT POLK / r( / 1/ 7 H 71 H c OO DUNNI CHIPPEWA sI.$y UCR.8( \LiN*t/ 'CHAGO % ) PINE La nia&net S pItt tiers at the Ctrenqtrettrrk Kee P—f s3t. Croft dw..I — lithe tovOieiett — -- — —— 0 • A o 1490 160 0 —I N LIce o.wi.6, eec.*esh.d tIt 5 I 101cr,. .ead — a90 of — &ecstor LIte locebon rd S.vIt(on 01 9SSS 91-f LIce US — -y otcp ci gius, Lake us Tied. ((Sec N — at? — — .Iatp of ØecII Lake Of.St.9 — 'of, 0tcti S gIt La. OailtbU5 o pci • o o 009_t -- H.yP-r $ w w— as, N H Red C — — —Isrun -It --— — — in.. — — - br — — S-lu, d.eN.S Gwist*so &lcO. kInd liar. II Sboc •INIt Sel of HeIs.cr ,d t.SwMt (1971) •ctn ol giec '-si us — sVn ci bted red tad brael S.asd — .ethn.nl �Figure Portion of of northwestern Wisconsin Wisconsin and and adjoining Minnesota Minnesota showing showing features associated associated with with the mostFigure 1-6.-1-6.- Portion recent induded to recent glacial glacial events. Spot elevations are included toshow showthat thatelevations elevationsincrease increasefrom fromcentral centralBurnett BurnettCounty Countyto tothe theSt. St. Croix ice margin. Based on their relative position, the Centuria, Luck, Fox Creek, and McKinley ice margins are correlated Croix Based on their relative position, the Centuria, Luck, Fox Creek, and McKinley are correlated with with the theTiger Tiger Cat Cat ice ice margin margin of Clayton (1984). (1984). Tiger Cat and Hayward Haywardice ice margins marginsfrom fromClayton Clayton(1984) (1984) and Attig and and others others(1985). (1985). Emerald, Emerald, St. St. Croix, Croix, Early Early Chippewa, Chippewa, and andLate LateChippewa Chippewaice icemargins marginsfrom fromJohnson Johnson(1986). (1986).Pine PineCity Cityice ice margin in Minnesota from Cooper (1935) and Hobbs and Goebel (1982). Location of glacial Lake Grantsburg and glacial margin in Minnesota from Cooper (1935) and Hobbs and Goebel(1982). Grantsburg and glacial Lake Lake Lind varved clay day in Minnesota Minnesota from Chris Hemstad and and myself myself (unpublished (unpublished data) data)and andGary GaryMeyer Meyer (personal (personal communication). Only tunnel channels in Wisconsin are shown. Extent of the glacial Lake Grantsburg in Minnesota is in in communication). Only tunnel channels in Wisconsin are shown. Extent of the glacial part location of Camp Sunrise. LL == townsite townsite of of Lind, Wisconsin. Till Till part from fromCooper Cooper (1935). (1935). CS CS (in (in eastern eastern Minnesota) Minnesota) == location fabric measurements in Minnesota from Chernicoff (1983). fabric measurements in Minnesota from Chernicoff (1983). �where overlain overlain by younger younger material. material. The Pierce Pierce till till is overlain in places by reddish-brown, sandy loam till The reddish-brown, sandy till and and outwash of which was was deposited deposited during the Baldwin outwash of the the River River Falls Falls Formation, Formation, which Baldwin of the Chippewa Chippewa Lobe probably over Phase of the Superior Superior Lobe and the Dallas Phase of over 130,000 years ago ago (Fig. (Fig.1-3, 1-3,1-5). 1-5).This Thismaterial materialisisweathered, weathered, as as shown shown by clay-mineral 130,000 years alterations and magnetite magnetite weathering weathering(Johnson, (Johnson, 1986) 1986) and thick soil soil profiles profiles (Baker (Baker interpret this this weathering weathering to have have likely likely occurred occurred during during the the and others, others, 1983). 1983). I interpret Sangamon Interglacial Interglacial interval. interval. Lobe and and Chippewa Chippewa advances advancesthat that occurred occurred during during the last part The Superior Lobe of the Wisconsinan Glaciation began began with with the Emerald Phase and early of Wisconsinan Glaciation Emerald Phase early Chippewa Chippewa 1-6). Deposits from from these these phases phases occur occur at at the surface underneath underneath the the Phase (Fig. 1-1, 1-6). gently rolling gently rolling topography topography of the the southern southern Barren Barren County, County, southeastern southeastern Polk Polk County, and and central central St. St. Croix Croix County. County. Part-way through through the thelate lateWisconsinan Wisconsinan Glaciation, Glaciation, the the Superior Superior Lobe Lobe changed changed behavior and and began different suite suite of of landforms landforms and sediment sediment types. types. behavior began to form form aa different These are associated positions in western These associated with more than 10 10 former former ice-margin ice-margin positions Wisconsin (Fig. (Fig. 1-6, 1-6, 1-7), 1-7),beginning beginningwith withthe theSt. St.Croix CroixPhase. Phase. During these events, Wisconsin events, the Superior and Chippewa left behind behind reddish-brown reddish-brown sandy sandy loam loam till and Chippewa Lobes Lobes left outwash of the the Copper Copper Falls Falls Formation, Formation, as well as as striations, striations, grooves, grooves, outwash outwash plains, outwash outwash fans, fans, tunnel tunnelchannels, channels,eskers, eskers, hummocks, hummocks, ice-walled-lake ice-walled-lake plains, plains, ice-dammed-lake plains, plains, end moraines, and the Spooner Spooner Hills of of northeastern northeastern Polk Polk Burnett County, County, and and central central Washburn Washburn County. County. The Superior County, southeastern Burnett Lobe ice-margin positions (Fig. 1-6) can can be be traced traced for for several several kilometers laterally and represent ice-margin stillstands, ice-margin advances, or sedimentologic events that imprint the the location location of of the the ice ice margin margin (for (for example, example, the tunnel-valley/outwash-fan tunnel-valley/outwash-fan pairs clearly indicate the position of the ice margin but do do not not require require an anice-margin ice-margin stilistand or readvance). stillstand readvance). As the Superior Superior Lobe Lobe retreated, glacial glacial Lake Lind formed in in the the preglacial preglacialSt. St. Croix River valley valley (Fig. 1-7A) 1-7A)and and lasted lasted about about 1000 1000years yearsbased basedon on the the number number of of varved silt silt and and clay clay couplets coupletsfound foundin inlake lakesediment sediment(Sunrise (Sunrise Member Member of of the the Copper Copper Falls Formation). Formation). 1-7D), The Grantsburg GrantsburgSublobe, Sublobe,an anoffshoot offshootof of the theDes DesMoines MoinesLobe Lobe(Fig. (Fig.1-7C, 1-7C,1-7D), advanced during during the the Pine Pine City City Phase Phase across a fluvial plain that developed on on top top of of glacial Lake Lind Lind sediments sediments(Fig. (Fig.1-7B). 1-7B). The Grantsburg Sublobe deposited gray, gray, loam till of the Trade Trade River River Formation and left behind end end moraines, moraines, till till plains, plains, iceicemarginal channels, Lake Grantsburg Grantsburg was channels, and and ice-dammed-lake ice-dammed-lake plains. plains. Glacial Glacial Lake 6 �-1 ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ drainage basin at this time. 7E—Clacial Lake Duluth drained through the study area along the St. Croix River. to advance to the Pine City margin and glacial Lake Grantsburg expanded. The Superior Lobe may have still been in the area. 71)—The Grantsburg Sublobe continued St. Croix River valley in the Taylor's Falls Crantsburg. The initial outlet of glacial Lake Grantsburg would have formed the modern St. Croix River, and formed glacial Lake Late Wisconsinan ice-margin positions of the Superior Lobe. 7B—Clacial Lake Lind filled in with sand deposited in prograding deltas and fluvial plains. 7C—.The Grantsburg Sublobe advanced across the sand plain, dammed the Superior Lobe at this time is shown by the heaviest line; the medium lines mark former events. 7A--Clacial Lake Lind formed In the lowland of the former St. Croix River. The area showing selected Late Wisconsinan Figure 1-7.—Five sketch maps of the field-trip I �dammed in front front of of the the advancing advancingice ice and and lasted lastedapproximately approximately100 100 years, years, based on the number of varved varved silt silt and and clay clay couplets couplets of the the Falun Falun Member Member of the Trade Trade River River Formation (see The location location of of the the lake's (see varve varve localities localities in inFig. Fig.1-6). 1-6). The lake's outlet outlet is is unknown. Numerous drainage events Numerous events from from ice-dammed ice-dammed Lake Lake Superior Superior (glacial (glacial Lake Lake Duluth, Fig. caused the the St. St. Croix Croix River Rivertoto incise incise its its valley valley and and created the Duluth, Fig. 1-7E) 1-7E) caused famous famous potholes potholes in the the basalt basalt around aroundSt. St.Croix Croix Falls. Falls. An interruption in these these drainage events events allowed drainage allowed aa large sand surface surface to develop develop in in northwestern northwestern Polk Polk County and in Burnett Burnett County. Dunes Duneslater laterdeveloped developed on on this thissurface. surface. IlL Ages of late Wisconsinan 111. Wisconsinan glacial events The date of the of northwestern Wisconsin the late late Wisconsinan Wisconsinan glacial events of Wisconsin is uncertain. AAradiocarbon radiocarbondate dateofof20,500 20,500years yearsB.P. B.P.± i400 400(1-5443) (1-5443)(Wright, (Wright,1972; 1972; Wright and others, organic matter matter in lake others, 1973) 1973) was obtained obtained from disseminated disseminated organic lake This lake lake is behind the sediments at Wolf Wolf Creek Creek in in central central Minnesota. Minnesota. This the St. St. Croix Croix until the ice ice margin had retreated 60 moraine and would not not have have been been ice-free ice-free until 60 km krn from the maximum maximum limit, limit, possibly post-dating the St. St. Croix Croix Phase maximum maximum by by hundreds of years. years. However, However,there thereisisaapossibility possibility of of contamination contamination of the sediment sediment by old Clayton and Moran by old carbon, carbon, and and the the date date may may not notbe bereliable. reliable. Clayton Moran(1982), (1982), Mickelson and others (1986)suggest suggestaa somewhat somewhat younger date others (1983), (1983), and Johnson (1986) for the years B.P. B.P. Their chronologies the St. St. Croix Croix Phase, Phase, approximately approximately18,000 18,000 to 15,000 15,000 years chronologies are based on on dates dates from from wood wood in in other other regions, regions, where where there there is is less less chance chance of of contamination. However, However, little little wood wood is associated associated with the deposits of the St. St. Croix Phase. The TheEmerald EmeraldPhase Phase(the (thepre-St. pre-St.Croix CroixPhase, Phase,Late-Wisconsinan Late-Wisconsinan advance advance in in western in press) to have western Wisconsin) Wisconsin) is considered by Johnson Johnson (1986; (1986; in have occurred occurred around 20,000 around 20,000 to to25,000 25,000 B.P. B.P. of the phases that occurred after the St. Croix Croix Phase Phase are are unclear unclear with with The dates of B.P. (Clayton, (Clayton, the exception of the Marquette Marquette Advance, Advance, which is dated dated around around9,900 9,900 B.P. 1984). 1984). IV. Landforms Landforms of western western Wisconsin Wisconsin The landscape created during overall retreat of of the Superior Lobe Lobe in western Wisconsin Wisconsin consists consists predominantly predominantly of hummock hummock tracts, tracts, ice-walled-lake ice-walled-lake plains, plains, of collapsed outwash, and and rolling to streamlined till pitted-outwash plains, regions of collapsed outwash, uplands. Tunnel Tunnelvalleys, valleys,eskers, eskers, and and the the Spooner Spooner Hills are also present. Pleistocene Pleistocene deposits are generally 30 30 to to 45 45 m m thick thick (up to 85 m m in places). places). Precambrian Precambrian basalt 8 �I r crops out out as in the the western and northern crops as striated striated and and grooved grooved knobs knobs in western and northern parts parts of of Polk Polk County, Barron Barron quartzite quartzite in in eastern Barron County, and and Cambrian Cambrian sandstones sandstones in in County, Barron County, southern Barron County. County. Drainage meltwater during retreat was generally generally to to the the Drainage of of meltwater south during duringdeglaciation deglaciation(see (seearrows, arrows,Fig. Fig. 1-6). 1-6). In the following section, section, II discuss discuss the the major majorlandform landform types types in in the the region, region, and In describe what each landform landform type type signifies. signifies. Moraines.--There are very few moraines, in the classic sense, in western Wisconsin. ---There The best-developed are along the Pine City Phase margin of of the Grantsburg Grantsburg Sublobe, Sublobe, but only in in places places (Fig. (Fig. 1-6). Few Few morainic morainic ridges occur at Superior Lobe ice-margin positions. The positions. The term term 'morainic 'morainic ridge' is is used used for for relatively narrow features deposited They contain contain little little hummocky hummocky topography, topography, and and are are at the at the margin margin of of the the ice. ice. They composed ofof various various types types ofof till till and and ice-contact ice-contactsand sandand andgravel. gravel. Much Much of of the the composed length of of the "St. Croix moraine" is not characterized by by morainic morainic ridges, ridges, but but consist consist of hummock tracts, outwash plains, and glacial thrust systems. of Hummocks and hummock tracts (Stop usethe the term term 'hummock' 'hummock' to to mean mean aa (Stop 1-3).--I 1-31.--1 use Hummocks occurring in in groups, groups, and associated hill or knob, irregular to circular to oval in plan, occurring This term term is with irregular to to circular circular to to oval oval hollows, hollows, depressions, depressions, or wetlands. wetlands. This regardless ofof the the type type of of sediment sediment composing composingthe thehummock. hummock. A A variety variety of of used regardless used has been applied to this type of landform in glaciated regions, terms regions, including including deaddeadice moraine, hummocky ice hummocky moraine, stagnation moraine, moraine, collapsed collapsed outwash, kame, 'hummock tract' to describe a distinct region region of and kame complex. I use the term 'hummock hummocks (in (in the the same same way way that that the the term group of hummocks term 'drumlin 'drumlin field' field' describes describes aa group of drumlins). hummocks within within the the field-trip field-triparea area are are 55 to to 20 20 m m high high and 25 25 to Individual hummocks Individual 400 m m in in diameter diameter with with a mean mean height height of of 10 10mmand andwidth width of of 130 130m. m. Hummocks Hummocks are are 400 irregularly spaced with respect to each other but show a frequency of of one hummock hummocks/km2. Hummock meters. There per 250 to 500 meters. There are are 15 15 to to 40 40 hummocks/km2. Hummock slope ranges from 2 to 14 degrees. degrees. 1-8)lie lieininaazone zoneparallel paralleltotoand and up up to 20 20 k km Hummock tracts (Fig. 1-8) m behind the St. Croix Croix and other Superior positions; hummocks hummocks are are absent along St. Superior Lobe ice-margin positions; The hummock hummock tracts tracts do certain lengths of of former former ice-margin ice-margin positions positions(Fig. (Fig.1-8). 1-8). The not form a continuous band but are are separated separated from each other by outwash plains, regions of tunnel valleys, valleys, and and rolling, rolling, upland upland till regions of collapsed-outwash, collapsed-outwash, tunnel till surfaces. surfaces. tracts in the form upland upland areas areas that have Hummock tracts the field-trip field-trip area area commonly commonly form have Hummock above above adjacent adjacent outwash outwash surfaces. surfaces. Outwash surfaces surfaces that lie adjacent to elevations the hummock hummock tracts are graded graded to to nearby nearby ice-margin ice-margin positions a few few kilometers kilometers 9 �, -i--' I 7 '.:.j:-._-- :3 — C .J2!k rTT pitted n CroixL.......J outwtsh Darn • ce-walled. lake plain hummocky ice-margin posi outwash o hummock tract 0 noii-humn,odcy suriace compos.d of till striation channel margin — cour bour Sb. 1 Figure part of Rgure 1-8.—A 1-8.-A part of western western Wisconsin Wisconsin showing the field-trip field-trip area area (black (black in in inset) inset) and and geomorphic geornorphicfeatures. features.Areas Areas left blank on the map map include includepredominantly predominantly rolling rolling to to dendritically-drained dendriticallydrained surfaces surfaces underlain by till (with a few few basalt basalt knobs knobs in in the the western western and northwestern northwestern parts parts of of the the study studyarea). area). NR=city NR=dty of New New Richmond, Richmond, SCF=city SCF=aty of St. Croix Croix Falls, Falls, TL=city TLscity of of Turtle Turtle Lake, Lake, C=Centuria ice-margin position, C-Centuria ice-margin position,BL=Balsam BL=Balsam lake lake ice-margin ice-marginposition, position,R=Range R=Rangeice-margin ice-margin position, PC=Pine City ice-margin position, position, P C = P i City ice-marginposition, SC=late SC=late St. Croix Croix ice-margin ice-margin position, position, GS=Grantsburg GS=GrantsburgSublobe. Sublobe. Dashed Dashed line line in in inset is is trace trace of the Superior Superior thbe Lobeice-margin ice-margin limit limit where where covered coveredduring duringthe thePine PineCity City Phase Phase of of the theGrantsburg GrantsburgSublobe; Sublobe; arrows arrowsin inset inset show general direction. general ice-flow ice-flow direction. 10 �I I I I I I I I I further up up ice further ice to to the the north north or orwest. west.In Inseveral severallocations, locations, the the outwash outwash plains plainslocated located between hummock tracts are collapsed into tunnel valleys valleys that that had been filled with thick, stagnant thick, stagnant ice. ice. In In part, part, the the tunnel tunnel valleys valleys may may have have controlled controlled the the location location of of outwash plains plains by by localizing localizing meltwater drainage in supraglacial troughs that that formed formed as ice flowed into the quiescent quiescent tunnels. Additionally, Additionally, tunnel-valley tunnel-valley formation formation may have affected location of of hummock tracts and and development development of of hummocks hummocks by by locally locally removing basal and and englacial englacial debris debris from from overlying overlying glacial ice as the tunnel tunnel formed. formed. The origin origin of of hummocks has has been been interpreted interpreted in in many many different ways. I have found at at least least twelve twelvedifferent differentmodels: models: 1- supraglacial 1supraglacial reworking reworking and and redistribution redistribution of of debris debris released released supraglacially supraglacially from from stagnant ice Clayton, 1967; 1967;Clayton Clayton and and Moran, 1974; stagnant ice (Boulton, (Boulton, 1967, 1967, 1972; 1972; Clayton, 1974; Paul, 1983). 1983). 2- slumping 2slumpingof ofsupraglacial supraglacialdebris debrisinto intocrevasses crevasses(Tanner, (Tanner,1914); 1914); 3- squeezing of of subglacial debris into basal crevasses or hollows under stagnant stagnantice ice (Hoppe, 1952; (Hoppe, 1952;Stalker, Stalker,1960). 1960). 4- molding of of basal till under active ice ice as as a transition form form between between drumlins and Rogen moraine moraine (Aario, (Aario,1977). 1977). deposition of s- patchy 5patchy deposition of lodgement lodgementtill till under underactive activeice ice(Menzies, (Menzies,1982); 1982); 6- melting 6melting of of simple simple or or stacked stacked layers layers of of debris-rich debris-rich ice ice producing producing melt-out melt-out till till hummocks (MOller, (Moller,1987). 1987). hummocks 7- deformation by rising diapirs of 7deformation of supraglacial supraglacial and englacial englacial debris by of clean clean ice ice (Minell, (Minell,1979). 1979). 8- rising diapirs 8diapirsof of subglacial subglacialdebris debris(Zelcs, (Zelcs,1993). 1993). 9- patchy 9patchy formation formation of of ground ground ice icebeneath beneathstagnant, stagnant,cold-based cold-based glaciers glaciers(Aario, (Aario, 1992). 1992). 10-melting of of debris-rich, stagnant ice ice containing containing extensive karst tunnels tunnels(Kemmis (Kemmis and others, and others,1994). 1994). 11-partial 11-partial erosion erosion of of till till plains plains by by subglacial subglacialmeltwater meltwater(Rains (Rainsand andothers, others,1993). 1993). 12-Extrusion of of proglacial sediment by glacier-forced glacier-forced groundwater groundwater flow (Boulton (Boulton and Caban, 1995). Caban, 1995). The hummocks in the the field-trip area are considered to have The hummocks in field-trip area considered to have formed formed as as stagnant-ice features features (#'s (#Is 11and and 6) 6)because because of of their their close close association association with with ice-walledice-walledformed from from the melting of stagnant, lake plains. plains. The hummocks formed stagnant, debris-rich debris-rich ice. ice. The The resulting topography formed as a result result of of collapse collapse and differential differential settling as the melting, the melting, buried, buried, debris-rich debris-rich ice ice lowered lowered the the overlying overlying supraglacial supraglacial debris. debris. Numerous show the the presence of faults, faults, folds, folds, and and steeply Numerous exposures exposures show presence of steeply tilted beds 11 I �a within within the the hummocks. hummocks. These Thesefeatures featuresare arebest best explained explained as as being being caused caused by collapse collapse due to to the the melting melting of of buried, buried, stagnant stagnant ice. ice. However, much of of the till in the hummocks is interpreted to be melt-out melt-out till. The interpretation of melt-out till in many of the hummocks is based primarily on the the strong strong pebble pebble fabric fabric parallel parallel to to regional regional ice ice flow flow (Fig. (Fig. 1-9). 1-9). I interpret the the diamicton with strong fabric as likely being melt-out melt-out till till (rather than lodgement fill till or deforming-bed (1) The The diamicton diamicton contains faults and deforming-bed sediment) sediment)for for three three reasons. reasons. (1) subtle The thin subtle stratification stratification that have have been been related related in in the the literature literature to to melt-out melt-out fill. till. The sand sand lenses lenses present present in in the thediamicton diamicton at at the the St. St. Croix Croix Falls dump and and speedway speedway sites sites are Möller uses these are similar similar totolenses lensesdescribed describedinindiamicton diamictonbybyMOller Moller(1987). (1987). Moller lenses as In over half half of of the samples as arguing arguing for for aamelt-out melt-out origin. origin. (2) In samples with with ice-flowice-flowparallel parallel fabric, fabric, the fabric fabric is stronger stronger than than those those reported reported for for lodgement lodgementfill. till. (3) Meltout and stagnant ice ice is is indicated out till till requires requires stagnant stagnant ice ice for for formation, formation, and indicated by the the hummocks till does does occur occur in in some some exposures, exposures,but but itit is not as hummocks themselves. themselves. Flow Flow till as common as the till Flow till till has has poor poor fabric development till II interpret interpret as as melt-out melt-out till. till. Flow and is fluvialsediment. sediment. is interbedded interbedded with withfluvial In terms hummockshave have been been used used to imply terms of of glaciologic glaciologic implications, implications, hummocks imply surging surging conditions conditions leaving leaving large large hummock hummock tracts tracts (Wright, (Wright, 1980; 1980; Johnson Johnson and and Savina, 1987) or that the 1987) or the hummocks hummocks indicate indicate extensive extensive freezing-on freezing-on of material material under under non-temperate non-temperateglaciers glaciers(Boulton, (Boulton,1972; 1972; Paul, Paul, 1983; 1983; Moller, Moller, 1987; 1987; Sollid and and Sørbel, Attig and others, 1990)and and therefore therefore indicate indicate cold Serbel, 1988; 1988; Attig others, 1989; 1989; Mooers, Mooers, 1990) conditions. conditions. The The ice-walled-lake ice-walled-lake plains and melt-out-till melt-out-till hummocks of of western Wisconsin Wisconsin represent the the coarse-grained coarse-grained end of of aa continuum continuum with with the the stagnant stagnant ice ice landscape landscape developed developed in in clayey clayey till till that thatwas wasdescribed describedininNorth NorthDakota Dakotaby byClayton Clayton(1967). (1967). In general, I suggest that sandier debris tends tends to to yield yield aa greater proportion proportion of of sandier glacial glacial debris melt-out till in glacial debris debris tends tends to produce in hummocks, hummocks, and more more clay-rich clay-rich glacial produce a greater greater proportion proportion of of flow flow till till and anddebris-flow debris-flow sediment sediment in in hummocks. hummocks. Ice-walled-lake plains in the I c e - w a l l e ~plains l a i n (Stop s(Stov 1-4).--There 1-4).--There are over 40 ice-walled-lake ice-walled-lake plains field-trip of them occur in hummock tracts, suggesting field-trip area area (Fig. (Fig. 1-8), 1-8), and nearly all of suggesting that that their their origin origin isisrelated related to tothe theorigin originof of the thehummocks. hummocks. Ice-walled-lake Ice-walled-lake plains plains form form initially initially as as supraglacial supraglacial lakes lakes on on stagnant, stagnant, debris-rich debris-rich ice. The lake water melts through through the thethin thinice, ice, and andsediment sedimentisisdeposited depositedin inthe thelake lakefrom fromadjacent adjacent debris-rich debris-rich ice. ice. Upon Uponmelting meltingof of stagnant stagnantice, ice, the the sediment sediment left behind forms a smooth, smooth, dishshaped shaped plateau plateauin inthe themidst midstof of aahummock hummocktract. tract. Ice-walled-lake plains in in the field-trip area range in Ice-walled-lake plains in size size from from 11toto13 13km2, km2, 12 �DIAMICTON FABRIC Figure Figure 1-9.--Map 1-9.-Map of of the study study area area showing showingrose rose diagrams diagrams of of fabric fabricin indiamicton. diamicton. Lake ice-margin position); stippled Balsam positions (B = ice-margin Hachured lines = ice-margin positions (B = Balsam Lake ice-margin position); stippled Hachured lines = Fabric measurements north. locations; arrows = site tracts; circles = hummock tracts; circles = site locations; arrows = north. Fabric measurements areas==hummock areas consist consistof of 25 25pebbles pebblesexcept exceptsite site44(75 (75pebbles pebbles combined combined from from three three places places in in the the places in each outcrop); sites 9, outcrop); outcrop);sites sites55aztd and66(50 (50 pebbles pebbles combined combimedfrom fromtwo two places in each outcrop); sites8,8,9, dipping stratification 11,and and 12 12(50 (50pebbles). pebbles). Diamicton at site site 4 contains contains steeply steeply dipping stratification 10,11, 10, showing showingthat thatfabric fabrichas hasbeen beenrotated. rotated.Rotation Rotation of of stratification stratificationto to 00 0Ârotates rotates dominant dominant fabricmode modetotoN70°W. W W . fabric 13 �plains commonly commonly have have aa rim with a typical typical size size around around 22 km2. km2. Ice-walled-lake Ice-walled-lake plains around their their margin that stands around margin that stands 3 to 10 10 m m above above the the center center of of the the lake lake plain. plain. Stream- and wave-sorted sand and and gravel gravel occur occur along the margins margins of of the the ice-walled ice-walled lakes. In Inplaces, places, the the rim rim sediment sediment is is interbedded interbedded with with till till that flowed flowed from from adjacent adjacent ice into the Coarse sediment sediment isis restricted restricted to to the the margins of the lake. lake. Coarse of the lake lake plain; plain; much of of the are underlain by silt, silt, with with as much the interior interior portions portions are underlain by as much much as as 20 20 m m underlying the the larger larger plains. plains. The sediment in the plains was deposited after active the ice-walled-lake ice-walled-lake plains active ice ice left left the area. plains cross known area. This is known known because because some some ice-walled-lake ice-walled-lake plains known iceicemargin positions, signifying that the ice that walled the lake came from two separate two separate advances. advances. Tunnelelvalleys and 1-8),--Tmel 1-SE--Tunnel valleys (Stom1-1. 1-1,1-2. 1-2,1-6.and valleys are are river river valleysand andeskers eskers(Stops valleys believed to have been carved valleys carved by subglacial subglacial streams streams that that became became incised incised into into the glacier bed. These These valleys valleys were were first first described in Denmark and later recognized in northern northern Germany. Germany. Numerous Numeroussubglacial subglacial river river channels channels associated associated with late late Wisconsinan Glaciation Glaciation in in the Upper Midwest have been described Wisconsinan described by by Mickelson Mickelson and Attig and others asbeing beingformed formed by by rapid rapid or catastrophic and others others (1983) (1983) and others (1989) (1989) as catastrophic drainage. these authors authors have have proposed proposed the term drainage. Therefore, Therefore, these term tunnel tunnel channel channel for for these features, suggesting that their formation occurred under bank-full conditions. conditions. Tunnel valleys are aa common common landform landform in western western Wisconsin, Wisconsin, the greatest greatest number is ice margin. margin. Half is associated associated with the the St. St. Croix Phase ice Half of of the the tunnel tunnelvalleys valleys in western westernWisconsin Wisconsincontain containeskers eskers(Fig. (Fig.1-6). 1-6). In western Wisconsin, link together tunnel valley valley segments segments Wisconsin, it is possible to link into a network 40 km. km. However, network with with some some valley valley systems as long as 40 However, breaks breaks in in the the sequences, development development of of outwash outwash plains plains of of different different ages graded to tunnel-valley sequences, different parts of of the the same same tunnel-valley tunnel-valley sequence, sequence, and the the presence presence of of the the bestbestdeveloped tunnel valleys suggest that the developed valleys next to to former former ice-margin ice-margin positions, positions, suggest the tunnel valleys valleys in in western western Wisconsin Wisconsin were formed as relatively short segments segments near near former ice-margin positions during during overall overall retreat. retreat. About half About half of the the tunnel tunnel valleys valleys in inwestern westernWisconsin Wisconsin also also contain contain central central eskers. The Theassociation association of of eskers eskers within within the the tunnel tunnel channels channels indicates indicates two two levels levels of of discharge during subglacial subglacial drainage. A A large large discharge discharge is shown by the large large size size of the tunnel channel channel as as well well as as the the fact fact that that itit isis an anerosional erosionalfeature. feature. It is suggested that the that the tunnel tunnel channel channel represents represents an an initial, initial, short-lived short-lived burst burst of of subglacial subglacial meltwater, perhaps under hydraulic head built up behind meltwater, behind aa frozen frozen margin margin (Wright, (Wright, 1973; Attig and and others, 1989). 1989). As discharge abates, the subglacial meltwater pathway 1973; Attig pathway 14 �isismaintained maintainedatataasmaller smallersize. size. This This smaller smaller tube tube later later becomes becomes filled filled with with stream stream sediment sedimentand andbecomes becomesan anesker eskerupon uponmelting meltingofofthe thesurrounding surroundingice. ice. Eskers Eskers that that do do not notoccur occur inintunnel tunnelchannels channels are are also alsopresent present ininwestern western Wisconsin. Wisconsin. The Thelargest largestoccurs occursin innorthwest northwestPolk Polk County County and and has hasits itsterminus terminusatatthe the lies. The elevation of this esker apex of the large outwash fan upon which Frederic apex of the large outwash fan upon which Frederic lies. The elevation of this esker rises feet at at its terminus, 1080 feet feet near near West West Sweden Sweden to to 1200 1200 feet terminus, indicating indicating that that rises from from1080 the thesediment sedimentin inthis thisesker eskerwas wasdeposited deposited as as water water flowed flowed up up regional regional slope. slope. Other Other prominent eskers include one, locally referred to as "The Hogsback," at the St. Croix prominent eskers include one, locally referred to as "The Hogsback," at the St. Croix County Countyline, line,and andone onerevealed revealedininaalarge largecollapse collapsepit pit 33km km north northof of Centuria. Centuria. Outwash Outwash plains plains (Stops (Stovs1-1 1-1and and1-2L--Outwash 1-21.~0utwashplains plains cover cover much much of of western western Wisconsin Wisconsin and and constitute constituteone oneof of the themost mostcommon commonlandforms landformsremaining remainingfrom fromthe the Wisconsinan 1-6). These These plains plains were were built built by by meltwater meltwaterstreams streams WisconsinanGlaciation Glaciation(Fig. (Fig.1-6). emanating emanatingfrom fromthe themelting meltingSuperior SuperiorLobe. Lobe. Outwash Outwash plains plainsare areclearly clearlyassociated associated with with former former ice-margin ice-margin positions, positions, and and the margins are are interpreted interpreted in part by the position positionof of former former Superior Superior Lobe Lobe ice margins by the the sharp sharp northern northern and andwestern westernup-slope up-slopelimits limits of of the the outwash outwash plains plains (Fig. (Fig. 1-5). 1-5). Near Near former former ice-margin the slope ice-margin positions, positions, the slope of of the the outwash outwash plains plains is is relatively relatively steep steep ranging ranging from as high high as as 8.5 8.5 m/km. m/km. InInmore from 2.0 2.0 to 4.0 4.0 mIlan, m/km, but but may may be be locally locally as moredistal distal positions, 1.0m/km. m/km. positions, the the slope slopeisis around around1.0 A A significant significant amount if not most of of the outwash in the the outwash outwash plains plains was was derived derived from from tunnels tunnels underneath underneath the theSuperior Superior Lobe Lobe discharging discharging meitwater meltwater and and plain has has aa fan sediment. sediment. In In several several places places in in the the county, county, the the outwash outwash plain fan shape shape at at former with the the mouths of former ice-margin ice-margin positions whose apex is coincident coincident with of a tunnel tunnel valley valley or or an anesker. esker. ItIt isis clear clear in in these these cases cases that that the the tunnel tunnel system system underneath underneath the the ice, ice, now indicated indicated by the the tunnel tunnel valleys valleys and eskers, was the source for the sediment that outwashplain. plain. that composes composes the the outwash Spooner Hills (Stop SpoonerHills Hillsrefer referto to aa line line of of hills of (Stov 1-1O).--The 1-I@.-The Spooner of high relief relief These hills are distinct from any other that 1-7). These hills are distinct from any other that contain containunlithified unlithifiedsediment sediment(Fig. (Fig.1-7). landform landform in the the field field trip trip area areaand andrepresent represent aalandform landform type typenot notcommonly commonly described described in inglaciated glaciatedregions. regions. I refer refer to to these these hills hills as as the the Spooner Spooner Hills Hills after after the the village of the band of village of of Spooner, Spooner, Wisconsin, Wisconsin, which lies in the center of of hills. hills. The The Spooner Spooner Hills range in area area from 11 to 55 km2 km2 and exhibit relief relief as high as 60 but a number 60 m. The TheSpooner SpoonerHills Hills are areroughly roughly equidimensional, equidimensional, but number of of them them are are elongate elongate to to the the southeast southeast parallel parallel to tothe thedirection directionof of regional regional ice ice flow, flow, suggesting suggesting that that they they may mayhave havebeen beensomewhat somewhatstreamlined. streamlined.Hill-top Hill-top elevations elevations in in the the Spooner Spooner Hills Hills generally generally increase increase from from the the northwest northwesttotothe thesoutheast southeast(Fig. (Fig.1-7). 1-7). 15 1 �Based on on this information, the following hypothesisisis offered offered as as an Based information, the following hypothesis explanation Because the the hills hills contain a explanation for the the formation formation of of the theSpooner Spooner Hills. Hills. Because of sediment types representing a variety of depositional environments, and variety of because because the sediment may may predate the most most recent glaciation, glaciation, itit is likely likely that the the Spooner Hills are lines of of evidence evidence suggest suggest that the are erosional erosional features. features. Several Several lines the erosion occurred subglacially. subglacially. The The Spooner Spooner Hills are commonly commonly covered with the the till of till of the the most most recent recent glaciation glaciation and are are somewhat somewhat streamlined streamlined in aa direction direction parallel to the the regional regionalice-flow ice-flow direction direction of of the the most most recent recentglaciation. glaciation. In addition, the orientation of the the band band of of the the Spooner Spooner Hills Hills parallels parallels the the St. St. Croix Croix ice ice margin margin valleys form a branching suggesting that they are suggesting are related. related. The inter-hill valleys branching network network that, in some some places, places, connects up with with prominent prominenttunnel tunnelvalleys. valleys. It is suggested suggested that these valleys by subglacial meltwater and and the these valleys were excavated excavated by subglacial meltwater the tunnel tunnel valleys valleys represent the outlets for meitwater meltwater and sediment. However, However, this this connection connection cannot be shown The water water and be shown convincingly convincingly along the the entire entire Spooner Spooner Hills Hills chain. chain. The and sediment was released sediment was released at the the glacier glacier margin margin and and the the sediment sediment was was deposited deposited proglacially in large outwash fans and outwash proglacially outwash plains. In this scenario, scenario, the Spooner Hills would have formed formed when the the ice ice was at at the the St. St. Croix Croix ice margin or the the Tiger Tiger Cat-McKinley ice margin margin(Fig. (Fig.1-6). 1-6). in the Midwest similar to Two published descriptions of landforms elsewhere in the Spooner Spooner Hills support the the suggestion suggestion that that subglacial subglacial meltwater meltwater erosion erosion may may Clayton (1986) (1986)describes describestill till ridges ridges in in Portage have created have created them. them. Clayton Portage County, County, Wisconsin, that that have have similar similar characteristics characteristicstotothe theSpooner SpoonerHills. Hills. He He suggests that Wisconsin, they In the they may may have have been been cut cutby bysubglacial subglacialmeltwater. meltwater. In the Puget Puget Lowland, Lowland, Washington, hills hills occur occur that that have have a size and shape Washington, shape similar similar to to the the Spooner Spooner Hills Hills (Booth and and Hallet, Hallet, 1993). 1993). The hills hills in in the the Puget Lowland Lowland occur occur among among channels that (Booth have been interpreted interpretedas ascut cutby by subglacial subglacialmeltwater. meltwater. V. fill discussed discussed on this V. Types of till this field field trip. trip. The of the glacial The interpretation interpretation of glacial landscape landscape requires requires that the the sediment sediment composing landforms be interpreted as as well. well. The The following following list list describes describes the the basic basic of lodgement till, till, melt-out melt-out till, till, flow flow till, till, and and deforming bed sediment. characteristics of sediment. All of of these sediment types may poorly sorted, pebbly), but All may look look similar similar (massive, poorly subtle differences allow interpretation interpretation in in some some places. places. Lodgement till.--Lodgement till till is is deposited deposited by by plastering of of glacial glacial debris from the JnfiOL-till.-Lodgement sliding base base of sliding of aa moving moving glacier glacier by pressure pressure melting melting and/or and/or other othermechanical mechanical processes (Dreimanis, (Dreimanis,1989), 1989), and and is is characterized characterizedby: by: 16 �I Laterally and and vertically vertically consistent consiste orientation of fabric elements, structures, and surface marks on on clasts. clasts. a.. parallel parallel striae striae on on lodged lodged clasts dusts b.. parallel parallel a-axes a-axes of pebbles c.. sediment smudges, thrust shear planes, and fissility showing shear thrust structures, str 2. 2. Comminution producing producing bi-modal grain-size with terminal modes in silt silt size. size. 3. Materials of local derivation nearer the base of the till. till. 4. Overconsolidated. Overconsolidated. of end moraines. 5. 5. Occurs in ground moraine, moraine, flutes, drumlins, proximal sides of Melt-out till.-t&- Melt-out till is deposited by a slow release of of glacial debris from ice that is and is characterized by: is not not sliding slidingor ordeforming deforminginternally internally(Dreimanis, (Dreimanis,1989), 1989), and 1. 1. Debris banding from ice preserved but with gradational contacts and flattening flattening of of structures. structures. Melt-out Melt-out till may may be be massive. massive. 2. 2. Clasts of unlithified material may be present. flow, but but may may be be transverse. transverse. Dip Dip of of pebbles pebbles is is upup3. Clasts aligned parallel to glacier glacier flow, 1. 1. Laterally I I I but lessened ice ice but lessened by by loss loss of of ice. ice. I I I I I i I I i 4. Grain-size may be coarser than lodgement till, till, and grain-size distribution may be more variable. variable. Striated clasts present, but 5. 5. Striated but faceted faceted clasts clasts are rare. 6. Draping Draping of of layers layersover over clasts clasts as as interstitial interstitialice ice is is lost. lost. 7. 7. Winnowing of fine particles and redeposition, perhaps as coats around around clasts. clasts. Sorted sediment sediment deposited deposited in 8. Lenses and veins veins of of sorted sorted sediment sediment cased cased in in till. till. Sorted englacial tubes. tubes. englacial 9. Normal consolidation. consolidation. 10. Associated with stagnant stagnant ice ice landforms. Flow till.--Flow till.--Flow tills tills (broadly (broadly speaking) speaking)may mayderive derivefrom fromany any glacial glacialdebris debris upon upon its Flow release from glacier ice or from a freshly glacier ice freshly deposited till, in direct direct association association with glacier ice. The The redeposition redeposition isis accomplished accomplished by gravitational gravitational slope process, mainly by gravity gravity flow, flow, or or by by squeeze squeeze flow, flow, and and ititmay maytake takeplace placeice-marginally, ice-marginally, supraglacially, or subglacially, 1989), subglacially, and and subaerially subaerially or or subaquatically subaquatically(Dreimanis, (Dreimanis,1989), and and is is characterized characterized by: by: Lithology (color, (color, grain-size, grain-size, mineralogy) mineralogy)inherited inheritedfrom fromparent parent ice ice (so (some sorting 1. 1. Lithology during flow). flow). 2. Common stratification and and interbedding with water-sorted sediments. 2. Depending on grain size sorting, grading grading (inverse or or normal) normal) 3. Depending 3. siz and water er content, sorting, may occur. occur. 17 17 �4. Fabric Fabric determined determined by (local slopes) slopes)and and stresses stresses are are low, low, producing producing 4. by local local stresses stresses (local random to to strong strong fabric fabric with with maxima maxima parallel parallel to transverse transverse stress stress orientation orientation (not (not ice flow). flow). 5. 5. Normally consolidated. consolidated. Deforming bed sediment.--Deforming bed sediment sediment forms forms under under aa sliding, -Deforming bed sliding, wetwetbased glacier. The is transmitted to the bed, causing based The glacier's glacier's basal basal shear stress is causing bed deformation. The thickness thickness ofof this this deforming layer is is hotly deformation. The deforming layer hotly debated debated among among glaciologists and and glacial geologists: is it centimeters glaciologists geologists: is centimeters or meters? meters? Deforming bed sediment ostensibly ostensibly has has the as lodgement sediment the same same characteristics characteristics as lodgement till, till, although although some some suggest that that deforming deforming bed bed sediment sediment has has a weak pebble authors (i.e., Hart, 1994) 1994) suggest pebble fabric. .. VI. Contrasts in glacial landforms landforms VI. One of of themes of this field field trip trip is to point out and discuss themes of discuss the variations variations in morphology of glacial deposits in the the terminus terminus region region of of the the Superior SuperiorLobe. Lobe. Emerald Phase Few hummocks Few collapse depressions No tunnel valleys valleys or eskers eskers No mappable outwash outwash plains plains Integrated, dendritic dendritic drainage drainage No drumlins(?) drumlins(?) St. Croix Phase and and- later phases 1 Many hummocks and ice-walled-lake ice-walled-lake plains plains behind multiple multiple ice-margin ice-margin positions positions Many collapse depressions Many tunnel valleys, some with with eskers, eskers, as well as as the the Spooner Spooner Hills Hills Extensive outwash plains plains Deranged drainage drainage Thrust (?) Thrust features features (?) No drumlins The landforms left behind during the the Emerald Emerald Phase of the Superior Superior Lobe Lobe are distinct from those formed during the St. Croix Croix and and later later phases. phases. Features Features formed formed by by widespread stagnant widespread stagnant ice ice (hummocks (hummocks and and ice-walled-lake ice-walled-lake plains) and extensive extensive discharge eskers, and outwash discharge of of subglacial subglacial meltwater meltwater (tunnel (tunnel valleys, valleys, eskers, outwash plains) plains) dominate left by by the the St. Croix Phase, Phase,but but are are absent absent or or rare rare in the dominate the landscape landscape left St. Croix landscape landscape left by the the Emerald Emerald Phase. Phase. I interpret interpret these phases to to have have occurred occurred during the the last last part partofofthe theWisconsinan Wisconsinan Glaciation Glaciation and that the the difference difference in in the the landform landform suites suites is is due due to to aachange changein incharacter character of of the the Superior Superior Lobe at the the beginning of the St. Superior Lobe changed from a cold, cold, nonSt. Croix Croix Phase. Phase. I suggest that the Superior 18 �[ "1 fl glacier during during the Emerald Phase, to to aa less less cold, cold, surging surging glacier glacier during during the surging glacier Emerald Phase, St. Croix Phase. The landforms of above), the the thin thin to patchy cover of of the Emerald Phase (listed above), of till deposited the till deposited during during the the Emerald Emerald Phase, Phase, and and the the presence presence of of well-developed well-developed permafrost features suggest suggest that that climate dimate during the Emerald Emerald Phase was colder than during the the St. St. Croix Croix Phase. Phase. The Theabsence absence of of tunnel tunnel valleys valleys indicates indicates less less subglacial subglacial meltwater present present during prevented meltwater during this this phase, phase, perhaps perhaps because because cold cold conditions conditions prevented meltwater from from draining draining through through the the glacier to the Meltwater formed meltwater glacier to the bed. bed. Meltwater formed flowed, for for the the most most part, part, over over dean clean ice ice and and had had a low predominantly supraglacially flowed, sediment load. Ice Iceflowed flowedinto intopre-Emerald-Phase pre-Emerald-Phase river valleys, which later became collapse depressions depressions when when warming warming allowed allowedburied buried ice iceto tomelt. melt. Following retreat retreat of of collapse the ice margin, conditions helped helped to to allow allow rapid rapid development of a the margin, permafrost permafrost conditions development of In part, part, the dendritic drainage drainage network much surface surface till till was was eroded. eroded. In dendritic network and likely much drainage network may have drainage have been been inherited inherited from from the the pre-Emerald-Phase pre-Emerald-Phase surface because it would not have been deeply buried by Poskin till. till. (Though (Though II suggest suggest that that because cold conditions, conditions, they they may may also also imply imply that that the Emerald Emerald Phase these features indicate cold did not last last long.) long.) During the St. subglacial drainage drainage of of the Superior During St. Croix Phase, large-scale large-scale subglacial Lobe began began and and formed formed tunnel tunnel valleys valleys and and eskers. eskers. As mentioned earlier, much much of of Lobe mentioned earlier, the meltwater stream sediment in in the outwash plains of western Wisconsin can be be Wisconsin can Additionally,the theSpooner SpoonerHills Hillsare arethought thought to to be be traced to tunnel-valley tunnel-valley mouths. mouths. Additionally, the result of erosion by subglacial meltwater. The meltwater subglacial meltwater. The increase in subglacial meltwater features is accompanied by the presence of of widespread stagnant stagnant ice ice features. features. suggestthat thatthe the Superior SuperiorLobe Lobesurged surged during during the the Johnson and Savina (1987) (1987) suggest St. Croix Croix and and later phases, and Clayton suggest that that many lobes of of Clayton and others others (1985) (1985) suggest Increased subglacial subglacial discharge discharge of of meltwater meltwater is the Laurentide Ice Ice Sheet Sheet surged. surged. Increased associated with surging (Kamb and others, 1985), and surging surging can leave large 1985), and large associated with (Kamb and Clapperton amounts of stagnant ice ice that that melts melts to toform formhummocks hummocks (Wright, (Wright, 1980). 1980). Clapperton (1975)suggests suggeststhat that large large amounts amounts of of debris debris are are frozen frozen on on to to the base of of the glacier (1975) surging. AA thick, layer in in aa mass mass of of stagnant stagnant ice ice would would during surging. thick, basal, basal, debris-rich debris-rich layer Surging isis aa periodic produce high-relief like those in Polk produce high-relief hummocks hummocks like Polk County. County. Surging behavior of of glaciers glaciers and and the size and geometry of the the tunnel valleys indicate that that behavior geometry of valleys indicate they operated only for a short time, and that they were not all operating at the same time (Attig and other, other, 1989; 1989; Patterson, personal communication). On the other On other hand, hand, the the hummocks hummocks may may simply simply indicate indicate cold cold conditions conditions rather than surging. Many are produced produced by by nonnonrather Many authors authors suggest suggest that hummocks hummocks are 19 �temperate glaciers temperate glaciers (glaciers (glaciers with with ice ice colder colder than than0°C) O°C(Boulton, (Boulton,1972; 1972; Paul, Paul, 1983; 1983; Mäller, 1987; Sollid and and Sørbel, Attig and Moller, 1987; Sollid Sorbel, 1988; 1988; Attig and others, others,1989; 1989;Mooers, Mooers, 1990). 1990). These These the process process of of meltwater meltwater generation generation where where the the bed bed is at 0°C authors describe, describe the P C and the subsequent freezing-on of of debris at the base of the glacier glacier as the the meltwater meltwatermoves moves subglacially towards towards the margin and ertcounters ice colder colder than than 0%. 0°C. This This process process subglacially encounters ice produces aa thick, zone. The produces thick, basal, basal, debris-rich debris-rich zone. The margin margin of of the the cold cold glacier glacier stagnates stagnates during melting and the melting of the debris-rich ice produces hummoclcy during melting and the melting of the debris-rich ice produces hummocky topography. Evidence of permafrost permafrost in in western suggests that that the topography. Evidence of western Wisconsin Wisconsin suggests the hummocks may may simply indicate a non-temperate glacier, and and not necessarily hummocks simply indicate non-temperate glacier, necessarily aa surging glacier. surging glacier. It is not the water water that cut not clear clear in in western western Wisconsin Wisconsin ifif the cut the the tunnel tunnel valleys valleys was melted from from the the bed or or from from the the surface surface of the the glacier. glacier. Wright Wright(1973) (1973) states that that tunnel valleys valleys formed under under the theSuperior SuperiorLobe Lobe because because subglacial subglacial meitwater meltwater was was held by aa frozen frozen margin margin of of the the glacier. glacier. Mooers Mooers(1989) (1989) argues that the Superior Superior Lobe Lobe was temperate and that that the the tunnel tunnel valleys valleys indicate indicate meltwater from the surface surface of of Gustavsonand andBoothroyd Boothroyd(1987) (1987) document document aa the glacier reaching the glacier glacier bed. Gustavson surficial source for subglacial tneltwater meltwater on on the the temperate temperateMalaspina MalaspinaGlacier, Glacier,Alaska. Alaska. The presence of ice-wedge casts behind behind the St. Croix limit in The presence of ice-wedge casts Croix Phase ice-margin ice-margin limit Wisconsin suggests suggests that that the ice surface would would have been well below below 00C and that 0OC and Wisconsin little surface meltwater would make it to to the the glacier glacier bed. However, cold conditions conditions were present when no no or few were present during the the Emerald Emerald Phase Phase when few tunnel tunnel valleys valleys were were formed. I suggest that that the the climate climate supported supported permafrost permafrost conditions conditions during both both the the Emerald and St. St. Croix Croix Phases, Phases, but was was gradually gradually getting gettingwarmer. warmer.Ice-wedge Ice-wedgecasts casts outside the Emerald outside Emerald Phase Phase ice-margin ice-margin limit are are numerous numerous and and well-developed well-developed (Johnson, 1986),whereas whereas those those behind behind the St. Croix Phase ice-margin limit limit are are few few (Johnson, 1986), During the St. Croix and less less well well developed. developed. During Croix Phase, even though though permafrost permafrost conditions were present, present, surface surface meltwater began to find pathways pathwaysto tothe theglacier glacierbed. bed. of increased water at the bed caused the lobe to surge, tunnel The presence of tunnel valleys valleys to to form, and left widespread widespread stagnant stagnantice. ice. VII. Bibliographic information VII. Bibliographic information on on the the glacial glacial geology geology of western western Wisconsin Wisconsin foraa north-south north-south band of The St. Croix moraine was named by Berkey Berkey (1897) (1897) for of occurring immediately immediately east east of of the town hummocks occurring town of of St. St.Croix Croix Falls, Falls, Wisconsin. Wisconsin. However, the the first comprehensive mapping and and description description of of the St. However, comprehensive mapping St. Croix Croix moraine and associated associated deposits deposits was was that that of ofStrong Strong(1880) (1880) and and T.C. T.C. Chamberlin Chamberlin 20 �•• I I fl I I I (1883). (1932)transferred transferredthe thename nametotoapply applyto to the the hummocky hummocky deposits deposits that that (1883). Leverett (1932) marked the Wright and Ruhe marked the edge edge of of the theSuperior Superior Lobe Lobe in in western western Wisconsin. Wisconsin. Wright (1965) called called the the event event that made these features the the St. St. Croix Phase. Along the St. Croix Phase Phase deposits deposits in Wisconsin, Wisconsin, aa number number of of geologists have have Along made several somewhat dissimilar interpretations ofof the the position position and and nature of the dissimilar interpretations St. Croix Croix ice-margin ice-margin position position(Chamberlin, (Chamberlin, 1905, 1905, 1910; 1910; Leverett, 1932; 1932; Mathieson, 1940; Black, Black, 1959; 1959;Berg, Berg, 1960; 1960;Wright, Wright,1972; 1972;Wright Wrightand and others, 1973; Johnson, 1986; 1973; Johnson, 1986; Johnson and Refinementsinin the the stratigraphy have Johnson and Savina, Savina,1987; 1987;Mooers, Mooers,1989). 1989). Refinements been made by by Baker Baker and andothers others(1983), (1983),Mickelson Mickelson and andothers others(1984), (1984),Johnson Johnson(1986; (1986; in press), The history history of press), and and Attig Attig and andothers others(1988). (1988). The of the glacier-dammed glacier-dammed lakes lakes (glacial Lake Lind and glacial glaaal Lake Grantsburg) occupying the St. Croix, Clam, and Yellow River drainage basins has has been been discussed discussed by by several severalworkers workers(Berkey, (Berkey,1905; 1905; Hansell, 1930; Johnson, 1992, 1994; Addis Addis 1930; Burkhead, Burkhead, 1931; 1931; Butz, Butz, 1931; 1931; Cooper, 1935; Johnson, and glacial period and others, 1996). A A regional regional understanding of of the details of of the last glacial has has been enhanced enhanced by by large-scale large-scale geologic geologic mapping of of Pleistocene Pleistocene deposits in the the Lake Superior Barron 1985), Barren Superior region region (Clayton, (Clayton, 1984), 1984), the Twin Cities region (Meyer, 1985), County, Hennepin County, County, Minnesota Minnesota (Meyer (Meyer and County, Wisconsin Wisconsin (Johnson, 1986), 1986), Hennepin Hobbs, 1989), Dakota County, County, Minnesota Minnesota (Hobbs (Hobbs and others, 1990), 1989), Dakota 1990), Washington Ramsey County, Minnesota (Patterson, County, Minnesota (Meyer (Meyer and and others, others, 1990), 1990), Ramsey 1992), and and Polk County, County, Wisconsin (Johnson, in press). VIII. References References cited Aario, R. ,1977, ,1977,Classification Classificationand andterminology terminologyofofmorainic morainiclandforms landformsininFinland: Finland: Boreas, Boreas, v. v. 6, 6, p. 87100. 100. 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Stop and Stop Stop 1-1 1-1and Stop1-2 1-2 St S t.Croix Croix Phase outwash outwash plain, plain, distal distal site site and and St. St. Croix Croix Phase outwash fan, proximal, ice-marginal ice-marginal site site Quadrangle: Haugen Haugen Quadrangle, Quadrangle,Wisconsin, Wisconsin, 7.5 7.5 minute minute series, series,sec. sec. 18, 18, T. T. 36 36 N., N., R. R. 11 W., sec. 13, T. T. 36 36 N., N., R R. 12 12W. 1 1W., W. Significance: These These stops stops show the character of sediment deposited by braided, character of braided, outwash streams, both immediately immediately next to a former former ice-margin position, as well as further away. away. Description: Lobe outwash outwash is probably the most common sediment Description: Superior Lobe sediment facies facies western and consists consists primarily primarily ofof sand, sand, slightly slightly gravelly gravelly sand, sand, and western Wisconsin Wisconsin and gravelly sand, with much much of of the the gravel gravel in in the thepebble pebblefraction. fraction. Stream sediment deposited within within 11km km of of former formerice-margin ice-margin positions positions is is commonly commonly much much coarser coarser and contains cobbly boulders. This This coarser coarser facies facies of of Copper Copper cobbly gravel with occasional boulders. Falls stream sediment is crudely horizontally horizontallybedded bedded and and is is more more poorly poorly sorted than stream sediment deposited in more distal positions. positions. Further Further away away from from former former iceicemargin positions, positions, the the stream stream sediment sediment is is dominated dominated by by sand in horizontal horizontal and and cross-bedded cross-bedded layers. layers. Gravel Gravel in the outwash, outwash, as as well well as as Superior Superior Lobe Lobe till, is composed primarily of of basalt, gabbro, granite, gneiss, rhyolite, rhyolite, and and sandstone. This This assemblage assemblage is typical typical of sediment sediment derived derived from from the theLake Lake Superior Superior basin. basin. proximal site is located on an outwash The proximal outwash fan fan associated associated with the the tunnel tunnel valley in which which Bear Bear Lake Lake lies. lies. It is suggested that all the outwash in this this outwash outwash plain emanated from from the the tunnel-valley tunnel-valley mouth at at Haugen. Haugen. Questions: Are rapid deposition? deposition? What Arethere thereany anyfeatures features present present here that suggest rapid would a catastrophic catastrophic deposit deposit look look like? like? Mileage from from Stop Stop1-2 1-2to to Stop Stop 1-3: 1-3:15 15 miles miles Stop 1-3 1-3 Stop Barron County hummock Barren hummock sites sites Quadrangle: Lower LowerVermillion VermillionLake LakeQuadrangle, Quadrangle,Wisconsin, Wisconsin, 7.5-minute 7.5-minute Series, Series, T. 36 N., R. R.13 13W. Significance: (1) Discussion of of the the occurrence of of melt-out till in hummocks (1)Discussion hummocks and and(2) (2) contrast between the landforms of the Emerald and St. Croix Phases. 1 25 �Description: Uniform Uniformdiamicton diamictonisisexposed exposed in infive fivehummocks hummocks in in northwestern northwestern Barron County exposures are are Barren County (sites (sites8, 8,9,9,10, 10,12, 12,13, 13,Figs. Figs. 1-8, 1-8,1-9). 1-9). In all cases, the exposures small and only pebble fabric fabric at these sites is strong only uniform uniform till till isis revealed. revealed. The pebble strong (Si=0.72, (1979) for melt(Si=O.72 0.80, 0.80, 0.74,0.72,0.85) 0.74, 0.72, 0.85)and andsimilar similartotothose thosereported reported by by Lawson (1979) out till till and and by byDowdeswell Dowdeswell and andSharp Sharp(1986) (1986) for melt-out melt-out till till and and undeformed undeformed lodgement till. Additionally,the the major major mode mode in in each each fabric fabric isis parallel parallel to the till. Additionally, the regional ice-flow direction as as determined determined by by local local striations striations and and the orientation of ice-flow direction of the nearby nearby ice-margin ice-margin position position (Fig. (Fig. 1-9). At At site site 12 12 (Fig. (Fig. 1-8), aa drill revealed 20 20 drill hole revealed m of of diamicton diamicton with with uniform uniform grain grain size size and anduniform uniform relative relativemagnetic magnetic beneath the base of of the surface surface exposure. exposure. Though these sites susceptibility beneath sites were were not not well-enough exposed to to investigate other structures well-enough exposed investigate other structures and contacts, contacts, the the strongly strongly oriented oriented pebble fabric parallel parallel to the the regional regional ice-flow ice-flow direction direction indicates indicates the diamicton is likely likely melt-out melt-out till. till. As discussed As discussed in the the text, text, features features formed formed by by widespread widespread stagnant stagnant ice ice (hummocks and ice-walled-lake plains) and extensive (hummocks and ice-walled-lake plains) extensive discharge discharge of of subglacial subglacial meitwater (tunnel valleys, valleys, eskers, eskers, and and outwash outwash plains) plains) dominant dominant the landscape left meltwater by the St. in the the landscape landscape left left by by the theEmerald Emerald St. Croix Phase, but are absent or rare rare in Phase. I have interpreted this Phase. this change change to represent a change change in ice dynamics, from a non-surging glacier cold, non-surging glacier to aa less-cold, surging glacier. See See text text for for discussion. discussion. Questions: Is it possible possible for for supraglacial supraglacial melt-out melt-out till to to survive survive collapse? collapse? Is it merely chance that till fabrics fabrics in hummocks are strong and parallel parallel to to regional regional iceiceflow direction? Do Do the thechanges changesseen seen from from the the Emerald Emerald to to St. Croix Phases represent changes in erosion erosion (and thus age)? changes in ice ice dynamics? dynamics? or merely merely differences differences in age)? Is it possible for supraglacial meltwater to ppenetrate through the thickness ckness of the the glacier glacier if if permafrost conditions conditions are are present? present? Mileage 16 miles from Stop Stop1-3 1-3 to Stop Stop 14: 14.16 Mileage from Stop 1-4 Stop 1-4 McKinley McKinley ice-walled-lake ice-walled-lake plain plain Quadrangle: McKinley, T.36 36N., N., R. R. 14 14W. W. Quadrangle: McKinley,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,sec. sec.31, 31,T. Significance: One Significance: Oneof of the thelargest largestice-walled-lake ice-walled-lake plains in in western western Wisconsin. Wisconsin. km2 and is is one one of of the the Description: The TheMcKinley McKinley ice-walled-lake ice-walled-lake plain is about about 77 km2 largest ice-walled-lake plains in western western Wisconsin Wisconsin (Fig. 1-8). About About 40 40 ice-walledice-walledlake plains occur in the the terminus terminus region region of of the the Superior Superior Lobe Lobe in in western western Wisconsin, Wisconsin, and another another 20 20 to to 30 30 occur occur in in the the continuation continuation of of these these deposits deposits in in Minnesota. Minnesota. Nearly of them occur in hummocky hummocky tracts, Nearly all of tracts, suggesting suggesting that that their their origin is related 26 �I I I I I I I I I I I the origin plains in in the the study study area to the to origin of of the the hummocks. hummocks. Ice-walled-lake Ice-walled-lake plains area range range in in size size from 1 to 13 km2, with a typical size around 2 km2. Ice-walled-lake plains from 1 to 13 km2, with a typical size around 2 km2. Ice-walled-lake plains commonly have a rim around their their margin margin that stands stands 33 to to 10 10 m m above above the the center center of of the the lake lake plain. plain. StreamStream-and andwave-sorted wave-sorted sand sand and and gravel gravel occur occur along along the the margins margins of of the lakes. In In places, places, the the rim rim sediment sediment is is interbedded interbedded with with till till that that flowed flowed the ice-walled ice-walled lakes. from adjacent ice ice into the lake. Coarse Coarse sediment sediment is restricted to the margins margins of the the lake plain; much lake plain; much of of the the interior interior portions portions are are underlain underlain by by silt. silt. Drill Drill holes holes at at Stop Stop 55 encountered encountered 20 20 m m of of silt siltoverlying overlyingSuperior SuperiorLobe Lobe till. till. The ice-walled-lake plains plains occur at elevations similar to those of the surrounding hummocks. The rim ridges occur at elevations similar to those of the surrounding hummocks. The rim ridges of the ice-walled-lake ice-walled-lake plains are approximately the same elevation or slightly slightly lower lower than the the tops topsof of hummocks hummocksadjacent adjacent to to the the lake lakeplain. plain. Ice-walled-lake described elsewhere may may occur in hummock tracts, Ice-walled-lake sediment described tracts, but within apparently ice ice was was thin thin enough enough that that the open within the the Southeastern Southeastern Sector, Sector, apparently water was able able to to melt melt entirely entirely through through the the stagnant stagnantice, ice, leaving leaving nicely nicely preserved preserved ice-walled-lake plains. plains. Questions: What is the relationship relationship of of permafrost permafrost to to the the ice-walled-lake ice-walled-lake plains? plains? Do Do the ice-walled-lake plains indicate indicate that that the the hummocks must be the ice-walled-lake plains hummocks must be stagnant stagnant ice ice What was the source of sediment for the ice-walled-lake plains? What do features? features? source ice-walled-lake plains? What do they indicate about sediment sediment distribution distribution in in the the ice? ice? Mileage (optional): 10 Mileage from from Stop Stop1-4 1-4to Stop Stop 1-5 1-5(optional): 10 miles miles Mileage Mileage from from Stop Stop1-4 1-4to Stop Stop 1-6: 1-6:16 16 miles miles 1-5 (optional) (optional) Stop 1-5 Turtle Turtle Lake ice-walled-lake plain delta Quadrangle: 7.5 minute minuteseries, series,sec. sec.6,6,T. T. 33 33N., N.,R. R. 14 14W. W. Quadrangle: Clayton, Clayton, Wisconsin, Wisconsin, 7.5 Significance: An Anexposure exposureof of aadelta deltathat thatprograded progradedinto intothe theTurtle TurtleLake Lakeice-walledice-walledSignificance: lake lake plain. 1-5to to Stop Stop 1-6: 1-6:23 23 miles Mileage from from Stop Stop1-5 Stop 1-6 Stop 1-6 Eskedahl tunnel valley and esker esker Big Round Lake, Wisconsin, 7.5 minute series, sec. sec. 28, 28, T. 36 N., R. R. 16 16 Quadrangle: Big Wisconsin, 7.5 w. Significance: Significance: A good example of of a tunnel valley with an an esker esker Description: The TheEskedahi Eskedahltunnel tunnelvalley valley and andesker eskerisis25 25 km km long long and and 0.5 0.5 to to 0.8 0.8 km krn relief of of the from the the bottom bottom ofof one one of of the lakes wide. The The relief the valley valley from lakes to to the the 27 �surrounding plain is is about about 25 25 m; the top top of of the the esker esker is is almost almost everywhere everywhere several several meters below below the top of the surrounding surrounding plain. plain. Many tunnel valleys end in an outwash fan, but the Many valleys end the Eskedahi Eskedahl tunnel tunnel valley valley with no no apparent apparent outwash outwash fan. fan. Tunnel Tunnel valleys valleys and esker ends in in Big Big Round Lake Lake with deeply buried buried by by outwash outwash tend tend to lose their straight shape and that later become become deeply and collapse into bulbous, elongate collapse elongate lakes, like Bone Bone Lake Lake or Big Big Round Lake. Lake. Very coarse outwash outwash occurs occurs at the head of Creek outwash outwash plain, plain, and it is coarse of the Fox Creek is likely likely that the tunnel tunnel valley valley fed fed the the Fox Fox Creek Creek outwash outwash plain. plain. of road cuts occur in the esker here and little is revealed about Only a couple of about of predominantly predominantly sand. the internal composition of of this esker. One outcrop consists of Questions: Does Doesthe thegeometry geometryof of the the tunnel tunnel valley valley and and esker esker indicate indicate the levels of of discharge? Or marking 'the meandering tunnel with the esker marking discharge? Or is is the the valley valley cut cut by a meandering last' position of of the tunnel? What last' What was was the the sources sources of of water? water? Does Does this this geometry geometry require a frozen frozen toe? toe? Mileage 1-6to to Stop Stop1-7: 1-7: 13 13miles miles Mileage from from Stop Stop1-6 Stop 1-7 1-7 Stop Erickson striations striations and and grooves grooves 7.5 minute minute series, SW1/4 SW1/4 sec. Quadrangle: Milltown, Wisconsin, Wisconsin, 7.5 sec. 11, 11,T. T.36 36 N., R. 18 18 W. w. Significance: Striations and Nye channels cut into basalt that Significance: that indicate indicate two two ice-flow ice-flow directions and and two twodifferent differentglacier-bed glacier-bed conditions. conditions. Description: Description: At Atthis thissite, site,broad, broad,shallow shallowgrooves grooves are are present present that that are are oriented oriented NENESW. These SW. These are are cut cutby byyounger youngerstriations striationsthat thatshow showice-flow ice-flowtotothe theSE SE(Fig. (Fig.1-10). 1-10). of basalt basalt in this area show a similar pattern, with the grooves, Numerous outcrops of grooves, interpreted to be interpreted be Nye Nye channels, channels, consistently consistently showing showing ice-flow ice-flow to the the SW. SW. The The and are likely cut by grooves resemble those described by Walder and and Mallet Hallet (1979) and subglacial meltwater. The striations within the grooves were cut by ice ice flowing flowing into into the grooves. grooves. We postulate postulate that the We the grooves grooves form during surges surges when when the the Superior Superior Lobe Lobe exhibited plug flow flow and and flowed flowed directly directly to to the the SW. SW. The Theexcess excess amount amountof of subglacial subglacial water present during during surging surging would have have cut cut the grooves. grooves. When surging stopped, a normal ice ice profile profile developed developed and and ice flowed flowed laterally laterally towards towards the the margins (to the normal SE). SE). Questions: Can Questions: Canice iceform formthese these grooves grooves or is water necessary? necessary? Is it possible possible that the grooves are are pre-Late-Wisconsinan? pre-Late-Wisconsinan? 28 �I LI Figure Figure1-10.-1-10.- Striations Striations and and grooves groovesin in Folk Polk County. County. Double Double arrows arrows== grooves; grooves; single single arrows striations. A: A: Orientation Orientation of grooves and striations showing showing ice ice flow flow to to the the arrows== striations. southwest places, southwestInInmost most places,cross-cutting aoss-cuttingrelationships relationshipswere wereapparent apparentand andalways alwaysshow show striations shown in B. 3. Striations inthis thisorientation orientation to be older than those shown Striationsat at striationsand andgrooves groovesin X are striations and crag-and-tail striations atop Eagle Peak and Observation Rock in X are striations and aag-and-tail striations atop Eagle and Observation Rock in Interstate C:Striations Striations Prominentsoutheast southeaststriations striationswith withsome somegrooves. erooves.C: InterstateState StatePark. Park. B:B:Prominent showing easterly flow and Pine City and Centuria ice-margin positions. The group showing easterly flow and Pine City and Centuria ice-margin positions. The groupat atZZ are are interpreted interpreted to tohave havebeen been cut cut by by the the Superior Superior Lobe Lobe but later than striations striations at the the same explanation. The group at Y was interpreted by same site site shown shown in in B. B. See See text for explanation. by Chamberlin Chamberlin(1905) (1905)to to have have been been formed formed by by the the Grantsburg GrantsburgSublobe. Sublobe. 29 �Mileage Mileage from from Stop Stop1-7 1-7to to Stop Stop 1-8: 1-8: 99 miles miles Stop 1-8 Stop 1-8 Frederic esker and fan fan Quadrangle: Quadrangle:Frederic, Frederic,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,sec. sec.21, 21,T. T.37 37 N., N., R. R. 17 17 W. Significance: AAprominent prominentesker eskerfeeding feedingan anice-marginal ice-marginaloutwash outwashfan. fan. Description: This Thispit pitcontains containsaacomplicated complicatedsedimentology sedimentology with large variations in grain size. Collapse Collapse features, antiform bedding, and possible possible injection injection features are are present. present. Questions: IfIfthis thisesker eskerisissurrounded surroundedby bycollapse collapsehummocks, hummocks, how how is is the the esker esker form form preserved? IsIs ititpossible possible that that the the antiform antiform bedding is primary? What does does this this esker esker indicate about the nature nature of of the the Superior Superior Lobe? Lobe? What What do doeskers eskersmean? mean? Mileage Mileage from from Stop Stop1-8 1-8to to Stop Stop 1-9: 1-9: 20 20 miles Stop 1-9 Stop 1-9 Searles varve site Quadrangle: Hertel, Quadrangle: Hertel,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,SW1/4 SW1/4NE1/4 NE1/4sec sec15, 15,T. T.38 38 N., N., R. R. 15 W. W. Significance: Proglacial Proglaciallake lakesediments sedimentsand and melting-out melting-out of of stagnant stagnantice ice Description: Description: This Thissandpit sandpitcontains containsaared, red,sandy sandySuperior SuperiorLobe Lobe till till that that is is overlain overlain by a coarsening coarsening upward upward sequence sequenceof of varved varved lake lakesediment. sediment. This This sequence sequence is is overlain overlainby by fluvial pebbly pebbly sand sand that is part of of an an outwash outwash plain plain that that grades grades to to the theHertel Herteliceicemargin position 3 km to the north. north. The Superior Lobe Lobe till, till, occurring occurringatatthe thebase baseofofthe thepit pit and and in a large knob in in the center of Lobe till fillfurther furthersouth. south. It is interpreted of the pit, is finer than Superior Lobe interpreted to to represent represent till deposited deposited during during aa readvance readvance of of the the Superior Superior Lobe Lobe during during overall overall retreat at at which which time time the theproglacial proglacial lake lake sediment sediment was was incorporated incorporated into into the theice. ice. Several outcrops of finer Superior Lobe till occur occur throughout the region region (triangles (triangles in in Fig. 1-6) and and suggest that this till may be associated associated with with an ice advance that reached the northernmost northernmost part part of of Polk Polk County. County. As ice retreated from an unnamed unnamed ice ice margin margin 3 km km to to the the south south(Fig. (Fig.1-6), 1-6), aa proglacial lake fronted the The pit pit contains a wonderful coarsening upward the ice. ice. The sequence of varved lake lake sediment. sediment. It is not not clear clear if this this lake lake sediment sediment belongs belongs to to glacial Lake Lake Lind, glacial glacial Lake Lake Grantsburg, or some other ice-marginal lake. If If it is glacial is glacial Lake Lake Grantsburg, Grantsburg, the the sediment sediment contains contains no no sediment sediment derived derived from the glacial the Grantsburg GrantsburgSublobe. Sublobe. 30 �I The 47 winter winter clay clay layers layers 22 to 10 The The varved section contains contains 47 10 mm mm thick. thick. The I I I I I I I I summer layers cm thick, thick, to to layers thicken thicken and and coarsen coarsen upward, upward, from from silty silty layers layers less less than than 11 cm fine-sand, ripple-bedded layers up to 40 crn cm thick. thick. The The varved section section is overlain by horizontally laminated sand sand with with laminations laminations of of segregated segregated heavy heavy minerals minerals(beach (beach fluvial sand. sand. turn overlain overlain by pebbly sand, interpreted to to be be fluvial sand?), which is in turn grades to to the theHertel HerteliceiceThe fluvial sand underlies an outwash plain that grades margin position that roughly 50 position (Fig. (Fig.1-6). 1-6). This This means means that 50 years passed from from the the uncovering of of this spot to the the filling filling in of the lake by sand derived derived from from the the nearby nearby Superior m/yr. Superior Lobe. This This suggests suggests an an ice ice retreat rate of 80 m/yr. The lake sediment is draped over the till knob, knob, but but faults and steeply dipping beds show that aa large large part partof of the therelationship relationship isis due duetotocollapse, collapse,presumably presumably by by melting of buried buried ice. ice. An angular unconformity unconformity in the varve varve sequence sequence indicates indicates progressively while while the the lake lake was was in in existence. existence. The cranberry that collapse occurred progressively bogs to the the south south of of the the pit pitoccur occur in inaalarger largercollapse collapse pit pit that thatindicates indicatesmelting melting of of buried buried ice ice continued continued after after the the lake lakewas wasfilled filled in. in. A possible ice-wedge cast was found at at this this site site in in 1990 1990 in the fluvial fluvial gravel. gravel. Questions: What of buried buried ice? There Whatisisthe therole roleof of lakes lakes in in hastening hastening the melting of There is a lot of detail is detail in in this this pit, pit, what whatelse elsecan can we we learn learn from from this thissequence? sequence? Mileage from Mileage from Stop Stop1-9 1-9 to to Stop Stop1-10: 1-10: 10 10 miles 1-10 Stop Stop 1-10 Spooner Hills The Spooner The Hills Quadrangle: Quadrangle:Timberland, Timberland,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,sec. sec.4,4,T,T.37 37N., N., R. R.14 14W. W. Significance: Significance: A stop in the midst midst of of the the Spooner Spooner Hills, suggested to have been cut by by subglacial meltwater. Description: As discussed in the text, the Spooner Hills is aa name given to this band Description: of hills hills that lie position. Some lie 15 15 to to 25 25 km km behind behind the the St. St. Croix Croix Phase Phase ice-margin position. Some key observations observations include: include: -- the the hills have have an an area areafrom from11to toS5km2, krn2, -- relief as high high as as 60 60 m, m, -- aa number of them are are elongate to the southeast parallel to the direction direction of regional flow, regional ice flow, -- hill-top elevations generally increase increase from from the the northwest northwest to the the southeast, southeast, - inter-hill inter-hill valleys tend to align with tunnel-valleys in places, -- the the hills are composed of a variety variety of unlithified unlithified materials. materials. The hypothesis isis offered offered as as an explanation for the formation The following following hypothesis explanation for formation of of the the - 31 I �S the hills hills contain contain a variety variety of of sediment types representing Spooner Spooner Hills. Hills. Because Because the representing aa variety of depositional depositional environments, environments, and because because the sediment may predate predate the the most recent glaciation, most glaciation, it is likely likely that that the the Spooner Spooner Hills Hills are are erosional erosional features. features. Several lines lines of Several of evidence evidence suggest suggest that the the erosion erosion occurred occurred subglacially. subglacially. The Spooner Hills are commonly covered covered with with the the till till of of the most recent glaciation and are somewhat somewhat streamlined streamlined in in aa direction direction parallel parallel to to the the regional regional ice-flow ice-flow direction direction of of the most recent of the band of the recent glaciation. glaciation. In addition, the orientation of the Spooner Spooner Hills parallels the St. Croix Croix ice ice margin margin suggesting suggestingthat that they they are are related. related. The The interinter- hill valleys that, in some up with hill valleys form a branching branching network network that, some places, places, connects connects up with prominent tunnel valleys. prominent valleys. It is suggested suggested that these these valleys valleys were were excavated excavated by by subglacial meltwater meltwater and the tunnel valleys represent the outlets for meltwater and and sediment. However, sediment. However, this connection connection cannot cannot be shown shown convincingly convincingly along along the the entire Spooner Hills water and sediment Hills chain. chain. The The water sediment was released at the the glacier glacier margin and the in large outwash fans and and margin the sediment sediment was was deposited deposited proglacially proglacially in outwash plains. In In this this scenario, scenario, the Spooner Spooner Hills would have formed formed when when the theice ice was at at the the St. St. Croix Croix ice ice margin marginor orthe theTiger TigerCat-McKinley Cat-McKinley ice margin margin (Fig. (Fig. 1-6). 1-6). We suggest that this type of landform may be more common than presently We recognized in in glacial glacial landscapes. landscapes. Questions: Questions: What Whatare arethe thecritical criticalquestions questionsto toask askto toascertain ascertainthe the origin origin of of these these hills? What of water water needed needed to cut these hills? What is is the the source source of of the the tremendous tremendous amount of these hills? What Whatare areother otherpossible possiblemechanisms mechanisms for for their their origin? origin? miles Mileage to Cable: 45 Mileage from fromStop Stop1-10 1-10 to 45 miles 32 �S I I I I I I I I I I I I OVERVIEW OF THE BEDROCK BEDROCK GEOLOGY GEOLOGY OVERVIEW - AREA, OF - HURLEY OF THE THE CABLE CABLE HURLEY AREA,WISCONSIN WISCONSIN �OVERVIEWOF OF THE ThE BEDROCK OVERVIEW BEDROCK GEOLOGY GEOLOGY OF ThE CABLE-HURLEY AREA, WISCONSIN THE CABLE-HURLEY AREA, by by W.F. Cannon and SW. Nicholson Nicholson W.F. Cannon and S.W. U. S. Geological Geological Survey, Reston, VA 22092 MS 954, Reston, Survey,MS I I I I I I I I I I I I I The area encompassing Field Field Trips Trips 2,4, 2,4, and and 55 is is underlain underlain by by bedrock bedrock ranging ranging in Proterozoic. Rocks of age from Late Archean to Middle Proterozoic. Rocks record three principal cycles cycles of deposition and deformation: volcanism and and sedimentation sedimentation in in Late deposition deformation: 1) submarine submarine volcanism Late Archean time, time, followed by major and granite 2) Archean followed by major deformation deformation and granite emplacement; emplacement; 2) Proterozoic time, time, followed followedby by weak weak to to epicontinental marine sedimentation in Early Early Proterozoic moderate faulting basaltic moderate faulting and and folding folding during duringthe the Penokean Penokean Orogeny; and 3) 3) extension, basaltic volcanism and related intrusions, and continental sedimentation sedimentation in in the Midcontinent volcanism Rift System System in in Middle Middle Proterozoic Proterozoic time, time, followed followedby byinversion inversionand and thrust thrust faulting. Rift Figure 11 shows of the the region, and Figure Figure shows the general general geology geology of region, and Figure 2 2 indicates indicates the approximate location trips 2,4, 2,4, and 5. approximate location of stops for trips GEOLOGY OF ARCHEAN ARCHEAN ROCKS ROCKS GY OF Volcanic and sedimentary rocks of late late Archean Archeanage ageare areexposed exposed in in aa westwardwestwardocks of tapering wedge Mellen, Wisconsin, Wisconsin,forming formingthe thebasement basement directly directly tapering wedge from from Huxley Hurley to near Mellen, rocks. The Thevolcanic volcanicrocks rocksgrade gradesouthward southwardand and westward westward beneath Early Proterozoic rocks. into gneiss and migmatite in a border zone of the Puritan Puritan Batholith, Batholith, a large granitic intrusion emplaced and others, 1977). West of of Mellen, volcanic volcanic intrusion emplaced at atabout about2750 2750 Ma (Sims and rocks are unknown and Early rocks rest rest directly directly on on gneiss and granite. rocks Early Proterozoic rocks Archean rocks are not a focus of the field trips but will be seen at one stop on Trip 2 (Stop 2-10). Details of Archean geology are imperfectly known because of very sparse exposures. sures. The The most most complete complete exposures are in the areas underlain underlain by volcanic rocks of basalt, basalt, andesite, andesite, and and between Hurley Hurley and and Upson. Upson. These Thesevolcanic volcanic rocks rocks consist mostly of 2-10)isisthe themost mostcommon commonrock rocktype type directly directly beneath beneath the rhyolite; dacite breccia (Stop 2-10) Middle Proterozoic Proterozoic rocks between Huxley Hurley and Upson (Greathead, (Greathead, 1975). The The volcanic rocks form form aa section at least and are overturned so that they face rocks section at least 66 km km thick, thick, and overturned so face northwestward and southeastward. northwestward and dip dip steeply steeply to moderately southeastward. 35 35 �CEOLOGY PROTEROZOIC ROCKS GEOLOGY OF OF EARLY EARLY PROTEROZOIC ROCKS Early Proterozoic rocks include strata of of the Marquette Range Supergroup Supergroup along along the Gogebic Iron hon Range. Range. These Theserocks rocks are arethe the focus focus of of Field Trip 5, and will also be seen on parts and 4. 4. The Thecontinuity continuityof of Early Early Proterozoic strata across the area is parts of of Trips Trips 2 and broken by the Mineral Lake intrusion, which truncates the sequence from near Mineral Lake westward westward to tothe theMarengo MarengoRiver, River,aadistance distanceof of about about10 10km. km. Area east of Lake intrusion: of Mineral M i n m East of of Mineral Lake, the Early Early Proterozoic Proterozoic sequence displays the Range stratigraphy stratigraphy with a basal the classical classical Gogebic Gogebic Range basal argilliteargillitequartzite unit by banded iron-formation unit (Palms (PalmsFormation) Formation) overlain overlain successively successively by iron-formation (Ironwood Iron-formation) and aa shale-graywacke shale-graywacke turbidite turbidite unit unit(Tyler (TylerFormation). Formation). From about about Ballou Creek westward westward a thin, possibly discontinuous, discontinuous, unit unit of of dolomite and chert breccia chert breccia of of the the Bad Bad River River Dolomite Dolomite lies between between the Palms Palms Formation Formation and and underlying Archean underlying Archeanbasement basement rocks. rocks. The Early section is is 2-3 2-3 km km thick and The Early Proterozoic Proterozoic section and records records sedimentation sedimentation successively on on aa stable stable craton, craton,passive passivemargin, margin,and andcompressional compressionalforeland. foreland. The oldest strata, represented by by the the Bad Bad River River Dolomite, Dolomite, were deposited deposited unconformably unconformably on on Archean rocks, The Bad Bad River River is a cherty rocks, apparently in aa stable stablecratonic cratonic setting. setting. The cherty dolomite, commonly metamorphosed metamorphosed to to tremolitic tremolitic marble. marble. It It also also includes includes aa distinctive distinctive breccia (Stops 2-9 2-9 and and 2-10) 2-10) that that constitutes constitutes most most of of the unit from chert brecaa from near near the. the Bad Bad River eastward eastward for about 10 km to near Ballou Creek. The River Ballou Creek. The breccia breccia appears to be be aa variably reworked residuum residuum of of chert chert nodules and and beds beds left left by solution solution of the dolomite dolomite during the the weathering weathering interval, interval, prior prior to to deposition deposition of of the the unconformably unconformably overlying overlying Formation. Palms Formation. The principal principal iron-bearing iron-bearing sequence sequence is the the Menominee Group, Group, consisting consisting of of the the and Ironwood bonwood Iron-formation. Palms Formation and Iron-formation We interpret the Menominee Group to have been deposited depositedon onaasouth-facing south-facing passive passive margin. margin. The ThePalms PalmsFormation Formation(Stops (Stops2-9 2-9 and 2-10) consists consists of of banded banded argillite argillite near near the the base, base, and and grades upward into into thickthickbedded quartzite near the unconformably on on Archean Archean rocks rocks and the Bad Bad the top. top. It lies unconformably River Dolomite. Dolomite. At its upper contact the Palms grades grades upward upward over a meter or two into Iron-formation. The Ironwood bonwood contains ferruginous beds of the Ironwood Iron-formation. contains numerous numerous lithologic types of iron-formation. East Eastof of Upson, Upson,Wisconsin, Wisconsin, itit consists consists of five laterally laterally continuous members that are alternating units of thin, even-bedded, carbonate ironformation and and thick, thick, wavy-bedded, wavy-bedded, hematitic hematiticiron-formation iron-formation(Hotchkiss, (Hotchkiss,1919; 1919; Huber, 1959). West of Upson Upson (Stops 5-B),these theselithologies lithologiesare arealso alsopresent, present, but but laterally (Stops 2-8 and 5-B), 36 �46° 46° 45 LAKE SUPERIOR 46° 00 46° 451 90° 00! 900 00! Figure 1: Geologic map of part of northern Wisconsin and Michigan showing region of field trips 2, 4, and 5. 91° 30 •S • • S S S SS S •• . . . S SS • • 91030 �L :: z, 3 : Chengwatana Kallander Creek Volcanics conglomerate - w ffl 3 3 3 Olivine gabbro and serpentinite Anorthosite and gabbro Granophyre Granite andesite and basalt Kallander Creek Volcanics 3 ffl2. 0 3- " 5 / SQ Siemens Creek Volcanics :a g 5' Copper Harbor Conglomerate rhyol ito Â¥ (A. xg 3 Nonesuch Formation s3 3-7; < = S ?= S Q n g,; % y s ss s 0- 3 conglomerate facies 3 -a r. 50 3 a ~ 3 sa $ s ¤g w 5 $? Freda Sandstone n8 > 5 m s s0 g0 u 77 m 0) 2 g m ^ Freda Sandstone 2s: a 77 Kallander Creek Volcanics 77 < m 6 Orienta Sandstone Lri:tJH 0- 0- w Portage Lake Volcanics w 0 0- Devils Island Sandstone w andesite and basalt " g^ 0 =s 0< 0" m Chequamegon Sandstone 3 Porcupine Volcanics 3. s 0 w 3 Jacobsville Sandstone 51 Middle Proterozoic g< Porcupine Volcanics rhyolite w Cambrian sandstone 2. 53" " 3 $6 à I 8 -B8- w 5 w 3. 0 3. n' Cu 3- EXPLANATION 2g 8 8 3. 8 ^ 01 Gneiss Early Archean Metavolcanic Rocks Gneiss and Amphibolite Puritan Quartz Monzonite Late Archean Bad River Dolomite and Palms Formation lronwood Iron-formation Blair Creek Formation Tyler Formation Metasedimentary and metavolcanic rocks Metadiabase Early Proterozoic �h I I I I I I p I I continuous members membersare are more more difficult difficulttoto define, define, in in part part because continuous because of of primary primary sedimentary changes, induced by by deformation and changes, but also also because of complications complications induced metamorphism. metamorphism. The Tyler Formation (Stops 2-7 2-7 and and 5-B) 5-B)overlies overliesthe the Ironwood Ironwood and is aa thick thick succession of succession of graywacke and slate deposited in a foreland basin during accretion accretion of of island Ma. We believe that the basal contact with island arc arc terranes terranes to to the the south southat atabout about1850 1850 Ma. the Ironwood Iron-formation unconformity, although the Iron-formation is most likely a low-angle unconformity, nature natureof of the the contact contact has has been been aa point point of of controversy controversy for many years. rocks are are essentially essentially unmetamorphosed unmetamorphosed east east of of Upson, Upson, but Early Proterozoic rocks metamorphic grade is progressively metamorphic progressively higher towards the the west west where whereassemblages assemblages including abundant abundant grunerite. grunerite. Near include garnet and aa variety variety of amphiboles, including Near the the contact with the Mineral Lake intrusion, assemblages include fayalite, orthopyroxene, and garnet in in iron-formation. iron-formation. The The metamorphism metamorphism was static and caused by Middle Middle Proterozoic thermal thermal events. events. Early Proterozoic Proterozoic rocks rocks dip steeply to vertical Early vertical nearly everywhere everywhere along along the the Gogebic Iron Iron Range. Range. This attitude attitude results Froterozoic deformation, deformation, results mostly from Middle Proterozoic discussed below, below, but we have have distinguished distinguished aa component component of relatively relatively strong Early Early Proterozoic deformation deformation as as well. well. The deformation is is part of the Proterozoic The Early Early Proterozoic Proterozoic deformation the Penokean of island island arcs arcs with with the southern southern edge Penokean orogeny, orogeny, caused caused by by collision collision of of a series of edge of the Superior and others, 1989). 1989). The area lies north north of 1850 Ma (Sims and Superior craton craton at atabout about1850 the suture and the suture andspans spansthe thetransition transitionfrom fromaa foreland foreland fold and and thrust thrust belt belt to to the the essentially essentially undeformed craton. undefonned craton. From Hurley to Upson, Penokean deformation is is nearly nearly nonexistent. nonexistent. A Penokean deformation A weak weak Formation but no folds slaty cleavage is developed locally in the Tyler Formation folds are are known. known. Westward deformation intensifies and is expressed both by Westward from Upson, compressional deformation thrust faults faults and and folds folds(Stops (Stops 2-10 2-10 and 5-8). 5-B). On OnMt. Mt. Whittlesey, Whittlesey, the Ironwood Ironwood IronIronformation is structurally thickened both by by folding folding and and repetition by by thrust faults. formation thickened both faults. Farther west, near Mineral nearly isoclinal isoclinalfolds foldswere were developed. developed. These Mineral Lake, large, nearly These folds originally were upright but but now now are are recumbent recumbent as as aa result result of of Middle MiddleProterozoic Proterozoic tilting. tilting. Ballou Creek Creekwestward westward there there appears appears to to be be aa detachment detachment fault at or From about Ballou so that that Early Proterozoic very near the the base base of of the theEarly EarlyProterozoic Proterozoicsection section (Stop (Stop 2-10) so Archean rocks rocksduring duringPenokean Penokeandeformation. deformation. The amount rocks were decoupled from Archean of structural shortening shortening in in the the Early Early Proterozoic Proterozoic strata is unmatched in in the the Archean Archean basement. �C — 1 25 I C 9'fl'ft'—k CCLJ J00.Io.,.o.,, r 0!.lI,M!. 20 I 5 F '41 (I LH/ J4_ckALI Jj Jf]}\ 17 0 I r- — — IS ; <'ii— 10 ________ — 20 i2-1 - -10 I — 0 0 f—1 • F-! 5 — — F—i 0 — 5 - — locations. detailed more for guides individual See 5. and 4, 2, trips field for stops of locations approximate the showing quadrangle 10x2° Ironwood the of Part 2. Figure - 5 �Area Area west west of of Mineral Mineral Lake I.ake intrusion: intrusion: West of of the Mineral Mineral Lake Lake intrusion, intrusion, Early Early Proterozoic strata are River to to the the north Proterozoic strata are present present from from the the Marengo Marengo River north side side of of Lake Lake Namekagon. Namekagon. These Thesestrata stratashare sharemany manysimilarities similaritieswith with their equivalents equivalents to to the the east east but but also alsodisplay displaysome someimportant importantdifferences. differences. The The Early Proterozoic succession includes an approximately approximately 300-rn 300-m thick section of of Bad Bad River River Dolomite, Dolomite, exposed exposed near near the the Marengo Marengo River River south south of of Grand Grand View, View, marble with with abundant lenses and beds of Wisconsin. Wisconsin. It It is is typically typically a gray gray dolomitic marble chert, partly replaced unconformably on on Archean Archean rocks. rocks. This is replaced by tremolite, tremolite, and lies unconformably the Group rocks rocks preserved preserved on on the the Gogebic GogebicIron Iron Range. Range. The the thickest thickest section section of Chocolay Group overlying laminated overlying Palms Palms Formation Formation is is much like that known to the east, consisting consisting of laminated argillite argillite near the the base and and thick-bedded quartzite quartzite near the top. The Ironwood lacks wavy-bedded wavy-bedded hematitic IronwoodIron-formation Iron-formation (Stops (Stops 4-1 and 5-A) lacks hematitic iron-formation iron-formationthat thatare arecommon commonto to the the east. east. However, However, it does does contain contain units units of laminated laminated cherty cherty magnetite magnetite iron-formation. iron-formation. The Ironwood grades laterally to the west into into nonnoncherty silicate iron-formation, magnetic and non-magnetic argillite, and black pyritic cherty silicate iron-formation, black pyritic shale. shale.Large Largesills sillsof ofmetadiabase metadiabase(Stops (Stops4-1 4-1and and5-B) 5-B) also occur in the iron-formation, iron-formation,in in contrast abundant. contrast to to areas areas farther farther east east where where mafic intrusions are much less abundant. Two unusual each as much as 20 m thick, are unusual breccia breccia units units(Stops (Stops4-1 4-1 and and 5-B), 5-B), each are exposed exposed in in the the iron-formation iron-formation near Atkins Lake. They have not been described prior to 1995 (Feher (Feher and and Flood, Flood, 1995). 1995). The The breccias breccias consist consistofofangular angular to to subrounded subrounded clasts as much sedimentary rocks in a matrix matrix of of dark dark much as as11m m across across composed composed of banded siliceous sedimentary gray-green clearly igneous and has a basaltic composition gray-green massive massive rock. rock. The matrix is clearly but but whether whetherthe theunits unitsare areextrusive extrusiveor or intrusive intrusive is uncertain. In In either either case, case, the presence of these indicates that igneous occurred very close deposition these breccias indicates igneous activity activity occurred dose in time to deposition of the the iron-formation iron-formationin in the the western westernpart partof of the theGogebic Gogebic hon IronRange. Range. The situation situation is similar to that observed in the eastern part part of of the the Gogebic Gogebic Iron Range in Michigan, Complexisis interlayered interlayered with with the Michigan, where the Emperor Emperor Volcanic Volcanic Complex bonwood hon-formation. Ironwood Iron-formation.Apparently Apparentlyquiescent, quiescent,platform-like platform-like conditions, expressed in the lateral of the Menominee Menominee Group Group in the central part of lateral continuity continuity of of lithologic units of the Gogebic Range, change into more volcanically-active volcanically-activeenvironments environments to to both both the the east and and west. west. Lateral Lateralchange changefrom fromcherty chertyiron-formation iron-formation common in the central part of the range, to non-cherty and ferruginous argillite in the west, also non-cherty silicate silicate iron-formation and suggests that diluted the chemically precipitated precipitated suggests proximity to to aa clastic clastic sediment source that components of the iron-formation. in the Ironwood, bonwood, iron-formation. The The increased detrital component in volcanism,atatboth boththe the east east and and west west end of of the range, along with contemporaneous volcanism, may indicate transition of extension and and rift-basin rift-basin development development that that marked transition to to a region of 39 �continental breakup continental breakupatatthe theoutset outsetof of the thePenokean Penokeanorogenic orogeniccycle. cycle. The Tyler Tyler Formation Formation isis unknown unknown west west of of the the Mineral Mineral Lake Lake intrusion intrusion but is The probably present, beneath low, low, swampy swampy country country north north of of the the Ironwood present, at at least locally, beneath outcrop belt. Magnetic traverses traverses across across these these areas areas show show extremely flat profiles outcrop belt. Magnetic profiles characteristic of the Tyler elsewhere. characteristic The western western termination termination of of strata strata of of the the Gogebic GogebicIron hon Range Rangeisis in in the the area area The between Lake Lake Namekagon Namekagon and and Cable, Cable, where where the the Atkins Atkins Lake Lake fault, fault, a Middle between Middle Proterozoic structure structure discussed discussed below, below, cuts cuts down down section section and and truncates Proterozoic truncates Early Early volcanicrocks. rocks. Outcrops are extremely Proterozoic strata against Middle Proterozoic Proterozoic volcanic sparse in that area, but the using magnetic magnetic data. the fault fault trace can be located using GEOLOGY OF MIDDLE MIDDLE PROTEROZOIC ROCKS GY OF ..,. Middle Proterozoic of continental continental volcanic rocks Middle Proterozoicrocks rocks consist consist of a thick sequence of overlain by red fluvial rocks and and lesser lesserlacustrine lacustrinedeposits, deposits, that that together together make up overlain fluvial clastic rocks the Keweenawan Supergroup. All All are are related related to the Midcontinent Rift Rift System System that that rift was was tectonically tectonicallyinverted inverted shortly shortly after it formed. developed at Ma. The rift developed at about about1100 1100 Ma. area, the the inversion inversion resulted resulted in in southward-directed southward-directed thrusting thrusting and and In the Hurley-Cable area, northward tilting northward tilting of of aa crustal-scale crustal-scale block, so that the Middle Proterozoic rocks now lie River monocline monocline (Cannon (Cannon in a northward-dipping northward-dippingmonoclinal monoclinal sequence, sequence, the Montreal River monocline provide provide aa complete complete history history of of the the rift rift and others, 1993b). 1993b). The rocks in the monocline including extension post-rift thermal thermal subsidence subsidence and and including extension and continental continental volcanism, volcanism, post-rift sedimentation, and sedimentation, and later later inversion inversion resulting from regional compression. Extension and volcavolcanism: The lower part of of the Keweenawan Keweenawan Supergroup Supergroup is composed of volcanic volcanic and and lesser sedimentary rocks rocks that that formed formed during during the the extensional phase phase of of of the rift and accumulated of as much as 12 krn km in in this this area, area, but but were as accumulated to a thickness thickness of km thick along the rift axis axis to to the the north. north. The much as 20 krn The lowest lowest unit unit is is the the Bessemer Bessemer Quartzite (Stop chieflygray grayto to white, white, thin-bedded thin-bedded quartzite, quartzite, mostly of of lacustrine Quartzite (Stop 2-6), 2-6), chiefly (akangas and Morey, made up up mostly mostly origin (Ojakangas and Morey,1982). 1982).AAmassive massivebasal basal conglomerate conglomerate is made of clasts of of Early Early Proterozoic and and Archean rocks rocks typical typicalof of those thoseexposed exposed south south of of the the of Bessemeroutcrop outcropbelt. belt. The TheBessemer Bessemerappears appearstotohave haveformed formedininaabroad broad basin basin that that Bessemer of extension contained a shallow lake. This This basin is apparently the first manifestation of related to the Midcontinent rift, and formed immediately prior to the initiation of related Midcontinent rift, immediately prior flood-basalt volcanism, which which was was soon soon to to dominate dominate the the region. region. continental flood-basalt The oldest volcanic sequence sequence is is the the 1.3-km 1.3-km thick Siemens Creek Volcanics (Stops 40 �I 4-3, volcanic rocks rockshave havenot notbeen beendated dated in in this area, but are 4-3, and and 4-7). 4-7). These These volcanic are probably equivalent equivalent to to the theOsler Osier Volcanics Volcanics on the north shore shore of Lake Superior where eruption 1985). We have made an eruption began at at about about 1109 1109 Ma (Davis (Davis and Sutcliffe, Sutcliffe, 1985). an informal into a thin, discontinuous discontinuous lower informal subdivision subdivision of of the the Siemens Siemens Creek Creek Volcanics Volcanics into lower unit unit and aa much much thicker thicker upper upper unit. unit. Flows Flows in the lower lower unit unit (Stop (Stop2-6) 2-6) are are geographically cinopyroxene phenocrysts, aa rarity geographically restricted basalts that have small clinopyroxene rarity in in Keweenawan Keweenawan volcanic rocks, and we recognize recognize a distinctive distinctive chemical composition composition(low (low Al203, MgO, and and steep steepREE REE patterns), patterns), indicating that that the theflows flowsreflect reflect Al2O3, high Cr, Cr, Ni, Ni, MgO, partial partial melts from a deep, enriched mantle source with little or no fractionation prior to eruption. eruption.The Theupper upperpart partofofthe theSiemens SiemensCreek CreekVolcanics Volcanics(Stops (Stops4-3 4-3 and and 4-7) 4-7) comprises comprises widespread flood more evolved evolved composition, composition, ranging from from basalt to to flood basalts basalts of of aa more andesite. indicates aa larger larger degree of of partial melting andesite. Their chemical composition indicates melting of of aa mantle source, during ponding within source, modified by fractional fractional crystallization during within or or at atthe the base base of of the lithosphere lithosphere prior to to eruption. eruption. The Thebasal basal1-3 1-3flows flowsof of the theSiemens SiemensCreek Creek Volcanics, erupted erupted into Quartzite was being deposited, into the the lake lake into into which the Bessemer Quartzite deposited, typically typically are are pillow basalt basalt and and pillow pillow breccia. brecaa. The The Bessemer Bessemer was unconsolidated unconsolidated at at the the time of eruption, and can be be found in places and Bessemer-like Bessemer-like sediments can places as as interfiow interflow accumulations above the lowermost lowermost flow. All remaining overlying flows appear appear to to be be subaerial subaerial based based on onlack lack of of pillow pillow structures. structures. The Kallander km thick) overlie the Siemens Kallander Creek Creek Volcanics Volcanics (1.2-4.5 (1.2-4.5 km Siemens Creek Creek Volcanics and consists of of a much higher proportion proportion of andesite andesite and and rhyolite rhyolite flows flows than than are are present present in in the theSiemens Siemens Creek. Creek. We Werecognize recognize two two informal informal units units in in the theKallander Kallander Creek Creek Volcanics. A A lower lower unit, unit, about abouthalf half of of the total stratigraphic stratigraphicthickness, thickness, is mostly andesite and and basalt basalt (Stop (Stop 4-6), 4-6), and appears to record continuation of of the widespread continental continental flood basalt eruption eruptionpresent presentin inthe theSiemens SiemensCreek Creek Volcanics, Volcanics, whereas the upper part part isismore morelocalized localized and andmost mostprobably probably represents represents aa central central volcano volcano near near Mellen. Mellen. The The upper upperpart partofofthe thesection sectioncontains containsabundant abundantrhyolite rhyolite and andconglomerate conglomerate (Stops 2-4 2-4 and 4-8) 4-8) in in addition to basalt, andesite, and other rocks rocks of intermediate intermediate composition 2-5). The composition (Stop 2-5). The lower unit is is very very similar similar to to the the lower lowerSiemens Siemens Creek Creek basalts basalts (small (small degree partial melts melts erupted from from deep deep in in the the mantle). mantle).However, However, our our analyses show that the analyses show the basalts basalts in in the the lower lower Kallander Kallander Creek Creek are are more more strongly strongly fractionated fractionated (high (high Ti02 and FeO, FeO, low MgO), and lack clinopyroxene as aa phenocryst phenocryst phase. AArhyolite rhyolitenear nearthe thetop topofofthe thelower lowerunit unitwas waserupted eruptedabout about1107 1107Ma Ma(Davis (Davisand and others, others,1995). 1995). In abundant In contrast contrast to to the the lower lower unit, the the upper upper Kallander Kallander Creek unit contains abundant rhyolite and and conglomerate conglomerate in addition addition to to basalt and andesite. Chemical Chemicalcompositions compositionsof of 2-6, 2-6, I I I I I I I I I fl I I 41 i �mafic and and intermediate rocks indicate that parent magmas were generated from largemafic fractional crystallization crystallization degree partial melts of of a mantle source, and that substantial fractional took place place within or near the base of of the crust. crust. Rhyolites took Rhyolites were generated, at least in of crustal crustal material. material. A A rhyolite rhyolitethat thatforms formsthe theuppermost uppermost unit unit of of part, by partial melting of (Stop 2-4) 2-4)was waserupted eruptedat at about about 1099 1099Ma Ma(Zartman (Zartmanand and the Kallander Creek Volcanics Volcanics (Stop others, 1995). and 4-5), 4-5),an an intrusive intrusive suite suite of of gabbroic 1995). The The Mellen Mellen Complex Complex (Stops (Stops 4-4 4-4 and Volcanics and and rocks, granophyre, and granite, granite, was emplaced into the Kallander Creek Volcanics older units at and probably probably represents represents aa at about about 1102 1102 Ma (Cannon and others, 1993a) 1993a) and shallow magma reservoir that fed eruptions eruptions from from the the central central volcano. formation of the central The area near Mellen remained a topographic high after formation volcano and and no further volcanic rockswere weredeposited. deposited. To To both both the east and west, volcano volcanic rocks additional flood basalt volcanism deposited a great thickness of of volcanic volcanic rocks, rocks, mostly mostly additional confined to the central graben of of the the rift. rift. These rocks are are represented represented by the These volcanic rocks Portage Lake Volcanics to the east and and the the Chengwatana ChengwatanaVolcanics Volcanics(Stops (Stops4-9 4-9and and 4-10) 4-10) to the west. The eachdominated dominatedby bybasalt basaltwith with The two two units units are are quite quite similar similar chemically, chemically, each lesser intermediate intermediate and felsic felsic rocks. rocks. In each, the the basalts basalts can canbe bedivided divided into into two two major major groups based on on whether whether the the Ti02 Ti02 content content is is greater greater or less less than than 2.5 2.5 wt % % (Nicholson The low-Ti02 low-Ti02basalts basaltsare arethe the most most abundant abundant and and represent 1990). The represent and Shirey, Shirey, 1990). widespread flood basalt volcanism: they they are are typically typicallyophitic ophiticin intexture texture and and commonly commonly than the high-Ti02 basalts. basalts. The Thehigh-Ti02 high-Ti02basalts basaltsform formthinner thinner and and form thicker flows than and commonly are are interlayered interlayered with with more more intermediate intermediate and felsic more localized flows, and rocks in in the section. continued for for rocks section. The The main main phase phase of of rift rift extension extension and volcanism volcanism continued about 55 m.y., until until about about1094 1094Ma Ma (Davis (Davisand andPaces, Paces, 1990). 1990). about The youngest youngest volcanic volcanicrocks rocksininthe thearea area are are basalt basalt and and andesite andesite flows flows of of the the The Porcupine Volcanics (Stop 2-3) 2-3)that thatmake makeup up aa central centralvolcanic volcaniccomplex complexcentered centeredto tothe the Porcupine of the Hurley-Cable Hurley-Cable area, area, near near the the Porcupine PorcupineMountains Mountainsin inMichigan. Michigan. Outcrops Outcrops of of east of in the the Hurley-Cable Hurley-Cable area area comprise comprisebasalt basalt and and andesite flows the Porcupine Volcanics Volcanics in and interflow conglomerate conglomerate and and sandstone. sandstone.AArhyolite rhyolitenear nearthe thetop top ofof the the unit unit was was erupted at erupted atabout about1094 1094Ma Ma (Zartman (Zartmanand andothers, others,1995). 1995). Thermal subsidence and sedimentation: Following eruption of of the the Portage Lake Lake and and Following eruption Chengwatana Volcanics, of the Porcupine Chengwatana Volcanics, and coincident with development of Porcupine Volcanics, changed. Earlier extension-driven subsidence subsidence and and related volcanism the tectonic regime changed. rapidlywaned waned and and further subsidence was was replaced by a regime in which extension rapidly The thermally thermally caused by by cooling cooling and and contraction contraction ofof the the hot hot root root zone zone of of the the rift. rift. The caused subsiding basin basin was was generally generally centered centeredover overthe the previous previousrift riftbasin basin but but was was much much subsiding 42 �I p broader. fluvialrocks rocksand andlesser lesserlake lakedeposits. deposits. As broader. This This basin was filled with red clastic fluvial much of sedimentary sedimentary rocks accumulated accumulated in in the the deepest deepest part part of of the the basin. basin. much as 7 km of The oldest sediments, sediments, comprising the Copper Copper Harbor Harbor Conglomerate Conglomerate(Stop (Stop2-2) 2-2) and perhaps perhaps the theoverlying overlyinglake lakebeds beds of of the theNonesuch NonesuchFormation Formation (stop (stop2-2), 2-2), were deposited in aa basin rift basin basin and and the basin transitional transitional between between the earlier extensional extensional rift successor thermally subsiding subsiding basin. A Aregional regional topographic topographic high high centered centered near near Mellen Mellen affected the distribution distribution and of nearby nearby sedimentary sedimentary units. units. The and lithology of The Copper Copper Harbor Harbor Conglomerate Conglomerate and and Nonesuch Nonesuch Formation Formation both pinch out against this highland so that the overlying Freda Sandstone locally lies lies unconformably unconformably on on volcanic volcanic and and Sandstone (Stop (Stop 2-1) locally intrusive intrusiverocks. rocks. The TheFreda FredaSandstone Sandstonenear near Mellen Mellen is atypically conglomeratic, reflecting proximity proximity of of the the nearby nearbyhighland highlandthat thatserved servedasasaasource sourceof of coarse coarseclastic clastic debris. debris. P U Rift Toward Rift inversion: inve& Towardthe theclose close of of the the thermal thermal subsidence phase and and coincident coincident with late late phases of of sedimentation, sedimentation, a period period of of regional regional compression compression began, that caused caused inversion inversion of of the the rift structure. structure.In Inthe theCable-Hurley Cable-Hurley area, area, compression compression resulted resultedin in aa series series of major listric thrust faults along which previously previously deeply deeply buried buried parts of the rift were thrust southward southward and and the the upper upper plates plates of of the the faults faults were were tilted tilted northward. northward. This thrusting in the the present present distribution distribution and structural thrustingevent eventisis the the major major controlling controlling factor in attitude attitudeof of the therocks rocksof of the the region. region. The principal fault in the area fault and its western extension, area is the Marenisco fault the the Atkins Atkins Lake fault. From From east east to to west west across across the area, the Marenisco fault gradually rises rises in in the the stratigraphic stratigraphicsection. section. In Inthe theeast, east,the the fault fault trace trace is is about about 10 10 km south south of the contact so so that that a large thickness thickness of of Archean Archean rocks rocks and and the Early Proterozoic-Archean contact Early entire entire Early Early Proterozoic Proterozoic and and Middle Middle Proterozoic Proterozoic section is in the upper plate plate above above the the structure was fault. The The importance importance of of the the Marenisco Marenisco fault as a Middle Proterozoic structure was not not fault. recognized until Rb-Srbiotite biotiteages agesdemonstrated demonstratedthat that the the upper upper plate had until 1992, 1992, when Rb-Sr been and others, 1993b). In the eastern been uplifted uplifted and andcooled cooled at at about about1060 1060 Ma (Cannon and part of of the upper plate has resulted in of the the area, area, thrusting and northward northward rotation of exposure exposureof of aa cross cross section section of nearly vertically dipping strata strata about about 20 20 km km thick as as well as basement rocks. rocks. This structure, the Montreal as about about 10 10 km of underlying Archean basement Montreal River 3/4 of of the the crust crust as as itit existed just after rifting and is the River monodine, monocline, exposes exposes about about 3/4 focus focusof of Field Field Trip Trip2.2. To rises to higher higher structural levels in To the west, west, the the Marenisco Marenisco fault gradually rises Archean Archean rocks rocks until, until, along alongthe the Marengo Marengo River, River, it cuts upward upward across acrossEarly Early Proterozoic Proterozoic strata. strata. From Fromthere therewestward, westward,the thefault faulthas hasthrust thrustMiddle MiddleProterozoic Proterozoicvolcanic volcanic rocks rocks southward rocks. The southward over over Early Early Proterozoic Proterozoic and Archean rocks. The fault fault is is traced traced mostly mostly by by 43 �aeromagnetic aeromagnetic data, data, but but extensive extensive exposures exposures of of intensely intensely sheared sheared and and rnylon.itized mylonitized rocks can been seen seen along along the the valley valley of of the the Marengo MarengoRiver River south south of of Grand GrandView, View, Wisconsin. Wisconsin. A second important important fault is the Lake Owen fault. Southwestward Southwestwardfrom fromCable, Cable, this fault separates separatesMiddle Middle Proterozoic Proterozoic volcanic volcanic rocks rocks of the the Chengwatana ChengwatanaVolcanics Volcanics from Archean Archean rocks. rocks. Northeastward the fault fault passes passes up section in the Northeastward from Cable Cable the footwall, so that footwall, that the theChengwatana ChengwatanaVolcanics Volcanics are are juxtaposed juxtaposed against against successively successively younger rocks. northeast of of Mellen, Mellen, the the fault fault passes younger rocks. Eventually, Eventually, northeast passes into the the Freda Freda Sandstone, where Sandstone, where its its expression expression is obscure and it appears to die out. Iceweenaw fault, fault, aa major major reverse reversefault fault to to the the east east of of the the area, area, also dies out out The Keweenaw within the within the volcanic volcanicsection section northeast northeastof of Mellen. Mellen. REFERENCES REFERENCES - Cannon, W.F., Cannon, W.F., Nicholson, Nicholson,SW., S.W., Zartman, Zartman,R.E., R.E., and andDavis, Davis,12W., D.W., 1993a, 1993a, The The Kallander KaUanderCreek CreekVolcanics Volcanics - aa remnant of a Keweenawan central volcano centered near Mellen, Wisconsin [abstract]: Institute on remnant of a Keweenawan central volcano centered near Mellen, Lake Superior Geology, Abstracts, v. 39, p. 20-21. Superior Geology, Abstracts, v. 39, p. 20-21. Cannon, WE., Crustal-scalethrusting thrusting and and origin Cannon, W.F., Peterman, Peterman,Z.E., Z.E., and and Sims, Sims, P.K., P.K.,1993b, 1993b, Crustal-scale origin of of the the Montreal Montreal River monocline -- aa 35 km-thick km-thick cross cross section sectionofofthe theMidcontinent Midcontinentrift riftin innorthern northern Wisconsin Wisconsin and and Michigan: Tectonics, v. 12, p. 728-744. Michigan: Tectonics, v. 12, p. 728-744. Davis, D.W., J.W., 1990, 1990,Time Timeresolution resolutionofofgeologic geologicevents eventson onthe theKeweenaw KeweenawPeninsula Peninsula and and D.W., and Paces, J.W., implications for development of the Midcontinent rift system: Earth and Planetary Science Letters, implications development of the Midcontinent rift system: Earth and Planetary Science Letters, v. 97, p. 54-64. Davis, D.W., D.W., and Sutcliffe, R.H., Ri-I., 1985, 1985,U-Pb U-Pbages agesfrom fromthe theNipigon Nipigonplate plate and and northern Lake Lake Superior: Superior: Geological Society Society of America America Bulletin, Bulletin,v. v. 96, 96, p. 1572-1579. 1572-1579. D.W., Green, J.3.and and Manson, Manson, M., M., 1995, 1995,Geochronology Geochronologyofofthe the1.1 1.1Ga GaNorth NorthAmerican American midcontinent midcontinent Davis, D.W., [abstract]: Institute rift [abstract]: Instituteon onLake LakeSuperior SuperiorGeology, Geology,Abstracts, Abstracts, v, v, 41, 41, p. p. 9-10. and Flood, T., 1995, Vesiclesand andbreccia brecciadue due to to injection injection of ofmafic maficmagma magma into partially partially lithified Feher, L., and 1995, Vesicles lithified sediments of the early NW Wisconsin sediments early Proterozoic Proterozoic Ironwood Iron-formation, Iron-formation, western western Gogebic Range, NW [abstract]: Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology, Abstracts Abstracts,, v. 41, p. 13-15. 13-15. Greathead, The geology geology and and petrochemistry petrochemistry of of the the greenstone greenstone belt south of Hurley Greathead, C., C., 1975, 1975, The Hurley and and Upson, Upson, Iron County, County,Wisconsin: Wisconsin: Milwaukee, Milwaukee, Wisc., Wise., University of of Wisconsin-Milwaukee, Wisconsin-Milwaukee, unpublished unpublishedM.S. M.S. Thesis, 191p. Thesis, 191 Hotchkiss, W.O., 1919, Geology Geologyofofthe theGogebic GogebicRange Rangeand andits itsrelation relation to to recent recent mining developments: developments: W.O., 1919, Engineering Engineeringand andMining MiningJournal, Journal,v.v.108, 108,p.443-452,501-507,537-541,577-582. p. 443-452,501-507,537-541,577-582. Huber, N.K., aspects of the origin origin of the the Ironwooci Iron-formation of Huber, N.K., 1959, 1959, Some aspects Ironwood Iron-formation of Michigan Michiganand andWisconsin: Wisconsin: Economic Economic Geology, Geology, v. v. 54, 54, p. 82-118. 82-118. Nicholson, S.W. S.W. and and Shirey, S.B., 5.8., 1990, 1990, Evidence Evidencefor foraaPrecambrian Precambrianmantle mantle plume: plume: A A Sr, Sr, Nd, and Pb Pb isotopic study Rift System System in in the the Lake Lake Superior Superior region: region: Journal Journal of of Geophysical Geophysical study of of the theMidcontinent MidcontinentRift Research, v. 95, P. p. 10851-10868. 10851-10868. Research, v.95, qakangas, R.W., Keweenawanpre-volcanic pre-volcanicquartz quartzsandstones sandstones and and related rocks Ojakangas, R.W., and andMorey, Morey,G.B., G.B., 1982, 1982, Keweenawan Rj., and and tectonics of of the Lake Superior region, in in Wold, R.J., and Hinze, H i ,W.J., W.J., (eds.), Geology and of the Lake Superior Superior 156,p.p.85-96. 85-96. SuperiorBasin: Basin: Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, P.K., Peterman, Peterman, Z.E., Z.E., and and Prinz, W.C., 1977,Geology Geologyand and Rb-Sr Rb-Srage ageofofthe thePrecambrian Precambrian W W Puritan Sims, P.K., W.C., 1977, Quartz 5, p. p. 185185QuartzMonzonite, Monzonite,northern northernMichigan: Michigan:Journal JournalofofResearch Researchofofthe theU.S. U.S. Geological GeologicalSurvey, Survey,v.v.5, 192. 192. 44 �I I I I I I I I I I I I I I I I I I I Sims, and Peterman, Z.E., Tectono-stratigraphic evolution Sims, P.K., P.K., Van Van Schmus, Schmus,W.R., W.R., Schulz, Schulz, K.J., K.J., and Pete-, Z.E.,1989, 1989,Tectono-stratigraphic evolutionof of the the Early EarlyProterozoic ProterozoicWisconsin Wisconsin magmatic magmatic terranes terranes of of the the Penokean Penokean orogen: orogen:Canadian CanadianJournal Journal of of Earth EarthSciences, Sciences,v.v.26, 26,p.p.2145-2153. 2145-2158. Zartman, Zartman,R.E., R.E., Cannon, Cannon,W.F., W.F., and andNicholson, Nicholson,S.W., S.W.,1995, 1995,U-Th-Pb U-Th-Pb ages agesof of some someKeweenawan Keweenawanrocks rocksfrom from western western Lake LakeSuperior, Superior,northwestern northwesternWisconsin, Wisconsin,and andeast-central east-centralMinnesota Minnesota[abstract]: [abstract]:Proceedings Proceedings of of International InternationalField FieldConference Conferenceand and Symposium Symposiumof ofInternational InternationalGeologic Geologic Correlation CorrelationProgram Program Project 336, Duluth, Duluth,Minn., Minn.,p.p.217-218. 217-218. Project336, 45 45 �. I U I I I I I I I I 1 I I I I I I I I FOR FIELD TRIP TRIP ##22 GUIDE GUIDE FOR FIELD OF RIVER GEOLOGY OFTHE THE MONTREAL MONTREAL RIVERMONOCLINE: MONOCLINE: GEOLOGY A THROUGH ATRAVERSE TRAVERSE THROUGH25 25KM KMOF OFTHE THE CRUST CRUST �I I I I I I U I fl FIELD TRIP TRIP #2 GEOLOGY RIVER MONOCLINE: MONOCLINE: GEOLOGY OF THE MONTREAL RIVER A ThROUGH 25 A TRAVERSE THROUGH 25 KM OF OF THE CRUST by by W.F. Cannon Cannon U. U. S. Geological Geological Survey, Survey,MS MS954, 954, Reston, Reston,VA VA 22092 22092 South border, aa remarkable remarkable cross cross South of Lake Superior, near the Wisconsin-Michigan border, section of the crust. This section displays displays what what had had been been the the upper upper 35 35 km of This section exposed as a sequence of nearly vertically dipping and north-facing volcanic volcanic and and sedimentary units of of Early Early and and Middle MiddleProterozoic Proterozoic age age and and underlying underlying Archean Archean rocks rocks (Figures (Figures 2-1 and 22). 2). This Thisstructure, structure,named namedthe theMontreal MontrealRiver Rivermonocline monocline by by Cannon Cannonand andothers others(1993), (1993), resulted resulted from from southward-directed southward-directed thrusting on a northward-dipping northward-dipping listric listric thrust of of crustal crustalscale, scale, the the Marenisco Marenisco fault. fault. The Theage ageof of thrusting thrustingisisknown knowntotobe beabout about1040-1060 1040-1060 Ma, rocks that that were were upthrust upthrust and Ma, the the date dateof of reset reset biotite biotite Rb-Sr Rb-Sr ages in Archean rocks andcooled cooled on on the the upper upperplate plateabove abovethe the fault fault(Cannon (Cannon and others, 1993). 1993). The trip begins at the mouth of vertically vertically dipping Freda mouth of the the Montreal Montreal River River where extensive exposures of Sandstone, Sandstone, the the youngest youngest unit unitexposed exposed in in the themonocline, monocline, form form bluffs bluffs along along the the Lake Lake Superior southward for for about about 25 25 km through through Superior shore. shore. The The traverse traverse progresses progresses southward successively older and and steeply successively older steeply dipping dipping to vertical vertical strata strata of of the theKeweenawan Keweenawan Supergroup, Supergroup,the theEarly EarlyProterozoic ProterozoicMarquette Marquette Range Range Supergroup, Supergroup, and and into intoLate Late Archean Archean metavolcanic metavolcanicrocks. rocks. STOP 2-1. Freda FredaSandstone Sandstoneatatthe themouth mouthofofthe theMontreal MontrealRiver River(Fig. (Fig.2-3) 2-3) STOP2-1. The The Freda Freda Sandstone Sandstoneisisthe theyoungest youngestunit unitexposed exposedin inthe theMontreal MontrealRiver River monocline monoclinebut but probably probably was was overlain overlain originally originally by as as much much as as aafew fewkilometers kilometers of of continental continental sandstones sandstones deposited deposited late late in the the history history of of the the rift. rift. The exposures seen seen here, here, representing representingthe the middle middleto toupper upperparts partsof of the theFreda, Freda, may may have have been been buried buried by by as as much much as as 3-5 3-5 km under under younger younger parts parts of ofthe theFreda Freda and andyounger youngersediments sedimentsof of the theBayfield Bayfield Group. Group. The Thesandstone sandstoneisiswell wellexposed exposedininhigh highcontinuous continuousbluffs bluffs along along the the Lake Lake Superior Superiorshoreline. shoreline. ItItisismostly mostlyaawell well bedded bedded and andcommonly commonly crossbedded crossbeddedfeldspathic feldspathic sandstone. sandstone. Dips Dips are areessentially essentiallyvertical. vertical. Volcanic Volcanic rock major rock fragments fragments are aa major constituent,indicating indicating that thatrift-derived rift-derived volcanic volcanic rocks rocks composed much of the the source source constituent, area. Muscovite Muscoviteisisalso alsoaacommon common detrital detrital mineral mineral in many layers indicating that a area. basementterrane terranewas wasalso alsoexposed exposedthat thatcontributed contributedaasubstantial substantialpart partof of the the detritus. detritus. basement 49 �00 Cii 0) NW Moho Archean White's Ridge mylield Group Bayfield Peninsula / MONTREAL MONTREAL RIVER RIVER Ml MONOCLINE S. S. shore shore of of Lake LakeSuperior Superior Moho I Archean Keweenawan Keweenawan I bio~~te ages diabase dikes S1 Figure the southern southernlimb limb of of the theMidcontinent Midcontinent rift rift showing regional structural structural context context of of the the Montreal Montreal River River monocline. monocline. The The Figure2-1. 2-1. Schematic Schematiccross cross section section ooff the showing the the regional section extends approximately from the Bayfield Peninsula to Mercer, Wisc., a distance of roughly 100 km. To the NW a prominent basement high, White's section extends approximately from the Bayfield Peninsula to Mercer,Wise., a distance of roughly 100 fan. To the NW a prominent basement high. White's Ridge, muchofofthe theKeweenawan Keweenawanvolcanic volcanicsection sectionand andremained remainedaapositive positivetopographic topographicfeature featureuntil untilthe theclose closeofofthe theextensional exiensional Ridge,limited limitedthe thedepositional depositionalextent extentofofmuch phase phase of of the the rift. rift.AsAsmore morewidespread widespreadthermal Ihennalsusiderice susidencesupplanted supplantedextension, extension,the theridge ridgewas wasburied buriedbeneath beneath the the Oronto Orontoand and Bayfied BayfiiGroups, Groups,which whichremain remain nearly nearly flatJying. flauying. Southeastward Southeastwardfrom fromWhite's White'sRidge Ridgetotothe thepresent present outcrop outcropbelt belt ofofthe thevolcanics, volcanics,the thevolcanic volcanicsection sectionbecomes becomes progressively progressively thicker. thicker. This This geometry part of thai the the deepest deepest part of the therift riftininthis thisarea areamay mayactually actuallyhave havebeen beentotothe thesouth southofofthe thepreserved preservedvolcanic volcanicrocks, rocks,ininananarea areasince sinceuplifted upliftedand and geometrysuggests suggests that deeply eroded. The Thepresent present steeply steeply northward-dipping northward-dippingattitude altitudeof ofthe therocks rocksininthe theMontreal MontrealRiver Rivermonocline monoclineisisbelieved believedtotobebethe theresult resultofofcrustal-scale crustal-scaleramping ramping deeply eroded. on to have have thrust thrust rift rift units and Archean on the the Marenisco Marenisco fault. fault. The TheMarenisco Mareniiofault faultisisinterpreted interpretedtotopenetrate penetrate the the entire entire crust crust and to units and and their their Early Early Proterozoic Proterozoic and Archean basement southward. The listric geomerty of the fault surface caused the upper plate to tilt northward, after which erosion has exposed the present crustal-scale basement southward. The listric geomerty of the fault surface caused the upper plate to tilt northward, after which erosion has exposed the present crustal-scale by the southerly dip dip of of originally and by by Middle Middle cross The involvement involvementof of Archean Archean rocks rocks in in the the monoclinal monoclinal structure structure is is shown shown by the southerly originallyvertical verticaldiabase diabase dikes dikes and cross section. section. The of biotite, was located Rb-Sr blocking temperature of uplift and cooling. 270°C isotherm, the which mark time The Proterozoic Rb-Sr ages of biotite, Proterozoic Rb-Sr ages of biotite, which mart lime of uplift and cooling. The 27WC isotherm, the Rb-Sr blocking temperature of biotite, was located by by of biodte determining determiningRb-Sr Rb-Sr closure closureages ages of biotitein in Archean Archean rocks. rocks. Rocks Rocks north north of of the the isothenn isotherm(originally (originallyabove abovethe theisotherm) isotherm)remained remainedcooler coolerthan than 270°C 27WCthroughout throughout ages reflecting reflecting Early Early Proterozoic and Keweenawan and retained retained ages Prot&ic and Archean Archean thermal thermal conditions. conditions. Rocks Rocksbetween between the theisotherm isothennand andthe the Marenisco Mareniscofault faultwere were Keweenawanburial burial and from about Ma and date the the time time of of heated heated above above 270°C 27WCby by Keweenawan Keweenawan burial burialand and Rb-Sr Rb-Sr biotite biotite ages ages were were reseL reset In In this this area area biotite bi& ages ages range range from about 1040-1060 1040-1060 Ma and date fault South uplift, andcooling coolmgcaused causedby bythrusting thrustingalong along the the Marenisco Marenisco fault Soothofofthe thefault, fault.Middle MiddleProterozoic Proterozoicburial burialwas was not notdeep deepand and biotite b i t eages agesagain again uplift,erosion, erosion,and reflect EarlyThoterozoic Proterozoicthermal thermalcvents. events. reflect Early �(ii 1 I 15 2 2' 2KM Figure 2-2. Cross section of the Montreal River monocline showing the location of field trip Figure 2-2.indicates Cross section of the Montrealburial Riverdepth along top estimated maximum duringshowing development of Midcontinent ri stops. Scale monocline the location of field trip along indicates estimated uplift top of the monocline. Agesmaximum of dated burial Middledepth Proterozoic units are shown in Ma.rift and prior to during igneous development of Midcontinent uplift of the monocline. Ages of dated Middle Proterozoic igneous units are shown in Ma. I 10 I— �/ 7T A721 / . / L - I. L -— '\ ' Freda Sandstone. I N 4 \\\ 1 15 — : \\ 1 n__ 11 I :- - - / I .1 II / — \; ___L___j_ // 7* 2 - H -\ ,- f 24 4 -ci 5CcPe t--- - x S lsaxUnI cOD - tC !I\X 4fl 0 ) MILE ? FEE! e._ I KILOMEtER Figure Bay Figure2-3. 2-3.Pans Partsofofthe theOronto Oronto Bayand andLittle LittleGirls GirlsPoint Point771/2' 112'quadrangles quadrangles showing 1 , 2, 2,and and3.3. showingthe thegeneral generalgeology geologyand andlocation locationof offield fieldtrip tripstops stops 1, 52 I �F' I I I I I 1 I I I I I r of numerous nearly An interesting secondary structural element is the presence of flatlying or very gently north-dipping faults. These These faults faults invariably invariably have only only aa few few centimeters to about a meter of of offset in which the upper plate plate has has moved moved relatively relatively north, as expressed by by drag on bedding and in some places by kinked, kinked, rather rather than places by broken, beds. Such along the the Montreal Montreal River. River. In Suchsmall small faults faults are are common in exposures along they cut clasts clasts that can be identified on opposite the Copper Harbor Harbor Conglomerate, Conglomerate, they displacements. The agee and cause of these small sides of the fault giving precise displ small faults faults are unknown. unknown. STOP 2-2. 2-2. Middle Middle part partof of Oronto OrontoGroup Groupalong alongParker ParkerCreek Creek(Fig. (Fig.2-3) 2-3) The top of the Copper Harbor Conglomerate, the Nonesuch Formation, and the lower part of of the the Freda Freda Sandstone Sandstonecan can be be seen seen along along the the incised inased bed bed of of Parker Parker Creek. Creek. of the the Nonesuch and adjacent The Parker Creek section is the most complete exposure of adjacent units in the Lake Superior region. region. Beds 75°N to to vertical. vertical. Detailed stratigraphy stratigraphy Beds dip from 75oN of of the Parker Parker Creek Creek section section was was described described by by Suszek Suszek (1991) (1991) on whose work the the following generalized description descriptionisisbased. based. The The upper upper part of the following generalized the Copper Copper Harbor Harbor Conglomerate of massive to to crudely crudelybedded bedded clast-supported clast-supported conglomerate with Conglomerate consists consists of of basalt and rhyolite cross-bedded, pebbly sandstone interbeds. Clasts Clasts consist consist mostly of with lesser granite granite and and gabbro, gabbro, all all probably probably derived derived from from slightly slightly older older Keweenawan Keweenawan jasper, quartzite, and chert clasts are are aa minor minor component component rocks. Banded iron-formation, jasper, rocks. but are but are widespread, widespread,indicating indicatingthat thatpre-Keweenawan pre-Keweenawanbasement basementwas wasalso alsoexposed. exposed. The Nonesuch Formation is about 130 m m thick thick and and comprises of of mostly mostly gray to pale brown siltstone, siltstone, sandstone, sandstone, and and minor minor shale, shale. It is generally thinly bedded to to laminated, but thicker thicker massive beds also occur. Small-scale Small-scale trough crossbedding crossbedding is is an an overall overall coarsening-upward coarsening-upward trend trend to to the the formation, formation, although although many common. There is individual units rocks of units display displayfining-upward fining-upward textures. textures. The fine-grained fine-grained rocks of the the Nonesuch Formation of the the Copper Copper Harbor. Harbor. A Formation lie on coarse conglomerate of A transitional transitional bed, one meter meter thick, thick, contains contains reddish-brown, trough-crossbedded sandstone at the base and grades grades upward upwardinto intogray-brown gray-brown calcareous calcareous siltstone. The The upper upper contact contact of the Nonesuch with the Freda Sandstone is gradational over about 20 m, in which gray siltstone and shale are interbedded interbedded with reddish-brown, reddish-brown, medium medium to to coarse sandstone. sandstone. Additional exposures exposures of the upper part of of the Copper Harbor Harbor Conglomerate Conglomerate can can be seen seen in in low low roadcuts roadcutsalong alongHighway Highway122 122ininthe theNW NW1/4 1/4ofofSec. Sec.30, 30,T. T.47 47N., N.,R. R. 11E. E. b I I 53 �I I I 0 1000 ----0 — — -l I1 1000 2000 5 5 3000 00 4 I MILE 5000 6000 -— 7000 FEET , 1 KIL0METCR KILOMETER 1 Figure Figure2-4. 2-4. Parts Parts of of the the Little LittleGirls Girls Point Point and and Iron Iron Belt Belt 7 1/2' 112'quadrangles quadrangles showing and 5. 5. showing the the general general geology geology and location of field trip trip stops stops 44and 54 I I I I I �— STOP STOP 2-3. Top Topof of Porcupine PorcupineVolcanics VolcanicsatatSaxon SaxonFalls Falls(Fig. (Fig.2-3) 2-3) Basalt flows flows and and interflow interfiow conglomerate conglomerateand andsandstone sandstoneofofthe theuppermost uppermost part part of of the River below below the dam at Saxon the Porcupine PorcupineVolcanics Volcanics are exposed along the Montreal River Saxon Falls flowage. The uppermost uppermost exposed unit is thin-bedded red sandstone and siltstone, which which is is underlain underlainby byaamassive massivebasalt basaltflow flow about about100 100 m m thick. This This flow is underlain by about interbedded conglomerate and sandstone. The about 30 30 m of interbedded The lowest lowest exposed exposed unit unit is is another partly brecciated brecciatedtop. top. About the upper half another basalt flow with an amygdular, partly half meter breccia, and and the the upper upper three meters are meter of of the the flow flow shows shows typical rubbly flow-top breccia, coarsely coarsely amygdular. amygdular.The Themost mostabundant abundantamygdule-filling amygdule-filling mineral is thomsonite, which occurs radiating blades blades in in the the larger larger amygdules. amygdules. The predominance predominance occurs in masses of coarse radiating of this this low low temperature temperature zeolite zeolite indicates indicates that rocks at this level of burial were only I weakly weakly heated heatedbefore beforeuplift. uplift. I STOP STOP2-4. 2-4. Rhyolite Rhyoliteatattop topofofICallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) I I I I I I I I The uppermost uppermostunit unitof ofthe theKallander KallanderCreek Creek Volcanics Volcanics is a thick, mostly massive, quartzrhyolite. We quartz- and and plagioclase-phyric plagioclase-phyric rhyolite. We informally designate this unit the Sheep Sheep Farm Farm rhyolite rhyolite and and this this stop stopisis our ourinformal informal type type locality. locality. The The reason reason for for the the name name isis obvious. obvious. The The unit unit is is at at least least 300 300 m thick and appears to be the product product of of aa single single eruptive eruptiveevent. event.ItItcan canbe betraced tracedfrom fromthis this locality locality westward for about about 30 30 km to Copper Copper Falls Falls State State Park near near Mellen, Mellen, where it is the the resistant resistant rock rock that that holds holds up upBrownstone Brownstone Falls Falls on on the theTyler Tyler Forks Forks River. River. At At that thatlocality, locality, we we have have located located by field measurement measurement the the horizon horizonof of the theprincipal principalmagnetic magnetic reversal reversal recorded recorded in in the theKeweenawan Keweenawansection. section. The The reversal reversal lies lies aa few fewflows flows beneath the rhyolite. The The rhyolite rhyolite has has been been dated dated atat1099 1099 Ma Ma (Zartman (Zartman and and others, others, 1995), 1995), so the age age of of the the magnetic magnetic reversal reversal must must also also be be approximately approximately 1099 1099Ma. Ma. At At this this stop, stop, the the exposures reveal the basal part of of the the flow, flow, which These blocks blocks which contains contains numerous numerous blocks blocks of rhyolite up to about about 20 20 cm across. These have haveaaslightly slightlydifferent differenttexture textureand andphenocryst phenocrystcontent contentthan thanthe thehost hostrhyolite. rhyolite. STOP STOP2-5. 2-5. Dacite DaateininKallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) The abundant rocks The upper uppermember memberof ofthe theKallander KallanderCreek Creek Volcanics Volcanics contains abundant rocks of of intermediate intermediatecomposition compositionin in addition additionto to basalt and rhyolite. We We have have proposed proposed that thatthe the upper upper part partof of the theKallander KallanderCreek CreekVolcanics Volcanics represents the partly eroded eroded remains remainsof of aa broad broad central centralvolcano, volcano, and and that thatthe theMellen Mellen Complex Complex is the crystallized remnants of aa magma magma chamber chamber that thatwas wasintruded intrudedinto intothe thevolcanic volcanic edifice edifice late in its eruptive eruptive history history (Cannon (Cannon and others, others, 1993). 1993). At At this this locality our data show that the rock knob in the gravelpit pitisisa afine-grained fine-grainedreddish-brown reddish-brown dacite (Si02=64-66wt%; wt%;Ti02=1.26 Ti02=1.26wt%; wt%; gravel dacite (SiO2=64-66 �I I I I I I I - -- - -- --3 7 I 0 U 1000 C I :000 2WX 5 3000 2000 - - ? . + - - , 0 0 4000 4000 -, 5000 5000 6000 60CC , 1 MILE 7000FEET I MILE 7000 FEET I KILOMETER I KILOMETER Figure 2-5. Part of the Saxon 7 112' quadrangle showing the general Figure 2-5.and Part of the Saxon geology location of field7trip stop 6. 1/2' quadrangle showing the general geology and location of field trip stop 6. 56 �I STOP STOP 2-3. Top Topof of Porcupine PorcupineVolcanics VolcanicsatatSaxon SaxonFalls Falls(Fig. (Fig.2-3) 2-3) Basalt flows and and interflow interfiow conglomerate conglomerate and and sandstone sandstone of of the the uppermost uppermost part Basalt flows part of of the Porcupine Volcanics are exposed along the Montreal River below the dam at Saxon the Porcupine Volcanics are exposed along the Montreal River below the dam at Saxon Falls flowage. The Falls flowage. The uppermost uppermost exposed exposed unit unit is is thin-bedded thin-bedded red red sandstone sandstoneand andsiltstone, siltstone, which underlain which is is underlain underlainby by aamassive massivebasalt basalt flow flow about about 100 100 m m thicic. thick. This This flow flow is is underlain by about mof about 30 30 m of interbedded interbeddedconglomerate conglomerate and sandstone. The The lowest lowest exposed exposed unit unit is is another basalt basalt flow flow with with an an amygdular, amygdular, partly partly brecciated brecciatedtop. top. About About the the upper upper half another half meter of the flow shows breccia, and and the upper three shows typical rubbly flow-top breccia, three meters meters are are coarsely amygdular. amygdular. The Themost mostabundant abundantamygdule-filling amygdule-fillingmineral mineral is is thomsonite, thornsonite,which which occurs in masses of of coarse coarse radiating radiatingblades bladesin inthe thelarger largeramygdules. amygdules. The predominance predominance of this of this low low temperature temperature zeolite zeolite indicates indicates that that rocks rocks at at this this level level of of burial burial were were only only weakly heated heated before before uplift. uplift. I STOP Rhyolite at attop topof ofKallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) STOP 2-4. Rhyolite I The uppermost uppermostunit unitof of the theKallander KallanderCreek CreekVolcanics Volcanics is aa thick, thick, mostly mostly massive, massive, rhyolite. We this unit quartz- and plagioclase-phyric rhyolite. We informally designate 'this unit the the Sheep Sheep I I I I I I I -. Farm rhyolite and this stop is our informal type locality. locality. The reason for the name is Farm The unit unit is at least m thick thick and and appears appears to to be be the the product product of obvious. The 300 m of a single single obvious. least 300 eruptive 30 km km to to Copper Copper eruptive event. event.ItIt can can be be traced traced from from this this locality locality westward for for about about 30 Falls State Park near Mellen, where where itit is is the resistant rock rock that holds up up Brownstone Brownstone River. At that Falls on the Tyler Forks River. that locality, locality, we have located by field measurement the horizon of the the principal principal magnetic magnetic reversal reversal recorded recorded in in the the Keweenawan Keweenawansection. section. beneath the the rhyolite. rhyolite. The rhyolite has been The reversal lies a few flows beneath been dated datedatat1099 1099 Ma (Zartman so the the age age of of the magnetic reversal must also be Ma (Zartrnan and others, others, 1995), 1995), so magnetic reversal Ma. At this stop, the exposures reveal the basal part approximately 1099 approximately 1099 Ma. part of of the the flow, flow, of rhyolite rhyolite up to about 20 cm across. These which contains numerous blocks of These blocks blocks have a slightly different texture and phenocryst content than the host rhyolite. STOP 2-5. Dacite Dacite in in Kallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) The upper upper member Volcanicscontains contains abundant abundant rocks of of The member of of the the Kallander Kallander Creek Volcanics intermediate composition basalt and and rhyolite. rhyolite. We have proposed proposed that the intermediate composition in addition to basalt represents the the partly partly eroded eroded remains of a upper part of of the the Kallander Kallander Creek Volcanics Volcanics represents broad central central volcano, volcano, and and that that the the Mellen Mellen Complex is the crystallized remnants of aa eruptive history magma chamber that was intruded intruded into into the the volcanic volcanic edifice late in its eruptive (Cannon and others, 1993). our data show that the rock 1993). At this locality locality our rock knob in in the the gravel pit pit isisaafine-grained fine-grainedreddish-brown reddish-browndacite dacite(SiO2=64-66 (Si02=64-66wt%; wt%;Ti02=1.26 TiO2=1.26wt%; wt%; 55 I �I I I I I $1 n I I I CeN/YbN=4.5) thatcontains containssmall smallplagioclase plagioclasephenocrysts. phenocrysts.The The rock rock has has a strong CeN/Yt>N=4.5)that primary and weathers weathers primary foliation, perhaps indicating that it is the basal zone of a flow, and into into platy platy fragments fragments parallel parallel to to the the nearly nearly vertical vertical foliation. foliation. Small Smalloutcrops outcropsnearby nearby show aa coarser, coarser, more more massive massive dacite. dacite. The Thedacite daciteisisoverlain overlainby bya abasalt basalt(Si02=50.24 (Si02=50.24 wt%; wt%; Ti02=3.78 Ti02=3.78wt%; wt%;CeNIYbrc_3.7) CeN/Yt>N=3.7)that is exposed in low outcrops along the power line north north of the the gravel gravel pit. pit. STOP 2-6. 2-6. Upson Upson Lake area--Siemens Bessemer Quartzite, Quartzite, and area--Siemens Creek Volcanics, Bessemer and Tyler Tyler Formation Formation (Fig. (Fig. 2-5) 2-5) of the Keweenawan section is is exposed exposed in contact with the At this locality the base o ft he Keweenawan underlying Tyler Formation. At underlying At the the top top of of the the prominent prominent bluff north north of of Upson Upson Lake Lake the Volcanicsare areexposed. exposed. They are pillowed lowermost basalt flows of the Siemens Creek Volcanics pillowed and brecciated brecciated as a result result of of eruption eruption into into aashallow shallow lake lake in inwhich whichthe theBessemer Bessemer Quartzite had been deposited. deposited. The Theflows flowshave haveaadistinctive distinctivechemical chemical composition composition marked by low (8-12wt%), wt%),and andhigh highCr, Cr,Ni, Ni,and andMgO. MgO. In In addition, rare earth low A1203 &03(8-12 earth element (REE) patterns patterns are and heavy heavy REEs REPs have have low element are quite quitesteep steep(CeN/YbN (CeN/YbN = about 15) and abundances. These indicate that that the the magmas magmas formed by a small abundances. These chemical characteristics indicate degree of partial melting of a deep, enriched mantle source (postulated to be a mantle plume), and that the plume), the magma magma erupted erupted directly directly to to the the surface surface without without undergoing undergoing significant crystallization and fractionation. fractionation. Flows Flows of of this this chemical chemical character character can can be recogi-uzed in the field by the phenocrysts of of clinopyroxene. clinopyroxene. These recognized the presence presence of small phenoaysts clinopyroxene-phyric flows flows have have been traced from near Bessemer, Michigan, to just just Bessemer, Michigan, west of this locality. They They apparently apparently represent represent aa unique unique magma magma composition compositionthat thatwas was erupted erupted only at the very outset outset of volcanism. volcanism. Identical Identical flows have been recognized at the base of the Minnesota, both both at at Ely's Ely's Peak Peak and at Pigeon the North North Shore Shore Volcanics Volcanics in Minnesota, Point Point and and Grand GrandPortage Portage(Green, (Green,1977). 1977). An interflow sedimentary bed is exposed between the first and second second flows. flows. The sediments are, in part, an algal laminite and and are are now now substantially metamorphosed metamorphosed so that that original original calcareous calcareous layers layers are are aa fine-grained fine-grained mat mat of of wollastonite. wollastonite. The The metamorphism was metamorphism was caused, caused, at at least least in in part, part, by by emplacement emplacementof the Potato Potato River Gabbro about 11km up-section. about up-section. Creek Volcanics Volcanicsare areunderlain underlain by by the the Bessemer Bessemer Quartzite, Quartzite, the oldest The Siemens Creek oldest unit in the Keweenawan Supergroup. Scattered of white white to to gray laminated Scattered exposures of quartzite are on the quartzite the slope slope below below the the basalt basalt exposures. exposures. Passing down-section, the Bessemer contains basal basal beds of coarse Bessemer contains coarse conglomerate conglomerate composed largely largely of of Early Early �•r -t ) i\ a-m / N V -: - $eiForma_yf vi; I — - -o •1475 !r •L 0 - • / Forts - - - °° F -4 Mlt€ 0 :OO 2O 3O o0 wo 7000 FEET KILOMETER Partof of the the Mt. Mt. Whittlesey Whittlesey 7 1/2' ~Figure i ~ u 2-6. r e Pan 112' quadrangle quadrangle showing the general geology geologyand andlocation locationof of field field trip trip stop stop 7. 7 general 58 N �I I Proterozoic metasedimentary metasedimentary clasts, Small garnet Proterozoic clasts, including including iron-formation. iron-formation. Small garnet porphyroblasts are common in the matrix. porphyroblasts are common in the matrix. A small small exposure exposure near near the base of the slope A slope shows an angular angular unconformity unconformity between basal conglomerate conglomerate of of the Bessemer Bessemer and thin-bedded argillite argillite of of the the Tyler Tyler Formation. Formation. This This is is the the only only exposure exposure known known to to us uswhere wherethe theunconformable unconformable relationship and the relationship between between the the Keweenawan Keweenawan Supergroup Supergroup and the Marquette Marquette Range Range Supergroup Supergroupcan can be be seen. seen. H STOP Tyler Formation Formation(Fig. (Fig.2-6) 2-6) STOP 2-7. Tyler I I This roadcut This roadcut exposes typical thin-bedded graywacke and argillite of the Early Early Proterozoic Tyler Formation. Although Althoughdips dipsare arenearly nearlyvertical, vertical, the the lack lack of of penetrative penetrative fabric indicates little fabric indicates little structural structuraleffect effect of the Penokean Penokean orogeny orogeny on on the the Tyler Tyler in in this thisarea. area. The highest grade common throughout the grade metamorphic metamorphic mineral is biotite, biotite, which is common matrix. a I I I I I I I I I a 1 STOP STOP 2-8. Ironwood Ironwoodhon-formation Iron-formationon onMt. Mt.Whittlesey Whittlesey(Fig. (Fig.2-7) 2-7) - The prominent held up by The prominent ridge of of Mt. Whittlesey Whittlesey isis held by the the Ironwood Ironwood IronIronformation. An Anunusually unusuallygreat greatthickness thickness of of iron-formation iron-formation is present here owing owing to to structural repetition structural repetition by thrust thrust faults faults and and folds folds produced during during the the Penokean Penokean orogeny. orogeny. shows our recent interpretation interpretation of Whittlesey area that of the the geology geology of the Mt. Whitdesey Figure 2-7 shows will be seen at Stops 2-9, and and 2-10. 2-10 Mt. easternmost extent will Stops 2-8, 2-8,2-9, Mt. Whittlesey lies at the easternmost extent of of Proterozoic)foreland forelandfold foldand andthrust thrust belt. belt. At the Penokean (Early Proterozoic) At Mt. Mt. Whittlesey, Whittlesey, a thrusts repeats series of thrusts series repeatsthe the Early Early Proterozoic Proterozoic section, having detached it from from Archean rocks along a basal decollement. The The thrusts thrusts all all rise rise in in the the section section to to the the east east along along aa series of of lateral ramps. ramps. Northward Northwardtilting tiltingof of the theregion region in inMiddle Middle Proterozoic Proterozoic time time results in the current results current map map pattern pattern that thatprovides provides an anunusual unusualcross-sectional cross-sectional view of the thrust complex. To To understand understand the thePenokean Penokean structural structural geometry geometry the map pattern pattern should be viewed as a longitudinal longitudinal cross cross section along the original trend of of the thrust thrust belt, so that the the upper upperplates platesof of originally originally nearly nearly flat-lying flat-lying faults would have have moved moved northward away from the viewer. Because Because of later tilting, these original thrusts thrusts now now mimic the geometry of of normal faults-that faults--that is, is, the the upper upper plates plates appear to have moved down to the north. The Theramps rampsthat thatrise risetotothe theeast eastare arelateral lateralramps rampsalong alongwhich which the the plates have have undergone undergone transcurrent transcurrent movement movement rather rather than thanoverthrust overthrustmovement. movement. Displacement along along the basal decollement diminishes eastward eastward as splays from the Displacement decollement diminishes the rise in the section. East decollement successively rise 2-10 the the Early Early Proterozoic Proterozoic decollement Eastof of Stop Stop2-10 section unconformably on section lies unconforrnably on Archean Archean rocks. �2 5/; ) U U — J (4\6(' itou — $ROMHfR 1 FEH /000 1 —- 6(X))) -_- 5000 afl I —: -- -a =——1 4(U) ) rrT _r 0 F X) I — I0 172 5 - -- I_i I 0 I Ft= : iLiT\ç ES?.. '-: o2:j '1;-c - 10. and 9, 8, stops trip field of location and geology general showing quadrangles 1/2' 7 MeIlen and Whittlesey Mt. the of Part 2-7. Figure , V$1? Y — (-) ' tvyt1 00J C' 1! ;iHI!t �S At Stop 2-8 2-8 excellent excellentexposures exposuresofofthe the Ironwood bonwood Iron-formation hon-formation occur At occur on on the the north face of of the ridge near the summit, and along a railroad grade near the Berkshire mine ruins. At Atthe theformer formerlocality, locality, aa large large area area was was cleaned cleaned of overburden overburdenin in the the 1920s 1920s in anticipation of open pit mining. mining. Only near the base base of of Only a small pit was developed near glacially polished, polished, exposure cleared area; the remainder remainder provides provides an an excellent, excellent, glacially exposure in which many At the many details details of of sedimentary sedimentary features features are are extraordinarily extraordinarily well well displayed. displayed. At mine ruins ruins an abandoned railroad grade provides a continuous cross section Berkshire mine of several several hundred hundredmeters metersof of section section and and aa tight tight fold fold is exposed in the cut. The iron-formation contains several several lithologic lithologic variations. The classic fivemember internal member internalstratigraphy stratigraphydefined definedtotothe theeast east(Hotchldss, (Hotchkiss,1919; 1919; Huber, Huber, 1959) 1959) consists of alternating alternatingmembers members of of even-bedded, even-bedded,carbonate carbonate iron-formation iron-formation (slaty (slaty iron-formation) iron-formation) irregularly-bedded hematitic jasper. jasper. This stratigraphy stratigraphy becomes more more complex complex and and and irregularly-bedded and irregular westward westward along alongthe the iron ironrange; range; we we have have not not been been able to apply apply itit west west of of Mt. has many lithologic Whittlesey. The iron-formation exposed here characteristically characteristically has Whittlesey. of variations on a small scale so that individual exposures may show a complete range of lithologies interbedded lithologies interbeddedon onaascale scale of meters or less. 2-9. Palms STOP 2-9. Palms Formation Formationand andBad Bad River River Dolomite Dolomite at at Eagles Eagles Peak Peak (Fig. ( ~ i ~2-7) .2-7) At the southwest prominent bluff, Eagles Peak, is is held held up up southwestend endof of Mt. Mt. Whittlesey a prominent by laminated At the laminated argillite argillite typical of the the lower lower part part of of the thePalms PalmsFormation. Formation. At westerost tiptip of the bluff thethe unconformable -westernmost of the bluff unconformablecontact contactbetween between the the Palms Palms and and underlying Bad Dolomite is is well well exposed. exposed. The Palms Palms can can be be seen seen to to be be draped draped underlying Bad River Dolomite which also has has a weathered into shallow depressions along the top of the Bad Bad River, River, which contact. The rusty color appears to be into rusty and rusty zone zone for for about about half a meter below the contact. caused by recent recent oxidation oxidationof small small amounts amounts of pyrite pyrite along along the the contact. contact. The breccia composed composed of of angular to The Bad River Dolomite at this locality is a chert breccia subrounded fragments subrounded fragmentsof of gray graychert chertcemented cemented mostly mostly by aa second second generation generationof of chert. chert. fill interstices interstices between between breccia breccia fragments, Locally, well-rounded well-rounded quartz quark grains grains partly partly fill Locally, matrix. At and magnetite magnetite is locally abundant as euhedral grains in the matrix. At other other localities localities nearby, magnetite of prospect magnetite was sufficiently abundant to have promoted the sinking of shafts in the early days days of of iron iron exploration. exploration. These These are are present present generally generally immediately immediately below the contact contact with with the the Palms Palms Formation. Formation. This This distinctive distinctive chert chert breccia breccia has been Locallyitit is is underlain underlain by by traced as aa mappable mappable unit unit for for about about12 12km km along along strike. strike. Locally marble River Dolomite Dolomite in inthis thisregion. region. We marble and and tremolitic tremolitic marble marble more more typical typical of the Bad River believe that the the breccia is a residual deposit, formed by solution of an originally thick section of of cherty dolomite during the weathering interval prior to to Palms Palms deposition. deposition. P 61 �The residue of insoluble chert was variably reworked into its present character and cemented by secondary silica. Magnetite Magnetite was apparently introduced introduced hydrothermally sometime sometime after after deposition depositionof of the the Palms PalmsFormation. Formation. STOP 2-10. 2-10. Contact of Early Proterozoic strata and Archean Archean metavolcanic rocks on the the southeast 2-7) southeastflank flankof of Mt. Mt.Whittlesey Whittlesey(Fig. (Fig.2-7) Low outcrops outcrops near near the the base base of a prominent ridge supported by the Low prominent ridge the Palms Palms Formation reveal the basal contact Proterozoic strata strata with with underlying contact of Early Proterozoic underlying dacite breccia of The breccia breccia has has a penetrative structural fabric, breccia of Late Archean Archean age. age. The fabric, best best expressed by the expressed the prominent prominent elongation elongation of of clasts. clasts. Long Long axes axes plunge plunge moderately moderately southward, southward, but but must musthave haveplunged plungedmoderately moderatelyto to steeply steeply northward northwardprior priortototilting tiltingof of the rocks into the monoclinal structure. structure. The Thebasal basalEarly Early Proterozoic Proterozoicunit unitisischert chertbreccia breccia of the Bad River Dolomite, Dolomite, the the same same unit unit seen seen at at stop stop 2-9. 2-9. Along Along the the contact contact the the upper meter or two two of of the the dacite dacitebreccia breccia is strongly sheared parallel to the contact, and the the overprinted by by this this secondary secondary fabric. fabric. Shearing Archean fabric typically is completely overprinted Shearing is weak to absent absent in in the the chert chertbreccia. breccia. To our knowledge these outcrops are the only ones in the western part of of the the Gogebic Range Range where where a basal detachment between the Early Proterozoic strata and Gogebic and observed. We Archean basement rocks can be directly observed. We believe believe the Early Early Proterozoic flatlying basal contact during the Penokean strata were thrust thrust northward northwardalong alongaanearly nearly flatlying orogeny. Because River monocline, monocline,the thepresent present apparent apparent Because of of later later tilting tilting of the Montreal River This fault fault can be traced displacement reflects a down-to-the-north down-to-the-north normal normal fault. fault. This traced westward, and westward, andabout about11km km to to the the west west of of these these exposures exposures it passes up-section up-section so so that that the the Bad River-Palms-Ironwood River-Palms-Ironwood sequence sequenceofofthe theupper upper plate plate is juxtaposed juxtaposed over Ironwood Bad Iron-formation in in the lower plate, plate, producing producing the the unusually Iron-formation unusually wide outctrop belt of of Whittlesey. Just east of of this stop the basal thrust Ironwood along higher parts of Mt. Whittlesey. appears appears to to pass pass upward upwardinto intothe theEarly EarlyProterozoic Proterozoic strata. strata. Exposures Exposuresnear nearBallou Ballou Creek Creek show that that the thebase baseofofthe theEarly EarlyProterozoic Proterozoicrocks rocks lies liesunconformably unconformably on onArchean Archean without an volcanic rocks without an intervening intervening shear shearzone. zone. The Archean Archean rocks rocks seen seen at at Stop Stop 2-10 2-10are arethe the structurally structurally lowest lowest parts parts of of the The monocline that the master that are are seen seen on on the the field field trip. trip. But But the the trace trace of the the Mareriisco Marenisco fault, the thrust that lies about about 88 km km to to the the south. south. Thus, thrust that formed formedthe theMontreal MontrealRiver River Monodline, Monocline, lies Thus, all of the stratigraphic seenon on the the trip, trip,plus plusan. an additional additional88 km km stratigraphicsection section to to the the north north that thatisisseen of Archean rocks to the south, form the upper of upper plate plate of of the the Marenisco Marenisco fault, a coherent structural unit structural unit that that was was uplifted uplifted and andtilted tilted late late in in the the Middle Middle Proterozoic history of the region. region. 62 I �— I I I I I I REFERENCES REFERENCES Cannon, Crustal-scale thrusting thrusting and Cannon,W.F., W.F., Peterman, Peterman,Z.E., Z.E., and andSims, Sims,P.K., P.K., 1993, 1993, Crustal-scale and origin originof of the theMontreal Montreal 35-km-thick cross section of the Midcontinent rift in northern Michigan River monocline a and River monocline - a 35-km-thick cross section of the Midcontinent rift in northern Michiganand Wisconsin: Wisconsin:Tectonics, Tectonics,v.v.12, 12,p.p.728-744. 728-744. Green, Green,J.C., J.C., 1977, 1977, Keweenawan Keweenawanplateau plateauvolcanism volcanismininthe theLake LakeSuperior Superiorregion, region,ininBaragar, Baragar,W. W.R.R.A., A.,and and others, (eds.), Volcanic regimes in Canada: Geological Association of Canada Special Paper 16, p. 407others, (eds.), Volcanic regimes in Canada: Geological Association of Canada Special Paper 16, p.407422. 422. Hotchkiss, Hotchkiss,W.O., W.O., 1919, 1919, Geology Geology of of the the Gogebic Gogebic Range Range and and its its relation relationtotorecent recentmining miningdevelopments: developments: Engineering Journal, v. v. 108, p. p. 443452, 501-507, 537-541, 577-582. Engineeringand andMining Mining Journal, 108, 44342,501-507,537-541,577-582. Huber, Huber,N.K., N.K., 1959, 1959, Some Some aspects aspectsof of the the origin originof of the the Ironwood IronwoodIron-formation Iron-formationofofMichigan Michiganand andWisconsin: Wisconsin: Economic p. 82-118. EconomicGeology, Geology,v.54, v. 54,p.82-118. Suzek, 1991, Suzek,T.J., T.J., 1991, Petrology and and sedimentation sedimentation of of the theMiddle MiddleProterozoic Proterozoic(Keweenawan) (Keweenawan)Nonesuch Nonesuch Formation, Formation,western westernLake LakeSuperior Superiorregion, region,Midcontinent Midcontinentrift rift system: system: Duluth, Duluth,Minn., Minn.,University Universityofof Minnesota, 198p.p. Minnesota,Duluth, Duluth,unpublished unpublishedM.S. MS.thesis, thesis,198 Zartman, 1995, U-Th-Pb U-Th-Pb ages ages of of some some Keweenawan Keweenawanrocks rocksfrom from Zartrnan,R.E., R.E.,Cannon, Cannon,W.F., W.F.,and andNicholson, Nicholson,S.W., S.W.,1995, western Lake Superior, northwest Wisconsin and east-central Minnesota [abstracti: Proceeding western Lake Superior, northwest Wisconsin and east-central Minnesota [abstract]: Proceedingofof International International Field FieldConference Conferenceand andSymposium, Symposium,International InternationalGeologic Geologic Correlation CorrelationProgram ProgramProject Project 336, 336, Duluth, Duluth,Minn., Minn.,p.p.217-218. 217-218. I I I I I I I I I I 63 �r I I I I I I I I I I I I I I I I I I I FIELDTRIP TRIP##44 GUIDE GUIDEFOR FOR FIELD PROTEROZOIC GEOLOGY OF EARLY EARLYTO TOMIDDLE MIDDLE PROTEROZOIC GEOLOGY OF THE REGION THE LAKE LAKENAMEKAGON NAMEKAGON REGION �I FIELD TRIP TRIP #4 I I I EARLY TO TO MIDDLE PROTEROZOIC GEOLOGY OF EARLY THE LAKE NAMEKAGON REGION GION by W. Cannonl, L. W. F. cannon1, L. G. G.Woodruff2, Woodruff2, and andS. S. W. W. Nicholson1 Nicholson1 Geological Survey Survey U. S. Geological 1Eastern Mineral Resources, eastern Mineral Resources,Reston, Reston,VA VA22092 22092 2Central Central Mineral Mineral Resources, Resources, St. St. Paul, Paul, MN MN55112 55112 This field trip offers offers new new interpretations interpretations of the structure, structure, geochemistry, geochemistry, and ana stratigraphy of the based on recent studies by the U. S. S. the Lake Lake Namekagon Namekagon region region based the U. Geological Survey. The Geological Survey. The trip trip will will emphasize emphasize the rocks of of the Powder Powder Mill Mill Group 1 I I I I I I n (Siemens Creek and Chengwatana Chengwatana Volcanics (Siemens Creek Volcanics Volcanics and Kallander Kallander Creek Volcanics) and Volcanics of the 'of the Keweenawan KeweenawanSupergroup, Supergroup,and andthe thecogenetic cogenetic Mellen Mellen intrusive intrusive complex, all rocks related Ga Midcontinent Midcontinent rift. rift. Stratigraphic and geochronologic data data from the the 1.1Ga related to the 1.1 different suggest a complicated differentrock rock units units of of the the Midcontinent Midcontinent rift in this region suggest complicated history of of volcanic eruption eruption and andmagma magma emplacement. emplacement. Early Earlyextrusive extrusivevolcanics, volcanics, flood flood basalts of the the Siemens Siemens Creek Creek Volcanics Volcanics and perhaps perhaps the thelower lowerKallander Kallander Creek CreekVolcanics, Volcanics, erupted subsiding basin basin throughout erupted from a number of of different different centers in a generally subsiding the the western western Lake Lake Superior Superior region. region. Development Development of of aa large largeshield shieldvolcano volcano complex, complex, possibly possibly centered centerednear nearthe thepresent presentlocation locationof of Mellen, Mellen, Wisconsin, was accompanied accompanied by intrusion shield. This produced the intrusion of multiple multiple magma magma chambers chambers in the volcanic shield. the Mellen Mellen intrusive complex complex and eruption eruption of of volcanic volcanic equivalents, the upper Kallander Kallander Creek Volcariics Volcanics (Cannon (Cannon and and others, others, 1993). 1993). With With aa decline decline in in shield shield volcano volcano activity, activity, floodfloodbasalt eruption eruptionfrom fromwithin withinthe thecentral centralgraben grabenof of the the rift rift became became dominant, dominant, forming forming aa thick series series of basalt flows, flows, the Chengwatana Chengwatana Volcanics. Volcanics. Sedimentary rocks deposited during glacio-fluvial during the thepost-extensional post-extensionalphase phaseof of the therift riftare arecovered coveredby byPleistocene Pleistocene glacio-fluvial and and lake lake deposits depositsand and are arenot not exposed exposed in in this this area. Post-rift Post-rift reverse reverse faulting faulting along the Lake Owen fault fault and andMarenisco-Atkins Marenisco-Atkins Lake fault during during late late Keweenawan Keweenawan time time rotated vertical in in some some areas. areas. As a rotated all all units units to to the the northwest, northwest, tilting tilting them to nearly vertical result, result, aa south-to-north south-to-north traverse traverse through through the the rift rift lithologies lithologies in the the area area north north of of Lake Lake Namekagon from older older to younger, younger, and and of of Namekagon provides provides aa cross cross section both through time, from crustal crustaldepth, depth,from fromrelatively relativelydeep deepto toshallow. shallow. The The first first stop stop will will be be in inan anEarly EarlyProterozoic Proterozoic sequence sequence of of iron iron and andsilica-rich silica-rich argillites argillitesof of the the bonwood Ironwoodhon-formation Iron-formationand andaametadiabase metadiabasesill. sill. This Thisstop stopis is notable notable for spectacular exposure exposure of of unusual unusual igneous igneous breccia breccia units units (Figs. (Figs. 4-1 4-1 and and 4-2). 4-2). All aa spectacular I i 67 �1'- KJIOMHFR 7 I 5000 40(W) r_3-__—_-i-z:==-- &)1X) 0 3000 0 2000 - 5 - I€0 _td L: 0 I 10® _______ - - 5. and 4, 3, 2, 1, stops trip field of locations and geology general showing quadrangle 1/2' 7 View Grand the of Part 4-1. Figure FEET ________ -: 144 -î I — — �I subsequent stops will will examine examine rocks rocks of of the the Middle Middle Proterozoic Proterozoic Midcontinent Midcontinent rift, rift, subsequent including 4-4, and includingthe theMellen Mellenintrusive intrusivecomplex complex(Stops (Stops4-2, 4-2,4-4, and4-5: 4-5:Fig. Fig. 4-1) 4-1)and and volcanic volcanic 4-6, rocks of the the Powder PowderMill MillGroup Group(Stops (Stops4-3, 4-3, 4-6,4-7, 4-7,and and 4-8: 4-8:Figs. Figs. 4-1 4-1and and 4-3) 4-3)and and rocks Chengwatana and ChengwatanaVolcanics Volcanics(Stops (Stops4-9 4-9 and4-10: 4-10:Figs. Figs.4-3 4-3and and4-4)). 4-4)). - STOP 1. Early Early Proterozoic Proterozoicdebris debrisflow flowand andmetadiabase metadiabase(Figs. (Figs.4-1 4-1and and4-2). 4-2). The topographic topographic highland highland extending extendingnortheastward northeastwardfrom fromForest ForestService ServiceRoad Road 379 numerous 379 hasThe numerousexposures exposuresof of bonwood Ironwoodhon-formation Iron-formationand andmetadliabase metadiabasesills sillstypical typical of the westernmost Range. Near the westernrnost extent extent of of the the Gogebic Gogebic Iron Range. the junction junction with with Forest Forest Service Road 201, just east of of Atkins Lake, Lake, two two unusual unusual breccia breccia units are 201,just are also also exposed. exposed. The breccia units contain angular to to subrounded subrounded clasts, clasts, up up to to 11 m in breccia units contain angular in length, length, of of metamorphosed, metamorphosed, banded banded siliceous siliceous sedimentary sedimentary rocks in a matrix matrix of of dark dark gray-green gray-green massive rock. Clasts Clastsmainly mainlyare aresiliceous siliceousargillite, argillite, aa very veryfew fewof of which whichare aremagnetic. magnetic. Most are are tabular tabular with with angular angularcorners, corners,but butsome someclasts clasts are are bent bent or orfolded, folded,suggesting suggesting that they Clastsconsist consist of of they were were not not fully fully lithified lithified when when incorporated incorporated in the matrix. Clasts alternating alternating layers layers of of recrystallized recrystallized quartz, quartz,fine-grained fine-grained chlorite, chlorite, biotite biotite or oractinolite, actinolite, garnet, garnet, and andgenerally generallyminor minoramounts amountsof ofmagnetite magnetite(Feher (Feherand andFlood, Flood, 1995). 1995). The The matrix matrix is aa fine-grained fine-grainedmafic mafic rock, rock, composed of fine- to medium-grained amphibole, amphibole, garnet, garnet, plagioclase, and magnetite, magnetite, with conspicuous conspicuous amygdules amygdules in in places. places. Metamorphic Metamorphic recrystallization has destroyed destroyed much much of the primary texture, texture, although although relict plagioclase phenocrysts phenocrysts are present present locally. locally. Preliminary geochemical geochemical data indicate indicate aa tholeiitic tholeiitic composition for the matrix Between the breccia units is is aa matrix (Feher (Feher and Flood, Flood, 1995). Between massive metadiabase 50 itt m thick. thick. The The top top of of the the sill sill is is chilled against againstthe thebase base metadiabasesill sill about about50 of the upper breccia breccia unit. The Thebase base of of the the sill sill is is separated separated from from the top top of of the the lower lower breccia unit by by aathin thinselvage selvageofofmagnetic magneticiron-formation. iron-formation. The breccia breccia units and interlayered km along along strike, but likely extend farther farther into into interlayeredsill sill can can be be traced traced for for about about11 km areas areas with with poor poor exposure, exposure. units may may be be extrusive extrusive basalt flows or ash ash that that incorporated incorporatedclasts clasts The breccia units The perfectly during eruption. eruption. Features suggestive of of an extrusive extrusive origin origin include: include: 1) perfectly concordant contacts sediments and concordant contacts between breccias and thinly laminated sediments and aa lack lack of any observed 2)strong strong lithologic lithologic contrast contrast between between the the breccias breccias observed cross-cutting cross-cuttingrelationships; relationships; 2) and undoubtedly undoubtedly intrusive intrusive metadiabase metadiabase exposed exposed in the the same same outcrop; outcrop; 3) 3)common common amygdular amygdular textures textures in in the the breccias breccias that are are absent absent in nearby nearby metadiabase; metadiabase; and and 4) 4)rare rare areas areas of rubbly rubbly matrix matrix that that resemble resemble pyroclastic pyroclastic textures. Alternatively Alternativelythe thebreccias brecaas may may be be related relatedto tothe themauic mafic sill, which could could have have been been emplaced sediments. Evidence consistent emplaced at at aa shallow shallow level into wet, semiconsolidated sediments. 69 �r — MAFIC MAlRCt El BRECCIA Br '9 BRECCIA IN IN AA MAFIC MATRIX Md Br —— — META DIABASE ——— c 50i Mg —— META GABBRO 0 ——— Mg / fl ci E a GIF —— — WAVY-BANDED WAVY-BANDED GRANULAR IRON FORMAT10 FORMATION GRANULAR ® FJELDSTOPS @ FIELDSTOPS GIP —— LAMINATED SILICATE SIUCATE LAMINATED IRONFORMATION FORMATION IRON — GIF 45 -" 5 — 0 0 0 OUTCROP 0 OUTCROPAREAS AREAS X mn 10 50 IXMm STRIKE AND AND DIP DIP STRIKE OF BEDDING OFBEDDING 'F # GEOLOGIC CONTACT CONTACT GEOLOGIC Fig. 4-2. area sshowing outcrops and and geologic geologic 4-2. Detailed map of the Atkins Lake area Fig. h o w i n g outcrops among iron-formation, iron-formation,bbreccia diabase and and gabbro. relationships among relationships r e c c i a uunits, n i t s , diabase gabbro. Unpublished map Unpublished mapprepared preparedby byKiasner Klasnerand andLaBerge. LaBerge. I I I I I I I I I I I 70 I I I I �with with an an intrusive intrusiveorigin originincludes: includes:1)1)occurrence occurrenceof of aa breccia breccia zone zone both both above above and and below below the metadiabase metadiabasesill sill (although (althoughthe thelower lowerzone zoneisis separated separatedfrom fromthe thesill sillby by aa thin thinseam seamof of iron-formation); War (initially lithified) lithified) and iron-formation);and and2) 2)incorporation incorporationinto intothe thebreccias brecciasof of tab tabular bent bent (initially (initiallyunlithified) unlithified)blocks blocks of of the the same same composition. composition. Neither Neither of of the the above above interpretations interpretationsseems seems to to explain explain all all observed observed relationships, relationships, and the the origin origin of of the the breccia breccia units thus thus remains enigmatic. An An especially especially problematic feature feature is that that nearly nearly all all of of the the clasts clasts are are exotic exotic and are not composed of immediately surrounding surroundingiron-formation, iron-formation, but but most mostclosely closely resemble resemble banded argillite argillite of of the the lower lower part part of of the the underlying underlyingPalms PalmsFormation. Formation. j STOP 2: 2: Granite Graniteof of the theMellen Mellenintrusive intrusivecomplex complex(Fig. (Fig.4-1). 4-1). The The metadiabase and iron-formation seen in Stop 4-1 are intruded by by several several dikes probably probably are offshoots offshoots of of a small granite body small granitic dikes. dikes. These These dikes in the open woods south of exposed in several outcrops east of Atkins Lake, Lake, in of Forest Forest exposed Service Road Road 379. 379. The granite is pink and and white, white, with with aa mediummedium-to tocoarse-grained coarse-grained minerals are potassium equigranular to porphyritic porphyritic texture. texture. Principal Principal minerals potassium feldspar, feldspar, plagioclase, biotite, and and quartz. The plagioclase, The granite granite intrudes intrudesEarly Early Proterozoic Proterozoic metasediments metasediments equigranularbiotite, of the Ironwood of metamorphic effects effects and and shearing shearing within within of Ironwood Iron-formation; Iron-formation; the lack of the granite suggests it is in age. age. The is Middle Middle Proterozoic Proterozoic in The granite granite is is very very similar similar in in appearance to appearance to the thewell-known well-knownMellen Mellen granite, granite, aaphase phaseof of the theMellen Mellen intrusive intrusivecomplex, complex, which is locally exposed over a large area more than 20 km to the northeast northeast of of this this locality. locality. intrusive complex is made up In addition addition to to this this small small granite granite body, body, the the Mellen Mellen intrusive of two large, intrusion and of large, layered layered gabbroic gabbroic bodies, the Potato River intrusion and the theMineral MineralLake Lake intrusion (Stop intrusion (Stop 44), 44), and andseveral severalrelated relatedigneous igneousbodies bodies including including the the Mellen Mellen granite, granite, the peridotitic Rearing peridotitic Rearing Pond Pond intrusion, intrusion,and andaaseries seriesof of gabbro gabbro and and granophyre granophyresills sills(Stop (Stop445). A Agranophyre granophyreofofthe theMineral MineralLake Lakeintrusion intrusionhas hasa aU-Pb U-Pbzircon zirconage ageofof1102.0 1102.0±Â2.8 2.8 Ma Ma and brecciates gabbro gabbro (Zartman and others, others, 1995). 1995). The Mellen granite, which intrudes and (Zartman of the Mineral Lake intrusion, has an an indistinguishable indistinguishableU-Pb U-Pb zircon age (within (withinerror) error)of ± 1.4 Ma Ma (Zartman (Zartman and 1100.9 andothers, others,1995). 1995). 1100.9 pyroxene hornfels 3. Siemens STOP 3. Siemens Creek Creek Volcanics Volcanics ---pyroxene homfels and and granophyre granophyre(Fig. (Fig.4-1). 4-1). Volcanics,the thelowermost lowermost unit unit of of the the Powder Powder Mill Group, is The Siemens Creek Volcanics, Wisconsin. It consists consists of a the oldest volcanic unit in the Midcontinent rift in northern Wisconsin. sequence erupted as as relatively relatively thin thin flows. flows. The TheMarenisco-Atkins Marenisco-AtkinsLake Lake sequence of flood basalts erupted fault bounds the the Keweenawan Keweenawan rocks rocks in this area area with with Keweenawan Keweenawan rocks thrust I 71 �I I I I p I I I I I I I I I extension of the larger intrusion extension intrusion to to the the east. east. The Therock rockconsists consistsof of mediummedium-to to coarsecoarsegrained grained plagioclase, plagioclase, pyroxene, and and magnetite, although although minerals minerals in in the the gabbro gabbro typically typically are altered. Because Because pyroxene pyroxene and and magnetite magnetite are are more more resistant resistant than thanplagioclase plagioclase to to weathering, a hackley hackley surface has developed on the outcrop, outcrop, with with knobs knobs of of mafic mafic minerals minerals prominent. prominent. STOP GranophyreofofLong LongMile MileLookout Lookout(Fig. (Fig.4-1). 4-1). STOP 5. Granophyre upper part The upper part of of the theMineral MineralLake Lake intrusion intrusion becomes becomes increasingly Fe-rich with the development development of ferrogabbro and granophyre. Seifert Seifert and and others others(1992) (1992) determined that intrusions associated anorthosite formed from that felsic intrusions associated with with the the Mineral Lake gabbroic anorthosite evolved mantle magmas that intruded along along older, mafic intrusive bodies and early with further crystal fractionation occurring occurringin in place. place. The granophyre granophyre at volcanics, with at this this stop stop is is an an offshoot offshoot from the upper upper part partof of the theMineral Mineral Lake Lake intrusion, intrusion, one one of of several several thin thin granophyric granophyric sills that interfinger with gabbroic sills in the western part part of of the theMellen Mellen intrusive complex. Granophyre exposed exposed in in the small hill of complex. Granophyre of Long Long Mile Mile Lookout Lookout typically typically is pink, pink, finefine- to to medium-grained, medium-grained, and contains contains small small phenocrysts phenocrysts of of plagioclase in aa graphic-textured of potassium feldspar and quartz. The plagioclase graphic-textured matrix matrix of potassium feldspar quartz. The granophyre typically weathers weathers brick red granophyre red because because of the presence presence of hematite. hematite. Basalt and andbrecciated brecuatedflow flowtop, top,lower lowerKallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.4-3). 4-3). STOP 6. Basalt The Volcanics consists consistsofof aa sequence sequence of of basalt, basalt, andesite, and The Kallander Creek Volcanics of flood basalts, similar to the rhyolite. The Thelower lowerKallander KallanderCreek CreekVolcanics Volcanics consists of Siemens Creek Creek Volcanics, Volcanics,but but the the upper upper Kallander Creek may may be an Siemens Kallander Creek an extrusive extrusive equivalent equivalentto to the the Mellen Mellen intrusive intrusivecomplex. complex. AAwedge wedgeof of the theKallander KallanderCreek CreekVolcanics, Volcanics, striking and dipping dipping to the northwest, striking northeast-southwest northeast-southwest and northwest, occurs occurs between the Marinesco-Atkins Lake Lake fault to to the south, the Lake Lake Owen Owen fault fault to to the the north, north, and the Marinesco-Atkins Mineral Lake intrusion intrusion to the the east. Largely Largelyunaltered unalteredvolcanics volcanicsof of the the Kallander KallanderCreek Creek can can be traced into into thin thin bands bandsof of metavolcanic metavolcanic rocks within the the Mineral Lake Lake intrusion, intrusion, caught up between thin thin sills sills of of gabbro gabbro and and granophyre, granophyre, attesting attesting to to aacomplicated complicated history eruption and and magma history of of volcanic eruption magma emplacement. emplacement. At this stop stop aabasalt basaltflow flownear nearthe thebase baseofofthe theKallander KallanderCreek CreekVolcanics Volcanics isis exposed, including a thick flow top-breccia. top-breccia. The basalt varies from massive to sparsely exposed, including sparsely amygdular, and and isis metamorphosed metamorphosedto toan anassemblage assemblageof of hornblende-epidote-biotitehornblende-epidote-biotitechiorite-plagioclase. breccia consists consists of of angular fragments of highly chlorite-plagioclase. The flow-top breccia highly fragmentsare are mostly mostly aa few few centimeters centimeters in in diameter diameter but amygdular basalt. Breccia Breccia fragments range Arnygdulesmainly mainly comprise quartz and epidote epidote with with minor range up up to to about about 11meter. Amygdules �I i-—-, — /&aHanai Vo - iI - y- -' o / - - 45' C- - - — -9-4r /J '-t v ptvnt/Crflk - I I —v --0 DavisLake xna2- — ç - — —— - Th — ans' ---\ f i: ste T 'N - C— ---1- - -- rt-_ - 2 - - - iemertsCreel(Votcanics 'LakeLizzie ci l 0 - "—HvM€sO-- - I 2 3 4 5 6 7 FEET 5 o KILOMETER 7 - Figure 4-3. Part Part of of the the Grand Grand View View 7 1/2' Figure 112' quadrangle quadrangle showing showing general general geology 8, and and 9. geology and and the the locations locations of of field field trip trip stops 6, 7, 8, u �I I I I I I I I I I I I I I I I I K-feldspar K-feldsparand and very verysparse sparsesulfide sulfideminerals. minerals.Locally, Locally,vesicles vesicles are are exceptionally large, as and some are incompletely filled filled with with secondary secondary minerals, minerals, leaving leaving open open much as 10 cm, and spaces. spaces. The matrix of the the flow flow top top breccia breccia is is aa very very fine-grained fine-grained clastic clastic rock, rock, now now metamorphosed metamorphosedto to chert-like chert-like material, material, although although clastic clastic textures are readily seen seen in thin thin secti on. Locally the matrix is finely laminated parallel to the orientation section. orientation of the the flow, flow, even though the the matrix matrix isis only only thin thinseams seamsdeposited deposited between between the the clast-supported clast-supported breccia. In In places places (best (bestseen seen in other outcrops) outcrops) the laminations laminations are highly contorted. contorted. We interpret this silty silty matrix to be wind-blown dust that rapidly rapidly settled settled onto onto basalt flows while they were still molten and moving, becoming incorporated incorporated into open spaces in flow top breccias. the sudden sudden eruption of breccias. Under Under some some climatic climatic conditions the of flood basalt basalt may have have generated generated intense wind wind and and dust dust storms, storms, which which quickly quickly deposited deposited aa layer layer of of dust dust over over the the erupting eruptingflow flow. A thin basalt dike cuts cuts the the basalt basalt flow flow near the northeast end end of of the the outcrop. outcrop. Field measurements of Field of magnetic magnetic polarity indicate that the basalt basalt flow flow isisreversely reversely elsewhere. The polarized, consistent with results results for for the the Kallander Kallander Creek Creek Volcanics Volcanics elsewhere. The dike has normal polarity, and possibly was emplaced during during the later eruption of the normally polarized normally polarizedChengwatana ChengwatanaVolcanics. Volcanics. STOP (Fig. Picritein inthe theSiemens SiemensCreek CreekVolcanics Volca~cs (Fig.4-3). 4-3). STOP 7: Picrite This stop is out out of of stratigraphic stratigraphic sequence, sequence, but the the significance significance of the outcrops outcrops makes it notable. The Thesmall smalloutcrop outaopjust just off off County County Road Road D, D, east east of of Lake Lake Knotting, Knotting, shows shows basalt basalt flows flowswithin withinthe thelowest lowestexposed exposedunit unitof of the theSiemens SiemensCreek CreekVolcanics Volcanics in in the the region. Immediately Immediatelytotothe thesouth, south,Keweenawan Keweenawanintrusive intrusiverocks rocks separate separatethe theflows flowsfrom from from this outcrop is the Marenisco-Atkins Lake fault. A A sample sample of these flows collected from 16.9 wt %; 0.72) and to date picritic (MgO picritic (MgO = 1 6.9 wt %; Mg# = = 0.72) date represents represents the the only only Keweenawan Keweenawan picrite identified on the south south shore shore of of western western Lake Lake Superior. Typically Typically the the lower lower member member of of the theSiemens SiemensCreek Creek Formation Formationhas hassubstantially substantiallylower lowerAl203 A1203(8(8to to<13 c13wt wt%) %) than any other Keweenawan elementpatterns patterns((Ce/Ybg and steeper rare earth element ce~/Yb =~ 15) than basalts. This well-documented picrites Thispicrite picriteisis different differentin in composition composition from the welldocumented picrites in the ICeweenawan section section at at Mamainse Point in eastern Keweenawan eastern Lake Lake Superior Superior (Berg (Berg and and Klewin, Klewin, Chemical modelling modelling suggests suggests that that the picritic composition sampled at this 1988). 1988). Chemical this outcrop represents an uncontaminated small-degree partial melt of the mantle plume outaop represents an uncontaminated small-degree mantle plume postulated to have postulated have produced produced the thevoluminous voluminous magmatism magmatism associated associated with the the Midcontinent rift. c Midcontinent rift. 75 75 �a STOP 8. STOP 8. Conglomerate and and rhyolite rhyolite of of the the Kallander Kallander Creek Creek Volcanics Volcanics at 'Davis 'Davis Hill' Hill' (Fig. (Fig.4-3). 4-3). The middle portion portion of of the theKallander Kallander Creek Creek Volcanics Volcanics in the the Lake Lake Namekagon Namekagon area mainly comprised comprised conglomerate conglomerate and rhyolite with subordinate subordinate amounts amountsof of basalt. basalt. Exposures at this stop of the the unit. unit. From stop illustrate illustrate the the lithologic variations of From Forest Forest Service 213, walk walk northward northward over the prominent Road 213, prominent bill hill (informally (informally known as as Davis Davis Hill Hill in older reports) immediately north of the road. The The best best exposures exposures of conglomerate are of the hill hill and along the the north slope. slope. Outcrops high on the western slope of Outcrops are are poorly poorly sorted and and crudely crudelybedded beddedvolcanogenic volcanogenic conglomerate conglomerate containing containing minor sandstone sandstone interbeds. Clasts Clastsof of cobble cobble to to boulder size are mostly rounded to subrounded subroundedrhyolite, rhyolite, and lesser basalt and and andesite. andesite. Some Someclasts clastsconsist consist of of basalt basalt containing containing large large pink pink phenocrysts of common in in Kallander Kallander Creek Creek flows, flows, but but phenocrysts of plagioclase; plagioclase; this lithology is fairly common is very rare elsewhere is elsewhere in in the theKeweenawan Keweenawan section. section. It appears, therefore, therefore, that the the conglomerate formed through conglomerate through erosion erosion of of the slightly older lower part part of of the the Kallander Kallander Volcanics. About Creek Volcanics. Creek About aa kilometer to the east, this same conglomerate unit is cut by a tongue Ma (Zartrnan (Zartman and tongue of of the the Mineral MineralLake Lake gabbro gabbrothat thatwas wasemplaced emplacedatat1102.0 1102.0±k 2.8 Ma and others, 1995), which which places places aa minimum minimum age age on on deposition deposition of ofthe the conglomerate. conglomerate. Cement Cement others, in the conglomerate of epidote and quartz, quartz, suggesting conglomerateis is mostly a mixture of suggesting that that relatively relatively high-temperature fluids high-temperature fluids permeated permeated this this part part of of the the section. section. AAlittle little copper copperstaining stainingcan can be seen rarely, but we have not identified any primary copper minerals. Continue walking northward for a few hundred meters to a prominent bedrock Continue exposed a rhyolite unit unit about 20 m thick. The knob. Along the south knob. southface face of this knob is exposed The rhyolite is purplish, phyric, and and mostly mostly massive. massive. In a few places near the purplish, plagioclase plagioclase phyric, base of the hill, faint outlines outlines of flattened pumiceous fragments fragments can be seen, seen, indicating indicating that the the rhyolite rhyolite probably probably is is aa welded welded tuff. tuff. The Theremainder remainderof of the theknob knobcontains containsgood good exposures of typical conglomerate. exposures conglomerate. From the the top of view to to the the north north can can be be seen. seen. The From of the knob a panoramic panoramic view The prominent prominent east-west east-westridge ridgeabout aboutaakilometer kilometerdistant distantisisunderlain underlainby byophitic ophiticbasalt basaltflows flows of the Chengwatana whichwill willbe beexamined examinedatatthe the next next stop. stop. The of Chengwatana Volcan.ics, Volcanics, which The Lake Lake Owen fault lies just south south of of the the ridge ridge and andhas hasthrust thrustthe theChengwatana ChengwatanaVolcanics Volcanics southward over southward overthe theKallander KallanderCreek CreekVolcanics. Volcanics. 9. Amygdaloidal STOP 9. Amygdaloidalophitic ophiticbasalt basaltflow flowin inChengwatana ChengwatanaVolcanics Volcanics(Fig. (Fig.4-3). 4-3). The Chengwatana Chengwatana Volcanics Volcanics records the main stage stage of flood-basalt volcanism of Basalts erupted erupted as a thick the Midcontinent thick series series of of Midcontinent rift rift in innorthern northernWisconsin. Wisconsin. Basalts subaerial flows into a subsiding central central graben. graben. Reverse Reverse faulting during a regional regional 76 I j I I fl p Ii �I I I I I I I I I I I I I I I I N. N 7 I - \\.. 1r MILE Figure 4-4. Parts of the Drumrnond and Upper Eau Claire Lake 7 112' Figure 4-4. Parts quadrangles showing geology and the location of field trip stop 10. of thegeneral Drummonä Upper Eau Claire Lake 7 1/2' quadrangles showing general geologyand and the location of field trip stop 10. 77 �compressional event inverted the the graben, graben, forming forming the the St. St. Croix horst, which which contains contains compressional Syncline. On Onthe thenorth northlimb limbof of the thehorst, horst,the theChengwatana ChengwatanaVolcanics Volcanicsare are the Ashland Syncline. along the the Douglas Douglas fault faultover over sediments sediments of of the the yourtger younger Bayfield Bayfield Group, while thrust along the southern southernlimb limbthe theLake Lake Owen Owen fault faultthrusts thrustsyounger youngerChengwatana ChengwatanaVolcanics Volcanics along the over over older olderKallander KallanderCreek CreekVolcanics. Volcanics. this stop stop flows flows of the upper upper Chengwatana Chengwatana Volcanics Volcanics are exposed along along aa steep steep At this The Lake Lake Owen Owen fault, fault, probably at the the base base of of the the bluff, bluff, cuts cuts up up south-facing bluff. bluff. The section so that the are not exposed here. The the lower lower Chengwatana Chengwatana Volcanics Volcanics are Theflows flowsare are Severalamygdular amygdular thick, monotonous ophitic basalts, typical typical of of this this part part of of the unit. Several variety of of secondary secondaryminerals, minerals, are well well exposed. exposed. Amygdules Amygdulescomprise comprise aa variety flow tops are including including quartz quartz and and epidote. epidote. STOP 10. 10. Ophitic near the top of of the Chengwatana Ophitic basalt and interfiow interflow conglomerate near Chengwatana Volcanics (Fig. 4-4). 44). These exposures upper flows, exposures show what what is is certainly certainly one of of the upper flows, and and may may be be the the uppermost flow, flow, of of the theChengwatana ChengwatanaVolcanics Volcanics and and an aninterfiow interflowconglomerate. conglomerate. Immediately north north of of the the road road are arelow lowoutcrops outcropsof of coarse coarse volcanogenic volcanogenic conglomerate and interbedded 30' to the the north. north. The conglomerate conglomerate is is interbedded sandstone sandstone that dip 20 20 -- 30° composed principally of of rhyolite rhyolite clasts. clasts. Cement Cement in the conglomerate conglomerate and sandstone sandstone varies from from calcite to epidote plus quartz, indicating that even in in this this stratigraphically stratigraphically high part part of of the thevolcanic volcanic section, section, relatively high-temperature alteration alteration has produced produced quartz-epidote quartz-epidoteassemblages. assemblages. Immediately to the north of of the the conglomerate conglomerate outcrops, along a low ridge, is is exposed of many many flows flows in in the the upper upper part of exposed coarse-grained ophitic ophitic basalt. This This is typical of of the Chengwatana predominate. Rocks ChengwatanaVolcanics Volcanics where where thick ophitic flows predominate. Rocksof of aasimilar similar type are m farther north. Whether are exposed exposed in in aa series series of of low outcrops for about 100 m Whether these outcrops are the same flows is is unknown. unknown. Magnetic same flow or additional flows Magnetic maps maps suggest suggest that that the thecontact contactwith with the theoverlying overlying Copper Copper Harbor Harbor Conglomerate Conglomeratelies lies just north north of of these outcrops, and that that the the featureless featureless sand plain to the north is underlain by the Copper Copper Harbor. Harbor . 78 �I I REFERENCES REFERENCES I I I I I I I I I I I I I I I I I Berg, J. H., H., and Klewin, High-MgOlavas lavas from from the the Keweenawan Keweenawan midcontinent midcontinent rift near Berg, 1. Klewin, K. K. W., 1988, 1988, High-MgO 16,p.p.1003-1006. 1003-1006. Mamainse Point, Point, Ontario: Ontario:Geology, Geology,v.v.16, Cannon, W. W. F., F., Nicholson, Nicholson, S. S. W., W., Zartman, Zartman, R. R. E., E., and and Peterman, Peterman, Z. Z. E., E., 1993, 1993, The The Kallander KallanderCreek Creek Volcanics -- a remnant of a Keweenawan Keweenawan central central volcano centered near Mellen, Mellen, Wisconsin [abstract]: Institute 39,p.p.20-21. 20-21. Instituteon onLake LakeSuperior SuperiorGeology GeologyAbstracts, Abstracts,v.v.39, Feher, Vesiclesand andbreccia brecciadue dueto to injection injectionofofmafic maficmagma magmainto into partially partially lithified Feher, L. and Flood, T., 1995, 1995, Vesicles sediments of the NWWisconsin Wisconsin sediments the early early Proterozoic Proterozoic Ironwood IronwoodIron-formation, Iron-formation,western westernGogebic GogebicRange, Range,NW [abstract]: Institute 41,p.p.13-15. 13-15. [abstract]: Instituteon onLake LakeSuperior SuperiorGeology GeologyAbstracts Abstractsv.v.41, M.W., 1954, 1954,Petrogenesis Petrogenesisof ofaa gabbro-granophyre gabbro-granophyre complex in northern Leighton, M.W., northern Wisconsin: Wisconsin:Geological Geological Society of America America Bulletin, Bulletin,v.v.65, 65,p. p.401-442. 401-442. Olmsted, J. Petrology of of the Mineral Lake intrusion, northwestern Origin of J. F., F., 1969, 1969, Petrology northwesternWisconsin, Wisconsin, in in Origin anorthosite and related rocks, Isachsen, Y. W. (ed.), New York State Museum and Science anorthosite and related rocks, Isachsen, Y. W. (4.). New York State Museum and ScienceService Service pp. 149-161. Memoir 18, pp. 149-161. Seifert, E., Peterman, Peterman, Z. E., and Thieben, F., 1992, 1992,Possible Possiblecrustal crustal contamination contamination of Midcontinent Seifert, K. E., E.,and Thieben, S. E., MidcontinentRift Rift igneous rocks: examples from the Mineral Lake intrusions, Wisconsin: Canadian examples from the Mineral Wisconsin: Canadian Journal Journal of Earth Sciences, v. 29, p. 1140-1153. p. 1140-1153. Sciences, Zartnian, RE., Cannon, U-Th-Pbages agesof ofsome someKeweenawan Keweenawan rocks from Zartman, R.E.,Cannon,W.F., W.F., and andNicholson, Nicholson,S.W., S.W.,1995, 1995, U-Th-Pb western Lake Superior, northwestern Wisconsin, and east-central Minnesota western Lake Superior, northwestern Wisconsin, and east-central Minnesota [abstracfl: [abstract]: Proceedings Proceedings of International Field Conference and Symposium of International Geologic of International Field Conference and Symposium of International Geologic Correlation Correlation Program Program Project 336, Duluth, Duluth, MN, MN,p.p.217-218. 217-218. Project �-- I I I I I I I I I I I I I I I I I I UIDEFOR FOR FIELD FIELDTRIP GUIDE TRIP # #55 LAKENAMEKAGON NAMEKAGON ANDPENOKEE PENOKEEGAP GAPAREAS, AREAS, LAKE AND WEST GOGEBIC RANGE, WISCONSIN �HELD TRIP FIELD TRIP #5 LAKE NAMEKAGON NAMEKAGON AND PENOKEE PENOKEE GAP GAP AREAS, AREAS, WEST GOGEBIC GOGEBIC RANGE, RANGE, WISCONSIN WISCONSIN by John S. Kiasner, Klasner, Department Department of of Geology, Geology, One University University Circle, Circle, Western Illinois Illinois University, Macomb, Illinois 61455, and Gene L. LaBerge, Department of Geology, 61455, LaBerge, Geology, Macomb, Oshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin54901 54901 University of Wisconsin Wisconsin -- Oshkosh, INTRODUCTION INTRODUCTION This field guide This guide focuses focuses on on two two regions regions of of the theWestern WesternGogebic GogebicRange: Range: Atkins Lake in the Lake Lake Naniekagon Namekagon area and and Penokee Penokee Gap near near Mellen, Mellen, Wisconsin Wisconsin Gogebic Range Range is is approximately approximately 120 120 kilometers kilometers long long and (Overview Fig. Fig. 1). 1). The Gogebic consists mainly mainly of consists of aa northwest-dipping northwest-dipping sequence sequence of of Early Early Proterozoic Proterozoic ironironrocks and and detrital sediments sandwiched between formation, interbedded volcanic volcanic rocks Archean basement rocks rocks on on the southeast Archean crystalline crystalline basement southeast and and Middle MiddleProterozoic Proterozoic (Keweenawan) volcanicand and sedimentary sedimentary strata strata of of the Midcontinent (Keweenawan) volcanic Midcontinent Rift on the the northwest. northwest. of the Gogebic Range Range that that lies west of of Mineral Lake Lake provides the The section of westernmost exposures exposures of of Early rocks of of the Marquette westernmost Early Proterozoic Proterozoic rocks Marquette Range Range Supergroup (Cannon and and Gair, Gair, 1970). 1970). Unlike Unlike the eastern eastern end end of of the theGogebic Gogebic Range Range where the Sunday Sunday Lake Lake Quartzite Quartzite underlies underlies the the dolomite, dolomite, the the Bad Bad River River Dolomite Dolomite at the western end end of of the the range rangerests restsdirectly directly on onArchean Archean gneisses gneisses and and volcanic volcanic rocks. rocks. In the Atkins Atkins Lake Lake area, the dolomite dolomite is aa 300 300 m thick gray dolomitic dolomitic marble with abundant lenses and beds dolomite thins thins towards towards the the east and isis beds of of chert. chert. The The dolomite Creek (east (east of discontinuously exposed. exposed. Near Near Ballou Ballou Creek of Mellen) Mellen) it is mostly mostly aa variegated chert breccia cemented by by chert chert and and (or) quartz, locally variegated breccia cemented locally with lenses of of dolomite near the base. This Thislithology lithology is interpreted as a residuum residuum of of chert chert nodules nodules dolomite and beds formed formed as as the the dolomite dolomite was dissolved during the weathering interval prior to deposition deposition of of the theunconformably unconformablyoverlying overlying Palms Palms Formation. Formation. Locally, magnetite and and hematite hematite concentrations concentrationsare arepresent present at at the top of Locally, magnetite of the the shafts were were sunk sunk on some of these magnetite-rich chert chert breccia. breccia. Exploration shafts magnetite-rich zones Penokee Gap and on the near the eastern eastern flank flank of of Mt. Mt. Whittlesey Whittlesey during during early early near Penokee Gap and exploration for for iron iron ores ores near near the turn of exploration of the the century. century. The occurrence of these these in conglomerate conglomerateatat the the top of the magnetite concentrations concentrations in the Bad Bad River River Dolomite Dolomite magnetite suggests that they are are paleo-placer paleo-placer deposits produced by streams streams flowing flowing on on the the prepre- I 83 �Palms erosion surface. Alternatively, Alternatively, they they may be of of hydrothermal hydrothermal or or metamorphic metamorphic origin. origin. The Palms Formation, which is is well well exposed exposed at at Penokee Penokee Gap Gap and at Atkins Formation, which Atkins Lake in the Lake area, is the basal unit of the Lake Namekagon area, the Menominee Menominee Group and unconformably overlies of a thinly bedded overlies the theBad Bad River River Dolomite. Dolomite. It is comprised of argillaceous lower unit unit and a thickly relatively pure, pure, quartzite quartzite upper unit. argillaceous lower thickly bedded, relatively unit. Ojakangas (1983) similarly similarly described described the the Palms Palms elsewhere elsewhere on on the Gogebic Range and suggested that the the Palms Palms Formation Formation was deposited in a tidal-flat environment in a transgressing transgressing sea. sea. Near Penokee grades across across 1 1 to to 2 m Penokee Gap, the uppermost Palms Formation Formation grades into the Here, the the base base of the overlying overlyingIronwood IronwoodIron-formation. Iron-formation. Here, of the Ironwood Ironwood has thin (3 Elsewhere aa one one meter meter thick thick zone of stromatolitic (3m) m) conglomerate conglomerate zone. zone. Elsewhere stromatolitic jasper occurs Detailed mapping mapping and and drill core occurs at at the the base base of ofthe theiron-formation. iron-formation. Detailed core analysis analysis by by U.S. U.S.Steel Steel geologists geologists in in the the late late1950's, 1950's, based based on onwork workof ofHotchlciss Hotchkiss(1919), (1919), subdivided the eastward from from Penokee Penokee Gap Gap into five the Ironwood Ironwood Iron-formation Iron-formation eastward five units. that alternating alternating units units of granular, units. Although Although our mapping indicates indicates that granular, wavy bedded and are present present west west of of Penokee Gap, it also and laminated laminated iron-formation iron-formation are Penokee Gap, also indicates that, except for the first west of of the gap, the first few few hills of iron-formation iron-formation west the five-fold division of of U. U. S. S. Steel Steeldoes doesnot notextend extendwestward. westward. In the the Lake Lake Namekagon Namekagon area the the Ironwood Ironwood hon-formation Iron-formation contains contains interbedded interbedded units of of granular, granular, wavywavy- bedded bedded and and laminated laminated cherty chertymagnetic magnetic iron-formation, iron-formation, similar similar to to exposures exposures elsewhere elsewhere along along the the Gogebic Gogebic Range. Range. The The iron-formation, iron-formation, however, is interbedded interbedded with with and andgrades gradeslaterally laterallyinto intomagnetic magneticand andnon-magnetic non-magnetic argillite, argillite, as as well well as asmafic mafic igneous rocks appear appear to be large sills of metadiabase igneous rocks. rocks. These igneous igneous rocks metadiabase with textures textures suggesting suggesting emplacement emplacement into into semi-consolidated semi-consolidated sediments (or (or basalt basalt flows flows interbedded just north of in the the Trapper Trapper Lake area, just of interbedded with with the the sediments). sediments). Drill Drill cores cores in Lake Lake Namekagon, Namekagon, intersected intersected granular granular and and laminated laminated magnetic magnetic iron-formation iron-formation with thin thin interbeds interbeds of of argillite, argillite, and and at atleast least 60 60 m m of of black black pyritic pyritic argillite, argillite, several several metadiabase Thus, the metadiabase sills, sills, and several several thin dikes dikes of of granite granite and and pyroxenite. pyroxenite. Thus, bonwood Ironwoodhon-formation Iron-formationgrades gradeswestward westward into intoaadeeper deeperwater, water,anoxic, anoxic, detritus-rich detritus-rich environment This is in environment with with penecontemporaneous penecontemporaneous igneous igneous activity. activity. This in marked marked contrast contrast to to the thecentral centralpart partof ofthe theGogebic GogebicRange, Range, where detrital detrital rocks rocks are are essentially essentially lacking lacking in in the the iron-formation, iron-formation, and andigneous igneousrocks rocksare arescarce. scarce. Recent work on the the east eastend end(LaBerge (LaBerge and and Ojakangas, Ojakangas, 1992; 1992; Anderson and Klasner, Klasner and and LaBerge, LaBerge, 1994A; 1994A; Klasner Kiasner et al., Klasner, 1993; 1993; LaBerge and Klasner, 1994; Klasner in press) press) and andininthe thecentral centralpart partand andwest westend end(Kiasner (Klasnerand andLaBerge, LaBerge,1994B; 1994B;LaBerge LaBerge 84 �• I I I I I I I I I I et a!., of the the Gogebic GogebicRange Rangeshows showsthat, that,inincontrast contrastto tothe the central central part, part, strata on al., 1995) of either end of of the the range range thicken thicken abruptly, abruptly, are are structurally structurally more more complex, complex, and contain contain volcanic strata interbedded with Ironwood hon-formation. Iron-formation. On Onthe theEastern EasternGogebic Gogebic Range abrupt lateral changes in stratigraphy Range stratigraphy and structure within within the the Ironwood Ironwood and interbedded rocks are are interpreted Iron-formation and interbedded volcanic volcanic rocks interpreted to indicate indicate the the development of grabens development of grabens in in an anextensional extensional tectonic tectonic environment environment (Klasner (Klasner and and on the the western western end of the LaBerge, 1994A; LaBerge and Kiasner, Klasner,1994). 1994). Likewise, Likewise, on range, deposition deposition of of detrital detrital sediments sediments(mainly (mainly argillites) argillites) and andcontemporaneous contemporaneous igneous activity also suggest a more tectonically active environment. environment. We igneous activity tectonically active We suggest suggest that these stratigraphic stratigraphic and structural structural relationships relationships indicate the development of of rift basins at both both ends ends of of the theGogebic Gogebic Range Range in aa divergent divergent tectonic tectonic regime regime during during deposition of platform platform sediments, sediments, including including iron-formation. iron-formation. The Tyler Formation overlies the Ironwood Iron-formation, and at at Penokee Penokee bedded black slate and Gap consists consists of about about 800 800 m of cyclically cyclically bedded and siltstone. siltstone.We We believe believe that the that the Tyler Tyler isis unconformable unconformable on the the Ironwood, Ironwood, as as isis the thestratigraphically stratigraphically equivalent Copps Formation in the Eastern Gogebic GogebicRange. Range. This This is is supported supported by an equivalent an outcrop of conglomeratic, sandy graywacke graywackethat that lies lies near near the the base outcrop conglomeratic, sandy base of the the Tyler Tyler Formation about 600 west of of Penokee Penokee Gap Gap along along the the north north slope of of the ridge of 600 m west of Tyler along the the contact iron-formation. Other Other remnants remnants of Tyler exposed exposed along contact with the the underlying underlying iron formation formation at Penokee Penokee Gap are are intensely intensely sheared sheared and and consist consist primarily of fine-grained quartz in an an anastomosing anastomosing matrix of opaque opaque carbonaceous carbonaceous material. In near the contact with the Inan anexposure exposureabout about22 km krn west west of of Penokee Penokee Gap, near Ironwood Iron-formation, the Tyler Tyler is is aa black, black, carbonaceous carbonaceous slate. slate. In thin thin section section the carbonaceous slate is quartz-rich with aa strongly strongly foliated foliated biotitic biotitic matrix matrix in in which which superimposed concentrically-zoned cordierite porphyroblasts porphyroblasts give give it a spotty superimposed concentrically-zoned cordierite spotty appearance. The Thecordierite cordieriteporphyroblasts porphyroblasts are arehexagonal hexagonal in in cross crosssection, section, about about 22 mm in length and 11mm mm wide wide and and display display remnants remnants of of aligned aligned mica mica flakes in their cores. cores. Farther north, north, in in a rock Farther rock cut cut along along the the railroad railroad tracks tracks that extend extend though though Penokee consistsbeds beds of of slate slate and and siltstone that show Penokee Gap, the Tyler Tyler Formation Formation consists show subtle grading from quartz-rich silt at the base base to to more more clay-rich clay-richunits unitsat at the the top. top. The The slate is carbonaceous with aligned flakes of of biotite, biotite, sericite sericite and and chlorite, chlorite, and and it also slate Although contains porphyroblasts activity was contains porphyroblasts of cordierite. cordierite. Although igneous igneous activity was depositionon on both both ends of the contemporaneous with iron-formation iron-formation deposition the Gogebic Gogebic Range, we we found no Early igneous rocks rocks within within or cutting the overlying Range, Early Proterozoic igneous overlying Tyler Formation Formation that that lies along most most of of the the Gogebic GogebicRange. Range. We We interpret the lack Tyler lack of 85 �igneous rocks within the gap between igneous rocks within the Tyler Tyler to to indicate indicate aa significant significant gap between deposition deposition of of the Ironwood the Ironwood and and Tyler Tyler Formations. Formations. In addition to to cordierite cordierite within within the the Tyler, Tyler, there are are numerous numerous other otherminerals minerals that indicate strata near that indicate that that the theEarly EarlyProterozoic Proterozoic strata near Penokee Penokee Gap Gap were were metamorphosed. Foliation metamorphosed. Foliation within the Tyler Tyler and and Palms Palms Formations, Formations, expressed expressed by by aligned aligned mica mica and and chlorite, chlorite, along along with with other other deformational deformational features features in in the the Early Early Proterozoic strata, indicate that that there Proterozoic strata, indicate there was was aaregional regional deformational deformational and and metamorphic event event in in the Penokee Gap region. region. Other porphyroblasts in the Early metamorphic Penokee Gap Proterozoic strata, strata, along with the cordierite, of a Proterozoic cordierite, however, however, suggest the occurrence of later metamorphic include garnet garnet within within the iron-formation later metamorphic event. event. These These include iron-formation and skeletal garnets in the the Tyler Tyler near near its its contact contact with with the theiron-formation, iron-formation,non-aligned non-aligned chlorite locallywithin within the the Palms Palms that that overprint chlorite porphyroblasts porphyroblasts locally overprint the the regional regional foliation, and possibly the euhedral euhedral magnetite magnetite crystals along the contact between the the Palms and Although the the origin of Palms and Bad Bad River River Formation. Formation. Although of these these metamorphic metamorphic minerals has not been studied in detail, the fact that some of of them overprint the minerals has regional deformational fabric clearly clearly indicates indicates that that they they postdate it. regional deformational fabric it. The most most obvious possibility possibility is that they they were were caused caused by by thermal thermal metamorphism metamorphism associated associated Lake Gabbro Gabbrothat thatlies liesabout about22 km km to to the the north of with intrusion of of the Mineral Mineral Lake Penokee Gap, Gap, but but further study of Penokee of metamorphism metamorphism in this region is needed needed to to fully fully confirm this. this. NOTE: Field stops at both the Atkins Lake Lake and and Penokee Gap Gap involve involve walking walking NOTE: Penokee Gap. Cap. Also, over steep, hilly terrane, especially at Penokee Also, a walk of of approximately approximately four miles is involved in in the the Penokee Penokee Cap Gap part of of this field field trip. trip. PART A: LAKE LAKE NAMEKACON NAMEKAGONAREA AREA(ATKINS (ATKINSLAKE) LAKE) Numerous exposures exposures of of the Ironwood and the Numerous Ironwood Iron-formation Iron-formation and the Palms Palms Formation are present in in aa 4,000 4,000 m long northeast-trending zone from Atkins Lake Lake units are are truncated to the the Marengo Marengo River, River, where where the Early Early Proterozoic Proterozoic units truncated by the the Marenisco-Atkins Lake fault The Palms Palms Formation Formation consists consists of of an an upper Marenisco-Atkins fault (Fig. (Fig.5-1). 5-1). The massive quartzite member and aa lower massive lower argillaceous argillaceous quartzite member, member, similar similar to to Range. (Note: exposures elsewhere on the Gogebic Gogebic Range. (Note: Due to time time limitations, limitations, we we will will The Ironwood Ironnot visit visit exposures exposures of of the the Palms Palms Formation Formation on this this trip). trip). The Ironformation consists of magnetic wavy-bedded and laminated laminated cherty cherty iron-formation iron-formation and argillite, argillite, some some of which is also also magnetic. Mafic Mafic sills sills or flows flows lie lie in in contact contact with with the of field field stops in this area, the iron-formation. iron-formation. Unusual Unusual breccia breccia units, the focus of area, are are associated with one one of of the the sills. sills. 86 H H �i_ '0% rsIIIn _j_. 0 2I) 5 L 3000 ——— 0 40% 5000 - -- — 70% FEET -i_: :-JnT] 6000 - MILE I +--: I—--4 I I 0 I f:j T-==-_=___ - KIt OMFTLR Figure 5-1. Part of the Grand View 7 1/2' quadrangle showing general geology and location of field trip stop A. 10% irCfleEiI jTV. Lt — :n—-i —- - I a— �The The breccia units contain contain angular angular to to sub-rounded sub-rounded clasts, clasts, up up to toseveral severalmeters meters in in length, length,of of banded bandedsiliceous siliceoussedimentary sedimentaryrocks rocks in in aa matrix matrix of of fine-grained, fine-grained,massive massive igneous igneous rock. rock. The Theigneous igneousrock rock isislocally locally fine-grained fine-grained near the margins margins where the the breccia breccia occurs but coarse-grained coarse-grained in the interior of of the igneous body, where it ranges ranges from from fine-grained fine-grained diabase diabase to tomedium-grained medium-grained gabbro gabbro (Feher (Feherand andFlood, Flood,1995). 1995). However, However, the the mineralogy mineralogy and, and, to tosome someextent, extent, the the textures textures have havebeen beenmodified modifiedby by Middle Clasts within the the breccia breccia are are Middle Proterozoic Proterozoic(Keweenawan) (Keweenawan)metamorphism. metamorphism. Clasts mainly mainly siliceous siliceous argillite: a few are magnetic. magnetic. Most Most clasts ciasts are are long, long, tabular tabular bodies. bodies. Bent or folded folded clasts clasts are are not not uncommon, uncommon, suggesting suggesting that the the sediments sediments were wereonly only semi-lithified semi-lithified when incorporated in the the breccia. breccia. The Theargillite argilliteconsists consistsof of alternating alternating layers layers of of recrystallized recrystallized quartz, quartz, fine-grained fine-grained chlorite, biotite or actinolite, garnet, and variable variable amounts amountsof of magnetite magnetite(Feher (Feher and and Flood, Flood, 1995). 1995). The The matrix matrix is is aa fine-grained fine-grained mafic rock with conspicuous conspicuous vesicles around some clasts. The Thematrix matrixisiscomposed composed of medium-grained medium-grained amphiboles amphiboles and plagioclase plagioclase laths, laths, probably probably aa relict relict ophitic ophitic phenocrysts are present texture texture (Feher (Feher and andFlood, Flood,1995). 1995). Plagioclase Plagioclase phenocrysts present locally. locally. Preliminary data indicates Preliminary geochemical geochemical data indicates a tholeiitic tholeiitic composition composition for the the matrix matrix (Feher (Feher and andFlood, Flood,1995). 1995). The origin of the the breccia breccia is problematic. problematic. The The breccia is a not not aa debris debrisflow flow because the matrix matrix is is igneous igneous and and not not fragmental: fragmental: the clasts appear to have have been been incorporated incorporated into into aamagma. magma. The Thepresence presenceof of angular, angular,and andin inplaces placesdeformed, deformed,blocks blocks of country country rock rock within within aamagma magma argues arguesfor forintrusion intrusioninto intosemi-consolidated semi-consolidated sediments at aa shallow shallow depth. depth. The Thepresence presence of of breccia breccia at both the upper upper and andlower lower margins of the igneous body argues for a common origin for both breccia units, margins of the igneous body argues for a common origin for both breccia units, most most likely the intrusion intrusion of of aa sill sill into into wet, wet, unconsolidated unconsolidated sediments, forming, perhaps, a peperite-like peperite-like body. body. Alternatively, the breccia may represent an extrusive breccia and mafic rocks may extrusive basaltic basaltic flow of the sediments flow that that incorporated incorporated blocks blocks of sediments over over which which it flowed, flowed, with with subsequent concordant concordant intrusion of aa mafic mafic sill separating the basalt basalt flow flow into into two two for this this origin origin are: are: 1) 1) perfectly perfectly concordant contacts contacts with with parts. Features arguing for parts. thinly laminated at several and the lack laminated sediments sediments exposed exposed at several outcrops, outcrops, and lack of of any any observed cross-cutting 2) marked marked lithologic lithologic contrast contrast between between the the cross-cutting contacts; contacts; and 2) breccia breccia and undoubtedly undoubtedly intrusive intrusivesills sillsofofcoarse-grained, coarse-grained,massive, massive,inclusion-free inclusion-free metadiabase within within the thesame sameoutcrops. outcrops. Regardless of whether whether the breccias breccias are are the the result result of Regardless of of an extrusive extrusive or or aa very very shallow intrusive igneous igneous event, event, they they indicate indicate that that igneous igneous activity activity was wasoccurring occurring contemporaneously with iron-formation iron-formationdeposition depositionininthe the western western part part of contemporaneously with of the the 88 �I Gogebic Range. The Gogebic Range. The situation situation is is similar similar to that of of the the eastern eastern part part of of the the Cogebic Gogebic I Range Complex isis interlayered interlayered with with the Ironwood Range where the Emperor Emperor Volcanic Volcanic Complex Ironwood Iron-formation Iron-formation (LaBerge and Kiasner, Klasner, 1994). 1994). In both areas areas platformal platformal sediments, sediments, including the the Bad the Palms Palms Quartzite, Quartzite, and and the Sunday including Bad River River Dolomite, Dolomite, the Sunday Lake Lake Quartzite in in the east, are rocks in in the the central Quartzite are similar similar to equivalent equivalent rocks central part of of the the I I Gogebic Range. Range. Igneous becomes a significant significant feature feature during the Gogebic Igneous activity, activity, however, becomes of deposition of the on both ends of time of the Ironwood Ironwood Iron-formation Iron-formation on of the the Gogebic Gogebic Range. Whereas Whereas igneous igneous activity activityininthe the central centralpart part ofof the the range range is limited to Range. (R. G. G. Schmidt, Schmidt, personal personal communication, communication, 1995), 1995), deposition of aa few few minor minor ash ashbeds beds(R. igneous deposits on igneous on either either end endof of the theGogebic Gogebic Range Range indicate indicate aa far far more morevolcanically volcanically active environment in in these these regions. regions. I I j I I I I I I I HELD STOPS ATKINS LAKE FIELD STOPS(see (seeFigure Figure5-2) 5-2) Our mapping mappingof of the thesill silland andbreccia breccia units unitsnear nearAtkins AtkinsLake Lake(Fig. (Fig.5-3) 5-3)reveals reveals aa body with breccia units up to 20 m thick along both the upper 70 m thick igneous body breccia units upper and lower margins. margins. STOP SA-1. STOP 5A-1. This outcrop consists of layered magnetic, magnetic, greenish, greenish, actinolitic actinolitic iron-formation with metadiabase, iron-formation metadiabase, and aa breccia breccia zone with with clasts clasts of of iron-formation iron-formation Bedding orientations orientations atat this this outcrop are in aa fine-grained fine-grained metadiabase metadiabase matrix. matrix. Bedding of bedding bedding elsewhere elsewhere in in the the area area indicating consistent consistent with orientations of indicating that the and not not aa raft raft of of iron-formation iron-formation entrapped in in the the igneous igneous rock. rock. outcrop is in place and Walk northeast about 60 m to the top top of of aa hill. hill. STOP 5A-2. 5A-2. At Atthis thislocation, location, large large thin thin slabs slabs of argillite argillite lie in aa matrix matrix of of locally vesicular metadiabase. locally metadiabase. The The slabs have various various orientations: orientations: some some are are contorted and folded, and one is contorted is rolled rolled into into aa ball ball with with aacentral central layered layered portion portion surrounded by Slabs zone of of smaller smaller clasts clasts in aa metadiabase metadiabase matrix. matrix. Slabs surrounded by aa concentric concentric zone range range from a meter or more more in in length length down down to to aa centimeter centimeter or or less. less. Walk east along the crest of the hill about 90 m to a north-northwest-trending north-northwest-trending of the hill toward the valley. valley. When in the valley valley follow follow the edge of the south-southwest south-southwest for about about 60 60 m. m. STOP 5A-3. Strongly Strongly magnetic, STOP 5A-3. magnetic, wavy-bedded, wavy-bedded, cherty cherty iron-formation. iron-formation. Lenticular chert chert beds beds are up to 15 Lenticular 15 cm thick. This This bedding bedding style styleisis typical typical of of wavywavybedded bedded iron-formation iron-formationfarther farthereast eastalong alongthe theGogebic GogebicRange. Range. Walk north-northeast along edge of of hill about about 25 25 m. m. 89 �S a Br BRECCIA INA MARC MATRIX Md Br META DIABASE ———— —— METAGABBRO ———— Mg ci / 60/ OW 0-- GIF -9 LAMINATED SILICATE IRON FORMATION D WAVY-BANDED GRANULAR IRON FORMATION OlE UF —— E -9— -9 © 45 STRIKE AND DIP Ø) OF BEDDING 0 OUTCROP AREAS 0 0 10 20 X mflt 60 GEOLOGIC CONTACT 1OO$. Fig. Fig.5-2. 5-2. Detailed Detailedmap mapof ofthe theAtkins Atkins Lake Lake area area showing showing outcrops outcropsand andgeologic geologic relationships units, diabase relationships among among iron-formation, iron-formation, breccia breccia units, diabase and and gabbro. gabbro. Unpublished Unpublishedmap mapprepared preparedbybyKiasner Klasnerand andLaBerge. LaBerge. 90 �I I I I I I I t I I I STOP 5A-4. non-magnetic chert-argillite chert-argillite or or argillaceous iron5A-4. Thin-bedded, non-magnetic formation. Some boudinaged. The formation. Some cherty cherty layers appear boudinaged. The argillite argillite unit unit is is about about 50 50 m m thick and grades grades into into aa more more argillaceous argillaceous unit with less cherty layers to the the north. north. Walk northeast about about 55 55 m. STOP (UFon onFig. Fig. 5-2) 5-2)is is STOP 5A-5. 5A-5. The top top of the the argillaceous argillaceousiron-formation iron-formationlayer layer(LIP in sharp sharp contact contact with with the the overlying overlying breccia breccia unit, unit, in which which argillite argillite clasts clasts are are surrounded by by aa metabasalt metabasalt matrix. matrix. Clasts in the breccia breccia tend to to become become larger larger higher in the section section (northward (northward from the contact). Remnants Remnants of what appears appears to to be be a thin slab slab of of iron-formation iron-formation lie lie along along the the top top of of the thebreccia breccia unit unit (Br (Br on onFig. Fig. 5-2) 5-2) at at stops 55 and both stops and 6. 6. m. Walk east-southeast east-southeast about about 10 10m. STOP SA-6. Observe the the southeast southeast continuation continuation ofof the the thin slab of 5A-6. Observe of ironironSTOP formation that lies along formation along the the contact contact between between the breccia breccia on the southwest southwest and and massive metagabbro on the the northeast. northeast. Walk northeast northeast about about 50 50 m. m. STOP 5A-7. 5A-7. Massive metadiabase/metagabbro. STOP Walk northwest northwest about about 35 35 m. m. Breccia. Clasts Clasts of of mainly STOP 5A-8. 5A-8. Breccia. mainly argillite in aa vesicular vesicular metabasalt metabasalt matrix. matrix. Argillite clasts are contorted. contorted. PART B: PENOKEE GAP Penokee Penokee Gap lies lies about about3.2 3.2 km km southeast southeastof of Mellen, Mellen, Wisconsin. Wisconsin. It is a water water formed by by the Bad gap in the the Gogebic Gogebic Range Range formed Bad River River as it cuts cuts across across the the Range. Range. by a 1.6 km km walk walk south south along the railroad tracks that Easiest access to Penokee Gap is by that follow the Bad Bad River. River. The Penokee Gap area itself itself and the area just west of the gap gap (Fig. (Fig. 5-3) provide abundant data on on local local stratigraphy stratigraphy and and structure structureof of the theGogebic GogebicRange. Range. It is is important to note, however, that the entire region important however, that region was tilted tilted steeply steeply northward northward the closing tectonisni so so that all during the closing phase phase of of Middle Middle Proterozoic Proterozoic tectonism all Early Early Proterozoic and Archean structural structural orientations orientations are not original original orientations. orientations. Strata at Penokee Gap consist of Archean gneiss overlain by Early Strata Early Proterozoic Proterozoic Bad River River Dolomite, Dolomite, Palms Palms Formation Formationwith with aa thin-bedded, thin-bedded, intensely intensely sheared lower Bad unit and and aamassive massivequartzitic quartziticupper upperunit, unit,Ironwood Ironwoodhon-formation Iron-formationand andcyclicallycyclicallybedded Tyler Tyler Formation, Formation, mainly mainly consisting consisting ofof slates slates and and siltstones. A thin Middle Middle Proterozoic (Keweenawan) (Keweenawan)diabase diabase dike dike intrudes intrudes the Tyler Proterozoic Tyler Formation. Formation. More More 91 �I - TABLE11: Summary of of structural structural components and our interpretation TABLE : Summary interpretation of of the thetectonic tectonic evolution at Penokee Penokee Gap. Gap. EVENT E YmI STRUCTURAL ELEMENTS Archean gneissic foliation SA- Archean foliation - OA-- Late Archean tectonism Discrete, narrow shear zones ss Ss -- Discrete, parallel to to gneissic gneissic foliation. foliation. 0o -- Divergent tectonism associated Do with rifting rifting of of Archean Archean continent. continent. Formation of passive passive continental continental margin. So So - Flat-lying Flat-lying beds unconformably unconformably Oi-- Convergent Convergent tectonism causing thin-skinned, north-verging north-verging folding folding and thrusting. thrusting. Regional Regionalgreenschistgreenschistgrade metamorphism. metamorphism. F1 -- Folds in 5o F1 So with Li Ll fold fold axes. axes. Ji - deposited on passive continental continental margin in the Penokee Penokee Gap Gap area. area. -- Continued Continued north-verging thinthin- - Axial planar foliation. Si Sl - Axial foliation. of boudins. boudins. LB LB -- Long axes of S; -- Spaced Spaced fracture fracture foIiation. foliation. F2 F; -- Kink folds folds primarily primarilyininS1 Sl with with L2 L2 fold fold axes. axes. skinned deformation deformationcoaxial coaxial with Di. Dl. L>M -- Middle Middle Proterozoic Proterozoic rifting rifting of the continental crust and and associated associated deposition of sediments and and igneous igneous activity. activity. Formation of of the Midcontinent Midcontinent Rift. Rift. Intrusion of Mineral Lake Gabbro Gabbro and, possibly, thermal metamorphism metamorphism to form porphyroblasts at at Penokee Penokee Gap. Gap. DK- Northward Northward lilting DKtilting of Archean Tilting resulted in formation formation of of a northwest-dipping northwest-dipping monoclinal monoclinal sequence of of Early and Middle Middle Proterozoic strata strata and formation formation of of north-northwest-striking, near vertical faults, including the formation joints and fractures. formation of Sic SKjoints fractures. and Early Early Proterozoic Proterozoic crust listric thrusts thrusts during along listric compressional phase of the Middle Middle Proterozoic Proterozoic Midcontinent Rift. Rift. 92 �I I I a I I I • p information information on the Early Early Proterozoic Proterozoic stratigraphy stratigraphy at Penokee Penokee Gap Gap is is covered coveredabove above in the introduction. discussions below below summarize the structural structural introduction. Table Table 1 and the discussions observed in in the Penokee Penokee Gap Gap area area and and our interpretation and stratigraphic features observed of the tectonic tectonic events that formed formed them. them. Archean deformation (DA) resulted in in the the formation of of the now near(DA)resulted nearLate Archean vertical, easterly-striking easterly-striking gneissic gneissic foliation foliation (SA (SAon Fig. 5-3) and parallel shear shear zones zones (Ss, not shown structural fabric fabric isis not not present present in any of the (Ss, shown on onFig. Fig.5-3). 5-3). This This structural the overlying Early Proterozoic Proterozoic strata that were were unconformably unconformably deposited on on it. it. The The time of of formation of the shear zones time formation of zones is not known: known: the shears may have formed formed during the subsequent convergent convergent phase of of Early Early Proterozoic Proterozoic tectonism, but they they have a different orientation than than structural structural features features in in the the Early Early Proterozoic Proterozoic strata. strata. Initial rifting of the Archean Do was accompanied accompanied by by unconformable unconformable Initial Archean crust Do on Archean Archean gneisses. gneisses. The rift event was deposition of Early Early Proterozoic Proterozoic strata (So) (SJ) on followed by convergent convergent tectonism. tectonism. At Penokee Penokee Gap, two phases phases (Di (Dl and andD2) D2)of of recognized in the Early Early Proterozoic Proterozoicrocks. rocks. Dl Di involved thindeformation have been recognized thinskinned, north-verging north-verging overthrusting overthrusting that detached Early Proterozoic strata from skinned, from the underlying underlying Archean Archean crust, folded it, and and formed formed multiple multiple bedding-parallel bedding-parallel shear shear zones within the the Early Early Proterozoic strata. Along Along the the Gogebic Gogebic Range, west of Upson, Wisconsin, numerous numerous upward-ramping (Cannon, personal Wisconsin, upward-ramping thrust thrust faults (Cannon, personal Kiasner and LaBerge, detach Early Early Proterozoic strata communication, 1994; 1994; Klasner LaBerge, 1994B) 1994B) detach strata deformation isis abundant from the underlying Archean basement. basement. Evidence Evidence for D1 Dl deformation the iron-formation, iron-formation, folds folds (F1) (Fl) in in Early Proterozoic Proterozoic strata near near Penokee Penokee Gap. Gap. In the bedding define gently gently northwest-plunging northwest-plunging fold see Figs. 5-3, 5-4A and bedding (So) (SJ) define fold axes axes (Li (Ll -- see 5-3,5-4A 45). 4B). AAfield fieldsketch sketchofofaarecumbent recumbentfold foldininiron-formation iron-formation isis shown shownin inFigure Figure5-5. 5-5. Similarly, northwest - plunging folds folds occur occur in in the Tyler Similarly, Tyler east of the Penokee Penokee Gap fault as shown by the 5-4C). Penetrative (Fig. 5-4C). the best best great great circle circle fit of poles to bedding (Fig. axial planar foliation foliation (Si) (Sl)to to the the F1 Fl folds in the Tyler Formation tends tends to to be be flat-lying flat-lying 5-4D). In the the iron-formation iron-formation Si Sl foliation foliation occurs as aa fracture fracture cleavage cleavage (see (see Fig. Fig. (Fig. 5-4D). 5-5). Prominent Prominent shear shear zones zones with with penetrative penetrative Sl S foliation 5-5). foliation occur occur at the base of of the Palms and top top of of the the Ironwood Ironwood hon-formation Iron-formation along along the the contact contact between the the Tyler Tyler and Ironwood strata (Fig. (Fig. 5-3). 5-3). Near Near its its lower lower contact, contact, the Palms is thinly-bedded and units units that that contain containfine-grained fine-grained quartz quartz in in aa sericite sericite matrix matrix are are intercalated intercalated with with finer grained, sericite-rich layerswith with ultra-fine ultra-finequartz quartzgrains. grains. Both the quartz-rich sericite-rich layers layers are foliated foliated and constitute constitute a broad zone of shearing and sericite-rich layers shearing within within the basal Palms: layers with ultra Palms: however, however, the the more more strongly-foliated, strongly-foliated, sericite-rich layers fine quartz are Si shear fine are more moreintensely intenselysheared. sheared. The The Sl shear foliation foliation generally generally dips dips - - • 1 1 �Penokee Gap )1. ? Sct BLOCK III Et Et 25 Et I p I Et 5- TO t Fa u ft 20 40 600 meters 100 2 00 feet Sect is Ss 16 BLOCK ll4 $ct 72 K A S_ 75 A , Middle Middle Proterozoic Proterozoic Keweenewan diabase dike El Early Early Proterozoic Proterozoic WlerFormation Formalon Tyler 1 1 Ironwood IronIronwood Ironformation Palms Formation Palms Formation Bad River DolomiBad River Dolomite Archean Archean G"dss Onelss ' Section comer, dashed Section corner, 11&on dashed 11H-- lines t section lines jS- Railroad Railroad tracks tracks Large exploration pit 4 Large exploration pit \ Fault Faulttrace trace Shearzom Sheer zone Thrust fault, Wangle* fault, triangles 44 Thrust on upthrown block on upthrown block Orientation of joint or \ Orientation of joint or f'=CtumplÇn — fracture planes (S^ 0 1 . II t (5K) Orientation of vertical joint Orientation vertical joint or fractureof planes or fracture planes Geologic contact Geologic contact 'j Strlkeand dlp of bddlng (SJ Strike and dip of bedding C) Strikeand dl of Eari 'V StrIke and dipfoiiation of Early ~roterozoic Proterozoic foliation (S.) SWke and dip of Archean Strike and(Sdip foliation ) of Archeen -C foliation L.1 K ' Strike Of vertical Archean Strike of vertical foliation (sA) Archeen foliation Plunge of first generation Plunge of (LJ first generation '^,fold fold axis axis (L) Plunge of Èçco generation '^,fold axis (L} Plunge of second generation fold axis (U d Fig.5-3: 5-3: Geologic sketch map of Penokee Gap area. Blocks I, II, and III represent Fig. Geologic sketch map of Penokee Gap area. Blocks I, U, and UI represent segments of the Gogebic range near Penokee Gap that are delineated by northwestsegments of the Gogebic range near Penokee Gap that by northwesttrending faults. Capital letters indicate general location of are datadelineated for stereoplots in Fig. 5-4. trending faults. Capital letters indicate general location of data for stereoplots in Fig. 5-4. 94 �I I I I I I I I r I I I I I I i northwest and strikes and constitutes constitutes the the zone along which strikes northeast northeast (Fig. (Fig. 5-4E), 5-4E), and which Early Proterozoic Proterozoic strata are Early are detached detached from from Archean Archean basement. basement. Likewise, a shear shear along the contact contact between the bonwood Ironwood and andTyler Tyler Formations Formations constitutes constitutes another another zone of of detachment of the from underlying underlying Ironwood honwood Iron-formation. hon-formation. We zone detachment of the Tyler Tyler from We consider that both both formation formation of of the the shear shear zones, zones, with withaccompanying accompanyingfoliation, foliation, and and of the Tyler and older strata, with folding of with accompanying accompanying axial planar foliation, were the same (Dl). That is, they they were were formed formed part of the same fold-thrust fold-thrust event event (D1). contemporaneously, and and we we therefore therefore label label both both the the shear foliation and the contemporaneously, the axial axial planar foliation foliation as as Sl. D2 deformation was characterized by continued continued north-verging thrusting thrusting that D2 characterized by resulted in further along the the Sl S shear resulted further deformation deformation along shear zones zones in inpre-Tyler pre-Tyler Early Early Proterozoic strata. Proterozoic strata. Within the lower lower Palms, Palms, prominent F2 kink folds in Si Sl shear shear foliation plunge plunge gently 5-4F) and and are prime foliation gently northwest northwest (Fig. (Fig. 5-4F) prime examples examples of of D2 D; deformation. Although Although F2 kink folds folds are are not not present present in in the Tyler, Si foliation Tyler, Si foliation in deformation. F; kink compared to to the generally northwest these strata tends tends to tobe beflat-lying flat-lying (Fig. (Fig. 5-4D) 5-4D) compared dipping Sl Sj foliation in pre-Tyler strata (Fig. (Fig.5-4E), 5-4E),and andSlS is is folded about a nearly dipping pre-Tyler strata northwest-trending fold fold axis axis that thatisisroughly roughlycoaxial coaxialwith withF2 F; fold foldaxes axes(Fig. (Fig.5-4F) 5-4F) in the sheared D2 sheared Palms Palms Formation. Formation. Thus, we think that that the the Tyler Tyler was was also alsoaffected affected by by D2 deformation. Sense of of structural vergence in the lower Palms shear zone is shown shown in in Fig. Fig. 556A, B 6A, B and C; C. Northward Northwardstructural structural vergence vergence along along a small, small, south-dipping south-dipping thrust Fig. 5-6A) 5-6A)in inwhich whichthe thehanging hangingwall wallmoves movestoward towardthe the north north as as shown by fault (see Fig. 5-6B)and andby by the the sigmoidal sigmoidal curvature curvature and offset a telescoped tabular layer (Fig. 5-6B) offset of of beds across across the the thrust thrustfault fault(Fig. (Fig.5-6C). 5-6C). Sense of of structural vergence Sense vergence in the Tyler Tyler Formation Formation at Penokee Penokee Gap is also also toward the north where where vertical vertical to overturned overturned graded beds of of siltstone siltstone and and slate slate stratigraphically face northward (even (evenafter after post-Early post-Early Proterozoic Proterozoic (Keweenawan) (Keweenawan) rotation is removed). Although rotation Although such such sense sense of folding and rotation of bedding is not proof of the northward northward sense of of rotation in Tyler strata proof of overall structural vergence, vergence, the agrees with kinematic indicators agrees indicators in the older older strata, strata, suggesting suggesting that that D1 Dl and and D2 D; represent represent a continuum continuum of of northerly-directed northerly-directed overthrusting overthrusting associated associated with the the convergent phase phase of of Early Early Proterozoic Proterozoic tectonism tectonism in the the Penokee Penokee Gap Gap area. area. Evidence for for the formation Evidence formation of of the the Middle MiddleProterozoic Proterozoic Midcontinent Midcontinent Rift Rift in Table Table 1) 1) lies lies mainly mainly north north of of the the Gogebic Gogebic Range. Range. Nevertheless, this (labeled DM DM in event affected Early Proterozoic Proterozoic and and Archean Archean strata at Penokee Gap. For example, example, the final the final phase phase of of tectonic tectonic evolution evolution of of the the Midcontinent Midcontinent Rift Rift involved involved aa �S 96 �S I I I I I I I I I I I I I Fig. 5-4: 5-4: Lower hemisphere, equal area stereo plots of of structural features observed in Fig. the Penokee Gap area. Stereoplots and according the Stereoplotsare arekeyed keyed to toFig. Fig. 5-3 5-3 by capital letters and according shown on observations. to blocks shown on Fig. 5-3. N N == number of observations. A. Poles to bedding primarily from iron-formation in blocks II bedding(So), (So), primarily Il and and ifi. in. Best fit great circle defines defines an 14O,N85°W. ~85¡W great an F2 F2 fold with an an axis that that plunges plunges14°, B. Orientation of Lz axes of of folds folds in in bedding bedding (So), (So),primarily primarily from from iron-formation, iron-formation, B. Orientation Soliddots dotsare arefield fieldmeasurements, measurements, best best fit fit orientation orientation (open in blocks blocks II J.I and and 111. in. Solid (open defines aa fold circle) defines fold axis axis that that plunges plunges17°, 17¡ N82°W. N82¡W C Poles primarily from from the the Tyler TylerFormation. Formation Best-fit C. Polesto tobedding bedding(So) (So) in block I,I, primarily Best-fit great that plunges great circle circle defines definesan anF1 Fi fold fold axis that plunges15°, 15O,N64°W. N64"W. D. Poles to Sl Si foliation foliation in in the the Tyler Formation. 8est-fit Best-fitgreat greatcircle circledefines definesan anF2 F; fold axis 04O,S62°E. S62OE. axis that that plunges plunges04°, IL Poles to to Sl S shear E. Poles shear foliation foliationin in the the lower lower Palms Palms Formation Formationof of block II. II. orientation F2 that plunges plunges 22°, Best-fit great circle defines the orientation Fa fold that 22O, N77°W. N77¡W F. Orientation Orientation of Si shear foliation in the lower of L2 L2 kink folds in Sl lower Palms, Palms, block block U. II. Solid Solia measurements, best-fit fold axis axis that that dots are field measurements, dots best-fit orientation orientation (open (open circle) defines aa fold plunges 31°, plunges 31°N75°W. N7W. �a —la/V Im •1 Im field sketch Fig. Fig.5-5: 5-5: Field Field sketch sketch of of recumbent recumbent fold fold in in Ironwood Ironwood Iron-Formation Iron-Formation just west of Penokee PenokeeGap. Gap. So ==bedding. bedding. S1 Si==axial axialplanar planarfracture fracturefoliation. foliation. ' 98 �99 photograph. in bed offset and folded Sigmoidally C. photograph. in layer Telescoped B. layering. shortened and fault thrust of sketch Hand A. fault thrust north) the toward wall (hanging north-verging small, a showing Formation Palms in zone shear Si within from photograph and Sketch 5-6: Fig. I I I I I I I I I I I I I I I * �compressional stage (Dic (DK on Table Table 1) that affected affected Early Proterozoic and Archean Archean strata at Penokee Gap. Gap. During OK deformation, deformation, rigid blocks of Keweenawan Keweenawan and During 0K Early strata, along Early Proterozoic Proterozoic strata, along with underlying underlying Archean Archean gneiss gneiss were tilted tilted northward along along north-dipping north-dipping listric listric thrust faults faults (Cannon (Cannon and others, 1993). 1993). This This northward northward tilting tilting created created the the north-dipping north-dipping monoclinal monoclinal sequence sequence of of Early Early Proterozoic strata that that characterize characterize most most of of the theGogebic Gogebic Range Range today. today. In addition, our mapping at Range to to the west of the gap at Fenokee Penokee Gap Gap and and along along the the Gogebic Gogebic Range gap indicates that the rotated blocks are divided into discrete segments (blocks I, II and ifi the rotated blocks are divided into discrete segments (blocks in on Fig. Fig. 5-3) 5-3) that are are bounded bounded by bysteeply-dipping, steeply-dipping,north-northwest-striking north-northwest-striking fault. fault. Besides the stratigraphic stratigraphic offsets across the the inferred inferred faults, numerous steeply-dipping, steeply-dipping, northwest-striking joints or closely northwest-striking joints closely spaced spaced fractures fractures (Sic) (SK)are are also also considered considered structural structural expressions expressions of of this thisphase phaseof of deformation deformation(Fig. (Fig. 5-3). 5-3). The Penokee Gap fault fault is perhaps the the most most prominent prominent of of these these faults, faults, and and itit created created aazone zoneof of weakness weakness along which the Bad River ultimately ultimately flowed flowed forming forming the the Penokee Penokee water water gap gap in the Gogebic Range. Steeply northwest-plunging northwest-plungingfolds folds adjacent adjacent to to these these faults are Range. Steeply are observed in outcrops of the Tyler Tyler and were were most most likely likely formed by drag drag along along the the faults. faults. Formation Formation of of the Midcontinent Rift Rift may may have have also also resulted in metamorphism of of Early Early Proterozoic Proterozoic strata. strata. As noted above, above, geologic geologic evolution of the Gogebic Range near Penokee Gap involved Gogebic Range involved at least two two metamorphic metamorphic events. events. The Dl The first first was was a adynamic, dynamic,low-grade• low-grade event event that thataccompanied accompanied regional regional D1 deformation. deformation. It is characterized characterized by formation of platy minerals minerals of of sericite, sericite, biotite, biotite, The second second metamorphic metamorphic event event was most and chlorite chlorite that lie lie along along Si SI foliation. foliation. The most likely related to to intrusion intrusionof of the theMiddle MiddleProterozoic ProterozoicMineral Mineral Lake Lake Gabbro, Gabbro, which whichlies lies about 1.6 km north This event event is is characterized by a suite of north of of Penokee Penokee Gap. Gap. This characterized by of metamorphic minerals including metamorphic minerals including cordierite, cordierite, garnet, garnet, chlorite, chlorite, magnetite, magnetite, and and deformational fabric and, thus, Dldeformational amphibole, some of of which clearly dearly overprint the D1 however, has has not not been been studied studied in in detail in this area and postdate postdate it. it. Metamorphism, however, is worthy of further further study. study. PENOKEE CAP PENOKEE GAPFIELD FIELDSTOPS STOPS(see (seeFig. Fig.5-7) 5-7) south from Walk south from County County Road Road GG GG at Foster Junction along railroad tracks tracks for for 1cmtotothe thefirst firstlarge largerock rockcut cut (Stop (Stop11on onFig. Fig.5-7). 5-7).Although Although most most field field stops about 1.3 1.3 krn will be be in stratigraphic order from oldest oldest to youngest, youngest, the the first first stop will will be in the will Tyler Formation, Formation, the the youngest youngest Early Early Proterozoic Proterozoicunit unit encountered encountered on on the walk Tyler southward southward along along the the railroad railroad tracks tracks to to the the older older strata. strata. 100 �I I I I I I I I I I I I I I I I map of the Penokee Gap area showing showing location location of field stops. stops. Geologic field map Fig. Fig.5-7: 5-7: Geologic 101 �Ti r STOP SB-i. Tyler Tyler Formation Formationand and Keweenawan Keweenawandiabase diabasedike: dike: SW SW 1/4, 1/4, NE NE 1/4, STOP 5B-1. SW 1/4, 1/4, 511, Sll, T44N, T44N, R3W R3W The Tyler Formation isis exposed exposed for for roughly roughly 100 100m m in in a rock cut along Tyler Formation along the the railroad railroad tracks and and consists consists of of multiple multiple beds beds of of black black carbonaceous carbonaceous slate and and siltstone, subtly subtly graded graded with stratigraphic tops tops toward toward the north. The TheTyler Tyler strata strata consist of of mostly silt-sized quartz grains in aa carbonaceous carbonaceous matrix of biotite, chlorite Small (—1 cm-diameter)cordierite cordieriteporphyroblasts porphyroblasts are are dispersed and sericite. sericite. Small (-1 cm-diameter) throughout the siltstone/slate. siltstone/slate. in the the Tyler Tyler at at the the northernmost northernmost end end of of the rock cut (east side of (So) in Bedding (So) the railroad railroad tracks) tracks) is overturned overturned toward toward the the north, north, but, but, progressing progressing southward, southward, most bedding dips dips steeply steeply northwest northwest and and strikes strikes northeast as shown shown in in Fig. Fig. 5-4C. 5-4C. Si Sl foliation lies at a large angle to bedding, is generally low-dipping to to flat-lying, and and is is that plunges plunges gently gently to to the the southeast as shown by the (1-2) that folded around aa fold fold axis axis (L2) great great circle circle on onFig. Fig.5-4D. 5-4D. zones of steeply-dipping, Isolated zones steeply-dipping, north-northwesterly-trending north-northwesterly-trending fracture fracture cleavage with steeply plunging folds (possibly drag drag folds) are found in cleavage with in outcrops outcrops especially along along the west side of especially of the the railroad railroad tracks. tracks. These, These, and other northwestnorthwesttrending joints joints and fracture fracture zones in the region, region, are considered part of of aa family family of of north-northwest faults in the the Penokee Penokee Gap area that divide divide the the Gogebic Gogebic Range Range into individual II, Fig. 5-3). 5-3). They They are are interpreted as Middle 1, and III on Fig. individual segments segments (blocks (blocks I, 1 of formation of of the - -- Proterozoic Proterozoic SK structures formed during the final closing phase of Midcontinent Rift. Midcontinent Rift. A 33 rn-wide diabase dike dike is is exposed exposed at the north m-wide undeformed Keweenawan Keweenawan diabase north end of the rock rock cut on on the the west west side sideof of the the railroad railroad tracks. tracks. Walk further south along the railroad tracks to to the first rock rock cut on the east Walk further railroad tracks east side side of the tracks, tracks, just past past the the second second bridge. bridge. STOP 5B-2. 5 5 2 . Archean Archean gneiss: gneiss: SE SE1/4, 1/4,NW NW1/4, 1/4,514, S14,T44N, TUN, R3W R3W Amphibolitic to granitoid granitoid gneiss. gneiss. The Archean Archean gneiss forms the basement basement The westupon which westupon which overlying overlying Early Early Proterozoic Proterozoic strata were were deposited. deposited. The northwesterly-striking gneissic foliation foliation dips dips steeply steeply south. Parallel shear northwesterly-striking gneissic shear zones zones wide occur occur in in the the gneiss. gneiss. Although the strike of the gneissic and several centimeters wide shear shear foliations foliations is roughly roughly parallel to the the strike strike of of Early Early Proterozoic Proterozoic structural structural features, there are no no structures structures in in the the overlying overlying Early Early Proterozoic Proterozoic strata that that have have similar dips. Other Otherthan thanpostdating postdatingthe thegneissic gneissicfoliation, foliation, the the age age of of shear shear formation formation is not known. known. The Theshears shearsmay maybe beEarly EarlyProterozoic Proterozoic in inage. age. Examine outcrops outcrops along both banks of Bad River, just just beneath railroad bridge. bridge. 102 j �I STOP STOP 5B-3. 5B-3. Bad Bad River Dolomite: NE NE 1/4, 1/4,SE SE 1/4, 1/4,NW NW1/4, 1/4,S14, S14,T44N, T44N, R3W R3W Exposures on the south side with side of of the the Bad Bad River are tan-colored tan-colored dolomite with chert Bedding is is oriented oriented N80'W, N80°W,45"N. 45°N.Note Note that that the dolomite chert lenses lenses and and layers. layers. Bedding rests directly on Archean gneiss. On directly on Archean gneiss. On the the eastern eastern end of of the the Range, Range, the the Sunday Sunday Quartzite occurs occurs between the the Archean Archean basement basement and and the theBad Bad River River Dolomite. Dolomite. Quartzite At Dolomite isis about about 20 20m m thick. thick. The basal portion At this this locality locality the the Bad Bad River Dolomite is is mainly mainly dolomite dolomite that that has hasvague vaguecross-bedding cross-bedding and andpossible possiblestromatolites stromatolites suggestive of of shallow water water deposition. deposition. The The upper part part of of the the Bad Bad River River Dolomite Dolomite (on the north side breccia. This side of of the the river) river) is a variegated chert and chert breccia. This lithology is is typical typical of exposures exposures for for about about 15 15 km krn in the western part of of the the Gogebic Gogebic Range. We We interpret interpret the the cherty chertyupper upperportion portionof of the theBad Bad River River Dolomite Dolomite to represent a residual concentration concentration of of chert layers and nodules nodules formed formed by solution solution of of dolomite dolomite during during erosion erosion that that preceded precededdeposition depositionof ofthe theoverlying overlyingPalms PalmsFormation. Formation. We of the cherty portion of the We will will examine examine another exposure of the Bad Bad River River Dolomite about about 515 m to the west at a later stop. stop. Walk north north from from the the railroad railroad bridge to to the first large outcrop on the the west west side side Walk of of the the tracks. tracks. STOP STOP 5B-4. 5B-4. Palms Palms Formation: Formation: SE SE 1/4, 1/4,NW NW 1/4, 1/4,NW NW1/4, 1/4,S14, S14,T44N, T44N, R3W R3W Alternating Alternating beds beds (So) (So) of silty silty to to finer-grained, finer-grained, more argillaceous strata are present present here. here. Thicker-bedded, Thicker-bedded, more more psammitic psamrnitic (silty) strata on the south end grade grade strata on the north end of into finer-grained, finer-grained, more mica-rich mica-rich strata of the the outcrop, outcrop, indicating indicating into that that stratigraph.ic stratigraphic facing is to the north. Both Both the the silty silty layers layers and and mica-rich mica-rich layers layers are are penetratively foliated, but the the argillaceous argillaceous layers have less quartz as well well as as finerfinerpenetratively grained (Si)isis grained quartz quartzininan anintensely-foliated intensely-foliatedsericite sericitematrix. matrix. Penetrative Penetrative foliation foliation (Si) generally parallel to to bedding. There are also F; generally oriented oriented N75°E, N75'E, 60°NW, 60°NWparallel also numerous numerousF2 kink kink folds folds in in Si Slfoliation foliationwith withL2 L; axes axesthat thatplunge plungeabout about16°, 16',N87°W. N8TW. These These penetratively-foliated strata are are considered consideredpart part ofof aa Di penetratively-foliated strata Dl shear shear zone zone that that was was subsequently kink folds. folds. We subsequently deformed deformed by by aaD2 D; deformational deformational event to form the F2 F; kink will will take take aa closer closer look look at at the the style style of of deformation deformation in this shear zone to the west at at Stops and7.7. Stops66and Walk Walk west west from from the the railroad railroad bridge bridge for for approximately approximately 515 515 m to to aa large largetalus talus slope hill. Climb slope along along the the steep steep south south flank flank of an easterly trending hill. Climb the the talus talus slope slope to to two twoexploration explorationpits pitsnear nearthe thetop topofofthe thesteep steepslope. slope. Note: Note: This Thiswalk walkisisstrenuous, strenuous,through through thick thick brush brush and and along along steep steep hillsides hillsides with with loose loose rocks rocksthat thatmay mayroll rolldown downthe thehillside hillsideififdisturbed. disturbed.BE BECAREFUL! CAREFUL! r 103 �STOP 50-5. 5B-5. Bad NW1/4, 1/4,NW NW1/4, 1/4,514, S14,T44N, T44N,R3W R3W BadRiver River Dolomite: Dolomite: SE SE 1/4, 1/4,NW The between the the Bad Dolomite and and the the Palms Bad River River Dolomite Palms Formation Formation is is The contact contact between exposed in in two pits at this exposed two exploration exploration pits pits at at this thislocality. locality. Other Other exploration exploration pits this stratigraphic horizon are are present present on on the stratigraphic horizon the eastern eastern flank flank of of Mt. Mt.Whittlesey, Whittlesey, approximately 9 km to the east. of magnetite magnetite are are localized Concentrations of localized in approximately 9 km to the east. Concentrations conglomeratic zonesatat the the top top of conglomeratic zones of the the cherty cherty breccia breccia portion portion of of the the Bad Bad River River Dolomite. The that surrounds angular and rounded Dolomite. The magnetite is in a sandy matrix matrix that chert fragments fragments up up to do not chert to at at least least 70 70 cm cm long. long. Magnetite-rich Magnetite-rich zones zones do not extend extend up up into the the magnetite into the overlying overlying Palms PalmsFormation. Formation. Therefore Therefore the magnetite concentrations concentrations appear to to be be pre-Palms. pre-Palms. Along Alongstrike strikefrom fromthe themagnetite magnetiteoccurrence, occurrence, the the Bad Bad River River Dolomite consists of of a spectacular breccia breccia with with some some rounded rounded and angular angular blocks blocks of of chert in tic matrix. in aa reddish reddishhemati hematitic matrix. The of magnetite in conglomeratic rocks at at an The local local concentrations concentrations of magnetite in conglomeratic rocks an unconformity argue for for a paleo-placer unconformity argue paleo-placer origin origin along along aa braided braided stream stream course. course. However, much of of the magnetite However, much magnetite is euhedral, showing no indication indication of rounding rounding that might be The euhedral magnetite may indicate be expected expected in in aa placer placer deposit. deposit. The indicate that these that these are are hydrothermal hydrothermal deposits, deposits, but but no nohydrothermal hydrothermal bleaching bleaching of of surrounding rocks is evident, evident, nor are are any any hydrothermal hydrothermal gangue gangue minerals, minerals, such such as as quartz crystals, the euhedral crystals, present. present. Alternatively, Alternatively, the euhedral magnetite magnetite crystals crystals may be be metamorphic in origin. origin. Clearly, Clearly, the origin of these peculiar magnetite magnetite occurrences occurrences is is problematic. A and report report that problematic. A mining mining company company has analyzed analyzed these conglomerates conglomerates and there are no no precious precious metals metals in in them. them. Walk north-northeast about 80 m to the crest and north flank Walk flank of of the the hill. hill. STOPS 5B-6 5B-6and and 5B5B-7.7. Sheared, Sheared, thin-bedded thin-bedded Palms Palms Formation: Formation: SE 1/4, NW 1/4, NW NW 1/4, 1/4,S14, S14,T44N, T44N,R3W. R3W. The purpose purpose of of these The these two stops stops is to to illustrate illustrate our our interpretation interpretation of the the kinematics of of deformation deformation in a D1 shear zone. zone. Lithology kinematics Dl shear Lithology at this stop stop is is similar similar to to that at at Stop Stop 44 where where layers layers of of silty silty Palms Palms are are intercalated intercalated with with finer-grained finer-grained micamicarich layers, both of which numerous small small which have have penetrative penetrative Si S1 foliation. foliation. At Stop 6 numerous boudins are formed formed in in thin thin quartz-rich quartz-rich layers layers that have have orientations orientations close to the the orientation of Si Also, several several F; F2 kink kink folds folds with L2 orientation Sl foliation foliation planes. planes. Also, L; fold axes axes deform the at this this stop. stop. At the S1 S1 shear fabric at At Stop Stop 7, about 70 m northwest of the area of Stop 6, there is is aa small, small, south-dipping south-dipping D1 Dl thrust thrust fault fault (Fig. (Fig. 5-6A) 5-6A) with telescoped telescoped layers (Fig. and a sigmoidal layers (Fig. 5-6B) and sigmoidaldrag dragfold foldwith withoffset offsetbeds beds(Fig. (Fig.5-GC). 5-6C). Si foliation, foliation, the the boudinaged boudinaged quartz layers and The three structural structuralelements: elements: Sl the small thrust fault fault provide provide information information to interpret the kinematics kinematics of of the shear shear 104 �I I I I N fl !+ [1 Fig. Fig. 5-8: 5-8: Lower Lower hemisphere, hemisphere, equal equal angle angle stereoplot stereoplot showing the orientations orientations of ofS1 foliation foliation(great (greatcircle), circle),orientation orientationof of the the long long axes axes of of boudins boudins(LB), (LB), orientation orientationof of the the axis (XI, and andorientation orientationof ofthe theaxis axis of of shortening shortening (Z) in in the the sheared shearedPalms Palms axisof ofstretching stretching(X), - (Z) Formation FormationatatStops Stops5B-6 5B-6and and5B-7. 5B-7.See Seetext textfor fordiscussion. discussion. 105 �j zone. structures. Penetrative zone. They are all considered to be D1 Dl structures. Penetrative Si SI foliation foliation formed as a result result of of simple simple shear shear along along an aninferred, inferred,now now steeply steeply north-dipping north-dipping to to vertical vertical shear Sense of of movement shear zone zone that that dips dipsmore moresteeply steeplythan thanSi SIfoliation. foliation. Sense movement in the the shear couple couple must have have been been down down to to the the north north to toform formSi Slfoliation. foliation. The general orientation of Si, SI, based based on on field field measurements, measurements, is shown by the the great great circle circle on the stereographic stereographic plot plot in inFig. Fig.5-8. 5-8. The boudins formed by stretching perpendicular to their axeslie lieroughly roughlyin inthe theST Siplane plane and and plunge about about 45° 45' toward their long longaxes axes(LB). (LB).LBaxes the northwest. in the shear zone can be northwest. The Theorientation orientationof of the theaxis axis of of stretching stretching (X) (X) in be estimated from the orientation of the boudins. The (X) orientation of the long axes of Thestretch stretchaxis axis(X) also lies in the the Si SI plane plane at atright rightangles anglesto tothe thelong longaxes axesof of the theboudins boudinsLB, LB, as shown on on Fig. Fig. 5-8. That That isis the therocks rocks in in the the shear shear zone zone were were stretched stretched along along an an axis axis (X) (X) that plunges plunges toward towardthe thenortheast northeastasasshown shownon onFig. Fig.5-8. 5-8. Finally, the small small thrust thrust formed formedinin aa region region where where Sl S foliation Finally, the foliation did did not develop. (Zon onFig. Fig.5-8). 5-8). develop. The Thethrust thrustlies liesparallel paralleltotothe theaxis axisofofmaximum maximumshortening shortening(Z That That is, is, itit developed developedat atright rightangles anglesto toSi S1foliation foliationas as shown shownon onFig. Fig.5-8. 5-8. Essentially, Essentially, the where Sl Si foliation the small small thrust thrust accommodated accommodated shortening in rocks rocks where foliation could not develop develop because because of of their theircomposition composition(see (seethe thephotograph, photograph,Fig. Fig.5-6). 5-6). The absence absence of similar similar structures structures in in the the underlying underlying Archean Archean basement basement requires requires that that Early Early Proterozoic Proterozoic strata must must be be detached detached from from them. them. Thus, we we interpret interpret the the intensely intensely foliated foliated strata strata in in the the lower lower part part of of the thePalms PalmsFormation Formation to to represent represent aa ductile ductile shear shear zone zone that that detached detached the the Early Early Proterozoic Proterozoic from from the the underlying underlyingArchean Archeangneiss. gneiss. Walk Walk north, north, across across aa narrow narrow valley valley for about 70 70 m to the next steep steep hill. hill. STOP STOP 5B-8. 5B-8.Uppermost UppermostPalms Palms Formation: Formation: SE SE 1/4, NW NW 1/4, 1/4, NW NW 1/4, 1/4,S14, S14, T44N, R3W. T44N, R3W. This This stop stop illustrates illustrates the the massive, massive, thickly bedded quartzite typical of the upper upper part bedded unit and the part of of the thePalms. Palms. Both Both this massively massively bedded the lower lower thin-bedded thin-bedded argillaceous argillaceous units units continue continue westward at at least least to to the the Atkins Atkins Lake Lake area, where outcrop outcrop dies diesout. out. The The Palms Palms Formation Formation generally generally strikes strikes N80°W N80'W and dips dips 65°NE 65'NE in this this area, area, shows shows cross-bedding, cross-bedding, and is aa clean clean orthoquartzite. orthoquartzite. Westward Westward from from Penokee Penokee Gap Gap the the quartzite quartziteisisaaprominent prominentridge-former ridge-formerwith withnumerous, numerous,excellent excellent exposures. exposures. Because of the exceedingly steep slopes slopes and loose rocks rocks it is dangerous for Because of for aa large large group group to toclimb climb to tothe thetop topofofthe thebluff blufftotoview viewthe thequartzite-iron-formation quartzite-iron-formation contact. contact. Walk Walk north north up up the therelatively relatively gentle gentle slope slope just just west of the the quartzite quartzite bluff bluff for for 106 fl I �L a about about 30 m. m. n fl-I I I I I I STOP 1/4, NW 1/4, STOP 5B-9. 5B-9. Ironwood Iron-formation: Iron-formation: NW NW 1/4, 1/4, S14, S14, T44N, T44N, R3W. R3W. The Ironwood Iron-formation overlies the the Palms The Iron-formation conformably conformably overlies Palms Formation Formation from which it grades through aa transition transition of of several beds of granular iron-formation iron-formation in the upper upper Palms. Palms. Locally, Locally,the thebase base of of the the Ironwood Ironwood has has aa thin thin (3 (3m) m) conglomerate conglomerate thick zone of of stromatolitic stromatolitic jasper jasper occurs occurs at at the base of the zone, elsewhere, locally a thick iron-formation. The eastward from Gap was The Ironwood Ironwood Iron-formation Iron-formation eastward from Penokee Penokee Gap was subdivided subdivided into five into five units units based based on onbedding beddingstyle styleand andmineralogy mineralogy(Hotchkiss, (Hotchkiss,1919). 1919). Our mapping west of of Penokee Penokee Gap shows that that the the iron-formation iron-formation consists consists of alternating alternating units of of granular, granular, wavy-bedded wavy-bedded iron-formation iron-formation and and laminated laminated iron-formation. iron-formation. However, except except in the first few west of of Penokee Gap, Gap, the However, few hills hills of iron-formation iron-formation west five-fold field field division of of Hotchkiss Hotchkiss and and U. U. S. S. Steel Steeldoes doesnot not extend extend westward westward along five-fold the Gogebic Gogebic Range. Range. basal 75 75 m m of of the the iron-formation iron-formationisismainly mainlyaagranular, granular, wavy wavy bedded bedded unit The basal with irregular lenticular layers that branch lenticular chert beds separated by magnetite-rich magnetite-rich layers unit may represent the and recombine recombine around the the cherty cherty lenses. lenses. This This unit the Plymouth Plymouth member of this wavy-bedded wavy-bedded unit unit is about 30 of Hotchkiss Hotchkiss(1919). (1919). Overlying Overlying this 30 m m of of mainly laminated, magnetic magnetic iron-formation with scattered intraformational breccia breccia units. This lithology may represent units. represent the the Norrie Norrie and andPence Pencemembers membersofofHotchlciss Hotchkiss (1919). The The uppermost exposures (1919). exposures are laminated, laminated, weakly weakly to to non-magnetic non-magnetic ironironformation. Some Some layers layers contain contain rounded rounded elongate elongate chert chert concretions concretions in aa somewhat somewhat matrix, possible representing the Anvill argillaceous matrix, Anvil1 member member of of Hotchkiss Hotchkiss(1919). (1919). Near the northernmost Near northernmost exposures exposures of the the Ironwood Ironwood Iron-formation, Iron-formation, the recumbent 5-5) mentioned mentioned above above isis present, present, and and the contact with with the Tyler Formation fold (Fig. 5-5) of the hill hill supported by by the iron-formation. iron-formation. There are no lies along the north flank of exposures of the Tyler Tyler in in this this region, region, however. however. END OF OF FIELD FIELD STOPS STOPS Walk east-southeast for for about 820 820 m m to to railroad railroad tracks along the Bad Walk Bad River, River, and then then about about 22 km km north northon onrailroad railroadtracks trackstotovehicles. vehicles. ACKNOWLEDGMENTS I We are grateful to the their help: Suzanne the following following persons persons for their SuzanneNicholson Nicholson for reviewing for reviewing the manuscript manuscript and and preparing preparing itit for forfinal finalpublication; publication; William William Cannon Cannon for reviewing reviewing the the manuscript; manuscript; Don Don Harrison, Harrison, of of Western Western Illinois Illinois 107 I �University, preparation of stereoplots; stereoplots; and Susan Susan Wilson, Wilson, also also of of Western Western University, for for preparation Illinois University, University, for computer drafting of the Illinois the figures. figures. Both and Both the reviews and field guide. guide. technical assistance aided considerably in preparation of this field REFERENCES REFERENCES Anderson, Mitchell, Mitchell, and Klasner, Klasner, John S., 1993, 1993, Geologic Geologicevidence evidencefor forthin-skinned thin-skinned deformation deformation in the Eastern Gogebic Gogebic Range Range [abstract]: [abstract]: Abstracts Programs, North-Central North-Central Section Section of the Eastern Abstracts with with Programs, of the Geological Society paper no. Geological Society of America, America, v. 25, 25, n. 3, paper no. 028211, 028211, p. 2. p. 2. J. E., E., 1970, 1970, A revision middle Precambrian Precambrian Cannon, W. F., and Gair, Gair, J. revision of of stratigraphic nomenclature of middle rocks in northern northern Michigan: Michigan: Geological GeologicalSociety Societyof of America America Bulletin, Bulletin, v. 81, p. 2843 2843 -- 2846. 2846. Z. E., E., and and Sims, Sims, P. K., K., 1993, origin of of the the Montreal Montreal Cannon, W. F., Peterman, Peterman, Z. Cannon, W. 1993,Crustal-scale Crustal-scalethrusting thrusting and and origin River rnonocline -- aa 35 kilometer-thick Northern River monocline -kilometer-thickcross cross section sectionofof the the Midcontinent Midcontinent Rift Rift in Northern Michigan: Tectonics, Tectonics,v.v.12, 12,p. p. 728 728 -- 744. Feher, L., Flood, T. P., 1995, 1995, Vesicles partially L., and Flood, Vesiclesand and breccia brecciadue due to injection injection of of mafic mafic magma magma into partially lithified sediments sediments of of Early Early Proterozoic, Proterozoic, Ironwood Iron-formation, western Gogebic Gogebic Range, N. W. Wisconsin [abstract]: [abstract]: 41st 41st Annual AnnualInstitute Instituteon onLake Lake Superior SuperiorGeology, Geology, Marathon Marathon Ontario, Ontario, v. 41, part Wisconsin 1., p. p. 13 13-- 15. 15. I., Hotchkiss, W. W. O., 0., 1919, Gogebic Range Rangeand and its its relation relation to to recent mining developments: ~otchkiss, 1919, Geology of the Gogebic developments: Journal, v. 108, p.p.443 507,537-- 541, and and 577 577-582. 452,501 - 507,537 - 582. Engineering and Mining Mining Journal, 443 --452,501Klasner, J. S., LaBerge, G. S., and and LaBerge, G. L., L., 1994A, 1994A,Structural StructuralEvolution Evolutionofofthe theEastern Eastern Gogebic GogebicRange, Range, Northern Northern Michigan [abstract]: 40th Annual Institute on Lake Superior Geology, Houghton, Michigan, v. 40, 40, [abstractj: on Lake Superior Houghton, Michigan, v. part 1, p. 23-24. 1, p. 23 - 24. and LaBerge, LaBerge, G. L., L., 19948, 1994B, Structural geology of the the Gogebic Gogebic Range, Range, Penokean Penokean Orogen, Orogen, Klasner, J. S. and Northern Michigan Michigan and and Wisconsin Wisconsin [abstract]: [abstract]: Abstracts with Programs, North-Central North-Central Section Section of of the Geological GeologicalSociety Society of of America, America, v. v. 26, 26, no. 5, paper paper 12069, 12069, p. 23. the p. 23. Klasner, J. S., LaBerge, the Eastern EasternGogebic GogebicRange, Range, Kiasner, LaBerge, G. G. L., L., and and Cannon, W. F., F., in press, Geologic Map of the Northern Northern Michigan: Michigan: U. U.S.S.Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations Map. LaBerge, G. L., L., Cannon, Cannon, W. W. F., F., and and Klasner, J.J. S., S., 1995, 1995,New Newobservations observationson onthe the geology geology of of the the Western Gogebic Iron Range [abstract]: 41st 41st Annual Annual Institute Institute on on Lake Superior Superior Geology, Geology, Marathon, Marathon, Ontario, Gogeb'ic v.41, v. 41, part part1,1,p.p.33-34. 33-34. LaBerge, C. L., and Klasner, LaBerge, G. L., Klasner, J.J. S., 1994, 1994, Tectonic Early Proterozoic Proterozoic Tectonic implications implications of of the Early lithostratigraphy on on the theEastern EasternGogebic Gogebic Range, Range, Northern Northern Michigan Michigan [abstract]: [abstract]: 40th Annual Annual Institute Instituteon on Lake LakeSuperior SuperiorGeology, Geology,Houghton, Houghton,Michigan, Michigan,v. v.40, 40, part part 1,1, p. 27 27 -- 28. 28. W., 1992, 1992, Archean Gogebic LaBerge, LaBerge, G. G. L. L. and and Ojakangas, R. W., Archean and and Early Early Proterozoic Geology Geology of of the Gogebic District, Northern Michigan and Wisconsin: District, Northern Wisconsin: 38th 38th Annual Annual Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology, Hurley, Wisconsin, v. v.38, 38, part part 2, 2, p. p. 11-40. - 40. Hurley, Ojakangas, W., 1983, 1983, Tidal Tidal deposits deposits in in the the Early Early Proterozoic Proterozoic basin of the the Lake Lake Superior Superior region region -- the the qakangas, R.R.W., Palms and Pokegama Formations: Formations: Evidence Evidence of sub-tidal deposition of the Superior-type banded in Maderis, Maderis, L. L. G., G., (ed), (ed.), Early Early Proterozoic Proterozoic Geology Geology of the the Great GreatLakes LakesRegion: Region: iron formation, formation, in Geological Society 56. Geological Society of America America Memoir Memoir 160, 160, p. 49 -- 56. 108 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1996 Description An account of the resource Institute on Lake Superior Geology. Cable, Wisconsin. May 15-19, 1996. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1996 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/3993ef81ee739d90f8703b1f07d9f6f0.pdf 08b32baa603f79ec4677898139749c26 PDF Text Text 43rd 43rd Annual INSTITUTE ON ON INSTITUTE LAKE SUPERIOR GEOLOGY GEOLOGY LAKE Sudbury, Ontario Ontario May 66-11, 1997 - 11,1997 and Proceedings Volume: Volume: Program Program and Abstracts Abstracts Volume 43, Part 11 Volume 43, Part �Institute on Lake Superior Geology 43rd 43rd Annual Annual Meeting Meeting May61997 May 6 -11, 11,1997 Sudbury, Ontario, Ontario, Canada Canada Sponsored Sponsoredby: by: Ministry Ministry of Northern Northern Development Development and and Mines Mines Ontario Geological Geological Survey Survey Resident Geologist's Geologists Office, Office,Sudbury Sudbury Proceedings Proceedings Volume Volume 43 43 Part I1--- Program Programand and Abstracts Abstracts Editors: Editors: Ron Ron Sage, Ontario Ontario Geological GeologicalSurvey Survey Wilf Geologists Office Wilf Meyer, Meyer, Resident Resident Geologist's Office �Contents Contents Patti Part I Program and Abstracts Institutes Institutes on on Lake LakeSuperior Superior Geology Geology to to 1997 1997..................................................i Constitution of the Constitution the (nstitute Institute on Lake Superior Geology..................................iiii ... iii By-Laws of the Institute Institute on on Lake Lake Superior Superior Geology Geology.......................................111 Proceedings Volumes and Field Trip Guidebooks Guidebooks ...........................iv Index of Proceedings Award Guidelines Guidelines for for Sam Sam Goldich Goldich Medal Medal.......................:.............................ix XI Board of Directors Directors.......................................................................................... xi Committees .......................................................................................... xi Local Committees xi .. Xii1 Student Paper Paper Committee Committee............................................................................ xi Session Session Chairs Chairs...................................... .. ...................................................... xii XII ; .. XII Goldich Goldich Medal Medal Committee Committee....................................................;.......................xii ... xiii Goldich Medal 1997 Goldich Medal Recipient Recipient.....................................................................xi11 xiii Goldich Medalists Past Goldich Medalists................................................................................ xm 0.. Banquet Speaker Speaker......................................................................................... ... Xlii xi11 1997 Goldich Medal 1997 Goldich Medal Recipient Recipient Citation Citation........................................................xv .. ... Report of the Chair Chair of the 42nd Annual Institute institute....:...................................xviii xvm Student Student Travel Travel Award Award.................................................................................xvii xvii xxi Calendar of Calendar of Events Events and and Program Program.................................................................xxi 1 Abstracts Abstracts.. ....................................................................................................... 1 �Institutes Institutes on Lake Lake Superior Geology Institute Institute Number Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Date Date 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Place Place Minneapolis, Minneapolis, Minnesota Minnesota Houghton, Houghton, Michigan Michigan East East Lansing, Lansing, Michigan Michigan Duluth, Minnesota Duluth. Minnesota Minneapolis. Minnesota Minneapolis, Minnesota Madison, Wisconsin Wsconsin Port Arthur, Ontario Port Ontario Houghton, Houghton,Michigan Michigan Duluth, Duluth, Minnesota Minnesota lshpeming, Michigan Ishperning, Michigan Paul, Minnesota St. Paul, Minnesota Sault Sault Ste. Ste. Marie, Marie, Michigan Michigan East East Lansing, Lansing, Michigan Michigan Superior, Wisconsin Superior, Wisconsin Oshkosh, Oshkosh, Wisconsin Wisconsin Thunder Bay, Thunder Bay, Ontario Duluth, Duluth, Minnesota Minnesota Houghton, Michigan Houghton, Michigan Madison, Wisconsin Sault Sault Ste. Ste. Made, Marie, Ontario Ontario Marquette, Michigan Marquette, Michigan St. Paul, Paul, Minnesota Minnesota Thunder Bay, Thunder Bay, Ontario Ontario Milwaukee, Milwaukee,Wisconsin Wisconsin Duluth, Duluth, Minnesota Minnesota Eau Eau Claire, Claire, Wisconsin Wisconsin East East Lansing, Lansing, Michigan Michigan International InternationalFalls, Falls,Michigan Michigan Houghton, Michigan Houghton, Michigan Wausau, Wisconsin Wsconsin Kenora, Ontario Kenora, Ontario Wisconsin Rapids, Wsconsin Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Marquette,Michigan Michigan Duluth, Minnesota Duluth, Minnesota Thunder Bay, Thunder Bay, Ontario Ontario Eau Eau Claire, Claire, Wisconsin Wisconsin Hurley, Hurley, Wisconsin Wsconsin Eveleth, Eveleth, Minnesota Minnesota Houghton, Houghton, Michigan Michigan Marathon, Ontario Ontario Cable, Cable,Wisconsin Wisconsin Sudbury, Ontario Ontario Chairman Chairman C.E. Dutton Dutton C.E. A.K. Snelgrove Sneigrove A.K. B.T. Sandefur Sandefur R.W. Marsden Marsden G.M. C. Craddock G.M. Schwartz & C. E.N. Cameron E.N. Cameron E.G. Pye E.G. Pye AX. A.K. Snelgrove Snelgrove Lepp H. Lepp A.T. A.T. Broderick Broderick P1<. Sirns Sims & & R.K. R.K. Hogberg Hogberg P.K. R.W. White White W.J. W.J. Hinze Hinze AR. A B. Dickas Dickas LaBerge G.L. LaBerge & E. E. Mercy Mercy Bartley & M.W. Bartley D.M. Davidson Davidson J.. Kalliokoski J Kalliokoski M.E. Ostrom Ottrorn M.E. P.E. Giblin Giblin J.D. J.D. Hughes Hughes M. Walton Walton M.M. M.M. Kehlenbeck Kehlenbeck G. Mursky Mursky D.M. Davidson Davidson P.E. P.E. Meyers Meyers W.C. W.C. Cambray Carnbray D.L. Southwick Southwick T.J. Bornhorst Bornhorst T.J. G.L. LaBerge LaBerge G.L. C.E. C.E. Blackburn Blackburn J.K. J.K. Greenberg Greenberg E.D. E.D. Frey & R.P. R.P. Sage LS. Klasner J.S. Klasner J.C. Green Green M.M. Kehlenbeck Kehlenbeck M.M. Meyers P.E. Meyers A.B. Dickas Dickas A.B. D.L. D.L. Southwick Southwick T.J. Bornhorst T.J. Bornhorst M.C. Srnyk Smyk M.C. L.G. Woodruff L.G. R.P. Sage Meyer R.P. Sage & W. Meyer �______________ Constitution of the Institute on on Lake Lake Superior Superior Geology Geology Constitutjon Article!I Article Name &gy+ Geology'. The name on Lake The nameof of the theorganization organizationshall shallbe bethe the"Institute "InsMute on Lake Superior Geologr. Article II Artidell Obieclives Objectives thii organization organization are: The objectives objectivesof of this A. To Toprovide provideaameans meanswhereby wherebygeologists geologistsin in the Great Great Lakes Lakes region region may may exchange exchangeideas ideasand and scientific data. scientitic B. To To promote promotebetter betterunderstanding understandingof ofthe the geology geology of of the the Lake Lake Superior Superiorregion. region. C. To trips. Toplan planand andconduct conductgeological geologicalfield fieldtrips. Article Ill Article Ill Status No to the the benefil benefit of of any any member member or No part pafi of the income income of of the the organization organization shall insure to or individual. in&idual. In dissolution the assets of the organization shall shall be distiibuted distributed to In the event event of diiltAion (some free organization). organuation). (some tax free ifo avoid should be be not only only "saen~c'~or "scientific" or (To avoidFederal Federaland andState Stateincome incometaxes, taxes, the organization should "educational", but "educational", but also also "non-profit".) "non-proiit".) Minn. Stat. Anno. Anno. 290.91, 290.91, SUM. subd. 4 Mnn. Minn. Stat. Anno. 290.05(9) 290.05(9) 1954 Internal 1954 InternalRevenue RevenueCode Codes.501 s.501(c)(3) (c)(3) Article IV Article IV Membership Membership The the Board of of Directors. Any The membership membershipof of the the organization organuation shall shall consist con& of the Anygeologist geologist interested thai! be to vote at at the the annual annual meetings. interested shall bepermitted perm~ed to attend attend and and participate participate in and vote meetings. Article V ArticleV Meetinas Meetings The organization shall meet once a year, year, preferably preferablyduring duringthe themonth monthof ofApril. April. The The place place and and organizationshall the Board Board of Directors. Directors. will be be designated designated by the exact date of each each meeting meetingwill Article VI A WeW Directors Directors Chairperson, Secretary-Treasurer, Secretary-Treasurer, and and the last three The Board Board of Directors Directors shall shall consist cons.& of the Chairpemon, past Chairpersons; Chairpersons; but time consist of of fewer than than five board should should at any time five persons, persons, by by past but ifif the board reason of unwillingness the above above persons persons to to serve serve as as directors, directors, the vacancies reason unwillingnessor or inability inabilii of any of the on so as as to to bring bring the the membership membership of the board on the board board may may be be filled filled by by the annual annual meeting so board up up to five fwe members. members. Article Article Vii Wl Officers The officers and Secretaiy-Treasurer. Secretary-Treasurer. thii organization organization shall be a Chairperson and The officers of of this beelected electedeach eachyear yearby by the the Board Board of of Directors, Directors, who who shall shall give g ~ due due e A. The TheChairperson Chairpetsonshall shallbe consideration the wishes of any group that may be promoting promoting the next annual meeting. consideration to the nexl annual meeting. His/her will terminate terminate at at the the close close of of the the annual annual meeting meeting over H i e r term of office office as Chairperson Chairperson will which successor shall shall have have been been appointed. appointed. He/she which he/she helshe presides presides or when the successor Helshewill will then then serve serve for for aa period periodof of three three years years as as aa member memberof of the the Board Boardof ofDirectors. Directors. B. The be TheSecretary-Treasurer Secretary-Treasurershall shallbe beelected elected at the annual meeting. The The term termof of office office shall shallbe two years or until the successor shall have been appointed. two years or until the successor shall have been appointed. Article Wl Vii Article Amendments Amendmenls This majority voteof ofthose thosepeffions personswho who are are personally personally present present This constitution constitution may be amended by a majotityvote participating in, and at, participating and voting at any annual annual meeting meeting of of the organization. organization. �By-Law By-LawII Duties Duties of the Officers Officers and and Directors Directors A. ItItshall shallbe bethe theduty duly of of the the Annual Annual Chairman Chairmanto: 1. 1. Preside Presideat atthe the annual annualmeeting. meeting. Aqpointall allcommittees w m m ~ e eneeded needed s forthe theorganization organizationof the annual annual meeting. meeting. 2. Appoint for 3. Assume the annual meeting meeting Assumecomplete completeresponsibility responsibiliifor for the the organization organization and financing of the over overwhich which he/she helshepresides. presides. B. B. ItIt shall shall be be the the duty duty of of the the Secretary-Treasurer Secretaw-Treasurerto: to: 1. Keep Keepaccurate accurateattendance attendancerecords recordsof ofall allannual annualmeetings meetings 2. 2. Keep Keepaccurate accuraterecords recordsof ofall allmeetings meetingsof, of, and andcorrespondence wrrespondencebetween, between, the the Board Board of of Directors. Directors. 3. Hold Holdall allfunds fundsthat thatmay mayaccrue accrueas asprofits protitsfrom *om annual annualmeetings meetingsor or field field hips tripsand and to to make make asrequired. required. these funds funds available available for forthe organizationand and operation operation of of future Mure meetings meetingsas these the organization C. annual meetings C. ItIt shall shall be be the the duty duty of of the Board Board of of Directors Directorsto plan plan locations locations of annual meetingsand and to to advise adhe on on the the organization organizationand andfinancing financingof ofall allmeetings. meetings. By-Law By-LawIII1 Duties Dutiesand andExpenses menses 1. There I. Thereshall shallbe beno noregular regularmembership membershipdues. dues. 2. 2.Registration Registrationfees feesfor forthe theannual annualmeetings meetingsshall shallbe bedetermined determinedby bythe theChairperson Chairpersoninin consultation consultationwith with the the Board Boardof of Directors. Directors. ItIt is is strongly recommended that these thesebe bekept keptto toaa recommended that minimum minimumto to encourage encourageattendance attendanceof ofgraduate graduatestudents. students. By-Law Rulesof of Order Order By-LawIllIll Rules The thisorganization organizationininall allcases casesininwhich which The rules mlescontained containedin in Roberts RobeesRules RulesofofOrder Ordershall shallgovem governthis they they are are applicable. applicable. By-Law IV Amendments Amendments By-Law IV These by-lawsmay maybe beamended amendedby by aa majority majorityvote vote of of those those persons persons who are are personally personallypresent present Theseby-laws at, at, participating paftiapatingin, in, and andvoting voting at at any any annual annualmeeting meetingof ofthe theorganization; organuation;provided providedthat thatsuch such modifications modificationsshall shallnot notconflict conflictwtih wtihthe theconstitution constitutionas aspresently preseniyadopted adoptedor orsubsequently subswuentlv amended. amended. Ill iii �Index of Proceedings Volumes and Field Field Trip Guidebooks Guidebooks of the Institute on Lake Superior Geology the Institute on Lake Superior Geology 1955 1955 -- 1997 1997 compiled by Compiled byMark MarkJissa, Jim, Secretary-Treasurer, Secretary-Treasurer, ILSO ILSG *Denotes abstracts volumes and guidebooks which can be ordered from from the the Secretary-Treasurer. Secretary-Treasurer. .Denotes abstracts and guidebooks UniversityAvenue, Avenue,SStt Paul, Paul, MN, MN,55114-1057, 55114-1057,Phone: Phone:6124274539, 612-627-4539,fax: fax:6124274778. 612-6274778, e-mail: 2642 Un~esity jirsaOOl@?maroon.tc.umn.edu jirsa001@maroon.tc.umn.edu complete list A complete liicontaining containingsuch such information informationas as author, author, editor, ed*or, chairperson, chairpemn, and andsponsoring sponsoringorganization organizationisis maintained Van Pelt maintained by Ms. Theresa Sanderson Sandeson Spence, archMst a r c h i d at at the J. Robert Robert Van PeltUbrary, Library, Michigan Michigan Technological Ml 49931 (906487-2505). (906-487-2505). Photocopies Photocopiesof of back backvolumes volumescan canbe beordered ordered Technolcgical University, Unwersity, Houghton, MI from Sanderson Spence some guidebooks were publiihed published separately separately by the the from Ms. Sanderson Spence at at the prevailing prevailingcopy rate. Some Mnnesota Survey MinnesotaGeological GeologicalSurvey Survey(MGS), (MGS), and and Wisconsin Wsconsin Geological Geolcgical and Natural Natural History Hiiory S u ~ e (WGNHS), y as indicated indicated below, below; however, however, most most are are no no longer longeravailable. available. (Each is a separate separate bound bound document) (Each italicized italicizeditem item is documenq Volume Location . Volume Year Location .--. . -- -.. 1 1955 Minneapolis, Minnesota 1955 Minnesota Program Program andAbsfracts andAbstracts (contains (contains no no record record of of field fieldtrips) trips) 2 1956 Houghton, Michigan 1956 Houghton, Michigan Program Abstracts Program and andAbstracts Geological GeologicalExploration ExplorationOnferred (inferred to to be be aa field field guide) guide) 3 1957 1957 East Lansing, Michigan Michigan Program and Abstracts h g r a m andAbshds 4 1958 Duluth, Minnesota 1958 Minnesota Program and and Abstracts Pfvgram 5 1959 Minneapolis, 1959 Minneapolii, Minnesota Minnesota Program and P -m andAbstracts Abstmcts 6 1960 Wisconsin 1960 Madison, W ~consin Program and Program andAbstracts AbsWs 7 1961 Port Arthur, Ontario Ontario 1961 Program and and Abstracts label reads reads 6th Program Abstracts (misprinted (misprinted label 6fh annual annualmeeting) 8 41962 962 Houghton, Michigan Michigan Program and and Abstracts Program Abstracts 9 1963 Duluth, 1963 Duluth, Minnesota Minnesota Program and Abstracts Program andAbstracts Field lfinera!y: Itineraty: Stratigraphy Strafigraphy of the Biwabik Iron m Fonnation Field of the Bwabik lmn ation 1964 10 Michigan 1964 lshpeming, Michigan Program andAbstracts Ptvgram andAbstrads Field Trip: Marquette imn-mining iron-mining d district and Republic Republic h trough Field Trip: Maque~e W and igh 11 1965 St. Paul, Minnesota 1965 Minnesota Program and and Abstracts Program Abstracts Field Trip Trip Guide Guidetto the St. St Cloud granite Idistrict Field o fhe Cloudgranite $&, central centralMinnesota Minnesota 12 1966 Sault Ste. Marie, Ontario Ontario 1966 Sauk Program and and Abstracts guides to: Program Abstractsincludes includesfield field guides to: 1. Regional Regional geology geology of I. of the Sault Sault Ste. Marie area 2. Geology Geologyand andmineral mtneraldeposits depositsof ofthe the Manitouwadge Manitouwadge Lake Lake area, Ontario 3. The Therelationship relationshipof ofmineralization mineralizationto to the the Precambrian Precambrianstratigraphy, stratigraphy, Blind River Rier area, Ontario 4. Sudbury Sudburynickel nickelirruptive irmptive tour, tour, Ontario Ontario 13 1967 3967 East Lansing, Michigan Michigan iv �Program tracts Programand andAbs Abstracts Field Field Trip: Trip: Grenville Grenville Province Province of of southeastern southeasternOntario, Bancroft-Madoc Bancrofl-Madoc area area Volume Location Volume Year Location 14 1968 Superior, Wisconsin Wisconsin 14 1968 Superior, Technical Sessions and and Abstracts Abstracts Technical Guide for Field complex F ~ e lTrip Trip d in in the fhe Duluth DU U IUI wm@x near nearEly, EM, Minnesota Minnesota Guide Wisconsin 15 1969 15 1969 Oshkosh, Wisconsin Technical Abstracts Technical Sessions Sessions and and Abstracts Wsconsin volcanic volcanic belt belt Guidebook: Central Central Wisconsin 16 1970 Thunder 16 1970 ThunderBay, Bay,Ontario Ontario Technical Sessions, Abstracts Abstracts and andField FieldGuides Guides Field Technical Sessions, Field Trips: A. A Proterozoic Proterozoicformations formations in in the the Thunder ThunderBay Bayarea area Sturgeon Riier River metavolcanic-metasedimentary metavolcanic-metasedimentary formations in the the Beardmore-Geraldton Beardmore-Geraldton area area B. Sturgeon C. The Port Coldwell alkalic alkalic.complex Port Coldwell complex Geology of the Atikokan area area (title not D. Geology not exact) Duluth, Minnesota 17 1971 17 1971 Minnesota Technical Sessions, Sessions, Abstracts Abstracts and and Field Field Guides Guides Field Technical FieldTrips: Trips: Group A. North Shore Volcanic Group B. Precambrian Precambrian rocks Cook County exposed along the the Gunflint Gunflint Trail Trail rocks of northwestern northwestern Cook County as e x w e d along C. Mesabi Mesabi Range Range magnetite magnelite taconite taconite 0. metavolcanic-metasedimentarybelt, belt, northeastern northeasternMinnesota Minnesota D. Geology Geologyof of the the Vermilion Vermilion metavolcanic-metasedimentary Houghton, 18 1972 18 1972 Houghton, Michigan Michigan Part L Technical Technical Sessions -Agenda - Agenda and and Abstracts (desmies (describes trips A-D) Partl. hips A-D) Field Trips: Field Trips. A. Penokean and PenokeanOrogeny Orogenyin in the the central centraland andwestern westernGogebic Gogebicregion, region,Wisconsin W~consin andMichigan Michigan B. Guide to to Penokean deformation deformation style style and and regional metamorphiim metamorphism at the the westem western Maquette Marquette Range, Michigan Michigan Madison, Wisconsin 19 19 1973 Abstracts* and Abstracts* Technical Program Program and Technical Field Trip: to the the geology geology and and mineral mineral deposits deposits of of the the central central part part of of Jackson Jacksoli County and part Field Trip: Guidebook to County and part County,Wisconsin W w n s i n (WGNHS) of Clark County, Field Trip: to the the Precambrian Precambrian geology geology of northeastern and and north-central north-central W Wisconsin Field Trip: Guidebook to mnsin Field Trip: to the the upper upper Miissippi MississippiValley Valleybase-metal base-metald'itrict district(WGNHS (WGNHSInformation Informationcircular circular No. No. Field Trip: Guidebook to 16) 16) Bibliography Lake Superior Superior Region Region ~ ! b l i o ~ r of of a Current ~Cutrent h ~ Research Researchin inThe tbe Lake Sault Ste. Marie, Ontario 20 1974 1974 SauR Marie, Ontario Field Middle I: Middle Keweenawan Keweenawan rocks rocks of of the the Batchawana-Mamainse Batchawana-MamainsePoint Pointarea area FieldTrip Trip 1: Field 2: unknown unknown FieldTrip Trip 2: Field Trip 3 3:: Precambrian Precambrian igneous rocks of the north shore of Lake Huron region Field Field Trip sedimentation of 4: Stratigraphy Stratigraphy and sedimentation of the Huronian Huronian Supergroup Supergroup Field Trip 4: Field Trip 5 5: belt. : The The Michipicoten Michipkoten greenstone belt Field Bibliography of Research in in fhe the Lake Lake Superior Superior Region Region (First Supplement) (first Supplement.) Bibliography of Current Cutrent Research Marquette, Michigan 21 1975 21 1975 Michigan Proceedings Proceedings Includes the following following field trip trip guides guides and and aa supplement supplement by Burton Burton Boyum Boyum containing containing aa mlour colour map map of the the Includes Marquette Marquette Mineral Mineral District District 1.. Glacial geology geology (trip cancelled, cancelled, no I Glacial no guidebook) guidebook) 2. Greenstone Greenstone 3. The The Jacobsville Jacobville Sandstone: Sandstone: Evidence Evfdencefor for aa Lower-Middle Lower-Miidle Keweenawan Keweenawanage age 4. Marquette Marquette Iron Iron Range Range 5 and and 6. The The Empire EmpireMine Mine and and Mill, Palmer, Palmer, Michigan Michiian Minnesota 22 1976 22 1976 St. Paul, Minnesota - V �Location Volume Year Location Proceedings Proceedngs Includes abstracts abstracts and Includes and guide guide to Field Field Trip B Field Trip A: A: Minnesota R River Valley field conference conference (no formal formal guidebook Field i ~ eValley r field guidebookprinted) printed) Field Trip B: Engineering Engineering and and Pleistocene Pleistocenegeology geologyin inthe the Twin TwinCities Ciies area area Thunder 1977 Thunder Bay, Bay, Ontario Ontario Proceedings Proceedings Field Trip Geology of the Coldwell alkaline Complex Trip A Geology Field Field Trip Trip B Proterozoic Proterozoicrocks rocks of of the the Thunder Thunder Bay Bay area, area, northwestern northwestern Ontario Ontario ("Proterozoic Trip") Trip") Field Field Trip South Sturgeon Trip C C Archean Archean metatlogeny rnetallogenyand and stratigraphy stratigraphy of of the South Sturgeon Lake Lake area area ("Mattabi ("Mattabi Trip") Trip? Field Wisconsin 1978 24 1978 Milwaukee, Wisconsin Abstracts Abstracts and andProceedings Procee&ngs Field zinc-lead district Trip IISouthwestern Southwestern Wisconsin Wiconsin zinelead d i i c t (WGNHS Field Field Trip Guide Guide Book Book Number Number1) I) FieldTrip Reid processing equipment manufacturers manufacturers in FieldTrip TripPI1Mineral Mineral extraction extraction and pro-hg in the Greater Greater Milwaukee Milwaukeearea area (no guidebook) guidebook) Field FieldTrip Trip lii IllPrecambrian Precambrianrhyolite rhyoMeand andgranite graniteinliers inliersin in south-central south-central Wisconsin Wiconsin (WHNHS (WHNHSField FieldTrip TripGuide Guide Book Number Number 2) Duluth, 25 1979 25 1979 Duluth, Minnesota Minnesota Technical Sessions Sessions and and Abstracts Abstracts Joint meeting meeting with North-Central Section Section GSA Technical Field Trip Trip Guidebooks: Guidebooks: some were published separately as MGS Guidebook referenced below, the the some were publiihed separately Guidebook Series referenced remainder are apparently unavailable. A in GSA GSA proceedings: proceedings: remainder A total total of of eight eight trips were listed in Precambrian volcanic and plutonic rocks 1. Middle Precambrian rocks of northern northern Wisconsin 2. Stratigraphy, Stratigraphy, structure structure and and mineral mineral resources resources of of east-central east-central Minnesota Mmnesota (MGS (MGS Field FieldTrip Trip Guidebook Guidebook series no. 9) no. 9) 3. Quaternav Quaternary geology geology of the Duluth Duluth area area Geology of the Mesabi 4. Geology Mesabi Iron Range Geologic history western Lake Lake Superior region 5. Geologic hiiory and engineering engineering geology of the western 6. Cambrian Cambrian and paleontology of southeastern Minnesota Minnesota and Ordovician Ordoviaan stratigraphy and paleontologyof (tipper Precambrian) v1GS Field 7. Keweenawan (Upper PrecambM) North NorthShore Shore Volcanic Volcanic Group, Minnesota (MGS Field Trip Tfip no 11) Guidebook no. 11) 8. Archean Archean volcanism volcanism and sedimentation of the w&em western Vermiliin Vermilion D District, northeastern Minnesota 8. and sedimentation k k t , northeastarn Mhnesota (MGS Guidebook Series Guidebook Series no. 10) 10) Eau Claire, Wisconsin Wisconsin 1980 1980 26 Proceedings Abstracts Proceedingsand andAbshcts Field Trip II Precambrian Precambriangeology geologyof ofthe the Chippewa Chippewa Valley, Wisconsin. Wsconsin Field Trip Field Trip 22 Precambrian Precambriantectonic tectonic history hiitow of the Black Black River Riier Valley Field Trip Field Field Trip Trip 33 Petrology, Petrology, geochemistly, geochemisby, and and contact contactrelations relations of of the the Wausau Wausau and andStettin Stettinsyenite syenite plutons, plutons, Central Wisconsin Central Wisconsin Reid Trip Trip44 Precambrian Precambriangeology geologyand andtectonics tectonicsof ofMarathon MarathonCounty, County, Wisconsin W~consin Field 1981 27 1981 East Lansing, Michigan Michigan Abstracts Abstracts and andProceedings Pmeedngs Field Excursion Guide Thessalon, District Algoma, D i i c t of Ngoma, FieldExcursion Guide The TheHuronian Huronianrocks rocksbetween betweenSault Sault Ste. Marie and Thesalon, Ontario Ontario 1982 28 International Falls; 1982 International Fans, Minnesota Minnesota Proceedings: Field Trips TripsQn (in one volume) h m d i n g s : Abstracts Abshcfs and andField Field Trip II Mineral Mineral deposits of the Fort Fott Frances-Mine FrancesMine Centre Centre area, Ontario Ontario Archean geology of the International International Falls-Kabetogama area, Minnesota III Archean Field Trip 1 29 1983 1983 Houghton, Michigan Volume I I::Abstracts Ropes gold mine geological setting Abstractsand andField FieldTrip Trip— Ropes mine and and its its geological setting Volume Volufne II: 11: Field guide to the the geology geology of of the the Keweenaw KeweenawPeninsula Peninsula 30 1984 Wausau, Wisconsin Wisconsin 1984 Wausau, Abstracts Abstracts 23 23 - vi �Volume Location Volume Year Location I Guide Guide to ofof thethe Early Proterozoic rocksrocks in northeastern Wisconsin Field Trip Trip 1 tothe thegeology geology Early Proterozoic in northeastern Wisconsin Field Field Trip tectonostratigraphic terraines of theof southern Superior region Trip22Early EarlyProterozoic Proterozoic tectonostratigraphic terraines the southern Lake Lake Superior region Field Field Trip Field Trip 3 3 The Wausau Wausau Syenite Complex 1985 31 31 1985 Kenora, Ontario Absfracts Abstracts Field Trip Field Trip Guidebook Guidebook The Cameron Cameron Lake 1. The Lake Deposit Deposit 2. Geologic the Lake Lake of of the the Woods Woods area Geologic setting setting and and style of gold mineralization in the 3. Geological Geologicalrelationships relationshipsin in the the vicinity of the Wabigoon-Winnipeg River River subprovincial subprovincialinterface interfaceininthe the Kenora Kenora area area 4. A volcanic volcanic fades 4. fades interpretation interpretationof of the the Berry BerryRiver River Formation Formation Granitoid related 5. Granitoid relatedmineralization mineralizationin in the Dryden Dryden area area 32 1986 32 1986 Wisconsin Rapids, Wisconsin Abs tracts AbsfnactsField Trip! The Field Trip I TheWolf WolfRiver RiverBatholith Batholithand andBaraboo Baraboointerval interval (published (published as as Field Field Trip Trip Guide Guide Book Book Number Number 12, 1 2,WGNHS) Il Penokean Penokean deformation and metamorphism metamorphism in central Wisconsin: volcanic volcanic rocks Field Trip Trip I1 rocks and and gneisses gneisses un-numbered Field Trip Guide Book Book of of the the WGNHS) WGNHS) (published as un-numbered . were adopted adopted to to conform conform to to ISSN standards standards in 1987) (compiler note: new new reference reference designations were 33 1987 Wawa, Ontario 1987 Ontario Pan' 1 1: Abstracts : 'Abstracts Part Part 2: *Geology Part2: "Geology of of the the Wawa Wawa area area and and gold gold mineralization mineralization Pail 3: 3: Geology 'Geology and andstratigraphy stratigraphyof ofthe theMichipicoten Michipicoteniron-Formation Iron-Formation Part *Glogy ofofthe Part 44: : 'Geology theHemlo HemloDeposit Deposit PantS: 5: TThe h eKapuskasing KapuskasingUplift UpliftArctiean Archeangreenstones greenstones and and granulites Part 1988 1988 Marquette, Michigan Michigan Pail I: Abstracts Parti: 'Abstracts Pant2:Field FieldTrip TripGuidebook Guidebook Part 1. An introduction introduction to to Archean Archean geology geology and and precious precious metal metal mineralization mineralization of of the the Marquette Marquette Greenstone Belt, Michigan Michigan 2. Marquette geology Marquette mineral mineraldistrict district of of Michigan, Michigan, mining mining history history and geology A structural traverse across aa part part of ofthe the Penokean Penokean orogen orogenillustrating illustrating Early Early Proterozoic Proterozoic overthrusting overthrusting in in 3. Astructural northern Michigan northern Michigan Duluth, 1989 1989 Duluth, Minnesota Minnesota Part : Abstracts Abstracts Part I:1 Part : Field Guidebook Pan' 22: Field Trin Dip Guidebook North Shore 1. ~o-rth Shore rhyolites, rhyolites, Minnesota Minnesota 2. Penokean PenokeanStructural StructuralTerranes Terranesinineast-central east-centralMinnesota Minnesota Mellen Complex. 3. Mellen Complex, Wisconsin Wisconsin 4. Archean Archean gold goldoccurrences occurrencesand andtheir their structural structuralsettings settings(Virginia (Virginia Horn) Horn) Thunder 1990 1990 Thunder Bay, Bay, Ontario Part I: tAbstracts Abstracts Part2 Part 2:Field FieldTrip TripGuidebook Guidebook and granitoid granitoid rocks rocks of of Lac des lies lies area 1. Mafic intrusions, PGE mineralization, and area 2. Geology Geology of of the the Shebandowan Shebandowan and and Quetico QueticoArchean Archean subprovinces subprovinces Granitoid-related mineral Lake Superior Superior region 3. Granitoid-related mineral deposits deposits in the western Lake region 4. Base Base metal metalmineralization mineralizationin in the the Shebandowan ShebandowanGreenstone GreenstoneBelt Belt 1991 Eau Wisconsin 1991 Eau Claire, Wisconsin Part *Abstracts Part I:1:*Abstracts Part Part 2: 2: *Fieid 'Field Trip Trip Guidebook Guidebook Mountain Shear post Penokean Penokean discrete discrete ductile ductile deformation deformation zone 1. Mountain Shear Zone Zone — - a a post zone 2. Features Featuresand and significance of of the the Precambrian-Cambrian Precambrian-Cambriancontact contactin in western westernWisconsin Wsconsin 3. Proterozoic Wisconsin Proterozoic volcanogenic volcanogenic massive massive sulfide sulfide deposits of NW NW Wisconsin - 34 35 36 37 . VII vii �Location Year Volume Year Location Volume Hurley, 38 1992 Hurley, Wisconsin Wisconsin 1992 38 Pad 1:*Program "Program and andAbstracts Abstracts Part1: Part 2:'Field Trip TripGuidebook Guidebook Pad2:Field 1. Archean and andEarly EarlyProterozoic Proterozoicgeology geology of of the the Gogebic GogebicDistrict District 1. Archean 2. Evolution Evolutionof ofthe the Keweenawan Keweenawansedimentary sedimentarysequence sequence 2. 3. 3. Geology Geologyof ofthe theKeweenawan KeweenawanSupergroup Supergroupat atPorcupine PorcupineMountains Mountains 4. late Archean paleosuture paleosuture 4. Geology Geologyof of the the Great GreatLakes LakesTectonic Tectonic Zone - Marquette area - a late Eveleth, 1993 39 1993 Eveleth, Minnesota Minnesota 39 Part 1: 1:'Program andAbstracts Abstracts Pan' Program and Part2: 2: Field 'Field Trip TripGuidebook Guidebook Pad 1. 1. Geology Geologyand andtaconite taconitemines minesof ofthe theMesabi Mesabirange range 2. 2. DNR DNRCore CoreUbrary LibraryBiwabik 'B'wabikIron IronFormation. Formation,Partridge PartridgeRiver Riverand andSouth SouthKawishiwi Kawishiiintrusions, intrusions,Regolith Regolithinin northernMinnesota) Minnesota) Rotasoniccores cores--northern Rotasonic 3. 3. Geology Geologyof ofArchean Archeangreenstone-granite greenstone-granite terrane: terrane: Cook-Side Cook-SideLake Lakearea area 4. Duluth DuluthComplex Complexat atDuluth Duluth Houghton, 40 1994 Houghton, Michigan Michigan 40 1994 Pad *Program and Part1: 1:"Program andAbstracts Abstracts Pad 2: *Self..guided geological Keweenaw Peninsula, Michigan (available from Part2:'Self-guided geological field trip to the Keweenaw from Dr. Dr. T.J. T.J. Bornhorst, 402 Emerald Street, Street,Houghton, Houghton,MI Ml 49931-1413 49931-1413 (906482-5507)) (906482-5507)) Part3: 3: Volcanic Volcanicgeology geologyof ofeastern easternIsle kle Royale, Royale, Michigan Michigan Pad Pad 4: Michigan "Michigankimberlites kimbetiiesand anddiamond diamondexploration explorationtechniques techniques Part4: Pad Part5: 5: Lessons 'Lessons from frommining miningcase casehistories: histories:West WestMenominee MenomineeRange, Range,Michigan Michigan Marathon, 1995 41 1995 Marathon, Ontario Ontario 41 Pad Part1: 1:*Program 'Program and andAbstracts Abstracts Pad Part2: 2: Field FieldTrip TripGuidebooks Guidebooks(some (some may mayalso also be beacquired acquiredfrom fromOntario OntarioGeological GeologicalSurvey, Survey,Ministry Ministryof of Northern 435 South NorthernDevelopment Developmentand andMines, Mines, Suite Suite 8002, B002.435 SouthJames JamesStreet, Street,Thunder ThunderBay, Bay,Ontario, Ontario, Canada Canada P7E P7E6E3 6E3 (807475-1331)). (807-475-1331)). 2a. Alkalic *Alkalicrocks rocksofofthe theMidconlinent MidcontinentRift Rift 2a. 2b. 2b.'Geology and andbase basemetal metaldeposits deposits of of the the Manitouwadge Manitouwadge Greenstone Greenstone belt belt 2c. 2c. Geology 'Geology ofofthe theSchreiber SchreiberGreenstone Greenstoneassemblage assemblageand andits itsgold goldand andbase basemetal metalmineralization mineralization 2 d Geology Geologyand and gold gold deposits deposits of of the Hemlo Hemloarea area 2d. 2e. 'Kimberlite, area *Kimberliie,base basemetal, metal,and andgold goldexploration exploration using using overburden, Wawa area Cable, Wisconsin 1996 42 1996 Cable, Wisconsin 42 Part1: 1:Program Programand andAbstracts Abstracts Pad Pad Part2: 2: Volcanogenic Volcanogenic Massive Massive Sullide Sulfide Deposits Deposits of Northern NorthernWisconsin: Wsconsin: A Commemorative CommemorativeVolume Volume (published (publishedin in conjunction conjunctionwith with Field Field Trip Trip 33 to to the the Flambeau FlambeauMine) Mine) Pad Part3: 3: Field FieldTrip Trip Guidebook Guidebook 1. Glacial Glacialgeology geologyof ofwestern westernWisconsin Wisconsin 1. 2. 2. Geology Geologyofofthe theMontreal MontrealRiver RiverMonocline: Monocline: A A traverse traverse through through 25 km km of of crust crust 4. 4. Early EarlytotoMiddle MiddleProterozoic Proterozoicgeology geologyof of the the Lake Lake Namekagon Namekagonregion region 5. Lake LakeNamekagon Namekagonand andPenokee PenokeeGap Gaparea, area, west west Gogebic Gogebic Range, Range, Wisconsin Wsconsin Sudbury, Ontario 43 1997 Ontario 43 1997 Pad 1: Program Parti: Programand andAbstracts Abstracts Pad2 Huronian Supergroup The Huronian Supergroupbetween betweenSault SaultSte. Ste.Marie Marieand andElliot ElliotLake Lake Part 2:The Pad 3: New Part3: NewDevelopments DevelopmentsininGrenville GrenvilleFront FrontGeology, Geology, Sudbury Sudbury Area, Ontario Ontario Pad 4: The TheSudbury SudburyStructure Structurewith with Emphasis Emphasis on on the the Whitewater Whitewater Group Group Part4: Pad 5: Magmatic Part5: MagmaticOre OreDeposits Depositsof ofthe the Sudbury Sudbury Igneous Igneous Complex Complex Part 6: 6: Alkalic Alkalicrocks rocksof ofthe theSudbury Sudbury Region Region Pad Pad Part?:7: Regreening Regreeningof of Sudbury Sudbury - Future Meeting Meeting Locations: Future 44 1998 ? 44 1998 ? 1999 45 1999 ? 45 VIII viii �Award Guidelines Award Guidelines Sam Goldich Sam Goldich Medal Medal Preamble Preamble The documented by by the the fact fact that that the 27th 27th The Institute Institute on on Lake Lake Superior Superior Geology Geology was born in or around 1955, as documented with those those aspects aspectsof of annual meeting meeting was was held held in in 1981. 1981. The TheInstitute's Institute's continuing continuing objectives objectives are are to to deal dealwith geology geology that that are are related relatedgeographically geographicallyto to Lake Lake Superior, to encourage encouragethe the discussion discussionof of subjects subjectsand and sponsoring sponsoring field field tips tripswhich whichwill willbring bringtogether togethergeologists geologistsfrom fromacademia, academia,government governmentsulveys, surveys,and andindustry, industry, and and to maintain maintain an an informal informalbut buteffective effective mode mode of of operation. During itsexistence existencethe the membership membershipof of the the Institute Institute(that (thatis, is, those those geologists geologistswho whoindicate indicatean an During the the course courseof ofits interest attending) has hasbecome become aware awarethat interest in the objectives objectives of the ILSG by attending) that certain certainof of their theircolleagues colleagueshave have made to the the understanding understanding of made particularly particularlynoteworthy noteworthyand and meritorious meritoriouscontributions to of Lake Lake Superior Superior geology geology and mineral mineral deposits. deposits. The was made to Sam Sam Goldich in in 1979 for for his many contributions contributions to the geology of of the the The first award award was made by by the the ILSG to region extending over some 50 years. region extending over some 50 years. Guidelines Award Guidelines The medal medal shall of Directors Directors to to a geologist geologist whose name 1) The shall be be awarded awarded annually annually by by the ILSG Board of name is substantial interest in, and and contribution contribution to, to, the the geology geology of the Lake associated with a substantial Lake Superior Superiorregion. region. 2) The the Nominating Nominating Committee. Committee. The The Board Board of of Directors Directorsshall shall appoint the The initial initial appointment appointment shall shall be be of three members, years, and and one for for one year. The member with the the members, one oneto to serve serve for for three three years, one for two years, memberwith briefest incumbency shall year, the the Board shall shall appoint briefest incumbency shall be be chairman. chairman. After the first year, appoint at at each each spring spring meeting meeting one new member member who will serve for three three years. years. In the third third year year this this member member shall shall be the the chairman. chairman. The The Committee membership membershipshould shouldreflect reflect main fields of interest geographic dbon ofofILSG thethe main fields of interest andand geographic distribution ILSG membership. membership. 3) By Committee shall shall make By November, November, the the Goldich GoldichMedal Medal Nominating Nominating Committee make its its recommendation recommendationto tothe theChairman Chairman of the Board Board of Directors inform the the Board of of the the nominee. Directorswho will then inform 4) The TheBoard Boardnormally normallywill willaccept acceptthe thenominee nomineeof of the the Committee, Committee, will will inform informthe the medallist medallistimmediately, immediately,and and will have meeting of the Institute. have the medal medalengraved engravedappropriately appropriately for presentation presentation at the next meeting recommended that set aside aside annually annuallyfrom from whatever whatever sources, sources, such such funds as will will be 5) that the the Institute Institute set 5) It is recommended required to support support the cosk of this award. required the continuing continuing costs Nomination Nomination Procedures Procedures 1) Nominations shall be taken at any any time lime by bythe theGoldich GoldichMedal MedalCommittee. Committee. Committee members members may themselves November 1. themselves nominate nominate candidates. The The deadline deadline for nominations nominations is November 1. supported by by appropriate appropriatedocumentation documentation such such as letters of 2) Nominations Nominations must must be be in in writing and supported recommendation, recommendation,lists listsof ofpublications, publications,c.v.'s, c.v.'s, and and evidence evidence on on contributions contributionsto to Lake LakeSuperior Superiorgeology geologyand andto to the Institute. Institute. 3) Nominations attendees but are open to anyone Nominations are are not notrestricted restrictedto to Institute Institute attendees anyone who who has hasworked workedon onand and contributed contributed to Lake LakeSuperior Superiorgeology. geology. ix �Selection Guidelines Selection Guidelines Nominees are Lake Superior 1) Nominees are to to be beevaluated evaluated on on the basis basis of their contributions to Lake Superiorgeology geology(sensu (sensulato) lato) including: importance of relevant a) importance relevantpublications publications b) promotion of natural natural resources promotion of of discovery discovery and utilization of natural history and environment c) contilbutions contributionsto to understanding understanding of the natural environmentof ofthe theregion region d) generation generation of new new ideas and concepts the training training and and education education of of geoscientists geoscientists and and the the public. public. e) contributions contributions to the - as demonstrated demonstrated by 2) Nominees Nomineesare are to to be beevaluated evaluatedon on their contributions contributionsto the Institute as by attendance attendance at at Institute meetings, presentation and service service on on Institute boards, committees, committees, and and field field Institute meetings, presentation of talks and posters, and trips. 3) The remain flexible The relative relativeweights weightsgiven given to each of the foregoing criteria must remain flexibleand andat atthe thediscretion discretionof of the the Committee members. Committee members. 4) There There are are several severalpoints pointsto to be be considered considered by the selection committee: balance of of medal medal recipients recipients from each a) an attempt attempt should should be be made made to maintain aa balance each of of the the three three estates, industry, academia, and and govemment. government. b) it must must be geoscientists are areat ataadisadvantage disadvantagein inthat that much much of their work is Is not not be noted noted that industry geoscientists published. published. one the the United UnitedStates, States,the theother otherCanada. Canada. This This is undoubtedly undoubtedly one of the the 5) Lake Lake Superior Superior has has two sides, one great strengths strengths and should should be be nurtured nurtured by equitable equitable recognition recognition of excellence excellence in Institutes' great in both both countries. x �Board Board of Directors Directors 1997 1997 Ronald Co-chainnan Ronald P. P. Sage, Co-chairman Wilt ned Meyer, Co-chairman Co-chairman Wilfried Ontario Ontario Geological GeologicalSurvey, Survey, Sudbury, Ontario Ontario 1996 1996 LaurelG.Woodruff Laurel G. Woodruff U.S. Geological Geological Survey, St. Paul, Paul, Minnesota Minnesota U.S. Survey, St. 1995 1995 Mark C. C. Smyk Ontario Geological Ontario GeologicalSurvey, Survey, Thunder Thunder Bay, Bay, Ontario Ontario 1994 1994 Theodore J. Bomhonst Bornhorst Michigan Technological Michigan TechnologicalUniversity, University, Houghton, Michigan Michigan Permanent Secretary-Treasurer Mark Jirsa Jirsa Mark Minnesota Geological Minnesota GeologicalSurvey Survey 2642 University 2642 UniversityAvenue Avenue St Paul, MN55114-1057 55114-1057 St. Paul.MN Committees Local Committees General Chair Ronald P. Sage Ronald Ontario Geological Geological Survey, Ontario Survey, Sudbury, Ontario Ontario Wilt ned Meyer Wilfried Geologists Program, Resident Geologist's Program,Sudbury, Sudbury, Ontario Ontario Program 'Committee Committee Program Ronald Ronald P. P. Sage Sage Geological Survey, Ontario Geological Survey, Sudbury, Sudbury, Ontario Wilfnied Meyer Wilfried Meyer Geologists Program, Resident Geologist's Program, Sudbury, Sudbury, Ontario Ontario Tracy Livingstone Resident Geologists Program, Resident Geologist's Program,Sudbury, Sudbury, Ontario Ontario Field Field Trip Trip Committee Committee P. Sagi Ronald P . Sage Geological Survey, Ontario Geological Survey, Sudbury, Sudbury, Ontario Ontario Wilfnied Wilfried Meyer Meyer Geologists Program, Resident Geologist's Program, Sudbury, Sudbury, Ontario Ontario Livingstone Tracy Livingstone Resident GeolgoisCs Geolgoist's Program, Resident Program, Sudbury, Sudbury, Ontario Ontario Secretary-Treasurer Secretary-Treasurer Tracy Livingstone Geologists Program, Resident Geologist's Program, Sudbury, Sudbury, Ontario xi �Student Paper Paper Committee Committee Kalliokoski Jorna Kalliokoski Technological University Professor Emeritus, Michigan Technological University Jim Miller Miller Senior Geologist, Geological Survey Geologist, Minnesota Minnesota Geological Darrell Long Long Department of Earth Earth Sciences, Sciences, Laurentian Laurentian University Session Chairs Chairs LaBerge Gene LaBerge of Wisconsin Wisconsin Oshkosh, Oshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin and and U. U.S. S. Geological GeologicalSurvey Survey University of Terrence Boerboom Boerboom Minnesota St. Paul, Paul, Minnesota Minnesota Minnesota Geological GeologicalSurvey, Survey, St. Mark Mark Smyk Ontario Ontario Geological GeologicalSurvey, Survey, Thunder ThunderBay, Bay, Ontario Ontario Jirsa Mark Jirsa Minnesota St. Paul, Paul, Minnesota Minnesota Minnesota Geological GeologicalSurvey, Survey, St. Gordon Gordon Medaris, Medaris, Jr. of Wisconsin-Madison, Wisconsin-Madison, Madison, Wisconsin Wisconsin University of Frank Luther Luther of Wisconsin-Whitewater, Wisconsin-Whitewater, Whiiewater, Whitewater, Wisconsin Wisconsin University of Theodore Bornhorst Michigan Michigan Technological TechnologicalUniversity, University, Houghton, Houghton,Michigan Michigan Phil Thurston Phil Thurston Ontario Ontario Geological GeologicalSurvey, Survey, Sudbury, Sudbury, Ontario Ontario 1996-97 Goldich Medal 1996-97 Medal Committee Committee Ken Card Ken Card (1997) (1997) Consulting (formerly Geological Consulting Geologist, Kanata, Ontario (formerly Geological Survey Survey of of Canada) England (1998) (1998) Dan England Eveleth Fee Office, Incorporated, Eveleth Incorporated,Eveleth, Eveleth, Minnesota Minnesota 999) (1999) John Klasner Klasner(1 Macomb, Illinois Western Illinois Illinois University, Macomb, Illinois XII xii �1997 GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT RONALD P. SAGE, SAGE, ONTARIO ONTARIO GEOLOGICAL GEOLOGICAL SURVEY SURVEY Past Goldich Goldich Medalists Medalists Samuel Samuel S. Goldich Goldlch not not awarded awarded Carl E. Dutton, Dutton, Jr. Jr. Carl E. Ralph Ralph W. Marsden Marsden Burton Burton Boyum Boyum Richard Richard W. Ojakangas Ojakangas Paul Paul K. Sims Sims G.B. G. 6.Morey Morey Henry Halls Henry H. Halls Walter S. Whit Whit Jorma Kalliokoski Kalliokoski Kenneth Kenneth C. C . Card Card William William J. J. Hinze Hinze William F. Cannon Cannon William F. Donald W. Davis Davis Donald W. Cedric Cedric Iverson Iverson Gene LaBerge LaBerge Southwick David L. Southwick 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Banquet Speaker Dr. Peter Lightfoot Lightfoot Inco Limited Limited Ontario Copper Cliff, Ontario Origin Origin of the Sudbury Sudbury Structure Structure and its its Mineral Mineral Wealth Wealth XIII xiii �Banquet Banquet Speaker Dr. D r.Peter Peter Lightfoot Lightfoot Inca Inco Limited Limited his BScdegree degreein inGeology Geologyfrom fromWorcester WorcesterCollege, Collee, Oxford, in Peter received h is BSc Oxford, England Englandin in 1980 1980 and and his MSc in Geology under the supervision of of A.J. A.J. NaldretI Naldrett from from the the University Universityof ofToronto Torontoin in1982. 1982. He returned returned to England England received his PhD in Geochemistry from from the Open University, Milton Keynes, Keynes, England England under under the supervision and received supervision C.J. Hawkesworth. .J.Hawkesworth. of C During the period 1985 through through 1987, 1987, Peter Peterwas was aa Post-doctoral Postdoctoralfellow fellowat atthe theUniversity Universityof ofToronto, Toronto,Canada Canada During the periodof of 1985 conducting diabase in in the Temagami Temagami and andNew NewLiskeard Uskeardarea areaof ofOntario. Ontario. conductingresearch researchon onthe the Nipissing Nipissing diabase joined the Ontario Geological Geological Survey Survey and became became Supervisor, Mineral MineralSciences SciencesSubsection, Subsection, In 1987 Peter joined Geoscience played aa major major role in in the the design design of of the the Ontario Ontario Geological Geological Survey Survey Geoscience Laboratories Laboratories until 1990. Peter played Geoscience Geosaence Laboratories Laboratoriesat at the the Willet Willet Green GreenMiller MillerCentre Centrein inSudbury. Sudbury. From conducted research research into into mafic mafic to to ultramafic ultramafic rocks rocks for for the the Ontario Geological Geological From 1992 1992 unth until 1996 Peter conducted Survey. During During his research has included included projects his career, his his research projects on the petrogenesis petrogenesis of of the the Nipissing Nipissingdiabase, Keweenawan Keweenawan flood flood basalt basalt sequences, sequences, Siberian Siberian Trap Trap lavas, lavas, Noril'sk-Tainakh Noril'sk-Tainakh intrusions intrusionsand andDeccan DeccanTraps. Traps.The The development rocks of mafic and ultramafic development of of suiphide sulphide accumulations accumulations in rocks ultramafic composition compositionhas has been been one one of of his his prime prime interests. interests. In at the the Ontario Ontario Geological Qeological Survey to to become become Senior 1996 Peter Peter resigned resigned his his position at Senior Geologist with Inco Inco In 1996 Limited in Sudbury, Ontario. Peter continues continues to to work work in in mafic mafic to ultramafic ultramafic rocks rocks and and their their associated associated sulphide sulphide Limited mineralization. One gabbro-hosted, Cu-Ni-Co hiscurrent currentinterests interestsis isthe the Voisey% Voise/s Bay, gabbro-hosted, C u - N i i deposit depositin in minerariuation. Oneof ofhis Newfoundland, Canada. Newfoundland, Peter resides with wife wife Nancy, Nancy,who whosupervises supervisescancer cancer research research projects projects at Laurentian Laurentian Peter resides in Sudbury, Ontario with Hospital, and Hospital, and daughter daughterMeagan. Meagan.- xiv . �CITATION CITATION Sage, 1997 1997 S.S. 5.5. Goldich Ronald Parker Sage, Goldich Medal Medal Recipient Recipient Ladies and Gentlemen: Gentlemen: Ladies my pleasure pleasure tonight to introduce to you Ronald Ronald Parker It is my Parker Sage, the the 1997 1997recipient recipientof ofthe theS. S. S. S. Goldich GoldichMedal. Medal. is the 43rd 43rd annual on Lake Lake Superior Superior Geology, and the 18th annual meeting meeting of of the Institute on 18th time the medal medal is is This is awarded. being awarded. IImet met Sam Goldich only once, and that that happened happened many manyyears yearsago agoat ataaconference conference on on iron ironformations. formations. From Sam Goldich became clear to me that he was was one one of of the the giants giants of of Lake Superior Superior geology. In Inaaheated heated the discussions it became debate the moderétor to challenge challenge Sam Sam Goldich this point"? point"? There There were were no no debate moderatorasked asked "Does "Does anyone wish to Goldich on on this years citation. citation,Glen GlenMorey Moreycompared comparedSam SamGoldich Goldichtotothe the"Drill "DrillInstructor Instructorwe wesee seeon onTV Wads ads for takers. In last years U.S. Marine Corps", tough, tough, expecting his people the U.S. people to perform perform at at their their best, yet yet aa wonderful wonderfulman. man. Before IIrecite recite to you the the many manyaccomplishments accomplishmentswhy why Ron Ronthe the scientist scientistis is the the worthy worthy 1997 1997 recipient recipient of the S. ~ efore Goldich medal, let S. Goldich let me me tell tell you you about Ron Ron the person. Ron was born the city where where he also also spent his childhood and his childhood and youth. Ron born in in 1938 1938 in in Pontiac, Michigan, the married Carol been happily In 1974, he married Carol Ann Raebiger from Philadelphia, and they have been happily married married for 23 23 years. honeymoon to to the the sunny sunny beaches and warm waters on some exotic While many many young couples couples travel for their honeymoon tropical tropical island, island. Ron Ron and and Carol Carol chose chose an anexotic exoticisland islandof of another anotherkind, kind, they theytravelled travelledto toIceland, Iceland,where wherethere there are Ron and and Carol have three three teenage children, Douglas, are glaciers, volcanic volcanic rocks, rocks, and no no tourists. Ron Douglas, Victoria, and and Alexandra. graduated in 1960 with with aa BSc BScdegree degreein ingeological geological engineering engineering from from Michigan Michigan Technological Technological Ron first graduated University Houghton. While While at at MTU, of his free free time lime wllec collecting MTU. Ron Ron spent spent moSt most of Univecsitv in Houahton. ting rocks rocksand and minerals mineralsin in the the copper and eaming him the the nickname nickname "Rocky". "Rocky". He Hewas wasaastudent ffirilSpiroff, Spiroff, the the "Mad "Mad copper and iron iron mining mining districts, earning studentof ofKiril remember, Ron holds his Alma Mater Russian", whom many many of you will remember. Mater in high hiiih esteem, his his son Douglas Douglas is L ~to1~ - -Scientific ~~.. enrolled there year 0study siuay oaenunc now enrolled there in in a premedicine premedicine program, and anddaughter daughterVictoria Victoriawill willfollow follownext nexi year and Technical technical Communications. Communications. .A..2~..-<--.<c. the early 1960s, 1960s,Ron Ronworked workedfor forthree threeyears yearsas asExploitation ExploitationEngineer Engineerfor forthe the Shell Shell Oil Oil Company Company in west west In the included well sitting, well well logging, well well workovers, and Texas. His duties included and other other production productionrelated relatedactivities. activities. graduated with aa Master's Master'sdegree degreein inGeology Geologyfrom fromthe the Colorado Colorado School School of Mines. It Itwas In 1966, Ron graduated was here here that to alkalic alkalic rocks, rocks, h his studytopic topicand andthesis thesisbeing being"Geology "Geologyand andMineralogy Mineralogyof ofthe theCripple cripple is study he was first exposed to Creek Teller County, County, Colorado". Colorado". This led to toemployment withAnaconda AnacondaAmerican AmericanBrass BrassLtd Ltdto to Creek Syenite Stock, Teller employmentwith investigate the Port Port Coldwell CoIdwell alkalic alkalic complex complex near near Marathon, Ontario. investigate Cu-Ni-PGE minerals in the During summer of During the summer of 1967, 1967, Ron Ron searched searched for basemetals basemetalsininthe theEly ElyGreenstone GreenstoneBelt BeltininMinnesota Minnesotafor forBear Bear Creek Mining. It was was in in that that year yearthat thathe hefirst first met met two two other other greats greats of of Lake Superior Superior geology, Ned Ned Eisenbrey Einbrey Creek and Gene Gene Laberge. Laberge. Ron again worked for Anaconda American American Brass Ltd, Ltd. this this time time north north of of Lake Superior in the the Schreiber Schreiber In 1969, Ron greenstone greenstone belt, belt, searching searching for for gold gold and and basemetals. fall of 1969, Geological Survey, Survey, his In the fall 1969, Ron Ron joined the Ontario Geological his professional professionalhome hometo to this this day. day. Ron's Ron's work for for the the OGS OGS has hastaken takenhim himto to many manyparts partsof of the the province, province, but but never never very very far far and andnever neververy verylong longfrom fromLake Lake Superior. helicopter reconnaissance reconnaissance in in Northern Ontario, then Superior. He He spent spent the first four years on aa helicopter thenmapped mappedthe the Slate worked on on aa multiyear multiyear program program to to study alkalic alkalic rocks rocks north Slate Islands Islands in in Lake Lake Superior, and next worked north of Port CoIdwell the Trans Trans Superior Superior Tectonic Tectonic Zone Zone and along along the Kapuskasing Coldwell along along the the northern northern extension extension of the Kapuskasing Structural greenstone belt. StructuralZone. Zone. In In1978, 1978,Ron Ronwas was assigned assigned to the Michipicoten Michipicoten greenstone belt.Here Herehe hespent spent10 10years years xv �mapping supracrustal rocks over approximately approximately 540 square miles, with emphasis on the the gold gold and mapping Archean supracrustal base metal potential. In 1993, Ron Ron was was assigned assignedto to aa province provincewide wideprogram program of of kimberliie kimberlite occurrences occurrences to to base metal stimulate diamond diamond exploration. Some Some of stimulate of this work was was again again in in the Michipicoten Michipicotenarea, area, where where diamond diamondindicator indicator minerals are common. minerals Despite his busy busy professional professional schedule, schedule, Ron was was able to complete complete his Despite hisPhD PhDdegree degreein in1986 1986for foraathesis thesis submitted to Carleton Catleton University in in Ottawa. Ottawa.The The topic: topic: "Aikalic submitted "Alkalic Rock Rock Complexes Complexesand andCarbonatites Carbonatitesof of Northem Northern Ontailo, and Ontario, and their their Economic EconomicPotential". Potential". xvi �Student Student Travel Travel Award Award The Travel Award to support support student The 1986 1986 Board Board of of Directors Directors established established the LL.S.G. I.L.S.G. Student Travel student participation participation at annual meeting Institute. The awards will be made from a special special fund fund set set up up for this purpose. This This the annual meeting of the Institute. award intended to help defray defray some some of of the the direct direct travel travel costs to to the the Institute and and includes a waiver waiver of of is intended award is The number numberof ofawards awards registration fees, fees, but but excludes excludesexpenses expensesfor formeals, meals,lodging, lodging,and andfield fieldtrip tip registration. registration. The and Chairman in Secretary-Treasurer and andwill willbe be and value value are are determined determined by by the annual annual Chairman in consultation consultation with the Secretary-Treasurer announced announced at at the the annual annualbanquet. banquet. The responsiblefor forthe theselection: selection: The following followinggeneral generalcriteria criteriawill will be be considered considered by by the the annual annual Chairman, Chairman,who who isisresponsible 1) resident (undergraduate (undergraduate or graduate) student student status 1) The applicants applicants must must have active resident status at at the time of of the annual annual meeting meetingof of the the Institute, Institute, certified by by the department departmenthead. head. 2) Students paper will be given Students who who are are the senior author on either an oral or poster poster paper given favoured favoured consideration. consideration. is desirable or more more students students to jointly requesttravel travelassistance. assistance. 3) ItIt is desirable for two or jointly request 4) In farthest away. In general, general, priority priority will be be given to those in the Institute region who are farthest away. 5) Each travel award writing, to to the the annual Chairman, Chairman, with with an Each travel award request request shall be made in writing, an explanation explanation of need, need, possible possible author author status status or or other other significant significantdetails. details. Successful Successful applicants applicantswill will receive receive their their awards awards at at the the time time of of registration registrationfor forthe theMeeting. Meeting. xvii xvii �Institute on Lake Lake Superior Superior Geology Geology 42nd Annual Institute Cable, Wisconsin Wisconsin - The Geology was 1996, at the Telemark Telemark Lodge The 42nd 42nd Annual Annual Institute Instituteon on Lake Lake Superior Geology was held held May May 15 15 - 19, 19,1996, Lodge in in Cable, Wisconsin. The (Chair, Laurel Laurel Woodruff, Reid U. S. Geological Geological Survey Survey (Chair, Field Themeeting meetingwas was organized organizedby by the U. Trip Oshkosh (Field - Oshkosh Trip Coordinators, Coordinators, William William Cannon Cannon and and Suzanne SuzanneNicholson), Nicholson),and andthe theUniversity Universityof of Wisconsin Wsconsin — Trip Secretary/Treasurer, Sally Trip Coordinator, Coordinator, Gene Gene LaBerge, Secretary~Treasurer, Sally LaBerge). The published inS The Proceedings Proceedings of of the 42nd 42nd ILSG ILSG were published in 3 parts: parts: Part Laurel woodruff Woodruff and Programand andAbstracts Abstracts (edited (edited by Laurel and Suzanne Suzanne Nicholson) Nicholson) Part I:1: Program Part of Northern Northern Wisconsin: Wisconsin: A Commemorative 11: Volcanogenic Volcanogenic Massive Massive Sulfide Deposits of CommemorativeVolume Volume (edited (edited by by Part II: Gene Gene L. L. LaBerge) LaBerge) Part Ill: Field Suzanne Nicholson Nicholson and Laurel Woodruff) FieldTrip TripGuidebook Guidebook(edited (edited by Suzanne Laurel Woodmfl) Part 111: Part 1: Glacial GlacialGeology Geologyof of Western Western Wisconsin Wisconsin (Mark (Mark 0. 0.Johnson) Johnson) Part 1: Part 2:: Overview Cable-Hurley Area, Wsconsin Wisconsin (William (William F F.. Cannon and and Part 2 Overviewof of the Bedrock Geology of the Cable-Hurley Suzanne Suzanne W. Nicholson) Nicholson) Part Traverse through through 25 25 km of the Crust Part 3: Geology Geologyof ofthe theMontreal MontrealRiver River Monocline Monocline— AA Traverse Crust (William (William F. F. Cannon) Cannon) Part Namekagon Region Part 4: Early Earlyto to Middle Middle Proterozoic Proterozoic Geology of the Lake Namekagon Region (William (William F. Cannon, Laurel Laurel G. G. Woodruff Woodruff and and Suzanne Suzanne W. Nicholson) Nicholson) Part LakeNamekagon Namekagonand and Penokee Penokee Gap Gap Areas, Areas. West West Gogebic Gogebic Range, Range, Wisconsin Wisconsin (John S. Klasner Klasner and and Part 5: Lake Gene L. LaBerge) LaBerge) - The the The commemorative commemorativemassive massivesulfide sulfide volume, volume, originally originallyconceived conceivedby byEdwarde EdwardeMay, May, consulting consultinggeologist geologistat atthe Flambeau and John John S. Phillips, early pioneers pioneers in In (he the exploration exploration FlambeauMine, Mine, and and dedicated to Edward H. Eisenbrey and and study sulfide deposits in In Wsconsin, Wisconsin, was was published published in conjunction conjunction with with aa post-meeting post-meetingfield fieldtrip trip and study of of massive massive sulfide to Wisconsin. The to the the Flambeau Flambeaugold-copper gold-copper mine mine in in Ladysmith, Ladysmith, Wsconsin. Thevolume volumecontains containsnine ninechapters: chapters: History for volcanogenic volcanogenic sulfides sulfides (Russell (Russell C. C. Babcock) History of exploration for L.LaBérge) LaBerge) Generalcharacteristics characteristics and and geologic geologic setting terrains(Gene (Gene L. General sethng of the Wsconsin Wisconsin magmatic magmatic terrains A A geologic geologic framework framework for for Early EarlyProterozoic Proterozoic volcanogenic volcanogenicmassive massivesulfide sulfidedeposits deposits in in Wisconsin Wsconsin (Theodore (Theodore A. DeMatties) DeMatties) An overview of of the the Flambeau Flambeau supergene supergene enriched enriched massive massivesulfide sulfidedeposit deposit Geology Geologyand andmineralogy, mineralogy.Rusk Rusk County, County, Wisconsin Wsconsin (Edwarde R. May May and and Stephen Stephen R. R. Dinkowitz) Dinkowitz) Case study of environmental environmental requirements for the permithng, permitting, operation, and reclamation of aa metallic metallicmine mine Case reclamation of in Flambeau Mine Mine (Jana (Jana E. E. Murphy Murphy and Richard Richard T. Dachel) in Wisconsin Wisconsin — Flambeau Oachel) Eisenbrey: AA structurally structurallycomplex complexProterozoic Proterozoiccopper-zinc copper-zincmassive massivesulfide sulfidedeposit, deposit. Rusk RuskCounty, County, Wisconsin Wsconsin(Edwarde (Edwarde R. R. May) May) Geological Crandon deposit (A. (A. J. Erickson GeologicalSummary Summary— Crandon Ericksonand and R. R. Cote) Cote) The AnEarly EarlyProterozoic Proterozoiccopper-gold coppergoldVMS VMSdeposit deposit(Theodore (TheodoreA. A. DeMatties DeMattiesand andWilliam WilliamF. F. The Bend Benddeposit depositAn Rowell) Rowell) Geology base-metal deposit, north-central north-central Wisconsin, A Adams) Geology of of the the Lynne Lynne base-metal Wsconsin, U.S.A. U S A . (Glen (Glen A. - - Gene the volume. volume. Most Gene LaBerge LaBerge undertook undertook the formidable task of organizing the Mostof of the the printing printing costs costs for the volume individuals and and corporations. corporations. Proceeds volumewere weregenerously generously donated donated by a number of individuals Proceedsfrom from the the sale sale of of the the volume volumewill willbe beused usedto to promote promotestudent studentparticipation participation in in future future ILSG ILSGmeetings. meetings. Motel 148people peopleregistered registeredfor forthe themeeting meetingininCable. Cable.Field Fieldtrips tripsassociated associatedwith withthe themeeting meetingwere wererobust, robust, A totalofof148 with 177 paid participants, including 11 for the glacial geology of northern Wisconsin, 43 on the Archeanwith 177 paid participants, glacial geology of northern 43 on the ArcheanMiddle MiddleProterozoic Proterozoictransect transect trip, 18 18 looking at the Early Early Proterozoic Proterozoicin in the Lake Lake Namekagon Namekagonregion, region,and and17 17on on the the trip trip to to the the Penokee Penokee Gap. The The tip triptotothe theFlambeau FlambeauMine Minewas wasone oneofofthe thelast lastofficial officialtrips tripsto tothe themine mineprior priorto to the 88 participants. participants. Many Manylogistical logisticaldetails detailsfor forthe thetrip tripwere were the start start of of planned plannedshut shut down down phase, and and had had 88 generously generouslysupported supportedby by Kennecott Kennecotl Copper Copper and and the Flambeau FlambeauMining Mining Company. Company. XVIII �annual banquet The annual banquetwas was attended attended by by 111 111 diners. The TheGoldich GoldichMedal Medalwas was awarded awardedto toDavid DavidSouthwick Southwickof ofthe the Geological Survey in in recognition recognition for for his his outstanding outstandingcontributions contributionsto togeology geology in inthe the Lake Lake Superior Superior Minnesota Geological Geological Survey, Survey, presented presentedthe the award. award. To region. Glen GlenMorey, Morey, also also from from the the Minnesota Geological To correct correct an an oversight during during the the annual meeting of of the the ILSG Board Board of of Directors, Directors,the the term term of of the the Secretaryrnreasurer Secretary/Treasurer v1ark (Mark E. approved by a belated, but unanimous The banquet banquetaddress addresswas wasgiven givenby byDr. Dr. Stephen StephenE. Jirsa) was approved unanimous act. The Kesler of the the University University of Michigan, presenting Kesler presenting aawell-received well-received lecture lecture titled, titled, Sustainable Sustainable Mineral Mineral Development Development — Fact Fact or or Fiction. Fiction. - Student Paper Paper Awards Awards were were given given to to Kimberly Kimberly Darrah Darrah(Kent (Kent State State University) University) for for her hertalk talkon onPetro Pefrographicand Student graphic and the srmoba rometic analysis the metamorphosedLittle LittleFalls FallsFormation, Formation,Central CentralMinnesota, Minnesota, with with implications implications thermobarometic analysis ofofthe metamorphosed for Early Early Proterozoic Proterozoic tectonism; tectonism; Susan Wilson Wilson (Western Illinois University) University)for for her her talk, talk, AA stmcfural structural and kinematic kinematic analysis analysis of of the McCaslin McCaslln Formation Formationnear nearMcCaslin Mccaslln Mountain, Mountain, Wisconsin, Wisconsin, and Zachary Zachary Naiman (Macalester Chengwatana Volcanic Group (Macalester College) College) for for his his poster, Metamorphism of Chengwatana Group near nearTaylors Taylors Falls Fateand and Osseo core. Five Fivestudent studenttravel travelawards awards totalling totalling$400 $400 were were presented presentedto to Zachary ZacharyNaiman, Naiman,Kim KimNeilsón, Neilson, from Osseo Andrey Bekker, Andrey Bekker, Susan Susan Wilson, Wilson, and andKimberly KimberlyDarrah. Darrah. The Board Lake Superior Geology Geology met met in in Cable Cable on May 16,1996. 16, 1996. Members Members of The Board of of Directors Directorsof of the the Institute Institute on Lake were: Laurel the Board Board in attendance were: LaurelWoodruff Woodruff (Chair), (Chair), Mark Jirsa (Secretary/Treasurer), Ted Ted Bomhorst, Bomhorst, David Southwick, and and Mark Mark Smyk. Smyk. Invited guests guestsincluded: included: Ken Card, Ron Sage, Wilf Meyer, Charles Blackburn, Blackbum, Gene Gene LaBerge LaBergeand and Sally Sally LaBerge. Actions Actions taken taken were: were: 1. Accepted Smyk), which which included included the the minutes of of the the last last Acceptedthe the Report Reportof ofChairman, Chairman, 41st 41st ILSG ILSG meeting (Mark Smyk), meeting Board meeting. 2. Approved Approved an anoffer offerby bythe the Ontario Ontario Geological GeologicalSurvey Survey to host host the 43rd Annual Institute on on Lake Lake Superior Superior Annual Institute Geology in Sudbury, Ontario. Ron Sage Sage and and Wilf Wilt Meyer Meyerwill willact actas asco-chairs co-chairs for for the the meeting. Geology 3. Approved host for the 44th 3. ApprovedKenora, Kenora,Ontario, Ontario, and and the the Ontario Ontario Geological GeologicalSurvey as host 44th ILSG ILSG in in 1998, 1998, with Charles Blackbum Charles Blackbumas as Chair. Chair. 4.. Accepted 4 AcceptedILSG ILSGFinancial FinancialReport Reportfrom fromthe theSecretary/Treasurer SecretarytTreasurerMark MarkJima. Jirsa. 5. Approved ApprovedDavid DavidSouthwick Southwickas as recipient recipient of of 1996 1996 Goldich Goldich Medal. 6 Approved Morton). 6. ApprovedJohn JohnKlasner Klasneras asnew newGoldich Goldich Medal Medal Committee member (replacing Penny Morton). 7. Discussed Discussedthe thefuture futureof ofthe theILSG ILSGNewsletter Newsletterand and the the establishment establishment of of aa home homepage pagefor forthe theILSG. ILSG.Results Results from from the the members memberspoll pollin inthe the llrst firstnewsletter newsletterwere were presented. presented. The The Board Board approved approvedthe thecontinuation continuationof ofthe the newsletterat at the the rate rate of of one/annum onelannumwith with Ted Ted Bomhorst Bomhorstcarrying carryingthe theinitiative initiativefor for both bothactivities. activities. newsletter 8. Discussed Discussedthe the distribution distributionand and continued continued sale of back back issues of ILSG Field Trip Guidebooks, Guidebooks, which are being being handled handledby by Mark Mark Jirsa Jirsa as as Secretary/Treasurer. Secretary/Treasurer. 9. Discussed the commemorative commemorative volume volume on -the 9. Discussedthe the recent recentpublication publicationof of Proceedings Proceedings Volume Volume 42, Part Part 22 — Wisconsin massive sulfides. The The Board agreed agreed to to send send aa letter letter of of thanks thanks to to all all the the contributors contributors who donated Wisconsin money for the publication of of the the volume. volume. Proceeds Proceedsfrom fromthe thesale salewill willbe beused usedfor forthe theencouragement encouragementof of student participation ILSG, and and will will be be kept kept separate separatefrom from the the general general working working fund. With participation in the ILSG, Withthe theBoard's Board's approval and sale sale of the the volume. volume. approval Ted Ted Borrihorst Bornhorstwill will promote promote the advertising and The Board Board approved voted on by the the participant the 10. The approved changes changes to the constitution constitution of the ILSG voted participantmembers membersof ofthe 11.80 duringthe themorning momingTechnical TechnicalSession Sessionon onMay May16, 1996. These These changes changes included included wording changes to to ILSG during 16,1996. make for the theterm term for for the the Secretaryfheasurer, Secretary/Treasurer, which was make the the constitution constitution gender gender neutral, and an extension for actually carried carried out at the annual actually annual banquet. banquet. To establish aa list list of of members members for for the ILSG, ILSG. the the Board agreed to to longcomprehensive mailing mailing list which includes (those participants participants with longcreate a comprehensive includes both both permanent permanent members members (those standing interest in Lake Superior geology) geology) and and aa list listof ofmembers members who who have have attended attended ILSG meetings in in the the past. The TheBoard Boardassigned assigned Laurel LaurelWoodruifto Woodruff tocomplete completethis thismembership membershipmailing mailinglist, list,which whichwill willthen thenbe be be assessed assessedat at this thistime. passed from Chair Chair to Chair for successive meetings. Membership dues dues will will not not be meetings. Membership 11. In a discussion discussion of requirements requirements and suggestions suggestions to ILSG Chairs, Chairs, itit was was determined determined that that the the Chair Chair needs needs 11, freedom to to act act independently independentlywithin reasonable intuitive the freedom intuitiveguidelines guidelinesthat that follow follow general general historical precedents. by Ken Ken Card Card on the standardization of the the selection selectionpolicy policyfor forthe the Board discussed discussedaa presentation presentationby 12. The Board standardization of Goldich Goldich Medal Medal award. The Thematter matterwas wastabled tabledfor forfuture futurereview. review. Board agreed agreed that that the Student Paper Committee independentlywithin 13. The Board Committee needs the the freedom freedom to act independently reasonable historical precedents. reasonableintuitive intuitive guidelines guidelines and and need need not not be be constrained constrained by historical precedents. xix xix �was done doneto tokeep keepcosts costswithin withinreasonable reasonablelimits, limits,and andnot notlose losemoney. money. This This was was Budgeting for the 42nd ILSG ILSG was successful, in excess excessof of $6000. $6000. However, However, as as much muchas as the the Chair successful, as as the the meeting meetingmade made an an approximate profit in would would like like to to claim claimcredit creditfor forthis, this, aa substantial substantial portion portion of this sum was a a result resultof of support supportfrom fromthe theElambeau Flambeau Mining Company Company for the Flambeau field trip. tip. InInaddition, withmany manyof ofthe thepublishing publishingcosts costsfor forthe the Flambeau Mine field addition,with Proceedings underwrittenby by the numerous numerous contributions contributionsfrom from individuals individualsand andcompanies companiesall allhsture future ProceedingsVolume Volume22underwritten sales will will directly student participation sales directlypràfit profitthe theInstitute's Institute'sstudent participationfund. fund. II enjoyed enjoyed my on Lake Lake Superior Superior Geology, Geology, and the opportunity my tenure tenure as as Chair Chair of of the the Institute on opportunity to interact interact with people associated organization. There are a number of people number of people involved involved with with the meeting meeting who were people associated with the organization. essential to its its overall overall success general well-being. well-being. I I thank thank Gene Gene and success and and the Chair's general and Sally SallyLaBerge, LaBerge,who who essential and guided guided me whom it would would have have been been nearly nearlyimpossible, impossible, and and coaxed and methrough through the the experience experience and without whom willingto todo do everything everythingIIasked askedher hertotodo, do,and andititwas wasalot. aId. Bill Bill Cannon Cannon Suzanne Nicholson Nicholson who was more than willing originally ILSG and then generously generously deferred originally conceived conceived of ofthe the USGS USGSsponsoring sponsoring an ILSG deferredthe the duties dutiesof ofChair Chairto to me, me, rather TedBornhorst Bomhorstand andMark MarkSmyk Smykwillingly willinglygave gaveadvice, advice, rather than than taking takingon onthe theglory gloryfor for himself, himself, former former Chairs ChainTed and and SecretaiyiTreasurer SecretaryrnreasurerMark MarkJirsa Jirsa covered covered all all the money money questions for me. Laurel Woodruff Laurel Woodruff Chairman, 42nd Chairman, 42nd ILSG ILSG Cable, Wisconsin Wswnsin xx �PROGRAM PROGRAM �Calendar Calendar of of Events Eventsand and Program Program Tuesday 1997 6,1997 TuesdayMay May6, - 8:00 8:00 a.m. a.m. - 7:00 7:00 p.m. p.m. Field FieldTrip Trip11 Field FieldTrip Trip 11--The TheHuronian HuronianSupergroup Supergroupbetween betweenSauft SaultSte. Ste. Marie Marieand andElliot ElliotLake Lake (day 1) (day 1) Leaders: Ken Ken Card Card(Geological (GeologicalSurvey Surveyof ofCanada, Canada,retired) retired) Leaders: Gerry Gerry Bennett Bennett (Resident (ResidentGeologist, Geologist, Sault Sault Ste. Ste. Marie, Marie, Ontario OntarioGeological Geological Survey) Survey) Wednesday, 1997 Wednesday, May May7, 7,1997 8:00 a.m. a.m. --6:30 p.m. Field 1,2, 3, 3,4 8:00 6:30 p.m. Field trips 1,2, 4 Field FieldTrip Trip 11-- The TheHuronian HuronianSupergroup Supergroup(day (day2) 2) Leaders: as as above above Leaders: Field New Developments Field Trip Trip 22 -New DevelopmentsininGrenville GrenvitleFront FrontGeology, Geology, Sudbury SudburyArea, Area, Ontario Ontario Leader Tony Tony Davidson Davidson(Geological (GeologicalSurvey Surveyof ofCanada) Canada) Leader: - FieldTrip Trip 33 The TheSudbuty SudburyStructure Structurewith withemphasis emphasison onthe the Whitewater WhitewaterGroup Group Field Leader Stu Stu Gibbons Gibbons(Falconbridge (FalconbridgeLimited) Limited) Leader 4 -Magmatic MagmaticOre OreDeposits Depositsof ofthe theSudbuiy SudburyIgneous IgneousComplex Complex FieldTrip Trip 4Field Leader: Steve Steve Prevec Prevec (Laurentian (LaurentianUniversity) University) Leader: Mike Mike Cosec Cosec (Resident (Resident Geologist's Geologist's Program, Program, Ontario Ontario Geological Geological Survey) Survey) 9:30 p.m. p.m. Registration, Registration,Poster Poster Set-up Set-up 7:30 p.m. p.m. -- 9:30 7:30 Alphonse Raymond Building, Alphonse Raymond Building, Laurentian Laurentian University UniversityCampus Campus , - 10:00 p.m. Icebreaker, Icebreaker, Cash Cash Bar Bar 7:30 p.m. - 10:00 Alphonse Alphonse Raymond Raymond Building, Building, Laurentian LaurentianUniversity University Campus Campus Thursday, 1997 Thursday, May May8, 8,1997 NOTE: NOTE: Technical TechnicalSessions Sessionsare arein inthe the auditorium, auditorium,Alphonse AlphonseRaymond RaymondBuilding, Building, Laurentian Laurentian University Campus Campus odi xxii �a.m. -- 4:30 4:30 p.m. p.m. Registration continues 8:00 a.m. Technical Session Technical Session11 Session Session Chairs: Gene GeneLaBerge LaBergeand and Terrence TerrenceBoerboom Boerboom 8:30a.m. Andy Andy Fyon Fyon Precambrian Geoscience Section, Ontario Senior Manager, Precambrian Ontario Geological Geological Survey 43rd Annual Annual Institute Institute on Lake Lake Superior Superior Geology Geology Opening Remarks - 43rd 8:40 Don Rousell Rousell Mineralization History The Tectonic, Magmatic Magmatic and Mineralization History of of the the Sudbury Sudbury Structure Structure 9:40 T. F. Morris Morris Results of modern alluvium alluvium sampling for kimberlite kimberlite indicator indicator minerals, Wawa-Kinniwabi Lake Lake Region Region and and the the implication implicationfor for kimberlite kimberliteexploration, exploration, Northeastern Northeastern Ontario Ontario 10:00 Coffee Break and Poster Session Session Limited Exploration Exploration Sponsored by Falconbridge Limited 10:20 Shawn M. M. Carlson and Glen W. Adams Adams. ultramafic lamprophyric WI The diamondiferous six-pak ultramafic lamprophyricdiatreme, Kenosha, Wl 10:40 Dean Dean M. Peterson Peterson GIS for Archean Archean gold gold exploration: exploration: using GIs applications for usingCanadian Canadianmining miningcamp camp GIS exploration in GIs queries to target gold exploration in Minnesota Minnesota 11:00 Ken Keri Anderson and Nigel Nigel Wattrus Wattrus Western Lake Superior A seismic stratigraphic study of Western 11:29 C. M. Mancuso, Mancuso,D. 0. K. K Hoim, KA Holm, U A.Foland Folandand andF. F. A. A. Hubacher Hubacher resultsof ofArIAr k/k mineral mineraldating datingfrom fromthe thePeavy Peavynode nodearea area of of northern Initial results northeastern Wisconsin Wisconsin Michigan and Dunbar dome area of northeastern 11:40 D. K. K Holmand Holm andD. D. H. H. Henderson Henderson of Early Proterozoic Proterozoic post-Penokean (1800-1600 Ma) Space-time patterns of metamorphism and and cooling cooling in in the the southern southern Lake Superior region region 12:00 p.m. Lunch Break Lunch Break XXIII �Technical Technical Session Session 22 MarkSmyk Smyk and and Mark Mark Jirsa Jirsa Session Chairs: Mark 2:00 2:OO L LaBerge LaBerae Gene L. The Early Early ~rotirozoic Implications of drill Proterozoic break-up of of the the Superior SuperiorCraton: Craton: Implications core and and geophysical geophysical data data south south of of the the Gogebic Gogebic range, range, northern northernWisconsin Wisconsin core 2:20 T. Arcuri Arcuri and and E. E. M. Ripley Ripley Interactionbetween between a Virginia Formation xenolith and mafic mafic magma magma at the Interaction Virginia Formation xenolith and Babbitt Babbitt Cu, Ni Ni deposit deposit Duluth Duluthcomplex, complex, MN MN 2:40 Edward R. Fridk Frick Edward M. Ripley, David David 0. D. Lambert Lambert and and Louise LouiseR. Re-Os, Sm-Nd Sm-Nd and and Pb Pb isotopic isotopicconstraints constraintson onmantle mantleand andcrustal crustal contributionsto to magmatic magmatic sulphide sulphide mineralization mineralizationin in the the Duluth Duluthcomplex complex contributions 3:00 Coffee Coffee Break Break and and Poster PosterSession Session Sponsored by Ministry of Northern Sponsored by Ministry of NorthernDevelopment Development&& Mines Mines 3:20 John John Siriunas Siriunas and and John John Wiebe Wiebe Overview Overview of the the Gregor Goldfields Goldfields Corp. Corp. Marathon Marathon (Wire (Wire Lake) Lake)Gold Gold Property Property in in the the Hemlo Hemlo Area of of central central Ontario, Ontario, Canada Canada 3:40 3:40 Tom Tom Muir Muir The The Hemlo HemloGold GoldDeposit: Deposit: It may be gold but its not black and white 4:00 4:OO Steve Steve Jackson Jackson Patterns of structure structure and and metamorphism metamorphism in in the Hemlo Hemlo greenstone greenstonebelt belt Patterns 6:30 --7:30 Mixer -- cash cash bar bar 7:30 Mixer Cavern, Science Cavern, ScienceNorth North 7:30 --9:30 9:30 Annual AnnualBanquet Banquetand andAwards AwardsPresentation Presentation Announcement of of the the 44th 44th Annual Annual Meeting Meeting location location Announcement 1997 1997 Goldith GoldichAward Award presentation presentationto to Ronald RonaldP. P. Sage Sage Banquet speaker speaker:Dr. Dr.Peter PeterLightfoot, Lightfoot,Inco IncoLimited, Limited,Copper CopperCliff) Cliff, Banquet Ontario: Oiigin Stwdure and Origin of of the Sudbury Structure and its its mineral mineralwealth wealth Friday, Friday, May May 9, 9,1997 1997 Technical Technical Session Session33 Session Gordon SessionChairs: Chairs: Gordon Medaris, Medaris, Jr. and and Frank Frank Luther Luther 8:30 8:30a.m. a.m. Registration Registrationcontinues continues xxiv �9:00 George Hudak George Hudak and and Ron Ron Morton Morton The evolution associated with the Sturgeon evolution of the hydrothermal hydrothermal systems associated Sturgeon Lake Lake Caldera Caldera complex, complex, northwestern northwestern Ontario Ontario 9:20 Jon Jon Devaney Devaney Stratigraphy, tectonics and mineralization of the Sioux Sioux Lookout Lookout orogenic orogenic belt, Western Wabigoon Wabigoon Subprovince Subprovince 9:40 Gerry Gerry Bennett Bennett The Huronian from the The Huronian--from thebottom bottomUp up 10:25 Coffee Coffee Break Break and and Poster Poster Session Session Sponsored Sponsored by by Laurentian Laurentian University University 10:45 Steve Jackson Steve Jackson Structural and metamorphic contraints contraints on on the the tectonic tectonic history of the Structural the Sault Ste. Marie Marie - Espanola area Southern Province in the - 11:05 Robert G. Tipping and Douglas Douglas Allen Hydrogeology of saline- and boron-bearing ground waters in in the North North Shore volcanic group - Minnesota Minnesota 11:25 Douglas Allen, W. E. Jr., and R. G. Tipping Tipping E. Seyfried, Jr., Douglas Allen, Boron, bromide and chloride in groundwaters and and rocks of the north north shore of incursion into the mid-continent Lake Superior - evidence for a seawater incursion mid-continent rift rift - 11:45 Richard W. Ojakangas Richard Ojakangas within the the Marquette Range Range Supergroup Supergroup (Michigan) Correlative sequences within and the Huronian Supergroup (Ontario): Glaciogenics, Huronian (Ontario): Glaciogenics, paleosols paleosolsand and orthoquartzites orthoquartzites 12:05 Woodard Hank Woodard The The Mckenzie McKenzieLake LakeAntiform Antiform and and the the Kawa Kawa Bay Bay Synform, Quetico Quetico Provincial Provincial Ontario Park, Ontario 12:30 p.m. Lunch 12:30 p.m. Lunch break break (remove posters) Technical Technical Session Session 44 Session Chair: Ted TedBomhorst Bornhorstand and Phil PhilThurston Thurston 2:00 2 :OO E. Zaleski, 0. 0.van van Breemen Breemenand and V. L. Peterson Peterson Age constraints on plutonism, metamorphism and deformation constraints on plutonism, metamorphism and deformationacross acrossthe the Manitouwadge Greenstone Wawa-Quetico Subprovince Subprovince boundary near the Manitouwadge Greenstone belt, northwestern northwestern Ontario Ontario xxv XXV �2:20 L. G. Medaris, Jr., L. P. Baumgartner, R. R. H. H. Dott Dott and and K. K. McSweeney McSweeney Sub-Baraboo Paleosol, Paleosol, Wisconsin: Wisconsin: geochemical evidence for The Sub-Baraboo Proterozoic weathering Proterozoic weathering and and metasomatism metasomatism 2:40 Keith Winterhalder Keith The greening The greening of Sudbury 3:05 Coffee Break Break 3:25 Masood Siddiqui Siddiqui and and Mark Mark Smyk Smyk Gerard Doiron, Masood investigations of the Pick Lake deposit, Winston Winston Lake Preliminary investigations Lake Mine, Mine, Ontario: AA remobilized massive suiphide orebody remobilized massive sulphide orebody 3:45 Theodore Bomhorst Bomhorst and Laurel Woodruff Woodruff copper precipitation precipitation by fluid-mixing, fluid-mixing, Keweenaw Peninsula, Michigan Michigan Native copper 4:05 Frank Frank R. Luther Luther The petrology of greenspar greenspar: aa Proterozoic Proterozoic porphyritic porphyriticdiabase diabase dike; dike; Pither Pifher and Irwin Irwin townships, Lake Lake Nipigon Nipigon Oistrict, District, Ontario Ontario 4:25 Presentation Presentationof of Student Student Paper Paper Awards Awards 4:30 Closing Remarks Closing Remarks Saturday, May Saturday, May 10, 1997 1997 p.m. Field Field trips 3, 4, 5, 6 6 8:00 a.m. -- 7:00 p.m. Field on the the Whitewater Group Field Trip 33 -- The The Sudbury Sudbury Structure with emphasis on Leader: Stu StuGibbons Gibbons(Falconbridge (FalconbridgeLimited) Limited) - Field Trip of the Sudbury Igneous Igneous Complex Field Trip 44 Magn7atio Magmatic Ore Ore Deposits of Complex Leader Leader Steve StevePrevec Prevec(Laurentian (LaurentianUniversity) University) Mike Cosec (Resident Geologist's Program, Ontario Ontario Geological Geological Survey) Mike Survey) - Field 5 Alkafic Alkalicrocks rocksof ofthe theSudbury Sudbury Region Region(day (day 1) 1) Field Trip Trip 5Leader: Ron RonSage Sage(Ontario (OntarioGeological GeologicalSurvey) Survey) Field 6--Regreening Regreeningof Sudbury Field Trip 6 Leaders: Keith KeithWinterhalder Winterhalder(Laurentian (LaurentianUniversity) University) John John Gunn Gunn (Laurentian (Laurentian University) University) XWi �Sunday, May May11, 1997 11,1997 8:00a.m. a.m. -- 7:00 7:00p.m. p.m. Field FieldTrip Trip55 8:00 Field Trip Trip 55 -AIkalic Alkalicrocks rocksof ofthe theSudbury SudburyRegion Region(day (day 2) 2) Field Leader Leader: Ron Ron Sage Sage (Ontario (Ontario Geological GeologicalSurvey) Survey) a Poster Poster Session Session Wednesday, Wednesday, May May 7, 1997 1997 (set-up begins begins at 7:30 p.m.) -Friday, May 9, 1997 (tear-down at 1997 (teardown at 12:00 12:OO p.m.) p.m.) Dave Dave DahI Dahl Minnesota Minnesota Department Department of of Natural NaturalResources Resources Gravity for Recognizing Recognizing Crustal Fabric Fabric and Gravity Aspect as a Tool for and Structure at Minnesota Minnesota Jon Devaney Devaney Ontario Ontario Geological Geological Survey Survey Stratigraphy, Stratigraphy, tectonics tectonics and and mineralization mineralizationof of the the Sioux SiouxLookout Lookoutorogenic orogenicbelt, belt, Western Western Wabigoon WabigoonSubprovince Subprovince Mike Mike Easton Easton Ontario Ontario Geological Geological Survey Survey S. James James R. S. Department Department of Geology, Geology, Laurentian Laurentian University University Revisiting Revisitingthe the disappearance disappearanceof of the the Huronian Huronianin inthe theSudbury-Crerar Sudbury-Crerararea: area: insight from the geochemistry of amphibolites and paragneisses paragneisses D. KK.HoIm Holm 0. Department Department of of Geology, Geology, Kent Kent State State University University D. R. Lux aR.Lux Department Geological Sciences, University University of of Maine Maine Department of Geological Results Results of Ar/Ar ArIAr dating of dikes in in central central Minnesota Minnesotaand andthe the Minnesota MinnesotaRiver River Valley Valley Tom Lawler Lawler and and Darold DaroldRiihiluoma Riihiluoma Tom Department of Natural Division of Minerals, Natural Resources, Division Minerals, State State of of Minnesota Minnesota Mineral greenstone belt using boulder boulder tracing, Ely-Bigfork Mineral potential potential study of aa greenstone area, Minnesota Minnesota xxV �F. Morris Morris T. F. Ontario Geological GeologicalSurvey Survey Ontario Results Results of of modern modern alluvium sampling for kimberlite kimberlite indicator indicatorminerals, minerals, Wawa-Kinniwabi Lake and the implication Lake Region Region and implicationfor for kimberlite kimberliteexploration, exploration, Northeastern NortheasternOntario Ontario Tom Muir Muir Tom Ontario Geological GeologicalSurvey Survey Ontario The area: aa surface The Hemlo Hernlo gold deposit area: surface perspective perspective Zachary Zachary Naiman Naimanand andKarl KarlR. R. Wirth Wirth Geology Department, Macalester Geology Department, MacalesterCollege College Petrogenesis volcanics, Minnesota Minnesota and Wisconsin Wisconsin Petrogenesis of Chegwatana volcanics, John John M. M. Siriunas Siriunas and and Neil Neil Willoughby Willoughby NR8J Resource ResourceAssociates Associates Limited Limited NR&J Copper mineralization in Eastern Eastern Sault Ste. Marie Copper and precious-metal mineralization Marie Mining Mining Division Division with focus on the Jentina Property, Property, Albanel Albanel and andNicholas Nicholastownships, townships, District Algorna District of of Algoma T.E. Wahl, Wahl, J.D. J.D. Miller MillerJr., Jr.,M.A. M.A.Jirsa, Jirsa, T.J. T.J. Boerboom, Boerboorn, V.W. Chandler, Chandler, A.C. A.C. Runkel Runkel • Minnesota Minnesota Geological Geological Survey Survey D. Dahl D.DahL Minnesota Resources, Division Division of Minerals Minerals Minnesota Department of Natural Resources, Severson M.J. Severson M.J. Natural Natural Resources Resources Research Research Institute, Institute, University Universityof of Minnesota Minnesota Geologic system (GeMS): (GeMS): A digital approach Geologic mapping system approach to bedrock bedrock geologic mapping mapping xxvii �ABSTRACTS ABSTRACTS xxix �groundwaters and Boron, bromide and chloride in groundwaters and rocks rocks of of the North North Shore Shore of of Lake Lake Superior, evidence for a seawater incursion into the Mid-Continent Rift E. Seyfried SeyfriedJr., Jr.,Dept. DeptofofGeology Geologyand andGeophysics, Geophysics,University University Douglas E. Allen and W. K of Minnesota, Robert C. E-mail: alle0167@maroon.tc.umn.edu, alle0167@maroon.tc.unm.edu, Robert G. Minnesota, Minneapolis, MN. E-mail: Tipping, Tipping,Minnesota Minnesota Geological Geological Survey, St S tPaul, Paul,MN. MN. geochemically distinctive distinctive groundwater groundwatertypes types have have been recognized in the Two geochemically the North Group (NSVG) (NSVG) rocks rocks of of the North Shore of Lake North Shore Shore Volcanic Volcanic Group Lake Superior, Superior, Northeast Minnesota. Minnesota. The The chemistry chemistry of of these these groundwaters groundwatersmay may contain contain evidence evidence of of aa Northeast incursion into the Mid-Continent Rift. seawater incursion Mid-Continent Rift. The most widespread widespread groundwater type is characterized by high pH and and boron boron concentrations, which reach reach values valuesof of 1 10.26 and 5.4 5.4 ppm, ppm, respectively. respectively. The Minnesota 0.26 and Minnesota concentrations, which imit, for boron in drinking water is 0 .6 ppm (STS Department of of Health, Health, Health Risk Risk L Limit, 0.6 Consultants Report, 1995), 1995), so so the the genesis genesis and distribution distribution of of these these waters waters is of some Consultants Report, some as being of of interest interestgeochemically. geochemically. The second groundwater type is a concern, as well as dissolved chloride chloride concentration concentrationnearly nearly twice twice that that of ofseawater, seawater, Ca-Cl brine, which has a dissolved and has a conspicuously conspicuously high Br/Cl ratio ratio (0.0089). (0.0089). Mineral-fluid equilibria equilibria calculations calculations reveal Mineral-fluid reveal that that the thehigh highp1-I pH groundwaters plot vithin the quartz-kaolinite-Iaumontite-calcite stability field (fig. 1). within the quartz-kaolinite-laumontite-calcite stability field (fig. 1). This assemblage of minerals is is ubiquitous ubiquitous in in the the North North Shore Shore basalts basalts (Schmidt, (Schmidt, 1993). 1993). As evidenced minerals evidenced by assemblage fixes fixes pC02 pCO2 at relatively low values I, the laumontite-bearing laumontite-bearing assemblage values (log (log figure 1, pCO2-5.2 atat25°C), pC02=-5.2 2S°C)which whichhelps helpstotoaccount accountfor forthe therelatively relativelyhigh highpH pH groundwaters groundwaters in in the NSVG rocks. 11 Preliminary boron boron isotope isotope data data for for the North North Shore groundwaters poundwaters reveal 8B Preliminary reveal SB11 I1 Typical SB values ranging from +21(Ca-Cl brine) to to +45.5. Typical 6B values for crystalline rock brines and and sedimentary sedimentary sources sources are arewell wellbelow below +20 (Barth, and non-marine brines (Barth, 1993). 1993). Rocks Rocks 11 =+39.5), formed and brines derived formed in marine marine environments environments and derived from seawater seawater (SB (5B =+39.5), II however, can have however, have SB' 5B greater than +50 Thus, interaction of NSVG (Barth, 1993). 1993). Thus, +50 (Barth, rocks with could have have with seawater derived derived fluids during late stage and post rifting events could resulted in uptake of seawater derived boron during basalt weathering and hydrothermal alteration. Indeed, Indeed, NSVG NSVG rocks rocks are are variably variably enriched in boron and have concentrations concentrations as high as 33 ppm (interflow Subsequent interaction of the (interfiow sedimentary sedimentary unit). unit). Subsequent the boron-rich boron-rich alteration minerals with high pH groundwater groundwater would enhance enhance mineral dissolution, dissolution, and and help to account for the high boron-bearing gmundwaters. groundwaters. A positive linear linear correlation correlation exists exists between between dissolved dissolved bromide bromide and chloride chloride concentrations in the groundwaters (fig. (fig. 2). 2). A positive correlation between mutually mutually conservative elements such as bromide bromide and chloride chloride suggests suggests a common common source source for for these these elements. This anendendThiscan canbe beexplained explained by bythe themixing mixingand andaccompanying accompanying dilution dilution of of an member brine. brine. There There isisaanegative negativecorrelation correlationbetween between boron boron and and chloride, chloride,however, however, which is consistent with a model involving boron uptake from seawater, seawater, decoupling decoupling the the controls controls on dissolved boron from from those those of of dissolved dissolved chloride chloride and and bromide. bromide. �- Boron Boron concentrations concentrations and and isotopic isotopic composition compositionof of NSVG NSVG groundwaters, groundwaters,as aswell well as the the bromide bromide and and chloride chloride data, da@ suggest suggest aa model model involving involving seawater seawater evaporation evaporation and and as subsequent subsequentrock rockalteration. alteration. ItItisisnot notunreasonable unreasonablethat thatsuch suchaaseawater seawaterincursion incmionresulted resulted in inthe thecharacteristic characteristicmarine marineboron boronisotopic isotopicimprint imprinton onthe therocks rocksand andresidual residualbrines brinesof ofthe the rift ofofthese riftInteraction Interaction thesealtered alteredrocks rocksand andbrines brineswith withmodern modem groundwater groundwatersystems syaemsresult result ininthe thedistinctive ditinctivenature natureof ofthe theNorth NorthShore Shoregroundwaters. groundwaters. Figure Figure1 I 20 Figure Figure22 18 // 2 16 14 10 'C t12 6 E a a 108 6 Ca-Cl brine 6 0 C 4 0 2 pg 0 0 0 -6 -5 -4 log aSiO2(aq) -3 -2 0 200 400 600 000 '000 1200 Cl (ppm) References References Barth, Barth,S., S.,1993, 1993,Boron BoronIsotope Isotope Variations Variations in Nature: Nature: a Synthesis. Geol GeolRundsch Rumkch v.82 v.82 p.640-652. p.640-652. Schmidt, PatternsofofLow-grade Low-gradeMetamorphism Metamorphismininthe the 1993,Regional Regionaland andLocal Patterns Schmidt,S.Th., S-Th.,1993, North N o dShore ShoreVolcanic VolcanicGroup, Group,Minnesota, Mimeso@USA. USA.Journ. JournMetamorphic MetamorphicGeoL Geol.v.11 v.11 p.401-414. p.401-414. STS STSConsultants ConsultantsReport Report (1995) (1995) Evaluation Evaluation of of boron boron impacted impacted wells. wells. To ToLTV LTVSteel Steel Mining Company. Mining Company. 2 1400 �A SEISMIC STFWTIGRAPHIC STRATIGRAPHIC STUDY OF WESTERN LAKE LAKE SUPERIOR SUPERIOR ANDERSON, Ken A., and WATTRUS, Nigel Ken A., and WATRUS, Nigel J., Large Large Lakes Lakes Observatory Observatory and and Department of of Geology, Geology, University of of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812, Depahnent and nwattrus@d.umn.edu nwatt~s@d.umn.edu knebe@d.umn.edu and profiles were collected Approximately 1000 I000 km of high high resolution resolution seismic profiles collected in in the the third of Lake Superior during three cruises in the summer of Of 1996. 1996. The western third The study study from Grand Portage, Minnesota area extends from Duluth, Minnesota to a line running tlom Minnesota to Houghton, Michigan. The The data data were were acquired acquiredwith with an an ORE ORE Geopulse Geopulse system system and and for later later processing processing with with the the Seismic UNIX software software system (Cohen digitally recorded for Stockwell, 1996). Post enhancement and Stockwell, Post acquisition acquisition processing processing of the data permits the enhancement of subtle features not visible visible in paper paper sections. sections. The The profiles profiles are are being being studied studied to to identify identify describe seismic seismic reflectors reflectorswithin withinthe thewestern westernbasin basinof ofLake LakeSuperior. Superior. The and describe interpreted profiles are are then then correlated correlated with with several several cores cores collected collected during previous mterpreted cruises In in th~s this part crulses parl of the lake. lake. are commonly commonly obsewed observedthroughout throughoutthe thebasin. basin. Each Four reflectors are Each has has a features in a representative representative distinct acoustic signature and can be correlated with features 1)) Scholz (1985). (1985). The first section (Figure I of Lake Superior sediments described by Schok strong and and continuous continuous and and is is associated associatedwith withthe thelake lakefloor. floor. The second reflector is strong strong, wavy wavy character characterwith withdiscernible discernibleinternal intemal reflections. reflections. This reflector has aa strong, discontinuous reflector is correlated correlated with with the the varved varved clay clay horizons. horizons. The third reflector reflector discontinuous acoustic acoustic character which which is correlative with with the the till horizon has a strong, discontinuous described by Scholz (1985). The Thefourth fourthreflector reflectorisisaastrong, strong,hard hardreflector. reflector. It's irregular surface and the presence of scattered channels throughout associate it with bedrock. bedrock. cover for for Western Western Lake Lake Superior Superior generated generatedfrom from this this data data: A map of sediment cover of the the basin basin where where sediment sedimentfocusing focusing is isoccurring. occurring. Acoustic Acoustic refle&we* reflectivity shows regions of (in conjunction with with data from from coring) coring) is used to to produce a distribution distribution map of sediment sediment type in the basin. This This information informationwill will further further our our understanding understanding of circulation circulation dynamics to improve sampling strategies for future within the western basin and will help to investigations sediment binding investigations of sediment binding contaminants. contaminants. 3 �Idealized Stratigraphic Stratigraphic Section Section of Idealized Lake Superior Sediments Sediments Lake Thickness (cm) {cm) Brown Brown clayey clayey sediment sediment Gray Clay Clay 10-350 15-400 Gray Gray Varves Vawes 257-900 Varves Red Varves Red 91-300 Red Clay Red Clay 100-3000 Brown Sand Brown Sand (After Scholz, 1985) Tilt Till Figure 1 References References cited cited J.K. and CWP/SU: Seismic Unix Cohen, J.K. and Stockwell, Jr. J. W., 1996, CWPJSU: Unix Release Release29: aa free free package for seismic research and processing, Center for Wave Phenomena, package Phenomena, Colorado Colorado School Schoolof of Mines. Mines. Scholz, C.A., and sedimentation sedimentation rates rates in the the western western arm of of C.A., 1985, 1985, Sediment distribution and Lake geochronology, Lake Superior Superiorusing using3.5 3.5 kHz kHzseismic seismicreflection reflectionprofiles profilesand and210Pb 210Pbgeochronology, M.S. thesis, thesis, 129 129pages. pages. 4 �INTERACTION AAVIRGINIA FORMATION XENOLLTR I N T E R A ~BETWEEN BEWEEN ON VIRGINIA FORMATION XENOLITH AND MARC MAGMA AT THE THE BABBITT -NI AND MARC MAGMA AT BABBJTF aCu-NI DEPOSIT, DULUTH COMPLEX, MN. DEPOSIT, DULUTH COMPLEX, MN. Arcuri, kcuri, T., T., and andRipley, Ripley, B. E. M., M., Department Department of Geological Geological Sciences, Sciences, Indiana IndianaUniversity, University, Bloomington, IN47405 47405 Bloomingtou,IN ., Previous Previouswork workon on the the Duluth Duluth Complex, Complex, MN, has shown shown the importance importanceof of the the interaction interaction between betweenVirginia VirginiaFormation Formationxenoliths xenolithsand andtholeiitic tholeiiticmagmas magmas in inthe theformation formationof ofsulfide sulfidemineralization. minerdimtion. In In this thisstudy studythe theeffects effectsof ofaasingle singlexenolith xenolithon onthe thesurrounding sumundiugigneous igneousrocks rocks were were examined examined from fromdrill &ill core factor coreininorder ordertotoassess: assess:I)1)ififininsitu situintroduction introductionofofsedimentary sedimenkuysulfur sulfurwas wasan animportant impo-t factorininthe the formation formationof ofthe themassive massivesulfide sulfidelayer layeratatthe thetop topof ofthe thexenolith, xenolith,2) 2)ifif aa flow flowpath pathof ofaapartial partialmelt meltderived derived from the xenolith can be determined from major element gradients, 3) if sulfur and oxygenisotopic isotopic from the xenolith can be determined from major element gradients, 3) if sulfur andoxygen gradientswere werepreserved preservedatatthe thexenolith xenolithcontacts, contacts,and andififso soto tomodel modeltheir theirorigins originsusing usingmass massbalance balanceand and gradients diffusion diffusioncalculations. calculations. Sulfur m yfrom fmrn12.4 12.4toto Sulfurisotopic isotopicvalues valuesof ofdisseminated disseminatedand andlenticular lenticularpyrrhotite pymhotitein inthe thexenolith xenolithvary 17.47~with prima^^ layer to layer differences in the the protolith pmtolith(Fig. (Fig. 1). 1). 17.4%o with the the variation variation thought to reflect primary differences in The Themassive massivesulfide d d eatatthe theupper uppercontact contactofofthe thexenolith xenolithisischaracterized c h a m m i dbyby6M5 6% values valnesof of 12.0 12.0 to l2.4%. 12.4%. In Inthe theigneous ignwusrock rockabove abovethe themassive massivesulfide, suEde,6M5 6% values valuesrange range from fmrn 10.7 10.7to to 111.5%0. The.sevalues valuesare are 1.5%. These strongly stronglysuggestive suggestiveof ofaasedimentary sedimentaqsource sourcefor forthe thesulfur sulfurin in the thesulfide sulfideminerals; minerals;taken takentogether togetherwith withthe the pyrrhotite-rich nature of the sulfide the 6'S values are also consistent with an in situ origin of the pymhotite-rich nature of the sulfide 6% values are also consistent with an in sim origin of the massive massivemineralization mineralizationat atthe the xenolith xenolith border. Andrews Andrewsand andRipley Kpley (1989) (1989) detected detectedaanegative negative correlation correlationbetween betweenwhole wholerock rockSScontent contentand andFe/Mg F&g ratios ratiosof of orthopyroxene orthopyroxeneand andbiotite biotiteininVirginia Virginia Formation Formationfootwall footwallrocks. rocks. This Thisrelationship relationshipwas wasattributed attributedto tosulfur sulfurfixation fixationininthe thecountry countryrocks rocksand andthe the sulfurization of Fe-bearing silicates. The opposite relationship was observed in the xenolith from sulfurization of Fe-bearing silicates. The opposite relationship was observed in the xenolith fromcore core BBl-127, 1-127, suggesting or process suggestingthat that sulfurization sulfurizatiouof of Fe-bearing Fe-bearingsilicates silicateswas wasnot notaamaj major process and and that thatFe/Mg F a g ratios betweenoriginal ariasedimentary sedimentary ratiosof ofminerals mineralsininthe thexenolith xenolithreflect reflectdifferences differencesininbulk bulkcomposition compositionbetween layers. 6S values layers. The 6% valuesof of the theigneous ignwus rocks rocksbelow below the the xenolith xenolith are are very very different differentfrom fmrnthose thosein inthe the igneous rocksabove abovethe thexenolith, xenolith,and andrange rangefrom fmrn-2.8 -2.8toto5.2%o. 52%. ignwusrocks Oxygen Oxygenisotopic isotopicvalues valuesalso alsoshow showvery verydifferent differenttrends hcnds above aboveand and below belowthe thexenolith xenolith(Fig. (Fig.1). 1). 6'o values of of thethe xenolith vary from 9.89.8 to to 1111.77m, .7%o, with 6'*0 values xenolith vary from withthe thelowest lowestvalue d u e near near the theupper upper contact. alsO 6% values values of 6.2%0 6.2% over valnesof ofthe theoverlying overlyingigneous igneousmaterial material gradually ddecrease e c m e to nnormal o d values over a 30 30 foot foot interval. gradient muchsharper sharper8O 6l80 gradientisisfound foundatatthe thelower lowercontact, contact,with with8180 P O values values of of 5.8 to 6.3% interval.AAmuch found foundininthe theigneous igneousrocks rockswithin withina adistance distanceofofless lessthan than1.5 1.5feet. fet. Major Majorelement elementanalysis analysisofofthe thexenolith xenolithindicate indicatethat thatitithas hasundergone undergoneextensive extensivepartial partialmelting, melting, with K-and andNa-bearing Na-bearingcomponent. component.Unmetamorphosed UnmetamorphosedVirginia VirginiaFormation Formation withthe theloss lossofofaaSi-rich, Si-rich,Ktypically wt. % % Si02, Si02,whereas whereas xenoliths contain from from 45 to 50. However, However, typicallycontains containsbetween between55 55and and65 65wt. gradients in Si02 content in the igneous rocks above the xenolith that might track the movement gradients in Si02content in the igneous rocks above the xenolith that might track the movementofofaa partial detected. The partialmelt meltand andalso alsoexplain explainthe the8180 6"O gradient w e n t are are not deected. Theabsence absenceof ofSi02 Si02gradients gradientsmay maybe be related magmadue duetoto relatedto: to:1)1)relatively relativelyrapid rapidmelt meltextraction extmctionand andmovement movementinto intothe thesurrounding surroundingmagma buoyancy, buoyancy,2)2)homogenization homogenizationininthe themagma magmadue dueto toconvection, convection, 3) 3) destruction destructioncaused causedby bythermal thermal perturbations resulting from later magma pulses. Modeling of SiC)2 transport into the surrounding melt perturbations resulting from later magma pdses. ModeIing of S O 2transpo~into the surroundingmelt via viadiffusion diffusionalone aloneindicates indicatesthat thatan aninitial initialSi02 Si02gradient w e n tcould couldbe behomogenized homogenizedwithin withinaamaximum rnaximumtime time ofof10,000 interpret thethe also proffle at the toptop of of thethe xenolith as being duedue to retrograde 18C).. 10.000years. years.We We interpret 6180 profile at the xenolith as being to retrograde l80exchange exchange(i.e. (i.e.developed developedafter afterthe theextraction extractionofofaagranitic graniticmelt meltfrom fromthe thexenolith xenolithand andhomogenization homogenizationofof the enclosing magma). Diffusion modeling indicates that a retrograde oxygen isotopic the enclosing magma). Diffusion modeling indicates that a retrograde oxygen isotopicexchange exchangeprofile profile could -3 x lO 10.'cm2/sec. cm21sec. couldbe beestablished establishedininasaslittle littleasas100 100toto500 500years, years,assuming assumingan anoxygen oxygendiffusivity diffusivityofof—3 The Thevery verydifferent differentisotopic isotopicprofiles profilesdeveloped developedatatthe theupper upperand andlower lowercontacts contactsofofthe thexenolith xenolith correlate correlatewith withdistinct distinctdifferences differencesbetween betweencomposition compositionand and mineralogy mineralogy of the the igneous igneous rocks. rock. The Theupper upper unit Ti02 and Si02 contents, and Fe/Mg ratio relative to the unit below the xenolith unitisismarked markedby by.higher higher TiO, and SiO, contents, and F&z ratio relative to the unit below the xenolith (Fig. ananevolved to gabbronorite is the (Fig.2). 2).This Thisunit unitisis evol<ednorite norite-to gabbronoritethat thatis themost mostfrequently frequentlymineralized mineralidrock rocktype type ininthe thePartridge PartridgeRiver Riverintrusion. intrusion,InIncontrast contrastthe thelower lowerigneous igneousunit unitisisaamore moreprimitive primitivetroctolite hctolitewith with only oxygen and onlysparse sparsesulfide s&de mineralization. mineralization.The Thewell welldeveloped developed-oxygen andsulfur sulfurisotopic isitopicprofiles profilesininthe the 55 �gabbronorite are are indicative indicative of the preservation of at gabbronorite of aa primary primaryxenolith-magma xenolith-magmainterface. interface. Isotopic values at the lower contact interface. Geochemical data suggest that the troctolitic contact are are indicative indicative of a secondary interface. magma was was aa later laterpulse pulsethat thatmay may have have intruded intruded after sulfur and oxygen isotopic equilibrationwith with mafic magma isotopic equilibration liquids had been been established establishedin in the the xenolith. Alternatively Alternativelythe the troctolitic tmctolitic magma magma may have have delaminated delaminated aa liquidshad portion of the the Virginia VirginiaFormation Formation that that formed f o n d the base t h i i e s s of portion base of of aa magma magmachamber. chamber. Because of the thinness the troctolitic troctoliticmagma magmasheet sheetisotopic isotopicgradients gradients did not develop due to rapid m liig. the cooling. REFERENCE: REFERENCE: Andrews, hdrews, M. M. and andRipley, Ripley,E. E. M., M., 1989, 1989,Mass Mass transfer and sulfur fixation in the contact contact aureole aureoleof ofthe the Duluth Duluth Complex, Complex, Dunk DunkaRoad RoadCu-Ni Cu-Nideposit, deposit,Minnesota: Minnesota: Can. Can. Mineralogist, Mimraiogist,v. v. 27, 27, p. 293-310. 293-3 10. &'S Depth 6% and and8180 ti1*0vs vs Depth 6180 (%) 6% (%) 22 44 66 88 I2 12 10 10 14 14 \Tirzinia Formation Tioctolite_____ -5 0 5 10 20 15 6S (%) Figure Figure1.1. 6180 6"Oand andoMS 6=S values valuesthrough throughaaVirginia Virginia Formation Formation xenolith and igneous igneous rocks rocksof of the thePartridge ParhidgeRiver River Intrusion, drillcore coreB1-127. Bl-127. Inmsion,drill SIC)2 SiO, vs vs Depth Depth(ft.) (ft.) FeO FeOand andMgO MgOvs vs Depth Depth wL% wL% 30 3 0 35 35 40 40 45 45 50 SO 55 55 Ti02 Ti02vsvsDepth Depth wt.% *% wL% wL% 0 10 20 30 40 50 0 2 4 6 8 10 Figure Figwe2.2.Variations Variationsininchemical chemicalcompositions compositionsthrough throughxenolith xenolithand andsurrounding surroundingigneous igneousrocks, rocks,Babbitt Bahbinarea, area,drill drill coreBl-127. wreB1-127. 66 �THE HURONIPJT UP THE HURONIAN -- FROM FROM THE THE BOTTOM BOTTOM —- UP G. G. Bennett, Bennett, Ontario Ontario Geological Geological Survey Survey The The HuronianSupergroup Huronian supergroupis is aa sequence sequence of of Early Early Proterozoic Proterozoic sedimentary sedimentary and minor volcanic rocks, up up to to 12 12 000 000 mm thick, thick,which unconfo±mably upon which lies lies unconfonnably minor volcanic Archean Huronian belt extends Archean rocks rocks of of the the Superior Superior Province. The Huronian extends eastward, eastward, about 450 tan km along the north north shore shore of of Lake Lake Huron Huron and and into into Quebec. The The age for about Huronian Supergroup is constrained by by the the ages ages of of basal basal volcanic volcanic rocks of the Huronian rocks (2.45 Ga) Ga) and Nipissing (2.45 Nipissing intrusions intrusions (2.2 (2.2 Ga). Ga). The Huronian HuronianSupergroup Supergroup subdivided, ascending order,into intothe the Elliot Elliot The is is subdivided, ininascending order, Lake, the Lake, the the Quirke and the the Cobalt Lake, the Hough Hough Lake, Quirke Lake Lake and CobaltGroups. Groups. The The Elliot Elliot Lake Lake Group Group contains contains the theonly onlyvolcanic volcanicrocks rocksand and important importanturanium uranium deposits. deposits. The abundanceofofdetrital detrital pyrite Matinenda The abundance pyrite and and uraninite uraninitein inthe the MatinendaFormation, Formation, and and the general lower, three Huronian the general lack lack of ofhematite hematitein inrocks rocksof o fthe the lower-three Huroniangroups, groups, points to points toaareducing reducingatmosphere atmosphere during during early earlyHuronian Huronian sedimentation. sedimentation. The The appearance of hematite hematite in in the marksthe the accumulation accumulation ooff free free appearance of theCobalt Cobalt Group Group marks oxygen in the Earth's atmosphere(Roscoe, 1968).Studies studies of oxygen in the Earth's atmosphere(Roscoe, 1968). of Huronian Huronian paleosols paleosols have also also provided valuable insight into into the the evolution evolution of of the the Earth's Earth's have atmosphere (References atmosphere (References in in Bennett Bennett et et al.l9Sl). al-1991). The 1-Juronian volcanicrocks, rocks,the theEast EastBull BullLake Lake Suite(EBLS) Suite(EBLS) of of layered layered mafic The Huronian volcanic mafic intrusions, intrusions, and and the the dikes dikes of of the the Matatchewan—Hearst Matatchewan-Hearst swarm swarm are are an an essentially essentially coeval(circa 2.45 Ga) igneous suite (Peck et al., al., 1995; 1995; Heaman, Heaman, 1997) (Peck et 1997) emplaced near The distribution distribution of EELS near the the base base of of the the Huronian Supergroup. The EBLS intrusions intrusions may form The northern northern group includes form two two approximately approximately linear arrays. The includes the the Agnew Lake A second Agnew Lake and and the the East East Bull Bull Lake Lake intrusions. intrusions. A second group group of of EELS EBLS intrusions west end end of of the the SudburyIgneous Sudbury Igneous Complex, intrusions extends extends from from near the west Complex, in in aa southwest direction, along the the base bise of of the the Huronian Huronian Supergroup. Supergroup. These These two two southwest groups magma chambers chambers emplaced emplaced under under two groups of of EELS EBLS intrusions intrusions represent magma two rift rift segments which joined joined just Sudbury Complex. segments which justwest westof ofthe thepresent present SudburyIgneous Igneous Complex. The proposed proposednorthern northern rift rift segment, The segment, which which contained contained the the Livingstone LivingstoneCreek Creek Formation andthe thevolcanic volcanicrocks rocksof of the the Thessalon Thessalon Formation Formationofofthe the Sault Sault Ste. Formation and Ste. Marie— ElliotLake Lakearea, area,has hasbeen beendeeply deeplyeroded, eroded,with withdeeper deepererosion erosion (i.e. (i.e. Marie- Elliot greater uplift) in The southern southern rift rift segment, segment, which which contains contains greater uplift) in the east. The volcanic much intercalated intercalated sandstone volcanic rock rock with with pillow pillow structures and much sandstone and and wacke wacke (Card, 1978) was was probably probably at a a much much lower lower topographic topographic level level during (Card, 1978) during erosion erosion of of the northern northern rift volcanic sequences sequences may may correspond correspond to the rift segment. These volcanic the "seaward dipping reflectors" margins. "seaward dipping reflectors" of of modern continental continental margins. Following was Following rifting, rifting,there there wascontinued continuederosion erosionand and an an eventual eventualsubsidence subsidence as as indicated and uraniferous uraniferous conglomerates conglomerates of indicated by the the deposition deposition of the arenites and of the Matinenda Formation. Formation. The Theturbidites turbidites of Formation which which overlie overlie the ~atinenda ofthe theMcKim McKim Formation - -- - the along aa foundering the Matinenda Matinenda Formation, Formation, suggest suaaest marine marine encroachment encroachment alona founderina continental margin. continental margin. It isissuggested Huronian It suggestedhere herethat thata a Huronian continental continentalflood floodbasalt basaltprovince provincemay may oncehave haveexisted existednorth northofofthe thepresent presentHuronian Huronian belt. so,at at least least the once belt. IfIfso, the southern portion of CFBP, must must have have been been eroded eroded prior to southern of this proposed CFBP, to the the deposition of the since the the latter latter has has a a mainly mainly granitic deposition the Matinenda Formation, since provinance. The sub—Matinenda disconformity (Bennett (Bennett et et al., al., 1991) marks this provinance. The sub-Matinenda disconformity potentially long potentially long erosion erosion interval. interval. Heaman(1997) mantle plume plume related, large large igneous Heaman(1997) provides provides evidence for a mantle igneous province at intrusive rocks rocks noted noted above. The 2 . 4 5 Ga Ga which includes includes the intrusive The model model province at 2.45 for the described here, here, although although arrived arrived at for the Elliot ElliotLake LakeGroup Group described atindependently, independently, supports of the supports many many of theconclusions conclusionsofofHeaman(l997). Heaman(1997). 7 �Following Following rifting rifting and and early early Huronian Huronian magmatic magmatic events, events, post—volcanic post-volcanic Huronian Huronian sediments were were deposited, deposited, either either along along aa passive passive continental continental margin, margin, or or (less (less sediments likely) within a continually sinking, sinking, intracratonic intracratonic basin. basin. Thecyclic Thecyclic likely) withina sedimentation groups above above the Elliot Elliot Lake Lake Group sedimentation of of each each of of the the three Huronian groups Group are and retreat retreat of of Huronian Huronian ice ice are generally generally believed to to record the advance and sheets.Each cycle cycle begins begins with with aa mainly mainly diamictite diamictite sequence(glacia1 sequence (glacial advance),• sheets: Each advance), overlain or carbonate carbonate (glacial overlain by by aa marine marine sequence sequence of of mudstones, siltstone or (glacial loading by a relatively thick thick arenite arenite loading and and marine marine transgression), transgression), followed followed by sequence . The sequence (interglacial (interglacialoutwash) outwash). The presence presence of of drop—stones drop-stones in in some some laminated units units of of all all three three groups supports the glaciogenic laminated glaciogenic model model by indicating the the presence presence of of floating floating ice ice (Roscoe, (Roscoe,1968). 1968). indicating The was variably variably deformed deformedand andfaulted faulted during during several The entire entireHuronian Huronian sequence sequence was several deformational of Nipissing deformational events, events,some some of ofwhich which preceded preceded the theemplacement emplacement of Nipissing sills 2.2 sillsatat 2.2Ga Ga(Card, (Card,1978). 1978). - - References References Bennett, Bennett, G., J.A. 1991. The The Huronian Euronian Supergroup Supergroup G., Dressler, Dressier, B.C. B.O. and Robertson, J .A. 1991. and and Associated Associated Intrusive Intrusive Rocks. Rocks. in in Geology Geology of Ontario Geological Geological of Ontario. Ontario. Ontario Survey, Survey, Special SpecialVolume Volume 4, 4, p. p. Card, Card, 633—641. 633-641. K.D. of the the Sudbury-Manitoulin Sudbury-Manitoulinarea, area,districts districts ofofSudbury Sudbury K.D. 1978. 1978. Geology Geology of and and Manitoulin; Manitoulin; Ontario Ontario Geological Geological Survey, Survey, Report Report 166, 166, 238p. 238p. Heaman, Heaman, L. L. M. M. 1997. 1997. Global Global mafic mafic magmatism magmatism at at 2.45 2.45 Ga: Ga: Remnants Remnants of of an an ancient ancient large large igneous igneous province?; province?; Geology, Geology, Vol. Vol. 25, 25, no. no. 4, 4, p. 299—302. 299-302. Peck, Peck, D.C., D.C., James, James, R.S., R.S., chubb, Chubb, P.T., P.T., Prevec, Prevec, S.A. S.A. and andICeays, Keays, R.R. R.R. 1995. 1995. Geology, Geology, Metallogeny Metallogeny and and Petrogenesis Petrogenesis of of the the East East Bull Bull Lake Lake Intrusion, Intrusion, Ontario; Ontario; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5929, 5929, ll7p. 117p. Roscoe, uraniferous conglomerates; Geological Geological Roscoe, S.M. S.M. 1969. 1969. Huronian Huronian rocks rocks and and uraniferous Survey Survey of of Canada, Canada, Paper Paper68—40, 68-40, 2OSp. 205p. - 8 �NATIVE NATIVE COPPER COPPER PRECIPITATION PRECIPITATION BY BYFLUID-MIXING, FLUID-MIXING, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN BORNHORST, Departmentof of Geological GeologicalEngineering Engineeringand andSciences, Sciences,Michigan Michigan BORNHORST,Theodore TheodoreI.J. Department Technological University, Houghton, MI 49931, tjbomho@mtu.edu; and Technological Houghton, MI 49931. tibornho@mtu.edu: and WOODRUFF, U.S. Geological Survey, WOODRUFF, Laurel G., G., U. s.Geological survey,St. St. Paul, Paul, MN MN 55112. 55112. woodruff@usgs.gov. woodruff@usgs.gov. Large billion kg kg of of refmed refined copper copperextracted) extracted)are arehosted hostedby bybrecciated brecciated Largenative nativecopper copperdeposits deposits(about (about 55 billion and andamygdaloidal amygdaloidaltops topsof of basalt basalt lava lava flows flows and and interfiow interflow conglomerates conglomeratesin inthe the1.1 1.1Ga GaMid-continent Mid-continent rift riftsystem systemalong alongthe theKeweenaw Keweenaw Peninsula, Michigan. AAsuite suiteof ofsecondary secondaryminerals mineralsparagenetically paragenetically associated associatedwith withthe thedeposition depositionof of native native copper copper includes includescalcite, calcite, epidote, epidote,quartz, quartz, and andprehnite, prehnite, in in addition numberof of other other low low temperature temperature minerals. Most Mostgenetic geneticmodels modelsfor forthe thenative nativecopper copper additionto toaanumber deposits from rocks deeper deeperwithin withinthe therift rift(e.g., (e.g.,White, White,1968; 1968;Bornhorst, Bomhors 1997). depositsderive deriveore ore fluids fluids fromrocks 1997). Mechanisms Mechanismsfor forprecipitation precipitationare aremore moreproblematic; problematic;proposed proposedmechanisms mechanismsinclude includecooling, cooling,fluidfluidrock rockinteraction interactionvia viametamorphic metamorphic reactions and fluid mixing. Cooling Coolingalone alonecannot cannotaccount accountfor fornative native copper complexedas asCu* Of (copper (1° (copper chloride), chloride), but precipitated as CuO copperprecipitation precipitationas as copper is likely complexed (native (nativecopper). copper).High Highwater/rock waterlrockratios ratiosininthe theore orezones zoneslimit limitthe theeffectiveness effectivenessof of fluid-rock fluid-rock interaction bodies. Wells interactionin inaccounting accountingfor for the the total mass of native copper found concentrated in ore bodies. Wells (1925) (1925)first firstsuggested suggestedmixing mixingof of dilute dilutewaters waters with with ore-bearing ore-bearingfluids fluidsas asaa mechanism mechanismfor fornative native copper 60years yearslater, later,Richards Richardsand andSpooner Spooner(1986) (1986) copperprecipitation precipitationbased basedon onchemical chemicalprinciples. principles. Some Some60 revived revivedthe theidea, idea,and, and,based basedon onfluid fluid inclusion inclusion studies, studies, suggested suggestedthe the mixing mixingof oflow-temperature, low-temperature,lowlowsalinity native copper copper precipitation. precipitation. Based salinityfluids fluidswith with ore-fluids ore-fluids as as a mechanism for native Based on on these these publications publicationsand andon onaareinterpretation reinterpretationof of stable stableisotope isotopedata dataof of Livnat Livnat(1983), (1983). Bomhorst Bornhorst(1992) (1992) proposed that"mixing "mixingofofore orefluids fluidswith withresident resident reduced reducedsemi-stratified semi-stratifiedfluids fluidsmay mayhave havebeen beenan an proposedthat important importantmechanism mechanismfor forprecipitation precipitation of native copper." Oxidized Oxidizedmeteoric meteoricwaters watersseem seemto tobe be eliminated eliminatedasasaapossible possibleend-member end-memberfluid fluidas asprecipitation precipitationof ofnative nativecopper copperrequires requiresreduction reductionofofthe the ore-fluid. ore-fluid. In Inorder ordertototest testthe thehypothesis hypothesis of fluid-mixing, fluid-mixing, aa suite suiteof of calcite calcitesamples sampleswas was collected collected for for12 12 km deposit. Samples kmalong alongthe thestrike strikeof ofthe theKearsarge Kearsarge deposit, the largest basalt-hosted basalt-hosted deposit. Sampleswere were from from mine range of drillcore. core. Calcites Calcitesfrom fromthe theKearsarge Kearsargedeposit deposithave haveaarange of6"O 8"0 from from20.1 20.1toto minerock rockpiles pilesand anddrill 11.3 %O and and8'3C 5° from from-1.7 -1.7 to to -3.1 -3.1 %, %o, based based on on 39 39analyses analyses from fromthis thisstudy studyand and16 16from fromLivnat Livnat 11.3 % (1983). (1983). The Thetemperature temperatureofofcalcite calcite(and (andaccompanying accompanyingnative nativecopper) copper)deposition depositionisisconstrained constrainedby by the minerals,alsO S"0 values values for for coexisting coexisting mineral mineral pairs pairs suggest suggestan anaverage average theassemblage assemblageofofgangue gangueminerals; temperature of about 215°C (Livnat, 1983). (215°q,calculated calculated 6O inin At this this temperature temperature (215¡C) 8"0_ temperature of about 215C (Livnat, 1983). At equilibrium +11.5%o %O (59 (59% %between between3.8 3.8and and5.8 5.8%o) %o) and andcalculated calculated equilibriumwith withcalcite calciteranges rangesfrom from+3.5 +3.5toto+11.5 rçrangesfmm-4to-l%o(71%between4.75and...3%0). 8°C ranges from -4 to -1 %o (71 % between -1.75 and -3 %). ForthesefluidsçandpHis For these fluids f,,, and p H is predicted to be an unimportant source of variation to account for Vc. predicted unimportant source of variation to account for 8 " To To~explain explain ~ the thedata databy byaa uniform assumed8'08O of of +5.0 % %O requires a temperature variation uniform ore ore fluid fluid with assumed +5.O requires a temDerature variationofof130 130toto260°C; 260¡Caa similar carbon in similartemperature temperature range range is is required required for an an assumed assumed uniform unifo&carbon inthe thefluid. fluid. The Thegangue gangue mineral mineralassemblage assemblageisisrather rathersimilar similarthroughout throughoutthe thedeposit depositand anddoes doesnot notsupport supportsuch suchaalarge largerange rangeinin temperature. lack of of correlation contlation between between8"'0._ 8"O and cannot Inaddition, addition, the lack and6'3C< 8'3~.,.,, cannotbebeexplained explainedby by temperature. In temperature data may maybe beinterpreted interpretedby bychanging changingtemperature temperatureand and However, the the data temperaturevariation variationalone. alone. However, mixing mixing of oftwo twoorormore morefluids. fluids. This This model model can can also alsoexplain explain the thewide widespread spreadininW'O 8"Ofor forquartz quartzasas reported Livnat(1983). (1983).The Theend-member end-memberore orefluid fluid(represented (representedby bymost mostofofthe thedata) data)has hasaa 8"0,,,,, reportedby byLivnat 9 �13cm ( - 8 " ~of~of ) about+5+5and and-2-2%c, %o, respectively respectively and is consistent with and '3C (—6'3C) about with derivation from the riftbewell welldefined, defined, but but has has 6"omand 60CQ S^Cm of of greater greater filling basalt Theother otherfluid fluidcannot cannotbe basalt section. section. The than + +11 11and andless lessthan than -3.5 -3.5 %4 %o,respectively. respectively. This fluid is interpreted as as water water resident resident at at the site of ore deposition. deposition. The Thedata datapresented presentedhere heresupport support the the hypothesis hypothesis that fluid-mixing fluid-mixing played a role role in in precipitation precipitation of native copper wpper in in the theKeweewan KeweewanPeninsula. Peninsula. Additional Additional studies studies are are in progress to further further test the the fluid-mixing fluid-mixinghypothesis. hypothesis. References References Bomhorst,Li, TJ.,1992, 1992, overview theKeweenaw KeweenawPeninsula Peninsulanative nativecopper copperdisthct, district,Michigan: Michigan: Bomhorst AnAn overview ofofthe Society GuidebookSeries, Series,v. v. 13, 13,p. p. 33-62. 33-62. Societyof of Economic EconomicGeologists GeologistsGuidebook Bomhorst, Bornhorst, TJ., TJ.,1997, 1997,Tectonic Tectoniccontext contextof ofnative nativecopper copperdeposits deposits of the North American American Midcontinent Special Paper 312, MidcontinentRift Rift System: System: Geological Geological Society Society of America Special 312, p. 127-136. 127-136. Livnat, 1983,Metamorphism Metamorphismand and copper coppermineralization mineralization of the Portage Portage Lake Lake Lava Lava Series, Series, Livnat, A., 1983, northern northern Michigan Michigan (Ph.D. (Ph.D.dissertation): dissertation): Ann Arbor, University of Michigan, 292p. 292p. Richards, J.P., and Spooner, high temperature, temperature, Spooner, E.T.C., E.T.C., 1986, 1986,Native Native copper copper deposition by mixing of high high cool dilute dilute groundwaters, groundwaters, high salinity salinity fluids fluids of possible possible magmatic association with cool Keweenaw Peninsula, Michigan: Geological Society of America Abstracts with Pmgrams, Keweenaw Peninsula, Geological Programs, v. v. 18, 18, p.730. p. 730. Wells, ltC., R.C,1925, 1925,Chemistiy Chemistryofofdeposition depositionofofnative nativecopper copperfrom fromascending ascendingsolutions: solutions:U.S. U.S. Geological Survey Bulletin 778.71~. 778, 'lip. Geological Survey 1968,The Thenative-copper native-copper deposits deposits of northern Michigan, in Ridge, J.D., J.D., ed., ed., Ore Ore White, W.S., 1968, White, deposits of of the the United United States States 1933-1967 1933-1967 (the (the Graton Sales volume): American Institute Institute of deposits Mining, Mining, Metallurgical Metallurgicaland andPetroleum PetroleumEngineering, Engineering,New New York, York, p. 303-325. 10 �THE DIAMONDIFEROUS SIX-PAK SIX-PAK ULTRAMAFIC ULTRAMAFIC LAMPROPHYRE LAMPROPHYRE DIATREME, KENOSHA, WISCONSIN, U.S.A. CARLSON, CARLSON, S. M., Ashton Mining Mining of of Canada Canada Inc., Vancouver, B.C., Canada Canada ADAMS, U. G. W., The The Doe Doe Run Company, Viburnum, MO, USA (former Chief Geologist Geologist for for Crystal Crystal Exploration Inc.) Diamond Diamond exploration exploration in in the the midwestern midwestern United States States began began with the the discovery Lake Ellen Ellen discovery of the Lake kimberlite kimberlite in in 1971. 1971. Early Early exploration exploration focused focused on on the the Upper Upper Peninsula Peninsula of of Michigan, Michigan, resulting resulting in in the the discovery of over over 20 20 kimberlite kimberlite bodies bodies in Iron, Iron, Dickinson Dickinson and and Menominee Menominee counties. counties. These These post-Ordovician post-Ordovician intrusives intrusivesrange range in fromnarrow narrow dikes dikes to to diatremes diatremes in in excess of 20 20 acres. acres. Diamonds are present present in in many of of the the Michigan Michigan in size size from kimberlites, but but to to date date no no economic economicdeposits depositshave havebeen been identified. identified. Further Furtherregional regional exploration explorationidentified identified concentrations concentrations of fresh fresh "kimberlitic" in glacial glacial "kimberiitic" indicator indicatorminerals mineralsin tilts tills in in southeastern southeasternWisconsin, Wisconsin, where at least least six six historic historic diamond diamond finds finds occurred, occurred, including including the the 21.5 21.5 carat carat "Theresa" major diamond diamond exploration exploration companies companies have have been active in "Theresa" stone. stone. Although Although several major in southeastern southeastern Wisconsin, the Six-Pak Six-Pak diatreme, diatreme, discovered by the Crystal Exploration-Ashton Exploration-Ashton Mining Joint Venture, Venture, is is the the only only pipe pipe ever everreported reportedininthis thisregion. region. Exploration Inc. carried out sporadic exploration Crystal Exploration exploration in in southeast southeast Wisconsin Wisconsin from from the the mid mid 1980's, and in in joint joint venture venture with with Ashton Ashton Mining Mining of Canada Canada Inc. Inc. from from 1992 1992 through through 1995. 1995. Target Target identification identification concentrated on kimberlitic kimberlitic indicator indicator mineral mineral anomalies and data data from from public publicairborne airbornemagnetic magneticsurveys. surveys. In In early 1994, 1994, Crystal Crystal Exploration Exploration acquired a little-known little-known airborne magnetic survey which had been been flown flownand and later donated to Case by a major oil company conducting base metal Case Western Western Reserve University University by metal exploration. exploration. From the new data, three "kintherlite-style" magnetic targets were recognized and ground checked. Two data, three "kimberlite-style" targets were recognized and ground checked. Twotargets targets were eliminated as cultural responses. eliminated as cultural responses. During During the spring and early summer summer of 1994, 1994,land landacquisition acquisition and and detailed ground magnetic surveys were completed completed on on the the third third target target and and in late August of 1994, 1994, the the Six-Pak Six-Pak diatreme intersectedininthe thefirst first of of eight eightexploration explorationdrill drill holes. diatreme was was intersected The The Six-Pak Six-Pak diatreme diatreme is is approximately 50 acres in size and is located within the the outskirts outskirtsof ofKenosha, Kenosha, Wisconsin. Reverse Reversecirculation circulationwith with selective selective core drilling was used to test the target. Between Betweenone oneand andseven, seven, one-ton samples of cuttings were recovered from each each hole. hole. A recovered from Aconcentrate concentrate was was generated generated from fromeach eachsample, sample, and and splits splitswere were submitted submittedto to Ashton Ashton Mining's Mining's laboratory laboratory facility facility in in Perth, Perth, Australia for for caustic causticfusion fusionprocessing. processing. The The remainder remainder of of this this"mini-bulk" "mini-bulk"sample sample was was processed processed through through Ashton's Ashton's one-tonne-per-hour one-tonne-per-hour dense densemedia media separation separationplant plant in inCrystal CrystalFalls, Falls,Michigan. Michigan. The upper upper portions portions of of the the diatreme diatreme are are complex, complex, containing containing sequences of fossiliferous fossiliferous dolostone dolostone and and red, bedded breccias at at depth. depth. The to80 80feet feetinintl1ickness thickness bedded arenites arenites which which grade grade into ultramafic breccias The arenites arenites range range up up to and minerals. They may represent andcontain containsparse sparsevolcaniclastic volcaniclastic fragments and indicator minerals. represent true true crater-facies crater-faciesrocks rocks or, after diatreme diatreme emplacement emplacement or, along alongwith withthe theminor minorcarbonate carbonaterocks, rocks,they they may may have formed formed long after Beneath rocks, the Six-Pak diatreme consists of fairly uniform uniform ultramafic ultramafic breccias breccias Beneath these these sedimentary sedimentary rocks, composed composedprimarily primarilyof ofserpentine, serpentine,calcite, calcite, mica, and various opaques; fresh olivine is is not not present, present, and and melilite meliliteor or pseudomorphs after melilite have not been recognized. Angular sedimentary xenoliths are common, ranging up pseudomorphs after melilite have not been Angular sedimentary xenoliths are common, ranging up to to five five feet feet across. across. Basement Basementxenoliths xenolithsare areextremely extremelyrare. rare. "Autolithic" "Autolithic" fragments fragmentsare arepresent presentininmany manysamples, samples, but but they they are aredifficult difficultto to characterize, characterize,making facies determinations determinations uncertain. Much Muchof ofthe the"diatreme" "diatreme"appears appearstoto be be hypabyssal hypabyssalin incharacter. character. many similarities similaritiesbetween between this this Classificationof of the the Six-Pak Six-Pak diatreme diatreme is not straightforward, as there are many Classification body body and and other other rock rocktypes typessuch suchasaskiinberlites kimberlites and andlamproites. lamproites. However, However, groundmass groundmass mica and and spinet spinel compositional trends are are inconsistent inconsistent with with both both kimberlites kimberlites and andtamproites. lamproites. The Six-Pak Six-Pak diatreme diatreme is is best best classified (Rock, 1991) 1991) or or a "melnoite" classified as an an ultramafic ultramafic larnprophyre lamprophyre (Rock, "melnoite" using using terminology terminology recommended recommended by Mitchell Mitchell(1994). (1994). ii �recovered from from processed processed concentrates concentrates include includethe thetypical typical"kimberlitic" "kimberlitic" indicator indicator Heavy mineral species recovered Cr-pyrope, low-Cr pyrope, pyrope, Cr-diopside, Cr-diopside, picroilmenite, picroilmenite,Cr-spinel Cr-spine!and andzircon. zircon. Apatite, rutile, minerals Cr-pyrope, mtile, amphibole, amphibole, barite and and celestite present, along along with with a variety of sulphide pyrite, galena and sulphide minerals minerals including pyrite, barite celestite are also present, millerite. The through red, red, and and exhibit exhibitlate-stage late-stage etching etching thought thought TheCr-pyrope Cr-pyrope garnet garnetsrange rangeinincolor colorfrom frompurple purplethrough to be These garnets garnet are are quite quite common common in in the the heavy heavy mineral mineral be produced produced by byinteractions interactions with with groundwater. groundwater. These concentrates, and contain up to to 6.5 6.5 wt% Cr203; Cr203; they are believed to be derived from garnet-bearing garnet-bearing peridotites. No subcalcic 10" varieties have been identified. subcalcic"G "G10" identified. Orange low-Cr pyrope is also common common in in Six-Pak Six-Pak concentrates, concentrates, often strongly strongly etched etched and and skeletal skeletalinin appearance with with deep deep corrosion corrosion sculpture sculptureand andinternal internaldecomposition decompositionchannels. channels. The The average average MgO MgO content content of of appearance these grains is 19.1 wt%, wt%, and andthe therange rangeisisbetween between13.9 13.9wt% wt%and and20.6 20.6wt%. wt%.Both BothCr203 Cr203 and and Ti02 Ti02 are are typically than 1.0 wt%. Most Most of of these these garnet garnetsare areprobably probablyderived derivedfrom from the the Cr-poor Cr-poor megacryst megacryst suite, although the less than lower MgO values found in in some somegrains grainssuggest suggestthat thatminor minoreclogitic eclogiticand andgranulitic granuliticgarnets garnet may may also also be bepresent present Cr-diopside is rare, appearing as as emerald-green emerald-green anhedral anhedralfragments. fragments. The diopsides are typically diopsides are typically coated coated with orange-white reaction products products and exhibit exhibit classic classic"cockscomb" "cockscomb" resorption resorptionmorphologies. morphologies. Green Green orange-white reaction amphibole is common, common, and and whereas whereas some some of of these these grains may be crustal, crustal, most are are probably probably derived derived from from amphibole modally-metasomatizedmantle mantlerocks. rocks. These These amphiboles amphibolescontain containup uptoto3.0 3.0wt% wt%Cr203 Cr203 and some are found as modally-metasomatized with purple purpleCr-pyrope Cr-pyropegarnets. garnet. mineral pairs with Picrojlmenjte Six-Pak concentrates. concentrates. It occurs occurs as asanhedral anhedral Picroilmenite is one of the most abundant minerals in the Six-Pak fragments with leucoxene reaction reactioncoatings coatingsand andcontains containsbetween between3.7 3.7wt% wt%and and9.8 9.8wt% wt%MgO. MgO. These These low low MgO MgO values, coupled coupled with with extremely extremely low low Cr203 Cr203 (<0.2 wt%) evidence that that the Six-Pak wt%) are supplementary supplementary evidence Six-Pak is is an an values, ultramafic lamprophyre, lamprophyre, not an archetypal kimberlite. kimberlite. spinels are are present present in in the the heavy heavy mineral mineralconcentrates. concentrates. Some are reasonably Cr-rich, with up to Various spinels wl% Cr203 Cr203 plus A12O3. Other spinels include magnetite and titanomagnetite. 58 wt% plus appreciable appreciable MgO and A1203. Coarse honey-yellow honey-yellowto to orange-brown orange-brownzircon zirconcrystals crystalsare arequite quitecommon. common. These grains are typically subhedral, and and are are mantled mantledby by fine-grained fine-grainedreaction reactionproducts, products,possibly possiblybaddeleyite. baddeleyite. A A date of anhedral, rarely subhedral, from these these zircons zirconsusing usingU/Pb U/Pbtechniques techniques(Ashton (AshtonMilling, Mining unpublished unpublished date). data). This 686 MY has been obtained from This Silurian carbonates; however, however, the age may may represent representaa is an unrealistic emplacement age as the diatreme intruded Silurian significant metasomatic significant metasomatic event event in in the the underlying underlyingmantle. mantle. Importantly,the the Six-Pak numeroussmall small diamonds diamonds have have been Importantly, Six-Pak lamprophyre lamprophyre isis diamondiferous; diamondiferous; numerous been recovered through caustic caustic fusion fusion techniques. techniques. Most Most diamonds diamonds are sharp-edged sharp-edged octahedra or macles, macles, some some showing intricate surficial surficial patterns including growth plates and trigons. trigons. Six-Pak does not not contain containeconomic economic of the large historic drift diamonds. diamonds. concentrations of diamonds, diamonds, and is unlikely to be the source ofthe The discovery of of the Six-Pak diatreme is is very very significant, significant, as as itit is the the first first recorded recorded mantle-sourced mantle-sourced Six-Pak diatreme diatreme to be be identified identified in in the thesoutheastern southeasternWisconsin Wisconsin region. region. The diatreme diatreme is also an enigma enigma as itit raises raises numerous questions regarding the the existence of of other other pipes pipes in in the the area and their economic economic potential. Do the Do the large large Wisconsin "drift" "drift" diamonds diamondshave haveaalocal localsource, source,ororare arethey theyindeed indeedderived derivedfrom fromrocks rocksfar farto to the the north north in Wisconsin Canada? Canada? authors wish to to thank Ashton AshtonMining MiningofofCanada CanadaInc. Inc.and and Crystal CrystalExploration ExplorationInc. Inc.for forpermission permission to topublish publish this this The authors givento toDr. Dr. Daniel DanielJ.I Schulze data. Additional Additionalappreciation appreciationLv is given Schufee at at the the University University of Toronto, Erindale College and and Mrs. Anne Anne Hall Hall of Winspear Resources ResourcesLtd. Ltdfor for critical critical reviews, reviewv,and andto to Dr. Dr. Ron Ron Sage of the Ontario Mrs. OntarioGeologjcal Geological for general general assistance. Survey for assistance. RH. (1994): 137-146. MITCHELL, RH. (1994): The TheLamprophyre Lamprophyrefacies. fades. MineraL Mineral.Petrology Petrology 51, 51,137-146. N.M.S. (1991): (1991): Lainprophyres. ROCK, N.M.S. Lamprophyres. Blackie Blackie& & Son, Son, Edinburgh. 12 �as aa Tool Toolfor forRecognizing RecognizingCrustal CrustalFabric Fabricand andStructure Structure Gravity Aspect as at Minnesota at 55746 D. A. Dahl, DahI, Minnesota Dept. Dept. of of Natural Natural Resources, Resources, Minerals Minerals Division, Division, Hibbing, Hibbing, Mn Mn 55746 Gravity aspect, the facing direction of Gravity gravity gradient, gradient, is is apparently apparently a sensitive sensitiveindicator indicatorof of of gravity crustal fabric, one that can can aid aid in in the therecognition, recognition,unmixing unmixingand andmapping mappingofof individual individual components of composite components composite gravity gravity signatures. signatures. Reported as a compass bearing (0-360). (0-360), aspect aspect records records the the direction direction normal normal to to the the strike of gradient. In the case of a potential field like gravity, aspect depicts the bearing bearing direction direction of of aa gradient In the case of a potential field like gravity, aspect depicts vector that is the components of gravity the sum sum of all all of the horizontal components gravity features featuresthat that affect affectaasite. site. Displayed in HSV (hue-saturation-value) color space, where hue (aspect) is valued in the (aspect) valued in the range range 0-360, gravity fabrics based on hue, and overlap of gravity gravity fabrics 0-360, fabrics can be recognized based fabrics can can be be recognized as vector-like color summing summing of of component component hues. hues. Conveniently, Conveniently, HSV color color space space also provides a means of comparing gravity aspect (hue) to Bouguer intensity, slope, slope, or or curvature (each plotted as gray scale value, with or without shadowing). curvature (1st and 2nd horizontal At MnDNR, terrain analysis tools such as slope and curvature horizontal derivatives) routinely used used to tocheck checkdata datasets setsfor foridiosyncrasies idiosyncrasies and and artifacts artifacts before before they are derivatives) axe are routinely included in a GIs-based GIS-based information system. system. Slope Slope and and curvature curvature provide provide an an excellent excellent means means of of caused by by inconsistencies inconsistenciesin indata datahandling handlingand andreduction. reduction. In the recognizing edge artifacts caused the case case Minnesota gravity of the Minnesota gravity data data set set (55,900 (55,900 points, Chandler and Schaap, 1991), 1991). terrain analysis analysis maps, and also to generate related maps of was used to generate slope slope and curvature haps, of aspect, aspect, profile curvature, curvature, and and planform planformcurvature. curvature. The aspect aspect pattern for for the Minnesota gravity data set is particularly interesting, interesting, because because itit reinforces structure in the Lake Superior reinforces several several interpretations of pre-existing structure Superior region region and and provides a basis for additional discussion discussion about about the the geologic geologic history history of of the the crust. crust. Readily Readily apparent apparent are are the the following: following: 1) 1) Overlapping Overlapping gravity gravity fabrics fabrics can be recognized. As As good good examples, examples,at at least least two two ancestral ancestral fabrics can be recognized beneath beneath the the Bayfield Bayfield basin basin of the the mid-continent rift system. gravity fabrics system. The Duluth Complex The gravity gravity aspect aspect pattern of the footwall of the ~ uluth Complex can also also be be reliably reliably traced tracedto to 30-40 30-40 km tan inside inside the the western westernmargin margin of of the the complex. complex. 2) Gravity Gravity aspect aspectcan can be be used used as an effective means of delineating the axes of gravity lows and highs. Elongate the statewide statewidepattern. pattern. Domal or bowl-like aspect gravity highs. Elongate "hinges" dominate the patterns patterns are, are, for for the the most part, part, restricted to individual intrusive intrusive features. features. 3) A A pervasive pervasivenorth-northwest north-northwest striking striking gravity fabric is parallel to the magnetic expression expression of 13 �similarly trending regional dike swarms. The The fabric fabrichas has aa much much broader broader "wavelength" "wavelength"than than the the of depth, and a general general lack spacing of the dikes. Curvature Curvatureprofile profile maxima, as a rough indicator of of magnetic that this this broader broader fabric fabric may may be be more more deeply deeply rooted than the magnetic expression expressionsuggest. suggest that the higher amplitude, amplitude, more more easily easily recognized recognized gravity gravity fabric fabric of the the east-northeast east-northeasttrending trending greenstone-granite-gneiss greenstone-granite-gneissterranes terranes that that overprint overprint it. it. 4) Pm-rift Pre-riftgravity gravityfabric fabricisisonly onlypartly partly obliterated obliterated by the the mid-continent mid-continent rift rift system system in in Minnesota. Minnesota. edge of of the the Penokean Penokean orogen orogen area in 5) A prominent gravity 5) gravity fabric parallels the northern edge completely interupts the north-south north-south aspect aspect pattern pattern that that can can be be traced on either Minnesota, but completely interuption. The side of the interuption, ThePenokean Penokean area, area,in in general, general, expresses expresses aa complex complex interplay interplay of of fabrics. fabrics. begseveral severalquestions. questions. What What is the geologic The patterns of gravity aspect in Minnesota beg significance significance of axial "hinges"? "hinges"? What What is is the the significance significance of the north-northwest trending fabric, and at what depth within or below the the crust crust does does that thatfabric fabricexist? exist? Can aspect be applied applied in interpretation interpretation of magnetic data? data? Will Will additional additionalgravity gravity data data increase increasethe the signal-to-noise signal-to-noiseratio ratioin in features can can be beresolved? resolved? Can algorithms be applied, in the aspect pattern so that more subtle features conjunction with aspect, to separate component fabrics? conjunction aspect, to separate component fabrics? References References Chandler, Anomaly Map Map of Minnesota, V.W., and and Schaap, Schaap, B.D., B.D., 1991, 1991,Bouguer Gravity Anomaly Chandler, V.W., Minnesota Minnesota Geological GeologicalSurvey, Survey,State StateMap Map Series Series Map Map S-16, S-16, 1:500,000. 1:500,000. 14 �STRATIGRAPHY, TECTONICS TECTONICS AND AND MINERALIZATION MINERALIZATION OF OF THE THE SIOUX LOOKOUT STRATIGRAPHY, OROGENIC BELT, BELT, WESTERI WESTERNWABIGOON WABIGOON SOBPROVINCE SUBPROVINCE Devaney, J.R., Ontario Ontario Geological Geological Survey, Lake Rd., Rd., Devaney, Survey, 933 933 Ramsey Ramsey Lake Sudbury, P3E 6B5, Canada Canada Sudbury, Ontario Ontario P3E Tectono-stratigraphic analysis of of the metamorphosed and variably Tectono-stratigraphic analysis deformed Archean Archean supracrustal supracrustal rocks rocks of of the the Sioux Lookout deformed Lookout Belt Belt (western Wabigoon Subprovince) Subprovince) suggests suggests the accumulation accumulation of (western Wabigoon of lower, lower, older, subaqueous basalt 2), 1, 2 ) , capped by by older, subaqueous basalt successions successions (Stages (Stages 1, sequences of more felsic volcaniclastic rocks (Stages 4), with sequences volcaniclastic rocks (Stages 3, 4), minor lavas lavas and and porphyries porphyries (at or small volcanic volcanic centres), centres), or near small overlain by by upper sedimentary rocks rocks (Stage 4), such as turbidite (Stage 4), deposits, by synchronous synchronous intermediate-felsic intermediate-felsic deposits, which which were were influenced influenced by volcanism (interbedded tuffs, volcanic pebble conglomerate, volcanism (interbedded tuffs, volcanic pebble conglomerate, magnetite iron formation). Minor magnetite iron formation). Minor volcanogenic sulphide volcanogenic sulphide mineralization sub-exhalite hydrothermal alteration are mineralization and and sub-exhalite hydrothermal alteration are rocks. A A relatively small small (3 km tan uncommon in the the volcaniclastic volcaniclastic rocks. thick) andesitic stratovolcano stratovolcano succession succession and thick) andesitic and its its comagmatic comagmatic subvolcanic subvolcanic intrusion intrusion (Stage (Stage 3, but undated) undated) are are well well preserved, preserved, but no no epithermal epithermal mineralization and only insignificant insignificant amounts mineralization and amounts of of porphyry copper-type copper-typemineralization mineralization have have been been found. foundNorthwest-southeast compression compression segmented the original original basin basin Northwest-southeast (arc on basalt, basalt:, buriedand andflanked flankedby byyounger younger volcanic volcanic (arc volcanics volcanics on buried detritus) thrust slices slices that detritus)into intoan animbricate imbricate stack stack of of numerous numerous thrust that generally 5, a a forelandforelandgenerally dip and young young to to the the southeast southeast (Stage (Stage 5, vergent fold-and-thrust fold-and- thrust belt). Fluvial polymict polymict conglomerates vergent belt). Pluvial conglomerates accumulated narrow, linear linear (strike-parallel), intra-orogenic accumulated in in a a narrow, (strike-parallel), intra-orogenic "molasse" basin basin and and were were overthrust overthrust by by oldervolcanic older volcanic rocks rocks forming forming nmolasse" the bases of thrust slices (relative ages confirmed by published Uthe bases thrust slices (relative ages confinned published UPb zircon dates). A large volume of basaltic strata zircon dates). large volume of basaltic strata (Northern (Northern Volcanic Belt) Volcanic Belt) was overturned overturned adjacent to to the the microcontinental microcontinental Winnipeg River River Subprovince Subprovince foreland; the overturning overturning was was likely likely Laramideproduced by by large-scale large-scalefaulting faulting (hypotheses (hypotheses include: include: aa Laramidetype uplift, uplift, or flower flower structures structures in cross-sectional cross-sectional views of of strike-slip to major faults strike-slip to oblique-slip oblique-slipfaults). faults). The The major faults appear appear to to be be sinistral strike-slip some of which strike-slip faults faults (Stage (Stage 6), which may may be be 6), reactivated thrust reactivated thrust faults faults (i.e., (i.e., Stage Stage 66 superimposed superimposed on on Stage Stage 5). 5). along some some of of these these major major faults. Late Granitoid plutons intruded along stage sinistral-sense a pullpullsinistral-sense motions motions produced produced features features such such as a apart Patara Fin.), Fm.), releasing releasing bend bend plutons, plutons, and apart basin basin (20 (20kin-long km-long Patara Quartz veins appear tension gashes. gashes. Quartz appear to be be thicker thicker and more more abundant, and contain near the major major deformation deformation zones zones abundant, contain more gold, near (thrust and/or and/or strike-slip faults). faults). At At a (thrust a regional regional scale, scale, gold gold occurrences appear to to be be located located along along lineaxuents lineaments which occurrences appear which resemble Riedel shear Riedel shear fracture fracture systems. systems. 15 �This left blank This page page left blank intentionally. intentionally. 16 �PRELIMINARY INVESTIGATIONS OF THE PICK LAKE DEPOSIT, WINSTON REMOBILIZEDMASSIVE MASSIVESULPHIDE SULPHIDEOREBODY OREBODY LAKE MINE, ONTARIO: ONTARIO: AAREMOBJLIZEI) LAKE DOIRON, Gerard, and SIDDIQUI, Masood, Imnet Inmet Mining Corporation, Winston Lake ON, POT POT 2SO; C., Resident Resident Division, P.O. Bag Bag 2, Schreiber, Schreiber, ON, Division, 2S0; and SMYK, Mark C., Geologist Northwest, Ontario Ontario Geological Geological Survey, Ministry of Northern Northern GeologistProgram Program- Northwest, Ministry of Development 435 S. James St., Thunder Bay, ON, Development and Mines, Suite Suite B002, B002,435 ON, P7E 6S7. P7E 6S7. - The The Winston Winston Lake Lake mine mine is is situated situated in in lower lower amphibolite-facies, amphibolite-facies,cale-alkalic calc-alkalicrocks rocksof ofthe the Neoarchean Schreiber-F{emlo greenstonebelt. belt. It comprises Schreiber-Hemlo greenstone comprises several volcanogenic volcanogenic massive massive suiphide sulphide (VMS), (VMS), zinc-copper zinc-copper deposits: deposits: Deposit Deposit Ore Ore (all (all categories) categories) (million (million tonnes) tomes) Winston Winston Lake Lake Zn Zn (%) (%) Metal Metal Grades Grades Cu Cu(%) (%) Ag Ag (g/t) (gft) Dilution4 Dilution* Au Au (gft) (glt) (%I (%) 3.1 3.1 15.90 15.90 1.00 1.00 30.3 30.3 1.02 1.02 20 20 Upper+Middle Upper + Middle 0.26 0.26 11.21 11.21 0.77 0.77 31.5 31.5 0.65 0.65 30 30 Lower Lower 1.2 1.2 15.90 15.90 0.86 0.86 38.0 38.0 0.46 0.46 25 25 Pick Pick Lake: Lake: (4 (* n.b. n.b. Possible Possible category category of of Pick Pick Lake Lake is is non-diluted) nondiluted) The The Pick Pick Lake Lake deposits deposits occur occur within within strongly strongly foliated, foliated,felsic felsicto to intermediate intermediatevolcaniclastic volcaniclasticrocks, rocks, approximately southwestof ofthe theWinston Winston Lake Lake deposit, deposit, and and 1 I km 1.31cm km southwest km lower lower in in the thefootwall footwall approximately 1.3 stratigraphic stratigraphic succession. succession. The Thedeposits deposits are are thin, thin, but but continuous, continuous, massive massive suiphide sulphide sheets sheetswith with aa down-plunge down-plungelength length of approximately 1000 1000 m. The TheUpper Upperand andLower Lower zones zones average average approximitely approximately2.0 2.0 and and 4.0 4.0 m m in thickness, respectively. Massive Massivesuiphide sulphide ore, ore, in in sharp sharp contact contact with to 400 400 m. m. ItIt forms formsaa dyke-like dyke-like with its its host host rocks, has a strike strike length which varies from 100 m to body body which which locally locallycrosscuts crosscutsboth bothfoliation foliationand andgranitic graniticdykes. dykes. Despite metal grades grades and and mineralogy mineralogy (sphalerite, (sphalerite, pyrrhotite, pyrrhotite, pyrite, pyrite,chalcopyrite), chalcopyrite), Despite similar similarmetal suiphide are markedly markedly different different. Finersulphidetextures textures in in the the Winston Lake and Pick Lake deposits are Finergrainecl ubiquitous development grained Pick Lake ore is characterized by the ubiquitous developmentof of durchbewegung durchbewegungtexture, texture, in the massive massive sulphide. Xenoliths, inwhich which brecciated wall-rock xenoliths comprise 10 to 15 % of the Xenoliths, generally ranging in size from <1 mm to 10 cm, are typically: (1) sub-rounded grains of quartz typically: (1) quartz±Â generally ranging in size from 4 rnm feldspar, chlorite, amphibole; feldspar, sericite; sericite;(2) (2) tabular tabular crystals crystals or aggregates aggregates of of biotite biotite ±Â±chlorite amphibole; or or(3) (3) subsubrounded rounded granitic granitic dyke dyke fragments. They Theymay may be be kinked, kinked, folded folded and/or andlor aligned aligned parallel parallel to to one one another and with suiphide banding. Large (>lm) ratted host rock xenoliths are also apparent. another sulphide banding. (>lm) rafted host rock xenoliths are also apparent. 17 �Piercement cusps and and injection injection structures are developed where massive sulphide sulphide has migrated migrated Piercement cusps into folded folded and and boudinaged boudiiaged host host rocks. The nature nature and and scope scopeof of these secondary textures at Pick Lake are characteristic of large-scale large-scale The characteristic of sulphide replacementand andannealing. annealing. The flowage sulphide remobilization, subsequent replacement flowage of massive sulphide, arising arising from from substantial substantial competency contrasts between competent silicate silicate xenoliths xenoliths and and incompetent incompetentsulphides sulphides during during deformation (Marshall and Gilligan 1989), 1989), has resulted resulted in in widespread widespread durchbewegt durchbewegt ore. The Thehigh high degree degree of of remobilization remobiiization at Pick Pick Lake Lake may may be be the the result result of Lake granite granite (averaging (averaging40 40 m) m) and and the the development development of of of the deposit's deposit's proximity proximity to the Winston Lake high fluids in in the the contact contact aureole. aureole. Crosscutting high strain strainzones zones and and hydrothermal flmds Crosscutting relationships relationships demonstrate suiphide deposition depositionpostdated postdatedthe theintrusion intrusion of of granitic demonstratethat that remobilized r e m o b i l i i sulphide granitic dykes, dykes, perhaps presumedprimary primaryVMS VMSdeposition deposition(ca. (ca. 2720 2720 Ma). Ma). The 35 million million years after the presumed The perhaps 35 location, suiphide deposit(s), from which location, size size and and characteristics characteristics of the primary sulphide which the the enigmatic enigmatic Pick Lake ore was derived, are as yet unknown. Pick Lake ore was derived, are as References: References: Marshall, piercement cusps Marshall, B. B. and and Gilligan, Gillipn, L.B. L.B. 1989. 1989. Durchbewegung structure, piercement cusps and and piercement suiphide deposits: Formation and interpretation. piercement veins veins in massive sulphide interpretation. Economic 11-2319. EconomicGeology, Geology,v.84, v.84, p.23 p.2311-23 19. 18 �THE HURONIAN IN THE SUDEURY-CRERAR AREA: REVISITING THE THE DISAPPEAffANCE DISAPPEARANCEOF THE SUDBURY-CRERAR AREA: THE GEOCHEMISTRY GEOCHEMISTRY OF AMPHIROLITES AMPHIBOLITES AND AND PARAGNEISSES INSIGHT FROM THE EASTON, RM., Rise!.,Precambrian PrecambrianGeoscience GeoscienceSection, Section,Ontario Ontario Geological Geological Survey, Survey, 933 933 Ramsey Lake Road, Road, Sudbury, Sudbury.Ontario Ontario P3E P3E 6B5, 6B5,eastonm@ndm.gov.on.ca and andLIMES, JAMES,R.S., R.S., Department Departmentof of Geology, Geology, Laurentian LakeRoad, Road,Sudbury, Sudbuiy, Ontario Ontario P3E 2C6 LaurentianUniversity, University, Ramsey Lake The Huronian Supergroup The presence presence of of high high grade grade metamorphic equivalents of Huronian Supergroup(Sgp.) (Sgp.) and and Nipissing Nipissing Suite Suite (GFTZ) in in Ontario has been long debated. A 5 km krn wide wide zone zone south south rocks in the Grenville Grenville Front Tectonic Zone (GFTZ) the Grenville Grenville Front in the Sudbury-Conision-Crerar of die Sudbury-Coniston-Orerar area provides provides an an opportunity opportunity to to test testthis thissuggestion suggestion geochemically. variety of of amphibolites, amphibolites, quartettes quartzites and muscovite±kyanite-bearin muscovite±kyanite-bearing In addition addition to containing a variety geochemically.In metapelites, the area and covered covered by by aa database database of of some some 155 metapelites, area is well mapped and 155 chemical analyses, including 80 major element element analyses analysesby by Kwak (1967), (1967). Pearson (1959) (1959) and and LaTour LaTour(1979), (1979). as aswell wellas as75 75newly newlyacquired acquired major and unpublished). RoughIy Roughly 80 (Easton,unpublished). 80 of these these analyses analyses are are of of amphibolites, amphibolites, and trace trace element element analyses analyses (Easton, with with another another60 60representing representingparagneisses. paragneisses. Amphibolites: Two types are are recognized recognized in in the the field: migrnadtic rnigmatiticamphibolites, amphibolites, typically typically Amphibolites: Twomain mainamphibolite ainphibolitetypes garnet-bearing, and diabasic textured, textured, typically typically clinopyroxene-b&ng, clinopyroxene-bearing, amphibolites. gamet-bearing, and non-miginatitic, non-mipatitic, locally diabasic Geochemic ally, all all datasets datasetsshow show33similar similargroups groupsof ofamphibolites amphibolites (Rg. (Fig. la); Ia); from most to to least least abundant, abundant, Geochemically, these are: (1) tholeiite group group corresponding corresponding to the migmatitic amphibolites. (2) a (1)aa tightly clustered high-Fe tholeiite magnesium-rich group with with Mg#70-78, Mg#70-78,Mg0=7.7-13.1%. MgO=7.7-13.l%, and Ca0=10.8-14.5%. CaO=l0.8-14.5%. Pods Podsof of orthopyroxene orthopyroxene homblendites in homblendites in the the area area may be related to this group, and (3) a high-Mg tl]oleiite tholeiite group, with Mg#=54-59, Mg#=54-59, MgO=7-9%, Both groups groups 22 and 3 show relict relict differentiation differentiationtrends trends within within individual individual Mg0=7-9%. and CaO=9.6-1ft5%. Ca03.6-10.5%.Both bodies (Fig. (Pig. Ia). la).In In the thefield, field.group goup 33 corresponds corresponds to diabasic-textured diabasic-texturedrocks rocks previously previouslyinterpreted interpretedas as Nipissing diabase; and chemically, itit lies lies in in die theHeld fieldof ofNipissing Nipissing diabase diabase chill chill margins. margins. In In die the field, group group 22 amphibolites locally show diabasic textures, but more typically are black; thinly layered rocks, with associated amphibolites locally show but more typically are black, thinly layered rocks,with gabbroic anorthosite. Chemically, group 2 corresponds corresponds to gabbrowrite gahbronorite cumulate cumulate rocks gabbroic rocks of of the the Nipissing Nipissingsuite. Group chemical similarities similarities with plutons of the Huronian Huronian magmafic magnialic suite suite Group 2 or or 3 amphibolites amphibolitesshow no clear chemical group 22 and 3 amphibolites amphibolites are (e.g. River River Valley Valley anorthosite). Consequently, group are interpreted interpreted as as equivalents equivalents of of the the 2.2 Ga Nipissing suite. Group I amphibolites plot in the field of Archean and Huronian metavolcanic rocks. Nipissing 1 amphibolites the field of Archean and Huronian metavolcanic rocks. In suiterocks rockswith withMg#=54-59 Mg#=54-59predominate, predominate,whereas, whereas,in inthe theGFIZ, GFrZ, to the Southern Southern Province, Nipissing suite interlayered gabbroic gabbmic anorthosite. anorthosite. One Oneexplanation explanationisis that that those with high Mg# (>70) (>70) are most common, as is interlayered the GFTZ, we see the mid-crustal magma chambers chambers of the Nipissing suite, postulated by various in die mid-cmstal "auxiliary" magma anorthositic cumulate cumulate rocks. so,this this leads leadsto tospeculation speculation workers, which would be dominated by mafic and anorthositic rocks. IfIf so, migmatization of the country countiy rocks may may be be related related to to wall wall rock-magma rock-magma chamber interaction. It is still that migmatizatiou unclear if these these magma magma chambers chambers are are hosted in Archean or or Paleoproterozoic Palwproterozoicrocks. rocks. Paragneisses: Kyanite-bearing chemical groups groups (Fig. (Fig. lb). ib). Most are intennediate are intermediate Paragneisses: Kyanite-bearing gneisses gneisses fall into two chemical composition micaceous micaceous gneisses gneisseswith withSi0~57-64%. SiO=57-64%,&03=19.9-26.855, AIO,=19.9-26.8%, Ti02=I.2-1.8%, Fe103t=4.5-8% Ti02=1.2-1.8%. P%03'=4.5-8% and and CIA=73-83. rocksare aremost mostlikely likelyof ofsedimentary sedimentaryderivation. derivation.Gamet-biotite Garnetbiotite gneisses CIA=73-83. Chemically, these rocks spatially associated contents (13spatially associatedwith withthe thekyanite kyanitegneisses gneisseshave havesimilar similarchemistry, chemistry,apart apart11Dm fromlower lowerA12O3 A@, contents contents (Fig. (Fig. lb). lb). The second second group group of of kyanite kyanitegneisses gneisses isis characterized characterizedby by 18%) and higher MgO and CaO contents high FfriO,' Fe103' contents (10-1255). (10-12%), varied varied Al,O, Al203content content(12-30%), (12-30%),and and high high CT, Cr, Ni, Ni, V V and and Ti Ti contents. contents. The The origin unclear, although although derivation derivation from from altered altered metavolcanic metavolcanic rocks is possible on on origin of these these kyathte kyanite gneisses is unclear, the trace and and REE REE abundances. abundances. the basis basis of of field fieldrelationships relationshipsand and trace garnet-biotite gneisses gneisses have havetrace traceelement element signatures signatures similar similar to to those those of of intercalated intemalated garnet garnet Many of the gamet-biotite intermediatetotofelsic felsicvolcanic volcanicrocks rocksor orvolcaniclastic volcaniclasticsediments. sediments.Some Someof of amphibolites, and could represent intermediate the garnet-biotite gamet-biotite gneisses have pronounced pronouncedpositive positiveCe Ceanomalies anomalies(Hg. (Fig. lc), lc), suggesting exposure to an oxidizing environment. weathering profiles, profiles, and and itit isispossible possiblesome someof ofthe the oxidizing environment. Similar Similar anomalies are common in weathering garnet-biotite gneisses represent a weathering profile developed on older metavolcanic rocks. No rare earth gamet-biotite gneisses represent developed older metavolcanic rocks. NOrare earth element element studies studieshave havebeen been conducted conducted on on any Huronian weathering weathering profiles, profiles, so soitit isisunknown unknownififHumnian Huronian 19 �regoliths possess similar similar cerium anomalies. Both the lcyanite and garnet-biotite garnet-biotite gneisses gneisses are associated with quartzose quart-zosegneisses gneisses(SiOy>74%), (Si02>74%), kyanite and quartzites, which locally show relict transposed bedding, and rare conglomerate conglomeratehorizons. Typically, Typically,quartzites quartzites have higher FGO," Fe203tand andTi02 Ti02contents contentsthan thando doany anyof ofthe theHuronian Huronianquartzitic quariziticor orconglomeratic conglomeraticunits units(Fig. (Fig. Ib), Ib), derivation of the metasedimentary metasedimentaiy gneisses gneisses from however, derivation from volcanic-derived volcanicderived sediments sediments such such as as those thosein inthe the Mm. and Stobie gneiss and associated quartzite quartzite Elsie Mtn. Stobie formations formations is not precluded. In In one one instance, instance, aa Icyanite kyanite gneiss present in in the the Pecors Pecors and McKim McKim formations (Fig. (Fig. Id). show REE patterns similar to those present Based on field relationships and geochemistry, it is most likely likely that that the the paragneisses paragneisses and and associated associated garnet theSudbury-Crerar Sudbury-Crerararea areaare arederived derivedfrom fromboth both an an Archean Archean metasedimentaiymetasedimentaryamphibolites in in the the GFTZ 0HZ ininthe succession and high grade grade equivalents equivalents of of the the Paleoproterozoic Paleopmtemzoic Elliot Elliot Lake Lake Group. Group. metavolcanic succession Feo* + TiC2 a) a 0 high-Mg# hioh-Mgf ençhibolites mnphlbolites u a modorate-Mg# moderate-Mflffaniphiboiftes amphibdtes • Nipissirq Nipissingdiabase dabase  o garnet 0 garnetampfllbolites amphbolites xx Opx-homblendites Opx-homblend'rtes 20  Slobb. E M Mtn.. CoppÈrO Fma. 0 0 A1203 A1203 (wt %) MgO 1000 1000 c) GARNET-BIOTITE GNE!S5€S 100 100 10 10 I .1 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sni Eu Gd Tb Dy Ho Er Tm Yb Lu Figure 1: and paragneisses paragneisses from from the the Sudbury-Crerar Sudbury-Crerar area. area. 1: Geochemical Geochemical characteristics characteristics of of amphibolites and Data Kwa/c(1967). (1967),Pearson Pearson (1959). (1959), LaTour LaTour (1979) (1979)and and Easton Easton (unpublished). (unpublished). A) Jensen Jensen plot Data from Kwak showing three main groups of amphibolites. amphibolites.Arrows Arrowsindicate indicatedifferentl&ion differentiationtrends trendsin inindividual individualbodies. bodies. B B)) showing Plot of total iron forStreet StreetTwp. Twp.paragneisses paragneissesand and1owerHuronian lower HuronianSgp. Sgp.units. units. C) C) Chondrite Chondrite iron versus versus A1203 A120,for normalized REEplot REE plot of gt-bi gt-bi gneissesfrom gneisses from Street SweetTwp. Twp.showing showing+ve +vecerium ceriumanomalies. anomalies. D) Chondrite Chondrite normalized REE REE plot plot of of Huronian tiuronian Sgp. units and metasedimentary metasedimentary rocks south of the the Grenville Grenville Front. Front. 20 �Space-lime patterns of Space-time patterns of Early Early Proterozoic Proterozoic post-Penokean post-Penokean (1800-1600 (1800-1600 Ma) metamorphism metamorphism and cooling iin Superior region n the southern Lake Superior DX. and Holm, D.K. andHenderson, Henderson, D.H., D.H., Dept. of Geology, Kent State State University, Kent, OH OH 44242 Introduction. The Precambrian terrane of of the southern Precambrian terrane southern Lake Superior region has has experienced experienced a protracted Proterozoic Proterozoic history history from accretion/colllsion accretion/collisionduring during the the Early Early Proterozoic ProterozoicPenokean Penokean orogeny omgeny to to rifling at 1100 Ma. Ma. Recognition Recognitionand and characterization characterization of of post-orogenic post-orogenic metamorphism, metamorphism, aborted cratonic rifting cooling, and thermal resetting is essential for understanding the evolution evolution from active active accretion/collision accretionlcollision et al., al., 1984, Geology). Geology). In to development of a stable craton (Rogers et In this thisregard, regard,considerable considerableadvances advances the excellent excellent overview overview of of Precambrian Precambrian metamorphism metamorphism by by Geiger Geigerand andGuldotti Guidotti have been made since since the Wisconsin v.v. 13). 13). We summarize differences in In the nature and extent summarize here important differences (1989, Geoscience Wisconsin Early Proterozoic post-Penokean thermal histories between olfferent different portions mst-Penokean (1800-1600 Ma) lhermal mrttons of the the of Eariy exposed exposed orogenic orogenic belt belt (I.e. (i.e. central Minnesota, Mhesota, northern northern Wisconsin, and and northern northern Michigan) Michigan) and and speculate speculate that some that some of of these thesedifferences differences may may reflect reflect Initial initial differences differencesIn in the the metamorphic metamorphicgrade grade(namely (namely.pressure) pressure) . attained attained during during the the Penokean Penokean Otugeny. Orogeny. - Central Minnesota. fades In increasesfrom from subgreenschist submeenschist fades in Central Minnesota.Penokean-age Penokean-aeemetamorphism metamomhismin inMinnesota Minnesotaincreases the north to ainphibolite near the amphibolite facies in the south southnear the first first appearance appearance of Penokean-age ~enokean^ageplutonic rocks (Morey, 1978, 78-10). New 1978, GSC Paper 78-10). New thermochronologic thcrmochronologic and thermobarometric thcrmobaromecric data from rocks of the internal zone of the the Penokean Penokean orogen in central central Minnesota ~innesotaindicate indicatethat that the the Early EarlyProterozoic Proterozoicsediments sediments initially during the Penokean Penokean Orogeny Orogeny (1870-1820 (1870-1820 Ma) Ma) and and again again during during an an were metamorphosed twice - initially at 1770-1760 Ma (Holm (Iloim and Lux, Darrah et et a!., al., episode of post-orogenic magmatism magmatism at Lux, 1996, 1996,Geology; Geology;Darrah 1996, ILSG). ILSG). Thermobarometric a]., 1981, 1981, GSAA; GSAA; Holm Holm and and Selverstone, Selverstone, 1990, 1990, Thermobarometric results (Labotka et al., kbar paleopressures pa!eopressures for both metamorphic Darrah et etal., al., 1996) 1996)indicate indicate—6 -6 kbar metamorphic events events suggesting suggesting Geology; Dauah little crustal uplift during during the theintervening interveningperiod. period. The The 66 kbar bar pressure pressureestimates estimatesfor for the the 1770-1760 1770-1760 Ma staurolite grade nildcrustal (13-15 km) emplacement emplacement depths of the the poststaurolite grade metamorphism in Minnesota, the midcrustal plutons, and the complete lack of of any Penokean-age hornblende AdAr Ar/Ar dates dates from from the the area area tectonic plutons, complete. lack Penokean-age hornblende (Darrah et al., 1996) 1996) argues against a simply contact contact related metamorphism metamorphism adjacent adjacent to mid-or mid-or shallow shallow crustal plutons. Instead, In tee the thickest portion portion of of the the orogenic orogenle crustal Instead, increased increased heat-flux heat-flux at the base of the crust in belt (the Internal zone) was was responsible responsible for for both both partial partial melting melting of of the lower crust and belt internal zone) and regional regional to staurolite staurolite grade gradeof ofthe themiddle middlecrust crust. The midcrustal mldcrustal rocks underwent underwent rapid rapid exhumation exhumation metamorphism to shortly after intrusion and metamorphism and may have even been exposed exposed before before 1700-1650 1700-1650Ma Ma (based (based on the the probable probable age age of the the Sioux Sioux Quartzite Quartzite in southwest southwest Minnesota, Chandler Chandler and and Morey, Morey, 1992, 1992, USGS USGS Bulletin 1904-N). 1904-N). The The1770-1760 1770-1760Ma Ma metamorphism, metamorphism,intrusion, intrusion, and and rapid rapid exhumation exhumationof ofthe theinternal internal zone of the Penokean orogen probably represents orogenic collapse and was the last major 'event' to have affected this region aside from the final formation of the McGrath gneiss dome dome around around 1700 1700Ma Ma (HoIm (Holm and Lux, 1996). 1996). Northern Early NorthernWisconsin Wisconsinand andnorthern northernMichigan. Michigan.Uniform Uniform EarlyProterozoic Proterozoicmetamorphic metamorphicpressures pressures from the internal in central Minnesota are greater than the typical 2-4 kbar paleopressure estimates for internal zone in throughoutmost most of of Wisconsin (Geiger (Geiger and Guldotti, Penokean metamorphism metamorphism throughout Guidotti, 1989). 1989). In contrast contrast metamorphic üodal patterns patterns in northern metamorphic nodal northern Michigan Michigan are are superposed superposed on onlow-grade low-grade greenschist greenschist metamorphism. metamorphism. The The origin origin of of the the prominent prominent nodal nodal metamorphic metamorphic patterns has been one one of of the the most most Interesting questions questions in in geologic geologicresearch researchofofthe thearea. area. Pressure differences among the nodes (4 kb at interesting Peavy, 2 kb at at Republic and 7 kb at Watersmeet) probably reflect initial differences differences in in crustal crustal thickness Orogeny (Attoh (Attoh and Klasner, 1989, Tectonics) TectonIcs) although for at least the attained during the Penokean Omgeny Watersmeet area, the uplift uplift and and doming doming of of the theisograds isogradsoccurred occurredsignificantly significantlylater later(at (at—1755 -1755 Ma; et al., aL, 1996, 1996,CJES). dES). Emilio Emilioetetal. al.(1996, (1996,Eos) Eos)have haverecently recentlysuggested suggestedthat thatthe themapped mapped nodal nodal Schneider et pattern at Peavy pattern Peavy isis actually actually aasimplification simplification of ofaamore morecomplex complexpolyphase polyphasemetamorphic metamorphichistory history characterized by possibly three three discrete metamorphic events. characterized The extent Mametamorphism metamorphism within withinthe the Penokean Penokean orogen in Wisconsin is just extent and and nature nature of of —1760 -1760 Ma unraveled. Van VanWyclc Wyck (1995, (1995, UW-Madison UW-Madison Ph.D.) Ph.D.) illustrated aa thermal thermal disturbance disturbance beginning to be unraveled. adjacent to Mapluton plutoninincentral centralWisconsin Wisconsin and and Romano Romano et et al. a]. (1997, (1997, GSAA) obtained obtained evidence to an an —1760 -1760 Ma evidence adjacent for partial thermal resetting interpreted to to be be related related to to -1760 -1760 Ma magmatism magmatism in in west-central west-central Wisconsin. 21 �However, these disturbances disturbances appear to be aa more more localized contact-related phenomenon phenomenonbecause becauseseveral several localities in Wisconsin (and upper datesthat that reflect reflect cooling from upper Michigan) Michigan) yield hornblende Ax/Ax ArIAr dates Schneider et et al., al,, 1996; Romano Romano et al., al., 1997; (i.e., 1800-1850 1800-1850 Ma; Sdmeider 1997; Mancuso Penokean-age metamorphism (i.e., with the the -1760 -1760 Ma granites In et al., al., 1997, 1997, ILSG). ILSG). This Thisinterpretation interpretation is also consistent consistent with in northwest northwest Wisconsin depths than similar Wisconsin having having been been emplaced emplacedatatsomewhat somewhatshallower shallower(9-11 (9-111cm) km) depths similar age agegranites granitesInin Minnesota (Anderson central Minnesota (Andersonet et al., al., 1980, 1980,CMP). The timing timing of unroofing unroofing of the the post-tectonic post-tectonic granites in northern Wisconsin is poorly poorly constrained constrainedbut but probably occurred fairly shortly after intrusion. In In northwest northwest Wisconsin, Wisconsin, an an area area little littleaffected affected by by later later reheating and deformational biotite cooling cooling dates dates (both (both RbISr Rb/Sr and ArIAr) Ar/Ar) are 1700-1730 defonnational events, biotite 1700-1730 Ma Ma (Peterman see spectrum spectrumbelow). below). Also, the 1760 (Petennan and Sims, 1988, Tectonics; see 1760 Ma Radisson Radisson granite granite in this area is Is overlain by the which, if If correlatable the Sioux Sioux Quartzlte Quartzite the undeforined undefonned Barron Quartzlte Quartzite which, cordatable with the (Chandler (Chandler and and Morey, Morey, 1992) 1992)might might indicate indicate exposure exposure by about about 1700 1700Ma. Ma. Precambrian rocks in Wisconsin Michigan were were also affected by younger Precambrian rocks Wisconsin and northern northern Michigan younger Early Early Pmterozoic at -1720 -1720 Ma Tlieseinclude includepossible possible contact contact metamorphism metamorphism at Ma In Innorthern northern Michigan Michigan Proterozoic events. These al., 1996). 1996), a cryptic cryptIc 1720 Ma node (Schneider (Schneideret a al., which may have created the Republic metamorphic metamorphic node metamorphic event in In Wisconsin (Van Wyck, Wyck, 1995) 1995) and and the the w widespread but little little understood 1630 Ma idespread but low-grade event which affected reeks rocks thmughout throughout much of Wisconsin and perhaps portions of of northern northern Michigan. Michigan. The Theabsence absenceof ofthese theseyounger younger overprinting overprinting events in in areas areas such suchasascentral centralMinnesota, Minnesota, northwest Wisconsin and portions of northern Michigan (i.e., (i.e., Watersmeet) Watersmeet) allow allow us us to learn learn much about the earliest and extremely metamorphic4ilutonic event event at at 1770-1760 1770-1760 Ma. extremely important important post-Penokean metaIII~rphidplIIt~ni~ Implications. Implications.Based Basedon onthe theabove aboveoverview, overview,ititappears appearsthat thatthe thenature natureand andextent extent of of post-Penokean post-Penokean Early Early Proterozoic metamorphism and cooling is distinctly different within different parts parts of of the theorogenic orogenicbelt. belt. areas where where the the We note that the the 1770-1760 1770-1760Ma post-tectonic post-tectonic plutons have deeper emplacement depths in areas paleopressure estimates are greater (i.e., (i.e., central Minnesota compared to northern Penokean paleopressure northern Wisconsin). Wisconsin). This suggests that little Ma but that little unroofing unroofing of of the the Penokean Penokean orogenic orogenic belt occurred prior prior to to —1770 -1770 Ma (and variable) variable) amounts amountsof of unroofing unroofingoccurred occurredrapidly rapidlythereafter thereafter(-10 (-10 tan km of of unroofing unroofing in In significant (and northern Wisconsin same time 1760 Ma and 1700 Ma but 15-20 km during the same time span span for for central central Wisconsin between 1760 Minnesota). We that the thedifferences differences may reflect initial differences iInn the amount amount of of crustal crustal Minnesota). Wespeculate speculatethat orogen. Post-orogenic metamorphism thickening attained across the Early Proterozoic orogen. metamorphism appears to have have grade) perhaps perhaps because because crustal thickening been more pervasive pervasive in central central Minnesota (reaching staurolite grade) thanin in the the island island arc arc terrane terrene of Wisconsin Wisconsin (Geiger and and Guidottl, Guidotti, 1989). 1989). was greater greater there there than of the complete Early Proterozoic Proterozoic unroofing unroofinghistory historyof of the the Penokean orogenic oregenic belt Is Knowledge of is critically dependent dependent on the age of the quartzites quaitzites mentioned mentioned above. above, If they they are are indeed indeed Early Early Proterozoic Proterozoicin in paleomagnetic data, thta, by ages of detrital zircons age (as seems to be suggested by palmmagnetic zircons in other other quartzites quartzitesof of the the region, Ma) then these quartzites region, and by the fact fact that that some some were were probably probably deformed at 1630 Ma) quartzites may represent of continental continental crust crust in in the the Lake Lake Superior region region after after a protracted history of represent stabilization of tectonic instability which lasted hundreds of millions of of years years (Greenberg (Greenberg and and Brown, 1983, 1983, J. Geology). the sudden sudden and and rapid rapid collapse collapse of the overthickened overthickened Penokean orogen orogen together together with withthermal thermal It appears appears that the re-equilibration of the lithosphere the Early Early Proterozoic Proterozoic re-equilibration lithosphere was a critical step in crustal stabilization during the etal., (ill). al., 1984; 1984; Nelson, 1991, GJI). (Rogers et 2000, Powell Kyanite Locality AGE' Northwest Wisconsin Ma: 1500- 1000— 0 1 Biotite — . . Tg = 1668±12 Ma Tp = 1696±13 Ma U • U %39Ar % 39 Ar I I U — 100 100 Complete citation of references will be available at at the the presentation presentation and andupon uponrequest request (dholm@kent.edu). (dholm@kent.edu). Complete citation 22 �Ar/Ar dating of dikes dikes in incentral central Minnesota Minnesota and and the the Minnesota River Valley Results of ArIAr D.K., Dept 44242 (dhoIm@kent.edu); HOLM, D.K., Dept.of ofGeology, Geology,Kent Kent State State University, Kent, OH 44242 (dholm@kent.edu); and LUX, D.R., D.R. Department of Geological Sciences, University of Maine, Orono, Orono, ME ME 04469 04469 Ma) magmatic magmatic suites suites of of central Minnesota Late- and and post-tectonic post-tectonic (1820-1770 (1820-1770 Ma) Minnesota are are crosscut crosscut by by mafic dikes east-west. Much of the dikes that that generally generally trend northeast-southwest northeast-southwest totoeast-west the region region affected affected by by the the Penokean orogeny, Minnesota, Wisconsin, Wisconsin, and the upper peninsula orogeny. including including central Minnesota, peninsula of of Michigan, Michigan, isis crosscut CJES; Chandler, Chandler, 1993, 1993,in in USGS USGS Prof. Prof. crosscut by similar similarlate latenortheast-trending northeast-trending mafic dikes (King, 1990, CJES; Paper 1556). 1556). Some Someofofthese thesedikes dikesare arecertainly certainly related related to to 1100 1100Ma Ma mid-continent mid-continentrift riftmagmatism magmatism(Green (Green 34). However, et al, 1987, 1987, In in GAC Spec Spec Paper 34). However, some are also significantly older and appear related to the -1770-1760 Ma mafic dikes dikes that that crosscut crosscut -1770 -1770 Ma InWisconsin. Wisconsin, northeast-oriented northeast-oriented mafic Ma magmatic magmatic suite. In plutons fades at 13W-MadIson Wyck,1995; 1995; UW-MadisonPh.D. Ph-D. plutons were weremetamorphosed metamoqhosedto to amphibolite amphibollte fades at-1720 -1720Ma Ma(Van (VanWyck, thesis). InInaddition, addition,Inincentral centralMinnesota MinnesotaPb PbIsotope isotopedata datafrom fromthe themafic maficdikes dikesare areconsistent consistentwith witha a—1800 -1800 thatthe thedikes dikesmay may have haveintruded intrudedonly onlyshortly shortlyafter afteremplacement emplacementofofthe the—1770-1760 -1770-1760 Ma age age suggesting suggestingthat Ma magmatic suite aL, 1987, 1987.Prec. Prec.Res.). Ret). Mafic Maficdikes dikesof of Early Early Proterozoic Proterozoicage agehave havealso alsobeen been suite (Horan et al.. reported (Hanson and Himmclberc. Hiinmelberg, 1967, rcoorted from from the the Minnesota Minnesota River River Valley Vallcv Manson 1967. GSAB). GSAB1. We (MRV-5A, MRV-3C, MRV-3C, &d and MRV-3) of andesite dated three three whole-rock whole-rock samples sampl&(MR~-5,4, kdesite dikes dikes from from the the We dated Granite AdArIncremental incremental Granite Fails Falls area, area,Minnesota MinnesotaRiver River Valley Valley (Himmelberg, (Himmelberg, 1968, 1968, MGS MGS Pub.) using usingthe theAr/Ar heating technique. No ATloss loss Noplateau plateau dates dates were were obtained. Rather, Rather,all allthree threespectra spectradisplay displaysignificant significantAr profiles and Ma)are aretherefore thereforemeaningless. meaningless. The The oldest increments for the and their total gas dates (1429-1551 Ma) three samples (1567 Ma, K-Armineral mineral Ma, 1685 1685 Ma, and 1723 1723 Ma) Ma) are are somewhat somewhat younger younger than than the theK-Ar (hornblende 1690-1930 Ma obtained on andesite dikes near Granite GraniteFalls Fallsby by Hanson Hanson (hornblende and and biotite) biotite) dates dates of 1690-1930 and Himrnelberg (1967). Because AI loss indicated by the spectra, spectra, the the oldest oldest increments increments we Himmelberg (1967). Because of the Ar minimumdates datesfor forintrusion intrusionofofthe thedikes. dikes. This is consistent consistent with the fact obtained should be considered minimum that at Ma -pluton (granite of section at least least one oneandesite andesitedike dikein inthis this area areaisisintruded intrudedby by an an—1850 -1850 Ma section 28; Goldich Goldich etetaL, al., 1970, 1970,GSAB). GSAB). We dated northeast trending basalt dikes dikes which cross-cut twowhole whole rock samples of noflheast cross-cut 1770 1770 Ma We dated two granites -2-95 and date(MN MN-2-95 andMN-37A), MN-37At. the the granites near near St. St. Cloud. Cloud Although AIthonehneither neithersample samoledisplayed dimlavedaaplateau nlateaudate spectra are total gas dates &bstantially substantially younger younger (1150-1200 &ma are considerably considerably less less disturbed and the btal (1150-1200Ma) ~ athan than ) River Valley. Valley. Feldspar separated from aa quartz-feldspar those obtained from the Minnesota Minnesota River quartz-feldspar porphyry yielded aa distinct distinctsaddle-shaped saddle-shapedspectra spectraindicative indicativeofofexcess excessargon argot In this case the dike in the same area yielded age minimum of 1456 wouldrepresent representaamaximum maximumage agefor forintrusion Intrusionof of the thedike. dike. Our 1456 Ma for this spectra would Ar/Ar whole-rock whole-rock basalt dates from the the St. St Cloud area are significantly younger than the three three whole-rock &/AT basalt K-Ar dates dates of of 1280 1280Ma, Ma, 1460 1460 Ma, and 1570 Ma obtained from this area by Hanson Hanson (1968, (1968, MGS MGS Rept. mv. isotope data Inv. 8). 8). Those Thosedates dateshave havecommonly commonly been interpreted as partially reset dates and the Pb isotope of Horan al. (1987) (1987) seem seem to to support support that interpretation. interpretation. However, However, we we interpret interpretour ourresults results from from the the Horan et et al. mafic dikes dikes (MN-2-95 indicating that that some some of of the northeast-oriented dikes in the St. MN-37A) as indicating St. (MN-2-95 and MN-37A) Cloud area are are Keweenawan in age. We We note note that the the morphology morphology of the the dike dike spectra spectrafrom from the the two two areas areas aredramatically dramatically different and this probably reflects a difference differenceIn in their theirintrusion intrusionages ages (MRV and CM) are post-Intrusion histories. and post-intrusion Our interpretation outside of the Our interpretation that that Keweenawan Keweenawan dikes were intruded outside the main mainrift rifttrough troughIn incentral central given the the evidence evidence for for Keweenawan dike dike swarms in northern Minnesota does not seem unreasonable unreasonable given Michigan (Baraga-Marquette) and in in central central Wisconsin Wisconsin (Green (Green et et al., al., 1987; 1987;KIng, King, 1990). 1990). Indeed, Indeed, (Baraga-Marquette) and position and and similarity similarity of of strike strike that that the the central central Wisconsin Wisconsin dike Chandler (1993) inferred on the basis of position swarm may correlate northeast -striking -strikingdike dikeswarm swarminincentral centraland andsouthwestern southwesternMinnesota. Minnesota. We correlate with the northeast conclude that conclude that there there are areprobably probably two two northeast-oriented dike populations in central central Minnesota: Minnesota: an an older older probably intruded intruded very very shortly shortly after after intrusion intrusion of the 1770 Early Proterozoic population that probably 1770Ma Ma postpostwith Keweenawan Keweenawan rift rift magmatism. tectonic granites granites and and aa younger younger population associated with dike swarms swarmsthroughout throughoutthe theLake LakeSuperior Superior region region may may cause cause at least Intrusion of Keweenawan Keweenawan dike locallzed of the older Early and localized thermal thermal overprinting overprinting and and complications complications of and Middle MiddleProterozoic Proterozoicregional regional thermal patterns. Schneider In Schneideretetal. al.(1996, (1996, CJES) CJES) reported Keweenawan disturbances of Ar/Ar MAT spectra in northern Michigan and Romano Ar/Ar biotite date from Romano et al. (1997, GSAA) obtained a Keweenawan AdAr west-central Wisconsin Wisconsinpossibly possiblyrelated relatedtotodike dikeresetting. resetting.The Thelocus locusof of <1.2 dates 4 2 Ga Ga Rb/Sr RhISr biotite biotite dates mapped in attributed to uplift in northeast northeastWisconsin Wisconsin (the (the Goodman Goodman Swell) has been attributed uplift associated associatedwith withloading loading 23 �__= Keweenawan rift rift trough trough (Peteman (Peterman and and Sims, Sims, 1988, 1988,Tecto~cs). Tectonics). We suggest lhat that Keweenawan along the Kewee~wan Keweenawan dikes and depth, if p pervasive enough, may provide provide an an alternative explanation explanation (see (see and associated associated plutons at depth, a s i v e enough, also also Coaldey Coakley and and Wang, 1992, lW2, Eos). bs). 2000: AGE Ma. %- U 1685 C Whole rock 1 ioooj, 1600 AGE: 1723 • '"' 1500 - 100 K-feldspar K-feldspar = Tg=1638±l2Ma Tg=1638*12 Ma —No -No Plateau Plateau ,m 100 MN-2-95 1000 - 1458 • Whole Whole rock rock Tg=1551±11 Tg=1551H 1 Ma Ma MN-4-95-FSP 0 16O0 Ma: 100 MN-37A - I 100- 1100 Whole rock Tg=1190±9Ma Whole rock Tg=1164±12 Ma Wv 0 0 2000, MRV-3 Whole rock Tg=1429±11 Tg=l&gkll Ma Ma S DUU 10 Ma: 15W MRV-3C 1150. TQ=1496±11 Ma 1000 ISO? = = 1500- AGE 1700• M RV-5A %39Ar - 10oowo %39Ar 100 , n r - swarms in the the Lake Superior Superior region region (after (afterChandler, Chandler,19G3). 1993). CM is central central Minnesota, Dike swarms MRV is is Minnesota Minnesota River Valley, Riled MRV Valley, KK is Kenora-Kabetogama Kenora-Kabetogamadike dikeswarm, swarm,M Mis isMarquette. Marquette. Filled circles are are Keweenawan region of Rb/Sr circles Keweenawan biotite biotite dates and and large large ellipse ellipse encloses encloses region RblSr biotite biotite dates dates (Goodman (Goodman Swell Swell of Peterman Peterman and Sims, 1988). 24 �The Evolution of the Hydrothermal Hydrothermal Systems Systems Associated Associatd with the Sturgeon Lake Caldera CalderaComplex, Complex, Northwestern Ontario George Hudak and Ronald Ronald L. L. Morton Morton George J. Hudak Research Lab, Duluth, Duluth, Duluth, h b , Geology Department, Depaament, University University of of Minnesota Minnesota-- Duluth, Economic Volcanology Research Minnesota, USA USA 55812 55812 The Archean Sturgeon Lake Caldera Complex (SLCC, (SLCC; Morton Mortonet et al., al., 1990) is is located within the Wabigoon volcan~sedimentaq volcano-sedimentarygreenstone greenstonebelt beltappruximately approximately200 200Km Kmnorthwest northwestof of Thunder Thunder Bay, Wabigoon Ontario. The Complex Complex is host host toto66known knownmassive massivesulfide sulfideorebodies orebodiesand andnumerous numeroussubeconomic subeconomic massive dsulfide lenses. Combined, these orebodies orebodies pproduced ore grading gradiig d e lenses. Combined, these r o d u d nearly 18.4 million tons of ore massive 8.5% 'Z Zn, Cu, 0.91% 0.91% Pb, and 3.73 ounces per ton Ag between 8.5% n, 1.06% Cu, W e e n 1971 1971 and 1991. 1991. Based on detailed mapping, core core relo.&g, relogging,petrographic petrographicinvestigations, investigations,and andevaluation evaluationof of whole rock and trace element analyses, the the caldera caldera wmplex complex has has been been divided into three rock element lithogeochemical lithogeochemical analyses, into three distinct volcanic volcanic sequences sequences (Hudak, (Hudak, 1996). 1996). The Pre-Caldera F're-Caldera Sequence Sequence (PCS) (PCS) represents a large, large, dominantly subaerial shield-type basalt volcano with with localized fields fields of of subaerial to shallow shallow subaqueous subaqueous basaltic tuff tuff and and cinder cone deposits 1988). The Early basaltic deposits (Groves (Groves et al., al.. 1988). Early Caldera Caldera Sequence Sequence (ECS) (ECS) represents the the onset onset of of explosive explosivefelsic felsicvolcanism volcanismand andthe thefonnation formationofofthe the major majorcaldera caldera structure. structure. The represents ECS comprises laterally very thick thick (up to 900 ECS laterally extensive extensive (up to 16 16 km km along along strike) strike) and locally locally very 9Cil m) m) mesobreccia and megabreccia deposits interlayered with and overlain by a series of shallow subaqueous mesobreccia and megabrecc~a overlain series of shallow subaqueous (<1000 m deep) quartz-phyric pyroclastic flow deposits deposits (up to 1200 i m thick) which which host host the F-Group and (<lo00 n thick) Mauabi massive sulfide orebodies. orebodies. The the change in volcanic Mattabi The Late Late Caldera Caldera Sequence (LCS) (LCS) represents the dominantly explosive explosive to to passive passiveeruptions. eruptions. The stratigraphic section in the LCS LCS progresses prupsses style from dominantly feldspar-phyric pyroclastic pyroclastic flow deposits deposits (which host the Sturgeon Lake, Lyon Lake, M e , Creek Creek from quartz ± feldspar-phyric orebodies) through through subaqueous andesite andesite and and kdacite Zone and Sub-Creek Zone o~bodies) i t e lava flows and and domes d o m s to to chemical sediments which include iron the formation of thick sequences of volcaniclastic sediments and chemical fonnation. Age rocks (Davis (Davis et et al., aL, 1985), 1985). as well well as as trace trace formation. Age dates datesof ofthe thecaldera-associated caldera-associated volcanic volcanic rocks element suggest that the element evidence evidence (Campbell (Campbell et et a!., al., 1981), 1981), suggest the Beidleman Beidleman Bay Bay Intrusive IntmsiveComplex Complex (trondjhemite to quartz diorite) was the subvolcanic magma chamber for the emptive eruptive material. (trondjhemite The style evolved during during the the development developmentof of the the SLCC. SLCC. Two style of of hydrothermal hydrothermal alteration alteration also evolved Two alteration suites suites have have been been identified: identified: a) a) an assemblage distinct hydrothermal hydrothermal alteration assemblage associated with massive sulfide mineralization mineralization early in the development of the SLCC, SLCC; and b) an assemblage assemblage associated associated with with iron iron formation which which formed formed during during the the later stages of the formation the SLCC. SLCC. Detailed Detailed mapping indicates that that both both alteration localized "pipe-like'' alteration suites suites illustrate semi-confonnable semianformable geometry geometry with with localized geometry near near "pipe-like" geometry synvolcanic fault zones. synvolcanic The massive sulfide associated alteration suite contains the following mineral fol1owing m i n e d assemblages: assemblages: a) aluminum pyrophyllite, sericite); sericite); b) b) aluminum silicate ++ chioritoid 2 pyrophyIlite, aluminum silicate chIoritoid aluminum silicate (andalusite/kyanite (andalusitdkyanite ± (andalusite/kyanite ± Fe-rich chlorite, pyrophyllite, pyrophyllite, sericite); sericite); c) c) sericite 2 ± pyrophyllite; (andalusitekyanite ++ chloritoid chloritoid 2 pyrophyllite; d) d) chioritoid + chlorite/Fe-rich &natq carbonate; e) e) Fe-rich Fe-rich chlorite 2 ± Fe/Mg-carbonate; + Fe-rich chloriteFe-rich Fehlg-carbonate; and 1) f) localized localii chloritoid zones of secondary secondary feldspar feldspar ++ Mg-rich chlorite. The The iron iron formation formation associated alteration alteration suite suite contains contains the the following following mineral assemblages: assemblages: a) a) FeFerich chlorite + magnetite + grunerite; b) chloritoid + chlorite ++ garnet + + Fe-rich carbonate carbonate ±2 pnerite; + Fe-rich chlorite ±2 FeFe+ Fe-carbonate rich carbonate; and c) Fe-chlorite + Fe-carbonate 2 sericite. ± sericite. There appears to be a change change in in the the style style of of alteration alteration in in the the caldera calderacomplex complex from from early, early, high high systems to to later, later, lower temperatum temperature Fe-formation temperature base-metal sulfide producing hydrothermal system Fe-formation * 25 �hydrothermal systems. systems. The change in alteration style appears to be temporally associated with producing hydrothermal pyroclastic to passive volcanism. the change from pyroclastic may be Archean Archean examples examples of "High "High The Cu-Zn Cu-231 orebodies orebcdies associated associated with with the the SLCC SLCC may massive sulfide sulfide deposits deposits as as described described by by Sillitoe Sillitoe (19951, (1995), Sillitoe. Sillitoe et al., aL, (1996), (1996), Sulfidation" volcanogenic massive et al. a!. (1997). (1997). The inpart, p ~ , and Gamo et The massive massive sulfide sulfideassociated associatedalteration alterationassemblages assemblagesmay may have haveformed, formed, in by reactions between originally glass-rich volcaniclastic rocks and pulses pulses of of metal-rich, metal-rich, magmatic magmatic fluids fluids which were were transported transported from from the the top top of of the Beidleman Bay intrusion which Beidleman Bay intrusion to the seafloor seafloor in in synvolcanic synvolcanic Mineralization appears to have structures structures during the early early stages stages of of caldera calderadevelopment. development. Mineralization appears have occurred occurred directly beneath beneath the the seafloor by of the strata. by sulfide sulfide replacement replacement of strata. The iron iron formation formation alteration alteration directly assemblages resulted from metasomatism by hydrothermal fluids composed of evolved assemblages evolved seawater seawaterwhich which occurred at at increasingly lower temperatures temperatures as as the Beidleman Bay intrusion occurred increasingly lower Beideman Bay intrusion continued continued to cool cool and and rnagmatic volatiles were less magmatic less abundant. abundant. References Campbell, I. H., Franklin, J. M., M., Gorton, M. M. P., P., Hart, Hart, T. R R., S.D. ., and Scott, S. D. (1981): (1981): The Therole roleof of subsubvolcanic 2248-2253. volcanic sills sills in in the the generation generation of of massive massivesulfide sulfidedeposits. deposits.Economic EconomicGeology Geology76, 76,2248-2253. Davis, D. W., Krogh, T. E., E., Hinzer, J., 1..and Nakamura, Nakamura, E. E. (1985): (1985): Zircon Zircon dating datingof of polycyclic polycyclicvolcanism volcanism at Sturgeon Lake and implications for base metal metal mineralization. mineralization. Economic Geology 80, 194219421952. 1952. . . Charlou, J.-L., J.-L., Auzende, J.-M., J.-M., Ishibashi, J., Shitashima, Gamo, T., Okamura, K., K.,Chadou, Shitashimq K., K., Chiba, Chiba, H.,and H.,and the the Shipboard Scientific Scientific Party of the MannsRux ManusFlux Cruise (1997): (1997): Acidic and sulfate-rich hydrothermal Shipboard hydrothermal basin, Papua Papua New Guinea. Guinea. Geobgy Geology 25 25(2), fluids from the Manus back-arc basin, (2). 139-142. 139-142. Groves, D. A, A., Morton, R. L., L., and Franklin, J. J. M. M. (1988): (1988): Physical Physical volcanology of of the the footwall m rocks near ks near massive sulfide sulfide deposit, deposit,Sturgeon SturgeonLake, Lake,Ontario. Ontario.Canadian CanadianJJournal of &ah Earth Science Science o u m l of the Mattabi massive 25, 280-291. 25,280-29 I. and hydrothermal hydrothermal alteration alteration associated associated with late caldera Hudak, G. J. (1996): The physical volcanology and volcanic rocks and volcanogenic massive sulfide deposits in volcanic and volcaniclastic volcaniclastic rocks volcanogenic massive in the the Sturgeon Sturgeon Lakee region of northwestern Ontario. Unpublished Ph. D. dissertation, M dissertation, University Universityof of Minnesota, Minnesota, Minneapolis, MN, 463 pages. Minneapolis, L., 0. J., S., and Franklin, I. J. M. (1990): Physical volcanology volcanology and h hydroMorton, R. L .,Hudak, G. 1.. Walker, Walker, 1. I. S., y b thermal alteration of the Sturgeon Lake Caldera Complex. Complex. In In Mineral Deposits of the Western Western Superior Province, Ontario, Geological Suwey Survey of Canada Open Open File File 2164,7494. 2164,74-94. Superior R. H. H. (1995): (1995): The influence of of magmatic magmatic hydrothermal hydrothermal models models on on exploration exploration strategies strategies for for Sillitoe, R. volcano-plutonicarcs: arcs:In In Mamas. Magmas.Fluids. Fluids,and and Ore Ore Deposits Deposits (Thompson, (Thompson,J.J. F. F. H. H. ed), ed),MAC volcano-plutonic Short Course Short Course Volume Volume 23, 23.5511-525. 11-525. .,Hannington, Hannington,M. D., and Thompson, J. F. H. sulfidation deposits deposits in in the Sillitoe., Sillitoe, R. R. H H., H. (1996): (1996): High sulfidation environment. Economic Geobgy Geology 91,204-212. 91, 204-212. volcanogenic massive sulfide environment. 26 �Patterns of structure structure and and metamorphism metamorphismin i nthe the1-lemlo Hemlo greenstone greenstone belt. belt. S.L. Jackson, Ontario Geological Survey, (705 670 jacksos@gov.on.ca) S.L. Jackson, Ontario Geological Survey, (70s5997; mo 5997; ja&so~@gov.~n.ea) Hemlo greenstone belt rocks generally possess possess a welt-developed well-developed (strong) (strong) penetrative planar penetrative planar fabric that is variably defined by combinations of mineral mineral shape foliation, metamorphic metamorphiciayering, layering. In In foliation, shape layering, and compositional compositional layering. map view the traiectories trajectories of this fabric are curvilinear and aenerallv generally strike maD " internal plutons. Within the subparallel to bounding biunding granitoid masses and larger internal stretch, mineral, and crenulation crenulation lineations lineations are plane of the strong fabric, stretch, common. Stretch Stretch and and mineral mineral lineations tend to be subparallel in a given area; crenulation crenulation lineations lineations may may or may not be subparallel to the stretch and and mineral mineral orientation although there is a lineations. lJneations Lineationshave have notable notable variation variation in orientation general granitoid general westward westward component to their plunges. Internal and external granitoid bodies development. Marginal phases of the bodies show show variable variable degrees of fabric development. Pukaskwa fabrics near the the granitePukaskwa and Black Black Pic batholiths exhibit strong fabrics greenstone belt well-developed fabric greenstone belt contact. The Dotted Doned Lake pluton has aa well-developed near its its margin margin that decreases decreases in in intensity intensity toward toward its its interior. interior. In contrast, the Heron appears to be weaklv weakly to to non-foliated. non-foliated. The The Cedar Lake Pluton Pluton Heron Bay Bav Pluton Pluton amears has weak'to weak to moderate developed at its margin and and aa weak weak foliation foliation in its moder&e fabric developei interior. interior. The variable orientation of the strong fabric within the the greenstone greenstone belt folding. At results, in part, from post-fabric folding. At Mussy Mussy Lake Lake the the granite-greenstone granite-greenstone boundary strong fabric are are sub~arallel subparalleland andfolded. folded. A well-develo~ed well-developed boundarv and strona crenulation fabric and iiss axial crenulathn cleavage cleavagi deforms deforms the earlier margin-parallel margin-parallel strong fabricand axial trace. Similarly, the the Heron Bay Pluton is is interpreted interpreted as planar to the fold axial trace. folded greenstone belt. &It. Again, folded along along with with an an earlier-formed earlier-formed strong fabric in the greenstone this this folding folding is is associated associated with a crenulation cleavage in the greenstone belt belt rocks. The TheGowan GowanLake Lake Pluton Pluton roughly roughly follows the contact between the granitegreenstone the pluton pluton greenstone belt belt which which is is concave concave to to the the northeast. northeast. It is unclear unclear if the configuration curved boundary boundary of the configuration resulted resulted from emplacement into an already cuwed greenstone folding. observations Observations by G.P. G.P. Beakhouse Beakhouse greenstone belt, belt, or from subsequent folding. (OGS) of magmatic magmatic flow flow foliations foliations in in the pluton pluton that that parallel parallelthe the granitegranitegreenstone supporl the interpretation interpretation of post-folding post-foldingemplacement. emplacement. greenstone boundary boundary support Metamorphic Metamorphic grade grade increases increases both both from west to east east and and as as one one approaches external and internal granitoid bodies. bodies. In metabasites, metabasites, the the increase approaches in metamorphic metamorphic grade is is reflected reflected by a decrease in in chlorite chlorite content content with with an an increase in hornblende content, content, the the appearance appearance of of garnet garnet andlor and/or cummingtonite cummingtonite increase and, at the highest the appearance appearance of ofclinopyroxene. clinopyroxene. In highest grades, the In metapelites, mineral assemblages progress from from west west to to east east from from garnet-chlorite garnet-chlorite to to staurolite .mineral to garnet-biotite-sillimanite assemblages exhibit a garnet-biotite-sillimanite assemblages. Calcareous assemblages transition from quartz-iron in the the west west to to quartz-calcitequartz-calcitetransition quartz-iron carbonate+/-chlorite in amphibole epidote-garnet+/-clinopyroxene, hornblende hornblende amphibole assemblages assemblages to epidote-garnet÷/-clinopyroxene, assemblages in assemblages in the the east. east. In In general, the the strong strong fabric in in the greenstone belt belt is is defined defined by by peak peak metamorphic deformed by metamor~hicmineral mineral assemblages. assemblaaes. This fabric is deformed bv the the later later crenulation internal plutons and crenulatibn cleavage that is is associated asskated with folding of internaiplutons andthe the boundary. The general westward component component of of plunge to granite-greenstone boundary. ~ 27 2~~ �and increase increase in in metamorphic grade from west west to to east east suggests linear elements and that deeper erosional levels levels of of the the greenstone greenstone belt belt are are exposed exposed in inthe the east. east. At deformation model is envisaged for the greenstone present a general two-stage deformation greenstone well-defined belt. An early, high-temperature, high-strain stage generated the well-defined foliation foliation that that is is parallel parallel to unit contacts and the granite-greenstone granite-greenstone boundary. There appears appears to be a paucity of map-scale folds related related to this deformation; T.L. Muir (OGS) has observed observed folds with strong axial planar fabric near however, T.L. deposit. A the Hemlo gold deposit. A low-temperature, low-temperature, regional, regional, compressive compressive deformation deformation stage followed and resulted resulted in folding of: the earlier-formed, high-strain high-strain fabric; internal plutons; and, and, the the granite-greenstone granite-greenstone boundary. boundary. This This later later deformation deformation internal stage, which may consist of more than than one generation of folding and faulting, is interpreted to be the main contributor to the current geometry of the graniteinterpreted greenstone belt. greenstone Pubhshed geochronology geochronology allows allows a a general general time frame to be Published be assigned assignedto to stages. The early high-temperature high-temperature deformation the deformation deformation sages. deformation occurred occur6d 2.695 Ga (aae (age of of metavolcanic rocks involved in the deformation) and between 2.695 H & ; Bay and Cedar Lake plutons). The younger lowlow- ' 2.688 Ga Ga (age of Heron temperature deformation occurred between 2.688 Ga (age of Heron Bay temperature deformation occurred between Ga (age of Heron Bay Pluton) Pluton) of Gowan Cowan Lake and, speculatively, 2.678 Ga (age of Lake Pluton). Pluton). At aa subprovince subprovince scale scale greenstone belt is similar to the Manitouwadge the general aeneral history historv of the Hemlo oreenstone Manitouwadae greenstone conjectural, the high grade metamorphism gre&stone belt. AAlthough I ~ ~ Oconje&ral, U ~ ~ the metamorphism and early ea& with comparable "D2" "D2' events rnav be correlative with events (Zaleski (Zaleski et et al. al. 1995) 1995) deformation may recorded Manitouwadge greenstone The late folding may correlate recorded in the ~ anitouwad~ greenstone e belt. The with formation "03" (Zaleski formation of the "D3 (Zalesk et et al. al. 1995) 1995)Manitouwadge Manitouwadgesynform. synforrn. REFERENCES REFERENCES Corfu Chem. Geol. Gaol. ,,79,201-233. 79, 201-233. Corh and Muir Mulr (1989) Chern. T.L Ont.GeoI.Surv. Report 289. 1.LMuir, Muir.1997, 1997.OnI.Geo1.S~~. ReDorl289. Zateski ei at al., at., 1.995. 1995,IISG LSG Field Field?ri; Trip Guidebook Guidebook Zaleski 28 �constraints on the tectonic history Structural and Metamorphic Metamorphic constraints historyof of the the Southern Southern Ste. Marie Marie - Espanola Province in i n the the SauD Sault Ste. Espanola area. area. Ontario Geological Survey, Sudbury Ontario (705 670-5997; S.L. Jackson, Jackson, Ontario Geological Survey, Sudbury Ontario (705 670-5997;Jacksos@gov.on.ca) Jacksos@gov.on.ca) - exhibit aa beauilinalv beguilingly sim~le simple concave to the north Southern Province rocks exhibit attributed to structural grain. Regional Regional structures structures are are commonly comrnonlyattributed to compression compressionduring during PenOkean Orogeny; however, structural, intrusive, and metamorphic relationships Penokean Oroaenv: however, structural, intrusive, and metamor~hicrelationships permit other interpretations. North of tthe h; Murray Murray Fault Fault rocks rocks of of low lowmetamorphic metamorphic grade grade are deformed about generally upright folds folds and reverse/thrust faults. faults. The folds affect Nipissing Gabbro and 2.22 Ga Nipissing and the 1.85 Ga Sudbury Sudbury complex complex and and are are commonly commonly weakly to to moderately moderately developed, developed, steeply steeply dipping, dipping, axial axial planar associated with weakly cleavage. Confusion Confusionabout aboutthe theage age of of folding foldingarises arisesbecause becausemany manygabbro gabbrodykes dykes structures parallel parallel to the axial trace trace of some regional folds which may indicate occupy structures deformation deformation prior to, or synchronous synchronous with, gabbro gabbro emplacement. Scenarios Scenariosthat that account account relationships include: 1) gabbro dykes and sills that were emplaced emplaced into for observed relationships structurally prepared faults/fractures); 2) crustal prepared sites (fold hinges and axial planar faultslfractures); crustal cover accompanied or or flexure resulting in fracturing and faulting of the basement and cover followed by emplacement of gabbro dykes and sills (subsequent compression resulted (subsequent compression resulted intrusive events may be confused confused as as aa single single in folding); and and 3) two or more mafic intrusive event (one represented by pre-folding 2.22 2.22 Ga gabbro sills and one by post-folding post-folding gabbro dykes). the Murray Fault there there is evidence evidence for at least deformationalevents events South of the least 33 deformational pre-Nipissing faulting and large-scale folding related related to syn-depositional syn-depositional including: 1) pre-Nipissing and/or post-depositional post-depositional unconsolidated deformation deformation of of strata; strata;2) 2)"Dl" "Dl" layer-parallel layer-parallel andlor structural pre to to syn peak structural elements reflecting high extensional strain that formed pre metamorphism; and 3) 3) "D2" "02" regional regionalfolds folds and andfaults faults parallel parallelstructures structures north north of the metamorphism; and fault that that deform metamorphic isograds isograds and and are associated associated with a crenulation Murray fault cleavage. Both D2structures structuressouth southof ofthe theMurray MurrayFault Fault affect affect Nipissing Nipissing D land and02 cleavage. Both Dl that D2 02 structures 1.75 Ga Ga gabbro; however, field observations indicate that structures post-date post-date the the 1.75 Cutler Batholith. Batholith. The origin involving staurolite and origin of high-grade high-grade metamorphic assemblages involving the Murray Fault is a perplexing biotite in the McKim McKim Formation south of the perplexing aspect aspect of of tectonics. High previously attributed attributed to Southern Province tectonics. High grade grade metamorphism metamorphism was previously crustal thickening during Although this this could explain the crustal thickening during the Penokean Orogeny. Although mesoscopic 01 structural oriented at a low angle to bedding, the lack structural elements oriented lack of mesoscopic Dl regional structural evidence for the required thickening during Dl and the observation regional structural for the required thickening during Dl and that metamorphism predates regional regional folding folding do do not support this this interpretation. Furthermore, geobarometry indicates relatively relatively low-pressure (2-3kbar; kbar; 6-10 6-10km) km) low-pressure (2-3 metamorphism at a crustal thickness thickness close close to, to, or less than, the estimated estimated thickness thickness of clastic prism prism which would also seem to preclude preclude metamorphism metamorphism related related to the Huronian Huronian clastic crustal thickening. Crustal Crustal extension and increased increased mantle mantle heat heat flow flow might might better better layer-parallel foliation, lack of structural evidence for significant explain the near layer-parallel significant crustal thickening, and andthe thelow-pressure low-pressuremetamorphism. metamorphism. - 0 . 29 �in general, extension of the Superior craton and deposition In deposition of the the Huronian Huronian 2.22 Ga, the age of Supergroup is thought to have occurred between 2.45 Ga and 2.22 and Nipissing gabbro, respectively. lower Huronian volcanic rocks and respectively. However, there is is aa well-established angular well-established angular unconformity unconformity between the 2.45 Ga volcanic rocks rocks and and units are reported overlying formations and no volcanic units reported from within strata strata above the unconformity. Conseauentlv. Consequently, crustal extension and resultant deposition deposition of units unconformitv. units above this mafic this unconformity unconformitymay may have have shortly shortly preceded preceded2.22 2.22 Ga GaNipissing ~i~issin; maficmagmatism. magmatism. Deep parts of the basin basin may have been subjected subjected to elevated elevatedheat heat flow flow during during Dll structural extension resulting in D structuralelements elements and and high-temperature, high-temperature, low-pressure low-Pressure inferred to to shortly shortly follow follow Nipissing Nipissing magmatism. magmatism. Post metamorphism inferred Post metamorphic metamorphic regional .75 Ga generated generated the regional folds and regional compression compression at -1 -1.75 and associated associated axial axial planar cleavage /I crenulation cleavage. cleavage. The The above above interpretation interpretationinvokes invokessubstantial substantial pre- and post-Penokean tectonic tectonic events, events, but does not require deformation or metamorphic metamorphic events in the 1.85-1.82 1.85-1.82 Ga Ga interval. interval. 30 �The The Early Proterozoic break-up of the Superior Superior Craton: Implications Implications of drill core core and and geophysical data south of the Gogebic range, northern Wisconsin. Gene L LaBerge, Gene L. LaBerge,Geology GeologyDepartment, Department, University University of of Wisconsin Wisconsin Oshkosh, Oshkosh, WI WI 54901 and U. S. Geological Geological Survey. Exploration drill cores cores and and geophysical geophysical data data reveal reveal several several nearly continuous continuous belts of Early Exploration thin Proterozoic rocks that extend extend northeasterly northeasterlv from from Proterozoic metasedirnentary metasedimentm and metavolcanic metavolcanic rocks Butternut, the south end of Lake Gogebic, Michigan. The Butternut, Wisconsin to thesouth Thebelts, belts, shown shownby by Menominee Sims (1992) as Blair Creek Formation and as undifferentiated Chocolay and Menominee Group granitoid rocks. rocks. The Group rocks, are separated by expanses of gneissic granitoid Thedistinct distinct geophysical on the the belts belts suggests suggeststhat thatthey theyare arefault ftult bounded. bounded. The boundaries on The - - aeromagnuic and provide information on the nature nature and and aeromagnedc and electromagnetic electromagneticgeophysical geophysical data provide distribution distribution of rock units encountered encountered in the the drill cores. cores. Some cores contain intercepts of up to 100 meters doloinitic mathle, 100 m eters of dolomitic ma~ble,some some of of which which Some inteabeddedbiodte biotiteschist schist Other bunOther cores cores contain contain granular and laminated ironcontains inteabedded massive quartrite, quartzite, which, in turn, grades grades formation that grades abruptly downward into massive into into more more thinly thinlv bedded quaitzite a d t e and and then then into intointerbedded intabeddedquartzite auartziteand and biotite biotiteschist. schist. Iron-formation is commonly interbedded breccias and hn-formationis ~ornmo&~ intobedded with basaltic basaltic pillow lavas, lavas, pillow breccias and hyaloclastite units. Some Somecores corescontain contain granular granularjasper and and hematite hematiteiron-formation iron-formation rocks. Several interbedded with basaltic rocks. Several cores cores intersected intersected zones of strongly foliated foliated gneiss. Some granitoid gneiss. Someof the the cores cores contain contain breccias breccias composed composed of tabular tabular clasts clasts of ironironformation, formation, quartzite, dolomite, or mixtures of these lithologies in a matrix of graphitic bioitite schist. Several Several of of these these breccia zones may be be present in a given core. Lithologies encountered in in the the cores cores are are similar similar to to rode rock units units exposed exposed to to the the northeast northeast in in the the Uthologies (LaBerge and Klasner, 1994). 1994). The The granitoid granitoid gneiss gneissmay may eastern Gogebic range in Michigan (LaBerge baseman, similar be slivers of Archean basement, similarto tothe thePresque PresqueIsle Islegranite graniteexposed exposed near nearMarenisco, Mareiusco, the Bad River Dolomite exposed exposed east eastof of Michigan. The Thedolomite dolomiteis is comparable comparableto the similarin in all all respects respects to to the the Palms Palms Formation Formation Wakefield, Michigan. The Thequartzite quartziteisissimilar of the length length of of the the Gogebic Gogebic range. range. The iron-formation with exposed throughout much of Theiron-formation with rocks is is very very similar similarto tothe theIronwood JronwoodIron-Formation hon-Formation and and interbedded interbedded interbedded volcanic rocks Marenisco, Michigan. The Emperor Volcanic Complex north of Marenisw, The geophysical geophysical data data indicate indicateaa and the the eastern eastern Gogebic Gogebicrange. range. Therefore, it near-continuity of units within these belts and likely that the units are correlative from the Gogebic Gogehic southward as suggested by appears Likely Allen and Barrett (1915) (1915) and and Dutton Dutton (1983). (1983). The volcanic rocks are largely restrictedto to units containing iron-formation, consistent with The volcanic stratigraphic eastern and western ends aids of stradgraphic relations on the &stern of the theCiogebic Gogebic range, (LaBerge (LaBergeand and others, the observations also supports smmorts the observations of Allen Alien and Barrett (1915, (1915. p.90o.90others. 1995). This This study studv also intertiedded with iron-formation are are widely distributed 91) that volcanic vol&c rocks hterbedded distributed in &I several several rocks south of of the the Gogebic Gogebicrange. range. Thus, belts of rocks Thus, volcanism volcanism contemporaneous with ironformation deposition is present present on the eastern and western ends of the Gogebic range and formation Gogebic rangeand iron-formation units along along the the length lengthof of the therange rangeto to the the south. south. The The widespread with iron-formation widespread occurrence (logebic range occurrence of volcanic rocks south of the Gogebic range indicates indicates aa broad distribution distributionof of volcanism southward toward the proposed margin of the Superior Craton. The sediments The breccia units are interpreted as depositional breccias, where shallow-water sediments (dolomite, quartzite, quartzite, and and iron-formation) slumped into deeper, deeper, stagnant basins basins in in which which carbonaceous, mud was was accumulating. accumulating. These These stagnant carbonam&, pyritic mud stagnant basins basks are interpreted to be restricted, fäult-bowrded fault-bounded basins into which miodic shallow-water sediments sediments periodic slumuine slumping of shallow-water occurred along along fault fault scarps. scarps. 31 �Collectively, formal environment environment at least 60-100 Collectively, the thedata data suggest suggest that 1) 1)aa plat platformal 60-100 km km wide wide extended range, on which dolomite dolomite and quartzite extended southward southward from from the present Gogebic range, quartzite of Marquette Ciange Supergroupaccumulated; accumulated; 2) volcanism commenced commenced during during ironironGange Supergroup the Marqueite formation demsition. deposition, mobablv probably associated with rifting rifling and the formation of fault-bounded fault-bounded formation basins. Volcanism the overlying ocean stagnant bas&. ~ol&sm may &ay have have contributed contributediron iron and and silica silica to theoverlying ocean water, which as iron-formation; iron-formation; 3) 3) breccias containing clasts breccias containing dasts of which was was then precipitated as that rifting rifling and the shallow-water sediments within carbonaceous sediments suggests that formation occuned along along the the margin marginof ofthe the Superior SuperiorCraton. Craton. In this formation of stagnant basins occurred inteipretation rocks in the several "ranges" to the south are prepminterpretationthe the Gogebic Gogebic range and the rocks coffision, and not related to foreland basin basin evolution. evolution. Available collision, Availableevidence evidenceindicates indicatesthat that the the overliethe theiron-formation. iron-formation. These Tyler and Copps Copps Formations unconformably overlie These formations formations are interpreted collisional tectonics, tectonics, and be foreland foreland basin basiin deposits related to wllisional and to to be be are interpreted to to be significantly younger significantly younger than the the iron-formation. Referfences Cited. Referfences Cited. Allen A lien ,,R.C., R.C., and Barrett, LP., 1915, 1915, Contributions Contributionsto tothe thePro-Cambrian Pre-Cambrian geology of Michigan and Wisconsin: Michigan Geological and Biological Biological Survey, Survey, northern Michigan Publication Publication 18, 18,Geology Geology Series Series15, 15, pp pp 65-139 65-139 Lithology and and geologic geologic setting settingof of Lower Lower Proterozoic Proterozoic iron-formation in Dutton, C. E., 1983, Lithology parts of northern Wisconsin: U.S. 15p. U.S. Geological Geological Survey, Survey, Open-File Open-File Report 8484- ,, iSp. LaBerge, G. L., Cannon, Cannon, W. F., and Klasner, J. S., 1995, 1995,New New observations observations on on the the range (Abstract): (Abstract): 41st 41st Annual Annual Institute Institute on on Lake Lake geology of the the western Gogebic iron range Superior Superior Geology, Geology, Marathon, Marathon, Ontario, vol. 41, 41, part part 1,1,p. p. 33-34. 33-34. L and LaBerge, G. L andKiasner, Klasner,I.J. S., S., 1994, 1994, Tectonic Tectonic implications implicationsof the the Early Early Proterozoic Proterozoic lithostratigraphy on the range, northern Michigan (Abstract): 40th Whostratigraphy the eastern eastern Gogebic range, 40th Annual Annual Houghton, Michigan, Michigan,vol. vol. 40, 40, part part 1, 1, p. p. 27-28. Institute on Lake Superior Geology, Houghton, P.K., 1992, Sims, P.K., 1992,Geologic Geologic map of Precambrian rocks, southern southern Lake LakeSuperior Superiorregion, region, Investigations Wisconsin Wisconsin and and northern northern Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey ,,Miscellaneous Investigations Series, Map 185. Series, Map1-2 1-21 85. 32 �Mineral Potential Study of a Greenstone Greenstone Belt Area, Minnesota Using Boulder Boulder Tracing, Tracing, Ely—Bigfork Ely-Bigfork Area, Minnesota Tom Lawler and Darold Darold Riihiluoma Riihiluoma of Natural Natural Resources, Resources, Division of State of Minnesota, Department of Minerals, Ave. E. 55746-1461 Minerals, 1525 1525 Third Ave. E. Hibbing, MN 55746—1461 Internet: lawler@dnr.state.mn us Internet: torn. tom.lawler@dnr.state.mn.us • Abstract Minnesota is an area of complex The Ely—Bigfork Ely-Bigfork area of northern Minnesota Archean bedrock geology. geology. Bedrock lithologies, structure, lithologies, structure, alteration, mineral occurrences and exploration exploration geochemistry alteration, mineral occurrences geochemistry indicate there thereshould should be be undiscovered undiscovered valuable valuable metallic metallic mineral mineral indicate deposits. sample site deposits. The The poster displays sample site locations locations and and anomalous anomalous results metal potential. The results which which indicate indicate gold or base metal The granite granite greenstone similar to those those hosting hosting economic greenstone belt (Morey, (Morey, 1996) is similar economic mineral deposits mineral deposits in in the the Archean of of Canada Canada and and Scandinavia. Scandinavia. - objective of this to provide provide a a reconnaissance reconnaissance study The objective this project is to of mineral mineral potential potential for for a a sixty—one sixty-one township township area area in in northern northern St. St. Louis County, southeastern Koochiching Koochiching County County and County, southeastern and northeastern northeastern Itasca achieved by by mapping mapping alteration alteration and analysis Itasca County. This This is achieved of mineralized rock samples found in glacial glacial drift drift deposits deposits from from pits. Anomalous gold values ranged 144 sites, mostly mostly gravel pits. ranged to to Base metal metal values values 3,598 ppb, with arsenic values up to 1,900 ppm. Base include zinc to 2,899 2,899 ppm, lead to to 248 248 ppm, copper to to 14,944 ppm and lead ppm, barium to to 1,980 1,980 ppm. ppm. Partial Partial analytical analytical results are ppm, also barium presented table with with anomalous anomalous areas areas designated designated as as Mineral Mineral presented in aa table Potential Areas (MPAs). The map map presents presents site number, number, designation Potential (MPAs). The as gold or or volcanogenic volcanogenic massive massive sulfide model, and and MPA MPA number. number. Samples of analyzed rock are displayed for many sites. The sites. The table table Mineral Potential Areas From Analysis displays selected Potential From displays selected analysis analysis used to to model model mineral mineral potential. potential. The location The location of of the the source source of mineralized samples samples is is indicated indicated by: by: 1. Development of mineralized—altered boulder 1. Development of mineralized-altered boulder dispersal dispersal trains. trains. 2. 2. amount of the sample The amount of mineralized rock at the sample site site which which decreases decreases denudation. 3. 3. Hand Hand lens classification classification with distal distal dispersion dispersion and denudation. lithologies contributing pebbles to a randomly selected sample of lithologies of 100 100 pebbles pebbles from from each each site site which which are are compared compared with with mapped mapped bedrock lithology bedrock lithology (Morey (Morey 1996). 1996). MPAs MPAs 1, 1, 2, 7, 7, 8 and 17 17 are are in in an an area mapped by Mooers, et al. al. (1996) as scoured scoured bedrock uplands uplands or (1996) as Lobe deposits. By all the the criteria criteria the the northern northern sites sites of MPA Rainy Lobe MPA5 7 and 17 are near the 1 and 2, and all of MPAs the bedrock bedrock source source of mineralized these MPAs, MPA5, Mooers, et mineralized rock. rock. West West 0of these et al. map additional additional dispersion by 3, 4, 5, 9, Kooochichinq Lobe. Lobe. 14PAs MPAs 3, dispersion by the the Kooochiching 9, 10, 10, 11, 11, 12, 12, 13, 14 and 15 their source 15 are are reasonably close to their source by by most most of of the the criteria. some distance distance from criteria. MPA MPA 6, 6, 88 and and 16 16 might be some from their their source. source. 33 �Morey, G.8., G.B., Compiler, Compiler,1996, 1996,Geologic GeologicMap Map of ofMinnesota, Minnesota, Minnesota Morey, Minnesota Geological Surveyl Digital Version Geological Survey, Digital Version H.D., et etal., al., 1996, 199G1Geomorphology Geomorphology of of the the Basswood Basswood Lake, Mooers, H.D., Mooers, Lake, Crane Lake, Little Fork, Ely, Vermilion Lake and Bigfork Crane Lake, Little Fork, Ely, Vermilion Lake and Bigfork 1: 1,000,000quadrangles quadranglesand and the the development developmentof of the the Land Land Type 1:1,000,000 Type Association layer of the Ecological Classification System, Association layer of the Ecological Classification System, MinnesotaDepartment Departmentof ofNatural Natural Resources Resources—-Division of Forestry Forestry Minnesota Division of MINERAL POTENTIAL AREAS I I P318 STUDY AREA • VMS BASE METAL CC:) MINERAL POTENTiAL AREA • GOLD SITES WITH NO MINERAL POTENTIAL SCALE 1:1mom SCALE 1:1.000,000 34 34 A �THE THE PETROLOGY PETROLOGYOF OFGREENSPAR: GREENSPAR: A A PROTEROZOIC PROTEROZOICPORPHYRITIC PORPHYRITICDIABASE DIABASEDIKE; DIKE; PIFHER NIPIGON DISTRICT, DISTRICT, ONTARIO PIFHER AND IRWIN IRWIN TOWNSHIPS, LAKE NIPIGON ONTARIO by Whitewater, Wl WI 53190 by Frank Frank A. R. Luther, Luther, Geology, UW-Whitewater, Whitewater, 53190 This This approximately approximately50 50 m mwide wide porphyritic porphyritic diabase diabase dike, dike, outcropping outcroppingininwestern western Irwin and Pifher Townships in the Lake Nipigon district, is locally known as greenspar. Irwin and Pifher Townships in the Lake Nipigon district, is locally known as greenspar. The The dike dike has has aa characteristic characteristic greenish greenish mottled appearance in outcrop as a result result of sausseritized sausseritized plagioclase plagioclaseglomerophenocrysts glomerophenocrysts in in aa diabase diabasegroundmass. groundmass. The The dike dike strikes strikes due due north northand anddips dipsvertically. vertically. ItIt is is located located approximately 15 15 km km east east of Lake Lake Nipigon Nipigon and and 5-20 5-20 km km north northof ofHwy Hwy11. 11. Mackasey off-set by by east-west east-westfaulting faulting Mackasey (1975) mapped mapped the dike as segments segments off-set and and suggests suggests that that only onlyone onedike dikewas was originally originallyintruded. intruded. Kresz Kresz and and Zayachivsky Zayachiiky (1989) observed chill borders borders on dike apophyses and stated that the the dike dike has has been been obsewed chill seen seen some some50 9km kmsouth southof of Irwin IrwinTownship. Township. Both Both reports reports stated stated that that the the glomerophenocrysts distribution; Mackasey reported glomerophenocrysts are erratic in distribution; ~ac-kasey reported aa segregation segregation of the the glomerophenocrysts glomerophenocrystsinto into bands bandsat at one one location. location. Alteration Alteration of of the the country muntryrock rockwas was not not reported reported by by these these workers workers nor nor was was itit seen seen by by the the author. author. The (1975) determined determinedthat that The greenspar greenspar dike dike isis of of Proterozoic Proterozoicage. age. Mackasey Mackasey (1975) this this dike dike is is cut cut by by the the large large middle middle or or late late Proterozoic Proterozoic (Keweenawan?) (Keweenawan?) sill in in Irwin Irwin Township. Township. There There are are no no radiometric radiometric dates dates on on this this rock rock or or associated associatedrocks. rocks. A A whole whole rock r w k chemical chemicalanalysis analysis of of the the greenspar greenspar isispresented presentedininTable Table1.1. The The texture textureand andmineralogy mineralogyof of this this rock rock were were studied studied by by petrographic petrographic and and electron electron microprobe microprobeanalysis. analysis. The The rock rockconsists consistsof of 20% euhedral, 20% glomerophenocryst g l o m e r o p h e n ~plagioclase: plagioclase: t euhedral, 1-5 1-5cm, cm,with withremnant remnantplagioclase plagioclase cores (an), the bulk of these crystals are altered to a very fine-grained cores (an83),the bulk of these crystals are altered to a very fine-grained mixture mixtureof of albite, albite,epidote, epidote,sericite, sericite,and andzeolite(?). zeolite(?). 45% (an) totorim 45% groundmass groundmassplagioclase: plagioclase: normally normally zoned core (ans) rim(an61), (an6,), subhedral subhedral laths, 0.5-1.O mm, mm, cores coresare are rarely rarelyaltered alteredto to aafine-grained fine-grainedmixture mixtureofof laths, 0.1-0.3 0.1-0.3 xx 0.5-1.0 sericite sericiteand andepidote. epidote. 30% Mg, minterstitial , interstitialtotosubhedral, subhedral,0.2-0.3 0.2-0.3 mm. mm. zonalcore coreMg70 Mg7,3to rim M 30% augite: augite:zoned 4% 4% opaques: opaques:euhedral euhedralmagnetite, magnetite,ilmenite, ilmenite,and andpyrite, pyrite,0.1-0.3 0.1-0.3mm. mm. <1% quartz: interstitial grains 0.1-0.3 mm. 4 % quartz: interstitial grains 0.1-0.3 mm. The haveremnant remnantcores coresofofanm an composition compositionwhile while the the The glomerophenocrysts glomerophemcrysts have bulk bulk of these these large large crystals crystals are are altered altered to aa mixture mixture of albite, epidote, sericite, sericite, and and zeolite(?). zeolite(?). The The glomerophenocrysts glomerophenocrystsare are interpreted interpretedas as phenocrysts phenocrystsbecause becauseof of their their euhedral form. No broken crystals, xenocrysts of other composition or mineralogy, euhedral form. No broken crystals, xenocrysts other composition or mineralogy, or or xenoliths xenolithswere wereobserved. obsewed. The The glomerophenocrysts, glomerophenocrysts, being being highly highly calcic, were were easily easily sausseritized during during sub-solidus sub-solidus events. The Thenormally-zoned normally-zonedplagioclase plagioclaseof of the the sausseritized wasnot notas assusceptible susceptibletotoalteration; alteration; groundmass with an average composition groundmass composition of of aanMwas some somecrystals crystals show show minor minor alteration alteration of of the the more more calciccores. calcic cores. Clinopyroxene Clinopyroxeneininthe the 35 �grouridmass in rims; there there is groundmass is is zoned zonedfrom fromMg70 MgTO in the the core core to to Mg40 MgdOin the rims; is minor minor alteration of of the clinopyroxene clinopyroxene to to actinolite actinolite and and zeolite(?). zeolite(?). Euhedral Euhedral Mn-bearing Mn-bearing ilmenite (sometimes skeletal or intergrown with with Ti Ti hematite?), magnetite, and pyrite pyrite groundmass. Olivine are present throughout the groundmass. Olivine was was not not observed. observed. It is The length is interesting interesting to speculate on the age age and and origin origin of the the greenspar. greenspar. The length of 15 vertical dip, uniform strike, and 15 (perhaps up to 65) km, minimal variation in width, vertical apparent over-all compositional homogeneity point point to to a deep-seated source and a long period of cooling at considerable depth to crystallize the exceptionally large large glomerophenocrysts. glomerophenocrysts. Following this period of quiescence, the magma magma was was intruded intruded into cooler Archean country rocks where the remaining remaining melt melt cooled cooled rapidly rapidly enough enough to to form zoned plagioclase and clinopyroxene. The glomerophenocrysts were zoned plagioclase and dinopyroxene. glomerophenocrysts were deuterically altered soon after emplacement while the groundmass plagioclase, less less minerals were less calcic in composition, and other groundmass minerals less affected. With mineralogical similar.@ similarity to to middle or late late Proterozoic Proterozoic respect to the time of intrusion, the mineralogical (Keweenawan?) diabases is (weak) evidence evidence that that this this rock may be an early early phase phase of Keweenawan Keweenawan activity. Logically, a lone dike in this location, given the characteristics characteristics enumerated above, with no compositional similarity to lamprophyre lamprophyre or kimber!ite, kimberlite, could easily be an early phase of Keweenawan Keweenawan magmatic magmatic activity. activity. Alternatively, Alternatively, the the east-west strike-slip offsets noted by Mackasey are not consistent with mostly mostly dip-slip dip-slip preKeweenawan faults resulting resulting from rifting. rifting. This faulting could indicate indicate a preKeweenawan origin of the greenspar. greenspar. Table of the greenspar. greenspar. (XRAL 1. A bulk chemical analysis of (XRAL Laboratories) LaMratories) Table 1. Si02 Si02 Al203 A 10 CaO CaO MgO MCJo Na20 NazO 1<20 K20 FeOt FeOt MnO MnO 1102 Ti02 P205 Pa5 Cr203 cr2m LOl LO1 TOTAL 48.9 13.2 13.2 11.0 11.0 6.02 1.94 0.28 14.2 0.21 0.21 1.33 0.15 <.01 c.01 Rb Sr V Zr Nb Ba 2 ppm 209 22 105 11 137 0.85 98.1 98.1 REFERENCES REFERENCES D.U. and Zayachiisky, Zayachivsky, B., Kresz, D.U. B., 1989, Precambrian Precambrian geology, Barbara, Meader Meader and and Townships; Ontario Geological Geological Survey, Survey, rpt rpt 270 270 with with maps 2536-2537, 2536-2537, 91 p. Pifher Townships; W.0., 1975, Dorothea, Sandra, and and Irwin Irwin Townships, Townships, District Districtof of Mackasey, W.O., 1975, Geology Geology of Dorothea, of Mines, r rpt Thunder Bay; Ontario Division of pt 122 with map 2294, 83 p. 36 �Initial results of ArlAr Ar/Ar mineral dating from the Peavy Peavy node nodearea area of ofnorthern northern Michigan and and Dunbar dome Dunbar dome area areaof of northeastern northeastern Wisconsin. Wisconsin MANCUSO, C.M. Cit. HOLM, OH MANCUSO, HOLWD.K., D.K.Dept k p t .of(Jeology, of Geology,Kent KentState StateUniversity, U ~ v e r s i t yKent, Kent, , OH 44242 (dholm@kentedu); (dholm@kent.edu); FOLAND, FOLAND, K.A., KA,and and HUBACHER, m A C H E R , F.A., FA, Dept. of of Geological Geological Sciences, The The Ohio Ohio State State University, University, Columbus, Columbus, OH OH 43210. 43210. The origin has The origin of gneiss gneiss domes domes and and metamorphic nodes exposed within the Penokean Penokean orogenic orogenicbelt belt has perhaps areas of of geologic geologic research research in in the the Lake Superior pexhaps been one of the most important and controversial areas region. have re$zion. Although Althouzhthe thenodal nodaJisograd isomadpatterns patlemsappear a o mgrossly mossl~similar similar In in map mm view, view. they they may mav actually actuall~ have very different tim&, times, and and may may evin even be the product veiy different diffmnt origins, 6rigjm. may hhave a k formed f o b & at dffere2 pbduit of polyphase po~bhase metamorphism. For For Instance, htance, Emiio Emilioetetal. al. (1996) (1996) on on the basis basis of textural relationships suggested that the node In in northern northern Michigan may be the result of three threediscrete disaetemetamorphic me$amotphieevents. events. metatnorphic node Peavy metamorphic Peavy node Winnet. (Winnet, 1981) ArIAr thermochronologlc t h e n n o c h r o ~ ~ l results o ~ c within tthe he Peaw 1981) are are suggestive su~~estive In addition Initial initial Ar/Ar post-orogenlc reheating episdes. episodes. Finally, numerous R Rb/Sr and mica d&s dates from within ~ I and'KlAr S ~ K/Ar &ca frogwitAin of several post-omgenic south) of the Peavy node also suggest a protracted history history of post-omgenic post-orogenic uplift uplift and outside (mainly south) andor reheating Petennan et al., aL, 1985). 1985). We (Aldrich et el al., al., 1965; 1965; Peterman We report here the the results results of of new new Ar/Ar ArlAr and/or reheating (Aldrich mineral mineral dates dates which whichfurther furtherelucidates elucidatesthe thethermal thermalhistory hisloryof ofthis thisarea. area dated one Result of hornblende hornblendedating. dating.We We dated onehornblende hornblendeseparate separate(96-MI-4) (96-MI-4) from froman anaxnphibolite amphiblite schist collected from the south kmwest westofofFoster FosterCity, City,MI). MI). lThis 3 i s sample sample yielded south side side of the the Feich Felch Trough (—7 (-7 km an excellent plateau date of 1799±6 total gas date of 1797 1799% Ma (and concordant concordant total 1797Ma). Ma). This date is comparable to the oldest post-Penokean K/Ar hornblende hornblendedate date from fromthis this area area obtained obtained by Aldrich et al. post-Penokean WAr a1. (1965) and is interpreted below interpreted to to represent represent the thetime timeofofinitial i ~ t i acooling cooling l below—500°C -51N° after after Penokean-age Penokean-age regional metamorphism. We Wenote notethat thatprevious previous hornblende hornblende Ar/Ar AdAr total gas dates d a m and and K/Ar WArdates datesobtained obtained Ma) and may well to the the west are are substantially substantially younger youngex (predominantly (predominantly 1730-1500 Ma) well represent representlocalized locaked thermal recognized 1630 thermal overprinting oveaprinting effects effects possibly possibly associated associated with the the.long recopizd 1630Ma Ma metamorphic m W o r p h i cevent went or or of the the Middle MiddleProterozoic Protozoic Wolf WolfRiver RiverBatholith. Batholith. even iintrusion n w o n of Result of muscovite muscovitedating. dating. Muscovite Muscovitefrom froman anArchean Archeanmuscovite-biotite m m v i m i o t i t e schist collected mUected at Foster l%stec City (94-MI-i) plateau date date of of 167335 1673±6 Ma oover the last last (94-M-1) showed showedsome somepossible possible recoil effects but yielded a plateau w the released. Coarse (96-MI-5) located located in in the the north ecentral part 50% of the gas released. Coam muscovite m m v i t e from a pegmatite (96-MI-5) n W part plateau date date of of 1653*4 1653±4Ma. Ma. nThese the oldest oldest mica mica dates dates of the Felch Trough gave an excellent plateau e s e dates are the aL, ArtAr or K/Ar WAr methods (see Aldrich et d .,1965 1965 and Winnet, Winnet, 1981). 1981). obtained from the area by either the Ar/Ar comparable to to the 1610-1680 Ma RbtSr Rb/Sr and and ArIAr Ar/Ar biotite biotite dates dates obtained obtained from from the the They are roughly comparable 1610-1680 Ma et al., aL, 1996) and may indicate the wan Schmus Sciunw and Woolsey, 1975; 1975: Schneider et Republic area to the north (Van regional time of initial i ~ t i aslow slow l regional cooling coolingthrough throughmica micaclosure closuretemperatures temperatures(—350-300°C) (-350-31N°C long after the Penokean Orogeny. Alternatively, Penokean Alternatively,these thesedates dates may may represent nearly complete complete thermal resetting resetting associated associated with the 1630 morphologyof of the the spectra spectrado do not not seem to support this 1630 Ma low-grade event although the morphology interpretation. Result of of biotite biotite dating. dating. We Wedated date4two twobiotite biotiteseparates separatesfrom from rock rock samples samples collected collected in in northeast northeast Wisconsin south southof of the the Niagara NiagaraFault Fault AAsample WI sampleof of aaPenokean Penokean pluton pluton collected collected near near Aniberg, Amberg, W I Wisconsin (southeast of of the the Dunbar Dunbar dome) dome) yielded yieldedaaplateau plateauage ageofof1456H 1456±4Ma. Ma. RblSr Rb/Sr biotite dates from (southeast fiom this locality younger (1350-1390 locality and and from fiom several severalsurrounding mounding localities lcalities are are substantially substantially youngex (1350-1390 Ma, Ma, Peterman Pemmanetetal., al., 1985). The meAr/Ar ArlArbiotite biotitedate dateisisnearly n w l y concordant concordant with with the intrusion age age of of the theWolf WolfRiver Riverbatholith batholith (exposed -25 -25 km to to the the southwest). southwest). The m enearest nearest exposed exposed portions portions of the the batholith batholith contain contain miarolitic miarolitic (exposed cavities composition which which suggests suggests cavities and a late late differentiate differentiate of of itit (the (theBelongia Belongia Granite) Granite) has has aacomposition Anderson and and Cullers, 1978). emplacement at shallow shallow crustal crustal levels levels (<4 (<4 1cm, km, Anderson 1978). Considering that the batholith extends for a considerable subsurface distance beyond beyond iB its map new view exposure exposure (Allen baU101ith extmds (Nlcn and and Hinze, Him, 1992), we suesxt suggest that the 1456 1992). we 1456 Ma Ma biotite biotite date date represents renresents thermal resetting resettine of shallow sliallowcrustal crustal rocks rocks intruded by th<-wolf the Wolf River intruhh R v a Batholith. km north north of of (WI-7) collected collected within the Dunbar Dunbar dome dome (—8 (-8 Ian Biotite from a biotite augen augen gneiss (WI-i) WI) yielded yielded aa near-plateau near-plateaudate dateof of 1128B 1128±3Ma Ma(and (andtotal totalgas gasdate dateofof 1116 1116Ma). Ma). This hDunbar, n b a r , WI) 'IXs date is nearly (Peterman et etal., al., 1985) 1985)and and nearly concordant concordant with with previous pxeviow Rb/Sr RbtSr biotite biotite dates obtained from this locality (FWexman - 37 �_____ ___________________ _________ from localities to the west (i.e., (i.e., the locus 01<1.2 of 4.2 Ga GaRb/Sr RblSrbiotitc biotitedates datescalled called the theGoodman Goodman Swell Swell by by from Peterman Peteand Sims, 1988). 1988). Our Ourdate daceisisconsistent consistentwith withthe theinterpretation intametationthat thatthis thisarea areacooled cooledduring durinz uplift be related to to loading loading along along the the Keweenawan Keweenawanrift riftbut but may mayalso alsoalternatively ~ltematively bcexplained, explained,perhaps, perhaps, by bi uplift related resetting igneousactivity. activity. m t t i n g due due to to subsurface subsurfaceKeweenawan Kcweenawanigneous References References Aldrich, LT., L.T., Davis, Davis,G.L, G.L.,and andJames, James,Hi., H.L.,1965, 1965, Ages mineralsfrom frommetamorphic metamorphicand andigneous igneous Aldrich, Ages ofof minerals rocks Petrology, 6: 445-472. 445472. rocks near near Iron Iron Mountain, Michigan: Journal of Pelrology, Allen, D.J., D.J., and and Hinze, Him,W.J., W.1,. 1992, 1992,Wisconsin Wisconsin gravity gravityminimum: minimum:Solution Solutionof ofaageologic geologicand andgeophysical geophysical Alien, puzzle evolution: Geology, p W e and and implications implications for for cratonic cratonic evolutiozx Geology, 20: :515-518 515-518 Anderson,J.L., J.L., and and Cullers, R.L., RL.,1978, 1978,Geochemistry Geochemistryand andevolution evolutionof ofthe theWolf WolfRiver RiverJ3athollth, Batholith, aa late late Anderson, Precambrian rapakvi massif in northern Wisconsin, Wisconsin, U.S.A.: U.S.A.: Precambrian PrecambrianResearch, Research,2 7:287-324 287-324 Ejnilio, IstC., MC., Johnson, Johnson, EL., EL., Matty, Mat& D., D., 1996, lW6,AACritique Critiqueof ofNodal Nodal Isograd Isograd Patterns P m in in the theUpper U p Emillo, Peninsula of Michigan: Michigait FLIS, as, 77: S285 Peninsula of SZ85 Petermnan, Z.E.,and andSim, Sims,P.K. P.K.,1988, 1988,lXe TheGooduma Goodman.% Swell: lithosphericflexure flexurecaused causedby bycrustal austal Peteman, 2.E.. WE AAJithospheric loading rift s system: Tectonics, 2 7:1077-1090. loading along the the Midcontinent rift ystem:Teuonics. 1077-10!90. Peterman, Z.E., Sims, P.K., P.K., Zartman, Zariman, RE., RE., and Schultz, K.J., Petem~an, ZE., KJ- 1985, 1985,Middle MiddleProterozoic F'mtemzoic uplift uplift events wen@in the Dunbar Dunbar Dome Dome of northeastern northeastan Wisconsin, Wimnsin, USA: USA: Contributions Contributionsto Mineralogy Mineralogy and Pemlogy, the Petrology, 91: 138150. 138-150. Schneider,D., D., HoIm, Holm, D., D., and and Lux, D., D., 1996, 1996,On Onthe theorigin originof ofEarly W l yProterozoic Proterozoicgneiss gneissdomes domesand and Schneider, metamorphic nodes, northern Michigan: Canadian Ekrth Science, 33: 1053-1063 1053-1063 metamorphic Canadian Journal of Earth Van Schmus, Schmus, W.R., W.R., and Woolsey, L.L., 1975,Rb/Sr RblSrgeochronology geochrono1ogyofofthe theRepublic Republicarea, area,Marquette Marquette Van Li., 1975, county, EarthSciences, Sciences,12: 1 21723-1733. 1723-1733. county,Michigan: Michigau: Canadian Canadian Journal Journal of of Earth Winnett, T.L., 1981, Middle Precambrian (PreCambrian thenualhistoiy historyofofnorthern n o d e mMichigan: Michigan: Winnett, tL, 1981, Middle PreCambrian (PreCambrian X)X)thermal Master's StateUniversity. U~versity. Master'sthesis, thesis,Ohio OhioState 94Mk1 iso- 1650- - Age Ma Ma .° 0 Muscovite Muscovite 1625 Tp=1673±6 Ma Age Ma Ma Tg=1640 Ma I I I 20 2 0 40 4 0 660 0 880 o l100W 00 : o0 9&M15 = 1150 - o-•_ 1100 4060 40 40 , 00 20 2 0 440 0 6 600 96-MM I, 4 1700 Ma 00 a.— — Homblencte Hornblende Tp=1799±6Ma T p l 7 9 W Ma 1Tg=1,7971'4a 20 20 40 40 60 60 %3OAr 38 80 80 100 iC Riotite Biotite Tp=1128+3Ma Tp=1128*3 Ma Tg-1116 a Tgflll6Ma %39Ar 1800 80 80 - %39Ar 1900 60 60 WI-7 - Age Ma 20 2 0 4 0 6 0 880o l100W P3 20 -— 1125 Biotite Biotite Tp=1456±4Ma Tp=1456*4 Ma 1Tg=lp7My Tg=1437 M Muscovite Muscovite Tp=1653*4 Ma Ma Tp=1653±4 Tg=1647 Ma Tg=1647 Ma I I I 00 WI-4 p 100 100 80 100 �THE SUIB-BARABOO PALEOSOL,WISCONSIN: WISCONSIN: GEOCHEMICAL GEOCHEMICAL EVIDENCE EVIDENCE FOR SUB-BARABOO PALEOSOL, PROTEROZOIC WEATHERING AND AN]) METASOMATISM METASOMATISM RH., Jr., Jr., Dept. Dept. of ofGeology Geology & & MEDARIS, L.G., MEDAKIS, L.G.,Jr., Jr.,BAUMGARTNJB, BAUMGARTNER,L.P. L.P.and andDO'IT, DOfl, 1CR, Geophysics; McSWEENEY, K, K,Soil SoilScience; Science;all allatatUniversity Universityof ofWisconsin-Madison, Wisconsin-Madis04 Geophysics; Madison, WI, 53706 53706 Precambrianpaleosols paleosolsprovide provideimportant importantdata data for for the the interpretation interpretation of ofpaleoclimates Precambrian paleoclimates and paleoatmospheres, but the chemical compositions of such ancient soils have paleoatmospheres, but the chemical compositions of such ancient soils havecommonly wmmonlybeen been modified by subsequent subsequent &genesis diagenesis or orm metamoiphisni. etamorph A A paleosol pdwsol has has recently recently been been discovered discoveredat at modified by the Chanite (Medaris (Medark et etaL, the base of the post-1760 Ma Baraboo Baraboo Quartzite Quartziteon onBaxter BaxterHollow HollowGranite al., 1996; have been obtained 1996%1996b), 1996b),and andchemical chemicalanalyses analyses have obtained to evaluate evaluate the conditions conditions of of weathering and possiile possible effects effects of of metasomatism metasomatisim The The geochemical geochemicalprofile profle of the sub-Baraboo sub-Baraboo paleosol palwsol is is consistent -withweathering weatheringunder wider conditions conditions of of mtense intense leaching, leaching, but but appreciable appreciable potassium potassium was condent with added added to saprolite saprolite and and the the associated associated pedogenic pedogeniczone m eduring duringlater latermetamorphism. metamorph f the sub-B sub-Barabm paleosol:the thequartzite-granite quaxtzite-ganite contact contactin inBaxter BaxterHollow Hollowisis Description ooft/ic araboo paleosol: not exposed in outcrop, but the the contact contact was was penetrated penetratedby by eight eight holes that that were were drilled drilled by the the U.S. Army Corps of Engineers in in 1959. Material the contact Materialfrom fiomthe contact zone zone was was recovered recoveredonly only in in drill from Hole No. 613, in which overlying pebbly quartzite d d core &om quartzite is separated separated from fromunderlying underlying granitic by aa 2.5 2.5 foot-thick, foot-thick, reddkh-pqle reddish-purple pedogenic gsa~ticsaprolite by pedoge~czone, consisting consisting of flne-grained he-grained hematite, quartz, quartz, and illite (kkaolinite). (±kaolinite). The The pedogenic pedogenic zone zone shows shows features features that are are commonly commonly associated with physical reorganization reorganization (e.g., (e.g., repeated repeated wetting wetting and drying) d q h g ) of of weathered weatheredrock rockin m soil-forming environments, which include: 1) aggregates of clay-size and larger grains with small soil-fonning w%ich include: aggegates of larger gains with wall intra-aggregate network of mtra-aggregate voids, 2) 2)a network of large largeinterconnected mtercomectedvertical, vertical, horizontal horizontaland andoblique obliquevoids voids separating the the aggregates, 3) discrete accumulations of claythy- and along andsilt-size silt-& materials matalong some some %changoK2O % dwge %charwK20 void walls and large grain edges, and 4) 4) stress stress orientation orientation .00 a -40 a a 0 SD2 , o a a 80 20 -$0 -40 0 40 -20 40 0.I 0.' within witbin some some clay-size clay-& accumulations. accumulations. 0.1 p p (iranitic texture is Granitic texture is preserved presewed in saprolite, saprolite, but but biotite biotite 3 .p p is largely largely replaced replacedby byhematite, hematite,and andfeldspar feldsparisiscompletely: completely I, replaced by illite; the the first feldspar in granite granite is is located located 2 P —30 feethelow belowthe thequamite. quartzite. We We presume presume that the -30 feet 10 I:10 10 intensity and fiequency frequency of processes processes driving intensiv driving physical physical aa G G reorganization reorganization of of the the soil-saprolite soil-saproliteprofile profile diminished dbbi&ed = ' G G Inn with IW surfice. with increasing maeasing depth below the land surfice. 1~ ha^ Na20 NaZO ~ CaOc ~ o %%change Geochemistry: XRF been obtained Geochemis~: XRF analyses analyseshave been obtained for for -125 %m.75change -25 -125 75 -25 42s -75 -25 00 25 25 -125 -75 .23 00 25 25 0.1 0.I major major and and selected selectedtrace traceelements elementsin mtwenty twentysamples. samples. p Data Data for for four four oxides oxidesare areplotted plotted in mthe theadjacent adjacentfigure figurein m p terms terms of% of %change changewith withrespect respect to to the the average averageof oftwo two , unweathered unweathered granite granite samples samples closest to saprolite, saprolite, and and normalized which is is assumed to be normalized to to A1203, %03,which be immobile immobile during duriag weathering. Some Somefeatures featuresof ofthe thepaleosol paleosol I38 10 ! chemical chemicalprofile profile resemble resemble those those of of modem mod& soils soilswhich which * are such as :: are produced produced by by intense intense chemical chemical leaching, such as aa 100 P = Pedogenic Zone P = Pedogenic Zone decrease in Si02 and severe depletion in CaO and Na20, deciease sio2 severe depletion C ~ O and N%O, S s== Saprolie sapr01te due quartz and release of Ca and Na fiom from G= due to solution solution of quartz = tJnvathered u-ath~ed Granite ~rmite Ki@.: . I ' • I8 2* 8 1 iG 1 43rd ILSG, 1997, p. 1 39 �plagioclaseduring during replacement by kaolinite. However, However, Ca Caand andNa Nadepletion depletionshould shouldbe be plagioclase accompanied by K depletion due to the exception exception of ofthe the accompanied to weathering of K K feldspar, but with Mth the uppermost the paleosol, is 30-40% 30-40% higher in m the paleowl, compared comparedto to average average granite. m e . We We uppermostsample, sample, 1(20 &O is believe believe that thatall a l l feldspar in the paleosol was altered altered during during weathering weatheringand andthat thatKKleaching leaching occuned, occurred,but butthat thatKKwas wasreintroduced reintroducedduring duringlater latermetamorphism metamoqhismby byfluid fluidflow flowalong alongthe the sub-Baraboounconformity. Note Notethat that detrital detritalfeldspar feldspar is israre rarein inquartzite, quartzite,and andinterlayered, interlayered,highly highly sub-Baraboo aluminous ofpyrophyffite+kaolinite+quartz, aluminous metapelites, consisting of pyrophyllite+kaolinite+q~are areimpoverished impoverishedininK, &Na, Na, and andCa. Ca. Similar Sjmilarchemical chemicalfeatures featureshave havebeen beendescribed descniedfrom fiomsub-Huronian sub-Huronianpaleosols paleowls on ongranite graniteat at Pronto, Ontario (Gay & Grandstag 1980), and Vile Marie, Quebec (Rainbird Pronto, Ontario (Gay & GrandstaK 1980), and ViUe Marie, Quebec (Rahbiid et et al, aL,1990), 19901,and and interpreted interpretedas asthe theresult re& ofK-metasomatism of K-metasomatismdating duringdiagenesis &genesis or orlow-grade low-grademetamorphism metamorphism of of pre-existing preexistingweathering weathe@ profiles. profiIes. The Therelative relative effects effectsof ofweathering weathering and and metasomatism m e t a s o m a h on onpaleosols paleowlscan canbe beevaluated evaluatedby byusing using aaplot (A),CaO+N%O CaO+N;O (CN), (CN), and q0 1(20 6). (K). A plotof ofmolar molar A1203 @03(A), A theoretical theoreticalweathering weathering trend trend for for Baxter BaxterHollow HollowGranite Granitewas wascalcuated calcuatedfrom fiomthe the AA CIPW CPWnorm normof ofaverage averagegranite graniteand and release releaserate rate constants Young, 1984). constantsfor forfeldspars feldspars(Nesbitt (Nesbitt& &Young, 1984). The the weathering Therelative relativepositions positionsof ofthe weatheringtrend trendand and analyses of sub-Baraboo paleosol indicate an analyses of sub-Ba~aboopaleosol indicate an addition additionof—1O of -10 mol% mol% 1(20 &O during duringmetasomatism, metasomatisq 5 which is comparable to the -44 mol% which is comparable to the -14 mol%estimated estimatedfor forC.) 070 the theVille V i eMarie Mariepaleosol paleowl(Fedo (FedoetetaL, aL,1995). 1995). The Thechemical chemicalindex indexof ofalteration alteration(CIA), (CIA),which whichisis defined defined as as A120J(A1203+CaO+N;0+}0), %OJ(@03+CaO+NQ+&O), can canbe be determined determinedfor forpre-metasomatized premetasomatizedpaleosol palms01by by Kcp extending extendinglines q0apex apexthrough throughthe the h e sfrom fiomthe the1(20 paleosol CN KK paleosolanalyses, analyses,to tointersect mtersectthe theweathering weatheringtrend, trend, CN yielding values ofSl-83. Such values are yielding of 81-83, Such values are significantly the effects signi6cantly higher higher than than those those obtained, obtained, ififthe effectsof ofK-metasoniatism K-metasomatismare areneglected. neglected. Conclusions: aawell-developed Conclus~om: well-developedweathering weatheringprofile profilewas wasestablished establishedon onthe theBaxter BaxterHollow Hollow Granite Graniteprior priorto todeposition depositionof ofthe theBaraboo BarabooQuartzite. Quamite. During Duringlater latermetamorphism metamoqhismand andfolding foldingof of thequartzite, quartzite,significant significantamounts amountsof ofKKwere wereadded addedtotothe thepaleosol paleowlby byfluids fluidschanneled channeledalong alongthe the the sub-B araboo unconformity. sub-Bamboo unwnfonnity. An Aninvestigation mvestigationof offluid &id inclusions mchwiom is is underway underway to todetermine determinethe the characteristics other characteristicsof ofthe themetasomatizing metasomatizing fluids. The Thetime timeof ofweathering weatheringremains remainsunknown, &OWJI, otherthan than being younger than 1760 Ma. An apparent Rb-Sr isochron being younger than 1760 Ma. An apparent Rb-Sr hcbronage ageofthe of thepaleosol paleowlisis1360±50 1360250Ma, Ma, raising raisingthe theintriguing mtriguingpossiblilty possiblilty that that K-metasomatism, K-metasomatism, metamorphism metamorphism,and andfolding foldingmight mighthave have been River events beenrelated relatedtotoWolf WolfRiver events(--1400-1500 (-1400-1500 Ma). Ma). REFERENCES REJBRENCESCITED CrnD Fedo, 92 1-924. Fedo,C.M. C.M.etetaLaL(1995) (1995)Geology, Geology,v.v.23, 23,921-924. Gay 349-373. Gay&&Grandstaff(1980) GrandstaE(1980)Precamb. Precamb.Res., Res.,v.v.12, 12,349-373. Medaris, aL(1996a) (1996a)42nd 42ndInst. Inst.Lake M eSuperior SuperiorGeoL, Ged,v.v.42, 42,31-32. Medaris,L.G., L.G.,Jr. Jr.etetaL 3 1-32. Medaris, L.G., Jr. et al (1996b) GeoL Soc. Amer. Absts. with Progs., Medark, L.G., Jr. et aL (1996b) GeoL SOC.h e r . Absts. with hogs.,v.v.28, 28,A-376. A-376. Nesbitt, Young, G.M. Nesbitt,11W. HW.&&Young G.M(1984) (1984)Geochini. G e o c hCosmochim. C o s m o c h Acta, Acta,v.v.48, 48,1523-1534 1523-1534 Rainbird v.v.98, 801-822. Rainbirdet et al. aL (1990) (1990) Jour. (led, (301, 98,801-822. . 43rdILSG, LSG,1997, 1997,p.p.22 43rd 40 �RESULTS OF MODERN A ALLUVIUM SAMPLING FOR KINIBERLITE L L U W M SAMPLING KIMBEJCLKTE INDJCATOR INDICATOR MINERALS, LAKEREGION, REGION, AND ANDTEIE THE JMPLICATION IMPLICATION FOR MINEMLS, WAWA-KTh4NIWABI WAWA-KINNIWABI LAKE FOR NORTHEASTERN ONTARIO. KIMBERLITE EXPLORATION, EXPLORATION, NORTEEASTERN ONTARTO. T.F. Morris, Ontario Survey, 933 933 Ramsey Ramsey Lake Lake Road, Road, Sudbury, Sudbury, Ontario, Ontario Geological Geological Survey, Ontario, Canada. P3E P3E 6115. 6B5. Quaternary till sampling samplingover overthe the Mlchipicoten Michipicoten greenstone greenstone belt, north and northeast Quaternary mapping and till northeast of Waw* Wawa, were i~tiated initiated in in 1990 1990 and and completed completed in in 1991. Following Following the discovery discovew of of diamonds in - the modem huvium alluvium by byaaprospector prospector in in 1993; 1993,the the Ontario Ontario Geological Survey conduAed conducted a modem modern alluvium sampling samplingprogram programin in 1994. 1994. The The area area sampled sampled included included the the region regionoriginally originally mapped in in 1990 1990 and 1991. At Atthe thesame sametime, time, Quaternary Quatemavmapping, mapping,modem modernalluvium alluviumsampling samplingand andtill till sampling were completed in the the Michipicoten Michipicoten River valley, south south of of Wawa. Wawa. the release release of of data data in in 1994, 1994, aa small smalldiamond diamondrelated related staking stakingrush rushoccurred. occurred. The The Following the distribution of kimberlite indicator indicatorminerals mineralssuggested suggested aa relationship relationship to to a northeast structural structural collected over over only aa part part of this structure during the the 1994 trend. As Asmodem modem alluvium alluvium was collected survey, the Ontario Ontario Geological Survey initiated a second second modem modemalluvium alluviumand andtill till sampling sampling Lake area, area, east east of of Wawa, in 1996. program in the Kirmiwabi Kinniwabi Lake 1996. indicator minerals mineralsrecovered recoveredinclude: include: 1) 1) chrome chrome pyrope pyrope garnetq.2) garnets; 2) chromite; 3) Kimberlite indicator magnesium-rich ilmenites chrome pyrope magnesium-rich ilmenitesand andchrome chromediopsides. diopsides.To Todate, date,aatotal totalofof 77 'GlO" "010" chrome chrome pyrope garnets, 60 60 "(39" "G9" chrome pyope garnets, 3 high chrome chrome chromites, 217 217 low low chrome chrome chromites, 292 ilmenitesand and3318 chromediopsides diopsideshave havebeen beenrecovered. recovered. The distribution 292 magnesium-rich magnesium-rich ilmenites 18 chrome and relative concentration of these these heavy minerals minerals clearly clearly illustrates illustrates aa correlation correlation with with northeastnortheasttrending regional fiiults fiults associated associated with withthe theKapuskasing Kapuskasing Stmctural StructuralZone. Zone. In In particular, a number trendiig regional of sample sites along the the fault controlled controlled Shikwamkwa River valley and and the the Shikwamkwa Lake Lake basin yielded yielded significant significantnumbers numbersand andtypes types of of kimberlite kimberlite indicator indicator minerals. minerals. These Theseminerals mineralsare are similar to to recovered recovered in in the the Trout Trout Creek Creek drainage drainage system, system, located along strike to the southwest, southwest, Dalton, situated situated along along strike striketo tothe the northeast. northeast. This and at Dalton, This may may suggest suggest that faults faults within the Kapuskasing Structural Zone, kom from Wawa Wawa to to the James Bay Lowland, could represent represent promising kimberlite kimberlite exploration exploration targets. targets. 41 �This page pageleft left blank blank intentionally. intentionally. This 42 �TIlE HEMILO GOLDDEPOSIT: DEPOSIT: IT MAY BE GOLD BUT IT'S NOT THE HEMLO GOLD NOT BLACK AND WHITE WHITE Ontario Geological Survey, Sudbury, Ontario, Ontario, P3E P3E 6B5. 6B.5. Muir, Tom L., Ontario Over 15 years have passed since the the "discove@' "discovery"of of the Hemlo gold deposit. A Aplethora plethoraof ofideas ideas as to its origin has has emaged. emerged. The diversity of interpretations, all drawing upon some type of The of interpretations, type of hydrothermal alteration system, reflects the complex geological history history of of the area, area, including including the the deposit. The interpretations regarding the deposit must be Theimplications implications for observations observations and interpretations integrated with an overall assessment of of events. events. The The establishment establishment of of fundamental hndamental relationships is paramount paramount to to developing an an appropriate appropriate depositional model and among geological events is ultimately a reliable exploration strategy. strategy. The deposit deposit currently currently lies within one of several high strain zones, largely at or or near near the the hanginghangingS-shaped, E2 F2fold. fold. The km amplitude, s-shaped, The ore ore overall overall transgresses transgresses wall side of the south south limb limb of of a 2.5 Ian units. In Inthe thewestern western part partof ofthe thedeposit, deposit, ore oreoccurs occurslargely largelyas as several several east-striking, east-striking, low-grade low-grade within massive massive (subvolcanic) (subvolcanic)and andfbgmental, fragmental,felsic, felsic,quartz-plagioclase-phyric quartz-plagioclase-phyricrocks. rocks. In In the the zones within central and eastern parts it occurs occurs mostly as 11 to 2 large, tabular, east-southeast-striking, east-southeast-striking,higher higher grade zones grade zones within within highly highly feldspathized feldspathized rocks. rocks. fundamental relationships relationships ffom from this thiswork work are are that that mineralization and alteration: 1) currently currently The hndamental are largely structurally 3) predate predate felsic to stmcturally controlled; 2) post-date regional-scale regional-scale (D2) (DJ folding; 3) intrusions (plutons (plutons and and dikes); dikes);4) 4)predate, predate, or or are are synchronous with, with, the development intermediate intmsions D2 high-strain zones; 5) 1)3ductile ductile and and brittle-ductile brittle-ductile flattening, which 5) predate predate regional scale D3 of D2 superposed dextral resulted in superposed dextral shear shear constrained constmined to to zones zonesof ofexisting existinghigh high strain strainand/or and/orfissile fissile rocks; rock, and 6) 6 ) predate predate regional regional metamorphism. By By inference, s e r e n e , the the mesoscopic mesoscopicand and microscopic microscopic features represent modiied modified primary primaryfeatures features and andthe the current current setting of of features which we presently observe mpresent the deposit does not accurately reflect the the original originaldeposit deposit characteristics. characteristics. The role of superposed superposed alteration and remobilization deposit-related metals is considered to have remobiiiition of deposit-related have been been generally generally underrated. The Therearrangement rearrangement of of primary primary characteristics impedes impedesaa simple simple reconstruction reconstruction of of the the mineralization/alteration events. mineralizatiodalteration events. Syngenetic and skarn models do not Syngenetic not account accountsufficiently sufficientlyfor for the the observed observedfield fieldrelationships. relationships. However, simple porphyry and shear-zone-hosted shear-zone-hosted models, models, as as presented, have notable shortcomings. Problems the deposit deposit to the origin of the quartzProblems revolve revolve around the relationship of the plagioclase-phyric rocks, rocks, the identification of of superposed alteratiodmineralization alteration/mineralization events, the role of of stmctural structural control and the present distribution initial role distribution of of various various mineral mineral phases phases (e.g., (e.g., muscovite, microcline). microcline). Most of the ambiguity arises from enigmatic relationships resulting Most of the ambiguity arises f?om enigmatic relationships resulting from fiom history of of superposed superposedevents. events. Nevertheless, Nevertheless, the H Hemlo the complex history e d o deposit does not appear to fit a single deposit model. model. Rather from an unexposed porphyry(?) porphyry(?) single classic deposit Rather itit may may be linked to fluids, fkom magma, which were channeled by by existing structural structural weaknesses weaknessesduring duringactive activetectonism. tectonism. 43 �This This page page l left e f t blank blank intentionally. intentionally. 44 �PETROGENESIS PETROGENESISOF OFCIIENGWATANA CHENGWATANA VOLCANICS, MINNESOTA MINNESOTA AND AND WISCONSIN WISCONSIN KarlR., R.,Geology GeologyDepartment, Department, Macalester Macalester College, St. Paul, NAIMAN, Zachary J., WJIRTH, WIRTH, Karl Paul, MN 55105, znaiman@macalester.edu, wirth@macalester.edu znairnan@macalester.edu,wirth@macalester.edu The Chengwatana Chengwatana Volcanics (CV), (CV), aa >3000 >3000 meter meter unit unit of of high high iron iron and and aluminum tholeiitic basalt interflow sediments, 2.0 with interflow sediments,were were erupted erupted south south of the presumed Penokean Penokeansuture suturezone zone(the (thesite siteof of 2.0 Ga southward dipping subduction) and are the southernmost exposed lavas of the 1.1 Ga Midcontinent Ga southward dipping subduction) the southernmostexposed Ga Midcontinent rift (MCR), studying magmatic magmaticprocesses processesalong alongthe the rift rift axis. axis. CV (MCR), making them ideal for studying CV flows flows contain An), clinopyroxene contain primary primary plagioclase plagioclase(—60% (-60% modal An,.), clinopyroxene(—30% (-30% modal modalWo35En45Fs), W o E n 4 F s ) ,and and Fe-Ti oxides modal). The The geochemistry geochemistryof of the the CV CV is is similar similar to to basalts from other eruptive (-8% modal). oxides (—8% centers MCR; the flows are characterized characterized by by low low magnesium magnesium (Mg#= (Mg# = 0.58-0.37), and can centers along along the theMCR; be divided divided into low-Ti02 groups, Volcanics (PLV). into high- and low-TiO, groups, resembling resemblingthe the Portage PortageLake LakeVolcanics (PLV). The TheCV CV are enriched in incompatible elements (TTE) (ITE) similar are enriched incompatibletrace elements similarto toPLV PLV basalts basalts as as well well as as basalts basalts from from the the Powder Mill Group of the Mamainse Point Formation (MPF), but exGroup (PMG), and group 6 flows of hibit more pronounced Nb and and Ta Ta anomalies. anomalies. ITE are negatively correlated with Mg# and are pronounced Nb positively positively correlated correlatedwith withTi02. TiO. Isotopic Isotopiccompositions compositions(ENd (Gfrom from 4fl V.11 to 4.5) -4.5)are arepositively positively correcorreabundances and and ratios ratios (eg. (eg.Y, Y, lated with the Nb anomalies and are negatively correlated with ITE abundances of fractional crystallization (e.g., (e.g., Mg#). Mg#). Petrographic La/Sm), Ti02 LdSm), T i 0 ,, and indices of fractional crystallization Petrographic observations observations coupled with geochemical CV were were derived derived from from an enriched enriched mantle source, coupled geochemical trends suggest that the CV similar and assimilated assimilated continental continental crust while fractional fractional crystallization similar to some some other MCR rocks, and crystallization occurred in in cmstal crustalmagma magma chambers. chambers. occurred Geochemical constraints on the petrogenetic petrogenetic processes processes involved Geochemicalmodeling modeling provides constraints involved in in CV CV genesis and evolution. Mass-balance Mass-balance models' models1demonstrate demonstratethat that the the major major element element trends trendsexhibited exhibited by by the CV CV flows flows can can be be accounted accounted for by 5-50% crystallization of varying varying proportions proportions of of olivine olivine(0(06%), clinopyroxene(0-15%), (0-15%),magnetite magnetite(0-5%), (0-5%),and and ilmenite ilmenite (0-5%). (0-5%). Al6%), plagioclase (5-20%), (5-20%), clinopyroxene though section, geophysical though no no olivine olivineis is observed observed in thin section, geophysicalstudies studiesof of the theMCR2 MCR2suggest suggest the the presence presence crust which which might mightbe bemafic maficcumulates. cumulates. Representative of high-velocity layers in the lower crust Representative models illustrated in in Figure Figure 1.1. are illustrated ClosedClosed- (Rayleigh) (Rayleigh)and andopen-system open-system(RFC)3 (RFC)3fractional fractional 3 crystallization crystallizationmodels models(using (usingmineral mineral proportions proportions predicted predicted by the mass-balance mass-balance equations equations and and from from petrographic petrographic analysis) successfully successfullymodel model the the enrichment enrichment of of some some trace trace analysis) elements (e.g., but fail fail to to model model highly $ elements (e.g., Zr, Zr, Hf, Y; Y;Fig. 2a), but incompatible trace elements and ratios (e.g., La/Sm, incompatible trace elements and ratios (e.g., LaISm, ZrlZr/X' 22 Nb; Nb;Fig. 2b,c). 0 fr< 5.1%0l Models of combined combined fractional crystallization and asfractional crystallization 11.9%plag 81%melt Fig. I similation similation have been used to account for the geochemical variation in basalts from various pans of the MCR. Simple variation basalts parts of the MCR Simple i1 0.4 0.5 0.6 03I 0.4 0.6 mixing models models between between CV CV and and average average Archean granumixing lite do do not not accurately accurately predict predict trace trace element element compositions compositions of CV flows, flows, but but Nd Nd isotopic isotopic compositions constrain the amount of cmstal crustal component in the CV to Combined assimilation assimilation and and fractional fractional crystallicrystallito <30%. <30%. Combined crustal compositions compositions zation (AFC) model? models4with with 15% 15%and and 30% crustal assimilation assimilation of a variety of crustal ; . 0 " 45 �250 I • I I I Alt (rO.I5) 200 - N 150 — Alt ( r03O) ;RFc(.cycles) F=0.95 S Fig. 2a AFC (-0.30) a 3 • •• • 85 (ID = 095 1P=0.95 41015 Ct — ,. A(r0.I5. 0.8 0.7 'Rayltith 20 XI RFC (# cycles) G cycles) 4 2 .0 iS .1 •• .. • z N 10 - •• . • •*• • .1 • .1 . 0 I I 20 I II I $ is RFC(# RFâ C cycles) Net) 5 25 2s Fig.2b Fig. 2b (lower, upper, upper, and and bulk bulk crust; ernst; granulite; shale) suc(lower, cessfully predict N4 E N and and most trace element element abunabundances of of enriched enriched CV CVflows flows (Fig. (Fig. 2a,b). 2a,b). AFC modpredict the the low Nb (high Zr/Nb, Fig. Fig. 2c). 2c). els do not predict The low Nb concentrations can be explained by by (1) assimilation of a crustal components with assimilation of with exextremely low concentrations concentrations of of Nb Nb relative to ITE, (2) (2) derived from from lithospheric lithospheric mantle melts derived mantle that that was was varivariin Nb Nbrelative relative to to other other ITE, ITE, or (3) melts melts ably depleted in asthenospheric mantle which which had incomincomderived from asthenospheric patible elements, elements, but butlittle littleNb, Nb, added added during during chemichemical interaction with lithospheric lithospheric mantle.5 Lithoscal pheric mantle could could have have become become enriched in incompatible elements elements (relative (relative to to Nb) Nb) by metasomatism metasomatism related to Penokean Penokean subduction. subduction. An An enriched enrichedmanUel mantle1 lithospheric mantle source source for for MCR rocks has lithospheric mantle has been been proposed for volcanics volcanics from from the early stages stages of riftrifting, including flows from from the the MPF MPFand andthe thePMG.678 PMG.6"x A modified mantle source has also modified lithospheric mantle also been proposed for the Portage Lake Volcanics.9'° volcanic^?^^^ Geochemicalmodels modelsindicate indicate that that a variety of Geochemical petrogenetic processes, processes, including including derivation derivation from mulpmgenetic mantle sources, sources, crustal crustal assimilation, and fractiple mantle tional crystallization, crystallization,operated operated to to produce the trace tional element and isotopic isotopic variations variations exhibited exhibitedby bythe theCV. CV. Fig.2c Fig. 2c II 40 30 40 Y (ppm) y(PP~) I I 0 50 50 0.95 -2 References References F = 0.35 (1) Bryan, Finger, L.W., Chayes, F., Bryan,W.B., W.B.,Finger, L.W.,and andChayes, F., 1969, 1969, Science 926-927. (2) Allen, D.J., Science 163, 163.926-927. (2)Allen. D.J.. Braile, Braile. L.W., L.W.. Hint, WJ., Mariano, J., Hinze. WJ..and &d~ariano, J.,1995, 1995,Continental continentiRifts: ~ifts: Evolution, Structure, Tectonics, 375-407. (3) O'Hara, Evolution, Structure,Tectonics, M.J., 1977, 503-507. (4) M.J., 1977, Nature, 266, 266,503-507. (4)DePaolo, DePaolo,D.J., D.J., 1981, Earth Earth Planet. Planet. Sci. Len., 53, 189-202. Lett., 53, 189-202. (5) (5) . -4 4 -6 -6 AFC(d.15) F = 02% AFC(r.3) AX (d.3) t 0 55 Fig. Fig. 3 1 10 10 Patchet, 1993, Patchet, P.J., RJ., Lehnert, M.R., M.R., and Sieber, Sieber, G., 0., 1993, Th Th ( PmP ~ Journal of Petrology, Petrology, 35, 35, 1095-1125. 1095-1125. (6) Shirey, Shirey, Steven B, Klewin, Kenneth Kenneth W., W., Berg, Jonathan H., H., W., 1994, Geochimica et et Cosmochimica CosmochitnicaActa, Acta,58,4475-44906. 58, 4475-44906. (7) Klewin, and Carison, Carbon, Richard W., Klewin, K.W., K.W., and and Berg, Berg, J.H., 1991, Journal of Geophysical Geophysical Research, 96,457-474. 96,457-474. (8) J.H., (8)Miller, Miller,J.D., J.D., and and Vervoort, J.D.. J.D., 1996, 1996,Institute Instituteon onLake Lake Superior Geology, 33-35. (9) GeochimicaetetCosmochimica CosmochimicaActa, Acta,53,2023-2035. 53, 2023-2035. (tO) Superior (9) Paces, J.B., J.B., and Bell, K., 1989, Geochimica (10) Nicholson, S.W., S.W., and Shirey, S.B., S.B., 1990, 1990, Journal of Geophysical Research, 95, 10,851-10,868. 10,851-10.868. 46 �CORRELATIVE SEQUENCES SEQUENCESWITHIN WItHIN THE MARQUETtE (MICHIGAN)AND AND THE THE MARQUETTERANGE RANGE SUPERGROUP SUPERGROUP (MICHIGAN) I-IURONIAN SUPERGROUP (ONTARIO): GLAaOGENICS, PALEOSOLS, AND ORTHOQUARTZ1ES HURONIAN SUPERGROUP (ONTARIO): GLAdOGENICS, PALEOSOLS, AND ORTHOQUARTZFTES - Ojakangas, Richard W W., Geology, University Universityof of Minnesota - Duluth Duluth ,. Department Department of Geology, Duluth, Minnesota 55812 55812 In the the Early of the Upper Peninsula subvertical Early Proterozoic ProterozoicMarquette MarquetteRange Range Supergroup Supergroup of Peninsula ooff Michigan, Michigan, subvertical diamictite and dropstone-beadng units that unconformably overlie Archean basement (the and dropstone-bearing units that unconformably overlie Archean basement (theFern FernCreek Creek Formation of the Iron Mountain area and the Enchantment Lake Formation of the Marquette Trough) Formation of the Iron Mountain area Lake Formation of Marquette Trough) have have been considered glaaogenic glaciogenic and and correlative correlative(Pettijohn, (Pettijohn, 1943; 1943; Gair, Gair, 1981; 1981; Ojakangas, Ojakangas, 1984). 1984). Orthoquartzite units which overlie these two units (the Sturgeon Quartzite and the Mesnard Orthoquartzite units which overlie these two units (the Sturgeon Quartzite and the MesnardQuartzite, Quartzite, respectively) also be be correlative correlative(e.g., (e.g., Morey, Morey,1972; 1972; Young, Young, 1983). 1983). respectively) have have long long been been assumed assumed tto o also Mother basal Archean basement on the the northern Another basalconglomeratic conglomeraticunit unitunconformably unconformably overlying overiying Archean northern CreekFormation) Formation)has hasbeen beeninterpreted Interpretedinindifferent different ways. ways. A edge of the the Marquette MarquetteTrough Trough (the (the Reany Reany Creek glacial origin origin has hasbeen beenclaimed daimedby byPuffett Puffett (1 (1960), Gair(1 (1981) Ojakangas(1(1984), but Mattson 960), Gair 981) and Ojakangas 984). but Mattson and glacial Cambray(1 (1983) without the Cambray 983) a,ued arguedfor fora amass-flow mass-flowmechanism mechanism of deposition without the lnwAvement involvement of of glaciers. glaciers. age was was proposed proposedby bySmall Smalland andBomhorst Bomhorst(1988). (1988).Sims Sims(1991) (1991) Interpreted Interpreted the A possible Archean age the Reany Creek Creekas as an an Archean Archean strike-slip strike-slip basin basinfill fill along along aa major major fault. fault. Reany The Reany Creek, Creek,which whichtops topssouth, south,isisshown shownonongeologic geologicmaps mapsas asbeing beingininfault fault contact contact with both MchigammeSlate Slate(Formation) (Formation)and andwith withsheared shearedrhyolite rhyolitetuff tuff of both the the overlying overiyingEarly Early Proterozoic Proterozoic Mchigamme the Archean Mona Schist. However, recent field work has verified an observation by Puffett (1974, Archean Schist. However, recent field work has verified an observation by Puffett (1974, p. 23) that a quartzite mapped Creekmight mightsomeday somedaybe beproven provent to belong tto that a quartzite mappedas asuppermost uppermostReany Reany Creek o belong oa I contend that this unnamed quartzite is a remnant of a faulted-out overlying different formation. that unnamed quartzite is a remnant of a faulted-out formation. quartzite unit unitthat thatisiscorrelative correlativewith withthe theSturgeon Sturgeonand andMesnard MesnardQuartzites. Quartzites. Creek Formation Formationisisoverlain overlainbybythe theSturgeon SturgeonQuartzite. Quartzite.AA two-meter two-meter thickness of The Fern Creek of just beneath the Sturgeon Quartzite and it it was. suggested by Trow was suggested sericite schist is is exposed exposed locally just Sturgeon Quartzite (1948) that ititrepresents Creek. A similar sericite schist is Interbedded (1948) representsaazone zone of ofweathered weathered Fern Creek. similar seriate interbedded with quartzite in the uppermost Enchantment Lake Formation near the contact with the overlying Mesnard quartzite in the uppermost Enchantment Lake near the contact with the overlyingMesnard Quartzlte. Similarly, In the upper Reany Creek, sheared sericite schist is Is present present beneath beneath the Quartzite. Similarly, In the upper Reany Creek, sheared seridte schist the unnamed unnamed quartzite units and quartzite unit unitmentioned mentionedabove. above. The Theseticite seriate schists schists between between the three glaclogenic gladogenic units and the the overlying quartzites are herein interpreted tto (i.e., e., paleosol paleosd or reworked reworked paleosol) paleosol) overiying o be be metaregolith metaregdith (I. units. The overlying oveilying quartzites quartzites are areinterpreted interpreted tto products of formed upon the glaciogenic gladogenic units. o be products of the the cover of of glaciogenic glaciogenicmaterial material (i(i.e., the paleosol) that erosion and reworking of a deeply weathered weathered cover .e., the thatwas was The tripartite tripartite sequence present on the the Early EarlyProterozoic Proterozoic land land surface. surface. The sequence of glaciogenic glactogenic rock, paleosol, paleosol, and quartzite thus interpreted interpreted as erosional remnants of quartzite ininthree threeareas areasof ofthe theUpper UpperPeninsula Peninsula of Michigan Michigan isis thus what was and likely likely continuous continuoussequence. sequence.This Thissimilarity similarityin in lithology, lithology, stratigraphy, stratigraphy, was once aa widespread widespread and and interpreted evidence that that the as strong strong circumstantial evidence the three threesequences sequences are are interpreted history historyisisherein herein cited cited as indeed correlative. correlative. The Huronian Supergroup Supergroup200 200 km tto the east o the east in in Ontario Ontario contains contains three threeglaciogenic glaciogenicunits—the units-the Ramsay Lake,the the Bruce, Bruce, and andthe the Gowganda GowgandaFormations Formations(e.g., (e.g.,Young, Young,1981a, 19813,1981b). 1981 b). The The uppermost, uppermost, Ramsay Lake, been units(e.g., (e.g.,Puffett, Puffett, 1969; 1969; Young, Young,1970, 1970, 1983; 1983; the Goanda, Gowganda,has has beencon-elated correlated with with the the Michigan Michigan units Ojakangas, 1988). Description Formation that that oveilies Ojakangas, 1988). Descriptionof ofan aninterpreted interpretedpaleosol paleosol within the the 10.-rain Lorrain Formation overlies the the Is in In preparation preparation by Mamio,and and R.R.Ojakangas; Ojakangas;this thispaleosol paleosol is Is being being Interpreted by K. K. Card, Card, .1. J. Manno, Interpreted Gowganda is as con-elative with those in (1983) correlative with in Michigan. Michigan. Young Young (1 983) emphasIzed emphasized that thatthe theMichigan Michigansequences sequences of of glaciogenic rock, quartzite, and (e.g., Kona Kona Dolomite) Dolomite) can can be be correlated correlated with glaaogenic and overlying dolomite (e.g., with the the Ontario Lonain, and and Gordon GordonLake LakeFormations. Formations. Recent RecentCCIsotope Isotope studies studies have Ontario sequence sequence of of Gowganda, Gowganda, Lonain, also been used as evidence Sdence for forcon-elation correlationof ofcarbonate carbonateunits unitsin inthe thedescribed describedsequences sequencesas as well well as as correlation with with Early Early Proterozoic Proterozoiccarbonate carbonate units 'oming (Bekker (Bekkeret et alal., 1996). Correlation correlation units in in Wyoming ., 1996). Correlation with with was proposed proposed earlier earlier (Marmo (Mamlo and similar Early Proterozoic Proterozoicsequences sequences in in Finland Finland and Russia Russia was andOjakangas, Ojakangas, 1984; 1984; Ojakangas, Ojakangas, 1985, 1985, 1988) 1988)and andthe thepossible possibleexistence existence of of an an Early Early Proterozoic Proterozoic supercontinent supercontinenthas has proposed (Ojakangas et al., been proposed (Ojakangas et at., 1991). The correlation Supergroupwith withthe thelower lowerpart part of of the correlation of of the the upper upper part part of of the the Huronian Huronian Supergroup the Marquette Range Supergroup Supergroupisissteadily steadilybeing beingstrengthened strengthenedininspite spiteofofthe the lack lackof of radiometric radiometric dates dates in in Marquette the the Marquette MarquetteRange RangeSupergroup. Supergroup. 47 �______ ______ ______ REFERENCES REFERENCES Bekker, A, A., Karhu, Karhu,J.,J.,and andBennett. Bennett,G.G., 1996, Lomagundi Lomagundievent eventin in North NorthAmerica: America: Application for , 1996, Bekker, stratigraphic correlation correlation (ethsj: (Abs,): Geological Geological Society Society of ofAmerica America Program Program and and Abstracts, Abstracts, Denver, CO. CO. Gair, 1981, Lower Proterozoic glacial glacial deposits deposits of of northern Michigan, Michigan,U.S.A.. U.S.A.:jaHambrey, jHambrey, M.J. Gair, J.1. . E.,E.,1981, MJ. and Harland, Hariand, W.B., W.B., (eds.), (eds.), Earth's Earth's PrePre- Pleistocene PleistoceneGlacial Glaaal Record, Record, Cambridge Cambridge University University Press, p. Press, p. 803-806. Marmo, J.S., Ojakangas, 1984, 1 984, Lower Lower Proterozoic Proterozoic glaaogenic glaciogenic deposits, deposits, eastern Marmo, J. S., and Ojakangas, eastern Finland: Finland: GeologicalSociety Societyof of America AmericaBulletin Bulletinv.v.95, 95, p. p. 1055-1062. Geological Cambray,FF. 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Geological __1 Glaciation: An An uncommon "mega-event" -1 988,988, Glaciation: uncommon "mega-event"asasaakey keytot ointracontinental intracontinentaland andintercontinental intercontinental correlation of Early basin fill, fill, North American and Baltic Baltic cratons: cratons: in in Kleinspehn, Kleinspehn, Early Proterozoic basin American and K.L. and Paola, C., (eds.), (eds.), New 1-444. New Perspectives Perspectives in in Basin Basin Analysis, Analysis, Springer-Verlag, Springer-Verlag, p. 43 431-444. K.L. Paola, C., Ojakangas, R.W., 1 991, Early Early Proterozoic Proterozoicglaciogenic glaciogenicdeposits: deposits: A R.W., Heiskanen, K.l., K.I., and and Marmo, Marmo, J.S., J.S., 1991, connection?j Ojakangas, North America-Baltic America-Baltic connection?& Ojakangas,R. R. W., W., (ed.), (ed.), Precambrian Precambrian Geology of the the Shield and and the the Eastern Southern Canadian Shield Eastern Baltic Baltic Shield, Shield, Minnesota Minnesota Geological Survey Survey Circular 34, 34, p. p. 83-91. Information Circular Pettijohn, F. F. J., J., 1943, 1943,Basal BasalHuronian Huronian conglomerates conglomerates of MenoMnee Menomineeand and Calumet Calumet districts, districts, MIchigan: Michigan: Pettijohn, Journal of of Geology, 51, p. Geology, v.v. 51, p. 387-397. Puffett, W. W. P., P., 1969, 1969,The TheReany ReanyCreek Creek Formation, Formation, Marquette MarquetteCounty, County, Michigan: Michigan: U.S. U.S. Geological Survey Survey Bulletin 1274-F, 1274-1, 25 p. Bulletin 1 974, Geology of of the Negaunee Quadrangle, Marquette Marquette County, Michigan: , 1974, Negaunee Quadrangle, Michigan: U.S. U.S. Geological Geological Professional Paper Paper788, 788, 53 p. Survey Professional Sims, P.K., for Archean Sirns, P. K., 1991, Great Great Lakes Lakes Tectonic Tectonic Zone Zone in in Marquette Marquettearea, area, Michigan—Implications Michigan-Implications for U.S. Geological GeologicalSurvey SurveyBulletin Bulletin 1904-E, 1 904-E, 17 17 p. tectonics in in North-Central North-Central United United States: U.S. 1 988 The The Reany Reany Creek Creek Formation, Formation, Northern Northern Marquette Marquette County, Small, JJ.R., and Bomhorst, 1. J., 1988 County, T. J., Small, .R., and Michigan:Archean ArcheanororProterozoic? Proterozoic?(Abs.) (Abs.):: Proceedings Proceedingsand andAbstracts, Abstracts,34th 34th Annual Annual Institute Michigan: on Lake Lake Superior Superior Geology, Geology, Marquette, Marquette, Ml, MI, p. p. 104105. 104-105. Trow, J.W., J.W., 1948, The The Sturgeon Sturgeon Quartzite of of the theMenominee Menominee district, district, Michigan: Michigan: Unpublished UnpublishedPh.D. Ph.D. Thesis, Thesis, University of of Chicago. Chicago. Young, G. 6. M., M., 1970, 1970, An An extensive extensive early early Proterozoic Proterozoic glaciation glaaation in in North NorthAmerica?: America?: Palaeogeography, Palaeogeography, Young, Palaeoclimatology, p. 85-101. 85-1 01. Palaeodirnatology, Palaeoecology, Palaeoecology, v. v. 7, p. 1981 a, The The early early Proterozoic ProterozoicGowganda GowgandaFormation, Formation,Ontario, Ontario,Canada: Canada:inj Hambrey, , 1981a, Hambrey, MJ., MJ., and and Hartand, W. B. (eds.), Record, Cambridge CambridgeUniversity University Press, Press, p. p. Harland, W . B. (eds.), Earths Earths Pre-Pleistocene Pre-Pleistocene Glacial Glaaal Record. 807-812. 807-81 2. 1981 b,b, Diarnictites Diamictites of of the Lake and and B Bruce Formations,north north shore shore -, 1981 the early eariy Proterozoic Proterozoic Ramsay Ramsay Lake N C ~Formations, in Hambrey, M.J. M.J. and and Hariand, Hailand, W W.B., (eds.), Earth's of Lake Lake Huron, Huron, Ontario, Ontario, Canada: Canada: in .B., (eds.), Earth's PrePreGlacial Record, Record,Cambridge CambridgeUniversity UniversityPress, Press,p.p. 790-794. 790-794. Pleistocene Glacial 1983, Tectono-sedimentary of Early Early Proterozoic rocks of the the northern northern Tectono-sedimentary history of Medaris,LL.G., Jr.(ed.), (ed.), Early EarlyProterozoic ProterozoicGedogy Geologyof of the the Great Lakes in Medaris, Great Lakes region: jn .G., Jr. Region, GeologicalSociety Societyof of America America Memoir Memoir 160, 160, p. p. 15-34. Region, Geological 15-34. 48 �Applications for for Archean Archean Gold Gold Exploration: Exploration: Using Using Canadian Canadian Mining Mining Camp Camp GIS Queries to GIS Applications Target Gold Exploration in Minnesota DEAN M. PETERSON Research Lab, Lab, Geology GeologyDepartment, Department, University of of Minnesota Minnesota - Duluth, Duluth, Economic Volcanology Research Duluth, Minnesota, Minnesota. USA USA 55812 55812 is to to discover discover ore ore mineralization mineralization before before funding is The objective objective of mineral exploration is in the the exploration exploration team. team.Exploration Exploration tends tends to to use use the exhausted or management loses confidence in simplest, cheapest, and lowest risk criteria, criteria, methods, methods, and and ore ore deposit deposit models models available. available. However, However, as as and deposits deposits become becomemore moredifficult difficultto todiscover, discover,exploration exploration risks risks increase, increase, and and the the mining camps mature and to mineral mineral exploration exploration increases. increases. In In this this case, case, the the exploration exploration amount of data potentially applicable to enhanced exploration methods and ore deposit models, that incorporate geologist must use enhanced incorporateadditional additional data, to continue to discover new ore deposits. data, continue to discover new ore explorationgeologist. geologist.This This Today, vast quantities of geological information are available to the exploration information includes field notes and measurements, geological maps, drill hole data, data, geochemical geochemicaldata, data, geophysical survey data, remote sensing data, data, and and geologic geologic literature. literature.Geologists Geologists must must integrate integrate vast vast quantities of data covering large areas in order to determine the best criteria for effective mineral quantities data covering in order to determine the best criteria for effective exploration. exploration. Currently, Currently, the the best best method to integrate integrate large data sets sets is to store store all all geologic geologicinformation informationinto into a Geographic overlays of (- <10km2), <10km2),simple light-table overlays GeographicInformation Information System System(GIS). (GIs). For small small areas areas (-. geological, geological, geochemical, geochemical, and geophysical data may be appropriate for interpretation. interpretation. However, However, small small analog data compilations typically do not answer the larger questions dealing with the fundamental compilations dealing with the fundamental controls types of of ore ore deposits. deposits. For Archean mesothennal mesothermal controls on the the formation and spatial location of specific types gold deposits, fundamental mineral exploration questions include: Which greenstone greenstone belt should should be be explored? explored? in the the greenstone greenstone belt beltshould shouldexploration explorationbe beconcentrated? concentrated? Where in What are are the best best criteria criteriafor for target target selection selection in inthe theconcentrated concentratedexploration exploration area? area? Geologic GIS format for the Hemlo, Timmins, Geologic compilations compilationshave been converted into GIs Timmins, and and Kirkland Lake Cadillac-Bousquet-Malarctic Lake gold camps of Ontario. An additional GIS data set from the Cadillac-Bouquet-Malarctic completion. The TheGIS GISdata dataincludes includesgeology, geology,1" ,l 2ndand gold camp in Quebec is near completion. and3r4 3"' order order shear shear zones zones (Figure (Figure 1), I), faults, faults, alteration, alteration, gold mines, gold occurrences, ore zones, and quartz-gold veins. veins. These TheseGIS GIs data 015 data set covering covering 6000 of northeastern Minnesota. The data sets sets are are being compared to a similar GIS 6000km2 km2of goal of the study of northeastern northeastern Minnesota Minnesota that that have have geological geological features features similar to to study is to highlight areas of present within those present within the the gold gold camps camps of of Canada. Canada. A series exploration models have series of Archean Archean mesothermal gold deposit exploration have been been developed developedfrom from 015 data data sets. sets. The The models models are are based based on on unique unique queries queries and spatial analyzes of the Canadian gold camp GIS analyzes that define define the the location location of of the the major major gold gold deposits deposits in analyzes of structural structural and lithological attributes that these < 1% 1% of the total area area of the the analog analogmining mining these mining mining camps. One One set of unique queries that defines < camps but hosts > > 90% 90% of all all gold mined is given below (Figure (Figure 2). 2). 2 1) Select Select compressional compressionaljog jogsegments segmentsofofI"1 Order Order shear shear zones zones(Figure (Figure lIa) a) Create aa 6-kilometer Order shear 22)) Create 6-kilometerbuffer around the selected F" Is Order 3) Intersect all 3) all data datalayers layerswith withthe the 1" I" Order Ordershear shearzone zone buffer 4) buffer, select select2"' 2" Order Riedel Riedel PP shears shears (Figure lb,c) Ib.c) 4 ) Within the buffer, 5) Order shears shears 5) Create Createaa 200-meter 200-meterbuffer buffer around around the the selected 2"" 2ndOrder 6) P-shear buffer 6)Intersect all all data datalayers layerswith withthe the 2"" 2"' Order P-shear 49 �Within the GIS environment, the outcome of these queries would would be a new subset of geological aspects of the original data data that incorporates all aspects data into a much smaller area. The geologist must now structural, lithological, geochemical, alteration data to target exploration use detailed structural, geochemical, geophysical, and alteration exploration programs in in these high potential areas. The Hollinger-McIntyre Hollinger-Mclntyre and Dome mines of the Timrnins Timmins camp; programs Kirkland lake lake gold the Ken Addison, Upper Canada, and the Kirkland Lake Main Main Break Break mines nines of the Kirkland camp; and and all all of of the the Hemlo gold gold mines are are defined defined by by the the simple queries queries listed listed above. above. Similar Similar queries are being applied to the Minnesota GIS to outline areas with high potential for hosting large Archean Archean gold deposits. deposits. 1st I Order Shear Zone Segment Classification " Order S h e a r Zone Classification Compressional Jog Compressional / A Extensional Jog Jog 7 A 2'"Order 2 '" Order Shear Shear Zones Zones (Riedel Shear Shear Arrays) (Riedel Arrays) CIS CIS Classification of of 2'td 2"i Order Shear Zones Zones zOrder Shears. Figure Figure 1. 1. A) Classification Classification of of 1" l order ordershear shearzone zonesegments segments B) 2nd ordershear shear zone zoneclassification classification based based on Riedel shear shear arrays 2* order arrays 2ndorder order shear shear zone zone classification classification C) GIS methodology for 2°' —R (8.6) —R'(2.3) P(98.6)— FIgure Figure 2. 2. Coffelation of mined gold and and 2" Correlation 2* order ordershear shearzone zoneclassification classification for for the the Timmins, Timmins, Kirkland Lake and Hemlo Gold Camps. Values in millions of ounces of gold. Values ounces of gold. 50 50 �RE—os,SM-ND, SM-ND, AND ANDPB PB ISOTOPIC ISOTOPICCONSTRAINTS CONSTRAINTSON ONMANTLE MANTLEAND AND CRUSTAL CoNTlunuTroNs TO RE-OS, CRUSTAL CONTRIBUTIONS MAGMATIC SULFIDE DULUTH COMPLEX. MAGMATIC SULPIDEMINERALIZATION MINERALIZATION IN THE DULUTH COMPLEX. Edward Ripley, Department Department of Geological Geological Sciences, Sciences, Indiana Indiana University, University, Bloomington, Bloomington, Edward M. Ripley, 47405; David IN 47405; David D. Lambert and Louise Louise R. Frick, Victorian Institute Institute of Earth Earth and and Departmentof ofEarth EarthSciences, Sciences,Monash MonashUniversity, Universy, Clayton, Planetary Sciences, Department Clayton, VIC 3168, 3168, Australia Australia Previous Previous petrologic petrologic and and stable stable isotopic isotopic studies studies of of sulfide sulfide mineralization mineralization in in the the Duluth Duluth Complex Complex have have led led to to the the premise premise that that sulfide sulfide genesis genesis is is strongly strongly linked to the the interaction interaction between between mantle-derived country rocks rocks in in aa rift riftzone zoneenvironment. environment. In order to mantlederived magmas and sedimentary country more fully evaluate evaluate the nature nature of this interaction, and to gain an insight insight into the possible possible importance of externally-derived externally-derived metals in the ore-forming ore-forming process, Pb, Sm-Nd, and and Re-Os Re-0s isotopic studies of the Babbitt Cu-Ni deposit were initiated. Rock-types Rock-types examined examined include include lowlowtroctolite that show evidence for contamination, disseminated sulfide troctolite show very little petrologic evidence disseminated contact with country sulfide-bearing troctolitic troctolitic to gabbroic rocks that occur occur close to the basal contact country metasedimentary xenoliths, and and massive massive sulfide. sulfide. Pb isotopic values of rocks and contain metasedimentary of whole whole rocks, plagioclase mineral separates, and massive sulfides show only subtle differences, differences, and are are contamination of a mantle-derived melt with a Proterozoic Proterozoiccrustal crustal compatible with 3 to 5% contamination cNd (1.1 (1.1 Ga) values of the troctolite and gabbro samples are chondritic, and only contaminant. Nd sulfides show strong the massive sulfides strong evidence for contamination based on Sm-Nd isotopic isotopic values. values. Massive be more more sensitive sensitiveindicators indicatorsof contamination contamination in in the the Sm-Nd Sm-Nd system system Massive sulfides sulfides tend tend to to be (apatite) because of late-stage late-stage incorporation incorporationof of aa light lightrare rareearth earthelement-rich element-richfluid fluidinto intoa aCa-PCI)4 Ca-PO4 (apatite) component ofthe theimmiscible immisciblesulfide sulfideliquid. liquid.Yes y (1.1 component of (1.1 Ga) values are also strongly anomalous, anomalous, and range from -500 to to1300 1300in indisseminated disseminatedsulfide-bearing sulfide-bearing troctolites troctolites and and massive massive sulfides. sulfides. contamination by Proterozoic sedimentary These values are also sedimentary also consistent consistent with from 3 to 5% contamination rocks. Elemental 30 to 60% 60% of the the Pb Pb Elementaland andisotopic isotopicmass massbalance balance calculations calculations suggest suggest that from 30 and 0 Oss in the sulfide mineralization have been been derived derived from from external external sources. sources. A corollary corollary is that other metals may also be in part derived from external sources, which would aid in explaining explaining the the mineralization. Selective compositional diversity of the sulfide mineralization. Selective assimilation of country country rocks by mantle-derived mantle-derived magmas may occur in crustal staging chambers, during ascent to shallower levels, or in situ as a result of devolatilization reactions and partial melting. 51 �T h i s page page left blank intentionally. intentionally. This left blank 52 �The Tectonic, MineralizationHistory Historyof ofthe the Sudbury Sudbury Structure Structure Tectonic, Magmatic and Mineralization Don H. Rousell Rousell and and Harold Harold H. H. Gibson, Gibson, Department Department of of Earth EarthSciences, Sciences,Laurentian LaurentianUniversity, University, Don H. Sudbwy, Ontario Ontario P3E Sudbury, P3E 2C6 The Sudbury Structure major components: components: 1) Structure consists of three major 1) the Sudbury Sudbury Basin; Basin, 2) the Sudbury Igneous Igneous Complex (SIC) which surrounds surrounds the basin as an elliptical collar; collar; and, and, 3) an outer zone of shatter-coned shatter-coned and and brecciated footwall rocks. The area has gained fame as a result of the SIC and the Ni-Cu-PGE ores ores which it hosts, as as well as the proposed proposed meteorite meteoriteimpact impactorigin origin for for the structure structure(Sudbury (Sudbury Event). Event). However, However, the thearea areahas hasundergone undergoneseveral severalsignificant significantArcheanArcheanProterozoic tectonic, magmatic and mineralization events which have been largely overshadowed Proterozoic tectonic, magmatic and mineralization been overshadowed by the Sudbury Sudbury Event. Event. extension and closure, namely a The Sudbury Sudbury area was was shaped shaped by two Wilson cycles of crustal extension Paleoproterozoic cycle and and aa Mesoproterozoic Mesoproterozoic cycle. cycle. The Sudbury Structure was apparently the the Paleoproterozoic site of a triple junction or Thefirst firstcycle, cycle, from from2500 2500tot o1700 1700Ma,, Ma, or hot-spot hot-spot during duringthese thesecycles. cycles.The included the following events: doming (uplift of Levack Levack gneiss complex); complex); NW-SE extension extension Ni-Cu-POE, (Matachewan dikes); N-S to NW-SE rifling rifting (faults, mafic intrusions, sedimentation, N-Cu-PGE, U); diabase,Ni-Cu-PGE, Ni-Cu-POE, Ag, Ag, Co); Co); and, NW-SE closure U ); NW-SE extension extension (Nipissing diabase, closure (Penokean Zn-Cu-Pb). Orogeny, 1900-1700 1900-1700 Ma) with imposed meteorite impact (1850 Ma; Ni-CU-POE, Ni-Cu-PGE, Zn-Cu-Pb). NThe second cycle, from 1700 1700 to 1000 1000 Ma, included: N-S extension (alkali metasomatism, Au); NS extension (homblende Murray fault set); NNE-SSW (hornblende diabase diabase dikes along Murray NNE-SSW extension extension(olivine (olivine diabase dikes); NE-SW extension (Fecunis Lake Lake fault fault set); set); and, and, NW-SE NW-SE closure closure (Grenville Orogeny). Orogeny). The extensive and rich mineralization which which is is characteristic characteristic of of the the Sudbury Structure, Structure,isis related related magmatism. Although Although the the Ni-Cu-PGE Ni-Cu-POE and ZnZnto endogenic endogenic and impact-triggered extension and magmatism. Cu-Pb ore are are located located within within an an impact structure, their age age and tectonic tectonic setting settingisis similar similar to to NiNiCu-POE the world. Geochemical arguments have been Cu-PGE and Zn-Cu-Pb deposits deposits elsewhere elsewhere in the presented which ascribe the origin of of the the SIC SIC and and its its ores ores to to aa melt melt sheet sheet or or to to contaminated mantle-derived magma. The melt sheet origin origin divorces divorces the the SIC and and its its ores ores from their geologic setting setting and pre-impact history, whereas the SIC and its ores are are consistent consistent with with evolutionary, evolutionary, global metallogenic events. Meteorite Meteorite impact impact is is interpreted interpreted as as aa triggering triggering event which focussed ore4orming processes long-lived ore-forming processesatatSudbury. Sudbury.IfIfviewed viewedin inthis thismanner, manner, layered layeredmaflc maficintrusions intrusions immediate host host rocks, rocks,both botholder olderand andyounger youngerthan thanthe the SIC, SIC, warrant warrant farther further and their immediate examination to assess assess their potential for for hosting hosting Ni-Cu-POE Ni-Cu-PGE ores. ores. 53 �This page page left blank intentionally. This left blank 54 �OVERVIEW OF OVEROF THE THE GREGOR GmGOR GOLDFIELDS GOLDFIELDS CORP. COW. MARATHON (WIRE LAKE) GOLD PROPERTY IN THE LAKE) GOLD PROPERTY IN THE HEMLO HEMLO AREA AREA OF OFCENTRAL CENTFLU ONTARIO, CANADA ONTAFUO, John M. Resource Associates Limited and John M. Siriunas, Siriunas,P.Eng., P.Eng,, NR&J NR&J Resource Associates Limited John John Wiebe, Wiebe, President, President, Gregor Gregor Goldfields Goldfields Corp. Corp. Gregor GoldfleldsCorp. Corp.(Gregor) (Gregor)has hasbeen been carrying carrying out out exploration work on Gregor Goldfields portions of of its its 4,000 ha Marathon-area property since since the the ground was first Marathon-area property ground was fist portions that staked in in 1983, 1983,during during the the rush" "rusP thatfollowed followedthe the1981 1981discovery discoveryof ofeconomic economic gold mineralization at ilemlo. There is no record of exploration work gold minerahation at Hemlo. is no rword of eqloration work being being to o that that time. time. Gold Gold mineralization mineralization was was carried out on the Gregor Gregor property prior t first located located on the property property in in1985 1985and andsubsequent subsequentprograms progrms of of diamond diamond drilling have have encountered encountered at at least four zones or areas drilling areas of of mineralization. mineralization. The property area area is is underlain underlainpredominantly predominantlyby bymafic malicvolcanic volcanic rocks; the auriferous auriferous mineralization is associated with zones of intense alteration that occur mineralization associated with zones of intense that occur within within these volcanic rocks. Much Much of of the detailed detailed exploration exploration work, work, especially especially the the volcanic rocks. drilling,has has been beencarried carried out outin in the the central central area of the property in the diamond drilling, vicinity of of Wire vicinity Wire Lake. Lake. The The best bestdiamond-drill diamond-drillintersection intersection of of gold-bearing gold-bearing mineralizationtto date is 7.39 o date 7.39 g Au/t Adt over ovw 3.04 3.04 m while while grab grab samples samples from fiom minerakation surface have returned up to 26.743 gAult. surface returned up ta 26.743 g Auk 55 �This left blank intentionally. This page page left blank intentionally. 56 �PRECIOUS-METAL MINERALIZATION IN COPPER AND PRECIOUS-METAL IN EASTERN SAULT STE. MARIE M A R E MINING MINING D1VISION DMSION WITH THE JENTINA JENTINA STE. WITH FOCUS FOCUS ON THE PROPERTY, ALBANEL AND AND NICHOLAS PROPERTY, ALBANEL NICHOLAS TOWNSHIPS, TOWNSHIPS, DISTRICT DISTRICT OF OF ALGOMA ALGOMA M. Siriunas, Siriunas,P.Eng. P.Eng. and andNeil Neil0.0. Willoughby,NR&J NR&J ResourceAssociates Associates John M. Willoughby, Resource Limited Limited Copper mineralization O n e o , though first &st Copper mineralizationin in the the Huronian Supergroup of of central Ontario, 1846, has importance discovered aatt Bruce Mines in 184S, has histofidly historically been overshadowed in importance deposits of of the copper-nickel copper-nickel deposits of by the ofthe the Sudbury Sudiburyarea, area, the the palmplacer paleoplacer uranium uranium deposits Elliot Elliot Lake Lake and andthe thesilver-arsenide silver-anenidevein veindeposits depositsof of the theCobalt-Gowganda Cobalt-Gowgandaregion. region. Previous have postulated postulated a variety F'revim investigations investigations have variety of origins origins for for the copper copper mineralization present within the the Huronian. H u r o n h . The Theemerging emergingconsensus consensusinineconomic economic geology in general general is that that regional-fault patterns and regional-fault patterns andzones mnesof ofdeformation deformationhave haveplayed played geology in aa major inthe theformation formationof of metallic-mineral metallic-mineraldeposits, deposits,irregardless irregardlessofofgeologic geologicera, era, majorrole rolein and that thatthe therecognition recognitionof of geological geological stactwe can lead leadto to the thediscovery discovery and structure and and alteration alteration can of signi6cant significant economic economicdeposits. deposits.The Thefact factthat that most most researchers researchers consider the the HuronianHuronianM e a n interaction interaction to to be beone oneofofcontinental continentalco]lision-subduction collision-subduction zone zone mechanics mechanics Archean invokes as invokes epithermal epithermal (Cordilleran-type) (Cordilleran-type) and mesothermal mesothermal (Archean-style) (Amhean-style) models models as being being applicable applicable to the the Huronian Huronian Basin. Basin. The Flack Lake Fault is is aa reverse reverse thrust thrust fault faultof of regional regional extent extent that thatisislocated locatedalong along The the the northern northernboundary boundaryof of the the Huronian Hmnian volcano-sedimentary volcano-sedimentary basin. bash. This Thisfault fault was was most most likely likely an an active active normal normal fault during during the the Archean Archean and and was wasre-activated re-activated during during the the Penokean Indications are are that that the thecurvilinear, curdinear,locally l d yeast-west east-westtrending, trending, Penokean Orogeny. Orogeny. Indications Hack Rack Lake Lake Fault FaultSystem Systemhas hasproduced produced considerable considerable ductile ductile shearing shearing and and brittle brittle deformation within within the the nearby nearby host rocks across the HuronianBasin. Basin. deformation the northern northern Huronian Major Major deposits deposits of of structurally-controlled structurally-mntmlled copper copper and and precious-metal precious-metal mineralization mineralization within Proterozoic Proterozoic terranes world in in such suchsettings settings as as within terranes can be found elsewhere in in the world northern northern Australia Australiaand andFennoscandia. Femoscandia. Within the the Huronian HuronianBasin Basinofofcentral centralOntario, Ontdo, the occurrencesare are associated associated with with the the Murray Murray Fault, themost most well-known well-known occurrences Fault, which which parallels pad& and and lies lies to to the the south south of of the Flack Lake Fault. Copper Ccpper mineralization mineralization in in this thisregion region has has been (43,000 tt Cu) Cu) and and the Pater been exploited exploited at at Bruce Bruce Mines (43,000 Pater Mine M h e(36,000 (36,000 ttCu, Cu,140 140kg kg Au, 4,300 of ckpper copper ocmrrenm occurrencesare are known known to to be present present along 4,300 kg kg Ag). A number of alongthe the northern northernmargin marginof of the the Basin Basin in in the the vicinity vicinity of the Flack Rack Lake Lake Fault; Fault; the theBi-Ore Bi-Ore Mine Mine at Cobre Lake produced 700 t Cu during its brief period of production (1948-49). at Cobre Lake produced 700 t Cu during its brief period of production (194849). 57 �The Jentina Property Property of AJ. AJ. Roy Roy of of Sudbury, Sudbury, Ontario, Ontario, is located located in Albanel Albanel and Nicholas Townships straddling the Flack Lake Fault. Several copper and Nicholas Townships straddling the Black Several copper and preciouspreciousmetal showings on the Jentina Property areindicated indicated to be be associated associated with with east-west east-west showings on PruperQ are striking striking shear shear and andfault faultzones zones associated associated with the the main main system systemof of faulting. faulting. The TheNo. No. 11 zone on the the Jentina Jenthia Property, mapping, iiss thought to have Pmperty, as as determined determined from surface mapping, have a strike The h. Thezone zonecomprises comprises quartz-carbonate quartz-carbonate veining veining with with strike length length of of about about11km. extensive albitization, silicification and chloritization chloritization of ofthe the host host Espanola Espanola Formation; silicification and Formation; massive mineralizationisislocally locallypresent. present. The The No. m k v e sulphide (chalcopyrite-bomite) (chalcopyrite-bornite) mineralization No. 22 zone zone is about about 1½ 1%km h in inlength. length. This 'l'his zone zoneincludes includes quartz quartz veining, veining, breccias breccias and and stockworks. Considerable chloritization ebloritizationand and sili&cation silicificationoccur occurwide while albitization albitization is stdcworks. Considerable is limitet limited Scattered h t k r e d pods pods ofofmassive massive chalcopyrite chalcopyrite occur occur within within this this zone zone which which transgresses several lithologies. On the Canamiska section of the claim bloclç a 3 transgresses several Iithologies Canamiska section the claim block, a 3kmIanlong and conductive conductive geophysical geophysicalanomaly anomalyhas has been been drill-tested drill-tested for only long soil geochemical and 75 m of of its its strike strikelength. length. Intersections Intersections of of up up to to1.44% 1.44% Cu Cu over over 19.5' 19.5' (5.9 (5.9 m) m) were were encountered during thatdrill drillprogram pmgram in in1965. 1965. during that Regional studies wwithin NTSSheet Sheet41J 41J have have demonstrated demonstratedthat that the available Regional studies ithin NTS available lake lake sediment geochemistry especiallymagnetics, magnetics, can can be used as as geochemistxy and airborne airborne geophysics, geophysics, especially effective tools toolsto tomap mapgeological geologicalstructures structuresand andbe beused usedtto locateother other areas, areas, similar o locate M a r to to the Jentina, Jentina, that thataxe are favourable favourable targets targets for mineral mineral exploration in the region. 58 �GEOIJXIICMAWINGSYSThM TO BEDROCK G E O L O G I C M A P P (CeM: N G ~A(DIGITAL A ~ : D AH1ROACH I ~ K ~ O GEOLOGIC A ~ MA ~ WNG B D WAHL, T.E., MILLER, J.D., J.D., JR., JIRSA, M.A., M.A., BOERBOOM, BOERBOOM, T.J., T.J., CHANDLER, V.W., WAHL, A.C., Minn. Mimi. Geological Suwev. Survey, 2642 2642 University University Ave., Ave., St. St. Paul. Paul, Mi~nn., Mimi., 55114: 55114; RUNKEL, A.C., D:, Mimi. Mii.Dept. of ~a-&d i i k l s , P.O. Box Box 567, 567, ~ ibbin~, DAHL, D., Natural ~esoukxs, Resources, Div. of M Minerals, Hibbing, Minn., 557M. and SEVERSON, MJ., Natural Natural Resources Eksources Research Institute, Institute. Univ. of Mint, 55746; Minn., 3051 3051 Miller Miller Trunk Tmnk Hwy., Hwy., Duluth, Duluth, Minn., 55811. 55811. Computers geophysical data Computers have have long long been bcen used nsed by geologists geologists to visualize remotely sensed gwphysical data and and manipulate point-source data. data. Increasingly in recent years, Geographic manipulate and image numerical point-source Information System System (GIS) (GIs) software software has been used to produce geologic maps and to archive archive the the raw data however, to make use of the data on on which which the the maps maps are arebased. based. Little has been done, however, exceptional data-management capabilities 015 for evaluating exceptional capabilities of GIs evaluating and sorting sorting geologic, geologic, structural, structural, geochemical, and geophysical creating a geologic map. geochemical, geophysical data, data, activities that must be done before creating the Miinesota Minnesota Geological Survey and other other agencies have developed developed Over the past several several years, the (Geologic Mapping GIS that consists of a graphical graphical user GeMS (Geologic MappingSystem), System), an Arc/Info-based Adhfo-based GIs user interface, image/grid base layers and data structures for storing and manipulating geologic interface,imagdgrid stmctures for storing and manipulating geologic field the capability capability for forgenerating generatingmaps. maps. The The utility utility of of GeMS GeMS as as itit has has been been and analytical data, and the current mapping in the notthwestem northwestern part part of of the the Duluth Duluth Complex Complex will will be be demonstrated applied to current at the the poster poster session. session. ' GeMS GeMS has has three three major major goals: goals: 1. use by by both both the the geologist geologist and and the the potential potential user. user. GeMS I. To make a system easy to use GeMS has has aa menu-driven, menudriven, point-and-click point-anddick interface for data entry, retrieval, manipulation, and imaging. This This reduces the time needed to learn how to use GIs GIS software and and allows allows geologists geologists to to focus on using GIS GIs as an aid in in making making geologic geologic interpretations. intetpretations. the subjective subjective nature nature of of most most 2. To Todevelop developaa flexible flexibledata-base data-base structure that accommodates the nonuniformity of nomenclahm, nomenclature, and and the the unique unique mapping mapping styles styles of of individual individual field data, the nonunifonnity geologists, retrieval and and sorting of of that that diverse and geologists, while while permitting permitting the straightforward straightforwad rettieval descriptive information. descriptive information. 3. To allow rendering prior prior data data bases bases To allowfor forexpansion expansionand and upgrading upgrading of the system without rendering obsolete. GeMS GeMSmay mayalways alwaysremain remainaawork-in-progress, work-in-progress, as as new new users users identify identify modifications modificationsto to describe aa particular particular geologic geologic terrane. tenane. better suit their style style of mapping or to better describe of five five gened general functions functions (Fig. (Fig. 1): 1): (1) The basic structure smcture of GeMS consists of (1) selection selection of of the the area, base maps, maps, and and overlays overlays[SETUP]; [SETUP];(2) (2)addition additionand andmodification modificationofof basic mapping area, geologic data (3) manipulation manipulation of of the the data using geologic data [OUTCROP, SAMPLES, and STRUCTURE]; (3) sorting, statistical, [TOOLS]; geologic interpretation interpretation [GFDLOGYI, [GEOLOGY], and (5) sortiug, statistical, and imaging ixnagiig tools W LS]; (4) gwlogic pLOTJ.This Thisbasic basicstructure structureisis outlined outlined in in the the startup stamp menu of GeMS. &MS. map plotting [PLOT]. Choices of the mapping area, base maps, maps, and transparent transparent overlays overlays for for all all other other GeMS Choices operations are made through the SETUP function. function. The operations The standard standard base for for detailed detailed bedrock bedrock Minnesota is the theUSGS USGS 1:24,00O-scale 1:24,000-scale(7.5') (7.5 topographic geologic mapping in Mimesotais topographic quadrangle quadranglemap, map, digital-raster-graphicand anddigital-elevation-model digital-elevation-modelformats. formats. Low-altitude which is available in digital-raster-graphic Low-altitude orthophotoquads and geophysical anomaly images images (aeromagnetic (aeromagnetic and and gravity) gravity) are are also also available. available. orthophotoquads outcrop patte.rns, patterns, sample sample lwations, locations, structure structure symbols, symbols, and and other Transparent overlays can include outcmp point- and line-source line-sowce data. Basic Basic field field and and analytical analyticaldata data are are entered e n t e d in three threegeologic geologic data data layers—OUTCROP, layers-OljTCROP, SAMPLES, STRUCTURE. Data constructed to tobe bemenudriven, menu-driven,whereby wherebythe the user user SAMF' LFS, and STRUCTURE. Jhta layers are constructed appropriate term termfor foraaparticular particularattribute. attribute. The outcrop-data selects from a look-up table the most appmpnate outcmpdata layer records the physical outcrop. Attributes physical characteristics of an outcmp. Attributes of three beerock rock types typesper per outcrop outcmp may be eentered tables, which which have have been been customized to pennit permit custom^ to n t e d through one of four menu-driven tables, description of intrusive-igneous, sedimentary, and and metamorphic metamorphic rocks. rocks. The description intrusive.-igneous, volcanic, sedimentaq, The sample sample 59 R ~ ~ �___________ _____________HArea _______ _____________ ______ __________ layer records the physical sample and the types of analyses conducted conducted on layer records physical state state of the sample on itit (e.g., (e.g., petrographic, petrogmphic, microprobe, microprobe, geochemical geochemical (whole-rock, (whole-rmk, isotopic, isotopic, and assay), assay), geophysical geophysicalproperties, properties, gemhronologic). These Thesedata dataare arestored storedin inassociated associated files filesand and are are indexed indexed to to aa unique unique sample sample geochronologic). identifier. The structure layer records the type of linear or planar feature and its orientation; its orientation; The structure layer records the type of linear or planar feature standard symbols type. A are assigned to each type. A fourth fourth data data layer layer containing conthimg drill-hole drill-hole infonnation information symbols are soon,and andfield fieldphotographs photographs may may constitute wnstitute aa fifth layer layer at a later later date. will be added soon, The TOOLS TOOLS function functionprovides provides subroutines subroutines for for sorting, sorting, numerical numerical manipulation, manipulation,and andimaging imaging The data from from the the three three geologic geologic data layers and related This function is is still still being beimg of data related data data tables. tables. This develop&, but butwill willinclude includeoptions optionslike likecolor colorcoding ccdimgof of outcrops outcropsby by specified specifiedattributes, attributes,and andthe the developed, calculation calculation and andplotting plottingof ofthe thevalues values of of geochemical geochemicalparameters parameters (e.g., (e.g., Fo Fo in in olivine, olivine,tracetraceelement elementratios, ratios, normative normativeabundances). abundances). The The GEOLOGY GEOLOGYlayer layerprovides provides for for the the creation creation and and description description of map map units units (polygons), (polygons),unit unit contacts contacts (polygon (polygonedges), edges), and and linear linear features features like like faults faults (lines). (lines). Lastly, to Lastly, the the PLOT PLOT function function permits permits layout layout and scaling scaling of printed p ~ t e maps d to include includeany any combination basematerial, material,raw raw or or processed processed data, data, and and geologic geologic interpretations. interpretations. combinationof of base The GeMSoffers offersan an increasingly increasingly useful useful tool tool for for the thecollection wllwtionand and Thecontinuing continuingevolution evolutionof ofGeMS manipulation manipulationof of geologic geologicinformation, information, map map production, production, and, and, most most importantly, imporfantly,interpretation interpretationof of bedrock geology. GeMS can be used from the beginning of a mapping project to the final map bdrock geology. GeMS can be used from the beginning of a mapping project to the final map creation with future future aquisitions aquisitions of of data. data. In creation and and allows allows for for straightforward straightforward upgrades with In addition, addition, users users have have easy easy access, access,in in aa geographic geographic context, context, to to all all the the original original information on which aa map map interpretation interpretation isisbased. based. GeMS H Backgroüi i j Jimage sample topography orlliophoto aeromag structure geology Joverlay(s) $PCWJ 9FEb14' SAMPLES (points) Jbiite j—JAdd J I I one frkgrounci data jsample description petrography probe phricalpropethes isotope assay geochrunology related data tables I—I v.ljole rock --ABl STRUCTURE STRUCTURE (points) F-* I OUTCROP lygons) I I!*°Y eIeJ I one background data twcture typj Jorientadj 9dily j I—kd 1bround data utcrop description elete )—jäean }-_oone ne f Jiled rock type(s) descriptions klteon J Intrusive Igneous Volcanic I Volcanic JsuildH I—J snta,y lidefomlation Metamoiphic TOOLS GEOLOGY ete F—F1ean1-—Pone Modify dd map unit descriptions jLOT I pir-l IQUIT edges F— contact relationships v t 1 " 8 jes —(ault&dikedescdptions faun & dike d m p t i o n s Figure Figure 1.1. Conceptual Conceptualframework frameworkfor forGeMS GeMS 60 Build I �HYDROGEOLOGY OF SALINE- AND AND BORON-BEARING BORON-BEARiNGGROUND GROUNDW WATERS INTHE ThE HYDROGEOLOGY AERS l h ' NORTH SHORE SHOREVOLCAMC VOLCANICGROUP, GROUP, MINNESOTA MINNESOTA TIPPING, TIPPING, Robert Robert G., G., Mimi. Miin. Geol. G a l . Survey, Survey, 2642 2642 University University Ave., St. St. Paul, Paul, Minn., 55114; 55114;and and Geol. Univ. of of Minn., Minn., 310 310 F~llsbury Pillsbury Dr. Dr SE, ALLEN, Douglas, Dept. of G a l . and Geophysics, Univ. SE, Minneapolis, Minn., 55455. Mimeapolis, Public levels of boron boron in ground water. Public concern concem grew grew in in late late 1994 1994 along the North Shore over high levels water, The The LTV LTV Mining Mining Company, which owns a large coal burning operation near the town of Schroeder, from the the plants plant's fly ash piles or initiated a study study to to determine determine whether boron in ground water was from from natural natud sources. sources. The Theresulting resultingreport(6) report(6)shows showsthat thatboron boron isis at at levels levels above abovethe therecommended mommended allowable limit of 300 North Shore Shore and and concluded concluded that that it is allowable 300 ppb in ground water all along the Nor&h saliie, coming from natural sources. In Inaddition, addition,the the LTV LTV study study sampled sampled two two wells wells that that were were highly highly saline, chloride concentrations concentrations greater than 40,000 ppm. The raisedtwo two questions questionsabout about with chloride The LTV LTV report report raised composition of ground water along the North North Shore: Shore: 1—What the composition 1-What is is the geologic geologic source sourceof of the the boron? Thisstudy studyuses uses chemical chemicaland and boron? and 2—What 2-What is is the the distribution and origin of the dsaline i n e water? This isotopic information on on the the shape shape and and evolution evolution of the isotopic analysis analysis of ground water, combined wmbined with new infomntion Portage resides under under the the lake, lake, at least in Portage Lake Lake volcanic volcanic basin(1,5) to propose that the saline water resides sedimentary unit located strat&aphicaIly stratigraphically at at the the base base ofthe of the (A0 m) interfiow interflow sedimenm part within withii a thick thick (>40 youngest Group (NSVG). (NSVG). Mien, youngest basalts of the the middle middle Proterozoic North Shore Volcanic Group Allen,D.E., D.E., eteta!. al. (this vol.) describe describe a possible model for the dissolution of boron boron in in ground ground water water and and offer offer evidence evidence basin. The for the presence presence of marine waters in the rift basin. Thepreliminary preliminary data data suggest suggest that that boron boron and and the the occurrence of saline occurrence salinewaters waters along along the the North Shore Shore are are genetically genetically related. are fractures fractures within within the thebasalts basalts of of the the NSVG. NSVG. Typical The primary source source of water for wells are Typical yields for per minute minute..Wells for these wells are 2-4 gallons per Wellsfmished finished in in the the interfiow interflow sedimentary sedimentaryrocks rocks generally of these these strata. strata. Interfiow generally have have higher higher yields due to the greater permeability of Interflowsedimentary sedimentary units are the the 70-rn-thick 70-m-thick unit unit units typically are are no more than a few meters thick(3). Notable Notable exceptions exceptionsare 40-rn-thickpolymict polymictconglomerate conglomerate partially partially Good Harbor Harbor Bay and an approximately 40-m-thick exposed at Good Little Marais MarS (Fig. 1). exposed near Little (Fig. 1). composed of of mediummedium- to to -grained coarse-grained sandstone sandstone grading grading into into The Good Harbor Hahor Bay unit is wmposed interbedded finewell-sorted sand sand and and shale shale beds beds;the theunit unit becomes becomes increasingly increasingly f m e to medium-grained well-sorted interbedded 10-15 degrees degreesto to shaly nnear e x the top. The Thebeds bedsin inthe the interfiow interflow rocks rocks and and the the overlying overlying basalts b d t s dip dip 10-15 the south-southeast Little Marais, Marais, like like the the Good Good Harbor south-southeast(Fig. (Fig. 1). 1). The The polymict conglomerate near Little Bay interfiow overlying Schroeder-Lutsen Schroeder-Lutsen basalts. basalts. The intefflow unit, unit, is is structurally conformable with the overlying The LTV study study demonstrated demonstrated that that the the water water from from wells wells finished finished in in both both sedimentary sedimentaryunits units contain containboron. boron. In addition, two wells sampled near near Little LittleMarais Maraisas aspart partof ofthe theLTV LW study had chloride 1eveLs levels greater than 40,000 40,OW ppm. These Thesesites siteswere were chosen chosen for foradditional additional water water and rock rock sampling sampling because because reasonable conceptual conceptual model model could could be be constructed constructed to to sampled from outcrop, and a monable the units could be sampled demonstrate the demonstrate the path path of of ground-water ground-water flow flow to to the wells. Marais and and Good Goad Harbor H&r Bay units units have not previously been correlated, correlated, Although the the Little Little Marais similar stratigraphic uncommon thickness imply these units units were their similar skitigraphic position position and uncommon imply that these were deposited depositedat at the same same time. Furthermore, Furthermore,the thelocation locationof of these theseunits units relative relativeto to the the shape shape of of the the Portage Porfage Lake Lake volcanic basin, as proposed by Mien, energy deposition D.J., et et aL(1), al.(l), fits fits a model of high energy depositionalong alongthe the volcanic Allen, D.J., cusp deposition farther farther from from the the basids basin's edge edge (Good (Good cusp of the basin (Little (Little Marais) and lower energy deposition Harbor basalts supports supports this Harbor Bay). AAbroad broadseismic seismicreflector reflectorat at the the base baseof of the the Schroeder-Laitsen Schder-Lutsen basalts depositional depositional model(l). model(1). From Fromaahydrostratigraphic hydrostratigraphicperspective, perspective, correlation of the two units provides for a laterally laterally extensive, extensive, porous porous aquifer aquifer extending extending along along the shore shore and and beneath beneath the the lake. lake. between dissolved dissolved bromide bromide and andchloride chloride concentrations concentrations in in A positive linear linear correlation exists between al.; this this vol.). vol.). the sampled sampled ground ground waters waters from from Little Little Marais Marais and Good Harbor Harbor Bay (Allen, (Allen, D.E., et et al.; results dilute waters waters moving movingdownslope dowuslopetoward toward the the lake lake The ~ s u l t fit s the conceptual model of fresh, dilute sites, saline saline ground ground water waterat ator ornezu near lake lake level. level. At mixing with, in the case of the Little Marais sites, At Harbor saline water was was sampled, sampled, the the similar similarbromide-to-chloride bromide-to-chlorideratio ratio may may be be Good H a b r Bay, where no salime result of meteoric waters moving through through sedimentary sedimentary units, units, which whichonce oncewere weresaturated saturated with with the mult compositionallysimilar similartotothe thewater wateratatLittle LittleMarais. Marts. Boron saline water that was compositionally Boron concentrations concentrations above at both both sites. sites. Boron was 600 ppb ppb were were found found in the majority of wells sampled at was also also found found in in above 600 61 �samples samples from from the the Good Good Harbor HarborBay Bay interfiow interflow unit, with with concentrations concentrationsgreater greaterthan than 30 30ppm ppm in in shaly shdy members. members. AApH pHmechanism mechanismfor forthe thedissolution dissolutionof of boron boron in in ground ground water waterfrom fromthese these shaly shaly members members is vol.). Based is presented presented in in Allen, Allen, D.E., D.E., et et at. al. (this vol.). Based on on their their preliminary preliminary boron boron isotopic isotopic results, results, the the boron beof ofmarine marineorigin. origin, boron in in the theGood GoodHarbor HarborBay Bayinterfiow interflow sedimentary sedimentaryrocks rocks isisthought thoughtto tobe implying implyingthe theporous porousinterflow interflowsedimentary sedimentaryunits units at at Little LittleMarais Marais and and Good GoodHarbor HarborBay Bay were were inundated inundated with with sea seawater waterat atsome sometime timeduring during the the development developmentof of the the rift rift basin. basin. Thepresence presenceof ofseawater seawaterisisunnecessary umece.ssary to account for saline s a h e waters in the rift. Hardie(2) Hardie(2) The demonstrates canproduce produce demonstrateshow howhydrothermal hydrothermalconvection convectionand andweathering w e a t h e ~reactions greactionsin in aa closed closedbasin basincan cakium-chloridebrines brinesfrom fromaawide widerange rangeof of source sourcewaters waters similar similarto to those thosesampled samuledin inthis thisstudy. studv. calcium-chloride i& utility utilityin in settings seniigs However,the the heavy heavy boron boron isotopic isotopicsignature signature of of the the waters waters analyzed analyzed highlights highlightsits However, like likethe therift, rift,where wheresedimentary sedimentaryevidence evidencefor formarine marineenvironments environmenbisisinconclusive. inconclusive. This thither work. This study studysuggests suggestsseveral seve& possibilities possibiiities for further work. The Theproposed proposedcorrelation comelationof ofthe theLittle Little Marais beinvestigated. investigated. Marais polymict polymictconglomerate conglomerateand andthe theGood Good Harbor Harbor Bay Bay interfiow interflow unit unit needs needsto tobe Detailed areanear near Good Good Harbor HarborBay(9) Bay@)has has revealed revealedaamore more.complex complex Detailedmapping mappingof ofthe theCascade CascadeRiver Riverarea stratigraphy stratigraphythan thandescribed describedin inthis this study. study. Although Althoughnot notas asconcentrated, concentrated,the thesaline salinewater waterisis chemically chemicallysimilar similartotothe thecalcium-chloride calcium-chIoridebrines brinesin inMichigan Michigancopper coppermines(4; mines(* see seealso also sfs. rifs.totoLane h e therein) 8).; these be therein)fluid FIuidmovement movementwithin withinthe thebasin basinisiscurrently cumntlybeing beiigmodeled(7, modeled(7,8).; thesemodels modelscould couldbe modified modifiedto toincorporate incovoratenew newinformation informationon on the the shape shapeof of the the rift rift and and the the possibility possibilityfor foraalaterally latedly continuous continuousporous porousunit unitatatthe thebase baseof ofthe theSchroeder-Lutsen Sctuoeder-htsenbasalts. basah. References: etal., 1997. MS. v.290, References:(1) (1)Allen, Allen,DJ., D.J. .etd.. 1997,GSA GSASpec. SF. Paper P a p312; 3 1 2 (2) (2) Hardie, Hadie. 1990, AN, v. 290,p.p. 43-106; 4 3 - I N (3)Jirsa, (3) Jirsa.1984, 1984, -~ MGS 30,20 p.; p.; (4) (4)Kelly Kellyet eta!., aI.. 1986, 1986, AJS, v. 286, p.281-308; p. 281-30%(5) (5)Miller. Miller. & &Chandler, 1997, GSA Spec. Spec Paper3l2, Papr312,p.p. MGS RI Rl30.20 v.286, Chandler, 1997, 73-96;(6) (6)STS STSConsultants, Consultants,I995, 1995.Eva!. Eval.ofofBoron BomnImpacted ImpactedWells; Wells;report repntotoLTV LTVSteel SteelMining MiningCo.; (7)(7)Swenson Swemon&& 73-96; Person,1995, 1995,IGCP 336,Duluth, Duluth.Minn., Minn.,p.p.187-188; 187-18%(8) (8)Woodruff Woodruffetetal., al..1995, 1995,IGCP IGCP336, 336,Duluth, Duluth,Minn., Mim.,p.p. 213-214; 213-21k(9) (9) Person, IGCP 336, Green, Green.1996, 1996.Geology Geologyon onDisplay. Display,Minn. Minn.DNR, D M ,69 69p.; p.;(10) (10)Green, Green,1982, 1982.Two TwoHarbors H h sSheet, Sheet,1:250,000, 1 : 2 5 0 , MGS. ~MGS. , a,; R6W , 95W R4W , + R3W • R2W , RIW R2W + Good Harbor Bay + e p * SamPled Wella Fauft Attitude of 15 Uttle Marais —r 26 volcanic rocks Attitude of Igneous layering /'Road 0 5 kilometers NORTh SHORE VOLCANIC GROUP Sd,roeder-Lutsen basafts red sandstone NSVG, undifferentiated H BEAVER BAY COMPLEX Marc and intermediate intrusions Felsicinfrusions Levaux porphyry • Feriodiorite River Figure I. Generalized geology of the Noflh 5hore of Lake Superior, Little Mania to Good Harbor Bay. Minnesou, and locations of sampled wells. Modified from Green ([0), and Figure 5 from Miller and Chandler (5) �The Greening of of Sudbury Keith Winterhalder Winterhalder Sudbury lies lies at the southern southern edge edge of of the Precambrian Precambrian Shield, Shield, in aa vegetation vegetation zone zone transitional between the boreal forest to to the north and the boreal coniferous co~ferous forest the deciduous deciduous to the the south. south.Prior Priortotothe theadvent advent of of the the miNng mining and smelting industry 1883, forest to industry in in1883, the area was characterized by extensive extensivestands standsofofred red pine pine and and white white pine. pine. One the characterized by One hundred years years of of logging, logging,fire, fire,soil soilerosion erosionand andenhanced enhancedfrost frost action, action,as as well well as hundred fumigationand and copper, copper, ~nickel iron particulate particulate fallout from from the sulphur dioxide fumigation c k e and land iron region's three smelt-, smelters, severely severelydamaged damaged the the Sudbury Sudbury landscape, landscape, giving giving rise rise to region's three 10,000 barrenland land forming forming concentric concentriczones zonesaround around the three smelters. 1 0,000 hahaofofbarren smelters. The The of the the barren barren zone zone are are stmngly strongly aadified, acidified, with with pH pH values values ranging fiom from 2.2 2.2 to to 4.4, 4.4, soils of and both Cu and and Ni Ni levels levels in in the the soils soils of of the the barren barren zone zone are are greatly greatly elevated, elevated, from several severalhundred hundred to to several severalthousand thousand&g. pg/g. As varying from As well well as as solubilizing solubilizing the Cu and Ni Ni that that has hasaccumulated accumulated in in the the soil soilfrom fromatmospheric atmospheric fallout, fallout, the the acidity acidity of of Sudbury soil releases aluminum ions ions from from aluminosilicate aluminosilicateminerals minerals such such as as days, releases aluminum clays, stunted, relict relict individuals individuals of of woody contributing to to the the soil's soil's phytotoxicity. phytotoxicity. A few stunted, woody plants such such as as red red maple, maple,red redoak oakand andaspen aspencan canbe befound found on on the otherwise barren slopes, which have have aa stony stony covering coveringthat thatresulted resulted from from the the combiied combined action of frostslopes, which frostthe barrens barrens is a heaving and erosion erosion on on the the glacial glacial till-derived till-derived soil. soil. Surrounding Sumounding the 36,000hectare hectarezone zone of of stunted, stunted, semi-barren semi-barren woodland, woodland, characterized characterized by patches of 36,000 of bare soil between the relict, relict, coppiced coppiced white white birch, birch, red red maple maple and red oak. In the the past past 25 25 years, years, some some areas of previously previously barren soil have been been colonized colonized by by species suchas astdted tuftedhair hairgrass, grass,tickle ticklegrass grassand anddwarf dwarfbirch, birch,asasaaresult result of of the speaes such evolution of of metal-tolerant metal-tolerant ecotypes. ecotypes. Furthermore, Furthermore, since sincethe the closure closure of of the Coniston CoNston smelter in 1 1972, thereappears appearstotohave have been been some some natural natural amelioration amelioration of of pH pH and 972, there smelter in metal levels levels in in that that vicinity, vicinity, and less plant such such as as white white birch birch and metal less metal-tolerant metal-tolerant plant wavy hairgrass hairgrass have begun to to colonize colonize the the area. area. The announcement by Inco Inco Ltd. Ltd. in in 1969 of its intention to construct 1%9 of intention to construct a 381 381 m The announcement by smokestack stimulated stimulatedthe theOntario OntarioDepartment DepartmentofofhLands andForests Forestsand and Laurentian smokestack n d s and University to iinitiate program. The frees University ~ t i a t ea joint experimental free-planting tree-planting program. trees planted planted barrens showed total mortality, mortality,but butititwas wasfound foundthat that the the soil could be on the barrens showed almost total detoxified suf£icientl sufficientlytoto initiate initiate colonization colonizationby bythe the surface-application surface-applicationof of p ground und detoxified limestone. Small-scaleexperiments experimentsinitiated initiatedinin1974 1974showed showedthat thatthe the surface surface of of the limestone. Small-scale 63 �stone-covered soil could be be detoxified by the stone-covered soil could detoxified by the manual manual application application of of ground ground limestone, and and that that seeds limestone, seeds were were trapped trapped by the the stony stony mulch, mulch, and andgerminated germinated successfully.The Theopen open structure structureofof the the resulting resulting grassy grassy sward was successfully. was beneficial beneficial for for colonization by native native plants plants with with wind-blown wind-blown seeds, seeds, since since itit offered offered numerous colonization by openings and microhabitats microhabitats for volunteer seedlings. In 1975 1975 and and 1977, 1977, small groups groups of elementary school pupils successfuUy successfullyestablished establishedgrass grass on on small small patches patches of of barren of land near near their their schools, schools, using using this this approach. approach. job-creation funds to the Regional Regional Municipality Municipalityofof Sudbury Sudbury appfied applied for In 1978, 1978, the for job-creation to employ one hundred and students to carry out and seventy-four seventy-four post-secondary post-secondaq students out largelargerevegetation employing employingthe the same same technique. technique.The Theprogram program reached reached its its peak peak in scale revegetation 1983, when when 1,277 1,277 unemployed unemployedpersons persons were were employed 1983, employed on combined combined federal, federal, provincial, m municipal industry funding. funding. So ha of of land land 3,500 ha provinaal, u ~ c i p a and land industry So far, far, approximately approximately 3,500 have been been greened greened in in this this way. way. More Inco has employed have More recently, recently, Inco employed aa commercial commercial crop-dusting company to apply limestone, limestone, fertilizer fertilizer and and seeds from the air.. aopdusting Spontaneous colonizationof ofthe thegrassed grassedland landby by larger larger woody woody plants plants is is so Spontaneous colonization so far far confined to birch, birch, poplar poplar and willows, willows, because confined because conifer seed source iiss scarce and the . seed bed conditions are poor. poor, More More than than 2.5 2.5 million million native native trees, trees, mostly mostly Jack Jack pine, red pine and and white white pine pine which which were were the the dominant dominant species species of the the pre-disturbance pre-disturbance landscape, have have been been planted planted since since1978 1978ininsmall smallinformal informalgroups, groups, which which break break up landscape, of the winter landscape, landscape, and and form form aa seed seed source source for for future future spread. the monotony of Plant communities communities that results from the revegetation revegetation procedure contains contains planted trees, trees, the seed rain, components derived from from the the seed seed mixture, mixture, planted rain, and any any metal-tolerant plants already on site. site.ItItisisassumed assumedthat that the the landscape will will ultimately ultimately metal-tolerant plants resemble the the original original pine pine forest, forest, but but concern concern exists existsas as to to how quickly resemble quickly the the typical typical understory species species will will move movein. in. The The usefulness usefulnessofofintroducing introducingplugs plugs of of soil soil that understory contain desirable understory understory species, species,aa seed seed bank, contain desirable bank, and and soil soilmicroorganisms microorganisms isis currently under investigation, and is meeting investigation, and meeting with with some some success. success. Another Another current current area of of interest interest isis the the use use of of liming liming and and revegetation on a watershed area revegetation on watershed basis, basis, thus thus dual problems of barren land and and acidified acidified lakes. lakes. solving the dual problems of the minimal the Sudbury Unique features Sudbury program program include include the minimal amelioration amelioration Unique features of of the approach, in which recolonizationplays playsa acritical criticalrole, role,and and the strong approach, in which natural natural recolonization strong manual component component and and resulting resultingjob-creation job-aeation benefits. benefits. 64 �THE MCKENZIE MCKENZIELAKE LAKEANTIFORM ANTIFORM AND THE KAWA BAY SYNFORM, PROVINCIAL THE SYNFORM, QUETICO PROVINCIAL PARK, PARK, ONTARIO ONTARIO WOODARD, H., Department of of Geology, Geology, Beloit Beloit College, College, Beloit, WOODARD, Henry H., Beloit, 53511and andPARHAM, PARHAM,Peter, Peter, P.O. P.O. Box 59510 Wis. 53511 Box 1647, Havre, Mont. Mont. 59510 The Mckenzie McKenzieLake Lake antiform antiform occurs occurs in in the the northeastern northeastern part part of Quetico QueticoProvincial ProvincialPark. Park. ItIt The was formed formedby bylate-stage late-stagetranspression, which of the the was which produced ductile deformation deformation of Quetico-Wawa subprovince subprovince boundary. The The fold fold measures measures at at least least 18 18 km km along alongits itsaxial axial Quetico-Wawa strike outcropwidth. width. The strike and and is is about about 55 km in maximum outcrop The crest crest of of the the fold fold defines definesthe the subprovincejunction junctionand andarches arches through through a distance of about 16 km; its hinge, which which does subprovince not correspond correspondto tothe thecrest, crest, is is very sharp. Both Bothlimbs limbsdip dip steeply steeplynorthwest, northwest,and andthe the not underlying very tight. tight, severelv severely stretched stretched and and dismembered. dismembered,. but underlyingKawa KawaBay Bay synform svnform is vew but still still traceable in outcrop and on Fig.1). Although traceablein outcropand on aerial aerial photographs (see Fig.l). Although the the plunge plungeof ofthe the Mckenzie McKenzieLake Lakestructure structureisisto to the the northeast, northeast, the degree of plunge plunge is is not not easily easilymeasured. measured. Lineation Lineationon on slickensided slickensidedsurfaces surfaces plunges plunges gently gently southwest southwest on on the the related relatedSide SideLake Lake zone zone of of backthrusting, backthrusting,and andthis thissuggests suggeststhat that the the folds folds plunge plungesteeply steeplynortheast. northeast.The TheSide Side Lake the antiform as a southwest-trending southwest-trending Lake shear zone zone emanates emanates from the crest of the backthrust of shear. shear. About backthrustwhich whichexhibits exhibitsleft-lateral left-lateral sense of About 28 28 km kmto to the thesouthwest, southwest, the the Side undeformed Lac La Croix Croix leucogranite leucogranite which Side Lake Lake shear shear zone zone cuts cuts a portion portion of the undeformed which is is dated datedat at 2,662 2,662 + 55Ma Ma(Woodard (Woodardand and others, 1995). This This age age is is approximately approximately30 30my my younger Ma)of of the theWawa Wawa subprovince, subprovince,and and15 15my my youngerthan thanthe thefolded foldedtonalite tonalitesills sills(2694 (2694 + 11Ma) younger younger than thanthe thefolded foldedquartz quartz monzonite sills (2678 + 6 Ma) in adjacent portions portionsof of the the Quetico synform is Quetico subprovince. subprovince. The Thesouthwest southwesthinge hingearea area of the underlying underlying Kawa Kawa Bay Bay synform is cut age for for this this granite should should allow cut by byaa stock-like stock-likebody bodyof of undeformed undeformed granite, and an age determination junction was wasfolded. folded. The determination of of the the time the junction The southwest southwest hinge hinge and and trough trough area area of fold axes, which of the theKawa KawaBay Bay synform synform is is broken broken into into aa mega-breccia, and major fold which were were developed developedin inWawa Wawasubprovince subprovincerocks rocksduring duringan an earlier earlier phase phase of the the juxtaposition, juxtaposition, are are secondarily are randomly randomly oriented. oriented. This secondarilyfolded foldedinto intomany many open open folds whose axes are This secondary accomplished by secondarydeformation deformationappears appears to to have have been been accomplished by aa process processwe we call call "backshoving" synform is "backshoving"where where the the trough trougharea area of of the the Kawa Kawa Bay synform is squeezed squeezedbackward backward (toward overriding-mass of the [toward the the southwest) southwest)under under the the northeastward northeastwardoverridina-mass the Mckenzie McKenzieLake Lake antiform (see Fig. 1). + + Figure 1 - - - Lake 9 4 15V '4 7 Km I Relationship of Side Lake Shear Zone to the Development of the Mckenzie Lake Antiform. 65 �This left blank intentionally. This page page left blank intentionally. 66 �AGE CONSTRAINTS CONSTRAINTS ON ON PLUTONISM, PLUTONISM, METAMORPHISM AND DEFORMATION DEFOWATION ACROSS THE SUEPROVINCE BOUNDARY NEAR THE THE WAWA-QUETICO WAWA-QUETICO SUBPROVINCE THE MANITOUWADGE GREENSTONE GFtEENSTONE BELT, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO Zaleski, E., and van of Canada (GSC), Ottawa, Zaleski, E., van Breemen, Breemen, 0., O., Geological Geologid Survey of Ottawa, ON ON K1A V.L., Department DepartmentofofGeosciences, Geosciences,Western Western Carolina CarolinaUniversity, University, KIA 0E8; OE8; and and Peterson, Peterson,V.L., Cullowhee, Cdowhee, NC NC 28723, 28723,U.S.A. U.S.A. The and the metasedimentary-migmatitic metasedimentary-migmatiticQuetico Quetico The volcano-plutonic volcano-plutonic Wawa subprovince subprovince and subprovince subprovincerepresent represent first &st order ordersubdivisions subdivisions of the Superior Superior Province; Province; yet yet our ourwork workalong along the Wawa-Quetico boundary and in the Manitouwadge greenstone belt (MOB) shows that the Wawa-Quetico boundary and the Manitouwadgegreenstone belt (MGB) that most of the structural history is is common commonto to both both terranes, terranes, and that structural and and metamorphic metamorphic history Quetico greywackes are correlative with greywackes in the MOB. The Quetiw greywackes are correlative with greywackes in the MGB. The Manitouwadge Mmitouwadge greenstone belt (MOB) (MGB) is is aahighly highly deformed deformed remnant of of supracrustal supracrustalrocks rockscomprising comprising a mafic-to-felsic volcanic succession successionofofcca. 2720Ma, Ma, the felsic component of which mafic-to-felsic volcaaic a. 2720 which isis intercalated intercalatedwith withiron ironformation formationand andassociated associatedmassive massivesulphide sulphidedeposits. deposits.AAsynvolcanic synvolcanic tronclhjemite was both both a magma volcanismand and aa heat source trondhjemite was magma reservoir reservoir for felsic felsic volcanism source for for mineralizing mineralizing hydrothermal hydrothermal activity. activity. U-Pb U-Pbages ages of of detritai detritalzircons zirconsfrom fromgreywackes greywackes in in the the MOB, immediatelytotothe the north, north, constrain the MGB, and in the the southern southern Quetico Quetico subprovince immediately depositional packagesto to younger youngerthan than ca. ca. 2690 2690 Ma Ma and and support support depositional ages of both sedimentary packages their correlation. correlation. The TheEverest EverestLake Lakepluton plutonintrudes intrudesthe theQuetico Queticogreywackes greywackes along along the the subprovince boundary. The age age of of the the Everest Everest Lake Lake pluton pluton constrains constrains the theminimum minimum subprovince boundary. depositional age of of the Quetico greywackestotoolder olderthan than ca. ca. 2680 2680 Ma. Ma. The Thenew new ages ages depositional age Quetiw greywa&es from the work in in the northern the southern southem Quetico, Quetiw, in in combination wmbiiation with previous work northern Quetico Quetico (Davis et a!., 1990), show that Quetico sediments were deposited over at least ca. 10 at 1-t ca. 10m.y. m.y. al., 19901, that Quetico sediments and and are are consistent consistentwith with southward southward younging, younging, a test test proposed proposed by by Percival P e r c i d and andWilliams Williams (1989) (1989) for their their accretionary accretionaryprism prism model model of of the the Quetico Queticosubprovince. subprovince. Regional Regional metamorphic grade increases increases northward, from from upper upper amphibolite amphibolitefacies facies without without migmatization migmatization in the the southern southern MOB, MGB, to to granulite granulite facies facie north north of of the theWawaWawaQuetico migmatizationininthe the southern southern Quetico Quetico and and northem northern Quetiw boundary, with extensive extensive migmatization Wawa subprovinces. Regional structural evolution can be modelled by aa four-phase four-phase sese Wawa subprovinces. quence of ductile deformation. In the MOB, D2 tectonic fabrics are defined by high grade quence ductile deformation. In the MGB, D2 tectonic fabrics are d&ed by high grade metamorphicminerals mineralsand andfolded foldedby by the theD3 D3Manitouwadge Manitouwadge synform, synform, with with relatively relativelyminor &nor metamorphic development of D3 fabrics, suggesting suggestingthat that peak metamorphic conditions were attained attained development of during Inthe theQuetico Queticosubprovince, subprovince,migmatitic migmatitic segregations segregationsvary vary from from during D2 D2 deformation. deformation. In in situ situmelts meltsdeveloped developed in in pelitic pelitic beds, beds, to to discordant discordant foliated foliated and and folded folded pegmatitic pegmatitic and and in tonalitic dikes, variations that are consistent with protracted migmatization contempotonalitic dikes, that are consistent with protracted migmatization contemporaneous raneous with withprogressive progressiveD2-D3 D2-D3 (and (andpossibly possibly D4) D4) deformation. deformation. Two the region region by U-Pb U-Pb Two major major syntectonic syntectonicplutonic plutonic events events have been documented in the dating dating of of igneous igneous zircon. zircon. Firstly, Firstly, hornblende-biotite hornblende-biotite diorite comprising the oldest phase phase of of the the Black Black Pic Pic batholith, batholith,and andthe theLoken h k e nLake Lake K-feldspar K-feldspar megacrystic granodiorite, are are both both ca. ca.2687 2687 Ma. Ma. These Theseplutons plutonswere were emplaced emplaced before or during D2 deformation, deformation, based on ontheir theirstrong strongD2 D2fabrics fabricswhich whichare arefolded folded by by the theD3 D3Manitouwadge Manitouwadgesynform. synform.Secondly, Secondly, 67 �ca. 2677—2680 Maplutonic plutonicrocks, rocks,including includingthe the Nama Nama Creek K-feldspar megacrystic 2677-2680 Ma megacrysticgragranodiorite, Banana monzodiorite, monzodiorite, and Everest Everest Lake Lake monzodiorite, monzodiorite, were were emplaced emplaced late during D2 or prior to to D3 D3 deformation. deformation. The TheEverest EverestLake Lakemonzodiorite monwdioriteintrudes intrudesQuetico Quetico greywackes and and is is veined veined by by anatectic anatectic segregations, hence hence constraining migmatization to greywackes to 2680Ma. Ma. In In the the MGB7 MOB, aa tonalite tonalite dike which which cuts cuts the the strong strong D2 fabric in the Loafter Ca. ca. 2680 ken Lake pluton, pluton, but also has a late-D2 foliation, constrains late D2 to to Ca.ca. 2675—2680 but also has a late-D2 foliation, constrains late D2 2675-2680 Ma. Ma. intrusive rocks, including foliated foliated to nearly massive aplites, Additional younger intmsive aplites, granites, granites, pegmatites pegmatite8 and and lamprophyres, lamprophyres, have not been dated. dated. The distribution distribution of U-Pb titanite titanite ages ages defines defines aa crude m d e gradient gradient ranging ranging from from ca. ca. 2686—2688 Masouth southofofthe theMGB, MOB,where wheretitanite titaniteages agesoverlap overlap with with the ages of igneous 2686-2688 Ma Maininthe thenorthern northernMGB, MOB, to to ca. Ca.2640 2640Ma Ma in in the the Everest Lake ca. 2650—2655 2650-2655 Ma zircons, to ca. pluton in in the theQuetico Queticosubprovince. subprovince. While While our our titanite titaaitegeochronology geochronology is still still in in progress, progress, preliminary indications are are that the prelimixiary indications the ages agea date dateregional regionalcooling cooling through through Ca. ca. 600°C, 6OO0C, the closure temperature of of the U-Pb system in titanite closure temperature titanite (Heaman (Heaman and andParrish, Parrish,1991). 1991). In In our work thus far, deviations from from the the northerly northerly younging 'ounging pattern are permissive of an pattern are permissive interpretation in terms of of D3 D3 or or D4 D4 deformation deformation of the the 600°C 6OO0Ccooling cooling surface in the southern MOB Ma. Structural southem MGB after ca. 2655 Ma. Structural relationships relationships and isotopic isotopic dating dating suggest suggest a prolonged migmatization event in the the Quetico Queticosubprovince, subprovince,possibly possibly commencing commencing during during or soon after the the emplacement emplacement of the Everest Lake pluton (ca. 2680 Ma), and continuing until foliated granitic granitic dike interpreted interpreted as until ca. ca. 2642 2642 Ma, the age of monazite from aa foliated a injected injected leucosome of local derivation. References References Davis, D.W., Pezzutto, F.,and and Ojakangas, Ojalcmgas, R.W., R.W., 1990: 1990: The age age and andprovenance provenance of of Davis7 D.W.? Pezzutto, F., metasedirnentary rocks in the rnetasedimentary the Quetico Quetico subprovince, subprovince, Ontario, Ontario,from fromsingle singlezircon zircon analyses: analyses: implications Archean sedimentation sedimentation and and tectonics tectonics in in the the Superior Province; Earth Earth and implications for Archean Planetary Science Planetary ScienceLetters Letters99, 99,195—205. 195-205. Heaman, L.M., and R.,1991: 1991:U-Pb U-Pbgeochronology geochronologyof of accessory accessory minerals; minerals;in in AppliAppliHeaman, and Parrish, Parrish,IL, cations of R.adiogenic Isotope Systems Systems to to Problems Problems in Geology, Short Short Course cations Radiogenic Isotope Course Handbook, Handbook, Mineralogical Association 59—102. 1g7 59-102. Mineralogical Association of of Canada, Canada,v.v.19, Percival, J.A., and and Williams, Williams, H.R., H.R., 1989: 1989: The late late Archean Archean Quetico Queticoaccretionary accretionarycomplex, complex7 Superior Province, Superior Province,Canada; Canada;Geology GeoIogy17, 17,23—25. 2S25. 68 � https://digitalcollections.lakeheadu.ca/files/original/3e6ca9983eab16833ef2eda88f3a6c48.pdf 4b6d21870aa8d2e4765dc27ef5fa0dbd PDF Text Text THE HIJRONIAN HURONIAN SUPERGROUP SUPERGROUP THE BETWEEN SAULT SAULT STE. STE. MARIE MARIE BETWEEN LAKE AND ELLIOT ELLIOT LAKE THE EARLY PROTEROZOIC EVIDENCE FOR THE PROTEROZOIC ATMOSPHERE, CLIMATE CLIMATEAND AND TECTONICS TECTONICS ATMOSPHERE, by by G. Card and G. Bennett, K. D. Card and K. Tomlinson K. Y. Y. Tomlinson (2-21G.) \\\\\\ NlpIulng Diabase Cobb,o. dlabae. gatr Bar River Fm. .\ \ Quarla areMe. sto*o.. manc, n,ud,tone. ttone. Gordon Lake Fm. '''''1 U,d. ne $UVJStOn. —' ' \ n m. \ \ \ \ \ \ \ '. '---c- Y9 \ Quartz areiPt QuaI12 pebu. cOngantot• Mire.. iuba*o.. ML.tone, rltdaie II Gowgida Fm. Mccse.eltstcrs Diarrictile. pdymbtlc ccnglom.rat. ,/ .-.-.-. —'—V - Seipeci Fm. / Esprola Fm. Biuco Fm. ''''I '' ,-. \ Msdua Fm. Suba¼o... waa. 0c. Diartlttt .anthtone &treta.., a.kre. . •g p a . ::-_1rs!T;rst p t_._c____t_ c'rc—r _j Pecon Fm. t.maton.. attton. McKlm Fm h*jthtont ttaw ¾i - '\\\\\\ \ \ \ \ \ \ \ 1- 'fr Matln.nda Fm '- Iheudon Fm tscwI +4 — A—. .jba&re. jath-p.bbIe conorner& $o. Mcc — p Ita r. pe ce. thffigsta* creek Ftt —- +++ 4, + + INSTITUTE INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 43 rd 11, 1997 rdANNUAL ANNUAL MEETING, MEETING,MAY MAY6,6,11,1997 SUDBURY, ONTARIO ONTARIO Field Trip part 22 Trip Guidebook, Guidebook,Volume Volume 43, part �RKUNI1 gYENI MIDDLE PROTEROZOIC Grenville Orogeny Grenville Midcontinent Rift Rift System ICeeweenawan volcanics, volcanics, sediments sediments Keeweenawan Dyke emplacement Sudbury Sudhury swarm - Anorogenic magmatism magmatism 1000-1200 Cu 1000-1200 Cu 1100 1100 1238 1238 Croker Island Island complex, Complex, Manitoulin Manitoulin Island Island intrusions intrusions 1450-1500 1450-1500 Chief Lake, Cutler Cutler batholiths batholiths 1700-1750 1700-1750 EARLY PROTEROZO$C Felsic plutonism Felsic plutonism Deformation and metamorphism Deformation metamorphism (late (latePenokean) Penokean) Sudbury Sudbuw Event Event Sudbury Sudbury Igneous Igneouscomplex Complex Whitewater Group Group Whitewater 1850 Ni, Ni, CU, 1850 Cu, PGE, Zfl PGE, Zn Pb Pb Deformation and metamorphism Deformation metamorphism (early Penokean) (early Penokean) Dykeemplacement, emplacement,rifting rifting Dyke (ocean opening?) (ocean opening?) Kenora-Kabetogama, Kenora-Kabetogama, Marathon swarms swam Mafic magtnatism Uafic magmatism Nipissing diabase diabase Nipissing -2150 2219 Ni, Mi, Cu, Cu, 2219 POE, ffiE, Ag, Ag, Co. Cu, Cu, CO, Au Deformation Deformation (Blezardian Orogeny) (Blezardian Orogeny) Oxyatmoversion Oxyatmoversion Upper Nuronian Kuronim Supergroup Superyroup Upper Si Si Sedimentation, Sedimentation, mafic mafic Huronian Supergroup Lower Kuronian Supergroup U V magmatism Matchewan dykes,mafic-felsic mafic-felsic volca m, Matchewan dykes, volca2450-2496 2450-2496Ni, Ni, Cu, gabbro-anorthosite gabbm-anorthosite intrustions intrustions - POE PGE Creighton, Creighton, Murray Murray granites granites N ARC A5uiEAM Late deformation Late deformation Late plutonism Late plutonism Au Algwan granites Algoman granites Early Early deformation deformation and and plutonism plutonism Levack Complextonalite tonalite gniess Levack Complex gniess Vocanism and sedimentation sedimentation —2650 -2650 U -2680 -2680 Abitibi Suhprovince Cu, Zn,Fe Subprovince greenstone greenstone belt belt 2735-2700 2735-2700Cu. Zn,Fe Table 1. Precambrian Precambrian rock units units and tectonic tectonic and and metallogenic metallogenic events events in in the the Lake Huron Region Region (After Card Jackson. 1995) 1995) CAfter Card and Jackson, �THE HURONIAN SUPERGROUP SUPERGROUP BETWEEN SAULT STE. MARIE BETWEEN AND ELLIOT ELLIOT LAKE L m EARLY PROTEROZOIC PROTEROZOIC EVIDENCE FOR THE E&Y AND TECTONICS TECTONICS ATMOSPHERE, CLIMATE AND by D. Card Card and G. Bennett, K. D. K. Y. Y. Tomlinson Tomlinson INSTITUTE ON LAKE SUPERIOR GEOLOGY rd ANNUAL MEETING, 43 rd MEETING,MAY MAY 6, 6 ,11, l l , 1997 ONTARIO SUDBURY, ONTARIO 43, part part 2 Field Trip Guidebook, Guidebook, Volume 43, �CONTENTS CONTENTS page Page Introduction Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 . The The Elliot Elliot Lake Lake Group Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44 The The Livingstone Livingstone Creek Creek Formation Formation......................44 Early Early Huronian Huronian Intrusive IntrusiveRocks Rocks . . . . . . . . . . . . . . . . . . . . . . .66 Huronian Huronian Volcanic Volcanic Rocks Rocks of of the the Sudhury Sudbury Area Area . . . . . . . . . .77 The The Huronian Huronian Volcanic Volcanic Rocks Rocksof ofthe theSault SaultSte. Ste . Marie-Elliot Marie-ElliotLake Lake area area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99 Sedimentary Sedimentary Rocks Rocks Associated Associatedwith withthe the Thessalon 14 Thessalon Formation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 The The Matinenda Matinenda Formation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 15 The TheF4cKim McKim Formation Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 18 Stratigraphic StratigraphicRelationships Relationshipswithin withinthe the Elliot Elliot Lake Lake Group Group of of the theSault SaultSte. Ste .MarieMarieElliot Lake Area Elliot Lake Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 19 Hough Hough Lake LakeGroup Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 20 Ramsay 20 RamsayLake LakeFormation Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Pecors PecorsFormation Formation .................................... 21 21 Mississagi MississagiFormation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2].21 Quirke QuirkeLake LakeGroup Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2222 Bruce 22 BruceFormation Formation ..................................... 22 Espanola EspanolaFormation Formation..................................2323 Serpent SerpentFormation Formation...................................2424 Cobalt CobaltGroup Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ..2424 . �GowgandaFormation. Formation. .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 24 Gowganda LorrainFormation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 26 Lorrain Gordon Lake Lake Formation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 27 Gordon Bar River River Formation Formation................................. 28 28 Bar Nipissing Intrusions Intrusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nipissing 28 Huronian Paleosols Paleosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Huronian 29 Regional Regional Tectonic Tectonic Patterns Patternsand and Metamorphism Metamorphism . . . . . . . 35 Tectonic Models Models for for the the Huronian Huronian Basin Basin . . . . . . . . . . . . Tectonic 40 Road Log Log -.Day Day 11 .................................. Road 42 Road Log Log -- Day Day 22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Road 56 �List List of of Figures Figures Figure 1. The The distribution distribution of of rocks rocks of of the the Huronian Huronian Figure 1. Supergroup Supergroup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure Figure 2. 2. Huronian Huronian stratigraphy, stratigraphy,Sault Sault Ste. Ste. Marie-ElliotLakearea Marie-ElliotLakearea.................................... 33 Figure Figure 3. 3. The The cyclicity cyclicity of of Huronian Huronian Sedimentation Sedimentation......55 Figure Figure 4. Stratigraphic Stratigraphic relationships relationships in in the the Elliot Elliot Lake Lake Group Group -. Sault Sault Ste. Ste. MarieMarie- Elliot Elliot Lake Lake area area.. . . . . . . . 55 Figure Figure 5. 5. Paleocurrent Paleocurrent roses roses for for the the Mississagi Mississagi and and Matinenda Matinenda formations formations................................ 8 Figure Figure 6. 6. The The distribution distribution of of the the Thessalon Thessalon Formation 10 Formation and and Livingstone Livingstone Creek Creek Formation Formation . . . . . . . . . . . . . . 10 Figure Figure 7. 7. Distribution Distribution of of Huronian Huronian volcanic volcanic rocks rocks . . . . .10 10 Figure Figure 8. 8. schematic Schematic stratigraphy stratigraphy of of the the Thessalon Thessalon Formation Formation . . . . . . . . . . . . . . . . . . . . . 11 Figure Figure 9. 9. Discrimination Discrimination diagrams diagrams for for volcanic rocks of the Thessalon Formation volcanic rocks of the Thessalon Formation. . . . . . . . . . . . . . 12 12 Figure Figure 10. 10. Pebble Pebble size size vs. vs. pyrite pyrite grains grains size size Matinenda Matinenda Formation, Formation, Elliot Elliot Lake Lake . . . . . . . . . . . . . . . . . . . . . . . 16 16 Figure Figure 11. 11. Concentration Concentration rations rations relative relative to to A1203 A1203 in in the the Pronto Pronto Paleosol Paleosol................................. 31 31 Figure Figure 12. 12. Concentration Concentration ratios ratios of of components components in in the the Denison Denison paleosol paleosol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 31 Figure Figure 13. 13. Concentration Concentration ratios ratios in in Sub-Matinenda Sub-MatinendaFm. Fm., Sub-Lorrain Sub-Lorrain Fm. Fm. and and sub-Matinenda sub-Matinenda Formation Formation paleosols paleosols .............................................. 32 32 Figure Figure 14. 14. Geological Geological cross-section cross-sectionof of the the Blind 34 Blind River River and and Sudbury-Maintoulin Sudbury-Maintoulinareas areas . . . . . . . . . . . . . . .34 Figure Figure 15. 15. Metamosphism Metamosphism of of the the Huronian Huronian Supergroup Supergroup .....37 37 �Figure Figure 16. 16 . The distribution distribution of of rocks rocks of of the the Huronian Huronian 43 Supergroup.. Sault Ste Ste.. Marie-Elliot Marie-Elliot Lake Lake area area . . . . . . . . . 43 Supergroup Thessalon area Figure 17. 17. Geology of the Thessalon area .............. 46 46 Figure 18. 18 . Plan Plan and section section of of the the Geology Geology of of the the Pronto Pronto Mine Mine area area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54 54 19.. Geology of the Elliot Lake 58 Figure 19 Lake area area . . . . . . . . . . . . 58 Precambrian rock units units and tectonic Table 1. Table 1 . Precambrian tectonic cover and metallogenic events events in in the the Lake Lake Huron Huron region. region. ..back back cover �ELLIOT LAKE THE BETWEENSAULT SAULTSSTE. THE HURCNIAN HURONIAN SUPERGROUP SUPERGROUP BETWEEN T E . MARIE MARIE AND ELLIOT LAKE Introduction Introduction The Huronian Earth's most studied The Huronian Supergroup Supergroup is is one one of the Earth's studied sequences of sequences of rocks. rocks. Since Since the turn of the century the results results of of hundreds of Huronian rocks have been published in hundreds of studies studies of Huronian in scientific journals and government publications. These studies scientific journals publications. studies Earth's have led geoscientists geoscientists to present evidence for the Earth's of free oxygen in earliest glacial glacial periods, the development of in the atmosphere paleoplacer atmosphere of of the the early early Earth, Earth, the deposition of paleoplacer deposits tectonic activity deposits of of uranium, uranium, and evidence evidence for for plate tectonic activity during the during the Proterozoic. Proterozoic. Much of the evidence presented is is based based on rock rock exposures exposures which which will will be be visited visited during during this this field field trip. trip. Paleoproterozoic The Huronian Huronian Supergroup Supergroup is a sequence of Paleoproterozoic sedimentary and unconformably upon sedimentary and minor volcanic rocks lying unconformably Archean rocks Archean rocks of of the the Superior Superior Province Province of of the the Canadian Canadian Shield. Shield. The Superior, along The Huronian Huronian belt belt extends extends eastward eastward from Lake Superior, along the the north shore of Lake Huron to Sudbury and then northward to the north shore of Lake Huron Sudbury northward to the Noranda area Noranda area of of Quebec, Quebec, aa distance distance of of about about 450 450 km km (270 (270miles) miles) (Figure 1). The Huronian Huronian Supergroup attains it greatest thickness thickness (Figure (40,000 feet) feet) southwest southwest of of Sudbury. Sudbury. The of 12,000 12,000 metres metres (40,000 The sequence sequence thins basal units, thinning thins northward northward due due to to the wedging out of basal thinning of clastic units, and erosion within the sequence (Roscoe, of clastic units, and erosion within the sequence (Roscoe,1969; 1969; Frarey and 1970). Frarey and Roscoe, Roscoe, 1970). The The 2219 2219 Ma Ma radiometric radiometric age age of the Nipissing intrusions intrusions places an an upper Supergroup, while while the upper limit limit on on the the age age of the the Huronian Supergroup, the is probably close to the date Copper Copper Cliff Cliff Ryolite Ryolite (2450 (2450Ma) Ma) probably to the date of of initial initial Huronian Huronian deposition deposition in in the the Sudhury Sudbury area. area. The Huronian Huronian Supergroup Supergroup consists of four groups, which in in ascending stratigraphic Elliot Lake Lake Group, Group, Hough ascending stratigraphic order are: The Elliot Lake 2,3). Lake Group, Group, Quirke Quirke Lake Lake Group Group and and Cobalt Cobalt Group Group (Figures (Figures 2,3) Formations of the with the exception of the Formations the three upper groups, with Serpent Formation, continuity, and and display display a Serpent Formation, show show stratigraphic continuity, remarkable cyclicity of lithological units; beginning with remarkable cyclicity of lithological matrix-supported conglomerate(diamictite), conglomerate(diamictite), followed followed by by mudstone, mudstone, matrix-supported siltstone or or limestone by coarse, coarse, cross-bedded cross-bedded siltstone limestone and capped by sandstone. sandstone. Many Many paleocurrent paleocurrent studies studies have have shown shown paleocurrent paleocurrent flowed being the predominant predominant flowed south south to to southeast, southeast, with southeast being direction(Figure 5) . direction (Figure 5). 1 �Whitewater Group __..'' Internal tonal boundary Provincial boundary Murray Foul, System Grenville Front Tectonic Zone Figure 1. The distribution of rocks of the Huronian Supergroup Poleo,oic rocks Huronion Supergroup Sudiry Igneous Complex Keweeriowan rocks Grertville Province Superior Province �______ __________ (2.21 Ga) Ga) (2.21 Nipissing Gabbro. diabase. gronophyre NipissingDiabcise Diabase Gobbro, diobase, gronophyre - NNNNNN NNNNNN Quartz arenfte, orenite,subarkose suborkose Bar B~~ River ~i~~~Fm. F ~ .Quartz minor minor mudstone, mudstone,siltstone. siltstone. -,-N__N N N N N N N NNN\ NNNN 4''' Slltstone, mudslone mudstone Slitstone, Gordon chert, sandstone GordonLake LakeFm. Ft-f~. chert, sandstone NN'NNN'\N\N \NNNNNNNNNNNN 'N --N N N N N N N NNNN\NNNN Lorrain Fm. Fm. NNN NN N N N N NN N N NN N N N N NN N N N N NNNN \N N N N N N N N NNNNNNNNNNNNN N N N' NNIX N N N N N - 0-C> - C' - Gowganda Arkose. slltslone Gowganda Fm.Fm. Arkose,slltstone Diamlctite, polymictic conglomerate conglomerate Diamictite, polymictic Unconformity Unconformity -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.. N NN N N N N NN N N N NN NNNNNN NNN N N N N N NNNN NNN NN N N N N N / / / / / / / / / / / / / / / /1A -c--V-CC Cc z_ SerpentFm. Fm. Serpent Subarkose. wacke Subarkose, wacke Espanola ppanola Fm. F ~ Dolostone hfostone slltstone. wooke sinstone. , wwke limestone limestone Bruce BruceFm. Fm. 0) C) x S Ca 0 -3 ¡ -' Diamictite. Diomictite. sandstone sandstone siltstone siitstone 'Do0 (U ;. 0 a 6 - Nj N NNN N N NNNNNNN Mississagi MississagiFm. Fm. N N N NN NNNN NNN N NN N NN N NNNNN NNN NNNNNNNN NNNN NNN N NNNNNNN NNNN NNN NNNNNNNNNNNN Pecors P ~ C OFm. Fm. ~S Subarkose. Suborkose,arkose orkose quartz-pebble quartz-pebble conglomerate conglomerate N 'Vc-VN--N-- McKim McKimFm Fm NN NNNNNNNNNNNNC NN NNNNNNNNNNNNNNNNN NN NNNNNNNNNNN NN N N NN NNNNNNNNNNNNN 'N \NNNNNNNNNNNN N N NN NNNNNNNNNNNNN 1' Mudstone, siltstone Mudstone.siltstone Disconformity Thessalon Fm. Arkose. subarkose quartz-pebble conglomerate Molt volcorks Livingstone Creek Fm. Areh4o, + + 8oqrtetd. + + 1 Dkconfo,,,,* DcOnfo,Th#)I Minor qtz. peb. cong. Disconformity 1 Layered gabbro, onorthosite + a0 a. ¡ -J 2 - 3 t (:5 i 0 0 0 x - Mudstone, Mudstone.siltstone siltstone wacke Mafinenda Fm a- 0) a, S x 6a) 00 Ramsay RamsayLake LakeFm. Fm.Diomictite Dfomictite .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. --:> : +j 0—0 00 00 Mudstone. Mudstone.siftstone siftstone NNNNNNNNNNNNNN -NN NNNNNNNNNN \NNNN NNNNNNN N 5 -3 ¡ no - 2 .: .: if:0: -o• :-. a a 0a ° a a 0 C> 'C> , C> C> Quartz arenne, arenlte, quartzquartzpebble conglomerate congbmerate pebble Arkose. subarkose Arkose. subarkose °- a) S 2o w Mefavolcanics, metasedirnents, gronitic rocks Figure Figure 2. 2. Huronian Huronian Stratigraphy Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake area area Stratigraphy -- Sault 3 �The The Elliot Elliot Lake Lake Group Group The Huronian groups groups The Elliot Elliot Lake Lake Group Group differs differs from the overlying Huronian in internal stratigraphy stratigraphy is is generally generally discontinuous discontinuous in that: that: (flits (1)its internal does not not show show the the diamictite-mudstonediamictite-mudstoneand less less extensive; extensive; (2)it does sandstone sequence; the only only important important uranium uranium sandstone sequence; (3)it (3)it contains the deposits; deposits; (4)and (4)and the the only only volcanic volcanic rocks rocks in in the the entire entire supergroup. supergroup. The Livingstone The Livinastone Creek Creek Formation Formation polymictic conglomerates The polymictic conglomerates and and sandstones sandstones of of the the Livingstone Livingstone Formation (Frarey, the lowermost lowermost Huronian Huronian Creek Formation (Frarey, 1967) form the formation. It formation. It is is the the only only Huronian Huronian formation formation known known to to precede precede some of the the Huronian Huronian igneous igneous activity. activity. The Livingstone in) The Livingstone Creek Creek Formation Formationis is at at least least1200 1200feet feet(400 (400 m) thick thick in in the the Sault Sault Ste. Ste. Marie Marie area area and and between between 300 300 feet feet (100 (100 m) m) Thessalon area. and 1000 in) and 1000 feet feet(300 (300 m) thick thick in the Thessalon area. The sandstone and The formation formation has has been correlated with grey sandstone conglomerate near Lake in Township (Bennett, conglomerate near Crazy Crazy Lake in Nicholas Township (Bennett,1978; 1978; member occurs Bottrill, 1971) A remnant of the conglomerate conglomerate member occurs as as Bottrill, 1971). A far far east east as as Pecors Pecors Lake Lake on on the the south south limb limb of the the Quirke Quirke Lake Lake (Figures 4, Syncline (Jensen, Livingstone Creek Syncline (Jensen,1990) 1990) (Figures 4, 6,). 6,). The Livingstone Creek Formation has Formation has not not been been recognized recognized east of the Quirke Quirke Lake Lake - Syncline. Syncline. of two two distinctive distinctive rock The Livingstone Livingstone Creek Creek Formation consists of types: an medium-grained arkose, arkose, subarkose subarkose and an upper upper finefine- to medium-grained subwacke; subwacke; and and aa lower lower clast-supported clast-supported polymictic conglomerate conglomerate with with cobble cobble to to boulder-sized boulder-sized megaclasts. megaclasts. The sandstone sandstone member of Formation may of the the Livingstone Livingstone Creek Formation may be be distinguished by the the uniform uniform grain distinguished from from other other Huronian sandstones by size Mudstone and and pebbly pebbly size (fine(fine- to to medium-sand) medium-sand) of the former. Mudstone units units (even (even isolated isolated pebbles) pebbles) are are lacking lacking within within the the sandstone sandstone member of Another characteristic member of the the Livingstone Livingstone Creek Creek Formation. Formation. Another characteristic feature of the sandstone units is the presence of carbonate feature of the sandstone units is of carbonate along along the foresets foresets of of the the commonly commonly well-developed well-developed trough trough cross-beds. cross-beds. Planar Planar cross-beds cross-bedsare are rare. rare. 4 �___ ______ ____ _____ ___ COBALT GROUP GROUP COBALT Bor River River Formation Formation Bar GordonLake LakeFormation Formation Gordon Lorrain Formation Formation Lorroin GowgandaFormation Formation Gowganda W I R K E LAKE LAKE GROUP GROUP QUIRKE m JW -.-----a MSn eefl -V •CRIO r0LW -----6 — I ———— I CI M"em,-& of 01 a ~ Mudstone. satafone. cothonote (Esponola Elm) MARINE 0 LCi1 E3 C Mississagi Mississagi Formation Formation Pecors Formation Formation Pecors Lake Formation Formation Ramsay Lake 0 0 S LakeGroup Group Elliot Lak. i)tarnlclfle. mudstone, sfltstone h k w e , m"d,~.'i"%,me clad suppotted conglomerate cm-dcmb-,,,e GLACIAL GLACIAL I____ lu II>- V (Melornoaphac grade mainly < m Mg ,wS b &W sst-gIreeoacbbt ~ " w ~lode,) l l ~ k , ~ Disconformity V 3 3 ~ FLU VIAL FLUVIAL 4 HOUGH LAKE LAKE GROUP GROUP HOUGH igure Figure Mose, m- soborkoso. m m - , qoodz q"om orenlte '"mu. quartz-pebble q w * conglomerate . ~ ~ m _____ Iii; rH!>. ki MalnRock RockTypos Types Mum -&" Ir 0 Serpent Formation Formation Serpent Espanola Espanola Formation Formation Bruce Formation Formation Bruce I I" / 'i Volcanic racks, morthe ond fluvial depoefta. Poleopbceruroruwnaeposns . The The cyclicity of of Huronian Huronian sedimention . LEGEND LEGEND HoughLakeGroup nough Lake Group fflIhHI MATINENDA MATINENDAFM FM m-. @I quatlz-peliue wa**-k.m=mte congianwate -- ri .... ..... - -, k - +1 + -P .-, tJ ThjJ.py —. —- —. N SAULT SAULT STE. STE. MARIE MARIE AREA AREA -. Uncønfonnhlyorthsconfonnity Paleosol on LMngstone Cr. Fm and basaltic dike (Ibessalon Fm.) -. -. 1., u.m. / —. L w " ! ~ ~ ~ , e ARCHE.AN BASEMENT G(arHtcgreenstone Quanz—pe4bIecongIooiemte loon C THESSALON FM. Dasal.sndeslerliyolileflows -at. -*e ,h"dde k basaJldce .,*e LNINGSTGNECREEK CREEKFM. FM, LMNGSTONE mey a*sxbrkme PolylilIclic conglomerate :LL -. ThESSALON THESSMONAREA AREA EIAUGHT0N-OrTER HAIJGHTONQTTERTWPS W S (DUNN'S (WNWS VALLEY V&Lâ‚ AREA) AREA) CRAZY C W LAXE LbKEAREA AREA NiCHOLAS NICHOUSTWP. W. -. -. -. , auoT LAKE 'ELLIM ME AREA AREA Stratigraphic relationships in the Elliot Elliot Lake Group — Figure 4. 4 . Stratigraphic Figure Sault Marie Elliot Elliot Lake Lake area. area. Sault Ste. Marie 5 5 e �Clast-supported, polpictic polymictic conglomerate is a a prominent prominent rock type Clast-supported, in the lower lower sections sections of of the the Livingstone Livingstone Creek Creek Formation. Formation. CobbleCobbleto boulder-sized clasts to boulder-sized clasts of of grey grey granitic granitic rocks rocks and and minor minor mafic mafic plutonic and metamorphic rock clasts clasts are set in a sparse matrix of coarse, of Huronian Huronian coarse, grey arkose arkose or arkosic grit. No clasts of recognized. Thin units units of of cross-bedded, cross-bedded, grey volcanic rocks were recognized. arkose are locally locally interbedded interbedded with with the the conglomerate conglomerate (Frarey, (Frarey, 1977, al., 1991). 1977, Bennett et al., 1991). The The grey grey granitic granitic mega-clasts mega-clasts of of the the conglomerate member is in contrast with with the predominantly predominantly reddish conglomerate hues hues of of the the underlying underlying Archean Archean basement basement rocks. rocks. This This colour colour difference of ferric iron in difference appears to be due to the reduction of the feldspars conglomerate, and feldspars of the red granitic clasts in the conglomerate, not a a result result of of differing differing provenance. provenance. This This conclusion conclusion is is supported supported by the the observation observation that that granitic granitic rocks rocks in in aa "paleosol "paleosol zone" few tens tens of of metres metres below below the the base base of of the the zonet9a few few metres to to aa few Livingstone Creek Livingstone Creek Formation Formation commonly commonly display display a a grey grey colour colour as as well. well. The The clast clast size, size, local local source source and and low low stratigraphic stratigraphic position position of of Livingstone Creek conglomerates the Livingstone conglomerates are are consistent consistent with with deposition mediumdeposition on on an an alluvial alluvial fan. fan. The The uniform, uniform, finefine- to to mediumgrained sand of the trough cross-bedded sandstone member sand of the trough cross-bedded sandstone member suggests suggests a different, different, although although probably probably related related depositional depositional environment environment than than that of the the conglomerate. conglomerate. The The sandstone sandstone member member may may represent represent a fault bounded bounded valley valley deposition by median streams flowing in a with scarps scarps covered by alluvial alluvial fans fans (Bennett (Bennett et et al., al., 1991). 1991). The The well sorted nature of the sandstone suggests an aeolian component sorted nature of the sandstone suggests an aeolian component (Meyer,W., W., 1983) 1983). or even aeolian aeolian deposition deposition (Meyer, Early Earlv Huronian Huronian Intrusive Intrusive Rocks Rocks Several petrographically petrographically distinctive, Several distinctive, mafic to to ultramafic ultramafic intrusive bodies intrusive bodies have been recognised recognised between the the eastern eastern end end of of the Sudbury Igneous Complex and the nose of the Quirke Lake Sudbury Igneous Complex and the nose the Quirke Lake Syncline. The intrusions Syncline. intrusions are are characterized characterized by the the presence presence of of anorthositic phases and locally well developed, primary rhythmic anorthositic phases and locally well developed, primary rhythmic layering of alternating layering alternating anorthositic anorthositic and and gabbroic gabbroic layers. layers. Segregations, Segregations, dikes dikes and and sheet-like sheet-like bodies bodies of of granophyre granophyre are are locally present (Card and Palonen, 1976; Peck et al., 1995). locally (Card and Palonen, 1976; Peck et al., 1995). Major intrusions Lntrusions of gabbro-anorthosite gabbro-anorthosite are are found found at at Agnew Agnew Lake Lake and Palonen, Palonen, 1976) and at East Bull Bull Lake Lake (Born (Born and and James, James, (Card and (1991) report report two 1978; 1978; Kamineni Kamineni et et al., al., 1984). 1984). Bennett, Bennett, et et al. a1.(1991) two 6 �additional additional bodies bodies between between Blind Blind River River and and Thessalon. Thessalon. All All gabbrogabbroanorthosite bodies bodies found found to to date date have have been been emplaced emplaced in in the the anorthosite Archean Archean basement basement at, at, or or just just below below the the Archean-Huronian Archean-Huronianboundary. boundary. Krogh (1984)reported reporteda aU-Pb U-Pbage age2491+5.5 2491 Ma al.(l984) Ma for for zircons zircons Krogh et et al. from the the gabbro-anorthosite gabbro-anorthosite intrusion from intrusion at at Agnew Agnew Lake Lake and and 2480+10-5 2480'° for for the the East East Bull Bull Lake Lake gabbro-anorthosite gabbro-anorthosite body. body. The The similarity similarity of of these these ages ages to to the the 245O2510Ma 2450+25.10 Ma (U-Pb (U-Pbzircon) zircon) age age of of rhyolite rhyolite of of the Huronian Huronian Copper Copper Cliff Cliff Formation Formation(Krogh (Kroghet et al., al.,1984) 1984) the indicates that that these these gabbro-anorthosite gabbro-anorthosite intrusions intrusions form form part part of of indicates the early Huronian volcanic events (Card, 1978a) the early Huronian volcanic events (Card, 1978a). The The north north to to northwest northwest trending trending Matachewan-Hearst Matachewan-Hearst dike dike swarm swarm is is the the second second largest largest dike dike swarm swarm of of the the Canadian Canadian Shield. Shield. The The 2.45 2.45 Ga Ga age age of of the the swarm swarm (Heaman, (Heaman,1988)is 1988)is essentially essentially the the same same as as that that of of the East Bull Lake Suite and the Huronian volcanic rocks of the the East Bull Lake Suite and the Huronian volcanic rocks of the Copper Copper Cliff Cliff Formation. Formation. Krogh report a U-Pb U-Pb age age of al. (1996) (1996) report of 2.48 2.48 Ga Ga for for the the Murray Murray Krogh et et al. Granite; Granite; one one of of several several granitic granitic intrusions intrusions cutting cutting the the lower lower part of the Huronian Supergroup near Sudbury. It is possible part of the Huronian Supergroup near Sudbury. It is possible that that these felsic volcanic volcanic these intrusions intrusions are are magma magma chambers chambers for for Huronian Huronian felsic rocks rocks in in the theSudbury Sudburyarea. area. Huronian Huronian Volcanic Volcanic Rocks Rocks of of the the Sudbury SudburyArea Area The The Huronian Huronian bimodal bimodal volcanic volcanic sequence sequence in in the the Sudbury Sudbury area area has has been been subdivided subdivided in in the the predominately predominately mafic mafic Elsie Elsie Mountain Mountain (1000 (1000mm thick) thick) and and Stobie StobieFormations Formations(1500 (1500mmthick) thick), and and the the felsic felsic Copper Cliff Formation (760 m thick) by (Card 1978a) Copper Cliff Formation (760 m thick) by (Card 1978a) (Figure (Figure7). 7). Krogh zircon) Krogh et et al.(1984) al. (1984)obtained obtained an an age ageof of24502510Ma 2450+25.10 Ma(U-Pb (U-Pb zircon) age age for for rhyolite rhyolite of of the the Huronian Huronian Copper Copper Cliff Cliff Formation; Formation; the the only only Huronian Huroniansupracrustal supracrustalrock rock for for which which there there is is an an absolute absolute age. age. The The volcanic volcanic rocks rocks of of the the Sudbury Sudburyarea area show show evidence evidenceof of submarine submarine eruption from fault controlled vents along the edge of eruption from fault controlled vents along the edge of aa depositional depositionalbasin basin into into which which arkosic arkosic sandstones sandstoneswere were being being transported Archean granitic granitic terrain terrain to to the the north, north, while while transported from from the the Archean turbidites turbiditeswere were deposited deposited from from sediment sediment from from both both the the volcanic volcanic 1978a). The The and rejuvenated rejuvenated basement basement marginal marginal to to the the basin basin (Card, (Card,1978a). and volcanic rocks of the Sudbury area differ in terms of internal volcanic rocks of the Sudbury area differ in terms of internal stratigraphy, stratigraphy,overall overall thickness thickness and and depositional depositional environment environment from from the the Huronian Huronianvolcanic volcanic rocks rocks in in the the Sault Sault Ste. Ste. Marie-Elliot Marie-ElliotLake Lake , area. area. 7 �00 Figure 5. Paleocurrent roses for the Mississagi and Matinenda fonnations. �The The Huronian Huronian Volcanic Volcanic Rocks Rocks of of the the Sault Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake area a Volcanic Volcanic rocks rocks overlying overlying the the Livingstone Livingstone Creek Creek Formation Formation were were named the the Thessalon Thessalon Formation Formation of of the the Elliot Elliot Lake Lake Group Group by by named Frarey(l967). Frarey(l967). Jolly(1987) Jolly(l987) concluded concluded the the Thessalon Thessalon Formation Formation is is aa continental continental flood flood basalt basalt sequence sequence associated associated with with continental continental rifting. Bennett Bennett et et al. al.(1991) volcanic rifting. (1991) proposed proposed that that the Huronian Huronian volcanic rocks of of the the Quirke Quirke Lake Lake Syncline Syncline should should also also be correlated correlated with with rocks the the Thessalon Thessalon Formation. Formation. Attempts Attempts to to obtain obtain an an absolute absolute age age determination determination from from rocks rocks of of the the Thessalon Thessalon Formation Formation have have so so far far been been unsuccessful. unsuccessful. However However the spatial spatial association association of of the the East East Bull Bull Lake Lake intrusions intrusions with with the the the Huronian of the the Quirke Quirke Lake Lake Syncline Syncline suggest suggest Huronian volcanic volcanic rocks rocks of Huronian Huronian volcanism volcanism in in that that area area occurred occurred about about the the same same time time as as the emplacement emplacement of of the the East East Bull Bull Lake intrusions intrusions (2480 (2480 Ma). Ma). Given Given the the the potential potential error error for for the the relevant relevant age age dates dates (Krogh (Kroghet et al., al., 1984), the age of the Thessalon Formation may not differ 19841, the age of the Thessalon Formation not differ significantly from from that that of of the the Copper Copper Cliff Cliff Formation Formation of of the the significantly Sudbury Sudbury area area (2450 (2450Ma). Ma) . The The maximum maximum thickness thickness of of the the Thessalon Thessalon Formation Formation in in the the Sault Sault Ste. Marie Marie area area is is approximately approximately 650 650 m m (2100 (2100 feet) feet) and and 820 820 mm Ste. (2700 (2700 feet) feet) (Frarey, (Frarey,1977) 1977). Diamond Diamond drilling drilling has has indicated indicated at at least least 670 670 mm (2200 (2200 ft) ft) of of Thessalon Thessalon volcanics volcanics under under Lake Lake Huron Huron south south of of the the town town of of Thessalon. Thessalon. The The Thessalon Thessalon Formation Formation may may be be as much much as as 1080 1080 mm (3500 (3500 feet) feet) thick thick at at Bass Bass Lake Lake in in Aberdeen Aberdeen as Township. Township. . Tomlinson(l996), Tomlinson(l996), who who studied studied the the geochemistry geochemistry of of the the Huronian Huronian volcanic volcanic rocks rocks between between Sault Sault Ste. Ste. Marie Marie and and Thessalon, Thessalon, concluded concluded that that the the lavas lavas of of the the Thessalon Thessalon Formation Formation are are divisible divisible into into 77 distinct distinct units units based based on on mapping, mapping, petrography petrography and and major major and and trace trace element units were were grouped grouped into into 8). The The 77 units element geochemistry geochemistry (Figure (Figure 8). two two "lava "lava series". series".The The upper upper lava lava series series (units (units66 and and 7, 7, of of Tomlinson, Tomlinson, 1996) 1996) is is equivalent equivalent to to the the upper upper tholeiitic tholeiitic basalt basalt sequence of Bennett et al. sequence of Bennett et al. (1991) (1991). The The lower lower lava lava series series (units (units 1-5, 1-5, of of Tomlinson, Tomlinson, 1996), 1996), consists consists mainly mainly of of basaltic basaltic andesite andesite with with subordinate, subordinate, local local rhyolite, rhyolite, mugearite, mugearite, andesite andesite and and high high magnesium magnesium basalt basalt flows; flows; and and corresponds corresponds to to the the "diverse "diverse member" member'' . of (1991). of Bennett Bennettetetal. al.(1991). 9 �___ 5 LEGEND PH Mesa-Proterazoic and Phanerozalc racks (Mngsfone Creek Fm. Sandstone. polymlctic conglomerate (tras, outcrop dabs. Upper Huronian rocks East Bull Lake Suite Goobro, onorthotite Thessalon Formation Sasolt. Ifli] Archean racks andesite. (waite etc •__s (Ftom outcrap and dre hale data) Quartz pebble conglemerote at baseotmessatonflows. (locaty rodioocttve) r' + / I -4.j/ c._r\7_ Se. a.......'4 + — —s 7 + + + + + + + + + + + + + + + ÷ + + + (Con, a hot. dot ,4' 4, NON — rocte (from Dtt4ltng =_) No mr÷+ —U— + + No I+aonla, thorn Fault J tO U Hi,oS, ÷ ± > .1*' -'sr -c + /e—' EtotL&o+++++J Murray Fault ——S——— —. Lake Huron Figure Figure 66 . . The Distribution of Thessalon Formation Formation The Creek Formation Formation. and Livingstone Creek 47°N orn7N km / ult St LAKE 46 it HURON Sudbury Structure Lillilill Poleozoic racks Huronion Supergroup Grenvitle Province Metasedimentary rocks - Metavolconic rocks Metovolconic rocks Exposed in in outcrop Exposed outcrop ~ m m Diamond-drill n d - d r r l indicated l 4ndtcote-d 7 ? Distribution D k ~ n a u ~ i ounknown unknown n Superior Province superior Province \ Quirke Ouifke Loke Loke Syncline Synclor ,' Fault Faulr Figure 7. 7. Distribution Distributionof ofHuronian Huronianvolcanic volcanic rocks. rocks. 10 �- unit f$* t t4 Livingstone Creek Fm 500m — unit 1 Bass Lake Figure 8. Schematic stratigraphy of the Thessalon Formation. Livingstone Creek Fm Radioactive \ Basalt to andesite cycles Rhyolite —.. Basalt —_- Thessalon unit I Urn 650 to 820m From Tomlinson (1996) Livirigstone Creek Fm unit 7 B as a 1200m Upper Island Lake �20 20 I basalts A - Within plate basalts 10 * 1 B - Island Island arc arc basalts basalts 0- Mid-ocean ridge basalts Z'/Y 5 0 I 1000 10 Zr Tc2 TO, 0 island arc basalts 0.5- i 200 200 IOU 100 40 40 300 300 400 400 Zr FeO* FeO* Nb * 2 A WPA ALAII WPT AII,C E 51 -56%SE02 - 56% 30, MOPS: S N MOPS: D VAB C,D y Zr/4 - Spreading Centre I -Spreading 1 Centre Island Island Orogeni 2 -- Orogenic 3 -- Ocean Ocean Ridge and Floor 4--Ocean 4 OceanIsland Island Continental 5 --Continental MgO Unit 1=0 Unit2=° Unit3=a Unit4='< Unit5 Unit6=° Umt7=x WPA = = within plaEetholeiite, tholeiite,E-MORB=enriched E-MORBenriched type mid-ocean within plate alkali basalt, basalt, WPT—within WPT=within plate mid-ocean ridge ridge basalt, basalt, N-MORB=normal N-MORB=nonnal mid-ocean mid-oceanridge ridgebasalt, basalt,VAB—volcanic VAB=volcanic arc arc basalt. basalt. Formation Figure 9. 9. Discrimination Discrimination diagrams diagrams for volcanic rocks of the Thessalon Formation (from Tomlinson, Tomlinson, 1996). 1996). 12 203 �Bennett et (1991) proposed proposed that that the the upper, upper, basaltic basaltic flows Bennett et al. al.(1991) flows of of probably represent the Thessalon Thessalon Formation (upper (upper lava lava series) series) probably represent part of of aa continental diverse continental flood basalt sequence, sequence, while the diverse member (lower (lower lava lava series) series) appears appears to to have erupted erupted from from central central member vents. The The Ruronian Huronian volcanic volcanic rocks rocks of the Quirke Lake Syncline Syncline Quirke Lake display lithological display lithological and geochemical similarities similarities to to the the lower lower lava lava series series of the Thessalon Formation Formation west of the the Quirke Quirke Lake Lake Syncline (G. (G. Bennett, Bennett, unpublished unpublished data). data). Syncline The The upper, upper, tholeiitic tholeiitic basalt flows flows of the Thessalon Thessalon Formation Formation (upper of Tomlinson, Tomlinson, 1996) are almost almost uniformly (upper lava series of uniformly greenish-grey finemedium-grained tholeiitic greenish-grey fine- to medium-grained tholeiitic metabasalt. metabasalt. The The essential minerals essential minerals are are albite, albite, actinolite, actinolite, chlorite, chlorite, clinozoisite, epidote and Fe-Ti Fe-Ti oxides. Primary clinozoisite, Primary clinopyroxene clinopyroxene is is present present in in only only aa few few samples samples of of basalt from from the the Sault Sault Ste. Ste. Marie Marie generally area. The andesitic rocks of the lower lava series are generally darker coloured and commonly contain stilpnomelane and biotite darker coloured and commonly contain stilpnomelane and biotite with with green green pleochroism (Fe3 (Fe+3rich?) rich?) in in addition addition to to albite albite and and actinolite actinolite (Bennett (Bennett et et al. al. 1991) 1991). Tomlinson(1996) the reports the Tomlinson(1996) reports presence of in some some flows. flows. Quartz is is a a minor component component presence of tremolite tremolite in metamorphic of basaltic and andesitic types. In In most areas the metamorphic grade of the Thessalon Formation flows grade flows is lower greenschist . fades. facies . Amygdules of quartz and Amygdules of epidote, epidote, chlorite, chlorite, calcite, calcite, quartz stilpnomelane, stilpnomelane, in in complex complex zonal zonal arrangements, arrangements, are are common. common. Flattened chlorite-filled amygdules a centimetre or Flattened chlorite-filled amygdules centimetre or less less across across Thessalon are a distinctive feature of most mafic flows of the Thessalon Formation. structures are rare but in most Formation. Pillow structures but were were observed observed in areas. areas. Scoriaceous Scoriaceous flow-tops flow-tops and and cross-cutting cross-cutting breccias breccias are are commonly filled filled with a fine-grained fine-grained mixture of quartz and grey grey to to commonly quartz and red secondary albite. red secondary albite. Tomlinson(1996) Tomlinson (1996)states: states: "The data indicate that that the lavas lavas are comparable comparable to "The field and geochemical data to modern day andesites but that their their source modern day continental continental basalt and andesites source was was similar 9 shows shows the the lavas lavas plotted plotted similar to to that that of of island island arc arc basalt. basalt. Figure Figure 9 variety of comparable to on a variety of discrimination discrimination diagrams where they are most comparable to modern Their arc-basalt modern within-plate within-platebasalt. basalt. Their arc-basalt geochemical geochemical characteristics characteristics result from upper mantle mantle that had been result from their derivation from an upper metasomatically enriched during subduction Kenoran orogeny. metasomatically subduction in in the Kenoran orogeny. Units Units within the generated from within the sequence sequence were generated from different pulses of of magma, magma, each each region of the relatively relatively homogenous of which which stemmed stemmed from from a different region homogenous Huronian mantle. lavas require generation generation from Huronian mantle. Only the unit 2 lavas from part of of 13 �the mantle with with slightly slightly different characteristics similar to to the characteristics to a source source similar that that required required to to generate generate island island arc arc basalt basalt 1D16 ID16 (a (a primitive basalt used used primitive basalt by (1996)inmaking making calculations) calculations). Different Different degrees degrees of of partial partial by Tomlinson Tomlinson (1996)in melting of of this this source source that that contains contains garnet in the residue (at less less than than melting residue (at 29.8% partial partial melting) are are responsible responsible for the REE characteristics of 29.8% characteristics of each generation of the the lower each unit. unit. In In the generation lower lava lava series, series, different different batches batches of or lesser of magma magma underwent underwent crustal crustal contamination contamination to a greater or lesser extent extent within within the the lower lower or or upper upper crust crust (or (or both) both) prior prior to to eruption. eruption. The The upper upper lavas lavas series series rocks rocks are are not not contaminated. contaminated. In In all all but the the unit unit 22 lavas lavas crystal fractionation fractionation occurred occurred both early, as magma to shallower shallower crystal magma ascended ascended to depths, depths, and and later, later, in in shallow shallow level level sills sills or or magma magma chambers. chambers. Early Early fractional Mg, Ni and Cr fractional crystallisation crystallisation was responsible responsible for the low Mg, Cr values values in in most most units, units, while while later later stage stage crystal fractionation fractionation was was responsible responsible for for the the major major element element and compatible compatible element trends trends within within single (Tomlinson, 1996). plots"(Tomlinson, single units, units, as as shown shown on on bi-element bi-elementplots" 1996). . On On the the geochemistry geochemistry and and tectonic setting setting of the Thessalon Thessalon volcanic volcanic rocks rocks Tomlinson Tomlinson (1996) (1996)states: states: "various "various lines lines of of evidence evidence from from the the Elliot Elliot Lake Lake Group Group as as aa whole whole can can be be used used to to characterize characterize the the Ruronian Huronian rifting rifting event. event. Active Active rifting rifting involves involves deep deep mantle mantle upwelling upwelling or or plume plume magmatism magmatism which which splits splits the the continental passive rifting continental crust; crust; whereas whereas passive rifting involves involves mantle diapirism diapirism and and adiabatic adiabatic upwelling upwelling induced induced by by differential differential stresses stresses and and stretching stretching in in the the lithosphere lithosphere (Wilson, (Wilson,1989) 1989). The The geochemical geochemical evidence Formation indicates that the evidence from from the the Thessalon Thessalon Volcanic Formation the source upper mantle mantle rather rather than a deep source of of the the lavas lavas was metasomatised upper deep mantle mantle or or plume plume component. component. Structural Structural subsidence subsidence patterns patterns in in the the Archean basement basement (Zolnai (Zolnai et et al., al., 1984) 1984) are thought to be responsible responsible Archean for for lithospheric lithospheric stretching, stretching, in-turn in-turn causing causing mantle mantle upwelling, upwelling, episodic episodic partial partial melting melting and and volcanism. volcanism. This This is is supported supported by by the the presence 400 metres of of Huronian Huronian syn-depositional faults faults in in up up to to 400 presence of of syn-depositional sedimentary sedimentary rocks rocks below below the the volcanics. volcanics. G. G. Bennett Bennett (personal (personal communication,1996) 1996) has has also also described described syndepositional syndepositional features features(at (at22 communication, locations sault Ste. Marie) Marie) where where sedimentary sedimentary locations near near Elliot Elliot Lake and Sault rocks ill fractures fractures in rocks of of the the Livingstone Livingstone creek Creek Formation Formationinf infill in the the underlying underlying Archean Archean basement. basement. These These features features indicate indicate that that initially initially volcanism volcanism was was aa consequence consequenceof ofrifting. rifting. In In active active rifts rifts just just one one uplift uplift and and melting melting event event occurs occurs as as aa plume plume impacts impacts the the lithosphere, lithosphere, but but in in passive passive rifts rifts uplift uplift and and melting melting are are episodic episodic (Williamson (Williamson and and Keen., . Multiple Keen.,1995) 1995). Multiple erosional erosional surfaces surfaces within within the the Elliot Elliot Lake Lake Group occurred. Based Group indicate indicate that that numerous numerous episodes episodes of uplift occurred. Based on on these these lines lines of of evidence evidence the the Huronian Huronian rifting rifting event event can can best best be be characterised characterised as as aa typical typical passive passive rifting riftingevent" event" (Tomlinson, (Tomlinson, . 1996) 1996). Sedimentary Sedimentarv Rocks Rocks Associated Associated with with the the Thessalon Thessalon Formation Formation In In the the Sault Sault Ste. Ste. Marie Marie area, area, thin thin units units (<10 (<I0m) m) of of radioactive radioactive and and pyritic, pyritic, quartz-pebble quartz-pebble conglomerate, conglomerate, with directly directly overlying overlying arkose arkose and and arkosic arkosic grit grit are are found found just just above above lowermost lowermost flows flows of of 14 �the the Thessalon Thessalon Formation. Formation. In In the the Thessalon Thessalon area area and and in in the the Quirke Quirke Lake Lake Syncline, Syncline, similar similar units units of quartz-pebble quartz-pebble conglomerate conglomerate and and arkose are found directly below the mafic volcanic rocks where arkose are found directly the volcanic rocks where they they lie lie upon upon the the Livingstone Livingstone Creek Creek Formation, Formation, or or upon upon the the Archean Archean basement, basement, where where the the former former is is not not present present (Hay, (Hay,1963; 1963; Bennett Bennett et et al., al., 1978; 1978; Meyer, Meyer, 1983). 1983). Bennett et et al. al.(1991) of these these Bennett (1991) proposed proposed that that the wide distribution distribution of units units (Figures (Figures4, 4, 6) 6) indicate indicate the the presence presence of of aa disconformity disconformity at at the base of the Thessalon Formation throughout the Sault Ste. the base of the Thessalon Formation throughout the Sault Ste. Marie-Elliot Marie-Elliot Lake Lake area area. The The Matinenda Matinenda Formation Formation The The Matinenda Matinenda Formation Formation of of the the Elliot Elliot Lake Lake Group Group (Roscoe, (Roscoe,1957) 1957) is is aa sequence sequence of of arenites arenites and and intercalated intercalated quartz-pebble quartz-pebble conglomerates which host the once important conglomerates which host the once important uranium uranium deposits deposits of of the the Elliot Elliot Lake Lake area area (Figure (Figure2) 2 ) . The The Matinenda Matinenda Formation Formation is is up up to to 180 180 mm (600 (600 feet) feet) in in the the Elliot Elliot Lake Lake area area (Robertson, (Robertson,1981) 19811, where volcanic rocks rocks and and Archean Archean basement. where it it lies lieson on1-luronian Huronian volcanic basement. In In the the Thessalon Thessalon and and Sault Sault Ste. Ste. Marie Marie areas areas the the Matinenda Matinenda Formation Formation consists predominantly predominantly of of fine fine to to medium medium grained grained subarkose subarkose and and is is consists probably probably less less than than 50 50 m(150 m (150ft) ft)thick thick(Bennett (Bennettet etal., al.,1978 1978). ). In In the the Sudbury Sudbury area area clastic clastic units units correlated correlated with with the the Matinenda Matinenda Formation Formation are are as as much much as as 600 600 mm (200 (200ft) ft) thick thick but but they they thin thin rapidly rapidly eastward eastward where where they they are are intercalated intercalated with with the the mainly mainly metavolcanic rocks of the Stobie Formation and the mudstones metavolcanic rocks of the Stobie Formation and the mudstones of of the the McKim McKim Formation Formation (Card, (Card,1978a). 1978a). . The The most most abundant abundant rock rock type type of of the the Matinenda Matinenda Formation Formation in in the the Elliot Elliot Lake Lake area area is is generally generally described described as as mediummedium- to to coarsecoarsegrained subarkoses, arkoses and grits consisting of poorly grained subarkoses, arkoses and grits consisting of poorly sorted sorted quartz quartz and and feldspar feldspar grains grains set set in in aa matrix matrix of of sericite sericite and and comminuted sodic feldspar feldsparis is comminuted fragments. fragments. The The ratio ratio of of K-spar K-sparto to sodic about about 8:1. 8:l. Minor Minor constituents constituents are are pyrite, pyrite, calcite, calcite, chlorite, chlorite, zircon zircon and and rarely, rarely, leucoxene leucoxene coated coated iron iron oxides oxides and and monazite monazite Variable (Robertson, 1968) (Robertson, 1968). Variable amounts amounts of of sericite sericite produce produce what what has has variously variously been been described described as as aa green, green, apple apple green green or or greenishgreenishyellow yellow colour. colour. Well Well sorted sorted quartz-pebble quartz-pebbleconglomerate conglomeratebeds, beds, containing containing well well rounded rounded pebbles pebbles and and cobbles cobbles of of quartz quartz and and chert, chert, and and pebbly pebbly subarkose subarkose units units are are scattered scattered throughout throughout the the coarse coarse subarkose units of the Matinenda Formation, but are more subarkose units of the Matinenda Formation, but are more common common near near the thebase. base. (Robertson, (Robertson,1968; 1968; Pienaar, Pienaar,1963). 1963). . Trough cross-bedding,scour scour and and fill fill structures structures are are common common in in Trough cross-bedding, 15 �Cl-) N U) 0.6 12 2.4 14 I 21 I 35 _I 42 I Pebble size (mm) 28 I S S S S 49 56 From Theis, 1976 S S Figure 10. Pebble size vs. pyrite grains size. Matinenda Formation, Elliot Lake. 7 I S S .... . S Correlation Coefficient = 0.93 . 63 . . �arkosic arkosic units units (Robertson, (Robertson,1968; 1968; Roscoe, Roscoe,1969) 1969). Paleocurrent Paleocurrent studies studies by by McDowell(1957) McDowell(1957) and and Long(1977) Long(1977) have have established established aa northwest northwest source source area area for for the the sediments sediments of the the Matinenda Matinenda Formation 5). Fralick Fralick and Miall(1989) suggest the the Formation (Figure (Figure5). Miall(l989) suggest Matinenda Matinenda Formation Formation was was deposited deposited from from shallow shallow braided braided streams streams flowing underwent tilting flowing down down aa south south dipping dipping paleoslope which underwent tilting to the southeast during deposition. Kimberly (1980) to the southeast during deposition. Kimberly (1980) reported reported that that the uraniferous uraniferous conglomerates conglomerates contained contained almost almost no no magnetitemagnetitethe ilmenite ilmenite and and had had very very high high potash/soda ratios. ratios. These These are are also also features features of of Huronian Huronian paleosols, paleosols, and and suggest suggest the the sediment sediment of of the the Matinenda Formation Formation was was formed formed by by the the intense intense weathering weathering of of aa Matinenda granitic source terrain as proposed by Roscoe(1969) granitic source terrain as proposed by Roscoe(1969). . Two Two southeast southeast trending trending ore ore zones zones were were recognized recognized since since the the early early days days of of uranium uranium mining mining in in the the Elliot Elliot Lake Lake camp. camp. The The Nordic Nordic zone, zone, east (1.6 Im) km) wide wide and and east of of the the City City of of Elliot Elliot Lake Lake is is about about 11 mile (1.6 3.6 3.6 miles miles (5.6 (5.6 km) km) long. long. The The Quirke Quirke Zone, Zone, in in the the Quirke Quirke Lake Lake area, is is about about two two miles miles (3.2 (3.2 km) km) wide wide and and six six miles miles (9(9km) km) long. long. area, Paleotopographic Paleotopographic features features of of the the basement basement are are thought thought to to have have had had aa determining determining influence influence on on the the position position and and orientation orientation of of the the zones. 0.1 % tJ3O3) % U,0.) conglomerate conglomerate occurs occurs as as zones. Ore Ore grade grade(circa (circa 0.1 persistent lenses lenses with with individual individual units units up up to to 15 15 feet feet (4.5 (4.5m) m) persistent thick. thick. The The uraniferous uraniferous quartz-pebble quartz-pebble conglomerates conglomerates are are commonly commonly well well developed developed at at the the base base of of the the Matinenda Matinenda Formation Formation but but also also occur occur within within the the arkose arkose up up to to 150 150 feet feet (45 (45 m) m) above above the the base base (Roscoe, (Roscoe,1968) 1968) . The The quartz-pebble quartz-pebbleconglomerate conglomerate consists consists mainly mainly of of well-rounded well-rounded pale-grey pale-grey to to dark-grey dark-grey quartz quartz and and chert chert pebbles pebbles set set in in aa matrix matrix of of pyrite pyrite with with some some quartz/feldspar quartz/feldspar grit grit and and sericite. sericite. Pyrite Pyrite usually usually forms forms about about 15% 15% of of minable minable units. units. Radioactive Radioactive minerals minerals include uraninite, brannerite, uranothorite (Roscoe, 1968) include uraninite, brannerite, uranothorite (Roscoe, 1968). Monazite Monazite and and zircon zirconare are characteristic characteristic heavy heavy minerals. minerals. The The sedimentological sedimentological and and mineralogical mineralogical features features of of the the uranium uranium bearing bearing zones zones of of the the Elliot Elliot Lake Lake camp camp are are now now generally generally believed believed to support a modified paleoplacer origin of the ores as outlined to support a modified paleoplacer origin the ores as outlined by supportingthe paleoplacer by Roscoe(1969). Roscoe(1969). Convincing evidence supportingthe paleoplacer hypothesis hypothesis was was provided provided by by Theis(l979) Theis(1979) who who demonstrated demonstrated that that aa direct direct relationship relationship exists exists between between the the size size of of quartz quartz pebbles pebbles and and pyrite pyrite grains grains (Figure (Figure10), 101, and and the the concentration concentration of of many many other other 17 �components accumulation of components of of the the ore ore zones. zones. Prior to the accumulation significant atmosphere, southeastward southeastward significant free free oxygen in the Earth's atmosphere, flowing pyrite and and uraniferous uraniferous minerals minerals flowing streams streams carried quartz, pyrite released by the extensive weathering of the Archean granitic released the of the Archean terrain, and terrain, and deposited deposited them them as as southeast southeast trending trending units units determined determined by by basement basement topography. topography. The McKim Formation Formation uppermost formation formation of of the Elliot Lake The McKim Formation Formation is the uppermost turbidite sequence It is mainly a turbidite sequence of generally generally dark dark grey, grey, subarkosic wackes, subarkosic wackes, mudstones, mudstones, subarkoses, subarkoses, lithwacke lithwacke and and litharenite which River area litharenite which extends extends from from the Blind River area to to the the Grenville Front. Grenville Front. Graded Graded beds, beds, parallel parallel laminations, laminations, ripple ripple marks, marks, ripple-drift cross-laminations and Bouma cycles, indicative ripple-drift cross-laminations Bouma cycles, indicative of of deposition by currents are are reported reported deposition by submarine submarine turbidity currents (Parvianen, (Parvianen, 1971; 1971; Card Card et et al., al.,1977). 1977). Group. Group. Robertson(1968) thickness of of 0-380 0-380 feet feet (0-100 (0-100 m) for the the Robertson(1968) gives gives aa thickness m) for McKim Formation of the the Quirke Quirke Lake Lake syncline. syncline. It Formation on on the south limb of It Formation is is missing on on the the north limb. limb. The McKim Formation is thickest thickest in in the Sudbury Sudbury area, area, where where it it is is up to to 2400 2400 metres metres (8000 (8000 feet) feet) thick. thick. The an important important influence The Murray Murray Fault Fault appears to have exerted an influence deposition of the McKim McKim sediments. sediments. North North of of the the Murray Murray on the deposition metres in Fault the the McKim McKim rarely rarely exceeds exceeds a few few hundred metres in thickness, thickness, whereas south of the fault the thickness of the McKim Formation south of of the McKim Card(1978a) noted noted that that the the change change from is at least 2400 2400 metres. Card(1978a) laminated siltstone laminated siltstone in in the west to more wacke in in the the east east indicated proximal facies, indicated aa change change from from more distal to proximal facies, in in turn turn suggesting more suggesting more tectonic tectonic activity activity and possibly a source source for for the the McKim sediments in the east. Fralick and Miall(l989)concluded sediments in the and Miall(1989)concluded the McKim that the McKim Formation Formation of the Elliot Lake area represents represents aa marine transgression transgression which which gradually gradually drowned drowned the the Matinenda Matinenda fluvial plain. fluvial plain. 18 �Straticrraohic Relationships Relationships within within the the Elliot Lake Lake Group Group of of the the Stratigraphic Sault Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake Area The stratigraphic stratigraphic relationship relationship between between the the Matinenda Matinenda Formation Formation The and the the Livingstone Livingstone Creek Creek Formation Formation is is revealed revealed on on aa rock rock face face and near near the the southern southern Boundary Boundary of of Otter Otter Township Township about about 30 30 km km (18 (18 miles) miles) north north of of the the town town of of Thessalon. Thessalon. At At this this location location pyritic pyritic quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation (Chandler, (Chandler, 1976) 1976) directly directly overlies overlies an an apple-green apple-green paleosol paleosol on on grey, grey, finefinegrained sandstone of the Livingstone Creek Formation. About grained sandstone of the Livingstone Creek Formation. About 600 600 metres metres (380 (380 feet) feet) northwest northwest of of the the above above occurrence occurrence arkose arkose and and quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation disconformably disconformably overlies overlies aa steeply steeply dipping, dipping, east-striking, east-striking, mafic mafic dike, dike, the the upper upper few few metres metres of of which which are are sericite-Jeucoxene sericite-leucoxene paleosol paleosol (Figures (Figures4, 4, 6). The The dike dike intrudes intrudes grey grey sandstone sandstone and and apple-green apple-green paleosol paleosol of of the the Livingstone Livingstone Creek Creek Formation Formation (Bennett (Bennett et al, al, 1991; 1991; Sutton Sutton and and Maynard, Maynard, 1992). 1992). Less Less than than 22 km km south south of of et the the above above location location Chandler(l976) Chandler(1976) identified identified aa fault-bounded fault-bounded block block of of Thessalon Thessalon Formation Formation volcanic volcanic rocks rocks with with aa minimum minimum thickness of approximately 500 m. thickness of approximately 500 m. The The above above observations observations show show clearly clearly and and unequivocally unequivocally that that there there was was aa period period of of volcanic volcanic activity, activity, as as well well as as aa significant significant period period of of erosion, erosion, separating separating the the Matinenda Matinenda Formation Formation and and the the Livingstone paleosols are are well well known known upon upon Livingstone Creek Creek Formation. Formation. Since Since paleosols Huronian Huronian flows flows in in the the Elliot Elliot Lake Lake area, area, the the sub-Matinenda sub-Matinenda unconformity extended to the Quirke Lake Syncline. unconformity extended to the Quirke Lake Syncline. In In addition, addition, the the above above observations observations imply imply that: that: 1. 1. The The mafic mafic dike dike referred referred to to above above was a a feeder feeder for for Thessalon Thessalon flows, flows, since since the the Thessalon Thessalon Formation Formation is is the the only only known known igneous igneous activity activity at at this this stratigraphic stratigraphicposition. position. 2. 2 . The The Thessalon Thessalon Formation Formation may may once once have have extended extended beyond beyond the the limit limit suggested suggested from from its its present present outcrop outcrop distribution. distribution. This This is is to to be exacted on consideration of Macdougall's(l988) statement be exacted on consideration of Macdougall's(1988) statement "Since 'Since many many CFB CFB provinces provinces have have been been uplifted uplifted and and occur occur as as elevated elevated plateaus, plateaus, dissection dissection and and removal removal is is rapid". rapid". He He notes notes as as well that the general scarcity of pre-Cretaceous Continental well that the general scarcity of pre-Cretaceous Continental flood flood basalt basalt provinces provinces is is probably probably due due to to their their erosion. erosion. 19 �Hough Lake Lake Group Group The Hough Lake Group (Robertson, (Robertson, et al., Hough Lake al., 1969; Roscoe, Roscoe, 1969) is groups which which display display the the cyclic cyclic the lowest lowest of of the the three three 1-luronian Huronian groups deposition deposition of of diamictite diamictite followed followed by by aa mudstone, mudstone, siltstone, siltstone, turbidite by aa cross-bedded cross-bedded turbidite or or carbonate carbonate sequence, sequence, and and overlairx overlain by arenite unit. represent a arenite unit. Each cycle is generally thought to represent sequence sequence of of glaciogenic glaciogenic -- marine marine -- fluvial fluvial and/or and/or shallow shallow marine marine deposition deposition (Figure (Figure3). 3) . Ramsay Ramsav Lake Lake Formation Formation The Ramsay formation of the Hough Ramsay Lake Lake Formation Formation is the lowermost formation Lake conglomerate units Lake Group Group and and is is the the oldest of three such conglomerate units which Quirke Lake Lake and Cobalt which define define the the base base of Hough Lake, Quirke Groups (Figures 2,3) 2,3). Groups (Roscoe, (Roscoe,1969; 1969; Piennar, Piennar,1963) 1963) (Figures The The Ramsay Ramsay Lake Lake Formation Formation is is aa widespread, widespread, relatively relatively thin thin unit unit which is which is up up to to 41 41 mm thick thick in in the the Dunns Dunns Valley Valley area area (Chandler, (Chandler, 1973) 1973). In In the Elliot Lake area the thickness of the the Ramsay Ramsay Lake Lake Formation is Formation is from from 00 to to just just over over 30 30 m. m. (Diamond logs (Diamond drill logs Assessment files, Sault Ste. Marie Resident Geologist's Assessment files, Sault Ste. Marie Resident Geologist's Office) Office). The Ramsay 70 to to 170 170 m thick thick in in the the The Ramsay Lake Lake Formation Formation is is from from 70 Sudbury-Manitoulin Sudbury-Manitoulinarea area (Card (Card1978a) 1978a). . Matrix Matrix supported supported polymictic polymictic conglomerate conglomerate (diarnictite) (diamictite) is the the most most abundant rock Lake Formation, Formation, especially especially near abundant rock type type in in the Ramsay Lake the base. of the formation formation usually usually the base. The lowermost few metres of reflects reflects the the underlying underlying rock rock type type (Robertson, (Robertson, 1968; 1968; Parviainen, Parviainen, 1973) Minor amounts of mudstone, wacke and arenite are 1973). Minor mudstone, wacke and arenite are locally locally present. present. . Subrounded to Subrounded to well well rounded rounded pebbles and cobbles cobbles of of grey grey granitic granitic rocks and angular of very very dark dark green green to black rocks angular to rounded clasts of volcanic rocks generally form less than 30 percent volcanic rocks generally form less than 30 percent of of the the total total volume of volume of the the diamictite. diamictite. The The dark dark matrix matrix consists consists of of quartz, quartz, feldspars, chlorite, muscovite-sericite-illite and and pyrite pyrite feldspars, chlorite, muscovite-sericite-illite (Parviainen, (Parviainen,1973). 1973). Although flow origin, origin, most Although some some writers writers have have argued for a debris flow 20 �writers writers now now accept accept the the Ramsay Ramsay Lake Lake Formation Formation as as having having aa significant significant glaciogenic glaciogenic component component (Roscoe, (Roscoe,1969; 1969; Robertson, Robertson, 1976). 1976). Fralick Fralick and and Maill(1989) Maill(l989) identified identified an an ice ice proximal proximal association association of of pebbly pebbly sandstone sandstone and and diamictite; diamictite; subaqueous subaqueous gravity gravity flows flows and and ice ice rain-out rain-out deposits; deposits; and and ice-proximal, ice-proximal, fluvial fluvial outwash outwash deposits. deposits. Pecors Pecors Formation Formation The Ramsay Lake Lake Formation Formation is is conformably conformably overlain overlain by by aa sequence sequence The Ramsay of of generally generally dark, dark, bedded bedded and and laminated laminated wackes, wackes, mudstone, mudstone, siltstones 1969). siltstones and and sandstones sandstones of of the the Pecors Pecors Formation Formation (Roscoe, (Roscoe,1969) The The Pecors Pecors Formation Formation is is 30 30 mm thick thick at at Quirke Quirke Lake Lake (Robertson, (Robertson, 1968) but is as much as 900 m thick south of the Murray 1968) but is as much as 900 m thick south of the Murray Fault Fault in in the Sudbury area area (Card, (Card,1978a) 1978a). It It was was not not identified identified in in the the the Sudbury area area between between Thessalon Thessalon and and Sault Sault Ste. Ste. Marie Marie (Frarey, (Frarey,1977). 1977). Ripple Ripple marks, marks, graded graded bedding, bedding, cross-laminations cross-laminationsparallel parallel laminations, clastic dikes dikes and and laminations, ball ball and and pillow pillow structures, structures, clastic slumpage slumpage features features have have been been reported reported in in the the formation. formation.The The basal basal part part of of the the formation formation is is commonly commonlylaminated laminated resembling resemblingvarves varves and, and, in in places, places, has has dropstones dropstones (Robertson, (Robertson,1968; 1968;Parviainen, Parviainen, 1973) 1973). Partial Partial Bouma Bouma sequences sequences are are common common (Card, (Card,1968; 1968;Robertson, Robertson, 1976) 1976). The The Pecors Pecors Formation Formation is is the the result result of of transgressive transgressive units units formed in deep water by turbidity currents (Card, l978a) formed in deep water by turbidity currents (Card, 1978a). The The presence presence of of drop drop stones stones is is evidence evidence of of aa cold cold paleoclimate, paleoclimate, and and provides provides supporting supporting evidence evidence for for the the glaciogenic glaciogenic origin origin of of the the underlying Ramsay Lake LakeFormation. Formation. underlying Ramsay . . . Mississagi Mississacri Formation Formation The The Mississagi Mississagi Formation Formation is is aa thick thick sequence sequence of of predominantly predominantly grey, grey, arenitic arenitic rocks rocks extending extending throughout throughout most most of of the the length lengthof of the outcrop belt. Within synclinethe the the Iluronian Huronian outcrop Within the the Quirke Quirke Lake Lake syncline Mississagi Formation is from 344 to 704 m thick. South of the Mississagi Formation is from 344 to 704 m thick. South of the Murray Murray Fault Fault the the formation formation is is notably notably thicker, thicker, being being more more than than 3000 3000 mm in in the the Sudbury Sudbury area area (Card, (Card,l978a; 1978a;Long, Long,1978). 1978). By By far far the the dominant dominant rock rock type type in in the the Mississagi Mississagi Formation Formation is is moderately moderately well well sorted, sorted,medium medium to to coarse coarse grained grained subarkose subarkose and and arkose. arkose.Small Smallto to medium quartz/chert pebble conglomerate is a minor component of medium quartz/chert pebble conglomerate is a minor component of the the formation, formation, but but is is more more common common in in the the western western and and northeastern northeastern parts foresets parts of of the the Huronian Huronian belt. belt. Fine-grained Fine-grainedpyrite pyrite along alongforesets 21 �commonly results results in in rusty rusty staining stainingof of outcrops. outcrops. Greenish, Greenish, thin, thin, commonly sericitic units units form form relatively relatively thin thin planar bedded units units between between sericitic cross-bedded sandstones. sandstones. Palonen Palonen (1971) (1971) provided provided evidence evidence cross-bedded supporting aa marine marine origin origin for for the the Mississagi Mississagi Formation; Formation; however, however, supporting Long (1978) (1978) argued argued that that the the abundance abundance of of mud-grade mud-grade matrix matrix in in the the Long immature paleocurrent immature arenites, arenites, and and the the predominance of unimodal paleocurrent arenites argued 5), and and the the lack lack of quartz arenites argued directions (Figure (Figure5) directions against against aa marine marine environment environment for for the the Mississagi Formation. Formation. He He concluded deposited from concluded that that the the Mississagi Mississagi Formation Formation was deposited from braided streams with low to intermediate sinuousity and braided streams with low to intermediate sinuousity and high high width to to depth depth ratios. ratios. width , Bedding Bedding units units are are commonly commonly about about aa metre thick but range range from from aa few cross-stratification few centimetres centimetres to to over over four four metres. Trough cross-stratification and ripple cross-stratification are common sedimentary and ripple cross-stratification are common sedimentary structures structures (Long, 1978). Individual Individual cross-stratified (Long, 1978). cross-stratified beds may so so show show grain grain size size gradation gradation (McDowell, (McDowell,1957) 1957). Long Long (1978) (1978) measured over over 2500 2500 cross-stratified cross-stratified units in in the the Two major stream systems Mississagi 5)5). . Mississagi Formation Formation(Figure (Figure Two systems were were recognized: a stream stream system system flowing flowing southeast to easterly from from the stream system the Sault Sault Ste. Ste. Marie Marie area area joined joined aastream system flowing flowing southwestward a southward flowing southwestward from from the Cobalt Cobalt Plain Plain to form a flowing system system southwest southwest of of the the Sudbury Sudbury area. area. These These observations observations suggest suggest that Complex was that the the area area now now occupied occupied by by the the Sudbury Sudbury Igneous Igneous Complex was elevated elevated during during the the period period of of Mississagi Mississagi deposition. deposition. Quirke Quirke Lake Lake Group Group Bruce Bruce Formation Formation The The Bruce Bruce Formation Formation extends extends from from the the Bruce Mines area to about about 70 70 km northeast northeast of of Sudbury. Sudbury. It It consists consists mainly of matrix supported supported km and and minor minor clast clast supported supported conglomerate. conglomerate. Pebbly Pebbly wacke, wacke, arkose, arkose, wacke reports wacke and and siltstone siltstone are are locally locally present. Robertson(1968) reports the the Bruce Bruce Formation Formation is is from from 79 7 9 mm (260 (260 feet) feet) to to 12 12 mm (40 (40 feet) feet) thick in the Elliot Lake area. It is 26 m (85 feet) to 37 thick in the Elliot Lake area. It is 26 m (85 feet) to 37 mm (120 (120 feet) feet) thick thick under under the the greater greater part part of of the the Quirke Quirke Lake Lake Syncline. Syncline. Pebble angular to subrounded clasts clasts generally generally Pebble to boulder sized, sized, angular 22 �consist of granitic rocks, consist of pale-grey pale-grey to whitish granitic rocks, Archean Archean supracrustal rocks supracrustal rocks and fine grained mafic clasts. clasts. The The upper upper parts parts of the 5% carbonate carbonate (Robertson, (Robertson, the formation formation may may contain contain up up to to 5% 1968) . 1968) Bruce Formation generally interpreted The Bruce Formation is is generally interpreted as as a a tillite tillite with with minor beds and lenses of glacially derived sandstone. Dropstones beds and lenses glacially derived sandstone. Dropstones been observed have been observed in in laminated laminated units units (Robertson, (Robertson,1964, 1964,1971). 1971). Casshyap (1969) Casshyap (1969) concluded the formation formation was deposited deposited from from terrestrial wet-base (1981) terrestrial wet-baseglaciers. glaciers. However HoweverSimms Simmsetetal. al.(1981) proposed that proposed that the the Bruce Bruce Formation Formation is is an an accumulation accumulation of of debris debris faulting, a sudden flows released as a result of normal faulting, sudden increase increase in paleoslope and in paleoslope and aa sudden sudden increase 'increasein in water water depth. depth. EsDanolp Formation Espanola Formation The Espanola widespread carbonate The Espanola Formation Formation is is the only widespread carbonate unit unit of of Huronian Supergroup. the Huronian Supergroup. It is present from from the the Sault Sault Ste. Ste. Marie area to to the the Maple Mountain Mountain area area about about 70 70 km km northeast northeast of of Sudbury.. Sudbury., Its widespread widespread distribution distinctive lithology Its distribution and distinctive lithology make it it the the most most useful useful stratigraphic stratigraphicmarker markerunit unitofofthe the1-luronian Huronian Supergroup. Supergroup. In the Elliot Lake area the Espanola Espanola Formation Formation can be subdivided can subdivided three parts: into three parts: a a lower lower limestone limestone member member (the (the Bruce Bruce Limestone) Limestone), a middle Greywacke) middle siltstone, siltstone, wake, wake, arenite arenite member member (the (the Espanola Espanola Greywacke) and an and an upper upper dolomitic dolomitic limestone limestone member member (the (theEspanola Espanola Limestone) Limestone) latter generally generally contains 4% total (Robertson, (Robertson,1968). 1968). The latter contains 33 -- 4% total iron which gives iron which gives a distinctly brownish colour colour to to weathered generally thinly bedded to surfaces. surfaces. All 3 members are generally to The threefold subdivision is not so well developed laminated. laminated. subdivision Contacts between between members members south of the Murray Fault (Young, (Young, 1982). Contacts tend to to be be gradational. gradational. Intraformational breccias, mud mud cracks, ripple ripple marks, marks, flame Intraformational flame structures and ball-and-pillow structures are common sedimentary structures and ball-and-pillow structures are common sedimentary features. (1980) described described stromatolites stromatolites in features. Hofmann Hofmann et et al. al. (1980) in the the Espanola Espanola Formation Formation at at Quirke Lake. Lake. These These features features suggest suggest deposition in a quiet shallow water environment with deposition in a quiet shallow environment with carbonate carbonate deposition deposition being being interrupted interrupted by by influx influx of of fine-grained fine-grainedsediment. sediment. Young (1973) proposed that the relatively sharp change from Young (1973) proposed relatively sharp change from the the diamictites diamictites of of the the Bruce Formation Formation suggests suggests warm climatic climatic However, the conditions conditions following following aa glacial glacial advance. advance. However, the recognition recognition 23 �of carbonate carbonate deposition deposition at high latitudes latitudes (Williams, (Williams, 1975) 1975) and and association of the association of detrital detrital uranium uranium with with intense intense chemical chemical weathering uncertainty to attempts weathering (Maynard (Maynard et al, 1991) 1991) adds uncertainty attempts to to model Huronian Huronian paleoclimate paleoclimate (Bennett (Bennett et et al, al, 1991) 1991). Serpent Formation Serpent Formation The Serpent Huronian The Serpent Formation Formation is found throughout much of the Huronian belt; however, however, it it is is locally removed by erosion during a period Gowganda of tectonic tectonic activity activity preceding deposition of the Gowganda Formation Formation of of the the Cobalt Cobalt Group. Group. Reported Reported thickness thickness estimates estimates of of the Serpent Serpent Formation Formation range range from from 150 150 up up to to 1500 1500 mm (Bennett (Bennett et et Robertson(l968) states states that nowhere nowhere in al., 1991). al., 1991). Robertson(1968) in the the Blind Blind River-Elliot Lake area is there any evidence that the total River-Elliot Lake area is there any evidence that the total thickness of thickness of the the Serpent Serpent Formation Formation has has been been preserved. preserved. The The Serpent Serpent Formation Formation is is mainly mainly fine fine to to medium-grained, medium-grained, quartz quartz arenite and arenite and arkose. arkose. Conglomeratic Conglomeratic units units have have been been noted, noted, especially especially near near the the base of the the Formation. Formation. Carbonate Carbonate is is aa significant significant component component near near the the base base of of the the formation formation in in the the Planar cross-bedding, cross-bedding, Elliot Lake area area (Robertson, (Robertson,1968) 1968). Planar Elliot Lake festoon festoon cross-bedding, cross-bedding, rip—up rip-up clasts, clasts, fine-laminations fine-laminations and and mud mud cracks have been Long(1976) proposed proposed that that the the Serpent Serpent cracks been reported. reported. Long(1976) Formation was was deposited distal braided stream Formation deposited in in a distal stream environment environment with calcareous calcareous units units representing representing aa sabkha sabkha environment. environment. presence of of very very large cross-beds cross-beds and Young(1982) noted that the presence bi-modal size a bi-modal size distribution distribution suggest suggest eolian eolian processes processes may may have have been been active active at at least least locally. locally. . Cobalt Cobalt Group Group Gowganda Formation Gowaanda Formation Gowganda Formation The Gowganda Formation is is a a complex complex sequence sequence of of conglomerates, conglomerates, sandstones, mudstones which sandstones, siltstones siltstones and mudstones which comprise comprise the the lowermost lowermost formation of the Cobalt Group. Its thickness is about 1070 formation the Its thickness is about 1070 mm in in Sault Ste. the Sault Ste. Marie area, area, from from 970 970 to to 1150 1150 m around around Whitefish Whitefish Falls, on the Huron, and from Falls, the North Shore Shore of Lake Huron, from 950 950 to to 2700 2700 mm near Sudbury. near Sudbury. Near Near Dunlop Dunlop Lake, Lake, in in the the Elliot Elliot Lake Lake area, area, the the 24 �Gowganda Gowganda Formation Formation is is about about 600 600 mm thick. thick. Matrix-supported Matrix-supported conglomerates conglomerates are are common, common, especially especially in in the the lower lower parts parts of of the the formation. formation. However, However, these these are are commonly commonly intercalated intercalated with with clast-supported clast-supported conglomerates, conglomerates, sandstone, sandstone, and and wacke wacke units. units. Laminated Laminated mudstones mudstones and and siltstone siltstone are are especially especially prominent prominent in in the the upper upper parts parts of of the the Gowganda Gowganda Formation. Formation. Many Many occurrences of of ice-rafted ice-rafted drop-stones drop-stones have have been been reported reported in in occurrences units. Individual Individual units units are are laminated mudstone/siltstone units. laminated generally generally relatively relatively thin thin and and discontinuous discontinuous making making subdivision subdivision of of the the Gowganda Gowganda formation formation difficult difficult except except in in well-exposed well-exposedareas. areas. Most Most granitic granitic clasts clasts of of Gowganda Gowganda conglomerates conglomerates have have aa distinctly distinctly pinkish pinkish or or reddish reddish hue, hue, in in comparison comparison to to the the grey grey granitic granitic clasts clasts in the matrix supported conglomerates of the stratigraphically in the matrix supported conglomerates the stratigraphically lower Ramsay Lake Lake and and Bruce Bruce Formations. Formations. Also, Also, pink pink and and red red hued hued lower Ramsay sandstones sandstones first first make make their their appearance appearance in in the the Gowganda Gowganda Formation. Formation. Roscoe(1969) Roscoe(1969) pointed pointed out out the the appearance appearance of of red red colouration colouration(i.e. (i.e. ferric ferric iron) iron) just just above above the the basal basal units units of of the the Gowganda Gowganda Formation, and argued that it represents the appearance Formation, and argued that it represents the appearance of of free free oxygen oxygen in in the the Earth's Earth's atmosphere, atmosphere, and and aa change change from from the the previously previously reducing reducing atmospheric atmospheric conditions conditions that that allowed allowed the the accumulation accumulation of of readily readily oxidized oxidized minerals minerals such such as as pyrite pyrite and and uraninite fluvial environment. environment. uraninite in in aa fluvial The depositional depositional environment environment of of the the diamictites diamictites in in the the Gowganda Gowganda The Formation Formation have have been been the the subject subject of of discussion discussion since sinceColeman(1905) Coleman(1905) proposed proposed aa glacial glacial origin origin for for the the matrix matrix supported supportedconglomerates. conglomerates. Many Many later later writers writers including including Ovenshine(1965), Ovenshine(1965),Cassyhap(1969), Cassyhap(1969). Lindsay(1971), Young Young and and Nesbitt(1985), Nesbitt(1985), and and others, others, have have also also Lindsay(1971), supported glaciolacustrine origin origin supported aa glacial, glacial, glacial-marine glacial-marine or or glaciolacustrine for for the the Gowganda Gowganda Formation. Formation. Card(1968) Card(1968) concluded concluded that, that, although although glaciation glaciation may may have have supplied supplied coarse detritus to the basin initially, debris flows and coarse detritus to the basin initially, debris flows and turbidity turbidity currents, currents, released released by by vertical vertical tectonic tectonic movement, movement, may may better better explain explain the the thickness thickness variations, variations, rock rock associations associations and and distribution Manitoulin area. area. distribution he he observed observed it it the the Sudbury Sudbury Manitoulin Roscoe(1969) Roscoe(1969) also also emphasized emphasized that that glaciation glaciation is is only only one one of of several processes responsible for the deposition of Gowganda several processes responsible for the deposition of Gowganda sediments. sediments. 25 �Lorrain Lorrain Formation Formation The The Lorrain Lorrain Formation Formation is is generally generally well well exposed exposed throughout throughout most most of the the Huronian Huronian belt, belt, where it commonly forms a background to some of the some the most scenic scenic views in in northern northern Ontario. Ontario. It It is is overwhelmingly overwhelmingly an an arenitic arenitic sequence, sequence, with with local local siltstone siltstone units units formation is up to present in in lower lower parts of the section. The formation 2500 2500 m thick thick near near Sault Sault Ste. Ste. Marie Marie and and in in the the LaCloche LaCloche Syncline, Syncline, southwest southwest of of Sudbury. Sudbury. It It is is up to to 2300 2300 m m thick thick in in the the Cobalt Cobalt Embayment.. Embayment In general, the In general, the lower lower part of the the Lorrain Lorrain Formation Formation is is dominated dominated by by pink, pink, arkosic arkosic sandstones, sandstones, the the middle middle by by hematite-rich hematite-rich subarkose and subarkose and quartz-arenite, quartz-arenite, and the the upper upper portion portion by by pale pale grey grey white mature, distinctive jasper-pebble jasper-pebble to white mature, quartz-arenite. quartz-arenite. A distinctive conglomerate conglomerate found found in in the the Sault Sault Ste. Ste. Marie Marie area area is is aa popular popular decorative decorative stone, stone, known known locally locally as as "pudding "pudding stone". stone". The The presence presence of of aluminous aluminous minerals is is a a characteristic characteristic feature feature of of the the upper, upper, piartz-arenites quartz-arenites of the Lorrain Lorrain Formation. Formation. Diaspore Diaspore and and kaolinite are kaolinite are common common in in the quartz-arenite quartz-arenite of of the the Sault Sault Ste. Ste. of Elliot Elliot Lake Lake (Wood, 1973) 1973) whilekyanite, whilekyanite, Marie area area and north of andalusite andalusite and and kaolinite kaolinite are are present present as as metamorphosed metamorphosed equivalents equivalents in the the LaCloche LaCloche Lake-Killarney Lake-Killarney area area (Card, (Card, l978a). 1978a). Young(1973) Young(1973) and Wood(l973) and Wood(1973) interpret interpret the the presence of of diaspore diaspore and and kaolinite kaolinite as the as the result result of of post-depositional post-depositional in-situ in-situ alteration alteration of of feldspar feldspar under hot under hot and and humid humid climatic climatic conditions. conditions. presence of The presence of abundant detrital hematite hematite in in the the Lorrain Lorrain Formation and Formation and the the occurrence occurrence of thorium-rich, thorium-rich, monazite-bearing, monazite-bearing, quartz-pebble quartz-pebble conglomerate conglomerate north north of of Elliot Elliot Lake Lake has has been been interpreted by Frarey Roscoe(l970) as interpreted Frarey and Roscoe(1970) as indicating indicating an an oxidizing oxidizing environment. environment. Planar Planar and and trough trough cross-bedding cross-bedding are are common, common, as as are are ripple ripple marks marks and other other primary primary depositional depositional structures. structures. There There is is no no consensus consensus as to to the the depositional depositional environment environment of the the Lorrain Lorrain Formation. Formation. Most Most of the sedimentary structures of the Lorrain Formation can be the sedimentary structures Lorrain Formation can be 26 �found found in in either either shallow shallow marine marine or or fluvial fluvial environments. environments. Wood(1973), Wood(1973) , Young(l973) Young(1973) and and Frarey(l977) Frarey (1977)favoured favoured aa fluviatile fluviatile model while while Pettijohn(1970) Pettijohn(l970) supported supported a a marine environment for for model the Lorrain Formation. Formation. Card(1976b) Card(1976b) proposed that that the the Lorrain Lorrain the Lorrain Formation Formation represents represents near-shore near-shore coastal coastal shelf shelf deposition deposition during during episodic marine transgression and regression. episodic marine transgression and regression. Gordon Gordon Lake Lake Formation Formation The The Gordon Gordon Lake Lake Formation Formation displays displays aa gradational gradational contact contact with with the the underlying underlying Lorrain Lorrain Formation. Formation. It It is is made made up up predominantly predominantly of of variegated variegated mudstone, mudstone, siltstone, siltstone,chert chert and and minor minor fine-grained fine-grained sandstone. sandstone. Robertson(1986) Robertson(1986) subdivided subdivided the the Gordon Gordon Lake Lake Formation Formation of of the the Flack Flack Lake Lake area area into into aa lower lower member member of of reddish reddish arenite, arenite, siltstone, siltstone, and and chert chert with with anhydrite anhydrite and and gypsum gypsum nodules, nodules, aa middle middle member member of of green green siltstone siltstone and and mudstone, mudstone, and and an an upper upper reddish reddish mudstone, mudstone, siltstone siltstone and and chert. chert. Abundant Abundant sedimentary sedimentary features features include include small-scale small-scalecross-bedding, cross-bedding,ripple ripple marks marks and and desiccation desiccation cracks. cracks. Some Some of of the the features features of of the the Gordon Gordon Lake Lake Formation Formation are are unique unique for for the Supergroup. Wood(1973) Wood(l973) noted noted the the abundance abundance of of the 1-Juronian Huronian Supergroup. feldspar feldspar in in the the formation, formation, aa marked marked contrast contrast to to rocks rocks of of the the immediately Lorrain Formation. Formation. He He also also described described immediately underlying underlying Lorrain hematite 0 . 0 2 to to 0.05 0.05 hematite ooliths ooliths and and the the abundance abundance of of grains grains in in the the 0.02 mm mm range, range, aa relatively relatively uncommon uncommon grain grain size size in in sedimentary sedimentary rocks. rocks. Since Since this this size size is is found found in bess loessdeposits, deposits, Wood(1973) Wood(1973) proposed proposed that that the the quartz quartz silt silt of of the the Gordon Gordon Lake Lake Formation Formation was was formed formed by by glacial glacial action action and and carried carried by by the the wind wind and and deposited deposited in in aa tidal tidal flat flat environment. environment. Jackson(1994) Jackson(1994) identified identified nodules nodules and and layers layers of of dolostone dolostone in in siltstone siltstone and and chert chert of of the the Gordon Gordon Lake Lake Formation Formation in in the the Aberdeen Aberdeen area, (1989) reported area, east east of of Sault SaultSte. Ste.Marie. Marie.Bennett Bennettetetal. al.(1989) reported aa unit unit of of dobostone dolostone in in Fenwick Fenwick Township, Township, near near Sault Sault Ste. Ste. Marie Marie and and proposed proposed aa correlation correlation with with the the Gordon Gordon Lake Lake Formation Formation in in the the Bruce Bruce Mines Mines area area and and to to the the Kona Kona Formation Formation of of the the Marquette Marquette Range Range Supergroup. Supergroup. 27 �Bar River Formation Formation The Bar River the uppermost formation formation of the the The River Formation Formation is is the 1-luronian Supergroup. It is characterized by quartz-arenite Huronian Supergroup. It is characterized by quartz-arenite with with siltstone. It is approximately approximately 300 minor ferruginous ferruginous arenite and siltstone. 300 m m thick thick in in the the Flack Flack Lake Lake area, area, north north of Elliot Lake. Wright and and Rust(l985) deposited Rust(1985) concluded concluded that the the Ear Bar River Formation was deposited in in a a tidal tidal environment. environment. Nipissing Nipissing Intrusions Intrusions Dikes, Dikes, sills, sills, and and cone cone sheets sheets of of gabbro, gabbro, diabase diabase and and granophyre, granophyre, Nipissing diabase" are the most commonly referred to as commonly referred to as " Nipissing diabase" are the most widespread igneous widespread igneous rocks rocks within within the the Huronian Huronian Supergroup. Supergroup. Baddeleyite from the Gowganda Gowganda area have Baddeleyite from Nipissing gabbro sills in the been dated at 2219 Ma U-Pb; u-pb; the minimum, minimum, age age for for the the Huronian Huronian Supergroup Card(1985) Supergroup (Corfu (Corfu and and Andrews, Andrews, 1986). 1986). Buchan Buchan and and Card(l985) report that paleomagnetic data suggest at least two report data suggest least two periods periods of of Nipissing Nipissing intrusive intrusive activity. activity. Olivine-bearing Olivine-bearing hypersthene hypersthene gabbro, gabbro, gabbro, gabbro, feldspathic feldspathic pyroxenite, pyroxenite, two-pyroxene two-pyroxene quartz quartz gabbro, gabbro, hornblende hornblende gabbro, gabbro, granophyric granophyre have been been identified in qranophyric qabbro gabbro and qranophyre bodies are Nipissing Nipissing intrusions. intrusions. Many of the the Nipissing bodies are characterized wide, overlain overlain by characterized by chilled margins 50 cm to 55 mm wide, 10-20 10-20 m of quartz quartz gabbro, gabbro, then then 100-500 100-500 m of hypersthene-poor hypersthene-poor gabbro-norite and vari-textured van-textured diabase gabbro-norite diabase (Lightfoot (Lightfoot and and Naldredt, Naldredt 1996) 1996) Nipissing Nipissing intrusions intrusions are are widely widely and and evenly evenly distributed distributed throughout throughout Huronian belt but, the Huronian but, with few few exceptions, exceptions, are not not recognized recognized intrusions may be within the Archean terrain. terrain. Individual intrusions be up up to to within the Archean several hundred metres thick several thick and and extend over an area area of of several several hundred hundred square square kilometres. kilometres. The form and orientation of Nipissing intrusions indicate intrusions indicate that their their emplacement may be controlled controlled by by older faults, folds and competency of the enclosing rocks (Card older faults, folds enclosing rocks (Card and and Pattison, Pattison, 1973) 1973). 28 �Lightfoot Lightfoot and and Naldredt(1996) Naldredt(1996) discuss discuss the the geochemical geochemical characteristics characteristics of of the the Nipissihg Nipissing magmas magmas and and the the potential potential for for platinum platinum group group metal metal deposits. deposits. They They conclude conclude that that the the Nipissing Nipissing magmas magmas were were emplaced emplaced into into the the Huronian Huronian sedimentary sedimentary sequence sequence over over a a period period of of less less than than 10 10 million million years. years. Parental Parental magmas magmas of of remarkably remarkably uniform uniform composition composition underwent underwent in-situ in-situ contamination contamination and and differentiation differentiation within within the the intrusions intrusions (Lightfoot (Lightfoot and and Naldredt, Naldredt, 1996) 1996) . AA spatial spatial association association between between Nipissing Nipissing intrusions intrusions and and both both magmatic magmatic and and vein-type vein-typemineralization mineralization has has long long been been recognized. recognized. Card Card and and Pattison(l973) Pattison(1973) noted noted also also that that there there is is aa variation variation in in style style and and type type of of mineralization mineralization associated with with Nipissing Nipissing intrusions intrusions from from the the Cobalt Cobalt area area in in the the east east to to the the Sault Sault Ste. Ste. Marie Marie area area in in the the west. west. Huronian Huronian Paleosols Paleosols and and Evidence Evidence for for the the Accumulation Accumulation of of Oxygen Oxygen in in the Huronian Atmosphere the Huronian Atmosphere It It has has long long been been recognized recognized that that the the study study of of Huronian Huronian paleosols paleosols (ancient (ancient soil soil profiles) profiles) could could provide provide information information pertaining pertaining to to the the development development the the Earth's Earth's atmosphere atmosphere and and climate climate during during the the Proterozoic. Since iron is much less soluble in the ferric Proterozoic. Since iron is much less soluble in the ferric state state than than when when in in the the ferrous ferrous state, state, the the behavior behavior of of iron iron in in paleosols paleosols should should provide provide some some indication indication of of the the oxygen oxygen partial partial pressure pressure of of the the environment. environment. Many Many of of the the best best descriptions descriptions of of Precambrian Precambrian paleosols paleosols have have been been from from those those associated associated with with Huronian Huronian unconformities unconformities (Gall, (Gall,1992) 1992). Grandstaff (1986) identified 8 features features of of paleosols, paleosols, most most al.(1986) Grandstaff et et al. of which can been observed in Huronian paleosols. These features of which can been observed in Huronian paleosols. These features are: are : 1. 1. Stratiform Stratiform 2. 2 . Relatively Relativelythin thin(<20 ( < 2 0 m) m) 3. Transitional lower boundary-sharp 3. Transitional lower boundary-sharp upper upper boundary boundary 4. 4. Colour Colour variations variations 5. 5 . Destruction Destruction of of primary primary rock rock textures textures accompanied accompanied by by the the development development of of soil soil textures textures 6. 6. Destruction Destruction of of primary primary minerals minerals with with formation formation of of clay clay 29 �minerals minerals or or metamorphic metamorphic equivalents equivalents 7. Dikes material from from overlying sediment washed down down 7. Dikes of material into desiccation cracks in in the the soil soil into desiccation cracks 8. Rip-up Rip-up clasts clasts of of overlying overlying sediments sediments Well preserved preserved paleosols paleosols below below the the Matinenda Formation Formation in in the the Well Elliot Lake area area have have been been described described by by many many workers workers (Roscoe, (Roscoe, Elliot Lake 1957a, 1969, 1969, 1973, 1973, 1981; 1981; Pienaar, Pienaar, 1963; Robertson, 1964; Frarey Frarey l957a, Robertson, 1964; and Roscoe, Roscoe, 1970; 1970; Freyer, Freyer, 1977; 1977; Gay Gay and and Grandstaff, Grandstaff, 1980; 1980; and Kimberly et et al, al, 1984; 1984; G-Farrow G-Farrow and Mossman, 1988; 1988; Prasad Prasad and and Kimberly Roscoe, Roscoe, 1991, 1991, Sutton Sutton and and Maynard, Maynard, 1991, 1991, 1993) 1993). Bennett et et al. al.(1991) Bennett (1991) have have proposed proposed that that there there are are three three disconformities disconformities or or unconformaties unconformaties within within the the Elliot Elliot Lake Lake Group Group which have have potential potential for for paleosol paleosol development (Figure (Figure 2). 2). These These which are in descending stratigraphic order: 1)the sub-Matinenda are in descending stratigraphic sub-Matinenda disconformity; disconformity, and 2)the sub-Thessalon sub-Thessalon Formation Formation disconformity, and disconformity; 2)the sub-Livingstone sub-Livingstone Creek Creek Formation Formation unconformity. unconformity. The The sub-Livingstone sub-Livingstone Creek Creek Formation Formation unconformity unconformity is is the the basal basal unconformity Supergroup and and is is the the only only entirely unconformityof of the the1-luronian Huronian Supergroup entirely sub-iluronian unconformity (Figure sub-Huronian unconformity (Figure2) 2). This This unconformity unconformity is is exposed metres of exposed in in the the Thessalon Thessalon area, area, where the upper few few metres of the the Archean Archean granitic granitic rocks rocks can can be be seen seen to to progress progress from from angular, angular, slightly grit and fine-grained slightly rotated rotated blocks, blocks, separated separated by grey grit fine-grained sandstone, boulders with with a higher sandstone, upward, upward, to to more rounded boulders proportion clastic material material (Collins, (Collins,1925) 1925). This This zone zone proportion of of finer finer clastic may be termed termed aa "paleo-regolith", "paleo-regolith",since since there is little little or or no no obvious development of the yellow, sericitic paleosol commonly commonly obvious development of the yellow, found found in in the the younger, younger, sub-Matinenda sub-Matinendapaleosols. paleosols. . . Prasad paleosols in the same Prasad and and Roscoe(1996) described two paleosols same drill drill core Denison Mine Mine at at Elliot Lake. A paleosol was was found found core from from the the Denison above Huronian volcanic rocks and another, less well developed above Huronian volcanic rocks and another, less developed paleosol, paleosol, was was found found upon upon Archean Archean tonalite tonalite below below aa short short section section of of quartz-pebble quartz-pebble conglomerate conglomerate and and grit grit (Prasad, (Prasad, personal personal communication, communication, 1997) 1997) below below the the 99 m thick volcanic unit (Figure (Figure 13). 13). The paleosols have The best best developed, developed, and and most most studied, studied, Huronian paleosols have been Formation. On On mafic been found found directly directly below below the the Matinenda Formation. mafic rocks, the sub-Matinenda paleosols can generally be recognized rocks, the sub-Matinenda paleosols can recognized by by the the presence presence of of an an upper, upper, distinctly distinctly apple-green apple-green to to yellowish, yellowish, 30 �0 0.5 5.5 0.03 0.01 0.03 3 II 10 Concentration Ratio Concentration Ratio Figure Figure 11. Concentration ratios relative relative to to A1203 A1203 of of components components paleosol. of the Pronto paleosol 0 0.3 0.6 3 a. a, C 4.5 6 8.5 8.5 - 1 0.5 10.5 LOSS I I I llllll 0.03 0.01 I I I 1 0.03 lllll A"*G 1 <wm. "-G&+ 1 I Ill 3 10 Concentration ConcentrationRatio Ratio Figure 12 12 Figure Concentration ratios of components . Concentration components of Denison Denison . paleosol paleosol relative relative to to A1203. A1203. 31 �CD H' 0 (0 0 8 -o 0 CD F--' 9 Di ID a a 0 0 3 a -U 0 m J S S -. HDi '-I 0 CD L1 r 7 0 C 9C (/, 0 CD breccia Forrnaflon Paleosd Heqnalitc N N N zone III! 0 9 II +>+..+++JN 8 F-) gronite Marie 'Idle Transition C)- Di S hPJ I I 0' 0CD N) 6 U, ID Di H 30 7 C 0 (0 CD S J 0 0 F Poleosol 0 upward weathered Increasingly - Tonailte ________ Coglornerate t:ijaF:,? a, ?lt)/49 '_ F>-' F-' Di 0) —— — 0, CD 0 I p F I I I S . 7 0 Ca 0 C CD CD 0 -U :, ——.1 0 L - 0 3 0 Co 0 F-'- çt Di Fl -n a a D 0 CD J a — Di F-I C C CD Co C) (paieoscj) WgiIIite I pcileosot rich sericile CNoriie. I upward weathered Metabadt-increastngFy LL 0 C) U) CD I-' C tO H- �sericitic zone grades downward, downward, over a few sericitic zone which grades few centimetres centimetres to to several metres, to an underlying, underlying, black, black, fine-grained, several fine-grained, chloritechloriterich eluvial eluvial zone zone up up to to several several metres metres thick. thick. Abundant Abundant pseudomorphs of titanium pseudomorphs titanium oxides oxides after after ilmenite ilmenite are are a a feature feature of of paleosols clast of of sericitic sericitic paleosols on on mafic mafic igneous igneous rocks. rocks. Rip-up Rip-up clast paleosol paleosol (the (the "argillite "argillite scraps" scraps'' of of mine mine geologists) geologists) are are commonly commonly found overlying Matinenda Matinenda found in in the the lower lower few few metres of the overlying Formation. Prasad and Roscoe(l996) Roscoe(1996) report significant Formation. significant amounts amounts of of carbonate carbonate and and pyrite pyrite in in sub-Matinenda sub-Matinenda paleosols paleosols in in the the Elliot Elliot Lake Lake area. area. The uppermost uppermost sections sections of sub-Matinenda sub-Matinenda Formation Formation paleosols paleosols on on Archean granitic rocks and arkosic sedimentary rocks, are Archean granitic rocks and arkosic sedimentary rocks, are generally apple-green yellowish rock composed generally apple-green to yellowish composed mainly of quartz quartz and sericite(Robertson, (1980); Sutton Sutton sericite(Robertson,1963; 1963; Gay Gay and and Grandstaff Grandstaff(l980); and and Maynard(l992). Where the texture texture of the protolith is is well replaced, the preserved, preserved, but but the the original original mineralogy mineralogy is is replaced, the paleosol paleosol may be (Rainbird et et al, al, 1990). 1990). The chloritechloritebe termed termed aa saprolith saprolith (Rainbird eluvial zone of paleosols on granitic rocks rocks is generally rich eluvial lacking or lacking or relatively relatively thin. thin. Sub-Matinenda Sub-Matinenda paleosols commonly commonly show show the pronounced loss loss of soda soda found 11) . Lime, found in in most most paleosols paleosols(Figure (Figure 11). Lime, and magnesia are are also also depleted, generally a large depleted, but there is generally large increase increase in in potash In content (Figure 12) (Gay (Gay and Grandstaff, Grandstaff, 1990) 1990). In most cases, cases, content (Figure12) iron iron and and manganese manganese are are depleted depleted in in upper upper parts parts of of the the paleosol. paleosol. weathering in This This is is held held to to provide provide good good evidence evidence of of weathering in aa reducing environment. However, Gay and Grandstaff (1980) reducing environment. However, Gay and Grandstaff(l980) noted an an upward increase upward increase in in total iron iron in in paleosol from from the the Pronto Pronto Mine 11). They concluded concluded this this upward increase increase in in iron iron area (Figure11) area (Figure . They content indicated the presence of free content free oxygen in in the early Huronian atmosphere although Huronian although at approximately 1% 1% of the present level (Gay and Grandstaff, 1980). They suggested suggested that the loss loss of of (Gay Grandstaff, iron iron shown shown in in most Huronian Huronian paleosols paleosols could could be be due due to to local local reducing environments. Some writers have concluded that the reducing increase in sericite) in Huronian paleosols is largely increase in potash (as (as sericite) largely due which may mask the due to to diagenetic diagenetic and metamorphic processes which the environmental and hydrologic conditions operative during paleosol environmental conditions operative during paleosol development (1980); G-Farrow G-Farrow and Grandstaff(l980); and development (Gay (Gayand and Grandstaff Mossman(1988) Mossman (1988). . geochemistry of Sub-Lorrain Sub-Lorrain Formation The mineralogy and geochemistry Formation paleosols have been described by Rainbird et al. (1990) and paleosols have been described by Rainbird et a1.(1990) 33 �84W 82W N 1 .5 Th / r — Elliot Lake tJ •1 -46N 46N Channel B 0 $ 60km AfterZolnaj Zolnaietetal. d.(1984) (1984) After Legend [1111 Paleozc rocks Thrust fault, teeth indicate Mesoproterozoic rocks (Grenv,lle Province) Normal fault, spat indicates bangi wall downthrown side [III] Cobalt Group rocks Fault (observed, assirned) Pre - Cobalt Group rocks fl Pee—Cobalt Grow rocks derived from Archean basement rocks Archean basement rocks (Swerior Province) Anticline, syncline Manitoulin Isto-id Discontiroity -' Grenville Front Tectonic Zone (traceable on surface, traceable in subsurface) Location of cross sections ELF FLF Flock FlockLake LokeFault Foul1 ALF Agnew Lake Fouls MF Murray Fault MFS MFS SS MGB MGE EF M w r qFault Foul1 System Murray System Sudbury Structure McGrqa6ay b y McGregor Unwmei fault fwlt 22km kmnorth nonhofof Unnamed Espanola E ~ 0 " 0 1Fault 0 Fa"!? Figure Figure14. 14: Geological Geological cross-section cross-section of of the the Blind Blind River River and andSudbury-Maintou!in Sudbury-Maintoulinareas. areas 34 �Sutton and and Maynard(1991). Maynard(l991). In In contrast contrast to to the the older, older, sub-Matinenda sub-Matinenda Sutton paleosols, Sub—Lorrain Sub-Lorrain paleosols paleosols commonly commonly show show an an enrichment enrichment of of paleosols, Fe3 without a significant Fei3at at the the expense expense of of Fe2 Fe+2without significant loss loss of of total total iron iron (Figure (Figure13) 13). Hematite Hematite is is a a common common mineral mineral in in the the upper upper parts parts of of sub-Lorrain sub-Lorrain paleosols, paleosols, in in contrast contrast to to the the presence presence of of pyrite pyrite in sub-.Matinenda sub-Matinenda paleosols. sub-Lorrain in paleosols. In In this this respect respect the sub-Lorrain paleosols paleosols resemble resemble many many post-Huronian post-Huronian paleosols paleosols and and are are consistent with weathering in an oxidizing atmosphere consistent with weathering in an oxidizing atmosphere (Prasad (Prasadand and Roscoe, 1990), Rainbird et et al., al.,1990). Roscoe, 1996; 1996;Rainbird . Since Since pyrite pyrite and and uraninite uraninite are are unstable unstable under under oxidizing oxidizing conditions, the the abundance abundance of of detrital detrital pyrite pyrite and and uraninite uraninite in in the the conditions, paleoplacer uranium uranium ore ore zones zones in in the the Matinenda Matinenda Formation Formation provide provide paleoplacer good good evidence evidence for for an an oxygen oxygen deficient deficient atmosphere atmosphere during during weathering, weathering, transport transport and and deposition deposition of of early early Huronian Huronian sediments. sediments. In clastic In marked marked contrast contrast to to the the common common red beds of of younger younger clastic sequences, sandstones sandstones (and (andmost most granitic granitic clasts clastsin inconglomerates) conglomerates) sequences, below below the the Cobalt Cobalt Group Group are are almost almost all all drab drab coloured coloured in in spite spite of of the the abundance abundance of of red red and and pink pink granitic granitic rocks rocks in in the the continental continental source (1970)noted noted source area area (Roscoe (Roscoe1969, 1969,1973). 1973). Frarey Frarey and and Roscoe Roscoe (1970) the the above above and and proposed proposed that that the the drab drab colour colour of of lower lower Huronian Huronian clastic clastic rocks rocks is is due due to to the the lack lack of of free free oxygen oxygen in in the the atmosphere atmosphere during I-iuronian during the theperiod periodofofdeposition depositionofoflower lower Huronian rocks. rocks. Red Red hued, hued, hematite hematite bearing bearing rocks, rocks, which which Roscoe(1969) Roscoe(l969) proposed proposed mark mark the the presence presence of of an an oxidizing oxidizing atmosphere, atmosphere, make make an an appearance appearance with with the the Gowganda Gowganda Formation Formation of of the the Cobalt Cobalt Group, Group, and and are are important important in in parts parts of of the the Lorrain Lorrain and Gordon Gordon Lake Lake Formations Formations of of that that group. group. What What may may be be the the first first true true red-beds red-beds are are found found in in the the purple Lorrain Formation Formation near near Sault Sault Ste. Ste. purple siltstone siltstone member member of of the the Lorrain Marie Marie (Frarey, (Frarey,1977). 1977). Regional Regional Tectonic Tectonic Patterns Patterns and and Metamorphism Metamorphism Major Major structures structures of of the the Huronian Huronian belt belt follow follow two two main main trends: trends: l)west-northwest 1)west-northwest trending trending folds folds and and faults faults of of the the Sault SaultSte. Ste. Marie-Elliot 2)east to to northeast northeast striking striking folds folds Marie-Elliot Lake Lake area; area; and and 2)east and and faults faults of of the the Sudbury-Manitoulin Sudbury-Manitoulinarea area (Figure (Figure14) 14). These These two two structural structural orientations orientations are are associated associated with with differing differing fold fold styles, metamorphic grade and metamorphic fabric. Changes styles, metamorphic yrade and metamorphic fabric. Changes are are . 35 �notable across across the the east-west east-west faults faults of the Murray fault most notable Murray fault system. system. This This fault fault zone zone (Figure (Figure14) 14) is is the most significant significant structural structural feature feature of of the the Huronian Huronian belt. belt. Since Since many many formations formations significant increase increase in in thickness thickness south south of of the the fault, fault,it it show aa significant show is generally generally interpreted interpreted as as an an inverted inverted growth growth fault. fault. (i.e. (i.e. an an is early listric listric normal normal fault, fault, active active during during sedimention, sedimention,which, which, early during aa later later compressive compressive regime, regime, was converted to a thrust thrust or or during converted to reverse reverse fault fault (Card, (Card,l978a; 1978a; Jackson Jackson (1997) (1997). The subjected to The rocks rocks of of the the Huronian Huronian Supergroup have been subjected to several deformational deformational events. This is particularly south several particularly evident evident south of of the the Murray Murray Fault Fault zone. zone. In In the Whitefish Falls Falls area area (south (south of of the Murray Fault) Young and Nesbitt(l985) conclude that some the Murray Fault) Young and Nesbitt(1985) conclude that some large-scale large-scale folding folding is is related related to to syn-depositional syn-depositional and/or and/or postpostdepositional sediment. Early depositional deformation deformation of of unconsolidated sediment. Early syndepositional syndepositional deformation deformation is is also also indicated indicated by by an an important important unconformity unconformity below below the the Gowganda Gowganda Formation Formation of of the the Cobalt Cobalt Group; Group; and the presence of ragged, slumped contacts and large slump and the presence of ragged, slumped contacts large slump blocks 1978a; Young, Young, 1983) 1983). blocks along along major major faults faults (Card, (Card,1978a; Convincing Convincing evidence evidence of of at at least least one one important important pre-Nipissing pre-Nipissing(2.2 (2.2 Ga) deformational deformational event, event, assigned assigned to to the the Blezardian Blezardian Ga) Orogeny(Stockwe11, 1982), 1982), is is provided by the observation that Orogeny(Stockwell, observation that Nipissing area transect Nipissing bodies bodies in in the the Sudbury-Whitefish Sudbury-Whitefish Falls area transact axial Jackson (1997) axial surfaces surfaces of of major major folds folds (Card, (Card, 1978a). Jackson (1997) did did not observe observe such such relationships relationships in in the areas north of the the Murray Murray not Fault. However, However, Jackson Jackson (1997) (1997) points out, noted by by Fault. out, as earlier earlier noted Robertson (1964), that the tendency of Nipissing dikes to occupy dikes to occupy Robertson (1964), that the Chiblow Anticline, Anticline, structures parallel parallel to to the the axial axial plane plane of of the the Chiblow structures suggests pre-Nipissing pre-Nipissing folding. folding. Jackson Jackson (l997)also (1997)also noted noted evidence evidence suggests of pre-Nipissing pre-Nipissing faults faults north north of of the the Murray Murray Fault Fault zone. zone. of Following intrusions but prior prior to Following emplacement emplacement of of the the Nipissing intrusions to the the emplacement emplacement of of the the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) (SIC) there there was was further further deformation deformation and and regional regional metamorphism. metamorphism. Rb-Sr Rb-Sr isotope isotope studies studies on on Huronian Huronian metasediments metasediments indicate indicate that that prograde prograde metamorphism metamorphism occurred occurred at at about about 1.90-1.85 1.90-1.85 Ga Ga (Fairbairn (Fairbairnet et al., al., 1969) Jackson(1995) state state that this this event event is is probably probably 1969). Card Card and and Jackson(1995) correlative correlative with with the the Penokean Penokean Orogeny Orogeny of of Michigan-Minnesota Michigan-Minnesota (Simms (Simms et et al., al., 1989). 1989). . After After the the emplacement emplacement of of the the SIC SIC and and the the deposition deposition of of the the Whitewater deformation and Whitewater Group, Group, there there is is evidence evidence of further further deformation and 36 �64W BrW Legend 4&N fl LI -- &gresd,ist fades —— Apgroximote meianorphic diogenetic and epigenelic zones — Low to middle reenscthsi fades cfilorite aid biotite zones Middle to tçper greerchSi tomes garnet aid ctiloriioid zones focies basidory Grenvulle Front Tectonic Boundary of Nuronion Supergroup aid Sutury — Struc tire Ariwhibohte tac'es stourolite zone Prnvinciol boundary rid/s Hornblende— horniels focus Cobalt FeIs.c nirustorts 40 0 N 80 km N 4rN 1' Superior Province - ,,tt 9'? —a Figure 15. 15. Metamorphism Metamorphism of of the Huronian Huronian Supergroup Supergroup(From (From Card, Card, 1978b) 19780) 37 �low-grade low-grade metamorphism, metamorphism, followed followed by by intrusion intrusion of of granite granite plutons plutons at about about 1.75 1.75 and and 1.5 1.5 GaGa. The The post-SIC post-SIC deformation deformation and retrograde retrograde at metamorphism metamorphism was was found found mainly mainly south south of of the the Murray Murray Fault, Fault, especially in in the the area area between between the the SIC SIC and and the the Grenville Grenville Front. Front. especially Shanks and and Schwerdtner(1991) Schwerdtner(1991) report report that that this this deformation deformation is is Shanks characterized by south-dipping south-dipping thrust faults faults or deformation zones zones characterized with northeast-trending northeast-trending foliation foliation and and southeast-plunging southeast-plunging with lineation. affecting lineation. The The last last recognized recognized deformational feature affecting Huronian rocks rocks is is the the movement movement along along faults faults which which post-date post-date the the Huronian diabase dikes dikes of of the the 1.25 1.25 Ga Ga Sudbury Sudbury swarm swarm (Card (Card and and Jackson, Jackson, diabase 1995). 1995) Recent Recent work work on on magnetic magnetic fabrics, fabrics, strain strain patterns, patterns, and and microstructures microstructures in in granitoid granitoid rocks rocks of of the the Creighton Creighton and Murray plutons Riller(1996) have have plutons and and their their Huronian Huronian host host rocks rocks by by Riller(1996) provided provided aa wealth wealth of of new new information information on on the the pre-2.2 pre-2.2 Ga Ga "Blezardian Orogeny" (Stockwell, Blezardian Orogeny" (Stockwell, 1982). 1982). Riller Riller concluded concluded that that major folding folding and and amphibolite amphibolite facies facies regional regional metamorphism in in the the Sudbury Creighton and Sudbury area area was coeval coeval with the the emplacement of the Creighton Murray Murray Plutons, Plutons, which which were were dated dated at at 2.3 2.3 Ga Ga by by Frarey Frarey et et al(1982) al(1982) (1984) and more recently at 2477 9 Ma by and Krogh et al. and more recently at 2477*'9 Ma by Krogh Krogh and Krogh et al. . Large-scale Archean et al. al. (1996) (1996). Large-scale dome-and-basin dome-and-basin structures structures in in Archean et basement and and Huronian Huronian cover cover rocks rocks represent represent major major north-vergent north-vergent nappes. nappes. The The Sudbury Sudbury Structure, Structure, aa deformed deformed relic relic of of an an astrobleme, astrobleme, is Archean is superimposed superimposed on on a a major major antiformal antiformal dome dome cored cored by by Archean granulite and granitoid rocks and flanked by overturned 1-luronian granulite and granitoid rocks and flanked by overturned Huronian strata strata on on the the south south and and several several remnant remnant rim rim synclines synclines of of Iluronian Huronian rocks on on the the north north (Riller, (Riller,1996). 1996). rocks In In the Sault Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake area area fault fault and and fold fold structures trend in general west-northwest to northwest. structures trend in general west-northwest to northwest. Folds Folds are are generally generally upright, upright, open open concentric concentric structures structures with with gentle, gentle, variably variably plunging plunging hinges hinges (Figure (Figure 14). 14). There There is is only only aa weak weak development development of of minor minor tectonic tectonic structures. structures. The The metamorphic metamorphic grade grade 1978b). The major major structural structural features features of of is subgreenschist subgreenschist(Card, (Card, is l978b) . The the Elliot Lake area include a gently south-dipping homocline the Elliot Lake area include a gently south-dipping homocline south south of the the Flack Flack Lake Lake Fault, Fault, the the open open fold fold of of the the Quirke Quirke Lake Lake Syncline Syncline and and the the Chiblow Chiblow Anticlinè Anticline between between the the Quirke Quirke Lake Lake Syncline Syncline and and the the Murray Murray Fault. Fault. Jackson Jackson (1997) (1997) found found no no evidence evidence of detachment detachment at at or or near near the the basement-cover basement-cover interface interface in in the the Elliot growthElliot Lake Lake area. area. He He also also proposed proposed that that the the "inverted "inverted growthfault" (1984) to fault" model model as as applied applied by by Zolnai Zolnaiet et al. al.(1984) to structuralstructuralstratigraphic stratigraphic relationships relationships in in the the Huronian Huronian may, may, in in some some cases cases at at 38 �least, be interpreted interpreted as thrust faults faults with flats flats following following least, depositional boundaries, boundaries, and and ramps ramps that that cut cut up up through through the the depositional stratigraphic stratigraphic section. section. Given Given the the data data available, available, neither neither model model could could be rejected rejected for for major major northwest northwest trending trending faults faults in in the the Sault Sault Ste. Ste. Marie Marie area. area. (Jackson, (Jackson, in in press). press). Jackson Jackson (1997) (1997) points points out out that that the the curvature curvature of of the the Flack Flack Lake Lake Fault Fault is is in in the the opposite opposite direction direction to to that that expected expected if if it it is is aa thrust thrust fault fault as as proposed (1984). Zolnaiet etal. al.(1984). In the the Sault Sault Ste. Ste. Marie Marie area area proposed by by Zolnai In the the presence presence of of trust trust faults, faults, as as suggested suggested by by out-of-sequence out-of-sequence units, has has been been confirmed, confirmed, in in at at least least one one location, location, by by diamond diamond units, Ste. Marie Marie Resident Resident Geologist's Geologist's drilling (Assessment (Assessment files, files, Sault Sault Ste. drilling Office). South-southwest South-southwest dipping dipping foliation, foliation, and and south-southwest south-southwest Office). plunging foliation foliation may may reflect reflect north-northwest north-northwest thrusting plunging thrusting (Jackson, (Jackson,1994) 1994) . The The Murray Murray fault fault zone zone separates separates the the moderately moderately deformed, deformed, low low metamorphic metamorphic grade grade rocks rocks to to the the north north from from the the multiply-deformed, multiply-deformed, higher higher grade grade rocks rocks of of the the Sudhury-Manitoulin Sudbury-Manitoulinarea area to to the the south. south. The The Sudbury-Manitoulin Sudbury-Manitoulin area area is is characterized characterized by by open open to to subisoclinal, flattened flattened buckle buckle folds folds with with upright upright to to northward northward subisoclinal, overturned axial axial surfaces. surfaces. Elongate Elongate domes domes and and basins basins are are formed formed overturned by by reversals reversals in in plunge. plunge. Penetrative Penetrative axial axial place place cleavage cleavage and and steeply rodding or or mineral mineral lineation lineation are are well well developed. developed. steeply plunging plunging rodding More More than than one one age age of of major major and and minor minor structures structures can can be be discerned discerned south south of of the the Murray Murray Fault Fault (Card (Cardand and Jackson, Jackson, 1995) 1995). Metamorphism Metamorphism south south of of the the Murray Murray fault fault ranges ranges from from low low greenschist fades (Card, (Card, l978b). 1978b). Rocks Rocks of of greenschist to to low low amphibolite amphibolite facies higher higher metamorphic metamorphic grade grade occur occur in in two two zones zones or or nodes, nodes, one one along along the the Murray Murray Fault Fault zone zone and and another another northwest northwest of of the the Grenville Grenville Front. Front. Both Both zones zones coincide coincide with with major major anticlinoria, anticlinoria, although although in in detail, detail, metamorphic metamorphic isograds isograds transect transect fold fold axes axes (Card (Card and and Jackson, Jackson, 1995). 1995). Higher Higher grade grade metamorphic metamorphic nodes nodes do do not not coincide coincide with with the the few few granitic granitic intrusions intrusions which which intrude intrude the the Huronian Huronian rocks rocks south south of of the the Murray Murray fault. fault. The The 1.850-1.900 1.850-1.900 Ga Ga age age of of metamorphism metamorphism is is much much younger younger than than the the Creighton-Murray Creighton-Murray granite granite (2.45 (2.45 Ga) Ga) and and older older than than the the 1.700-1.750 1.700-1.750Ga Ga of of the the Chief Chief Lake Lake and and Cutler Cutler granites. granites. Jackson Jackson (1997) (1997) considers considers the the origin origin of of the the high-grade high-grade staurolitestaurolitebiotite biotite assemblages assemblages of of the the McKim McKim Formation Formation in in the the hanging hanging wall wall of of the the Murray Murray Fault Fault as as one one of of the the most most enigmatic enigmatic aspects aspects of of the the tectonic tectonic history history of of the the Southern Southern Province. Province. He He concludes concludes that that 39 �geobarometry metamorphism (2geobarometry indicates indicates a a relatively relatively low low pressure metamorphism (233 kbar) kbar) at at high high temperature temperature. These These conditions conditions differ differ significantly from from the the 6-7 6-7 kbar kbar pressures pressures estimated estimated for for the the significantly Penokean metamorphism in in Minnesota as determined by Holm and Penokean Balm and Silverstone(1990). Silverstone(1990). He He concluded concluded that that the the high-temperature high-temperature metamorphism was at or below pressure corresponding metamorphism was at or below pressure corresponding to to the the thickness thickness of of the the Huronian Huronian rock rock column, column, thereby thereby precluding precluding crustal crustal thickening thickening as as the the origin origin of of the the metamorphism. metamorphism. Jackson Jackson (1997) (1997) concluded areas of concluded that that a a high high heat flow flow regime developed in in areas of crustal crustal extension extension and and related related mantle mantle upwelling. upwelling. Such Such aa model model is is Card's(1964) view that the high-grade compatible with compatible with Card's(1964) view that the high-grade metamorphism metamorphism may may be be the the result result of of rapid, rapid, focused focused heat heat flow. flow. Tectonic Huronian Basin Basin Tectonic Models Models for for the the Development Development of the Huronian There for the early There have have been been various tectonic tectonic models proposed for early development basin. Many Many development and and later laterdeformation deformationofofthe the1-luronian Huronian basin. reconstructions reconstructions are are essentially essentially modifications modifications of of the the model model put put forth Holden(1966)which whichstated statedthat thatthe theJ-Iuronian Huronian forth by by Dietz Dietz and and Holden(1966) Supergroup represents a rift and passive margin sequence Supergroup represents a rift and passive margin sequence that that was was compressed, compressed, partly tectonically tectonically buried and metamorphosed during during aa collision collision with with the the Superior Superior craton craton and and another another mass mass which Zolnai et et al. al. (1984), (1984), Bennett Bennett which overrode overrode its its southern southern edge. edge. Zolnai et et al. al. (1991) (1991) accept the essential aspects of the Dietz Dietz and and Holden Holden (1966) (1966) model. They They propose that rifting rifting and continental continental breakup breakup was was coeval coeval with with Huronian Huronian volcanism volcanism (2.45 (2.45 Ga) Ga) and and that that the the much much later later deformation deformation was was equivalent equivalent to to the the Penokean Penokean Orogeny Orogeny (1.860-1.835 (1.860-1.835Ga) Ga). This This model model does does not not attempt attempt to to account account for for the the multiple multiple deformation deformation events events affecting affecting Huronian Huronian rocks rocks and and the the origin of the Nipissing magmatic event. origin of the Nipissing magmatic event. . Young Huronian Supergroup Young (1982) (1982) proposed proposed that the the Huronian Supergroup was deposited deposited in in an an aulocogen, aulocogen, an an easterly easterly trending trending fault fault bounded bounded trough trough which which opened opened towards towards an an ocean ocean in in the the area area now now occupied occupied by by the the Grenville Grenville Province. concluded that that the the Huronian Huronian Province. Sims Sims et et al. al. (1980, (1980, 1981) concluded Supergroup, Animikie rocks rocks Supergroup, the the Marquette Marquette Range Range Supergroup Supergroup and and Animikie were were deposited deposited as as intracontinental, intracontinental, fault fault controlled controlled basins basins developed along a major, late Archean structure, the Great Lakes developed along a major, late Archean structure, the Great Lakes Tectonic Tectonic Zone. Zone. More More recently, recently, Roscoe Roscoe and and Card Card (1992), (19921,noting noting the the close close stratigraphic stratigraphic correlation correlation between between the the Early Early Proterozoic Proterozoic sequences sequences 40 �of Supergroup, proposed of the the Wyoming Wyomingcraton cratonand andthe theI-iuronian Huronian Supergroup, proposed that that the the Superior Superior and and Wyoming Wyoming cratons cratons are are rifted rifted portions portions of of what what was was once once aa single single continental continental land land mass. mass. They They suggest suggest the the direction direction of of the the Matachewan-Hearst Matachewan-Hearst dike dike swarm swarm (2.45 (2.45 Ga) Ga) indicates indicates an an easteastwest west tensional tensional regime regime which which resulted resulted in in aa Huronian Huronian basin basin elongated elongated in in aa north-south north-south direction. direction. On On this this larger larger craton craton the the Huronian sediment was deposited in a southward deepening Huronian sediment was deposited in a southward deepening intracratonic intracratonic basin. basin. Roscoe Roscoe and and Card Card (1992) (1992) propose propose that that it it was was during during the the Nipissing Nipissing igneous igneous event event (2.2 (2.2 Ga) Ga) that that successful successful rifting rifting of of the the Superior Superior Province Province took took place place with with the the eventual eventual drifting drifting of of part part of of the the missing portion portion to to its its present present location location as as the the Wyoming Wyoming craton. craton. They attribute attribute pre-Nipissing pre-Nipissing folding folding to to the the Blezardian Blezardian Orogeny Orogeny of Stockwell Stockwell (1982) (1982) and and the the later later more more important deformation deformation to to be coeval coeval with the Penokean Penokean Orogeny Orogeny of of important Michigan, 1992). Michigan, Wisconsin Wisconsin and and Minnesota Minnesota (Roscoe (Roscoeand and Card, Card,1992). Jackson Jackson (1997) (1997) supports supports the the model model of of Roscoe Roscoe and and Card Card (1992) (1992) since since the the high high heat heat flow, flow, which he he considers considers necessary necessary to to give give the the observed observed features features of of the the high-grade high-grade metamorphic metamorphic rocks, rocks, would would be be aa necessary necessary effect effect of of mantle mantle upwelling upwelling during during continental continentalbreak-up. break-up. He He also also interprets interprets some some of of the the early early high-strain high-strain deformation deformation as as being being consistent consistent with with aa Nipissing Nipissing age age break-up break-up of of the the Superior Superior craton. craton. 41 �ROAD ROAD LOG LOG -- HURONIAN SUPERGROUP SUPERGROUP BETWEEN BETWEEN SAULT SAULT STE. S T E . MARIE AND AND ELLIOT E L L I O T LAKE LAKE INTRODUCTION INTRODUCTION Some Some of of the the outcrops outcrops briefly briefly described described below below will will not not form form aa part part of of the the present present ILSG ILSG field field trip. trip. They They are are included included to to allow allow those those interested interested to to visit visit them them if if travelling travelling in in the the area area at at some some future future date. date. UTN UTM coordinates coordinates have have been been provided provided for for some some locations locations for for those on a map, map, or those who who may may wish wish to to plot the locations locations on or who who may may have have aa GPS GPS device. device. The The accuracy accuracy is is about aboutSO 50m. m. ROAD LOG ... DAY 1 Proceed Proceed east east along along Highway Highway 17 17 from from Sault Sault Ste. Ste. Marie. Marie. The The road road log log starts starts at at the the intersection intersection of of Highway Highway 638 638 and and Highway Highway 17 17 East East in in the the Town Town of of Echo Echo Bay Bay 0.0 638 at 0.0 km km -- 0.0 0.0 miles miles -- Highway Highway.638 at Echo Echo Bay Bay -- continue continue east east on on Highway Highway 17. 17. 44 km km -- 2.5 2.5 miles miles -- Start Start of of divided divided highway highway 7.9 7.9 km km -- 4.9 4.9 miles miles -- At At sign sign for for Calabogie Calabogie Road Road (UTH (UTM 1616- 55 144 144 004 Sub-Jacobsville 004 N, N, 725 725 322 322E). E). Sub-Jacobsvilleunconformity unconformity Outcrop Outcrop on on west west side side of of Highway Highway 17. 17. The The most most southerly southerly outcrop outcrop is is white white and and grey grey quartzite quartzite (quartz (quartzarenite) arenite) of of the the white white orthoquartzite (Frarey,1977) 1977) of of the the Lorrain LorrainFormation Formationis is orthoquartzitemember member (Frarey, overlain overlain by by aa basal basal sharpstone sharpstone conglomerate conglomerate of of the the Keweenawan Keweenawan Jacobsville Formation. The conglomerate conglomerate is is comprised comprised of of angular angular Jacobsville Formation. The clasts Lorrain quartzite quartzite up up to to 60 60 cm cm across across in in aa red red siltstone siltstone clasts of of Lorrain matrix. matrix. The The contact contact is is irregular. irregular. No No stratification stratificationwas was observed. observed. 20.0 20.0 km km -- 12.7 12.7 miles. miles. Highway Highway to to St. St. Joseph Joseph Island. Island. Continue Continue east east on on Highway Highway 17. 17. 42 �a U) 4 + / + -I- + 4 + + -t- + + -p-"- + I + + + 'I- + ++ + + 7 + ± ¼, + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +_.i- + + + + + + + .p• + + + + + + + 4 + + + + + + r + + + 4+ ++ -' 4 — . _+ + + + + + + + + + + + + + + + + + + + + + ++ +-F+ + + + + + + + + + + + + (' + + + + + + + +_-'{+ + + + + + area. + + + IL,j: 4 + + Archean rocks — + + + + + + + + +•'+ +/+ + + + + + + + + + #+ + + + + + + + + + + + + + + +)+ 50km + +'tf- -k •'_+ + + + + + ,* + + + 4 + + + + + + + + + + + + + + + +%, + +_•.+ + + + + + + + + + *.+ + + + + + 4- + East Bull Lake Suite (Gabbro-Anormosite) ,_+ Murray Fault + Elliot Lake, -lough Lake and Quirke Lake Grouos Huronlan Supergroup Cobalt Group + ++1+ -+ + +.+ ' + .+-'+ ++ + - +,I' + + See Flr7rjrer 16,17 & 181cr remair-ng stops eIdtripatop Faults Cutler Granite + LEGEND + Paleazolc and Keweenawan racks .AKE HURON + + + —.— T1IIIfl Thessalon ,+ '1- + —'+ + + + + + + + + —______ +—c+ + + +#.. + + + + + Figure 16. The distribution of rocks of the Huronian Supergroup. Sault Ste. Marie-Elliot Lake + t t North '-1:, �25.0 25.0 km km -- 15.5 15.5 miles miles STOP Lorrain Formation Formation 1: Lower Lower red red quartzite member of the Lorrain STOP 1: (Frarey, (Frarey,1977) 1977). (Refer (Refer to to Figure Figure 16) 16). . - On On the the north north side side of of Highway 17 steeply dipping beds of the the lower lower member well preserved preserved member of of the the Lorrain Lorrain Formation Formation reveal well oscillation oscillation ripples ripples on on aa large large south south facing facing surface. surface. red red Note: Note: the the differing differing ripple ripple directions directions and and local local interference interference ripples. This This impressive impressive outcrop outcrop is known locally "Ripple ripples. locally as the "Ripple Rock". Rockw. Main Street Street in in the the town town of of Desbarats Desbarats (pronounced (pronounced"Debarah" "Debarah" 1 Main 26.8 26.8 km km -- 16.6 16.6 miles miles STOP STOP 2: 2: Purple Purple siltstone siltstone member member of of the the Lorrain Lorrain Formation. Formation. Dark Dark red red to to purple purple siltstone siltstone and and sandstone sandstone constitute constitute true true redredbeds 1977) in in the the Huronian. Huronian. These These hematite-rich hematite-rich rocks rocks beds (Frarey, (Frarey,1977) display the the reduction reduction along along fractures fractures typical typical of of red red beds, beds, and and aa display good good indicator indicator of of deposition deposition in in an an oxidizing oxidizing environment. environment. The The bedding 140 and and dipping dipping bedding is is faint, faint, but but locally locally distinct, distinct, striking striking 140° 10° 1O0 south. south. 27.7 27.7 km km -- 17.2 17.2 miles miles Lake Lake Huron Huron Drive Drive in in the the town town of of Desbarats Desbarats 28.0 28.0 km km -- 17.4 17.4 miles. miles. STOP STOP 3: 3: Basal Basal Arkose Arkose Member Member of of Lorrain Lorrain Formation. Formation. UTM UTM Zone Zone 17. 17 275461N, 275461N, 5l36234E. 5136234E. Large Large outcrops outcrops of of pink, pink, medium—grained medium-grained , rather rather massive massive arkose arkose beds beds with with hematite-rich hematite-richspots spots about about one one centimetre centimetre across. across. Pale Pale laminations in outcrop on south side of the road indicate shallow laminations in outcrop on south side of the road indicate shallow dips loowest. west. The The unit unit is is about about 1700 1700 feet feet thick thick in in dips of of about about10° this this area area (Frarey, (Frarey,1977). 1977). , 40.5 km -- 25.0 25.0 miles miles copper copper bearing bearing quartz quartz vein vein in in town town of of Bruce Bruce 40.5 km Mines. Mines. In 17, in in the the town town of of In aa rock-cut rock-cut on on the the north north side side of of Highway Highway 17, 44 �Bruce Bruce Mines, Mines, is is aa 33 metre metre wide wide quartz quartz vein vein in in Nipissing Nipissing diabase. diabase. The The vein vein contains contains small small amounts amounts of of chalcopyrite, chalcopyrite,chalcocite, chalcocite, bornite bornite and and malachite. malachite. It It is is one one of of the the few few remaining remaining remnants remnants of of the the copper copper mineralization mineralization that that once once made this this town town known known throughout throughout the the mining mining world. world. Mining Mining began began here here in in 1846 1846 and and continued continued to to 1875, 1875, making making Bruce Bruce Mines Mines the the first first mining mining town town in in Canada. Please do do not not take take samples samples from from this t h i s outcrop. outcrop. Canada. Please About 75 metres metres north north of of this this outcrop outcrop there there is is aa reconstruction reconstruction About 75 of of aa copper copper mining mining operation operation of of that that period period built built on on one one of of the the original mine workings, known as the "Simpson Shaft". original mine workings, known as the "Simpson Shaftn. During During the the summer summer months months the the Simpson Simpson Shaft Shaft site site is is open open as as aa tourism tourism operation. operation. 42.6 42.6 km km -- 26.5 26.5 miles miles Entrance Entrance to to the the quarry quarry of of Ontario Ontario Trap Trap Rock Rock (R.W. (R.W. Tomlinson Tomlinson Limited). Limited)'.The The quarrying quarrying of of trap trap rock rock (Nipissing (Nipissing diabase) diabase) at at Bruce Bruce Mines predecessor near near the the lake lake operated operated Mines resumed resumedin in1990. 1990. AA predecessor during during the the First First World World War. War. 45.1 45.1 26.0 28.0 Highway 17-5 Highway 17 17 17-5 129 129 846N, 846N, 289 289 Sl2E, 512E, Low Low outcrops outcrops of of Mississagi Mississagi Formation. Formation. Waltonen Waltonen Road Road at at 45.4 45.4 km km or or 28.2 28.2 miles miles at at east east end end of of outcrop. outcrop. Medium-sand Medium-sand to to grit-sized, grit-sized,grey1 grey, subarkose subarkose with with thin thin quartzquartzpebble pebble beds beds and and prominent prominent planar planar cross-bedding cross-bedding are are well well exposed exposed along along the the north north side side of of the the highway. highway. Rusty Rusty staining staining on on the the outcrop detrital(?) pyrite pyrite along along the the foreset foresetbeds. beds. outcrop reflects reflects minor minor detrital(?) Black Black chert chert pebbles pebbles in in pebbly pebbly beds, beds, minor minor pyrite pyrite and and metre metre scale scale bedding bedding are are common commonfeatures featuresof of the the Mississagi Mississaqi Formation. Formation. Roscoe, Roscoe, (1969) (1969) concluded concluded that that the the drab drab colour colour and and presence presence of of detrital detrital pyrite pyrite in in Huronian Huronian sandstones sandstones and and conglomerates conglomerates is is evidence evidence of of the the reducing reducing nature nature of of the the early early Huronian Huronian atmosphere. atmosphere. 60.6 60.6 km km -- 37.6 37.6 miles miles Intersection Intersection of of Highway Highway 17 17 and and Highway Highway129. 129 UTM Zone 17 303590E, 17-5126450N UTM Zone 17 - 303590E, 17-5126450N STOP STOP 4: 4: Thessalon ThessalonFormation Formationtholeiitic tholeiiticbasalt. basalt. Refer Refer to toFigure Figure17. 17. Dark Dark green, green, fine fine to to medium medium grained grained basalt basalt is is exposed exposed on on the the east east 45 �+ ± + + + + -I + -l + ÷ -I + + -l + + -I ÷ -I -4 4 4 at— -1 + 2"/j5S 4jçr74Cv Thessalon -l Lake Huron IL EGEND EGEND Thessalon lhessalonFm Fm Basalt, andesite. rhyolite rflyolite Basait. andesite. Nipissing Nipissing Gabbro. Gobbro.diabase. diabase,granophyre granophyre A MississadFm. Fm. Mississagi Subarkose,pebble pebbk conglomerate conglomerate Subarkose, 3 AAA AAA High magnesium basalt High magnesium basalt felsic pyroclastic rocks fetsfc flows, flows, pyroclostic rocks Frn MdinendaFm Malinendo Subarkose. arkose %barkose.ark- Arkose, quartz-pebble conglomerate conglomerate Arkose, quartz-pebbk (localty pyriticand and radioactive) radioacWe) (iocalty pyritic quartz-pebble quartz-pebble conglomerate conglomerate Iivlngstone Cr.Fm. Fm. livingstoneCr. Anticlinal ax // X Nkose. conglomerate Arkose, polymictic conglomerate Synclinal axis Archeon Afchean Plutonic and and gneissic gneissicgranite graniterocks, rocks, rnigmatite migmatite N 25 00 Bedding attitude attitude Fault Fault * / 1 I * + 22 d km krn I I Field trip stop - Figure 17. Figure 17. Geology of of the the Thessalon Thessalon Area Area 46 �north of the intersection intersection with Highway side of Highway 129 just north 17. Thessalon 17. This tholeiitic tholeiitic basalt forms the top of the Thessalon Formation Formation in in the Thessalon area and is typical of the thicker thicker tholeiitic tholeiitic sequences sequences which which make make up up the the upper upper parts parts of of the the Aberdeen Township Township Thessalon Formation in the Sault Ste. Marie and Aberdeen The rocks areas. The rocks consist consist of albite, albite, chlorite, chlorite, epidote, epidote, clinozoisite, leucoxene minor quartz clinozoisite, leucoxene and minor quartz and and oxides. oxides. The The metabasalt contains amygdules albite, quartz, quartz, epidote, epidote, calcite s of albite, contains amygdule calcite and chlorite. relatively small, monomineralic monoimineralic chlorite slatively small, chlorite chlorite. The .. The . r< . buttons") .. , are amygdules amygdules ("chlorite ("cniorite buttons"; are characteristic cnaracteristic of of the the mafic mafic volcanics Ste. Marie and and volcanics of the Thessalon Formation between1 Sault Ste. Elliot Lake. Elliot Lake. 7 7 Glacial striae and cnaci-er chatter marxs marks are we± well aeveloped developed on the the striae ana outcrop surface. outcrop surface. Proceed north 129. Reset Reset odometre odometre to to 00 00 at at Proceed north on on Highway Hi< Intersection of Higl Highway 17 andd Highway Highway 129. 129. Intersection 1.0 miles km -- 0.62 0.62 miles 1.0 km STOP 5: Outcrop of Matinenda Formation Formation on east side of Highway 129. 129. This pink to greenish grey, grey, subarkose which This fine-grained, fine-grained, pale pink directly Thessalon area directly overlies the Thessalon Formation in the Thessalon has been correlated with with the Matinenda Matinenda Formation of of the Elliot al., 1991). Faint outlines of trough Lake Group (Bennett (Bennett et al., cross-bedding, visible on the upper cross-bedding, upper surface surface of of the the outcrop, outcrop, indicate paleocurrent directions directions from the northwest. northwest. The The greenish greenish (sericitic) units and and the the trough trough cross-beds cross-beds are typical of the (sericitic) units the Matinenda Formation, but the fine grain size is not. At Thessalon Formation, At Thessalon Point about 4 contain 4 km southwest of this location these rocks contain thin quartz pebble conglomerate thin quartz conglomerate units, units, but but the the pyrite pyrite and and radioactivity, radioactivity, characteristic characteristic of of the the Matinenda Matinenda Formation Formation of of the the Elliot Lake Lake area, area, are are lacking. lacking. village of Warncliffe 23.0 km -- 14.9 14.9 miles The village 23.0 km north end 29.1 km km -- 18.4 end of of Appleby Appleby Lake. Lake 18.4 miles north 47 �30.3 3 0 . 3 km km -- 19.4 19.4 miles miles UTM UTM 17, 17, 5 144 748N, 320 320 904E 904E STOP 6: 6: Laminated Laminated siltstone siltstone of the Gowganda Formation Formation on on scarp scarp STOP west west of of Highway Highway 129. 129. (Refer (Refer to to Figure Figure 16.) 16.) Proceed Proceed up up steep steep slope slope to to scarp scarp located located aa few few tens tens of of metres metres into into the bush. bush. the Vertical Vertical joint joint faces faces in in laminated laminated siltstones-mudstone siltstones-mudstoneof of the the Gowganda Formation Formation form form an an impressive impressive cliff just just west of of Highway Highway Gowganda 129. The The bedding bedding comprises comprises regular regular and and remarkably remarkably continuous continuous 129. mudstone-siltstone couplets from 0.5 to 2 cm thick. mudstone-siltstone couplets from 0.5 to 2 cm thick. The The grey grey siltstone siltstone unit unit at at the the base base of of each each couplet couplet grades grades up up to to aa darker darker mudstone mudstone which which is is in in sharp sharp contact contact with with the the siltstone siltstone base base of of the the resembles varves vanes of overlying overlying couplet. couplet. The sequence closely resembles of Pleistocene few pink, pink, discontinuous, discontinuous,fine, fine, Pleistocene glacial glacial lakes. lakes. AA few sandstone sandstone beds beds are are also also present. present. Widely boulder-sized Widely scattered scattered through through the sequence are pebble to boulder-sized Archean granitic granitic rocks. rocks. In In the the "drop stones", stones", predominantly predominantly of Archean "drop absence absence of of volcanic volcanic activity activity within within the the Gowganda Gowganda Formation, Formation, the the only plausible source of the drop stones is the presence of only plausible source of the drop stones is the presence of floating floating ice ice which which released released its its rock rock load load during during melting. melting. This This outcrop, outcrop, and and many many others others of of aa less less spectacular spectacular nature, nature, provide provide some some of of the the best evidence evidence for for aa cool cool climate climate during during Gowganda Gowganda time. time. interpret the the laminated unit unit as a varved Church and and Young, Young, (1972) interpret Church sequence. They They also note the presence of small small sedimentary sedimentary sequence. clasts, lithologically similar to the enclosing rocks. clasts, litholoqically similar to the enclosing rocks. They They interpret interpret the the clasts clasts of sedimentary sedimentary rocks rocks as as having having been been derived derived from upper surface from the the ablation ablation of sediment sediment on on the upper surface of of the the glacier. glacier. reported pyritic, pyritic, carbonaceous carbonaceous inclusions inclusions and and Jackson, (1971) reported Jackson, "fossil fossil gas gas bubbles", bubbles", which which he he considered considered to to be be biogenic biogenic origin, origin, associated associated with with drop-stones drop-stones at at this this location. location. 30.9 km km -- 19.5 19.5 miles. miles. Intersection Intersection with with Highway Highway 554. 554. Return Return to to 30.9 Thessalon along Thessalon along Highway Highway 129. 129. Intersection of Highway 17 and 30.9 km km -- 19.5 miles. Intersection and Highway Highway 19.5 miles. 30.9 129 at at Thessalon. Thessalon. Reset Reset odometer odometer to to 0.0. 0.0. 48 �2.6 miles. 2.6 km km -- 1.6 1.6 miles. 17- 126567N. 126567N. Green Lane. Lane. Cross Cross UTM 306085E, 306085E, 17railway tracks (with (with care) and immediately immediately turn left then then south south railway tracks to short short section section of of unpaved unpaved road road between between private private properties. properties. Outcrops of Thessalon Formation felsic metavolcanics lie at the Outcrops end end of of the the road. road. STOP 7: Rhyolite Rhyolite of of the the Thessalon Thessalon Formation. Formation. (Refer STOP 7: (Refer to Figure Figure 17) . 17) Volcanics are Volcanics are fine fine grained, grained, grey to to pink and maroon rhyolite rhyolite (Table consisting of a fine (Table 2) consisting fine grained grained mosaic mosaic of of albite, albite, K-feldspar, and K-feldspar, and quartz quartz with minor minor green green pleochroic pleochroic biotite. biotite. Amygdules Arnygdules are are filled filled with with quartz, quartz, biotite biotite and and stilpnomelane. stilpnomelane. Collapsed iron staining Collapsed vesicules are also present. Local iron staining and darker chloritic darker chloritic areas areas indicate indicate the the presence presence of of iron iron sulfides. sulfides. 5.9 km 3.6 miles. miles. km -- 3.6 At Pine Pine Ridge Ridge Road Road Reset odometre odometre to to 000 000 Intersection of 17 and and Pine Pine Ridge Ridge Road. Road. Intersection of Highway Highway 17 (south) onto Pine (south) Pine Ridge Ridge Road. Road. 2.9 1.8 miles. miles. 2.9 km km -- 1.8 property. property. At Lake Lake Huron. Huron. Turn right Turn right Causeway to Causeway to private private NOTE: In residents there will be NOTE: In consideration consideration of the privacy of residents no road road log log for for the the next next four four stops. stops. STOP STOP 8: 8: Sub-Livingstone Sub-Livingstone Creek Creek Formation Formation regolith. regolith. NOTE: NOTE: High High water water levels levels on on Lake Lake Huron may prevent access to part of this this area. area. Supergroup is exposed near The granitic granitic basement to the Huronian Supergroup the predominantly the shore shore of of Lake Lake Huron. Huron. The granitic rocks rocks are predominantly red to red to grey grey coloured coloured with with zones zones of of mafic mafic xenoliths. xenoliths. sub-Livingstone Creek This will be a brief stop to examine sub-Livingstone Formation regolith Archean granitic granitic rocks. rocks. This This Formation regolith on on the the lowermost lowermost Archean sub-Livingstone Creek sub-Livingstone Creek Formation Formation unconformity unconformity is is the the lowermost lowermost unconformity A saprolitic paleosol is is unconformity in in the the Huronian Supergroup. A not as sub-Matinenda as well developed developed as at the well studied sub-Matinenda 49 �paleosol of paleosol of the the Elliot Elliot Lake Lake area. area. On fine-grained On a a 22 by S5 m outcrop at the waters edge, grey, fine-grained arkosic sandstone sandstone surrounds arkosic surrounds sub-rounded sub-rounded blocks blocks of grey to reddish reddish granitic basement. granitic basement. The The granitic blocks appear appear to to be in in place or place or only slightly slightly dislocated. dislocated. only tens of of metres metres further east, east, very very On shoreline shoreline outcrops a few tens fine-grained steeply dipping, silicious fine-grained steeply dipping, silicious veins veins may may also also be be related related Locally, sandstone to the the pre-Livingstone pre-Livingstone Creek Creek weathering. weathering. Locally, sandstone filled seams (fissure or crack filling) appear to dip filled seams (fissure filling) appear to dip steeply steeply to to the east, east, i.e. i.e. about about perpendicular perpendicular to to the the paleosurface. paleosurface. the Return to Return to the the driveway. driveway. STOP 9: STOP 9: Base of the Livingstone Livingstone Creek Creek Formation. Formation. About 3 3 m m of of fine-sand fine-sand to to grit-sized, grit-sized, grey grey sandstone sandstone of of the the Livingstone Livingstone Creek Creek Formation Formation is is exposed exposed in in outcrops outcrops along along the the short short ascent ascent to to the the driveway. driveway. Although Although neither neither the the contact, contact, nor nor a complete Archean basement complete transition transition zone zone between the Archean basement granite granite and 1-juronian Supergroupare areexposed, exposed,these these sandstones sandstones are are only only a and Huronian Supergroup few few metres (stratigraphically) (stratigraphically) above the Livingstone Livingstone Creek Creek Formation—Archean unconformity. Formation-Archean unconformity. At the section, the Livingstone Creek the base base of of the the short exposed section, sandstone sandstone is is massive and has a few few scattered scattered (matrix (matrix supported), supported), well-rounded well-rounded to to sub-rounded sub-rounded granitic granitic cobbles cobbles and and boulders. boulders. The The diffuse edges and embayments of of some some clasts clasts suggests suggests that that they they diffuse have have undergone undergone little little transportation transportation and and may may be be core core stones stones of of weathered granitic blocks, weathered granitic blocks. Widely distributed distributed rusty rusty areas areas up to to 4 4 cm cm across across indicate indicate the presence of sulfide sulfide concentrations concentrations (nodules?). The basal basal portion portion of this section section may may be be paleosol or paleosol or material derived from paleosol. The material from adjacent adjacent paleosol. The upper upper part part of of the the exposed sandstone The exposed sandstone section section shows shows trough trough cross-bedding. cross-bedding. The recessive weathering pattern indicates indicates that carbonate recessive carbonate is is prominent along foreset beds. beds. prominent along the the foreset STOP STOP 10: 10: member of of the Livingstone Livingstone Creek Formation Conglomerate member Formation A A low low outcrop outcrop adjacent adjacent to to the the driveway driveway on on private private property. property. 50 The The �rocks are are clast.-supported clast-supported polymictic commonly rocks polymictic conglomerate conglomerate which which commonly forms the the lowermost lowermost member member of of the the Livingstone Livingstone Creek Creek Formation. Formation. forms The boulder-sized clasts The conglomerate conglomerate is is made made up of cobble cobble and boulder-sized clasts to white-weathering white-weathering massive, and of pale-grey pale-grey to massive, porphyritic porphyritic and gneissic granitic rocks rocks with with some some foliated foliated amphibolite amphiboliteand andmat mafic gneissic granitic ic plutonic plutonic rocks. rocks. There There are a few few thin beds of intercalated coarse intercalated coarse arkose. arkose. No No clasts clasts of of Huronian Huronian volcanic rocks rocks have have been been identified identified in the the Livingstone Livingstone Creek Creek Formation. Formation. The polymictic polymictic clast clast population, population, sorting sorting and size size indicate indicate The deposition in in aa high high energy energy environment environment such such as as an an alluvial alluvial fan. fan. deposition Although the the grey grey colour colour is is dominant dominant in in these these conglomerates, conglomerates, the the Although pink to basement rocks, rocks, is is to red red colour, colour, common common in in the the Archean basement scarce scarce or or lacking lacking in in the the conglomerate conglomerate clasts. clasts. This This colour colour difference between between the the clasts clasts and and the the source source granites granites may may be be due due difference preto reduction reduction of of ferric ferric iron iron in in the the feldspar feldspar lattice lattice during during preto Huronian Huronian weathering weathering or or diagenesis. diagenesis. STOP STOP 11: 11: Base Base of of the the Thessalon Thessalon Formation Formation -- Sedimentary Sedimentary rocks rocks of of the the Thessalon Thessalon Formation. Formation. Fine Fine to to medium medium sand-sized, sand-sized, cross-bedded cross-bedded dark-grey dark-grey sandstone sandstone marks marks the top top of of the the Livingstone Livingstone Creek Creek Formation Formation is is this this area. area. The The the grey grey colour, colour, recessive recessive weathering weathering along along the the foreset foreset beds, beds, and and the the restricted range range of of clast clast size, size, is is characteristic characteristic of of the the restricted sandstone member member of of the the Livingstone Livingstone Creek Creek Formation. Formation. sandstone Near Near the the water water line line on on the the west west side side of of the the outcrop, outcrop, aa thin thin unit unit (a few cm cm thick) of radioactive, radioactive, quartz-pebble quartz-pebble and and cobble a few cobble conglomerate, 040' and and dipping 45"west, lies on on the the conglomerate, striking striking O4O 45west, lies upper upper surface surface of of the the grey grey sandstone sandstone of the Livingstone Livingstone Creek Creek Formation. The The conglomerate conglomerate consists consists predominantly of pale-grey pale-grey Formation. predominantly of and dark-grey pebbles and dark-grey to to black, black, well-rounded well-rounded quartz pebbles and cobbles cobbles up bed is, in turn, turn, overlain 10 cm cm across. across. The conglomerate bed overlain up to to 10 by by aa unit unit of of massive massive to to cross-bedded, cross-bedded, grey grey grit grit and and arkose arkose which which forms forms the the basal basal unit unit of of the the Thessalon Thessalon Formation Formation in in the the area. area. displacement of of the the quartz quartz pebble pebbleconglotherate conglomerate Note: the the 55 mm displacement Note: along along aa steeply steeply dipping dipping dextral, dextral, northwest northwest striking striking fault. fault. Diamond Huron in Diamond drilling drilling done done from from the the ice ice of Lake Huron in the the 1970's 1970's indicates indicates that that the the volcanic rocks rocks which form the the bulk of of the the Thessalon are at at Thessalon Formation Formation directly directly overlie overlie the the grit grit unit unit but are 51 �this this location location covered covered by by the the lake lake waters. waters Measurement gamma ray Measurement of of gamma gamma radiation radiation made with a McPhar TV1A gamma ray spectrometer are spectrometer are given given below: below: Livingstone Tl=2,000; T2=60; T2=60; T3=30 T3=30 Livingstone Creek Creek sandstone: sandstone: Tl=2,000; Quartz Pebble Quartz Pebble Conglomerate Conglomerate (Thessalon (ThessalonFormation) Formation) T2=700; T3=6O T2=700; T3=60 T2=U+Th; Th. where Tl=K÷U-i-Th; Tl=K+U+Th; T2=U+Th; T3 == Th. where : : T1=20,000; Tl=20,000; measurements in measurements in counts/mm counts/min Earlier radioactive Earlier writers writers have have (reasonably) (reasonably) concluded that the radioactive conglomerate conglomerate is is aa unit unit of of the the underlying underlying Livingstone Livingstone Creek Creek concluded that the Formation. However, Formation. However, Bennett Bennett et et al. al. (1991) concluded the radioactive stratigraphically radioactive conglomerate conglomerate at this locality is stratigraphically equivalent and significantly significantly equivalent to to the the Thessalon volcanic rocks and younger than younger than the the Livingstone Livingstone Creek Creek Formation. Formation. Some Some of of the the evidence evidence for for this this conclusion conclusion is is as as follows: follows: 1. Radioactive conglomerates occur within within the the volcanic volcanic flows near 1. Radioactive the base of the Thessalon Formation in the Sault of the Thessalon Formation in Sault Ste. Ste. Marie Marie area area (Hay, 1963) 1963) and the Aberdeen Aberdeen Lake (Hay, Lake area area (Bennett, (Bennett,1982) 1982). 2. At At a few few localities localities in in the Quirke Lake Syncline Syncline radioactive radioactive conglomerate below the Thessalon Thessalon conglomerate and and arkose are found directly below Formation Formation flows flows upon upon the the Archean Archean basement where where the the Livingstone Livingstone Creek Formation Creek Formation is is not not present. present. 3. No quartz-pebble 3. quartz-pebble conglomerate conglomerate has has been identified identified anywhere anywhere within within the the Livingstone Livingstone Creek Creek Formation. Formation. 4. 4. The The resistate resistate nature nature of of the the minerals minerals in in the the conglomerate conglomerate suggests extensive area and suggests extensive weathering of the source source area and the the presence presence of a disconformable relationship with the underlying unit. disconformable relationship with the underlying unit. Proceed Proceed from from west west end end of of causeway causeway northward northward along along Pine Pine Ridge Ridge Road. Road. STOP 12: Archean Granitic Basement Rocks Rocks STOP 12: Saprolith Saprolith on on Archean gneiss, up to Blocks of pale-weathering pale-weathering granitic granitic gneiss, to 11 m across, across, are are separated by separated by brownish-weathering brownish-weathering arkosic sandstone sandstone filled filled cracks, cracks, 52 �which which appear appear to to be be products products of of the the paleoweathering paleoweathering of of the the gneiss. gneiss. The The grain grain size size of of quartz quartz in in the the inter-block inter-block sandstone sandstone is is consistent consistent with with derivation derivation from from weathering weathering of of the the surrounding surrounding granite. In places the prominent gneissosity in the granite. In places the prominent gneissosity in the granitic granitic rocks rocks shows shows that that no no rotation rotation of of the the blocks blocks has has taken taken place place during during the the development development of of the the sandstone sandstone units. units. The The sandstone sandstone units units are are up wide, and and in in places places include include numerous numerous sub-angular sub-angular to to up to to 22 mm wide, sub-rounded sub-roundedblocks blocks of of granitic graniticgneiss. gneiss. The The very very thin thin arkosic arkosic units units appear appear to to be be no no more more than than altered altered seams seams in in the the granitic granitic basement. basement. At At the the west west end end of of the the outcrop outcrop the the sandstone sandstone units units are are fined fined grained, grained, grey grey and and resemble resemble the the sandstones sandstones of of the the overlying overlying Livingstone Livingstone Creek Creek Formation. Formation. Proceed Proceed north north on on Pine Pine Ridge Ridge Road Road to toHighway Highway17. 17. then then proceed proceed east east on on Highway Highway17. 17. Reset odometer odometer Reset Reset Reset odometre. odometre. 13.5 13.5 km km Melwell Melwell Road Road 14.1 14.1 km km Chalcopyrite Chalcopyrite bearing bearing quartz quartz carbonate carbonate vein vein cut cut pebbly pebbly siltstone siltstone of of the the Gowganda Gowganda Formation Formation on on the the south south side side of of Highway Highway 17. 17. The The vein vein and and mineral mineral assemblage assemblage (quartz-carbonate-pyrite(quartz-carbonate-pyritechalcopyrite-hematite) chalcopyrite-hematite) is is typical typical of of many many in in such such occurrences occurrences between between Sault Sault Ste. Ste. Marie Marie and and Sudbury. Sudbury. 47.6 47.6 km km Downtown Downtown Blind Blind River River(at (atTim TimHorton's). Horton's). 66.7 66.7 km km Pronto Pronto Road Road Turn Turn north north onto onto the the Pronto Pronto road road and and continue continue until until prevented prevented by by aa gravel gravel barrier barrier from from proceeding proceeding further. further. Continue Continue on on foot foot past past the the barrier barrier to to the the west west end end of of aa beaver beaver pond pond just just north north of of the the road. Proceed along along aa trail trail across acrossthe the west west outlet outletof ofthe thepond, pond, road. Proceed then then around around the the north north end end of of the the pond pond and and up up aa steep steephill. hill. Turn Turn left (to the north) on a gravel road at the top of the hill. left (to the north) on a gravel road at the top of the hill. Continue Continue to to an an area area of of outcrop outcrop and and gravel gravel fill fill which which marks marks the the former stope of of the the Pronto Pronto mine. mine. If If not not accompanied accompanied by by aa former open open stope guide, guide, please please do do not not attempt attempt to to access access this this site site without without aa compass compass as as well well as as suitable suitablefootwear footwearand andclothing. clothing. NOTE: NOTE: During During the the field field trip trip we we hope hope to to arrange arrange for for access access from from the the normally normallyrestricted restrictedmine mineproperty. property. 53 �(13) '7',' 7,,,, +—+-- -:—:-:::÷:÷ 7,',, 7,,,, .7/,, '7,, ''/, 7,' ''7 '77, ::÷::t:*::t.. LEGEND HIJRON1AN + 4 + + + + * + + * ++ + + >/ formations above the Motinenda 7, 7 7 / + * + + , + + + +4 +,+ 4+, + + + + + [V71 Matinendo, conglomerate + + +4 + 4-4 + + Poieosol + 4 + + + ++4 +-*+ ++ ++ + ARCHEAN + +++++ + + + + ftfterRobrtsorj(197O) fl Gronitic rocks + y;ç' y Pond"\ / —. c-:: :v- 1/ 12 / —'- Pond c_f /''///' '''','''' •'''C t%_ _*++,+e,,,,, -70- z,zz,,,,,z / / //'/'/ —4- /7/ ,, ,,,,,,,,,/,-,, /7/7/7/7/7/7/, /17/7/7/7' / ,,,,,,,,,,,,,, /4 ,,• • -0. ,f',/ ,+,-////////7//,+/1/ /7/ + 7 +-..2yc 7/fly /7/77/7/7/7 ,,,,,,,,,'''''' -,r,,,,,,,,,,,,,,,,,,,,,,,,,,,, ////////f7////////////7///////// /71/7/'//'// ,,,,,, ,,,,,,, / /77/7/. C t.+ +V V - VVV, VVVVVVVV 0/'''' /' /''/'''/'' /7+,,,,,, VVVVVVVVVV,VV, ,,,,, 7,,,,,,, 7'//'// 7,7,7,,,,,, VVVVVVV VVVVVV VVV /7/7/7/' -C '',,,,, 0 /////,/////7.///// / / VVVVVV VVVVVVVVVVVVV 7,, +1-''// /7/' ,,,,,,,,,,,, c+,,, , 0_,,//,,4.__j", /7/7/7/77 , - + '+ V VVVVVVVVV VVVVVVVV'VVVVV VVVVVV VVVVV VVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVVVVVVVVVZ '-VVVVVVVVVVVVVVVVVVV""""-4 VV VVV VVVV VV V V V V VV VVVV V ,,,, /77177+V-V0" / 4\iV' - //VVVVVVVVV 77vV'VVVØ4 VV4Sk1i.& VVVVVV VVVVVVVV'+ VVVVVVVVVVVVVVVV VVVVVVVVVV VVVVVVVVVV V/ JVVVV VVVVV V VVVVV — VVVVVVVVVVVVVVVVVVV +r'+' V1 VVVV V V V V V V V V V V V V V V V .VVVVVVVV'' . t V V,VW V V V V V V V V V V V V V V V V V'VVVV V V V V V V V V V V V V V V V VVV'V V V_-—' / VVVVVVVV'+ VVVV I VVVVVVVVVVVVVV.+M - V - VVVVVVVVVVVV V V V V V VVVVVV V V V V VV'L+_-+ - '1 HURONIAN Formations above the Matinenda -.- Hi Matinenda Formatloin Pat~F.xmat#m a fl Gronilic rocks Gron8ltc rocks Fautt Fault c<^ Bedding attitude Bedding attitude 0Paler Formation ARCHEAN ARCHEAN SYMBOLS SYMBOLS — '13' ,_ ----4 13 Fieldtrip stop Fieldtnp slop -d I Projection ore body Projection ofdoriginal original ore body , 1 krn 1 km ? . Figure Plan and section of of thethe Geology ofof the Figure18.18. Plan and section Geology thePronto ProntoMine Minearea. area. 54 �STOP STOP 13: 13: Pronto Pronto Mine Mine (past (pastproducer) producer) -- This This property property is is currently currently undergoing restoration restoration to to a a condition condition as as closely closely as as undergoing possible possible to to it's it's original original state. state. (Refer (Refer to to Figure Figure 18). 18). This This is is one one of of the the few few locations locations where where exposures exposures of of uraniferous uraniferous quartz quartz pebble pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation can can be be found found on on surface surface in in the the Elliot Elliot Lake-Blind Lake-BlindRiver River area. area. In In the the depression depression south south of of the the road road are are exposed exposed rusty-weathering rusty-weathering outcrops outcrops of of radioactive, radioactive, pyritic, pyritic, quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation which which mark mark the the base base of of the the ore ore bed bed of of the the Pronto Pronto Mine. Mine. The The conglomerate conglomerate lies lies directly directly upon upon yellowish, yellowish, sericitic Archean granitic granitic baAement. basement. sericitic paleosol paleosol developed developed on on Archean Proceeding Proceeding in in aa general general northerly northerly direction direction some some features features of of the the original granitic rocks, displayed as dikes and irregular bodies original granitic rocks, displayed as dikes and irregular bodies of of aplite aplite and and pegmatite, pegmatite, can can be be recognized recognized in in the the paleosol paleosol (saprolith). southward sloping sloping outcrop outcrop the the (saprolith). Continuing Continuing up the the southward yellowish yellowish colour colour of of the the paleosol paleosol can can be be seen seen to to take take on on aa pinkish pinkish and Archean granitic granitic rocks rocksof of the the area. area. and reddish reddish hue hue normal normal to to the the Archean Continuing north and west to near the highest point on the Continuing north and west to near the highest point on the outcrop outcrop one one can can discern discern the the faint faint outline outline of of core-stones core-stonesin in the the granitic rocks. granitic rocks. Return Return to to Highway Highway 17. 17. Continue Continue east east along along Highway Highway 17 17 to to Highway Highway 108 108 to to Elliot Elliot Lake. Lake. Continue Continue eastward eastward for for aa few few hundred hundred metres metres past to low low outcrops outcrops in in an an open open area area just just south south of of 108 to past Highway Highway 108 Highway 17. Highway 17. STOP STOP 14: 14: McKim McKim Formation Formation —- Staurolite Staurolite schist. schist. Low Low outcrops outcrops aa few few tens tens of of metres metres south southof of Highway Highway17. 17. (Refer (Referto to Figure Figure16) 16). This This outcrop, outcrop, which which lies lies aa few few hundred hundred metres metres south south of of the the Murray Murray Fault Fault Zone, Zone, displays displays the the higher higher metamorphic metamorphic grade grade and and deformation deformation common commonto torocks rockssouth southof of the thefault. fault. At At this this location location argillaceous argillaceous units units of of the the McKim McKim Formation Formation contain contain pale pale prismatic prismatic crystals crystals of of staurolite staurolite which whichhave have undergone undergone retrograde retrograde metamorphism metamorphism to to sericite-quartz sericite-quartzaggregates. aggregates. AA few few pseudomorphs pseudomorphs show show the the characteristic characteristic cruciform cruciform twinning twinning of of staurolite. staurolite. The The enhanced enhanced growth growth of of staurolite staurolite crystals crystals in in the the originally originally more more 55 �argillaceous argillaceous upper upper portions portions of of the the beds beds has has resulted resulted in in graded bedding" graded bedding" in in aa few few places. places. "reverse "reverse Return Return to to the the intersection intersection of Highway Highway 17 17 and Highway 108. Proceed Proceed north north along along Highway Highway 108 108 to to the the Town Town of of Elliot Elliot Lake. Lake. ROAD LOG ... DAY 2 Day Day 22 of of the the field field trip trip begins begins in in the City of Elliot Lake at the intersection 108 and and Hillside Hillside Drive DriveNorth. North. (Refer (Refer to to intersection of of Highway Highway 108 Figure Figure 18). 18) . Turn Turn west west onto onto Hillside Hillside Drive Drive North. North. Continue Continue west west on on Hillside Hillside Drive Drive North North for for about about 11 km km to to Spine Spine Road. Road. Turn Turn west west onto onto Spine Spine Road Road 1.9 1.9 km km Spine Spine Road Road at at Lawrence Lawrence Ave Ave (End (Endof of Spine Spine Road). Road). UTM UTM 370525E, 17-5137802N 370525E. 17-5137802N STOP 15: 15: Radioactive Radioactive quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation. Formation. The The low low outcrops outcrops on on the the north north side side of of Spine Spine Road Road are are grey, grey, buff buff and dark-grey dark-grey arkose arkose and and radioactive, radioactive, pyritic, pyritic, quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation. Formation. Pebble Pebble units units are are about about 20-30 cm thick and dip about 10 degrees to the north. 20-30 cm thick and dip about 10 degrees to the north. Pebbles in Pebbles in this 1-2 cm cm across across and and are are generally generally much much this outcrop outcrop are are about about 1-2 smaller smaller than than the the pebbles pebbles in in the the ore ore zones zones of of the the Elliot Elliot Lake Lake mines. LeCheminant, (1984) (1984) report radioactive mines. Ruzicka Ruzicka and and LeCheminant, report the radioactive conglomerate conglomerate contains contains : "rare-earth-elements-bearing uranothorite (7) large 'rare-earth-elements-bearing uranothorite(?), large zircons, ?), zircons, aa Ti-U-Si-Fe Ti-U-Si-Fephase phase (brannerite (brannerite7), chalcopyrite chalcopyrite and and chromite. chromite. The The distribution distribution of of radioactive radioactive minerals minerals in in the the conglomerate conglomerate displays displays layering thus indicating layering thus indicating aa detrital detrital origin origin of of these these grains" grains " , The The dark-grey dark-grey areas areas in in the the radioactive radioactive beds beds are are due due to to the the presence known in presence of of minor minor amounts amounts radioactive radioactive carbon carbon generally known in 56 �_______ LEGEND For figure 18 POST-HURONIAN MAFIC INTRUSIVE ROCKS Ramsay Lake Formation NIPISSING DIABASE [Li "1 Conglomerate Dabase, gabbm, melagabbm, INTRUSIVE CONTACT ELLIOT LAKE GROUP McKirn Formation HURONIAN SUPEROROUP COBALT GROUP Sttston., argIIIIts,wecks Bar River Formation MatInanda Formation Ouartz arentle p.— pn. p., a. O,bnL..ty'. tJ x-1 Subaricosa, adios., conglomerate, Gordon Lake FormatIon uranhini-beer%ng conglomerate SlIlatone, argilItte, subail<ose DISCONFORMITY Lorraln Formation Thessalon FormatIon (5) Ouarft erenlte, subarkose, eikose, conglomerate, thorium-bearing conglomerate Basalt, andaste, mInor mugeadte-hawallte, rtiyollte, metabasalt, and Intercalated sedImentary rocka Gowganda FormatIon Conglomerate, argllilte, wacke, subarkoes, sittetone DISCONFORMITY? HIATUS HIATUS LMngetone Creek Formation QUIRK LAKE GROUP Mlcose, polymicec conglornerata Serpent Formation UNCONFORMITY Subaricose, conglomerate ARCHEAN Espanola FormatIon (3) LImestone, dolomIte, calcareous alltetone Plutonic granldc rooks, gnelsees, Bruce Formation (3) FeIslo to motto metavolcanlc rooks, metasedimentary rocks Cong?omerata HOUOHLAXEGROUP UOUGH IAKE QROUP Mlssissagl Formation Mls~i~s Fomallon e~l Subalcose, añcoes, $%behem, ahme,conglomerate mngbmemle Peoors PemmFormation Fomatlon(4) (4) flglItits alllstone r Shaft-fornior uranium mine Fault @ Field Field trip tripstop stop so_ w eeO5& sad L•IM'(lflsI --wmm �c4(4c :o'o.go.0 ç ',,".", v a 0 0 0 0 00 00C0 :o:c:00o: 0 d. 00 0 0 2°°° 99090909 ° 0cc' (4\ I, 0 Figure 19. Geology of the Elliot Lake area. 00 00000000'0 000 0000000000000000oo ):o:o:c,o:o:o,c:c:o:o:o:o:o:o:o:oo*o*o* 0,o,c. ,c.oo, .o,o:6:o:c:o, o:o:o:oo:c,o,c:o:oo:o:oo:o oCc0c\0c0o r—tc. ,, 7))*e ;::zz:k fl0 OtQ 09 Lake U - 0 (1.CÔ 0j0 g° sr-- 00000000 ' Quince * ——— 6 — $,* — — —— a 000 2 r!d1:1T :00 000000t a e Lake Hake �the thucoliteT but also referred the Elliot Elliot Lake Lake area area as as "thucolite" referred to to as as aa hydrocarbon hydrocarbon kerogen. kerogen. Ruzicka Ruzicka and and LeCheminant, LeCheminant, (1983) that (1983) note note that several several generations generations of carbon carbon occur in the conglomerates conglomerates of of the the Matinenda generation occurs occurs as Matinenda Formation. Formation. The earliest generation as layers layers concordant with the bedding or a component of the matrix matrix and and appears to appears to have have been been deposited deposited in in areas areas of of quiescent quiescent sedimentation during the last phase phase of an upward fining sedimentation fining sedimentary cycle. Later generations generations are probably probably remobilized remobilized sedimentary phases of phases of the the first first generation generation of of carbon. carbon. The carbonaceous carbonaceous matter matter in in the the Elliot Elliot Lake Lake ores ores is is comparable comparable in in occurrence occurrence and and composition hydrocarbon in the Witswatersrand Witswatersrand gold composition to to similar similar hydrocarbon gold reefs; interestingly LeCheminant(l984) report report reefs; interestingly Ruzicka and LeCheminant(l984) elevated gold 2000 ppb) ppb) in in the the Elliot Elliot Lake Lake elevated gold content content (1000 (1000 -- 2000 carbonaceous matter. carbonaceous matter. The radioactive radioactive carbon carbon at this this site site is is although the gold content is is not reported to be auriferous, although available. available. A drill drill hole hole was was drilled drilled about 30 30 m south south of this this location location by by Rio Rio Algom Mines Mines Limited Limited in in 1955. The logs logs of this this hole hole indicate indicate that that radioactive beds exposed here are about 35 metres above the radioactive above the the basement of Archean granitic granitic rocks. rocks. Diamond Diamond drilling drilling has has basement of Archean indicated that indicated that there there are are no no ore-grade ore-grade units units in in this this area. area. Grab returned up to Grab samples samples collected by G. Bennett in 1982 1982 returned to .80 .80 lbs/ton tJ308 and 0.78 0.78 lbs/Ton lbs/Ton Th02. Th02. AA continuous continuous chip chip sample lbs/ton U308 and returned lbs/ton U308 U308 and and 0.53 0.53 lbs/ton lbs/ton Th02. Th02. returned 0.31 0.31 lbs/ton Return Return to to Highway Highway 108 108 and proceed north on Highway 108 108 to to Milliken Milliken Road Road (about (about 1.5 1.5 km km north north of of Hillside Hillside Drive Drive North). North). Reset odometer odometer at at Milliken Milliken Road. Road. miles 1.0 0.63 miles 1.0 km km -- 0.63 Mississagi Formation, STOP 16: 16: Subarkose Subarkose of the the Mississagi Formation, Rough Hough Lake Lake Group. Group. Grey subarkose Formation displays wellwellsubarkose of the Mississagi Formation developed developed trough trough cross-bedding cross-bedding in bedding units about a metre thick. thick. Paleocurrents Paleocurrents are from the west. The rusty iron-staining iron-staining on pyrite content on the face face of of the outcrops reflects the minor pyrite content beds. The grey grey which commonly commonly is is deposited along the foreset beds. colour presence of apparently apparently colour of these these sandstones, sandstones, and the presence detrital pyrite, pyrite, is held to indicate very very low partial partial pressure of detrital 59 �free free oxygen oxygen of of the the atmosphere atmosphere in in this this time. time 1.4 km km -- 0.9 0 . 9 miles miles 1.4 17: Nipissing Nipissing Diabase/Gabbro, DiabaselGabbro, altered altered Mississagi Mississagi Formation, Formation, STOP 17: STOP Bruce Bruce Formation. Formation. AA sill-like sill-likebody body of of Nipissing Nipissing gabbro/diabase gabbro/diabase is is exposed exposed on on the the east side side of of Highway Highway 108. 108. Rhythmic, Rhythmic, compositional compositional layering layering is is east visible on on the the vertical vertical face face of of the the exposure. exposure. Near Near the the north north end end visible of of the the Nipissing Nipissing sheet sheet the the present present erosion erosion surface surfacedisplays displays evidence evidence of of water water erosion erosion presumably presumably as as aa result result of of melting melting of of adjacent adjacent Pleistocene Pleistocene glacial glacial ice. ice. North North of of gabbro gabbro sill, sill, the the upper upper portion portion of of the the Mississagi Mississagi Formation Formation is is exposed exposed along along the the east side side of of the the highway. highway. The The sandstones sandstones here here have have been been east subjected subjected to to metasomatism, metasomatism, presumably presumably related related to to the the adjacent adjacent Nipissing metasomatic effect Nipissing intrusion. intrusion. The The metasomatic effect is is visible visible as as the the distinctly distinctly pinkish pinkish hue hue of of the the sandstone, sandstone, which which is is probably probably due due to to The dark-green dark-greento to black black chlorite chlorite the development development of of albite. albite. The the deposited deposited along along thin thin fractures fractures may may also also reflect reflect metasomatic metasomatic alteration by by fluids fluids circulated circulated by by the the hot hot diabase. diabase. alteration Continue Continue northward northward on on foot foot for for aa few few tens tens of of metres. metres. Here Here the the Mississagi Mississagi Formation Formation is is overlain overlain by diamictite diamictite of of the the Bruce Bruce Formation Formation at at the the base base of of the the Quirke Quirke Lake Lake Group. Group. The The dispersed dispersed megaclasts megaclasts of of the the Bruce Bruce Formation Formation are are predominantly predominantly grey grey granitic granitic rocks rocks with with smaller smaller mafic mafic clasts clasts of of what what appear appear to to be, be, at at least least in in The abundant matrix of the part, part, Huronian Huronian volcanic volcanic rocks. rocks. The abundant matrix of the conglomerate conglomerate is is dark-grey dark-grey to to black. black. Sand-sized Sand-sized quartz quartz grains grains have have a a glassy, glassy, black black appearance, appearance, aa reflection reflection of of the the chlorite chlorite content content There is no evidence of significant disconformity of the the matrix. matrix. There is no evidence of significant disconformity of at the the base base of of the the Bruce Bruce Formation. Formation. at Proceed Proceed by by vehicle vehicle to to near near the the top top of of the the hill. hill. 1.8 km km -- 1.4 1.4 miles. miles. 1.8 STOP 18: 18: STOP Espanola Espanola Formation Formation and and Nipissing Nipissing diabase diabase sills. sills. The The base base of of the the Espanola Espanola Formation Formation is is aa green green laminated laminated unit unit about overlain by laminated about aa metre metre or or so so thick. This is overlain laminated silty silty limestones limestones of of the the Bruce Bruce Limestone Limestone member, member, Espanola Espanola Formation. Formation. At At this this location location the the proximity proximity of of Nipissing Nipissing intrusions intrusions has has led led to to 60 �the development skarn with grossularite garnet, idocrase development of a skarn garnet, idocrase (vesuvianite) (vesuvianite), diopside, diopside, and wollastonite. The The latter latter can can be be and wollastonite. found, found, just just below below the the north-dipping north-dipping diabase diabase sill sill near near the the north north end of the the exposure. exposure. Wollastonite Wollastonite occurs occurs as as sub-parallel sub-parallel groups groups of of pale-grey pale-grey to to white white prismatic prismatic crystals crystals about about one one mm mm wide. wide. The The pink (KFCa4[Si8020]8H20) (KFCa4[Si802,,l8H20) an an pink coating coatingon onjoint jointsurface surfaceisisapophyllite apophyllite uncommon mineral, mineral, sometimes sometimes found found in in amygdules amygdules in in basalts, basalts, but but is is uncommon also associated with cab-silicates. Young(l99l) states that the also with calc-silicates. Young(l991) states that the small small scale scale thrust thrust faults faults and and folds folds displayed displayed in in the the limestone limestone on on the the west side side of of the the highway highway are are probably the result of slumping slumping during during early early tectonic tectonic activity. activity. , ferruginous dolostone-bearing dolostone-bearing member of the the Espanola Espanola The upper, upper, ferruginous The Formation present at Formation and and the the overlying overlying Serpent Serpent Formation Formation are are not present at They have have probably probably been been removed removed during during a a period period of of this this location. location. They pre-Gowganda pre-Gowganda erosion. erosion. The The basal basal units units of of the the Gowganda Gowganda Formation Formation are are visible visible on on the the west west side side of of the the highway. highway. 2.0-2.5 1.3-1.6 miles miles Gowganda Gowganda Formation Formation diamictite. diamictite. km -- 1.3-1.6 2.0-2.5km Massive Massive diamictite diamictite of of the the Gowganda Gowganda Formation. Formation. Megaclasts Megaclasts of of pink pink granite, granite, grey grey granite granite and and granitic granitic gneiss gneiss and and mafic rocks rocks are are widely distributed in a dark green matrix. widely distributed in a dark green matrix. Most Most geologists geologists now now consider consider at at least least some some of of the the diamictites diamictites in in the the Gowganda Gowganda Formation Formation to to be be tillites, tillites, although although a a debris-flow debris-flow origin, origin, either either glaciogenic glaciogenic or or as as sub-marine sub-marinedebris debris flows flows is is also also reasonable. reasonable. Roscoe, Roscoe,.(1969) (1969) places of free free oxygen oxygen in in the the places the appearance appearance of atmosphere ("oxyatmoversion") ("oxyatmoversion")as as coinciding coinciding with the the appearance appearance atmosphere of of the the reddish reddish hue hue of of hematite hematite just just above above the the base base of of the the Gowganda Formation. Gowganda Formation. 3.8 3.8 km. km. -- STOP STOP 19: 19: 2.4 2.4 miles. miles Stratified Stratified Gowganda Gowganda Formation. Formation. Park Park just just south south of of the the rock-cut rock-cut on on east east side side of of the the highway. highway. This This is is an an impressive impressive exposure exposure through through aa stratified stratified sequence sequence of of diamictites diamictites and and sandstones sandstones of of the the Gowganda Gowganda Formation. Formation. The The base base of of the the sequence sequence at at the the extreme extreme southern southern end end of of the the exposure exposure on on the the west side of Highway 108 consists of massive diamictite overlain west side of Highway 108 consists of diamictite overlain 61 �by a thin thin unit of of laminated laminated mudstone mudstone siltstone siltstone with with drop drop stones. stones. About 11 m of stratified Gowganda overlies the siltstone. m stratified Gowganda overlies the siltstone. Diamictite, Diamictite, sandstone, sandstone, pebbly sandstone and clast clast supported polymictic conglomerate conglomerate are are present. present. Some Some conglomerate conglomerate units units polymictic display normal normal and and reverse reverse grading grading suggestive suggestive of of debris debris flows. flows. display The The rocks rocks displayed displayed here here may may be be interpreted interpreted to to represent represent aa depositional environment environment proximal proximal to to aa retreating retreating glacial glacial margin. margin. depositional Note: the predominance of red and pink granitic clasts, Note: clasts, is is in in marked contrast contrast to to the the pale grey grey clasts clasts of of the the Bruce Bruce and and Livingstone Creek Livingstone Creek Formations Formations seen seen earlier. earlier. 4.7 km. 2.9 miles. Pink sandstones 4.7 km. -- 2.9 sandstones and diamictite diamictite of of the the Gowganda Formation. Gowganda Formation. 6.7 km 4.2 miles. Diamictite 6.7 km -- 4.2 Diamictite with with large large boulder, boulder, Gowganda Gowganda Formation. Formation. Pink and red arkose arkose with pebbly and bouldery bouldery mudstone mudstone Relatively (diamictite). Relatively massive bed of pink arkose arkose with with (diamictite).. scattered pebbles and a boulder of red granite on on the the west west side side of the the highway. highway. The The continuity continuity of of strata strata is is broken broken by by faulting, faulting, channelling and deformed arkose bodies in grey pebble siltstone siltstone (near south end (near south end of of rock-cut) rock-cut). 8.2 8.2 km. km. 11.4 - 5.1 5.1 miles Stanrock Stanrock Road Road Denison Mine east. Denison Mine Road Road -- Turn Turn east. Reset odometre odometre to to 000 km km 3.6 km. 3.6 km. Serpent Formation STOP Gowganda Formation Formation -- Serpent Formation disconformity disconformity STOP 20: Gowganda 376l02E, 5150299N 376102E, 1717partially removed The Serpent Formation Formation has been partially removed during during aa period period pre-Gowganda erosion in the southwestern of pre-Gowganda southwestern part of of the the Quirke Quirke Lake Syncline and the Blind River Sault Ste. Marie area. Lake Syncline and the Blind River Sault Ste. Marie area. At this this location, south side of the road, road, well-sorted well-sorted sandstone location, on the south sandstone of of Formation is overlain by polymictic conglomerate the Serpent Formation conglomerate of of contact is the the Gowganda Gowganda Formation. Formation. The contact is sharp sharp but but irregular. irregular. disconformity at this Evidence of a sub-Gowganda sub-Gowganda disconformity this location location is is given by the given the presence presence of pebble and and cobbles cobbles of the the Serpent Serpent 62 �Formation Formation near near the the base base of of the the Gowganda Gowganda Formation. Formation. Return Odometre, turn Return to to Highway Highway 108 108 Reset Odometre, turn north north 000 000 0.5 km km -- 0.5 0.5 miles. miles. Disseminated Disseminated carbonate carbonate in in sandstone sandstone of the the Serpent Formation Serpent Formation on on east east side side of of Highway Highway 108. 108. 0.8 miles. Outcrop Limestone Member 1.4 km km -- 0.8 Outcrop of of Espanola Espanola Limestone Member of of the the Espanola Formation Formation with ripple is exposed on on the east side side Espanola ripple marks is of Highway Highway 108. 108. The carbonate carbonate units units of of the the Espanola Espanola Limestone Limestone are actually actually ferruginous ferruginous dolomite dolomite containing containing approximately approximately 3% 3% total total iron. iron. 1.6 1.6 km km -- 1.0 1.0 miles. miles. Road to to Quirke Quirke Lake Lake and and former former Panel Panel Mine. Mine. Turn onto Turn onto Panel Panel Mine Mine road. road. Reset Reset odometre odometre to to 000 000 1.3 km miles 1.3 km -- 0.8 0.8 miles STOP 21: STOP 21: Espanola Espanola Member Member of of the the Espanola Espanola Formation. Formation. Rock-cut Rock-cut in in ferruginous ferruginous dolomite dolomite and and siltstone siltstone of of the the Espanola Espanola Limestone The Espanola Limestone Member Member of of the the Espanola Espanola Formation. Formation. The Espanola Limestone Limestone Member Member is is the the uppermost uppermost member member of of the the thee thee members members of of the the Espanola Espanola Formation Formation recognized recognized in in the the Elliot Elliot Lake Lake area. area. It It is is characterized by intercalated characterized intercalated siltstone siltstone and and reddish-weathering, reddish-weathering, ferruginous ferruginous dolostone dolostone beds containing containing 3-4% 3-4% FeO. FeO. Intraformational Intraformational breccia, breccia, ripple ripple marks, marks, small small scale scale cross-bedding, cross-bedding,and and various various present. Near soft sediment features features are present. Near the the east east end end of of the the outcrop a grey, complex clastic dike crosses the stratification stratification outcrop grey, complex at a a high high angle. angle. 4.1 km 2.5 miles miles. 4.1 km -- 2.5 STOP STOP 22: 22: Ramsay Lake Formation Formation overlain overlain by by Pecors Pecors Formation. Formation. Diamictites of the Ramsay Lake Formation contain contain cobbles of grey Diamictites granitic rocks, granitic rocks, mafic clasts clasts of of Huronian Huronian volcanic volcanic rocks rocks and and Archean dark-grey to Archean felsic felsic volcanic clasts clasts in in an an abundant dark-grey to black sandy matrix. The Ramsay Lake Formation is overlain by dark Lake Formation is overlain by dark sandy matrix. laminated mudstone of laminated siltstone siltstone and and mudstone of the the Pecors Pecors Formation. Formation. The The 63 �latter latter contains contains aa few few drop-stones. drop-stones. Note: Note: the the Matinenda Matinenda Formation Group, expected Formation of the Elliot Lake Group, expected between the the basement basement and Ramsay Lake Lake Formation, Formation, is is truncated truncated by by the the Ramsay Ramsay Lake Lake and the the Ramsay Formation Formation in in this this area. area. The The Matinenda Matinenda Formation Formation does does occur occur in in the the mine mine workings workings down-dip down-dip from from this this location. location. Continue Continue east east to to the the end end of of the the Panel Panel Mine Mine road. road. This This is is the the rehabilitated rehabilitated area area of of the the former former Panel Panel Mine. Mine. There There is is little little evidence mill complex complex that was on evidence of of the the uranium uranium mine mine and. and mill on this this site site until until 1993. 1993. Return Return to to Highway Highway 108. 108. Continue Continue north north on on Highway Highway 108. 108 Tailings Tailings dam dam of of the the Quirke Quirke Mine Mine is is visible visible west west of of the the Highway. Highway. Highway Highway 108 108 ends ends and and Highway Highway 639 639 begins. begins. Reset Reset odometre. odometre. 0.8 0.8 km km -- 0.5 0.5 miles. miles. Diamictite Diamictite of of the the Bruce Bruce Formation Formation is is exposed exposed west west of of the the Highway. Highway. 1.5 0 . 9 miles. miles. Outcrops Outcrops of of Mississagi Mississagi Formation Formation are are exposed exposed 1.5 km km -- 0.9 along along Highway Highway 639. 6 3 9 . Note Note the the yellowish yellowish colour colour characteristic characteristic of of the the Mississagi Mississagi Formation Formation where it lies directly on on the the Archean Archean granitic granitic basement basement (Robertson, (Robertson,1968) 1968) . 2.2 2.2 km km -- 1.4 1.4 miles miles STOP STOP 23: 23: Huronian Huronian volcanic volcanic rocks rocks of of the the Thessalon Thessalon Formation Formation (Dollyberry (DollyberryVolcanics) Volcanics) . Road Road leading leading west west from from Highway Highway 639 639 leads leads to to the the Quirke Quirke Mine Mine tailings tailings dams. dams. Park Park near the the gate gate and and walk a a short short distance distance along along the road to a snowmobile bridge over the stream from the the road to a snowmobile bridge over the stream from the tailings tailings dam. dam. Follow Follow the the trail trail from from the the bridge bridge to to outcrops outcrops of of mafic (Dollyberry mafic volcanics volcanics of of the the Thessalon Thessalon Formation Formation (Dollyberry Volcanics)near Vo1canics)near the the crest crest of of aa low low hill. Chemical Chemical analyses analyses of of the the Huronian Huronian volcanics volcanics in in this this area area indicate indicate the the volcanic volcanic rocks rocks include include transitional transitional alkalic alkalic types, types, hawaiite hawaiite and and mugearite. mugearite. The The unconformity unconformity between between the the Archean granitic granitic basement basement rocks rocks and and Huronian Huronian volcanic volcanic is is visible visible in in this this area. area. There There is is no no visible visible paleosol paleosol at at this this location. location. Near Near the the trail trail aa thin, thin, quartz-pebble quartz-pebble 64 �conglomerate unit of angular conglomerate angular to to subrounded, subrounded, quartz-clasts, quartz-clasts, overlies overlies the the granitic granitic rocks rocks at at the the base base of of the the volcanic volcanic unit. unit. Walking eastward from-this from this point scattered, scattered, isolated, isolated, pebblepebble- and and cobble-sized cobble-sized clasts of quartz can be found found along along the the unconformity. A similar unconformity. similar quartz-pebble quartz-pebble conglomerate conglomerate occurs occurs at at the the base where they Archean base of of the the Huronian volcanic rocks rocks where they overlie overlie Archean mafic mafic volcanic volcanic rocks rocks in the haulage drift of the Stanleigh Stanleigh Mine on on the the south south limb limb of the Quirke Lake Syncline. Syncline. A few few kilometres kilometres west of this this location, location, occurrences of this this conglomerate conglomerate unit unit contain clasts, and are contain more rounded quartz clasts, are commonly commonly overlain overlain by by a thin thin arkosic arkosic unit. unit. Quartz-pebble Quartz-pebble conglomerate, conglomerate, which which locally locally contains significant pyrite pyrite as well as uranium, uranium, occurs occurs sporadically base of the Huronian Huronian volcanic sequence sporadically at the base sequence of the the Quirke Syncline and and westward westward to to the the Sault Sault Ste. Ste. Marie Marie area. area. Quirke Lake Lake Syncline The The conglomerate conglomerate at this location is is correlated correlated with with the the radioactive, 11. radioactive, quartz-pebble quartz-pebble conglomerate conglomerate of of Stop Stop 11. Return to Return to Vehicle and and continue continue north north on on Highway Highway 639. 639. Archean Archean granitic granitic rocks rocks cut cut by by diabase diabase outcrops outcrops along along the the highway. highway. 8.8 km 8.8 km 5.5 miles 5.5 miles STOP 24: STOP 24: Archean pillowed (Refer to Figure pillowed metavolcanics. metavolcanics. (Refer Figure 16). 16). Archean well-developed pillow Archean mafic metavolcanics displaying displaying well-developed pillow structures are exposed on on a north north sloping outcrop outcrop on the east structures side deformed, but facing side of of highway. highway. Pillows Pillows are deformed, facing directions directions can can easily easily be determined. Small amygdules are concentrated near the upper surface upper surface of of many many pillows. pillows. Lake fault occupies a valley near this 9.4 5.8 miles. Flack Lake 9.4 km km -- 5.8 point. point. 9.9 km 6.1 miles. miles. Outcrops Outcrops of of 9.9 km -- 6.1 the the Bar Bar River River Formation. Formation. 10.5 miles. 6.5 miles. 10.5 km km -- 6.5 hematite-stained sandstone hematite-stained sandstone of Entrance Entrance to to Mississagi Mississagi Provincial Provincial Park. Park. 10.8 10.8 km km -- 6.7 6.7 miles. Pale grey sandstone sandstone of of the the Formation with Formation with herringbone herringbone cross cross bedding. bedding. 11.4 11.4 km km -- 7.2 7 . 2 miles. Christman Christman Lake Lake 65 Bar River River �STOP STOP 25: 25: Bar Bar River River Formation Formation Sandstones Sandstones of of the the Bar Bar River River Formation Formation display display ripple ripple marks, marks, mud cracks cracks and and sinuous sinuous structures structures which which have have been been described described as as possible possible worm worm casts. casts. Comparison Comparison with with desiccation desiccation structures structures in in the the Gordon Gordon Lake Lake Formation Formationled ledYoung, Young, (1969) (1969) to to suggest suggest that that these these features features are are the the result result of of the the transportation transportation of of consolidated consolidated desication fracture fillings. desication fracture fillings. 15.3 15.3 km km -- 9.5 9.5 miles. miles. STOP STOP 26: 26: Gordon Gordon Lake Lake Formation Formation Laminated, Laminated, maroon maroon buff buff siltstone siltstone and and chert chert with with reduction reduction spots spots in in the the upper upper part part of of the the Gordon Gordon Lake Lake Formation. Formation. This This is is another another red-bed occurrence within the Cobalt Group. red-bed occurrence within the Cobalt Group. 16.6 10.3 miles miles 16.6 km km -- 10.3 StoD Stop 27: 27: Gordon Gordon Lake Lake Formation. Formation. Siltstones Siltstones and and sandstones sandstones of of the the Gordon Gordon Lake Lake Formation Formation display display ripple ripple marks, marks, desiccation desiccation cracks, cracks, cross cross bedding bedding and and aa late late cleavage. cleavage. Note: Note: the the presence presence of of pyrite pyrite in in contrast contrast to to the the generally generally hematitic hematitic nature nature of of the the Gordon Gordon Lake Lake Formation Formation near near the the top of the formation. top of the formation. 19.7 12.2 miles. miles. View View of of the the Boland Boland River River valley. valley. 19.7 km km -- 12.2 21.0 21.0 km km -- 13.0 13.0 miles miles STOP STOP 28: 28: Lorrain LorrainFormation Formation White White to to pale pale pink pink quartz quartz arenite arenite of of the the upper upper portion portion of of the the Lorrain Lorrain Formation Formation is is exposed exposed on on the the east east side side of of the the highway. highway. 22.8 22.8 17.8 17.8 miles. miles. Junction Junction with with Little Little White White River River road road (Highway (Highway 546.) 546.) End End of of field fieldtrip. trip. 66 �REFERENCES REFERENCES Bennett, Bennett, G. G. 1978. 1978. Huronian Huronian volcanism, volcanism, districts districts of of Algoma Algoma and and Sudhury; in Summary Summary of of Field Field Work, Work, 1978; 1978; Ontario Ontario Geological Geological Sudbury; in Survey, Survey, Miscellaneous MiscellaneousPaper Paper82, 82,p.105-111. p.105-111. Bennett, Bennett, G. G. 1982. 1982. 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Marie Marie and and Blind Blind River, River, Ontario; Ontario; Geological Geological Survey Survey of of Canada, Canada, Memoir 383, Memoir 383, 87p. 87p. Frarey, Frarey, M.J. M.J. and and Krogh, Krogh, T.E. T.E. 1986. 1986. U-Pb U-Pb zircon zircon ages ages of of late late internal plutons and eastern eastern Wawa Wawa subprovinces, internal plutons of of the the A.bitibi Abitibi and subprovinces, Ontario and of Canada, Canada, paper paper Ontario and Quebec; Quebec; Geological Survey of 86-lA, 86-1A, p.43-48. p.43-48. 69 �- Frarey, N.J., W.D. and and Sullivan, Sullivan, R.W. R.W. 1982. A A U-Pb U-Pb Frarey, M.J., Loveridge, Loveridge, W.D. zircon age or the the Creiqhton Creighton granite, granite, Ontario; Ontario; in in Rb-Sr Rb—Sr and and U-Pb U-Pb zircon age ffor Isotopic Age Studies, Report 5, Current Research, Part C, 5, Research, Part C, Isotopic Studies, Geological Survey Geological Survey of of Canada, Canada, Paper Paper 82-1C, 82-1C, p.129-132. p.129-132. Frarey, The Huronian Huronian Supergroup Supergroup north Frarey, N.J. M.J. and and Roscoe, Roscoe, S.M. 1970. The of Geosynclines of the in Symposium Symposium on Basins and Geosynclines of Lake Lake Huron; Huron; in Canadian Canadian Shield; Shield; Geological Geological Survey Survey of of Canada, Canada, 70-40, 70-40,p. p. 143-158. 143-158. Gall, Q. Q. 1992. 1992. Precambrian Precambrian paleosols paleosols in in Canada; Canada; Canadian Canadian Journal Journal Gall, of Earth Earth Sciences, Sciences, Vol. Vol. 29, 29, p. p. 2530-2536. 2530-2536. G-Farrow,C.E. D.J. 1988. Geology of Precambrian Precambrian G-Farr0w.C.E. and and Mossman, D.J. paleosols paleosols at at the the base base of of the the Huronian Huronian Supergroup, Supergroup, Elliot Elliot Lake, Lake, Ontario, Canada; Precambrian Research, v.42, p.107-139. Ontario, Canada; Precambrian Research, v.42, p.107-139. Gay. Gay. A.L. A.L. and and Grandstaff, Grandstaff, D.E. D.E. 1980. 1980. Chemistry Chemistry and and mineralogy mineralogy of of Precambrian paleosols Lake, Ontario; Ontario; Precambrian Precambrian paleosols at Elliot Lake, Precambrian Research, v.12, v.12, p.349-373. p.349-373. Research, Grandstaff, D.E. Grandstaff, D.E. 1980. 1980. Origin Origin of uraniferous uraniferous conglomerates conglomerates at at Elliot Lake, Lake, Canada Canada and and Witwatersrand, Witwatersrand, South South Africa: Africa: implications implications oxygen in atmosphere; Precambrian Precambrian Research, for oxygen in the the Precambrian Precambrian atmosphere; Research, v. 13, p. v. 13, p. 1—26. 1-26. Ste. Marie Hay, Hay, R.E. R.E. 1963. 1963. The Geology of the Sault Ste. Marie map map area; area; unpublished PhD PhD thesis, thesis, McGill McGill University, University, Nontreal, Montreal, Quebec, Quebec, unpublished 325p. 325p. Heaman, U-Pb zircon age for a Hurst dike; dike; in Heaman, L.M. L.M. 1988. 1988. A A precise U-Pb Program with Program with Abstracts, Abstracts, Annual Annual Meeting Meeting Geological Geological Association Association of of Canada-Mineralogical Canada-Mineralogical Association Association of of Canada, Canada, v. v. 13, 13, p. p. A53. A53. Holm, D. Rapid growth growth and strain Holm, D. K. K . and and Silverstone, Silverstone, J. 1990. Rapid strain rates rates inferred inferred from from synkinematic synkinematic garnets, garnets, Penokean Penokean Orogeny, Orogeny, Minnesota; Minnesota; Geology, Geology, 18(1). 18(1). Innes, D.G. 1977. 1977. Proterozoic Proterozoic volcanism in in the the Southern Southern Province Province Innes, D.G. MSc thesis, thesis, Laurentian Laurentian of the the Canadian Canadian Shield; Shield; unpublished MSc University, 150p. University, Sudbury, Sudbury, Ontario, Ontario, lSOp. Innes, Metallogenetic development Innes, D.G. D.G. and and Colvine, Colvine, A.C. 1979. 1979. 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R.A. and and Helmstaedt, Helmstaedt, H. cross-section of cross-section of the the Southern Southern Province Province adjacent adjacent to to Lake Lake Huron, Huron, Ontario: implications Ontario: implications for for the the tectonic tectonic significance significance of of the the Murray fault fault zone; zone; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v.21, v.21, p.447-456. p.447-456. 76 � https://digitalcollections.lakeheadu.ca/files/original/2d6c621da28d3b6ef1ab078bea8bc378.pdf 03bc1a08726e8b70887f134fc605f576 PDF Text Text NEW INFORMATION ON THE THE GRENVILLE GRENVILLE FRONT FRONT NEAR NEAR SUDBURY SUDBURY BY A. 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INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 43rd MEETING, MAY 66- 11, 1997 43rd ANNUAL MEETING, 11,1997 SUDBURY, ONTARIO ONTARIO - Field Trip Part 33 TripGuidebook, Guidebook, Volume Volume 43, Part �Frontispiece: Line Linedrawing drawingfrom frompart partof ofGLIMPCE GLIMPCE Seismic Seismic reflection reflectionLine LineJ, J, W W to to EEline line crossing crossing the the Grenville GrenvilleFront Frontin inGeorgian GeorgianBay Bay(from (fromGreen Greenet etat, al, 1988, Geology, v. 16, p. 790, Figure 2) 1988, Geology, 16, p. 790, Figure 2) �NEW DEVELOPMENTS DEVELOPMENTS IN IN NEW GRENVILLE GRENVILLE FRONT GEOLOGY, GEOLOGY, SUDBURY AREA, ONTARIO SUDBURY AREA, ONTARIO A. Davidson Davidson Geological Survey of Canada, Canada, 601 601 Booth Street, Street, Ottawa, Ontario Ontario K1A KIA0E8 OE8 Geological Survey of of Canada Canada contribution contribution no. no.1997031 1997031 �NEW DEVELOPMENTS DEVELOPMENTS IN IN NEW GRENVILLE GRENVILLE FRONT GEOLOGY, GEOLOGY, SUDBURY SUDBURY AREA, AREA, ONTARIO ONTARIO A. A. Davidson Davidson Geological Geological Survey Survey of of Canada, Canada,601 601Booth Booth Street, Street, Ottawa, KIA0E8 OE8 Ottawa,Ontario OntarioK1A Geological Geological Survey Survey of of Canada Canadacontribution contributionno. no.1997031 1997031 �. ... IllI l l LIST LISTOF OFCONTENTS CONTENTS Southern Province . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 11 Southern Province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 GrenvilleProvince Province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Grenville TheGrenville GrenvilleFront Front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 The Sudbury dyke swarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Sudbury dyke swarm Fieldtrip tripsummary summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313 Field Roadlog logand andstop stopdescriptions descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1515 Road Mississagi sandstone, Stop 1 Mississagi sandstone.Nipissing Nipissinggabbro gabbroand andSudbury Sudburydiabase diabase . . . . . . 1515 Stop 1 Stop22 Slaty Slatyargillite, argillite. Pecors PecorsFormation, Formation. and and"trap "trapdyke" dyke" . . . . . . . . . . . . 1616 Stop Stop33Conglomerate, Conglomerate.Ramsey RamseyLake LakeFormation Formation . . . . . . . . . . . . . . . . . 17 17 Stop 18 Stop44 The TheGrenville GrenvilleFront, Front.Highway Highway69 69 . . . . . . . . . . . . . . . . . . . . . 18 Stop Metasedimentary rocks in the Grenville Province Stop 5 Metasedimentary rocks in the Grenville Province . . . . . . . . . . . 20 20 Stop 5 21 . Stop66 Truncation Truncationof of the theGrenville GrenvilleFront Frontmylonite mylonitezone zoneatatAlice AliceLake Lake . . . 21 Stop . . . Stop77 Comparison ComparisonofofSouthern Southernand andCrenville GrenvilleProvince Provincerocks rocks Stop 24 on onopposite oppositesides sidesof ofthe theWanapitei Wanapiteifault fault . . . . . . . . . . . . . . . . 24 Stop88 Grenville Grenville Front Front relationships relationships near near the theStinson Stinsonhydroelectric hydroelectricdam dam . . 25 25 Stop Stop Stop99 Metamorphosed MetamorphosedSudbury Sudburydiabase diabasedyke dykesegments segments inmetasedimentary metasedimentarygneiss gneiss . . . . . . . . . . . . . . . . . . . . . . . 27 27 in Comments problemsof of correlation correlation and andhistory historyof ofthe theGrenville GrenvilleFront Front problems Comments —. References References . . . . . . 2929 .......................................... 33 33 LIST LISTOF OFILLUSTRATIONS ILLUSTRATIONS Figure1.1. Figure Figure2.2. Figure Figure3.3. Figure Figure4.4. Figure Figure5.5. Figure Figure6.6. Figure Figure7.7. Figure Figure8.8. Figure Generalizedgeology geology of of the the Sudbury Sudburyregion region . . . . . . . . . . . . . . . 33 Generalized The The Sudbury Sudbury dyke dyke swann, swarm. Southern Southernand andGrenville Grenvilleprovinces provinces . . . . . 10 10 Geology of of the the Grenville Grenville Front Front southeast southeastof of Sudbury Sudbury . . . . . . . . . 14 14 Geology 19 Detailed Detailedgeology, geology. the the Grenville GrenvilleFront Frontat atStop Stop4, 4. Highway Highway69 69 . . . . . . 19 22 . The The Grenville Grenville Front Front between between Highway Highway 69 69 and andConiston Coniston . . . . . . . 22 Fault interpretations interpretations in in the theConiston Coniston area area . . . . . . . . . . . . . . . . 23 23 Fault 26 . . . . . . . . . . . . . . . The Grenville Grenville Front Front at at Stop Stop 7, 7. near near Stinson Stinson 26 The Metadiabase Metadiabase dyke dyke remnants; remnants; relics relics of the the Sudbury Sudburyswarm swarm . . . . . . . 28 28 . . Table1.1. Table Huronian HuronianSupergroup Supergroupstratigraphic stratigraphic succession succession in the the Sudbury Sudbury area area . . . . . . 22 �NEW DEVELOPMENTS IN GRENVILLE DEVELOPMENTS IN GRENVILLE FRONT GEOLOGY, SUDBURY SUDBURY AREA, AREA, ONTARIO GEOLOGY. INTRODUCTION INTRODUCTION The Grenville orogen, formed formed during during the the latter part The Grenville orogen, part of ofmid-Proterozoic mid-Proterozoic time, time, Scandinaviato toTexas Texasand andbeyond. beyond. The Grenville Crenville Province is that part extends from Scandinavia of the orogen which is exposed exposed in in the the southeastern southeastern Canadian Canadian Shield. Shield. Its Its northwest northwest boundary with older Shield provinces is known as the Crenville Front, boundary Shield provinces is known as Grenville Front, and is aa major lineamentmarked markedby by faults faults and and mylonite mylonite zones zones inclined inclined to to the major tectonic tectonic lineament southeast. southeast. It is a stnictural structural front in the sense that it truncates the structural trends the older older provinces provincestotothe thenorthwest. northwest: It is aa metamorphic that characterize characterize the metamorphic front in the sense that that high-grade high-grade metamorphic metamorphic rocks characterize characterize the the marginal marginal Crenville Grenville metamorphic grade grade varies varies along along the the footwall of of the front, dependorogen, whereas metamorphic ing on the level exposed exposed in in the different provinces that abut it. the exhumed exhumed crustal level different provinces The high-grade high-grade metamorphism metamorphismin in the the immediate immediate hangingwall hangingwall is not everywhere The everywhere Grenvillian in in age; age; itit attests attests to to uplift uplift in Grenvillian time of the Grenvillian the Crenville Grenville orogen orogen relative to the the adjacent adjacent Shield Shield provinces. provinces. The Grenville Front is is well well exposed exposed in the Grenville Front the vicinity vicinity of of Sudbury, Sudbury, Ontario, Ontario, 1). It has been the the subject subject footwall (Fig. (Fig. 1). where the the Southern Southern Province Province constitutes constitutes its its footwall of attention—and controversy—forseveral several decades, decades, and and shadows of attention-and in retrospect, controversy-for former attempts some of of the the more enigmatic features of of this structure former attempts to explain explain some enigmatic features Crenvillian terrane terrane that that forms its hangingwall are still evident and the the complicated complicated Grenvillian in recently recently compiled compiled maps maps(e.g. (e.g.Card Cardand andLumbers Lumbers1977; 1977;Dressier Dressier1984). 1984). It must be admitted that the Southern Provinceisis known known in in much much more more detail, detail, and is admitted Southern Province is thus thus better understood, than the better understood, than the adjacent adjacent Crenville, Grenville, despite despite recent recent advances advances in in interpreting the interpreting thelatter latter(Davidson (Davidson1986a, 1986a,1995; 1995;Easton Easton1992). 1992). This is not to say that there is consensus on the interpretation of the geologic history of there consensus on interpretation of geologic history of the Southern Southern Province—there are several severaltopics topicsofofdispute dispute outstanding, outstanding, and reinterpretations Province-there are reinterpretations to to of many of be made (e.g.Davidson Davidsoneteta!. 01. 1992; 1992; Card Card 1992). 1992). Resolution of of these these will will made (e.g. have have a direct direct bearing bearing on how how the the rocks rocks in in the theadjacent adjacentCrenvilie Grenville Province Province are are viewed. Before outlining outlining the the historical development of of ideas Before historical development ideas concerning concerning the the Crenville Front Front in in the the area area southeast southeast east east of of Sudbury, Sudbury, it is Grenville is advantageous advantageous to be be presently known known about about the local geology. geology. Brief familiar with what is presently Brief summaries of of the geology geology of of the the Southern Southern and Grenville our current knowledge of Grenville provinces in this area are are therefore presented below. below. �Southern SouthernProvince Province The Southern Province in in Ontario, Ontario, which which isis characterized above all all by wellThe Southern Province characterized above wellpreserved supracrustal strata of of the Huronian Supergroup, Supergroup, early early Proterozoic Proterozoic in age (<2.5>2.22Ga), Ga),can canbe bedivided divided into into two parts: i), (<2.5>2.22 1),aa northeastern northeastern region, region, the Cobalt Embayment, in in which which these these strata strata are little deformed and barely Embayment, barely metamorphosed, metamorphosed, and ii), ii), aa southwestern southwestern belt of steeply folded and variably variably metamorphosed metamorphosed strata (though with a less-deformed northern fringe). fringe). The Huronian Supergroup, less-deformed northern Supergroup, at at least least km thick within the fold belt, lies unconformably on Archean cratonic cratonic rocks. It is 12 krn divided into four four groups, groups, each each group consisting consisting of of at least least three three formations formations (see (see Table 1). The groups generally have immature dastic (gladogenic in part) sedimenhave immature clastic (glaaogenic Table 1). shaly to to silty silty rocks rocks in in the the middle, middle, and sandstone at the top, tary rocks at the base, shaly top, defining upward-maturing cycles with with each cycle cycle reaching reaching greater greater maturity maturity than the preceding one. InInplaces, places,notably notablynear nearSudbury, Sudbury,both bothmafic mafic(Elsie (Elsie Mountain, Mountain, Stobie Stobie formations) and felsic volcanic rocks rocks occur occur at at the base of felsic (Copper Cliff) volcanic of the the Elliot Elliot Lake Group; the mafic flows may may be related to to coeval coeval diabase diabase dykes dykes (Matachewan (Matachewan swarm) and anorthositic complexes that that intrude the adjacent anorthositic gabbro complexes adjacent basement, and the Copper Cliff Cliff rhyolite to granites (Murray, (Murray, Creighton, Skead) which occur only of note within the the volcanic volcanic formations. formations. Other Other features features of note are are the the restriction restriction of of Huronian Supergroup stratigraphic succession succession in in the Sudbury Table 1. Table 1 . Huronian Supergroup stratigraphic Sudbury area area Thickness, m Cobalt Group Group Bar River Bar Gordon Lake Lorrain Gowganda Gowganda Quirke Lake Group Serpent Serpent Espanola Espanola Bruce Bruce Hough Lake Lake Group Group Mississagi Mississagi Pecors Ramsey Lake Lake Elliot Lake Group McKim Matinenda Copper Cliff Copper Stobie Stobie Elsie Mountain orthoquartzite, orthoquartzite, minor iron iron formation formation siltstone, minor argillite, argillite, sandstone arkose, and ortho- quartzite quartzite arkose, feldspathic and polymictic conglomerate, argillite >1220 1060-1280 1500-2400 180-1200 feldspathic quartzite quartzite calcareous siltstone, limestone, dolomite dolomite polymictic conglomerate conglomerate 180-1500 150-550 60-460 cross-bedded feldspathic feldspathic arenite arenite shale, siltstone, wacke wacke polymictic conglomerate conglomerate 760-3000 60-600 60-180 laminated shale, siltstone, wacke wacke conglomerate, wacke, wacke, feldspathic feldspathic arenite arenite conglomerate, felsic flow flow and pyroclastic roclcs pyroclastic rocks flows, intercalated wacke pillowed mafic flows, wacke pillowed mafic flows flows 1500-1800 180-300 730 1500 1000 Abstracted Abstractedfrom fromCard Cardcietal. al.(1977), (19771, Frarey Frarey (1985) (1985) and and Bennett Bennetteteta!. al.(1991). (1991). �- Grenville GrendeProvince Province =1.75 -1.75 Ga plutonic plutonicrocks rocks I.''' IF I'''# # / Paleozoic Paleozoic - =1.45 1.GGa Ga metaplutonic metaplutonicrocks rocks 1.45 1.45 Ga plutonic p l u t o ~rocks crocks B88 1.85 1.85 Ga Ga Sudbury Sudburycomplex complex 1Whitewater WhitewaterGroup Group Murray, Murray, Creighton Creightongranites granites Huronian HuronianSupergroup Supergroup m- 1111111 L 3 LI =2.45 =2& Ga Ga gabbro, gabbro, anorthosite anorthosite Archean Archeanrocks, rocks, undivided undivided =1.7 = 1.7Ga Ga metaplutonic metaplutonicrocks rocks a F ...m.. nfl.. Undated Undatedmetaplutonic metaplutonicrocks rocks Wanapitei Wampiteimafic maficcomplex complex Metagabbro, Metagabbm, anorthosite anorthosite ''IllIllI Gneissic undivided Gneissic rocks, mcks, undivided Front 4 Grenville GrendeFmnt mylonite mylonitezone zone geology ofof the the Sudhury Figure Figure 1.1 . Generalized Generalized geology Sudbury region. region. Plutonic Plutonic units units Killarney; Islands; K mentioned in the the text text are: are: CC -- Cutler; Cutler; CI C1 -- Croker Croker - Killarney; mentioned in B --Bell k k e ; FE -- Eden Eden Lake; lnke; CL -- Chief Chief Lake; W -- Wanapitei. Wanapitei. B Bell Lake; �carbonate rocks rocks to the middle of the Quirke Quirke Lake Lake Group (Espanola (Espanola Formation), and the immense immense thicknesses thicknesses of Cobalt Group Group of extremely extremely pure pure orthoquartzite orthoquartzite in in the Cobalt (upper Lorrajn Lorrain and Bar Bar River fiver formations). Where Where basement-cover basement-cover relationships relationships are are preserved in the Cobalt Embayment, Embayment, it is evident in places that younger younger cycles cycles well presewed successively overlap onto tothe thebasement basement(Bennett (Bennetteteta!. al.1991). 1991). overlap northward northward on Voluminous masses masses of of Nipissing gabbro (formerly Voluminous (formerly called Sudbury Sudbury gabbro, gabbro, now commonly referred Nipissing diabase) formations of of the now commonly referred to to as Nipissing diabase) intrude intrude all formations Huronian Supergroup and has and its itsadjacent adjacentArchean Archean basement. basement. Nipissing gabbro has Ga W-Pb (U-Pbbaddeleyite baddeleyite age age 2219 2219 Ma; Ma; Corfu Corfu and Andrews been dated dated at at—2.22 -2.22 Ga Andrews 1986; 1986; 1993). Although Although folded folded with with its its Huronian Huronian host in the Southern Noble and Lightfoot 1993). Southern Province fold fold belt, belt, there there is is some some evidence evidence that that its its intrusion intrusion postdated postdated an earlier Province earlier (Blezardian orogeny orogenyof of Stockwell Stockwell1982). 1982). stage of folding folding (Blezardian Major, upright, upright, east-west east-westfolds foldsinin the the fold fold belt belt are generally attributed Major, attributed to Penokean orogeny, dated in 1239 and and 1.83 1.83 in its its type type area area(northern (northernMichigan) Michigan) between between1.89 Ga (Bickford a!.1986). 1986). Metamorphic Metamorphicculminations culminationswithin withinthe thefold fold belt, belt, in in part Ga (Bickford etetal. associated with intrusion intrusion of of sanitoid granitoid rocks, rocks, isis of of low low pressure pressure type type and and appears to associated with overprint an earlier, overprint earlier, regional, regional, low-grade low-grade dynamothermal dynamothermal metamorphism metamorphism (Card (Card rocks with with ages in the Penokean range have yet to 19780). to be be identified; identified; 1978a). Plutonic rocks determinations for Cutler (titanite) (titanite) and Eden Eden Lake Lake plutons plutons recent U-Pb U-Pb age determinations for the Cutler Ma (Davidson (Davidson et et al. a!. 1992; 1992;Sullivan Sullivan and and Davidson Davidson (monazite), for example, example, are are—1750 -1750 Ma 1993) 1). 1993) Pig. (Fig. 1). Although not a player in the the Grenville Grenville Front story, a world-renowned feature feature of 01.1984). 1984). of this area area is is the theSudbury SudburyIgneous IgneousComplex, Complex,dated datedatat1849 1849Ma Ma(Krogh (Kroghetetal. Now widely accepted as the product of a massive impact (though not without vocifwithout vociferous detractors; to which which breccias brecciasand and shatter shatter cones cones in in its et a!. al. 1984), 1984), to detractors; see Pye et country rocks rocks are are attributed, attributed, thii this feature feature serves serves to to constrain constrain the the age age of of part part of of the deformation affecting affecting the the Southern deformation Southern Province Province fold belt. belt. The The south south half half of the the Sudbury structure, including including the the sedimentary sedimentary Whitewater Whitewater Group which which itit encloses, encloses, 1978a), displaying northerly, thrust-sense thrust-sense deformed (Card (Card l978a), is metamorphosed and deformed displacement on faults and ductile deformation zones (Shanks and Schwerdtner displacement on ductile deformation (Shanks Schwerdtner 1991). 1991). A belt belt of of elongate elongate granitoid granitoid plutons plutons (Killarney (Killarney batholithic batholithic complex complex of Lumbers the Lumbers 1975) 1975)intrudes intrudes folded folded Huronian Huronian Supergroup Supergroup strata strata adjacent adjacent to to the Grenville Front Front from from near near Sudbury Sudbury to to the coast Grenville coast of Georgian Georgian Bay, Bay, where where the Killarney granite granite and associated, predominantly felsic volcanic volcanic and and hypabyssal rocks Killaney dated atat—1740 -1740 Ma have been dated Ma (U-Pb (U-Pbzircon; zircon;van vanBreemen Breemenand and Davidson Davidson 1988). 1988). A for a phase of the similar age was obtained by Krogh Krogh and and Davis Davis (1970) (1970) for the Chief Chief Lake Lake batholith nearer to Sudbury, but aa new batholith new U-Pb U-Pb analysis analysis of of zircon zircon from from coarse, coarse, pink pink granite of this this unit unitsuggests suggestsan anage ageofof—1465 -1465 Ma (Davidson and and van vanBreemen Breemen1994). 1994). This much younger age is comparable to those reported earlier for the Bell This much younger comparable those earlier for the Bell Lake Lake Ma; van van Breemen Breemen and and Davidson 19881, 1988), and and for the granite farther southwest (1471 (1471 Ma; Croker Island Islandcomplex complexwest westofofKillarney Killarney(—1465 (-1465 Ma; Van Schmus %hmus 1965). 1965). All these rocks are cleanly cut by southeast-trending, vertical dykes of fresh (Uolivine diabase to the the Sudbury Sudburyswarm, swarm,now nowreliably reliablydated datedatat -1235 Ma Ma (Udiabase belonging to —1235 Pb, baddeleyite; Krogh Dudàs eet a!. 1994). 1994). The The importance importance of these Krogh et ef a!. nl. 1987; 1987; Dud& f 01. these dykes dykes is elaborated later in this text. A younger set of east-trending dykes of quartz-bearing A younger set of east-trending dykes of quartz-bearing �5 diabase, diabase, belonging to to the the Grenville Grenville swarm swarm and anddated datedatat595 595Ma Ma(Kamo (Kamoeteta!. al.1995), 19951, 600 the Southern Southem Province Province through the the Grenville Grenville Province Province for for at atleast least600 extends from the km. km. Grenville Province Geological maps of of the the Grenville Provinceadjacent adjacenttotothe the front front in the Sudbury Geological maps Grenville Province Sudbury region (Lumbers Frarey 1985; 1985;Card Card and and Lumbers 1977) portray this terrane 197'7) portray terrane (Lumbers 1975; 1975; Frarey primarily as a 'sea 'sea of of gneisses', gneisses', a large large proportion proportion of which is interpreted interpreted to to be be sedimentary in in origin. origin. The gneisses gneisses include undoubted metasediments metasediments such as as quartzite, gneissand and marble, marble, but but many many are rather calc-silicate gneiss quartzite, pelitic gneiss, and rare calc-silicate ordinary quartzofeldspathic protoliths are uncertain. These quarkofeldspathic rocks whose specific speafic protoliths uncertain. These gneisses are interlayered with with mafic maflc gneiss gneiss and and metagabbro metagabbro near near the the front southeast of Sudbury, and with with anorthositic anorthositic gneiss farther northeast; northeast; they are are interspersed interspersed with irregular and and commonly commonly sinuous units units of of foliated foliated or or gneissic gneissic granitoid, granitoid,particparticularly Bay. A ularly toward Georgian Georgian Bay, A few few small small plutons plutons have have more more equant equant outlines. outlines. Notable among these these is an Notable among an oval oval body body of of mafic mafic rock, rock, the theWanapitei Wanapiteicomplex complex (Lumbers 1975;Rouse11 Rouselland andTrevisiol Trevisiol1988), 1988),situated situatedclose closetoto the the front east of (Lumbers 1975; of Sudbury, which more more information informationisisgiven givenbelow. below. Also Also present present in this area Sudbury, about which of pegmatite, pegmatite, as well well as numerous small pegmatite are several large masses of pegmatite dykes dykes and lenses, and small bodies of mafic rock mapped as 'cataclastic metadiabase' small bodies of mafic rock mapped as 'cataclastic metadiabase' (Lumbers 1975). 1975). The The latter latter are are now now confidently correlated correlated with with Sudbury Sudbury diabase on the grounds outlined below. grounds outlined below. itIt isis easy easytotoassume assumethat thatthe themetasedimentary metasedimentary gneisses gneisses and and interlayered interlayered metagabbro were derived derived from metagabbro were from the Huronian Supergroup Supergroup and and Nipissing Nipissing gabbro gabbro respectively, but ifif this is the case, of stratigraphic stratigraphic order permitting case, all semblance of respectively, but direct correlation with the well-known Huronian succession has been been obscured or well-known Huronian succession has destroyed destroyed during deformation deformation and and high-grade high-grade metamorphism. metamorphism. Northeast Northeast of of Sudbury, metasedimentary biotite biotite schist schist and gneiss gneiss (Red (Red Cedar Cedar Lake Lake formation), formation), formerly interpreted as aa coarse clastic facies of of Huronian sediment sediment by by Lumbers Lumbers coarse clastic (1978), are now now considered considered to to be be Archean, Archean, probably representing reworked wacke (1978), are wade and siltstone siltstone of of the the Pontiac Pontiac Group Group of of the the adjacent adjacent Superior Superior Province; Province; Archean Archean ages ages are preserved units in this p r e s e ~ e din metagranitoid metagranitoid units this area. area. On the the other other hand, hand, some some metasedimentary rocks in in the marginal metasedimentary rocks marginal Crenville Grenville Province Province south of of Sudbury, Sudbury, extending extending to to the the north north shore shoreof of Georgian Georgian Bay, Bay, have Nd-model Nd model ages ages (2.32 (22.32Ga, Ga,Dicldn Dickin and McNutt 2.12 Ga, McNutt 1989; 1989; 22.12 Ga, P.O F.O Dudas, Dud&s,pers. pers. comm., comm., 1991) 1991) which are are too tooyoung young (unless disturbance of of Nd systematics systematics isis admitted) admitted) for for them them to to be be correlated with the Huronian Supergroup, whose sediments sediments have have Archean Archean provenance provenance and Nd model model ages; for example, Nd isotopic analyses of sedimentary rocks from the Lorrain ages; example, isotopic analyses of sedimentary the Lorrain Formation northeast of Sudbury (Lightfoot and Naldrett Naldrett 1989) 1989) yield depleted depleted mantle mantle 2.85 Ga. Ga. model ages agesof of 2.85 model In the same U-Pb zircon zircon ages ages provide provide reason to correlate same region, region, however, however, U-Pb correlate metamorphosed granitoid rocks rocks with those in the the Southern Southern Province, Province, both 1.74 1.74 and 1.47 Ga Ga age age groups being being represented represented (Davidson (Davidsoneta!. el al.1992; 1992; van van Breemen Breemeneta!. et al.1986; 1986; van Breemen pers. comm. 1993). 1993). van Breemen Breemen and and Davidson Davidson (1988) (1988) suggested suggested corcorrockswith withthe the—1.75-Ga -1.75-Ga graniterelation of the the Killarney Killamey granite granite and and allied alliedvolcanic volcanicrocks �rhyolite association of the the Central Central Plains Plains orogen orogen in the association of the mid-continent mid-continent (Sims (Sims and itselfpart part of of the the larger larger Yavapai/Mazatzal Yavapai/Mazatzal province exposed farther Peterman 1986), 19861, itself 19%). They also noted that the the 1.47-Ca 1.47-Ga age of the Bell Bell Lake granite west (Hoffman 1988). lies within the lies the range range of of the the older olderofoftwo twoso-called so-calledanorogenic anorogenicgranite-rhyolite granite-rhyolite a!. 1986). provinces et al. 1986). In the the adjacent adjacent provinces in the the buried buriedmid-continent mid-continent (Bickford (Bickford et Grenville Rovince, Province, the the supracrustal supracrustal rocks rocks which which originally originally hosted hosted the the older of of the two granite suites and which appear to be younger than the Huronian Supergroup, the Huronian Supergroup, for this event has have presumably presumablyundergone undergone—1.7-Ga -1.7-Ga orogeny. orogeny. Evidence Evidence for has been been recognized in in the Key Harbour area of the Georgian recognized Key Harbour Georgian Bay Bay coast, where the oldest oldest associated with with deformed granite dated migmatitic gneisses are assoaated dated at at1685 1685Ma (Corrigan 1990). In addition, it now appears that this 1990). this part part of of the theGrenville Grenvilleorogen orogen also also underunder-1.47-Ga plutonwent widespread widespread metamorphism metamorphism and anddeformation deformationshortly shortlyafter afterthe the—1.47-Ca ism. Monazite al. 1994) 1994) and titanite Monazitein inhigh-grade high-grade metasedimentary metasedimentary gneiss gneiss (Dudas (Dud& et a!. in 1.74-Ga et a!. al. 1993), 1993), both the front, front, 1.74Ga metagranitoid rocks (Haggart (Haggart et both within within 10 km of the leucosomes farther farther into the Crenville and zircon zircon in in orthopyroxene-bearing orthopyroxene-bearing leucosomes Grenville orogen orogen (Ketchum 1994), all record record ages ef a!. al. 19941, agesofof—1.45 -1.45 Ga. Ga. (Ketchurnet orogeny in in this this comer corner of of the the province province appears appears to be restricted to Grenvillian orogeny deformation and metamorphism metamorphism late in the age-range age-range ofof1.3-—1.0 51.3--1.0 Ga Gaaccorded accordedtoto and presumthe broader 'Crenvillian 'Grenvillian orogenic orogenic cycle' (Moore and Thompson 1980), and ably associated with tectonic burial accompanied by deep-seated, deep-seated, large-scale thrust imbrication directed directed toward toward the the front, followed followed shortly shortly thereafter thereafter by by rapid rapid uplift and imbrication and a!. 1993; Culshaw exhumati on accompanied by by extensional tectonics (Haggart (Haggart et al. Culshaw et ef a!. al. exhumation 1994). related to tothe theonset onsetof ofGrenviUian Grenvillian 1994). There are no supracrustal rocks that can be related orogeny, and no plutonic rocks marking its culmination. culmination. A A growing growingdatabase databaseof of UUorogeny, rocks marking and titanite from this region Pb ages for zircon, zircon, monazite monazite and region suggests suggests that that tectonic tectonic activity was Ma(thii (thisseems seems aa relatively short short was restricted restricted totobetween between—1040 -1040 and —980 -980 Ma period in terms, but but nevertheless nevertheless is is equivalent equivalent to to the whole whole of the the in Precambrian Precambrian terms, Tertiary!). Much earlier Ma; van van Breemen Tertiary!). Much earlier ductile ductile deformation deformation (—1160 (-1160 Ma; Breemen and Davidson 1986) was associated associated with with emplacement emplacement of of the Parry Sound 1986) was Sound granulite granulite allochthon kmfrom from the the front, front, but so so far far there there isis allochthon in the the interior interiorof of the theprovince, province,—100 -100 km no geochronological evidence evidence for forany any event event of of this this age age closer doser to to the the front. front, The Grenville GrenvilleFront From Georgian Bay Bay to Coniston, Coniston, the Grenville Front is marked marked byby a zone of of faults faults inclined generally generallyatatmoderate moderate angle angle to to the the southeast, southeast, that cut all but and mylonites, inclined dykes, the the Grenville Grenvilleswarm. swarm. It has been well documented documented that the youngest diabase dykes, dykes disrupted by by faults and dykes of of the the Sudbury Sudbury swarm, swarm, although although disrupted and not not traceable traceable individually zones, do cut earlier, front-parallel fabrics within faultindividually across across mylonite zones, within faultbounded bounded panels panels(Henderson (Henderson1967; 1967; Brooks Brooks 1976; 1976; Frarey 1985; Bethune and Davidson Davidson 1988). A means means is is thus thus available available to to distinguish distinguishprepre-and andpost-1235-Ma post-1235-Ma structures. structures. 1988). First, some lingering lingering misunderstandings misunderstandings about about the Grenville Front are First, however, however, some the historical historical development development of of interpretation interpretation of of thii this major best assessed by following following the structure. structure. Long before the the Shield Shield was was divided into structural h n g before structural provinces provinces (Gill (Gill1948), 1948), the boundary between the Southern Southern and and Grenville Grenville Provinces was recognized recognized by Collins Collins �(1916, 1925) as as the locus of major (1916, 1925) major change, change, where where well-preserved, well-preserved, broadly-folded broadly-folded Huronian Huronian sedimentary sedimentary rocks rocks and Nipissing Nipissing gabbro gabbro intrusions, intrusions, at at relatively relatively low low metamorphic metamorphic grade, give give way way southeastward to to aa complex complexterrane terrane of of high-grade high-grade gneissic gneissic rocks. rocks. Mapping Mapping across across this boundary in in the the late late 1920s 1920s led to the idea that that granitization on aa huge huge scale scale was was responsible responsible for for the the"disappearance "disappearance of of the the granitization Huronian" (Quirke (Quirke and and Collins Collins 1930). 1930). This Thii hypothesis hypothesis was was championed championed particularly particularly Huronian" by Quirke Quirke(1927, (1927, 1940), 1940), although hotly hotly disputed disputedby byothers others(e.g. (e.g.Jones Jones1930); 1930);tracts tractsof of by metasedimentary gneiss gneiss as far as 40 40 km from the the boundary boundary were werecorrelated correlatedwith with metasedimentary speafic Huronian Huronianformations formations(Quirke (Quirke1930). 1930). specific in Inthe thearea areadirectly directly southeast southeastof of Sudbury, Sudbury, the theboundary boundarybetween betweenthe theSouthern Southern and Grenville Grenville provinces provinces was interpreted as as aa metamorphic metamorphic transition iransition by by Phemister Phemister and (1961; Grant et et al. a!. 1962) 1962)where whereHuronian Huronian sedimentary sedimentary rocks and Nipissing (1961; Grant Nipissing gabbro gabbro were were abruptly abruptly metamorphosed metamorphosed and granitized g r a n i i k d to to make makethe thegneissic gneissicand andmigmatitic migmatitic rocks rocks of of the the Grenville Grenville Province. Province. Kwak Kwak(1968) (1968) and and La La Tour Tour(1981) (1981) documented documented an an Daiziel et a!. (1969) abnormally high metamorphic gradient across this transition. abnormally metamorphic across this transition. Dalziel et al. (1969) recognized was an an important factor in this transition, and that recognized that mylonitization mylonitization was metamorphism preceded preceded the the earliest earliest recorded recorded folds. folds. They They expressed expressed some some doubt doubt metamorphism about about the the equivalence equivalence of of rocks rocks on opposing sides of the front, front, but but did didnot notinvoke invoke large-scale displacement to to explain explain the the possibility large-scale displacement possibility that different different rocks rocks had had been been juxtaposed juxtaposed or or that that metamorphic metamorphic isograds had been been 'telescoped'. 'telescoped'. Without Withoutthe thebenefit benefit of modern Dalziel (1974, (1974, p. 1577) 1577) contended that the the modern geochronology, geochronology, Brocoum Brocoum and Dalziel rocks of the including the the Sudbury Structure, and those the Southern Southern Province, Province, including those in in the the "... all all underwent underwent the thesame samemajor majordefordeforpart of of the theGrenville GrenvilleProvince Province"... adjacent part mational event after the intrusion intrusion of the the Nipissing Nipissing diabases diabases (2.15 (2.15 b.y. b.y. ago) and the Nickel Irruptive Irruptive (2.0 (2.0 b.y. ago) and prior prior to to the theintrusion inirusionofofthe thenorthwest-southeast— northwest-southeasttrending olMne olivinediabase diabasedyke dykeswarm swarm(1.46 (1.46b.y. b.y. ago) ago)...", ...",which, which, they they stated, stated, cuts a.16the the trending gneisses in the northwestern Province. This Thii major major event event was was attributed attributed northwestern Grenville Grenville Province. to a wider age-range (2.0—1.6 to the the Penokean Penokeanorogeny, orogeny,which whichwas wasatatthat thattime timeaccorded accorded a wider age-range (2.0-1.6 (1976)pointed pointed out out that the today. However, However, Brooks Brooks (1976) the same same olivine olivine Ga) than itit isis today. diabase swarm) are are deformed deformed and andmetamorphosed metamorphosed farther farther diabase dykes dykes (Sudbury (Sudbury swarm) southwest he did not dispute southwest along the front, although although he dispute the the fact fact that that they theyalso alsocut cut earlier deformation deformation fabrics fabrics in granitoid granitoid rocks rocks adjacent adjacent to to the the front. front. earlier Phemister recognizedthe theGrenville GrenvilleFront Frontinin this this area area to have Phemister (1961) (1961) recognized have two two distinct distinct manifestations, manifestations, a metamorphic transition southwest southwest of of Coniston, Coniston, and and aadisdkcrete cit., p. 61): "One of the features that makes this Crete fault to the east. He Hestated stated(op. (op. 61): "One the features that makes this region of special is that here the Wanapitei fault is seen special interest is seen to to cut cut across across the the "front" of of metamorphiim metamorphismleaving leavingno nodoubt doubt therefore therefore that that it marks a younger event the structural structural history history of of the region.... region.... Thus Thus ... ...the the boundary boundary in inthe thewestern westernsection section in the Dalziel et a!. is aa metamorphic "front" while in the eastern part it is a fault." (1969, metamorphic "front" while in it is a fault." Dalziel ei al.(1969, 211) described described the the Wanapitei Wanapitei fault fault as aa brittle brittle fracture, fracture, being being aa later latereffect effectwhich which p. 211) . The obscures"... ... the the fundamental fundamental tectonic character of front ...". The westward westward conconof the front obscures " tinuation tinuation of of the the Wanapitei Wanapitei fault in in the the Southern Southern Province Province aligns aligns with with the thewellwellknown Murray fault, passing south of of Sudbury and extending extending for at at least least aa further further to the the west west(Fig. (Fig.1). 1). 150 km to An alternative interpretation alternative interpretation was advanced advanced by by Lumbers Lumbers(1975), (1975), who who comcombined the of the front as a single the two two different different segments of single feature feature referred to to as as the the �'Grenville Front Boundary Boundary Fault'. Fault'. His map shows the Murray Murray fault fault as asremaining remaining within the Southern Province instead of being continuous with the Wanapitei Southern Province of Wanapitei fault interpretation has has been been reproduced 6, A). A). This This interpretation reproduced on subsouth of of Coniston Coniston (Fig. (Fig. 6, sequent geological compilations compilations (Card (Card and and Lumbers Lumbers1977; 1977; Dressler Dressier1984). 1984). Reaffirming the faulted nature of the Grenville Front mylonite zone east in the Coniston of the Grenville mylonite the Coniston Davidson (1992) (1992) argued post-Grenvillian normal displacement on the the area, Davidson argued that post-Grenvillian normal displacement Wanapitei fault (i.e. side down) down) best best explains explains the the abrupt opposition (i.e. Grenville Grenville side opposition of of Wanapitei high-grade high-grade gneisses gneisses and andlittle-affected little-affected Southern SouthernProvince Province rocks. rocks. Zone' is is commonly commonly used in conjunction The term 'Grenville 'Grenville Front Tectonic Tectonic Zone' conjunction First coined by Lumbers with the northwest northwest margin margin of ofthe theGrenville Grenville Province. Province. First Lumbers (1971a), itit was defined defined as as aa zone zoneof of northeast-trending northeast-trending cataclastic cataclastic foliation foliation with with (1971a), manifested mainly mainly in the gneissic attendant southeast-plunging southeast-plunging lineation manifested gneissic rocks rocks of of Province, but but also also including includingaa narrow narrow strip strip in the adjacent the Grenville Province, adjacent Superior of the 'Grenville and Southern Southern provinces, provinces, northwest northwest of 'Grenville Front Boundary Boundary Fault', Fault', in in occur. The which similarly oriented structures occur. The northwest boundary boundary of of the theGrenville Grenville Province, however, however, was was placed placed at at the boundary Province, boundary fault. fault. Wynne-Edwards (1972) Wynne-Edwards (1972) defined the the tectonic zone aa little confiningitit to to southeast of the defined tectonic zone little differently, differently, confining southeast of Grenville Front, Front, while while recognizing that front-related deformation is present Grenville recognizing that front-related deformation present northwest of the front in the ForelandZone'. Zone'. The southeast margin of of northwest of the 'Grenville 'Grenville Foreland the Grenville Front Tectonic Zone was not defined rigorously by either author. Tectonic Zone was not defined rigorously either author. Subsequently, Rivers et a!. (1989)used usedthe the term term 'Parautochthonous Belt' to describe al. (1989) describe the marginal part of the Grenville orogen containing reworked rocks the marginal of the Grenville orogen containing reworked rocks of of the the adjacent, older older Shield provinces, and and not not coincident adjacent, Shield provinces, coincident with the the Grenville Grenville Front Front Tectonic Zone. To confusion,neither neitherofofthese these two two terms terms is is used used in Tectonic Zone. To avoid avoid possible possible confusion, this guide. guide. Application of of modern kinematic kinematic analysis to fabrics in in the themylonitic myloniticrocks rocks along the Grenville along Grenville Front between between the coast of Georgian Georgian Bay Bay and Sudbury Sudbury conconsistently yields evidence for thrust-sense displacement toward toward the northwest (Pryer (Fryer thrust-sense displacement 1988). The position of this c; Davidson and Bethune Bethune 1988). 1985, 1993; Davidson Davidson1986b, 1986b,C; segment of of the front, however, Frarey and however, has been a matter of of some some contention. contention. Frarey Cannon (1969; Frarey 1985) 1985)placed placedthe thefront frontalong along the the northwest northwest contacts of the (1969; Frarey the and Bell Lakegranites, granites,on on the thebasis basisthat that these these contacts contacts are are faulted faulted in many Bell Lake Killarney and places and cut across fold trends in the Huronian rocks. rocks. The places The northeast northeast extension extension of of was shown shown to pass into the southern part this 'front', 'front', however, however, was part of of the theChief Chief Lake Lake In their Card and Lumbers granite. In their regional regional compilation, compilation, Card Lumbers (1977) (1977) placed placed the the 'Grenville Front Front Boundary Boundary Fault' Faultton onthe thesoutheast southeastside sideofofthese these granites. granites. Davidson Davidson (1986b)favoured favoured the the latter latter position, position, modified modified to to a somewhat more (1986b) more southeasterly southeasterly position near Georgian it coincided with a major Georgian Bay, Bay, because because it coincided with major zone zone of of mylonitizmylonitization across which the most pronounced change change in in structural style and orientation orientation Farther northeast, northeast, this this zone zone also also coincides coincides with with an abrupt increase occurs. occurs. Farther increase in in metamorphic grade; in in addition, metamorphic grade; addition, it marks marks the the southeast southeast limit limit of ofcontinuously continuously traceable Sudbury dykes dykes (Bethune (Bethune 1993) 1993)and andisisthus thus identifiable identifiable as as a feature traceable Sudbury feature of Grenvillian age. that a distinction must be made It has has now now become become clear clear that distinction must made between between the respective northwestern limits limits of of the the pre-Sudbury pre-Sudbury dyke dyke deformation that postdated respective the —1.47-Ga granitesand and post-Sudbury post-Sudbury dyke deformation. deformation. If the Grenville Grenville Front Front is is -1.47-Ga granites �taken as the northwest northwest limit of penetrative deformation and metamorphism related to Grenvillian Sudbury dykes dykesbecomes becomes Grenyillian orogeny, then the state of preservation of the Sudbury a crucial factor in locating locating the front. front. The youngest pre-Sudbury dyke dyke structures structures northwest of this limit northwest of limit are are unlikely unlikely to to represent represent an an early early phase phase of ofGrenvillian Grenvillian orogeny because the the Sudbury dyke swarm, swarm, which which cuts them, them, was was presumably presumably orogeny because Sudbury dyke emplaced into stable stable continental continental crust. crust. It seems more likely that aa distinctly distinctly earlier earlier Ga,recorded recordedon onboth bothsides sides of of the the Grenville Front as orogenic event at at —1.45 -1.45 Ga, as defined defined above, was was responsible responsiblefor forthe theyoungest youngeststructures structurescut cutby bythe theSudbury Sudburydykes. dykes. At above, present, present, no counterpart counterpart of of this this event event has has been been recognized recognized elsewhere elsewhere outside outside the the Grenville Province; coeval coevaligneous igneousactivity activityinin the the buried mid-continent Grenville Province; mid-continent to the the a!. Windley southwest is a al. 1986; 1986; 1989). Based on is regarded regarded as as'anorogenic' 'anorogenic' (Bickford (Bickford et 1989). less comprehensive geochronology than is is available available today, today,Stockwell Stockwell(1982, (1982, p. p. 68) 68) proposed that the ill-defined 'Killarriean orogeny', to which he ascribed a terminal terminal that the ill-defined Killarnean orogeny', to which age of of —1.5 Ga,has hasitsitstype typeregion regionwithin withinthe theGrenville GrenvilleProvince. Province This -1.5 Ga, This now now seems seems prophetic in the prophetic in the light light of of the themore morerecent recent identification identification of of widespread, widespread, prepreGrenvillian plutonism within the the adjacent adjacent Grenville Grenville orogen. orogen. Stockwell, however, (-1.74 and and had no no knowledge knowledgeof of the thetwo twodistinctly distinctlydifferent differentages agesofofgranitic graniticrocks rocks(—1.74 —1.47 Ca)that thatisisconsistently consistentlyemerging emergingfrom fromgeochronological geochronologicalstudies studies in in this area; -1.47 Ga) area; the concept of of 'Killarnean orogeny' now now seems seems inappropriate inappropriate in that the 'Killarnean orogeny' the time-span time-span assigned to it embraces embraces both age groups. groups. The ages and events in the and expression expression of of post-Penokean, post-Penokean, pre-Grenvillian pre-Grenvillian events the Southern Province are are poorly poorly documented. documented. For example, the age of Southern Province of deformation deformation and metamorphism of of the southern southern part part of of the Sudbury Structure, Structure, and how far the effects of of this this event extend extend into the neighbouring Huronian rocks, are not not known. known. It is quite possible possible that the the rocks rocks in in the the Grenville Grenville Front Front region region were were affected affected by by two two post-Penokean events before before emplacement of the the 1235-Ma 1235-Ma Sudbury Sudburydyke dykeswarm swarm—related to the of major orogens farther farther southeast that have events related the development development of major orogens been largely overprinted and obscured by later Grenvillian orogeny in the the interior interior of of Province. Displaced the Grenville Province. Displaced and telescoped remnants of these orogens, whose tectonic fronts appear appear to to coincide coincide so so closely closely with with the the Grenville GrenvilleFront Front(Bethune (Bethune1993), 19931, may may explain explain the the abundant abundant evidence evidence for for pre-Grenvillian pre-Grenvillian deformation deformation and and metamorphism within this part part of of the theGrenville Grenvilleorogen. orogen. referenceshave have been been made made to the Sudbury Throughout the foregoing, several references Sudbury diabase dyke swarm, implying usefulness as as a time-marker for discerning diabase implying its usefulness discerning the effects of of Crenvillian effects Grenvillian orogeny orogeny in this this poly-orogenic poly-orogenic terrane. Therefore Therefore a more more detailed account of of this this swarm swarm and its recognition within the Crenville detailed recognition within Grenville orogen is given below. below. The Theextent extent of of the the Sudbury Sudbury swarm swarm in in the the Southern SouthernProvince Province southwest southwest of of Sudbury and and the the known known distribution distribution of of equivalent equivalent metadiabase metadiabase dykes dykes and and remnants in 2. in the the Grenville Grenville Province Province are shown shown in in Figure Figure 2. Sudbmy dyke Sudbury dyke swami swarm Lumbers (1975)mapped mappedtwo two types types of of diabase diabase dykes dykes in the Lumbers (1975) the Southern Southern Province Province of Sudbury, Sudbury, which which he he referred referred to to simply simplyas as 'olivine 'divine diabase' and southeast of and 'diabase', 'diabase', and which are part of what what are are now now known known as the the Sudbury Sudbury and and Grenville Grenville swarms swarms olivine diabase dikes respectively (Fahrig (Fahrigand and West West1986). 1986). He He stated stated that the "... "... olivine dikes respectively �The Sudbury Sudburydyke dyke swarm swarm in inthe theSouthern SouthernProvince Provincesouthwest southwestofof Sudbury, Sudbury, Figure2.2. The Figure dykes in the Grenville and anddistribution distributionofofmetamorphosed metamorphosedand anddeformed deformedSudbury Sudbury dykes in the Grenville Province(solid (solidlines linesand anddots). dots). East-west East-westdashed dashedlines linesare areGrenville Grtimilledykes. dykes. Province areconfined confinedtotothe theSouthern SouthernProvince Provinceportion portionof of the thearea areaand andare arepart partofofa aregional regional are northwest-trending northwest-trending swarm swarm that that intrudes intrudesrocks rocksof ofboth boththe theSouthern Southernand andSuperior Superior Provinces Provinces but but which which does does not notextend extendacross acrossthe theGrenville GrenvilleFront FrontTectonic TectonicZone Zoneinin (op.cit., cit.,p.p.109). 109). Although Although he he mapped mappedoccurrences occurrencesof of theGrenville GrenvilleProvince." Province."(op. the metadiabase' in metadiabase metadiabase in inthe theadjacent adjacentGrenville GrenvilleProvince Province(termed (termed'cataclastic 'cataclastic metadiabase' in his map map legend), legend), he he did did not notequate equatethese thesewith withthe the Sudbury Sudbury dykes. dykes. Farther Farther his (1977) also documented two different types of diabase southwest,Palmer Palmer aeta!. al. (1977) two different types of diabasein inthe the southwest, Southern SouthernProvince Province south southofofLake LakePanache, Panache,but butFrarey Frarey(1985), (1985). while whileacknowledging acknowledging the the distinction, distinction, included included both types types in in the thesame samemap mapunit. unit.Frarey, Frarey, however, however, did did recognize recognize that that "Olivine "Olivine diabase diabase dykes dykes of of the the "Sudbury "Sudbury swarm", swarm", so sonumerous numerous in inthe the Province Southern Province, continue east-southeastward into the Grenville Southern Province, continue east-southeastward into the Grenville Province atat (op.cit., cit., p.p. 47). 47). His Hismap mapshows shows leastas asfar faras asTyson TysonLake Lake and andpossibly possiblymuch muchfarther." farther."(i. least several severaldyke dykesegments segmentswith withvarious variousorientations orientationsininthe theGrenville GrenvilleProvince; Province; some someof of Grenvillian "...curved curved traces, traces, suggesting suggesting late late folding folding that that isispresumably presumably Grenvillian thesehave have"... these .."(op. (op. cit., cit., p. 48), and he he recognized recognized the the'cataclastic' 'cataclastic' nature nature of of the thediabase diabasein inthin thin the Grenville section. At At the theeastern eastern edge edge of of his hismap maparea, area,some some18 18km km into into the Grenville section. Province, he mapped one dyke whose eastward continuation in Province, one dyke whose eastward continuation in the theBurwash Burwashmap map 'cataclastic metadiabase'. Farther areawas wasclassified classifiedby byLumbers Lumbers(1975) (1975)as as 'cataclastic metadiabase'. Farthereast eastnear near area within a ductile gneiss Key Harbour, 'cataclastic metadiabase' occurs as isolated pods Key Harbour, 'catadastic metadiabase' occurs as isolated pods within a ductile gneiss medium(Davidson (Davidsonand andBethune Bethune1988). 1988). medium �It is clear clear that geologic geologic units foreland of an units which which are are undisturbed undisturbed in in the foreland orogen, orogenic front front may may be be used to constrain the tectonic history history of of the adjacent orogen, provided they can can be be recognized recognized within it. it. With respect to the Grenville Front, the Sudbury dykes Southern Province and are are Sudbury dykes in in the Southern Province foreland forelandare are such such aa unit, and particularly important for for the the following following reasons: reasons: 1) they they are are oriented oriented orthogonally orthogonally to the front; front; 2) the theacross-strike across-strikewidth widthofofthe theswarm swarmisisatatleast least200 2001cm; km; 3) many many dykes dykes are are thicker thicker than than 30 30 m, some some being more than than 100 100 in; m; 4) individual individual dykes dykesare arecontinuous continuousfor formany manytens tensof of kilometres; kilometres; 5) the the diabase diabase has has aa distinctive, distinctive, evolved evolved chemistry chemistry (undersaturated, enriched in iron, alkalis and high high field field strength strength elements); elements); 6) the known (—1235 theage ageof ofthe theswann swarmisis known (-1235 Ma). Ma). The first first four four attributes attributes make make it reasonable reasonable to to expect expect them them to to be be found within the the Grenvile Province provided provided that the Grenville the Grenville Grenville Front is not not aa post-1235-Ma post-1235-Ma suture juxtaposing exotic crust crust against against the the Superior and Southern Province craton, or that that juxtaposing exotic there has been lateral displacement displacement along the front. been no no large largescale, scale, post-1235-Ma post-1235-Ma lateral front. Their distinctive distinctive chemistry chemistryshould should allow allow them them to to be be recognized Their recognized within the GrenGrenville Province, Province,provided provideditithas hasnot notbeen beenunduly unduly disturbed disturbed during during metamorphism. metamorphism. If If ville be traced traced into the front and recognized beyond beyond it, it, their known age would they can be make them them an invaluable make invaluable time marker for distinguishing distinguishing pre- and and post-emplacepost-emplacement structures. structures. Mapping along the the Grenville Front has has failed failed to trace individual Mapping along Grenville Front individual Sudbury Sudbury dykes from the Southern into the Grenville Province. Correlation of Sudbury the Southern into the Grenville Province. Correlation of Sudbury diabase and inetadiabase metadiabase must therefore therefore rely rely on on comparative comparativewhole-rock whole-rock chemistry chemistry and isotopic age. The characteristic chemistry of Sudbury diabase, documented by The characteristic by (1965),Merz Merz(1976) (1976)and andCondie Condieetetal. a!.(1987), (1987),and andunlike unlikethat that of of any any other other Fahrig et al. (1965), diabase dyke swarm in the Shield, has been corroborated by major and trace trace element element analyses of of 40 40 samples samples between between Sudbury Sudbury and and Georgian Georgian Bay, Bay,ranging ranging up up to 45 km km analyses northwest of the Grenville Front. A northwest of Grenville Front. A similar similar number number of of analyses analyses of of metadiabase metadiabase samples from the the Tyson Tyson Lake Lakearea, area,up up to to 16 km km from samples from from the front, front, and and smaller smaller numbers from both Key Harbour, —40 km from the front, and closer to the front both Key Harbour, -40 km from the front, and front east east of Sudbury, all have identical identical chemical chemicalsignatures signaturesto tofresh fresh Sudbury Sudbury diabase. diabase. These of Sudbury, results are summarized and reported reported fully in Bethune (1993). summarized in in Bethune Bethune (1989) (1989) and (1993). The U-Pb age of of 1238±4 Maobtained obtained by by Krogh Krogh eet a!. (1984) (1984)on onbaddeleyite baddeleyite in Sudbury U-Pb 1238±Ma t al. Sudbury diabase from from Espanola, Espanola,65 65km kmwest westofofSudbury Sudburyand and40 40km from the front, has been diabase km from corroborated by U-Pb U-Pb baddeleyite baddeleyite ages ages determined determined for for three three other other Sudbury dykes corroborated by northwest of the front (1994),who who also also obtained obtained similar similar ages for ef a!. al. (19941, northwest of front by by Dudãs Dudas et metadiabase in the the Grenville Grenville Province. Province. The The average average age age for for the the three dykes in the metadiabase in Southern Province, at at locations 30, 16 and 33 km from the Southern Province, locations 30, the front, front, isis1234±7 12349 Ma. Ma. Baddeleyite was separated from metadiabase at locations 2,3 2, 3 and 12 km southeast Baddeleyite was southeast of of the front at Tyson Lake, and 5 km from the front at Wahnapitae, east of Sudbury. Tyson Lake, at Wahnapitae, east of Sudbury. Ma), but all U-Pb analyses The average age for metadiabase metadiabase is slightly slightly older older (1243 (1243 Ma), analyses lie lie on a discordia whose upper intercept is 1233±4 Ma. In addition, metamorphic zircon intercept is 1233±Ma. metamorphic zircon obtained from two two of of the themetadiabase metadiabasesamples samplesgave gaveages agesofof—1000 -1000 Ma, agreeing agreeing well well with a Nd-Sm metamorphic mineral mineral isochron isochron age age obtained obtained from from the sample 12 12 km from the the front. front. In from In summary, summary, there is little reason to doubt that diabase dykes of the �Sudbury swarm are represented in the the Crenville Grenville Province Province by metadiabase metadiabase preserved preserved as folded dyke segments the area area that that segmentsand and isolated isolatedpods. pods. It is the only rock unit in the records solely the effects of younger Grenvillian deformation and and metamorphism, metamorphism, both adjacenttoto the the front both in the the Southern Southern Province Province adjacent front and within within the the Crenville Grenville orogen. Approaching the front from from the northwest, the dykes dykes are are offset offset by by subsidiary subsidiary faults faults near which which they they may may show show internal internal cataclasis cataclasis and and low-grade low-grade alteration alteration (chlorite, epidote, epidote, fibrous (chlorite, fibrous amphibole amphibole and sericitized sericitized plagioclase). plagioclase). In the the Lake Lake Panache area they swing to a more easterly trend where they cross the Bell Lake Panache area they swing to where they cross the Bell Lake granite granite and turn turn abruptly abruptly northeast northeast at the the main main Crenville Grenville Front Front mylonite mylonite zone zone (Frarey 1985; 1985; Bethune and Davidson Davidson1988; 1988;Bethune Bethune1989, 1989,1993). 1993). Although several several large metadiabase dykes are are present present immediately immediatelyto to the the southeast, large metadiabase dykes southeast, there there is no no match in in the pattern of of dyke sparing spacing on on opposing opposing sides of of this zone. zone. In obvious match In the the Chief Sudbury dykes dykes immediately immediately northwest northwest of of the mylonite Chief Lake Lake complex, complex, Sudbury mylonite zone zone follow irregular courses within fault-bounded fault-bounded panels panels(Davidson (Davidsonand andKetchum Ketchum1993). 1993). Farther northeast, northeast, dykes dykes can can be be traced traced directly directly to to the front, but have have no no potential potential counterparts counterparts in in the theGrenville Grenville hangingwall. hangingwall. In all all of of these these localities, localities, an important important and consistent consistent observation observation is that that Sudbury dykes within fault-bounded panels adjacent to the front frontfault-bounded panels front cut cut across across frontfabrics in in their host rocks; shear-sense indicators, particularly parallel mylonitic fabrics particularly in in the Chief Lake complex, imply penetrative penetrative northwest-directed thrust complex, imply thrust displacement. displacement. mylonitization is is strongly strongly developed Since this pre-1235-Ma pre-1235-Ma mylonitization developed in inthe the1.46-Ma-granitic 1.46-Ma-granitic rocks, deformation deformation must must have have been been active active along along the the Grenville Grenville Front Front in in the interval rocks, is possible between granite emplacement and dyke intrusion. It between granite emplacement and dyke intrusion. possible that this this metamorphism within within the adjacent -1.45-Ga metamorphism adjacent Grenville Grenville deformation is related to to the the—1.45-Ga orogen. Whatever Whatever the the age age of of deformation, deformation, the dykes' dykes' host host rocks rocks are are likely likely to to have have cooled suitable for for ductile ductile deformation deformation to those cooled from conditions conditions suitable those cool cool and and stable stable enough for emplacement of of a typical continental mafic dyke swarm. swarm. In the the Tyson Tyson Lake Lake area close to Georgian Georgian Bay, Bay, Sudbury metadiabase metadiabase dykes dykes display a remarkable progressive progressive change change in in structural structural style and metamorphism over over several kilometres kilometres as as they they are are traced into several into the the Grenville Grenville Province Province (Bethune (Bethune and Davidson 1988; 1988; Bethune Bethune 1989, 1989, 1993). 1993). Conditions of of metamorphism derived derived from from garnet-pyroxene assemblages within 6 km of of the the front frontare areestimated estimatedatat—6.5 -6.5 kbar and and 690°C, increasing southeastward to —7.7 kbar and a similar temperature at a distance 690°Cincreasing southeastward to -7.7 kbar and a similar temperature at of 16 from the front atatdepth) of 16 km krn (perhaps (perhaps 12 12 km km orthogonally. orthogonally. from depth)(Bethune (Bethune1993). 1993). similar change change is is evident evident in in metadiabase dykes southeast of of the Closer to Sudbury, a similar Chief Lake Lake granite granite complex, complex,where wherethe thefront frontisisalso alsomarked marked by by mylonites mylonites in in aa zone zone at at Chief In the Wahnapitae Wahnapitae area, however, however, contrasting contrasting with the least aa kilometre kilometre thick. thick. In situation recorded situation recorded farther southwest, southwest, Sudbury dykes in the the Crenville GrenvilleProvince Province as as little as 400 m from the front are represented by misoriented and dismembered little 400 front are represented by misoriented and dismembered metadiabase dyke dyke segments, in places arcuate, whose metadiabase segments, in whose sides sides commonly commonly preserve preserve chilled contacts cutting cutting across acrossgneissic gneissicfoliation foliationinintheir their host host rocks, rocks, but but whose ends chilled mobilized by by ductile ductile flow. flow. Dyke are truncated by gneiss mobilized Dyke segments segments are are cut cut by by coarse coarse pegmatite, near which which the the diabase diabase is is hydrated hydrated to coarse biotite biotite amphibolite. amphibolite. Where Where not hydrated, hydrated, itit contains contains metamorphic metamorphic garnet, garnet, clinoproxene clinoproxene and and orthopyroxene orthopyroxene with typical coronitic structure around former olivine and Fe-Ti with typical coronitic structure around former and Fe-Ti oxide oxide grains. grains. �13 Coronitic metadiabase metadiabase commonly commonly contains twisted laths of of relict relict plagioclase plagioclase whose whose Coronitic cores cores are are densely densely clouded clouded with with spinel spinel dust. dust. Farther Farther southwest, southwest, similar similar structural structural and metamorphic metamorphic features features are not attained attained until until at atleast least15 15km km southeast southeast of of the the front front and (Bethune 1993). 1993). A A remarkable remarkable variation on the the theme theme of of Sudbury Sudburydyke dykepreservation preservation (Bethune in the the Crenville Grenville Province Province is is offered offered by by the theoccurrence occurrence ofofnon-deformed non-deformed yet yet in thoroughly metamorphosed metamorphosed dykes in the theWanapitei Wanapitei mafic maficcomplex, complex, mentioned mentioned thoroughly previously, for which more detailed detailed information informationisisgiven given atat the the end of previously, for which more of this this guidebook. guidebook. Field trip trip summary summary Field This This field trip trip is is designed designed to to allow allowevaluation evaluationof of both bothaspects aspectsof ofthe theGrenville Grenville Front including the the truncation truncation of of the mylonite Front discussed discussed above, above, including mylonite zone zone by by the the Murray-Wanapitei fault, and to demonstrate Murray-Wanapitei fault, demonstrate the the dilemma dilemma concerning concerningcorrelation correlation of of metasedimentary metasedimentary gneiss in the Grenville Grenville Province Province with the the Huronian HuronianSupergroup. Supergroup. The geology in in the field trip area are 3, on on The main elements of the geology are illustrated illustrated in inFigure Figure3, which the the first first seven seven stops stops are areidentified. identified. In In the the morning, morning, the the first first three three stops stopswill will which examine rocks in the Southern Southern Province near the the Grenville Grenville Front, but but unaffected unaffected by by Grenvillian tectonism.Next Nextwill willcome comeaa stop stop to to look Grenvillian tectonism. look at the the highly highly deformed deformed equivalents footwall of of the theGrenville GrenvilleFront Front equivalents of some of these these rocks in the the immediate immediate footwall on Highway by a short traverse Highway 69, followed followed by traverse across across the the highly highly deformed deformed contact contact between quartzite and and Chief Chief Lake Lake granite granite lying structurally beneath between Mississagi Mississagi quartzite beneath mylonite and ultramylonite that are typical of the Grenville Front south of of Sudbury. This will be followed by stops on pelitic politic gneiss, quartzite and and mafic mafic rock rock near near the the southeastern southeastern edge edge of of the theGrenville GrenvilleFront Frontmylonite mylonitezone. zone. In be examined examinedwhere where In the the afternoon, afternoon, the the Grenville Grenville Front Front mylonite mylonite zone will will be itit isis truncated truncated by bythe theMurray-Wanapitei Murray-Wanapitei fault fault south southof of Coniston, Coniston,just justeast eastofofAlice Alice Lake. This will be followed by a traverse across the Grenville Front near the Stinson traverse across the Grenville Front near the Stinson This will be followed hydroelectric hydroelectric plant during during which which aa tectonic tectonicslice slice of of possible possible Archean Archean basement basement will will be seen, south of which metasedimentary rocks derived in part from conglomerate seen, south of which metasedimentary in part from conglomerate contrast strongly with the Mississagi Formationon onthe the north north side side of of the front. The Mississagi Formation The last stop visits spectacular outcrops of kyanite gneiss showing evidence for extreme stop visits spectacular kyanite gneiss evidence for extreme ductility ductility and and enclosing enclosing segments segments of highly highly metamorphosed metamorphosedSudbury Sudburydliabase diabasedykes. dykes. The road log induded in the following section is intended for those who for those who wish wish included in the following section run the the field field trip trip on on their their own. own. It It gives cumulative cumulative distances distances in inkilometres kilometres to run between each stop in the left hand column, and a cumulative cumulative log for the whole whole trip trip - this guidebook guidebook should should be sure to the right right hand hand column. column. Persons following following this to in the obtain obtain permission permission from owners of private land land for for stops stops22 to to66inclusive. inclusive. �/ /,&nis gnei in GreniIle Provthce (SE of GFMZ and Wanapitei fault) Southern Province: yI% antldine syncline Sudburydiaba ft Daisy L granodiorite Nipiing gabbro Miissagi Formation (fadng dired ion indite Pecors Formation Ramy L Formation Mokirn Formation A. Figure 3. A. Geology of the Grenville Front southeast of Sudbury; GFMZ is the Grenville Front mylonite zone. Locations of stojv 1 —7 are indicated by circled numbers. B. Regional setting; triangles in Lake Nipissing are alkaline corn plexes associated with Neoproterozoic rifting. Box shows area of A. �ROAD LOG AND STOP STOP DESCRIPTIONS DESCRIPTIONS km rum. cum.km km 0.0 0.0 0.0 Proceed southfrom from Sudbury Sudbury to to the Proceed south the intersection intersection oof f Paris and and Regent streets (Four Regent streets (Four Corners), Corners), and set set odometer odometer to zero. zero. Turn Turn 3.4 3.4 10.2 10.2 10.2 10.2 left (east) on Regent Regent Street Street (old (old Highway Highway 69). 69). Take the ramp ramp just just after and go go east Take the after the the underpass, underpass, and east on the the Sudbury bypass Outcrops along along the roadside 17E). Outcrops roadside for bypass (Highway (Highway 17E). the next 33 km krn are areNipissing Nipissinggabbro, gabbro, and and beyond beyond this, this, Mississagi Mississagi sandstone which dips dips steeply sandstone which steeply south south and isis overturned. overturned. right shoulder shoulder at at aadark darkoutcrop outcropofofmassive massiverock. rock. Stop on on the right Stop 1. Mississagi sandstone, Nipissing Nipissing gabbro gabbroand and Sudbury Sudbuiy diabase This stop lies within the Southern Province 900 900 m m northwest northwest of of the Murray fault, This 3 km km west-southwest west-southwest ofof where where this this fault truncates the Crenville truncates Grenville Front Front mylonite mylonite zone; from the the Grenville GrenvilleFront. Front. Here a southeast-trending, zone; it is only two kilornetres kilometres from vertical, 65-m-thick 65-rn-thickolivine olivine diabase diabase dyke dyke of of the 1235-Ma Sudbury swarm swarm cuts vertical, 1235-Ma Sudbury cuts across across Formation (south (south side of the road) the contact between sandstone of the Mississagi Mississagi Formation road) and Nipissing metagabbro (north side). The of the The sandstone sandstone exposed here is typical of quartz-rich and lighter in colour upper part part of of the the Mississagi, Mississagi, being somewhat more quartz-rich colour than in the lower lower part of of the the formation. formation. Cross-bedding Cross-bedding in the the sandstone sandstone indicates indicates we are on the southeast limb of that the steeply dipping beds face face north-northwest; north-northwest; we syncline, illustrated illustrated in Figure 3). The the Coniston syncline, The Nipissing metagabbro metagabbro is is massive massive secondary green green amphibole, amphibole, epidote epidote and chlorite. but metamorphosed, containing secondary chlorite. This assemblageisis typical typical of of Nipissing Nipissing gabbro gabbro throughout throughout the This metamorphic metamorphic assemblage Southern Province Provinceand anddoes doesnot not appear appear to to be be aa function of proximity to the Southern function of proximity to Grenville Front, Front, aa conclusion corroborated by by the the fact Grenville conclusion corroborated fact that the the pre-Grenvillian pre-Grenvillian Sudbury diabase cuts itit is is not not metamorphosed. metamorphosed. diabase which cuts The Sudbury Sudbury olivine olivine diabase diabase exposed exposed at at this this stop illustrates the pristine The pristine of cataclased adjacent to to the Grenville Grenville Front, Front, which which we we will will see see at protolith of cataclased diabase adjacent Stop 8, and of equivalent equivalent coronitic metadiabase in the Grenville Province, to be seen seen 9. The all but but exposed exposed on on the the south side at Stop 9. The Sudbury Sudbury dyke's northeast contact is all of the road, and of and must must have have been been excavated excavated during during road road construction, construction, as as blocks blocks its chilled chilled contact contact with with Miissagi Mississagisandstone sandstonecan canbe befound found at at the the roadside. containing its Close to this contact the diabase is fine grained grained and contains xenocrysts of of plagioclase plagiodase which in turn turninclude includeearlier-crystallized earlier-crystallizedolivine olivinecrystals crystals— - a common feature near which the margins of Sudbury dykes. dykes. In Inthin thinsection, section, there there is is no no evidence evidence whatsoever whatsoever for for reaction between between these these two two minerals minerals at at this this location location (it is principally metamorphic reaction this reaction which gives gives rise rise to the garnet reaction which garnet and and secondary secondary pyroxenes pyroxenes present in metamorphosed olivine olivine diabase). diabase). In the same same dyke on the southeast southeast side of of the the Murray fault and closer closer to to the the Grenville Grenville front, front, however, however, the plagioclase plagioclase xenocrysts xenocrysts become clouded with with fine fine epidote, epidote, and rims become clouded rims of of fine fine actinolite actinolite appear appear between between olivine and plagioclase. plagioclase. This This particular particular dyke dyke cannot cannot be traced across across the the Grenville Grenville �Front fault, Front fault, but where where Sudbury Sudbury dykes have have been been identified identified in in the the immediate immediate hangingwall of of the front, of front, olivine olivine in plagioclase plagioclase xenocrysts has reaction coronas of pale orthopyroxene with outer rims of pargasite-spinel symplectite, and Fe-Ti oxide orthopyroxene outer rims of pargasite-spinel symplectite, and Fe-Ti oxide grains are surrounded vicinity of the surrounded by by Ti-biotite Ti-biotite and and garnet garnetsymplectite. syrnplectite. In the vicinity Grenville Front 50 50 km km to to the southwest, Sudbury dykes cut across across and are are chilled chilled Grenville Front against a pre-existing mylonitic mylonitic fabric fabricthat that isis developed developed in in granitoid granitoid rocks rocks as young as 1470 Ma Ma (Bethune 1989; 1989;Davidson Davidson and and Ketchum 1993), pointing to the existence 1993), pointing existence of some kind of of pre-Crenvillian pre-Grenvillian tectonic front roughly coincident with the the Grenville Grenville In this regard it is pertinent that, sensu stricto. stricto. In that, in in the the hangingwall hangingwall within a Front sensu few kilometres of al. of the front, front, metamorphic metamorphic monazite monazite in in pelitic politic gneiss gneiss (Dudas (Dudasetet al. 1994) and and zircon from pegmatitic 1994) pegmatitic leucosomes leucosomes(Krogh (Krogh1994) 1994) record recordan anage ageofof—1445 -1445 Ma. Ma. km 0.0 5.8 5.8 65 6.5 cum.k,n CUM.^ 93 9.3 19.5 19.5 9.7 19.9 10.2 16.0 16.7 Turn around around and and return to tothe theinterchange. interchange. Take thefirst first exit exit ramp ramp to the Take the the right. right. light, turn At At the the traffic light, turn left left on on Highway Highway 69, 69, and and proceed proceed through the the next through next traffic traffic light. light. Turn right right at at the theintersection intersection with with Poitvin Poitvin Road Road and and follow follow itit round round to the the left. left. Park on the before rejoining rejoining Highway Highway 69. 69. Park the shoulder shoulder just before 2. Slaty argillite, argihite, Pecors Formation, Formation, and and "trap "hap dyke" Stop 2. Stop This stop stop and the This the next next illustrate illustrate rock types of of the the two two formations, formations, Pecors and Ramsey Lake, Lake, that that precede precede the the Mississagi Mississagi in in the Huronian stratigraphic Ramsey stratigraphic succession. succession. Both are well exposed in the City of Sudbury along the north shore and west of Both are well exposed in the City of Sudbury along the north shore Ramsey Lake, Lake,where wherethey theylie lienorth northofof the the Creighton Creighton fault fault (Fig. (Fig.3). 3). Here, Here, most of of the Ramsey low-lying area around Richard and MacFarlane lakes lakes is is devoid of of outcrop, although it is shown shown as as underlain underlain by by Mississagi Mississagi Formation on the most most recent recent compilation compilation of 1984)and andon on the the regional regional map map that preceded Sudbury geology (DressIer (Dressier 1984) preceded itit (Lumbers (Lumbers and Card 1977). The surrounding hills are underlain underlain by by Mississagi Mississagi sandstone or Card1977). in aa few fewplaces places Nipissing diabase, but sparse exposures at the the base base of of these these hills, and and in in the valley, valley, are of of sedimentary sedimentary rocks rocks that are are not not typical typical of of the theMississagi Mississagi Formation. This This was was recognized long ago by Collins (1936) who assigned recognized long by Collins (1936) assigned conglomerate that that crops crops out out along along the north side conglomerate side of of Richard Richard Lake Lake to to the the Ramsey Ramsey Lake Formation, which will be seen at the next stop. stop. At this stop, outcrop on the bill hill to the south south is is well-bedded well-bedded sandstone of the Mississagi Formation,but butatat the the base base of of the the slope slope a few metres of of grey argililte Mississagi Formation, argillite are exposed. Similar Similar exposures occur along the south side side of the the Richard Lake valley to the east. South Southof of MacFarlane MacFarlane Lake, Lake, to the southwest, southwest, argillaceous rocks in the same stratigraphic position beneath the stratigraphic the Mississagi Mississagi are represented represented by by fine finemicaceous micaceous schist schist of altered altered staurolite staurolite and andalusite; this higher grade of with small porphyroblasts of of metamorphism is is apparently associated associated with with a number of metamorphism of nearby nearby small small intrusions intrusions �17 of granodiorite and granite dated at Ma. Low Lowoutcrops outcropsaround around the east end of of at —1745 -1745 Ma. MacFarlane Lake Lakeexpose exposerocks rocksthat that are are stratigraphically stratigraphically lower lower than the argillaceous MacFarlane argillaceous rocks immediately immediately beneath beneath the the Mississagi MississagiFormation. Formation. These These are are of of fine fine wacke wacke and rocks siltstone which which have have aa greensish greensish hue hue and lack siltstone lack the the thin, thin, rusty-weathering, rusty-weathering, shaly shaly so typical typical of of the the Mississagi. Mississagi. What What is more, more, they preserve graded bedding interbeds so and and elements elements of of Bouma Bouma cycle cycle sedimentation, sedimentation, suggesting suggesting aa depositional environment altogether different different from from that that which produced environment altogether produced the the cross-bedded cross-bedded Mississagi sandstone. Taken sub-Mississagi sedimentary rocks match Mississagi sandstone. Taken together, these these sub-Mississagi of the Pecors Pecors Formation Formationin in its its type type area area and, given their stratigraphic those of stratigraphic position, position, should be assigned to to this this formation. formation. At this stop, an added feature feature is is the the presence presence of a fine-grained, fine-grained, greenish grey, diabase. Several altered diabase. Several narrow dykes of this this swarm, swarm, known as as "trap "trap dykes", dykes", trend trend east-west in this area. They They have not been dated, dated, but but are are known knownto tocut cut"offset "offset dykes" dykes" of the 1850-Ma Sudbury Intrusive Intrusive Complex, Complex,and and to to be cut by the the 1235-Ma 1235-Ma Sudbury of 1850-Ma Sudbury swarm. These Thesedykes dykesare arenot, not, therefore, therefore, related related to toNipissing Nipissinggabbro. gabbro. cum. km km cum. km get into into the right lane. left on on Highway Highway 69,; 69,;immediately immediately get lane. 19.9 Turn left 19.9 20.2 2 0.2 Turn right. right. At sharp 20.5 2 0.5 At sharp left-hand left-hand bend, bend, go go straight straight into into parking parking area area by by Walk Richard Lake Lake Homecare Hoinecare Building Building Centre Centre and and park. Richard park. Walk 0.0 0 .0 0.3 03 0.6 0.6 ahead throughgate, gate,and andgo go to to outcrop outcrop on on hill hill to to the left ahead through left of of the the buildings. buildings. Ramsey Lake Lake formation formation Stop 3. Polymictic conglomerate, Ramsey At this stop, stop, grey, grey, ill-sorted ill-sorted wacke supports sparse sparse pebbles pebbles and and cobbles, cobbles, some some of of granitoid rock; rock; aa few few are are of of boulder-size. boulder-size. Look granitoid Look for small, bluish grains of quartz, quartz, which typify much much of of the the Ramsey RamseyLake Lakeconglomerate conglomerateininits itstype typearea. area. Bedding dips southward, but but is poorly southward, poorly developed developed and facing facing direction direction cannot cannot be determined. determined. and quartz wacke are exposed exposed in a few places closest dosest to to the the Argillite and to Richard Richard Lake Lake to east, and are are similar similar to to the therocks rocks at atthe theeast eastend endofofMaciFarlane MacFarlane Lake, Lake, assigned assigned above above Pecors — Mississagi to the Mississagi from the Pecors Pecors Formation. Formation. The Thesuccession successionRamsey RamseyLake Lake—- Pecors north to to south south across across the the valley valley is is in in accord accord with with aahomoclinal homoclinal succession, succession, although although it is possible that faults and folds are concealed beneath the valley floor. of low hills hills along along the north shore of Richard The line of Richard Lake, all underlain by conglomerate, separatedfrom fromthe thehigher higherridge ridgeto to the the north north by by a strip in conglomerate, isisseparated in which which which conceals concealsthe theMurray Murrayfault. fault. The ridge is underlain by there is no outcrop, and which sandstone which faces north, north, being the same subvertical strata of of Mississagi Mississagi sandstone same limb limb of of facing on on opposite opposite side of the 1. Sedimentary Sedimentary facing the the Coniston syncline syncline as at Stop Stop 1. Murray fault fault is thus thefault fault occupies occupieswhat what may may be be a breached Murray thus "back-to-back"; "back-to-back"; the breached anticline, and and has has a net north-side-down north-side-down displacement. displacement. To the west, anticline, west, however, however, the Murray fault fault truncates fault, west Murray truncates aa north-trending north-trending fault, west of of which which the the Mississagi Mississagi Formation occupies occupies the the south south side side of of the fault and is Formation is also also north-facing. north-facing. �km cum.km km cum.km 0.0 20.5 20.5 0.3 20.8 03 20.8 2.1 2.1 22.6 33 23.8 3.3 Turn around around and and go go back back to to Highway Highway 69. 69. Turn left on Highway Turn left Highway 69. 69. Roadcuts here expose steeply inclined Mississagi Mississagi Formation. Formation. here expose steeply inclined the right Just after after the end end of of the the roadcut roadcut on on the the right, right, park park on on the at swampy swampy valley. valley. Please note that that this thisisisaavery verybusy busy highway highway with w i t h fast-moving traffic; traffic; travelling south south must must merge mergeinto into one one lane lane aatt this ttwo w o lanes of vehicles travelling this point after extreme caution; point after coming coming round round aa blind blind corner. comer. Exercise Exercise extreme keep an eye eye on on traffic traffic and and other other participants, participants, and do not step back onto keep an onto the roadway roadway when when taking taking photographs. photographs. 4. The Stop 4. The Grenville GrenvilleFront Frontat atHighway Highway69 69 Figure 4 gives some some details details of of the the geology geologyat at this thislocation. location. Looking to the the west west from from Highway 69 69 at this stop, Highway stop, mylonite mylonite and ultramylonite ultramylonite marking the Grenviile Grenville Front Front are well exposed along the south side of the broad swamp; swamp; mylonitic mylonitic foliation foliation dips dips thesoutheast southeastand and contains contains numerous numerous shear-sense shear-sense indicators of northwest-—35° 3 5 O totothe northwestdirected thrust displacement. passes through through the low point in the displacement. The front passes the skyline skyline to the left of of the island in the swamp. swamp. The The island island and the high high part part of of the the hill hill behind it are underlain by coarse granite of the Chief Lake complex, continuous are underlain by coarse granite of the Chief Lake complex, continuous in in krn to the the southwest southwest where where aa U-Pb U-Pb zircon zircon age ageof of1465 1465Ma Ma outcrop with aa locality locality 77 km was recently determined determined (Davidson (Davidson et et a!. al. 1992). 1992). Mississagi sandstone is is in in contact contact with the granite on with on the the right right (north) (north) flank flank of of this this hill. hill. The contact dips dips steeply steeply south-side-up sense, sense, but but the displacement is south and is is the the locus locus of of shearing with south-side-up Mississagi Formation north north probably not great, as dykes dykes of granite are present in the Mississagi of The ridge ridge to the right of the contact. contact. The right of of the the swamp swamp is is Nipissing Nipissing gabbro, gabbro, and and Mississagi Formation is exposed sporadically along the lower lower slope. slope. Walk north on the Walk the west west side side of of Highway Highway 69 69 to examine examine aa small, small, duplex-like duplex-like structure in Mississagi exposed in in the the roadcut structure Mississagi sandstone sandstone exposed roadcut beneath beneath Nipissing Nipissing metagabbro. Metamorphic is greenschist greenschist facies; fades; the metagabbro contains contains metagabbro. Metamorphicgrade grade here here is the assemblage assemblagealbite-chlorite-epidote-actinolite. albite-chlorite-epidote-actinolite. Cross the the highway highway when when traffic trafficpermits permitsand and walk walk back back to to the nearest point Cross where the ditch can be crossed to have have access accessto to outcrop outcrop on on the the south side of where of the the of the highway. The the Chief Chief Lake swamp east of The first first outcrop is deformed granite of the complex. Continue along the edge of of the the swamp swamp to to the the higher, higher, bare bare outcrop beyond; complex. beyond; Mississagisandstone sandstoneand and the the granite, granite, both intensely deformed, the contact between Mississagi deformed, finely laminated laminated nature of is exposed exposed here. here. Note the the extremely extremely finely of the theMississagi Mississagi quartzite, locally thrown into small small box boxfolds. folds. These rocks rocks are quartz mylonite; is it possible that that the laminae represent extremelyattenuated attenuatedbedding? bedding? The possible represent extremely The overlying overlying Chief Lake Lake granite granite is is strongly strongly foliated foliated with with aa consistent consistentsoutheasterly southeasterly dip dip of 3 35° and a 5' and Chief pronounced dip-parallel lineation. lineation. It has undergone principally brittle deformation, deformation, but with with ductile ductile flattening flattening of of its its quartz quartz content. content. Thin sections show show cataclasis cataclasis of feldspar quartz with highly feldspar and thin, thin, sinuous sinuous laminae laminae of finely finely polycrystalline polycrystalline quartz highly �19 A p4 S p. 44 4 / 4 / 1' 200m Sketch map of the the geology geology at the the GrenvÜle Grenville Front, Highway Highway 69. 69. The arrow arrow Figure 4. Sketch shows the location of the small duplex in the Mississagi Formation immediately shows the location of the small duplex in the Mississagi Formation immediately line indicates indicates the the traverse traverse described described in in the second of the the front. front. The The black black line second part north of of this stop. stop. of neoblasts of of chlorite, chlorite, pale pale green Fine interstitial interstitial neoblasts green biotite, biotite, orientation. Fine preferred orientation. epidote, microcline and albite attest to low-grade metamorphism overprinting epidote, microcline and albite attest to low-grade metamorphism overprinting deformation features. The exposed on on this this ridge ridge are considered to be in in the the deformation features. The rocks rocks exposed immediate footwall of what Lumbers (1975) referred to as the "Crenville Front "Grenville immediate footwall of Lumbers (1975) referred to as boundary boundary fault" fault" Cross the wooded valley to the south. The The next next ridge ridge of of outcrop outcrop exposes exposes dark dark mylonite that do not appear to have mylonite and ultramylonite ultramylonite that have been been derived derived from from Chief Chief Lake complex complex rocks. rocks. The mylonitic rocks rocks exposed exposedbetween betweenhere here and and the driveway driveway to to the south south are are mainly mainly derived derived from frommafic mafic and andsemi-pelitic semi-pelitic precursors. precursors. Large Large 'porphyroblasts of garnet occur locally in the latter, but despite their euhedral 'porphyroblasts' of garnet occur locally in the latter, euhedral shape, thin sections show that they are porphyrodasts porphyroclasts with late late rim rim overgrowths. overgrowths. Oriented X-Z thin sections also show a pronounced, oblique subgrain orientation in X-Z also show a pronounced, oblique subgrain quartz lamellae, to the northwest. lamellae, indicating indicating thrust-sense displacement to northwest. On the driveway, go west west to Highway 69 and examine examine the the On reaching reaching the driveway, go Highway 69 mylonitized pegmatite for for kinematic kinematicindicators indicatorsininthe thefirst firstroadcut roadcut to to the south on mylonitfzed pegmatite on the east east side side of the the highway. highway. �km km cum.km cum.km 23.8 Continue south south on Highway 23.8 Continue Highway 69. 69. 0.7 24.5 Turn right right on on Gladu Gladu Road. Road. 1.1 24.9 Stop on on the right by 1.1 24.9 Stop by open open grassy grassy area. area. Follow across open open Follow track across area to fairways to outcrop to golf golf course; course; cross cross path path between between fairways outcrop in in area open wooded area. open wooded area. 0.0 0.0 Stop 5.5. Metasedimentary Metasedimentaryrocks rocks in in the Grenville Stop Grenville Province Province margin correlatives Huronian Supergroup? correlatives of the Huronian Supergroup? - — The first outcrops are fine-grained, fine-grained, highly deformed deformed and and grain-comminuted grain-comminutedmafic mafic rock, probably probably ultimately ultimatelyderived derived from from gabbro. gabbro. Beyond rock, Beyond this is a unit of feldspathic feldspathic which shows some quartz metasandstone metasandstone which some remarkably remarkably convolute convolute fold patterns, patterns, followed by by outcrops of muscovite is present present in in this rock, but is followed muscovite schist. schist. Kyanite Kyanite is is colourlessand andhard hard to to identify. identify. Garnet is pale pale and easier easier to to spot. spot. Staurolite colourless Staurolite is also present as small grains. grains. The The metamorphic metamorphic grade grade recorded recorded by the pelitic schist at this outcrop, m on on the ground from outcrop, a mere 900 900 m from the the northwest northwest margin margin of of the the Grenville Grenville Front mylonite zone and perhaps only 500 m perpendicularly, is clearly Front mylonite zone and perhaps 500 perpendicularly, clearly much much facies) than than that in the higher (middle amphibolite facies) the Southern Southern Province Province immediately immediately across the the front. front. A of the the Pecors Pecors across A comparable comparable parent rock would be the shaly part of Formation (seen (seen at at Stop 2), 21, which which itself itself has hasdeveloped developed andalusite-staurolite andalusite-staurolite Formation assemblagesin in nearby nearby parts parts of of the the Southern Province. Province. The assemblages The presence of kyanite at at this locality indicates aa distinctly distinctly higher higher pressure pressure than than that that recorded this locality indicates recorded by the the andalusite-bearing knotted knotted schists in the the the thePecors Pecors Formation. Formation. In fact this schist records a complex kyanite and and staurolite staurolite are partly complex metamorphic metamorphic history. history. Early Early kyanite replaced by phengitic mica mica and margarite, and spongy garnet cores cores have secondary secondary overgrowths containing staurolite inclusions. P-T estimate estimate on the the younger younger overgrowths inclusions. A P-T assemblage, obtained obtained by by D.M. D.M. Carmichael, Carmichael, Queen's Queen's University, University, isis 77 kbar at 670°C, assemblage, S670°C "... the evidence of of earlier and "... the garnet garnet core core inclusion inclusion assemblage assemblage ... ... gives gives evidence earlier equilibration at about 4 kbar." 1991). As documented by La kbar." (Davidson (Davidson et a!. at. 1991). La Tour Tour equilibration (1981),the theapparent apparentgradient gradientacross acrossthe thefront frontisis too too steep steep to to be be anything (19811, anything but tectonically telescoped, telescoped, particularly particularly if if the paleoisotherms paleoisotherms are are inclined. inclined. At a locality 1994), approximately 2 km locality 1.2 1.2 km to to the the southeast southeast(Davidson (Davidson 1994), km from Front and and well beyond from the Grenville Grenville Front beyond the the zone zone of of intense intenseinylonitization mylonitization defining the front in this area, area, metasedimentary metasedimentary rocks rocks include include pelitic gneiss, quartzquartzgneiss, and and a thin, discontinuous gneiss. These rich feldspathic gneiss, discontinuous layer layer of calc-silicate calc-silicate gneiss. These are interlayered with thick are interlayered with thick units of of coarse coarse garnet garnet amphibolite amphibolite and gedritegedritehornblende gneiss of uncertain Association of of both both kyanite and uncertain origin. origin. Association and sillimanite sillimanite were reported reported to occur in this with K-feldspar K-feldspar were this area area by by Kwak Kwak (1968), (1968), although the prevalent assemblage assemblage iii in pelitic gneiss gneiss here here isisquartz-plagioclase-biotite-muscovitequartz-plagioclase-biotite-muscovitegarnet-kyanite-sillimanite; stauroliteisisabsent. absent. A garnet-kyanite-sillimanite; staurolite A P-T P-T estimate estimate obtained obtained by byD.M. D.M. Carmichael is —8 kbarat at 710° 71 0°C(Davidson (Davidsonetetal.a!.1991). 1991).The Theisograd isogradmarking marking the the first -8 kbar appearance of of sillimanite sillimanite (which (which here here texturally texturally overprints overprints kyanite), kyanite), trends trends northnorthwest toward the Wanapitei northwest toward Wanapitei fault segment segment of the the Grenville Grenville Front Front between between �21 Coniston Coniston and and Wahnapitae Wahnapitae village village(Stop (Stop7). 7). A feature of o f the the pelitic pelitic gneiss gneiss in i n this this vicinity is ( u p to to II) 10 vicinity is the occurrence occurrence within within itit of of quartz quartz pods pods with coarse blue kyanite (up cm) and minor garnet. km km cum.km cum. km 0.0 Return to Gladu 0.0 24.9 Return Gladu Road Road and Highway Highway 69, and and retrace retrace route route back back 6.9 31.8 18.5 43.4 24.1 49.0 26.5 50.4 27.6 51.5 toward Sudbury. toward Sudbury. At turn left At traffic traffic light light just just before before overpass, overpass, turn left onto onto ramp ramp for for Sudbury bypass Beyond Stop Stop 1, 1, note 17E). Beyond Sudbury bypass (Highway (Highway 17E). note that that bedding in the bedding the Mississagi Mississagi Formation Formation changes changes dip dip direction direction from from northwest northwest to south as as one onecrosses crosses the theConiston Coniston syncline. syncline. The big big roadcuts on the roadcuts on the hills hills after after the the long long left-hand left-hand curve curve The expose spectacular spectacular examples expose examples of of shatter-cones shatter-cones related related to the the impact that that caused impact caused the Sudbury structure. Take right lane lane at at traffic 17., Take right traffic light light and and go go east east on on Highway Highway 17., two defunct of Coniston passing by passing by the town of Coniston with its its two defunct The barren barren blackened rocksininthis this area area are are the smokestacks. smokestacks. The blackened rocks the èevere erosion, of vegetation result of vegetation kül, kill, subsequent severe erosion, and staining by fumes fumes from from this this former former smelter. smelter. staining by Turn right on the road to Turn to the Coniston hydroelectric road, crossing generating station. Keep on main generating station. Keep on main gravel gravel road, crossing railway. railway. Gate at entrance entrance to to ICI ICI explosives explosives plant. plant. Obtain permission permission to drive through drive through the the fenced fenced compound. compound. along the the south south side of End End of of the the road; road; park. park. Walk Walk along of the the valley valley to the the powerline. powerline. Stop 6. Truncation Truncationof of the theGrenville GrenvilleFront Frontmylonite mylonitezone zoneat at Alice Lake Two major faults faults ooff the the Murray Murray fault system in the T w o major the Southern Southern Province Province (Card 1978b), theCreighton Creightonfault faultand andthe the Murray Murray fault fault itself, converge convergeeastward eastward and and meet 1978b), the East-northeast ooff this this juncture, juncture, a narrow valley in just north 5). East-northeast in just northof o fAlice Alice Lake Lake (Fig. (Fig.5). with the Murray Murray fault fault marks marks the the Grenville Crenville Front. Front. North of line with o f this valley valley are wellpreserved sandstonestrata strata and and Nipissing preserved Mississagi Mississagi sandstone Nipissing gabbro at low l o w metamorphic metamorphic grade, and south of gneiss ooff the the Grenville Crenville Province. Province. The o f it, high-grade migmatitic gneiss covered interval interval between between the the two two conceals conceals the the Wanapitei Wanapitei fault, fault, and and iiss as little little as as covered 25 m m wide wide in places places between between Alice Alice Lake Lakeand and the village village ooff Wahnapitae Wahnapitae 66 km km to to the 25 There is is nno evidence tto suggest that the Murray northeast. There o field field evidence o suggest Murray and and Wanapitei Wanapitei faults are not one and the the same, same, contrary contrary to t o published published maps maps of o fthis thisarea area(Lumbers (Lumbers 1975; Dressier1984); 1984);the thetwo twointerpretations interpretations are are illustrated in 1975; Dressier i n Figure Figure 6. 6. The southeast-dipping zone ooff mylonitization which marks marks the Grenville The southeast-dipping zone mylonitization which Grenville Front ttoo the southwest Front southwest converges converges with the the Murray-Wanapitei Murray-Wanapitei fault fault at at Alice Alice Lake. Lake. �22 Figure 55 The The juncture juncture between between the the Grenville Grenville Front Frontmylonite mylonitezone zone and and the theMurrayMurrayFigure Wanapitei Wanapitei fault south southofofConiston. Coniston. Four Four elements elements of of the theCrenvile GrenvilleFront Frontmylonite mylonitezone zone also alsoconverge convergeatatthis thisjuncture; juncture; fromnorthwest northwesttotosoutheast southeastthese theseare: are: from 1) highly highly attenuated attenuatedHuronian Huronianmetasedimentary metasedimentary rocks, rocks, mainly mainlyMississagi Mississagi 1) Formation Nipissingmetagabbro, metagabbro,and andprotomylonitic protomylonitic Formation like like that thatseen seenatatStop Stop1,1,Nipissing �23 granitoid rocks rocksofofboth boththe theDaisy DaisyLake Lake (7-1.75 Ga) Ga)and andChief ChiefLake Lake(—1.46 (-1.46 Ga) Ga) granitoid (?—1.75 plutonic units; units; 2) migmatitic migmatiticgranitoid granitoidorthogneiss orthogneiss of unknown unknown affinity; affinity; 3) metasedimerttary metasedimentarygneiss gneiss and and schist, schist, induding includingmicaceous micaceouskyanite-bearing kyanite-bearingschists schists 3) like that that seen seen at atStop Stop5; 5; 4) Migmatitic with mafic layers layers and and pods. 4) Migmatitic quartzofeldspathic quartzofeldspathic gneiss with pods. of these elements is separated separated by by aa relatively narrow narrow (a few metres), southeastEach of dipping zone zone of of mylonite mylonite and ultramylonite carrying thrust-sense indicators. These These intense mylonite zones, themselves included within within the overall intense themselves included overall Grenville Grenville Front Front mylonite from their their truncation Murraymylonite zone, zone, diverge diverge southwestward southwestward from truncation by by the theMurrayWanapitei fault the Grenville Crenville Front itself fault (La (LaTour Tour1981). 1981). Conventionally, Conventionally, the itself is is designated as the themylonite mylonitemarking marking the the southeastern southeasternlimit limit of of recognizable recognizableSouthern Southern designated as Province rocks rocks (Grenville (Grenville Front boundary boundary fault faultof of Lumbers Lumbers1975). 1975). interpretations in in the Coniston Coniston area. area. Figure 6. 6. Fault interpretations A, after afterLumbers Lumbers (1975); (1975); B, B, modified modified after DressIer Dressier (1984). (1984). �24 this stop, stop, the the granitoid granitoid rocks rocks of of the the Daisy Daisy Lake and Chief Chief Lake Lake plutons At this exposed west of Alice Lake, Lake, have have been been cut out by the Murray-Wanapitei fault, so that only the Mississagi Mississagi and Nipissing Nipissing units, both both of of which which have have suffered suffered extreme extreme tectonic flattening, represent represent element I1(above). (above). The The migmatitic migmatitic granitoid granitoid of of tectonic flattening, element 22 is also missing, although itit may may be be represented in the pink mylonite missing, although represented in mylonite element structurally above 1. structurally above element element 1. After examining the outcrops close to Alice Alice Lake, Lake,climb climbthe thehill hill to to the the east east to gneiss of of element element 4, 4, noting noting shear see the nature of of the the heterogeneous heterogeneous migmatitic migmatitic gneiss sense in in the underlying mylonite, sense mylonite, and the ductile ductile style of deformation, deformation, including sheath folds, folds, in in the gneiss above. above. Thin sheath Thin units units of of pelitic politic gneiss gneiss are are present present locally locally within this unit. between the migmatitic quartzowithin unit. There There is some some resemblance resemblance between quartzofeldspathic gneiss seen seen here and migmatitic granitoid granitoid at Stop 8, several several kilometres to the northeast, but there there is is no no continuity continuityin inoutcrop. outcrop. 0.0 1.8 1.8 51.5 51.5 53,3 533 Return through compound. compound. Park on the the right right just justbeyond beyond the therailway railway crossing. crossing. Stop 7. Comparison on opposite opposite Comparison of Southern Southern and and Grenville Grenville Province rocks on Coniston hydroelectric hydroelectric dam dam sides of the Wanapitei fault near the Coniston This outcrop outcrop shows shows similar similarfeatures featurestotothose thoseininelement element44atatthe the last last stop, stop, and This includes narrow narrow mylonite mylonite zones zones that diverge includes diverge southwestward southwestward from the the MurrayMurrayWanapitei fault line. state of of the Wanapitei line. The The remarkably remarkably well-preserved well-preserved state the Mississagi Mississagi sandstone north of sandstone north of the fault fault can can be be examined examined on the hillside north of of the the valley, valley, where cross-bedding cross-bedding shows shows that that the succession facesnorthwest, northwest, away away from from the where succession faces Wanapitei fault. fault. To the southeast, the dark high ground ground on on the the other other side side of of the theWartapitei Wanapitei River and the Coniston plant is is underlain Coniston hydroelectric hydroelectric plant underlain by predominantly mafic mafic River and rocks of of the the Wanapitei Wanapitei complex. complex. There There is is not not time timeon onthis this trip trip to to visit this 3 x 8 k km m rocks body of of rock, whose northern contact Field work has body contact is only only 500 500 m from here. here. Field shown that this complex is not not an in situ but in fact shown that complex is situ intrusion intrusion but fact aa huge huge tectonic tectonic 1992). remnant wrapped by by aa carapace carapaceof of ductile ductilegneiss gneiss (Davidson (Davidson and andKetchum Ketchum1992). This topic topic is elaborated in the notes This notes that that follow follow the the stop stop descriptions. descriptions. Suffice it to gneiss with with garnet garnet and and both both kyanite kyanite and sillimanite say that metasedimentary gneiss sillimanite lies within the valley north of the thefact factthat that this this is less than half the Wanapitei Wanapitei complex; complex; the a kilometre from the low-grade Mississagi Formation Formationexposed exposedat at this this stop attests to to an enormous fault/Grenville Front Front at this this enormous net displacement displacement along the Wanapitei Wanapitei fault/Grenville locale. locale. �25 1.8 53.3 55.1 4.4 57.7 10.7 11.8 64.0 13.2 66.5 0.0 14.0 65.1 67.3 Continue Continue back back to Highway Highway 17. 17. Highway 17, 17, turn right. Highway right. Bridge Bridge over over the the Wanapitei Wanapitei River. River. The The highway highway crosses crosses the the Wanapitei fault and Wanapitei fault and enters enters the the Grenville Grenville Province Province at this point. Railway crossing. Turn keeptoto the the left left at at all Turn left left on on road road to to Stinson Stinson Hydro; Hydro; keep all turnings. At At the the bottom bottom of of the the hill hill after afterpassing passing under undersecond secondpowerline, powerline, take a track to the left, just before the entrance to the take a track the left, just before entrance the parking parking area by the plant (alternatively, park and area the hydroelectric hydroelectric plant (alternatively, park and walk walk along the track). along track). Park and walk the weir over the End End of of track. track. Park walk ahead, ahead, crossing crossing the the Follow instructions under Stop 8, below. river. river. Follow instructions Stop 8, below. 8. Grenville Front relationships relationships near the Stinson Stinson hydroelectric Stop 8. hydroelectricdam; dam; Mississagi Formation, Formation, ultramylonite and cataclasite, metasediMississagi and an mentary gneiss and schist including metaconglomerate, metaconglomerate, and (?)migmatitic migmatitic granite granite slice slicesouth southof ofthe the Grenville Grenville Front Archean (?I This stop requires a walk of about 2 km (Fig. 7) 7) and and will will illustrate illustrate the the abrupt abrupt changes T his stop changes of structural style and metamorphic grade associated associated with with this this part part of the Crenville Grenville Front, here marked marked by by the eastward continuation of the the Wanapitei Wanapitei fault. fault. From Front, here continuation of From the the end of the track track which which leads west from from the the lower lower road to to the the Stinson Stinsonhydroelectric hydroelectric plant, cross the weir over the Wanapitei Wanapitei River River and and follow followthe the track track until until it meets an improved gravel road, where grey sandstone sandstone beds of the the Mississagi Mississagi Formation are are Bedding dips dips steeply steeply northeast, northeast, and exposed on the north side 7). Bedding well exposed side (a (a in inFig. Fig. 7). cross beds indicate that it also faces in that direction, away from the Grenville Grenville Front. Beddingstrikes strikessoutheast southeastatatan an angle angle to to the Bedding the trend trend of of the theWanapitei Wanapitei fault. fault. Metamorphic grade is is clearly clearly low, low, and and there is no evidence of of folding or foliation Metamorphic grade foliation parallel to the nearby fault. fault. weir, but before crossing crossing it, it,go goto tothe theoutcrop outcrop on on the the north bank Return to the weir, (b). Here bedding in the the Mississagi Mississagi Formation Formation has of of the the weir weir (b). of the river east of with the Wanapitei fault, which which lies lies aa short distance to swung toward parallelism parallelism with Wanapitei fault, the south. The Therocks rocksdisplay displayaafoliation foliationand andseveral severalsmall-scale small-scale folds. folds. Cross the weir, walk back back along along the the track, track, and and take take a side-track weir, walk side-track that leads Beforereaching reachingthe thecleared clearedstrip, strip, cut cut to to the left south to to the the powerline powerlineclearing. clearing. Before through open bush toward toward rising rising ground ground below below the the powerline powerline (c). (c). All the outcrop outcrop here is brittle-ductile mylonite mylonite and ultramylonite that has aa grey, grey, closely-fractured closely-fractured surface. Foliation Foliation is is sub-vertical. At Ataalow, low,west-facing west-facing vertical outcrop outcrop face face on on the the side of the hill, small-scale kinematic kinematic indicators indicatorscan canbe beseen seenwith with the the naked eye and and hand-lens that show south-side-up south-side-up sense sense oof displacement This f displacement. This sense sense is is corroborcorroborhand-lens that ated in in oriented oriented thin thin section section by by aaspectacular spectacularC-and-S C-and-S fabric fabric formed formed by by oblique oblique subgrains in in thin quartz layers, by rotated porphyroclasts, and by by back back rotation rotation of of porphyroclasts, and �26 fl.wwwn,wr,wwrrrw,wrr ++++++++++++++++++++++ - - - +++++++++++++++++++ fin +++++++++++++++ U. - '• 'Stinson a a a a Ufl•_ S + .p*-+ + n-+.s+ + + + +! + ++ + + + + + +* + + + + :..... • * * a- -S - S S S S • tt# • S S S SSSqSSS•SS t.-l.a. / S •_S S S SSSS— []] 2 I::: I S ' — 2- .5-S • S S • 500 in 9 Ir.iza4 Sudbury Sudbury diabase diabase t.af #5 — - metasedimentary schist, metasedimentary schist, rnetaconglomerate : rnetacongiornerate mylonite ultramylonite, cataclas!te I''1 granitoid_.— ,'' Iti,',j migmatiticCgranitoid Nipissing Nipissing gabbro g&bm mixed metasedimentary %hl; mixg m amphiblite e t a ~ d i m e m ~, amphibolite schist, Mississagi Fm Mississagi Fm plagioclase gneiss garnet-hornblende plag~cclase Figure 7. Geological relationships Front near Figure 7. Geological relationships at the Grenvifle Grenville Front near the the Stinson Stinson hydroelectric hydr~decfricgenerating station. station. broken feldspar grains ("collapsed dominoes"). The The zone of of ultramylonite is parti("collapsed dominoes"). cularly thick at this locality because itit is where cularly thick locality because where two two mylonite mylonite strands sfrands converge converge westward. To To the the east, east, the the northern northern strand strand separates separates mylonitized mylonitized quartz sandstone granitoid rocks rocks to to the the south; south; the southern to the north north from from migmatitic migmatitic granitoid southen strand &anitoid unit from metasedimentary schist and gneiss to the south. separates this granitoid Walk south south through through the narrow uncut strip that separates the Walk the two two powerlines powerlines to the outcrop outaop near the base base of of the hill (d). (dl. Dark Darkmetasedimentary metasedimentaryrocks rocks here here are are well layered and contain contain biotite and garnet; garnet; some some are are derived derivedfrom fromconglomerate, conglomerate, although the evidence for this is not particularly convincing at this outcrop. outcrop. Walk back to to the the northern northern powerline powerline and and follow follow the the higher higher ground ground to the Walk back (e). Outcrop which shows a structural trend, Outaop on on this this hill is migmatitic mipatitic granitoid which east (el. given primarily by the orientation of of leucosome, leucosome, that that strikes strikes northwest northwest at a marked angle to the curves into parallelism the mylonite mylonite strands. strands. This foliation foliation curves parallelism with both both mylonite strands that enclose the granitoid lens, having an overall Z-sense. mylonite strands enclose the granitoid lens, having overall Z-sense. The The lineation within within these these rocks rocks is clearly not aa typical steep northwesterly-plunging northwesterly-plunging lineation typical Grenvillian orientation. Neither the the age age of of the granitoid nor of GrenviIIian orientation. Neither granitoid protolith protolith nor of its its migmatization is is known, known, but but both both may be older than the mipatization the metasedimentary metasedimentaryrocks rocks to to the south, given that the latter latter are are not not migmatitic. migmatitic. In addition, the granitoid and its are locally locally cut cut by by thin thin dykes dykes of of metamorphosed metamorphosed mafic rock rock which are not leucosome are �27 found in found in the the metasedimentary metasedimentary rocks. rocks. It is possible that the granitoid granitoid lens lens is is aa slice slice of Archean crust, but this remains to be tested by U-Pb dating. of the the powerline powerline clearing, clearing, Follow side of Follow the the high high ground ground eastward eastward on on the north side and where the ground ground begins north toward toward the the and where begins to to slope slope away away to to the east, go north River. On On reaching a steep, narrow gully (f), (0,go down-slope to the the right. right. Wanapitei River. Here a narrow Here narrow zone zone of of intensely intensely cataclased cataclased rock derived derived from from the the migmatitic migmatitic granitoid is exposed on the south south side side of of the gully. Cross Crossthe thegully, gully, which which conceals conceals the Crenville boundary fault; fault; on on the north side is an anoutcrop outcropof of mylonitized mylonitized Grenville Front boundary side is quartz This is is cut by a dyke 4. This dyke of of Sudbury Sudbury quartz sandstone sandstone not not unlike unlike that seen seen at at Stop Stop 4. diabase that is replete with with cataclastic cataclasticfractures fracturesand andshears. shears. It it is hard to tell whether or not the the dyke dyke actually actually cuts the mylonitic foliation in the deformed sandstone; the impression that this this is the case may be explained as the result explained alternatively alternatively as result of of impression that competency contrastduring during deformation. deformation. This dyke cannot be traced on the competency contrast the south south (Crenville) side side of of the the gully; gully; continuous outcrop of (Grenville) of migmatitic granitoid along along the the powerline crosses crosses the the strike strikeprojection projectionofofthis thisdyke. dyke. Neither Neither can the dyke be traced to the northwest; northwest; itit is, is, however, offset from outcrop of similarly cataclased Sudbury diabase at the south just below the dam, which south shore of the Wanapitei River River just which lines dyke can can be traced traced northwest northwest for for 10 10 km up with with aa thick thick dyke dyke on the north side; this dyke (Dressler,1984). 1984).AAmere mere 500 500mm northwest northwest of of the the river, river, this toward Falconbridge Falconbridge (Dressier, undisturbed as that that seen seen at at Stop Stop1. 1. diabase is as fresh and undisturbed powerline and and go go east east to to the road, then follow the road south Return to the powerline south to to powerline (g). (g). Up-slope Upslope to the left, on the north north side side of of the the the edge of the second second powerline powerline clearing, is an outcrop of in which pebbles are well clearing, is of metaconglomerate metaconglomerate in well preserved. strand lies lies farther farther up up the hill to the north, preserved. The The southern southern mylonite mylonite strand north, and has been traced northeastward for two kilometres kilometres along along the the south slope of the high northeastward for ground, everywhere markingthe thecontact contactbetween betweenthe thegranitoid granitoid unit unit and and the ground, everywhere marking metaconglomerate-bearing metasedimentary rocks. metamnglomerate-bearing 0.0 2.2 2.2 4.8 67.3 69.5 69.5 72.1 72.1 Turn round round and and return to to Highway Highway 17. 17. Highway 17, turn right. right. After lookfor for the the Norvic After the the railway railway crossing, crossing, look Norvic Motel Motel on on the the left, cross cross the the highway highwayand and park park just just beyond the motel lefi, beyond the motel (at an Walk south south to inoperativerestaurant restaurantaat the time inoperative f fhe time of of writing). writing). Walk to the west of the motel, and take a track into the woods until aa the woods the west of the motel, and take a track Go to to the top low appears to the l m ridge ridge of of outcrop outcrop appears the left. l q t . Go top of of this this outcrop. outcrop. Stop 9. Metamorphosed Sudbury diabase dyke segments segments in metasedimenmetasedintenStop tary gneiss showing extreme ductility ductility Having seen a fresh, fresh, undeformed undeformed Sudbury dyke at at Stop Stop 1, 1,and and cataclased cataclasedSudbury Sudbury diabase to see the the form that Sudbury Sudbury dykes diabase at the last stop, it is instructive to dykes assume assume in in the highly ductile medium of metasedimentary gneiss that is the common country ductile of the common country of the the front front in in this this area. area. At rock southeast of At this this stop stop (Fig. (Fig. 8), 81, two parallel, northeast- �28 oriented dyke?) are are oriented segments segments of relatively relatively thick thick dykes dykes (perhaps (perhaps parts parts of of the same same dyke?) enclosed enclosed in in kyanite-bearing kyanite-bearinggneiss. gneiss. They They terminate terminate to to the the northeast northeast with rounded ends wrapped wrapped by by gneiss. gneiss. Along Along their however, they cut cut across across gneissic gneissic their sides, however, foliation in their host rocks; this is best observed at the southeast contact of the the foliation in their rocks; this best observed contact of northern of the two segments. segments. Note Note the the prolific prolific growth of garnet porphyroblasts in the dykes dykes near near their their contacts. contacts. of Sudbury Sudbuy metadiabase metadiabase dyke dyke Figure 8. 8. Detail of remnants in in metasedimentary mefasedimentary sclzist schist and gneiss, 1200 m south south of of the the Wanapitei Wanapitei fault. fault. gneiss, No more detached segments of Sudbury metadiabase have been found along along strike to the northeast, mafic rocks rocks exposed exposed there there are strike northeast, despite despite plentiful plentiful outcrop; outcrop; mafic amphibolite derived from The southern southern segment from metagabbro. metagabbro. The segment can be be followed followed southwestward before itit disappears disappears beneath beneath cover; cover; itit reappears as aa southwestward for for nearly nearly 300 m before area beyond beyondthe thecovered coveredinterval. interval. in detached pod in the well-exposed well-exposed area In the the central central where it is 27 m wide, wide, the the outcrop surface of of the least part of this dyke segment, where altered metadiabase shows the speckled texture typical typical of altered metadiabase shows speckled texture of Sudbury metadiabase. metadiabase. Whole rock rock analysis analysis of of this rock rock confirms its chemical chemical affinity affinity with with the Sudbury Whole confirms its Sudbury swarm. In remnant, 5.5 km from the Inaddition, addition,metadiabase metadiabase from from another another tectonic tectonic remnant, front south of the relics of of primary baddeieyite front the village village of of Wahnapitae, Wahnapitae, contains contains relics baddeleyite Ma; six sixfractions fractionsofofmetamorphic metamorphic zircon zircon from coronas 1243 Ma; coronas which gave a U-Pb age of 1243 around baddeleyite 1026to to988 988 baddeleyite in in the the same same rock gave 207Pb/2Pb 207PbPPbages agesranging rangingfrom fiom1026 from a late, late, undeformed pegmatite that cuts Ma (Dud& et uI. al. 1994). 1994). Zircon Zircon from undeformed pegmatite cuts this this (Dudas et enclave gave gavean anage ageofof97= 97 Ma Ma(A. (A.Davidson Davidsonand and0.0.van vanBreemen, Breemen,unpublished). unpublished). enclave narrow wooded wooded draw draw flanking flanking the the north north side side of of the the central part of Cross the narrow of in the the open open area area beyond. beyond. Here, homogenized' this dyke and go to outcrop in 'homogenized' kyanite kyanite gneiss encloses twisted twisted fragments of of mafic mafic rock, rock, representing representing either either a small dyke dyke or or �29 pieces This outcrop the extremely extremely ductile ductile pieces tom torn from from aa larger one. one. This outcrop bears testament to the behaviour kyanite gneiss gneiss aa mere mere 1200 1200 m south-southeast south-southeast of of the the Wanapitei Wanapitei behaviour of of the kyanite fault fault. Return to to the the highway highway and and totoSudbury. Sudbury. (If (If time time permits, permits, an extra extra stop stop will be be made made totosee seethe thesuccession successionkyanite kyaniteschist-quartzite-calcareous schist-quartzite-calcareous will gneiss in the of aa fold fold just just north north of of the fhehighway highway nearby.) nearby.) the core core of - COMMENTS - PROBLEMS PROBLEMS OF CORRELATION AND AND HISTORY OF THE GRENVILLE FRONT Metasedimentary schist and and gneiss immediately southeast of of the Grenville Metasedimentary schist immediately southeast Grenville Front Front boundary fault rocks of fault in in this this region region bear no no strong strong resemblance resemblance to the sedimentary sedimentary rocks the Huronian which here Huronian Supergroup Supergroup in the the adjacent adjacent Southern Southern Province, Province, which here are represented by the the Mississagi Mississagi Formation characterized by a monotonous monotonous succession succession of cross-bedded cross-bedded feldspathic feldspathicsandstone sandstonebeds bedstotalling totallingasasmuch muchasas33km kmthick. thick. In the of Grenville Province, Province, the the metasedimentary metasedimentary rocks rocks display display an an alternation of contrasting Grenville contrasting rock types types in in units only ten to a few hundred metres thick, thick, and although one may rock appeal to thinning thinning during duringductile ductiledeformation, deformation, the the successions successions themselves do not not satisfactorily match any any parts of satisfactorily match of the the well-documented well-documented Huronian Huronian succession succession (see (see If, for example, the metaconglomerate and kyanite kyanite schist schist present in this Table 1). 1). If, metaconglomerate and thii area are are equated equated with, with, say, say,the theRamsey Ramsey Lake Lake (Stop (Stop 2, conglomerate) and Pecors Pecors (Stop (Stop 3, slaty argillite) formations, which lie stratigraphically below the Mississagi, Mississagi, then garnet-hornblende-quartz-plagioclase gneiss, gneiss, their association association with with well-layered well-layered garnet-hornblende-quartz-plagioclase presumably derived derived from from calcareous calcareous sedimentary rock, cannot be explained explained in in stratistratigraphic terms, as the only calcareous unit of consequence in the Huronian only calcareous of consequence in Huronian sucsucgraphic terms, cession k is the Espanola Formation Formation (composed (composed of of calcareous calcareoussiltstone siltstone and and wacke with cession limestone at at its base and dolomite limestone dolomite at its its top), top), which which lies lies above above the Mississagi Mississagi and Bruce formations; formations;this thiscorrelation correlationproblem problemisiscompounded compoundedby bythe the fact factthat that aa thin but Bruce persistent quartzite quartzite unit unit lies between persistent between the kyanite kyanite schist and and the thecalcareous calcareous gneiss. Equating metasedimentary gneiss. Equating the the metaconglomerate metaconglomerate with conglomerate higher succession, either either the the Bruce Bruce or or Gowganda Cowganda formations, is equally in the Huronian succession, equally since both both these formations formations are are overlain overlain by by thick thick quartz-rich quartz-rich sandstone problematic since formations respectively) respectively)that thatare arenot not present present in in this units (the Serpent and Lorrain formations part of the the Grenville Grenville Province. Province, One is left with with four four alternatives, alternatives, namely: namely: 1) the metasedimentary rocks rocks are are facies equivalents of conjecture formerly formerly favoured by of Huronian Huronianformations formations—- aa conjecture Lumbers (1975, 1978);2)2)they theyrepresent representsedimentary sedimentaryrocks rocksofof formations formations higher higher in (1975, 1978); the Huronian Table 11)) than than are curHuronian succession succession(i.e. (i.e. above above the the Bar Bar River Formation; Table 3) they they represent represent a younger rently preserved in the the Southern Southern Province; Province; 3) younger succession succession that may on the may have have been been deposited deposited unconformably unconformably on the Huronian Huronian Supergroup Supergroup (perhaps equivalent in age to the the Marquette Marquette Supergroup in the the Southern Southern Province Province of northern Michigan?); 4) they are are an an entirely entirelydifferent differentsuccession successiontectonically tectonically of Michigan?); 4) juxtaposed the Southern Southern Province. Province. The jury jury is still out on this juxtaposed at some time against the this - �matter, but, as stated matter, but, stated earlier, earlier, an inkling inkling that the the metasedimentary metasedimentary rocks rocks are not correlative comes from isotope studies studies which which correlative with with the Huronian Supergroup comes from Nd isotope show provided Nd isotope systematics show that, provided systematics have have not not been been disturbed disturbed during the metarocks, the metapolyphase structural and metamorphic history history imposed imposed on these rocks, sedimentary Grenville Province have Nd depleted depleted sedimentary rocks rocks in in the the Crenville Provincenear near the the front front have mantle model ages younger on this this basis basis younger than than those those of of the the Huronian Huronian Supergroup. Supergroup. IfIf on would probably have favoured, juxtaposition juxtaposition would the last alternative alternative given above is favoured, occurred before before -1750 —1750Ma, Ma, theage ageofofplutonic plutonicrocks rocksfound foundon onboth both sides sides of of the occurred the Grenville Front. Is this part of the front front therefore therefore coincident coinadent with aa pre-Grenvillian pre-Grenvillian Grenville suture? Penokean in in age? age? Note suture?—- perhaps Penokean Note that that Dickin Dickin and andMcNutt McNutf (1989) (1989) placed a Penokean suture much farther south within the the Crenville Grenville orogen. orogen. Two other rock Two other rock units northwest northwest of the the front front have have potential potential counterparts counterparts within within the marginal marginal part part of of the theCrenville GrenvilleProvince. Province. One of the the characteristic characteristic geologic units units in in the Southern Province,and and also also in in the neighbouring part of the geologic Southern Province, the Superior Province, Province, is is the the Nipissing Nipissing gabbro, gabbro, occurring occurring as large, sill-like intrusions. as large, sill-like intrusions. Amphibolitebodies bodiesofof similar similar size, size, derived derived from Amphibolite from gabbro, gabbro, occur occur within within the the metasedimentary rocks rocks in the Grenville metasedimentary Grenville Front zone. zone. Another characteristic characteristic unit, found near the base of the Huronian Supergroup in the Sudbury found Sudbury region region and and also also (-2.45 Ga) Gal adjacent to the front front 50 50 km km to to the thenortheast, northeast,forms formsaanumber numberofofolder older(—2.45 intrusions of gabbro and anorthosite. of similar composition, now mainly infmsions anorthosite. Rocks Rocks of mainly metamorphosed hornblende gneiss gneiss but but locally retaining relict metamorphosed to plagioclase-rich plagioclase-rich hornblende igneous texture where where not not strained, occur occur within the adjacent part of igneous of the the Crenville Grenville Province, ifIf itit isis considered Province. considered that these two two units units are are correlative correlative across across the the front front (and (and it does seem likely that the older suite suite is is correlative, correlative, as as itit can can be be traced traceddirectly directlyacross across the front at then it becomes at River River Valley), Valley), then becomes difficult to accept accept that that the theassociated assoaated If they are metasedimentary rocks rocks in in the Grenville are not Huronian Huronian equivalents. equivalents. If Huronian, then then all all that that can be said said is that during Huronian, can be during their their tectonic tectonic history history they they have been so severely sliced sliced up up and stacked together out of sequence that all semblance sequence that all semblance of Huronian Huronian stratigraphic stratigraphic order order has has been been obliterated. obliterated. With regard to the With regard the potential potential severity of tectonic tectonic 'rearrangement', 'rearrangement', two other units within the Grenville Frontzone zonemust mustbe beconsidered. considered. The The first is the narrow Grenville Front wedge of migmatitic granitoid granitoid examined examined at at Stop 8, 8, and other, smaller slivers slivers of the tucked in with metasedimentary rock and amphibolite same rock that occur tucked amphibolite toward toward Wahnapitae. The of protolith is not not known, known, but it is possible that it Wahnapitae. The age o f the granite protolith is Archean, Archean, and if so, so, that that itit represents represents basement basement to to the the Huronian Huronian Supergroup Supergroup brought up in in tectonic tectonic slices slices at the the front. front. Its migmatitic nature nature isischaracteristic; characteristic; similar is not not present similar leucosome leucosome is present in in orthogneiss orthogneiss derived derived from from post-Huronian post-Huronian granitoid rocks Chief Lake Lakegranite) granite)adjacent adjacent to to the the front front south of (e.8. Chief of Sudbury. Sudbury. granitoid rocks (e.g. The second is the fascinating fascinating Wanapitei mafic complex, mentioned mentioned at at Stop Stop7, 7, which time has not allowed allowed to be examined examined on on this this trip trip(see (seeDavidson Davidson1994 1994for for field field guidance). This This 33 xx 8-km body is composed in part part of of layered, layered, differentiated differentiated gabbro, gabbro, metamorphosed but but not deformed, deformed, and in part of of an an incredible incredible jumble jumble of of equant to to mafic rocks rocksin inaa matrix matrix of of variably variably ductile ductile material material derived from distorted blocks of mafic and an invading invading swarm swarm of of ggranite dykes. Where the dykes cut unr a ~ t edykes. both the gabbro and deformed gabbro, they are straight-walled and composite, with abundant abundant evidence evidence of gabbroic gabbroicand andgranitic graniticmagma. magma. The The granite granite from one of these dykes for comingling of �31 has a U-Pb U-Pb zircon age of 1747 1747 Ma Breemen, unpublished), Ma (Davidson (Davidson and and van Breemen, unpublished), the (1992)on (although itit is is same age as as that that obtained obtained by by Prevec Prevec (1992) on zircon from metagabbro (although possible that the zircon from All of these rocks are cut from the the gabbro gabbro is is metamorphic). metamorphic). All by straight, north-trending, north-trending, vertical dykes of of coronitic coronitic olivine metadiabase metadiabase (just (just like that in the the core core of the dyke remnant seen at at Stop Stop 9), whose chemistry is identical to diabase. In In addition, addition, the dykes dykes retain retain chilled chilled margins, margins, close to which may Sudbury diabase. be found xenocrysts and and small, found large large plagioclase plagioclase xenocrysts small, angular xenoliths xenoliths of quartz quartz 1). The outer part of do Sudbury Sudbury dykes in the Southern Province (Stop I). of sandstone, as do the Wanapitei complex, wellexposed exposedalong alongits its north north and west complex, well west sides, sides, isis entirely entirely tectonic, formed of ductile, recrystallized gneiss whose foliation tectonic, foliation wraps wraps the thecomplex. complex. in the the undeformed undeformed gabbro gabbro is is truncated truncated at this contact, and neither Primary layering in - in fact, the granite granite nor nor olivine olivine metadiabase metadiabase dykes dykes penetrate penetrate the theductile ductilecarapace carapace— large boudins of metadiabase are incorporated within the ductile rim, and metadiabase are incorporated within and occur occur as as segments in in the more distal country disconnected and disoriented segments country rocks. If the coronitic metadiabase metadiabase dykes dykes within within the Wanapitei complex are indeed If Sudbury dykes, then then itit follows that the incorporation of the as a Sudbury dykes, follows that incorporation of the complex complex as 'megaboudin' within within a ductile ductile medium, medium, was was an effect of Grenvillian Crenvillian orogeny. orogeny. The 'megaboudin' effect of fact that the the northern northerncontact contact of of the the Wanapitei Wanapiteicomplex, complex, in in contact contact with withsillimanitesillianitebearing gneiss, lies less than 500 500 m from from outcrops outcropsof ofgreenschist-facies greenschiit-fades Mississagi Mississagi Formation with preserved sedimentary structures facing away from the front front (Stop (Stop remarkably steep steep gradient gradient in in metamorphic grade and 7) belies a remarkably and style style of of deformation deformation across this part of across of the the Grenville Grenville Front. Front. It seems clear clear that that the the Grenville Grenville Front Front boundary fault, particularly particularly where coincident with the Wanapitei Wanapitei fault, exhibiting exhibiting brittle deformation, manifestation of of considerable considerable uplift uplift along along part part of deformation, is the latest manifestation margin, probably probably post-dating introduction the Grenville orogenic margin, introduction of of pegmatite pegmatite at at980 980 Ma, Ma, and perhaps related related to rebound of of the the Grenville Grenville orogen orogen induced by by southeastsoutheastdirected extensional extensional unloading of the the tectonically tectonically thickened thickened Grenville Grenville interior. interior. A word remains to be said about about possible possible renewed renewed displacement, displacement, of of normal normal of the sense (south-side-down) along the Wanapitei-Murray Wanapitei-Murray fault, fault. The truncation of 61, moderately southeast-dipping Grenville Front mylonite mylonite zone zone at atAlice Alice Lake Lake (Stop (Stop 6), metamorphic isograds isograds to the southeast, by and of the the parallel parallel Grenvillian Grenvillian metamorphic by the the subsubvertical fault isis hard hard to with uplift of vertical Wanapitei Wanapitei fault to reconcile reconcile geometrically geometrically with of the the Grenville side alone, unless unless the the preexistent pre-existent Murray-Wanapitei Murray-Wanapitei fault fault acted acted as a ramp 4) was was deflected deflected against which moderately-indined, moderately-inclined, thrust-sense thrust-sense displacement displacement(Stop (Stop 4) the Wanapitei-Murray Wanapitei-Murray fault fault may may have been reactivated vertically. vertically. Alternatively, Alternatively, the reactivated during during post-Crenvillian post-Grenvillian rifting associated with late Neoproterozoic Neoproterozoic development development of rift system, system,centered centeredfar fartotothe the east east and and related related to opening of of the the St. Lawrence Lawrence rift In this regard, some 50 50 krn km east of Sudbury the lapetus Ocean. Iapetus Ocean. In regard, some the Wanapitei Wanapitei fault curves from its position Front boundary boundary fault into the curves position as the Grenville Grenville Front the Grenville Grenville Province, cuffing across acrossthrust thrustfaults faults and and mylonite mylonite that that mark the Province, cutting the continuation continuation of of the Crenville Grenville Front Front to the northeast; northeast; it projects eastward toward toward south-side-down south-side-down faults that that mark mark the the northern northern edge edge of of the theOttawa Ottawagraben graben(Lumbers (Lumbers1971b) 1971b)in in which which Lake Nipissing Nipissing lies, lies, and and with with which are associated Lake associated several alkalic alkalic and and carbonatite carbonatite complexes dated complexes datedatat—585 -585 Ma. Ma. dearly In conclusion, (sensu late) lato) in the Sudbury region clearly conclusion, the Grenville Grenville Front Front (sensu albeitsporadic, sporadic,that that lasted lasted for for aa lot longer than the duration has a history of activity, activity, albeit duration �32 of the the Crenvillian Grenvillianorogeny orogeny itself. itself. It may have been the the locus locus of of juxtaposition juxtaposition of of of crust (based on differences differences between between the the Huronian Supergroup different blocks of Supergroup in in the Southern Grenville) Southern Province Province and the the metasedimentary metasedimentary rocks in the the adjacent adjacent Crenville) Ma. It was active before being being sealed sealed by by igneous igneous rocks rocks at at—1740 -1740 Ma. active following followingemplaceemplacement of granite plutoris at —1470 Ma, but quiescent at the time of intrusion of of the the granite plutons at -1470 Ma, but quiescent at the time of continental Ma. ItIt was was strongly strongly active during -1235 Ma. during continental Sudbury Sudbury diabase diabase dyke dyke swarm swarmat at—1235 at least least the the latter latter part partofofCrenvillian Grenvillian orogeny, orogeny, with with ductile ductile followed followed by brittle brittle Ma,and andpart partofofititmay mayhave havebeen been reactivated reactivated during during the late -1000 Ma, late deformation at —1000 Neoproterozoic. �33 REFERENCES REFERENCES Bennett, G, B.O., and and Robertson, Robertson,J.A. J.A. 1991. C, Dressier, B.O., 1991. The Huronian Supergroup and associated intrusive rocks. In InGeology Geologyof of Ontario. Ontario. Edited Edited by by P.C. P.C. Thurston, Thurston,H.R. H.R. Williams, RH. R.H. Sutcliffe Williams, Sutcliffe and G.M. G.M. Stott. Stott. Ontario Geological Geological Survey, Survey, Special Special Volume pp.549—591. 549-591. Volume4,4,Part Part1,1,pp. Bethune, K.M. 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T.E. 1994. 1.45 1.45 Ga Ga granulites granulites in in the southwestern 1994. southwestern Grenville Grenville province: province: geologic geologic setting, P-T 22:22: 215—218. setting, P-T conditions, conditions,and andU-Pb U-Pbgeochronology. geochronology.Geology, Geology, 215-218. Krogh, T.E. agesfor forGrenvillian Grenvillian and and pre-Grenvilhian T.E. 1994. 1994. Precise Precise U—Pb U-Pb ages pre-Grenvillian thrusting thrusting of Proterozoic Proterozoic and Archean Archean metamorphic metamorphic assemblages assemblages in the the Grenville Grenville Front Front tectonic zone, 963—982. 963-982. tectonic zone,Canada. Canada.Tectonics, Tectonics,13: 13: Krogh, T.E., ages along the Grenville Krogh, T.E., and and Davis, Davis, G.L. G.L. 1970. 1970. Isotopic Isotopic ages Grenville Front Front in in Ontario. Yearbook 68,68, pp.pp. 309—313. 309-313. Ontario. Carnegie CarnegieInstitution InstitutionofofWashington, Washington, Yearbook Krogh, Krogh, T.E., T.E., Corfu, F., F., Davis, Davis, D.W., D.W., Dunning, G.R., G.R., Heaman, Heaman, L.M., L.M., Kamo, Kamo, S.L., S.L., Machado, N., 1987. Precise U-Pb isotopic N., Greenough, Greenough, J.D., J.D., and Nakamura, E. E. 1987. ages of diabase diabase dykes dykes and mafic mafic to ultramafic ultramafic rocks using trace trace amounts amounts of of dyke swarms. swarms. Edited baddeleylte baddeleyite and and zircon. zircon. In Mafic Mafic dyke Edited by by H.C. H.C. Halls and and W.F. W.F. Fahrig. Geological GeologicalAssociation Association of of Canada, Canada,Special Speaal Paper Paper34, 34, pp. 147-152. pp. 147—152. 1984. Precise U-Pb. zircon and and baddeleyite Krogh, T.E., T.E., Davis, D.W., D.W., and Corfu, F. F. 1984. U-Pb zircon ages for the The geology geology and ore deposits deposits of of the the Sudbury Sudbury the Sudbury Sudbury area. area. In The Structure. Edited Pye, A.J. 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Associationof of Canada, Canada,Special SpecialPaper Paper � https://digitalcollections.lakeheadu.ca/files/original/0b1e124eba531637fe45b2fc2ebef497.pdf 40b8bec228577a177ab4473d7cc44f96 PDF Text Text THE THESUBBURY SUDBURYSTRUCTURE STRUCTURE WITH ONTHE THE WITHEMPHASIS EMPHASISON WHITE WATER GROUP WHITEWATER GROUP BY BY S.F. F. M. M.GIBBINS GIBBINS S. INSTITUTE INSTITUTEON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY 43rd 43rdANNUAL ANNUAL MEETING, MEETING, MAY MAY6-11,1997 6 - 11,1997 SUDBURY, ONTARIO ONTARIO SUDBURY, Field Field Trip TripGuidebook, Guidebook,Volume Volume 43, 43, Part Part44 �2 The The Sudhury Sudbury Structure Structure with Emphasis Emphasis on on the the Whitewater Group Group by S.F.M. Gibbins Gibbins Falconbridge FalconbridgeLimited Limited Kidd Kidd Creek CreekDivision DivisionGeology Geology P.O. Bag2002 2002 P.O. Bag Timmins, Ontario Ontario P4N P4N 7K1 7K1 Frontispiece: Frontispiece: Schematic diagram diagram illustrating illustratingthe thestyle style of of development and hyaloclastite emplacement of intrusive hydroclastic breccias and hyaloclastite deposits of the Sandcherry Sandcherry member Formation member of the Onaping Formation (modified from Smith Smith and and Batiza Batiza1989, 1989, Hanson Hanson 1991, 1991, and and Gibson, Gibson, unpublished) unpublished) �3 ACKNOWLEDGMENTS ACKNOWLEDGMENTS This possible without without the the support of Falconbridge This field field trip trip guidebook would not have been possible Limited, Harold Gibson of Laurentian University and Ron Sage Sage of of the the Ontario Ontario Geological Geological Survey. Survey. INTRODUCTION INTRODUCTION The The Sudbury Sudbury Structure Structureis is located located in in south-central south-centralOntario Ontarioat atthe thepresent presentboundary boundarybetween between metavolcanic and and metasedimentary metasedimentary rocks, and granitic granitic the Archean Superior Superior Province Province (,gneissic, (gneissic, metavolcanic intrusions) metasedimentary rocks), and intrusions) and the Proterozoic Southern Province (metavolcanic and metasedimentaq lies approximately approximately 10 of the the Grenville Grenville Province Province(high (high grade gradegneisses) gneisses)(Figure (Figure1). 1). 10km north-west of a!. 1984) Sudbury Structure Structure is known world-wide for for its its NiNiThe 1.85 Ga Ga old (Krogh et al. Cu-POE Cu-PGE ore ore deposits and its debated origin: endogenic endogenicvolcanic volcanicexplosion explosionversus versus meteorite meteorite impact. Two Twocarbonate carbonatehosted hosted Zn-Cu-Pb-Au-Ag Zn-Cu-Pb-Au-Ag massive massive sulphide sulphide deposits deposits also occur in the interior of the Sudbury Structure, located located at atthe thetop top of ofthe the Onaping OnapingFormation Formation of of the the Whitewater Whitewater Group. Group. The Sudbury Sudbury Structure Structure is defined by three components: 1) the Sudbury Sudbury Igneous Complex footwall rocks rocks (both (both Superior Superior and and Southern Structural Provinces) (SIC), 2) surrounding brecciated footwall that SudburyBasin, Basin, comprising comprising rocks rocks of of that extend extend some some 80 80 km away from the Complex, and 3) the Sudbury the Whitewater Group, found in the the interior interior of of the the Complex Complex (Figures (Figures 1and and 2). 2). The The Sudbury Sudbury Igneous Complex, which which has has aa noritic noritic base base and granophyric top, occurs occurs at at the the base base of of the the the surrounding surrounding brecciated brecciatedfootwall footwallrocks. rocks. The The Whitewater Whitewater Group and overlies the Group, Sudbury Basin, comprises, within the Sudbury comprises, from base base to to top, top, initially initiallyglass-rich glass-rich Group, found found only only within breccias of breccias of the the Onaping OnapingFormation, Formation, carbonates carbonatesand anda.rgillites argillites of of the the Vermilion Vermilion and and Onwatin Onwatin Formations, Formations, and and arkosic arkosic sandstones (waekes) (wackes) of the Chelmsford Formation. Formation. The The SIC SIC has has been been dated at 1850 1850Ma Ma (Krogh (Krogh et et al. al. 1984) 1984)and andisisinterpreted interpretedto tohave havebeen beenemplaced emplacedshortly shortlyafter afteror or during 984c). In during the deposition of the Onaping Formation (Rousell I1984~). Inplan, plan,the theSIC SICisiselliptical ellipticalin in shape by 27 km in in size. size. In that the the In section, section, seismic seismic reflection shows that shape and approximately 60 km by north margin (North Range) of the the Sudbury Sudbury Structure consists of, shallowly dipping dipping strata strata of of and layered layered rocks rocksof ofthe the SIC SIC and and footwall footwallgneisses gneisses.. In Incontrast, contrast,the thesouth south sediments, breccias and margin (South Range) is dominated by a series of moderately south dipping reflectors interpreted thrust fliults to be thrust faults or or shear shear zones zones on on which which considerable considerablenorth-west-south-east north-west-south-east shortening shorteningof ofthe the Sudbury et al. 1992). Sudbury Structure Structure has occurred (Milkereit et 1992). The Thepresent presentshape shapeof ofthe theSudbury Sudbury Structure, Structure, as as delineated delineated by the SIC, is due to the combination combination of structural structuralshortening shortening and and subsequent erosion. The The Sudbury Sudbury Structure, Structure,in in plan, plan, isis interpreted interpreted to to have have been originally more circular, circular, with with dimensions dimensions in in the 150 150 -- 200 200 km range (Grieve (Grieve et al. 1991). 1991). Schwerdther (1991) attributed the present elliptical shape Shanks and Schwerdtner shape of the Sudbuiy Sudbury Structure to be the result of north-westerly directed thrusting thrusting related to the Penokean Orogeny, Structure This wasresponsible responsiblefor for several several low-angle low-angle dated at 1750 1750 Ma (Rousell l984c). 1984~). Thisthrusting thrustingevent eventwas flults that reverse faults that cut cutacross acrossthe the SIC SICand androcks rocks of of the the Whitewater Whitewater Group, Group,from from the the south-west south-west to to the south-east. Deformation has also resulted in the formation of isoclinal folds and a slaty Deformation has also resulted in formation cleavage within the Onwatin Formation, open, concentric folds cleavage open, uprighf uprightconcentric folds in in the the Chelmsford Chelmsford 984c). The Formation, and locally overturned rocks in the South Range (Rousell 11984~). The effects of structural deformation are confined primarily primarilyto to rocks rocks of ofthe the South South Range Range and andthe thecentral centralpart part of of structural the Sudbury Sudbury Basin. Rocks Rocksinin the the North North Range Range are are metamorphosed metamorphosed to greenschist greenschist facies, those in South Range are metamorphosed to to lower amphibolite facies facies (Dressier 1984a; the South 1984a; Shanks Shanks and Schwerdtner Schwerdtner1991). 1991). Structure has been attributed The origin of the Sudbury Structure attributed to to volcanism volcanism or or meteorite meteorite impact of aa meteorite meteoriteimpact impactorigin originspecify speci shock (see below for authors). authors). Advocates Advocates of shockfeatures features and and breeciation associated with the Sudbury Structure, the extreme crustal contamination of brecciation Sudbury Structure, the extreme crustal contamination of the the SIC, SIC, glasses and and rapid rapid deposition of of the the Onaping Onaping Formation, Formation, and and the the original original circular circular shape heterolithic glasses �SUDBURy STRUCTURE CHELM$Fo Fm E2:ONWA11N Fm : EZi ONAPft4Q Fm SUDHURY IGNEOUS COMPLEX — - -:-:-:-:r_ - : : :--:- :T::E7 : + + + -c::z' *:- +f i-:.-t:';;:'. ..ERNGTON -- ..'..- - + + + + + •+ ± + + + + 4* FIGURE 1 0 (modified after Gibbins 1994) t + + /4 +! i + + + + 4 L Km I 10 4 + I—T_ i / -- -. + + + + + + + + + + + + + + + + 4 + + + + + __±___+ + + + + + + + + i÷ + —tç ÷ + • + + + +1+ * + * + + -+ + +/+ + + + + + * + + #7+ 4 + + -f + + + 4 +7-f + + + + + �__ 5 NOMENCLATURE NOMENCLATURE THISPAPER PAPER THIS PREVIOUS FREVIO(S CHELMSFORD FORMATION CHELMSFORD FORMATION 0 0 - - - .4 44 MIOOLEIJIITS 0z I— • 44 D6WLJNG MEMBER :±• : & 64: bc6 RitIITS - - C z 0 IL I C', z a- o-o-o-o-o-o- MEMBER C INTR1SION÷:.+.;.. z 0 x Lu Ill UPPER ZONE -J _1 r0! GRANQPf4'y C- z a 0 0 u C C-) N- RIGHT) (SEERIGHT) (SEE MIDDLE ZOWE-QU GAB p 3 0 0 wIll z 2 010 >>- cr LOWERZONE FELSIC NORITE 3 m 0 -5 cn Co XXXxx,ç4 I'tAFIC NORITE: 2 3 I0 00 (SEERIGHT) RIGHT) (SEE ll. C Q Lu UJ I— IIC < 0 u C-) u LU I l l a: 0' m m Figure Figure2:2: StratigraphicSection Section of ofthe Sudbury Structure (modifiedGrieve et al. 1991) Stratigraphic the Sudbuiy Stmctum (modified Grieve et al. 1991) �6 of the Sudbury for aa meteorite meteorite impact. impact. Proponents of a volcanic origin argue Sudbury Structure Structure as evidence for that features features such such as as Sudhury SudburyBreccia Breccia dykes dykes cutting cutting across acrossother other Sudbury SudburyBreccia Brecciadykes, dykes, composite composite fragments ("breccia within breccia") and igneous activity activity within within the Onaping Onaping Formation, Formation, and events/structures that predate and various various regional regional endogenic eventslstructures predate and and post-date post-datethe the"Sudbury "SudburyEvent" Event" are evidence that the Sudbuiy Structure is the result of prolonged endogenic processes, are Sudbury Structure is the result of prolonged endogenic processes, unexplainable unexplainable by aa one one time event such as a meteorite meteorite impact. impact. An extensive amount of literature exists on the geology and evolution of the Sudbwy Sudbury Structure, compilationcontained containedwithin withinPye Pyeetetal. ai.(1984). (1984). The withthe the most recent comprehensive compilation The Structure, with Onaping Errington and Vermilion Vennilion deposits, has been described Onaping Fonnation, Formation, the the footwail footwall rocks to the Enington product of: of: 1) volcanism volcanism (Bell (Bell 1893; Coleman Coleman 1905; Burrows and and interpreted to be the product Rickaby 1930; Williams 1957; 1957; Stevenson Stevenson 1961% 1961a, 1961b, 1972, 1990; Muir 1981, 1930; Thomson 1957; Williams 1981, 1984, 1986; 1986; discussion by Muir in Muir and Peredery 1984); 1984); 2) meteorite impact (French 1968; 1968; Dence 1972; Peredeiy Peredery 1972a, 1972a, 1972b; 1972b; discussion discussion by Peredery Peredery in Muir Muir and and Peredery Peredery 1984; 1984; Peredery Peredery and Morrison a!. 1987; Brockmeyer Brockmeyerand andDeutsch Deutsch 1989; 1989; Stoffler Stoffleret eta!. Monism 1984; 1984; DressIer Dressler et al. al. 1989; 1989; eta!. Brockmeyer 1992; 1992; Krogh Kroghet eta!. Grieve et al. 1991; 1991; Avennanu Avennann 1992; Avennann and Brockmeyer al. 1996, Deutsch et a!. (Thomson 1969; Muir 1982, al. 1995); 1995);or or 3) 3) impact-induced impact-induced volcanism (Thomson 1982, 1983; 1983;Dietz Dietz 1964; 1964; Gibbins 1994). Gibbii 1994). Additional Additional research researchhas has been been directed directed towards towards specific specificfeatures featureswithin within the the Onaping Onaping Fonnation, including (Peredery 1972% I 972a, 1972b; I 972b; Paakki Paakki 1990; Formation, including intrusive rocks (Peredery 1990; McKinley 1992), 1992), mineralization (Chubb 1990; 1990; Drake 1992), 1992), geochemistry geochemistry(Ding (Dmgand andSchwarcz Schwarcz1983; 1983;Schandl Schandleteta!. al. geochemistry, stratigraphy stratigraphy and mechanisms of emplacement 1986; McKinley 1992), geology, geochemistry, 1995and andAmesetal. Abriefsummaryofthe 1994)andalteration(AmesetaL Ames et al. 1996). 1996). A brief summary of the (Gibbins 1994) and alteration (Ames et al. 1995 (Gibbins Onaping Formation is presented presented by by Dressler Dressier et et aI. al. (1991) (199!) in an overview of the Sudbury in an Sudbury Structure. Structure. ford formations formations are are contained within Detailed descriptions of the Onwatin and Chelms Chelmsford contained within Coleman (1905), Burrows and Rickaby (1930), Martin (1957), Thomson Thomson (1957), (1957),Williams Williams (1957), (1957), Sadler Rousell (1972, !984a), Sadler (1958), Cantin (1971), Cantin and Walker (1972), Rousell(1972, 1984a),Beales Beales and and Lozej Lozej (1975), Arengi (1977), and Vezina Vezina (1992). (1992). Mineralization Whitewater Group has been Mineralization in the Whitewater discussed by Burrows and Rickaby (1930), (!930), Martin (1957), Desborough Desborougb and Larson Larson (1970), Card Card and Hutchinson Hutebinson (1972), Arengi (1977), Rousell(1983, Rousell (1983, 1984b), 1984b), Davies Davies et et al. al. (1990), (1990), Whitehead Whitehead et et a!. (1994) and and Gray Gray (1995). The al. (1990), and Paakki (1992), Gibbins (1994) Thestructural structuralgeology geologyof ofthe the by Martin Martin (1957), Rouse11 Rousell (1984c), Whitewater Group has been addressed by (1984c), Cowan Cowan and and Scbwerdtner (1991), and Milkereit et al. (1992). Schwerdtner (1990), Shanks and Schwerdtner (1991), SUDBURY STRUCTURE STRUCTURE of; in ascending ascending stratigraphic stratigraphic order, brecciated breceiated footwall footwal! rocks, The Sudbury Sudbury Structure Structureis composed of, the Sudbury Igneous Complex, and the Whitewater Group. Sudbury Igneous Complex, Whitewater Group. Brecciated FootwaH Brecciated Footwall Rocks Breccias in the footwall are are divided dividedinto intotwo twotypes: types: Sudbury Sudbury Breceia Breccia and Footwall Breccia Breccia. Their al.1991). 1991). Theirorigin originisisaasubject subjectof ofconsiderable considerabledebate debate(Dressier (Dressleret eta!. Sudbury Breccia bodies (pseudotachyiites) occur within all footwall Sudbury bodies(pseudotachy1ites) footwall rocks rocks that that predate predatethe the event,and andextend extendas asfar fir as as 80 km km away away from the the SIC, but are most Sudbury Structure-forming event, abundant in a 10 zonethat that surrounds surroundsthe theSIC SIC (Dressler (Dressier 1984a). The 10 km wide zone The breccias breccia form form subsubvertical irregular from a few millimetres to to zones 0.5 by 11 11 km km in in vertical irregular dyke-like dyke-like bodies ranging in size from size (Dressier 984a). The matrix of of Sudbury Breccia Breceia is is gray gray or or black and consists of of (Dressler 11984a). wealdy recrystallized recrystailized rock rock (Dressler (Dressier 1984a). Large microscopic, weakly Largefragments, fragments,predominantly predominantly of of the the ones are are more more angular angular (Dressler (Dressier et al. a!. 1991). 1991). Igneous Igneoustextures, textures, host rock, are are rounded, rounded, the smaller ones amygduies, and flow banding are not uncommon. Contacts with surrounding amygdules, surrounding host host rocks rocks are aresharp. sharp. Sudbury Sudbuiy Breccia Sudbury Breccia Breccia dykes cutting across other Sudbury Breccia dykes, and fragments fragments of of Sudbury Sudbury Sudbury Breccia have havebeen beenobserved observed(Dressler (DressIeretetal. al.1991). 1991). The The Sudbury Breccia udbu~ Breccia Breccia within S �7 by sudden, explosive brittle brittle failure leading leading to to a violent milling and and is interpreted to have formed by crushing 984a). crushing process process that that involved involved little little or or no no melting melting (DressIer (Dressler 11984a). The as "late granite granite breccia" and "leucocratic "leucocratic breccia" The Footwall Breccia, also described as (Langford 1960; Pattison 1979; Muir Muir 1981, 1960; Souch et al. 1969; Greenman 1970; Paitison 1981, 1983; 1983; DressIer Dressler 1984a; Lakomy 1986, 1989), bodies up up to to 150 m thick, parallel to the contact 1989), occurs as sheet-like bodies contact with the base of of the SIC, SIC, and and hosts hosts much of of the the Ni - Cu ore in the North Range (Dressier (Dressler et al. al. 1991). Contacts Contactswith withthe theoverlying overlying SIC SIC are are sharp, sharp, whereas whereas contacts contactswith with the the underlying underlyingfootwall footwall rocks are gradational (Pattison 1979). The The matrix matrix of of the Footwall Breccia is light coloured with granoblastic granoblasticand and granophyric granophyric textures. Fragments Fragmentsof ofvariable variablesize sizeand andlithology lithologyare arederived derivedfrom from (Dressier et et al. al. 1991). Dressier Dressler et et al. al. (1991) (1991) inteipreted interpreted the the Footwall Footwall Breccia to the local footwall (Dressler shock-metamorphosedrocks, rocks, similar similarto to Sudbury Sudbury Breccia, Breccia, that formed be a mass of crushed and shock-metamorphosed or meteorite meteoritecrater, crater, before before the the deposition deposition of of the the along the walls of the original endogenic-volcanic or lower Onaping Formation and the intrusion of the Sudbury Igneous Complex. Complex. - Sudbury Igneous Sudburv Imeous Complex Complex The into Sublayer Sublayer (Contact (Contact Sublayer The Sudbury Sudbury Igneous Complex (SIC) is subdivided into Sublayer and Offset Offset Sublayer) Sublayer) and and the Main Mass (norites, (norites, quartz quartz gabbros, gabbros, and and granophyres) granophyres)(Pye (Pye et et al. al. 1984). 1984). In plan view, the SIC is elliptical in in shape shape with with aa long long axis axis of of 60 60 km km and and aa short axis of 27 km. et al. al. 1992), to one cross-section, shows the threeSeismic reflection data (Milkereit et 1992), albeit limited to of at least the the north north half half of of the the Sudbury Sudbury Igneous Igneous Complex Complexto to be be similar similar to to aa dimensional shape of sheet-like sill, rather than a fiumel-shaped funnel-shaped intrusion as previously suggested by, amongst amongst others, others, Wilson (1956); (1956); Naldrett Naldrett and and Kullerud Kullerud (1976). (1976). The Sublayer, a fineto medium-grained mafic to to intermediate rock (quartz diorite The Sublayer, fine- to diorite -(Contact Sublayer) Sub!ayer) and as dykes in norite) occurring at the base of the Sudbuiy Sudbury Igneous Complex (Contact surrounding country rocks (Offset Sublayer), the surrounding Sublayer), is host to to much much of of the the Ni Ni -- Cu sulphide ores of (DressIer et et al. al. 1991). The the Sudbury Structure (Dressler The Contact Contact Sublayer Sublayer and Offset Sublayer Sublayerhave have described in detail detail by by Naldrett Naldrett et et al. al. (1984) and by Grant and Bite been described Bite (1984), (1984), respectively. respectively. Dressier that at at least some of of the the Sublayer Sublayer post-dates post-dates the Main Dressler et al. al. (1991) (1991) provided provided evidence that Mass of of the the SIC. SIC. The SudbuvIgneous Igneous Complex Complex is is subdivided subdivided into into aa Lower, Lower, Middle Middleand and The Main Main Mass Mass of of the the Sudburv an Upper zone (Pye et al. 1984; 1984; DressIer Dressler 1984b). 1984b). The Thelower lower zone zone consists consistsof ofmafic maficand and felsic felsic consists of of quartz quartz gabbro, gabbro, and and the the Upper Upper Zone Zone of of granophyres. granophyres. The The norites, the Middle Zone consists contacts between these major phases are gradational (DressIer et a!. 1991). The granophyres contacts major phases are gradational (Dressier et al. 1991). The granophyres of of the the by Peredery Peredery and and Naldrett Naldrett (1975) into an early plagioclase-rich plagioclase-rich Upper Zone have been divided by phase phase. The phase and and aa contemporaneous contemporaneous to slightly later "normal" phase. The SIC SICdoes doesnot not exhibit exhibitfine-scale fine-scale to other large, mafic mafic igneous complexes complexes such suchas as the the Bushveld Bushveld Complex. The The layering common to abnormally rich rocks of the Sudbuiy SudburyIgneous Igneous Complex Complex are are also also unique unique in being abnormally rich in in normative normative SiO2 SiO; and K20. This to suggest Thisobservation observationled led Irvine Irvine (1975) (1975) and and Naldrctt Naldrett and Macdonald (1980) to suggest that the Sudbury strongly contaminated by silica-rich silica-rich country country SudburyIgneous Igneous Complex Complex represented a magma strongly rocks. rocks. Naldrett and Rewins the published published literature literature on the the Main Hewins (1984) summarized much of the Mass Mass of of the the Sudbury SudburyIgneous IgneousComplex, Complex, and and stated stated that that three three main main models models have have been been proposed proposed for for (Dressier et et al. al. 1987). 1987). These the Igneous Complex (Dressler Theseare: are: 1) 1)the the Complex Complex is is aa folded folded differentiated differentiated sill; 2) both the norite and granophyre intruded intruded separately separately as as ring ring dikes, dikes, and and 3) 3) the the Complex Complex is is aa flinnel cataclastic fracturing fracturing of three models require an initial cataclastic of the earth's funnel shaped intrusion. These These three crust crust with the formation of a crater into which a basic magma, rising from depth (possibly from a reactivated Nipissing magma chamber), chamber), intruded intruded and andformed formedthe theSIC. SIC. The Main Mass Mass of of the the Sudbury Sudbury Igneous Igneous Complex has also also been interpreted to be the clast-free component of a melt sheet, impact (Faggart (Faggart et eta!. al. 1985, 1985, Brockmeyer Brockmeyer 1990; 1990; Grieve Grieve et et al. al. 1991). 1991). formed in situ by meteorite impact �8 The upper contact of the SIC Onaping Formation has has been been described described as SIC with the overlying Onaping both gradational gradational and sharp intrusive contact relationships (Dressier et al. at. 1991). exhibiting both 1991). Whitewater Group stratigraphic order, a The Proterozoic Whitewater Group consists of, in ascending stratigraphic conformable conformable sequence sequence of initially glass-rich breccias and melts of the Onaping Onaping Formation, Formation, carbonates and gray argillites of the Vennilion Formation, carbonaceous argillites and siltstones siitstonesof of carbonates the Vermilion Formation, carbonaceous argillites and Onwatin Formation, and and wackes wackes of of the the Cbelmsford Chelmsford Formation. Formation. the Onwatin Onaping Formation Onapine Formation Onaping Formation is the lowermost formation of the Proterozoic Proterozoic Whitewater Whitewater Group. Group. The Onaping The formation consists of a 1400 m thick succession of initially glass-rich breccias and igneousThe consists 1400 m succession breccias ignwustextured rocks within the Sudbury Basin (53 by by 17 km). km). Rocks Rocks of of the Onaping Onaping Formation are are underlain by intrusive granophyres of the Upper Zone of of the the Sudbury Igneous Complex and and are overtain by carbonates and argillaceous conformably overlain argillaceous rocks rocks of of the the Vermilion Vermilion and and Onwatin Onwatin Formations. The TheOnaping OnapingFormation Formation isis the the stratigraphic stratigraphicfootwall footwall to the carbonate-hosted Vermilion and Emngton Errington Zn-Cu-Pb-Au-Ag Zn-Cu-Pb-Au-Ag deposits that that are are found in the the south-west quadrant of the Sudbury Onaping Formation has been Sudbury Basin (Figure 1). Coeval Coevalwith with the the Sudbury Sudbury Event, Event, the Onaping interpreted interpreted as as aa meteor metwr impact impact faliback fallback breccia breccia or oraavolcanic volcanicdeposit. deposit. The Onaping Formation consists of 33 major major units'that unitsthat are are discontinuous discontinuous around around the from the the base base upward, upward, they they are are the the Basal Basal Intrusion, Intrusion,the the Sandcheny Sandcherry Member and Sudbury Basin; from the Dowling member member [Gibbins (Gibbins 1994). These Theseare are different different subdivisions subdivisions than than described described by other other workers. Figure Figure22illustrates illustratescorrelative correlativenomenclature nomenclatureused used in in this this paper paperand andmost mostrecent recentprevious previous workers. Previous Peredery 1984; 1984; Grieve Grieve et al. 1991; 1991;Avermann Avermann 1992; 1992; Previous workers, workers, such such as as Muir Muirand and Peredery Avermann and Brockmeyer Brockxneyer1992, 1992,subdivided subdividedfragmental fragmentalrocks rocksof the Onaping Onaping Formation Formation into into aa of the lower Gray Member, an upper Black Member, and a middle Green member, member, distinguished, distinguished, as as their by colour. colour. The and fluidal-texfured fluidal-textured rocks rocks of of names suggest, by The same same authors authors subdivided the igneous- and Formation into into Basal Basal member memberand andMelt MeltBodies. Bodies. Table Table 1 I summarizes the Onaping Formation summarizes the stratigraphic subdivision nomenclature and stratigraphic subdivision used by previous workers. workers. Stratigraphic subdivision breccias by by Gibbins (Jibbins (1994) using a Stratigraphic subdivision of the Onaping Formation breccias non-genetic, detailed detailedmapping mappingapproach approachbased basedon onFisher's Fisher's classification of fragmental systematic, non-genetic, rocks (Fisher (Fisher 1966), 1966), in conjunction with standard bedrock mapping criteria and detailed morphological examination of of 'glass' fragments, fragments, showed showed that that carbonaceous carbonaceousmaterial materialwithin within the the matrix of the breccias is not time stratigraphic stratigraphic and is, therefore, not a viable criterion for matrix for the the stratigraphic subdivision of the the Onaping Onaping Formation. Formation. Gibbins stratigraphic Gibbins(1994) (1994)noted notedaapronounced pronounced stratigraphic percentage, size and and type type of of fragments fragments (Figure (Figure 3), 3), the stratigraphicdifference in the percentage, the morphology morphology forthe thevarious various depositional depositionalunits unitsthat that were were of glass shards, and in the mechanisms of emplacement for delineated. Based Based on on these these differences Gibbins Gibbins (1994) (1994) proposed proposedaa revised revied stratigraphic stratigraphicclassification scheme for the Onaping Formation that thatisisnot notbased basedon oncolour colour(i.e. (i.e.carbon carboncontent) content)(Figure (Figure4). 4). area, the Onaping Formation is aa 1400 m thick succession of devitrified In the Dowling area, glass-rich breccias and hypabyssal intrusions that dips gently at 25" 25° towards towards the interior of the the Sudbury Sudbury Igneous Complex. According Sudbury Basin and strikes parallel to the contact with the Sudbury According to Gibbins (1994), the succession consists of (1) a coarse, shard-rich, shard-rich, matrix-poor, lower lower member, that that is subdivided into into Fluidal Fluidal Fragment-rich Fragment-rich and Shard-rich Sandcherry member, Shard-rich units, units,(2) (2)aa finer, shard-poor, matrix-rich upper upper Dowling Dowling member, that that is is subdivided subdivided into into Lower, Lower, Middle Middle and and referred to to as as sheet-like sheet-like and and pipe-like pipe-likebodies bodiesof of Basal Upper Units, and (3) coeval intrusions, referred Intrusion and Aphanitic dykes dykes (Figures (Figures 44 and and 5). 5). The the Sandcherry Sandcheny and The contact between the �PRESENT PRESENT PAPER PAPER PAST PAST STUDiES STUDIES GIBB1NS GIBB1NS (1997) (1997) AVERMANN AVERMANN && BROCKMEYER BROCKMEYER (1992) (1992) MUIR & MUIR & PEREDERY PEREDERY (1984) (1984) MUIR MUIR (1983, (1983, 1981) 1981) BURROW & & BURROW STEVENSON THOMSON THOMSON(1957) (1957) RICKABY RICKABY COLEMAN COLEMAN (1972a, 11972b) (1 11972b) (1961, 1972) 1972) WILLIAMS (1957) (1957) (1930) (1905) (1930) (1905) Dowling Cowling Member Member Upper Upper and and Middle Middle Units Units Upper Upper Black Black Member Member Black Black Member Member Black Black Member Member black black Onaping Onaping Lower Lower Black Black Member Member Green Green Member Member Lower Lower Units Units Sandtherry Sandcherry PEREDERY PEREDERY gray gray Onaping Onaping Gray Gray Member Member Gray Gray Member Member Green Green Member Member Melt Melt Body Body Melt MeltBody Body Grey Grey Member Member melt melt rock rock melt mett body body Basal Basal Member Member Basal Member basal basal Basal Member Member Sasal black black tuft tuff Basal Basal Intrusion Intrusion Pipe-like Pipe-like Bodies Bodies Sheet-like Sheet-like Bodies Bodies Table Table 1: 1: breccia breccia - Nomenclature - Present Present and and Past Past (after (afterMuir Muirand andPeredery Peredery1984) 1984) andesitetuft, tuff, andesite tuff-breccia tuff-breccia volcanic volcanic luff, tuff, flow flow breccia breccia grey grey tuff tuff lapilli-tuff, lapilli-tuff, glowing glowing avalanche avalanche deposits deposits pepper-andpepper-andsalt salt micromicropegmatite pegmatite (chilled) (chilled) andesite andesitewith with rhyolite rhyolite fragments fragments lavas lavas quartzite quartzite breccia breccia (tectonic) (tectonic) rhyolite, rhyolite, rhyolite rhyolite breccia breccia rhyolite, rhyolite, Member Member Shard-rich & Shard-rich & Fluidal Fluidal Fragment-rich Fragment-rich Units Units BELL BELL (1893) (1893) pyroclastic pyroclastic sediments sediments siliceous siliceous volcanic volcanic breccia breccia part of part (unspecified) (unspecified) Trout Lake Lake Trout Conglomerate Conglomerate (with igneous(withigneouslooking looking matrix) matrix) Trout Lake Lake quartzite Troul quartzite agglomerate Conglomerate Conglomerate conglomerate conglomerate agglomerate '0 �To SANDCHERRY SANDCHERRY MEMBER MEMBER D 60 E E VITRIC FRAGMENTS FRAGMENTS VITRIC LITHIC FRAGMENTS FRAGMENTS LITHIC 50 A DOWLING DOWLING MEMBER MEMBER (I) zId I— 4° C) IL 30 LI- 0 Id C) zLi P 20 15 0 10 Li a- 5 — 0 SMFL SMFL SMSR SMSR SMSRC SMSRC I DMLCT DMLCT DML DML DMM DMM I DMU DMU UNITS DEPOSITIONAL UNITS Figure3:3: Figure Average percentage ofjunvenile and basement lithic fragments gitater than 1 mm in size in the fragmental units of the Onaping Formation (SMFL= Fluidal Fragment-rich units of Sandcheny Member, SMSR = Shard-rich units of Sandcheny Member, SMSR = Conductive Shard-rich units of Sandcheny Member, DMLCT = Lower Contact Unit of fowling member, DML = Lower units of Dowling Member, DMM = Middle units of fowling Member, DMU = Upper units ofDowling Member. (after (Jibbins 1994) �11 Dowling members change in the percentage of matrix, matrix, morphology and and members marks marks aa rapid rapid stratigraphic stratigraphic change size of shards, percentage of lithic fragments, and depositional depositional character character of of units. units. shards, percentage The description of of the the Onaping Formation is based on work presented The following detailed description by Gibbins Gibbins (1994). (1994). Sandcherry Member Sandcheny The Sandcherry average of 250 Sandcheny member (an average 250 m m thick) thick) is is distributed distributedalong alongthe the base baseof ofthe the Onaping Fragment and Shard-rich Onaping Formation Formation and is subdivided into Fluidal Fragment Shard-rich Units Units (Figure (Figure5). 5). Sandcheny mm in in size), size), that that are are Sandchenymember member rocks contain at least least 60% 60% fragments fragments (>1 (>1 mm predominantly altered "andesitic" "andesitic" glass glass shards with approximately 5% 5% lithic, lithic, basement fragments fragments (Figure (Figure 4). Glass Glassshards shardswithin withinthe theSandcherry Sandchenymember memberare areweakly weakly vesiculated vesiculated (<15% (<15% vesicles) vesicles) and of two predominant types: (1) equant, blocky shards (average (average <1 xx 11cm cmin in size), size),characteristic characteristic of Shard-rich Shard-rich Units and (2) tabular tabular to to ribbony, ribbony, flow flowbanded banded(fluidal), (fluidal),lapilli-sized lapilli-sizedshards, shards, characteristic characteristicof of Fluidal Fluidal Fragment Fragment Units. Units. Sandcherry member units, as defined by mapping, are massive, extremely extremely poorly bedded, laterally discontinuous (<3 km), kin), irregular-shaped breccia breccia deposits deposits that that range rangein in thickness thickness from from 50 50 or to 350 m. Contacts Contactsbetween between units are characteristically characteristically gradational, may be conformable or represent aa facies-like ficies-like change. The discordant, and commonly represent The Sandcherry Sandcherry member member encompasses encompasses units. Where both carbon-poor and carbon-bearing units. Where carbon-bearing, carbon-bearing, the the matrix matrix of ofthe the units units isis conductive. conductive. Fluidal Fragment Units Units (SMFLa, (SMFLa, SMFLb ,SMFLc, SMFLtr) SMFLtr) -- 2a, 2b, 2c, 3 Fluidal Fragment Units comprise four distinct and7) 7)based basedon onthe the distinct map units (Figures (Figures66and percentage percentage and size of fragments that characteristically characteristicallycontain contain aa prevalence prevalence (50 (50- 90%) of tabular to ribbony, flow flow banded shards, lapilli, blocks and bombs bombs (fluidal (fluidal fragments) fragments) of of aphanitic aphanitic 'andesite', 'andesite', aa relatively relativelyminor minor amount of white, equant, blocky shards (0.5 - 1.0 1.0 cm in size), and an extremely low percentage percentageof offine fineash-sized ash-sizedmatrix matrixmaterial. material. The matrix ground mass consists consists primarily of increasingly diminutiveshards shardsof ofthe thesame sameflow flowbanded bandedaphanitic aphanitic'andesite'. 'andesite'. The increasingly diminutive The 10% lithic fragments fragments units may also contain up to 5% 5% dark dark green green chlorite-actinolite chlorite-actinolite fragments, 2 - 10% and blocks, and 3% composite fragments fragmentsof ofother other Sandcherry Sandcherry member memberunits. units. Fluidal Fragment Units are are massive, massive, non-bedded, non-bedded,dense, dense,coarse, coarse,fluidal fluidalfragment-rich fragment-richbreccias. breccias. The four units lapilli-tuff and transitional) (autobreccia, lapillistone, lapilli-tuff, transitional) are are differentiated based on clast size size and percentage percentage and represent a continuous sequence from coarse, semi-massive, flow-banded, 'andesite' autobreccia material of of similar composition. composition. The transitional unit autobrecciathrough to tuff-sized material (SMFLtr) is is a hybrid unit contlining containing fluidal fluidal fragments fragments as as well well as as equant, equant, blocky blocky shards shards that that are are characteristic below. The characteristic of the Shard-rich Units, described below. The transitional transitionalunit unit isis included included within this subgroup subgroup due due to to the the abundance abundanceof of fluidal fluidal fragments. fragments. spatially associated associated with Aphanitic dykes and Fluidal Fragment Units are commonly spatially grouped together represent "Fluidal Breccia bodies of Basal Intrusion and when grouped Breccia Complexes". Complexes", Fluidal Breccia Breccia Complexes typically are several hundred metres to kilometres in size, and are the strata strata of the the Sandcherry member member (sometimes (sometimes"stacked"), 'stacked'), but but are aremore more found throughout the towards the the base. base. Fluidal Fluidal Fragment Fragment Units are are conformable conformable with other fragmental units common towards tuffs), but also intrude discordantly discordantly through (including carbon-bearing tuffs), through them. - - - Shard-rich Units Units (SMSRa, (SMSRa, SMSRb, SMSRc, S 4c,5 SMSRc, SMSRC) SMSRC) -- 4a, 4b, 4c, The Shard-rich that are aredistinctive distinctivefrom fromthe theFluidal Fluidal Shard-richUnits consist of four mappable mappable units units that (Figures 66 and and 7). 7). Characteristic Characteristicof ofthe the Shard-rich Shard-richUnits Units isisthe the prevalence prevalence of of 40 40 Fragment Units (Figures - �12 85%, moderately moderately well sorted, white to pinkish-white, equant, blocky shards, shards, (<1 ( 4 xx 11cm cmininsize) size) 85%, within a fine fine ash-sized microcrystalline light Where carbonaceous carbonaceousmaterial materialoccurs occurs within light green greenmatrix. matrix. Where within the matrix of the Shard-rich Units, Units,the thematrix matrixisisdark darkgray grayto to black black and and conductive. conductive. The Shard-rich units also <10% also contain up to 15% 15% cored bombs, 4 0 % fluidal fluidal fragments, fragments, 1-5% 1-5%accretionary accretionary lapilli, <5% fragments of other Sandcherry <5% lithic lithic fragments, and up to 5% 5% composite fragments Sandcheny member units. The The Shard-rich Shard-rich Units Units are are distinguishable distinguishable from the Fluidal Fragment Units by the occurrence occurrence of of moderately moderately well sorted sorted blocky white shards shards within aa fine finematrix, matrix. were mapped mapped as lapillistones, lapilli-tuffs lapilli-tuft's or or tuffs, tiffs, Non-carbonaceous Shard-rich Units were the size size and and percentage percentageof offragments. fragments. Carbonaceous depending on the Carbonaceous (black (black matrix), matrix), predominantly predominantly Shardrich Units mapped as as SMSRC SMSRC (Unit (Unit 5). 5). Except conductive Shard-rich Units were mapped Except for for the the occurrence of carbon throughout throughout the matrix, this unit is lithologically the carbon the same same as as the the other Shard-rich units. Contacts carbonaceous and andnon-carbonaceous non-carbonaceousShard-rich Shard-richUnits Unitsare aregradational. gradational. The Contacts between carbonaceous Shard-rich Shard-rich Units Units are arethick, thick,confonnable, conformable,laterally laterallycontinuous continuous(several (several1cm) km) sheet-like sheet-like depositional depositional units packed, originally originallyglass-rich glass-richbreccias. breccias. The units of of massive, massive, non-bedded, densely packed, The units units may may locally locally The units units are are situated situatedthroughout throughoutthe the strata strata have a bomb- and block-rich-base, block-rich-base, and/or and/or aa finer finertop. top. The of to pinch and and swell along along strike. Shard-rich of the the Sandcherry Sandchenymember and appear locally to Shard-richUnits Units overlie, underlie, are grade laterally are intruded intruded by, and grade laterally into into Fluidal Fluidal Fragment FragmentUnits Units of ofthe theSandcherry Sandcheny member. Generally, Sandcheny member. Generally, the the Shard-rich Shard-rich Units mark the top of the Sandcheny member. Interpretation Interpretation Shards passive Shardscharacteristic characteristicof of the Fluidal Fragment Units formed by relatively passive fragmentation processes (auto-brecciation) caused caused by by the the interaction interaction of of melt melt with with surrounding surrounding fragmentation water and/or and/or "wet" "wet" (water-rich) breccias. Emplacement Emplacementand and deposition deposition of of the the Fluidal FluidalFragment Fragment Units varied from repeated shallow level intrusion and auto-brecciation to explosive explosive eruptions eruptions characterized by submarine and and subaerial subaerial fountaining fountainingand andspattering. spattering. Passive fragmentation appears to appears to have have been been widespread widespread along the base of the Sandcherry Sandchenymember, member, where where Fluidal Fluidal Fragment Units Units occur occur as as "crusts" "crusts" to to underlying bodies of Basal Intrusion, and also also higher up Fragment section Basal Intrusion intruded wet section where where Aphanitic Aphanitic dykes and pipe-like bodies of Basal wet breccias breccias and and auto-brecciated. auto-brecciated. The TheFluidal FluidalFragment FragmentUnits Unitswere were emplaced emplaced contemporaneously contemporaneouslywith with the the ShardShardrich Units of member as as both discordant, brecciated brecciated intrusive bodies and of the Sandcherry Sandcherry member confonnable conformableinterbedded interbedded units. Contacts Contactsbetween between these these two two Units, Units, where where gradational, gradational,are are represented by LMFLtr, LMFLtr, a transitional transitional unit. Emplacement Emplacementof ofFluidal FluidalFragment FragmentUnits Unitscontinued continued during the Dowling Dowling member. member. In duringand and after afterthe the deposition deposition of the Lower Units of the In conjunction conjunction with the Basal Basal Intrusion Intrusionand and Aphanitic Aphanitic Dykes, Dykes, the Fluidal Fragment Units record a complex history of continued continuedmultiple multiple intrusion, auto-brecciation, and and explosion explosion and and may may spatially spatiallyrepresent represent"vent" "vent" areas areas within within the the Onaping Onaping Formation. The Theemplacement emplacementand and deposition deposition of of Fluidal Fluidal Fragment FragmentUnits Units are are interpreted interpretedto tobe besimilar similarto to the theemplacement emplacement of (1) (1) peperites peperites described describedby by Hanson Hansonand andWilson Wilson (1993), (2) intrusive intrusivehydroclastic hydroclastic breccias breccias described by Hanson (1991), and/or and/or(3) (3)vent-fäeies vent-facies (1993), (2) deposits summits, described described by by Smith and and Batiza (1989) deposits of of hyaloclastic hyaloclastic eruptions on seamount summits, (Figures (Figures 8, 8, 9, 9, and and10). 10). The The Shard-rich Shard-rich Units Units of of the the Sandcherry Sandcheny member are are interpreted interpretedto to have haveformed formedfrom fromthe the same Units. The same melt that formed the Fluidal Fragment Units. The Shard-rich Shard-richUnits Units are arethe theresult resultof ofmore more explosive explosiveinteraction interactionand and eruption eruption of of large large volumes of predominantly juvenile material comprising comprising mostly equant, blocky shards and fine ash-sized material. The Shard-rich Units were deposited mostly equant,blocky shards The Shard-rich Units were deposited throughout throughout the the Sandcheny Sandchenymember member strata strataand and are arethe the explosive explosiveproducts products of ofthe therepeated repeated emplacement melt into into its its own ownbreccia brecciapile. pile. The emplacement and brecciation of melt The occurrence occurrenceof of accretionary accretionary lapilli lapilli indicate indicatethat that eruption eruptioncolumns columns associated associated with the deposition deposition of of the the Shard-rich Shard-richUnits Unitswere, were, in in part, part, subaerial. subaerial.The Theshard-rich shard-richUnits Unitswere weredeposited depositedrapidly rapidlyas asvoluminous, voluminous,essentially essentiallynonnonbedded, particle concentration), subaqueous subaqueous "pyroclastic" bedded, dense dense (high particle "pyroclastic" falls falls of ofslurry-like slurry-like hyaloclastic contemporaneouslydown downslope slopeas asmass massflows. flows. The hyaloclastic flows flows that likely sloughed contemporaneously �1994) GibbS (after Stnicture Sudbury Formation, Onaping the of units map of subdivision and column Stratigraphic -1 '3 ONAPING FORMATION -i<i 4: Figure �ONAPING FORMATION if. SUDBURY IGNEOUS COMPLEX GRANOPHYRE WHITEWATER GROUP CHELMSFORD FORMATION I ONWATIN FORMATION I ONAPING FORMATION DOWLING MEMBER I SANDCHERRY MEMBER SHARD-RICH UNITS FLUIDAL FRAGMENT UNITS 0 INTRUSIONS APHANITIC DYKES BASAL INTRUSION a �LEGEND LEGEND [] 15 MiDDLE MIDDLE PROTEROZOIC PROTEROZOIC Diahose tYykas (1245—1460 t/— 130 Ma) EARLY EARLY PROTEROZOIC PROTEROZOIC SUDB%JRY IGNEOUS COMPLEX (1849.6 +3.4/-3.0 Ma) ORMOPI-IYRE WHITEWATER GROUP CHELMSFORI) FORMAtiON M<oslc to lithic aricosic sandstones (wockes), minor mudstones ONWA11N ORMA1iON Black carbonaceous argllfites. minor ttones ONAPING FORMA11ON INTRUSIONS — iiwmc DYXES (commonly flow bonded, xenoflth—poor) aASAL INIRUSION (medkan to fine—grainS. ccmrnon3' xenslth—ttcsi) — Shoot—like bodies Bib - Border phase with 0rortopl'rn Sic - Pipe-4Ike bodies I 2 OM—DOWUNG MEMBER (lenficulor to plots—Se shads, >60% mabtx) UPPER UNITS (reworked, block carbonaceous matrix) OIhUc — Conductive fine bitt. CX kiplTh—zed fmgmecits (noted In drill hole only) DMUb - fine bitt, <3% cpU—ted fragments DMUo — Redded tuft. lnterbsds of UMUb and UMMc MIDDLE UNITS (<3% block-sized fmgrnenth, carbonaceous matrix) DUMo - topifilatone UMMb - Loplol-tuff DMMc — tuft LOWER UNITS (Matrix Is locally non—carbanooeous >3% block—sIzed fragments) DMb - Loplifistone/ruff BrecS OMLI, - Lopilli-tuff [El [J DMLo — Tuft DMt.CT — Cant Unit — Tuff/Lcpltil-b.sft, eutoxitic bxtur., fine motstc <10% fragments >2cnt and bombtiict base SMSANDCHERRY MEMBER W [J [J (<40% matrIx) SHARD—RICH UNITS (equant. blocky shards) tuft, grades 100* to lapifhitne ad tiff. block carbonaceous matrix SMSRC - onductive C (locally non—conductive), <3% accredonary kipilil SMSfa — Lopifiletone, nan—carbonaceous matrIx SMSRb — LoplIll—tuff. non—carbonaceous matrix SMc — luff, non—carbonaceous mattc 5 FLUIDAL FRAOMtNT UNITS (fiuldal. ribbon-like, flow bonded fragments common, ror* and locally block carbonaceous matctc) SMFIk - Thff/Tu <t%. .rt>flctn in te. equant blocky shards also SMRA — Mt.ct,reccla, 'C20% matrix, block— and bomb—rich StIFLb — Lopilistone SMELo - La$U-tiff U NDEAND UNITS (lower units, significant matrix recsystallizatlan and pervasive sftklfIoatlon) SM— — Tuft—brecalo - tn_one SM--- - Lopilli—tuiff case letters (a. b. e) In unit codes do not necessarily denote time etrotigraphic order. Figure figure6:6: Detailed Detailed legend legend and and stratigraphic d g a p h i c subdivision s u H ~ s i o nof the theOnaping OnapingFonnation FormationofThe oftheSudbury Suhy Structure GibbS 1994) Structure(after (&er Gibbii 1994) �I j I Q'a 1 ClassXcation scheme and terns used in the detaiIed legend and stratigraphic subdivision of the Cnapin~Formation of the Sudbuv S t n ~ c h ~(Figure re 6) ( a b Gibbiis 1994). LapiHi 64—2mm Ash <2mm (Modified after Fisher 1966) Blocks and Bombs >64mm 6 4 3 2 1 pre—existing sulphides sulphide fragment — fragmentary mineralization derived fran, fluldal fragments — aftered Juvenile fragments that display contorted flow banding block — fragment >B4mm ejected in a solid condition bomb — glassy fragment >64mm ejected in a molten state matrix — fragments <1mm in size shards — lapilil—sized or smaller, aftered glass fragments NON—GENETIC TERMS TO DESCRIBE FRAGMENTAL ROCKS CSSIFICATION TERMS USED HEREIN ARE �17 hyaloclastic debris was likely deposited deposited quenched quenchedor or wol, cool, as as there there is is no evidence evidence of of welding. welding. Fire hyaloclastic fountaining, fragmentation of fountaining, ejection of bombs, and explosive explosive fragmentation of ash-, ash-, lapillilapilli-and andblock-sized block-sid and composite) composite)were wereongoing ongoingprocesses processesdurini during deposition. deposition. Emplacement material (juvenile, fiivenile, lithic and hyaloclastie flows on seamount of the Shard-rich Units is interpreted to be similar to hyaloclastic seamount summits, and Batiza Batiza (1989) (1989) (Figure (Figure 8). 8). The described by Smith and The source sourceof of the the Shard-rich Shard-richUnits Units isis interpreted interpreted to be the same Fragment Units. Units. Eruption the he same vent sites as for the Fluidal Fragment Eruptionand andemplacement emplacement of both t Shard-rich and Fluidal Fragment Units occurred contemporanwusly; contemporaneously; the two Units reprSent U ~ t likely s represent different merent vent ticies faciesof ofthe thesame sameeruptive eruptiveprocess p m s that that varied variedin ineffusion e6sionrates ratesand andexplosivity explosivitywith with time. Unit U NLMFLtr ~ LMFLtrlikely likelyisis the the product product of of both both the the eruption emption mechanisms mechanisms characteristic characteristic of the Fluidal Fluidal Fragment Fragment and and Shard-rich Shard-richUnits. Units. The Sandcherry due to to fragmentxtion fragmentation and emption eruption pprocesses Sandcheny member was eemplaced m p l d due r m s e s that involved both passive and explosive interaction of water water with melt, melt, that that was wasrepeatedly repeatedlyemplaced emplaced into its own breccia pile. pile. IfIf there was aa meteorite meteorite impact, "failback" "fallback" is is not represented represented by the there was Sandcherry Intrusion (i.e. Sandcheny member, but is possibly represented by some components of the Basal Intmsion lithic lithic xenoliths). xenoliths). Dowling Member Member member comprises comprisesthe theupper upper 75% 75% (1000 m) of the Onaping Ouaping Formation, and The Dowling member consists of at least wnsists least 10 10 glass-rich, glass-rich, weakly bedded, fragmental units that that are are grouped grouped into into Lower, Lower, Middle, and Upper Units (Figures 5, 6 and 7). 7). Units Unitsofofthe theDowling Dowlingmember memberdefine defineuniform, unifom laterally continuous deposits tthat hat characteristically 60% fine fine ash-sized characteristically consist of more than 60% material material (matrix) (matrix) and and are are essentially essentially carbonaceous, carbonamus, with the the exception exception of of the the lower lower Contact Contact Unit Unit (DMLCT -- U Unit i t 6) 6) (DMLCT member rocks rocks contain contain less lessthan than40% 40% fragments fragments (>l (>1 nun mm in size) that that are Dowling member predominantly glass shards with approximately 15% predominantly altered "andesitic" glass 15%lithic fragments fragments (Figure 4). Glass Glass shards shards of of the the Dowling Dowling member, compared to shards of the Sandeherry Sandcherrymember, are are smaller, smaller, contain fewer, torn4ooking, fewer, but larger larger vesicles, display less flow banding and have a more wispy, torn-looking, lenticular lenticular to plate-like shape. Dowling Dowling member member depositional depositiod units are are of of considerable considerablestrike strikelength length (2 to more than 10 km),are uniform in thickness (25 -- 300 300 in), m), and conformable to 10 kin), and display display conformable lower contacts. contacts. Sedimentary unconformable erosional lower Sedimentarystructures stmcturesare areevident evidenttowards towardsthe thetop topof ofthe the Dowling member. Member Lower Units of the Dowling Member Dowling member member wmprises comprises four four distinct distinct map map units, including the the This subgroup of the Dowliig Lower "chioritic shard horizon'' horizon" or h w e r Contact Contact Unit Unit (DMLCT (DMLCT - Unit 6), previously known as the "chloritic member". The "Green memkr". TheLower LowerUnits Units are aredistinguishable distinguishablefrom &om Sandeherry Sandcherrymember memberunits units essentially essentially by aa greater greater percentage percentage of ash-sized a s h - s d matrix and different shard morphology, and from Middle Units of the Dowling member by by the the presence presenceof ofblock-sized block-sizedfragments fragmentsof ofcountry countryrock rock and and 'andesite' 'andesite' comprise aa reverse ggraded package (increasingly coarser coarser bombs. Collectively, Collectively, the the Lower Units wmprise d e d package crudely channellized ehannellized units, units. Individual depositional units units up section) section) of thick, thick, non-bedded, cmdely are normally graded) TheLower LowerUnits Units have have an an average average true thickness of 200 m, graded)..The in, but range than 55 in than 300 m. The locally from less than m to more than TheLower Lower Units Units were were mapped mapped as as tuffs, tuffs, lapillilapilliand aa considembly considerably coarser lapillistone tuft' breccia. breccia. ttufTs, u s , and lapillistone to tuff - - Unit (DMLCT) (DMLCT) -66 Contact Unit - green The most distinguishing feature feature of of D DMLCT the predominance predominance of 20 20 - 45% m C T unit is the 45% p n to chloritic shards (less than than 55 mm mm in insize) size)within withinaavery veryfine finematrix. matrix. The matrix is dark green ehloritic normally a pale bluish green, but may be dark gray to black due due to to fine fine carbonaceous carbonamus material, material, �Figure 8: A BY./; — //jz>'>,> — rn K//'. :'>' — 7. Schematic model for the development of intrusive hydroclastite breccias (Hanson 1991) S EM ENT SE DIM EN -_ WATER /7.;'C., — — - oc �cJ• Figure 9: • %— RHYOLITE PEPERITE --__ 1993) - PEPERITE Schematic model for the development of peperites (Hanson and Wilson FEEDER CONDUITS' - - o:. 'I REDEPOSITED _____ _ - WATER WET SEDIMENTS _ 'C �20 e. non explosive formation of splinter shards zone of explosive mixing of magma and sea water: fluidal and blocky shards produced density flow entrains vent -.J. 5 metres Schematicdiagram diagramillustrating illustratingstyle styleofoferuption eruptionenvisioned envisioned to produce the Schematic to produce the hyaloclastitedeposits depositson onseamount seamountsummits summits(Smith (Smith and Batiza 1989) hyaloclastite and Batiza 1989) Figure 10 10: Figure �21 which usually occurs the unit. unit. The which occurs towards the top of the The DMLCT Unit contains some (<15%) ( 4 5 % ) blocky shards characteristic of the the Sandcherry Sandcherry member, member, but butthe the majority majority are are finer, finer, angular angular shards similar similar to those characteristic glass glass splinters splinters and and plate-like shards. The Theunit unit commonly commonly displays displays a eutaxitic-like eutaxitic-liketexture texture (incipient (incipient welding), defined by the alignment of of plate-like plate-likelenticular Icnticularshards. shards. Locally, flow flow features features are arevisible visible around the margins of blocks blocks and and bombs. bombs. The unit also contains 5% fluidal 5% fluidal lapilli, 5% 5% bombs, The <5% fragments,and and<3% <3% composite fragments of Sandcherry member <5% lithic lithic fragments, composite fragments of Sandcheny member units, units, This unit outcrops outcropsasasdiswntinuous discontinuous lenses to several kilometres in at length at the contact lenses up toup several kilometres in length the contact between the Sandcherry and Dowling Dowlingmembers. members. The lower contact contact of of the the DMLCT DMLCT Unit is bombs, 0.5 --22 m commonly marked by an an increase increase in percentage percentage (5 -- 45%) of blocks and bombs, m in in size, size, units. Where with respect to underlying units. Where a block- and bomb-rich base is not observed, the contact contact is gradational over decrease upwards gradational over a distance distance of of 33 to to S5 m and is indicated by a decrease upwards (in (in section) section) in in shard shard in shard shard morphology. morphology. The upper contact contact of of the the DMLCT DMLCT size and percentage, as well as a change in Unit, though not typically observed, is sharp and marked by an increase (up section) section) in in lapilli-sized lapilli-sized fragments and and an an absence absence of of eutaxitic-like eutaxitic-liketextures. textures. The Contact Unit may extend around the where the the unit unit was was deposited deposited above water. basin but the "welded texture" may only be developed where compacted (not deposited Elsewhere, the Contact Contact Unit Unit is is not not welded or compacted deposited hot) and and looks looks like like other other units that that were deposited deposited below belowwater water (subaqueous (subaqueous deposition). deposition). In Dowling member units In other other words, words, = subaerial deposition and non-welded = subaerial deposition = subaqueous subaqueous deposition. Welding Welding is is aa good good welding = paleoenvironment indicator. indicator. The The DMLCT DMLCTUnit Unit isis the the first first stratigraphic stratigraphicoccurrence occurrencecontaining containingdepositional depositionalfeatures features characteristic underlying units units of the Sandcheny Sandcherry member, characteristic of of the the Dowling Dowling member.. Compared to underlying the DMLCT DMLCTUnit Unit shows shows an an increase increase in percentage percentage of composite fragments, lithic litbic fragments, fragments, bombs, and having aa block- and bomb- rich base and cored cored bombs bombs (both (both simple and complex), locally having that clearly clearly separates separates this this unit unit from from underlying underlying Shard-rich Units of the Sandcheriy Sandchenymember. member. Lower Units ((DMLa, 7a, 7b, 7c D M 4 DMLb, DMLc) -- 7% 7c Differentiated by size and percentages percentages of of similar similar fragments fragments types, types, these three three units, lapillistone to tuff breccia, lapilli tuff, and tuff, represent represent a discontinuous, discontinuous, crudely crudely interlayered interlayered sheet that comprises the the bulk bulk volume volumeof ofthe theLower LowerUnits. Units. Contacts between the the various various units are typically indistinct, but can be sharp. Lower Lower contacts contacts are locally channelized. Tuff Tuff (DMLc), (DMLc), where where preserved, preserved, is is commonly commonly the the lowest of the three units and usually usually directly directlyoverlies overliesthe the DMLCT Unit (Unit DMLCT (Unit 6). 6). Lapillistone (DMLa) is normally found near the the top top of of the the Lapillistonetototuff tuffbreccia breccia(DMILa) with lapilli-tuff lapilli-tuff(DMLb). (DMLb). Individually, Individually, the the units units are are crudely, crudely, but but normally nonnally sequence, intercalated with graded. Together, sequence. The Together,the thethree threeunits units define define a reversely graded sequence. The units units are aredistinguished distinguished from the underlying DMLCT DMLCT unit by by aa coarser coarser appearance appearance and and the the absence absence of of eutaxitic eutaxitic textures textures in in the matrix. Overlying Overlyingunits units are arebetter better sorted, sorted, and and lack lack coarse coarse lapilli lapilli and and block sized fragments. fragments. The units normally have a dark gray to black carbonaceous carbonaceous fine fine ash-sized ash-sized matrix, matrix, which which represents more than 60% of the rock. rock. The units also contain 15 25% wispy, lentieular to The units also 15 25% lenticular cuspate cuspate shards, shards, 55 - 95% flow flow banded, tabular and fluidal fluidal lapilli lapilliof ofaphanitic aphanitic 'andesite', 'andesite', 3 -- 40% of aphanitic, aphanitic, poorly poorlyvesicular vesicular'andesite' 'andesite', 5 - 10% bombs, cored bombs and blocks of lithic fragments fragments 10% lithic Sandcherry and Dowling member and blocks, and up to 10% 10%composite composite fragments of underlying Sandcheny units. Rare Rarediscontinuous diswntinuouslenses lensesof offine finetuff tuffare arelocally locallyinterbedded interbedded with with the the coarser coarserunits. units. Bedding or layering layering is is not not evident evident at the outcrop outcrop scale. scale. - - - 8a, Sb, 8c 8c Middle Units (DMMa, DMMb, DMMe) DMMc) -- Sa, The memberconsist consistof ofsimilar, similar, thick thickdepositional depositional units units of of The Middle Units of the Dowling member and lapillistone. lapillistone. The tuff, lapilui-tuff lapilli-tuff and The three map units that comprise comprise the Middle Units are are different different only in the percentage percentage of of lapilli-sized, lapilli-sized,dark, dark,chloritic chloriticshards shardsand andlithic lithicfragments. fragments. The The units units m inin true true represent the majority majority (>60%) (>60%) of of the the Dowling Dowling member, and collectively collectively average average 600 600 m �22 gradational. thickness. Contacts with underlying DML Units and overlying DMU Units are mostly gradational. the field from underlying underlying DML DML Units by the absence of blockMiddle Units are distinguished in the and bombs. bombs. Overlying sized lithic fragments and Overlying DMU DMU Units are are finer finer grained and more distinctly bedded. bedded. contain more than than 65% matrix, mostly dark gray to black due to presence of DMM Units wntain carbonaceous 35% wispy, lenticular to cuspate shards, 11 -carbonaceous material. The Theunits units also alsocontain wntain 15 15-- 35% 5% equant, flow banded 'andesite' fine lapilli-sized fragments, <7% lithic fragments (<4 (<4 cm in 5% banded fine 8% shiny, dark, rounded size) and and 2 -- 8% rounded quartz quartz grains, grains, <1-2 mm mm in in size. size. Shards size) Shards in DMM Units display similar DML Units. Some similar features to shards shards contained in underlying DML Some shards shards appear appearto tobe be coated or surrounded by fine ash-sized material material and carbonaceous material. Composite Compositeblocks blocks and and irregular clumps irregular clumps of of coarser coarser and and finer finer underlying underlying breccia breccia units units are arecontained containedin in DMM DMMUnits. Units. Upper Units of the Dowling Member This subgroup This subgroup of the Dowling member marks the top top of the Onaping Onaping Formation Formation and and isis divided into into three three map map units. units. In stratigraphic order DMU Units comprise a basal bedded In stratigraphic order DMU Units wmprise a basal bedded tufT tuff Unit 9a), a fine tuff (DMUb -- Unit Unit 9b), 9b), and and an an upper upperconductive, conductive,fine finetufT tuff (DMUe (DMUc -- Unit (DMUa - Unit 10). Overall, Overall,DMU DMUUnits Units comprise comprise aa normally normally graded graded sequence sequence that has an average average true thickness of 170 m. DMU Units are much finer than underlying units (Figure 4), and display 170 m. DMU Units are much finer than underlying units (Figure 4), and displayfeatures features suggestive of reworking suggestive reworking and and re-deposition. redeposition. - Bedded Tuff Tuff-- (DMUa) (DMUa) -- 9a This tufT(DMUa) (DMUa) occurs occurs at at the the transitional transitional contact zone between DMM and DMU This bedded tuff DMU Units and contains alternating alternating beds of material characteristic of both. DMUa DMUaisisdistinguished distinguishedfrom from underlying DMM Units by the first stratigraphic stratigraphicoccurrence occurrenceof oflaterally laterallycontinuous, continuous,shard-poor, shard-poor, fine ash-sized interbeds intercalated with the relatively coarse tuffs tufTsand and lapilli-tuffs lapilli-tuffsthat that are are characteristic characteristic of of DMM DMM Units. Units. DMUa consists consists of alternating alternating coarse coarse beds beds of of Dowling Dowling member member Middle Units and and fine beds of Dowling member member Upper Upper Units. Units. Individual beds vary considerably in thickness, but but generally average cm thick. The Theaverage averagethickness thickness of of DMUb DMUb beds beds increases upwards. DMUb DMUbbeds beds average55 to to 50 50 cm consist of fine ash-sized ash-sized fragments fragments of ofjuvenile juvenile and lithic material; fragments greater than 2 mm are uncommon. Normal beds isis absent absentto toweakly weaklydeveloped; developed; contacts contacts unwmmon. Normal grading gradingwithin within individual individual beds between beds are sharp, with uncommon soft sediment slump features and small, channel-like structures. structures. - TufT-- (DMUb) Fine Tuff (DMUb) - 9b Contacts Contacts are are conformable conformable and and gradational, gradational,marked marked by by an anabsence absenceof ofthe theDMM DMMUnit-like Unit-like comnon in (Unit9a) 9a) and and by by aa generally coarser appearance appearance and interbeds common in the theunderlying underlying DMT.Ja DMUa (Unit and lack of conductivity, compared compared to to the the overlying overlyingDMUc DMUc (Unit (Unit 10). 10). DMUb is is well sorted sorted with material finer finer than than 1 mmm insize. size. Much of the fine ash ash material material is is subsubm in greater than 95% of the material rounded lithic lithie fragments and and rounded rounded (abraded) (abraded) shards. shards. Rare, Rare, larger largeraltered altered glass glass shards shardsmay mayalso also occur. DMUb DMUbisislocally locallyinter-layered inter-layered with with beds beds of of angular angularto torounded rounded argillaceous argillaceous and cherty cherty fragments, less than 2 cm in size. Individual Individual beds are are commonly commonly less than 40 cm thick, and may contain up to 80% fragments. Many 80% of these dark gray to black fine sedimentary fragments. Many of of the the fragments fragments wntain give give the impression of of being rip-up elasts. clasts. �23 - - Conductive ConductiveFine Fine TufT Tuff - (DMUc) (DMUc) - 10 10 tuft' (DMUc) (DMUc)was was described described by by Paakki Paakki (1992) (1992) as "Conductive This conductive fine tuff 'andesite' tuft". tuff". Conductivity Conductivityisisattributed attributedto tothe the presence presence of of fine carbonaceous material. Lower Lower underlying DMUa DMUa and and DMUb DMUb are are marked marked by by aa gradational gradational fining finingand andthe theonset onsetof of contacts with underlying associated with with aa stratigraphic stratigraphic increase increase in in carbonaceous carbonaceous material. material. The conductivity, associated The upper upper contact contact with overlying sediments and and carbonates carbonates of the Vermilion Formation is sharp sharp and and conformable. conformable. from the the similar similar looking looking Onwatin Onwatin Formation Fonnation by the absence of fine DMUc is visually distinguished from laminations and siltstone laminations siltstone interbeds. interbeds. The The upper 55 to 10 10m m of DMUc DMUc is is black, black, fine, fine, poorly poorly bedded bedded to to massive, massive, and and strongly strongly conductive. Towards Towardsthe thebase baseof ofDMUc DMUcconductivity conductivitydecreases decreasesand andwispy wispylenses lensesof oflighter lighterand and slightly coarser, dark gray apparent. gray tuff tuff become apparent. Interpretation The The morphology morphology and internal internal characteristics characteristicsof ofshards shardswithin withinthe theDowling Dowlingmember memberindicate indicate that vesiculation (volatile (volatile exsolution) played a role, though though aa minor minor one, one, in in the the predominantly predominantly hydroelastic hydroclastic fragmentation fragmentation and eruption of the Dowling member. The The Dowling Dowling member member Lower Lower Contact Unit represents a deposit formed by by fragmentation processes that changed from the Contact relatively passive to moderate explosive generation of Fluidal Fragment Fragment Units (proximal, (proximal, intrusive/extrusiveauto-breccia deposits) and co-genetic Shard-rich Units (more widespread intrusive/extrusive hyaloclastic activity and and basin-wide deposition deposition of of voluminous voluminous falls, hvaloclastic deposits) to more explosive activity falls. flows and subsequent mass mass flows. Consistent and consistent with the greater explosivity expiosivity is a fine grain size &d minor (10%) in the the lithic lithicfrwment fragment content of depositionai units. The Sandcheny (10%)enrichment in content of depositional units. The Sandchem member/Dowling member contact is suggestive of an evolving hydroclastic hydroclastic eruption that that was was initially initially relatively passive, passive, but but with with time timebecame becamemore moreexplosive. explosive. The Contact Unit (the DMLCT DMLCT Unit) is interpreted interpreted to have been deposited relatively hot, possibly in aa subaerial to shallow subaqueous environment, subaerial to shallow subaqueous environment,and andisisincipiently incipientlywelded welded (where (where deposited subaerially). The TheDMLCT DMLCTUnit Unitisisthe theproduct productofofthe theexplosive explosiveintroduction introductionof ofnew newmelt melt at at surface. surface. The majority of the Dowling member units units are interpreted interpreted to have have been deposited deposited subaqueously as a prolonged, explosively erupted erupted series series of of "pyroclastic" falls, flows and subaquwusly subsequent debris or mass flows. Nearly in the the Nearlycontemporaneous contemporaneousslumping slumpingand and sloughing sloughingresulted resulted in transportation transportation and re-deposition redeposition of tuffaceous material down slope in the form of pyro-turbidite mass flows (Figure 111). 1). Cored, Cored, aerodynamic aerodynamicbombs bombs indicate indicate that that eruption eruptioncolumns columns and debris-like mass were, in part, subaerial subaerialand and associated associated with lava lava fountaining fountaining during during the the deposition of the Lower Units. Lower LowerUnits Unitswere weredeposited deposited on on fairly fairly irregular irregularpaleo-topography paleo-topographyas aspoorly poorlysorted, sorted, ehannellized sheets of significant thickness. In contrast, the Middle Units arc interpreted channellizcd of significant thickness. contrast, the Middle Units are interpreted to to have have been deposited as a series 10 m) "pulses" series of frequent, frequent, thin (1 - 10 "pulses" of generally better sorted, sorted, finer finer (block(block- and bomb-poor), possibly possibly graded graded material; material; there there isis no noevidence evidence of of significant significantsedimentary sedimentary re-working. Deposition was rapid and mass slumping destroyed primary depositional Deposition was rapid and mass slumping destroyed primary depositionalfeatures. features. The "pulses" are are typical typical of of hydroclastic hydroclastic explosions explosions where water water intermittently has access access to to melt. Deposition of the laterally continuous and uniform Middle Middle Units of of the the Dowling Dowling member marks marks aa change to a more tectonically stable stable depositional depositional environment, compared to that that of of the the Lower LowerUnits Units member. The of the Dowling member. The Upper Upper Units Units represent represent the final final deposition of fine ejecta and subsequent subsequent sedimentary sedimentary reworking. reworking. - Basal Intrusion Intrusion subdivided into intothree threeseparate separatemap mapunits. units. These are (I) The Basal Intrusion is subdivided (1) Sheet-like Sheet-like bodies (BIa), which occur occur as discontinuous sheets or or sills, up to 300 m thick, at the base base of of the the �24 Sandcheny bodies (BIG), (Bk), which occur Sandcherry member, (2) Pipe-like bodies occur as as irregularirregular-to toovoid-shaped ovoid-shapedintrusive intrusive masses Sandcheny and fragmental units of the Sandcherry and Dowling members (pipe-like bodies are masses within fragmental commonly commonly exposed in clusters, clusters, and range in size from less than 2 xx 22 in in to over 50 x 100 100 m), and and (3) Border phase with Granophyre (Bib), (BIb), which which represents represents aa transitional transitional contact zone up to 65 m thick between sheet-like bodies bodies of of Basal Basal Intrusion Intrusionand andGranophyre. Granophyre. The The border border phase phase was was not not Granophyre and fragmental units units of of the the Sandcheny Sandcheny member are in direct contact. contact. noted where Granophyre (Ma) -- 1Ia Sheet-like (Ha) l a and and Pipe-like Pipe-like Bodies (BIc) (BIc) -- lie 1l c 1 pipe-like bodies bodies of ofBasal Basal Intrusion Intrusion are are igneous-textured phases of the same Sheet-like and pipe-like same unit, and and are aredifferent differentonly only in in their their morphology morphology and stratigraphic stratigraphiclevel level of of exposure. exposure.The Themost most distinguishing 85% (ave. 35%) xenoliths of a variety of distinguishingfeature feature of of the the Basal Basal Intrusion Intrusion isis S5 - 85% leucocratic basement rock types (quartzites, granitoids). leucocratic rock types (quartzites, granitoids). Xenoliths Xenoliths are are randomly randomlyoriented, oriented, subangular to rounded, sub-equant,.and .sub-equant,and range in size from from <5 <5 mm to to 30 m, but average average 30 30 - 40 subangular cm. rounded. The cm. Locally, Locally,xenoliths xenolithsare arewell well sorted sorted and well rounded. The xenoliths xenoliths decrease decrease in size and are better higher in in strata. strata. Pristine better sorted sorted in in bodies of Basal Intrusion exposed higher Pristineto tocorroded corroded(melted) (melted) textures bleaching, recrystallization, recrystallization, assimilation textures are are common, common, with with xenoliths xenoliths showing minor bleaching, assimilation andior andlor partial partialmelting, melting, the the last lastof ofwhich which isis demonstrated demonstratedby by embayments, embayments,rounded rounded margins, margins, cavities, other fragments. fragments. This cavities, apophyses, apophyses, and and annealed margins with other This "melting" "melting" indicates indicatesmelting melting and assimilation at "depth" and then transportation to surface and this is farther evidence of assimilation at and transportation surface and this is farther evidence of the the Onaping melts being emplaced from below and not as fall Onaping fall back. back. The The matrix matrix isis medium medium greenish-gray, greenish-gray, fmefine- to medium-grained, and has a massive, salt-andsalt-andtexture. Fine pepper texture. Fineprisms prismsofofamphibole amphiboleare aretypically typically visible visible in in the the coarser-grained coarser-grainedbodies. bodies. Generally, there is a decrease decrease in in matrix matrix grain grain size size in intrusive intrusive bodies exposed exposed higher higher in in stratigraphy. 10% quartz-, chlorite-, and/or stratigraphy. Pipe-like Pipe-likebodies bodies higher higher in strata strata also contain 5 - 10% andlor sulphide-fillcd mm in size. sulphide-filled amygdules, amygdules, that that range range from from 22 - 55 rnm Contacts sharp, vertical Contacts with all all but the Fluidal Fragment Units are intrusive, sharp, vertical to to horizontal horizontal surfaces. The and usually obvious obvious on outcrop surfaces. Thelarge largesheet-like sheet-like bodies bodies display display chilled, chilled, fine-grained fine-grained generally have a thin thinchilled smaller pipe-like bodies generally chilled to aphanitic, aphanitic, xenolith-poor margins. The Thesmaller margin. Contacts with the Eluidal Fragment Units are gradational, marked by an aphanitic, Contacts with the Fluidal Fragment brecciated brecciated and and xenolith-poor margin. Where Wherethese these brecciated brecciated contact contact margins margins are arerelatively relatively large large they have have been beenmapped mappedas asAutobreccia Autobreccia(SMFLa). (SMFLa). Contact relationships suggest or extensive they emplacement emplacement of Basal Intrusion Intrusion is is contemporaneous with, pre-date predate and and post-date postdate the the emplacement emplacement of the fragmental fragmental units. Locally, Locally,where wherethe the Basal BasalIntrusion Intrusionintrudes intrudescarbon carbonbearing bearingfragmental fragmental rocks, aa 22 to to 15 15m m contact contactzone zone of of carbon-poor carbon-poor tuffs tuffs surrounds surrounds the the intrusive intrusive body. body. The The Basal Basal Intrusion Intrusionisis envisioned envisioned to represent represent an xenolith-bearing xenolith-bearing melt that that intruded intruded the the fragmental fragmental rocks of the Onaping Formation. Bodies Bodies of of Basal Basal Intrusion Intrusionwere were emplaced emplaced before, before, the Sandcherry. Sandcherry.and Dowling members. members. During during, and shortly shortly after, the deposition of the and Dowling During intrusion intrusion most of of the the fragmental fragmental units were unconsolidated and, at least least locally, locally, bodies bodies of of the the Basal Basal Intrusion for the the Fluidal Fluidal Fragment Fragment Units Units (SMFL), (SMFL), in similar Intrusion are interpreted to be the melt source for fashion fashion to to peperites. peperites. Xenoliths with@ within the Basal Intrusion are interpreted to be remnants remnants of of basement basement rocks. rocks. The variety of xenolith xenolith rock types indicates mixing of basement fragments before and during their asSimilation into, or or transportation transportation by, by, the the Basal Basal Intrusion. Intrusion. Locally, assimilation into, Locally, xenoliths were rounded and sorted according according to size sizç before or during emplacement. emplaeement. Because of the high percentage of xeholiths and relative small size of the intrusions, partial melting of the xenoliths is interpreted to xenoliths have have occurred occurred before before incorporation incorporation into into the intrusive intrusive bodies that transported transportedthem them to totheir theirpresent present site. Other Otherxenoliths xenolithsare arefresh freshand andunmelted, unmelted, suggesting variation in melt temperatures or, more likely, in the timing of incorporation. The The cataclastic cataclastic event event that that formed the Sudbury SudburyStructure Structureisis interpreted to have have formed the xënoliths, x'enoliths, that are presently found within the Basal Basal Intrusion, Intrusion,by by - - - - �25 A BEGINNING OF ERUPTION Schematicdiagram diagramof ofinferred inferred submarine eruption Schematic submarine eruption 1964) (Fiske and Matsuda (Fiske and Matsuda 1964) Figure11: 11: Figure �26 basement rocks. rocks. The brecciation of the basement The"melted" "melted" appearance appearanceof ofsome somexenoliths xenoliths may may be be evidence of impact melting: melting. Border Border Phase Phase of of the the Basal Basal Intrusion Intrusion (BIb) (Bib) -- 11lb BIb (iranophyre and bodies of the Basal Bib represents represents a gradational contact contact zone between Granophyre Intrusion. BIb Bibhas hasfeatures featuresof ofboth both these these units, units, in in varying varying percentages. The Thecontacts contactsbetween between the the bodies of of Basal Basal Intrusion (BIa) border phase of the Basal Intrusion (BIb) (Bib) and both the sheet-like bodies and and Granophyre Granophyre are are gradational gradational over over 11-- 55 m. Close Closeto tothe theGranophyre, Granophyre,the the matrix matrix of of BIb Bib isis similar Thesole soledifference differencebetween betweenthe thetwo twobeing being the the presence presenceof of55 -- 10% 10% similar to Granophyre. Granophyre. The xenoliths. xenoliths. Near Nearthe thecentre centreof ofBib, Bib,the thematrix matrixisisincreasingly increasinglyfine-grained, fine-grained,but butcommonly commonlydisplays displays aggregates of coarser coarser andlor Rareamphibole amphibole needles are visible. Lithic Lithic aggregates and/or finer crystals within within it. Rare xenoliths account account for for 15 15- 65% 65% of the rock, and and commonly commonly have a mafic mafic reaction reaction rim rim that that extends extends22 -- 77 mm into the surrounding matrix. Close Closeto toBIn, BIa,the thematrix matrixisisfine-grained fine-grainedand and homogeneous, homogeneous, and and except except for forrare rarelong longneedles needles of ofamphibole, amphibole,isisindistinguishable indistinguishablefrom fromElla. BIa. Bib bodies of of lower border phase/contact phaselcontact zone of the sheet-like bodies Bib is is interpreted interpreted to to be the lower Basal Intrusion and Granophyre. No No sharp sharpintrusive intrusivecontact contact between between Granophyre Granophyre and Bib Basal BIb has been noted. BIb Bibmay mayrepresent representaazone zoneofofmixing mixingbetween betweentwo twonearly nearlycontemporaneous contemporaneousmelts. melts. The Basal Basal Intrusion has been described described as a conglomerate (Coleman 1905), a rhyolite (Thompson 1957; 1957; Williams 1957), 1957), aa tectonic tectonic quartzite quartzite breccia (Stevenson 1972), 1972), aa breccia (Thompson 1972b), and part of of an an impact impact melt melt system system also also meteorite fall-back breccia (Peredery 1972a, 1972b), Stevenson (196 (1961a) that comprising the Sudhury Sudbury Igneous Complex (Brockmeyer (Brockmeyer 1990). Stevenson la) proposed that the matrix matrix was wasoriginally originallyaa highly highly pulverized pulverized mixture mixture of of country countryrock rock fragments, fragments,subsequently subsequently the Alternatively, the the matrix matrixhas hasbeen been recrystallized by the intrusion of the the upper upper phases of the SIC. Alternatively, 1989; interpreted to have been initially igneous-textured and intrusive (Brockmeyer and Deutsch 1989; Paakki Paakki 1990). 1990). - - Aphanitc Aphanitc Dykes (APHDYK) (APHDYK) - 12 12 Aphanitic Aphanitic dykes (APHDYK) are narrow, to irregular-shaped, irregular-shaped, intrusive intrusive aphanitic aphanitic 'andesite' dykes that are are xenolith xenolith poor, commonly commonly display regular regular to to contorted contorted flow flow banding, banding, and and are are similar similar appearanceand and composition composition to to fluidal fluidal fragments fragmentsand and bombs bombs within within the the fragmental fragmentalunits units of ofthe the in appearance Sandchenyand and Dowling Dowling members. APHDYK APHDYK occurs occursspatially spatiallyassociated associated with the margins of Sandcheny sheet-like bodies of Basal Intrusion, as narrow, narrow, or or lens-shaped lens-shaped intrusions intrusionswithin within the the Sandcherry Sandcherry member, and and uncommonly as small, thin dykes within the Lower, Middle, and Upper Units of of the the Contactsbetween between APHDYK APHDYK and and the the fragmental fi-agmental units units may may be be locally locally knifeDowling member. Contacts sharp, sharp, intrusive, intrusive, and and normally steeply steeply dipping. Elsewhere, Elsewhere,these these contacts contacts tend tend to to be be highly highly irregular and and brecciated, brecciated, with with numerous numerous apophyses apophysesextending extending outwards outwardsfrom fromthe themain main body body in in irregular lobe-shaped structures, of structures, surrounded surrounded by hyaloclastite, hyaloclastite, in similar fashion to the emplacement of peperites. Contacts Contactsof ofAPHDYK APHDYK with with bodies bodies of of Basal Basal Intrusion Intrusion are are gradational gradational over 10 10 cm and are towards the the Basal Basal Intrusion. Intrusion, The are characterized characterized by a coarsening of grain size towards The margins of APHDYK are typically strongly flow flow banded bandedparallel parallelto tocontacts. contacts. Conehoidal Conchoidal fractures and sharp flinty flinty to to cherty-like cherty-like broken edges are are characteristic characteristicof ofthe theunit. unit. APHDYK APHDYK contains contains less than 5% 5% subrounded subrounded quartz-rich lithic fragments (1 - 10 10cm cm in in size), up to 10 pyrrhotite and chalcopyrite. Spherulitic 10 % % quartz/chlorite-filled quartz/chlorite-filled amygdules, and 1% 1% pyn-hotite Spherulitic texturesare arealso alsolocally locally common. common. Higher Higherininstratigraphy stratigraphythe theunit unitisismore morevesicular vesicularand andspherulitic. spherulitic. textures APFIDYK similar in appearance appearance to bombs APHDYK is similar bombs and and fluidal fluidal fragments fragmentswithin within the the fragmental fragmental units. units. Aphanitic Aphanitic dykes are are interpreted interpreted to to be be the the less less contaminated, contaminated, lithic-poor, lithic-poor, more more rapidly rapidly crystallized crystallized equivalents (end members) of the Basal Intrusion. Intrusion. Aphanitic Aphaniticdykes dykesand andpipe-like pipe-like bodies of Basal Intrusion may represent different different phases of the same intrusion. Aphanitic Aphanitic dykes dykes - �27 hypabyssal intrusions of of non-brecciated non-brecciatedmelt meltof of 'andesite' 'andesite' are interpreted to represent small hypabyssal composition that intruded the fragmental rocks of the Onaping during and shortly after their deposition. The Theoccurrence occurrenceofofAphanitic AphaniticDykes Dykesmay may defme define "vents" and structures structures that that controlled emplacement of the Onaping breccias, fluid migration, alteration, alteration, and mineraliziation. Locally, APHOYK APHDYK represents represents sites sites where where massive massive 'andesite' 'andesite' locally locallyintruded intrudedand andflowed, flowed, tongue-like, tongue-like, into into unconsolidated, unconsolidated, wet piles of glass-rich fragmental rock, interacted with water and passively passively to explosively fragmented. Aphanitic Aphaniticdykes dykes represent represent feeders, feeders, at at least leastlocally, locally,for forthe thefragmental fragmentalunits units of the lower Onaping Formation. The The dykes dykes show show many features features similar similar to "peperites" described and Wilson Wilson (1993) (1993) (Figure (Figure9) 9) and and "intrusive "intrusivehydroclastic hydroclasticbreccias" breccias"described describedby by by Hanson and Hanson (1991) (1991) (Figure (Figure 8). 8). Aphanitic Aphaniticdykes dykesare arelikely likely representative representative of the original melt from which the fragmental fragmental rocks rocks of of the the Onaping Onaping Formation Formationwere werederived. derived Carbon Carbon Contact Contact Carbonaceous Carbonaceous material material occurs occurs locally locally within the Sandcherry Sandcherry member and is pervasive through much of the overlying Dowling Dowling member. member. The contact The wntact between between carbon-poor carbon-poor and and carboncarbontransects lithological contacts contacts and is gradational bearing fragmental rocks transects gradational over over 55 to to 20 m. Where Where carbonaceous material occurs within the the Sandcherry member member Shard-rich Shard'rich Units, the rocks are conductive. The wnductive. TheDowling Dowling member, member, though significantly significantly more carbonaceous carbonaceous than than the the Sandcherry Sandcherry conductive (due to to high high amorphous amorphous carbon carbon contents) only in in its its upper upper 50 m, directly member, is wnductive the Vermilion Vermilion Formation. Formation. Conductivity within the the Shard-rich Shard-rich Units Units of ofthe the Sandcherry Sandeheny beneath the to high high amorphous amorphous carbon contents, member, however, is not attributed solely to Carbonaceous Sandcheny rocks support support subaqueous Sandcherry and and Dowling member fragmental rocks deposition for both members. Carbonaceous Carbonaceousmaterial materialmust musthave havebeen beenrelatively relativelyabundant abundantwithin within the water of both both the the Sandcherry Sandcheny and water column and on the depositional floor during the emplacement of Dowling Dowliig members. This This suggests suggeststhe the early early incorporation incorporation of of carbonaceous carbonaceous material, locally at least, Onaping Formation. Formation. least, during during deposition deposition of of the the Onaping The The carbon carbon contact wntact isis interpreted interpreted to to mark mark either either (1) (1) the the boundary boundary between between oxic oxic and and anoxic anoxic depositional environments, or (2) an alteration front, or contact, wntact, between lower rocks (carbon-poor) (carbon-poor) and upper rocks material has has been preserved. preserved. All of the Sandcheny rocks in which the carbonaceous material Sandcherry member depositional units units may may have havebeen beeninitially initiallycarbonaceous. carbonaceous Deep Deep circulation circulation of of fluids, presumably marine water, driven by the heat of the Basal Basal Intrusion Intrusion and SIC, SIC, may may have have been been responsible responsible for the removal of the carbonaceous carbonaceous material material out outof ofmuch much of ofthe theSandcherry Sandcherrymember. member. Later cooling of the SIC may have subsequently caused the "drawing down" and and redistribution of carbonaceous material. carbonaceous material. Perederv (1972a, 1972b), Peredery and Momson Morrison (1984), Avermann (1992), (1992), and Peredery (1972a, Avcrmann Avermann and Brockmeyer (1992) proposed that the carbonaceous carbonaceous material material within the fragmental fragmental material, derived from surrounding surrounding pelagic sediments, that that was washed into units is is fine fine organic organic material, the crater fallout material. material. Alternatively, crater and and redeposited redeposited along with reworked meteorite fallout Alternatively, that the source of of the the carbon carbon is is the the result result of of aa mass mass killing of of Whitehead et al. (1990) proposed that organisms subsequently settled through the water organisms within the Basin Basin - the dead organisms subsequently water column column and were incorporated incorporated into into the the initially initially glassy glassy breccias brecciasbeing being deposited depositedon on the the crater craterfloor. floor. - Alteration The Onaping Formation displays pronounced stratigraphic stratigraphic lithogeochemical variation, variation, upwards in wt.% wt.% Si02, TiO2, Ti02, Al203, Na20, K20 K10 and illustrated by progressive apparent losses upwards A1203, NazO, MgO, and progressive progressiveapparent apparentgains gainsupwards upwardsininwt.% wt.%COz, CO2.CaO, CaO,FeiOs, Fe203, MnO, C, and S (Table (Table MgO, MnO, Cm, 13, 14, 14, and and 15). 15). The The base base of of the Sandcheriy Sandchenymember shows a marked apparent 2, Figures 12, 12, 13, Si02. Variations increase in SiO;. Variationsin in composition, composition, except for the occurrence of particulate organic (C), are carbon (Cm), areattributed attributedlargely largelytotoalteration. alteration.All Allfragmental fragmentalunits unitsofofthe theSandeherrv Sandcherrymember member �28 of aa similar andesitic andesitic composition composition(Gibbins (Gibbins 1994). 1994). Aphanitic are interpreted to have initially been of Aphanitic dykes best represent the precursor precursor composition wmposition of the glass-rich breccias. breccias. lithogeochemicalstratigraphic stratigraphic variation variation (zonation) (zonation) Glass composition wmposition heterogeneity and lithogeochemical the Onaping Formation Formation isisattributed attributed largely largely to to various various types types displayed by the fragmental rocks of the of alteration. alteration. These Theseconsist wnsistofof(1) (I)aabasal basalsilicification, silicification,(2) (2)an anoverlying, overlying,lower lowersemiconformable semiconformable + orthoclase) feldspar (albite + orthoclase) alteration alteration (similar (similar to spilitization), (3) an an overlying, overlying, upper upper semiconformable calcium carbonate alteration that increases in intensity upwards, toward the the semiconfonnable that in intensity upwards, toward contact temperature, (semiconformable?) (semiconfonnable?) wntact with the the overlying overlying Vermilion Formation, and (4) a low temperature, potassie alteration, potassic alteration, at at the the top top of of the the Onaping Onaping Formation. Sulphide Sulphide Showings Showings Base metal suiphide sulphide occurrences occurrences within Onaping Formation area are are predominantly predominantly fragmental fragmentalin in nature natureand, and,in indecreasing decreasingorder order of of mineral mineral abundance, abundance,consist consistof ofpyrrhotite, pyrrhotite, chalcopyrite and pyrite. Stringer-like sphalerite, chalcopyrite Stringer-likevein vein mineralization has been observed. All All sulphide occurrences are nickel-poor. In Instratigraphic stratigraphicorder, order,suiphide sulphideshowings showingsoccur occur at atfour fourmain main sulphide "horizons". These Units of of the the Sandcherry Sandcherry member; member; (2) (2) at at the the Theseare: are:(1) (1)ininthe thesilicifled silicified Undefined Undefined Units carbon member, and and (4) 100 carbon contact; wntact; (3) (3) within coarse Lower Units of the Dowling member, 100 - 200 200 m above above the carbonate the Dowling Dowlingmember. member. Mineralization also occurs carbonate contact contact within within the Middle Units of the occurs adjacent to pipe-like pipe-like bodies bodies of of Basal Basal Intrusion Intrusionand andinincalcite calciteveins veinsassociated associatedwith withfaults. thults. Most Most of of the sulphides occur occur as as fine fine disseminations disseminationsand replacement of glass shards, shards, but but some someof ofthe the mineralization may be the result of of brecciation and reworking of older intra-Onaping Formation Formation sulphide sulphide occurrences. occurrences. - Concluding Concluding Remarks Remarks The Sandcherry Sandcherryand and Dowling Dowlmg members constitute constitute a sequence sequence of initially glass-rich fragmental rocks (breccias) composition. The (breccia) of intermediate composition. The two members, distinguished from fragments consist each other by percentage, size, size, and and morphology of glass fragments consist of numerous numerous distinct distinct depositional units that show show an an overall overall fining upwards along with an increase, first, first, in in fine fine carbonaceous material followed by byan anupwards upwardsincrease increaseinincalcium calciumcarbonate. carbonate. Both Both carbon carbon and and carbonaceous lithological contacts. contacts. The carbonate boundaries transcend (overprint) lithological The upper upper 170 170m m of of the the Onaping Onaping Formation, Formation, compared compared to to the the rest rest of of the the sequence. sequence, isis characterized characterized by by aa pronounced pronounced decrease decreasein in grain size, greater internal stratification, and stronger evidence of sedimentary reworking. grain size, greater internal stratification, and stronger evidence of sedimentary reworking. In terms of the Onaping Formation, terms of of the the interpretation interpretation of of mechanisms of emplacement of the origin or source of the melt is inconsequential. The assumption is made, simply, that the emplacement and deposition of the breccias of the Onaping Formation was preceded and initiated lithicclast-bearing clast-bearingmelt melt of ofan anintermediate intermediate by the emplacement of a high level, "shocked" lithic composition. This wmposition. Thismelt melt may may represent represent (1) (1) aa meteorite meteorite impact melt sheet, (2) a melt generated by intracrustal ("impact-induced anatexis", anatexis", Lowman Lowman 1993), or intracmstal bulk melting beneath an impact crater ("impact-induced magma. The (3) a hypabyssal intrusion of contaminated magma. The occurrence occurrence of of shock shock features features within within lithic lithic fragments glass-rich of fragments and and zircons zircons (both (bothof of basement basement origin) origin) within within the glass-rich of the the Onaping Onaping Formation Formation melt for the breccias was at least partially produced by a meteorite impact. The suggests the source melt AphaSic dykes Basal Intrusion and, particularly, Aphanitic dykesare areinterpreted interpretedto to represent represent the the remnants remnants of of the melt source source for for the the fragmental fragmental rocks. rocks. The morphology of glass glass fragments fragments within within the Onaping Onaping Formation indicates that the the fragmental fragmental rocks (breccias) formed by the rapid cooling and fragmentation of melt upon interaction rocks (breccias) formed by the rapid cooling and fragmentation of interaction with with fragmentation and water. "Magmatic" "Magmatic"degassing degassing(vesiculation) (vesiculation)played played only a minor role in clast fragmentation of the the Onaping Onaping Formation. Formation. Deposition of the the Onaping Onaping Formation Formation is is emplacement of Deposition and emplacement of passive to explosive was continiously fed from the result of prolonged passive explosive fragmentation of melt, which was below, upon interaction with water. Deposition Depositionand andemplacement emplacementinvolved involved repeated repeated brecciation, brecciation, �29 ejection, re-deposition of of earlier earlier deposited, deposited, altered, altered, and and lithified lithified breccias breccias. Deposition ejection, and redeposition Deposition of of the the Onaping Formation occurred over a prolonged period of time, too long of a period to accommodate accommodate 'simple" meteorite impact fallback failback models. "Secondary" "simple" "Secondary"and and renewed renewed eruptive eruptive processes processes must must have occurred occurred during during emplacement emplacementand and deposition. deposition. Assuming Assuming a meteorite impact, fàllback fallback breccias were either (1) (1) deposited beneath the Sandcherry member and subsequently "eliminated" !feljinatedII or assimilated Sandcherry assimilated by the underlying underlying Basal Basal Intrusion Intrusion and SIC, or by the emplacement of the Sandcherry member, or (2) were never actually deposited emplacement Sandcherry within the crater enter defined defined by by the the Sudbury SudburyBasin. Basin. The upper contact wntact of of the the Onaping Onaping Formation Formation with the overlying argillites of the Onwatin Formation gradational and Formation has been described as gradational and conformable conformable (Muir (Muir and and Peredery Peredery 1984; 1984;Rousell Rousell 11984a; 984a;Avermann Avennann 1992; Avermann Avennann and and Brockmeyer Brockrneyer1992) 1992)to to geochemically geochemicallyand and lithologically lithologically sharp al. 1990; Paakki 1992, Gibbins 1994, Grey Grey 1995). The sharp (Whitehead et al. The upper upper 40 40 metres metres of of fine-grained, rich rich in inorganic organiccarbon, carbon,and andas as stated stated by by Martin Martin (1957) can the Onaping Formation is fine-grained, be difficult difficult to distinguish visually from from the the pelagic pelagic sediments sediments of the Onwatin Onwatin Formation. Formation. Vermilion Formation The (Martin 1957, 1994),previously previously known known as as the the The Vermilion Formation (Martin 1957,Stoness Stoness 1994), of the the Onwatin Formation (Rousell 11982a), 982a), is is situated situated at the contact wntact between Vermilion member of the Onaping and Onwatin Formations. Stoness Stoness(1994) (1994)upgraded upgraded the the member member to to formation formation status status and distinct geological geological character. character. The because of its Basin-wide occurrence and TheVermilion VermilionFormation Formation hosts the Vermilion and Emngton Errington Zn-Cu-Pb-Au-Ag Zn-Cu-Pb-Au-Ag Deposits, located in the south-west quadrant quadrant of the Sudbury Formation rocks, rocks, 1 to to 30 Sudbury Basin. While Whilediamond diamond drilling drilling has intersected Vermilion Formation m thick, elsewhere in the the North North and South Ranges, the continuity of the formation is unknown (Arengi 1977; Gibbins et eta!. al.1992). 1992).InInthe thevicinity vicinityofofthe thedeposits depositsthe theVermilion Vermilion Formation Formation has has an an average average thickness of 43 m (Martin (Martin 1957; 1957;Rousell Rousell 1982a). 1982a). The Vermilion Formation comprises fine- to coarse-grained, warse-grained, commonly commonly pyritiferous pyritiferous and and base-metal-bearing carbonate; cherty carbonate, carbonate, chert chert breecia, breccia, interbedded interbedded flne-grained fine-grained gray coarse grained granular granular to pisolitic argillite, and fine- to coarse pisolitic carbonate. carbonate. Rapid lateral lateral lithological lithological variation within the Vermilion Vermilion Formation Formation in in the the vicinity vicinityof ofthe thedeposits depositsisiscommon. common. The Vermilion Formation has been described as a syngenetic stratabound deposit (mainly recrystallized, altered by Card Card and Hutchinson Hutchinson (1972), a sedimentary-exhalitive deposit deposit (Rousell micritic limestone) by 1984b; Davies et al. 1990; 1990;Whitehead Whitehead et et a!. al. 1990; 1990;Paalcki Paakki 1992), 1992), and and an an epigenetie epigeneticvein vein deposit deposit turbiditic argillite argillite (Martin 1957). Most Mostrecently, recently,the theVermilion Vermilion Formation has been subdivided into turbiditic and carbonate exhalite exhalite sinter sinter deposits deposits(Gray (Gray 1995). The The exhalites exhalites deposits (Stoness 1994) and comprise Carbonate member of the 50 m Formation;. The comprise the Lower Carbonate m thick Vermilion Formation;. Themiddle middle member is the Grey Argillite member and consists of fine-grained grey turbidites that have Grey Argillite wnsists of turbidites that have basinbasincarbonate wide continuity; and the Upper Carbonate member is a thin hydrothermal concretionary carbonate (Gray (Gray 1995). 1995). Onwatin Formation Formation The Onwatin Formation (Coleman 1905; Burrows and and Rickaby 1930; Martin 1957; 1957; Thomson 1957; Lozej 1975; 1975;Rousell Rousell 1984a) 1984a)consists wnsistsof oflaminated laminated 1957; Sadler Sadler 1958; 1958;Beales Beales and and Lozej carbonaceous carbonates and wackes. carbonaceous and pyritic pyritic argillites argillites and siltstones, siltstones, with minor fine-grained carbonates wackes The Sudbuiy Basin, but The Onwatin Onwatin Formation is poorly exposed in the Sudbury but where where present, present, aa well well developed slatey slatey cleavage cleavagepredominates predominates(Paakki (Paakki1992). 1992). Carbonate concretions, though though rare, rare, are developed also evident. The Theformation, formation,based based on drill hole data and stratigraphic stratigraphic reconstruction reconstruction (Gibbins et al. 1992), thickness of of 600 600 m. m. The al. 1992), is interpreted to have an original thickness The formation has been �DOVVLING DOWLING MEMBER MEMBER FLU IDAL FLUIDAL ILLITE ILLITE MIDDLE UNITS MIDDLE UNITS BASAL BASAL ONW DMUc DMLJbDMUa DML)aDMMb,a DMMb,aDMMc DMMc DMLa DMLb DMLc DMLC1 SMSRC SMSRSMFLtr SMEL1FMU DMLb DMLc DMLCT DMUc DMUb DMLa SMSRC SMSR SMFL ONW SO2 SiO, wt% wL% wt.% wt.% 55.97 55.97 52.32 57.50 wt.% v,t.% 59.00 60.36 wt.% wt,% wt% wt.% 60.76 61.33 51.00 61.22 TIC2 DO2 0.63 0.63 0.44 0.44 0.40 0.43 0.48 0.49 A1203 A1203 14.33 14.33 8.77 8.77 8.64 9.62 10.61 10,77 0.59 6.27 1.17 1.84 5,23 0.14 0.14 10.24 3.87 0.14 2.10 4.00 9.02 0.54 0.40 2.22 3.70 0.15 1.89 4.13 9.26 0,39 0.01 0.01 CDI 0.01 6.99 2.34 6.11 5.81 4.38 2.04 1.84 Na20 Na20. 0.90 0.90 0.42 0.42 GaO CaO P205 P205 0.78 0.78 0.12 0.12 4.04 4.04 0.16 0.16 1<20 K20 3.62 3.64 3.32 3.32 1,23 2.00 MgO MgO Fe203 Fe20, MnO MnO Cr203 Cr2Os 2.32 2.32 3.83 3.83 3.66 8.09 8.09 12.75 12.75 11.10 0.23 0.23 0.58 0.58 0.59 3.95 Lol LO1 Clot Ca Corg C,,, 002 C02 S S 8.93 8.93 0.01 0.01 9.39 9.39 3.19 3.19 6.11 6.11 0.65 0.65 4.26 4.28 1.01 o.eg 0.99 0.18 0.49 6.81 6.81 6.49 6.48 0.37 0.37 1.25 1.25 4.46 0.72 3.92 0,43 2.94 0.28 0.94 0.48 0.01 0.01 INTRUSIONS INTRUSIONS APHAN. BASAL APHANBASAL INTRUSION INTRUSION SHARD-RICH SHARD-RICH FRAGMENT DFRAGMENT SAN ITIC SANDITIC BORDER GRANOBORDER GRANOLOWER UNITS LOWER UNITS UNITS UNITS UNITS CHERRY DYKES PIPES UNITS CHERRY DYKES PIPES SHEETS SHEETS PHASE PHASE PHYRE PHYRE ARGARO- UPPER UPPER UNITS UNITS ., sc SIC ONAPING ONAPING FORMATION FORMATION SANDCHERRY_MEMBER SANDCHERRY MEMBER wt% SM-- APHOYK APHDYK Blo EIc Bla Ela BIb Bib SICG SlOG 0,55 0.55 wt.% 61.62 0.56 0.66 0.56 wt.% $3.12 0,57 0.48 0.58 0.57 0.49 0.45 0,78 11.88 11.88 11,91 12.07 11.98 12,37 12.71 12.82 I1.61 12,94 13.21 12.62 13.12 12.31 4.21 5.07 3,54 0.15 4.41 4.78 3,44 0,14 3,94 3,68 4.00 4.00 4,04 3,45 0.14 3.03 2.21 1.70 223 1.55 0.11 0.13 0.11 0.12 1.61 1.58 2.41 1,87 2.31 3,77 3.82 6.97 0.16 0.02 3.64 0.15 2.39 3.37 3,04 1.59 0.18 2,76 1,35 0.86 6.21 6.53 3.29 5,99 5.66 4.04 5,79 0.18 0.15 0.13 0.13 0,09 0,41 0.02 0.02 0.02 0.02 0.01 0.04 1.47 1,50 1.63 1.63 1.38 1,20 0.07 1.36 0,08 0.04 0.05 0.56 62.04 0,55 wt.% 63,00 3.56 3.69 0.15 2.04 3.79 3.70 3,98 4.08 0.15 0.15 4.38 3.85 0.15 2.32 2.25 1.64 2.21 1.31 421 4.33 4.28 4,36 4,12 8.26 0.26 0.02 2.67 0.69 8.60 8,79 0.26 0.27 0.23 0.02 0.02 0.02 6.04 0.20 0.02 4.07 7,43 0,19 2.03 2.15 1.51 0.80 0,19 0.36 0.50 0.79 0.26 0.33 o.4i 62.88 3.75 0.15 1.84 3.79 7.08 0.17 0.02 1.46 wt.% 66.13 wt.% 63.44 0.09 2.15 0.41 0,02 1.32 0,08 0.14 0,06 0.37 0,03 0.03 0,04 0.03 0.03 0.10 0.31 0.13 0.05 0.32 0.03 0.38 0,17 0,10 0.13 0.23 0.09 0.16 0.11 0.35 0.02 wt% wt,% wt,% wt% 65.01 66.40 68.61 69.08 ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Cu 63 54 165 12 24 34 31 33 25 33 28 23 16 33 24 19 30 157 124 89 82 74 64 50 49 52 42 49 45 56 44 50 25 9 II 12 8 9 8 7 9 9 7 14 8 14 12 9 10 Ni 70 44 47 60 59 53 62 59 46 51 4 807 861 773 772 860 46 54 60 120 180 142 111 80 108 238 1198 121 138 Zr 132 97 126 552 66 138 849 Sr 404 50 85 413 149 804 52 49 674 68 215 18 626 60 457 52 710 59 782 61 Ba Rb 22 68 856 119 II 50 Pb 82 8 22 48 11 Zn 35 56 133 16 13 14 124 124 205 205 131 115 130 129 130 62 818 80 99 126 'I 22 14 12 Il 13 12 10 12 15 Nb 18 23 16 19 14 15 10 15 14 63 597 58 74 139 15 14 202 202 38 38 27 27 45 45 213 213 468 468 Ii 11 64 64 111 111 Its 115 Pts. Pts. 61 847 77 91 135 81 111 138 16 Table 2: Avetage Table2 Averagelithogeochemical lithogeochemicalcomposdion compositionofofOnaping OnapingFormation Formationunits units (after (afterGibbins Gibh'ms 1994) 1994) 52 59 SI 61 135 121 161 132 138 145 140 400 210 ¶21 121 146 217 13 14 12 14 11 11 12 23 12 13 13 12 12 I? 10 16 57 57 86 86 54 54 51 51 18 18 79 79 15 15 83 99 0 �or U 8 I I 2. �I n I I 32 ! I —0 QJ h___ H 9____ Uafl__ 2r___ fl! III!HI4HHJ HHHHHL4H} 1HHHHHEI Ø2VUI8&, tB1RP1 £ . 0 Figure Figure13:13: 0 0) 0 0 Q 0 a C a - In Lithogeochemical Lithogeochemicalstratigraphic stratigraphiccolumn column- Average - Averagecompositions compositions(major (majoroxides#2 oxides#2+ +Corg, Core,C02, C02, S,S,Zn) Zn)and andthicknesses thicknessesofofunits (afterGibbins Gibbiis1994). 1994) units (after �-'3 Figure14: 14: Figure - Lithogeochemical stratigaphic i i Average AvcrageC02/CaO CO2tCaO molar ratio and thicknesses o f LithogeochemicaJ stratigraphic w column molar ratio and thicknesses of units(after (afterGibbins Gibbims1994). 1994). units �AL2D3/TlflE 4ff I Q.BQyATIN I 0 I I I ISIDE/T102 500 J DHUb I I I INA2D/TIIJ2J I 2500 DMLJQ 300 it' II I I —t 600 DMMc I I x ' DMLb DML 900 I DNLCT 'SMSRC SMSR 1200 ciri +v r SPIFL ySM--- JfG 1500 I meters i j ' I K2IJ/T102 200 I I — — — — ZR/TIIJ2 MGEI/T102 I I I 200 ii — I I C I 200 I y - - I I I I 500 IJI — —-1 I liii- (I i J E a �35 structurally particularlyininthe theSouth SouthRange. Range.Whitehead Whiteheadetetal. at (1990), Paakki (1992), structurallythickened, thickened, particularly Stoness Gray (1995) showed Stoness (1994), Gibbins (1994) and Gray showed the Onwatin Onwatin Formation Formation (and Vermilion Formation) distinct from from the the underlying underlying Onaping Formation Formation) to to be chemically chemically and lithologically distinct to be be (Table 2). The Theupper uppercontact contactisis gradational gradational with with the Chelinsford Chelmsford Formation and is considered to at the the base base of of the the first first thick thick wacke wacke bed. The The pelagic rocks of the Onwatin Formation were deposited in a restricted restricted basin basin with with (Rousell 1984a). 1 984a). They Theygrade grade upwards upwards into into the the coarser sediments of of the the anoxic bottom conditions (Rousell Cbehnsford Formation, indicating a transition to a higher energy depositionai Chelmsford depositional environment et al. at 1991). (Dressier et 1991). Chehns ford Formation Chelmsford Formation The and Rickaby Rickaby 1930; Williams 1957; The Chelmsford Formation (Burrows and 1957; Cantin Cantin 1971; 1971; Cantin and 1972; Vezina 1992) and Walker 1972; 1972; Rousell Rousell1972; 1992) is the uppermost formation formation of of the the Wbitewater Group and has a preserved thickness similar similar to to that that of the underlying Onwatin Whitewater Formation, approximately approximately 600 m. The TheChelmsford ChelmsfordFormation Formation isis aa turbidite turbiditesuccession successionof ofmassive massive wackes, siltstones, siltstones,and andcarbonaceous carbonaceous mudstones. mudstones. Sedimentary to normally graded lithic wackes, Sedimentary structures structures carbonate concretions, rip-up clasts, clasts, U-shaped U-shaped channels, channels, climbing climbing ripples ripples and and crossinclude carbonate concretions,rip-up laminations,and andload loadstructures. structures. Paleocurrent bedding, convolute laminations, Paleocurrent studies studies indicate indicate that that the the predominant was to to the the south-west, south-west,parallel parallel to to the the long long axis axis of of the the Sudbury Basin predominant flow direction was (Cantin and and Walker Walker 1972; 1972;Rousell Rousell 1972). 1972). Errington and Emneton and Vermilion Deposits Deposits are are Paleoproterozoic carbonate-hosted carbonate-hosted Zn-Cu-PbThe Errington Emngton and Vermilion Deposits Zn-Cu-PbThe Au-Ag massive suiphide sulphide deposits located locatedin inthe thesoutheast southeastcomer cornerof ofthe the Sudbury Sudbury Basin. Basin. The deposits occur the Vermilion Formation. Formation. The occur at at the the top of Onaping Formation and partially within the The Errington toimes grading grading 4.21% Emngton deposit deposit contains contains an undiluted mineral inventory of 6.27 M tonnes 4.21% Zn, Zn, g/tonne Au Au and and 62.06 62.06gltonne g/tonneAg Ag(Severin (Severinand andGates Gates 1981). 1981). The 1.22% Cu, 1.09% 1.09% Pb, 0.86 gkome proven-probable-possible mineral mineral inventory of 2.44 m Vermilion deposit contains an undiluted, proven-probable-possible tonnes grading 5.11% Zn, 1.49% tomes 1.49% Cu, 1.37% 1.37% Pb, 1.10 1.10gltonne gltome Au and and 66.17 66.17g/tonne gltomeAg Ag (Severin (Severin the mid mid to to late late 1920's and and Gates 1981). 1981). The Thetwo twodeposits, deposits, 88 km apart, apart, were discovered in the later poor later developed developed for for production. Attempts Attemptsto toexploit exploitthe thedeposits depositswere wereunsuccessThl unsuccessful due due to topoor metal recoveries, lowmetal lowmetalprices prices and and overall overall marginal marginal grades. grades. Gray (1995) (1995) described the the deposits deposits to to be hosted by the Vermilion Formation within a CaMg carbonate complex that that grades grades laterally laterally into into Mn-Fe-rich Mn-Fe-rich carbonates carbonates (up to carbonate exhalite exhalite sinter vent complex wt% MnO and and 33 33 wt% wt%Fe203). Fe203). The TheVermilion Vermilion Deposit Depositisis underlain underlain by lower discordant 9.5 wt% chlorite zone and an upper discordant silicification silicificationand andstratiform stratiform Ca-Mg Ca-Mg carbonate carbonate stockwork zone. Gray Gray(1995) (1995)proposed proposedthe thedeposits deposits fbnned formedin in aa sub-seafloor sub-seafloorenvironment environmentby by the theinitial initiallow low temperature pyrite-sphalerite infilling of of carbonate porosity within sinters followed by later temperature later higher temperature chalcopyrite-rich mineralization that that replaced earlier pyrite pyrite and temperature and sphalerite sphaleriteand and secondary hydrothermaldissolution dissolutionleaching leachingof ofthe thecarbonates. carbonates. The carbonate secondary porosity from hydrothermal carbonate sinter host host is is attributed attributedto tosub-seafloor sub-seafloorboiling boiling and and carbonate carbonateprecipitation precipitationby byventing ventinginto intoan analkaline, alkaline, that enabled the sinter mounds to grow. grow. anoxic basin and and by successive successive replacement events that Carbonates were preserved from dissolution dissolutionby bythe theemplacement emplacementof ofturbidites. turbidites. The hydrothermal Carbonates underlying Sudbury system responsible responsible for for the Vermilion Deposit was long-lived, the underlying SudburyIgneous Igneous Complex, or precursor to drive and sustain convection cells precursor melt melt provided the thermal energy to within within the the Onaping OnapingFormation Formation (Gray (Gray1995). 1995). �36 LOCATION AND DESCRIPTION DESCRIPTION OF OF GEOLOGICAL GEOLOGICAL TOUR STOPS Tour Tour stops stops are are indicated on Figures 16 --22. 22. STOP 11 STOP SUDBURY BRECCIA An easily accessible outcrop of Sudbury Breccia is located on Highway 144, 144, 3.2 3.2 km km north north of the junction junction of Highway 144 tumofi). 144 and Regional Road 8 (Levack turnoff). The Sudbuiy Sudbury Basin is surrounded by a zone of Sudbury Breccia about 50 km wide. The wide. The to rocks rocks outside outsidethe theSudbury SudburyIgneous IgneousComplex. Complex. Fragments Fragments in the the breccia brecciation is limited to of the the same same material materialas asthe thewall wallrocks rocksand andare arerounded roundedtotovarying varyingdegrees. degrees. The generally consist of comminuted wall wallrock rockmaterial material that that has has been recrystallized matrix of the breccia consists of finely comminuted to to aa coherent coherentmass. mass. STOP 2 STOP FELSIC FELSIC NORITE This stop junction of Highway Highway 144 144 and Regional Road Road 88 stop is located located 1.4 1.4 km north of the junction (Levack turnoff), near the Elk's Elk's Club Club Road. Road. Felsic norite is the main member member of ofthe the Sudbury Sudbury Igneous Igneous Complex Complexon onthe theNorth North Range. Range. ItIt hypidiomorphic granular granular rock consisting consisting of is approximately 450 m thick and is a coarse grained hypidiomorphic plagioclase, hypersthene and augite (ration 2: 2:1), biotite, interstitial granophyre, granophyre, quartz, and l), biotite, and minor minor pyrite, apatite apatiteand and ilmenite. ilmenite. No Nolayering layeringisisevident, evident, but but the the mineralogy mineralogy changes changes gradually gradually producing producing "cryptic layering". layering". STOP STOP 33 QUARTZ GABBRO AND GRANOPHYRE QUARTZGABBROANDGRANOPHYRE Stop Stop 33 consists consists of of rock outcroppings outcroppings on either side of Regional Road 8 at the junction of of Highway 144. 144. Quartz Quartzgabbro gabbrocan canbe beseen seenin in the the road cuts cuts to to the the north north and and south south of of the the road; road, the the granophyre is thither further to to the the southwest. southwest. Complex consists consists of of granophyre, granophyre, which is pink The upper member of the Sudbury Igneous Complex plagioclase. in colour and comprises about three parts micrographic intergrowth to one part plagioclase. Quartz, biotite, biotite, amphibole, amphibole, chlorite chlorite and opaques opaques are are also alsopresent. present. granophyre, occurs occurs aa thin thin member member known knownas asquartz quartz gabbro gabbro (or transition zone), Below the granophyre, which is is more more mafic mafic than the the granophyre granophyre and and consists consists principally principally of of plagioclase, plagioclase,cimopyroxene, clinopyroxene, amphibole and intercumulus micrographic intergrowth and quartz. STOP 4 STOP CONTACT BETWEEN GRANOPHYRE AND BASAL INTRUSION, AND THE THE BASE BASE OF OF THE THE SANDCHERRY APHANITIC DYKES, AND MEMBER Stop 44 is between Granophyre Granophyre and and the the Basal Basal Intrusion Stop is a walking tour over the contact zone between glass-rich breccias and over a variety of exposures exposures of Basal Intrusion, Aphanitic Dykes, and glass-rich breccias at atthe the member of ofthe theOnaping OnapingFormation. Formation. Access Access to to the the area area is gained from aa base of the Sandcherry member private dirt private dirt road road (Gravel (Gravel Lake LakeRoad), Road), which which extends extends south south of of Falconbridge FalconbridgeLimited' Limited'ss main mainaccess access road to Strathcona Mine, approximately 4.8 km past the main gate entrance. Permission to main gate entrance. Permission to use use Strathcona Mine, approximately from Falconbridge Falconbridge Limited, Limited, as as the the area area is on mine the road and to view the outcrops is required from property. Turn Turnright rightoff offthe themine mine access access road on to Gravel Lake Road, which parallels the eastern eastern the shore shore of of the the lake lake until until aa yellow shore of a nearby lake, and continue south along the yellow road road gate gateisis �+ + + + + + FIGURE + S UD B U ONAPING Fm ONWA11N Fm + + + + + + ++ + .+ I +. + + + + -p + + + + + + + + GEOLOGICAL + + + + + -t + + + + + + + + + TOUR STOPS + 16 (modified after Glbbins 1994) * + + CHELMSFORD Fm c;:: COMPLEX fj• EE: EI OUTCROP STOPS + + - .4. - RINGTON 4 0 LCI Km 10 + + + + + + + + + + + + + • + + + + 1- + + + + ÷ + + + • + + + + + + * + + + + + + + + + + + + + I + -f .- / -e Y /4 + 1+ _*_— + + + + + +1+ + +7+ +7+ + +7+ + + ft + + + + + * ++ + + + + + + * • + + —4 �Figure 17 TOUR STOPS SUDBURY BASIN 'H:) - ix Bowling Area A WHITEWATER GROUP EH CHELMSFORD Fin C.. S, ONWATIN Fm fji:J ONAPING SUDBURY fi33 IGNEOUS COMPLEX GEOLOGICAL TOUR STOPS 1 0 00 �ONAPING FORMATION TOUR STOPS SUDBURY IGNEOUS COMPLEX WHITEWATER GROUP CHELMSFORD FORMATION ONWATIN FORMATION DOWLING MEMBER SANDCHERRY MEMBER APHANITIC DYKES BASAL INTRUSION \0 �40 ( reached (= 2 kin). reached km). The Thewalking walking tour tour begins 200 south of the gate by leaving the gravel road and following a stream eastwards for 600 m to to reach reach exposures exposures of of granophyre granophyre along along the the north north shore shore of of a small Figure small lake. The Thewalking walkingtour tour route routeisis marked marked in detail from this point onwards on Map A, Figure 19. 19. following exposures exposures will willbe beseen: seen: granophyre, granophyre, xenolith-bearing During the tour the following xenolith-bearing granophyre, both coarse grained xenolith-rich basal intrusion and fine-grained, well sorted, coarse basal Dykes and and various various 'glass'-rich 'glass' -rich units units of of the the xenolith-poor basal intrusion, flow banded Aphanitic Dykes Sandcherry tour offers offers one of of the the best exposures of Sandcheny member. Although Although a bit of a hike, the walking tour the base base of of the the Onaping Onaping Formation and of flow banded Aphanitic Dykes. The Thewalking walkingtour tourbegins begins and ends at the same same spot. spot. STOP 5 STOP FLUIDAL FRAGMENT-RICH FRAGMENT-RICH AND SHARD-RICH SHARD-RICH BRECCIAS BRECCIAS OF OFTHE THE SANDCHERRY MEMBER. MEMBER. THE CONTACT BETWEEN BETWEEN THE THE SANDCHERRY MEMBER MEMBER AND ANDLOWER LOWERUNITS UNITSOF OF THE THE DOWLING AND PIPE-LIKE MEMBER. AND MEMBER, PIPE-LIKE BODIES OF THE THE BASAL INTRUSION that extends extends eastward eastward from fromGravel GravelLake Lake Road, Road, 200 200 m south of aa Stop 5 is a walking tour that gravel pit, which is approximately 1.5 km further along Gravel Lake Road from 1.5 krn from the the yellow yellow gate gate described in the previous previous stop. After a walk of 200 m eastward from Gravel Lake Lake Road, aa small small ridge of rock is reached which marks the the beginning beginningof ofaageological geologicaltraverse traverseover over (1) (I) Fluidal Fragment-rich and Shard-rich units of of the the Sandcherry Sandcheny member, (2) a rare rare well exposed contact (running (running along along the the top of of aa steep, steep, large large ridge) between the Sandcherry Sandcherry and and Dowling Dowling members, members, with with both sharp (3) pipe-like bodies bodies of of the the sharp and and gradational gradational characteristics characteristics over its 400 400 m length, and (3) Basal Intrusion. in detail detail on onMap MapB, B,Figure Figure20. 20. The Intrusion. The Thewalking walking tour is marked in The Lower Lower Contact Unit of the Dowling member member ("chlorite ("chlorite shard shard horizon") horizon")and andthe thecarbon carbon boundary boundary are also well the southern flank flankof ofthe theridge. ridge. Alteration (silicification (silicification and albitization) exposed locally along the albitization)of the 'glass' shards shardsatatthe thetop topof ofthe theSandcheny Sandcherrymember memberisis well well featured featured within within the the vicinity vicinity of the near the the western westernend endof ofthe theridge ridgeof ofoutcrop. outcrop. From pipe-like bodies of Basal Intrusion, near From this this area, area, return to Gravel Gravel Lake Lake road by walking 150 150 m due west through through the the bush. STOP 66 STOP MIDDLE AND AND UPPER UPPER UNITS UNITS OF OF THE THE DOWLING DOWLING MEMBER MEMBER Gravel Lake Lake Road Road at at the junction junction with Morgan Road. Stop 6 is located at the south end of Gravel south of of Stop Stop 55 in inGravel GravelLake LakeRoad, Road, Stop Stop 66 must must be reached Unfortunately due to a wash-out south from the south. To 144, by by the the same same route taken in, and travel travel south, south, Toget getthere, there, return return to to Hwy. Hwy. 144, through the town of Dowling and and turn turn left left onto onto Morgan Morgan Lake Lake Road, Road,just just before the bridge on Hwy. 144 that crosses Vermilion River Rivernear near Larchwood. Larchwood. Stop crosses over the Vermilion Stop 6, 6, at at the the junction junction between between Gravel Gravel 144. Lake Road and Morgan Morgan Road is approximately approximately 3.5 km north of Hwy. 144. Stop on Map Map C, C, Figure Figure 21. 21. Representative Stop 66 is shown in detail on Representative units of of the the Middle and well exposed exposed at at this this stop, including Upper Units of of the the Dowling member are well including rarely rarely exposed exposed characteristic features bedding within withinthe theUpper UpperUnits. Units. The characteristic features of of reworking and bedding The stop stop provides providesaa good good example of the unaltered and undeformed undefonried equivalents equivalents of of the the immediate immediate footwall footwall rocks rocks to to the at the top top of the Onaping Formation Errington and Vermilion deposits located at Formation along along the the southern southern margin of the Sudbury Sudbury Basin. Basin. STOP 7 STOP CARBON BOUNDARYWITHIN WITHINSHARD-RICH SHARD-RICH UNITS OF THE CARBON BOUNDARY AND AN AN INTRUSIVE INTRUSIVE F1,UIDAL FLUIDAL BRECCIA SANDCHERRY MEMBER AND COMPLEX Offset road that Located near Sandcherrv Sandcherry Creek, Stop Stop 77 is accessed via Nickel Offset that extends extends The Nickel Nickel Offset Offset Road Road is located 5.75 km krn northwards from Morgan Road (Montpellier Road). The �- -geologic I contact - . -geologic contact gradational + -fault 4 o ,* 1 II lithie blasts I traverse route I a �42 Figure 20: Figure 20: Detailed geology geoloey of of Stop Stop55 (after (after Gibbins 1994). 1994) �43 Figure 22!: 1: Detailed geology of Stop Stop 66 (after (after(Jibbins Gibbii 1994). 1994) �44 LEGEND l l l l l t t l ~ r s eroute --- , EeOlogical contact .......carbon boundary fault ---road o blocks --- - Figure22: 22: Figure Detailedgeology geologyofofStop Stop7 7(alter (after Gibbiis 1994). Detailed Gibbins 1994). �45 Morgan Road. Road. Drive 5.5 km north on Nickel Offset Road east of Stop 6, further along Morgan Road until until the the second of two bridges that cross Sandcheriy Sandcheny Creek is reached. Park Park the the vehicle vehicle before before crossing crossingthe the 2nd bridge and walk 500 m further up Nickel Offset Offset Road Road to to aajunction junction with with aa second, second, but butless less Map D, D, Figure Figure 22. 22. Though a bit of as indicated on Map of bush bush crashing crashingand and climbing climbing traveled dirt road, as idal Fragment Fragment Units and Pipe-like is involved (50 (50 m), Stop 7 provides an excellent exposure of Flu Fluidal Pipe-like bodies of Basal Intrusion Intrusion (Fluidal (Fluidal Breccia Complexes) Complexes) intruding intruding into the Lower Contact ContactUnit Unit of ofthe the Dowling member. Only exposure of the carbon Only350 350m m to to the south south is a representative representative exposure carbon boundaiy/contact Within units of of the the Sandcheny Sandcheny member. within Shard-rich units boundarylcontact STOP 8 STOP CHELMSFORD FORMATION FORMATION Easily accessible road cuts of the Chelmsford Formation Formationare are to to be be found found on on both both sides sides of of 144and and Gordon Gordon the Gordon Lake road approximately 3.5 km south of the junction between Hwy. 144 Lake Road. The TheGordon GordonLake Lake Road Road turn off from Hwy. 144 is located 200 m south of the bridge near Larchwood. Larchwood. The that crosses over the Vennilion Vermilion River near The Chelmsford Chelmsford Formation Formation is is the the youngest youngest the Whitewater Whitewater Group Group and and occupies occupiesthe thecentral centralportion portionof ofthe theSudbury SudburyBasin. Basin. The The member of the Formation consists consists of of turbidites, turbidites, with partial to to complete complete Bouma sequences, sequences, which mark mark aa change change in the the pattern of sedimentation within within the the Basin Basin (the (theunderlying underlyingOnwatin Onwatin Formation Formation is a series of mudstones). Rusty are carbonaceous and pyritic siltstones and mudstones). Rusty weathering weathering concretions concretions and lenses are and represent concentrations concentrationsof offerruginous ferruginouscarbonate. carbonate. At this locality, a partial common and partial Bouma Bouma and dewatering dewatering structures structures also also present. sequence is present with cross bedding and STOP 9 STOP ONWATIN FORMATION FORMATION Stop 9 is located on Vennilion Vermilion Lake Road, 11 km east of the junction between between Vermilion Lake Road and Gordan Gordan Lake Lake Road. At Atthis thislocality, locality, in in the the hangingwall hangingwall to to the the Errington Errington and and Vermilion deposits and in the mid-zone mid-zone area area between betweenthe thetwo twodeposits, deposits,the the carbonaceous carbonaceous Onwatin Formation contains s. contains elevated elevated amounts amounts of of pvrite p*te and and rare rarepyritic pyriticcarbonate carbonateconcretion concretions. STOP 10 STOP 10 VERMILION FORMATION VERMILION FORMATION Stop of Gordon Gordon Lake Lake road, road, approximately approximately 75 m south of the Stop 10 10 is is located on the south side of Vermilion River. River. Varved-looking, cm thick thickbands bands of of carbonate carbonate and grey grey argillite bridge over Vermilion Varved-looking, 1-2 cm representative of the non-carbonaceous Vermilion Vermilion Formation, Formation, and and host host to to the Emngton Errington and representative Vermilion can be be seen seen at at this this rare rareexposure. exposure. Vermilion deposits, deposits, can STOP 11 11 STOP LOBATE PEPERITELIKE PEPERITE-LIKE INTRUSIVE BODIES OF OF SPHERULITIC SPHERULITIC WITHIN UPPER UNITS OF THE DOWLING APHANITIC DYKES WITHIN DOWLING MEMBER MEMBER west side side of ofGordon GordonLake Lakeroad, road,approximately approximately 200 200 m m south south of of Stop 11 11 is located on the west the Vennilion km southwest southwest of the Gordon Gordon Lake Lake road road bridge bridge over over Vermilion Mine Mine road road turn turn og off,which whichisis221cm spherulitic devitrified devitrifled as these these strongly strongly altered (silicifled) (silicified) and spherulitic the Vermilion River. Exposures Exposures such such as lobes of aphanitic 'andesite' are level of of the the Onaping Onaping Formation. Formation. They areextremely extremely rare at this level They have not been related to the mineralization at the Vermilion Vermilion or or Errington Errington deposit, deposit, but they may define structures structures that that also alsocontrolled controlled the the location location of the deposit. STOP 12 STOP 12 VERMILION FORMATION FORMATION of the the Errington Errington #1 #1 shaft, shaft, 700 m east east of of the the Stobie Stobie Stop 12 12 is located within the vicinity of Dam on Vermilion River. Though Thoughreclamation reclamationactivities activitieshave have been been recent recent in in the the area, area,trenches trenches �46 showing showing folding of the Vermilion Formation, weak mineralization and strong strong carbonate carbonate alteration alteration can still be observed. The folding is representative of the structure pattern in the deposit area The folding the structure area. STOP 13 STOP13 DISCOVERY SITE SITE Stop east side side of Highway 144, 144, 1.9 1.9 km krn north north Godfrey Godfrey Drive, Drive, or or 4.4 4.4 Stop 13 13 is is located located on the east km Nickel Mine Mine Road. Road. Look for a small paved area with an Heritage Foundation krn north of the Big Nickel historical plaque and an American Society of Metals commemorative plaque plaque marking marking the the site. site. Be Be careffil! Train hea'y. Train traffic traffic on on the railway can be heavy. careful! Though Nickel was first reported in in 1856 near near the the Creighton CreightonMine Minesite siteby byA. A.Murray Murray of of the Geological Survey was not not until 1883, 1883,during during the the construction constructionof of the the Canadian Canadian Survey of Canada, Canada, itit was Pacific Railway, that Pacific that aa railway railway rock-cut rock-cut near nearthe the site siteexposed exposed nickel-copper mineralization, which was was subsequently subsequently developed as the Murray Mine ore body. The Theoriginal originaldiscovery discoveryoutcrop outcropwas was located close to the rim of the present Murray Murray Mine Mine open open pit pit and and remained remained intact intact until untilthe themidmid1970's, when the highway and railway were relocated to to permit permit mining mining of of the the ore. ore. The TheClarabelle Clarabelle No. 22 Open Open Pit Pit and and headftame headframeof of the the inactive inactive Murray Murray Mine Mine are are visible, visible, across acrossthe thehighway. highway. the paved paved area, area, toward toward the the railway railwaytracks tracks is is aa rust-covered rust-covered outcrop outcrop of of Thirty meters from the weakly mineralized Sublayer of the Sudbury Igneous Complex and host for the nickel-copper ore Sudbury for the nickel-copper ore minerals (pyrrhotite, pentlandite, and and chalcopyrite). chalcopyrite). The outcrop is the eastern continuation of the mined-out ore ore body. body. On Onthe theeast eastside sideof ofthe the railway railway track, track, quartz-rich norite is exposed. exposed This This isis the basal unit of the Complex on the the South Range. Range. The The quartz-rich quartz-rich norite differs differs from the homogeneous and and the the quartz quartz has has a Sublayer, in that it contains contains few ore minerals or inclusions, it is homogeneous distinct blue tint. The TheSublayer Sublayerdips dipsnorthward northward at atabout about60° 60"beneath beneath the the norite. norite. STOP STOP14 14 SHATTER CONES Stop 14 14 is located on Ramsey Lake Road, on the south side in a rock cut about about 200m 200m long, long, 1.4 km east of Paris Street. Street. The fracture structures Theshatter shattercones, cones, feathery-looking feathery-looking conical striated fracture structures in the host quartzite quartzite and greywackes of the Mississagi Formation of the Huronian Supergroup, Supergroup, are are illuminatedby bythe thelate lateafternoon afternoonlight. light. The site on Ramsey Lake best observed when obliquely illuminated Road is one of the best and most easily accessible. There Thereare arenumerous numerousshatter shattercones conesininthese these exposures, exposures, most being 20 to 30 cm in size. Please Pleasedo donot not break breaksamples samplesfrom fromthis thissite. site. First noted in the early 1960's by Dr. Robert Robert Dietz, the shatter cones, which were traveling through through the the rock, rock, occur occur in in all all rocks rocks outside of the the produced by strong shockwave(s) traveling Sudbury Sudbury Basin, Basin, but but not not within, within, and and have havebeen been attributed attributedto tothe theSudbuzy SudburyEvent Eventwhich whichformed formedthe the Sudbury asevidence evidenceof ofaameteorite meteoriteimpact. impact. Sudbury Structure. Structure.The Theshatter shattercones conesare arewidely widelyaccepted acceptedas �47 REFERENCES REFERENCES Ames, D.E., Jonasson, I.R., Parish, Parish, R., R., Watlcinson, Dii. and Gibson, Ames, D.E., Jonasson, I.R., Watkinson, D.H. Gibson, H.L. 1996. 1996. 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The base of of the the Onaping Onaping Formation, Formation, Sudbuiy, Sudbury, Ontario; of Toronto, Toronto, Toronto, Toronto, Ontario, Ontario, 366p. Ontario; unpublished PhD. thesis, University of Peredery, W.V. W.V. and and Momson, Mothson, G.G. G.G. 1984. Discussion of the the origin origin of of the Sudbury Structure; Peredery, Discussion of Structure, in The Geology Gwlogy and Ore Deposits Deposits of the the Sudbury Sudbury Structure, Structure, Ontario Ontario Geological Geological Survey, Survey, Special Special volume 1, p.491-511. of the upper Peredery, W.V. W.V. and Naldrett, Peredery, Naldrett, A.J. A.J. 1975. 1975. Petrology Petrology of upper Irruptive Irruptive Rocks, Rocks, Sudbury, Sudbury, Ontario; Economic Geology, v.70, p. p.164-175. 164-175. Pye, P.E. (eds.) and ore deposits A.J. and and CIiblin, Giblii P.E. (4s.) 1984. The geology geology and deposits of of the the Pye, E.G., E.G., Naldrett, Naldrett, A.J. Structure; Ontario Volume 1, I, 603p. Sudbury Structure; Ontario Geological Survey, Special Volume 603p. Rouse!!, D.H. 1972. The Chelmsford of the Sudbury Rousell, D.H. Chelmsford of Sudbury Basin -- a Precambrian turbidite; in in New New Geology, Gwlogical GeologicalAssociation AssociationofofCanada, Canada,Special Special Paper, Paper, no.10, p.79p.79Developments in Sudbury Geology, 91. 91. Rouse!!, D.H. 1983. Nature and Rousell, D.H. and Origin Origin of of mineralization mineralization inside inside the Sudbury Sudbury Basin; Basin, Ontario Ontario 53p. Geological Survey, Open File Report 5443, 5443,53p. 984a. Onwatin Onwatin and and Chelmsford Chelmsfordformations; formations;ininThe TheGwlogy Geologyand and Ore Ore Deposits Deposits of Rousell, D.H. 11984a. -217. the Sudbuiy SudburyStructure, Structure,Ontario OntarioGeological GeologicalSurvey, Survey,Special Specialvolume volume 1,1,p.211 p.2 11-2 17. Rousell, D.H. D.H. l984b. 1984b.Mineralization Mineralization in the Whitewater Group; in The Geology and Ore Deposits Rousell, 19. of the Sudbury Sudbury Structure, Structure,Ontario OntarioGeological Geological Survey, Survey, Special Special volume volume 1, 1, p.2 p.219. Rousell, D.H. 1984c. 1984c. Structural StructuralGeology,of Geologyof the Sudbury Basin; in The The Geology Geology and and Ore OreDeposits Deposits of the Sudbuty Sudbury Structure, Structure,Ontario OntarioGeological Geological Survey, Survey, Special Special volume 1, 1, p.83-95. �52 Sadler, J.F. 1958. 1958. A A detailed detailed study study of of the the Onwatin Onwatin Formation; Formation; unpublished unpublished MSc. thesis, Queen's University, Kingston, Ontario, 184p. l84p. Severin, P.W.A. P.W.A. and Gates, B.I. 1981. 1981.Giant Giant Yellowknife Yellowknife Mines Limited Limited Ore Reserve Calculation Erringtonfveimilion Deposits. Falconbridge Limite Internal, unpublished, Enington/Vennilion Falconbridge Limite Internal, unpublished, 21p. 2 lp. Sehandi, E.S., Schandl, E X , Martin, Martin, R.F. and and Stevenson, Stevenson, J.S. 1986. 1986.Feldspar Feldsparmineralogy mineralogy of the Sudbury Sudbury Igneous Complex and the Onaping Formation, Fonuation, Sudbury, Ontario; Canadian Mineralogist, v.24, p.747-759. Shanks, W.S. W. S. and and Schwerdtner, Schwerdtner,W.M. W.M. 1991. Structural analysis of the central central and and southwestern southwestern Sudbury Sudbury Structure, Structure, Southern Southern Province Canadian Shield; Canadian Journal of Earth Earth Sciences, Sciences, v.26, no.3, p.411-430. 110.3, Smith, Smith, T.L. and Satin, Batiza,R.R.1989. 1989.New Newfield fieldand andlaboratory laboratoryevidence evidencefor forthe theorigin originof ofhyaloelastite hyaloclastite flows on seamount 1, p.96-114. seamount summits; summits; Bull. Bull. Volcanol. Volcanol.v.5 v.51, Soueh, B.E., B.E., Podolsky, Souch, Podolsky, T. and Geological Geological Staff, The The International International Nickel Company of Canada, Canada, Limited 1969. The sulphide ores of Sudbury: their particular particular relationship relationshipto to aadistinctive distinctiveinclusioninclusionbearing facies fàcies of Nickel Memoir 4, bearing Nickel Irruptive; Irruptive; in Magmatie Magmatic Ore Deposits, Deposits, Economic Economic Geology, Geology, Memoir p.252-261. p.252-261. Stevenson, J. S. 1961a. 1961 a.Origin Originofofquartzite quartziteatat the the base base of the Whitewater Series, Stevenson, J.S. Series, Sudbury SudburyBasin, Basin, Congress, 21st 21st Session, pt.26, Supplementary Ontario; International Geological Congress, Supplementary Volume, section 121, p.32-41. 21,p.32-41. Stevenson, J.S. J. S. 1961b. 196 lb.Recognition Recognitionofofthe the quartzite quartzite breccia breccia in in the Whitewater Stevenson, Whitewater Series, Series, Sudbuiy Sudbury Basin, Ontario; in Transactions p57-66. Transactions of the Royal Society of Canada, v.60, Third Series, p.57-66. Stevenson, J.S. J.S. 1972. The Onaping ash-flow ash-flow sheet, sheet, Sudbury, Sudbury, Ontario; Ontario; in New Developments Stevenson, Developments in Sudbury Geology, Geological Association of Canada, Special 1-48. Sudbury Special Paper, Paper, no. no. 10 10p.4 p.41-48. 1990. The The volcanic Stevenson, Stevenson, J.S. J.S. 1990. volcanic origin origin of the theOnaping Onaping Formation, Formation, Sudbury, Sudbury, Canada; Canada; Tectonophysics, no. no.171, Tectonophysics, 171, p.249-257. 1994. The stratigraphy, and depositional of the Stoness, Stoness, J.A. 1994. stratigraphy, geochemistry geochemistry and depositional environment environment of the Formation,host hostto to the the Emngton Enington and Vermilion Zn-Cu-Pb massive suiphide Proterozoic Vermilion Formation, sulphide deposits, Sudbury, Ontario; Ontario; unpublished MSc. thesis, thesis, Laurentian Laurentian University, University, Sudbury, Sudbury,Ontario. Ontario. M., Bushoff, Bushoff, L., L., Brockmeyer, Brockmeyer, P., P., Deutsch, A., Dressier, B .0., Lakomy, Stoffler, D., Avermann, Avermann, M., B.O., Lakomy, R. and Muller-Mohr, V. 1989. Sudbury, R. Muller-Mohr, V. Sudbury,Canada: Canada:Remnant Remnant of of the the only only multi-ring(?) multi-ring(?) impact basin Earth; Abstract, Annual Meeting, Meteoritical Society. on Earth, Thomson, J.E. J.E. 1957. Thomson, 1957. Geology Geology of the Sudbury Sudbury Basin; Basin; Ontario Ontario Department Department of of Mines, Mines, Annual Annual Report, 1956, 1956, v.65, pt.3, p.1-56. Thomson, J.E. 1969. Thornson, 1969. A discussion of Sudbury Sudbury geology and sulphide sulphide deposits; Ontario Ontario Department Department of Mines, Miscellaneous Paper, 22p. Vezina, J. 1992. 1992. Origin Origin of of concretions concretions in in the the Proterozoic ProterozoicChelrusford Chelmsford Formation, Formation, Sudbury SudburyBasin, Basin, Ontario; unpublished BSc. thesis, Queen's University, Kingston, Ontario, Ontario, 43p. 43p. �53 R.E.S., Davies, J.F., Whitehead, R.E.S. J.F.,and andGoodfellow, Goodfellow, W.D. W.D. 1990. 1990.Jsotopic Isotopicevidence evidencefor forhydrothermal hydrothermal anoxie seawater, Sudbury Sudbuiy Basin, Ontario; 49-63. discharge into anoxic Ontario; Chemical Chemical Geology. v.86, 49-63. Williams, H., H., 1957. avalanche deposits depositsof of the the Sudbury Sudbuiy Basin; Ontario Department Williams, 1957. Glowing Glowing avalanche Department of Mines, Annual Report, 1956, v.65, pt.3, p.57-89. 1956, pt.3, p.57-89. Wilson, A.B. 1956. Societyof ofAmerica, America,v.67, v.67,p.289-300. p289-300. 1956. Structure Structure of lopoliths; Geological Society � https://digitalcollections.lakeheadu.ca/files/original/a067484278c2263efba7df81dae0e8f2.pdf ea0b653c4701179ab932b501e767cb6c PDF Text Text MAGMATIC ORE ORE DEPOSITS DEPOSITS OF OF TIlE THE MAGMATIC COMPLEX SUDBURY IGNEOUS COMPLEX BY BY S. S. A. A. PREVEC PREVEC INSTITUTh INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY 43rd 43rdANNUAL ANNUALMEETING, MEETING,MAY MAY66- 11, 11,1997 1997 SUDBURY, SUDBURY,ONTARIO ONTARIO - Field TripGuidebook, Guidebook,Volume Volume43: 43:Part Part55 FieldTrip �THE MAGMATIC ORE DEPOSITS OF THE SUDBURY IGNEOUS COMPLEX COMPLEX INSTITUTE ON LAKE SUPERIOR GEOLOGY 43rd ANNUAL ANNUAL MEETING, MEETING, MAY MAY6-11, 6-11,1997 43rd 1997 SUDBURY, ONTARIO ONTARIO Field Trip Trip Co-leaders Co-leaders S.A. Prevec Prevec (Laurentian (Laurentian University, University, Sudbury) Sudbury) M. Cosec Cosec (Resident (Resident Geologist's Geologist's Office, Office, Sudbury) Sudbury) Conference Co-chairs Co-chairs R.P. Sage Sage (Ontario (Ontario Geological Geological Survey, Survey, Sudbury) Sudbury) Meyer (Resident (Resident Geologist's Geologist's Office, Office, Sudbury) Sudbury) W. Meyer �ILSG '97 '97 Field Trip TripGuidebook Guidebook Magmatic Magmatic Ore OreDeposits Deposits of of the Sudbury Sudbury Igneous Igneous Complex Complex S.A. Prevec Prevec of Earth EarthSciences Sciences Laurentian hurentianUniversity Universi@ Sudbuzy, Ontario Su&ury, Ontario CANADA P3E2C6 CANADA P3E 2C6 Dept. Dept. Introduction Introduction Objectives Objectives of of this this excursion excursion Acknowledgements Acknowledgements Geological Sudbury Geological Introduction Introduction to Sudbury Introduction Introduction to to the the mineralized mineralized environments environments Sublayer Sublayer Footwall Footwall Offsets Offsets Sudbury Sudbury Breccia Breccia Mineralization Mineralization T r i ~Part Part : II -- Whistle Whistle Mine Mine sField e l d Trip: Stop 1: Introduction to Whistle Whistle Mine Mine Stop Stop Stop 2: 2: Main Main Mass Mass norites nontes Stop 3: Sublayer Subhyer Stop 4: Inclusion Inclusion Sublayer Sublayer Stop 4: Stop Stop 5: 5: Footwall Footwall Footwall Breccia Breccia II-- Strathcona Trin: Part II Strathcwa Footwall Stop Stop 1: 1: Sublayer Sublayer (breccia) (breccia) Stop Stop 2: 2: Footwall Footwall Breccia Breccia Mineralized Sudbury Sudbury Breccia 3: Mineralized Breccia Stop 3: Stop Field Field Trip: a Frontispiece: Idealized sketch of aa mining mining operation that appeared on some some stationery stationery of the former Ontario Department of Mines, circa 1972. the former Ontario Department of Mines, circa 1972. Frontispiece: �Introduction Introduction 1883 Since the initial discovery of copper sulphide ores in the Sudbury area in 1883 during construction of the trans-Canadian railway, and the subsequent discovery of high nickel contents in these ores, Sudbury has remained the single largest source of in the world. For nickel in For the the first first half of this century, Sudbury produced this has has dropped to less than 20% 20% approximately 80% of the world's nickel, although this of Ni-deposits Ni-depositselsewhere elsewherein inthe theworld. world. In in recent decades with the development of addition to nickel, Sudbury also produces significant quantities of both copper and lesser amounts amounts of gold, gold, silver, silver, cobalt, cobalt, the platinum group elements (PGE), plus lesser selenium, selenium tellurium and sulphur. This This and andfurther furtherhistorical historicalinformation information isis summarized by Giblin (1984). (1984). In addition to its anomalously high abundances of base- and precious-metals, precious-metals, Sudbury is also distinguished by its somewhat unique distribution distribution of silicate silicate and and or at at least controversial controversial models for sulphide components, and the resultant enigmatic or its origin. ItIthas haslong longbeen been recognized recognized that that aa discrete, discrete, igneous-textured igneous-textured noritic noritic phase phase pockets along the interface interface between the of the complex occurs in discontinuous pockets Sudhury (SIC) and and the the footwall. footwall. This is known as the Contact Sudbury Igneous Complex (SIC) Contact Sublayer- and is characterized by the presence of a high proportion of inclusions of Sublayer~and various types (including relatively ultramafic ones), bits of assimilated footwall, and residence of the majority of the nickel most significantly, represents the residence nickel sulphides. sulphides. Offshoots of less nmfic mafic material which extend out from this interface into the footwall, or which may be emplaced into linear zones in the footwall footwall running running parallel to the SIC-footwall contact contact are are known known as as Offset OffsetDykes. Dykes. The ore mineralization in Sudbury is largely associated associated with these three thee environments, environments,as as �summarized by Morrison Momson et et al. al. (1994): (1994): 1. contact-~pe contact-type deposits depositsthat thatoccur occurat at or or near near the basal contact contact of of the the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) (SIC)with with Proterozoic and and Archean basement of SIC SIC material material that extend many 2. offset dykes of kilometres into infothe th.e basement basement foorwall-tvpe deposits deposits that that occur occur as sheet-like veins 3. footwa~&ype within brecciated brecciated basement up to 2 and vein stockworks within outside the the SIC SIC ana7or and/or basement basement contact contact km outside The emplacement emplacement of the SIC SIC was a catastrophic catastrophic event, involving extensive fracturing and brecciation of the host rocks, including the appearance appearance of of shockshock- Ramsey Lake Road, west induced features such as shattercones (well-preserved on Ramey building)and andplanar planarlamellae lamellaein inquartz quartzgrains. grains. In of the Ontario Geological Survey building) the footwall footwall this fracturing fracturing has not only provided potential conduits for the introduction of magmas (such as the Offset Dykes) and heated fluids introduction fluids (which (which may may carry suiphides, sul<hdes, as as may may the the magmas), but also a distinctive pseudotachylitic-textured pseudotachyfitic-texmed rock known known as as Sudbury Sudbury Breccia, Breccia, which which has also provided a conduit conduit for later later migration migration of sulphides sulphides and and other other material. material. 2 �Objectives Objectives of this this excursion excursion This excursion will provide access to some of the best aboveground aboveground examples examples of of the the in the the Contact Contact Sublayer Sublayer (at (at Whistle Whistle pit), pit), and in the environments of mineralization in associated with footwall, associated with Sudbury Sudbury Breccia emplacement (at the Barnet Barnet showing). showing). one-half day dayexcursions. excursions. Part The trip has been arranged as two onehalf Part 11 involves involves a trip to Limited property property located located at at the northeast corner the Whistle mine, an active Inco Limited comer of the SIC. SIC. This Thisisisan anexcellent excellentexample exampleof of the the Contact Contact Sublayer-type Sublayer-typemineralization, mineralization, and displays the the transition transition from from the Main Mass to the Sublayer Sublayer to the footwall footwall environments extremely well. The Thetransition transition of of mineralization styles styles is is also alsovery very evident through this this sequence. Part will take take place place at the Part 2 of this excursion will northwest of the SIC, Levack. Here SIC, near the town of kvack. Here we we will will observe observethe thetransition, transition, breccia to to mineralized mineralized footwall footwall breccia to a bit more discontinuously, discontinuously, from Sublayer breccia mineralized Sudbury Sudbury Breccia within the footwall, courtesy of Falconbridge FalconbridgeLimited. Limited. Acknowledgements Acknowled~ements Acknowledgements Acknowledgements are are due due first fist and foremost to both Inco Limited and Falconbridge Limited, collaboration this excursion L~mited,without whose cooperation and collaboration - would not be possible. Both Boththese thesecompanies companies have provided access to their properties, logistical properties, logistical advice advice and assistance, assistance, and scientific support support and and expertise. expertise. Specific acknowledgements are due to Andy Bite and Bill Dyck (Inco) and John Fedorowich and Mike Mike Sweeny Sweeny (Falconbridge) for their assistance in preparing preparing this guidebook and and supporting supporting the the pre-excursion fieldwork involved. 3 �Introduction to Sudhury Geological Introduction Sudbury The "Sudbury "Sudbury Structure' Structure"refers refers to tothe theentire entirepackage package of of igneous-textured, igneous-textured, metamorphic rocks which which are aregenetically geneticallyinter-related inter-related or were mtamorphic and sedimentary rocks shaped by the the geological geological episode which produced this complex. These include the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) (SIC) itself, the Onaping Formation (the later later subaqueous sedimentaq package package which overlies it), and the complex complex marginal marginal subaqueous sedimentary assemblage textured material materialbetween between the the main main body body of of assemblage of igneous and metamorphic textured the SIC and the the footwall, footwall, which which is the area area of of interest interest in terms of of mineralization mineralization and and indeed of many many other other aspects aspectsof of this this complex complex structure. structure. The SIC occurs occurs at at the the southern southern boundary boundary of of the Superior superior Province, Province, in in the the granitegraniteAbitibi Subprovince. Subprovince. The greenstone terrains of the late Archean Abitibi The Abitibi Abitibi has has been been overlain in this area by a thick pile of volcanogenic and sedimentary rocks known known as as the Huronian between 2480 Huronian Supergroup Supergroup (of the Southern Province), F'rovince), sometime between 2480and and 2220 Ma. The TheSIC SICwas wasemplaced emplacedat at 1850 1850Ma Ma into into these two basement basement types, such such that the "north tonalitic, "north range" range" of of the the SIC SIC is hosted by by granodioritic granodioritic to tonalitic, heterogeneous high grade gneisses and granitoids of of the the kLevack heterogeneous v a c k Gneiss Complex and Abitibi granitoids, granitoids, and and in the "south range" by more mafic, less evolved evolved low low % grade metavolcanics, metavolcanics, metasediments metasediments and granitoids of the Huronian. upper sequence sequence known known as the Main Mass, The SIC itself may be subdivided into an upper downward through consisting of an an upper granophyric granophyric sequence which grades downward through aa quartz gabbroic gabbronoritic gabbroictransition transition zone zone into into an an igneous, cumulate-textured cumulate-textured gabbronoritic rock known as "Felsic "Felsic Norite". The The sequence sequence from fiom Granophyre down through the Felsic Norite can (i.e., can be be broadly broadly viewed viewed in terms of a differentiation differentiation sequence sequence (i.e., 4 �becoming more evolved with increasing height in in the the sequence), sequence), although evidence for geochemical discontinuities and other apparent inconsistencies suggest that simple differentiation differentiation represents represents an an oversimplified oversimplifiedmodel. model. At the base of the Felsic Norite, at the contact contact with the the country country rock (footwall), (footwall), the relationships relationships become become more complex. complex. The SIC SIC is is geographically geographically described describedin in terms terms of of its its three three ""sides", North, sides", into the North, (ca. 2710 2710 to to TheNorth NorthRange Rangeisishosted hostedby byLate LateArchean Archean(cci. South and East Ranges. The granitic and heterogeneous heterogeneous gneissic gneissic rocks of the southernmost southernmost Abitibi Abitibi 2665 Ma) granitic Subprovince Province. The Subprovince of the Superior Province. The gneissic gneissic footwall suite which borders much of the North Range Range is is called called the the Levack Levack Gneiss Complex Complex (a "typical" "typical" section section of which is well-displayed along the Highway 144 just north of Windy 144 roadcut just TheSouth SouthRange Rangefootwall footwallconsists consistsmainly mainly of of volcanics and sediments sediments of of the the Lake). The Supergroupof of the the Early Early Proterozoic ProterozoicSouthern SouthernProvince Province(cci. (ca. 2480 2480 to 2200 2200 Huronian Supergroup Ma). These Theseinclude includebasaltic basalticand andrhyolitic rhyoliticvolcanics volcanics and and intercalated intercalated sediments, sediments, overlain by glacially-deposited glacially-deposited sedimentary sedimentary sequences sequences in a rift rift environment, environment,and and intruded by gabbroic gabbroic to leucogabbroic dykes and intmded and sills sills of of various variousages. ages. The South Range Range has been been much much more more extensively extensively metamorphosed than has the North Range, Range, - probably probably as as aa result resultof ofboth bothPenokean Penokean(cci. (ca. 1950 1950to 1850 1850 Ma) and and later later Grenvillian Grenvillian (ca. 1100 1100 to 950 Ma) activity. The TheEast East Range Range reflects reflects some some characteristics of both (cci. environments. In Ingeneral, general,preservation preservation of of igneous igneous textures and compositions compositions is much better in in the the North North Range Rangerocks rocks than thanelsewhere. elsewhere. 5 �Introduction Introduction to to the the mineralized mineralized environments environments The mineralized environments margins of of the the SIC Main Mass environments occurring along the margins Mass can be broadly therefore of of magmatic-origin) magmatic-origin) broadly subdivided subdividedinto into igneous-textured igneous-textured (i.e., therefore Figure 1, and and the metamorphicContact Sublayer Sublayer and Offset dykes, as shown in Figure footwall rocks recently, the igneoustextured footwall rocks which which host host them. them. Until relatively recently, igneousSublayer matrix ("lTSM't) textured Sublayer ("ITSM") and the more felsic equivalents in the Offset Offset ("QD"), had had been been grouped grouped together together as as Contact Contact dykes, referred to as quartz diorite ("QD"), petrography (e.g., 1984). Evidence Evidencefrom frompetrography (e.g., Pattison, Pattison, Sublayer (e.g., Naldrett et al., 1984). 1979), incompatible trace aL, in press), press), and and trace element element geochemistry (e.g., Lightfoot et aL., radiogenic isotope aL, 1997) suggests that the matrices of isotope geochemistry (Prevec et al., different magmas. magmas. Thus, the Offsets Offsetsand andthe theSublayer Sublayerrepresent represent distinctly distinctly different Thus, although although theft inclusion populations populations and and emplacement emplacement styles styles suggests suggests a close the similarity of their genetic relationship, relationship, they will be treated here as separate separate entities. entities. An additional subunit of the Main Mass gabbronorites known known as as "Mafic Norite" has Norite (which (which comprises comprises the the bulk of the been identified, occurring below the Felsic Norite Main Mass). Mafic MaficNorite Noriteisisparticularly particularly evident evident in locations where Sublayer and/or Offsets occur below the Main Mass. This andlor This relationship is depicted depicted in Figure Figure . petrologic grounds; 2. Mafic MaficNorite Noriteisisdistinguished distinguishedfrom fromFelsic Felsic Norite Norite on petrologic grounds; geochemicaHy the the two norites reflect a gradationally upwards upwards evolving sequence. geochemically sequence. be provided in the Specific distinctions between these two Main Mass subunits will be descriptions for for stops stopsin in the the Whistle WhistleMine Mine pit. pit. 6 �Sublayer The most recent recent formal formal publication dealing specifically with this subunit subunit of the SIC SIC (Naldrett et al., 1984) 1984)used the the term term "Contact "Contact Sublayer" Sublayer" to define define that that part part of of the the Sublayer adjacent to the Main Mass of the complex complex and not that included in (Offset) (Offset) dykes. However, However,its itsusage usageeven evenin in that that article article was was ambiguous, ambiguous, and and more more recent recent prominent distinction distinction between between study, as mentioned previously, has indicated a more prominent Contact Sublayer and Offset Dyke magmas. magmas. Therefore, Therefore, our our working working terminology terminology will henceforth refer merely merely to to "Sublayer" "Sublayer" and and "Offset" "Offset"rocks. rocks. The Offsets will be discussed in more more detail detail in in the the next next subsection. subsection. The discontinuous discontinuous marginal embayments known collectively as the Sublayer, Sublayer, as as characterized by by Pattison (19791, (1979), contain the the bulk bulk of of the the Ni-Cu-PGE ores. originally characterized This unit is characterized characterized by an an igneous-textured igneous-textured noritic matrix mamx hosting disseminated disseminated to massive sulphides and a relatively relatively large large proportion proportionof ofinclusions. inclusions. The inclusion populations may be divided into two groups; those obviously derived from the adjacent footwall, and more enigmatic mafic mafic to ultramafic ultramafic inclusions, inclusions, the the latter latter of of which appear to be spatially associated associated with sulphide occurrences (e.g., (e.g., Souch Souch and Podolsky, 1969). 1969), Sublayer Sublayerinclusion inclusiontypes types include includesmall-scale small-scalefelsic/anorthositic felsic/anorthositic . blebs (generally (generally cm-scale) cm-scale) which which are are most most abimdant abundant in, but not unique unique to, to, the the cm-scale inclusions of fine-grained, often porphyritic, hornfels-textured Sublayer, cm-scale material ("anhedral ("anhedral porphyries"), and cm- to metre-scale metre-scale inclusions inclusions of of ultramaflc ultramafic material. Although Althoughthese theseinclusion inclusionpopulations populations comprise comprise a significant significant proportion proportion of of the Sublayer (up to 25%), 25%), they are not at all well-represented well-represented in the surrounding surrounding basement. basement. 7 �Footwall Footwall The term term "footwall" "footwall" is used as a general general term to denote basement rocks underlying has been variably km surrounding surrounding the SIC has the SIC. The Thefootwall footwallwithin within about about 11 km thermally recrystallized by the contact aureole therma1Iy aureole of the SIC, producing concentric concentric epidote-albitecontact metamorphic zones from from pyroxene- to hornblendehomblende- to epidote-albite- hornfels, in order of increasing distance distance from from the thecontact. contact. It has been o observed b s e ~ e dthat mineralization in the footwall is largely associated the mineralization associated with the the most most proximal, proximal, highest temperature, temperature, pyroxene hornfels aureole aureole (Coats (Coats and Snajdr, Snajdr, 1984). 1984). In addition to the thermal aureole, fractured, both aureole, the footwall is extensively extensively fractured, both radially and concentrically around the SIC. SIC. These These fractures fractures provide conduits for the noritic magma magma bodies bodies known known as as Offset Offset Dykes injection of relatively homogeneous noritic and of distinctive shock-induced pseudotachylitic-textured rocks known as Sudbury Sudbury Breccias, Breccias, both both of of which which represent represent environments environments for hosting significant significant Cu-rich mineralization. In Inaddition addition to to the the Sudbury Sudbury Breccias, Breccias, additional additional breccia-type breccia-type environments which may host mineralization include rifootwall breccia", "late environments r'footwallbreccia", granite breccia" and Sublayer (breccia; (breccia; see see pg. pg. 21). 21). The The latter latter two reflect reflect terminology used mainly by Falconbridge Limited, Limited, and and will willbe be discussed discussed further in the text for Part Part IIIIof of this this excursion. excursion. Offsets fxfsets Offset Dykes are intrusive, igneous- to metamorphic-textured bodies occurring as elongate dykes into the footwall, 10to to 15 15km kminto footwall, occasionally occasionally dykes which which may extend extend 10 Offset in in the theNorth NorthRange). Range). These dykes upwards of 25 km (in the case of the Foy Offset occur both radiating outwards from the contact with with the base base of the SIC and also 8 �out in in the the footwall, footwall, as as in in Hess Hess and Falconbridge aligned parallel to the contact, lying out Townships. The Thesilicate silicatemineralogy mineralogy of the Offset Dykes is dominated by Pattison, plagioclase, orthogranophyre (e.g., Pattison, plagioclase, ortho- and and clinopyroxenes, clinopyroxenes, quartz and ganophyre 1979). As As the thedyke dykeextends extends further further into the footwall, this assemblage is replaced by its metamorphic equivalent, whereby the pyroxenes pyroxenes in particular particular are replaced by quartz, feldspar feldspar and and gsanophyre granophyre are recrystallized. amphibole and then biotite, and quartz, Sudbury Breccias Sudburv Breccia the SIC, where their Sudbury Breccias also occur in a wide zone surrounding the alignment, as with the Offsets, is a function of of the the local local fault fault geometries. geometries. They Theyhave have been identified identified as far as 80 80 km distance away from Sudbury (both near Lake Agnew Lake Lake to to the the west). west). They Temagami to the northeast and Agnew They consist consist of of aa very very within which whichblocks blocksof ofcountry countryrock rockare areentrained. entrained. The clast fine-grained matrix within xenocrystic grains grains to to outcrop outcrop size blocks, where size may vary enormously, from xenocrystic the rotation of regional fabrics (foliations, lineations, lineations, etc.) etc.) allow these blocks to be identified as breccia clasts. The The matrix matrix of of Sudbury Sudbury Breccia is texturally comparable consist to a low-viscosity low-viscosity liquid in terms of its fluid dynamics, although it appears to consist of the the local local country country rock, rock, displaying displaying sharp sharp contacts contacts with of the pulverized equivalent of - it but with with no no thermal thermal contact contactaureole. aureole. Mineralization Mineralization The vast majority of the ores at Sudbury are incorporated into an assemblage assemblage dominated by pyrrhotite, pentlandite, pentlandite, chalcopyrite chalcopyriteand andpyrite. pyrite. Variation in the relative proportions of these minerals within aa given given deposit deposit are atmbutable attributable to the effects of fractionation solid solution solution (Mss), (Mss), such that fractionation of a monosulphide solid 9 �fractionated liquids enriched in Ni, Cu, Pt, Pd and Au are differentiated from Fe, Co, Co, FUI, Rh, Ru, Ru, Ir Jr and and 0Oss (Naldrett, 1984). residual cumulate sulphides enriched in Fe, 1984). Differences in Cu. Ni and PGE tenor between different deposits may be attributed attributed to progressive depletion depletion of of these these elements elements from from a given batch of magma by segregation segregation of successive successive batches batches of of sulphide. sulphide. While most of the Ni is is concentrated concentrated into into pentlandite, exsolved exsolved at at low-temperatures low-temperatures (2000 250°C) from pyrrhotite, pyrrhotite pyrrhotite itself itself may may also also retain retain up up to to 1.2 wt% Ni. (200' to 250°C Cu is largely concentrated concentratedin in chalcopyrite, chalcopy&e, with lesser amounts amounts occurring occurring in in cubanite cubanite PGE are largely concentrated in the platinum-group platinum-group minerals minerals (PGM) (CuFe2S3). PGE (PtAs2). A michenerite (PdBiTe), (PdBiTe), moncheite moncheite (PtTe2) (PtTeJ and sperrylite (Pas*). A relatively relatively at Sudbury Sudbury is is provided by complete list of the metalliferous minerals occurring at Naldrett (1984). (1984). Typical Typicalaverage averagegrades grades of of these these elements elements in 100% 100% sulphide sulphide are a R as as al. follows, based on on values values given given in Naklrett Naldrett (1984), Cochrane (1984), Binney et aL (1994) (I 994) and Naldrett Naldrett et etaL ul.(1994). (I 994). Ni Cu Co Pt Pd Au (wt%) (wt%) (wt%) (ppb) (ppb) (ppb) Sublayer— S ublap 3.8 2.2 0.19 1391 1798 583 0.58 6.8 Offset 4.0 3.6 0.17 2130 3170 868 0.90 5.3 F. Breccia 4.5 2.3 0.16 756 802 122 0.51 25 S. S, Breccia 4.9 3.8 0.12 1042 1026 105 0.78 93 Cu zones 1.6 30.1 0.06 1753 2994 85 18.8 897 Unit Unit CuJNI (Pt+Pd)/ (Ru+Jr+Os) These values are are based based on on arbitrarily arbitrarily chosen data from available literature, and are intended as a very general guide to relative relative abundances. abundances. Sublayer deposits deposits are are thought to to have have CdNi CuiNiranging rangingbetween between0.1 0.1and and0.5 0.5(Morrison (Morrisonetetal.,' at, generally thought 10 10 �1994), than presented presented here. here. The 19941, which is lower than The concentrations concentrations of PGE PGE and and Au Au in between deposits, deposits, so "average" particular may vary by orders of magnitude between be treated treated with with caution. caution. The CdNi Cu/Ni ratio ratio of of the the SIC deposits as a abundances should be whole is considered to be around 1.0, 1.0, where where Sublayer deposits deposits have have Cu/Ni<l, Cu/Nici, 1, and the Offset Dyke and Sudbury Breccia (or Footwall deposits) deposits) have have Cu/Ni> Cu/Ni>l, copper and Cu>>Ni. deep copper and stringer stringer zones zones have have Cu>>Ni. 11 �Trip: Part Part I -- Whistle Field Trio: Whistle Mine The following three page page description description of the environment and history of the Whistle Whistle Mine was written written by by Inco Inco Ltd. Ltd. for for geological geological visitors to the mine site. site. It is here reproduced for courtesy of ofInco kco Limited as of January, 1997, for this field trip guide courtesy 1997, with minor updating updating courtesy courtesyof of A. A. Bite Bite (Inco (Inco Ltd.). Ltd.). WHISTLE MINE Whistle Mine Mine is located locatedin in the the extreme extreme north-east corner comer of the Sudbury SudburyBasin, Basin, of the the town town of of Capreol Capreol in in concession concession IV approximately twelve kilometres north-east of of Norman Township. Township. orebody lies lies within within the the Whistle Whistle embayrnent embayment which plunges to the west southsouthThe orebody west at about forty degrees. The Theore oreoutcropped outcropped in the form of a large hill facing to the south and is reasonably continuous to to aa depth depth of of about aboutfive fivehundred hundredfeet. feet. The ore is of two two primary primary varieties, varieties, the the most most abundant abundant type being disseminated disseminated inclusion inclusion norite in which the blebs in in aa noritic noritic matrix. matrix. Also Also within within the' sulphide sulphide exists as distinct blebs % the norite are are large large inclusions inclusions of of greenstone, amphibolite and a variety of ultramafics ultramafics (generally dark coloured rocks). The The second second most common type of ore is inclusion suiphide. ItItisischaracterized characterizedby by large large rock inclusions (as described above) above) massive sulphide. in aa matrix matrix of of massive massive sulphide. sulphide. The orebody itself itself is is overlain by a thick "floating" in layer of medium-grained, medium-grained, light light grey barren main mass felsic norite. 12 �The footwall of the Sudbury Igneous Complex (SIC) comprises partly barren However, the the true footwall footwall to the ore ore body body is is sublayer andlor inclusion basic basic norite. norite. However, a pink granite breccia breccia which is well exposed exposed on on the the north north wall wall of of the thepit. pit. The ore is made up predominantly of copper plus nickel with minor amounts of cobalt and precious metals. The The copper/nickel copperlnickelratio ratio is is approximately approximately 0.3:1 0.3:l while the pyrrhotite/nickel 23.5: 1. pyrrhotitelnickel ratio ratio is is 23.5:1. There are no major offsetting structures transecting the ore zone; however, strong strong localized joints joints are encountered and many are quite rusty in appearance, indicating significant historic historic water water movement. movement. This may be due in part to the fact that the area had previously been developed as a mine near the turn of the century. 4.5 million tons of rock and 2.7 million tons of ore have been mined To date, some 4.5 from the pit. January 15, 15,1991 1991 13 �WHISTLE WHISTLE MINE MINE HISTORY and and STATUS STATUS 12 lan km north of Capreol -LOT #6, concession concession #5 #5 -- Norman Township Township -- 12 1897 -- Isaac 1897 Isaac Whistle discovers the property 1900 - A mining patent is issued issued 1900 1903 -- Property ownership is transferred from Dominion Nickel Copper Company Company 1903 to British American Nickel Nickel Company. Company. 1910 - Exploration begins in the form 1910 form of diamond drilling and drifting drifting along along ore ore veins accessible accessible through an an adit. adit. 1912 - Whistle is abandoned in favour of the Murray prospect. 1912 1912 -- 1929 The property 1929 -- The property stagnates stagnates 1912 1929 -- The The property reverts to INCO INCO through through the the merger. merger. 1928 -- 1988 1988 -- The ore body is delineated by several series of diamond diamond 1928 programs. drilling programs. 1988 -- INCO INCO develops an open pit in January, 1988 1988 contractually contractually mined by 1988 MacIsaac MacIsaacMining Miningand and Tunnelling. Tunnelling. 1991 3,285,000 1991 -- Pit production ceases and the mine is placed on standby after 3,285,000 tons of ore are extracted along with nearly 4,868,000 tons of waste. Approximately 1.3 million tons tons of of ore remain remain to be be extracted from from the open pit. Additional Additionalmineral mineral below below the the pit could become mineable mineable if economic economic conditions become favourable. conditions favourable. in the footwall of the pit locates aa small 1993 1993 -- Exploration Exploration diamond drilling in small occurrence of high grade copper with substantial substantial precious precious metals metals between levels. -1500 and 2000 levels. 1995. to be be ready for submission by 1995. -- Closure Closure plans are being formulated to 1994 -- Exploration Exploration diamond drilling continues continues to reopen reopen Whistle. Whistle. The 1994 -- In November plans are established to The mining mining contract contract 1994 is let to Carman Construction Construction with the intention to mine approximately 1.3 1.3 million tons to the 12th 12th bench. bench. expansion which which will will access access an additional 1.0 1995 -- Plans are finalized for an expansion 1995 1.0 million tons of of ore ore and and development developmentbegins. begins. Mining will now go to cut million tons #14. -- The The mine closure plan is completed and submitted. 14 �Canmet initiates to characterize a living growing wastewaste - Canmet initiatesaaproject projecttotoattempt attempt to characterize a living growing pile. -- A rare earth earth magnet magnet is purchased to facilitate ore cobbing in an an attempt attempt to to rock" and enhance the remove significant volumes of "floatable rock the mine mine feed feed grade. grade. Mining 1996 for the the fall fullyear yearatataarate rateofof2500 2500tons tonsper perday. day. The is planned for 1996 place and and about about 70% 70% of the ore is being magnetic separation circuit is in place treated. treated. 1997 mine until until September September of this year Reserves indicate that we will be able to mine 1997 -- Reserves day. This at a rate of 2500 tons per day. This will take the pit to a depth of 14 14 benches. benches. Summary (as of June 1, 1, 1996): 1996): Total rock removed to date -Total ore shipped -shipped to date date 6.11 6.1 1 million tons tons 4.80 million tons tons 15 �At the Whistle Whistle mine, mine, the the geology geology exposed exposed in the pit includes both both felsic felsic and and mafic mafic Main Mass norites norites at at the the southwest, southwest,the the Sublayer Sublayer in its various forms, and finally corner. The The trip trip will traverse traverse these these units units in this the footwall contact at the northeast comer. order, in theory, theory, depending depending on on pit logistics, as depicted depicted in in Figure Figure 2. 2. Stop 1: Stop 1: Introduction Introduction to to Whistle Whistle Mine This stop is technically technically not a geological stop, as it will not involve involve looking looking closely closely at at the rocks, but will will provide provide aa geological geological and historical overview of the the mine, mine, courtesy of Inco courtesy Inco Limited, Limited, much of which has been provided in the previous previous text, for for your convenience. Stop 2: Stop 2: Main Main Mass Mass norites norites (south (south ramp) and the the contact contact between between them. them. The This stop includes the two Main Mass norites and The felsic norite is distinguished from the mafic norite on the basis not only of colour modal mineralogical change), but also by inclusion content content index (and therefore therefore aa modal and sulphide content. The Thefelsic felsicnorite norite isis aa two-pyroxene-plagioclase-granophyre two-pyroxene-plagioclase-granophyre massive and and homogeneous. homogeneous. Towards the base, the rock, which is relatively massive clinopyroxeneincreases increases from from roughly equal (about (about 20% 20% and and proportion of ortho- to dinopyroxene \ orthopyroxene-dominant. The 15% of the rock, respectively), to orthopyroxene-dominant. The mafic mafic norite norite dinopyroxene at all, and consists underlying it does not contain clinopyroxene consists of approximately approximately 35-45 modal% orthopyroxene, which becomes progressively more poikiliticpoikilitictextured with depth. The Theporportion porpordon of quartz and granophyric-textured quartzofeldspathic quartzofeldspathicmaterial also decreases decreases from about 10% 10% in the felsic norite to norite. The The mafic mafic norite contains contains cm-sized cm-sized less than 2 or 33 modal% in the mafic norite. felsic clasts thought to to represent anorthositic melt droplets, which have have subsequently subsequently 16 �been recrystallized and hornfelsed. Inclusions Inclusions of dark, fine-grained fine-grained massive massive "gabbro-hornfels" comprise the the other other main main inclusion inclusionpopulation populationhere. here. Minor Minor (2 (2 wt%) disseminated suiphides sulphides appear appear in the mafic norite, consisting consisting of pyrrhotite. pyrrhotite. Stop Stop 3: 3: Sublayer: Sublayer:upper upper contact contact At this stop the contact between the base of the mafic norite and the uppermost uppermost Sublayer is observed. The Thecontact contactisis irregular, irregular, and and is represented by by aa decrease decreasein in grain size, significant decrease in the abundance of coarse-grained feldspar, and an increase in suiphide sulphide content. The The mafic mafic norite here is characterized by the presence presence of coarse-grained interstitial biotite, as well. The Sublayer here here may may be broadly described as opx-rich Sub lover,and andconsists, consists,atatthe thetop, top,of of a medium-grained rock Sublayer, containing about about 40% 40% plagioclase plagioclaseplus plustwo twopyroxenes pyroxenes(ortho~clino). (ortho>>cino). Granophyre but decreases decreases with with depth depthand anddisappears. disappears. Suiphide is also present again, but Sulphide consists of pyrrhotite, grading about about 250 250 ppb ppb Ni, Ni, plus five to ten percent disseminated pyrrhotite, associated pentlandite. associated Stop Stop 4: 4: Inclusion Inclusion Sublayer Sublayer This "stop" "stop" is a sequence sequence of stops stops as we we move move progressively progressively into the more more mineralized Sublayer down down towards towards the the footwall footwallrocks. rocks. The Sublayer can be discriminated discriminated petrographically into a variety variety of of sub-groups, sub-groups, including includingolivine-opxolivine-opx- rich Sublayer, porphyritic opx-Sublayer and variations thereon, as distinguished distinguished variant at atthe thetop topof ofthe theSublayer Sublayer.. The from the opx-rich variant The presence of porphyritic- textured pyroxene distinguishes Sublayer rocks from mafic norite, which is characterized by poikilitic textured textured pyroxene. pyroxene. As the footwall contact is the Sublayer Sublayer referred referred to to as as inclusion basic approached, a relatively thin subunit of the 17 �no rite is is present, present, characterized characterized by by aa "salt "saltand andpepper" pepper"texture. texture. This is a somewhat norite leucocratic variant one time time to to be be more leucocratiic variant of of the the Sublayer, Sublayer, and and has has been thought at one representative of a possible parental composition for the Sublayer (e.g., Morrison et aL, 1994). 1994). The Theinclusion inclusionbasic basicnorite norite may may also also reflect reflect differentiation differentiation of of Sublayer Sublayer al., extends outwards from the Whistle rock into the "root" of the Offset Dyke which extends Sublayer to the northeast (forming the the Whistle Whistle and and Parkin Parkin Offsets). Offsets). The The application application of terminology such as inclusion basic norite and quartz diorite to Offset Offset rocks rocks this point. point. Many becomes somewhat subjective at this Many workers apply apply the term term "quartz "quartz diorite" to Offsets Offsets in the South South Range Range only. Sulphide textures vary through through the the Sublayer Sublayer from fromthe the interstitial interstitial pyrrhotite pyrrhotite observed observed at the top top to to progressively progressively more more interconnected, interconnected, higher sulphide sulphide content content equivalents equivalents the inclusion inclusionbasic basicnorite). norite). These include towards the core of the Sublayer (above the suiphide, ragged-textured sulphide, gabbro-peridotite disseminated (blebby) sulphide, (GPIS) and inclusion massive-sulphide. The The inclusions inclusions in in inclusion suiphide sulphide (GPIS) inclusion massive sulphide tend to consist of locally derived footwall material, whereas those in gabbro-peridotite gabbro-peridotite inclusion sulphide are thought to represent material. This potentially more exotic material. This interpretation interpretation depends depends on on knowing knowing the the source source inclusions, which whichisisunclear. unclear. Alternatives include &ore ultramafic ultrarnafic inclusions, of these more (i.e., cumulates), cumulates), a pre-existing Proterozoic Proterozoic maficmaficderivation from the Main Mass (i.e., ultramafic body, Archean footwall, or or picritic picritic mantle. mantle. The source ultrarnafic source of of these these inclusions therefore has further potential implications regarding the origins of the metals and the sulphur. sulphur. 18 �Stop 5: 5: Footwall Footwall The footwall footwall exposed exposed along along the north side of the pit consists of granitic granitic material of Complex, cut cut by bymafic maficdykes dykeslocally. locally. [Note [Note that that the cliffface cl(ffface in the Levack Gneiss Complex, in pit at the footwall footwall in particular particular is relatively unstable, due to the extensive the pit particular awareness and caution should be fracturing in in this this brecciated brecciated rock, rock, so particular Blocksofoffootwall footwallrock rockare arepresent presentwithin within the the exercised at all all times times in in this area.] area.]Blocks adjacent inclusion adjacent inclusion basic basic Sublayer, Sublayer, and and may contain Cu-enriched Cu-enriched suiphides sulphides may also be observed, particularly dominated by chalcopyrite. Pyrite-rich Pyrite-rich sulphide may associated with the and footwall footwall granite granite breccias. associated the more more "granitized" "granitized Sublayer and mineralization, can can also be observed "gash-type"copper mineralization, observed Sudbury Breccia, hosting "gash-type" breccias. The presence of well-defined Sudbury amongst and below the footwall breccias. Sudbury Breccia Breccia can can be be used used to to imply imply that that the host footwall rock is (probably) (probably) insitu, insitu, and and is is not, itself, a breccia breccia block. block. LUNCH -- Onanin Onaoins Falls Falls LUNCH 19 �Field Trip: Part Part H I1 -- Stratheona Strathcona Footwall Breccia In contrast to the Sublayer-hosted, pyrrhotite-dominated ores at Whistle mine, the along the the northwest northwest margin margin of of the the SIC SIC are are dominantly dominantly footwafl-hosted, footwall-hosted, deposits along (1984), Thefollowing followingtable, table,modified modified from from Coats Coats and and Snajdr Snajdr(1984), copper-rich deposits. The summarizes activity in this 10 10km km wide wide belt. belt. summarizes the mining activity Deposit Ownership Ownership Depth (fret) (feet) Production Production Hardy Falconbridge Falconbridge 1427 1427 1954 to 1978 1978 1954 Boundary Boundary Falconbridge 952 1961 to 1973 1973 Onaping Onaping Falconbridge Falconbridge 5348 5348 1961 to 1982 1982 McCreedy West Inco 1600 1600 1973 1973 to present Craig Craig Falconbridge Falconhridge Levack Levack Inco Inco 3915 3915 1913 1913 to present Fecunis Fecunis Falconbridge 3993 3993 1957 to 1977 1977 North Falconbridge Falconbridge 4430 4430 1964 1964 to present McCreedy East McCreedy Inco Inco Fraser Falconbridge Falconbridge 5250 5250 1981 to present Strathcona Strathcona Falconbridge Falconbridge 3205 3205 1968 to present Colemar Coleman- Inco Inco 2278 2278 1970 to 1982 1982 Lower Coleman Coleman Inco Inco Longvack Falconbridge Falconbridge open pit 1956 to to 1961 1961 1956 Longvack South South Falconbridge Falconbridge 1289 1289 1968 1968 to 1977 1977 Big Levack Inco Inco developed not developed developed not developed developed not developed not developed developed of sulphides in in the the area in 1888, production of Ni-Cu Following initial discovery of ores began in 1913, 1913, and production and reserves for the deposits in this area exceed 20 �200 million tons. A A summary summary of the so-called "North Range deposits" located located in from whom whom the the Levack Township is provided by Coats and Snajdr (1984), from following information has been derived. derived. corresponding mafic The Sublayer, Sublayer, as as characterized characterized previously, along with its corresponding noritic protrusion from poorly developed at the surface from the Main Mass, is relatively poorly surface in this area, although well-developed well-developed in in the the subsurface. subsurface. No Offset Offset Dyke Dyke projects projects outwards outwards into into the the footwall, although offset rocks hosted by Archean granitoids do occur parallel Hess and and Harty Harty parallel to to the the footwall footwall contact about 15 15 km to the north in Hess I). The Townships (Fig. 1). Thefootwall footwall in Levack LevackTwp. Twp. consists consists of of aa heterogeneous heterogeneous Gneiss Complex), Complex), in its type high-grade Archean gneiss complex (the Levack Gneiss location (or near enough). This Thiscomplex complex includes includes a mixture mixture of granitic, granitic, tonalitic, tonalitic, mafic and occasionally occasionally ultramafic rocks which have seen granulite granulite grade grade metamorphism metamorphism(and subsequently retrogressed to amphibolite facies, for the most part). The 2.5kin kmout outfrom fromthe the Thecomplex complexisisexposed exposedatatsurface surfaceto toaa width width of of about about2.5 SIC, beyond which more heterogeneous, greenschist-grade granitoids occur. The stops stops on on this this section section of of the the excursion will pass from basal Sublayer Sublayer into - Footwall Breccia Breccia and and then into the footwall proper, where mineralization is associated associated with with aa Sudbury SudburyBreccia Breccia zone. zone. Stop (garbage dump Stop 1: 1:Sublayer Sublaye~(garbage dump outcrop) outcrop) The Sublayer between the the base base of the Main Mass Sublayer here here is inclusion-rich Sublayer between and the footwall proper. ItItisisbroadly broadly equivalent equivalent to undifferentiated inclusion Sublayer between the inclusion basic basic norite described described the opx-rich Sublayer and the inclusion 21 �previously. This This rock rock type typemay may be be considered considered a breccia, given that a large have been been derived derived fiom fromthe the Main Main Mass Mass above it (as proportion of the inclusions may have Falconbridge, as opposed to the Inco perspective which which treats treats the the it is interpreted by Falconbridge, exotic). As footwall increases, increases, inclusions as largely potentially exotic). As the the proportion proportion of of footwall this becomes analogous to the footwall footwall breccias brecciasobsewed observedat atWhistle. Whistle. Inclusions gneiss, iron-rich iron-rich pyroxenite, and a identifiable here include fragments of footwall gneiss, variety of mafic inclusions in a variably crystalline crystalline felsic felsic matrix. matrix. The The granitic granitic footwall proper is evident evident in the the cliff cliff face, about 100 100 m to the north. Stop 2: Stop 2: Footwall Footwall Breccia Breccia (Strathcona (Strathcona cliff cliff face, water tower) mines, (at (at the the lefthandmost lefthandmost extreme extreme of of In front of the Strathcona and Coleman mines, Figure 3, but not shown), the contact between Sublayer breccia breccia and footwall breccia is well displayed. The Thetwo two breccias breccias represent represent a transition from a norite-dominated inclusion-rich breccia into aa granitoid-dominated granitoid-dominated environment with mafic mafic inclusions. inclusions. the water water tower, tower, access access permitting), permitting), late-granite late-granite Further up on top of the hill (under the breccia is is evident. evident. This Thiscontains containsfewer fewermafic mafic inclusions inclusions in a much more granitic matrix and is characterized characterized by by aa stockwork stockworkof of relatively relatively fine finefractures fracturesinfihled infilled with with granitic material. Mineralization this stop occurs at the base of the cliff in Mineralization evident at this \ the footwall breccia, consisting consisting of blebby pyrrhotite plus pentlandite, with chalcopyrite present locally. locally. Stop Sudburv Stop 3: 3: Mineralized M M Brecciai i(Barnet (Bametshowing) showing) This location, shown example' of footwall footwall shown in Figures 33 and 4, is an excellent example (Sudbury Breccia)-hosted mineralization, and has been summarily described by Morrison and Sweeny (1994). ItItisislocated locatedapproximately approximately 400 m into the footwall 22 �extension of the from the SIC contact, and is interpreted to be the up-plunge extension Strathcona Copper Copper Zone, characterized characterized by high-Cu, low-PGE contents contents in in the ores. ores. Limited (since (since 1979), and and the outcrops This showing is the property of Falconbridge Limited were stripped in 1987 1987 and 1989 1989 for subsequent subsequent detailed mapping and sampling. The footwall here consists of Levack Gneiss Complex gneisses and migmatites, cut by plagioclase-phyric ("Matachewan-type") ("Matachewan-type") mafic dykes, with later Sudbury Breccia units. Sudbury Sudbury Breccia pseudotachylite occurs as small cutting both of these units. veinlets at the south end of the outcrop and as a large east-west east-west trending trending dyke dyke at at the the of the mineralization mineralizationisishosted. hosted. Thin veinlets of north end, where the bulk of extensively epidotized epidotized and and hematized, hematized, cross-cut cross-cut pegmatitic feldspathic material, extensively footwall, dykes and breccias, and are also associated associated with Cu-mineralization. Cu-mineralization. This showing is located within the hornblende-hornfels homblende-homfels aureole induced in the footwall footwall by the intrusion of the SIC (as mentioned earlier). Both Both mineralization mineralizationand and alteration alteration are very strongly fractured andlor footwall and/or structurally structurally controlled in the footwall environment. environment. Mineralization is dominated by by chalcopyrite, and occurs as disseminated sulphide, h4ineralization stockworks of of veinlets. veinlets. The veins and stockworks as discrete veins, or as fine stockworks evident evident within the Sudbury Breccia body represent the best-mineralized section, where the the distribution distribution of veins and stringers stringers is controlled controlled by two two main main orientations orientations of fracture sets. The TheSudbmy SudburyBreccia Brecciaisismore more prone prone to to extension extension than than is is the the footwall, providing more zones of weakness and therefore a relatively relitively high high suiphidesulphidereservoir potential. This the Thisextensional extensionalfracture-fill fracture-filloccurrence occurrence is is equivalent equivalent to to the 23 �deep-Cu deposits, deposits, but does not display the wide mineralized zones required to produce the more massive, higher-grade ores present present at at depth. depth. 24 �References Binney, W.P., R.Y.,Sweeny, J.M. W.P., Poulin, R.Y., J.M. and Halladay, Halladay, S.H. S.H. (1994) The Lindsley Ni-CuPGE deposit Sudbury -- Noril'sk deposit and and its its geological geological setting In Proceedings of the Sudbury Norifsk Symposium (editedbyby P.C. Lightfoot Naldrett). Ontario Geological Survey, Symposium (edited P.C. Lightfoot andand A.J. A.J. Naldrett). Ontario Geological Survey, Special Special Volume 5, p. p. 91-103. 91-103. Coats, C.J.A. and and Snajdr, Snajdr, P. P. (1984) (1984) Ore Ore deposits deposits of the North Range, Onaping-Levack area, Structure (edited (edited by by E.G. E.G. Pye, Pye, Sudbury In The geology and ore deposits of the Sudbury Structure A.J. Naldrett P.E. Giblin). Giblin). Ontario Ontario Geological Geological Survey, Special Special Volume Volume 1, 1, p. 327-346. 327-346. A.J. Naldrett and and P.E. (1984) Ore Ore deposits deposits of of the Copper Cliff Cochrane, L.B. (1984) Cliff Offset OffsetIn In The The geology geology and and ore ore deposits deposits of of A.J. Naldrett and P.E. Giblin). the Sudbury Structure Structure (edited (edited by E.G. Pye, A.J. Giblin). Ontario Ontario Geological Geological Survey, Survey, Special Special Volume 1, p. 347-359. Giblin, P.E. P.E. (1984) development, of of geological geological studies studies and Gibh, (1984) History History of exploration and development, development and ore ore deposits of the Sudbury development of geological geological concepts In The geology and Sudbury Structure Giblin). Ontario Ontario Geological Survey, Structure(edited (editedby by E.G. E.G. Pye, Pye, A.J. A.J. Naldrett Naldrettand andP.13. P.E. Giblin). Special Volume 1, 1, p. 3-23. 3-23. Lightfoot, R.R., Moore, M. and Pekeski, D. (in press, K., Keays, R.R., Lightfoot, P.C., P.C., Doherty, Doherty,W., W., Farrell, Farrell, K., Mass, Sublayer, Offsets, Offsets, and and inclusions from from the Sudbury 1997) Geochemistry of the Main Mas, Igneous Igneous Complex, Complex, Ontario. Ontario. Ontario OntarioGeological GeologicalSurvey SurveyOpen Open File File Report. Report. White, T.L. T.L. (1994) (1994)Footwall Footwall mineralization mineralization of the the Sudhury Sudbury Morrison, G.G., Jago, Jago,B.C. B.C. and andWhite, Igneous Igneous Complex Complex In In Proceedings Proceediigs of of the the Sudbury Sudbury - Norifsk Noril'sk Symposium (edited (edited by P.C. Lightfoot Li&tfoot and and A.J. A.J. Naldrett). Naldrett). Ontario Ontario Geological Geological Survey, Special Volume 5, p. 57-64. 57-64. Morrison, surface tour. tour. CIM (1994) Sudbury ore environments surface CIM Geological Geological Morrison, G. and and Sweeny, Sweeny, M. (1994) Society, trip guidebook, guidebook, 35 pp. Society, Fourth Fourth Annual Annual Field Field Conference, Conierence, field field trip pp. Naldrett, In The The geology geology and and Naldrett, A.J. A.J. (1984) (1984)Mineralogy Mineralogyand and composition composition of the Sudbury Sudbury ores h ore deposits deposits of of the the Sudbury Sudbury Structure Structure (edited (edited by E.G. Pye, A.J. Naldrett Naldrett and and P.E. P.E. Giblin). Giblin). p. 309-325. Ontario Geological Geological Survey, Survey, Special Special Volume 1, p. Naldrett, R.,Asif, Asif, M. M. and and Li Li C. (1994) (1994) Compositional Compositional variation varjiition in the Sudbury Sudbury Naldrett, A.J., A.J., Pessaran, Pessaran,R., of footwall copper-PGE copper-PGE bodies In Proceedings of the ores and prediction of the proximity of 25 �Sudbury Noril'sk Symposium (edited Sudbury -- Norilsk Ontario (edited by by P.C. P.C. Lightfoot Lightfoot and AJ. A.J. Naldrett). Ontario Geological Survey, 143. Geological Survey, Special Special VolumeS, Volume 5,p.p. 133133-143. E.F. (1979) (1979)The TheSudbury SudburySublayer. Sublayer.Canadian Canadian Mineralogist, Mineralogist,v. v. 17, 17, p. Pattison, E.F. Pattison, p. 257-274. 257-274. S.A., Keays, Keays, R.R. R.R. and and Lightfoot, Lightfoot,P.C. P.C. (1997) (1997)Genesis Genesisof ofinclusions inclusionsin in the themineralized mineralized Prevec, S.A., Contact Sublayer,Sudbury Sudbury Igneous Igneous Complex: Sm-Nd Sm-Nd isotopic, isotopic, geochemical geochemicaland and Contact Sublayer, In Geological Geological Association of Canada/Mineralogical petrographic evidence evidence In petrographic Canada/Mineralogical Association of Canada Program Canada Program with Abstracts, Abstracts, v. v. 22. 22. Podolsky, T. T. and and geological geological staff of Inco Limited (1969) The sulphide ores at Souch, B.E., Podoisky, Souch, Sudbury: their particular relation to a distinctive inclusion-bearing facies facies of of the Nickel 4, p. 252-261. Irruptive. Economic Geology, Monograph 4, Recommended references: references: 1. 1. The geology and ore deposits of the Sudbury Structure Structure (edited by by E.G. E.G. Pye, A.J. A.J. Naldrett and P.E. Giblin). Giblin). Ontario Geological Geological Survey, Special Volume 1, 1984. 1984. 2. Proceedings (edited by by P.C. P.C. Lightfoot and and A.J. A.J. Proceedings of the the Sudbury Sudbury - Noril'sk Symposium (edited Naldrett). Ontario 1994. Ontario Geological Geological Survey, Survey, Special Special Volume 5, 1994. 3. Sudbury tour (prepared (prepared by by Gordon Gordon Morrison and Inco Sudbury ore environments surface tour geological staff and Mike Mike Sweeny Sweeny and andFalconbridge Falconbridgegeological geologicalstaff). stam. CIM geological CIM Geological Geological Society, Fourth field trip trip guidebook, guidebook, 35 pp., 1994. Society, Fourth Annual Field Conference, field 1994. 26 �____ 15km W4E Part I Whistle Mine (Figure 2) Whistle Offset Strathcona Fraser s.._Rigure 3) Levack West Mine -. C) Mine — a) -c Offset :- A I Frood-Stobie Offset '7 ..:.. e... r") SIC Main Mass ......................... ...^.$^$ ................. .................... ...... ...... .,:......... :..,.: :....:,: :,:...: ....... ....... .....:.: SIC Main Mass Sublayer norite 0 Sublayer noritediorite Offset quartz Offset quartz diorite Faults Faults A , Sample locations Sample locations Figure1:1: Map Mapof of the the Sudbury SudburyIgneous IgneousComplex Complex(SIC) (SIC)showing showing Sublayer and Offset Figure locations, plus plus excursion excursion stop stop areas areas (modified (modifiedfrom from Lightfoot Lightfoot et Sublayer at., 1997).and Offset locations, et at., 1997). �+++++++ aa — — a a a - aaa a -" a + + + aa LSJ J a a a L L 111ff Ii L Li. ill 11;::: EEJ Leucocrafic noifte alhopyoxene-dch rinite Olvinenorite Tvo pyroxerfe noilte ILfl MDflcNoilte Felsic t'blte Mjln Mass — — Fojit SuW&y &-eccla SCm 0 QJ Qnlzcio,ffe Cet Altered math> UItranc4lc indthlon Fresh macaria IndIcn - +++ ++- < bdIcn mczslvo sulpilde Sudbury Igneous Complex + °° X A ++++ IndLtct Gniltojd rockB Leucocrafic brecda Anof1hc6Ite4roctcMte,tho Dczo hckaris aid ratls ftpilte Gceybmdedgnes FoofclI and indusions +±++++++ +++ c ++ NJ,Cu=60 aa çaa ++++++++ + + + + ++++++ aaaaaaaaa a a aaaaaaaI aaa aI a++++ +++ a a a a a a a a a a a aa a a + + Y+ + — ,Ifr-a a a a +1 aaaaa a aaaaa aaaaaaaa + + ++ u= O.oolf + in Offtef 1- Figure 2: Geology of the Whistle pit, from Lightfoot et al. (1997). Approximate positions of stops are indicated by circled numbers. - a a a aaa aaaaa a a ++++++ ++++ ++++ ++++ +++++++++-ftlfiu=55+ L. ++-EI-++/ct++++y+++ +++ Mapped:1993-94 ++ ++++ +++++++++ + ++++ L -L +++++++++ + + cu<o.1 ++++++ ++++++++++.+++C?) SCHEMA11CANAToM WiSThEEMR'yMENff �___ ___ Strathcona-Longvack area area Strathcona-Longvack GeologicalPlan Plah map map Geological V/ ] Footwall SIC Levack Oneiss Sublayer Diabase IT'1 Fe/sic Norite as r&..a.i SudbuoiBreccia Grid 7' / / // // // // II! / //////// V -'] FootwallBrecc/a 200m //////////////// ////// / / / / / // / / / / / / / / / / ?/// •.••+. /// //////..,..+•• N / Barnet Showing '1 : /// ////// / / ///// /// / aa:asas ////// Aa A . A * . . . . . . . . . . . . . . . £ Asaaasaaaaasaaaaaaaaaaasa ALAS LA Lsaasaasaaaaaassasaaaasaa LLsLaasaaaaaAssaaaLAsLaAsaAa as a a La aLa a aLa Laa s a aa a AL A a AL as a a a a £ Aaaassaaasaaa ALL Laaaaaaaa A Lsssas A La £ As ALL a a LA Las £5 A Las £LLLLAALLSaL AL La AL Las Las LLLALSLLSaL545 Figure 3: Strathcona to Longvack area geolo9ical map, showing mine locations and location of stripped outcrops of the Barnet showing (modified after Morrison and Sweeny, 1994). �Barnet Barnet Showing Showinq Trench Map Sulphides (cpy) (cpy) Suiphides maficlultramafic inclusions inclusions mafic/ultramafic (including plag-phyric plag-phyricdykes) dykes) (including Sudbury Breccia Breccia Sudbury fr,,, I,,,,,, m j Tonalitic gneiss (Levack) gneiss (Levack) d*<*<:v*;;<;;;, 40m 40 m Figure 4: Outcrop Outcropmap mapof of Barnet Barnetshowing, showing, displaying displaying mineralized mineralized Sudbury Sudbury Figure Breccia in in Archean Archean footwall, footwall, modified modified after after Morrison Morrison and and Sweeny Sweeny(1994). (1994). Breccia � https://digitalcollections.lakeheadu.ca/files/original/4afc55d14de13fcdcaa0443badf9ba58.pdf ed2258139e0613bbe04baa280822e4ed PDF Text Text ALKALIC ROCKS ROCKS OF OF THE THESUDBURY SUDBURY REGION REGION BY R. P. P. SAGE SAGE INSTITUTE ON SUPERIOR GEOLOGY INSTITUTE ON LAKE LAKE SUPERIOR GEOLOGY 43rd ANNUAL MEETING, MEETING, MAY 43rd MAY 66 -11, -11, 1997 1997 SUDBURY, ONTARIO ONTARIO Field Trip Part 66 Trip Guidebook, Guidebook, Volume 43: Part �Alkalic Rocks of the Sudhury Sudbury Region Region by R. R. P. P. Sage Sage Precambrian PrecambrianSection Section Ontario OntarioGeological Geological Survey Survey Ministry Ministry of of Northern NorthernDevelopment Development and and Mines Mines 7th 7th floor floor 933 Ramsey Lake Road Road Sudbury, Sudbury, Ontario Ontario P3E 6B5 P3E 6B5 of aa Carbonatite Carbonatite Frontispiece: Frontispiece: Idealized Cross Section of Intrusion(modified Intrusion(modifiedfrom fromSage, Sage,1991) 1991) �ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This This field field trip trip guidebook guidebook would would not not have have been been possible possible without without the the assistance assistance of of Wilf Wilf Meyer, Meyer, Resident Resident Geologist, Geologist, and and Mike Mike Cosec, Cosec, Staff Staff Geologist, Geologist, Ontario Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario. Ontario. Excluding Excluding the the Spanish Spanish River River Carbonatite, Carbonatite, author had no prior exposure manifestations the author exposure to the the many manifestations of of alkaline alkaline magmatism magmatism in in the the region. region. �1 INTRODUCTION INTRODUCTION magmatism within the Sudbury region Alkaline magmatism region manifests itself in many forms forms and in in differing differing structural structural settings(Figures 1 1 and 22). Alkaline magmatism magmatism occurs from settings(Figures ) . Alkaline the middle Proterozoic Proterozoic to to Middle Cambrian Cambrian and and expresses expresses discrete plutons and as metasomatic events itself as discrete as metasomatic events with with no no clearly recognizable recognizable magmatic magmatic phase. phase. The The various various alkaline alkaline features features are are widely widely spaced; spaced; therefore, therefore, all all will will not not be be seen seen on the field field trip. trip. Due Due to to the the wide wide spacing spacing of of the the accessible accessible sites, two sites, two days days will will be be spent spent examining examining the the alkaline alkaline rocks. rocks. alkaline rocks Day one will be spent spent examining alkaline rocks in in the the immediate area immediate area of of Sudbury Sudbury and and will will include include the the Spanish Spanish River River Carbonatite, Carbonatite, Nemag Lake fenites fenites and the French French river river nepheline-cancrinite pegmatites. The Spanish nepheline-cancrinite Spanish River River Carbonatite occurs the Sudbury Carbonatite occurs in in Archean rocks northwest of the Complex(SIC), the Nemag Nemag Lake fenites fenites occur in Igneous Complex(SIC), Supergroup at the deformed rocks rocks of the Huronian Huronian Supergroup the western western end Great Lakes of the Great Lakes Tectonic Zone southwest of Sudbury Sudbury and the French River River alkalic pegmatites occur occur in in a syenite syenite intrusion intrusion within within the the Grenville Grenville structural structural province. province. On On the the day, two second day, two alkaline alkaline intrusions of lower lower to to middle Cambrian age Cambrian age will will be be examined examined in in the the Lake Lake Nipissing Nipissing area area and and a a visit to to the the Scadding Scadding mine is is planned to to examine examine the the effects metasomatism. The effects of regional regional sodium sodium metasomatism. The visit visit to to the the Lake Lake Nipissing Nipissing area area will will require require boat boat transport. transport. �2 * • Mesozoic kimberlite (120-1507 Ma) Mesozoic kimberlrte (120-150? Ma) Mesozoic (90 125 Mat Mesozoic (90-125 Ma) £ Paleozoic (275-570 Ma) Paleazoic (275-570 Ma) • Prolerozcuc (570 2500 ~ a ) Proterozajc (570-2500 Ma) • Archean (2500 Ma) Archean (2500 Ma) K K * * * @ Cr~ptoexplosionstructures Cryptoexpiosron Structures Fault Zone Phanerczojc and Precambrian boundary Sporosimute timri of rate Precambrian supracrustar racks Parts ol St. Lawrence Graben System affec1ed by Phanerozoic faulting and recent earthquakes Midconrinenm Rrfm System Unknown age Unknown age Figure 1: Regional distribution of alkalic rock-carbonatite Figure 1: Regional distribution of western complexes in eastern Ontario and Figure alkalic Quebec. rock- carbonatite complexes in eastern ( 1 9 7 8 ) and western Sage ( 1 9 9 Quebec. 1) . modified from Lumbers Ontario Figure modified from Lumbers(l978) and Sage(lg9l). �G.ology 505111.5 PRQVINCE SUPERIOR PROVINCE - - North.,0 All.',. Map. 2197 •nd 2393 PROVINCE - sodium metasornatism) Crater; - - . - - - - - Figure 2: Distribution of alkali0 rock-carbonatite complexes in the Sudbury region. Modified from Sage(l99l) Brent 3 Callander Bay Alkalic Rock Complex; 4 (2- Manitou Island Alkalic Rock Complex; 5 Burritt Island Alkalic Rock Complex; 6 Iron Island Alkali0 Rock Complex; 7 Carbonatite; S Spanish River Carbonatite; 45 NemagLavergne iKusk Lake Fenites; 46 Allen Lake Carbonatite; 52 and Sullivan Island Carbonatite complex; A French River (Rotter Pluto0j Alkalic Rock Complex and B Scadding mine area of rem OntarIo O.plrtm.n t or Ml COBALT EMBAYMENT GREENSTONE BELTS NEOARCHEAN SUDBLJRy IGNEOUS COMPLEX DOMINANTLY METASEDIMENTS PALEOPROTEROZOIC DOMINANTLY METASEDIMENTS GRANITIC ROCKS M E SO PR 01 EROZO IC All *9•• CARBONATITE AND RELATED ROCKS LEGEND �4 SITES SITES TO TO BE BE VISITED VISITED DAY DAY 11 1. ISLAND COMPLEX 1. MANITOIJ MANITOU ISLAND COMPLEX 2. 2. CALLANDER BAY BAY COMPLEX COMPLEX 3. 3 .SCADDING SCADDINGMINE MINE DAY DAY 22 4. 4 . SPANISH SPANISHRIVER RIVERCARBONATITE CARBONATITE 5. 5 .NEMAG NEMAG LAKE LAKE AND AND KUSK KUSK LANE LANE FENITES FENITES 6. 6.FRENCH FRENCHRIVER RIVERALKALIC ALKALICROCKS ROCKS �FIGURES FIGURES Figure Figure 1: 1: Regional Regional distribution distributionof ofalkalic alkalicrocJc—carbonatite rock-carbonatite complexes complexes in in eastern eastern Ontario Ontario and and western western Quebec. Quebec. Figure Figure modified modified from from Lumbers(1978) Lumbers (1978)and and Sage(l991). Sage (1991). Figure Figure 2: 2: Distribution Distribution of of alkalic alkalic rock-carbonatite rock-carbonatitecomplexes complexes in in the the Sudbury Sudbury region. region. Modified Modified from from Sage(l99l). Sage(1991). (2 (2 -- Brent Brent Crater; Crater; 33 -- Callander Callander Bay Bay Alkalic Alkalic Rock Rock Complex; Complex; 44 -- Manitou Manitou Island Island Alkalic Alkalic Rock Rock Complex; Complex; 55 -- Burritt Burritt Island Island Alkalic Alkalic Rock Rock Complex; Complex; 66 -- Iron Iron Island Island Alkalic Rock Rock Complex; Complex; 77 -- Lavergne Lavergne Carbonatite; Carbonatite; 88 -- Spanish Spanish River River Carbonatite; Carbonatite; 45 45 Nemag Nemag and and Kusk Kusk Lake Lake Fenites; Fenites; 46 46 -- Allen Allen Lake Lake Carbonatite; Carbonatite; 52 52 -Sullivan Sullivan Island Island Carbonatite Carbonatite complex; complex; AA -- French French River River[Rutter [Rutter Pluton] Plutonl Alkalic Alkalic Rock Rock Complex Complex and and BB -- Scadding Scadding mine mine area area of of sodium sodium metasomatism) metasomatism) Figure Figure 3: 3: Geology Geology of of the the Manitou Island Island Complex(from Complex(from Lumbers, Lumbers, 1971, 1971,p. p. 82) 82). Figure 4: Aeromagnetic Aeromagnetic map map of of the the Manitou Manitou Island Island Figure 4: complex(from complex(from ODM-GSC ODM-GSC1965c) 1965c) Figure Figure 5: 5: Geology Geology of of the the Callander Callander Bay Bay Complex(from Cornplex(fromLumbers, Lumbers, 1971, 1971, p.84). p.84). Figure 6: 6: Aeromagnetic Aeromagnetic map map of of the the Callander Callander Bay Bay Complex(from Complex(from Figure ODM-GSC ODM-GSCl965a,b). l966a,b) . Figure Figure 7: 7: Topographic Topographic and and road road map map for for the the Callander Callander Bay Bay area(from topographic topographic maps maps obtained obtained from from the the Resident Resident area(from Geologist's Office, Office, Ontario Ontario Geological Geological Survey, Survey,Sudbury) Sudbury) Geologist's Figure 8: 8: Geological Geological sketch sketch map map of of the the Scadding Scadding Gold Gold Figure Mine (modified after Mine (modified after Harper, Harper, 1983) 1983) . Figure Figure 9: 9: Topographic Topographic and and road road map map for for the the Scadding Scadding Gold Gold Mine area(from area(from topographic topographic maps maps obtained obtained from from the the Resident Resident Mine Geologist's Geologist's Office, Office,Ontario Ontario Geological Geological Survey, Survey,Sudbury). Sudbury). Figure Figure 10: 10: Aeromagnetic Aerornagnetic map map of of the the Spanish Spanish River River Carbonatite(from Carbonatite(from ODM-GSC ODM-GSCl965d). 1965d). �7 DAY DAY 11 MIDDLE MIDDLE TO TO EARLY EARLY CAMBRIAN CAMBRIAN ALKALIC ALKALIC INTRUSIONS, INTRUSIONS, LAKE LAKE NIPISSING NIPISSING AREA AREA Introduction Introduction Within Within the the Lake Lake Nipissing Nipissing area area there there are are 77 alkalic alkalic rock rock intrusions intrusions into into the the gneissic gneissic rocks rocks of of the the Grenville Grenville Subprovince Subprovince of of the the Canadian Canadian Shield Shield or or areas areas of of extensive extensive alkalic alkalic metasomatism(Sage, metasomatism(Sage, 1991) 1991). These These are are Brent Brent Crater, Crater, Callander Callander Bay, Bay, Manitou Manitou Island, Island, Burritt Burritt Island, Island,Iron IronIsland, Island, Lavergne Lavergne and and Allen Allen Lake. Lake. These These alkalic alkalic rock rock complexes complexes occur occur where where the the Ottawa-Bonnechere Ottawa-BonnechereGraben Graben splits splits into into an an east-west east-west trending trending deformation deformation zone zone and and the the northwest northwest trending trending Lake Lake Timiskaming The Ottawa-Bonnechere Ottawa-Bonnechere Timiskaming Structural Structural Zone(LTSZ) Zone(LTSZ) . The Graben Graben system system is is aa branch branch of of the the St. St. Lawrence Lawrence valley valley system system which which Kumarapeli Kumarapeli and and Saull(l966) Saull(1966) compare compare to to the the East East African African rift rift valley valley system. system. Existing Existing isotopic isotopic dating dating of of the the alkalic alkalic rocks rocks of of the the Lake Lake Nipissing Nipissing area area indicates indicates that that these these alkalic alkalic intrusions intrusions were were emplaced emplaced during during the the middle middle to to early early Cambrian. Cambrian. Lying Lying to to the the east east of of this this east-west east-weststriking striking cluster cluster of of intrusions intrusions is is the the Proterozoic Proterozoic Sullivan Sullivan Island Island Carbonatite Carbonatite intruded intruded into into the the Ottawa-Bonnechere Ottawa-Bonnechere Graben(Luinbers et al., al., 1990). The GrabentLumbers et The Ottawa-Bonnechere Ottawa-BonnechereGraben Graben system system was was most most likely likely in in existence existence during during the the Proterozoic Proterozoic and and has has been been periodically periodically reactivated reactivated throughout throughout geologic geologic history(Sage, history(Sage,1996) 1996). The The St. St. Lawrence Lawrence rift rift system system and and its its many many branches branches are are seismically seismically active active to to this this day(Adams day(Adams and and Basham, Basham, 1986; 1986; Bent, Bent, 1992, 1992,1996) 1996). . . Table 1: Summary Summary of of Alkalic Alkalic Rock Rock geochronological geochronologicaldata data for for Table 1: the the Lake Lake Nipissing Nipissing area area Intrusion Intrusion Age (MA) Age(MA) Method Method Reference Reference Manitou Manitou Island1 1sland1 560 570 560 568 566 +- 38 576 +- 45 K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar 558 ÷ 14 K-Ar K-Ar K-Ar K -Ar K-Ar K-Ar 1 1 2 3 4 4 Caliander Callander Bay2 ~a~~ 568 575 5 3 3 �8 576 ÷- 3 Pb-Pb 6,4 Brent Crater Crater 40 576 576 ++ - 40 K-Ar KAr 7 7 Footnotes Footnotes ages cited 4 are the same same as as references references 1. The ages cited by reference reference 4 1 and 2 using using different different decay decay constants. constants. 2. Except for for the the 575 575 Ma Ma age age on on nepheline nepheline syenite syenite the the cited cited isotopic ages ages are are on on lamprophyre lamprophyre dikes dikes interpreted interpreted to to be be isotopic related to to the the Callander Callander Bay Complex Complex References References 1. 2. 3. 3. 4. 5. 6. 7. Gittins et Gittins et al., al., 1967 1967 Lowden et Lowden et al., al., 1963 1963 Currie, 1976 Currie, 1976 Symons and Symons and Chiasson, Chiasson, 1991 1991 Ferguson and Ferguson and Currie, Currie, 1972 1972 Kamo et et al., al., 1989 1989 Shafiqullah et Shafiqullah et al., al., 1968 1968 The only only regional regional mapping mapping in in which which most of of the the intrusions intrusions were were examined examined was was by by Lumbers(1971). Lumbers(1971). Currie(l976) Currie(1976) prepared prepared aa brief description description of of each each of of the the occurrences occurrences in in an an abstract abstract format format but has has restricted restricted most of of his his field field investigations investigations to the Callander Callander Bay Bay complex. complex. Extensive sampling sampling for for paleomagnetic studies Symons, paleomagnetic studieshas has been beencompleted completedbybyID. D . Symons, University of University of Windsor, Windsor, on on the the Callander Callander Bay, Bay, Manitou Manitou Island Island and Iron Iron Island Island Complexes, Complexes, however however only only the the work work on on the the Callander Callander Bay Bay complex complex has has been been completed(Symons completed(Symons and and Chiasson, Chiasson, 1991) 1991). STOP STOP 1: 1: Manitou Manitou Island Island Complex Complex I I I The The Manitou Manitou Island Island complex complex lies lies in in the the east east central central portion portion Lake Nipissing of Lake Nipissing and and is is only only accessible accessible by by boat. boat. Road Log Log Proceed 112.9 km east east along along highway highway 17 17 measured measured from from the the intersection of highway intersection highway 17 17 and and the the by-pass by-pass south south of of Sudbury. Sudbury I 1 At intersection intersection with with highway highway 17B 17B in in North North Bay Bay turn turn right. right. I Go (Note: If Go 4.1 4.1 km km to to Memorial Memorial Street Street and and turn turnright. right.(Note: If you you turn turn left left you you will will be be on on Murray Murray Street) Street) �Go Go 0.6 0.6 km krn to to parking parking lot lot at at boat boat landing. landing. Travel Travel time time by by boat boat to to Newman Newman Island Island is is approximately approximately45 45 minutes minutes and and distance distanceis isapproximately approximately1010kin km or or 66 miles. miles. Geology: Geoloqv: The The Manitou Manitou Island Island Complex Complex is is outlined outlined by by aa circular islands consisting consisting of of fenitic fenitic circular distribution distribution of of 55 islands rocks. rocks. The The actual actual intrusion intrusion located located central central to to the the islands islands is is unexposed. unexposed. The The site site to to be be visited visited is is located located on on Newman Newman Island Island where where exploration exploration for for uraniferous uraniferous pyrochlore pyrochlore took took place place in in the the late late l9SOs. 1950s. Most Most of of these these islands islands are are now now included included in in the the Manitou Manitou Islands Islands Provincial Provincial Park Park even even though though the the mineral mineral rights rights are are retained retained by by the the mining mining company. company. Lumbers(197l) Lumbers(1971) describes describes the the fenite fenite aureole aureole as as consisting consisting of of an an outer outer zone zone of of quartz quartz fenite fenite approximately approximately 400 400 feet feet wide wide and and an an inner inner aureole aureole of of aegirine-potassic aegirine-potassicfeldspar feldsparfenite feniteas as much much as as 1,500 1,500 feet feet wide. wide. These These fenites fenites have have been been derived derived from from Grenville Grenville granitic granitic gneisses. gneisses. The The central central portion portion of of the the complex complex is is poorly poorly known known from from scattered scattered diamond diamond drill drill holes. holes. Lumbers(l97l) Lumbers(1971) states states that that the the west west central central portion portion of of the the complex complex consists consists of of massive massive coarse-grained coarse-grainedto to pegmatitic pegmatitic pyroxene-rich pyroxene-richrocks rocks younger younger than than the the enclosing enclosing fenites. fenites. The The carbonatite carbonatite occurs occurs as as fine fine to to coarse coarse grained grained dike-like dike-like intrusions intrusions into into the the fenites fenites and and consists consists of of aegirine, aegirine,sodic sodic amphibole, amphibole, biotite, biotite, magnetite, magnetite, apatite apatite and and locally locally pyrochlore pyrochlore and and pyrite pyrite in in addition additionto to carbonate. carbonate. On On the the west west side side of of Little Little Manitou Manitou Island, Island,located locatednorthwest northwest of of Newman Newman Island, Island, fossiliferous fossiliferouslower lower Ordovician Ordovician limestone limestone is is exposed exposed on on the the shoreline. shoreline. Attempts Attempts to to make make cement cement from from this this material material were were made made in in the the early early days days of of settlement settlement in in the the region. region. Figure Figure 33 presents presents the the geology geology of of the the Manitou Manitou Island Island Complex(Lumbers, illustrates the the airborne airborne Complex(Lumbers,1971) 1971) and and Figure Figure 44 illustrates magnetic magnetic response response of of the the intrusion(ODM-GSC, intrusion(0DM-GSC,l965a,b). 1965a,b). The The complex complex is is approximately approximately 22 miles miles long long and and 1.7 1.7 miles miles wide(Lumbers, wide (Lumbers,1971) 1971) . Economic Economic Geology: Geoloqv: Upon Upon discovery discovery of of pyrochlore pyrochlore and and uraniferous uraniferous pyrochiore pyrochloreon onNewman Newman Island Islandin inthe theearly early1950's, 19501s, testing verticalshaft shaft442 442 testing of of the the discovery discovery took took place. place. AA vertical feet feet deep deep was was sunk sunk on on Newman Newman Island Island and and 2,500 2,500feet feetof of lateral lateral drifting drifting completed(Lumbers, completed(Lumbers, 1971). 1971). This This work work outlined U303 and and 0.69% O.69 outlined 2,962,000 2,962,000tons tons averaging averaging 0.04fl 0.041% U3O8 Nb205 Nb205 all all 200 200 feet feet below below lake lakebottom(Lumbers, bottom(Lumbers,1971) 1971). The The . �10 0 0r;ft.covered areas; no subsurface data available. @ Mddle Ordovhian sedimentary rocks, . a Umi.3n PYrochlore-bearing rocks. Mahly altered feldspathic rocks. C and alkalic Mafic ~ Wsyenite Pyroxenrte. Aegirfne-potassic feldspar fe Wining minor carbonatite in a a Quart.?fenite. Geological boundary, (defined. assumed). Fautt. lsomagnetic lines. Shaft. Scale in feet !m 0 , 2 y O.D.M. €4 Figute Figure 3: 3: Geology Geology of of the the Manitou Manitou Island Island Complex(from Complex(from Lumbers, 1971, p. 82) Lumbers, 1971, p. 8 2 ) . �I I I I t - A— -k 1 1mIle mile Figure Figure4: 4: Aeromagnetic Aeromagneticmap mapof ofthe theManitou ManitouIsland Island ODM-GSC1965c) 1965~) complex~£ro complex(from ODM-GSC �12 pyrochlore mineralization mineralization occurs occurs with with fenitic Eenitic rocks rocks and and pyrochiore carbonatite. carbonatite. Newman Newman Island: Island: On On the the inner inner or or north north side side of of Newman Newman island island brecciated, brecciated, red, red, syenitic syenitic fenite fenite is is exposed exposed along along the the lakeshore. veined and lakeshore. At the the shaft, shaft, blocks of fenite Eenite veined and cemented cemented with with white white carbonate carbonate can can be observed. observed. Along Along the the shoreline shoreline an an occasional, occasional, narrow, narrow, yellow-brown, yellow-brown,fine-grafted fine-grained carbonate carbonate dike dike can can be be observed observed cutting cutting the the fenite fenite and and white white carbonate. carbonate. Towards Towards the the east east end end of of the the island island and and to to the the south south side side gneissic gneissic textures textures are are well preserved preserved and and the the rocks rocks take take on on the the appearance appearance of of Grenville Grenville gneisses. gneisses. The The general general gneissic gneissic trend trend is is 260 260 degrees degrees with with aa steep steep north north dip. dip. Locally Locally these these gneisses gneisses may may appear appear brecciated brecciated and and are are irregular white white carbonatite carbonatite dikes dikes and and on on occasion occasion by cut by irregular younger, younger, very very narrow, narrow, fine-grafted, fine-grained,brown brown carbonatite carbonatite dikes. dikes. Return Return to to the the boat boat landing. landing. STOP Bay Complex Complex STOP 2: 2: Callander Callander Bay The The Callander Callander Bay Bay Complex Complex lies lies at at the the eastern eastern end end of of Lake Lake Nipissing Nipissing and and most most of of the the complex complex lies lies beneath beneath the the water water of of Callander Callander Bay. Bay. Road Road Log Log to highway highway 17 17 and and zero zero the the odometer odometer Return to Return Proceed Proceed eastward 7.8 km km to to where where highway highway 11 11 splits splits from from eastward 7.8 highway highway 17. 17. Take Take highway highway 11 11 to to the the town town of of Callander. Callander. At 13.2 13.2 km km take take the the exit exit to to the the town town of of Callander. Callander. The The road road goes qoes right right and and then then jogs jogs left. left. km turn turn left left on on Pinewood Pinewood Drive Drive and and go go south south towards towards 13.7 km At 13.7 Callander(4 Callander ( 4 km). km). At the highway highway splits. Take highway 94 At 17.2 17.2 1cm km the 94 to to the the left left and and continue continue south. south. At 19.1 19.1 km k m Landsdowne Landsdome St. St. intersects intersects the the highway. highway �Zero the odometer Zero odometer at at Landsdowne Landsdowne St. St. and and continue continue on. on. km Main Main St. St. intersects intersects the the highway. highway. Park Park at at the the side side At 1.65 1.65 km of the the road road for for Stop Stop 2A. 2A. Geology: Geoloqy: As As with with the the Manitou Manitou Island Island Complex, Complex, the the Callander Callander Bay Complex Complex is is poorly poorly exposed exposed and and largely largely lies lies beneath beneath the the waters of Lake Lake Nipissing. Most exposures are of fenite fenite border border rocks rocks with with only only aa limited limited number number of of exposures exposures of nepheline nepheline syenite syenite towards towards the the centre centre of of the the complex. complex. Nearly all of the the exposures exposures of of nepheline nepheline syenite syenite are are on on private private property property and and not not easy easy to to access. access. Lumbers(l971) Lumbers(l971) interpreted interpreted the the Callander Callander Bay Bay complex complex to to be be approximately approximately 2.25 2.25 miles miles in in diameter diameter and and to to consist consist of of cone cone sheets of (Figures 5, sheets of fenite fenite and and nepheline nephelinesyenite syenite(Figures 5, 6) 6). Lumbers(1971) Lumbers(l971) predicts the the centre centre of the the intrusion intrusion may consist of carbonate-rich consist carbonate-richrocks rocks and and alkalic alkalic mafic mafic rocks. rocks. Lamprophyre, basaltic Lamprophyre, basaltic and and phonolitic phonolitic dikes dikes cut cut across across rocks rocks of the the fenite fenite zone zone and and these these are are in in turn turn cut cut by by barite barite and and calcite veIns calcite veins(Lurnbers,l971) (Lumbers,1971) . Currie(l976) Currie (1976) has has also also interpreted interpreted the the Callander Callander Bay Bay Complex Complex to to consist consist of of cone cone sheets sheets of of fenite fenite and and alkalic alkalic rocks rocks enclosed enclosed in in aa crescentic crescentic zone of nepheline zone nepheline syenite. syenite. The The fenitic fenitic rocks rocks were were observed observed by Currie(l976) Currie(l976) to to be be cut cut by by dikes dikes of of carbonatite, carbonatite, lamprophyre, trachyte lamprophyre, trachyte and and nepheline nepheline syenite. syenite. The The alkalic alkalic dikes dikes intruding intruding the the fenitic fenitic rocks rocks are are considered considered coeval coeval with with Callander Bay the Callander Bay complex complex and and have have been been the the most most intensely intensely studied studied rock rock group group within within the the complex. complex. . The fenitic fenitic rocks rocks are are derived derived from from Grenville Grenville gneissic gneissic rocks rocks adamellite(granitic) composition composition and and form form aa zone zone up up to to of adamellite(granitic) 1000 1000 m wide wide along along the the eastern eastern margin margin of of the the complex complex where where are well they are well exposed(Currie exposed(Currie and and Ferguson, Ferguson, 1971, 1971, 1972). 1972). Currie and Ferguson(1971) Currie F'erguson(l971) subdivide subdivide this this metasomatic metasomatic halo halo enclosing the enclosing the Callander Callander Bay Bay Complex Complex into into inner, inner, middle middle and and outer zones. outer zones. The The inner inner zone zone is is characterized characterized by by aa loss loss of of gneissosity, igneous igneous textures and miarolitic cavities cavities and the outer outer zone zone is is characterized characterized by by regional regional gneissosity, gneissosity, reddening of the the rock, rock, hematized fractures fractures and rare brecciation(Currie and Ferguson, Ferguson, 1971). 1971). The The middle zone is is brecciation(Currie and middle zone transitional between transitional between the the outer outer and and inner inner zones. zones. The The alkalic alkalic dikes were studied studied by Ferguson Ferguson and Currie(l971) and interpreted by them interpreted them to to have have formed formed by by liquid liquid immiscibility. immiscibility. the basis basis of of the the studies studies on on the the dikes dikes the the Callander Callander Bay Bay On the ,complex has has been been interpreted interpreted to to result result from from aa carbonated, carbonated, mantle-derived, magma(Fergus0n and and Currie, Currie, mantle-derived,nephelinitic nephelinitic magma(Ferguson 1971, 1972) 1971, 1972). The The fenitic fenitic rocks rocks were derived derived by fluids fluids emanating from from the the fractionating fractionating nephelinitic nephelinitic magma magma which which . �Figure 5: Geology of the Callander Bay Complex(from Lumbers, 1971, p.84). 4:- �ODMGSC1965ab) Figure 6: Aeromagnetic map of the Caflander Bay Complex(from 1 mile �16 underwent underwent liquid liquid immiscibility immiscibility in in its its late late stages stages giving giving rise rise to to aa carbonate carbonate magma(Ferguson magma(Ferguson and and Currie, Currie, 1971, 1971,1972; 1972; Cullers Cullers and and Medaris, Medaris, 1977). 1977). Since Since the the Callander Callander Bay Bay Complex Complex is is of of middle middle to to lower lower Cambrian Cambrian age age and and untilted, untilted, it it has has been been the the subject subject of of recent recent studies paleomagnetism(Chiasson, 1989; 1989; Symons Symons and and studies in in paleomagnetism(Chiasson, Chiasson, Chiasson, 1991) 1991). Economic Economic Geology: Geolocrv: The The Callander Callander Bay Bay Complex Complex has has undergone undergone prospecting prospecting and and some some diamond diamond drilling. drilling. While While anomalous anomalous niobium niobium values values have have been been encountered encountered nothing nothing of of potential potential economic economic interest interest has has been been identified identified to to date. date. STOP STOP 2A: 2A: Stop Stop 2A 2A is is located located within within the the inner inner to to middle middle fenite fenite zone(Figure zone(Figure7) 7). Numerous Numerous alkalic alkalic dikes dikes cut cut the the fenites the ont h e east east side side fenites and and can can be be observed observed in in the the road road cut cut on of highway. One of the the.highway. One should should observe observe the the diverse diverse rock rock textures textures within within the the fenites fenites and and the the variety variety of of dike dike rocks rocks available available to to study. study. . STOP STOP 2B: 2B: Continue Continue south south from from Stop Stop 2A 2A for for 2.3 2.3 km. km. AA scenic scenic lookout lookout occurs occurs on on the the right right hand hand side side of of the the road road and and provides provides aa good good parking parking spot. spot. Opposite Opposite the the lookout lookout is is an an outcrop outcrop of of granitic granitic gneiss gneiss intruded intruded by by biotite biotite porphyry porphyry mm and and the the lamprophyre. The The biotite biotite phenocrysts phenocrysts are are up up to to 44 mm lamprophyre. dike dike trends trends 010 010 degrees degrees and and dips dips approximately approximately 45 45 degrees degrees east. east. The The dike dike may may be be up up to to 55 metres metres in in width width and and is is one one of of the the widest widest dikes dikes observed observed in in the the road road cuts. cuts. The The outcrop outcrop shows shows many many sample sample sites sites and and it it is is obvious obvious that that it it has has served served as as aa source source of of material material for for aa number number of of studies studies on on dike dike rocks rocks in in the the area. area. Continue Continue south south along along the the east east side side of of the the highway highway for for approximately approximately 760 760 feet feet and and aa small small point point outcrop outcrop of of nepheline nepheline syenite syenite can can be be found. found. Contact Contact relations relations are are not not exposed exposed but but this this is is likely likely one one of of the the nepheline nepheline syenite syenite cones cones sheets sheets of of Lumbers(1971). Lumbers (1971). STOP STOP 2C: 2C: Return Return to to the the junction junction of of Main Main Street Street and and highway highway 94 (Stop 2A) 2A) and and turn left onto Main Street 94(Stop Street towards towards the the town town of km and and on on the theright rightside(east) side(east) of Callander. Callander. Proceed Proceed for for 1.8 1.8 km of of Main Main street street an an outcrop outcrop of of medium medium to to coarse coarsegrained, grained, massive, massive, equigranular equigranular nepheline nepheline syenite syenite can can be be found. found. This This is is one one of of the the very very few few outcrops outcrops of of this this rock rock type type that that is is currently currently accessible accessible to to sampling. sampling. To To avoid avoid problems problems with with flying flying rock rock chips chips since since this this is is aa highly highly travelled travelled street street II would would strongly strongly recommend recommend collecting collectingthe thesamples samplesyou youwish, wish, �N CD CD C Hi 0Q H o Ofl C) 1-"-'- HI MI Figure 7: Topographic and road map for the Callander Bay area(from topographic maps obtained from the Resident Geologist's Office, Ontario Geological Survey, Sudbury) !( \ di e - - \ 1"'tH ('- - -. - -f ''L- ) I ,WH(iN - _\ ?'Y ,i, C) rtc LIa' V Fr - I / 7 / I - -; 'Q r L —-'t' --,-- :- — \7: y, —JTh' —--'' / tH2-1 >' vtca4>'..7— ,J çX4''" H /1 �18 and and we will transport transport them them to to another another site site for for trimming trimming and and selection. selection. A thin thin section section prepared prepared from from aa sample sample collected collected of of this this coarse grained grained inequigranular inequigranular seriate senate outcrop displayed aa coarse allotriomorphic texture allotriomorphic texture with lobate lobate to to serrate serrate grain grain boundaries. boundaries. The The potassium potassium feldspar feldspar is is aa string string perthite perthite that that sometimes displays sometimes displays Carlsbad twining. The The nepheline nepheline is is fresh fresh . with sericite with sericite alteration alteration along along grain grain boundaries boundaries and and cleavage cleavage planes. ic mineral mineral is is aa dark dark greenish greenish brown brown amphibole planes. The The mat mafic amphibole appears interstitial that appears interstitial to the feldspar feldspar and and nepheline. One One possible grain possible grain of of clinopyroxene clinopyroxene was was noted noted that that was was mantled mantled with amphibole. amphibole. Biotite, Biotite, sphene, sphene, apatite apatite and and chlorite chlorite are are present as as accessory accessory or or alteration alteration phases. The The rock rock is is visually visually estimated estimated to to consist consist of of 10 10 to to 15% 15% amphibole, amphibole, 45 45 to to potassium feldspar 55% potassium feldspar and and 35 35 to to 45% 45% nepheline. nepheline. Return to Return to Sudbury Sudbury ALKALIC ROCKS OF THE ALKALIC ROCKS THE IMMEDIATE IMMEDIATESUDBURY SUDBURY REGION REGION Within the the immediate area of of Sudbury Sudburythere there are are three Within immediate area three distinct alkaline events which are not likely distinct alkaline likely coeval. coeval. The The events events are are represented represented by by the the Spanish Spanish River River carbonatite, carbonatite, regional regional sodium sodium metasomatism metasomatism and and the the development development of of the the Nemag Lake Lake and and Kusk Kusk Lake Lake fenites. fenites. The The age age relationships relationships of of these three three events events remains remains speculative speculative since since only only one one feature feature has been been accurately accurately dated, dated, one one has has been been dated dated in in aa general fashion fashion and and no no attempt attempt to to age age the the third third has has been been undertaken. undertaken. The The existing existing isotopic isotopic studies studies suggest suggest these these alkalic alkalic rocks rocks are are of of middle middle Proterozoic Proterozoic age. age. STOP STOP 3: Scadding Scadding Mine NOTE: THIS THIS SITE SITE WILL WILL LIKELY LIKELY BE BE VISITED VISITED ON ON THE THE RETURN RETURN TRIP TRIP FROM BAY FROM NORTH NORTH BAY Road log log from from the the intersection intersection of highway highway 17 17 and and the the by-pass by-pass around Sudbury Sudbury near near the the town town of of Coniston. Coniston. from the the bypass along along highway highway 17 17 to to Proceed 19.7 km east from Kukagami t(north). Kukagami Road. Road. Turn Turnlet left (north). �11 16.8 north along along the the Kukagami Kukagami Road Road there there is is aa skid skid road road 16.8 km km north or or overgrown overgrown road road to to the the left(west) left(west) . Turn left left and go 0.6 0.6 km km to the Scadding Scadding Mine Site Geology: Sodium Geoloqy: Sodium metasomatism metasomatism is is common common within within the the Sudbury region region but has has been been poorly poorly documented documented and and has has been been the the subject of only subject only one one serious serious attempt attempt to to interpret interpret the the phenomenon. Sodium phenomenon. Sodium metasomatism metasomatism is is characterized characterized by by the the development development of of albite albite feldspar feldspar which which imparts imparts aa tan, tan, pink, pink, buff, grey, buff, grey, white white to to yellow yellow color color to to the the rocks. rocks. Occurrences Occurrences of sodium sodium metasomatism metasomatism are are found found as as far far east east as as Cobalt Cobalt and and as as far far west west as as Bruce Bruce mines, mines, aa distance distance of of approximately approximately 400 400 km(Meyer, 1995) km(Meyer, 1995). Occurrences of of sodium sodium metasomatism metasomatism are are perhaps best developed developed between Espanola Espanola and the area immediately immediately east east of of Lake Lake Wanapitei(Meyer, Wanapitei(Meyer, 1995). 1995).Meyer(1995) Meyer(1995) reports reports that that the the sodium sodium metasomatism metasomatism affects affects the the Proterozoic Proterozoic rocks more than rocks than the the Archean rocks. rocks. The effects of sodium metasomatism metasomatism varies varies from from incipient incipient to to nearly nearly 100 100 percent albite replacement albite replacement with sodium sodium contents of some some altered rocks approaching approaching 11.0% Na20 indicating rocks 11.0% Na2O indicating a rock of nearly pure pure albite albite composition. composition. Meyer(1995) Meyer(1995) describes describes the the effects effects of of sodium sodiummetasomatistu metasomatism as as occurring in occurring in vein-like vein-like or or dike-like dike-like features features up up to to several several kilometres kilometres in in length length associated associated with with faults faults or or fractures fractures and and as irregular irregular shaped shaped masses. masses. The The extensively extensively altered altered rock rock can can easily easily be mistaken mistaken for for chert chert due due to to the the development development of of aa conchodial conchodial fracture fracture and and very fine-grained fine-grainednature nature and and can can be be missed in in outcrop outcrop if if color contrast color contrast is is absent(Meyer, absent(Meyer, 1995). 1995). The The tan tan to to pink pink color color of sodium metasomatism(a1bitization)blends blends into into or or with with the the sodium metasomatism(albitization) normal normal colors colors of of arkoses arkoses and and granites. granites. Within the Within the Sudbury Sudbury region region breccias breccias are are of of common common occurrence. occurrence. With respect respect to to sodium sodium metasomatism metasomatism three three breccia breccia types types have have been recognized recognized by by Meyer(1995) Meyer(1995). These are 1) 1) in-situ in-situ These are brecciation brecciation of of metasomatically metasomatically altered altered rock, rock, 2) 2) metasomatic metasomatic alteration of alteration of aa pre-existing pre-existing breccia breccia and and 3) 3) breccias breccias that that contain contain fragments fragments of of altered altered rock rock mixed mixed with with fragments fragments of of other other rock rock types. types. . When is associated associated with with other other alteration When sodium sodium metasornatism metasomatism is alteration events it is is always always the the earliest, earliest, followed followed by by carbonate, carbonate, quartz, quartz, chlorite chlorite and and possibly possibly the the introduction introduction of of Fe, Fe, As, As, Cu Cu Schandl et suiphides and sulphides and gold(Meyer, goldtMeyer, 1995) 1995). Schandl et al., al., (1994) (1994) have have completed the only detailed study on the sodium sodium metasomatism within the the region. region. Two Two generations generations of of hydrothermal hydrothermal REE . I �20 minerals were minerals were identified identified in in albitized albitized Huronian Huronian sediments. sediments. The minerals found The minerals found were were monazite, monazite, bastnasite, bastnasite, synchysite synchysite and and gadolinite. An An U-Pb U-Pb isotopic isotopic age age of of 1700 1700 ÷+ - 22 Ma Ma was was gadolinite. obtained on obtained on hydrothermal hydrothermal monazite monazite and and on on hydrothermal hydrothermal rutile(Schandl rutile (Schandl et et al., al., 1994). 1994) . The very high high light light REE enrichment enrichment within within the the albitized albitized rocks rocks prompted prompted Schandl Schandl at et al., al., (1994) the (1994) to to propose propose that the sodium-rich sodium-rich fluids fluids were derived from from a carbonatitic carbonatitic or or alkali intrusion approximately alkali intrusion at depth. depth. The The isotopic isotopic age is approximately Ma younger younger than 150 Ma than the the formation formation of of the the Sudbury Sudbury Igneous Igneous Complex(SIC) that Complex(S1C) that was was emplaced emplaced at at approximately approximately 1850 1850 Ma(Krogh Ma(Krogh at et al., al., 1984; 1984; 1996). 1996). Geoloqy Mapping Napping of the mineral occurrences east of Economic Geoloqv Lake Wanapitei by by Gates(l991) Gates(1991) has has shown shown most most mineral mineral occurrences in occurrences in the area display associated sodium metasomatism. Gates(1991) metasomatism. Gates(1991) proposed that that the the sodium sodium metasomatism has which upon metasomatism has developed developed a hard brittle rock which upon fracturing produced channelways fracturing channelways for for the the introduction introduction of of chlorite, gold chlorite, gold and and sulphide sulphide minerals. minerals. Scadding Mine(go1d) Mine(gold) is The Scadding is one of of two small mines in in the the region that display display associated associated sodium sodium metasomatism, region metasomatism, the other being the Norstar gold-copper Scadding Mine other gold-copper mine. The Scadding extracted gold from extracted from four four chlorite zones zones containing pyrite arsenopyrite within within the the Serpent Serpent Formation Formation arkose arkose near near and arsenopyrite the contact contact with with Espanola Espanola Formation Formation limestones(Gates, limestones(Gates, 1991). 1991). The The chlorite chlorite zones zones are are within within carbonate-rich, carbonate-rich, argillaceous argillaceous siltstones near the base of the Serpent Formation. The zones zones are described as as breccias(Gates, breccias(Gates, 1991) 1991) and the east-west east-west 100-300 metres in zone had an approximate dimension of 100-300 length and 30-50 30-50 metres in in width. width. The other other zones zones were much length smaller(Meyer, smaller(Meyer, 1996, 1996, Resident Geologist, Geologist, Sudbury, Sudbury, personal communication) communication). At the the site site of of the the Scadding Scadding mine, mine, samples samples of the the metasomatized Serpent Formation Formation are are abundant abundant and and large large metasomatized Serpent blocks of altered altered rock rock display display reddish-brown reddish-brown weathering weathering carbonate rhombs carbonate rhombs up up to to 11 cm cm or or more. more. The The carbonate carbonate alteration alteration post dates dates the the albitization. Samples Samples of sulphidesulphidebearing chlorite chlorite rock rock that formed formed the the gold ore can can also also be collected at at the the site. site. At At the the Scadding Scadding Mine Mine site, site, collected Gates(1991) reported total total rock rock analysis analysis of of 8.40 and and 8.15% 8.15% Gates(1991) reported Na20 (1994) reported reported values values of 7.68 Na20 and and Schandl Schandl et et al. al.(1994) 7.68 and and 7.65% 7.65% Na20 from from albitized albitized rocks. rocks. One of of the Scadding Scadding mine samples(SC-5) was isotopic dating dating of of the sodium samples(SC-5) was used used in in ti-Pb U-Pb isotopic sodium metasomatism(Schandl et metasomatism(Schand1 et al., al., 1994). 1994). �The The Scadding Scadding Mine Mine operated operated from from Septeniber September 1987 to February February 1988 milled ore July 1990. 1990. Estimated Estimated production production is is 1988 and milled ore until until July 11,000 11,000 ounces ounces from from ore ore grading grading 0.159 0.159 ounces ounces per per ton(Canadian ton(Canadian 347). Mines Handbook, Handbook, 1990-1991, 1990-1991,p. p. 347) Figure Figure 88 presents presents the the geology geology as as reported reported by by Harper(l983) Harper(1983) and Figure Figure 9 9 presents presents the the local local road road and geographic geographic features. features. �2 LEGEND LEGEND 0Upper Quartz;te Upper Quartzite a Upper Upper Chlorite. Chtorite Internediate quartz;te quartzite Intermediate Lower quartzite quartzite Lower 1Lower chlorite LI Lower Chkwite Linestone Linestone Bruce Fornoton Fornation Bruce 3 Diabase Diabase Fi~ure 8:Geotogcat Geologicat sketch nap of' o f the the Figure 8: sketch nap Scaddng ScaddingGotd GotdM;ne(nod;F;ecl Minehodif ied from from Harper, H a r p e r ,1983) 1983) �————— — — a a — — Figure 9: Topographj and road map for the Mine area (from tOpograph Scadding Gold Geologist's Office, Ontariomaps obtained from the Resident Geologi Sii,ny. �24 DAY DAY TWO TWO The second second day day of of investigating investigating alkali alkali rocks rocks of of the the Sudbury Sudbury region region will be be spent spent examining examining genetically genetically and and structurally structurally unrelated unrelated occurrences occurrences northwest, northwest, southwest southwest and and south south of of Sudbury. Sudbury. Stop Stop 4: 4: Spanish Spanish River River Carbonatite Carbonatite The The Spanish Spanish River River Carbonatite Carbonatite occurs occurs northwest northwest of of Sudbury Sudbury and west west of of Lievack. Levack. The log to to the the intrusion intrusion is is and The road log measured t to (Figure measured from fromthe theturn turnofoff to Levack Levack on on highway highway144 144(Figure 10) Proceed km to to Cartier. Cartier. Proceed north north along along highway highway 144 144 for for 16.4 16.4 km Turn t(south) along along a a road from the centre Turn let left(south) centre of of Cartier Cartier and and go km towards towards the the Fox Fox Lake Lake Lodge Lod3e where where road road splits. splits. go 10.2 10.2 km Take Take right right fork fork to to Macaulay Macaulay Lake(Fox Lake(Fox Lake) Lake) and and continue continue to to 24.0 There is is aa short short dirt dirt road to the extreme extreme northeast 24.0 kin. km. There northeast corner corner of of Macaulay Macaulay Lake Lake at at this this point. point. Continue km and and turn turn right right on on an an unmarked unmarked skid skid road road Continue to to 24.2 24.2 km through through former former cut cut over over area. area. At km road road splits, splits, take take right right fork. fork. At 26.1 26.1 km At 26.2 km aa skid skid trail 26.2 km trail to to the the left left leads leads to to several several trenches trenches recently recently dug dug into into carbonatite carbonatite regolith. regolith. Continue Continue to to 26.4 26.4 km km where where weathered weathered carbonatite carbonatite outcrops outcrops on on the the left(west) left(west) side side of of the the road. road. I I I If If one one continues continues along along this this skid skid road road to to 27.2 27.2 km km one one comes comes to to aa popular popular local local campsite campsite on on the the elbow elbow of of the the Spanish Spanish River. River. Return Return to to the the fork fork in in the the road road at at 26.1 26.1 km km and and take take the the right right fork (you are are now now on on the the return trip fork(you trip traveling traveling south) south). �___ 21 I I N in + I I Figure 10: 10: Aeromagnetic map map of of the the Spanish Spanish River River Figure ODM-GSC1965d). 1965d). Carbonatite(fr0m ODM-GSC Carbonatite(from I I �At 0.4 0.4 km k m aa skid skid road road on on the the east east side side of of the the road road leads leads to to several recent several recent trenches trenches in in carbonatite carbonatite regolith regolith at at the the top top of the the hill. hill. Geology: Geolocw: The The Spanish Spanish River River Carbonatite Carbonatite lies lies within within the the Abitibi Abitibi Subprovince Subprovince of of the the Superior Superior Structural Structural Province Province and and is one one of of 66 known known middle middle Proterozoic Proterozoic carbonatites carbonatites within within the the Province of Ontario(Sage, Ontario(Sage, 1987; 1987; Sage Sage and and Watkinson, Watkinson, 1991) 1991). Province of On On the the basis basis of of isomagnetic isomagnetic contours contours the the carbonatite carbonatite is is elongated in in a a direction direction east of north, north, however however the the lack lack of of outcrop, brecciation outcrop, brecciation and and fenitization fenitization make the the positioning of of the the contacts contacts difficult(Sage, difficult (Sage,1987) 1987)(Figure (Figure 11). 11) . The The carbonatite carbonatite has has been been emplaced emplaced into into Archean Archean granitic granitic rocks rocks of of quartz quartz monzonitic monzonitic composition composition and and the the process process of of fenitization has fenitization has desilicated these these rocks rocks close close to to the the carbonatite intrusion carbonatite intrusion creating creating syenitic syenitic compositions. compositions. The The carbonatite carbonatite occurs occurs within within aa regional regional trend trend of of Proterozoic Proterozoic outliers outliers suggesting suggesting some some regional regional structural structural control control along along the northern northern margin margin of of the the Sudbury Sudbury Igneous Igneous Complex Complex that that is is not well 1987) (Figure . Isotopic Isotopic studies not well defined(Sage, defined(Sage, 1987) (Figure12) 12). studies by Bell and and Blenkinsop(l980), Blenkinsop(1980), using using the the Rb-Sr m - S r system, system, obtained obtained an age age of of 1838 1838 ÷+ - 95 95 Ma which, which, due to the large large calculated calculated error, brackets error, brackets the the U-Pb U-Pb isotopic isotopic age age of 1850 1850 ++ - 11 Ma Ma obtained obtained on on the the Sudbury Sudbury Igneous Igneous Complex Complex by Krogh Krogh et et al. (1984). The The Spanish Spanish River River Carbonatite Carbonatite and the al.(l984). the Sudbury Sudbury Igneous Igneous Complex Complex could could be coeval coeval within within the the present present limits limits of of isotopic isotopic age age dating. dating. Within the Within the past past year, year, deep deep trenches trenches have have been been dug dug into into the the weathered(rego1it.h) surface surface of of the the carbonatite carbonatite making making it it one one weathered(regolith) of the the best best if if not not the the best best exposed exposed carbonatite carbonatite in in Ontario. Ontario. This will be This be aa very very short short lived lived feature feature since since the the regolith regolith will collapse collapse and and the the trenches trenches will will quickly quickly fill fill returning returning it to its its former former mysterious mysterious presence. presence. Over Over the the years, years, this this intrusion intrusion has has been been largely largely represented represented by the the single single weathered outcrop outcrop along along the the access access road road to to the the Elbow Elbow on on the the weathered Spanish River. Spanish River. The The one one other other outcrop outcrop area area was was exposed exposed by by the the trenches Manville Company Company Ltd., Ltd., but which which in in recent recent trenches of Johns Johns Manville years became years became filled, filled, overgrown overgrown and and essentially essentially nonexistent. nonexistent. The The present present trenching trenching has has re-exposed re-exposed this this earlier earlier area area of of weathered outcrop weathered outcrop and and removed removed all all traces traces of of the the earlier earlier work. work. Samples of of carbonatite carbonatite and and related related rocks rocks can can be be collected collected Samples from from the the regolith regolith for for study. study. In In general general terms terms the the rock rock types types recognized are recognized are syenite, syenite, sovite, sovite, silicocarbonatite, silicocarbonatite,ijolite, ijolite, pyroxenite and pyroxenite and biotitite(glimmerite). biotitite(g1immerite). The The syenitic syenitic rocks rocks are are likely the product of likely of extreme extreme fenitization fenitization of of granitic granitic wall wall rocks and the rocks the biotitites biotitites are are likely likely derived from from the the pyroxenites. The pyroxenites. The relationship relationship of of the the pyroxenites pyroxenites to to the the carbonatite is carbonatite is uncertain uncertain and the the ijolite ijolite is is likely likely an an early early �_______ 21 I I I . . . .. ..... •:•:cc•i Suc1bury Sudbury Igneous Igneous Complex Complex wA E;'i;rozoic V/////A Proterozoic V/////A Rocks I=] LEGEND LEGEND i I Grenviue E;irsille Rocks k.N\'N'J 4rchecn Archean Greenstone Greenstone BeLt Belt I I 1 Archean Granitoids I Granitoids I 1 Figure 11' RegionaL geotog;col River Carbonatite Figure 11s Regional geological s e tsetting t i n g o of f tthe h e Spanish Spanish River Carbonatite (compiledfrom from Ontario Ontario Geological (compiled Geological Survey SurveyCompilation Compilation Map Map 2543) 2543) �Figure 12: Topographic and road map for the area of the Spanish River Carbonatite(taken from topographic map 41 I/NW) 1 km + N j N) �29 phase of the carbonatite carbonatite intrusion. intrusion. The The silicocarbonatite silicocarbonatite likely has several several origins; origins; ie: ie: sovite sovite with with high high accessory accessory mineral content content and and as as aa carbonate-rich carbonate-richalteration alteration product product of xenolithic xenolithic fragments fragments from from several several sources. sources. Economic Geoloqv: Geology: The River Carbonatite The Spanish Spanish River Carbonatite has been prospected prospected over over the the years years for for asbestos, asbestos, niobium, niobium, vermiculite vermiculite and phosphate. The The present present efforts efforts are are directed directed towards towards vermiculite vermiculite of of which which examples examples can can be seen seen in in some some of the the trenches. trenches. Stop 5: Lake Fenites Stop 5: Nernag Nemag Lake Fenites The The Nemag Nemaq and and Kusk Kusk Lake Lake Fenites Fenites lie lie within within the the boundaries boundaries of of cannot be accessed accessed Whitefish Lake Lake Indian Indian Reserve Reserve 66 and cannot without permission of the the residents. residents. We will be visiting only only the the Nemag Nemag Lake Lake occurrence. occurrence. The road road log log starts starts at at the the intersection intersection of of Highway Highway 55 55 and and Regional Road 24. 24. From From the stop stop light at the intersection intersection Regional Road 24 Regional 24 goes goes north north across across the the CPR CPR railroad railroad tracks tracks into into Lively Lively and and south south of of the the intersection intersection the the road road is is known known Black Lake as Black Lake road. road. 3 . 6 km km west along along highway 55 towards towards Naughton Naughton to the turn Go 3.6 Whitefish Lake off to the the Whitefish Lake First First Nations Nations settlement. settlement. This This will be a left left turn turn going going south(see southfseeFigure Figure 13) 13). At 0.6 Whitefish 0.6 km km is is the the Administration Administration building for for the the Whitefish Nations on Lake First Nations on the the left left side side of of the the road. road. 3.0 km km there there is is a a culvert culvert on on the road between Fly Fly Lake At 3.0 and and Whitefish Whitefish Lake. Lake. Whitefish Lake Lake can can be be seen seen on on the the left hand hand side At 5.1 5.1 kin km Whitefish side of the road road and and at at 7.1 7.1 km, km, opposite opposite Makada Makada Lake, Lake, aa logging logging road splits splits from from the the main main road road and and goes goes west. west. Turn Turn right right onto this this logging logging road. road. Continue on the rough rough logging road till where a skid trail leads leads north from the right on the skid trail and continue to may wish to to park the the vehicle at the the top top reach 12.9 km you reach logging road. Turn 14.15 km where you of of the the hill and and �30 11 mIle mile Figure Figure N N 4 + 13: 13: Topographic Topographic and road road map map for for the the area area around around the the Nemag (taken from Nemag Lake Lakefenites fenites(taken from topographic topographic map map 41 41 1/6). 1/6). �31 continue on on foot. foot. The The road road will will be be swinging swinging almost almost due due west west continue as you you continue continue north north from from the the parking parking site. site. as At At approximately approximately 850 850 metres metres from from the the parking parking site site one one must must walk 90 90 to to 100 100 metres metres south south into into the the bush bush and and up up to to the the top top of a ridge ridge of of outcrop outcrop consisting consisting of Nemag Lake Lake Fenite. Fenite. If If you you reach reach Nemag Nemag Lake Lake you you have have gone gone too too far. far. NOTE: NOTE: If If the the roads roads are are muddy muddy the the site site may may be be inaccessible. inaccessible. A four four wheel wheel drive drive vehicle vehicle is is recommended. recommended. Geoloqy: Geoloqv: One One of of the the best, best, if if not not the the best, best, example example of of fenitization fenitization occurs occurs within within Proterozoic Proterozoic feldspathic feldspathic quartzite quartzite Mississagi Formation Formation southwest southwest of of Sudbury. Sudbury. The The fenite fenite of. the the Mississagi of occurs occurs in in an an explosive explosive breccia breccia and and represents represents extensive extensive replacement replacement of of the the Mississagi Mississagi Formation Formation by by aegirine, aegirine, riebeckite, riebeckite, albite, albite, potassium potassium feldspar feldspar and and rutile(Siemiatkowska rutile(Siemiatkowska and and Martin, Martin, 1975; 1975; Figure Figure 14) 14). The The brecciation brecciation and and fenitization fenitization are are part part of of the the same same event event and and represent alteration alteration by sodium-rich sodium-rich fluids fluids under under subsolidus subsolidus represent conditions conditions perhaps perhaps derived derived from from a magma of essexite essexite or or ijolite ijolite composition(Siemiatkowska composition(Siemiatkowska and and Martin, Martin, 1975) 1975). Siemiatkowska and and Martin(1975) Martin(l.975) subdivide subdivide the the brecciation brecciation and Siemiatkowska fenitization fenitization in in great great detail detail into into seven seven stages. stages. For For the the details details of of this this subdivision subdivision the the reader reader should should refer refer to to Siemiatkowska Martin(1975). The The fenitizing fenitizing fluid fluid was was Siemiatkowska and and Martin(1975). poor poor in in 002 C02 and and potassium potassium appears appears to to be be significant significant only only in in the late late stages stages of of the the fenitization fenitization process. process. The The Nemag Nemag and and the Kusk Kusk Lake Lake fenites fenites are are dominantly dominantly aa process process of of desilication desilication accompanied by by extensive extensive additions additions of of iron iron and and accompanied sodium(Siemiatkowska and and Martin, Martin, 1975). 1975). Siemiatkowska Siemiatkowska and and sodium(Siemiatkowska Martin(1975) report report aa K-Ar K-Ar isotopic isotopic age age of of 1196 1196 ÷+ - 11 11 Ma Ma on on Martin(1975) biotite biotite obtained obtained from from the the fenite. fenite. This This age age would would place place the the fenitization fenitization event event within within Grenville Grenville time time or or development development of of the the mid mid continent continent rift. rift. . The discovery discovery of of the the Nemag Nemag and and Kusk Kusk Lake Lake fenites fenites was was made made The during during regional regional mapping mapping of of the the Ontario Ontario Geological Geological Survey Survey and and they they occur occur on on opposite opposite sides sides but but near near the the northeast northeast trending trending Kusk Fault(Card et et al, al, 1975). 1975). The The region region contains contains Kusk Lake Lake Fault(Card numerous numerous faults. faults. The The northeast northeast trending trending faults faults display display aa tendency to to swing swing to to more more east-west east-west strikes strikes in in the the western western tendency portion portion of of the the map map area area perhaps perhaps parallel parallel to to the the trend trend of of the the regional (Card et et al., al., 1975). Northwest Northwest trending regional Murray Murray Fault Fault(Card trending faults are are also also common common in in the the area area and and they they are are oriented oriented faults approximately orthogonal orthogonal to to the the Grenville Grenville Deformation DeformationZone. Zone. approximately In In Figure Figure 1, 1, aa very very broad regional regional interpretation interpretation by by Lumbers(1978), Lumbers(1979), the the Nemag Nemag and and Kusk Kusk Lake Lake Fenites Fenites would would occur occur �_______ 32 LEGEND FENITIZATION ZONE (STAGE I STAGE 3,2) 3.21 LATE DIABASE DIKES (SUDBLFRY SWARP.I)b r— Olivine diabase dikes 71 Albite veins AIRicbeclsite—aegis-ine veins thermal L_i LATE ,"LkFIC LATE ,WIG DIKES DIKES 1:tv i Metagabbro Xetegabbro dikes dikes Riebeckite veins rl:T4 Granulated, L1113 L'ia)J Sphalerite—bearing ankerite vein Breccia replaced by riebeckite and aegirine in aegirine matrix (Nemag Lake) Albite—aegirinc area Breccia partly replaced by by riebeckite riebeckice sod and ragnetite snagmecite cut c n t by by albite albite veins veins Breccia e c c i a partly p a r t l y replaced r e p l a c e d by aegirine aegirine and riebeckite r i e b e c k ~ t ecut c u t by by albite a l b i t e veins wins STAGE 4 Breccia partly replaced by riebeckite and/or aegirine in aegirine matrix (Nemag Lake) Breccia partly replaced by rieberkite, aegirine and K—feldspar in aegirine, riebeckite matrix (Kusk Lake) deforred quart zitc5 [TiTT Metagabbro5 ^ctaeabbnoa MISSISSAGI FORMATION Feldspathic quartzito comonly displaying incipient fenitization Lake) Lake 1 STAGE S 5' -STAGE Rutile vein Brecciated NIPISSING GABBRO GABBRO INTRUSION INTRUSION NIPISSINC Breccia B r e c c i a replaced r e p l a c e d by byK—feldspar K - f e l d s p a r and and aegirine i n in i n aegirine a e g i t - i n e matrix m t r i x (Kusk (Kusk NiAJOR BRECCIATION AND FENITIZATION W O R B-iECCIATIOH FEMTIZATION ZONE ZONE shock zone DEFOR'tajION ZONE ( STAGE 1) CAR BONATEb FENITIZATION FENITIZATION AND AND BRECCIATION BRECCIATIOK (STAGE ( S T A G E 1,6) 7.61 I a Occurs only at Nemag Lake b. Occurs only at Frisk lake SYMBOLS SYMBOLS LIIJ Area of obedrock Area f bedrockoutcrop outcrop Bedding, B e d d i n g , top t o p unknown unknown ,= E, Bedding, ~ e d d i n g ,top t o p from f r o m cross—bedding cross-bedding Foliation Folia~~o" - Geological G e o ~ o g i c a l boundary, b o u n d a ~ ~assumed assumed , Boundary of o f outer i u c e r fenitization fenlt~zation zone, zone. assured essumd Figure 14: 14:Geology Geology of ofthe theNernag Nemaq Lake Lake Fenites(modif Fenites(modified from Figure led from Siemiatkowska and Martin, 1975; Card et al., 1975). Siemiatkowska and Martin, 1975; Card et al., 1975). �3: at the the intersection intersection of of the the eastern eastern extension extension of of the the Great Great Tectonic Zone Lakes Tectonic Zone and and the the Grenville Grenville Deformation Deformation Zone. Zone. Siemiatkowska enites may may Siemiatkowska and and Martin(1975) Martin(l.975) suggest suggest that that the the if Eenites in some some way by related to the Murray fault system system which would would follow follow the the trend trend of of the the Great Great Lakes Lakes Tectonic Tectonic Zone. Zone. At the the Nemag Lake Lake Fenite Fenite site, site, fragments fragments up to to a a metre in in maximum maximum dimension dimension can can be be observed observed concentrically concentrically mantled mantled with aegirine aegirine and riebeckite. Late Late stage stage pegmatitic pegmatitic albite albite with riebeckite riebeckite and and aegirine aegirine are are present present as as well well as as late late stage stage breccia breccia veins. veins. Economic Geology: Geolow: The The fenites Eenites are are geochemically geochemically anomalous anomalous in in niobium niobium but under under existing existing conditions conditions they they are are not not likely likely to be of of economic economic interest. interest. One One small small occurrence occurrence of of sphalerite sphalerite has has been been reported(Meyer, reported(Meyer, 1996, 1996, Residept Resident Geologist, Geologist, Sudbury, Sudbury, personal communication) personal communication) Stop 6: French French River River Alkalic Alkalic Rocks Rocks Stop 6: The French French River River Alkalic rocks rocks occur occur within the the Grenville Grenville Structural Province Structural Province on private property. Permission Permission to to access the the site site should be obtained obtained from from the property owner before entering. before entering. The The road road log log starts starts at at the the intersection intersection of of the the Sudbury Sudbury bybypass and pass and highway highway 69 69 south south of of Sudbury. Sudbury. Drive south to Bigwood Bigwood and turn Drive south on on highway highway 69 69 for for 59.9 59.9 1cm km to turn right right on on to to Hartly Hartly Bay Bay Road(see Road(see Figure Figure 15). 15). Continue Continue along along the the Hartly Hartly Bay Bay Road Road until until aa distance distance of of 65.2 65.2 km is reached reached and turn turn left towards towards a camp camp on on the the French French River. This This is is aa private private road. road. 6 6 . 6 kin krn aa dump to the the a final final distance distance of of 66.6 At a dump appears appears just to east of the road. Park at this dump site site and examine examine the exposed syenite syenite outcrops outcrops in in the the eastern eastern portion portion of of the the cleared area. cleared area. Geology: Geoloqy: The The alkalic rocks rocks have been described described by The alkalic Hewitt(1960; Figure 16) 16) and and Lumbers(l975) Lumbers(1975). The Hewitt(l960; Figure alkalic syenites were subdivided syenites subdivided into into the the French French River River nepheline nepheline syenite, syenite, French French River River alkaline alkaline syenite syenite and and Rutter Rutter nepheline nepheline syenite by by Hewitt Hewitt (1960); syenite (1960); however, however, Lumbers(1975) Lumbers(1975) refers to . �34 N — a 1 mIle Figure 15: 15: Topographic Topographic and and road road map map Figure French River a l k a l i c s y e n i t e s taken French River alkalic syenites taken 1/2) 1/2) + of the t h e area a r e a around around the the of from topographic map 41 from topographic map 41 �I Figure 16: Simplified ge0l09ic s k e t c h nap o f t h e R u t t e r Figure 16 SirnptiP;ed alkalic syenite intrusion(nodified f r o mRutter Hewitt, geoLogic sketch nap of the atkalic 1960, syeni-te p. 167) intrus:on(nod;f;ed from Hewitt, 1960, p. 167) �36 all all the the alkali alkali syenites syenites in in this this pluton pluton as as the the Rutter Rutter Pluton. Pluton. The The alkaline alkaline syenites syenites occur occur in in an an elongated elongated body body of of approximately approximately seven seven miles miles length length with with its its long long axis axis just just west west of of north. north. The The maximum maximum width width is is approximately approximately one one mile(Hewitt, mile(Hewitt, 1960; 1960; Lumbers, Lumbers, 1975). 1975). The The syenites syenites are are dominantly dominantly leucocratic, leucocratic,medium-grained, medium-grained, gneissic (Lumbers, gneissic with with streaks streaksand andlenses lensesofofmafic maficminerals minerals(Lumbers, 1975) pink leucocratic leucocratic phase phase is is the the latest latest in in the the 1975). AA pink sequence. sequence. The The mineralogy mineralogy of of the the syenites syenites is is albite, albite, nepheline, nepheline, potassium potassium feldspar feldspar and and biotite biotite with with accessory accessory hastingsite, hastingsite, aegirine-augite, aegirine-augite,magnetite, magnetite, sphene, sphene,zircon, zircon, apatite, apatite, graphite, graphite, corundum, corundum, carbonate, carbonate, sodalite sodalite and and cancrinite(Lumbers, cancrinite(Lumbers,1975). 1975). Hewitt(1960) Hewitt(1960) proposed proposed that that aa regional regional potassium potassium metasomatic metasomatic event event has has occurred; occurred;however, however, Lunibers(1975) reported that that he he found no evidence Lumbers(1975) reported evidence for for this this event rarely exposed exposed contacts contacts were were sharp sharp and and event and and that that rarely display display no no evidence evidence for for aa potassium potassium metasomatism. metasomatism. Hewitt(1960) reports that that aa lead lead alpha alpha decay decay age age of of 975 975 Ma Ma Hewitt(1960) reports was was obtained obtained on on zircons zircons from from this this body. body. This This method method of of age age dating dating is is no no longer longer in in use use and and additional additional geochronological geochronological study study is is warranted. warranted. . The The syenites syenites at at the the site site display display aa strong strong fabric fabric that that strike strike west west of of north north and and dip dip east. east. Within Within these these syenites syenites are are very very coarse-grained coarse-grainedalkali alkali peymatites pegmatites containing containing potassium potassium feldspar, feldspar, nepheline, nepheline, cancrinite, cancrinite, sodalite, sodalite, aegirine aeqirine and and magnetite. magnetite. The The pegmatites pegmatites display display aa well well developed developed pinch pinch and and swell swell structure structure along along strike strike with with the the gneissosity, gneissosity,however however the the coarse-grained coarse-grainedminerals minerals in in the the pegmatites pegmatites do do not not appear appear deformed deformed or or fractured. fractured. Samples Samples of of graphite-bearing graphite-bearingsyenite syenite have have been been found found at at the the site site and and molybdenite molybdenite flakes flakes over over 11 cm cm in in diameter diameter are are occasionally occasionally found. found. Pockets Pockets of of weathered weathered very very coarse-grained coarse-grainedbiotite biotite are are exposed exposed at at several several locations locations within within the the stripped strippedarea. area. Corundum Corundum is is present present at at the the community community dump dump site site north north of of the the road road leading leading to to this this stop, stop, however however it it is is not not abundant abundant and and no no plans plans have have been been made made to tovisit visit the thelocation. location. �BIBLIOGRAPHY BIBLIOGRAPHY Adams, '3. and Basham, Basham, p., Adams, J. and P., 1986. Seismicity and and 1986. The Seismicity Seismotectonics of Seismotectonics of Canada Canada East of the the Cordillera; Cordillera; Geoscience Geoscience Canada, v. 16, p. Canada, v. 16, p. 3-16. 3-16. 1980. Ages and Initial and Blenkinsop, Blenkinsop,'3., J., 1980. 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Age Age for for aa Kamo, Lamprophyre Dike, Dike, Callander Callander Bay, Bay, Ontario: Ontario: Use Use of of Ti-bearing Ti-bearinq Lamprophyre Minerals Minerals as as aa Potential Potential Geochronometer; Geochronometer; Geological Geoloqical Association of of Canada Canada Program Program with with Abstracts, Abstracts, v. v. 14, 14, p. p. A41. A41. Association Krogh, Kroqh, T.E., T.E., Davis, Davis, D.W. D.W. and and Corfu, Corfu, F., F., 1984. 1984. Precise Precise U-Pb U-Pb Zircon Zircon and and Baddeleyite Baddeleyite Ages Aqes for for the the Sudbury Sudbury Area; Area; p. p. 431431446, 446, in The The Geology Geoloqy and and Ore Ore Deposits Deposits of oC the the Sudbury Sudbury Structure, Structure, edited edited by by E.G. E.G. Pye, Pye, A.J. A.J. Naldrett Naldrett and and Giblin, Giblin, P.E.; 1, 603p. 603p. P.E.; Ontario Ontario Survey Survey Special Special Volume Volume 1, Krogh, Kroqh, T.E., T.E., Kamo, Kamo, S.L. S.L. and and Bohor, Bohor, S.F., B.F., 1996. 1996. Shock Shock Metamorphosed Metamorphosed Zircons Zircons with with Correlated Correlated U-Pb U-Pb Discordance Discordance and and �Melt Melt Rocks Rocks with with Concordant Concordant Protolith Protolith Ages Ages Indicate Indicatean an Impact Impact Origin Origin for for the the Sudbury Sudbury Structure; Structure; American American Geophysical Geophysical Union Union Geophysical p. 343-353. Geophysical Monograph Monograph 95, 95, p. 343-353. Kumarapeli, V.A., 1966. 1966. The The St. St. Lawrence Lawrence Kumarapeli, P.S. P.S. and and Saull, Saull, V.A., Valley Valley System: System: aa North North American American Equivalent Equivalent of of the the East East African Rift Valley System; Canadian Journal of Earth African Rift Valley System; Canadian Journal of Earth Sciences, Sciences, v. v. 3, 3, p. p. 639-658. 639-658. Lowden, Lowden, 1LA., J.A., Stockwell, Stockwell, C.H., C.H., Tipper, Tipper, H.W. H.W. and and Wanless, Wanless, R.K., R.K., 1963. 1963. Age Age Determinations Determinations and and Geological Geological Studies; Studies; Geological p. 93-94. 93-94. Geological Survey Survey of of Canada Canada Paper Paper 62-17, 62-17,p. Lumbers, Lumbers, g.E., S.B., 1971. 1971. Geology Geology of of the the North North Bay Bay Area, Area, Districts Districts of of Nipissing Nipissing and and Parry Parry Sound; Sound; Ontario Ontario Department Department of Mines Mines and and Northern Northern Affairs Affairs Geological Geological Report Report 94, 94,lO4p. 104p. Lumbers, Lumbers, S.B., S.B., 1975. 1975. Geology Geology of of the the Burwash Burwash Area, Area, Districts Districts of of Nipissing, Nipissing, Parry Parry Sound Sound and and Sudbury; Sudbury; Ontario Ontario Division Division of of Mines Geological Report 116, 158p.; Map 2271, Scale 1 inch 158p.; Map 2271, Scale 1 inch Mines Geological Report 116, to to 22 miles. miles. Lumbers, 1978. Geological Geological setting Lumbers, 5.13., S.B., 1978. setting of of alkali alkali rockrockcarbonatite p . 81-89, 81-89, in carbonatite complexes complexes in in eastern eastern Canada; Canada; p. Proceedings Proceedings of of First First International International symposium symposium on on Carbonatites; Carbonatites; Pocos Pocos de de Caldas Caldas Minas Minas Gerais, Gerais,Brazil; Brazil; Ministerio Mhisterio Das Das Minas Minas EE Energia, Energia, Department Department Nacional Nacional de de Producao Producao Mineral, Mineral, 324p. 324p. I Lumbers, S.B., Heaman, Heaman, L.M., L.M., Vertolli, Vertolli, V.M. V.M. and and Wu, Wu,T.-W., T.-W., Lumbers, G.E., 1990. 1990. Nature Nature and and Timing Timing of of Middle Middle Proterozoic Proterozoic Magmatism Magmatism in in the j & the Central Central Metasedimentary Metasedimentary Belt, Belt, Ontario; Ontario; p. p. 243-276, 243-276,in Mid-ProterozoicLaurentia-Baltica, Laurentia-Baltica,Geological Geological Association Association of of Mid-Proterozoic Canada Canada Special Special Paper Paper38. 38. Meyer, Meyer, W., W., 1995. 1995. Soda Soda Metasomatism Metasomatism in inthe theSouthern SouthernProvince; Province; unpublished unpublished manuscript manuscript prepared prepared for for the the Ontario Ontario Geological Geological Survey, 2p. Survey,2p. ODM-CSC, ODM-GSC,1965a. 1965a. Sturgeon Sturgeon Falls, Falls,Ontario OntarioDepartment Departmentof ofMinesMinesGeological inch to to 11 Geological Survey Survey of of Canada Canada Map Map 1488G, 1488G, Scale Scale 11 inch mile. mile. I I �ODM-GSC, ODM-GSC, l965b. 1965b. Nipissing; Nipissing; Ontario Ontario Department Department of of MinesMinesGeological Geological Survey Survey of of Canada Canada Map Map 1487G, 1487G, Scale Scale 11 inch inch to to 11 mile. mile. ODM-GSC, ODM-GSC, l965c. 1965c. Powassan; Powassan; Ontario Ontario Department Department of of MinesMinesGeological Geological Survey Survey of of Canada Canada Map Map l477G, 1477G, Scale Scale 11 inch inch to to 11 mile. mile. ODM-GSC, ODM-GSC, 1965d. 1965d. Cartier; Cartier; Ontario Ontario Department Department of of MinesMinesGeological Geological Survey Survey of of Canada Canada Map Map l524G, 1524G, Scale Scale 11 inch inch to to 11 mile. mile. Sage, Sage, R.P., R.P., 1987. 1987. Geology Geology of of Carbonatite Carbonatite -- Alkalic Alkalic Rock Rock Complexes Complexes in in Ontario: Ontario: Spanish Spanish River River Carbonatite Carbonatite Complex, Complex, District District of of Sudbury; Sudbury; Ontario Ontario Geological Geological Survey Survey Study Study30, 30, 62p. 62p. Sage, Sage, R.P., R.P., 1991. 1991. Chapter Chapter 18; 18; Alkalic Alkalic Rocks, Rocks, Carbonatite Carbonatite and and Kimberlite Kimberlite Complexes Complexes of of Ontario, Ontario, Superior Superior Province; Province; p. p. 683— 683709, in Geology Geology of of Ontario; Ontario; Ontario Ontario Geological Geological Survey Survey 709, & Special Special Volume Volume Number Number 4, 4,pt. pt. 1, 1, 7llp. 711p. Sage, Sage, R.P. R.P. and and Watkinson, Watkinson, D.H., D.H., 1991. 1991. Alkali Alkali rockrockcarbonatite carbonatite complexes complexes of of the the Superior Superior Structural Structural Province Province northern northern Ontario, Ontario, Canada; Canada; Chronique Chronique de de la la Recherche Recherche Miniere Miniere N. N. 504, 504, p. p. 5-19. 5-19. R.P., 1996. 1996. KirnberlItes Kimberlites of the Lake Lake Timiskaming Timiskaming Sage, R.P., Sage, Structural Structural Zone; Zone; Ontario Ontario Geological Geological Survey Survey Open Open File File Report Report 5937, 5937, 435p. 435p. Schandi, Schandl, E.g.; E.S.; Gorton, Gorton, M.P. M.P. and and Davis, Davis,D.W., D.W.,1994. 1994. Albitization Albitization at at 1700 1700 ÷+ - 22 Ma Ma in in the the Sudbury-Wanapitei Sudbury-WanapiteiLake Lake Area, Area, Ontario: Ontario: implications implications for for deep-seated deep-seated alkali alkali magmatism magmatism in in the the Southern Southern province; province; Canadian Canadian Journal Journal of of Earth Earth Sciences, v. 31, 31, p. p. 597-607. 597-607. Sciences, v. Shafiqullah, Shafiqullah, N.; M.; Tupper, Tupper, W.M. W.M. and and Cole, Cole, T.J.S., T.J.S., 1968. 1968. K-Ar K-Ar Ages Ages on on Rocks Rocks from from the the Brent Brent Crater, Crater, Ontario; Ontario; Earth Earth and and Planetary 5, p. p. 148-152. 148-152. Planetary Science Scie~lceLetters, Letters,v. v. 5, Siemiatkowska, K.M. K.M. and and Martin, Martin, R.F., R.F., 1975. 1975. Fenitization Fenitization of of Siemiatkowska, the Mississagi ~ississagiQuartzite, Quartzite, Sudbury Sudbury Area, Area, Ontario; Ontario; Geological Geological the Society p. 1109-1122. 1109-1122. Society of of America America Bulletin, Bulletin, v. v. 86, 86,p. �41 Syrnons, D.T.A. D.T.A. and and Chiasson, Chiasson, AA.D., 1991. Paleoma9netism Paleomagnetism of Symons, . D . , 1991. Callander Complex the Callander Complex and and Cambrian Cambrian apparent polar wander path for for North North America; America; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. 28, pp. . 3355363. 55-363. � https://digitalcollections.lakeheadu.ca/files/original/4a485eaf390ab9a722b362ed4d66ab3d.pdf 16c0001f51f6fb6b73bc94a0d28369f4 PDF Text Text I I I I I I I I I I I I I I I I I I I THE GREENING THE GREENING OF OF SUBBURY SUDBURY BY K. WINTERHALDER LAKE SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON LAKE ANNUALMEETING, MEETING,MAY MAY66-11,1997 43rd ANNUAL - 11,1997 SUDBUIRY,ONTARIO ONTARIO SUDBURY, Trip Guidebook, 43, Part Part 7 Field Trip Guidebook, Volume 43, �I I 1 THE GREENING OF OF SUDBURY SUDBURY I I May 10,1997 10, 1997 Leader: Leader: Prof. Keith Winterhalder Department of Biology Biology Laurentian Lawentian University University I 1 I I I I I I I I I I I Institute Institute on Lake Superior Superior Geology Geology Sudbury, Sudbury, 1997 1997 �Institute on on Lake Lake Superior Superior Geology Geology Greening of of Sudbury Field 1997 Greening Field Trip, May May 10, 10, 1997 I Winterhalder Keith Winterhalder (Ipe w e hundred years years of of logging, logging, fire, addification acidification by sulphur sulphur dioxide, dioxide, particulate metal metal deposition, enhancedfrost frost action action and and erosion particulate deposition, enhanced erosion have have created 10,000 hectares of of barren land and 36,000 10,000 hectares 36,000 hectares of stunted, stunted, I I I I I I I I I I I open birch woodland woodland around around the the Sudbury Sudbury copper copper and nickel smelters. smelters. It was found found that the which have have been addifled was the steep, steep, stony barren barren slopes, slopes, which acidified and can be be detoxified by aluminum, can and contaminated contaminatedwith with copper, copper, nickel and alu.minum, the manual manual application application of of pulverized pulverized doloniitic dolomitic limestone. limestone. Revegetation Revegetation began on an operational scale in 1978, and approximately 3,500 hectares operational hectares soil have have been been detoxified deiadfled by of surface soil by manual manual application application of of limestone, limestone, by and revegented revegetated using using aa grass/legume grass/legurne seed mixture. mixture. Rapid invasion invasion by birch, poplar occurred spontaneously, and the birch, poplar and willow willow seedlings seedlings occurred spontaneously, and woody deciduous dedduous cover coverhas has been been enriched enriched by by the planting resulting woody planting of than 2.5 2.5 million tree seedlings, seedlings, the majority of them native native pines. pines. more than species in in blocks blocksofoftheir their own ownssoil arebeing beingintroduced introduced at at an oil are Understory species experimental level, level,to to facilitate facilitateand and accelerate accelerate the the establishment establishment of of an experimental appropriate herb and shrub stratum, microflora and microfauna. Unique herb and shrub stratum, microflora and microfauna. Unique its community-based format, the features of of this features this program program include include its community-based format, manual approach approach employed, employed,and andthe the use use of aa minimal predominantly manual minimal colonization by amelioration approach that relies heavily on spontaneous s species and other natural dynamic processes. native other natural dynamic p addition to to the degraded natural landscape, landscape, deposits of materials materials that that In addition discarded after the ore is are discarded is separated separated by by milling milling flotation, flotation, known known as tailings, cover cover more more than than 2,000 hectares. hectares. Experimental Experimental reveg revegetation began on the tailings in in the the 1950s in in response response to to a dust problem, and the Inco Inco Ltd. Ltd. tailings which all all non-active non-active tailings tailingsareas areas are in various has has reached the point at which stages of of revegetation. The revegetation process includes includes liming liming and stages revegetation. The revegetation process seeding with a grass-legume mixture, use of a cereal rye nnurse fertilizing, fertilizing, with a grass-legume mixture, use of a cereal rye crop, and ultimately plantingofof trees, trees, many many of of which crop, and ultimately planting which are are grown gr underground underground at atthe the4600' 4600' level. level. Tower,3.5 3.5 fccn km northeast # 11- McKim Street Transmission Stop Transmission Tower, Stop # of the Copper Copper Cliff Cliff smelter previously barren barren area was grassed 1981 by the the Regional Regional Land This previously grassed in 1981 Program, and planted with red and jack pine in Reclamation Program, and planted with red jack in 1983. 1983. Also this area area were were smaller smaller numbers numbers of white spruce, white ash, planted in this maple, silver silver maple, maple,white whitecedar cedarand andred redoak. oak.As Asyou youwalk walkuup the sugar maple, volunteer trembling trembling and and large-tooth bill, you will hill, will also see volunteer large-tooth aspen, white birch will see see the the city city of ofSudbury Sudbury to Se cherry.From From the top, you will birch and and pin pin cherry. �-2- east and south-east, 20 hectares hectares of of grassed grassed barrens barrens to to the the west, west, and and a an. south-east, 20 untreated area across across the the railway railwaytracks trackstotothe the north north that that has been untreated area beex colonized by by aa metal tolerant strain of dwarf or bog- birch (Betula colonized (Betula -pumila var. glandulifera). u I Stop # 22 -- Barren Stop # Barren site II On On the way 18 U m lI I II i II II II II II I I I Copper Cliff Cliff smelter. smelter. east of Clarabelle, elle, 2 km northeastt of the to this site, we shall see a slag disposal disposal area, area, and and the process of grinding of railway grinding slag slag for construction construction of railway beds beds (coarse (coarse slag) slag) and and driveways driveways (fine (fineslag slag mixed mixed with with sand, sand,known knownasas'TDrypack"). "Drypack"). You willsee seeaamosaic mosaicofofland landthat thatisistotally totallybarren, barren,and and in in the the early u will early stages stages of revegetation, includingbare bare rock rock outcrops, outcrops, soil soil pockets pockets and stony revegetation, including stony slopes, with large white white pine stumps lopes, with stumps indicating indicating the the original originalvegetation. vegetation. The rare,, coppiced of red red maple maple and and red oak, coppiced and stunted individuals individuals of oak, which pre-date and are often predate denudation, denudation, arise arise from from large large stools, stools, and often surrounded by a litter litter of of earlier, earlier, much much larger larger stems. stems. The soil soil is is highly highly acidic, between 3.5 3.5 and 4.5, 4.5, and plant-available copper, nickel acidic, with a pH between and aluminum can each exceed ppm. Some Someofof this this land land has has been exceed 100 ppm. aluminum can aerially Ltd. in in 1990 and and 1991, and is aerially limed, fertilized and seeded seeded by by Inco Ltd. 1991, and is grass-covered. grass-covered. The sole colonizer colonizerof ofthe theuntreated untreated land is (tufted is Deschampsia Descbampsia caespitosa (tufted hairgrass), hah-grass),which which has has been beenshown shownby byCox Cox& & Hutchinson Hutchinson (New (NewPhytologist Phytologist 84: 631-647:1980) to have evolved tolerance. AA few 631-647:1980) to evolved multiple-metal multiple-metal tolerance. few individuals sca bra(tickle (ticklegrass), grass),also alsoa ametal-tolerant metal-tolerant ecotype individuals of Agrostis scabra (Archambault Botany 73:766-775), 73:766-775), (Archambault & Winterhalder, Canadian Journal of Botany have havealso alsobegun begunto tocolonize. colonize. As As we leave the area, area, aa site site opposite opposite aa school school building will be pointed out. OUT. This techniquewas wastried tried out out at the This is where where the manual manual technique the "semi"semioperational" pupils, on on one one acre of operational" level in 1975 by elementary elementary school school pupils, land beside their school. school.ItItwas wasthe the success successofof this this trial trial that encouraged encouraged the MunicipalityofofSudbury Sudburyto to apply apply for for job-creation job-creation funds funds to the Regional Regional Municipality establish establish its its ongoing ongoing land land reclamation reclamation program. program. Stop : # 33 -- Inco Inco Ltd. tailings, Copper opperCliff. Cliff. Your guide: will will be Bob Bob Stanzel Stanzel of Inco's Inco's Environmental Environmental Control Control . is my my hope hope that thatyou youwill will be be shown shown the the spigotting spigottingprocess, process, Department. ItIt is �I and the end product at stages in vegetation establishment, and stages at the the 'C-I)" "C-Darea, area, the results initiated over over 30 30 year which shows shows the results of of revegetation revegetation initiated year ago, ago, the originally originally seeded seeded grasses grasses and and legumes, iincluding n c l m the legumes, some spontaneous spontaneous colonizers, and planted pines. colonizers, and planted I I You willalso alsosee seeattempts attemptsto todivers@ diversifythe thepine pineplantations plantations by by intbducing introducing You plots or plugs of plant and their native soil from undisturbed forest. plots of plant from undisturbed forest. I I Lake,44 km km south south of of the Copper # 4 -- South shore of Kelly Stop Kelly Lake7 Copper Stop # Cliff smelter. Cliff smelter. I I Our W W walk k ~ ibegins n a ninmana area t h that a t was w hlimed, & f ~fertilized e d a n and d ~seeded e d e in d 1982, i1982, n red and jack jack pine in 1984. The The grasses grasses are are a mixture of of and planted with red tufted hairgrass and tickle grass with seeded species. The metal-tolerant metal-tolerant hairgmss and tickle seeded species. The seeded legumes Alsike clover and birdsfoot trefoil are also seeded legumes Alsike clover and birdsfoot trefoil are also present. present Colonists include include white white birch, birch, trembling trembling aspen, balsam poplar, fireweed, Colonists fireweed, well as as acid-tolerant sheep pearly everlasting, yarrow and hawkweed, hawkweed7as well sheep sorreL Relict red maple and red oak are common. We eventually emerge sorrel. Relict red maple and red We emerge Note that that here, here, at a greater untreated area.. area. Note greater distance distance from the into an untreated smelter than than Site 2, there is is an an almost almost complete complete cover of metal-tolerant metal-tolerant tufted relictred red maple maple and and red red oak. Some t ufted hairgrass, hairgms, with occasional relict Some white were also planted in this area in 1984, and one of them pines were also planted in this area in 1984, and one them has has survived and and grown grown on on the the untreated soil, survived soil, but exhibits &bits necrotic needle tips. I I I I I I I I I l I I You can of the lake, lake, with with aa clear line marking see the north shore of marking the point at at which liming stopped. stopped. return by from the smelter, We return by way way of of aa south-facing south-facing slope, slope, facing away from smelter? on there is on which there is aa relict relict community community of large red oaks. - Stop ## 55 - South of southeast Stop South of southeast bypass, bypass? north of of Richard Richard Lake, Lake, approximately midway midway between between the the Copper approximatdy Copper Cliff Cliff and and Coniston Coniston smelters. shall walk transition") We shall walk through through aa typical typicalsemi-barren semi-barren ("birch ("birch transition") community, with with birch7 birch, red red maple and red oak, some of which may have have lost some stems stems to to the combined of drought drought and gypsy lost some combined effects efFects of gypsy moth defoliation. The The larger larger red red pines pines are are native native here, here, but but some some planting planting of of tree tree seedlings (pine and and spruce) has has also occurred. occurred. ItIt is is not not necessary necessary to lime s e d b g s (pine lime before planting planting trees trees in the the soil before the semi-barren semi-barren zone. zone. The understory understory hair grass consist of tufted hak grass and and two two spedes speciesof of blueberry, blueberry, with withmosses mosses �1 I I i I I I I I I I I I I I I I I I (Poh.lia urn)and and lichens7 lichens, and and Labrador Labrador tea tea in (PohZia and Po/ytrich Polytnkhum) damp damp sites. sites. Returning of the gully, where the the soil is deeper, Labrador tea isis Returning by way of gully, where more and the Ere-tolerant fire-tolerant clubmoss known known as as ground cedar more common, and cedar can can be be seen. seen. Stop ## 66 -- north of Highway 17E, 44 km km northwest northwest of the Highway 17E7 the Coniston Coniston smelter. smelter. We by walking up the overgrown road that irt road that was was We shall shall begin begin by walking up overgrown ddirt constructed by the land reclamation reclamation crew crewin in 1979 for for the transportation of ground limestone. limestone.InIn1979? 1979,the thearea areato to the the west west of of the road, partly partly sheltered sheltered from from the the Coniston Coniston fumes, fumes?supported birch birch transition transitionwoodland, woodland, but but the the area area to the the east of the road was barren barren except except for for aa few few scattered scattered relict birches and maples. The upper section of the road crosses birches maples. The upper section of crosses the the revegetated revegetated area areaobliquely obliquelyon onits itsway way to to the thetop topof ofthe thehill. hill.Young Young birches birches predominate, relict white white birch, birch, red red maple and red predominate, with occasional occasional relict red oak. oak. Larger shrubs shrubs include include beaked beaked hazel hazel and andwillows, willows?with the the N-fixing N-fixing shrub shrub sweet fern and blueberries in the understory with hair moss sweet fern and blueberries in the understory with hair moss (Polytrichwn). (Polytri&m). At At some points along the trail trail we shall still see some of the the originally seeded seeded species species such as birdsfoot trefoil, clover and tall trefoil7Alsike Msike clover tall fescue. Note the small plantation of European fescue. Note small experimental experimental plantation European larch. The The main native herbaceous colonists are pearly everlasting, rough and main herbaceous colonists are pearly everlasting, rough and Canada and yairow, Canada goldenrod, goldenrod, fireweed firewed and yarrow, accompanied accompanied by weedy weedy non-native as the theyellow yellowand andorange orangehawkweed. hawkweed. Woody Woody nm-native species species such as colonists include pin pin cherry and colonists include and staghorn staghom sumac. sumac. Native Native woody woody plants plants such as bush honeysuckle and trailing arbutus have been seen here, such honeysuckle and trailing arbutus have here, but but we them. Near Near the treated/untreated treateWuntreated junction junction is aa we may may not not encounter encounter them. healthy red pine healthy red pine that that has has become become rooted rooted in in untreated untreated soil. soil. This This isis probably probably because the the active active physical physical weathering of rock in in this this microsite microsite has has created createdaarooting rootingenvironment environmentthat thatisisnot notmetal-toxic. metal-toxic. Emerging stopped, we see that hill7where liming stopped? that birch bircn isis Emerging at at the the top topof of the the hill, actively colonizingthis this site, site, which whichhas has been been relatively unaffected actively colonizing unaffected by by smelter in 1972. In In the the last last 20 years? years, the average average soil soil smelter fallout since closure in pH risen from from around around 35 3.5totoaround around4.5. 4.5.You Youwill will also also see see pH in in this area has risen relict relict coppiced birch, and red redmaple mapleundergoing undergoingregressive regressivedieback. dieback. The The metal-tolerant metal-tolerant grass grass is is tickle tickle grass. This hilltop may be too isolated isolated from from the the moist moist valley valley to have have been beencolonized colonized by bymetal-tolerant metal-tolerant tufted tufted hairgrass. commonare are the the moss PohZia, Pohlia, and and blueberry blueberry bushes Also common bushes which which hairgrass. Also may be relicts. relicts. Note the the signs signs of frost frost activity activity visible in in the the soil. soil. may be Looking acrossthe the highway? highway,you youwill willsee seem anarea areathat that was was limed limed but not not Looking across seeded. know that that this use of an seeded. We We know of limestone limestone as a "trigger "trigger factor" factor" is an effective regreening, but effectivemethod of regreening but the theRegional Regional authorities authoritieslike like the the �I I I1 I 1 I I1 II iI II I I I bright bright green grass in the spring. 1979, the revegetation crew ran out of spring, In in 1979, seed, demonstration site. seed, providing a useful demonstration site. On the way down, we we shall shall see see aa small small experimental plantation of white v e pine. White pine, pine, once the the dominant dominant tree tree species species in in this this area, area, is is extremely extremely again under under current current atmospheric atmospheric SO2-sensitive, but can can survive survive again 9)2-sensitive, conditions. conditions. En En route to to Stop Stop #7: #7: On the left hand side turnoff, you side of the bus, just prior to to the the Coniston Coniston turnoff, you will will see 11acre of of sloping slopingland landthat that was wastreated treated by elementary elementary school school students students in in 1975. 1975. Stop Stop #7 -- just east of of Coniston Coniston smelter smelter - I I I 1 I I I After passing passing a small industrial complex, you will will see untreated ban-en complex, you barren land on your we drive onto the your right. right. As As we the net net slag-surfaced slag-surfaced area, area, you you wifi will see aa good good transition between two-year and and three-year-old three-year-oldgrassing. grassing. We We shall area so shall take a walk on the grassed area so that that you you can cansee seethe thecolonization colonization process, rocess, mostly mostly by poplar and andwillow willow seedlings. seedlings. The second-year second-year area area seems to have probablydue duetto the right woody colonization, colonization, probably o the right have more more woody combination when the the seeds were shed. Much of the on of weather, wind etc. when the limed ground has been colonized by by the moss Fanaria hygrometrica.. moss F m ' a hygromemka.. Note how grass grows grows better at at the thesoil-rock soil-rock interface. interface. Pine Pine seedlings seedlings have already been en planted planted here. here. Stop ## 88 -- north of Highway Highway 17E, 17E, 1.5 1.S km km northeast northeast o of the Coniston ston smelter. smelter. This area a was was treated treated in 1978, no 1978, and and the theseed seedmixture mixture contained contained no legumes.. Nevertheless, Nevertheless,trefoil trefoiland and clover cloverhave have colonized colonizedfrom from aa nearby Inco Redand and white whitepine pinewere wereplanted planted here in o seeded site. Red in1983. 1983.We We shall shall examine an experiment experiment in which typical understory species species have been transplanted in blocks so-called blocks of of their th& own ownsoil soil(the (the so-called"nucleation" "nucleation" approach). successfulwere werethe thewoody woodyground groundcover cover bearberry bearbeny ch). Especially Especially successful and the nitrogen-fixing shrub soapberry soapberry (or (or buffalo berry). Note nitrogen-fixing shrub buffalo berry). Note that many other ther species species were w e introduced introduced with with the the woody woody plants, plants, wild wild strawberry and and starry starryfalse falseSolomon's Solomon'sseal sealbeing beingespecially especiallyconspicuous. conspicuous. The later nonnally limestone soils, soils,and and its its success here is success here is normally favours favours limestone probably the used.Some Sometree treespecies, species, the result result of of the thelimestone limestonetreatment treatmentused. such uch as & balsam balsam fir and and white white spruce, spruce, have have also also been been acddentally acad&aUy introduced troducedin inthe thesoil soilblocks. blml-- �I I I I I 1 I I I I I I I I I I I I Stop #9- smelter. Coniston Hydro road, 2 km east of the Coniston From point, it is possible to see land treated in 1978, 1981, From this vantage van 1987, 1993 and 1994, as well well as as untreated untreated land and 1994, respectively, respectively7as and land land aerially-limed by Inco in 1995 and 1996 in the distance. Note that the aerially-limed Inco 1995 1996 the distance. Note the untreated barren, while that to to the the east east is is untreatedland landcloser closerto to the thesmelter smelteris is still still barren7 undergoing rapid colonization white birch. birch. Plantings Plantings of of pines, black colonization by white locust and red oak can also be seen here. Some of the red and jack pine seen o. was propagated propagated underground u n d ~ r o u nby dbyInc Inco. seen here here was IfIf we we drive drive further further down down the the Hydro Hydro road, road, we we can get a close-up view of barren withbirches birchesbeginning beginningtotocolonize. colonize. barrenterrain, terrain,with Stop 10 -- north north Stop (or (or drive-by) drive-by) ## 10 km km east of of the theConiston Coniston smelter. smelter. and south of Highway 17E, 3.5 Following grassinginin1978, 1978,container container and bare-root stock of red and Jack Following grassing pine were planted here, here7plantation-style, plantation-style, in 1979. 1979. Later planting in in this this area natural-looking style. If If we we stop at this area were in aa more more informal, informal. natural-look in^ stvle. this site, site, we shall have the opportunity to look at ano&er-understory another unders tory transplanting trm trial using soil blocks. trial wing soil Stop Stop # # 11 11 -smelter. Coniston-Garson road, 4 4 km k m north north of of the theConiston Coniston Prior to initiation of manual liming of hillsides, this sandy valley bottom was limed, fertilized and seeded with Canada Canada bluegrass bluegrass in in1974. 1974.Some Some areas showed rapid, diverse colonization, while while others others remained remained bare. bare. The The latter areas were probably short of organic matter and and phosphorus phosphorus(see (see experimental plot). The nitrogen-fixing shrub called called sweet sweet fern fern is is spreading rapidly. Interesting herbaceous species now found found at s now at this thissite site include rattlesnake ferns, lathes' tresses orchids and a small small blue blue early early s and violet (Viola adunca). olet ( Viola admca). Thee red red and andJack Jack pine pine plantations plantations at at this this site sitewere wereestablished establishedfollowing followin grassing 1976, using using paper-pot container container stock. stock. Seedlings Seedlings planted in in rassing in 1976, neighbouring eighbouringungrassed ungrassedareas areasshowed showed almost almost total total mortality. mortality. �I I En route to Stop Stop # 12 12 -- north of Garson Garson I I I I I I I I I I I I I I I Here you you will will see see extensive extensive tracts tracts of blueberries, Here bluebemies, with scattered scattered pines. pines. Tree planting planting here here has has been been kept to Tree to the thenhinimuni, minimum, to to conserve conserve the the blueberry stands. stands. Past the airport airport turnoff, turnoff, on on the the Falconbridge Falconbridge road, you will d l see see extensive extensive grassing and and pine grassing pine planting planting carried carried out by byFalconbridge Falconbridge Ltd. Ltd. in collaboration collaboration with the the Region. Region. Stop (roiling (rolling stop?) ## 12 - south of Falconbridge Falconbridge Here see very very early early revegetation revegetation work work carried carried out by Tom Tom Uoyd Lloyd Here we shall see Falconbridge Ltd. Ltd.Carolina Carolinapoplars poplarswere wereplanted plantedin in large large pits filled filled with of Falconbridge black loam, loam, in in plantation plantation fashion. fashion.This Thisisisaa very very different approach from from what we would take today. Stop (rolling stop?) stop?) ## 13 community Stop (rolling 13 - Falconbridge Falconbridge communiv We Park, which is a a park We shall shall drive drive past pastCentennial Centennial Park, which is park built built on on first tailings Falconbridge's first tailings deposit. deposit. We We shall shall also also view view Fakonbridge's Falconbridge's "conservation area",aabarren barren peatland peatland that that has been restored to a cattail uconservation area", cattail marsh by flooding it with alkaline mine waste water and sewage sludge. flooding and sewage sludge. This currently being upon by slag, and This is currently being encroached encroached upon by granulated granulated slag, negotiations are underway between the Environmental Environmental and Smelter Smelter negotiations are underway between officials alternative dumping dumping site. officials to find an alternative En route, re-entering re-entering Sudhury Sudbury by by the theKingsway Kingsway As we enter enter Sudbury, you will will notice notice that the the semi-barren semi-barren woodland woodland has has As we grassy understory. Only occasionaJly occasionallyare are woodland woodland sites sites grassed grassed in this a grassy this way. way, �-8PARTIAL CHECK OF VASCULAR VASCULAR PLANT PLANT SPECIES SPECIES PARTIAL CHECK LIST LIST OF FOUND ON BARREN AND REVEGETATED m G E T A T E D SITES SITES BARREN AND CB CR P R S T * COLONIZING SPECIES CommIN'G sF'Ecm (BARRENS) (BARRENS) COLONIZING (REVJXETATED) COIDNIZING SPECIES (REVEGFFATED) PLANTED (NURSERY STOCK) PLANTED (NURSERY STOCK) RELICT RELICT SPECIES SPECIES SEEDED SPECIES SEEDED SPECIES SUSPECTED SEED SEED CONTAMINANT CONTAMINANF TRANSPLANTED TRANSPLANTEDSPECIES SPECIFS PART "WILDFLOWER" MIXTURE MIXTURE PART OF OF "WIU)FLOWER" Mosses and lichens lichens Ceratodon Cmtodon purpureus Funaria Funaria hygroinetrica hygromemica Pohlia nutans nutans Polytrichwn Poljtachum commune commune Ciadonia cI. d&omBs deformis CIa&n.ia cf. Stereocaulon paschale cf. paschaie Stereocaulon ci. Ferns and and fern-allies fern-allies Bolrychium Botrychium multifidum multifidurn Dennstaedtia Dennstaedtia punctiloba punctiloba Equisetum &uisetum arvense arvense Ophioglossum turn Ophioglossumvulga vulgatum Conifers conifers Cedar, easternwhite eastern white Cedar, Larch, European WOF larch, Japanese Japanese Pine, Jack Larch,Jack Pine, Mugo Mugo red Pine, red Pine, Pine, Pine,white white Spruce, Spruce, black black Spruce, white white Spruce, J=a I I I CR CR CB, CR GB GB 03 CR R 03 CR Thuja Thujaoccidenta.lis wadentab Larix decidua decidua larix leptolepis Larix leptolepis Pin us banksiana banksia.na l?inus Pinusmugho Pinus mugho Pin resinosa l?inus resinosa Pin us strobus Pinus su-obus Picea mañana Rcea m arha Picea Rcea glauca glauca p P P P P P P P P �I I I I I I I I I I I I I I I I I I Grasses Grasses Bluegrass, Canada Canada Bluegrass, Bluegrass, Kentucky Fescue, creeping red Fescue, tall Fescue, tall Hairgrass, wavy wavy Hairgrass, Hairgrass, tufted tufted Orchard Orchard grass grass Qpack QW& grass grass Redtop Redtop Tickle Tickle grass grass Timothy Timothy Poa compressa SS compressa Poa pratensis S Festuca rubr.a mbra SS Festuca m arundinacea dinaca S Deschainpsia Lkschampsia flexuosa KR Descharnpsia Lkschampsiacaespitosa caespitosaCB, CB,CR CR Dactylis glomerata glornerata CR CR(SC?) (SC?) Agropyron CR Agropyron repens repens Agrostis gigan tea 5, S, CR a Agmstis gigantea Agrostis CB, Agmstis scabra scabra a,CR a Phleum tense S Phleum pra pratense Other Ot31erMonocotvledons Monocotvledons False Solomon's-seal, Solomon's-seal, starry starry Lady's tresses, tresses, nodding Lady's Lady's tresses, tresses, slender slender Sedge Sedge Sedge Sedge Sedge, Sedge, wool Smilacina stellata AT stellata Spiranthes CR (moist (moist sand) Spirauthes cernua c a m sand) Spiranthes CR (moist (moist sand) sand) gradis Spirauthesgradilis Carexhoughtoniana Grexhoughtoniana CR CX Juncus brevicaudatus Jmcus brevicaudatus CB(wet) CB(wet) Scirpus cyperinus CB (wet) Herbaceous Herbaceous Dicotyledons Dicotyledons Alfalfa Alfalfa Alsike clover clover Alyssum, Alyssum, yellow Bindweed Black-eyed Susan Susan Bristly sarsaparilla sarsaparifia Cornflower cornflower Cow Cow vetch vetch Dam&s rocket Dame's rocket [)evil's Devil's paintbrush Fireweed Flax Flax Foxglove Foxglove Grass-leafed goldenrod Grass-leafed Grass-leafed stitchwort Grass-leafed Hawk's beard Heal-all Horseweed Iceland WPPY Icehd poppy Moth mullein mullein Medicago offlcinalis officit~ah Trifoliuni hybridwn TMolium hybndum Alyssum tile * Alyssum saxa saxatile* Polygonum Polygon urn &ode cilinode hirta Rudbeckia h irta** Aralia hispida Amlia hispida Can ta urea cyan us * G?Ll&Ureacyanus* Vicia cracca Hcia mcca CR CR 5, S, CR CR S 5 CB, CR 5, 1', T CRa CR CR s, 5s CR CR Hesperis matronalis **5S Heqmis matronalis Hieraciwn aurantiacwn fieraciumamtiacum Epiobiwn Epilobiutn angustifolium angustifolium Linurn pet-anne h u m p e r e m e ** Digitalis ppurpurea q m ** Solidago granilnffolia &lidago gmnhifofia Stellaria graininea S t W a graminea Crepis -pis tectorwn tectortun Prwiella h e l l a vulgaris vulgaris Conyza canadensis canaciensis Conyza Papavernudicaule Papaver nudicade ** Verbascwn blattaria Verbascum b1am.a CR CR CR CR SS S CR CR CR CR CR CR A AT T CR CR S5 CR * CR* �I I I I ' I I I I -10Muflein Mullein Northern Nodern willow-herb willow-her1 Oxeye daisy Oxeye daisy Pearly Pearly everlasting everlasting Philadelphia Philadelphia fleabane fleabane Red clover clover Rock Rock harlequin harlequin Rough cinquefoil cinquefoil Rough goldenrod goldenrod Scentless Scentless mayweed mayweed Sheep Sheep sorrel sorrel Sulphur Sulphur cinquefoil cinquefoil Tickseed Tickseed White bedstraw bedstraw White White sweet-clover sweet-clover Wild strawberry strawbeny Yarrow Ymow Yellow hawkweed hawkweed Verbascum CR Verbascum thapsus thapsus QZ Epilobiwn ulosum CR Epilobiumgland glanddosum QZ Chrysanthemum leucanthemwn CLuysanthemumleucanthemum Anaphalis Anaphalis margaritacea margm-tacea CR a Erigeron philadeiphicus CR Erigmn philadelphim CR Trifoliani tense CR TMoliumpra vratense at Coiydslis sempervirens CR a corydalis iempelvirens Potentiila norvegica CR CR Potentilla norvegica Solidago rugosa CR solidago mgosa CR Anthemis SI SI A n t h e - s cotula cotda Rumex acetosella CR acetosella CR Potentiila recta T, Potentilla recta T, CR a Coreopsis lanceolam lanceolata ** S s Galium mollugo moliugo CR Galium CR MeiLlotus a/ba Melilotus alba CR CR QZ Fragaria Fmgm-avirginiana vir&iana Achillea mulefoliuni AchiUea mill&olium Hieracium florentinum Hkracium florentillum 1, T,CR Populus balsamifera balsamifera Salix pyrifolia salixpyf%olia Arctostaphylos uva-ursi uva-ursi Robinia pseudo-acacia pseudo-acacia Prunus virgilliana l?runusvirginiana Vaccinium angustifolium Vacciniumangustifolium Vaccinium niyrtilloides Vacciniummyrtilloides II, CR a s CR, CR,S CR CR Woody woodv Dicotyledoms Dicotyledom Balsam poplar poplar Balsam willow I I I I I I I I Bearberry Black locust locust Choke cherry cherry Common blueberry blueberry Downy-leaf blueberry Downy-leaf blueberry Dwarf birch Large-toothed Largetoothed aspen Pin cherry F'in cherry Pussy Pussy willow willow Red elderberry elderberry maple Red maple Red Red Oak oak Silver Silver maple maple Slender Slender willow willow Soap or buffalo berry Sugar Sugar maple maple Sweet fern sweet fern Trembling aspen aspen White White Ash Ash White white birch birch Witherod Betula Betula pumula pumila Populus grmdidentata grandidentata Prunus l?runus pensylvanica peusylvanica Salixhumulis Salixhumilis Sam bucus ppubens Sambucus uhs Acer rubrum rubrum Quercus borealis Querm borealis Acer urn Acer saccharin saccharinum SaThcgracilis gradilis salix Shepherdia Shepherdia canadensis canadensis Acer sacsacdiarum Comptonia peregrina peregrina Populus tremuloides tiemuloides Fraxinus americana Fmxinus ameficana Betula papyrifera papyrifera Viburnum Viburnumcassinoides casinoides R,a CR CR T T P P R, CR? CR? R, CR R R R,a CB, a,CR CR CR R, R, CR? CR? CR CR CR CR R R R PP CR CR T T pP a CR CR CR P P R, R, CR CR R R �3 (ti)- 2 mIllionth free (Nickel Cenn Welcome Cean) cm - millionth vee (Tiny Pn Caphx) rtt14MJt__44_th Tree 't- a S km GREENING MAP: MAP A ,. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1997 Description An account of the resource Institute on Lake Superior Geology. Sudbury, Ontario. May 6-11, 1997. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1997 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/d31e5e66626ffb77a8d6cff650edfda2.pdf f889347321a92c3ecf21c0564230434d PDF Text Text Program and and Abstracts 94th ANNUAL MEETING Minneapolis, Minnesota May 1998 May 6-10, 6-10,1998 Organized by MINNESOTA MINNESOTA GEOLOGICAL GEOLOGICAL SURVEY UNIVERSITY OF MINNESOTA UNIVERSITY MINNESOTA �44th Annual Meeting INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE parts: Volume 44 contains the following parts: Part Part 1: Program Program and and Abstracts Part 2: Field Part 2: Field Trip Trip Guidebook Guidebook i—Early 1-Early Proterozoic Proterozoicintrusive intrusive rocks of east-central Minnesota 2—Geology 2-Geology of the southeastern southeastern portion of the Midcontinent Midcontinent Rift Rift System, eastern Minnesota and western Wisconsin 3—Glacial 3-Glacial exotica exotica of the Twin Cities Cities area 4—Stratigraphy and hydrogeology 4ÑStratigraph hydrogeology of Paleozoic rocks of southeastern southeastern Minnesota 5—Minnesota 5-Minnesota River River Valley and vicinity, vicinity, southwestern southwestern Minnesota Minnesota Reference to the material in Reference in this volume volume should should follow follow the example example below: below: P.K., Neymark, L.A., Sims, P.K., L.A., Peterman, Z.E., Z.E., and and Kotov, Kotov, A.B., 1998, 1998, Nd isotope isotope evidence evidence for for Middle Middle and and Early Early Archean Archean crust crust in in the the Wawa Wawa subprovince subprovinceof of the the Superior SuperiorProvince, Province, U.S.A., [abstract]: Institute on Lake Superior logy Proceedings, Proceedings, 44th Michigan, U.S.A., Superior Geology MN, 1998; v. v. 44, 44, Part Part 1, 1,p. p. .: Annual Meeting, Minneapolis, MN, Volume Volume 44 is is published by the Institute on Lake Superior Geology and distributed by the Institute Institute Secretary-Treasurer: Secretary-Treasurer: Mark Mark Jima Jirsa (term (term 1994-2000) 1994-2000) Minnesota Minnesota Geological Geological Survey Survey 2642 University Avenue MN USA 55114-1057 St. Paul, MN 55114-1057 (612)-627-4780 (6 12)-627-4780 email: jirsa001@tc.umn.edu jirsa001 @tc.umn.edu http://www.geo.mtu.edu/great_lakes/ilsgl ILSG website http://www.geo.mtu.eddgreat_lakes/ilsg/ ISSN 1042-9964 1042-9964 �INSTITUTE ON LA SUPERIOR GEOLOGY 4th Annual Annual Meeting Meeting 44th May 6-10, 1998 Minneapolis, Minnesota Sponsored Sponsored by: by: Minnesota MinnesotaGeological GeologicalSurvey Survey University University of Minnesota Minnesota PROCEEDINGS PROCEEDINGS Volume 44 44 Part Program and Part 11-Program and Abstracts �CONTENTS CONTENTS Proceedings Volume Volume 44 44 Proceedings Part1—Program 1-Program and andAbstracts Abstracts Part Instituteson onLake LakeSuperior SuperiorGeology, Geology,1955-1998 1955-1998 ...............................................iviv Institutes Constitution Constitution of of the theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology..........................................vv .. vu By-Laws By-Lawsofofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology.. .........................................vii ... GoldichMedal MedalGuidelines Guidelines ........................................................................ viii vm Goldich PastGoldich GoldichMedalists Medalists. ............................................................................. x.x Past x GoldichMedal MedalCommittee Committee ...........................................................................x Goldich xi Citationfor for1998 1998Goldich GoldichMedal MedalRecipient Recipient.. .....................................................xi Citation .. ... Student Student Paper Paper Awards Awards ............................................................................. xiii xm ... StudentPaper PaperCommittee Committee ......................................................................... xiii xm Student StudentTravel TravelAwards Awards.. ........................................................................... xii xu Student Boardof ofDirectors Directors ................................................................................. xiv xiv Board LocalPlanning PlanningCommittee Committee.. ......................................................................xiv xiv Local SessionChairs Chairs ...................................................................................... xv xv Session BanquetSpeaker Speaker.. .................................................................................. xv xv Banquet xvi Reportof ofthe theChair Chairofofthe the43rd 43rdAnnual AnnualInstitute InstituteMeeting Meeting.. ...................................xvi Report ... Program.. .......................................................................................... xviii xvm Program Abstractsfor forSpecial SpecialSession: Session: Abstracts 1 Geolo~ical Overviewof ofthe theLake Lake Superior SuperiorRegion Region ..........................................1 Geolo2ical Overview Card,Ken Ken D. D. Card, Archean Archean geology geology of of the the Great Great Lakes Lakes region region of of North NorthAmerica America ................................33 Ojakangas,Richard RichardW. W. Ojakangas, Generalized GeneralizedEarly EarlyProterozoic Proterozoichistory, history,Lake LakeSuperior Superiorregion region ................................ .55 Cannon,William WilliamF. F. Cannon, Understanding Understandingthe theMiddle MiddleProterozoic Proterozoichistory history of of the theLake LakeSuperior Superiorregion: region: What's What's new? new? What's What'snext? next?. ...............................................................19 19 Runkel, Anthony Anthony C. C. Runkel, Paleozoic Paleozoicrocks rocksin inthe thenorthern northernpart part of of the thecentral centralmidcontinent midcontinentof of North North America America Patterson, Carrie CarrieJ.J. Patterson, Models Models for for interpreting interpreting the the Quaternary Quaternary history of the the Lake Lake Superior Superior region region L. Southwick, David David L. Southwick, 25 .........25 .................33 33 37 ...................................... .37 39 Abstracts for forGeneral GeneralTechnical TechnicalSessions Sessions ...................................................... .39 Abstracts What's What'snext nextfor forgeology geologyin inthe theLake LakeSuperior Superiorarea9 area? Ill �INSTITUTES ON INSTITUTES ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY, GEOLOGY,1955-1998 1955-1998 # DATE DATE PLACE PLACE C HAIRS CHAIRS 1 1955 2 1956 3 1957 4 1958 5 6 1959 1960 7 1961 8 10 1962 1963 1964 11 1965 12 13 14 1966 15 16 1969 1970 17 1971 18 1972 9 1967 1968 19 1973 20 1974 21 1975 22 23 24 25 26 27 28 29 30 1976 1977 1978 1979 31 1985 32 33 34 35 36 37 38 39 40 1986 1987 1988 41 42 43 44 1980 1981 1982 1983 1984 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 Minneapolis, Minnesota Minneapolis, Houghton, Michigan East Lansing, Lansing, Michigan Duluth, Duluth, Minnesota Minnesota Minneapolis, Minneapolis, Minnesota Madison, Wisconsin Port Arthur, Ontario Ontario Houghton, Houghton, Michigan Duluth, Duluth, Minnesota Ishpeming, Ishpeming, Michigan Michigan St. Paul, Minnesota Sault Ste. Marie, Michigan Michigan East Lansing, Michigan Superior, Wisconsin Superior, Oshkosh, Wisconsin Thunder Thunder Bay, Bay, Ontario Ontario Duluth, Duluth, Minnesota Houghton, Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Ontario Marquette, Marquette, Michigan Michigan St. Paul, Minnesota Thunder Thunder Bay, Ontario Ontario Milwaukee, Wisconsin Duluth, Duluth, Minnesota Minnesota Eau Claire, Claire, Wisconsin Wisconsin East Lansing, Lansing, Michigan International Falls, Minnesota International Houghton, Michigan Michigan Wausau, Wausau, Wisconsin Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Marquette, Michigan Michigan Duluth, Minnesota Thunder Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Ontario Cable, Wisconsin Sudbury, Ontario Minneapolis, Minneapolis, Minnesota C.E. Dutton C.E. A.K. Sneigrove A.K. Snelgrove Sandefur B.T. Sandefur R.W. Marsden Marsden G.M. Schwartz & C. Craddock E.N. Cameron Cameron E.G. Pye Pye A.K. Sneigrove Snelgrove H. H- Lepp L~PP A.T. Broderick Broderick P.K. Sims & R.K. R.K. Hogberg Hogberg R.W. White White WJ. W.J. Hinze Hinze A.B. Dickas Dickas G.L. LaBerge LaBerge Bartley & E. Mercy M.W. Bartley D.M. Davidson J. Kalliokoski Kalliokoski M.E. Ostrom Ostrom P.E. Giblin Giblin J.D. Hughes Hughes M. Walton Walton Kehlenbeck M.M. Kehienbeck G. Mursky D.M. Davidson P.E. Myers Myers W.C. Cambray Cambray D.L. Southwick Southwick T.J. Bornhorst G.L. LaBerge LaBerge C.E. Blackburn Blackburn J.K. Greenberg Greenberg E.D. & R.P. Sage Sage E.D. Frey & J. S. S. Klasner Klasner J.C. Green Green M.M. Kehlenbeck M.M. P.E. Myers A.B. Dickas D.L. Southwick D.L. Southwick T.J. Bornhorst M.C. Smyk M.C. L.G. Woodruff R.P. Sage, W. Meyer R.P. J.D. Miller, M.A. Jirsa J.D. iv �_________(some CONSTITUTION OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Board—May 8, 1997) (Last amended by the Board-May 8,1997) Article Article II Name The name of the organization organization shall be the "Institute "Institute on Lake Superior Superior Geology". Geology". Article II II Objectives Objectives are: The objectives objectives of this this organization organization are: A. To Toprovide provideaameans meanswhereby whereby geologists geologists in in the the Great Great Lakes Lakes region region may may exchange exchange ideas ideas and and scientific scientificdata. data. Topromote promotebetter betterunderstanding understandingof of the the geology geology of of the the Lake Lake Superior Superior B. To region. region. C. To Toplan planand andconduct conductgeological geologicalfield field trips. trips. Article III ifi Status Status to the the benefit benefit of any No part of the income of the organization shall insure to member or individual. In the event of dissolution, the assets of the organization organization shall be distributed distributed to free organization). organization). (some tax free To avoid Federal and State income taxes, the organization should be not only "scientific" "scientific" or or "educational, "educational,but also also "non-profit". "non-profit". Minn. Stat. Anno. 290.01, subd. 4 Minn. Stat. Anno. 290.05(9) Mim. 1954 Internal Revenue Code Code s.501(c)(3) s.501(c)(3) Article IV Article Membership Membership The membership of the organization organization shall shall consist consist of persons who have have registered for an annual meeting within the past three years, and those who approved by the indicate interest in being a member according to guidelines approved Board of Directors. Directors. Article V Meetings organization shall meet once a year, preferably preferably during during the the month month of The organization April. The Theplace placeand andexact exactdate date of of each each meeting will be designated designated by the Board of Directors. Directors. Article VI Directors The Board of Directors shall consist of the Chair, Secretary-Treasurer, and the last three past Chairs; but if the board should at any time consist of fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve serve as directors, directors, the vacancies vacancies on the board may be be filled filled by the Chair Chair so so as to bring the membership membership of the board board to to five five members. members. V �Article Article VII Officers Officers The The officers officers of of this this organization organizationshall shallbe be aa Chair Chairand and Secretary-Treasurer. Secretary-Treasurer. A. A. The TheChair Chairshall shallbe beelected electedeach eachyear year by by the the Board Board of Directors, Directors, who shall give due consideration consideration to the wishes of any group that may be promoting promoting the next annual meeting. His/her Hisher term of office office as Chair will terminate he/she presides, or terminate at at the close close of the annual meeting over which helshe hisher successor shall have been Helshe will then serve serve when his/her been appointed. appointed. He/she for as aa member member of the the Board Board of Directors. Directors. for aa period period of of three three years as B. The the annual annual meeting. meeting. Hisher His/her TheSecretary-Treasurer Secretary-Treasurer shall shall be elected at the term term of of office office shall shall be be four four years, years, or or until his/her hislher successor successor shall shall have have been been appointed. appointed. Article Article Vifi VIXI Amendments Amendments This vote of of the the membership membership of This constitution constitution may be amended by a majority vote the the organization. organization. vi �BY-LAWS BY-LAWS OF THE INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY I. Duties Dutiesof of the the Officers Officers and and Directors A. ItItshall shallbe bethe theduty dutyof ofthe theAnnual AnnualChairman Chairmanto: to: 1. Preside Preside at at the the annual annual meeting. meeting. 1. Appointall allcommittees committeesneeded neededfor forthe theorganization organizationof of the the annual annualmeeting. meeting. 2. Appoint 3. Assume Assumecomplete completeresponsibility responsibility for for the organization and financing of the annual meeting over over which he/she helshe presides. B. ItItshall shallbe bethe theduty dutyof of the theSecretary-Treasurer Secretary-Treasurerto: 1. Keep Keepaccurate accurateattendance attendancerecords recordsof of all allannual annualmeetings. meetings. 2. Keep Keepaccurate accuraterecords recordsof of all all meetings meetings of, of, and and correspondence correspondence between, the Board of Directors. Directors. 3. Hold Holdall allfunds fundsthat that may may accrue accrue as as profits profits from from annual annual meetings meetings or or field trips for the the organization organization and and operation operation of of and to make these funds available for future meetings as required. C. ItItshall shallbe bethe theduty dutyof of the the Board Board of of Directors Directors to to plan locations locations of annual meetings and and to to advise advise on on the the organization organizationand and fmancing financingof of all all meetings. meetings. II. 11. Duties Dutiesand and Exoenses Expenses A. There Thereshall shallbe beno noregular regular membership membership dues. dues. B. Registration Registrationfees feesfor forthe the annual annual meetings meetings shall shall be determined by the Chair in The registration fees can include consultation with the Board of Directors. Directors. The expenses to cover cover operations operations outside of the annual meeting as determined by expenses the Board of Directors. ItIt isis strongly strongly recommended recommended that registration fees be kept at a minimum minimum to encourage encourage attendance attendance of graduate graduate students. students. ifi. Rules In. Rules of of Order Order The The rules rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shall govern govern this this organization organizationin in all all are applicable. applicable. cases to which they are IV. Amendments Amendments These These by-laws may be be amended amended by a majority vote of the membership of the organization; organization; provided that such modifications shall not conflict conifict with the constitution presently adopted adopted or or subsequently subsequently amended. amended. constitution as presently vu vii �GOLDICH MEDAL GUIDELINES GOLDICH MEDAL GUIDELINES (Adopted by the Board of Directors, 1981; 1981;amended 1997) 1997) Preamble Institute on Lake Superior Geology was born in 1955, as as documented documented by by the the fact fact that that The Institute the 27th annual meeting was held in 1981. The The Institute's Institute's continuing continuing objectives are to deal are related geographically to Lake Superior; Superior; to encourage encourage with those aspects aspects of geology that are discussion of subjects subjects and and sponsoring sponsoring field trips that will bring together geologists from the discussion academia, government government surveys, surveys, and industiy; industry; and and to maintain an informal informal but highly effective mode mode of operation. operation. During the course course of its existence, existence, the membership of the Institute (that (that is, those geologists geologists by attending) attending) has has become become aware aware of of who indicate an interest in the objectives of the ILSG by noteworthy and and meritorious meritorious the fact that certain of their colleagues have made particularly noteworthy contributions to the understanding understanding of Lake Lake Superior Superior geology and mineral mineral deposits. deposits. The first award was made by ILSG to Sam Goldich in 1979 for his many contributions to years. Subsequent the geology of the region extending over about 50 years. Subsequentmedalists medalists and and this this year's recipient recipient are are listed listed in in the the table table below. below. Award Guidelines Guidelines 1) The Themedal medal shall shallbe be awarded awardedannually annually by by the the ILSG ILSG Board Board of of Directors Directors to to aa geologist geologist with aa substantial substantial interest interestin, in,and and contribution contribution to, to, the thegeology geologyof of whose name is associated with the Lake Superior Superiorregion. Medal Committee. Committee. The initial 2) The TheBoard Boardof of Directors Directors shall shall appoint the Goldich Medal appointment will be of three members, one to serve for three years, one for two years, and appointment one for one year. The Themember memberwith withthe thebriefest briefestincumbency incumbencyshall shallbe be chair chair of of the the Nominating Committee. After Afterthe thefirst firstyear, year,the the Board Board of of Directors Directors shall shall appoint appoint at at each each years. In hisfher third third year year this this spring meeting one new member who will serve for three years. In his/her member shall be the chair. The TheCommittee Committeemembership membership should should reflect the main fields of interest and geographic interest geographic distribution distribution of ILSG ILSG membership. membership. November , the Goldich Medal Committee shall make its recommendation of November, 3) By By the the end of to the the Chair Chair of of the the Board Board of of Directors, Directors,who who will will then then inform inform the the Board Board of of the the nominee. nominee. 4) The TheBoard BoardofofDirectors Directorsnormally normallywill willaccept acceptthe thenominee nominee of of the the Committee, Committee, will will inform inform the the medalist medalist immediately, immediately, and and will will have have one one medal medal engraved engraved appropriately appropriately for for presentation presentation at the next meeting of the Institute. 5) ItItisisrecommended recommendedthat thatthe theInstitute Instituteset set aside aside annually annually from whatever sources, such funds as will be required to support support the continuing continuing costs of this award. Nominating Procedures Nominatin~ 1) Nominations Nominations shall shallbe be taken taken at at any time by the Goldich Medal Committee. Committee Committee members may themselves nominate candidates. The The deadline deadline for for nominations nominations is November 1. 1. 2) Nominations Nominationsmust mustbe beininwriting writingand andsupported supportedby by appropriate appropriatedocumentation documentationsuch such as as letters letters of recommendation, recommendation, lists of publications, curriculum vita's, and evidence of contributions contributions to Lake Lake Superior Superior geology geology and and to to the the Institute. vifi �Nominationsare arenot notrestricted restrictedto toInstitute Instituteattendees, attendees,but but are arc open open to anyone anyone who has has 3) Nominations worked on and contributed contributed to the understanding understanding of Lake Superior Superior geology. Selection Selection Guidelines Guidelines 1) Nominees Nominees are are to to be be evaluated evaluated on on the the basis of their contributions to Lake Superior geology (sensu lato) including: a) importance importanceof ofrelevant relevant publications; publications; b) promotion promotionof ofdiscovery discoveryand andutilization utilization of of natural natural resources; c) contributions contributionsto tounderstanding understandingof of the the natural natural history and environment environment of the region; region; d) generation generationof of new new ideas ideas and and concepts; concepts; and e) contributions contributionsto tothe thetraining training and and education education of geoscientists geoscientists and the public. Nomineesare aretotobe beevaluated evaluatedon ontheir their contributions contributionsto the Institute as demonstrated by 2) Nominees attendance at Institute meetings, meetings, presentation service on Institute Institute presentation of talks and posters, and service boards, boards, committees, committees, and andfield fieldtrips. trips. 3) The Therelative relativeweights weightsgiven givento to each each of of the the foregoing foregoing criteria criteria must remain flexible and at the the discretion discretion of of the the Committee Committeemembers. members. 4) There Thereare areseveral severalpoints pointsto tobe beconsidered consideredby by the theGoldich Goldich Medal Medal Committee: Committee: a) An Anattempt attemptshould shouldbe be made made to to maintain maintain a balance of medal recipients from each of the three three estates—industry, estates-industry, academia, academia, and and government. government. that much much of b) ItItmust mustbe benoted notedthat that industry industry geoscientists geoscientists are arc at a disadvantage in that their work in not not published. published. U.S., and the the other Canada. Canada. This 5) 5) Lake Lake Superior Superior has two sides, one the U.S., This is is undoubtedly undoubtedly Institute's great strengths and should be nurtured by by equitable equitable recognition recognition of one of the Institute's excellence excellence in in both both countries. countries. ix �GOLDICH MEDALISTS 1979 Samuel SamuelS. S. Goldich Goldich not awarded 1980 not 1989 Jorma Jorrna Kalliokoski Kalliokoski 1981 Dutton, Jr. 1981 Carl E. Dutton, 1990 Kenneth Kenneth C. Card 1982 Ralph RalphW. W. Marsden Marsden 1991 William William Hinze 1983 Burton Burton Boyum Boyum F. Cannon 1992 William William F. 1984 Richard RichardW. W. Ojakangas Ojakangas W. Davis 1993 Donald DonaldW. 1985 Paul PaulK. K. Sims Sims 1994 Cedric Cedric Iverson 1986 G.B. G.B. Morey Morey LaBerge 1995 Gene GeneLaBerge H. Halls Halls 1987 Hemy HenryH. L. Southwick Southwick 1996 David DavidL. 1988 Walter WalterS. S. White White 1997 Ronald Ronald P. P. Sage Sage 1998 1998 Zell Peterman Peterman GOLDICH MEDAL GOLDICH MEDAL COMMITTEE—1997-1998 COMMITTEE-1997-1998 (Committee membership membership through the meeting year shown) shown) Dan England England (1998) (1998) Eveleth Fee Office, Office, Eveleth, Minnesota John Kiasner Klasner (1999) (1999) Western Illinois University, University, Macomb, Macomb, Illinois Mark Mark Smyk Smyk (2000) (2000) Ontario Ontario Geological Geological Survey, Survey, Thunder Thunder Bay x �CITATION CITATION Zell Zell E. E. Peterman Peterman 1998 Goldich Medal Medal Recipient Recipient my personal personal pleasure pleasure to to introduce introduce Zell E. Peterman, this years Goldich medalist. Zell Zell It's my deserves this this highest highest honor honor of the Institute Institute on Lake Superior Superior Geology because of his richly deserves many outstanding outstandingcontributions contributions to to Precambrian Precambrian geology geology and and geochronology geochronology of of the the Lake Lake Superior Superiorregion. region. Zell received received aa Geologic GeologicEngineering Engineeringdegree degreefrom fromthe the Colorado ColoradoSchool Schoolof of Mines, Mines,aamasters masters Zell Geology from from the the University University of Minnesota, Minnesota, Minneapolis, and a Ph.D. in Geology Ph.D. in Geology in 1962 from the University of Alberta. At AtMinnesota, Minnesota,Zell Zellwas wasaastudent studentof of Sam SamGoldich. Goldich. 1962 Zell has 1994Ñwit the theGeologic Geologic has spent spent all all of ofhis hiscareer—except career-except for forthe theyears yearssince since1994—with Division Division of of the the U.S. U.S. Geological Geological Survey, Survey, and it was in this capacity that he carried out most of of his his geochronologic geochronologicresearch researchthat thatwe weacknowledge acknowledgetoday. today. Over aa period period of of several several years, years, working working with with field field geologists, geologists, Zell Zell has has been been mainly mainly responsible for for the the isotopic isotopictime time framework framework for for the the pre-Keweenawan pre-Keweenawan that that we we accept accepttoday. today. responsible A A major majorcontribution contributionwas wasaastudy studyof ofArchean Archeanrocks rocksacross acrossthe theGreat GreatLakes Lakestectonic tectoniczone zoneinin the the Marenisco-Watersmeet Marenisco-Watersmeet area in Michigan. This Thisstudy study established established that that gneisses gneisses in in the the Minnesota Minnesota River RiverValley Valley subprovince subprovinceare are as asold oldas as3,550 3,550 Ma Ma and and flanking flankingmetavolcanicmetavolcanicmetasedimentaryrocks rocksininthe theWawa Wawasubprovince subprovince(to (tothe thenorth) north)are arein inthe therange range2.6-2.8 2.6-2.8 Ga. Ga. metasedimentary This Thispattern pattern has hasproved proved to tobe becharacteristic characteristicof of Michigan-Wisconsin. Michigan-Wisconsin. In 1980's,in in an aninnovative innovativestudy study utilizing utilizing Rb-Sr Rb-Sr ages of biotite, Zell outlined the In the the late late 1980's, uplift uplift history history of of the theGoodwin GoodwinSwell Swellininnortheastern northeasternWisconsin—a Wisconsin-a lithospheric lithosphericflexure flexure caused by by crustal crustal loading loading along along the Midcontinent Rift System. This This isis the the sort sort of of thing thing that caused has been been characteristic characteristic of Zell. More Morethan than most most people, people, he he has has the the ability ability to use use various has geochronologic geochronologictechniques techniquesto tosolve solveproblems problemsmost mostof ofus usmortals mortalsdon't don'tknow knoweven evenexist. exist. Since Since 1994, 1994,Zell Zell has has been been involved involved in in DOE's DOE'SYucca Yucca Mountain Mountain Project, and some of the the successful successfultechniques techniquesused usedto tosolve solveprojects projectsjust just blow blowyour yourmind. mind. II should duties and and skills. skills. From should mention mention Zell's Zell's administrative administrative duties From 1971 1971to to 1976, 1976,he hewas was branch branch chief chief of of the theUSGS's USGS's Branch Branchof ofIsotope IsotopeGeology, Geology, aatime timewhen whenthe theIsotope IsotopeBranch Branch was Since 1994, 1994, he he has has assembled assembled an an isotope isotope hydrology hydrology team team under under the the was flourishing. flourishing. Since Yucca Yucca Mountain Mountain Project Project that that isisdoing doingmany many marvelous marvelousthings, things, particularly particularly using using Rb-Sr Rb-Sr tracers. tracers. P.K. Sims Sims P.K. xi �STUDENT TRAVEL AWARDS STUDENT AWARDS The 1986 Awards to support 1986 Board Board of of Directors Directors established established the ILSG Student Travel Awards the annual annual meeting meeting of ofthe theInstitute. Institute. The awards will will be be made made from from aa student participation at the fund set up for this purpose. purpose. These special fond These awards are intended to help defray some of the direct travel costs of attending Institute Institute meetings, meetings, and include a waiver of registration fees, fees, but exclude exclude expenses expenses for for meals, lodging, and field trip registration. The The number number of of awards awards and value are determined determined by the annual annual Chair Chair in consultation consultation with the Secretary-Treasurer. Secretary-Treasurer. Recipients Recipients will will be be announced announced at at the the annual annualbanquet. banquet. The following following general general criteria will be considered by the annual Chair, who is responsible for the selection: selection: 1) The The applicants applicantsmust must have have active active resident (undergraduate or graduate) student status at the the time time of of the the annual annual meeting meeting of of the the Institute, Institute, certified certified by the department department head. 2) Students Studentswho whoare arcthe thesenior seniorauthor authoron on either either an an oral oral or or poster paper will be given favored consideration. consideration. 3) ItItisisdesirable desirablefor fortwo twoor ormore morestudents studentsto to jointly request request travel assistance. assistance. 4) In Ingeneral, general,priority prioritywill willbe begiven givento tothose thosein in the the Institute Institute region region who are are farthest farthest away from the meeting location. 5) award request request shall shall be made in writing to the annual Chair, and should 5) Each travel award explain need, student student and and author author status, status, and and other other significant significant details. details. Successful applicants Successful applicants will will receive receive their their awards awards at at the time time of registration registration for for the meeting. meeting. xli �STUDENT STUDENTPAPER AWARDS AWARDS Each year, the Institute selects the best of the student presentations and honors presenters with a monetary award. award. Funding with Funding for for the the award award isis generated generated from from registrations registrations of the the annual meeting. meeting. The TheStudent StudentPaper PaperCommittee Committeeisisappointed appointedby by the the annual annual meeting meeting Chair Chairin in annual such a manner as to to represent represent aa broad broad range range of of professional professional and and geologic geologic expertise. expertise. Criteria for for best best student student paper—last paper-last modified modified by the the Board Board in in 1997—follow: 1997-follow: Criteria 1) The Thecontribution contributionmust mustbe bedemonstrably demonstrablythe thework work of of the the student. student. 2) The Thestudent studentmust mustpresent presentthe thecontribution contributionin-person. in-person. to grant, grant, and and whether whether or or 3) The TheStudent StudentPaper Paper Committee Committee shall shall decide how many awards to not to give give separate separateawards awards for for poster poster vs. vs. oral oral presentations. presentations. 4) In Incases casesof ofmultiple multiplestudent studentauthors, authors,the the award award will be made to the senior author, or the award award will will be be shared shared equally equally by by all all authors authors of of the the contribution. contribution. amount of the awards 5) The The total amount awards is left left to the discretion discretion of the meeting Chair Chair and and 5) Secretary-Treasurer, but in the the amount amount of of about about $300 $300US. US. Secretary-Treasurer, but typically typically is is in 6) 6 ) The TheSecretary-Treasurer Secretary-Treasurermaintains, maintains,and andwill willsupply supply to to the the Committee, Committee,aa form form for for the the numerical ranking of presentations. This by Student Paper Paper This form form was created and modified by Committees an effort effort to to reduce reduce the the difficulties difficultiesthat that may may arise arisefrom from Committeesover over several severalyears years in in an background. The selection by raters of diverse background. The use of the form is not required, but is left to the discretion of the Committee. discretion the Committee. 7) The Thenames namesofofaward awardrecipients recipientsshall shallbe beincluded includedas aspart part of of the the annual annual Chair's Chair's report reportthat that appears appears in in the the next next volume volume of of the the Institute. Institute. 1998 1998 STUDENT STUDENT PAPER COMMITTEE COMMITTEE Nancy Nelson—Committee Nelson-Committee Chair Chair North Shore Shore Technical Technical Communications Randy Van Schmus Schmus University University of Kansas Kansas Peter Whelan Whelan University University of Minnesota—Morris Minnesota-Morris ll �1998 BOARD OF DIRECTORS BOARD OF DIRECTORS (Board membership membership through the close of the meeting year shown) shown) James Co-chair (2001) (200 1) James D. Miller, Jr., Co-chair Mark A. A. Jirsa, Jirsa, Co-chair Co-chair and and Institute InstituteSecretary-Treasurer Secretary-Treasurer (2000) (2000) Minnesota Minnesota Geological Geological Survey Survey Ronald P. Sage Sage (2000) (2000) Ronald P. Ontario Ontario Geological Geological Survey—Sudbury, Survey-Sudbury, Ontario Ontario Laurel G. G. Woodruff Woodruff (1999) (1999) U.S. Geological Geological Survey—Mounds Survey-Mounds View, View, Minnesota Minnesota Mark Mark C. C. Smyk Smyk (1998) (1998) Ontario Ontario Geological Geological Survey—Thunder Survey-Thunder Bay, Bay, Ontario Ontario 1998 1998 LOCAL LOCAL PLANNING PLANNING COMMITTEE COMMITTEE James D. D. Miller, Miller, Jr.—Co-chair Jr.-Co-chair Mark MarkA. A. Jirsa—Co-chair Jirsa-Co-chair and andmeeting meeting Treasurer Treasurer Terrence TerrenceJ.J.Boerboom—Field Boerboom-Field Trip TripCoordinator Coordinator Lori LoriDay—Meeting Day-Meeting Coordinator Coordinator Assistance Assistanceto to the thelocal localCommittee Committeewas wasprovided providedby by the thefollowing followingindividuals individualsfrom fromthe the Minnesota MinnesotaGeological GeologicalSurvey: Survey: David David L. L. Southwick Southwick Director Directorof of host host organization organization G.B. G.B. Morey Morey Manuscript Manuscriptreview review Alan Alan Knaeble Knaeble Field Field and and meeting meeting preparation preparation Barb Lusardi Lusardi Manuscript Manuscriptpreparation preparation xiv �1998 SESSION SESSION CHAIRS CHAIRS (In (In order of appearance) appearance) P.K. P.K. Sims Sims U.S. Geological Geological Survey—Denver Survey-Denver G.B. G.B. Morey Morey Minnesota Geological Minnesota Geological Survey Survey Lundy Jim Lundy Minnesota Minnesota Pollution Pollution Control Control Agency Agency Laurel Woodruff Woodruff U.S. Geological GeologicalSurvey—Mounds Survey-Mounds View View Johnson Rod Johnson Bitterroot Resources Resources Ltd. Mark Smyk Smyk Ontario Geological Geological Survey—Thunder Survey-Thunder Bay John Green Green University University of Minnesota—Duluth Minnesota-Duluth Paul Weiblen Weiblen University University of Minnesota—Twin Minnesota-Twin Cities Cities 1998 BANQUET BANQUET SPEAKER Bevan French Smithsonian Institution Smithsonian "When the thesky skyfalls: falls: Large Large meteorite impacts impacts and and 'When of earth earth and other worlds" the history of worlds" xv �43rd ANNUAL INSTITUTE 43rd ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY MEETING SUDBURY, SUDBURY, ONTARIO The 43rd annual meeting of the the Institute Institute on on Lake Lake Superior Superior Geology Geology was held on on the the Laurentian University University in Sudbury, Sudbury, Ontario from May 6, through May 11, 11, 1997. 1997. campus of Laurentian The meeting was organized organized by the Precambrian Section and the Resident Geologists Office of the Ontario Ontario Geological Geological Survey. Ron Ron Sage, Sage,Precambrian Precambrian Section, Section, and Wilf Wilf Meyer, Meyer, co-chaired the the event. event. Mrs. Resident Geologist, Sudbury, co-chaired Mrs. Tracy Tracy Livingstone, Livingstone, Resident Resident Geologist's Office, helped organize and coordinate all all activities activitiesrelating relatingto tothe the meeting. meeting. All the guidebooks and individual abstracts were reviewed by W. Meyer, R.P. Sage, and T. Livingstone. The Proceedings Proceedings of of the the 43rd 43rd ILSG ILSGwere were published publishedin in 77 parts: parts: Part 1: Part 1: Program ProgramandAbstracts and Abstracts(edited (editedby byRon RonSage Sageand and Wilf Wilf Meyer); Parti: TheHuronian HuronianSupergroup Supergroupbetween betweenSault Sault Ste. Ste. Marie and and Elliot Lake: Evidence Part2: The for the the Early Proterozoic atmosphere, atmosphere, climate, and tectonics (G. (G. Bennett, K.D. Card, and K.Y. Tomlinson); K.D. Tomlinson); Part Part 3: 3:New Newinformation informationon onthe the Grenville Grenville Front Front near nearSudbury Sudbury (A. (A.Davidson); Davidson); Part Group (S.F.M. Part 4: 4: The TheSudbury SudburyStructure, Structure, with with emphasis emphasis on the Whitewater Group Gibbins); Gibbins); Part 5: Part 5:Magmatic Magmaticore oredeposits depositsofofthe theSudbury Sudbury Igneous Complex (S.A. (S.A. Prevec); Part 6: Part 6: Alkalic Alkalicrocks rocksof of the the Sudbury region (R.P. (R.P. Sage); and Part 7: Part 7:The Thegreening greeningof of Sudbury Sudbury (K. (K.Winterhalder). Winterhalder). A total of 101 101 people registered registered for the meeting in Sudbury and most of the field trips were well attended. There Therewere were13 13paid paid participants participantsfor for the the Huronian Supergroup Supergroup field trip, 22 for the Grenville Grenville Front, 15 15 for for the the Sudbury Sudbury Structure, 36 for the Magmatic ore deposits, deposits, 6 the greening greening of of Sudbury Sudburyfield fieldtrip. trip. Access to local mining for the Alkalic rocks, and 3 for the sites was granted granted by by INCO INCO Limited Limited and and Falconbridge Falconbridge Limited. Limited. Coffee breaks were supported by Laurentian University, University, Falconbridge, Falconbridge, and Ministry of of Northern Northern supported by Laurentian and the the Ministry Development and Development and Mines. Mines. The annual banquet banquet was attended attended by 83 83 diners and held in the Cavern of Science Science North on Ramsey Lake. The TheGoldich GoldichMedal Medal was was awarded awarded to to Ron Ron Sage Sage of of the the Ontario Ontario Geological Geological Survey geology in in the the Lake Superior Superior region. region. The Survey for his contributions contributions to geology The award award was was presented by by Wilf presented Wilf Meyer, Meyer, Resident Resident Geologist, Geologist, Sudbury, Sudbury, Ministry Ministry of of Northern Northern Development and Mines. The Thebanquet banquet address address was was given given by by Dr. Dr. Peter Peter Lightfoot, Lightfoot, INCO INCO talkwas was"Origin "Originof ofthe theSudbury SudburyStructure Structureand andits itsmineral mineral wealth". wealth". Limited. The Thetitle titleof ofthe thetalk The best Student Student Paper Paper Award, Award, consisting consisting of $270 $270 (Can), (Can), was won by Craig Craig Mancuso Mancuso for for his paper "Initial "Initial results of Ar/Ar ArIAr mineral dating from the Peevy node area of northern Michigan and Dunbar dome area of northeastern Wisconsin". Zachary Zachary Naiman Naiman won won $150 $150 for his poster "Petrogenesis of Chengwatana volcanics, volcanics,Minnesota Minnesotaand andWisconsin". Wisconsin". Three student travel awards of $150 $150 each each were were granted granted to to Terry Terry Arcuri, Arcuri, Zachary Zachary Naiman, Naiman, and and Dean Peterson. The Board Board of Directors Directors of of the the Institute Institute on on Lake Lake Superior SuperiorGeology Geology met met in in Sudbury Sudbury on on May May 8, 1997. Members Membersof of the the Board Board in in attendance attendancewere were Mark Mark Smyk, Smyk, Jim Miller (representing (representing Laurel Woodruff), Mark Jirsa (Secretary-Treasurer), Ted Ted Bornhorst, Bornhorst, Ron Ron Sage, Sage, and and Wilf Wilf Meyer. Invited LaBerge. Actions Actions taken were: Invitedguests guestswere were Tracy Tracy Livingstone Livingstone and Gene LaBerge. xvi �1) Accepted Acceptedthe thereport report of of the the Chair, Chair,42nd 42nd ILSG, ILSG, Laurel Laurel Woodruff, including the minutes of the last board meeting. the 1998 meeting. meeting. Jim 2) Approved Approvedan anoffer offerby by the the Minnesota Minnesota Geological Survey to host the Jim the meeting. meeting. The offer by Charles Blackburn to to chair chair Miller and Mark Jirsa will co-chair the the meeting meeting in Kenora Kenora in 1998 1998had to be withdrawn due due to circumstances circumstances beyond beyond his his control. The The1998 1998meeting meetingwill willbe be held held in in Minneapolis, Minneapolis,Minnesota Minnesota on on May 6-10. 6-10. 3) Approved Approvedthe the1996-1997 1996-1997financial financialreport reportpresented presentedby by Mark MarkJirsa. Jirsa. 4) Approved ApprovedRon RonSage Sageas asthe theGoldich GoldichMedal Medal winner winner for for 1997. 1997. 5) Goldich Medal guidelines guidelines prepared by Ken Card. 5) Approved the Goldich 6) Approved Approvedthe thereplacement replacementof of Ken Ken Card Card by Mark Mark Smyk Smyk on the Goldich Medal Committee. Committee. 7) Discussed Discussedthe theILSG ILSGnewsletter newsletter and and web site. The Thenewsletter newsletterhas has been been well well received received and and will be continued. We Wemay mayeliminate eliminatethe the annual annual publication of the Constitution Constitution and place (http://www.geo.mtu.edu/great_lakes/ilsg). The web a general preamble on the web site (http://www.geo.mtu.edu/great-lakeslilsg). site includes information information about about the organization organization and its constitution, constitution, award guidelines, guidelines, publications by the list of publications the Institute Institute and and Goldich Goldich Medal Medal recipients. recipients. 8) Approved Approvedthe themembership membershipguidelines guidelinesfor forthe the ILSG ILSG prepared prepared by Mark Mark Jirsa Jirsa and and Ted Ted in an an effort effort to reduce its size and lower mailing Bornhorst. Mailing Mailinglist listwill will be be revised revised in costs. 9) Discussed was tabled tabledfor forfurther furtherreview. review. A Discussed the the Eisenbrey Eisenbrey Fund and action on this fund was committee consisting committee consisting of Gene LaBerge, Mark Jirsa, and Mark Smyk was formed to study and make make recommendations recommendationson on how how the the monies monies in in the the Eisenbrey Eisenbrey Fund Fund are are to to be be used. Interest Interestearned earnedfrom fromthis thisfund fundmay maybe beused usedto to support supportstudent studenttravel travel to to the the annual annual Institute meeting, and corporations and individuals may may donate donate to to the the fund. fund. Criteria to Institute receive funding receive funding from from the the Eisenbrey Eisenbrey Fund Fund need need to to be be established. established. 10) Discussed Discussed the the ILSG ILSG mailing mailing list. list. Mark MarkJirsa Jirsaisisto tobe be in in charge charge of of the the list. list. 11) Discussed DiscussedUS-Canada US-Canada currency currency exchange. exchange. ItItwas wasagreed agreedthat that prices prices for for Canadian Canadian meetings should should always always list list aa US currency currency price price because many US US participants participants have have difficulty difficulty obtaining obtaining Canadian Canadian funds. funds. Budgeting for the 43rd ISLG was done with an attempt to keep cost down and and not not lose lose money. This Thiswas wassuccessful, successful, in in part, part, due due to to logistical logistical support support provided by the Ontario Ontario Geological Geological Survey. Survey. We enjoyed serving as Co-chairs of the 43rd Institute on Lake Superior Geology meeting. Organizing the meeting was a challenge, Organizing challenge, as the the Ontario Ontario Geological Geological Survey was going going through a difficult period of reorganization, reorganization, and two of the three individuals planning the height of of the the planning planningprocess. process. A special thanks meeting received surplusing notices at the height is due to Wilf Meyer Meyer and and Tracy Tracy Livingstone Livingstone for for staying staying with with the the planning planning and and organization organization of the meeting while their lives were were being being upset upset due due to to reorganization. reorganization. Without Without their their efforts, the meeting meeting could could not not have have been been organized. organized. Ronald P. Sage Wilf Meyer Co-chairs, 43rd ILSG Sudbury, Sudbury, Ontario Ontario xvii �PROGRAM �CALENDAR OF EVENTS EVENTS AND PROGRAM CALENDAR AND PROGRAM WEDNESDAY. MAY 6 0730-0800 0730-0800 0800-1800 0800- 1800 REGISTRATIONIPRE-REGISTRATTONPACKET PACKET PICK-UP PICK-UP REGISTRATIONIPRE-REGISTRATION -Function Area Holiday Inn Pre Pre-Function PRE-MEETING FIELD TRIPS TRIPS Pre-Function Area Depart from: Holiday Inn Pre-Function EARLY PROTEROZOIC PROTEROZOIC INTRUSIVE INTRUSIVE ROCKS ROCKS OF OF EAST-CENTRAL EAST-CENTRAL 11)) EARLY MINNESOTA MINNESOTA Leaders: Terry Boerboom, J i m , and Daniel Daniel Hoim Holm Boerboom, Mark Mark Jima, 2) 2 ) GEOLOGY GEOLOGY OF OF THE THE SOUTHEASTERN SOUTHEASTERNPORTION PORTION OF OF THE THE MINNESOTA AND MIDCONTINENT RJFF RIFT SYSTEM, SYSTEM, EASTERN MINNESOTA AND WESTERN WISCONSIN Leaders: Karl Wirth, Bill Cordua, Bill Kean, Mike Middleton, and Zach Naiman Naiman GLACIAL EXOTICA 3) GLACIAL EXOTICA OF OF THE THE TWIN TWIN CITIES CITIES AREA AREA Leaders: Howard Hobbs, A1 Al Knaeble, and Gary Meyer 1600-2200 REGISTRATION/PRE-REGISTRATION PACKET REGISTRATIONPRE-REGISTRATION PACKET PICK-UP PICK-UP PUBLICATIONS FOR SALE PUBLICATIONS Pre-Function Area Holiday Inn Pre-Function 1700-2200 POSTER SET-UP Pre-Function Area Holiday Inn Pre-Function 1800-2200 WELCOMING WELCOMING RECEPTION/POSTER RECEPTIONPOSTER SESSION SESSION Free Beer and Hors d'oeuvres; Cash Bar /Aragon Ballroom Holiday Inn Pre-Function Area /Aragon Ballroom A-B xd XXI �THURSDAY, MAY 7 0730-1630 0730-1630 REGISTRATIONIPRE-REGISTRATIONPACKET PICK-UP PICK-UP REGISTRATION/PRE-REGISTRATION PUBLICATIONS PUBLICATIONS FOR SALE SALE Holiday Inn Pre-Function Area 0730-0820 0730-0820 COFFEE COFFEE AND TEA TEA Pre-Function Area Holiday Inn Pre-Function SESSION I: 1: GEOLOGICAL SESSION GEOLOGICALOVERVIEW OVERVIEW OF OFTHE THELAKE LAKE SUPERIOR SUPERIOR REGION REGION Aragon Ballroom D-E-F Session Session Chairs: Chairs: P.K. Sims Sims (U.S. (U.S. Geological Geological Survey) Survey) G.B. Morey (Minnesota (Minnesota Geological Geological Survey) Survey) 0820-0830 0820-0830 WELCOME (Jim Miller—Meeting WELCOME Miller-Meeting Co-chair, Minnesota Geological Survey) Survey) 0830-0900 0830-0900 Card,Ken KenD. D.(Card (Cardand andAssociates AssociatesGeosearch) Geosearch) Card, America Archean geology of the Great Lakes region of North America 0900-0930 0900-0930 Ojakangas, Ojakangas,Richard RichardW. W.(University (UniversityofofMinnesota—Duluth) Minnesota-Duluth) Generalized Generalized Early Proterozoic history, Lake Superior region 0930-1000 Cannon, Cannon, William William F. F.(U.S. (U.S.Geological Geological Survey) Survey) Understanding the Middle Middle Proterozoic Proterozoic history of the the Lake Lake Superior Superiorregion: region: What's new? What's What's next? next? Pre-Function Area) AND POSTER POSTER SESSION SESSION (Holiday (Holiday Inn Pre-Function Area) 1000-1030 COFFEE COFFEEBREAK BREAK AND 1030-1100 1030-1 100 Runkel, Anthony Runkel, AnthonyC. C.(Minnesota (MinnesotaGeological Geological Survey) Survey) Paleozoic rocks in the northern part of the central midcontinent midcontinent of North Paleozoic America 1100-1130 1100-1 130 Patterson, Carrie Patterson, CarrieJ.J.(Minnesota (MinnesotaGeological Geological Survey) Survey) Models for interpreting the Quaternary Quatemary history of the Lake Superior region. 11130-1200 130-1200 Southwick, David L. (Minnesota (MinnesotaGeological GeologicalSurvey) Survey) What's next for geology in the Lake Superior Superior area? 1200-1400: LUNCH LUNCH BREAK ILSG BOARD MEETING (Grill (Grill Room Restaurant, Holiday Inn) Inn) POSTERS (Holiday -Function Area) Area) POSTERS (HolidayInn Inn Pre Pre-Function xdi �SESSION II SESSION I1 Aragon Ballroom D-E-F D-E-F Session Chairs: Session Jim Lundy (Minnesota (Minnesota Pollution Control Control Agency) Agency) Laurel Woodruff Woodruff (U.S. Geological Geological Survey) Survey) 1400-1420 1400-1420 Pfannkuch, H.0, H.O, and Paulson, Pfannkuch, Paulson, Richard A. A. assessments of groundwater Improved geologic geologic sensitivity sensitivity and vulnerability assessments groundwater pollution potential potential through fuzzy logic logic pollution through application application of fuzzy 1420-1440 1420-1440 Campion, Moira Ground water recharge, recharge, discharge discharge and and residence residence time time in Rice Rice County, County, Minnesota: Implications Implications for land use planning 1440-1500 1440-1500 Cannon, Cannon, W.F., W.F., Kolker, Alan, and and Westjohn, Westjohn, D.B. D.B. water in southeastern Michigan Michigan The geological source of arsenic in ground water -Function Area) AND POSTER POSTER SESSION SESSION (Holiday (Holiday Inn Pre Pre-Function 1500-1520 COFFEE COFFEEBREAK BREAK AND 1520-1540 1520-1540 Fralick, P.W., Fralick, P.W., and and Kissin, Kissin, S.A. S.A. The age and provenance of the Gunflint Gunflint lapilli tuff 1540-1600 1540-1600 Medaris, L.G., L.G., Jr., and Medaris, and Fournelle, Fournelle, J.H. J.H. Svanbergite Significance for diagenetic diagenetic processes Svanbergite in the Bamboo Baraboo Quartzite: Significance and phosphorus phosphorus flux flux in Precambrian Precambrian oceans oceans 1600-1620 1600-1620 Medaris, L.G., L.G., Jr., Brown, Medaris, Brown, P.B., P.B., and and Bunge, Bunge, R.J. R.J. PostT 1.76low-grade low-grademetamorphism metamorphismof ofthe theBaraboo Bamboo Quartzite Quartzite Post-1.76 1620-1640 1620-1640 Mudrey, M.G., M.G., Jr. Mudrey, aeromagnetic data for regional geology Use of high-resolution aeromagnetic investigations, investigations, southeastern southeastern Wisconsin Wisconsin (Where's (Where's the the kimberlite!) 1830-1900 1830-1 900 MJXER(Holiday Inn Pre-Function Pre-Function Area) MSXER(Ho1iday Area) Cash Bar 1900-2200 1900-2200 ANNUAL BANQUET BANQUET AND AND AWARDS AWARDS PRESENTATION PRESENTATION Aragon Ballroom D-E-F D-E-F • Announcement Announcement of 45th Annual Meeting Meeting location location • 1996 1996 Goldich Goldich Award Award presentation to Zell Peterman Peterman • Banquet speaker: Bevan French, French,Smithsonian SmithsonianInstitution Institution falls: Large meteorite impacts "When the sky sky/alls: impacts and the history of Earth and other other worlds" worlds" xll �FRIDAY, MAY 8 0730-1200 07301200 REGISTRATION/PRE-REGISTRATION PACKET PICK-UP REGISTRATION/PRE-REGISTRATION PICK-UP PUBLICATIONS FOR SALE (coffee (coffeeand and tea tea 0730-0800) 0730-0800) Holiday -Function Area Holiday Inn Inn Pre Pre-Function SESSION 111 III SESSION Aragon Ballroom D-E-F Session Session Chairs: Chairs: 0820-0840 0840-0900 0900-0920 0920-0940 0940-1000 Rod Johnson (Bitterroot (Bitterroot Resources Ltd.) Mark Smyk Smyk (Ontario (Ontario Geological Survey) Survey) Jirsa, Mark MarkA., A., Boerboom, Boerboom, Terrence Terrence J., and Chandler, Chandler, Val Val W. W. ursa, J., and Geologic setting of subeconomic in the Virginia Horn, subeconomic gold deposits in Minnesota: A horn of plenty or a or hornswoggle? hornswoggle? northeastern Chandler, Val W., W., Jirsa, Mark A., Chandler, Val A., and and Lively, Lively, Richard L. Gravity and magnetic studies studies in the Virginia Virginia Horn area, area, northeastern northeastern Minnesota Saini-Eidukat, Bernhardt, and Saini-Eidukat, and Bernatchez, Bernatchez, Raymond Raymond Herontrack silver-zinc-copper Preliminary ore mineralogy of the Herontrack occurrence, occurrence, Lumby Lake area, Ontario, Canada *Salo, *Salo, R.W., R.W., and and Kissin, Kissin, S.A. S.A. Kremzar Alteration and metamorphism metamorphism in an Archean lode gold deposit, deposit, Kremzar mine, Goudreau-Lochalsh gold camp, Ontario Ontario Hudak, George George J., J., Morton, Ron L., L., and Franklin, James M. Hudak, Morton, Ron M. to the Archean The recognition of a lava dome complex and its relationship to Sturgeon Sturgeon Lake caldera, caldera, northwestern northwestern Ontario Ontario 1000-1020 1000-1020 COFFEE COFFEEBREAK/FINAL BREAKfFINALPOSTER POSTER SESSION SESSION Pre-Function Area Holiday Inn Pre-Function 1020-1040 Sims, P.K., Neymark, L.A., and Peterman, Sims, P.K., Neymark, L.A., Peterman, Z.E. Z.E. Nd isotope isotope evidence evidence for Middle and Early Archean crust in the Wawa Subprovince Subprovince of the Superior Superior Province, Michigan, USA 1040-1100 Schulz, Klaus J., and Schulz, Klaus and Ayuso, Ayuso, Robert Robert A. A. Crustal Crustal recycling recycling in the evolution evolution of the Penokean Orogen: Isotopic Isotopic evidence evidence for for Archean Archean contributions contributions to crustal crustal growth growth in the the PembinePembineWausau terrane, northern northern Wisconsin Wisconsin Wausau terrane, 1100-1 120 Hoim, Daniel K., K., Schneider, David, and and Coath, Chris Holm, Daniel Schneider, David, Chris D. D. Age Age and and deformation deformation of Early Proterozoic Proterozoic quartzites quartzites in the southern southern Lake Lake Superior region: Implications Implications for extent of foreland deformation deformation during Superior during fmal final assembly of Laurentia *Czeck, Dyanna Dyanna M., M., and and Hudleston, Peter J. *Czeck, Hudleston, Peter Evidence for for aa modified modified Kinematic fabrics near Mine Centre, Ontario: Evidence transpression model Corfu, Corfu, F., and and Easton, Easton, R.M. R.M. 1140-1200 Extension of the Huronian magmatic magmatic suite suite inside the Grenville Grenville Province: New zircon U-Pb evidence from the Grenville Front Front Tectonic Tectonic Zone Zone in Street Township, Sudbury region, Ontario Ontario 1200-1400 LUNCH LUNCHBREAK BREAK(posters (postersto tobe beremoved; removed;publication publicationsales sales end) end) 1120-1 140 xxiv XXIv �SESSION IV SESSIONIV Aragon Aragon Ballroom Ballroom D-E-F D-E-F Session Session Chairs: Chairs: 1400-1420 (University of Minnesota—Duluth) John C. Green (University Minnesota-Duluth) ~ e i b l e (University n(university of Minnesota—Twin ~innesota- win Cities) Cities) Paul W. Weiblen Nicholson, Suzanne W., W., and Woodruff, Nicholson, Suzanne Woodruff, Laurel Laurel G. G. The Powder Powder Mill Mill Group Group revisited: revisited: Basal volcanic rocks of the Midcontinent The Midcontinent Rift Rift System System on on the the south south shore shore of Lake Lake Superior Superior 1420-1440 *Najman, Zachary J., J., and Wirth, Karl R. *Naiman, Zachary R. Composition Compositionand and source(s) source(s)of of Midcontinent MidcontinentRift Rift lavas lavas (Chengwatana (Chengwatana Volcanics) Volcanics) near near Clam Clam Falls, Falls, Wisconsin Wisconsin 1440-1500 *Vislova, *Vislova, Tatiana Tatiana The The relevance relevanceof of the the geology geology of of the the mid-ocean mid-ocean ridges ridgesand andophiolites ophiolitesto tothe the understanding understanding of layered layered intrusions in the Midcontinent Rift: Part Part I.I. Geometry; Geometry;Part Part II. 11.Internal Internal structure structureand and petrology petrology 1500-1520 *Maki, *Maki, John C., C., and and Bornhorst, Bornhorst, Theodore Theodore J. J. New New field field observations observations of the Clarksburg Volcanics, Upper Peninsula of Michigan Michigan 1520-1540 re-Function Area) 1520- 1540 COFFEE COFFEEBREAK(Holiday BREAK(Ho1idayInn InnPPre-Function Area) 1540-1600 Tikoff, Tikoff, Basil, Bauer, Bauer, Bob, Bob, Vigneresse, Vigneresse, Jean-Louis, Jean-Louis, and and Haggeman, Nick Nick A A gravity, gravity, magnetic, magnetic, and and structural structuralstudy study of of the the Wakemup Wakemup Bay Bay Tonalite, Tonalite, Minnesota Minnesota 1600-1620 Myers, Myers, Paul Paul E. E. Xenolithologies Xenolithologiesas asindicators indicatorsof of intrusion intrusionmechanisms mechanisms in in the theWausau Wausau Syenite SyeniteComplex, Complex,Wisconsin Wisconsin 1620-1640 BEST BEST STUDENT STUDENTPAPER PAPER AWARDS AWARDS CLOSING CLOSING 1905 BASEBALL: (HHH Metrodome) BASEBALL: TWINS TWINS vs. YANKEES (HHHMetrodome) xxv XXV �SATURDAY. SATURDAY. MAY MAY 9 0800-1800 0800-1 800 POST-MEETING FIELD TRIPS TRIPS Depart from: Holiday -Function Area Depart Holiday Inn Inn Pre Pre-Function 4) STRATIGRAPHY STRATIGRAPHY AND HYDROGEOLOGY OF PALEOZOIC ROCKS OF SOUTHEASTERN MINNESOTA Leaders: Tony Tony Runkel Runkel and and Bob Bob Tipping Tipping MINNESOTA RIVER VALLEY AND VICINITY, SOUTHWESTERN 5) MINNESOTA MINNESOTA MINNESOTA Leaders: Dave Dave Southwick Southwick and and Carrie Carrie Patterson Patterson SUNDAY, MAY MAY 10 SUNDAY, 10 0800-1800 08001800 FIELD TRIP TRIP 5, 5, DAY 2 FIELD Returns Returns to to Holiday Inn Inn Metrodome Metrodome xxvi �PRESENTATIONS POSTER PRESENTATIONS 1700 hrs. Wednesday, May May 66 through through 1400 1400 hrs. hrs. Friday, Friday, May 8 *Abbott, Kathleen *Abbott, Kathleen M., M., Thole, Thole,Jeffrey JeffreyT., T., and and Wirth, Wirth, Karl R. Petrography and and geochemistry of Midcontinent Rift rhyolite (Chengwatana Petrography (Chengwatana Volcanics) Volcanics) near near Clam Clam Falls, Falls, Wisconsin Bernatchez, Raymond Bernatchez, Raymond A. A. detailed geological geological description description of the new high grade grade silver-base silver-base A preliminary detailed metal discovery discovery in the the Lumby Lake Lake metavolcanic metavolcanic belt northeast of Atikokan, metal Ontario, Ontario, Canada Canada Boerboom, Terry, Terry, and Oberhelman, Boerboom, Oberhelman, Matt Dimension Dimension stone stone products products of Minnesota Chandler, V.W., V.W., Jirsa, M.A., Morey, Morey, G.B., G.B., and Lawler, Lawler, T. T. Chandler, Jirsa, M.A., Mineral potential assesment assesment of northern St. Louis County, southeastern Koochiching Koochiching County, County, and northeastern northeastern Itasca County, Minnesota Cannon, W.F., W.F., Laberge, Laberge, G.L., G.L., Klasner, Kiasner, J.S., J.S., and Schulz, Cannon, Schulz, K.J. K.J. Reinterpretation of the Penokean continental margin in part Reinterpretation part of of northern northern Wisconsin Wisconsin and Michigan Michigan Cannon, W.F., Cannon, W.F., McRae, McRae, M.E., M.E., and and Nicholson, Nicholson, S.W. S.W. Geographic information information system system on the geology and and copper copper deposits deposits of the the Geographic Keweenaw Keweenaw Peninsula Peninsula Daniels, D. L., Daniels, D. L., Snyder, Snyder, S. S. L., L., Nicholson, Nicholson, S. W., W., and and Cannon, Cannon, W.F. W.F. New aeromagnetic aeromagneticsurveys surveys in m Wisconsin Wisconsin by the the U.S. Geological Geological Survey Survey *Deangelis,M.T., M.T., Peck, Peck, W.H., W.H., and and Valley, *Deangelis, Valley, J.W. J.W. Polymetamorphism of skarns Polymetamorphism skarns related to the Morin Anorthosite Complex, Grenville Province, Quebec Quebec *Gramstad, Sally *Gramstad, Sally D. D. Minnesota River Valley Pre-Wisconsinan gray till in the Mankato area of the Minnesota Han, Han, T.M. T.M. A mineralographic mineralographic study of magnetite in the Biwabik Iron lion Formation, Mesabi Range, Minnesota Minnesota *Hensel, Erin, *Joslin, *Hensel, Erin, *Joslin, Rick, Rick, and Lehrmann, Lehrmann, Dan Dan Facies Ironwood Iron lion Facies and and depositional depositional environments environments of the Early Proterozoic Ironwood Formation, Formation, Mt. Whittlesey, Whittlesey, Wisconsin Wisconsin Kjerland, Kjerland, Dean Dean W., W., and Kjerland, Kjerland, Marc Marc Effects Effects of of electric-pulse electric-pulsedisaggregation disaggregation on on microfossil-bearing microfossil-bearing argillaceous argillaceous limestone of the Middle Ordovician limestone Ordovician Decorah Decorah Shale Shale xxvii �*Loofboro, Jeff, and Holm, *Loofboro, Jeff, Holm, Daniel Daniel Results of modeling Proterozoic thermal histories: Evaluating the the possible possible effects effects of of Wolf River River Batholith Batholith reheating reheating on on thermochronologic therrnochronologic data data from from northern northern Wisconsin Wisconsin Luther, Frank R. Luther, R. An Archean subaqueous subaqueous heterolithic debris flow, Irwin, Pifher, and Meader Townships, Lake Townships, Lake Nipigon Nipigon region, region, Ontario Ontario McRae, M.E., M.E., Cannon, Cannon, W.F., W.F., and and Woodruff, Woodruff, L.G. L.G. McRae, Post-glacial shorelines shorelines of Isle Isle Royale Royale -- Where are are they now? now? McSwiggen, Peter L. McSwiggen, Peter L. Electron microprobe Electron microprobe study of the Pt-Pd and related mineralization in the Minnamax/Babbitt Cu-Ni deposit MinnamaxIBabbitt *peterson, Dean Dean M., M., and Morton, *Peterson, Morton, Ronald Ronald L. GIS-based GIs-based mineral potential potential analysis analysis for lode-gold and massive sulfide sulfide deposits deposits in an Archean terrane terrane of northern Minnesota *Rausch, Deborah E., E., and and Wattrus, Nigel *Rausch, Deborah Nigel J. Seismic Seismic evidence evidence of pre-Nickerson Quaternary sediments in western Lake Superior *Schaper, D., *Suess, W., *Katzer, *Katzer, L., L., and Kean, *Schaper, D., *Suess, W., Kean, W. W. Additional paleomagnetic results for a 1500 Wisconsin 1500 Ma mafic dike at Waterloo, Wisconsin Schmidt, Susanne Susanne Th., Th., and Seifert, Schmidt, Seifert, Karl Karl Metamorphism, hydrothermal Metamorphism, hydrothermal alteration, and lateritic weathering of drilled MRS volcanic rocks in Iowa Schulz, Klaus Klaus J., J., and Schulz, and Ayuso, Ayuso, Robert Robert A. A. Crustal Crustal recycling in the evolution of the Penokean Orogen: isotopic isotopic evidence evidence for for Archean contributions contributions to crustal growth in the Pembine-Wausau terrane, northern Wisconsin *Soofi, M.A., M.A., and King, *Soofi, King, S.D. S.D. A thin viscous viscous sheet sheet approach approach to investigate investigate the post-rift post-rift evolution evolution of the the Midcontinent Rift System Grenville Orogeny Midcontinent System under the influence of Grenville *Thomas, C., C., Kean, Kean, W., W., and and Luther, F. *Thomas, F. Paleomagnetic studies Pither and Paleomagnetic studies of a Proterozoic Proterozoic porphyritic diabase dike, Pifher and Irwin Townships, Lake Townships, Lake Nipigon district, district, Ontario Wirth, Karl R., Wirth, R., and and Gehrels, Gehrels, George George E. E. Precise U-Pb zircon ages of Midcontinent Rift rhyolite (Chengwatana Volcanics), Clam Clam Falls, Falls, WI xxviii �ABSTRACTS SPECIAL SESSION: SPECIAL SESSION: Geological Geological Overview Overview of the Lake Superior Region The The 1998 1998ILSG ILSG planning planning committee committeeasked asked six six leading leading geologists geologists for for aa summary summary of of their their special specialsubfields subfieldsof of Lake Lake Superior geology, geology, including including what's new and what's next. The following following is is their their response. response. 1 �ARCHEAN ARCHEAN GEOLOGY OF THE THE GREAT GREAT LAKES LAKES REGION REGION OF NORTH NORTH AMERICA AMERICA CARD, CARD, K.D., Card Card and and Associates' Associates' Geosearch, Geosearch,Kanata, Kanata, ON, ON, K2K K2K 1M1, 1M1,email email culau2ag3@aol.com cu 1au2ag3@aol.com Archean Archean rocks rocks of of the the southern southern Canadian Canadian Shield Shield in in the the Great Great Lakes Lakes region form form the the world's world's largest km.) Archean craton, the Superior Province. These These ancient ancientrocks rocks largest (2 (2 million million sq. sq. km.) were were formed formed during during several several major major cycles cycles of volcanism, volcanism, sedimentation, sedimentation, plutonism, and and tectonism—mainly Archean(2.5-2.8 (2.5-2.8 Ga), Ga), but but also alsoin in the the Middle Middle(2.8-3.4 (2.8-3.4 Ga) Ga) tectonism-mainly in in the the Lake LakeArchean and and Early Archean (>3.4 (>3.4 Ga). Superior SuperiorProvince Province consists consists of northern and southern highgrade grade gneiss gneiss subprovinces subprovincesand and aa broad broad central central region region of of alternating alternatinggranite-greenstone granite-greenstoneand and sedimentary sedimentary belts belts (Figure (Figure X). Some Someof ofthe thehigh-grade high-grade rocks rocksrepresent represent exposures exposuresof of lower lower crust crust of of Superior SuperiorProvince Provinceuplifted uplifted in in the the Early Early Proterozoic; Proterozoic;others, others, notably notably the the Minnesota Minnesota River Archean crust. crust. The The volcanic and related River Valley Valley gneisses, gneisses, are exotic blocks of Early Archean plutonic plutonic rocks rocks are are similar similar to to those those of modern modem island island and and continental continental arcs formed formed along along convergent oceans. Middle convergent margins. The Themetasedimentaiy metasedimentary belts may mark Archean oceans. Middle Archean Archean rocks, rocks, including includingplutonic plutonicgneisses gneissesapproximately approximately3.0 3.0 Ga Gaold oldare areoverlain overlain unconformably unconformablyby by ca ca 2.8 2.8 Ga Ga platformal platformalsequences sequencesincluding includingquartzite, quartzite,quartz quartzpebble pebble conglomerate Incontrast, contrast,the theLate LateArchean Archean volcanic volcanicand and conglomerateand and komatiitic komatiitic volcanic rocks. In sedimentary sedimentarysequences sequencesare aremainly mainlyjuvenile, juvenile, derived deriveddirectly directlyfrom fromthe themantle mantleor orfrom fromcrustal crustal sources sourcesless less than than 200 200million millionyears yearsolder, older,and anddo donot nothave havestratigraphic stratigraphicbases; bases;many many greenstone greenstonebelts belts may may be beallochthonous. allochthonous. Superior SuperiorProvince Provinceisisrich rich in in minerals mineralsincluding includingcopper, copper,zinc, zinc,and andnickel nickelmassive massivesulfide sulfide and and lode lode gold gold deposits. deposits. Most Mostofofthe themineral mineraldeposits depositsoccur occurin in the the granite-greenstone granite-greenstonebelts belts where 100million million years years or orless less by by processes processesrelated relatedto tothe the where they they were were formed formedin in aa period period of of 100 major the Archean. Archean. These major volcanism, volcanism, plutonism, plutonism, and tectonism that marked the end of the These processes processes also alsoled ledto to the the formation formationof of aa large, large, stable stable craton craton called Kenorland. Kenorland Kenorland may supercontinent~oneof the ffirst i r t of Earth's supercontinents. ItIt was was may have have been been part part of aa supercontinent—one broken broken up upin inthe theEarly EarlyProterozoic, Proterozoic,parts parts of of itit migrating migrating westward westward to to Wyoming, Wyoming, and and other other parts parts going goingback backto tothe theold oldcountry countryto toform formthe theBaltic BalticShield. Shield. Archean Earthwas was significantly significantlydifferent different from modern modem Earth in many ways. The The ArcheanEarth Archean Archeanatmosphere, atmosphere,for forexample, example, lacked lacked free free oxygen oxygen and and was rich in ammonia, ammonia, carbon carbon dioxide, dioxide,and and methane. methane.Meteorite Meteoriteimpacts impactswere weremuch muchmore morefrequent, frequent,and anduntil untilabout about4.0 4.0Ga Ga probably Earthhistory history isiscalled calledthe the probably kept kept the the crust crust well-stirred. well-stirred. This Thisearly earlyperiod periodof ofEarth Hadean, Hadean, probably probably with with justification. Heat Heatflow flowwas wasalso alsohigher, higher,resulting resulting in in aa thicker thicker mantle Archean, the the rocks, rocks, mineral mineral mantle and and aa volcanically volcanically active active crust. crust. However, However,by bythe theLate LateArchean, deposits, are remarkably remarkably similar similarto to those those of of deposits,and andstructures structuresbeing being formed formedand and preserved preserved are modern modemaccretionary accretionaryorogens, orogens,notably notably those those around around the the Pacific Pacific Rim. Although Althoughcurrently currently the ArcheanSuperior SuperiorProvince Provincewas wasformed formedby by the subject subjectof ofdebate, debate,ititwould wouldappear appearthat thatthe theArchean subduction-driven subduction-drivenorogenic orogenicprocesses processessimilar similarininmost mostrespects respectstotothose thoseoperating operatingtoday. today. Additional Additional Reviews: Reviews: Card, Card,K.D., K.D.,AAreview reviewofofthe theSuperior SuperiorProvince Provinceofofthe theCanadian CanadianShield, Shield,aaproduct productofofArchean Archeanaccretion: accretion: Precambrian 48,p.p.99-156. 99-156. PrecambrianResearch, Research,v.v.48, Hamilton, Hamilton,W.B., W.B.,Evolution Evolution of of Archean Archeanmantle mantle and and crust, crust,p. p. 597-614 597-614in in Reed, Reed,J.C. J.C.Jr., Jr.,Ball, Ball,T.T., T.T.,Farmer, Farmer, G.L., G.L.,and andHamilton, Hamilton,W.B., W.B.,1993, 1993,AA broader broader view, view, in in Reed, Reed,J.C.Jr., J.C.Jr.,Bickford, Bickford,M.E., M.E.,Houston, Houston,R.S., R.S., Link, Link,P.K., P.K.,Ranking, Ranking,D.W., D.W.,Sims, Sims,P.K., P.K., and andVan VanSchmus, Schmus,W.R., W.R., eds., eds.,Precambrian: Precambrian:Conterminous Conterminous U.S, U.S, Geological GeologicalSociety SocietyofofAmerica, America,The TheGeology Geologyof of North North America, America,v.v.C-2, C-2,p.597-636. p.597-636. 3 �Figure Figurex. x. Subprovinces Subprovincesof of the the Superior Superior Province Province 4 �GENERALIZED GENERALIZED EARLY EARLY PROTEROZOIC PROTEROZOIC HISTORY, HISTORY, LAKE LAKE SUPERIOR SUPERIOR REGION REGION Department RichardW., W , Departmentof ofGeology, Geologyf Ojakangas, 0j akangas , Richard University Duluth, MN MN55812 55812 Minnesota-Duluthf Duluthf UniversityofofMinnesota-Duluth, rojakang@d*m*edu rojakang@d.umn.edu INTRODUCTION INTRODUCTION Over the the'last last century, centuryf countless countless geologists ueolouists have have worked worked to to Over decipher ~r&eroGoic geological geological history history of of decipher the the fascinating fascinating Early Early Proterozoic to this region. region* Unfortunately, Unfortunatelyf it it is is impossible impossible in in aa short s h o review review ~ to this acknowledge all all the the important important works, worksf but but each each cited cited reference reference acknowledge contains aa bibliography. bibliography* Two Two compendiums compendiums are are especially especially valuable valuable contains and and include include more more than than 500 500 and and 700 700 Precambrian Precambrian references, referencesf respectively respectively (Sims (Simset et al, alf1993; 1993; Sims Situs and and Carter, Carterf1996). 1996). As As in in any any limited limited review, reviewf the the bias bias of of the the reviewer reviewer will will be be present. present* The The integration history* integration of of plate plate tectonic tectonic theory theory permeates permeates this this history. HURONIAN HURONIAN After the the supercontinent supercontinent of of Kenorland Kenorland was was assembled assembled about about 2.7 2.7 Ga Ga After (Card, (Cardf 1990; 1990; Williams Williams et et al, alf 1991) 1991) during during the the Algoman Algoman (Keewatin) (Keewatin) orogeny, erosionf and and sedimentation sedimentation orogenyf aa long long period period of of weathering, weatheringf erosion, occurred on on this this stable stableand and thick thick crustal crustalplatform. platform* The The oldest oldest occurred sedimentary sequence, sequencef the the Huronian Huronian Supergroup, Supergroupf was deposited deposited sedimentary between 2-45Ga Ga and and 2.2 2.2 Ga, Gaf mainly mainly north north of of Lake Lake Huron. Huron* As between 2.45 As thick thick as km and and thinning thinning northward, northwardf this this is is aa sequence sequence quite quite unlike unlike 12 km as 12 in that "uncommon" glacial deposits, Archean sequences sequences in thatititcontains contains ffuncommon'fglacial depositsf Archean quartzose paleosolsf carbonates, carbonatesf and and abundant arkosic to to quartzose paleosols, sandstones. from sandstones* An An upper upper part part of of this this supergroup supergroup is is aa sequence, sequencef from the the bottom bottom up, upf of of glaciogenic glaciogenic rocks, rocksf paleosol, paleosolf quartz quartz sandstone, sandstonef and (evaporites). AA similar similar and carbonate carbonate rocks rocks with with sabkha sabkha minerals minerals (evaporites). sequence sequence is is present present as as erosional erosional remnants remnants in in the the Upper Upper Peninsula Peninsula Group, Marquette Marquette Range of Michigan, Michiganf 200 200 km km to to the the west west (Chocolay (Chocolay Groupf Range of An even even more more complete complete similar similar sequence sequence is is found found in in Supergroup)* An Supergroup). southeastern southeastern Wyoming, Wyomingf the the Snowy Snowy Pass Pass Supergroup. Supergroup* The The glacial glacial units units of of these these three three sequences sequences were were first first interpreted interpreted by by Young Young (1970) (1970)as as remnants remnants of of aa major major continental continental glaciation, glaciationf and and additional additional work work (e.g., ( e - g O fOjakangas, Ojakangasf 1984, 1984f 1985, l98Sf 1988) 1988) further further strengthens strengthens this this idea. idea* As an an interesting interesting aside, asidef Williams Williams and and Schmidt Schmidt (1997) (1997)stated stated that that paleomagnetic paleomagnetic data data indicate indicate that that this this Huronian Huronian glaciation glaciation occurred occurred 4-110 of of the the equator. equator* Further E'urther evidence evidence of the the correlation correlation within 4-11° within of these these three three sequences sequences was was provided provided by by Bekker Bekker and and Karhu Karhu (1996) (1996) and and Bekker Bekker (1998), (1998)fwho who found found similar similar high high values values of of 13C_enrichment 13C-enrichment and 'BO—depletion 180-depletion in in carbonate carbonate units. units* and Supercontinent Supercontinent Kenorland Kenorland began began to to undergo undergo extension extension at at 2.45 2.45 Ga, Gat as as indicated indicated by by mafic mafic igneous igneous rock rock units units at at the the base of of the the Huronian Huronian Supergroup Supergroup (e.g., ( e * g O Heaman, fHeamant 1997; 1997; Cheney, Cheneyf 1998; 1998; Balls, Hallsf 1998). 1998). Actual Actual breakup breakup occurred occurred at at 2.2 2.2 to to 2.1 2.1 Ga Ga with with emplacement emplacement of of Nipissing Nipissing diabase diabase sills sills and and major major dike dike swarms s w a m (Roscoe (Roscoe and and Card, Cardf 1993). 1993)- The The Kenora-Kabetogama Kenora-Kabetogama mafic mafic dikes dikes (2145 (2145 +1+/- 45 45 Ma) Ma) in in northern northern Minnesota 1983) that that show show up up so so well well on on Minnesota (Southwick (Southwickand and Day, Dayf 1983) aeromagnetic aeromagnetic maps maps (Chandler, (Chandlerf1991; 1991; Chandler Chandler et et al, alf 1984) 1984) appear appear to to be products products of of this this final final extensional extensional event. event* The The breakup breakup of of 5 �Kenorland has has an an even even broader broader intercontinental intercontinental significance; significance; aa Kenorland similar similar sedimentary sedimentary sequence sequence with with similar similar igneous igneous activity activity is is also also present in in Finland Finlandand and adjacent adjacentRussia Russia (Marmo (Mannoand and Ojakangas, Ojakangasf present 1984)fand and correlation correlation seems seems likely likely (e.g., (e.gOfOjakangas, Ojakangasf1984, 1984f1988; 1988; 1984), Ojakangasfet et al, alf1991). 1991). In In summary, summaryf Kenorland, Kenorland# which which formed formed in in Ojakangas, Archean, apparently apparentlybroke broke up up in inthe theEarly Early Proterozoic, Proterozoicf the Late Late Archean, the with with the the Wyoming Wyoming craton craton heading heading west west and and the the Svecofennian Svecofennian craton craton east* heading east. heading CORRELATION CORRELATION Correlation Correlation of of Early Early Proterozoic Proterozoic rock rock units units of of Michigan Michigan and and Ontario has has long long been been aaproblem. problem* Glacial Glacial units units have have been been used used as as Ontario marker marker units units (e.g., ( e - g oYoung, fYoungf1983; 1983; Ojakangas, Ojakangasf1988); 1988);on on this thisbasis, basisf the the lower lower portion portion of of the the Marquette Marquette Range Range Supergroup Supergroup (the (the Chocolay Chocolay Group) Group) is is correlated correlated with with the the upper upper part part of of the the Huronian Huronian Supergroup, Supergroupfincluding includingthe theGowganda Gowganda Formation Formationand and overlying overlyingunits. units. Correlation Correlation within within the the Lake Lake Superior Superior region region itself itself has has also also long long been been controversial controversial(Morey (Moreyand and Van Van Schmus, Schmusf1988; 1988;Morey, Moreyf1996). 1996). Correlationshave have long longbeen been made made on on lithostratigraphic lithostratigraphicgrounds; grounds; Correlations for for example, example! it it had had been been assumed assumed that that the the various various iron-formations iron-formations of the the Lake Lake Superior Superior region region were were correlative, correlativef but but this this is is now now of questioned* Correlations Correlations are are complicated complicated by by deformation deformation (both (both questioned. thin-and thick-skinned thick-skinned tectonics) tectonics)and and the thelack lackofofexposures exposures thin-and approaches, suchas C— because of extensive extensive glacial glacialcover. cover* New New approachesf such-as Cbecause isotopic studies studies of of carbonate carbonate units, unitsfhave have been been interpreted interpreted as as isotopic evidence evidence that that not not all all of of the the carbonate carbonate units units are are correlative, correlativef as as Unless 1998). long assumed assumed (Bekker (Bekkerand andKarhu, Karhuf1996; 1996; Bekker, Bekkerf1998). Unless the the long C-ratios have have been been affected affected by by diagenesis/metamorphism, diagenesis/metmrphismf they C-ratios they indicate indicate that that the the Kona Kona Dolomite Dolomite may may be be younger younger than than the the Bad Bad River River Dolomite Dolomite (WI (WIand and MI), MI)! the the Saunders Saunders Formation Formation (MI), (MI)fthe the Randville Randville Dolomite (MN) units units that that have have all all been been (WI)#and and the the Rabbit Rabbit Lake Lake (MN) Dolomite (WI), "correlative "correlative units". unitsw*An An excellent excellent summary summary of of the the sedimentation sedimentation and and correlation correlation of of the the continental continental margin margin assemblage assemblage is is by by Morey Morey (1996). (1996). IRON-FORMATION IRON-FORMATION Naturally Naturally enriched enriched iron iron ores ores of of the the Lake Lake Superior Superior region region made made the the U.S.A. U-S.A. an an industrial industrial giant, giantf but but only only two two of of the the many many ranges, rangesf the the are still still producing iron ore Mesabi and and the the Marquette, Marquettef are producing iron ore (taconite (taconite Mesabi Superior-type" siliceous known known pellets). "Lake "Lake Superior-typew siliceousiron-formation iron-formationisis pellets). world-wide, world-widef and and similar similar units unitshave havebeen been described described from from other other continents* For For nearly nearly aa century, centuryf geologists geologists had had thought thought they they continents. inrecent recent years years it it has were all allabout about2.0 2.0 Ga Ga old. old. However, Howeverf in has been been were deposition* In In suggested that that there there was was more more than than one one period period of of deposition. suggested Minnesotaf there thereappear appear to tobe bethree threeages agesranging rangingfrom from about about 2.2 2.2 Ga Ga Minnesota, to1 1.9 to •9 Ga Ga (Southwick (Southwickand and Morey, Moreyf 1991; 1991; Morey Morey and and Southwick, Southwickf1995); 1995); the oldest oldest two two are are laminated laminated and and fine-grained fine-grained (deposited (deposited below below the wave—base basin^?)^ in in contrast contrast to to the the younger younger wave-base in in extensional extensional basins?), Biwabik Biwabik Iron-formation Iron-formation that that contains contains sand-sized sand-sized grains grains of of chert chert and iron iron minerals, mineralsf is is cross-bedded, cross-beddedf and and contains contains two two stromatolite stromatolite and horizons shelf* In In horizons indicative indicativeof of deposition deposition on on aa shallow shallow shelf. Michigan-Wisconsinf there theremay may be be two two major major periods periods of of deposition deposition Michigan-Wisconsin, (e.g., Ojakangas, (e*go fOjakangas!1994; 1994;Morey, Moreyf1996). 1996)-The The older older Negaunee Negaunee IronIron- 6 �formation of of the t h eMarquette Marquette district d i s t r i c tappears appearstot ohave havebeen beendeposited deposited formation w a t e r s of i ndeeper deeper waters ofa adown-faulted down-faulted graben graben (with (with the t h e addition a d d i t i o n of of in t e r r i g e n o u s material material by by turbidity t u r b i d i t y currents c u r r e n t s from from the t h e south s o u t h side side as as terrigenous noted by by LaRue, LaRuef 1981), 1981)! whereas whereas the t h e Ironwood Ironwood Iron-formation Iron-formation of of the the noted Gogebic range range (Schmidt, (Schmidtf 1980) 1980) and and the t h e Bijiki B i j i k i Iron-formation Iron-formation member member Gogebic of the t h e Michigamme Michigamme Formation Formation appear appear to t ohave have been been deposited d e p o s i t e don on aa of stable marine marine shelf. s h e l f - Interesting I n t e r e s t i n g spirally s p i r a l l y coiled, coiled! megascopic megascopic stable e u k a r y o t i c algae a l g a e have have been been found found in i n the t h e Negaunee Negaunee (Han (Han and and eukaryotic Runnegar, 1992). 1992)Runnegar, The The Biwabik Biwabik Iron-formation Iron-formation (as (asthick t h i c k as as 225 225 m) m) on on the t h e Mesabi M e s a b i range range (Morey, t h e Gogebic Gogebic range range (Morey! 1992) 1992) and and the t h e Ironwood Ironwood Iron-formation Iron-formation on on the appear to t o have have aa common common origin; o r i g i n ; part p a r t of of the t h e evidence evidence is i s found found in in appear t h e underlying underlyingPokeama Pokegamaand andPalms Palms formations formationswhich which have have been been the i n t e r p r e t e dasashaving havingformed formed in i na atidal t i d aenvironment l environment(Ojakangas, (Ojakangas! interpreted 1996)- These These studies s t u d i e s indicate i n d i c a t e that t h a t the the G o W., W O f1996). 1983; Ojakangas, Ojakangas! G. 1983; marine tidally—influenced tidally-influenced iron-formations were were deposited deposited on on aa marine iron-formations shelf, s h e l f ! seaward seaward of of the t h e land-derived land-derived sand sand and and muds muds of of the t h e Pokegama Pokegama Palms formations. formations- Lougheed Lougheed (1983) (1983) also a l s o proposed proposed aa tidal tidal and Palms and environment, environment! with w i t h siderite-rich s i d e r i t e - r i c h limestone limestone the t h e primary primary preprediagenetic type- Deposition Deposition appears appears to t o have have been been related related to t o aa d i a g e n e t i c rock rock type. major marine marine transgression t r a n s g r e s s i o n (Simonson ( S h o n s o nand and Hassler, Hassler! 1996). 1996). major There There are are two two oft-cited o f t - c i t e d sources sources for f o r the t h e iron i r o n and and the t h e silica—silica-hydrothermal hydrothermal activity a c t i v i t yassociated a s s o c i a t e dwith withvolcanism volcanismiii ih the t h e basin basin ( e - g e, t Carrigan Carrigan and and Cameron, Cameron! 1991; 1991; Isley, I s l e y f 11995) 9 9 5 ) and and weathering weathering of of t h e Archean Archean craton c r a t o n ( e m g, oLepp, tLepp, 1987). 1987)- The The Ironwood Ironwood Iron-formation Iron-formation the on the t h e Gogebic Gogebic is i s interbedded interbedded with with volcanics volcanics (Klasner (Klasner et et al, alf on 1998)! the t h e Gunf G u n flint l i n t Iron-formation (once continuous with w i t h the the 1998), Iron-formation (once Biwabik Biwabik Iron-formation Iron-formation prior p r i o r to t o intrusion i n t r u s i o n of of the t h e 1.1 1.1 Ga G a Duluth Duluth Complex) i s aa prominent prominent ashy ashy bed bed in in Complex) contains c o n t a i n s tuff t u f f beds, beds, and and there t h e r e is t h e Biwabik. Biwabik- Hoffman Hoffman (1987) (1987) tied t i e d the t h e iron-formations iron-formations of of the t h e Lake Lake the and 00 isotopes i s o t o p e s of of the the t o foredeep foredeepvolcanism. volcanism- CC and S u p e r i o r region r e g i o n to Superior hydrothermal source source for f o r the t h e Fe+2 Fe+2 and and the the G u n f l i n t indicate i n d i c a t e aa hydrothermal Gunf silica! with w i t h siderite siderite being being the t h e primary primary iron i r o n mineral mineral in i n aa silica, basinward facies f a c i e s (Winter (Winter and and Knauth, Knauth! 1992). 1 9 9 2 ) - The The lower lower part p a r t of of basinward the beds t h e overlying o v e r l y i n g Virginia V i r g i n i a Formation Formation contains c o n t a i n s numerous numerous ash a s h beds (Lucente and and Morey, Morey! 1983). 1983)- Thus Thus there t h e r e is i s aa growing growing body body of of (Lucente of the evidence w a s the t h e main main source source of t h e iron iron evidence indicating i n d i c a t i n g that t h a t volcanism volcanism was silica! but b u t continental c o n t i n e n t a l weathering weathering may may indeed indeed have have been been and silica, and Drevet! 1974). 1974). Biota Biota have have long long been been touted touted a n o t h e r source source (e.g., ( e - g o ,Drever, another as as important important in i n the t h e precipitation p r e c i p i t a t i o n of of the t h e iron i r o n minerals (e.g., ( e - g O fLa La Berge! 1967; 1967; Lougheed, Lougheed! 1983; 1983; LaBerge LaBerge et e t al, a l f 1987). 1987)Berge, lint When When was w a s the t h e Biwabik Biwabik Iron-formation, Iron-formationf the t h e largest l a r g e s t and and probably probably the the P a r t of of the the youngest youngest iron-formation iron-formation in i n the t h e region, region! deposited? deposited? Part evidence comes from from the t h e less-metamorphosed less-metamorphosed and and correlative correlative evidence comes Gunf Iron-formation tthat G u n flint l i n t Iron-formation h a t iis s on sstrike t r i k e with and was once once continuous continuous with w i t h the t h e Biwabik. Biwabik. Faure Faure and and Kovach Kovach (1969) (1969) reported r e p o r t e d aa whole-rock whole-rock Rb-Sr Rb-Sr isochron isochron age age of of 1.64 1-64 +1+/- 0.2 0.2 Ga G a for f o r the the AA Sm-Nd isochron aageon Sm-Nd isochron ge-on deposition lint. ordiagenesis d i a g e n e s i sofofthe t h eGunf Gunflintd e p o s i t i o n or argillites was determined at a t 2.08 2-08 +1+/- 0.25 0.25 Ga Ga a r g i l l i t e s in i n the t h e Gunf G u n flint l i n t was (Stille whole-rock isochron o of ( S t i l l e and Clauer, Clauer! 1986). 1986)- A Sm-Nd Sm-Nd whole-rock f 2100 +1+/52 52 Ma M a was w a s reported r e p o r t e d for f o r "slaty" 88slatywportions p o r t i o n s of of the t h e Biwabik, Biwabik! but b u t this this 7 �probablya amixing mixingage ageofof Archeanand andProterozoic Proterozoic components isisprobably Archean components (Gerlach et et al, alf 1988). 1988). Quartz Quartz veins veins in in the the underlying underlying Pokegama Pokegama (Gerlach +/- 25 25 Ma Ma (Hemming (Hemminget et al, alf1990). 1990). Probably Probably most most were dated dated at at 1930 1930 +1were +/- 22 Ma Ma on on indicative of of the the age age is is aa new new U-Pb U-Pb date date of of 1876 1876 +1indicative euhedral lint euhedral zircons zirconsfrom fromaareworked reworkedtuff tuffbed bedininthe thelower lowerGunf Gunflint (Fralick and and Kissen,1998). Kissenf1998)*This This date date has has major major tectonic tectonic (Fralick implications, implicationsffor for it it indicates indicates that that these these two two iron-formations iron-formations were were deposited deposited on on the the peripheral peripheral foreland foreland bulge bulge of of the the Animikie AnMkie foreland basin, basinfrather rather than than on on the the continental continental margin margin prior prior to tothe the foreland development of of the the foreland foreland basin. basin. In development In this this scenario scenario of of aa northward-migrating northward-migrating foreland foreland basin, basinfthe the terrigenous terrigenous clastic clastic Palms Palms Formation Gogebic range rangeof of Formation and and the the Ironwood Ironwood Iron-formation Iron-formation on on the the Gogebic Wisconsin-Michigan Wisconsin-Michigan may may be be continuous continuous with with but but older older (i.e., (i.eOf diachronous) diachronous) than than the the more more northerly northerly (by (by100 100 km) km) terrigenous terrigenous clastic Pokegama Pokegama Formation Formation and and the the Biwabik Biwabfi Iron-formation Iron-formation on on the the clastic Mesabi range range of of Minnesota Minnesota (Ojakangas, (Ojakangasf1994). 1994). Mesabi PENOKEAN OROGEN OROGEN PENOKEAN of aa big big supercontinent, supercontinentf The Archean Archean ended ended with with the the formation formation of The Kenorland, Kenorlandf the the product product of of the the amalgamation amalgamation of of volcanic arcs arcs and and granitic granitic intrusive intrusivebodies, bodies! and and history history repeats repeats itself. itself* The The Penokean Penokean (Hudsonian) (Hudsonian)orogeny orogeny occurred occurred on on the the southern southern edge edge of of the the Superior Superior craton, cratonIextending extending over over aa distance distance of of 1100 1100 km km from from the the Grenville ONf westward westward to to the the area area just just west west Grenville Front Front near near Sudbury, Sudburyf ON, of of Lake Lake Superior, Superior! deforming deforming the the sedimentary sedimentary units units deposited deposited on on the the passive passive continental continental margin margin when when volcanic volcanic arcs arcs (the (the Wisconsin Wisconsin magmatic terranes) terranes) and and microcontinents microcontinents (that (that included included Archean Archean magmatic rocks) collided collided from from the the south south with with northward-directed northward-directed thrusting rocks) thrusting over over aa southward-dipping southward-dipping subduction subduction zone zone (e.g., (e.gOfMorey Morey and and Southwickf 1995; 1995; Sims, S h I1996). 1996). Southwick, The The Penokean Penokean has has long long been been an an enigma enigma for for it it seems seems to to have have been been long-lived, Ma to to 1770 1770 Maf Ma, with withthe long-lived! lasting lasting from from at least 1982 Ma the earliest earliest Proterozoic Proterozoic sedimentary sedimentary units units in in Minnesota Minnesota deposited deposited Southwickf1995). 1995). Volcanic Volcanic rocks rocks of of the the about 2200 2200 Ma Ma (Morey (Moreyand and Southwick, about orogen range range in in age age from from 1880-1840 1880-1840 Ma, MaI plutonic plutonic rocks rocks from from 19801980orogen 1770 1770 Ma, Maf and and deformation deformation from from 1982-1770 1982-1770 Ma Ma (e.g., (e.gOfSouthwick Southwick and and Moreyf 1991; 1991; Sims S h s et et al, alf1993). 1993). Volcanogenic Volcanogenic massive massive sulfide sulfide Morey, deposits CutZn, ZnIand and Pb, Pbf about about 1860-1840 1860-1840 Ma, Maf deposits and and occurrences occurrences of of Cu, are are abundant abundant based based on on extensive extensive exploration exploration drilling drilling of of geophysical geophysical anomalies; anomalies; more more than than 13 13 bodies have been identified identified (DeMatties, (Flambeau) has has been been mined mined to to ( M a t t i e s f 1994), 1994)f although although only only one one (Flambeau) date. Post-Penokean Post-Penokean rhyolites rhyolites and and granites granites occur occur in in Wisconsin Wisconsin date. ( S d et al, alf 1989) 1989) and and post-orogenic post-orogenic metamorphism metamorphism and and coeval coeval (Sims plutons plutons in in east-central east-central Minnesota Minnesota have have been dated at 1770-1760 1770-1760 Ma with with rapid rapid cooling cooling at at 1760-1750 1760-1750 Ma Ma (Holm (Holmet et al, alf 1998). 1998). Two !lWo deformations Formation have deformations in in the the southern southern portion portion of the the Thomson Formation been described, describedfwith with F1 Flisoclinal isoclinal recumbent recumbent folds folds and and F2 F2 upright upright been folds (Holstf1982, 1982f 1984). 1984)folds that that refolded refolded the the earlier earlier folds folds (Holst, Excellent Excellent interpretations interpretations of of Penokean Penokean deformation deformation can can be be found, found, S h e.gOf in in Holst Holst (1991), (1991)fKlasner Klasner et et al a1 (1991), (1991)fKiasner Klasner and and Simse.g., (1993), (1993)f Gregg Gregg (1993), (1993)! and and Sims S h and and Carter Carter (1996). (1996). 8 �By removing removing the t h e 60 60km-wide kxu-wide Middle Middle Proterozoic Midcontinent Rift Rift Proterozoic Midcontinent By System from from aa regional r e g i o n a l geological geological map, map, thereby thereby bringing b r i n g i n g Minnesota Minnesota system and Wisconsin-Michigan Wisconsin-Michigan into i n t o juxtaposition, juxtaposition, the t h e fold-and-thrust fold-and-thrust and belts of of the t h e two two areas areas become become one one continuous continuous zone. zone- Southwick Southwick and and belts Morey (1991) (1991) correlated c o r r e l a t e d the t h e Niagara ( W I ) and and Niagara fault f a u l t zone/suture zone/suture (WI) Morey t h e Malmo Malmo ddiscontinuity i s c o n t i n u i t y(MN). (MN). Similarly, S i m i l a r l y , the t h e various v a r i o u s turbiditeturbiditethe shale s h a l e units u n i t s (Thomson, (Thomson, Rove, Rove, Virginia, Virginia, Tyler, Tyler, Copps, Copps, and and Michigamme Michigamme onecontiguous contiguousuunit become one n i t ffilling i l l i n gthe t h eAnimikie Animikie Formations) then t h e n become Formations) Basin- This, This, however, however, does does not n o t imply imply that t h a t all a l l of of these t h e s e formations formations Basin. are the t h e same same age, age, for was migrating migrating northward northward during during f o r the t h e basin basinwas are d e p o s i t i o n of of these t h e s e units; u n i t s ; some some sediment sediment deposited in i n the t h e earlier earlier deposition s t a g e s of of basin b a s i n development development was was likely l i k e l y cannibalized cannibalized and and stages redepositedredeposited. asa anorthward-migrating northward-migrating The Animikie Animikie bbasin a s i n has been iinterpreted n t e r p r e t e d as The has been f r o n t of of (on (on the t h e north n o r t h side) s i d e ) of of f o r e l a n d basin b a s i n that t h a t developed developed in foreland in front of tthe t h e fold-and-thrust fold-and-thrust belt beltdue dueto t othe t h eweighting weighting down down of h e crust crust by by the t h i sfolded foldedand andthrusted t h r u s t e mountain d mountainrange rangethat t h a then t t h e nbecame became aamajor major this s o u r c e of of sediment sediment for f o r the t h e basin basin (e.g., ( e - g oHoffman, , Hoffman, 1987; 1987; Southwick Southwick source e t al, al, et 1988; Barovich Barovich et e t al, a l , 1989; 1989; Southwick Southwick and and Morey, Morey, 1991; 1991; 1988; Ojakangas, 1994; 1994; Morey Morey and and Southwick, Southwick, 1995). 1995)Ojakangas, N d isotope isotope data data determined determined by by Barovich Barovich et e t al a1 (1989) (1989) indicate i n d i c a t e that that Nd sampleshad hadananArchean Archeanprovenance provenancet ototthe some Michigainme Michigamme samples h e north n o r t h and and some some had had an a n Early E a r l y Proterozoic Proterozoic provenance provenance to t o the t h e south. southsome P a l e m u r r e n t data data for f o rthe t h Michigamme e Michigamme and h e Tyler n d i c a t e aa andt the Tyler iindicate Paleocurrent northward transport t r a n s p o r t of of sediment sediment from from the t h e south south side side of of the the northward southward transport t r a n s p o r t of of sediment sediment from from the the Animikie Basin Basin and and aa southward Animikie n o r t h side side of of the t h e basin b a s i n as as summarized summarized in i n Ojakangas Ojakangas (1994). north (1994). Hemming Hedng e t al a1 (1995), (19951, on on gochemical geochemicaland and isotopic i s o t o p i c evidence, evidence, described d e s c r i b e d the the et provenance of of the t h e Virginia V i r g i n i a Formation Formation as as aa young young differentiated differentiated provenance v o l c a n i c arc arc to t o the t h e south south of of the t h e basin. basinvolcanic The magmatic terranes t e r r a n e s were were located l o c a t e d just j u s t to t o the t h e south s o u t h of of The Wisconsin Wisconsin magmatic t h e fold-and-thrust fold-and-thrust belt. belt- The The Pembine-Wausau Pembine-Wausau terrane t e r r a n e is is comprised comprised the of older older (1889-1860 (1889-1860 Ma) M a ) magmatic magmatic rocks rocks that t h a t formed formed in i n an a n island island of arc and/or and/or back-arc back-arc basins b a s i n s above above aa south—dipping south-dipping subduction subduction zone zone arc magmatic rocks rocks ( t h e Niagara Niagara fault f a u l t zone zone or o r suture) s u t u r e ) and and younger younger magmatic (the (1845-1835 Ma) M a ) that t h a t formed formed above above aa north-dipping north-dipping subduction subduction zone, zone, (1845-1835 t h e Eau Eau Pleine P l e i n e shear s h e a r zone zone (Sims ( S h et e t al, a l , 1989, 1989, 1993). 1993)- Deep Deep seismic seismic the p r o f i l i n g indicates i n d i c a t e s that t h a t both both the t h e Niagara Niagara fault f a u l t and and the t h e Eau Eau Pleine Pleine profiling shear e t al, a l , 1991). 1991)- An ~n s h e a r zone zone may may penetrate p e n e t r a t e the t h e entire e n t i r e crust c r u s t (Cannon (Cannon et o p h i o l i t e sequence sequence in i n the t h e Quinnesec Quinnesec Formation Formation of of northeastern northeastern ophiolite Wisconsin basinWisconsin (Schulz, (Schulz, 1987) 1987) indicates i n d i c a t e s the t h e closure c l o s u r e of of an an ocean ocean basin. In I n the t h e southerly s o u t h e r l y Marshfield Marshfield terrane, t e r r a n e , 1860 1860 Ma M a rocks rocks were were deposited deposited on Archean Archean crust crust and and amalgamation amalgamation of of the t h e two two terranes t e r r a n e s along along the the on Eau Eau Pleine P l e i n e suture s u t u r e occurred occurred at a t about about 1840 1840Ma M a (Sims ( S h et e t al, a l , 1993). 1993)Three episodes episodes of of post-orogenic post-orogenic magmatism m a g m a t i s m followed, followed, dated dated at a t 1835 1835 Three Ma, M a , 1760 1760 Ma, ~ aand and , the t h e 1469+/1469+/- 28 28 Ma Ma Wolf Wolf River M v e r batholith b a t h o l i t h (Sims ( S h et et al, a l , 1989). 1989)- Nd N d isotopic i s o t o p i c data data of of Barovich Barovich et e t al a1 (1989) (1989) indicated i n d i c a t e d the the major growth growth of of new new crust crust from fromthe t h e mantle. mantlemajor The Penokean Penokean (Hudsonian) (Hudsonian) Orogen Orogen was was part p a r t of of the t h e reassembly reassembly The (Hoffman, new supercontinent supercontinent that t h a t Williams W i l l i a m s et et al a1 (1991) (1991) (Hoffman, 1988) 1988) of of aa new 9 �This supercontinent supercontinent also a l s o included included the the dubbed Hudsonland. Hudsonland. This dubbed (as did d i d the t h e Archean Archean supercontinent supercontinent of of Fennoscandian Shield S h i e l d (as Fennoscandian Kenorland). i s comparable comparable Kenorland). The The Svecokarelian Svecokarelian orogeny orogeny of of that t h a t shield s h i e l d is t o the t h e Penokean Penokean Orogen Orogen in i n many many aspects. aspects. to Q U A R T ZITES ITES QUARTZ The Penokean Penokean Orogen Orogen and and adjacent a d j a c e n t rock rock units u n i t s continued to t o be be The weathered weathered (Southwick (Southwick and and Mossler, Mossier, 1984) 1984) and and eroded for f o r about 100 100 Ma following the mountain-building culmination at about 1850 (?) M a following t h e mountain-building culmination a t about 1850 ( ? ) M a . Several S e v e r a l quartzite q u a r t z i t e units u n i t s were w e r e deposited deposited to t o the t h e south south of of the the Ma. orogen, orogen, including i n c l u d i n g the t h e Sioux Sioux Quartzite Q u a r t z i t e of of Minnesota, Minnesota, South South Dakota, Dakota, Weber, and Iowa Iowa (e.g., , Morey, Morey, 1984; 1984; Ojakangas and W e b e r , 1984; 1984; Southwick Southwick and e t al, a l , 1986) 1986) and and the t h e Baraboo Baraboo (Dott, (Dott, 1983), 1983), Barron Barron (Rozacky, (Rozacky, 1987), 1987), et Flambeau (Campbell, (Campbell, 1986), 1986), and and McCaslin McCaslin (Olson, (Olson, 1984) 1984) Quartzites Quartzites Flambeau of problem of Wisconsin. Wisconsin. Their Their ages ages and and correlation c o r r e l a t i o n have long been a problem e t al., a l e , 1991; 1991; Chandler Chandler and and Morey, Morey, (e.g., Brown, 1986; 1986; LaBerge LaBerge et (e.g., 1992; 1992; Ojakangas, Ojakangas, 1993), 1993), especially e s p e c i a l l y because because the t h e Baraboo, Baraboo, Flambeau, Flambeau, and and McCaslin McCaslin are are deformed deformed whereas whereas the t h e Sioux Sioux and and the t h e Barron Barron are are relatively r e l a t i v e l y horizontal. h o r i z o n t a l . These These "Baraboo "Baraboo Interval" I n t e r v a l w quartzites q u a r t z i t e s pose pose the t h e "Proterozoic "Proterozoic red r e d quartzite q u a r t z i t e enigma" enigmawof of Dott Dott (1983). (1983). Dott Dott (1983) (1983) e t al a1 (1993) (1993) suggested suggested that t h a t aa plate p l a t e suture s u t u r e exists exists and Van Van Schmus Schmus et and beneath the t h e Paleozoic Paleozoic cover cover to t o the t h e south, south, and tthat beneath h a t a southerly southerly t e r r a n e collided c o l l i d e d with with the t h e then-passive then-passive margin of h e continent continent terrane of tthe s o u t h e r l y dipping dipping subduction subduction zone. zone. Chandler over aa southerly Chandler and and Morey Morey over (1992) interpreted (1992) i n t e r p r e t e d paleomagnetic paleomagnetic data d a t a to t o indicate i n d i c a t e that t h a t there t h e r e are are two ages ages of of quartzite q u a r t z i t e bodies, bodies, one one late l a t e Penokean Penokean and and the t h e other other two post-1760 Ma. M a . Recent Recent U-Pb detrital d e t r i t a l zircon z i r c o n ages of 1730—1710 1730-1710 Ma M a for for post-1760 t h e Baraboo Baraboo and and the t h e McCaslin McCaslin and and Pb/Pb Pb/Pb ages on d e t r i t a l zircons z i r c o n s of the detrital 1730-1850 for f o r the t h e Sioux, Sioux, 1745—1880 1745-1880 for f o rthe t h eFlainbeau, Flambeau, and and 1750—1880 1750-1880 1730—1850 et al, a l , 1998) 1998) and and similar similar ages ages for for (Schneider et f o r the t h e Barron Barron (Schneider for d e t r i t a l zircons z i r c o n s in i n the t h e Baraboo Baraboo and and McCaslin McCaslin quartzites q u a r t z i t e s (Van detrital (Van Wyck, Wyck, 1995; Dott D o t t et e t al, a l , 1997) 1997) can can be be interpreted i n t e r p r e t e d to t o indicate i n d i c a t e that t h a t these these 1995; "Baraboo Interval" I n t e r v a l f fquartzites q u a r t z i t e s may may be be correlative. c o r r e l a t i v e . Holm "Baraboo H o l m et et al a1 (1997) have have located l o c a t e d aa 1630 1630 Ma M a thermal thermal front f r o n t in i n northwest northwest Wisconsin Wisconsin (1997) based on on cooling c o o l i n g ages ages in i n Ar/Ar A r / A r dates d a t e s on on mica; mica; this t h i s front f r o n t coincides coincides based with the t h e deformational deformationalboundary boundary between between tthe h e Barron Barron and the the with . Flambeau Flambeau. If I f one one assumes assumes tthat h a t the t h e quartzites q u a r t z i t e s are areerosional e r o s i o n a l remnants remnants of of aa l a r g e r sheet s h e e t of of quartz q u a r t z sand sand locally l o c a l l y >1500 >I500 m m thick t h i c k and deposited deposited larger on on the t h e continental c o n t i n e n t a l margin, margin, aa tremendously tremendously large l a r g e and and deeply deeply weathered must be be assumed. assumed. even weathered quartz-bearing quartz-bearing source source terrane t e r r a n e must Even without without the t h e assumption assumption of of aa single s i n g l e large l a r g e basin, basin, the t h e volume of quartz q u a r t z is i s enormous. enormous. Wheras Wheras aa fluvial f l u v i a l origin o r i g i n is i s most likely l i k e l y for for most most of of the t h e quartzites q u a r t z i t e s (e.g., (e.g., Southwick Southwick et e t al, a l , 1986), 1986), aa marine marine origin o r i g i n for f o r the t h e upper upper Sioux Sioux (Ojakangas (Ojakangas and and Weber, Weber, 1984) 1984) and and for for Baraboo (Dott, ( D o t t , 1983) 1983) has has been been proposed. proposed. p a r t of of the t h e Baraboo part REFEREHCES REFERENCES Patchett, P. P. J., J., Peterman, Petennan, Z. Z. E., E., and and Sims, Sims, P. P. K., K., 1989, 1989, Nd Nd Patchett, isotopes and and the the origin origin of of 1.9-1.7 1.9-1.7 Ga Ga Penokean Penokean continental continental crust crust of of the the Lake Lake isotopes Superior region: region: Geological Geological Society Society of of america America Bulletin, Bulletin, v. v. 101, Superior 101, p. p. 333—338. 333-338. Barovich,K. 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Bulletin implications and implications and suggested suggested correlations: correlations: U. . Geological Survey Bulletin 1904—R, 31 1904-R, 31 p. p. Ojakangas, Ojakangas, R. R. W., W., Heiskanen, Heiskanen, K., K., and and Marmo, Marmo, J. J. S., S., 1991, 1991, Early Early Proterozoic Proterozoic giaciogenic connection? in Ojakangas, R. R. W. W. glaciogenic deposits: A North America-Baltic connection? Precambrian Geology Geologyofofthe the Southern Southern Canadian CanadianShield Shieldand andthe the Eastern Eastern (ed.), Precambrian p. 83—91. 83-91. p. Geological Survey SurveyInformation InformationCircular Circular 34, Baltic Shield: Shield: Minnesota Minnesota Geological 34, Baltic R. W W. paleocurrents of Ojakangas, Ojakangas, R. . and and Weber, R. E., E., 1984, 1984, Petrography and paleocurrents of the the Lower Southwick, Lower Proterozoic Proterozoic Sioux Sioux Quartzite, Quartzite, Minnesota Minnesota and and South South Dakota: Dakota: in in Southwick, D. L. 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C-2, Geological Society Society of of Project series, pp. America Decade Decade of of North North American American Geology Geology Project . 11—120. 11-120. P. K., Schulz, K. 3., E., Petrography Schulz, K. J.8 DeWitt, DeWitt8 E ., and Brasaemle, BB., ., 1993, Petrography of Early magmatic and geochemistry geochemistry of Early Proterozoic Proterozoic granitoid rocks rocks in Wisconsin magmatic terranes of terranes of Penokean Penokean Orogen, Orogen, northern northern Wisconsin: Wisconsin: U.S. U.S. Geological Survey Survey Bulletin 1904-J8 31 31 p. p. Bulletin 1904—3, Sims, Sims, P. K., Schulz, K. K. J 3., Peterman, Z. Sims, w. R., R., ., and Peterman# Z. E., E., 1989, 1989, Sims8 P. K., K., Van Van Schmus, Schmus8 W. Tectono—stratigraphic evolution Wisconsin magmatic magmatic Tectono-stratigraphic evolution of of the the Early Proterozoic Proterozoic Wisconsin terranes v. terranes of of the the Penokean Pen0kea.nOrogen: Orogen: Canadian Canadian Journal Journal of Earth Sciences, v . 26, p. p. 2145-2158. 2145—2158. petrology of Proterozoic Southwick, Southwick, D. D. L., L., and and Day, Day, W. W. C., C., 1983, 1983, Geology Geology and and petrology Proterozoic mafic mafic dikes, dikes, north—central north-central Minnesota Minnesota and and western western Ontario: Ontario: Canadian Canadian Journal Journal of of Earth v. 20, 20, p. p. 622—638. 622-638. Earth Sciences, v. Southwick, Southwick8 D. D. L., L., and and Morey, G. G. B., B., 1991, 19918 Tectonic Tectonic imbrication imbrication and foredeep foredeep development development in in the the Penokean Penokean Orogen, Orogen, east—central east-central Minnesota——An Minnesota--An interpretation interpretation U. based on on regional regional geophysics geophysics and and the the results results of test—drilling: test-drilling: U . S. Geological Geological Survey Survey Bulletin Bulletin 1904-C, 1904-C8 17 17 p. p. Southwick, L., Geologic map G. B., B., and and McSwiggen, P. P. L ., 1988, 1988# Geologic Southwick8 D. D. L., L., Morey, Morey, G. (scale 1:2508000) 1:250,000) of the Penokean Penokean orogen, orogen, central central and and eastern eastern Minnesota8 Minnesota, and (scale accompanying accompanying Minnesota MinneS0ta Geological Geological Survey Survey Report of Investigations Investigations 37, 3T8 25 25 p. Fluvial origin Southwick, D. Southwick, D. L.. L.. Morey, Morey, G. G. B., B e 8and and Mossier, Mossler, 3. J. H., He, 1986, 1986, Fluvial origin of of the Minnesota: Geological Geological the lower lower Proterozoic Proterozoic Sioux Sioux Quartzite, Quartzite, southwestern southwestern Minnesota: Society of America America Bulletin Bulletin v. v. 97, 97, p. p. 1432—1441. 1432-1441. Society of Southwick, Southwick, D. D. L., L.8 and and Moasler, MoSSler, 3. J. B., H e 81984, 1984, The The Sioux Sioux Quartzite and subjacent subjacent regolith regolith in in the the Cottonwood Cottonwood County County basin, basin8 Minnesota: in Southwick, D. D. L., L., Quartzite (Early (Early (ed.), Contributions to to the Geology of the Sioux Quartzite (ed.)# Shorter Contributions Proterozoic), Southwestern Proterozoic), Southwestern Minnesota: Minnesota: Minnesota Geological Geological Survey Report of of Investigations Inveatigations 32, 32, p. p. 17—44. 17-44. 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M., M., 1970, 1970, An An extensive extensive early early Proterozoic Proterozoic glaciation glaciation in in North North america:? Palaeography, v. 7, p. America:? Palaeography, Palaeoclimatology, Palaeoclimatology, Palaeoecology, v. p. 85—101. 85-101. , 1983, 1983, Tectono—aedimentary Tectono-sedimentary history of early Proterozoic rocks rocks of of the the northern Great northern Great Lakes Lakes region: region: in in Medaris, Medaris, L.G., L.G., Jr., Jr., (ed.), (ed.), Early Early Proterozoic Proterozoic Geology of of the the Great Great Lakes Lakes Region: Region: Geological Geological Society Society of of inerica America Memoir Memoir 160, 160, p. 15—32 p.15-32. 17 �UNDERSTANDING THE UNDERSTANDING THEMIDDLE MIDDLEPROTEROZOIC PROTEROZOIC HISTORY HISTORY OF OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION: WHAT'S REGION: WHAT'S NEW? NEW? WHAT'S WHAT'S NEXT? NEXT? W.F. Cannon, Cannon, US Geological Geological Survey, Survey, Reston, Reston, VA VA Middle Proterozoic Proterozoic time encompasses 700 million Middle million years years (1600-900 (1600-900Ma) Ma)of ofgeologic geologichistory. history. In the Lake Superior Superior region only a small part of that 1470 Ma Lake that time time is is recorded recorded in inthe therock rockrecord. record. At about 1470 large anorogenic granitic plutons plutons were were emplaced emplaced in innorthern northernWisconsin. Wisconsin. Between 1108 and about about 1108 and 1060 1060 Ma the Midcontinent rift, a 2200 km-long volcanic and subsequent sedimentary basin, formed and was was structurally structurallymodified. modified. AAbrief briefsummary summaryof ofthe thecurrent currentunderstanding understandingof ofthese thesetwo twoevents eventsisis and emphasizing findings during the presented below emphasizing the past past 15 years. years. An extended list of references for the Midcontinent Midcontinent Rift Rift presents presents some some of of the principal publications since the detailed papers in the 1982 1982 Geological Society Societyof of America America Memoir Memoir 156, 156, "Geology and Tectonics Tectonics of the Lake Superior Superior Basin". Geological For anorogenic anorogenic plutons, plutons, references references include include original original research from the 1970's 1970's and and more more recent recent For summary summary papers. papers. Anorogenic Anorogenic plutons AAsuite suiteof oflarge largegranitic graniticplutons plutons was emplaced in a broad belt spanning most of the North American continent to Arizona Arizona between betweenabout about 1500 1500and and 1450 1450Ma. Ma. The continent from Labrador to plutons plutons intruded intruded older older continental continentalcrust crust during a period generally devoid of major orogeny, orogeny, hence the name anorogenic anorogenic plutons. That Thatsuite suiteof of plutons plutons is is represented in the Lake Superior region by the Wolf River River batholith and Waussau and Stettin plutons plutons in in Wisconsin. These Theseplutons plutonswere werestudied studied extensively with the the exception exception of of extensively in the 1970's 1970's but but have have received received relatively relatively little attention since, with being discussed discussed in regional summary papers. The The Wolf Wolf River batholith, with an exposed area of about were emplaced emplaced at at about about 1470 Ma. Ma. The about 10,000 10,000km2, km2, and the smaller plutons were The Wisconsin Wisconsinplutons plutons share share characteristics characteristics with the other members of the suite in being emplaced at shallow depths in Early Proterozoic Proterozoic crust crust and and consisting consistingof of large large volumes volumes of granite granite with rapakivi affinities, affinities, and lesser lesser volumes volumes of of more mafic rocks, largely mangerite mangerite and and anorthosite. anorthosite. The Thegranites granitesof ofthe thesuite suiteare are interpreted (20±10%) of Proterozoic interpreted to have formed by relatively relatively low percentage of partial melting (20±10% granitic granitic rocks rocks in in the the lower lower crust. crust. Anorthosite Anorthosite may be derived from basaltic basaltic magma produced, produced, in part, by partial partial melting melting of mantle lithosphere. Studies Studiesof of the the Wolf Wolf River batholith indicate that mangerite magma C. Crystallization magma was was derived derived at at aa depth depth of of 21-32 21-32 km and and a temperature temperature of 950±90° 950±90C. Crystallizationof of the the granite 0-840°C and 650-840° and at at shallow shallow depths depths of of 2-4 2-4 km. km. The The granite now now exposed exposedoccurred occurredatattemperatures temperaturesof of65 cause cause of of widespread widespread melting melting of of lower lower crust crust in in a belt of continental dimensions dimensions remains obscure. obscure. Midcontinent Midcontinent rift The TheMidcontinent Midcontinentrift rift extends extendsin in an an arc arc from Kansas, through the Lake Superior basin, basin, into into southern southernMichigan. Michigan. The The physical physical character character of the rift (rock types, geometry, structure, structure, approximate decades. Research in the past 15 approximate age) age) have been well known for many decades. 15 years has added critical critical information informationto to allow allow the thekinematic kinematic and and dynamic dynamic aspects aspects of evolution evolution of the rift to be deciphered. Deep crustal seismic surveys, precise age determinations, deciphered. Deep crustal seismic surveys, precise age determinations, petrochemical petrochemical research, and experimental experimentaland and theoretical theoretical studies studiesof of mantle mantle and and lithospheric lithospheric processes can be integrated to understand understandthe the rift rift in in the the broad broad context context of of the the evolution of the North American continent continent and and globalglobalscale scale processes. processes. Seismic comprising the entire crustal Seismic surveys surveys have have shown shown that that the rift is is very deep, in places comprising thickness. thickness. Subaerial Subaerialbasalt basaltflows flowsform formthe thelower lowerpart part of of the the rift-fill rift-fill and are as as much as 20 km thick along km along the rift axis. axis. Continental Continentalclastic clasticsedimentary sedimentaryrocks rocksoverlie overliethe thebasalt basaltand andare areas asmuch muchas as10 10km thick. thick. Basalt Basalteruption eruptionand andcoeval coevalrift riftsubsidence subsidencewas was rapid rapid and and of of relatively relatively short short duration. duration. The The volcanic volcanic phase of of the the rift rift lasted lasted about about 14 14 my (1108-1094 (1 108-1094 Ma). Rates of volcanism and subsidence subsidence were were not entirely entirely uniform uniform and and appear appear to have have been greatest near the close of the volcanic phase. Subsidence Subsidenceof of volcanic volcanic basins, basins, as as inferred inferred from seismic seismic profiles, appears appears to have been by a combination combination of of normal normal faulting faulting and and broad flexure. Large Largevolumes volumesof ofmafic maficmagma magmawere werealso also 19 �emplaced both within the crust and as crustal underplating during during this this same same period. period. Basalt Basalt eruption eruption ceased rather abruptly at about 1094 Ma and subsidence rates rates declined correspondingly. correspondingly. Further filling of the rift was with continental sedimentary rocks, mostly mostly red red sandstone, sandstone, and and minor minor reduced reduced lacustrine rocks. The Theduration durationof ofsedimentation sedimentationisis not not well well constrained constrained but but most most likely likely continued, continued, lacustrine During along with subsidence, at declining rates for at least several tens tens of of millions millions of of years. years. During sedimentation, sedimentation,inversion inversion of of the the central central portions portions of of the the rift rift took took place place along along aa set set of of major majorreverse reverse faults. These Theseevents eventscombined combinedto toform formthe thepresent present geometry geometry of of the the rift. rift. A A central central horst horst contains containsthe the originally of volcanic volcanic rocks. rocks. Flanking originally deeper central parts of the rift, including thick sections of Flanking basins basins contain contain wedges of of thinner thinner volcanic volcanic sequences sequences and and overlying overlying sedimentary sedimentary rocks. rocks. The great volume of basaltic rocks and related intrusive rocks in in the the rift, rift, combined combined with with limited amounts hot during during rifting; rifling; probably amounts of lithoshperic lithoshperic extension imply that the mantle was anomalously hot about 200°C 200° hotter than present day asthenosphere. Petrochemical Petrochemical studies studies indicate indicate that much of of the the magma was generated by partial melting melting of of primitive, primitive,enriched enrichedmantle mantle.. Together, Together, these these features features point to the existence that the the rifting rifling existence of a mantle plume beneath the rift, and more specifically, suggest that the initiation of of aa new new plume plume and andthe the arrival arrival of of aa plume plume head head at at and volcanism was a consequence of the the base of the lithosphere. Modelling and numeric simulation of plume behavior shows that that when aa large mushroom-shaped mushroom-shaped head head of of hot hot new plume forms and rises from depth, it generates aa large asthenosphere. The head grows asthenosphere. grows as as it rises rises slowly slowly and is fed by its its own own narrower narrower but but faster faster rising risingstem. stem. The arrival arrival of a plume head at at the base of the lithosphere lithosphere and at at depths depths where where adiabatic adiabaticpartial partial magma generation. generation. Under suitable melting occurs creates a short period of intense magma suitable stress stress conditions conditions in the lithosphere, the plume can also initiate extension and and rifting. rifting. The The arrival arrival of of aa new new mantle mantle plume at the base of the lithosphere lithosphere at at about about 1108 1108 Ma provides the most most coherent coherentexplanation explanationfor forthe the origin of the rift and its its great great volume volume of of igneous igneous rocks. rocks. than the the volcanic volcanic basin. basin. The Rift sedimentation occurred in basins somewhat broader than The sedimentary sedimentary basins do not appear to be strongly controlled by faulting. Rather, Rather, they they appear appear as as smooth smooth flexural flexural depressions depressions on seismic seismic reflection sections. Subsidence Subsidencewas was most most likely likely aa result result of of cooling cooling of of the the head spread and and cooled cooled conductively. conductively. Sediments lithosphere as the initial plume head Sediments were initially initially derived dominantly progressed, however, however, more more older dominantly from volcanic rocks in the rift. As sedimentation progressed, with continued continued erosion erosion of of rift rift terranes outside outside of the rift were tapped as a sediment source along with volcanic volcanic rocks. Inversion of the central portion of of the the rift rift occurred occurredduring duringthe thelater laterstages stagesofofsedimentation. sedimentation. A A set set of of high angle produced displacements displacements of as angle reverse reverse faults and thrusts, in part reactivated normal faults, produced much as several tens of kilometers. The Thetime timeof offaulting faultingisis imprecisely imprecisely known, known, but but most most movement movement must have been in in the the interval interval 1080-1040 1080-1040Ma. Ma. Viewed on a more more regional scale, the Midcontinent rift has been historically somewhat of an enigma in that it is a major extensional feature feature which formed formed immediately immediately west of of the the seemingly seeminglycoeval coeval Grenville orogen. In recent years, however, precise radiometric dating shows that the short In recent years, however, precise radiometric dating shows that short interval interval (1108-1094 Ma) of extension in the Midcontinent rift appears to coincide with an interval of tectonic tectonic rift appears to coincide with an interval of (1 108-1094 quiescence, orogeny. Thus, quiescence, or possibly extension, in the multi-phase Grenvillian orogeny. Thus, aa mantle mantle plume plume arriving arriving at 1108 1108Ma Ma could could have have begun aa period period of of extension extension during during this this Grenvillian Grenvillianquiescent quiescentperiod. period. was renewed renewed and and aa period period of of northwestnorthwestAt about 1090 1090 Ma compression in the Grenville Province was directed thrusting, the Ottawan orogeny, orogeny, continued continuedfor fortens tensof ofmillions millionsofofyears. years. The The onset onset of of thrusting ininthe theGrenville GrenvilleProvince Provincecoincides coincidesremarkably remarkably closely closelywith with the the end end of of extension extensionin in the the Mideontinent Midcontinent rift rift and and the the onset onset of of compressive compressive deformation. deformation. rift marks marks the the arrival arrival of of aa new new plume plume head head at at the the It appears then that development of the Midcontinent rift at about about 1108 Ma. Ma. Melting base in the lithosphere of the Lake Superior region at Melting of the plume plume head head and and 20 �stresses generated by lateral spread of the plume caused the intensely volcanic rift. Under Undersome some stresses circumstances this event might have led circumstances led to to continental continentalbreakup. breakup. In this case, however, however, initiation of the Ottawan orogeny in the adjacent Grenville Province, transmitted northwest-southeast northwest-southeast directed stresses into the Lake Superior region. This Thisnewly newlyapplied appliedstress stressfield field not not only only terminated terminatedrift rift extension, initiated aa period period of of compressive compressive deformation deformation and and rift rift inversion. inversion. extension, but initiated The processes that formed the rift were also important in forming the major mineral deposits for which the rift is well known. The The vast vast new igneous rocks were fertile starting material for for metalmetalprocesses. Some crystallization of of concentrating processes. Someconcentration concentration occurred occurred early, during fractional crystallization magma. The Thevery verylarge large Cu-Ni Cu-Ni sulfide sulfide deposits deposits of the theDuluth Duluthcomplex complexand and other other intrusions intrusions formed formed at at this stage, as did concentrations of of platinum platinum group groupelements. elements. The rifting and related related processes processes in in the the mantle also provided a large heat engine that drove hydrothermal circulation. Those Thosehydrothermal hydrothermal systems sediment-hosted systems formed the Keweenaw native copper district, the White Pine and related sediment-hosted copper deposits, and polyrnetallic polymetallic vein vein deposits. deposits. The heat generated by the the rift rift also also caused regional regional metamorphism that converted Early Proterozoic iron-formations from non-magnetic to magnetic taconite in places such such as as the the Mesabi Mesabi Range Range and and Gogebic Gogebic Range. Range. Much progress has been made in the past 15 years in understanding fundamental causative factors of refinements the Midcontinent rift. The The data data gathered gathered in in that period lay the foundation for continued refinements of knowledge knowledge of this important structure. Research continues on refining knowledge of the age of rifting events, events, internal stratigraphy stratigraphy of rift units, the nature of plume-lithosphere interaction, and and alteration. alteration. Advances in the detail and precision precision of patterns of regional metamorphism and information information on the geometry, age, and composition of the rift from recent and continuing research, combined quantitative numerical combined with modem modem computational computational techniques, allows allows a new phase of quantitative undertaken. Examples of this new phase of research research are current research on rift evolution to be undertaken. studies studies of the transient transient thermal history of the rift, and the paleohydrology of the rift as it related to formation formation of of mineral mineral deposits. deposits. 21 �References on on the the Midcontinent Midcontinent Rift (post Selected References (post 1982) 1982) Allen, Wi., Dickas, &en, D.J., Hinze, W.J., Dickas,A.B., A.B.,and andMudrey, Mudrey,M.G., M.G., Jr., Jr., 1997, Integrated geophysical modeling of the North American Midcontinent Midcontinent Rift System: System: new interpretations interpretationsfor for western Lake Lake Superior, Superior, in northwestern Wisconsin, Wisconsin, and eastern eastern Minnesota, Minnesota, in Ojakangas, R.W., and others, others, eds., Middle Middle Proterozoic to Cambrian Proterozoic Cambrian rifting, central central North America: Geological Society Society of of America America Special Special Paper 312, p. 47-72. Cannon, Cannon, W.F., and and Hinze, Hinze, W.J., W.J., 1992, 1992,Speculations Speculationson onthe the of the the North North American American Midcontinent Midcontinentrift: rift: origin of Tectonophysics, v. 213, p. 49-55. Hinze, W.J., W.J., and Mariano, Mariano, J., J., 1995, 1995, Allen, D.J., Braile. L.W., Hinze, The Midcontinent Midcontinent rift rift system, system, U.S.A.-a major major Proterozoic in Olsen, Olsen, K.H., K.H., (ed.), (ed.), Proterozoiccontinental continental rift: in Continental rifts: evolution, evolution, structure, structure, tectonics, tectonics, International Lithosphere Lithosphere Program Program Publication Publication no. no. 264, 373-407. 264, p. p. 373-407. Cannon, W.F., W.F., and ten ten others, others, 1990, The The Midcontinent Midcontinent rift beneath Lake Superior from GLIMPCE seismic reflection profiling: Tectonics, Tectonics, v. v. 8, 8, p.305-332. p.305-332. Cannon, showing mineral Cannon, W.F., W.F., and McGervy, T.A., 1991, Map showing Midcontinent rift. rift, Lake Superior deposits of the Midcontinent region, United States and Canada: U.S. Geological Miscellaneous Field Studies Survey Miscellaneous StudiesMap Map MF-2153, MF-2153, 1:500,000. scale 1:500,000. Z.E., and and Sirns, Sims, P.K., P.K., 1993, CrustalCrustalCannon, W.F., Peterman, Z.E., scale thrusting and origin of the Montreal River monocline—a 35-km-thick cross section of the monocline-a Midcontinent rift in northern Michigan and Wisconsin: Tectonics, Tectonics, v. 12, 12, p. p. 728-744. 728-744. Behrendt, J.C., and seven Behrendt, seven others, others, 1988, 1988,Crustal Crustal structure structureof of the the Midcontinent Midcontinent rift rift system: system: results results from from GLIMPCE GLIMPCE seismic reflection profiles: Geology, v. 16, deep seismic 16, p. 81-85. 81-85. 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Nelson, B.K., B.K., and and DePaobo, DePaolo, D.J., 1985, 1985, Rapid production production of of Nelson, continentalcrust crust 1.7-1.9 1.7-1.9 b.y. b.y. agoago- Nd and and Sr Sr isotopic isotopic continental evidence from from the basement basement of of the North American American evidence midcontinent: midcontinent:Geological Geological Society Society of of America America Bulletin, Bulletin,v. v. 96, 96, p. p. 746-754. 746-754. Anderson, Anderson, J.L., J.L., 1983, 1983,Proterozoic Proterozoicanorogenic anorogenic granite granite plutonism plutonism of of North North America, America, in in Medaris, Medaris,L.G., L.G., Jr., Jr., and and others, others, eds., eds., Proterozoic Proterozoicgeology: geology:selected selectedpapers papersfrom from an an International International Proterozoic ProterozoicSymposium: Symposium:Geological Geological Society Society of of America AmericaMemoir, Memoir, 161, 161,p. p. 133-154. 133-154. Sims,P.K., P.K., 1996, 1996,Early Earlyand andMiddle MiddleProterozoic Proterozoicintracratonic intracratonic Sims, rocks, rocks,in in Sims, Sims,P.K. P.K. and and Carter, Carter, L.M.H., L.M.H., eds., eds., Archeanand and Proterozoic Proterozoicgeology geology of of the the Lake Lake Archean Superior region, U.S.A.: U.S.A.: U.S. Geological Geological Survey Survey Superior ProfessionalPaper Paper1556, 1556,p.p.57-60. 57-60. Professional Anderson, Anderson,.LL., J.L., 1980, 1980, Mineral equilibria equilibria and and crystallization crystallization conditions conditionsin in the the late latePrecambrian PrecambrianWolf WolfRiver River rapakivi rapakivi massif, massif, Wisconsin: Wisconsin: American Journal of Science, Science,v. v. 280, 280, p. p. 289-332. 289-332. Van Medaris, L.G., L.G., and andBanks, P.O., 1975, 1975, Van Schmus, Schmus,W.R., W.R., ,,Medaris, Banks, P.O., Chronologyof ofPrecambrian Precambrianrocks rocksininWisconsin, Wisconsin,I:I: Chronology theWolf WolfRiver Riverbatholith, batholith,aarapikivi rapikivimassif massif the approximately1500 1500 m.y. my. old: Geological Geological Society Society of of approximately AmericaBulletin, Bulletin,v.v.86, 86,p.p.907-9 907-914. America 14. Anderson, Anderson,J.L., J.L., and andCullers, Cullers,R.L., R.L.,1978, 1978,Geochemistry Geochemistryand and evolution evolutionof of the the Wolf WolfRiver Riverbatholith, batholith,aalate late Precambrianrapakivi rapakivimassif massifininnorthern northernWisconsin, Wisconsin, Precambrian USA: v.7,7, p.p. 287-324. 287-324. USA: Precambrian PrecambrianResearch, Research,v. 24 �ROCKS IN THE THE NORTHERN NORTHERN PART OF THE THE CENTRAL CENTRAL PALEOZOIC ROCKS MIDCONTINENT OF NORTH NORTH AMERICA AMERICA RUNKEL, RUNKEL, Anthony Anthony C., C., Minnesota Minnesota Geological Geological Survey, Survey,2642 2642University University Ave AveSE, SE,St St Paul, Paul, MN, MN, 55114-1057 55 114-1057 INTRODUCTION Paleozoic Paleozoic strata strata in the central central midcontinent region of North North American American consist consistof of thin thin units of carbonate, carbonate, sandstone, sandstone, and and shale shale distributed across tens of thousands of square square kilometers. kilometers. This This overview overview focuses focuses on the northernmost extent of lower Paleozoic strata which were were deposited deposited on on the the stable stable cratonic cratonic shelf northwest northwest of the Illinois and Michigan Michigan basins sinuous belt of outcrops outcrops in southern southern basins (Figs. (Figs. 11and and 2). 2). They They are are exposed exposed in in a sinuous Minnesota, Minnesota, Wisconsin Wisconsin and and northern northern Michigan, Michigan, on the southern southern flanks flanks of the Transcontinental Transcontinental arch arch and and the the Wisconsin Wisconsin dome dome and and arch. arch. Deposition Late Cambrian Cambriantime. time. Coarse Coarse Depositionof of Paleozoic Paleozoicsediments sedimentsbegan began in in Middle Middleto to Late siliciclastic siliciclastic sediments sediments of the the Mt Mt Simon Simon Sandstone Sandstone covered covered the eroded eroded Precambrian Precambrian surface. surface. Overlying Overlying strata stratawere were deposited deposited in in two broad, laterally equivalent equivalent facies belts across the central inset) (Palmer, (Palmer, 1960). 1960).An An inner innerdetrital detritalbelt belt was was central midcontinent midcontinentregion region (Fig. (Fig.11inset) composed composed of shallow shallow marine marine siiciclastics siliciclasticsderived derived from from subaerially subaerially exposed exposed Precambrian Precambrian shield shield areas areas on on and and totothe thenorth northof ofthe theWisconsin WisconsinDome. Dome. Thin, Thin, laterally laterally extensive extensive units units dominated quartzose sandstone, sandstone, very fme fine sandstone, or dominated by either either fmefine-to tocoarse-grained coarse-grainedquartzose shale shalewere were deposited depositedin in the the inner innerdetrital detritalbelt. belt. The The middle middle carbonate carbonatebelt belt consisted consistedof ofsubtidal subtidal to to intertidal intertidal carbonate carbonate and and shale shale deposits deposits that accumulated accumulated to the south. The boundary between belts shifted, belt sedimentation shifted, with inner detrital belt sedimentation dominant during Cambrian and part part of of Middle MiddleOrdovician Ordovician time, time, and and middle middle carbonate carbonate belt sedimentation sedimentationdominant dominantduring during the as in in Silurian Silurianand and Devonian Devoniantime time (Fig. (Fig. 2). 2). the Early Early and and Late LateOrdovician, Ordovician,as as well well as Early Early Paleozoic Paleozoicdeposition depositionoccurred occurred on on aavirtually virtuallyhorizontal, horizontal,cratonic cratonicshelf shelfwith withaavery very low lOrn1m.y. (Sloss, (Sloss, low subsidence subsidence rate. Late LateCambrian Cambriansubsidence subsidenceaveraged averaged less lessthan thanlOrn/m.y. 1988), 1988),about about one-fifth one-fifth to to one-tenth one-tenth the the rate rate in in the the contemporaneous contemporaneousIllinois IllinoisBasin Basin (Sargent, (Sargent, 1991) 1991) and orders orders of magnitude magnitude slower slower than than that that of better known, known, younger younger basins basins in in North North America. (e.g. Byers Byersand and Dott, Dott, America. Maximum Maximumpaleobathymetry paleobathymetrywas was typically typically less lessthan than100 100m m(e.g. 1995; 1995; Ludvigson Ludvigson and and others, others, 1996) 1996)and and the shelf had a low gradient gradient slope slope of about about 0.1 rn/km. O.lm/km. The The Wisconsin Wisconsinarch arch and and dome dome and and Transcontinental Transcontinentalarch arch were were positive structural structural features featuresthat that influenced influencedearly early Paleozoic Paleozoic sedimentation sedimentation patterns, patterns, and and eventually eventually controlled controlledthe the distribution distribution and and configuration configurationof of gently gently folded folded and and faulted faulted Paleozoic Paleozoic strata strata today. In In northern are northern Iowa, Iowa,southern southernMinnesota, Minnesota,and and southwestern southwesternWisconsin Wisconsin Paleozoic Paleozoic strata strataare preserved preserved in in what what is is known known as as the the Hollandale Hollandale Embayment, which is a broad syncline syncline that lies lies between between these these two two positive positive features. features. South Southand andeast eastof ofthe theWisconsin Wisconsinarch archand anddome dome Paleozoic Paleozoic rocks rocks dip dipless lessthan than 11degree degreeinto into the the Illinois Illinois and and Michigan Michigan basins. basins. DEPOSITIONAL MODELS MODELS The The depositional depositionalhistory history of of lower lowerPaleozoic Paleozoicsiliciclastic siliciclasticstrata strata of of this this region regionremains remains poorly understood despite an despite over 100 100 years of study. Many Many workers workers have have lamented lamented an apparent apparent absence absenceof of modern modem or or ancient ancientdepositional depositionalanalogues. analogues.In In addition, addition,dozens dozensof of local local studies studies have have been conducted conducted (e.g. (e.g. Nelson, Nelson, 1954; 1954; Haddox and Dott, 1990) 1990) but there are few regional-scale regional-scaleinvestigations investigationsthat that incoiporate incorporate several several lithofacies lithofaciesinto into aa temporally temporally constrained constrained stratigraphic stratigraphic framework. framework.Present-day Present-day understanding understanding of early Paleozoic Paleozoic siliciclastic siliciclastic deposition deposition is is based based mostly mostly on on work work conducted conducted since since 1950, 1950,beginning beginning with with the the predominantly (1954), Nelson Nelson (1956), (1956), Berg Berg and and others others predominantly stratigraphic stratigraphic investigations investigations of of Berg Berg (1954), (1956), Bell and others (1956), and Ostrom (1964, 1970). Subsequent work has been (1964,1970). chiefly chiefly sedimentologic, sedimentologic, focusing focusing on the interpretations of near-shore marine facies (Fraser, (Fraser, 1976; 1976; Driese Driese and and others, others, 1981; 1981;Dott Dott and and others, others, 1986; 1986; Haddox Haddox and and Dott, Dott, 1990; 1990;Barnes Barnes and and 25 �Figure1.1.Location Locationmap mapshowing showing Figure earlyPaleozoic Paleozoictectonic tectonicfeatures, features, early major paleotopographic paleotopographichighs highs of of major Precambrian rocks (stippled) and the Precambrian rocks (stippled) and the approximate distribution of approximate distribution of (C),Ordovician Ordovician (0), (0), Cambrian (C), Cambrian Silurian (S), and Devonian (D) Silurian (S), and Devonian (D) stratain in the thenorthern northernpart partof ofthe the strata centralmidcontinent midcontinentregion. region. The The central inset shows the study area relative inset shows the study area relative toto theLate LateCambrian Cambrianinner inner(stipple) (stipple) the detritalbelts belts and and and outer outer(dashes) (dashes)detrital and the middle carbonate belt (block the middle carbonate belt (block pattern)of ofPalmer Palmer(1960). (1960).Modified Modified pattern) from Runkel Runkeland andothers others(1998) (1998) from GROUP! FORMATION LITHOLOGY ; i. Cedar VaHey J — I — —L —I -— I——I Manustique Burnt Bluff Cataract I—I- J —— — . Maquoketa Dubuque Galena Decorah Platteville ood !:!. — •• E •. -: • Figure2.2.Generalized Generalizedstratigraphic stratigraphiccolumn column(no (no Figure scale)for for lower lowerPaleozoic Paleozoicrocks rocksininthe thenorthern northernpart part scale) of the central midcontinent region. The Cambrian of the central midcontinent region. The Cambrian andOrdovician Ordoviciannomenclature nomenclatureisisthat thatused usedinin and southeastern Minnesota Minnesota and and Wisconsin, Wisconsin, the the southeastern Silurianfrom from eastern easternWisconsin Wisconsinand and northern northern Silurian Michigan,and and the the Devonian Devonianfrom from southernmost southernmost Michigan, Minnesotaand andnorthern northernIowa. Iowa. Minnesota Engadune Jde Group Jordan St Lawrence Franconia Ga (Wonewoc) Eau Claire and Bonneterre — . Mt. Simon E l (uatzose -sandstone sandstone sdtstone, shale (] Very Very fine fine s.s.,s.s., siltstone, shale (LoneRock) — (dashedwhere whereshaly) shaly) Carbonate(dashed Carbonate Norecord record No Unconfonnity Unconformity �others, others,1992; 1992;Mossier, Mossler,1992; 1992;Runkel, Runkel,1994). 1994).In Inaavery veryimportant importantand andwidely widelycited citedstudy study Dott Dottand andothers others(1986) (1986)examined examinedthe thetransition transitionfrom fromnonmarine nonmarinetotomarine marineenvironments environments recorded recordedin inquartzose quartzosesandstones, sandstones,and andprovided providedthe thefirst fmt set setof of criteria criteriafor foridentification identificationof of nonmarine facies.They described described an an early early Paleozoic Paleozoic terrestrial terrestrial setting setting with broad braided braided nonmarinefacies.They streams streamsand andeolian eoliansheet sheetand anderg ergsystems systemsthat that delivered delivered sand sand to to aa shallow shallowmarine marine environment environmentdominated dominatedby by small smallthree threedimensional dimensionaldunes. dunes.Dott Dottand andothers others(1986) (1986)stressed stressed the as the the lack lack of of vegetation, vegetation, between between early early Paleozoic Paleozoic depositional depositional the differences, dzfferences, such such as environments A environmentsand andthose those inferred inferredfor forboth both younger younger rocks rocks and and modem modemsettings. settings.A depositional depositional model model ofofaasimple, simple,storm-dominated, storm-dominated,texturally texturallygraded gradedshelf shelfwas wasproposed proposedby by Runkel Runkel and and others others(1998), (1998),and and isis noteworthy noteworthy in in its its similarity similari~to to models modelsbased basedon onboth both younger youngerrocks rocks and andmodem modemsystems. systems.Their Theirstudy studywas was essentially essentiallyaaregional-scale regional-scaleoutgrowth outgrowth of of the the excellent excellentoutcrop outcropwork workof of Charlie CharlieBell Belland andhis his students studentsfrom fromthe the University University of of Minnesota Minnesotain in the the 1950's. 1950's.Runkel Runkeland and others others(1998) (1998)suggested suggestedthat that early early Paleozoic Paleozoic depositional areanalogous analogousto to those thosedepicted depictedin inwell-known well-known depositionalprocesses processesand andfacies faciesdistribution distributionare models modelsof of the the Cretaceous Cretaceousinterior interior seaway and the modem Bering Bering Shelf. Shelf. The The thin widespread widespread siliciclastic chamcteristic of lower lower Paleozoic strata strata result from large largelateral lateralfacies facies siliciclasticunits units characteristic migrations relativesea sealevel. level. migrationswhich whichoccurred o c c m din inresponse responseto tocontinental-scale continental-scalechanges changesininrelative Taylors Falls Precambrian lava flow rrdges, (J,/ Mayor sand 0 — SILIcICLASTIC OFFSHORE SHELF — CARBONATEI — — — —(M0StIV — — SHELF — — — - — — — — — — o — — — Storm—t,anspolt of !° sand. suit. shale !rom shoretace — — 0 — — — — —— = — — - — — 0 — — — 0 — — — — — — Rudge : — — — — - — — — 'mmodks - Tempestltes- 01 0 0 00 — Depth 5Pm = -o — — — — 0 4OUI — -o 2O4O= I •.: 0 00 00 00 : 0 —— — .._- on Arch 0 —0 — — — — source sandstone Tudal - — — FLUVIAL& o . EOLIAN 0 SANDPLAIN sand transport by storms s.. — - Dome • — SHOREFACE 0 — ORE Figure Figure3.3.Conceptual Conceptual source from — — — — 0000 0000 0 0 0 0 (East) 0 depositional depositional model model of Late Late Cambrian Cambrianstorm-dominated, storm-dominated, texturally textxrailygraded gradedshelf. shelf. Quartzose Quartzosefmefme- to to coarsecoarsegrained gained sand sandaccumulated accumulatedin in nearshore nearshoreterresirial terrestrial and and shoreface shorefaceenvironments. environments.Finer Finer grained feldspathic grained,,feldspathic siiciclastic siliciclasticsediments sedimentsand and subtidal subtidalcarbonates carbonates accumulated accumulated in in deeper deeperwater water of the the offshoreshelf. offshoreshelf. Carbonate Carbonaterocks rocks within within the the lower lower Paleozoic Paleozoic sequence sequence have have historically historically been regarded regarded as as more more amenable amenableto to comparison comparisonwith with both both modem modem and and ancient ancientfacies facies models. models. Deposition Deposition occurred occurred in in environments environmentsthat thatrange m g efrom fromevaporitic, evaporitic,supratidal supratidalconditions conditionsfor forparts parts of of the the Prairie du Chien Chien Group Group(Smith (Smithand andothers, others,1993) 1993)to to subtidal subtidalsettings settingsin indepths depthsof of 100 100m mor or Prairie du more more for for parts parts of of units units such suchas asthe theDecorah DecorahShale Shale(Ludvigson (Ludvigsonand andothers, others,1996). 1996).Most Most investigations in scope scoperelative relativeto to the the great g m t lateral lateral extent extent of of these these units units and and investigationshave havebeen been local localin there aretoo too many many to tocite cite them them individually. individually. Ordovician Ordovician carbonate carbonatestrata strata of of the the Hollandale Hollandale thereare embayment embayment are are the the focus focus of of aa monograph monograph edited edited by by Sloan Sloan (1986). (1986). Silurian Siluriancarbonates carbonateson onthe the westem westem flank flankof of the the Michigan Michigan Basin Basin have have recently been studied studied by Harris Harris and and Waldhuetter Waldhuetter (1996). There are many excellent excellent studies studies of Ordovician through Devonian age strata strata in There are northern northem Iowa, Iowa, largely largely conducted conducted by the Iowa Geological Survey; the results can often be extrapolated several papers in Witzke and others, 1996) 1996) extrapolated to to Minnesota Minnesota and and Wisconsin Wisconsin (e.g. several Some Some regional regional scale scalestudies studies have have recently recently been been completed; completed;aa stratigraphic stmtigxaphicframework frameworkhas has been been developed developedfor for the the Prairie Fhkie du du Chien Chien Group Group from the Michigan basin to the Hollandale Hollandale embayment 1996; Barnes embayment (Smith (Smith and others, 1993, 1993,1996; Barnesand and others, others, 1996). 1996).Simo Simoand and others others (1997) are currently currently constructing constructingaa large large scale scale stratigraphic stratigraphic framework framework for for Ordovician Ordovician rocks rocks (1997) are of as identification identification of the the central centralmidcontinent midcontinentin in order order to to address address long-standing long-standing problems problems such such as of the controls responsible for the the apparently synchronous regional-scale changes from from "tropical" to %opicalV1 to "temperate" "temperate1'styles stylesof of carbonate carbonatedeposition. deposition. . 27 �NOTABLE FEATURES FEATURES AND AND LONGSTANDING LONGSTANDING PROBLEMS PROBLEMS NOTABLE LowerPaleozoic Paleozoicstrata strataininthe thecentral centralmidcontinent midcontinentregion regionare areamong amongthe thelongest longeststudied studied Lower sedimentary sedimentaryrocks rocksin in North North America. America. They Theyare arewell wellknown knownto togeologists geologistsoutside outsideof ofthe thearea area forseveral severalenigmatic enigmaticfeatures features(Dott (Dottand andByers, Byers,1980). 1980).Most Mostnotable notableisisthe theextreme extremetextural textural for andmineralogical mineralogicalmaturity maturityofofthe thefme fineto tocoarse-grained coarse-grained sandstones, sandstones,and andthe the sheet-like sheet-like and geometryofofthese theseand andother othersiliciclastic siliciclasticunits. units. The Theoverall overalldearth dearthofofshale shalehas haspuzzled puled geometry sedimentologists, sedimentologists,and andthe thefundamental fundamentalcontrols controlson onthe theepisodic episodicchange changefrom fromsiliciclasticsiliciclasticdominated dominatedto tocarbonate-dominated carbonate-dominatedsedimentation sedimentationremain remain poorly poorly understood. understood. Lastly, Lastly, the the presence, presence,position positionand andmagnitude magnitudeofofunconformities unconformitieshas hasbeen beendebated debatedfor fordecades. decades.The The remainderof ofthis thisabstract abstractsummarizes summarizesthe theprogress progressmade madeininunderstanding understandingthese theseenigmatic enigmatic remainder features featuressince sincethe theoverview overviewpublication publicationby byDott Dottand andByers Byers(1980) (1980)on onlower lowerPaleozoic Paleozoicstrata. strata. Sheet Sheetgeometry geometryAAlong-standing long-standingquestion questionhas hasbeen beenhow howsheet-like sheet-likesiliciclastic siliciclasticlayers layerswere were initially initiallydeposited depositedand andthen thenpreserved preservedacross acrosstens tensof ofthousands thousandsof ofsquare squarekilometers kilometersof ofthe the cratonic cratonicshelf. shelf.Most Mostworkers workershave haveattributed attributedthe theformation formationof ofsuch suchsheets sheetsto todepositional depositional processes aremarkedly markedlydifferent differentfrom fromthose thosedescribed describedfor formost most processesand andenvironments environmentsthat thatare younger youngerrocks rocksand andmodern modernsettings. settings.Lochman-Balk Lochman-Balk(1970) (1970)inferred inferred the the presence presence of of enormous kilometersperpendicular perpendiculartotothe the enormoustidal tidalflats flatsextending extendingwell wellover overtwo twohundred hundredkilometers shoreline. shoreline.Dott Dottand andByers Byers(1980) (1980)suggested suggestedthat that quartzose quartzosesand sandaggraded aggradedmore more or or less less vertically verticallyinto intoaasheet sheetunder underhigh-energy high-energy conditions conditions across across a vast shallow shallow sea. sea. The Themost most widely widelycited citedhypothesis hypothesisisisone onewhich whichattributes attributesthe theorigin originof ofquartzose quartzosesandstone sandstonesheets sheetstoto fluvial fluvialand andeolian eolianprocesses processesthat thatdispersed dispersedsand sandacross acrossaa vegetation vegetation free freelandscape landscapeprior priorto to marine marinereworking reworkingduring duringaatransgression bansgression(Dott (Dottand andothers others1986). 1986).Recent Recentstudies, studies,however, however, have havedemonstrated demonstratedthat thatsome somequartzose quartzosesheets sheetswere weredeposited depositedentirely entirelywithin withinthe themarine marine realm realmunder underregressive regressiveconditions conditions(e.g. (e.g.Runkel, Runkel, 1994, 1994,Hughes Hughes and and Hesselbo, Hesselbo,1997, 1997,Runkel Runkel and and others others1998), 1998),and andthat thatthe thedepositional depositionalprocesses processes responsible responsible for for the the dispersal dispersalof of siliciclastic siliciclasticsediments sedimentswere were similar similar totothose thoseoperating operatingduring duringthe the deposition deposition of of ancient ancient sandstones that are not sheet-like. sheet-like. sandstones The Thelateral lateralpersistence persistenceand andsheet-like sheet-likegeometry geometryof oflower lowerPaleozoic Paleozoicsiliciclastic siliciclasticunits units probably probablyreflect reflectthe theroles rolesof ofbasin basinphysiography physiographyand andtectonics tectonicsin in controlling controllingthe the lithostratigraphic lithostratigmphicarchitecture, architecture,rather ratherthan thanthe theexistence existenceof ofatypical atypicalsedimentary sedimentary environments. environments.Deposition Depositionwas was characterized characterized by a continuous continuous and abundant supply of sediment sedimenttotoaarelatively relativelystable, stable,nearly nearlyfiat flatbasin basin with with aa slow, slow,uniform uniformrate rateof ofsubsidence. subsidence. Individual (e.g.Fig. Fig.3) Individual sheets sheetsof of siliciclastic siliciclasticsediment sediment were were deposited when whendiscrete discretefacies facies(e.g. 3) migrated migratedgreat greatdistances distancesduring duringchanges changesininsea sealevel. level.Deep Deepincision incisionof ofthe theindividual individualsheets sheets during duringepisodes episodesof of subaerial subaerialexposure exposuredid did not not occur, occur, resulting resulting in in more more or or less less uniform uniform preservation. preservation. Textural Texturalmaturity maturitvof ofsandstones sandstonesThe Theextreme extremetextural textural and and mineralogical mineralogical maturity maturity of of the the finefineto to coarsecoarse-grained grainedsandstone sandstoneunits, units, such such as as the the St St Peter Sandstone, Sandstone, may maybe bethe thebest bestknown known and andlongest longeststudied studiedfeature featurein in the the lower lowerPaleozoic Paleozoicstrata strataof ofthe thecentral centralmidcontinent. midcontinent.The The sandstones are moderately moderately to to well wellrounded. rounded. sandstonescontain containmore morethan than 98% 98%quartz quartzand andmost most grains grainsare Such Suchtextural texturaland andcompositional compositionalmaturity maturitycould couldnot not have have been been achieved achievedsolely solelyby by fluvial fluvialand and marine marine abrasion abrasioneven evenover overtransport transportdistances distancesof of hundreds hundreds of of kilometers kilometersifif the the grains grainswere were derived derived directly directly from from crystalline source rocks. Rare Rare grains grains with abraded overgrowths are are reworked reworkedfrom fromolder oldersedimentary sedimentaryrocks, rocks,but butthe thevolumetric volumetricsignificance significanceof of such suchrecycling recyclingisis uncertain uncertain and and aa source source of of suitable suitable sedimentary rock has never been identified. Odom Odom (1975, (1975, 1978) 1978)conducted conductedthe the most mostcomprehensive comprehensivemineralogical mineralogicalstudy studyof of lower lowerPaleozoic Paleozoic sandstones; sandstones;he henoted noted that thatthe thevery very fme finegrained grainedfraction fractionis is feldspathic, feldspathic,whereas whereas the the fine fine to to coarse-grained coarse-grainedfraction fractioncontains containsmore more than than 98% 98%quartz quartz (with (with the exception exception of some some lower lower Mt Simon Simon Sandstone Sandstonebeds). beds). He He suggested suggested that that aa long history of abrasion in a marine setting 28 �could account account for for both the maturity of the quartzose grains and the reduction in size of feldspar first to to clearly clearly identi@ identify the thepresence presence of of feldspar grains. Dott and others (1986) were the fmt substantial eolian deposits quartzose sandstones, and they suggested that deposits within some quarkose eolian abrasion abrasion could contribute contribute to the textural and mineralogic features features described described by Odom Odom (1975, 1978). 1978). Lastly, Lastly,chemical chemicalweathering weatheringin inthe thesource sourcearea area must mustbe be taken taken into into consideration (Morey, consideration (Morey, 1972). 1972). Odom Odom (1975, (1975, 1978) 1978)noted that the the very very fine fine grained, grained, feldspathic sandstones are arerich rich in in K-feldspar K-feldspar but have have only a "trace" "trace" amount of plagioclase grains, even though though plagioclase plagioclase was presumably dominant dominant in in the the source source area area of of the the Precambrian shield. Selective plagioclase grains grains from from the the sandstone Precambrian Selective diagenetic leaching of plagioclase chemical weathering weathering probably preferentially dissolved was discounted by Odom. Thus, chemical plagioclase crystals and reduced reduced the thesize sizeand and amount amount of of other other relatively unstable unstable minerals minerals prior prior to to mechanical mechanicalabrasion abrasionduring during transport transport to to the the shoreline. shoreline. While each of the processes processes described above above could have been responsible responsible in part for for the the mineralogic and textural attributes of lower Paleozoic sandstones, they do not entirely mineralogic that virtually virtually all all fmeaccount for the compositional record that appears to indicate that fine- to coarse-grained sand sand was was exceptionally exceptionally mature mature when itit arrived arrived to to the the early early Paleozoic Paleozoic shoreline. shoreline. Fine- to coarse-grained coarse-grained immature immature sand would have almost certainly been abrasion model modelof ofOdom Odom(1975) (1975)were wereaccurate. accurate. It It is difficult difficult deposited locally if the marine abmion in which whichall all sand abrasion sand is subjected to prolonged eolian abrasion to reconstruct a terrestrial setting in (Dott and others others 1986) 1986) prior to deposition deposition in a marine marine environment. centmlmidcontinent midcontinent region region are are noted noted for for aa Dearth of Shale Shale Lower LowerPaleozoic Paleozoicrocks rocksof of the thecentral dearth of shale shale compared compared to other shallow marine deposits. Two Twovery very different d i f f e ~ nhypotheses hypotheses t have been proposed to account account for this dearth of shale. In a "marine bypassing" model, were delivered to the Pettijohn and others (1973) suggested that clay- and silt-sized particles were shoreline, shoreline, but subsequently subsequently carried carried in suspension suspension by repeated storms across the shallow shallow shelf before final burial in basinward areas. In contrast, Dalrymple Dairymple and others (1985) suggested that strong kilometers strongwinds windsblew blewclay clayand andsilt siltparticles particleshundreds hundredsto to thousands thousands of of kilometers offshore, to be ultimately ultimately deposited deposited in the outer detrital belt (Fig 1). Recent investigations investigations of Upper Cambrian siliciclastic siliciclastic strata support the marine bypassing well known known dearth of shale isis model of Pettijohn and others (1973), demonstrating that the well of the the outcrop outcrop belt on the flanks of the Wisconsin dome and arch characteristic only of (McKay, 1988, Wisconsin arch, subsurface 1988, Runkel and others, 1998). Basinward of the Wisconsin records from Minnesota Minnesota and and Iowa Iowa show show that facies facies dominated by shale shale and and siltstone siltstoneare are equivalents to the shale-poor offshore equivalents shale-poor common. The The shale shale and and siltstone siltstone dominated facies are offshore sandstone facies of the sandstone theoutcrop outcropbelt, belt, and and their their geographic geographic position changed through time in response outcrop belt has response to to changes changes in in the the position position of the storm-fairweather storm-fairweather wave base. The outcrop a dearth of shale shale simply because the depositional depositional record is dominated by highstand shoreface shoreface base. This facies deposited above fairweather wave base. This stratigraphic stratigraphic and sedimentologic sedimentologic attribute is not unique attribute unique to the the lower lower Paleozoic Paleozoic rocks of the central central midcontinent midcontinentregion-it region-it is is landward margins margins of of common in many younger wave-dominated wave-dominated sequences along the landward shale-free early earlyPaleozoic Paleozoicepeiric epeiricsea seaisis a deeply individual basins. The notion of a shale-free entrenched idea ideathat thatsimply simply reflects reflectsthe thebias biasof ofthe theoutcrop outcropbelt. belt. The The dearth dearth of of shale shale in in lower Paleozoic Paleozoic rocks should should be removed from the list of enigmatic enigmatic features unless the scarcity scarcity can can be be demonstrated demonstratedto to exist exist on on aa scale scale larger larger than than that that of of the the outcrop outcropbelt. belt. Siliciclastic-Carbonate Thefundamental fundamentalcontrols controlson on the the transition transition from from nearshore nearshore Siliciclastic-Carbonatecycles The siliciclasticsiliciclastic- to carbonate-dominated carbonate-dominated deposition deposition have have never never been been satisfactorily satisfactorilyunderstood. understood. the For example, example, in Early Ordovician time carbonate deposition apparently dominated across the entire region even in the shallowest water water conditions conditions (Smith and others 1993). Both older Sandstone) and younger (St Peter Sandstone) shallow marine environments were (Jordan Sandstone) dominated dominated by siliciclastics. siliciclastics. Only speculative speculative and vague hypotheses have been suggested suggested to to account account for for such such fundamental fundamental changes. For example, Adams (1978) suggested that the Early Ordovician Ordovician change change in in depositional depositionalstyles styles may have have been in response response to drowning drowning of of the the 29 �siliciclastic siliciclastic source source area by a shallow sea or the result of siliciclastics being "deflected" "deflected" to another l y Paleozoic carbonate-dominated systems another region. b Early systems developed developed following following extended extended highsea sealevel level(Smith (Smithand andothers, others,1993) 1993)which which suggests suggeststhat that the the siliciclastic siliciclastic periods of high source area may have been covered with a blanket of carbonate rocks. rocks. The The spread of certain source forms of terrestrial life such as bacterial encrustation, and later the development development of vascular vascular plants, may may have have also also reduced reduced siliciclastic siliciclasticinput. input. Crvntic of lower lower Paleozoic Paleozoic strata strata of of the the central central C w t i c unconformities Previous investigations of midcontinent region have also been hindered by an inability to recognize midcontinent recognize unconformities. unconformities. The are fairly fairly well well The unconformities unconformities bounding bounding the the major major sequences sequencesof of Sloss Sloss (1963) (1963) are established within the strata of the outcrop belt. The presence and position of "lesser" "lesser" unconformities, within siliciclastic siliciclasticunits, have have been aa matter matter of of considerable considerable unconformities,especially especially within relations and interpreted depositional histories indicate that such debate. Stratigraphic Stratigraphic relations unconformities "should" "should" be present. However, However, little or no evidence evidence for for regionally regionally extensive extensive subaerial erosion has been documented. Such sequence-bounding unconformities unconformities are are they are are contained containedwithin withincoarse coarsesiliciclastics siiciclastics because because they they difficult to recognize where they are texturally and mineralogically similar, similar, and because because separate quartzose quartzose sandstones sandstones that are that occurred occurred on they are relatively flat-reflecting erosion that on aa loose, loose, sandy sandy substrate substrate along along aa low, uniform gradient, gradient, and in a nonvegetated terrestrial terrestrial environment. environment. Furthermore, Furthermore, the the ultra ultra development of a distinctive mature mineral composition composition of the exposed substrate substrate inhibits inhibits development distinctive weathering profile. Recent work has shown some promise for identifying subtle subaerial surfaces of of regional regional erosion. Recognition Recognition of cryptic unconformities requires interpretation of stratigraphic at individual outcrops stratigraphic relations in conjunction with physical evidence collected at and high resolution resolution biostratigraphic biostratigraphic data. Smith and others (1993) interpreted local deposits of silica cement cement in uppermost Cambrian Cambrian and Lower Ordovician Ordovician strata strata as subaerially subaerially formed formed silcrete. Runkel fronton Runkeland andothers others(1998) (1998)suggested suggestedthat that cryptic cryptic unconformities unconformities within the Ironton and at at the the top of the Jordan Jordan Sandstone Sandstoneand andcan canbe be identified only and Galesville Sandstones and the coarsest coarsest bed bed within within nearshore nearshore by overlying lag deposits. These lags deposits are the sandstone sandstone successions; successions; they separate separate a regionally traceable, decameter-scale, coarseningupward interval interval below from from a decameter-scale, fming-upward fining-upward sequence sequence above. Preliminary Preliminary results of high resolution resolution biostratigraphic biostratigraphic dating using conodonts has verified the presence of an erosion erosion surface surface on top of the Jordan Sandstone, Sandstone, and demonstrates demonstrates promise for for measuring the measuring the magnitude magnitudeof of such such cryptic cryptic unconformities unconformities with with detailed detailedpaleontologic paleontologicwork. work. REFERENCES Adams, Adams, R. R. 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A., A., and andDay, Day,J., J., Formation, Upper Upper Mississippi Mississippi Valley, in Witzke, eds., eds., Paleozoic Paleozoic Sequence SequenceStratigraphy: Stratigraphy: Views Views from from the the North North American American Craton:Geological Craton:Geological Society Societyof of America AmericaSpecial SpecialPaper Paper306, 306,p.67-86. p.67-86. McKay, McKay, R. R. M., M., 1988, 1988,Stratigraphy Stratigraphyand andlithofacies lithofaciesof of the the Dresbachian Dresbachian(Upper (UpperCambrian) Cambrian)Eau Eau Claire Ludvigson,G. G. A., A., and and Bunker Bunker B. B. Claire Formation Formation in in the the subsurface subsurface of eastern Iowa: in Ludvigson, A., A., eds., eds., New New perspectives perspectives on on the the Paleozoic Paleozoic history history of the Upper Mississippi Mississippi Valley, Valley, Guidebook Guidebookfor forthe the18th 18thField FieldConference Conferenceof of the the Great GreatLakes Lakessection, section,Society Societyof ofEconomic Economic Paleontologists Paleontologistsand andMineralogists, Mineralogists,p. p. 33-53. 33-53. Morey, Sims,P. P.K., K., and andMorey, Morey,G. G. B., B., eds., eds., Morey, G. G. B., B., 1972, 1972,Pre-Mt Pre-Mt Simon Simon Regolith, in Sims, Geology Geology of of Minnesota: Minnesota: A A Centennial CentennialVolume: Volume: Minnesota Minnesota Geological GeologicalSurvey, Survey,p. p. 506-508. 506-508. Mossler, Mossier,J.J. H., H., 1992, 1992,Sedimentary Sedimentaryrocks rocks of of Dresbachian Dresbachian age age (Late (Late Cambrian), Cambrian), Hollandale Hollandale Embayment, Embayment,southeastern southeasternMinnesota: Minnesota:Minnesota Minnesota Geological Geological Survey SurveyReport Reportof of Investigations 71 p. 40,71 p. Investigations40, Nelson, Nelson, C. C. A., A., 1956, 1956,Upper UpperCroixan Croixanstratigraphy, stratigraphy,Upper UpperMississippi MississippiValley: Valley: Geological Geological Society Society of of America America Bulletin, Bulletin,v. v. 67, 67,p. p. 165-183. 165-183. 31 �Odom, I. E., 1975, 1975, Feldspar-grain size relations in Cambrian arenites, Upper Mississippi Valley: Journal Journal of Sedimentary Petrology, v. 45, no. 3, p. 636-650. Odom I. E. 1978, 1978,Mineralogy Mineralogyof of Cambrian Cambriansandstones, sandstones, Upper Upper Mississippi Mississippi Valley: Wisconsin Geological and Natural History Survey Field Trip Guidebook 3, p. 23-45. Ostrom, M. E., 1964, Ostrom, 1964, Pre-Cincinnatian Pre-Cincinnatian Paleozoic cyclic sediments in the Upper Mississippi 1-398. Valley: A A discussion: discussion: Kansas KansasGeological GeologicalSurvey SurveyBulletin Bulletin169, 169,p.p.38 381-398. Ostrom, M. E., 1970, Ostrom, 1970, Sedimentation Sedimentation cycles cycles in Lower Lower Paleozoic Paleozoic rocks of western western Wisconsin: Wisconsin: Wisconsin Geological Geological and and Natural History History Survey Survey Information Information Circular Circular11, 11,p. p. 10-34. 10-34. Palmer, A. R., 1960, 1960,Some Some aspects aspects of the the early early Upper Upper Cambrian Cambrian stratigraphy stratigraphy of of White White Pine Pine County Geology of of east east Central Central Nevada: Intermountain Intermountain County ,, Nevada, and Vicinity, in Geology Association 1lth Annual Field Conference, Conference, p. 53-58. 53-58. Association of Petroleum Petroleum Geologists Geologists Guidebook Guidebook 11th Pettijohn, F. J., Potter, Potter, P. E., E., and and Siever, Siever, R., R., 1973, 1973,Sand Sand and and Sandstone:New Sandstone:New York, York, Springer-Verlag, 618p. 6 18p. Runkel, A. C., 1994, 1994,Deposition Deposition of the uppermost uppermost Cambrian Cambrian (Croixan) (Croixan) Jordan Sandstone, Sandstone, and and the the nature nature of of the the Cambrian-Ordovician Cambrian-Ordovician boundary boundary in in the the Upper Upper Mississippi MississippiValley: Valley: Geological Society Society of America America Bulletin, Bulletin, v. 106, 106, p. 492-506. 492-506. Runkel, A. C., McKay McKayR. R.M., M., and andPalmer, Palmer, A. A. R.,1998, R.,1998, Origin Origin of a classic cratonic sheet sandstone:Stratigraphy across the Sauk 11-Sauk Il-Sauk I11 III boundary in the Upper Mississippi sandstone:Stratigraphy Valley: Geological Geological Society Society of America Bulletin Bulletin v. 110, 110, no. 2, p.188-210 Sargent, M. L., 1991, 1991, Sauk Sequence: Cambrian System through Lower Ordovician Series, F., and Eidel, J. J., J., eds., Interior cratonic in Leighton, M. W., Kolata, D. R., Oltz, D. F., basins: American p.75-86. American Association Association of Petroleum Petroleum Geologists Geologists Memoir 51, p.75-86. P., Byers, C. W., Dott, Doft, R. R. H., H., Jr., and Saylor, B., 1997, 1997, Simo, J. A., Choi, L, Freiberg, P., Sedimentology, Sequence Sedimentology, Sequence Stratigraphy, Stratigraphy, and Paleoceanography of the Middle Ordovician of eastern Wisconsin, Wisconsin, in, Mudrey, M. G., ed, Guide to Field trips in Wisconsin Wisconsin and and adjacent areas areas of Minnesota: Wisconsin Geological Geological and and Natural History History Survey, Survey,p. p. 9595114. 114. Sloan, R. E., ed, 1986, 1986, Middle Middle and Late Ordovician Ordovician lithostratigraphy lithostratigraphy of the Upper Upper 232p. 35,232~. Mississippi Valley: Minnesota Minnesota Geological Geological Survey Survey report report of Investigations Investigations 35, Sloss, L. L., 1963, 1963, Sequences Sequences in the cratonic interior of North America: Geological Society of America Bulletin, America Bulletin, v. v. 74, 74,p.p.93-1 93-114. 14. in Phanerozoic Phanerozoic time, time, in in Sloss, 1988, Tectonic evolution of the craton in Sloss, L.L., ed., Sloss, L. L., 1988, Sedimentary American craton, craton, United United States: States: The The Geology of North Sedimentarycover—North cover-North American America, DNAG America, DNAG Volume Volume D-2, p. 25-51. 25-5 1. Smith, G. L., Byers, C. W., and Dott, R. H., Jr., 1993, 1993, Sequence Sequence stratigraphy of the Lower Ordovician Prairie in the the Michigan MichiganBasin: Basin: Ordovician Prairie du du Chien Chien Group Group on on the the Wisconsin Wisconsin Arch Arch and and in American Association Association of of Petroleum Petroleum Geologists Geologists Bulletin, Bulletin, v. 77, 77, p. 49-67. Smith, G. L., Byers, C. W., and Dott, R. H., Jr., 1996, 1996, Sequence stratigraphy of the Prairie du Chien Group, Group, Lower Lower Ordovician, Midcontinent, USA, in, Witzke, B.J., Ludvigson, Ludvigson, 0. G.A., A., and andDay, Day,J., J.,eds., eds.,Paleozoic PaleozoicSequence SequenceStratigraphy:Views Stratigraphy:Views from from the the North North American American Craton: Geological Geological Society Society of America Special Special Paper 306, p.23-34. Witzke, B. J., Ludvigson, Ludvigson, G. A., and and Day, Day, J., 1991, 1991, eds., eds., Paleozoic Paleozoic Sequence Sequence Stratigraphy:Views from the North American Craton: Geological Society of America 446p. Special Paper 306, 306,446~. 32 �MODELS FOR INTERPRETING INTERPRETING THE THE QUATERNARY QUATERNARY HISTORY OF THE THE LAKE SUPERIOR SUPERIOR REGION PATTERSON, PATTERSON, Carrie Carrie J., Minnesota Minnesota Geological GeologicalSurvey Survey The interpretation interpretation of the Quaternaiy Quaternary glacial and interglacial history for the Lake Superior as aa result result of of two twonew newmodels. models. Firstly, oxygen isotope region is in the midst of change as data have provided evidence leading to the development of a model that indicates a large during the the last lasttwo twomillion millionyears. years. Secondly, a new number of glaciations occurred during mechanical model for the dynamics of ice flow has been developed. In In order orderto to integrate integrate the new models into into our our interpretations, interpretations,aa broad broad geographic geographicperspective perspectiveisis required. required. Rather than provide a summary of the history of the investigations in the Lake Superior in the the context contextof ofthese thesenew newmodels. models. Even ifif region, I will present relevant observations in to look beyond the confines the models are eventually eventually replaced, they will have forced us to of the Upper Midwest Midwest and and the the traditional traditional glacial glacial interpretations. interpretations. Number of Number of glaciations glaciations Evidence indicates indicates that the number of Quaternary glaciations is significantly greater than the turn turn of the century the four-fold glacial chronology devised for North America around the which included the Wisconsinan, Illinoian, Kansan and Nebraskan glaciations (Flint, 1957). The The new new precision precisionisis based based on on nonterrestrial nonterrestrial records records of global global ice ice volume, record of of ocean ocean carbonates. carbonates. During glaciation, 160 is is including the oxygen-isotope record the ice ice sheets, enriching enriching the preferentially evaporated evaporated from the oceans and is stored in the Fluctuationsin in the the amount amount of 160 160 and 180 180 can be measured measured in glacial oceans in 180. Fluctuations used to to determine global ocean sediments sediments and ice cores (Shakleton and others, 1984) and used of oxygenice volume. Based Based on on these these calculations calculations for for global ice volumes, a series of represent isotope stages has been identified. Even Even numbered oxygen-isotopes stages represent periods. There glaciations, and odd numbers represent interglacial periods. There were were 40 40 glaciallinterglacial oscillations volumes between between 2.4 2.4 Ma Ma glacialhterglacial oscillations involving moderate global ice volumes and .9 Ma, and andthere therewere were 22 22 oscillations oscillations involving involvinggreater greaterice icevolumes volumes between between .9 .9 Ma Ma al., 1984). For the most recent 11 glaciations, oxygenand the present (Shackleton et al., 6, 12 2,6, 12 and 16 16 show the greatest ice volumes, possibly possibly corresponding correspondingto to isotope stages 2, traditional four-fold four-fold record record of terrestrial terrestrial glaciations glaciations in in North America. America. that the the most most extensive Another feature of the traditional four-fold record of glaciations is that glaciation formerly formerly recognized, recognized, (the (the Nebraskan) Nebraskan) was was also also interpreted interpreted to to be be the the oldest. oldest. Successively Wisconsinan) were Successively less extensive extensive glaciations, (the Kansan, Illinoian and Wisconsinan) younger (Flint, (Flint, 1957). 1957). This chronology is probably probably an interpreted to be successively younger of terrestrial terrestrial glacial glacial sediments. sediments. While there were clearly more artifact of the preservation of than four glacial periods during the past 0.9 my, each glacial advance obscures, either by of previous, previous, less less extensive extensiveadvances. advances. If, for example, there there erosion or burial, the record of random distance, probability probability were ten successive successive glacial advances, each advancing some random the surface and the oldest anaylsis suggests suggests that only three glacial limits will survive at the surviving advance advance will be the most extensive (Gibbons and others, 1984). ItIt isis therefore therefore 11 most recent glaciations we have historically recognized only not surprising surprising that of the 11 four glacial limits limits at at the the surface. surface. i r t half of the Pleistocene did The oxygen isotope record shows that glaciations in the ffirst (Shaldeton and others, not have as great great a global ice volume as those in the latter half (Shakleton 1984). However, However, these theseearly early advances advances of of ice ice were were apparently apparently extensive extensive enough enough in in North North 33 �America to to reach reach Iowa Iowa and and Nebraska Nebraska (Hallberg, (Hallberg, 1986) 1986)and and the the foothills foothillsof of the the Canadian Canadian America Rockies (Kiassen, (Klassen, 1989). 1989). The Thesediment sedimentof ofthese theseearly earlyadvances advancesmay may be be preserved preserved in in Rockies Minnesota (e.g. (e.g. Meyer, Meyer, 1997; 1997;Patterson, Patterson, 1997) 1997)and and in in Canada Canadain in the the subsurface subsurface(e.g. (e.g. Minnesota Klassen, 1989) 1989)in in areas areasof of net net glacial glacialdeposition, deposition, but but the the record record is is discontinuous discontinuousand and Kiassen, localized localized in in deep, deep, preglacial preglacialvalleys. valleys. Discontinuous,subsurface subsurfaceglacial glacial sediment sediment is is difficult difficultto to place place in in aa stratigraphic stratigraphic Discontinuous, framework because: (1) (1)absolute absolutedating datingof of the theunits units isis difficult; difficult;(2) (2) till till of of different differentglacial glacial framework terranetraversed traversedby by the the periods isis lithologically lithologicallyand andtexturally texturally similar similarifif the the source sourceterrane periods glacier (3)although althoughtill till may may change changecomposition compositiongradually graduallywith withdistance distanceinin glacierisisthe thesame; same;(3) the the ice-flow ice-flow direction, direction,isolated isolatedexposures exposuresof of till till may may be be dissimilar dissimilarenough enoughto toprevent prevent correlation. correlation. Radiocarbon Radiocarbondating datingof oforganic organicremains remainsisis only only useful useful for for Wisconsinan-age Wisconsinan-age deposits scattered predeposits because because of the limitations of the half life of 14C. A few dates from scattered Wisconsinan Wisconsinansamples sampleshave havebeen been secured securedusing using vertebrate vertebratepaleontology paleontology (e.g. (e.g.Klassen, Klassen, 1989), 1989), dating of volcanic ash present in the glacial glacial sediment (summarized (summarized in in Richmond Richmond and 1986),studies studiesof of remnant remnant magnetization magnetizationin in till till and andlake lakesediment sediment(e.g. (e.g. and Fullerton, Fullerton,1986), Baker Baker and and others, others, 1983), 1983),and and cosmosgenic cosmosgenic isotope isotope age age estimates estimates of of striated striatedrock rock surfaces surfaces (Bierman (Bierman and and others, others,1998). 1998). Owing Owingto to the thedifferent differentsubstrates substratesover overwhich whichthe theice iceflowed, flowed,ititisispossible possibleto todistinguish distinguish tills tills using using matrix matrix color, color,texture texture and and mineralogy, and clast lithology. During Duringthe theLate Late Wisconsinan, Wisconsinan,Minnesota Minnesotawas wasnearly nearlyequidistant equidistantfrom from the the two twomajor majorice iceaccumulation accumulation centers centersof of the theLaurentide Laurentideice icesheet sheetand andreceived received ice icefrom fromboth both (Dyke (Dykeand andPrest, Prest,1986). 1986). Minnesota's Minnesota'sunique uniqueposition position has hasfacilitated facilitatedprovenance provenancestudies studiesto to determine determineice-flow ice-flow paths paths and and source sourceareas. areas. The Theglacial glacialstratigraphy stratigraphyof ofCanada Canadaand andMinnesota Minnesota(Fulton, (Fulton, 1989; 1989; Meyer, Meyer,1997) 1997)indicate indicatethat thatice icesheets sheetshad had similar similargeometries geometriesthroughout throughoutthe theQuaternary. Quaternary. At At least leastfive fiveice icelobes lobesadvanced advancedinto intoMinnesota Minnesotaduring duringoxygen-isotope oxygen-isotopestage stage22(Late (Late Wisconsinan). Wisconsinan). Many Manyof ofthese theselobes lobeshad had multiple multiple readvances. During Duringadvance advanceeach eachlobe lobe had had the the potential potentialto toerode erodeolder oldersediment sedimentand androck, rock, and andto to deposit depositits itsown ownglacial glacial sediment. sediment.Therefore, Therefore,aasingle singleglacial glacialperiod periodmay maybe berepresented representedby by ten's ten'sof of compositionally -each each compositionallyand andtexturally texturallydifferent, different,incompletely incompletelypreserved preserved glacial glacialunits units— having having several severaldepositional depositionalfacies. facies. Interpretation Interpretationof of the themost mostrecent recentadvances advancesisismost most straightforward straightforwardbecause becausethe thedeposits deposits are are continuous, continuous,and and the the associated associated landforms are well preserved. For Forthis thisreason, reason, research research in in Minnesota Minnesota and and neighboring neighboring states states has historically focused of the activity of ice ice lobes lobesduring during the the Late LateWisconsinan Wisconsinan(for (forregional regional summaries summariessee seeWright, Wright,1972; 1972;Clayton Clayton and and Moran, Moran, 1982). 1982). Dynamics Dynamicsof ofice iceflow flow During 12 and Duringoxygen-isotope oxygen-isotopestage stage22(Late (LateWisconsinan), Wisconsinan),and andprobably probably during duringstages stages6,6,12 and 16 an ice ice sheet sheet that that extended extended 16 (all (all pre-Late pre-Late Wisconsinan), Wisconsinan),Minnesota Minnesota was was marginal marginal to to an across across most most of of Canada. Canada. Minnesota Minnesotaand andthe theGreat GreatLakes Lakesregion regionwere wereaffected affectedmainly mainlyby by thin, thin, dynamic dynamicice ice lobes lobes that that advanced advanced beyond the main body of the ice sheet. Much Much effort efforthas has been been made madeto tocorrelate correlatethe theadvances advancesof of these theselobes lobes(Clayton (Claytonand andMoran, Moran,1982; 1982; Mickelson Mickelsonand andothers, others,1983) 1983)but butitithas hasbecome becomeapparent apparentthat thatthey they were werenot notsynchronous synchronous on on aa time time scale scaleof of hundreds hundreds to to thousands thousands of of years. Movement Movementof ofthe theice icelobes lobesisis ultimately ultimatelydriven drivenby by the theoverall overallmass massbalance balanceof of the theice icesheet, sheet,which whichisiscontrolled controlledby by climate. climate.Ice Icelobes, lobes,however, however,respond respondquickly quicklytotochanges changesininmass massbalance balanceand andbed bed 34 �conditions of their their respective respective icesheds and may therefore appear to be out of phase with conditions nearby nearby lobes lobesand andregional regionalclimate. climate. Because km Because the the ice icelobes lobeswere werecomparatively comparativelythin—decreasing thin-decreasing from fromapproximately approximately11km where they they left leftthe the ice ice sheet— sheet- exisiting exisiting structural structural and and alluvial alluvial lowlands lowlands controlled controlled the where direction of of ice ice flow. flow. These Theselowlands lowlandswere weredeepened deepened even even more more owing to the enhanced enhanced direction glacial erosion erosion resulting resulting from fast, focused flow of the The Great Great Lakes are well glacial the ice. ice. The known examples examplesof of basins basins that that controlled controlled the flow flow of lobes; lobes; others others include include Great Great Bear known MacKenzie, Lake Lake Lake in in the the Northwest Northwest Territories, Territories, Great Great Slave Slave Lake in the District of MacKenzie, Lake Athabasca, on on the the Alberta-Saskatchewan border, Reindeer Reindeer Lake Lake in Saskatchewan, Saskatchewan, and and Athabasca, Lakes Winnipegosisin inManitoba. Manitoba. Lakes Winnipeg Winnipeg and andWinnipegosis Evidenceindicates indicatesthat that the the development development of of ice ice lobes (or (or 'outlet lobes') may be the result result Evidence of of ice ice streams streams(Patterson, (Patterson,1997). 1997).Ice Iceflow flowhundreds hundredsof ofkm kmup-ice up-icefrom fromthe theoutlet outletlobes lobes may may begin begin to toconverge convergeinto intoaanarrow, narrow,fast-moving fast-movingstreams streamsof ofice ice(Dyke (Dykeand andPrest, Prest,1986; 1986; Fulton, Fulton,1989; 1989;Thorliefsson Thorliefssonand and Kristjansson Kristjansson 1993; 1993; Fulton, 1995). The The nature nature and and distributionof of glacial glacialsediment sedimentand andlandforms landformsimplies impliesthat thatice iceflow flowwas wasmuch muchdifferent differentinin distribution thesenarrow narrowconvergent convergentzones. zones.Till Tillassociated associatedwith withice icestreams streamsisismore moredistally distallyderived, derived, these homogenous, homogenous, traceable traceablefor for hundreds hundreds of of km, and and typically has a level-to-streamlined level-to-streamlined surface surfaceexpression. expression.Tills Tillsdeposited depositedoutside outsidethese thesenarrow narrowconvergent convergentzones zonesare areusually usually thin thinand andlocally locallyderived. derived. are based based on on the the study study of of modem modem ice ice Modelsfor forthe themechanics mechanicsof of ice icemovement movementthat that are Models sheets (Fowler and Johnson, 1995) predict that slow, uniform flow of ice is unstable and sheets (Fowler and Johnson, 1995) thereforeunlikely. unlikely.What Whatisispredicted predictedand andobserved, observed,by bycontrast, contrast,isisaabimodal bimodalstyle styleofofice ice therefore flow, (km/yr)moving movingwithin within slower slower ice ice (cm/yr). (cdyr). The Thelocation locationofofice ice flow,with withfast fastice icestreams streams(km/yr) streams streamsappears appearstotochange changeover overtime, time,but butisisinfluenced influencedby bybed bedtopography topographyand and hydrogeology. Ice Icestreams streamsand andtheir theiroutlet outletlobes lobesare arethe themajor majordischarge dischargeareas areasfor foran anice ice hydrogeology. sheet, sheet,and andtheir theirdevelopment developmentisislargely largely aa function function of of subglacial subglacialwater. Ice Icestreams streamsdraw draw down downthe theice icemass massin inthe theice iceaccumulation accumulationcenters. centers. Ice-lobe Ice-lobeadvances advancestherefore thereforerepresent represent aa redistribution redistributionof ofice, ice,and andmay may actually actually signal signalthe the overall overall decay decay of the the ice ice sheet sheet rather rather than thanan anincrease increaseininvolume volumeofofthe theice icesheet. sheet. The LateWisconsinan Wisconsinan Laurentide Laurentideice ice sheet sheet indicates indicates that that in in the the Thedeglacial deglacialrecord recordof ofthe theLate areas areasof of continuous continuousice icecover coverin inCanada, Canada,ice ice streams streamsdeveloped developed within within the the ice ice sheet sheet and and fed fedthe theice icelobes lobesthat thatmoved movedthrough through the the Great Great Lakes Lakes basins basins into into the the upper upper Midwest Midwest (Dyke Hicockand andDreimanis, Dreimanis,1992; 1992;Thorleifson Thorleifsonand andKristjansson, Kristjansson, (Dykeand andPrest, Prest,1986; 1986;Hicock 1993). 1993).The Theice icestreams streamswere wereactive activethroughout throughoutthe theretreat retreatof ofthe theice iceacross acrossCanada Canadaas as documented documentedin inthe thepattern patternof of moraines moraines(Dyke (Dykeand and Prest, Prest, 1986; 1986;Fulton, Fulton, 1995). 1995).ItItisis unclear growthbecause because the theeffects effectsof of unclearififice icestreams streamswere werealso alsoimportant importantduring duringice-sheet ice-sheetgrowth subglacial subglacialwater waterare aredifficult difficultto toascertain. ascertain.This Thismodel modelofofice iceflow flowcan canbe becautiously cautiously extended extendedto toearlier earlierglaciations, glaciations,bearing bearingininmind mindthat thatbed bedconditions conditionscould couldhave havebeen beenvery very different differentfrom fromthose thoseof ofmore morerecent recentevents. events. The Theadvantages advantagesofofstudying studyingthe thegeological geologicalrecord recordofofQuaternary Quaternaryglaciations glaciationsinclude: include:(1) (1) the (2) the the therelatively relativelyexcellent excellentpreservation, preservation, continuity continuity and and accessibility accessibilityof of the the deposits; deposits; (2) location locationof ofthe thedeposits depositswithin withinaawell wellestablished established paleogeographic, paleogeographic, paleomagnetic, paleomagnetic,and and tectonic (4)records recordsfor forfloral floraland andfaunal faunalsuccession successionand andpluvial pluviallake-level lake-level tectonicsetting; setting;(4) histories (4) direct direct historiesthat thatallow allowthe theconstruction constructionof of predictive predictiveglobal globalcirculation circulationmodels; models; (4) evidence evidenceof ofglobal globalice icevolume volumefrom fromthe theocean oceanoxygen oxygen istope istoperecord record as as well well as as the the record record of ofcrustal crustalrebound; rebound;and and(5) (5)fairly fairlyeasy easyaccess accessto to modem modemanalogs analogs(for (forexample, example,the thestudy study 35 �of Antarctic chamber). Antarctic ice is relatively easy compared to the study of a deep magma chamber). These advantages advantages also provide the greatest greatest challenge challenge to Quaternary researchers, researchers, who are are required to integrate data across a wide range range of of disciplines disciplines and and geographic geographic areas. areas. The ultimate goal is to provide provide a integrated picture of the geosphere, geosphere, hydrosphere and biosphere for a specific specific period of earth's history, and to extend this understanding understanding to more more obscure glacial periods in the geologic record. REFERENCES REFERENCES Baker, R. W., Diehi, Diehl, J. F., Simpson, Simpson, T. W., W., Zelazny, Zelazny, L. L. W., W., and and Beske-Diehl, Beske-Diehl, S., S., 1983, 1983,Pre-Wisconsinan Re-Wisconsinan paleomagnetics of of west-central west-central Wisconsin: Wisconsin: Geological glacial stratigraphy, chronology, palmmagnetics Geological Society Society of America Bulletin, Bulletin, v. 94, p. 1442-1449. 1442-1449. Bierman, P. R., Marsella, K. A., Patterson, Patterson, C., Davis, P. T. Caffee, M., 1998, 1998, Mid-Pleistocene cosmogenic Mid-Pleistocene cosmogenic minimum-age pre-Wisconsinan glacial surfaces in southwestern minimum-age limits for pre-Wisconsinan southwestern Minnesota Minnesota and southern southern Island --- aa multiple nuclide approach. Accepted Accepted for for publication publication in Geomorphology. Geomorphology. Baffin Island Clayton, L., and Moran, S. R., 1982, 1982, Chronology Chronology of late Wisconsin glaciation in middle North America. America. Quaternary Quaternary Science Science Reviews, v. 11 p. 55-82. Dyke Dyke A. S. S. and and Prest, Prest, V. V. K., K., 1986, 1986,Paleogeography Paleogeographyof northern northern North America, America, 18,000-5000 18,000-5000 years years ago. ago. Geological Survey of Canada, Map Map 1703A, scale scale 11::12,500,000. 12,500,000. Hint, R. F., 1957. 1957. Glacial Glacialand andPleistocene PleistoceneGeology. Geology.New NewYork, York,John JohnWiley Wileyand andSons, Sons,553 553p.p. Flint, 1995, Hydraulic run-away: A mechanism mechanism for thermally regulated surges of Fowler, A. C., and Johnson, C., 1995, run-away: A ice sheets: 1. sheets: Journal JournalofofGlaciology, Glaciology,v.v.41, 41,p.p.554-56 554-561. Fulton, R. J., 1989, 1989, Foreward in Fulton, Fulton,R. R. J., J., ed., ed., Quaternary Quaternary geology geology of Canada Canada and Greenland: Greenland: Ottawa, Ottawa, Geological Survey Survey of Canada, Canada, Geology Geology of Canada series, v. 1;(Geological l;(Geological Society Society of America, America, Geological Geology of North America, v. v. K-1), K-i), p. 1-11. 1-11. Fulton, R. J., 1995, 1995, Surficial Surficial map of Canada: Geological GeologicalSurvey Survey of Canada Canada Map 1880A, 1880A, scale 1:5,000,000. 1:5,000,000. Gibbons, A. B., Megeath, Megeath, J. D., and Pierce, K. L., 1984, 1984, Probability of moraine survival in a succession succession of glacial advances. Geology, Geology,v. v. 12, 12,p. p. 327-330. 327-330. Hallberg, Hallberg, G. G. R., 1986, 1986,Pre-Wisconsin Pre-Wisconsin glacial glacial stratigraphy stratigraphyof the the central central plains plains region region in in Iowa, Iowa, Nebraksa, Nebraksa, Kansas, and Missouri. Quaternary Quaternary Science Science Reviews, Reviews, v. 5, p. 11-15. Dreimanis, A., 1992, Deformation till implications for rapid Hicock, S. T., and Dreimanis, till in in the the Great Great Lakes Lakesregion: region: implications of the the Laurentide Laurentide Ice Ice Sheet. Sheet. Canadian Journal of Earth flow along the south-central margin of Sciences, Sciences, v. 29, 29, p. 1565-1579. 1565-1579. Kiassen, Klassen, R. W., W., 1989, 1989,Quaternary Quaternarygeology geology of of the the southern southern Canadian Canadian interior interior plains, plains, in in Fulton, Fulton, R. R. J., J., ed., ed., and Greenland: Greenland: Ottawa, Quaternary geology of Canada and Ottawa, Geological Survey of Canada, Geology of of America, America,Geology Geologyof ofNorth NorthAmerica), America),v.v.K-1, K-i, p. p. 138Canada series, v. 1; (Geological Society of 174. 174. Mickelson, D. M., Clayton, L., Fullerton, D. S., S., and Boms, Borns, H. H. W. W. Jr., Jr., 1983. 1983. The late Wisconsin glacial S, C., LateLaterecord of the Laurentide ice sheet in the United States, in Wright, H. E., Jr., and Porter, S. Quaternary Environments of of the the United United States, States, Vol. Vol. 1, 1,The TheLate LatePleistocene. Pleistocene. Univeristy of Minneapolis, p. 3-37. Minnesota Press, Minneapolis, Meyer, G. N., 1997, of north-central north-centralMinnesota. Minnesota. Minnesota 1997, Pre-late Wisconsinan till stratigraphy of 48, 67 p. Geological Survey Survey Report of Investigations Investigations no. 48,67 Patterson, in Patterson, Patterson,C. C. J., J., Contributions Contributionsto to Patterson, C. C. J., 1997, 1997,Quaternary Quaternarygeology geology of of southwestern southwesternMinnesota, in the Geology Geology of Southwestern Southwestern Minnesota, Minnesota, Minnesota Geological Geological Survey Report of Investigations Investigations 47, p. 1-45. 1-45. Richmond, Richmond, G. G. M., M., and and Fullerton, Fullerton, D. D. 5., S., 1986, 1986,An An introduction introductionto to Quaternary Quaternaryglaciations glaciationsin in the theUnited UnitedStates States of America, Quaternary Quaternary Science Science Reviews, Reviews, v. 5, p. 3-10. Shackelton, N. J. and others, Shackelton, others, 1984, 1984, Oxygen isotope isotope calibration calibration of the onset of ice-rafting ice-rafting and history history of glaciation in the North Atlantic region: region: Nature, Nature, v. 307, p. 216-219. Thorleifson, L. H., and Kristjansson, Kristjansson, F. J., 1993, 1993, Quaternary Quaternary geology and drift prospecting, prospecting, BeardmoreBeardmoreGeraldton area, Ontario: Geological GeologicalSurvey Survey of of Canada Canada Memoir 435, 146 146 p. of Minnesota, Minnesota, in in Sims, Sims,P. P.K. K.and andMorey, Morey,G. G.B, B,eds., eds.,Geology Geologyof of Wright, H. E. Jr, 1972, 1972, Quaternary History of Minnesota: AAcentennial centennialvolume. volume. Minnesota MinnesotaGeological GeologicalSurvey, Survey,p.p.5515-547. 36 �WHAT'S NEXT FOR GEOLOGY GEOLOGY IN IN THE THE LAKE LAKE SUPERIOR SUPERIOR AREA? WHAT'S NEXT SOUTHWICK,David David L., L., Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642University University Ave. Ave. W., W., St. St. Paul, Paul, MN MN SOUTHWICK, 55114-1057 55114-1057 Marvelous Marvelous progress progress has has been been made madein indeciphering decipheringthe thecomplex, complex,diverse diversegeological geological framework frameworkof of the the Lake Superior Superior region over the past twenty years. In particular, our comprehension comprehension of the Precambrian rock record has progressed progressed remarkably remarkablythrough throughexcellent excellent programs programs of of geologic mapping, regional geochronology, and and related related topical research research supported supported largely by government government and geophysics, geochronology, and justified understanding of on the premise that that geologic understanding of Precambrian terranes terranes will will lead to to discovery discovery of of economic mineral be sustained sustained and and that intellectual and mineral deposits. One hopes that this momentum can be progress toward the goal of finding and developing technological progress developing viable ore deposits deposits will continue. continue. Sustaining it will not not be be easy easy in in the theprevailing prevailingpolitical politicalclimate, climate, however. however. of democratic governments governments are determined Ultimately, albeit indirectly, the policies of determined by by public public opinion that is transmitted transmitted to to elected elected representatives. At the present time the public is not particularly p&ticularly concerned about mineral commodities commodities and therefore minerals issues do not have aa high high political political profile. There are no pressing shortages, prices are moderate moderate and stable, stable, unemployment unemploymentis is generally generally issues greatly greatly outweigh outweigh concerns concerns for for the the long-term long-term low, and concerns concerns for present-day "quality "quality of life" issues of mineral and energy availability of energy resources resources in in the the minds mindsof of most most people. people.As As aa consequence, consequence, elected elected representatives are representatives are being urged by their constituents to preserve and promote promote environmental environmentalquality, quality, provide provide recreational recreational opportunities opportunitiesin inwilderness wildernessareas, areas, improve improveurban urbaninfrastructure, infrastructure,combat combatcrime, crime, opportunites, and reduce taxes. They are are not not being being urged urged to improve health care, extend educational opportunites, of aa mining mining industry industry that we geologists geologists know know is is vital vital to to the the long-term long-term provide for the well-being of sustainability of because there there is is aa powerful powerful human human tendency not to worry about sustainability of the quality quality of life, because about future difficulties until circumstances absolutely demand demand it. Instead of of mining, mining, the the plexus plexus of of future affect human human health health and and happiness will be the primary environmental issues that immediately affect primary driver driver of public resource policy and derivative of derivative geological investigations in the Lake Superior region over the the next twenty twenty years. Although Although metal metal mining and and related related industries industries surely surelywifi will remain remain significant significant to local and will receive passive passive political politicalsupport, support, they they will wifinot notin in themselves themselvesprovide provide the the rationale rationale economies and for increasing public expenditures expenditureson ongeological geologicalinvestigations. investigations. be growth areas for applied geologic thinking thinking and research in the Lake The following will be Lake Superior Superior Detailed characterization of of unconsolidated unconsolidated materials within the uppermost region. (1) Detailed uppermost100 100m m of of the the This work work will involve collaboration among among glacial glacial geologists, geologists, stratigraphers, stratigraphers, geologic section. This hydrogeologists,and and soil soil scientists scientistsand and will will have have direct direct application to a geophysicists, geochemists, hydrogeologists, number number of of societal societalconcerns. concerns. It will will also also benefit mineral exploration, exploration, but itit wifi will not be justified on on that that basis. (2) The The development development and deployment deployment of improved geophysical geophysical tools for obtaining information mapping of about the the shallow shallow subsurface. subsurface.(3) (3) Detailed geologic geologic mapping of surficial deposits, deposits, especially especially in in urban, urban, mapping to to provide provide the stratigraphic framework of of the the urbanizing, and agricultural agricultural areas. Regional mapping Quaternary materials Quaternary materials will will be necessary as well, but the more pressing need will will be for detail. detail. (4) (4) Hydrogeologic studies studies on on aa variety variety of of scales, scales, with particular particular emphasis emphasison onthe thegeological geologicalcontrols controlsof of ground-water flow. be a developing area of of research research in in which which ground-water flow. Fractured-rock Fractured-rock hydrogeology will be sedimentologists, petrologists, sedimentologists, petrologists, and and structural structuralgeologists geologistswill willbecome become increasingly increasinglyinvolved. involved.(5) (5)LowLowtemperature rock-water of surface-water surface-water and and groundgroundtemperature rock-water geochemistry, geochemistry, with applications to problems of The mapping mapping and (6)The water composition composition and and the the transport transportof of dissolved dissolvedchemical chemical species. species. (6) of mined mined land and mine waste, characterization characterizationof of aggregate aggregateresources. resources.(7) (7) Characterization Characterization and control of in which the brought to the full full spectrum spectrumof of hydrogeological hydrogeological and and geochemical geochemical methodologies are brought to bear. bear. (8) (8) Geological and geophysical studies within Lake Superior Superior itself itself that that will will be be predicated predicated on calibration Geological and of the paleoclimate record but but will will extend extend to to investigations investigations of of lake-basin lake-basin evolution. evolution. As the geological profession profession becomes becomes ever evermore moredependent dependent on on government government policies, policies, our our near-term near-term research opportunities inevitably will reflect public priorities. This need not and will not mean opportunities inevitably This need not mean the the total demise of economic economic geology geologyand andthe thehard-rock hard-rockdisciplines disciplinesthat thatsupport supportit.it. However, traditional hard-rock work work will will diminish diminish in in favor favor of of non-traditional non-traditional investigations investigationsin in which which hard-rock hard-rock thinking thinking and skills skills can can be applied. applied.Flexibility Flexibility of training training and andoutlook outlookwifi willbe be critical criticalto to professional professionalsuccess. success. 37 �ACTS ABSTRACTS GENERAL TECHNICAL SESSIONS 39 �PETROGRAPHY AND GEOCHEMISTRY O OF F MIDCONTINENT RIFT RIFT RHYORHYOVOLCANICS) NEAR NEAR CLAM CLAM FALLS, FALLS, WISCONSIN LITE (CHENGWATANA (CHENGWATANA VOLCANICS) R.,Geology Geology Department, Department, ABBOTT, Kathleen M., THOLE, THOLE, Jeffrey Jeffrey T., T., WIRTH, WIRTH, Karl KarlR., Macalester College, St. Paul Paul MN, MN, 55105; 55105; kabbott@macalester.edu; kabbott@macalester.edu; thole@macalester.edu; wirth@macalester.edu The southwest southwest limb of the Midcontinent Rift (MCR) includes includes the the poorly-exposed poorly-exposed Chengwatana Chengwatana Volcanics (CV) (CV) which which are comprised of predominantly tholeiitic basalts (Wirth et al., Volcanics al., 1997, 1997, Naiman et al., this volume), volume), with minor rhyolites which are believed to be the the southernmost southernmost exposed rocks of this type within the the MCR. MCR. Recent analysis of these rhyolites found near Clam exposed Falls, Wisconsin, provides physical, chemical, and isotopic data data which which has has helped helped constrain constrain the the processes (Naiman (Naiman and Wirth, this timing (Wirth and Gehrels, this volume), and magmatic processes and the the southern southernMCR. MCR. These data are also used volume) involved in the generation of the CV and . rhyolites of northern Michigan to compare compare the CV rhyolites rhyolites with the Portage Lake rhyolites Michigan (Nicholson, (Nicholson, 1992, Nicholson Nicholson and Shirey, 1990), and the felsic rocks of the the North North Shore ShoreVolcanic Volcanic Group Group (Green (Green and and Fitz, Fitz, 1993, 1993,Vervoort Vervoort and and Green, Green, 1997). 1997). Two exposures exposures of rhyolite rhyolite are are found just west of Clam Clam Falls Falls including including about about 55 meters of rhyolite (KC-302) which is approximately 640 meters above the base of the exposed volcanic volcanic section. The The only only other otheroutcrop outcropof of rhyolite rhyolite (KC-310) (KC-310) is exposed exposed near the base of of the the section section approximately 3 kilometers south of KC-302 and is is less less than than 10 10meters metersthick. thick. No flow contacts contacts approximately or foliations are are present present but but the the outcrops outcrops appear appear to to be beconcordant concordantwith withsurrounding surroundingbasalts basalts which trend northeast and dip approximately 15 degrees to the northwest in this area. The northeast and dip approximately 15 degrees Thebase base with the underlying basalt basalt and of the outcrop at KC-302 appears to be an intrusive contact with the rhyolite contains contains subangular subangular inclusions inclusionsof ofophitic ophiticbasalt. basalt. The nature of emplacelocally, the ment ment of these these rhyolite rhyolite bodies bodies isis unclear. unclear. porphyritic small phenocrysts phenocrysts(-(—.1mm) The rhyolites rhyolites are generally weakly (<5%) (4%) porphyritic containing small lmm) The euhedral to and trace trace amounts of subhedral of euhedral to subhedral subhedralplagioclase plagioclase(avg. (avg.Ab94 Abo4An2 An2 Or4) and subhedralFe-Ti Fe-Ti locally. Amphiboles, oxides. Quartz Quartzphenocrysts phenocrysts and and albite albite glomerocrysts glomerocrysts are present only locally. Amphiboles, partly replaced replaced by chlorite/epidote/carbonate, chlorite/epidote/carbonate,are are rare. rare. The Thegroundmass groundmassisiscommonly commonlyspheruspherucontaining tabular quartz (tridymite (tridymite paramorphs), paramorphs), with phenocryst phenocryst nuclei, nuclei, containing litic (up to 22-- 3 mm) with Or95),very veryfine-grained fine-grained disseminated disseminated Fe-oxides, Fe-oxides, Ani Org5), dusty, anhedral anhedral alkali alkalifeldspar feldspar(avg. (avg.Ab4 Ab4An1 and local poikilitic anhedral quartz. quartz. Accessory zircon cessory zircon is present present as as minute minute I I I a euhedral prisms prisms in in most most samples. samples. The euhedral The C1fl Falls Clam Falls (CV) (CV) presence of minor epidote epidote and and carbonate carbonate BSa1t a Basalt D within the groundmass groundmass is is ubiquitous. ubiquitous. -3 . . Rhyolite Rhyolite samples contain minor diktytaxitic Some samples contain minor diktytaxitic Some a cavities. The presence of of tridymite tridymite g cavities. paramorphs pararnorphsindicate indicatethese theserocks rocks are are simisimi-Do 22 -lar to some rhyolites of the NSVG which a & erupted at athigh highterntern- 0 C are believed to have erupted I L7 f-4 peratures (Green and Fitz, 1993). No ap00° o na ° parent flow foliation or pyroclastic pyroclastic texn o 1 00 observed in the exposures exposures near tures were observed Falls. Clam Falls. Only basalt and rhyolite are present I I I 0 in the Clam Clam Falls' section; section; no rocks rocks of 50 60 40 50 60 70 70 80 intermediate intermediate composition compositionhave have been been idenidenS.1 2 wt /0 SiO, % tifled. tified. Rocks of of intermediate intermediate composicomposiI I I ^ 1 I 41 - �_______________________________ DI 0 I I 0 NSVG Granophyres \ ocJJ om 0 0a Portage Lake Portage Lak  0a -4 — -8 NSVG Icelandites Icelandi -12 NSVG Rhyolites Clam Clam Falls Falls (CV) (CV) -16 0 Basalt Basalt I Rhyolite Portage Lake Type II -20 40 50 60 70 80 Si02 wt % both the the NSVG NSVG and and the thePortage PortageLake LakeVolcanics. Volcanics. Chengwatana Chengwatana basalt basalt geochemgeochemtions are found in both Naiman et al., a!.,this thisvolume. volume. The The felsic felsic Chengwatana Chengwatana rocks rocks can can be be classified classified istry is discussed by Naiman as tholeiitic rhyolites. The Therocks rocks are are metaluminous metaluminous and and only only one one sample sample has normative normative coruncorundum (0.16%). In In general, general,the therhyolite rhyolite chemistry chemistry is is similar similar to to both both NSVG NSVG and and Type Type I Portage Portage Lake rhyolites. Si02 (7 (71-72%), rhyolites.Notable Notablevariations variationsfrom fromthese thesetwo two groups groups include include slightly less Si02 1-72%), higher 13higher total total Fe Fe (4.87 (4.87 to to 5.78 5.78Fe203%), Fe203%),higher Th (25-27 ppm), and significantly significantlyhigher higherZr Zr(7 (713986 986 ppm). Initial ENd (1100Ma) Ma)values valueson ontwo twoChengwatana Chengwatanarhyolites rhyolitesare are0.95 0.95and and-0.06. -0.06. These ENd (1100 Chengwatana basalts of of the the Clam ClamFalls Fallsregion region(-2 (-2toto+3.4). +3.4).The TheChengwatana Chengwatana values are similar to Chengwatana rhyolite similar to Portage Lake (Type I) rhyolites rhyolites which which range rhyolite ENd ENd values are most similar range from from-0.3 -0.3to to -4.7 (Nicholson (Nicholson and andShirey, Shirey, 1990) 1990)and and are are distinct distinct from rhyolites of the NSVG which range from -2.3 to ENd to -14.8 -14.8 (Vervoort (Vervoort and Green, Green, 1997). 1997). NSVG NSVGgranophyres granophyresand andicelandites icelanditeshave haveENd values with a smaller and these these values values are also lower than smaller range range than NSVG rhyolites rhyolites and rhyolites. Large degrees of crustal melting melting are are invoked invoked as as a major process in in Chengwatana rhyolites. forming forming the the NSVG NSVG rhyolites rhyolitesas asindicated indicatedby bythe thelow lowENd ENd values values (Vervoort (Vervoort and and Green, Green,1997). 1997). The Chengwatana rhyolites at Clam Falls lack the pronounced crustal Nd isotopic isotopic signature signature evident in the NSVG rhyolites rhyolites and are are believed to be fractionates fractionates of a primary basaltic basaltic magma magma derived from an enriched enriched mantle mantle source. References Cited Green, v. 54, 54, p. p. 177-196. Green, J.C. J.C. and and Fitz, Fitz, T.J., T.J., 1993, 1993, Journal of Volcanology and Geothermal Research, v. Nicholson, S.W., S.W., and Shirey, S.B., 1990, Journal of Geophysical Research, v. 95, p. 10,851-10868. Nicholson, S.W., U.S.G.S. Bulletin 57 pp. S.W., 1992, U.S.G.S. Bulletin 1970, 1970,57 K.R., Vervoort, J.D., J.D., Naiman, Z.J., 1997, Canadian Journal of Earth Sciences, v. 34, no. 4, p. 536-548. Wirth, K.R., 536-548. J.C., 1997, Vervoort, J.D., and Green, Green, J.C., 1997, Canadian Journal of Earth Sciences, Sciences, v. 34, p. 521-535. 42 �A PRELIMINARY DETAILED GEOLOGICAL GEOLOGICAL DESCRIPTION DESCRIPTION OF OF THE NEW A PRELIMINARY DETAILED NEW IN THE LUMBY HIGH GRADE SILVER-BASE SILVER-BASE METAL DISCOVERY DISCOVERY IN LUMBY LAKE METAVOLCANIC BELT BELT NORTHEAST METAVOLCANIC NORTHEAST OF ATIKOKAN, ATIKOKAN, ONTARIO, ONTARIO, CANADA BERNATCHEZ, Raymond A., President & Consulting Geologist to Atikokan Resources Inc., P.O. Box Box 1376, 1376,126 126Willow Willow Rd., Rd., Atikokan, Atikokan,Ontario, Ontario,Canada, Canada,POT POT1CO. 1CO. Tel. 807-597-4526, Fax 807-597-4636 (rbernatc@atikokan.lakeheadu.ca) (rbernatc @ atikokan.1akeheadu.ca) A high mineraloccurrence occurrencehas hasbeen beendiscovered discoveredwithin within an an east-west east-west high grade grade silver—zinc—lead silver-zinc-lead mineral stratabound felsic volcaniclastic horizon at the southern edge of the Lumby Lake Metavolcarnc Metavolcanic Belt. Located Locatednorth northof ofthe thecreek creekconnecting connectingLumby Lumbyand and Herontrack HerontrackLakes, Lakes,the thediscovery discovery occurs at the southern margin of a 1.5 1.5 km thick east-west trending felsic volcanic volcanic package package near Marmion Lake tonalite the southern contact of the Lumby Lake Metavolcanic Belt with the Marmion of batholith to the south. The The Lumby Lumby Lake Lake volcanic belt is located 23 air miles northeast of Atikokan, Ontario, Canada and forms the northeasterly extension extension of of the the Steep Rock and Finlayson Lake volcanic stratigraphy. This This discovery discoveryisis contained containedwithin within highly highly (hydrothermally) (hydrothermally) altered felsic volcaniclastic rocks having geological and geochemical geochemicalfeatures features similar to other Archean massive sulphide deposits. However, the felsic volcanic rocks hosting metaloccurrence occurrence have have been been dated dated at 3.0 Ga (Mesoarchean; this high grade grade silver—base silver-base metal (Mesoarchean;Davis Davis and Jackson, 1988), 1988), whereas all other base metal deposits found in the Archean in Ontario have been dated at 2.7 2.7 Ga. The The occurrence occurrence contains contains unusually high silver content with some random grab samples assaying as high as 416 ounces/ton (14,265 (14,265 gm/tonne) gdtonne) or or270 270ozfton ozlton samples assaying as high as 416 ounces/ton over 1.1 1.1 meter (9292 (9292 gm/tonne). gdtonne). The Lumby Lake greenstone greenstone belt is located within the Wabigoon subprovince, 30 km north of the Wabigoon-Quetico Wabigoon—Queticosubprovince subprovinceboundary boundaryand and 37 37 air airkm km northeast northeast of Atikokan, Ontario. Ontario. The Lumby Lake km xx 20 20 km km synclinal synclinalsupracrustal supracrustalsequence sequence Lake greenstone greenstonebelt belt consists consists of of aa 60 60 km of rocks composed of mafic (pillowed and massive), ultramafic (komatiitic), and felsic (tuff, lapili lapillituff, tuff,tuff tuffbreccia, breccia,massive), massive),metavolcanic metavolcanicrocks rockswith with lesser lesseramounts amountsof of metasedimentary metasedimentary rocks (chert, (chert, argillite, argillite, arkose, arkose, conglomerate conglomerateand and iron iron formations). formations).The Themetavolcanic— metavolcanicmetasedimentary assemblage Mannion Lake Batholith to the south and the assemblage is in contact with the Marmion White Otter Batholith to the northwest. The The belt belt has has been been intruded intruded by two larger oval oval and monzodiorite-granite plutons, the Norway Lake and van Nostrand Lake Stock heterogeneous monzodiorite-granite and smaller ones (the Bar Lake and Viking Lake Lake stocks). The Belt has been subjected subjected to four major structural structural events: at least two folding events and two faulting-shearing events. The TheBelt Belthas has had had aa major major synclinal synclinal folding folding event event with with its its axis axis trending east-west east-west through through the central central portion of the the belt through through Seahorse-Garnet Seahorse-GarnetBayBayPinecone-Hematite Lakes system. The The van van Nostrand Lake stock intrudes this axis in the central part of the belt. AAsecond secondfolding foldingevent event occurs occurs within within the the interfiow interflow sedimentary sedimentaryunits. units. belt to to the the west. west. Two The Redpaint Lake Fault truncates the Lumby Lake belt Two east-west east-west Spoon Lake Deformation Deformation Zone and the deformation zones have been noted: the Bufo Lake - Spoon Garnet Garnet Bay-Viking Lake-Hematite Lake-Hematite Lake Lake Deformation Deformation Zone. Zone. The silver—base metaldiscovery discoveryisislocated locatedin inthe thewestern westernblock block of of claims claims known known as the silver-base metal Herontrack Herontrack Lake Lake Block Block and and within within the the southwest southwestportion portion of of the the Lumby LumbyLake Lakegreenstone greenstonebelt. belt. A 130 krn grid has been established established in the the central central portion of this block from Lumby Lumby Lake Lake to to 130 km Hutt Lake. AAdetailed detailedexploration explorationprogram programover overthis this grid grid consisting consistingof of geological geologicalmapping, mapping, lithogeochemical soil geochemical sampling, magnetic and partial VLF EM and IP surveys, lithogeochemical 43 �sampling sampling and overburden overburden mechanical stripping has identified and exposed exposed numerous numerous suiphide sulphide bearing felsic volcaniclastic horizons horizons containing containing economic economic to to subeconomic subeconomicvalues valuesin in zinc, zinc, copper, silver, lead and gold. gold. The detail detail geological geological mapping mapping has identified identified five five rock rock types: mafic mafic volcanic, volcanic, massive massive and and pilowed; pillowed;felsic felsicvolcanic, volcanic,tuff, tuff, lapili lapillituff, tuff,tuff tuffbreccia brecciaand andcoarse coarse breccia, breccia, massive massive rhyolite rhyolite as feldspar feldspar and/or andfor quartz quartz porphyries porphyries and and cherty cherty rhyolite; rhyolite; mafic mafic to to intermediate intermediateintrusive intrusiverocks rocks (gabbro and diorite) as dykes and sills intruding the above; Marmion Lake batholith (tonalite) Lake batholith (tonalite) and finally felsic dikes intruding intruding the the felsic felsic volcanic volcanic rocks. rocks. The bulk of the mineralization is contained within stratabound stratabound interflow interflow sediments. sediments. Pyrite, Pyrite, and in some some interfiow interflow units, units, pyrrhotite pyrrhotitemake makeup upthe thebulk bulkofofthe thesulfides. sulfides.The Thehigh highgrade gradesilver— silverzinc—lead discovery zone contains significant amounts of pyrite, sphalerite, galena, acanthite zinc-lead discovery zone contains significant amounts of pyrite, sphalerite, galena, acanthite and native silver with minor chalcopyrite. This This mineralization mineralization is is contained contained within within highly highly altered felsic volcanic rocks. The The felsic felsic rocks rocks have have been been altered altered to sericite sericite and chlorite chlorite in some some locations. The Thesericite sericitewas waspreviously previouslyinterpreted interpreted as as an an altered altered and and sheared shearedquartz quartz diorite; diorite; itit now appears that this alteration was caused as the result of the footwall alteration associated with massive sulphide deposits. This This has has been been partially partially confirmed confirmed by some some limited limited lithogeochemical lithogeochemicalrock rock sampling. sampling. The exploration exploration program carried out out to date has identified three highly altered base metal mineralized horizons. The The most most economically economically significant significanthorizon identified to date is the Lake—SpoonLake LakeHorizon Horizonwhich whichhosts hosts the the high high grade grade silver silver discovery. Several Lumby Lake-Spoon Several other other been discovered discovered along along this 250 to to significant silver and base metal-bearing occurrences have been 300 meter wide sulphide horizon that has now been traced for a strike length of about about 66 km by surveys. Two additional suiphide base metal mechanical stripping and geophysical surveys. additional altered sulphide bearing felsic volcanic horizons (Delos Lake and Pond Lake Horizon) have been located a few hundred meters north of the silver discovery horizon. Geophysical Survey The Questor Airborne Geophysical Survey carried out by the Ontario Geological Survey in Lake mineralized mineralized 1980 did not identify any input input anomalies anomalies along along the the Lumby Lumby Lake—Spoon Lake-Spoon Lake horizon. However, a broad magnetic low covers the area over the newly identified However, a broad magnetic low covers the area over the newly identified felsic felsic strata. This Thismagnetic magneticlow lowcan canbebetraced tracedeast—west east-west along alongthe thesouthern southernvolcanic—granite volcanic-granite contact contact for over 12 km km from from Bufo Bufo Lake Laketo toHutt Hutt Lake. Lake. Other similar of the Lumby Lake greenstone belt for of over 13 km. km. Similar Similarfelsic felsic magnetic lows can be traced eastward to Old Man Lake a distance of volcanic rocks have been identified in these areas. A new copper—zinc—silver occurrence has rocks have been identified in these areas. A new copper-zinc-silver occurrence been found along this magnetic low response response near a series of airborne input anomalies anomalies at the west end of Old Man Lake. The TheOGS OGSairborne airbornegeophysical geophysicalsurvey survey has has detected detected numerous numerous other anomalies anomalies in the Lumby Lake greenstone greenstone belt, of which most have never been examined or tested. What Whatother otherbase basemetal metaldiscoveries discoverieswill will the the Belt Belt reveal? reveal? References References cited: Davis, D.W., and Jackson, M.C., 1988, 1988, Geochronology of the Lumby Lake greenstone belt: a 3 Ga complex within the Wabigoon Subprovince, northwest Ontario: Bull. G.S.A., G.S.A., v. v. Ontario: Bull. 100, p. 818-824. 44 �L5 r I Ii 0 z 0 -' Ic ii I 45 �DIMENSION STONE PRODUCTS DIMENSION PRODUCTS OF OF MINNESOTA MINNESOTA BOERBOOM, BOERBOOM, Terrence Terrence J., Minnesota Minnesota Geological Geological Survey, Survey, 2642 University University Avenue, Avenue, St. St. Paul, MN 55114; 55114;boerbO01@tc.umn.edu; boerbOOl@tc.umn.edu; and and OBERHELMAN, OBERHELMAN, Matt, Matt, Minnesota Minnesota Division of Minerals, 1525 E. 3rd Street, Hibbing, Department Department of Natural Resources Resources - Division matt.oberhelman@dm.state.mn.us 55746-1461;matt.oberhelman@dnr.state.mn.us MN 55746-1461; The first fmt dimension dimension stone stone quarry was opened in 1868, 1868, to supply gray granite granite from the St. St. Paul Customs Customs House House and and Post Post Office. Office. Since Cloud District for construction of the St. Paul Since then, grown considerably. considerably. At present there are the dimension stone industry in Minnesota has grown are fourteen active fourteen active dimension dimension stone stone quarries quarries in in the the state, state, and and several several others others that that are are active activeon on an an intermittent basis. Dimension Dimension stone stoneproducts products from from Minnesota are marketed worldwide, and are used for for a variety of purposes purposes that that include include interior interior tiling, counter counter tops, monuments monuments and and memorials, "surface memorials, "surface plates" platest' for for precision machine mounts, acid-resistant acid-resistant industrial applications, decorative decorative and structural structural exterior panels for major buildings, and grinding mill liners liners and and balls. balls. The Resources' dimension stone The results of a recent Minnesota Department of Natural Resources' stone inventory potential for for krther further development development of of inventory show show that northern Minnesota offers excellent potential high quality dimension dimension stone products. Field Field investigations investigations have identified twenty-two for quarry quarry development. development. Prospects prospect sites that exhibit potential for Prospectshave havebeen been identified identified in in Middle Proterozoic Proterozoic rocks (ca. 1100 1100 m.y.) of the Duluth Complex and Archean rocks (ca. 2700 m.y.) rock units. units. Prospects may.)of the Vermilion Vermilion Granitic Complex and other granitoid rock Prospects include include black, green, with aa variety variety of of textures. textures. Prospect green, pink, beige, and multi-colored stone with Prospect evaluation evaluation included included outcrop outcrop observations observationsthat that considered consideredjoint spacing, spacing, color, color, texture, texture, and and deleterious deleterious materials. Results Resultsof ofthe theinventory inventoryare aredescribed described in in the the following followingthree three MDNR MDNR reports: Dimension Dimension Stone StoneInventory Inventory of of Northern Northern Minnesota Minnesota 1991, 1991,Report Report 289; 289; Dimension Dimension and Dimension Dimension Stone Inventory Inventory of Stone Inventory of Northern Minnesota 1993, Report 298; and Northern Minnesota Minnesota 1995, 1995, Report Report 298-2. Cold Spring Spring Granite Granite Co. is currently currently leasing three of the prospect sites identified by the have opened opened quarries quarries on ontwo twoof ofthese theseleases. leases. Both dimension stone inventory study, and have utilize gabbroic h m these these sites sites is is marketed gabbroic anorthosite anorthosite of the Duluth Complex; the the stone stone from under Lake Superior SuperiorGreen. Green. under the the names names Mesabi Mesabi Black Black and and Lake This poster display shows shows products from all of the currently active quarries in the state state of Minnesota, along with samples of dimension stone prospects that were collected and prepared Minnesota, along with samples of dimension stone collected and prepared by the Minnesota Minnesota DNR-Minerals Division (see below). The The numbers numbers on on the the samples samples refer refer to locations on the index map. The table on the following page summarizes the geologic The table on the following page summarizes the geologic aspects aspects of the various various dimension stone dimension stoneproducts products of of Minnesota. Minnesota. ACKNOWLEDGMENTS AcmowLEDGMENTs All of the quarry companies listed on companies listed on the the following following table table kindly contributed contributed samples samples of of their their products to the Minnesota Geological Survey for this display. products to the Minnesota Geological Survey for this display. 46 �Sample Sample Company Company Trade Trade Name Name Geologic Geologic Unit 1 1 CSG Mesabi Black Complex Duluth Complex 2 CSG Lake Superior Superior Green Green 3 CSG Indian Iridian 4 CSG 5 Texture -1090 Ma —1090 Dominant Mineralogy P, cpx, urn ilm Duluth Complex Complex -1090 Ma —1090 P, cpx, gp, ilm p, very cgr, porph Isle Granite Isle Granite 18121770 Ma Ma 1812 - 1770 K, P, Q, Q, bi m-cgr, porph porph Charcoal Charcoal Black Reformatory Reformatory granodiorite granodiorite 1812±9 Ma 11 18 1Z?HMa P, K, Q, P, Q, bi, hbl, sph m-cgr, si. sl. porph. porph. CSG Diamond Diamond Pink Rockville Rockville Granite Granite 11812±9 8 1 2 s Ma Ma 11 K, P, Q, Q, bi, hbl, sph m-cgr, porph, rkv, 6 CSG Rockville Rockville Beige Beige Rockville Rockville Granite Granite Ma 11 1812±9 1812&9Ma K, P, Q, Q, bi, hbl, sph cgr, porph, rkv, 7 CSG Rockville Rockville White White Rockville Rockville Granite Granite Ma 11 11812±9 8 1 2 s Ma K, P, Q, Q, bi, hbl, sph cgr, porph, porph, rkv, rkv, 8 CSG Agate Agate Unnamed 2618±1 Ma 22 261833 Ma K, P, Q, Q, bi cgr ClY 9 DGC Bellingham Granite Granite Unnamed 2618±lMa? 2618klMa ? bi K, Q, Q, P, K, P, bi cgr C lY 10 JSC Quartzite Sioux Quartzite 1700Ma 1700 - 1750 Ma Q recrystallized recrystallized quartzite quartzite 11 CSG Rainbow Rainbow Morton Gneiss Gneiss 2600 2600- K, P, Q, bi, hbl gneissic banded, gbl 12 MKS Varieties Varieties of pink-gray Oneota Dolomite Dolomite Earliest Ordovician Earliest Ordovician dolomite dolomite bioturbated bioturbated micro-xln. micro-xln. 13 VSC vsc Varieties pink-gray Varieties of pink-gray Oneota Dolomite Dolomite Earliest Earliest Ordovician dolomite dolomite bioturbated bioturbated micro-xln. micro-xln. 14 BSC Winona Dolomite Dolomite Oneota Dolomite Dolomite Earliest Ordovician Earliest Ordovician dolomite dolomite bioturbated bioturbated micro-xln. micro-xln. Age - - 3600 Ma mgr, lam, lin, un, oph Company abbreviations: abbreviations: CSG -- Cold Spring Granite, JSC JSC -- Jasper Stone Stone Company, DGC - Dakota Granite Company, Company, MKS MKS -- Mankato-Kasota Stone, Inc., Company VSC Co., BSC -- Biesanz Stone Co. VSC -- Vetter Stone Co., Mineral abbreviations: abbreviations: P - plagioclase, plagioclase, K -- potassic feldspars, Q jim - ilmenite, ilmenite, sph sphene, Q - quartz, quartz, cpx - clinopyroxene, hbl -- hornblende, hornblende, bi -- biotite, ilm sph -- sphene, Mineral granophynic quartz/feldspar, gp - granophyric quartdfeldspar, xln xln -- crystalline crystalline Texture abbreviations: abbreviations: mgr mgr - medium-grained, Texture medium-grained, cgr cgr -- coarse-grained, coarse-grained, lam - igneous igneous lamination (cumulus or trachytoid), trachytoid), tin lin -- lineated, lineated, rkv rkv -- rapakivi, gbl-rapakivi, gbl granoblastic, oph oph -- ophitic, ophitic, porph porph -- porphyritic 1U-Pb I u - P ~zircon date (Goldich pers. commun., as reported in Horan and and others, others, 1987) 1987) MassachussettesInstitite Instititeof ofTechnology, Technology, pers. pers. comm., comm., 1998) 22U.Pb ~ - zircon ~ b date (Mark Schmitz, Massachussettes �GROUND GROUND WATER WATER RECHARGE, RECHARGE,DISCHARGE DISCHARGE AND AND RESIDENCE RESIDENCETIME TIMEIN INRICE RICE FOR LAND USE PLANNING IMPLICATIONS COUNTY, COUNTY,MINNESOTA MINNESOTA---- IMPLICATIONS FOR LAND USE PLANNING CAMPION, CAMPION?Moira Moira---- Minnesota Minnesota Department Department of of Natural Natural Resources Resources e-mail moira.campion@d~.state.mn.us e-mail--- moira.campion@dnr.state.mn.us Rice Rice county county is is located located 40 miles miles south south of of the Minneapolis-St. Paul metropolitan metropolitan area. The The county county contains containsurban, urban, suburban, suburban,and and rural rural areas areasand and faces facesincreasing increasingdevelopment developmentpressure pressure for for housing housing as as well as as for for recreational and high intensity agricultural agricultural purposes. Water Watersupply supply in in the the county county isis primarily primarily from fromground groundwater waterand andmost mostof ofthe the1600 1600wells wellsininthe thecounty countydata data base base are are completed completed in in the St. St. Peter-Prairie du Chien-Jordan aquifer. This Thisbedrock bedrockaquifer aquiferisis confined throughout the western and southeastern portions of the county and is unconfined confined throughout the western and southeastern portions of the county and is unconfinedinin the the east-central east-central and and northeast. northeast. The Thepotentiometric potentiometricsurface surfaceshows showsaaregional regionalhigh highin insouthwest southwest Rice Rice County Countyand and lows lowsin inthe the central centraland andnortheast northeastparts partsof ofthe thecounty countywhere wherethe theaquifer aquifer discharges dischargesinto intolocal localstreams. streams. Throughout Throughout most most of of the the county county the the aquifer aquifer isis protected protected from fromdirect directsurface surfacerecharge rechargeby by various consolidated and unconsolidated low permeability materials, except in the northeast various consolidated and unconsolidated low permeability materials, except in the northeast where where the the aquifer aquifer is is exposed exposed at at or or near near the surface. surface. The Thevarious variouslow lowpermeability permeabilitydeposits deposits and and their their distribution distribution result in different different recharge conditions conditions to the bedrock aquifer. In In the the northeast, northeast, where where the the aquifer aquifer is is not not protected protected by by overlying overlying material, material,recharge recharge to to the the aquifer aquifer occurs occurs directly through percolation from the land surface. In Inwestern westernRice Rice County, County,there there are are abundant lakes and wetlands in a hummocky terrain of thick supraglacial tills. Recharge to abundant lakes wetlands supraglacial Recharge to the the bedrock bedrock aquifer occurs occurs in complicated flowpaths flowpaths through the lakes and tills in this part of the the county. county. InInthe thesoutheast, southeast,the theDecorah-Platteville-Glenwood Decorah-Platteville-Glenwoodconfining confiningunit unitand andsome some older older tills tills cover cover the the aquifer. aquifer.Where Where this this relatively relatively thin thin package package of ofshales shalesand andlimestones limestonesisis continuous, continuous7the the St. St. Peter-Prairie Peter-Prairie du du Chien-Jordan Chien-Jordanaquifer aquiferreceives receivesvery verylittle littlevertical verticalrecharge recharge from the surface. Conversely, near the edge of this confining unit, recharge may be as from the surface. Conversely, near the edge of this confining unit, recharge may be asmuch much as fiomthe theaquifer aquifer as 30 30 times times greater greater than underneath this unit (Delin, (Delin, 1991). 1991). Discharge Dischargefrom occurs occurs where where ground ground water water drains drainsinto into the the Cannon CannonRiver, River, the the Straight StraightRiver, River,and andPrairie Prairie Creek. Creek. Residence Residencetime timeofofground groundwater waterwas wasestimated estimatedusing usingtritium tritiumand and14C 1% age-dating. age-dating. These These isotopic isotopic age age estimates estimatesconfirm confirmthe the conceptual conceptualmodel model of ofrecharge rechargein inthe thecounty. county. Ground water is youngest in the northeast where low permeability cover is absent youngest in the northeast where low permeability cover is absent and and oldest oldest in in the the southeast southeast under the Decorah-Platteville-Glenwood confining unit. Isotopic Isotopicresults resultsin in western western Rice Rice County County show showages agesgreater greaterthan thantritium tritium dating datinglimits limitsbut butless lessthan thanaafew few centuriesold. old. centuries Knowledge Knowledge of of these these differing differing recharge recharge conditions, conditions, coupled coupled with with geologic geologic and and hydrologic hydrologic information, provides county planners with an important water resource management information, provides county planners with an important water resource managementtool. tool. This This information information allows allows county county staff staff to to decide decidewhere where modification modificationto to current currentland land use use practices would minimize potential negative impacts on ground water quality. Basing Basing land land use planning decisions on resource management concepts rather than on politically based planning decisions on resource management concepts rather than on politically based situations situationswill will increase increasethe the chance chanceof of resource resource protection. protection. 48 �RICE RICE COUNTY, COUNTY, MINNESOTA Hydrogeology of the Hydrogeology St. Peter-Prairie Peter-Prairie du du Chien-Jordan Chien-Jordan Aquifer Aquifer -5m 5) 5 (0 ln - *- 64 - 0 0 0 2 4 I 1 I 6 Miles I Cross Section Section Legend Cross Legend Map Legend /V Potentiometric Potentiometric contour Cross section section Cross A A Well sampled Well sampled for chemistry + + Well measured for water level, level, but not sampled sampled Saturated thickness in feet LIII 0-100 R E 0 Aquifer absent '1 Aquifer ix Aquiferunconfined; unconfined; aquifer confined to west + 100-200 200-300 300-400 400-500 500-600 From: Rice Counly County Geologic Atlas, Atlas. Part 6.1997 6,1997 Original Scale l1:100,000. : l C J O , O ~ . Fmm: Copyright: Minnesota Minnesota Dept. Dept. of of Natural Natural Resources Cop*ght: 49 Unsaturated Unsaturated Recent waters; waters; tritium tritium >10 sf0TU TU Mixed waters; waters 1< 7c tntium tritium <10 c70 TU TU Vintage waters; tritium c <1 Vintage 7 TU and between 50 50 to 5,000 5,000years old Vintage waters; tritium e <1 l TU and Vintage 5,000to to 10,000 70,000years old more than 5,000 Decorah-Platteville-Glennwood Decorah-Plaffeville-Glennwmd Confining Confining unit unit St. Peter-Prairie Peter-Prairie du Chien-Jordan ChienJordan aquifer — Direction ofofgroundwater Direction groundwater flow flow �THE THE GEOLOGICAL GEOLOGICALSOURCE SOURCE OF OF ARSENIC ARSENIC IN IN GROUND WATER IN SOUTHEASTERN MICHIGAN MICHIGAN W.F. W.F. Cannon Cannon and and Alan Alan Kolker, Kolker, U.S. U.S. Geological Geological Survey, SurveyyReston, Reston?VA VA D.B. Westjohn, Westjohn?U.S. U.S. Geological Geological Survey, SurveyyLansing, Lansing?MI MI The ground ground water water in in parts parts of of nine counties in southeastern Michigan contains anomalous quantities of The dissolved arsenic, arsenic?presumably presumably derived from a natural source. Many Manywells wellstested tested by bythe theMichigan Michigan dissolved Department U.S.Environmental Protection Department of of Community Community Health and by the USGS exceed the U.S.Environmenta1 Agency's maximum maximum contaminant contaminant level level (MCL) of 50 pg/L Extreme values values are are as as Agency's .tg/L for drinking water. water. Extreme high as as 350 350 jtg/L. pgL. In In one one county county (Huron) (Huron) about about 30% of the tested wells exceeded the MCL for arsenic. high Most Sandstone, but other Most wells wells with with elevated elevated arsenic arsenic were completed in the Mississippian Marshall Sandstone? units, units?particularly particularlyglacial glacial aquifers, aquifers?can can also alsoyield yield arsenic-contaminated arsenic-contaminatedwater. water. The nine nine affected affected counties countieshave have aa combined combinedpopulation populationof of more more than than 22 million millionpeople. people.The TheMarshall Marshall The Sandstone Sandstone is is the principal bedrock bedrock aquifer aquifer in in most most of of the the affected affected counties countiesand and in in some someareas areasisisthe the sole-source aquifer. aquifer. These Theseconditions conditionscombine combineto to make make knowledge knowledge of of the the natural natural source source for for arsenic arsenic aa sole-source critical critical aspect aspectin in designing designingaa strategy strategyto to provide provideaa continued continuedsupply supplyof ofsafe safedrinking drinkingwater waterfor forthis this region. region. As As part part of of aa larger larger study study of of this this problem, we have been examining the lithology, mineralogy, and chemistry stratigraphic, and mineralogic chemistry of of the the Marshall Marshall Sandstone Sandstoneto better define the geographic, geographic?stratigraphic? distribution distribution of arsenic arsenic in bedrock. In InOctober October1997, 1997?aa well well was was drilled drilled and and cored cored to to collect collect aa complete complete stratigraphic overlying and and underlying underlying units. units. The stratigraphic section of the Marshall Sandstone and immediately overlying The hole County?near nearone oneof ofthe themost mostcontaminated contaminatedwells wellsknown knownininthe thestudy studyarea. area. hole was was drilled drilledin in Huron HuronCounty, Core Core from from that that hole hole and and cuttings cuttings and and core core from other producing wells have formed the basis for this study. study. The The Marshall Marshall Sandstone Sandstoneis is aa fluvial .fluvialto marginal marine sequence that is present at subcrop in a belt encircling the central part of the encircling the central part of the Michigan Michigan Basin. Arsenic-contaminated Arsenic-contaminatedground groundwater waterisisknown knownonly only along along the the eastern eastern flank flank of of the the basin. basin. As Asseen seenininthe theHuron HuronCounty Countycore, core,the theMarshall Marshallisisaavery very heterogeneous interbedded with massive heterogeneousunit unit of of mediummedium- to to coarse-grained, coarse-grained, gray to brown sandstone sandstone interbedded to to laminated laminated gray gray and and red red siltstone siltstoneand and thin units of black to gray shale. Fossil Fossilplant plantdebris debrisisispresent present and and pyrite pyrite isis common commonin in accessory accessoryamounts amountsin inmany manyunits. units. Arsenic Arsenic isis very very unevenly unevenly distributed distributed in in the Marshall. Highest Highestvalues valuesin inthe theHuron HuronCounty Countycore, core,up upto to 255 mg/kg, are in black shale units. Most sandstone and siltstone have an arsenic content below the 255 m a g yare in black shale units. Most sandstone and siltstone have an arsenic content below the analytically mglkgarsenic. arsenic. analyticallydetectable detectablelimit limit (5 (5 mg/kg), mgkg) but butsome somesandstone sandstonebeds bedscontain containas asmuch muchas as25 25mg/kg Average Average sandstones sandstonescontain contain about about 22 mg/kg mgkg arsenic, arsenic?and so even these relatively low values are anomalous. adjacentLapeer LapeerCounty Countycontain contain as as much much as as 350 350 mg/kg mgkg arsenic. arsenic.The The anomalous. Cuttings Cuttingsfrom fromwells wellsininadjacent strongly strongly anomalous anomalousarsenic arseniccontent content of of the the Marshall Marshall Sandstone Sandstonein in the the area area of of arsenic arseniccontaminated contaminated ground ground water water lends lendsstrong strongsupport supportto to the the earlier earlierbelief belief that that the the source sourceof of arsenic arsenicisisnatural naturaland andwithin within the the Marshall Marshallaquifer. aquifer. Electron Electron microprobe microprobe studies studies of of well cuttings cuttings from Lapeer and Tuscola Counties show that essentially all all arsenic arsenic is is in in pyrite. pyrite. Pyrite Pyriteisisubiquitous ubiquitousininthe theMarshall MarshallSandstone, Sandstone?typically typicallyin in trace traceconcentrations, concentrationsy but locally rock, mostly as porelocally constitutes constitutesfrom from aa few few percent to as much as 20 percent of the rock? occluding occluding cement. cement. Pyrite Pyrite formed formed during during several stages of diagenesis. Early Earlydiagenetic diageneticpyrite pyriteformed formed coatings on detrital grains. Framboidal pyrite formed in intermediate stages of diagenesis and coatings on detrital grains. Framboidal pyrite formed in intermediate stages of diagenesis and precipitated overgrowths. Late precipitated on on authigenic authigeniccarbonate carbonate and chlorite chlorite or on authigenic quartz overgrowths. Latestage stage pyrite pyrite encapsulated encapsulatedframboids framboidsand andin inplaces placesformed formeddisplacive displacivepyrite pyritemasses. masses. 50 �Arsenic Arsenic is very unevenly distributed in pyrite at virtually all scales, even to the limit of resolution of the microprobe. Many Manypyrite pyritegrains grains have have little little or no arsenic arsenic at the limit of detection (about 0.01 mass percent), whereas enrichment. whereas nearby grains grains (within the same rock chip) may have extreme arsenic enrichment. Individual 6.5 mass percent arsenic. Arsenic Arsenic shows a variety of Individual analyzed analyzed points points contain contain as as much much as as 6.5 modes of occurrence, but the most common is as strong enrichments enrichments in rims on individual framboids framboids (see figure). ItItappears appearsthat that aa majority majorityof of arsenic arsenic was introduced during an intermediate stage of pyrite diagenetic growth, at the end of framboidal pyrite formation. Both Both framboid framboid cores cores and and later laterovergrown overgrown pyrite are not enriched in arsenic. Some Someother othertrace traceelements elementsalso alsoshow showenrichment. enrichment.Some Somearsenicarsenicenriched enriched pyrite contains contains as much as 0.7 mass % Ni Ni and and0.5 0.5 mass mass% %Co. Co. A critical critical remaining remaining question question is where and how arsenic is released from pyrite to contaminate ground water. In Ingeneral, general,the theoxidation oxidationof ofarsenic-bearing arsenic-bearingpyrite pyritemust mustbe bethe thefundamental fundamentalcontrol controlof ofarsenic arsenic release. Most Mostarsenic arsenicseems seemsto to be be contained contained in in black shale units, which are not aquifers and have not been observed to be undergoing undergoing oxidation. oxidation. It seems likely, therefore, that arsenic is introduced to concentrations in the coarser sandstones that that form form the the aquifers aquifers within the ground water from smaller concentrations 25 mg/kg mglkg over several Marshall Sandstone. Observed Observedarsenic arseniccontent contentof of coarse coarse sandstone sandstoneisis as as high high as as 25 feet, or tens of feet, of section. The Thesandstones, sandstones,therefore, therefore,have have concentrations concentrationsseveral severalhundred hundredtimes times in quantitative terms terms to to provide provide enough arsenic to greater than the MCL for drinking water and are able in contaminate contaminate a large volume of ground water. Results Results to to date dateindicate indicate that that the the potential potentialfor for natural natural contamination of ground water is controlled by a variety variety of of factors factors including total total arsenic arsenic contamination characteristics of the the rock, rock, and by by poorly poorly know factors such as content of the rock and hydrologic characteristics biological mediation of pyrite solution and variable redox conditions of ground water in both time and place. in arsenic-rich pyrite, in Electron microprobe microprobe map showing showing framboids of arsenic-poor pyrite encased in turn overgrown overgrown by arsenic-poor pyrite. Map of iron distribution (left) outlines large pyrite grains (lightest shade) shade) that have grown in pore space between quartz clasts (black). Authigenic clay (intermediate gray) also fills pore space. space. Arsenic distribution is shown on the the right, right, the the same same field field of of framboids now completely enclosed view as the iron map. Arsenic is concentrated on rims of pyrite frarnboids within late late stage stage pyrite. pyrite. 51 �REiNTERPRETATION REINTERPRETATIONOF OF THE THE PENOKEAN PENOKEAN CONTINENTAL CONTINENTAL MARGIN MARGIN IN IN PART PART OF NORTHERN NORTHERN WISCONSIN WISCONSIN AND AND MICHIGAN MICHIGAN W.F. W.F. Cannon, Cannon, U.S. U.S. Geological GeologicalSurvey, Survey,Reston, Reston,VA VA G.L. G.L. Laberge, Laberge, UW-Oshkosh, UW-Oshkosh, Oshkosh, Oshkosh, WI WI J.J. S. Klasner, Kiasner, Western Illinois Illinois University, University, Macomb, Macomb, IL IL K.J. Schulz, U.S. Geological Survey, Reston, K J. Schulz, U. S. Geological Survey, Reston,VA VA The Thedepositional depositionaland and tectonic tectonic history history of of part part of of the the Penokean Penokean continental continental margin margin has has been clarified clarifiedby by field field studies, studies, and and examination examination of of previously previously proprietary' proprietary1magnetic, magnetic,electroelectromagnetic, drillcore coredata. data. AAcontinental continentalmargin marginterrane, terrane,informally informallycalled calledthe theMarquette Marquette magnetic,and anddrill terrane, terrene, inasmuch inasmuchas asitit isis composed composed largely largely of of rocks rocks of of the Marquette Marquette Range Range Supergroup Supergroup and and its Archeanbasement, basement,consists consistsof ofthree threesubterranes, subterranes,each eachwith withits itsown owncharacteristic characteristicdepodepoitsArchean sitional sitional and and tectonic tectonic history (see figure). The Thesubterranes subterranesare areseparated separatedby bymajor majorPenokean Penokean faults, faults,each eachprobably probablyaanorthward-directed northward-directedthrust. thrust. POWELL POWELLSUBTERRANE SUBTERRANE LAKESUBTERRANE SUBTERRANE PINE LAKE Marquette Vflyj metasedimentary MarquetteRange RangeSupergroup Supergroup metasedirnentary & metavolcanic metavolcanicrocks rocks [i] Graywacke. metavolcanic rocks, Graywacke, metavolcanic rocks,schist schist & Archeangranitic graniticrocks rocks Archean Basal Basalferrugenous ferrugenousunit unit Archean Archeangreenstones greenstones Archean Archean gneiss gneiss WISCONSIN TERRANES WISCONSINMAGMATIC MAGMATICTERRANES PARK PARK FALLS FALLS SUBTERRANE SUBTERRANE ±Xg Granite Graywacke, Graywacke,schist, schist, metavolcanic metavolcanicrocks rocks gi Archeangneiss - Metavolcanic rocks - Keweenwan thrustfaults faults — A.. — Keweenwan thrust Penokean 7 Penokeanthrust thrust faults faults y 1 'We Corporation for permission penuission to We thank thank Cominco ComincoAmerican American Incorporated and and Kerr-McGee Corporation to publish publish detailed detailed aeromagnetic area aeromagneticand and electromagnetic electromagnetic data data for for parts of our study a rea 52 52 �The Marquette terrane includes those areas where the Marquette Range Supergroup was deposited in a tectonically unstable environment for at least part of its depositional history and was subsequently significantly deformed and metamorphosed during the Penokean orogeny. The Theterrane terrane isis bounded bounded on on the north by areas where the Marquette Range Supergroup Supergroup was deposited in a stable cratonic or foreland setting and was not appreciably deformed during the Penokean orogeny (central Gogebic Iron Range for instance), and on the south by the volcanic arcs of the the Pembine-Wausau Pembine-Wausau terrane. terrane. The essential characteristics characteristics of each subterrane subterrane are outlined below. Pine Lake subterrane subterrane 0 Archean granite, granite, greenstone, greenstone, and and metagraywacke. metagraywacke. • Basement is Late Archean 0 Early Proterozoic has quartzite and dolomite of Proterozoic has quartzite and dolomite Chocolay Group at base. • Formation, iron-formation iron-formation including including shallow-water shallow-water oolitic ooliticjasper, jasper, and and • Menominee Group consists of Palms Formation, abundant volcanic volcanic rocks. rocks. Group abundant Group was was deposited deposited in in tectonically tectonically active region, probably in syndepositional grabens. Early Proterozoic rocks were strongly deformed, generally with increasing intensity of deformation deformation to the • south. south. basement rocks rocks were were not not deformed deformedpenetratively penetratively during duringthe thePenokean Penokeanorogeny. orogeny. • Archean basement Penokean granitic rocks are rare. • Penokean granitic rocks are rare. grade ranges ranges from from chlorite chloriteto to garnet garnet (locally (locally staurolite). staurolite). • Metamorphic grade Powell subterrane subterrane Powell • Basement is is Early and and Late Late Archean Archean gneiss. gneiss. 0 Proterozoic rocks widespread basal ferruginous slate slate and and lean leaniron-formation, iron-formation, Early Proterozoic rocks include include a widespread basal unit of ferruginous • Early quartzite, and black suffidic sulfidic slate and an overling succession of metapelitic metapelitic and and lesser lessermetavolcanic metavolcanicrocks. rocks. correlative with the Marquette Range Supergroup, The rocks are probably broadly correlative Supergroup, but details detailsof of correlation correlation are not known. known. basement was penetratively penetratively deformed deformed along along with with Early Early Proterozoic cover during the Penokean Penokean • Archean basement orogeny. orogeny. • Dikes and segregations segregations of of Penokean Penokean granitic granitic rocks rocks are are widespread. widespread. pressure metamorphism metamorphism occurs throughout throughout. Pelitic assemblages are biotitebiotite• High temperature and high pressure gamet-staurolite-kyarnte. garnet-staurolite-kyanite. Park Falls subterrane • Basement is is Archean Archean gneiss. gneiss. 0 politicschist, schist,carbonaceous carbonaceoussulliclic sulfidicslate, slate, and and subordinate subordinatemetavolcanic metavolcanicrocks. rocks. • Early Proterozoic rocks are peitic equivalent to the Marquette Range Supergroup but details of correlation The rocks are probably broadly equivalent correlation are are unknown. unknown. 0 are intensely folded folded in in multiple multiple folding foldingevents. events. • Rocks are 0 segregationsof of Penokean Penokean granitic graniticrocks rocks are are abundant. abundant. • Dikes and segregations Peliticassemblages assemblagesare arebiotite-garnet-sillimanite. biotite-garnet-sillimanite. • Metamorphism is moderate temperature and pressure. Pelitic The assemblage assemblage of subterranes subterranes hereby defined in Wisconsin and Michigan is similar to the assemblage known in analogous parts of the Penokean orogen in Minnesota. In Inparticular, particular, we suggest suggest that the Flambeau Flowage Fault in Wisconsin and Michigan is the eastward extension of the Malmo discontinuity discontinuity in in Minnesota. Minnesota. Both structures structures thrust Archean gneiss and highly metamorphosed Early Proterozoic strata northward over less deformed and metamorphosed Early Proterozoic Proterozoic strata. strata. 53 �GEOGRAPHICINFORMATION INFORMATIONSYSTEM SYSTEMON ONTHE THE GEOLOGY GEOLOGYAND AND COPPER COPPER GEOGRAPHIC DEPOSITS DEPOSITSOF OFTHE THEKEWEENAW KEWEENAW PEMNSULA PENINSULA W.F. W.F.Cannon, Cannon,U.S. U.S.Geological GeologicalSurvey, Survey,Reston, Reston,VA VA Michele MicheleE. E.McRae, McRae,Oak OakRidge RidgeAssociated AssociatedUniversities, Universities,Reston, Reston,VA VA Suzanne Reston, VA VA Suzanne W. W. Nicholson, Nicholson, U.S. U.S. Geological Geological Survey, Survey,Reston, Twonew newproducts productson onthe thegeology geologyand andmineral mineraldeposits depositsof ofthe theKeweenaw KeweenawPeninsula Peninsulaand and Two surroundingarea areahave haverecently recentlybeen beendeveloped: developed:aatraditional traditional1:100,000 1:100,000scale scaleU.S. U. S.Geological Geological surrounding Surveygeologic geologicmap map(now (nowininpress) press)and andaageographic geographicinformation informationsystem system(GIS) (GIs)database. database. Survey These Theseproducts productsare arebased based largely largelyon ondetailed detailedgeologic geologicmaps, maps, many manyatat aascale scaleof of1:24,000, 1:24,000, published during during the the past past 50 50 years. years. They Theypresent presentnew newdata dataand andinterpretations interpretationsininparts partsofofthe the published area.The Thepaper paperproduct productwas wascompiled compileddigitally digitallyand anddigital digitalproduction productiontechniques techniquesare arebeing being area. used usedtotostreamline streamlinethe theprinting printingprocess. process. /1 \ Formations Paleozoic undivided J Jacobsville Sandstone Freda Sandstone Nonesuch Formation Copper Harbor Conglomerate Indiana Felsite Portage Lake Volcanics Diabase dikes Siemens Creek Volcanics Michigamme Formation Granitic gneiss Geology Geologyofofthe dieKeweenaw KeweenawPeninsula Peninsulaand andvicinity vicinitygeneralized generalizedbybyformation. formation. 54 �The The data data were were developed developed using using the Environmental System Resource Institute's Institute's ARC/INFO ARCIINFO softwareand and exported exported to to ArcView. ArcView. ArcView ArcViewisisaadesktop desktopmapping mappingsoftware softwarepackage packagethat that software provides provides aa variety variety of of tools tools for for the display, display, query, analysis, and output of geographically geographically referenced data sets. sets. This Thisparticular particular GIS GIs consists consistsof of coverages coverages and tabular data on on the the geology,structure, structure,mines, mines, mineral mineral deposits, deposits, hydrography, hydrography, and and transportation transportation networks networks of of the the geology, area. Most Mostofofthe thedetail detailfrom fromthe thesource sourcemaps maps has has been incorporated incorporated into the database. database. Map Map area. views showing showingfull fall detail detail can can be be constructed; constructed; however, however, the the data data have have been structured structuredto to allow allow views generalizationby by age, age, rock rock type, type, tectonic tectonic setting, setting, or or stratigraphic stratigraphicrank. rank. The Thefigure figureabove above was was generalization generated in inArcView, ArcView,by by generalizing generalizingthe thegeologic geologicunits unitsbased basedon onstratigraphic stratigraphicformation. formation. generated ArcView ArcView also alsoallows allows the the user user to to access accessinformation information either either by interactively interactivelyselecting selecting features features on on aa map map view, view, or or by by performing performing logical logical selection on the data tables. For Forexample, example,clicking clicking on tool will will open open aa window window that that provides provides tabular on aa mineral mineral deposit deposit with the 'identify' tool information informationon onmines minesthat thatworked workedthe thedeposit, deposit,amount amountof ofproduction, production,years yearsofofproduction, production, and and an an estimate estimate of of the the amount amount and and grade of remaining identified resources. resources. AAlogical logicalsearch search could could be be used to to identify identify native native copper copper lodes lodes with greater than 1% 1% Cu. Finally, Finally,this thisproduct product will will include includegeologic geologiccross crosssections, sections,aa correlation correlation chart, chart, aa description description of of map map units, units, and and interpretative interpretativetext. text. The Thecross crosssections sectionsare aredynamically dynamicallylinked linkedto tothe thecross crosssections sectionslines lineson on the themap mapview. view. 55 �GRAVITY VIRGINIA HORN HORN AREA, AREA, GRAVITY AND AND MAGNETIC MAGNETIC STUDIES STUDIES IN IN THE VIRGINIA MINNESOTA NORTHEASTERN MINNESOTA CHANDLER, Val W Minnesota CHANDLER, Va! W.,.,JIRSA, Mark A., and LIVELY, Richard L. Minnesota Geological Survey, 2642 2642 University Ave., St. St. Paul, Paul, MN MN 55114 551 14 Geological Survey, (chandOO4@maroon.tc.umn.edu) (chand004@maroon.tc.umn.edu) and magnetic magnetic data data were were used used to to supplement supplement geologic geologic field field mapping mapping of of Archean Archean rocks rocks Gravity and of the Virginia Horn area of northeastern Mimesota. Minnesota. Although Although outcrop outcropcontrol controlisis locally locally excellent, gravity gravity and and magnetic magnetic data data assist assist to a minor minor degree degree in mapping mapping areas areas covered covered by by excellent, glacial deposits and mine dumps. More More importantly, importantly, they provide additional information on geologic structure at depth. Preexisting Paleoproterozoic Preexisting subdivisions subdivisionsof the Archean and Paleoproterozoic rocks were used to guide mapping and geophysical work. Although the gross lithologic divisions divisions have have remained remained essentially essentiallyunchanged, unchanged, many many details detailsof of their their stratigraphic stratigraphicand and structural relations are now much better better known. known. Gravity data used in this study consist of of together with with 203 203 new new stations. stations. The new preexisting stations in the state-wide database together gravity stations development of a 50 km stations fill fill gaps in the previous coverage, and allow development northeast-southwest Virginia Horn area, area, together together with northeast-southwest profile profile across across the the Archean rocks of the Virginia (5-15 km) northwest-southeast profiles. The The magnetic magnetic data data are are from from the high shorter (5-15 five shorter resolution aeromagnetic resolution aeromagneticsurvey survey of of Minnesota; Minnesota; line line spacing spacing in in the the Virginia Virginia Horn Horn area area is is 400 400 Subsurfacestructure structurewas wasinvestigated investigatedusing using gravity gravity and and magnetic modeling on the long m. Subsurface profile. The gravity gravity and and magnetic data data were interpreted using grid images of processed data. Unfiltered and Unfiltered and derivative-enhanced derivative-enhanced versions versions of the the gravity and and aeromagnetic aeromagneticgrids grids reveal reveal many details of the bedrock geology. The Thenorthern northern part part of the the study area is underlain by Archean granitic rocks of the Giants Range Batholith. ItIt isis characterized characterizedby by aa strongly strongly negative Bouguer negative Bouguer gravity gravity anomaly anomaly and and aa busy, busy, moderatemoderate- to to high-amplitude high-amplitude magnetic magnetic mafic phases phases within within the the batholith is indicated indicated by signature. The Thepresence presenceof ofintermediate intermediateto to mafic signature. more more magnetic areas areas that that are are associated associated with highs in the derivative-enhanced derivative-enhanced gravity gravity data. Derivative-enhanced magnetic magnetic data data also delineate several previously unidentified northweststriking faults that extend across the batholith. A discontinuous discontinuous sliver sliver of high-grade strildng batholith. A metavolcanic metavolcanic and metasedimentary rocks, the Mimtac Minntac sequence, occurs along the the southern margin of the batholith. AAnegative negativeBouguer Bouguergravity gravity anomaly anomaly implies implies that the supracrustal supracrustal rocks of the Mimtac Minntac sequence are under-plated under-plated by by granitic graniticrocks rocksatatshallow shallowdepths. depths. The Minntac sequence sequence is separated separated from Archean rocks to the south by the east-west striking Laurentian fault. South Laurentian Southof ofthe theLaurentian Laurentianfault faultsubsub- to to low-greenschist low-greenschist grade grade metavolcanic metavolcanic and metasedimentary metasedimentary rocks rocks of the the Archean Archean Mud Lake Lake and and Midway sequences sequences are are characterized by aa positive characterized positive gravity gravity anomaly anomaly and and an an extremely extremely subdued subduedmagnetic magnetic signature. signature. Rocks of the Mud Lake sequence form aa broad broad southwest-plunging southwest-plungingsyncline. syncline. To the south are and west, the supracrustal supracrustal rocks rocks of the the Minntac, Midway and and Mud Lake Lake sequences sequences are Group. Regional covered by the Paleoproterozoic Animikie Group. Regional gravity data indicate that the major belt beltbeneath beneaththe theAnimikie Animikiebasin. basin. The The Biwabik Biwabik Archean rocks extend southwest as aa major Formation of the high-amplitude Iron Formation the lower lower Animilde Animikie Group Group is associated with complex, high-amplitude magnetic signatures; signatures; magnetic magnetichighs highsdelineate delineateoxide-rich oxide-richtaconites taconitesand andmagnetic magneticlows lows delineate natural ores and faults. delineate natural ores and faults. Gravity constmined by surface geologic mapping and rock Gravity and and magnetic modeling was constrained the properties determined from surface samples. The The models indicate that most structures in the Archean rocks have near-vertical dips. The Giants Range Batholith and the low-grade supracrustal extend to to about about 55 km km depth. depth. The supracrustal rocks of the Midway and Mud Lake sequences extend The composition Minntac sequence composition of the the crust crust below 5 km remains uncertain, although the Mimtac (which we infer to have been uplifted along the Laurentian fault) may yield clues because it has been extensively extensively invaded invaded by tonalitic and other early phases of the Giants Range Batholith. Models sedimentaryrocks rocksof of the theMud Mud Lake Lake Modelsclearly clearlyshow showthat thatthe thelow-grade low-gradesedimentary as thick thick as as 1 km km are are underlain underlain sequence lie within a structural structural trough; low-density sediments as 56 �by by moderately moderately high-density high-density rocks rocks inferred inferred to be largely basaltic. Thickness Thicknessof of the the sedimentary rocks rocks increases increases in in stepwise stepwise fashion fashion northwestward northwestward towards the center center of the sedimentary basin against againstnortheast-striking northeast-strikingfaults. faults. Sediment Sedimentthickness thicknessisisalso alsointerpreted interpretedto to increase increase basin appreciably to to the the northeast. northeast. These Theseresults resultsdemonstrate demonstratethat that gravity gravity and and magnetic studies are appreciably valuable valuableto to aa geologic geologicmapping mappingprogram, program,even evenin inareas areasof ofabundant abundantoutcrop outcropcontrol. control. ACKNOWLEDGMENTS ACKNOWLEDGMENTS This This study studywas wassupported supportedby by the theMinnesota MinnesotaLegislature Legislaturethrough throughthe theState StateSpecial Special Appropriation an appropriation appropriationrecommended recommended by the Minnesota Minnesota Minerals Coordinating Coordinating Appropriationand and an Committee. U.S.S.Steel SteelCorporation, Corporation,Inland InlandSteel SteelMining MiningCompany, Company, Committee. The Theauthors authorsthank thankU. Cliffs LTV Mining Mining Company, Company, American American Shield Company, the Cliffs Mining Mining Services ServicesCompany, Company, LTV Duluth Duluth Mesabi Mesabi and and Iron Iron Range Range Railway Railway Company, Company, and and the Minnesota Minnesota Power Power Company Company for for access access to their their properties properties and and for for providing providing elevation data. 57 �MINERAL POTENTIAL POTENTIAL ASSESSMENT ASSESSMENT OF NORTHERN ST.LOUIS ST.LOU1S COUNTY, COUNTY, SOUTHEASTERN KOOCHICHING COUNTY, AND NORTHEASTERN ITASCA COUNTY, SOUTHEASTERN MINNESOTA Va! Chandler, M.A. Jirsa, and G.B. Morey, Minnesota Geological Survey Survey Val W. Chandler, Presented Presented by Tom Tom Lawler, Lawler, Department Department of Natural Resources, Division Division of Minerals Minerals Minnesota Geological Survey The Minnesota Survey in a contract with the Department of Natural Resources, Resources, Division of Minerals Minerals produced a geologic map and mineral-potential assessment assessment of a contiguous contiguous township area twenty-six township area in northern St. Louis, southeastern southeastern Koochiching, and northeastern northeastern Itasca Counties, Counties, Minnesota. Six Six tholeiitic to caic-alkaline calc-alkaline volcanic sequences sequences of the Archean Archean Wawa subprovince subprovince are resolved that are usually separated by faults or metasedimentary belts, and are intruded intruded by a variety of syn- to late tectonic granitoid plutons. Eight criteria criteria are identified identified which indicate indicate potential for twenty-two lode gold deposits; Six Six criteria criteria identify identifj potential potential for for two two iron-formation hosted replacement gold deposits; Seven criteria identify potential for four iron-formation Seven criteria identifj potential four volcanic associated massive sulfide deposits; Seven Seven criteria criteria identify identi@ potential for maficultramafic intrusion intrusion hosted Cu-Ni-PGE deposits; Six Six criteria criteria identify identifj potential potential for for komatiite komatiite associated Ni-Cu-PGE deposits deposits (although (although the criteria criteria were developed only one area with PGE potential was identified); identified); and Two Two criteria identify identifj potential for two kimberlite kimberlite hosted diamond diamond deposits. All of these W h e r evaluation evaluation these areas areas are to be regarded with appropriate caution and further would require require detailed detailed exploration explorationincluding including drilling. The compilation map (Plate compilation of the bedrock geologic map (Plate 6), 61, the magnetic and gravity gravity model crosssections (Plate 7) and the mineral mineralpotential potential assessment assessment map map (Plate (Plate 9) used available available geologic geologic data combined combined with gravity gravity and and airborne airborne magnetic data. The interpretation interpretation used gridded gridded forms forms of of geophysical phenomena. Using geophysical data data that have have been enhanced enhanced to emphasize near-surface geologic phenomena. Using polarization the UTM based grid grid the aeromagnetic aeromagnetic data were enhanced by reduction to vertical polarization and calculation calculation of the second second vertical derivative. These procedures shift anomalies anomalies more directly directly over their sources anomalies to help clarify fiom regional scale anomalies clarifj the sources and eliminate eliminate interference from short wavelength wavelength signatures signatures of shallow shallow sources sources that lie at or near the Precambrian Precambrian surface. surface. With With aa similar similar procedure the gravity data data were enhanced by the calculation of the second second vertical derivative after smoothing by continuation to a level of two kilometers above derivative smoothing continuation kilometers above surface surface to eliminate eliminate "noise" caused caused by by variations variationsin in overburden overburden thickness. thickness. Much Much of of the the quantitative quantitativeanalysis analysisof of this this study are based on the Werner deconvolution method of inverse modeling using the approach approach proprietary software and proprietary software developed developed by by R.J. R.J. Ferderer Ferderer (1988). (1988). The contract resulted in a twenty-seven page open-file report 97-5: Chandler, V.W., Jirsa, M.A. and Morey, G.B., (1997) Mineral potential assessment of northern St. Louis County, southeastern southeastern Koochiching Koochiching County, County, and northeastern Itasca County, Minnesota. The report report includes includes a detailed detailed account of analytical procedures and results, rock property data, six cross cross sectional studies using gravity and magnetic modeling, five tables and nine plates displaying displaying results. This report and the plates plates are available in hard copy and digital digital format format at the Minnesota Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota, 55114-1057, 551 14-1057, Phone (612) (612) 6276274780 also the Minnesota Department of Natural Resources, 1525 Third Avenue East, Hibbing, Minnesota Department of Resources, 1525 Hibbing, Minnesota Minnesota 55746-1461, 55746-1461, Phone Phone (218) (218) 262-6767. 262-6767. 58 �EXTENSION OF THE HURONIAN MAGMATIC SUITE INSIDE INSIDE THE THE GRENVILLE PROVINCE: PROVINCE: NEW ZIRCON ZIRCON U-Pb EVIDENCE FROM THE THE GRENVILLE FRONT TECTONIC TECTONIC ZONE ZONE IN IN STREET STREETTOWNSHIP, TOWNSHIP,SUDBURY SUDBURY REGION, ONTARIO. F. Corfu, Museum, 100 100Queen's Queen'sPark, Park,Toronto, Toronto,ON ON M5S 2C6 and C o f i , Royal Ontario Museum, R.M. Easton, Precambrian Precambrian Geoscience Geoscience Section, Section, Ontario Ontario Geological GeologicalSurvey, Survey,933 933 Ramsey Lake Road, Sudbury, Sudbury, ON ON P3E P3E 6B5 6B5 The Sudbury region is characterized by very complex geological relationships relationships due to to the confluence and overlapping of multiple geological domains ranging in age from Archean to rifling of the Archean crust led to the the deposition of Neoproterozic. Early Paleoproterozoic rifting extensive ian Supergroup and was initially extensive clastic clastic sedimentary sedimentaryassemblages assemblagesof of the the Huron Huronian accompanied by the emplacement emplacement of bimodal mafic mafic and felsic, felsic, intrusive intrusiveand and extrusive extrusiverocks. rocks. Although the distribution distribution and petrogenetic features of these magmatic rocks is well understood in the region west of Sudbury, Sudburyythe fate of the Huronian remains a matter of speculation farther to the Frontythe only only exception exception being being the the previously previously dated dated River RiverValley Valley east and south of the Grenville Grenville Front, gabbro-anorthosite. In conjunction program gabbro-anorthosite. conjunction with an Ontario Ontario Geological Geological Survey S u ~ e mapping mapping y program along alongthe the Southern-Grenville Southern-GrenvilleProvince Province boundary, we have examined examined two examples examples of of metamorphosed metamorphosed granitic bodies and a metapyroxenite plug straddling the Grenville Front Front tectonic tectonic zone in Street 15 km east of Sudbury. Sudbury. Township, roughly 15 The metapyroxenite is part of a suite of small bodiesy bodies, generally less than 500m in size, that occur Coniston and and River River Valley. Valley. Mineralogically, Mineralogically, within the Grenville Grenville Front Front tectonic tectonic zone zone between between Coniston these bodies consist of roughly equal amounts of orthopyroxene phenocrysts (0.5-5 cm in size) in locally olivine phenocrysts are preserved. Metamorphic crystallization in an amphibole matrix; locally these bodies increases with increasing increasing distance from the Grenville Front, consequently, sampling was conducted on a body located only 250m southeast of the Grenville Front. The metapyroxenite contains highly resorbed, prismatic zircon yielding a U-Pb U-Pb data data array array that that points points toward toward an an upper upper intercept age of about 2490 Ma. The age corresponds corresponds approximately approximately to to that that of of the the East-Bull East-BullLake Lake and Shakespeare-Dunlop intrusionsyemplaced emplaced in in Archean crust crust at at the the margin margin Shakespeare-Dunlop (a.k.a. Agnew Lake) intrusions, Huronian basin basin east east of of Sudbury. Sudbury.On On the the basis basis of of SEM SEM examination, examinationymost mostof ofthe thezircon zirconfound found of the Huronian in this sample is located within the orthopyroxene orthopyroxene phenocrysts, in in conjunction conjunctionwith with Cr-spinel Cr-spineland and chromite. In addition, the matrix of the metaproxenite is chemically differentiated. Thus, we are confident that the zircon fraction yielding the upper intercept age of 2490 Ma dates emplacement metapyroxenite was metamorphosed and developed metamorphic zircon during of these rocks. The metapyroxenite an event at about about 1700-1600 1700-1600Ma, Ma, and and was was subsequently subsequentlyoverprinted overprintedby by Grenvillian-age Grenvillian-age metamorphism. metamorphism. Two granitic bodies were sampled. The first was a foliated monzogranite located in an area south of the Ess Creek fault and north of the Grenville Front boundary fault as mapped by Lumbers 59 �(1973). This fault-bounded fault-bounded region has been variously variously assigned assigned to the Southern Southern or or Grenville Grenville provinces, and has been subjected subjected to middle to upper amphibolite amphibolite facies facies metamorphism. metamorphism.The The second body is located about about 15 15 km south of the first, and is is one one of several several similar similar bodies bodies located located within the Grenville Grenville Province. Province. Both sampled granites, granites, as as well as as other other bodies bodies south south of of the the Grenville Grenville plutonic body or a suite of Front, are chemically similar, suggesting they form part of a larger plutonic FeOt0 >35% intrusions. intrusions. In particular, particular, they they are are characterized characterizedby by Si02 Si0266-72%, 66-72%, Al203 A120311.9-12.6%, 11.9-12.6%, FeotO&' >3.5%, CaO >1.5%, La/Yb >IS%, EufEu* Eu/Eu* .55-.70, -55--70,L a b 5-8, and Gd/Yb GdNb 1.2-1.65, 1.2-1-65, and are identical identical in major major and and REE geochemistry with Stobie Formation Formation dacites from both the Sudbury Sudbury and Street Street Township Township areas. areas. On On they plot plot in in the the Within-Plate Within-Plate granite granite field. field. In In various geochemical discrimination diagrams, they contrast, felsic rocks of the Murray and Creighton granites granites and the Copper Copper Cliff Cliff rhyolite rhyolite have have lower Feotoh' FeOt0 contents contentsand andhigher higherSi02 Si02and andalkali alkalicontents. contents.In Inaddition, addition,REE REEdata, data,only onlyavailable available from the Copper Cliff rhyolites, have Eu/Eu* EufEu* c.5, <.5, LLa/Yb <5.5and andGdffb Gd/YbC.75. <.75. The foliated a b -3.5 monzogranite monzogranite defines defines a U-Pb zircon age age of about about 2460-2450 Ma, which overlaps overlaps the the age age of of some some of the youngest magmatic expressions of the Huronian Huronian rifting rifting event event such such as as the the Copper Copper Cliff Cliff rhyolite rhyolite and the Hearst Hearst dyke dyke swarm. swarm. The The granite granite was was overprinted overprinted by by Grenvillian Grenvillianmetamorphism metamorphism that strongly, strongly, but not not totally totally reset reset the the titanite titanite ages. ages. The The zircon zircon data data for for the the second secondgranitic graniticbody body display more pronounced effects of both a 1700-1600 1700-1600 Ma event and the Grenvillian Grenvillian orogeny orogeny at at about 990-980 Ma, but are nevertheless nevertheless consistent consistent with a Huronian Huronian age and with the the chemical chemical similarities similarities between these granitic granitic intrusions. intrusions. are consistent consistent with field field relations relations which which show show aa close close spatial spatial The ages on the bodies reported here are relationship between the metapyroxenites, metapyroxenites,the the granites, granites, and and mesocratic mesocratic to to anorthositic anorthositicgabbros gabbros relationship likely correlative with the ca. 2475 Ma River Valley gabbro-anorthosite. gabbro-anorthosite. In addition, addition, the foliated foliated monzogranite is spatially associated with a thin sliver of mafic and felsic metavolcanic rocks that monzogranite that correlated with the the Huronian Huronian Stobie Stobie Formation. Formation. The The latter latter are are the the only only Huronian Huronian have been correlated volcanic rocks so so far far identified identified east east of of Sudbury. Sudbury. These These field field relationships, relationships,in in conjunction conjunctionwith withthe the geochronological results results reported reported herein, herein, suggest suggest that that the the Huronian Huronian magmatic magmatic province provinceisismore more geochronological extensive extensive east of of Sudbury Sudbury than previously previously recognized. In In addition, addition, felsic felsic magmatism magmatismof ofHuronian Huronian longer confined confined to to the the vicinity vicinity of of Copper Copper Cliff, Cliff, and and indeed, indeed, could could be be more more extensive extensivethan than age is no longer previously thought, thought, particularly particularly in in the the area area of of the the little littlestudied studiedeastern easternCobalt Cobaltplate. plate. previously Reference: 1973. River Valley area; Ontario Ontario Division of Mines, Preliminary Map, P.844. Lumbers, S.B. 1973. P.844. 60 �KINEMATIC KINEMATIC FABRICS FABRICS NEAR MINE MINE CENTRE, CENTRE, ONTARIO: EVIDENCE EVIDENCE FOR A MODIFIED MODIFIED TRANSPRESSION TRANSPRESSION MODEL. MODEL. Czeck, and Hudleston, Hudleston, P. J., Department Department of Geology and Czeck, D. M. and Geophysics, Geophysics, University of Minnesota, Minnesota, 310 3 10 Pillsbury Pillsbury Dr. Dr. SE, SE, Minneapolis, MN 55455 55455 The The boundary boundary between between the the Quetico Quetico and and Wabigoon Wabigoon subprovinces subprovinces of the the Archean Archean Superior Superior Province is characterized by ductily deformed GreenschistGreenschist- Arnphibolite Amphibolitefacies faciesrocks. rocks. The two subprovinces continental accretion accretion processes. processes. The subprovinces have been amalgamated through continental working working kinematic kinematic model model to to describe describe this this area area is is transpression, transpression, which which explains explainsthe the dominant dominant flattening flattening fabric fabric in the vertical vertical plane and the evidence for noncoaxial strain noted in the horizontal plane. Theoretical Theoreticalwork workon onclassical classicaltranspression transpression has has shown shown that that the the long long axis of the the strain strain ellipsoid,' ellipsoid,and either vertical or or axis and thus the mineral lineation, are necessarily either horizontal. horizontal. Structural Structuralfield fieldwork workin inthis thisstudy studyhas hasshown shownthat that the the lineations lineationsalong along the the Wabigoon-Quetico boundary plunge between 0-90' 0-90° within within the the foliation foliationplane. plane. Therefore, a modification modification to to the the three-dimensional three-dimensionaltranspression transpressionmodel model isis necessary necessaryto toadequately adequately describe describe the deformation deformation process. One Onepossible possiblemodification modificationto to transpression transpression which which explains explains the the oblique oblique lineations lineations is is heterogeneous heterogeneous extrusion extrusion due due to anastomosing anastomosing shear shear zones. zones. 61 �New New Aeromagnetic AeromagneticSurveys SurveysininWisconsin Wisconsinby bythe theU.S. U.S.Geological GeologicalSurvey Survey David DavidL. L.Daniels, Daniels,Stephen StephenL. L.Snyder, Snyder,Suzanne SuzanneW. W.Nicholson, Nicholson,William William F. F. Cannon, Cannon,U.S. U.S.Geological Geological Survey, Survey, MS MS 954 954National National Center, Center,Reston, Reston, VA VA20192 20192 Aeromagnetic Geological Aeromagneticsurveying surveyingin in Wisconsin Wisconsin over over the the past past 10 10years yearsby by the theU.S. U. S.Geological Survey Survey(USGS) (USGS)has has added addedconsiderably considerably to to the the coverage coveragein in the the state stateand and to tothe thedigital digital aeromagnetic database of the USGS Mineral Resources Program. Initial efforts aeromagnetic database of the USGS Mineral Resources Program. Initial effortswere weredirected directed toward towardcompleting completingthe thecoverage coverageininthe thenorthern northernpart partofofthe thestate stateininwhich whichPrecambrian Precambrianbedrock bedrockisis atatthe thesurface surfaceor orcovered coveredby byglacial glacialdeposits. deposits.The Theflight-lines flight-lineswere wereflown flownin in aa N-S N-S direction direction because because of of the the predominant predominanteasterly easterly or or northeasterly northeasterly grain grain of of the the geology, geology, were were spaced spaced '/2-mile %-mile apart, apart,and andflown flown at at 500 500or or1000 1000ftftabove aboveterrain. terrain. The Thesurveys surveyswere weredesigned designedto toextend extendthe thelarge large survey 1990), surveyconducted conductedby byJohn JohnKarl Karlofofthe theUniversity UniversityofofWisconsin, Wisconsin,Oshkosh Oshkosh(Karl, (Karl, 1986; 1986;King, King,1990), priorto to1977. 1977. prior In In1988, 1988,the theUSGS USGSflew flewaa3900 3900line-mile line-mileaeromagnetic aeromagneticsurvey surveyin in the thenorthwestern northwesterncorner comer of ofWisconsin Wisconsin south south of of Lake Lake Superior. Superior.In In 1996, 1996,USGS USGSsurveying surveyingwas was continued continued in in two two areas areas adjacent to the 1988 survey (see index map) for an additional 6700 line-miles. These two adjacent to the 1988 survey (see index map) for an additional 6700 line-miles. These twosurveys surveys completed completed the the coverage coverageof ofthe thevolcanic volcanicand andsedimentary sedimentaryrocks rocksin in the theMidcontinent Midcontinentrift riftsystem. system. These Thesenew new data datahave haveled led to tonew newinterpretations interpretationsofofstructures structuresininthe thehighly highlymagnetic magneticKeweenawan Keweenawan basalt basalt flows flows in in the the St. St.Croix Croixhorst horst (Cannon (Cannonand and others, others,1997). 1997).In Inthe themost mostrecent recent(10/97-3/98) (10197-3198) survey, survey, aeromagnetic aeromagneticdata datahave havebeen beenacquired acquiredininthree threeblocks blocksin in aabroad broadswath swaththrough throughthe the central central part part of ofthe the state, state,ininthe theMarinette-Green Marinette-GreenBay Bay area, area, the theWisconsin Wisconsin Rapids Rapids area, area, and and the the Mississippi Mississippi River River area area (about (about16,000 16,000line-miles). line-miles). In In addition, addition,two two small small areas areas along along the the Wisconsin-Michiganborder borderwere werefilled filledin. in. Wisconsin-Michigan In 50m) veneer (<150m) veneer of of In much much of ofthe thearea areacovered coveredby bythe themost mostrecent recentsurvey, survey,aathin thin(<1 magnetically magnetically transparent transparentCambrian Cambriansandstone sandstoneoverlies overliesthe themore morehighly highly magnetic magneticEarly Earlyand andMiddle Middle Proterozoic Proterozoicrocks; rocks;ininthe thewestern westernpart partnon-magnetic non-magneticMiddle MiddleProterozoic Proterozoicsedimentary sedimentaryrocks rocksform form part part of of the the basement. basement. Thus, Thus,although althoughthis thisisisan anarea areaof ofvery very little little outcrop, outcrop, the the aeromagnetic aeromagnetic data data effectively effectively delineate the structure structureand and character characterof ofthe theburied buried basement basement rocks. rocks.The Theenhanced enhanced understanding understandingof of the the basement basement geology geologyprovided providedby by the theaeromagnetic aeromagneticsurvey surveywill will allow allow better better evaluation evaluationof of the the mineral mineral potential potential of of this this region region and and aid aid in in regional correlations correlationsof of basement terranes terranesin in the the region. region. Maps Maps of of the the new new aeromagnetic aeromagneticsurvey survey and the current current aeromagnetic aeromagnetic compilationof ofWisconsin Wisconsinwill will be be shown. shown. compilation References Cited Cited References Cannon, Cannon, W.F., W.F.,Daniels, Daniels, D.L., D.L., Snyder, Snyder,S.L., S.L.,1997, 1997,New Newaeromagnetic aeromagneticmap mapofofthe theMidcontinent Midcontinent Rift Rift in in Northwestern NorthwesternWisconsin Wisconsin and and adjacent adjacent Minnesota; Minnesota;Geological Geological Society Society of of America America 1997 1997 abstractswith with programs, programs, v. v. 29, 29, no. no. 4, 4, p. p. 9.9. abstracts Karl, Karl, J.H., J.H.,1986, 1986,Total Totalmagnetic magneticintensity intensitymap mapof ofnorthern northernWisconsin; Wisconsin;Wisconsin Wisconsin Geological Geological and and Natural History Survey, Map 86-7, scale 1:250,000. Natural History Survey, Map 86-7, scale 1:250,000. King, King, E.R., E.R.,1990, 1990,Precambrian Precambrianterrane terraneofofnorth-central north-centralWisconsin: Wisconsin:an anaeromagnetic aeromagneticperspective; perspective; Canadian Journal Journal of of Earth Earth Science, Science, v. v. 27, 27, pp. pp.1472-1477. 1472-1477. Canadian 62 �Index of Recent Aeromagnetic Aeromagnetic Surveys Surveys in in Wisconsin Wisconsin 93 93- 91 91' 9T 92' 88 88- 89 89' 9O 90' 8T 87' 46 45 44 43 92 0 50 88° 89° 90° 91° 150 100 63 200 KM �POLYMETAMORPHISMOF OF SKARNS SKARNS RELATED RELATED TO TO THE MORIN POLYMETAMORPHISM MORIN ANORTHOSITE ANORTHOSITE COMPLEX, GRENVILLE COMPLEX, GRENVILLE PROVINCE, PROVINCE, QUEBEC. QUEBEC. DEANGELIS1, DEANGELIS l , M. T., PECK, W. H., and VALLEY, VALLEY, J.J. W., W., Department Department of Geology Geology and Geophysics, University of Wisconsin, Wisconsin, Madison, Madison, Madison, Madison, WI, WI, 53706, 53706, william@geology.wisc.edu. william@geology.wisc.edu.1student ^student author caic-silicate assemblages Skarn calc-silicate assemblagesassociated associated with with the the Mona MorinAnorthosite AnorthositeComplex Complexare areexposed exposed—2 -2 km west of the town of St. St. Jovite, Jovite, Quebec, Quebec,and anddisplay displayfield fieldrelations relationsand andreaction reaction textures textureswhich whichindicate indicateaa polymetamorphic origin. small dioritic dioritic and and monzonitic monzonitic intrusive intrusive bodies, bodies, which which are are located located -25 small polymetamorphic origin. A set of —25 between two mapped bodies bodiesofofmangerite mangerite(Martignole (Martignoleand andConiveau, Corriveau,1993) 1993)outcrop outcropinina a—300 -300 meter meter long long These bodies bodies are are rimmed rimmed by by 10-20 cm cm thick thick series of four roadcuts in calcite marble along Highway 117. These skarns containing containing metasomatic metasomatic banding of garnet, diopside, and wollastonite. wollastonite. This This locality locality occurs occurs adjacent adjacent ± 3 Ma (Doig, 1991). to the western margin of the Morin Anorthosite Anorthosite Massif which was emplaced at 1155  bodies that that were were emplaced emplaced 1135 1135 ±3 The anorthosite is associated with mangerite bodies 3 Ma (Doig, 1991). The The area was metamorphosed anorthosite massif metamorphosedunder granulite granulite facies facies conditions conditions following emplacement of the anorthosite of 650-775 650-775 O °C Martignole, 1989). 1989). This to pressures of 6-8 kb and temperatures of C (Indares and Martignole, metamorphism metamorphism has been been dated dated at at 1070-1100 1070-1100Ma Ma by Rb-Sr Rb-Sr whole whole rock isochrons isochrons (see (see Doig, Doig, 1991). 1991). Descriptions of skarns Descriptions of skarns Well developed developedskarns skarns appear appear on both diorite diorite and monzonite bodies. We Weinterpret interpretthese thesebodies bodies as as intrusive relict igneous igneous textures. textures. On intrusive because because of cross-cutting cross-cutting relationships relationships between different intrusions and relict exposed with diameters diameters exposed surfaces, surfaces, diorite diorite bodies bodies vary vary in in both both size size and and shape, shape,but but are are typically typically circular circular to to oval oval with ranging from 11 to 10 10 meters. meters. The Thediorite dioriteintrusives intrusivesare arecomposed composedprimarily primarily of of plagioclase plagioclase with with minor minor amounts of clinopyroxene, amphibole, biotite, magnetite, pyrite, and sphene. Metamorphic Metamorphicminerals minerals and clinozoisite. which are are made made up upof of include calcite, garnet and clinozoisite. Surrounding Surroundingthe the diorite diorite intrusives are skarns which concentric garnet-, clinopyroxene-, cinopyroxene-, and and wollastonite-rich wollastonite-rich bands. Next Next to to the the diorite, diorite, garnet-rich bands are —10cm cmthick. thick.Wollastonite-rich Wollastonite-richbands bands(in (inthe themiddle middleof ofthe theskarn) skarn)are arethinner thinner(51 (1 cm) cm)and andsometimes sometimesare are -10 cmthick thick and gradually not present. Clinopyroxene-rich Clinopyroxene-richbands bands are are —15 -15 cm gradually grade grade into the marble. The Thegarnetgarnetplagioclase, quartz, calcite, sphene, and small amounts of pyrite. pyrite. rich bands contain garnet, clinopyroxene, clinopyroxene, plagioclase, plagioclase, garnet, The wollastonite-nich wollastonite-rich bands are composed of wollastonite, clinopyroxene, calcite, plagioclase, and pyrite. pyrite. The clinopyroxene-rich bands are are made made up up of of quartz, sphene, and small amounts of graphite and clinopyroxene, calcite, garnet, clinopyroxene, garnet, plagioclase, plagioclase, quartz, quartz, sphene, sphene, with minor amounts amounts of graphite and pyrite. monzomte intrusives The monzonite intrusives are composed of potassium feldspar feldspar and plagioclase plagioclase with minor amounts of clinopyroxene, and sphene. Metamorphic quartz, clinopyroxene, Metamorphic minerals minerals include include calcite, calcite, garnet, garnet, and Fe-vesuvianite (Fe/Fe+Mg=0.65 determined determined by electron microprobe). FeFevesuvianite is visibly zoned in hand sample, with Fe-rich rims (Fe/Fe+Mg=0.67) (FeIFe+Mg0.67) and andless less Fe-rich Fe-rich cores (Fe/Fe+Mg=0.61). Fe-vesuviamte Fe-vesuvianitecrystals crystalscan can reach reach lengths cmand andare are found found within within the the monzonite monzonite and lengths of —6 -6 cm the inner most skarn band. Within Withinone onemonzonite monzonitebody, body, an unusual unusual texture texture consisting consisting of of aa cylinder cylinder of of matrix matrix minerals minerals (potassium (potassiumfeldspar, feldspar,plagioclase, plagioclase,garnet, garnet,and and quartz) quartz)encased encasedby byaasingle singlecrystal crystalofofelongate elongate(—2-6 (-2-6 cm cm long, width50 mm)clinopyroxene clinopyroxene(En26Fs23Wo50Ac1) (En2(;Fs23W050Acl) width90mm) occurs. This gives these crystals a "hollow" appearance in thin section and on the outcrop. Monzonite Monzonite occurs occurs both Fragmented diorite dioriteintrusion. intrusion. Figure 1. Fragmented semi-circular bodies (1-10 as semi-circular (1-10 m in diameter) diameter) as as well as Skam is developed Skam developed where where hot hot diorite diorite contact with with marble. marble. Brittle came into contact Brittle dikes which cross cut diorite. Skarns Skarns around the deformation of of diorite and skarn postdeformation monzonite consist of small (3-5 cm) garnet- and intrusion. dates intrusion. clinopyroxene-rich bands. Garnet-rich clinopyroxene-rich Garnet-rich bands contain clinopyroxene, calcite, garnet, clinopyroxene, calcite, potassium potassium feldspar, feldspar, Fe-vesuvianite, and sphene. Clinopyroxene-rich plagioclase, Fe-vesuvianite, Clinopyroxene-rich bands bands contain contain clinopyroxene, clinopyroxene, calcite, calcite, garnet, potassium feldspar, primarily feldspar, plagioclase, plagioclase, and sphene. sphene. Away from the igneous bodies, marble is composed of primarily equigranular calcite with small amounts of clinopyroxene, garnet, sphene, sphene, and and feldspar. feldspar. Trace amounts of equigranular graphite and pyrite are also observed. Bogoch (1997)report reportsimilar similarmineralogies mineralogiesof of calcite, calcite, potassium potassium Bogochetetala1(1997) feldspar, vesuvianite, quartz, clinopyroxene, cinopyroxene, plagioclase, spbene in a body body 2.5 2.5 m m plagioclase,wollastonite, wollastonite, graphite, and sphene long and 50 cm wide in calcite krn west of the field area. calcite marble marble approximately 12 12 km 64 �Deformation Deformation and and mineral mineral reactions reactions The majority of the exposed skarns skarns parallel the edge of the igneous igneous bodies bodies and and maintain uniform uniform thickness. However, However,some someskarns skarnsand and igneous igneous rock are Someigneous igneousbodies bodies and and their their skarns skarns locally deformed. Some are folded and boudined, boudined,2-25 2-25 cm cm size size skarn skarn fragments fragmentsare are common away from from igneous igneous rock; rock; some some of which are are variably folded. Skarn Skarnfragments fragments and and skarn skarn minerals are observed being transported by ductile flow of the marble (e.g. into boudin necks and out of fold hinges). Some Some igneous bodies and their skarns skarns show brittle deformation, breaking both skarn and intrusion intrusion into fragments fragments (see Fig. 1). The intrusionThe lack lack of of skarn skarndevelopment development on on some someintrusionmarble contacts contacts of dismembered dismemberedigneous igneous bodies bodies indicates indicates that brittle deformation deformation (of (of igneous igneous rock rock and and skarn) skarn) Figure 2. Calcite rimmed with garnet occurred after after igneous crystallization and skam skarn formation. formation. (Gç)). This texture (G texture and and garnet garnet rimming nmnung Mineral wolliastonite is Mineral textures textures show show that that original original skarn skarn wopastonite is evidence for the the reaction calcite+ quartz+ quartz+ anorthite+ anorthite+ mineralogies have mineralogies have been been modified modifiedby by aa later later granulite-facies granulite-facies wollastonite-> grossular+ wollastonite-> grossular+CO2. COT metamorphic metamorphic event event (see (see also also Martignole Martignole and and Schriver Schriver 1970). Garnet Garnet(Gr92) (Gr92)rims rimssurrounding surroundingcalcite, calcite, wollastonite, wollastonite,and and plagioclase plagioclaseindicate indicatethe the reaction reaction calcite calcite ++ quartz ++ anorthite anorthite ++ wollastonite wollastonite -> -> grossular + + + wollastonite C 0 2 (see Fig. 2). Garnet-quartz Garnet-quartz intergrowths intergrowthsindicate indicate the the reaction anorthite + ->grossular ++ CO2 wollastomte ->grossular quartz. quartz. The The univariant univariant assemblage assemblageof of garnet garnet(Gr95), (Gr95),plagioclase plagioclase(An19), (An19),quartz, quartz,wollastomte wollastoniteisisobserved observedas as fine-grained intergrowths. Dilution Dilutionof ofthe theanorthite anorthitecomponent componentof of plagioclase plagioclase by albite albite moves moves the fine-grained univariant univariant assemblage assemblage to to lower lower pressures pressures and and temperatures temperatures(Windom (Windom and and Boettcher Boettcher 1976), 1976),consistent consistent with the estimates estimates of regional regional metamorphism metamorphism (Indares (Indares and Martignole 1990). 1990). The Thepresence presenceof of wollastomte+ wollastonite+ vesuvianite, garnet+ plagioclase+ quartz+ wollastonite, wollastomte, clinozoisite+ plagioclase+ plagioclase+ quartz, quartz, and and sphene sphene vesuvianite, indicate metamorphism was was fluid fluid saturated. saturated. These Xu20 ifif metamorphism These assemblages assemblages also also consistent consistent indicate conditions conditions of high high XH2O with estimates of low H2O activityfrom from granulite granulitefacies facies terrains terrains if conditions are fluid absent or if non CH20 activity 0-H fluid 0-H fluid species speciesare are important important(Valley (Valley et et al., al., 1990). 1990). Comparison to the Comparison the Adirondacks Adirondacks Economic wollastonite deposits depositsin in the the Adirondack AdirondackHighlands Highlands(—250 (-250 km Economic wollastonite kmto tothe the south) south) are are skarns skarns associated with the the Marcy Marcy Anorthosite Anorthosite Massif Massifand andrelated relatedgranitic graniticrocks rocks.. Skarn formation adjacent to to the the anorthositewas was due due to to the the infiltration infiltration of of oxidizing oxidizing meteoric meteoric water water into the high temperature contact Marcy anorthosite zone of a shallow (<10km) anorthosite body. The Adirondacks Adirondacks underwent regional granulite facies body. The facies metamorphismwith withhigh highpressure, pressure,fluid-absent fluid-absentconditions conditions—100 -100 Ma later later (McLelland (McLellandand andChiarenzelli, Chiarenzelli, metamorphism 1990), wollastonite and 1990), but wollastonite and other other skarn skarn minerals minerals remained remained stable stable through through this this later later metamorphism metamorphism due due to to fco2 "fluid-absent" "fluid-absent"conditions conditions(Valley (Valley et et al. al. 1990). 1990). Post-intrusion Post-intrusiondeformation deformation and and mineral mineral textures in low fc02 Morin Complex Complexskarns skarnssuggest suggestpolymetamorphism, polymetamorphism,but butpublished publishedgeochronology geochronology(i.e. (i.e. dating datingof ofhigh high Monn temperature temperature metamorphic metamorphicminerals) minerals)atatpresent presentdoes doesnot notallow allowaadistinction distinctionbetween between two twoseparate separate metamorphicevents, events, or or aa continuum continuumof of metamorphism metamorphismunder underchanging changingconditions conditionsfollowing followinganorthosite anorthosite metamorphic intrusion or depth of intrusion. intrusion. References Bogoch, R., Kumarapeli, S., Can Mm Min 35:1269-1275. 351269-1275. S., and Matthews, A. A. (1997) Can Geology 99: 99: 729-738. 729-738. Doig R. (1991) J Geology J., Corriveau L. (1993) Geol Geol Surv Surv Can Can Open Open File 2640. Martignole J., Martignole J., Schrijver Schrijver K. K. (1970) (1970)Geol Geol Soc SocFinland Finland Bull Bull 42: 42: 165-209. 165-209. Chiarenzelli, J. J. (1990) (1990)JJ Geology Geology 98:19-41. 98:19-41. McLelland, J., Chiarenzelli, 1-386. (1989)Can CanJJEarth EarthSci Sci27: 27:37 371-386. Indares A., Martignole MartignoleJ.J. (1989) 1:555-596. R., Essene, Essene, E. E. J., J., and and Lamb, Lamb, W. W. (1990) (1990) J JPetrology Petrology331555-596. Valley, J., Bohlen, S. R., Am Mm Min61:889-896. 61:889-896. Windom, K. E., Boettcher, A. L. (1976) Am 65 �THE OF THE THE GUNFLINT LAPILLI LAPILLI TUFF THE AGE AND PROVENANCE OF TUFF and KISSIN, KISSIN, S.A., S.A., Department Department of of Geology, Geology, Lakehead Lakehead FRALICK, P.W. and University, Thunder Bay, Ontario, P7B University, P7B 5E1, 5E1, and and DAVIS, DAVIS, D.W., Royal Ontario Ontario Museum, Museum, 100 100 Queen's Park, Park, Toronto, Toronto,Ontario, Ontario,M5S M5S 2C6. 2C6. forms the the middle middleunit unit of ofthe the Animikie Animikie Group Group in northwestern The Gunflint Formation forms proximally to to the western end of Ontario, outcropping proximally of Lake Lake Superior. Superior. It consists of an assemblage assemblage of chemical and fine-grained elastic sediments deposited in the strand-proximal zone of a south facing (1996). facing shelf shelf as recently interpreted by Pufahl Pufahl(1996). Previous attempts at assigning an age to the Gunflint Formation (or the conformably conformably overlying Rove Formation) and equivalents equivalentscan can be be classified classified into into three three groups: groups: (1) ages from (Hurley et et a!., al., 1962; 1962;Peterman Peterman 1.556 to 1.63 Ga based on whole-rock Rb/Sr or KIAr K/Ar techniques techniques (Hurley 1969; and Franklin, 1978); 1978); (2) ages from 2.08 to 2.111 2.1 11 Ga Ga based on on 1966; Faure Faure & Kovach, 1969; a!, 1988); and (3) 1.86 1985; Gerlach et al, 1.86 and whole-rock NdJSm NdlSm techniques (Stille & Plauer, 1985; Hemmings et al; 1995). 1995). 1.99 Ga based on whole-rock PbIPb Pb/Pb from the the Virginia Virginia Formation Formation ((Hemmings Petrographic the upper upper Gunflint at Kakabeka Kakabeka Petrographicexamination examination of of aa lapilli lapilli tuff unit present in the Falls identified euhedral zircons forming a small portion of the silt population together with large, monomineralic clasts of of quartz quartz and and sanidine likely from an explosive, volcanic source. source. stratigraphic section section present present here has aa large large algal algal bioherm bioherm complex complex at at its its lowest lowest level level The stratigraphic (Figure sporadic (Figure 1). 1). This Thisisis overlain overlainby by aa thick thick sequence sequence of parallel-laminated black shale with sporadic development of layer rip-ups rip-ups caused causedby bycurrent currentactivity. activity. A A series of what what has been described as lapilli tuff beds beds occurs midway midway through through this thissequence sequence(Shegelski, (Shegelski, 1982). 1982). These are massive to disorganized disorganizedbedded. bedded. Mudstone rip-ups rip-ups are are common. common. The to cross-stratified and graded to The lapilli consist of Fe-rich Fe-rich chlorite chlorite and and are areinternally internallymassive. massive. The The above above strongly suggests suggests that the lapilli are not accretionary volcanic-rainout debris, but but rounded rounded volcaniclastic volcaniclastic mud mud rip-ups, and transported transportedby bystorm-induced storm-inducedcurrents. currents. The The black black shale unit which were eroded, abraded and is correlated with a find-grained, fmd-grained, resedimented, volcaniclastic shale, which which extends throughout upper Gunflint equivalents equivalents in the U.S.A. U.S.A. It may also be correlated correlated with aa small small region region containing containing basaltic basaltic flow flow rocks. rocks. Approximately 100 tuffs, including including altered, 100 zircons were recovered from the reworked tuffs, altered, abraided and euhedral euhedral brown brown populations. populations. Although the majority of the population analysed concordant age of 1878± gave reset Archaean ages, a euhedral zircon gave aa concordant 1878Â2Ma BP (Figure (Figure 2). 2). This most likely represents the age of of volcanism volcanism that was penecontemporaneous penecontemporaneous with sedimentation. sedimentation. volcaniclastic sediment Preliminary geochemical geochemical data data for Gunflint basalts and volcaniclastic sediment indicates indicates possibility of deep mantle mantle source for the melts melts and rules out out any any involvement involvement of the possibility of a deep Similaritieswith with the the Emperor Emperor and and Hemlock Hemlock volcanics volcanics suggest suggest a subducting lithosphere. lithosphere. Similarities eruptive event, event, which which may may in in part part overlap overlap northward time-transgressive, extensional, intraplate eruptive chronologically with the commencement commencement of arc volcanism to the south. south. 66 �References References Faure?G., G.?& & Kovach? SOy 1725-1736. Faure, Kovach,J.J.(1969). (1969). Geol. Geol.SOC. Soc.Amer. Amer.Bull. Bull. , 1725-1736. Franklin, J.M. (1978). Geol. Sum. Can. Pap. 77-14,35-39. Franklin, J.M. (1978). Geol. Surv. Can. Pap. 77-14, 35-39. D.C.? Shirey, 1515. GerlachyD.C., Gerlach, Shirey, S.B. S.B.& &Carlson, Carlson,R.W. R.W.(1988). (1988).EOS EOS@, , 1515. Hemming,S.R., S.R.?McLennan, McLennan,S.M. S.M.& & Hanson, Hanson, G.N. G.N. (1995). (1995). Jour. Jour.Geol. Geol.jQ., 147-168. 147-168. Hemming, Hurley, P.M., Fairbairn, H.W., Pinson? W.HSy & Hower, J. (1962). Jour. Geol. 489-492, Hurley, P.M., Fairbaim, H.W., Pinson, W.H., & Hower, J. (1962). Jour. Geol. 489-492. PetermanyZ.E. Z.E. (1966). (1966). Geol. Geol.Soc. SOC.Amer. Amer. Bull. Bull. fl, 103 lo31-1044. 1-1044. Peterman, Pufahl,P.K. P.K.(1996). (1996).M.Sc. M.Sc.Thesis, Thesis,Lakehead LakeheadUniv., Univ.,167 167 p. Pufahl, p. R.J. (1982). Geol. Assoc. CanJMineral. Assoc. Can.Field FieldTrip TripGuidebook Guidebook4, 4?15-31. 15-31. Shegelski, Shegeiski, R.J. (1982). Geol. Assoc. Can./Mineral. Assoc. Can. my a, , a, Breccia Breccia Stromatolites Stromatojites Wavy Beddin( '' Wavy Beddinc . .34 Cross- '..-.. Cross Stratification Stratification Brown euheclral .338 1878 +I-2 Ma .336 .334 20'Pb / 236U .332 5.2 5.25 5.3 5.35 5.4 5.45 10-01-1997 Fig.2. 2.Pb/U Pb/Uplot plotfor foreuhedral, euhedralybrown brown Fig. zircons from fiomthe thelapilli lapillituff tuffunit. unit. zircons a Granulesto to / Granules .smallPebbles Pebbles small Sandstone Sandstone siltstone .--. Siltstone .-. .:. .:... .. .. .. .. .. .. . .............. . . . . . . Shale Chert Fig. 1.1.Stratigraphic Stratigraphicsection sectionof ofthe theupper upper Fig. GunflintFormation Formationcontaining containinglapilli lapilli Gunflint tuff units in the Kakabeka Gorge. tuff units in the Kakabeka Gorge. 67 �PRE-WISCONSINAN AREA OF THE MINNESOTA PRE-WISCONSINANGRAY GRAY TILL IN THE MANKATO AIZEA MINNESOTA RIVER RIVER VALLEY GRAMSTAD, Sally D., student, Department of Geological Geological and Atmospheric Atmospheric Sciences, Sciences, Iowa Iowa University,Ames, Ames,IA IA5001 50011, sgramstaiastate.edu State University, 1, sgramsta@iastate.edu Exposures of pre-Wisconsinan gray till in the Mankato area of the the Minnesota Minnesota River River Valley Valley show that that continuous. Low shale content, moderate moderate carbonate carbonate this unit is up to 30 m thick and is somewhat continuous. content, and NW-SE trending fabrics fabrics indicate indicate aaWinnipeg Winnipegprovenance. provenance. The The texture texture and and lithology lithology of of this unit are similar to those of other pre-Wisconsinan tills in the Midwest, including the Browerville Browewille and Elmdale tills in north-central north-central and central Minnesota, and unit 1 at Salisbury Hill, which is twenty miles northeast of the study study area. The topography topography of of the bedrock bedrock valley valley that is is present present in in the the Mankato Mankato area area may may have have affected affected ice flow of the glacier that deposited the pre-Wisconsinan gray till unit. Influence Influenceof of this thisbedrock bedrock that the the thick thick till till unit is interrupted valley may explain several several anomalous anomalous fabrics, as well as the fact that by sand and gravel gravel layers layers at at some some sites sites and and is is completely completelyundisturbed undisturbedat at others. others. 68 �A A MINERALOGRAPHIC MINERALOGRAPHICSTUDY STUDYOF OFMAGNETITE MAGNETITEIN IN THE THE BIWABIK BIWABIK IRON-FORMATION, IRON-FORMATION,MESABI MESABI RANGE.M[NNESOTA MrNNESOTA RANGE, T. T.M. M.Han, Han,Senior SeniorResearch ResearchScientist Scientist(Retired), (Retired),Cleveland-Cliffs' Cleveland-Cliffs'Research ResearchLaboratory Laboratory A A substantial substantial number number of ofpolished polishedsections sectionsprepared preparedfrom from specimens specimenscollected collected from from the the Biwabik BiwabikIronIronFormation Formation were were microscopically microscopically examined examined before before and after an induced oxidation procedure. The TheBiwabik BiwabikIronIronFormation Formation is is simply simply classified classified here as cherty and slaty members. ItIt isisconsidered considered aa regionally regionally metamorphosed metamorphosed sediment sediment before before the the the the intrusion intrusion of of the the Duluth Duluth complex. complex. Based Basedon onthe the nature nature and and magnitude magnitude of of the thechanges, changes, the the existing existing iron-formation iron-formationmay may be be divided dividedinto intothree three metamorphosed metamorphosed sectors sectors progressing from west to to east, east, i.e. i.e. hematite functioned functioned as aa regionally, thermally, thermally, and andpyrometasomatically. pyrometasomatically. During During regional regional metamorphism, metamorphism, hematite regionally, "starting much of of the the magnetite magnetitethrough through~Fe Thermal "starting point" point" for for the development development of much e +diffusion. difhsion. + Thermalmetamorphism metamorphism involves involves mineralogical mineralogical transformations transformations of an isochemical isochemical nature, which may be be subdivided subdivided into into transitional, transitional, process involved amphibole, amphibole, and and pyroxene pyroxene zones. zones. Pyrometasomatism Pyrometasomatism process involved advanced advanced recrystallization recrystallization and and replacement replacementby bygabbro gabbroadjacent adjacentto, to,and andwithin, within,the theintrusion. intrusion. This This poster poster focuses focuses on on the the genesis genesisof ofmagnetite magnetiteinin the theregionally regionallymetamorphosed metamorphosed iron-formation iron-formation and and the metamorphismand andpyrometasomatism. pyrometasomatism. Most Most of the the textural textural and and mineralogical mineralogical changes caused by thermal metamorphism features features observed observed during during the the course course of of study study are are photographically and photomicrographically shown. ItIt covers: covers: A. fiomdifferent differentmetamorphic metamorphiczones. zones. A. Lithological Lithologicalcharacteristics characteristicsfrom The The irregularly irregularlyand andevenly evenlybanded bandedmacrostructures macrostructuresofofthe theregionally regionallymetamorphosed metamorphosediron-formation iron-formation show show little little change, change, whereas whereasthe themineralogical mineralogicalcomposition composition and and microstructures microstructures have have experienced experienced significant significant progressive progressive elimination eliminationand andtransformation transformationdue duetotothe thethermal thermalmetamorphism metamorphismand andpyrometasomatism. pyrometasomatism. B. B. Hematite-Magnetite Hematite-MagnetiteRelations Relationsininthe theRegional RegionalMetamorphosed MetamorphosedIron-Formation Iron-Formation occur either Before Induced Induced Oxidation. Oxidation. The hematite hematite and magnetite magnetite occur either in separate separate layers layers or or inin 1. Before 1. intimate intimate relations in in the same same layer. layer. Hematite Hematiteisisalmost almostalways alwaysmuch muchfmer fmerand andless lessabundant abundantthan thanmagnetite. magnetite. The The replacement of of hematite by magnetite is readily evident. The The magnetite magnetite differs differs in in external external morphology, morphology, i.e. i.e. octahedral octahedral and and pseudomorphs pseudbmorphs after afterother otherminerals. minerals. After Induced Induced Oxidation. Oxidation. The Themorphologies morphologiesand andarrangement arrangement of of precursor precursor hematite hematite in in existing existing magnetite magnetite 2. 2. After significantly. In the the evenly evenly banded banded slaty slaty lithology, lithology, the the precursor precursor hematite hematite isis almost almost exclusively exclusively lathlathvary significantly. shaped shaped and exhibits exhibits aa decussate decussate microstructure. In Inthe the irregularly irregularlybanded banded lithology lithology of both the slaty and cherty cherty members, the the precursor precursor hematite hematite exhibits exhibits aawide widevariety varietyofofmorphologies. morphologies. It is is either either randomly randomly arranged arranged or or displays displays vuggy vuggy or or microgeodic microgeodic structures structures within within magnetite magnetite that isis present present as asirregular, irregular,coalesced coalescedcrystals, crystals, granules, or or pinch-and-swell pinch-and-swell layers. layers. The The external external morphology morphology of the present magnetite magnetite is governed governed by by the the granules, hematite. Some Some of the the precursor precursor hematite hematite might might have have been been enlarged enlarged by by authigenesis authigenesis before before precursor hematite. inclusions isis present present in nearly all magnetite development. development. Magnetite Magnetite with precursor precursor hematite hematite inclusions all the the mineral mineral magnetite assemblages fiom assemblages of of the the iron-formation. iron-formation. The Thesize sizeand andmorphologies morphologiesof ofprecursor precursorhematite hematitein inmagnetite magnetite differs differsfrom the the existing existing hematite, hematiteyeither either coexisting coexisting with or or playing host hostto tothe themagnetite. magnetite. C. C. Effect EffectofofThermal ThermalMetamorphism Metamorphismon onHematite Hematiteand andMagnetite Magnetite In In the the transitional transitional zone, zoneymore more than than one one stage stage of of overgrowth overgrowth on euhedral magnetite (with or without the the precursor hematite inclusions) inclusions) is frequently frequently observed. Two Twoto tothree threeexternal externalmorphologies morphologiesof ofmagnetite magnetitewere were also seen in in coexistence. coexistence. The Theinduced inducedoxidation oxidationpattern patternprogressively progressively changes changes from from grain grain boundary boundary oxidation oxidation along planes of of the existing along the the precursor precursor hematite hematite to cleavage cleavage oxidation oxidation along octahedral octahedral planes existing magnetite magnetite as the metamorphic grade grade increases. increases. The Thehematite hematiteofofthe theregionally regionallymetamorphosed metamorphosediron-formation iron-formationisisprogressively progressively replaced by magnetite. magnetite. The Theeuhedral euhedralmagnetite magnetiteisisprogressively progressively changed changed to subangular subangular to nearly round grains. However, the outlines granules are still preserved. Magnetite outlines of of the the magnetite magnetite pseudomorphs pseudomorphs and magnetite granules Magnetite porphyroblasts appear in the fine-grained coalesced subangular magnetite. fine-grained magnetite. Some Some siliceous siliceous magnetite magnetite blades blades or or 69 �cubic cavities are are occasionally occasionally observed observed in in magnetite magnetite distributed distributed in the the pyroxene pyroxene zone. zone. However, However, some some hematite coexisting coexisting with with magnetite magnetitehas has also alsobeen been found foundinin the the pyroxene pyroxenezone. zone. D. Effect Effectof ofPyrometasomatism Pyrometasomatismon on Hematite Hematite and Magnetite Advanced Recrystallized Recrystallized Zone. The Themagnetite magnetite here here is is substantially substantially coarser than 1. Advanced than in the regionally and thermally metamorphosed metamorphosed zones. zones. The hematite, hematite, magnetite magnetite pseudomorphs, and magnetite magnetite granules granules no no longer exist. Two Twogenerations generationsof ofmagnetite magnetiteand andthe theintroduction introductionof ofhercyanite hercyanitealong alongmagnetite magnetitecleavage cleavageplanes planes fmeparallel parallelto tosubparallel subparallelfractures, fractures,whereas whereas the the host hostdoes does are evident. The Themagnetite magnetitegrains grainscommonly commonlyhave havefme not. The Thefractured fracturedmagnetite magnetitesometimes sometimesresembles resembles specular specular hematite. Minute Minuteeuhedral euhedral gangue gangue inclusions inclusions are are commonly present. Cleavage Cleavageoxidation oxidationisistypical. typical. Magnetite Magnetiteinclusions inclusionswithin withinmagnetite magnetiteare areeither eitheroutlined outlinedby by the effect of differential differential oxidation oxidation or or by their their grain grain boundaries. boundaries. The advanced Gabbroized Zone. 2. Gabbroized Zone. The advanced recrystallized recrystallized magnetite magnetite gradationally gradationally transforms transforms to to a 2. titanomagnetite approaching the gabbroized zone. The The latter latter contains contains minute inclusions of hercyanite, ilmenite, and ulvospinel, mineral. Most phases are are products products of of exsolution. exsolution. Both ulvospinel, and an unidentified unidentified mineral. Most of these mineral phases Both magnetite and titanomagnetite may be observed observed in in adjacent adjacent layers layers of of the thesame samespecimen. specimen. Small octahedral octahedral the same composition and texture as inclusions of titanomagnetite are occasionally seen and exhibit essentially the as titanomagnetite contains contains apatite, apatite, pyroxene, pyroxene, and and other other gangue grains; some titanomagnetite host. host. Some titanomagnetite some their titanomagnetite exhibits aa myrmekitic intergrowthtexture textureinin pyroxene; pyroxene;and and some some appears appearstoto be be replaced replaced by by ilmenite and exhibits myrmekitic intergrowth ilmenite and sulfides. sulfides. Economically, regional regional metamorphism metamorphism isis the the key key contributor in in generating generating magnetite magnetite for for the present Economically, Thermal metamorphism metamorphismhas has aa negative negative impact impact on on magnetite magnetite size size liberation liberation but but a positive mining industry. industry. Thermal positive recovery. Advanced effect on magnetite weight recovery. Advanced recrystallization recrystallization has a positive effect on both both size size liberation liberation ore. and weight recovery, whereas whereas the gabbroized gabbroized iron-formation can no longer be considered iron ore, The details details relative relative to to this this study study were were reported reported in in the the following followingpapers papersand andabstracts. abstracts. T. M. Han (1978) "Microstructures "Microstructures of of Magnetite Magnetite as as Guides Guides to Its Origin in Some Precambrian IronFormations." Fortschr. Fortschr. Mineral. Mineral.56, 56,105-142 105-142 (1982) "Iron-Formation of of Precambrian PrecambrianAge: Age: Hematite-Magnetite Hematite-MagnetiteRelationships RelationshipsininSome SomeProterozoic Proterozoic (1 982) "Iron-Formation MicroscopicObservation." Observation."Ore Ore Genesis - State of the Art, Springer-Verlag, Deposits -- A Microscopic Genesis - The The Springer-Verlag, Berlin, Berlin, Iron Deposits Heidelberg, New York. (1988) "Origin of of Magnetite Magnetite in Precambrian Iron-Formations of Low Metamorphic Grade." Proceedings of Dof the Seventh Seventh Quadrennial Quadrennial IAGOD IAGOD Symposium, Symposium, E Schweizerbart'sche Schweizerbart'sche Verlagsbuchhandlung, Verlagsbuchhandlung,D7000 Stuttgart Stuttgart II (1996) "Mineralogical Evolution Evolution of of Precambrian Precambrian Iron-Formation of Low Metamorphic Grade and Its Contribution to the U.S. Steel Steel Industry" (Abstract), (Abstract), 30th IGC, Beijing, China G . Graber, and Ruth Kramer (1992) "Effect of Duluth Gabbro Intrusion on Ore Mineralogy of T. M. Han, R. G. the Biwabik Iron-Formation, Iron-Formation, Lake Superior Superior District," District," USA International International Symposium on Mineralization Related to Mafic and Ultramafic Rocks, Rocks, 8th 8th Quadrennial Quadrennial IAGOD Symposium, Symposium, Orleans, France (Abstract) 70 �FACIES DEPOSITIONAL ENVIRONMENTS ENVIRONMENTSOF OFTHE THEEEARLY PROTEROZOIC FACIES AND DEPOSITIONAL A m Y PROTEROZOIC IRONWOOD IRONWOOD IRON FORMATION, MT. WHITTLESEY WISCONSIN. *EJ Joslin, Dan *EMHensel, Hensely*ck *Rick J o s hand , and DaLehrmann; n LehrmaqDept. Dept.ofofGeology, Geoloa,University Universityof of WisconsinWisconsinOshkosh, .54901 Kl54901 Oshkosh7Oshkosh, Oshkosh, Wi There are numerous models of depositional depositional environments environments of ofEarly EarlyProterozoic Proterozoiciiron fonnation. The k n formation. The puipose of the study was to evaluate which which of of these these models modelsbest bestfit fitthe thesedimentary sedimentaiyfacies faciesand and stratigraphic stratigraphic purpose patterns in the the Ironwood Ironwood iron iron formation formation exposed e x p o d at the Whittlesey, in the patterns in the Berkeshire Mine Ruins, at Mt. Whitfiesey, Gogebic were stripped stripped from from this this area by the the abandoned Gogebic District, near Mellen Wisconsin. Soil and vegetation were mining miningeffort. &ort. Approximately Approximately 100 100 meters meters of of stratigraphic stratigraphicsection sectionwas was described describedbed bed by by bed bed at at aa decimeter decimeter scale. bed in reconnaissance cut and and d e . An An additional additional150 150 meters was descr described reconnaissance sections. Samples were collected, cut described described in in detail detail to to help help understand understanddepositional depositionalenvironments. environments. fades were recognized from outcrop observation observation and and sample sample descriptions. descriptions. These These are are Five different facies summarized facies consists s u m a r i d as as follows. 1) 1) The The horizontal horizontallaminated hmin'atedfiia consistsof ofcontinuous continuousand anddiscontinuous discontinuouslaminae laminae of alternating alternating inagnetite structures include includethin, thin, graded graded laminae, laminae, scour scour marks, marks, vmagnetite and and chert. chert. Sedimentary structures shaped ?), and and discontinuous shaped cracks cracksthat that probably probably resulted resulted from from differential Merentid compaction compaction(j)ossibly (possibly desiccation ?), discontinuous lenses thick and commonly pinch out within a few lenses of granular granularfacies. The lenses lenses range range from fiom a few to 15 cm thick meters laterally. 2) The wavy wavy hminatedfacies consists of wavy wavy laminae laminaeof of magnetite magnetiteand and chert chertwith with few few 2) The laminated facies consists intraclasts of cheit are horizontal horizontal intraclasts chert.Sedimentary Sedimentarystructures structuresinclude includecrinidey crinkleylaminations laminationsthat thatprobably probably are stromatolites, convolute convolutelaminae, laminae,and andlenticular lenticularlayers. layers.3)3)The Theinfracladcfacies intraclasticfacies consists consistsof of intraclasts of of stromatolites, magnetite magnetiteand andchert chertderived derivedfrom fromthe thewavy wavyand andgranular granularfacies. facies.The Theclasts clastswere werecemented cementedearly earlyby bysilica. silica. include, planar cross beds, beds, imbricated clasts, clasts, differential differential syn-sedimentary syn-sedimentaiy compaction, compaction, Sedimentary structures include7 autoclastic penetrating the margins autoclastic breccia, breccia, and abundant abundant v-shaped cracks penetrating margins of of intraclasts. intraclasts. These Thesemay may be be desiccation of the the intraclasts intraclasts are are rounded roundedand andare areconcentrically concentricallycoated coatedwith withchert. cheit 4) 4) The The desiccation cracks. Some of stromatolitefacies contains ~omatolifefacies containsdomal domalstromatolites stromatolitescomposed composed of of chert chert and and magnetite. magnetite. Intraclastic Intraclastic material, containing occursbetween betweenthe the containingstromatolite stromatolite fragments hgments and and clasts clasts of of granular granular fades, facies*isisinterbedded interbeddedwith withand andoccurs stromatolites. 5) facies consists 5)The Thegranular granuhrfacies consistsof ofcoarse coarse to fine fine sand and minor silt sized chert and magnetite grains. ooids. The The granular granular facies grains. Most Mostofofthese thesegrains grainsare arepeloids peloids(featureless (featureless rounded grains), some are mids. appears appears to to be winnowed with little fine grained matrix and locally contains ripple ripple cross-lamination. cross-lamination. The stratigraphic pattern at Mt. Whittlesey is a meter- to decimeter-scale intercalation intercalation The most obvious stratigraphic of the wavy, granular, granular, and and intraclastic intraclasticfacies facies (fig. (fig. 1). 1). Careful Carefid observation obsemtion reveals, however, that that there there is is also a larger-scale are lithologic cycles. These cycles are larger-scale change change in in facies facies associations associations in the the outcrop outcrop that defines 3 lithologic approximately50 m thick. thick Within Within the the cycles cycles there there is a preferential association association in which which the the following following facies facies approximately more frequently granular and and wavy laminated facies, 2) the intraclastic intraclastic and and stromatolitic stromatolitic frequently occur together: 1) the granular three facies associations 3) the the horizontal horizontal laminated laminatedfacies. facies. The The cycles cycles consist of a repetition of the three facies, and and 3) stmmatolitic facies facies above. Interestingly, the cycles are are asymmetric in in the sense that that the intraclastic and stromatolitic associationalways always occurs beneath the the horizontally horizontally laminated laminatedfacies faciesand andnot notabove aboveitit(fig. (fig.2). 2). association Our interpretation that in aa shallow-marine, intertidal Our data data supports supports the interpretation that the the iron formation was deposited in to subtidal subtidal shelf environment. This Thisisissimilar similarto tothe theenvironments environments that that have have been been most most widely interpreted for iron Lougheed, 1983; M LaBerge, (cf. Simonson, 1985; hugheed, e r g e , 1987; Simonson Simonson and and Hassler, Hassler, 1996). 1996). iron formations formations(CL Sedimentary fatures interpretation include the stromatolites, ooids, mi&, ripple ripple cross lamination, lamination, features that that support this interpretation and and cross cross bedding. We interpret interpret that that the theiron ironformation formationformed formed as as aa biochemical biochemical precipitate precipitateof of iron iron and and silica silica minerals marine carbonate supports the minerals from from sea-water. sea-water. The The similarity similarityto to Proterozoic Proterozoic or Early Paleozoic marine carbonate facies supports idea to support the interpretation interpretation that are biochemical biochemical rocks. We found no evidence to that these these were idea that that these these are originally carbonate carbonate sediments sediments that that were were diagenetically diagenetically replaced by h w a t e r deposition that has originally by silica or for hfreshwater been postulated by 1973). by other other authors authors (Hough, (Hough, 1958; 1958;Eugster Eugsterand andChou; Chou;and and Trendall, 1973). In our laminated facies facies formed formed on on the the tidal tidal flats, the granular, granular, our preferred p r e f e d depositional model, the wavy laminated intraclastic, further seaward in shallow, wave agitated subtidal intraclastic, stromatolite, stromatolite7facies facies formed formed progressively progressively fiuther environments environmentsand and the the horizontally horizontallylaminated laminatedfacies faciesformed formed in in deeper deeper environments environmentsbetween nonnal normalwave wavebase base and and storm storm wave wave base base (fig. 3). The The horizontal horizontallaminations laminationsare are interpreted interpretedto tohave haveformed formedin inquiet quietwaters watersbelow below granular facies found found in in the the The abundant abundantscour scour structures structuresand discontinuous lenses of granular normal wave base. The horizontally laminated horizontaIly laminated facies are interpreted interpreted to to represent represent agitation agitation and and "spill "spill over over lobes" lobesnof of granular granularmaterial material 71 �___ Originally we entertained the idea that the horizontally laminated washed seaward during storms (fig. 3). 3). Originally facies formed formed landward landward of of the the oolite oolite shoals shoals in in tidal tidal flat flat ponds. ponds. If If the the v-shaped v-shaped cracks crackswere were desiccation desiccationfeatures, features, facies that that would support support such such an an interpretation. interpretation. The Thev-shaped v-shaped cracks cracks are more commonly associated with syndepositional depositional deformation deformationstructures structureshowever, however, and and the the horizontally horizontallylaminated laminatedfacies faciesisisrarely rarelyassociated associatedwith with laminatedfacies. facies. This, This, along alongwith withthe theasymmetrical asymmetricalpattern pattern of of the thelarge-scale large-scaledepositional depositionalcycles cycles the wavy laminated facies associations associations would represent supports the deeper deeper offshore offshore environment. In this this model, model, the the cycles in facies represent long long term (—million (--million year) intraclastic term year)asymmetric asynunetrictransgressions transgressions and and regressions regressions of ofthe the shelf. shelf. The The stromatolites stromatolites and intraclastic facies formed preferentially during initial transgressions, due to increased wave energy energy and and increasing increasing water Maximum deepening deepening is is represented represented by the horizontally laminated facies and regression is represented depths. Maximum by the shift facies association. association. shift back to to the the wavy laminated laminated - granular facies studies have commonly interpreted the horizontally laminated laminated facies Previous studies facies as as being being aa deep deep water water In some some cases cases itit has has been been interpreted interpretedto tobe be aa vezy very deep, pelagic and turbiditic Our data datasuggests suggests deposit. In turbiditic facies. Our that, at units interbedded interbedded in in the the horizontal horizontal facies are are at Mt. ML Whittlesey Whittlesey at least, this is not the case. The granular units far too discontinuous discontinuousto to represent represent distal distalturbidites turbiditesand andthey they lack lack Bouma Bouma sequences. sequences. - Eugster, H. P., Chou, Chou, I.M., I.M., 1973, 1973,The The depositional depositional environments environments Precambrian banded iron iron formations: formations: Economic Geology and the Bulletin Bulletin of the Society for for Economic Economic Geology, Geology,v. v. 68, 68, n. n. 7, 7, p. p. 1144-1168. 1144-1168. Economic Hough, J. L., L., 1958, of Precambrian Precambrian banded banded iron iron formation: formation: Journal Journal of of 1958, Fresh Freshwater waterenvironment environmentof of deposition of Sedimentary Sedimentary Petrology, v. 28, n. 4, p. p. 414-430. 414-430. LaBerge, G. L., L., Robbins, E. E. I. Schmidt, R K 0., G.,1987, 1987,AAmodel model for for the the biological precipitation of Precambrian iron Pubi., Athens, p. 69-96. iron formations: formations: Precambrian Precambrian Iron Iron Formations, Formations, Theophrastus Theophrastus Publ., 1983, Origin Origin of of Precambrian Precambrian iron iron formations formations in the lake superior superior region: region: Geological Geological Society Lougheed, M. S., 1983, of America Bulletin, Bulletin, v. 94, 94, ii. n. 3, 3, p. 325-340. 325-340. M., 1985, the origins of of Precambrian Precambrian iron formations: Simonson, B. M, 1985, Sedimentological Sedimentological constraints on the Geological Geological Society of America Bulletin, v. 96, n. 2, p. 244-252. Simonson, B. M M. and Hassler, S. W., of large large Precambrian Precambrian iron formations linked to W., 1996, 1996, Was the deposition of major marine marinetransgressions?: transgressions?:Journal Journalof ofGeology, Geology, v. 104, 104,n. n. 6, 6, p. p. 665-676. 665-676. Trendall, A. F.,1973, 1973,Iron Ironformation formationof ofthe theHamersley HamersleyGroup Groupof of Western Western Australia; Australia; type typeexamples examplesof ofvarved varved Trendall, A. F., Earth arth Science Science (Paris), v. 9, p. 257-270. 257-270.evaporites: E Fades Fades TO- ,"- nfradasc Fades Associations 1 HorizontallyE HorizontallyLaminated Intraclastic I Intraclastic Stromatolitic Strornatolitic Wavy Laminated /I Granular 3 I1 urn FIom Figure Figure11 ."-- Figure 2 Fades Wavy Iamânated Wavy laminated Granu [S Intradastic t.nbad&c a HorizontallyLaminated Figure Figure 3: Depositional Depositional Model Model 72 �AGE DEFORMATION OF EARLY PROTEROZOIC PROTEROZOIC QUARTZITES AGE AND DEFORMATION QUARTZITESIN IN THE THE SOUTHERN SOUTHERN LAKE SUPERIOR SUPERIOR REGION: REGION: IMPLICATIONS IMPLICATIONSFOR FOR EXTENT EXTENTOF OF FORELAND FORELAND DEFORMATION DEFORMATION DURING DURING FINAL FINAL ASSEMBLY OF LAURENTIA Daniel Daniel Hoim, Holm,Department DepartmentofofGeology, Geology,Kent KentState StateUniversity, University,Kent, Kent,OH OH44242 44242 David David Schneider, Schneider,Dept. Dept.of ofEarth Earth and and Environmental Sciences, Sciences, Lehigh Lehigh University, University, Bethlehem, PA PA Christopher ChristopherD.D.Coath, Coath,Department DepartmentofofEarth Earthand andSpace SpaceSciences, Sciences,UCLA, UCLA,Los LosAngeles, Angeles,CA CA90095 90095 Post-accretion stabilization stabilization in the Lake Superior region at 1770-1760 1770-1760 Ma resulted in deposition of locally thick successions successions of Early Early Proterozoic Proterozoic mature mature quartzites quartzites in Wisconsin Wisconsin and and southern southern Minnesota. Minnesota. Their Their age age of of deposition deposition and and the theage ageof of the thedeformation deformationwhich which caused causedwidespread widespreadfolding foldingof ofmany manyof ofthe the quartzite units has long been aa matter importance and and controversy. controversy. We matter of of considerable considerable importance We present present new new evidence these quartzites. quartzites. Also, we document evidence for both the maximum and minimum age of these document the spatial coexistence of aa thermal with a deformational front in the thermal front front in in Precambrian Precambrian crystalline crystalline basement basement with deformational front overlying quartzite units. The Theage ageofofthe thefront frontsuggests suggeststhat thatpost-Penokean post-Penokeanshortening shortening of of the thePenokean Penokean province province is is likely likely related related to to the the final final stages stages of formation formation of the Laurentian Laurentian supercontinent supercontinent at at -1650 Ma. 1650 Ma. The The bulk bulk of Laurentia Laurentia formed formed by rapid aggregation aggregation of Archean continents at 1900-1800 1900-1800 Ma during the Trans-Hudson and Penokean orogenies (Hoffman, 1989). Subsequent Subsequent accretion accretion of of juvenile crust crust along along the the southern southern margin margin of of pre-1800 pre-1800Ma Ma Laurentia Laurentiaformed formedthe theTranscontinental TranscontinentalProterozoic Proterozoicprovinces provinceswhich which consist broadly of aa northern northern 1800-1700 1800-1700 Ma inner accretionary belt and a southern 1700-1600 1700-1600 Ma outer tectonic belt. The Thetransition transition zone zone between between the the two two tectonic tectonic belts belts of the the TPP TPP represents represents the region of known Ma during during formation formation of of the outer known pre-1700 pre-1700 Ma Ma rocks rocks metamorphosed metamorphosed and and deformed deformed at at —1650 -1650 Ma tectonic belt. The Theeastward eastwardcontinuation continuation of of this this transition transition zone zone and and of the the outer outer tectonic tectonic belt from the central central plains plains is is problematic problematicas as no no 1800-1600 1800-1600Ma Majuvenile juvenile crust crustexists existsin inthe theentire entiresouthern southernGreat GreatLakes Lakes region region (Van (Van Schmus Schmus et et al., al., 1993). 1993).However, However,on onthe thebasis basisof of1680-1640 1680-1640Ma Maorogenic orogenicdeformation deformationand andthe the existence of 1650 1650 Ma Ma batholithic batholithic intrusive rocks in Labrador, Labrador, Van Schmus et al. al. (1993) (1993) have have proposed proposed that that the the outer outer tectonic tectonic belt belt was was aa single single coherent coherent continental arc extending extending from California California to Labrador. Labrador. The arc/microcontinentcollision collisionalong alongthe the southern southernpassive passivemargin margin The Penokean Penokean orogeny orogeny involved involvedisland island arc/microcontinent of of the the Superior Superior Province Province at at 1870-1830 1870-1830Ma. Ma. InInnorthern northernWisconsin Wisconsinthe thesouth-dipping south-dippingNiagara Niagarafault faultzone zone represents represents the the main main suture suturewhich whichseparates separatesuniformly uniformlymetamorphosed metamorphosed (upper (uppergreenschistllower greenschist/lower amphibolite facies) island arc arc rocks rocks of of the thePembine-Wausau Pembine-Wausauterrane terrane from fromdeformed deformedcontinental continentalmargin margin rocks rocks which whichexhibit exhibitaanodal nodalmetamorphic metamorphicpattern patternimposed imposedduring duringcollapse collapseof ofthe theorogen orogen(Schneider (SchneideretetaL, al., 1996; 1996; Marshak Marshak et et al., al., 1997). 1997). Abundant Abundant mica mica Ar/Ar ArIAr cooling cooling dates dates from from central central Minnesota Minnesota and and northernmost northernmost Wisconsin Wisconsin and and Michigan Michigan indicate indicate that that collapse collapseand andorogenic orogenicunroofing unroofingoccurred occurredatat175017501700 1700 Ma shortly shortly after after an anepisode episodeof ofwidespread widespreadmagmatism magmatismatat1770-1760 1770-1760Ma Ma(Holm (Holmand andLux, Lux,1996; 1996; Schneider Schneider et et al., al., 1996). 1996).InIncontrast, contrast,Rb-Sr Rb-Srwhole wholerock rockisocbron isochronand andbiotite biotitemineral mineraldates datesininnorthern northernand and central central Wisconsin Wisconsin (Peterman (Petermanand and Sims, Sims,1988) 1988)are are mostly mostly Middle Middle Proterozoic Proterozoic (1600-1100 (1600-1100Ma) Ma) and and reflect reflect variable variable thermal thermal resetting resettingassociated associatedwith withaalow-grade low-grade—1630 -1630 Ma metamorphic event (Van Scbmus Schmus and and Woolsey, Woolsey, 1975; Van Van Schmus Schmus et al., al., 1975), 1975), intrusion intrusion of the the 1470 1470 Ma Ma Wolf Wolf River River batholith, batholith, and and Keweenawan Keweenawan activity. activity. Post-accretion Post-accretion rapid rapid stabilization stabilization resulted resulted in in the the accumulation accumulation of of post-tectonic post-tectonic quartz quartz arenites arenites in in the the southern southern Lake Lake Superior Superior region region (Van (Van Schmus Schmus et al., 1993). 1993). Deformed Deformedquartzite quartziteunits units in in central central and and southern southernWisconsin Wisconsin yield yield post-Penokean post-Penokean detrital detrital zircon Pb-Pb ages (Van (Van Wyck, 1995). 1995). The The folded folded Baraboo Baraboo quartzite quartziteis is depositional depositionalon on aa 1752 1752Ma Ma granite granite(Medaris (Medariset et a!., al., 1996) 1996)and and contains contains detrital detrital zircons zircons as as young young as as 1712 1712Ma Ma (Dott (Dott et et a!., al., 1997). 1997). The Theminimum minimumage ageof ofthese thesequartzite quartziteunits unitsisisconstrained constrained only only by by the the fact factthat thatsome someare areintruded intrudedby bythe the1470 1470Ma MaWolf WolfRiver Riverbatholith, batholith,although althoughDott Dott(1983) (1983)and and Van Van Schmus Schmuset et al. al. (1993) (1993)speculated speculatedthat that they they may may have have been been deformed deformed during during the the 1630 1630Ma Ma event. event. The The predominantly predominantly Middle Middle Proterozoic Proterozoic mica mica mineral mineral dates of central central Wisconsin contrast sharply with the the well-grouped well-grouped 1750-1700 1750-1700Ma Ma mica mica dates dates obtained obtainedfrom from central centralMinnesota, Minnesota,northernmost northernmost Wisconsin, Wisconsin, and and northern northern Michigan. Michigan. The The1750-1700 1750-1700Ma Madates datesare arethe theoldest oldestmica micadates datesobtained obtainedfrom fromthe theinternal internal portions portions of of the thePenokean Penokeanorogen orogenand andthus thusalmost almostcertainly certainlyreflect reflect primary primary cooling cooling through through mica mica closure closure temperatures temperatures following following Penokean Penokean metamorphism. metamorphism. Considering Considering that that primary primary cooling cooling atat1750-1700 1750-1700Ma Ma was An—1630 -1630 Ma Maage age was orogen orogen wide, wide, ititisislikely likelythat thatthe theyounger youngermica micadates datesrepresent representthermal thermalresetting. resetting.An contour contour thus thus separates separates basement basement with with typical typical post-Penokean post-Penokean cooling cooling ages to the the north north (and (and west, west, in in Minnesota) Minnesota)from frombasement basement with with thermally thermally reset reset ages ages to the south. The Theeastward eastwardextent extentof ofthe thechrontour chrontourisis not not precisely preciselylocated, located,however, however,north northof ofthe theFlambeau Flambeauquartzite quartziteininnorthwest northwestWisconsin Wisconsinthe thechrontour chrontourisis sharply sharplydefined definedby byRb-Sr, Rb-Sr,K-Ar, K-Ar,and andAr-Ar Ar-Armica micadates. dates. Importantly, Importantly,the theFlambeau Flambeauthermal thermalfront frontin innorthwest northwestWisconsin Wisconsincoincides coincidesspatially spatiallywith withan anapparent apparent deformational deformational front front ininoverlying overlyingpost-Penokean post-Penokeanquartzites. quartzites. In In Minnesota, Minnesota, the thesubhorizontal subhorizontal Sioux Sioux 73 �quartzite quartzitelies liesjust justsouthwest southwestofofPenokean Penokeaninternal internalzone zonerocks rockswhich whichcooled cooledrapidly rapidlythrough throughmica micaclosure closure temperatures Ma. In temperaturesatat—1750 -1750 Ma. Innorthwest northwest Wisconsin, Wisconsin,the theBarron Ban-onquartzite quartziteisisessentially essentiallyflat-lying flat-lyingand andisis depositional depositional on on Precambrian Precambrian basement basement with mica ages between 1730-1700 1730-1700 Ma. South Southof ofthe thethermal thermal front, front,and andonly only25 25km kmsouth southofofthe theBarron Barronquartzite, quartzite,are areexposures exposuresofofsteeply-dipping steeply-dippingFlambeau Flambeauquartzite. quartzite. Here Herethe thequartzite quartziteisisfolded foldedinto intoaamoderately moderatelywest-plunging west-plungingsynform synform(Myers, (Myers,1974) 1974)similar similarto to the thestyle styleof of deformation McCaslin quartzites. quartzites. The Therelatively relativelyundeformed undeformedBarron Barronand and deformationexhibited exhibitedby by the theBaraboo Barabooand andMcCaslin Sioux SiouxProterozoic Proterozoicquartzites quartzitesmust musteither eitherlie lieoutside outsidethe theregion regionofofsignificant significantpost-Penokean post-Penokeandeformation deformation (as (asseems seemssuggested suggested by by the thespatial spatialcoincidence coincidence of of aathermal thermalfront frontwith withaadeformational deformationalfront) front)ororbebe younger younger quartzite quartzitepackages packagesdeposited depositedafter aftersignificant significantpost-Penokean post-Penokean deformation. deformation. To Totest testwhether whetherthe the subhorizontal subhorizontalquartzites quartzitesare arecorrelatable correlatablewith withthe thedeformed deformedquartzites quartziteswe weobtained obtainedsingle-grain, single-grain,singlesinglespot ages spot207Pb/206Pb 2 0 7 ~ b / 2 0 6ages ~ b on detrital zircons separated from from the the Sioux, Sioux,Barron, Barron,and andFlambeau Flambeauquartzites. quartzites. Because Becausewe weare aremostly mostlyinterested interestedininconstraining constrainingthe themaximum maximumage ageofofeach eachquartzite quartzitewe weconcentrated concentratedour our efforts possible. All efforts on ondating dating euhedral euhedral or or subhedral subhedral crystals crystals wherever wherever possible. All three three quartzite quartzite bodies bodies yielded yielded Early Early Proterozoic Proterozoic and and Late Late Archean Archean detrital detrital zircon zircon dates dates comparable comparable to to dates dates obtained obtained by by Van Van Wyck Wyck (1995) (<2000Ma) Ma)dates dates (1995)for fordeformed deformedquartzite quartzitebodies bodiesin in Wisconsin. Wisconsin. Many Manyofofthe thelate lateEarly EarlyProterozoic Proterozoic(<2000 fall fallalong alongaadiscordia discordiawith withaalower lowerintercept interceptatator ornear nearthe theorigin originindicating indicatingrecent recent lead lead loss lossattributed attributedto to upper Proterozoic uppercrustal crustalfluid fluidcirculation. circulation.Reliable Reliable207Pb/206Pb 207Pb/2w~b Proterozoicages agesare arebetween between1730 1730and and1850 1850Ma Mafor for the theSioux Sioux(9 (9grains), grains),between between1714 1714and and1880 1880Ma Mafor forthe theFlambeau Flambeau (9 (9 grains), grains),and and between between 1750 1750and and 1880 1880 Ma Mafor forthe theBarron Barron(6 (6grains). grains).These Thesedata dataattest attesttotothe thefact factthat thatall allthree threequartzite quartzitebodies bodiespost-date post-datethe the1760 1760 Ma Mamagmatic magmaticevent eventin inthe theLake LakeSuperior Superiorregion. region. Thus Thusfar farthere thereisisno noevidence evidencetotosuggest suggestthat thatthe theBarron Ban-on and andSioux Siouxquartzites quartzitesare areyounger youngerthan thanthe thedeformed deformedquartzites quartzitesfound foundthroughout throughoutmost mostofofWisconsin. Wisconsin. Abundant Abundant new new thermocbronologic thermochronologic data in the Lake Superior Superior region allow us to make make aa simple simple but but important importantfirst-order first-orderobservation observationthat thatprovides providesthe thefirst firstdirect directstructural structuralevidence evidencethat thatthe thequartzites quartziteswere were deformed deformedduring duringthe thelow-grade low-grade—1630 -1630 Ma event in the Lake Superior region. We Wenote notethat thatsubhorizontal subhorizontal post-Penokean post-Penokean quartzites quartzites consistently consistently overlie overlie crystalline crystalline basement basement with with primary primary post-Penokean post-Penokean cooling cooling ages, ages, whereas whereas highly highly deformed deformed quartzites quartzites everywhere everywhereoverlie overliecrystalline crystallinebasement basementwith withsecondary secondary (thermally (thermally reset) reset) cooling coolingages. ages.We Weare arefortunate fortunatethat thatthe theproximity proximityofofthe thedeformed deformedFlambeau Flambeauquartzite quartzitetoto the the subhorizontal subhorizontal Barron Barron quartzite quartzite in in northwest northwest Wisconsin Wisconsin allows allows us to to precisely precisely locate locatethis this deformational/thermal deformationalhhermal front. front. An Anage ageofof1650-1630 1650-1630Ma Mafor forthe thedeformation deformationseems seemsreasonable reasonablegiven giventhat that coolingages agessouth southof ofthe thefront frontprobably probablypost-date post-datethe thedeformation deformationsomewhat. somewhat. cooling The The thermal thermal front front extends extends eastward eastward into into northern northern Michigan, Michigan, the the geology geology of of which which isisdominated dominated by by gneiss gneissdomes domesand and classic classic nodal nodal metamorphic metamorphic isograds. No NoEarly EarlyProterozoic Proterozoicpost-Penokean post-Penokeanquartzites quartzitesare are known known north north of of the the McCaslin McCaslin quartzite. quartzite.However, However,it's it'sinteresting interestingtotonote notethat thatthe theRepublic Republicmetamorphic metamorphic node node located locatednorth north of of the thethermal thermalfront frontisisconcentric concentricwhereas whereasthe thePeavy Peavymetamorphic metamorphicnode nodelocated locatedsouth south of the the thermal thermal front frontisiselongate elongateeast-west. east-west. ItIt isis tempting tempting to to speculate speculate that that the the Penokean Penokean isograds isograds of the the of Peavy Peavy metamorphic metamorphic node node have have been been shortened shortenednorth-south north-south and and may may therefore therefore be be yet yetanother anotherstructural structural manifestation of of the the1630 1630Ma Madeformational deformationalevent. event. If If our our interpretations interpretations are are correct, correct, then thenthe thesimilar similar manifestation orientation orientation of of post-Penokean post-Penokean folds folds and and Penokean-age Penokean-age folds (north (north of the the front) front) requires requires that that caution caution be be used usedwhen whenattributing attributingbasement basementstructures structuressouth southofofthe thefront fronttotoPenokean Penokeandeformation. deformation. The Ma metamorphism metamorphism has has been one of the most Thelow-grade low-grade—1630 -1630 Ma most poorly poorly understood understood events events in inthe the Lake Lake Superior Superior region. region. Although Althoughitithas haslong longbeen beenspeculated speculatedupon uponthat thatthe thequartzites quartzitesmay mayhave havebeen been deformed deformed during during this this event event (Dott, (Dott, 1983; 1983; Van Van Schmus Schmus et al., al., 1993), 1993), until now there has been no no direct direct evidence evidence of of any any intrusive intrusive or or deformational deformational event of that age. We Webelieve believethat thatthe thedata datasummarized summarizedhere here provides provides the the missing missing structural structural link link to to that that event. event. The Thetiming timingand andthe thestrong strongapproximately approximatelynorth-south north-south shortening shorteningstyle styleof of post-Penokean post-Penokeandeformation deformationtogether together are are consistent consistentwith with itit being being the theresult resultof offoreland foreland deformation deformation associated associated with emplacement emplacement of the outer outer tectonic tectonic belt belt onto onto the the southernmost southernmost margin margin of of Laurentia Laurentia during the the Mazatzal Mazatzal orogeny orogeny (Van (Van Schmus et al., 1993). 1993). The Therocks rocksofofthe theTranscontinental Transcontinental Proterozoic Proterozoic provinces provinces were were subjected subjected to to aa major major magmatic magmatic event event during during the theMiddle MiddleProterozoic Proterozoicfrom from 1500-1300 1500-1300 Ma. The Theundeformed undeformedWolf WolfRiver Riverbatholith batholithinincentral centralWisconsin Wisconsinisissurrounded surroundedby byand andlocally locally intrudes intrudesthe the deformed deformedquartzite quartzitebodies, bodies,leading leadingsome someto tosuggest suggestthat thatquartzite quartzitedeformation deformationwas wascaused causedby by Middle Middle Proterozoic Proterozoic epeirogenic epeirogenic doming doming and and igneous intrusion (Greenberg and Brown, 1984). However, However, the the existence existenceof of the theFlambeau Rambeau deformational deformationalfront front(located (locatedover over 100 100km km from fromexposures exposuresof of the thebatholith) batholith) shows showsthat that the the deformation deformationdoes does not not wane wane away away from from the the batholith. Rather, Rather,the theabrupt abruptnature natureof ofthe thefront front is is characteristic characteristic of of tectonic, tectonic, not not intrusion intrusion related, deformation. This This study studysupports supportsDott's Dott's (1983) (1983) model model which which attributed attributed post-Penokean post-Penokean deformation deformation in in Wisconsin Wisconsin to to Early Early Proterozoic Proterozoic plate plate collision collisionfrom fromthe the south 1700-1600Ma Ma outer outer tectonic tectonic belt belt south and and supports supports the the hypothesis hypothesis of of Van Van Schmus Schmus et et al. al. (1993) (1993) that that the the 1700-1600 was was aa single single coherent coherentbelt belt extending extendingfrom fromCalifornia Californiato to Labrador. Labrador. References Referenceswill will be be made madeavailable availableatatthe themeeting meetingor orupon uponrequest request(dholm@kent.edu). (dholm@kent.edu). 74 �THE THERECOGNITION RECOGNITIONOF OFAALAVA LAVADOME DOME COMPLEX COMPLEXAND AND ITS ITS RELATIONSHIP RELATIONSHIP TO TO THE THEARCHEAN ARCHEANSTURGEON STURGEONLAKE LAKE CALDERA, CALDERA,NORTHWESTERN NORTHWESTERNONTARIO ONTARIO GEORGE RONALD L. MORTON GEORGEJ.J.HUDAK HUDAKAND AND RONALD MORTON Economic EconomicVolcanology VolcanologyResearch ResearchLab, Lab,Geology GeologyDepartment, Department,University Universityof ofMinnesota Minnesota —-Duluth, Duluth, Duluth, Duluth,Minnesota, Minnesota, USA USA 55812 55812 JAMES JAMES M. M. FRANKLIN FRANKLIN Geological GeologicalSurvey Survey of of Canada, Canada,601 601Booth Booth Street, Street, Ottawa, Ottawa,Ontario, Ontario,Canada CanadaK1A KIA0E8 OE8 Detailed has led to the Detailed volcanic facies mapping mapping has the recognition recognition of of the the Archean Archean Sturgeon Sturgeon Lake Caldera Caldera Complex Complex in northwestern Ontario (Morton This complex complex is isup uptoto Lake (Morton et et al., al., 1991). This 25 kilometers kilometers in in strike strike length, length, contains contains up up to to 4500 4500 meters meters of of caldera calderafill fillmaterial, material,and andhosts hosts 25 six six known known volcanogenic volcanogenic massive massive sulfide sulfide (VMS) (VMS)orebodies orebodiesand andnumerous numeroussubeconomic subeconomic massive sulfide sulfide lenses. The Thevolcanic volcanicrocks rockswithin withinthe thecomplex complexhave havebeen beendivided dividedinto intoten ten massive distinct based on the types distinct stratigraphic stratigraphic successions successions based types of ofvolcanic volcanicand andsedimentary sedimentaryrocks rocks present present (Hudak, (Hudak,1996). 1996). The TheLyon LyonCreek CreekSuccession Successioncomprises comprisesthe theuppermost uppermostof ofthese thesesuccessions. successions.Historically, Historically, these these rocks rocks were were called calledthe theNBU NBUrhyolite rhyolite(Harvey (Harvey and andHinzer, Hinzer, 1981; 1981;Severin, Severin,1982), 1982),and and were were interpreted interpreted as as rhyolite rhyolite tuffs, tuffs,lapilli lapillituffs, tuffs,agglomerates, agglomerates,and andgraphite-rich graphite-richsediments. sediments. However, However, our our detailed detailedfield fieldmapping, mapping,core corelogging, logging,and andpetrographic petrographicinvestigations investigationsindicate indicate that that little littleor ornone noneof ofthese theserocks rocksare arepyroclastic pyroclasticininorigin. origin. Instead, Instead,this thissuccession successionhas hasbeen been interpreted interpretedto torepresent representaasubaqueous subaqueouslava lavadome domecomplex. complex. krn in strike strike length length and and up up to to 540 540 A plagioclase-phyric plagioclase-phyric dacite A dacite lava lava dome dome that that is is 2-3 2-3 km meters meters thick thick forms formsthe thebase baseofofthe thesuccession. succession. This Thisdome domeoccurs occurswithin withinthe thecaldera calderaedifice edifice krn west west of of aa major major caldera caldera margin margin fault. fault. An Anabsence absenceofofflow flowcontacts, contacts, approximately 1-2 1-2 km approximately and andan anincrease increaseininthe thesize sizeofoffeldspar feldsparphenocrysts phenocrystsfrom fromthe themargins marginstoward towardthe the core coreof ofthe the dome, suggests suggests that thatthe thedome's dome'sgrowth growthwas wasendogenous. endogenous.AAseries seriesofofpredominantly predominantlydomedomedome, derived matrix-supportedbreccia breccia derived clastic clastic sediments sediments overlies overliesthe thedome. dome. These Theseinclude: include:a)a)matrix-supported deposits depositswhich which contain contain up up to to75% 75%dome domefragments; fragments;b) b) arkosic arkosicgreywacke greywackedeposits; deposits;c) c) veryveryfine finegrained grainedtuffaceous tuffaceoussandstone sandstoneand andsiltstone siltstonedeposits; deposits;and andd) d)graphite-rich graphite-richshale shaledeposits. deposits. The Theclastic clasticsediments sedimentslack lackan anabundance abundanceofofpumice pumice(rarely (rarely>3%) >3%)and andcross-bedding cross-beddingisisabsent. absent. Silica-, carbonate-, carbonate-, oxide-, oxide-, and/or and/or sulfide-facies sulfide-facies iron iron formations formations and and associated associated chert chert are are Silica-, interlayered interlayeredwith withthe theclastic clasticsediments sedimentsand, and,locally, locally,directly directlyoverlie overliethe thelava lavadome. dome. Detailed Detailedfacies faciesmapping mappingindicates indicatesthat thatthe thebreccia brecciadeposits, deposits,the thegraphite-rich graphite-richshales, shales,and and theiron ironformation formationwere wereformed formed ininrestricted, restricted,fault-bounded fault-bounded basins within the top top of ofthe the the dome. dome.The Theiron ironformation formationresulted resultedfrom fromrelatively relativelylow lowtemperature temperaturehydrothermal hydrothermalactivity activitythat that occurredproximal proximal to to the the basin basin marginal marginal faults. faults. The Thelack lackofofpumice, pumice,the theabsence absenceofofevidence evidence occurred suggestive suggestive of of reworking reworking by by surface surfacecurrents currents(e.g. (e.g.cross-bedding), cross-bedding), and andthe the presence presence of of graphitic graphitic shales shales suggests suggests aarelatively relativelydeep deepwater water(>500 (>500meters), meters),anoxic anoxicenvironment, environment, although althoughno noabsolute absolutewater waterdepth depthestimate estimateisispossible. possible. Detailed studies studies on onfelsic felsicvolcanic volcanic centers centers indicate indicate that that the the final finaltwo twostages stagesofofcaldera caldera Detailed development development involve involve major major ring ring fracture fracture volcanism volcanism and and terminal terminal hot hot spring springand andfumarolic harolic activity activity (Smith (Smith and andBailey, Bailey,1968). 1968). The The strata stratacomprising comprisingthe theLyon LyonCreek CreekSuccession Succession represent these these final final two two evolutionary evolutionary stages stages in in the the development development of of the theSturgeon SturgeonLake Lake represent Caldera CalderaComplex. Complex. 75 �References References Harvey, J. D., and Hinzer, J. J. B., 1981, 1981,Geology Geology of of the the Lyon Lyon Lake Lake ore ore deposits, deposits, Noranda Noranda Mines Mines Ltd., Ltd., Sturgeon SturgeonLake, Lake, Ontario: Ontario:Canadian CanadianInstitute Instituteof ofMining Miningand and Metallurgy Bulletin, Bulletin, v. 74, 74, no. 833, 833, p. 77-84. 77-84. Hudak, G. J., 1996, 1996, The The physical physical volcanology volcanology and and hydrothermal hydrothermal alteration alteration associated with with late late caldera caldera volcanic volcanic and and volcaniclastic volcaniclastic rocks rocks and and volcanogenic volcanogenicmassive massive sulfide sulfide deposits deposits in in the the Sturgeon SturgeonLake Lake region region of of northwestern northwestern Ontario, Ontario, Canada: Canada: unpublished unpublished Ph. Ph. D. D. dissertation, dissertation, University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, MN, MN, 463 463 pages. pages. Morton, Morton, R. L., Walker, Walker, J. J. S., S., Hudak, Hudak, G. G. J., J., and and Franklin, Franklin, J.J. M., M., 1991, 1991,The The early early development developmentof of an an Archean Archean submarine submarine caldera calderacomplex complex with with emphasis emphasison onthe the Mattabi Mattabiash ash flow and its its relationship relationshipto to the the Mattabi Mattabi massive massive sulfide sulfidedeposit: deposit:Economic EconomicGeology, Geology, flow tuff and v. 86,p. 86, p.1002-1011. 1002-1011. Severin, P. W. A., 1981, 1981, Geology Geology of the Sturgeon Sturgeon Lake Lake Cu-Zn-Pb-Ag-Au deposit: deposit: Canadian Canadian Institute Instituteof of Mining Mining and and Metallurgy MetallurgyBulletin, Bulletin, v. v. 75, 75, no. no. 846, 846,p. p. 107-123. 107-123. Smith, R. L., and Bailey, R. A., 1968, of 1968, Resurgent Cauldrons: Geological Society of America 13-662. AmericaMemoir Memoir116, 116,p.p.661 3-662. 76 �GEOLOGIC SETTING OF SUBECONOMIC GOLD GEOLOGIC GOLD DEPOSITS DEPOSITSIN INTHE ThE VIRGINIA HORN, NORTHEASTERN MINNESOTA: MINNESOTA.A AHORN HORNOF OFPLENTY PLENTY OR A HORNSWOGGLE? NORTHEASTERN HORNSWOGGLE? JIRSA, Geological JIRSA, Mark Mark A., BOERBOOM, BOERBOOM,Terrence Terrence J., J.,and and CHANDLER, Val Val W.-Minnesota W.—Minnesota Geological Survey(MGS), (MGS),2642 University Avenue,St. St.Paul, Paul,MN, MN,55114-1057 55114-1057(jirsa001@tc.umn.edu) (nrsaOOl@tc.urnn.edu) Survey University Avenue, Several significant-though, significant—though, to to date date subeconomic-gold subeconomic—gold deposits deposits occur occur within within Archean Archean bedrock bedrock in the area known as the Virginia Horn. Three Three prospects prospects were were worked worked to to varying varying degrees degrees by exploration exploration companies in the late late 1980's, 1980'~ and ~ one of of these, the "Viking prospect", The and prospect",was was extensively extensivelydrilled. drilled. The exploration focused focused on pervasively pervasively altered altered felsic felsicporphyry porphyry intrusions intrusions having having variably variably well well developed deformation envelopes and and associated associated carbonate-sericite alteration. Recent mapping mapping by by the theMGS MGS (Jirsa (Jirsa deformation envelopes alteration. Recent and others, others, 1998), 1998), together together with with geochemical work work by by the the Natural Natural Resources Research Research Institute Institute (Englebert and Hauck, 1991; 1991; and information on on the the lithological lithological and work work in in progress) progress) has has provided provided further further information and structural structuralframework, framework, potential potential sources sources of of Au, and relative timing of mineralization mineralization in these prospects and the surrounding surroundingarea. area. à 'I ''''''I, ,,,,,,,,, ,f/f,, ,,,,,,,,,,, MINNTAC SEQUENCE \- %, 'S .. , .' .' \ \ '. 'S S S 'S ,1 , S.''' / / /1 / /, /1 •5%.'.'\\'SI / / / / / / /1 '''''S.''''' '''''S'S'S'''' '''''''S'S''', ,,/,//,/,,, 'S'S5'S'S'S'S'S 'S 'S 'S 'S'S.' 'S 'Ss 'S 'S '''''S ''''S'S'S' '''"'S /, MUD LAKE SEQUENCE Graywacke (stippled) and volcanic rocks (white) Figure 1—Schematicblock blockdiagram diagramofofthe theVirginia VirginiaHorn. Horn.Map Mapsurface surfacedimensions dimensions approximately approximately Figure 1-Schematic 30X30 km. km. 30x30 The Archean rocks of the Virginia Horn lie within the Wawa subprovince subprovinceof of Superior SuperiorProvince. Province. The rocks are are subdivided subdivided into northern and southern of metamorphic metamorphic grade grade and and southern panels on the basis of deformation style. The The northern northernpanel, panel,immediately immediatelysouth southofofthe theGiants GiantsRange Rangebatholith, batholith,contains contains intensely lineated, schists having having volcanic volcanicand and clastic clasticprotoliths. protoliths. The southern heated, amphibolite-grade schists southern panel that were metamorphosed to much lower grades, panel contains contains lithologically similar rocks that grades, ranging ranging from prehnite-pumpellyite to low greenschist. The two panels are separated by the east-trending, post-metamorphic, Laurentian Laurentianfault fault (Figure (Figure1). 1).The Themetamorphic metamorphiccleavage-forming cleavage-formingevent event in in both both panels of 33major majordeformations-the deformations—theother othertwo twodeformation deformationevents eventsproduced produced no no panels was was the the second second (1)2) (D2) of metamorphic affects. affects. The first (Dl) (Di) involved upright discernible metamorphic upright folding, folding, soft-sediment soft-sediment deformation, deformation, and complex faulting; the third third (D3) (D3) produced produced localized localized semi-brittle semi-brittle crenulation crenulation of of D1 Dl and and D2 D2 structures, brittle fractures, of earlier-formed earlier-formed faults. faults. Amphibolite structures, fractures, and and selective selective reactivation of Amphibolite grade grade sequence; the the low low and and sub-greenschist sub-greenschist grade grade rocks north of the Laurentian fault comprise the Minntac sequence; 77 �strata south of the Laurentian fault are subdivided The Minntac subdivided into Mud Lake and Midway sequences. The sequence contains strongly banded banded schists schists having geochemical geochemical and outcrop-scale outcrop-scale characteristics characteristics of mafic to intermediate volcanic and volcaniclastic volcaniclastic strata, strata, subvolcanic subvolcanicmafic maficsills, sills,and andgraywacke. graywacke. Although of the Minntac sequence, sequence, relict relict grading grading and bedding the possibility of tight folding is great in rocks of Incontrast, contrast,the the Mud Mud Lake Lake sequence sequence forms forms a broad, southward stratigraphic stratigraphic facing. facing. In consistently indicate southward southwest-plunging, D1 D l syncline synclinethat that isis cored cored by by graywacke, graywacke, slate, slate, and and minor minor felsic felsic tuff; and and has has outer outer southwest-plunging, of calc-alkalic calc-alkalic and limbs of and tholeiitic tholeiiticstrata. strata. The Mud Lake strata are cut by several variably The Mud Mud Lake Lake sequence and the intrusions are porphyritic, quartzofeldspathic intrusions. The and are are locally locally in fault contact with, fluvial conglomerate and and subaerially subaerially unconformably overlain by, and deposited trachyandesite trachyandesite flows flows and and pyroclastic pyroclastic rocks that comprise the Midway sequence. seauence. The The deposited Tirniskaming -like strata in the Kirkland Lake and Shebandowan gold attributes of of Timiskaming Midway has many attributes Like the the Timiskaming Timiskaming rocks of mining districts of Ontario. Like of Ontario, those those in in the Virginia Virginia Horn Horn are have been deposited deposited in in aa fault-bounded fault-boundedpull-apart pull-apartbasin basinthat thatformed formedbefore beforethe theonset onsetofof1)2 D2 inferred to have deformation and metamorphism. datingback back to tothe thedays daysof of J.W. J.W. Gruner Gruner and and The Virginia Horn has a long history of of gold "shows", 'shows', dating F.F. Grout Grout (Grout, and some some visible visible gold gold can can still still be be found found locally in in altered altered rocks in and and adjacent (Grout, 1937), and adjacent to quartz quartz veins. Sampling Samplingby byexploration explorationcompanies companiesfocused focused largely largely on the quartzofeldspathic intrusions, and the country rocks were rarely rarely analyzed. analyzed. From those data and the current study, the generalizations can be made about the distribution distribution of of gold gold in in the the region: region: following generalizations 1. Gold 1. Gold is is most abundant abundant in in quartzofeldspathic quartzofeldspathicdikes. dikes. Thegreatest greatestgold goldcontents contents(as (aslarge large as as 50,000 50,000 ppb) 2. The ppb) occur occur in in rocks rocks that that are are pervasively pervasively altered and cut by quartz-rich veins. Anomalousquantities quantitiesofofgold gold(50(50-500 500 ppb) also also exist in sedimentary sedimentary and and volcanic volcanic wall-rocks wall-rocks of of 3. Anomalous the porphyritic intrusions. intrusions. 4. Gold Goldconcentrations concentrationsgreater greaterthan thana a"mineable" "mineable"cut-off cut-offof ofabout about1000 1000ppb ppb (0.029 (0.029 OPT) are recorded exclusively from samples of quartzofeldspathic quartzofeldspathic dikes. dikes. Inrocks rocks uniformly uniformly affected affected by carbonate-sericite alteration, 5. In alteration, gold gold is is most most abundant abundant in zones of of anomalous arsenic content. anomalous arsenic content. carbonate-sericite alteration and The carbonate-sericite alteration associated associated with with gold mineralization mineralization varies from pervasive and having textures that imply strong involvement in shearing. not obviously related to to the the rock rock fabric, to having Pyrite typically is associated with carbonate and sericite; sericite; and arsenopyrite and and chalcopyrite chalcopyrite occur occur locally. Alteration is inferred to have taken place during or just after D2 deformation, as the Alteration is inferred to have taken during or are variably variably affected affected by 82. That alteration is best developed along major fault alteration products are S2. That zones, lithologic contacts, contacts, and and adjacent adjacentto to and and within within the the quartzofeldspathic quartzofeldspathic intrusions. intrusions. Although Although the the shallow subsurface subsurface have been evaluated in in some some detail, detail, comparisons with analog analog deposits deposits surface and shallow imply that that unexplored unexplored potential potential exists; exists; 1) 1) at depth in in the the low-grade low-grade rocks rocks of of the the Midway Midway in Canada imply and and Mud Mud Lake Lake sequences; sequences; and and 2) 2) throughout throughout the thehigh-grade high-gradeMirintac Minntac sequence. sequence. ACKNOWLEDGMENTS Mapping Mapping and and geochemical geochemical study study was was supported supportedby by the the Minnesota Minnesota Legislature Legislatureon on recommendation recommendationof of the Minerals Coordinating CoordinatingCommittee. Committee. REFERENCES REFERENCES Englebert, and Hauck, 1991,Bedrock Bedrockgeochemis geochemistryofofArchean Archeanrocks rocksin innorthern northern Minnesota: Natural Natural Englebert, J.A., J.A., and Hauck, S.A., 1991, Institute Technical Report NRRI/TR-91/12, 200 p. NRRI TR-91/12,200 Resources Research Institute 7 Grout, Petrographic study F.F., 1937, Petrographic studyof of gold goldprospects prospectsofofMinnesota: Minnesota:Economic EconomicGeology, Geology,v.37, v.37,P. p.56-68. 56-68. Grout,F.F., Jirsa, Bedrockgeolo geologic map of of the the Virginia Horn, Horn, Mesabi Ran e,St. St. Jirsa,M.A., Boerboom, Boerboom, T.J., and Morey, Morey, G.B., 1998, Bedrock 'c map Mesabi Iron IronRange, Louis County, County,Minnesota: Minnesota:Minnesota MinnesotaGeological GeologicalSurvey SurveyMiscellaneous MiscellaneousMap MapM-85 M-85(digitial), (digitial),scale scale1:48,000. 1:48,0%. 78 �EFFECT EFFECI' OF OFELECTRIC ELECI'RICPULSE PULSEDISAGGREGATION DISAGGREGATION ON ON MICROFOSSIL-BEARING MICROFOSSIL-BEARING ARGILLACEOUS ARGILLACEOUSLIMESTONE LIMESTOM OF OF THE THE MIDDLE MIDDLE ORDOVICIAN ORDOVICIAN DECORAH DECORAH SHALE SHALE KJERLAND, KJERLAND, Dean Dean W., W., and andKJERLAND, KJERLAND, Marc MarcP., P., amateur amateurpaleontologists, paleontologists, 73563,3520@compuserv.com E-mail: 73563,352O@compuse~.com 8007 MN 55431 S, Bloomington, Bloomington, MN 8007 Xerxes Ave S, 55431 E—mail: The The Middle Middle Ordovician Ordovician Decorah Decorah Shale is a fossiliferous fossiliferous shale with lenses and thin beds beds of of coquinoidal coquinoidal limestone limestone and and calcareous calcareous shale (Rice). The Thecalcitic calciticmacrofossils macrofossilsand andphosphatic phosphatic conodont conodont microfossils microfossils have been been studied studied (Sloan, (Sloan, Webers). Webers). Though Though known known from from acid acid processing processingresidues, residues,other othernon—calcitic non-calcitic microfossils have have not not been beendocumented. documented. We samples of of limestone from Decorah We collected collectedover over250 250typical typicalhand—sized hand-sized samples Decorah Shale Shale beds beds disturbed disturbed during during the the reconstruction reconstruction of Hwys 110, 55 & 13 13 at at Mendota, Mendota, Minnesota Minnesota in in 1993. 1993. Our Our selection selection criteria criteria was was the the presence presence of of phosphatic phosphatic microfossils or fragments fragments visible visible with with Our photographic photographic documentation of 200 of of these these aa hand hand lens lens on oneither eitherororboth bothsurfaces. surfaces, Our surface surface microfossils microfossilsusing using optical optical microscopy reveals a wide variety of microfossils including including lithified lithifiedmud mud internal internalcasts castsof of bryozoans bryozoans(Cuffey), (Cuffey), laminated laminated plates, plates, and and gastropod gastropodsteinkerns. steinkerns. Separation Separation of microfossils microfossils from the the matrix matrix isis necessary necessary for for more more efficient efficientcollection collectionand and documentation. documentation. Full Fullviewing viewingof of specimens specimensisis useful useful for for classification. classification. Mechanical Mechanicalcrushing crushing is is not not an aneffective effectivemethod methodfor forcleanly cleanlyseparating separatingeither eithermacrofossils macrofossils or ormicrofossils microfossilsfrom from matrix. matrix. Acid Acidprocessing processingyields yieldsclean cleanmicrofossil microfossilspecimens specimensbut but artificially artificially selects selects for for either either calcitic or phosphatic material. material. Both Both Ca Ca and P, as well as Fe, 5, S, Al, A,Si, Si, and and Mg, Mg, have have been been confinned confirmed from from our our S.E.M. S.E.M. analyses analyses of of aa sample sample of of several severaldozen dozen typical typical microfossils. microfossils. Saini—Eidukat andWeiblen Weiblenreported reportedthe theuse use of of an an Electric Pulse Pulse Disaggregator (EPD) for Saini-Eidukat and fossil extraction extraction (see (see References). References). In In our our study study we we evaluated evaluated the potential potential of the the EPD EPD for for separating visible microfossils from the surface 'fossil hash' of Decorah Shale limestone and separating microfossils Shale limestone and also for sampling matrix of of this this rock. rock. We sampling for microfossils microfossils buried in the matrix We used the the specialized, specialized, upgraded version EPD EPD at the University of Minnesota which is upgradedlaboratory—scale laboratory-scale version is based based on on the the electric—pulse facility in St. Petersburg, Russia (Saini—Eidukat and Weiblen). electric-pulse facility Petersburg, Russia (Saini-Eidukat Weiblen). A cm long long xx 12.5 12.5 cm cm wide weighing about 1.2 1.2 kg, was quartered quartered A lenticular lenticularslab slab fragment, fragment,16 16cm with aa rock hammer and further fragmented/delaminated with a cold chisel to rock hammer and further fragmentedldelaminated with cold chisel toproduce produce walnut—sized fragments for electric walnut-sized fragments electric pulse pulsedisaggregation. disaggregation. The rock rock consisted consistedofofnon— nonweathered, crystalline calcite calcite with with typical weathered, compact, compact, dark dark blue—gray blue-gray crystalline typical cemented cemented calcitic calcitic macrofossil clay on both sides and macrofossil fragment fragment debris and gray interstitial surface clay and phosphatic phosphatic microfossils microfossils and and fragments fragmentsvisible visible on ononly onlyone onesurface. surface. The The slab slab pieces pieces were were hand hand fed fed in in two two batches batches into into the hollow cathode of the EPD over over aa 66 mm pulses at approximately 100 kV. kV. All mm integral integral sieve sieve and and subjected subjected to approximately approximately 200 pulses All material except except the the suspended suspended fines fines was was air air dried driedand andmechanically mechanicallysorted sorted through through brass brass sieves sieves (Table (Table 1.) 1.) The Thematerial materialwhich whichpassed passedthrough throughthe the0.25 0.25 mm mm sieve sievewas wasprocessed processeddry dry through through aa series series of of teflon teflonmeshes meshes(Table (Table2.). 2.). The aggregate calcite and yellow clay and aggregate produced produced by the the EPD EPD isis fragmented fragmented crystalline calcite and mud-sized fines. fines. Only Only aa small small fraction fraction consists consists of whole whole calcite calcite fossils fossils or or fragments fragments and and mud—sized non—calcitic microfossils and orpartly partlyenclosed enclosed in in calcite calcite matrix). matrix). non-calciticmicrofossils and fragments fragments(either (eithermatrix—free matrix-free or 79 �Table 1: 1:Grading Grading criteria criteria and and results: results: Table 2. Grading of of Class VIII Material Weight(in g) and % % Class Sieve(in mm) Weight(in 31.2 >6.0 31.2 2.5% ~6.0->4.0 297.8 24.0% 24.0% I1 II <6.0—>4.0 297.8 I11 ~4.0->2.0 397.3 32.1% 32.1% III <4.0—>2.0 397.3 IV 207.6 207.6 16.8% 16.8% Iv c2.0->1.0 <2.0—> 1.0 65.6 5.3% ~1.0->.701 vV <1.0—>.701 <.701—>.495 46.7 <.701->.495 46.7 3.8% VI c.495->.250 62.9 5.1% <.495—>.250 62.9 VII <.250 129.1 10.4% 10.4% 129.1 VIII e.250 Total Total 1238.2 1238.2 100.0% 100.0% Note: The material which passed through the Note: 0.25 mm brass brass sieve sieve was wasre—graded re-graded using using meshes. Results teflon meshes. Results are from top of mesh. II Class Class VIlla VIIIa VIIIb VIIIb VIlic VIIIc VIlId VIIId Mesh# (mm) Weight(m Weight(ing) g) and and % 6.4 #60 (>.250) 5.0% 15.9 12.3%; #80 (>.177) (>.I771 15.9 12.3%; #100(>.149) 13.0 13.0 10.1%; 10.1%; thru #100 #lo0 93.8 72.6%. Total 129.1 100.0% Total 100.0% materialsfrom fromthe theteflon teflonmeshes mesheswere werenot notexamined examinedatatthis thistime. time. The VIIIa-d materials The Class VIIIa—d Class ClassII—- VII materials were were examined examined with with an an optical opticalmicroscope microscopeand andsampled sampledfor fora).a).non— nonfossils, fragments fragments and fossil crystalline crystallinecalcite, calcite,b). b).fossil—bearing fossil-bearing calcite, and c). non—calcitic non-calcitic fossils, and unknowns. Based Basedon onsubjective subjectivecriteria criteria (i.e. typical, interesting, unusual or trophy categories) 654 fossils, fragments and unknowns were were collected. collected. Specimen Specimen counts counts are: are: 11.8% 11.8%calcitic calcitic fossils, crystalline calcite, fossils, 9.8% 9.8% phosphatic fossils fossils in crystalline calcite, 74.9% 74.9% loose loose phosphatic phosphatic fossils fossils and fragments, and 3.5% fossils and fragments, 3.5% unknown. unknown. Virtually all of of the thematrix—free matrix-free non—calcitic non-calcitic fossils recovered from from the top of the sieves fragments are from that portion of the aggregate (31%) recovered sieves .250 mm sieve in the the 2.0 2.0mm mm—- -250 sieveset set(Class (ClassIV—VII). IV-VII). Conclusion: provides aa new new method method for for disaggregating disaggregating rocks for for isolating isolating Conclusion:The The EPD EPD provides microfossils mm to to 0.25 0.25 mm. mm. EPD processing microfossils in the size range from 2.0 mm processing effectively effectively separates separates microfossils from allows efficient efficient phosphatic, calcitic, and pyritic microfossils from their calcitic matrix and allows testing of rocks for the the presence presence of buried specimens. Although Although some some specimens specimens may may break break in processing or during preserved in shale are during sample sample preparation, preparation, many fossils preserved are commonly commonly fractured naturally in the matrix. We Webelieve believethat that EPD EPDprocessing processingsimply simply separates separatesalready already damaged fragments or whole whole fossils fossils along along existing existing fractures. fractures. References: References: Cuffey, Roger J., Professor of Paleontology, Department of of Geosciences, Pemsylvania Pennsylvania State correspondence 1997 1997 and and 1998. 1998. University; personal correspondence Rice, William F.; "TheSystematics Systematicsand and Biostratigraphy Biostratigraphy of the Brachiopoda of the Decorah F.; "The St.Pau1, Minnesota", Mimesota", 1985, 1985,Unpublished M.S. thesis, University of Minnesota, Mimesota, Mpls. Shale at St.Paul, Saini-Eidukat, B., Saini—Eidukat, B.,and andWeiblen, Weiblen,P.W., P.W., 1996; 1996; "A "ANew New Method Method of of Fossil Fossil Reparation, Preparation, Using High-Voltage Pulses", references therein. therein. High—Voltage Pulses", Curator Curator 3912, 39/2, and references Sloan, Robert E, E, editor, editor, Middle Middle and and Late LateOrdovician Ordovician Lithostratigraphy Lithostratigraphy and Biostratigraphy Biostratigraphy of the Upper #35, Mimesota Minnesota Geological Survey, Upper Mississippi Mississippi Valley, Report of Investigations #35, University of Minnesota, university Mimesota, 1987. 1987. Webers, Gerald F.; "The Middle Mimesotat': Middle and Upper Ordovician Conodont Faunas of Minnesota": Mimesota Geological Geological Survey Survey Special SpecialPublication PublicationSeries SeriesSP—4, SP-4, 1966 1966 Minnesota 80 �RESULTS OF MODELLING MODELLING PROTEROZOIC PROTEROZOIC THERMAL THERMAL HISTORIES: HISTORIES: THE POSSIBLE POSSIBLEEFFECTS EFFECTS OF OF WOLF WOLF FUVER RIVER BATHOLITH BATHOLITH EVALUATING THE REHEATING THERMOCHRONOLOGIC DATA =HEATING ON THEMOCHRONOLOGIC DATA FROM FROM NORTHERN NORTHERN WISCONSIN WISCONSIN Jeff Jeff Loofboro Loofboro(student) (student) and and Daniel DanielHoim, Holm,Department Departmentof of Geology, Geology, Kent Kent State StateUniversity, University, Kent, OH 44242 Introduction. Mica MicaRb/Sr RblSrand andAr/Ar ArlArthermochronologic thermochronologicresults results across across northern northern Wisconsin Wisconsin and northern Michigan (Peterman and Sims, 1988, 1988, Tectonics; Schneider and and others, others, 1996, 1996, CJES; CJE!S;Hoim Holm and and others, 1997, 1997, GSAA) reveal a 1630-1600 1630-1600 Ma chrontour chrontour which separates separates basement basement rock with with primary primary cooling ages of 1760-1750 Ma Ma to the north from 4<1630 6 3 0 Ma ages to the south. The Thechrontour chrontourcoincides coincides physically with an apparent deformational front in overlying, Early Proterozoic, post-Penokean quartzites Hoim and others (1998, ILSG; and in review) to interpret complete leading Holm interpret the the chrontour chrontour to to represent representcomplete thermal resetting resetting of of micas associated with foreland deformation deformation related related to to accretion accretion from the south. thermal associated with However, we note that the chrontour also appears appears to surround surround the known known subsurface subsurface extent extent of of the the Middle Middle Wolf Mver River batholith batholith(Fig. (Fig. 1) 1) raising raising the the possibility possibilitythat that itit might might be be an an artifact of partial partial Proterozoic Wolf resetting. In Inthis this case, case, the the1630-1600 1630-1600Ma Ma chrontour chrontour may may represent represent aa collection collection of meaningless "mixed" ?nixed'' resulting from from partial partial resetting of of the older primary 1760-1750 Ma dates at 1470 dates resulting 1760-1750 Ma 1470 Ma Ma when when the the batholith intruded. Using Using the the MacArgon MacArgon program (Uster (Listerand andBaldwin, Baldwin,1996, 1996,Tectonophysics) Tectonophysics) we we have have various Proterozoic Proterozoic thermal thermal histories histories in in an attempt to evaluate modelled various evaluate the possible effects effects of of Middle Middle Proterozoic Proterozoic reheating on thermochronologic data data from from northern Wisconsin. Initial Initial conditions conditions and andmodel modelparameters. parameters.We Weinitially initiallyconsider consideraarock rockcontaining containing muscovite muscovite with a plateau ArIAr Ar/Ar date of 1765 Ma and biotite biotite with with a plateau plateau date date of of 1755 Ma. Ma. Precambrian Precambrian basement rock north of the chrontour chrontour in northwest northwest Wisconsin are are near near the the Early Early Proterozoic Proterozoic nonconformity nonconformity suggesting suggesting these rocks were at shallow Ma. Considering this, we chose three shallow crustal depths by —1700 -1700 Ma. three different different ambient temperatures temperatures(loo0, (100°, 150° 150°,and and200') 200°) and and imposed imposedaa thermal thermal pulse pulse at at 1470 Ma Ma to simulate ambient intrusion of the batholith. batholith. We We varied varied the the peak peak temperature temperature of of the the pulse pulse between between 200° 200O and and 450°C 450° (using (using 50°C to 22 my my (using (using 0.5 0.5 my my increments). In In 50° increments) and the duration of heating from instantaneous to all cases the duration of cooling back to ambient temperatures lasted 2 my and hence the total duration duration of the pulse varied in our models models from from 2-4 2-4 my. my. The plutonism on country rock The duration duration of thermal effects effects of plutonism is normally normally shorter than this (Carslaw (Carslaw and Jaeger, Jaeger, 1959, 1959, Clarendon Press), but we chose chose such such long long durations in in order order to to maximize maximize the the effects effects of of partial partial resetting resettingby bythe the batholith. batholith. We assume no other affects after after intrusion intrusion of of the the Wolf Wolf River batholith, batholith, ending ending the the thermal thermal history with thermal overprinting affects slow cooling cooling from from the the chosen chosen ambient ambienttemperature temperaturetotoO° 0°Catat600 600Ma Ma(Fig. (Fig.2). 2). The variables in the modelling thus include the peak temperature obtained, the duration of the thermal pulse, and the the initial initial temperature. The ambient temperature. The affect affect of each each of these these parameters on argon diffusion in muscovite and biotite is is described described below. Results thermal modeling. modeling.AsAsmight mightbebeexpected, expected,the thedominant dominantfactor factorinfluencing inlluencingpartial partial resetting Results of thermal is the peak temperature obtained by by the the rock rock during during the the imposed imposedthermal thermalpulse. pulse. Peak thermal pulses at or below the closure temperature of biotite (300°C) (3W°Cor muscovite (350°C) (350°Chad little affect on on the the initial initial cooling age regardless of the duration of heating. Peak Peakthermal thermalpulses pulsesof of50°C 50°above aboveclosure closuretemperature temperature resulted in considerable considerable partial partial resetting. resetting. In this case the duration of the heating interval did have a moderate degree of resetting total gas gasages ageswhich whichare are moderate affect on the degree resetting with 2 my my heating intervals intervals resulting resulting in in total —50 myyounger youngerthan than in in the case for Because of of the difference in closure -50 my for instantaneous instantaneous heating. heating. Because closure temperature between biotite and muscovite, the modelling reveals that large differences in the degree of partial resetting resetting (and hence apparent ages obtained) are expected for 1470 1470 Ma Ma peak peak thermal thermal pulses pulses between 300 and 450°C 450°C. Temperatures Temperatures100°C 100OCabove above the the mineral's mineral's nominal nominal closure closure temperature temperature resulted in nearly complete resetting resetting of of the the isotopic isotopic systematics systematics regardless regardlessof ofthe theduration durationof ofheating. heating. Varying the initial ambient temperature between 100-200°C 100-200OC had little little affect affect on the apparent apparent ages ages obtained. obtained. Implications. Existing Existingthermochronologic therm6chronologicdata data from from northern northern Wisconsin Wisconsin show nearly concordant muscovite and biotite dates near the chrontour (with muscovite around 1620 1620 Ma and biotite around around 1600 1600 GSAA). We Ma; Romano and others, 1997, GSAA). Weare areunable unableto toobtain obtainnearly nearlyconcordant concordantpartially partiallyreset resetages ages with any of our simulations and conclude that Middle Proterozoic intrusion of of the the Wolf River batholith was probably probably not responsible for generating the 1630-1600 1630-1600 Ma chrontour by partial resetting. This is indirectly indirectly supported supported by by two two independent independent lines lines of ofevidence. evidence. First, the degree of deformation conclusion is deformation Proterozoic quartzites in in Wisconsin Wisconsin does does not not wane away from the the Wolf Wolf River batholith as of the Early Roterozoic deformation. The would be expected for intrusion related deformation. The sharp sharp deformational deformational front front (which (which coincides coincides Second, with the 1630-1600 1630-1600 Ma clirontour) chrontour) is more more characteristic characteristic of tectonic-related tectonic-related deformation. Second, 81 �thennal thermaleffects effectsof ofthe theDuluth DuluthComplex Complexon onArchean Archeancountry countryrock rockininnortheastern northeasternMinnesota Minnesotaexist existonly onlytotoaa map-view distance distance of 10 10 km away from the intrusion (Hanson (Hanwn and others, 1975, GCA). By By comparison, comparison, the 40km kmaway awayfrom fromthe theknown known the 1630-1600 1630-1600Ma Ma chrontour chrontour in in northern northern Wisconsin Wisconsin isis located locatedmore more than than 40 subsurface extent of the Wolf River batholith (l3g. (Fig. 1). Our Ourresults results support supportthe the conclusion conclusion of of Hoim Holm and and others U G )that that the the1630-1600 1630-1600Ma Machrontour chrontourrepresents represents complete completethermal thermal resetting resetting of of micas micas others (1998, (1998, ILSG) tectonism. associated with latest Early Proterozoic tectonism. Lister, Lister, G.S., G.S., and andBaldwin, Baldwin,S.L., S.L., 1996, 1996,Modelling Modellingthe theeffect effectof of arbitrary arbitraryP-T-t P-T-t histories historieson onargon argondiffusion diffbsion in in minerals minerals using using the the MacArgon MacArgonprogram program for for the the Apple Apple Macintosh: Macintosh: Tectonophysics, Tectonophysics, v. 253, p. 83-109. #%. ../ %t %/% %/%/ &S:S:S:::S 3:S::S / . F. /. /. / / / FS. %S.F SaS. —:-xc-t-:.:-: %'..—.. % . KEWEENAWAN S. subhoilzontal, , Ba ffonF % ,, S ,,,- .. .. % % % .. - S. S. S. S. S. S. S. S. S. CM%S.S.S.S.S.S.S.S.1 S. S. S. ' —46 - :Penoke ambeau ightly fold I, fit ,f' a 50km Edge of Late Prol/ Phanerozoic cover / Baraboo qtzite I 1(tightly folded) / Approximate sub . -! surface extent of WRB I 91 I I 90 89 I 88 Figure I.Simplified Simplifiedtectonic tectonicmap mapof of the the central central Penokean Penokeanorogen, northern northern Figure 1. Wisconsin and Michigan, U.S.A. (after Sims, 1992; Holm and others, Wisconsin and Michigan, U.S.A. (after Sims, 1992; Holm and others, in in review). review). CM = continental margin; EPSZ = Eau Pleine shear zone; NSZ = Niagara suture CM = continental margin; EPSZ = Eau Pleine shear zone; NSZ = Niagara suture zone; MT Archean Marshfield Marshfieldterrane; terrane; WRB WRB == Wolf Wolf River River batholith. batholith. MT == Archean E 92 PeakT Peak T 3 + 2 tzE \ a 1 1800 1800 tt == duration duration of thermal thermal pulse pulse AmbientT Ambient T ,t 1470 Age(Ma) Age (Ma) 1470 600 600 Figure Figure 2. Temperature-time Temperature-timegraph graphshowing showing modelled modelledparameters. parameters. 82 �An Archean subaqueous heterolithic debris flow, Irwin, Irwinl Pifher, Pifher! and Meader Townships, Townshipsl Lake Nipigon Nipigon Region, Ontario ft Luther, Whitewater, Wl WI 53190 Frank R. Luther!Geology GeologyDepartment, Departmentl UW-Whitewater, UW-Whitewaterl Whitewatery 53190 lutherf@mail.uww.edu lutherf@mail.uww.edu This extensive body body of volcanic breccia breccia is is located located in in northern northern Irwin, Irwinl southeastern southeastern Meader, Meader! and and aa large large part part of of southern southernand andeastern easternPifher PifherTownships. Townships. It is 10-25 10-25 km east of Lake Lake Nipigon Nipigon and and 17-28 17-28km km north-northeast north-northeastof of Beardmore. Beardmore. Mapping by Mackasey (1975) and Kresz and Zayachivsky (1989) shows this rock to be enclosed in a thick sequence of typical greenstone greenstone assemblage rocks -flows, intermediate to felsic pyroclastics pillowed and massive basalt flowsl pyroclastics and and flows, flowsl and lesser amount amount of of spatially-associated spatially-associatedvolcanogenic volcanogenic sediments. sediments. It is cut by small granitic intrusions through most of its its exposure exposure area and and by by larger larger granitic granitic intrusions in Pifher Twp to to the the northeast. northeast. Metamorphism Increases to to the the northeast, perhaps caused by these these intrusions. Keweenawan northeast! Keweenawanintrusions intrusions which which cut cut the breccia breccia include a large diabase sill which dips gently to the south and a small dike, locally termed greenspar (Luther, Thomas, Kean, Keanl and and Luther, Luther! diabase dike! (Lutherl 1997; Thomasl in preparation). preparation). fragments ranging from from c <1l mm up to over The breccia contains rounded rock fragments 1 Im m in in maximum maximum dimension. dimension. Most fragments are disk-shaped disk-shaped to cigar-shaped cigar-shaped in in form although although irregular irregular on on smaller smaller scale; some some smaller smaller (5-20 (5-20 cm) cm) fragments fragments are are of fragments is, more competent more competent and and nearly nearly spherical. spherical. Sorting and alignment of isl in in some locations, locationsl poorly-developed poorly-developed primary primary bedding while, whilel in other locations, locationsl the sorting and alignment is a result of later strain. The smaller fragments fragments vary in in Larger composition from that of the composition the matrix matrix to to mafic mafic or or ultramafic ultramaficto to carbonate-rich. carbonate-rich. Larger fragments tend to be be similar to to the the matrix matrix in in composition composition although although minor minor differences differences in composition or consolidation consolidation cause the fragments to to weather weather high high or or low. low. The matrix of fine mm), matrix of the breccia is composed of fine quartz quartz grains grains (<0.05 (~0.05 mm)l euhedral to broken 4 . 1 to to euhedrai broken crystals of plagioclase (now albite) ranging in in size size from <0.1 1 mm, a minor pelitic fraction (now muscovite), and, locally, quartz, I muscovite)l and! locallyl fragments of quartzl and/or hornblende hornblende(now (nowchlorite) chlorite)up uptoto0.5 0.5mm. mm. The primary pyroxene andlor primary texture is epidotel actinolite, actinolitel over-printed by a metamorphic metamorphic assemblages of chlorite, chloritel epidote, Representative whole rock analyses of the matrix muscovite, muscovitel and and biotite. biotite. Representative matrix and and fragments are presented Theseanalyses analysesshow showthe theaverage average(igneous (igneous presented in Table 1. These rock equivalent) composition of of the matrix to be dacitic while the fragments vary from from dacitic dacitic to to mafic. mafic. fragments, (2) the relative relative In summary (1) (I) the heterogeneity of the fragments! homogeneity of the matrix, (3) the shape, and rounding of the fragments, matrix?(3) the shape! and rounding the fragmentsl (4) (4) the the 83 �great variability variability in in size size of of the the fragments, fragments, (5) (5) the the poorly poorlysorted sortedcharacter characterof of the thewhole whole great body of of rock, rock, and and(6) (6)the thespatial spatialassociation associationwith withpillowed pillowedvolcanics volcanicsand andbedded bedded body of aasubaqueous subaqueous tuffs lead leadthe the author author to to conclude conclude that that this this rock rock isisthe the product productof tufts debris flow flow or or flows flows off offthe the side side of of aavolcanic volcanic edifice. edifice. The Theslopes slopes presumably presumably debris consisted of of poorly-consolidated poorly-consolidatedvolcanogenic volcanogenic debris debrisincluding includingfinely-crystalline finely-crystalline consisted quartz and and clay clay which which was was transported transported from from nearby nearbyweathered weathered felsic-tofelsic-toquartz intermediate volcanics volcanics and and an an admixed admixedquantity quantityof of pyroclastic pyroclasticdebris. debris. intermediate Table 1. 1.Whole Wholerock rockanalyses analysesofofthe thematrix matrixand andselected selectedfragments fragmentsof of the the Table volcanic breccia. (XRAL) (XRAL) volcanic fraaments matrix matrix fraaments LN97-6-1BB LN97-6-2A ~~97-7-9~* LN97-6-2 LN97-7-9-2 LN97-7-9-2 LN97-6-1 LN97-6-2 LN97-6-2A LN9779A* Si02 Si02 Ti02 Ti02 A1203 A12 0 3 Fe203 Fe203 Feo FeO MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 p205 LO1 LOI TOTAL 643 0.49 15.8 1.85 3.2 0.08 2.92 4.87 4.54 1.05 0.10 0.55 99.75 60.5 0.53 63.2 0.51 0.51 16.0 1.38 4.9 0.09 4.63 3.53 4.18 1.15 0.12 2.4 16.5 1.85 16.0 1.73 5.4 0.09 4.36 4.42 3.47 2.18 99.41 3.1 0.07 2.15 6.03 3.53 1.49 0.11 0.85 99.39 57.8 1.45 45.4 0.36 22.2 7.34 0.8 0.12 0.88 17.7 0.88 0.30 0.08 2.0 97.52 98.06 0.11 95%epidote epidote ** 95% REFERENCES REFERENCES Kresz, D.U. D.U. and and Zayachivsky, Zayachivsky, B., B.,1989, 1989,Precambrian Precambriangeology, geology, Barbara, Barbara, Meader Meader Kresz, and Pifher Pifher Townships; Townships;Ontario Ontario Geological Geological Survey, Survey, rpt rpt270 270with withmaps maps2536-2537, 2536-2537, and 91p.p. 91 Mackasey, W.O., W.O., 1975, 1975, Geology Geology of of Dorothea, Dorothea, Sandra, Sandra, and and Irwin IrwinTownships, Townships, District District Mackasey, of Thunder Thunder Bay; Bay;Ontario OntarioDivision Divisionof of Mines, Mines,rpt rpt122 122with withmap map2294, 2294, 83 83 p. p. of F., 1997, 1997, The The Petrology Petrologyof ofgreenspar: greenspar: aaProterozoic Proterozoicporphyritic porphyriticdiabase diabase Luther, F., Luther, dike; Pifher Pifherand andIrwin IrwinTownships, Townships, Lake LakeNipigon NipigonDistrict, District,Ontario Ontario (extended (extended dike; abstract):43rd 43rdAnnual Annual Institute Instituteon onLake LakeSuperior SuperiorGeology Geologymeeting, meeting,Sudbury, Sudbury, abstract): 43. Ontario,v.v.43. Ontario, 84 �UPPER PENINSULA PENINSULA OF NEW FIELD OBSERVATIONS OBSERVATIONS OF THE CLARKSBURG VOLCANICS, UPPER MICHIGAN MICHIGAN MAKI, John C. and Bornhorst, Theodore J., J., Department of Geological Engineering and MAIU, MI 49931 4993 1 Sciences, Michigan Technological TechnologicalUniversity, University,Houghton, Houghton, MI The Clarksburg Volcanics are a member of the the Early Early Proterozoic Proterozoic Michigamme Michigamme Formation, Baraga Baraga Group, Marquette Supergroup and crop crop out near US-4 Group, Marquette Supergroup and US-41I between between Champion Champion and west Ishpeming, Ishpeming, Marquette County, County, Upper Upper Peninsula, Michigan (Cannon, (Cannon, 1974, 1975; Cannon and Klasner, Marquette Peninsula, Michigan Klasner, 1977; 1977; Simmons, 1974). 1974). The TheClarksburg ClarksburgVolcanics Volcanicsare are stratigraphically stratigraphically above above the the Greenwood Greenwood Iron-formation Iron-formation member of of the the Michigamme Michigamme Formation Formation and and are are laterally Member and below the Lower graywacke member restricted over a 19 19 km strike length and only crop out on the southern southern limb limb of of the Marquette Marquette trough. trough. These only provides provides data on on stratigraphic These rocks rocks dip dip about about 60 60 degrees degrees or more, hence the exposed section only and strike parallel variation. Despite metamorphism to the amphibolite amphibolite facies in most most exposures exposures and and fades in greenschist facies in aa few, few, primary primary textures textures are are well preserved in the outcrops. Clarksburg Volcanics Volcanics are composed mostly of volcanic rocks with lesser amounts The Clarksburg amounts of of clastic clastic sedimentary rocks and iron-formation. Field Field observations and available chemical data suggest that the volcanic rocks are dominantly basalt with less amounts amounts of of andesite. andesite. In general, general, the volcanic rocks are tuffs and agglomerates agglomerates containing containing fragments 0.5 to 1.5 1.5 cm in diameter. Near Near the thetowns townsof ofHumboldt Humboldtand and clast size is considerably larger larger than than elsewhere, elsewhere,up upto to 30 30 cm cm in in diameter. diameter. Laterally, Clarksburg, clast Laterally, the the typical clast clast size size is is considerably considerably finer finer in both the extreme eastern and western exposures with argillite argillite being common in the west Ishpeming exposures. These These observations observations suggest suggest a proximal proximal or or near near vent vent environment environment in the central central exposures exposures and a distal environment towards the east and west. Since Sincemafic mafic pyroclastic pyroclastic rocks rocks often often do do not not travel travel large large distances distances from from the volcanic volcanic vent, itit is is likely likely that that the the volcano volcano was quite near the central exposures of the Clarksburg Volcanics. central exposures Clarksburg Within the Clarksburg Volcanics there there are are several areas with Within Clarksburg Volcanics with interbedded interbedded banded banded ironironformation. The layers (I (1 to to44 mm mm Theiron-formation iron-formationisiscomposed composed of of mixed magnetitemagnetite- and detrital-bearing layers (< 1 mm thick). Metamorphism thick) and poorly defined chert layers (< Metamorphism has has produced produced quartzite quartzite textures textures in the iron-fonnation. iron-formation. As Asthe theexposures exposuresof ofiron-formation iron-formationare arein in the the proximal proximal section section of of the the Clarksburg Clarksburg Volcanics, we suggest suggest that the interbedded iron-formation has a volcanogenic volcanogenic origin. origin. Throughout the immediate immediate region, diabase sills, dikes, and other shaped bodies bodies are are common. common. Cannon (1974) (1974) suggested suggested that that the the diabase was was approximately approximately equivalent equivalentinin age age to to the Clarksburg Cannon Volcanics. The Themajor majorelement elementchemical chemical composition composition of the the diabase diabase and and Clarksburg Clarksburg Volcanics Volcanics are are large body body of of diabase diabase with with a surface similar. Just south of the town of Clarksburg Clarksburg is a relatively large exposure of approximately km. This approximately 1.5 1.5 by 1.5 1.5 krn. Thisbody body of of diabase diabasecuts cuts rocks rocks stratigraphically stratigraphicallyolder olderthan than the Clarksburg Volcanics and is spatially adjacent to to the the proximal proximal section. section. We suggest this diabase is part of the subvolcanic subvolcanic roots roots of of the the Clarksburg Clarksburg volcanic volcanic system. system. References Marquette County, County, Michigan: Michigan: U.S. U.S. Cannon, W. F., 1974, 1974, Bedrock geologic map of the Greenwood quadrangle, Marquette Geological 168. Geological Survey Survey Geologic GeologicQuadrangle QuadrangleMap MapGQ-l GQ-1168. Michigan: U.S. U.S. Cannon W. F., 1975, 1975, Bedrock Bedrock geologic geologic map of the the Republic Republic quadrangle, quadrangle, Marquette County, Michigan: Geological Survey Geological Survey Miscellaneous MiscellaneousInvestigation InvestigationSeries SeriesMap Map 1-862. 1-862. Klasner, J. S., 1977, 1977, Bedrock geologic map of the southern part of the Diorite and Champion Cannon, W. F., and Kiasner, minute quadrangles, quadrangles, Marquette Marquette County, County, Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigation Investigation Series 7-112 minute Map 1-1058. 1-1058. map of of the the Ishpeming Ishpemingquadrangle, quadrangle,Marquette MarquetteCounty, County,Michigan: Michigan: U.S. Simmons, G. C., 1974, 1974, Bedrock geological map Geological Survey Geological SurveyGeologic GeologicQuadrangle QuadrangleMap MapGQ-1 GQ- 1130. 130. 85 �ROYALE -- WHERE ARE THEY POST-GLACIAL SHORELINES OF ISLE ROYALE THEY NOW? NOW? M.E. McRae, Oak Ridge Associated Universities, Universities, Reston, VA W.F. Cannon, Cannon, U.S. Geological Survey, Reston, VA Woodruff, U.S. Geological Survey, Mounds View, MN L.G. Woodruff, Well-developed Well-developed shoreline shoreline features features at at elevations elevations higher higher than the the present day day lake lake level level are are basin. These well documented in the Lake Superior basin. These shorelines shorelines formed approximately approximately 10,000 10,000 to 4,500 years years ago as the last glacier to occupy western Lake Superior Superior receded to the northeast. Further, Further,mapping mapping of of stranded stranded shoreline shoreline features features has demonstrated demonstrated that these once flat-lying lake planes are now tilted from northeast to southwest as a consequence consequence of differential isostatic rebound. Previous Previousresearchers researchers have been able able to construct construct isobases of better-developed lake lake levels. levels. These Washbum and rebound for several of the better-developed These include include Lakes Washburn Lake Minong B.P.), Beaver Bay Minong(—9500 (-9500 B.P.), Lake Houghton Houghton(—8000 (-8000 B.P.), Beaver Bay(—9800 (-9800 - 9700 B.P.), Lake and Lake Lake Nipissing Nipissing(—5500 (-5500 -4700 - 4700 B.P.). Beach ridges are common features features on Isle Royale, particularly particularly on the lower lower elevations elevations of of the the southwest portion of the island where glacial debris debris is is widespread. widespread. A few wave-cut features features in bedrock have also been mapped in the the northeastern northeastern half half of of the the island. island. However, However, all of and discontinuous. discontinuous. Consequently, these features are scattered and Consequently, the exact exact positions of former shorelines shorelines are not precisely known from observable observable features features for most of the island. island. (GIs) software, we constructed constructed a series series of gridded gridded Using geographic geographic information information systems systems (GIS) surfaces surfaces representing representing lake level level planes from from the isobases of glacioisostatic glacioisostatic rebound described described above. Subtracting Subtractingeach eachgridded gridded surface surfacefrom from the the present-day digital digital elevation elevation model (DEM) (DEM) new DEM7s DEM's showing the island's morphology morphology at at several several of Isle Royale yields a sequence of new different different lake lake stages. stages. We then displayed the modeled shorelines shorelines with the known beach and wave-cut features. features. The The Beaver Bay do not correlate correlate with with two highest modeled shorelines, shorelines, Lake Washburn and Lake Beaver any of the mapped features. This This may may indicate indicatethat that the the island island was not yet free free of ice at these Minong shoreline. shoreline. Lengthy times. All All mapped mapped features features fall fall either either on or below the Lake Minong on the the modeled modeled Minong Minong shore. shore. Evidence sections of mapped beach ridges lie on Evidence also seems seems to shore. No features support the position of the modeled Nipissing shore. features seem seem to correlate correlate with the Houghton Houghton shoreline. shoreline. By overlaying overlaying the the modeled modeled shorelines shorelineson on the the modern modem digital digital elevation elevation model, model, itit isis possible possibleto to the post-glacial post-glacial shores shores around around the the island. island. This determine the approximate elevation of the knowledge could serve serve as a guide to future future mapping particularly if combined with information such as vegetation type, surficial surficial material, abundance of outcrop, outcrop, and and information accessibility accessibility to trails. 5,000 years ago, and possibly possibly earlier. earlier. Lastly, prehistoric mining of native copper copper began about 5,000 the prehistoric prehistoric discovery discovery and and mining mining of of We hypothesize that former lake levels influenced the copper. Copper would have been easily accessible and recognizable in wave-washed Copper would have been easily accessible and recognizable prehistoric shorelines shorelines seems seems probable. probable. Because shoreline rock exposures, so discovery along prehistoric Because wave-washed exposures exposures remain largely barren of vegetative material for for prolonged prolonged periods periods 86 �after afterthey theyare areabandoned, abandoned,they theyremained remainedfavorable favorablepoints pointsfor fordiscovery discoverylong longafter afterthe thelake lake levels levelshad hadreceded. receded.Major Majorprehistoric prehistoricworkings workingsatatthe theMinong MinongMine Mineare areininextensive extensivebedrock bedrock exposures exposuresatatororjust justabove abovethe theprojected projectedMinong Minongshore. shore.During Duringa abrief briefreconnaissance reconnaissanceinin 1997 1997we weobserved observedprehistoric prehistoricworking workinginintwo twoother otherareas areasof ofextensive extensiveexposure exposureatatthe the Minong Minongshore. shore.Did Didearly earlyinhabitants inhabitantsofofthe theLake LakeSuperior Superiorregion, region,such suchasasthe thePlano PianoIndians Indians who whoinhabited inhabitedthe theMinong Minongshore shorenear nearThunder ThunderBay, Bay,visit visitthe theisland islandand anddiscover discovercopper copper duringthe theLake LakeMinong Minongstage, stage,well wellbefore before the the generally generally accepted accepted date of first mining? Or Or during did didbarren barrenrock rockexposures exposuresfrom fromthe theformer formerMinong Minongshore shorefacilitate facilitaterecognition recognitionofofnative native copper eithercase, case,we wesuggest suggestthat thatthe theprojected projectedlocation locationof ofthe the copperthousands thousandsofofyears yearslater? later?InIneither Minong Minongand andyounger youngershorelines shorelinescan canprovide providea aguide guidetotofuture futurearchaeological archaeologicalstudies. studies. Projected Projecteddigital digitalelevation elevationmodel modelof ofIsle IsleRoyale Royaleduring duringthe thetime timeof ofLake LakeMinong. Minong. Shoreline Shorelineof ofthe the modem modemisland islandisisshown shownininwhite. white. 87 �ELECTRON MICROPROBE STUDY STUDY OF THE Pt-Pd Pt-PdAND AND RELATED RELATED MINERALIZATION IN THE Cu-Ni DEPOSIT MINERALIZATION THE MINNAMAX/BABBITT MINNAMAXIBABBITT Cu-Ni McSWIGGEN, Peter L., Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 551 14 The Minnamax deposit deposit is is one one of several several copper-nickel copper-nickel sulfide sulfide deposits deposits that occur occur along along the the base of the the Duluth Duluth Complex, Complex, which which is is aa series series of mafic intrusions intrusions that are part of the Keweenawan (1100 and Miller, Miller, 1993). The Keweenawan (1 100 Ma) Midcontinent Rift system (Paces and The ore ore body consists inclusions derived derived from from consists of troctolitic and ultramafic rocks, as well as hornfelsic homfelsic inclusions Paleoproterozoic metasedimentary rocks, and unconforrnably unconformably overlying Mesoproterozoic Mesoproterozoic Paleoproterozoic volcanic rocks. The Thecopper copperand andnickel nickel are are contained contained predominantly predominantly in disseminated disseminated sulfides that make rock. The make up between 11 and 5 percent of the rock. The sulfides sulfides consist largely of chalcopyrite, cubanite, pyrrhotite and pentlandite (Severson, 1991; chalcopyrite, 1991; Severson and Barnes, 1991). In In addition additionto tothe thecopper copperand andnickel, nickel,the the deposit depositalso alsocontains containssignificant significant concentrations of platinum concentrations platinum (Pt), (Pt), palladium palladium (Pd), (Pd), gold gold (Au), (Au), silver silver (Ag) (Ag)and and cobalt cobalt(Co). (Co). Sections Sections of core core ranging ranging from from 55 to 10 ft long have as much as 7.0 ppm Pd, 3.1 ppm Pt, and 13.1 13.1 ppm Au. As Aspointed pointed out outby by Severson Severson(1991), (1991), the high values for the platinum group elements other precious precious metals, and Co have been shown by others to be elements (PGE's), other associated associated with the the high-grade high-grade copper copper zones zones (Kuhns (Kuhns and and others, others, 1990). 1990). This This electron electron microprobe microprobe study study has has shown shown that that rocks rocks at at the the Minnamax Minnamax site sitecontain contain at least two platinum group minerals (PGM's) -froodite (PdBi2) and cabriite -- froodite cabriite (Pd2SnCu). (PdzSnCu). They are are commonly commonly associated associated with massive massive sulfide sulfide mineralization and are less common common in in samples samples consisting consisting mostly of silicates. silicates. Of Ofthe the14 14samples samplesinvestigated investigatedin indetail, detail,55 were were found to contain either froodite or cabriite. Although Although the number of PGM grains is small, small, just aa few few of of the the 1-2 1-2micron micron size sizegrains grains could could account account for for the the reported reported whole whole rock rock values. values. Therefore there is no need to invoke invoke PGE-sulfide phase solid solution solution to account for the Therefore there PGE whole-rock whole-rock values values reported reported from from these these rocks. Numerous found in in these these rocks. rocks. The Numerous examples examples of silver mineralization were found The silver silver is typically typically present either either as as solid solid solution solution in maucherite maucherite or as discrete discrete grains grains of native native silver. Significant Significantgold goldwas was found found in in aa few few of the native silver grains. Values Values as as high high as as 16 wt. percent Au were measured in 55 to 100 micron size grains of silver, but values were more typically typically in the 11 percent range. Cobalt Cobaltwas was found foundat at significant significantlevels levels only only in in maucherite maucherite and pentlandite. Detailed Detailedinspections inspections of of these these samples samples shows shows that they contain contain numerous altaite (Ni,As), shadlunite shadlunite[(Pb,Cd)(Fe,Cu)8S8], [(Pb,Cd)(Fe,Cu)$J, altaite numerous rare rare phases phases including includingdienerite dienerite(Ni3As), (PbTe), laurionite (PbTe), laurionite[PbCl(OH)} [PbCl(OH)]and and cotunnite cotunnite(PbCl2). (PbClJ. Kuhns, M.P., Hauck, S.A. and Barnes, R.J., 1990, Origin and occurrence of platinum group elements, copper-nickel mineral group elements, gold and silver, silver, in the South Filson Creek copper-nickel mineral deposit, Lake County, Minnesota. Natural Natural Resources Resources Research Institute, NRRUGMIN-TR-89-15,6Op. 60p. Univ. Minn., Duluth, Duluth, Tech. Tech.Report, Report,NRRI/GMIN-TR-89-15, Paces, J.B. and and Miller, Miller, J.D., J.D., Jr., Jr., 1993, 1993,Precise Precise U-Pb U-Pb ages ages of Duluth Complex and and related related mafic intrusions, intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, petrogenetic, paleomagnetic, and tectonomagmatic tectonomagmatic processes associated with with the the 1.1 Midcontinent Rift System. Journal Journal Geophysical Geophysical Research, Research, v. 98, no. B8, 13,997-14,013. p. 13,997-14,013. Severson, MinnamaxlBabbitt Severson, M., 1991, 1991, Geology, Geology, mineralization, mineralization, and geostatitics of the Minnarnax/Babbitt Cu-Ni Deposit (Local Boy Area), Minnesota. Natural Resources Resources Research Research Institute Institute Technical Report NRRIITR-91/13a, 96 96p. p. Severson, Severson, M.J. and Barnes, Barnes, R.J., 1991, 1991, Geology, mineralization, and geostatistics geostatistics of the the Minnamax/Babbitt MinnamaxBabbitt Cu-Ni Cu-Ni deposit deposit (Local (Local Boy Area), Area), Minnesota; Minnesota; Part II: II: Mineralization Mineralization and geostatistics. Natural Natural Resources Resources Research Research Institute Institute Technical Report NRRI/TR-91/13b, NRRIITR-9 1/13b, 216 p. 88 �POST- 1.76 Ga Ga LOW-GRADE LOW-GRADE METAMORPHISM METAMORPHISM OF THE BARABOO QUARTZITE POST-1.76 G., Jr., J., Dept. of Geology Geology & & Geophysics, MEDARIS, MEDA1US,L. L.G., Jr., BROWN, BROWN, P.B. P.B. and BUNGE, BUNGE, R R.J., Wisconsin-Madison,Madison, Madison,WI WI53706; 53706;medaris@geology.wisc.edu medarisgeology.wisc.edu Univ. of Wisconsin-Madison, It has long long been been recognized recognized that the the Baraboo Baraboo Quartzite Quartzite is is folded folded and and metamorphosed, metamorphosed, and recent U-Pb dating of of detrital detrital zircons zircons in the quartzite quartzite requires requires that deformation deformation and and recrystalrecrystallization were were post-1.76 Ga events. Although Although the the structure structureof ofthe theBaraboo Baraboosyncline syncline has been well studied, little attention has been devoted to to metamorphism metamorphism in the Baraboo Baraboo Range, Range, other other identifyingpyrophyllite pyrophyllite in inmetap metapelite and recognizing recognizing that that metamorphism metamorphism was was than identii'ing elite layers and low-grade. low-grade. We Wehave haveundertaken undertakenaapetrologic petrologicinvestigation investigation of of the theBaraboo BarabooQuartzite Quartziteand and post-1.76Ga Gametamorphism. metamorphism. underlying granite and rhyolite to to determine the the conditions of ofpost-1.76 Rock types, chemical compositions, well-developed paleosol paleosol compositions. and and mineral assemblages AAwell-developed occurs in granite and rhyolite at the unconformable base of the Baraboo Quartzite. Intense rhyolite the unconformable the Baraboo Quartzite. Intense chemical weathering and sedimentary chemical weathering sedimentary processes processes Table I1 produce marked geochemical combined to a combined a geochemical Chemical Compositions, Compositions, Baraboo Baraboo Rocks Rocks differentiation among basement basement rocks, paleosol, and avg avg avg pelitic layers in the Baraboo 1). pelitic layers Baraboo Quartzite Quartzite (Table (Table 1). rhyolite granite granite saproliie soil pelite saprolite soil pelite (1) (2) (10) (5) (1) Ca, (1) (2) (10) ( 5) (1 Ca, Na, Na, and and KKwere wereleached leached from from granite granite and and wt% wt% rhyolite, and and A1 Al and Fe were were concentrated concentrated in the the Si02 rhyolite, 5102 70.51 59.70 70.51 56.41 56.41 59.70 72.80 69.25 69.25 72.80 0.26 0.25 0.36 0.87 Ti02 0.26 0.25 0.36 paleosol (saprolite and soil) 0.87 1.03 1.a3 soil) and and pelitic layers in the Ti02 1AJ203 13.30 15.15 17.18 20.89 25.40 A1203 13.30 15.15 17.18 20.89 25.40 sedimentary section, which which consisted of sedimentary section, consisted originally originally of Fe203 2.99 3.46 2.82 10.18 8.04 2.99 3.46 2.82 10.18 8.04 kaolinite and variable amounts of silt-size quartz kaolinite and variable amounts salt-size quartz Fe203 MnO 0.07 0.09 0.00 0.00 0.00 0.01 MnO 0.07 0.09 0.00 0.01 elites MgO aluminousofofthree threeanalysed analysedppelites grains. The Themost mostaluminous MgO 0.14 0.89 0.07 0.38 0.38 0.04 0.14 0.89 0.07 0.04 is listed listed in Table Table 1, 1, and and two two other othersamples samples are are CaO 1.16 1.55 0.14 0.09 0.09 0.03 1.16 1.56 0.14 0.03 CaO 4.93 4.40 0.34 0.32 0.32 0.04 0.34 0.04 Na20 4.93 4.40 equally lowinin Ca, Ca, Na, Na, and meta- Na20 equally low and K During meta3.17 3.14 4.75 5.72 0.21 4.75 5.72 0.21 K20 K20 3.17 3.14 morphism, K K was was reintroduced re-introduced into the paleosol by P205 0.03 0.09 morphism, 0.13 0.10 0.10 0.12 P205 0.03 0.09 0.13 0.12 1120-tich fluids that were H,0-rich fluids that were channeled channeled along along the the LLOl 1.25 1.53 2.51 3.65 4.70 4.70 O1 1.25 1.53 2.51 3.65 sub-B araboo unconformity; unconformity; this K-metasomatism sub-Baraboo K-metasomatism SSum 100.10 99.78 98.80 98.62 um 100.10 99.78 98.80 98.62 99.32 99.32 was orethindiasp diasporewas accompanied accompaniedby by formation formationof ofthin quartz pyrophyffite-white pyrophyllite-white mica veins in basal quartzites. quartzites. The compositions compositions of Baraboo rocks are projected projected into in which which the the positions positions into the the system, system, KASH, KASH, in in Fig. Fig. 1,1,in microcline of selected selected minerals minerals are also also plotted. plotted. The KASH KASH equilibrium metamorphic metamorphic assemblages assemblagesfor for these these rocks equilibrium + quartz + microcline are: granite and and rhyolite, microcline + are: granite rhyolite, quartz muscovite; metapelite, muscovite; paleosol, paleosol, quartz ++ muscovite; metapelite, hydrothermal veins, veins quartz pyrophyllite; and hydrothermal quartz ++ pyrophyllite; + diaspore. diaspore. Kaolinite is pyrophyllite Kaolhute pyrophyllite ++ muscovite + present in elite and hydrothermal in metap metapelite hydrothermal veins, but only only as a retrograde retrograde product. Inhiaddition additiontotoKASH KASHminerals, minerals, granite and rhyolite contain albite, epidote, and chlorite. chlorite. Hematite isis abundant abundant in these these rocks, rocks, especially especially in Hematite K20 A1203 diaspore paleosol common in in paleosol and metapelite, metapelite, and and rutile rutile is common Fig. 1 Compositions Compositions of of Baraboo Baraboo metapelite. metapelite. plane rocks projected projected into into the KAS plane system, KASH KASH of the system, 89 �Metamorphic Metamorphic conditions conditions Mineral reactions and and chemographic chemographic relations relations in m the thesystem, system, KASH for unit unit activity activity of of H20), KO), are aresummarized summarized in in Figure Figure 1.1. Minimum KASH (calculated (calculated for temperatures temperatures of of metamorphism metamorphism are are defined defined by by the themetapelite metapeliteassemblage, assemblage, quartz ++ pyrophyllite, pyrophyllite, which is stable stable above above the reaction, reaction, Kin K h ++ Qtz Qtz == Pr! Prl ++ V, V, and and by the the absence absence of stable kaolinite from all observed T,, assemblages, indicating that temperatures were T- assemblages, indicating that temperatures were above above stable fiom the kaolinite. Maximum the stability stability limit of kaohite. Maximum temperatures temperatures are are defined defined by the the absence absence of of kyanite kyanite ore, in from pyrophyllite ++ diasp diaspore, in hydrothermal hydrothermal veins, vems, which which isis fiom the the assemblage, assemblage, muscovite muscovite ++ pyrophyffite stable below the reaction, Pr! Prl ++ Dsp Dsp == Ky Ky ++ V, V, and and by by the theabsence absencekyanite lqmniteininmetapelite, metapelite, which limitof of pyrophyllite. pyrophyllite. which indicates mdicates that temperatures temperaturesdid didnot not exceed exceedthe thestability stabilitylimit Fluid were analysed from quartz m in a folded vein in inmetapelite. metapelite. The The a d inclusions inclusions were analysed fiom folded quartz quartz vein quartz contains contains aa single single population population of ofabundant abundantaqueous aqueousinclusions mclusions that thathave havefinal finalmelting meltmg points corresponding points of-15 of -15toto-18°C, -lS°C corresponding to to 18 18to to20 20equivalent equivalent wt% wt% NaCL NaCL First Firstmelting meltmg below below -35OC divalent cations. H o m o g ~ t i o temperatures ntemperatureslie lie between between -3 5°C suggests suggests the the presence presence of divalent cations. Homogenization 165 the 175-185°C 175-lW°range. range. 165 and 215°C 215OC with a peak in the Intersection of with the thelimiting limiting mineral mineral reactions reactions constrains constrains of the the fluid fluid inclusion mclusion isochore isochore with temperature-pressure conditions conditions for for the the Baraboo BarabooQuartzite Quartzitetotolieliebetween between—320°C, -320°C2.7 kbar kbar and —385°C, 4.0kbar. kbar. Such values correspond correspond to aa thermal -385OC, 4.0 thermal gradient gradient of of25-30°C/km. 25-30°C/kmwhich is is typical terranes and is notably notably elevated elevated over that for typical for Barrovian-type Barrovian-type metamorphic terranes for stable stable cratons cratons(--17°C/km (-17OCh at comparable comparable depths). depths). 8 6 4 2 0 250 300 350 T,°C 400 450 Fig. Fig. 2 Mineral Mineralassemblages assemblagesand andreactions reactionsin inthe the system, systeml KASH, KASH, aa fluid fluid inclusion inclusionisochore isochorefor for quartz quartzin inaa folded foldedquartz quattzvein, vein, and and metamorphic metamorphicconditions conditions for for the the Baraboo Barabm Quartzite Quarfziie Conclusions Folding and metamorphism metamorphism of the Baraboo Baraboo Quartzite Quartzite mark mark an animportant important Conclusions the age of this post-l.76 post- 1-76Ga Gatectonothermal tectonothermal event event in in the theLake LakeSuperior Superiorregion. region. Although Although the event remains remains uncertain, uncertain, itit could could be be related related to an an eastern eastern extension extension of the the Mazatzal Mazatzal belt at at -1.63 Ga. However, However,andalusite-bearing andahsite-bearingassemblages assemblagesin the the Waterloo Waterloo Quartzite Quartzite are are probably probably -1.63 Ga. due due to to contact contactmetamorphism metamorphismassociated associatedwith withWolf WolfRiver Rivermagmatism magmatismatat—4.43 -1.43 Ga. 90 �SVANBERGITE SVANBERGITEiN INTHE THEBARABOO BAMBOOQUARTZITE: QUARTZITE:SIGNIFICANCE SIGNIFICANCEFOR FORDIAGENETIC DIAGENETIC PROCESSES ANDPHOSPHORUS PHOSPHORUSFLUX FLUXIN INPRECAMBRIAN PRJXAMBRIANOCEANS OCEANS PROCESSESAND MEDARIS, Geophysics, MEDARIS,L.G., L.G.?Jr. Jr.and andFOURNELLE, FOURNELLE?J.H., J.H.,Department DepartmentofofGeology Geology&&Geophysics, University Madison,WWI 53706;medaris@geology.wisc.edu medarisgeology.wisc.edu I 53706; University of of Wisconsin-Madison, Wisconsin-Madison, Madison? Authigenic Authigenicminerals mineralsof ofthe thebeudantite beudantiteand andcrandallite crandallitegroups groupshave haverecently recentlybeen beenrecognized recognizedasas widespread widespreadconstituents constituentsofofArchean ArcheantotoCretaceous Cretaceoussedimentary sedimentaryrocks rocks(Rasmussen, (Rasmussen71996). 1996). Although Althoughthe theabundance abundanceofofthese thesealuininophosphate-sulfate alumhophosphate-dte minerals minerals is is small, small, on the the order order of of wt%ininaagiven givensample, sample7they theyappear appearto tobe bemore moreabundant abundantthan thanauthigenic authigenicapatite apatite 0.2to to0.01 0.01wt% 0.2 and phosphorusbalance balanceininthe theoceans. oceans. andplay playan animportant importantrole roleininphosphorus The general formula i%e beudantite beudantite and andcrandaiite cranddlitemineral mineralgroups w m pThe The general formulafor forthe thebeudantite beudantite groupisisAB3(XO4XSO4XOH)6, AB3(X04)(S04)(OH)6, whereAA ==Ba, Ba7Ca, Ca7Ce, Ce7Pb, Pb7Sr; Sr;BB==Al, Al,Few; Few;and andXX==As, As7P; P; group where and where AB3(X04)2(O13,F)547 whereAA ==Ba, Ba7Bi, Bi,Ca, Ca7Ce, Ce,La, La7Nd, Nd,Sr, Sr7Th; Th; andfor forthe thecrandallite crandallitegroup groupisisAB3(XO4)2(OH,F)5, P, Si. Electron microprobe analysis of Baraboo svanbergite B = Al, Fe3+; and X = As7 P7 S i Electron microprobe analysis of Baraboo svanbergite Fe3+; and X = As, B = Al, demonstrates which demonstratesthat thatits itscomposition compositioncan canbe beportrayed portrayedby byaadistorted distortedpyramid pyramid(Fig. (Fig.1)1)ininwhich members of the beudantite group lie along the front edge of the pyramid and members members of the beudantite group lie along the fiont edge of the pyramid and membersof ofthe the crandallite crandallite group group lie lie in m the the fir fiuface face(note (notethat thatCa Caand andBa Bahave havebeen beencombined combmedfor forprojection projection purposes). purposes). florencite florencite CeAJ3(P04)2(OH)6 ce%p04)2(0H) Crandallite group SrsAJ3Q'Q4 )2(H)5 . HO goyazite (Ca,Ba)A13(P04)(S04)(OH)6 SrAI3(P04)(S04 )(OH)6 svanbergite Fig. Fig. IICompositional Compositionalspace spaceofofBeudantite Beudantiteand andCrandallite Crandallite groupminerals mineralsfrom fromBaraboo Baraboometapelite metapelite group svanbergite Small Occurrenceand andchemical chemical composition compmition of o fBaraboo svanberdte S d amounts amounts of Occurrence svanbergite elite layers layers m in the the Baraboo Baraboo Quartzite7 Quartzite, where where it is inmetap metapelite is svanbergite are are widespread widespreadin associated with pyrophyllite, quartz, hematite, and rutile. Svanbergite grains are equant associated with pyrophylbe7 hematite7 Svanbergite grains are equantand and have smallsize, size7are arereadily readilyvisible vkiile have diameters diametersof of10-20 10-20microns, microns7but butdespite despitetheir theirsmall microscopically microscopically because because of of their their marked marked difference &erence in relief compared to associated associated pyrophyllite. <1 pyrophyllite. Baraboo Baraboosvanbergite svanbergitecontains contains<2 < 2wt% wt%Fe203, Fe203? 4wt% wt%As205, 4 O s 7and andhas hasnegligible negligiile amounts ofAAl3(PO4XSO4XOH)6 solidsolution solution of ALUJPO~)(SO~)(OH)~ amountsof ofBi, Bi,Pb, Pb7Th, Th7Si, Si,and andF;F;itsitscomposition compositionisisa asolid Ca + Ba + REE, which lies near the base of the + Ba + W E 7 which lies near the base of the Ca Sr> where A = AAl&P04)2(OH)5*q07 where A = Sr AAI3(P04)2(OH)5'H20, pyramid in m Fig. 11 between between svanbergite svanbergiteand and goyazite goyazite(Fig. (Fig. 2). 2). - 91 �"crandallite" "crandallite" goyazite goyazite Ba Ba REE REE 0 0 + 0 U) 0 U) Ca Ca 0 0.2 0.4 0.6 0.8 Ba Sr - Fig. 33 Proportions Promtions of of cations cations in in the A-site of Baraboo Bamboo svanbergite-goyazite svanbergite-goyazite 1.0 "woodhouseite" "woodhouseite"Sr/(Sr+Ca+Ba) Srl(Sr+Ca+Ba) svanbergite svanbergite Fig. 2 Projection Projectionof ofmineral mineralcompositions compsitions onto onto the the base of the Beudantite-Crandallite Beudantite-Crandallite prism prism Baraboo svanbergite The The Baraboo svanbergite solid solid solution solution ranges ranges l m m from fiom almost pure svanbergite (beudantite group) to —70% goyazite(crandallite (crandallite group) group) with with a concomitant concomitant -70% goyazite in Sr/(Sr+Ca+Ba) (Fig. 2), decrease m 2)?and and A-site 10000 is dominated dominatedby by Sr Sr(Fig. (Fig.3). 3). Many occupancy is grains are svanbergite grains svanbergite are strongly strongly zoned, zoned, with with rims rimsbeing bemg in crandallite component7 component, m in which whichthe the sum sum of of enriched in reaches 5.3 wt %, La203, Ce203, %? L%O3? Ce203?and and Nd203 N&03reaches amounting to --27% -27% occupancy occupancy of of the the A-site (Fig. (Fig. 3). 3). present, they Although other RE RE elements elements may be present? Nd can't readily re&ly be determined by electron microprobe Fig. 44 Representative Representativechondrite-normalized chondritenormalized techmques due to their techniques their low low abundances abundances and spectral spectral La, contentsof of Baraboo Baraboo La, Ce, and Nd contents svanbergite-goyazite interferences. mterferences. The light REE contents contents in m svanbergite svanbergite 5000 toto40,000 times are 407000 timesgreater greaterthan thanin mchondrites, chondrites7 are -5000 Nd by by aa fhctor factor of 2 to to 3 (Fig. 4). There nomarked markedCe Ceanomaly, anomaly7 and La is enriched over Nd Thereisisno with respect respect to to La and Nd. although two samples samples may have a slight Ce enrichment with Geological simificance significance of svanbergite Precipitation Geolokcal ofsvanberkte Precipitation of ofauthigenic authigenic aluminophosphatesulfate minerals has been ascribed to bacterial decomposition of P-beakg P-bearing organic matter m in an d t e minerals has been ascriied to bacterial decomposition of within the zone of d sulfate methanogenesis ithin the a t e reduction and methanogenesis Al-rich environment, such as shale, shale?w (Rasmussen, so7the theoccurrence occurrenceof ofsvanbergite-goyazite svanbergite-goyazite in m Baraboo metapelites (Rasmussen71996). IfIfso, that such a process process may have been operative m mid-Proterozoic mid-Proterozoictime. time. signifies that operativein The widespread occurrence occurrence of of authigenic authigenic aluniinophosphate-sulfate alumhophosphate-dte minerals represents a unrecognized repository for phosphorus m in the the oceans. Rasmussen previously unrecognized Rasmussen has has estimated estimated that fluxof of7.6 7.6xx1010 10" moles that aluminophosphate alumhophosphateprecipitation precipitation accounts accountsfor for aaphosphorus phosphorusburial burialflux yr, which is comparable to that resulting from authigenic phosphates and P-bearing which is comparable to that resultmg fiom authigenic phosphates and (2.2-9.1 xx 10" moles yfl). yf'). However, However7Rasmussen Rasmussenused used the the composition composition of carbonates (2.2-9.1 florencite florencite (2 (2 moles of of P phi) pfb) in m his his calculation, calculation, and using the compositional compositional range range of of Baraboo Baraboo svanbergite-goyazite (1.0(1.0-1.7 estimate by 15 15 to 50%. 50%. 1.7 moles moles of of P pfli) pfi) reduces reduces the the burial flux estimate Regardless, factor in m oceanic oceanic P-flux. P-flux. Regardless?aluniinophosphate-sulfate aluminophosphate-dte minerals are an important fhctor REFERENCE CITED 296?601-632. 601-632. Rasmussen, B. (1996) (1996) American Journal Journal of of Science, Science?v. 296, . 92 �HIGH-RESOLUTION AEROMAGNETIC DATA DATA FOR USE OF HIGH-RESOLUTION FOR REGIONAL REGIONAL (WHERE'S THE GEOLOGY INVESTIGATIONS, INVESTIGATIONS, SOUThEASTERN SOUTHEASTERN WISCONSIN (WHERE'S KIMBERLITE!) MIJDREY, M.G., Jr., Jr.?Wisconsin WisconsinGeological Geologicaland and Natural NaturalHistory History Survey, Survey73817 3817Mineral Mineral MUDREY, Road, Madison, Point Road? Madison?WU 53705-5 100, 100, mgmudreyfacstaff.wisc.edu mgmudrey@facstaff.wisc.edu Between 1876 Between 1876 and and 1913, 1913, diamonds diamonds were found in at least seven localities in southern and central Wisconsin. All All were were found found in in Pleistocene Pleistocene gravel gravel deposits depositsor orHolocene Holoceneriver rivergravel. gravel. The bedrock unknown, but was presumed to be in bedrock kimberlite source for these diamonds is unknown7 northern northern Canada, Canada?the the only only area area north north of ofWisconsin Wisconsin previously previously known known to to contain containkimberlite. kimberlite. County, Michigan? Michigan, Cannon and With the discovery discovery of the Lake Lake Ellen kimberlite in Iron County? Mudrey (1981) (1981) suggested suggestedthe thedrift driftdiamonds diamondsin in Wisconsin Wisconsin may have come from a more more local source. source. Carison southeastern Wisconsin about 280 m Carlson and Adams (1997) described a kimberlite in southeastern across. The Thepreliminary preliminaryidentification identificationwas wasbased basedon ondrilling drillingsmall, small,highly highly magnetic magnetic anomaly anomaly identified from a little known aeromagnetic survey from the 1980s 1980s (800-meter (800-meter flight-line flight-line have aeromagnetic spacing). Only recently have aeromagneticsurveys surveysbeen been sufficiently sufficiently detailed to determine determine the presence of absence of kimberlite kimberlitein insoutheastern southeasternWisconsin. Wisconsin. Prior Prior to to the the most most recent survey? strong, small small survey, limited flight-line spacing of 110-krn 0-km precluded precluded the the identification identification of strong, magnetic bodies at the the shallow shallow bedrock bedrock surface. surface. Analysis of the aeromagnetic aeromagnetic survey survey indicates indicates that that flight-line flight-line spacing less than 800 800 m m will be ineffective in the identification identification of of small, small?highly magnetic kimberlite at at the the bedrock/surficial bedrock/surficial material material surface surface in southeastern southeasternWisconsin. Wisconsin. The identification identification of the kimberlite, and analysis of available aeromagnetic maps, indicate that other other kimberlitic kimberlitic bodies may occur occur in southeastern southeasternWisconsin and possibly northeastern Illinois and may be the source source for for the the diamond diamond discoveries discoveriesin in Wisconsin Wisconsin and and Illinois. Illinois. However, urbanization However? urbanization in in the the Milwaukee-Chicago Mlwaukee-Chicago corridor corridor may may discourage discourage further hrther geologic geologic and geophysical analysis and competing competing land use may make further hrther exploration explorationand and ultimate ultimate development difficult. development difficult. REFERENCES: REFERENCES: Cannon, W.F., and Mudrey, Cannon? Mudrey, M.G., M.G., Jr., Jr., 1981, 1981,The Thepotential potentialfor fordiamond-bearing diamond-bearingkimberlite kimberlite in northern Michigan and Wisconsin: U.S. Geological Survey Circular 842, 15 15 p. p. Carison, S.M. Carlson, S.M. and Adams, G.W., G.W., 1997, 1997,The Thediamondiferous diamondiferousSix-Pak Six-Pak Ultramafic Ultramafic U.S.A. (abs.): Institute Institute on Lake Superior Lamprophyre Diatreme, Kenosha, Wisconsin, U.S.A. Superior Geology, Proceedings, Part 1-Program Geology?Proceedings? 1-Programand and Abstracts, Abstracts?v. v. 43, 43, p. p. 11 11 Wisconsin, kimberlite, Wisconsin, kimberlite, aeromagnetic data 93 �_____________ AS INDICATORS INDICATORS OF OF INTRUSION INTRUSIONMECHANISMS MECHANISMS XENOLITHOLOGIES AS IN THE THEWAUSAU WAUSAU SYENITE SYENITE COMPLEX, COMPLEX, WISCONSIN WISCONSIN MYERS?Paul E., Geology Department, Department?University of Wisconsin, Eau 54701 MYERS, Eau Claire? Claire, WI WI 54701 area west of Wausauy (2) Wausau, Wausau, In the area Wausau, four alkaline subvolcanic subvolcanicplutons: plutons: (1) Stettin, (2) (Figure)?were intruded in a southeastward southeastward sequence sequence (3) Rib Mountain, and (4) Ninemile (Figure), into Lower Lower Proterozoic Proterozoic metavolcanic, metavolcanic, metasedimentary, and and granitic granitic intrusive intrusive rocks rocks into (Myers and others, 1984). 1984). Whereas Whereas the first three syenite plutons are concentrically concentrically (Myers plutons are zoned and and pipelike in structure, structure, the theyoungest, youngest,Ninemile Ninemilepluton, pluton, although althoughpossessing possessing an an zoned stopedits itsway wayto toaashallow shallowdepth depthunder underthe the aplitic core core rim, rim, isisaastock-like stock-likebody bodywhich whichstoped aplitic volcanoes. This paper shows the connection between magma now-eroded volcanoes. between xenolithologiesy xenolithologies, magma emplacement, emplacement?and andwalirock wallrockalteration. alteration. EXPLANATION EXPLANATION qp qp quartz quartzmonzonite monzoniteporphyry porphyry ng ng Ninemile Ninemile granite granite ga ga granite granite aplite aplite sy sy syenites syenites vv volcanic rocks rocks qq quartzite quartzite bs bs biotite biotiteschist schist fault fault 4 ', , -1 contact, infened contact, dashed where inferred 1 1 0 Scale: Scale:1 - 1 -, 1 2 . Zmiles mles 012-3. 7 -? kilometers kilometers Figure --- Map Map of of Wausau Wausau syenite syeniteplutons plutons The The Stettin Stettin pluton, plutony(Figure) (Figure) which is the oldest, oldest, most alkaline alkaline intrusion of the Wausau of 8.8 and Wausau syenite syenite complex, 8.8 xx 6.4 6.4 km. by and has has aa complexyis oval in plan with dimensions of concordant concordant NE NE elongation. elongation. Its Its outer outer wall zone zone consists of strongly strongly syenitized volcanic volcanic rocks rocks and and syenite syeniteaplite, aplite,which which grade grade inward inward into into concentric, concentricysheet-like sheet-like masses masses of gneissic gneissic nepheline nepheline and and tabular tabular syenites. syenites. The The indistinctly indistinctly bounded bounded intermediate intermediate zone zone consists consists mainly mainly of of flow-lineated flow-lineatedamphibole amphibolesyenite, syenite,and andthe the cylindrical cylindricalcore, core?with with aa diameter diameterof of 22 km kmhas hasaa rim rim of of lineated heated nepheline nephelinesyenite syeniteand and an an inner inner core core of coarse, coarse, pyroxene pyroxene syenite syenite identical identical with Stettin pluton is is separated separated from from the the syenite syenite bodies bodies to to with that that in in the the intermediate intermediatezone. zone. The The Stettin the the SE SE by by aa fault. fault. In the the Wausau Wausau pluton, pluton, coarse, coarse?massive massive pyroxene pyroxene and and amphibole amphibole syenites syenitesform form aa partial partial outer outer rim rim on on the the north and and east sides. AAbroad broad intermediate intermediatezone zone of of lensoidal lensoidal syenite syenite and and quartz quartz syenite syenite are are crowded crowded with lenticular lenticular xenoliths xenoliths of mica schist, schist?sillimanite-bearing sillimanite-bearing 94 �syenitized volcanic rocks. rocks.Xenolith Xenolith volume volume locally locally exceeds exceeds the the volume volume of of quartzite, and syenitized the the quartz quartzsyenite. syenite.As Asthe thecontact contactbetween betweenthe theWausau Wausauand andRib RibMountain Mountainplutons plutonsisis obscured by by aa broad strip strip of of Rib Rib River alluvium, its itscore coremay maynot notbe bevisible visiblein in outcrop. outcrop. obscured The Rib Rib Mountain Mountainpluton pluton produces produces aa crescentic crescenticmap map pattern pattern with with an an opening openingto to the the The south The most most striking strikingfeature feature of of this this south where where itit is engulfed engulfed by younger Ninemile granite. The concentric concentric pluton is the 8km 8km ring of very large, lenticular lenticularquartzite quartzite and and mica mica schist schist xenoliths xenoliths embedded embedded in in foliated foliated quartz quartz syenites syenites in in its its intermediate intermediate zone. zone. The The Ninemile NinemilePluton, Pluton,isisan anelliptical, elliptical, stock-like stock-likebody body which whichwas was intruded intrudedat at 1500 1500 Ma. (Van (Van Schmus Schmusand and Bickford, Bickford, 1981) 1981) into into the core core and south rim of the Wausau Wausau pluton. pluton. According According to to Anderson Anderson (1983) (1983)itit isis comagmatic comagmaticwith with rapakivi rapakivi granites granitesof of the the Wolf Wolf River River batholith. Although Althoughclassed classed as as aa granite, the theNinemile Ninemile pluton is mainly mainlycoarse coarsebiotitebiotiteamphibole amphibolemonzonite monzonitecontaining containingup up to to 30 30percent percent strained, strained,polycrystalline polycrystallinequartzite quartzitegrains grains usually accompanied accompanied by occasional occasional mica schist and quartzite xenoliths. A A crescentic crescentic mass mass of of granite graniteaplite aplite defines defines the the core corerim rim of of the the larger larger southern southernlobe lobe of of the the Ninemile Ninemilepluton. pluton. The The Wausau Wausau plutons plutons thus thus show show aa distinctive distinctive magmatic magmatic differentiation differentiationsequence, sequence, beginning Stettin pluton and and ending ending with with pegmatite pegmatite dikes dikesin in beginning with with nepheline nephelinesyenite syenitein in the the Stettin the the Ninemile Ninemile pluton. pluton. As As these these dikes dikes are are shallow-dipping shallow-dippingand and contain contain miarolitic miarolitic cavities cavitieswith with autoclasts autoclasts of of early early crystalline crystallinephases, phases,Falster Falster (1985) (1985)concluded concludedthat thatthey theycrystallized crystallized shallow shallow enough enough for for hydrothermal boiling. Several small small porphyritic quartz monzonite monzonite plugs plugs cut cut post-syenite post-syenite faults faults outside outside the Wausau complex complex and probably represent the "last gasp" Ninemile magma. magma. gasp" of of the the differentiated differentiatedNinemile Xenoliths Xenoliths in in the the Wausau, Wausau, Rib Rib Mountain Mountain and and Ninemile plutons are unassimilated wallrock wallrock fragments fragmentscarried carriedup up and and down down in in the the magmas magmas during during intrusion. intrusion. Where Wherethere therehas has been been considerable considerablevertical vertical transport, as asfor forinstance instancealong along caldera calderawalls, walls, xenoliths xenoliths show show great great diversity diversity of of protolithology protolithologyand and metamorphic metamorphicgrade. grade. They They include include upper upper amphiboliteamphibolitegrade, amphibolite, metadiorite, andesitic grade, sillimanite-bearing sillimanite-bearing quartzite, quartzite, mica schist, and arnphibolite, andesitic metavolcanics metavolcanicsand andmetasediments, metasediments,and andeven evencognate cognateinclusions inclusionsof ofearlier-phase earlier-phasesyenites. syenites. Their Their shapes shapes are are most most commonly commonly lenticular lenticular and and sheet-like with a preferential orientation orientation parallel Stettinpluton. pluton. parallel to to cylindrical cylindricalwalls. walls. Xenoliths Xenolithsare areuncommon uncommonininthe theStettin In In the the Wisonsin Wisonsin River River channel channel east east of of the the power power dam dam at at Wausau, Wausau, the the relationships relationships between betweenxenoliths xenolithsand andflow flowstructures structuresin in enclosing enclosing felsic felsic and and mafic mafic quartz quartz syenites syenites are are well displayed. with swirled swirledlineation lineation,, give displayed. Biotite amphibolite xenoliths with give way way southward southward in the outcrop outcrop to to sheet-like sheet-like masses masses of of felsic felsic and and mafic mafic rocks. The folded and fragmented mafic mafic xenoliths advanedmetasomatic metasomaticreplacement replacementand anddeformation. deformation. xenolithsare arebiotite-rimmed, biotite-rimmed, showing showingadvaned The Theenclosing enclosingamphibole amphibolequartz quartzsyenite syenitehas has highly highly discordant discordant flow flow lineation lineation with with swirls swirls and and eddies eddiessuggesting suggestingconsiderable considerableviscosity viscosity and andturbulence. turbulence. Late-stage Late-stagesyenite syenitepegmatite pegmatite veins veins with with quartz quartzcores corespobably pobably represent representresidual residual liquid liquid segregations segregations along along incipient incipient thermal thermalcontraction contractionfractures fracturesininquartz quartzsyenites syenitescontaining containingincompletely incompletelyassimilated assimilatedquartzite quartzite xenoliths. xenoliths.The Theoccurrence occurrenceof of several severalsmall smallxenoliths xenoliths of of unaltered, unaltered, porphyritic porphyritic trachyte trachyte in in the the north northend endof ofthe theoutcrop outcropsuggest suggestaadownward downwardmovement movementof ofsome someof ofthe theclasts clastsfrom fromthe the overlying overlyingvolcanic volcanicpile. pile.As Aselsewhere elsewherein inthe theWausau Wausausyenite syenitecomplex, complex,the theconsiderable considerable concentric concentricheterogeneity heterogeneityof ofxenoliths xenolithssuggests suggestsconsiderable considerablevertical, vertical,somewhat somewhatlaminar laminar transport transportof of xenoliths xenolithsalong alongcaldera calderawalls walls as as aa consequence consequence changes changes in the level of magma magma in in the the conduit. conduit. Future Future field fieldstudies studiesshould shouldinclude include detailed, detailed, comprehensive comprehensive mapping mapping of of xenolithologies. xenolithologies . References: References: Anderson, Anderson,J.J.L., L.,1983, 1983,Proterozoic Proterozoicanorogenic anorogenicgranite graniteplutonism plutonismofofNorth NorthAmerica, America,Geological Geological Society Society of of America AmericaMemoir Memoir161, 161, P.p.133-154. 133-154. Myers, Myers,P.E., P.E.,Sood, Sood,M. M. K., K.,Berlin, Berlin,L.A., L.A.,and andFaister, Falster,A.A.U., U.,1984, 1984,The TheWausau Wausausyenite syenitecomplex, complex, central central Wisconsin, Wisconsin,30th 30thAnnual AnnualInstitute Instituteon onLake LakeSuperior SuperiorGeology, Geology,58 58 pages. pages. Van VanSchmus, Schmus,W.R., W.R.,Medaris, P.O.,1975, 1975,Chronology Chronology of of Precambrian Precambrian rocks rocksin in Medaris,L.G., L.G.,and andBanks, Banks,P.O., Wisconsin, TheWolf WolfRiver Riverbatholith, batholith,aarapakivi rapakivimassif massifapproximately approximately1500 1500m.y. m.y.old, old,Geological Geological Wisconsin,I:I:The Society 14. Societyof of America, America,Bulletin, Bulletin,v.v.86, 86,p.p.907-9 907-914. 95 �COMPOSITION COMPOSITIONAND AND SOURCE(S) SOURCE(S)OF O FMIDCONTINENT MIDCONTINENTRIFT RIFTLAVAS LAVAS (CHENGWATANA VOLCANICS) NEAR NEAR CLAM FALLS, WISCONSIN (CHENGWATANA VOLCANICS) NAIMAN, NAIMAN,Zachary ZacharyJ., J.,Department Departmentof ofGeosciences, Geosciences,University Universityof ofArizona, Arizona,Tucson, Tucson,AriArizona, WIRTH, Karl znaiman@geo.arizona.edu; WIRTH, Karl R., R., Geology Geology Department, Department, zona, 85716, 85716, znaiman@geo.arizona.edu; MacalesterCollege, College,St. St.Paul, Paul, Minnesota, Minnesota, 55105, 55 105,wirth@macalester.edu. wirth@macalester.edu. Macalester Most well-exposed volcanics Moststudies studiesof of the the1.1 1.1Ga Ga Midcontinent Midcontinentrift rift (MCR) (MCR) have have focused focused on the well-exposed volcanics in the Lake Superior region from the central part of the rift. Studies of the Chengwatana Volcanics in the Lake Superior region from the central part of the rift. Studies of the Chengwatana Volcanics (CV), (CV),the the southernmost southernmostexposed exposedvolcanics volcanicsof of the the MCR, MCR, provide provide information informationabout about variations variationsin in rift rift processes processesalong alongthe theaxis axisof of the the MCR. MCR. Here Herewe wereport reportmajor majorelement, element,trace traceelement, element,and andNd Nd isotopic isotopicdata datafrom frommafic maficand andfelsic felsicCV CVflows flowsnear near Clam Clam Falls, Falls, Wisconsin. Wisconsin. Approximately Approximately3000 3000 meters of mafic volcanics, minor interfiow sediment, and rare rhyolite are exposed in the Clam meters of mafic volcanics, minor interflow sediment, and rare rhyolite are exposed in the Clam Falls Falls area. area.The Thepetrography petrographyand andgeochemistry geochemistryof ofthe therhyolite rhyoliteare arediscussed discussedby by Abbott Abbott et et al. al. (this (this volume). volume). New, New,precise preciseU-Pb U-Pbzircon zirconages ages(1,102±5 (1,102±Ma) Ma)of of rhyolite rhyolitenear near Clam ClamFalls Falls (Wirth (Wirth and and Gehrels; Gehrels; this this volume) volume) provide provide aa means means for forcorrelation correlation of of the theChengwatana ChengwatanaVolcanics Volcanics from from Clam Clam Falls Falls and and Taylors Taylors Falls Falls with volcanics from other parts of the rift. Recent Recentaeromagnetic aeromagnetic data data (USGS) (USGS)suggest suggestthat that Clam ClamFalls Fallsflows flowsare arestratigraphically stratigraphicallylower lowerand andtherefore thereforeolder olderthan than CV flows flowsexposed exposedin inthe theTaylors TaylorsFalls Fallsregion. region. CV The The mafic mafic volcanics volcanics from from the the Clam Clam Falls Falls region region are are classified classified as as basalt basalt based based on onmajor major and and trace trace element elementabundances. abundances.The Thebasalts basaltsare aremostly mostlyolivine olivinenormative, normative,but butsome someflows flowsconcontain (Mg# = = tain small smallamounts amountsof of normative normative quartz. Most Mostflows flows have have moderately moderately low Mg-numbers Mg-numbers (Mg# and Si02 contents (45-53 wt. %) indicating that they have under0.58) M ~ / [ M ~ + F = ~ 0.40 + ~ ] 0.58) and Si02 contents (45-53 wt. %) indicating that they have under= 0.40 Mg/[Mg+Fe2I gonesignificant significantfractionation, fractionation,similar similarto toflows flowsfrom fromthe the Taylors Taylors Falls Falls section section of the the Chengwatana Chengwatana gone Volcanics1. Volcanicsl. Clam ClamFalls Fallsbasalts basaltsexhibit exhibitincreasing increasingincompatible incompatibleelement elementabundances abundances(e.g., (e.g.,P,P,Ti, Ti, Y) Y) with with decreasing decreasingcompatible compatibleelement element abundances abundances (e.g., (e.g., Mg, Mg, Ni, Ni, Cr) Cr) similar similarto tothose thoseof ofthe the Taylors Taylors Falls Falls region, region, and and can can be be modelled modelled by fractional fractional crystallization processes2. processes2. Clam ClamFalls Falls flows have Ti02 concentrations which are similar to the low-Ti group (<2.3 wt. %) of basalts flows have Ti02 concentrations which are similar to the low-Ti group (42.3 wt. %) of basalts recognizedininthe theTaylors TaylorsFalls Fallssection1. section1. recognized Neodymium Neodymiumisotopic isotopicanalysis analysisof ofeight eightbasalts basaltsand andtwo tworhyolites rhyolitesfrom fromthe theClam ClamFalls Fallsarea area values between -2.0 and 3.4. Initial ENd values decrease with stratiyield initial ENd loo Ma values between -2.0 ""3.4. Initial ENd values decrease with stratiyield initial ENd(1 iOO Ma') graphic ( igure 1), 1 ,and and all all of of the the values values are are in in general general displaced displaced toward toward more more positive positive graphicheight height (1!gure values values relative relative to to those those of of the the overlying overlying flows flows of of the the Taylors Taylors Falls section1 section1 (Figure 2). AlAlthough similarly similarlyhigh highNd Ndvalues values(initial (initialENd ENd = 2) +2)have havebeen beenobserved observedininother othervolcanic volcanicsesethough quences in the Midcontinent rift quences in the Midcontinent rift 3000 3000 I rn I I I (e.g., (e.g., Group Group 66 and and 77 flows flows of of Clam Falls Region Mamainse Mamainse Point3, ~ o i n t 3Portage ,Portage Lake Lake • basalt basalt Volcanics Volcanicsand and "late "late basalts" basalts" of of northnorth- 'a i   '.' Q r yo ite em Wisconsin4), ~isconsin4),flows with with initial initial w em Â¥ . U ENd values > +2 2 are ENd values arerare rareininthe theearly early 2000 2000 .stagesof of rift riftevolution evolution(time (timeequivaequivastages lent to to upper upper Kallander Kallander Creek Creek ForForlent 0 5 lavas). Furthermation or Group mation or Group 5 Further- 3 more, Taylors Taylors Falls Falls flows flows which which 2 more, rn 1000 -overlie the the Clam Clam Falls Falls basalts basalts (and (and ^. 1000 overlie U  maybe becorrelative correlativewith withPortage PortageLake Lake .may cd 0 j=!  Volcanics Volcanics and Group Group 66 flows) flows)have have w epsilonNd Nd values valuesthat thatare aregenerally generally epsilon  45 -ENd == -4.5 more negative negative(initial (initialENd more I I n I 00 44 22 33 11 -1 00 O1) than ""0.1) thanhas hasbeen beenobserved observedinincorcor-2 -2 -1 relativemain mainstage stagelavas lavas(initial (initialENd ENd relative Initial Ed &srd Initial ^ \ s - 6 a 4-à - 96 - �12 -1 -- 4) +4)elsewhere elsewherein in the therift. rift. == -l Most models models of of the the magmagmatic evolution evolution of the the matic Midcontinent rift assume that the Midcontinent rift assume that the large volume volume of of magmas magmas were were produced primarily from from an an enenriched riched mantle mantle plume plume with with initial initial eNdnear zero3'4. zero3'4. Lavas with with ENd negative ENd values have have been been negative ENd modelled by contamination contamination of of mantle mantle plume plume melts melts with with conticontinental nental lithospheric lithosphericmantle mantle(ENd (ENd near near 9) -9)or orwith withcontinental continentalcrust crust -12 -10 -8 -6 -4 (ENd < -10). -10). In In contrast, contrast, lavas lavas (ENd with with positive positiveENd ENd values values has has been been Initial ENd £\ Initial modelled modelled by aa combination combination of of enriched enriched mantle mantle plume plume and and dedepleted pleted asthenospheric asthenosphericmantle mantle(ENd (ENd > 6) that may have been entrained in the plume head5. FolFollowing valuesof ofChengwatana Chengwatana basalts basalts suggest suggest aa progression progression of mantle lowingthis this model, model, the the initial initial ENd ENd values sources sources from from enriched enrichedmantle mantle plume+depleted plume+depletedasthenospheric asthenosphericmantle mantle(flows (flowswith withENd>>11near near the base of the the Clam Clam Falls Falls section) section) to to enriched enriched mantle plume that has been variably variably contamicontaminated nated with with lithosphere lithosphere(the (theremainder remainderof of the theClam ClamFalls Fallssection sectionand andthe the overlying overlyingTaylors TaylorsFalls Falls section). The inferred progression of mantle sources observed in the Chengwatana Volcanics section). The inferred progression of mantle sources observed in the Chengwatana Volcanics (plume+asthenosphere (plume+asthenosphere—> -> plume plume+1+I- continental continental lithosphere) occurs at a time when when mantle mantle sources sources elsewhere elsewherein in the the rift rift are are inferred inferred to to be changing changing from from plume+continental plume+continental lithosphere lithosphereto to plume+asthenosphere. IfIfthe thedepleted depletedmantle mantlecomponent component of of early early Clam Clam Falls Falls flows flows originated originated from from material material that that was was entrained entrainedin in the the plume plume head, head, as as has been suggested suggested by several several for for other other parts the proportion proportion of melts melts produced produced from entrained entrained asthenospheric asthenospheric mantle rift3'4y5 then the mantle parts of the the rift3'4'5 in the plume plume varied varied in in space space and and time time throughout throughout the rift. rift. Alternatively, Alternatively,the thedepleted depletedmantle mantle component component may may have have been differentially incorporated into plume-generated melts as they traveled continental lithosphere. lithosphere. The eled through the the asthenosphere asthenospherebefore reaching the continental The relatively relativelylow low initial values observed observed in flows of the Taylors Taylors Falls Falls and and upper upper Clam Clam Falls Falls sections indicate initial ENd EM values indicate greater greater involvement involvementof of aa continental continentallithosphere lithosphere(crust (crust and/or andlor mantle) mantle) component componentthan than has hasprepreviously been recognized during the early part part of of "Main "Main Stage" Stage" volcanism volcanism in inthe the rift. rift. In all all of these cases, cases, the the observed observed isotopic isotopic differences differences between between the the Chengwatana ChengwatanaVolcanics Volcanics and and other other volcanic "off-axis" position of the Chengwatana volcanic sequences sequencesof of the the MCR MCR might be related to the "off-axis" Volcanics relative to the location of the inferred inferred plume plume head. head. References Cited Cited (1) Jeffrey D., D., and and Naiman, Naiman, Zachary ZacharyJ,J, 1997. (1) Wirth, Karl R., Vervoort, Jeffrey 1997. The TheChengwatana ChengwatanaVolcanics, Volcanics,Wisconsin Wisconsin and Minnesota: Petrogenesis Petrogenesisof ofthe thesouthernmost southernmostvolcanic volcanic rocks rocks exposed exposed in in the the Midcontinent Midcontinent rift. rift. Canadian Canadian Journal 536-548. (2) (2)Naiman, Naiman, Zachary Zachary J., 1997. 1997. Petrogenesis Petrogenesisof of the the ChengwatanaVolcanics: ChengwatanaVolcanics: Journal of Earth Science, Science, 34: 536-548. 1.1 Wisconsin. Bachelors Thesis, Macalester College. (3) 1.1 Ga Midcontinent rift lavas in Minnesota and Wisconsin. (3)Shirey, Shirey, S.B., Klewin, K.W., Berg, J.H., J.H., and and Carlson, Carlson, R.W.. R.W.. 1994. K.W., Berg, 1994. Temporal Temporal changes changes in the the sources sources of of flood flood basalts: basalts: isotopic and 1100Ma Ma old old Keweenawan Keweenawan Mamainse Marnainse Point Formation, Formation, Ontario, Ontario, and trace trace element element evidence evidence from from the the 1100 Canada: Geochimica Geochimica et et Cosmochimica Cosmochimica Acta, Acta, 58: 58: 4475-4490. 4475-4490. (4) Nicholson Nicholson Suzanne Suzanne W., W., Shirey, Shirey, Steven Steven B., B., Shultz, Klaus J., and and Green, Green, John John C., C., 1997. 1997.Rift-wide Rift-widecorrelation correlationofof1.1 1.1Ga GaMidcontinent Midcontinentrift riftsystem systembasalts: basalts: implications for multiple mantle sources during rift development. Canadian Journal of Earth Science, 34: 504520. 520. (5) (5)White, White,Robert RobertS., S.,1997. 1997.Mantle Mantletemperatures temperaturesand andlithospheric lithosphericthinning thinning beneath beneath the the Midcontinent Midcontinent rift system: evidence from magmatism and subsidence. Canadian Journal of of Earth Earth Science, 34: 34: 464-475. 97 �MILLGROUP GROUPREVISITED: REVISITED: BASAL BASALVOLCANIC VOLCANIC ROCKS ROCKS OF OF THE ThE THE POWDER MILL MIDCONTINENT RIFT MIDCONTINENT RIFTSYSTEM SYSTEM ON ON THE THE SOUTH SOUTH SHORE SHOREOF OF LAKE LAKE SUPERIOR SUPERIOR NICHOLSON, SuzanneW. W.USGS, USGS, National NationalCenter, Center,MS MS954, 954,Reston, Reston,VA VA20192 20192 NICHOLSON, Suzanne and WOODRUFF, and WOODRUFF,Laurel LaurelG., G.,USGS, USGS, 2280 2280 Woodale Woodale Drive, Mounds View MN 55112 55112 In northern Wisconsin and Michigan the Powder Mill Group comprises the oldest volcanic Michigan Group oldest volcanic rocks related to the 1.1 Ga Ga Midcontinent Midcontinentrift rift system system (MRS). (MRS). In In the the more more than than twenty years years since Hubbard (1975) (1975) first separated separated the thePowder PowderMill MillGroup Groupfrom fromthe theoverlying overlyingPortage Portage Lake isotopic, and Lake Volcanics, Volcanics, an abundance abundance of of geophysical, geophysical, structural, structural, geochemical, geochemical, isotopic, chronological data data for for Midcontinent Midcontinentrift riftrocks rockshas has become becomeavailable. available. This report integrates integrates new and existing information to to provide provide a better existing information better understanding understanding of the the early earlymagmatic magmatic history historyof of the theMRS. MRS. Powder Mill MillGroup Groupconsists consistsofof the the basal basal Bessemer BessemerQuartzite, Quartzite, and and the reversely The Powder reversely magnetized igneous rocks of the the Siemens Siemens Creek Creek Volcanics Volcanics and and overlying overlying Kallander Kallander Creek Creek Volcanics. The outcrop outcrop distribution distributionextends extendsfor formore morethan than 180 180 km km along strike, from just Volcanics. The west of the Lake WI discontinuously eastward to toSilver Silver Mountain, Mountain, Lake Owen Owen fault fault near near Cable, Cable, WI ML The Thetrue trueextent extent of of the thegroup group is is unknown unknown because or Ml. because itit is is either structurally truncated or unconformably overlain by younger rocks. However, seismic reflection proffles suggest that unconformably by younger rocks. profiles that the Powder Powder Mill Mill volcanic volcanic rocks rocks extend extend laterally laterally beneath beneath Lake Lake Superior. Superior. The Siemens CreekVolcanics Volcanicsisissubdivided subdividedinformally informallyinto intoupper upper and and lower lower The Siemens Creek members and isotopic isotopiccharacteristics. characteristics. The The lower lower member member of of the members based based on on field, field, geochemical, geochemical, and Siemens Creek Creek Volcanics Volcanicsisisdominantly dominantlybasalt, basalt, but but includes indudes recently recently recognized basal highhighMgO has limited limited regional extent, and and MgO picritic flows. The Thelower lower member memberis is thin thin (<50 ( ~ 5m 0 thick), has is distinctive distinctive because because some someflows flowscontain containaugite augitephenocrysts, phenocrysts,uncommon uncommonamong amongyounger younger MRS basalts. basalts. Pillows Pillows formed formed in the the basal few basalt basalt flows flows that that directly overlie the MRS the Bessemer Bessemer Quartzite. Basalt Basalt with minor basaltic andesite and and andesite andesite dominates dominates the the upper uppermember, member, which is more widespread and 1.5km) km)than thanthe thelower lowermember. member. No No ages have and thicker (up to 1.5 for the Siemens Creek of been determined determined for CreekVolcanics, Volcanics,but butby bycorrelation correlationwith withthe the basal basal units of Osler Group in Ontario and the sills, volcanism volcanismprobably probablywas was initiated initiated about the Nipigon Nipigon sills, the Osier 1108 Ma. Ma. High-MgO High-MgO(picritic) (picritic)rocks rocksrelated relatedtoto the the Midcontinent Midcontinentrift rift magmatism magmatism are are now known of the section sectionin inthree threeareas: areas:1) 1)in inthe theNipigon Nipigonarea area in in Ontario known to to occur occur near the base of associated with with dikes dikes and andsills sills(Sutdiffe, (Sutcliffe,1987); 1987); 2) associated 2) at at Mamainse MamainsePoint Point in in the the basal 500 m of the MRS section (Berg (Bergand andKlewin, Kiewin,1988); 1988);and and3)3)ininthe the Club Club Lake, Lake, WI WI area area west of the MRS section the Mineral Lake Lake intrusion intrusion as as recently identified picritic picriticflows flowsnear near the the base base of the recently identified the Siemens Siemens Creek The high-MgO flows in in the Siemens Creek Volcanics Volcanicsare are strongly strongly altered altered to high-MgO flows Siemens Creek Creek. The serpentine, chlorite chlorite and and talc: no primary serpentine, primary mineralogy is is present. present. An average of of three three analyses of these of these high-MgO high-MgO flows (Ti02 (Ti02= = 1.95 1.95 wt wt %; %; A1203 A1203= 8.89 8.89 wt %; %; MgO MgO == 16.09 16.09 wt %) %) is is chemically chemically most most similar similar to to an an analysis analysisof of a Nipigon Nipigon picritic picritic dike dike (Ti02 (Ti02== 1.88 1.88 wt %; A1203 A&03== wt %; 7.72 higher Ti02 Ti02 and and lower A1203and and MgO MgOthan than a 7.72 wt %; %; MgO MgO == 17.1 17.1 wt %) in having higher picritic average wt %; %; A1203 A l a == 9.79 wt %; %; MgO MgO average reported reportedfrom fromMamainse MamainsePoint Point(Ti02 (Ti02== 0.90 wt = 19.89 wt %; and Klewin, = 19.89 %; Berg and Klewin, 1988). 1988). Picritic flows in the the Siemens Siemens Creek Volcanics show with derivation derivation from steep 18.6), consistent consistent with from partial partial steep REE-element REE-element patterns patterns(CeN/YbN (CeN/YbN= 18.6), melting melting of an an enriched enriched mantle mantle source source at at a depth depth of of more more than than about about 80 80 km. Basalts Basalts from fromthe thelower lowerSiemens SiemensCreek Creek Volcanics Volcanics show show moderate moderateTi02, Ti02,lower lowerA1203 higher MgO MgO than and higher than basalts basalts from the the upper upper Siemens SiemensCreek. Creek. REE REEpatterns patterns are steeper Creekthan thanfor foroverlying overlyingunits. units. In In addition, addition, the two = 14.2), two (CeN/YbN 14.2), for the lower Siemens Creek (CeN/YbN = of the Siemens Siemens Creek CreekVolcanics Volcanicscan canbebedistinguished distinguishedon onthe thebasis basisofof Nd Nd isotopic members of composition: lower lower Siemens SiemensCreek Creekbasalts basalts have have initial initial £v Ed == -1 -1 whereas the upper upper Siemens Siemens Creek EM,, == -3.6. Creek basalts basaltshave haveinitial initialENd Volcanics overlies overliesthe theSiemens SiemensCreek CreekVolcanics, Volcanics,and and also also has The Kallander Creek Volcanics has been informally divided into upper and lower members. members. Both Both members membersrange range from from basalt basalt to to andesite and andesite and rhyolite. rhyolite. The Thelowermost lowermost1.5 1.5km km of of the the Kallander Kallander Creek Creek consists consists of flood basalt phenocrysts,which whichlocally, locally,form formlarge largeradiating radiatingclusters. clusters. A typically containing plagioclase phenocrysts, 98 �rhyolite flow near near the the top of the lower Kallander Kallander Creek Creek gives gives an an age age of of 1107.3 rhyolite flow 1107.3 ± Â1.6 1.6 Ma Ma and Green, Green, 1997). 1997). The upper upper member (about 22 krn km thick) thick) is is dominated dominated by andesite (Davis and member (about andesite and is is considered considered to to represent representthe the extrusive extrusive products of of aa localized localized magmatic magmatic system, the the Mellen complex complex(Cannon (Cannonetetal. al.1993). 1993). A A thick thick laterally laterally extensive extensiverhyolite rhyoliteatat the the top of the the upper member upper memberofofthe theKallander KallanderCreek Creekgives givesan anage ageofof1099.0 1099.0±Â2.6 2.6 Ma (Zartman (Zartmanetetal. al.1997). 1997). Basalts of the Volcanics are are characterized characterized by the lower lower member member of the Kallander Creek Volcanics and low MgO, MgO,Cr Crand andNi, Ni,suggesting suggestingstrong strongfractionation. fractionation. Although Although the REE TiODand their high Ti02, patterns for this Creek basalts, basalts, the patterns this group group are are similar similar to those those for for the the lower lower Siemens Siemens Creek elemental REE REEabundances abundancesare aresubstantially substantiallyhigher higherfor forthis thisgroup. group.InInaddition, addition, not not only are incompatible trace trace element elementratios ratiossuch suchas as C CeN/YbN andTa/Th Ta/Th similar similarfor for both both lower incompatible e N / m and lower members of of the their Nd members the Kallander Kallander Creek Creek and andSiemens Siemens Creek CreekVolcanics, Volcanics, their Nd isotopic isotopic compositionsare are similar similar as as well well (initial (initial ENd Nd == -1). In basalts of of the In contrast, contrast, basalts the upper upper compositions Creek show show lower lower incompatible incompatible trace trace element elementratios ratios and and much less steep Kallander Creek steep REE REE patterns than despite the fact that patterns than the thelower lowerKallander Kallander Creek Creek member, member, despite that their theirmajor majorelement element of the the upper upper Kallander Creek yields compositions are similar. The The Nd isotopic composition of yields slightly lower than the an initial initialEyy d == -1.5, slightly the lower lower member. member. The Siemens Creek and and Kallander Creek Volcanics Volcanicsrepresent representthe the initiation initiation of of aa The Siemens Creek Kallander Creek continental upweiling of of aa mantle mantle plume beneath continental rifting event that has been attributed to the upwelling beneath the Lake Superior Superior region. region. The diversity diversity of of basalt basalt compositions, compositions, including induding picrites, picrites, that that are representative the first years ofof rifting rifting are are characteristic of other representative ofof the first several several million million years characteristic of other continental rift settings mantle plumes plumes play play a dominant which mantle dominant role. role. Based Based on the the continental rift settings in which geochemical and isotopic both the the lower lowerSiemens SiemensCreek Creekand and lower Kallander isotopic characteristics, both Kallander Creek units are probably the of partial melting the products products of of varying varying degrees of melting of an an enriched enriched source (mantle plume) at great great depth depth with withthe thelower lowerKallander Kallander Creek Creekhaving havingundergone undergone significant fractionation. fractionation. The upper Siemens Siemens Creek Creek member member probably represents represents larger larger degrees of of partial partial melting meltingof ofaaplume plumesource sourceatatshallower shallowerdepths, depths,producing producingmelts meltsthat that may have interacted with with lithosphere lithosphereand andundergone undergonelimited limitedfractionation. fractionation. The upper Kailander Kallander Creek probably in in shallow crustal Creek appears to to have haveundergone undergone significant significant fractionation fractionation probably crustal magma magma chambers chambersnow now seen seen as as layered layered intrusions. intrusions. References: References: Berg, J.H., J.H, and 1988, High-MgO High-MgOlavas lavasfrom fromthe theKeweenawan Keweenawanmidcontinent midcontinent rift rift near Berg, and Kiewin, Klewin, K.W., K.W., 1988, near Mamainse MarnainsePoint, Point, Ontario: Ontario:Geology, Geology,v.v.16, 16,pp. pp.1003-1006. 1003-1006. Cannon,W.F., W.F., Nicholson, Nicholson, S.W., S.W., Zartman, Zartman, R.E., R.E., Peterman, Peterman,Z.E., Z.E.,and and Davis, Davis, D.W., D.W., 1993, Cannon, 1993, The Kallander remnantof ofaa Keweenawan Keweenawan central central volcano centered near Mellen, Kallander Creek Creek volcanics—a volcanics-a remnant Mellen, Wisconsin: Institute Institute on Lake Superior Superior Geology GeologyProceedings, Proceedings,Program Programand and Abstracts, Abstracts, v. 20v. 39, 39, p. p. 2021. Geochronologyofofthe theNorth North American American Midcontinent Midcontinentrift rift in Davis, D.W., D.W., and andGreen, Green, J.C., J.C., 1997, 1997, Geochronology western Lake Superior Superior and and implications implications for for its geodynamic evolution: Canadian Journal of western Lake geodynamic evolution: Earth Earth Sciences, Sciences,v.v.34, 34, pp. pp.476-488. 476-488. 1975, Lower Lower Keweenawan Keweenawanvolcanic volcanicrocks rocksofofMichigan Michigan and and Wisconsin: Wisconsin: U.S. U.S. Hubbard, H.A., H.A., 1975, Geological Journal of Research, v. v.3, 3, no.5, no. 5,pp. pp.529-541. 529-541. Geological Survey, Journal Sutcliffe, R.H., of Middle Middle Proterozoic Proterozoicdiabases diabasesand andpicrites picrites from from Lake Lake Nipigon, Nipigon, Sutcliffe, R.H., 1987, 1987, Petrology Petrology of Canada: Canada: Contributions ContributionstotoMineralogy Mineralogyand andPetrology, Petrology,v.v.96, 96,pp. pp.201-211. 201-211. Zartman, R. 1997, U-Th-Pb zircon zircon ages ages of Zartman, R. E., E., Nicholson, Nicholson, S.W., S.W., Cannon, W.F., W.F., and Morey, G.B., G.B., 1997, of some some Keweenawan Supergroup Supergrouprocks rocksfrom fromthe thesouth south shore shore of of Lake Lake Superior: Superior: Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences,v.v. 34, 34, pp. pp.549-561. 549-561. 99 �GIS MINERAL POTENTIAL GIs BASED MINERAL POTENTIALANALYSIS ANALYSIS FOR FOR LODE-GOLD LODE-GOLDAND AND MASSIVE MASSIVE SULFIDE TERRANE OF NORTHERN SULFIDE DEPOSITS DEPOSITS IN IN AN AN ARCHEAN TERRANE NORTHERN MINNESOTA MINNESOTA DEAN M. PETERSON PETERSONand and DR. DR. RONALD RONALD L. L. MORTON DEANM. MORTON Economic Economic Volcanology Volcanology Research Lab, Geology Geology Department, University University of Minnesota - Duluth, Duluth, Duluth, 55812 Duluth, Minnesota, Minnesota,USA USA55812 The last decade change. The decade has been a period of worldwide political and economic change. The globalization globalization of of the world's world's economy economy has has created creatednew new challenges challengesand and opportunities opportunities for the mining and mineral exploration exploration industry. industry. Many Manyareas, areas,which whichpreviously previouslywere were strictly strictly the the domain domain of of nationalist nationalistenterprises enterprises (Southeast Asia, South America, and the former Soviet Union), are now open to mineral exploration (Southeast Asia, South America, and the former Soviet Union), are now open to mineral exploration by companies companies from North America and Europe. Many Many exploration exploration companies companiesare are focusing focusinglarge large portions of their resources resources away from North America and into these recently opened countries. This This switch in regional area selection selection has had aa negative negative impact impact on on the the amount amount of mineral mineral exploration exploration conducted conducted in the Archean terranes terranes of Minnesota. Aside Asidefrom fromthe the changes changesin in global global economics, economics, other other specific specific reasons reasons for the lack of recent mineral mineral exploration exploration in the the Archean Archean terranes terranes of of Minnesota Minnesota include the following: following: > no no local local prospectors are are "beating "beatingthe the bush" bush"and anddiscovering discoveringprospects prospects in in Minnesota Minnesota >>misconception that mine misconception that minepermitting permittingwould wouldbebeasascumbersome cumbersomeasaswith withWisconsin WisconsinVMS VMSdeposits deposits >>absence ofofsuccess absence successininprevious previousgold goldand andmassive massivesulfide sulfideexploration exploration programs programs > most most mineral industry industry geologists geologists have have little little knowledge knowledge of of the the geology geology of of Minnesota, Minnesota,and and > the identification identificationof of specific specificexploration exploration target target areas areas are are normally normally not not included includedin in geological geological ' reports reports and and maps maps The The discovery discovery of economic economiclode-gold lode-gold and and massive massive sulfide sulfidedeposits deposits will will only only occur occurfollowing following prolonged exploration by the mineral mineral industry. industry. To exploration in the Archean terranes of Minnesota by To increase increase exploration exploration activity, activity, state state agencies agenciesin in Minnesota Minnesota have have completed completed extensive extensivegeological geologicaland and geophysical mapping, mapping, completed completed several several mineral mineral potential potential studies, studies, and and currently currentlyare arepromoting promoting geophysical Minnesota's Minnesota's geology geology and and mineral mineralpotential potential to to the the mineral mineral industry. However, However,because becauseof ofextensive extensive glacial glacial cover, cover, an an absence absence of of producing producing mines, mines, and and the the aforementioned aforementionedreasons, reasons, the the mineral mineralindustry industry requires additional Archean additional geological geologicalincentives incentives in in order order to to start start exploration exploration programs programs in in the the Archean terranes terranes of Minnesota. Minnesota. These Theseincentives incentivescould couldinclude includedetailed detailed descriptions descriptionsof of known known prospects, prospects, detailed mineral mineral potential potential studies, studies, and and specific specifictargets targetsand and geologic geologic criteria criteriaupon upon which whichto tobase base detailed exploration exploration programs. programs. This This study study is is an attempt attempt to to generate generatespecific specific lode-gold lode-gold and and massive massive sulfide sulfidetarget targetareas areasthat thatthe the mineral the state. Current mineral industry industry can use as a premise to begin exploration programs in the Currentore ore deposit deposit models GIs databases databasesof of important important Canadian Canadian mining mining camps camps(Timmins, (Tirnrnins, models have have been been integrated integratedinto into GIS Kirkland Lake, Lake, Hemlo, Hernlo, and and Sturgeon Sturgeon Lake Lake(Figure (Figure1)), I)), and and lode-gold lode-gold and and massive massive sulfide sulfideexploration exploration Kirkland models developed from detailed spatial analysis. Exploration target areas in the Minnesota developed detailed Exploration target areas in the Minnesotastudy study area area have have been generated generated from fromthe the integration integrationof of these these models modelsinto intoaa detailed detailedGIS GIs of of aalarge largeArchean Archean tenane 2). terraneof ofnorthern northernMinnesota Minnesota(Figure (Figure2). The The methods methods developed developedto to complete completethis thisstudy studycomprise comprisefive fiveseparate, separate,but but related relatedthemes: themes: >9Thorough research Thorough researchononthethetheory theoryand andmethods methodsofofore oredeposit depositmodeling, modeling,and andthe thegeological geologicalsetting setting of of Archean Archean lode-gold lode-gold and andmassive massivesulfide sulfidedeposits. deposits. 100 �_____________________________________ Standardized from the Superior Province of of Standardized geological compilations compilations of four analog mining camps from Ontario, Canada. These Thesecompilations compilationsare areintegrated integratedwith with Ontario Ontario Geologic GeologicSurvey Survey(OGS) (OGS) drill drill hole, geochemical geochemical and and mineral mineral deposit deposit inventory inventory databases databasesand and have have been been converted convertedinto intoGIS GIs format. format. I ) Standardized geological, Standardized geological,geophysical, geophysical,and geochemical geochemical compilation compilation of the Minnesota study area, area, and and the the conversion conversionof of this this compilation compilation into into GIS GIs format. format. Development of mineral mineral exploration models and targeting targeting criteria generated from knowledge-based queries queries of of the the analog analogGIS GIs datasets. These Thesemodels modelsintegrate integrateArchean Archean massive sulfide lode-gold and massive sulfide deposit deposit models models with spatial features in the analog GIS analog GIs databases. Specific Specificgeological geological criteria criteria have been developed developed that define define the location of the lode-gold and massive sulfide deposits within the analog GIS GIs datasets. datasets. I Figure 11 Location map of the the study study areas. areas. Figure I Thoroughmineral mineralpotential potentialevaluation evaluationfor forlode-gold lode-goldand andmassive massivesulfide sulfidedeposits deposits in in the > Thorough Minnesota study area. This Thisevaluation evaluationisisbased based upon upon spatial spatialanalysis analysisof of the the Minnesota MinnesotaGIS GIs of database using targeting criteria developed from the exploration models generated from queries of the analog analog GIS GIs databases. databases. Simvlified Simolified Geology Geoloey Ely* Ely' Towns ....— 10 Figure Figure 22 0 Major MajorShear S k a Zones Zones ~ 10 20 Kilometers = Proterozoic Protemzaic Rocks Rocks Wawa Subprovince Subpronnce Vennilion Vemilion Granhtic G r a ~ t i cComplex Complex Greenstone Terrane GreenstoneTemne Internal Plutons Plutolw Giants Range Range Granitic Gramtic Complex Complex Mammnt& Simplified geology and location of USGS 1:24,000 Simplified 1 : 2 4 , 0 scale scale quadrangle quadrangle maps maps of of the the Minnesota Minnesotastudy study area. area. 101 �IMPROVED VULNERABILITY ASSESSMENTS ASSESSMENTS OF IMPROVEDGEOLOGIC GEOLOGIC SENSITIVITY SENSITIVITY AND VULNERABILITY OF GROUNDWATER GROUNDWATER POLLUTION POLLUTION POTENTIAL POTENTIALTHROUGH THROUGHAPPLICATION APPLICATIONOF OFFUZZY FUZZYLOGIC LOGIC PFANNKUCH, PFANNKUCH, H.O., H.O., and and PAULSON, PAULSON, Richard, Richard, A., Department Departmentof of Geology Geology and andGeophysics, Geophysics, University of of Minnesota, 310 Pillsbury Drive S.E. Minneapolis, MN University Minnesota, 310 Pillsbury Minneapolis, MN 55455 55455 Vulnerability/sensitivity assessments assessmentsbelong belongto to the the general general problem class of Vulnerability/sensitivity of suitability suitability assessments. In general, these these are management tools to to evaluate evaluate the feasibility, reliability assessments. management tools or risk of of using using aa given given physical physical entity entity or or process. process. In In the the environmental environmental or geologic geologic context context it is is aa decision decision aid aid ininaaresource resourceprotection, protection,or ormanagement managementplan. plan. In generall general, the procedure has three components: components: aa phvsical physical model that describes the process process in a risk analysis analvsisframework, framework, and andaamethodology methodology to to aggregate aggregate individual individual partial partial vulnerability indices indices to to aa global vulnerability alobal vulnerability vulnerabilitv index. index. In In the the context context of of aa vulnerability vulnerability assessment to groundwater contamination contamination the physical physical model model simulates simulates contaminant contaminant transport along pathways from the land surface to the groundwater groundwater body. The pathway pathway is is subdivided into a sequence sequence of of zones zones in in which which different differenttransport transport processes processesand andparameters parameters predominate. These compartments compartments are are surface surface parcell parcel, soil soil zone, zone, vadose zone, capillary fringe, and the groundwater flow zone zone which which may may be be further further subdivided subdivided ifif more more detail detail is fringe, groundwater flow wanted. wanted. In a perfectly perfectly deterministic deterministic world where all transport transport processes processes can be be described described as as mathematically exact, where flow boundary physicoboundary geometry, geometry, boundary boundary conditions conditions and and physicochemical parameters are known everywhere in the domain domain of of interest, interest, the the transport transport process process can be be modeled modeled exactly exactly along along continuous continuous pathways, pathwaysl given given appropriate appropriate computational computational power. power. Then, concentration of the contaminant Its residence residence contaminant everywhere everywhere in space and time is known. known. Its time in in the the system system and and its its exposure exposure to to and and impact impact of of exposure exposure on on the the target target can canbe bequantified. quantified, From this, choices about protection protection of the the resource, resource, the the environment, environment, or or human human targets targets can can be made. This is all that is is needed needed for solving the problem, and no further steps are necessary. necessary. Alas, the world is is not notisotropic, isotropic, homogeneous homogeneousand and perfect, perfect, and and mathematical mathematicalsimulation simulation models even less models less so. so. Therefore, Therefore, severely severely restrictive restrictive approximations approximations and and simplifying simplifying assumptions have have to to be introduced to represent the transport transport process process in in an half-way assumptions represent the adequate manner. The approximations concern the mathematical description of the process, process, limited by insufficient insufficient and and infrequent infrequent information, information, and by inadequate inadequate knowledge of impacts. impacts. the greater greater the the uncertainty that the the model The greater the simplifications, simplificationsl the uncertainty that model results results reflect reflect reality and produce reliable predictions or vulnerability designations. and produce reliable predictions or vulnerability designations. This uncertainty traditionally has been handled by a risk risk analysis analysis approach. approach. The The likelihood likelihood of aa contaminant contaminant particle particle reaching reaching the the groundwater groundwater target and its its likelihood likelihood to to produce produce unwanted unwanted consequences has been expressed in terms of conditional conditional probabilities probabilities and and statistical estimates as confidence limits or ranges. Inadequacies in the geologic database estimates as confidence limits or ranges. Inadequacies in the geologic database have been handled handled by by statistical statistical methods methods such such as as Monte-Carlo Monte-Carloapproaches approaches or or kriging. kriging. A groundwater groundwater system system is is extensive, extensive, three three dimensional, dimensional, dynamic dynamic and and non-homogeneous. non-homogeneous.Its Its properties and states must be be spatially spatially referenced referenced for most most efficient efficient analysis analysis and and map map representation. Georeferencing is best carried out by by aa Geographic Geographic Information InformationSystem System (GIS) (GIs) which also also performs performs aggregation aggregation functions functions able able to to handle handlemap mapoverlay-index overlay-index procedures using built in algorithms. procedures using algorithms. The information information for each hydrogeologic hydrogeologic flow as an an information layer layer in in the the GIsl GIS, and and can can be combined into an compartment is represented as aggregate or monothematic monothematic layer such as aa global global vulnerability vulnerability map map layer. layer. Traditional methods of groundwater translate the the protection afforded Traditional groundwater sensitivity assessment assessment translate by various elements elements of the the geological geological conditions conditions and materials between the surface and the groundwater body body into into vulnerability vulnerability indices, indices, from from which, which, pollution pollution potential potential can can be groundwater 102 �estimated. estimated.One Onesuch suchmethodology methodologyisisUSEPA's USEPA's DRASTIC. DRASTIC.Many Manyof of these theseprocedures procedureslack lack internal consistency, and give no explicit rationale for assigning rating indices, internal consistency, and give no explicit rationale for assigning rating indices, range range intervals and and thresholds, thresholds, weights to the various various factors, and leave leave the choice choice of of an an additive additive intervals aggregation aggregationmodel modelunexplained. unexplained. The Minnesota MinnesotaDepartment Department of of Natural Natural Resources' Resources' (MN (MN DNR) DNR) guidelines guidelines stand stand on on aamuch much The firmer firmer conceptual conceptual basis. basis. They They link link geologic geologic sensitivity sensitivity to to travel travel time time of ofaaconservative conservative tracer tracer from from the the surface surface to to the thegroundwater. groundwater. Long Long travel travel times times are are equated equated to low low sensitivities, and and short short travel travel times times to to high high sensitivity. sensitivity. In In order order to to take take into intoaccount account the the sensitivities, availability of of information information for for mappable mappable factors factors ititmakes makessome somesweeping sweepingsimplifications. simplifications. ItIt availability uses three three factors: factors: depth depth to to water, water, geologic geologic material material in the vadose vadose zone and material material at at the the uses water water table table and andobtains obtainsthe theaggregate aggregateindex indexthrough throughaabinary binarydecision decisiontree treeprocedure. procedure. Because Because of of these these simplifications simplificationsthe the degree degreeof of uncertainty uncertaintyand andthe theconfidence confidencelimits limits are are large. large. Introduction Introduction of of aa fuzzy fuzzy set set methodology methodology will will lead lead to to aa greater greater internal internalconsistency consistency of of the the rating ratingprocess processand andfacilitate facilitate the the use use of of vague vague and and descriptive descriptive data data in in aa more moreappropriate appropriate way. way. Fuzzy Fuzzy logic logic isisaabranch branchof ofset settheory theorythat thatallows allowsobjects objectsdegrees degreesof ofbelonging belongingto toaaset setrather rather than than aabinary binaryyes yesororno nodescription. description.Fuzzy Fuzzynumbers numbersare aredefined definedby bymembership membershipfunctions functions that thatdescribe describetheir their degree degreeof of belonging belongingto to one one set set or or another, another, and and thereby thereby are are able able to to deal deal with with verbal verbal descriptors descriptors or or linguistic linguistic variables, variables, and and to to take take into intoaccount accountthe thenatural natural vagueness vaguenessand anduncertainty uncertaintyinherent inherentiningeologic geologicdata. data.Fuzzy Fuzzymethodology methodologyprovides providesthe the algorithms algorithmsto tooperate operateon onvague vaguerating ratingclasses classesininaaconsistent consistentway. way.Fuzzy Fuzzymethodology methodologywill will also alsogive givemore morerealistic realisticboundary boundarydefinitions definitionsbetween betweenrating ratingcategories categoriesand andclasses. classes. This This research researchcasts caststhe thedefinition definitionof ofthe theMN MNDNR DNRrating ratingfactors factorsinto intoaafuzzy fuzzycontext. context.This This approach more (I) moreadequate adequaterepresentation representation of of linguistic linguistic variables variables such such as as approach isiscapable capableof: of:(1) lithologic lithologic descriptions descriptions from from well well log loginformation informationinto intomanipulable manipulableindex indexnumbers, numbers, (2) (2) combining combining of layer layer information information in in aa GIS GIsthrough throughfuzzy fuzzyrule rulebased basedinstructions, instructions,and and (3) (3) to to extend extendthe thenumber numberof of factors factorsthat thatgo gointo intothe theoverall overallevaluation evaluationto to geohydrologic geohydrologic and and land landuse uselayers. layers. Fuzzy Fuzzy methodology methodology application: application: The The technique technique for for performing performing aa Level Level 22geologic geologicsensitivity sensitivity analysis analysis as as set set forth forthby bythe theMN MNDNR DNRisisrelatively relativelysimple simple and and straightforward. straightforward. The The techniques techniques were were intentionally intentionally designed designed so so that that water water resource resource managers managers (or (or others) others) who who may maynot nothave havetraining trainingon, on,ororaccess accessto, to,a ageographic geographicinformation informationsystem system(GIS), (GIs),would wouldstill still be beable abletotoimplement implementaahand-performed hand-performedoverlay overlayanalysis. analysis. This This can canbe beaavery verytime timeconsuming consuming and andtedious tedioustask taskfor forthe theanalyst. analyst. InInan aneffort efforttotospeed speedup upand andsimplify simplifyespecially especiallythe the preliminary preliminaryassessment assessmentor orproject projectstage, stage,an anExcel Excelspreadsheet spreadsheetbased basedprogram programisisbeing being developed MicrosoffVisual VisualBasic. Basic.ItItaccepts acceptsthe thevarious variousMN MNDNR DNRspecified specifiedvadose vadosezone zone developedusing usingMicrosoft parameters parametersunder underconsideration considerationas as input. input. The Theinput inputdata datalayers layersinclude: include:depth depthtotowater watertable table below belowthe theland landsurface, surface,aquifer aquifermatrix matrixmaterial materialtype typeatatthe thewater watertable, table,cumulative cumulative thickness thicknessofofany anylow lowand andmoderate moderatepermeability permeabilityunits unitsininthe thevadose vadosezone. zone.AAsecond secondversion versionofof the theprogram programincorporates incorporates the the principles principles of of fuzzy fuzzy methodology methodology into the analysis. The The sensitivity sensitivityratings ratingsproduced producedby bythe the"fuzzy" "fuzzy"version versionare arecompared comparedtotothose thoseproduced producedusing using the thepresent presentMN MNDNR DNRtechnique. technique. 103 �SEISMIC EVIDENCE OF Pm-NICKERSON PRE-NICKERSON SEDIMENTS IN SEISMIC WESTERN LAKE SUPERIOR SUPERIOR Deborah E. Rausch and and Nigel J Wattrus Wattrus Large Lakes Observatory, University Universiiy of Minnesota Duluth, MN 55812 558I2 email:nwattrus@d. umn.edu email:nwattrus@dumn.edu The Superior Superior lobe of the Laurentide Laurentide Ice Sheet advanced and retreated out of the western basin of Lake Superior Superior several several times during during the Wisconsin glaciation. glaciation. Wright et al. (1973) recognized recognized four four they are (in order of decreasing age): separate phases of ice advance out of the Lake Superior basin, they the St. Croix; Automba; Split Rock and Nickerson Nickerson phases. phases. The tills of the last two phases show an which represents represents the the incorporation incorporationof of proglacial lacustrine sediments with each enrichment in clay, which advance. As As the the ice ice retreated retreated during during the Nickerson phase, a series of proglacial lakes formed against the edge of the retreating ice. The position of ice margins bordering these lakes have been determined by correlating correlating subaerial subaerial moraines on either side of western Lake Superior Superior (Farrand, (Farrand, 1969; 1969; Isle Royale (Huber, 1973). A Saarnisto, 1974) and Isle A series series of of subaqueous subaqueous recessional recessional moraines, moraines, presumably associated with this sequence of proglacial lakes, have been described in the western arm of Lake Superior Superior near near Isle Isle Royale Royale (Landmesser (Landmesseret et al., al., 1982). 1982). The sediment sediment record contained contained in western Lake Superior Superior is intimately related to the retreat of the An idealized idealized soft soft sediment sediment section section for western Lake Superior based upon Laurentide Ice Sheet. An coring (Farrand, (Farrand, 1963; 1963; Dell, 1971; 1971; Thomas and Dell, 1978) 1978) and high resolution seismic surveying surveying consists of of till till overlain overlain by by aa glaciolacustrine clay (Johnson, 1980; Scholz, 1985; Anderson, 1997), consists sequence followed by a thin post-glacial Holocene clay. Recent Recentdata data collected collectedby by the the Large LargeLake Lake from Observatory (LLO) suggests the presence of a relict sediment section below the till, presumably fiom advances into earlier advances into the Lake Lake Superior Superiorbasin. basin. Since 1996, the Large Lakes Observatory (LLO) has collected over 2500 km km of high resolution single channel seismic reflection data in western Lake Superior. The surveyed area extends from Duluth to Isle Royale and southeast to Houghton, Michigan. Most of this this new data was collected with a ORE Geopulse system. The firing rate was 0.5 seconds and the the average vessel vessel speed was 6.5 milliseconds/sample for later post-survey knots. The data were digitally recorded at rate of 0.5 milliseconds/sample processing. Positioning Positioninginformation information was was derived from fiom the ships GPS navigation system. Images of the recently acquired data show most of the soft sediment section and bedrock-soft sediment interface (acoustic basement). In In water water depths depths of less than 100 100 meters, the development/preservation of the g1aciaVpost-glacial and Holocene clays above the till is negligible negligible developmentlpreservation glacial/post-glacial due to current action on the lake floor. floor. In In the deeper deeper portions of the lake, the near surface reflections are associated with the post-glacial Holocene clays, glaciolacustrine glaciolacustrine clays and a thin basal till (less than six meters thick). Presumably, glaciallpost-glacial sequence is associated with the last Presumably, this glacial/post-glacial advance/retreat in the Lake Superior (Nickerson/post-Nickerson deposition). Many of recent advancehetreat Superior basin (Nickersodpost-Nickerson seismic lines, especially those in the western portion of the survey area, exhibit buried channels containing thick sequences sequences of pre-Nickerson deposits (Figure 1). There is often a well defined unconformity separating the pre-Nickerson sediments sediments from the overlying younger section. The unconformity clearly represents represents a period of erosion, perhaps associated with the last advance advance of ice across across the basin. basin. 104 �Seismic facies analysis suggests that the pre-Nickerson pre-Nickerson material material is is composed composed of of aa sequence sequence of of glacial glacial tills and glaciolacustrine sediments. Presumably Presumably these represent represent relict relict sediments sediments preserved preserved from from earlier advances of the Superior Lobe in in western Lake Lake Superior. Superior. Very few of of the the cores cores collected collected in in Lake Superior penetrated penetrated sediment sediment below below the the glaciolacustrine glaciolacustrine vvarved clays. One a n e d clays. One long long core collected Minnesota North North Shore, Shore, however, however, recorded over 190 of Split Rock on the Minnesota 190 meters of glacial and glaciolacustrine sediments glacio1acustrine sediments (Zumberge and Gast, 1961). 1961). References. Anderson, K.A., K.A., 1997, Lake Superior Superior (M.S. (M.S. Thesis): Thesis): University University of of Anderson? 1997, A seismic stratigraphic study of western Lake Minnesota, Mimesota, Duluth, Minnesota, Minnesota, 82 82 p. p. C.!., 1971, (Ph.D. Dissertation): Dissertation):University Universityof ofMichigan, Michigan, Dell, C.I., 1971, Late Quaternary Quaternary sedimentation sedimentation in in Lake Lake Superior Superior(Ph.D. Ann Arbor, Michigan, Michigan, 184 184 p. W.R., 1963, Preliminary report report of Lake Superior Coring Program, Program, Core Core Study, 33 p. p. Farrand, W.R., W.R., 1969, The Quaternary history of Lake Superior: International Farrand, W.R., InternationalAssociation Association of of Great Great Lakes Lakes Research, p. 181-197. 181-197. Huber, N.K., 1973, 1973, Glacial and postglacial history of Isle Royale National Park, Michigan: U.S. U.S. Geological Geological Survey Professional Professional Paper 754-A. Johnson, T.C., 1980, 1980, Late Late glacial and postglacial sedimentation sedimentation in Lake Superior based on seismic-reflection profiles: Quaternary QuaternaryResearch, Research, p. 380-391. 380-391. Landmesser, Landmesser, C.W., Johnson, Johnson, T.C., T.C., and and Wold, Wold, R.J., R.J., 1982, 1982,Seismic Seismicreflection reflectionstudy studyof ofrecessional recessionalmoraines moraines 173beneath Lake Superior and their relationship to regional deglaciation: Quaternary QuaternaryResearch, Research, p. p. 173190. 190. C.A., 1985, Scholz, C.A., 1985, Sediment Sediment distribution distribution and sedimentation sedimentationrates rates in the the western western arm arm of of Lake LakeSuperior Superiorusing using 3.5 kHz kHzseismic seismicreflection reflectionprofiles profilesand and210Pb ''qb geochronology University of of Minnesota, Minnesota, geochronology (M.S. (M.S. Thesis): Thesis): University Duluth, Minnesota, Minnesota, 129 129 p. Thomas, Thomas, R.L. and and Dell, Dell, C.I., C.I., 1978, 1978,Sediments Sedimentsof of Lake LakeSuperior: Superior: Journal Journal of Great Great Lakes Lakes Research, Research, p. p. 264-275. 264-275. Wright, H.E., H.E., Matsch, C.L., E.J., 1973, Superior and Des Moines Moines Lobes: Lobes: Geological GeologicalSociety Society of of C.L., and Cushing, E.J., America Memoir 136, 136, p. 153-185. 153-185. J.H., and Gast, P.G., P.G., 1961, Geological investigations in Lake Lake Superior: Geotimes, Zumberge, J.H.? Geotimes,p. p. 10-13. 10-13. sP p 0 C" I •1 C I -I -r'" . — -- Figure 1. North Shore southwest southwest of of 1. Geopulse seismic reflection data collected off the Minnesota North Grand Marais, Minnesota. Relict Relict sediments sediments are are clearly clearly preserved p r e s e ~ e in din aa broad broad channel channel and and are are unconformably overlain by by younger till and and glaciolacustrine glaciolacustrine sediments sediments of of the the Nickerson Nickerson phase. phase. 105 �____ PRELIMINARY ORE OREi MINERALOGY OF THE HERONTRACK SILVER-ZINC-COPPER OCCURRENCE, OCCURRENCE, LUMBY LAKE LAKE AREA, AREA?ONTARIO, ONTARIO, CANADA CANADA SAINI-EIDUKAT, Geosciences, North Dakota State SAINI-EIDUKAT?Bernhardt, Bemhardt, Department of Geoscien~es~ University, Fargo, Fargo?ND 58105-5517 USA (sainieid@badlands.nodak.edu). (s~fieid@badlands.nod&.edu). Inc., Box 1376, BERNATCHEZ, Raymond, Atikokan Resources, Inc.? 1376?126 126 Willow Road, Atikokan, Ontario, Canada (rbernatc@atikokan.lakeheadu.ca) Road? (rbernatc @atikokan.lakeheadu.ca) The Herontrack silver-zinc-copper silver-zinc-copper occurrence occurrence occurs near Herontrack Lake Lake in the the Lumby Lumby Lake greenstone belt. It lies in the southwestern part of the Archean Superior Province, near Atikokan, Atikokan?Ontario. Recently discovered in the region of the famous Steep Rock iron mine, the Herontrack occurrence contains numerous stratiform mineralized horizonsy horizons, some of which contain contain significant significant Ag Ag mineralization. mineralization. The Lumby Lake greenstone near its border border greenstone belt occurs occurs in the Wabigoon subprovince, subpro~ince~ near its with the Quetico subprovince (Fig. 1, 1 from Davis and Jackson, 1988). It comprises a 60 km x mafic, ultramafic (komatiitic) and felsic 20 km synclinal supracrustal assemblage of mafic? metavolcanic packages with subordinate metasedimentary units (Jackson and Chevalier, Chevalier? contacts the the older Marmion Lake tonalite batholith to the the southy south, and is intruded by 1985). ItIt contacts north, and by mafic dikes. Felsic units include lapilli the younger Norway Lake granite to the north? tuffs, quartz porphyriesy porphyries, and rhyolite flow breccias. tuffs? breccia. To the west of the Lumby Lake area, area?the northeasterly trending Red Paint Lake fault zone truncates the assemblage. '-..-_.4+.' ..L—r..JJ I *+T —: I ! ,./ \ • * * + + * * Finlays0 Lake '* Belt. • * ++ A * + e't * — . Marmion Lake Batholith * —---—-——- : + * * : --+ kilornetres Figure 1. Geologic map showing the location map of the the western western Wabigoon Wabigoon subprovince, showing location of the Lumby Lumby Lake area. From Davis and Jackson, 1988. 106 �I The The lack lackof of aametamorphic metamorphicaureole aureolein inthe thesupracrustal supracrustalsequence sequence against againstthe theMarmion Marmion Lake Laketonalite tonaliteindicates indicatesthat thatthe thebatholith batholithwas wasaabasement basementunit unit upon upon which whichthe theLumby LumbyLake, Lake, and and possibly possibly the the Steep Steep Rock Rock Lake Lake group, group,were were deposited deposited (Davis (Davis and and Jackson, Jackson, 1988). 1988).Davis Davis and and Jackson Jackson (1988) (1988) dated dated felsic felsic samples samplesfrom from the the Lumby Lumby Lake Lake area area and and the the Marmion Mannion Lake Lake batholith batholith to to approximately approximately 33 Ga, Ga, an an age age older older than than most most greenstone greenstone belts. belts. During 1990's,Atikokan AtikokanResources, Resources,Inc. Inc. prospected prospected the the Lumby LumbyLake Lakearea areaand and During the the mid mid 1990's, discovered discovered aa high-grade high-gradesilver silveroccurrence occurrenceon onthe thewest westside sideof of Herontrack Herontracklake. lake.The The occurrence km thick thick east-west east-westtrending trending intermediate intermediateto to felsic felsicvolcanic volcanic occurrenceisis hosted hosted in inaa1.5 1.5km sequence sequencein in the the area areabetween betweenHerontrack Herontrackand andLumby LumbyLakes Lakes(Staargaard, (Staargaard,1997). 1997).This This sequence sequence thins thinsto to the theeast eastand andwest, west,indicating indicatingititmight mightbe bean aneruptive eruptivecenter. center.The Thefelsic felsic units units are are fragmental, fragmental, often often containing containing quartz quartz eyes, eyes, and and can can contain contain significant significant cherty chertyunits. units. Chip Chip samples samples (over (over one onemeter) meter)indicate indicategreater greaterthan than40 40g/tonne ghonneAg. Ag. Thin Thin and and polished polished block block sections sections of of ore ore horizon horizon samples samples are are being being investigated investigated using using transmitted transmitted and and reflected reflected light lightmicroscopy microscopyanalysis analysis to to determine determine the the host host rock rock and and ore ore mineralogy mineralogy and and genesis. genesis. The Therelationship relationshipbetween between fold fold structures structures recognizable recognizable on onboth both outcrop outcrop and and thin-section thin-section scales scalesand and mineralization mineralizationindicates indicatesthat that the the silver silvermineralization mineralization may may be be locally locally remobilized. remobilized. These Thesefold fold structures, structures,however, however, may may be be related related to to mafic mafic dike dike intrusion intrusion and and not not to to regional regional shear. shear. Mineralization Mineralizationoccurs occurs in in chert chert units units as as disseminated disseminated sphalerite, sphalerite, galena, galena, native native silver, silver,acanthite, acanthite,chalcopyrite chalcopyriteand and pyrite. pyrite. Native Native silver silverand andacanthite acanthite occur pm in diameter diameter and and as as veinlets veinlets 10—20 10 - 20 p.m pm wide. No Au Au was was occur as as isolated isolated grains grains 10 10to to 30 30p.m detected detected in in the the Ag Agor orthe theacanthite acanthiteusing using EDS EDSanalysis. analysis.Electron Electronmicroprobe microprobe analyses analysesare are being being undertaken undertaken to to determine determinethe theamount amountof of Ag Ag contained containedin in galena galena and and trace traceelement element composition composition of of sphalerite. sphalerite.Continued Continuedmapping mappingmay may show showthat that the the Herontrack Herontracksilver silver occurrence occurrence represents represents aa locally locally remobilized remobilized silver-rich silver-rich distal distal portion portion of of aa larger larger massive massive sulfide system. system. sulfide Referencescited: cited: References Jackson, Jackson, M.C. M.C. and and Chevalier, Chevalier, P., P., 1985, 1985,Precambrian Precambrian Geology Geology of of the the Lumby Lumby Lake Lake Area, Area, Western Preliminary Western Part, Part, Kenora Kenora District; District; Ontario OntarioGeological Geological Survey, Survey, Geological Geological Series Series-- Preliminary Map P.2828. P.2828. Map Davis, D.W., and Jackson, M.C., M.C., 1988, 1988,Geochronology Geochronology of of the Lumby Lake Lake greenstone greenstone belt: belt: aa Bull. G.S.A., G.S.A., v. v. 100, 100,p. p. 3 Ga complex within the Wabigoon Subprovince, northwest Ontario: Bull. 8 18-824. 818-824. Staargaard, C.F., 1997, 1997,Private Private report report to to Atikokan Atikokan Resources, Resources, Inc. Staargaard, 107 �ALTERATION AND METAMORPHISM METAMORPHISM IN AN ALTERATION AND AN ARCHEAN ARCHEAN LODE GOLD GOLDDEPOSIT, DEPOSIT, KItEMZAR KRJZMZARMINE, MINE,GOUDREAU-LOCHALSH GOUDREAU-LOCHALSHGOLD GOLDCAMP, CAMP,ONTARIO ONTARIO SALO, R.W. and Lakehead University, andKISSIN, KISSIN,S.A., S.A., Department Departmentof ofGeology, Geology, Lakehead University, SALO, RW.* Thunder P7B SE! SEl ThunderBay, Bay, Ontario, Ontario,P7B The TheKremzar KremzarMine h4heisislocated located45km 45km northeast northeast of of Wawa, Wawa, Ontario Ontarioin in the theMichipicoten Michipicoten Greenstone GreenstoneBelt. Belt.The TheKremzar Kremzarisisone oneofofseveral severalformer formergold-producing gold-producingmines minesin inthe thevicinity vicinity including well as as aa number of smaller properties. The including the Magino and Edwards Mines, as well The mine mine was was most most recently recently operated operatedby by Canamax CanamaxResources ResourcesInc. hc. in in the thelate late1980s, 1 9 8 0with with ~ ~ aa total total production productionof of 46798 46 798oz ozAu Au(Domville, (Domville,1998). 1998). The Thepresent presentstudy studywas was undertaken undertakenwhile whilethe the property is under redevelopment as the Island Gold Project of Patricia Mines Inc. property is under redevelopment as the Island Gold Project of Patricia Mines Inc. The TheNo.2 N0.2 Zone, Zone,aagold-bearing gold-bearingvein veinsystem systemwell well exposed exposed on on the the surface, surface,was was channelchannelsampled sampled in order order to tostudy studythe thealteration alterationassociated associated with with the thequartz-carbonate quartz-carbonate vein. vein. Petrographic Petrographicstudies studieswere werecarried carriedout outon on25 25samples samplescollected collectedatatO.5m OSm intervals; intervals; 13 13of these these were analyses of of major, major, minor minor and and trace elements by XRF and were selected selected for for whole-rock whole-rock analyses and NAA, respectively. respectively. NAA, The Thevein vein system system cuts cuts metavolcanic metavolcanic rocks of intermediate intermediatecomposition, composition,which which contain contain the chlorite chloritezone zonemineral mineralassemblage assemblagechiorite-sericite-albite. chlorite-sericite-albite. Alteration Alteration is is marked marked by by the intense carbonate carbonate and quartz quartz flooding, flooding, as well well as aa number number ofofchanges changesininaccessory accessory mineralogy. Primary Primaryilmenite ilmeniteisisprogressively progressively replaced by sphene, and allanite allanite occurs occurs only only within the the alteration alterationzone. zone. Zoisite, Zoisite, not present in in the the country country rock, rock, is abundant abundant in the the within altered zone. zone. Weakly Weakly pleochroic, fine-grained fie-grained biotite is is closely closely associated associated with with quartz quartz altered veining and andflooding. flooding. veining Among major components, CaO increases increases inward inward toward the the vein vein system, system, whereas components, CaO normally mobile components components Na20 Na20and and K20 K20show show little little variation. Ti02 Ti02decreases decreasesslightly, slightly, Among trace elements, W shows a marked increase. although itit usually usuallyimmobile. immobile. Among elements, shows a marked increase. although Although REE REE are areconsidered consideredtotobe beimmobile immobileiningold goldvein veinsystems systems(McCuaig (McCuaig & & Kerrich, Kemch, 1994), the the light light REEs, LLaa and Ce, are markedly markedly enriched in the alteration alteration zone. zone. The presence and prehnite and abundant presence of of euhedral euhedral zoisite, zoisite, minor minor wollastonite wollastonite and abundant The skarnoid calcite produce an an assemblage assemblage resembling resembling that of of aalow-grade low-gradeskarn. skarn. The skarnoid assemblage is the result result of of regional regional metamorphism metamorphism subsequent to formation formation of of the the vein vein and carbonate-enriched system, which has operated system, which operated on onthe thecompositionally compositionallymodified modified carbonate-enriched alteration zone. zone. Multiple Multiple metamorphic events are consistent consistent with three three deformational deformational alteration regimes &Helmstaedt Helmstaedt(1989). (1989). regimes documented documented by by Arias Arias & References References Arias, Z.G. & of central and east& Helmstaedt, Helmstaedt, H., H., 1989. 1989. Grant 343 343 Structural Structural evolution of eastcentral Michipicoten (Wawa) Greenstone Greenstone Belt, Belt, Superior Superior Province, Province, p. p. 210-226 210-226hj Michipicoten (Wawa) Milne, V.G., Research Grant V.G., ed., Geoscience Research Grant Program, Program,Summary Summary of Research Research 198819881989, 237 p. p. 1989, Ont. Geol. Geol. Surv. Sum. Misc. Misc. Pap. Pap. 143, 143,237 Domville, 1-32. J., 1998. 1998. Patricia Patricia Mines. Mines. Ont. Ont.Prospector Prospector1998, 1998,p.p.331-32. Domville, J., McCuaig, T.C. & Kerrich, of lode gold McCuaig, T.C. Kemch, R., R., 1994. 1994. P-T-t-deformation-fluid P-T-t-deformation-fluid characteristics of gold deposits: Evidence from from alteration alteration systematics, systematics,p.p.339-380 339-380 j Lentz, D.R., ed., ed., deposits: Evidence Lentz, D.R., Alteration AlterationProcesses ProcessesAssociated Associatedwith with Ore-forming Ore-formingProcesses. Processes. Geol. Geol.Assoc. Assoc. Can. Can.Short Short Course Course Notes, Notes, v. v. 11, 11,467p. 467p. *student *studentauthor author 108 �— ADDITIONAL PALEOMAGNETIC RESULTS FOR A 1500 Ma MAFIC DIKE AT WATERLOO WISCONSIN Schaper*, D. , Suess*, W. , Katzer*, L. ,and Kean, W. Department of Geosciences,University of Wisconsin—Milwaukee P.O. Box 413, Milwaukee, Wi. 53201 (* student authors) Recent expansion of the Michels Materials Quartzite Quarry (Gillen Quarry) at Waterloo Wi. has exposed additional outcrops of a near vertical mafic dike which cuts the quartzite in a North-South direction. The new exposure is approximately 1.5 meters wide and about 50 meters long located on the NE top surface of the quarry. The other exposure previously reported by Kean(1994) is on a vertical wall in the Southwest corner of the quarry (Luther,1997). The two exposures are on line and appear to be the same dike. The age of the dike is assumed to be 1500 Ma, which is the age of mafic material from a drill core in the nearby Portland Quarry (Aldrich et.al., 1959) and similar to the age of a pegmatite (1440 Ma, Aldrich 1959) in the area. Luther(personal communication, 1994) identified the dike as basalt which has been metamorphosed to possibly greenshist fades. Thirty six cores were collected from both locations, as well as from the surrounding quartzite. The edges of the dike show evidence of weathering and mineral alteration, so the majority of the mafic samples were collected from the center of the dike. Cores from all sites were subjected to detailed thermal demagnetization to either 600° or 750° C. Several dike samples were also A.F. demagnetized to lOOmT. The demagnetization characteristics and the Saturation Isothermal Remanent Magnetization characteristics (SIRN) indicate that magnetite is the primarily carrier of the magnetism. There is one primary magnetic direction for the dike which is removed with thermal demagnetization to 600°C. The magnetism of the quartzite is carried by hematite, as is evident from thermal demagnetization to 750°C., and SIRM studies.The magnetic directions of all samples including those reported by Kean, 1994, are presented in Figure 1. The dike shows negative inclinations (-30° to -50°)and declinations in the NNW-NNE direction. The quartzites have positive inclinations (30° to 40) and westerly declinations, which is similar to the earlier results of Mercer(1984). The magnetic directions for the dike show streaking, which may represent an alteration component in some of the samples. Nonetheless, the overall direction provides a pole position consistent with other 1400—1600 Ma. rocks in the Lake Superior region,and significantly different than that of the quartzite. 109 �References: References: Aldrich,L.T., Wetherill,G.W., ~etheri1l~G.W.~ Bass, MN.., M.N., Compston, Compston, W., Davis, Aldrich,L.T., Bass, W,Davis, G.L., and and Tilton,G.R.,1959, Tilton,GÈR.,1959Mineral Mineral age age measurements: measurements: G.L., 58, p.245—247. p.245-247. Carnegie Institute Washington Year Book Carnegie Institute Washington Year Book. 58, Kean, WF., W.F., 1994, 1994,Paleomagnetism Paleomagnetismofofa a1500 1500Ma. Ma. mafic maficdike dikeat at Kean, Institute on Lake Superior Geology abstracts Waterloo Wi. Waterloo Wi. Institute on Lake Superior Geology abstracts Vol.40, p.17. p.17. and proceedings, proceedings, Vol.40, and Luther, F., F., 1997, 1997, The The precambrian precambrian Waterloo waterloo quartzite, quartzite, Dodge Dodge and and Luther, Counties, Wisconsin-petrology, structure, and Jefferson Jefferson Counties, Wisconsin—petrology, structure, and Field Trip Trip No.5, No.5, in in Guide Guide to to Field Field Trips Trips in industrial uses, uses, Field industrial Wisconsin and Adjacent Areas of Minnesota. 31st annual Wisconsin and Adjacent Areas of Minnesota. 31st annual meeting of of the the NCGSA, NCGSA, Madison Madison , Wi. Wi. Ed. Ed. M.G. MçG Mudrey, Mudrey, Jr. Jr. meeting , Mercer, D., Paleomagnetism of of the theBaraboo BarabooQuartzite, Quartzite,tJW— UWMercer,. D., 1984, 1984, Paleomagnetism Milwaukee M.S. thesis, 294 p. Milwaukee M.S. thesis, 294 p. FIGURE 11 FIGURE FOR WATERLOO WATERLOO BASALTIC BASALTIC DIKE DIKEAND AND WATERLOO WATERLOO MAGNETIC DIRECTIONS DIRECTIONS FOR MAGNETIC HAS NEGATIVE INCLINATIONS AND NORTHERLY QUARTZITE. DIKE MATERIAL QUARTZITE. DIKE MATERIAL HAS NEGATIVE INCLINATIONS AND NORTHERLY DECLINATIONS. THE QUARTZITE HAS POSITIVE INCLINATIONS AND DECLINATIONS. THE QUARTZITE HAS POSITIVE INCLINATIONS AND WESTERLY DECLINATIONS. THE DATA REPRESENTS TWO DIFFERENT WESTERLY DECLINATIONS. THE DATA REPRESENTS TWO DIFFERENT EXPOSURES IN IN THE THE SAME SAME QUARRY QUARRY EXPOSURES N o EXPOSIJ( H(Z NES DC smir. £ EflU( 1(6 IPC RA.T s. HORIZ EXPO$UI( P06 DC OUNflZITE * WRT OPOSU( P06 DC IW1TZITE 110 I �I METAMORPHISM,HYDROTHERMAL HYDROTHERMALALTERATION ALTERATION AND AND LATERITIC LATERITIC METAMORPHISM, WEATHERING OF OF DRILLED MRS VOLCANIC ROCKS IN IOWA WEATHERING SCHMIDT, Susanne Th.! Th., Mineralogisch-Petrographisches Mineralogisch-Petrographisches Institut, SCHMIDT/ Susanne Institut/ Bernoullistr. Bernoullistr. 30, 30/ CH CH 4056 4056 Basel, Basel/ Switzerland, Switzerland/ schmidts~ubac1u.unibas.ch;SEIFERT, SEIFERTt Karl! schmidts@ubaclu.unibas.ch; Karl, Departement Departement of Geological & Atmospheric AtmosphericSciences, Sciences/ Iowa Iowa State StateUniversity, University/Ames, Ames/IA IA50011, 500111 kseifert@pop-2.iastate.edu. kseifertapop-2.iastate.edu. and cuttings from deep wells into the Precambrian igneous rocks Well cores and of the buried buried Midcontinent MidcontinentRift RiftSystem System in in Iowa Iowa (Iowa (Iowahorst, horst/Anderson, Anderson/1990) 1990) were studied to to identify identify primary primary and and secondary secondary mineral mineral assemblages assemblages and the compositionwas was determined determined by by instrumental instrumental neutron neutron bulk geochemical composition activation analysis (INAA) for trace elements and and by inductively inductively coupled coupled for major major elements. elements. The results indicate a complex plasma (ICP) analysis for alteration history with metamorphic and hydrothermal hydrothermal stages, stages! followed followed by lateritic weathering on the Precambrian erosion surface. surface. Minerals Minerals were analyzed analysis/clay clay minerals minerals by by X-ray X-ray diffraction diffraction analyzed by by electron electron microprobe microprobe analysis, (air-dried and gly~olated)~ and the theisotopic isotopic composition compositionof of calcite calcite was was (air-dried and and glycolated), determined. The large majority of these Midcontinent Rift samples were originally & Anderson, Anderson/ 1996) 1996) compositionally similar to basalts or diabases diabases(Seifert (Seifert & intermediate olivine olivine tholeiites tholeiites as as described described by by Brannon Brannon (1984) (1984) from the exposed north north of Midcontinent Rift or North North Shore Shore Volcanic Volcanic Goup (NSVG) (NSVG) exposed Duluth in Minnesota. Minnesota. Although Although alteration alteration has greatly modified modified the primary samples/ relicts relicts of the original original magmatic magmatic composition and texture texture of of most most samples, mineral assemblage can still be be observed observed in in some some samples. samples. Based on amygdule frequency frequency and and degree degreeof of alteration alteration itit is is possible possible to to differentiate differentiate morphological flow flowunits. units. Flow tops with a large between the various morphological Flow tops number of amygdules and and highest highest degree degree of of alteration alteration can be distinguished distinguished without any amygdules and a less from massive flow interiors without less intensive Massive alteration. In some flow tops no primary igneous texture is visible. Massive of alteration but but the primary texture is flow interiors show various degrees of often preserved. A relativly homogenous regional metamorphic alteration alteration pattern is observed based on the highly amygdaloidal amygdaloidal flow tops and amygdule amygdule minerals. In addition, some massive flow interiors have preserved part of addition/ some of the the early early alteration history. history. The Theassemblage assemblageepidote-Fe-rich-chlorite-albiteepidote-Fe-rich-chlorite-albitequartz±pumpellyite±sericite is characteristic characteristic for for all all studied studied drill sites of of the quartz~umpellyite~ericite facies. The Iowa horst and and indicates indicates conditions conditions of the beginning greenschist facies. The same facies is also observed in the lowermost part of the ca 8 km thick NSVG the lowermost part of the ca 8 k m thick NSVG in Minnesota near Duluth which is interpreted to be the result of of burial metamorphism (Schmidt, 1990; 1993). metamorphism (Schmidt/ 1990; 1993). 111 �The Sharp #1 core documents the complex alteration history that affected at least part of the Midcontinent Rift System in Iowa. A sequence of secondary alteration stages can be established. In the massive flow interior of Sharp #1 (sample 2206.4), an early Fe-poor, Si-rich phyllosilicate replaces pyroxene along grain boundaries. Fe-poor, Si-rich phyllosilicates (smectites) are also reported from massive flow interiors of the NSVG indicating an earlier alteration stage under lower temperatures (Schmidt & Robinson, 1997). The Fe-poor, Si-rich phyllosilicate is in turn replaced by a late Fe-rich chlorite which also occurs in veinlets. This Fe-rich chlorite also forms part of the epidote-Fe-rich-chlorite-albite-quartz ± pumpellyite ± sericite assemblage in the amygdaloidal flow tops. In samples, a late potassic alteration is present with K-feldspar as a frequent overgrowth not only of silicates (albite and pyroxene), but also of chalcopyrite. All samples which were derived directly from the original Precambrian erosion surface are partly intensively altered to kaolinite which is attributed to a tropical lateritic weathering (Seifert & Anderson, 1996). This correlates well with the suggested position of Iowa near the equator at the end of the Precambrian time. No kaolinite is present deeper in the drill cores. Anderson, R.R. (1992) The Midcontinent Rift of Iowa. Ph. D. thesis, University of Iowa, Iowa City, 324p. Brannon, J.C. (1984) Geochemistry of successive lava flows of the Keweenawan North Shore Volcanic Group. Ph. D. Thesis, Washington University, St.Louis, 3l2p. Schmidt, S.Th. (1990) Alteration under conditons of burial metamorphism in the North Shore Volcanic Group, Minnesota - Mineralogical and geochemical zonation. Heidelberger Geowisscnschaftliche Abhandlungen, Band 41, 309 p. Schmidt, S.Th. (1993) Regional and local patterns of low-grade metamorphism in the North Shore Volcanic Group, Minnesota, USA. Journal of metamorphic Geology, 11, 401-414. Schmidt, S.Th. & Robinson, D. (1997) Metamorphic grade and porosity and permeability controls on mafic phyllosilicate distributions in a regional metamorphic zeolite to greenschist facies transition of the North Shore Volcanic Group. Geological Society of America, Bulletin, 109, 683-697. Seifert, K. & Anderson, R.R. (1996) Geochemistry of buried Midcontintent Rift volcanic rocks in Iowa: Data from well samples. Jour. Iowa Acad. Sci. 103 (3-4), 63-7. 112 �CRUSTAL CRUSTALRECYCLING RECYCLINGIN INTHE THEEVOLUTION EVOLUTIONOF OFTHE THEPENOKEAN PENOKEANOROGEN: OROGEN:ISOTOPIC ISOTOPIC EVIDENCE EVIDENCEFOR FORARCHEAN ARCHEAN CONTRIBUTIONS CONTRIBUTIONS TO TO CRUSTAL CRUSTAL GROWTH GROWTH IN IN THE THE PEMBINE-WAUSAU TERRANE, TERRANE, NORTHERN NORTHERN WISCONSIN WISCONSIN PEMBINE-WAUSAU Schulz,Klaus KlausJ.J.and andAyuso, Ayuso,Robert RobertA., A.,U.S. U.S.Geological GeologicalSurvey, Survey,954 954National NationalCenter, Center,Reston, Reston, Schulz, VA20192 20 192(kschulz@usgs.gov) (kschulz@usgs.gov) VA Continental Continentalgrowth growthmodels modelsdepend dependon oninformation informationregarding regardingthe theage ageofofbasement basementininorogenic orogenic belts beltsand andon onestimates estimatesof ofthe theamount amountof ofcrustal crustalrecycling recycling involved involvedin in their theirevolution. evolution. The Thedistribution distribution and androle roleof ofArchean Archeanbasement basementininthe theEarly EarlyProterozoic ProterozoicPenokean Penokeanorogen orogenininthe theLake LakeSuperior Superiorregion region has haslong longbeen been aa topic topic of of debate debate and and speculation. speculation. Early Earlyworkers workersviewed viewed the the Early Early Proterozoic Proterozoic history history of theregion regionin interms termsof ofintracratonic intracratonicdeposition depositionand andreactivation reactivation of of Archean Archean crust crust of of the the Superior Superior the Province Province(e.g., (e.g.,Sims, Sims,1976). 1976).More Morerecently recentlythere therehas hasbeen beenaageneral generalconsensus consensusthat thatthe theEarly Early Proterozoic Proterozoicrocks rocksevolved evolvedthrough throughplate platetectonic tectonicprocesses processesincluding includingcontinental continentalrifling riftingand andsubduction, subduction, with wasaccreted accretedtotothe theArchean Archeancraton craton withformation formationofofsignificant significantvolumes volumesofofjuvenile juvenilecrust crustthat thatwas (Hoffman, (Hoffinan,1988; 1988;Sims Sirns and and others, others, 1989). 1989).However, However,isotopic isotopicstudies studieson onrocks rocksfrom fromthe theWisconsin Wisconsin maginatic magmaticterranes terraneshave haveagain againraised raisedquestions questionsabout aboutthe thedistribution distributionand androle roleofofArchean Archeancrust crustininthe the Penokean Penokeanorogen orogen (Barovich (Barovichand and others, others, 1989; 1989;Van Wyck and Johnson, 1997). 1997). In Inparticular, particular,Van VanWyck Wyck and and Johnson Johnson(1997) (1997)proposed proposedthat thatthe thePenokean Penokeanorogen orogenevolved evolvedthrough throughback-arc back-arcrifling riftingofofthe thesouthern southern Superior SuperiorProvince, Province,followed followedby bycollision collisionof ofaacontinental continentalarc arcterrane terrane(the (theMarshfield Marshfieldterrane) terrane)from fromthe the south. south. One Oneof ofthe theprimary primarylines linesof ofevidence evidenceused usedby byVan VanWyck Wyckand andJohnson Johnson(1997) (1997)totosupport supportaamodel model of of continental continentalback-arc back-arcrifling riftingfor forthe thePembine-Wausau Pembine-Wausauterrane terranewas wasan aninferred inferredcorrelation correlationbetween betweenthe the degree degree of of crustal crustal contamination contamination and and distance distance from the northern margin of the terrane, the Niagara fault zone, (i.e.,€Nd(T) eNd(T)values valuesbecome becomemore morepositive positive zone, in in which whichcontamination contaminationdecreased decreasedsouthward southward(i.e., southwards). southwards). To Totest testthis thismodel modelfor forthe thePembine-Wausau Pembine-Wausauterrane terraneand andfurther furtherrefme refineestimates estimatesfor forthe the involvementof of older oldercrust, crust,14 14volcanic volcanicrocks rocksand and14 14granitic graniticrocks rocksfrom fromacross acrossthe thePembine-Wausau Pembine-Wausau involvement terranein innorthern northernWisconsin Wisconsinwere wereanalyzed analyzedfor forNd Ndand/or andlorPb Pbisotopes. isotopes. These Thesesamples, samples,collected collectedfrom from terrane thethree three principal principal outcrop outcropareas areasin innorthern northern Wisconsin—the Wisconsin-the Dunbar-Pembine Dunbar-Pembine area area located located in in the northeastern northeasternWisconsin Wisconsinjust justsouth southofofthe theNiagara Niagarafault faultzone, zone,the theMonico Monicoarea arealocated locatedabout about45 45 km krn south south of ofthe theNiagara Niagarafault faultzone zoneininnorthcentral northcentralWisconsin, Wisconsin,and andthe theMarathon MarathonCounty Countyarea arealocated locatedatatthe the southern southernmargin marginof ofthe thePembine-Wausau Pembine-Wausauterrane terraneinincentral centralWisconsin—significantly Wisconsin-significantly expand expandthe the sampling sampling density density in in these thesethree threeareas areasand andfor forthe thefirst firsttime timeprovide provideisotope isotopedata datafor forseveral severalvolcanic volcanic units units within within the the Pembine-Wausau Pembine-Wausau terrane. terrane. Results Resultsare aresummarized summarizedininthe thetable tablebelow. below. The Theanalyzed analyzedmafic maficvolcanic volcanicrocks rocks from from the the Monico Monicoand and Marathon Marathon County County areas areasare are light light REEREEenriched from +1.3 +1.3 to to +3 +3 and and relatively relatively primitive primitive p values. These enrichedbut but have havepositive positiveENd(T) ENd(T)from TheseNd Ndisotope isotope data dataare are slightly slightlymore more enriched enriched than than the the Nd isotope isotope results of of Beck and and Murthy Murthy (1991) (199 1) for for the the +4.2 )from fromthe thePembine Pembinearea areaand andsuggest suggestderivation derivationfrom fromdepleted depletedEarly Early Quinnesecbasalts basalts(€Nd(T) (eNd(T) +4.2) Quinnesec Proterozoic (10%) addition contrasttoto Proterozoic mantle mantle with possibly a small (510%) additionofofolder oldercrustal crustalcomponents. components.InIncontrast the the mafic mafic volcanic volcanic rocks, rocks, the the felsic felsic volcanic volcanic rocks rocks from throughout throughout the Pembine-Wausau Pembine-Wausau terrane terrane have eNd(T) values ranging ranging from -0 —0toto-4 -4and andrelatively relativelyhigh highppvalues values >10 >10 suggesting suggesting variable but significant eNd(T) values significant input inputof of older, older, probably probablyArchean Archean crustal crustalcomponents. components. Surprisingly, Surprisingly,the thefelsic felsicvolcanic volcanicrocks rocksfrom fromthe the Monico Monico area area show show the the greatest greatest crustal crustalcontamination. contamination. The Thegranitic graniticrocks, rocks,like likethe thefelsic felsicvolcanic volcanicrocks, rocks, also alsohave havemostly mostlynegative negativeENd(T) eNd(T)values valuesbut butshow showaagreater greaterrange rangefrom from—0 -0 to to—7.4, -7.4, and relatively high high pp values values >10; >lo; younger youngergranites granitestend tendto tohave havethe themost mostnegative negative€Nd(T) e ~ d ( Tand ) highest p values values in in both both the the Dunbar-Pembine Dunbar-Pembine and and Marathon Marathon County County areas. areas. The Theisotope isotopedata datalie liealong alongmixing mixinglines linesbetween betweendepleted depleted Early Proterozoic mantle and Archean Superior Province crust; mixing models suggest from 20 Early Proterozoic mantle and Archean Superior crust; mixing models suggest from to to >70% >70%Archean Archeancrustal crustalcontamination contaminationfor forfelsic felsicvolcanic volcanicand andgranitic graniticrocks. rocks. - 113 I �I Areas Dunbar-Pembine (North) Dunbar-Pembine (North) • Pemene Pemene Rhyolite Rhyolite (2) (2) • Dunbar Dunbar Dome Dome (5) (5) • Bush Bush Lake Lake Granite Granite (1) (1) • Twelve Foot Falls Falls (1) Quartz Quartz Diorite Diorite Monico Monico Basalt (2) (2) • Basalt • Dacite/Rhyolite DaciteRhyolite (3) (3) • Quartz Quartz Porphyry Porphyry (1) (1) Marathon Marathon County County (South) (South) Basalt/Andesite (4) • BasaltIAndesite • DaciteIRhyolite Dacite/Rhyolite (3) (3) • Pre/Syn-Tectonic PrefSyn-TectonicGranite Granite (3) (3) Syn/Post-Tectonic Granite Granite (3) • SynPost-Tectonic TDM TDM(in Ga) Ga) ENd(T) e~d(T.1 - — M.35 +0.35 p (8U/204Pb) (*8~/20"~b) 12 --10.4 11.5 .7.4 -7.4 -3.2 2.3 2.3 2.2 to 2.9 2.9 2.8 +2.1 +2.1 -3.1 -3.1 •1 -4.7 2.1 —2.6 2.6 2.5 --9.811 9.4 +3 to +1.3 +1.3 to -2.0 2.0 -0.8 to 4.0 -1.0 42 -4.2 2.0 to 2.2 2.2 to 2.3 2.3 2.8 2.8 9.8 ---10.6 - 10.9 13.2 -0.9 to -4.2 - -- -- 12 10.4 11.5 - — 9.8 11 9.4 9.8 10.6 10.9 .-. 13.2 The new new data datapresented presented here here do donot notsupport supportaacorrelation correlationof ofincreasing increasing6Nd eNd with distance from Niagara fault zone. zone. The the Niagarafault The felsic felsic volcanic rocks from throughout the terrane show isotopic evidence greatest crustal crustal component component in in rhyolites rhyolites from fromthe theMonico Monicoarea. area. The for crustal contamination with the greatest granitic rocks from throughout the terrane also show isotopic evidence for significant significant crustal contamination. However, However, the the isotope isotope data datado do suggest suggest that that crustal contamination was greatest for syn- to post-tectonic granites emplaced near the northern and southern margins of the Pembine-Wausau terrane. post-tectonic isotope data data for for the Pembine-Wausau terrane suggest suggest that: (1) (1) input input of of Archean crustal crustal The new isotope greater and more widely distributed than previously components to Penokean crust crust formation was greater (2) there there isisno noclear clearcorrelation correlationbetween betweenENd EN^ and and distance from the northern (Niagara) recognized; (2) suture zone, although contamination appears to have been greatest for syn- to post-tectonic granites shown by the emplaced near the margins of the terrane; and (3) the high levels of crustal components shown felsic igneous rocks probably result from crustal assimilation and mixing and not from contamination contamination of a depleted mantle source by subduction of Archean derived sediments. References cited Barovich, KM. Cia KM.,Patchett, Patchett,P.J., P.J.,Peterman, Petennan,Z.E., Z.E.,and andSims, Sims,P.K., P.K.,1989, 1989,Nd Ndisotopes isotopesand andthe theorigin originof of1.9-1.7 1.9-1.7 Ga Penokean Penokean continental continental crust crustof of the the Lake Lake Superior Superiorregion: region: Geological GeologicalSociety Society of of America AmericaBulletin, Bulletin,v. v. 101, 101, p. 333-338. Beck, W. and and Murthy, V.R., V.R, 1991, 1991,Evidence Evidence for for continental continental crustal crustal assimilation assimilation in in the the Hemlock Hemlock Formation Formation flood flood basalts basalts of of the the Early Early Proterozoic ProterozoicPenokean Penokean Orogen, Orogen, Lake Lake Superior Superiorregion: region: U.S. U.S. Geological Geological Survey Survey Bulletin 25p. Bulletin 1904-I, 1904-1,25p. Hoffman, P.F., 1988, Hoffinan, 1988,United United plates plates of of America, America, the the birth birth of craton: craton: Early Proterozoic Proterozoic assembly assembly and and growth growthof of Laurentia: Laurentia:Annual AnnualReviews Reviews of of Earth Earth and and Planetary Planetary Sciences, Sciences, v. 16, 16,p. p. 543-603. 543-603. Sims, Sims, P.K., 1976, 1976, Precambrian Precambrian tectonics tectonics and and mineral deposits, deposits, Lake Lake Superior Superior region: Economic Economic Geology, Geology, v. 71, 71, p. 1092-1177. 1092-1177. P.K., Van Schrnus, W.R., Schulz, KJ., K.J., and Peterman, Petennan, Z.E., 1989, Sims, P.K., Schmus, W.R, 1989, Tectono-stratigraphic Tectono-stratigraphic evolution evolution of the Early Early Proterozoic ProterozoicWisconsin Wisconsin magmatic magmatic terranes terranes of the the Penokean Penokean Orogen: Orogen: Canadian CanadianJournal Journalof of Earth Earth Sciences, v. 26, p. 2145-2158. Van Wyck, N. and Johnson, Johnson, C.M., C.M., 1997, 1997, Common Common lead, lead, Sm-Nd, Sm-Nd, and and U-Pb constraints constraintson on petrogenesis, petrogenesis, crustal crustal architecture, architecture,and and tectonic tectonic setting setting of of the the Penokean Penokean orogeny orogeny (Paleoproterozoic) (Paleoproterozoic)in in Wisconsin: Wisconsin: Geological Geological Society of America Bulletin, Bulletin, v. 109, 109, p. 799-808. , 114 " - II I �I ND ISOTOPE EVIDENCE EVIDENCE FOR FOR MIDDLE MIDDLE AND AND EARLY EARLY ARCHEAN ARCHEAN CRUST CRUST IN THE WAWA SUBPROVINCE OF THE SUPERIOR PROVINCE, MICHIGAN, U.S.A. IN Sims, P.K., Neymark, L.A., L.A., and and Peterman, Petennan, Z.E., Z.E., U.S. U.S. Geological Geological Survey; Survey; Kotov, A.B., A.B., Institute Institute of Precambrian Precambrian Geology Geology and and Geochronology, Geochronology, St. St. Petersburg, Petersburg, Russia Russia Kotov, New Sm-Nd New Sm-Nd isotopic isotopic data on Late Late Archean Archean granitic granitic rocks rocks from from the theWawa Wawasubprovince subprovince(a(agranite-greenstone granite-greenstone terrane) indicate aa Middle to Early Archean crustal source for the rocks. rocks. terrane) of the Superior province, northern Michigan, Michigan, indicate Early Archean model ages between between 2.7 and 3.6 Ga At 2.7 Ga pNd values vary from -6.4 to +3.3, which correspond to depleted mantle mantle model Previous Nd-isotope Nd-isotope studies studies in in granite-greenstone terranes in in the the southern part of the (see table). Previous granite-greenstone terranes the Superior Superior province province indicated that that most most granitoid rocks are juvenile, juvenile, i.e. i.e. mantle derived, with little identifiable participation from older have indicated crust or recycled material. Samples were taken from the Puritan batholith (Fig. I), I), which which lies lies astride astride the Michigan Michigan -- Wisconsin Wisconsin border, batholith (Fig. border, and the northern complex of the Marquette district district (Fig. (Fig. 2); both igneous igneous bodies bodies have have crystallization crystallization ages agesof of—2.7 -2.7 Ga. Ga. Candidatesfor for the the source source of of the Middle Candidates Middle and Early Early Archean Archean rocks rocks in the the Michigan Michigan segment segment of the the Wawa Wawa subprovince have not been been identified, identified, but these rocks mainly constitute ancient ancient continental continental crust, crust, perhaps a proto-craton proto-craton block like that in the Sachigo and Minto subprovinces subprovinces (Percival (Percival and and other, other, 1994) 1994)to to the the north. north. Not unexpectedly, high-grade gneisses from the adjacent Minnesota River Valley subprovince, to to the south, which which contains the oldest rocks in the Superior province, have have comparable comparable old old Nd-depleted Nd-depleted mantle mantlemodel modelages ages(see (seetable), table), ranging from 2.9 to 3.3 Ga. d Table. Sm-Nd Sm-Ndisotope isotopedata datafor forgranites granitesfrom from Wawa WawaSubprovince Subprovinceand andfelsic gneisses and and granites granites from from Minnesota felsic gneisses Subprovince. River Valley Suburovince. '47Sm/ 143Ndt T(Ga) Nd Sample Sm d(t) d(O) TDM TDM '44Nd '44Nd (ppm) (ppm) Subprovince (Granite-Greenstone (Granite-Greenstone Terrane) Wawa Subprovince Terrane) 182B 183B 198 215B 0919-1-89 0919-3-89 0920-4-89 l36R M169 Ml70 177 179 D1044 D1731 D2493 D2494 D2495 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 8.88 19.7 5.70 2.76 4.06 8.08 3.56 0.79 1.60 2.98 40.9 98.2 32.2 17.0 30.2 57.7 17.9 3.11 11.5 17.4 2.53 13.8 1.01 4.67 4.10 16.7 2.08 10.5 1.26 6.48 5.06 33.6 5.60 33.6 0.0980 0.1214 0.1074 0.0982 0.0815 0.0925 0.1205 0.1545 0.0848 0.1041 0.1107 0.1315 0.1486 0.1200 0.1176 0.0913 0.1012 0.510695 (13) 0.511072 (5) 0.510842 (8) 0.510672 (13) 0.510594 (12) 0.510707 (6) 0.511397(10) 0.511781 (9) 0.5 10708 (10) 0.511040(10) 0.510912 (10) 0.511415(9) 0.511572(7) 0.511070(7) 0.511266(7) -3.7 -4.5 0.510928 (7) 0.510792(4) 3.3 -37.9 -30.5 -35.0 -38.4 -39.9 -37.7 -24.2 -16.7 -37.6 -31.2 -33.7 3202 3394 3276 3237 2922 3044 2840 3478 2863 2908 3277 -23.9 -20.8 -30.6 -26.8 -33.4 -36.0 3182 3646 3347 2959 2744 3163 3334 3123 3358 3347 2966 2758 3256 -39.8 -32.1 2971 3037 -31.4 -31.6 3192 3309 3072 3226 3325 3104 -6.4 -36.0 3358 3456 -2.3 -2.3 -31.8 3068 3127 -4.1 -4.2 0.1 -1.5 2.3 -2.1 1.2 1.0 -3.8 -1.2 -4.1 -4.0 0.7 -2.9 213 2.8 2.8 2.8 Subprovince (Gneiss Terrane) Terrane) Minnesota River Valley Valley Subprovince 44.9 0.0841 0.510600(8) 0.8 6.22 44.9 0.0841 0.5 10600 (8) 0.8 0.510993(11) 0.510993 (1 1 ) 2.35 12.8 0.1117 -1.5 12.8 0.11 17 2.35 0.1170 0.511027(10) 1 1027 (10) 0.5 38.2 -2.7 38.2 0.1 170 7.36 0.511018(8) 21.2 0.1089 0.0 0.1089 0.0 3.80 3.80 21.2 3-90 2.6 10.5 10.5 34-90 161-B 211 2.8 3319 3384 3352 3361 3012 3144 2839 3193 2924 2943 Tilden Granite Granite 59.2 0.510791 0.5 1079 1 (8) 0.1078 0.1078 Gwinn Granite 226-89 2.6 5.65 5.65 31.6 31.6 0.511006(10) 0.511006(10) 0.1082 0.1082 2 within-run **)) Data Data corrected to La La Jolla Jolla '43Nd/'44Nd=0.5 '"Nd/'"Nd=0.5 1 11860, 1860, 2,-r within-run errors errors are are given given inin parentheses. parentheses. 12ininthe the source source of of rocks before T Ga ** *) * ) Two-stage Two-stage Nd-model age age assuming assuming47Sm/'41Nd=0. '"Sm/'"Nd=O. 12 Ga ago. ago. 115 �________________________________ W" 89' 88O I 1 LAKE SUPERIOR 47% Figure 1. 1.Geologic Geologicmap mapofofPrecambrian Precambrianrocks rocksininnorthern northernMichigan Michiganand and adjacent adjacent Figure Wisconsin, showing showing localities Sm-Nd samples. Figure 2 is an enlargement of area outWisconsin, - localities of Sm-Nd samples. Figure 2 is an enlargement of area outlined lined south south of of Marquette. Marquette. n EXPLANA11ON EXPLANATION EXPLANATION —Contact Paleozoic Paleozoicrocks, rocks,undivided uncfwidd (1,600-900Ma) Ma) MIDDLEPROTEROZOIC PROTEROZOIC(1.600-900 MIDDLE ROCKS subprovinces '—Mylonde (ca. 1 ,I 00Ma) Ma) Rocksof ofmidcontinent midcontinentrift riftsystem system(ca. Rocks 1,100 Sm-Nd age locality . Wawa / Sub- Palmer EARLY (2,500—I .600 Ma) EARLYPROTEROZOIC PROTEROZOIC (2,500-1,600 Ma) province '.k)lcanic Volcanic.and andgranitoid granitoidrocks rocksofofWisconsin Wisconsin 1618 magmatic zone (—1.880—1,860 (-1.880-1.860Ma) Ma) magmatlc zone Sedimentary Sedimentaryand andvolcanic volcanicrocks rocksofofMarquette Marquette Range RangeSupergroup Supergroup •3.90 Puritanbatholith batholiih (-2,700 Ma) Puritan (—2,700 Ma) Granitoid Granitoidrocks rocksofofnorthern northerncomplex complexofof Marquette district (—2,700 Ma) Marquette district (-2,700 Ma) ' SAND COVER B 828 34-90 ' Minnesota A subprovince ARCHEAN ARCHEAN(2,500 (2,500Ma Maand andolder) older) ':2 PRO TEROZOIC . MinnesotaRivervalley Jacobsville JacobsvilleSandstone Sandstone n 1361 Approximate boundary between Wawa and Valley 21 21 '\\ 5 MILES 5 KILOMETERS Metavolcajijc Metavolcanicrocks rocks "3 7- 1 Gneiss (2,750—2,640 Ma) Gneissand andamphibolite amphiboliie (2.750-2.640 Ma) mat3icgneiss gneissofofMinnesota MinnesotaRiver RiverValley Valley Migmatitic prwlnce(3,550—2,800 (3,550-2,800 Ma) subprovince Ma) GLTZ, GLTZ, Ma, Ma, Mar, Mar, Me, Me, Great GreatLakes Lakestectonic tectoniczone zone Marquette, Marquette,Michigan Michigan Marenisco, Marenism,Michigan Michigan Mellen, Mellen,Wisconsin Wisconsin Sm—Nd Sm-Ndage agelocality locality Figure2.2.Geologic Geologicsketch sketchmap mapofofPrecambrian Precambrian Figure rocksininan anarea areasouth southof ofMarquette, Marquette,showing showing rocks localities of Sm-Nd samples. The Great hkes localities of Sm-Nd samples. The Great Lakes tectoniczone zoneseparates separatesgranite-greenstone granite-greenstonetertertectonic rane(Wawa (Wawasubprovince) subprovince)from fromgneiss gneissterrane terrane rane (MinnesotaRiver RiverValley Valley subprovince). subprovince). (Minnesota 116 I �I A THIN SHEET APPROACH TO A T H I N VISCOUS VISCOUS S HEET A PPROACH T O INVESTIGATE INVESTIGATE THE POST POST OF THE RIFT EVOLUTION O FT H E MIDCONTINENT M I D C O N T I N E N T RIFT RIFT SYSTEM SYSTEM UNDER UNDER THE INFLUENCE OF O F GRENVILLE GRENVILLE OROGENY OROGENY Soofi, M. A., A., and and King, King, S. S.D., D., Department Department of of Earth Earth and Atmospheric Sciences, Purdue Purdue Soofi, M. West Lafayette, Indiana University, West Indiana 47907 47907 The cause of the termination termination of of rifting rifting along along the the Midcontinent Midcontinent Rift Rift system system(MCR) (MCR) and the the presence presence of reverse faults along along the rift margins margins are are still still troublesome troublesome for the the investigators of the MCR. Suggestions for the cause of rifting investigators of Suggestions for rifting range range from fiom aapassive passive mechanism, where where processes processesatat plate plate boundaries responsible (e.g. (e.g. Hinze Hinze et al., mechanism, boundaries were were responsible al., 1982), to to an active mechanism, where where aa mantle mantle plume plume ascended ascended and and initiated initiated rifting (e.g. 19821, (e.g. the formation of reverse reverse faults faults has been suggested Cannon and Hinze, 1992). Similarly, the to be under the loading due to rift be aaconsequence consequence of plate flexure under rift related related rocks rocks (e.g. (e.g. stresses from from the the plate boundaries, which Nyquist, 1986), 19861, or an effect effect of compressive compressive stresses which thrusting along the original rift bounding not only terminated the the rifting but also also caused thrusting normal faults (e.g. (eg. Cannon, Cannon, 1994). 1994). study focuses on the evolution of of the the MCR under the the influence of plate plate boundThis study influence of forces from from the the Grenville Orogeny. We are ary forces, forces, particularly particularly the compressive compressive forces Grenville Orogeny. using the thin using thin viscous viscous sheet sheet model model (TVS) (TVS) of of England England and and McKenzie McKenzie (1983) (1983) which which is implemented in in aa finite element element code code by by Houseman Houseman and and England England (1986). (1986). This model implemented model has been used in the the study studyof of India-Asia India-Asia collision collision (England and Houseman, Houseman, 1986) 1986) and (Sobouti and and Arkani-Hamed, 1996), where where it has successArabia-Eurasia convergence convergence (Sobouti successfully reproduced reproduced the topography and deformation in the overriding Eurasian Eurasian deformation observed observed in plate. The Themodel modeluses usesincompressible, incompressible,vertically vertically averaged, averaged,power-law power-law rheology rheology for the the lithosphere. lithosphere. For a given geometry,boundary boundary conditions, conditions,stress-strain stress-strainexponent exponent(n) (n) and and Argand For given geometry, Number (Ar) (Ar) values, stresses, strain rates and Number values, the the model model calculates calculates crustal thickness, stresses, and rotation. rotation. These These can can then thenbe becorrelated correlatedwith withtopography topography and and deformation deformation in in the theover over riding plate. A assumed such such that that there is no discontinuity in the A continuous continuous medium is assumed velocity field. Fault Fault planes cannot be defined defined explicitly explicitlybut, but, information information on on the the type of of velocity field. faulting can be inferred from from the the stress and strain rate rate distribution. distribution. results indicate indicate that even (i.e. n=10) Our results even in the case case of aa very very weak weak lithosphere lithosphere (i.e. n=lO) stresses from the the Grenille GrenilleEont Front (GF) (GF) can can be be transmitted transmitted inland inland to interact with stresses from with the the processes that that were were occuring occuringalong along the the MCR. MCR. Also, Also, depending dependingon on the thesize sizeof of the the colliding colliding microcontinents (i.e. indenters) indenters) and and their their position position along alongthe the GF GF itit is is possible possiblethat that the microcontinents (i.e. MCR was subjected to different magnitude of of stresses stresses along along its its length length and itit evolved was subjected difFerent magnitude evolved through the the superposition superposition of of these stresses. The Thevarying varying degree degree of thrust thrust faulting faulting obobserved along along the the MCR could style. The models could be a manifestation manifestation of such a collision collision style. models also predict significant of crust crust next to the significant thickening of the indenter, indenter,the thethickening thickeningdecreases decreases away from the collision boundary. For For a comparatively rigid lithosphere lithosphere (n=l,Ar=l) (n=1,Ar=1) away fiom collision boundary. comparatively rigid crustal thickening is as much much as as 2 km where for a weak lithosphere (n=lO,Ar=l) (n=10,Ar=1) thickening is where as for weak lithosphere crustal thickening is as much as 19 km. Assuming kg/m3 and Assuming crustal density density of 2700 2700 kg/m3 mantle density density of of 3300 3300 kg/m3 kg/rn3 and and assuming assumingthe the surface surfaceof ofthe the 35 35 km km thick thick crust to mantle to be at at the thesea sealevel level the thechange changein in crustal crustalelevation elevation is is 0.36 0.36 km for for rigid lithosphere and 3.4 km km for for the relatively weak lithosphere. lithosphere. The high elevations elevations predicted predicted by by the the TVS 3.4 relatively weak for the the Tican initiate local local extension, as suggested by England and McKenzie McKenzie (1982) (1982) for betan betan plateau. plateau. Such Suchaamechanism mechanismmay may had hadbeen beenresponsible responsiblefor for the the late latestage stageextension extension reported for the the Grenville Grenville Orogeny (e.g. (e.g. Easton, Easton, 1992). 1992). 117 �We are also studying along the the GF studying the the effect effect of of oblique oblique convergence convergence along GJ? on on the theevoluevolution of the the MCR. MCR. For For fixed fixed boundary boundary conditions conditions and and rheology, rheology, the length length scale scale of of dede formation decreases with increasing obliquity. As discussed for the normal convergence, formation decreases increasing As discussed the normal convergence, microcontinents convergingobliquely obliquelyalong alongthe the GF GF can produce stresses microcontinents of various sizes converging magnitudes along the the MCR. Oblique convergence convergenceproduces producessame samepattern pattern of of of different magnitudes crustal thickening as observed for normal convergence except that it is not symmetric. observed for normal convergence except that it One between oblique oblique and and normal convergence is the the significant area area One significant significant difference between of (indenter). This thinning repof crustal thinning next to to the the colliding colliding microcontinent microcontinent (indenter). resent extension in the over over riding plate. For For normal normal convergence convergence the thinning is is very very localised and produced produced in a very localised and very small small area area that thatdoes doesnot notchanges changessignificantly significantly with with rheology. this area of rheology. For oblique convergence this of extension extension increases increases for for weaker weaker rheology (increasing nn value). We together with a weak We hypothesize hypothesize that that oblique oblique convergence, convergence, together weak lithosphere (due subduction), may had helped, (due to thermal thermal anomaly anomaly resulting resulting from fiom subduction), helped, if if not initiated, the the rifting rifting process. process. REFERENCES CITED CITED of Grenvillian Cannon, Cannon, W. F., F., 1994, 1994,Closing Closing of the Midcontinent Midcontinent rift rift -- A A far-field effect of compression: Geology, Geology, v. 22, 22, p. p. 155-158. 155-158. on the the origin of of the the North AmerCannon, W. F., and Hinze, Hinze, W. J., 1992, 1992, Speculations on ican Midcontinent rift, in Ziegler, P. A., ed., Geodynaniics of rifting, an Ziegler, P. A., ed., Geodynamics of rifting, Volume Volume 2. 2. Case History History Studies Studies on on Rifts: Rifts: North and and South South America America and and Africa: Africa: TectonoTectonophysics, v. 213, 213, p. 49-55. 49-55. Easton, R. R. M., M., 1992, 1992, The The Grenville Grenville Province and the the Proterozoic Proterozoic history history of of Central Central and Southern Ontario, in an Thurston, Thurston, P. P. C., C., Williams, Williams, H. R., Sutcliffe, Sutcliffe, R. H., H., and Stott, Stott,G. G.M., M.,eds., eds.,Geology Geologyof of Ontario, Ontario,Ontario OntarioGeological GeologicalSurvey, Survey,Special SpecialVolume Volume 4, Part 2, p. 715-904. Part 2, p. 715-904. England, P., and and Houseman, Houseman, G., G., 1986, 1986, Finite strain straincalculations calculationsof of continental continental defordeformation 2. 2. Comparison Comparisonwith with the theIndia-Asia India-Asiacollision collision zone: zone: Journal Journalof ofGeophysical Geophysical Research, v. 91, p.3664-3676. 3664-3676. 91, p. England, P., and and McKenzie, McKenzie, D., D., 1983, 1983, Correction to,: to: A thin thin viscous viscous sheet sheet model model for for continental continental deformation: deformation: Geophysical Geophysical Journal Journalof ofthe theRoyal RoyalAstromomical AstromomicalSociety, Society, v. 73, 73, p. p. 523-532. 523-532. Hinze, W. J., Wold, R. J., J., and and O'Hara, O'Hara, N. N. W., W., 1982, 1982,Gravity Gravity and and magnetic magnetic anomaly anomaly Hinze, W. studies of of Lake Lake Superior, Superior, an in Wold, Wold, R. R. J., J., and and Hinze, Hinze, W. J., J., eds., eds., Geology Geology and and tectonics of the Lake Superior basin: Geological Society of America Memoir 156, the Lake Superior basin: Geological Society of America Memoir 156, 203-222. p. 203-222. Houseman, G., and and England, England, P., 1986, 1986, Finite strain strain calculations calculations of continental deformation 1. Method and general results for convergent 1. Method and general results for convergent zones: zones: Journal Journalof of Geophysical Geophysical Research, v. v. 91, 91,p.p.3651-3663. 3651-3663. of the the Mid-Continent Mid-Continent rift rift [Ph.D. Nyquist, J. E., 1986, 1986, Thermal and mechanical models of thesis]: University Universityof of Wisconsin-Madison, Wisconsin-Madison,193p. 193p. Sobouti, F., and of the the deformation of of and Arkani-Hamed, Arkani-Hamed, J., 1996, 1996, Numerical Numerical modelling of the Iranian plateau: plateau: Geophysical Geophysical Journal Journal International, International, v. v. 126, 126,p. p.805-818. 805-818. 118 I �U PALEOMAGNETIC STUDIES OF AA PROTEROZOIC PORPHYRITIC PORPHYRITIC DIABASE DIABASE DIKE, PIFHER AND IRWIN DIKEf IRWIN TOWNSHIPS, TOWNSHIPS LAKE LAKE NIPIGON NIPIGON DISTRICT, DISTRICT ONTARIO ONTARIO T h ~ m a s *C., C~S fKean, Keanf W., Department Department of of Geosciences, Geosciencesf Thomas*, University of Wisconsin-Milwaukeef 53201 Wisconsin—Milwaukee, Milwaukeef Milwaukee, WI 53201 and Luther, Lutherf F., F e fGeology Geology Department, Departmentf UW—Whitewater, UW-Whitewaterf Whitewater, student author) Whitewaterf WI WI 53190 53190 (* ( * student author) This approximately This approximately 50 50 m m wide wide porphyritic porphyritic diabase diabase dike, dikef outcropping outcropping in western Irwin Irwin and Pifher Pifher Townships Townships in in the the Nipigon district, districtf is is locally locally known known as as greenspar. The The dike dike has has a characteristic characteristic greenish greenish mottled appearance appearance in in outcrop outcrop as as aa result of saussaritized saussaritized plagioclase glomerophenocrysts glomerophenocrysts in in aa diabase (Luther,1997). The The dike dike strikes strikes due due north north diabase groundinass groundmass (Lutherf1997). and dips verticallyf vertically, and is off-set by by is found found as as segments, segmentsf off—set east—west east-west faulting(Mackasey,1975). faulting(Mackasey,l975). There There are are no no radiometric radiometric dates on on this this rock rock or or associated associated rocks, rocks, although, althoughf it it is is cut cut by by middle or late Proterozoic sill a large middle sill in Irwin Irwin Township 1975).. Township(Mackasey, (Mackaseyf1975) Paleomagnetic studies were completed on 2—3 2-3 cores cores from from each of 5 locations. Each location represents represents one one dike dike segment. Samples Samples from each location location were subjected subjected to to both alternating field alternating field (A.F.) (A.F.) and and thermal thermal demagnetization demagnetization studies. studies. The is The samples samples show show one one primary primary magnetic magnetic direction direction which which is removed at demagnetization demagnetization temperatures temperatures of of 5700 570 C. or or by by A.F. fields of 60 mT. All but one location normal polarity fields 60 mT. location shows shows normal with inclinations of with northwesterly northwesterly declinations(200°-300°) declinations(200~-300') and inclinations of 40°-80°. The northern northern most most section section of of the the dike dike which which we we sampled 40'-80° The is reversally reversally magnetized magnetized with with declinations declinations of of about about 90°—100° 90'-100~ and inclinations inclinations of of —75°. -75'- These magnetic directions directions are are consistent with Keweenawan age age paleomagnetic directions directions in in the the Lake Superior Superior Region. Region. References References Luther, Proterozoic Lutherf F.,1997, F.f1997f The The Petrology Petrology of of Greenspar: Greenspar: A Proterozoic Porphyritic Porphyritic Diabase Diabase Dike; Dike; Pifher Pifher and Irwin Irwin Townships, Townshipsf Lake Lake Nipigon District, Districtf Ontario. Institute Institute on on Lake Lake Superior Superior Geology Geology Vol.43. abstracts abstracts and and proceedings proceedings Vo1.43. , Mackasey, Mackaseyf W.O.,1975, W.0.f1975f Geology Geology of of Dorothea, Dorothear Sandra, Sandra, and and Irwin Irwin Townships, Townshipsf District District of of Thunder Thunder Bay; Bay; Ontario Ontario division division of of Mines, Minesf 83 p. p. rpt 122 122 with with map map 2294, 2294# 83 119 �., GRAVITY, MAGNETIC, AND STRUCTURAL STUDY OF TJ3E THE WAKEMUP WAKEMUP BAY A GMVITY, TONALITE, MINNESOTA TIKOFF, Basil, Department of Geology and Geophysics, Rice University, Houston, TX 77005-1892, 770051892, USA, BAUER, Robert Department of Geological Sciences, University of Missouri, Columbia, Columbia, MO, 65211, 652 11, USA, VIGNERESSE, VIGNERESSE, Jean-Louis Jean-Louis Vigneresse, Vigneresse, CREGU, 54501 54501 Vandoeuvre, Vandoeuvre, Nancy Cedex, France, and HAGGEMAN, HAGGEMAN, Nick, Nick, of Mimesota, Minnesota, Minneapolis, Minneapolis, MN MN Department of Geology and Geophysics, University of 55455, USA Wakemup Bay The wakemuP Bay tonalite tonalite is is aa small small intrusive intrusive body that intrudes intrudes amphibolite-grade amphibolite-gradebiotite biotite schist on the extreme extreme southern southern edge of the Quetico sub-province sub-province in the western part of Lake Lake Minnesota. The tonalite is part of of the the Wakemup Wakemup Bay Bay block, block, which which is is bounded bounded by by Vermilion in Minnesota. the Vermilion fault to the north and the Haley fault to the south. The Haley fault has a dip-slip component that separates separates amphibolite-grade amphibolite-grade rocks of the Quetico sub-province to the north greenschist-grade rocks of the Wawa sub-province to to the the south. south. The The primary primary purpose purpose of of from greenschist-grade our investigation was to evaluate the mechanism of emplacement of the Wakemup Bay pluton and its relationship to local doming by determining its 3D shape and internal magnetic fabric. conducted aa gravity gravity survey survey over over the the pluton, and use the gravity gnvity inversion inversion to to evaluate evaluatethe the We conducted pluton shape. shape. We Wecollected collectedanisotropy anisotropyof of magnetic magnetic susceptibility susceptibility(AMS) (AMS) data data to to evaluate eval~latethe the magnetic fabric mdgnetic fabric of the pluton. pluton. Bauer Bauer (1985, (1985, 1986) 1986)reports reports previous previous structural structural analysis analysis and mapping mapping of the the Wakemup Wakemup Bay pluton. The pluton comprises a medium-grained biotite tonalite, with sphene, apatite, magnetite, appearance, magnetite, and and zircon zircon as as accessory accessory minerals. minerals. The tonalite typically has a layered appearance, indicate solidand the microstructures throughout throughout the pluton, particularly at the pluton margin, indicate soliddeformation. Foliation dips outward (20-60°) (20-60') from the middle of the pluton, in a state deformation. plagioclase, quartz, and biotite concentric concentric pattern. pattern. Biotite Biotite schist schist -- consisting dominantly of p1agioclase7 surrounds the tonalite tonalite on on all all sides, sides, and and has has foliation foliation that that also also dips dips away away from from the the center centerof of the the pluton on all sides. On On aa more more regional scale, the foliations of the schist defines a doubly plunging, EW-trending anticline with moderately moderately dipping dipping limbs. limbs. The tonalite is spatially B auer(1985, (1985, 1986) 1986)interpreted interpreted as as an an F3 F3 fold fold associated with the hinge area of this fold, which Bauer in the local deformation biotite schist deformation sequence. A hornblende hornblende diorite unit that intruded the biotite The center of of the pluton pluton is is capped by by outcrops on both the north and south sides of the tonalite. The abovethe thetonalite tonalitecontact. contact.The The roof roof consists consists of both the wallrock that that extends extends—40 -40 mmabove a roof of walirock biotite schist schist and and aa relatively relatively flat-lying flat-lyinglayer layer of of the the hornblende hornblende diorite. diorite. The Anisotropy Anisotropy of Magnetic Susceptibility Susceptibility (AMS) is a technique that is widely used in the study = K x H, where M is defmed by M = study of granitic granitic fabrics. fabrics. The The magnetic magnetic susceptibility is defined the induced magnetization and H is the inducing magnetic field. The variation induced magnetization and H is the inducing magnetic field. The variationof of this thismagnetic magnetic susceptibility with the sample placed in different orientations produces an AMS ellipsoid, sample ellipsoid, kmin, which similar to the finite strain ellipsoid. The principle AMS axes are kmax > > kint > > kmin7 plane) or magnetic lineation kint lineation may be interpreted interpreted in terms terms of a magnetic foliation (kmax (kmax orientation). orientation). The bulk susceptibility values varied widely widely in in the the Wakemup Wakemup Bay tonalite 10-1 SI), SI), interpreted as representing the presence or absence of magnetite. The (5 x 10-4 to 10-1 AMS foliation essentially essentially parallels parallels the measured field foliation. foliation. The The major major insight insight from from the the AMS study comes comes from from the orientation orientation of the magnetic lineation. Throughout the Wakemup Bay tonalite, tonalite, the the magnetic magneticlineation lineationisis oriented oriented dominantly dominantly EW, EW, plunges plunges shallowly, shallowly,and andisis generally parallel to the long long direction direction of the Wakemup Bay pluton and parallel to the trace trace of the F3 fold hinge. This This observation observation has has significance significance with respect respect to to emplacement emplacementmechanism. mechanism. We selected gravity study study because: because: 1) 1)ItIt had had selectedthe the Wakemup Wakemuptonalite tonalite for for our our detailed detailed gravity with aa previous structural structural mapping mapping (Bauer, (Bauer, 1985); 1985); 2) It has a single surrounding surrounding lithology lithology with significant and consistent ± 0.04 for the tonalite and 2.75 k ± 0.04 for the consistent density density contrast contrast (2.67 k surrounding 3) A A walirock wallrock roof exists over the center of the pluton, despite despite the surrounding schists); schists); and and 3) (<40 40 m). m). Thus, Thus, the depth recorded by the gravity inversion relatively low relief of the area (< represents represents the the true true depth depth of of the the pluton, within the limitations limitations of the gravity inversion inversion technique technique (e.g., method of Vigneresse, Vigneresse, 1995). 1995). To achieve resolution obtained in structural measurements, Wakemup pluton and immediate measurements,142 142gravity gravity stations stations were collected collected on the Wakemup immediate 120 I ' �I surroundings surroundingsusing using aa Lacoste Lacoste & & Romberg, Romberg, model model G G gravitimeter. gravitimeter. Laser theodolite theodolite from from benchmarks and the controlled-elevation shoreline Of Lake Lake Vermilion provided the existing benchmarks Bouguer anomalies is is provided provided (Fig. (Fig. la). Using a critical elevation controls. A map of the Bouguer gravimetric three-dimensional gravirnetric three-dimensional iterative technique, resulted in a good first-order picture of the (Fig. ib). lb).Most Mostofofthe thepluton plutonisisvery verythin, thin,less lessthan than0.5 0.5 km km thick. thick. There There are aretwo two root root pluton (Fig. zones, both of which which indicate depths of up to 4.0 km, using the calculated densities. The depth krn anomaly in the southwest southwest part of the pluton has a linear, NW trend and is approximately 5 km thus adjacent to the the Haley Haley fault. fault. The The long. It lies adjacent to the SW part of the pluton and is thus contains aa NW depth anomaly anomalyin in the thecenter centerof ofthe thepluton plutonisisslightly slightlyless lessdeep deep(—3 (-3 km). It also contains NW NW-SE oriented trend. trend, although the depth depth is clearly at a maximum in the SE part of the NW-SE interesting to note that the deepest portion of the tonalite does not sit under the present It is interesting exposure of the pluton. As a result of the structural geology, magnetic analysis, and gravity measurements, the Wakemup Bay pluton is interpreted as intruding a broad anticlinal hinge, hinge, during during the the folding folding Wakemup event (F3). This was one of the possibilities suggested by Bauer (1986) and consistent with the very thin nature of of the the pluton pluton (<0.5 ( ~ 0 . km). 5km).The The walirock wallrock preservation preservation in in the the roof represents representsthe the anticlinal anticlinal hinge. hinge. The The hornblende diorite unit on the north side, south side, and above the pluton is a good indication indication of of this this situation. situation. The The two NW-root zones zones were presumably presumably were were feeder feeder zones for the magma, magma, although although given the very high exposure level this claim is impossible to support by geological may have have initiated initiated on on NW NW geological or or magnetic measurements. The feeder zones may oriented fractures. oriented fractures. This This type type of of cross-faulting cross-faulting is commonly commonly seen seen in in folds, folds, particularly particularly those those with a component component of of hinge-parallel hinge-parallel extension. extension. The The large large southern southern root root zone zone may may have have affected affected the subsequent subsequent movement movement of the Wakemup Wakemup block, between the Haley and Vermilion faults. occurs just south of the deep southern root zone, and the root of the the The Haley fault occurs tonalite may have fault shows tonalite have acted acted as as a strong strong heterogeneity in the schist. The Haley fault indications of some inferredto some dextral dextral strike-slip faulting, which is inferred to have have occurred occurred after afterits its earlier normal normal movement movement (e.g., (e.g., Bauer, 1986). 1986). This type of small rigid block moving between major fault fault systems systems is is inferred inferred in other other orogenic orogenic belts. REFERENCES REFERENCES Minnesota. Minnesota Bauer, R.L., 1985, 1985, Norwegian Bay Quadrangle, Quadrangle, St. Louis county, Minnesota. Minnesota Geological Geological Survey, Survey, Miscellaneous Map Series, Map MapM-59, M-59, 1:24,000. 1:24,000. Bauer, R.L., 1986, 1986,Multiple Multiple folding folding and pluton emplacement emplacement in Archean migmatites rnigmatites of the the southern complex,- northeastern northeasternMinnesota. Minnesota. Canadian Journal of Earth Earth southern Vermilion granitic eranitic com~lex, Sciences, v. 23, 23, p. p. 1753-1764. 1753-1764. I I I I I I I I I I I I 5314.00 5312.00 5310.00 5308.00 5306.0 5304.00 5302.00 5300.00-' I I b ! t I I 53002.00 522.00 524.00 524.00 526.00 526.00 528.00 528.00 530.00 530.00 532.00 532.00 534.00 534.00 536.00 536.00 538.00 538.00 540.00 540.00 542.00 542.00 I 544.00 544.00 Fig. Fig. 1. Gravity Gravityinversion inversion model model for for Wakemup Wakemup Bay tonalite. Heavy Heavy dashed dashed line line represents represents current outcropping outcropping of the pluton. Light Lightlines linesare are inferred inferred depth depth of of the pluton, pluton, contoured contoured for for km. The 0.5 km. Thetonalite tonaliteisisgenerally generallyaathin thinsheet sheet(<0.5 ( ~ 0 . km), 5km), with with two two deep deep root root zones. zones. 121 �THE RELEVANCE OF THE GEOLOGY AND OPHIOLITES TO GEOLOGY OF OF MID-OCEAN MID-OCEAN RIDGES AND UNDERSTANDING OF MIDCONTINENT RIFT: RIFT: THE UNDERSTANDING OF LAYERED LAYERED INTRUSIONS INTRUSIONS IN IN THE MIDCONTINENT AND PETROLOGY PETROLOGY PART I. GEOMETRY; GEOMETRY; PART PART II. 11. INTERNAL STRUCTURE STRUCTURE AND Tatiana TatianaVislova, Vislova,Department DepartmentofofGeology Geologyand andGeophysics, Geophysics,University Universityof of Minnesota, Minnesota, USA USA Part Insightsfrom fromcurrent current research research on on mid-ocean mid-ocean ridges and ophiolites remain to be applied Part I.I.Insights to studies studies of ofintracontinental intracontinental rift rift systems. systems. Dynamic Dynamic magma magma chambers chambers where where fractional fractional crystallization and and formation formation of of layered with spreading are crystallization layered cumulates occur simultaneously simultaneously with being ocean island island and and mid-ocean mid-ocean ridge ridge systems. systems. But But layered layered being defined defined by by seismic data for ocean intrusions in in continental continentalcrust crustare are still still generally generallystudied studiedfrom fromthe the point point of of view view of fixed intrusions fixed geometry. conclusion that the Duluth Duluth Complex Complex and and associated associated geometry. However, However, ifif we we accept the conclusion intrusions such as the Sonju Lake and the Bald Eagle intrusions formed in an an intracontinental intracontinental rift system, the concept concept of of dynamic dynamic magma magma chambers chambers during during crystallization crystallization of of layered layered gabbro gabbro must be considered. considered. There is a growing database on the geometry geometry and dynamic dynamic processes processes of of crystallization crystallization and the formation of layered gabbro based based on seismic studies along along the the fast spreading (>-lo (>-10 cm/yr.) cmlyr.) East Pacific Rise (Sinton, 1992; 1992; Wang, 1996; 1996; Barth, Barth, 1996) 1996) and and the theslow-spreading slow-spreading (<-5 crnlyr.)Mohns Mohns Ridge Ridge (Geli, (Geli, 1994) 1994)and and Mid-Atlantic Mid-Atlantic Ridge Ridge (Rommevaux, (Rommevaux, 1994). 1994).These These (<-5 cm/yr.) studies demonstrate studies demonstrate that active active magma magma chambers: chambers: 1) are are segmented segmented and and centered centered under under and active vents along the ridge axes (McKenzie, 1997 topographic highs and 1997 and and Wright, Wright, 1995), 1995), 2) pinch and swell 15 km (Geli, swell in in plan plan view view with withtypical typicalwidths widthsand andalong-axis along-axislengths lengthsofof5 5—- 15 2.5 km below the seafloor. These features are best 1994), and 3) are are found found at atdepths depthsofof1.5 1.5— - 2.5 developed along slow spreading rifts such as the Mohns Ridge (Geli, 1994). 1994). Because ophiolites are fragments of oceanic crust, they provide an opportunity opportunity to to study study the processes that occur along along ridge axes. axes. Recent Recent detailed detailed mapping mapping and interpretation interpretation of of the the Oman generally confirm confirm the the segmental segmental structure structure of of ridge ridge magma Oman ophiolite ophiolite generally magma chambers chambers as described above above (Nicolas, (Nicolas, 1996 1996and and references referencestherein). therein). The geophysical expressions expressions of present-day oceanic oceanic ridges and the 1.1 1.1 Ga Ga Midcontinent Midcontinent bulls-eye structure on on a scale of 100-1000 Rift in North America America show the same same segmented segmented bulls-eye 100-1000 km. On aa scale scaleof ofI 1—- 100 100 km, the geophysical geophysical data on active active magma magma chambers chambers along along ridge ridge axes and the first first derivative derivative of the the aeromagnetic aeromagnetic data on the the Bald Bald Eagle Eagle Intrusion Intrusion have have aa pinch and and swell geometry. geometry. These These similarities similarities on on large large and and small small scales scales imply imply that that our similar pinch current understanding of the processes processes responsible responsible for for the the structure and and petrologic petrologic features features of of understanding of ridge magma chambers and and layered layered gabbro in ophiolites ophiolites can can be be used to explain the origin of similar features features in in layered rifts. The geometries similar layered intrusions intrusions in intracontinental intracontinental rifts. geometries of intrusions intrusions formed in dynamic or static magma chambers are related to spreading rates and continuity of static With fast, fast, continuous continuous spreading spreadingrates ratesititisis possible possibleto to produce produce layered layered gabbro gabbro at at aa spreading. With lateral scale of many kilometers from a relatively narrow, growing magma chamber which is never more than 1-2 km wide at any p.17,842). On the other any given time (e.g., Nicolas, Nicolas, 1996, p.17,842). hand, rates the the lateral lateral extent extent of layered hand, with with slow, slow, episodic episodic spreading spreading rates layered gabbro gabbro could could be restricted to the dimensions dimensions of the active active magma magma chambers. chambers. Thus Thus the the Sonju Sonju Lake Lakeintrusion, intrusion, with its sill-like could have have formed sill-like geometry geometry (Miller, (Miller, 1996), 1996), could formed in a static static magma magma chamber; chamber; whereas the Bald Eagle intrusion, with its funnel shape, could have formed in a more dynamic dynamic environment. environment. Part II. Part It.The Thefunnel-shaped funnel-shaped layering layering in in the theBald BaldEagle Eagleintrusion intrusioncontrasts contrastsremarkably remarkably with near-horizontallayering layeringofofthe the other other intrusions intrusionsinin the the Duluth Duluth Complex Complex and and in the near-horizontal the Oman Oman ophiolite. Unfortunately the current interpretations of the layering in ophiolites do not provide Unfortunately the current interpretations layering do provide 122 �readyexplanation explanation for for the the layering layering in in the the Bald Bald Eagle Eagle intrusion. intrusion. There aaready Thereisisananactive activedebate debateinin the literature literature concerning concerning the the processes processes that would would lead lead from from the the isotropic isotropic crystal crystal mushes mushes of the of active active ocean-ridge ocean-ridge magma magma chambers chambers to the the near-horizontal near-horizontal layering layering in gabbro gabbro of ofthe theocean ocean floorand andininophiolites ophiolites(Quick, (Quick,1993, 1993,and and Nicolas, Nicolas, 1996). 1996).In Inessence essenceQuick's Quick'sanalysis analysisimplies implies floor that the thelayering layeringand andthe theigneous igneouslamination laminationare arepost-crystallization post-crystallizationphenomena, phenomena,produced produced that whencrystal crystalmush mush isiscarried carried away away from from the the active activemagma magma chamber. chamber. IfIfthis thisidea ideaisisapplicable applicableto to when theDuluth Duluth Complex, Complex, the the Bald Bald Eagle Eagle intrusion intrusion could be aa frozen frozen active active chamber chamber thus thus far far not not the observed in in ophiolites. ophiolites. Layered Layered gabbro gabbro of ofadjacent adjacentSouth SouthKawishiwi Kawishiwiintrusion intrusioncould couldbe bethe the observed equivalent equivalentof oflayered layeredgabbro gabbroininophiolite ophioliteproduced producedduring duringspreading spreadingaway awayfrom fromaaridge ridgeaxis. axis. One One might might expect expect that thatthe thecryptic, cryptic,compositional compositionalvariations variations ofofcumulus cumulusminerals minerals formed formedininstatic staticchambers chambersmight mightdiffer differfrom fromthose thoseformed formedinindynamic dynamicchambers. chambers.AAsuggestion suggestion of ofsuch suchdifferences differencescan can be be seen seenin inFigure Figure1.1.All Allthree threedata datasets setslie lieon onaacommon commontrend. trend.Gabbro Gabbro inthe theOman Omanophiolite ophiolite and and rocks rocks in inthe theBald BaldEagle Eagleintrusion intrusion show show more more restricted restricted ranges ranges of of in differentiation than rocks in the Sonju Lake intrusion, and the Oman magma is the most differentiation than rocks Sonju intrusion, Oman magma is the most primitive. primitive. Additional Additional electron electronmicroprobe microprobe mineral mineral and and minorminor- and and tracetrace-element elementrock rockanalyses analyses ofthe theBald Bald Eagle Eagleintrusion intrusionare areplanned planned to toevaluate evaluatethe thesuggestion suggestionthat thatthe thechemical chemicalvariations variations of produced produced in in dynamic dynamic chambers chambers are are 100 100 definitively definitively distinct distinct from from those those L-..-.-.---L-.-..-----^---.....--i^<---.. . 90 jp. established establishedfor forstatic staticchambers. chambers.  + .ac ::80 ^n- ; - 1..-.....---- ---.--.....L--~-.~.---L-..-......L-------.-.~---------- -3 1 70 70 = 0, 0 5 " 3 - - - - -1 ; ; ; + +--+wt*^.+ Hi"++--?--.: ---------- ; L . -------..... - ------- -. Fig. Fig. 1.1.Mg/(Mg+Fe) Mgl(Mg+Fe) variation variationin inpyroxene pyroxeneand and olivine. All the data are electron microprobe olivine. All the data are electron microprobe ..--.-------------___t+ 50 analyses. analyses. Sonju SonjuLake Lakeintrusion intrusion(Miller, (Miller,1996); 1996); + Sonju Lakelnbusion Lake intrusion d.+f? - - - - - - - - - [ - - - - - - - - +SOOjU 40 --..-.40 points are averages Bald Eagle intrusion data Bald Eagle intrusion data points are averages ++ OBaldEagle Eaglelnfrusion Intrusion OBald So --------.---: ---------.; ----xman . - -ophiolite gabbro SIIISof ofover over200 200analyses analysesof ofrepresentative representativesamples samples I I 20 of oftroctolite, tructolite,olivine olivineand andoxide oxidegabbros; gabbros; Oman Oman 20 40 60 80 loo 40 20 0o ophiolite ophiolite—- data data from from gabbro gabbrosills sills(Korenaga, (Korenaga, fitom% %Mg!(Mg+Fe) Ma/(Mg+Fe)in in olivine olivine Pom 1997). 1997). , 60.-----------~----------p.++ --------~.---------~---------60  - ¥  ¥  ¥  I l D References: References:Barth, Barth,G. G.A., A ,and andJ.J.C.C.Mutter, Mutter,Variability Variabilityininoceanic oceaniccrustal crustalthickness thicknessand andstructure: structure:Multichannel Multichannel seismic resultsfrom fromthe thenorthern northernEast EastPacific Pacific Rise, J. Geophys. Res., 17,951-17,975, seismic reflection results Rise, J. Geophys. Res., 10101, 1 17,95 1 17-975,1996. 1996. Geli, Geli, L., L., and andV. V. Renard, Renard, Ocean Ocean crust crust formation formation process at very slow slow spreading spreading centers: centers: A A model model for for the the Mohns Mohns ridge, 2995-3013, 1994. basedon onmagnetic, magnetic,gravity, gravity,and andseismic seismicdata, data,J.J.Geophys. Geophys.Res., Res.,99, 99,2995-3013, 1994. ridge,near near72 72N, N,based Korenaga, Korenaga, J., J., and and P. P. B. B. Kelemen, Kelemen, Origin Origin of of gabbro gabbro sills sills in in the the Moho Moho transition transition zone zone of of the theOman Omanophiolite: ophiolite: Implications magma transport transportin in the the oceanic oceanic lower lower crust, cmst, J. Geophys. Res., 102,27,729-27,749, 102,27,729-27,749,1997. 1997. Implicationsfor formagma McKenzie, McKenzie, D., and and D. D. Fairhead, Fairhead, estimates estimates of of the the effective effective elastic elastic thickness thickness of of the the continental continental lithosphere lithosphere from from Bouguer 27,523-27,552, 1997. Bouguerand andfree freeair airgravity gravityanomalies, anomalies,J.J.Geophys. Geophys.Res., Res.,102, 102,27,523-27,552, 1997. Miller, Ripley, Layered LayeredIntrusions Intrusionsofofthe theDuluth DuluthComplex, Complex, Minnesota, USA, RG.Cawthorn Cahom Miller, J. J. D., and E. M. Ripley, Minnesota, USA, hi:In: RG. (ed) Layered Layered Intrusions, Intrusions,Elsevier ElsevierScience, Science,1996 1996 (ed.) Nicolas, crustalthickness thickness in inthe theOman Omanophiolite: ophiolite: Implication Implication for for Nicolas, A., A , F. F. Boudier, Boudier, and andB. B.ildefonse, Ildefonse,Variable Variable crustal oceaniccrust, Geophys. Res., Res., 101, 101,17,941-17,950, 17,941-17,950,1996. 1996. oceanic crust, J.J. Geophys. Quick, Quick, J.J. E., E., and and R. R P. P. Denlinger, Denlinger, Ductile Ductile deformation deformation and and the origin origin of layered layered gabbro gabbro in in ophiolites, ophiolites, J. Geophys. Geophys. Res., 98, 98, 14,015-14,027, 14,015-14,027,1993. 1993. Res., Rommevaux, study of of the theMid-Atlantic Mid-AtlanticRidge: Ridge:evolution evolution Ronunevaux,C., C., C. C. Deplus, Deplus, and andP. P. Patriat, Patriat,Three-dimensional Three-dimensional gravity gravity study of 3015-3029, 1994. of the thesegmentation segmentationbetween between 28° 28Oand and29°N 2g0Nduring duringthe thelast last10 10my, my, J.J.Geophys. Geophys.Res., Res., 99, 99,3015-3029,1994. Sinton, and R it S. 197-216, 1992. M yand S.Detrick, Detrick,Mid-ocean Mid-oceanridge ridgemagma magmachambers, chambers,J.J.Geophys. Geophys.Res., Res., 97, 97,197-216,1992. Sinton,J.J. IvL, Cochranand andG.G.A.ABarth, Barth,Gravity Gravityanomalies, anomalies,crustal crustalthickness, thickness,and andthe thepattern pattern of of mantle mantle flow flow at at Wane, X., J.J. itRCochran Wan& Res., the EastPacific PacificRise, Rise,9-10 9-10N: N:evidence evidencefor forthree-dimensional three-dimensionalupwelling, upwelling, J.J.Geophys. Geophys. Res., 101, 101, the fast fastspreading spreadingEast 17,927-17,940,1996. 1996. 17,927-17,940, Wright, D. J., Fomari, Wright, D. J., itR.MM.Haymon, Haymon,and andD.D.J. J. Fornari,Crustal Crustalfissuring fissuringand anditsitsrelationship relationship to tomagmatic magmatic and and hydrothermal processes on the East Pacific Rise crest (9°12' to 54'N), J. Geophys. Res., 100, 6097-6120, 1995. hydrothermal (9O12' to 5479, J. Geophys. Res., 100,6097-6120, 1995. - 123 �PRECISE PRECISE U-Pb U-Pb ZIRCON ZIRCON AGES AGES OF O F MIDCONTINENT RIFT RHYOLITE RHYOLITE (CHENGWATANA VOLCANICS), CLAM FALLS, WI CLAM FALLS, WI WIRTH, Karl Karl R., R.,Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN MN55105, 55105, WIRTH, wirth@macalester.edu; E.,Department Departmentof ofGeosciences, Geosciences,UniUniwirth @macalester.edu;and and GEHRELS, GEHRELS,George, George,E., versity versity of of Arizona, Arizona, Tucson, Tucson, AZ 85721, 85721, gehrels@geo.arizona.edu. gehrels@geo.arizona.edu. Recent Recent studies studiesof of the the southwestern southwesternsegment segmentof of the the Keweenawan KeweenawanMidcontinent Midcontinentrift riftalong alongthe theSt. St. Croix River River have have focused focused on on the the structural structural (Leslie (Leslie et et al., al., 1994), 1994),paleomagnetic paleomagnetic(Kean (Keaneteta!., al., 1997), evolution of the poorly-exposed poorly-exposed Chengwatana 1997),and and magmatic magmatic (Wirth (Wirthet et al., 1997) 1997) evolution ChengwatanaVolcanics Volcanics (Minnesota (Minnesotaand and Wisconsin). Wisconsin). Comparison Comparisonof ofChengwatana ChengwatanaVolcanics Volcanicsfrom from this this segment segmentof of the the rift with the those of the better-studied portions of the rift in the Lake Superior region (e.g., the those of the better-studied Superior (e.g., Nicholson Nicholson et al., 1997) 1997) have have been been hindered hindered by the the lack lack of of well-constrained well-constrained ages for for the the Chengwatana ChengwatanaVolcanics. Volcanics. The Theonly onlyprevious previousgeochronologic geochronologicstudy studyof of these thesevolcanics volcanics(Zartman (Zartman et exposed in the Ashland syncline et al., al., 1997) 1997)resulted resulted in in an an age age of 1094.6 1094.6± zk 2.1 Ma for rhyolite exposed syncline in northern Wisconsin; rhyolite from drill core in Hudson-Afton Horst (SE of Minneapolis) in northern Wisconsin; rhyolite drill core in Hudson-Afton Horst (SE of Minneapolis) yielded yielded an an anomalously anomalouslyold old(1130 (1130Ma) Ma) age. age. Here Herewe wereport reportprecise preciseU-Pb U-Pbzircon zirconages ages(1102 (1102±k55 Ma) Ma) for for rhyolites rhyolitesexposed exposedin in the the lower lower part part of of the the volcanic volcanic section section along along the the Lake Lake Owen Owen Fault, Fault, which rhywhich bounds bounds the theeastern easternmargin marginof of the therift. rift. Petrographic Petrographic and and geochemical geochemical studies studies of of the the rhyolitic and basaltic flows of this segment of the rift are described by Abbott et al. and Naiman olitic basaltic flows segment Abbott Naiman et a!. al. (both this volume). volume). Rhyolite exposed one kilometer east of Clam Falls, WI contains phenocrysts of plagioplagioclase spherulitic groundmass of tabular tabular quartz quartz and and potassium potassium feldspar. feldspar. The clase and rare quartz quartz in a spherulitic The rhyolite is typically typically finefine- to to medium-grained medium-grained and massive massive (sample (sample KC-302a), but becomes becomes more coarse-grained coarse-grained near near its its base base (sample (sample KC-302d) KC-302d) and and contains containssubangular subangularclasts clastsof ofbasalt. basalt. Flow structures the large large rhyolites rhyolites of of structuresare are not apparent, apparent, but the rhyolites are otherwise similar to the the the North Shore Shore Volcanic Group. Rhyolite Rhyoliteis is rare rare in in this this portion portion of of the Midcontinent Midcontinentrift rift and and is is estimated estimated to to compose compose less less than than one one percent percent of the the exposed volcanic volcanic and and sedimentary sedimentary sections. sections. Zircons (1ength:width ratios ratios == 2:1 2: 1 to to Zircons from from both samples samples have have relatively simple simple prismatic (length:width 8:1) 8: 1) forms, forms, are are translucent, translucent, and and vary vary in in color color from from reddish-brown, reddish-brown, to to honey honey brown, brown, and andto to pale pale pink. Dark Darkgrains grainstypically typicallycontain containabundant abundant inclusions inclusions and were not selected selected for analysis. analysis. Analyses Analyses were were conducted conducted by conventional conventional isotope isotope dilution-thermal dilution-thermal ionization ionization mass mass spectromspectrometry, as described by Gehrels et al. a!. (1991). Six Six euhedral crystals (175-250 jim pm in length) from KC-302a analyzed as as individual individual grains. grains. Three KC-302awere were abraded abraded to to 75% 75% their original size and were analyzed Three ages of the grains grains yielded yielded concordant concordant ages ages with mean 2o6Pb*P38U 2 0 6 ~ b * / 2 3and and 8 ~2o7Pb*/2o6Pb* 207~b*/206~b* ages of 1102 1102 Ma; an uncertainty of k5 ±5 Ma Ma (2a) uncertainty of (20) is is assigned assigned to this age on the basis of the errors errors of the the individual individual determinations, determinations, rather than the error of the mean of the three concordant concordant analyses. analyses. Three Three additional additional grains grains are are slightly slightly discordant, presumably due to small amounts of lead loss. A discordia through these points, projected from from 1102Ma, Ma,yields yieldsaalower lowerintercept interceptofof196 196±205 5 205 A discordia Ma (MSWD (MSWD == 0.15). 0.15). Analyses of KC-302d were conducted on two multigrain fractions, one Ma unabraded unabraded single singlegrain, grain,and andfive fiveabraded abradedsingle singlegrains. grains.The Thesingle singlegrains grainswere wereallall—200 -200 .tm pminin length jim 125 pm length originally, originally, and and the the multigrain multigrainfractions fractionsconsisted consistedof: of:1)1)seven sevengrains grainsmeasuring measuring—125 in length, and 2) thirty grains —80 jim in 1enth. The three abraded grains are analytically 2) thirty grains -80 pm in length. The three abraded grains are analytically Ma k± 5 Ma. Ma. Three concordant concordant and yield mean mean 2o6Pb*/238U 2 0 6 ~ b * / 2 3and and 8 ~ZO7pb*/2O6pb* 2O7pb*/2O6pb*ages of 1101 Ma Three additional grains grains and and the the two two multigrain multigrain fractions fractions are are slightly slightly discordant; discordant;aa discordia discordiathrough through these ±217 217 Ma Ma (MSWD (MSWD==0.45). 0.45). these points, points, projected projectedfrom from 1101 1101Ma, Ma, yields a lower intercept of 63 k Given the uncertainties of ±5 Ma on each of the ages, the 1 Ma age difference between the two Given the uncertainties of k5 Ma on each 1 difference samples samples is is probably probably not not significant. significant. Analyses of the Chengwatana rhyolites near Clam Falls indicate indicate that magmatism magmatism began began by at least least 1102 1102 Ma in in this this portion portion of the rift, considerably considerably earlier than the age age reported reported by by Zartman et al. (1997) for rhyolite (1094.6 ± 2.1 Ma) exposed near the base of the Chengwatana Zartman et al. (1997) for rhyolite (1094.6 k base of the Chengwatana - 124 - I �U 0.190 0.186 00 en 0.182 0.178 Lower Intercept = Lower Intercept = 196 ±205 Ma (MS WD=0.15) I 0.174 1.82 1.90 I I 2.06 1.98 / 63±217Ma(MSWD=0.45) 1.82 1.90 1.98 2.06 207Pb / 235 u 207pb / 235 u section section in the southeastern limb of the Ashland syncline. This This implies implies that flows flows exposed exposed near near Clam Falls likely formed formed contemporaneously contemporaneously with the Upper Kallander Creek Volcanics and the Mellen Conglomerate of Mellen Complex Complex of of Northern Northern Wisconsin, Wisconsin, and the Group 5 flows and Great Conglomerate Mamainse Point. The Maage ageofofChengwatana ChengwatanaVolcanics Volcanics in in the the Clam ClamFalls Fallsregion region The1102 1102±Â55Ma implies implies that that the the Clam Clam Falls flows flows may have "reversed" paleomagnetic paleomagnetic directions directionssince sincethey they are are coeval with the time of the reverse-to-normal magnetic polarity change (1105-1100 Ma) that the time of the reverse-to-normal magnetic change (1 105-1100 has throughout the Lake Superior region. region. New aeromagnetic has been widely observed observed throughout aeromagnetic data data (USGS) (USGS) suggest Falls, MN, MN, are younger than suggest that Chengwatana Chengwatana Volcanic flows exposed near Taylors Falls, those those near Clam Clam Falls. Flows Flowsnear nearTaylors Taylors Falls Falls have predominantly "normal" paleomagnetic paleomagnetic directions (Kean et al., 1997) and are likely younger than the regionally documented reversedirections (Kean et al., 1997) and are likely younger than the regionally documentedreverseto-normal to-normal polarity polarity shift; shift;these theseflows flowsmay may be be correlative correlativewith with Portage PortageLake LakeVolcanics Volcanics (northern (northern WI) and Group Group 66 flows flows (Mamainse (Mamainse Point). A A few few Taylors Taylors Falls flows have "reversed" paleomagnetic directions (Kean reversal event that that is younger than the mean et al., 1997) 1997) and record a reversal regionally observed reverse-to-normal magnetic regionally observed reverse-to-normal magnetic Upper Mich Mich Michipicoten Is. Is. Minnesota Minnesota polarity change. NW Wisconsin NW Wisc Wisc Mamainse Mamainse Point Point polarity change. ' References Cited Cited Gehrels, G.E., W.C., Samson, Samson, S.D., and G.E., McClelland, McClelland, W.C., Patchett, SciPatchett, P.J., P.J., 1991, Canadian Journal of Earth Sciences, p. 1285-1300. 1285-1300. ences, v. 28, P. Green, J.C. and and Fitz, Fitz, T.J., T.J., 1993, 1993, Journal Journalof ofVolcanology Volcanology and Geothermal 177-196. Geothermal Research, Research, v. 54, p. 177-196. Kean, W.F., W.F., Williams, I., Chan, L., and and Feeney, Feeney, J., J., 1997, 1997, Geophysical Geophysical Research Research Letters, Letters, v. 24, p. 1523-1526. 1523-1526. Leslie, M., Wetzel, Wetzel, T., Wirth, K.R., and and Craddock, Craddock,J.P., J.P., 1994, 40thAnnual Meeting 1994,40thAnnual Meeting of of the the Institute Institute on on Lake Lake Superior Houghton, MI, May 11-14, 11-14, Part Superior Geology, Houghton, II -- Program Abstracts, v. 40, p. 35-36. Program with Abstracts, 35-36. Miller, J.D., Nicholson, Nicholson, S.W., S.W., and and Cannon, Cannon,W.F., W.F., 1995, 1995, Minnesota MinnesotaGeological GeologicalSurvey SurveyGuidebook GuidebookSeries, Series,p.p. 1-22. 1-22. Nicholson, Nicholson, S.W., S.W., Shirey, S.B., S.B., Schulz, K.J., Green, Green, J.C., J.C., 1997, Canadian Journal Journal of Earth Earth Sciences, Sciences,v.v. 34, 34, p. p. 504-520. 504-520. Wirth, K.R., Vervoort, J.D., J.D., Naiman, Z.J., Z.J., 1997, Canadian Canadian Journal of Earth Sciences, Sciences, v. 34, no. 4, p. 536-548. Zartman, Zartman, R.E., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., and Morey, G.B., 1997, 1997, Canadian Canadian Journal Journal of of Earth EarthSciences, Sciences,v.v. 34, p. p. 549-561. 549-561. 125 � https://digitalcollections.lakeheadu.ca/files/original/ef817c5c00f1dd4aa45ca2f7d4b1ff20.pdf e9633852122cc432ccfd00cdfe5f1152 PDF Text Text Minneapolis, Minnesota May 6-10,1998 Organized by MINNESOTA GEOLOGICAL SURVEY OF MINNESOTA UNIVERSITY �44th 44th Annual AnnualMeeting Meeting INSTITUTE ON GEOLOGY INSTITUTE ONLAKE LAKESUPERIOR SUPERIOR GEOLOGY Volume Volume44 44 contains contains the the following followingparts: parts: Part1: 1:Program Programand andAbstracts Abstracts Part 2: Field FieldTrip TripGuidebook Guidebook Part2: Part 1—Early 1-Early Proterozoic Proterozoic intrusive intrusiverocks rocks of of east-central east-centralMinnesota Minnesota 2—Geology 2ÑGeolog of of the the southeastern southeasternportion portionof of the theMidcontinent MidcontinentRift Rift System, stern,eastern easternMinnesota Minnesotaand andwestern westernWisconsin Wisconsin 3—Glacial 3-Glacial exotica exoticaof of the theTwin TwinCities Citiesarea area 4—Stratigraphy &Stratigraphy and andhydrogeology hydrogeologyofofPaleozoic Paleozoicrbcks rocksof of southeastern southeastern Minnesota Minnesota 5—Minnesota 5-Minnesota River River Valley Valley and vicinity, southwestern southwesternMinnesota Minnesota Reference Referenceto to the thematerial materialin inthis thisvolume volumeshould shouldfollow followthe theexample examplebelow: below: Sims, Sims,P.K., P.K., Neymark, Neymark,L.A., L.A., Peterman, Peterman,Z.E., Z.E., and andKotov, Kotov,A.B., A.B., 1998, 1998, Nd isotope isotope evidence evidence for forMiddle Middleand andEarly EarlyArchean Archeancrust crustin inthe theWawa Wawasubprovince subprovinceof of the the Superior SuperiorProvince, Province, Michigan, 44th Michigan,U.S.A., U.S.A., [abstract]: [abstract]:Institute Institute on onLake Lake Superior SuperiorGeology GeologyProceedings, Proceedings,44th Annual MN, AnnualMeeting, Meeting,Minneapolis, Minneapolis, MN,1998; 1998;v.v.44, 44,Part Part1,1,p.p.10-11. 10-11. Volume Volume44 44 is is published publishedby by the the Institute Instituteon onLake LakeSuperior SuperiorGeology Geologyand and distributed distributedby bythe theInstitute InstituteSecretary-Treasurer: Secretary-Treasurer: MarkJirsa Jirsa Mark MinnesotaGeological Geological Survey Survey Minnesota 2642 University University Avenue Avenue 2642 MNUSA USA55114-1057 55114-1057 St.Paul, Paul,MN St. (612)-627-4780 (612)-627-4780 email:jirsa001@tc.umn.edu jirsaOOl@tc.urnn.edu email: /www.geo.mtu.edu/great_lakes great-lakes /ilsg /ilsg // ILSG website http: // /www.geo.mtu.edu/ ILSG website http: ISSN ISSN1042-9964 1042-9964 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 44th 4th Annual Meeting May 6-10, 1998 Minneapolis, Minnesota Sponsored by: Sponsored by: Minnesota Minnesota Geological Survey University University of Minnesota Minnesota Field Trip Guidebook Volume 44 Volume 44 2—FieldTrip Trip Guidebook Guidebook Part 2-Field EDITORS: EDITORS: Terrence J. J. Boerboom Boerboom and and Barbara A. Lusardi Lusardi Terrence Minnesota Minnesota Geological Geological Survey Survey �PROCEEDINGS VOLUME 44, 44, PART 2—FIELD %FIELD TRIPS CONTENTS CONTENTS 1: Early EarlyProterozoic ProterozoicIntrusive IntrusiveRocks Rocks of of East-Central Minnesota Trip 1: Introduction Field Trip Stops 3 18 Leaders Terry Boerboom, Boerboom, Minnesota Minnesota Geological Survey Mark Jirsa, Minnesota Minnesota Geological Geological Survey Daniel K. Hoim, Holm, Kent State State University Trip Trip 2: The TheGeology Geologyof of the the Southeastern Southeastern Portion Portionof of the the Midcontinent MidcontinentRift Rift System, System, Eastern Eastern Minnesota Minnesota and andWestern WesternWisconsin Wisconsin Introduction .................................................................................................. 33 Introduction.. 33 44 Field Trip Stops Stops............................................................................................. 44 Leaders: Karl Wirth, Wirth, Macalester Macalester College College William S. Cordua, Cordua, University University of of Wisconsin-River Wisconsin-River Falls Falls William F. Kean, Kean, University University of of Wisconsin-Milwaukee Wisconsin-Milwaukee Mike Middleton, Middleton, University of Wisconsin-River Falls Zachary J. Naiman, University of Arizona Trip 3: Glacial Trip GlacialExotica Exoticaof of the the Twin Twin Cities Introduction Field Trip Stops Leaders: Howard Hobbs, Hobbs, Minnesota Minnesota Geological Geological Survey Survey Alan Knaeble, Minnesota Minnesota Geological Geological Survey Survey Minnesota Geological Survey Gary Meyer, Minnesota 79 82 Trip 4: 4: Stratigraphy Stratigraphyand andHydrogeology HydrogeologyofofPaleozoic PaleozoicRocks Rocks of of Southeastern Southeastern Minnesota Minnesota Trip Introduction Field Trip Stops 103 113 Leaders: Anthony C. C. Runkel, Runkel, Minnesota Minnesota Geological Geological Survey Robert G. Tipping, Minnesota Geological Robert G. Tipping, Minnesota GeologicalSurvey Survey Trip Trip 5: 5: Archean Archeanand andQuaternary QuaternaryGeology Geologyofofthe theMinnesota MinnesotaRiver RiverValley Valley Introduction to Precambrian Geology 133 Geology.......................................................... 133 Field Trip 137 Trip Stops, Stops, Day Day 11................................................................................ 137 Introduction 148 Introduction to to Quaternary Quaternary Geology Geology............................................................ 148 Field Trip Stops, Day 2 154 Stops, ................................................................................ 154 Leaders: D. L. Southwick, Southwick, Minnesota Minnesota Geological Survey Carrie J. Patterson, Minnesota Minnesota Geological Geological Survey Survey ��FIELD FIELD TRIP TRIP#1 #1 EARLY PROTEROZOIC PROTEROZOIC INTRUSIVE INTRUSIVE ROCKS ROCKS OF OF EAST-CENTRAL EAST-CENTRALMINNESOTA Leaders: Terry Boerboom, Mark Mark Jirsa, Jirsa, and Leaders: and Daniel Hoim Holm INTRODUCTION rocks of the St. Cloud District The Early Proterozoic (Paleoproterozoic) granitoid rocks District in in east-central east-central Minnesota Minnesota(Fig. (Fig.1) 1)have have long long been been aa source source of both building building materials materials and and geologic geologic controversy. Quarrying Quarrying for for dimension dimension stone stone began in the St. Cloud District in the late 1800's 1800's 1930-1940, were some some 18 different differentquarry quarrycompanies companies operating operating and peaked at about 19301940, when there were in the district (Thiel (Thiel and Dutton, 1935). 1935). Currently, Currently, Cold Cold Spring Spring Granite Granite is is the the only only dimension dimension operating, with 5 active quarries stone company operating, quarries here, and and 4 others others in different different parts parts of of the the state. state. Meridian Aggregates Company also operates a large crushed-stone operation in the St. Cloud Cloud TheSt. St.Cloud Cloudarea areacontains containsabundant abundant active active and inactive quarries, as well as natural District. The outcrops. Despite Despitethese theseexposures, exposures,many many of of the the critical critical relationships relationships between various intrusive units are concealed—leaving concealed-leaving details of the magmatic history unknown and speculative. Until Until recently, geologic geologic maps reconnaissance-style (Morey recently, maps of the district were reconnaissance-style (Morey and and others, others, 1981), 1981),and and little geochronologic work had had been been conducted. conducted. This This field field trip highlights the results of more current and thorough thorough mapping mapping endeavors endeavors that utilized quarry and natural exposures, drill core, These include include the the Stearns Steams County Geologic Atlas (Boerboom and geophysical interpretation. These and others, 1995; 1995; Boerboom, Boerboom, 1996a), 1996a),and and mapping mapping north north and east of St. Cloud (Jirsa and others, 1995a; 1995b; Jirsa and Chandler, 1997). In In addition, addition,we we review review both pre-existing pre-existing and and newly newly acquired geochronologic data (e.g., Hoim Holm 1997, 1997, 1998) 1998) in light of the field, field, petrographic, petrographic, and and geophysical observations. observations. Intrusions Intrusions of the the St. St. Cloud Cloud District District were were emplaced emplaced relatively relatively late late in in development developmentof of the the Penokean orogen—a Penokean orogen-a belt belt of of Early Early Proterozoic Proterozoic volcanic, volcanic, sedimentary, sedimentary,and and plutonic plutonic rocks rocks affected affected the Penokean Penokean orogeny, orogeny, which which culminated culminated at approximately approximately 1870 Ma (Van (Van Schmus and by the 1981). Rocks Rocksofofthe theorogen orogenare aredivided dividedfrom fromnorth north to to south south(Fig. (Fig. 1) 1)into intoaavariably variably Bickford, 1981). deformed foreland basin; a fold and thrust belt; and what what has has been been inferred inferred to to be be an accreted broadly equivalent to the Wisconsin Wisconsin magmatic magmatic terranes terranes (Jirsa (Jirsa and others, island-arc terrane, broadly 1995b, Boerboom, 1996b). All All of of these these terranes terranes were were deposited deposited upon or or accreted accreted against against the the southern margin of the Archean Superior Province. Province. Using Using the terminology of Southwick Southwick and into distinct distinct segments on on the the basis basis of of others (1988), (1988), the fold fold and thrust belt is further subdivided into of the Animikie Group and lithologic and structural attributes: 1) an external zone comprised of related outliers; 2) a medial medial zone zone characterized characterized by fault slices of interlayered interlayered volcanic and related clastic including the Cuyuna north internal zone, zone, clastic strata including north and south (iron) ranges; ranges; and 3) an internal containing fault-bounded fault-bounded blocks blocks of of various metamorphic and and plutonic plutonic rocks. rocks. The The Early Proterozoic Proterozoic granitoid granitoid rocks rocks of the St. Cloud District occur within the internal zone of the western Penokean orogen, where they form a physically continuous mass of lateand post-orogenic post-orogenic intrusions. intrusions. They Theyrepresent represent some some of the most deeply emplaced magmas of the 3 �orogenicbelt. belt. Regionally, Regionally, the the Early Early Proterozoic Proterozoic supracrustal supracrustalcountry country rocks—including rocks-including the the orogenic Little Falls Formation to the north and west, and unnamed volcanic and clastic strata to the east Little Falls Formation to the north and west, and unnamed volcanic and clastic strata to the east andsoutheast—were southeast-were metamorphosed metamorphosedatatdepths depthsofof22-25 22-25km krnduring duringthe the Penokean Penokeanorogeny orogeny(Holm (Holm and andSelverstone, Selverstone,1990). 1990).Reconstruction ReconstructionofofP-T-t P-T-thistories historiesindicate indicatethat thatthe therocks rocks currently currentlyexposed exposed and remained at those depths until well after the orogeny, then were rapidly exhumed at about 1770 remained at those depths until well after the orogeny, then were rapidly exhumed at about 1770 Ma during during emplacement emplacement of of post-tectonic post-tectonic magmas magmas (Hoim (Holm and and others, others, 1998). 1998). The Thesignificant significant Ma depth of emplacement and the great volume of igneous rock provide an excellent opportunity to depth of emplacement and the great volume of igneous rock provide an excellent opportunity to midcrustal magmatic magmatic processes processes that that occurred occurred immediately immediately after after the the orogenic orogenic belt belt investigate midcrustal investigate was constructed, constructed,and andlater lateras asthe theorogen orogencollapsed. collapsed. was 950 940 930 92° b IIArchean Archean (A) (A) I I 1 Superior Province 47O 46' sland arc rocks (Equivalent to Wisconsin agma 45O thePenokean Penokeanorogen, orogen,showing showingmajor major Figu 1. Simplified geologic map of)fthe Figure tectcLLL.w.-iLLuLLLo. bciLbuuaL-Lbb~nic Penokeanintrusions intrusionsshown shownininblack. black. tectonic elements. LatetoLu post-tectonic Penokean GEOLOGYOF OFINTRUSIVE INTRUSIVEROCKS ROCKS GEOLOGY Intrusionsof ofthe theSt. St.Cloud CloudDistrict District(Fig. (Fig.2) 2)are arecomprised comprisedof of several several discrete discrete units units that that Intrusions includethe theReformatory Reformatorygranodiorite, granodiorite,the thecharnockitic charnockiticRichmond Richmondgranite, granite,the theRockville RockvilleGranite, Granite, include the St. St.Cloud CloudGranite, Granite,the theFoley Foleybatholith, batholith,and andseveral several types types of of granitic graniticand anddiabasic diabasicdikes. dikes. the Only untry rocks are recognized within the intrusions, Only scattered xenoliths of metamorphic country rocks are recognized within the intrusions, 4 �but numerous numerous mafic maficenclaves enclavesinterpreted interpretedto to be be comagmatic comagmaticwith withthe theenclosing enclosing granitoid granitoidrocks rocks but are present in some units. The intrusions can be divided on the basis of composition and relative are present in some units. The intrusions can be divided on the basis of composition and relative 1) gray gray to to pinkish-gray pinkish-gray to to greenish greenish gray gray granitic, granitic, temporal setting setting into into three three categories: categories: 1) temporal granodioritic,and and dioritic dioriticrocks—Reformatory rocks-Reformatory granodiorite, granodiorite,Richmond Rchmond granite, granite,and and Rockville Rockville granodioritic, Granite; 2) red and pink granitic intrusions-St. Cloud Granite, Foley batholith, and associated Granite; 2) red and pink granitic intrusions—St. Cloud Granite, Foley batholith, and associated aplite; and and 3) 3) diabasic diabasic and and porphyritic porphyritic microgranite microgranite dikes. Colorisis not not always always an an adequate adequate aplite; dikes. Color distinguishing characteristic between various intrusions because components of the "gray" distinguishing characteristic between various intrusions because components of the "gray" intrusionscan canbe be quite quite pink. pink. Other Otherattributes attributesthat that distinguish distinguish "gray" "gray" from from"red" "red" varieties varietiesinclude include intrusions the observation observationthat that "gray" "gray" intrusions intrusionscontain containmafic maficenclaves, enclaves,and andhave have aa better better developed developedand and the more pervasive magmatic foliation than do the "red" ones. These differing attributes have more pervasive magmatic foliation than do the "red" ones. These differing attributes have A description description importantimplications implicationsabout about the the magmatic magmatic history history that that will will be important be discussed discussed below. below. A of individual individualplutonic plutonic units unitsfollows. follows. of EARLYVPROTEROZOIC PARI PRCTFPfl7flI ', NW-striking diabase dike ..NW-strikingdiabasedike Maficto toultramafic ultramaficintrusions intrusions Mafic D St.Cloud CloudGranite Granite St. Foleybatholith batholith Foley RockvilleGranite Granite Rockville Richmondgranite granite Richmond Reformatotygranodionte granodiorite Reformatory Gabbroicintrusions intrusions Gabbroic = 0 Granite,undivided undivided Granite, AnimikieGroup Group(slate) (slate) Animikie \ LittleFalls FallsFormation Formation Little (garnet-stauroliteschist) schist) (gamet-staurolite Volcanicand andclastic clasticrocks, rocks, Volcanic iron-formation; largely large1 of of iron-formation; Mille Lacs Lacs Group, Group, undivided unchided Mule Strike- or or dipdipStrikeslip fault. slip fault. Thrustfault. fault. Thrust El ARCHEAN ARCHEAN Sartell Gneiss(may (maybe beEarly Early Sartell Gneiss Proterozoicininpart) part) Proterozoic 'NS Lithologic Lithologic contact. contact. 0 Gneissterrane terrane 0Gneiss Figure 2. 2. An An extremely extremely busy busy and and largely largely illegible illegibleregional regional geologic geologic map map of of the the Figure area around Steams County (outlined). Inset map references location within area around Steams County (outlined). Inset map references location within 1). Penokeanorogen orogen(Fig. (Fig.1). Penokean 55 �Reformatory Reformatory granodiorite granodiorite Reformatory granodiorite granodiorite (Reformatory (Reformatory Granite 1978) is presently presently The Reformatory Granite of Morey, 1978) (trade name Charcoal Granite), just city of of St. St. extracted from only one quarry (trade just south of the city Cloud. However, However,there thereare aredozens dozensof of inactive inactive pits pits from from which which this this rock rock has been quarried quarried in the the Cloud. past, including those that supplied stone to the the unit's unit's namesake-the namesake—the State State Reformatory! Reformatory! The rock is mediummedium- to dark-gray, mediummedium- to to coarse-grained, coarse-grained, weakly wealdyporphyritic porphyriticbiotite-hornblende biotite-hornblende granodiorite characterized by small small tabular tabular plagioclase plagioclase phenocrysts (oligoclase to andesine; andesine; Johnson, Johnson, 1978) 1978)in in aa groundmass groundmassof of plagioclase, plagioclase, microcline, microcline, homblende, hornblende, biotite, biotite, and and accessory accessory pyroxene, pyroxene, sphene, and apatite. apatite. AAweak, weak,generally generally subhorizontal subhorizontal trachytoid trachytoid fabric in the the granodiorite granodioritecan canbe be observed observed in in many places. Small Smallovoid ovoid mafic enclaves are scattered throughout the the intrusion. intrusion. Richmond granite granite The charnockitic Richmond granite is well exposed between the towns of Richmond and Cold Spring, but has never been significantly exploited as as a dimension stone. Although Although generally generallydark dark greenish-pink, greenish-pink,ititlocally locallyretains retainsaa unique unique deep deep green green color color where where the rock has not been been subjected subjectedto to oxidation oxidationalong alongtight tight brittle brittle fractures. fractures. The Thegranite granitedisplays displaysaa prominent prominentrapakivi rapakivi 2-6 cmlong longK-feldspar K-feldsparmegacrysts, megacrysts,as as well well as as a consistent texture defined defined by plagioclase-mantled, texture plagioclase-mantled, 2-6cm consistent Hypersthene, redeast-northeast magmatic trachytoid fabric defined by by aligned aligned phenocrysts. phenocrysts. Hypersthene, brown biotite, and and green green homblende hornblende are are the the dominant dominant mafic mafic minerals; minerals; apatite, apatite, ilmenite, ilmenite, and and zircon mafic minerals. minerals. Quartz zircon form form abundant abundant accessory accessoryphases phases concentrated concentrated with the late-formed mafic Quartz typically occurs occurs as as more-or-less more-or-less equant, equant, but anhedral-interstitial, anhedral-interstitial,monocrystalline monocrystalline clots clots as as large large typically as 11 cm. cm. Although Althoughelongate elongategrains grainsofofquartz quartzoccur occurin inlocalized, localized,meter-scale meter-scale shear shear bands, bands, the the of the the intrusion intrusion contains contains aawell-developed well-developed magmatic magmatic foliation foliation and no evidence evidence of bulk of metamorphic recrystallization. recrystallization. Scattered Scatteredoutcrops outcropsand and geophysical geophysical maps (Fig. 3) indicate that metamorphic the Richmond charnockitic intrusion intrusion Richmond granite may be be one one component component of of aa large large composite composite charnockitic composed largely of gabbroic and noritic intrusive rocks. composed largely of gabbroic and noritic intrusive Rockville Granite Granite The Rockville Rockville Granite is presently presently taken from from three separate separate quarries and marketed marketed under under the the trade trade names namesof ofDiamond DiamondPink, Pink,Rockville RockvilleBeige, Beige,and andRockville RockvilleWhite. White. It is is aa very very coarse-grained, coarse-grained, pinkish- to grayish-white grayish-white rapakivi granite characterized characterized by zoned 1-3 1-3 cm cm microcline microcline phenocrysts phenocrysts and and smaller smaller plagioclase (oligoclase; Johnson, Johnson, 1978) 1978)phenocrysts phenocrysts in in aa groundmass groundmass of of coarse coarsequartz, quartz,feldspar, feldspar, biotite, biotite, and and hornblende, hornblende, with with accessory accessoryzircon, zircon,apatite, apatite, sphene, epidote, and allanite. The Rockville locally shows a weak trachytoid fabric, defined sphene, epidote, and allanite. The Rockville locally shows a trachytoid fabric, defined by aligned generally N-S N-S and and dips dips variably variablyto to the the west. west. This aligned feldspar phenocrysts, that strikes generally This granite granite contains containsscattered scatteredenclaves enclavesthat that vary vary from from coarse-grained coarse-grainedblack black diorite, diorite, to to fine-grained, fine-grained, gray gray quartz quartz monzonite; monzonite; both both having having abundant abundant homblende hornblende and biotite. The Thedioritic dioriticenclaves enclaves commonly commonlycontain containmicrocline microclinephenocrysts phenocrystsor orxenocrysts; xenocrysts;whereas whereasthe the monzonitic monzoniticones ones contain contain scattered microcline, scatteredplagioclase plagioclasephenocrysts phenocrystsin in aa pristine pristine igneous-textured, igneous-textured, trachytoid trachytoid matrix matrix of microcline, quartz, biotite, and homblende. hornblende. Dikes Dikes5-30 5-30cm cmwide wideof of rock rocklike likethe thecoarse-grained coarse-grained dioritic dioritic phase phaselocally locallycut cut the the Rockville RockvilleGranite. Granite. These Thesetwo twoconflicting conflictingoccurrences occurrencesof of the the coarse-grained coarse-grained diorite (as both rphenocrysts' in in the thecoarsecoarseboth enclaves enclaves and and dikes), dikes), the the presence presence of of microcline microcline 'phenocrysts' grained grained enclaves, enclaves, the pristine pristine trachytoid trachytoid igneous texture of the finer grained enclaves, and the rapakivi mafk and and felsic felsic magmas magmas during during rapakivi texture, texture, all all imply imply an an origin origin by by the the commingling comminglingof of mafic magma magma ascent ascent(see (seeDISCUSSION). DISCUSSION). 66 �Figure anomaly map of Stearns Figure 3. 3. First vertical derivative, derivative, reduced to pole aeromagnetic anomaly S t e m s County (white dashed line, also also see Figure 2) and the fringing area. Outlines Outlinesonly only shown shown for for rock rock units units discussed discussed in in text. text. St. Cloud Granite Granite The The St. St. Cloud Cloud Granite Granite occurs occurs as as aa zone of variably wide dikes and sills that permeated into the Reformatory Reformatory granodiorite, granodiorite,resulting resulting in a complex geometry not easily depicted at small into map map scales. scales.At Atlarger largerscale, scale,dikes dikesof ofSt. St.Cloud CloudGranite Graniteare are irregular irregular in in shape, shape, and and contacts contacts most most commonly trend trend to to the the north north and and northeast. Small Smalldikes dikesand and irregular irregular pods pods of of pink pink aplite aplite that that commonly are associated associated with with the the St. St. Cloud CloudGranite Granite also also cut cut Reformatory Reformatory granodiorite. granodiorite. The St. extensively in in the the past, past, but but no no longer. longer. It is a St. Cloud Cloud Granite has been quarried extensively coarse-grained, coarse-grained,deep-colored, deep-colored,grayish-pink grayish-pinkto tored, red, hornblende hornblendegranite granite having having a weak porphyritic texture texture defined defined by by pink pink microcline microcline phenocrysts phenocrysts only slightly larger than the matrix. The Themain main 19781, quartz, hornblende, microcline, plagioclase (albite to oligoclase; minerals are microcline, oligoclase; Johnson, 1978), and biotite, apatite, zircon, zircon, sphene, sphene, and and rare rare epidote. epidote. Using biotite, with with accessory accessory Fe-Ti oxides, apatite, Using Maitre (1979), (19791, the the St. St. Cloud Cloud varies varies in in modal modalmineralogy mineralogy Streckeisen and and Le Le Maitre terminology of Streckeisen from alkali-feldspar (Fig. 4). 4). A alkali-feldspar granite to syenogranite (Fig. A vague vague trachytoid trachytoid fabric fabric defined defined by by aligned feldspar and hornblende crystals is common and is parallel to the margins of the dikes aligned feldspar and hornblende crystals is common and is parallel to the margins of the dikes and and sills sills in in which which the the St. St. Cloud Cloud Granite Granite occurs. Narrow Narrowdikes dikesof of pink pink aplitic apliticgranite granitelocally locallycut cut the St. St. Cloud Cloud and and Reformatory, Reformatory, and and are are inferred inferred to to be be late late differentiates differentiatesof of the the St. St.Cloud Cloudon onthe the the basis of of lithologic lithologic similarity. similarity. Coarse Coarsepegmatite pegmatiteis is exceedingly exceedingly (and (and conspicuously) rare. The The St. St. Cloud Cloud commonly commonlycontains containsangular angularxenoliths xenoliths of of Reformatory Reformatorygranodiorite, granodiorite,along alongwith withrare rare xenoliths xenoliths of of metamorphic metamorphiccountry countryrock. rock. 77 �Foley batholith batholith Foley The salmon-colored, coarse-grained, coarse-grained, hornblende-biotite homblende-biotite granite TheFoley Foley batholith batholith is is a red to salmon-colored, granite that that is is cut cut by by minor minoramounts amountsof ofgranitic graniticporphyry porphyry and andaplite—similar aplite-similar in in nearly nearly all allrespects respectsto to the km),ovoid ovoidgravity gravitylow lowthat thatextends extendsfrom fromthe the the St. St. Cloud Cloud Granite. Granite. ItItforms formsaalarge large(60 (60xx20 20km), east east side sideof of St. St.Cloud, Cloud, northeastward northeastward to to near Mule Mille Lacs Lake (Jirsa and Chandler, 1997). The The batholith batholith is is moderately moderately well well exposed exposed along along its its western western terminus, terminus, where where its its intrusive intrusive contact contact against againstReformatory Reformatorygranodiorite granodioritecan canbe beseen, seen,and andin inseveral severalplaces placeseast eastof ofthe themap maparea areashown shown on on Fig. Fig. 2. 2. Small Smallquarries quarriesininthe thewestern westernpart partofofthe theunit unitoperated operatedduring duringthe theperiod period1896-1909. 1896-1909. The The Foley Foley isismassive massiveto tovaguely vaguelyfoliated, foliated,having havingaapoorly poorlydeveloped developedand andlocalized localizedtrachytoid trachytoid fabric. fabric. Although Althoughititwill willnot notbe bevisited visitedduring duringthis thisfield fieldtrip, trip,the theFoley Foleyisis described describedhere herebecause because itit isisaalarge largeand anddistinctive distinctiveunit unitthat thatappears appearsto tobe bemagmatically magmatically related related (parental?) (parental?) to to the the St. St. Cloud Granite. Granite. Cloud Porphyritic (AKAQFP) QFP)dikes dikes Porphyriticmicrogranite microgranite(AKA Thin Thin northeast-trending northeast-trendingdikes dikesof of distinctively distinctively textured porphyritic porphyritic microgranite microgranite cut cut the Reformatory Foley batholith. batholith. None of Reformatory granodiorite, granodiorite, Rockville RockvilleGranite, Granite, St. St. Cloud Granite, and Foley these these dikes dikes were were noted noted in in the the Richmond Richmond granite, granite, but but they they would would logically logically post-date that unit. unit. Most 2-4 m m wide, wide, but but one one is is at at least least 30 30 m wide, and and another another may may be as as much much Most of of these these dikes dikesare are 2-4 as as 100 100m m wide, wide, although although correlation correlation of of the the latter latter with this dike set is tenuous. The Themargins marginsof of these dikes dikes are are chilled chilled and and locally locally flow-banded, flow-banded, texturally similar to volcanic rhyolite. The The porphyries porphyries are are characterized characterized by by 3-10 3-10 percent percent quartz quartz phenocrysts as large as 4 mm across across that have primary euhedral have aa primary euhedralshape shapemodified modified by by resorption, resorption,and and 3-10 3-10 percent percent microperthite microperthiteor or sanidine sanidine phenocrysts phenocrysts as as large large as as 10 10mm. mm. The Thefine-grained fine-grainedgroundmass groundmassvaries variesin intexture texturefrom fromanhedralanhedralgranular to spherulitic. spherulitic. InInaddition additiontotothe themain mainquartz quartzand andfeldspar, feldspar,the the rock rock contains contains minor minor amounts of of fine-grained fine-grained biotite, biotite, homblende, hornblende, actinolite, actinolite, and and chlorite, chlorite, and and accessory accessory fluorite, fluorite, apatite, apatite, Fe-Ti Fe-Ti oxides, oxides, epidote, epidote, sphene, sphene, zircon, zircon, and and allanite. allanite. Diabase dikes dikes Diabase There There are are two two main main groups groupsof of diabase diabase dikes dikes recognized recognized in in the the area: a northeast-trending northeast-trending set, and a northwest-trending northwest-trending set. Both Both sets setsare are steeply steeply dipping dipping and are interpreted to be the youngest rocks in the St. youngest Precambrian rocks St. Cloud Cloud area, area, as as they they cut cut nearly nearly all all other other rock rock types. types. Northeast-trending Northeast-trendingdiabase diabasedikes dikesare aretypically typically non-magnetic non-magnetic and andlack lackgeophysical geophysicalexpression, expression, but throughout the area. They but are are exposed exposedin in several several outcrops outcropsand and old old quarries quarries throughout They are are most most commonly commonly 1-3 m thick, but some m,and anddike dikemargins margins are aresharply sharplychilled chilled against against the the some are are as as wide wide as as 88m, neighboring metamorphism neighboringgranitic graniticrocks. rocks. These Thesedikes dikescontain containfresh fresh plagioclase, plagioclase, but low-grade metamorphism or actinolite, chlorite, or deuteric deuteric alteration alteration(?) (?)has has altered alteredthe the primary primary mafic minerals minerals to actinolite, chlorite, and and dusty dusty oxides. oxides. Northwest-trending Northwest-trendingdiabase diabasedikes dikesare arerarely rarely exposed, exposed,but are are inferred inferred from geophysical geophysical data 100m wide. They They are are geophysically geophysicallytraceable traceableby by their their distinctive, distinctive,generally generally data to to be be as as much much as as 100 reversely polarized, aeromagnetic signature (Fig. (Fig. 3). 3). One exposed northwest dike (Fig. F6 of One exposed stop descriptions) has has sharply sharply chilled chilled margins, margins, and and compared compared to to the the northeast-trending northeast-trendingset setisis strongly magnetic magnetic (pyhrrotitic) (pyhrrotitic) and and is is less less altered/metamorphosed, alteredmetamorphosed, having having substantially substantiallymore more fresh clinopyroxene. This Thisdike dikeisisnormally normally polarized polarized and and only 6 meters thick—attributes thick-attributes that contrast somewhat somewhat with the the geophysically-defined geophysically-defined northwest northwest swarm, making correlation correlation 8 �uncertain. Another Anothersmall smalloutcrop outcropof of apatitic apatiticferrodiorite, ferrodiorite,in in northwestern northwestern Stearns Steams County, County, lies over one of the reverse-dike reverse-dike anomalies and is probably part of this swarm, swam, but no no magnetic magnetic polarity tests have been performed. performed. GEOCHEMISTRY A standard standard alkali-silica alkali-silica chemical chemical classification classificationplot characterizes characterizesthe the granitoid granitoidrocks rocksas as subalkaline to alkaline composition. As As shown shown in in Figure Figure 4, 4, both both the the St. St. Cloud Cloud and and Rockville Rockville alkalic Granites plot as subalkalic subalkalic using the dividing line of Irvine and Baragar (1971), but as alkalic Miyashiro (1978). (1978). This alkalic tendency reflects the perthite-dominated perthite-dominated using the dividing line of Miyashiro mineralogy of the St. Cloud Granite. In In addition, addition, the all the granitoid rocks in Stearns Steams County are peraluminous, and I-type, I-type, consistent consistent with with the abundance of biotite peraluminous, calc-alkaline, calc-alkaline, and biotite and and hornblende and lack of muscovite. DISCUSSION DISCUSSION Temporal Relationships—Field Temporal Relationships-Field Evidence Evidence Based on field and petrographic petrographic observations, observations, geophysical geophysical maps and measurements, measurements, and and limited geochronologic geochronologic data, the following following sequence—from sequence-from oldest to youngest—summarizes youngest-summarizes the emplacement history of igneous igneous rocks in the St. St. Cloud Cloud District: 1) Reformatory granodiorite, and Rockville and Richmond granites—emplaced granites+mplaced at at about about 1812 Ma; Granite and associated associated aplite, and Foley batholith+mplaced batholith—emplaced at approximately 2) St. Cloud Granite approximately 1770 Ma; northeast-trending dikes of porphyritic 3) northeast-trending porphyritic microgranite microgranite and diabase; diabase; and 4) northwest-trending northwest-trendingdiabase diabase dikes. dikes. 10 + 0 9 z 5 SO feldspar 70 75 VDiabua dike 8W w a i n R v G ~ P w p b @ c ~ ~ARichond+te t e SL CI-4 w e 0 Refemwary pnodiaite Figure 4. Modal rocks from from the the St. St. Cloud Cloud area. area. (a) Modaland andchemical chemicalvariation variation diagrams of intrusive rocks selected selected modal modal analyses analyses compiled compiled from from Dittman (1971), (1971), Morey (1972), (19721, Johnson (1978), (19781, Skiliman Skillman (1946), and Boerboom (in prep.); (b) (19461, (b)alkali-silica alkali-silicaclassification, classification,with with dividing dividing lines lines of of Miyashiro Miyashiro (1978, solid line) and Irvine k i n e and Baragar (1971, (1971, dashed line). 9 �The TheSt. St.Cloud CloudGranite Graniteintrudes intrudesthe theReformatory Reformatory granodiorite, granodiorite,as as established establishedabove above and and by by earlier earlierworkers workers(Morey, (Morey,1978 1978and and references references therein). therein). The Theintrusive intrusiverelationships relationshipsbetween between the the Rockville Rockville Granite Granite and and other other granitoid granitoid rocks cannot be seen in outcrop. outcrop. Although Although geochronological geochronologicaldata dataimply implythat thatthe theRockville Rockvilleand and Reformatory Reformatory are are generally generally synchronous synchronous(as (as discussed discussedbelow), below),some someoutcrops outcropsof ofRockville RockvilleGranite Granitecontain containinclusions inclusionsof ofrock rockequivocally equivocally similar to to the theReformatory Reformatorygranodiorite. granodiorite. Geophysical Geophysical maps maps imply imply that that the thenon-magnetic non-magnetic similar Rockville Rockville Granite Granite forms forms an an eastward-thinning eastward-thinning wedge wedge that that overlies overlies the the more moremagnetic magnetic Reformatory 3);however, however, the the observations observationscontribute contributelittle little to to their theirrelative relative Reformatorygranodiorite granodiorite(Fig. (Fig.3); emplacementhistory. history. emplacement Porphyritic dikes are inferred inferred to to be either cut by or Porphyritic microgranite microgranite dikes or synchronous synchronous with with northeast-trending northeast-trendingdiabase diabasedikes. dikes.ItItisisinteresting interestingto tonote notethat thatthe the microgranite microgranitedikes dikescommonly commonly have have aa similar similar northeast-trending northeast-trendingdiabase diabase dike dike near them. At At one one locality locality aa thin thin diabase diabase dike dike is is chilled chilledagainst againstthe theRockville RockvilleGranite Graniteon on one one side, side, but but retains retains felty-textured felty-textured plagioclase plagioclase against against the the contact contactwith withaaporphyritic porphyriticmicrogranite microgranitedike dikeon onthe theother, other,implying implyingthat thatthe themicrogranite microgranite was porphyrywas still stillhot hot when when diabase diabase was was emplaced. emplaced. The Thediabase diabasecontains containsabundant abundantxenocrysts xenocrystsof ofporphyryderived derived quartz and feldspar grains adjacent to this contact. These Thesetextures textures indicate indicate that that the the diabase diabasemay may be be comagmatic comagmaticwith with the the microgranite, microgranite, or or that that diabase diabase post-dates post-dates microgranite micrograniteonly only slightly. A northwest-trending diabase dike exposed in a quarry in Waite Park (Fig. F6 of slightly. A northwest-trending diabase dike exposed in a quarry in Waite (Fig. F6 stop stop descriptions) descriptions)unequivocally unequivocally cuts cutsand andisis chilled chilledagainst against aa small smallnortheast-trending northeast-trendingdiabase diabasedike. dike. If If this this northwest-trending northwest-trendingdike dikeisisrepresentative representative of of the the aeromagnetically aeromagneticallydefined defined dikes dikes having having the the same same orientation, orientation,they they are are the the youngest youngest intrusive intrusive rocks in the area. Temporal TemporalRelationships—Geochronologic Relationships~GeochronologicData Data All All the the intrusions intrusionsdescribed describedabove aboveare areinferred inferredto to be be Early Early Proterozoic, Proterozoic,with withthe theexception exception of somewhat equivocal dates. Unfortunately, of diabasic diabasicdikes dikesthat that cut cut the the granitoid granitoid rocks rocks and and yield somewhat Unfortunately, U-Pb data data are are rare, rare, and andfield fieldobservations observations together together with with Ar-Ar Ar-Ar and and K-Ar K-Ar dates dates make make much much of of the the emplacement emplacementhistory historyinferential. inferential.Reported ReportedU-Pb U-Pbdates datesof of1,770 1,770Ma Ma for for the the St. St. Cloud Granite, Granite, and 1,812 Â9Ma Mafor forboth boththe theRockville Rockvilleand andReformatory Reformatory(Goldich, (Goldich,pers. pers.comm., comm.,as asreported reportedin in and 1,812±9 Horan Horan and and others, others, 1987) 1987)are are consistent consistentwith with the the field field observations observationsthat that show show Reformatory Reformatory cut cut by St. St. Cloud Cloud Granite. Granite. Although Althoughnot notdated datedby by the the U-Pb U-Pb method, method, the Richmond granite has Nd and Pb isotope and trace element systematics consistent with and Pb isotope and trace element systematics consistent with it being Early Proterozoic (Spencer, (Spencer, 1987). 1987). Most Most controversial controversial are are the dates dates for diabasic dikes. Hanson Hanson(1968) (1968)gives gives K-Ar K-Ar wholewholerock ages northeast-trending diabase diabase dikes. dikes. Of these, the ages of 1280, 1280, 1460, 1460, and 1570 1570 Ma for the northeast-trending 1570 considered aa minimum consistent 1570Ma Ma date date is considered minimum age, age, and and some some of the dikes yield Pb isotope data consistent with northeastwith an an age age of approximately approximately1800 1800Ma Ma (Horan (Horan and others, 1987). 1987). Using Using these these data, data, the northeasttrending with enclosing enclosing granitic granitic rocks. rocks. By trending diabasic dikes may be more or less comagmatic with By contrast, contrast, Holm Holm and andLux Lux (1997) (1997)report reportAr-Ar Ar-Ar whole-rock ages of 1164±12 1164k12 Ma and 1190±9 1190±Ma two of of the thenortheast-trending northeast-trendingdiabase diabasedikes. dikes. Field relationships relationships do not permit us to to from two However, some field, geophysical, and unequivocally unequivocally resolve resolve these these contrasting contrasting age age dates. dates. However, and petrographic petrographicobservations observationsraise raisequestions questionsabout aboutthe theyounger younger(Keweenawan) (Keweenawan)emplacement emplacementdate. date. For example, example, nearly nearly all all of the diabase diabase dikes—including dikes-including those those dated dated by Holm and Lux (1997)— (1997)show alteration of mafic minerals to actinolite. The The northeast-trending northeast-trending dikes dikes in in the the St. St. Cloud Cloud District dikes exposed elsewhere elsewhere Districtare are only only weakly weakly to to non-magnetic, non-magnetic,in in contrast contrast with Keweenawan Keweenawan dikes that are strongly magnetic. Furthermore, paleomagnetic measurements on a limited suite of are strongly magnetic. Furthermore, paleomagnetic 10 10 �samples samples failed failed to to isolate isolate any any magnetization magnetization direction direction that that is is consistent consistent with with either either the the reversed reversed or normal normal directions directions typical typical of of Keweenawan Keweenawan dikes dikes (Val (Val Chandler, Chandler, unpub. data, Minnesota Minnesota Geological GeologicalSurvey). Survey).The Thegranites granitessurrounding surroundingthe thediabase diabasedikes dikesare are not metamorphosed, metamorphosed,implying implying that the the alteration alteration of of mafic mafic minerals minerals to to actinolite actinolite in the diabase diabase may be of of deuteric deuteric rather rather than than metamorphic origin. In Ar-Ar ages ages in in the the range range of of 1152-1199 1152-1199 Ma Ma may may indeed indeed Inthis thiscase casethe theAr-Ar reflect emplacement, related to the onset emplacement, or alternatively alternatively a weak metamorphic metamorphic overprint related onset of of Keweenawan different ages of northeastnortheastKeweenawanigneous igneousactivity activityto to the the east. A A third third scenario scenariois is that two different trending trending dikes dikes exist; exist; however, however, no systematic systematic differences differences between dikes of this trend have been observed observed in the field field or during during subsequent subsequent petrographic and geochemical study. The The apparent apparent conflict conflict of of dates dates and and observations observationsfrom from diabasic diabasic and and quartzofeldspathic quartzofeldspathicdikes, dikes,and and uncertainties uncertainties about the age age of of other other plutonic plutonic elements elements in in east-central east-central Minnesota, Minnesota, underscores underscores the need need for for modern modem U-Pb U-Pb zircon zircon or or baddelyite baddelyitedates. dates. Mafic microgranular microgranularenclaves-evidence enclaves-evidence for for magma magma mingling mingling Mafic Mafic microgranular microgranular enclaves that occur in many intrusions of the St. Cloud area are interpreted interpreted as as the the product product of of commingled, commingled, coeval felsic and mafic magmas. The Thetextural texturaland and mineralogical attributes of mafic mafic microgranular microgranular enclaves enclaves in the Rockville Rockville Granite Granite and and Reformatory rapakivitexture textureof of the the Rockville Rockvilleand and Richmond Richmondgranites, granites,are are Reformatorygranodiorite, granodiorite,and andthe therapakivi similar commingling of mafic and felsic magmas. Although similarto to features featuresattributed attributedelsewhere elsewhereto to the commingling Although some some of of the the enclaves enclavesmay may have have originated originatedby by the the reincorporation reincorporationof of chilled chilled intrusion intrusionmargins margins by upwelling upwelling magma, magma, textural texturalevidence evidenceclearly clearly shows shows that that some some of the the enclaves enclaves coexisted coexisted as as aa melt melt with with the the host host granite granite magma. magma. Textures Texturesimplying implyingcommingling comminglingof ofmafic maficand andfelsic felsicmagmas magmas beg the question: Under what conditions are these coeval yet disparate magmas generated? beg question: Under conditions coeval yet disparate magmas generated? The mingling mingling of of mafic mafic and and felsic felsic magmas magmas is is most likely likely to occur in regions where crustal melts are generated generatedby by underplating underplatingof of continental continentalcrust crust by mafic mantle-derived magma. Melt Meltgenerated generated by this process process and and in in aa quantity quantitysufficient sufficient to to accumulate accumulate at at the the base base of of the the crust crust can can become become fully (Cruden fully mobilized mobilized and and ascend ascend rapidly, rapidly, entraining entraining the underlying underlying mafic magma as it rises (Cruden and and others, others, 1995, 1995,and and references referencestherein). therein). We suggest suggest that that the the numerous numerous mafic mafic enclaves enclavespresent present in in the the 1812 1812 Ma intrusive intrusive suite suite give give evidence evidence that that melting meltingof of the the lower lower crust crust by mafic mafic mantle mantle underplating underplatinggave gave rise rise to to the the latelatetectonic tectonicsuite suiteof of granitic graniticintrusions, intrusions,during duringthe the waning waning compressive compressivestages stagesof of Penokean Penokeanorogeny. orogeny. Furthermore, Furthermore, the numerous numerous gabbroic to noritic intrusions such as that that associated associated with with the the Richmond Richmond granite granite (Fig. (Fig. 2) 2) may may represent represent mafic mafic end-members end-members of this same same late-Penokean late-Penokean suite suite of intrusions. intrusions. of In the case Masuite suite of ofpost-tectonic post-tectonic granites, granites, mantle mantle underplating underplating as the case of of the the —1770 -1770 Ma result of mantle (e.g., Holm Hoim and and Dahl, Dahl, 1996; Cruden mantle lithospheric lithospheric delamination (e.g., Cruden and andothers, others, 1995; Turner and others, 1992) may have generated the melts. In this model, delamination 1995; Turner and others, 1992) may generated In this model, delaminationand and thinning of the the orogenically orogenically overthickened overthickened crust allows hot asthenosphere to well up, up, raising raising the asthenosphere-lithosphere asthenosphere-lithosphereboundary and increasing the thermal input into into the the base base of of the the crust. This Thisprocess processisisattractive attractivebecause because granitic granitic melt melt generation is delayed until some 40-50 m.y. after the peak of orogenesis, orogenesis, coincident coincident with the time necessary for orogenic collapse and thinning of the mantle lithosphere thinning of the mantle lithosphere(Turner (Turner and and others, others, 1992). 1992). There are post-orogenic granites of the are several several lines of evidence which indicate that the post-orogenic St. Cloud area may have formed from crustal crustal underplating underplating by by high-temperature high-temperature mantle material material following following crustal crustal collapse collapse and and mantle mantle lithospheric lithosphericdelamination. delamination. - 11 �high temperatures temperatures 1. The The granite granite melts are are inferred by Spencer (1987) to have formed at high (800-1000°C), and and are nearly coeval with the (800-1000°C) the isotopically isotopically similar similar mantle-derived mantle-derived diabasic diabasic rocks rocks (Horan (Horan and and others, others, 1987). 1987). 2. The Theclose closeand andprobable probablecogenetic cogeneticassociation associationof ofthe theporphyritic porphyritic microgranite microgranitedikes dikes with diabase dikes. This This may may reflect reflect bimodal bimodal magma generation, a common feature of post-orogenic post-orogenic plutonic plutonic complexes complexeselsewhere elsewhere (Turner (Turner and and others, others,1992). 1992). 3. The Theemplacement emplacementofofgranite granitelags lagsbehind behindpeak peakorogenesis orogenesisby by—50 -50 Ma. 4. Holm 4. Holm and and others others (1998) (1998) concluded concluded from garnet garnet and and staurolite staurolite core-rim core-rim thermobarometric, geobarometric, geobarometric, and and thermochronologic thermochronologic studies studies (see following thermobarometric, section) that crust crust thickened thickened by the the Penokean Penokean orogeny orogeny remained remained so so for for50-60 50-60m.y. m.y. before collapse, collapse, which then may then have triggered sudden lower crustal melting. 5. Spencer Spencer(1987, (1987,p. p.174, 174,e.g.) e.g.) interpreted interpreted from from isotopic isotopic evidence evidence that the granite melts were generated at aa convergent convergent continental margin that recycled a source source material material with a short-lived crustal history. However, he allows for an extensional extensional environment environment superimposed superimposedon on an an earlier earlier orogenic orogenic event, event, to produce produce basic mantle mantle melts melts beneath beneaththe the crust to melt the crustal rocks. the crustal rocks. Thermobarometric data The significant significant proportion of igneous rocks, together with the regional staurolite grade of metamorphism of of the country rocks, implies implies that that outcrops outcrops in this area represent one of metamorphism of the the deepest exposed levels of the entire entire Penokean Penokean orogenic orogenic belt. belt. Holm Hoim and others (1998) recognized recognized deepest that Early Proterozoic country rock within the internal internal zone zone (Little (Little Falls Falls Formation) Formation) were were metamorphosed twice. Thermobarometric Therrnobarometricestimates estimatesindicate indicate that early, Penokean-age, garnetgrade (Ml) metamorphism occurred at pressures of 5-6 kbar and temperatures of 450-500°C 450-500°C. (Ml) metamorphism occurred at pressures Thermobarometric estimates metamorphism yield similar pressures, pressures, and and only only slightly slightly Thermobarometric estimatesof the M2 metamorphism temperatures (500-550°C) (500-550°C). This indicates plutons exposed exposed in in the St. higher temperatures indicates that Penokean plutons District were Cloud District were emplaced emplaced during during the the interim interim between between the the two metamorphic metamorphic events events at at 19-23 19-23 depths. The km midcrustal orogenic depths. The age age of of M2 M2 metamorphism must be older than the 1750Ma mica mica Ar/Ar Ar/Ar cooling cooling ages obtained obtained throughout throughout the the region region because because of of the the 300° 300°C closure closure 1760 Ma temperature of biotite Hoim and Lux, 1997;Holm Holm and and others, others, 1998). These These ages indicate indicate temperature biotite (Fig. (Fig. 5; Holm been reheated reheated to temperatures temperatures above 300° 300°C since since that that time. time. Five hornblende hornblende that the area has not been Ar/Ar dates obtained from central Minnesota are concordant with the 1760-1750 Ar/Ar 1760-1750 Ma mica mica temperatures dates. Hornblende Hornblendehas hasaa typical typical closure closure temperature temperature of 500°C, 500°Cwhich matches the temperatures obtained for M2 metamorphism (500-550°C). This is strong evidence that the rocks of the strong the metamorphism (500-550°C) remetamorphosed to to staurolite internal zone of the orogen in central central Minnesota were widely remetamorphosed grade during the same same event event responsible for for generating generating the post-tectonic magmas at 1770 1770Ma. Ma. 5-6 kbars kbars indicates indicates that little or or no no unroofing unroofing of of the the Penokean Penokean The M2 pressure estimate of 5-6 midcrustal root occurred occurred between between about about 1820 1820and 1770 1770 Ma. Emplacement Emplacement pressure estimates estimates using an igneous barometer indicate that some of the 1770 Ma post-Penokean plutons were intruded at 4.6 kbar pressures (17 km depth); depth); whereas, whereas, others were emplaced at lower pressures of 3.5 kbar, or about 13 km depth (Darrah, lower kbar, about 13 km depth (Darrah, 1996). 1996). These contrasting contrasting pressure estimates—derived estimatesÑderive from suites of rock tentatively inferred to be be comagmatic—indicate comagmatic-indicate that post-tectonic magma emplacement was synchronous with crustal uplift (Fig. (Fig. 6). 6). 12 �________ _________________________________________ Early Proterozoic Proterozoic tectonomagmatic tectonomagmaticmodel Our mapping observations and analytical results of the last five years indicate that there significant differences in the overall character of the & vs. -Penokean plutons are significant m-Penokean plutons(Table (Table that must be explained in any tectonic model. model. We believe these differences differences reflect two very 1) that tectonomagmatic settings; different tectonomagmatic settings; one that occurred at the end of orogenic orogenic belt construction, construction, and one during its demise demise approximately approximately 40-50 40-50 my later. (I)- ci) 4-- 0 0 "0- S I- a) E z 1800 Ml metamor hism Late- Penokean plutonism ) ) ) I I I II I I '1 11 j Ar/Ar, ArIAr,hornblende hornblende H Ar/Ar, mica McGrath gneiss dome dates S Ii' 1.1.1.1 ——l I 1700 I 1600 I 1500 AGE (Ma) Post-tectonic plutonism, M2 metamorphism metamorphism Figure Figure 5. Histogram Histogramof ofAr/Ar ArlAr dates dates from from the the EarlyProterozoic EarlyProterozoic of central Minnesota Minnesota (after Holm and Lux, 1996; 1996; Holm Holm and and others, others,1998). 1998). Figure 7 presents a Temperature (*C) (C) schematic synopsis of of our schematic synopsis our interpretation of pluton 300 400 500 600 300 400 the emplacement after compressive phase phase (Fig. (Fig. 7A) 7A) of compressive semi-brittle shears Penokean deformation in central n Rapid cooling Minnesota. The Richmond, Richmond, Reformatory, and Rockville-the Rockville—the Reformatory, 1770-1760 Ma "gray granites"—represent lower granites9'-represent \ 1 post-tectonic crustal crustal melts intruded into the the midcrust (20-22 km) km) of the midcrust (20-22 the Penokean orogen (Fig 7B). These These Penokean magmas were generated during generated during metamorphism Ml the waning stages stages of of Penokean Penokean compression hence, compression and 1 late-tectonic plutons developed a moderate magmatic fabric. fabric. Figure 6. Summary Summaryof of P-T-t P-T-t diagram diagram showing showing the relation The The evidence for (M 1and andM2), M2),plutonism, plutonism,and and forforbetween metamorphism metamorphism (Ml commingled commingled mafic mafic and felsic mation of semi-brittle shears in the internal zone of the these rocks indicates magmas in Penokena orogen Penokena orogen (modified (modifiedafter after Hoim Holm and and others, others, 1998). 1998). 13 13 �TABLE 1—Comparison post-Penokean intrusions intrusions 1-Comparison of late and post-Penokean TYPEIAGE TYPE/AGE Composition/Color Composition/Color LATE LATE PENOKEAN/—1812 PENOKEXNI- 1812 Ma Ma Granodiorite-granite——typically Granodiorite-granite-typically gray—with gray-with mafic maficenclaves enclaves POST-PENOKEAN/--1770 POST-PENOKEANI- 1770 Ma Granite Granite (alkali-feldspar (alkali-feldspargranite granite to to syenogranite)—typically syenogranitel-typically red— redwith with few few mafic mafic enclaves enclaves Magmatic Fabric Fabric Magmatic Moderately Moderatelydeveloped, developed, NE NE orientation, orientation,commonly commonlyflat flat Very weak to absent absent Pluton Pluton Shapes Shapes Broad Broad and and irregular irregular Dikes, Dikes, sills, sills, and and larger larger plutons plutons with a tendency for for NE orientation orientation Geophysical Characteristics Characteristics Variable Variable -- moderate moderate and busy busy magnetic magnetic signature; signature;dense dense Typically non-magnetic, non-magnetic, pronounced pronounced gravity gravitylows lows Depth Depth Emplaced Emplaced 20-22 20-22 km km(5-6 (5-6 kbar) kbar) 13-17 13-17 km (3.5-4.5 (3.5-4.5 kbar) kbar) Associated Metamorphism Metamorphism Garnet Garnet grade grade Ml M 1(5-6 (5-6 kbar) kbar) Staurolite M2 (5-6 (5-6 kbar) kbar) Staurolitegrade gradeM2 Solid-state Solid-state Fabric Fabric Cut Cut by by semi-brittle semi-brittleshears shears Cut Cut by semi-brittle semi-brittle shears shears that that crustal crustal underplating underplatingmay may have have played played an an important important role in their generation. However, However, these these crustal melts were not able to penetrate the stronger upper crust of the orogen, but instead not able to penetrate the stronger the orogen, but instead formed formed irregular irregularshaped shaped plutons plutons at at depths depths of of 20-22 20-22 km km where where they remained for approximately approximately 40 Penokean orogeny 40 m.y. The Theperiod period of of tectonic tectonic quiescence quiescenceand and amagmatism amagmatismafter after the Penokean orogeny (during (during the the period period approximately approximately1812-1770 1812-1770Ma) Ma)was wasterminated terminatedby byaashort-lived short-livedperiod periodof of post-tectonic post-tectonic magma magma generation, generation,metamorphism, metamorphism,and and rapid rapid midcrustal midcrustal uplift uplift and and cooling coolingat at about about 1770 1770Ma. Ma. This This abrupt abrupt episode episode may may have been triggered by mantle-lithospheric mantle-lithospheric delamination delaminationthat that would would have midcrustto to temperatures temperatures have caused causedboth bothmelting meltingof ofthe thelower lowercrust crust(Fig. (Fig. 7C) 7C)and and heating heatingof of the the midcrust above above 500°C 5OO0Cduring during M2 M2 metamorphism. metamorphism. This Thisthermal thermalheating heatingsoftened softenedthe the overthickened overthickenedcrust, crust, causing At this this time time significant significant unroofing occurred and shears shears causing itit to collapse collapse and and thin (Fig. 7D). At formed as as the the rocks rocks cooled cooled and and became more brittle. The TheSt. St.Cloud CloudGranite, Granite,Foley Foley batholith, batholith, and associated associated plutons—the plutons-the "red, "red, massive massive granites"—were granites9'-were advected advected during during this this event event into into uplifting orogenic shortening uplifting crust crustthat that was was extending extendingNW-SE, NW-SE, parallel parallel to to the the previous orogenic shorteningdirection. direction. Early Proterozoic Proterozoic diabasic diabasic and and quartzofeldspathic quartzofeldspathic dikes apparently lagged behind a bit bit and and were emplaced just after after brittle brittle shears shearsformed, formed, using using the the shears shearsas as conduits conduits(Fig. (Fig. 7E). 7E). were emplaced ACKNOWLEDGMENTS ACKNOWLEDGMENTS This This field field guide guideis is an an outgrowth outgrowth of studies studies by the Minnesota Geological Survey Survey (MGS) (MGS) that were were supported supportedby by several several programs programs of the State Legislature. The The Stearns StearnsCounty County segment segment (Boerboom and others, 1995, 1996a) was funded through the Legislative Commission 1995, 1996a) was funded through the Legislative Commission on on Minnesota Resources; funding for drilling drilling and and mapping mapping east of of St. St. Cloud Cloud (Jirsa (Jirsaand andothers, others, 1995a) was made available available on on recommendation recommendation of the the Minnesota Minnesota Minerals Minerals Coordinating Coordinating Committee. On-going On-goingmapping mapping and and analytical analytical work work in in both areas areas has been supported supported by the MGS. was supported supported thermobarometricand andgeochronologic geochronologicwork work of of Daniel Daniel Holm and others was MGS. The Thethermobarometric by a National Science Foundation grant (EAR-9304070). We are grateful to Mr. Frank Lyons Science We and and the the Meridian MeridianAggregates AggregatesCompany Companyfor foraccess accessand andguidance guidancein in the theaggregate aggregatequarry, quarry,and andfor for permission to to visit visit their their developing developingsouthern southern property property (before (before the the natural natural outcrops outcropsare aregone!). gone!). A very special special thanks thanks to to Charles Charles Muehlbauer Muehlbauer and and other other employees employees of the the Cold Cold Spring SpringGranite Granite Company Company for for assistance, assistance,advice, advice, samples, samples, permission, permission, and and guidance guidance (on their their day day off!). off!). 14 �___ Schematic Schematic N ++ + — Timing Timing Penokean orogeny Penokean orogeny Mj Mi metamorphism metamorphism \ crust cmst mantle- B s* s Penokean Penokean highlands Orogenic Orogenic features features —1850Ma Ma -1850 strong upper ccrust wt —_ Late-Penokean magma emplacement emplacement _..______S2022 datum 20-22 km depth depth datum mantle km manti —1812Ma Ma -18l.2 basaltic underplating? ---- ———, I --—-—- M2 metamorpinsin metamorph Generation Generation of post-tectonic post-tectonic magmas in the lower crust 1775-1770 Ma 1775-1770 Ma Mantle delamination, basaltic underplating? underplating? D E —- H — - - a- a- magma emplacement emplacement Post-tectonic magma Crustal unroofing/cooling crustal ~ o f ~ / c o o ~ Semi-brittle shears shears developed Semi-brittle Ma km depth depth datum datum 1770-1750 \20-22 20-22 km 1770-1750 Ma Diahase and QFP dikes <1750 MaKeweenawan? —. post orogenic plutons, plutons, Figure 7. Proposed Proposed tectonomagmatic tectonomagmaticmode mode for for generation generation of late- and post central Minnesota. Minnesota. Heavy dashed lin un represents 20internal zone of the Penokean orogen, central 22 km depth datum prior to crustal crustal unroofing unroofing (B (B and andC). C). Crustal Crustal unroofing unroofing and and exhumation exhumation causes upwarping upwarping of this this datum datum livel live1 in (D (D and E). E). 15 �REFERENCES FWFERENCES CITED CITED B arbarin, B., B., and and Didier, J., 1991, Macroscopic features of mafic microgranular enclaves, Barbarin, enclaves,in in Didier, J., and Barbarin, Barbarin, B., eds., Enclaves and granite petrology: Elsevier, Elsevier,p. p. 253-262. 253-262. in Meyer, Meyer, G.N., G.N., Boerboom, T.J., 1996a, 1996a, Precambrian geology of Steams S t e m s County, County, Minnesota, in and Swanson, supplement to the Geologic Atlas, Stearns Steams County, Swanson,L., eds; eds; Text supplement County, Minnesota: Minnesota: Survey County CountyAtlas AtlasSeries SeriesC-10, C-b, Part C, p. 1-6. Minnesota Geological Survey Boerboom, T.J., 1996b, Boerboom, 1996b, Southward Southward extension of the Penokean terrane through Stearns Steams County, County, Part 1- programs and abstracts; central Minnesota: Institute on Lake Superior Geology, Part 42nd annual annual meeting, meeting, Cable, Cable, Wisconsin. Wisconsin. Boerboom, T.J., Setterhoim, f Boerboom, Setterholm,D.R., D.R., and andChandler, Chandler,V.W., V.W., 1995, 1995, Bedrock geologic map, plate 2 oof GeologicAtlas Atlasof ofStearns SteamsCounty, County,Minnesota: Minnesota: Minnesota Minnesota Meyer, G.N., project manager, Geologic Geological Survey County County Atlas AtlasSeries SeriesC-10, C-b, Part A, scales 1:200,000 and 1:100,000. Part scales 1:200,000 and 1:100,000. A.R., Koyi, H., and Schmeling, Cruden, A.R., Schmeling, H., 1995, 1995, Diapiric basal entrainment entrainment of mafic mafic into into 321-340. felsic magmas: Earth Earthand andPlanetary PlanetaryScience ScienceLetters Letters 131, 131, p. 321-340. internal zone zone of of the the Early Early Proterozoic Proterozoic (1870Darrah, K.S., 1996, 1996,An exhumation history of the internal 1830 Ma.) Penokean orogenic belt, central central Minnesota: Minnesota: Unpublished Unpublished M.S. M.S. thesis, thesis, Kent Kent State State University, University, 99 99 p. Hanson, G.N., 1968, 1968, K-Ar ages for hornblende hornblende from granites and gneisses and for basaltic intrusives in Minnesota: Minnesota 8, 20 p. Minnesota Geological Geological Survey Survey Report of Investigations 8,20 Hoim D.K., and Selverstone, synkinematic Holm Selverstone,J., 1990, 1990,Rapid growth growth and strain rates inferred from synkinematic garnets, garnets, Penokean orogeny, Minnesota: Geology, Geology, v. v. 18, 18, p. 166-169. 166-169. Hoim D.K., and Dahl, delamination an an important important process process in the Holm Dahl, P.S., P.S., 1996, 1996, Was lithospheric delamination evolution of Early Proterozoic collisional orogens? Institute on Lake Superior Institute on Lake Superior Geology, Part 11- programs and abstracts; 42nd 42nd annual annual meeting, meeting, Cable, Cable, Wisconsin. proposed for gneiss gneiss dome dome development development Holm D.K., and Lux, D.R., 1996, 1996, Core complex model proposed during collapse v.24, 24, no. no. during collapseof of the the paleoproterozoic paleoproterozoicPenokean Penokeanorogen, orogen,Minnesota: Minnesota:Geology, Geology,-v. 4, p. 343-346. Minnesota and Holm D.K., and and Lux, Lux, D.R., 1997, 1997,Results Results of of Ar/Ar ArIAr dating of dikes in central Minnesota and the the Minnesota River Valley: Valley: Institute on Lake Lake Superior SuperiorGeology, Geology,Part Part11-program - program and abstracts; Minnesota 43rd annual annual meeting, meeting, Sudbury, Sudbury, Engineers, Engineers, Reston, Reston, Va., 141 141 p. Holm D.K., D.K., Darrah, Darrah,K.S., K.S., and andLux, Lux,D.R., D.R., 1998, 1998,Evidence Evidencefor forwidespread widespread—1760 -1760 Ma metamormetamorphism and rapid crustal (1870-1820 crustal stabilization stabilization of the early Proterozoic (1 870- 1820 Ma) Penokean orogen, 298, p. 60-81. orogen, Minnesota: American AmericanJournal Journal of of Science, Science,vol ~01298, 60-8 1. Horan, M.F., M.F., Hanson Hanson G.N., G.N., and Spencer, K.J., 1987, Pb Pb and Nd isotope and trace element Spencer, K.J., element constraints constraints on on the the origin origin of of basic basic rocks rocks in an early Proterozoic Roterozoic igneous igneous complex, Minnesota: Precambrian PrecambrianResearch, Research,v. v. 37, 37, p. 323-342. 323-342. Irvine, W.R.A., 1971, A guide guide to to the the chemical chemical classification classification of of the the common common Irvine, T.N., and Baragar, W.R.A., 1971, A volcanic rocks: Canadian Journal of Earth Sciences, v. 8, p. 523-543. 16 �Jirsa, M.J., Chandler, J.M., and Meints, J.P., J.P., 1995a, Bedrock geologic map of Chandler, V.W., V.W., Cleland, J.M., east-central Minnesota: Minnesota east-central Minnesota: Minnesota Geological Geological Survey Survey Open-file Open-file Report 95-1, 95- 1, scale scale :100,000. 11:100,000. Jirsa, T.J., 1995b, Jirsa, M.J., Chandler, Chandler,V.W., V.W., and Boerboom, T.J., 1995b, Extension of the Wisconsin Magmatic Magmatic Terranes into the Minnesota segment of the Penokean orogen: orogen: Institute Institute on Lake Lake Superior Geology, Part 1- programs and abstracts; 41st 41st annual annual meeting, Marathon, Marathon, Ontario. Ontario. test drilling and mapping in east-central Jirsa, M.J., and and Chandler, Chandler, V.W., V.W., 1997, Scientific test east-centralMinMinnesota, 1994-1995: 1994-1995: Summary of lithologic results: Minnesota Geological Survey Information Circular Circular 42, 42, 105 105p. Johnson, M.C., east-central MinJohnson, M.C., 1978, 1978, Mineral Mineral chemistry chemistry of four quartz-bearing monzonites in east-central Minnesota: Unpublished UnpublishedM.S. M.S. thesis, thesis,University Universityof of Iowa, Iowa, 227 227 p. Miyashiro, A., 1978, Nature of alkalic volcanic volcanic rock rock series: series: Contributions Contributions to mineralogy mineralogy and petrology, 1-104. petrology, v. v. 66, 66,p. p. 991-104. Morey, G.B., 1978, Middle Precambrian Precambrian stratigraphic stratigraphic nomenclature nomenclature for east-central east-central 1978, Lower and Middle Minnesota: Minnesota 52 p. MinnesotaGeological GeologicalSurvey SurveyReport Report of of Investigations Investigations 21, 21,52 Morey, G.B., Olson, B.M., and Southwick, Southwick, D.L., 1981, 1981, Geologic map of Minnesota, Minnesota, east-ceneast-central Minnesota, bedrock geology: Minnesota Geological Survey, scale 1:250,000. Minnesota, Minnesota Geological Survey, scale 1:250,000. Muehlbauer, C.J., and Fuchs, J.P., J.P., 1997, 1997, Modern dimension stone quarrying and fabrication fabrication technologies, in Labuz, J.E, J.F.,ed., ed.,Degradation Degradationof ofnatural naturalbuilding buildingstone: stone:proceedings proceedingsof of22 technologies, in sessions sponsored by the Rock Mechanics Committee of the Geo-Institute Geo-Institute of the Amerisessions can Minneapolis, can Society Society of Civil Civil Engineers Engineers in conjunction conjunction with the ASCE Convention in Minneapolis, Minnesota, Reston,Va., Va.,141 141p. p. Minnesota,October October 5-8, 5-8, 1997: 1997:American AmericanSociety SocietyofofCivil CivilEngineers, Engineers,Reston, Southwick, D.L., Morey, G.B., and McSwiggen, P.L., 1988, Geologic Geologic map map (scale 1:250,000) Southwick, 1:250,000) of the Penokean orogen, accompanying text: text: Minnesota orogen, central and eastern Minnesota, and accompanying Minnesota Geological 25 p. Geological Survey Survey Report Report of of Investigations Investigations37, 37,25 p. Spencer, K.J., 1987, constraints on the sources of granites in 1987, Isotopic, Isotopic, major, and trace element constraints an 1800 near St. Cloud, Minnesota: 1800 Ma-old Ma-old igneous igneous complex complex near Minnesota: Unpublished Unpublished Ph.D. Ph.D. dissertation, dissertation, SUNY-Stony SUNY-Stony Brook. Brook. Streckeisen, A chemical chemical approximation to to the modal QAPF Streckeisen, A.L., and Le Maitre, Maitre, R.W., R.W., 1979, A classification classificationof of the the igneous igneousrocks: rocks:N. N. Jb. Jb. Miner. Miner. Abh., Abh., v. v. 136, 136, p. 169-206. 169-206. Thiel, G.A., and Dutton, C.E., 1935, monumental stones of of 1935, The architectural, structural, and monumental Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey Bulletin Bulletin 25, 25, p. 63-87. Turner, Sandiford, M, and Foden, J., 1992, Some geodynamic geodynamic and compositional compositional constraints constraints Turner, S., Sandiford, on "postorogenic" magmatism: magmatism: Geology, Geology,v.v.20, 20,p.p.93 931-934. 1-934. Van Schmus, W.R., W.R., and Bickford, M.E., M.E., 1981, Van 1981, Proterozoic chronology and evolution of the the Midcontinent region, Precambrian plate in Kroner, Kroner, A., ed., Precambrian plate tectonics: tectonics: New New Midcontinent region,North North America, America,in York, Elsevier, p. 261-296. 261-296. 17 �FIELD FIELD TRIP TRIP STOPS STOPS The shown on on figure figureFFl. The general general locations locations of all stops are shown l. A A more more detailed detailed location and geologic geologic map map is is included included with each each stop stop description. description. The Thevarious various rock rock units units are are fully fully described in in the the field field trip trip introduction, introduction,and and only only the the details details pertinent pertinent to to the the individual individualsites sites described are given given below. below. are I A KILOMETERS MILES 1 ------- 1 0 0 2 1 1 3 4 2 8 6 - 3 4 7 8 5 0 10 6 Figure Fl. Fl. Locations Locationsof offield fieldtrip trip stops. stops. STOP STOP 1. 1. STEARNS STEARNSCOUNTY COUNTYQUARRY QUARRY PARK • Location: Location:T.T.124 124N., N.,R.R.2828W., W.,Section Section19 19DDA. DDA. • St. St.Cloud Cloud(red) (red)Granite, Granite,diabase diabasedikes, dikes,semi-brittle semi-brittleshears shearsin in granite, granite, outcrops. glacially polished outcrops. This This area area contains containsseveral severalinactive inactivequarries quarries(Figs. (Figs. F2 F2 and and F3), F3), and and was was recently recently made made into into a unique unique county county park. The Thepark parkprovides providesexcellent excellent exposures exposures in which which one can can view view the the relationship between the Reformatory granodiorite and the St. Cloud Granite, as well as several relationship between the Reformatory granodiorite and the St. Cloud Granite, as well as several diabase dikes. Although Althoughthe thepark parkhas hasexposures exposuresof ofboth bothnortheastnortheast- and andnorthwest-trending northwest-trending diabase dikes, we will will only only see seenortheast-trending northeast-trending ones and St. St. Cloud Cloud Granite, Granite, due due to to time time constraints. constraints. 18 18 �________-- Diabase dike (single line for thin dike; dashed where inferred) Porphyritic microgranite Outcrop IA Ii —450 32 30 .4 QUirri - I DM7 4 0 092 -. / C J -- — z I /Y kI -'zr? )( (JU :-- Q'II. rI 0 -'S 1094 - '':i • t074 p - ç— — I c..j Â¥ Mhi =;, ON jl FÑ 1 3.',, 3 1,- ' 6282 kilLS MILS 15 15MIS MgLS I ,' i 00 ^ ^ ^ - - . 2 - - , 0 1000 1000 , È I - 1 -0 I1 - - 1000 1 2000 200C 3000 3000 4SOO 4001) 5 00 .55 - - - - - , 1 MILC MILE - - 5000 5000 6000 7000FEfT 701.51 FEri 1 I KILOMETRE 11KILOMETRE i CONTOUR CONTOUR INTERVAL INTERVAL 10 10FEET FEET DOTTED LINES RPR.SNT 5.FOO1 CONTOURS DOTTED LINES REPRrSFNT 5-FOOT CONTOURS Figure FigureF2. F2. Map MapofofWaite WaitePark, Park,southwest southwestof ofSt St.Cloud, Cloud,showing showinglocations locationsof ofoutcrops outcropsand anddikes dikes in 1:24,000. in parts parts of of the theSt. St.Joseph Joseph and andSt. St.Cloud Cloud 7.5-minute 7.5-minute quadrangles. quadrangles. Scale Scalereduced reduced from from 1:24,000. 19 �2, and 3. Scale Figure F3. Location Locationmap map for for stops stops 1, 1,2, Scale1:24,000; 1:24,000;St. St. Cloud Cloud 7.5-minute quadrangle. quadrangle. At least seven different different quarry companies were active in what is now the park area—all area-all utilizing the St. Cloud Granite. Production Production started in the early 1900's, peaked in about 1940, variety of of "red" "red" and ceased in the mid-1950's. The Thestone stonethey they produced was marketed under a variety "Mahogany Red," Red," "Indian "Indian Red," Red," and and"Rose "Rose Red." Red." Most of names, including "North Star Red," Red," "Mahogany the pits were (and (and still still are!) 60 60 to to more more than 100 100 feet feet deep deep (Thiel (Thiel and Dutton, Dutton, 1935). 1935). PLEASE PILES ARE ARE NOT NOT PLEASE EXERCISE EXTREME CAUTION! THE THEQUARRY QUARRY PILES STABLE, AND AND THE THE PITS PITS ARE ARE DEEP! DEEP! parking area. From Follow the park road south from the park entrance to the parking From here here walk walk trail on on the the right right (west) (west)that thatleads leadsup upto toquarried quarriedarea. area. Proceed 400 feet south on a dirt road to a trail up this trail to the edge edge of of aa small small quarry quarry and and Stop Stop 1A 1A (Fig. (Fig. F4). F4). 20 �Diabase Dike St. Cloud (Red) Granite Reformatory (Grey) Granite Quarry Figure F4. Outcrop Outcrop map map of Stop 1A and lB. IB. STOP lA—Three-dimensional 1A-Three-dimensional view view of diabase and quartz-epidoteshears shearsin inSt. St.Cloud Cloud STOP and quartz-epidote Granite. Granite. Directly Directlywest, west, across across the the rubble rubble in the pit, is an excellent exposure in pit, is an excellent exposure of a northeast-striking, northeast-striking, steeply steeply southsouthdipping, dipping,meter-thick meter-thickdiabase diabasedike dikethat that cuts cuts St. St. Cloud Cloud Granite. Granite. The Thedike dikewas was sampled sampledfor for both both paleomagnetic paleomagneticstudy study and and Ar/Ar ArIAr dating dating (see (seeintroduction). introduction). This This is is typical typical of of the the diabases diabases in in the the area, area, having having chilled chilled margins margins and and Diabase dikes ~iab&e dikes Quartz-epidote Quartz-epidoteshears shears scattered cm-scalexenoliths xenolithsof ofgranite granite scatteredcm-scale wallrock. wallrock. The Thegranite graniteadjacent adjacentto tothe the Figure F5. F5. Stereographic Stereographicprojections projectionsof oforientations orientations Figure dike dike contains contains numerous numerous thin, thin, diabase dikes dikes (A) and and quartz-epidote-filled quartz-epidote-filledsemiserniof diabase northeast-trending, northeast-trending, quartzquartz- and and brittle brittle shears shears(B). (B). epidote-lined, epidote-lined,semi-ductile semi-ductileshears shearsthat that 21 �truncated by by and are probably probably in in part part occupied occupied by by the the diabase diabase dike. dike. This are clearly truncated This nearly nearly coincident trend typical of the regional pattern shown on the stereoplots stereoplots in coincident trend of dikes dikes and and shears shears is typical figure F5. Two Two other other diabase diabasedikes, dikes, up up to to 22 meters meters thick, thick, can can be be seen seen north north of of this this dike. dike. Although the majority of blocks in the the waste waste rubble rubble before you are are indigenous, indigenous, several several exotic rock types are present, including including blocks of Reformatory granodiorite granodiorite (gray) (gray) that we we will will see in place at Stop 3. The Reformatory granodiorite is presently extracted from a quarry The Reformatory granodiorite is presently extracted quarry just by the Cold Spring Granite south of the city of of St. St. Cloud, Cloud, marketed marketed as "Charcoal "Charcoal Granite" Granite" by Company. The Company. The maroon-colored maroon-colored granite granite blocks are probably probably imported from quarries near South Dakota. Dakota. Blocks of grayish-pink, complexly banded Ortonville, Minnesota and Milbank, South Morton gneiss are are from from the the Minnesota Minnesota River River Valley. Valley. Several Several other blocks of pink granite granite and and pale pink gneiss are from unknown localities, but are not indigenous. Return to the dirt road, Return road, and and walk walk south south (to (to the the right) right) approximately approximately 250 feet to to the the switchback right. Note the spheroidally-weathered granite along along the the switchback trail on the right. spheroidally-weatheredoutcrops of red granite west (right) edge of the road between the two trails. The The aggregate aggregatecovering covering the the switch-back switch-back trail illustrates illustrates one of the many uses of crushed stone from the Meridian Aggregates one stone Aggregates Quarry Quarry that that polished outcrop on on the the north north we will visit at Stop 2. At At the the next quarry proceed to a glacially polished (right) side of the pit. pit. STOP Granite. STOP 1B—Diabase 1B-Diabase dike in St. Cloud Granite. The diabase dike splits and rejoins along its length, and has small, 4-10 cm, north-south 'jogs' at at its its northeast northeasttrend. trend.There Thereare areno noobvious obviouscross-fractures cross-fracturesin in the the granite granite that that might might have have controlled the these small small offsets, offsets, making them somewhat enigmatic. xenoliths, as well as This stop stop affords affords a better look look at the chilled dike margins and granite xenoliths, of granite wallrock walirock torn torn partly partly loose loose during during dike dike emplacement. emplacement. Granite xenoliths in slivers of various stages of assimilation assimilation can be seen, seen, and xenoliths xenoliths are concentrated concentrated in the the center center of of the the ±0.5 main dike, presumably by flow entrainment. Also Also visible here, with some searching, are ±0. cm amygdules filled with fibrous fibrous actinolitic actinolitic amphibole. side, where where two two subparallel, subparallel, northeast-trending northeast-trending diabase Walk around the quarry to its south side, diabase approximately 3 m thick—the this thick-the maximum thickness of dikes in this dikes occur. These These dikes dikes are approximately set. They They are are cut cut by by thin, thin, white, white,silicic, silicic,and and sugary-textured sugary-textured veinlets veinletsthat that emanate emanatefrom from the the dike dike margins and pinch out in the dike interiors. The Theveinlets—interpreted veinlets-interpreted as partial melts of of the the presumably because because narrower wallrock granite—are granite-are rarely rarely present present in in dikes dikes less less than 2.5 m thick, presumably narrower dikes were not capable of heating the wallrock to temperatures sufficient for melt generation. polished outcrop mineralogy and The polished outcropsurface surfaceprovides provides aa good good look look at at the mineralogy and coarse coarse texture texture of black and white white mottled, mottled, red red color. color. The the St. Cloud Granite, characterized characterized by its distinctive black The imparted by microcline, red color is imparted microcline,the the black black by hornblende hornblendeand and minor minor biotite, biotite, and and the the white white by by saussuritized plagioclase. The The granite granite has has aa very very weak weak trachytoid trachytoid foliation, foliation, via alignment alignment of blocky feldspar and hornblende crystals. Where Where discernible, discernible, this fabric parallels the granite granite coarse-grained phase) phase) dike or sill margins. This This granite granite has has an amazing amazing lack of pegmatite (very coarse-grained and a preponderance preponderance of homblende hornblendeas as the the mafic mafic phase. Glacial features are are well well displayed displayed here here and and include include polished polished outcrops, outcrops, striations, striations, and and differential diabase/granite contacts. contacts. Most Mostof of the the subsurface subsurfacebedrock bedrock in in Minnesota Minnesota differential scouring scouring of the diabaselgranite is covered by variable variable thicknesses thicknesses of of weathered weathered bedrock bedrock residuum (saprolite) (saprolite) that has has been been highs by by glacial scouring. scouring. Saprolite stripped away from bedrock topographic highs Saprolite developed developed on on 22 22 �granite is typically pale gray-green. Many Many of of the the active active quarries in this area have exposures of granite of this saprolite saprolite along along the the margins margins of of the the pits. pits. interesting hydrologic hydrologic observation is the approximately 10-foot 10-foot difference in water An interesting level level between this pit and the small one to the south. The The two two quarries quarries are are separated separated by little little more than than the the diabase diabase dike's dike's width, width,and and the the hydrologic hydrologic gradient gradient exists exists despite despite the the abundance abundanceof of more cross-fractures cross-fractures in in the the diabase. diabase. Addendum Addendumto toStop Stop11 The The sketch sketch map shown shown on figure figure F6 is included for those who wish to visit the park to Of particular particularinterest interestisis aa pit pitatatthe theeast eastside sideof ofthe thepark park view other exposed geologic features. Of northwest-trending diabase to the the where aa northwest-trending diabase dike dike cuts cuts aa northeast-trending northeast-trendingone. one. The next pit to northwest of that thatshows showsSt. St.Cloud CloudGranite Granitehaving havingmany manyangular, angular,meter-scale meter-scale xenoliths xenoliths of of Reformatory Reformatory granodiorite—typical granodiorite-typical of of regional regional intrusive intrusiverelationships relationships between between the the two twounits. units. Diabase Dike St.Cioud(red) Granite ' Reformatory(gray) granodiorite j Mixed St. Cloud Granite and Reformatory granodiorite .# Cross—country ski trails Figure Figure F6. F6. Sketch Sketchmap mapofofthe theQuarry QuarryPark Parkshowing showingoutcrop outcropdistribution distributionand andsimplified simplifiedbedrock bedrock geology. geology. Modified Modifiedfrom fromStearns SteamsCounty CountyPark Parkwinter wintertrail trailmap. map. 23 23 �STOP STOP 2. 2. MERIDIAN MERIDIANAGGREGATES AGGREGATESQUARRY QUARRY • Location: Location:T.T.124 124N., N.,R.R.28 28W., W.,south southhalf halfofofSection Section18. 18. • Quarry Quarryoverlook, overlook,crushing crushingfacilities, facilities,restrooms. restrooms. Due to constraints constraints of time, time, safety, safety, and group size, we will will not not go go into into the the Meridian Meridian Aggregates Aggregates quarry, quarry, but we we will will get get an an excellent excellentview view of of the the pit pit from froman anoverlook overlookpoint. point. 1.2 million million tons tons of of crushed crushed Meridian Aggregates Aggregates Company produces an average average of 1.2 The Meridian rock aggregate aggregate per year. Mining Miningand andcrushing crushingoperations operationsrun run 77 months months of of the the year, year, although although stockpiled stockpiledproduct productisis shipped shippedyear-around. year-around. This Thisquarry quarryutilizes utilizes the the complex complex mixture mixture of igneous igneous rock rock types types present present in in the the pit, pit, mainly mainly the the Reformatory Reformatory granodiorite granodiorite and St. Cloud Red Granite, and and lesser lesser proportions proportions of of diabase diabaseand andquartz-feldspar quartz-feldsparporphyry porphyry dikes, dikes, such such as as will will be be seen seenatat Stop Stop 3. 3. Unlike Unlikedimension dimensionstone stonequarries, quarries,joints jointsand andfractures fracturesin inthe therock rock are are not not detrimental— detrimentalblast blast away! away! Quarrying Quarryingmethods methodsinvolve involvedrilling drillingand andblasting, blasting,primary primary crushing crushingin inaagyratory gyratory crusher, crusher, and and secondary secondary crushing crushing to various sizes. The The primary primary use use of of the the aggregate aggregate is is railroad railroad ballast, ballast, followed followed by by road road construction construction and and other other uses, uses, including including breakwater breakwater walls, decorative decorative stone, stone, and and driveway drivewaymaterial. material. A A substantial substantialfraction fractionof of the therock rockin in this this quarry quarry consists consistsof of fine-grained fine-grainedgray gray granodiorite granodiorite interpreted interpreted by by earlier earlierworkers workersas asinclusions inclusionsofofmetamorphosed metamorphosedand andmetasomatically-altered metasomatically-altered country rock in in the the Reformatory Reformatory granodiorite. granodiorite. Although Although there there are are undoubtedly undoubtedly some some small small xenoliths, finexenoliths,textural texturaland andgeochemical geochemicalevidence evidenceindicates indicatesthat thatthe thebulk bulkof ofthis thisgray graymaterial materialisisfinegrained grained border border phase phase of of the the Reformatory Reformatory granodiorite. granodiorite. If If the the light lightconditions conditionsare areproper, proper,aacross-section cross-sectionisisvisible visibleon onthe thefar farwall wallof of the the pit pit showing showing fresh fresh rock, rock, transitionally transitionallyoverlain overlainby weathered weathered bedrock residuum residuum (saprolite), (saprolite),overlain by glacial deposits. deposits. STOP STOP3. 3. MERIDIAN MERIDIANAGGREGATES AGGREGATESCOMPANY—SOUTH COMPANYÑSOUT PROPERTY PROPERTY • Location: Location:T.T.124 124N., N.,R.R.2828W., W.,Section Section19 19AB. AB. • St. quartzSt.Cloud Cloud(red) (red) Granite, Granite,aplite, aplite, Reformatory Reformatory granodiorite, granodiorite,diabase diabase dikes, quartzfeldspar feldsparporphyry porphyry(aka (akaporphyritic porphyriticmicrogranite) microgranite)dikes. dikes. This This stop stopisislocated locatedin inan anarea areaof of planned planned large-scale large-scalemining mining like like that that in in Meridian's Meridian's main main pit pit (Stop (Stop2) 2) just across acrossHighway Highway 23 23 to to the the north. north. There Thereare areaafew fewsmall smallabandoned abandonedquarries quarrieson on the the property, property, but but most most of of the the outcrops outcrops are natural (Fig. F7). Permission Permission must must be be obtained obtainedfrom from Meridian Meridian Aggregate Aggregate Company, Company, which has kindly kindly granted granted access access for for this this trip, trip, before before entering entering their their property, property,but but these these outcrops outcropswill will soon soonbe be mined mined out. out. STOP Cloud (red) (red)Granite Granite intrusive intrusive into into Reformatory Reformatory STOP3A—NE-trending 3A-NE-trending dikes dikes of St. Cloud (gray) (gray)granodiorite. granodiorite. The TheSt. St.Cloud CloudGranite Graniteisisnot notaadistinct distinctsingle singlebody, body, but but rather rather an an intricate intricate series series of of vertical vertical and and horizontal horizontal dikes dikes emplaced emplaced into into the Reformatory granodiorite. As As represented represented in this series series outcrops, outcrops,the theintrusions intrusionshave havecomplex complexgeometries geometriesand andvaried variedthicknesses thicknessesfrom fromfew fewcentimeters centimeters to to more more than than 50 50meters. meters. 24 �3B-A variety units, including including (oldest (oldest to toyoungest) youngest) STOP 3B—A variety of of intrusive rock units, St. Cloud Cloud Reformatory granodiorite, St. Cloud Granite, aplite related to the St. Granite, Granite,and anddiabase. diabase. The aplite aplite occurs occurs as as small, small,irregular irregularpod-shaped pod-shaped masses masses that that apparently apparentlycut cutboth boththe thered red The and gray gray intrusions. intrusions. Although Althoughthe thetiming timingof of emplacement emplacement of of the the aplites aplites relative to that of the and quartz-feldspar porphyry porphyry and and diabase diabase dikes dikes is is uncertain, uncertain, the the irregular irregular shapes shapes of of the the former former vs. vs. quartz-feldspar the straight straight and andcontinuous continuous(fracture-controlled (fracture-controlled emplacement) of the latter two two leads leads to to the the the inference that that the the aplites aplites are are a late late differentiate differentiate of the St. Cloud Granite. At this this site site and and the the inference Granite. At next (stop (stop 3C), 3C),note note the the contrast contrast in in jointing jointing pattern pattern of the aplite aplite and porphyry porphyry compared compared to to the the next surrounding surroundingplutonic plutonicrocks. rocks. Early Proterozoic Intrusive Rocks --------e Diabase dikes QFP (Porphyritic microgranite) dikes Aplite pods related to St. Cloud Granite (?) St. Cloud Granite Ref ormatory granodiorite Outcrop Geolo ical contacts, \ - - dashe where inferrec Small or discontinues diabase dike 0 8 ' 200 feet I 50meten I . Trails I Figure FigureF7. F7.Outcrop Outcropand andgeologic geologicmap mapofofStop Stop3.3. 25 % �STOP 3C-Porphyritic 3C—Porphyritic microgranite (aka quartz-feldspar quartz-feldspar porphyry). porphyry). This dike strikes strikes N45E, is 4-5 4-5 m thick, and has 4-6 percent percent glassy glassy subhedral subhedral quartz quartz phenocrysts and 3-4 percent subhedral phenocrysts in in an aphanitic, siliceous, phenocrysts subhedral K-feldspar K-feldspar phenocrysts groundmass. Dikes Dikes such suchas asthis thisare arescattered scattered around around the the St. St. Cloud Cloud area, area, and like the diabase the St. St. Cloud Cloud Granite. Granite. The dikes, they cut the Reformatory granodiorite, Rockville Granite and the phenocrysts vary from the 2-4 mm cm elsewhere. elsewhere. The margins phenocrysts rnm size here, to as large as 22 cm margins of the quartz-feldspar dikes are chilled, and in some cases flow-banded. A similar dike in quartz-feldspar dikes are chilled, and in some cases flow-banded. A similar dike in the the aggregate aggregate quarry north of here is clearly clearly comagmatic comagmatic and commingled with a diabase dike that contains fresh ophitic clinopyroxene, olivine, and chromite. However, However, that diabase dike contrasts with not altered/metamorphosed altered/metamorphosed all the other diabase diabase dikes dikes in this area in that the mafic minerals are not to actinolitic actinolitic amphibole. amphibole. STOP xenolith of of garnet garnet amphibolite amphibolite in St. Cloud Granite. Granite. STOP 3D—Small 3DÑSmal xenolith True xenoliths of external origin (vs. cogenetic mafic enclaves) are are rare rare in in all of the St. Cloud District intrusions. Xenolith types noted in the St. Cloud area include garnet-magnetiteCloud District intrusions. Xenolith types noted in the St. Cloud area include garnet-magnetiteamphibole schist (probably (probably metamorphosed metamorphosed iron-formation), biotite-quartz-feldspar schist of graywacke magnetite, and abundant graywacke protolith, protolith, granulitic granuliticgneiss gneiss that that contains contains garnet, sillimanite, sillimanite, magnetite, abundant cordierite, charnockitic garnet-biotite-orthopyroxene garnet-biotite-orthopyroxenegranofels. The The general general metamorphic metamorphic cordierite, and chamockitic mineral assemblages indicate that the country rock was metamorphosed to amphibolite and higher retrograde metamorphism metamorphism caused higher grade grade prior prior to to incorporation incorporationinto into the granites, granites, with minor retrograde caused by contact with with granite granite magma. magma. On the way to Stop 4 watch for the the derrick derrick in in the the deep deep quarry quarry north north (right) (right) of of the the highway highway on the east edge of the town of Rockville. Rockville. This This is the "Rockville Beige" quarry operated operated by the Cold Spring Spring Granite Granite Company. Company. STOP STOP 4. COLD COLDSPRING SPRINGGRANITE GRANITEQUARRY QUARRYAND AND PROCESSING PROCESSINGPLANT PLANT • Location: T.T.123 Location:(quarry) (quarry) 123N., N.,R.R.29 29W., W.,Section Section19 19BDAB. BDAB. • Rockville Rockville Granite, Granite,quarry quarrymethods, methods,production productionof offinished finisheddimension dimensionstone. stone. -- '—, —..__/ .1 -/ J/4 ((Gr.v • — u)j Highway 23')c-StOp 4A Figure F8. Location Location of of Stop Stop 4A. Other Otheroutoutcrops of Rockville Granite shown in black, Granite shown in black, except over the two quarries. STOP 4A—Cold 4A-Cold Spring Granite Granite Rockville Rockville White quarry quarry(Fig. (Fig. F8), F8), Rockville Rockville Granite, Granite, mafic mafic enclaves. enclaves. This is the "Rockville L'RockvilleWhite" quarry, quarry, one one of the three Cold of Cold Spring Spring Granite Granite quarries quarries developed granite developed in in Rockville Rockville Granite. Granite. The granite from the other Rockville quarries is marketed Beige" and and "Diamond "Diamond Pink." Pink." Due as "Rockville Beige" we will not be able to enter to safety concerns we the quarry, but will have ample opportunity to view the Rockville Granite Granite up close. close. This quarry uses the "drive-in This "drive-in quarry quarry method," method," a system that replaces the traditional cable-operated cable-operated derrick derrick method method of stone stone removal. Surprisingly, Surprisingly, the method was developed only in 26 �the mid-1970's mid-1970's (Muehlbauer (Muehlbauerand andFuchs, Fuchs,1997). 1997).The Thedrive-in drive-inmethod method utilizes utilizes aa series series of benches, the from which which the the stone stone is is removed removed as a series series in large "loaves" "loaves" that vary in size—15-25 size-15-25 feet (5from 8m) high high xx 20 20 feet feet (6m) (6m) wide wide xx 30-150 30-150feet feet (lO-50m) (10-50m) long. long. These Theseloaves loavesare aresubsequently subsequently 5.5 x 5.5 5.5 x 10.5 drilled off into smaller blocks that that are optimally optimally 5.5 10.5 feet feet in in size, size, weighing in at approximately 25,000 kg, or nearly 28 tons. This Thissize sizeisissmall smallenough enoughto totransport transportlegally legallyby by approximately flatbed trailer trailer without without aa special specialpermit, permit, and and allows allows for for minimum minimum wastage wastage during during processing. processing. flatbed Charles Charles Muehlbauer of Cold Cold Spring Spring Granite Granite will give a more extensive overview of the the quarry, quarry, and will will also also answer answer questions questions about about the the quarry quarry and andstone stone quarrying process at the products products in in general. general. There are many near the quarry viewing area to many blocks blocks of of Rockville Rockville Granite stacked near examine. examine. The Thefollowing followingfeatures featurescan canbe beseen seenin inthe theblocks: blocks: 1. Porphyritic Porphyritictexture, texture,rapakivi rapakivifeldspars. feldspars. 2. Mafic Maficenclaves, enclaves,some somewith with feldspar feldspar phenocrysts phenocrysts in them. The Theenclaves enclavesare areinterpreted interpreted as as the the product product of of the themingling minglingof ofmafic maficand andfelsic felsicmagmas magmas(see (seeINTRODUCTION). INTRODUCTION). Most Most occur occur as as ovoid ovoid inclusions, inclusions, although although discontinuous discontinuousand and irregular irregular dike-like dike-like masses masses of of the the same same composition compositionhave have been been noted noted in in another another quany. quarry. 3. Weak phenocrysts. This Weak trachytoid trachytoidtexture texturedefined defined by aligned aligned feldspar feldspar phenocrysts. Thisisistypical typicalof ofthe the "gray g r a y granites." granites." Stop Granite Company Processing and and Fabrication Fabrication Plant. Stop 4B—Cold 4BÑCol Spring Granite Plant. Cold two different different buildings. buildings. One Cold Spring Springpersonnel personnelwill will guide guide us in small groups through two One is is the the facing facing plant, plant, where where rough rough quarry quarry blocks blocks are are cut, cut, finished finished (polished (polished vs. vs. the the rougher rougher "fire"firefinish"), product specifications. The finish"), and and made made into into facing facing panels of varied size, depending on product The other polished, and and engraved. engraved. Notice other is the the monument monument plant, where the stone is cut, shaped, polished, surprisingly surprisinglyornate ornateworks! works! ****PLEASE * *PLEASE OBSERVE OBSERVESAFETY SAFETY REGULATIONS— REGULATIONS- HARD HARDHATAND HAT ANDSAFETY SAFETYGLASSES GLASSESMANDATORY*** MANDATORY*** STOP STOP5. 5. RICHMOND RICHMONDGRANITE GRANITE • Location: Location:T.T.123 123N., N.,R.R.3030W., W.,Section Section29 29BB BB center. center. • Charnockitic, prominent trachytoid trachytoid K-feldspar Charnockitic,rapakivi rapakivi granite granitewith with prominent K-feldspar phenocrysts. phenocrysts. ***PRIVATE PERMISSION OF *** ***PRIVATEPROPERTY—MUST PROPERTY-MUST HAVE HAVE PERMISSION OFHOMEOWNER HOMEOWNERTO TOENTER ENTER*** —HAMMERING -HAMMERING AND AND SAMPLING SAMPLJNG PROHIBITED— PROHIBITED- The TheRichmond Richmondgranite granitewas wasinterpreted interpretedby byearlier earlierworkers workersas asaahigh-grade high-grademetamorphic metamorphic gneiss gneissof ofArchean Archeanage. age. By Bycontrast, contrast,this thisstop stopdemonstrates demonstratesthat thatthe thegranite granitehas hasaa primary primary igneous igneous texture, texture, which which isis typical typical of of the the unit unit overall. overall. ItItcontains containsundeformed undeformedunit unitquartz quartzgrains grainsas aslarge large as 1 cm and euhedral feldspar phenocrysts as large as 5 cm. Because quartz is one of the as 1 cm and euhedral feldspar phenocrysts Because quartz is one of the first first minerals mineralsto toexhibit exhibitstrain strainand and recrystallization recrystallizationduring during deformation deformationand and metamorphism, metamorphism,the the rock rock clearly semiclearly has has not notexperienced experienced substantial substantial amounts amounts of of either either process, process, and and only only localized localized semibrittle brittle shearing shearing exists. exists. We Weinterpret interpretthis thisand andother otherlithologic lithologic evidence evidence to to indicate indicate that that the the Richmond emplacedafter aftermost mostof of the the regional regional deformation deformationceased, ceased, and and infer infer that that itit Richmondgranite granitewas wasemplaced probably probablyhad hadan anemplacement emplacementhistory historylike likethat thatof of the theReformatory Reformatorygranodiorite granodioriteand andthe theRockville Rockville Granite. Granite. 27 �Key features features at at stop stop 5: 5: 1. Dark green charnockitic charnockitic granite. This Thiscolor colorphase phasegrades gradesinto intothe the more moretypical typicalpink-tinted pink-tinted 1. Richmond granite, Richmond granite, due due to oxidation oxidation introduced introduced along along fracture fracture planes. At At first first glance, glance, the the green green phase looks like gabbro, gabbro, but if you trace trace across the gradation gradation to the pinker pinker phase, phase, you will will see see that it actually actually contains contains abundant abundant quartz quartzand and K-feldspar. K-feldspar. 2. Euhedral, Euhedral, carlsbad-twinned carlsbad-twinnedK-feldspar K-feldspar (microperthite) (microperthite) phenocrysts. Some Someof these are mantled by a thin rim of plagioclase, plagioclase, giving giving rise rise to rapakivi texture—best texture-best observed observed on on vertical, vertical, slightly slightly weathered faces, where plagioclase plagioclase is bleached white. 3. Magmatic-trachytoid Magmatic-trachytoidalignment alignmentof of feldspar feldsparphenocrysts phenocrysts (see (see Fig. F9). dark-colored mafic mafic enclaves. enclaves. From From aa petrographic petrographic standpoint, standpoint, these enclaves are 4. Small dark-colored mineralogically identical to aa fine-grained, mineralogically fine-grained, trachytoid, trachytoid, apatitic, apatitic,quartz-orthopyroxenequartz-orthopyroxeneclinopyroxene ferrodionte outcrops clinopyroxene ferrodiorite(orjotunite, (orjotunite,in incharnockite charnockiteterminology) terminology)that that occurs occurs in several outcrops 1/4 mile to the the west west of of this this location. location. This diorite diorite contains contains abundant abundant zircon zircon and small phenocrysts 114mile small phenocrysts phase that is of both plagioclase plagioclase and K-feldspar, K-feldspar, and locally grades into a coarser-grained coarser-grained phase compositionally and compositionally and texturally texturally similar similar to the Richmond granite as exposed here. The Thediorite dioriteto to the west is inferred inferred to to be be aaborder border phase phase of of the theRichmond, Richmond,and andthe the small smallenclaves enclavesscattered scattered throughout the Richmond throughout Richmond are are interpreted interpreted as as cognate cognate xenoliths derived from from this dioritic dioritic border border phase. •END FiELD TRIP. TRIP. THANKYOUFORATITENDING! END OF FIELD THANK YOU FOR ATTENDING!---------------You are are encouraged encouraged to to visit the poster titled You "DIMENSION "DIMENSION STONE STONE PRODUCTS PRODUCTS OF OF MINNESOTA" MINNESOTA" on display at the poster session. 28 �A ——- Strike and dip of ductile shear fabric Strike and dip of brittle shear fabric Strike and dip of trachytoid foliation vertical, inclined Figure F9. Map of central part of the Cold Spring 7.5-minute quadrangle, showing outcrops of Richmond granite. Structure symbols touch the outcrop from which they were taken. OAD �PHOTOGRAPHS OF QUARRIES QUARRIESININTHE THEST. ST.CLOUD CLOUDAREA AREAFROM FROMTHE THE EARLY 1900's. Top, QUARRIES PHOTOGRAPHS OF EARLY 1900's. TOP, QUARRIESOPERATED OPERATEDBY BY NORTH STAR GRANITE COMPANY, NOW OVERRUN AGGREGATES QUARRY?; NORTH STAR GRANITE COMPANY, NOW OVERRUNBY BYTHE THEPRESENT-DAY PRESENT-DAY MERIDIAN MERIDIAN AGGREGATES QUARRY?; BOTBOTTOM,AAQUARRY QUARRY OPERATED OPERATED BY GRANITE COMPANY, LOCATED IN FIELD TOM, BY THE MELROSE MELROSE GRANITE COMPANY, LOCATED IN THE THE VICINITY VICINITYOF OFSTOP STOP 1 1 OF FIELD TRIP 1.1. REPRODUCED FROM JOURNAL COLORED GRANITES FOUND IN TRIP REPRODUCED FROM JOURNALARTICLE ARTICLE OF OFTHE THEBRILLIANT BRILLIANT COLORED GRANITES FOUND IN AMERICA'S AMERICA'S GREAT NORTHWEST AMERICAN STONE STONE TRADE, PUBLISHED GREAT NORTHWEST ININ AMERICAN TRADE, PUBLISHEDMAY, MAY, 1931. 1931. 30 30 ��FIELD TRIP TRIP #2 FIELD THE SOUTHEASTERN FIELD GUIDE GUIDE TO THE GEOLOGY OF THE RIFT SYSTEM, PORTION OF OF THE THE MIDCONTINENT RIFT SYSTEM, EASTERN AND WESTERN WESTERN WISCONSIN WISCONSIN MINNESOTA AND Leaders: Leaders: Karl KarlR.R.Wirth, Wirth,William WilliamS.S.Cordua, Cordua,William WilliamF. F. Kean, Kean, Mike Middleton, Zachary Zachary J. J. Naiman Naiman INTRODUCTION The Middle Proterozoic Midcontinent rift rift system system extends extends over over 2,000 Proterozoic (Keweenawan) (Keweenawan) Midcontinent kilometers in an arc across central North America America from from Kansas Kansas to tocentral centralMichigan. Michigan. Magmatic kilometers Magmatic continental lithosphere lithosphere and sedimentary sedimentary rocks rocks in in this this major major tectonic tectonic feature feature record the evolution of continental million years years ago. ago. Rifting as it interacted with a mantle plume 1100 million Rifting was was aborted aborted before the production of oceanic lithosphere lithosphere began. Field, production Field, geochemical, geochemical, geochronologic, geochronologic, and and geophysical geophysical studies during the past decade have made significant contributions contributions to our understanding understanding of the evolution of of the Midcontinent rift rift system. system. The interested reader is referred to several recent evolution reviews (Van Schmus Schmus and Hinze, 1985), volumes (Tectonophysics, 213, 1992; Canadian Canadian reviews 1985), special volumes (Tectonophysics,v. 213,1992; Journal of Earth Science, Science, v. v.31, 1994; Canadian 34, 1997; Ojakangas Ojakangas Journal 3 1,1994; Canadian Journal Journal of Earth Science, Science, v. 34,1997; et al., 1997), 1997), and and guidebooks guidebooks (Miller (Miller et al., al., 1995) 1995) on on the the Midcontinent Midcontinent rift rift for for additional additional information. information. Geophysical Geophysical studies studies have provided much information about the nature of the rift, which lies buried beneath younger deposits along much much of of its its length. length. Regional gravity and magnetic surveys were important in establishing the extent and character of the rift (e.g., Hinze Hinze et et al., al., 1992). Our Our knowledge knowledge of of the the detailed detailed structure structure and and stratigraphy stratigraphy of the rift has has been been greatly greatly of the COCORP (Serpa et al., 1984; enhanced by several seismic surveys, most notably those of 1984; Zhu and and Brown, 1986) 1986)and and GLIMPCE GLIMPCE (Behrendt (Behrendt et al., 1988; 1988; Cannon et al., 1989) 1989)programs. programs. These surveys basins filled filled with with thick sequences of surveys revealed the presence of fault-bounded basins sedimentary rock. Detailed Superior volcanic and sedimentary Detailedseismic seismicimages imagesof the eastern portion of Lake Superior indicate the percent of oforiginal original thickness) thickness) in in some portions portions of the indicate the extent extentof of crustal crustalthinning thinning(—30 (-30 percent kilometers deep deep and and consists consists of of roughly roughly 20 kilometers kilometers rift; the rift in this region is more than 30 kilometers of basalt overlain by 10 10 kilometers of Keweenawan sedimentary rock. The voluminous tholeiitic basalt flows voluminous volcanic volcanic rocks of the rift consist predominantly of tholeiitic flows and minor rhyolite (Green, (Green, 1977; 1977; 1983) 1983) that were erupted during a relatively short short time time span span (1110-1090 Ma; Davis and Green, 1997). Trace element and isotopic studies indicate that the (1 110-1090 Trace element and isotopic studies indicate the basalts were derived from mantle melts that basalts that were were variably variably contaminated contaminated by continental continental lithospheric mantle Nicholson et lithospheric mantle and and crust crust (Nicholson (Nicholsonand and Shirey, Shirey, 1990; 1990;Shirey Shirey et al., 1994; 1994; Nicholson et al., 1997). The Thecombined combinedpetrologic, petrologic,structural, structural, and and geophysical geophysical evidence are consistent with a "hot-spot" "hot-spot" origin originfor for the the Midcontinent Midcontinentrift rift system system(Hutchison (Hutchisonet et al., al., 1990). 1990). 33 �SOUTHWESTERN ARM OF THE MIDCONTINENT RIFT SYSTEM SOUTHWESTERN THE MIDCONTINENT RIFT SYSTEM Most Most ground-based ground-based studies studies of the the Midcontinent Midcontinent rift have have been been conducted conducted in in the the Lake Lake Superior Superior region region where where Keweenawan Keweenawan volcanic and sedimentary rocks are well-exposed. Along Along much much of of the the southeastern southeastern (Michigan) (Michigan) and and southwestern southwestern (southern (southern Minnesota Minnesota to Kansas) Kansas) extensions extensions of the rift, rift, these these rocks rocks are are largely largely buried beneath thick Phanerozoic deposits. The The objective objectiveof of this this field fieldtrip trip is is to to provide provide an an overview overview of of recent recent studies studiesof of the the Midcontinent Midcontinentrift riftin in east-central east-centralMinnesota Minnesotaand andwest-central west-centralWisconsin. Wisconsin. Despite Despitethe therelatively relativelypoor poorexposure exposurein inthis this region, region, there there are are several several compelling compelling reasons reasons for for studying studying this portion of the rift. Most Most studies studies of of the rift in of the rift formed near the in the the Lake Lake Superior Superior region region have focused on the portion of location Peterman and Sims, Sims, locationof of the the inferred inferred Keweenaw Keweenaw plume plume beneath northern northern Wisconsin (e.g., Peterman 1988). New (e.g., Campbell Campbell and and Giffiths, Giffiths, 1990) 1990) have have New models modelsof ofmantle mantleplume plumeprocesses processes (e.g., contributed contributed significantly significantly to our understanding understanding of large igneous provinces and suggest that rift processes processes may vary with distance distance from the plume center. Unfortunately, Unfortunately, the distal portions of the Midcontinent rift system are buried, making geologic study difficult and costly. The Midcontinent rift system are geologic The rocks rocks of the the Taylors Taylors Falls Falls-- Clam Clam Falls Falls region region are are the southernmost southernmostexposures exposures of the Midcontinent Midcontinentrift rift of system system and and provide provide an an opportunity opportunity to to examine examine variations variations in rift geology geology and and processes processes along along the length length of of the the rift. rift. AAsecond secondreason reasonfor forstudying studyingthis thissegment segment of of the the rift rift relates relates to to regional regional geologic geologic provinces. provinces. The TheMidcontinent Midcontinentrift riftsystem systemcrosses crossesseveral severalmajor majorgeologic geologicprovinces provincesas as itit traverses In northern northern Minnesota Minnesotaand and Ontario Ontario traverses from from Minnesota Minnesotato to Kansas Kansas (Van Schmus, 1992). In the the rift rift is superimposed superimposedon on Late Late Archean Archean granite-greenstone granite-greenstoneterranes terranes (2.6-2.8 (2.6-2.8 Ga) Ga) of of the the Superior Superior Province. Province.South SouthofofLake LakeSuperior, Superior,the therift riftcrosses crossesaa younger younger east-west east-west belt belt of of immature immaturevolcanic volcanic and southward-dipping subduction and sedimentary sedimentaryrocks rocks (Southwick (Southwicket et al., al., 1989) 1989)that formed formed in a southward-dipping subduction zone Ga). Subduction Subduction processes processes during zone during duringthe the Penokean Penokeanorogeny orogeny(—1.85 (-1.85 Ga). during the Penokean Penokean may may have modified the mantle beneath these terranes, and thus might have had an effect on mantle an effect on the the Keweenawan magmas erupted through them. Studies Studiesof of Keweenawan Keweenawan volcanics south of the Malmo Structural Structural Discontinuity Discontinuity (Minnesota) (Minnesota) and and Niagara Niagara Fault Fault Zone Zone (Wisconsin) (Wisconsin) provide provide an an opportunity opportunity to to study study these these effects. effects. PREVIOUS PREVIOUS STUDIES STUDIES Studies of the the Taylors Taylors Falls - Clam Clam Falls region date back to the time before Minnesota became became aa state state in in 1858. 1858.AAthorough thoroughreview reviewof ofthe thehistory historyof ofinvestigations investigationsisis beyond beyondthe thescope scope of this guide, and the interested reader is referred to the review by Craddock (1972). Since this guide, and the interested reader review by Craddock (1972). Since the early 1900'sitithas hasbeen beenrecognized recognizedthat thatthe therocks rocksof ofthe theTaylors Taylors Falls Falls - Pine early 1900's Pine City City region region constitute constitute a thick, fault-bounded fault-bounded volcanic and sedimentary sedimentary sequence that has been broadly folded into a synform Hall, 1901). The synforrn (Strong, 1880; 1880; Berkey, 1897, 1898; Hall, The term term "Chengwatana" "Chengwatana" was was first first assigned by Hall in 1901 1901 to to refer refer to to aa sequence sequence of flows flows and interfiow interflow sediments of "unusual extent" that are exposed along the Snake River east east of of Pine Pine City City (Fig. (Fig. 1). As As stated stated by by Hall Hall (1901) (1901) "The flood floodof of 1898, 1898,which whichtore toreaway away the the dam dam at at the the foot foot of Cross Cross lake lake and and poured poured down down the river gorge gorge a vast volume volume of water, cleaned cleaned out in an admirable admirable manner manner for for examination examinationthe the channel channel of the the stream stream for for several several miles." At At the the time, time, Hall Hall (1901) (1901) was was able able to to describe describe aa nearly nearly continuous continuous sequence sequence consisting consistingof of 65 65lava lava flows flows and and 55 interfiow intefflow sedimentary sedimentaryunits, units, as aswell wellas as the relationships relationships of the bounding Douglas fault. He also recognized the typical three-fold flow He also morphology and described the igneous and metamorphic minerals. minerals. Unfortunately, Unfortunately, the rocks rocks along the Snake Snake River River are not not nearly nearly so so well-exposed well-exposed today. today. Later, Later, the the term term "Chengwatana "Chengwatana volcanics" volcanics" was wasused usedto torefer referto to Keweenawan Keweenawanvolcanic volcanicrocks rocks exposed exposed over over aa much much broader broader region region 34 �_______ ______ _______ ______ 2: Croix Falls 1982) (Modified from Morey Morey eta], eta!, 1982) 0 I I kilometers kilometers I I I 50 50 I Q .:. .:. .:. .;. ........... +;,:>:..:: .... :..:... .......... * * * * Ordovician Ordovician 0 N 0 Lower-Middle Lower-Middle Proterozoic Quartzite Proterozoic Cambrian Metavolcanic Rocks Metavolcanic Rocks U. Animikie Animikie Group Group Slate Metagreywacke Slate & Metagreywacke Bayfield Baytield Group Group Copper Copper Harbor Harbor Iron Iron Formation Formation Conglomerate Conglomerate Group L. Animikie Group Quartzite & wacke Duluth Duluth Complex Complex Gabbro & Anorthosite Gabbro Anorthosite F,,, - 5) Prot. Archean-L. h ot. Granite & Gneiss Mellen Complex, Complex, Basalt & Sediment Sediment Basalt Basalt (NSVG and and Chengwatana ChengwatanaVolcanics) Volcanics) 1. Generalized Generalizedbedrock bedrockgeology geologyof ofthe thesouthern southernLake Lake Superior Superiorregion region showing showing Figure 1. location of of the the field fieldtrip tripin inthe theTaylors Taylors Falls Falls -- Clam Clam Falls region. (Modified (Modified from from the location Morey et al., 1982). al., 1982). 35 35 �between the Douglas fault (west) and Lake Owen fault (east) in east-central Minnesota and between west-central Wisconsin (Morey west-central (Morey and Mudrey, 1972; 1972; Hassan and Mudrey, 1980). 1980). The distribution distribution and stratigraphy stratigraphy of the Chengwatana volcanics in the Taylors Falls - St. St. Cordua (1989a and b; b; unpublished unpublished mapping). mapping). He Croix Falls region was established by Cordua He divided divided the nearly 3,000 meter thick thick volcanic volcanic section section into into seven seven flow units based on on field field and and textural textural relationships (Fig. 2). The by Themapping matmin~ bvCordua Corduaalso alsodelineated delineated several several east-west east-west faults faults in in the the region. Nearly 3,000 meters of volcanic and sedimentary rock are also dso exposed in the Clam Nearly 3,O region, however corresponding mapping and stratigraphic been ~ h i cstudies have not been Falls Frederic regi Falls -- Frederic conducted conducted there there yet. ye1 meters above base Figure 2. Lithostratigraphic column of Chengwatana volcanics in the Taylors Falls region (Modified from Wirth et al., 1997). Top and bottom 2500 of the section are unexposed. Geochemical sample locations are shown with tick marks along the right side of the column. Flow unit abbreviations are from Cordua 2000 (1989): K!, Lotus lake; Kd, Dresser; Kt, Traprock Alley; Kep, Eagle Peak; Ks, Skitrail; Kp, Pipeline; Ky, unnamed. 1500 1000 Unexposed Interfiow Sediment Interflow Sediment Intersertal to Ophitic Ophitic Plag. phyric, intersertal 500 ....... ....... ....... Intersertal Intersertd ... Ophitic Ophitic [ Sub-ophitic Sub-ophitic 0 36 GEOPHYSICAL STUDIES Gravity, magnetic, ~agnetic,and and seismic studies lies were essential to developing developing detailed models of the buried the buried zontinent parts of the Midcontinent rift system in Minnesota mesota and and Wisconsin (see:review by Craddock, 1972). 172). The regional magnetic tic character of the Keweenawan iwan Rift E f t in eastern Minnesota lesota and and western Wisconsin sin is given given in Chandler et In Lnanuler eL a!. al. (1989) and Allen et al. al. (1997). Allen et (1997). The The rocks of the Taylors Falls Clam Clam Falls Falls region are part of the St. Croix horst, which is is bounded by by the Douglas bounded Douglas (northwest) and Hastings Hastings (northwest) (southeast) faults (Fig. 3). (southeast) 3). On On the the basis basis of of threethreedimensional dimensional gravity gravity models, models, the thickness ooff Chengwatana volcanics volcanics in Chengwatana this region ranges from 4 kilometers at Clam Falls to to 14 kilometers north of 14 kilometers north Frederic, and vertical uplift of the horst ranges from 3 kilometers in the northwest northwest to 8 kilometers in �Emerald Basin + + 0 20 kilometers strike/dip of flows and bedding I trend of aeromagnetic anomalies inferred structuraJ/strañgraphic I discontinuity 450 15' + + 920 15' 92° 00' Falls - Clam Falls region Figure 3. Sketch Sketchmap mapof ofaeromagnetic aeromagneticanomalies anomalies in the Taylors Falls interpreted from interpreted from new new aeromagnetic aeromagneticmaps mapsof of western western Wisconsin Wisconsin (Cannon (Cannonet et al., al., 1997; 1997;in in prep). prep). the southeast southeast(Allen (Allenetetal., al.,1997). 1997).Thick Thick(—5 (-5 km), wedge-shaped wedge-shaped accumulations accumulationsof of Keweenawan Keweenawan sediment (Oronto (Oronto and Bayfield Bayfield Groups) Groups) occur occur in in basins basins on the margins of St. Croix sediment Croix Horst Horst (Allen et a!., al., 1997). 1997). The magnetic character of Polk County is provided by Reich (1989), (19891, who conducted aa primarily N-S ground magnetic magnetic survey survey at 0.1 mile intervals, transecting the county along seven primarily Time-corrected raw data and 3-point smoothed data for line one are and E-W lines (Fig. 4). Time-corrected presented in Fig. 5. This This line covers some of the outcrops seen on this this field trip, trip, and shows the strong magnetic signature of the Chengwatana flows that is about 1000 nanotesla (nT) above the regional value. The Theminimum minimumin in the the magnetic magnetic line line at approximately approximately 15 15 kilometers kilometers from from the the 37 �___________ in the the bedrock bedrock caused caused west end of the line is interpreted interpreted by Reich (1989) as the result of offset in by the Cottage Grove fault. The Thehigh-frequency high-frequency nature nature of of the the magnetic magnetic signal signal on on the the west west end end of the flows. flows. These of the line is common to all the lines that cross outcrops of These high-frequency high-frequency by lightening. lightening. Lightening magnetic "spikes" may in part represent locations hit by Lightening strikes strikes on highly magnetic rock can produce produce large large localized localized anomalies. Many Many outcrops outcropsin in this thisregion regionare aremagnetically magnetically significantly deflect a compass! compass! Reich variations in the strong enough to significantly Reich (1989) interpreted interpreted the variations half-graben faults faults that thatparallel parallelthe theCottage CottageGrove Grovefault. fault. Recent Recent filtered data as resulting from half-graben work by Cannon et al. (1997; in prep.) suggest that these features are the result of folding work Cannon et (1997; suggest these features folding within within in the the magnetic susceptibility of of the the different different flows flows may may also be aa the flows. flows. Variations Variations in magnetic susceptibility contributing factor. Recent Recentstudies studiesby by Kean Kean (1992, (1992, 1993, 1993,1995) 1995)and and Kean Kean et et al. al. (1997) (1997) on on the the paleomagnetic paleomagnetic character characterof of Chengwatana Chengwatanaflows flows in in the the Taylors Taylors Falls region are described described in in the the 2. section for Stop Stop 2. et al., al., 1997; in prep.) provide New aeromagnetic data from western Wisconsin (Cannon et additional constraints on the stratigraphy stratigraphy and structure of the Chengwatana Chengwatana volcanics in the the Falls region. Previously, the relationship between the stratigraphic sections Taylors Falls Falls -- Clam Clam Previously, relationshipbetween the stratigraphic sections Taylors Taylors Falls Falls and and Clam Clam Falls Falls regions regions was wasnot notwell wellunderstood. understood. Preliminary interpretation interpretation in the Taylors suggest that the stratigraphy stratigraphy continues trending of the data suggest continuesnorth north of of the the Taylors Falls region before trending to the east east around around aa northeastnortheastsouthwest southwest antiformal antiformalstructure structure(Fig. (Fig. 3). No Nomajor majorstructural structuralbreaks breaks are are STUDY AREA POW COUNTT apparent. apparent. If this this interpretation interpretation is correct, then then the correct, the flows flows in the the Frederic - Clam Falls region are Frederic are stratigraphically below those of the stratigraphically the Falls section. section. Also apparent apparent Taylors Falls aeromagnetic map on the aeromagnetic map are are several several stratigraphic structural or stratigraphic discontinuities surrounding surrounding the the Ashland syncline, syncline, and northwest of Frederic. These relationships, relationships, combined with the results of recent geochemical geochemical and geochronologic geochronologic studies, suggest that that there may be significant differences between the flow flow sequences sequences and that further further stratigraphic subdivision of the stratigraphic subdivision the ICALI I US.SC CMLII • Chengwatana volcanics volcanics may be • C S ISKI.OMITICS warranted. warranted. U U SA8R STATION Location map map for Figure 4. 4. Location magnetic profiles of Polk magnetic profiles Polk Co., Co., 1989). Wisconsin (after (after Reich, Reich, 1989). 38 �WI., LVIE I A. A GAMMAS I .J'jii*w DATA 61500.0 •:". U.TIRCD DATA 60500.0 MM.I$ Plot of raw and filtered data for line 1 (A—A'I. - Figure Figure 5. 5. -- Magnetic Magnetic profile profile of Line Line 11 in in Figure Figure 44 (after (after Reich, Reich, 1989). 1989). METAMORPHISM IVETAMORPHISMAND AND MINERALIZATION MINEXALIZATION The The secondary s e c o n d q minerals minerals in in the the Keweenawan Keweenawan volcanic rocks form by aa combination combination of of burial metamorphism, activity and and contact contact metamorphism. metamorphism. They metamorphism, hydrothermal hydrothermal activity They form form 20-80 20-80 percent percent of of aa typical typical sample. sample. They Theyreplace replacephenocrysts phenocrystsand andgroundmass, groundmass,fill fillamygdules, amygdules,form form veins and line line joint and and fault fault planes. planes. The Theminerals mineralsreplacing replacing ground ground mass mass and and phenocrysts phenocrysts typically albite epidote+actino1ite~hlorite+qu~z+ albite+1+I- calcite calcite +1+Itypically consist consist of ofthe theassemblage assemblageepidote+actinolite+chlorite+quartz+ muscovite +/-titanite +1Fe-Ti muscovite +/-titanite +I- Fe-Ti oxides. oxides. The Thecommon commonminerals mineralsfilling filling amygdules amygdules are are quartz, quartz, chlorite, crystalline material chlorite,epidote, epidote,K-feldspar K-feldsparand andcalcite. calcite.The Thequartz quartz may may be present as coarse crystalline material or, or, more rarely, as agate. Joint Jointsurfaces surfacesand and fault fault planes planes may have veins or coatings of any of the and chrysotile. chrysotile. Minor the above above mentioned mentioned minerals, minerals, but may also show tremolite, tremolite, and Minor copper copper mineralization mineralizationin inthe theform formof of native native copper, copper, chalcopyrite, chalcopyrite, bornite, bornite, chalcocite chalcocite and and malachite malachite and and azurite occurs in amygdules, flow-top breccias or later gash veins (Grant, 1901; Dutton, 1972; azurite occurs in amygdules, flow-top breccias or later gash veins (Grant, 1901; Dutton, 1972; White, White, 1978; 1978;Cordua CorduaetetaL, al., 1979). 1979). Epidote Epidote occurs occurs as as both both granular granularand and crystalline crystalline grains. grains. Granular Granularepidote epidoteisiscommonly commonly observed observed in in the the groundmass groundmassor orasasalteration alterationofofthe theplagioclase, plagioclase,whereas whereascrystalline crystallineepidote epidote occurs occurswithin withinthe theamygdules. amygdules.Actinolite Actinoliteisispresent presentmainly mainlyininthe thegroundmass, groundmass,but butalso alsoreplaces replaces clinopyroxene clinopyroxeneand andoccurs occursin inamygdules. amygdules.Chlorite Chloriteisisubiquitous ubiquitousininall allof of the the flows flows and and is is present present in intwo two forms: forms: ripidolite ripidolite(brown (brownbirefringence) birefringence)and andpycnochlorite pycnochlorite(anomalous (anomalousblue bluebirefringence). birefringence). Although both types are present throughout the sequence of Chengwatana flows Although both types are present throughout the sequence of Chengwatana flowsthe theFe-poor Fe-poor variety variety (pycnochlorite) (pycnochlorite) is is most most abundant abundant in in the theuppermost uppermostflows, flows, and andthe thehigh-iron high-ironvariety variety (ripidolite) (ripidolite)isis more morecommon commonin inamygdules amygdules(Wirth (Wirthet. et. al., al., 1996). 1996). The The pressure pressure and andtemperature temperature conditions conditions during during metamorphism metamorphism in in these these rocks rocksare are constrained the actinolite. actinolite. The constrainedby bymineral mineralreactions reactions(Liou (Liouet etal., al., 1987) 1987)and and by the Na content of the The minimum minimum temperature temperatureof ofmetamorphism metamorphismof of the theChengwatana Chengwatanavolcanics volcanics isis constrained constrainedby bythe the 39 39 �presence of actinolite and epidote (Fig. 6) and presence and by by the the absence absence of of coexisting coexisting prehnite prehnite and and pumpellyite. The upper temperature temperature boundary of metamorphism is constrained by the lack of with epidote, chlorite, actinolite actinolite and and quartz. quartz. The hornblende coexisting with The maximum maximum pressure pressure conditions of metamorphism metamorphism (4-6 kbar) are constrained constrainedby bythe theabsence absenceofofglaucophane. glaucophane. Further Further conditions constraints on the pressure constraints pressure conditions conditions during during metamorphism metamorphism can can be estimated estimated from from the Na and and Al contents of the calcic amphiboles in the presence of of quartz + + albite + + chlorite + + magnetite A1 (Brown, 1977). Analyses (SEM-EDS) of actinolite indicate that it contains Na (M-4 site) 1977). Analyses (SEM-EDS) of actinolite indicate site) and tetrahedral A1 Al (AlIV). (Ala'). The found in in the tetrahedral Theresults resultsare are similar similar to to the the composition composition of amphiboles found Batholith and suggest suggest low low pressure pressure burial burialmetamorphism metamorphism contact aureoles aureoles of the Sierra Nevada Batholith Group. This of the Chengwatana Volcanic Volcanic Group. This suggests suggests that the the presently presently exposed exposed Chengwatana Chengwatana sediment. This flows were overlain by an additional 6-7 kilometers of volcanic flows or sediment. This estimate estimate is greater than the estimated burial depths made by Cordua (1980; 1989b) and Cavaleri (1987) by analogy Group in the Keweenaw Peninsula, Peninsula, but are consistent consistent analogy with with the the Portage PortageLake LakeVolcanic Group with the amount of uplift (<8 km) (<8 km) estimated from geophysical geophysical models models al., 1997). Assuming Assuming a peak (Allen et al., metamorphic temperature of approximately350' 350° C and a burial approximately km., the depth of approximately 7.5 km., metamorphic data from the Chengwatana flows suggest Chengwatana flows suggest aa geothermal gradient of approximately geothermal approximately 0.6 45-50° 45-50' CCwithin within this this portion portion of the midcontinental midcontinental rift. rift. Similar results were were obtained obtained by Livnat (1983) (1983) using using oxygen isotopes in the Portage Lake volcanic sequence sequence on on the the Keweenaw Keweenaw Peninsula. Peninsula. The metamorphic minerals in Polk County are are distinctly distinctly different different from those those seen seen further from further north in content of aci Wisconsin. Wisconsin. In the volcanic volcanic rocks rocks pr-s exposed in northern Douglas County cz-i-tr+H20 (south shore of Lake (south Lake Superior), Superior), \X, prehnite, laumontite and other prehnite, laumontite and other X #' \X zeolites are common common secondary secondary 9 .1. minerals (Grant, 1901, 1972, minerals (Grant, 1901, Dutton, 1972, 0 400 500 300 200 300 100 Cordua, 1990,1991). 1990,1991). In White, 1978; Cordua, southern Douglas County, southern Douglas County, in the Temperature Temperature (°C) (OC) region between Dairyland to Solon region Solon Figure 6. P-T P-Tdiagram diagramfor forunivariant univariant reactions reactionsrelevant relevant Springs, prehnite is found, but the Springs, prehnite the to low-grade low-grade metamorphism metamorphism of of mafic mafic volcanic volcanic rocks rocks zeolites zeolites are rare to absent absent (Grant, (Grant, (modified from from Wirth Wirth et al., (modified al., 1997). 1997). Estimated 1901). 1901). To To the the east, east, in in the the Minong Minong conditions conditionsof of metamorphism metamorphismof of Chengwatana Chengwatanavolcanics volcanics Copper Range, which stretches from are shown in shaded regions. Minong Minong through through Grandview Grandview in in 40 �Washburn, Washburn, Bayfield and Douglas Douglas Counties, Counties, prehnite is is common common and and pumpellyite pumpellyite has hasbeen been reported. Mi, 1982). Zeolites reported. (Grant, (Grant, 1901; 1901;Smith, Smith, 1947; 1947; Dutton, 1972; White, 1978; AH, Zeolites such such as as natrolite natroliteoccur occuralong alonglater laterjoint joint surfaces surfacesnear near Chittamo Chittamo and and heulandite heulandite and and natrolite natroliteare are reported reported occurring occurring in in amygdules amygdules with with quartz, quartz, epidote epidote and and chlorite chlorite near nearGrandview Grandview (LaPoint, (Lapoint, 1976). 1976). South South of of Grandview, Grandview, southeast southeast of of the the Lake Lake Owen Owenfault, fault,epidote, epidote,chlorite, chlorite,actinolite, actinolite,quartz, quartz, biotite zeolites (LePoint, biotiteand and ferrostilpnomelane ferrostilpnomelaneoccur, occur,with with no no prehnite, pumpellyite or zeolites (LePoint, 1976). 1976). A hornblende-epidote-biotiteassemblage assemblageisislikely likelydue duetotothe thepresence presenceof ofnearby nearbyMellen MellenIntrusive Intrusive A hornblende-epidote-biotite Complex plutons (Cannon et al., 1996). Toward the Michigan border, at Saxon Falls Complex al., 1996). Toward the Michigan border, at Saxon Fallsnear near Hurley, Hurley, prehnite prehnite and and zeolites, zeolites, such such as as thomsonite thomsonite and and laumontite, laumontite,are areagain againreported reported(Irving, (Irving, 1883; 1883;Cannon, Cannon,1996). 1996). The The higher higher metamorphic metamorphic grade grade of of the the Chengwatana Chengwatana basalts could could reflect reflect either either deeper deeper burial burialin inthe thevolcanic volcanicpile pilethan thanrocks rocksto tothe thenorth, north,or or the the presence presence of of aa higher higher geothermal geothermalgradient gradient in in that that part part of of the the Keweenawan Keweenawan terrain. Allen Allen et etal. al. (1997) (1997)estimate estimatethat that the the St. St. Croix CroixHorst Horst has has undergone undergone 3-8 3-8kilometers kilometers of of uplift uplift in in the the Taylors Taylors Falls-Clam Falls region. This This contrasts contrastswith with estimated estimateduplift upliftofof2-4 2-4kilometers kilometersininthe theAshland Ashlandsyncline synclineand and1-2 1-2kilometers kilometersininthe theTwin TwinCities Cities Basin Basin(SE (SEMinnesota). Minnesota). GEOCHEMISTRY GEOCHEMISTRY Petrographic Petrographicand andgeochemical geochemicalstudies studiesof ofthe theChengwatana Chengwatanavolcanics volcanicsin inthe theTaylors TaylorsFalls Falls -- Clam Clam Falls Falls region region have have been been conducted conducted by by Cordua Cordua(1980; (1980;1989b), 1989b),Cavaleri Cavaleri(1987), (1987),Leslie Leslieetet al. (1994), (1994),Wirth Wirthet et al. al. (1995; (1995;1996; 1996;1997), 1997),Naiman Naiman et et al. al. (1996; (1996;1997; 1997;in in press), press), and and Abbott Abbott et et al. al. al.(in (in press). press). These Thesestudies studiesestablished establishedthe thetholeiitic, tholeiitic,high-alumina high-aluminaand andhigh-iron high-iron character characterof of the the basalts basaltsin inthe theregion region(Table (Table1;1;Fig. Fig. 7); 7);intermediate intermediate and and felsic felsicrocks, rocks, with with the the exception exceptionof of rare rarerhyolite rhyolitenear nearClam ClamFalls, Falls, are are not observed. observed. Most Mostflows flows are are weakly weakly olivine-normative olivine-normative (0-15 (0-15 percent percent norm norm ol) 01) and and the theremaining remaining flows flows have have trace trace amounts amounts of quartz quartz in in their their norms norms (0-5 (0-5 percent percentnorm normqz). qz). Nickel Nickel abundances abundances (36 (36 -185 185ppm) ppm)and andMg#'s MgWs(Mg# (Mg#==Mg! Mg/ [Mg+Fe2] [Mg+Fe+2]== 0.37 0.37 -- 0.58) 0.58) are are Fe2 F ~ ++ Fe3 + Ti generally generallylow, low,suggesting suggestingthat thatthe the Chengwatana Chengwatana Volcanic Volcanic Group Group flows flowshave haveundergone undergonesignificant significant fractionation. fractionation. Chengwatana Chengwatana basalts can be subdivided basalts can be subdividedon onthe the basis basis of of TiO2 T i 0 2 (less (less than than and and greater greater than than 2.3 2.3 weight weight %), %), aa distinction distinction that that has has been been recognized recognized elsewhere elsewhere in in the the Midcontinent Midcontinentrift. rift.InIngeneral, general,the the high-Ti02 high-Ti02 basalts basalts are aremore more abundant in the upper part of abundant in the upper part ofthe the St. Croix Croix Falls Fallssection sectionand andare are St. characterized characterizedby byhaving havinggenerally generally low low Mg# Mg# (<0.5) (<0.5) and and high high A Al A1 Figure Figure7.7.Plot PlotofofChengwatana Chengwatanavolcanics volcanicsfrom fromthe theTaylors Taylors Falls region on a Jensen cation plot (Jensen, 1976) (after Falls region on a Jensen cation plot (Jensen, 1976) (after Wirth et al., 1997). Wirthetal., 1997). 41 �Table 1. Representative Representative analyses analyses of basalt and sediment from the Taylors Taylors Falls and Clam Clam Falls Falls region. region. Si02 Si02 Ti02 A1203 *l2O3 Fe203 Fe203 MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 P2° LOT LO1 basalt KC-lb basalt KC-7 basalt KC-70 KC-70 47.60 48.30 1.69 15.57 13.34 1.71 48.13 2.64 14.07 16.40 0.21 5.17 15.65 13.61 0.19 6.69 9.56 0.19 7.48 8.14 2.38 0.16 3.09 64.75 0.93 59.64 0.84 11.11 13.55 8.75 1.63 8.41 2.45 1.43 0.31 1.25 7.37 0.08 0.97 11.92 0.21 0.73 0.10 2.02 2.60 0.55 0.19 1.13 sediment sediment sediment KC-331f KC-330g KC-330g KC-33 1f 0.10 2.66 11.55 1.28 0.61 0.13 1.59 Total Total 100.77 100.68 100.47 100.19 100.70 Mg# Mg# 0.57 0.43 0.42 0.23 0.48 39.54 0.57 — qz qz — — — — — — hy hy ol 01 17.73 17.01 20.38 9.24 6.41 2.66 ne Rb Ba Th Nb La Sm Sm Yb Zr Y 42 206 Cr Cr Ni — 9 26.68 — 16 15 128 — 206 — 13 9 11 — — — — — — — — — 108 23 121 209 42 122 23 142 165 185 125 124 128 79 67 105 248 254 169 161 1.03 9.58 3.50 2.15 Initial ENd Initial CNd+0.101 Locations: Sample Sample Locations: -KC-lb KC-1b KC-7 KC-7 KC-70 KC-70 KC-330g KC-310 48 546 14 11 V v 277 — -- -- -- 6.94 26 82 318 -1.7— -1.7 - — 19 -1.86 -1.86 NW1/4, section 5, T T 33 33 N, N, R R 18 18W NE114, NW114, W NE1/4, 1/4, NE NE 114, 1/4, section 6, T T 33 33 N, N, R R 18 18W SE W (Stop (Stop 1) 1) SE 114, NW 114, 1/4, section 14, T T 33 33 N, N, R R 19 19W NW 1/4, 114, NW W T 33 N, N, R R 18 18W NEll4, NEl14, section 6, T W NE1/4, NE1/4, T 37 37 N, N, R R 17 17W NE114, SW114 of section 11, T W (Stop 5) NE1/4, SW1/4 42 — 50 �the Taylors Taylors Falls basalts are are subsubincompatible trace-element trace-element abundances. abundances. REE patterns of the and variably variably enriched enriched in in the the light light REE, REE, with with abundance abundance levels levels 40-100 40- 100times times chondritic chondritic parallel and values for La, and from Most samples samples have have prominent prominentnegative negative from 12-22 12-22 times chondrites chondrites for Yb. Most Eu anomalies, feature that is consistent with the widespread petrographic evidence of plagioclase anomalies, aa feature petrographic evidence plagioclase Normalized trace trace element element abundances abundances (Fig. 8) of the flows are enriched in the fractionation. Normalized highly incompatible elements (e.g., Th, Nb, La) relative to the the less less incompatible incompatible trace elements incompatible elements (e.g., Th, I.) a -4 10 ID I I I I I Nd La Ce 5o I I I I I I I I I YbLu Tb Sm Eu I b : 10 I I I I I I I I I I I I I I I I I Th Nb Ta La Ce Sr P Nd Sm Zr Hf Eu Ti Th Y Yb Lu Figure 8. (a) (a)Chondrite-normalized Chondrite-normalizedplot plotof of REE REE abundances abundancesin in representative Figure 8. volcanics from from the Taylors Taylors Falls Falls region region (after Wirth Wirth et al., Chengwatana volcanics trace-element abundances normalized to primitive mantle. (b) Plot Plot of trace-element abundances normalized 1997). (b) (e.g., Zr, Y, Y,Yb); Yb);Ta, Ta,Nb, Nb,and andSr Srare arerelatively relativelydepleted. depleted. These These relationships relationships suggest that at least some of the major major and and trace trace element element variations variations exhibited by the Chengwatana Chengwatana volcanics volcanics are are aa fractional crystallization contamination. Basaltic result of fractional crystallizationand variable contamination. Basalticflows flows of the the Chengwatana Chengwatana volcanics exhibit a relatively narrow narrow range range of of Nd Nd isotopic isotopic compositions compositions (Fig. (Fig. 9). 9). Although Although flows range range from from+3.4 3.4 to initial ENd ENd values of the flows to 4.5, -4.5,the themajority majority of of samples samples plot within a initial more limited range (-1.5 and -3.0). -3.0). The The combined combined geochemical geochemical data suggest that the basalts originated contaminated by by continental continental lithospheric lithospheric originated from from plume-derived plume-derived melts that were variably contaminated mantle EM values mantle or or crust crust (Wirth (Wirth et et al., 1997). 1997).Rhyolites Rhyolitesfrom fromthe theClam ClamFalls Fallsregion regionhas hasinitial initialENd ENd of ++1.0 Thesevalues valuesare areclose closeto tothe thecomposition compositionof ofthe theinferred inferredplume plume(initial (initialENd 1.0 and -0.1. These value = = 0) 0) implying that the rhyolites formed by crystal fractionation fractionation (Abbott (Abbott et al., al., in in press). press). ' 43 43 �12 Clam Falls Rhyolite • Clam Falls Basalt 10 Falls Basalt 8 6 L 4 2 0 -12 -10 -8 -4 -6 0 6 Initial Nd £\ Initial Figure Figure 9. 9. Histogram Histogramofofinitial initialENd EM values values (1100 (1100Ma) Ma) of Chengwatana Chengwatana volcanics volcanics from from the the Taylors TaylorsFalls Falls and and Clam ClamFalls Falls regions regions(after (afterNaiman Naiman etetal., al.,in inpress). press). ITINERARY ITINERARY This in Minneapolis, Minneapolis, Minnesota. Minnesota. A This guide guide describes describes aa one-day one-day trip beginning and ending in regional regionalmap mapof ofthe theroute routeisisgiven givenin inFigure Figure10, 10,and andmore moredetailed detailedmaps mapsof ofthe thestops stopsare aregiven giveninin Figures Figures11 11and and12. 12.AAbrief briefdescription descriptionofofthe theroute routeisisgiven givenbelow: below: Proceed from from Minneapolis Minneapolis about 45 miles to Osceola Wisconsin. One One route route to to Osceola Osceola Proceed would wouldbe beas asfollows: follows:Take Take 1-35 1-35 north to the exit for Minnesota 97 east bound. Follow FollowRoute Route97 97 for 11 11miles miles to to its its intersection intersection with with Minnesota 95. Turn Turn left left (north) (north) on on Minnesota Minnesota 95 for 66 for miles. Turn Turnright righton onroute route243, 243,cross crossthe theSt. St.Croix CroixRiver Riverand andfollow followititto toits itsintersection intersectionwith with miles. Wisconsin Route 35. Wisconsin Route 35. Go Go north north on on Route Route35. 35. InInabout about4.5 4.5miles miles(about (about11mile milenorth northof ofDresser DresserWisconsin) Wisconsin)turn turnright right on Ravine Drive. Follow Ravine Drive a short distance to the entrance of the Dresser Trap Rock on Ravine Drive. Follow Ravine Drive a short distance to the entrance of the Dresser Trap Rock Company CompanyQuarry Quarry(Stop (Stop1;1;Fig. Fig.13). 13). Return Return to to Route Route 35. 35. Turn Turnleft left(south). (south). Go Go1 1mile miletotoState StateStreet. Street.Turn Turnright right(west) (west)on onState State Street. milestotothe theintersection intersection Street. This Thissoon soonbecomes becomes100th 100thAvenue. Avenue. Follow Followthis thisroad roadabout about33miles with with County County S. S.Turn Turnnorth northand andgo goabout about1/2 112mile miletotothe thepipeline pipelinecrossing crossingofofCount CountSS(Stop (Stop2;2; Fig. Fig. 15). 15). Return Return to to Route Route 35. 35. Turn Turnleft left(north). (north).Go Gothree threemiles milestotothe thecity citylimits limitsof ofSt. St.Croix CroixFalls. Falls. Turn Turn left leftinto intoInterstate InterstatePark, Park,Wisconsin Wisconsin side side (fee (fee area). area). Follow Followthe thepark parkroad road to toEagle EaglePeak Peakand andthe the group groupcamp camparea area(Stops (Stops3a 3aand and3b; 3b;Fig. Fig.17). 17). 44 �Figure Figure10. 10.Scanned Scannedimage image(not (notshown showntotoscale) scale)ofofUSGS USGSStiliwater, Stillwater,Minnesota Minnesota- -Wisconsin Wisconsin topographic topographicquadrangle quadrangle(1 (1xx22degree degreeseries; series;1:250,000 1:250,000scale) scale)showing showingthe thelocations locationsofofthe the field fieldtrip tripstops. stops. Return ReturntotoRoute Route35. 35.Turn Turnleft. left.Follow Followthe thesigns signstotomerge mergeonto ontoU.S. U.S.Highway Highway8 8- -WEST bound. WEST bound. Cross Crossthe theSt. St.Croix CroixRiver Riverinto intoMinnesota. Minnesota.Immediately Immediatelyafter afterthe thebridge bridgeturn turnleft leftatatthe thetraffic traffic light lightinto intoInterstate InterstatePark Park- -Minnesota Minnesotaside side(a(adifferent differentfee feearea) area)(Stop (Stop4;4;Fig. Fig.17). 17). Return Turnright right(east). (east).Recross Recrossthe theSt. St.Croix CroixRiver. River.Follow FollowU.S. U.S.88for for55miles miles ReturntotoHighway Highway8.8.Turn totothe theexit exitfor forRoute Route35 35north. north.Follow FollowRoute Route35 35north northabout about25 25miles. miles.About About2.5 2.5miles milesnorth northof of Frederic, Frederic,turn turnleft leftonto onto130th 130thStreet. Street.InInabout about0.5 0.5miles milesturn turnleft lefton on345th 345thStreet. Street.InIn0.7 0.7miles, miles, look anoutcrop outcropininthe thefield fieldtotothe thenorth north(Stop (Stop5;5;Fig. Fig.19). 19). lookfor foran Return for Returneast easton on345th 345thStreet StreettotoLewis. Lewis.Cross CrossRoute Route3535and andcontinue continueeast eastononCounty CountyRoad RoadEEfor 55miles; turn south on 65th Street to the town of Clam Falls. Turn west at the junction with miles; turn south on 65th Street to the town of Clam Falls. Turn west at the junction with County CountyRoad RoadI.I.Stop Stop55isisNNE NNEofofthe thejunctioin junctioinwith with73rd 73rdStreet. Street.(Stop (Stop6;6;Fig. Fig.20). 20). 45 �Figure 11. 11. Scanned Scannedimage imageof of aaportion portion of of the the USGS USGS Stiliwater, Stillwater, MinnesotaMinnesotaWisconsin topographic quadrangle (30 x 60-minute series; 1:100,000 1:100,000 scale) scale) image (not (not shown shown to to scale) Figure 12. 12. Scanned Scanned image scale) of a portion portion of of the the USGS USGS topographic quadrangle (30 x 60-minute series; Grantsburg, Wisconsin Minnesota Grantsburg, topographic quadrangle (30 60-minute series; . 1: 100,000 scale) scale) showing showing the locations locations of the the field field trip trip stops stops 5-7. 5-7. 1:100,000 46 �AlternateStop Stop66isisreached reachedfrom fromstop stop66by by continuing continuingsouth southon on73rd 73rdto tothe thejunction junction with with3315th Alternate 15th Ave. Continue Mckenzie Trail south and around Continuewest weston on315th 3 15thAve Ave to Mckenzie Trail. Follow Mckenzie the bend to to the the east. east. The Theroad roadveers veerssouth southaround around an an outcrop outcropon on the the north north side side of the the road road (Stop (Stop the 6b; 6b; Fig. Fig. 23). 23). 3 15th Ave and continue west to 90th Street along the east side side of of Sommers Sommers Lake. Lake. Return to 315th Turn north north and and continue continueon on 90th 90th Street Street to to the junction with 320th Ave. Continuewest west on on 320th 320th Turn Ave. Continue 15thAve. and on County Road I until the junction junction with with 3315th Ave. Continue Continue west west on on 315thAve. 315th Ave. Outcrops Outcrops on on north north side sideof of road road near neartop topof ofhill hill(Stop (Stop7;7;Fig. Fig.24). 24). Return 15th Ave., Return to to Frederic Fredericand andRoute Route35 35by bytravelling travellingwest weston on3315th Ave., south south on on120th 120thAve., Ave., and and west west on on 310th 3 10thAve. Ave. A Asimple simpleway way to to return return to to Minneapolis Minneapolis isis to to follow follow Route Route 35 35 south southto to U.S. U.S. Highway Highway 8. 8. Follow FollowU.S. U.S.88east easttotoits itsintersection intersectionwith with1-35. 1-35. 1-35 1-35southbound southboundleads leads direcily directly to to the the Twin Twin Cities Cities of of Minneapolis Minneapolisand andSt. St.Paul. Paul. Stop Trap Rock Quarries. Stop 1—Chengwatana 1-Chengwatana Lava Lava Flows Flows in the Dresser Trap Quarries. Location: NW 1/4 114Sec. Sec.55 Location: Approximately Approximatelyone onemile mileNNE NNE of of Dresser, Dresser, Wisconsin. North North Quarry Quarry -- NW andNEl/4Sec.6,T33N,R18W. and NE 114 Sec. 6, T 33 N, R 18W.EastQuarriesEast Quarries - SW1/4Sec.5,T33N,R18W. SW 114 Sec. 5, T 33 N, R 18 W. The The lava lava flows flows at at Dresser Dresserhave havebeen been mined mined for "trap rock" since "trap rock" since 1855. The Thelarge largequarry quarry complex, complex, owned owned by by Dresser Dresser Trap Trap Rock Rock Inc., Inc., currently produces currently produces 750,000 750,000 tons tons per per year year in in crushed crushedstone stoneof ofall allsizes. sizes. The rock rock isis extremely extremely tough an4 durable, duein in tough and durable,due large large part part to to the the interlocking of of microscopic microscopic unoriented unoriented crystals crystals of of chlorite chlorite and and actinolite. actinolite.All Allvisitors visitorsare are urged urg6d to to seek seekpermission permission to to enter, enter, and and to to use use Figure WIFigure 13. 13.Scanned Scannedimage imageof. of portions portions of of the the USGS USGS Osceola, Osceola,WIfundamental rules of fundamental rules of MN MN and and St. St.Croix CroixDalles, Dalles,WI-MN WI-MN topographic topographicquadrangles quadrangles(7.5(7.5caution. caution. The Therock rockwalls walls minute minuteseries; series;1:24,000 1:24,000scale) scale)showing showing the the location locationof of Stop Stop1.1. are are shear, shear, blasting blasting isis frequent, frequent,rock rockpiles pilesare areunstable, unstable,and andquarry quarrytruck truckdrivers driversexpect expectyou you to to yield yield right-of-way. right-of-way. We We will will visit visitseveral severalspots spotsininthe thequarry, quarry,the theexact exact localities localitiesdependent dependenton onthe theareas areasaccessible accessibleatatthe the time of the field trip. time of the field trip. Both Both quarries quarries expose expose basaltic basaltic lava lava flows flows that that have have been been recrystallized recrystallized incipiently incipiently to to completely completelyto togreenschist greenschistfacies ficiesminerals mineralsby bystatic staticburial burialmetamorphism, metamorphism,due duetotoburial burialwithin within the thevolcanic volcanicpile. pile. 47 �Geology of of the the north north quarry quarry The north north quarry quarry is is aa large largequarry quarry cut cut into into aa single singlelava lava flow flow over over 35 35 meters meters thick, thick, which which The is informally informally named the Trap Rock Alley flow. The flow is a generally subophitic subophitic to diabasic diabasic porphyritic basalt. The Themajority majority of of the the phenocrysts are plagioclase. Augite Augite shows shows up as lighter porphyritic patches on on weathered weathered surfaces, surfaces, giving giving the rock aa distinctly distinctly mottled appearance appearance (Fig. (Fig. 14 14aa gray patches Otherprimary primary igneous igneous minerals minerals are are plagioclase and ilmenite. In In places places these minerals minerals and b). Other are relatively fresh, but usually they are incipiently to completely replaced replaced by by a mixture of chlorite, titanite. The groundmass usually consists entirely chlorite, epidote, epidote, actinolite, actinolite, albite, albite, zoisite and titanite. of this mix of secondary secondary minerals minerals .Locally, bodies of coarse gabbro are present as sill-like sill-like masses. masses. Particularly Particularly common common on on the lowest lowest level level of of the the quarry, quarry, they they average average 0.5-1.0 0.5-1.0 meters meters in in thickness, thickness, and and consist consistof ofcoarse coarse augite, plagioclase and magnetite. Elongated to 44cm cmlong. long. Secondary augite, plagioclase Elongated augite augitecrystals crystals may be up to minerals, commonly developed minerals, such such as as those those found found in the surrounding surroundingbasalt, basalt, are are commonly developed at at the expense expense of the primary minerals. Angular Angularvesicles vesicles occur occur in in these these gabbros, gabbros, and are filled with euhedral quartz, quartz, epidote epidote and and felted felted masses of chlorite. chlorite. These Thesegabbros gabbrosare areinterpreted interpretedas as lenses lensesof of slowly slowly cooled intrusions. The cooled magma magma trapped trapped within within this this exceptionally exceptionallythick thick flow, flow, rather than as later intrusions. The lack lack of of chilled chilled margins margins in in the the gabbro gabbro against against the the basalt basalt support support this this conclusion. conclusion. Flow-top quarry. Here an interfiow Flow-top features features are are common common along the west wall of the quarry. interflow zone is found, basalt. The found, containing containing clasts clasts of of fine-grained fine-grained and extremely amygdaloidal basalt. The clasts clasts are are angular consisting angularand and up up to to 20 20 cm cm in diameter. Interstitial Interstitialto to these these clasts clasts in a fine-grained matrix consisting of of angular angular quartz quartz and and feldspar. feldspar. This Thismay maybe bean aninterfiow interflowsediment sedimentconsisting consistingof ofwind-blown wind-blown scoriaceous scoriaceous flow-top flow-top material material or or perhaps perhaps pyroclastic pyroclastic debris debris from a nearby cinder cone. Burial Burial metamorphism has resulted in the recrystallization of the matrix and growth of secondary the recrystallization matrix and growth of secondary minerals, minerals,especially especiallyquartz, quartz,epidote, epidote,and and chlorite. chlorite. Pay Payclose closeattention attentionto to the the sedimentary sedimentaryfeatures features at at this this stop stop for for later later comparison comparisonwith with sediments sedimentsexposed exposed at at Stop Stop 5. 5. Amygdules Amygdules are are ubiquitous ubiquitous throughout throughout the the flow, flow, but but increase increase in in size size and andnumber numbertoward toward the top of the the flow. flow. The Theminerals mineralscommonly commonly found found filling filling the the amygdules amygdules are are quartz, chlorite, epidote, K-feldspar, calcite and actinolite. The Theamygdules amygdulesare are usually usually zoned, zoned, with with chlorite chlorite forming forming the the rinds. rinds. Growing Growingon onthese theserinds rindsare areinward inward projecting projecting crystals crystals of of quartz, quartz, epidote epidote and and pink pink perthitic perthitic K-feldspar. K-feldspar. Calcite, Calcite,or oraasecond secondgeneration generation of of chlorite, chlorite, occupies occupiesthe the centers centers of the amygdules. Actinolite Actinoliteoccurs occursas asmicroscopic microscopic fibers fibers projecting from the groundmass into the amygdules amygdules and and intergrown intergrown with with the the other other amygdule amygdule minerals. Another joint surfaces surfaceswithin withinthe thebasalt. basalt. The Another group group of minerals minerals form form veins or occur along joint most prominent veins are a series reverse faults. faults. These series of of quartz quartz veins veins formed along reverse These veins veins range from 10-40 10-40 cm cm in in thickness thickness and andare aresurrounded surrounded by by zones zonesof ofparticularly particularly extensive extensive chioritization chloritization and and epidotization epidotization of the basalt. The Thequartz quartzisis coarsely coarsely crystalline crystalline and and milky. milky. At At times crystals up to 15 cm long. long. Locally Locally times the the veins veins open open up up into into vugs vugs containing containing euhedral euhedral quartz quartz crystals calcite occurs occurs on on the the quartz quartz as asyellow-green yellow-green flattened flattened rhombohedral rhombohedral or globular clusters of radiating crystals. Pink Pinktotowhite whiteK-feldspar K-feldspardruses, druses,radial radialgroups groups of of dark-green dark-green chlorite, chlorite, and and copper minerals such such as as chalcocite, chalcocite, cuprite and malachite also occur from time to time in the veins. veins. Joint chlorite, hematite, hematite, tremolite Joint surfaces surfacesmay may be be coated coated by by aa variety of minerals, including chlorite, tremolite (growing (growing in in fibers fibers up up to to 33cm cmlong), long),white whitecleavable cleavablecalcite, calcite,chrysotile, chrysotile,chalcopyrite, chalcopyrite,bornite, bornite, malachite, malachite,and andnative native copper. copper. 48 �Figure Figure 14. 14.(a) (a)Photomicrograph Photomicrograph(crossed (crossedpolars) polars)of of "ophimottled" "ophimottled"basalt basalt(scale (scalebar bar along alongleft left mrn long). long). (b) Photomicrograph Photomicrograph (uncrossed polars) of augite augite exhibiting exhibiting ophitic ophitic side is 55 mm mm long). Groundmass in (a) and (b) contains plagioclase texture (scale bar along left side is 2.5 texture (scale bar along left side is 2.5 rnrn long). Groundmass in (a) and (b) contains plagioclase microcrysts, microcrysts, Fe-Ti oxides, oxides, chlorite, chlorite, quartz, quartz, epidote, epidote, actinolite, actinolite, and and calcite. calcite. 49 �Nuggets Nuggets of native copper copper massing up to several kilograms have been found in the quarry, but the author has not seen any in place. place. These Thesereportedly reportedly are are most most common common when when quarry quarry corner of the quarry. These operations are active in the flow-top area in the northwestern comer These can can effects on the crusher, and are thus not viewed as a resource have disastrous effects resource by the the quarry quarry owner. quarry are arecut cutby bynumerous numerousfaults. faults. Numerous Numerouseast-dipping east-dipping(45O (45°)) The flows of the north quarry cross-cut by a west-dipping (35° north-south across thrust faults are cross-cut (35O ) thrust fault that trends north-south across the center of the quarry (Leslie et al., 1994). Along most of the west-dipping fault surface is (Leslie 1994). Along most of west-dipping fault surface is massive massive and milky-white milky-white quartz. epidote-filled en-echelon en-echelon fractures, fractures, quartz. Also Alsofound found within within the the gouge gouge zone are epidote-filled striated and stepped chlorite-quartz-epidote chlorite-quartz-epidote surfaces, and late-stage syntaxial calcite fillings. kinematic indicators indicators indicate indicate that the hanging wall moved up and and east east relative relative to to All of these kinematic the footwall. Motion Motionalong alongthis thissurface surfaceoffsets offsets other other thrust faults in the quarry that dip to the east; the magnitude of the motion is not known known but but is is likely likely minor. minor. The age of faulting is not known, but the similar metamorphic minerals found in both the host rock and the gouge zone suggest that motion occurred occurred while the rocks were still relatively deeply buried. Geology of of the the east east quarries quarries across the the railroad railroad tracks, tracks, is another Approximately 0.5 0.5 km km SSE of the north quarry, across complex. These quarry complex. Thesequarries quarriesexpose exposetwo twoflows flowsunderlying underlyingthe theTrap TrapRock RockAlley Alley flow flow seen seen in in the north quarry. These These flows flows are are informally informally named the Dresser flows. Ten to twelve meters of each flow are exposed. The flows The flows dip dip westerly at about 10 10 degrees. The The contact contact between between the the two flows is well exposed. exposed. been converted Both flows flows are are subophitic subophiticdiabase, diabase,and andlike likethe the Trap Trap Rock Rock Alley flow, have been to greenstones greenstones during burial metamorphism. metamorphism. The The lower lower flow flow contains contains aa primary primary igneous igneous ilmenite. The rock is microporphyritic. microporphyritic. The assemblage of augite, plagioclase and ilmenite. The groundmass groundmass phenocrysts are titanite, and phenocrysts are incipiently incipiently to completely completely replaced replaced by a mixture of chlorite, epidote, titanite, actinolite, albite albite and and zoisite. zoisite. The plus white white quartz quartz and and pink pink K actinolite, The same same mineral mineral assemblage, plus Feldspar occur in the amygdules. The top of this flow is well exposed, and has been virtually amygdules. The top of this flow is well exposed, and has been virtually entirely entirely recrystallized recrystallizedto to aa metamorphic metamorphic greenstone. greenstone. Large Largeamygdules amygdulesare areabundant, abundant,and and contain contain coarse-grained assemblage yellowan attractive coarse-grained assemblageof white white quartz, quartz, pink K-feldspar, K-feldspar, red hematite, hematite, yellowgreen epidote, and dark green chlorite. Only Onlyminor minor flow-top flow-top breccia breccia can be seen. seen. subophitic The upper flow has a fine-grained chilled base grading upward into a diabasic subophitic interior. The Theprimary primaryigneous igneousand andsecondary secondary minerals minerals are are the the same same as as that that of of the the lower lower flow. flow. The The upper flow flow contains contains fewer fewer amygdules, amygdules, and and these these are are dominated dominated by nearly isotropic isotropic chlorite chlorite with minor intergrown epidote and quartz. The Thetop topof of this thisflow flow isis not not exposed. exposed. 50 �Stop %Magnetic Characteristics of the the Chengwatana ChengwatanaLava LavaFlows. Flows. Stop 2—Magnetic Characteristics of Location: Outcrops are are located located on on both both sides sides of of the the road road near near the the intersection intersection between between the the Location: Outcrops NE 1/4, 114, NE 1/4, 114, Sec. 11, 11, T 33 N, R 19W. 19 W. pipeline and County Road S. NE Figure 15. 15. Scanned Scannedimage imageof ofaaportion portionof ofthe theUSGS USGS Osceola, Osceola,WI-MN WI-MN topographic topographic quadrangle (7.5-minute (7.5-minute series; series;1:24,000 1:24,000 scale) scale) showing showing the the location location of of Stop Stop 2. 2. quadrangle examine and discuss the magnetic characteristics characteristics of the Chengwatana Chengwatana At this stop we will examine lava flows as exposed in Polk County, Wisconsin. Wisconsin. Paleomagnetic studies have been been conducted conducted in this region over the past 10 relationship of these 10 years to better understand the stratigraphic relationship flows within within the the context context of of the the regional regional Keweenawan Keweenawan magmatic sequence. paleomagnetic studies studies for for this this region region are arereported reportedby byKean Keanetetal. al.(1997). (1997). Here Detailed paleomagnetic only on on the the general general interpretation interpretation of of the the paleomagnetic paleomagnetic results results that that help helpto to place place we concentrate concentrate only the Chengwatana flows in the context context of of the the other other Keweenawan Keweenawan rocks in the Lake Lake Superior Superior region. Keweenawan Keweenawan paleopole paleopole positions positions for the craton are well known and a major polarity reverse to normal transition from fromreverse normal occurred occurred during during the the middle middle Keweenawan Keweenawan (1105-1102 (1 105-1102 Ma) has been documented by Palmer (1970) and Halls and Pesonen (1982). Table Table 22 shows shows this this Lake Superior polarity change change as as determined determined in some some of the major basalt flows of the southern Lake predominantly region. Feeney Feeney(1990) (1990)determined determinedthat that the the lava lava flows throughout Polk Co. have predominantly a-95=15.5° ;;which is consistent D=27S0 ,,1=41.5° 1=41S0,, a-95=15.5O normal polarities, polarities, with with aa mean direction direction of D=275° consistent Pesonen, 1982) 1982) such as the the North North Shore with other other Keweenawan Keweenawan directions directions(Table (Table 2) (Halls and Pesonen, Volcanic Group Group (Books, (Books, 1972). 1972). He Volcanic He also also noted noted several several locations locations with with reversed reversed directions. directions. St. Croix CroixFalls Fallsrendered renderedamore amore precise correlation correlation Insufficient geologic geologic control controlnorth north of the city of St. impossible impossible for for those those locations. locations.However, However,the thevolcanics volcanicssouth southof of St. St. Croix Croix Falls Falls are are better exposed exposed and have been mapped in detail detail by Cordua Cordua (1989a and b) which allowed for a more detailed study. Sixty-five Sixty-fiveoriented orientedcores coreswere were collected collectedat at the 66 sites noted in ~FIgure i g u r e16. Sampling Samplingwas was 51 �Table 2. Magnetic Magnetic polarity polarity and anddirections directionsfor formany many Keweenawan Keweenawan rocks rocks in in the the Lake Lake Superior region (from Superior (from Halls Halls and and Pesonen, Pesonen, 1982). 1982). Formation DeclinDeclination Jacobsville Jacobsville Sandstone Sandstone 263 263 Freda Sandstone Sandstone Apha 95 Pole Position Polarity -11 6 183°E, -0.9°S N 271.3 271.3 0.7 2.8 179.5°E, 1.2°N N Nonesuch Shale Shale 279.8 279.8 9.8 6 176.5°E, 10.3°N N Portage Volc (Avg) (Avg) Portage Lake Lake VoIc 288.6 34.9 2.5 181.2°E, 26.5°N N Upper North Shore Shore Vol. Vol. (Avg) (Avg) 290.3 290.3 44.5 4.7 183.8°E, 32.4°N N Lower Lower North Shore Shore Vol. Vol. (Avg) (Avg) 120.9 120.9 -63 7.8 197.8°E, 9.6°N N Logan Logan Sills Sills 1111 11 -72 2.5 219°E, 49.4°N N 74 74 -71.5 4.8 232.4°E, 28.9°N N Upper Powder Mill Gr. Gr. InclinInclination and 2), 2), and and concentrated in the areas areas where where Feeney Feeney (1990) (1990) found found reversed reversed directions directions (sites (sites 11 and equivalent. Most which are considered stratigraphically equivalent. Most of of the the samples samples (Table (Table 3) 3) have have high high intensities of natural remanent magnetism (NRM) (1.0-2,0 AIm) and volume magnetic natural remanent magnetism (NRM) (1.0-2.0 Alm) and volume magnetic susceptibility (4 x 10-2 SI). SI). The Themagnetic magneticproperties propertiesdiffer differ somewhat somewhat between between flows.. flows. The The remanent intensities middle flows flows (Pothole (Potholetrail, trail, Trap Trap Rock Rock Alley and Dresser flows) have remanent intensities and and which are are at least an order of magnitude less than the other magnetic susceptibilities which other flows flows (Table 3). For Forsamples sampleswith withvery very strong strong remanent remanent values, values, the intensities intensities are typically reduced A.F. demagnetization to to 20 20 millitesla millitesla (mT). (mT). Petrographic studies 100 fold with A.F..demagnetization studies of the the opaque opaque minerals in samples from each each site site also also show show differences differences which are consistent with the bulk magnetic parameters of susceptibility susceptibility and intensity. intensity. The The upper upper lava lava flows flows (sites (sites 1-4; 1-4; Fig. 16) 16) have a high percentage percentage of coarse-grained magnetic minerals (25 percent), which are generally coarse-grained magnetic minerals (25 percent), which are generally more altered than the older flows (sites 5 and 6), 6),and and which appear to have been produced during metamorphism. metamorphism. Samples during Samplesfrom fromsites sites55and and66have haveonly only about about 10 10percent percent magnetite magnetitegrains grains and the grains are smaller smaller than the upper flows. Principal Principalcomponent componentanalysis analysisof of the the magnetic magnetic directions directions (Kirschvink, (Kirschvink,1980) 1980)for for samples samplesfrom fromthe the various various sites sitesreveals reveals two two directions directionsthat that are are approximately antiparallel to to each other. other. The most prominent direction, after removal of The most prominent direction, after removal of aa viscous component is a northwesterly with inclinations of of about 430 43O (normal (normal northwesterly declination, with magnetization). A approximately -50 500 A second seconddirection direction with with aa southeasterly southeasterly declination and approximately inclination (reverse in some some samples samples at at sites sites 11and and2.2. There are (reverse magnetization) is present only in no significant significant differences petrographic characteristics characteristics or in the the rock rock magnetic magnetic properties properties differences either either in petrographic between the normal magnetized samples and the reversely magnetized samples at both sites 11 normal samples and 2. Wirth the entire entire sequence sequence of of Wirth et et al. al. (1997) (1997)report report only minor geochemical differences for the flows. The Thedetailed detailedmagnetic magneticinformation information for for these these sites sites is is given given in Table 4. Combined Combined data data from both components yield yield a Virtual Virtual Geomagnetic GeomagneticPole Pole(VGP) (VGP)atat30.9' 30.9° N, N, 186' 186° E, which which 52 �92 42 3O Oc 1 Ouarternary Alluvium. Colluviurn. Drift d 45 25 ST CROIX FALLS 8 PRECAMBRIAN PRECAMBRIAN KEWEENAWAN KEWEENAWANVOLCANIC VOLCANIC SERIES SERIES Ky Kv 0Kp Kp 0KsKs 0Kep Kep tO Kt Kd Kd Kpt Kpt --0 Q Unnamed Unnamed Flows Flows Pipeline P~pehneFlows Flows Skitrail Skltra!lFlows Flows Eagle Eagle Peak Peak Flows Flows Traprock TraprockAlley Alley Flows Flows Dresser Dresser Flows Flows Pothole Pothole Trail Tra~lFlows Flows Exposed Exposed Contact Contact Unexposed Contact Contact Unexposed Sample Location LocatlonNormal Normal Sample Location Locat!onReversed Reversed Sample Location LocatlonMixed Mlxed 1 MILE G 0 iKM t 45 20 92 $2'42 42'30 3W 92 37 30 Figure Figure 16. 16. Map Mapshowing showingpaleomagnetic paleomagneticsampling samplingsites sites(after (after Kean Kean et et al., 1997). 1997). 53 �Table 3. NRM NRM intensities intensitiesand and susceptibility susceptibility values for the Chengwatana volcanics in the St. St. Croix Croix Falls Falls area. area. Flow Name Number of samples samples Ky Kv NRM Intensti Intenstity ty AIM A514 Magnetic Susceptibility x10i5 Volume S.I. units xlO-5 9 2.3 3591 Pipeline Pipeline 14 2.0 5118 SkiTrail Ski Trail 16 2.1 5326 Eagle Peak Peak Eagle 14 0.15 1061 6 0.14 23 0.057 299 742 Trap Rock Alley Dresser 11 Pothole Trail 6 0.05 LotusLake h t u s Lake 6 2.1 3647 Paleomagnetic data for the sites indicated in Figure 16 Paleomagnetic 16 (after Kean et a!., al., 1997). 1997). Table 4. N DecinDeclination Inclination K 288.9 49.5 5.2 6.9 29.2 36.7 17 Apha -95 (R) (3) 7 7 114.8 55.0 -57.8 Site 2 (N) (N) 7 274.0 51.1 13 -47.5 33.2 14 23.1 20.8 31 16.3 14.1 45.5 42.6 43.4 45.8 11.2 18.8 11.2 Site I1 (N) (N) (R) (3) Site 33 Site 4 Site 55 Site 66 (N) Avg (N) (N&R) Avg @&R) 10 10 88 106.7 5 280.0 88 77 88 285.1 306 6 6 88 287.9 286.8 287.5 6.7 25.4 43.9 48.5 10.2 8.04 VGP Lat(N) L atO Long(E) Long@) SITE SITE L ato L ong0 Lat(N) Long(W) 45.33 92.65 24.6 31.2 193.4 193.4 198.4 187.9 45.37 92.67 19.9 183 22 43 178.9 29.6 29.7 30.9 183.6 184.9 186.1 45.39 45.39 45.36 45.37 92.66 92.66 92.64 92.63 41 173 agrees well with published published Keweenawan Keweenawan paleopoles for stable North American (Halls and and Pesonen, the area, area, because because Pesonen,1982). 1982).ItItisispossible possiblethere thereare areother other exposures exposuresof of the reversed flows in the detailed magnetic studies have not been conducted over the full length of the two prominent ridges in the area. area. Paleomagnetic Correlation Correlation The appear wimn within aa thick thick series series of of The reversed flows in this area are important because they appear flows that are normally polarized and considered to be equivalent in age, or younger than, the 54 �NorthShore Shorevolcanics. volcanics.Past Pastinterpretations interpretationssuggested suggestedthat thatallallthe theKeweenawan-age Keweenawan-ageflows flowsequivaequivaNorth lentororyounger youngerthan thanthe theNorth NorthShore Shorevolcanics volcanicswere werenormally normallypolarized polarized(Green, (Green,1977; 1977;Halls Halls lent and andPesonen, Pesonen,1982), 19821,and andthose thoseflows flowsolder olderthan thanthe theNorth NorthShore Shorevolcanics volcanicswere werereversely reverselypolarpolarized. ized.Similar Similarshort shortreversals reversalsatatapparent apparentequivalent equivalentstratigraphic stratigraphiclevels levelshave havebeen been documented documented onlyaafew fewother otherlocations locationsin inthe theLake LakeSuperior Superiorregion. region. The Thebasalt basaltflows flowsatatMamainse MamainsePoint Point atatonly theeastern easternLake LakeSuperior Superiorregion regionshow showa asimilar similarshort shortreversal reversal(Palmer, (Palmer,1970; 1970;Robertson, Robertson, ininthe 1973). 1973).The Thedikes dikesininthe thealkali alkalisyenite-carbonatite syenite-carbonatitecomplexes complexesininthe theKapuskasing Kapuskasingstructural structural zone zoneininCanada Canadadated datedatat1097 1097Ma Mayears yearsshow showreversals reversalsin in aanormal normal polarity polarity sequence sequence(Symons (Symons etetal. al.1994). 1994).The Thegeochemical geochemicaldata dataofofWirth Wirthetetal. al.(1997) (1997)are areconsistent consistentwith withthis thisequivalence equivalenceinin age agebetween betweenthe theChengwatana Chengwatanaflows flowsand andthe themiddle middlesection sectionat atMamainse MamainsePoint. Point.AAshort shortreverreversal salatatthis thistime timeisisalso alsoconsistent consistentwith withrecent recentages agesby by Wirth Wirth and and Gehrels Gehrels (in (in press). press). They Theyreport report Mafor forslightly slightlyolder olderChengwatana Chengwatanarhyolites rhyolitesnear near preciseU-Pb U-Pb zircon zircon ages ages of of 1102 1102Ma Ma ± 55Ma precise Clam ClamFalls, Falls,which whichisison onthe theeastern easternextreme extremeofofthe theChengwatana Chengwatanaexposures. exposures. Field FieldIdentification IdentificationofofReversed ReversedFlows Flows Unfortunately, Unfortunately,ititisisnot notpossible possibleto tovisually visuallyrecognize recognizenormalnormal-from fromreverse-polarity reverse-polarityrocks rocks ininthe thefield. field.Occasionally, Occasionally,the thereversed reversedflows flowsininthis thisarea areawill willcause causeaacompass compassneedle needleto todeflect deflect by but bymore morethan than90°, 90° butthen thenso sowill will areas areasstruck struck by lightening. lightening. Only Onlydetailed detaileddemagnetization demagnetizationof of samplesin inthe thelaboratory laboratorycan canresolve resolvethe thepolarity polarityquestion. question. samples Stop Interstate Park, Stop3a—Chengwatana 3a-Chengwatana Volcanic Volcanic Flows Flows of Interstate Park,WI. WI. Location: Location: Access AccesstotoEagle EaglePeak Peakisisfrom froma ahiking hikingtrail trailleading leadingwest westfrom fromthe thegroup groupcamping camping area, (WI).NW NW1/4, 114,SE SE1/4, 114,Sec. Sec.36, 36,TT3434N,N,RR1919W. W.(Fig. (Fig.17). 17). area,Interstate InterstatePark Park(WI). NOTE: NOTE: Specimen Specimencollecting collectingisisnot notallowed allowedininthe thepark! park! Thecrest crestof ofEagle EaglePeak Peakisison ontop topof of the thedipping dippingEagle EaglePeak Peakflow, flow, aa porphyritic porphyritic basalt basalt with with The large largeplagioclase plagioclase phenocrysts. phenocrysts. The Thepanoramic panoramicview viewfrom fromthe thecrest crestallows allowsvisitors visitorstotosee seethe the contrasting contrastingtopography topographyon oneast-facing east-facingflow flowfronts frontsversus versuswest-sloping west-slopingflow flowtops, tops,the thegeneral general distribution distributionof ofCambrian Cambriansedimentary sedimentaryrocks rocksdeposited depositedaround aroundbasaltic basalticislands, islands,and and the the Quaternary Quaternary featuresof ofthe theDalles Dallesofofthe theSt. St.Croix CroixRiver. River. features TheEagle EaglePeak Peakflow flowmap mapunit unitconsists consistsof ofseveral severalflow flow units units containing containingconspicuous conspicuouspink pink The plagioclasephenocrysts phenocrystsup uptoto66cm cmlong longin inaafine fine crystalline crystallinematrix. matrix. The Thematrix matrixand andphenocrysts phenocrysts plagioclase minerals such as epidote, arepartly partlyto tocompletely completelyreplaced replacedby bysecondary secondarymetamorphic metamorphic minerals such as epidote,chlorite, chlorite, are actinolite Kactinolite and and albite. albite. The Theflow flowtop topcontains containsmany manyamygdules amygdulesfilled filledwith withquartz, quartz,epidote, epidote,Kfeldspar feldsparand andchlorite. chlorite.The Theflows flowsdip dipgently gentlywestward westwardatatan anangle angleofofabout about15 15degrees. degrees. This Thisflow flowisisan animportant importantstratigraphic stratigraphicmarker, marker,traceable traceablein inthe thearea areafor forover over99kilometers kilometers along alongstrike. strike. InInplaces placesthe theunit unitconsists consistsofofonly onlyone oneflow; flow;in inothers othersititthickens thickensto to as asmuch muchas as60 60 meters meters and and includes includesat atleast least33 flow flow units, units, one one on on top top of the other. In Inthe theEagle EaglePeak Peakarea, area,only only oneflow flowisisevident. evident. one The Theslope slopecontinuing continuingdown downto tothe thewest westisisthe thedip dipslope slopemarking markingthe thetop topof ofthe theEagle EaglePeak Peak flow. flow. This Thisisisinincontrast contrasttotothe thesteep steepeast-facing east-facingescarpment escarpmentone oneascends ascendstotoreach reachthe thesummit summit from the group camping area. A small escarpment in the trees marks a quarry exposing from the group camping area. A small escarpment in the trees marks a quarry exposing the the overlying overlyingflow. flow. This Thisemphasizes emphasizesthe thestair-step stair-steptopography topographyof of the the terrain terrain formed formed by the dipping dipping flows. flows. 55 �Figure 17. 17. Scanned Scannedimage imageof of aaportion portion of of the the USGS USGS St. St. Croix Croix Dalles, Dalles, WItopographic quadrangle MN topographic quadrangle(7.5-minute (7.5-minute series; series; 1:24,000 1:24,000 scale) scale) showing showing the locations of Stops Stops 3a, 3a, 3b, and 4. One can see see outcrops outcrops of of Cambrian Cambrian sediments sediments deposited unconformably on the complex in the Chengwatana Chengwatana flows. flows. Looking slightly south of west, across the landscape developed in sandstones exposed in road cuts along U.S. river, one sees buff-colored Cambrian Mazomanie sandstones Highway 8. Cambrian Cambrianstrata strata continue continue down down to river level on the west side of the St. Croix Croix Highway River. The fiver. The sandstone sandstoneisistraceable traceablethrough through the the trees trees along along the the bluffs north nearly to the town of Taylors Falls. Falls. Here Taylors Hereaaridge ridgeofofbasalts basalts(predominantly (predominantlythe the Eagle EaglePeak Peak and andTrap TrapRock RockAlley Alley flows) rise up from which the the town town rests. rests. The scenic gorge called from the river to form the hills on which the St. Croix Dalles is cut cut through through these flows. Locally Locally along along the the contact contact of of the the Cambrian Cambrian sediment, is aa coarse coarse basalt basalt boulder boulder conglomerate conglomerate facies called the Mill Street Street conglomerate. conglomerate. the next next stop. stop. Another ridge of basalt is found near This is not visible here, but will be visited at the Northern States Falls is is built. built. East the Northern States Power Power Plant Plant and forms the highlands on which St. Croix Falls East of the river are many outcrops A few few exposures exposuresof of Cambrian Cambrian sandstone, sandstone,particularly particularly outcrops of basalt. A along along the bluffs bluffs to to the the east, east, can can also also be be found. found. 56 �Reconstruction Reconstructionof of the the paleogeography paleogeography of of the the Cambrian-Precambrian Cambrian-Precambrian unconformity unconformity was was done done using using outcrop outcrop and and water-well water-well data. The Theunconformity unconformity is is complex complex and and shows shows aa relief relief of of over over 100 100meters meters (Scott (Scott and and Anderson, Anderson, 1983). 1983). In Insome someareas, areas,the the relief relief occurs occurs along along buried buried shear shear cliffs, Cambrian sea rose. The as the Cambrian The Mill Mill Street Street conglomerate conglomerate cliffs?which whichwere wereprogressively progressively covered covered as marks these environments. In other areas, calmer embayments and lagoons formed marks these environments. In other areas, calmer embayments and lagoons formed in in areas areas of lower lowerrelief, relief?sometimes sometimesisolated isolated behind behind basaltic basaltic islands. islands. Fine Finesandstones sandstonesand andshales shalesof ofthe theEau Eau Claire Claireand and Mazomanie MazomanieFormations Formations were were deposited deposited in in these these areas. areas. The Theshapes shapesofofthese theseislands islands were of the the flows? flows,joint joint sets, sets, and and small small faults. faults. The were controlled controlled by the the stair-step stair-step topography topography of The continuity continuity of of the the Eagle Eagle Peak Peak flow flow from from island island to toisland island suggests suggests that thatfaults faultswith withmajor major displacement displacementdid didnot notcontrol controlthe theshapes shapesof ofthe theislands. islands. Knowledge Knowledge of the the distribution distribution of of basalt basalt in inthe thesubsurface subsurfacehas hasconsiderable considerablepractical practical importance. A company building a pipeline through the area in the 1970's went bankrupt importance. A company building a pipeline through the area in the 1970's went bankruptbecause because they they failed failedto totake takeinto intoaccount accountthe theexpenses expensesinvolved involved in in blasting blastingthrough throughthese theseburied buriedbasalt basalt ridges ridgeswhen when submitting submittingtheir theirbid. bid. ItItisisalso alsonot notuncommon uncommonfor forone oneparcel parcel of of land land to to have have basalt near near the the surface surfaceto to have have little little or or no no ground ground water, while a neighboring parcel a few 100 100 meters away away will will have have aa plentiful plentifulsupply supply of of water water from fromaathick thicksection sectionof ofPleistocene Pleistoceneand andCambrian Cambrian sediments. sediments. The The scenic scenic dalles dalles of of the the St. St.Croix CroixRiver River are arewhere wherethe theriver, river,after afterexcavating excavating the the soft soft Cambrian sediments in a gap between paleo-islands, has finally cut down to the hard basaltic Cambrian sediments in a gap between paleo-islands, has finally cut down to the hard basaltic shoal shoal separating separatingdeeper deeperCambrian Cambrianembayments. embayments. Immediately Dalles, aa possible possible whirlpool whirlpool or Immediately to the north, one can see see the Lake Lake of the the Dalles, plunge more easterly easterly course. course. Finally, numerous plungepool pool formed formedwhen whenthe the St. St. Croix Croix flowed along a more glacial glacial striations striationsand andchatter chattermarks marks can canbe be found foundon on the the bedrock bedrock surface surfaceat atEagle EaglePeak. Peak. Stop Interstate Park, Stop 3b—Cambrian 3b-cambrian Rocky Rocky Shoreline Shoreline Deposits of Interstate Park,WI. WI. See Figure Figure 17 17for forlocation locationmap. map. See Location: Lmation: Ravine Ravineimmediately immediatelysouth southofofSkyline SkylineTrail, Trail,approximately approximately 400 400 m m from from trailhead trailhead at at group Park (WI). (WI). SE1/4, SE1/4, Sec. 36, 36, TT 34.N7 34N, R 19W. group campground in Interstate Park SEl14, SElI4, 19W. NOTE: Specimen Specimencollecting collectingisisnot notallowed allowedin inthe the park! park! The meters. ItIt then The Skyline SkylineTrail Trail skirts skirts aa low, marshy area for its first 150 meters. then begins begins its its slow slow ascent ascent onto onto the the Trap Trap Rock Rock Alley flow of the Precambrian Chengwatana Chengwatana basalt, basalt, with with outcrops outcropsof of basalt basalt prominent prominent on on both both sides sides of of the the trail. After Afterapproximately approximately400 400 m, m, aa steep-walled, steep-walled,narrow narrow ravine can be be seen seen by by looking lookingdown down to to the the right right (south) (south) of of the the trail. trail. This ravine ravine marks marks the the approximate approximatecontact contactbetween between Precambrian Precambrian basalts basalts and Cambrian sedimentary deposits. deposits. Basalt Basalt outcrops outcropsoccur occuron on the the floor floor of of the the ravine ravine and along the north wall. Along Along the the south south wall, wall, 88 m of Upper Mazomanie Formation Formation UpperCambrian Cambrianconglomerates conglomeratesand andsandstones sandstonestentatively tentatively assigned assigned to the Mazomanie of of the the Tunnel Tunnel City City Group Group (Mazomanie (Mazomanie Member Member of the Franconia Franconia Formation in Minnesota) Minnesota) lie lie directly directlyabove aboveand andlateral lateralto to the the basalts. basalts. The TheCambrian Cambriansediments sedimentscan canbe betraced tracedfor forsome some240 240m m to to the the east east up up the theravine, ravine,but but the the best best exposures exposuresare are in in the the first first 70 70 m. m. On the south south wail wall of of the the ravine, ravine, aa basalt basalt boulder boulder conglomerate conglomerate facies ("the Mill Mill Street Street conglomerate" of of Berkey, Berkey, 1897) 1897)lies lies against against the the lava lava flows and grades grades vertically vertically and and laterally laterally into in this this area area (Fig. (Fig. 18). In into the sandstone sandstone facies facies more typical of the Cambrian section in In sharp sharp contrast contrastto to the the gray-green gray-greenbasalt basaltflow flowoutcrops outcropson onthe the north north side sideof of the the ravine, ravine, the the basalt basalt boulders boulders in the conglomerate are heavily weathered and stained orange-brown by iron oxides. The conglomerate are heavily weathered and stained Thelargest largest 57 57 �- - - - - I 10 meters meters Figure 18. Sketch Sketch of south south wall wall of of ravine ravine along along Skyline Skyline Trail (Stop 3b) showing vertical and and boulder conglomerate conglomerate and and sandstone sandstonefacies. facies. Covered areas lateral relationships between basalt boulder indicated by lack of pattern. No No vertical vertical exaggeration. exaggeration. boulders boulders near the the base base of the exposure exposure are over 1 m in diameter. The boulders are rounded but perhaps due to to original originaljointing jointing in in the thebasalt. basalt. A quartz sandstone matrix with of low sphericity, perhaps inarticulate brachiopods brachiopods fills boulders. No abundant inarticulate fills the spaces between the boulders. No trace trace of bedding bedding is is present within the main body of the conglomerate, although a few thin conglomerate beds present the conglomerate, extend out into the sandstones. These These beds beds contain contain rip-up clasts of sandstone as well as basalt cobbles and pebbles, pebbles, in basalt conglomerate conglomerate in which sandstone sandstone cobbles in contrast contrast to to the main body of the basalt clasts have not been seen. They Theyalso alsoshow showweak weakimbrication imbricationsuggesting suggesting current current flow flow to to the the west. conglomerate and and sandstone sandstonefacies faciesisissurprisingly surprisinglysharp. sharp. The The contact between the conglomerate The sandstone sandstone beds beds thin- to medium-bedded quartz arenites. arenites. The sandstones are orange-brown, thinmedium-bedded quartz vary in texture from fine- to coarse-grained, coarse-grained, from sub-rounded to rounded, rounded, and from moderately moderately to well-sorted. Some Somefinefine-to to medium-grained medium-grained sandstone sandstoneunits units contain contain scattered scattered coarse, coarse, frosted frosted quartz grains. A A few few beds beds are aregraded, graded, and and some some contain contain quartz pebbles and rip-up clasts of sandstone with foresets foresets dipping dipping sandstone and siltstone. Many Many units units show show high-angle planar cross-bedding, with to the west. fron-oxide Iron-oxidestaining stainingand andconcretions concretions are are common, common, as are inarticulate brachiopod shell- hash layers. AAlarge trough cross-bed set (or possibly a slump) near the center of the large trough cross-bed set (or exposure exposure is indicated indicated by aa curved curved erosional erosional surface surface marked by basalt cobbles near its base, and sandstone beds which dip slightly to the east, in contrast to the slight westward westward dip dip of of most of the sandstone sandstone beds in in the the outcrop. outcrop. Interpretation Interpretation The Taylors Falls-St. Falls-St. Croix Croix Falls Falls area of Minnesota and and Wisconsin Wisconsin isis one one of the few localities in North North America America where where Upper Upper Cambrian Cambrian conglomerates conglomerates lie lie unconformably unconformably on on Precambrian rocks rocks (Webers (Webers and and Austin, Austin, 1972; 1972;Cavaleri Cavaleri et. al., 1987). 1987). 58 �Apparently, Apparently, the the Cambrian Cambrian Sauk Sauksea seatransgressed transgressedonto ontoaaland landsurface surfaceof ofvery verylow lowrelief reliefas as itit flooded advanced. At a few localities localities flooded the the North North American American craton, craton, leaving leaving a blanket of sand as itit advanced. such such as as Taylors TaylorsFalls-St. Falls-St.Croix CroixFalls Fallsand andBaraboo, Baraboo,Wisconsin Wisconsin (Dalziel (Dalzieland andDott, Dott,1970; 1970;Dott, Dott, 1974), 1974), resistant bedrock bedrock hills hills stood stood above above the the subdued subdued land land surface surface and and acted actedas aslocal localsources sources for for coarse coarse conglomerate conglomeratedeposits depositsas as the sea advanced. In In Baraboo, Baraboo, the conglomerate conglomeratewas was formed formed of quartzite quartzite boulders boulders from from local local outcrops; outcrops; in in the the Taylors Taylors Falls-St. Falls-St. Croix Croix Falls Falls area, area, the the conglomerate conglomerate was was formed formed of of basalt basalt boulders boulders from from the the local local lava lava flows. flows. The basalt boulder boulder conglomerates, conglomerates, informally called the "Mill Street conglomerate" are are exposed exposed at at only only aa handful handful of of sites sites on on both both sides sidesof of the the St. St. Croix Croix River River south southof of Taylors Taylors Falls-St. Falls-St. Croix Croix Falls. Falls. Of Ofthese thesesites, sites,the theSkyline SkylineTrail Traillocality, locality,shows showsmost most clearly clearlythe the vertical verticaland andlateral lateral relationships relationships between between the Precambrian Precambrian basalts and Upper Upper Cambrian Cambrian conglomerates conglomerates and sandstones. sandstones. As Ascan canbe beseen seenin in the the ravine, ravine, the the basalt boulder conglomerate conglomerate was deposited deposited on on top of and and against against aa steep steep face face cut cut into into the the basalt basalt lava lava flows. Very Very high high energy energy conditions conditionsmust musthave have been been present present to to round round the the corners comers of the basalt boulders. Dott Dott(1974) (1974)estimated estimatedthe theheight heightof ofthe the waves required to round boulders of similar size in Baraboo. Baraboo. His His conservative conservative estimates estimates of m high suggest suggest storms storms were important in producing producing these conglomerates. conglomerates. A A waves 55 m paleogeographic paleogeographic reconstruction reconstructionof of the the Taylors Taylors Falls-St. Croix Falls area as the Sauk Sauk sea sea began began to submerge submerge the the basalt basalt highlands highlands shows shows that the the lava flows along the Skyline Trail would have been fully exposed to waves from the west or southwest. ItIt isis tempting tempting to to envision envision basalt basalt sea sea cliffs on the windward windward side side of of islands islands or or headlands, headlands,with with storm-generated storm-generatedwaves waves crashing crashinginto into and the base base being being pounded pounded and jostled jostled and undercutting undercuttingthe the cliffs, cliffs, and and the the rubble rubble in the surf zone at the to produce rounded boulders. Such an environment evokes images of the Hawaiian Islands or rounded Such an environment evokes images the Hawaiian or perhaps perhaps the the Pacific Pacific Northwest Northwest coast coast today. today. However, However, very very little little has been written written in the geologic geologic literature literature on on the characteristics characteristics of of rocky shoreline shoreline deposits (Johnson, 1988) 1988) and care should be taken in reconstructing reconstructing the the exact exact depositional depositionalenvironment. environment. The The sharp sharp contact contact between between the conglomerate conglomerateand and sandstone sandstone and the difference in lithology between between the the two two facies facies suggest suggestthat that the the sands sands came came from from a more distant distant source source and and were were washed washed along basalt boulders. boulders. The along the shoreline shoreline and and deposited deposited against against and between the basalt The graded graded bedding, bedding, rip-up clasts and shell-hash layers show that periodic storms may have been more important and shell-hash layers been more important in deposition deposition of of the the sandstone sandstone beds beds than normal day-to-day events. Storms Stormscould couldalso also account accountfor for the two conglomerate beds extending out into the sandstone; each each bed bed with a mix of basalt basalt cobbles and sandstone rip-up clasts from the ocean floor. and sandstone rip-up clasts from the ocean floor. The The sandstones sandstones are are tentatively tentatively assigned assigned to to the the Mazomanie MazomanieFormation Formationof of the theTunnel TunnelCity City Group Group by their their similarity similarity to to outcrops outcrops of of that formation formation across across the St. Croix River in Minnesota. However, they they may represent a near-shore Ironton Member Member of ofthe theWonewoc Wonewoc near-shore facies facies of of the the fronton Formation as well. The Mill Street conglomerate varies in age from Dresbachian to Franconian Formation as well. The Mill Street conglomerate varies (Webers and Austin, 1972) 1972) and and thus thus may may grade grade laterally laterally into into sandstones sandstonesof of either eitherformation. formation. Detailed Detailed study of of the the fossil fossil assemblages, assemblages, particularly particularly the trilobites, trilobites, in the the sandstone sandstone and and conglomerate would be the best method method to tell the age age and and formation, formation, but as as yet yet this this has has not not been attempted. attempted. Such Suchaastudy studywould would be be especially especially valuable valuable since the Mill Street conglomerate is known known to to contain contain an an unusual unusual assemblage assemblage of of trilobites, trilobites, inarticulate inarticulate brachiopods brachiopods and and monoplacophoran monoplacophoran molluscs molluscs representing representing an an intertidal, intertidal, shoreline shoreline environment environment (Webers, (Webers, 1972). 1972). According to Johnson (1988), the oldest known known rocky-shore rocky-shorefaunas faunasare areOrdovician Ordovicianininage. age. It may well be be that that the theunusual unusualUpper Upper Cambrian Cambrian conglomerate conglomerate deposits deposits around around St. St. Croix Croix Falls Falls and Taylors Falls contain contain the the oldest oldest rocky rocky shoreline shorelinefaunas faunasin in the the world. world. 59 �Stop Stop4—Potholes &Potholes of ofInterstate InterstatePark, Park,MN. MN. SeeFigure Figure17 17for forlocation locationmap. map. See Location: Paths Pathsleading leadingfrom fromthe theparking parkinglot lotbybythe theinterpretative interpretativecenter, center,Interstate InterstatePark Park Location: (Minnesota). SW 1/4, SW 1/4, Sec. 30, T 34 N, R 18 W. (Minnesota). SW 114, SW 114, Sec. 30, T 34 N, R 18 W. NOTE: NOTE:Specimen Specimencollecting collectingisisnot notallowed allowedininthe thepark! park! This Thisstop stopprovides providesan anopportunity opportunity totoexamine examineoutcrops outcropsof ofbasaltic basalticlava lavaflows flowswith with spectacular spectacular potholes. potholes. From Fromthe theparking parkinglot, lot,follow followthe theservice serviceroad road(also (alsocalled calledTrap TrapRock Rock Alley) Alley)aashort shortdistance. distance.Many Manyshort, short,well-marked well-markedtrails trailstotothe theeast eastimaginatively imaginativelyand andconveniently conveniently lead over, around and through world-class potholes cut in the top of the Dresser basaltic lead over, around and through world-class potholes cut in the top of the Dresser basalticlava lava flow. flow. The Thebase baseofofthe theTrap TrapRock RockAlley Alleyflow, flow,here here at at its its type typelocality, locality, is is well well exposed exposedalong alongthe the west westside sideof ofTrap TrapRock Rock Alley. Alley. The Thetop topof of the the Dresser Dresser flows flows is exposed to the east. This Thisflow flow dips dips gently gently west westunder underthe theTrap TrapRock Rock Alley. Alley. The Theflow flowtop topisistypically typicallyamygdaloidal amygdaloidaland and extensively extensivelyepidotized. epidotized.ItItisiswell wellexposed exposedininabundant abundantoutcrops, outcrops,asaswell wellasasalong alongthe thesides sidesof ofthe the manyenormous enormouspotholes. potholes. many The Thepotholes potholesformed formedon onthe theDresser Dresserflows flows are arethought thought to to be be some someof of the thedeepest deepestin inthe the world world(Crawford, (Crawford,undated). undated).They Theyrange rangefrom fromfist-size fist-sizedepressions depressionsto to"giant's "giant's kettles" kettles"that thatcan can be beover over66meters metersacross acrossand andmore morethan than 20 20 meters meters deep. deep. The Thepotholes potholesare aregenerally generallypartly partly filled filled with withaamixture mixtureof ofsilt, silt,mud, mud,peat peatand andcoarse coarsegrind grindstones stonesranging rangingfrom frompebble pebbletotoboulder bouldersize. size. The Thesediments, sediments,swirled swirledby bythe theturbulence turbulenceof ofthe theriver riveras asititraced racedover overthe the basalt, basalt,were werethe thetools tools cuttingthese thesepotholes. potholes. cutting These Thesepotholes potholesare arepart partofofaalarger largerregion regionof of river-scoured river-scouredterrain. terrain. InInaddition additiontotothem, them,the the bedrock bedrocksurface surfaceisisscoured, scoured,smoothed smoothedand andpolished polished in in many areas. The Thepotholes potholes were were produced produced when when localized localized areas, areas, facilitated facilitated by by joint joint intersections, intersections, wore wore down down slightly slightly faster faster than than the the surrounding rock. Eddies formed over these low spots, trapping sediment. Large boulders surrounding rock. Eddies formed over these low spots, trapping sediment. Large boulders occasionally occasionally were were stranded strandedin in these these depressions. depressions. The Thestrong strongcurrent currentswirled swirledthem themabout, about,but but lacked lackedthe theforce forceto to free free them. them. This Thisaction actioncut cutthe thepotholes. potholes. Notice Noticeininplaces placesthe thegrooves groovescut cutin in the the sides sidesof ofthe thepotholes potholesas aslarge largeboulders boulders ground ground their their way way down. down. The Theboulders bouldersthemselves themselves were were shaped shaped by by the theprocess. process. Grind Grindstones stonesrecovered recoveredfrom fromthe thepotholes potholesare areasassmooth smooth and and roundedas ascannon cannonballs. balls. rounded The Thepotholes potholes here hereare are7.5-18 7.5-18 meters metersabove above the the current current river river level. level. Some Somepotholes potholeshave have beenfound foundasashigh highasas34 34meters metersabove aboveriver riverlevel. level. been The Thepotholes potholesformed formedwhen whenwater waterfrom fromthe themelting meltingglaciers glaciersfilled filledGlacial GlacialLake LakeDuluth Duluthto to the thenorth north(Cahow, (Cahow,1975; 1975;Ojakangas Ojakangasand andMatsch, Matsch,1982). 1982).The Thewater waterovertopping overtoppingthis thislake lakeflowed flowed south southdown downthe the ancestral ancestralSt. St.Croix CroixRiver. River. At AtInterstate InterstatePark, Park,these thesewaters waterswere werefurther furtherfunneled funneled down down the the narrow narrow channel channel now now seen seen as as the Dalles. Dalles. Below Belowthe theDalles, Dalles,the the river river encountered encounteredsoft soft Cambrian Cambriansandstones sandstonesand andshales, shales,which whichcut cutaway awayfaster fasterthan than the the basalt. This Thisresulted resultedininaamajor major knickpoint in in the the St. St.Croix Croixatatthe the Dalles. Dalles. This Thishigh highgradient gradientsped spedup upthe thewater, water, increasing increasing its its knickpoint ability abilityto to gouge gougeout outthe thepotholes potholesas asititexcavated excavatedits its valley valley into into the the resistant resistant basaltic basaltic bedrock. bedrock. Many Many of of the thepotholes potholeshere herehave have been been given given names names by the park service. service. Be Besure suretotoenjoy enjoy the the Lily Lily Pond, Pond,Devil's Devil'sParlor, Parlor,Cauldron, Cauldron,Bottomless BottomlessPit Pit and and Bake Bake Oven Oven as as time time permits. permits. Also Also note note the the west-dipping west-dipping thrust thrust fault fault exposed exposed in in the the cliff cliff by by the the riverboat riverboat dock dock just west west of of the the potholesarea. area. potholes 60 60 �Stop Stop 5—Volcanic 5-Volcanic Flows and Interfiow Interflow Sediments Sedimentswest west of of Lewis, WI. Location: Outcrops Outcropsare arelocated locatedon on345th 345thAve AveOne-half one-half mile west of the intersection intersection with with 130th 130th Location: Street. Street. NN1/2, 112,SE SE1/4 114and and5S1/2, 112,NE NE1/4, 114,Sec. Sec.11, 11,TT37 37N, N, RR 17 17W; W, Lat. Lat. 450 45' 42' 42' 07.6" 07.6" N, N, Long. Long. 092° 092' 26' 26'25.8" 25.8"W. W. Figure 19. Scanned Scanned image image of of a portion of the Figure 19. the USGS USGS Frederic, Frederic, Wisconsin Wisconsin topographic topographicquadrangle quadrangle(7.5-minute (7.5-minuteSeries; Series;1:24,000 1:24,000scale) scale)showing showing the the location location of of StopS. Stop 5. These permission before before entering. entering. Basalt Theseoutcrops outcropsare areon on private private land land and you should seek permission Basalt and and interfiow intefflow sediments sedimentsare areexposed exposedin inaaseries seriesof ofoutcrops outcrops20-100 20-100meters metersnorth northof ofthe theroad. road. Near Near the the road, road,fine-grained fine-grainedbasalt basalt isis exposed exposed in in aa flow that is at least 4 meters thick. Near Near the amygdules. the top top of of the theflow, flow, the the basalt basalt contains containsrare rare large large quartz-filled quartz-tilledamygdules. Interflow Intefflow sediment sedimentisis exposed exposed further furthernorth north and andisisparticularly particularly well-exposed well-exposed in inan aneasteastwest west trending trendingcliff cliff face. face. Please Pleasedo donot nothammer hammeron onthis this face. face. Excellent Excellentexamples examplesofofthe theinterfiow interflow sediment sediment can be found found in in the the many many loose loose blocks along the base of the cliff. The Thebasalt basaltisis overlain Thesediment sediment overlain by aa mixed mixed basalt basalt and and sediment sediment zone zone that is roughly 3 meters thick. The weathers weatherspale palereddish-orange reddish-orangeand andconsists consistsof offine-grained, fine-grained,poorly poorly sorted, sorted,and andthinly thinlylaminated laminated quartz, quartz, feldspar, feldspar, and and volcanic volcanic fragments. fragments. The Thefine-grained fine-grainedmatrix matrixmaterial materialisiscompletely completely recrystallized minerals. Beds recrystallized to epidote epidote and and other other greenschist greenschist facies minerals. Beds typically typically show show planar planar bedding bedding structures, structures,although although some somecross-beds cross-beds(ripple (ripplestructures), structures),channel-fill channel-fillstructures, structures,and and convoluted convoluted beds are are also also visible. Bedding Beddingstructures structuresoften often trend trend uninterrupted uninterrupted right up to the margins margins of of clasts, clasts, though though in in some someplaces places bedding bedding surfaces surfaces appear appear to to be be deflected deflected by by clasts. clasts. There There are are also also patches patches of of sediment sedimentthat that are are surrounded surrounded by basalt and appear "isolated" in in the the two-dimensional two-dimensionaloutcrop outcropface. face.'These, These,asaswell wellas asmany many narrow narrow sub-vertical sub-vertical"veins" of of sediment, sediment, exhibit exhibitwell-defined, well-defined,sub-horizontal sub-horizontallayering layeringthat thatisissharply sharplytruncated truncatedalong alongits itsmargins. margins. 61 , �Fragments of basalt range from less than than aa millimeter millimeter to to more morethan than 15 15centimeters. centimeters. The microcrystalline plagioclase, plagioclase, and are are highly highly vesicular vesicular clasts are typically sub-angular, consist of microcrystalline (1-5 mm mrn diameter); the outer outer surfaces surfaces of many many clasts are are highly highly embayed embayed and and exhibit exhibit very very "sponge-like" textures. textures. Some delicate "sponge-like" Some clasts clasts are are sub-rounded sub-rounded and exhibit decreasing vesicle sizes near their outer edges; the long long axes axes of of highly highly elliptical elliptical vesicles also parallel the clast clast surfaces. Many Many of of these thesefeatures featuresare aresuggestive suggestiveof of chilled chilled margins margins surrounding surrounding some of the clasts. clasts. Many Manylarger largerclasts clastsalso also have have numerous numerous small small "floating" fragments fragments around around their margins. margins. Viewed closely, many of these these fragments fragments appear appear to to be bedisrupted disrupted"glassy" "glassy" walls walls between between adjacent adjacent vesicles. fragments are typically filled with with coarse coarse epidote. epidote. Near the vesicles. Vesicles Vesicles in in the interiors interiors of fragments continuous layer of vesicular basalt has a highly irregular top of the outcrop, a nearly continuous irregular base base that that in some places cross-cuts layering in the underlying sediment. All All of of these these features features point point to to aa highly immature sediment. Elsewhere Elsewherein in the the rift, rift, interflow sediments are interpreted to record deposition in predominantly environments (e.g., (e.g., Jirsa, Jirsa, 1984). However, predominantly sedimentary environments However, some some features features at at this this stop stop are are suggestive suggestiveof hyaloclastites, hyaloclastites,in in which which basaltic basaltic melt melt interacts interactswith with water, water, or water-saturated water-saturated sediment. sediment.Preliminary Preliminaryinitial initialCNd EM^values valuesof ofthese thesesediments sediments(—-2.0; (--2.0; Naiman, unpublished data) are are similar similar to to those those of of the the surrounding surrounding basalts (Table 5) suggesting that the source of the sediments sediments is primarily immature rift volcanics. Stop Stop 6a—Rhyolite 6a-Rhyolite and Basalt Basalt near near Clam ClamFalls. Falls. Location: 435 435m mNNE NNE of of the the intersection intersection between County Rd I and 73rd St. SE SE 1/4, 114,SE SE 1/4, 114, 09.8" N, N, Long. Long. 092' 092° 18' 27.4"W. Sec. 14, T 37 N, R 16W; 16W,Lat. Lat. 450 45O 41' 41'09.8" 18'27.4" W. image of of a portion Figure 20. 20. Scanned image portion of the the USGS USGS Clam Clam Falls, Falls, Wisconsin topographic topographic quadrangle quadrangle (7.5 minute minute series; series; 1:24,000 1:24,000 scale) scale) showing the location of Stop Stop 6a. 6a. 62 62 �Table Table 5. 5. Representative Representativeanalyses analysesof ofbasalt basaltand andrhyolite rhyolitefrom fromthe theClam ClamFalls Fallsregion. region. Si02 Si02 Ti02 Ti02 Al203 *l2O3 Fe203 Fe203 MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 basalt basalt KC-301b KC-301b basalt basalt KC-303 KC-303 rhyolite rhyolite KC-302a KC-302a rhyolite rhyolite KC-302d KC-302d rhyolite rhyolite KC-310 KC-3 10 47.08 47.08 49.89 49.89 1.60 15.66 14.10 0.18 1.84 14.91 13.61 72.46 72.46 0.49 71.34 7 1.34 0.49 11.52 5.30 0.06 72.18 72.18 0.48 11.93 5.78 0.12 0.40 '25 P2° 0.56 0.15 LOl LO1 1.72 0.17 5.10 8.61 3.17 0.55 0.20 2.31 Total Total 100.20 100.36 Mg# Mg# 0.53 6.84 10.00 2.31 qz qz or ab ab an an hy hy 01 ol 3.41 20.08 31.54 14.07 9.23 4.87 0.09 0.48 1.36 2.32 2.63 4.11 1.01 1.32 3.52 4.21 0.09 0.40 99.69 100.22 100.43 0.47 0.19 0.37 0.14 0.56 3.36 27.66 25.60 21.60 31.39 30.56 24.75 3.65 6.43 31.85 24.62 22.51 7.55 29.75 25.02 29.90 4.30 7.24 1.08 2.89 5.10 0.08 0.54 0.08 8.21 13 151 91 82 216 1036 80 889 123 831 108 90 12 178 68 794 62 713 38 141 118 67 965 155 205 117 24 133 281 76 299 14 6 21 Rb Rb Ba Ba Sr Sr 19 115 Nb Zr Y Y 8 Cr Cr Ni Ni v V InitialENd EN^ Initial 11.61 164 111 31 +34 "'"3.4 — -0.10 Sample Sample Locations: Locations: T 37 N, R 16W. 16 W. SW114, SW1/4, SW114, section section 13 13 KC-301b KC-301b -- SW1/4, SE 1/4, 114, SE 1/4, 114, section section 14 14 (Stop (Stop 6) 6) KC-302a -- SE KC-302a KC-302d -- SE SE 1/4, 114, SE 1/4, 114, section 14 14 (Stop (Stop 6) 6) KC-302d SE114, NW1/4, NW114, section section 13 13 KC-303 -- SE1/4, KC-303 SE114, SE1/4, SE114,section section 26 26 (Stop (Stop 66 Alt.) Alt.) KC-310 KC-310 -- SE1/4, 63 14 26 19 9 17 095 �These outcrops outcrops are are on on private private land and permission to access access them them should should be sought sought before before the intersection intersection of of Country Country entering. The The outcrops outcropscan can be be accessed accessed from from the property (north of the 73rd St. approximately 1 mile mile west west of of Clam ClamFalls. Falls. Direct access to the the outcrops outcrops from Rd I with 73rd County Rd Rd I requires landowner. An alternate County requires permission permission from another another landowner. alternate stop (6b) (6b) near near the the McKenzie McKenzie Creek Creek State State Hunting HuntingGrounds Groundsisisgiven given below. below. The purpose of this stop is to examine an example example of ofrhyolite. rhyolite. Rhyolite is extremely rare in this part of the rift rift and and only only two two localities localitiesare are known known in in the the area area extending extendingfrom fromTaylors TaylorsFalls Falls to Clam Falls. This Thisisisin instark starkcontrast contrastto tothe the relatively relatively abundant abundant rhyolites rhyolites (up (up to 25 25 percent percent of of the volcanic volcanic section; section;Green Greenand andFitz, Fitz, 1993) 1993)that that are are exposed exposed on on the North Shore Shore of Lake Lake Superior. Superior. This locality was also also sampled sampled for for U-Pb zircon studies studies (see (see below). At this exposure, that measures measures approximately approximately 150 x exposure, the rhyolite is exposed over an area that 75 meters. The the exposure exposure trends trends N N 50 50° E and Theupper uppersurface surfaceof of the the outcrop outcrop at at the north end of the dips 15° 15O NW, NW, sub-parallel sub-parallelto to the the trend of flow layering in the area. At the southern southern end of the outcrop, exposures outcrop, the the basal basal contact contact with with the underlying underlying basalt basalt flow can be seen. In a few isolated exposures approximately 3-4 3-4 meters meters below below the the top top of of the knoll one can observe isolated exposures exposures in in approximately which basalt and rhyolite are complexly inter-fingered. Sub-angular Sub-angularto to rounded rounded clasts clasts consist consist of fine-grained basalt, up to 15 cm in diameter, diameter, can can be befound foundin inrhyolite. rhyolite. The upper upper contact of of the rhyolite rhyolite with with the the overlying overlying flows flows isis not not exposed. exposed. Weakly porphyritic (An2Abo40r4)and porphyritic rhyolite rhyolite consists consistsof of phenocrysts phenocrystsof of euhedral euhedralalbite albite(An2Ab94Or4) rare quartz quartz occur occur in in aa groundmass groundmassof ofintergrown intergrownquartz quartzand andpotassium potassiumfeldspar feldspar(An0Ab5Or95); textures spherulitic (Fig. 21). textures range from from fine-grained fine-grained intergranular intergranular to medium-grained medium-grained spherulitic Spherulitic Spheruliticintergrowths intergrowths are are commonly commonly nucleated nucleated on on phenocrysts. phenocrysts. Minor Minoranhedral anhedralFe-Ti Fe-Tioxides, oxides, rare calcic amphibole and accessory apatite and zircon are amphibole (ferro-edenite-hornblende), (ferro-edenite-hornblende), and are also also commonly commonly present. present. Groundmass Groundmassquartz quartzisistypically typicallyeuhedral euhedralto to subhedral subhedral and tabular to elongate (length:width (1ength:width ratios == 10:1 10:1 to 50:1) 50: 1) indicating crystallization as tridymite, the orthorhombic, high temperature (>867O (>867° C) C) form form of of quartz. quartz. The Thepreservation preservation of of these these delicate delicate devitrification textures is remarkable remarkable given given the metamorphic metamorphic alteration alteration and and recrystallization recrystallizationthat that has has occurred occurred in this portion of the rift. The rhyolites of the Clam Clam Falls Falls region region are classified as rhyolite or rhyodacite on most diagrams (Abbott (Abbottetetal., al.,ininpress). press). The major and trace major and trace element discriminant diagrams element compositions icelandites and granophyres granophyres from the North element compositions(Table (Table 5) 5) are are similar similar to some icelandites Shore Green, 1997) to type type IIrhyolites rhyolites from from the the Portage Portage Lake Lake Shore Volcanic Group (Vervoort and Green, 1997) and to volcanics (Nicholson, (Nicholson, 1992; 1992; Nicholson and Shirey, 1990). Nd Nd isotopic isotopic studies studiesof of the the rhyolites rhyolites (Abbott ENd values = (Abbott et et al., al., in in press; press; Naiman Naiman and andWirth, Wirth, in in press) press) indicate indicatethat that they they have have initial initialENd This evidence, combined with their relatively minor abundance in the volcanic 0. their relatively abundance the volcanic section, section, 0. by magmatic fractionation. fractionation. This suggests that they originated as residual melts by This is is in contrast contrast to to many values and are interpreted interpreted many of of the the rhyolites rhyoliteson onthe theNorth NorthShore Shorethat thathave havenegative negativeinitial initialENd ENd values to be the and Green, Green, 1997). 1997). Basalt from this part of the the result result of of crustal crustal melting melting (Vervoort (Vervoort and volcanic volcanic section section (e.g., (e.g., KC-301b KC-301band andKC-303; KC-303;Table Table5) 5) isis similar similarto to low-Ti low-Ti basalt basalt of of the the Taylors Taylors Falls region and has initial ENd valuesranging rangingfrom from00toto+3.4, 3.4, consistent ENd values consistent with with derivation derivation from multiple asthenosphere (Naiman multiple mantle mantle sources, sources, including includingenriched enriched mantle mantle plume plume and depleted asthenosphere (Naiman and Wirth, in press). 64 �Figure21. 21.(a) (a) Photomicrograph Photomicrograph (plane-polarized (plane-polarized light) light) of of spherulitic Figure intergrowths of of tridymite pararnorphs paramorphs and and feldspar feldspar in Clam Falls rhyolite intergrowths bar along (sample KC-302a). KC-302a). Scale bar along left side is 0.25 0.25 mm mm long. long. (b) (b) Photomicrograph showing plagioclase (albite) phenocryst with spherulitic spherulitic mrn long. sideis 1.25 1.25 mm intergrowths around the margin. Scale Scale bar bar along along left sideis 65 �One of the major difficulties in integrating geologic information from this portion of the rift with models of of the the rift rift has has been been the thelack lackof ofgeochronologic geochronologic control control in in the the Chengwatana Chengwatana volcanic s. With this objective collected from both Stop volcanics. objective in mind, large samples of rhyolite were collected Stop 10) has not 6a and Stop 6b for U-Pb zircon dating. The Thesample samplematerial materialfrom fromStop Stop6b 6b(KC-3 (KC-310) been processed processed at at this this time, time, but two, two, nearly identical identical ages ages were determined determined for for different different rhyolite rhyolite phases (KC-302a and and KC-302d) KC-302d) from from Stop Stop 6a. 6a. Zircons from both samples samples have have relatively relatively simple reddish-brown, to honey brown, simple prismatic prismatic forms, forms,are are translucent, translucent,and and vary vary in in color color from reddish-brown, brown, and pale pink. Three Threezircon zircongrains grainsfrom fromKC-302a KC-302a yielded yielded concordant concordant ages ages (Fig. (Fig. 22) 22) with mean mean 2O6pb*/238U and 2o7Pb*PO6Pb* of 1102 k ± 5 Ma (2a). 206Pb*/238U and 207~b*/206Pb* ages of (20). Three Threeadditional additionalgrains grainsare are slightly slightly discordant, discordant,presumably presumablydue dueto to small smallamounts amountsof of lead lead loss, loss, and and aa discordia discordiathrough through these thesepoints, points, projected from ± 205 Analyses 205 Ma Ma (MSWD (MSWD== 0.15). 0.15). Analyses from 1102 1102Ma, Ma, yields yields aa lower lower intercept of 196 196 k of three and yield mean 2O6Pb*/238U three abraded abradedgrains grainsfrom fromKC-302d KC-302dare areanalytically analyticallyconcordant concordant and yield mean ^Pb*/238U ages 1101Ma Mak ±55Ma Ma(Fig. (Fig.22). 22). Three additional grains and the two and 2o7Pb*PooPb* 207~b*/206Pb*ages ofof1101 multigrain fractions are slightly discordant; a discordia through these points, projected from uncertainties o of± 1101 Ma, Ma, yields yields a lower intercept intercept of 63 63 k± 217 Ma (MSWD = 0.45). 0.45). Given the uncertainties 1101 ft 5 Ma on each of of the the ages, ages, the the 11Ma Ma age agedifference difference between between the the two two samples samples is is probably probably not not significant. significant. 0.190 Rhyolite Rhyolite 0.186 00 I Age = Age = 1080 1102 ±5Ma 1080 1101 ±5Ma 0.182 0.178 Lower Intercept 196 ±205 Ma (MSWD=0.15) 0.174 I I Lower Intercept = 63 ±217Ma (MSWD=0.45) • 1.98 2.06 1.98 1.82 1.90 1.90 1.90 1.98 2.06 1.82 1.90 1.98 2.06 2O7pb 235 u 2O7pb 235 u 207Pb / 235 U 207Pb / U Figure 22. Concordia Concordiadiagrams diagramsfor forChengwatana Chengwatanavolcanics volcanics from from the the Clam Clam Falls Falls area area (Stop (Stop6a). 6a). Error ellipses ellipses and and regression regression age age uncertainties uncertainties represent represent 95 95 percent percent confidence confidencelimits limits(after (afterWirth Wirth and Gehrels, in press). 1.82 1.82 Analyses of the the Chengwatana Chengwatana rhyolites near Clam Clam Falls indicate indicate that magmatism magmatism began began by at least 1102 1102 Ma Ma in in this this portion portion of of the the rift, rift, considerably considerably earlier than the age reported by Zartman et ± 2.1 Zartman et al. (1997) (1997) for for rhyolite rhyolite (1094.6 2 2.1Ma) Ma)exposed exposednear near the the base base of the the Chengwatana Chengwatana section section in the southeastern southeasternlimb limb of the Ashland syncline. This This implies implies that that lower lower flows flows exposed exposed near Clam Clam Falls Falls likely likely formed formed contemporaneous contemporaneouswith with the the Upper Upper Kallander Kallander Creek Creek volcanics volcanicsand and Conglomerate of the Mellen Complex Complex of of Northern Northern Wisconsin, Wisconsin, and the Group 5 flows and Great Conglomerate Mamainse Point (Fig. 23). The The 1102± 1102 k55Ma Maage ageofofChengwatana Chengwatanavolcanics volcanics in in the Clam Falls 66 �Age (Ma) Minnesota Wisconsin Wisconsin Upper Mich Michipicoten Is. Is. NW Wise Wisc Mamainse Point Point 1085 1090 1095 1100 1105 1110 Figure23. 23. Diagram Diagramillustrating illustratingthe thecorrelation correlationof ofMidcontinent Midcontinentrift riftrocks rocks from from Figure Taylors Falls-Clam Falls region with those those of of northern northern Wisconsin Wisconsin and and the Taylors Superior. The The upper upper limit limit of of the theChengwatana Chengwatana volcanics volcanics is eastern Lake Superior. Zartman et et al. al. (1997) (1997) in in the the estimated on on the the basis basis of of U-Pb U-Pb zircon zircon studies studies by by Zartman estimated Ashland syncline; syncline; the the lower lower limit limit is is based on on the the age age of of Clam Clam Falls Falls rhyolite. rhyolite. Ashland The The age age of of Taylors TaylorsFalls Falls flows flows isisbased basedon ontheir theirpredominantly predominantly "normal" "normal" paleomagnetic paleomagneticsignature signature(Kean (Keanetetal., al.,1997) 1997)(after (afterWirth Wirthand andGehrels, Gehrels,in inpress). press). 67 �region implies that the lower Clam Falls flows may may have have "reversed" "reversed" paleomagnetic paleomagnetic directions directions since they are approximately 105approximately coeval with the the reverse-to-normal reverse-to-normal magnetic magnetic polarity polarity change (1 (11051100 Ma) zk 55 Ma) that that has has been been widely widely observed observedthroughout throughoutthe theLake LakeSuperior Superiorregion. region.The The 1102 1102± age of the the Clam Clam Falls Falls rhyolites rhyolitesalso also implies impliesthat that this this section section of of the the Chengwatana ChengwatanavOlcanics volcanics Ma age during a period regarded as the was erupted erupted during the transition transition between between the the"latent" "latent" and and "main-stage" "main-stage" of rift magmatism (Millerand 1996). magmatism (Miller andVervoort, Vervoort, 1996). Stop 6b -(Alternate) —(Alternate) Rhyolite Rhyolite near near the McKenzie McKenzie Creek Creek State State Hunting Hunting Grounds. Outcrops Outcrops are located on on 310th 3 10th Ave approximately 0.8 miles south and east of the intersection intersection Ave. SE with 315th Ave. SE 1/4, 114,SE SE 1/4, 114, Sec. 26, T 37 N, R 16W; 16 W; Lat. Lat. 450 45O 39' 15.1" N, 092° 18' Long. 092O 18'28.4" 28.4" W. W. Scannedimage imageof of aaportion portion of of the the USGS USGS Clam Clam Falls, Falls, Wisconsin Wisconsin topographic topographic Figure 24. Scanned quadrangle (7.5 minute series; quadrangle series; 1:24,000 1:24,000 scale) scale) showing showing the location of Stop 6b. This stop is an region. Although an alternate alternate stop stop in the the rhyolites rhyolites of the Clam Falls region. Although the the contact stop does does permit permit examination examination contact with with surrounding surroundingbasalts basaltsisisnot not exposed exposed at at this locality, the stop of a large exposure exposure of rhyolite. The Theoutcrops outcropsare arelocated locatedalong alongthe thenorth northside sideof of 310th 3 10thAve Ave after after the end of the pavement near near where where the the road curves south south around around outcrop. outcrop. This outcrop is the the eastemmost easternmostexposure exposure of of Chengwatana Chengwatana volcanics in the Clam Falls Falls region and defines the base of the region the exposed exposed section. At At this thislocation, location,aaseveral-meter-thick several-meter-thick section of rhyolite is exposed over an area area several severalhundred hundredsquare squaremeters. meters. The The rock rock consists consists of of rhyolite. No layering is is observed. observed. The pale purple and aphanitic rhyolite. No compositional compositional or textural textural layering outcrop outcrop is cut by several sets of closely-spaced sub-vertical sub-verticalfractures fracturesthat that have have coatings coatings of iron iron oxides and other alteration alteration minerals. Quartz-rich Quartz-richveins veinsup up to to several several millimeters millimetersthick thick are are also also commonly observed. commonly 68 �Stop near Godfrey Stop 7—Porphyritic 7-Porphyritic flows near Godfrey Lake, Lake, WI. Outcrops are located 0.72 miles west of of County County Rd RdIIon on 315 St. SE SE1/4, 1/4,NW NW1/4, 1/4,Sec. Sec.29, 29,TT 37 37 N, R 16 W; Lat. Lat. 45O 45° 39' 43.0" N, Long. 092O 092° 22' 16 W, 22' 43.4" 43.4" W. W. purpose of this stop is to examine some of the strongly plagioclase-porphyritic plagioclase-porphyritic flows The purpose flows features can be observed in the exposures of the Clam Falls region. Several Severalinteresting, interesting-features exposures along along the north north side side of of the road road at this stop. The the Theeastern eastern end end of of the the exposure exposure consists consists of coarse basalt with porphyritic basalt* large (<3 cm cm long) long) large plagioclase phenocrysts phenocrysts plagioclase (40-60 percent) in aa (40-60 percent) groundmass groundmass consisting consisting of microcrysts of and plagioclase secondary minerals; secondary minerals; no minerals primary mafic minerals are present. Possible zoning structures are zoning still apparent is some of the feldspar phenocrysts. The The rock has been extensively extensively altered as evidenced evidenced by altered 25. Scanned image image of a portion of the strongly Figure 25. the USGS USGS Clam Clam Falls, Falls, the tpographic quadrangle and 1:24,000scale) scale) saussuritized Wisconsin topographic quadrangle(7.5-minute (7.5-minuteseries; series;1:24,000 showing the location epidotized plagioclase, plagioclase, location of Stop Stop 7. abundant chlorite, disseminated iron-oxides, quartz, and secondary feldspar (pink). Near the top of the the porphyritic porphyritic disseminated iron-oxides, quartz, centimeter thick "epidosite" "epidosite" that is is sub-parallel sub-parallel to toflow flowlayering. layering. This This epidosite epidosite is basalt is a ten centimeter similar interfiow sediments sediments seen at other localities. localities. Further similar to many intefflow Further west is a sparsely porphyritic basalt and vesicular basalt that basalt, which is overlain overlain by repeating layers of fine-grained basalt might represent several thin flow units. Some Somecross-cutting cross-cuttingvesicular vesicular basalt is also also observed. observed. Other coarse coarse porphyritic porphyritic basalts basalts can be found found several hundred meters south south of this this stop. stop. plagioclase phenocrysts phenocrysts typically comprise 15-25 percent percent of ofthe therock. rock. Intefflow Interfiow sediment sediment There, plagioclase is also found. Other exposures of coarse porphyritic basalt are also found further south and Other exposures of coarse porphyritic west of this stop (one mile NW of Straight Lake). Lake). The The orientations orientations of flows in this area are NW On poorly known, known, but but they theygenerally generallytrend trendNNE NNEand anddip dipgently gently(—15° (-15' ) to the NW. On the the basis of these considered to be these general general trends, trends, and and the the similarity similarityof rock types, these units are tentatively considered the same same stratigraphic stratigraphicunit. Considering Consideringthat thatflows flowswith with coarse coarse porphyritic porphyritic textures textures are are relatively relatively rare in the Chengwatana volcanics (Eagle Peak flows near St. Croix Falls and stop in the Clam Clam Chengwatana Falls in the region), it is also Falls region), also tempting tempting to suggest suggest that these geographically disparate disparate flow units units might might event. A be a roughly roughly coeval coeval eruptive event. A large large sample sample from this outcrop outcrop was processed processed for baddeleyite and zircon, but did not baddeleyite and not yield yield either either in in sufficient sufficient quantity quantity for for U-Pb U-Pb analysis. analysis. Preliminary Preliminaryinterpretation interpretationof of new new USGS USGS aeromagnetic aeromagneticdata data suggests suggeststhat that the the porphyritic porphyritic basalts basalts at Stop 7 are are stratigraphically stratigraphically below those of Stop Stop 3a. 3a. 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Z.J. and andWirth, Wirth, K.R., K.R., (in (in press), press), Composition Compositionand and source(s) source(s)of of Midcontinent Midcontinentrift riftlavas lavas (Chengwatana Volcanics) Volcanics) near near Clam Clam Falls, Falls, Wisconsin: Wisconsin: 44th Annual Institute Institute on on Lake Lake Superior SuperiorGeology, Geology,Proceedings. Proceedings. 73 �Naiman, Zachary, Zachary, Wirth, Karl R., R., Morey, G.B., and Miller, James D., 1996, 1996, Metamorphism Metamorphismof of Naiman, Chengwatana 42nd Annual Annual Chengwatana Volcanic Group near Taylors Falls Falls and and from from Osseo Osseo drill drill core: core: 42nd Meeting Meeting of of the the Institute Instituteon on Lake Lake Superior Superior Geology, Geology, Cable, Cable, WI, Proceedings, Proceedings, v. 42, p. 4041. 41. Nicholson, S.W., 1992, 1992,Geochemistry, Geochemistry,petrography, petrography,and and volcanology volcanologyof of rhyolites rhyolitesof of the the Portage Portage Nicholson, S.W., Lake Geological Survey Bulletin Lake volcanics, volcanics, Keweenaw Keweenaw Peninsula, Peninsula, Michigan: Michigan: United States States Geological Survey Bulletin 1970-B. 1970-B. Nicholson, S.W., and Shirey, S.B., 1990, Nicholson, 1990, Midcontinent rift volcanism in the Lake Lake Superior Superior region: Sr, Nd, and Pb isotopic evidence for mantle mantle plume plume origin: origin: Journal Journal of of Geophysical Geophysical Research, 1-10868. Research,v. v. 95, 95, p. p. 1085 10851-10868. Nicholson, S.W., S.W., Shirey, Shirey, S.B., S.B., Schulz, Schulz, K.J., K.J., and and Green, Green, J.C., J.C., 1997, Evolution Nicholson, Evolution of 1.1 1.1 Ga Ga Midcontinent Midcontinentrift basalts: basalts: rift-wide rift-wide correlation correlation and interaction of multiple multiple mantle mantle sources sources during rift development: development: Canadian Canadian Journal Journal of of Earth EarthScience, Science,v. v. 34, 34, p. p. 504-520. 504-520. Ojakangas, Green, J.C., editors, editors, 1997, Proterozoic to Ojakangas, R.W., Dickas, Dickas, A.B., and Green, 1997, Middle Proterozoic to Cambrian Cambrian rifting, 322 p. rifting, central central North North America: America: Geological Geological Society Society of of America America Special SpecialPaper Paper 312, 3 12,322 p. Ojakangas, R.W. Matsch, C., C., 1982, Minnesota's Minnesota's Geology: University R.W. and Matsch, University of Minnesota Minnesota Press, Press, Minneapolis, Minneapolis,225 225 p. p. Palmer, H.C., 1970, 1970, Paleomagnetism Paleomagnetism and and correlation correlation of some some middle middle Keweenawan Keweenawan rocks, rocks, Lake Lake Superior: Canadian Canadian Journal Journal of of Earth Earth Science, Science,v. v. 7, 7, p. p. 1410-1436. 1410-1436. Peterman, Z.E. and Sims, P.K., P.K., 1988, The Goodman Swell: a lithospheric flexure caused by rift system: system:Tectonics, Tectonics,v. v. 7, 7, p. 1077-1090. 1077-1090. crustal loading loading along along the the Midcontinent Midcontinentrift Reich, L., 1989, Reich, 1989, Geomagnetic Geomagnetic model of the the St. St. Croix Croix horst horstininPolk PolkCounty, County,Wisconsin: Wisconsin: Unpublished M.S. M.S. Thesis, Thesis, University University of of WisconsinWisconsin- Milwaukee, Milwaukee, 141 141p. p. Robertson, W.A., W.A., 1973, 1973, Pole Pole positions positions from from Mamainse MamainsePoint Pointlavas lavasand andtheir theirbearing bearing on on aa Robertson, Keweenawan pole path and polarity sequence: Canadian CanadianJournal Journalof ofEarth EarthScience, Science,v.v.10, 10, p. 1541-1555. 1541-1555. relief of of the Precambrian-Cambrian contact in Scott, D. and Anderson, G., 1983, 1983, Topographic relief Chisago County, Minnesota: Chisago Minnesota: 17th 17thAnnual Meeting Meeting of the Geological Geological Society Societyof of America, America, p. 255. 255. North-Central Section, Section,Madison, Madison,WI, WI, Abstracts Abstracts with with Programs, Programs, p. Serpa, L. Setzer, Setzer, T., Farmer, Farmer, J., J., Brown, Brown, L., L., Oliver, Oliver,J., J., 1984, 1984,Structure Structureof ofthe thesouthern southern Keweenawan Keweenawan Serpa, COCORP surveys Midcontinent geophysical geophysical anomaly rift from COCORP surveys across across the Midcontinent anomaly in northeastern northeastern Kansas: Tectonics, Tectonics, v. 3, p. 405-421. 405-421. S.B., Kiewin, Shirey, S.B., Klewin, K.W., K.W., Berg, J.H., and Carlson, Carlson, R.W., R.W., 1994, 1994, Temporal Temporal changes in the the sources of flood basalts: basalts: Isotopic and trace element evidence from the 1100 1100 Ma old old Keweenawan Mamainse Point Formation, Ontario, Ontario, Canada: Canada: Geochimica Geochimica et Cosmochimica Cosmochimica Keweenawan Mamainse Acta, v. 58, p. 4,475-4,490. 4,475-4,490. Wisconsin: U.S. Bureau of Smith, M.C., 1947, 1947, Copper deposits of Douglas County, County, Wisconsin: of Mines Mines 4088,7 p. Report of Investigations 4088,7 Southwick, D.L., D.L., Morey, G.B., G.B., and McSwiggen, P.L., P.L., 1989, Geologic Geologic map map of the Penokean orogen, central central and eastern Minnesota: Report of of orogen, Minnesota: Minnesota Minnesota Geological Geological Survey Survey Report Investigations 37, Investigations 37, scale scale 1:250,000. 1:250,000. 74 �Strong, Moses, 1880, 1880, The geology of the the upper upper Saint Saint Croix Croix district: district: Geology Geology of of Wisconsin, Wisconsin, Wisconsin Wisconsin Geologic GeologicSurvey, Survey,v. v. III, Ill, p. p. 363-428. 363-428. Symons, D.T.A., Symons, D.T.A., Lewchuk, Lewchuk, M.T., Dunlop, Dunlop, D.J., Costanzo-Alvarez, Costanzo-Alvarez,V., V., Halls, Halls, H.C., H.C., Bates, Bates, M.P., M.P., Palmer, H.C., H.C., and Vandall, T.A., 1994, 1994, Synopsis Synopsis of of paleomagnetic paleomagnetic studies studies in in the Palmer, Vandall, T.A., Kapuskasing structural zone: Canadian Canadian Journal Journal of Earth Earth Science, Science, v. 31, 3 1, p. 1206-121. 1206-121. Van Schmus, W.R., W.R., 1992, Tectonic Tectonic setting setting of of the the Midcontinent Midcontinent rift rift system: Tectonophysics, Tectonophysics,v. v. 1-15. 213, p. 1-15. Van W.R. and Hinze, W.J., W.J., 1985, The The Midcontinent Midcontinent rift rift system: system: Annual Annual Review Review of of Van Schmus, W.R. Earth and and Planetary PlanetarySciences, Sciences,v. v. 13, 13,p. p. 345-383. 345-383. 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G.S., 1972, Webers, G., and Austin, G.S., 1972, Field trip guidebook for Paleozoic and Mesozoic rocks of 4, 91 p. southeastern Minnesota: Minnesota Geological Geological Survey Guidebook Series 4,91 theoretical basis for exploration White, W.S., 1978, 1978,A theoretical exploration for for native copper copper in in northern northernWisconsin: Wisconsin: U.S. Geological Survey Circular 769, 19 p. Geological Survey Circular 769, 19 p. J.D., 1995, Geochemistry Geochemistry of southernmost Wirth, K.R., Grotta, Grotta, S., S., Sadofsky, Sadofsky, S., and and Vervoort, J.D., southernmost Midcontinent Midcontinent rift lavas lavas in Minnesota Minnesota and and Wisconsin: International Field Conference Conference and and Symposium on the Petrology and Metallogeny Metallogeny of Volcanic and Intrusive Rocks of the the Midcontinent p.211-212. Midcontinent Rift Rift System: System: Aug. 19-Sept. 19-Sept. 1, Duluth, Minnesota, Proceedings, p. 21 1-212. Wirth, Karl R., Naiman, J.D., Miller, James D., and Naiman, Zachary, Zachary, Vervoort, J.D., and Morey, Morey, G.B., G.B., 1996, 1996, Volcanic Group Group near near Taylors Taylors Falls Falls and from Osseo drill Geochemistry of Chengwatana Chengwatana Volcanic core: core: 42nd Annual Meeting of the the Institute Institute on on Lake Lake Superior Superior Geology, Geology, Cable, Cable, WI, WI, Proceedings, Proceedings, v. v. 42, p. 66-67. 66-67. Wirth, Karl, Vervoort, J.D., and and Naiman Naiman Z.J., Z.J., 1997, Petrography Petrography and and geochemistry geochemistry of of the the Wirth, Vervoort, J.D., southernmost volcanic rocks exposed in the the Midcontinent Midcontinent rift: rift: Canadian southernmost Canadian Journal Journal of Earth Science, v. 34, p. 536-548. 536-548. of Midcontinent Midcontinent rift rift rhyolite rhyolite Wirth, K.R. and Gehrels, G.E., in press, Precise U-Pb zircon ages of (Chengwatana volcanics), Annual Institute on Lake Superior Superior Geology, 44thAnnual (Chengwatana volcanics),Clam Clam Falls, WI: 44th Proceedings. Zartman, Zartman, R.E., R.E., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., and Morey, G.B., 1997, 1997, U-Th-Pb zircon zircon ages ages of of rocksfrom fromthe thesouth southshore shoreofofLake LakeSuperior: Superior: Canadian some Keweenawan Supergroup rocks Journal of Earth Earth Science, Science, v. v. 34, 34, p. 562-575. 562-575. Zhu, Consortium for continental continental reflection reflection profiling Michigan Michigan surveys: Zhu, T., and Brown, L., 1986, 1986, Consortium surveys: reprocessing and results: results: Journal of Geophysical Geophysical Research, Research, v. 91, p. 11477-11495. 11477-11495. 75 ��FIELD FIELD TRIP TRIP#3 #3 GLACIAL GLACIAL EXOTICA OF OF THE THE TWIN TWIN CITIES CITIES AREA Leaders: Leaders: Howard HowardHobbs, Hobbs, Alan Alan Knaeble, Knaeble, Gary Gary Meyer Meyer OVERVIEW OF OF LATE QUATERNARY QUATERNARY GEOLOGIC OVERVIEW GEOLOGIC HISTORY Howard Howard Hobbs Hobbs The The landforms landformsand andsurface surfacesediments sedimentsof of this this area area formed formed during during the the most most recent recent glaciation— glaciation- the late Wisconsinan. The Thearea areawas was covered covered by by previous previous glaciations some 10 10 to 20 times, but sediments sediments from from these these earlier earlier glaciations glaciationshave have been been partially partially eroded eroded by by subsequent subsequentglaciations glaciations and are are now now deeply deeply buried buried by sediments sediments deposited during the last glaciation. Although Although the the volume of late Wisconsinan drift in Minnesota is less than half the volume of all the older drifts volume of late Wisconsinan drift in Minnesota is less than the volume all older drifts put put together, together, the the amount amountremaining remainingper per glaciation glaciationisisso somuch muchmore morethat that itit can can be be explained explainedonly only by recycling new drift drift sheet. In recycling large large amounts amounts of older glacial sediment into each new In other other words, words, only aa portion portion of of the the sediment sediment that that we we will will see see was was brought brought from from its bedrock bedrock source source to its its present present position position in in one one glaciation. glaciation. The The Twin Twin Cities-St. Cities-St. Cloud Cloud area area is is dominated dominated by by the the deposits deposits of of two two ice ice lobes, lobes, each each from fromaa different direction (Fig. 1). 1). The TheSuperior Superiorlobe lobeadvanced advancedinto intocentral centralMinnesota Minnesotathrough throughthe the Lake Superior Superior basin from from northeast. Its Itstill tillisisreddish-brown, reddish-brown,sandy sandyto toloamy, loamy,and andrich rich in inred red and and black black rocks rocks from from the the Superior Superiorbasin and and the north shore of Lake Superior. Typical Typical rocks are red sandstone basalt and and gabbro. gabbro. Within the Superior sandstone and siltstone, rhyolite and granophyre, granophyre, basalt basin, basin, the the Superior Superiorlobe lobedrift drift contains containspractically practically no no carbonate carbonaterocks rocks or or matrix matrixcarbonate, carbonate,but butin in the field field trip trip area area ititcontains containsaamodest modestamount, amount,presumably presumably recycled recycledfrom fromolder, older,calcareous calcareous drifts. drifts. The St. St. Croix Croix moraine moraine roughly roughly marks marks the the late late Wisconsinan Wisconsinan maximum of the Superior Superior lobe. lobe. There Thereisisevidence evidencefrom frombeyond beyondthe themoraine moraineof of aa somewhat somewhat more more extensive extensive lobe that may have preceded moraine-building, but but this this zone zone is is not not very very wide. wide. On the southeast southeast side of the the lobe, the moraine moraine is is wide wide and andhigh. high. It ranges lobe, from from south south of Minneapolis Minneapolis to the St. Croix River, the from 5-10 5-10 miles miles wide, wide, and and the the thickness thicknessof of morainic morainicmaterial material ranges ranges from from100-300 100-300feet. feet. Its Its surface development surface morphology morphology is is highly highly collapsed, collapsed, indicating indicating that the final event of moraine development was was the the melting melting of of stagnant stagnantice icefrom frombemeath bemeath thick thickdebris. debris. At the west west end end of this this same same segment, segment, the moraine moraine turns sharply sharply and and runs northwest northwest to to the the St. Cloud area. Most Mostof ofthis thissegment segmentisisburied buried by by glacial glacial sediment sediment of of the the Des Des Moines Moines lobe, lobe, so so is not known in detail. Only the highest parts (generally kames) are exposed at the surface (for Only the highest parts (generally kames) are exposed surface example, Stop 1). 1). These Thesekames kamesmay may represent represent fans fans of of sand sand and and gravel built at the edge of the ice by subglacial subglacial tunnel tunnel valleys valleys (Fig. (Fig. 1.1). 1.1). The Thetop topof ofthe themoraine morainein inthis thissegment segmentisislower, lower,due due to a combination combination of the following following factors: the thebase baseon on which whichitit was was built built seems seems to to be lower; lower; the the average thickness of moraine material is less; and some of the material was eroded off by the overriding overridingDes Des Moines Moines lobe. lobe. Inasmuch Inasmuchas asthis this segment segmentrepresents represents the frontal frontal part of the moraine, the debris debris may may have have been been spread spread over over aa wider wider zone zone by minor minor fluctuations fluctuations of of the the ice ice front. front. 79 �EII1 Park 1/ 4 - do . '- :' 4Bodu I, ok A pr1 pers C 0O 0 EXPLANATION hp td do Terraces of the Mississippi River Des Moines lobe outwash (includes sandy lake sediment in eastern part) dag, dpg, Des Moines lobe ground moraine dbg Des Moines lobe stagnation moraine das dpe, dbe Des Moines lobe end moraine Superior lobe outwash so Superior lobe ground moraine ssg Superior lobe end moraine sse Figure Figure 1. 1.Simplified SimplifiedQuaternary Quaternarygeology geologyofofthe thefield fieldtrip triparea, area,showing showingmajor majorroads roadsand andlocation locationofofstops. stops. �About 15 15 miles miles south south of of St. St. Cloud, Cloud, the the moraine moraine begins begins to to emerge emerge from from under under its its Des Des About Moines Moines lobe lobe cover. cover. The Thehigher higherparts partsof ofthe themoraine moraineform formisolated isolated bumpy bumpy knobs, knobs, while while the the lower lowerparts partsare arecovered coveredwith withoutwash outwashof of the the Des Des Moines Moines lobe. lobe. Many Manyof ofthe thehigher higherparts parts appear appear to to be be ice-thrust ice-thrustfeatures, features,such suchas asthe theone oneatatStop Stop2.2. The The Des Des Moines Moineslobe lobeadvanced advanced from from the the northwest, northwest,following following the the broad broad lowland lowland now now occupied occupiedby bythe theMinnesota MinnesotaRiver RiverValley. Valley. Its Its till till isisgray gray(oxidizing (oxidizingto toolive olivebrown), brown), loamy loamy to to clayey, clayey, and and rich rich in in sedimentary sedimentaryrock rock fragments—mainly fragments-mainly carbonate carbonate and and gray shale. shale. Granite Graniteand and Anoffshoot offshootof ofthe theDes DesMoines Moineslobe, lobe,called calledthe the greenstonefragments fragmentsare are also alsofairly fairlycommon. common. An greenstone Grantsburg Grantsburgsublobe, sublobe,extended extendednortheast northeastfrom fromthe themain mainlobe, lobe,burying buryingthe theSt. St.Croix Croixmoraine, moraine,and and advancing over land that had recently been vacated by the Superior lobe. advancing over land that had recently been vacated by the Superior lobe. ItIt appears appearsthat thatthe theGrantsburg Grantsburg sublobe sublobe was was aa late late advance, advance, during a time when when the the main main Des Moines lobe was retreating. The retreat was interrupted by many minor re-advances, each Des Moines lobe was retreating. The retreat was interrupted by many minor re-advances, each one lobeApparently the the Bemis Bemis advance advance of of the the Des DesMoines Moineslobe— one less less extensive extensive than than the thelast. last. Apparently 14,000 14,000years years ago— ago- was was blocked blocked and and diverted diverted by the St. Croix moraine. How Howwas wasthis thismoraine moraine able ableto toblock blockthe theearliest, earliest,most mostextensive extensiveadvance, advance,and andyet yet was was overridden overriddenby by aa later, later, less less powerful powerful pulse? pulse? The Themost mostreasonable reasonableexplanation explanationisisthat thatearly earlyon onstagnant stagnantice iceburied buriedininthe themoraine moraine made madeititeffectively effectivelyhigher. higher.As Asthe theice icemelted, melted,the thebarrier barrierbecame becamelow lowenough enoughto tobe bebreached breachedby by the theadvancing advancingice. ice. One One could could postulate postulate that that at at the the time time of of the theBemis Bemisadvance, advance, the the St. St. Croix Croixmoraine moraine was was backed sublobeto to backedby byactive activeglacier glacierice, ice,which whichlater laterretreated retreatedenough enoughto toallow allowthe theGrantsburg Grantsburgsublobe cross crossthe themoraine. moraine.However, However,glacial glaciallake lakedeposits depositshave havebeen beendiscovered discoveredwell well back back from fromthe the St. St. Croix moraine, underneath sediments of the Grantsburg sublobe. Johnson and Hemstad (in Croix moraine, underneath sediments of the Grantsburg sublobe. Johnson and Hemstad (in prep.) varve couplets couplets from from the the thickest thickest part part of of the the lake lake sediments sediments as as prep.) estimate estimate at at least least 900 900varve extrapolated extrapolatedfrom fromthinner thinnercounted countedsections. sections.This Thissuggests suggeststhat thatactive activeice ice had had melted melted back back from from the themoraine morainelong longbefore beforethe theGrantsburg Grantsburgadvance. advance. The TheDes DesMoines Moineslobe lobeadvance advanceover overthe theSt. St.Croix Croixmoraine morainewas was in in two two phases: phases:first firsttotocross cross was wasthe theDuelm DuelmBulge Bulge(Stops (Stops44and and5). 5). The Thenorthern northern limit limit of of this thisadvance advanceisisdefined definedby by the the Duelm Duelmchannel, channel,which whichcarried carriedthe thedischarge dischargeof ofthe theupper upperMississippi MississippiRiver Riveraround aroundthe thebulge bulgeof of ice. The eastern limit of the bulge is less certain, but it may have been pinned by the high ice. The eastern limit of the bulge is less certain, but it may have been pinned by the high ground groundnorth northofofElk ElkRiver River(Stop (Stop7). 7).This Thisadvance advanceappears appearstotohave havebeen beenshort-lived, short-lived,and andquickly quickly succeeded succeededby bythe theadvance advanceofofthe theGrantsburg Grantsburgsublobe. sublobe. The TheGrantsburg Grantsburgsublobe sublobecrossed crossedthe theSt. St.Croix Croixmoraine moraineover overaabroad broadfront, front,and andadvanced advancedtoto the thenortheast, northeast,past pastthe theSt. St.Croix Croixriver rivertotothe thetown townof ofGrantsburg, Grantsburg,Wisconsin. Wisconsin. ItItwas washemmed hemmedinin by bythe theback backside sideofofthe theSt. St.Croix Croixmoraine moraineon onthe thesoutheast southeastside, side,and andby byhigh highground groundtotothe thenorth. north. The TheGrantsburg Grantsburgappears appearstotohave havebeen beenone onemain mainpulse, pulse,followed followedby bywidespread widespreadstagnation stagnationand and melting. melting. Till Tillof ofthe theGrantsburg Grantsburgadvance advanceisisquite quitevariable variablein in composition; composition;ininplaces, places,ititisisessentially essentially the thesame sameasastill tillofofthe theDes DesMoines Moineslobe. lobe.InInothers, others,ititisisbanded bandedred redand andgray, gray,on onthe thescale scaleofoffeet feet totoinches. inches.InInother otherplaces, places,ititappears appearsthe thesame sameasastill tillofofthe theSuperior Superiorlobe, lobe,except exceptfor foraatrace traceof of shale. sublobeincorporated incorporatedaalarge largeamount amountof ofSuperior Superior shale.Apparently, Apparently,the theice iceofofthe theGrantsburg Grantsburgsublobe lobe lobedebris debrisasasititwas waspassing passingover overthe theSt. St.Croix Croixmoraine. moraine. This Thisdebris debriswas waspartially, partially,but butnot not completely, completely,mixed mixedwith withsediment sedimentalready already in in the the ice. ice. InInplaces, places,especially especiallyininthe thecenter centerofofthe the lobe, lobe,Grantsburg Grantsburgtill tillisisthin, thin,orormissing missingaltogether. altogether. 81 �The ice melted melted more rapidly in the center center than along along the margins, presumably presumably because it GlacialLake Lake Anoka Anoka formed formed in the center center of the sublobe, sublobe, fed by large large had less of a debris cover. Glacial amounts Of of meltwater amounts meltwater from the upper Mississippi (a continuation of the same flow that eroded the Duelm Channel). Channel). The Thelake lakedeclined declinedin instages stagesas asice icemelted melted out out of of the the margins, margins,uncovering uncovering successively lower outlets into the St. Croix Croix River, River, and finally finally drained drained altogether altogether down down the the Mississippi River. This This drainage drainageevent event connected connectedthe the upper upper and and lower lower parts parts of the the Mississippi Mississippi for the first time in its modern course. course. of two two parts: parts: the The Anoka Sand Plain is composed of the lakebottom lakebottom sediment sediment (mostly (mostly fine fine plain-delta which extends from the Mississippi valley train train into the outwash plain-delta sand), and a sandy outwash lake. The Thelake lakewas wasshallow, shallow,and and apparently apparentlymost most of of the the silt silt and and clay clay from from the the meitwater meltwater stayed stayed until it was carried downstream. between the the delta and the in suspension suspension until downstream. The The boundary boundary between lakebottom sediment lakebottom sedimentisisdifficult difficultto to pin pin down, down, because becausethe the texture textureof of the the sand sand is is not much much different, different, and because the boundary boundary shifted shifted as as the lake filled in. STOP 1—Superior ValleyFan Fan Sand Sand and and Gravel Buried by Superior 1ÑSuperio Lobe Tunnel Valley SuperiorLobe Lobe and and Grantsburg GrantsburgSublobe SublobeTill. Till.(Gary (GaryMeyer) Meyer) A radiocarbon radiocarbon date 32,300±2000 obtained from from wood fragments fragments date of 32,300 k2000years yearsB.P. B.P. (Beta-40098) (Beta-40098) obtained in a core core sample sample taken taken below below 130 130 feet feet of of Superior Superior lobe lobe sand sand and and gravel gravel in Ramsey Ramsey County County (Meyer, 1992), 1992), gives a possible maximum age for the advance advance of the Superior Superior lobe lobe into into easteastcentral Minnesota. As Asthe thefront frontof of the the Superior Superiorlobe lobe became stabilized, stabilized, it formed the St. Croix moraine—a complex the east, east, south, south, and and moraine-a complexlinear linear series seriesof of high high hills encircling encircling the Twin Cities on the paralleling the Mississippi Cloud area area (Fig. (Fig. 1.1). 1.1). During the eventual west, and paralleling Mississippi River to the St. Cloud retreat of the ice front, front, meltwater meltwater issuing issuing from the Superior lobe became channelized through the moraine. The TheSuperior-provenance Superior-provenance(Table (Table 1.1) 1.1) sand sand and gravel deposit at Maple Grove in northeast Hennepin Hennepin County County (Fig. (Fig. 1.1), 1.l), extensively exposed in gravel pits (Fig. 1.2), was likely deposited during formation of the North 1992),which which mark mark a retreatal retreatal deposited during formation of the North Ramsey Ramsey mounds mounds (Patterson, (Patterson, 1992), position of the Superior Superior lobe lobe behind the the St. St. Croix Croix moraine. Table 1.1. General Generalcharacteristics characteristicsof of mapped mapped glacial glacial deposits of ofthe theTwin Twin Cities Cities area. area. texture Till texture Mountain Riding Mountain Provenance Provenance loamy Superior Superior Provenance Provenance sandy sandy Color oxidized oxidized unoxidized unoxidized yellow brown to olive olive brown gray gray red brown gray to to red red gray gray gray common common uncommon to common common rare to uncommon common to abundant abundant rare to uncommon uncommon uncommon to abundant abundant common absent absent Feature Pebble type white to to buff carbonate carbonate dark gray to gray-green rocks red felsite and sandstone sandstone gray shale shale 82 �u lMTED STATES Figure moraine in east-central east-central Minnesota Figure 1.1. 1.1. Tunnel Tunnelvalleys, valleys,valley-mouth valley-mouthfans, fans, and and the St. Croix moraine and adjoining counties in Wisconsin. Wisconsin. Lettered features are landforms landforms discussed discussed in inthe thetext: text: M, Maple Grove fan; E, Elk River fan complex. complex. Modified Modified from Patterson (1994). The The Maple Maple Grove Grove sand sand and and gravel gravel deposit depositwas was laid laid down down as as aa fan fan at at the the mouth mouth of of aa tunnel tunnel valley—a drainageway (Patterson, (Patterson, 1994). 1994). The trend valley-a deeply incised, broad, subglacial drainageway trend of of the the tunnel valley that fed the fan is is marked marked to to the the northeast northeast in in Anoka County by aa chain chain of of lakes lakes (Fig. 1.1) 1.1) formed formed when thick thick ice filling filling the valley later melted. The The sand sand and and gravel gravel laid laid down down at the mouth of the valley evidently buried stagnant ice, as the fan deposit is deeply pitted (Fig. 1.2). The The buried buried ice ice was was well-insulated, well-insulated, as as it apparently was still melting during a readvance of the Superior gravel below reddish reddish sandy till, and then then during during an Superior lobe, lobe, which which buried buried the the sand sand and grave1 which further buried buried the the sand and gravel with yellowish advance of the Grantsburg sublobe, which clayey till. The Thesand sandand andgravel gravelisis thickest thickest where where the the buried ice was thin, forming ridges in the postglacial landscape. landscape. Areas Areasunderlain underlain by by the the thickest thickest ice became depressions into which first Superior lobe till from Superior from the the readvance readvance (Automba?) (Automba?) phase flowed, flowed, and and then, then, following following final final deglaciation, both finally completely completely deglaciation, both Superior Superiorlobe lobe and and Grantsburg Grantsburg sublobe sublobe tills flowed flowed as the ice finally melted, deposited. A log at the base of collapsed melted, apparently apparently thousands thousandsof of years years after after it was first deposited. lake sediments and Superior Superior lobe lobe tills, tills, exposed in a Maple sediments overlying overlying collapsed Grantsburg Grantsburg and Maple Grove fan pit, yielded a date date of of 11,930±60 11,93e60radiocarbon radiocarbon years years B.P. B.P. (Beta-23746; Meyer and Hobbs, 1989), 1989), indicating indicating that that buried buried St. St. Croix Croix phase ice was still melting less than 12,000 12,000 years years ago. ago. 83 83 �9/ yr- jj ci o a Q J)I Ik0 TH II 0 0 / a 0riggI lemT I t U— - - r Y.°'— .'c 4r'/t9r( _.; . .. . . . Figure 1.2. 1.2. Topographic Topographicmap mapwith with Maple Maple Grove Grove fan deposit outlined. The The landform landform likely likely extended extended to to the Figure sublobe meltwater. meltwater. Area shown is is about about 2.8 2.8 miles miles wide; wide; northeast prior to being planed off by Grantsburg sublobe contour contour interval interval 10 10 feet. feet. (U.S. (U.S. Geological Geological Survey Survey Osseo Osseo quadrangle, quadrangle, 7.5-minute series, series, 1967.) 1967.) The movement depressions during during differential differential ice-block ice-block movement of the bulk of overlying tills into depressions melt-out melt-out reduced reducedthe the"overburden" "overburden7'thickness thicknessabove abovethe thesand sandand andgravel, gravel,allowing allowingitit to to be exploited exploited for construction construction aggregate. aggregate. Gravel Gravelmining mininghas hasinverted inverted the the topography once once again, again, turning the gravel ridges into deep pits and the till-filled depressions into into hills. hills. Gravel from the Maple till-filled depressions Grove Cities area area as as ititconsists consistsmostly mostly of ofPrecambrian Precambrian Grove fan fan deposit deposit is is the most durable durable in the Twin Cities rock clasts (Meyer and Jirsa7 ursa, 1984). 1984). Superior Superiorlobe lobe deposits deposits to to the the east east and and southeast southeast contain greater greater amounts amountsof of locally-derived, locally-derived,relatively relativelysoft softPaleozoic Paleozoicclasts, clasts,eroded erodedas asthe thelobe lobemoved movedup up the escarpment others, 1986). Des Moines lobe and escarpment formed formed by the Oneota Dolomite (Jirsa and others, Grantsburg sublobe deposits contain clasts of both Paleozoic carbonate and Cretaceous shale, as they are of Riding Riding Mountain Mountainprovenance provenance (Table (Table 1.1). 1.1). 84 �%Powder Ridge Site-Glacial Thrusting Cretaceous STOP 2—Powder Ridge Borrow Borrow Pit Site—Glacial Thrusting of of Drift and Cretaceous (Alan Knaeble) Knaeble) Bedrock. (Alan A located in the St. Croix moraine (Fig. 2.1). The moraine was deposited A large large borrow borrow pit pit is located deposited prior prior to to 16,150 16,150years years BP BP (Birks, (Birks,1976) 1976)when when the the Superior Superior lobe was at its maximum. This Thissite siteisis perched Moines lobe lobe outwash outwash plain plain (Fig. (Fig. 2.2). 2.2). The perched about about 225 ftft above above the surrounding Des Moines borrow to0build up the summit of the ski hill and and regrade borrow pit pit was was excavated excavated to to supply supply material 1 existing existing ski-run slopes. The The pit pit isis 1/4 114mile mile long long and and oriented oriented north-south. north-south. There There are are good good exposures wails (Fig. 2.3). 2.3). Six texturally and lithologically distinct exposureson on the the north, north, west, and east walls (K); pre pre Wisconsin Wisconsin sand sand (S); (S); are recognized recognized in in the the pit pit including: including: Cretaceous Cretaceous shale shale (K); units are unoxidized, dark dark gray, gray, clayey clayey pre-Wisconsin pre-Wisconsin till (Elmdale (Elmdale till) till) (wt-w); (wt-w); unoxidized, unoxidized,dark darkredredunoxidized, brown pre-Wisconsin till ("Old ("Old Red Red till") till") (st-x); (st-x);oxidized, oxidized,yellow-brown yellow-brown or orunoxidized, unoxidized,gray gray pre-Wisconsin pre-Wisconsin till (wt-x); (wt-x); and and reddish-brown, reddish-brown, sandy sandy late late Wisconsin Wisconsin till, till, lake lake sediments, sediments,and and sandlgravel identification sand/gravel (Superior (Superior lobe deposits) (st). Fossil Fossil and and mineral mineral content content have helped identification of of the Cretaceous Cretaceousdeposits, deposits,and and texture texture and and grain grain count count analyses analysesindicate indicate that that at at least least four four glacial glacial advances advances are are represented represented(Table (Table2.1; 2.1; Fig. Fig. 2.4) 2.4) (Knaeble, (Knaeble,1996). 1996). - E St. Croix moraine Payn.wC. Thrusthills IOMILES o • Thrust site I Fo a 10 - --- 15 KMOMETERS . . Figure 2.1. Simplified Simplifiedmap mapof ofStearns steamsCounty Countyshowing showingthe thelocation locationof of thrust thrust masses masses Figure (hills) (hills) within the St. St. Croix Croix Moraine and 22 thrust sites. From FromKnaeble Knaeble(1996). (1996). Exposures in the the pit pit walls walls show show that that these these sediments sediments form slabs slabs 50-250 50-250 ft thick, thick, which which appear appear to extend extend laterally for more than 400 ft. The The slab slab contacts contacts dip dip 30°-60° 30°-60north-northeast, north-northeast, in for the the Superior Superiorlobe. lobe. The The internal internal stratification stratification in what would would have been the up-glacier direction for ft 50-100 ft within these slabs slabs largely largely subparailels subparallels slab slab boundaries, although although two zones, each 50-100 withiI these thick, are intensely deformed; the sediments are sheared, streaked, mixed and, in the intensely eaked, mixed and, in the intensely thick, are intensely deformed; the sediments are sheared, str rned zone, 7nne dicnlmr distorted dictnrtpd overturned nvprhirnpd fnldc Rnqpd on deformed display folds. Based ----on comparisons comparisons with with undeformed undeformed defonAawu uALw, exposures exposures in in Stearns SteamsCounty, County, the the sequence sequence of sediments sediments in in this pit can be divided into at least 6 thrust blocks. Each Eachthrust thrustblock blockcontains containstwo twoor ormore moredistinct distinctunits unitsdifferentiated differentiatedby by color, color, texture, and lithology. block. Superior lithology. The The youngest youngest till (unit st) caps each thrust block. Superior lobe lobe ice, ice, associated with deposition of this youngest till, is interpreted to have caused the thrusting associated deposition of youngest (Knaeble, (Knaeble, 1996). 1996). 85 85 uawy*aJ -au..-A.-- �I I glaciotectonic thrusting Figure 2.2. 2.2. Topographic Topographicmap map showing showing the powder ridge ski pit, a site of glaciotectonic Figure on N., R. R. 29 29W.). on the the St. St. Croix Croix Moraine Moraine (sec. (sec. 27, 27, T. 22 N., W.). Hachured Hachured lines lines indicate indicate scarps; scarps; hachures hachures on on downslope downslope side. Area Areashown shownisis2.3 2.3 miles miles wide; wide; contour contourinterval interval10 10feet feet(U.S. (U.S.Geological Geological Survey Kimball quadrangle, 7.5-minute series, 1967). From Knaeble (1996). From Knaeble (1996). 86 �EXPLANATION Fill Unexpose area or Slope wash Superior lobe lull (Pierz). in places Containing inlerbegs of Superior lobe lacuustrine sedumenf (.1) and Superior lobe sand and gravel deposits (so) Winnipeg provenance n till )Sauk Centre or Meyer Lake) v till (Old Red) Winnipeg provenance w till (Elmdale) Sand (pre-lafe Wisconsin) Cretaceous marine Shale Thrust fault; sawteeth in upper plate Fault, Showing relative horizontal motion; approximate location where dashed —— — Unit confacl, approximate location where dashed Highly deformed mined malerial Superior provenance I. 0 tOO 300 feet Vertical exaggera(l Figure thrust blocks. blocks. Quaternary sediments sediments and Cretaceous Figure 2.3. Powder PowderRidge Ridgeski ski pit showing showing interpreted thrust clays are exposed on the north, east, and west west walls walls of of the the pit; pit; the exposure exposure on the west wall has been extended through to the outside face face of ofthe theblock blockdiagram. diagram. See Seefigures figures 2.1 2.1 and.2.2 and 2.2 for forpit pitlocation. location. From Knaeble Knaeble (1996). (1996). Table 2.1. Matrix Matrixtexture textureof of glacial glacialtills tills in in the the Powder Powder Ridge Ridge ski ski pit. Unit Percent of Sand Sand Silt No. of Samples Samples Clay Clay wt-w 4 29 29 40 31 31 st-x st-x 6 41 41 34 34 25 25 Meyer Lake 5 28 57 57 15 15 Sauk Sauk Centre Centre 8 8 41 41 41 41 18 18 20 58 58 29 29 wt-x wt-x St st 87 . 13 13 �Clay Clay 100% 100% UMTS • wt-w + st-x • wt-x o wt-x St Figure 2.4. Triangular Triangular plot of matrix texture of glacial till units in the Powder Ridge ski ski units Powder Ridge pit. From FromKnaeble Knaeble (in (in prep.). U.. U ••S• c&o • 100% Sand Sand 100% 50% Silt The The exposure exposure on on the west west wall at at the south south end of the pit, shows Cretaceous marine shale shale 10-foot-thick packet of deformed deformed Superior lobe till, which contains contains streaks streaks of of overlying a 10-foot-thick incorporated older till. The deformed Superior lobe till overlies 25-30 ft of very well sorted, The deformed Superior finely bedded, finepre-late Wisconsin, Wisconsin, which in turn finely bedded, fine- to medium-grained medium-grained sand sand interpreted interpreted to to be pre-late overlies overlies more Cretaceous Cretaceous shale. shale. The Thecontacts contactsbetween betweenthese theseunits units dip dip 30°-60° 30°-60north and and indicate indicate south-directed thrust block block overlying overlying younger south-directedthrusting thrustingwith withaa Cretaceous Cretaceousunit unit at at the base of one thrust units in another another thrust thrust block. Drill Drillcore coreof of the the Cretaceous Cretaceousshale shale at at the south south end of the pit shows them to extend to a depth of at least 56 ft, where the drill core ended. The elevation at the the top of extend ft, where the drill core ended. the Cretaceous shale is about about 1300 1300 ft; ft; yet well well logs logs show show the highest undisturbed Cretaceous level. Some Some of the thrust blocks contain contain bedrock in the region to be less than 1100 1100 ft above sea level. Cretaceous top of of other other thrust thrust Cretaceous shale, shale, which which is is interpreted interpreted to have been exhumed and stacked on top blocks to form form the moraine moraine during during ice ice advance advance (Knaeble, (Knaeble, 1996). 1996). wide at the the Powder PowderRidge Ridge ski skipit. pit. Water-well Water-well The St. Croix end moraine is about one mile wide records for mile northwest northwest records for three three wells wells located located on on the flanks flanks of the end moraine (two about a half mile of the pit, one one located located about about aa quarter quarter mile northeast northeast of the pit) also describe materials that appear appear to be thrusted thrusted (i.e., (i.e., Cretaceous Cretaceousdeposits depositsover over till, till, and and repetitive repetitive sequential sequentialcolor color changes changes in the till units). units). There is evidence evidence that that the the presence presence of permafrost (Mackay (Mackay and Mathews, Mathews, 1964; 1964; Clayton Clayton increase in in pore-water pore-water pressure pressure and Moran, 1974; 1974; Bluemle and Clayton, Clayton, 1984; 1984;Aber, 1988), an increase in the underlying underlying sediment sediment(Clayton (Claytonand andMoran, Moran,1974; 1974;Bluemle Bluemleand andClayton, Clayton,1984; 1984;Aber, Aber,1988), 1988), Aber, 1988) are conditions that and sufficient ice-flow velocities (Clayton and Moran, 1974; Aber, contribute to thrusting thrusting of substrata substrata at ice margins. When Whenthe theSuperior Superiorlobe lobeadvanced advancedover over soft soft bedrock, such as Cretaceous shale, or older glacial deposits, these conditions may have been as Cretaceous shale, or older glacial deposits, these conditions have been present and appear appear to to have have fostered fostered thrusting thrusting (Fig. (Fig. 2.5) during during the formation formation of the the St. St. Croix Croix moraine at Powder Powder Ridge. Ridge. 88 �Zuul—. 'I // \—_;.u__ \'_ — — —— 7, .. ,, -u '' 7,s_... • /\ 7/._.. . , _'•- —' — — - #•%S _ /' - — _% 'ui — , %_ \ 'S - 1s __u_u— — —I —S — -. _ .. — F I Is/i ,%7.,I, — 55 .2s I5./ ,./ — .2 .. — — '.. I ..S_I_\ — sI —,.;.. * — -' — %s '%S '\ ,%—;_ S_ — .. ',, \S S Ss1 — ' 7 — —-' ,• .'' _'L. — .2 •S__4•. I S , / 5, '5 — _.g_l' — :L L''-'.7' '•'_i r''——— '—''——— '—'r5 — Bedrock Surface Cretaceous Precambrian — — 5,5 J ———'5' 7,5,,,—5—— — —— i, — I_,,\ \_ 7, I_5—%_'S_ 5, SJ 1_ — — . .2 ': %___ ,: — — -__S... S — • _''_—— —' s._ ''SA \__ '_/t _.ez.' 'ui SS .— . ,','_',/_'. _,'..'/_!.I — __ _SS — __ — — I !. '—S . _,— L .2 .. ' —— '\ '11ui'' ' S/*'S'' I_ \__ '_'—, — '—— ,./ —— I, 5 __/% —,';— •__ us/u / z _;'u•_ ,— — .b —— — — ;_ : I—I / .j. ---I... _'5. Ice-Thrust Sites Figure 2.5. 2.5. Geologic Geologicmap mapofofSteams StemsCounty Countyshowing showingthe theSt. St.Croix Croix Figure moraine and the association of ice-thrusts with the underlying moraine and the association of ice-thrusts with the underlyingbedrock. bedrock. Powder POW^& Ridge Ridge Borrow Borrow Pit Pit STOP Thrusting of Cretaceous STOP3—Merden 3-Merden Lake Lake Esker EskerGravel GravelPit—Small-scale Pitamall-scale Thrusting Cretaceous Bedrock Bedrock and and Glacial Glacial Drift. Drift. (Alan (Alan Knaeble) Knaeble) The gravel gravel pit cuts through a section section of the Merden Lake esker and provides evidence for small-scale thrusting that is not associated with with end-moraine end-moraine formation formation(Fig. (Fig.2.1). 2.1). The esker formed formed beneath beneath the the Superior Superiorlobe lobeas asthe the ice ice advanced advanced towards towards the the southwest. southwest. Typical esker esker deposits deposits are are exposed exposedalong alongthe theeast eastwall wallof ofthe the pit. pit. Here, Here, about about 20 20 ftft of of Superior Superiorlobe lobe sand sand and and gravel gravelare are overlain overlain by aa thin 5-foot 5-foot layer layer of sandy sandy Superior Superiorlobe lobe till till (Fig. (Fig. 3.1). In represent Inthe the northwest northwestwall, wall,aa Superior-lobe-source Superior-lobe-sourcesand sand and and gravel gravel is also interpreted to represent the Superior lobe lobe till that has incorporated incorporated the core core of an an esker. Mantling Mantlingthis thiscore coreisis aa 5-10-foot 5- 10-footcap cap of Superior aa 3-5-foot Cretaceous shale 3-5-foot slab slab of old 'Elmdale 'Elmdale till' till' of of Meyer (1986). Thin Thin layers layers of dark gray Cretaceous are present present at the base of the Superior Superior lobe till cap. The The Cretaceous Cretaceous shale shaleand and the the older older Elmdale Elmdale till till are are interpreted interpretedas as substrata substratathat that were were picked up up by Superior-lobe Superior-lobe ice, transported transported at the base of the glacier, glacier, and and then deposited deposited on top top of the esker esker as as the ice ice wasted wasted (Knaeble, (Knaeble, 1996). 1996). Scattered in the sand and gravel on the pit floor you can find pebbles and cobbles of pisolitic lateriticclay. clay. These Theseclasts clastsare areinterpreted interpretedto tobe be derived derived from from the the uppermost uppermost weathering weathering pisolitic lateritic profile Precambrian igneous saprolith, and transported transported here by by Superior Superior profile of the Precambrian igneous and metamorphic saprolith, lobe landscape lobe ice ice and and meitwater. meltwater. Setterholm Setterholm(1990) (1990)states, states,"The "The pisolitic pisolitic layer layer marks marks aa soil soil of the landscape upon which which the the bulk of of the the Upper Upper Cretaceous Cretaceous rocks rocks in in Steams S t e m sCounty Countywere weredeposited." deposited.'' 89 �andravel east ____— west Cretaceous Cretaceous shale shale iiorlobetil1_ Superior lobe till sand and gravel . . . . . . .. Figure 3.1. Merden MerdenLake Lake Esker Esker gravel gravel pit: profile profile of of exposed exposed east and west walls. Brothers Gravel STOP STOP 4— 4- Bauerly Brothers Gravel Pit. Pit. (Howard (Howard Hobbs) lobe drumlin drumlin (Fig. (Fig.4.1). 4.1). The near side of the This pit is dug into the side of a Superior lobe drumlin is truncated by the the edge edge of of the theMississippi Mississippivalley valley train. train. There is about about 25 25 feet feet of Superior outwash overlain by by as much as 25 feet of reddish-brown till. The till cover reddish-brown till. cover gets thinner on the lower flanks of the drumlin. ItItisisnot not unusual unusual for for drumlins drumlins of of the the Pierz Pierz drumlin drumlin field to contain meltwater meltwater sediment, sediment, presumably deposited deposited in an earlier phase of glaciation, glaciation, as as well as till. are typical typical of ofSuperior-provenance Superior-provenancedeposits. deposits. They are reddish reddish Both the till and the gravel are brown, and contain many many red and black pebbles; pebbles; carbonate carbonatepebbles pebblesare aresparse. sparse. The till is aa brown, rocky gravelly gravelly sandy sandy loam. In Insharp sharpcontrast, contrast,this thissequence sequenceisis overlain overlain in in places places by aa thin layer layer of buff-colored buff-colored loamy till, which which contains contains only a few rocks and pebbles. This material material is is interpreted interpreted as as till deposited deposited by the Duelm Duelm bulge of the Des Moines lobe. This This site site is is only only aa few few miles from Benton and Sherburne Counties, from the the edge edge of the bulge, bulge, judged by the soil surveys of Benton and by the position of the Duelm channel. The interpreted as Thethin thin and and patchy patchy nature nature of the till is interpreted as a sign that the the ice ice did did not not persist persist long. long. 90 �I- 4 ) H .7 / Wa?j% P.... h- t: 6 ____arr t \1C4Ie 309\ t-- / _ LJ c 31 0 0w . — ?—4 - . (: UIN1 cl.1BENTON rr hl: '' M& c-o. . ii// Figure 4.1. Duelm Channel and Mississippi valley train. ________ ._/ ). r y BovJ sr c j, o.i �_ STOP STOP 5— 5- Duelm Channel Channel (Howard (Howard Hobbs) Hobbs) vantage point, on on an an erosional erosional remnant of till, till, the the essential essential elements elements of of the the From this vantage 4. I). The Thechannel channelstretches stretchesas asfar faras asthe the eye eye can can see see to to the the east east Duelm channel channel can can be be seen seen (Fig. (Fig. 4.1). Duelm Thenorthern northernbank bank of ofthe thechannel channel isis about about 1/2 I12 mile mile away, away, rising from 30-60 feet and west. The floor. The The land landsurface surface to to the the north north isismade madeup upofofdrumlinized drumlinizedtill, till, above the flat channel floor. underlain in places by outwash, outwash, of the Superior lobe. To To the the south, south, the edge edge of the channel channel is is underlain not so so well well defined. defined. In Inplaces, places,the thechannel channelcuts cutsseveral severaltens tens of of feet feet into into a drumlinized drumlinized topography topography not similar similar to the north north side, side, but but in in other other places places there there is is scarcely scarcely any any elevation elevation difference difference between between the channel channel bottom bottomand and the the land land outside outside the the channel. channel. In Insome someplaces, places,the the land land actually actuallydrops dropsoff off the to dificult to to see see how how the the channel channel could could have have held in any any water water unless unless itit was was to the the south. south. ItIt is is difficult fronted fronted by by glacial glacial ice ice on on the the south southside. side. This This channel channel defines defines Duelm channel ,Duelm channel the limit limit of of what what II have have Princeton0 called called the "Duelm bulge" bulge'' (Fig. 5.1). 5.1). ItItisislobate, lobate,but but (Fig. too small small to to be be an an ice ice lobe lobe too or even even aa sublobe, sublobe, in in the the usual usual sense. sense. All the the Duelm meltwater flowing down meltwater flowing down 0 /1 the the Mississippi Mississippi valley valley 0 0 bulge train was diverted around train was diverted around this this bulge bulge in in the the ice ice front, front, on on its its way way to to the the Mississippi Mississippi south south of of St. St. Paul. Paul. The The thin thin skim skim of of -. gray, gray, shale-bearing shale-bearing till till atat Stop Stop 44 indicates indicates that that this this was was aa bulge bulge of of the the Des Des Figure Figure 5.1. 5.1. Duelm Duelmchannel channeland andDuelm Duelmbulge. bulge. Moines Moines lobe, lobe, which which was was otherwiseheld heldback backby by the the otherwise St. St. Croix Croixmoraine. moraine. Because the till till is is thin, thin, and and has has not notaltered alteredthe theunderlying underlyingdrumlinized drumlinized topography topographyinherited inheritedfrom fromthe theSuperior Superiorlobe, lobe,IIinterpret interpretthe theDuelm Duelmbulge bulgeas asaashort-lived short-livedevent. event. ItIt was was probably probably aasingle singlepush pushfollowed followedby by stagnation. stagnation. \ The The Duelm Duelm channel channel originates originates just east east of of St. St.Cloud. Cloud. Its Its original original junction junction with with the the Mississippi Mississippi valley valley train train cannot cannot be beobserved, observed,because becauseof of subsequent subsequenterosion erosionalong alongthe thevalley valley train. train.At Atthe theupper upperend, end,the thewatercourse watercourseisisbroad broadand andits itsedge edgeisispoorly poorly defined, defined,suggesting suggestingthat that itit was Inthe themiddle middlesection, section, itit isis as aswe we see seeitithere—wellhere-wellwas not not very very erosive erosive in this this section. section. In defined definedand anderosive erosiveon on the the north northside, side,variable variable on on the the south south side. side. At Atits itslower lowerend, end,the thechannel channel gradually Anoka Sand Sand Plain. Plain. South graduallyloses losesits itsidentity identityas asitit is is buried buried by younger deposits deposits of the Anoka South of the the Duelm Duelm channel channelisisaa set setof of smaller, smaller,anastamosing anastamosingchannels channels at lower elevations. They They range range from fromwell-defined well-definedto toobscure, obscure,and andcontain containmany manyshallow shallowdepressions, depressions,apparently apparentlyaaresult resultof ofice ice collapse. Like the main channel, they trend east to southeast, and disappear beneath the Anoka collapse. Like the main channel, they trend east to southeast, and disappear beneath the Anoka Sand SandPlain. Plain.These Thesechannels channelsrepresent representshort-lived short-liveddiversions diversionsaround aroundthe theice iceas asitit was was advancing, advancing, and andpossibly possiblyalso alsoas asititwas wasmelting meltingback. back. 92 �northwestern part part of the the Duelm Duelm bulge advanced over relatively high drumlinized drurnlinized till The northwestern subsequently covered after the ice melted off. By By contrast, contrast, of the Superior lobe, which was not subsequently the southern and eastern eastern parts parts of of the the bulge bulge passed passed over over lower lower ground, ground, which which was was covered coveredby by Here, itit is is impossible impossible to to tell tell where where the the sand of the Anoka Sand Plain after the ice melted off. off. Here, boundary of the bulge was, or where the Duelm channel went. Clearly, Clearly, the the water water must must have have found its way eventually eventually to to the the Mississippi MississippiRiver River below below the the Twin Twin Cities. Cities. Stop &The 6—The Lake LakeAnn AnnDunes, Dunes,East-Central East-Central Sherburne Sherburne County, Minnesota. Minnesota. (Gary (Gary Meyer) Meyer) see figure figure 7.1 for location]. [From Stop 2 by Kerry Keen in Goldstein (1987); see Sand dunes are an uncommon uncommon feature feature of of Minnesota's Minnesota's landscape. landscape. They typically occur as small distinct areas on much much larger larger glacial outwash plains or on terraces terraces along along rivers rivers (Cooper, (Cooper, Grigal and and others, others, 1976). 1976). Dunes also occur adjacent to to lakes lakes and and on beach beach ridges ridges of of 1935; Grigal Glacial Lake Agassiz in northwestern Minnesota. Some Some of of the the largest largest tracts tracts of well developed developed dunes are scattered scattered across across the the Anoka Anoka Sand Sand Plain, Plain, just north north of of the theTwin Twin Cities CitiesMetropolitan Metropolitan Area. Of Ofthese, these,the thelargest largestareas areasof of dunes dunesare are north north of of Elk Elk River River in eastern eastern Sherburne Sherburne County. These dune areas are best best described described as parabolic parabolic dune blankets (David, 1977) that contain narrow, elongate, parabolic parabolic dunes dunes and and en en echelon echelon dune dune ridges. ridges. the typical typical geometry geometry of of dune dune blankets blankets on on the the Anoka Anoka The Lake Ann dunes (Fig. 6.1) display the Sand Plain (Fig. 6.2A). This Thisdune duneblanket's blanket's distinct distinctsoutheast southeastlobe lobeappears appearsto tohave have advanced advanced Ann. The dune blanket is highly asymmetric, with an indistinct into the southern area of Lake Ann. wing. ItIt isis composed southeastsouthwest margin and a well-developed northeast wing. composedof of several severalsoutheasttrending dune dune ridges, ridges, which with northeast northeast slopes slopes steeper steeper than than trending which also are very asymmetric, asymmetric, with outwash plain, plain, southwest slopes. The Thedune duneblanket blanket grades gradesnorthwestward northwestward into into wind-deflated wind-deflated outwash containing a number number of northwest-southeast elongate elongate deflation deflation depressions. depressions. The eolian features of the Anoka Sand Plain were originally attributed to formation by Cooper, 1935). 1935). However, study of air photos southwest winds (Leverett and Sardeson, 1932; Cooper, — the dune blankets and other data indicates that the major eolian features of the sand plain — were were formed by northwest winds (Keen, 1985). Modification Modification by by west, west, southwest, southwest, and and south south winds created the asymmetry asymmetry of of the the dune dune blankets blankets and and dune dune ridges. ridges. Sand was eroded and transported transported to the the northeast northeast over over the the dune dune ridges, ridges, steepening steepening their their northeast northeast slopes. slopes. This modification was so parabolic dune shapes were nearly obliterated modification so severe severe that the original parabolic obliterated (Fig. (Fig. 6.2B). The Thepresent presentwind windregime regime of of the thesand sandplain plain isisdominated dominated by by northwest northwest winds winds that that are are strongest in spring and fall. During Duringthe the summer, summer, winds winds from from the west and south would result in of sand. sand. The present wind appears to be similar to that a smaller net northeastward movement of responsible for eolian activity on the Anoka Sand Plain, although components of this regime regime probably varied in importance importance during during the Holocene. Holocene. A number of vegetational vegetational communities occur on the dunes of the Anoka Sand Plain and are well displayed in the Lake Ann Ann area. area. Prairie of Prairie grows on the dry sunny southwest sides of dune ridges, whereas oak woods occupy the moister northeast slopes. An An area area of of low low dunes dunes in in Ann dunes dunes supports an oak oak savanna savannacommunity. community. Various Variouswetland wetlandcommunities communities occupy occupy the Lake Ann dune depressions. depressions. Sediments from from Lake Lake Ann were studied studied with the the goal goal of of interpreting interpreting the the vegetation vegetationand and eolian history of the adjacent Lake Ann Ann dunes dunes (Keen (Keen and and Shane, Shane, 1990). 1990). As determined determined by 93 �Ann dune field. field. Area Figure 6.1. Topogaphic Area Topogaphic map map showing showing part of the Lake Ann shown (U.S. Geological GeologicalSurvey Survey shown is about 2.8 miles wide; contour contour interval interval 10 10 feet. (U.S. Orrock Orrock quadrangle, quadrangle, 7.5-minute 7.5-minute series, series, 1991). 1991). 94 �I\. Deflation area limb Obscure southwest southwasl margin parabolic dunes 4i 1 . B. WENDS WINDS 1km m .k MAP MAPVIEW VIEW CROSSSECTION SECTION CROSS Figure 6.2. 6.2. A. A.Typical Typicalasymmetic asymmeticdune dune blanket on the Anoka Proposed stages stages Figure Anoka Sand Sand Plain. Plain. B. Proposed in in the thedevelopment developmentof ofmodified modifiedparabolic parabolicdunes: dunes: A. A. Initial Initial development developmentof of symmetric symmetricparabolic parabolic dunes dunes by by strong strong northwest northwestwinds. winds. B. Modification Modificationby bycross-winds. cross-winds.Northwest Northwestdunes dunesare arestill stillstrong, strong,but butan animportant importantsouthsouthB. west wind component exists. west wind component exists. C. Stabilization Stabilizationand andrevegetation revegetation of of the the dunes. dunes. Minor Minoreolian eolianerosion erosion under under variable variable wind wind C. directions. directions. Steep Steep slope slope (slipfaces) (slipfaces)represented represented by by lined linedpattern; pattern; less less steep, steep,eroding eroding slopes slopes(backslopes) (backslopes)represented representedby by dotted dottedpattern. pattern. (Stop (Stop 22 by by Keen, Keen,from fromGoldstein, Goldstein,1987) 1987) 95 �O\ "S [H [TLTi. p.,..., •i •i•i ... —.-. I. ,:$ ,P s •' lI0 'be' !. - 'il-::j - --F— -, Istiflid b t C S $54.5. IRS, '1.! — I- ;Q' , 0.s (or rsd Din.) forest Birch-Aider forest Spruce woodland — Jack pine Prairie Oak savanna Oak I VEGETATION TYPES and sample of the spruce pollen decline). From Keen (1985). The estimated time scale was constructed by linear extrapolation between dated materials (surface lacustrine sediment, radiocarbon dated samples, Figure 6.3. A. Abbreviated pollen diagram for Lake Ann, Sherburne County, Minnesota: B. Eolian component of magnetic susceptibillity of core F, Lake Ann. Depth is estimated from the frozen lake surface. "1 4..— — 'S.— 'S..— '405— '7,.— — 6 Shi'burns Coirnuy . UInn.,oI. •5SS— CoreA lw's.. aOl ? A. CorSF C-' D??S LAKE ANN 1400- 1300. 1200. 1100. 900. SOD' 700 I 10 I 9 II I 20 I -3000 -2000 -bOO (yr. B.P.) Estkn.t.d 'C B?) (WIS-I4S2 7420*90 (WIS-1453) 43910 (yr. —8000 —4000 W — 10.000 — 9000 $000 -7000 -.000 0 w z U I- .. Radiocarbon dates Dipm AdusI.d Inagnstic auscepIty (ciTu) (.muIO.) a 1O bsss of B EOLIAN COMPONENT OF MAGNETIC SUSCEPTIBILITY CORE F. LAKE ANN, SHERBURNE COUNTY. MINNESOTA ___________ �pollen analysis (Fig. 6.3A), the postglacial vegetation vegetation history history of of spruce spruce woodland, woodland, birch-alder birch-alder forest, pine forest, and finally oak woodland other studies studies forest, prairie, and woodland is similar similar to that inferred from from other Minnesota. The in east-central Minnesota. The degree degree of of representation representation of prairie-indicator prairie-indicator species implies conditions on on the the Anoka Sand Plain during the mid-Holocene. mid-Holocene. very dry conditions The chronology of eolian eolian activity activity for the dunes dunes near Lake Ann, derived from analyzing lake sediment for eolian coarse silt and and very very fine fine sand, sand, correlates correlates extremely well with the vegetation history determined from pollen analysis. Because sediment is found history determined Because no wind-derived sediment in early Holocene Holocene sediments, present on the the sandplain sandplain in late late sediments, it appears appears unlikely that dunes were present glacial or early Holocene time, when forest covered the land. land. Eolian Eolian activity activity appears appears to to have have begun around 8000 8000 years ago, ago, when the percentage of tree pollen falls to its lowest postglacial 6.3B), Majoreolian eolianactivity, activity,as as shown shown best best by by the the magnetic magnetic susceptibility susceptibility curve curve (Fig. (Fig. 6.3B), value. Major occurs during prairie conditions occurs conditions of the mid-Holocene, mid-Holocene, until until about about4000 4000years yearsago. ago. Minor eolian activity activity follows follows throughout throughout the the late late Holocene. Holocene. Stop 7. The The "Feature" "Feature"(Howard (HowardHobbs) Hobbs) North of Elk River, an extensive extensive highland rises above the Anoka Sand Plain (Fig. 7.1). 7.1). Its largest dimensions east-west direction and a little less than 15 dimensions are are aa little little over 15 15 miles in the east-west miles north-south. Its about 100 feet; feet; local relief ranges Itsaverage average height height above the sandplain is about up to 100 100 feet, feet, but but many many parts parts are areflatter. flatter. highland has been interpreted interpreted as a tunnel-valley fan (Fig. 1). However, The origin origin of this highland However, it has been mantled mantled and and modified modified since since its its formation, formation,so so its surficial surficial sediments sedimentsare are quite quite variable. variable. Much of it has been mantled by reddish-brown sandy till, similar to till till of of the the Superior Superior lobe. lobe. In In places, places, banded banded red red and and gray gray till has been observed. The The till-covered till-covered part part of of the the feature feature is is crossed crossed by eskers, eskers, some from the Superior some of which which appear appearto to be Grantsburg, Grantsburg, some some of which which are are left left over over from Superior lobe. On gravel. They are similar Onthe thewest westside sideof of the the highland highland is is aa set of north-south ridges of gravel. to eskers, but are straighter. Stop Stop77isisaalarge largegravel gravelpit pit in in one oneof of them. them. in most most of of the the pit pit at The gravel is clean and rather coarse in at first first glance, glance, itit looks looks just like like Superior gravel. gravel. It has lots lots of of black black and and red red pebbles pebbles from from the the Superior Superior basin basin and and the the North North Shore. But Butlook lookclosely, closely,and andyou you will will find find aa few few gray gray shale shale pebbles, pebbles, which are are never found in pure Superior Superior gravels. ItItappears appearsthat thatmost most ifif not not all all the shale shale is coming out of the upper part of the exposure, but this is difficult to confirm, because the lower parts slump over so quickly. Our best interpretation interpretation of these ridges is that they were formed as a sort of ice-marginal meitwater by the the highland. highland. Most meltwater deposit where the Duelm bulge was hemmed in by Most of of the the gravel gravel is reworked from the existing existing fan, but aa little little gravel gravel was was derived derived from from the the Des Des Moines Moines lobe. lobe. This is where where the the shale shale came came from. from. 97 �Figure 7.1. Location Locationmap mapfor forstops stops66 and and 7. 7. 98 98 �REFERENCES CITED Aber, J. S., 1988, with glaciotectonic glaciotectonic examples: examples: Winston-Salem, Winston-Salem, 1988, Structural Structural geology exercises with N.C., Hunter HunterTextbooks, Textbooks,p.p.881-84. 1-84. Birks, H.J.B., 1976, 1976, Late LateWisconsin Wisconsinvegetational vegetational history history at at Wolf Wolf Creek, central Minnesota: Minnesota: Ecological Ecological Monographs, Monographs, v. v. 46, p. 495-529. glacial thrusting and related processes in Bluemle, J.P., J.P., and Clayton, L., 1984, 1984, Large-scale glacial North Dakota: Boreas, Boreas,v.v. 13, 13,p. p. 279-299. 279-299. Clayton, process-form model, Clayton, L., and and Moran, Moran, S.R., S.R., 1974, 1974,A glacial process-form model, in in Coates, Coates,D. D. R., ed., ed., Glacial Glacial geomorphology—Geomorphology Binghamton, N.Y., N.Y., 1974: 1974: Binghamton, geomorphology-Geomorphology Symposium, Symposium,5th, 5th, Binghamton, 89-119. State University University of New York, p. 89119. Cooper, W.S., 1935, Mississippi River in late Wisconsin Wisconsin and postglacial postglacial Cooper, W.S., 1935,The history of the upper Mississippi time: Minnesota MinnesotaGeological GeologicalSurvey SurveyBulletin Bulletin 26, 26, 116 116p. p. David, P.P., Sand dune dune occurrence occurrencein inCanada: Canada: A theme and resource resource inventory study study of of P.P., 1977, Sand eolian David, Dept. Dept. of Geology, Geology, University University eolian landforms landformsof of Canada: Canada: Available Availablefrom fromDr. Dr. Peter Peter P. David, of Montreal, 183 183 p. Goldstein, Goldstein, B., 1987, 1987, Geomorphology Geomorphology and and Pleistocene Pleistoceneglacial glacial geology geology of of central central Minnesota, Minnesota,in in Balaban, N.H., N.H., ed., Field trip guidebook for Quaternary and Cretaceous geology of westcentral Minnesota Minnesota and adjoining South Dakota: Minnesota Minnesota Geological GeologicalSurvey Survey Guidebook Guidebook Series No. 16, 16, p. 16-19 16-19 (Stop (Stop 2). Grigal, Grigal, D.F., Severson, Severson, R.C., and Goltz, G.E., 1976, 1976, Evidence of eolian activity in north-central Minnesota 8,000 to 5,000 years years ago: ago: Geological Geological Society Society of of America America Bulletin, v. v. 87, p. 125 1-1254. 1251-1254. Bedrock geologic geologic and topographic topographic maps Jirsa, M.A., Olsen, Olsen, B.M., and Bloomgren, B.A., 1986, Bedrock of the seven-county seven-county Twin Cities Cities Metropolitan MetropolitanArea, Area,Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Miscellaneous Miscellaneous Map Map M-55, scale scale 1:125,000. 1:125,000. Johnson, M.D., M.D., and Hemstad, Chris, in prep., Glacial Lake Grantsburg: a short-lived lake Johnson, recording recording the advance and retreat of the the Grantsburg Grantsburg sublobe, sublobe, in in Patterson, Patterson, C.J., C.J., ed., ed., Contributions to the Quaternary of Minnesota: Minnesota: Minnesota Quaternary of Minnesota Geological Survey Report of Investigations Investigations49. 49. Keen, K.L., 1985, Plain: Unpublished 1985, Sand dunes on the Anoka Sand Plain: Unpublished M.S. M.S. thesis, thesis, University University of Minnesota, Minneapolis, 191 p. Minnesota, Minneapolis, 191 Keen, K.L., and Shane, Shane, L.C.K., L.C.K., 1990, 1990,A A continuous continuous record record of of Holocene Holocene eolian eolian activity activity and and vegetation change at Lake Ann, east-central Minnesota: Minnesota: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 102, 102,p. p. 1646-1657. 1646-1657. A.R., 1996, Knaeble, A.R., 1996, Glaciotectonic thrusting along the St. St. Croix Croix moraine, moraine, Stearns StearnsCounty, County, Minnesota, Geologic Atlas, in Meyer, Meyer, G. G. N., and and Swanson, Swanson, L., eds., Text supplement to the Geologic Minnesota, in Stearns S t e m s County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey SurveyCounty CountyAtlas Atlas Series SeriesC-1O, C-10, Part C, p. 40-47. Knaeble, A.R., in prep., Superior Knaeble, Superior lobe glacial thrusting of drift and bedrock along the St. Croix Croix moraine, Stearns County, Minnesota, in in Patterson, Patterson, C. J., County, Minnesota, moraine, J., editor, Contributions Contributions to the the Quatemary Quaternary geology of Minnesota: Minnesota MinnesotaGeological Geological Survey Survey Report Report of Investigations Investigations 49. 99 �Leverett, F., and Sardeson, Sardeson, F.W., Minnesota and parts Leverett, F.W., 1932, Quaternary geology of Minnesota parts of adjacent adjacent states: U.S. U.S. Geological GeologicalSurvey Survey Professional Professional Paper Paper 161, 161, 149 149 p. Mackay, K.R., and Mathews, W. W. H., H., 1964, The The role role of of permafrost permafrost in in ice ice thrusting: thrusting: Journal Journal of of Geology, v. 72, p. 378-380. p. 378-380. Meyer, G.N., 1986, 1986, Subsurface Subsurface till till stratigraphy stratigraphy of of the the Todd Todd County County area, area, central central Minnesota: Minnesota: Minnesota 40 p. Minnesota Geological GeologicalSurvey SurveyReportof ReportofInvestigation Investigation34, 34,40 p. Meyer, G.N., 1992, plate 55 in in Meyer, 1992, Quaternary stratigraphy, stratigraphy, plate Meyer, G.N., G.N., and and Swanson, Swanson, L., L., eds., eds., Geologic atlas of Ramsey County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey County CountyAtlas Atlas Series C-7. Meyer, G.N., in Balaban, G.N., and Hobbs, Hobbs, H.C., 1989, 1989, Surficial Suficial geology, plate 3 in Balaban, N.H., ed., Geologic Geologic atlas of Hennepin County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey County County Atlas Atlas Series Series C-4, scale 1:100,000. 1:100,000. Twin Cities Metropolitan Meyer, G.N., and Jirsa, M.A., 1984, 1984,Aggregate resources inventory, Twin Area, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey Information Information Circular 20, 16 16 p. Patterson, C.J., 1992, in Meyer, G.N., G.N., and and Swanson, Swanson, L., L., eds., eds., Geologic Geologic Patterson, 1992, Surficial Surficial geology, plate 33 in atlas of Ramsey County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey SurveyCounty CountyAtlas Atlas Series Series CC7, scale 1:48,000. 1:48,000. Patterson, C.J., 1994, Tunnel-valley fans of the the St. St.Croix Croixmoraine, moraine,east-central east-centralMinnesota, Minnesota, U.S.A., U.S.A., Patterson, 1994,Tmnel-valley in Warren, W.P., W.P., and and Croot, D.G., D.G., eds., Formation and deformation of glacial glacial deposits: deposits: Rotterdam, Balkema, Rotterdam, Balkema,p.p.69—87. 69-87. Setterhoim, D. R., 1996, Setterholm, 1996, Geology Geology of of the the Late Late Cretaceous Cretaceous Strata Strata and and Pre-Late Pre-Late Cretaceous Cretaceous Weathering Profile, Steams Stearns County, County, Minnesota, Minnesota, in in Meyer, Meyer,G. G. N., N., and and Swanson, Swanson, L., L., eds., Weathering Atlas, SStearns County,Minnesota: Minnesota: Minnesota Minnesota Geological Geological Text supplement to the Geologic Atlas, t e m s County, Survey County Atlas Atlas Series Series CC-b, 10,Part PartC, C,p. p. 7-15. 7- 15. 100 ��FIELD FIELD TRIP TRIP #4 #4 STRATIGRAPHY STRATIGRAPHYAND AND HYDROGEOLOGY HYDROGEOLOGY OF OF PALEOZOIC PALEOZOICROCKS ROCKS OF OF SOUTHEASTERN SOUTHEASTERNMINNESOTA MINNESOTA Leaders: Leaders: Anthony AnthonyC. C.Runkel Runkeland andRobert RobertG. G. Tipping Tipping Paleozoic Paleozoicstrata strataof of the thecentral centralmidcontinent midcontinentregion regionare areamong amongthe thelongest longeststudied studiedand andbest best known America. This known sedimentary sedimentary rocks in North America. This field field trip tripwill willprovide provide an anopportunity opportunityto to examine examinethe thediverse diversesuite suiteof of lower lowerPaleozoic Paleozoicrocks rocks exposed exposedalong alongthe the Mississippi MississippiRiver Riverand andits its 1) the depositional tributaries in southeastern Minnesota, focusing on two interrelated topics: tributaries in southeastern Minnesota, focusing on two interrelated topics: 1) the depositional history history of of these thesestrata, strata,highlighting highlightingadvances advancesmade madeover overthe thepast pastfifteen fifteenyears yearsin inunderstanding understanding the the origin originof of their their well well documented documented enigmatic enigmatic features, features, and 2) 2)the thehydrogeologic hydrogeologicproperties propertiesof of these these strata, strata,with withparticular particularemphasis emphasison oncharacterization characterizationof ofhydrostratigraphic hydrostratigraphiccomponents. components. INTRODUCTION INTRODUCTION Paleozoic Paleozoicstrata stratain inthe thecentral centralmidcontinent midcontinentregion regionof ofNorth NorthAmerica Americaconsist consistof ofthin thinunits units of of carbonate, carbonate, sandstone, sandstone,and and shale shaledistributed distributed across across tens tens of of thousands thousands of of square squarekilometers. kilometers. This Thisoverview overviewfocuses focuseson onthe thenorthernmost northernmostextent extentof of lower lowerPaleozoic Paleozoicstrata stratathat thatwere weredeposited deposited on the stable cratonic shelf northwest of the illinois and Michigan basins (Figs. 1 and 2). The on the stable cratonic shelf Illinois basins (Figs. and 2). The rocks rocks are areexposed exposedin in aa sinuous sinuousbelt beltof of outcrops outcropsalong alongthe the southern southernflank flankof of the theTranscontinental Transcontinental arch Minnesota, Wisconsin and northern Michigan. Michigan. archand and the the Wisconsin Wisconsindome dome and and arch in southern Minnesota, Deposition began in in the the Middle Middle to Late Cambrian. Deposition of Paleozoic Paleozoic sediments sediments began Cambrian. Coarse Coarse siliciclastic Sandstone covered the eroded Precambrian Precambrian siliciclasticsediments sedimentsof of what whatisis now now the Mt. Simon Sandstone surface. surface. Overlying Overlyingstrata stratawere weredeposited depositedinintwo twobroad, broad,laterally laterally equivalent equivalent facies facies belts belts across across the composed the central central midcontinent midcontinentregion region (Fig. (Fig.11 inset) inset) (Palmer, 1960). An inner detrital belt was composed of of shallow shallowmarine marinesiliciclastics siliciclasticsderived derived from from subaerially subaerially exposed exposed Precambrian Precambrian Shield Shieldareas areason on and to to the the north north of of the theWisconsin Wisconsin Dome. Dome. Thin, Thin,laterally laterallyextensive extensiveunits unitsdominated dominatedby by either either and fineto coarse-grained quartzose sandstone, very fine gralned sandstone, or shale were deposited fine- to coarse-grained quartzose sandstone, very fine grained sandstone, in intertidal carbonate carbonate subtidal to intertidal in this this inner inner detrital detrital belt. The Themiddle middlecarbonate carbonatebelt belt consisted consisted of subtidal and and shale shale that that accumulated accumulated to the south. south. Over Overtime, time,the theboundary boundary between between these thesedepositional depositional belts shifted: shifted: sedimentation sedimentationininthe theinner innerdetrital detritalbelt beltwas wasdominant dominantduring during the theCambrian Cambrianand and part of of the the Middle Middle Ordovician; Ordovician; and and sedimentation sedimentation in in the the middle middle carbonate carbonate belt belt was was dominant dominant during during the the Early Early and and Late LateOrdovician, Ordovician,as aswell well as asin in the theSilurian Silurianand andDevonian Devonian(Fig. (Fig.2). 2). Early Early Paleozoic Paleozoicdeposition depositionoccurred occurredon on aa virtually virtually horizontal, horizontal, cratonic cratonic shelf shelf that that subsided subsided very slowly. slowly. Late LateCambrian Cambriansubsidence subsidenceaveraged averaged less less than than 10 10m/m.y. m/m.y. (Sloss, (Sloss,1988)—about 1988)-about one-fifthto to one-tenth one-tenth the the rate rate in the contemporaneous Illinois 199I), and orders one-fifth illinois basin (Sargent, (Sargent, 1991), magnitude slower slower than that that of of better known, younger basins in North America. Maximum Maximum of magnitude 1995; Ludvigson and typically less than 100 m (e.g., Byers and Dott, 1995; paleobathymetry was typically others, 1996) 1996)and and the theshelf shelfhad hadaalow low gradient gradientslope slopeof of about about0.1 0.1 rn/km. mlkrn. others, The Wisconsin Wisconsin dome dome and and arch arch and Transcontinental Transcontinental arch were positive structural The structural features features influenced patterns patterns of of early early Paleozoic Paleozoic sedimentation, sedimentation, and and eventually eventually controlled controlled the the that influenced distributionand and configuration configurationof the gently folded and faulted Paleozoic distribution Paleozoic strata we we see see today. today. In 103 �____ Figure 1.1.Location Location map map showing showing Figure early Paleozoic Paleozoic tectonic tectonic features, features, early major paleotopographic pdeotopographic highs of major Precambrian rocks rocks (stippled) (stippled) and and the the Precambrian approximate distribution dismbution of approximate Cambrian (C) Ordovician (0), Cambrian (C),, Ordovician (0), ( S ) ,and and Devonian Devonian (D) (D) Silurian (S), strata in the northern part of the central midcontinent midcontinent region. region. The The central area relative relative to to shows the study study area inset shows the Late Late Cambrian Cambrianinner inner (stipple) (stipple) the detrital belts belts and and and outer outer (dashes) (dashes)detrital and the the middle middle carbonate carbonatebelt (block (block Palmer (1960). (1960). Modified Modified pattern) of Palmer others (1998). from Runkel and others GROUP! FORMATION UTHOLOGY .e. < Cedar Valley J ::::" — —l -— Burnt Bluff Cataract -——— —— Maquoketa Dubuque J —— Figure Figure2.2.Generalized Generalizedstratigraphic stratigraphiccolumn column(no (no scale) scale) for for lower lower Paleozoic Paleozoicrocks rocksininthe thenorthern northernpart part of the the central central midcontinent midcontinentregion. region. The The Cambrian Cambrian and and Ordovician Ordoviciannomenclature nomenclatureisis that that used used in in southeastern southeastern Minnesota and Wisconsin, the the Silurian from eastern eastern Wisconsin Wisconsinand and northern northern Silurian from Michigan, Michigan, and and the the Devonian Devonianfrom fromsouthernmost southernmost Minnesota Minnesota and and northern northern Iowa. Iowa. ngadine Manistique ——— Galena Decorah PttevilIe - St Peter ShakoPeejPrane O' I j-L--. — 2 - \_ ..: . —. —. . . Group Jordan St Lawrence Franconia (Lone Koch) (Worwwoc) EauClaireand Bonneterre • Mt. Simon Quwtzose sandstone @atzosesandstone Very shale Very fine fines.s., s.s., siltstone. s~lmone, shale - Carbonate (dashedwhere whereshahy) sbl~) Carbonate(dashed No Norecord record Unconformity Unconfonn~ty 104 �northern Iowa, southern Minnesota, Minnesota, and southwestern southwestern Wisconsin, Wisconsin, Paleozoic Paleozoic strata are are preserved preserved northern in what is known known as as the the Hollandale Hollandale embayment, embayment, which is aa broad broad syncline syncline that that lies lies between between these two positive features. South Southand andeast eastof of the theWisconsin Wisconsin dome dome and and arch, arch, Paleozoic Paleozoic rocks rocks dip less than 11 degree degree into into the Illinois Illinois and and Michigan Michigan basins. DEPOSITIONAL MODELS DEPOSITIONAL MODELS Despite over 100 100 years of study, study, the depositional depositional history of lower lower Paleozoic Paleozoic siliciclastic siliciclastic strata of this region remains poorly understood. Many poorly understood. Many workers workers have lamented an apparent apparent absence of modern or ancient depositional analogues. In addition, addition, while dozens of local studies have been conducted (e.g., Nelson, 1956; 1956; Haddox and Dott, Dott, 1990), 1990), few few are are regional-scale regional-scale investigations that incorporate several lithofacies into a temporally constrained stratigraphic framework. framework. Present-day Present-dayunderstanding understandingof of early early Paleozoic Paleozoic siliciclastic siliciclasticdeposition depositionis is based mostly mostly on work conducted since since 1950, 1950,beginning beginning with the predominantly predominantly stratigraphic stratigraphic investigations investigations of Berg (1954), (1956), Bell Bell and others (19561, (1956), and Ostrom (19541, Nelson (1956), (19561, Berg and others (19561, (1964, 1970). Subsequent sedimentologic—focusing on the interpretations interpretations (1964,1970). Subsequentwork work has has been chiefly sedimentologic-focusing of near-shore marine facies (Fraser, (Fraser, 1976; 1976; Driese and others, 1981; 1981; Dott Dott and and others, others, 1986; 1986; Haddox and Dott, 1990; 1990;Barnes Barnes and and others, others, 1992; 1992;Mossler, 1992; 1992; Runkel, Runkel, 1994). 1994). In a very important important and widely cited examined the transition cited study, study, Dott and others (1986) examined transition from nonmarine to marine environments recorded recorded in quartzose sandstones, and provided the of nonmarine nonmarine facies. facies. They described an early Paleozoic first set of criteria for identification of terrestrial setting with broad braided streams and eolian sheet and erg systems that delivered sand to a shallow marine environment dominated dominated by by small smallthree-dimensional three-dimensionaldunes. dunes. Dott and of vegetation, between between early early Paleozoic others (1986) stressed the differences, difherences, such as the lack of depositional environments environments and those inferred inferred for both younger rocks and and modern modern settings. settings. depositional model A depositional model of a simple, simple, storm-dominated, storm-dominated, texturally texturally graded graded shelf shelf was was proposed proposed by Runkel and others (1998) (Fig. 31, 3), and is noteworthy noteworthyin inits itssimilarity similarity to models based on both younger younger rocks regional-scale outgrowth rocks and modern systems. Their Their study study was essentially a regional-scale of the excellent students from the University University of Minnesota Minnesota excellent outcrop outcrop work work of Charlie Charlie Bell Bell and his students in the 1950's. Runkel Runkeland andothers others(1998) (1998)suggested suggestedthat that early early Paleozoic Paleozoic depositional depositional processes distribution are analogous analogous to those depicted in well-known and facies distribution well-known models models of of the the Cretaceous Cretaceous interior seaway and the modern Bering Shelf. Shelf. The thin, widespread siliciclastic seaway and modern Bering The thin, widespread siliciclastic units units characteristic migrations that occurred characteristic of lower lower Paleozoic Paleozoic strata strata result from large lateral facies migrations in response to to continental-scale continental-scalechanges changes in in relative relative sea sea level. Carbonate rocks within within the lower lower Paleozoic sequence sequence historically historically have have been regarded regarded as as more amenable comparison with both modern and ancient ancient facies facies models. models. Deposition occurred amenableto comparison occurred in environments supratidal conditions conditionsfor for parts parts of of the the Prairie Prairie du environments that range from evaporitic, evaporitic, supratidal Chien Group Group (Smith (Smith and and others, others,1993) 1993)to to subtidal subtidalsettings settingsin in depths depths of of 100 100m m or or more more for for parts parts of the Decorah Shale (Ludvigson and others, 1996). Most Most investigations investigations have have been local local in in scope relative relative to to the great lateral extent extent of of these these units, units, and and there there are are too too many many to cite them scope individually. Ordovician individually. Ordovician carbonate carbonate strata strata of of the the Hollandale Hollandale embayment embayment are are the the focus focus of a monograph edited by Sloan (1986). Silurian Siluriancarbonates carbonates on the western flank of the Michigan basin have recently been studied by Harris and Waldhuetter Waldhuetter (1996). (1996). There are many excellent studies of OrdovicianOrdovician- through through Devonian-age Devonian-age strata strata in northern northern Iowa, Iowa, largely largely conducted conducted by by the the Iowa Geological extrapolated to Minnesota and Wisconsin (for Geological Survey; Survey; the the results results can often be extrapolated 105 �Taylors FaNs Precambrran ava flow ndq SILICICLASTIC (WSMOPE SHELF - — — MO3ft — — — — — — sand — — — -4,:;— — - — — — — 0 trom ahotataco — — — —— ' —o Q\AILW%.PUI Iranspolt by storms Sand 0 — — — '' Storm — naport ot fn sand. Ol. srral. — — — — .'.,, 0 0 - Ternp,sIiI.I — D Wasfi Figure3.3.Conceptual Conceptualdepositional depositionalmodel modelofofLate LateCambrian Cambrianstorm-dominated, storm-dominated, texturally Figure texturally graded shelf. Quartzose fineto coarse-grained sand accumulated nearshore terrestrial graded shelf. Quartzose fine- to coarse-grained sand accumulated ininnearshore terrestrial andshoreface shorefaceenvironments. environments.Finer Finergrained, grained,feldspathic feldspathicsiliciclastic siliciclasticsediments sedimentsand and subtidal and subtidal carbonatesaccumulated accumulatedinindeeper deeperwater waterofofthe theoffshore offshoreshelf. shelf. carbonates example,several severalpapers papersininWitzke Witzkeand andothers, others,1996). 1996).Some Someregional-scale regional-scalestudies studieshave have recently example, recently been completed; a stratigraphic framework has been developed for the Prairie du Chien Group been completed; a stratigraphic framework has been developed for the Prairie du Chien Group fromthe theMichigan Michiganbasin basintotothe theHollandale Hollandaleembayment embayment(Smith (Smithand andothers, others,1993, 1993, 1996; Barnes from 1996; Barnes andothers, others,1996). 1996).Simo Simoand andothers others(1997) (1997)are arecurrently currentlyconstructing constructingaalarge largescale scalestratigraphic stratigraphic and frameworkfor forOrdovician Ordovicianrocks rocksofofthe thecentral centralmidcontinent midcontinentininorder orderto toaddress addresslong-standing long-standing framework problemssuch suchasasidentification identificationof ofthe thecontrols controlsresponsible responsible for forthe theapparently apparently synchronous problems synchronous regional-scale changes from "tropical" to "temperate" styles of carbonate deposition. regional-scale changes from "tropical" to "temperate" styles of carbonate deposition. NOTABLEFEATURES FEATURESAND ANDLONGSTANDING LONGSTANDINGPROBLEMS PROBLEMS NOTABLE LowerPaleozoic Paleozoicstrata strataininthe thecentral centralmidcontinent midcontinentregion regionare arewell wellknown knowntotogeologists geologists Lower outsideof ofthe thearea areafor forseveral severalenigmatic enigmatic features features(Dott (Dott and and Byers, Byers, 1980). 1980). Most Most notable is the outside notable is the extreme textural and mineralogical maturity of the fineto coarse-grained sandstones, and the the extreme textural and mineralogical maturity of the fine- to coarse-grained sandstones, and sheet-likegeometry geometryofofthese theseand andother othersiliciclastic siliciclasticunits. units.The Theoverall overalldearth dearthofofshale shale has puzzled sheet-like has puzzled sedimentologistsyand and the thefundamental fundamentalcontrols controls on onthe theepisodic episodicchange changefrom from siliciclasticsedimentologists, siliciclasticdominatedtotocarbonate-dominated carbonate-dominatedsedimentation sedimentationremain remainpoorly poorlyunderstood. understood.Lastly, LastIy, the presence, dominated the presence, position,and andmagnitude magnitudeofofunconformities unconfonnitieshas hasbeen been debated debatedfor for decades. decades. The Theremainder remainder of this position, of this discussion summarizes the progress made since Dott and Byers (1980) published a similar discussion summarizes the progress made since Dott and Byers (1980) published a similar overviewyand andoffers offersaaguide guideto totopics topicsthat thatcan canbe bediscussed discussedatatthe theindividual individualfield fieldtrip trip stops. overview, stops. Texturalmaturity maturityofofsandstones sandstones Textural Theextreme extremetextural texturaland andmineralogical mineralogicalmaturity maturityofofthe thefinefine-totocoarsecoarse-grained grainedsandstone sandstone The units,such suchasasthe theSt. St.Peter PeterSandstone, Sandstone,may maybe bethe thebest bestknown knownand andlongest longeststudied studied feature in the units, feature in the lower Paleozoic strata of the central midcontinent. The sandstones contain more than 98 percent lower Paleozoic strata of the central midcontinent. The sandstones contain more than 98 percent quartzand andmost mostgrains grainsare aremoderately moderatelyto towell wellrounded. rounded. Such Suchtextural texturaland andcompositional compositionalmaturity maturity quartz could not have been achieved solely by fluvial and marine abrasion, even over transport distances could not have been achieved solely by fluvial and marine abrasion, even over transport distances 106 �of hundreds of kilometers, if the grains grains were were derived derived directly from crystalline source rocks. Rare grains with abraded abraded overgrowths overgrowths are reworked reworked from older sedimentary rocks, but the the volumetric significance of suitable suitable sedimentq sedimentary rock volumetric significanceof such such recycling is uncertain and a source of been identified. identified. Odom 1978) conducted the most comprehensive comprehensive mineralogical mineralogical has never been Odom (1975, (1975,1978) Paleozoic sandstones. He fine grained grained fraction fraction is is feldspathic, feldspathic, study of lower Paleozoic He noted that the very fine whereas the fine- to coarse-grained contains more more than than 98 percent percent quartz (with the coarse-grained fraction contains exception of some lower Mt. Mt. Simon Simon Sandstone Sandstonebeds). beds). He suggested exception of suggested that a long long history history of of abrasion abrasion in aa marine marine setting setting could could account account for for both both the maturity of the quartzose quartzose grains grains and and the the reduction in size of feldspar grains. Dott Dott and and others others (1986) (1986) were the first to clearly identify the presence of substantial substantial eolian eolian deposits deposits within within some some quartzose quartzose sandstones, sandstones, and and they they suggested suggested that eolian mineralogic features features described described by Odom eolian abrasion abrasion could could contribute contributeto the textural and mineralogic Odom be taken taken into into consideration consideration (1975, 1978). Lastly, Lastly, chemical chemical weathering weathering in the source area must be 1978) noted that the very fine grained, feldspathic sandstones sandstones are (Morey, 1972). Odom Odom(1975, (1975,1978) rich in K-feldspar "trace" amount of of plagioclase plagioclase grains, grains, even even though though plagioclase plagioclase K-feldspar but have only a "trace" of the Precambrian Precambrian Shield. Shield. Selective was presumably dominant in the source area of Selective diagenetic diagenetic leaching of of plagioclase plagioclase grains grains from from the the sandstone sandstone was was discounted discountedby by Odom Odom (1978). (1978). Thus, leaching Thus, chemical weathering probably preferentially dissolved plagioclase crystals and reduced reduced the the amount of other relatively unstable unstable minerals prior to mechanical mechanical abrasion abrasion during during transport size and amount transport to the shoreline. shoreline. been responsible responsible in part for the While each of the processes described above could have been mineralogic mineralogic and and textural textural attributes attributes of lower Paleozoic sandstones, they do not entirely account for the compositional record that appears to indicate that virtually all fine- to coarse-grained coarse-grained exceptionally mature the early early Paleozoic Paleozoic shoreline. shoreline. Finesand was exceptionally mature when it arrived to the Fine- to to coarsecoarsegrained immature sand would have almost certainly been deposited locally if the marine abrasion grained immature sand would have almost certainly been deposited locally marine abrasion model accurate. Similarly, terrestrial setting model of Odom Odom (1975) (1975) were accurate. Similarly,itit is difficult to reconstruct a terrestrial in which all all sand sand isissubjected subjectedto toprolonged prolonged eolian eolian abrasion abrasion prior prior to to deposition deposition in in aa marine marine environment environment as suggested suggested by Dott Dott and and others others (1986). (1986). Sheet geometry geometry layers were were initially initially deposited deposited Another long-standing long-standing question question is how sheet-like siliciclastic layers of thousands of of square kilometers kilometers of of the the cratonic cratonic shelf. shelf. Most and then preserved across tens of workers have attributed the formation of such sheets to depositional processes and environments workers have attributed the formation such sheets processes and environments that are markedly markedly different different from those described for most younger rocks and modern settings. Lochman-Balk (1970) inferred the presence of enormous tidal flats extending well over over two two the shoreline. shoreline. Dott and Byers (1980) (1980) suggested suggested that that hundred kilometers perpendicular to the quartzose sand under high-energy high-energy conditions conditions across quartzose sand aggraded aggradedmore more or or less less vertically into a sheet under across a vast shallow sea. The most widely cited hypothesis is one that attributes the origin of quartzose The widely cited that attributes the origin of quartzose sandstone sheets to fluvial fluvial and and eolian eolian processes processes that that dispersed dispersed sand sand across across aavegetation-free vegetation-free reworking during during aa transgression transgression(Dott (Dottand andothers, others, 1986). 1986). Recent landscape prior to marine reworking studies, however, have demonstrated demonstrated that that some some quartzose quartzose sheets were deposited entirely within the marine realm under under regressive conditions conditions (e.g., Runkel, Runkel, 1994; 1994; Hughes and Hesselbo, Hesselbo, 1997; 1997; Runkel and others, 1998), and that the depositional processes responsible for the dispersal of 1998), depositional siliciclastic ancient sandstones sandstones siliciclasticsediments sedimentswere were similar similarto to those those operating operating during during the deposition of ancient sheet-like. that are not sheet-like. 107 �The lateral lateral persistence persistence and and sheet-like sheet-like geometry geometry of of lower lower Paleozoic Paleozoic siliciclastic siliciclastic units units probablyreflect reflectthe theroles rolesof of basin basin physiography physiographyand and tectonics tectonics in controlling controlling the lithostratigraphic probably lithostratigraphic architecture, rather rather than than the the existence existence of atypical atypical sedimentary environments. Deposition Deposition was was architecture, characterizedby byaacontinuous continuousand andabundant abundantsupply supplyof of sediment sedimentto to aa relatively stable, stable, nearly flat flat characterized basin that that had had aa slow, slow, uniform uniform rate rate of of subsidence. subsidence. Individual basin Individualsheets sheetsof ofsiliciclastic siliciclasticsediment sediment (e.g., Fig. Fig. 3) 3) migrated migrated great great distances distances during duringchanges changesin in were deposited deposited when when discrete discrete facies facies (e.g., were sea level. level. Deep Deepincision incisionofofthe theindividual individualsheets sheetsduring duringepisodes episodesof ofsubaerial subaerialexposure exposuredid didnot not sea occur, resulting in more or less uniform preservation. occur, resulting in more or less uniform preservation. Dearth Dearthof ofShale Shale LowerPaleozoic Paleozoicrocks rocksof ofthe thecentral centralmidcontinent midcontinentregion regionare arenoted notedfor foraadearth dearthofofshale shale Lower compared comparedto toother othershallow shallowmarine marinedeposits. deposits.Two Twovery verydifferent differenthypotheses hypotheseshave havebeen beenproposed proposed to "marinebypassing" bypassing" model, model,Pettijohn Pettijohnand and others others (1973) (1973) to account accountfor for this this dearth dearth of of shale. shale. In Inaa"marine suggested that that clayclay-and andsilt-sized silt-sizedparticles particleswere weredelivered delivered to to the the shoreline, shoreline,but but subsequently subsequently suggested carriedin insuspension suspensionby byrepeated repeatedstorms stormsacross acrossthe theshallow shallowshelf shelfbefore beforefinal finalburial burial in in basinward basinward carried areas.InIncontrast, contrast,Dairymple Dalrympleand andothers others(1985) (1985)suggested suggestedthat thatstrong strongwinds windsblew blewclay clayand andsilt silt areas. particles hundreds hundredsto to thousands thousandsof of kilometers kilometersoffshore, offshore, to to be ultimately ultimately deposited deposited in in the the outer outer particles detrital detrital belt belt (Fig. (Fig.1). 1). Recentinvestigations investigationsof of Upper Upper Cambrian Cambrian siliciclastic siIiciclastic strata strata support support the marine bypassing Recent model model of of Pettijohn Pettijohnand andothers others(1973), (1973),demonstrating demonstratingthat thatthe theabsence absenceof ofshale shaleisischaracteristic characteristic only only of of the the outcrop outcropbelt belt on on the the flanks flanksof of the the Wisconsin Wisconsin dome dome and and arch arch (McKay, (McKay, 1988; 1988; Runkel Runkel and and others, others, 1998). 1998).Basinward Basinwardofofthe theWisconsin Wisconsinarch, arch,subsurface subsurfacerecords records from from Minnesota Minnesota and and Theseshale shaleand and siltstone siltstone Iowashow showthat that facies faciesdominated dominatedby by shale shale and and siltstone siltstone are common. These Iowa facies facies are are the the offshore offshoreequivalent equivalent of of the the shale-poor shale-poor sandstone sandstone facies facies of of the the outcrop outcrop belt, belt, and and their geographic geographicposition position changed changed through through time time in in response response to to changes changes in in the the position position of of the the their storm-fairweather wave storm-fairweather wave base. base. The The outcrop outcrop belt belt has has aadearth dearth of of shale shalesimply simply because because the the depositional depositional record record isisdominated dominatedby byhighstand highstandshoreface shorefacefacies faciesdeposited depositedabove abovefairweather fairweather wavebase. base.This Thisstratigraphic stratigraphicand andsedimentologic sedimentologicattribute attributeisisnot notunique uniquetotothe thelower lowerPaleozoic Paleozoic wave rocks rocks of of the thecentral centralmidcontinent midcontinentregion—it region-it is is common common in many many younger wave-dominated wave-dominated sequences along along the the landward landward margins margins of of individual individual basins. The Thenotion notionof ofaashale-free shale-freeearly early sequences Paleozoic epeiric epeiric sea seaisisaadeeply deeplyentrenched entrenchedidea ideathat thatsimply simplyreflects reflectsthe thebias biasof ofthe theoutcrop outcrop Paleozoic belt. belt.The Thedearth dearthofofshale shaleininlower lowerPaleozoic Paleozoicrocks rocksshould shouldbe beremoved removedfrom fromthe thelist listofofenigmatic enigmatic featuresunless unlessthe thescarcity scarcitycan canbe bedemonstrated demonstratedtotoexist existon onaa scale scalelarger largerthan than that that of the outcrop features outcrop belt. belt. Siliciclastic-Carbonate Siliciclastic-Carbonatecycles cycles The The fundamental fundamental controls controls on onthe thetransition transitionfrom fromnearshore nearshoresiliciclasticsiliciclastic-to tocarbonatecarbonatedominated understood. For dominated deposition deposition have have never never been satisfactorily satisfactorily understood. For example, example, in in the the Early Early Ordovician, carbonate carbonate deposition deposition apparently apparently dominated dominated across across the the entire entire region, region, even even in in the the Ordovician, shallowestwater waterconditions conditions(Smith (Smithand andothers, others,1993). 1993).Both Botholder older(Jordan (JordanSandstone) Sandstone)and andyounger younger shallowest (St. (St. Peter PeterSandstone) Sandstone)shallow-marine shallow-marineenvironments environmentswere weredominated dominatedby bysiliciclastics. siliciclastics. Only Only speculative kndamentalchanges. changes. speculativeand andvague vaguehypotheses hypotheseshave havebeen beensuggested suggestedto toaccount accountfor forsuch suchfundamental For Forexample, example,Adams Adams(1978) (1978)suggested suggestedthat thatthe theEarly EarlyOrdovician Ordovicianchange changeinindepositional depositionalstyles styles may mayhave havebeen beenin inresponse responsetotodrowning drowningof of the thesiliciclastic siliciclasticsource sourcearea areaby by aa shallow shallow sea sea or orthe the result resultof ofsiliciclastics siliciclasticsbeing being"deflected" "deflected"to toanother anotherregion. region. Early EarlyPaleozoic Paleozoiccarbonate-dominated carbonate-dominated 108 �systems developed following level (Smith (Smith and and others, others, 1993), which which systems following extended periods of high sea level siliciclastic source area may have been covered by a blanket of of carbonate carbonate suggests that the siliciclastic rocks. The Thespread spreadof of certain certainforms formsof of terrestrial terrestriallife life such such as as bacterial bacterial encrustation, encrustation, and and later later the the development development of vascular vascular plants, may have also reduced siliciclastic siliciclastic input. Cryptic Cryptic unconformities unconformities Previous investigations investigations of lower Paleozoic strata of the central midcontinent region have also been hindered by an inability to recognize unconformities. unconformities. The unconformities bounding the major sequences sequences of Sloss Sloss (1963) (1963) are are fairly well established established within the strata strata of of the the outcrop outcrop belt. The The presence presence and and position position of "lesser" "lesser" unconformities, unconformities, especially especially within siliciclastic units, have been a matter of considerable debate. Stratigraphic Stratigraphicrelations relations and and interpreted interpreted depositional depositional histories indicate that such unconformities "should" be present. However, However, little little or or no evidence evidence for regionally extensive subaerial subaerial erosion erosion has has been been documented. documented. Such Such sequence-bounding sequence-bounding they are contained within coarse siliciclastics unconformities are difficult to recognize where they texturally and and mineralogically mineralogically similar, and and sandstones that are texturally because they separate quartzose sandstones because they are relatively flat—reflecting erosion that occurred on a loose, sandy substrate relatively flat-reflecting sandy substrate along a low, uniform uniform gradient, gradient, and and in in aa nonvegetated nonvegetatedterrestrial terrestrialenvironment. environment. Furthermore, Furthermore, the ultra-mature mineral ultra-mature mineral composition compositionof of the the exposed exposed substrate substrateinhibits inhibits development developmentof of aa distinctive distinctive weathering profile. Recent work has shown some promise for identifying subtle subaerial erosion surfaces. Recognition of cryptic unconformities interpretation of regional stratigraphic stratigraphic relations Recognition unconformities requires requires interpretation outcrops and high resolution in conjunction with physical evidence collected at individual outcrops biostratigraphic data. data. Smith deposits of of silica cement cement in biostratigraphic Smith and and others others (1993) (1993) interpreted local deposits formed silcrete. Runkel uppermost Cambrian and Lower Ordovician strata as subaerially formed Runkel and and others (1998) suggested that cryptic unconformities within the fronton and Galesville Sandstones Ironton Galesville Sandstones others (1998) suggested that cryptic unconformities within and at the top top of of the the Jordan Jordan Sandstone Sandstone and and can can be be identified identified only by overlying overlying lag deposits. deposits. These lags deposits are the coarsest bed within nearshore sandstone successions; they separate a regionally traceable, traceable, decameter-scale, decameter-scale, coarsening-upward interval below from a decameterdecameterscale, fining-upward sequence above. above. Preliminary Preliminary results of of high high resolution resolution biostratigraphic biostratigraphic verified the the presence presence of of an an erosion erosion surface surface on on top top of of the Jordan dating using conodonts has verified Sandstone, and magnitude of such cryptic cryptic unconformities unconformities Sandstone, and demonstrates demonstratespromise promise for for measuring the magnitude with detailed paleontologic paleontologic work. HYDROGEOLOGY The Paleozoic Minnesota are are the the most most widely widely used used source of Paleozoic strata of southeastern southeastern Minnesota groundwater in the state. state. Groundwater Groundwatermanagement management and andscientific scientificinvestigations, investigations, including including ground water models, models, estimates estimates of of aquifer yields and predictions of contaminant transport, ground water well construction codes have, in the past, relied on a generally accepted hydrogeologic framework that we believe believe is inaccurate inaccurate in in many many important important respects. respects. This commonly framework that commonly used classification of aquifers and confining beds beds (e.g., (e.g., Kanivetsky Kanivetskyand andWalton, Walton,1979; 1979; Delin and Woodward, 1985) assumption that Paleozoic lithostratigraphic lithostratigraphic units in Minnesota Minnesota Woodward, 1985)is based on the assumption are more or or less less internally internally homogeneous homogeneous in in hydrogeologic hydrogeologic character, character, and that they they have have boundaries. Furthermore, this paradigm is boundaries that correspond to hydrostratigraphic boundaries. based chiefly on the the hydrogeologic hydrogeologic characteristics of the Paleozoic strata in the Twin Cities Metropolitan from equivalent equivalent strata stratain insoutheastern southeasternMinnesota. Minnesota. A Metropolitan Area, which differ markedly from 109 �more accurate accurate hydrogeologic hydrogeologic framework framework is necessary to advance our understanding of groundwater flow in this region. region. We have have recently changes in the methods We recently made fundamental fundamental changes methods used used to to characterize characterize hydrogeologic attributes focusingon onhydrostratigraphic hydrostratigraphic components components rather rather hydrogeologic attributes of Paleozoic strata, focusing than lithostratigraphic lithostratigraphic units. Fig. 4 shows our preliminary results in delineating hydrostratigraphic Fig. 4 shows in delineating hydrostratigraphic components, permeability. The Paleozoic components, distinguished distinguishedand and characterized characterized by their porosity and permeability. bedrock hydrostratigraphic components components that bedrock of southeastern southeastern Minnesota Minnesota consists consists of four distinct hydrostratigraphic have been described described in in studies studies at at both both the regional regional and local scale scale (e.g., Setterholm Setterholm and and others, others, Miller and and Delin, Delin, 1993; Runkel, Runkel, 1996a, 1996b). 1996b). They are: 1) fine clastic; 2) coarse 1991; Miller coarse clastic, 3) carbonate rock, rock, and 4) mixed mixed carbonate carbonate and and clastic. clastic. The values for porosity and permeability permeability of these these components, components,discussed discussed below, below, have been determined determined through through laboratory laboratory tests of plug samples samples and and through through hydraulic hydraulic testing testing of of boreholes boreholes in in southeastern southeasternMinnesota. Minnesota. grained, feldspathic feldspathic sandstone, sandstone, siltstone The fine-clastic component consists of very fine grained, strongly to to moderately moderatelycemented. cemented. This component and shale in thin to medium beds that are strongly orders of of magnitude less than that of the has low to very very low low relative relative permeability—several permeability-several orders coarser-grained sandstone coarser-grained sandstone of the quartzose quartzose component component described described below. Vertical Vertical conductivity conductivity based on on pumping pumpingtests testscommonly commonlyranges ranges from i0 to i0 ft/day for interbedded from 1 0 to 10'~ft/day for interbedded very very fine sandstone and sandstone and shale shale (Miller (Millerand and Delin, Delin, 1993), 1993),to to as low as iO7 10'~ft/day ft/day for units composed composed almost almost entirely entirely of shale shale (Freeze (Freeze and and Cherry, 1979). In In the the former, former, horizontal horizontal permeability permeability is is typically typically more than 100 100times times greater greater than than vertical vertical permeability permeability (Miller, (Miller, 1984; 1984;Setterholm Setterholm and and others, others, 1991; 1993). 199 1;Miller and Delin, 1993). coarse-clastic component The coarse-clastic componentis is aa mostly uncemented, uncemented, moderately moderately to to well-sorted, well-sorted,finefine-to to coarse-grained sandstone composed of about 98 percent quartz. Plug-sample Plug-sampletests tests indicate indicate itit has aa high high to tovery veryhigh highpermeability permeability and andporosity porosity due due to torelatively relatively large, large, well-connected well-connected intergranular intergranular pore spaces. spaces. Pump Pumptests testsof ofwells wellsopen openmostly mostlyto tothis thiscomponent componenttypically typicallyrange range from from about about 2-20 2 -20ft/day, ft/day, indicating indicatingaamoderate moderateto to high high conductivity, conductivity, corroborating corroborating the results results of the plug tests 1 996a). tests (Miller, (Miller, 1984; 1984;Setterholm Setterholmand and others, others, 1991; 1991;Miller Miller and and Delin, Delin,1993; 1993;Runkel Runkel1996a). The carbonate-rock component consists of limestone or dolostone with minor shale and sandstone. Porosity features, and karst features. sandstone. Porosityand andpermeability permeabilityisisdue dueto to fractures fracturesand solution features, The permeability permeability varies varies substantially substantiallyfrom from place place to to place place depending dependingon on the the size, size, extent, extent, degree degree and interconnectivity interconnectivityof of fractures fracturesand andsolution solutionfeatures features(Libra (Libraand andHallberg, Hallberg,1985; 1985;Visocky Visockyand and others, 1985). Pumping Pumping tests tests indicate indicate that that this this component component in most places is moderately moderately to highly permeable permeable where where such such features features are are well developed—typically developed-typically ranging from 1-40 1-40 ft/day Woodward, 1985). 1985). However, (Delin and Woodward, However, in places where fractures and solution features are minimally developed, developed, such such as as where where deeply deeply buried by younger bedrock, the component component has has aa very low conductivity, even at a large scale (Libra and Hallberg, 1985; Visocky and others, large scale (Libra and Hallberg, 1985; Visocky and others, 1985). 1985). The mixed carbonate and clastic component is composed of interbedded siltstone, very sandstone, sandy dolostone, dolostone, and shale (Setterholm (Setterholm and others, 1991; fine to very coarse grained sandstone, 1991; Cementationisisvariable; variable; beds beds of of mediummedium- to to coarse-grained coarse-grained sandstone sandstone are are Runkel, 1996b). Cementation typically friable, but very fine to fine-grained sandstone and siltstone are commonly strongly permeability from from bed bed to tobed. bed. Coarsecemented. As As aa heterolithic heterolithic unit, unit, it varies markedly in permeability grained grained sandstone sandstone beds beds that that are are too too weakly weakly cemented cemented to to provide provide coherent coherent samples samplesare are likely likelyto to be highly permeable. Laboratory Laboratorytests testsof ofthe themore morestrongly stronglycemented, cemented,finer-grained, finer-grained, clastic clastic 110 �0 Group, Formation. Member - ,.-% 5 - Natural Gamma Log D Lithology Increasingcount LIMESTONE LIMESTONE 100 API-G units DOLOSTONE DOLOSTONE SANDY SANDY SANDSTONE SANDSTONE TO FINE VERY FINE FINETO FINE Prosser Limestone FINE TO MEDIUM FI NE TO MEDIUM M EDIUMTO COARSE MEDIUM SHALY Cummingsville Formation SILTSTONE SILTSTONE SHALE Vugs Vugs (commonly (commonlytilled filledwith with coarse coarse calcite) calcite) Decorah Shale Chert Chert K-bentonile K-bentonitebed bed(altered (altered volcanic volcanic ash ash bed bed Oolites Oolites Glaucorrite Glauconite Iron Ironstain stain Goethite-hematite ore Goethite-hematite St. Peter Sandstone Phosphate pellets Phosphate pellets AaI mats Abal mats atromatolites Algal domes; stromatolltes Fossiliferous; fossils (symbols Fossiliferous; (symbolsnot not limestone and dotostone dolostone used in limestone units) units) bored Worm bored Pebbles (gravel Pebbles (gravelIn in unconsolidated units) unconsolidated Shakopee Formation Flat-pebble conglomerate Flat-pebble Cross-bedded Cross-bedded(testoon) (festoon) Cross-bedded (planar to tangential) - Ripple cross-laiThnatlons "TT^- Ripple cross-laminations ^S- 7 J- -r 7 J. J. Dolomitic Dolomitic Calcereous Calcareous Contact Contact marks marks aa major majorerosional erosional surface surface ,,'\ .f': .-"ÂFades Fadeschange change Low permeability permeability and porosity; Low hodzontal horizontal bar shortened shortened where lateral lateralextent extent is is limited limited high permeability Moderate to high permeability end porosity porosity and Oneota Dolomite l a Outcrop Intervals. intervals. Number Number refers refersto stop number number In the the field field guide guide in Coon valley Member column showing showing units units from from the the Prosser Prosser Limestone Limestone of of the Figure Figure 4. 4. Bedrock stratigraphic column Upper Ordovician Ordovician Galena Galena Group Group to the Upper Upper Upper Cambrian CambrianEau EauClaire ClaireFormation. Formation. Column Colunm includes hydrostratigraphic hydrostratigraphicunits units based based on on estimated estimated permeability permeability and and porosity. porosity. 111 �Group, Formation, Member - Natural Gamma Log Increasingcount - O 100 API-G units Coon Valle) Member Jordan Sandstone St. Lawrence Formation Birkmose Member Ironton and Galesville Sandstones Eau Claire Formation Figure 4. Continued Continuedfrom fromprevious previous page. beds, indicate aa low beds, low permeability permeability (Setterholm and and others, others, 1991). 1991). These These latter beds beds make make up up the the bulk latter bulk of this heterolithic meager heterolithic component, and meager pumping data data indicates a horizontal pumping horizontal conductivity conductivity of of about one-fifth that of the coarse coarse clastic clastic facies facies (Runkel, (Runkel, 1996a). 1996a). Lateral and vertical variability variability in abundance and interconnectivity of abundance and fractures can markedly markedly affect affect the the hydrologic behavior of each of the four components described above. above. Such features features are most abundant abundant and best best interconnected where the bedrock is at or near (within (within 100 100 feet) feet) the the surface. surface. Siliciclastic components componentssuch such as as the fine Siliciclastic which has low to clastic component, component, which very low intergranular intergranular permeability, may be orders orders of of magnitude magnitude higher higher in in conductivity where they they lie near the conductivity where the surface because because there there is a substantial surface substantial amount of flow along fractures. amount of flow along fractures. Conversely, some carbonate units may may have a relatively relatively low low conductivity conductivity and and act as confining confining beds where they they are are covered by younger covered by younger bedrock bedrock and and secondary porosity is not well developed secondary porosity is developed (Libra (Libra and Hallberg, Hallberg, 1985; 1985;Visocky and others, 1985). 1985). Additionally, Additionally, fracture flow may be be dominant even in the flow may dominant even coarse-clastic component, which which has a high intergranular intergranular permeability permeability where it lies near the surface. surface. aquifers and Delineation of aquifers and confining confining beds Given the hydrostratigraphic hydrostratigraphiccharacter character of the components components described described above, above, the Paleozoic Paleozoic section can be divided and low low permeability permeabilityunits units(Fig. (Fig.4). 4). The The coarse coarse divided into moderate/high moderatehigh and clastic that contribute contribute most most clastic and carbonate carbonate rock rock component component (where (where karstic) karstic) are likely the sources that of the yield yield to to water water wells wells developed developed in in Paleozoic Paleozoic strata. The Thefine-clastic fine-clasticcomponent component can can potentially yield particular where it is fractured near the surface, potentially yield moderate moderatequantities quantitiesof of water, water, in particular but more importantly itit acts acts as as aa confining confiningunit unit separating separatingcoarse-clastic coarse-clastic and and karstic karstic aquifers aquifers (e.g., Wenck and Associates, Associates, Inc., 1997). The component contains The mixed carbonate carbonate and clastic component contains individual beds that can yield moderate quantities of water, but where greater than 10 feet individual beds that can yield moderate quantities of water, but where greater than 10 feetthick, thick, this unit apparently apparently also (Setterhoim and and others, others, 1991). Unfractured Unfractured carbonate also acts as an aquitard (Setterholm carbonate rock can also Visockyand andothers, others, 1985; 1985;Donahue Donahueand andAssociates, also serve serve as a confining bed (e.g., Visocky Associates, 1991; Barr Engineering, Engineering, 1996). 199 1;Ban1996). 112 �Of particular particular importance this more more rigorous rigorous hydrogeologic hydrogeologic approach importanceto to this this field field trip is that this approach indicates that that two two widely widely used used aquifers, aquifers,the the Prairie Prairie du du Chien-Jordan Chien-JordanAquifer Aquifer and and the the FranconiaFranconiaindicates Ironton-GalesvilleAquifer, Aquifer, are are not single, hydraulically connected aquifer systems as commonly Ironton-Galesville commonly believed believed (e.g., (e.g., Kanivetsky Kanivetsky and and Walton, 1979). Pumping Pumping tests (Miller, (Miller, 1984; 1984;Delta Environmental Consultants, Inc., Inc., 1992; 1992;Miller Miller and and Delin, Delin, 1993) 1993)and and carefully carefullycollected collectedlocal localstatic staticwater waterlevel level Consultants, measurements measurements(Delta (DeltaEnvironmental EnvironmentalConsultants, Consultants,Inc., Inc.,1992; 1992;Wenck Wenckand andAssociates, Associates,Inc., Inc.,1997) 1997) demonstrate that that the the fine fineclastics clasticsof ofthe theFranconia FranconiaFormation Formationhydraulically hydraulicallyseparate separate clearly demonstrate ground ground water water in in the the fractured, fractured, upper upper part part of of the the Franconia Franconia Formation Formation from from ground ground water water in in coarse below. Some fractured, fractured, carbonate-cemented carbonate-cemented coarseclastics clastics of the Ironton-Galesville Sandstones below. rock rock in in the the lower lower part part of of the the Franconia, Franconia, where it occurs at or near the surface, is the source of many many springs springs in in the the area area and andisisperhaps perhapsthe theonly onlyhighly highlypermeable permeableconduit conduitfor forgroundwater groundwater within the the Franconia Franconia Formation. Formation. The ThePrairie Prairiedu duChien-Jordan Chien-JordanAquifer Aquiferisis likewise likewisetwo two distinct distinct within and coarse clastic clastic aquifer-separated aquifer—separated and separate separateaquifers—an aquifers-an upper upper carbonate carbonateaquifer aquiferand and a lower, coarse by clastic component. component. Hydraulic by an an intervening intervening aquitard aquitard composed composed of the mixed carbonate and clastic Hydraulic separation separationof of the the carbonate carbonateand and coarse-clastic coarse-clasticaquifers aquifersisis indicated indicatedby by several severallines lines of hydrologic hydrologic evidence including: Donahue and andAssociates, Associates,1991; 1991; including: potentiometric potentiometric data data (Kanivetsky, (Kanivetsky, 1988; 1988; Donahue N.O. pumping tests (Barr N.O. Janick Janick ,,Winona Winona State University, University, oral communication communication 1994), pumping (Barr Engineering, Engineering, 1996; 1996;N.O. N.O. Janick, Janick,Winona Winona State StateUniversity, University, oral oral communication, communication,1994), 1994),and andby by ground-water ground-waterchemistry chemistry(Alexander, (Alexander,1990; 1990;Setterholm Setterholmand andothers, others,1991, 1991,Wall Wall and and Regan, Regan, 1994). 1994). FIELD FIELDTRIP TRIPSTOPS STOPS Introduction Introduction As enigmatic features As we we examine examinethese these rock rock exposures, exposures,think think about about the enigmatic features and and long-standing long-standing sedimentologic sedimentologic problems associated with these units. For For example, example,what what created created the the extreme extreme maturity of the fine to coarse-grained sandstones? sandstones? Is there really a dearth dearth of of shale? shale? Why is it difficult to place your hand on an unconformity in these rocks? In addition, difficult unconformity in these rocks? In addition, think think about about the water-bearing water-bearing characteristics that are are determined determined by grain grain size, size, cementation, cementation, fractures, fractures, and and dissolution dissolutionfeatures. features.With Withthis thisininmind, mind,judge judgefor foryourself yourselfthe thevalidity validityof of some someof of the the commonly commonly accepted accepted depictions depictions of of the the hydrogeologic hydrogeologiccharacteristics characteristics of the Paleozoic Paleozoic rocks. For Forexample, example, does doesthe thePlatteville PlattevilleFormation Formationlook looklike likeaaconfining confiningunit unit that that will will impede impedethe the downward downwardtransport transport of of contaminants, contaminants,as asititisis commonly commonlyshown shownto to be on maps? maps? Compare Comparethe theFranconia FranconiaFormation Formationtoto the try to to determine determine why the former is most often often regarded as an an the Eau Eau Claire Claire Formation, Formation, and and try aquifer aquifer and and the the latter latteras asaaconfining confiningbed. bed. Examine Examinethe thedramatic dramaticvariability variabilityininthe theporosity porosityand and permeability ChienGroup Group and and Jordan Jordan Sandstone Sandstone and ask yourself whether permeabilitywithin withinthe thePrairie Prairiedu du Chien the the commonly commonly accepted accepted hydrogeologic hydrogeologic depiction depiction of of these these units units as asinternally internallyhomogenous, homogenous, hydraulically connected aquifers is accurate. hydraulically connected aquifers is accurate. The 8, 10, Thelocation locationof of individual individualstops stops is is shown shown on Figures 5, 7, 7,8, 10,and and 11. 11. Directions Directionsfrom from major major road road intersections, intersections,or orstreet streetaddresses, addresses,are arealso alsoprovided providedfor foreach eachstop. stop. STOP STOP1—Rochester I-Rochester Public PublicUtilities, Utilities,4000 4000E.E.River RiverRoad RoadNE, NE,Rochester, Rochester, Minnesota. Minnesota. An An overview overview of of the thedepositional depositionalhistory history and andhydrogeologic hydrogeologicattributes attributes of of the thePaleozoic Paleozoic strata strataof of southeastern southeasternMinnesota Minnesotawill willbe bepresented presentedatatthis this stop. stop. Paleozoic Paleozoicbedrock bedrockininthe theRochester Rochester area areaare arenearly nearly flat flat lying, lying, and and have have been eroded into an upper and lower plateau. The The resistant resistant limestone and dolomite formations of the Galena Group form an upper plateau that skirts limestone and dolomite formations of the Galena Group form an upper plateau that skirtsthe the 113 �8, 10, Figure 5. 5. Index Index map map of of field field stops. Black Blackboxes boxes refer refer to to maps maps in in Figures Figures 7, 7,8, 10,and and 11. 11. Figure perimeter perimeter of of Rochester. Rochester. The Themostly mostlycarbonate carbonaterocks rocksof of the the Prairie Prairie du du Chien Chien Group Group form form a lower plateau along the South Fork of the Zumbro River and the lower ends of its tributaries, in and along the South Fork of the Zumbro around around the the city city of Rochester. These Thesetwo twoplateaus plateausare areseparated separatedby by an an escarpment, escarpment, composed composed of of Decorah Sandstone, which exposed DecorahShale, Shale,Platteville PlattevilleFormation, Formation,Glenwood GlenwoodShale, Shale,and and St. St. Peter Peter Sandstone, which is exposed on steep city. We will examine most steep bluffs within and around the city. most of of these these units units on on the the trip trip today, as well as as several several older older units, units, such such as as the Jordan Sandstone. Sandstone. The hydrostratigraphic attributes of of many many of the Paleozoic units that we will will examine examine today have have aa direct direct or orindirect indirectimpact impacton onthe theavailable availablewater watersupply supplyfor forthe thecity cityof ofRochester. Rochester. The understanding the The city city has has devoted devoted aa considerable considerable amount amount of of effort effort and resources to understanding the geologic geologic controls controlson on ground-water ground-waterquality qualityand andquantity quantityin in their their region. region. An Aninvestigation investigationof of variable variableyield yield from Dolomite from city city wells wells that that draw draw water water from from the Jordan Sandstone Sandstone and and lower part of the Oneota Dolomite (Runkel, 1996a) 1996a) provides provides an an example example of of where where lithostratigraphic lithostratigraphic and and hydrostratigraphic hydrostratigraphic boundaries do not coincide. coincide. The Theopen-hole open-holeinterval interval of of these these city city wells wells cross cross three three or or more more distinct hydrostratigraphic hydrostratigraphic components—the components-the fine-clastic, fine-clastic, coarse-clastic, coarse-clastic, and mixed carbonate carbonate 114 �and clastic components (Fig. 6). Permeability Permeability values values of of these these components components vary by as much as four orders of magnitude. magnitude. Grain permeability Grainsize, size,sorting sortingand and degree degree of cementation cementation affect affect the permeability of these rocks, all within boundaries of what is currently designated as a single aquifer unit— unitthe Prairie du Chien-Jordan Aquifer. Pumping records of municipal wells finished in these Chien-Jordan Aquifer. Pumping municipal components, all three components, all considered considered "Jordan" wells, wells, show show that the productivity productivity of individual individual wells wells is directly proportional to the thickness of the coarse-clastic component exposed in the openhole interval (Runkel, (Runkel, 1996a). 1996a). This stop Formation in the the large large quarry quarry west west of of stop shows shows the sandy dolomite of the Shakopee Formation the road. Notable Notablefeatures featuresinclude includethe thethin thincover coverof of the the bedrock bedrock and and the the highly highly fractured fractured nature nature rock hydrostratigraphic hydrostratigraphic component. component. The high density density of of fractures fractures isis typical of of the carbonate rock all bedrock units near the land surface surface in this region. region. Also visible visible to the southeast southeast is the quartzose quartzose facies of the St. Peter Sandstone Sandstone and the overlying Glenwood Shale and Platteville Limestone. recharge to to the the Prairie Prairie du du Chien Group and Jordan Delin (1991) showed that ground-water ground-water recharge Sandstone is focused along along the the edge edge of of the the plateau plateau above abovethe the St. St. Peter Peter Sandstone. Sandstone. Ongoing investigations into into the the phenomena phenomena of of focused focused recharge recharge by by the the USGS USGS based based on earlier work investigations (Delin, 1991; 1991; Delin and Almendinger, 1991) 1991) will provide better data on the hydrologic budget of the region by quantifying quantifying the amount amount of water recharging recharging from from upper plateau. plateau. STOP 2—Bailey Quarry near STOP %Bailey Quarry nearSt. St.Charles, Charles,Minnesota. Minnesota.West Westside sideof ofMinnesota Minnesota Highway 74, about 1.2 1.2 miles south south of Interstate Interstate 90. Winona County, Minnesota (Fig. 7). This quarry has one one of of the the most most accessible, accessible, continuous continuous exposures across the upper upper St. St. Peter Sandstone, Glenwood Shale, and Platteville Formation in Minnesota. Our work on this part of the Paleozoic reconnaissance nature at this time. Most Paleozoic section section is of a reconnaissance Most workers workerswho whohave have studied these units have suggested suggested that they are part of an overall transgressive sequence (e.g., Dott and others 1986; Mossler, 1985). A 1986; Mossier, 1985). A rise rise in in sea sea level level is is recorded recorded by the the facies facies change change upsection from fine- to coarse-grained coarse-grained quartzose sandstone deposited in a shoreface (St. Peter deposited in deeper offshore shelf areas (Glenwood (Glenwood Shale), culminating culminating in rnicritic micritic SS.), to shale deposited carbonates offshoreconditions conditions (Platteville (PlattevilleFormation). Formation). While While carbonatesthat that accumulated accumulated in the most distal offshore this scenario scenario is plausible, plausible, some some features features suggest that the depositional depositional history may be more more complex. For example the upper half to two-thirds of the St. Peter Sandstone coarsens upward For example the upper half to two-thirds of the St. Peter Sandstone coarsens upward in southeastern wh,ich in in other other sheet sheet sandstones sandstones is is indicative indicative of shallowing shallowing rather rather southeastern Minnesota, Minnesota, wh,ich than deepening. Workers Workersin inother otherstates states(e.g., (e.g., Simo Simoand and others, others,1997) 1997)have have suggested suggestedthat that the the St. Peter Sandstone Sandstone is capped by an unconformity, which also suggests that its deposition was culminated by a regressive event. Additionally, Additionally, the Glenwood Glenwood Shale contains discrete beds of medium- to coarse-grained sandstone, some with with a channel-shape, channel-shape, and and the the lower lower part part of the Platteville Formation Formation contains contains matrix-supported, matrix-supported,coarse coarsequartz quartzgrains. grains. These attributes are incompatible incompatible with with deposition depositionin in aa relatively relatively deep, deep, distal distal offshore offshore shelf shelf setting. setting. here. The There are three hydrostratigraphic hydrostratigraphic components exposed here. The Platteville Platteville Formation Formation consists fractured carbonate carbonate rock component, the Glenwood Glenwood Shale Shale consists consists mostly mostly consists chiefly chiefly of the fractured of the fine clastic clastic component, component, and Sandstone consists coarse clastic and the the St. St. Peter Sandstone consists of the coarse clastic component. component. Hence, across this part of of the the Paleozoic Paleozoic section section lithostratigraphic lithostratigraphic boundaries nearly (within a meter) coincide with the principle hydrostratigraphic boundaries. We We will see examples at principle hydrostratigraphic boundaries. subsequent stops where the lithostratigraphic lithostratigraphic boundaries do not correspond to the principal principal hydrostratigraphic hydrostratigraphic boundaries. boundaries. 115 �____ ____ _____ NORTH /—/ f • - - . . . ___ .. . . . . - S . a — . ••' * _z___7__. . . . .-r in - . ,— . ci - •—---— • s . . . coarse clastic . ._.— . .—- •'. ._._—e—t'-—-':; . .. s. — — ———— — • / . . . . . • coarse clastic . . - . mixed carbonate and clastic.,- ' ' ——-k SOUTI+ . ., __ - coarse clastic ——— .--fineclastj,. - — — . St. Lawrence Formation St. Lawrence Formation L Lines on section dashed where control is poor 434041 161425 mcc rncct 220166 1 mcc mcc cc Ic fc I I Ic xl 2C64 21ca11 222525 2226S - - mcc cc cc E)QLANATION mcc mixed mixedciastic clasticand andcarbonate carbonatecomponent component Ic mixed clastic ciastic and and carbonate carbonatecomponent component fc cc cc mixed clastic clastic and and carbonate carbonate component component mcc SI St. Lawrence Formation sl St. Lawrence Formation - - Ic fC — cc cc Ic fc Ic cc Ic SI Figure 6. West-east West-eaststratigraphic stratigraphiccross-section cross-sectionand andcorresponding correspondinggamma gammalogs logsfor forthe theJordan JordanSandstone Sandstoneand andthe thelower lowerpart partof ofthe theOneota Oneota Figure Dolomite in the Rochester Metropolitan area, showing the variable thickness of the coarse-clastic and fine-clastic fine-clastic components of the Jordan beneath the mixed carbonate and clastic Coon Valley Valley Member Member of of the the Oneota. Oneota. (Modified from from Runkel, Runkel, 1996a.) 1996a.) �Figure 7. Map Map11on onindex indexmap map(Fig. (Fig. 5) 5) showing showing the the location location of of stop stop 2. 2. quarry is a good example example of the geologic geologic controls on ground-water ground-water recharge recharge discussed This quarry discussed carbonate Platteville Formation is through through horizontal at Stop 1. Ground-water Ground-waterflow flow through through the carbonate vertical joints. joints. Matrix fractures along bedding planes and vertical Matrix porosity and permeability does not contribute substantially Platteville bench contribute substantiallyto to ground-water ground-water flow. flow. Water Water pools pools on on top of the lower Platteville because the underlying underlying Glenwood Glenwood Shale Shale restricts restricts the downward downward movement of ground ground water. water. conductivity of of the the Glenwood Shale Shale is is estimated estimated to to be be similar to values for shale Hydraulic conductivity reported in in the the literature literatureof of iO to toiO rn/day &day(Freeze (Freezeand andCherry, Cherry,1979). 1979). The Thesurface surfacewater water Platteville bench bench and and onto onto the the top top of of the Glenwood Shale entering the quarry runs across the Platteville before spilling quarry. This stream does not account for all the spilling into the St. Peter section of the quarry. recharging the St. Sandstone. Joints water recharging St. Peter Sandstone. Jointsare arevisible visiblein in the the Platteville Plattevillethat that extend extend into into the the Glenwood Shale. The ThePlatteville PlattevilleFormation Formation and and Glenwood Glenwood Shale form aa flat flat plateau plateau across across much of the Twin Cities area. The Glenwood Shale is an important confining bed in Twin area. The Glenwood an important bed that it restricts contaminant contaminant transport transport to to lower lower bedrock aquifers aquifers where where it is is not not crossed crossed by by fractures. fractures. STOP 3—Road >Road Cut Cut near nearHomer HomerMinnesota. Minnesota.From Fromintersection intersectionofofState StateHighway Highway 43 43 and and U.S. 61 61 inWinona, in Winona,take takeState StateHighway Highway 61 61 south south for 3.5 miles. Turn right on County Road 15 (at Homer) and travel 2.2 miles to large large road cut (Fig. (Fig. 8). 8). This exposures of the Jordan Sandstone This is one one of the most complete, complete, readily accessible accessible exposures Sandstone in the entire central mid-continent region. The mid-continent region. The section section is is continuously continuously exposed from the upper part of the St. Lawrence Lawrence Formation, Formation, through the entire Jordan Sandstone, Sandstone, and most of the the Oneota Dolomite. cycleisisrecorded. recorded. The very fine grained complete regressive-transgressive regressive-transgressive cycle grained Dolomite. AA complete sandstone, shale and dolostone dolostone of the St. Lawrence Lawrence Formation Formation was deposited deposited in relatively relatively deep deep water during a high high stand stand of of sea sealevel level (Hughes (Hughes and and Hesslbo, Hesslbo, 1997), 19971,which which was was followed followed by by 117 �KILoMmERs MILES 1 -1 - 0 - 1 0 - 2 I 3 4 2 5 3 6 1 4 7 8 5 9 $0 6 Map22on onindex indexmap map(Figure (Figure5) 5) showing showing the the location location of of Stop Stop3. 3. Figure 8. Map progressive shallowing recorded in the coarsening coarsening upward Jordan Sandstone, culminated by subaerial erosion marked by aa pebbly pebbly sandstone sandstone lag. lag. The Oneota Oneota Dolomite Dolomite above above the the unconformity unconformityrecords recordsthe thereturn returnof ofthe theshoreline shorelineand andgradual gradualdeepening deepeningin inthe theEarly EarlyOrdovician. Ordovician. Lowermost Oneota strata (Coon Valley Member) are mixed clastic carbonate deposits that Oneota strata (Coon Valley accumulated in supratidal to shallow subtidal conditions. conditions. Upper Upper Oneota Oneota strata strata (Hagar (Hagar City City Member) dolostonedeposited depositedin in deeper, deeper, entirely entirely subtidal subtidal conditions. conditions. Member) are are mostly mostly sand-free sand-freedolostone Particularly include large-scale, large-scale, high-angle high-angle Particularly interesting interestingsedimentologic sedimentologicfeatures features at this stop include cross cross strata stratawith with reactivation reactivationsurfaces surfacesand and shale shaledrapes drapesin in the the Jordan Jordan Sandstone Sandstonethat that may may record record a strong influence of tidal currents, and bbcabbage-head" "cabbage-head" stromatolites stromatolites in the lower Oneota. Oneota. The The depositional can account account for for the the sedimentologic sedimentologic and stratigraphic stratigraphic depositional model depicted depicted in in Figure Figure 33 can attributes of the St. Lawrence Formation and Jordan Sandstone, but does not readily explain the attributes Lawrence Formation and Jordan Sandstone, attributes attributes of the overlying overlying Oneota Oneota Dolomite Dolomite This exposure example,whereaa major major hydrostratigraphic hydrostratigraphicboundary boundary does does not not exposure includes includes an an example.where correspond hydrostratigraphic variability correspondto to aa lithostratigraphic lithostratigraphicboundary, boundq, and and also also shows shows the great hydrostratigraphic variability within internally homogenous homogenous in in hydrogeologic hydrogeologic within lithostratigraphic lithostratigraphicunits units that that are are widely regarded as internally properties. properties. The TheSt. St.Lawrence Lawrence Formation Formation and and lower lower part of the the Jordan Jordan Sandstone Sandstone are both composed confining composedof of the the fine-clastic fine-clastic component. component. The TheSt. St.Lawrence Lawrence is is commonly commonly regarded regarded as as a confining bed and the the Jordan Jordan as as an an aquifer, aquifer, yet yet there there is is no no distinct distinct hydrogeologic hydrogeologic boundary between the two lithostratigraphic units as is commonly believed. believed. As As you you walk walk up up the the outcrop, outcrop, consider consider where where you would would define define the the bottom bottom and and the the top top of the "Jordan Aquifer." Aquifer.'' The The mixed mixed carbonate carbonate and and clastic clastic component componentthat that composes composesthe the Coon Coon Valley Member of the Oneota Dolomite (Prairie (Prairie du du Chien Chien Group) Group) isis markedly markedly lower lower in in porosity porosity and and permeability permeability than than the the coarse coarseclastics clasticsof ofthe the uppermost Jordan Sandstone. The Theoverlying overlying carbonate carbonate rock rock component component of of the the Hagar Hagar City City Member fractures. Fracture Member is tightly cemented, cemented, with primarily horizontal fractures. Fracture tops show evidence 118 �of dissolution. Larger scale scale vertical vertical dissolution along dissolution. Larger along aa vertical verticaljoint joint isis also also visible visible here. here. If such fractures and dissolution dissolution features features were not developed in the subsurface subsurface this unit would be be a confining bed. BIOSTRATIGRAPHY OF OF CONODONTS CONODONTS FROM FROM JORDAN JORDAN SANDSTONE SANDSTONEAND AND LOWERMOST ONEOTA LOWERMOST ONEOTA DOLOMITE DOLOMITENEAR NEAR HOMER, HOMER,MINNESOTA MINNESOTA J.F. Miller* and and Anthony C. C. Runkel Runkel *Southwest *Southwest Missouri Missouri State State University, University, Department Departmentof of Geography, Geography,Geology, Geology, and and Planning, 901 South South National National Avenue, Springfield, Missouri 65804-0089 The physical evidence for the presence presence of aa large large magnitude, magnitude, regional regional unconformity unconformity associated with the Jordan Sandstone has been been debated for decades. Smith Smith and and others others (1993) (1993) described subaerially formed silcrete that occurred at or or below below the the Jordan Jordan Sandstone-Oneota Sandstone-Oneota Dolomite contact at at a few outcrops Wisconsin. Runkel that a pebbly Dolomite contact outcrops in Wisconsin. Runkel (1994) suggested suggested that sandstone that caps the Jordan Jordan Sandstone Sandstone at many outcrops in Wisconsin and Minnesota is an erosional lag of regional extent. ItIt everywhere everywhere separates separates a major, decameter-scale coarsening decameter-scale fining upward upward sequence sequence above, above, and and was was formed formed upward sequence sequence below from a decameter-scale extreme basinward basinward positions positions in inlatest latestCambrian Cambriantime. time. The when the regressive shoreline was in extreme to be be more more deeply deeply truncated beneath this lag on the margins of of Jordan Sandstone was shown to the Hollandale Embayment Embayment (Runkel, (Runkel, 1994). 1994). The work described above suggests that that an unconformity unconformity is is present present near near or or at at the the top top of of evidence is subtle and and cannot cannot be be recognized recognized at at all all outcrops outcrops the Jordan Sandstone Sandstone but the physical evidence (Fig. 9). In unconformity and and determine determine its magnitude, magnitude, In an an effort effort to substantiate substantiate the presence of an unconformity Jordan Sandstone and from the conodont samples samples were were collected collected at the Homer section from the Jordan overlying Coon Valley Member of the Oneota Dolomite overlying Coon Dolomite by A. C. C. Runkel Runkel and were processed processed by J.F. Miller. Samples J.F. Samples from the Jordan Sandstone Sandstone contain contain only two conodont conodont species, species, Proconodontus muelleri muelleri (Miller) Proconodontus (Miller) and and Eoconodontus Eoconodontus notchpeakensis notchpeakensis (Miller), (Miller), which which range range America and and are are diagnostic diagnostic of of throughout the Jordan. These These species species are widespread in North America of the theEoconodontus Eoconodontus Zone, Zone, approximately approximately of middle middle the Eoconodontus notchpeakensis Subzone of Age. This from samples samples 1 through through 10. 10. Sample 11 Trempealeauan Age. This fauna fauna has been recovered from 11 is from the Coon Coon Valley Valley Member of the Oneota Oneota Dolomite Dolomite and and yielded yielded aa completely completely different different conodont fauna. This Thissample sampleincludes includesAcanthodus uncinatus uncinatus (Furnish), (Furnish),Aloxoconus Aloxoconus iowensis iowensis (Furnish), Aloxoconuspropinquus (Furnish), Cordylodus intermedius (Furnish), (Furnish), Aloxoconuspropinquus (Furnish), Aloxoconus sp., Cordylodus (Furnish), Cordylodus lindstromi lindstromi (Druce (Druce & & Jones), Jones), aa new species of Cordylodus known known from from Utah Utah and and Polycostatus oneotensis oneotensis (Furnish). Many Texas, and Polycostatus Many of of these these species species were named by Furnish (1938) (1938) from from the Oneota Oneota in the Iowa-Minnesota area. The The presence presence of of these these species species in in the the Coon Coon Valley Member indicates a close age relationship between sandstones of the Coon Valley and Valley overlying dolomite the assignment assignment of these these sandstones sandstones the overlying dolomite member of the Oneota, and supports the to the Oneota rather than to the Jordan. This This assemblage assemblage of species species is at least as young as the Cordylodus angulatus angulatus Zone Rossodus manitouensis manitouensis Zone. Cordylodus Zone but but could could be from from the the overlying overlying Rossodus These two zones are are from from the the middle middle to to upper upper part part of of the the Skullrockian Skullrockian Stage Stage of of the the Ibexian Ibexian Series (Lower (Lower Ordovician) Ordovician) in the Ibex Ibex area area of western Utah (Ross (Ross and and others, others, 1997). 1997). Sandstone and Coon Valley Valley Member Member are are separated separated These faunas indicate indicate that the Jordan Sandstone by a large hiatus hiatus compared compared with with the the continuous continuous succession successionin in the the Ibex Ibex area area of of Utah, Utah, which which was was 119 �ZONATION CONODONT CONODONT ZONATION MIller MIIler (1988) ( 1 988) one I oneI z e = conodonts conodonts LU <I-. 0 wO a z-J 0 Rossodusmanitouensis Ii z 0 I— (1, 0 z Cordylodus lindstromi . 20 15 I.—. 'Jb z 0 0 . . , .5 .4 '3 C,, 7 I,,,,, It 1 1 7 .1 & 7' T1 0• liii VF FMCVC pJg Burrows B Intraclasts gpJ l r l ~ l a s t s Hunmocky cross-strata @Dolostone O ~ o r l e Ripple cross-strata R i i cross-strala =EEzL Z hlntzei HirsutodontUS simplex ... Clavohamulus elongatus d1 -. )< LU Fryxellodontus inornatus Hirsutodontus 10 z< Clavohamulus hirsutus Cambroistodus minutus 5. • LU lapetog,wthus w C-) UJ Cordylodusangulatus 25 z Subzone Subzone 1t•D• 5 < I- EoconodontUS notchpeakensis — z= < < <x WQ ILl o '- Proconodontus mueller! Trou mTang8nMl o w cross-strata cross-stram Tangentlel cross-strata cross-stmm thick thick hnes h e s are are shale shale drapes drapes MedP.sn to ccoarse-graied M d b m to o a r s w n e dS.S. S.S. m .•: nFimt+gmmd S.S. Fine-gravied S.S. Pebbles Po- Figure9. 9.Measured Measuredsection sectionofofthe theJordan JordanSandstone Sandstoneand andadjacent adjacentunits unitsatatHomer, Homer, Minnesota Minnesota Figure outcropyhighlighting highlightingbiostratigraphic biostratigraphicinterpretation interpretationbased basedon onconodonts conodontsasasreported reportedherein. herein. outcrop, Thevertical verticallines linesshow showthe therelative relativemagnitude magnitudeof of the the hiatus hiatus represented The represented by the unconformity unconformity on top of the Jordan Sandstone. on top of the Jordan Sandstone. deposited rapidly subsiding subsidingmiogeoclinal miogeoclinal carbonate platform. The Thefollowing followingconodont conodont deposited on on aa rapidly units known known in in Utah Utahare aremissing missingbetween betweenthe theJordan Jordanand andCoon CoonValley ValleyatatHomer: Homer: biozonal units Cambrooistodus Cambrooistodus minutus Subzone Subzoneof ofthe theEoconodontus Eoconodontus Zone Zone(uppermost (uppermostTrempealeauan, Trempealeauan, Upper Cordylodusproavus Zone Zone(basal (basalSkullrockian, Skullrockian,Lower Lower Upper Cambrian), Cambrian),three three subzones subzonesof of the Cordylodusproavus Ordovician), Ordovician), two two subzones subzones of the Cordylodus intermedius Zone, Zone, the the Cordylodusprolindstromi Cordylodusprolindstromi Zone, Zone, the Cordylodus Cordylodus lindstromi lindstromi Zone, Zone,and andthe thelapetognathus IapetognathusZone Zone(approximately (approximatelymiddle middle Skulirockian). Skullrockian). InInthe theIbex Ibexarea areaofofUtah, UtahyUpper UpperCambrian Cambriancarbonate carbonatestrata strataare areapproximately approximately 2850 2850ftft (870 (870m) m)thick thickand andare areoverlain overlainby by approximately approximately5000 5000ftft(1525 (1525m) m)of ofOrdovician Ordovicianstrata. strata. The The missing missinginterval intervalat atHomer Homerisisequivalent equivalentto to more more than than 500 500 ftft (150 (150 m) m) of of limestone limestonein in Utah. Utah. The The interval intervalincludes includesseveral severalstratigraphic stratigraphicsequences sequencesthat that include include at at least least two two major major lowstands lowstands of A similar similarlarge large hiatus hiatus is is of sea sealevel, level, as as well well as as several several transgressive transgressive and highstand sequences. A known known on on the the crest crestof ofthe theTranscontinental Transcontinentalarch archin inwestern westernColorado Colorado(Myrow, (Myrow, Ethington, Ethington,& & Miller, Miller,1995), 19951,which whichisisaawestern western extension extensionof of the the Minnesota Minnesota craton. craton. 120 �STOP 4—Road &Road cut cut along alongnorth northside sideofofCounty CountyRoad Road3030(time (timepermitting). permitting).From From County County STOP road 14, 14,travel travel east east on on County County road road 88 for for one one mile mile (becomes (becomesCounty Countyroad road 30 30in inWinona Winona road Continueeast easton onCounty Countyroad road 30 30for for about about 0.7 0.7 miles miles to to road road cut cut (Fig. (Fig. 10). 10). County). Continue The upper upper part part of of Oneota OneotaDolomite Dolomiteand and lowermost lowermost Shakopee ShakopeeFormation Formationof of the the Prairie Prairiedu du The Chien Group are exposed at this stop. The TheOneota OneotaDolomite Dolomite consists consists chiefly chiefly of of tan tan to to gray gray microcrystalline dolostone dolostone in thick to medium irregular beds. The Shakopee Shakopee consists of sandy, microcrystalline beds. The The New Richmond Sandstone Sandstone oolitic and intraclastic dolostone, with intercalated sandstone. The of the Shakopee uppermost part part of of this this exposure. exposure. Deposition Shakopee Formation forms the uppermost Deposition of of these these strata occurred occurred on a carbonate-dominated, laterally extensive strata carbonate-dominated, laterally extensive platform in environments ranging from from supratidal supratidal to to shallow shallow subtidal subtidal (Smith and others, 1993). The The Oneota Oneota Dolomite Dolomite and and Shakopee Shakopee Formation are separated by an unconformity unconformity less meters below below the the New New Richmond Richmond less than than 22meters Sandstone. Features Featuresdiagnostic diagnosticof ofdepositional depositionalorigin, origin,as aswell wellas asthe theunconformity, unconformity, are arelargely largely Sandstone. Stop99will willprovide provide aa better better opportunity opportunity to to more more closely closely inaccessible in this steep road cut. Stop examine the Prairie Prairie du Chien Chien Group. Group. The primary primary purpose purpose of this this stop stop is is to to discuss discuss the the karst karst features features exposed exposed in in this this road roadcut. cut. A well developed developed cave in the Oneota exists at the solution solution horizon near the Oneota-Shakopee Oneota-Shakopee contact. The Theunconformable unconformablecontact contactshows showssubaerial subaerialexposure, exposure,as as evidenced evidenced by by considerable considerable karst development development below below it, and and is is characteristic characteristic of of this this contact contact throughout throughout southeastern southeastern Minnesota and and western western Wisconsin (Smith and others, 1993, 1996). Sinkholes Sinkholes occur occur near near this this contact Maki, 1988; 1988;Magdeline Magdeline and and Alexander, Alexander, contact (Dalgleish (Dalgleishand andAlexander, Alexander,1984; 1984;Alexander Alexander and and Maki, 1995) catastrophic collapse treatment lagoons 1995) and have resulted in catastrophic collapse of several several sewage treatment lagoons (Alexander (Alexander and and Book, Book, 1984; 1984;Alexander Alexander and and others, others, 1993; 1993;Jannik Jannik and and others, others, 1991). 1991). The SW. Evidence for the The cave cave at this outcrop apparently formed in aajoint joint trending trending NE to SW. development development of this solution feature is visible. Ground Groundwater water originally originally flowed flowed horizontally horizontally along along aa permeable permeable bedding beddingplain, plain,widening wideningitself itself through throughdissolution dissolutionas as itit became became the the dominant dominant hydraulic conduit at this horizon. At the intersection of a vertical joint, water moved downward, hydraulic conduit at this horizon. At the intersection of joint, downward, dissolving dissolving the the bedrock bedrock and and increasing increasing the size of the cavity. This This feature feature widened widened from from top top to to bottom, ground-water flow. Characteristic bottom, as as the the conduit conduit captured captured increasing increasing amounts amounts of ground-water Characteristicfeatures features include fracture—and sinuous include aa flat-topped flat-topped ceiling—top ceiling-top of of the original original hydraulic fracture-and sinuous walls formed by the water water dissolving dissolving beds beds of of variable variable permeability. permeability. A A large largecollapse collapse adjacent adjacent to to the thecave, cave, presumably into a void extending into the outcrop, and the alignment of this feature with void extending with aa creek dissolution creek bed on on south south side side of of the the highway, highway, indicate indicate the extensive extensive nature of this type of dissolution within within the the Prairie Prairie du du Chien. Chien. The regional regional direction direction of ground-water ground-water flow with the Prairie du Chien Group is is to to the the southeast—perpendicular southeast-perpendicular to to the the trend of this large dissolution feature. Monitoring Monitoringof of groundgroundwater quality quality within within the the Prairie Prairie du du Chien Chien is complicated complicated by these types of features throughout southeastern southeastern Minnesota. Dye-trace Dye-trace studies studies have have documented documented cases where local flow is in aa direction perpendicular to the regional gradient (Donohue 1991). The The presence presence direction perpendicular to the regional gradient (Donohue and Associates, 1991). of of these these large-scale large-scaledissolution dissolutionfeatures featuresleads leads to to extreme extreme variability in transmissivity, and preclude the isotropic porous media in ground-water ground-water monitoring the treatment treatmentof of the the Prairie Prairie du du Chien Chien Group Group as as isotropic monitoring and and modeling. modeling. 121 �KILOMETERS MILES 1 1 - -0 0 2 - 1 1 3 4 2 6 .-7 8 3 ' 4 8 5 0 10 6 Figure 10. 10. Map Map33on onindex indexmap map (Figure (Figure 5) 5) showing showingthe the locations locationsof of stops stops44 through through 8. 8. STOP overlook of of Mississippi Mississippi River River Valley Valleynear nearWabasha. Wabasha. On STOP 5—Scenic 5ÑSceni overlook On north side of State State Highway Highway 60 60 about about 1.3 1.3miles miles east east of of U.S. U.S. 61 61 (Fig. (Fig. 10). 10). This This overlook overlook provides provides aa visual visual estimate estimate of of the the thickness thickness of of the the lower lower Jordan Jordan Sandstone, Sandstone, St. that lie lie below below our our feet. feet. The St. Lawrence, and Franconia Formations that The upper upper 50 50 ftftof ofJordan Jordan Sandstone, Sandstone,and andlower lower20+ 20+ftftof ofOneota OneotaDolomite Dolomite(Coon (CoonValley Valley Member) Member)are areexposed exposedhere. here.This This outcrop provides an excellent opportunity to examine the sequence bounding unconformity provides an excellent opportunity to examine the sequence bounding unconformity that quartzose Jordan Jordan Sandstone Sandstone below from from the that separates separates well-sorted, well-sorted,finefine- to to coarse-grained, coarse-grained,quartzose overlying overlyingheterolithic heterolithicCoon CoonValley Valley Member. Member. The TheCoon CoonValley Valley Member Member consists consists of very finefine- to coarse-grained coarse-grainedsandstone, sandstone,siltstone, siltstone,shale, shale, and and sandy dolostone. dolostone. The The erosional erosional lag lag marking marking the the unconformity Minnesota (Stop (Stop 3) 3) but but here consists of an unconformity was poorly developed developed at Homer, Minnesota an 2 m thick—that contains intraclastic, poorly sorted, complexly cross-bedded sandstone—i - 2 thick-that contains cross-bedded sandstone-1 abundant abundant pebbles pebbles of of Precambrian Precambrianrocks rocksas aslarge largeas as22cm cminindiameter. diameter. 122 �Note the the considerable considerable difference difference in grain grain size size and and degree degree of of cementation cementation between between the the Note Jordan JordanSandstone Sandstoneand andthe theCoon CoonValley Valley Member. The Theformer formerisisdominated dominatedby bythe the coarse coarseclastic clastic hydrostratigraphic hydrostratigraphic component, the latter by the the mixed mixed carbonate carbonate and and clastic clastic component. component. Permeability of the the mixed mixed carbonate carbonate and clastic component component is as much as three three orders orders of of Permeability magnitude magnitude less less than than that that in in the the underlying underlying coarse clastics. In Inunfractured unfracturedsubsurface subsurfacesettings, settings, this this unit unit and and overlying overlyingunfractured unfractured carbonate carbonate rocks rocks of of the the Hagar Hagar City City Member Member of of the theOneota Oneota Dolomite Dolomite can can act actas asaaconfining confiningbeds, beds, hydraulically hydraulically isolating isolating ground ground water water in in the the Jordan Jordan from from ground groundwater waterininthe theupper upperPrairie Prairiedu duChien. Chien.This Thisseparation separationcan canbe beseen seenininchemical chemical(Alexander, (Alexander, 1990; Setterholm and others, 1991; Smith and Nemitz, 1996; Wall and Regan, 1990; Setterholm and others, 1991; Smith and Nemitz, 1996; Wall and Regan, 1995) 1995) and and hydraulic hydraulicdata data(Barr (Ban-Engineering, Engineering,1996). 1996). STOP STOP6—Lower &Lower Franconia FranconiaFormation Formationnear nearWabasha, Wabasha,Minnesota. Minnesota.Outcrop Outcropisisalong alongwest west side sideof of U.S. U.S. Highway Highway61, 61,1.2 1.2miles milesnorth northof ofState StateHighway Highway60 60(Fig. (Fig.10). 10). The Thelower lowerFranconia FranconiaFormation Formationatat this thisstop stopisisan anexcellent excellentexample exampleof ofthe theheterolithic, heterolithic, very very fine finegrained grainedsandstone sandstoneand andshale shalefacies faciescharacteristic characteristicof of Cambrian Cambrian storm storm and and fairweather fairweather deposits that accumulated on the offshore shelf seaward of the quartzose shoreface sands. deposits that accumulated on the offshore shelf seaward of the quartzose shoreface sands. Thin Thin to tomedium mediumbeds bedsof offeldspathic, feldspathic,variably variablyglauconitic glauconiticsandstone, sandstone,siltstone, siltstone,and andshale shalecommonly commonly occur occurin innormally normallygraded gradedsequences sequencesas asmuch muchas as30 30cm cm thick. thick. Sandstone Sandstonebeds bedspinch pinchand andswell swellasas form form sets setsofofsmall-scale small-scalehummocky hummockycross-stratification, cross-stratification, which which in in aacomplete complete depositional depositional sequence, sequence,pass passtransitionally transitionallyupward upwardinto intoripple ripplecross-stratified cross-stratifiedor orstructureless, structureless,very veryfine finegrained grained sandstone sandstone and andsiltstone, siltstone,which which in in turn turn passes passes upward upward to to shale. shale. Bioturbation Bioturbationisiscommon, common,and and ranges rangesfrom fromisolated isolatedburrows burrows(Planolites (Planolitesand andSkolithos) Skolithos)totonearly nearlyhomogenized homogenizedsediment. sediment. The Thefine-clastic fine-clasticcomponent componentofofthe thelower lowerFranconia FranconiaFormation Formationisishydrostratigraphically hydrostratigraphically similar similarto tothe thesame samecomponent componentthat thatmakes makesup upthe thebulk bulk of of the theSt. St.Lawrence LawrenceFormation Formationseen seenatat Stop Stop3.3.The TheSt. St.Lawrence Lawrenceisiswidely widelyregarded regardedasasaaconfining confiningbed, bed,yet yetthe theFranconia Franconiaisiscommonly commonly designated designatedasasan anaquifer aquiferalong alongwith withthe theunderlying underlyingcoarse coarseclastics clasticsofofthe thefronton Irontonand andGalesville Galesville Sandstones. Sandstones.We Webelieve believethat thatthis thischaracterization characterizationof of the the Franconia Franconia is inaccurate. This Thispart partof of the onia has theFranc Franconia has permeability permeabilityvalues valuesseveral severalorders ordersof of magnitude magnitudelower lowerthan than underlying underlyingcoarse coarse sandstones sandstones(Miller (Millerand and Delin, Delin, 1993). 1993).Core Coresamples samplestaken takenfrom fromoutcrop outcrophad had permeabilites permeabilites of of 0.01 0.006md. md.(MGS (MGSunpublished unpublisheddata, data,1997). 1997).InInaddition, addition,wells wellsfinished finishedabove aboveand andbelow below 0.01--0.006 this thispart partofofthe theFranconia Franconiahave haveover overaa40-foot 40-footdifference differenceininhydraulic hydraulichead head(Wenck (Wenckand andAssoc., Assoc., 1997). 1997). STOP STOP7—Road 7-Road cut cuton onU.S. U.S.Highway Highway61 61near nearWabasha. Wabasha.From FromState StateHighway Highway60, 60,take takeState State Highway Highway61 61south south1.8 1.8miles milestotoroad roadcut cuton onwest westside sideofofroad road(Fig. (Fig.10). 10). The metersofoffronton IrontonSandstone Sandstoneand andabout about44meters metersof ofthe theoverlying overlyingFranconia Franconia Theuppermost uppermost55meters Formation are exposed here in a steep road cut. The fronton consists of poorly sorted sandstone Formation are exposed here in a steep road cut. The Ironton consists of poorly sorted sandstone that thathas hasaapervasive pervasivebioturbated bioturbatedtexture, texture,with withburrows burrowsasasmuch muchasasa acentimeter centimeterinindiameter. diameter. Shale Shaleand andsiltstone siltstoneoccur occuras asaamatrix matrixbetween between sand sandgrains grains and and as as lenticles. lenticles. Moderately Moderatelytotowellwellsorted sortedsandstone sandstonebeds bedsare areinternally internallystructureless structurelessororcontain containill-defined ill-definedtrough troughand andtangential tangential cross-strata cross-stratawith withrare rareshale shaledrapes drapesand andreactivation reactivation surfaces. surfaces. These Thesefeatures featuresare areindicative indicativeofof deposition deposition in inaashoreface shorefaceand andtidal tidalflat flatenvironment. environment. The Theoverlying overlyingstrata strataofofthe theFranconia Franconia Formation Formationconsists consistsmostly mostlyofoffeldspathic, feldspathic,glauconitic, glauconitic,finefine-totovery veryfine finegrained grainedsandstone sandstonewith with hummocky hummockycross-strata cross-strataand andtempestites tempestitesthat thatwere weredeposited depositedon onthe theoffshore offshoreshelf. shelf.These Theselower lower 123 �Franconia Franconia Formation Formation strata strata are are better better exposed exposed at at Stop Stop 6. 6. The The contact contact between between the the Ironton Ironton Sandstoneand andFranconia FranconiaFormation Formationisistransitional transitionaland and records records gradual gradual flooding flooding during duringan an overall overall Sandstone rise rise in in sea sealevel. level. The quartzose quartzosesandstone sandstoneof of the the fronton Ironton exposed exposed includes includesaa pebbly pebbly sandstone sandstonebed bed that that may may The mark aa regional regional unconformity. unconformity. The Theupper upper part part of ofthe theunderlying underlyingEau Eau Claire ClaireFormation Formation and and mark lower lower approximately approximately two-thirds two-thirds of of the the fronton/Galesville Ironton/Galesville Sandstones Sandstones (below (below level level of of this this exposure)form formaacoarsening-upward coarsening-upwardsequence sequencethat thatrecords recordsdeposition depositionininprogressively progressivelyshallower shallower exposure) water Ironton/GalesvilleSandstones Sandstones fines fines upward, upward, water conditions. conditions. The Theupper upperone-third one-thirdofofthe thefrontonlGalesville recordingdeeper deeperwater waterconditions. conditions.The Thenearly nearlystructureless, structureless,resistant resistantbed bedabout about22mmabove abovethe the recording base base of of this thisoutcrop outcropisisaa1.5-2 1.5-2mmpebbly pebblysandstone sandstonelag lagthat thatseparates separatesthese thesedecameter-scale decameter-scale sequences. sequences.This Thispebbly pebblylag lagcan canbe bephysically physicallytraced tracedfrom fromthe theTwin TwinCities Citiesarea areasouth southinto intoIowa, Iowa, and andfrom fromsouthwestern southwesternWisconsin Wisconsinwestward westwardatatleast least80 80kilometers kilometersinto intothe thesubsurface subsurfaceof ofsouthsouthcentral centralMinnesota. Minnesota.ItItmay mayrepresent representaatransgressively transgressivelyre-worked re-worked lag lag that that developed developed subaerially subaerially when when the the "Ironton-Galesville "Ironton-Galesville shoreline" shoreline"was wasininextreme extremebasinward basinwardpositions. positions. Compare Compare the the hydrostratigraphic hydrostratigraphic properties of the the Franconia Franconia Formation Formation and and Ironton Ironton Sandstone.The Thefronton Irontonisiscomposed composedmostly mostlyof ofthe thecoarse-clastic coarse-clasticcomponent, component,specifically specificallyof of aa Sandstone. poorly poorlycemented cementedmostly mostlyfine fine-- very verycoarse coarsegrained, grained,shaly shalysandstone sandstonewith withmoderate moderateporosity porosityand and permeability. The TheFranconia Franconiaabove aboveisisdominated dominatedby by the thefine fineclastic clastic component, component, which which is is finer finer permeability. grained Ironton,and and contains contains discrete, discrete, continuous continuous laminations laminations of of grainedand andbetter bettercemented cementedthan than the the fronton, shale. fronton. The shale.ItItisismarkedly markedlylower lowerin in porosity porosity and and permeability than the Ironton. The common common practice practice of of lumping lumpingthese thesetwo twounits unitstogether togetheras asaasingle singleaquifer aquiferis is not not reasonable, reasonable,and and gives gives the the erroneous erroneous impressionthat thatthey theyshare sharesimilar similar hydrogeologic hydrogeologicattributes attributes (see (see Stop 6 for impression for additional additional discussion). discussion) STOP STOP8—Road %Road cut cuton onU.S. U.S.Highway Highway61 61near nearWabasha. Wabasha.From FromState StateHighway Highway60, 60,take takeU.S. U.S. 61 61south south2.3 2.3miles milesto toroad roadcut cuton onwest westside sideof ofroad road(Fig. (Fig.10). 10). Intethngering InterfingeringEau EauClaire ClaireFormation Formationand andIronton-Galesville Ironton-Galesville(Wonewoc) (Wonewoc)Sandstones Sandstonesare are exposed in this long road cut. There are several interesting sedimentologic features, including exposed in this long road cut. There are several interesting sedimentologic features, including hummocky cross-strata, cross-strata, tempestites, tempestites, trough trough cross cross stratified stratified sandstone, sandstone, and and coarse coarse sand sanddune dune hummocky forms formsdraped drapedby byshale. shale.Trilobite Trilobitemolds moldsare areabundant abundantatatthis thisstop stopininthe thehummocky hummockystratified stratified sandstone sandstonefacies. facies.This Thisoutcrop outcropisisone oneofofonly onlytwo twoknown knownexposures exposuresininthis thisarea areathat thatrecord recordthe the boundary boundarybetween betweenthe theMarjumiid Marjumiidand andPterocephaliid Pterocephaliidbiomeres, biomeres,aamajor majorisochronous isochronousextinction extinction event correlatable across all of North America. event correlatable across all of North America. This Thisexposure exposureisisaagood goodexample exampleofofthe thesame samefine-clastic fine-clastichydrostratigraphic hydrostratigraphiccomponent component that thatdominates dominatesthe thelower lowerFranconia Franconia and and St. St. Lawrence Lawrence Formations seen at stops 3 and 6. Core Core samples samples from fromall allthree threeunits unitsshow showaaconsiderably considerablylower lowerdensity densityofoffractures fracturesalong alongbedding bedding planes. planes. STOP west STOP9—Vern 9-Vern Keller KellerQuarry. Quarry.Along Along westside sideofofCounty CountyRoad Road6,6,1.15 1.15miles milessouth southof ofState State Highway Highway19. 19.Goodhue GoodhueCounty County(Fig. (Fig.11). 11). About About30 30mmofofthe themiddle middlepart partofofthe thePrairie Prairiedu duChien ChienGroup Groupisisexposed exposedininthis thisquarry. quarry. Relatively Relativelypure puredolostone dolostonebeds bedsof ofthe theuppermost uppermostOneota OneotaDolomite Dolomiteare areunconformably unconformablyoverlain overlain by ShakopeeFormation Formationabout about22meters bysandy sandydolostone dolostoneand andsandstone sandstoneofofthe theShakopee metersabove abovethe thefloor floorofof the thequarry. quarry. This Thisunconformity unconformityisisregional regionalininextent, extent,traced tracedfrom fromthis thisarea areainto intothe theMichigan Michigan basin basin by bySmith Smithand andothers others(1993). (1993).Deposition Depositionofofthe thePrairie Prairiedu duChien ChienGroup Groupoccurred occurredon onaa shallow shallowcarbonate carbonateplatform platformduring duringaarelatively relativelyhighstand highstandof ofsea sealevel levelthat thatflooded floodedmost mostof of North North 124 �Map 4 KILOMETERS MILES 11 1 00 00 I1 — 22 1 1 33 — 22 44 = 55 33 6B = It 17 88 55 90 —10$0 6 Figure Figure 11. 11.Map Map44on onindex indexmap map(Figure (Figure5) 5) showing showingthe the locations locationsof of stops stops99and and10. 10. Americaduring duringthe the Early Early Ordovician Ordovician (Smith (Smith and and others, others, 1993; 1993; Smith Smith and Clark, 1997). 1997). These These America strataare are typical typical of of "tropical" "tropical" carbonate carbonatesystems, systems,dominated dominatedby oolitic oolitic and peloidal grainstones grainstones strata subtidal andpackstones, packstones,and andstromatolitic stromatoliticand andwavy-laminated wavy-laminatedboundstones boundstonesdeposited depositedininshallow shallowsubtidal and tosupratidal supratidalsettings. settings.Stromatolites Stromatolitesare areabundant abundantininthis thisquarry: quarry:digitate digitateforms formscan can be be discerned discerned to inaafew fewplaces placesininthe theuppermost uppermostOneota, Oneota,and andcabbage-head cabbage-headstromatolites stromatolitesare arecommon commonininthe the in Shakopee.Evidence Evidencefor forsubaerial subaerialexposure exposureincludes includesabundant abundantmud mudcracks, cracks,intraclastic intraclasticbreccias, breccias, Shakopee. and andsilicified silicifiedand andmoldic moldicanhydrite. anhydrite. Thereare aresome someinteresting interestingquestions questionsthat thathave haveyet yetto tobe be answered answeredabout aboutthe thedeposition depositionof of There the ChienGroup: Group: thePrairie Prairiedu duChien 1) 1)What What isis the the fundamental fundamentalcontrol control that that blocked blocked detrital detrital input input when when most most of of the the Oneota Oneota was deposited? deposited?Much Muchofofthe theOneota Oneotaconsists consistsofofstrata stratathat thatwere wereapparently apparentlydeposited depositedalong alongaa was regional shoreline in which siliciclastics were nearly absent. regional shoreline in which siliciclastics were nearly absent. 2)What What are arethe thefundamental fundamental controls controls that that led led to to an an arid, arid, tropical tropical carbonate carbonate style style of of 2) deposition,when whenboth bothyounger youngerand andolder oldercarbonate carbonatedeposition depositionwas wasreminiscent reminiscentof of modern modemcoolcooldeposition, water, water,temperate temperateconditions? conditions? This Thispart partof ofthe thePrairie Prairiedu duChien ChienGroup Groupconsists consistschiefly chieflyof of the the carbonate-rock carbonate-rockcomponent. component. ItItisisan anexcellent excellentexample exampleof of the the importance importancein in delineating delineatingthe the presence presence and and position position of of fractures fractures that that are arethe theprincipal principalgroundwater groundwaterconduits. conduits. AAprominent prominenthorizontal horizontalinterval intervalofofdissolution dissolution features, features,some somewith withstalactites, stalactites,occurs occursalong alongthe theOneota-Shakopee Oneota-Shakopeeunconformity unconformityininthis thisquarry. quarry. AAsecond seconddissolution dissolutionlayer layerisisvisible visiblehigh highon onthe thequarry's quarry's south southwall, wall,just just below belowaa1-2 1-2m mbed bedof of coarse coarsesandstone. sandstone.Work Workby byCalvin CalvinAlexander Alexanderfrom fromthe theUniversity University of of Minnesota Minnesota suggests suggests that that these these dissolution dissolution horizons horizons have have an animportant importantcontrol control on on the thehydrogeologic hydrogeologicattributes attributes of of the the Prairie Theyare arelikely likelymajor majorconduits conduitsfor forground-water ground-waterflow, flow,and andenhance enhancethe the Chien. They Prairie du du Chien. development developmentof ofsinkholes sinkholeswhere wherethey they are are nearer nearer the surface. surface. Other Othernotable notablefeatures featuresinclude includethe the 125 �the carbonate carbonate rock rock exposed exposed on the the south south wall wall of of the thequarry—in quarry-in tight, unfractured nature of the contrast with with the the carbonate carbonaterock rock of of the the Shakopee Shakopeeseen seen at at Stop Stop 11 where it is closer to the surface, contrast surface, and and secondary secondary porosity porosity isisbetter betterdeveloped. developed. Stop 10—Spring 10ÑSprin near nearVern VernKeller KellerQuarry. Quarry.From Fromquarry quarrycontinue continuesouth south0.7 0.7 miles miles on County Stop Road Road 6. 6. Turn Turneast easton onto togravel gravel road road and and travel travel 0.1 miles (Fig. 11). 11). Spring Springisison on north northside side of road on PRIVATE PROPERTY. of road on PRIVATE PROPERTY. Elevation Elevationof of this this resurgent resurgent spring spring approximately approximatelythe the same same as as the Oneota-Shakopee Oneota-Shakopeecontact contact seen seen at at the the previous previous stop. stop. This supports supports the hypothesis hypothesis that dissolution dissolution features along along the the unconformity unconforrnitymay maybe beaamajor majorconduit conduitfor forgroundwater groundwaterflow. flow. REFERENCES REFERENCES CITED CITED Adams, R. R. L., L., 1978, 1978,Stratigraphy Stratigraphy and and petrology petrology of of the the lower lower Oneota Oneota Dolomite Dolomite(Ordovician), (Ordovician), south-central Wisconsin: Wisconsin Wisconsin Geological Geological and and Natural Natural History Survey Field Trip Guidebook Guidebook3, 3, p. p. 82-90. 82-90. Alexander, Alexander, E.C.., E.C.., 1990, 1990,Anion Anion analysis analysisof of selected selectedwells wellsand and springs: springs:Oronoco Oronocodye dyetrace tracestudy: study: Unpublished Unpublishedstudy, study,Investigations InvestigationsReport Report90-408 90-4081,1,101 101p. p. Alexander, Beck,B.F., B.F., logoon collapses, collapses,ininBeck, Alexander, E.C., E.C., Jr., Jr., and andBook, Book,P.R., P.R., 1984, 1984,Altura, Altura, Minnesota Minnesota logoon ed., ed., Sinkholes: Sinkholes:Their Theirgeology, geology,engineering engineeringand andenvironmental environmentalimpact— impact- Multidisciplinary Multidisciplinary Conference Proceedings: Boston, Conference on Sinkholes, 1st, lst, Orlando, Florida, Oct. 15-17, 1984, Proceedings: Boston, A.A. Balkema, p. 3 11-318. A.A. Balkema, p. 3 11-318. Alexander, E.C., Jr., Jr., Broberg, Broberg, J.S., J.S., Kehren, Kehren, A.R., A.R., Graziani, Graziani, M.M., M.M., and and Turn, Turri,W.L., W.L., 1993, 1993, Bellechester in Beck, Beck, B.F., B.F., ed., ed., Sinkholes: Sinkholes:Their Theirgeology, geology, Bellechester Minnesota Minnesota lagoon lagoon collapse, collapse, in engineering engineeringand andenvironmental environmentalimpact—Multidisciplinary impact-Multidisciplinary Conference Conference on on Sinkholes, Sinkholes,4th, 4th, Orlando, Orlando, Florida, Florida, Jan. Jan. 25-27, 25-27,1993, 1993,Proceedings: Proceedings: Brookfield, Brookfield,Vermont, Vermont,Balkema, Balkema, p. p. 636372. Alexander, Alexander,E.C., E.C., and andMaki, Maki,G.L., G.L., 1988, 1988,Sinkholes Sinkholesand and sinkhole sinkholeprobability, probability, plate plate 77 in in Balaban, Balaban, N.H., ed., Geologic Atlas of Olmsted County, Minnesota: Minnesota Geological N.H., ed., Geologic Atlas of Olmsted County, Minnesota: Minnesota GeologicalSurvey Survey County CountyAtlas Atlas Series SeriesC-3. C-3. Barnes, Barnes,D.A., D.A., Harrison HarrisonIII, 111,W.B., W.B., and andShaw, Shaw,T.H., T.H., 1996, 1996,Lower-Middle Lower-MiddleOrdovician OrdovicianLithofacies Lithofacies and in Witzke,B.J., B.J.,Ludvigson, Ludvigson,G.A., G.A.,and and and interregional interregionalcorrelation, correlation,Michigan MichiganBasin, Basin,USA, USA,inWitzke, Day, Day, J., J., eds., eds., Paleozoic Paleozoicsequence sequencestratigraphy: stratigraphy: Views Views from from the the North North American American craton: craton: Geological GeologicalSociety Societyof ofAmerica AmericaSpecial SpecialPaper Paper306, 306,p.p.35-54. 35-54. Barnes, Barnes, D.A., D.A.,Lundgren, Lundgren,C.E., C.E., and andLongman, Longman,M.W., M.W., 1992, 1992,Sedimentology Sedimentology and and diagenesis diagenesisof of the St. Peter Sandstone, Central Michigan Basin, United States: American Association of the St. Peter Sandstone, Central Michigan Basin, United States: American Association of Petroleum PetroleumGeologists GeologistsBulletin, Bulletin,v.v.76, 76,no. no.10, 10,p.p.1507-1532. 1507-1532. Barr Barr Engineering, Engineering,1996, 1996,Dakota DakotaCounty Countygroundwater groundwatermodel modelsummary summaryreport: report:90 90p. p. 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R.T., and Delin, Delin, G.N., G.N., 1993,Field Field observations, observations, preliminary preliminary model model analysis, analysis, and and aquifer aquifer Miller, R.T., thermal efficiency: U.S. Geological Survey Professional Professional Paper Paper 1530-A, 1530-A,55 55 p. 128 �1972, Pre-Mt Simon regolith, in Sims, Sims,P.K., P.K., and and Morey, Morey, G.B., eds., Geology Geology of of Morey, G.B., 1972, Minnesota: Minnesota:A A centennial centennialvolume: volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey, p. p. 506-508. 506-508. Mossler, J.H., 1985, 1985,Sedimentology Sedimentologyof of the Middle Ordovician southeastern Mossler, Ordovician Platteville Platteville Formation, Formation, southeastern Minnesota Geological Geological Survey Survey Report Report of of Investigations Investigations 33, 33,27 p. Minnesota: Minnesota 27 p. 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A discussion: discussion:Kansas KansasGeological GeologicalSurvey SurveyBulletin Bulletin169, 169,p.p.38 381-398. Ostrom, M.E., M.E., 1970, 1970,Sedimentation Sedimentation cycles cycles in in lower lower Paleozoic Paleozoic rocks rocks of of western westernWisconsin: Wisconsin: Ostrom, Wisconsin Wisconsin Geological Geologicaland and Natural Natural History History Survey Survey Information Information Circular Circular11, 11,p. p. 10-34. 10-34. Palmer, Palmer, A.R., 1960, 1960,Some Someaspects aspectsof of the the early early Upper Upper Cambrian Cambrian stratigraphy stratigraphyof of White WhitePine PineCounty County ,Nevada, Nevada, and and vicinity, vicinity, in Geology Geologyof of east eastcentral central Nevada: Nevada: Intermountain Intermountain Association of Petroleum PetroleumGeologists GeologistsGuidebook Guidebook11th 11thAnnual Annual Field Field Conference, Conference, p. 53-58. 53-58. 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Runkel, Runkel, A.C., 1994, 1994, Deposition Deposition of of the the uppermost uppermost Cambrian Cambrian (Croixan) (Croixan) Jordan Jordan Sandstone, Sandstone, and and the the nature natureof of the the Cambrian-Ordovician Cambrian-Ordovicianboundary boundaryin inthe theUpper UpperMississippi MississippiValley: Valley: Geological Geological Society Societyof of America AmericaBulletin, Bulletin,v.v. 106, 106,p. p. 492-506. 492-506. Runkel,A.C., Runkel,A.C.,1996a, 1996a,Geologic Geologicinvestigations investigationsapplicable applicableto to groundwater groundwatermanagement, management,Rochester Rochester Metropolitan Metropolitanarea, area,Minnesota: Minnesota:Minnesota MinnesotaGeological GeologicalSurvey SurveyOpen-File Open-FileReport Report96-1, 96- 1, 27p. 27 p. Runkel., Minnesota: Minnesota Runkel., A.C., 1996b, 1996b,Bedrock Bedrock geology of Houston County. Minnesota: Minnesota Geological Geological Survey Survey Open File Report 96-4, 1lip. lp. 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Thesis, University Sargent, M.L., 1991, 1991, Sauk Sequence: Sequence: Cambrian System through Lower Ordovician Series, in D.F., and Eidel, J.J., J.J., eds., Interior cratonic basins: Leighton, M.W., Kolata, D.R., Oltz, D.F., basins: American Association of Petroleum Geologists Memoir 551, 1, p. 75-86. Setterholm, D.R., Runkel, Runkel, A.C., Cleland, Cleland, J.M., Tipping, R., Mossier, J.M., Kanivetsky, R., and Hobbs, H. C., 1991, 1991, Geologic Geologic factors affecting the sensitivity sensitivity of of the Prairie du ChienJordan Jordan Aquifer: Aquifer: Minnesota MinnesotaGeological GeologicalSurvey SurveyOpen-File Open-FileReport Report991-5,18 1-5,18 p. Simo, J.A., J.A., Choi, L., Freiberg, Simo, Freiberg, P., P., Byers, C.W., C.W., Dott, R.H., R.H., Jr., and and Saylor, Saylor, B., B., 1997, 1997, Sedimentology, sequence stratigraphy, and paleoceanography of the Middle Sedimentology, Middle Ordovician Ordovician Wisconsin, in Mudrey, M.G.,ed., M.G.,ed., Guide to field trips trips in in Wisconsin Wisconsin and and adjacent adjacent of eastern Wisconsin, areas of Minnesota: Minnesota: Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, p. 95-114. 95-1 14. Sloan, R.E., ed., 1986, 1986, Middle and Late Ordovician lithostratigraphy of the Upper Mississippi Valley: Minnesota Geological Survey Report of Investigations 3 5 ,232p. 232~. Valley: Investigations 35, Sloss, L.L., 1963, 1963, Sequences in the cratonic interior of North America: Geological Society of America Bulletin, Bulletin, v. 74, p. 93-114. 93-1 14. 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Wenck and Associates, Associates, Inc., Inc., 1997, Phase 11: II: Detailed site investigation report and Phase II Wenck investigation report I1 workplan for the hydrogeologic of the proposed proposed Red Wing Wing ash disposal hydrogeologic investigation investigation of facility facility expansion, expansion, 36 36 p. p. Witzke, B.J., Ludvigson, Ludvigson, G.A., G.A., and and Day, Day, J., eds., 1996, 1996,Paleozoic Paleozoic sequence sequencestratigraphy: stratigraphy:Views Views from from the North North American American craton: Geological Geological Society Society of America Special Paper 306, 446 p. 130 ��FIELD FIELD TRIP TRIP#5 #5 MINNESOTA MINNESOTA RIVER RIVERVALLEY VALLEYAND AND VICINITY, VICINITY, SOUTHWESTERNMINNESOTA MINNESOTA SOUTHWESTERN Leaders: D.L. D.L.Southwick Southwick and and Carrie CarrieJ. J. Patterson Patterson Leaders: INTRODUCTIONTO TOTHE THEGEOLOGY GEOLOGYOF OFPRECAMBRIAN PRECAMBRIANROCKS ROCKSIN INTHE THE INTRODUCTION MINNESOTA RIVER VALLEY MINNESOTA RIVER VALLEY D. D.L. L.Southwick Southwick The Precambrian Precambrian rocks rocks exposed exposed in inthe theMinnesota MinnesotaRiver RiverValley Valley are are within within an anArchean Archean The gneiss terrane terranethat thatconstitutes constitutesthe thesouthernmost southernmostsubprovince subprovince of of the the Superior SuperiorProvince Provinceof ofthe the gneiss CanadianShield. Shield.The TheMinnesota MinnesotaRiver RiverValley Valley(MRV) (MRV) subprovince subprovince is is further further subdivided subdivided into into Canadian fourtectonic tectonicblocks blocks by byregional regionalENE-trending ENE-trending shear shear zones zones (Fig. (Fig.1;1;Southwick Southwickand andChandler, Chandler, four 1996).This Thistrip tripwill willfocus focuson onexposed exposedrocks rocksof ofthe theMorton Mortonand andMontevideo Montevideoblocks, blocks,which whichare are 1996). EXPLANATION' EXPLANATION TECTONIC TECTONICELEMENT ELEMENT Sioux Quartzlto P.nok.an Ponokoanoreg.n orogon (undlvld.d) (undivided) ROCKTYPES TYPES ROCK AGE AGE Red sandstone and shale Middle Middle Proterozotc Proterozoic a (51,100Ma) Ma) (1,100 Quartzite Quartzite Early Early Pmterozok Proterozoic (1,630-1,770Ma) Ma) (1,630.1,770 'fl /1 Supracrustal SuPracrustal endIntrusive Intrusiverocks rocks and manytypes; types: ofofmany alsoArchean Archeangnelss gneiss also Penokean rewwked reworked InInPenokean events events Early Early Proterozoic Proterozoic (depositional (depositional andemplacement emplacement and 80681.770-2.200 1,770-2.200 ages Ma) Ma) Greenstone-belt Greenstone-belt 1tNcassociation. association, Nthlc granitoidIntrusions Intrusions granitold LateArchean Archean Late Ma) ('2.700Ma) (2,700 Greenatone-beft NtNc association, Uncertain;Late Late Uncertain; Archeanand/or and/or Arctiean EarlyProterozoic Proterozoic Early SuperiorProvince Province Superior Wawa W a w subprovlno. aubprovlnco (undivided) (undlvldod) ' VaMoy mibprovlnce ffffl'Jffl) Ilifirnillil lowtotomoderate moderate low orade rnetarnor~hic metamorphic . grade 4-; Location Map Regionalshear shearzone zoneorortectonic tectoniccontact; contact;barbs barbs Regional indicatedirection directionofofdip dipasasInterpreted interpreted from Indicate from geophysical models. geophysical models. IOWA 0 30 - Quartzofeldspathic Quartzofeldspathic MiddletotoLate Late Middle gneiss,granitold granitoid gnelsa, Archean(3,600(3,600Archean ~ ~ ~ I U S I O ~ S Intrusions 2,600Ma) Ma) 2,600 60 KNOm.tws Figure Figure1.1.Tectonic Tectonicsketch sketchmap mapof ofPrecambrian Precambrianterranes terranesin insouthwestern southwesternMinnesota. Minnesota.The TheMinnesota Minnesota River RiverValley Valley subprovince subprovinceconsists consistsof of the the Benson, Benson, Montevideo, Montevideo, Morton, Morton, and and Jeffers Jeffers blocks. The The Taunton Tauntonbelt beltisisa anarrow narrowseptum septumofofrelatively relativelylow lowgrade grademetavolcanic metavolcanicrocks rocksalong alongthe theYellow Yellow Medicine shear zone, which marks the boundary between the Montevideo and Morton blocks. Medicine shear zone, which marks the boundary between the Montevideo and Morton blocks. The Theline lineindicates indicatesthe thelocation locationofofgeophysical geophysicalprofiles. profiles.From FromSouthwick Southwickand andChandler Chandler(1996). (1996). 133 �central two two blocks blocks of the the subprovince. subprovince. The Theboundary boundarybetween betweenthese theseisisthe theYellow Yellow Medicine Medicine the central shear zone (YMSZ), (YMSZ),aamajor majorcrustal crustal feature feature that that is is well well delineated delineated aeromagnetically aeromagnetically but does does not crop crop out. The TheYMSZ YMSZcrosses crossesthe the Minnesota MinnesotaRiver River between betweentrip trip stops stops66 and and 77 (Figs. (Figs. 11 and and 2). 2). At stops stops 11 through through 6, 6, south south of the the YMSZ, we will see features of the Morton block and at Stops 6 through ii11we wewill willsee seefeatures featuresof ofthe theMontevideo Montevideoblock. block. The characteristic characteristicrock rock type type of of both blocks blocks is a modally layered gneiss gneiss that falls falls generally generally tonalite to granodiorite granodiorite range in bulk composition (Goldich and others, 1980a 1980a and b). within the tonalite irregular blocks of mafic gneiss, gneiss, This rock type, together together with less less abundant abundant layers, layers, lenses, lenses, and irregular amphibolite, constitutes that Morton Gneiss amphibolite,and and various various types types of aluminous alurninous gneiss, constitutes Gneiss south south of the YMSZ and the Montevideo Montevideo Gneiss north of it. Alert readers will note note the the correspondence correspondence of the the principal principal map mapunit unitwithin withinit. it. Mineral-assemblage between the block name and the name of data indicate that the Morton and Montevideo gneisses were metamorphosed metamorphosed under under conditions conditions of the upper upper amphibolite amphibolite and and granulitic granulitic facies (Grant, (Grant, 1973; 1973; Perkins and Chipera, Chipera, 1985). 1985). Retrograde processes Montevideo Gneiss Retrograde processeshave have affected affectedaa considerable considerablearea area of the Montevideo Gneissbut are are evident evident only locally in the Morton. The Morton and by granite (adamellite, and Montevideo Montevideo gneisses were invaded by (adamellite, in the the terminology favored favored by by Goldich Goldich and and others, others, 1980a and and b) b) at two different different times during the terminology Archean. 1 of 980a) Archean. The Thefirst firstepisode episodeof ofgranite graniteemplacement emplacement(adamellite(adamellite-1 of Goldich Goldichand and others, others,11980a) fabric in in the gneissic host rocks; preceded the development of the predominant metamorphic fabric that fabric passes passes through the the granite granite bodies, bodies, most most of of which which are are aplitic aplitic or or pegmatitic, pegmatitic,without without discernable change in in orientation. orientation. In addition, addition, much granite of this this generation generation possesses possesses of Goldich metamorphic texture. The The second second episode episode of of granite granite emplacement emplacement (adamellite-2 of and others, 11980a) 980a) occurred occurred after after the the main main fabric-forming fabric-forming events. events. Most intrusions intrusions of of this this generation generationlack lack internal internalfabric, fabric,although although some someshow show aa weak foliation foliation and therefore therefore may be latelateAdamellite-2 intrusions intrusions range from to post-tectonic. post-tectonic. Good Good igneous igneous textures textures are the norm. Adamellite-2 aplitic to medium-grained granitic in grain size and from thin dikes and sills to batholiths in form and scale. The TheSacred SacredHeart HeartGranite Granite(Stop (Stop6) 6)forms formsaa regional-scale, regional-scale, sheet-like sheet-like intrusion intrusion several kilometers kilometers in in thickness thickness that that is is interpreted interpreted to to be be of of the adamellite-2 generation. generation. The Ortonville and Fort Ridgeley granites are late- to post-tectonic post-tectonic masses that also are of of the the adamellite-2 adamellite-2 type and and are are assumed assumed to to be approximately approximately coeval with the Sacred Sacred Heart. Between colleagues devoted huge efforts efforts to to pioneering pioneering Between 1950 1950 and 1980, 1980, S.S. Goldich and colleagues geochronologic studies geochronologic studies of the the Morton Morton and and Montevideo Montevideo gneisses gneisses and and the various various granitic granitic rocks rocks that are associated associated with with them them (Goldich (Goldich and and Wooden, Wooden, 1980; 1980; Goldich and others, others, 1980a 1980a and and references therein). components of both the Morton references therein). The Thegneisses gneissesproved provedto tobe be (1) (1)very very old, old, with components and Montevideo as old as about 3,600 Ma, and (2) geochronologically as about 3,600 Ma, and (2) geochronologically complex, complex, with with several several Archean events events recorded recorded isotopically. isotopically. Moreover, Moreover, the the Goldich Goldich group group found found the discernable Archean "adamellite 1" the geologically geologically straightforwardstraightforward"adamellite 1" rocks rocks to to be be isotopically isotopically complex complexas as well, and even the "adamellite 2" rocks rocks to to yield yield less less than thandefinitive definitive crystallization crystallization ages. ages. Goldich's appearing "adamellite interpretation of interpretation of the the geologic geologichistory historyof of the theMRV MRV subprovince subprovinceisis presented presentedin inTable Table1.1. Goldich emphatically type represented represented genuine Goldich emphaticallybelieved believedthat that the the granite graniteof the the adamelliteadamellite- 1 type igneous i.e., true true intrusion. intrusion. Others contended Others have contended igneous importation importationof of magma magma from from a distant source; i.e., that some, some, if not not all, all, of the the early early granite granite was derived more or less locally through partial partial melting melting of the gneis sichost. host. A major question persists as to to whether whether the the pink pink leucosomatic leucosomatic components components gneissic of the Morton 1 Morton Uneiss Gneissin inthe thevicinity vicinityof ofMorton Mortoncrystallized crystallizedfrom frominjected injectedmelt meltofofadamelliteadamellite-1 134 �Figure 2. Locations of field-trip stops for Day 1. More detailed location maps accompany the individual stop descriptions. �Table1.1.Summary Summaryofofprincipal principalPrecambrian Precambrianevents eventsininthe theMinnesota MinnesotaRiver RiverValley Valley subprovince. subprovince. Table Modified and and interpreted interpreted from from Goldich Goldich and and Wooden Wooden (1980); Goldich and others others (1980a). (1980a). Modified 1800 Ma Ma event event(Proterozoic): (Proterozoic): Emplacement Emplacement of of small small intrusions; intrusions; local local 1800 retrogade retrogademetamorphism, metamorphism,shearing shearing 2600 2600Ma Maevent eventEmplacement Emplacementofofpost-kinematic post-kinematicaplite apliteand andpegmatite pegmatitedikes dikes Emp1acemen.tof of Sacred SacredHeart Heart Granite, Granite, other other granite granitebatholiths, batholiths,and and Emplacemen.t associated associated minor minor intrusions intrusions ("adamellite-2"; ("adamellite-2"; late-kinematic) late-kinematic) High-grade High-grade metamorphism, metamorphism, deformation deformation of of gneiss gneiss 3100 Ma event 3100Maevent High-grade High-grademetamorphism, metamorphism,deformation deformationof of gneiss gneiss Emplacement Emplacementof ofminor minorgranitoid granitoidintrusions intrusions("adamellite("adamellite-1") 1") 3600 3600 Ma Ma event event Intrusion Intrusionof oftonalite, tonalite,granodiorite granodioriteinto intoheterolithic heterolithicprecursor precursorof of layered layered gneiss gneiss typeor orfrom frommelts meltsdeveloped developedthrough throughanatexis anatexisof ofpre-existing pre-existinggranodioritic granodioritictototonalitic tonaliticgneiss. gneiss. type We and2A. 2A. We will will have have an anopportunity opportunityto toform formour ourown ownconclusions conclusionsatatstops stops22and Although the theprincipal principalrock-forming rock-forming events events responsible responsible for for the theformation formationof ofthe theMRV MRV Although subprovinceoccurred occurredover overaabillion-year billion-yearinterval intervalof ofArchean Archeantime, time,there thereare areclear clearindications indicationsof of subprovince further furthergeologic geologicactivity activityin in the the Early Early Proterozoic. Proterozoic. The Thesubprovince subprovincelay lay in in the the cratonic cratonicforeland foreland (Superiorcraton) craton)with with respect respectto toPenokean Penokeantectonism tectonism in in the the interval interval between between 2.1 2.1 and and 1.7 1.7Ga. Ga. (Superior We are arejust just beginning beginningto torecognize recognizeand andquantify quantifyevents eventsand and responses responses recorded recorded in in the the foreland foreland We rocks rocksthat thatwere wereengendered engenderedby bytectonic tectonicprocesses processeswithin withinthe thePenokean Penokeanorogen orogen (Southwick (Southwickand and Chandler,1996; 1996;Holm Holmand andothers, others,1998), 1998),the the axis axis of of which which lies lies only a few 10's 10's of kilometers kilometers to to Chandler, theeast eastof ofpresent presentMRV MRV exposures. exposures. Proterozoic Proterozoicevents eventsinclude include(1) (1)the theemplacement emplacementof of at at least least the twoand andpossibly possiblyasasmany manyas asfour fourswarms swarmsof ofdiabase diabasedikes; dikes;(2) (2)the the emplacement emplacementof of small smallintrusive intrusive two plugsthat thatrange rangein incomposition compositionfrom fromperidotite peridotiteto togranite; granite;and and(3) (3) differential differential vertical vertical movement movement plugs on onblock-bounding block-boundingshear shearzones, zones,with withconcomitant concomitantdevelopment developmentof of brittle brittlestructures structuresand and retrograde retrograde metamorphic metamorphiceffects. effects. No No discussion discussionofofthe theMRV MRVsubprovince, subprovince,regardless regardlessofofbrevity,, brevity,.is is complete completewithout withoutan an acknowledgment 1956) over acknowledgmentof ofthe theexcellent excellentgeologic geologicmapping mappingdone doneby by Ernest ErnestLund Lund (1950, (1950,1956) over45 45 years Lund'swork workwas wasthe thestarting startingpoint pointfor forsubsequent subsequentgenerations generationsof offield fieldinvestigations investigations yearsago. ago.Lund's (Himmelberg, (Hirnmelberg, 1968; 1968; Grant, Grant, 1972; 1972; Bauer, Bauer, 1980) 1980) and and was was the the principal principal framework framework for for the the geochronologicinvestigations investigationsofofGoldich Goldichand andcolleagues. colleagues.Those Thoseofofus usworking workingtoday todayfind findLund's Lund7s geochronologic maps mapstotobe beproof proofofofthe themantra mantrathat thatcareful carefulgeologic geologicobservations observationsand anddescriptions descriptionsare aretimeless; timeless; their theirvalue valuewill willoutlast outlastthe theinterpretational interpretationalframework frameworkwithin withinwhich whichthey theywere weremade. made. 136 �FIELD TRIP FIELD TRIPSTOPS—DAY STOPS-DAY 11 Stop 1—MRV 1-MRV geomorphology; geomorphology; Proterozoic diabase dikes and and walirock wallrock of of Archean Archean Morton Morton Stop Morganquadrangle, quadrangle,T. T.112 112N.-R. N.-R. 34 34W.-Section W.-Section 23AAC. 23AAC. Gneiss. Morgan At this locality locality south Franklin, newcomers can readily comprehend comprehend several south of Franklin, several elements elements of post-Precambrian geologicalhistory history that that bear bear on the condition and distribution post-Precambrian geological distribution of the the Precambrian Precambrian rock outcrops on the valley Point (1): (1): The ThePrecambrian Precambrianrocks rocks were were deeply deeply weathered weathered valley floor. floor. Point prior to continental glaciation in the Quaternary. Quaternary. Actually, Actually, most of the weathering weathering occurred prior to the Late Cretaceous. ManyMRV MRV outcrops, outcrops, such such as these, are incipiently substantially Cretaceous. Many incipiently to substantially weathered; they represent material that lay just pre-Cretaceous weathering just at the base of the pre-Cretaceous profile. Upper the Upper parts parts of of the weathering profile, remnants of of weathering Late Cretaceous marine strata, and the overlying glacial deposits deposits were were stripped away as the Glacial River Warren (a high-discharge, Warren high-discharge, lowlowgradient gradient meltwater meltwater river river ancestral ancestralto to the Minnesota) eroded downward. downward. River River downcutting downcutting slowed slowed or or perhaps ceased perhaps ceased where where hard rock was encountered at the the base of encountered at of the the (2): The The weathered section. section. Point (2'): present valley-floor outcrops were rapids and islands rapids islands in the Glacial Glacial River Warren. Warren. Their morphology morphology is due primarily due primarily to river river erosion. erosion. (31: Because Because of of the the Scoured cuts (former shoots in rapids) and and potholes potholes are are common. common. Point (3): history knobs of approximately history discussed discussedin inpoints points(1) (1)and and(2), (21, outcrops outcropstend tend to to be clusters clustersof low knobs approximately the same height. InIngeneral generalthey theydo donot notoccur occuron onthe thevalley valley walls, walls,Grand-Canyon Grand-Canyon style, style, but instead are located toward the middle middle of the the valley valley floor floor where where the the stream stream velocity velocity and and downcutting greatest. The commonly downcuttingpower power of of the the River River Warren were greatest. The sides sides of the valley floor are commonly occupied by constructional terraces (as here) and the valley walls are chiefly the Quaternary sediments sediments through through which whichthe the River RiverWarren Warren cut. cut. Diabase dikes of of Proterozoic Proterozoic age age form form prominent prominent valley-floor valley-floor ridges ridges at at this thislocality. locality. Compositionally, tholeiites. They are very similar in in composition composition Compositionally,the dikes dikes are good continental tholeiites. and petrographic characteristics characteristics to to tholeiitic tholeiitic dikes dikes near Granite Granite Falls, Falls, some some 40 40 miles miles up-river, up-river, that yield K-Ar dates of about 2,080 Ma (Hanson and Himmelberg, 1967). Several of of the the larger larger az. 095-100, approximately parallel to the dikes dikes here tholeiite dikes dikes at at Granite Granite Falls Falls strike strike about about az. tholeiite approximately parallel at Franklin. Franklin. Some Somebetter bettergeochronology geochronologyand andaalittle littlepaleomagnetic paleomagneticwork workwould wouldbe bevery very helpful helpful in deciding Falls tholeiitic tholeiitic diabase diabase dikes dikes are are or or are not deciding whether whether the Franklin Franklin and Granite Granite Falls genetically genetically related. related. that is held up up by by the the Cedar About a mile northwest northwest of Stop 11 is a prominent brushy knob that Mountain Complex, a compositionally zoned zoned igneous igneous plug plugof ofProterozoic Proterozoicage. age. The outer part of the plug plug isis melanocratic melanocratic hornblende hornblende diorite that has aa chilled chilled external external rind rind of of olivine olivine trachybasalt homblende trachybasalt porphyry. The Thecore core of of the the plug is granite and granodiorite. Biotite and hornblende from the core core yield yield essentially essentially identical identicalK-Ar K-Ar ages ages of of 1,750 1,750Ma Ma (Hanson, (Hanson,1968). 1968). from :&, 137 �1.5 miles to the east of Stop 11 is a small plug of highly silicified and carbonatized About 1.5 Thisbody body isispost-Archean post-Archean but but is is unconstrained unconstrained otherwise otherwise as to age. serpentinite. This wallrock to the dikes and other intrusions is a granodioritic granodioritic variant The walirock variant of the middle Archean Morton Gneiss. Gneiss. Because Becausethe thegneiss gneisshere hereisis in in such such poor condition (incipient (incipient weathering), Archean Morton weathering), it has not been studied in any great detail. We We will see much better outcrops of the Morton at 4, and Stops 2, 2,4, and 5. 5. Features to see: see: • Grain Grain size sizeand andfabric fabricvariations variationswithin within diabase diabasedikes; dikes; chilled chilled margins. margins. • Paleomagnetic Paleomagneticdrill drillholes: holes: Where Where are are the the paleomagnetic paliomagnetic data?? data?? owned and operated operated by by the Cold Spring Stop 2—Morton %Morton Gneiss, Morton Quarry owned Spring Granite Granite Company. Morton W.-section 3lDAA. 31DAA. Hard hats must be Morton quadrangle, quadrangle, T. 113 113 N.-R. 34 W.-section worn everywhere everywhere on company company property. quarried here here isis aa variant variantof ofthe theMorton MortonGneiss. Gneiss. It is a The flamboyant dimension stone quarried classic migmatite migmatite in which a pink, granitic of the neosome classic granitic to pegmatitic pegmatitic component component of neosome (the "adamellite-1" rock suite of Goldich and others, 1980b) is unusually unusually abundant. More "adamellite-1" More typical typical Morton Gneiss from the standpoint standpoint of areal areal abundance abundance is aa predominantly predominantly gray rock of of granodioritic to to tonalitic tonalitic composition composition that that is is more more uniform uniform in in texture texture than than the the gneiss gneiss in the granodioritic Morton complex metamorphic metamorphic Morton area. area. This Thisisisanother anothercase casewhere where the the concept concept of "type locality" for a complex rock turns out to be flawed. flawed. The TheMorton Mortonarea areasupplied suppliedthe the name name for for the the gneiss gneiss because because the the many quarries provided accessible, unweathered, unweathered, clean exposures to study, study, not not because because the rock exposed is particularly exposed is particularly typical of aa mappable mappable geologic geologic unit. gneiss from u q The gneiss from this qquarry is marketed marketed under under the the trade trade name name granite." ItIt can "rainbow granite.'' can be seen ornamental stone as a facing and ornamental stone on buildings throughout buildings throughout the the Nation, Nation, and and in in recent recent years years itit has become a favorite favorite material material for for up-scale up-scale kitchen counters counters and and tabletops. The patterns, plastic, suggestive of inhomogeneous bulk inhomogeneous bulk deformation deformationunder under conditions conditionsat at which which the the rock rock was was in in aa partially partially molten molten state, attractive and intriguing intriguing to architects architects and interior designersas designers as they are to to geologists. geologists. state, are as attractive Features to to see: see: • Paleosomatic Paleosomatic"enclaves" "enclaves" of of several several types. types. • Evidence Evidenceof of rheological rheologicalcontrasts contrastsamong amongdifferent differentrock rock types during partial melting and deformatio.n. deformati0.n. • Gently dipping, tight folds folds reoriented reoriented into the dipping, broadly undulating gneissosity; small, tight undulating undulating "regional" "regional" fabric. fabric. 138 �• Zones Zones of of extensional extensional ductile ductile shear, shear, many many of of which which contain contain granitoid granitoid segregations segregations interpreted interpreted to to have have formed formed as as partial partial melts. melts. Stop Stop 2A 2A (Alternative (Alternative to to Stop Stop 2)—Morton 2)-Morton Gneiss, Gneiss, small small quarry quarry behind behind former former school school building in in town building town of Morton. Morton. Morton Morton quadrangle, quadrangle, T. T. 113 113 N.-R. N.-R. 34 34 W.-section W.-section 3 1BCBA. 1BCBA. Because of insurance insurance liability liability considerations, considerations, the Cold Spring Granite Company does not quarry. As of press time we were not normally permit field-trip field-trip groups groups into the active Rainbow quarry. many of of the cleared for quarry access. The The small small quarry quarry behind the old Morton school shows many described under Stop 2 (above), but but the the rock rock surfaces surfaces are are smaller smaller and and less less features of the gneiss described spectacular than those in the Rainbow quarry. Please spectacular Please read read the the discussion discussion of of Stop Stop 22 and and transfer transfer it to the Stop 2A exposures. exposures. move about about Stop Stop 2A. 2A. Rock surfaces that are shaded most of the Be very careful as you move time acquire a slimy slimy coating coating that can be treacherously treacherously slick. slick. Stop 3—Weathering Morton Gneiss Gneissprior priorto tothe theLate LateCretaceous. Cretaceous. Redwood Redwood Stop &Weathering profile developed on Morton Falls Falls quadrangle, quadrangle,T. T. 113 113N.-R. N.-R.35 35W.-section W.-section3ODAB. 30DAB. Clay-rich saprolith of the general type exposed here here occurs occurs widely widely in in the the subsurface of of southwestern Minnesota. southwestern Minnesota. Where WhereLate LateCretaceous Cretaceousmarine marinestrata stratahave havenot notbeen been removed removedby by postpostCretaceous erosion they overlie the saprolith saprolith directly, confirming that most of the weathering weathering occurred before Late Cretaceous Cretaceous marine transgression transgression and the the deposition deposition of of marine marine sedimentary sedimentary occurred rocks. In places where where the Cretaceous Cretaceous rocks rocks were eroded away prior to glaciation, remnants of the weathering weathering profile profile directly underlie Quaternary glacial deposits. The The clay, clay, grus, and corestones from from the the weathered Precambrian rocks undoubtedly contributed contributed substantially substantially to the mass of subsequent Cretaceous shales and and Quaternary tills. Quaternary Reworked and inReworked deposits of Late situ clay deposits Cretaceous and postCretaceous Cretaceous age are mined at several sites mined sites along the Minnesota along Minnesota River, including one River, one about a mile southeast of 139 �these exposures. Theclay clayisisused used mainly mainly in in the the manufacture manufacture of portland portland cement cement and and for for various various exposures. The agricultural purposes. The weathering profile at this stop was was studied studiedby bySam SamGoldich Goldichininthe the1930's; 1930's; his classic the weathering weathering stability stability of of rock-forming rock-forming minerals minerals (Goldich, (Goldich, 1938) 1938) was was based based on on paper on the Thatfundamental fundamentalpaper paper on onweathering weathering has has probably probably achieved achieved wider wider materials collected here. That all of of Sam's Sam's geochronological geochronologicalcontributions contributionscombined. combined. notoriety than all Features Features to to see: see: Upwardloss lossof ofsource-rock source-rockminerals mineralsand andfabric fabricin in the the bottom bottom two-thirds two-thirds of the weathering • Upward weathering profile. profile. • Pisolitic Pisoliticclay claylayer layertoward towardthe thetop top of of the the section. section. Beddedclay clay(reworked (reworkedby by streams?) streams?)above abovethe the pisolitic pisolitic layer layer and and below Quaternary Quaternarytill. till. • Bedded Stop Stop4—Morton &Morton Gneiss Gneisscut cut by by adamellite adamellitedikes. dikes. Vicksburg quadrangle, quadrangle,T. T. 114 114N.-R. 36 36 W.-section W.-section 33DDD. 33DDD. The gray tonalitic gneiss exposed in these outcrops is a common, widespread variant of of the Morton. Much Muchof ofthe therock rock mapped mapped as as Morton Morton Gneiss Gneiss is basically basically this lithology lithology with varying included mafic "enclaves" "enclaves7'and and varying degrees degrees of intrusion intrusion by younger younger granitoid granitoid quantities of included rock types. The The gray gray gneiss gneiss inclusionhere is about as inclusionas it free gets. Furthermore,this this is is a Furthermore7 locality where where there there is a locality intrusive clear-cut relationship between between .late late relationship granite of the Sacred Heart type (sharp-walled dikes, dikes, including an easily accessible one about two accessible meters thick) thick) and meters and the the can tonalitic Morton Morton Gneiss. Gneiss. The Therelative relativeage ageof of the the two two is is not a matter of great debate, in that it can be reliably reliably inferred inferred from from textural textural evidence evidence in the rocks and from field relationships observed at a number of places in the Valley. Valley. Accessible outcrops that show the critical field relations are rather rare7however. however. rather rare, Samples of tonalitic Morton Gneiss from this this site site form form part part of of the the dataset dataset for for the the "old" Rb-Sr isochron age of about about 3,500 3,500 Ma (Goldich (Goldich and Wooden, 1980) that is widely cited in the literature. Data the Rb-Sr Rb-Sr diagram diagram (Goldich (Goldich literature. Datafrom fromhere hereanchor anchorthe the lower lower or less radiogenic end of the and Wooden? Wooden, 1980; 1980; their their fig. fig. 2 and and data data from from locality locality 5). 5). In addition, addition, zircons from from the gneiss at this locality yield an interpreted interpreted U-Pb age age of 3,662 3,662+1+I-42 42 Ma (Goldich (Goldich and and Fischer, Fischer, 1986). 1986). details is beyond beyond the scope and purpose of this Lengthy discussion of geochronologic details this out7however, however, that that healthy disagreements exist as to the exact field guide. ItItmust mustbe bepointed pointedout, antiquity of the Morton Morton Gneiss Gneiss and and the the significance significanceto to be be attached attached to to the the dates dates determined. determined.A A derives from the the complexity complexity of of the the neosomatic neosomatic components components of of major source of controversy derives migmatitic rocks rocks (as seen in the quarries migmatitic quarries at at Stops Stops 22 and and 2A, 2A, for forexample) example) and andconflicting conflicting sequence of ofprocesses processesinvolved involvedinin neosome neosome genesis. genesis. The interpretations of the processes and sequence 140 �more straightforward straightforward sequence sequence of of cross-cutting cross-cutting relationships relationships displayed at the the present present stop stop isis more informative informativebecause becauseitit eliminates eliminatessome someof of the theinterpretational interpretationalambiguities ambiguitiesassociated associatedwith withthe the more morecomplex complexphases phasesof ofthe theMorton. Morton. Featuresto tosee: see: Features • Fabric Fabricand andfabric fabricvariations variationsinintonalite tonalitegneiss. gneiss. • Folded Foldedmafic maficlayer layerinterpreted interpretedas asaadeformed deformeddiabase diabasedike. dike.(Do (Doyou youagree?) agree?) • Textural Texturaland andfabric fabricvariations variationswithin withinpostpost-Morton Mortonadamellite adamelliteintrusions. intrusions. Stop5—Morton 5-Morton Gneiss Gneissthat thatdisplays displaysaavariety varietyofofenclaves enclavesand andsmall-scale small-scalestructures. structures. Stop Iverson IversonLake Lakequadrangle, quadrangle,T. T.114 114N.-R. N.-R. 37 37W.W.- section section21CB. 21CB. These 0.5mile mile south southof of the the the the largest largestexposed exposedmass massof of Sacred Sacred Theseoutcrops outcropsare arelocated locatedabout about0.5 Heart Heart Granite Granite in in the the Minnesota Minnesota River River Valley. Valley. The The gneiss gneiss here here isis characterized characterized by by abundant abundant amphibolitic amphibolitic inclusions inclusions of of tholeiitic tholeiitic and andkomatiitic komatiiticcomposition, composition, complex complex fold foldstructures structures indicative indicative of of multiple multiple folding folding events, events,deformed deformed(boudinaged, (boudinaged,folded) folded) aplitic aplitic dikes dikes presumably presumably of the "adamellite 1" suite, and straight, undeformed granite dikes of Sacred Heart the "adamellite 1" suite, and straight, undeformed granite dikes of Sacred HeartGranite. Granite. The The quartzofeldspathic quartzofeldspathic gneiss gneiss that that encloses encloses the various various mafic rock types is variable variable in modal modal composition composition and and texture. texture. Its Itsoverall overallcomposition compositionisisapproximately approximatelyin in the the granodiorite granodioriterange. range. Wander Wander around among the cedars cedars and and thombushes thornbushes to to find find examples examples of of the thefeatures features mentioned above. Look before you kneel or sit! Little cacti with big spikes grow all over these mentioned above. Look before vou kneel or sit! Little cacti with big spikes grow all knobs. knobs. Stop Stop6—Sacred &Sacred Heart Heart Granite Granite and and associated associated rock types. Iverson Iverson Lake Lake quadrangle, quadrangle, T. 114 114 N.-R. 37 37 W.-section 7DD, 7DD, near prominent prominent knob knob named named Middag MiddagKnutea. Knutea. The The Sacred SacredHeart HeartGranite Graniteisisone oneof of several severallarge large granite granite masses masses that that intruded intrudedMRV MRV gneisses gneisses 2.55 -- 2.7 2.7 Ga Ga time time interval. interval. Available Availableradiometric radiometricage age determinations determinationson on these these intrusions intrusions in the the 2.55 in are rather imprecise, owing to the scarcity and poor poor quality quality of of the the contained contained zircons. zircons. Further efforts to obtain high-precision dates would be most welcome. efforts obtain high-precision dates would be most welcome. 141 �I / :::: Most of of the the Sacred Sacred Heart Heart is is aa Most rather ordinary ordinary medium-grained medium-grained rather granite that that consists consists of of subequal subequal granite amountsof of quartz, quartz,oligoclase, oligoclase,and andKKamounts I '7 M —p \) c !'sA - - -- 8 - N , —_.) ))c ,J) - feldspar. It was quarried as dimension stone in an earlier era but is not being worked now. Although much of the rock mapped mappedas asSacred SacredHeart Heartisisquite quite rock uniform in in texture texture and andcomposition, composition, uniform thereare areparts partsof ofthe themass massthat thatdisplay display there '-'c.-zz C' quartzstronglygneissose gneissosefabric fabricand andquartzstrongly ° poor compositions compositions trending trending toward toward poor ) " ' monzonite. Some Somefeatures featuresindicative indicative monzonite of aa complex complex intrusive intrusive history history are are of displayedin in the the road roadcuts cutsatatthis thisstop. stop. displayed Featuresto tosee: see: Features • Massive, Massive,uniform uniformSacred SacredHeart HeartGranite Granite(road (roadcuts cutsabout about1,000 1,000ftftsouth southof of Middag MiddagKnutea). Knutea). • Gneissose Gneissosefabric fabriciningranite; granite;modal modaland andtextural texturallayering layering(SE (SEflank flankof ofMiddag MiddagKnutea). Knutea). • Monzonite Monzonitewith withpyroxene pyroxenegranulite granuliteinclusions. inclusions. ;Q I 'ci, tfl i U — I Drive DrivetotoStop Stop7—The 7-The bedrock bedrocksurface surfaceexposed exposedhere herewas wasexhumed exhumedby byGlacial GlacialRiver RiverWarren, Warren, however, however, significant erosion of fresh rock was not required to form form this smoothly smoothly undulating undulating bedrock bedrocksurface surfacewith with rounded rounded bedrock bedrock knobs and boulders. Such Suchsurfaces surfacescan can be formed simply by by the the removal removal of of deeply deeply weathered weathered bedrock. bedrock. Large Largerounded roundedboulders boulderswere werenot notshaped shapedduring during fluvial fluvial and and glacial glacial transport; transport; they they represent represent chemically chemically rounded corestones resting at or near their source. source. their Pre-Cretaceous weathering penetrated to an average depth of 30 m, but the rock, the fresh fresh rock/ of relief. Joints m weathered rock interface is irregular and undulates with as much as 45 Joints and and weathered rock interface is irregular and undulates with as much as 45 m fractures isolating fracturesare are preferentially preferentiallyexploited exploitedand andpenetrated penetratedto to depths depthsof of 60 60 m in places, locally isolating meter-sized volumes volumes of fresh fresh rock. The Therounded, rounded,fresh fresh rock rock remnants remnants are are known as corestones corestones and are are aa common common feature feature of of the theweathered weathered bedrock bedrock residuum residuum in in Minnesota Minnesota and and when when incorporated incorporated into into glacial glacialsediment, sediment,may may be be misinterpreted. misinterpreted. On Homme-Kollin Unit, Scientific Scientificand and Natural Natural On the south south side side of the road is Swedes Forest, Homme-Kollin Area. quarries that that are are hibernating hibernating Area. Its Itsmain mainscientific scientificsignificance significanceisisthat thatititisisthe the site site of several old quarries areas for the rare, blue-tailed lizards lizards and and "blue "blue devils"). devils"). They rare, five-lined five-lined skink (also called blue-tailed They prefer sunny woodlands. The sunny bedrock exposures near oak woodlands. The main main range range of of this this species species is is the the eastern eastern United United States Statesand andthese theseare arean anisolated isolatedpopulation. population. 142 �Stop7—Garnet-biotite-quartz-feldspar 7-Garnet-biotite-quartz-feldspar gneiss gneiss (Montevideo Gneiss). Granite Granite Falls quadrangle, quadrangle, Stop T. 115 N.-R. 39 W.-section W.-section 10AA. bAA. 115 N.-R. The Yellow Medicine Minnesota The Medicine shear zone (YMSZ), a major crustal structure structure within the Minnesota River Valley subprovince subprovince (Southwick (Southwick and and Chandler, Chandler, 1996), 1996),crosses crosses the the Minnesota MinnesotaRiver Riverabout about River two miles miles southeast southeast of here. The The shear shear zone zone rocks rocks do do not two crop out; out; the the zone zone was first recognized from geophysical geophysical crop recognized from mapping and and the existence existence of sheared sheared rock within within itit was mapping later verified verified through core drilling. The TheYMSZ YMSZ isisnow now later informally defined defined as as the the boundary between between the the Morton Morton informally Gneiss Gneiss (to (to the the south) south) and and the the Montevideo Montevideo Gneiss Gneiss (to (tothe the north). north). The The rock rock in the rubbly rubbly road road cuts cuts at at this this locality locality is is aa garnet-biotite-quartz-plagioclasegneiss, gneiss,aamappable mappablesubsubgarnet-biotite-quartz-plagioclase unit unit of of the the Montevideo Montevideo Gneiss Gneiss that that is is fairly fairly abundant abundant in in the (Himmelberg, 1968). the Granite Granite Falls area (Hirnmelberg, 1968). Lund Lund (1950) (1950) mapped mappeditit as as the Granite Granite Falls Falls garnetiferous garnetiferousquartz quartzdiorite diorite gneiss, aa name name that never caught on. The The protolith protolithof of the the gneiss, unit as a whole is not immediately apparent. Parts Parts of of itit unit are are quite quite aluminous, aluminous, suggestive suggestive of a sedimentary sedimentary origin, origin, and and other other parts parts are are very very feldspathic, feldspathic,at at least least locally locally suggestive suggestiveof of igneous igneous derivation. derivation. This This and and other other rock rock units units in in the the Granite Granite Falls Falls area area are are folded folded broadly broadly about about east-trending, east-trending, gently F2 structures. structures. gently east-plunging east-plungingaxes axes(Himmelberg, (Himmelberg,1968) 1968)that that Bauer Bauer (1980) (1980) interpreted interpreted as as F2 The Thecomplete completedeformational deformationalhistory historyinvolves involvesfour four folding foldingevents, events, which which Bauer Bauer (1980) (1980) discusses discusses in in detail. detail. Faults Faultsand andbrittle-ductile brittle-ductileshears shearsatatand andnear nearthe thesouth southedge edgeof of the the garnet garnet gneiss gneiss outcrop outcrop belt belt are are probably probably related related to to late late deformation deformationalong along the the nearby nearby YMSZ. There Therealso alsoisisscattered scattered evidence evidence of of earlier, earlier,more more deep-seated deep-seated shear sheardeformation deformationthat that may may have have been been related relatedto toearlier earlier YMSZ activity. YMSZ activity. Features Featuresto tosee: see: • Lithologic Lithologicvariations variationsin in the the gneiss. gneiss. • Late Lateshear shearzones. zones. • Rotational Rotationalstructures structuresindicative indicativeof ofductile ductileshear. shear. Stop Stop8—Granulite-facies 8-Granulite-facies mafic mafic and and pelitic pelitic gneiss gneiss (Montevideo (Montevideo Gneiss). Gneiss). Granite GraniteFalls Fallsquadrangle, quadrangle, T. 3BBD. T. 115 115N.-R. N.-R. 39 39W.-section W.-section 3BBD. Garnet-bearing Garnet-bearinggneiss gneisssimilar similarto tothat thatatatStop Stop77 is is in in contact contactwith withgranulite-grade granulite-grademafic maficgneiss gneiss(cpx(cpxopx-plag) opx-plag)in inthese theseroad road cuts. cuts.Small Smallamounts amountsof ofbiotite biotite in in the the granulite granulite may may record record retrograde retrograde rereequilibration. The garnet gneiss is quite micaceous equilibration. The garnet gneiss is quite micaceous and and well well layered, layered, and and has has been been regarded regarded as as aa metamorphosed metamorphosedsedimentary sedimentaryrock. rock.The Themafic maficgneiss gneiss may mayhave havebeen beenaabasalt basaltflow floworiginally, originally,although althoughother other mafic maficprotoliths protolithsare arecertainly certainlypossible. possible. 143 �Stop 9—Mafic 9-Mafic gneiss gneiss (Montevideo Gneiss). Shear Shear zones zones and pseudotachylite veins. Granite Granite Stop 4AAB. Falls quadrangle, quadrangle, T. T. 115 115 N.-R. 39 39 W.-section 4AAB. Shear structures in these outcrops have been studied by John Craddock and several of his Thefollowing followingsummary summary is is taken taken from from material material provided provided by by students at Macalester College. The John. Twenty-two discrete discrete shear zones have been Twenty-two found here that contain pseudotachylite seams. The The subparallel, trend 070 on on average, average, zones are subparallel, trend about about az. az. 070 and dip and dip subvertically. subvertically. This This orientation orientation is is approximately that of approximately of the the regional-scale regional-scale Yellow Yellow Medicine shear zone and several of the Proterozoic diabase dikes dikes in in the the area. Within diabase Within aa given given zone the individual pseudotachylite pseudotachylite seams seams (black) (black) are of individual diverse orientations. orientations. pseudotachylite matrix is compositionally compositionally The pseudotachylite layered and preserves preserves flow-foliation layered flow-foliation swirls swirlsand and relics relics of glass. Dextral Dextralwinged wingedporphyroclasts porphyroclastsin in the the pseudotachylite pseudotachylite preserve dextral and sinistral kinematic kinematic displacement, displacement, primarily primarily opposite opposite the the sinistral sinistral sense sense of of S-C S-C structures structuresin in the the country country rock and and of sinistral rock sinistral fault fault drag drag indicators indicators along the strike-slip strike-slip zones that contain the pseudotachylite seams. Seam-margin pseudotachylite seams. Seam-margin forking forking directions directions are are dominantly dominantly toward toward the the west; west; poryhyroclast imbrication imbrication within the pseudotachylite is dominantly dominantly up and easterly. pseudotachylite seams yield Calcite in veins that appear to be contemporaneous with the pseudotachylite twinning strains indicative indicative of zone-parallel and zone-normal horizontal shortening. Magnetic Magnetic pseudotachylite seams give Krnax Kmax subvertical, Krnin Kmin subhorizontal fabric meaurements on the pseudotachylite and zone-normal. zone-normal. IfIfthe themagnetic magneticfabric fabriccorrelates correlateswith withflow, flow, these these results results indicate indicate that the flow of pseudotachylite pseudotachylite glass glass was was upward upward within withinthe thezone zoneof ofshear. shear. Features Features to to see: see: • Discrete Discrete shear shearzones zones (many (many are are reddened). reddened). • Pseudotachylite Pseudotachyliteseams. seams. • Sense-of-shear Sense-of-shearindicators indicatorsin in shear shear zones. zones. Stop lO—Proterozoic Gneiss. Granite Stop 10ÑProterozoi "Section "Section 28" intrusion and wallrocks of Montevideo Gneiss. Granite Falls quadrangle, quadrangle,T. T. 116 116N.-R. 39 39 W.-section 28BCA. At this locality a small plug of Proterozoic granite is in complex contact contact with with a body body of hornblende hornblende andesite andesite (also (also Proterozoic). Proterozoic). Contacts Contactswith withthe the Montevideo Montevideogneiss gneiss are are not not exposed, exposed, but they can be mapped rather closely. closely. The The granite granite yields a zircon Pb-Pb age of 1825 1825 Ma (Catanzaro, 1963). 1963). The standard standard explanation explanation of of the the relationships relationships seen seen here is as follows: andesite. Dikes (1) The body of dark rock is a dike of hornblende andesite. Dikes of of this this composition composition occur elsewhere elsewhere in the the Granite Granite Falls area area (e.g., (e.g., Stop Stop 11). 11). (2) The granite intrudes the dike and thus is the younger rock, by classical geological reasoning. reasoning. contact relations relations necessarily necessarily imply imply the the interpretation interpretation outlined outlined Do we agree that the observed contact above? above? 144 �______ _______ Stop Gneiss,Proterozoic Proterozoic dikes dikes in inthe theYellow Yellow Medicine Medicine quarry quarry owned owned and an( Stop11—Montvideo 11- -MontvideoGneiss, 115N.-R. N.-R.39 39 operatedby bythe theMeridian MeridianAggregates AggregatesCompany. Company.Granite GraniteFalls Fallsquadrangle, quadrangle,T.T.115 operated W.-section W.-section 33BB. 33BB.Hard Hardhats hatsmust mustbebeworn worneverywhere everywhereon oncompany companyproperty. property. TheYellow Yellow Medicine Medicine quarry produces crushed stone, much of which which is is used used as as railroad railroad The ballast ballast for for the theBurlington Burlington Northern Northern Railroad. Railroad. Aggregate Aggregatefrom fromhere here isisused used on onrailroad railroadtracks tracks across acrossthe theDakotas Dakotasand andMontana Montanatotothe theRocky RockyMountain Mountainfront. front. The principal principal rock rock in in the the quarry quarry isis aa The granitic granitic gneiss gneiss composed composed of of quartz, quartz, plagioclase, microcline, microcline, and and biotite biotite that that isis plagioclase, modally layered layered on on various various scales. scales. Scattered Scattered modally withinititare areconformable conformablelenses lensesand and layers layersof of within hornblende-pyroxenegneiss. gneiss.This Thisgeneral generalrock rock homblende-pyroxene '' type is is the thecommonest commonest variant variant of of the the type MontevideoGneiss Gneissin in terms termsof ofmap maparea areaand and Montevideo D / essentiallythe therock rockexposed exposedup-river up-riveratatthe the isisessentially 33L4F "type locality" locality" outcrops outcrops near near the thetown town of of "type Montevideo. Samples Samplesof ofgneiss gneissfrom fromthe the Montevideo. quarry were were used used by by Goldich Goldich and andothers others quarry = (1980a, locality 4) 4) to to identify identifyaasequence sequence (1 980a, their locality ofRb-Sr Rb-Srisotopic isotopicevents eventsthat thatrange rangefrom from3,530 3,530 of toto2,265 2,265Ma. Ma.Various Variousinterpretations interpretationsofofthese these v' )\ ranité11s rriS I \ ) iriYfA 1ru • I I :11: E5!T 145 �I isotopic results results are are discussed discussed at at length length by the original authors. U-Pb zircon data reported for an isotopic "older" adamellite adarnelliteintrusion intrusioninto into the the layered layered gneiss gneiss yield an interpreted age of 3,230 3,230 Ma Ma (Goldich (Goldich and others, 1980a). others, 1980a). Dikes of of Proterozoic Proterozoic hornblende hornblende andesite andesite are are prominently prominently displayed displayed in in the the quarry quarrywalls. walls. Dikes all other other rocks rocks in in the the quarry quarry are are shot shot through through with chioritized, chloritized, slickensided, slickensided, brittle These and all shears on all all orientations. orientations.This Thistype typebrittle brittleshearing shearingand andassociated associatedevidence evidenceof ofhydrothermal hydrothermal shears activity (chlorite (chlorite films; films; calcite-quartz calcite-quartz veins) veins) are are associated associated with a pronounced reddening of the activity disseminated hematite. The Thereddening reddeningphenomenon phenomenon affects affects many many rocks, presumably due to disseminated MRV exposures exposures north north of of the the YMSZ YMSZ but is uncommon uncommon south south of it. it. END OF OF DAY DAY ONE. REFERENCES REFERENCES CITED CITED Bauer, R.L., 1980, 1980, Multiphase deformation in the Granite Granite Falls-Montevideo area, Minnesota River in Morey, Morey,G.B., G.B.,and andHanson, Hanson,G.N., G.N.,eds., eds.,Selected Selected studies studies ofkchean ofArchean gneisses River Valley, in gneisses and lower Proterozoic rocks in the southern Canadian Shield: Geological Society lower Proterozoic the southern Canadian Society of America America Special SpecialPaper Paper 182, 182,p. p. 1-17. 1-17. Catanzaro, southwestern Minnesota: Journal of Geophysical Geophysical Research, Catanzaro,E.J, E.J, 1963, 1963,Zircon Zircon ages ages in southwestern Research, v. 68, p. 2045-2048. 2045-2048. Goldich, Goldich, S.S., S.S., 1938, 1938,A A study study of of rock rock weathering: weathering:Journal Journalof of Geology, Geology,v. v. 46, 46, p. p. 17-56. 17-56. Goldich, S.S., and and Fischer, Fischer, L.B., L.B., 1986, 1986,Air-abraison Air-abraison experiments experiments in U-Pb U-Pb dating dating of ofzircon: zircon: Chemical ChemicalGeology, Geology, v. v. 58, 58, p. 195-215. 195-215. Goldich, J.B., and North, R.M., 1980a, Goldich, S.S., S.S., Hedge, Hedge, C.E., C.E., Stern, Stem,T.W., T.W., Wooden, J.L., Bodkin, J.B., 1980a, Archean rocks of of the the Granite GraniteFalls Falls area, area, southwestern southwestern Minnesota, Minnesota, in Morey, Morey, G.B., and Hanson, G.N., G.N., eds., eds., Selected Selected studies studies of of Archean genisses and lower Proterozoic rocks, southern southern Canadian Canadian Shield: Geological GeologicalSociety Societyof of America America Special Special Paper 182, 182, p. 19-43. 19-43. Goldich, Goldich, S.S., and and Wooden, J.L., 1980, 1980, Origin of the Morton Gneiss, southwestern southwestern Minnesota: Minnesota: Part Archean Part 3. Geochronology, Geochronology,ininMorey, Morey,G.B., G.B., and andHanson, Hanson,G.N., G.N., eds., eds., Selected Selectedstudies studiesof ofkchean gneisses and lower Proterozoic rocks, southern Canadian Shield: Geological Society of gneisses Canadian Shield: America America Special Special Paper Paper 182, 182,p. 77-94. 77-94. Goldich, Goldich,S.S., S.S., Wooden, Wooden,J.L., J.L.,Ankenbauer, Ankenbauer,G.A., G.A.,Jr., Jr., Levey, Levey, T.M., and Suda, Suda, R.U., 1980b, 1980b,Origin Origin of the Morton Morey, G.B., G.B., and and Morton Gneiss, Gneiss, southwestern Minnesota: Part Part 1. 1. Lithology, Lithology,ininMorey, Hanson, G.N., eds., eds., Selected Selected studies studies of of Archean Archean gneiss and lower lower Proterozoic Proterozoic rocks, southern southern Canadian Canadian Shield: Shield: Geological GeologicalSociety SocietyofofAmerica, America,Special SpecialPaper Paper182, 182,p.p.45-56. 45-56. Grant, Grant, J.A., J.A., 1972, 1972,Minnesota MinnesotaRiver RiverValley, Valley, southwestern southwestern Minnesota, Minnesota,in in Sims, Sims,P.K., P.K., and and Morey, Morey, G.B., eds., Geology of Minnesota: A A centennial centennial volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey, 177-196. p. 177-196. Grant, Grant, J.A., 1973, 1973,Phase Phase equilibria equilibriain in high-grade high-grade metamorphism metamorphism and partial melting of pelitic pelitic rocks: rocks: American American Journal Journalof of Science, Science,v. v. 273, 273, p. p. 289-317. 289-3 17. Hanson, G.N., 1968, 1968, K-Ar K-Ar ages ages for for hornblende hornblende from from granites granites and gneisses gneisses and and for for basaltic basaltic intrusives 20 p.p. intrusives in in Minnesota: Minnesota: Minnesota MinnesotaGeological GeologicalSurvey SurveyReport ReportofofInvestigations Investigations8,8,20 Hanson, Granite Falls, Minnesota: Minnesota: Hanson,G.N., G.N., and andHimmelberg, Himmelberg,G.R., G.R., 1967, 1967,Ages Ages of mafic mafic dikes near Granite Geological GeologicalSociety Societyof ofAmerica AmericaBulletin, Bulletin,v.v. 78, 78,p. p. 1429-1432. 1429-1432. 146 �G.R., 1968, Geology Geology of Precambrian rocks, Granite Granite Falls - Montevideo Himmelberg, G.R., Precambrian rocks, Montevideo area, area, southwestern Minnesota: Minnesota Geological Survey Special Publication Series Series SP-5, SP-5, 33 p. 33 Hoim, D.K., Holm, D.K., Darrah,K.S., Darrah,K.S., and and Lux, Lux, D.R., D.R., 1998, 1998,Evidence Evidencefor forwidespread widespread—1760 -1760 Ma metamorphism and rapid crustal stabilization of the Early Proterozoic (1870-1820 Proterozoic (1870-1820 Ma) Ma) Penokean orogen, orogen, Minnesota: Minnesota: American American Journal Journal of of Science, Science,v. v. 298. 298. p. p. 60-8 60-81. 1. Igneous and metamorphic rocks of the Minnesota Minnesota River River Valley: Valley: Unpublished Unpublished Lund, E.H., 1950, 1950, Igneous Minneapolis. Ph.D. dissertation, dissertation, University of Minnesota, Minneapolis. Valley: Geological Lund, E.H., 1956, 1956, Igneous Igneous and metamorphic rocks of the Minnesota River Valley: Geological Society Society of America Bulletin, Bulletin, v. 67, p. 1475-1490. 1475-1490. Moecher, D.P., ffi, Leier-Englehardt, Leier-Englehardt, P.J., and and Medaris, Medaris, L.G., L.G., Jr., Jr., 1986, Metamorphic Metamorphic Moecher, D.P., Perkins, D. in, conditions of late high-grade gneisses, conditions late Archean high-grade gneisses, Minnesota Minnesota River River valley, U.S.A.: Canadian Canadian Journal of Earth Journal Earth Sciences, Sciences,v. v. 23, 23, p. 633-645. 633-645. Perkins, D., ifi, in,and and Chipera, Chipera, S.J., S.J., 1985, 1985,Garnet-orthopyroxene-plagioclase-quartz Gmet-orthopyroxene-plagioclase-quartz barometry: Refinement and application to the English River subprovince and the Minnesota River Valley: Contributions to Mineralogy and Petrology, Petrology, v. 89, p. 69-80. 69-80. Southwick, D.L., and architecture of the Minnesota Minnesota Southwick, and Chandler, Chandler,V.C., V.C., 1996, Block and shear-zone architecture Valley subprovince: subprovince: Implications for Late Archean Archean accretionary accretionary tectonics: Canadian Canadian River Valley Journal of Earth v. 33, 33, p. 831-847. 831-847. Journal Earth Sciences, Sciences,v. 147 �I INTRODUCTION TO THE INTRODUCTION THE GLACIAL GLACIAL HISTORY OF OF THE THE MINNESOTA RIVER VALLEY Carrie Carrie J. Patterson Patterson Contrary to the four-fold devised around around the the turn of the century for four-fold glacial chronology devised terrestrial glacial sediments (Wisconsin, Illinoian, Kansan Kansan and and Nebraskan Nebraskan (Flint, 1957)), 195711, the current model for the Quaternary Quaternary record of glaciations is much more elaborate (Ruddiman and more elaborate Wright, 1987). 1987). The Theoxygen oxygenisotope isotoperecord record of of ocean ocean carbonate carbonate sediments sediments records records the the effects effects of glaciations. glaciations.During Duringglaciations, glaciations,160, 160,which whichisispreferentially preferentiallyevaporated evaporatedfrom from the the oceans oceans because because of it lesser mass, is stored enriching the glacial glacial oceans stored on land in the ice sheets, enriching oceansin in 180. 180. According to this record record of of global globalice icevolume, volume,there therewere were40 40glacial/interglacial glacialhnterglacialoscillations oscillationsinvolving involving moderate global Ma and and there therewere were22 22oscillations oscillations involving involving moderate global ice ice volumes volumes between 2.4 2.4 Ma and 0.9 Ma greater ice volumes from .9 Ma to the present present (Fig. (Fig. 3) 3) (Shackleton (Shackleton et et al., al., 1984). 1984). Counting back from our current oxygen isotope stage, stage 1, odd-numbered stages represent interglaciations interglaciations stages, glaciations. glaciations.Oxygen-isotope Oxygen-isotopestages stages2,2,6,12 and16 16show show the the greatest greatest and even-numbered even-numbered stages, 6, 12 and ice volumes, perhaps perhapsexplaining explainingthe the historical historical recognition of a four-fold record of terrestrial glaciation. glaciation. SPECMAP SPECMAP COMPOS!TE. COMPOSITE. 4 0.0 6180 6"0 (cr) (a) 0 2 —2 6"=0 ö'o (c) (a) 4 —4 0.0 • $_ 7 , $ —2 --4 7 10 0.5 0.5 a 2$-uz 1.0 0 2 25 1.0 1 .o - • 1.5 - 52 ' • 60 • 52 63 - Figure 3. Oxygen-isotope Oxygen-isotope profile derived from four cores (2 Atlantic Atlantic and 2 Pacific), Pacific), showing showing the the dominance dominance cores of the 41,000-year 41,000-year frequency before about 700,000 the 100,000-year 100,000-year frequency frequency after. after. Note years ago, and the the higher values values (and thus larger ice volumes) volumes) for 12, and and 16, 16,perhaps perhaps representing representing times times stages 2, 6, 12, when the Laurentide Laurentide ice sheet extended extended into the Great Lakes region and and beyond (from (from Williams Williams et et a!; al; 1988). 1988). Lakes data are compared compared with the the SPECMAP SPECMAP These data compilation compilation (Imbrie et al., 1984). 1984). . 2.0 148 . �oxygen-isotopestage stage 2 (the late Wisconsin7 During oxygen-isotope Wisconsin, retained retained from from the the former former chronology) chronology) and possibly possibly during during stages stages6, 6?12 12and and 16, 167Minnesota Minnesota was at the edge of an ice sheet that covered and most most of of Canada Canada (Fig. (Fig. 4). 4). thin7dynamic dynamic ice ice lobes lobes that that advanced, advanced?stagnated, stagnated?and and Minnesota was was affected affectedmainly mainly by by thin, Minnesota retreated independently independently of one another another (Wright, (Wright?1972). 1972). Ice-lobe Ice-lobedynamics dynamics were were controlled controlled by by retreated the mass mass balance balance and and bed conditions conditions of their respective icesheds. Owingto to the the different different substrates substrates the icesheds. Owing the ice ice flowed flowed over, over7it is possible possible to to distinguish distinguish the till of of the the different different ice ice lobes lobes using using matrix matrix color?texture texture and and mineralogy, mineralogy?and and clast clast lithology, lithology7and and thus thus reconstruct reconstructthe the activity activityof of the the lobes. lobes. color, few advances and aid in the reconstruction of the nature of ice ice Landforms remain for the last few advance advance and and retreat. retreat. Figure 4. Laurentide Laurentideice icesheet sheetatat14 14Ka. Ka. (Modified (Modifiedfrom fromDyke Dykeand andPrest, Prest?1986). 1986). Figure 4. Absolute dating dating of of the the late lateWisconsin Wisconsin glacial glacial sediments sediments is is possible possible using using radiocarbonradiocarbondating methods ifif organic organic remains remains are are found. found. Pre-late Pre-late Wisconsin units are difficult difficult to to date date absolutely Wright?1987). 1987). AAfew fewscattered scattereddates dateshave have been been secured securedin in the the area area absolutely (Ruddiman (Ruddiman and and Wright, using usingthe the presence presenceof of volcanic volcanicash ash (Richmond (Richmondand and Fullerton, Fullerton71986), 1986)?magnetic magneticreversals reversals preserved preserved in till and lake sediment (Patterson, 1993), amino-acid dating of shells (Gilbertson, 1990) and lake sediment (Patterson?1993)?amino-acid (Gilbertson71990) and cosmosgenic cosmosgenic isotope isotope age age estimates estimatesof of striated striatedrock rock surfaces surfaces(Bierman (Bierman et et al., al.?in in press). press). 149 �The basic stratigraphy stratigraphy was was described described by Matsch Matsch (1972). The history history of of work work in this area and the basic oldest glacial glacial sediment sediment in in southwestern southwestern Minnesota Minnesota is at least of mid-Pleistocene age age (Fig. (Fig. The oldest (Patterson,1997) 1997)and and may may even even be be of of Late Late PliocenefEarly Pliocene/Early Pleistocene Pleistoceneage age(2.1-1.2 (2.1-1.2 55 A and B) (Patterson, Ma) based based on on correlations correlations with glacial sediment in Ma) in Iowa Iowaand andNebraska Nebraska(Hallberg, (Hallberg,1986). 1986). These depositsare are attributed attributedto to northwest-sourced northwest-sourcedice iceadvances, advances,which which deposited depositedgray, gray, loam-to-clayloam-to-claydeposits loam tills tills containing containingclasts clasts of of Paleozoic Paleozoic carbonate carbonate and Cretaceous Cretaceous shale. There Thereare areatatleast leasttwo two loam tills tills of this age age that are are difficult diflicult to differentiate. Similar Similartills tills in South South Dakota are thought to be .6 Ma to 2.1 Ma (Gilbertson, 1990). (Gilbertson, 1990). / Figure 5. Ice Iceadvances advancesinto intothe the region. region. A. A.Early EarlyPleistocene Pleistoceneadvances, advances,greater greater that 0.6 Ma; B. B. Ice Ice Figure5. advance advance from from the northwest; C. C. Ice Ice advance advance from the northeast; D. D. Ice Iceadvance advancefrom fromthe thenorth, north, deposition 0-20 depositionof ofGranite GraniteFalls Fallstill till>40 >40ka; ka; E. E.Late LateWisconsin Wisconsinadvance advanceofofearly earlyDes DesMoine Moinelobe, lobe,330-20 ka; F. Late Wisconsin advance of the Des Moine lobe, 14 ka. (From Patterson, 1993). ka; F. Late Wisconsin advance of the Des Moine lobe, 14 ka. (From Patterson, 1993). 150 �Stratigraphicallyabove above these these gray gray tills tills is is aa northeast-sourced northeast-sourced glacial glacial sediment sediment(Fig. (Fig.5C) 5C) Stratigraphically that can can be be distinguished distinguishedby by its itsred-brown red-brown color, color, sandier sandier texture, texture, and and clasts clasts originating originating in in the the that Lake Superior Superiorarea area including including banded banded iron iron formation, formation, agate, agate, red Thisunit, unit, Lake red clastics clastics and and basalt. basalt. This the Hawk Creek till (Matsch, 1972) is only locally preserved and its southwestern extent is not the Hawk Creek till (Matsch, 1972) is only locally preserved and its southwestern extent is not known. ItItisisthought thoughtto tobe be >50 >50 ka ka (Gilbertson, (Gilbertson,1990). 1990). known. Thelast lastpre-late pre-lateWisconsin Wisconsinglacial glacial advance advancewas was from from the the north-northwest (Fig. 5D) 5D) and and is is The north-northwest (Fig. similarto to the theolder oldergray grayunits unitsbut but has has less less Cretaceous Cretaceousshale. shale.Wood Woodininthis, this,the theGranite GraniteFalls Fallstill, till, similar is A0,OOO years old (Matsch, 1972). is >40,000 years old (Matsch, 1972). The surficial surficial glacial glacial sediment sediment in in the the Minnesota Minnesota River River basin basin was was deposited deposited by by the the late late The Wisconsin Des Moines lobe, which advanced, stagnated and retreated repeatedly. Its first advance Wisconsin Des Moines lobe, which advanced, stagnated and retreated repeatedly. Its first advance may have have been been as as early early as as 30-20 30-20 ka ka (Fig. (Fig. 5E) 5E) (Gilbertson, (Gilbertson, 1990) 1990) The Theadvance advanceto to Des Des Moines, Moines, may Iowa is is dated dated at at 14 14ka ka (Fig. (Fig. SF) 5F) (Clayton (Clayton and 1982; Hallberg The Iowa and Moran, Moran, 1982; Hallberg and and Kemmis, Kenimis, 1986). 1986). The loam-textured till is gray when unoxidized and has Cretaceous shale and Paleozoic carbonate loam-textured till is gray when unoxidized and has Cretaceous shale and Paleozoic carbonate clasts.ItItgenerally generallycontains containsPierre PierreShale, Shale,whereas whereasthe theolder oldergray graytills tillscontain containother otherCretaceous Cretaceous clasts. formations such as the Greenhorn and Carlisle. The base of the Des Moines lobe till is locally locally formations such as the Greenhorn and Carlisle. The base of the Des Moines lobe till is marked by by aa planar planar concentration concentrationof offaceted, faceted,striated striatedboulders. boulders. marked GlacialLake LakeAgassiz Agassiz and and Glacial Glacial River River Warren Warren Glacial commonfor forlakes lakes to toform formin infront frontof ofaaretreating retreatingglacier, glacier, with with meltwater meltwater ponding ponding ItIt isiscommon between aa moraine moraine and and the the ice ice front. front. AAproglacial proglaciallake lakemay maynot notbe bevery verylarge large or or long-lived long-lived between because of the instability of the moraine dam and ice margin. However, an unusually stableand and because of the instability of the moraine dam and ice margin. However, an unusually stable large proglacial proglaciallake lakebegan began to to form form in in west-central west-central Minnesota Minnesota at approximately approximately12 12ka ka as as the theice ice large retreatednorth north of of the the Big Big Stone StoneMoraine Moraine and and the the nonspectacular nonspectacular continental continental divide divide at at Brown's Brown's retreated Valley (Fig. 6). Valley (Fig. 6). For much muchof ofits itsearly earlyhistory, history,Glacial GlacialLake LakeAgassiz Agassizwas wasdrained drainedby byGlacial GlacialRiver RiverWarren, Warren, For which flowed southeast from the southern tip of the lake (Upham, 1883, 1895; Matsch and which flowed southeast from the southern tip of the lake (Upham, 1883, 1895; Matsch and Wright, 1967). 1967). Initially Initially Glacial Glacial River Rver Warren Warren cut series of of anastomosing anastomosing channels channels with with Wright, cut aa series streamlined residual bars and boulder lags (Matsch, 1983). The style of channel formation streamlined residual bars and boulder lags (Matsch, 1983). The style of channel formation isis characteristicof ofsudden suddenand andlarge largedischarge dischargefrom fromaa lake lake that that overwhelms overwhelms the the existing existing drainage drainage characteristic system (Kehew (Kehew and and Lord, Lord, 1986). 1986). Flow Flowwas waseventually eventuallyfocused focused in inone onemain mainspillway spillwaywhich which system became more deeply incised, stranding earlier channels (Fig. 7). became more deeply incised, stranding earlier channels (Fig. 7). Continuedretreat retreatof ofthe theice icefront fronteventually eventuallyopened openedlower lower outlets outletsfor for Glacial GlacialLake Lake Agassiz Agassiz Continued to the northeast (Clayton, 1983) and possibly the northwest (Smith and Fisher, 1993) and to the northeast (Clayton, 1983) and possibly the northwest (Smith and Fisher, 1993) and Glacial Glacial River Warren was abandoned abandoned as as an an outlet. outlet. Tributaries Tributaries to to Glacial Glacial River River Warren, Warren, which which had had River steepened their their gradients gradients in in response response to tothe thedowncutting, downcutting,were were now now contributing contributingtoo toomuch much steepened sediment to be carried away by the reduced flow of the river. Fans spread across the valley floor sediment to be carried away by the reduced flow of the river. Fans spread across the valley floor partiallydamming dammingit,it,forming formingaaseries seriesof oflong longlakes lakes(Wright, (Wright,1972; 1972;1990) 1990)including includingLake LakeTraverse, Traverse, partially Big Stone Lake, Marsh Lake and Lac qui Parle. The levels of these lakes are now controlled by Big Stone Lake, Marsh Lake and Lac qui Parle. The levels of these lakes are now controlled by damsfor for recreation recreationand andflood floodabatement. abatement. dams Thefield fieldstops stopswill willfirst firstaddress addressthe the most most recent recent event event related related to to glaciation, glaciation,the the formation formation The of the the Minnesota MinnesotaRiver RiverValley, Valley, and then move move to to progressively progressively older older events events that that are are exposed exposed of because of of river river downcutting. downcutting. See Seeplate plate11(page (page168) 168)for forstop stoplocations. locations. because 151 �KM Figure Figure6. 6.Early Earlystages stagesofofGlacial Glaciallake lakeAgassiz. Agassiz.(Adapted (Adaptedfrom fromTeller, Teller,1987). 1987). 152 �pPpLrmw hf Hermanstage stagedownstream downstreamfrom fromOrtonville. Ortonville. Herman Thewide wideshallow shallowRiver RiverWarren Warren(in (inblack) black) The flowsacross acrossaaflat flatstretch stretchofoftopography, topography, flows "'i" around branching aroundislands islandsofofdrift. drift. r-d i—J 1 I I0 ost-Tintah stage downstream from rtonville. The auxiliary channels are bandoned as River Warren (in black) enches more deeply. A few islands, ome of bedrock, appear in the channel ownstream from Ortonville. 7 r-l- .-A resent valley. Alluviation by tributarie as segmented the valley abandoned by Warren into a series of long, shallow lakes, connected by the Minnesota River. r - Figure Figure 7.7.A.A.Initial Initialstages stagesofofdevelopment developmentof ofGlacial Glacial River Warren. Warren. B. B. Formation Formationofofmain mainriver rivertrenches. trenches. Abandoned Abandoned channels channels may may be be marked marked by river lags. C. C. Present-day Present-day Minnesota MinnesotaRiver River Valley. Reproduced Reproduced from from Matsch, Matsch, 1983. 1983. 153 �FIELD TRIP FIELD TRIPSTOPS—DAY STOPS-DAY 2 Stop 1—Ingebretsen's 1-Ingebretsen's Landing, Landing, or "the clay banks" on Lac qui Parle. Milanquadrangle, quadrangle, Stop Pane. Milan T. 119 42 W.-section 32 32 119 N.-R. 42 and low bank are formed in 2-3 m of reddish matrix has 43The beach and reddish brown brown till. till. The till matrix 48 percent sand and and the the clasts clasts have have aa northeastern northeastern provenance; provenance; you may find find Lake Lake Superior Superior clastic rocks on the beach. This Thiscolor, color,texture textureand and agates, banded iron formation, formation,basalt basalt and and red clastic agates, banded iron grain type are unusual for tills in this general area. area. This is not the surface till in the region but but is normally found deeper deeper in the glacial glacial section section and was exhumed by river downcutting. In places there are are remnants remnants of of another anothertill till overlying overlying this this red red till. till. It can be distinguished distinguished by its siltier northwest, including siltier texture texture and and clasts clasts typical typical of of an an ice ice advance advance from from the northwest, includingPaleozoic Paleozoic carbonate and Cretaceous Cretaceous shale. shale. discontinuous boulder A discontinuous boulder lag lag represents represents the erosional discontinuity created as Glacial River Warren, Agassiz, cut into the the glacial glacial sediments, sediments, selectively removing removing Warren, the spillway spillwayfor for Glacial Glacial Lake Lake Agassiz, the finer grains. The Thefollowing followingsections sectionsfrom from aa paper paper by Kehew Kehew and Lord (1986) describe the general formation of glacial-lake glacial-lake spiliways spillways (Fig. 8). The instability of the the spillway spillway rivers rivers was was exceptional; exceptional; torrential torrential discharges discharges no sediment from glacial-lake glacial-lake outlets, following following dam failure, had high energy and no load. Consequently, Consequently,flows flowswhich whichincised incisedspillways spillwayswere were highly highly erosive, erosive, and and channel channel sediment from these events is scarce. The The flood flood deposits deposits which do exist consist of homogeneous masses of very poorly sorted, pebbly homogeneous masses pebbly cobble cobble gravel, gravel, which indicates water. p. 165 rapid aggradation in very turbulent water. 165 154 �The morphological morphologicd characteristics characteristics of of spiliways. spillways....indicate indicate that the spiliways spillways were channels that that contained contained flow flow at at bankfull bankfull stage stage during during one one or more highly Thesize sizeof of the thespillways spillwaysqualitatively qualitatively demonstrates demonstrates that the the flood flood erosive floods. The discharges were enormous, and the estimated volumes of most proglacial proglacial lakes lakes (Kehew and Clayton, 1983) require that that bankfbll banklull discharges couldn't have been (Kehew sustained for more than aa few few weeks. weeks. In short, spiliways spillways in the the mid-continent mid-continent region geologically instantaneous instantaneous events of colossal colossal magnitude magnitude region were were incised incised by a few, geologically in comparison comparison to modern modern river discharges. p. 165 165 . At this location in Glacial Glacial River River Warren, two subparallel channels were incised rather than one main channel: channel: Lac Parleand andWatson Watson Sag. Sag. They Theyare areseparated separated by the erosional Lac qui qui Pale residual is located located on. on. According to Kehew and and Lord, Lord, (1986) (1986) erosional erosional residua1that the the town of Watson is residuals are key to identifying floods that overwhelmed existing drainage systems. residuals are identifying floods that overwhelmed existing drainage systems. organic horizon horizon associated associated with with the theboulder boulder lag. lag. A A silty silty lake lake sediment sediment In places there is an organic caps the section. The organic horizon and lake sediment may represent Glacial River section. The organic horizon and lake sediment may represent Glacial River Warren overbank deposits deposits or more recent overbank E X PP L AANAT N A T IION ON Holocene deposits. An examination examination of the organics of organics for pollen pollen to to determine their approximate determine approximate age age fihallow Channel before radiocarbon before radiocarbon dating was was considered yielded no identifiable considered yielded identifiable 9 Erosional Erosional Residual Residual grains. The bank The bank has has retreated significantly in recent years and the DNR-fisheries is planning to riprap Longitudinal it to prevent prevent further further retreat. retreat. Their Groove concern is that sediment loading of lake is negatively the negatively affecting affecting fish fish Boulder Lag habitat. habitat. Features to see: Features see: • Lake LakeSuperior Superioragates, agates, banded iron formation, basalt basalt and red elastic formation7 clastic rocks on the beach indicative indicative of a northeastern provenance provenance for the northeastern till. • Joints Joints in in till till with with narrow zones of reduced indicating reduced till indicating water water Figure 8. There Thereare are two two basic spillway levels: (1) (1) the movement along the joints. trench-like, channel; and (2) the trench-like, low sinuosity, inner channel; • Boulder lag and associated associated organic organic broad outer zone with: (a) slighity of slighlty scoured areas of honzon. horizon. channels; and anastamosing channels; and (b) (b) the the deeply deeply scoured scoured v / displays longitudinal longitudinal grooves, zone which displays grooves7streamlined erosional residuals residuals and and boulder boulder lags. lags. From erosional From Kehew Kehew and Lord (1986). (1986). 155 �Stop2—Glacial %Glacial Lake Lake Benson Benson sediment sediment exposed exposed along the Chippewa River. Bend City City Stop River. Big Bend quadrangle, T. T. 120 120N.-R. N.-R. 41 41 W-section W-section 36 36 Glacial Lake Lake Benson, a moraineGlacial morainedammed, 2800 sq km, proglacial lake in dammed, 2800 west-central Minnesota, formed formed during during the the west-central Minnesota, late Wisconsin Wisconsin retreat retreat of of the Des Moines lobe (Fig. 9). It was the last in a series of of retreated lakes before the Des Moines lobe retreated north of the divide to form form Glacial Glacial Lake Lake Agassiz (Diedrick and and Rust, Rust, 1975; 1975; Agassiz (Diedrick Patterson, Cotter Cotter and Knaeble, Patterson, Knaeble, 1998; 1998; Rittenour, Geiger and Cotter, Cotter, in prep.) Two-rn-thick exposures exposures of of lake Two-m-thick lake sediment Chippewa River in Swift sediment along along the Chippewa and Chippewa counties counties show show as many as 23 23 rhythmically bedded couplets interpreted as annual interpreted annual layers layers (varves) (varves) by Des Moines lobe till. In a underlain by series of undergraduate undergraduate and and NSF-sponsored NSF-sponsored for REU (Reseach (Reseach Experience supervised by Jim Undergraduates) studies studies supervised Cotter of University of Minnesota, Minnesota, Morris, Morris, students students have described described and counted counted varves at five five sites; 44 4 4 varves were were correlated correlated (Rittenour, (Rittenour, 1994; 1994;1995). 1995). exposure you will note that in some areas the beds beds are are overturned. overturned. We interpret interpret this In this exposure this as a result of the lake forming forming in an area where there was stagnant glacial ice which melted out, out, been deposited deposited in in a disrupting some of the beds. The Theupper, upper, massive massive silt and clay may have been shallower lake that was was unfavorable varve to development because the wave base base disturbed disturbed the the bottom bottom sediment. sediment. Features to see: see: • Difference in grain size of the winter and summer layers. • Upward decrease in thickness of summer layer indicating lessening sediment load and aid retreating glacier. retreating glacier. • Overturned beds. • Dropstones. Dropstones. • Nature of of contact contact with underlying Des Moines lobe lobe Figure 9. Approximate Approximateextent extent of of Glacial Glacial Lake Lake Benson till. till. (from Rittenour Rittenour et al., al., in in prep). prep). 1 156 �Stop 3—Ice-confined &Ice-confined streams. Montivideo Montivideo landfill landfill and nearby pits. Montevideo Montevideoquadrangle, quadrangle, Stop 117 N.-R. 40 W.-section 12; Asbury W.- section section 13 13and and T. T. T. 117 Asbury quadrangle, quadrangle, T. 1. 117 N.-R. N.-R. 40 40W.117 117 N.- R. R. 39 39 W.-section W.-section 33. 33. These These three three pits pits have have been been developed developed in in southeast-oriented, southeast-oriented?discontinuous discontinuousridges ridgesthat thatare are generally less less than than 77 m high. We We may may only only visit visit one one or two of the pits depending generally depending on the quality of the exposures exposures and time constraints. These transverse to them form These ridges ridges and others oriented transverse a rectilinear rectilinear pattern pattern that that is is common common in in the the interior interiorof of the the Des Des Moines Moines lobe. lobe. Ridges Ridges parallel to to ice ice flow, flow, and therefore to former ice surface surface slope, slope?are are predominantly predominantly composed of sorted sorted sediments. The Thetransverse transverse ridges ridges are are composed composed of sediment sediment ranging ranging from from diamicton to to sand sand and and gravel. gravel. Most Mostof of the thesampled sampledtransverse transverse ridges ridges were were only only slightly slightlycoarser coarser diamicton and more more sorted sorted than than the the underlying underlying and and surrounding surrounding till. till. ridges are result of The ridges are intepreted intepreted to to be be a result the pervasively pervasively crevassed crevassed deposition localized in the stagnant stagnant ice of the Des Des Moines Moines lobe lobe (Fig. (Fig. 10) 10) (Matsch, (Matsch, 1972; 1972; Patterson, Patterson?1997). 1997). Crevasses oriented oriented paralled paralled to to the the ice ice surface surface Crevasses slope were preferentially used by by supraglacial supraglacial streams. streams. Final melting melting of the ice ice walls walls of of the the streams inverted the the topography topography and left sorted sorted stream sediment sediment as a positive positive element element in in the the landscape. landscape. iceBenson outlets were were iceGlacial Lake Benson confined and the pits east and north of the landfill landfill are interpreted as part part of a late-stage interpreted as late-stage outlet of Glacial Lake northern pit, pit, well well Glacial Lake Benson. Benson. In the northern sorted sand is unconformably unconformably overlain by poorly sorted sorted pebbly pebbly sand which which has an an indistinct, indistinct, conformable contact with with the the overlying diamicton. This is is overlying diamicton. This interpretedas as steady steady discharge discharge interpreted followedby by aa larger, larger?short-lived followed short-lived discharge causing causing the the collapse collapse discharge of of stagnant stagnantice ice resulting resultingin inflow flow of diamicton into the channel. channel. Features Featuresto to see: see: • Climbing Climbingripples. ripples. • Uncollapsed Uncollapsedbeds beds indicating indicating no ice ice beneath beneath the the stream stream when when the sediments sediments were were deposited. deposited. 157 157 �Figure 10. 10. Heavily crevassed, postsurge Bering Glacier, surge ice surface surface of the Bering Glacier, Alaska. Photograph reproduced Photograph reproduced with with the the permission permission of of B. B. Molnia. Molnia. 158 �Stop4—Glacial &Glacial Stratigraphy, Stratigraphy,Upper UpperSioux SiouxAgency Agency State StatePark, Park, exposure exposureon on the theyellow Stop Yellow Medicine Medicine LoneTree TreeLake Lakequadrangle, quadrangle,T. T. 115 115 N.-R. 38 38 W.-section 30 River. Lone WARNING This is an unstable Be aware awareof of the the position position of others on the slope. Do not unstable outcrop. Be another person before digging digging or descending. descending. follow another personup upaagully. gully. Look Lookfor forpeople peoplebelow below you before Climbing up up is is easier easier than than getting getting down. down. Hardhats Hardhats are are recommended. If you chose not to climb around on this outcrop, samples of the till and and washed washed pebbles from the different different units will be provided for for viewing viewingon ontop topof ofthe thebluff. bluff. Do not step too close There are are rotational rotational slump slump blocks blocks waiting to descend; avoid close to to the the edge. edge. There becoming colluvium. colluvium. Nearly of glacial glacial sediment sediment is is exposured exposured along this meader bend of of the the Yellow Yellow Nearly 100 ft of Medicine River (Fig. 11). This This is almost almost the entire thickness of glacial glacial sediment at this this location. location. constructed from from waterwaterCross sections constructed well data show show the regolith regolith surface surface at at approximately immediate approximately 930 930 ft ft in the immediate just a few feet below the river area; this is just bed. bed. uppermost unit is a 2-3 m layer The uppermost of Des Moines lobe till. It accessible It is not accessible from this outcrop. Please do not Please do not try! try! There is aa discontinuous There discontinuous boulder boulder pavement pavement at the base of the Des Des Moines Moines lobe till. till. The boulders are faceted and and striated and and form form aa planar planar surface. surface. The The boulder pavement, although not continuous, is found at this stratigraphic stratigraphic position the position over over most most of of the interior of the I/i ,—ih,Des Moines lobe in Minnesota (Wright (Wright et et 1973). The Thefaceting facetingand andstriating striatinghad had to todevelop develop beneath beneath aa moving moving glacier glacier that did did not, not, al., 1973). however, however, have the shear stress to move move the theboulders boulders very very far farbecause becauseunderlying underlying beds beds are are generally generally not disturbed. Theboulders bouldersmay mayhave havebeen been concentrated concentratedat at the the surface surfacebefore before the glacier glacier overrode overrode disturbed. The them by water or periglacial processes. processes. Alternatively, some have proposed that the Alternatively, some have proposed that the boulder boulder concentration settling through an incompetent incompetent till matrix concentrationdeveloped developedsubglacially, subglacially, by large large clasts settling (Clark, 1991). 1991). The Theissue issueisisstill stillunresolved. unresolved. The exposure of the The next next unit unit is exposed exposed is is the the Granite Granite Falls Falls till. till. This may be an atypical exposure Granite Falls till; it is siltier than normal and layered layered with with sorted sorted sediment. sediment. Toward the base base of this unit, near near the the contact contact with with the the underlying underlying fine fine sand, sand, discrete discrete lobes of of diamict diamict can can be be recognized. These Thesefeatures featuresare areinterpreted interpretedas as the the result result of of flow flow of of the the till till into into standing standing water. water. This is a very plausible scenario given the unit immediately below which has been interpreted plausible scenario given unit which has been interpreted as a lake sediment. sediment. is mainly mainly aa fine fine sand sand with with silt silt and and some some clay. clay. In The unit interpreted as lake sediment is In places it is finely finely bedded. bedded. The Theextent extentof of the the lake lake sediment sediment beyond beyond this outcrop is not well 159 �Figure 11. 11. Yellow Yellow Medicine Medicine River River exposure exposure in Upper Sioux Sioux Agency State Park looking downriver. Photograph Photographby by Star Star Mulder known. From Fromthis thisexposure exposureitit appears appearsto to be be aarelatively relatively deep deep lake and therefore could have covered a large large area. area. Beneath the the lake lake sediment sedimentis a thick, gray loamy Beneath loamy till. till. Note the many well-striated Paleozoic Paleozoic carbonate clasts. clasts. The Thelower lowertill tillhas hasnot not been been well well exposed exposed here here but at other cuts along this river carbonate there are are two two gray tills tills separated separatedby aa glacial glacial stream stream sediment sediment at at this stratigraphic stratigraphicposition. Features Features to to see: see: • Striated, Striated,bullet-shaped bullet-shaped clasts clastsof of Paleozoic Paleozoic limestone limestonefrom from lower lower till. till. • Path Path of of groundwater groundwater flow through glacial units. Note Note areas areas of of lateral lateral flow. flow. • Contact of the Granite Falls till with underlying lake sediment. Contact of the Granite Falls till with underlying lake sediment. • Evidence Evidence for for depositional depositional environment environmentof of Granite GraniteFalls Falls till. • Boulder Boulder pavement pavement (from (from aa distance, distance,please). please). 160 �Stop5—Inge 5-Inge Kea's Kea's climbing climbingripples. ripples. Iverson IversonLake Lakequadrangle, quadrangle,T. T. 114 114 N.-R. 37 W.-section 23 Stop (this stop is out of stratigraphic stratigraphic order along the field trip route) located in an an This sand pit is located upper terrace along the Minnesota Minnesota The deep deep channel channel below us is River. The the Glacial Glacial River River Warren Warren part of the spillway. spillway. Glacial outwash outwash streams streams flowed from from the retreating retreating Des Des flowed Moines general area of Moines lobe lobe in the general Glacial Warren prior prior to its Glacial River River Warren formation. formation. This exposure is most most likely likely a remnant of an earlier earlier outwash stream. stream. The The depositional depositionalenvironment environment is distinctly different different from the first stop of the the day. day. Features to see: Variation in migration and migration and aggradationrates rates (angle (angle of climb). climb). aggradation Stop6—Rush &Rush River River Wayside; Deformation of Henderson quadrangle quadrangle T. 112 Stop of glacial glacial sediment. sediment. Henderson N.-R. 26W-section 15 The downcutting of this east-flowing east-flowing Minnesota River has exposed exposed tributary to the Minnesota glacial units glacial units that display display deformation deformation induced by the advance a glacier. induced by the advance a glacier. Mark Mark Johnson Johnson of Gustavus Gustavus Adolphus College has directed undergraduates from his school directed undergraduates from school and from an NSF-sponsored NSF-sponsored field program program in in work work on the details details of this outcrop outcrop (Fig. (Fig. 12). 12). The lowest lowest unit is a gray The gray loamy loamy till till and it is conformably conformably overlain by lake sediment, sediment, that, judging judging by the color, formed in front of the retreating, gray-till-bearing gray-till-bearing ice lobe. lobe. The gray lake sediment sediment grades into a red red layers. This sandy unit records sand with silt layers. the northeast. the advance advance of an ice lobe from the northeast. The next unit is a mixture of the underlying sand sand with with aa red red sandy sandyloam loamtill. till. There is a sharp contact between this and the final unit exposed, exposed, a homogenous red sandy till. Folds: The lower two units are folded into three anticlines anticlines that span the outcrop. outcrop. sand displays displays a subparallel subparallel series series of high-angle high-angle normal faults. faults. Faults: The red sand Faults: Fabric: The long axis of prolate pebbles in a till till are are commonly commonly measured measured and plotted plotted on Fabric: a Rose diagram. Pebbles Pebblesin in aa subglacial subglacialtill till may be oriented oriented by the the shear shear stress stress of the overriding overriding glacier; glacier; pebbles pebbles are are generally generally parallel parallel to to flow, flow, with a slight slight upsuggesting ice flow from from the the north-northeast. north-northeast. glacier dip. The The red red till till has a fabric suggesting 161 - ll rn �Si .5Z $2 .38 53 .10 SI .4 53 .44 53 .o Elgen Values Si .55 51 .5S 52 .38 SZ .31 53 .13 53 .0? * F,t Ta., • zs Mlyi Siiuple T.n w 0000 OlyL1y MSfldOnud RhvwO (rscxit) DdR.d Old Grey Grey EJ Hs$d LayW Leysre eI 1*. Sam.nts iiwougl.on — S Faà. Tp-.* sew Figure Figure12. 12.Structural Structuraldata datafor forRush RushRiver Riveroutcrop. outcrop.Unpublished Unpublishedwork workofofAmy AmyMoe, Moe,Gustavus Gustavus Adolphus AdolphusCollege Collegestudent, student,1996. 1996. 162 �Ouestion structural data consistent with the simple interpretation of proglacial deformation Is the structural and eventual overriding overriding by the advance of the the red-till-bearing red-till-bearing ice ice lobe lobe from from the the north-northeast north-northeast (Fig. (Fig. 13)? 13)? - p_se. — -.p mmmbwlI@ll .I—_ =-- V v - —_ V v Vv 1401 wt-mmma A. Advacing Advacing glacial glacial ice with attached frozen frozen-unfrozen substrate. Shear Shear forces forces along the frozen-unfrozen boundaryat boundaryat the base base of the slab slab initiate i ~ t i a t thrustthmste block movement. movement. —— \ • B. Thrusted Tbrustedsubglacial subglacialslabs slabs are are deformed deformed and attacked Snout. attacked at the the glaciers glaciers~ snout. C. Glacial Glacialice ice ovemdes ovenides the the thrust thrust slabs, causing more more deformation. deformation. 13. Sequence Sequenceof ofproglacial proglacialdeformation deformationA A and and B B with with eventual eventual overriding by Figure 13. advancing glacier glacier (from (fromAber, Aber, 1988). 1988). the advancing TERRACES THE MINNESOTA RIVER NEAR SHAKOPEE, SHAKOPEE,MINNESOTA MINNESOTA TERRACES ALONG THE Barbara Lusardi Lusardi The Minnesota Minnesota River River Valley near near Shakopee is almost almost 200 200 feet feet deep deep and and over over 33 miles miles wide wide in places. highlands on on either either side side of of the valley rise to an elevation places. Till highlands valley rise elevation of over 900 feet. Distinct terraces terraces step step down into into the valley where the undefiit across underfit Minnesota River meanders across a broad alluvial alluvial plain. based on on elevation. elevation. The Three terraces are distinguished based The uppermost uppermost terrace, terrace 3 (Qft3), is visible just to the the south south of of highway highway 169 169 between between Marschall Marschall Road and Marystown Marystown Terrace33 is is at at an an elevation elevation of about 850 feet-150 Road. Terrace feet—iSO feet feet above abovethe themodern modernfloodplain. floodplain. A distinct scarp separates the terrace from the till upland to the south, and smaller channel scars crisscross the surface "islands" above terrace above the level of terrace crisscross surface breaking breaking the the terrace terrace up into three small ''islands" thick over overbedrock. bedrock. Data from water 2 (Qft2). Alluvial Alluvial sediments sediments of of terrace terrace 3 are up to 40 feet thick well logs indicate that sand and gravel extends suggests that extends south beneath beneath the the till till upland. upland. This suggests the terrace sediments outwash deposits deposits that that have have been eroded eroded to form form the the terrace. terrace. sediments may may be be outwash follows the middle terrace, terrace, terrace terrace 2, 2, at atan anelevation elevationof ofapproximately approximately The new highway 169 169 follows feet—i 10 feet above the modern modern floodplain. Numerous 810 feet-1 Numerous shallow shallow channels crisscross the terrace surface. Alluvial Paleozoic bedrock. bedrock. Just south of Alluvial sediments sediments are are 10-50 10-50 feet thick over Paleozoic Shakopee, terrace miles wide. wide. It narrows to the southwest southwest and and eventually eventually disappears disappears Shakopee, terrace 2 is about 1.5 miles (Qftl) near Meniam. Many Manygravel gravel pit pit operations operations occur occur within sediments of against terrace 1 (Qftl) near Merriam. terrace 2 and and into into the the bedrock bedrock below. below. 163 �_ ___ 14. Terraces Terracesof ofthe theMinnesota MinnesotaRiver River Valley Valley near Shakopee and Chaska. Figure 14. ; \G1ajidepsits \i . ' ;7i / 2 / I :/ / ' Qf / ( / /_ /I * wa f -., — . SCALE 1:62 162500 SCALE 500 2 1/2 1 1 1 ~ (sand and gravel and till) i .. 3/4 — : I . }/' 1 / ... _,$7 I' - •— 1.1 — ikt j $ r — . L 1 . / . Lower terraces cut into glacial p- sediments and bedrock I .. : I 1 KILOMmER KILOMETER preserved as terraces above the floodplain of the modern Minnesota River Highest terrace cut into glacial sediments Z / I 0 : ALLUVIAL TERRACES—Cilacial River Warren sediments - / -.. U 11MILE MILE 0 5 .5 H - 1 Qft3 Alluvium of Terrace 3—Elevation —850 ft 150 ft (46 m) above present floodplain Silty loam to sandy loam (fine grained in shallow channels) grading into loamy shale; increasing percentage of gravel with depth. Qft2 above present floodplain Loam to sandy loam (fine grained in shallow channels) 1 2mm coarse sand than 1 percent percent shale; shale increasing fraction contains less than percentage of gravel with depth Qftl Alluvium of Terrace 1—Elevation 750 ft 50 ft (15 m) above present floodplain Variable thickness of predominantly medium to coarse coarse sand. sand. 1 / c I 1 / GLACIAL DEPOSITS—Sediment deposited by the Des / Moines lobe Contains abundant shale fragments .- 1 PALEOZOIC BEDROCK—Prairie du Chien dolostone and Jordan Sandstone mapped within 10 feet of surface. L This map consists of portions of the Shakopee and Jordan East 7.5-minute quadrangles that have been modified and reduced in scale Linework and descriptions are taken from Lusardi (1997) and Lusardi (in prep). Hennepin I Carver ---I)ak ota Scott L -Dig ram Location Digram I@ 164 �The lowest lowest terrace terrace is is at at an elevation elevation of approximately 750 feet—50 feet-50 feet feet above above the the modern modern The approximately 750 floodplain. In Inmany manyplaces places the the underlying underlying bedrock is at or near the Ordovician Prairie Prairie floodplain. the surface. surface. Ordovician du Chien dolostone is the principal source for crushed stone. Cambrian Cambrian Jordan Jordan Sandstone Sandstoneisis exposed limited areas just west exposed in limited areas near Merriam and Baden. The The only only known sandstone sandstone quarry, just of Baden, Baden, is is now now abandoned. abandoned. On the opposite terraces are narrow narrow or or obscured. obscured. Just northeast opposite side of the river, the terraces northeast of Chaska, sediments sediments of terrace terrace 11 are are buried by colluvial sediments eroded from from the the valley valley wall. Chaska, small remnants remnants of this this lowest lowest terrace terrace are visible above the floodplain. Terrace22 is is present present Only small floodplain. Terrace 114 mile as a very narrow strip, less than 1/4 mile wide, wide, between between Chaska Chaska and and Carver. Carver. Terrace 3 is is present present south of Chaska dramatically south south of Carver. Sand Sandat at the the same same elevation elevation of of terrace terrace south Chaska and widens dramatically 3 continues to the south south in aa band band almost almost 2.5 2.5 miles miles wide wide along along the the river, river, although although no no distinct distinct scarp is obvious. Unlikethe the other other terrace terracesurfaces, surfaces, this this area is pitted and channeled, scarp obvious. Unlike channeled, and may be related to to an an earlier earlier flood flood event. Similarly, Similarly,thick thick sand sand buried buried by 50-100 50-100feet feetof of glacial glacialtill till on on the the related north side side of of the the valley, valley, north north of of Shakopee, Shakopee, suggests suggests that that the the river river valley valley at at one one time timeextended extended north further further to the the north. The Thesand sandwas wascovered coveredby by glacial glacial sediment sediment during during the the last last glacial glacial advance advance and was never re-excavated re-excavated by subsequent subsequent floods. floods. REFERENCES WFEWNCES CITED CITED Aber J.S., 1988, 1988, Structural Structural geology exercises with glaciotetonic examples: WinstonSalem, 1-84. Salem, North North Carolina, Carolina,Hunter HunterTextbooks, Textbooks,p.p.881-84. Bierman, Bierman,P.R., P.R., Marsella, Marsella, K.A., K.A., Patterson, Patterson, C., C.,Davis, Davis,P.T., P.T., Caffee, M., in press, press, MidMidPleistocene Pleistocenecosmogenic cosmogenicminimum-age minimum-agelimits limitsfor for pre-Wisconsinan pre-Wisconsinan glacial glacialsurfaces surfacesin in southwestern southwestern Minnesota Minnesota and and southern southern Baffin Island—a Island-a multiple nuclide nuclide approach: approach: Geomorphology. Geomorphology. Clark, pavements: Products Clark, P.U., P.U., 1991, Striated clast pavements: Products of deforming subglacial subglacial sediment? sediment? Geology, Geology, v. v. 19, 19,p. p. 530-533. 530-533. Clayton, Clayton, Lee, Lee, 1983, 1983,Chronology Chronologyof ofLake LakeAgassiz Agassizdrainage drainagetotoLake LakeSuperior, Superior,ininTeller, Teller, J.T., and Clayton, Lee, eds., Glacial Lake Agassiz: Agassiz: Geological Association of Canada Special 1-307. 291-307. SpecialPaper Paper26, 26,p.p.29 Clayton, Clayton, L., and and Moran, Moran, S.R., S.R., 1982, 1982,Chronology Chronology of of late late Wisconsin Wisconsin glaciation glaciation in in middle middle North America: Quaternary QuaternaryScience ScienceReviews, Reviews,v.v. 1,1,p. p. 55-82. 55-82. Diedrick, Diedrick,R.T., R.T., and and Rust, Rust, R.H., R.H., 1975, 1975,Glacial Glaciallake lake evidence evidencein in western western Minnesota Minnesotaas as interpreted interpreted from from the the soil soil survey: Journal Journalof of the the Minnesota Minnesota Academy Academy of Science, Science, v. v. 41, 9-12. p. 9-12. Dyke Dyke A.S., and and Prest, Prest, V.K., V.K., 1986, 1986, Paleogeography Paleogeography of northern northern North North America, America, 18,00018,0005000 5000 years years ago: ago: Geological GeologicalSurvey Surveyof ofCanada CanadaMap Map1703A, 1703A,scale scale1:12,500,000. 1:12,500,000. Flint, Flint, R.F., R.F., 1957, 1957, Glacial Glacial and and Pleistocene Pleistocenegeology: geology: New NewYork, York, John John Wiley and Sons, Sons, 553 553 p. p. Gilbertson, Gilbertson,J.P., J.P., 1990, 1990, Quaternary Quaternary geology along along the eastern flank flank of the Coteau Coteau des des Prairies, Prairies, Grant Grant County, County, South Dakota: Unpublished UnpublishedM.S. M.S. thesis, thesis, Univeristy Univeristy of of Minnesota, Duluth, 108 p. Minnesota, Duluth, 108 p. Hallberg, Hallberg, G.R., G.R., 1986, 1986,Pre-Wisconsin Pre-Wisconsin glacial glacial stratigraphy stratigraphy of of the the central central plains plains region region in in Iowa, Iowa, Nebraksa, Kansas, Kansas, and Missouri: Missouri: Quaternary QuaternaryScience ScienceReviews, Reviews, v. v. 5, 5, p. 11-15. 11- 15. 165 i m-' �Hallberg, G.R., and and KenuTlis, Kemmis, T.J., glacial T.J., 1986, Stratigraphy Stratigraphy and correlation of the glacial deposits of the Des Moines and James lobes and adjacent areas in North Dakota, Minnesota,and and Iowa: Iowa: Quaternary QuaternaryScience ScienceReviews, Reviews,v. v. 5, 5, p. 65-68. 65-68. Minnesota, Imbrie, J., and and others, others, 1984, 1984,The The orbital orbital theory of Pleistocene climate; climate; Support Support from from aa Imbrie, n Berger, A.L., the marine marine 8 8 0 record, iin revised chronology of the A.L., and others, eds., Boston,Mass., Mass., D. D. Reidel, Reidel, p. p. 269-305. 269-305. Milankovitch and climate: Boston, 1986, Origin and large-scale erosional features of glacialKehew A.E., and Lord, M.L., 1986, lake spillways spillways in the northern Great Plains: Geological Society of America Bulletin 97, p. 162-177. 162-177. Lusardi, B.A., 1997, quadrangle: Carver, Scott, and 1997?Surficial geology of the Shakopee quadrangle: Counties?Minnesota: Minnesota MinnesotaGeological Geological Survey Survey Open-File Open-File Report Report 97-6, 97-6? Hennepin Counties, scale scale 1:24,000. 1:24,000. of the the Jordan Jordan East East quadrangle: quadrangle: Scott Lusardi, B.A., in prep., Surficial geology of Scott County, County7 Minnesota: Minnesota Geological Survey, scale 1:24,000. Minnesota: Minnesota Geological Survev. scale 1:24.000. " geology Minnesota, in Matsch, C.L., 1972, 1972, Quaternary gec )logy of southwestern Minnesota, in Sims, Sinns, P.K. and nK:....-"-+,.. A ...:-I -.-I..--. nK:-* Morey, G.B, G.B, eds., eds., Geology Geology of of lvuuuc>uLa. Minnesota: fi A centennial volume: Minnesota Geological LCLILCIIIIW V U ~ U I I I G . 1~111111esota Geological Survey, Survey?p. 548-560. 548-560. Matsch, C.L., 1983, 1983,River River Warren, the southern southern outlet outlet of Glacial Glacial Lake Lake Agassiz, Agassiz, in in Teller, Teller, J.T., and Clayton, Lee, eds.? eds., Glacial Lake Lake Agassiz: Agassiz: Geological Association Association of of Canada Canada J.T., Special Special Paper 26, p. 231-244. C.J., 1993. Mapping Patterson, C.J., Mappingglacial glacialterrain, terrain, southwestern southwestern Minnesota, Minnesota, U.S.A., U.S.A.7 in J.S., ed., Glaciotectonics Aber, J.S., Glaciotectonicsand and mapping mapping glacial glacial deposits: deposits: Regina, Saskatchewan, Saskaichewan, University of Regina, Regina, Canadian Canadian Plains Plains Research Research Center, Center, p. p. 155-176. 155-176. Patterson, C.J., 1997, 1997, Quaternary Quaternary geology geology of southwestern Minnesota, in Patterson, C.J., Contributions to the geology Contributions geology of southwestern southwestern Minnesota: Minnesota Geological Geological Survey Report Report of Investigations Investigations 47, 47?p. 1-45. 1-45. Patterson, Patterson, C.J., C.J., Cotter, Cotter,J.F.P., J.F.P., and Knaeble, Knaeble?A.R., 1998, 1998, Des Moines lobe advanced advanced into into Glacial Lake Benson to form the Big Stone Stone Moraine, Moraine?west-central Minnesota: Geological Society Geological Society of of America America Abstracts Abstracts with Program, Program, v. v. 30, 30, no. 2, p. 66-67. 66-67. Richmond, Richmond, G.M., and and Fullerton, Fullerton,D.S., D.S., 1986, 1986,An introduction introduction to Quaternary Quaternary glaciations glaciations in in the the United States States of America: America: Quaternary Quaternary Science Science Reviews, Reviews, v. v. 5, 5, p. 3-10. 3-10. Rittenour, T.M., 1994, 1994, Lacustrine Lacustrinedeposits depositsin in the the Minnesota MinnesotaRiver River Valley, Valley, west-central Minnesota; evidence for Glacial Lake Benson? Abstracts Abstractswith with Program, Program, 5th 5thAnnual Annual Minnesota; evidence Argonne Symposium Symposium for Undergraduates Undergraduates in Science, Science, p. 102. 102. 1995, Strand lines and lacustrine lacustrine deposits deposits in in the the Minnesota Minnesota River River Valley, Valley? Rittenour, T.M, 1995, Benson exist? exist? Geological Society west central Minnesota; Minnesota: Did Glacial Lake Benson Society of America no. 3, 3, p. 82. 82. An 2l7?no. ierica Abstracts Abstracts with with Programs, Programs, v. v. 27, Rittenour, Geiger, K.L., K.L., and Cotter, J.J.F.P., prep., Evidence Evidence for Glacial Lake Lake Benson, F.P., ininprep., r, T.M., Geiger? Rittenou -+ ..-I XK:....--..+,. L. Dn++a..nAwest-central in W ~ ~ L - L G I I Minnesota, ~ LVLU ~ U EJ W L ~ , w Patterson, =UUWU,C. C. J., ed., Contributions to the Quaternary geology of Minnesota: Minnesota MinnesotaGeological Geological Survey Survey Report of Investigations 49. d d 166 , �Ruddiman, W.F., and Wright, 1, in Ruddiman, W.F., and Wright, H.E., H.E., Jr., 1987, Introduction, Chap. 1, Ruddiman, W.F., H.E., Jr., Jr., eds., North America and the adjacent oceans during the last Wright, H.E., Wright, TheGeology Geologyof ofNorth NorthAmerica, America, volume volume K-3, Geological Geological Society Society of deglaciation: The America, America, p. p. 1-12. 1-12. Shackelton, N.J., and and others, others, 1984, 1984,Oxygen Oxygen isotope isotope calibration calibrationof of the the onset onset of of ice-rafting ice-raftingand and Shackelton, history of glaciation region: Nature, glaciation in the North Atlantic region: Nature, v. v. 307, p. 216-219. 216-219. Smith, D.G., and and Fisher, T.G., 1993, 1993, Glacial Lake Agassiz: The The northwestern northwestern outlet outletand and Smith, paleoflood: paleoflood: Geology, Geology,v. v. 21, 21, p. p. 9-12. 9-12. Teller, J.T., J.T., 1987, Proglacial lakes and the southern margin of of the Laurentide Laurentide Ice Sheet. Ch. Ch. 3, in Ruddiman, Ruddiman,W.F., W.F., and Wright, H.E., Jr., eds, North America and the adjacent adjacent 3, in oceans oceans during during the the last last deglaciation: deglaciation: The TheGeology GeologyofofNorth NorthAmerica, America,volume volumeK-3, K-3, Geological GeologicalSociety Societyof of America, America, p. p. 39-69. 39-69. Upham, Upham, Warren, 1883, 1883, The The Minnesota Minnesota valley valley in in the the ice ice age: age: American American Association Association for forthe the Advancement 1. Advancementof of Science ScienceProceedings, Proceedings,v.v.32, 32,p.p.213-23 213-231. Upham, Agassiz: U.S. Upharn, Warren, 1895, 1895, The Glacial Lake Agassiz: U.S. Geological Geological Survey Survey Monograph Monograph25, 25, 658 p. Williams, Thunell, R.C., Tappa, E., Rio, D., and Raffi, I., 1988, 1988, Chronology Chronology of of the the Williams, F.F., F.F., Thunell, Pleistocene Pleistocene oxygen isotope record: 0-1.88 0-1.88 my. my. B.P.: B.P.: Paleogeography, Paleogeography, Paleoclimatology, Paleoclimatology, Paleoecology, Paleoecology, v. 64, no. 3-4, p. 221-240. Wright, in Sims, Sims,P.K., P.K., and Morey, G.B., Wright, H.E., H.E., Jr, Jr, 1972, 1972,Quaternary Quaternary history history of of Minnesota, Minnesota, in eds., Geology of Minnesota: A centennial volume: Minnesota eds., Geology Minnesota: A centennial MinnesotaGeological GeologicalSurvey, Survey, p.515-547. p.515-547. Wright, Jr. 1990, 1990,Geologic Geologichistory history of of Minnesota Minnesota rivers: rivers: Minnesota Minnesota Geological GeologicalSurvey Survey Wright, H.E., H.E., Jr. Educational 20 p. EducationalSeries SeriesNo. No. 7, 7,20 p. Wright, E.J., 1973. Superior in Wright, H.E., Jr., Matsch, Matsch, C.L., and Cushing, E.J., Superiorand and Des Des Moines Moines lobes, lobes, in Black, H.B., eds., The Wisconsinan Black, R.F., R.F., Goldthwait, Goldthwait,R.P., R.P., and Whillman, H.B., Wisconsinanstage: stage: Geological GeologicalSociety Societyof ofAmerica AmericaMemoir Memoir136, 136,p.p.153-185. 153-185. 167 i m- �..:. '(1 \'' \\\(\ Ir Plate Plate 1. 1. Preliminary Preliminarysurficial surficialgeologic geologicmap mapof of the theupper upper Minnesota Minnesota River River basin showing showing stop locations. locations. 168 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1998 Description An account of the resource Institute on Lake Superior Geology. Minneapolis, Minnesota. May 6-10, 1998. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1998 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/9660caf940f66fd29e7fe32eae6eae00.pdf 6d73e78d6c61bec84aba951e925d06e6 PDF Text Text ~ake Institute on Lake Superior Geology 45th 45th Annual Annual Meeting Meeting Ramada mi Ramada IInn Marquette, Maquette, Michigan Michigan 1999 May 4-8, 4-8, 1999 Sponsored Sponsoredby Northern Northern Michigan Michigan University and University and Michigan Michigan Technological Technological University Proceedings Volume 45: Program and Abstracts Robert S. Regis and Theodore J. Bornhorst, editors �45TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Volume Volume 45 consists of Pan 1: Program Partl: Programand andAbstracts Abstracts Pan Part2: 2: Field FieldTrip TripGuidebook Guidebook Reference to material material in this this volume should should follow follow the the example example below: Ams, Arns, D. and Hoim, Holm, D., 1999, 1999, Characterization Characterization and timing constraints constraints of post-Penokean post-Penokean meso-scale structures in the Watersmeet and Republic gneiss domes structures domes of northern northern Michigan (abst.): Institute Instituteon on Lake Lake Superior Superior Geology Proceedings, 45th Annual Meeting, Marquette, Marquette,MI, MLv.v.45, part 1,I, p. p.2. 2. 45, pan distributed by Volume Volume 45 45 Published Published and distributed by Institute Institute on Lake Lake Superior SuperiorGeology Geology Mark Jirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer,I.L.S.G. I.L.S.G. Minneosta Minneosta Geological Geological Survey Survey 2642 University University Avenue Avenue St. Paul, MN USA USA 55114-1057 551 14-1057 (612)-627-4780 (61 2)-627-4780 email: jirsaOOl jirsaOOl@tc.umn.edu @tc.umn.edu ILSG websitehttp://www.eeo.mtu.edu/ereat http://www.geo.mtu.edu/great lakes/ilsg/ ILSG website lakes/Us$ ISSN 1042-9964 1042-9964 All volumes are are available available for photocopying costs All costs from Michigan Technological TechnologicalUniversity UniversityLibrary Library Archives �INSTITUTE ON LAKE SUPERIOR GEOLOGY PROCEEDINGS Volume 45 AND ABSTRACTS ABSTRACTS Part 1: 1 :PROGRAM PROGRAM AND *~ ~ ~ .- .> . . .. . -.. . ... ~, . .. .. .~ , , 1 !; ! I Editors: Robert S. Regis and Theodore Theodore J. J. Bornhorst Bornhorst Editors: �CONTENTS CONTENTS PROCEEDINGS VOLUME VOLUME 45 45 PROCEEDINGS ABSTRACTS PART 1 1 -- PROGRAM PART PROGRAM AND ABSTRACTS Editors: Robert S. Regis and Theodore Theodore J. J. Bornhorst Bomhorst Institutes Institutes on on Lake Lake Superior SuperiorGeology Geology to to 1955-99 1955-99......................................... Constitution Constitution of of the the Institute Institute on on Lake Lake Superior Superior Geology Geology...................................... ii iii By-Laws BY-Lawsof of the the Institute Institute on on Lake Lake Superior Superior Geology Geology ..........................................................iii iv Goldich Goldich Medal Medal Guidelines Guidelines ................................................................................................. iv Goldich Goldich Medal Medal Committee Committee.................................................................. .................v Past Goldich Past Goldich Medalists Medalists ......................................................... vi ................vi 1999 Goldich Goldich Medal Medal Recipient 1999 Recipient ............................. ....................... VIvi .. vii ............vll Citation Citation for for 1999 1999Goldich Goldich Medal Medal Recipient Recipient ............. Student Paper Paper Awards Student Awards .................................................................. ........ ... Viii .............vlll ... Student Student Paper Paper Awards Awards Committee Committee ...................................................................................~Viff 111 Student Travel Travel Award Student Award ......................................................................................... Student Travel Travel Award Student Award Application Application Form Form ............................................................ ........ ix IX. . ix ix Board of of Directors Directors ............................................................................................................... xx Board x Local Local Committees Committees ...............................................................................................................x xi Banquet Banquet Speaker Speaker................................................................................................................. xi xii Report of the Chair Chair of the the 44th 44th Annual Annual Institute Institute ...............................................................xii Program Program xv ............................................................................................................................ xv Abstracts ....................................................................................................................... 1 Abstracts �INSTITUTE ON LAKE SUPERIOR GEOLOGY DATE PLACE CHAIRS 4 1955 1956 1957 1958 5 1959 6 1960 7 8 1961 Minneapolis, Minnesota Minneapolis, Minnesota Houghton. Michigan Houghton, East Lansing, Lansing, Michigan Michigan East Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Madison. Port Arthur, Arthur. Ontario Houghton. Michigan Houghton, Duluth, Minnesota Ishpeming, Michigan Ishpeming, Michigan St. Paul, Minnesota Marie. Michigan Sault Ste. Marie, East Lansing. Michigan Superior. Wisconsin Superior, Wisconsin Oshkosh, Wisconsin Oshkosh. Thunder Bay. Ontario Thunder Duluth, Minnesota Duluth. Houghton. Michigan Madison, Wisconsin Madison. Marie, Ontario Sault Ste. Marie. Marquette. Michigan Paul. Minnesota St. Paul, Thunder Bay. Bay. Ontario Ontario Milwaukee. Wisconsin Milwaukee. Duluth. Minnesota Duluth, Eau Claire. Wisconsin East Lansing. Michigan Falls, Minnesota International Falls. Houghton. Michigan Wausau. Wisconsin Wausau. Kenora. Ontario Ontario Kenora, Wisconsin Rapids. Wisconsin Wisconsin Wawa, Ontario Marquette, Michigan Marquette. Duluth, Minnesota Thunder Bay, Bay. Ontario Thunder Eau Claire. Claire, Wisconsin Eau Hurley, Wisconsin Eveleth. Minnesota Eveleth, Houghton, Michigan Houghton. Michigan Marathon, Ontario Marathon. Cable, Wisconsin Sudbury. Ontario Minneapolis, Minnesota Marquette, Michigan C.E. Dutton . . . AK. Snelgrove A.K. Snelgrove B.T. Sandeflir Sandefur R.W. Marsden R.W. E.N. Cameron & & R.A. Hoppin E.N. E.N. Cameron E.N. E.G. Pye E.G. A.K. Snelerove Snelgrove *,. . A.K. H. L Lepp H. ~PP A.T. Broderick A.T. P.K. Sims & & R.K. R.K. Hogberg P.K. R.W. White R.W. W.J. Hinze A.B. A.B. Dickas G.L. G.L. LaBerge M.W. Bartley & E. Mercy Bardey & D.M. Davidson D.M. J. Kafliokoski Kalliokoski M.E. Ostrom Osuom P.E. Giblin P.E. J.D. Hughes M. Walton M.M. Kehlenbeck M.M. C. Mursky G. D.M. Davidson i-'fr ' D.M. P.E. Myers P.E. W.C. Cambray W.C. DL. Southwick D.L. Southwick T.J. Bornhorst T.J. Bomhorst -' -st CL. LaBerge G.L. LaBerge CE. Blackburn C.E. Blackburn J.K. Greenberg J.K. E.D. Prey Frey & R.P. R.P. Sage E.D. J. S. Klasner .J.C. Green Green J.C. M.M. Kehlenbeck M.M. P.E. Meyers P.E. A.B. Dickas Dickas A.B. DL. Southwick D.L. Southwick T.J. Bornhorst Bomhorst M.C. Smyk M.C. L.G. Woodruff L.G. R.P. Sage & W. Meyer R.P.Sage&W.Meyer J.D. Miller Miller & M.A. M.A. Jirsa ursa J.D. T.J. Bornhorst Bomhorst & & R.S. Regis Regis INSTITUTE NUMBER INSTITUTE NUMBER 1 2 3 9 10 11 12 13 14 15 16 17 18 19 20 2] 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 t982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 ~--., �CONSTITUTION OF OF INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY CONSTITUTION Article Article II Name Nams The be the the "Institute "Institute on onLake LakeSuperior SuperiorGeology". Geology. The name of the organization shall be Article I IIl Article Article IU III Article Objectives Obiectlves The objectives objectives of of this organization organization are: are: geologists in in the the Great Great Lakes Lakes region region may may exchange exchange ideas ideas and and A. To provide a means whereby geologists scientific data. scientific data. B. Superior region. B. To promote better understanding understanding of the geology of the Lake Superior C. To plan plan and conduct C. To conduct geological geological field trips. Status Sam? No part of to the benefit benefit of any member or individual. of the the income income of the organization shall insure to In the event of dissolution the assets of the organization shall be distributed to ______________ tax free organization). organization). (some (some tax (To avoid Federal and State State income taxes, the organization should be not only only "scientific "scientific" or also "non-profit".) "educational, but also "non-profit".) .. ,2.. Minn. Stat. Slat. Anno. 290.01, subd. subd. 44 Minn. Stat. 290.05(9) S t a Anno. ~ Internal Revenue 1(c)(3) 1954 Internal RevenueCode Code5.50 s.501(~)(3) Article Article IV IV ,. Membership rasmkmm The membership of the organization shall consist of persons who have registered for an an annual annual meeting or who have indicated interest in being a member according according to to membership membership guidelines guidelines approved by the board approved board of directors directors and have paid any applicable applicable dues. Article V Meetin2s &!dlws The organization shall shall meet meet once once aa year, year, preferably preferablyduring duringthe themonth monthof ofApril. April. The The place place and and exact directors. exact date date of of each each meeting meeting will be designated by the board of directors. Article VI Article VI Directors Directors The board and the the last last three three past board of of directors directors shall shall consist consist of the the Chair, Chair, Secretary-Treasurer, Secretary-Treasurer, and Chair; but if the by reason reason of Chair, but the board board should should at any any time time consist consist of fewer fewer than five persons, persons, by unwillingness or inability of any of the above persons to serve as as directors, directo& the the vacancies vacakies on on the the board may board up to five members. may be be filled filled by by Chair Chair so as to 10 bring the the membership of the board Article VH Officers smcsls The The officers officersof this this organization organization shall be a Chair and Secretary-Treasurer. A. be elected of directors, A. The Chair Chair shall shallbe elected each each year year by by the the board boardof directors, who who shall give due due consideration to the wishes of any group DUUD that that may may be be promoting promoting the the next next annual annualmeeting. meetine. His/her terminate at at the cl&c close of theannual the annual meeting over which Hisher term of office office as Chair Chair will $lt&nate he/she presides or when hisher his/her successor shall have have been been appointed. appointed. He/she hdshe presides Hdshe will willthen thenserve serve for for a period period of of three three years years as as aa member memberof of the theboard boardof of directors. directors. B. shallbe beelected electedby by aa majority majority vote of of members B. The Secretary-Treasurer Secretary-Treasurer shall members at the the annual annual . . vote meeting. His/her of years or ~ i s / h eterm term r ofoffice officeshall shall be be four fouryears or until until his/her hisher successor successorshall shall have have been been appointed. appointed. Article VIII Amendments This may be be amended amended by by aa majority of those This constitution constitution may majority vote vote (majority (majority of those voting) voting) of of the the membership membership of of the the organization. organization. �BY-LAWS OF OF INSTITUTE INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY "9.. !!i !',vp..,. Duties of the the Officers and Directors Directors I. Duties A. It shall be the duty of the the Annual Annual Chair Chair to: to: >, .,,, , . 1 -"-< I.. Preside at the annual meeting. - ,, Appoint all committees committees needed for the organization organization of the annual meeting. . . ..,.&;, 2. Appoint .. 3. Assume and of the the annual *. . ! 3. Assumecomplete completeresponsibility responsibility for for the the organization organization and financing financine annual meeting meetine - of over which he/she h&he presides. B. It shall be the duty of the B. the Secretary-Treasurer Secretary-Treasurerto: to: 1. 1. Keep accurate accurke attendance attendance records &cords of all annual meetings. 2. Keep Keep accurate accurate records records of of all meetings of, and correspondence between, the the board board of of 2. meetings of, correspondence between, directors. directors. 3. Hold all funds that may may accrue accrue as as profits profits from from annual annual meetings meetings or or field field trips trips and and to make 3. these funds available available for the organization and operation operation of future future meetings meetings as as required. required. C. It shall be the duty of the board of directors to plan locations locations of annual meetings and to advise on the organization organization and and financing financingof of all all meetings. meetings. 8 ,, Expenses and E IH. I. Duties and xuee s - I. Regular lesson 1. Regularmembership membership dues dues of $5.00 $5.00 or or less on an an annual annual basis basis shall shall be be assessed assessed each member member as determined by the board board of directors. directors. 2. Registration Registration fees for the annual meetings shall shall be be determined determined by by the Chair in consultation with the board of The registration fees can can include expenses to cover the of directors. directors. The registration fees expenses to cover operations operations outside of of the annual outside annual meeting meeting as as determined determined by the the board hoard of of directors. directors. It is strongly strongly recommendedthat thatregistration registrationfees feesbebekept keptatat aa minimum to encourage attendance of of recommended minimum to encourage attendance graduate students. ILL. Rulesof ofOrder Order ;z F .lQW The rules contained in Robert's Rules of Order shall govern this organization in all cases to which The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are are applicable. applicable. LV. Anw>nflnw*nfc Amendments N. . I , These by-laws may be amended by by aa majority majority vote vote (majority (majority of of those those voting) voting) of of the the membership membership of the organization; provided provided that that such such modifications shall shall not not conflict conflict with with the the constitution as as ;;-of adopted or subsequently amended. 5 ~ i i ~ .presently presently is adopted or subsequently amended. . . , . ..;. Last Amended May, 1996 Amended -- May, 1996 .'t . �GOLDICH GOLDICH MEDAL GUIDELINES GUIDELINES Preamble Preamble Institute on on Lake The Institute Lake Superior Superior Geology Geology was was born born on on or or around around 1955, 1955, as as documented documented by by the the fact fact that that the the 27th 27th The annual meeting annual meeting was was held held in in 1981. 1981. The TheInstitutes Institutesare areexemplary exemplaryin intheir theircontinuing continuingobjectives objectivesof ofdealing dealingwith withthose those aspects of aspects of geology geology that that are are related related geographically geographically to to Lake ~ a k eSuperior; ~ u p e r i oof ofr ;encouraging encouraging the the discussion discussion of of subjects subjects and and sponsoring field trips which will bring surveys, and industry; and of swnsoring brine together together geologists eeoloeists from academia, government surveys. maintaining an an exceedingly exceedingly informal but highly effective mode mode of of operation. operation. maintaining i n f o d buthighiyeffective During the course of of its existence, existence. the membership membership of the Institute (that is, those geologists who indicate an interest colleagues have made in the objectives of the ILSG by by attending) attending) has has become aware aware of the fact that certain of their colleagues made particularly noteworthy noteworthy and of Lake Lake Superior and particulaily and meritorious meritorious contributions contributions to to the the understanding understanding of Superior fgeology $eolo&' and mineral mineral deposits. deposits. The toSam SamGoldich Goldichin in 1979 1979for forhis hismany many contributions contributionsto to the the geology geologyof ofthe theregion region The first award award was was made made by by ILSG ILSG to extending below. extending over about 50 50 years. Subsequent Subsequentmedalists medalistsand and this this year's year's recipient are listed in the table below. Award Award Guidelines Guidelines I) The medal shall to a geologist whose whose name name is is associated associated 1) shall be awarded awarded annually by the ILSG Board of Directors to contribution to, the geology of the Lake Lake Superior region. with a substantial interest in, and contribution 2) The Board Committee. The three Board of of Directors Directors shall shall appoint appoint the Goldich Medal Committee. The initial initial appointment appointment will be of three members, members, one to serve for three three years, years, one for for two two years, years, and and one one for for one one year. year. The member with the the briefest briefest incumbency shall be chair of the firstyear, year,the the Board Boardof ofDirectors Directorsshall shallappoint appoint the Nominating Committee. After Afterthe the first at each spring three years. In his/her hidher third year year this member member shall shall be be spring meeting meeting one one new new member member who who will will serve serve for for three the chair. The Committee of interest interest and and geographic geographic distribution distribution of of ILSG ILSG Committee membership membership should reflect the main fields of membership. membership. 3) By to the the Chair Chair of of the 3) By the the end end of of November, November, the the Goldich Goldich Medal Medal Committee Committee shall shall make make its its recommendation recommendation to the Board of Directors, Directors, who who will then inform inform the Board of the nominee. 4) The 4) The Board Board of ofDirectors Directorsnormally normally will will accept accept the thenominee nominee of ofthe theCommittee, Committee. will will inform inform the themedalist medalist immediately, and will have one medal engraved appropriately appropriately for presentation at the next meeting of the Institute. 5) It is recommended recommended that that the the Institute Institute set set aside aside annually annually from from whatever whatever sources, such funds as will be be required required to to continuing costs of this award. support the continuing Nomination Procedures Procedures Nomination Nominations shall be taken 1) Nominations taken at at any anytime timeby bythe theGoldich GoldichMedal MedalCon-imittee. Committee. Committee Committeemembers membersmay may themselves themselves candidates. The nominate candidates. The deadline deadline for for nominations nominations is is November 1. 1. 2) Nominations Nominations must be in writing and supported by appropriate appropriate documentation such as letters of recommendation, recommendation, publications. curriculum contributions to Lake Lake Superior geology and to to the Institute. lists of publications, curriculum vita's, and evidence evidence of contributions are not not restricted restricted to to Institute Institute attendees, attendees, but are are open open to to anyone anyone who who has has worked worked on on and and contributed contributed 3) Nominations Nominations are to the understanding understanding of of Lake Lake Superior Superiorgeology. geology. iv �Selection Guidelines Nominees are to be evaluated 1) Nominees evaluated on the basis of their contributions contributions to Lake Superior Superior geology geology (sensu lato) lato) including: including: a) importance importance of relevant relevant publications; publications; b) b) promotion promotionof of discovery discoveryand andutilization utilizationof ofnatural natural resources; resources; c) contributions contributions to to understanding understandingof of the the natural natural history history and and environment environmentof of the the region; d) generation generation of new ideas ideas and concepts; concepts; and e) contributions contributions to to the the training training and education educationof of geoscientists and the the public. nublic. - and -geoscientistsand # ., ...,:,{ m, . P,:~:, ,y 2 : 2) 2) Nominees Nominees are are to tobe beevaluated evaluatedon ontheir theircontributions contributionsto tothe theInstitute Instituteas asdemonstrated demonstratedby byattendance attendanceatatInstitute Institute meetings, meetings, presentation presentationof of talks talksand andposters, posters. and andservice serviceon onInstitute Instituteboards, boards, committees, committees,and andfield fieldtrips. trips. 3) 3) The The relative relative weights weights given given to to each each of of the theforegoing foregoing criteria criteria must must remain remain flexible and at the discretion discretion of of the the Cornniittee Committee members. members. - . ..q .* ? ,' 4) 4) There There are are several several points points to to considered considered by by the the Goldich Goldich Medal Committee: . "...., * . . . a) of the a) An An attempt attempt should should be be made madeto to maintain maintain aa balance balanceof of medal medal recipients recipientsfrom from each each'of thethree threeestates-industry, estates-industry, academia, academia, and government. government. b) It It must must be be noted noted that thatindustry industry geoscientists geoscientistsare areat at aa disadvantage disadvantagein in that that much much of of their their work work is is not not published. published. .# 5) 5 )Lake Lake Superior Superiorhas hastwo twosides, sides,one onethe theU.S., US., and andthe theother otherCanada. Canada. This Thisisisundoubtedly undoubtedlyone one of ofthe theInstitute's Institute's great great strengths strengths and should should be be nurtured nurtured by by equitable equitablerecognition recognition of of excellence excellencein in both both countries. countries. Last Last Amended Amended 1997 1997 GOLDICH GOLDICHMEDAL MEDAL COMMITTEE COMMITTEE1998-99 1998-99 John John Klasner Klasner (1999) (1999) Western Western Illinois IllinoisUniversity, University, Macomb, Macomb, Illinois Illinois Mark Smyk MarkSmyk (2000) (2000) Ontario Ontario Geological Geological Survey, Survey, Thunder Thunder Bay, Bay, Ontario Ontario Rod Johnson Johnson (2001) (2001) Rod Rod Johnson Johnson and and Associates, Associates, Negaunee, Negaunee, Michigan ~ichi'n V *' k' * �,; :G?L GOLDICH GOLDICH MEDALISTS MEDALISTS '' 1991 991 William WilliamJ. Hinze 1992 William F. Cannon Cannon 992 F. 1993 993 Donald W. W. Davis 1994 994 Cedric Cedric Iverson 1995 995 Gene Gene LaBerge 1996 David L Southwick 996 L. Southwick 1997 997 Ronald P. Sage 1998 Zell Peterman Petennan 998 Zell 1999 Tsu-Ming Han 999 Tsu-Ming Hun 1979 Samuel S. £ Goldich Goldich 1980 not awarded E. Dutton, Jr. Jr. 1981 Carl Carl IL 1982 Ralph W. Ma Marsden 1983 Burton 1983 Burton Boyum Boyu 1984 Richard Richard W. W Ojakangas Ojakangas 1985 Paul Paul K. 1985 K. Sims Sims 1986 1986 G.B. Morey 1987 Henry H. Halls 1988 Walter £ White Walter S. White 1989 JormaKalliokoski Kalliokoski 1989 Jonna 1990 1990 Kenneth C. Card Card '' 1999 19999 Goldich Medal Recipient -.. Tsu-Ming Han vi !:- �- I I : ,.. . . ,. Citation Citation Tsu-Ming HHan an 1999 Recipient 9 Goldich Medal Recipien The 1999 1999 c3oldich Goldich Medal recipient epitomizes the characteristics characteristics required to receive receive this unique and prestigious award. He life to to solving nature's nature's this prestigious award. He has has devoted devoted his professional professional life myriad challenges challenges in in the field myriad field of of geology geology and and sharing sharing his his findings findings with with colleagues colleagues both both verbally and through published and unpublished unpublished mineral mineral papers. r He born during the 1920's of China. China. His He was was born during the 1920's in in the the Hunan Hunan Province Province of His family familystressed stressed the importance importance of of education. education. He the He pursued pursued his his education education during during a series series of of difficult difficult periods periods that included being kidnapped kidnapped and and held held by by bandits, pursued by by Japanese Japanese forces, forces, and and the that included being bandits, pursued imposition of of Nationalist Nationalist control control followed followed by by the the cultural cultural upheaval upheaval caused caused by by the the ascendancy ascendancy imposition of the Communists from Northwest Northwest University in Sian of Communists after after World War War II. U. After graduating from Province in in 1945 Province 1945 and a brief stint stint with with the the Bureau Bureau of of Mineral Mineral Exploration, he immigrated immigrated to to the U.S. the U.S. in in 1947 1947 to tocomplete complete graduate graduate work work at at the the University University of of Cincinnati Cincinnati and and the the University of Minnesota. Minnesota. His Drs. Goldich, His mentors mentors at the University of Minnesota included Drs. Gruner, and Schwartz. Gmner, Schwartz. ;, ,. ,,, After summer employment with Clevcland-Cliffs in 1952, After Cleveland-Cliffs in 1952, he he accepted accepted permanent permanent employment at at the the Ishpeming Ishpeming Research Researchfacility. facility. Soon Soon after, after, he he met met and and married married Joy. Joy. They They employment have have advanced have three three children children who who,, have also alsobenefited beqegted,professionally professionally by b yachieving .achiev&g *-* advanced .,.~ , ,. educational educational degrees. degrees. , t He has published numerous articles on the genesis of iron formations with emphasis on textural textural relations relations during duringdiagenesis diagenesisand and metamorphism. metamorphism. What is not generally known known is that he is an expert on all facets of the beneficiation and pelletizing pelletizing process process that that has has dominated dominated the the North North American Americaniron ironore ore industry industry for for half half aa and His studies have assisted in the pelletizing process to century. century. His assisted in continual continual improvement improvement in industry competitive. keep the industry competitive. He in several He has has aa special special interest interest in in the the preserved preserved algae algae present present in several areas areas of of the the Negaunee Iron-formation Iron-formation at at the the Empire Empire Mine Mine and and has has published his his findings. findings. It should be noted noted that he delivered delivered a paper at the first Institute Institute meeting in 1955 1955 and and continues his scientific inquiry as evidenced by his current presentation at the Institute. continues his scientific inquiry evidenced by current presentation the Institute. his formal formal retirement retirement in in 1992 is is that that he he now now wears Indeed, the only change noticeable since his tennis shoes shoes to the office. office. It is my pleasure to to introduce introduce to the Institute Institute the the 1999 1999 recipient recipient of the the Goldich Goldich Medal, Medal, friend and our my friend our colleague, colleague, Tsu-Ming Tsu-Ming Han. Han. Tom Wagonner vii �STUI)ENT STUDENT PAPER PAPER AWARDS AWARDS Each year, the Institute selects the best of the and honors presenters presenters with with aa monetary award. Each the student student presentations and Funding for for the Funding the award award is is generated generated from from registrations registrations of of the the annual annual meeting. meeting. The The Student Student Paper Paper Committee Committee isis appointed by appointed by the the annual annual meeting meeting Chair Chair in in such such aa manner manner as as to to represent represent aa broad broad range range of of professional professionaland andgeologic geologic expertise. Criteria expertise. Criteria for for best best student student paper-last paper-last modified modified by the the Board in 1997-follow: 1997-follow: 1) The The contribution contribution must 1) must be be demonstrably demonstrablythe the work work of of the thestudent. student, 2) The The student student must present the contribution 2) contribution in-person. 3) The Student shall decide decide how how many many awards awardsto to grant, grant, and and whether whether or or not not to give separate 3) Student Paper Committee shall separate awards awards for for poster poster vs. vs. oral oral presentations. presentations. 4) In will be be made made to to the the senior author, author, or or the the award will be 4) In cases cases of of multiple multiple student student authors, the award will be shared shared equally equally by all authors authors of of the the contribution. contribution. 5) The but The total total amount amount of of the the awards awards isisleft lefttotothe thediscretion discretionof ofthe themeeting meetingChair Chairand andSecretary-Treasurer, Secretary-Treasurer, but typically is in the amount of about $300 $300 US. 6) The maintains, and and will will supply supply to to the 6) The Secretary-Treasurer Secretary-Treasurer maintains, the Conmiittee. Committee, aa form form for for the the numerical numerical ranking ranking of of presentations. This form form was was created and modified modified by Student Student Paper Paper Committees Committees over several years in in an an effort effort to to reduce the the difficulties that that may may arise arise from selection by by raters raters of of diverse background. background. The The me "Se of of the the form form is not reduce required, but but is is left left to to the the discretion discretion of of the the Committee. Committee. 7) The 7) The names names of of award award recipients recipients shall shall be be included included as a s part part of of the the annual annual Chair's Chair's report that that appears appears in in the the next next volume volume of of the the Institute. Institute. STUDENT PAPER PAPER COMMITTEE COMMITTEE 1999 STUDENT .~ .. ~,,. Allan Blaske, STS STS Consultants, Consultants, LTD. LTD,Lansing, Lansing, MI MI Woodruff, U.S. Laurel Woodruff, U.S.Geological Geological Survey, Survey, St. Paul, MN vii . ' . B; .. , . .. . , . . .: ,, .. �I 1 STUT)ENT TRAVEL TRAVEL AWARD STUDENT AWARD The Travel Award Award to to support student participation participation at at the the The 1986 1986Board Board of of Directors Directorsestablished established the the LL.S.G. I.L.S.G. Student Student Travel support student annual find set annual Institutes. Institutes. The The awards awardswill will be be made made from from aa special special fund set up up for for this this purpose. purpose. This Thisaward awardisisintended intendedtoto help help defray defray some some of of the the direct direct travel travel costs costs to to the the Institute Institute and and includes includes aa waiver waiver of of registration registration fees, fees, but but excludes excludes expenses and field field trip trip registration. registration. The and value by the the expenses for for meals, meals, lodging, lodging, and The number number of of awards awards and value are are determined determined by annual annual Chairman Chairman in in consultation consultationwith with the the Secretary-Treasurer Secretary-Treasurerand and will will be be announced announcedat at the the annual annualbanquet. banquet. The beconsidered consideredby bythe theannual annualChairman, Chairman,who whoisisresponsible responsiblefor forthe theselection: selection: Thefollowing followinggeneral generalcriteria criteriawill willbe 1) 1) The or graduate) graduate) student student status status at at the the time time of of the the The applicants applicants must must have have active active resident resident (undergraduate (undergraduate or Institute, Institute, certified certified by by the the department department head. head. who are are the the senior author on on either either an an oral 2) Students who senior author oral or or poster poster paper paper will will be be given given favored favored 2 ) Students consideration. consideration. 3) is desirable desirablefor fortwo two or or more more students students tojointly to jointly request requesttravel travel assistance. assistance. 3) ItIt is In general, general,priority priority will will be be given given to to those thosein in the the Institute Institute region region who who are are farthest farthest away. 4) 4) In with an an explanation of 5) Each travel travel award award request request shall shall be be made made in in writing, writing, to to the the annual annual Chairman, Chairman, with explanation of 5 ) Each need, need, possible possibleauthor authorstatus statusor orother othersignificant significantdetails. details. Successful Successfulapplicants applicantswill willreceive receivetheir theirawards awardsat atthe thetime timeof of registration registration for forthe the Meeting. Meeting. INSTtTUTh ON SUPERIOR GEOLOGY ONLAKE -SUPERIOR GEOLOGY Student A want Application Student Travel TravetAwardAppUcdon Please Pleaseprint: print: Student Student Name: Name: _______________________________ Date: Date: _______________ Address: Address: _______________________________________________________ :. Icertify 1certifythat thatthe theabove abovenamed namedperson personisIsan anactive activeresident residentstudent. student. .; ;; .,>'. , .. .,." v.., Department DepartmentHead Head--Typed Typed .. - ..>i.; ;.( <: ... , ,, Date Date Department DepartmentHead Head- Signature Signature L Educational Educational Status: Status:___________________ Are an oral reyou you the theSenior Senior Author Author of ofan oral or orposter poster paper? paper? Yes Yes Will Willany anyother otherstudents studentswill willbe betraveliag (revelingwith withyou? you? c . ~,.. : ___ ___ No No-_____ How Howmany? many? - Statement (If:(Ifyou statementofofNeed: ~eed youneed needmole moreloom, room,please pleaseuse usethe theback backof ofthe thepage.) Page.) Other OtherSignificant SignificantDetails: Details: Please Please return returnto: to: ix : �BOARD BOARD OF OF DIRECTORS DIRECTORS fheodoreJ. J. Bornhorst, Bornhorst, Chair Chair(2002) (2002) Theodore Michigan MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton,Michigan Michigan James JamesD. D.Miller Miller(2001) (2001) Minnesota Minnesota Geological GeologicalSurvey, Survey,St. St.Paul, Paul,Minnesota Minnesota Ronald RonaldP. P.Sage Sage(2000) (2000) Ontario OntarioGeological GeologicalSurvey, Survey,Sudbury, Sudbury,Ontario Ontario <. Laurel LaurelG. G. Woodruff Woodruff(1999) (1999) U.S. US. Geological GeologicalSurvey, Survey,Mounds MoundsView, View,Minneapolis Minneapolis Mark MarkA. A.Jirsa J i m(2000) (2000)Institute InstituteSecretary-Treasurer Secretary-Treasurer Minnesota MinnesotaGeological GeologicalSurvey, Survey,St. St.Paul, Paul,Minnesota Minnesota LOCAL LOCAL COMMITTEES COMMITTEES GENERAL Co-CHAIRS Robert RobertS.S.Regis Regis Department Northern Michigan Departmentof ofGeography/Earth Gwgraphy/EarthScience, Science,Northern MichiganUniversity, University, Marquette, Marquette,Michigan Michigan49855 49855 Theodore TheodoreJ. J. Bornhorst Bornhorst Department Department of of Geological GeologicalEngineering Engineeringand andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University.Houghton, Houghton, Michigan Michigan 49931 49931 PROGRAM AND EDITORS PROGRAM AND ABSTRACTS EDITORS ,* . Robert RobertS. S.Regis Regis Department Departmentof ofGeography/Earth Geography/EarthScience, Science,Northern Northern Michigan MichiganUniversity, University, Marquette, Marquette,Michigan Michigan 49855 49855 Theodore TheodoreJ. J. Bornhorst Bornhorst Department of of Geological GeologicalEngineering Engineering and andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity. University, Houghton, Houghton, Michigan Michigan 49931 49931 FIELD TRIP GUIDEBOOK EDITOR Theodore Theodore J. J. Bornhorst Bornhocst Department of of Geological Geological Engineering Engineering and andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton, Michigan 49931 49931 x �SESSION CHAiRS SESSION CHAIKS Dave DaveBaxter, Baxter,PayDay PayDayResources, Resources,Lansing, Lansing,MI MI Shawn Shawn Carison, Carlson, Ashton AshtonMining, Mining,North North Vancouver, Vancouver,BC, BC, Canada Canada Ron Ron Graber, Graber, Cliffs CliffsMining Mining Services ServicesCompany, Company, Ishpeming, Ishpeming, MI MI John John Green, Green,University Universityof of Minnesota, Minnesota, Duluth, Duluth, MN MN Rod Rod Johnson, Johnson, Rod RodJohnson Johnson& &Associates, Associates,Inc., Inc.,Negaunee, Negaunee, MI MI Gene Gene Laberge, Laberge, University Universityof of Wisconsin, Wisconsin,Oshkosh, Oshkosh, WI WI Jim Jim Small, Small, Edward Edward Kraemer Kraemer & &Sons, Sons, Burnsville, Burnsville, MI MI Tom Tom Waggoner, Waggoner, retired retired Cliffs CliffsMining MiningServices ServicesCompany, Company,Ishpeming, Ishpeming, MI MI " a, 1999 999 BANQUET BANQUET SPEAKER SPEAKER ' Nelson R. R. Ham Ham Department Department of Geology Geology St. Norbert College St. College De De Pere, Pere, Wisconsin Wisconsin , . . , Ice-Flow Dynamics and Landform Landform Development Development Along the Southern Southern Margin Margin of of the the Laurentide LaurentideIce Ice Sheet Sheet xi , �REPORT REPORTON ONTHE THE44th 44thANNUAL ANNUAL MEETING MEETINGOF OFTHE THE INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY MINNEAPOLIS, MINNEAPOLIS,MINNESOTA MINNESOTA The The44th 44thAnnual AnnualMeeting Meetingof ofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geologywas washeld heldinin Minneapolis, Minneapolis,Minnesota Minnesotaon on May May 6-10, 6-10, 1998. 1998. The Themeeting meeting was was sponsored sponsored by by the the Minnesota Minnesota Geological GeologicalSurvey Surveyand andwas washeld held at atthe the Holiday Holiday Inn Inn on on the the West West Bank Bank of of the the University University of of Minnesota Minnesotacampus. campus. Proceedings Volume44 44of ofthe themeeting meetingwas waspublished publishedinintwo twoparts: parts: ProceedingsVolume Pan Abstracts Part1:1:Program Programand and Abstracts(including (includingextended extendedabstracts abstractsofofthe thespecial specialoverview overview session) session) Part Part2:2:Field FieldTrip TripGuidebook Guidebook 1—Early 1-Early Proterozoic Proterozoicintrusive intrusiverocks rocksof of east-central east-centralMinnesota Minnesota 2—Geology 2-Geology of of the the southeastern southeasternportion portionofofthe theMidcontinent MidcontinentRift RiftSystem. System,eastern eastern Minnesota Minnesotaand andwestern westernWisconsin Wisconsin 3—Glacial ofthe theTwin TwinCities Cities area area 3ÑGlacia exotica exoticaof 4—Stratigraphy hydrogeology of M t r a t i g r a p h y and andhydrogeology of the the Paleozoic Paleozoic rocks rocks of of southeastern southeastern Minnesota Minnesota 5—Minnesota River Valley and vicinity, southwestern Minnesota (Precambrian and 5-Minnesota River Valley and vicinity, southwestern Minnesota (Precambrian and Quaternary Quaternarygeology) geology) By By most most measures, measures,the themeeting meetingwas wasaagreat great success. success. We Wesaw sawaaconsiderable considerablejump jumpinin attendance attendancethis thisyear yearto to200 200participants, participants.compared comparedwith withrecent recentaverage averageattendance attendanceon onthe the order of 125. Fifty-six participants were first-time attendees to the ISLG; split about order of 125. Fifty-six participants were first-time attendees to the ISLG. split aboutequally equally between betweenstudents studentsand andrelated relatedfields fieldspeople—that people-that is. is, those those involved involved in in Quaternary, Quaternary, Paleozoic, Paleozoic, environmental, are not not traditional traditional topics topics of the the Institute. Institute. We We environmental,and andengineering engineeringgeology geology that that are attribute attributesome someof of this thisincrease increasesimply simplyto to the the metropolitan metropolitan location location of the the meeting meeting and and our our fairly fairly aggressive aggressiveappeal appealto to the thelocal localgeoscience geosciencecommunity. community. To Toattract attractlocal localand andmore more broadly broadlybased basedinterest, interest,we webroke brokesomewhat somewhatwith withtradition traditionby byconducting conductingaaspecial specialhalf-day half-day session region. To session overviewing overviewingthe geology of the Lake Superior region. Tomake makethe themeeting meetingeven even more moreattractive attractiveto tonew-comers, new-comers,we weoffered offeredaafirst-day-only first-day-onlyregistration registrationatataareduced reducedrate ratefor for those thoseinterested interestedin inattending attendingjust justthe thespecial specialoverview overviewsession; session;however, however,few fewtook tookadvantage advantage of of the the offer. offer. The talksthat thatoutlined outlinedcurrent currentideas ideasand and The special specialoverview overviewsession sessionconsisted consistedof ofsix six30 30minute minutetalks new new research researchdirections directionson onthe themain maingeologic geologicprovinces provincesof of the theLake LakeSuperior Superiorregion. region. Presentations (Archean),Dick DickOjakangas Ojakangas(Early (EarlyProterozoic), Proterozoic),Bill Bill Presentationswere weregiven givenby by Ken KenCard Card(Archean), Cannon Cannon(Middle (MiddleProterozoic), Proterozoic),Tony TonyRunkel Runkel(Paleozoic), (Paleozoic),Carrie CamePatterson Patterson(Quaternary), (Quaternary),and and Dave talkswere werewell wellpresented presented Dave Southwick Southwick(New (Newdirections directionsin in Lake Lake Superior Superior geology). The Thetalks and and well well received; received; comments commentsfrom fromthe the participants participants were overwhelmingly overwhelmingly favorable. The The general 23oral oralpresentations presentationscovering coveringnot not only only the the typical typical fare fareof of general sessions sessionsincluded included23 Precambrian to groundwater. groundwater. In Inaddition, addition,24 24 Precambriantopics, topics,but but also alsoincluded included several severaltalks talks related related to poster of the the meeting. meeting. The poster presentation presentation were were on on display display during during the course of Thebanquet banquet speaker speaker was was Dr. Dr. Bevan Bevan French Frenchof ofthe theSmithsonian SmithsonianInstitution, Institution,who whogave gavean anexcellent excellenttalk talkon onthe therole role of of meteorite meteoriteimpacts impactson on the the geologic geologic history history of earth earth and other planets. At At the thebanquet, banquet,Zell Zell Peterman Petennan of of the theUSGS USGSwas wasawarded awardedthe theGoldich GoldichMedal Medalfor forhis his important importantgeochronologic geochronologicand and xii �geologic studies studies of of Precambrian Precambrian geology geology in in the the Lake LakeSuperior Superiorregion. region. Another Another highlight highlight of of geologic the meeting for 40 40 participants participants was was aa night night of of baseball baseball at at the the Metrodome. Metrodome. This meeting excursions that covered a meeting also also broke broke the the mold mold a bit by offering five field excursions similarly wide breadth similarly breadth of geology gwlogy as as was was presented in the the special special overview overview session. session. Although the emphasis highlighting the Paleozoic Although-the emphasis remained remained with Precambrian geology, trips highlighting and Quaternary geology of central and southern Minnesota Minnesota were were also also included. included. Three Threeprepremeeting the Early Early Proterozoic Proterozoic gwlogy geology of meeting field field trips trips were were run run on on Wednesday, Wednesday,May May 6th; 6th. 1) the east-central Minnesota Minnesota led by Terry Boerboom, Mark Jirsa, and Daniel Holm (26 participants); Wirth, Bill participants); 2) the Keweenawan geology of the Taylor's Falls area led by Karl Wirth, Cordua, Cordua, Bill Kean, Kean, Mike Mike Middleton, Middleton, and Zach Naiman Nairnan (46 (46 participants); and 3) Glacial exotica exotica of the the Twin Twin Cites Citesarea area led led by by Howard Howard Hobbs, Hobbs, Alan Alan Knaeble Knaebleand and Gary GaryMeyer Meyer(21 (21 participants). Two the Paleozoic Paleozoic stratigraphy, stratigraphy, Twopost-meeting post-meetingtrips trips included included aa one-day trip on the sedimentology, sedimentology,and hydrogeology hydrogeology of southeastern southeastern Minnesota led by Tony Runkel and Bob Tipping Tipping (11 (1 1 participants), and a two-day excursion investigating the Quaternary and Archean geology of the Minnesota Minnesota River Valley led by Carrie Patterson and David Southwick (33 participants). participants). The meeting was also is to to at least also a financial success; that is, if your measure of success is break even (which has been the traditionally held held view). view). We actually turned turned aa small small profit profit of of several hundred dollars. dollars. Although Althoughregistration registrationwas wasmore morecostly costlythan than we we had had hoped, hoped, the thecost cost was unavoidable unavoidable given the metropolitan metropolitan location. Part Partof of the theregistration registrationwe we all all pay pay is is applied to encouraging Institute by by granting granting awards awards for for student student encouraging student student participation in the Institute travel and best student student papers. Eight Eighttravel travelawards awardstotaling totaling$750, $750, and and two two best best paper paperawards awards of $150 each were granted. granted. Best Bestpaper paperawards awardswent went to to Kathleen Kathleen Abbott Abbott (Macalester (MacalesterCollege) College) for her undergraduate undergraduate work work on on geochemistry geochemistryand and petrography petrography of of Keweenawan Keweenawan Chengwatana Chengwatana volcanic rocks of Minnesota and Wisconsin, and to Dean Peterson (University of MinnesotaMinnesota Duluth) Duluth) for for his his graduate graduate presentation presentationon on (3IS-based GIs-based mineral potential analyses analyses of Archean Archean rocks in Minnesota. Congratulations Congratulationsto to you you both! both!. The Institute's Institute's Board Board of Directors Directors met on May 7th, 7th. and the following is generalized from minutes of that meeting: 1. Accepted Acceptedthe the Report Report of of the the Chair Chair 43rd 43rd ILSG ILSG 2. Accepted Acceptedthe the1997-1998 1997-1998JLSG ILSG Financial Financial Report. Report. 3. Approved ro rovedZell ZellE. E.Peterman Petermanas as1998 1998Goldich Goldich Medal Medal recipient. recipient. 4. Modified 4. Modifiedthe thelanguage languagefor forGoldich GoldichAwards Awards regarding regarding dates dates for for receipt receipt of nominations nominations (now November 1) 1) and final decision (now the end of November). 5. Approved Approvedthe theend-of-term end-of-termreplacement replacement of of Dan Dan England England (Eveleth Fee Office) Office) as committee member member hy y Rodney Goldich Medal committee RodneyJohnson Johnson (Trans (Trans Superior Superior Resources). Rod begins a 3-year term in Novemuer Novemner of 1998. 1998. title to to "Eisenbrey "EisenbreyStudent StudentTravel TravelAwards". Awards'. This 6. Changed Changedthe the student student travel award's title satisfies a request from satisfies from individual individual and corporate corporate contributors contributors to the 1996 1996 meeting meeting that that such a fund be established in honor of Ned Eisenbrey, and permits the use of & l established =senbrey, investment income income for for encouraging encouraging student student participation participation in the Institute. ILSG meeting. meeting. Co-chairs will 7. Approved Approvedthe the host host location—Marquette—for location-Marquette~for the 1999 ILSG will Bomhorst (Michigan Bob Regis Regis (Northern be Ted Bomhorst (Michigan Technological University) and Bob Michigan University). University). xiii xiii �8.8.Discussed Discusseda apotential potentialY2K Y2Kmeeting meetinglocation—Thunder location-Thunder Bay Bayororother otheraccess accesspoint pointtoto the theAtikoken Atikokenarea. area. 9. 9.Discussed Discusseda apotential potential2001 2001meeting meetinglocation—Sault 1ocationÑSaulSte. Ste.Marie, Marie,MI. MI. 10. the 10. Other Otherbusiness—contact busines-ontact thesecretary-treasurer secretary-treasurerfor fordetails details We Wehope hopethat thatwith withthe thesuccess successof ofthe the1998 1998meeting, meeting, the the ILSO ILSGtook took an an important important step steptoward toward achieving achievingthe thegoal goalof ofexpanding expandingits itsreach, reach,both both in in terms termsof of the the range range of of geological geological topics topics and and the thebackground backgroundof of participants. participants. While Whilewe wemay maynot notbe beable ableto torepeat repeat the the attendance attendancesuccess success of of this thismeeting meetingas aswe wemove moveto tothe themore moretypically typicallyremote remoteconference conferencesites, sites, future futureorganizers organizersand and those thoseof ofus uswho whoare arelong-time long-timeparticipants participantsmust mustdo doall allwe we can can to to actively actively promote promote the the ]LSG ILSG to the broadest possible audience. If we had to pinpoint one reason for the success to the broadest possible audience. If we had to pinpoint one reason for the successofofthe the 1998 1998 meeting, meeting, itit would would be be our ourrelentless relentlesspromotion promotionof ofthe themeeting meetingto tolocal localgeoscience geoscience organizations, organizations,colleges, colleges,and andindividuals. individuals.For Forour ourpart, part,we wewill willencourage encourageTwin TwinCities Cities geoscientists geoscientiststo tocontinue continuetheir theirinvolvement, involvement,now nowthat thatthey they have have been been exposed exposed to to what what the the ILSO ILSGhas hasto tooffer. offer. We Wewish wishto tothank thankall allof ofthe thepresenters, presenters,in inparticular particularthe the special special session session speakers speakerswho who wrote wrote extended extendedabstracts abstractsthat thatwill willserve serveas assummaries summariesof of their their fields fieldsfor for years years to to come. come. This This institute institutewas was built built on onits itstradition traditionof of fine finefield field trips, trips, and and this this year's year's trips trips maintained maintained that that tradition, tradition,thanks thanksin inlarge largepart partto toefforts effortsof of the theleaders. leaders. Acknowledgment Acknowledgmentisisalso alsodue duetotothe the session sessionchairs, chairs,the thebest beststudent studentpaper paperaward awardcommittee, committee,the thelocal localplanning planningcommittee, committee,and andthe the LLSG board members members for for making jobs much easier by by doing theirs well. ILSG board making our our jobs much easier doing theirs well. AAspecial specialthanks thanks to to Terry Terry Boerboom Boerboomfor forhis hisflawless flawlessorganization organizationof ofthe thefield fieldtrips tripsand andguidebook, guidebook,and andtotoLori Lori Day, it takes. takes. Finally Day, the the meeting meeting coordinator, coordinator, for for doing doing all all that that it Finally we we want want to to thank thank our our director directorof ofthe theMinnesota MinnesotaGeological GeologicalSurvey, Survey,David David Southwick, Southwick, for for giving giving us us the the freeboard freeboard and andstaff stafftime timeneeded neededto topull pullthe themeeting meetingtogether. together. Jim JimMiller Millerand andMark MarkJirsa Jirsa Co-chairs Co-chairsof ofthe the44th 44thAnnual AnnualILSG ILSG xiv xiv �45TH 4 5ANNUAL ANNUAL ~ ~ MEETING MEETING INSTITUTE GEOLOGY INSTITUTEON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY Program Program �Program Program of of Events Tuesday, Tuesday, May May 4 4 0800-1730 0800-1730 Field Trip 2 Field Trip 2: Archean Ishpeming Greenstone Belt and Gold Mineralization, D.J. Duskin, R.C. Mineralization, Michigan - Leader T.J. Bornhorst, D.J. Johnson, R.A. Mahin, T.O. Quigley, and G.W. Scott Mahin, T.O. Quigley, Scott Wednesday, May Wednesday, May 5 5 ,:-3. ,.. :. .;:, ;+?, 0800-1730 0800- 1730 Field Trip 1I and 2 Field Trip Trip 1: 1: Early Early Proterozoic Proterozoic Strata Strata of the Marquette Marquette Iron Iron Range, Range, Michigan Leader: W.F. Cannon Michigan - Greenstone Belt and Gold Field Trip 2: Archean Ishpeming Greenstone Leaders: T.J. T.J. Bornhorst, D.J. Duskin, R.C. Mineralization, Michigan Michigan - Leaders: Johnson, R.A. Mahin, T.O. Quigley, and G.W. Scott - Registration -- Ramada Inn, Inn, Marquette, Marquette, Michigan Michigan 1700-2000 Registration 1700-2000 1900-2100 Poster Session and cash bar in Ramada Inn 1900-2100 (Authors at posters 1930 1930 to 2100) xv �1 J Thursday, Thursday,May Mav 66 All All technical technical sessions sessions are arein inRamada RamadaInn, Inn,Marquette, Marquette,Michigan Michigan 0730-1600 0730-1600 J Registration Registration-- Ramada Ramada Inn Inn Technical Technical Session SessionII Session Session Chair: Chair: Gene Gene LaBerge LaBerge (University (University of Wisconsin, Wisconsin, Oshkosh) Oshkosh) Shawn Shawn Carison Carlson (Ashton (AshtonMining) Mining) 0820-0830 Opening Opening-- 45 45thAnnual Annual Institute Instituteon on Lake Lake Superior Superior Geology Geology R. R. S. S. Regis Regis and and T.J. T.J. Bornhorst, Bornhorst, Co-Chairs Co-Chairs J J 0830-0930 0830-0930 Invited Invited Presentation Presentation Sarah Sarah A. A. Green Green and and Judy Judy Wells-Budd Wells-Budd Cross Cross Margin Margin Transport Transportin in Lake LakeSuperior Superior . !' .,: . ' . ... . 0930-1000 0930- 1000 Invited InvitedPresentation Presentation Charles Kerfoot, W. : ~. W. Charles Kerfoot,John John A. A. Green, Green, and and Lawrence Lawrence J. J. Weider Weider , A New Approach to Historical Reconstruction: Combining A Approach to Historical Reconstruction: Combining Descriptive Descriptiveand and Experimental ExperimentalPaleolimnology Paleolimnology J 1000-1030 1000-1030 Coffee CoffeeBreak Break J " . 1030-1050 1030-1050 Ojakangas, Ojakangas, R.W. R.W. Sedimentology Sedimentology of of two two Deep Deep Wells Wells in in the the Keweenawan Keweenawan Midcontinent Midcontinent Rift Rift System System Near Munising, Munising, Upper Peninsula, Peninsula, Michigan Michigan 3'. 1050-1110 Puschner,U., U., Schmidt, Schmidt,S.Th., S.Th., and and Bornhorst, Bornhorst,T.J. T.J. 1050-1110 Puschner, Low Grade Metamorphism and Hydrothermal Low Grade Metamorphism and Hydrothermal Alteration Alteration of the the Upper Upper Keweenawan Keweenawan Portage Portage Lake Lake Volcanics, Michigan J 1110-1130 1110-1130 Maki, Maki,J.C. J.C.and andBornhorst, Bornhorst,T.J. T.J. The Gratiot Chalcocite Chalcocite Deposit, Keweenaw Peninsula, Michigan 1200-1340 LunchBreak Break 1200-1340 Lunch 1200-1340 1200-1340 Board BoardofofDirectors DirectorsMeeting Meeting xvH xvi i J �Technical II Technical Session Session H Session Chairs: Rod Johnson (Rod (Rod Johnson & & Associates, Associates, Inc.) Inc.) Jim Small (Edward Jim (Edward Kraemer Kraemer & & Sons) Sons) 1340-1400 Easton, 1340-1400 Easton, R.M. R.M. Metamorphic Map Map of the Canadian Canadian Shield Shield of Ontario, Ontario, Michigan, Michigan, Minnesota, Minnesota, and and Wisconsin Wisconsin 1400-1420 Vitton, 1400-1426 itt ton, S.J. and and Subhash, Subhash. G. G. Dynamic and Static Strength of of Aggregates: Aggregates: An Estimate Estimate of of Static Strength Strength Rate Sensitivity of Geological Materials Rate Sensitivity Geological Materials . ,. . .. . . , : .: :>: , , i.#&: ..' , 3B ?:'$ .A, '3 1420-1440 1420-1440 Yeo, Yeo, G.M. Is the Janice Lake Unconformity a Link between the Hearne Craton and the La Ronge Ronge -- Lynn Lynn Lake Volcanic Arc? . .. . . .. . ! I . - . .... : 1440-1510 1440- 15 10 Coffee CoffeeBreak Break 15 10-1530 Czeck, 1510-1530 Czeck, D.M. and and Hudleston, Hudleston, P.J. P.J. Structural Structural Fabric Fabric and and Strain Strain for for the the Seine Seine River River Conglomerates Conglomeratesat at the the Wabigoon-Quetico Wabigoon-QueticoSubprovince Subprovince Boundary Boundary Near Mine Mine Centre, Centre, Ontario Ontario 1530-1550 Cannon, Cannon,W.F. W.F.and andWoodruff, Woodruff,L.G. L.G. Isle Mercury Distribution in Bedrock, Distribution in Bedrock, Native Copper Copper Ore Ore and and Soils Soils -- Isle Royale National Park, Michigan Michigan 1830-1930 Social Cash Bar 1830-1930 Social - Cash . . . . . . . ?:. 1930-2130 Annual Banquet at Ramada Inn xvii i xvii .:i"> ,. : . . .S t . + . . . ., . . , . . ,. . . .. . . .,. , . "' �j Friday, Friday, May 7 Technical Session ffl III Technical r-Â¥f Session Chair. Chair: Ron Graber (Cliffs Mining Services Co.) Tom Waggoner (Cliffs (Cliffs Mining Services Services Co.) 0830-0850 LaBerge, 0830-0850 LaBerge,G.L. G.L. Regional Patterns on the Peno Penokean Continental Margin in the ~e~ional Southern Lake Superior Superior Region Regio 0850-0910 0850-0910 Ottke, D. Ottke,D. i.g,. , ,, , .~*: Early Descriptions of the Natural Features on the Marquette 1Iron r o Range n ~ a n ~- e ,: --. J J U j L 0910-0930 Webster, Webster,C., C.,Cambray, Cambray,W., W., Scott, Scott,0., G.,Nordstrom, Nordstrom,P., P., Wilson, Wilson, E. E. Palmer Gneiss: A Large, Low-grade Low-grade Shear Shear Zone Zone ., , '.!, , 0930-0950 Diedrich, Diedrich,T.R., T.R., and andMorton, Morton,P. P. Investigation of CaO at Thunderbird Mine, Mesabi Range: Range: Mineral and Stratigraphic StratigraphicRelationships Relationships j 0950-1020 0950- 1020 Coffee CoffeeBreak Break 1020-1040 Medaris, Medaris,L.G., L.G., Fournelle, Foumelle,J., J., Boszhardt, Boszhardt, R., R., and and Broihahn, Broihahn, J. T* Chemical and Mineralogical Comparison Comparison of Baraboo, Barron, Ban-on, and Sioux Sioux Argillite, Metapelite, Metapelite, and Pipestone Pipestone 1040-1100 1040-1100 Graber, Graber,R.G. R.G.and andStrandlie, Strandlie,A.J. A.J. Where are the Metamorphosed Natural Orebodies of the Mesabi Range? Range? j 1100-1120 1100-1120 Scott, G.W. and Lukey, Lukey, H.M. Geology of the Tilden Mine, Marquette iron range, Michigan J 1120-1140 1120-1140 Meier, Meier,J.G. J.G. Republic Wetland Preserve 1140-1300 1 140-1300 Lunch Lunch U J xix j �I Technical TechnicalSession SessionIV IV Session Session Chair: Chair: John John Green Green (University (University of of Minnesota, Minnesota,Duluth) Duluth) Dave DaveBaxter Baxter(PayDay (PayDayResources) Resources) 1300-1320 1300-1320 Boerboom, Boerboom,T.J. T.J.And AndSeverson, Severson,M. M. Geologic Geologic Map Map of of the the Western Western Penokean Penokean Orogen, Orogen, East-Central East-Central Minnesota Minnesota :. 4 8 -?-# 1320-1340 1320- 1340 Daniels, Daniels,D.L., D.L.,Nicholson, Nicholson,S.W., S.W.,Cannon, Cannon,W.F., W.F., and andBracken, Bracken,R.E. R.E. Preliminary Aeromagnetic Map of Wisconsin Preliminary Aeromagnetic Map of Wisconsin 1340-1400 1400 Johnson, Johnson,R.C. R.C.and andBornhorst, Bomhorst, T.J. T.J. Ishpeming Ishpeming greenstone greenstone belt belt -- Evidence Evidence for for Archean Archean tectonic tectonic evolution evolution of the southern edge of the Superior Province in Michigan of the southern edge of the Superior Province in Michigan 1400-1420 1420 Yeo, Yeo,G.M. G.M. Low-Resolution Low-Resolution Sequence Sequence Stratigraphy Stratigraphyof of Early Early Proterozoic Proterozoic Paragneisses, Paragneisses, Wollaston Wollaston Domain, Domain, Saskatchewan Saskatchewan I I I I I I 1420-1450 1420- 1450 Coffee CoffeeBreak Break 1450-15 10 Bickford, 1450-1510 Bickford, M.E. M.E. and and Steinhart, Steinhart,W.E. W.E. Distribution Distribution of of the the Archean Archean to to earliest earliest Paleoproterozoic Paleoproterozoic Sask Saskcraton craton beneath beneath deformed deformed orogenic orogenic rocks rocks in in the the Trans-Hudson Trans-Hudson orogen orogen and andits its tectonic implications: Evidence from common Pb and Sm-Nd isotopic tectonic implications: Evidence from common Pb and Sm-Nd isotopic data data 1510-1530 Miller, Miller, J.D. J.D. Jr. Jr. 1510-1530 Potential Potential for for stratiform stratiformPGE PGE mineralization mineralization in in mafic mafic layered layered intrusions intrusions of of the the Duluth Duluth Complex Complex - 1530-1550 Peterson, Peterson.D.M. D.M.and andMorton, Morton,R.L. R.L. Development Development of of Volcanogenic Volcanogenic Massive Massive Sulfide Sulfide Deposit Deposit Exploration Exploration Targets Targets in in Northern Northern Minnesota Minnesotafrom from GIS GIs Spatial SpatialAnalysis Analysis of of Geological, Geological, Geochemical, Geochemical, and Geophysical Geophysical Criteria 1550-1610 1550-16 10 Loughry, Loughry, J.E., Johnson, Johnson, Matthew Matthew M., and Cotter, J.F.P A Geochemical Geochemical and and Petrologic Petrologic Study Study to Determine the Origin of the the Crowduck Crowduck Lake Lake Group, Group, Kenora, Kenora, Ontario: Ontario: A A Problematic Problematic Metaconglomerate Metaconglomerate xx �—I Poster Session Poster Session J Posters will be Friday 1200 Posters be up up from from Wednesday Wednesday 1900 1900 to to Friday 1200 Authors will will be be at at posters posterson onWednesday Wednesdayfrom from1930 1930to to 2100 Authors Ams, D. and Holm, D., Characterization Characterization and Timing Timing Constraints Constraints of Post-Penokean Post-Penokean Meso-Scale Structures in the Watersmeet and Republic Gneiss Domes of Northern Structures Michigan Barber-Delach, R.D. and and Cannon, Cannon, W.F., Re-examining Stream Stream Sediment Sediment Geochemical Data from the National Uranium Resource Evaluation Program Program Geochemical (NURE), Wisconsin and Northern Michigan (NURE), and Michigan Han, T.M., T.M., Megascopic Megascopic Fossils and Their Their Possible Possible Contribution Contribution to to the the Han, Development of the Silicate Silicate Unit Unit of of the the Negaunee Negaunee Iron Iron Formation, Formation, Empire Empire Mine, Mine, Marquette Range, North Michigan Marquette Michigan Holm, D., Romano, D., and Mancusco, C., Comparison of Mica Ar/Ar AdAr and Rb/Sr Thennochronology Results from Northern Wisconsin and Northern Michigan j J J lUasner, J.S., Klasner, J.S., Cannon, Cannon, W.F., Schulz, Schulz, K.J., and LaBerge, G.L., G.L., The Iron River Syncline: An Allochthonous Structural in the the Penokean Penokean Foreland Foreland of of Structural Panel in Syncline: Northern Michigan Miller, J.D. Jr, and Miller, and Chandler, Chandler, V.W., V.W., New Geologic Geologic Map of the Central Central Duluth Duluth Complex Complex Rausch, D.E., and Wattrus, N.J., Rausch, N.J., Lake Superior's Rings: Clues to the Origin of Polygonal Fault Systems Polygo J J j xxi j �Saturday. May Saturday. Mav 8 8 0800-1730 0800-1730 Field and 4 Field Trip Trip 3 and Field of the the Marquette Marquette Iron Iron Range, Range, Field Trip Trip 3: 3: Tilden Tilden and and Empire Mines of Michigan G.W. Scott, Scott, P.M. P.M. Nordstrom Nordstrom and and H.M. H.M. Lukey Lukey Leaders: G.W. Michigan -- Leaders: Field Trip 4: Paleozoic and and Glacial Geology from Au Train to Grand Trip 4: Marais, R.S. Regis Regis and and J.B. LB. Anderton Anderton Leaders: R.S. Marais, Michigan Michigan -- Leaders: xxi xxi i �45TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Abstracts Abstracts �CHARACTERIZATION AND AND TIMING TIMING CONSTRAINTS CHARACTERIZATION CONSTRAINTS OF POST-PENOKEAN POST-PENOKEAN MESO-SCALE STRUCTURES STRUCTURES IN IN T THE MESO-SCALE H EWATERSMEET WATERSMEET AND REPUBLIC REPUBLI~GNEISS GNEISS DOMES OF OF NORTHERN MICHIGAN MICHIGAN David Ams (undergraduate student) and Daniel Hoim, Holm, Department Department of Geology, Kent State Ams (undergraduate University, Kent OH 44242 OH 44242 We have measured late, meso-scale, structures present present in in Early Proterozoic Proterozoic gneiss gneiss meso-scale, ductile and brittle structures in order to to assess assess their their origin. origin. The Watersmeet and Republic gneiss gneiss domes domes domes of northern Michigan in lie north north of of the the region regionofofpervasive pervasivepost-Penokean post-Penokean 1600-1650 1600-1650 Ma shortening shortening (Hoim (Holm et a!., al., 1998, 1998, Geology) and southeast which closed the Keweenawan Keweenawan rift rift at ca. 1080-1860 southeast of thick-skinned thrusting which whether meso-scale meso-scalebrittle brittle and andductile ductile 1994, Geology). The The challenge challenge then is to determine whether Ma (Cannon, 1994, shear zones formed during during the late stages stages of Early Proterozoic gneiss dome formation or if they represent deformation associated defamation associated with these these younger younger events. events. Watersmeet gneiss Watersmeet gneiss dome. observations were made on the north-east side of the dome, south of its contact with the overlying Our observations metasedimentary rocks rocks (Hwy (Hwy 45 45 exposures). exposures). The dominant steep east-west fabric fabric in in Archean Archean rocks rocks of of metasedimentary brittle shear shear zones. zones. The ductile the dome are cross-cut by steep ductile, semi-brittle, and brittle ductile and larger semiand dip dip steeply steeply both both north north and and brittle to brittle shear zones show a dominant N70-80E strike orientation and etc.), the apparent sense sense south (Fig. 1). Where Where relative relativemotion motion indicators indicators exist (offset dikes, pegmatites, etc.), up. Small to be be oriented oriented NS NS (with (with steep steep east east of motion is south-side up. Small scale scale brittle brittle faults and fractures tend to dips) dips) or NW (with steep steep southwest dips). Slickenlines Slickenlineson on the the NW NW oriented oriented set set plunge plunge gently gently to to the the NW NW Pie. 1 (Fig. 1). .--o- *1 The coarse, more gentle gentle to to the the north north toward toward the the contact contact coarse, steep, steep, EW fabric fabric of the dome interior becomes more rocks and and shows shows aareduction reductioniningrain grainsize sizedue duetotoductile ductileshearing. shearing.We Weattribute attribute with the metasedimentary rocks this to ductile ductile overprinting shear zone. zone. The overprinting of the steep fabric along a basement-cover shear The timing timing of shearing shearing during gneiss gneiss dome dome formation formation is is constrained constrained by aa 1765 1765 Ma Ma hornblende hornblende Ar/Ar ArIAr plateau date date obtained obtained from from the core rocksjust just from aa concordant concordant muscovite plateau date obtained from metasedimentary rocks core rocks and from north of the see also also Schneider Schneider et et al., al., 1996, 1996, CJES). CJES). the contact contact (Fig. (Fig. 2; 2; see We propose that ductile and semi-brittle shear zones zones Conned formed during during the thelate latestages stagesof ofunroofing unroofingofof thal the theductile of the the footwall footwall In our our model model they thev represent remesent internal deformation of the gneiss dome (at ca. 1765-1755 1765-1755 Ma). In dome rocks as they were unroofed from beneath the metasedimentary cover rocks along a north-dipping detachment fault fault at at the basement-cover contact. The brittle shear zones have a completely different detachment basement-cover contact. ones. Their orientation from the ductile and semi-brittle ones. Their orientations and subhorizontal lineations suggest rift. they may be related to closure of the Keweenawan rift. Republic gneiss dome. Republic fracture zones zones which which occur occur in in the the Republic We focused on the numerous chlorite mineralized brittle fracture Ma post-tectonic post-tectonic alkali alkali red red granite granite gneiss dome north of Republic (Fig. 3). They Theycross-cut cross-cutthe the—1735 -1735 Ma be younger younger than than mica mica cooling cooling ages ages within within the the dome dome (1680-1720 (1680-1720 Ma). Ma). (Xgaf of Sims. Sims, 1992) 1992) and must must be They have a dominant north-northwest north-northwest strike strikeand anddip dip moderately moderatelytotosteeply steeplytotothe thewest. west. Most of the They lineations plunge gently gently to to the the northwest. northwest. Kinematic fiber steps) steps) on on a few few of these Kinematic indicators (crystal fiber show left-lateral, reverse motion. Ductile Ductileshear shear zones zones within within the dome dome strike dominantly northwest and dip steeply and must be older older than the mica cooling coo1i.i; ages. ages. related to to the older ductile shear zones along The brittle fractures do not appear to be kinc:iiatically kincniatically related uplifted. The which the gneiss dome block was probably uplifted. Thedominant dominant left-lateral left-lateral strike-slip strike-slip motion and be defonnational deformational features features associated associated with withclosure closureof of north-northwest attitude indicates they might be also be the Keweenawan rift. This Thisinterpretation interpretationisisconsistent consistentwith with prior prior thermochronologic thennochronologic evidence evidence for a low temperature Keweenawan CJES). temperature Keweenawan age age disturbance disturbance of this region (Schneider (Schneider et al., 1996, 1996, CJES). 2 �Ductile shear zones Smaller britile fracture zones Fig. Fig. 1. Stereonet Stereonet plots of of ductile, ductile, semi-brittle, semi-brittle, and and brittle brittle shear shear zones zones within the Watersmeet the Watersmeet gneiss gneiss dome. 1 -1 Schist outside of the dome — 2000J 2000: Amphibolite imnhibolite within within the the dome AGE 1 Ma 1500 - - 1000-0_ 94-MI-3-H 94-MI-3-H Hornblende Hornblende Tg=1751±l3Ma T g = 1751k13Ma - Tp=1765±l3Ma %39Ar 100 0 UP-i OA-M UP-1 0A-M Muscovite Muscovite Tg=1760±i4Ma Tp=1767±l7Ma 100 %39Ar Fig. 2. Ar/Ar mineral Fig. mineral age age spectra from from the the Watersmeet Watersmeet gneiss gneiss dome region. region. date. Tg Tg Is is total gas Tp is plateau date. gas date. Fig. 3. 3. Stereonet plots plots of ofrepresentative representativeductile ductileshear shear zones zones and and mineralized mineralized Fig. brittle fracture brittle fracturezones, zones. Republic Republic gneiss gneiss dome dome region. region. 3 1 �Re-examining stream sediment data ffrom National U Uranium Re-examining sediment geochemical geochemical data r o m tthe h e National r a n i u m Resource Resource Evaluation Program and nnorthern o r t h e r n Michigan Michigan Evaluation P r o g r a m (NURE), (NURE), Wisconsin Wisconsin and Robert D. Barber-Delach, Oak Oak Ridge Ridge Associated Associated Universities, Universities, at at U.S. U.S. Geological Geological Survey. Survey, Mail Mail Stop Stop 954, Reston, VA VA 20192 20192 W.F. W.F. Cannon, U.S. Geological Geological Survey, Survey, Mail Mail Stop Stop 954, 954, Reston, Reston, VA VA 20192 20192 In the In the latter latter 1970's 1970's a astream streamsediment sedimentgeochemical geochemical survey survey was was conducted conducted in in parts parts of ofnorthern northern the United United States Department Department of of Energy. Energy. A A Wisconsin and northern Michigan by the NURE program of the data set consisting I °x2° data consisting of of multi-element multi-element analyses analyses of of 3185 3 185 samples samples was was developed developed spanning spanning eight eight l0x2' quadrangles. The but also quadrangles. The data datawere wereintended intended for foruse use ininevaluating evaluatingundiscovered undiscovered uranium uranium resources, resources, but have application geochemical background background and and baseline have application for for establishing establishing regional regional variations variations in geochemical baseline concentrations. The The U.S. is concen&itions. U.S. Geological ~ e o l o ~ i c Survey Survey al is ____________________________________________ expanding research research on on regional regional geochemical geochemical Figure I. 1. Comparison of unadjusted (a) (a) and patterns, and and the the NURE data set patterns, MURE data set is is being being rerenormalized (b) (b) cobalt cobalt concentrations concentrations for for use use in in normalized examined as as part of of that that effort. effort. displaying NURE stream sediment sediment data. data. In many places places the the NURE NURE data datashows showsobvious obvious biases in in values values between between adjacent adjacent quadrangles, quadrangles, visual in some some cases cases apparent only by visual examination of element concentration maps. For instance, Figure llaa shows shows significant discontinuities of cobalt values values between quadrangles in the original original NURE NURE data. data. Biases were probably introduced introduced by by somewhat somewhat different sampling, processing, sampling, processing, and analytic analytic techniques techniques between various quadrangles, between quadrangles, and probably also changes in analytical by time-dependent time-dependent changes instrument calibration that that appear appear not not to have instrument calibration have been fully accounted for over the duration of the NURE program. program. These Thesequadrangle-based quadrangle-based biases biases render use of render of the thedata dataproblematical problematical without without careful assessment careful assessment and correction correction of of analytical analytical biases. Here Here we present present two two approaches approaches by by which the NURE NURE data data set set can can be be corrected corrected for for which the quadrangle biases. in analytical data First, systematic biases in between can be normalized between quadrangles quadrangles can normalized by by quadrangle as as a displaying data for each each quadrangle function of the statistical function statistical distribution distribution of values values for only that quadrangle. Figure lb for quadrangle. Figure I b shows shows the the same data for cobalt as shown in Figure Ia, same la, but but each of with the values within within each of the the eight separately into quadrangles quadrangles classified separately percentiles of the data data set set from from that that quadrangle. quadrangle. The between-quadrangle bias bias is is largely largely removed removed and natural patterns patterns of of cobalt cobalt variation variation are are more more 4 a. Unadjusted data . . ,do.- adom. b. Data normalized within quadrangles �evident. that standard standard desktop desktop G GIS software evident. This Thistechnique technique has has the the advantage advantage of of ease ease and and simplicity simplicity in in that I s software can perform statistical manipulation manipulation of of data data and and time time required required for for perform and display the results with minimal statistical processing. Also, Also, the technique However, two two technique does not require acquisition acquisition of new analytical analytical data. However, important shortcomings shortcomingsof of the the technique only relative of element are: 1) presents only relative variations variations of element important technique are: I) itit presents concentrations and and does does not not improve the the overall overall accuracy accuracy of of the the NURE NURE data, data, 2) 2) itit masks masks true true variations variations concentrations quadrangle. that occur at the approximate scale of a l°x2° l0x2"quadrangle. A second In the the 1980's, A second technique technique requires requires new new analytical analytical data. data. In 1980's, the the USGS USGS became became the the official official archiving agency agency for for NURE NIJRE data and maintains repository in in Denver, Denver, Colorado archiving data and and samples, samples, and maintains aa sample sample repository Colorado in which all N'URE samples samples are are accessible accessiblefor for restudy. restudy. We re-analyzed aa subset subset of of those those samples samples We have have re-analyzed in which all NURE for the Ashland and Rice Rice Lake Lake l°x2° Iox2' quadrangles quadrangles in northern Wisconsin and compared the results of our re-analyses to to the the original original data data reported reported by by the the NURE NUREprogram. program. Our Our analyses analyses were were done done using using routine routine re-analyses 40-element inductively 40-element inductively coupled coupled plasmaplasmaatomic emission spectroscopy Figure 2. 2. Scatterplot Scatterplot of of magnesium magnesium concentration concentration spectroscopy (ICP-AES) (ICP-AES) Figure technique supplemented supplemented by by more (ppm) demonstrating demonstrating the the quad quad bias bias of of original original NURE NURE technique more precise precise (ppm) single-element techniques for arsenic and data, with with fitted fined regression regression lines lines and and correlation correlation single-element techniques and data, selenium. Analytical precision and and Analytical indices (R2). indices (R'). accuracy were monitored accuracy were monitored by by replicate replicate 2.1 2.1 analyses of standard samples. ,, 1 , -, — 1 Comparison of our new new values values to to 1.8 •0 concentrations reported reported by by NURE NURE show show $b —, quadrangle-based quadrangle-based biases in virtually all 1.5 elements elements for which which aa significant significant number number —— 000 of samples exceed exceed detection limits (about (about ,. elements). Figure 20 elements). Figure 2 shows shows an extreme 0 case in which NURE magnesium analyses 09 are strongly and and consistently consistently quadranglequadrangle0.9 dependent and in which which both both quadrangles quadrangles vary significantly from our new analyses. j, vary significantly from analyses. of bias bias within within aa 0.6 This consistency of quadrangle allows derivation of equations •Rice Lake Lake Quad Quad Â¥Ri that can adjust the original original NURE data to 03 correct for previous analytical biases and and oAshland Quad Quad OAshland , new produce a better accord with new 0 data. Although Although this technique analytical analytical data. technique 1.8 2.1 0.6 0.9 1,2 1.5 0.3 has 00 0.3 0 .6 0.9 1.2 1.5 1.8 2.1 has inherent inherent statistical statistical uncertainty, uncertainty, that that the and the uncertainty is quantifiable, and Re-Analyzed Mg MgConcentration Concentration Re-Analyzed element maps are resulting element are significantly significantly L more accurate accurate than than those made from more from the the Although this this technique techniquedoes doesrequire requirethe the cost cost and and time time of original NURE data. of re-analyzing re-analyzing aa original data. Although significant number number of of NURE NURE samples, samples, the the result result produces producesaamuch much improved improveddata dataset setwithout withoutthe thecost costof of re-analyzing the entire sample set. We plan to proceed with this technique during the coming year. re-analyzing the entire set. We to the year. , . 7 • , 7 i. • — - 7 5 I �Distribution Distributionof ofthe theArchean Archean to to Earliest Earliest Paleoproterozoic PaleoproterozoicSask Sask Craton Craton Beneath Beneath Deformed Deformed Orogenic OrogenicRocks Rocksin inthe theTrans-Hudson Trans-HudsonOrogen Orogenand andits itsTectonic TectonicImplications: Implications:Evidence Evidencefrom from Common Common Pb Pb and and Sm-Nd Sm-Nd Isotopic IsotopicData Data M. E. Steinhart, III, ifi, Department M. E. E. Bickford Bickford and and William William E. Departmentof of Earth Earth Sciences, Sciences, Heroy Heroy Geology Geology Laboratory, Syracuse University, Syracuse, NY 13244-1070 Laboratory, Syracuse University, Syracuse, NY 13244-1070 Late, Late, undeformed, undefonned ,ca. ca.1.8 1.8Ga Gapegmatites, pegmatites,leucogranitic leucograniticsheets, sheets, and and post-orogenic post-orogenic plutons plutons in in the Glennie, Hanson Lake, and La Ronge Domains, and parts of the Hearne Province, were studied Glennie, Hanson Lake, and La Ronge Domains, and parts of the Hearne Province, were studied to melting ofjuvenile ofjuvenile orogenic orogenic crust crust or or of Archean todetermine determinewhether whetherthey they were werederived derived by melting Archean lower structuralwindows windowsin inthe theGlennie Glennieand andHanson Hanson lower crustal crustalrocks rocksequivalent equivalentto tothose thoseexposed exposedin instructural Lake isotopic composition of of PbPb from feldspars (206Pb/2°4Pb == 14.3 14.3-- 15.2; 15.2; LakeDomains. Domains.The The isotopic composition from feldspars (20Èpb/== 15.1 15.1-- 15.25; 15.25;208Pbf°4Pb ^"Pb/'^Pb ==34.4-36.4) 34.4 - 36.4) and andSm-Nd Sm-NdTDM TDM ages of of ca. ca. 3.2 3.2 Ga Ga m7~b/2d4pb ages for forca. ca.1.8 1.8Ga Gapost-orogenic post-orogenicintrusions intrusionsreveal revealthat thatArchean Archean rocks rocks are arenot not only onlyexposed exposedin inthe the windows, windows,but butalso alsoextensively extensivelyunderlie underlieparts partsof ofthe theGlennie Glennieand andHanson HansonLake LakeDomains Domainsininwhich which only Incontrast, contrast,feldspar feld arPb Pbfrom frompegmatites pegmatitesin inthe the only juvenile Paleoproterozoic Paleoproterozoicrocks rocksare areexposed. exposed. In La similar == 15.1 b/-b 15.1-- 15.2; 15.2; 15.4 - 15.6; 15.6;207Pb/2"Pb LaRonge Ron eDomain Domainisisisotopically isotopically similar(2°6Pb/2°'Pb ('"'Pb/^'Pb ==15.4208Pb/204Pb plutons with TDM "'PW b =34.8 34.8-- 35.2) 35.2)to tothat thatofjuvenile, ofjuvenile,ca. ca.1.85 1.85Ga GaPaleoproterozoic Paleoproterozoic plutons with TDM ages oceanic materials. materials. Sm-Nd data agesof ofca. ca.1.80-2.0 1.80-2.0Ga, Ga,indicating indicatingderivation derivation from similar oceanic data from from two yield TDM ages twoLa LaRonge RongeDomain Domainaplites, aplites,ininwhich whichSm Smand andNd Ndare areapparently apparentlyunfractionated, unfl-actionated, yield TDM ages of 19 Ga. Surprisingly, feldspar Pb data (2°'Pb/2°4Pb 207Pb/204Pb = 15.1 Surprisingly,feldsparPbdata (""Pb/^Pb== 15.515.5 - 15.8; 15.8;^Pb/^'Pb= 15.1-- 15.2; 15.2; of1.8-. 1.8-.19Ga. 35.0--35.2) 35.2) from frompegmatites pegmatitesthat that intrude intrudeArchean Archean rocks rocksof ofthe theHearne HeameProvince, Province,in in m'~b/-b ==35.0 the thehinterland hinterlandwest westofofthe theNeedle NeedleFalls FallsShear ShearZone, Zone,also alsoindicate indicatederivation derivationfrom fromjuvenile juvenilesources. sources. Thus, viewthat thatan anArchean Archeanmicrocontinent microcontinent("Sask ("SaskCraton") Craton") Thus,while whilethese thesedata datasupport supportthe theview underlies underliesparts partsof ofGlennie Glennieand andHanson HansonLake LakeDomains, Domains, they they suggest suggest that that crust crustbeneath beneathLa LaRonge Ronge Domain, Domain,and andalso alsobeneath beneathatatleast leastparts partsofofHearne HeameProvince, Province,isisofjuvenile ofjuvenilemantle mantlederivation. derivation. Alternatively, LaRonge RongeDomain Domainand andHearne HearneProvince, Province, Alternatively,Archean Archeancrust crustmay maybe bepresent presentbeneath beneaththe theLa but ca.1.8 1.8Ga Gapegmatites pegmatiteswere wereformed. formed.These These butwas wasbelow belowthe thezone zoneofofmelting meltingwhen whenthe theca. observations observationsare areconsistent consistentwith withinterpretation interpretationofofnorthwesterly-dipping northwesterly-dippingreflectors reflectorsbeneath beneath Hearne revealedby byCanadian CanadianLithoprobe Lithoprobeseismic seismic data, data, as asrepresenting representingsubducted subducted H e m eProvince, Province,asasrevealed oceanic oceaniclithosphere. lithosphere.The Thepresence presenceofofoceanic oceaniclithosphere lithospherebetween betweenHearne HeameProvince Provinceand andGlennie Glennie Domain Archeanmicrocontinent microcontinentbeneath beneaththe theGlennie GlennieDomain Domainisisprobably probablynot not Domainindicates indicatesthat thatthe theArchean subducted subductedHearne H e m ecrust, crust,but butmore morelikely likelyan anexotic exoticcrustal crustalfragment. fragment. =% 4 6 �GEOLOGIC MAP GEOLOGIC MAP OF OF THE THEWESTERN WESTERN PENOKEAN PENOKEAN OROGEN, OROGEN, EAST-CENTRAL EAST-CENTRAL MINNESOTA BOERBOOM, Terrence Terrence J., J., Minnesota Minnesota Geological Geological Survey, Survey,2642 2642 University UniversityAve., Ave.,St. St.Paul, Paul,MN MN 55114; BOERBOOM, 55114; boerboOl @maroon.tc.umn.edu; @maroon.tc.umn.edu; and boerb00l and SEVERSON. SEVERSON, Mark, Mark, Natural Resources Resources Research Institute, Institute, University University of Minnesota, Duluth. Duluth, MN 55811; 5581 1;mseverso@sage.nrri.unm.edu mseverso@sage.nrri.umn.edu The Natural Resources Resources Research Research Institute, Institute, has has recently recently The Minnesota MinnesotaGeological Geological Survey, Survey, in cooperation with the Natural completed Orogen in east-central east-central Minnesota. Minnesota. comnleted aa revised revised geologic eeoloeicmap man of the the western portion nortion of the Penokean Oroeen The geologic framework western Penokean framework for for the thewestern ~ e n o k e Orogen kOrogen has has been been previously previously interpreted interpreted by by Southwick Southwick and others (1988) using plate-tectonic theory theory (see discussion discussion below). below). This This map map builds builds on on that that base base by by data. Although utilizing new drilling information and better geophysical geophysical data. Although thousands thousands of of exploratory exploratory holes holes were drilled in this area area from the late l800s 1800sto tothe the 1950s, 1950s.nearly nearly all all focused focused on locating locating iron, iron, manganese, manganese, or or sulfur ore. As Asaaresult, result, the thedistribution distributionand and form form of of the the major major iron-formations both within and outside the iron-mining districts are fairly well established, but but little little is is known known about aboutthe the areas areas in in between. between. Thus, any geologic compilation compilation necessarily relies relies heavily on geophysical interpretations. interpretations. GEOLOGIC FRAMEWORK Southwick (1988) interpreted interpreted the Penokean Orogen to consist of several structural panels that range from sedimentary sedimentary rocks rocks filling filling aa foreland foreland basin, basin, through through aa main main fold-and-thrust fold-and-thrust belt belt of sedimentary sedimentaryand and volcanic volcanic rocks, to a complex terrane. The major terranes, referred referred to as panels in the list rocks, complex metamorphic-plutonic metamorphic-plutonic terrane. list below, are separated by linear, linear, northeast-trending northeast-trending aeromagnetic aeromagnetic anomalies, which are are interpreted interpreted as as thrust thrust faults that truncate stratigraphy-related stratigraphy-relatedaeromagnetic a e r ~ r n a ~ e tanomalies ainc o d i e s within the panels. The Thefollowing followingsummary summary of the structural I), and modified accordingly accordingly structural panels panels is is condensed condensed from from Southwick Southwick and others others (1988) (1988) (Fig. (Fig. 1), for this study study based based on on new new information. information. 1. The Animikie basin is filled with essentially essentially unmetamorphosed unmetamorphosed sedimentary 1. The Animikie sedimentary rocks rocks (Pokegama (Pokegama Quartzite, Quartzite, Biwabik Iron Formation, Formation,and and Virginia Formation). The TheAnimikie Animikie strata strata generally generally have have aa shallow shallow south south dip, but along along the the southern southern basin basin margin, margin, and and hence hence this this map map area, area, are are deformed deformed into into fairly fairly tight tight upright upright folds. folds. In Inthis thisarea areaofofthe themap, map,these thesestrata strataunconformably unconformablyoverlie overlierocks rocks of of the the foldfold- and and thrust-belt. thrust-belt. 2. The North Range 2. Range panel panel isisdominated dominatedby byweakly weaklymetamorphosed metamorphosedargillite, argillite, siltstone, siltstone, quartzite, quartzite,ironironformation, graphitic slate, graywacke, and minor limestone and and chert. chert. Volcanic and hypabyssal mafic rocks rocks are are a minor component componentof the the North Range. Structurally, Structurally,the the North North Range Range is is dominated dominatedby by aa large large northwest-inclined, northwest-inclined, doubly plunging synclinorium. synclinorium. Geophysical Geophysicalmodels models (Carlson, (Carison, 1985) 1985) show that the folded Animikie Basin. The folded Trommald Trommaldiron-formation iron-formationcontinues continuesto tothe theeast eastbeneath beneath rocks rocks of of the thehimikie Thestructural structural of those deposited in an external and stratigraphic attributes of North Range rocks are characteristic of tectonic zone. zone. 3. The 3. The South South Range Rangepanel panel also alsocontains containsan an abundance abundanceof of slaty slaty and and argillaceous argillaceousrocks, rocks, but but unlike unlike the the North North Range, rocks, all of which Ranee. it has aa substantial substantial component comoonent of mafic rnafic volcanic volcanic and hypabyssal hvpabyssal intrusive rocks, have undergone low-grade inthe theSouth SouthRange Rangeresembles resemblesAlgomaAlgomahaveundergone low-grade metamorphism. metakorphism. The Theiron-formation iron-formationin type iron-formations iron-formations in in that that itit occurs occurs as as aa series seriesof of Jenses lenses closely associated with mafic volcanic rocks and graphitic anomalies. The graphitic slate. slate. This Thispanel panel isis characterized characterizedby narrow linear aeromagnetic anomalies. The structure structure of the the South South Range Range isis dominated dominatedby by elongate elongateeast-northeast-trending east-northeast-trending overturned overturnedfolds. folds. The South Township panel panel to to the the south south by byaa South Range Range panel panel is is separated separated from from the Moose Lake-Glen Township narrow zone of graphite-rich, graphite-rich, crenulated crenulated phyllitic schist that curves from northeast to east-west. This This graphitic schist schist may have absorbed absorbed aa great great deal deal of strain strain during during thrust thrust faulting. faulting. 4. The TheMoose MooseLake-Glen Lake-GlenTownship Townshippanel panel isis dominated dominated by by quartz-rich quartz-rich metaclastic rocks and by mafic mafic volcanic graphitic argillite argillite and and schist; schist; all were subjected volcanic and hypabyssal intrusive rocks, along with graphitic subjected to lower greenschist-facies greensehist-facies metamorphism. This Thispanel panel includes includes the the Glen Glen Township Formation, a sulfiderich graphitic schist schist grading grading into into aa sulfide sulfideiron-formation iron-formation that that contains contains pyrrhotite, pyrrhotite, pyrite, pyrite, lesser lesser chalcopyrite, and consists of ofamygdaloidal amygdaloidal chalcopyrite, and minor minor sphalerite. sphalerite. The Thestratigraphic stratigraphicsection section at at Glen Township consists basalt overlying overlying the the sulfidic-graphitic sulfidic-graphiticschist, which in turn overlies graywacke. In In places places the the latter lattertwo two are separated by slaty iron-formation. iron-formation. The Thebase base of of the thesequence sequencecomprises comprises quartz-rich quartz-rich sedimentary sedimentary moderate magnetic magnetic anomaly. rocks that typically contain contain up up to several several percent magnetite, which causes a moderate Several prominent linear linear aeromagnetic anomalies anomalies apparently reflect some combination of thrust faults faults with relatively minor displacement, displacement, and stratigraphic and lithologic variation. variation. The GlenTownship Glen Township strata strata have undergone undergone at least least two two generations generationsof of folding folding that that produce produce complex complex aeromagnetic aeromagneticpatterns. patterns. �A previously unrecognized, synsyn- to to late-orogenic late-orogenic monzonitic intrusion intrusion with with aa well-defined well-defined circular circular aeromagnetic anomaly core drilline drilling iust just northwest northwest of ofMille Mule Lacs Lacs Lake. Lake. Another Another core core aeromaenetic anomalv was intersected by bv core hole hole drilled drilled on on this this anomaly anomaly intersected intersected ten ten feet feet of o faabrick-red, brick-red,unmetamorphosed unmetamorphosed quartz-pebble quartz-pebble conglomerate. This Thisunit unitisisgeophysically geophysicallyinvisible invisibleand and its its extent extent is is thus thus unknown, unknown, but but itit may may represent represent conglomerate that was deposited durine during Meso~roterozoic Mesoproterozoic time time in in aa shallow shallow basin basin on on the the backside backside of of aa conelomerate the Midcontinent Midcontinent rift, and the and thus thus is is correlative correlative with with Keweenawan Keweenawan rocks rocks to to the the east. east 5. The McGrath-Little 5. The McGrath-Little Falls Falls panel, panel, the the southernsouthern- and and internal-most internal-most component component of of the the foldfold- and and thrust-belt, thrust-belt, comprises comnrises granitic eranitic to to tonalitic tonalitic gneiss, eneiss. amphibolite-facies amnhibolite-facies pelitic nelitic schist, schist. and and latelate- to post-tectonic nost-tectonic granitic eranitic intrusions. An uncommon dike that Penokean granites of fresh, comnosed fresh. intr6sions.~n uncommon that nost-dates ~enokekn =m~ i t e s is composed -~~ ~- ~ ~ ~lamprophyre -la&ronhvredike -~~~~~ r~ ~ - r ~ ~- , ~ ~~~-~~ ~ post-dates - -~~ -~~~~-~~~ ~ euhedral be traced across across the entire entire map area area euhedral clinopyroxene clinopyroxenein in aa groundmass groundmass of of poikilitic feldspar; feldspar; it can be by its its pronounced pronounced reverse reverse aeromagnetic aeromagnetic anomaly. Abundant Abundant small small circular circular to to elongate elongate positive positive magmagnetic anomalies anomalies are areindicative indicative of of mafic-ultramafic mafic-ultramafic plugs plugs similar similar to to those that have been drilled at several locations to to the the south locations south and and east. east. Based Basedon onaeromagnetic aerom&$etic data, data, these these plugs plugs post-date post-date the the lamprophyre lamprophyre dike. The Thedike dikeisisconjectured conjecturedtotobe berelated relatedto tothe thewaning waningstages stagesof ofPenokean Penokean granite granitemagmatism. magmatism. ~ ~ ~~~~ -~ ~~~~ ~ ~ is ~ ~ References: References: Carlson, Carlson, K.E., K.E.,1985, 1985, A A combined combined analysis analysis of of gravity gravity and and magnetic magnetic anomalies anomalies in in east-central east-central Minnesota: Minnesota: M.S. 138p. p. M S . thesis, thesis. University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, 138 Southwick, Geologic map map (scale (scale 11:250,000) of the the Penokean Penokean Southwick, D.L., Morey, Morey, G.B., and McSwiggen, McSwiggen, P.L., P.L., 1988, Geologic :250,000) of Orogen, and accompanying accompanying text: text: Minnesota Report Orogen, central central and and eastern eastern Minnesota, Minnesota, and Minnesota Geological Geological Survey Survey Report of Investigations 37, 25 p. 37.25 p. Figure 1. 1. Regional Regional tectonic tectonicinterpretation interpretation elements discussed in in showing the tectonic elements the abstract- From Southwick and others (1998). This map does not reflect changes made on the map accompanying this poster. Area of revised geologic map 8 �Mercury distribution National Park, Park, Mercury distributionin inbedrock, bedrock,native nativecopper copperore, ore, and andsoils—Isle soils-Isle Royale National Michigan Michigan W.F. Cannon, U.S. W.F. U.S. Geological Geological Survey, Survey, Reston, Va L.G. Woodruff, U.S. Geological Geological Survey, Survey, St. Paul, MN In response response to recent recent findings findings of elevated elevated mercury in fish in some inland lakes on Isle Royale, we have begun a study of mercury concentration study of concentration in natural geologic materials of the island. Initially Initially we aimed to determine determine if elevated elevated mercury from native copper deposits could be contributing mercury to the impacted lakes. Small Smallnative nativecopper copperdeposits depositson onthe the island island were were mined mined the 1800's. Those sporadically in the Thosedeposits, deposits,waste waste dumps dumps at at abandoned abandoned mines, and wastes from small processing operations, do contain anomalous amounts of of mercury. mercury. Our Our analyses analyses have have found individual as much as 14 14 parts per million (ppm) mercury, and stamp sands individual samples samples with as were found to contain contain from 0.6 to 0.7 ppm. In Incontrast, contrast,typical typicalbedrock bedrockof of the the island, island, aa sequence sequence of volcanic Sampleswe we have have volcanic basalt flows, appears appears to be uniformly very low in mercury. Samples analyzed all had no detectable parts per billion (ppb). detectable mercury at at aa detection detection limit limit of of 55 parts (ppb). determine if mercury contained To determine contained in in mineral mineral deposits deposits could wuld be be aa source source of of mercury mercury to to impacted impacted lakes we sampled and analyzed analyzed soil soil and and glacial glacial deposits deposits on on which which the the soils soils formed formed in in two two test test wextaken takenaround aroundthe theMinong Minong mine, mine, the the largest largest mine mine on on the the island, island, to to determine determine areas. Samples Sampleswere the extent extent to which which anomalous anomalous metal content content of the ore and surrounding altered rocks affected the drainage drainage basins basins of of the trace element content of soils. Also, Also, samples samples were taken within the mercury in in fish. fish. No copper Sargent Lake and Lake Wagejo, two of the lakes with elevated mercury copper basins, but but deposits depositscould wuld be concealed concealed beneath beneath extensive extensive deposits are known known within within those those basins, mercury. In glacial deposits, and, if present, could be a contributor of mercury. In total, total, samples samples were were taken taken was taken from from the theAAsoil soilhorizon, horizon, aa dark dark organic organic mineral soil, soil, at 65 sites. At Ateach eachsite siteaa sample samplewas 1-6 inched below the surface. A second sample was taken from a depth of about 2 feet, A second sample was taken from depth consisting of either consisting either reddish reddish sandy sandy glacial glacial till till or or till till slightly slightly modified by soil-forming soil-forming processes processes (referred to here as BC horizon). as BC (referred Results show Results show that that the the copper copper deposit depositat at Minong Minong mine mine produces produces aa very very distinct distinct trace trace element element anomaly in soil, soil, especially especially the copper copper content of the BC horizon. Mercury Mercury also also is is somewhat somewhat elevated in samples closest to tothe thecopper copperdeposit. deposit. Mean Mean copper copper content content of of BC samples of the BC horizon closest ppm and that of of mercury mercury is is 44 44ppb. ppb. Highest values are 1160 1160 soils in the Minong mine area is 342 pprn ppm copper and 110 ppb mercury. The A soil horizon near the Minong mine averages 290 ppm pprn 110 The A soil horizon near the Minong averages pprn Cu and 70 thedrainage drainagebasins basinsfeeding feedingLake LakeWagejo Wagejoand and Sargent Sargent Lake, BC soils 70 ppb ppb Hg. Hg .InInthe ppm Cu, nearly five times lower than near Minong Minong mine, mine, and and 38 ppb Hg, essentially essentially average 60 pprn A-horizon soils soilsin inthe the Sargent-Wagejo Sargent-Wagejo drainage drainage average average 63 63 ppm pprn the same as at Minong mine. A-horizon Cu and 133 133 ppb ppb Hg. Hg. The The maximum maximum value value for for Hg Hg is is 370 370 ppb, ppb, an an exceptionally exceptionally high high value value for for soil soil For comparison, similar soil geochemical studies that we are conducting in the in this this region. region. conducting Chequamegon National Forest in Chequamegon in northern northern Wisconsin show A-horizon soils soils to have a mean mean Hg content of about 54 ppb with a maximum detected concentration of 260 ppb. C-horizon content about 54 of 260 ppb. C-horizon soils soils in in that area have a mean of 19 ppb. With 19ppb ppbHg Hg and and aa maximum maximum of 80 ppb. With respect respect to to soils, soils, Isle Isle 9 �than northern northern Wisconsin. Both Royale appears to be a more Hg-rich environment than Both A A and and BC BC horizon soils soils are are at least least twice twice as as high high on on the the island island as as in in northern northern Wisconsin. Wisconsin. The results results suggest suggest that the very elevated mercury content of soils in the Sargent Sargent Lake-Lake Wagejo area is not caused by concealed concealed native native copper copper deposits depositsbecause because there there is is little littleor orno no elevated elevated copper copper content of those soils. soils. Results from the Minong mine area show that concealed deposits, if present, would produce readily detectable elevated copper content of the soils. Neither is there reason reason to conclude conclude that local bedrock is the source for mercury because all tested chemically very uniform bedrock have very low mercury mercury content. content. Because samples of the chemically Becauseof of the the general lack of mercury in the most common occurrence common rocks of the island and the very limited occurrence of native copper copper deposits deposits that that do do contain some mercury, the mercury content of the soils on Isle Royale seems very very likely likely to to result result largely largely from from airborne airborne deposition. deposition. The The processes processes causing causing the the great variability variability of mercury content content of similar similar appearing soils over short distances that thatwe wehave have observed in our survey remain only speculative. Nevertheless, it appears certain that mercury must be very mobile in the soil soil zone zone in order to redistribute what must be a relatively uniform mobile in amount of deposited mercury into the highly variable observed concentrations. 10 10 �STRUCTURAL STRUCTURALFABRIC FABRICAND AND STRAIN STRAINFOR FOR THE THE SEINE SEINERIVER RIVER CONGLOMERATES CONGLOMERATESAT AT TIlE THE WABI000NQUETICO WABIGOONQUETICOSUBPROVINCE SUBPROVINCEBOUNDARY BOUNDARYNEAR NEARMINE MINECENTRE, CENTRE,ONTARIO. ONTARIO. CZECK, Peter I., J., Department Department of of Geology Geology and M. and and HTJDLESTON, HUDLESTON, Peter and Geophysics, Geophysics,University University of of CZECK, Dyanna Dyanna M. Minnesota, Minnesota, 310 310 Pillsbury Dr. SE, Minneapolis, MN 55455, 55455, dyanna@geolab.geo.umn.edu dyanna@geolab.geo.unm.edu INTRODUCTION The The Superior Superior Province Province consists consistsof of approximately approximatelyeast-west east-west trending trending subprovinces subprovinces defined defined by by lithological lithological differences, & Ciesielski Ciesielski 1986). This This study study differences,metamorphic metamorphic grade, and structural boundaries (Card & concentrates concentrates on on the the boundary between between the the Quetico Quetico metasedimentary metasedimentary subprovince subprovince and and the the Wabigoon Wabigoon metavolcanic subprovince. The Seine River Metasedimentary Group, including the Seine River metavolcanic The Seine River Metasedimentary Group, conglomerates, are distinctive rocks found within a wedge along this boundary. along this conglomerates, are distinctive rocks found within a Structural Structural work along the Quetico Quetico and Wabigoon describes subvertical foliation overprinting overprinting large Hudieston 1991). 1991). These These structures structures indicate a strain large lithological folds (Poulsen 1986, 1986, Tabor & Hudleston history history consisting consisting of an early early recumbent recumbent nappe nappe deformation deformation followed by a more more ubiquitous ubiquitous overprinting overprinting of a subvertical flattening fabric and shear zones attributed to dextral transpression. Strain is pervasive flattening attributed to dextral transpression. throughout throughout the the boundary, boundary, but but also also localized localized into into more more discrete discrete shear zones zones including including two two main, main, connecting connecting shear shear zones zones coincident coincidentwith with the the Rainy Rainy Lake-Seine Lake-Seine River River and Quetico Quetico Faults. These Theselarge large shear shear zones zones are are interconnected interconnected with with smaller smaller shear shear zones zones forming an anastomosing anastomosing pattern. The TheSeine Seine River conglomerates conglomerates are are located located in in aa wedge wedge between between these two shear shear zones zones west west of their intersection. intersection. Poulsen (1986) (1986) interpreted interpreted the the Seine Seine River River conglomerates conglomeratesto to have have formed formed syn-kinematically syn-kinematically during during transpression, transpression, possibly possibly in in structures structuressimilar similarto topull-apart pull-apanbasins. basins. This This preliminary preliminary structural structuralwork work made made itit clear clear that that the the WabigoonWabigoon- Quetico Quetico subprovince subprovince boundary is is not not merely aa discrete discrete suture suturebetween between two two tectonic tectonic microplates, microplates, but is instead instead a complex complex network of shear zones which together accommodated oblique collision. The Thegoal goalof ofthis thisstudy studyisisto todescribe describehow how this complex shear zone geometry is reflected in spatially variable strain magnitudes and structural complex shear zone geometry is reflected in spatially variable magnitudes structural fabrics. fabrics. - STRUCTURAL FABRIC Foliations Foliations in in the the field field show show aa consistent consistent regional regional orientation orientation with strike strike of approximately approximately 080 080 and and subvertical dips. This Thisstrike strikeisisconsistent consistent with with the the dextral dextral transpression model. One Oneexception exceptionto to this this is is in the area of Shoal 045,creating creatingan anoverall overallS-like S-likegeometry geometry Shoal Lake Lake where where the the strike strikechanges changesto toapproximately approximately045, with a map pattern analogous analogous to to a dextral shear sense indicator. The Thesame sameshear shearsense senseisisobserved observedatataa smaller scale within the conglomerate clasts that often form sigma and delta dextral shear smaller scale within the conglomerate clasts that often form sigma and delta dextral shearsense senseindicators indicators on the sub-horizontal sub-horizontalplane. plane. Mineral chlorite and amphiboles. Mineral lineations lineationsin in the field field are are predominantly defined by chlorite amphiboles. General General transpression 1993). However, However, transpression theory predicts either vertical or horizontal lineations (Fossen & Tikoff 1993). lineation orientations orientations in the field field vary remarkably within the foliation plane. Typically, Typically,the theSeine SeineGroup Group lineations are spatially similar on the scale of 0.5-1 km. Therefore, the lineation variations are not Therefore, the lineation variations are not caused caused similar by small-scale-phenomena by some regional regional phenomenon. phenomenon. Rather small-scalephenomena such as clast interaction, but by Rather than than reflecting different different bulk kinematic kinematic conditions conditions along the boundary (such as partitioned triclinic transpression). transpression), the lineation lineation variations variations may reflect reflect anastomosing anastomosing shear zone patterns and variable pressure gradients gradients within within the therock. rock. 11 �Taken together, the finite strain ellipsoid Taken together. foliation and lineation match the variations in the orientation. The Thefoliation foliationpole polealigns alignswith withthe theminimum minimumstretching stretchingdirection, direction,and andthe thelineations lineationsparallel parallel the maximum stretching direction. direction. STRAIN ANALYSIS The Seine River conglomerates are useful strain recorders. recorders. Qualitative observations and quantitative strain analyses indicate heterogeneous heterogeneous strain distributions within the Seine River conglomerates. Analysis Analysis confinns confirmsaaflattening flatteningstyle stylestrain strainthat that could could only only be aa result result of of aa threethreedimensional deformational phenomenon such as transpression rather than the two-dimensional strain strain produced by wrench or thrust movements. Results to date show that the longest axis corresponds to the mineral lineation longest lineation measured . principal in the field and the shortest principal axis corresponds well with the foliation pole. This Thissupports supportsthe theidea idea that structural fabric measured in the field may reoresent the orientation of the finite finite strain mav be used to represent ellipsoid. ellipsoid. The variations in strain ellipsoid orientations orientations and magnitudes could be used to argue argue for multiple multiple deformation events or complex and variable kinematic kinematic boundary boundaryconditions. conditions. However, the geometry of of the anastomosing shear zone pattern can be used to explain the variations in the orientation of the strain ellipsoid and and the the heterogeneous heterogeneous strain magnitudes within the Seine Seine Group Group within a simple dextral ellipsoid transpressional setting. Poles to to foliation foliation 138 Measurements Measurements (equal (equal area) area) Mineral lineations 113 Measurements Measurements (eaual (equal area) Card. K. IC.D. D.& &Ciesielski, Ciesielski, A. A. 1986. 1986. DNAG DNAG Subdivisions Subdivisions of of the the Superior Superior Province Province of the Canadian Card, Geoscience Canada Canada 13, 5-13. Shield. Geoscience 13.5-13. Fossen, H. & Tikoff, B. 1993. 1993. The deformation matrix for simultaneous simple shearing, pure shearing and volume change, and its application to transpression- transtension tectonics. tectonics Journal 15, 413-422. Journal of o fStructural Structural Geology Geoloxv IS. 4 13-422. -. Poulsen. example of of an an Archean Archean Subprovince Subprovince boundary boundary Poulsen, K. H. 1986. 1986. Rainy Lake Wrench Zone: An example in Northwestern Ontario. Tectonic evolution evolution of greenstone belts Technical Technical Report Report (edited (edited Ontario. In: In: Tectonic Ashwal, L. L. D.) D.) 86-10. Houston TX, TX, Lunar and planetary Inst., 177-179. 1. Sc & Ashwal, 177-179. by de Wit, M. J. Tabor. J. J. R. & & Hudleston, P. 1 J.. 1991. Deformation at an an Archean subprovince boundary, boundary, northern Tabor, Minnesota. Canadian Canadian Journal 292-307. Journal of of Earth EarthSciences Sciences 28, 28,292-307. 12 �Preliminary PreliminaryAeromagnetic AeromagneticMap Mapof ofWisconsin Wisconsin David DavidL. L. Daniels, Daniels,Suzanne SuzanneW. W.Nicholson, Nicholson,William WilliamF. F.Cannon, Cannon,U.S. US. Geological GeologicalSurvey. Survey,MS MS 954 954National National Center, E.Bracken, Bracken,U.S. U.S. Geological GeologicalSurvey, Survey,MS MS 964, 964, DFC DFCBox Box 25046, 25046, Center,Reston, Reston,VA VA20192, 20192,Robert RobertE. Denver, Denver,CO CO80225 80225 The The Mineral MineralResources ResourcesProgram Program of of the the U.S. U.S. Geological GeologicalSurvey Survey (USGS) (USGS) has has conducted conducted aeromagnetic the magnetic coverage coverage of of the the aeromagneticsurveys surveys in in Wisconsin Wisconsin during during the past three years to improve the state. state. State Statecoverage coveragewas was completed completed with with aa survey survey carried out in 1998/1999. 199811999. The The new new aeromagnetic aeromagnetic survey survey fills fills the the southern southernthird third of of the the state statenot not covered covered by existing existing good quality surveys (see figure). Right are:north-south north-southflight flightlines linesatat½Vimile mile(800 (800m) m) separation separation draped draped at at 1000 1000ftft (305 (305 m) m) Flightspecifications specificationsare: mean mean terrain terrain clearance. clearance. Right Flightlines linesare areeast-west east-westfor foraapart partof ofsoutheast southeast Wisconsin. Wisconsin. The 4' meeting of the ILSG in 1998 1998 The results resultsof ofthe thefirst firsttwo twoyears yearsofofflying flyingwere wereshown shownatat44th (Daniels and others, 1998). These data have been released since that meeting as paper contour (Daniels and others, 1998). These data have been released since that meeting as paper contourmaps maps (Snyder, (Snyder,1998; 1998;USGS USGS Open-File Open-File Reports Reports 98-431 through 439). Digital Digital data data for for the the 1997/1998 199711998survey survey have have now now been been released released(Open-File (Open-FileReport Report99-28) 99-28)on on CD-ROM CD-ROM (Daniels, (Daniels, Nicholson, Nicholson, and and Cannon, Cannon, 1999). 1999). The accompanying figure shows a shaded image of the aeromagnetic field for current data in The accompanying figure shows a shaded image the aeromagnetic field for current data in Wisconsin years data data are are blocked and labeled. Three Threeaeromagnetic aeromagneticsurveys surveys Wisconsin and and the the areas areas of of the the first first22 years obtained (M.Mudrey, Mudrey, obtainedfrom fromindustry industrysources sourcesby by the theWisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey(M. personal for the the new new survey survey are are still still personal communication, communication, 1997) 1997)are are shown shown in southern Wisconsin. The data for preliminary. Blocks 1-5 and A-D represent the areas of the new survey that will be shown and the will Blocks 1-5 and A-D represent the areas of the new survey contour be available available later later in in 1999. 1999. contour maps maps that that will will be The been to to provide provide higher higher resolution resolution data data The rationale rationale for for continued continued aeromagnetic aeromagnetic surveying has been with with which which to to interpret interpretbasement basementgeology geologyin inWisconsin. Wisconsin.The Theaeromagnetic aeromagneticdata data image image basement basement structures by glacial glacial structures in in detail detail and and give give clues clues to to the the structural structural evolution of the Precambrian crust, covered by and and Paleozoic Paleozoiccover. cover. References References D.L., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., 1999, 1999,Aeromagnetic ~eromahetic surveying in Wisconsin Wisconsin 1997-98: 1997-98: Daniels, D.L., Daniels, surveying Digital Digital data datafiles: files:U.S. U.S. Geological GeologicalSurvey SurveyOpen-File Open-FileReport Report99-28, 99-28, CD-ROM. CD-ROM. Daniels,D.L., D.L., Snyder, Snyder,S.L., S.L., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., 1998, 1998,New New aeromagnetic aeromagnetic surveys surveysin in Daniels, Wisconsin part 1, 1, Wisconsin by by the theU.S. U.S. Geological GeologicalSurvey: Survey:Institute Instituteon on Lake Lake Superior SuperiorGeology Geology Proceedings Proceedings v. 44, part p. 62-63. 62-63. p. Snyder, S.L., 1998, areas: 1998, Aeromagnetic Aeromagnetic map map of of part part of of northwestern Wisconsin and and adjacent areas: U.S. U S . Geological Survey Survey Open-File Open-File Report Report 98-228, 98-228, Scale Scale 1:125,000, 1:125,000,22 sheets. sheets. 13 �Index Index Map Mapof of'Wisconsin Wisconsin Aeromagnetic Data Data 93E 936 92E 926 91E 916 89 9oE cct SEE 87E 46E 46E 45E 45E 44E 43E 43E 92E me. 9oE 90fi 91E 916 ssE 'O'5°20 KM 50 50 0 89E 100 • 14 150 200 KM siE 876 �INVESTIGATION INVESTIGATIONOF OFCaO CaOAT ATTHUNDERBIRD THUNDERBIRDMINE, MINE,MESABI MESABIRANGE: RANGE:MINERAL MINERALAND AND STRATIGRAPHIC STRATIGRAPHICRELATIONSHIPS RELATIONSHIPS DIEDRICH, DIEDRICH,Tamara TamaraR., R.,and andMORTON, MORTON,Penelope, Penelope,Dept. Dept.of ofGeology, Geology,University Universityof ofMinnesota Minnesota Duluth,Duluth, Duluth,MN, MN,55812, 55812, tdiedric@unnd.edu tdiedric@umn.d.eduand andpmorton@unmA.edu pmorton@umn.d.edu Duluth, Mine Minegeologists oeolomstsatatEVTAC's EVTAC'sThunderbird ThunderbirdMine, Mine,aataconite taconitemine mineininEveleth, Eveleth,Minnesota, Minnesota,have havebeen been tracking variation ofofnaturally trackingthe thevariation naturallyoccurring occurringCaO CaOinmiron ironore oreconcentrate concentratefor foratatleast leastnine ninemonths. months. Information Informationabout aboutthe theCaO CaOisishelpful helnfulininformulating formulatino thepartial fluxpellets nelleis that that EVTAC EVTAC produces. produces. The The -the .vartialflux CaO-bearing CaO-bearinephase phasewas wasunidentified, unidentified,but butpresumed presumedto to be be aa carbonate. carbonate. The Theobjective objectiveof ofthis thisstudy studywas wasto to investigate investigatethe thenature natureof ofthis thisCaO CaOininterms termsof: of:1.) I .)The The identification identificationof of its its phase or phases; 2.) Location of major majorsiratigraphic stratigraphiccontributors; contributors;and and3.) 3.)The Theininsitu situtextural texturalrelationship relationshipbetween betweenthe theCaO-bearing CaO-beanng phase(s) phase(s)and andthe themagnetite. magnetite. Manual Manualinterpretation interpretationof ofX-ray X-raydiffraction diffractionresults resultsidentified identifiedthe theCaO-bearing CaO-bearingphase phasein inthe the concentrate concentrateto tobe beankerite. ankerite.Other Otherconstituent constituentminerals mineralsinclude includequartz, quartz.hematite, hematite,siderite, siderite.greenalite, greenalite, stilpnomelane, stilpnomelane,talc, talc,and andgoethite. goethite. Thunderbird ThunderbirdMine Mineexcavates excavatesore orefrom fromthe theBiwabik BiwabikIron IronFormation, Formation,aaPrecambrian Precambrianunit unitcomposed composed of areUpper UpperUpper Upper ofseveral severalhorizons horizonsof ofbanded bandediron ironformation. formation.From Fromtop toptotobottom, bottom,these thesehorizons horizonsare Cherty, Bottom Lower Lower Cherty,Middle MiddleUpper UpperCherty, Cherty,Lower LowerUpper UpperCherty, Cherty, Lower Lower Slaty, Slaty, Top Top Lower Cherty, Cherty,and Bottom Cherty. Cherty.Horizons Horizonsdiffer differininphysical physicalcharacteristics, characteristics,such suchasasthickness thicknessand andtexture, texture,and andchemical chemical composition. areblasted blasted and and composition.When Whencollecting collectingore orefor forthe theinitial initialore oremix, mix,aacombination combinationof ofhorizons horizonsare blended achieveaadesirable desirablemagnetic magneticiron ironconcentration. concentration.Statistical Statisticalanalysis analysisdemonstrated demonstratedaastrong strong blendedtotoachieve positive the amount amount of of positiverelationship relationshipbetween betweenthe thepercentage percentageof ofore orederived derived from from the the Top Top Lower Lower Cherty Cherty and and the ankerite ankeritein inthe theresulting resuitingconcentrate. ~oncen~te. Textural Texturalrelationships relationshiosbetween betweenthe theankerite ankeriteand andmagnetite mametitewere wereobserved observedand andphotographed. photographed. Ankerite ankerite Ankexiteoccurs occursininatatleast leastfour fourdistinct distincthabits, habits,relative relativethe themagnetite: magnetite:1.) 1.)Rhombohedral ~hombohedrd ankeritecrystals crystals are granoblastic,recrystallized recrystallizedquartz, aresurrounded surroundedby bymuch muchsmaller, smaller,granoblastic, quartz,and andminor minormagnetite; magnetite;2.) 2.) FineFinegrained, areintergrown intergrownwith withmagnetite magnetiteof ofapproximately approximatelythe thesame samesize; size;3.) 3.)An An grained,irregular irregularankerite ankeritecrystals, crystals,are ankerite ankeritecrystal crystalcan canbe beentirely entirelyenclosed enclosedwithin withinaasingle singleor orcluster clusterof ofmagnetite magnetitecrystals; crystals;and and4.) 4.)A Asingle single or orcluster clusterof i fankerite ankeritecrystals crystalsencapsulates &apsulates aamagnetite mapetite crystal. crystal. The Theiron ironore oreat atEVTAC EVTACis isprocessed processed by by magnetic mameticseparation. senaration.Examining Examininothe thetextural texturalrelationship relationshipbetween betweenthese thesetwo twominerals mineralscan can produce produce information informationrelevant relevanttotomake makethe theisolation isolationof ofmagnetite magnetitemore moreefficient. efficient. ~~ ---- ~~~ - - - .~ ~ ~ ~ ~ 15 �METAMORPHIC THE CANADIAN SHIELD SHIELD OF OF ONTARIO, METAMORPHIC MAP MAP OF THE ONTARIO, MICHIGAN, MICHIGAN, MINNESOTA MINNESOTA AND AND WISCONSIN WISCONSIN R.M Easton, Ontario R.M. Easton, Ontario OntarioGeological GeologicalSurvey, Survey,933 933Ramsey RamseyLake Lake Road, Road, Sue/bury, Sudbuty, Ontario J'3E 6B5, and R. G. Berrnan. Berman, Geological Geological Survey P3E 6B5, eastonrm@vianet.Ofl.Ca eastonrm@yianet.on.ca and R G. Survey of of Canada, Canada, 601 Booth Booth Street. Street, Ottawa, OE8 607 Ottawa. Ontario Ontario K1A KIA 0E8 The Geological The Geological Survey Surveyof ofCanada's Canada's undertook undertookaaproject projectseveral severalyears yearsago ago to toproduce produce an an updated updated metamorphic map for for the Canadian Canadian Shield Shield (GSC (GSC Map Map 1475A), l475A), which which would wouldalso alsobe be used used to produce aa metamorphic map map of of the the world world (in (in conjunction conjunction with with the for the Geologic M Map World). ap of of the the World). metamorphic the Commission Commission for the Geologic At of the Geological Survey Ontario was was asked askedto to compile compile aa metamorphic metamorphic map map of of At the the request request of the Geological Survey of of Canada, Canada, Ontario the Canadian Canadian Shield Shield in in Ontario. the Ontario. In addition addition to to simply simply compiling this project project with with In compiling metamorphic metamorphic information, information, Ontario Ontarioapproached approached this the goal of the goal of attempting attempting to to integrate integrate metamorphic metamorphic information informationwith withthe thetectonic tectonicsynthesis synthesisproduced produced as a s part part of the Ontario project, with the aim of of developing mineral exploration exploration models. of the Geology Geology o f Ontario project, with the aim developing improved improved mineral models. As As aa of consequence,the the metamorphic metamorphic map map of of Ontario as to to complement complement the existing existing set set of of consequence, Ontario was was designed so as 1: 1.000,000 1.000,000bedrock, bedrock, suficial surficial geology, geology, geophysical, geophysical,and andtectonic tectonicassemblage assemblagemaps mapsand andtime-space time-space charts charts released in in 1991-92 part of of the the Geology Geology o Ontario series. released 1991-92 aas s part f Ontario series. A draft draft of of this this map, map, at roughly roughly 1:2,500,000 1:2,500,000 of scale, will will be scale, be presented presented here. here. Also at of the Geological Survey to produce produce aa Also at the the request request of the Geological Survey of ofCanada, Canada, Ontario Ontario has has undertaken undertaken to preliminary in Wisconsin, Wisconsin, Michigan, preliminary metamorphic metamorphicmap mapof ofthose those portions portions of ofthe theCanadian Canadian Shield Shield exposed exposed in Michigan, and Minnesota. One One of ofthe thereasons reasons for requesting reauestine the involvement of of the the Ontario Ontario Geological Geological Survey Survey in in this compilation, wasso soas as to to best best integrate integrate the metamorphic met-orphic pattern compilation,as asopposed opposed to toother otherorganizations, or&izations, was present in the the shield shield in in the the United United States with that that oresent present across acrossthe theborder borderininOntario. Ontario. In In addition. addition, fast fast present in States with approaching deadlines for completion of deadlines for of the the project project factored factored into into this this decision. decision. Thus. the main focus of this presentation will be preliminary draft Thus, presentation will be on on presentation presentation of a preliminary draft of ofthe the adjoining Ontario, metamorphic map for for the the shield shield rocks rocks in in the the areas areas adjoining Ontario, for forthe thepurposes purposes of of discussion discussion regarding: regarding: the style style of presentation, 1) the ,,,:~ i. . , , 2) the accuracy accuracy of ofthe the data data presented, presented, and 3) solicitation bringing this solicitation of ofpossible possible assistance assistance in bringing this project project to to aa conclusion. concl&on. The metamorphic map of the Shield is being being produced produceddigitally. digitally. In Inthe the case case of Ontario, the Tectonic used as the geologicalbase. geological base. Key aspects of of the project include as the Key digital digitalaspects the project include Tectonic Map Map of ofOntario 0ntariowas wasused digitization of representing different metamorphic facies (grade) and of linework (e.g. dieitization ofpolygons nolveons reoresentine different metamomhic facies (grade) and of linework (e.e. isoerads. . . . - isograds, facies boundary boundary information), information), into a-CAD a CAD program. facies program. In In addition, addition, point-source point-source information information (e.g. (e.g. assemblage data.P-T P-Tdeterminations) determinations) is is beinginput being input into a database. database. The final final map product will willbe bean an assemblage data. attributed map. releasedon onCD-ROM. CD-ROM.containinc containingall allthe thecom~iled compiledinformation. information. The artnbuted attributed map map will will mao. released accompany aa standard standardcoloured, coloured,hard hardcopy copymap, map,which whichwill will mainly mainly display display metamorphic metamorphic facies facies distribution. will be distribution. This Thissame sameapproach approach will be taken taken in compiling compiling the the information information for forWisconsin Wisconsin Michigan Michiganand and ofofCanada, based Minnesota, except that here, the digital digital base base is being being supplied supplied by by the the Geological GeologicalSurvey Survey Canada, based , . on a previously previously released released US geological compilation compilationmap mapof ofthe theregion. region. -- - in the Two Canadian Mineralogist on "Tectonometamorphic Twospecial special issues issues of of The The CanadianMineralogist "~ectonom&&phic Studies Studiesin the Canadian Shield Shield" are are being being produced producedaas partofthis of thisproject. project. The first (vol. (vol. 34, 34, part pan 5, 5, October October 1997), 1997). Canadian s part includes results results obtained obtained from from aa variety variety of of ancillary to the the compilation compilation effort. includes ancillary metamorphic metamorphic studies studies related related to effort The second issue, issue, which which is is in in the the process process of of being being assembled, assembled, includes regional overviews overviewsrelated related to tothe the metamorphic map well as map of of the the Canadian Canadian Shield, Shield, as as well a s additional, additional, detailed detailed metamorphic metamorphic studies. studies. 16 16 �WHERE ARE OREBODIES WHERE ARE THE THE METAMORPHOSED METAMORPHOSED NATURAL NATURAL OREBODIES OF THE MESABI RANGE? OF THE MESABI RANGE? RONALD G. 0. GRABER RONALD GRABER AND AND ALAN ALAN J. J. STRANDLJE STRANDLIE CLIFFS COMPANY,ISHPEMING, ISIIPEMING, MI. ML 49849 49849 C U F F S MINING MINING SERVICES SERVICES COMPANY. (graber@ponup.com) (graber@portup.corn) The nearly nearly century-old century-old debate regarding The regarding the genesis genesis of the hematite-goethite hematite-goethite iron iron ore deposits the Mesabi Mesabi Range Range has has recently recently been been revisited revisitedby byMorey Morey(1999). (1999). The The ore deposits of of the historic debate for the the combined combined oxidation oxidation historic debate centers centers on on the the origin origin of of the the fluids fluids responsible responsible for and leaching of the Biwabik iron-formation to form the deposits — they upward were and leaching of the Biwabik iron-formation to form the deposits moving hydrothermal moving hydrothermal fluids fluids (hypogene) (hypogene)or or downward downward moving movingmeteoric meteoricwaters waters (supergene)? (supergene)? Morey presents conceptual model model for for the the genesis genesis of of the the ores ores that that Morey presents an an interesting interesting conceptual utilizes Early Proterozoic, Proterozoic, driven driven by by uplift utilizes continental-scale continental-scale groundwater groundwater flow flow during during the the Early uplift in fold-thrust belt belt to to the the south south of of the the Mesabi Mesabi Range. Range. This This model model relies relies on on in the the Penokean Penokean fold-thrust the as aa regional regional the Pokegama Pokegama Quartzite, Quartzite, which which underlies underlies the the Biwabik Biwabik iron-formation, iron-formation, as aquifer for for the aquifer the movement movement of of basinal basinal waters waters to to the the northern northern margin margin of of the the Animike Animike basin. basin. A Ma when when loss loss of the A minimum minimum age age for for ore ore genesis genesis in in this this model model is is believed believed to to be be 1650 1650 Ma of the hydraulic gradient for the groundwater flow system occurred due to erosion of the hydraulic gradient for the groundwater flow system recharge area. This ThisEarly EarlyProterozoic Proterozoicage age for for ore ore genesis genesis is significantly significantly older than the Jurassic-Cretaceous over the Jurassic-Cretaceous age age that has been generally, generally, albeit not universally, accepted over last 30 plus plus years years (Sloan, (Sloan, 1964; 1964;Morey. Morey, 1972). 1972). last Constraints Constraints on on the the timing timing of of the the hematite-goethite hematite-goethiteores ores are are few few due due to to the the scarcity scarcity of geologic geologic events events impacting the the Mesabi Mesabi Range Range between between the the Early Early Proterozoic Proterozoic and and the the of Late Cretaceous. ItItisison onthe theeast eastend endof of the theMesabi Mesabi Range Range where where intrusive intrusiveevents eventsand and contact metamorphism associated with the Middle Proterozoic Duluth Duluth Complex provide a potential opportunity to put additional time time constraints constraints on onthe thegenesis genesisof ofthe theores. ores. Hence Hence the title of this paper. IfIf ore oreformation formation occurred occurred prior to the Middle Proterozoic, the opportunity equivalents of of the the soft soft hematite-goethite hematite-goethite opportunity should exist to find metamorphosed equivalents ores. Detailed Detaileddrilling drillingboth bothalong alongthe theiron-formation iron-formation outcrop outcropbelt belt and and downclip downdip as part of exploration to find these metamorphosed metamorphosed equivalents. equivalents. In In exploration for for Cu-Ni Cu-Ni deposits deposits has has failed failed to find these fact the distinct distinct absence absence of of enriched enriched orebodies orebodies of any sort east of the Duluth Complex's post-Middle Proterozoic Proterozoic age age metamorphic aureole aureole has long been utilized as support for aa post-Middle for ore ore genesis. genesis. Alternatively, Alternatively, thinning thinningof of the the Pokegama Pokegamaquartzite quartzitein in this thissame samegeneral general area is cited by Morey Morey to to explain explain the the absence absence of enriched enriched ores ores on on the the East East Mesabi. Mesabi. The The relative relative abrupt abrupt absence absence of of enriched enriched ores ores in in the the Biwabik Biwabik iron-formation iron-formationoccurs occurs within the mining operations Mining Company, Company, managed managed by by aa subsidiary subsidiary of of operations of LTV Steel Mining Cleveland-Cliffs, which has been active 1). Detailed Detaileddata data active for over 40 years (Figure 1). acquired acquired through through both both field field observations observationsand and thousands thousands of of drill drill holes holes provide provideinsight insighton on the controls controls of the the ore-forming ore-forming process. The Thefollowing followingfeatures featuresof of the the geology geology at at LTV LTV Steel Mining Company are are in in conflict conflict with with an an Early Proterozoic Proterozoic genesis genesis of the the hematitehematitegoethite ores: goethite ores: 17 �1. 1. Due to the economic economic significance significance that metamorphism has on the processing of the magnetic taconites, considerable effort is placed on mapping the metamorphic isograds at this operation. Further Further refinement refinement of the original zonation of the Duluth Complex's contact resulted. The Complex's contact metamorphic metamorphic aureole (French, 1968) has resulted. The relationship of metamorphic metamorphic grade with the the eastern eastern limit limit of of iron-formation iron-formation enrichment enrichment relationship stronger than the correlation with either the thickness or distribution of the appears stronger Pokegama Pokegama Quartzite. This Thisisismanifested manifestedby: by: the abrupt termination of enrichment enrichment and oxidation oxidation along along the the Wentworth Wentworth a) the abrupt termination a) structure structure due due to increasing increasing metamorphic metamorphic grade; grade; and, and, b) the b) the thepresence presenceof ofenrichment enrichmenteast eastof ofthe the Siphon Siphon structure structure which which is is the controlling structure for aa dramatic dramatic decrease decrease in in Pokegama Pokegama Quartzite Quartzite thickness. thickness. controlling structure for 2. the Biwabik Biwabik iron-formation in 2. The Aurora sill, sill, aa sizeable sizeable syenitic syenitic body that intrudes the the western portion of the mining operation, appears to have contributed to the localization James and and the the Miller-Mohawk Miller-Mohawk mines. mines. This sill localization of ore formation in the St. James has visual similarities to granophyres associated elsewhere with the Duluth Complex similarities granophyres elsewhere and as such has long been considered Keweenawan (White. 1954). Jf ore genesis in long (White, 1954). If ore genesisin these mines constrain ore mines were Early Early Proterozoic, how could a Keweenawan sill constrain formation? formation? Likewise, Likewise,no nometamorphic metamorphic overprint overprint has has been reported from these % orebodies. Definitive Definitiveage agedating dating though though is is lacking lacking for for this intrusive. ri 3. AAlarge largenumber numberofofthe theenriched enrichedorebodies orebodiesat at the the LTV LTV Steel Steel Mining Company operation are very shallow. Drilling of a Drilling has has been been conducted conducted through the bottom of number of the natural ore magnetic taconite taconite ore pits successfully successfully finding fresh, unaltered magnetic reserves below. The Thelack lackof of alteration alteration between between the the Pokegama Pokegama Quartzite Quartzite and the orebodies orebodies is is problematical problematical for for ascending ascendinggroundwater groundwaterflow flowmodels. models. French, B.M. 1968, of the the Biwabik Biwabik iron-formation, iron-formation, 1968, Progressive Progressive contact metamorphism of Mesabi Range, Minnesota, p.103. Minnesota, Minnesota Minnesota Geological Survey Bulletin 45, p. 103. Morey. Morey, eds.. eds., Geology Geology of of Morey, G.B., G.B., 1972, 1972, Mesabi Range; Range; in P.K. Sims Sims and G.B. Morey, Minnesota: Minnesota: A A Centennial Centennial Volume, Volume, Minnesota MinnesotaGeological GeologicalSurvey. Survey,pp. pp. 204-217. 204-217. Morey, Mesabi Range, Range, MinnesotaMinnesotaMorey, G.B., G.B., 1999, 1999, High-grade High-grade iron iron ore ore deposits deposits of of the the Mesabi Product of a continental-scale ground-water system. Econ. Geology, vol. 94, pp 133-142. continental-scale ground-water system, Geological Survey Sloan, R.E., R.E., 1964, 1964, The Cretaceous system in Minnesota: Minnesota Geological 5 . 64p. 64~. Report of Investigations Investigations 5, White, D.A., White, D.A., 1954, 1954,The The stratigraphy stratigraphyand and structure structureof of the the Mesabi Mesabi Range, Range, Minnesota: Minnesota: Minnesota 92p. Minnesota Geological Geological Survey Survey Bulletin Bulletin 38, 38,92p. 18 �Figure 1. Map of of LTV Steel Steel Mining Mining Company Company Figure 1. Geologic Geologic Map 19 �Cross Cross Margin Margin Transport Transport in in Lake Lake Superior Superior GREEN, GREEN,Sarah Sarah A. A. and and BUDD, BUDD, Judith Judith W., W., Dept. Dept. of of Chemistry Chemistry and Dept. of Geological Geological Engineering Engineeringand andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University, Houghton, Houghton,MI MI49931 4993 1 The The Keweenaw Keweenaw Interdisciplinary InterdisciplinaryTransport Transport Experiment Experiment in Superior Superior (KITES) (KITES) is focused focused on on cross-margin cross-margintransport transportprocesses processesalong alongthe thewestern westernshore shoreof ofLake LakeSuperior's Superior's Keweenaw Keweenaw Peninsula. Peninsula. The Thedominant dominantfeature featureofofthis thisregion regionisisthe theshore-parallel shore-parallel Keweenaw Keweenaw Current, Current,which whichflows flowsto tothe thenortheast northeastand andisisstongest stongestnear nearEagle EagleHarbor. Harbor. Water, Water, sediment, sediment,and andhydrographic hydrographicdata dataare arebeing beingcorrelated correlatedwith with satellite satelliteimagery imageryto to obtain obtain an an integrated integrated view view of of transport transport of of suspended suspended sediments, sediments, nutrients, and organic organic material material near near and and across acrossthe thecurrent. current. Time show cross cross margin margin transport Time series series SeaWiFS SeaWiFS images from May to September, 1998 show events in Lake Superior. These chlorophyll and turbidity maps reveal a highly events in Lake Superior. These chlorophyll and turbidity maps reveal a highly productive productive southern of the the Keweenaw. southern corridor corridor from Duluth Harbor to the tip of Keweenaw. Distinctive Distinctivesediment sediment and and chlorophyll chlorophyll plumes plumes can can be be seen seenoffshore offshorewest west of of the the Ontonagon Ontonagon River Riverand andnear nearthe the tip of the the Keweenaw Keweenaw Peninsula. Movement Movementofofthe theplumes plumesoffshore offshorewas washighly highlyvariable variable depending dependingupon upon the thedirection directionofofprevailing prevailingwinds windsprior priortotothe thesatellite satelliteband bandpass. pass. Simultaneously Simultaneouslyacquired acquiredSeaWiPS SeaWiFS(Sea-viewing (Sea-viewing Wide Wide Field-of-View Sensor) Sensor) and AVHRR 23,1998 1998were were AVHRR(Advanced (AdvancedVery VeryHigh HighResolution ResolutionRadiometer) Radiometer)images imagesfrom fromMay May23, used used to to verify verify cross cross margin margin transport transport events events in in Lake Lake Superior. Superior. The TheAVHRR AVHRRlake lakesurface surface temperature temperatureimage imagereveals reveals aa dramatic dramatic northward northward flowing flowing offshore offshore eddy eddycurrent currentat atthe thetip tip of of the the Keweenaw Keweenaw Peninsula. Peninsula. AASeaWiFS SeaWiFSturbidity turbidity map mapacquired acquiredwithin withinhours hoursof ofthe the AVHRR AVHRR SST SSTimage imagesuggests suggeststhat that materials materials were weretransported transportedoffshore offshorenorth northof ofEagle Eagle Harbor, Harbor, providing providingevidence evidenceof of crosscross- margin margin transport. transport. These Thesepatterns patternswere werenot notpresent presentin in AVHRR 23rdevent event(on (onMay May20 20 AVHRR and and SeaWiFS SeaWiFSimages imagesobtained obtainedbefore beforeor orafter afterthe theMay May23rd and and May May 27). 27). Sediment Sedimentpatterns, patterns,in-water in-wateroptical opticalmeasurements, measurements,and andphysical physicalmodels modelsare arehelping helping clarify in the the KITES KITESstudy study region. region. clarify transport transport mechanisms mechanismsand andpathways pathwaysin 20 �Megascopic Fossils and and Their Megaswpic Fossils Their Possible Possible Contribution Contribution to to the theDevelopment Development of of the theSilicate SilicateUnit Unit of Iron-Formation, Empire of the the Negaunee Negaunee Iron-Formation, Empire Mine, Mine, Marquette MarquetteRange, Range, North NorthMichigan Michigan T. M. Han, Senior Research Scientist (Emeritus), Cleveland-Cliffs Inc. Abstract The fossils discovered discoveredin in the the Early Early Proterozoic Negaunee Iron-Formation Iron-Formation are The megascopic megascopic fossils Proterozoic Negaunee are the the world's have been been reported reported as as eukaryotic eukaryotic algae algae similar similar to to world's oldest oldest known known fossils. fossils. These These fossils fossils have Grypania may have have played Grypania spiralis spiralis (Han (Han and and Runnegar Runnegar 1992). 1992). Their Their existence existence may played a a key key role role in in the the development of of the the thin thin banded banded "silicate unit" unit" of the the Negaunee Negaunee Iron-Formation Iron-Formation at at the the Empire Empire Mine. Mine. This of magnetite-rich magnetite-rich layers layers alternating alternating with layers having This unit is is composed wmposed of having a mineral mineralassemblage assemblage of of chert, chert, siderite, siderite, ankerite, ankerite,minnesotaite ininnesotaiteand and stilpnomelane stilpnomelane in various various proportions. proportions. Two fossil types typesare are recognized. recognized. One filaments that that are long One type type is is fine fine filaments long and and uniform uniform in in width width Two fossil and "springs". The The other other type type is is short, short, coarse, coarse, in inwhole whole and andsectional sectional forms, forms, and and and coiled wiled like like "springs". resembles "coiled garden garden worms". worms". These were apparently apparently transported transported by resembles "coiled Thesefossils fossils were by direct direct current current and and deposited at at distances from their origin. Based on the relationship between the current marks distances between the marks and and the orientation coils on on the the outcrops outcrops measured, measured, the direction orientation of of the the fossil fossil patches patches and and oval-shaped oval-shaped coils of the paleocurrent where Archean rocks paleocurrent at at the the time timeof of sedimentation sedimentation was from from the the southwest southwest where rocks are are distributed. distributed. • 'a-".: z"& ,. Fossil remains resembling resembhg "coiled "coiledgarden garden worms" worms" 21 �An An induced induced oxidation oxidation study study reveals reveals that that much much of of the themagnetite magnetitewas wasdeveloped developed and andenriched enriched through Fe+ nuclei. These These laths laths are are randomly randomly arranged, arranged, through Fe+ + diffusion, diffusion, using using lath-shaped lath-shaped hematite hematite as as nuclei. either scattered, either scattered, or or in in irregular irregularclusters clustersand andexisted existedbefore beforethe themagnetite magnetitedevelopment. development. The gangue layers are believed to be derived from a highly sfficeous gel with with carbonaceous carbonaceous matter The gangue layers are believed to be derived from a highly siliceous gel matter and other and replaced and other impurities. impurities. They Theywere weresubsequently subsequently recrystallized recrystallized and replaced by by siderite, siderite, ankerite, ankerite, minnesotaite and and stilpnomelane and low-grade regional metamorphism. minnesotaite stilpnomelane during during diagenesis diagenesis and low-grade regional metamorphism. + --f -. Magn eliteand and magnetite magn elitegranule granule layers, white; Microstructrure of Magnetite white; 250x Micmstructrure of aa magnetite magnetite layer. layer. 250x gangue layers, dark. Magnetite, gray; gray; hematite grayish white dark. and gangue, gangue, black. black. Magnetite, hematite grayish white and According to LaBarge LaBarge et et al is reasonable According to a1(1987), (1989, it it is reasonable to to assume assume that that the theheavily heavilypopulated populated megascopic eukaryotic eukaryotic algae algae were were probably probably one the principal megascopic one of of the principal oxygen oxygen suppliers suppliers for for precipitating precipitating Ee+ + ± as as Fe(OH)3. Fe(OH)3. The Theclusters clustersof ofthe thelath-shaped lath-shapedmagnetite magnetite pseudorph pseudorph in in magnetite magnetitelaininae laminae and and Fe+ granules hematite . The effect of granules probably probably represent represent dehydrated dehydratedand andcrystallized crystallized Fe(OH)3 Fe(OH)3 flocculi, flocculi, hematite flocculation, if any, any, would flocculation. if would cause cause the the segregation segregation between between the the siliceous siliceous gel gel and and the theEe(OH)3. Fe(Om3. Furthermore, the gravity of of the theFe(OH)3 Fe(Om3 is is significantly significantly greater greater than thanthe thesificeous siliceousgel. gel. the specific specific gravity Consequently,the the interbanded interbanded structure structure of of the unit is Consequently, the lithological lithologic111 unit is believed believed to to be be deposited deposited simultaneously through processes of selective flocculation and and differential differential settling between simultaneously through processes of selective flocculation between the Fe(OH)3 and siliceous gelunder under aa rhymatic rhymatic and and cyclic cyclic manner maimer regulated regulated by by the the life life and and death Fe(OH)3 and siliceous gel death of of the organism, i.e. the off-season is aa period period of growing season season is aa period period of of deposition deposition while the off-season is the i.e. the the growing solution. Furthermore, Furthermore, the solution. the carbonaceous carbonaceous matter associated associated with the precipitates precipitates may may generate generate Fe+ ++during duringdiagenesis diagenesisand andmetamorphism metamorphismfor forthe thedevelopment development of of various various types types of hon iron minerals, minerals, particularly, particularly, the the development development and and enrichment enrichment of of magnetite. magnetite. . References ,. , . 1. Han, T. M. 1. M. and andRunnegar, Runnegar,B. B.(1992) (1%) Megascopic MegascopicEukaryotic EukaryotiiAlgae &ae from fromthe the2.1 2.1 Billion-YearBillion-YearAmerican Association for the Advancement Oldd Negaunee Iron-Formation, Iron-Formation.Michigan. Michigan. American Association for the Advancement of Science, science, Vol. Vol. 237, 237, pp. pp..232-235 .232-235 2. 2. Han, T. M. M. (1978) (1978) Microstructures Microstructuresof ofMaguetite Magnetite as as Guides Guides to to Its Its Origin Origin in in Some Some Precambrian Precambrian Iron-Formations. Fortschr.Miner. Miner.Vol. Vol.56 56pp. on.105-142 105-142 Iron-Formations. Fortschr. (1988) Origin of Magnetite Magnetite in inPrecambrian Precambrian Iron-Formations Iron-Formations of Low Low Metamorphic Metamorphic Grade Grade (1988) Proceedings of the Seventh Symposium. pp.641-656 Seventh Quadrennial JAGOD IAGOD Symposium. pp.641-656 3. Laflerge, LaBerge, C. G. L., L., Robbins, Robbins, E. E. I., I.,and andHan, Han,T.T.M. M.(1987) (1987)AAModel Modelfor forthe theBiological Biological Precipitation Precambrian Iron-Formations Evidence. Precambrian Precambrian Iron of Precambrian Iron-Formations- A: GeologicalEvidence. IronFormations. Formatt.ons. Publication, SA. Athens, Greece. Editors: Peter and Gene Gene LaBarge. LaBarge. Theophrastus Publication, SA. Athens, Peter Appel Appel and pp.69-96 pp. 69-96 ~ - 22 �COMPARISON OF O F MICA Ar/Ar ArIAr AND AND Rb/Sr RblSr THERMOCHRONOLOGY THERMOCHRONOLOGY RESULTS RESULTS FROM NORTHERN WISCONSIN AND NORTHERN MICHIGAN WISCONSIN AND Daniel HoIm, Holm, Denise Romano, Romano, and andCraig CraigManeuso, Mancuso,Dept. Dept.ofofGeology, Geology,Kent KentState StateUniversity, University, Kent, OH 44242; Ken Foland, Dept. of Geological Sciences, The Ohio State Poland, Dept. of Geological Sciences, The Ohio State University, University, Columbus, OH OH 43210. 43210. Columbus, Thermochronologic data from from the the southern Lake Superior Thermochronologic data Superior region has historically historically been been dominated by the RblSr Rb/Sr method method on biotite (Fig. (Fig. 1; Peterman Peterman and and Sims, Sims. 1988, 1988, ~&Q&J. Tectonics). We We summarize the results of 45 45 new new mica mica Ar/Ar ArlAr age age dates dates from from northern northern Wisconsin Wisconsin and and northern northern Michigan (Fig. Rb/Sr data. data. Because (Fig. 2) and compare these with the RbISr Because the Rb/Sr RbISr and K/Ar systems in biotite thissummary summaryprovides providesan an biotite are are known known to to have have similar similarclosure closuretemperatures temperatures(300°±50°C), (300¡±50°this excellent opportunity opportunity to to compare how susceptible these these systems systems are are to to partial partial or or complete complete excellent resetting. Northwest to 1730 M ML Northwest Wisconsin. Wisconsin. Rb/Sr RbISrbiotite biotitedates datesfrom fromthis thisregion region vary vary from from 1309 1309 to a In In contrast, Ar/Ar ArIAr mica mica dates dates fall fall tightly tightlyinto intotwo twogroups, groups,an anolder older—1755 -1755 Ma group and a younger —1600Ma Magroup. group. The two groups of Ar/Ar -1600 Ar/Ar dates dates are are separated separated by by aa sharp sharppost-Penokean post-Penokean deforinational front in the overlying defonnationallthennal defonnational front overlying Early Proterozoic quartzites. The ThedeformationalJthermal in the front here probably probably represents represents the northern northern limit of of Mazatzal Mazatzal foreland foreland deformation deformation in southern Lake Superior Superior region. Northern 1630-1650 Ma ArIArchrontours, chrontours,which whichcoincide coincidein in Northern Michigan. Michigan.The The 1630-1650 MaRb/Sr RbISrand andAr/Ar northwest Wisconsin, diverge diverge eastward eastward into into northern northern Michigan. Michigan. Given northwest Wisconsin, Given the the absence absence of of postpostPenokean quartzites quartzites in in this region, region, we suggest that the Ar/Ar proxy for for Penokean ArIAr ages can serve as aa proxy determining the northern limit of Mazatzal deformation. We suggest that the Republic area determining the northern limit of Mazatzal deformation. area escaped significant Mazatzal related deformation deformation and higher-temperature higher-temperature metamorphic affects but did undergo some form of lower-temperature, possibly hydrothermal, metamorphism metamorphism at undergo some form of lower-temperature, possibly hydrothermal, —1630 1630 Ma. - Northeast Wisconsin. largearea areaofof<1200 el200Ma MaRb/Sr Rb/Srbiotite biotitedates dates(the (theGoodman GoodmanSwell) Swell) Northeast Wisconsin. AAlarge north of the Wolf River batholith has been been interpreted as an uplifted flexural bulge created by rapid loading along Fig. 1). In In contrast, contrast, along the mid-continent rift axis to the north (dashed ellipse of Fig. Ar/Ar dates mica ArIAr dates from the the same same region region define define aa much much smaller smaller region region of <1200 c1200 Ma Ma dates dates (dashed (dashed ellipse of Fig. 2). An isolated 1170 Ma Ar/Ar biotite date has also been obtained from basement An isolated 1170 Ma ArlAr biotite date has also swell. We over 100 100 km southwest of the swell. Weinterpret interpretthe the <1200 c1200 Ma dates for both systems to reflect shallow intrusion-related resetting. The larger locus of The larger locus of anomalously anomalously young young Rb/Sr RbISr dates dates probably reflects reflects the the fact fact that that the the Rb/Sr RWSrsystem systemisismore moresusceptible susceptibleto tolower-temperature lower-temperatureresetting resettingthan thanthe the Ar/Ar system. This Thisinterpretation interpretationalso alsoprovides providesan anexplanation explanation for for the the problematic problematic Rb/Sr RbISr and and AdAr Ar/Ar dates that fall between between 1200 and and 1400 Ma. Ma. Because AdAr Because much of the 1470 1470 Ma Wolf River batholith and associated intruded into into shallow shallow crust and batholith associated plutons (Wausau (Wausau Syenite complex) complex) intruded cooled through Ma (Fig. (Fig. 1 and 2). 2), it is likely through 300°C 300OCby by —1400 -1400 Ma likely that that the the surrounding surroundingPrecambrian Precambrian country rock to the north and west was also shallow. We We suggest, suggest, therefore, therefore, that the 1200-1400 1200-1400 Ma country rock mineral dates for for both systems systems indicate indicate incomplete mineral resetting related to shallow Keweenawan intrusions. 23 �Fig. Fig.1 1Rb/Sr RbISrBIOTITE BIOTITEAGE AGEDATA DATA Republic iis 4'— KEWEENAWAN 4 - ,,____,__,__ S'S.. — - — 1686. Peavy -1018=-— W:.1537+4+!.&ioa.thJ. ifs8l c*rtJL:i 4. +.ff rj¼l63:.llss.. '..5%& 1l03j.j..j tmbeau quartz'te 1249, r ' tfQightly foldedrL!:.', .'i'!! 1516 'us-i 620 ti's 1354S 1739 IZ3Sbj 1354 1360 1384"74// a, g 408 4/ .:.LLJ.:L1.J.J.:.Lth1455 'IV. ::15e2 1385 Edge of Late Proterozol Phanerozoic cover' After Peterman and Sims (1988) but excluding data of Aldrich et al. (1965) • Biotite Fig. 2 Ar/Ar MICA AGE DATA <4 ff011 '111 4', % — —.-- KEWEENAWAN "p ,',',',','.\.'.','l 696-,' 0 MuscovIte ___ ept I R7A "'%"' 10,natIonah11ft0i , , '..'' - IA! — tTrrrrrrrw1576;n.:.E.:n cm067'r*101 r.trhTrTnT.Tr:!Tr:,Tr:tT:-r-'.r' - 1358t -. Qua 1605-— _._.._j_ _,ø.__; -- -— r,-n11366rrtt1456 -'--1 HFlambeau quarizute :1-1372t:h-htr t1753I'r!." — 4 (tughtlyfolded) 1581 - S LJ.:1461 -! - 1A7 1616 415 Edge of Late Proti Phanerozoic covei Compiled Compiledfrom fromRomano Romano(1999, (1999.Kent KentState StateM.S. M.S.thesis), thesis),Mancuso Mancuso(1999. (1099.Kent Kent State CJES), StateM.S. M.S.thesis), thesis).Hoim Holmand andLux Lux(1998, (1998. CJES).Hoim Holmetelal. al.(1996, (1998.GSAA). GSAA),and and . Schneideretetal. al.(1996, (1996,CJES). CJES). Schneider 24 24 �ISHPEMING ISHPEMING GREENSTONE GREENSTONE BELT BELT --EVIDENCE EVIDENCEFOR FOR ARCHEAN ARCHEANTECTONIC TECTONIC EVOLUTION OF THE SOUTHERN EDGE OF THE SUPERIOR EVOLUTION OF THE SOUTHERN EDGE OF THE SUPERIOR PROVINCE PROVINCE IN IN MICHIGAN MICHIGAN JOHNSON, JOHNSON,Rodney RodneyC., C., Rod Rod Johnson Johnson& &Associates, Associates,Inc., Inc., Negaunee, Negaunee, MI MI 49866, 49866, MinerDoc@aol.com; MinerDoc@aol.com;and andBORNHORST, BORNHORST, Theodore Theodore J., J., Department Department of of Geological Geological Engineering Engineeringand and Sciences, Sciences,Michigan MichiganTechnological Technological University, University, Houghton, Houghton, MI MI 49931, 4993 1, tjbomho@mtu.edu tjbomho@mtu.edu The The Ishpeming Ishpeminggreenstone greenstonebelt belt is is the the southernmost southernmostgreenstone greenstone belt of of the the Superior Superior Province. The southern boundary of the Superior Province and the Ishpeming Province. The southern boundary of the Superior Province and the Ishpeming greenstone greenstone belt zone. Late k m long long Great Great Lakes Lakes tectonic tectonic zone. LateArchean Archean greenstone greenstone and i d belt is is the the 1,000 1,000km granite graniteterrane terraneto tothe thenorth north(Ishpeming (Ishpeminggreenstone greenstone belt) belt) are are juxtaposed against against Early Early to to Middle migmatite-gneiss-amphiboliteand and Late Late Archean Archean granite granite terrane terrane MiddleArchean Archeanmigmatite-gneiss-amphibolite (southern (southern complex). complex). The TheIshpeming Ishpeminggreenstone greenstonebelt belt consists consistsof of subaqueous subaqueous tholeiitic tholeiitic basalt thickness. New calc-alkalic rhyolite, rhyolite, 10-15 10-15km in total thickness. basalt to to calc-alkalic New U-Pb U-Pb zircon zircon data data establish establishthe the age ageof of volcanism volcanism at at 2705.8+/-1.6 2705.8+/-1.6 Ma. (Table (Table 1) Recent Recent field field studies studiesdefine define aa sequence sequenceof of multiple multipledeformation deformationand and intrusive intrusiveevents events following followingvolcanism. volcanism. The The volcanic volcanic rocks rockswere wereenveloped envelopedby by aatonalite tonalitesuite suite just before before and and during during the the northnorthdirected directed thrusting thrustingand and nappe nappe formation. formation. This Thiswas wasfollowed followedby bydevelopment developmentof ofstrike-slip strike-slip shear zones and the deposition of clastic sediments into pull-apart basins. A second second shear zones and the deposition pull-apart basins. phase suite intruded the belt phase of of folding folding produced upright folds. A Atrondhjemite trondhjemiteto to granite suite and and deformed deformedearlier earlierfabrics. fabrics. The Thetiming timingof ofdeformation deformationisisconstrained constrainedwith withnew newU-Pb U-Pb zircon zircon data data yielding yielding an an age age of 2668.4÷2.l/-l.8 2668.4+2.1/-1.8 Ma Mafor foran anintrusion intrusionin inthis thissuite. suite. Intrusions Intrusionsof of hornblendite homblenditeto to syenite syenite (appinite (appinite suite) suite) and and continued movement along along shear shear zones zones represent represent the the end end of of deformation. deformation.An Anundeformed undeformedpost-tectonic post-tectonicgranite graniteintrusion intrusion has has an an age ageof of 2585 2585(Sims (Simsand andPeterman, Peteman, 1992). 1992). This are readily readily interpreted in a This sequence sequenceof of deformation deformationmagmatic/volcanic magmatic/volcanicevents events are modern modem plate plate tectonic tectonic context. context. The Thevolcanic volcanicarc arcrocks rocksare arethe theresult resultof of north-directed north-directed subduction. Tonalite-suite plutons intruded the arc just prior to collision subduction. Tonalite-suite plutons intruded the arc just prior to collisionof ofaasmall small continent from the south (southern complex) along the Great Lakes tectonic continent from the south (southern complex) along the Great Lakes tectoniczone zone (suture). (suture). Collision Collisionoccurred occurredover overan anextended extendedperiod periodof oftime timewith withmultiple multipledeformation deformation and and magmatic magmatic events. events. The Theappinite appinitesuite suiteisischaracteristic characteristicof ofmodern modemcollision-related collision-related magmatism. magmatism. The Thefield-based field-basedsequence sequenceof ofevents eventsand andnew new age agedates datesare areimportant importantdata datain in continuing continuing to to unravel unravel the the tectonic tectonic evolution evolution of the southern southern edge of the Superior Superior Province. sProvince. References: Sims, Sims, P.K. P.K. and and Peterman, Peterman, Z., Z., 1992, 1992, Guide Guideto tothe thegeology geologyof of the theGreat GreatLakes Lakestectonic tectonic paleosuture: Institute zone zone in in the the Marquette Marquettearea, area,Michigan Michigan -- A A late late Archean Archean paleosuture: Instituteon on Lake LakeSuperior SuperiorGeology GeologyProceedings, Proceedings,38th 38"' Annual Annual Meeting, Meeting, Hurley, Hurley, WI, WI, v. v. 38. 38, part part 2, 2, p. p. 105-135. 105-135. 25 �1 Table 1. and constraining constraining age age dates dates for for the the Table 1.Summary Summaryof ofdeformation deformation sequence, sequence, volcanic/magmatic volcanic/magmatic activity activity and Jshepming greenstone Ishepming greenstone belt. belt. Event Characteristic ., VolcanicfMagmatic Vnlcanic~MaematicActivity Activity Age Dates Undeformed Undeformed post-tectonic post-tectonic granite granite 2585 Ma Kink bands Kink bands with with north-easterly north-easterly striking kink kink planes planes and striking and steeply steeply plunging hinges :,'',,->$ '.f03'] D5 Ds Dip slip motion along shear zones. U4 D4 Folding associated associated with Folding with intrusion of plutons. D3 D3 Upright folding. Appinite suite Di U2 Strike-slip shearing. Trondjhemite-granite suite Tmndjhemite-granite suite U1 Di Recumbent folding. Recumbent folding. Tonalite suite Tonalite suite : yw; .8fel. Extrusion of mafic ma ic and an felsic sic volcanic rocks. 26 2668.4+2.11-1.8 2668.4+2.1/- 1.8 Ma Ma ,". ,,. , . . , : ,. :* : : 2705.8+/-1.6 Ma ; , , b �A NEW APPROACH APPROACH TO TO HISTORICAL HISTORICAL RECONSTRUCTION: COMBINING DESCRIPTIVE AND DESCRIPTIVE AND EXPERIMENTAL EXPERIMENTAL PALEOLIMNOLOGY W. W. Charles CharlesKerfoot, Kerfoot,Lake LakeSuperior SuperiorEcosystem EcosystemResearch Research Center Center and and Department Department of of Biological BiologicalSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University, Houghton, Houghton, MI MI 49931 4993 1 John John A. A. Robbins, Robbins,NOAA NOAAGreat GreatLakes LakesEnvironmental EnvironmentalResearch Research Laboratory, Laboratory, 2205 2205 Commonwealth CommonwealthBlvd., Blvd., Ann Ann Arbor, Arbor,MI MI 48105 48105 Lawrence LawrenceJ. 1.Welder, Weider,Max-Planck-Institut Max-Planck-Institutfür f i rLimnologie, Limnologie,Postfach Postfach165, 165,D-24302 D-24302PlOn, PlOn, Germany* Germany* Here Here we we introduce introduce aa combined combined experimental experimental and and descriptive descriptive approach (termed "Resurrection Ecology") Ecology") to toreconstructing reconstructinghistorical historicalperturbations, perturbations,pointing pointing out out how how direct direct tests tests with with sediments sediments and and hatched hatched resting resting eggs eggs complement complement the traditional descriptive calculation of microfossil microfossil fluxes. fluxes. This Thisapproach approachisisbeing beingstudied studiedin in both both NSFINOAA NSF/NOAA Cooperative sites, the KITES Project in in Lake LakeMichigan. Michigan. Additional core KITES Project in Lake Superior Superior and the EGLEE Project studies studies involve involveBaltic Baltic German German lakes lakes and and the Caspian Sea. In the the Keweenaw Keweenaw Waterway, Waterway, aa freshwater freshwater estuary estuary off Lake Superior, turn-of-the-century copper coppermining mining impacted impactedthe the resident residentbiota. biota. Remain Remain fluxes fluxes document document that that diatom, diatom, rhizopod. rhizopod, and production all declined declined during stamp sand discharges, but recovered rapidly and Bosmina production after moving above background levels due to developing developing eutrophication. eutrophication. In addition addition after WWLI, WWII, moving to biogenic biogenic silica, silica, we we discovered discovered that that bromine bromine flux holds promise as an indicator of diatom production production and and confirmed confirmed that that this this element element is present in several genera. Fluxes of Daphnia resting eggs also the 1940's. 1940's, dominated by by aa hybrid hybrid apparently apparently also increased dramatically since the produced produced from from crosses crosses between offshore offshore and interior interior Waterway species, after channeling promoted promoted greater greater mixing mixing of of water water masses. masses. Toxicity Toxicity studies studieswith with sediments sediments and and Daphnia Daphnia clones clones directly directly tested tested recovery recovery of environments environments after concentrations and after cessation cessation of of mining mining activities. activities. The The studies studies document document that increased concentrations fluxes fluxes of of copper copper in in the the Waterway Waterway during during mining mining discharges discharges were toxic to invertebrates. Once stamp stamp sand sand discharges discharges ceased, ceased, the the biota biota recovered recovered rapidly due to a combination of decreased copper copper cycling cycling and and organic organiccomplexation. complexation. Although Although sedimentation sedimentation has returned to nearbackground background conditions conditionsand and surficial surficial sediments sediments in much of Portage Lake are no longer toxic, eutrophication eutrophicationand and faunal faunal exchange exchange with with Lake Lake Superior Superior make it unlikely that the original zooplankton zooplankton community communitycomposition composition will will return return to to the Waterway system. 27 �THE IRON IRON RIVER RIVER SYNCLINE: AN AN ALLOCHTHONOUS ALLOCHTHONOUSSTRUCTURAL STRUCTURALPANEL PANELIN INTHE THE PENOKEAN PENOKEANFORELAND FORELANDOF OF NORTHERN NORTHERN MICHIGAN MICHIGAN KLASNER, John S., Survey Western S., Department Department of of Geology Geology and U. S. Geological Survey, Western Illinois Illinois University, University. Macomb, Macomb, IL IL61455, 61455. jklasner@macomb.com; jklasner@macomb.com; CANNON, CANNON, William William F. F. and and SCHULZ, SCHULZ, Klaus Klaus J., U. U. S. Geological Geological Survey, Survey, National NationalCenter, Center, MS. MS. 954, 954, Reston, Reston, VA VA 20192; 20192; and and LABERGE, S. Geological Geological Survey, Survey, University Universityof of LABERGE, Gene Gene L., L., Department Department of of Geology Geology and and U. U. S. Wisconsin 54901 Oshkosh, Oshkosh, Oshkosh,WI Wl54901 Wisconsin -- Oshkosh, The The Iron IronRiver Riversyncline syncline(James (Jamesand andothers, others, 1968) 1968)lies liesnear nearthe the southern southernmargin marginof ofthe the Penokean strata of of the Penokeanfold fold and and thrust thrust belt beltin innorthern northernMichigan. Michigan. It It contains sedimentary strata the Paint Paint River River Group Group and and underlying Badwater BadwaterGreenstone. Greenstone. The Thesyncline synclinehas has aa triangular triangular map map pattern pattern and and is is flanked flankedby by strata strataof ofthe theMichigamme MichigammeFormation Formationon onits itsnorth northand andeast eastsides sidesand andby by intensely comolex. intensely deformed deformed Early Earlv Proterozoic Proterozoic strata on its southwest side. An An unusually unusuallvcomplex, multiply-folded structure within the multiply~folded structurewithin the syncline synclinehas hasbeen beenrecognized recognizedsince since the the detailed detailedstudies studiesby by James James and and others others (1965). (1968). Traditional Traditionalstratigraphic stratigraphicinterpretation interpretationhas hasbeen beenthat that the the strata stratain inthe the syncline syncline are are stratigraphically stratigraphicallyabove abovethe the Baraga BaragaGroup Groupand and that that the the Badwater BadwaterGreenstone Greenstoneand and Paint Paint River River Group Group are are the the youngest youngest parts parts of the Marquette Marquette Range Supergroup. More Morerecently, recently, an an allochthonous allochthonousorigin originfor forthe thesyncline syncline has hasbeen beenadvocated advocated(Sims, (Sims, 1996) 1996)and andthe the exact exact correlation correlationof of units unitsin inthe thesyncline synclinewith with autochthonous autochthonousunits unitselsewhere elsewhere in inthe the foreland foreland is is uncertain. uncertain. Our Ourrecent recentre-examination re-examinationof of the the region region lends lends support to tothe theview view that that the the syncline syncline is is an anallochthon allochthonemplaced emplacedby bygenerally generallynorthward-directed northward-directed thrusting. A A thrust thrust of of considerable considerable magnitude This thrust thrust forms forms the the magnitude is is interpreted interpretedto to lie lie at at the the base base of the Badwater Greenstone. This base base of of the the allocthon allocthonand andseparates separatescomplexly complexlydeformed deformedstrata strataabove abovefrom from more moresimply simply deformed deformed strata strata below. below. Several Severalsets setsof ofstructural structuralobservations observationsargue arguefor for the the allochthonous allochthonous nature nature of of the the Iron IronRiver Riversyncline, syncline,the theprincipal principalargument argumentbeing beingthat that the the syncline synclinehas hasaafolding folding history history and and fold fold geometry geometrymore morecomplex complexthan thansurrounding, surrounding,and andpresumably presumablyunderlying underlyingrocks. rocks. ItIt must must therefore thereforehave haveacquired acquiredsome someaspect aspectof ofits itsstructure structureeither eitheras asaageographically geographicallyseparated separated terrane terrane or or during duringthin-skinned thin-skinnedemplacement emplacementover overthe thefootwall footwallrocks. rocks. ~~~~ Structures Structures in in the the allocthon allocthon Studies Studies of of outcrops outcropsof ofthe thePaint PaintRiver RiverGroup Groupshow showthat that at atleast leasttwo twoand andprobably probablythree threeor ormore more generations generations of of fold fold axes axes occur occur in in the the Iron Iron River River syncline. Most Mostfolds folds are are tight tight to to isoclinal isoclinalwith with steeply-plunging steeply-plungingaxes. axes. Similar Similarsteeply-plunging steeply-plunging fold fold axes axes are are common common in in fault fault panels panelswithin within the the Niagara Niagara fault fault complex, complex, part partof of which which bounds bounds the the syncline syncline on on the the south, south, but but are are rare rare elsewhere elsewhere in in the the foreland. Bedding Beddingand andaxial axialplanar planarfoliation foliationare are variably variably oriented, oriented, but but generally generally dip dip steeply. steeply. Remnants Remnantsof of sub-horizontal sub-horizontal foliation foliation occur occur in in aa few places places suggesting suggesting that that recumbent recumbent folds of folding. folding. AAcross folds may may have have been been significant significant during early stages of crosssection section(James (Jamesand and others, synclinenear near others,1968) 1968)from fromiron ironmine mineworkings workingsat atthe thewest westend endof ofthe theIron IronRiver Riversyncline Staumbaugh, steeplyStaumbaugh, Michigan Michigan shows shows a a recumbent recumbentfold foldthat thatisisonly only moderately moderately overprinted overprinted by by steeplydipping dipping structures. structures. The The Badwater BadwaterGreenstone, Greenstone,although althoughlargely largelymassive, massive,does doescontain containstructures structuressimilar similarto tothose those shown history. The shown in in the the Paint Paint River River Group Group and and appears appears to have the same structural history. The Badwater Badwater Greenstone Greenstoneis is therefore thereforeconsidered consideredpart partof ofthe theallochthon. allochthon. 28 �syncline Structures iinn rocks surrounding the Iron Iron River syncline Rocks within the Niagara fault fault complex, south south of of the the syncline, syncline, have havenorthwest-striking, northwest-striking,steeply steeply south-dipping foliation and tight tight to to isoclinal folds folds that that are are steeply steeply plunging, plunging,like likethose thosewithin withinthe the Structures in Baraga Group rocks (primarily (primarily Michigamme Michigamme Formation), Formation),which whichbound boundthe the syncline. Structures the north and east, are much different and and generally generally have havewest-northwest-striking west-northwest-striking syncline on the foliation to sub-horizontal sub-horizontal fold fold axes axes that that foliation that dips moderately to steeply south, and horizontal to trend fold axes axes are are rare rare in in the the Iron Iron River River trend west-northwest. Such Such sub-horizontal, west-trending fold first generation recumbent folding foldingwith with sub-horizontal sub-horizontalaxial axialplanar planar syncline. Several areas of first foliation foliation have have been been found found over over the the past past several several years years within within the the Baraga Baraga Group Group rocks, rocks, small recumbent recumbentfolds foldswith with sub-horizontal sub-horizontal suggesting the formation of nappes. Most recently, small foliation of the the Iron Iron River River foliation have have been been documented documented near Watersmeet, Michigan, northwest of structures north north and andeast eastof ofthe the Iron Iron syncline. Together Together with with previous previous observations observations of similar structures River syncline, there is now widespread evidence evidence of of an early phase of recumbent folding and an early phase foliation, now now variably variably overprinted overprintedby bymore moreupright upright generation of low angle axial planar foliation, structures. structures. Interpretation Interpretation Recumbent Recumbent folds documented documentedby by underground underground mapping mapping in in the Iron Iron River River syncline syncline (James (James and and others, 1968) and remnants of flat-lying foliation found in outcrops of the Paint River Group remnants found in outcrops of the Paint River Group Baraga Group Group had had aa similar similarearly early suggest that both both the Iron Iron River syncline and adjacent Baraga structural history history of recumbent folding and development of of low low angle anglefoliation. foliation. However, structural However, multiple generations generations of of steeply-plunging steeply-plungingfold axes axes and and steeply-dipping, variably-oriented variably-oriented axial axial planar foliations of the Iron River syncline, are distinct from the gently west-plunging fold axes Iron distinct from the gently west-plunging fold axes found in the the Michigamme Michigamme Formation Formation north northand andeast eastof of with south-dipping south-dipping axial planar foliation found the syncline. Similar Similarsteeply steeplyplunging plungingfold foldaxes axes are are common common in in very highly highly strained rocks rocks along to events events related related to to suturing suturing of ofthe thevolcanic volcanic the Niagara Niagara Fault Fault and seem clearly to be integral to terranes south south of the fault. This Thissuggests suggeststhat thatthe theIron IronRiver Riversyncline syncline was was detached detached from from folding history. history. The base interpreted to underlying rocks during much of its folding base of the allocthon is interpreted be a thrust fault along the the base base of of the the Badwater Badwater Greenstone, Greenstone, along which the allochthon allochthon has has been thrust thrust northward over foreland basin turbidite turbidite deposits deposits of ofthe the Michigamme MichigammeFormation. Formation. We folding within within the the Iron Iron River Riversyncline synclineisisaaresult resultof of suggest that the unusual unusual complexity of folding zone. During thrusting of earlier earlierdeformed deformedrocks rocks northward northward from the suture zone. During this thrusting, an earlier set of recumbent folds was intensely redeformed. In In contrast, contrast, rocks rocks in in the structural structural the fact fact that that the the Iron Iron River Riversyncline synclinecross-cuts cross-cutsthe the footwall were little little deformed as shown by the west-trending, sub-horizontal west-trending, sub-horizontal fold fold axes axes in in the the adjacent adjacent Michigamme Michigamme Formation. Formation. REFERENCES REFERENCES J., and Wier, Wier, K. K. L., L., 1968, 1968, Geology Geology and andOre Ore Deposits Depositsof of James, H. L., L., Dutton, C. E., E., Pettijohn, F. J., the Iron Iron River-Crystal River-Crystal Falls Falls District, District, Iron Iron county, county, Michigan: Michigan: U. S. Geological Geological Survey Professional Paper 570, 134 134 p. P.K., 1996, L.M.H., eds., Sims, P.K., 1996,Structure Structureof of continental continentalmargin, margin, in in Sims, P.K., P.K., and Carter, L.M.H., Archean and Proterozoic geology of the Lake Superior region, U.S.A., 1993: Proterozoic of the Lake Superior region, U.S.A., 1993: U.S. Geological Professional Paper Paper 1556, 1556, p. p.44-51. Survey Professional 44-51. 29 �REGIONAL PATTERNS PAYIERNS ON THE ON THE THE PENOKEAN PENOKEAN CONTINENTAL MARGIN IN THE SOUTHERN SOUTHERN LAKE SUPERIOR REGION Gene , Oshkosh, Oshkosh, WI L. LaBerge, M e r g e , UW UW Oshkosh Oshkosh , W I 54901 and U. U.S. S. Geological Geological Survey Survey Gene L. Studies of outcrops outcrops and exploration drill cores reveal several cores during the past decade decade reveal several regional patterns in the deposition deposition and subsequent deformation deformation and metamorphism metamorphism of of the the Early Proterozoic Earl Proterozoic Penokean continental continental margin margin rocks rocks in in northern northern Wisconsin Wisconsin and and northern northern Michigan. These datahelp helpconstrain constrain models models of of the the depositional depositional and tectonic history of the ~ichigan. Thesedata region. . region. I. Regional depositional depositional patterns. patterns. A. Thinning westward of the basal arenite of of the the Chocolav Chocolay Grouo. Group. The A. The Mesnard and Sturgeon Formations are are prominent arenite arenite units in the Marquette ~ a r ~ b e tand te Sturge& Formations Menominee districts, Menominee districts. respectively, resuectivelv. and the the Sunday Sundav Quartzite Ouartzite forms forms a thin basal unit on the eastern Gogebic &nee. range. However, basal arenite &&te is is absent absent on on the thewestern rfowever, aabasal Gogebic range, where the the the dolomite dolomite unit characteristic characteristic of the upper part of the Gogebic range, Group rests directly on on Archean basement. basement. Drill Chocolay Group Drill core coredata data from from the the Park Park Falls -- Mercer area of northern Falls northern Wisconsin suggests suggests that this this pattern pattern extends extends southward toward toward the the proposed continental continental margin. southward increase in politic pelitic rocks rocks southward toward the proposed continental B. An increase margin. Drill pelitic ParkFalls Falls -- Mercer area intersect abundant ~elitic marein. Drillcores coresfrom from the the Park schists, some of which contain interbedded carbonate carbonate units. units. Bedded Bedded sulfides sulfides are are present locally within the politic pelitic rocks. rocks. The Thestratigraphic stratigraphicposition positionof of the thepelitic politicunits units has not been ascertained, but they may be broadly correlative correlative with the Chocolay (Cannon and others, 1998). 1998). Group (Cannon C. A consistent pattern of litholoeies lithologies within the Palms formation of the Menominee Menominee Penokean platform. platform. The Group throughout the Penokean The thin-bedded argillaceous lower member and the thick-bedded thick-bedded orthoquartzite are recognizable orthoauartzite upper uooer member membea are r e c o b b l e from from member the Marenisco are also ~amekaion.These Thesemembers membekare also Marenisco area westward to Lake Namekagon. recognizable recoenizable in drill drill cores cores from from the the Pine PineLake LakeSubterrane Subterrane(Cannon (Cannonand andothers, others. 1998) from the Lake Gogebic Gogebic area southwestward WI area, area, southwestward at least to the Butternut, WI suggesting a uniform platformal depositional environment. platf-1 suggesting D. Rift-related ironRift-relatedvolcanic volcanicrocks rocks(Sims (Sims and and others, 1989) 1989) are are associated with ironformation of the Menoninee ~Group G u on p the proposed shelf. The The Emperor Emperor Volcanics Volcanics are interbedded interbedded with iron-formation on the the eastern eastern Gogebic Gogebic (LaBerge (LaBereeand and Klasner, Klasner, 1994), and volcanics are present within the iron-formation iron-formation on & the western w-&tern end end of the Gogebic ((LaBerge M e r g e and others, 1995). Volcanic Volcanic rocks rocks as as well as carbonaceous sediments are associated with iron-formation south of the Gogebic range in a belt that extends extends from from near near Lake Lake Gogebic Gogebic southwestward southwestward at at least least to to the the Butternut, Butternut, Wisconsin area, (LaBerge, (JaBer e, 1997). This Thissuggests suggeststhat that rifting, rifting, with with associated volcanism and stagnant stagnant basin development, development, occurred occurredafter after deposition deposition of of the the Palms Palms Formation on the continental margin. On Onthe themain mainGogebic Gogebicrange, range,then, then, the the ironironformation accumulated accumulated on a shallow shallow platform bounded bounded on on the the east, east, south south and and west west basins with active active volcanism. by rift basins II. deformation/metamorhpic 11. Regional Regional defonnation/metamorhmcpatterns. " A. Metamorphism ~ & o r p h i s m of ofcontinent &tin& margin margin sediments sedimentsthat that increases increasesin in intensity intensity associated with with intense intense folding foldingand andnorth-directed north-directedthrusting. thrusting. A A zone zone of of southward associated high pressure pressure metamorphism metamorphism characterized characterized by kyanite and a high temperature zone 30 �sillimanite(the Powell Subtenane Subterrane and the Park Falls Subterrane, Subterrane, characterized by sillimanitefthe respectively of Cannon and others, 1998). 1998). pegmatitic, granites, some of of B. Emplacement of post-tectonic potassic, commonly pegmatitic, two-mica granites, or garnet, garnet,typical typicalof of which are two-mica granites, or which contain sillimanite or anatectic granites. later deformational deformational event eventwith withassociated associatedretrograde retrogrademetamorphism. metamorphism.This Thisisis C. A later widespread alteration alteration of of high grade minerals such such as as sillimanite sillimaniteand and expressed as widespread rocks)to topyrophyllite pyrophylliteand andserpentine, serpentine,respectively. respectively. This This olivine (in carbonate rocks) the post-tectonic post-tectonic granites granitesassociated associatedwith withthe theearlier earlier deformation has locally affected the deformation. References: Cannon, W.F., W.F., LaBerge, G.L., G.L., Klasner, Kiasner, J.S., J.S., and Schulz, K.J., K.J., 1998, Reinterpretation Reinterpretation of the Penokean continental margin in part of northern Wisconsin and Michigan (Abstract): 44th Annual Institute on Lake Superior Geology, vol. vol. 44, 44, part part 1, p. p. 52-53. J.S., and M LaBerge, G.L., 1994, Klasner, J.S., e r g e , G.L., 1994, Structural evolution of the eastern Gogebic Michigan (Abstract): (Abstract): 40th 40th Annual AnnualInstitute Instituteon onLake LakeSuperior Superiot range, northern Michigan vol. 40, part part 1, p. 23-24. Geology, vol. LaBerge, G.L., G.L., 1997, break-up of of the the Superior SuperiorCraton: Craton:Implications Implicationsofof Merge, 1997, Early Proterozoic break-up drill core and geophysical data south of of the the Gogebic range, range, northern northern Wisconsin Wisconsin (Abstract), 43rd Annual Annual Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology,vol. vol.43, 43,part part1,1,p.p. 3 1-32. 31-32. LaBerge, G.L., G.L., Cannon, Cannon, W.F., and andKiasner, Klasner,J.S., J.S., 1995, 1995,New New observations observations on the geology of the western Gogebic range (Abstract): Institute on Lake (Abstract): 41st Annual Institute Superior Geology, vol. 41, part I,1,p.p.331-32. 1-32. LaBerge, G.L. G.L. and Klasner, J.S., J.S., 1994, Tectonic Tectonic implications implications of the Early Proterozoic lithostratigraphy on the eastern Gogebic range, northern Michigan (Abstract): 41st on the eastern Gogebic Annual Institute on Lake Superior Geology, vol. vol. 41, part part 1, p. p. 33-34. Sims, P.K., P.K., Van Schmus, W.R., W.R., Schulz, K.J., K.J., and Peterman, Z.E., Z.E., 1989, TectonoTectonostratigraphic evolution evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatictenanes terranesof ofthe the Penokean Orogen: Canadian Journal of Earth Sciences, v. 26, p. 2 145-2158. Orogen: Canadian Journal of Earth Sciences, v. 26, p. 2145-2158. 31 �1 I DETERMINE THE THE ORIGIN ORIGIN OF A GEOCHEMICAL AND PETROLOGIC STUDY TO DETERMINE CROWDUCK LAKE THE CROWDUCK LAKE GROUP, GROUP. KENORA, ONTARIO: A PROBLEMATIC METACONGLOMERATE. METACONGLOMERATE. JOHNSON, Matthew M. M.and and COTTER, COTTER, J.F.P., J.F.P., LOUGHRY, Joy LOUGHRY, Joy E., JOHNSON, Geology Geology Discipline, Discipline, University University of of Minnesota, Minnesota, Morris, Morris, Morris 56267 Morris MN M N 56267 The The Crowduck Crowduck LakeLake Group is is a sequence sequence of of argillite argillite and aa poorly poorly sorted sorted conglomerate (Archean (Archean ? age) age) exposed exposed near near Kenora, Kenora, Ontario. Ontario. Smith Smith (1988) may be be a debris debris flow flow (1988) suggested suggested that that the the Crowduck Crowduck Lake Lake Group Group may deposit, deposit, however however lithology lithology and and geographic geographic location location suggest suggest that that it may may be be aa correlative correlative of of the the"Gowganda "Gowganda tillites' tillites" (polymictic (polymictic conglomerates conglomerates deposited deposited during during the the Gowganda Gowganda glaciation glaciation 1.8 1.8 billion billion years years ago). ago). The goal goal of Crowduck Lake Lake Group Group is is glacial glacial in in of this this study study is is to todetermine determine ifif the theCrowduck origin. origin. Extensive research has has been been done done on Extensive research on the the deposits deposits of of the the Gowganda Gowganda Glaciation of the Glaciation (Summarized (Summarized by by Young Young 1969, 1969, 1973. 1973, 1999). 1999). Outcrops Outcrops of the Gowganda Gowganda are are located located in in Chibougamau, Chibougamau, Quebec, Quebec, Wyoming. Wyoming, and and Northern Northern Michigan. Geochemical analysis analysis indicate indicate that that there Geochemical there are are broad broad similarities similarities in diamictite constituents. Additionally. Chemical Index in constituents. Additionally, Chemical Index Alteration Alteration studies studies provide provide evidence evidence of of regionally regionally cold cold climatic climatic conditions conditions (Young, (Young, 1999). 1999). Young on the Young (1969), (1969). on the basis basis of of outcrop outcrop distribution, distribution, suggests suggests that that elsewhere in Canada there elsewhere in Canada there are arepolymictic polymictic conglomerates conglomerates which which on on detailed detailed analysis may well turn out to be tillites. analysis may well turn out to be tillites. For For this this study study an an outcrop outcrop at at the the type type locality locality of of the theCrowduck Crowduck Lake Lake Group Group was was described described and and sampled. sampled. Hand Hand samples samples were were analyzed analyzed for for sedimentary structures, Geochemistry structures, clast provenance provenance and and clast clast shape. shape. Geochemistry of matrix matrix samples samples was was determined determined using using ICP. ICP. Thin Thin sections sections of of matrix matrix were were used used for for petrographic petrographic analyis. analyis. Geochemistry of the Crowduck Lake Lake Group Group is is similar similar to to that that of of the the Geochemistry of the Crowduck type of these type Gowganda Gowganda Fotmation Fofmation of of Ontario. Ontario. However, However, interpretation interpretation of these results is results is restricted restricted because because little little is is known known about about the the geochemistry geochemistry of of the the bedrock at at the Additionally, the age age of of the the Crowduck bedrock the time time of ofdeposition. deposition. Crowduck Additionally, the Lake Group Lake Group is is poorly poorly constrained. constrained. Thus, Thus, several several possible possible origins origins of the the Crowduck Crowduck Lake Lake Group Group remain remain plausible: plausible: glacial glacial tillite, tillite, turbidite/debris turbiditeldebris flow, and flow, and basal basal conglomerate. conglomerate. Although Although the sedimentology. sedimentology, location location and and age of of the the Crowduck Crowduck Lake Lake Group Group make make aaglacial glacial origin originattractive, attractive, evidence evidence is Additional is not conclusive. conclusive. Additional petrographic petrographic analysis analysis are are underway. underway. 32 �THE GRATIOT CHALCOCITE DEPOSIT, KEWEENAW PENINSULA, MICHIGAN MAKI, John C., Department of of Geological Geological Engineering Engineeringand andSciences, Sciences,Michigan Michigan Technological Technological University. Houghton, MI 49931, jcmaki@mtu.edu; and BORNHORST, Theodore J., Department Department of of University, 4993 1Jcmaki@mtu.edu; and BORNHORST, Theodore J., Geological University, Houghton, Houghton, MI 49931, Geological Engineering and Sciences, Sciences, Michigan Technological University, tjbomho@mtu.edu tjbomho@mtu.edu ABSTRACT ABSTRACT Michigans Michigan's Keweenaw Keweenaw Peninsula Peninsula is is well well known for world-class world-class native copper deposits and the lack of significant amounts of copper sulfides. Twelve copper Twelve copper sulfide sulfide (chalcocite-dominated) (chalcocite-dominated) deposits depositshave have Peninsula. Robertson (1975) described one small deposit near Mt. been discovered in the Keweenaw Peninsula. Bohemia. Chalcocite-dominated deposits are are concentrated concentratedininthe the lower lowerquarter quarter of of the the Portage Portage Lake Lake Bohemia. Chalcocite-dominated deposits to Mt. Mt. Bohemia Bohemia (Figure (Figure 1). 1). The Gratiot chalcocite Volcanics from Suffolk to chalcocite deposit (previously termed 543-S) is the largest of the deposits and and contains about about 4.5 4.5 million metric 5434) the copper copper sulfide sulfide dominated dominated deposits tons of ore with an average average grade grade of of 2.3% 2.3% copper. copper. The The Gratiot chalcocite chalcocite deposit deposit is is hosted hosted by the Portage Lake Volcanics and is about 1.4 1.4 km from from the In vicinity of the ore, basalt lava flows are Keweenaw fault, a major reverse fault of regional extent. reverse fault of regional In vicinity of dikes. These to the the orientation orientation of of the the lava lava flows. flows. cut by two dacite-andesite dikes. These dikes are nearly subparallel to flow tops, although lesser amounts are Ore grade intercepts occur mostly in brecciated brecciated amygdaloidal flow found in flow interiors and and dikes. dikes. The both dikes are present present The highest highest grade and tonnage exists where both both dikes dikes are are thick. thick. Faulting and both dikes dikes and where both and fracturing fracturing are most prevalent in rocks where both exist. The deposit zone, the the Gratiot-Suffolk Gratiot-Suffolkfault, fault, that has a stratigraphic exist. deposit is within a 12 12 km long fault zone, displacement of about 7 meters and is sub-parallel to to the the attitude attitude of of the the basalt basalt flows flows and and sub-parallel to to fault. Two deposit are are the the Cross-Gratiot Cross-Gratiot fault fault that that is is the Keweenaw fault. Two other other significant significant faults that cut the deposit basalt flows flows with with aa stratigraphic stratigraphic displacement displacement of of about roughly perpendicular to the attitude of the basalt about 15 15 meters and and the the Gratiot fault that that is sub-parallel to the the attitude attitude of of the the basalt basalt flows flows with with very meters Gratiot fault sub-parallel to very little little The highest grades are associated with the intersection of the Gratiotstratigraphic displacement. displacement. highest grades associated with the intersection the GratiotSuffolk fault, the Gratiot Gratiot fault fault and and the the Cross-Gratiot Cross-Gratiot fault. fault. fill amygdules amygdules and and fractures fractures within within the the basalt lava A suite suite of of secondary secondary hydrothermal hydrothermal minerals minerals fill lava flows and dikes. Chlorite was the earliest secondary mineral, followed by epidote, potassium feldspar, Chlorite was the earliest secondary by epidote, potassium feldspar, Deposition of of native copper and native silver, prehnite prehnite and quartz and calcite (approximate order). Deposition pyrite clearly follows native copper and was itself followed by by chalcopyrite, bomite, bornite, chalcocite chalcocite and and hematite. The Thelast lastphase phaseof ofsecondary secondarymineral mineral deposition deposition was adularia, laumontite and more calcite. Chalcocite Chalcocite is by far far the the major majorcopper-bearing copper-bearing mineral mineral in the Gratiot Gratiot deposit, deposit, other other copper-bearing copper-bearing minerals are trace to rare in occurrence. The deposit The relative relative age of mineral deposition in the Gratiot deposit matches the relative age of mineral mineral deposition deposition in the large native copper deposits in the the Keweenaw Keweenaw Peninsula. Butler an early early suite of of minerals associated associated with with native native Butler and and Burbank Burbank (1929) (1929) documented documented an Native copper copper in in the copper followed by late adularia, adularia, laumontite and calcite. Native by chalcocite and then late Keweenaw Peninsula is interpreted to be temporally and and genetically genetically related related to to compressional tectonics The close temporal produced reverse motion motion along along the the Keweenaw Keweenaw fault (Bornhorst, (Bomhorst, 1997). 1997). The temporal that produced also chalcocite is also relationship of native copper and chalcocite relationship of chalcocite in the Gratiot deposit suggests that chalcocite are interpreted interpreted as as very Native copper copper ore-depositing ore-depositing fluids are very tectonics. Native related to to compressional compressional tectonics. related Chalcocite ore must Chalcocite ore fluids must sulfur poor and derived from basalts within the rift (Bomhorst, 1997). sulfur poor and derived from within the rift (Bomhorst, 1997). 33 �have have carried carried more moresulfur sulfurthan thannative nativecopper copperfluids. fluids. However, However, the the genesis genesis of offluids fluidsgenerating generatingthe the chalcocite chalcocitedeposits depositsisiscurrently currentlyspeculative. speculative. Gratiot-Suffolk Fault Gratiot Lake Mt Bohemia Deposit Gratiot GratiotDeposit Deposit Suffolk Deposit 1111111 Jacobsville Sandstone KXI Oronto GrOLQ I Portage Lake Volcanics I 20 0 km FIGURE FIGURE 1: 1: LOCATION LOCATIONOF OFCOPPER COPPERSULFIDE SULFIDEDEPOSITS DEPOSITS References References - ,< . Bornhorst, Bomhorst, T. T. J., J., 1997, 1997,Tectonic Tectoniccontext contextof ofnative nativecopper copperdeposits deposits of of the the North North American American Midcontinent Midcontinent Rift Rift System: System: Geological GeologicalSociety Societyof ofAmerica AmericaSpecial SpecialPaper Paper 312, 312, p. p. 127-136. 127-136 Butler, deposits of of Michigan: Michigan: U. S., 1929, 1929, The copper deposits U. S. S. Geol. Geol. Survey Survey Prof. Prof. Butler, B. S. and Burbank, W. 5., Paper 238 p.p. Paper 144, 144,238 Robertson, Robertson, J. M., M., 1975, 1975, Geology Geologyand andmineralogy mineralogy of of some somecopper coppersulfide sulfidedeposits depositsnear near Mount Mount Bohemia, Bohemia, Keweenaw Keweenaw County. County, Michigan: Economic Economic Geology, Geology, v. v. 70, 70, p.p.1202-1224. 1202-1224. 34 �CHEMICAL AND AND MINERALOGICAL MINERALOGICAL COMPARISON COMPARISON OF OF BARABOO, BARABOO, BARRON, BARRON, AND AND SIOUX SIOUX CHEMICAL ARGILLITE, METAPELITE AND PIPESTONE ARGILLITE, METAPELITE AND PIPESTONE MEDARJS, L.G., Jr., of MEDARIS, L.G., Jr., and and FOURNELLE, FOURNELLE, J.H., J.H., Dept. Dept. of of Geology Geology & & Geophysics,Univ. Geophysics,Univ. of Wisconsin-Madison,53706, 53706,medaris@geology.wisc.edu, inedarisgeology.wisc.edu, johnf@geology.wisc.edu; johnfgeo1ogy.wisc.edu; Wisconsin-Madison, BOSZHARDT, BOSZHARDT, RI., RF.,Mississippi MississippiValley ValleyArchaeology ArchaeologyCenter, Center,Univ. Univ.ofofWisconsin-La Wisconsin-LaCrosse, Crosse, 54601, rboszhar@uwlax.edu; J.H., State rboszhar@uwlax.edu, BROII{AHM, BROBHAHN, J.H., State Historical Society Society of of Wisconsin-Madison, 53706, John.Broihahn@ccmail.adp.wisc.edu 53706, John.Broihahn@ccmail.adp.wisc.edu Early Early Proterozoic Proterozoic (1760-1630 (1760-1630 Ma) Ma) red red quartzites quartzitesin in the the southern southern Lake Lake Superior Superiorregion region place place important important constraints on the climatic, sedimentary, and tectonic history of North America, and fine-grained constraints on the climatic, sedimentary, and tectonic history of North America, and fine-grained sedimentary and hydrothemially hydrothermally altered rocks in sedimentaly in the quartzite sequences sequences have provided material for for Native Native artihcts. Although American artifacts. Althoughargillites argilhtesand andpipestones pipestonesfrom fromseveral severallocalities localities have have been been investigated investigated freviously by previously by X-ray X-ray diffiaction, diffraction, little littleattention attentionhas hasbeen beenpaid paid so sofar firto totheir theirchemical chemical compositions compositions and and textural details. Representative samples of Baraboo, Barron, and Sioux argillite, metapelite, and pipestone Representative samples of Barabw, Ban-on, and Sioux have been investigated by by petrographic petrographic microscope, XRF, XRD, and EMP to determine textural characteristics to determine their textural characteristics and and chemical and and mineralogical mineralogical compositions. compositions. Such chemical Such information information provides provides aa basis basis ibr for evaluating evaluatingpossible possibleregional regional variations variations in in chemical compositions and metamorphic metamorphic conditions among conditions among the artifact determining artifact the quartzite quartzite localities localities and and for for determining provenances. provenances. Bamboo: fine-grained metasedimentary metasedimentary layers, Barabw: layers, several several to several several feet feet in inthickness, thckness, are interbedded interbedded with inches to quartzite and vary varyfrom frompink pink argillite argillite(metasiltstone) (metasiltstone) to gray phyllonite (metapelite), depending on on the the proportions proportions of quartz and pyrophyllite. Pipestone occurs Pipestone occursin in several several small pipestone quarries and one outcrop near the base of the quartzite sequence sequence in the south south limb of the the Bamboo Baraboo syncline. syncline. The pipestone is a dark purplish-red argillite, aigillite, consisting of quartz, quartz, pyrophyllite, and and hematite, hematite, which which is is cut cut by by thin thin white white hydrothermal veins containing pyrophyffite, muscovite, and hydrothermal containing pyrophyllite, and diaspore. In several pipestone samples, argillite itself has In several pipestone samples, argillite been altered to an assemblage assemblage of of muscovite-pyrophyllitemuscovite-pyrophyllitediasp ore-hematite, in in which which quartz quartz has been replaced diaspore-hematite, replaced largely largely by pyrophyllite (Fig. 1). Small amounts of kaolinite in 1). Small amounts of kaolinite inthe the metasedimentary rocks and and pipestone pipestone are are retrograde retrogradein in origin, origin, replacing replacing pyrophyllite pyrophyllite or or muscovite. muscovite. Barron: four samples fow samples of of discarded discardedpipestone pipestone were collected in the vicinity of a pipestone pipestone quarry quarryin in the the Doyle Doyle Barron County. The Forest Unit, Barren Thepipestone pipestoneisis aamassive massive to laminated red argillite, which contains quark, quartz, hematite, hematite, and and large vermicular grains of vermicular-grains of kaolinite kaolmite (Fig. 2). 2). Sioux: two samples M: samples of of pipestone pipestone from from Pipestone Pipestone National Monument and one of flaggy aigillite argillite from the Jasper quadquadrangle (sec. 32, Tl 04N, R4W) T104N, R4W) were were provided by David and Tony Tony Runkel. Runkel. The Southwick and Thepipestone pipestone samples samples are are typical catlinite, catlinite, being being fine-grained fine-grainedand and deep deepred red in in color, color, m: 35 �I locally with small pale orange-red reduction spots and pale gray elliptical domains. The Thepipestone pipestone mineral mineral assemblage assemblage is pyrophyllite-diaspore-muscovite-hematite, pyrophyllite-diaspore-muscovite-hematite,and the pale pale gray gray elliptical elliptical domains domains are are largely largely pyrophyllite with minor diaspore and muscovite (Fig. 3). Small Smallamounts amountsof ofkaolinite kaoliniteare are retrograde retrogradeafter after argillitecontains containsquartz, quartz,hematite, hematite,pyrophyllite, pyrophyllite,and and traces tracesof of detrital detrital pyrophyllite and muscovite. The Theargillite muscovite. muscovite. Chemical Comoosition Composition Six are Six samples samples of Baraboo, Barron, Barron, and Sioux Sioux argillite and metapelite are of Na,0 Na20 and CaO CaO and and contain wntain less than than essentially devoid of 0.39 wt% wt% K20, K,0, attesting attestingto totheir theirextreme extreme chemical chemical Rock Compositions in the q Baraboo Baron ICASH System matunty and maturity and contrasting contrastingmarkedly markedly with with the the composition composition of Projected onto tle KAS Plane Sioux average shale (Fig. (Fig. 4). Relative argillite and average Relative to to argiuite shale, the K-rich and Si-poor Si-poor compositions wmpositions of Bamboo Baraboo and and 19 Si Sioux pipestones (0.66-5.62 wt% lC,O Sioux K,0 and 40.90-54.20 wt% SiOJ 5i02) indicate wt% indicate that they may have have formed from ppestone argillite by addition of K and removal of Si through argilhte hydrothermal activity. Such Suchaa process processcould could account account for kin estone and replacement of quartz quartzin inBaraboo Baraboopip pipestone and the replacement suggests suggests that that the the elliptical ellipticalpyrophyllite pyrophyllite domains domains in in Sioux Sioux K pipestone may also be the result of quartz pipestone replacement. replacement. 8 Metamorphic Metamomhic Conditions: the Barron Ban-on argillite argiUite assemblage, quartz-kaolinite, assemblage, quartz-kaolimte, is limited to 6 at 22 kbar kbar (Fig. (Fig. 5). 5). The temperatures below 3300°C 0 0 T at The Bamboo and Baraboo and Sioux Siouxargilhite argillite assemblage, quartzquartzpyrophyllite, is stable stable between 300 and 390°C 3 9 0 T at 2 -. kbar, and and the the pipestone pipestone assemblage, assemblage, pyrophyllitepyropbyllite22 muscovite-diaspore, is is more more narrowly narrowlyconfined confined between 3315 and 360° 360°C (Fig. (Fig. 5). 5). The Baraboo and hetween 15 and Sioux assemblages assemblages cannot cannotbe be due due to to burial burial alone, alone, o o 450 350 400 250 300 because depths on the order of 18-19 18-19 km k m would be 250 300 350 400 450 T C T, "C required to reach reach 300°C 'raton quiredm 3000c for a typical stable craton 5 Reactions Fig. 5 Fig. Reactions in in the the KASH KASH system system and and assemblages assemblages conductive g geotherm. conductive ~ t h e n n The .Theage ageand andsource source of the u Bamboo, Barron, in Ban-on, and and Sioux Sioux rocks rocks thermal pulse responsible responsible for for Baraboo Baraboo and and Sioux Sioux metamorphism remains uncertain. In Inaddition, addition,kaolinite kaolinite is is widely reported in the Sioux Quartzite, and it is was ubiquitous in the the Sioux Quartzite (as it was was in the Baraboo quartzite), unclear whether metamorphism was or restricted restricted to to zones zones of of hydrothermal hydrothermal activity, activity, perhaps perhapsrelated relatedto tofaulting. faulting. Conclusions: Conclusions: the thechemical chemicalcompositions wmpositionsof ofargillite argilliteand andmetapelite metapeliteconfirm confirmthe the chemical chemicalmaturity maturity of of all all sedimentary members of the Bamboo, Barron, and Sioux sequences, consistent with derivation from a Baraboo, Barren, and Sioux sequences, consistent with derivation from a deeply weathered, weathered, low-relief low-relief source source in in an an Early Early Proterozoic Proterozoic warm, warm, humid humid climate. climate. Comparable Comparable mineral assemblages in Bamboo assemblages Baraboo and and Sioux Siouxpipestones pipestonesdemonstrate demonstratethat thatthe thepromotmg promotinghydrothennal hydrothermalactivity activitydoes does not coincide with the 1630 1630 Ma thermal front in the southern Lake Lake Superior Superiorregion, region, postulated postulatedby by Hoim Holm et et al. (1998); (1998); whether whether they are are contemporaneous remains remains to be seen. Regarding Regarding artifact artifactprovenance, provenance, Barron Barron pipestone is easily easily distinguished distinguished from Bamboo Baraboo and and Sioux Siouxpipestone pipestone by by the the presence presence of of vermicular vermicular kaolinite. kaolinite. Comparable Comparable mineral mineral assemblages assemblagesand and textures texturesmake makediscrimination discriminationbetween between Baraboo Baraboo and and Sioux Siouxpipestones pipestones more difficult. Baraboo Baraboopipestone pipestonemay maycontain wntainquartz, quartz,isislocally locallycut cutby bythin, thin,white white veins, veins, and and is is dark dark purplish purplish red red in in color; color; Sioux Siouxpipestone pipestoneis isdevoid devoid of of quartz quartzand andveins, veins, commonly commonly has has reduction reduction spots spotsand and conspicuous, conspicuous, small, small, pale pale gray, gray,elliptical ellipticalpyrophyllite-rich pyropbylhte-rich domains, domains, and and isis deep deep red red to to orange orangein in color. color. 36 �REPUBLIC REPUBLIC WETLAND PRESERVE John G. G. Meier - District DistrictManager Manager— Environmental Environmental Affairs Affairs Cliffs Cliffs Mining Milling Services Company Iron Iron ore ore mining, mining, by by its its very very nature, nature, causes causes large large potential impacts to natural resources. Development Developmentof of mine mine pits, pits, rock rock stockpiles stockpiles and and tailings tailings basins basins impacts impacts wetlands wetlands from time to to time. time. Permits Permitstotoimpact impactwetlands wetlandsare areissued issuedby by the the Michigan Michigan Department Department of Environmental EnvironmentalQuality Quality ifif the the impacts impacts are are "unavoidable" "unavoidable" and and are are "minimized "minimized to to the the greatest greatest extent extent possible". possible". Each Eachpermit permitrequires requiresthat that"compensatory "compensatory wetland wetland mitigation" mitigation" be be provided. provided. The The Republic RepublicWetland WetlandPreserve Preserveisis being being created created at at the the former former Republic Republic Mine Mine tailings tailings basin basin to to provide providecompensatory compensatorywetland wetland mitigation mitigation for for those unavoidable unavoidable impacts to wetlands wetlands at at other other mining operations. operations. Instead Insteadof of merely merely draining draining the water from the various various tailings tailings and and water water clarification clarification ponds and converting the land to upland at Republic, Cliffs, with MDEQ oversight, is in these these areas. areas. Several is constructing wetlands in hundred hundred acres acres of creditable creditable wetland will be created. This This wetland area, area, along along with adjacent upland and external external preservation area, will be placed in a Conservation Easement Easement for for the the benefit benefit of the the State State for long term protection. 37 �POTENTIAL PGE IN POTENTIALFOR FORSTRATIFORM STRATIFORM PGEMINERALIZATION MINERALIZATION IN MAFIC LAYERED INTRUSIONS COMPLEX MAFIC LAYERED INTRUSIONSOF OFTHE THEDULUTh DULUTH COMPLEX MILLER, 55114 MILLER,James JamesD., D.,Jr., Jr.,Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAve., Ave.,St. St.Paul, Paul,MN MN 55114 (mille066@maroon.tc.unm.edu) (mille066@maroon.tc.umn.edu) Economic Economicconcentrations concentrationsof ofplatinum platinumgroup groupelements elements(PGEs) (PGEs)ininmeter-thick, meter-thick,stratiform, stratiform,sulfide-bearing sulfide-bearing horizons horizons(reefs) (reefs)have havelong lonebeen beenknown knowntotobebeassociated associatedwith withultramafic-mafic ultramafic-maficlayered layeredintrusions intrusionssuch suchasas the theBushveld ~ u s h i e land dA dStillwater Stillwatercomplexes. complexes. Recent Recentdiscoveries discoveriesofofPGE PGEmineralization minerali&on ininthe theSkaergaard Skaergaard Intrusion Intrusionand andrelated relatedbodies bodiesininGreenland Greenland(Bird (Birdetetal., al.,1991, 1991,1995; 1995;Neilsen Neilsenand andBrooks, Brooks,1995; 1995;Aranson, Aranson,etet - al., al., 1997; 1997;Andersen Andersenetetal., al.,1998) 1998)have haveshown shownthat thatstratiform stratiformPGE PGEmineralization mineralization can can also alsooccur occurinin tholeiitic tholeiiticlayered layeredintrusions. intrusions.The Thepresence presenceofofmany manytholeiitic tholeiiticmafic maficlayered layeredintrusions intrusionsassociated associatedwith withthe the 1.1 1.1 Ga GaMidcontinent MidcontinentRift Riftsuggests suggeststhat thatthe theLake LakeSuperior Superiorregion region isisfertile fertileground groundfor forexploration explorationof ofthis this newly newlyrecognized recognizedtype typeof ofPGE PGEmineralization. mineralization. With Withthe thesupport supportofofthe theState StateofofMinnesota's Minnesota'sMinerals Minerals Coordinating the been assessing coordinatingCommittee ~ommi'ttee theMinnesota MinnesotaGeological GeologicalSurvey Surveyhas hasbeen assessingthe thepotential potentialfor forstratiform stratiform PGE PGE mineralization mineralization in in two twointrusions intrusionsof ofthe theDuluth DuluthComplex—the Complex-the Layered Layered Series Series at at Duluth Duluth and andthe the Sonju SonjuLake Lakeintrusion intrusion(Miller (Millerand andRipley, Ripley.1996). 1996). Based Skaergaardand andother othertholeiitic tholeiitic Based on onempirical empiricalobservations observations of ofPGE PGEmineralization mineralizationin inthe theSkaergaard intrusions, intrusions, and andon ontheoretical theoreticalconsiderations considerationsof ofsulfur sulfurand andPGE PGEbehavior behaviorinindynamic, dynamic,differentiating differentiating intrusions, intrusions, the the conditions conditions that that favor favorthe theformation formationofofPGE-enriched PGE-enrichedhorizons horizonsinintholeiitic tholeiiticlayered layered intrusions intrusionsare: are: 1.1.The undersaturated Theparent parentmagma magmaisisinitially initiallysulfide sulfideundersaturated. 2.2.The parent magma has a high initial PGE experiences &h experiencesaaconsiderable considerableamount amount The parent magma has a high initial PGEconcentration concentrationand/or of offractional fractionalcrystallization crystallizationtotobuild buildup upnoble noblemetal metalconcentrations concentrationsprior priorto tosulfide sulfidesaturation. saturation. of sulfide 3.3. The Theinitial initial segregation segregation of sulfide melt melt is is triggered triggered by by aaprocess processsuch suchasasmagma magmamixing, mixing, decompression, decompression, assimilation, assimilation, or or simple simple differentiation differentiation that that promotes promotes aa large large R-factor R-factor (silicatdsulfidemelt meltratio). ratio). (silicate/sulfide These Theseconditions conditionsimply implythat thatan anintrusion intrusionthat thatformed formedfrom fromananinitially initiallysulfide-undersaturated, sulfide-undersaturated,tholeiitic tholeiitic parent parentmagma magmahas hasthe thebest bestchance chancefor forsignificant significantPGE PGEmineralization mineralizationin in the themidmid- to toupper-level upper-level horizon horizon that that marks marksthe thefirst first"cumulus "cumulusarrival" arrival"ofofimmiscible immisciblesulfide sulfidemelt. melt. Theoretically, Theoretically, aa gabbro gabbrocumulate cumulate crystallized crystallizedfrom fromaamagma magmasaturated saturatedininsulfide sulfideshould shouldcontain containgreater greaterthan than400 400ppm ppmsulfur sulfur(Boudreau (Boudreauand and McCallum, McCallum, 1992). 1992).Regardless Regardlessofofhow howsulfide sulfidesaturation saturationisistriggered, triggered,ororthe theway wayininwhich whichsulfide sulfide melt melt arrives arrives at atthe themagma magmachamber chamberfloor, floor,ititisislikely likelythat thatthe thefirst firstsignificant significantsulfide-saturated sulfide-saturated melt melt has has the the greatest greatestchance chanceof ofencountering encounteringthe themost mostPGE-enriched PGE-enriched silicate silicate magma. magma. Thus, Thus, exploration exploration for foraaPGEPGEenriched enrichedhorizon horizonshould shouldattempt attempttotoseek seekout outthe thestratigraphically stratigraphicallylowest lowestgabbroic gabbroiccumulates cumulatesthat thatcontain contain 400 ppm ppm SSor ormore. more. The The Cu/Pd Cfld ratio ratioindicates indicatesthe theeffectiveness effectiveness of of the thesulfide-saturated suicide-saturated melt melt inin 400 scavenging of magnitude scavengingchalcophile chalcophilemetals metalsfrom fromthe thesilicate silicatemagma. magma. Because BecausePd Pdisisseveral severalorders. ordersof magnitude more more compatible Cu,an anefficiently efficientlyscavenged scavengedsilicate silicatemelt meltshould shouldrecord recorda asignficant signficant compatiblewith with sulfide sulfidemelt meltthan thanCu, increase increasein inCu/Pd CuIPdafter afteraasulfide-segregation sulfide-segregationevent. event. These (DLS,Miller, Miller,1998). 1998). Thesegeochemical geochemicalcriteria criteriawere werefirst firstapplied appliedtotothe theLayered LayeredSeries SeriesatatDuluth Duluth(DLS, The TheDLS DLSisisaa3.53.5-toto4-km-thick, 4-km-thick,well-differentiated, well-differentiated,layered layeredintrusion intrusionemplaced emplaced into into the the basal basal section section of of comagmatic Keweenawan Keweenawan volcanics volcanics in in the the vicinity vicinity of of Duluth. Duluth. The The DLS DLS isis composed composed of of aa comagmatic unidirectionally troctolite(P1+01) (Pl+01) to gabbro gabbro unidirectionally differentiated differentiatedsuite suiteof of mafic maficcumulates cumulatesthat that grades grades up up from from troctolite and (Pl+Aug+Fem±O1±Ap and displays displays aa complementary complementary cryptic cryptic variation variation inin cumulus cumulus mineral mineral (Pl+Aug+Fe0±0l±Ap), compositions. 1-km-thickinterval interval compositions. The Thetransition transitionfrom fromtroctolitic troctolitictotogabbroic gabbroiccumulates cumulatesoccurs occurs in inan an1-km-thick called called the thecyclic cycliczone zonewherein whereinP1+01 Pl+01cumulates cumulatesgrade gradeupward upwardto toPl+Aug+Fe0,,+0l Pl+Aug+Fe-+01 cumlates, cumlates, and and regress regress abruptly abruptly back back to to P1+01 Pl+01 cumulates. cumulates. The Thecyclic cyclic zone zone isismade made up upof ofasasmany manyasassix sixsuch suchmacrocycles, macrocycles, 38 �which implies that despite despite being being well-differentiated, well-differentiated, the DLS magma system was open open to to recharge rechargeand and venting (Miller and Ripley, 1996). (Miller and Ripley, 1996). Sulfur concentrations indicate that that the DLS was initially sulfide undersaturated undersaturated and and did did not reach Cu/Pd ratios begin to show sulfide saturation until the onset begin show irregular irregular onset of of cyclic cyclic zone zonecrystallization. crystallization. CuRd upsection from from the the base base of of the the cyclic cyclic zone. zone. The though significant increases upsection The irregular irregular increase in Cu/Pd CuIPd ratios probably reflects the open nature of the DLS system. Interestingly, Interestingly,the theanomolous anomolous concentrations concentrations of sulfur sulfur and PGEs occur occur at macrocycle macrocycleboundaries, which I interpret interpret to to indicate indicate venting venting and/or and/or recharge recharge events. These observations suggest that a PGE-enriched sulfide reef may exist near the base of cyclic These observations suggest that a PGE-enriched reef may zone, and may correspond correspond to to aa horizon horizon indicative indicativeof of open-system open-system perturbations perturbations to to the the DLS DLSmagma. magma. the stratiform PGE PCE potential potential of of the Sonju Lake Geochemical studies were recently initiated to study the intrusion (SLI) near Finland, Minnesota. The The SLI SLI isis aa 1-km 1-km thick, sheet-like sheet-like intrusion that was emplaced beneath beneath a granophyre granophyre body. body. It is is aa completely completely differentiated differentiated intrusion intrusion that displays a very very regular, regular, unidirectional cumulus paragenesis: Ol—>Pl+Ol—>Pl÷Aug+Ol—>Pl+Aug+Fe—>Pl+Aug+Fe+Ol+ unidirectional paragenesis: 01->P1+01->Pl+Aug+01->Pl+Aug+Fe_->Pl+Ang+Fe_+Ol+ Ap. This Thisphase phaseprogression progressionand andaasmooth smoothcryptic crypticvariation variationin inmineral mineral composition composition indicate indicate that that the the SLI SLI crystallized as an almost The SLI is the intrusion most most similar to the crystallized almost closed closed system. system. The the Keweenawan Keweenawan intrusion the Skaergaard. Geochemical analyses of sulfur and PGEs have not yet been completed for the SLI. Skaergaard. Geochemical analyses of sulfur and PGEs have not yet been completed for SLI. Previous analyses included Cu which provides indirect evidence for for the the abundance abundance of of sulfide in in the SLI cumulates. The TheCu Cuconcentration concentrationshows shows aa dramatic dramatic 5-fold Sfold increase increase (from cl0Oppm e100ppm to >500 >500 ppm) ppm) at at aa level equal to 2/3 2.13 of of its itsthickness. thickness. This change is level above above the base base of of the theintrusion intrusion approximately approximately equal approximately midway midway through cumulate interval; interval; notably, notably, it is at approximately through the Pl+Aug+Fe0, Pl+Aug+Fe cumulate at the theequivalent equivalent stratigraphic level, and within the same cumulate type as the Platinova reef of the Skaergaard stratigraphic the same cumulate as the Platinova reef of the SkaergaardIntrusion Intrusion ILSGmeeting. meeting. (Andersen et al., 1998). 1998). I anticipate anticipate reporting reporting geochemical analyses for the SLI SLI at at the theILSG horizon in They will provide more direct evidence of the potential potential for aa PGE-enriched PGE-enriched sulfide-bearing horizon the upper part of SLI. may exist in the In conclusion, these studies studies suggest suggest that that significant significant PGE mineralization mineralization may the medial medial orupper parts of the DLS and SLI intrusions, as well as in other tholeiitic layered intrusions of the the orupper parts of DLS and SLI intrusions, as well as in other tholeiitic layered intrusions of Midcontinent Rift. Moreover, demonstrate that that geochemical geochemical criteria criteria can can be be used (1) to Moreover, these studies demonstrate to evaluate the overall potential for stratiform stratiform PGE mineralization in tholeiitic mafic intrusions, and (2) to Because potential PGEassist in assist in identification identification of of favorable favorableintervals intervalswithin within individual individual intrusions. intrusions. Because PGEmineralized horizons horizons are likely likely to be meter-scale and contain contain only only a few modal percent meter-scale in thickness, thickness, and sulfide, core drilling drilling and and systematic systematicgeochemical geochemical sampling sampling are are necessary necessary to to confirm confirmtheir their existence. existence. References :.,!, J.C.ø., Rasmussen, J.G., 1998, The Triple Group and the Platinova gold and palladium Andersen, J.C.0.. Rasmussen, H., H., Neilsen, Neilsen, T.F.D., T.F.D., Rønsbo, R~nsbo.J.G., reefs in relations: ECONOMIC ECONOMIC GEOLOGY, 488-509. reefs in the the Skaergaard SkaergaardIntusion—stratigraphic Intusion-stratigraphicand andpetrographic petrographic relations: GEOLOGY, v.93, v.93, p. 488—509. DX., Bernstein, PB., 1997, J.G., Bird, D.K., Bernstein, S. and and Kelemen, Kelemen, P.B., 1997, Gold Goldand andplatinum-group platinum-groupelement element mineralization mineralization in the Aranson, J.G., Kruuse ECONOMIC Kmuse Fjord FjordGabbro Gabbrocomplex. complex.East EastGreenland: Greenland: ECONOMICGEOLOGY, 490-501. GEOLOGY,v.92, v.92, p. 490—501. Bird, D.K., Bird, D.K., Brooks, C.K., C.K., Gannicott, Gannicott, R.A., R.A., Turner, P.A., P.A., 1991, 1991, A A gold-bearing gold-bearing horizon horizon in the the Skaergaard Skaergaard Intrusion, Intrusion, East East Greenland: GEOLOGY, v. 092. ECONOMIC GEOLOGY, v. 86, 86,p.p.1083—1 1083-1092. Greenland:ECONOMIC Brandriss. ME., M.E., Nevle, Nevle, R.J., Kelerotn, P.R., P.B., 1995, 1995, Bird, Bird, D.K., D.K., Aranson, J.G., IC., Brandriss, It)., Radford, G., C., Bernstein, S., Gannicott, R.A.. R.A., and Kelemen, A gold-bearing gold-bearing horizon East Greenland: ECONOMIC ECONOMICGEOLOGY, 90. p. 1288—1300. 1288-1300. A horizonininthe theKap KapEdvard EdvardHoIm HolmComplex, Complex, East Greenland: GEOLOGY,v.v.90, by magmatic fluids in layered intrusions: Boudreau, A.E. A.E. and McCallum, McCallum, 1.8., IS., 1992, 1992, Concentration of platinum-group elements by intrusions: ECONOMIC GEOLOGY, v. 87, ECONOMICGEOLOGY, 87.p.p.1830—1848. 1830-1848. J.D., Jr., 1998, 1998,Potential Potential for for stratiform stratiform POE PGE deposits deposits in sulfide-undersaturated, sulfide-undersaturated, tholeiitic layered intrusions of the Duluth Miller, J.D.. Complex. Complex, Minnesota, Minnesota, USA. USA. 8th 8th International International Platinum Platinum Symposium Symposium Abstracts, Abstracts, Rustenburg, Rustenburg, South South Africa, Africa, GSSA GSSA and and SAIMM Symposium Symposium Series Series 518. S18,p.263—266. p. 263-266. J.D.. Jr.. Jr., and Ripley, Ripley, E.M., E.M., 1996, 1996,Layered Layeredintrusions intrusions of of the the Duluth Duluth Complex, Complex, Minnesota, Minnesota, USA, USA, in in Cawthorne, R .G.,ed., Miller, J.D., R.G., Layered Layered Intrusions: Intrusions:Amsterdam, Amsterdam,Elsevier ElsevierSci., Sci..p.p.257—301. 257-301. T.F.D. and Brooks, East Greenland: Greenland: Factors Factors important important to tothe themineralization mineralization Neilsen, T.F.D. Brooks, C.K., C.K., 1995, 1995,Precious Preciousmetals metals in in magmas magmas of of East in ECONOMIC GEOLOGY, v. 90, ECONOMICGEOLOGY, 90,p.p.1911—1917. 1911-1917. in the theSkaergaard SkaergaardIntrusion: Intrusion: 39 �NEW GEOLOGIC MAP OF THE CENTRAL DULUTH COMPLEX MILLER, James D., D., Jr., Jr., and and CHANDLER, CHANDLER, Val. Val. W., Minnesota Minnesota Geological Geological Survey, Survey, University of of Minnesota, 2642 University Ave., Ave., St. Paul, MN MN 55114 orchand004@tc.umn.edu) 551 14(milleO66 (mille066 or chand004@tc.umn.edu) The Minnesota The Minnesota Geological Geological Survey Survey is is preparing preparing aa new new interpretation interpretation of of the the geology geology of of the the central central part pan of of the Duluth Complex, 00,000-scale man mapthis thissummer. summer. The map 1: 100.000-scale mao will cover cover Comnlex. which which will be published nublished as a 1:1 and lat. rectangular area and 9101510011 aa rectangular areaof ofabout about1,100 1,100square squaremiles milesbounded boundedbybylong. long.92°07'30" 92007'30 and 91°15'00 andlat. 47°37'30" and Both the the southeastern southeastern comer corner of of the the map map area, area, which which is is anchored anchored to to the the Lake Lake 47'37'30 and 47°15'OO". 47°15'00" Both Superior shoreline contact of Superior shoreline near near Silver Silver Bay, Bay, and and the the northwestern northwestern corner, comer, which which covers the the basal basal contact of the the Duluth Complex, Duluth Complex, have have adequate adequatebedrock bedrock exposure exposure that that has has been been mapped mapped at at the the scale scale of of 1:24,000 1:24,000 (Miller, (Miller, Miller and others, 1993; 1988; Miller 1993; Severson and Hauck, 1990; Severson and Miller, 1999). However, However, the the intervening area, area, roughly roughly 90% 90% of of the the map map area, area, contains contains little little or orno nobedrock bedrockexposure. exposure. Geologic Geologic intervening evaluation of of aeromagnetic aeromagneticand andgravity gravitydata. data. Geologic interpretations in in this area largely depend on evaluation control for the the geophysical geophysical data data is is limited limited to to widely widely and and unevenly unevenly dispersed dispersed drill cores as as well well as as scattered scattered outcrop (Severson, 1971). areas of outcrop (Severson, 1995; 1995; Chandler Chandler and others, others, 1991; 1991;Bonnichsen, 1971). The bedrock geology geology of the the map area area is is dominated by intrusive intrusive rocks that were emplaced emplaced into into the the basaltic North North Shore Shore Volcanic Volcanic Group Group (NSVG) (NSVG) during during the the main main lower and medial portionS portions of the largely basaltic stages of the Midcontinent Rift magmatism (Paces and and Miller, Miller, 1993). 1993). The intrusive rocks can be grossly subdivided into those belonging to the more plutonic Duluth Complex and those more subdivided into those belonging to the more plutonic Duluth Complex and those composing composing the the more intrusions of the Beaver Bay Complex. The complexes hypabyssal intrusions The boundary boundary between between two intrusive complexes corresponds to a semi-continuous semi-continuous septa septa of strongly hornfelsed homfelsed volcanic rocks, locally containing minor corresponds the middle middle of of the the map maparea area(Fig. (Fig. 1). 1). Large-scale intrusions of of intrusions, that trends northeasterly through the differentiated mafic cumulates, cumulates, gabbroic gabbroic anorthosites, &orthosites. gabbros, gabbros, and &d granophyres pnophyres compose the Duluth Complex northwest of the volcanic septa. Southeast Southeast of of the the volcanic volcanic septa, septa, smaller scale, sheet-like bodies and dikes dikes of mafic mafic cumulate cumulate rocks, rocks, gabbro, gabbro,diabase. diabase, diorite dionte and granophyre granophyre constitute constitute multiple multiple intrusions intrusions of the Beaver Beaver Bay Bay Complex Complex that that were were emplaced emplaced into into higher higher levels levels of the the volcanic volcanic edifice. edifice. A number of intrusive components can be be distinguished distinguished within within the theDuluth DuluthComplex. Complex. The oldest is a structurally structurally complex complex assemblage assemblageof of mostly mostly leucogabbroic leucogabbroic to to anorthositic anorthositic rocks, small bodies of olivine olivine oxide hornfels (collectively (collectivelytermed termedAGV AGVin inFigure Figure IA). 1A). This oxide gabbro, and scattered inclusions of volcanic homfels assemblage assemblage corresponds correspondsto to aa very very heterogeneous heterogeneous aeromagnetic aeromagneticsignature signature of variable variable amplitude amplitude in the to aa more more subdued subdued signature signaturetotothe theeast east(upsection). (upsection). The The western part of the complex but gives rise to consistently anorthositic anorthositic compositions. compositions. Irregular masses of change may indicate a transition to more consistently granophyre granophyre occur occur within the the eastern eastern part of the the AGV, AGV, but contact contact relationships relationships are not exposed in the study area. Aeromagnetic Aeromagneticpatterns patternssuggest suggestthat thatthe thesubcircular subcircularto tolensoidal lensoidalgranophyre granophyrebodies bodieswere were emplaced emplaced into into the the AGV, AGV, but but exposures exposures outside outside the map map area (Boerboom (Boerboom and Miller, 1994) 1994) indicate indicate that large granophyre granophyrebodies bodies can can be be older olderthan than the the anorthositic anorthositic rocks. More than half half of of the the Duluth Duluth Complex Complex in in the the map map area area is composed of six discrete mafic layered layered intrusions intrusions which were were emplaced emplaced beneath beneath and and within the AGV and, in one case, beneath a body of granophyre. granophyre. The Thestratiform stratiforminternal internalstructure structureofofthese theselayered layeredintrusions intrusionsgives givesrise riseto toaacrudely crudelybanded banded aeromagnetic aeromagnetic pattern. pattern. Truncations Truncationsofofthe thepatterns patternsimply implyaageneral generalsequence sequenceof ofemplacement emplacementand andsuggest suggest that successive successiveintrusions intrusions overplated overplated previous intrusions. intrusions. Although Althoughthe theigneous igneousstratigraphy stratigraphyof ofeach each intrusion is generally generally poorly known, known, some some notable differences differences are evident. Apparently, Apparently, the theoldest oldestlayered layered mafic intrusion intrusion is is the the Partridge Partridge River River intrusion intrusion (PRI), which forms the basal contact in the northwestern by frequent frequent PRI suggests suggests that it formed by part of the map area. The Thepreponderance preponderanceof of troctolite troctolitein in the the FRI truncated by by the impulses of magma and little internal differentiation. The The northeast end of the PRI is truncated South Kawishiwi South Kawishiwi intrusion intrusion (SKI). (SKI). Where Whereititisismore morecompletely completelyexposed exposedin inthe theGabbro GabbmLake Lakequadrangle quadrangle dominatedby bytroctolite. troctolite. At its southern end, end, the the to the north (Green and others, 1966), 1966). the SKI is also dominated PRI is overplated overplated and and ultimately cut cut out out by another another intrusive intrusive body that is almost entirely unexposed except for a few drill except drill holes holes along along its its basal basal contact contact and some some troctolite emplaced into the AGV hanging wall of the PRI. This Thisintrusion, intrusion,which whichwe wetentatively tentativelycall callthe theWest-central West-centralmargin marginintrusion, intrusion,has hasaa subdued subdued aeromagnetic aeromagnetic signature signature indicative indicative of troctolitic troctolitic cumulates. cumulates. The Thesubdued subduedpattern pattern passes passesupsection upsection into a busy, high-amplitude high-amplitude signature signature that that shows shows some some banding and thus may indicate the presence of roof zone. The upper gabbroic cumulates beneath an AGV roof The Greenwood Lake intrusion (GLI) is a somewhat isolated somewhat isolated intrusion intrusion that that truncates truncates the the SKI SKI but otherwise otherwise intrudes AGV and granophyre rocks. troctolite The GLI is unique in in that that itit contains contains aa complete complete differentiation differentiation sequence sequence that grades from lower troctolite 40 �cumulates cumulatesto to upper upper oxide oxide gabbro gabbro cumulates. The Thenorthern northern extent extent of of the the GLI GLI is is truncated by the southern margin margin of of the the troctolitic troctolitic Bald BaldEagle Eagleintrusion, intrusion,apparently apparentlythe the youngest youngest major major mafic mafic layered layered intrusion intrusion in in the the map map area. area. The TheOsier OsierLake Lakeintrusion intrusionisisaasmall, small,plug-like plug-likebody body of of troctolite troctolite cored by gabbro gabbro cumulates that that is is known known from from two two drill drill core core and a bull's-eye aeromagnetic signature. It It was was emplaced entirely entirely into anorthositic anorthositicrocks rocks of of the the AGV, AGV, and andthus, thus,its itsage agerelative relative to to other other layered layered intrusions intrusions is is unknown. unknown. Intrusions Intrusionsof of the the Beaver BeaverBay Bay Complex Complexoccur occuras asseveral severalsuites suites of of east-dipping, east-dipping, half-saucer-shaped half-saucer-shaped sheets, anomaly patterns. patterns. The largest and sheets, which which produce produce very very distinctive, concentric concentric aeromagnetic anomaly earliest to be be aa nested nested set set of of earliestintrusive intrusivesuite suiteis is the the Cloquet Cloquet Lake Lake layered layered series (CLLS), which appears to sheet-like sheet-like intrusions. intrusions.ItItisisdifficult difficulttotoaccurately accuratelydetermine determinethe thecompositional compositionalvariability variability of of the the CLLS CLLS because dozen or so drill drill core. core. In In general, general, the the lower lower becauseitit is is completely completely unexposed unexposed and and penetrated penetrated by only a dozenor part part of of the the series seriesappears appearsto tobe becomposed composedof ofatatleast leasttwo twodifferentiated differentiatedsequences sequencesof of troctolitic troctolitic to to gabbroic gabbroic cumulates. cumulates.The Theupper upperpart partofofthe theseries seriesappears appearstotocontain containmore moreevolved evolvedintrusive intrusiverocks, rocks, including including gabbro, ferrodiorite,monzodiorite, monzodiorite,and andgranophyre, granophyre,as aswell wellas gabbro, ferrodiorite, asan an unknown unknown amount amountof of volcanic volcanic hornfels. hornfels. A A complex complexaeromagnetic aeromagneticpattern pattern emanating emanatingfrom fromthe thesouthern southernmargin margin of of the the CLLS CLLS may may be be caused caused by by numerous numeroussatellite satellitedikes dikesand and sheets sheetsemplaced emplaced into into volcanic rocks. The Theeastern easternside side of of the the CLLS CLLS is is cut cut by another anothersheet-like sheet-likebody—the body-the Sonju Sonju Lake Lake intrusion intrusion (SLI). This Thisstrongly stronglydifferentiated differentiated mafic mafii layered layered intrusion in the theFinland Finland quadrangle quadrangle(Miller (Millerand and others, others, intrusion isiswell wellexposed exposedjust just to tothe theeast eastof ofthe themap maparea areain 1993) of the the Finland Finland granite. granite. Good exposure 1993) and is is capped capped by ferromonzonitic to granophyric rocks of exposure in the the southern southernDoyle DoyleLake Lakeand andSilver SilverBay Bayquadrangles quadrangles(Miller, (Miller,1988; 1988;Miller Millerand and others. others, 1993) 1993)shows showsthat that the of the the Lax Lax Lake Lake gabbro. gabbro. Both the Finland Finlandgranite granitecuts cutsan an early early suite suiteof of gabbroic gabbroic to ferromonzonitic rocks of the the Finland Finlandgranite graniteand andthe theLax LaxLake Lakegabbro gabbromay mayoriginally originallyhave havebeen been part part of of the the CLLS CLLS but but were were disassociated are the disassociatedfrom fromitit by by the the intrusion intrusion of of the the SLI. SLI. The Theyoungest youngestintrusions intrusionsin in the the map map area area are anorthosite-inclusion-bearing is anorthosite-inclusion-bearing dikes dikes and and sills sills of the Beaver River diabase. This This intrusive intrusive swarm, swarm, which which is well exposed exposed in in the the southeastern southeastern corner comer of of the the map map area, area, is is bounded on the west by a prominent dike dike that feeds feeds into into southeast-dipping southeast-dipping sheets. sheets. The Theupper upperparts partsof ofthese thesesheets sheetscommonly commonly contain contain ferrogabbroic ferrogabbroic cumulate cumulatebodies, bodies, collectively collectivelytermed termedthe theSilver SilverBay Bay intrusions. intrusions. The 00,000-scale map of of the central Duluth Duluth Complex Complex will will represent represent aa significant significant improvement improvement on on The 1:1 1:100,000-scale previous previous regional regional geologic geologic maps maps of of the the complex. complex. Because Becausethis this map map will will be be digitally digitally compiled, compiled, we intend to to revise revise itit periodically periodically as as new new data data become become available. An Animportant importantcontribution contribution of this this new geologic map map isis that that itit will willidentify identifymany manypreviously previouslyunrecognized unrecognizedintrusive intrusivebodies bodies that that should should provide provide new new exploration explorationtargets targetsfor forstratiform stratiformPGE PGEdeposits. deposits. References References Bonnichsen, Bonnichsen, 8., B.,1971, 1971,Outcrop Outcropmap mapofofsouthern southernpart partofofDuluth DuluthComplex Complexand andassociated associatedKeweenawan Keweenawan rocks, rocks,St. St. Louis 1, scale Louis and and Lake LakeCounties, Counties,Minnesota: Minnesota:Minn. Minn. Geol. Geol. Surv. Surv. Misc. Misc. Map Map M-l M-11, scale 1:24,000. 1:24,000. Boerboom, Boerboom, T.J., T.J., and and Miller, Miller,J.D., J.D., Jr., Jr., 1994, 1994,Geologic Geologicmap map of of the the Wilson Lake Lake quadrangle and parts of the Silver Silver Island Lake and Toohey Lake quadrangles. quadrangles, Lake and and Cook Cook Counties, Counties,Minnesota: Minnesota: Minn. Minn. Geol. Geol. SUN. Surv. Misc. Misc. M-81, scale scale 1:24,000. 1:24,000. Map M-81, Map Chandler, V.W.,Miller, Miller,J.D., J.D., Jr., Jr.,and and Venzke, Venzke,E. E. A., A,,1991, 1991,Central Central Duluith Dululth Complex drilling drilling project; Minn. Geol. Chandler,V.W., S w . OFR 91-4,2 sheets,accompanying accompanyingtext. text. Surv. 91-4,2 sheets, Green, County, Minnesota: Minn. W.C., and and Weiblen, Weiblen,P.W., P.W., 1966, 1966,Gabbro GabbroLake Lake quadrangle, quadrangle. Lake County, Green, J.C., J.C., Phinney, Phinney,W.C., Surv. Misc. Misc. Map Map M-2, M-2, scale scale 1:24,000. 1:24,000. Geol. Surv. Miller, County, quadrangles. Lake County, Miller, J.D., J.D., Jr., Jr., 1988, 1988,Geologic Geologicmap mapof of the the Silver SilverBay Bay and and Split Split Rock Rock Point NE quadrangles, Minnesota: Minn. Minn. Geol. Geol. Surv. SUN.Misc. Misc. Map Map M-65, M-65, scale scale 1:24,000. 1:24,000. Minnesota: Miller, J.D., J.D., Jr., Jr., Green, Green,J.C., J.C., Chandler, Chandler,V.W., V.W., and and Boerboom, Boerboom, T.J., T.J., 1993, 1993,Geologic Geologic map of the Finland and Doyle Miller, Lake Lake quadrangles, quadrangles, Lake Lake County, County,Minnesota: Minnesota: Minn. Minn. Geol. Surv. Misc. Map M-72, scale 1:24,000. Paces, intrusions, Paces, JR., J.B., and andMiller, Miller,J.D., J.D.,Jr., Jr.,1993, 1993,Precise PreciseU-Pb U-Pbages agesof of Duluth Duluth Complex and related mafic intrusions, northeastern, northeastern, Minnesota: Minnesota: new new insights insightsfor for physical, physical, petrogenetic, paleomagnetic and tectono-magmatic 13997-14013. processes rifting: J. J. Geophys. Geophys.Res., Res.,v.v.98, p. 13 processes associated associated with 1.1 1.1 Ga Midcontinent rifling: 98, p. 997-14 013. Severson, Severson, M.J., 1995, 1995,Geology Geology of of the the southern southern portion portion of of the Duluth Complex: Univ. of Minn. Natural Resources Res. Inst., Inst.,Tech. Tech.Rept. Rept.NRRITI'R-95126, NRRI/TR-95/26, 185 185 p. Res. Severson, Severson, M.J., MJ., and and Hauck, Hauck, S.A., S.A., 1990, 1990,Geology, Geology, geochemistry, geochemistry, and stratigraphy of a portion of the Partridge River NRRIIGMIN-TR-89-l 1,236 p. intrusion: Univ. of of Minn. Minn. Natural Resources Resources Res. Inst., Tech. Rept. NRRIIGMIN-TR-89-11.236 Severson, quadrangle, Minnesota: Minn. Geol. M.J.. and and Miller, Miller, J.D., J.D., Jr., Jr., 1999, 1999,Bedrock Bedrock geologic geologic map of the Allen quadrangle, Severson, M.J., Surv. Misc. Map M-91, M-91, scale scale 1:24,000. 1:24,000. 41 �A. —fSBl Footwall Beaver Bay complex Miscellaneous Volcanic Shale Iron-formation Grariute Duluth Complex NSVG —-" — "BRD Mafic Granophyre Anohositic Rocks ftGranophyre Rocks Gabbroic Rocks Gabbroic Cumulates Gabbro, Ferrodiotite, Monzodiorite Fault Volcanic Homlels LilTroctolite Cumulates Diabase, 01 Gabbro, Troctolite • Oxide Ultramatic Metavolcanic Rocks 10 Miles =20 Kilometers FIGURE 1. A) Preliminary generalized geologic map of the central Duluth Complex. Specific intrusive units are: AGV-Anorthositic-gabbroicvolcanic assemblage (rock types distinguished in the northwest area), PRI-Partidge River intrusion, WCMI-West-central margin intrusion, SKI-South Kawishiwi intrusion,OLl-Oreenwood Lake intrusion. BEt-Bald Eagle intrusion, OLI-Osier Lake intrusion, CLLS-Cloquet Lake layered series. SLISonju Lake intrusion, FO-Finland granite, LLG-Lax Lake gabbro, BRD-Beaver River diabase, SBI-Silver Bay intrusions. Crosses mark 7.5' quadrangle corners. B) First-vertical-derivative, reduced-to-pole image of data, which forms basis for the geologic interpretation shown in A. aeromaic �SEDIMENTOLOGY OF TWO DEEP MIDGONTINENT SEDIMENTOLOGY DEEP WELLS IN THE KEEWANAWAN MIDCONTINENT RIFT SYSTEM NEAR MUNISING, UPPER RIFT UPPERPENINSULA, PENINSULA,MICHIGAN MICHIGAN OJAKANGAS. Richard Richard W., W., Department Department of of Geology, OJAKANGAS, Geology, University of Minnesota-Duluth, Duluth, MN 55812, rojakang@d.umn.edu Minnesota-Duluth, MN 55812, rojakang@d.umn.edu Amoco Production Production Company Companydrilled drilled the the St. St. Amour Amoco Amour stratigraphic stratigraphic test well well in 1987. six miles south-southeast of Munising, Ml. The well bottomed well bottomed at at 1987, miles south-southeast Munising, MI. Eight mites to the southeast 7,241 ft. ft. Eight miles to southeast of the the St. St. Amour Amour welt, well, at at Mickey Hickey 7,241 Creek, Cliffs Cliffs Mining Mining Services Services Company Companyhad haddrilled drilledaa 5,345 5.345 ftft deep Creek, deep well well in in 1969. 1969. These These wells wells are located located on on the the southwest southwest flank flank of of the theMidcontinent Midcontinent Rift System where the the rift Rift System (MRS) (MRS) where rift starts starts bending bending towards towards the the south. south. Except for for the the Pleistocene (110ftft thick thick in in the the St. Except Pleistocene (110 St. Amour Amour and and 88 ft thick thick in in the Mickey Creek), both both wells wells were the Hickey Creek), were cored from from top to to bottom. bottom. The The youngest youngest bedrock is is the the Ordovician Au Train Train Formation, Formation,about about280 280ftft thick thick in in the St. bedrock Ordovician Au St. Amour well well and and 235 Amour 235 ft thick thick in inthe theMickey Hickey Creek Creek well. well. The The Au Au Train Train overties the the Upper (?) Munising Munising Formation, Formation, a quartz quartz arenite arenite unit unit overlies Upper Cambrian Cambrian (?) that is 135 ft thick in the St. Amour and 310 ft thick in the Hickey Creek. that 135 thick in the St. Amour and 310 ft thick in the Hickey Creek. The Keweenawan rocks in in the St. Keweenawan rocks St. Amour Amour well well from from the thebase basedownward downward include QIF/L= =2200 ft of feldspatholithic sandstone (N=8: QlF/L= 72.2/20.7/ 72.2120.71 include -2200 feldspatholithic sandstone (N=8: interpreted as as Jacobsville Jacobsville Fm.; Fm.; =3000 -3000 ft of of lithofeldspathic lithofeldspathic 7.2) interpreted 725 ft sandstone (N=7: (N=7: Q/F/L=58.1/19.3/22.6) interpreted as Freda Freda Fm.; Fm.; 725 ft sandstone QIF/L=58.1/19.3/22.6) interpreted of basalt flows 400 ftft of basalt flows of quartz .4/5.0): 400 of quartz sandstone sandstone(N=4: (N=4:Q/F/L=93.6/1 QlFIL=93.611.4/5.0); with interflow with interflow black black shales shales and and red red to tobrown browncoarse coarseclastics elasticsincluding including conglomerateand and lithic lithic sandstone sandstone (N=2: (N=2: QlFlL=65.010.5134.5); QIFIL65.0I0.5/34.5); and and 300 300 ftft conglomerate of of dacitic dacitic (?) (?) ignimbritic flows. flows. - The Keweenawan rocks in in the The Keweenawan rocks the Hickey Hickey Creek Creek welt well from from the the base basedownward downward include include =1720 -1720 ft ft of of dominantly dominantly feldspatholithic feldspatholithic sandstone sandstone (N=6: (N=6: Q/F/L=78.2/16.7/5.1) interpreted interpreted as as Jacobsville Q/F/L=78.2116.715.1) Jacobsville Fm. Fm. and and —2845 52845 ft ft of dominantly lithofefdspathic sandstone (N=9: QIF/L= 54.8/19.0/26.3) dominantly lithofeldspathic sandstone (N=9: Q/FlL= 54.8119.0126.3) interpreted as Freda main two two types types of of sand-sized sand-sized rock rock interpreted as Freda Fm. Fm. The main In the fragments in the two fragments in two wells wells are aremetamorphic metamorphic and and fetsic felsic volcanic. volcanic. In the St. St. Amour well, metamorphic rock fragments (schist and greenstone) are on Amour well, metamorphic rock fragments (schist and greenstone) are on average twice as abundant average twice abundant as as felsic felsic volcanic volcanic fragments, fragments, whereas whereas in in the the Mickey Creek Creek well, well, felsic fetsic volcanics volcanics are are three three times times as Hickey as abundant abundant as as metamorphic rock fragments. metamorphic rock fragments. Porosity Porosity decreases decreases downward downward in both both wells, wells, with with virtually virtually no no porosity porosity present present below below 2750 2750 ft. ft. 43 �I I The in the the two The mineralogy mineralogy in two wells wells is is quite quite similar similar for for the the upper upper 5300 5300 ftftand and the formations, not unexpectedly, correlate well. They also correlate well the formations, not unexpectedly, correlate well. They also correlate well with with Keweenawan Keweenawan outcrops outcrops in the the Lake LakeSuperior Superior region region(Ojakangas, (Ojakangas, 1986; 1986; However, the lower portion of the St. Amour does not Adamson, 1997). However, the lower portion of the St. Amour does not Adamson, 1997). correlate correlate well well with with the theexposed exposedBayfield Bayfield and andOronto OrontoGroups. Groups. Quartz Quartz sandstones occur low low in the sandstones occur the well, well, in in direct direct contrast contrast to toexposed exposedsections sections where deep in in the rift where they they are are near near the the top. top. Quartzose Quartzose sediments sediments deep rift are arealso also present present in in the the Eischeid Eischeid ## 11 well well in in Iowa Iowa(Ludvigson (Ludvigson et et at, al, 1990). 1990).Clearly, Clearly, the the search search for for uniformity uniformity and andcorrelation correlationwhere wheredeposition deposition likely occurred occurred in in aaseries seriesofofsub-basins sub-basins(haif-grabens) (half-grabens) is is aa tenuous tenuous pursuit, pursuit, as asnoted noted earlier earlier by by Mauk Mauk(1991). (1991). Soreghan Soreghan and and Cohen Cohen (1993) (1993) interpreted interpreted relatively relatively quartzose quartzose sands sands (Q (Q to to 79%) 79%) on onhinged hingedmargins marginsofofmodern modernLake LakeTanganyika Tanganyika to to be be the theresult resultofofreworking reworkingininshallow shallowwater. water. This This may may be be aa partial partial analogue for these but eolian analogue for these quartz quartz sandstones, sandstones, but eolian activity activity in in the the vegetationless vegetationless Middle Middle Proterozoic Proterozoic terrestrial terrestrial environment environment is is also also likely. likely. Cliffs Cliffs Mining Mining Services Services Company Company kindly kindly purchased purchased the the thin thin sections. sections. REFERENCES REFERENCES Adamson, k.F, 1997, Adamson, K.F., 1997,Petrology, Petrology, stratigraphy, stratigraphy, and and sedimentation sedimentation of of the the Middle Middle Proterozoic Proterozoic Bayfield Bayfield Group. Group, Northwestern NorthwesternWisconsin: Wisconsin: Unpublished M.S. thesis. thesis, University of Minnesota, Unpublished M.S. University of Minnesota, Duluth, Duluth, 203 p. p. Ludvigson, Ludvigson, G.A., G.A., Mckay, McKay, H.M., P.M., and andAnderson, Anderson, R.R., R.R., 1990, 1990,Pekrology Petrology of of Keweenawan sedimentaryrocks rocksinin the the MG. drillhole: in in Keweenawan sedimentary M.G. Eischeid Eischeid ## 1 drillhole: Anderson, DeepPetroleum PetroleumTest, Test, Anderson, R.R., R.R., ed., ed.. The The Amoco Amoco M.G. M.G. Eischeid Eischeid ## 11Deep Carroll Carroll County, County, Iowa, Iowa, Iowa Iowa Department Department of of Natural NaturalResources Resources Special Special Report Report Series Series No.. No., 2, p. p. 77-112. 77-112. Mauk, J. J. L., L., 1991, 1991, Sub-basins Sub-basins in in the theProterozoic Proterozoic Midcontinent Midcontinent Rift: Rift: Mauk, Stratigraphic Stratigraphic evidence evidence from from Upper Upper Michigan Michigan (Abs.): (Abs.): Geological Geological Society Society of of America America Abstracts Abstracts with with Programs, Programs, San San Diego, Diego, CA, CA, p. p. A59. A59. Ojakangas, R.W., 1986, Reservoir characteristics of the keweenawan Ojakangas, R.W., 1986, Reservoir characteristics the Keweenawan MG. Jr., Supergroup, in Mudrey, M.G. Jr., ed., ed., Supergroup, Lake Superior Superior region: region: in Precambrian Precambrian Petroleum Petroleum Potential, Potential, Wisconsin Wisconsin and and Michigan. Michigan, Geoscience Wisconsin, V. V. 11, 11. p. p. 25-31. 25-31. Geoscience Wisconsin. Soreghan, M.J.. and Cohen, Soreghan, M.J., Cohen, A.S., A.S., 1993, 1993, The The effects effects of of basin basinasymmetry asymmetry on on in Examples from from Lake Lake Tanganyika. Tanganyika, Africa: Africa: in sand sand composition: composition: Examples Johnsson, Johnsson, M.J., M.J., and and Basu, Basu, A.. A., eds.. eds., Processes ProcessesControlling Controlling the the Geological Composition Composition of Clastic Clastic Sediments: Sediments: Geological Society Society of of America America Special Special Paper 284. 284, p. p. 285-301. 285-301. 1 44 �DESCRIPTIONS OF MARQUETTE EARLY DESCRIPTIONS OF THE THE NATURAL NATURAL FEATURES ON THE MARQUETTE IRON RANGE Doug Ottke, U.S. Geological Survey, 12201 Sunrise SunriseValley ValleyDr. Dr. Reston, Reston, Virginia Virginia 20192 -, -- -- r The peninsula of of Michigan Michigan is is integrally integrally linked linked to to The history history of the Marquette Iron Range in the upper peninsula the environment. The the mode mode of of production production on Thenatural naturalfeatures features of of the the Marquette Marquette Range defined the on the the Range, Range, and and conversely, conversely, as as human human systems systems became more adept in these modes of production they they became became the the most most important importantmodifiers modifiersof of the the natural natural systems. systems. Settlement natural Settlement on the the Marquette Marquette Iron Iron Range was closely related to two factors of natural environment: environment: the the iron iron ore ore formations formationsand and the the hardwood hardwood forest. The distribution of three iron ore ore formations--principally formations-principally the the Negaunee, Negaunee, but but also also the the Bijiki Biiiki and other other Iron-formations Iron-formations within the Michigamme --determined the the locations locations of of the sites sites of of extraction of iron ore Michigamme Formation Formation --determined ore in the the area. area. Stands Standsof of hardwood hardwood forest, forest, particularly particularly maple maple and yellow birch were the major factor determining determiningthe the location location for for processing pro&ssing operations operations that converted iron ore into pig pig iron. iron. The location of beehive kilns where the hardwood was converted into charcoal, the early forges, and and beehive kilns charcoal, the early forges, the of hardwood. hardwood. The iron ore formations the blast blast furnaces furnaces were reliant foremost on the availability of formations and and the the hardwood hardwood forest forest of of the the Range Range defined defined the physical subdivision of the land into tracts owned the mines, mines, forges, forges, owned by individuals. individuals. Because Becauseaareadily readilyavailable available workforce workforce was needed at the kilns, kilns, and and furnaces furnaces of of the the area, area, locations locations of of settlement settlement on the Range were within very close proximity proximity to to the the sites sites of of extraction and processing operations. Transportation, from the earliest trails to the plank road, trails to the plank road, strap straprailroad railroad and and the the Iron Iron Mountain Railroad completed in the 1857 1857 were were defined defined by by the the natural natural location location of of the the ore ore and and the processes processes involved with extracting it. In 1850's, with withadvances advancesinintransportation transportationassociated associatedwith with the the completion completion of of the the railroad railroad In the the mid mid 1850's, to to the the mining mining areas areasnear near Negaunee Negaunee and and lshpeming Ishpeming and the completion of the Sault Locks near Sault By 1868 that that Sault Saint SaintMarie, Marie, the the production production of of iron iron ore ore reached reached a level of 11,343 tons per year. By number 508,000 tons mined. The Thedepression depression of of 1873 I873 caused aa sharp sharp drop drop number had had reached reached aa level level of of 508,000 in in production. production. However, However,for forthe theyear yearbefore beforethe thedrop dropone onemillion million tons tonshad had been been withdrawn withdrawn from from 40 rose to to 40 pits pits carved carved into into the ore bodies. In In 1880 1880two two million million tons were mined and that number rose seven seven million million tons tonsmined mined during duringthe the year year of of 1890. 1890. The Thequarrying quarryingoperations operationsprogressed progressed deeper deeper into into the earth earth until until by by the the 1880's 1880's shaft shaftmining miningbecame became aa necessity, necessity, calling calling for for advancement advancement in in technological applications and forcing many of the less wealthy operations out of business. The technological applications wealthy operations out of business. The large large amounts amounts of of capital capital involved involved in in diamond drilling drilling exploration, and the operations underground underground forced forced industrial industrial consolidation consolidation of of the many small operations into a few large companies companiescommanding commandinglarge largeresources. resources. As Asmines mineswent wentunderground, underground,the the need need for for timber timber also also increased became aa necessity. necessity. Between .72 and .92 increased as as supports supports for for the underground workings became cubic cubicfeet feetof oftimber timberwas wasneeded neededper perton tonof ofore oreextracted. extracted. In In 1868 1868eleven elevenblast blast furnaces furnaceswere were in in operation operation on the Marquette Range. Twenty Twentyfive fivefurnaces furnaces total total were were built built ininMarquette MarquetteCounty. County.Numerous Numerous beehive beehive kilns kilns dotted the countryside. These These kilns pine, and and other softwoods softwoods kilns converted converted maple, maple, yellow yellow birch birch and, and, in in some instances, hemlock, pine, into iron produced produced in in furnaces furnaces varied varied from from 110 110 into charcoal. charcoal. The Thecharcoal charcoalconsumed consumedper per ton ton of of iron bushels to 140 bushels, with a bushel consisting of 20 pounds of charcoal. The Pioneer Furnace, bushels to 140 bushels, with a bushel consisting of 20 pounds of charcoal. The Pioneer Furnace, the theoriginal originalblast blastfurnace furnaceininthe thearea arealocated locatedin in Negaunee, Negaunee, used used the timber from 1,500 1,500 acres in the year year of of 1869 1869to to produce produce 9,500 9,500 tons tons of pig iron. One Oneacre acreof ofwood wood could could produce produce 14 14 tons of iron. iron. ItIt isis estimated the kilns of the the estimatedthat thatby by 1903 1903thirty thirty acres acresof of hardwood hardwood per day was needed to supply the Marquette MarquetteRange. Range.InInthe thefirst firsthalf halfcentury centuryofofiron ironproduction production330,000 330,000acres acreswere were cut. cut. In In order orderto to understand understand more more thoroughly thoroughly how natural and human systems have modified each other on pre-major European European settlement settlement natural environment must be on the the Marquette MarquetteRange, Range, the the pre-major 45 �I delineated. delineated. Beginning Beginninginin1838, 1838,the theMichigan MichiganGeological GeologicalSurvey Surveyand andthe the Linear LinearSurvey Surveyof ofthe the U.S. U.S.Land Land Office Officecreated createddescriptions descriptions of ofthe thenatural naturalenvironment environmentof ofthe theMarquette MarquetteRange. Range. These These descriptions descriptionsbetter betterenable enablethe theunderstanding understanding of ofthe thepre-major pre-majorsettlement settlementnatural naturalenvironment. environment. The Thedescriptions descriptions contained contained within withinthese these reports reports of of the location location of of the the original originaloutcrops outcropsof ofiron ironore ore and andthe thestands stands of of trees trees shows shows how how important importantthese these factors factors were were to to the the early early settlement settlement of ofthe the Marquette MarquetteRange. Range. The Thedescriptions descriptionsalso alsoallow allowus usto tosee see how how influential influentialthat thatsettlement settlementwas wasin in modi1'ing modifyingthe thenatural naturalsystems systemsofofthe theRange. Range. 46 �DEVELOPMENT OF VOLCANOGENIC VOLCANOGENIC MASSIVE MASSIVE SULFIDE SULFIDEDEPOSIT DEPOSITEXPLORATION EXPLORATION OF TARGETS IN NORTHERN MINNESOTA FROM GIS GIs SPATIAL SPATIAL ANALYSIS OF GEOLOGICAL, GEOCHEMICAL, GEOPHYSICALCRITERIA CRITERIA AND GEOPHYSICAL GEOLOGICAL, GEOCHEMICAL, AND DEANM. M. PETERSON PETERSONand andDR. DR. RONALD RONALDL. L. MORTON MORTON DEAN Economic Volcanology Research Research Lab, Lab, Geology Department, Department, University ofMinnesota of Minnesota --Duluth, Duluth, Economic Duluth, Minnesota, Minnesota, USA USA 55812 massive sulfide (VMS) deposits are are syngenetic syngenetic stratifm stratiformiron ironand andbase-metal base-metal(Cu-Zn-Pb) (Cu-Zn-Pb) Volcanogenic massive systems in in subaqueous subaqueousvolcanic volcanicenvironments. environments. At the accumulations that form out of large geothermal systems "bottom" of VMS-producing systems are subvolcanic intrusions, which which produce produce focused focusedheat heatsources sourcesthat that "bottom" provide the energy for circulating hydrothermal fluids and leaching reactions, reactions, and and may may add addbase-metals base-metals into the geothermal system. Above Above the the subvolcanic subvolcanicintrusions, intrusions, the strata have undergone extensive highmetal depletion, alkali alkalimodification, modification,and andextensive extensive temperature alteration, which can include metal silicification. silicification. Over the last twenty years, a VMS ore ore deposit deposit model has been developed from the work of many researchers. Important features of the model Important features of the model include include the the following: following: • • • • • • deposits are associated VMS deposits associated with with submarine submarine volcanic volcanic rocks, and typically are are spatially spatially associated associated with felsic volcanic rocks in greenstone terranes. with age age or or petrochemistry petrochemistrybut butdo dooccur occurin indistinct distinct VMS deposits occur with no obvious correlation with provinces, camps or clusters. Deposits often occur at one or more distinctive favorable stratigraphic stratigraphichorizons horizonswithin withinaacamp. camp. These Deposits represent quiescent horizons represent quiescentperiods periods in in volcanic volcanic activity, activity, tops tops of volcanic volcanic cycles, cycles, or a major volcanicor aa sediment interface. The Thedistal distal extent extentof of ore ore horizons horizons may be marked by a siliceous, ferruginous, or tuff. base metal bearing bearing sediment sediment and/or and/or felsic felsic tuff. Footwall subvolcanic subvolcanic intrusions intrusionsare are typically typically sill-like, sill-like, with with irregularly irregularly distributed distributed porphyritic and non-porphyritic phases. The intrusions may contain minor porphyry copper occurrences. The intrusions may contain minor Synvolcanic fault controls are recognized in some deposits, and may control the location of rhyolite some Synvolcanic controls deposits. Proximal facies volcanic rocks associated with with domes that occur in the footwall of some deposits. synvolcanic faults are generally generally the most favorable favorable horizons for ore deposition. alteration may include semi-conformable and cloud-like Footwall alteration include a pipe-like zone and/or andlor widespread semi-confmable alteration. alteration. The massive-sulfide nature of the ore ore typically makes them conductors conductors of electricity, and therefore can be detected by airborne and ground-based electro-magnetic (EM) surveys. airborne feature of the ore deposit deposits have been based on only one feature Many exploration programs for for VMS deposits specifically, the blind drilling of airborne EM EM conductors. conductors. Although this method of exploration model, specifically, has discovered many major major deposits deposits in the the past, strictly strictly EM-based VMS exploration has many shortcomings. The The drawbacks drawbacks include include any any or or all of the following: • • • • Poor geologic control of conductor location block Poor ranking of conductors in a survey block High cost of drilling tens tens to hundreds hundreds of barren or graphitic EM conductors prior to discovery 1% of drilled EM conductors conductors lead to mines) Poor rate of discovery discovery (less than 1% 47 �This study study formulates formulates a GIS-based GIs-based exploration exploration model model that that incorporates incorporates all all facets facets of of the the VMS VMS ore deposit deposit Thesemaps maps have have ultimately ultimately led led to to the generation of specific s p e c i f VMS icps model into a series of digital maps. These exploration targets in the study area of northern Minnesota. The km The study study integrates integrates a new 5880 5880 km geologic compilation map with with mapped mapped alteration alteration zones, zones, over over 5400 5400 ground ground and airbome airborne EM EM anomalies, anomalies, and approximately 21,000 copper and zinc assays. Intermediate Intermediate maps maps used to predict VMS potential include stratigraphy, stratigraphy, heat generation, generation, alteration, Cu-Zn Cu-Zn geochemistry, geochemistry, and and EM EM conductors. conductors. The methodology inFigure ~ i &1.1. e methodology used used to to create create the the 015-based GIs-basedmodel modelisispresented presentedin STEP STEP I1 Build luild Spatial Spatial Data Base Base STEP STEP22 Collect Collect spatial Spatial Data Data and and Input Input into into GIS CIS Extraction of 015 CIS Extraction of Features Relevant Relevant to the VMS Ore to the VMS Ore Deposit Deposit Model Model S S BEDROCK BEDROCK GEOLOGY GEOLOGY S MAPPED MAPPED ALTERATION ALTERATION ZONES ZONES -H———— ———--H— I. Extractqtz.cpidote 2. Extract chlorite 2.Extractchlonu t.1.Reclassii RecUmfy 2. 2 Extract . m - contacts 3. Qeale buffers 3.0cçEbufiei 3. 3 .CYeate O m e bbuffers ufim I.1.Classifymiervals aassi& intervals 2. Grid soil & lake aSs 2.Gndsoil&lateseds 3. Buffer rock & axe 3.Bufferrock&core Data Data Processing Processing Preliminary Preliminary Maps Maps of of Selected Selected GIS GIs Features Features S ROCK, CORE, SOIL SOIL AIRBORNE ROCK. CORE. AIRBORNEAND AND & & LAKE LAKE SEDIMENT SEDIMENT GROUND GROUND EM EM CONDUCTORS GEOCHEMISTRY CONDUCTORS tontacts ;contscts Volcanic-Sedin.t contacts Greanstone Subvókar.ac 5eq lntrusio,.s Qsarfl- Chlorite A -A- Cu Zn Cu Zn Cu C"aC"a m Zna Epidote I I. Extnct ground EM 1-ExtractcrowdEM 2. airborne EM 2. Classil5, Classify airbornem soils Soik Lake Lake Rocks Reeks Gromd t EM EM EM EM Assign Assign Weights Weights of ofEvidence Evidence hny,gIits(O.on . t.) F-wriflte(0m-lm) STEP STEP33 Integration Integration Modelling Modelling Map Map Overlay Overlay to Produce to Produce Interrnedtate Intermediate Factor Factor Maps Maps 1 STRATIGRAPHY STRATIGRAPHY HEAT HEAT Factor Factor Factor Factor 1 ALTERATION ALTERATION Factor Factor 1 GEOCHEMICAL GEOCHEMICAL Factor Factor 1 EM EM Factor Factor Overlay of Overlay of Intermediate Intermediate Factor Factor Maps Maps to to Produce Producethe the Final Predictive Final Predictive Map Map Figure Figure 1. 1. VMS NJFEWflAL MAP VMS NERAL MINERAL-POTENTIAL MAP L Flowchart Flowchart for for the the 3-step 3-step GIS GIs modelling modelling of the VMS potential of the Archean Vermilion District District and and its its western western extension, extension, northeastern, northeastern, Minnesota. Minnesota. The Thethree threesteps stepsin inthe thestudy study are: are: 1) 1)Detailed Detailedgeologic geologicmapping mappingand andcompilation compilationof ofall allavailable availablegeological, geological, geochemical, geochemical,and and geophysical geophysical data. data. Conversion Conversionof ofall alldata datainto intoprimary primaryGIS GIsdatasets; datasets; 2) 2) Extracting Extractingand and enhancing enhancing the the features featuresof of the the primary primary datasets datasets that are important important for predicting VMS and 3) 3) Integration Integration of of the preliminary prelimhry maps using GIS GIs modelling p~dicting VMS deposits; deposits;and techniques techniquesthat that predict predictmineral mineralpotential. potential. 48 �LOW-GRADE LOW-GRADEMETAMORPHISM METAMORPHISMAND AND HYDROTHERMAL HYDROTHERMAL ALTERATION ALTERATION OF OF THE THE UPPER KEWEENAWAN PORTAGE LAKE VOLCANICS, MICHIGAN UPPER KEWEENAWAN PORTAGE LAKE VOLCANICS, MICHIGAN PUSCHNER, PUSCHNER, Ulrich, Ulrich, SCHMIDT, SCHMIDT,Susanne SusanneTh., Th., Mineralogisch-Petrographisches Mineralogisch-PetrographischesInstitut, Institut, Base!, J.. Department Department of Geological Basel. Switzerland Switzerlandand and BORNHORST, BORNHORST. Theodore Theodore J., Engineering Sciences, University, ~ n ~ i n e e rand and in~ Sciences,Michigan Michigan Technological ~echnolo~ical university, Houghton, ~ o u ~ h t o Michigan n,-~ichi~an 49931 4993 1 The ThePortage PortageLake LakeVolcanics Volcanicsin inthe theKeweenaw KeweenawPeninsu!a Peninsula of Michigan Michigan consists consists of aa thick thick succession interfiow sedimentary sedimentary successionof of subaerial subaerialtho!eiitic tholeiiticbasalt basalt !ava lava flows with scattered interflow !ayers. layers. These Theserocks rockshave havebeen beensubjected subjectedtotolow-grade low-grademetamorphic metamorphicand andhydrothermal hydrothermal alteration. emplaced during during this alteration alteration alteration.The Theworld-class world-classnative nativecopper copperdeposits depositswere were emplaced event. In the Keweenaw Peninsula, and elsewhere, the Portage Lake Volcanics are not event. In the Keweenaw Peninsula, and elsewhere, the widely widely exposed exposed at at the the surface surface because because of overlying overlying unconsolidated glacial sediments. However, Peninsula during However, subsurface subsurfacedrill drill core core were were obtained obtained in the Keweenaw Peninsula during exploration explorationfor for native native copper. Much Muchdrill drillcore, core,some someover over 100 100years old, still exists in excellent and locations. locations. Mr. Gordon Peterson excellent condition condition and and with original dri!l drill core logs and of of Calumet Calumetowns ownsand and continues continuesto to maintain maintain much much of the the existing existing drill drill core core and and allowed allowed us us to to sample samnlethe the core core for for our our research. Stoiber Stoiberand and Davidson Davidson (1959a, (l959a. b), in part, part. used a drill core portage Lake Lake Volcanics. Volcanics. corecross-section cross-sectionto topostu!ate postulatemetamorphic metamorphic zonation zonation within within the the Portage Four Fourdrill drillcore corecross crosssections sectionsthrough through the thePortage PortageLake Lake Volcanic Volcanic have been studied studied using using aa combination combinationof of microscopic microscopicinvestigation, investigation, XRD XRD technique, technique, and electron electron microprobe analysis, by Stoiber Stoiber & &Davidson Davidson(1959a. (1959a,b). b). These analysis, including including the drill core section studied by four are located located between Ahmeek and Copper Harbor and four dril! drill core core cross cross sections sections are provide km provide coverage coveragethrough through 3000m 3000m of of the the Portage Portage Lake Volcanics over a distance of 60 k m along alongstrike. strike. Interlayered Interlayeredsediments sedimentsand andse!ected selectedlava lavaflows flows can can be be used used as as marker marker horizons horizonsto to corre!ate correlatethe the stratigraphic stratigraphic zones zones between the different individual drill holes. Initial distinguished within Initial results resultsdemonstrate demonstratethat that two two main main minera! mineral associations associations can be distinguished the the amygdaloidal amygdaloidal tops tops of of the the basaltic basaltic !ava lava flows of the upper part of the Portage Lake Vo!canics Volcanics (above (above the the Greenstone Greenstone flow) flow) in the Copper Harbor to Ahmeek sections: (1) a zeolite-dominated laumontite-chlorite-corrensite±wairakite±quartz± zeolite-dominated assemb!age assemblage with laumontite-chlorite-corrensite±wairakite±quart calcite, with chloriteiquartz* chlorite±quartz± calcite, and and (2) (2) aa pumpellyite-epidote-dominated assemblage with calcite±prehnite±laumontite. The zeolite-dominated assemblage is more frequent in the the calcite±prehnite±laumontit upper upper part part of of the the section, section,but butwairakite wairakiteoccurs occurs only below the Hancock Conglomerate. The pumpellyite-epidote-dominated assemblage of the the lower part of the The pumpellyite-epidote-dominated assemblage is characteristic of sequence. sequence. Zeolite Zeoliteminerals mineralsare arepresent present throughout throughout the whole vertical section. Along strike, strike, aa temperature temperature gradient gradient is is observed observed with lower temperature conditions in the Copper Copper Harbor Harbor section section and and higher higher temperature conditions in the Ahmeek section near Ahmeek Ahrneek to the southwest. southwest. This Thiscorrelates correlateswith with the the distribution of native copper deposits increasing in frequency and size from Copper Harbor Ahmeek. increasing in frequency and size from Copper Harbor towards towards Ahmeek. The The most most abundant abundantphyllosilicates phyllosilicates in in the the upper part of the Portage Lake Volcanics are chlinochlore units of of aa lava lava chlinochlore and corrensite. Chlinoc!ore Chlinoclore is present in all morphological units flow, within all flow, i.e. in in the the amygdaloidal amygdaloidal flow top and in the massive interior, and within stratigraphic as determined determined by by electron electron stratigraphichorizons. horizons. The Themean meanof ofthe theinterlayered interlayeredcations cationsas microprobe microprobe analysis analysisis is around around 0.1 0.1 indicating indicatingon!y only very low mixed-layered mixed-layered components. components. Corrensite amygdaloidal flow flowtops. tops. In the eastern eastern most most Copper Copper Corrensite is more abundant in the amygdaloidal 49 �Harbor Harbor section, section, smectites smectites (saponite, (saponite,montmorillonite) montmorillonite)as as well well as asparagonite paragoniteand and pyrophyllite pyrophyllite are are also also present present in in the the zeolite-dominated zeolite-dominatedassemblage. assemblage. The complexmetamorphic metamorphicand andhydrothermal hydrothermal The Portage Portage Lake Lake Volcanics Volcanicswas was subjected subjectedto to aacomplex alteration event (Stoiber & Davidson, 1959, Bornhorst, 1997). The initial 1997). The initialresults resultsof ofthis this alteration event (Stoiber & Davidson, 1959, continuing continuing research research suggest suggest that the abundant laumontite-chlorite assemblage in most of the the upper upper part part of of the the Portage Portage Lake Lake Volcanics Volcanicswas was likely likely the the result result of of regional regional zeolite zeolite fades pumpellyite-prehnite-epidoteassemblage assemblageis is faciesmetamorphism metamorphism during duringburial. burial. The Thepumpellyite-prehnite-epidote likely In the the Copper CopperHarbor Harbor to to Ahmeek Ahmeek section sectionthe the likely related to a hydrothermal hydrothermal phase. In hydrothermal hydrothermalevent eventoccurs occursonly onlylocally, locally,but but when when present present itit is ispervasive. pervasive. References References . Bornhorst, Bornhorst, T.J., T.J., 1997, 1997,Tectonic Tectoniccontext context of of native native copper copper deposits depositsof of the the North NorthAmerican American Midcontinent Midcontinent rift rift system: system: Geological Geological Society Society of America Special Paper, 312, 312, p. p. 127127136. 136. Stoiber, E.S., l959a, 1959a.Amygdule Amygdulemineral mineralzoning zoningin inthe thePortage PortageLake Lake Stoiber, R.E. R.E. and and Davidson, Davidson, E.S., Lava v. 54, 54. p.1250Lava Series, Series, Michigan Copper Copper district. district. Part I: Economic Geology, v. p.12501277. 1277. Stoiber, R.E. and and Davidson, Davidson, E.S., E.S., l959b, 1959b.Amygdule Amygdulemineral mineralzoning zoningin in the thePortage PortageLake Lake Stoiber, R.E. Lava Lava Series, Series, Michigan Michigan Copper Copper district. district.Part Part H: IT Economic Economic Geology, v. 54, 54, p. p. 144414441460. 1460. 50 �Lake Superior's Superior's lUngs: Fault Systems Lake Rings: Clues Clues to to the the origin origin of of Polygonal Polygonal Fault Systems Deborah J. Wattrus Deborah E. E. Rausch Rausch and and N/gel NigeI J. Wattrus Large Lakes Minnesota Large Lakes Observatory, Observatory, University University of ofMinnesota Duluth MN 55812 55812 Duluth MN email: drausch2(did.umn.edu Polygonal Fault Fault Systems Systems (PFS) (PFS) are are aa recently recently recoenized recognized class class of of soft-sediment soft-sedimentstructures. structures. They result They result Polygonal from volumetric contraction contraction triggered triggered by by s&eresis-during syneresis during early early compaction compactionof ofultra-fine ultra-finesediments. sediments. PFS PFS from-volumetric were first described in Paleoeene Paleogene clavstones claystones from from the the North North Sea Seabasin basin (Cartwrieht. (Cartwright, 1994). In 2D cross1994). . sections, PES appear appear be be small small extensional extensional faults and in in map map view, view, the the faults faults have have aa polygonal polygonal appearance. sections, PFS faults and appearance. Cartwright and and Lonergan Lonergan (1996) measured measured the extensional Camwight extensional strain and determined determined that apparent apparent extension extension on any any given given horizon horizon was was uniform uniform in in all all directions. directions. They this that that the the fault fault systems systems could could on They concluded concluded from from this not not have have aa tectonic tectonic origin origin and and that that the the faulting faulting was was related related to to volumetric volumetric contraction contraction of of sediments sedimentsduring during early burial burial and and compaction. compaction. From North Sea, Cartwright Cartwright and and Dewhurst Dewhurst early From 3D 3D seismic seismic data data collected collected in the North (1998) identified identified specific specific criteria criteria of of PFS. PFS. These in other other (1998) These criteria criteria are are used used to to delineate delineate systems systems in sedimentary basins. Based normal faults faults with with small small sedimentary basins. Based on on these these criteria, criteria, PFS PFS are are typically typically close close networks networks of of normal throws that that occur occur over over aa large large area area in in sedimentary sedimentary basins. basins. The bound and and are are throws The systems systems are are layer layer bound occasionally tiered. They Theyonly onlyoccur occurin in very very fine-grained fine-grained sediments sediments (<2 (<2 micron). There Thereare areno noknown known modern analogues. analogues. - < Doughnut-shaped rings rings and and subcircular depressions have been observed in in the the side-scan records collected Doughnut-shaped subcircular depressions side-scan records collected in Lake Lake Superior (Bergson (Bergson and Clay, 1973; et al., 1984; Flood and and Johnson, Johnson, 1984; in 1973; Johnson et 1984; Flood 1984; Flood, 1989; 1989; and Anderson, 1997). The The described describedfeatures features are are 100-300 100-300 meters in diameter. diameter, 10-3- meters wide and 5 meters deep. Side-scan Side-scandata datacollected collectedby by the the Large Large Lakes Lakes Observatory Observatory (LLO) confirms confirms the widespread development of of ring ring structures structures throughout throughout much much of of the the basin. basin. The rings rings commonly commonly occur occur wherever wherever finefinedevelopment grained glacio-lacustrine glacio-lacustrine sediments sediments are are found. found. High-resolution reflection data data collected collected with with grained High-resolution seismic reflection boomer A and d echosounder echosounder systems systems show show that that the the nngs ringsare areassociated associated with with deformation deformationthat thattypically typically disrupts the the thir thifl Holocene Ilolocene surface sediments sediments and and elacio-lacustrine glacio-lacustrinesediments sedimentsbelow. below. The echosounder dismots data clearly shows that the underlying underlying glacio-lacustrine glacio-lacusmne exhibits extensive fracturing and small-scale small-scale ring or or faulting. Some Someof of these these fractures fractures and and faults faults continue to the surface where they coincide with a ring partial ring structure. Many, Many,however, however,are aretruncated truncated at at the the Holocene Holocene boundary. Throws Throwson onthe thesmall small faults are often less than 50 cm and the apparent displacement on these faults is typically normal. Some Some echosounder records show evidence apparently genetically unique deformation deformation sequences sequences in the of the echosounder evidence of apparently fine-grained sediments. sediments. These poorly resolved resolved horizon horizon with with little little coherent coherent These sequences sequencesare are separated separated by a poorly internal reflections. reflections. The well developed Thesequences sequencesabove aboveand andbelow belowexhibit exhibitwell developedinternal internalreflections reflectionsthat thatdo do not appear appear to be concordant. concordant: Both Bothsystems systemsshow showwell-developed well-developedfracture fractureand andmicro-faulting micro-faultingpatterns. patterns. observation suggests that these systems in the subsurface, and are This observation systems are confined to distinct intervals in therefore genetically genetically unique. unique. . ~ ~ ~ ~~ - ~ ~ It is proposed that the rings in Lake Superior expressions of PFS developed in the near surface surface Superior are surface expressions clays. AAcomparison comparisonwith withthe thecriteria criteriaoutlined outlinedby byCartwright Camwightand andDewhurst Dewhurst(1998) (1998)show showthat thatthe thenearnearsurface requirements for PFS development. surface sediment sediment and data from Lake Lake Superior Superior meet nearly all of the requirements development. The seismic data collected thus far indicate indicate that there are basinwide layer bound normal fault systems systems with small throws. The TheLake LakeSuperior Superiorglacio-lacustrine glacio-lacustrinesediments sedimentsare arecharacterized characterizedby by fine finegrain grainsize, size, high water content, content, and and aa clay clay fraction fractioncomposed composedpredominantly predominantlyof ofillite. illite. 51 �The following following model is proposed proposed to explain explain the the origin origin of the the rings rings on the floor of Lake Superior. High High sedimentation sedimentation rates associated with the retreat of ice ice out of the basin produced produced deposits deposits with with high high water water Sometimeafter after deposition, deposition, syneresis syneresis in the sediments sediments contents, which behaved like a colloidal fluid. Sometime tothe thedevelopment developmentof of fractures fracturesand and faulting faultingin in the the initiated volumetric volumetric contraction. This Thisprocess pocess led ledto initiated clays. The Thegrowth-fault growth-faultappearance appearanceof ofsome someof ofthe the faults faultssuggests suggests that that deformation deformation and and faulting faulting was was clays. syndepositional syndepositional and continued for some time. Since Since many of of the fractures fractures and and faults faults truncate truncate against against the the Holocene the deposition of Holocene boundary, we believe that most of the volumetric contraction ceased before the the the Holocene Holocene sediment. sediment. Some Somefractures fractureswhich whichcontinue continueto tothe thesurface surface appear appear to to act act as asconduits conduitsfor forthe the expressed expressed water. This Thisisissupported supportedby bysubmersible submersibleobservations observations(Flood, (Flood, 1989) 1989) that that appear appear to to suggest suggestthat that water in water venting venting from from the the lake lake floor floorremoved removed or or prevented prevented the the deposition depositionof of the the fine fineHolocene Holocenematerial materialin the the vicinity vicinity of of the the ring. ring. REFERENCES REFERENCES Anderson, graphic study Anderson,K.A., K.A., 1997, 1997,A A seismic seismic strati stratigraphic study of of western western Lake Superior Superior(M.S. (M.S. thesis). thesis): University University of of Minnesota, 74p. 74p. and Clay, Clay. C.S., C.S., 1973, 1973. Possible Possiblesyneresis syneresisorigin originof ofvalleys valleyson on the thefloor of ofLake Superior: Berkson, J.M.. f.M., and Lake Superior: Nature, Nature, 245:89-91. 24589-91. Cartwright, from geopressured Cartwright,f.A.. J.A., 1994, 1994.Episodic Episodicbasin-wide basin-widefluid fluid expulsion expulsionÂ¥fro geopressuredshale shale sequence sequencein in the the North 2222:447-450. :44 7-450. NorthSea Seabasin: basin:Geology, Geology, J.A., and sediments: Cartwright,.J.A., Cartwright. and Dewhursi, Dewhurst, D.N., D.N., 1998. 1998, Layer-bound Layer-bound compactionfaults faults infine-grained infine-grained sediments: Geol. 7. Geol.Soc. Soc. Am. Am. Bull., Bull., 110:1242-125 110:1242-1257. Cart-wright, .14. and Lonergan. Lonergan, L., Cartwright,J.A. L., 1996, 1996,Volumetric Volumetriccontraction contractionduring duringthe thecompaction compactionofofmudroc/cy: mudrocks: AA mechanism cale polygonal polygonalfault mechanismfor the the development development of regional-s regional-scale fault systems: systems: Basin BasinResearch, Research,v.8, v.8, p 183-193. 183-193. Flood. topography in Lake Superior: Superior: .1 Flood, RD., R.D., 1989. I989,Submersible Submersiblestudies studiesof of current-modified current-modified bottom topography J. Great GreatLakes Lakes Res., Res., 15:3-14. 15:3-14. Flood. C., 1984, for bedforms and Flood. R. R. D. and and Johnson, Johnson,TT.C., 1984,Side-scan Side-scan targets targetsin in Lake Lake SuperiorSuperior- evidence evidencefor sediment sediment transport: transport:Sedimentology, Sedimentology,v.v.31, 31,p. p. 311-333. 311-333. Johnson, and currents andfish Johnson,T. T.C.. C.,Halfman, Hal/man,J.D., J.D., Busch, Busch,W.H., W.H., and Flood, Flood,R.D., R.D., 1984, 1984,Effects Effects of bottom currents and fish on on sedimentation sedimentationin inaadeep-water. deepwater,lacustrine lacustrineenvironment.' environment:Geol. Geol.Soc. Soc.Am. Am.BulL, Bull., 95:1425-1436, 95:1425-1436. Mollard, patterns ononthe J.D.,1983, 1983,The Theorigin originofofreticulate reticulateand andorbicular orbicularpatterns thefloor floorofofthe theLake LakeAgassiz Agassiz basin basin Mollard. ID., in IT. and in Teller, Teller, J.T. andClayton, Clayton,L., L., eds.. eds.. Glacial GlacialLake Lake Agassiz: GeoL Geol. Assoc. Can. Can. Sp Sp. Paper, Paper,p. p. 355355374. 3 74. 52 �GEOLOGY OF THE TILDEN MINE, MINE,MARQUETTE MARQUEflE IRON IRONRANGE, RANGE, MICHIGAN MICHIGAN Glenn W. Scott Scott and Helene Helene M. Lukey, Lukey, Mine Engineering Engineering Department, Department, Tilden Tilden Mining Mining Company, P.O. Box 2000, 2000, Ishpeming, MI 49849 The Tilden hon Formation, Tilden Mine Mine produces produces iron iron ore ore from from the Negaunee Iron Formation, Menominee Menominee Group, Group, Marquette Range Supergroup in the Upper Peninsula of Michigan. As the base of the iron peninsula iron Marquette ~ a n ~ e ~ u p e r ~ r o u p formation is not exposed exposed at at the the Tilden Tilden Mine, the stratigraphic thickness is unknown. The The thickness exceeds 1000 feet and is probably underlain by and is gradational into thickness exceeds 1000 feet and is probably underlain bfand is gradational into Mine. The undifferentiated elastics and iron formation of the Empire Mine. The iron iron ore ore deposit deposit at at the the Tilden Mine hut, more Mine has has been divided divided into into geologic geologic domains based in part on lithology but, importantly on on the the metallurgical metallurgical response response based based on on bench bench tests tests and and in in the the processing processingplant. plant. The interaction of sedimentation sedimentation and diagenesis within growth fault controlled basin, metamorphism and metamorphism and supergene supergeneoxidation oxidationhas has resulted resulted in in aa complex complexsuite suiteof of ore oretypes, types,each each with specific, problems. Production specific, if not entirely entirely objective, blending characteristics and problems. Production since 1974 million long long tons tons of ore at a 1974 has been 126 126 million long tons of pellets from 355 million 1999, the Asof ofJanuary January1,1,1999, the proven proven and and probable long long range (30 (30 year) stripping ratio of 0.94. As mine mine plan reserve reserve was 628 628 million long tons of ore containing 233 million long tons of pellets at a stripping ratio 0.77. at a stripping ratio of of 0.77. Chlorite Chlorite schist schist defines defines the footwall footwall of the Tilden ore body. The The Martite Martite and and main main pit pit Carbonate Carbonate domains domainsdomains domainslie lie stratigraphically stratigraphicallybelow below the the CDffl CDffl Footwall Footwall and and Main Main Pit Pit Hanging wall intrusives. This is metallurgically "good ore" and is typically characterized This is metallurgically "good ore" and is typically characterizedby by high weight recovery (35-45+%), (35-45+%), low phosphorous, phosphorous, low slime slime iron and good grinding grinding media. The West PitJCDffl Pit/CDin Hematite domain in the west pit is stratigraphically stratigraphically between the CDffl CDIII this is is metallurgically metallurgically 'poor' 'poor' In contrast contrast to the martite domain, this hanging wall and footwall. In ore with higher slime iron, phosphorous and poor grinding. Mineralogically Mineralogically and and texturally, martite domain domain in in being being dominantly dominantly platey hematite hematite with with thin thin this domain domain differs differs from from the the martite (mm scale) chert laminae. The equivalent to the (mrn The Magnetite Magnetite domain domain is is the the stratigraphically stratigraphically equivalent West PitJCDIII. Pit/CDffl. Mineralogically, Mineralogically,the the ore oreconsists consistsprimarily primarily of of magnetite-siderite-chert magnetite-siderite-chertwith with variable hematite and silicates. silicates. This Thismineralogy, mineralogy, along along with with the the thin laminations, laminations,appears appears to to indicate a restricted basin and a reduced environment of deposition. environment There are several igneous igneous horizons horizonsatatthe theTilden TildenMine. Mine.The Theterm term'intrusive' 'intrusive' or or 'dike' 'dike' is is used for diabasic to porphyritic porphyritic to aphanitic aphanitic bodies, which vary from (semi) conformable sill-like horizons, usually interpreted as interpreted as synsedimentary sills but may be flows, to obviously crosscutting bodies, interpreted as dikes that may may be be feeders. feeders. The sills and majority of the crosscutting andlor the dikes appear appear to be of early early Proterozoic Proterozoic age, related to the Clarksburg Clarksburg Volcanics and/or Hemlock and Emperor Emperor Volcanics, but there there are are several several dikes that are interpreted interpreted to be of Keweenawan based on Keweenawan age agebased on the the magnetic magnetic signature. signature. 53 �AN ESTIMATE OF RATE DYNAMIC AND STATIC STATICSTRENGTH STRENGTH OF AGGREGATES: AN SENITIVITY OF SENITIVITY OF GEOLOGIC GEOLOGIC MATERIALS MATERIALS STANLEY J. VITTON, Department of & &Environmental Environmental Engineering, Engineering,GHATUPARTHJ GHATUPARTHI STANLEY J. S UBHASH, Department Mechanics, Michigan Michigan SUBHASH, DepartmentofofMechanical MechanicalEngineering—Engineering Engineering-Engineering Mechanics, Technological University, Technological University,Floughton, Houghton, Michigan Michigan49931 4993 1 The Michigan Michigan Department Department of ofTransportation Transportation (MDOT) (MDOT)has has initiated initiatedresearch research into into the dynamic dynamic fracture fracture characteristics of cement concrete concrete(PCC) (PCC) pavements. pavements. The main focus of this characteristics of aggregates aggregates in Portland cement this aggregateportion portion in PCC. research is to study the fracture fractureand and strength strcngth characteristics of the coarse aggregate wide range Due to the wide range of of rock rock types types inin Michigan, Michigan,there thereisisaacorresponding correspondingrange range of ofcoarse coarse aggregate aggregate used PCC. PCC. In used In addition, addition,aasignificant significant amount amountofofblast blastfurnace furnaceslag slag isis produced produced and used used in PCC. To study unconfined uniaxial uniaxial compressive of study the static static and dynamic dynan~icstrength strength of of the the aggregates. aggregates, unconfined compressive strength of three limestones, limestones, four fourdolomites. dolomites,two twobasalts basaltsand andthree three blast blastfurnace furnaceslags slags were were conducted. conducted. InIn addition, conditions. The addition,tests tests were wcre also also conducted conducted under dry dry and and saturated saturated conditions. The studies studies revealed that that the the aggregates exhibited exhibited the lowest compressive strcngth, strength,followed followed by the limestones and dolomites. slag aggrcgates aggregates exhibited exhibited the the highest highestcompressive compressivestrength. strength. The The compressive compressive strcngth strength data dataof of The basalt aggregates rocks were were found found to to have haveaastrong strongcorrelation correlationtotothe thebulk bulkdensities. densities. Both the dry thy dry and saturated rocks and saturated aggregates revealed revealed aahigher higher compressive compressive strength strength under under dynamic dynamic loads compared compared to to in dynamic compressive strcngth strength over over its static strength is the static loads. The Thepercentage percentage increase increase in identified as which may identified as aa measure measure of the rate sensitivity sensitivityofofthese these aggregates, aggregates, which may have have considerable considerable geologic interpretation. relevance in applications applicationssuch such as rock blasting, underground construction, and geologic interpretation. The aggregate used used in in the thestudy studywere wereobtained obtainedfrom fromquarries quarriesininMichigan, Michigan, Ohio Ohio and and Ontario, Ontario, while while blast furnnace ftrnnace slags obtainedfrom from steel steelmills mills in in Sault Stc. Ste.Marie. Marie, Ontario Ontario and and Detroit. Detroit, the blast slam were obtained Michigan. The limestones investigated Michigan. Thethree threelimestones investigated were from the Fibron Limestone Limestone Formation of of middle middle Silurain City Limestone Silurain age age (Port Inland Inland Quarry), Quarry), the the Roger City Limestone Formation of of middle middle Devonian Devonian age age (Presque Isle Quarry), Quarry), and the the Bay Bay Port Port Limestone Limestone of of late Mississippian Mississippian age age (Bay (Bay County County ~ Road (Presquc Isle oad Commission Quarry). The Dolomite Formation of middle Thedolomites dolomiteswere wcre from from the the Engadine Dolomite middle Silurian Silurian (Cedarville Quarry), age (Cedarvillc Quarry), the the Raisin Raisin River River Dolomite DolomiteFormation Formationofoflate lateSilurian Silurianage age(France (FranceStone Stone Quarry). the Lucas Dolomite Dolomite Formation of Quan-y), of middle middleDevonian Devonian age age (Rockwood Quarry), Quarry), and a stratigraphically later dolomite from the Lucas Formation (Denniston Quany). stratigraphically later dolomite from the Lucas Formation (Denniston Quarry).The Theigneous igneous rocks rocks tested were were from from the Portage Lake Lake Volcanics Volcanics (Moyle (Moyle Quarry) Quarry)and and the the Paleoproterozic Paleoprotcrozic volcanics near near Bruce Mines, Ontario Ontario (Ontario (OntarioTraprock Traprock Quarry). Quarry). The aggregates weresubjected subjectedtotouniaxial uniaxial compressive compressiveloads loadsatattwo twodifferent different strain strain rates. rates. Low Low strain aggrcgates were strain rate (static) wcre were conducted conducted on on aa MTS servohydraulic and high strain rate experiments experiments (static) sc~ohydraulicmachine machine and strain rate rate experiments (dynamic) (dynamic) were conducted conducted on on aa modified modified split Hopkinson Hopkinson pressure pressure bar (MSHPB). (MSHPB). The The experiments Split bar (also çalsocalled calledaa Kolsky Kolsky bar, bar, Kolsky, 1949) Split Hopkinson Hopkinson pressure pressure bar 1949)technique technique has has been been widely used for for dynamic testing testing of of materials materialsatathigh highstrain strainrates ratesininthe therange rangeofof10'-104 IO'-l 4 s"' s' (Ravichandran used (Ravichandran and and Subhash, 1995). It consists consists of aa striker strikerbar, bar, an anincident incidcntbar barand andaatransmission transmission bar, bar, as as shown shown Subhash, 1995). schematically in Figure I.1. The schematically in Thespecimen specimen totobe becharacterized characterized isis placed placed between between the incident incident and and transmission bars. bars.The Thefree freeend endof of the theincident incident bar bar isis impacted impactedby by the the striker striker bar, bar, which which is launched transmission launched from aa gas gun, at aa predetermined predetermined velocity. velocity. The pulse in in the incidcnt incident The impact impact generates generates aa compression pulsc from specimen,subjecting subjectingitit to to the the required required compressive compressiveloading. loading.AApart part of of bar which travels towards the specimcn, and the the rest rest is is rcflected reflected back back into into the the incident bar as a this pulse is transmitted to the transmitter bar and tensile pulsc. pulse. Strain Strain gages gages are are mounted mountedat at the the center center of of each bar to measure the magnitude and tensile each bar measure the magnitude and duration of of these these stress stress pulses. pulses. Based Based on on one-dimensional one-dimensional calculations, calculations, it can can be be shown shown that that the the magnitude of the transmitted pulse gives a measure of the stress to which the specimen is subjected the transmitted pulsc gives a measure which the specimen is subjected and the the magnitude and magnitude of the reflected reflected wave gives aa measure measure of the the strain strain rate rate within withinthe thespecimen. specimen. 54 �integrating Integratingthe the strain strainrate ratewith withrespect respecttototime timeyields yieldsthe thestrain strainin in the the specimen. specimen.Thus, Thus. the thestress-strain stress-strain a material can be obtained at high strain rates. response response of a material can be obtained at high strain rates. A A minimum minimum often of tensamples sampleswere weretested testedfor foreach eachaggregate aggregatetype type in in each each condition, condition, e.g. e.g. thy, dry,saturated, saturated, static, and dynamic dynamic conditions. The Theresults results of of the the static static and and dynamic dynamic testing for thy dry conditions conditions are arc presented in Figure slags arc are identified identifiedas as sample sampletypes types I.1. 2, 2, and 3; the 2, where whcre the the blast blast fi1rnace furnace sla&s the Figure 2, and the basalt and 6; the dolomites are sample types 7 through 10; lirnestones are sample types 4, 5, limestones are sample types 4, 5. and the dolomites arc 10; and the basalt sample sample types are II11and and12. 12. In addition, the bulk density of the rock types are are also alsopresented. presented. ItIt can can be be seen seen from from this thisdata datathat thatthe theslags slagsexhibited exhibitedthe thelowest lowest strength strength followed followed by the the limestones limestones and and addition, itit can can be be sccn seen that that there there is is aa good dolomites dolomites with withthe thebasalts basaltshaving havingthe thehighest higheststrength. strength. In In addition, good of the the slag!,, slags, all of the correlation with with bulk bulk density. density. With the partial exception cxception of the materials materials tested tested showed an increase indicating that that these materials are increase in in dynamic dynamic strength strength over o v a the static strength, strength, indicating rate rate sensitive. sensitive. The blast blast furnace furnacc slag slag showed showed relatively relatively low low strength strength both both in in satic satictesting testingand anddynamic dynamictesting. testing. However, it can be strength and strength in the range of the be seen that that the the air air cooled cooled slag had both low strcngth the limestoncs dolomites. The liniestones and dolomites. The two two data data sets sets shown shown for for the the air air cooled cooled slag slag represent represent samples samples form form two different blocks of slag slag material material assumed assunicd to have been been cooled cooled at different rates depending on where it was deposited. The blast fijrnacc slag is formed from the gangue gangue and and secondary secondaryconstiuents constiuents whcre deposited The blast furnacc slag is formed from the in iron ore as and has has aa chemical chemicalcomposition compositionof ofCaO, CaO,Si02, Si02, A103 Al03 as well as coke residue and limestone and and MgO with trace amounts of of.sulphur and some some alkalis alkalis (Smolczyk, (Smolczyk,1980). 1980). The final structure of sulphur and the slag depends on the cooling conditions conditionsof ofthe themolten moltenslag. slag. When When itit is allowed to cool slowly it forms into into aadense densecrystalline crystallinestructure structurewith with properties properties similar similartotorock. rock. When the molten molten slag slag isis quenshed quickly with limited amonts of water, it traps steam in the mass and produces a porous, quenshed quickly with limited amonts of water, mass and produces a porous, glassy properties. However, slag is formed it also glassy material material with poor mechanical propcriies. Howcvcr, when the air cooled slag has different rates of cooling depending on its location when when deposited deposited for for cooling. cooling. The The molten moltenslag slag exposed to the then the slag at the the atmosphere atmosphere (top) will cool more more quickly then the bottom bottom of ofthe thedeposit. deposit. The appearance of pores. The statification statification when when cooling cooling isis cieariy clearly observed observed by a color straification and the appearance The test data data shows shows this this with with aa significant significant increase increase in strength strcngth with test samples from two different blocks from from the the same same deposit. deposit, i.e., i.e., top topand and bottom bottom locations. locations. In the case of the tested, itit can can be be sccn seen that that the the trap trap rock rock basalt basalt has aa higher strength then the the basalt.s basalts tested, Portage Portage Lake Lake volcanic volcanic basalt. basalt. in In a simplied simplied framework it is assumed that the cooling rate of the trap trap rock basalt was longer which were were formed formed formed formed near near or or at the longer than the Portage Portage Lake voleanics, volcanics, which the surface. surface. This is also also seen in in the the crystalline crystallinc structure structurc of the two basalts, with the trap trap rock rock basalt basalt having a more uniform crystallinc crystalline structure structure and and the the Portage Lake Lake volcanics volcanics a more inconsistent and random crystalline crystallinestructure. structure. The The sedimentary sedimentarylimestones limestones and and dolomites dolomitesalso alsoshow showrate ratesensitivity. sensitivity. It is interesting interesting to note in the the limestones that the the static strength strength for the three three limestones limestones tested tested are relatively relatively close, close, while the the limestones that dynamic dynamic strength strength are archigher. higher. In particular, the Silurian limestone (Port Inland) showed significantly significantly higher rate sensitivity than does the Devonian limestone (Preque Isle) or the Mississippian limestone sensitivity (Prcque Islc) limestone With the exception However, this same trend is not seen in the doloinites. trend seen in the dolomites. With cxception of the the (Bay County). County). Howcvcr, this Silurian dolomite (Cedarville) (Cedarvillc)there thereisis an an increase increase in in both Silurian dolomite both the static static and and dyanmic dyanmic strength strength with with geologic geologic age. age. Previous research has has shown shown that that for Previous research for aa brittle brittle material, material, the the damage damage evolution evolution under under applied applied compressive microeracking at defects such a pores, inclusions, second compressive loading is intimately related to microcracking second phase particles, twin grain boundary intersetcions and triple point grain boundary boundary junctions junctions (Lanford, (Lanford, 1977). However, strain rate the the rate rate sensitivity of a However, under dynamic loading conditions above a critical strain atiributted to to the the inertia-dominated inertia-dominateddynamic dynamiccrack crackgrowth growthfrom fromprc-existing pre-existingflaws. flaws. Thus, material is attributted 55 �response responseofofaadefect defecttotoloading loadingisisinertia inertiadependent, dependent,i.e. i.e,the thetime timeitittakes takestotoovercome overcomethe theinertia inertiaofofthe the strength. Therefore, microcrack, more defects are loaded in the material leading to higher microcrack, more defects are loaded in the material leading to higher strength. Therefore, ititisis speculated speculated that thatififdynamic dynamicloading loadingstresses stressesaalarger largerportion portionofofa amaterial's material'sdefects, defects,then thenititmay maybebe lithification may possible possiblethat thatgeologic geologicmechanism mechanismsuch suchasasformational formationalhistory, history,compaction compactionand and lithification maybebe better bcncrobserved observedunder underdynamic dynamicfracture fracturetesting. testing. References References Koisky, Kolsky,H., H.,1949, 1949,AnAnInvestigation Investigationofofthe theMechanical Mechanicalproperties propertiesof ofMaterials MaterialsatatVery VeryHigh HighRates Ratesofof Loading. Proc.R.R.Soc. Sue.London, London,B62, B62,pp. pp.676-700. 676-700. Loading,Pmc. Ravichandran. Ravichandran,G. G.and andSubhash, Subhash, G., G., 1995, 1995, A A Micromechanical MicromechanicalModel Modclfor forHigh HighStrain StrainRate RateBehavior Behavior 32 Ceramics,lifiernalional International.Journal JournalofofSolids Solidsand andSiructures. S/ruc/ure.~. 32[17/IS], [I 71181,pp. pp.2627-2646. 2627-2646. ofofCeramics, Smolczyk, 1950, Smolczyk,H.G.. H.G., 1980.Slag SlagStrcture Strctureand andIdentification IdentificationofofSlags, Slags,Inter. Inter.Congress Congressononthe theChcmistry Chemistryofof Cement, editions Septima, Cement,7"7*ed. ed.1980. 1980.Paris Parisa aeditions Septima,pp. pp.3-17. 3-17. High HighSpeed, Speed,44Channel Channel Digital DigitalOscilloscope Oscilloscope PR040) (NicoletPRO4O) (Nicolet I I Wheatstone Bridge Strain gage - 1 Striker StrikerBar Bar - specimen m m Incident IncidentBar Bar I Transmission TransmissionBar Bar Modifidied ModifidiedSplit SplitHopkinson HopkinsonPressure PressureBar Bdrwit witMomentum MomentumTrap. Trap. Figure Figure I 1 0 = 0 S d 22 Q F - 700 V 0 H 0 ii Ji 1' 3.5 ID — 600 m U. 5 C 0 3.0 Stat 500 C., E Dens 0 0 > 0 C 0 1 400 I I 300 I .4: 2.5C I 0 C, V C 1 I I; 200 2' VA = 0 C 2.0 00 0 0 1.5 1 2 3 4 5 6 7 6 9 10 11 Sample SampleType Type Figure Figure22 Dynamic Dry Conditions. Dynamicand and Static Static Strength Strength Tests Tests in Dry Conditions. 56 56 12 13 �8 Palmer Palmer Gneiss; Gneiss; aa large, large, low-grade low-grade shear shear zone zone ' 1 ~ e b s t e rC. C. , L., 'Cambray 'cambray W. W. F., F., 2Scott, '~cott,0., G.,'~ordstrom, 'Webster, 2Nordstrom, P. P. 'Widson, 'Wilson, E. 'Dept. Sciences, Lansing, MI 48824 ' ~ e ~Geological Geological t. Sciences, Michigan State State University, University, East Lansing, 22Cleveland Cliffs Mining Co, lshpeming, MI Cleveland Cliffs Ishpeming, MI The Marquette Marquette Trough Trough is is interpreted interpreted to to be be an an asymmetric asymmetricrift-related rift-related basin; basin, truncated truncatedstratigraphy stratigraphy southern margin and a rollover on the southern rollover structure structure to to the the north north provides provides evidence evidencefor for this this interpretation, Marking interpretation. Markingthe thesouthern southernboundary, boundary,between between the the Archean Archeangneiss gneiss and and the the Early Early Proterozoic Proterozoic metasedimentary metasedimentary rocks of the Marquette Marquette Range Supergroup, is the Palmer Gneiss (PG). Van Hiseand andBayley Bayley(1897) (1897)first firstinterpreted interpretedthe the PG PG as as aa comminuited, comminuited, sericitzed and VanRise partly silicified silicified phase of of the lower lower Precambrian Precambrian gneiss. In In1968, 1968,Gair Gairand andSimmons Simmonsconcurred concurred with theft their interpretation and offered offered three three possible modes of genesis: (1) alteration and shearing of Precambrian Precambrian rock during during faulting, faulting, (2) (2) migration migrationof of fluids the contact contactbetween betweenlower lowerand and fluids along along the middle Precambrian rocks, and (3) alteration of of aa regolith regolith during duringfolding. folding. Since the the time time of of mapping by Gair Gair and Simmons, Simmons, Tilden Tilden open pit mining mining operations have exposed the PG. Large Large shear bands, with approximately approximately2.5 2.5 meter meter spacing, spacing,indicate indicatethe the importance importanceof of ductile ductile zone (Figure (Figure 1). Foliation deformation during the formation formation of the PG in a low-grade shear zone Foliation measurements show measurements show aa steep steep NNE NNE dipping dippingS-foliation S-foliation being being cut cutby by aa shallow shallowNNE NNE shear shearband, band, indicating a reverse sense sense of shear (Figure 2). The Thefolds foldsmeasured measuredin in the the adjacent adjacent iron ironformation, formation, at the Tilden Tilden and and Empire Empire mines, mines, consistently consistentlyplunge plunge gently gently towards towardsthe the WNW, WNW,reflecting reflectingthat that they were formed zone. The formed under under the same strain strain conditions conditions as the shear zone. TheNNE-SSW NNE-SSW compressive compressive direction direction corresponds corresponds to previous studies in the area (Myers, 1984). Whole Whole rock rock chemical analysis chemical analysis of of the PG PG suggests suggeststhat that these these altered altered rocks rocks are are not not granitic granitic in in origin, origin, but but rather rather basaltic. The age. The The basaltic basalticnature nature indicates indicates that the PG is of Proterozoic age. The Penokeon Penokeon Orogeny, collision of an island island arc arc with with the the Lake Lake Superior Superior Craton, Craton,caused caused closure closure of of the the Marquette MarquetteTrough Trough that reactivated preexisting normal faults and resulted in a reverse dip dip slip. slip. Strain Strain was was concentrated concentrated in in aa portion portion of of aa metadiabase metadiabasesill sillthat that was was dragged dragged into into the the shear shearzone zone causing causing 57 �alterationand andshearing shearingofofthe therock rocktotoform formthe the PG. A 34% loss of volume is the calculated effect alteration PG. A 34% loss of volume is the calculated effect alterationfrom fromthe themetadiabase metadiabaseprotolith protolith to the PG (Gresens, 1967). ofofalteration to the PG (Gresens, 1967). References: References: Gair, J. E., and Simmons, G. C, 1968, Palmer Gneiss-an example of retrograde metamorphism Gair, J. E., and Simmons, G. C, 1968, Palmer Gneiss-an example of retrograde metamorphism alongan anunconformity: unconfonnity:U.S. U.S.Geological GeologicalSurvey Survey Professional Paper, 600-D, p. D186along Professional Paper, 600-D, p. D186D194. D194. Gresens, R L., 1967, Composition-volume relationships of metasomatism: Chemical Geology, v. Gresens, R. L., 1967, Composition-volume relationships of metasomatism: Chemical Geology, v. 47-65. 2,2,p.p.47-65. G., 1984, Structural analysis of foliated Proterozoic metadiabase dikes in the MarquetteMyers, Myers, G., 1984, Structural analysis of foliated Proterozoic metadiabase dikes in the MarquetteRepublicregion regionofofNorthern NorthernMichigan: Michigan:Master's Master's Thesis, Michigan State University. Republic Thesis, Michigan StateofUniversity. Van Hise, C. R . , and Bayley, W. S., 1895, The Marquette iron-bearing district Michigan: U.S. Van Hise, C. R., and Bayley, W. S., 1895, The Marquette iron-bearing district of Michigan: U.S. 28, p. 608. GeologicalSurvey SurveyMonograph Monograph28, Geological p. 608. East West 2.5 Fig.11Footwall FootwallShear ShearZone, Zone,Tilden TildenMine Mine Fig. N\ . -*- (Palmer Gneiss) (Palmer Onees} o • Pole to mean C'-foliation Pole to mean C-foliation Pole to mean S-foliation Pole to mean S-foliation Slip direction Mean S-C' intersection A Slip direction * Mean S-C. intersection S-C' intersections S-foliation plane S-foliation plane Top of shear zone S-C' intersections \ Top of shear zone C'-foliation plane C-foliation plane StereonetofofFootwall FootwallShear ShearZone, Zone,Tilden Tilden Fig.22Stereonet Fig. 58 58 �IS ISTHE THEJANICE JANICELAKE LAKEUNCONFORMITY UNCONFORMITYAALINK LINKBETWEEN BETWEENTHE THEHEARNE HEARNE LAKE VOLCANIC ARC? CRATON CRATONAND ANDTHE THELA LARONGE RONGE- LYNN LYNN LAKE VOLCANIC ARC? YEO. YEO,Gary GaryM., M.,Saskatchewan SaskatchewanEnergy Energyand andMines, Mines, 1914 1914Hamilton HamiltonSt., St.,Regina, Regina,SK, SK, - S4P 4V4, gary.yeo@sem.gov.sk.ca The TheWollaston WollastonDomain, Domain,aaNE-trending, NE-trending, 75km 75 kmwide widebelt beltofof2076-1860? 2076-1860?Ma Maparagneisses, paragneisses, overlying Archean orthogneisses along the eastern edge of the Heame Craton overlying Archean orthogneisses along the eastern edge of the Hearne Cratonin in Saskatchewan, Saskatchewan,isis separated from 1910-1875 Ma arc volcanics and sediments of the La Ronge Domain by (a) (a) separated from 1910-1875 Ma arc volcanics and sediments of the La Ronge Domain by Archean Archeanorthogneisses, orthogneisses,poorly poorlyknown known supracrustal supracrustalrocks, rocks, and and minor minor Proterozoic Proterozoic plutons plutons of of the the Peter PeterLake LakeDomain, Domain,(b) (b)1855 1855Ma Mamonzogranite monzograniteto toquartz quartzdiorite diorite of of the the Wathaman Wathaman Batholith, Batholith, and and (c) (c)the theRottenstone RottenstoneDomain, Domain,aamigmatitic migmatiticbelt beltof of sediments, sediments,similar similarto to those those of of the the La La Ronge Ronge Domain, Domain, intruded intrudedby by tonalite. tonalite. The Theboundary boundarybetween betweenWathaman Wathaman Batholith Batholith and and Wollaston and Lake Shear Zone. While this Parker Peter PeterLake Lakedomains domainsisisthe theNeedle NeedleFalls Falls-- Parker Lake Shear Zone. While thisisisaafundamental fundamental break breakbetween betweenancient ancientcrust crustto tothe thewest westand andjuvenile juvenile crust crustof of Trans-Hudson Trans-Hudson Orogen Orogen to to the the east, east, there thereisisno noevidence evidencethat thatititisisaacollisional collisionalsuture. suture. Within Within the theWollaston Wollastonsupracrustal supracrustalsuccession, succession,the the Janice Janice Lake Lake Conglomerate, Conglomerate, which can be traced discontinuously for 245 km along the eastern margin of the belt, be traced discontinuously for 245 km along the eastern margin of the belt, marks marks aa major major unconformity. The conglomerate is polymictic, with clasts derived from underlying unconformity. The conglomerate is polymictic, with clasts derived from underlying strata strata predominating. predominating.Locally, Locally,ititincludes includesfanglomerate. fanglomerate.Although Althoughthe theconglomerate conglomeratecannot cannotbe betraced traced westward, westward,younger youngercalc-silicate calc-silicatebearing bearingstrata, strata,locally locally resting restingon on various various older olderlithostratigraphic lithostratigraphic units, units,mark markthe thepresence presence of of aa profound profound unconformity. AAcorrelative correlativeunconformity unconformityhas hasbeen been recognized recognizedininthe theManitoba Manitobasegment segmentof of Wollaston Wollaston Domain, Domain, another another200 200 km km to to the the northeast. northeast. In In the the absence absence of of any any evidence evidence for for thermal thermal uplift (ie. igneous igneous activity), uplift and extension extensionin in Janice Janice Lake Lake time time must must be be due due to to mechanical mechanical flexure flexure of the crust. AAprobable probablecause causeisis Lynn Lake tectonic tectonicloading loadingof of the the eastern eastern margin margin of of the the Hearne H e m e craton craton as as the the La Ronge --Lynn Lake volcanic volcanic arc LaRonge Ronge-arcconverged convergedtowards towardsitit over overan an east-dipping east-dippingsubduction subduction zone. zone. Volcanism Volcanismininthe theLa Lynn LynnLake Lakearc arcbegan beganabout about1910 1910Ma Maand andreached reachedaa peak peak about about 1880 1880Ma. Ma. Following Followingarc-craton arc-craton collision collisionat at about about1860 1860Ma, Ma, the the sense senseof of subduction subductionwas was reversed reversed and the Wathaman Batholith was was emplaced emplaced at at about about 1855 1855 Ma. Geochemical Geochemicalevidence evidencesuggests suggests that the La Ronge segment of the thearc arcdeveloped developedin in aatransitional transitionalcrust crust setting, setting, close close to to or or partly partly over marginal continental crust. Tectonic Tectonic loading loadingof of the the outboard outboard margin margin of of the the Heame Heame Craton Craton would have resulted in an inboard flexural bulge, with consequent normal faulting and erosion over its crest and deposition inboard flexural bulge, with consequent normal faulting of coarse clastics on its flanks. As convergence proceeded, the bulge of coarse clastics on its flanks. As convergence proceeded, the bulgewould would have have migrated migrated cratonward cratonward and and died died out, out, creating creatingaa diachronous diachronous regional unconformity. Preservation Preservationof of coarse coarse clastics clasticswould would be be favoured favoured only only on the the trailing, eastern flank of the bulge, however. The The approaching approachingvolcanic volcanic arc arc would would have have become a bather barrierto tothe the open open ocean, ocean, and and accumulation accumulation of evaporites evaporitesand and carbonates carbonates in in the the resulting resulting restricted restricted basin would have been increasingly favoured. This by the the This hypothesis hypothesisalso also explains explains the the dramatic dramatic change change in sedimentation recorded by Wollaston of Wollastonparagneisses. paragneisses. Following Following2100 2100Ma Marifting, rifting, the the widespread widespread Lower Sequence of psammopelites, psammopelites,pelites, pelites, and and feldspathic feldspathic psammites accumulated accumulated on a passive margin. As As arcarcahead of of craton craton convergence convergenceproceeded, proceeded,coarse coarseclastics clastics were were shed shedoff off aa migrating migrating flexural flexural bulge bulge ahead the arc. Upper Sequence calc-silicate rich strata subsequently accumulated in the developing the arc. Upper Sequence calc-silicate subsequently in the developing foreland basin. basin. foreland 59 �- (a) Rift Rift Sequence (Courtenay (Courtenay - Cairns Cairns Lake LakeBelt): Belt):2100 2100 Ma Ma Rift Stretched continental crust sediments—_ * + t ÷ j* + %+ + L+ + ± Superior Cratori? - Hearne Craton ÷+ ÷ + %+ + A+ + + ±1 ++ ÷ 4• + Oceanic crust - ,.., La Range Volcanic Volcanic Arc Arc (1910- 1860 Ma) (b) Lower LowerSequence: Sequence:2100 2100- 1880 1880Ma I - (c) Upper Sequence: 1880 1880-1860 1860 Ma Ma Restricted basin Restricted basin Uplift and erosion (uncónforrMy) Uplift (uncbnformity) (d) Cord illeran Margin: 1860 - 1830 Ma Foreland sedimentation tharnan (1855 Ma) Reference Reference +'>, : <;s Yeo, ci. G. 1998. 1998 A systems tract approach oach to totthe stratigraphy of paragneisses isses in in the the southeastern southeastern Wollaston Domain: Wollaston Domain: Saskatchewan Saskatchewan Energy Energy and and Mines, Mines, Misc. Misc. Rep. Rep. 98-4, 98-4, p36-47. p36-47. 60 �LOW-RESOLUTION OFF EARLY PROTEROZOJC LOW-RESOLUTION SEQUENCE SEQUENCE STRATIGRAPHY STRATIGRAPHY O EARLY PROTEROZOIC PARAGNEISSES, PARAGNEISSES, WOLLASTON WOLLASTON DOMAIN, DOMAIN, SASKATCHEWAN SASKATCHEWAN YEO, Saskatchewan YEO, Gary Gary M., M., SaskatchewanEnergy Energy and andMines, Mines,1914 1914Hamilton HamiltonSt., St.,Regina, Regina,SIC, SK. S4P S4P4V4, 4V4, gary.yeo @sem.ov.sk.ca The Wollaston Wollaston Domain 75 km km wide wide belt belt of of of of early early Proterozoic Proterozoic paragneisses, paragneisses, The Domain is is aa NE-trending, NE-trending, 75 overlying Archean orthogneisses the eastern eastern edge edge of of the overlying Archean orthogneisses along along the the Hearne Hearne Craton; Craton; west west of of the the TransTransHudson Hudson Orogen. Orogen. Bimodal Bimodal volcanics volcanics near near the the base base of of the the paragneiss paragneiss succession succession give give aa U-Pb U-Pb zircon zircon age granitic plutons plutons range range from from 1.81 to 1.84 Ga. A age of of 2.08 2.08 Ga. Ga, while while minor minor gabbro gabbro and and granitic 1.81 to 1.84 Ga. A threethreeyear, year, 1:20,000 1:20,000 scale scale mapping mapping project project was was begun begun in in 1997 1997in in the the southern southern part part of of Wollaston Wollaston Domain Domain to to improve improve understanding understanding of of the the stratigraphy stratigraphy and and structure structure of of the the guesses, gnesses, which which underlie underlie the unconformity-type unconformity-type uranium the uranium deposits deposits of of Athabasca Athabasca Basin. Basin. A A basic basic strategy strategy of of the the project project is is to to map outward from Archean inliers so as to be able to work out the stratigraphic succession in map outward from Archean inliers so as to be able to work out the stratigraphic succession in spite of of complex complex deformation deformation and spite and high high metamorphic metamorphic grade. grade. Four episodes of of regional regional deformation deformation can can be be distinguished. distinguished. D Dll involved Four episodes involved isoclinal isoclinal folding, local local basement basement ovenhmsting, overthrusting, and and transposition transposition of of primary primary layering layering into into the the SSIl foliation, foliation. folding, D2 involved involved tight tight to D2 to isoclinal isoclinal folding folding about about NE-trending NE-trending axes, axes, superposition superposition of of aa strong strong 52 S2 foliation, and and local local thrust thrust faulting. faulting. D3 foliation, D3 involved involved local local open open folding folding about about SW SW to to NW N W axes, axes, and and local brittle-ductile fault fault movement. movement. D4 D4 involved involved minor minor sinistral sinistral offset offset on on aa series series of of N N to to NNW NNW local brittle-ductile trending brittle trending brittle faults. faults. Two lower granulite facies) (upper amphiboIite amphibolite - lower Two episodes episodes of of high high T T -- low low P (upper metamorphism are associated associated with Dl and Peak with Dl a n 1)2 d ~ deformation. def&mation. 2 Peak P-T PITconditions, conditions. reached reached during during metamorphisk are D2, 750°C and and 55 kbar. kbar. Along the eastern margin of the belt, however, metamorphic D2, were were about about 750° Alone the eastern margin of the belt. however, metamorphic grades are are relatively relatively low lower amphibolite facies). grades low (upper (upper greenschist greenschist - lower Two widespread Two widespread paragneiss paragneiss successions successions are are distinguished distinguished in in Wollaston Wollaston Domain: Domain: aa lower lower Pelite Pelite Unit, Unit, and and an overlying overlying Psammite Psammite Unit. Unit. These These can can be be subdivided subdivided into into at at least least eight eight subunits subunits in the the Foster Foster -- Daly lakes area. Two lakes area. Tworestricted restricted successions successions are are also also recognized: recognized: aa basal basal package package in (Courtenay Lake Lake and (Courtenay and Souter Souter Lake Lake Formations), Formations). preserved preserved locally locally along along the the eastern eastern margin margin of of the the domain, and the heterogenous Hidden Bay Assemblage of interlayered quartzites, pelites. domain. pelites, amphibolites. calc-silicates, amphibolites, calc-silicates, and and marbles, marbles, which which likely likely overlies overlies or or is is correlative correlative with with the the Psammite Unit Unit near near Wollaston Wollaston Lake. Lake. The demonstrated to to Psammite TheCourtenay Courtenay Lake Lake Formation Formation has has been been demonstrated be a rift succession, while a passive margin margin setting is inferred inferred for for the the overlying overlying Pelite and Attempts to to determine the depositional setting of individual lithologic units, Psanunite units. Attempts Psammite however, have been restricted to to the the low-grade low-grade rocks rocks along along the eastern margin of of the the domain. domain. Although sequence Although sequence stratigraphy stratigraphy has has become become aa standard standard technique technique for for analysis analysis of of platform platform and craton margin strata, there have been few attempts to apply it to metamorphosed and deformed rocks. rocks. As which deformed As demonstrated demonstrated here, here, itit has has great great potential potential in in interpreting interpreting strata strata in in which obliteration of primary primary features limits application of facies models or comparison with modern obliteration modem sedimentary environments. environments. Two major sequence boundaries subdivide the succession. succession. The The unconformity on Archean basement can be recognized recognized without without difficulty. difficulty. The Thebase baseof ofthe theJanice JaniceLake LakeConglomerate Conglomerate(Unit (Unit Wo) marks a second unconformity. unconformity. To To the the west, west, where where the the conglomerate conglomerate is is absent, this unconformity corresponds to the base base of of the the calcareous rocks rocks that that overlie overlie it. it. Within each unconformity sequence, the mapped lithofacies lithofacies units can be asigned to a succession of of systems systems tracts. 61 �Lower Sequence: Lower Sequence:Ferruginous Ferruginous(garnet), (garnet),anoxic anoxic(graphite), (graphite), muddy muddy sediments sediments of Unit Wna fine upward upward into aluminous (clay-rich) (clay-rich) muddy muddy sediments sediments of of Unit Unit Wnps. Wnps. Such retrogradation is consistent with transgressive systems is consistent with aa transgressive systems tract. tract. The quartzite quartzite beds in Unit Unit Wna may be stormstormgenerated flows. Less aluminous muddy sediments of Unit Wns are transitional through Unit Wnsp to Unit Wrn Wm sands. Such a progradational sequence is consistent with a highstand systems systems tract. Upper Sequence: Upper Sequence:Polymict Polymictconglomerate conglomerateof ofUnit UnitWo Womarks marksaaperiod periodof of uplift uplift and and succession. Although erosion. Most Most clasts clasts are are derived derived from the underlying sedimentary succession. restricted to the eastern margin of Wollaston Domain, Domain, the Janice Janice Lake Lake Conglomerate Conglomerate can can be be for at at least least 245 245 km. km. This unit is interpreted interpreted as as alluvial alluvial fan fan deposits. deposits. Nontraced along strike for tract. An marine conditions indicate that it is a lowstand systems tract. An upward upward decrease decrease in in clastic input is suggested between calc-silicate calc-silicate bearing bearing Unit Wmc Wrnc and and calc-silicate calc-silicate rich rich Unit Unit Wnc. Wnc. This suggests another transgressive transgressive systems tract. tract. The rocks may may be evaporitic The calc-silicate calc-silicate rich rich rocks deposits. LIthelpay LuhtMY C, 0 C C, C. C, Cl) IC, C. a Wnc lnterDretatipn Gale-silicate Gale-silicate rocks rocks Wrnc Wo Transgressive Transgressive Systems Tract Systems Tract Gale-silicate -bee ring Calc-silicate-bearing arkose 1 I - Gale-silicate-bearing Calc-silicate-bearing conglomerate and arkose Lowstand Lowstand Systems Tract Systems Tract C, 0 C C, Wnsp = C. C, Cl) Wns C, -I0 Wnps Wna I Arid zone zone alluvial fan deposits alluvial deposits Coastal sands sands Arkose and subarkose wbarkose Highstand Highstand Systems Tract Systems Tract Biotite psarn mite and psammopelite Transitionat Transitional shell shelf sands sands and muddy muddy sands and Biotite psammopeiite psammopelite and psammite psammite Shelf muddy sands Shell Sillimanite-cordieriteiimanite-cordieritebiotule psammopelite biotite ~ sammo~eiite and psammite Graphite-garnet-biotute psammopelite and psammopeiite and pelite pelite with quartzite interbeds shell muddy Outer shelf muddy sands sands and sandy muds Transgressive Transgressive Systems Tract Unconformity strain zone) (and high high strai Unconformity (and Basement 1 Carbonate-cemented Carbonate-cemented coastal sands coastal Uplift Uplift and and erosion erosion Unconformity Unconformity Wrn Sauna or restricted restricted basin basin Salina calcareous sediments calcareous sediments and and evaporites evaporites Anoxic shell shelf muds muds and and sands sands Uplift and erosion erosion Granitoid rocks rocks with with local local amphibolite, amphibolite, metased. metased. xenoliths, chsrnockie xenoliths, and charnockile References Delaney. G GD.. and Tisdale. Tisdale, D D., 1997, Geological investigations investigationsof ofthe theCounenay CourtenayLake. Lake. D Jankovic, Jankovic, Z., Z . MacNeil, MacNol. A.. A . McGowan, McGowan. J.. J .and 1997. Geological Cairnss Lake Fold Belt and the H Hill Embayment, Johnson Johnson River River Intier. Intier, Wollasion Wollaston Domain. Domain, northern northern Saskatchewan. Saskatchewan: C i l l Lake Embayment, Saskatchewan SaskatchewanEnergy Energy and and Mines, Mines. Misc. Misc Rep. Rep 97.4. 97-4,p90-1O1. p90-101 Tran, G.M., Geology of of the the Burtudge BurbidgeLake Lake'- northern Lake area, aica. eastern eastern Wollaston Domain Yeo, O M . . 1997. 1997. Geology northern Upper Upper Foster Lake Wollasion D omn Tran, H.T. H T and and Yeo, (NTS 74A-14): Saskatchewan Energy and Mines. Misc. Rep. 97-4. 97.4. p72-89. N T S 74A-14)- Saskatchewan Tran, H.T., Yco, G., Bradley. S. and Lowry, Jl*, 1998. Geology of the Daly-suttle-Middle Foster lakes asea, eastern wollaston S. and Lewry. J.F. 1998. o f the My-Sutile-Middle area. eastern Wollasion Tran. H.T.. Yeo. G.. and.12): -12)Saskatchewan Saskatchewan Energy E n e m and and Mines, Mmcs, Misc. Misc Rep. Rep 98-4. p36-47. Domajn (NTS Domain (NTS 74A-5, 74A-5, -I -Il.I, and p36.47. paragneisses iinn the the southeastern southeastern Wollaason Domain: Saskaichewal Saskatchewan G., 1998. A systems systems tract approach to to the stratigraphy of of para&sses Yeo, G.. 1998, A ~oliaston Domain: Energy and Mines, Misc, Rep. 98.4. Mines. Misc. 984. p36.47. p3647. . . 62 � https://digitalcollections.lakeheadu.ca/files/original/23d76f1727e6bc080350abdf1335866d.pdf 54d5b014057f0f987f6c366c6fc057ee PDF Text Text Trip 1: Early EarlyProterozoic Proterozoic Strata Strata of the Maquette Marquette Iron of Range, Michigan Ishpeming Trip 22:: Archean Arc1 Greenstone Belt and Ore, G01d Golf Mineralization H-<o<a 3: Tilden Trip 3: Tilden and and Empire Empire A tc.* ~ c . \6 6 A\~ Mines 0f the Marquette Mines of Marpette Iron Range, Michigan Trip 4: Paleozoic andIGlacial Glacial Geology from1 Au Train to to Grand Marais,3, Michigan I on ~Lake Institute on ake Superior Geology 45th 45th Annual Annual Meeting Meeting Ramada da IInn nn Rama Marquette,,Michigan Maquette ~ichigan May 4-8, 4-8, 1999 1999 Sponsored by Sponsored Northern Northern Michigan Michigan University and Michigan University and Michigan Technological University Proceedings Volume 45: Field Trip Guidebook Theodore J. Bornhorst, editor �45TH ANNUAL MEETING SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON LAKE SUPERIOR Volume 45 consists of Part Part 1: 1:Program Programand and Abstracts Abstracts Part 2: 2: Field FieldTrip Trip Guidebook Guidebook Reference to material in this volume should follow the example below: Holm, D., 1999, 1999, Characterization and timing constraints of post-Penokean Ams, D. and Hoim, meso-scale structures in the Watersmeet and Republic gneiss domes of northern Michigan (abst.): (ahst.): Institute Institute on on Lake Lake Superior Superior Geology Proceedings, 45th Annual Meeting, Marquette, MI, v. 45, part 1, 1, p. 2. 2. Volume 45 Published and distributed by Institute on Lake Superior Geology Mark .G. Mark Jirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer,I.L.S I.L.S.G. Minneosta Geological Survey 2642 University Avenue St. Paul, MN USA 55114-1057 551 14-1057 (612)-627-4780 email: jjrsaOOl @tc.umn.edu email: jirsaOOl @tc.umn.edu ILSGwebsite websitehtto://www.eeo.mtu.edu/ereat http://www.geo.mtu.edu/great lakes/ilse/ lakes/ilsg/ ILSG ISSN 1042-9964 1042-9964 All volumes volumes are are available for photocopying All photocopying costs costs from Michigan Technological Technological University University Library Library Archives Archives �INSTITUTE ON LAKE SUPERIOR GEOLOGY PROCEEDINGS Volume 45 45 Part 2: Field Trip Guidebook �CONTENTS PROCEEDINGS VOLUME VOLUME 45 PROCEEDINGS PART 2: FIELD TRIP GUIDEBOOK GUIDEBOOK PART2: FIELDTRIP Editor: Theodore J. Bornhorst Field Trip 1 :: Early Proterozoic Strata Strata of the Marquette Marquette Iron Iron Range, Range, Michigan Leader: W.F. W.F. Cannon Early Proterozoic Strata Strata of the Marquette Iron Range by W.F. Cannon ........................ 22 Field Trip Trip 2: 2: Archean Archean Ishpeming Ishpeming Greenstone GreenstoneBelt Belt and and Gold Gold Mineralization, Mineralization,Michigan Michigan Leaders: T.J. Bornhorst, D.J. Duskin, R.C. Johnson, R.A. R.A. Mahin, Mahin, T.O. TO. Quigley, Quigley, and and G.W. G.W. Scott and An Introduction to the Archean Ishpeming Greenstone Belt, Michigan by R.C. Johnson and 12 T.J. Bornhorst .......................................................................................... 12 Introduction to the Ropes Gold Deposit in the Ishpeming Greenstone Belt, Michigan abstracted from R.A. Brozdowski by T.J. Bornhorst, S.E. Bair, and G. W. Scott ............ 29 29 Geologic Field Excursion to the Ishpeming Greenstone Belt by R.C. Johnson and T.J. T.J. 45 Bornhorst ............................................................................................... Bomhorst 45 Shear Zones and Gold Mineralization in the South Half of the Ishpeming Greenstone Belt, Michigan by D.J. Duskin and T.O. Quigley ................................................57 Examples of Gold Mineralization in the Northern Block of the Ishpeming Greenstone 97 Belt by T.O. Quigley and R.A. R.A. Mahin ............................................................... 97 of the the Marquette Marquette Iron Range, Michigan Field Trip 3: Tilden and Empire Empire Mines of Leaders: G.W. Scott, P.M. Nordstrom and H.M. Lukey Geologic setting of the Tilden and Empire Mines, Michigan by T.J. Bornhorst ............ 108 108 Geologic Field Trip to the Tilden Mine by G.W. Scott and H.M. Lukey .................... 114 114 Geologic Field Trip to the Empire Mine by P.M. Nordstrom ..................................129 129 Trip 4: Paleozoic and and Glacial Glacial Strata Strata from Au Au Train Train to Grand Grand Marais, Field Trip Marais, Michigan Michigan Leaders: R.S. Regis and J. Anderton Regis and J. Anderton Paleozoic and Glacial Geology from Au Train to Grand Marais, Michigan by R.S. Regis and J. J. Anderton ......................................................................136 136 �Field Trip Trip11 Early Early Proterozoic Proterozoic Strata Strataof of the the Marquette MarquetteIron IronRange, Range,Michigan Michigan Leader: Leader:W.F. W.F. Cannon Cannon 2 �FIELD TRIP #1 EARLY PROTEROZOIC PROTEROZOICSTRATA STRATA OF OF THE THEMARQUETTE MARQUETTEIRON IRONRANGE RANGE LEADER: W.F. GEOLOGICAL SURVEY W.F.CANNON, CANNON, U.S. GEOLOGICAL INTRODUCTION preserved in the Marquette Iron Range Early Proterozoic strata of the Marquette Range Supergroup preserved the south edge of the the Archean Superior craton. record the tectonic evolution of a continental margin along the That evolution spans an imprecisely known period culminating in suturing with volcanic arcs to the south at about 1855 Ma. Ma. Lower the Chocolay Chocolay Group Group(Stops (Stops1,2,3,5), 1,2,3, 5), are mostly a sequence of Lower parts parts of the section, the pure quartzite, dolomite, and shale believed to have formed in a stable cratonic setting. They They were were deposited deposited now most commonly a fault (Stop I). unconformably on Archean greenstone and granite, but the contact is now 1). A low angle unconformity separates the Chocolay Group from the overlying overlying Menominee Group (Stop 5). The Menominee Group consists of a basal quartzite-shale unit (Stop 5) overlain overlain by the principal principal ironproducing unit in the range, the Negaunee Iron-formation The Menominee Menominee Group Groupwas was Iron-formation (Stops 6, 7, 10). The deposited in actively subsiding grabens, probably on the rifting continental margin, although a foreland researchers in in the the region. region. Strata basin setting is possible and is favored by some current researchers Strata of of the the Baraga Baraga 9, 11) are widely accepted accepted as products products of sedimentation sedimentation in in aa foreland foreland basin basin during during 8,9, Group (Stops 4, 8, preserved in in northern northern Wisconsin. Wisconsin. The accretion of volcanic terranes now preserved The Baraga Baraga Group Group which lies lies with with aa prominent low angle unconformity unconformity on rocks of the the Menominee Menominee Group Group (Stop (Stop 4), 4), is is composed composed mostly mostly of a prominent turbidite sequence of graywacke and shale (stop 11), and conglomerate conglomerate (stop (stop 4), 4), lesser 1I), quartzite and lesser black black shale shale (stop 8), and minor volcanic rocks rocks (stop (stop 9). 9). The Marquette Iron Range Range is is aa complexly complexly folded folded and faulted, faulted, gently gently west-plunging west-plunging synclinorium synclinorium composed of strata of the Marquette Range Supergroup and intrusive intrusive diabase diabase sheets. sheets. Deformation Deformation occurred occurred during the Penokean orogeny at about 1850 Ma. The synclinorium is bounded on both the north and 1850 Ma, The synclinorium is bounded on both the north and south south by Archean volcanic and granitic rocks, which are most most commonly in in fault fault contact contact with with the the Early Early Proterozoic strata. The Theintense intense penetrative penetrative deformation deformation seen seen in in the the Early Early Proterozoic Proterozoic strata strata isis not not present present in in the Archean basement rocks, which were last penetratively deformed in in Lake Lake Archean Archean time. time. This has led to penetratively deformed the interpretation that the Archean rocks behaved as relatively relatively rigid, rigid, fault-bounded fault-bounded blocks blocks during the Penokean orogeny, and were structuraliy highly deformed deformed Early Early Proterozoic Proterozoic strata. By structurally decoupled from the highly By that interpretation, the Marquette synclinorium is a graben with with respect respect to to Archean Archean basement basement rocks. rocks. The synclinorium synclinorium of of Early Early Proterozoic Proterozoic rocks rocks lies lies within within that that graben. graben. localities that that have have been been visited visited by by literally literally The Marquette area contains many classic geologic localities thousands of geologists during the past century. The TheInstitute Institute on on Lake Lake Superior SuperiorGeology Geology has has visited visited the the area area during several past meetings, but the the Marquette Marquette Range stratigraphy has has not not been been examined examined since sincethe the Twenty-first Annual Meeting in 1975. 1975. This Thisguidebook guidebook isis based based very very largely largely on on the the guidebook guidebook prepared prepared for for that meeting and other guidebooks guidebooks (Cannon (Cannon and and others, others, 1975; 1975; Prinz, Prinz, and and others, others, 1975; 1975;Margeson, Margeson,1989; 1989; Morey, 1989). 1989). For Forthose thosewho whohave havetoured toured the the region region before, before, the the stops stops will will be be largely largely the the same same and and the the rocks rocks familiar; only the interpretations have changed. The stops are arranged, arranged, to to the the extent extent practical, practical, to to view view the the beginning at the base of the the section section and and progressing progressing up-section. up-section. To streamline logistics and stratigraphy beginning minimize driving distances a few stops are out of proper stratigraphic order. 3 �a n - 00 1 1 22 33 44 1 5 miles 5miles 4- C; �frt? + C- 7p2 5 �Stop 1. Enchantment EnchantmentLake LakeFormation Formationand andArchean Archeanvolcanic volcanic rocks. rocks. The Enchantment Lake Formation is is a discontinuous unit at the base of of the Marquette Marquette Range Range Supergroup. ItIt consists arkose, and and slate. slate. Most geologists who have studied it Supergroup. consists of of conglomerate, conglomerate, graywacke, arkose, believe that itit is of of glacial glacial origin, origin, although although that that interpretation interpretation remains remains in in dispute. dispute. It conformably underlies underlies hills immediately immediately south south of of stop stop 1, I, but the Mesnard Quartzite. The The transition transition to the Mesnard can be seen in hills will not be visited on this trip. hip. Immediately north of the Old State State Road are are several exposures of of basal basal conglomerate conglomerate of of the the fragments of of tonalitic tonalitic gneiss gneiss and and greenstone. greenstone. The matrix is Enchantment Lake Formation, containing fragments is rich rich in in chlorite. The The conglomerate conglomerate can can be be seen seen in in sharp sharp vertical vertical contact contact with slaty, highly sheared greenstone greenstone of the underlying Mona Schist (Archean). About About 100 100 feet feet north of the contact, the Mona becomes mostly massive massive greenstone. Both Both the the greenstone greenstoneand and conglomerate conglomerate are are strongly strongly foliated foliated near the contact and and steeply steeply plunging to vertical lineations lineations are are common on on foliation surfaces. surfaces. The contact of the Mona Schist and Enchantment Lake Lake Formation Formation has has been been interpreted interpreted as as aa fault. In In addition to the highly sheared rocks along along the contact, contact, the two units units are are stratigraphically stratigraphically "back "back to to back". back". Pillows in the Mona Schist Schist in in nearby nearby outcrops outcrops are are uniformly uniformly north-facing, north-facing, whereas whereas the the Enchantment Enchantment Lake Lake and overlying formations are south-facing. The present attitude of the rocks is probably a result of vertical The present attitude of rocks is probably a of vertical rise of aafault faultblock blockof ofMona MonaSchist Schistand and passive passive draping draping of of the the Enchantment Enchantment Lake Lake Formation Formation over over the block. block. Stop 2. Mesnard Quartzite Quartzite and and Jacohsvitle Jacobsville Sandstone. Sandstone. In this lakeshore outcrop the Mesnard Quartzite, the basal orthoquartzite unit of of the the Chocolay Chocolay Group, is overlain with with aa sharp sharp angular angular unconformity unconformity by by the the Middle Middle Proterozoic Proterozoic Jacobsville Jacobsville Sandstone. Sandstone. strikes eastward and and dips dips White-weathering vitreous Mesnard Quartzite in beds 4 to 88 inches thick strikes 80°S to vertically. vertically. Cross 80's to Cross beds beds and and ripple ripple marks indicate top direction to the south, in conformance with the position of the quartzite on the north limb limb of the Marquette synclinorium. Reddish Jacobsvillle Jacobsvillle Sandstone Sandstone dips 10-15° 10-15' eastward to southeastward and the contact with the Mesnard is visible at several places on on the the outcrop. Patches of Jacobsville are plastered against the north side of the quartzite outcrop, and on the south side outcrop, and on the south side the contact is steep. Evidently Evidently during during deposition deposition of of the the Jacobsville, Jacobsville, the Mesnard at this locality formed formed a low topographic ridge, much as it does now. Flat-lying Flat-lying Jacobsville Jacobsville is is on the flank of Mt. Mesnard, about about 3/4 miles west of here and 370 feet above current lake level, which indicates a pre-Jacobsville topographic Vs miles relief and ruggedness approximately the same same or or greater than that adjacent to the present present shore shore of of Lake Lake Superior. Superior. 3. Kona Kona Dolomite Dolomite Stop 3. on the the Mesnard Mesnard Quartzite. Quartzite. The formation is mostly dolomite, The Kona Dolomite lies conformably on fine- to to medium-grained medium-grained clastic clastic rocks. rocks. The outcrops on the north siliceous dolomite, and lesser amounts of fineside of the highway show exceptionally exceptionally well preserved sedimentary textures indicative of of aa shallow shallow water water to to intratidal environment, probably open tidal tidal flats at at this this stratigraphic stratigraphic interval. interval. Many beds are algal carbonates with large stromatolites stromatolites exceptionally well displayed and accentuated by differential differential weathering. weathering. visitors. Other Please help preserve these features for future visitors. Other well preserved features features include dessication and rip-up structures, ripple marks, and rip-up beds beds probably probably produced produced by tidal currents. 6 �4. Goodrich Quartzite Stop 4. This stop, for the sake of economizing economizing driving drivingtime, time, isisnot notininproper properstratigraphic stratigraphicorder. order. We We have have temporarily skipped over the Menominee Group and will examine the basal conglomerate of the Baraga Group. At At this this stop, stop,just just south southof ofthe the village village of of Palmer Palmer and and near near the the old old Isabella Isabella Mine, Mine, coarse coarse conglomeratic conglomeratic Goodrich Quartzite are exposed. exposed. The rocks forming the lower part of the Goodrich The Goodrich Goodrich Quartzite, Quartzite, the the basal basal unit unit of the Baraga Group, unconformably overlies the Negaunee Iron-formation. Here Here aa basal basal conglomerate containing clasts of iron-formation iron-formation as as much as 0.5 0.5 m m diameter can be seen. The angular angular clasts clasts have have features features seen. The indicative of brittle fracturing, implying that the Negaunee Negaunee was was well well lithified lithified prior prior to to the the time that that these clasts were eroded. Well Wellrounded rounded clasts clastsof ofvein vein quartz quartz are are also also common, common, most most likely likely derived derived from from aa locally locally exposed basement basement terrane. terrane. The lack of other basement rock types in clasts may mean that the surface of The lack of in clasts may mean that the surface of vein material material persisted persisted in coarse fragments. The exposed basement rocks was deeply weathered so that only vein The exposures seen here are only a few feet above the unconformity and and Negaunee Negaunee Iron-formation Iron-formation was mined from small pits immediately immediately south south of of the the outcrop. outcrop. Conglomerate Conglomerate units such as seen here are typically lenticular. They range up to a few hundred feet thick locally but pinch out along strike so that quartzite commonly lies on the Negaunee with with little or no conglomerate. The Thecoarse coarseconglomerate conglomeratelenses lenses may mayhave have been been alluvial alluvial fans fans along along the the scarps scarpsof offaults faultsthat that were active during deposition. The Thefeatures featuresseen seenhere here suggest suggestaa rather rather long long time time interval interval across across the the unconformity and renewed deposition during reactivation reactivation of basement faults. One One interpretation interpretation isisthat that the the Menominee Group was deposited during continental margin and that the Baraga Group, continental breakup on a rifting margin beginning with the Goodrich Quartzite, was deposited deposited in in aa foreland foreland basin basin at at the the outset outset of of collision collision with with volcanic terranes now now seen seen in in northern northern Wisconsin. Wisconsin. 5. Chocolay Group and lower Group (Ajibik Quartzite Quartzite and Siamo Slate) lower part part of of Menominee Group Stop 5. The series of roadcuts along U.S. Highway much of the the stratigraphy stratigraphy of the the lower part of Highway 41 exposes much the Marquette Range Supergroup. The Theeasternmost easternmost cut cut shows shows aa few few tens tens of of feet feet of of green green chloritic chloritic slate slate Formation. Here mapped as the upper part of the Enchantment Lake Formation. Here the the Enchantment Enchantment Lake Lake differs differs significantly from that seen at stop I1 in in being being much much thinner, probably not much thicker than the section section exposed here, and it lacks conglomerate beds. The The Enchantment Enchantment Lake Lake grades grades over over aa few few feet feet into into the the overlying vitreous quartzite of the Mesnard Mesnard Quartzite, essentially similar similar to to that that seen seen at at stop stop 2. 2. The The Ajibik Ajibik Quartzite is exposed in the next set of roadcuts to the west. Although Although similar similar in in appearance appearance to to the the Mesnard, Mesnard, the Ajibik in general is somewhat more feldspathic. The The geology geology near near here here was was mapped mapped in in detail detail by by Willard Willard Puffett Puffen to document the rdationship relationshipbetween between the the two two quartzite quartzite units. units. Puffett Puffett was was able able to to trace trace aa distinctive distinctive granule bed, about 10 Ajibik and show that the the Ajibik Ajibik cuts across the 10 inches inches thick near the base of the Ajibik Mesnard at a low angle, demonstrating the angular unconformable nature of the the contact. contact. The The thinness thinnessof ofthe the Chocolay Group here and the absence of the Kona Dolomite reflect reflect the westward westward beveling of the group by the Ajibik. Within Withinaamile milewest westof ofhere herethe theChocolay ChocolayGroup Group isis absent absent and and the the Ajibik Ajibik rests rests directly directly on on Archean rocks. The Ajibik grades upward into the Siamo Slate seen in in roadcuts roadcuts about about 1000 feet feet farther farther west west on the south side ofthe of the highway. highway. The The Siamo Siamo is is a lithologic lithologic mixture of slate, slate, arkosic arkosic quartzite, and graywacke, generally in beds from a few inches to a few feet thick. thick. The The rock rock here here has has aa prominent prominent cleavage cleavage that that dips dips southward more steeply than bedding, consistent with the location location on the north limb limb of of the the Marquette Marquette synclinorium. An An interesting interesting and and controversial controversial feature feature of of this outcrop outcrop is is lenses lenses of graywacke that lie lie within 7 �the cleavage and transect bedding. Various Variousauthors authors have have interpreted interpreted these these as as clastic clastic dikes dikes or or as as lithified lithified beds beds tectonically forced into into cleavage cleavage planes. planes. Stop 6. 6. Negaunee Iron-formation (carbonate fades) facies) This stop, near the old Athens Mine, shows carbonate carbonate facies facies iron-formation iron-formation typical typical of of much much of of the the lower lower part of the Negaunee Iron-formation. Iron-formation. The here consists consists mainly mainly of of alternating alternating laminae laminae of of The iron-formation iron-formation seen here sideritic carbonate and 5% minnesotaite, which imparts a and chert, chert, but but some some layers layers contain contain as as much much as as 115% greenish color. Some Somelayers layerscontain contain small smallamounts amounts of of magnetite, magnetite, but but in in general general the the rock rock isis only only weakly weakly foot thick, are are also also present present in in the exposure. exposure. magnetic. Thin Thin sills sillsof ofaltered altered metadiabase, metadiabase, less less than than aa foot This exposure provides striking striking examples of the effects of of surface surface weathering weathering and and oxidation oxidation and and replacement of sideritic iron-formation. iron-formation. The The weathering weathering has has taken place in in the relatively few decades decades since since the road cut (originally a railroad cut) was excavated. Oxidation Oxidation has has advanced advanced inward inward from from cracks cracks and and exposed surfaces, first converting converting layers layers rich rich in in carbonate carbonate into into yellow yellow brown brown to to reddish reddish brown brown goethitic goethiticiron iron laminae into iron iron oxide. oxide. These oxide, and eventually changing even chert laminae These surficial surficial effects effects are analogous analogous to to those that formed the "soft ores" of the region. The major ore bodies in the eastern end of the iron range, The major ore bodies in the eastern end of the iron range, including those in the immediate immediate vicinity vicinity of of this stop, stop, were replacement masses of of iron iron oxides oxides and and hydroxides formed by low low temperature alteration alteration of of carbonate carbonate and and silicate silicate iron-formation iron-formation accompanied accompanied by by dissolution and replacement replacement of of chert. chert. Stop 7. Negaunee Negaunee Iron-formation (hematite-jasper (hematite-jasper fades) facies) Classic exposures exposures of of the jaspillitic upper upper part part of of the the Negaunee Iron-formation Iron-formation are are seen seen on on Jasper Jasper Knob. Knob. These exposures just north north of of the the major major fold fold axis of the exposures are in in the central part of the Marquette synclinorium, just district. The Theknob knob itself itself isison on aa west-plunging west-plunging anticline anticline so so that the base of the Goodrich Goodricb Quartzite wraps around the west end of the knob and is is exposed in in some of the fenced mined areas areas near near the the base base of of the the west west slope. The alternating thin thin beds beds of of specular hematite and bright The iron-formation iron-formation here here characteristically characteristically has alternating jasper. Specularite red jasper. Speculariteplates plates are are strongly strongly oriented oriented parallel parallel to bedding in the hematitic layers. Folds having drag folds on their limbs and themselves being drag folds on the limbs of still still larger larger folds are strikingly shown shown in in many many exposures. exposures. Fold axes are horizontal horizontal to to gently gently plunging. plunging. Small breccia zones are common and appear to lie roughly along axial axial planes planes of of folds. folds. In these zones fractured jasper beds are surrounded by crystalline hematite. hematite, theories have have been been advanced advancedfor forthe theorigin originofofthejaspillite. oxidation of Two theories the jaspillite. One advocates oxidation siderite-chert iron-formation iron-formation during the post-Negaunee erosional interval and its recrystallization recrystallization to to Penokean deformation deformation and and metamorphism. metamorphism. This theory accounts for patches of specularite-jasper during Penokean specularite-jasper within carbonate facies iron-formation near contacts between the two rock types, types, as, as, for for example, in the Cliffs Shaft mine about '/2 ¼ mile mile to to the the west. west. The second theory advocates a primary origin for the hematite and jasper in in a more more oxidizing oxidizing depositional depositional environment than that responsible responsible for for carbonate carbonate iron-formation. The Theeven-bedded even-bedded and and thin-bedded thin-bedded nature nature of of the jaspillite on Jasper Knob is very similar to iron-formation. ItIt contrasts the bedding characteristics of carbonate iron-formation. contrasts sharply sharply with wavy bedding and oolitic structure common common in injaspillite jaspillite elsewhere elsewhere in the district. district. At At the the Kloman Kloman Mine, near Republic (stop 10), lo), a convincing case can be made made for aa primary primary depositional depositionalorigin originofjaspillite. ofjaspillite. Here, at Jasper Knob, an origin origin by oxidation of carbonate iron-formation iron-formation is more possible. 8 �Stop 8. Michigamme Michigamme Formation, Formation, lower lower slate slate member. member. black sulfidic slate well well represented by the The lower part of the Michigamme Formation consists of black outcrops along the south side of Highway 41. This Thisoutcrop outcropisisnear near the the axis axisof of the the Marquette Marquette synclinorium, synclinorium. Subtle beds show mostly low dips and gentle folds with nearly horizontal axes. A A steep steepaxial axial plane planecleavage cleavage is well developed. Very Very fine-grained fine-grained pyrite pyrite is is abundant in many beds. This This black black slate slate facies facies lies lies on on the the Goodrich Quartzite and is overlain by the Greenwood Iron-formation Iron-formation Member, a lean silicate-magnetite iron-formation. iron-formation. Stop 9. Michigamme Michigamme Formation, Formation, Clarksburg ClarksburgVolcanics Volcanics Member. Member. The Clarksburg Volcanics is is a local unit resting on the Greenwood Iron-formation Member. The volcanic rocks are restricted to the south limb of the Marquette synclinorium, where they are exposed along length of about about 15 miles miles and and range range up upto toabout about 1I mile mile thick. thick. The absence of volcanic rocks on the a strike length away, shows that that deposition deposition in in the the Marquette trough trough north limb of the synclinorium, only a few kilometers away, was very assymetrical at this time and and that that the the trough trough was was probably probablymuch muchdeeper deeperon onthe thesouth. south. Lenses of lean iron-formation horizons throughout throughout the the volcanic volcanic section section indicate that that iron-formation at numerous stratigraphic horizons volcanism was mostly or or entirely entirely submarine. submarine. The volcanics are almost exclusively mafic and pyroclastic. pyroclastic. This This outcrop outcrop along alongthe the north north side sideof ofthe the which layering is shown shown distinctly by by variations in abandoned railroad grade is representative of the unit in which highly vesicular mafic rock, rock, and and the the matrix is rich in fragment size, most fragments are angular pieces of highly carbonate minerals. Fragments of argillite and chert are also present. Rocks here are Fragments of argillite and Rocks here are metamorphosed metamorphosed to to garnet grade and original mafic minerals are converted to amphibole and biotite. biotite. In In spite spite of ofthe the recrystallization, original igneous textures are very well preserved, even at microscopic microscopic scales. Low Low outcrops south of the railroad grade show lean, impure iron-formation typical of lenses that that are widespread iron-formation typical in the the Clarksburg Volcanics. Volcanics. The rocks consist of of alternating alternating layers layers of of magnetic magnetic biotite biotite argillite argillite and and siliceous in beds with abundant abundant fine-grained fine-grained muscovite. muscovite. Stop 10. Negaunee Iron-formation at a t Kioman Kloman Mine. Mine. the Negaunee Negaunee Iron-formation. Iron-formation. Interbedded Exposures here are of the uppermost units of the Interbedded on on aa scale scale iron-formation, aa wavy-bedded, wavy-bedded, oolitic oolitic jaspillite jaspillite of one to three feet are two contrasting lithologic types of iron-formation, and even-bedded cherty grunerite-magnetite gmnerite-magnetite iron-formation. The The features features seen seen in in this this exposure exposure were were instrumental in Hal James' formulation formulation in in the 1950's 1950'sof ofhis his concepts concepts of of sedimentary sedimentary facies facies of ofiron-formation iron-formation mineral assemblages assemblages during during high high grade grade metamorphism. metamorphism. A as well as oxygen-buffering by contrasting mineral A critical feature feature very well shown shown here here isis aa correspondence correspondence between between bedding bedding characteristics characteristics and andoxidation oxidation state. Relatively Relatively reduced reduced rocks, rocks, now now grunerite-magnetite grunerite-magnetite assemblages, assemblages, are invariably invariably in thin, even beds, beds, probably reflecting deposition in in quiet, quiet, poorly poorly oxygenated oxygenatedwater. water. Interbeds ofjaspillite ofjaspillite invariably invariably show show irregular wavy wavy beds and oolites are common, common, especially especially in in thicker thickerjasper jasper beds. beds. These These units are are believed believed to to formed in agitated, more oxygenated oxygenated water. water. James have formed James used used this correspondence of sedimentary sedimentary features features and mineral assemblages to argue argue that the different different lithologies lithologies and and their oxidation oxidation states, states, although although metamorphosed to sillimanite grade grade here, here, still still reflect reflect differences differences in in primary primary depositional depositional settings. settings. 9 �Stop 11. Michigamme Michigamme Formation. the Michigamme Michigamme Formation Formation in in the the axis axis of the the This roadcut shows very highly deformed deformed schist of the northwest-plunging Republic trough. The The rock rock here here consists consists of of iron-rich iron-rich metasediments, now now consisting of of biotite-garnet-amphibole schist. The The light-colored light-colored bladed bladed amphibole amphibole is is commonly commonly mistaken for for sillimanite, sillimanite, but although this exposure is is within the sillimanite sillimanite metamorphic zone, detailed petrographic petrographic examination examination failed to find sillimanite in this outcrop. Thicker has failed Thicker beds, beds, up up to a few few inches, inches, of impure impure quartzite form form readily traceable marker beds and reveal very tight folds with amplitudes many times greater than beds and reveal very folds with amplitudes many times greater than wavelength, and highly attenuated limbs. Fold Fold axes, axes, even even in in adjacent adjacent folds, folds, diverge diverge by by as as much much as as 600. 60'. The The compression of of the the metasediments metasediments between between two two blocks blocks of of very tight folding is caused, in large part, by compression Archean gneissic rocks that flank flank the Republic Republic trough on on the northeast northeast and and southwest southwest sides. sides. References Cannon, W.F., Gair, J.E., Klasner, J.S., and Boyum, B.H., 1978, Marquette Marquette Iron Iron Range: Range: Twenty-First Twenty-First Annual Institute on Lake Superior Geology, Field Trip Guidebook, p. 125-173. 125-173. Prinz, W.C., Gair, J.E., and Cannon, W.F., 1975, 1975, Greenstone: Twenty-First Annual Institute Institute on on Lake Lake p.41-85. Superior Geology, Field Trip Guidebook, p. 41-85. and metal metal occurrences, occurrences, Michigan's Michigan's upper peninsula: Society of Margeson, G.B., 1989, Precambrian Precambrian geology and Economic Geologists Geologists Fall Field Conference, 154 154 p. Morey, G.B., 1989, 28"' International Geological 1989, Early Proterozoic rocks of the Great Lakes region: 28th 63 p. Congress Field Trip Guidebook T145, T145,63 10 �Field Field Trip Trip22 Archean ArcheanIshpeming IshpemingGreenstone GreenstoneBelt Beltand andGold Gold Mineralization, Mineralization,Michigan Michigan Leaders: Leaders:T.J. T.J.Bornhorst, Bornhorst,DJ. D.J.Duskin, Duskin,ftC. R.C.Johnson, Johnson,R.A. R.A. Mahin, Mahin,T.O. T.O.Quigley, Quigley,and andG.W. G.W.Scott Scott 11 �An Introduction Introduction to to the the Archean Archean Ishpeming Ishpeming Greenstone GreenstoneBelt, Belt, Michigan Michigan Rodney Johnson & & Associates, Associates, Inc., 1550 1550 Baldwin Baldwin Ave., Ave., Negaunee, Negaunee, MI MI Rodney C. Johnson, Rod Johnson 49866 Theodore of Geological Theodore J. J. Bornhorst, Bornhorst, Department Department of Geological Engineering Engineering and and Sciences, Sciences, Michigan Technological Technological University, University, Houghton, Houghton, MI MI 49931 49931 Introduction Introduction The Ishpeming belt (IGB) (1GB)covers coversan anarea area of of about about 300 300 km2 km2 and and is located Ishpeming greenstone greenstone belt located in Michigan's Upper Upper Peninsula. Peninsula. It is is on on the the southernmost southernmost edge of the Superior Superior province and is is part of the composed of of tholeiitic tholeiitic pillowed pillowed basalt basalt the Wawa Wawa subprovince subprovince (Figure 1). 1). The belt is composed flows and lesser amounts to felsic volcanic flows amounts of intermediate intermediate to volcanic rocks rocks and minor minor clastic clastic and and chemical sedimentary sedimentary rocks. rocks. The 1GB IGB is about 2,700 2,700 Ma Ma (Bornhorst (Bornhorst and and Johnson, Johnson, 1998; 1998; Hammond, 1978). 1978). The The1GB IGB is is north north of of the the Great Great Lakes tectonic zone, an Archean Archean continentcontinentcontinent In Michigan, the Archean rocks south Michigan, the Archean rocks south of the the Great Great Lake Lake continent suture suture (Sims, (Sims, 1991). In tectonic tectonic zone zone are composed composed of old old Archean Archean gneiss gneiss and and migmatite migmatite intruded intruded by younger younger Archean granites granites and and is is part part of of the the Minnesota Minnesota River River Valley Valley Subprovince Subprovince(Sims, (Sims,1996). 1996). Tholeiitic to caic-alkalic calc-alkalic volcanism volcanism of of the the 1GB IGB belt resulted resulted from from north-directed north-directed subduction subduction (Hoffman, 1989; Card, 1990) Archean time. Successive Archean Archean accretion resulted in 1990) during Archean southward younging younging of of greenstone greenstone belts belts in in the the Superior Superior province. province. The Great Lakes tectonic tectonic zone (GLTZ) km long longArchean Archean paleosuture paleosuture (Sims, (Sims, 1991), 1991), the the most most significant significant (GLTZ) is aa 1,000 1,000km Archean boundary within within the the U.S.A. U.S.A. Sims Archean tectonic tectonic boundary Sims (1991) (1991) has has studied studied aasignificant significant shear shear zone, just south south of of the the 1GB, IGB, that he has interpreted as the only exposed segment of of the the GLTZ GLTZ (Figure 1). The buried. A The Minnesota Minnesota segment segment of the GLTZ is buried. A result result of of detailed detailed and andregional regional field studies, studies, including including structural structural geology, geology, is is the the synthesis synthesis of of the the lithostratigraphy lithostratigraphyof ofthe the1GB IGB in close close proximity proximity to to the the Great Great Lakes Lakes tectonic tectonic zone. zone. Structure Structure stratigraphic correlation correlation depends depends on on good good understanding understanding of of deformation deformationhistory. history. Accurate stratigraphic studies have have shown shown that that the the rocks rocks of of the the 1GB IGB have been effected by six periods of of Recent studies deformation (Table (Table 1)(Johnson, l)(Johnson, 1993; 1993;Nachatilo Nachatilo and and Bauer, Bauer, 1993). 1993).D1 Dldeformation deformation Archean deformation produced axial-planar cleavage (Johnson produced recumbent folds with a flat-lying penetrative, nearly axial-planar and Bornhorst, 1991). 1991). D2 D; deformation deformation produced large-scale strike-slip strike-slip shear shear zones zones that that Dadeformation deformation produced produced upright uprightfolds folds define the the boundaries boundaries of of lithostratigraphic lithostratigraphic blocks. blocks. D3 define axial-planar cleavage cleavage that is is developed best best in in felsic felsic volcanic volcanic (Figure 2) with a near-vertical axial-planar D4 deformation is associated with the intrusion of late interflow sedimentary units. D4 and interfiow trondjhemite-granite suite suite plutons plutons that that reorient reorient earlier earlier fabrics. fabrics. D5 Dsdeformation deformation produced produceddipdiptrondjhemite-granite slip motion in shear shear zones. zones. D6 D6 deformation deformation produced produced crenulation cleavage, cleavage, local local kink kink bands, bands, Archean rocks rocks of of the the 1GB IGB were not significantly deformed TheArchean and strike-slip shear zones. The Orogeny (Nachatilo (Nachatilo and and Bauer, Bauer, 1993). 1993). during the Early Proterozoic Penokean Orogeny strata of the southwest southwest block (Figure (Figure 2) 2) form form aa steeply steeply west-plunging synformal synformal The strata This fold foldisisdefined defined by by the the orientation orientation of bedding. Fieldwork Fieldwork has has identified identified northnorthanticline. This 12 �' I '00 700 I I 700KM Explanation Explanation Phanerozoic Phanerozoic 111111 - Precambrian Precambrian 1----] Middle Proterozoic Proterozoic volcanic and sedimentary sedimentary rocks rocks Early Proterozoic Proterozoic sedimentary and volcanic rocks V//A - Grenville front boundary boundary fault fault Sedimentary rocks rocks -- Fault Margins of Great Lakes Lakes tectonic tectonic zone; zone; short dashed where inferred inferred or or covered covered greenstone-granite complexes Archean greenstone-granite complexes Archean gneiss gneiss and and local local granitoid granitoid rocks rocks Regional geologic setting of the Archean Ishpeming greenstone belt and Archean Figure Figure 1: Regional Great Lakes tectonic zone. 13 �____ 87°30' - 0 I T. 50 2 Mi. 0 1 2 3 K m . N T. 49 N ++++++ T. ++++++ +++++++ 48 N. 46°30 Explanation Explanation Mona Mona Formation Formation Upper tuff unit lapilli-tuff unit unit and and lapilli-tuff IN '1 Basalt flow unit unit Kitchi Formation Kitchl Formation Tuff unit and lahar I- — — —l lahar unit unit Basalt flow unit Proterozoic Proterozoic Sedimentary Sedimentary rocks rocks Archean Archean Intrusive Rocks intrusive Rocks Granodiorite k'."J Granodiorite Ii Tonalite Tonalite Deer Lake Lake Peridotite Peridotite P Sedimentary Rocks Rocks £S&S1 Timiskaming-type Timiskaming-type sedimentary sedimentary rocks Volcanic Rocks Rocks Lighthouse Lighthouse Point Point Basalt Basalt Basalt Basalt V//I Reany Lake pyroclastic Reany Lake pyroclasticunit unitand and Fire Center mine iron-formation iron-formation unit unit PL.JLJ Nash Creek glomerophyric glomerophyric basalt unit unit a I\ /1 0 I I a I Bedding Bedding Overturned Overturned bedding bedding Facing of pillows pillows 'C Plunging anticline anticline syncline 'C Plunging syncline Plunging overturned anticline anticline \ Shear zone & - 87 f 87+ A % Figure 2: Generalized Figure Generalized geologic geologic map map of o f the the Ishpeming Ishpeminggreenstone greenstone belt. belt. 14 �Table Table1.1.Summary Summaryofofdeformation deformationsequence sequenceand andvolcanic/magmatic volcanic/magmaticactivity activity and and constraining constraining age agedates datesfor forthe the Ishepming greenstone belt. belt. Event Event - Characteristic Characteristic Volcanic/Magmatic Activity Volcanic/Ma~matic Activity Age Dates Ace Dates Undeformed post-tectonic post-tectonic granite granite 2585 Ma Ma D6 Kink Kink bands bands with with north-easterly north-easterly striking kink kmk planes and steeply plunging hinges D5 Ds Dip slip motion along shear shear zones. D4 D4 Folding associated Folding associated with with intrusion of plutons. plutons. D3 Upright Upright folding. folding. Appinite suite D2 Strike-slip Strike-slip shearing. shearing. Trondjheniite-granite suite Trondjhemite-granite DI Recumbent Recumbent folding. folding. Tonalite suite Extrusion of mafic and felsic volcanic rocks. 15 2668.4+2.11-1.8 Ma 2668.4+2.1/-1.8 2705.8+/-1.6 Ma �northeast-lacing beds in tuffaceous tuffaceous units on the northern northern limb limb of of th'is this D3 D3fold. fold. Tuffs Tuffs of and northeast-facing the southwest block have a well-developed axial planar foliation foliation (S4. (53). Pillow basalts of of the the southeast block consistently consistently young to the north and and have have aa poorly poorly developed developed cleavage. cleavage. Interfiow sedimentary rocks rocks dip dip steeply steeply to to the the north. north. Tuffs that overlie the basalts basalts have two Interflow well-developed cleaviges cleavages that defini define a-moderately a moderately plunging plunging D3 D3synform. synform. The The strata of the well-developed sedimentary and felsic volcaniclastic volcaniclastic rocks define a north block have been re-folded, and sedimentary pattern (Johnson (Johnson and and Bornhorst, Bornhorst, 1991). 1991). The low density of broad Z-shaped outcrop pattern sedimentary rocks necessitates relying on pillows pillows in pillow pillow lava for defining younging directions (Figure 2). AAwell-developed well-developed foliation foliation in in amphibolite-facies amphibolite-faciesbasalt basalt was was subsequently refolded by D3 deformation. deformation. D3 folds are are upright, upright, open open to to tight tight and have D3 folds shallow to steeply plunging fold axes. axes. Stratified Rocks Stratified lithostratigraphic blocks that comprise Bornhorst (1988) subdivided the 1GB IGB into three lithostratigraphic comprise units bounded boundedby bydeformation deformationzones zones (Figure 3). 3). As internally consistent stratigraphic units As aa whole, the belt is bounded to the south by Early Proterozoic Proterozoic sedimentary rocks along the Carp River Falls shear zone, a structure that was active from the Archean Archean through the Proterozoic (Puffett, 1974). 1974). The Thesouthwest southwest block block isis bounded bounded to to the the west west by by Archean Archean granitoid rocks. This Thiscontact contact may may be be aafault fault since since the the boundary boundary is is not not transitional transitional lit-par-lit lit-par-lit as found near the intrusive greenstone-granitoid contact of of the the north north block block of of the greenstone greenstone-granitoid contact belt (Johnson and Bornhorst, Bomhorst, 1991). The The Carp Carp River River shear zone separates the southwest interpreted to be a dextral shear zone with uncertain block from the southeast southeast block. It is interpreted displacement. The stratigraphic displacement. The dextral dextral Dead Dead River River shear shear zone separates separates the two southern southern blocks from the north block. The north block is bounded bounded to the east, north north and west by Archean granitoid rocks that have intrusive relationships relationships with with the volcanic rocks rocks (Wilkins and Bornhorst, 1992; 1992; Johnson and Bomhorst, Bornhorst, 1991). 1991). Southwest Block The southwest block is composed of mafic flows and intermediate to to felsic volcanic and volcaniclastic rocks of the Kitchi Formation which are subdivided into vokaniclastic into three three informal informal units: units: basalt flow, tuff, and lahar units (Figure 44 and 5). The The basalt flow unit, at at the base of of the the Kitchi Formation is composed of 1,800 1,800 meters of dominantly pillowed basalt flows, flows, but but includes massive basalt flows as well. The The basalts basalts are are dominantly dominantly magnesian tholeiites tholeiites composed of hornblende-actinolite-albite-chlorite-clinozoisite hornblende-actinolite-albite-chlorite-clinozoisitewith minor amounts amounts of of sphene, sphene, magnetite, and (or) pyrite. The The base base of of the the basalt basalt flow flow unit unit is is in probable fault fault contact contact with with beds of of chert and and dacite dacite to to rhyolite rhyolite tuff tuff are are interlayered interlayered Archean granitoid rocks. Several thin beds basalt flow unit. Near near the middle of the hasalt Near the the top ton of of the the basalt flow flow unit is is aa 30-meter30-meterplagioclase phenocrysts phenocrysts up up to to 22 cm cm in in diameter. diameter. The The thick glomerophyric flow containing plagioclase uppermost basalt flows intercalate with intermediate volcanic rocks of the overlying tuff intermediate overlying unit. - - tuff unit. Formation is composed composed of of 5,000 meters meters of of tuff tuff with with lesser lesser amounts amounts ~Thei tuff e unit of the Kitchi Formation of interlayered lahar with the thicker beds of lahar separated separated into into the the lahar lahar unit. unit. The The tuff tuff unit unit ash tuffs, tuffs, dominantly dominantly calccalcand lithic lithic tuffs, with minor lapilli-ash and ash consists of crystal and alkalic andesite in composition. The Therocks rocks are are schist schist composed composed of of quartz-feldspar-sericitequartz-feldspar-sericitechlorite containing quartz and feldspar phenocrysts. phenocrysts. Pillowed Pillowed basalt basalt flows flows interfinger interfinger with with 16 �T 50 N T 49 N T 48 N 4630 R2SW R2JW 0 R26W 5 111111 R25W 10 KILOMETERS Explanation Explanation Middle Proterozoic Proterozoic (900-1,600 (900-1,600 Ma) Ma) Metavolcanic rocks Metavolcanic rocks LAttJ ,Jacobsville JacobsvilleSanstone Sanstone(Midcontinent (Midcontinentrift rift system) system) Early Proterozoic Proterozoic (1,600-2,500 (I ,600-2,500 Ma) Ma) I Sedimentav Sedimentary rocks 0 rocks of of Marquette MarquetteRange RangeSupergroup Supergroup I Archean -- - Contact Contact +f - Shear zone Approximate trace of of axial axial plane of plunging plunging anticline anticline +i f- Approximate trace of axial axial — plane planeof ofplunging plungingsyncline syncline I÷++4 Granitoid Granitoid rocks rocks Figure 3: Lithostratigraphic Figure Lithostratigraphicblocks blocks of the the Ishpeming Ishpeminggreenstone greenstone belt. belt. 17 �8r4 8fl0 AAA A Y 4t32'30" 66 A AA A Aa A A'St'/?s —4 A A A A A A A'S {/? z A A A A A 2- A A A A A% M&io - - r4 2' - A A 'a a FJA.Je5 A C - - eq -, -— aa , V 0lshpemiig e3cy 0 88 KILOMETERS KILOMETERS 0 I Explanation Explanation Early Proterozoic Proterozoic 0Undifferentiated Undifferentiated metasedimentary metasedimentary rocks rocks I LAAAAAJ Tuff unit Tuff unit ---- Basalt flow flow unit unit Basalt + App~ximate Approximate trace of axial plane of anticline anttcl~ne I Archean Archean - Contact Contact Undifferentiated Undifferentiatedrocks rocks —r Metagabbro Metagabbro 65 Strike and dip dip of of beds beds "- Shear zone Shear zone Deer Lake Peridotite Peridotite Kitchi Formation Formation Lahar unit unit #— Note: All rocks are metamorphosed metamorphosed Figure 4: 4: Generalized geologic map of southwest block block of the Ishpming n s t o n e belt. Mi. of the southwest lshpeming p greenstone 18 �METERS METE1 0 0 500 500] 1000 1000 Tuff unit Lahar unit unil unit cc: Lahar unit J Basalt flow unit Formation within the southwest block Figure Figure 5: Generalized stratigraphy of the Kitchi Formation of the Ishpeming greenstone greenstone belt. belt. 19 �the tuff unit near the top and base of the unit. The Thelahar lahar unit unit of of the the Kitchi Kitchi Formation Formation isis composed of of beds and and lenses lenses of of polymictic volcanic conglomerate containing clasts of thinly laminated, laminated, porphyritic, porphyritic, and and holocrystaline holocrystaline rocks that are calc-alkalic andesite to dacite dacite in in composition. The polymict volcanic volcanic conglomerates conglomerates are are more more common near the base of the Thepolymict tuff unit unit and and are are interpreted interpreted as as lahar lahar deposits deposits (Bornhorst (Bomhorst and andJohnson, Johnson,1993). 1993). Southeast Southeast Block Block The southeast southeast block is is composed of basalt flows and felsic volcanic and volcaniclastic rocks of the Mona Formation, which which is subdivided subdivided into informal units: basalt flow, lapiffi-tuff, and and upper tuff units (Figure 6). The Thebasalt basalt flow flow unit, unit, at at the the base of the Mona Formation, is a 5,500-meter-thick 5,500-meter-thick sequence of pillowed with minor massive basalt flows. The basalts are dominantly magnesian tholeiite basalt flows. Within the basalt flow unit are thin interfiow interflow chert-magnetite iron formations and schistose schistose quartz-sericite quartz-sericiterocks rocks (tuffs). (tuffs). The most notable occurrence of interflow sedimentary sedimentary rocks in the Mona Formation occurs north of the Pine Hill Hill Quarry Quarry (Figure (Figure 6). 6). At Atthis thislocation, location,chert-magnetite chert-magnetiteand andchert-pyrite chert-pyriteiron-formation iron-formationare are intercalated with graphite and quartz-sericite schist (tuffs) (tuffs) as as interflow interfiow units. units. Diamond quartz-sericite schist drilling drilling along along this interval interval has indicated that these units have a combined thickness of approximately approximately 10 10 meters. meters. The Thelapilli-tuff lapilli-tuffunit unitoverlies overliesthe thebasalt basalt flow flowunit unit (Figure (Figure7) 7)and andisis composed of calc-alkalic rhyolite lapilli in a quartz-sericite-chlorite matrix supporting quartz of calc-alkalic quartz-sericite-chlorite and, less commonly, feldspar phenocrysts. This unit is interpreted as subaqueous pyroclastic flow and fall fall deposits deposits (Bornhorst (Bornhorst and Johnson, 1993). 1993). The Thelapilli-tuff lapilli-tuff unit unit grades gradeslaterally laterally and vertically into the upper tuff unit. This quartz-feldspar-sericiteThisunit unitisiscomposed composedof of quartz-feldspar-sericitechlorite chlorite schist schist with with aa bulk bulk calc-alkalic calc-alkalic dacite dacite composition. composition. It is interpreted as interbedded tuffs tuffs and and volcanic volcanic derived derived graywacke (Bomhorst and Johnson, 1993). The The combined combined thickness thickness of of these these felsic felsicvolcanic volcanic and andvolcaniclastic volcaniclastic units units isis900 900meters. meters. North North Block Block The The north north block block isis composed composed of of the the 3,100-meter-thick 3,100-meter-thick Lighthouse Point Basalt (Figure 8). 8). The Lighthouse Point Basalt is dominantly pillowed tholeiitic-magnesian basalt flows with The Lighthouse Point Basalt is dominantly with minor minor massive massive flows. flows. AAglomerophyric glomerophyric(Nash (NashCreek) Creek)basalt basaltflow flowoccurs occursnear nearthe thebase base (Figure 9). 9). Within Withinthe theLighthouse LighthousePoint PointBasalt, Basalt,the theReany ReanyLake Lakepyroclastic pyroclastic unit unitisiscomposed composed (Figure of interbedded interbedded ash ash to to lapilli lapilli ash ash tuffs tuffs of of caic-alkalic calc-alkalic dacite composition. ItItisisininturn tumoverlain overlain of by thinly bedded chert-magnetite chert-magnetiteiron-formation iron-formation by the the Fire FireCenter Centermine mineiron-formation iron-formationunit unit—- aa thinly with with lesser lesseramounts amountsof ofassociated associatedchlorite-magnetite chlorite-magnetite schist schistand andchert-pyrite chert-pyrite iron-formation. iron-formation. Over-lying Over-lyingthe the iron-formation iron-formation isisintercalated intercalated chlorite-carbonate-feldspar chlorite-carbonate-feldspar and andquartz-chlorite quartz-chlorite schist schist (tuffs). (tuffs). Above Aboveand andbelow belowthe theiron-formation iron-formationare areisolated isolatedlenses lensesand andpods podsof ofgraphitegraphitepyrite pyrite schist. schist. This Thisinterval internalofofsedimentary sedimentaryrocks rocksisispoorly poorlyexposed, exposed,but buthas hasan anestimated estimated thickness thickness of of approximately approximately 100 100meters. meters. The TheReany ReanyLake Lakepyroclastic pyroclastic unit unitalso alsocrops cropsout outinin the the vicinity vicinity of of Hills Hills Lakes Lakes where where itit is is composed composed of lapilli and ash tuffs of calc-alkalic dacite to to rhyolite rhyolite composition. composition. The TheLighthouse LighthousePoint PointBasalt Basaltrepresents representsaasuccession successionofofsubaqueous subaqueous tholehite tholeliitebasalt basalt flows flowswith with intercalated intercalated distal distal to to nearly nearly proximal proximal felsic felsic volcanic volcanic rocks rocks (Johnson (Johnson and andBornhorst, Bornhorst,1991). 1991). 20 �3fl5 8740 a 4 ___ -A t ......................... A A A A A A £e/Lt, —— A A fr - & DeadRiver StorageBasin AA 8t25 87% 87'30 \D A A. -- - A A A Ah —---" A A A A A SMarquette -_ 4632 30 - - - -C4 • - - - - - - - "s/i CARP RIVER FALLS SHEAR ZONE 0Negaunee 10lshpeming 4630 10 KILOMETERS KILOMETERS j0 5 0 1 Explanation Explanation 0Undifferentiated Undifferentiated metasedimentary rnetasedimentary rocks rocks I I V//A Lapilli-tuff unit unit Basalt flow unit unit ARCH EAN ARCHEAN - -- L1 Undifferentiated rocks Undifferentiated rocks - Metagabbro Metagabbro Mona Formation Formation '4-+ unit LA.AI Upper tuff unit — Contact--Dashed where concealed concealed Shear zone Approximate trace of axial axial plane plane of of plunging syncline plunging syncline Note: All rocks rocks are metamorphosed metamorphosed Figure 6: Generalized geolgic map of off the Ishpeming greenstone greenstone belt. o f the southeast block o 21 �Upper upper tuff unit *tuff unit Lapilli-tuff Lapilli-tuff unit unit METERS METERS 0 Basalt Basalt * flow flow unit unit 500 1000 Figure 7: 7: Generalized Generalizedstratigraphy stratigraphy of of the the Mona Mona Formation Formation within within the the southeast southeast block block Figure the Ishpeming Ishpeming greenstone greenstone belt. belt. of the 22 �_____ ______ ______ 0 10 5 Explanation Explanation 0Sedimentav rocks of Middle and EaW Proterozoic ages ages Sedimentary rocks of Middle and Early I Fire Center center mine iron-formation and and Reany Lake pyroclastic pyroclastic units units I ARCHEAN ARCHEAN a to a a] Nash Nash Creek glomerophyric glotnerophyric basalt basalt unit unit where inferred - Fault—Dashed Fault-Dashed where inferred --- Reany Creek Reany Creek Formation Formation Granodiorite near Rocking Granodiorite Rocking Chair Lakes Lakes Gneissic granite Gneissic granite to to tonalite tonalite Strike and dip of overturned overturned bedding bedding %5 +f I.. Lighthouse Point Lighthouse Point Basalt Basalt Hills Lakes Hills Lakes pyroclastic pyrodastic unit unit Shear Shear zone zone — '-{T - Approximate Approximate trace of axial plane plane of plunging plunging anticline anticline Approximate Approximate trace trace of of axial axial plane planeof of plunging syncline plunging syncline Figure 8: Generalized geologic map map of of the north block of of the Ishpeming Ishpeming greenstone greenstone belt. belt. 23 �Local unconformil unconformity + Hills Lakes pyroclastic unit unit Main lithology of Lighthouse Point Basalt Fire Center mine iron-formation unit Reany Lake pyroclastic pyroclastic unit unit Nash Creek glomerphyric basalt unit Base unknown unknown Figure 9: Generalized stratigraphy of the Lighthouse Point Basalt within the north block of the Ishpeming greenstone belt. 24 �Stratigraphic Relationships Stratigraphic Relationships Among Among Lithostratigraphic Blocks Blocks Stratigraphic correlations made across major maior shear zones are tenuous. The folded rocks in in the the southwest block comprise a steep westward plunging synformal anticline, with tops to bedding on the north limb facing northward (Figure (Figure 2). 2). Pillows Pillows in in the the southeast southeast block block consistently consist&tly young to the north, thus strata strata of the southeast block could be be interpreted interpreted as as younger than and overlying strata of the southwest southwest block. block. Displacement Displacement along along the the Carp Carp River shear zone may have eliminated eliminated some of of the the stratigraphic stratigraphic section. section. However, itit could could also be argued that the stratigraphy of the southwest and southeast blocks may have been juxtaposed by thrusting along the Carp River shear zone making stratigraphic relationships between them indeterminate but evidence for thrusting is lacking. & The stratigraphic stratigraphic units of the north block and the southeast block face each other other across across the the Dead River Basin, Basin, but but are separated separated by bythe theDead DeadRiver Rivershear shearzone zone (Figure (Figure 2). 2). The strata strata of the southeast block consist of pillowed and massive tholeiitic basalt flows overlain calcoverlain by by calcalkalic tuffs and lapilli-tuff. lapilli-tuff. The alkalic The Lighthouse Lighthouse Point Basalt and the Mona Formation may represent the opposing limbs of a synform. This This is is much much more more speculative speculative than the stratigraphic correlation between the southeast southeast and and southwest southwest block. block. If each block is stratigraphically unique and represents distinct and separate separate strata, strata, the the total total stratigraphic thickness is 16,000 16,000 meters. If all three blocks are correlatable with one another, the cumulative cumulative thickness thichess isis 13,000 13.000meters. meters. Intrusive Intrusive Rocks Rocks have been been intmded intruded by by multiple multiple episodes episodes of of Archean Archean mafic and felsic The rocks of the 1GB IGB have magmas. The and peridotite peridotite sills. sills. The gabbros Theoldest oldest intrusive intmsive rocks rocks are synvolcanic gabbro and are chemically indistinguishable from the surrounding basalt flows and likely represent subvolcanic intmsions intrusions (Bornhorst (Bornhorst and and Johnson, Johnson, 1993). 1993). The Deer Lake Peridotite is intmded intruded subvolcanic between the basalt and tuff units of the Kitchi Formation. Formation. Contacts with surrounding volcanic rocks are conformable, conformable, but lack of quench textures (spinifex), pillow structures, structures, or or other features typical tpical of ultramafic flows lead to the interpretation of the peridotite body as as aa (Bornhorst and and Johnson, Johnson, 1993; 1993; Brozdowski, Brozdowski, 1990, 1990,Bornhorst Bomhorstet et al., al., 1986). 1986). The sill complex (Bornhorst peridotite is lherzolite lherzolite to harzburgite in composition (Rossell, 1983) 1983) and similar to ultramafic ultramafk flows and sills from other Archean greenstone belts. sills from other Archean greenstone belts. The oldest felsic intrusive intmsive bodies are foliated diorite to granite gneiss batholiths that intrude intmde the margins of the greenstone belt. These These intrusions intmsions post-date post-date mafic volcanism in the greenstone belt and were deformed along with volcanic rocks during the earliest stage of quartz-feldspar porphyry dikes cut deformation. Archean granodiorite to syenite stocks and quartz-feldspar greenstone belt and Dzthrough through D4 D4deformation deformation the greenstone and are are interpreted interpreted to tobe besynchronous synchronouswith withD2 (Wilkin and Bornhorst, Bornhorst, 1992). 1992). 25 �Discussion Structural Stmctural studies studies in the 1GB IGB have led to a more accurate picture of stratigraphic thickness within lithostratigraphic Iithostratigraphic blocks and and possible possible correlations correlations between between blocks. blocks. Geological studies prior to 1988 1988 (Bornhorst) (Bomhorst) did not recognize the stratigraphic significance of lithostratigraphic Iithostratigraphic blocks. The Therecognition recognition of of the the synformal synfonnal anticline anticline in in the the southwest southwest block allows the true thickness of the volcanic strata of the Kitchi Kitchi Formation to be estimated 1,500 meter thickness estimated by Morgan at 6,800 6,800 meters, a four fold increase increase over over the the ++1,500 and DeCristoforo (1980). polyphase deformation in the Lighthouse Point (1980). The recognition of polyphase Basalt of the north block lead to a thickness estimate of 3,000 meters, compared to an earlier estimate of 4,500 meters (Morgan (Morgan and DeCristoforo, DeCristoforo, 1980). 1980). The stratigraphy of the 1GB can be be compared compared to tothat thatof ofthe theAbitibi Abitibigreenstone greenstonebelt. belt. In IGB can particular, the volcanic stratigraphy can be compared to the Tisdale Group, which stratigraphy compared the Tisdale Group, which isis composed of komatiites and basaltic komatiites at the base overlain overlain by tholeiitic basalts, calc-alkalic volcaniclastic volcaniclastic rocks rocks (Pyke, (Pyke, 1982). The Tisdale subsequently overlain by calc-alkalic Tisdale Group Group has a total thickness of from 950 to 4,000 meters. The The 1GB IGB has a similar volcanic stratigraphy: tholeiitic basalt (the basalt basalt flow units units of of the the Kitchi Kitchi and and Mona Mona Formations, Formations, and the Lighthouse Point Basalt) at the base, succeeded by calc-alkalic volcaniclastic rocks rocks (the (the tuff unit of the Kitchi Gtchi and and the upper upper tuff tuff unit unit of the Mona Mona Formations, Formations, and and the the Reany Reany Lake Lake pyroclastic unit of the Lighthouse Point Point Basalt). Basalt). The stratigraphy is even more comparable ifif the Deer Lake Lake Peridotite Peridotite represents represents subvolcanic subvolcanic sills sills analogous analogous with with komatiitic komatiitic volcanism. volcanism. Thus, in terms of lithology lithology and and thickness thickness the the stratigraphy stratigraphy of of the the 1GB IGB is directly comparable comparable to the Abitibi greenstone belt. The The1GB IGB represents an Archean volcanic arc assemblage as characterized characterized by Thurston Thurston and and Chievers Chievers (1990). (1990). The environment of deposition is important in identifying identifying potential potential ore deposits deposits with'in within the JOB. Significant occurrences of volcanogenic massive sulfide deposits are not known in the IGB. the 1GB. Chalcopyrite and sphalerite associated with chert in the Reany Lake pyroclastic unit of IGB. Chalcopyrite the Lighthouse Point Basalt was interpreted by Johnson and Bomhorst Bornhorst (1991) as a massive sulfide deposit incorporated incorporated in the pyroclastic pyroclastic flow. flow. Typically, Typically, volcanogenic massive greenstone belts belts that that have have aa greater greater than than average average volume volume of of sulfides are hosted in greenstone volcanic and sedimentary sedimentary rocks rocks (Franklin, (Franklin, 1990). The intermediate volcanic, felsic volcanic The JOB IGB is favorable for VMS deposits because of its considerable considerable stratigraphic stratigraphic thickness. thickness. The The Ropes Ropes 18901s,and more recently from 1985 1985 to to 1989, 1989,is is gold mine, which was in production in the 1890's, 1990). controlled by a shear zone (Bornhorst (Bomhorst et al., 1986; 1986; Brozdowski, 1990). Card (1990) suggested that the Superior province grew by Archean accretion, accretion, and and that that of north directed directed subduction. subduction. A similar sequence of Archean volcanism was the result of of events events could explain the Archean geology of the IGB. 1GB. The mafic to felsic volcanism could have subduction. Extra-belt been the result of northward directed subduction. Extra-belt tonalite tonalite batholiths, batholiths, intra-belt intra-belt granodiorite stocks, and appinite stocks intrude intrude the the greenstone greenstone belt. belt. The transition transition from from subduction to collision is is preserved by the volcanic rocks (subduction (subduction related arc) arc) and and by by intrusive rocks as described by Wilkin and and Bornhorst (1992) (1992) (transition from from subduction subduction to to collision). 26 �1GBcan canbe beplaced placedininan ananalogous analogousmodem modemenvironment. environment. As As a The volcanic strata of the IGB directed subduction subduction thick thick accumulations accumulations of pillowed tholeiitic tholeiitic basalt basalt flows flows result of north directed (basalt flow units of the Kitchi and Mona Formations and the Lighthouse Point Basalt) were were Subsequently, dome dome complexes complexes developed developed on on the the mafic mafic erupted from shield volcanoes. Subsequently, shield volcanoes. Subaqueous pyroclastic and lahar flows (tuff and lahar units of the Kitchi Kitchi Formation, upper tuff and lapilli-tuff units of the Mona Mona Formation, Formation, and and pyroclastic pyroclastic units units of of the Lighthouse Point Basalt) erupted erupted from the dome complexes. The Therocks rocksofofthe the1GB IGB Continent-continent collision collision caused caused the the represent coalescing volcanoes in an arc complex. complex. Continent-continent cessation of volcanism volcanism and and complex complex post-deposition post-deposition deformation. deformation. Summary Summary The Tshpeming Ishpeming greenstone belt consists of subaqueous tholeiitic basalt to calc-alkalic calc-alkalic rhyolite, 10-15 !an in total thickness. thichess. U-Pb U-Pb zircon zircon data data establish establish the the age age of of volcanism volcanism at at 10-15 km 2705.8 +1—i .6 Ma Ma (Bornhorst Johnson, 1998). The 2705.8+/-1.6 (Bomhorst and Johnson, The volcanic rocks were enveloped by tonalite suite suite plutons just before before and and during the beginning of recumbent folding folding (Table (Table 1). 1). Strike-slip Stnke-slip shear shear zones zones and and the the deposition deposition of clastic sediments into pull-apart basins followed followed recumbent folding. The folded. A The belt belt rocks rocks were were then upright folded. A trondhjemite trondhjemite to granite suite suite intruded the belt and folded earlier fabrics. The timing of deformation is constrained with UThe timing of deformation is with Udata yielding yielding an an age age of of 2668.4+2.1/-1.8 2668.4+2.1/-1.8 Ma for an intrusion in this suite suite (Bornhorst (Bornhorst Pb zircon data and Johnson, 1998). 1998). Intrusions Intrusions of of hornblendite homblendite to to syenite syenite (appinite (appinite suite) suite) and and continued continued movement along shear zones represent represent the end of of deformation. deformation. An undeformed post-tectonic granite (Sims,1991). 1991). granite intrusion intrusion has has an an age age of of 2585 2585 (Sims, These events are readily interpreted in a modem modern plate plate tectonic tectonic context. context. North-directed arc. Subduction-related subduction produced a volcanic arc. Subduction-related tonalite intruded the arc just prior to collision of a small km long long small continent continent from from the south (southern complex) along the 1000 1000 kin Great Lakes tectonic zone (suture). Collision Collision occurred occurred over over an an extended period of time with multiple deformation and magmatic events. events. The The appinite appinite suite suite is characteristic of modem collision-related magmatism. magmatism. Continuing Continuingstudies studiesof ofthe the1GB IGB and and vicinity vicinity will will help help to to unravel unravel the tectonic evolution evolution of of the the southern southem edge edge of of the the Superior SuperiorProvince. Province. Acknowledgments Acknowledgments We thank thank Shannon Shannon E. E. Bair Bair for forcomputer computerdrafting drafting of of the thefigures. figures. We References References T.J., 1988, 1988,Geological Geological overview overview of of the Marquette greenstone greenstone belt, Michigan Michigan ThirtyThirtyBornhorst, T.J., annual meeting, meeting, Institute Institute on Lake L&e Superior Geology, Field Trip Guide Books, Books, part part 2, 2, p. p, fourth annual Al-A31. ALA3 1. 1998, Archean evolution of the southern southem edge of the Superior Superior Bornhorst, T.J., and Johnson, R.C., 1998, 30, p. AProvince in Michigan: Geological Society of America Abstracts with Programs, v. 30, 159. 159. and Johnson, R.C., 1993, 1993, Geology of volcanic rocks in the southern half of of the the Bornhorst, T.J. and U S . Geological Survey Bulletin 1904-P, 1904-P, l3p. 13p. Ishpeming greenstone belt, Michigan: U.S. 27 �Bornhorst, T.J., Shepeck, Shepeck, A.W., and Rossell, D.M., 1986, 1986, The Ropes gold mine, Marquette County, Michigan, U.S.A.-- an Archean hosted lode gold deposit: MacDonald, A.J. (ed), (ed.), Proceedings of Gold '86, an International Symposium on the Geology of Gold, Toronto, p.213-227. bend, Marquette greenstone Brozdowski, WA., R.A., 1990, 1990, Ropes pyritic gold deposit in a dilational bend, belt, Michigan: University of Western Ontario, London, Ph.D. dissertation, 592 p. Card, K.D., 1990, 1990, A review of the Superior Province of the Canadian Shield, a product of of Archean Archean accretion: Precambrian 56. accretion: PrecambrianResearch, Research,v.48, v.48,p.99-1 p.99-156. Card, K.D. and Ciesielski, A., A,, 1986, 1986, DNAG No.1. Subdivisions of the Superior Superior Province Province of of the the Canadian Shield. Shield. Geoscience Geoscience Canada, Canada, v.13, v.13, p.5-13. Franklin, J.M., 1990, massive sulphide sulphidedeposits, deposits,inin Ho, Ho, S.E., SE., Robert, 1990, Volcanic-associated massive Robert, F., F., and and Groves D.I. (eds.), Gold and and Base-Metal Base-Metal Mineralization in the Abitibi Ahitibi Subprovince, Subprovince, Canada, Canada, With Emphasis 1-242. Emphasis on on the the Quebec Quebec Segment, Segment,Short ShortCourse CourseNotes, Notes,p.21 p.211-242. Hammond, R.D., 1978, 1978, Geochronology and origin of Archean rocks in Marquette County, Upper Upper Michigan: University of Kansas, Lawrence, Kansas, M.S. thesis, 69 p. University Kansas, Lawrence, Kansas, M.S. thesis, 69 p. Hoffman, P.F., 1989, 1989, Precambrian Precambrian geology and tectonic tectonic history history of North America, America, in in Bally, Bally, A.W., A.W., and Palmer, A.R. (eds.), (eds.), The geology geology of North North America: America: an an overview: overview: Boulder, Boulder, Colorado, Colorado, Geological society society of America, The Geology Geology of North America, America, v.4, v.4, p.447-512. p.447-512. Johnson, R.C., 1993, structural, tectonic, tectonic, and and economic economic studies studies of the Archean Johnson, R.C., 1993, Stratigraphic, Stratigraphic, structural, the Archean Ispheming greenstone belt, Marquette County, Michigan: Michigan Technological University, University, Houghton, Ph.D. Dissertation, Dissertation, 119 119 p. Johnson, R.C. and Bornhorst, of the the Ishpeming Ishpeming Bomhorst, T.J., 1991, 1991, Archean geology of the northern block of Bulletin 1904-F, 20 p. greenstone belt, Marquette County, Michigan: U.S. Geological Survey Bulletin Morgan, J.P., J.P., and and DeCristoforo, DeCristoforo, D.T., 1980, 1980, Geological Geological evolution of the the Ishpeming Ishpeming Greenstone Greenstone Belt, Michigan, Michigan, U.S.A.: U.S.A.: Precambrian Research, Research, v.11, v.11, p.23-41. p.23-41. Nachatilo, Nachatilo, S.A., and Bauer, R.L., 1993, 1993, Structural Structural analyses analyses of Archean Archean rocks rocks in in the theNegaunee Negaunee area, Michigan ---- constraints constraints on Archean versus versus Proterozoic Proterozoic deformation: deformation: U.S. U.S. Geological Geological Survey Survey Bulletin Bulletin 1904-0. 1904-0. Puffett, W. p., U.S. P., 1974, 1974, Geology of the Negaunee Quadrangle, Marquette County, Michigan: U S. Geol. Survey Professional Paper 788, 53 p. Survey Professional Paper 788,53 Pyke, D.R., 1982, Timmins area, District of Cochrane: Ontario Geological Survey 1982, Geology of the Tirnrnins Report 219, 219, l4lp. 141p. Rossell, Rossell, D.M., 1983, 1983, Alteration of the Deer Lake peridotite in the vicinity vicinity of the the Ropes Ropes mine, mine, Marquette County, Michigan: Michigan Technological University, Houghton, Michigan, County, Michigan: Michigan Technological University, Houghton, Michigan, M.S. M.S. thesis, thesis, 83 83 p. p. Subprovince (Archean (Archean Gneiss Gneiss Terrane): Terrane): in in Archean Archean and and Sims, P.K., 1996, 1996, Minnesota River Valley Suhprovince Proterozoic Proterozoic Geology of the Lake Superior Superior Region, U.S.A., U.S.A., 1993: 1993: U.S. U.S. Geological GeologicalSurvey Survey Professional Professional Paper Paper 1556, 1556,p. p. 14-23. 14-23. Sims, P.K., 1991, Great Lakes Lakes tectonic tectonic zone zonein inMarquette Marquettearea, area,Michigan Michigan--implications - implications for for Archean tectonics in north-central United States: U.S. US. Geological Geological Survey Survey Bulletinl9O4-E, Bulletin1904-E, 77 p. p. Thurston, P.C., and Chievers, K.M., 1990, Secular variations in greenstone sequence development, P.C., Chievers, 1990, Secular variations greenstone sequence development, emphasizing emphasizing Superior Superior Province, Province, Canada: Canada: Precambrian Research, Research, v.46, v.46, p. 21-58. 21-58. Geology and and geochemistry geochemistry of of granitoid rocks in the T.3., 1992, Geology Wilkin, R.T., R.T., and Bornhorst, Bornhorst, 713., Archean Northern complex, complex, Michigan, Michigan, U.S.A.: U.S.A.: Can. Journal of Earth Science, Science, v. v. 29, 29, p. 167416741685. 1685. 28 �INTRODUCTION INTRODUCTION TO THE THE ROPES GOLD DEPOSIT DEPOSIT IN THE THE ISHPEMING GREENSTONE GREENSTONE BELT, MICHIGAN ABSTRACTED H PERMISSION FROM GEOLOGY OF ABSTRACTED WIT WITH OF THE ROPES ROPES GOLD GOLD DEPOSIT BY R.A. BROZDOWSKI BROZDOWSKI (1988) (1988) Theodore J. Bornhorst and Shannon E. Bair, Department of Geological Engineering Engineering and and Sciences, Michigan Technological University, Houghton, MI 49931; 4993 1; and Glenn Glenn Scott, Scott, Tilden Tilden Mining Company, company, Ishpeming, MI 49849 Introduction Introduction The southwest part of the greenstone belt (Figure 1) 1) consists of, of, from west west to to east: east: pillowed and massive basalt, hypabyssal gabbro, dacite tuff and subordinate tuff breccia, breccia, fine-grained peridotite peridotite of of the the Deer Deer Lake Lake Peridotite. Peridotite. Volcanic rocks strike serpentinitic, fine-grained northeast, with a major bend to the east northeast at the Bjork-Lundeen prospect, 1.5 1.5km km west west of the Ropes deposit. Rocks face consistently to the southeast, based on pillows and graded and graded bedding The Ropes deposit is southeast of a transition from dominantly basalt to the the northwest northwest to dominantly dacite tuft to the southeast (Figure (Figure 2). 2). Meter-thick banded iron formation formation and and several meter thick greywacke are within the dacite up section from the interlayered basalt basalt and dacite. Sericite Sericiteprogressively progressively overprints overprints and and finally finally totally pesudomorphs feldspar feldspar phenocrysts in dacite tuff as the Ropes gold deposit is approached from the west. The deposit is in quartz-sericite-chlorite quartz-sericite-chloriterock which is interpreted as quartz-sericite altered altered dacite dacite tuff. tuff. Major Rock Types within Major within the the Ropes Ropes Deposit The four major rock types in or immediately bounding the Ropes deposit are are (Figures (Figures quartz-sericite-chlorite rock which encloses ore, strikes 070' 070° 3 and 4): 1.) fine grained quartz-serieite-chlorite overall, but 080' 080° where where it hosts the the Ropes deposit, deposit, and and dips dips steeply steeply south south or vertical. This This rock type is bounded north and south by 2.) fine grained carbonate-quartz-chlorite rock which is massive to compositionally layered on a scale of several millimeters. It and the the quartz-sericite-chlorite rock are locally complexly interlayered, particularly in the west part quartz-sericite-chlorite of the deposit, and have have generally generally sharp sharp contacts. contacts. Carbonate-quartz-chlorite rock is flanked successively, on both the north and south sides by, 3.) fine grained, massive to moderately rock, and 4.) 4.) fine foliated, carbonate-talc rock, fine grained, grained, serpentinitic peridotite which commonly original olivine olivine and and lesser lesserpyroxene. pyroxene. This is variably has pesudomorph texture after original with carbonate-talc carbonate-talc rock. rock. Contacts between carbonatecarbonate-bearing near its contacts with quartz-chlorite rock and carbonate-talc rock and between the carbonate-talc rock and the serpentinitic peridotite are generally gradational over one to several meters. Quartz-Sericite-Chlorite Quartz-Sericite-ChloriteRock Rock The main host for gold is light green, massive to slightly foliated, fine grained, quartz-sericite-chlorite thick on the 800 quartz-sericite-chlorite rock. This This rock rock is is aa 080°-striking 080'-striking layer up to 40 m thick mine level, but narrows toward the surface and toward the east to less than 6 m thick. It is is level. 29 �0 km 2 EXPLANATION EXPLANATION PROTEROZOIC PROTEROZOIC 1 graywacke and slate 2 quartalte ARCH LAN 3 serpentinillc peridotila 4 volcanIc conglomerate, subordinate daclte tuti 5 banded Iron lorniatton 6 daclle tutt, lull breccta and ltows 7 tonallIe and granodlorlte a gabbro 9 basalt 10 gtornerophyrlc basalt Figure1:1:Geologic Geologicsetting setting theRopes Ropesmine mineininthe thesouthwest southwestblock blockofofthe theIshpeming Ishpeming Figure ofofthe greenstone greenstonebelt. belt. 30 , �EXPLANI4 TION EXPLANA JION 0 0 0 ii GRAYWACKE GRAYWACKE 10 QUARTZITE QUARTZITE w F- 0 a- SERPENTINITIC PERIDOTITE LJ SERPENTINI11C PERIDOTITE EIJ CARBONATE RICH, SERPENnNITIC CARBONATE RICH, SERPENTINITICPERIDOTITE PERIDOTITE 1 a - CARBONATE TALCROCK ROCK ED CARBONATE-TALC COMPOSITIONALLY LAYERED TO MASSIVE COMPOSKIONALLY LAYERED MASSIVE CARBONATE QUARTZ - CHLORITE CHLORITE ROCK ROCK CARBONATE- QUARTZ - - TUFF, TUFF TUFF BRECCIA, BRECCIA, AND FLOWS; FLOWS; DACITE TIJFF, (ALTERED TO QUARTZQUARTZ-SERICITESERICITE- CHLORITE CHLORITE ROCK IN INROPES ROPESDEPOSE!) DEPOSIn S " = - ED BANDED BANDEDQUARTZ QUARTZ - MAGNETrrE MAGNETITE IRON FORMATION FORMATION GRAYWACKE ANDSILTSTONE SILTSTONE ED GRAYWACKE AND E1J FINE GRAINED FINE GRAINEDGABBRO GABBRO 1' L S BASALT (INCLUDES (INCLUDES PILLOWED PILLOWED AND GLOMEROPHYRIC VARIETIES) VARIETIES) PROJECTION TO SURFACE OF OF OREBODIES OREBODIES UPDIP PROJECTION TO SURFACE A = main main ore ore zone zone northwest ore B = northwest ore zone zone Figure 2: Surface Surfacegeologic geologic map mapof o f the the Ropes Ropes mine m i n e and vicinity. 31 �1 300 level 1152 level 200 Ft CI I 61 M I N 200E 400E 6006 BODE I000E 12006 EXPLANATION EXPLANATION I i I I 2 I i 3 i a [5 a Quartz-Sericite SerpentiniticFeridotite Peridotite L41 Quartz-Seridte chlorite Rock -. Serpentinitic Chlorite Rock locally carbonate carbonate rich rich locally Carbonate-Talc Carbonate-Talc Rock Rock Carbonate-Quartz -Carbonate-Quadz Chlorite Rock Rock Chlorite I Orebody Orebody >2 2 , g /tonne ,tonne Au Au Figure 3: Geologic Geologicplan planmap mapof ofthe the300 300and and1152 1152levels levels of of the the Ropes Ropes mine. mine. Figure 32 �ROPES R O P E S MINE MINE 600 E E Cross-Section Cross-Section Looking LookingS80°W S80° i Elevation Elevation(ft) ( 1 Serpentinitic Peridotite Peridotite Serpentinitic locallycarbonate carbonaterich rich locally I a 121 Carbonate-Talc Carbonate-TalcRock Rock 1400 1401 I 1200 1201 Carbonate-Quaflz -Carbonate-Quartz Chlorite Rock Rock Chlorite 3 4 i Quartz-Sericite Quartz-Sericite ChloriteRock Rock Chlorite Orebody 151 Orebody gltonneAu Au >>22g/tonne 1000 1001 C 0mine minelevels levels 800 80C Scale 0 600 600 100 200ff 61 m 100 400 40C 200 ft 61 m 200 200 Sea SeaLevel Level -200 -200 Figure Figure4:4:Geologic Geologiccross crosssection sectionofofthe theRopes Ropesmine minelooking loohngS80°W S80° along alongthe the600E 600Esection. section, 33 �complexly interlayered with carbonate-quartz-chlorite rock, especially west of the Ropes main ore zone and in the mine. Randomly Randomlyoriented orientedto tomoderately moderately aligned, aligned, 11to to22 mm, mm, angular, rectangular mats of felted sericite up to 2 mm in length, comprised of individual sericite grains less than 10 10 microns in size, and minor quartz, are enveloped in this matrix and have an external habit identical to plagioclase In dacite dacite tuff tuff immediately immediately plagioclasephenocryst. phenocryst. In west of the deposit there are plagioclase phenocrysts. The Therectangular rectangular mats matsare areinterpreted interpreted as as pseudomorphs after the plagioclase phenocrysts. phenocrysts. The rock is layered locally with 5 mm thick, lens-like, sericite-rich sericite-rich and and alternating alternating more more chlorite-rich chlorite-rich laminae. laminae. Sericite quartz-sericite-chloriterock rock decreases decreases Sericite in in relict relict feldspar feldspar and and lithic lithic clasts clasts in in the the quartz-sericite-chlorite gradationally westward from the Ropes main ore zone over a distance of of several hundred meters into aa large large body of of dacite dacite tuff tuff that that has has moderately moderately aligned aligned twinned twinned plagioclase plagioclase phenocrysts phenocrysts with with only only very very minor minor sericite sericite internal to the phenocrysts, bipyramidal quartz, and volcanic volcanic rock rock fragments fragments in in an an aphanitic aphanitic quartz-sericite feldspar-chlorite matrix. The Thedacite dacite tuff outside of the Ropes deposit, proper, has local lapilli-sized fragments as well as tuff tuff outside of the Ropes breccia breccia layers. layers. Gold abundance abundance is generally greatest where very fine to aphanitic pyrite is 5 to 8% 8% of the the rock, rock, quartz quartz and and sericite sericite are are most most abundant, and chlorite is least abundant. However, However,this this generality generality does does not not apply apply to to the the chioritic, chloritic, pyritic, pyritic, eastern eastern most most rim rim of of the the Ropes Ropesmain mainore ore zone. zone. Anastomosing Anastomosingquartz quartzveinlets veinletsless lessthan than11mm mmthick thickmake makeup upseveral severalpercent percentof ofthe the rock. rock, Rock Rockoutside outsideofofthe theore orezones zonescontains containsless lessthan than2% 2%very very fine finepyrite. pyrite. The The overall overall 070° quartz-sericite-chlorite rock rock which which hosts hosts the theRopes Ropes 070' striking striking trend trend of of quartz-sericite-chlorite main main and and northwest northwest ore ore zones zones interfingers interfingers with with carbonate-quartz carbonate-quartz chlorite chloriterock rockwest westof ofthe the deposit, and does not continue west of the northwest ore zone (Figure 2). East of the deposit, deposit, and does not continue west of the northwest ore zone (Figure 2). East of the deposit, the the trend trend of of quartz-sericite-chlorite quartz-sericite-chlorite rock does not continue at surface beyond 300 m east of the the Ropes Ropes main main ore ore zone. zone. A A zone zone of of carbonate-talc carbonate-talc rock rock within within the the serpentinitic serpentinitic peridotite peridotite marks marks the the east-northeast east-northeastprojection projection of ofthe thetrend. trend. Carbonate-Quartz-Chlorite Rock Carbonate-Quartz-Chlorite Rock Carbonate-quartz-chlorite Carbonate-quartz-chloriterock rock envelopes envelopes the the quartz-sericite-chlorite quartz-sericite-chloriterock rockand andisis complexly complexly interlayered interlayered with with it, it, particularly particularly toward toward the the west west end end of of the the Ropes Ropesdeposit. aeposit. Carbonate-quartz-chlorite rock rock isis restricted restricted largely largely to to the the deposit deposit although although layers layersup uptoto22mm Carbonate-quartz-chlorite thick thick occur occur up up to to 400 400 m m west of the Ropes main ore zone. The The thickest thickest layers layersof of carbonatecarbonatetalc talc rock rock are are immediately immediately north north and and south south of of the the deposit; deposit; however, however, thin thin layers layersof oftalc-rich talc-rich rock rock are are at at numerous numerous localities localities atat the the contacts contacts of, of, and and also also within within serpentinitic serpentiniticperidotite peridotite along along the the northwest northwest contact contact of of the the peridotite peridotite up up to to 500 500 m m away away from from the the deposit. deposit. Carbonate-quartz-chlorite Carbonate-quartz-chlorite rock rock contains contains abundant abundant ferroan ferroan dolomite, dolomite, and andlesser lesserquartz quartz and and chlorite. chlorite. Minor Minorsericite sericiteisisininsome someparts partsand andvariable variable amounts amounts of of talc talc in inothers, others,but butthese these two quartz-sericite-chloriterock rock two minerals minerals are are generally generally mutually exclusive. Contacts Contactswith with quartz-sericite-chlorite are are sharp sharp in in aa direction direction across acrossthe the strike strikeof of the the rock rock type, type, but but are arelocally locallygradational gradationalalong along strike. strike. Barren Barrenmilky milkyquartz quartzveins veinsup uptoto10 10cm cmthick thickoccur occurlocally locallyand andare areconformable conformabletotothe the contact. contact. Minor Minorcarbonate carbonateminerals mineralsare arepresent presentininthe thequartzquartz-sericite-chlorite sericite-chloriterock rocknear nearits its contacts contacts with with the the carbonate-quartz-chlorite carbonate-quartz-chloriterock, rock, and and minor minor sericite sericiteisispresent presentininthe the carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock near near its itscontacts contactswith with quartz-sericitequartz-sericite-chlorite chloriterock. rock. Carbonate-quartz-chlorite rock rock has has up up to to150 150ppb ppb Au, Au, and and quartz quartzrich richparts partsof ofthe thecarbonatecarbonateCarbonate-quartz-chlorite 34 �quartz-chlorite rock only very locally contain several percent pyrite and up to 11 ppm Au. Locally the carbonate-quartz-chlorite rock is brecciated, with angular fragments of carbonate carbonate veined carbonate-quartz-chlorite rock in a chlorite rich matrix particularly at the south south side side of of the deposit. Carbonate-quartz-chlorite rock is generally compositionally layered on a scale of several millimeters, but but locally locally is is massive. massive. Layering is defined by hy fine to medium grained white cxbonate carbonate lenses, chlorite foliation, foliation, and and quartz-chlorite quartz-chloriterich richlaminae. laminae. The rock is white increasingly talcose toward the contact with carbonate-talc rock. Coarse grained, barren, white dolomite veins up to 5 cm thick cut across all other features and are several percent of rock. Carbonatethe rock. Carbonate- quartz-chlorite quartz-chlorite rock rock is is not only within the deposit but also in a zone up to 60 m thick on its north side, where it contains thin layers of the other three main rock types. Carbonate-quartz-chlorite types. Carbonate-quartz-chlorite rock rock is is in local lenses along the northeast striking contact of and northwest northwest of of the the Ropes Ropesdeposit. deposit. The carbonatethe Deer Lake Peridotite, southwest and quartz-chlorite rock is interpreted as an alteration product of a serpentinitic peridotite protolith. Serpentinitic Peridotite and Carbonate-Talc Serpenrinitic Carbonate-Talc Rock Rock quartz-sericite-chlorite rock and carbonate-quartz-chlorite rocks are The interlayered quartz-sericite-ihlorite are bounded on north and south by elongate masses of serpentinitic peridotite. There are also several smaller serpentinitic peridotite bodies enclosed within the carbonate-quartz-chlorite of the Ropes Ropes deposit. deposit. The largest of these bodies is the north wall of rock on the north side of the Ropes deposit. The The rock rock is is dark dark gray gray to green, green, mostly fine grained, with major serpentine, subordinate talc and carbonate, carhonate, minor chlorite, and accessory chromite and magnetite. The The serpentine serpentine isis aa mixture mixture of of felted felted chrysotile and oriented plates of antigorite. Commonly it has a relict texture of 11 to 3 mm serpentine pseudomorphs after major olivine pyroxene. The and subordinate pyroxene. The pseudomorphs pseudomorphs are surrounded by rims of talc, carbonate and accessory accessory fine-grained fine-grained magnetite magnetiteand andchromite. chromite. Locally the the rock rock is is dark green, minerals and felted textured serpentine which which lacks lacks aa pseudomorphic pseudomorphic texture. texture. The serpentinitic peridotite is increasingly carbonate-rich toward its borders, although the relict texture is commonly preserved. Fibrous continuously preserved. Fibrous chrysotile chrysotile veinlets in the serpentinite are locally pseudomorphed by carbonate. Au abundance is typically less than 30 ppb, even in close proximity to the deposit. deposit. Massive to well foliated, gray to dark green, very fine grained carbonate-talc rock margins of of serpentinitic serpentinitic peridotite. peridotite. Chlorite, serpentine, magnetite and occurs around the margins pyrite are minor phases. phases. The carbonate-talc The carbonate-talc rock has gradational contacts over one to several meters with serpentinitic peridotite and with talc-rich parts of the carbonate-quartz-chlorite subequal. The carbonate rock. Talc Talc and and carbonate carbonate contents contents are generally generally subequal. carhonate mineral in the ferroan dolomite dolomite with with minor minormagnesite. magnesite. Au abundance is carbonate-talc rock is dominantly ferroan from less than 30 ppb to approximately 100 100 ppb locally in the carbonate-talc rock. The Gold Ore g/ton Au, including production and The Ropes deposit is 2.8 million tonnes with 3.24 glton reserves. There Ninety five percent percent of the ore all categories of reserves. There are are two two main types of ore: 1.) 1.) Ninety dispersed pyrite pyrite in in quartz-sericite-chlorite quartz-sericite-chloriterock. rock. This ore has several subtypes is gold with dispersed proportions of of quartz, quartz, sericite, sericite, chlorite, chlorite, and andpyrite. pyrite. 2.) Five percent of the ore is with varying proportions 35 �auriferous quartz veins with saccharoidal saccharoidal texture and tetrahedrite, pyrite, galena, galena, and and chalcopyrite. ItItisisgenerally generallyatator ornear nearthe thesouth southside sideof of the the deposit. deposit. Dispersed Pyrite in Quartz-Sericite-Chlorite Gold With Dispersed Quartz-Sericite-ChloriteRock Rock The Ropes main ore zone is steeply dipping, 335 m in maximum strike length, 12 12 m in average thickness, and 600 m in known down dip extent (Figures 4). It is within the quartz-sericite-chlorite rock, and gold is associated associated with dispersed pyrite with only minor quartz veins. veins. The Ropes main ore zone can be divided longitudinally into three ore subtypes section. Subtype (Figure 5). These These subtypes subtypes are, are, from west to east, in long section. Subtype 11 is is light light gray gray to to pale green, siliceous quartz-sericite rock, containing minor lenses of of light gray cherty quartz rock with pyrite, tetrahedrite, chalcopyrite and galena. galena. Pyrite Pyrite abundance abundance does does not not correlate correlate with gold grade. Subtype quartz-sericite-chlorite Subtype11has hasan aninterdigitating interdigitatingcontact contact with with barren barren quartz-sericite-chlorite and carbonate-quartz-chlorite rock to the west, and a gradational contact to the east with is 6.8 6.8 glton. g/ton. Subtype subtype 2. The average gold concentration is Subtype 2 is is light green green quartzquartzsericite-chlorite-pyrite rock with a positive correlation between fine-grained pyrite pyrite content content and Au abundance. Subtype 2 is the thickest part of the ore zone and, therefore, therefore, the most volumetrically important. ItIt has with subtype 3. The has aa relatively relatively sharp contact to the east with The average Au concentration ranges from 2.6 glton, g/ton, rarely up to 6.2 glton. g/ton. Subtype dark Subtype33isisdark green quartz-chlorite-pyrite consistently large fine-grained fine-grained pyrite pyrite content. ItIt has quartz-chlorite-pyrite rock with a consistently has barren quartz-sericite-chlorite rock rock to to the the east. east. The a sharp contact with barren The average average Au Au concentration is is 10.3 10.3g/ton. glton. Zones of greater than 4 g/ton glton Au abundance, defined by assay data, are are contained contained centrally within the Ropes main ore zone. The middle parts of these greater than The middle parts of these greater than 44 g/ton glton Au Au zones strike echelon fashion at approximately strike across the 080° 080' trend of the orebody in en echelon 055°, 055', whereas their extremities have a nearly 070° 070' strike, thus forming forming a low low angle angle sigmoidal sigmoidal pattern across the ore ore zone. zone. This This pattern pattern is is most most pronounced pronounced at at and and below below the the 1152 1152level level toward the east end of of the the Ropes Ropes main main ore ore zone zone (Figure (Figure 6). 6). Above the 650 level, ore is separated from carbonate-quartz-chlorite rock on on the the north north by slightly auriferous quartz-sericite-chlorite rock, but but below below the the 650 level level the east end of the ore is in contact with carbonate-quartz-chlorite carbonate-quartz-chlorite rock (Figure 3). 3). The north side side of of the the ore ore strikes 070° 070" and dips very steeply north whereas the contact between quartz-sericite-chlorite quartz-sericite-chlorite rock and the carbonate-quartz-chlorite rock strikes 080° 080Âwithin the deposit and dips dips steeply steeply south. Therefore, Therefore, atatdepth, depth, the the ore ore abuts abuts the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock contact contact on on the the north, with the east limit of the Ropes main ore zone plunging to the west at at deeper deeper levels levels along the line defined by the intersection of the planes of the orebody and the the carbonatecarbonatequartz-chlorite rock contact on the north. Below Below the the 1284 1284 level, the 25 25 to 40 m m thick quartzquartzsericite-chlorite rock thins markedly to the east and interfingers along strike strike to to the the east east with with quartz-sericite-chlorite rock rock plunges plunges carbonate-quartz-chlorite rock. The The thickest thickest part part of of the the quartz-sericite-chlorite approximately 45° 45' east and is coincident with the bend in strike of the trend of quartz-sericite-chlorite rock from 080° 070° east of the main ore zone. 080' within the deposit back to 070' zone. There are several other gold bearing bodies bodies near the the main main ore ore zone zone (Figure (Figure 5). The The northwest ore zone is a small ore zone of 101,000 tons tons with with 4.6 4.6 glton g/ton Au, Au, 170 m m northwest northwest of of the Ropes main ore zone, and is dominantly ore subtype 2. 2. Auriferous, Auriferous, pyritic pyritic quartzquartz36 �_____ _____ long section section of of the the Ropes Ropes deposit in in the the Vertical long N80° plane, with gold gold ore ore subtypes: subtypes: N80°E 1 1 2 3 - QUARTZ SERICITE SERICITE ROCK, ROCK, QUARTZWITH WITH GRAY GRAY QUARTZ QUARTZ LENSES LENSES QUARTZ SERICITE -- CHLORITE CHLORITE ROCK, ROCK, QUARTZ -- SERICITE GOOD Au AU :: PYRITE CORRELATION CORRELATION - QUARTZ CHLORITE - PYRITE PYRITE ROCK ROCK QUARTZ -- CHLORITE FigureS: Figure 5 : Vertical Vertical long long section section of of the the Ropes Ropes mine mine in in the the N80°E N8O0E showing gold gold ore ore subtypes. subtypes. 37 37 �0 50 meters meters ROPESMINE MINE 1152 1152 LEVEL LEVELPLAN PLAN ROPES tonne Au Au ore orezones zones >> 44 gg I1tonne I 0quartz quartz-- sericite sericite-- chlorite chloriterock rock 1 Figure6:6:Geologic Geologicplan planmap mapofofthe the1152 1152level levelofofthe theRopes Ropesmine mineshowing showinghigh highgrade gradeore orezones. zones Figure 38 �Ropes Ropes Mine Mine Level 1620 Level Geologic Plan Geologic Plan IN ul m C L, + cu "1" 50 50 m EXPLANATION EXPLANATION serpentinitic peridotite a serpenthitic peridotite C >2g/tonneAu 0 > 2 g I tonne Au carbonate - talc rock C] >4g/tonneAu 0 > 4 g I tonne Au a carbonate - quartz - chlorite rock rock - A,, Au LIII quartz rock quartz -- sericite -- chlorite rock auriferous quartz vein (Lower Secondary Secondary Drift Drift Vein) Vein) LI microcrystalline a rnicrocrystallinecarbonate carbonate - quartz rock rock Figure 7: Geologic Geologic plan plan map map of of the the 1620 1620 level of the Ropes mine. mine 39 �south south of of the the central central part part of of the the main main ore ore zone. zone, Non-Aunferous Non-Aur$erous Veins Veins Milky white, white, vitreous, vitreous, medium to coarse-grained quartz veins commonly cut the east northeast foliation in the quartz-sericite-chlorite quartz-sericite-chlorite rock at a high angle. Some Somedip dipsteeply, steeply, whereas others are shallowly dipping veins offset in north side up stepwise fashion along foliation parallel structures. The The veins veins are are not not auriferous auriferous and are commonly up to 10cm 10 cm thick and several meters in length. They are approximately 1% of the quartz-sericite-chlorite quartz-sericite-chlorite rock. rock. Quartz Quartzininthe theveins veinshas hasfull fullextinction extinctionunder undercrossed crossedpolars, polars,simple simplegrain grainboundaries, boundaries, and locally locally has has minor minor pyrite. pyrite. Banded dolomite veins commonly strike 015' 015° and dip nearly vertical. vertical. They cut the auriferous quartz veins. Massive, planar sided, coarse crystalline white white dolomite veins up to 10 10 cm thick thick cut cut all all other other veins veins and andare areundeformed. undefonned. Structure Structure An 065° 065' striking striking near vertical foliation is defined by planar alignment of sericite and chlorite chlorite in in the the quartz-sericite-chlorite quartz-sericite-chlorite rock. This Thisfoliation foliationisisinterpreted interpreted as astectonic tectonic schistosity schistosity or or SS fabric fabricbecause because the the sericite sericite and and chlorite chloriteare aresecondary secondaryminerals mineralsthat thatcut cutand and locally locally displace displace relict relict primary primary magmatic features, such as domains of former feldspar phenocrysts, phenocrysts, and and lithic lithic fragments. fragments. Locally LocallyS-C S-Cfabric fabricisisdeveloped, developed, especially especiallyin incarbonatecarbonatetalc talc and and carbonate-quartz-chlorite carbonate-quartz-chlorite rocks. rocks. Contacts Contacts between between the the quartz-sericite-chlorite quartz-sericite-chlorite rock rock and and rocks rocks derived derived from fromaaperidotite peridotite protolith protolith defined defined planes planes of of weakness weakness that favored development of a shear zone. The The orientation orientation of of reactivated reactivated zones zones of of weakness such as contacts between rock types are not strictly strictly governed governed by by the the exact exact orientation orientation of of the the stress stress that that causes causesthe the movement. movement. Ore Ore Related Related Structure Structure The The Ropes Ropes main main ore orezone zone trends trends 080° 080' overall, overall, but but is is internally internally comprised comprised of of 055° 055' to to 065° 065O trending trending zones zones of of greater greater Au concentration, concentration, which host most of the gold. These Theseoccur occur in glton Au Au concentration concentrationwithin within ore ore in low low angle angle sigmoidal sigmoidalzones zones of of greater greater than than 44 g/ton characterized characterized by by dispersed dispersedpyrite pyrite or or in in auriferous auriferous quartz-tetrahedrite quartz-tetrahedrite oblique obliqueshear shearveins veinswith with similar similar geometry geometryand andorientation. orientation. Zones Zones with withgreater greaterthan than44g/ton @on gold goldconcentration1 concentration, defined defined by by assay assaydata, data,are aremore more centrally centrally within within the the Ropes Ropes main main ore zone (Figures 6 and 7). The Themiddle middle parts partsof ofthese thesehigher higher grade grade zones zones strike strikeen en echelon echelon across acrossthe the overall overall 080° 080" trend trend of of the the ore orebody bodyatatapproximately approximately 055" whereas their extremities extremities nearer nearer the contacts contacts with the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock 0550 strike strike approximately approximately070°, 070°forming formingaalow low angle angle sigmoidal sigmoidal pattern pattern across acrossthe thezone, zone,which whichisis most most prominent prominent on onthe theeast eastend endof ofthe the1152 1152level level (Figure (Figure6). 6).This Thisgeometry geometryisisconsistent consistentwith with greater movement movementbeing beingaccommodated accommodated near nearthe themargin margin of ofmore moreductile ductiledeforming deforming greater carbonate-quartz-chlorite carbonate-quartz-chloriterock, rock,where wherethe theoriginally originally formed formed 055° 055' to to065° 065' schistosity schistositywas was flattened 080' plane plane of of shear, shear, represented represented by by the the contact contact between between contrasting contrastingrock rock flattened to tothe thelocal local080° types. types. 40 �sericite-chiorite sericite-chlorite rock rock was was encountered encountered in in deep deep drilling drilling at at the the Ropes Ropes deposit, deposit, in in aa zone zone separate separate from, from, and and deeper deeper to to the the east east of, of, the the Ropes Ropes main main ore ore zone. zone. Ore Ore Minerals Minerals and and Textures Textures and and Metal Metal Distribution Distribution Gold is with pyrite pyrite less less than than 100 100 microns microns in in diameter diameter dispersed dispersed throughout throughout the the mass mass of of the the quartz-sericite-chlorite quartz-sericite-chloriterock, rock, and and with with this this pyrite pyrite on on fractures, fractures, foliations, foliations,and and within within and and along the margins of millimeter-thick quartz veinlets. veinlets. Native Native gold, gold, of of variable variable fineness, fineness, isis 11 to to 10 10micron micron grains grains isis attached attached to to the the surface surface of of the the fine fine grained grained pyrite, pyrite, included included as asround round blebs hlebs within within fine fine grained grained pyrite, pyrite, on on fractures fractures within within fine fine grained grained pyrite, pyrite, and andatatgrain grain boundaries boundaries of of fine fine grained grained quartz quartz and and sericite. Minor Minorcoarse coarsegold goldisison onfractures fracturesin inquartz quartz veins. veins. Silver Silver isis in in electrum, electrum, native native silver silver isis with with fine fine pyrite, pyrite, argentiferous argentiferous tetrahedrite, tetrahedrite, argentiferous argentiferousgalena, galena,and andrare raredyscrasite. dyscrasite. Pyrite Argentiferous galena, galena, Pyrite is is 97% 97% of of the the metallic metallic minerals followed by 1% chalcopyrite. Argentiferous argentiferous tetrahedrite, tetrahedrite, sphalerite, millerite, bravoite, magnetite, and argentiferous tetrahedrite, tetrahedrite, sphalerite, millerite, bravoite, magnetite, and rutile rutile are are present present in in trace trace amounts. amounts. The The gold gold is is silver silver bearing and metallic silver is gold bearing. bearing, The The low low bulk bulk Au/Ag AulAg of of 0.65 0.65 for for the the Ropes Ropes gold gold deposit deposit differs differs from from ratios ratios reported reported for for Precambrian Precambrian gold-quartz gold-quartz veins veins and and lodes lodes (Boyle, (Boyle, 1979), 19791,which which range range from from1.37 1.37to to12.5 12.5and and average average about about 4.2. 4.2. Both BothAu Auand andAg Aghave havecontinuous continuouspositively positivelyskewed skewed log log normal normal distributions, distributions, each each with with aa single singlemaximum, maximum, interpreted interpretedasasindicating indicatingonly onlyone oneperiod periodof of mineralization. mineralization. Distribution. Distribution.Geometry Geometryand andAu Au Concentration ConcentrationofofAur?ferous Auriferous Quartz QuartzVeins Veins Auriferous Auriferous quartz quartz veins veins are are concentrated concentrated at the south side of the deposit. Individual Individual veins average 20 cm thick and extend 12 m horizontally and 15 m vertically, but collectively veins average 20 cm thick and extend 12 m horizontally and 15 m vertically, but collectively these these veins veins are aregrouped groupeden enechelon, echelon,and andlocally locally they they form formore oreshoots shoots88to to11 11mmthick, thick,with withthe the quartz quartz-sericite-chlorite rock. The Theveins veinsstrike strikeen en quartz veins veins separated separated by by auriferous auriferous foliated foliated quartz-sericite-chlorite echelon echelonatat055° 055' to to065° 065' across acrossthe the080° 080' trend trend of of the the quartz-sericite-chlorite quartz-sericite-chloriterock rocktype, type,dip dip vertically geometry. They vertically to to 85° 85' south, south, and and have a slight sigmoidal geometry. They occur occur progressively progressively further further east east in in successively successively deeper deeper mine mine levels. Eight Eightmajor majorshoots shootsmade madeup upof of these these veins veins were were mined mined in in the the 1800's 1800'sand and 1890's 1890's above above the 800 level. Broderick Broderick (1945) (1945)implied implied that that single single large largequartz quartz veins veinsranged ranged up up to to11 11m m thick, thick, 60 60m m in in horizontal horizontal extent, extent,and and76 76m m vertical vertical extent, extent,but but examination examinationof of the the old old mine mine workings workings concurrent concurrent with with development developmentof ofthe the modern modern Ropes Ropes mine, mine, and anddetailed detailedhistoric historic descriptions descriptions indicate indicate the the old old stopes stopeswere were ore oreshoots shoots made made up upof of aaseries seriesof ofsmaller smallerindividual individualquartz quartz veins veins and and intervening interveningauriferous auriferousfoliated foliated quartz-sericite-chlorite quartz-sericite-chlorite rock. rock. The Theveins veinsare aresaccharoidal saccharoidalwhite white to tolight lightgray grayquartz, quartz,with with pyrite pyrite and andminor minorargentiferous argentiferoustetrahedrite, tetrahedrite, galena, galena, and and chalcopyrite; chalcopyrite;and and rare rare free freegold, gold, molybdenite, molybdenite, dyscrasite, dyscrasite, tourmaline, tourmaline, and and native silver. Overall, Overall,metal metal concentrations concentrations in inthe the veins veins range rangefrom from20 20to to75 75g/ton gltonAu Au with with Au/Ag AulAgratio ratio from from 0.08 0.08 to to 1.76. 1.76. Thequartz quartzveins veinshave havegreater greaterconcentrations concentrationsof ofgold goldthan thanmost mostof ofthe thegold goldwith withdispersed dispersed The quartz-sericite-chloriterock, rock,but butthe thezones zonesof ofgreater greaterthan than44g/tonne gltonneAu Au pyriteininquartz-sericite-chlorite pyrite concentrationin inthe thequartz-sericite-chlorite quartz-sericite-chloriterock rock are are not not generally generally zoned zoned about about the theveins, veins, concentration rather,they they occur occurmore morecentrally centrallywithin within the the quartz-sericite-chlorite quartz-sericite-chloriterock rock north northof ofthe theveins. veins.In In rather, some instances, Au concentrations of greater than 4 glton in the gold with dispersed pyrite in some instances, Au concentrations of greater than 4 g/ton in the gold with dispersed pyrite in quartz-sericite- chlorite chloriterock rockextend extendalong alongthe the same same055° 055' to to 065° 065' trend trend eastward eastwardfrom fromthe the quartz-sericitewest end endof ofold oldstopes stopeswhich which mark markconcentrations concentrations of of quartz quartz veins, veins,particularly particularlyfor forold oldstopes stopes west 41 �westward plunging plunging auriferous auriferous quartz-tetrahedrite quartz-tetrahedrite veins Vertically dipping, steeply westward occur progressively further east in successively deeper levels of the mine. These banded, auriferous, tetrahedrite-bearing tetrahedrite-bearing quartz veins with aligned schistose inclusions of sericitequartz-chlorite wall rock are at or near the south side of the main main ore zone and have an orientation the same as the zones of schistosity parallel gold concentration with dispersed pyrite, which are more centrally within within the the trend trend of of quartz-sericite-chlorite quartz-sericite-chloriterock. rock. The veins are oriented nearly parallel to the schistosity, and therefore therefore nearly nearly perpendicular to the inferred maximum principal principal stress. They They contain schistose septa identical in composition to the quartz-sericite-chlorlte wall rock and have quartz with undulose undulose extinction and subgrain development textures indicating grain size reduction. reduction. These characteristics are compatible with an origin as oblique shear veins formed in the direction of of shear movement movement (Hodgson, 1989). Oblique shears Oblique shear shear veins veins are are inclined inclined to to shear shear zone zone margins margins in the same same way as as PP shears and show the same sense of en echelon stepping as the sense of of movement movement across the zone containing them (Hodgson, 1989). In In the case of the Ropes deposit, this indicates a dextral component in plan view. An An origin origin for for the the quartz-tetrahedrite quartz-tetrahedrite veins, veins, and and the the en en echelon echelon zones of Au concentration with dispersed pyrite, pyrite, as tension tension shears, extension extension veins, or Riedel shears in a sinistral shear zone is not indicated indicated because the the low low angle orientation of the tips of the veins with respect to the shear zone margin, margin, and the similar orientation of of the ends of the en echelon zones of Au concentration with dispersed dispersed pyrite, pyrite, is not not consistent with the sense of rotation expected in sinistral sinistral shear. shear. The sigmoidal zones of gold concentration with dispersed dispersed pyrite pyrite and the oblique shear veins have orientations nearly parallel parallel to the S fabric, fabric, consistent with with an origin as P shears. PP shears commonly form at approximately 10° 10' to the shear shear zone zone boundaries, boundaries, after after peak peak deformation, when resistance to shear is decreased decreased by by the the presence presence of of well well developed planar fabric (Tchalenko, (Tchalenko, 1970). 1970). Inferred Direction of Shear Movement direction in aa shear zone is commonly considered considered to to be he in in the the line line perpendicular to the intersection of of the shear zone margin with the plane plane of of the the oblique obliqueSS fabric, and the sense of movement is inferred from the the sense of of obliquity obliquity of of the the fabric fabric to the shear zone margin. In In aaductile ductile environment environmentthe the acute acute angle angle between between the the SS fabric fabric and and the the shear plane faces away from the direction of movement. The The sigmoidal sigmoidal zones zones of of greater greater gold gold concentration with dispersed pyrite follow an SS fabric, fabric, interpreted as as aa largely largely compressive, compressive, ductile feature. Contacts Contactswith with nonfoliated nonfoliated serpentinitic serpentinitic peridotite peridotite north north and and south south of of the the Ropes deposit are considered considered shear planes parallel to the C C direction. direction. The The orientation orientation of of the the SS fabric relative to the C direction indicates a dextral dextral component component of of movement movement when when viewed in the horizontal plane, with the south south side side of of the zone moving west southwest southwest and and the the north north side moving east northeast. (Figure 8). Offsets Offsets along along northeast northeast trending trending faults faults in in the the deposit, deposit, and the Z sense of warping of layering between between the the rock rock types types at at the the south south side of of the the deposit (Figure 7) 7) also support support a dextral component of movement. Localization of the Deposit Within Within a Dilational Jog quartz-sericite-chlorite rock strikes strikes 070° 070' overall overall but but 080° 080" where where itithosts hosts The trend of quartz-sericite-chlorite the main ore zone (Figure 8). This This080° 080Âpart part of of the the trend trend acted acted as as aa dilational dilational jog or or releasing releasing of movement movement in in plan view view (Figure (Figure 8). 8). bend during the indicated dextral component of Releasing bends are are commonly commonly sites sites for for ore ore deposits, deposits, even even if if the the main main fault fault trend trend isis barren barren 42 �0 1 km r N 2 3 1 1 Ropes deposit quartz vein prospect - 18 svucture anspg, s'rn obliqu, m, v.i,,., nd.s nht Loan 01 gvSr Au conc.,Wi,flon slTh .p.nnpjfl, Numbered quadrants mathed by dashed lines are ranges of possible orientations of horizontal components of maximum principal stresses which could account for dextral components of strain at: I. Bjork -- Lundeen prospect 1. Lundeen prospect 2. 2. I-I -18 18Structure Structure 3. Ropes Ropesdeposit deposit 4. range 4 Possible Poss~ole rangeof 01 horizontal horizontalcomponent component 01 maximum maxfmumprincipal pr,nc~paI stress which wnlcn could co~ld of stress s ~ m ~ l t a n e o usatisfy sat~sfv s l ~ requirements requmvnentsfor lor simultaneously sites 2, and sqles 1, 1.2. and33 above above Figure 8: 8: Structural Structuralmodel model for for the the Ropes Ropes mine, mine. 43 �(Sibson, 1987). Both Both the the sigmoidal sigmoidal zones zones of of Au Au concentration concentration with with dispersed dispersed pyrite, pyrite, and and the the auriferous quartz veins are interpreted as indicating local extension within aa dilational dilational jog. jog. There is a component of positive volume change in the shear zone, in an otherwise compressive tectonic regime. Increased Increased pore pore pressure pressure within within the the shear shear zone zone as as microfractures filled with fluid, combined with the extensional effect effect of of the dilational jog, jog, local extension. extension. Slip jogs involves extensional may have contributed to local Slip transfer in dilational jogs fracture openings localized in the jog, jog, or step over. Formation Formation of of dilational dilational jogs involves involves local loss of cohesion, or brittle failure, in an an otherwise ductile ductile environment. environment. The trend of quartz-sericite-chlorite rock which hosts hosts the Ropes main ore zone narrows to the east of the deposit, as well as toward toward surface up up dip from the deposit, where it 70° south dip at shallow shallow levels. levels. This bends from a near vertical dip at depth to a 70" This change change in in thickenss and attitude may have caused barrier barrier conditions conditions for ascending hydrothermal fluids, thickens addition to to the the dilational jog jog controlling resulting in another control on localization of ore in addition of the overall setting setting of of the the deposit. deposit. References References Anderson,E.M., Anderson, E.M., 1951, 1951,The The Dynamics Dynamics of of Faulting: Faulting: London, England. Oliver and Boyd, Boyd, 191 191 p. p, Geochemistry of Gold and Its Deposits: Deposits: Geological Geological Survey of Boyle, R.W., 1979, 1979, The Geochemistry Canada Bulletin 280, 584 p. 280,584 p. Broderick, T.M., 1945, 1945, Geology Geology of the Ropes Ropes Gold Mine, Mine, Marquette Marquette County, County, Michigan: Michigan: Economic Geology, Geology, v.40, v.40, p.115-128. p.115-128. of Economic Brozdowski, R.A., 1989, 1989, Geology of The Ropes Mine, Society of Economic Geologists Geologists Fall Fall Field Conference Guidebook, Guidebook, Precambrian Geology and and Metal Metal Occurrences, Occurrences, Michigan's Michigan's Upper Peninsula Field Conference, Conference, p. 38-75. Groshong, R.H., Jr., 1988, 1988, Low Temperature Temperature Deformation Mechanisms Mechanisms and and Their Their v. 100, p. 1329-1360. 1329-1360. Interpretation: Geological Society of America Bulletin, v.100, Hodgson, C.J., 1989, 1989, Patterns Patterns of of Mineralization, Chapter Chapter 3, 3, in: in: Mineralization and Shear Zones, Geological Association of Notes v.6, Montreal, Quebec, May 12-14, 12-14, p.51-88. Lisle, R.J., 1989, Dike Sets: Geol. 1989, Paleostress Analysis from Sheared Dike Geol. Soc. Soc. Am. Am. Bulletin, Bulletin, v. v. 101, p. 968-972. Sibson, R.H.,1987, Earthquake Rupturing as a Mineralizing Agent in Hydrothermal Systems: Systems: Geology, v.15, v. 15, p 701-704. 701-704. Tchalenko, J.S., 1970, 1970, Similarities Similarities Between Shear Shear Zones of Different Magnitudes: Magnitudes: 625-1640. Geological Society Society of of America America Bulletin, Bulletin,v.81, v.81,p.1 p.1625-1640. 44 �Geologic Field Field Excursion Excursion to to the the Ispheming Greenstone Greenstone Belt Rodney C. Johnson, Johnson, Rod Rod Johnson Johnson & & Associates, Associates, Inc., Inc., Negaunee, MI MI 49866 49866 Theodore J. Bornhorst, Department Department of Geological Geological Engineering Engineering and and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, Houghton,MI MI49931 4993 1 Introduction Introduction This geologic field excursion to the Ishpeming Ishpeming greenstone belt consists consists of of 88 selected selected stops stops (Figure 1). These These stops stops are are designed designed to to cover cover the major varieties of volcanic lithologies found in the belt and several localities of structural structural significance. significance. Johnson and and Bornhorst Bomhorst (this volume) provide an overview of the greenstone belt and explanation of stratigraphic stratigraphic terminology used in this guide. AA detailed detailed topographic topographic map map is is provided provided to to identify identify the the location of the stops, however users should refer to larger scale maps in order to navigate stops, order to navigate roads to the stops. stops. Trip Stops Field Trip Stops Stop Stop A -- Lighthouse Point Purpose: View: View:1)1)amphibolite amphibolite schist schist of of Lighthouse Lighthouse Point Point Basalt, Basalt, 2) 2) Dead Dead River Shear Shear Zone, Zone, and 3) cross-cutting relationships of Archean and Proterozoic rocks (Figure 2). Note: You Guard to to visit visit this this locality. locality. No rock You must must obtain obtain permission permission from from the U.S. Coast Guard rock hammers or specimen collecting are allowed at this this stop. Park Park in in the the parking lot across across from from the Coast Coast Guard Guard office. office. At this stop excellent shoreline exposures on Lighthouse Point and along the adjacent beach provide a view of Archean and Proterozoic Proterozoic rocks rocks (Figure (Figure 3). 3). Gair Gair and and Thaden (1968) (1968) mapped these rocks in detail. detail. Part I. The Theoutcrop outcrop in in the the middle middle of of the the beach beach near the parking lot is composed of Archean thinly layered, amphibolite schist (basalt). The basalt here is part of the Lighthouse Point generally strike E-W E-W and and dip dip 70°N 70°N. The layers in Basalt. The The layers layers on on Lighthouse Lighthouse Point generally highly flattened flattened pillows. pillows. The flattening is interpreted to be a the basalt are interpreted as highly result of north verging recumbent folding (Johnson and Bomhorst, 1991). 1991). Part 11. II. The Theoutcrop outcropon on the the southwest southwest end end of of the beach is composed of chlorite-sericite schist, again part of the Lighthouse Point Basalt (see Johnson and Bornhorst, Bomhorst, this volume). The chlorite-sericite schist is interpreted to be deformed pillow basalt and are Kinematic indicators indicators (S-C fabric in particular) metamorphosed to greenschist facies. metamorphosed facies. Kinematic indicate a dominantly left-lateral shear sense, but on close inspection right-lateral and northnorthindicators are also present. present. This locality is interpreted to be the eastern extension of side-up indicators block of of the Ispheming greenstone the Dead River Shear Zone that separates the northern block belt from the southern 1). southern two two blocks blocks (Figure (Figure 1). 45 �____ T. 50 N T. 49 N T. 48 N. 46°30' R.28W. R.27W. R.26W. R.25W. Explanation Explanation Proterozoic Proterozoic Sedimentary rocks 0Sedimentary rocks I Mona Mona Formation Formation Upper tuff unit unit and lapilli-tuff lapilli-tuff unit unit Basalt Basalt flow unit unit Kitchi Formation Formation Kitchi Tuff unit and lahar unit Basalt unit Basalt flow unit l\ /1 I Archean Intrusive Intrusive Rocks Rocks k''-4 Granodiorite Granodiorite 177771 Tonalite Tonalite 1 Deer Lake Peridotite Deer Lake Peridotite Sedimentary Rocks Sedimentary Rocks K"Xl Timiskaming-type Timiskaming-typesedimentary sedimentaryrocks rocks Volcanic Rocks Rocks Lighthouse Lighthouse Point Point Basalt Basalt Basalt Basalt V/A Reany Reany Lake pyroclastic pyroclastic unit unit and and Fire Center mine mine iron-formation iron-formation unit unit HP_Li Nash NashCreek Creek glomerophyric glomerophyric basalt basalt unit unit 3 L\1 m Bedding Bedding 87 f Overturned bedding bedding 87+ Facing of pillows A Facing pillows Plunging anticline Plunging anticline Plunging syncline syncline 'C Plunging overturned anticline Plunging overturned Shear zone 1 @ Location Location of stops stops & - A % Figure 1: 1: Generalized geologic geologic map of the Ishpeming greenstone belt showing location location of stops. stops. 46 �R. 25W. T. 48 N. Figure 2: 2: Stop StopAA- Lighthouse Lighthouse Point Point Figure 47 �100 0 200m 0 50rn I Explanation Middle Middle Proterozoic Proterozoic /,%j Keweenawan Keweenawandiabase diabasedike dike Early Early Proterozoic Proterozoic 'dt*S Metadiabase Metadiabasedike dike Archean Archean I Intrusive IntrusiveRocks Rocks Rhyolite Rhyolite 0 I Lighthouse Lighthouse Point PointBasalt Basalt Basalt, Basalt,outcrops outcropsinindarker darkershade shade Figure Figure3: 3:Geologic Geologicmap mapof of Lighthouse LighthousePoint Point (modified (modifiedfrom fromGair, Gair,1959). 1959). 48 I �Within the basalt dominated outcrop there are lenticular pods of quartz-chert (hematite (hematite The interpretation of the the quartz-chert stained) and small texturally different different quartz quartz veins. veins. The with deposition deposition of of the the basalts. basalts. Small Small quartz quartz pods is not clear, they could be synchronous with veins are found in rocks throughout throughout the the Ishpeming Ishpeming greenstone greenstone belt. belt. Most of of these were were Archean deformation deformation and and metamorphism. metamorphism. However, at at least some some likely emplaced during Archean 1998). were emplaced during the Proterozoic (Bornhorst (Bomhorst and others, 1998). Part III. 111. The main outcrops of Lighthouse Point are northeast of the first two localities. localities. This trip will only only visit visit the the shorline shorline ouctrops ouctrops on on the the northeast end of of the the beach, beach, near near aa house. house. Here, Archean thinly layered, amphibolite schist (basalt) is cut by a tabular, porphyritic rhyolite dike trending roughly parallel to the layering. The layered basalt is part of the the Lighthouse Point Basalt and the rhyolite is interpreted as synchronous with the synorogenic late trondjhemite-granite suite plutons that reorient earlier fabrics. are The Archean rocks are cut by two N-S trending Proterozoic diabase dikes that are metamorphosed to greenschist facies as compared to the surrounding Archean rocks that are are metamorphosed to amphibolite facies. The The crest crest of the ridge (not visited today) is underlain by a relatively unmetamorphosed E-W E-W trending diabase dike dike of Keweenawan Keweenawan age. age. White Bear Drive Stop B -- White Drive Purpose: View Viewthe theupper uppertuff tuffunit unitof ofthe theMona Mona Formation Formation and andS3 S3crenulation cleavage cleavage (Figure (Figure 4). 4). The rocks at this stop are part part of of the the upper upper tuff tuff unit unit of of the the Mona MonaFormation. Formation. The rocks of the quartz-feldspar-sericite-chlorite schist. schist. Thin primary layering subupper tuff unit consist of quartz-feldspar-sericite-chlorite parallel to S S,foliation foliationcan canbe beobserved observed in in some some of the outcrop in this area. Based Based on on the the presence of sand-sized, sand-sized, lenticular lenticular volcanic volcanic fragments, and lack of sand-sized quartz quartz and and feldspar in an intact framework, most of these schist beds are interpreted as tuff. On the north side of the outcrop nearest White Bear Drive we can see the hinge of a fold. This allows us to see S3 crenulation crenulationcleavage. cleavage. On the limbs of westward plunging F3 fold. S and Bornhorst, this volume, andS3 S3are are parallel parallel and and indistinguishable (see Johnson and Bomhorst, the fold S, Table 1). 1). Stop C - Tower Purpose: View Viewthe thelapilli-tuff lapilli-tuff unit unitof ofthe theMona MonaFormation Formation and andS3 S3crenulation cleavage cleavage (Figure 5). 5). Note: Park Parkatatthe thecommunication communicationtower towerand andwalk walkabout about lOOm loom downhill in a southerly direction to aa series series of of outcrops outcrops alongside alongside the the hill. hill. The rocks at this stop are part of the lapilli-tuff lapilli-tuff unit unit of of the the Mona MonaFormation. Formation. The rock is composed of calc-alkalic rhyolite lapilli in a quartz-sericite-chlorite matrix with quartz and and 49 �R. 26W. T. 48 N. Figure 4: Stop Stop B-White B-White Bear Drive Drive R. 26W. T. 48 N. Figure Figure 5: 5: Stop Stop C-Tower C-Tower 50 �R. 26W. 1.48 N. Figure Figure 6: 6:Stop Stop D-Shunk D-Shunk Furniture Furniture R. 26W. T. 48 N. StopE-Tuff E-Tuff Unit Unitof ofthe theKitchi KitchiFormation Formation Figure7:7:Stop Figure 51 �less commonly, feldspar phenocrysts. Flattened Flattened apple apple green green lapilli lapilli (muscovite (muscoviteand and chlorite; chlorite; Puffet, 1974) are also common at this stop. This This unit unit isis interpreted interpreted as as subaqueous subaqueous pyroclastic flow and fall deposits. At this stop an earlier shallowly easterly dipping foliation (S1) (Si) is crenulated by a later E-W foliation and and elongated elongated in the (S3). The The lapilli lapilli are are flattened along the S1 S, foliation trending foliation (53). direction of the intersection of Si and S3. The Dead River Shear zone (D2, D4) is interpreted 83. The Dead River Shear zone (Dz,D4) to be located on the north side of the tower hill. Stop D - Shunk Furniture Purpose: View Viewpillowed pillowedbasalt basalt of ofthe theMona MonaFormation Formation (Figure (Figure 6) 6) Note: Park Parkalongside alongsideof ofthe theroad roadacross acrossfrom fromShunk ShunkFurniture, Furniture, but but be be very very careful careful of oftraffic. traffic. There are excellent views of relatively undeformed pillowed pillowed tholeiitic basalt in outcrops pillowed basalts are part part of of the the basalt basalt flow flow unit unit of of the the Mona Mona alongside of U.S. The pillowed 30 cm cm X X 1.5 1.5 m; m; Formation. The Thepillows pillows are are ellipsoidal ellipsoidal in in shape shape with with dimensions dimensions about about 30 E-W and and dips dips 85' 85° N. N. Cusps on pillows indicate attitude of bedding strikes approximately E-W that stratigraphic top is to the north. There There are are characteristic characteristic well-developed well-developed pillow pillow rinds, rinds, radial fractures, and interpillow void spaces filled with quartz and carbonate. carbonate. Overall, Overall, pillowed and massive tholeiitic basalt is the dominant lithology in the Ishpeming greenstone belt. Stop EE— Kitchi Formation Stop - Tuff Unit of the Kitchi Purpose: View View tuff tuff unit unit of of the the Kitchi Kitchi Formation Formation and and evidence evidence for for superposed superposed folding folding (Figure 7). 7). Kitchi At this stop we will see some of the lithologic variation within the tuff unit of of the the Kitchi folding. Cross-bedding, Formation and evidence for large scale folding. Cross-bedding, graded graded bedding, and and cut cut and and Kitchi Formation, Formation, but but in in this this area area clearly clearly indicate indicate tops tops to to fill structures are uncommon in the Kitchi the east. AA foliation foliation atatright right angles angles to to bedding bedding indicates indicates this this area area is is near aa vertically vertically plunging fold nose. Stop F - Teal Teal Lake Purpose: View View the theCarp CarpRiver River Falls Falls shear shear zone, zone, tuff tuff unit unit of of the Kitchi Kitchi Formation and and Ajibik Ajibik 8). Quartzite of the Menominee Group of the Marquette Range Supergroup (Figure (Figure 8). At this stop we will cross the Carp Carp River Falls shear zone from Lower Proterozoic metasedimentary rocks into Archean We will will begin the the traverse in in the the Archean metavolcanic metavolcanic rocks. rocks. We steeply dipping Ajibik Quartzite of the Lower Proterozoic Marquette Marquette relatively undeformed steeply TheCarp CarpRiver River Falls Falls shear shear zone zone is is aa high high strain strain zone zone indicated indicated by by Range Supergroup. The The foliation foliation in in the the schist schist is is near near vertical vertical and and has has aa quartz-sericite-feldspar-chlorite schist. The steep mineral lineation. As As the the shear shearzone zone isis traversed traversed there there is is aa noticeable noticeable increase increase in in the the 52 �R. 27W. T. 48 N. Figure 8: 8: Stop Stop F-Teal F-Teal Lake Lake R. 27W. T. 48 N. Figure Figure 9: 9: Stop Stop G-Alorig G-Along Deer Deer Lake Lake 53 �amount of chlorite in the schist. On Onthe thenorth north side side of of the the Carp Carp River River Falls Falls shear shear zone zone isis quartz-feldspar-sericite-chlorite schist schist of of the the tuff tuff unit unit of of the the Kitchi Kitchi Formation. Formation. Stop G --Along Along Deer Lake Lake Purpose: View View lahar laharunit unitof ofthe theKitchi Kitchi Formation Formation (Figure (Figure 9). 9). At this stop polymictic volcanic conglomerate is exposed in in a glacially glacially polished polished outcrop along the north side the road road towards towards Deer Deer Lake. Lake. Park alongside of the road. road. This This volcanic volcanic part of the the lahar lahar unit unit of of the the Kitchi KitchiFormation. Formation. On the polished polished surface, the conglomerate is part volcanic clasts vary from 25 cm X 35 cm in cross section, section, down down to to the the size of the matrix grains. Larger 1.2mminincross crosssection, section, are are present present in in the the nearby nearby lake lake Larger clasts, clasts, up up to to 60cm 60 cmXX1.2 shore outcrops. Clasts Clastsgreater greater than than 11cm cm make make up up about about 20 20 % % of of the the rock rock and and there there isis an an obvious stratification in clast clast size. Shape very angular to to rounded. rounded. The Shape of clasts varies from very The volcanic clasts are caic-alkalic calc-alkalic andesite andesite to dacite dacite in composition with with most most clasts clasts at at this this locality being near the andesite to dacite division division with with small small chemical chemical variation variation (Bomhorst (Bornhorst unpublished holocrystalline. The unpublished data). Most Most clasts clasts are are porphyritic and some are holocrystalline. The volcanic volcanic conglomerate is interpreted as a subaqueous lahar deposit. deposit. Stop H - Shoreline of Deer Lake Purpose: View ViewDeer DeerLake LakePeridotite Peridotite (Figure (Figure10). 10). road. Park Note: There There isis aa small small pullover pullover on on the east side of the road. Park and and walk walk along along the the road road to to the north where you can find a small small trail that leads through the woods to to the the tip tip of of the the point. point. Outcrops occur along the shoreline of this small point into into Deer Lake. At this this stop stop serpentized peridotite of the Deer Lake Peridotite is exposed along the shore shore of of Deer Deer Lake. Lake. Elongate pods of massive serpentized peridotite with closely spaced spaced fractures fractures are are surrounded surrounded by 2 to 5 cm wide ribbons of 11 to 22 mm subparallel veins of cross cross cross-fiber serpentine serpentine (Bornhorst fine(Bomhorst and others, 1986). 1986). The Thedark dark grey grey to to green green massive massive serpentized serpentized peridotite peridotite is is fineto medium-grained and lacks obvious foliation. lit In hand sample one can find well-developed well-developed 1 to to 55 mm mm pseudomorphs pseudomorphs after olivine and and pyroxene pyroxene outlined outlined by by thin thin selvages of white carbonate or talc. No No spinifex spinifex or or pyroxene "string beef' beef' textures textures indicative indicative of of komatiite komatiite flows have been found. The Thechemical chemical composition composition indicates indicates an an olivine olivine to to pyroxene ratio ratio from about 0.25 to 2 and most samples samples are are in the harzburgite field and and some some are are in in the the Iherzolite lherzolite field. The The Deer Deer Lake Lake Peridotite Peridotite is is interpreted interpreted as as a sill complex. This locality is only a few 100 Ropes gold gold mine. mine. The 100 meters from the Ropes The shear shear zone zone that that hosts hosts the Ropes gold mine projects immediately immediately north north of of this this small small point. point. The The serpentized serpentized peridotite has a strong, veinlets and and streaks streaks strong, contorted contorted foliation with magnetite as irregular irregular veinlets along the foliation foliation planes indicating the shear zone that hosts gold at at the Ropes ~ o ~mine mine e s continues into the Deer Lake Peridotite. Adjacent Adjacent to to the the gold gold ore ore body body the the serpentized serpentized peridotite is altered altered to a talc-carbonate rock (Bornhorst (Bornhorst and and others, this this volume). volume). 54 �R. 26W. T. 48. N. Figure 10: 10:Stop Stop HH- Shoreline Shoreline of of Deer Deer Lake Lake Figure R. 26W. T. 48 N. Figure 11: 11:Stop StopI-I-County CountyRoad Road510 510 Figure 55 �StopiStop I -County County Road Road 510 Purpose: View Purpose: View fire fire Center Center Mine Mine iron-formation iron-formation of the Lighthouse Point Basalt (Figure (Figure 11). 11). Note: Park Parkalongside alongsideof ofthe theroad, road, but but be be careful careful to to watch watch for for logging logging trucks trucks moving moving at at high high speeds. There are several outcrops outcrops on both sides of County Road 510 510 at at this stop. stop. The The particular particular outcrop of interest is near the top of the slope slope on the east side of the road, itit may may take take aa little little effort to find the iron-formation. iron-formation. At At this this stop stop the the Fire Fire Center Center Mine Mine iron-formation iron-formation unit unit of of the the Lighthouse Point Basalt is overlain and underlain by massive tholeiitic basalt of of the the Lighthouse Point Basalt. The Theiron-formation iron-formation isis approximately approximately 1.5 1.5 m m thick thick and and strikes strikes N30°W. N30¡WItIt isis composed composed of of fine, fine, black black chert chert that contains scattered magnetite grains and pyrite. To Tothe thewest west of of this thislocality, locality, the the iron-formation iron-formation is is layered layered with 1.5 1.5 cm cm thick chert chert and and magnetite bands. Despite Despitevariable variable magnetite magnetite content, content, this this iron-formation iron-formation produces produces aa strong strong magnetic signature signature and can be traced from north to south in this stratigraphic stratigraphic block block of of the the greenstone belt. This marker. The This iron-formation iron-formation is an excellent stratigraphic marker. The basalt is dark dark amphibolite green to black, fine-grained and relatively non-foliated and metamorphosed to amphibolite grade. grade. Acknowledgments We thank Shannon E. Bair for computer drafting of the figures. References Bomhorst T.J., T.J., Shepeck, Shepeck, A.W., A.W., and and Rossell, Rossell, D.M., D.M., 1986, 1986, The The Ropes Ropes gold gold mine, mine, Marquette Marquette County, Michigan, gold deposit: deposit: MacDonald, - an Archean hosted lode gold MacDonald, E.J. E.J. Michigan, U.S.A -(ed.), Proceedings of Gold '86, an International Symposium on the Geology of Gold, Toronto, p. 13-227. Toronto, p. 2213-227. Bornhorst, Bomhorst, T.J., Thorpe, R.I., R.I., and Johnson, R.C., 1998, 1998, Lead isotope study of veins in in the the Archean Ishpeming greenstone belt, Michigan: Econ. Geol., v. 93, pp. 102-107. 102-107. Gair, J.E. and Thaden, R.E., 1968, 1968, Geology of the Marquette and Sands Sands Quadrangles, Quadrangles, Marquette County, Michigan: U.S. Geol. Survey Professional Paper397, 77 p. Johnson, R.C. and Bornhorst, T.J., 1991, Archean Archean geology geology of of the the northern Johnson, R.C. Bomhorst, T.J., northern block block of the the Ishpeming belt, Marquette Ishpeming greenstone greenstone belt, Marquette County, County, Michigan: Michigan: U.S. U S . Geological Geological Survey Survey Bulletin 1904-F, 1904-F, 20 20 p. p. Puffett, W. P., 1974, 1974, Geology of the Negaunee Quadrangle, Marquette County, Michigan: U.S. 53 p. U S . Geol. Survey Survey Professional Professional Paper Paper 788, 788,53 p. 56 �Shear Shear Zones Zones and and Gold Gold Mineralization Mineralization in the the South South Half Half of of the the Ishpeming Ishpeming Greenstone GreenstoneBelt, Belt, Michigan Michigan by D.J. Duskin Duskin Consulting Consulting Geologist Geologist 210 21 0 Union Street Street Camden, SC 29020 29020 and and T.O. T.O. Quigley President Minerals Minerals Processing Processing Corporation Corporation 4547 4547 County County Road Road 601 60 1 Champion, MI 49814 49814 57 �Foreword Foreword Much of this field trip is devoted to gold occurrences. occunences. At Atmost moststops, stops,the theguidebook guidebookdescriptions descriptions will include the the results results of of sampling sampling and and assaying assayingfor forgold. gold. The term "grab sample" means a small reconnaissance-style sample deliberately chosen chosen by by an an exploration exploration geologist to have, in his experience, the maximum chance of yielding gold in the assay because of the presence of alteration, sulfides, sulfides, gossan, gossan, etc.. etc.. If our reported result contains contains gold, gold, this this doesn't doesn't necessarily mean mean that that someone someone else's else's subsequent sample the same value. value. This phase of sampling is deliberately subjective, and and gold gold distribution distribution is is far far will give the from uniform in Archean deposits, deposits, varying varying greatly greatlywithin withinsmall smalldomains, domains,even evenatatproducing producingmines. mines. More representative sampling will will be be discussed at some of the field trip stops as either "channel" or "chip" samples across an exposure. exposure. Channel front diamond blade rock saw cuts or hand-cut Channel samples, samples, taken either from by hammer and moil, are meant to be volumetrically equivalent to a ¼ '/2 split of BQ (1.5-inch (1 S-inch diameter) drill core. Chip Chipsamples samples are are more more representative representative of the exposure than a grab sample, but not as rigorously taken as a channel sample. sample. Unless otherwise specifically noted, all gold values reported herein are from samples samples crushed, ground, split and assayed at the former Callahan Mining Corporation assay lab in the Humboldt (Ropes) Gold Mill, now owned and operated by Minerals Processing Processing Corporation Corporation (MPC). (MPC). MPC's MPC's assays assays were were all all done by the fire fife assay-gravimetric finish finish method, method, using usingaa 1-assay I-assay ton ton (29.167 (29.167 gram) gram) subsplit. subsplit. MPC's MPC's lower detection limit by by this this technique technique isis ,003 .003 odton oz/ton (103 (103 ppb) ppb) Au. Au. The terms "no gold", gold, or or "below "below detection" refer to this limit. In Insome somecases caseswhere wherewe we felt feltititimportant importantto toknow knowthe thepresence presenceof ofeven evenlower lower Au values, separate subsplits were sent to Chemex Labs in Vancouver, B.C. for analysis by a lower detection limit technique, noted herein where so done. This This technique technique is is the the fire fire assay assay -- atomic absorption finish fmish process (FA-AA), (FA-AA), and has has aa lower lower detection detection limit limit of of 10 10ppb. ppb. Chemex Labs also performed whole rock rock major major oxide analyses. analyses. Results Results from samples samples taken at (Grunsky, 1983; Jensen, 1976) some of the field trip stops are shown on Jensen cation plots (Gnmsky, 1976) that have been routinely used for characterizing the lithochemisby lithochemistry of of the the rocks rocks from from this this region (Bomhorst (Bornhorst and Johnson, 1993). Figure lisa 1993). 1 is atemplate templateJensen Jensenplot. plot.The TheJensen Jensenplots plotswere weredone doneby byconsulting consulting geologist geologist R.A. Campbell, Burlington, Ontario, using "Newpet" "Newpet" software developed and distributed by the Earth Sciences Sciences Department of Memorial Memorial University Universityof ofNewfoundland Newfoundland.. Mr. Mr. Campbell's Campbell's assistance assistance is is gratefully acknowledged. acknowledged. 58 �Chemex Chemexalso alsodid didaa32-trace 32-traceelement elementanalysis analysisusing usingthe theX-ray X-rayfluorescence fluorescencetechnique techniquefor forall all samples samplessubmitted submittedfor forassay; assay;results resultsare arediscussed discussedwhere wheresignificant. significant. All thinsections sectionsexamined examinedwith withthe theassistance assistanceofofR.L. R.L. Allpetrographic petrographicdescriptions descriptionsare arefrom frompolished polishedthin Bamett BamettofofBameti BamettGeological GeologicalConsulting, Consulting,London, London,Ontario. Ontario. Mineral Mineralcompositions compositionswere weredetermined determined using JEOLModel Model733 733five fivespectrometer spectrometerscanning scanningelectron electronmicroprobe. microprobe.Mineral Mineral usingBaniett BamettGeological's Geological'sJEOL percentages percentagesare arevisual visualestimates; estimates;no no point point counts counts were done. Mr. Mr.Bamett's Barnett'svaluable valuablehelp helpisisalso alsogratefldly gratefully acknowledged. acknowledged. FeO* + 1102 Cation % Jensen (1976) PJ203 A1203 Mgo MgO Figure 1: 1 :Fields Plot Figure Fieldsfor forthe theJensen JensenCation Cation Plot 595 9 I �CONTOUR INTERVAL 20 FEET 0.. ) 20 Zr.C .5 r CQ 0 t%Z 0 0 �Stop SC-I: SG1: Variably basalt of ol'Mona Mona Formation Formation near near M Marquette Harbor Variably sheared sheared pillow basalt a q u e t t e Harbor (Location 2). (Location map, Figure Figure 2). Gair and (1968) and Thaden Thaden (1 968) last mapped this locality and assigned it to the lower member of the Mona Schist. Recently (1993)have have revised revised the the stratigraphic stratigraphic nomenclature nomenclature of of the the Recently Bornhorst Bomhorst and and Johnson Johnson (1993) lshpeming Ishpeming Greenstone Belt; this locality would now be assigned to the informal basalt flow of the Mona lowermost unit unit.. Pillowed Formation, its lowermost Pillowedmetabasalts metahasaltsof ofgreenschist greenschistfacies facies are are the the predominant Ethology lithology in this this unit. unit. The exposures here are best seen in a three-part sequence. After After parking in in the the abandoned abandoned railroad railroad yard, head east and take the trail along the south side of of Whetstone Whetstone Brook Brook to to the the lakeshore lakeshoreto tosee seeglacially glacially polished outcrops of pillow lavas. The Theoutcrops outcropsdisplay displaywell wellpreserved preservedglacial glacial grooves grooves and andstriae striaetrending trending 198°; 19S0; some of the grooves contain contain classic classic examples examples of of crescent-shaped crescent-shaped chaffer chatter marks pointing down-ice. down-ice. The two outcrops here show show a layer of massive massive non-pillowed non-pillowed basalt basalt conformably conformably sandwiched sandwiched between two pillowed pillowed layers. layers. The layering shown by by this "sandwich" "sandwich" trends trends approximately approximately 305'. 305°. The The pillows are pristine and and undeformed, undeformed, some some of of them them up up to to six six feet feet across. across. They display internal cooling cooling fractures, well preserved rinds, and cusps cusps consistently consistently showing showing tops to to the the north. north. The next point of interest is about about 100 feet feet south south on on the the rocky rockypoint pointof of the thelakeshore. lakeshore. Please he be careful while making your wav way southward over over this this slioperv slippery outcro~. outcrop. On On the the south south side side of of this this rocky rocky point point are pillowed basalt and thin discontinuous lenses of chert interbedded interbedded with the pillows, pillows, some someforming forming pillow selvages. Some brecciated red Someof ofthe thechert chertcontains contains patches patches of ofbrecciated red jasper; this this texture is is probably the the deformation. None of result of soft sediment deformation. of these cherts is magnetic. A A great great deal of of excess calcite is also present with the pillows. This This probably probably contributed contributed to to the the development development of of shearing, shearing, which which can can be be to be increasing rapidly rapidly in in intensity intensity southward southwardin inthis thisoutcrop. outcrop. We think that the calcite and clearly seen to the result result of of degassing degassing and and seawater seawaterprecipitation precipitationininand andnear nearaaflow flowtop. top. In our experience chert lenses are the such interpillow zones containing discontinuous thin cherts are very common. path from the beach beach westward westward back back to to the the railroad railroadyard yard the the progressive progressive deformation deformation of of Taking the path best seen. seen. Entering pillow basalt here is perhaps best Entering the yard, the outcrop exposure on the right (north) again marks the north edge of the developing shearing. Here Here the rock is moderately and variably sheared but the outlines of pillows can still be seen seen despite a penetrative penetrative foliation striking striking 290°, 290°85°N 85'N (photo, (photo,Figure Figure3). 3). The pillow rinds are pinkish weathering calcite, and the pillows here are much smaller than those earlier seen to the north, again a possible contributing contributing factor to the development development of of shearing shearing here. here. 61 �Figure northwest Figure3.3.Looking Looking northwestatatsheared shearedgreenstone greenstoneoutcrop outcropononeast eastside sideofofrail railyard, yard,Stop StopSG-1. SG-1. Hammer Hammerpoint pointtouching touchingcalcareous calcareousflattened flattenedpillow pillowrind. rind. Moving is is itsitswest Movingwest westacross acrossthe therailroad railroadyard, yard,the thethird thirdpart partofofthis thisstop stop westwall. wall.The The features here features here 50yards yardswest westofofhere hereand andabove aboveususininthe theU.S. U.S.Highway Highway4141road roadcut; cut; aremore morecontinuously continuouslyexposed exposedabout about50 are that vexydangerous dangeroushigh highspeed speedIraffic trafficlocation locationand andwe've we'vechosen chosentotoshow showthe thesame sameunits unitsinindetail detailatat thatisisa avery this instead. thisrail railyard yardexposure exposure instead. 62 �'V p/I/sawed 4.ilr 1 n.bbl caicgreo4Jt —-—---— ZontS ii 4n14 a 71 Careen /1/1 Th— r--sheand 2 i4/ pt/al- p//Iota c,_.rinds —'-c re/ic4.. p1/ala 0 20 —'- Peer 7R2-2 - -4-- /1/in Jo.sper £he-rt 71 P/I/a Ec/kt p//loots v Shea rtd X Acsay .capIe ® u/kale- rock mj#trtJ ,tiaiQa d1 te. e-'-- ,-._, _iCoeapsss and Tape. ao Figure Figure4. 4. Compass Compassand andtape tapemap mapofofwest westwall wall of of railroad railroad yard, Stop SG-l. SG-1 63 Ca inple -Thea £ —A... ....LL__ C -at ny �Figure 4 is a map of the rail rail yard yard exposure. exposure. From From north north to to south, south, the the first exposed exposed unit unit is is dark blackish green non-amygdaloidal non-aniygdaloidal pillowed pillowed basalt basalt with with calcareous calcareousepidote-rich epidote-richpillow pillowrinds. rinds. The pillows are quite large, some up to four feet across. Blobs Blobs of ofcalcite calcite and and calcite-cemented calcite-cemented breccia fill some some of the pillow interstices. Within Withinthis thisunit unitthere thereare areshallow shallownorth-dipping north-dipping rubbly rubbly zones zonesthat thatmay may represent represent irregular flow tops. Many Many of ofthe thepillow pillowcusps cuspsindicate indicatefacing facingto to the thenorth, north, but butthis thisisiseasily easilyarguable arguableatatthis this outcrop. The Thepillows pillows themselves themselvesare arenot not megascopically megascopically foliated. foliated. Moving southward, there is an 8-foot covered interval critical to the relationship between the pillowed basalt and the next unit. unit, In In the the Highway Highway 41 exposure exposure to the west, this zone is occupied by a sheared-off lens of gray chert and highly sheared rusty weathering chlorite chlorite rock rock with with abundant abundant oxidized oxidized pyrite along along shear shearplanes. planes. (grab (grab sample sample HIWAY-1, HIWAY-l, .013 fine cubic pyrite ,013 ozlton Au). The The remainder remainder of the unit, exposed past the covered interval here, is highly sheared and light gray-green, with with aa strong Si S foliation foliation striking 269", 269°, 8O0N, 80°N, defined by chloritic slip planes with vertically plunging lineations. Oblique Obliqueto toS1 Sl and dipping more shallowly to the north are discontinuous blobs of white calcite and feathery seams of light brow!] ankerite. ankerite. These appear to to be flattened and and sheared-out sheared-out pillow pillowrinds. rinds. Both textural features are cut brown S1,striking strikingapproximately approximately300' 300°and and dipping dipping 30'-4O0N, 30°-40°N, defined by by a tensional cleavage conjugate to Si, seamlets. There thin fibrous calcite searnlets. There are are also also wide wide spaced spaced flat-dipping flat-dipping relief relief fractures fractures with with fibrous fibrouscalcite. calcite. At first sight this this rock rock might mightbe betaken takenfor foraamafic mafictuff. tuft However, However, itit lacks definitive features of such a protolith, i.e., lapilli, crystals, lithic fragments or bedding. Instead, Instead,itit appears appearsto tohave have been been derived derived from shearing of massive rock, save for the relict pillow rinds, which here indicate that the pillows were quite small and probably more susceptible to shearing than the more massive large pillows to the north. Southward there is another another 10-foot covered covered interval. interval, in In the Highway 41 exposure to the west, a highly sheared rusty sericite-chlorite-ankerite sericite-chlorite-ankeritezone with traces of oxidized cubic cubic pyrite pyrite occupies occupies this. this. (grab sample HIWAY-2, .009 odton ozlton Au). Past Past this this covered covered interval, the exposure is of moderately sheared gray-green rock. rock. SSifoliation vertical; foliationisisapproximately approximately270°, 270° vertical;the theshallow shallowdipping dipping cleavage cleavage isis weakly developed. Blobs Blobsof ofchlorite chlorite in in the the plane plane of SSlshow showvertical verticalalignment, alignment,and and the the rock rock carries carries disseminated coarse cubic pyrite with vertically aligned aligned calcite calcite pressure pressure shadows; shadows; in in thin thin section section both both of of these exhibit porphyroblastic development, rather than a pre-existing textural fabric. This Thischlorite-spotted chlorite-spotted unit has a higher MgO content than the adjacent rocks, plotting in in the the komatiitic field field (see (seeJensen Jensencation cation plot, Figure Figure 5). 5). Further south within this sheared rock rock is a 1.5 -foot bed of non-magnetic jasper chert that almost 285°, dipping 73'N. 73°N. The surely surely defmes defines an an original originallayering layering(So). (So). It strikes 285', Thepatchy patchy bright bright red red jasper zones zones 64 �in this chert are brecciated in in places, as seen seen in in the the outcrop outcrop east east across across the the railroad railroad tracks. tracks. The chert is is not foliated, but carries a trace of fine cubic pyrite on late white quartz fractures. A A grab grab sample sample here here yielded yielded oziton gold gold;;FA-AA 0.003 0 3 odton FA-AA re-analysis re-analysis by by Chemex Chernex gave gave 51 5 1ppb ppb Au. Au. Good examples of relict pillows are a couple of feet north of the hanging wall of the chert. This sheared lithology southern contact contact is is hthoáogy grades grades southward southward into intonon-foliated non-foliatedpillowed pillowedbasalt. basalt. The basalt's southern This a thin discontinuous 0-4" 0-4" nonmagnetic non-magnetic chert-jasper breccia breccia that that gave gave no no gold gold in in aa grab grab sample. sample. This Beyond its its cherty cherty southern southern contact contact the the foliation-resistant pillow basalt unit is about 15 feet thick. Beyond remainder of the exposure consists consists of of highly highly sheared, sheared, light light gray-green gray-green rock with arguable arguable relict relict pillow pillow "vein" S i at 260°, 260°70°N. 70°NWithin this southernmost part of the exposure is a 2-foot calcareous "vein" textures, S1 oblique to S,, S, strike foliation. A grab sample strike 315°, 3 15O, 72°N. 72'N. ItItexhibits exhibitsslickensides slickensides and and drag of the S1 S, foliation. yielded no gold. In In thin thin section sectionthis this rock rock consists consists of of alternating alternating parallel bands of of fine fine grained grained calcite and and plagioclase aggregates in nearly equal amounts, both carrying interstitial high magnesian chlorite that constitutes about 10% 10% of the rock. The Thecalcite calcitebands bands contain contain lozenge-shaped lozenge-shaped ankeritic ankeritic domains. Accessory minerals include apatite, zinc-rich cbromite chromite and abundant chromian titanornagnetite titanomagnetite commonly displaying atoll textures, a feature of of ultramafic rocks. rocks. Other Other indications indications of of an an ultramafic ultramafic parentage parentage are are the the high magnesian chlorite and a trace element analysis that includes 296 ppm Ni, an unusually high result in comparison to the nickel content found in in the dozens dozens of of other other rocks rocks analyzed analyzed in in the the study studyfor forthis thisfield field trip. We altered ultramafic ultramafic dike. dike. Gair and Thaden (1968, Wethus thus consider consider this this "vein" to be be a hydrotherrnally hydrothemally altered pl. 1) showed southernmost end of of what what was was then then the the p1.1) showed an an outcrop outcrop of of "hornblende "hornblende lamprophyre" at the southernmost Highway 41 road cut. Their Their outcrop outcrop cannot cannot be be found found today, today, but hut this this dike dike may may represent represent its its eastward eastward extension. extension. Marked on Figure 4 are five samples taken for for whole rock major oxide oxide and and 32-element 32-element trace trace analysis. Two Two are are from from unfoliated unfoliated pillow pillow basalts, basalts, two are are from from the the sheared sheared lithologies, and the fifth is The whole whole rock rock results results are are shown shown on Figure 5. from the ultramafic dike. The Discussion In this exposure chemically very similar rock rock units unitsexhibit exhibit shearing shearingthat that isispreferentially preferentially developed in weaker units (zones of small pillows, lava interfiow interflow beds, more more magnesian magnesian layers). layers). to shearing. The Intervening more massive buttress units are resistant to The sense sense of of shearing shearingisis nearly nearly vertical. vertical 65 �FeO* + 1102 SAMPLES Cation % Cation % Jensen Jensen(1 (1 976) 976) S RRCVN • PR-i A V RR-2 RR-3 • RR-4 S BK V A1203 MgO Figure 5: Stop SG-1 Figure 5: Stop SG-1 66 �Gait outcrop on on their their map map of of the the Marquette Marquette quadrangle, quadrangle,but but didn't didn't Gair and Thaden (1968) noted this outcrop indicate shearing or or slaty lithology lithology here. here. A couple of of miles miles to to the the southwest southwest they did describe describe east-west shearing at the southern contact of the Mona greenstones and the overlying overlying Proterozoic Proterozoic Enchantment EnchantmentLake Lake conglomerate. Mapping Fails Mapping the the next next quadrangle quadrangle west, Puffett (1974, p.43) recognized the Carp River Falls shear zone near that same contact and correlated it with the shearing in the Marquette quadrangle quadrangle by Gair and Thaden. Both previously noted by Both authors authors pointed pointed out out that that the the sense sense of of shearing shearing isis strongly strongly vertical. Puffett and noted noted (p. (p. 45), 45), "The "The Puffett (1974) (1974) also also recognized recognized and named the Dead River shear zone and projection of the shear zone to the southeast southeast across the Marquette quadrangle quadrangle meets meets aa conspicuous conspicuous rereentrant in the shoreline of of Lake Lake Superior." Superior." Thus Thus neither neither of of these these two two major major later-recognized later-recognized block boundary shear zones is actually actually shown shown on onGair Gait and andThaden's Thaden's 1968 map. map. This This was was left left to to later later authors of maps at various smaller scales, who usually place the Dead River shear shear zone zone as as aa west-northwest west-northwest trend trend meeting the lakeshore at the approximate contact with the Mona formation basalt basalt flow unit of the southern unit of of the the northern northern block block of of the the Ishpeming lshpeming Greenstone Belt. This block and the Lighthouse Point basalt unit This the Dead Dead River River shear shear zone zoneabout about'/< ¾mile miledue duenorth northof ofthis thisfield fieldtrip tripstop. stop. (Figure 2) 2) The would place the The zone seen here is a probable parallel, sympathetic sympathetic structure. Discussing the structural framework of the Ishpeming Greenstone Belt, Bornhorst Bomhorst and and Johnson Johnson (1993, event (Dl) (Di) was was recumbent recumbent folding. folding. This was followed by (1993, p. 4) stated, stated, "The oldest recognized event axes (Dz). (D2). Shear zones are interpreted to to have formed during and upright folding about east-west oriented axes later than 1)2 andmay mayhave havebeen beenreactivated reactivatedduring duringthe theearly earlyProterozoic Proterozoic Penokean Penokean deformation." deformation." They D; and They "Rock units in all blocks are also cut by by minor shear zones. zones. These went on to point out, out, "Rock These high-strain high-strain zones zones are characterized by by rocks that that are more more intensely intensely foliated foliatedthan thanthe thesurrounding surroundingrocks." rocks." We agree with these interpretations and offer the exposure at this stop as a case in point. point. Whether Whether or or not not this this particular particular major or minor one has yet yet to to be be determined. To shear zone is a major To the the west west itit projects projects into into an an urbanized urbanized area area with no outcrop. outcrop. The sheared lithologies at this locality exhibit varying levels of propylitic alteration (pyrite, carbonate, chlorite); significant significant trace amounts of gold can can be found where pyrite andlor carbonate are are well developed. As Asaapractical practicalmatter, matter, further further exploration exploration for for gold gold in in this this shear shear zone zone isis ruled ruled out out by by its its location. 67 �56-2: Stop SG2: Dead with gold gold mineralization mineralization at at Marquette Marquette Mall (Location map, Dead River Shear Zone with Figure 2). Figure 2). After parking at the head of the ski trail in the southeast comer corner of the Marquette Mall parking lot, walk about 500 feet ESE up the trail to an outcrop knob knob of undeformed metabasalt. This This greenstone greenstone has unusually high high number number of of blocky blocky hematitic hematiticfractures. fractures. The northern limit limit of of this this outcrop outcrop is isaa cliff an unusually cliff face face that is controlled by by foliation foliation planes planes striking striking280° 280°,85% 85°S. This cliff cliff face face represents representsthe thesouthern southern margin margin of of was exposed exposed in man-made outcrops in the bank of the Holiday Inn parking lot until it was shearing that was recently covered covered by by landscaping. landscaping. R. Brozdowski (personal communication, 1988) reported anomalous recently gold values from Callahan's Callahan's sampling sampling of of that that sheared sheared rock. rock. Returning about 400 feet westward down the trail, a makeshift wooden bridge crosses crosses the stream leading to the motel's duck pond. Intermittently Intermittentlyexposed exposed along along the the stream stream are are small outcrops outcrops of sheared chiorite-sericite rock rock with with brown brown carbonate carbonate weathering weathering rinds rinds and and oblique oblique quartz quartz veinlets. veinlets. Some chlorite-sericite Some of of this this phenocrysts, indicating aa crystal crystal tuff tuff protolith. protolith. Of rock has small gray quartz phenocrysts, Of three threewidely widely spaced spacedgrab grab took here, here, one one gave gave ,023 .023 odton or/ton Au, the the other other two two were were below below MPC's MPC's detection limits. The samples we took The sample that yielded the gold value was taken aa couple of feet below the little wooden bridge. Mail parking lot and moving west along its south bank, bank, there is a 650 foot Back at the Marquette Mall rock. Bornhorst long exposure of highly sheared rock. Bomhorst and Johnson (1993, p. 9) 9) gave aa brief description of this "..... tuffaceous rock and a graphitic zone crop out." outcrop: ". rock is badly badly slumped northward towards the the parking parking lot throughout throughout This sheared phyllonitic rock much of its length. At At its its eastern easternend end itit is is more more hematitic hematitic than elsewhere, elsewhere, with reddish reddish foliation foliation planes planes in the the relatively relatively underformed underformed greenstone greenstone to to the the east. east. Throughout resembling the fractures in Throughout its its entirety entirety there on foliation planes, planes, with with much much of the rock exhibiting a is a strong presence of chlorite and sporadic sericite on color due due to to weathering weathering of of chlorite chloriteand andferroan ferroancarbonate. carbonate. Where not not slumped, slumped, foliation maroon-reddish color measurements measurements cluster cluster closely closely about about 280°, 280°vertical. vertical. probable tuff There are some zones of chlorite-poor rock with small quartz eyes indicating aa probable protolith, similar to that found in the stream to the east. Near Near the the eastern eastern end end of of the the outcrop outcropisisan an irregular irregular to 2 feet layer of nearly pure graphite. Our Our grab sample of the graphite gave foliation-parallel two inches to no Au. One Oneorortwo twofeet feetacross acrossfoliation foliationfrom fromthe thegraphite graphiteisisaathin thinsemi-parallel semi-parallel layer layer of of rusty rusty to to black gossan with selvages of massive and semi-massive semi-massive pyrite carbonate carbonate breccia. breccia. From From the the pyrite-gossan pyrite-gossanzone, zone, Gleason (1986) reported values values up up to to 22 gmltonne gmltonne (.06 (.06 ozlton) or/ton) Au. Au. Our Our grab grab sample sample of of the the gossan g o w n gave gave .037 gave .028 .028 odton or/ton Au. Au. A 0 3 7 or/ton odton Au, Au, while our sample of pyrite breccia selvages gave A polished polished thin thin section section sample of the pyrite breccia shows shows that there are are two generations generations of of pyrite pyrite in in aa quartz-calcite-chlorite quartz-calcite-chlorite 68 �gangue, with the calcite late late in in the the paragenetic paragenetic sequence. sequence. The first generation pyrite is large and often framboidal, corroded and and partially partially replaced replaced by by quartz quartz and and second secondgeneration generationpyrite pyrite in in smaller, smaller,euliedral euhedral crystals. Heavy as inclusions inclusions in the second generation pyrite and as tiny Heavy traces traces of of covellite covellite (CuS) (CuS) occur occur as gangue. Other free grains in the gangue. Other inclusions inclusionswithin within pyrite pyrite found found by by the the microprobe microprobe include include chalcopyrite and sphalerite as as lesser trace sulfides. Accessory Accessory minerals minerals found found in in this this breccia breccia are are monazite monazite and and ilmenite ilmenite rutile, a common hydrothermal alteration. alteration. No grains common result of hydrothermal partially altered to mtile, grains of of free gold were found in this thin section sample. Besides Besides the the highly anomalous gold in in the corresponding corresponding assay assay grab grab sample, sample, anomalous trace trace elements elementswere werepresent present(ppm): (ppm): Ag-3; Ag-3; As-252; As-252; Cu-1700; Cu-l700; Pb-68; Zn-124; Uthe following anomalous 10. 10. About 150 150 feet from the western end of this exposure is a 2-foot complexly brecciated chloritecalcite-quartz-graphite vein vein with with strong strong vertical verticalhematitic hematiticslickensides slickensidesand andminor minorcopper copperstain. stain. The slickensided hangingwall of of this this vein vein strikes, strikes, 290' 290° 75'N. 75°N. Our Our grab grab sample sample yielded .005 .005 ozlton odton Au, Au, as aswell well as 244 pprn ppm Cu and 100 ppm Zn. Study Study of ofaa corresponding corresponding polished thin section did not fmd any gold grains but confirmed the presence of of very fine grained grained chalcopyrite chalcopyrite and and covellite covellite in in irregular irregular trains trains following late fractures and rimming graphite. This This vein vein appears to be cut cut off off by by aa northerly northerly cross cross fault. fault. About 75 feet from the western end of the exposure is a thin discontinuous vein vein of similar composition; our grab sample sample yielded yielded no no Au. Au. About 100 100 yards southward and uphill uphill from the west end off the Mall exposure is a slumped-in and partially flooded small open open cut cut next next to to the the north-flowing creek. In to the the south south wall of of this old mine pit there is an exposed patch of of rusty rusty weathering, weathering, ankeritic phyllonite similar to the Mall exposure exposure lithology. lithology of the the ore ore mined. mined. This There are no dumps or other present evidence of This is is the the Eureka Eureka mine mine (Williams, (Williams, 1890). 1890). Gair and Thaden (1968, p. 69) provided the following: "The "Theprincipal principaloccurrence occurrenceof ofiron ironininthe the Marquette-Sands area was at the old Eureka mine ... ... Perhaps Perhaps as much as several hundred tons of earthy goethitic iron ore was mined from from aa shear shear zone zone about about 55 feet feet wide wide in in chloritic chloritic slaty slatygreenstone greenstone (Mona (Mona Schist). Secondary Secondaryquartz quartz and and iron-bearing iron-bearing carbonate carbonate were deposited along the shear zone in places, prior to formation of of the iron ore. The Theore oreresulted resultedfrom fromoxidation oxidationof ofcarbonate carbonateand andchlorite, chlorite,the theconcentration concentration of iron, iron, and and the the removal removal of of silica, silica, MgO, MgO, CaO CaOand and alumina alumina by by ground groundwater watercirculating circulatingalong alongthe theshear shear zone. Virtually Virtually all all mining mining was was done done prior to to 1880, 1880,and and whatever whatever ore ore was extracted was shipped shipped to to local smelters. There were several unsuccessful attempts to to renew renew mining mining in in the the 1880's and charcoal-burning smelters. three test holes were drilled at the site in the 1920's". 1920's". 69 �Discussion Discussion This (1968, P1, 1). Their Thislocality locality was was last last mapped by (3air Gair and Thaden (1968, PI. 1). Their map shows shows only only aa couple couple of members of of small small exposures exposureshere, here, marking marking the contact between their Lower and Lighthouse Point members of the the Mona MonaSchist. Schist.We Webelieve believethat thatthe theoutcrops outcropshere hererepresent representthe thesouthern southernmargin marginof ofthe theDead DeadRiver Rivershear shear zone. zone. The Thepresence presenceofofgold goldand andbase basemetals metalsininthe theMaIl Mallexposure exposureisisdirect directevidence evidence of of their their localization localization by by major major shear shearzones, zones, and and we we suspect suspect that some some of of the the ore ore produced produced by by the the Eureka Eureka mine mine may have have been, been, in in aftersuluides. sulfides. part,gossan gossanafter part, The The trend trend of of shearing shearingprojects projects from from here here westward westward along along the the valley of an E-W creek. creek. No No exposures exposures could could be be found found along along itit except except aa few few outcrops outcropsof of aanarrow narrowE-W E-W magnetic magnetic diabase diabase dike dikeon on its its south 4,200feet feetwest west of ofhere, here, probably probably emplaced emplaced atator orclose closeto tothe thesouthern southernmargin margin of of the theshear shearzone. zone. southside side4,200 Thatdiabase diabaseisisnot noton onany anypublished publishedmap. map. That StopSG—3: SG3: Stop Archean metavolcanics metavolcanics (Location map, Keweenawan diabase in hornfelsed, foliated Archean (Location map, Figure Figure2). 2). Loojeuvs &4.cr '4 C -c -a C U '4 '7 sphero,Sc 'a 0" S'a 6atc h. h b It pg S -c 1 -z Lj :W40/e t-k/Occay scnsp.'e SM 0 U. a m rr AFPCg m&>C o% . reE Figure6. 6. Sketch Sketch cross cross section of outcrop outcrop at at Stop StopSG-3, SG-3,looking lookingeast. east. Figure 70 �This outcrop was last mapped by by Gair Gair and and Thaden Thaden (1968, (1968,P1. PI. 1) 1) as as Late Late Precambrian Precambrian diabase diabase with with a small adjoining patch of site" belonging to their lower unit of the Lighthouse Point Member of "fel "felsite" Member of of the the Mona Schist. There There is no outcrop description in their text. This This one one is is part of of a series series of outcrops outcrops of of a long narrow diabase dike that Gair and and Thaden traced eastward eastward into into Lake Lake Superior Superior at atLighhouse Lighhouse Point. Point. Here it strikes 250° 250°, dip 8O0N. 80°N. ItIt appears not appears to to be be about about 50 50 feet feet thick, thick, although its southern contact is not exposed. The Thediabase diabaseisisnon-foliated non-foliatedand andisismagnetic magneticthroughout. throughout. Figure 6 isisaa sketch sketch cross cross section section of this exposure. At Atthe thesouth south end end the the diabase diabase is is medium medium jointing grained, has a felty texture and contains rare vugs lined with drusy calcite. calcite. It shows shows rectangular rectangularjointing that controls incipient spheroidal spheroidal weathering weathering at the erosion surface; surface; the joint planes planes are are hematitic hematitic and and calcareous. The The diabase diabase grain grain size size lessens lessens northward to a fme fine grained but still magnetic chilled margin at the host rock contact. This Thiscontact contactisisstrongly strongly foliated foliated parallel parallel to to the the dike dike margin margin for for aa few few inches. inches. Beyond that the immediate immediate host host rock rock is is aablack, black,non-magnetic, non-magnetic,aphanitic aphanitichomfels homfelswith with strong strong foliation foliation defined mostly by prominent pink K-spar-quartz laminae. This Thisrock rock carries carries aa trace trace of of disseminated disseminated extremely fine-grained pyrite, and some some discontinous discontinous foliation-parallel foliation-parallel lenses lenses of of coarsely coarselyciystallized crystallized quartz. greenish gray. gray. Outward to the north, the host rock becomes rusty weathering, quartz. It weathers light greenish "baked"-lookthg, all the while exhibiting strong foliation planes closely slaty and less "baked"-looking, closely clustered clustered around around 280°, 80%. 80°N. The source 280" source of of the rusty color appears to be numerous foliation partings of ferroan carbonate; no pyrite is visible on a fresh surface. An An irregular irregular 4-6 4-6 inch inch foliation-parallel foliation-parallel quartz-iron oxide oxide vein marks marks the transition northward to non-thennally non-thermally altered altered grainy-light grainy-light greenish-gray greenish-gray sheared sheared rock rock with with rusty rusty 275°, 85¡ 85°N continuing continuing to the northern limit of the exposure. exposure. foliation planes at 275¡ Four grab samples of the host rock are shown on the sketch sketch cross cross section. section. Two Two of of these these were were clearly below below MPC's MPC's detection limit for gold (samples DBS-2 DBS-2 and and 3). 3). The other two returned values at or near the detection limit and were re-analyzed by Chemex using FA-AA, returning weakly anomalous gold values: DBS-l, DBS-1,51 5 1ppb; ppb;HFEL, HFEL,33 33ppb. ppb.No Nounusual unusualtrace traceelement elementsignatures signatureswere werepresent presentininany anyof ofthese these samples. samples. Study of a polished thin section of a sample corresponding to assay sample HFEL HEEL confirmed that that the pink bands consist of quartz phenocrysts phenoctysts in a K-spar groundmass. The The darker-colored darker-colored domains domains of of this this phenociysts/ciystals of albite-oligoclase, rock have a porphyritic texture with scattered phenocrysts/crystals albite-oligoclase, quartz quartz (often (often in in with pyrite), pyrite), and and composite composite large large grains grains or or fragments fragments of of quartzquartz- plagioclase. plagioclase. The dark biminerallic grains with color appears to be mainly due to biotization biotization of of numerous numerous foliation-defining foliation-defining chlorite-quartz-plagioclase chlorite-quartz-plagioclase to ruhle. rutile. The laminae and to an overall content of about 5% opaques: pyrite and ilmenite altered partially to The nature of the coarse grained components suggests that that this this rock rock was was originally originallyaa crystal crystallithic lithictuff. tuff. The 71 �thermal metamorphic effects effects near the contact of the diabase diabase dike dike appear appear to be limited limited to to prograde prograde alteration of chlorite to biotite biotite and recrystallization recrystallization of quartz and feldspar. feldspar. Figure 7 is a Jensen cation plot of of the the whole rock analyses analyses of the four four samples samples taken at this stop. stop. Discussion Discussion The foliation in the weakly hornfelsed country rock here is at an oblique angle to the diabase diabase dike, can best best be be seen seen at at the the top top of of the the outcrop outcropknob). knob). Because of this, we (which can webelieve believethis thisfoliation foliationprepreexisted the emplacement of the dike. We We also also believe believe that much of the foliation foliation in the host rock here is the result of shearing, shearing, and that this outcrop lies near the middle of the Dead River River shear shear zone. The The southern southern boundary of this shear zone would lie lie near near the the Marquette Marquette Mall Mall outcrop outcropatatStop Stop SG-2. SG-2. The emplacement of this diabase diabase dike dike within such such aa large large zone zone of of weakness weaknesswould would not notbe beunexpected. unexpected. Gaff and and Thaden Thaden (1968), (1968), though noting shearing in in their their text text from from place place to to place in the Archean Gair Quadrangle, did did not not emphasize emphasize its its importance, importance,nor norillustrate illustrateititon ontheir theirmap. map. They They rocks of the Marquette Quadrangle, also found very few outcrops of their lower unit of the Lighthouse Point Member, most of which are are shown as "felsite". "felsite". About About 1200 1200feet feet NNW NNW of ofhere, here, theft their map map shows showsaa cluster cluster of of 44 small small outcrops outcrops on on aa low low bill, "felsite". The hill, marked as ""felsite". TheWestwood WestwoodMall Mall and and its its parking parking lots lots now cover cover them, but we suspect that have exhibited exhibited shearing shearingsimilar similartotohere. here. About 500 feet further north in in the the woods woods these outcrops would have and sewer line line were were being being constructed constructed in in the the fall fall of of 1998. The behind the Mall, a new east-west street and The construction equipment tore up the tops of several small subcrops of sheared rock whose composition chioritic to nearly pure pure massive massive sericite. ItIt was was not not possible possible to to obtain obtain dips, but the strike varies from highly chloritic of the shearing is east-west. east-west. These exposures lie he near the probable northern contact contact of of the the Dead Dead River River shear zone. Since Since it's it's unlikely unlikely that that they'll they'll be bestill still available availablein in the the spring spring of of 1999, 1999, we we offer offer Stop Stop SG-4 SG-4 as as an alternative. alternative. 72 �FeO* + 1102 SAMPLES • • Cation Cation % % Jensen (1976) Jensen (1 976) A DBS-1 DBS-2 DBS-3 v HEEL BK A1203 A1203 MgO Figure 7: Stop SG-3 Figure 7; Stop SG-3 73 �Stop Stop SG-4: SG4: margin of Dead River Shear Northern margin Shear Zone on Wright Wright Street Street (Location map, Figure Figure 2). 2). This is an optional optional stop stop that that is is included included here here for for those those interested interestedin in seeing seeing more moreof of the theDead DeadRiver River Zone in in the the Marquette Marquette area. area. This exposure be Shear Zone exposure is very close to a busy highway, and care should be exercised when when visiting visitingit. it. About About 65 65 feet feet of of sheared sheared greenstone greenstone is exposed here on the east side of Wright Street. The The lower lower level level of of the the exposure exposurewas wasrecently recently created created by by widening wideningthe the road, road, and andwas wasnot notavailable available to Gair and Thaden (1968), who showed showed the the upper upper part part of of the the exposure exposureas as aa lithology lithologylabeled labeled"interlayered "interlayered ) massive basalt(?)" on on their their map map(P1. (PI. I1). The degree of shearing is variable here, here, but but much much of of itit is is intense. intense. Foliation The Foliation becomes generally more strongly developed from north to south, and strikes E-W, E-W, nearly nearly vertical. vertical, hi In the the small small cut above above the forms similar to to the the sheared shearedpillows pillows at at Stop StopSG-1 SO-i are present. Figure lower ledge, curvilinear sheared forms Figure 88 isis a photograph of pencil cleavage cleavage developed developed further further south south as as shearing shearing intensifies. intensifies. There Thereisisweak weakcarbonate carbonate alteration in some of the most heavily sheared rock, but it is not pyritic; we didn't sample samplefor forgold goldhere. here. Figure 8. Figure 8. Looking Lookingdue dueeast eastatatpencil pencilcleavage cleavagedeveloped developedby by shearing shearingin in greenstone greenstonein in low low roadcut, east side side of of Wright Wright Street, Street, Stop StopSG-4. SG-4. 74 �The northern part of this outcrop consists of nearly chaotic chloritic foliation that appears to result from the contact with a shear-resistant dike of non-magnetic gabbro that is only weakly foliated. Only Onlyaa couple of feet of this gabbro gabbro are exposed exposed in the roadcut, but a larger, glacially smoothed outcrop outcrop of of itit lies lies above above and and aa few few yards yards east east of of here. here. ii D is c u S 5 Discusssion About 400 feet to the north, on the east side of of the road road is an an outcrop outcrop of of relatively undeformed metabasalt; glacially polished outcrops outcrops of similar rock are exposed exposed in the south side side of the gravel pit being development aa couple couple of of hundred hundred yards yards further furtherENE. ENE. These rocks appear appear to to be be converted to a housing development Point basalt basalt typical typical of of this this area area(Johnson (Johnsonand andBomhorst, Bornborst,1991). 1991). So we would would place place the the Lighthouse Point northern boundary of the Dead River Shear Zone, if not at this outcrop, then no more than a few hundred feet north of here. Figure Figure22shows showswhat what we we think think are are the the approximate approximatelimits limits of of the the shear shear zone, zone, which which corresponds roughly to the lower unit imit of the Lighthouse Point Point Member of of the the Mona Mona Schist of of Gair and corresponds Thaden (1968), (1968), in turn corresponding roughly to the "Eureka Group" of Williams Williams (1890), nomenclature nomenclature that was discarded by Van Hise and Bayley (1897). This Thiswould wouldmake makethe theDead DeadRiver RiverShear ShearZone Zone3,000 3,000 feet wide at this point. Puffett Puffett (1974, (1974, p. p. 44) 44) noted noted that that the the Dead Dead River River Shear Shear Zone four miles west- northwest of here is about 3,400 3,400 feet feet wide. wide. To better define define and and understand understand the the Dead Dead River River Shear ShearZone Zone in in this this important importanthinge hinge area areabetween between the northern and southern blocks of the Ishpeming Greenstone Belt, Belt, remapping re-mapping and and structural study study of of existing and newly newly created created outcrops outcrops are areneeded, needed,before beforeit's it's too too late. late. The ex-urban growth around Marquette, Marquette, although presently presently creating creating new outcrops, outcrops, will will eventually eventually result in a net loss loss of of exposures. exposures. 75 I I I �Figure 9. Location map for Stops SG-5,6 and? 76 �Stop SG-5: Stop SG5: Progressively shearedlaltered sheared/altered metavolcanics metavolcanics in Carp River Falls Shear Shear Zone. 9). (Location map, Figure Figure 9). Puffett Puffett (1974) (1974) last mapped this this locality locality as as "undifferentiated "undifferentiated greenstone" greenstone" within within the Carp River Falls shear zone. Dealing Dealing with with this this exposure exposurespecifically, specifically,he he included included aa photograph photograph of ofits itsmost mostsheared sheared part, and described it as follows (p. 43): "Sericite, and altered part. "Sericite,chlorite, chlorite,carbonate, carbonate,and andleucoxene leucoxeneare arethe the products. Weathered brown from from oxidized oxidized most conspicuous alteration products. Weathered surfaces are commonly stained brown minerals. Quartz-carbonate iron minerals. Quartz-carbonate veinlets fomi form an an anastomosing network in some rock. Copper Copper minerals minerals are present locally. Analytical Analytical data datasuggest suggestthat that the the altered altered rocks rocks are are enriched enriched in CaO CaO and Co2 Co2(Table 12)." value, 90 90 ppm. ppm. W.A. Puffett's analysis from here gave an anomalous copper value, W.A. Bodwell Bodwell (personal (personal communication, 1998) 1998) reports having noted trace chalcopyrite and copper staining here, hut but they are not not easily found. found. This exposure was a 1988 follows (Bornhorst (Bomhorst and 1988 I.L.S.G. field trip stop stop described, described, in part, as follows others, 1988): 1988): "The "The rocks rocksin in this this roadcut roadcut have have aa well developed close-spaced foliation (N75-88W, dip 7089°S) which produces produces a slate-like appearance. appearance. These 89OS) These rocks rocks are are within within the Archean Carp River Falls Shear Zone. There two lithologies lithologiesin in this outcrop: chlorite chloriteschist schistfrom fromaabasaltic basaltic parent, parent, and and quartz-sericite quartz-sericite Thereare are two schist from a rhyolitic parent." Bornhorst Bomhorst and others (1988) also pointed out that near the very eastern end of the outcrop are probable relict pillow rinds. As probable Asseen seenelsewhere elsewhereon onthis thisfield fieldtrip, trip,these these are are gradually gradually obliterated obliterated by by shearing as one moves westward westward along the outcrop. outcrop. The The chioritic chloritic sheared sheared metabasalt metabasalt gives way progressively to more and and more more rusty rusty weathering weathering carbonate-sericite carbonate-sericitealtered altered rock; rock; we we believe believe itit represents represents aa progressively progressive change from from propylitic propylitic alteration alterationto to weak weak potassic potassicalteration alterationin in aa rock rock of ofthe thesame sameparentage. parentage. progressive lighter colored colored carhonate-sericite carbonate-sericitealtered alteredrock rocknear nearthe thewestern westernend endthere thereisisaa 6-inch 6-inch pyritic In the lighter pyritic carbonate zone. Our Our grab grab sample sample of of this this gave .005 oz/ton odton Au (sample STOP 3). AA70-foot 70-footchip chip sample sample across across the entire entire sericite-carbonate sericite-carbonate altered altered zone here (not including including the pyritic pyritic grab grab sample) sample) gave gave undetectable AU Au (sample STOP-3A) STOP-3A)..An AnFA-AA FA-AAre-analysis re-analysisby by Chemex Chemex of of the the pyritic pyritic grab sample gave a value of 90 ppb Au, Au, confirming MPC's MPC's results. We Wealso alsotook tookwhole wholerock rocksamples samplesfrom fromthe thevery veryeastern eastern exposure in the pillowed pillowed greenstone greenstone(sample (sample 5-1), 5-l), one onefrom frommoderately moderatelysheared shearedrock rocknear nearthe the end of the exposure (5-I), and one at the western end of the outcrop in approximately the same spot sampled and middle (5-1), photographed by Puffett (our sample 5-3). Whole Whole rock analyses analyseswere were also also done done on on the the two samples samples taken for gold assay; sample STOP-3A is the themost mostrepresentative representativeof of the the light light colored colored sheared sheared rock at at the western end of the exposure, exposure, since since itit was aa composite composite chip chip sample sampleacross across 70 70 feet feetof ofit. it. Figure 10 10 is a 77 �Jensen plot showing the Note that that sample sample STOP STOP33 is is anomalously anomalously high high in in iron iron because becauseititwas was Jensen the results. results. ((Note chosen chosen for for best bestpyrite pyritecontent). content). + FeO* FeO* + 1102 Ti02 Cation% % Cation Jensen (1976) (1 976) Jensen SAMPLES SAMPLES • 5-1 5-1 • 5-2 5-2 5-3 5-3 "v STOP3 STOP 3 A A • STOP-3A STOP-3A PJ203 MgO Figure Figure 10: 10: Stop Stop SG-5 SG-5 78 �A polished thin section was made of a specimen corresponding corresponding to to pyntic pyritic grab grab sample sample STOP STOP 33 that yielded anomalous gold. Megascopically Megascopicallythis thisspecimen specimenisisaa chlorite-sericite chlorite-sericiteschist schist hosting hostingaa foliationfoliation¼-inch veinlet veinlet of of carbonate. carbonate. Under conformable %-inch Under the microscope microscope and electron microprobe the host rock is 1%tiny tiny a fine grained mixture of 50% quartz, 30% 30% chlorite chlorite and 20% 20% niuscovite/sericite, muscovite/sericite, containing containing about about 1% rutile grains. The grains of disseminated chalcopyrite, as well as trace amounts of tiny disseminated mtile The dolomite with high-manganese cores, with about carbonate veinlet is a mosaic of coarse grains of zoned dolomite 10% high-iron chlorite. chlorite. This 10% interstitial high-iron This vein vein assemblage assemblage hosts hosts schlieren texturally similar to the host rock except that these fragments have no quartz. quartz, consist primarily of zoned ankerite with dolomitic cores and contain about 25% opaques, mostly Mn and Fe oxides, but also abundant fine fine grained euhedral pyrite and subordinate chalcopyrite. One Oneof of the thechalcopyrite chalcopyritegrains grains was was found found to to have have inclusions inclusions of of nonnonand one 3-micron grain of of high-gold high-gold electrum electrum (photo, (photo, Figure 11). This argentiferous tetrahedrite and Thiswas was the the only gold grain found in in this this sample. sampie Arsenopyrite Arsenopyritewas wasnot notfound, found,but but trace traceelement elementanalysis analysis of of the the corresponding assay sample yielded 170 170 ppm As. 'I, 3e+ Figure 3, White Figure II. 11.Polaroid Polaroidphoto photoofofbackscattered backscatteredelectron electrondetector detectorimage, image, sample sample STOP 3. White vertical scale bar at lower left is 10 10 microns. Bright 3-micron grain of of high gold gold electrum electrum in in (teØ. Black chalcopyrite (cpy) that also contains larger inclusions of tetrahedrite (tet). Black areas areasare are gangue. gangue. 79 �Discussion Puffett (1974, (1974, P. p. 43-44) 43-44) noted noted copper copper minerals minerals at at more more than one locality in the Carp Carp River Falls shear zone, an encouraging base metal association from kom the gold exploration explorationpoint point of ofview, view,since sincegold gold mineral here. here. This occurs directly with a copper mineral This outcrop outcrop is is close close to to the the north notth margin margin of the shear shear zone. zone. margin appears to be marked by bluffs that are coneolled controlled by by E-W foliated greenstone, across across The south margin behind Ball Moving and Storage, makiig making the the zone zone about about 400 400 feet wide wide at at this this point point, mostly mostly the highway behind covered by U.S.Highway 441. 1. We Wewill will cross crossthe the highway highway here to to see see more more evidence evidence of of gold gold mineralization. mineralization. Stop SG-6: Stop SG& Gold-bearing gtacial erratic erratic (Bill Bodwell'sBoulder) Boulder).. Location Gold-bearing glacial (Bii Bodwell's Location map, map, Figure Figure 9. first noticed noticed and and sampled sampled by by Bill BillBodwell Bodwellininthe the1980's. 1980's. His This was fust His attempts attempts to find fmd a bedrock source in the immediate immediate vicinity were unsuccessfid. unsuccessful. However, However, judging judging by byits itslarge largesize sizeand andangularity, angularity,this this boulder hasn't traveled traveled very very far. far. The Theeastern easternend endof ofthe theboulder bouldershows showsthe thepreserved preservedremains remainsof ofan an original bedrock surface. snrface. This rectangular 5 by 10 I0 foot foot block block was was unearthed unearthed in in sandy sandy glacio-fluvial glacio-fluvial sediments sedimentsduring during site site clearing for the moving and storage facilities, and and has has lain lain in inits itspresent presentposition positionfor forabout about 30 30years. years. It up to to one one foot thick. thick. The consists of about about 50% 50% close-spaced, close-spaced, sub-parallel sub-parallelen en echelon white quartz veins up veins contain l0%-20% 10%-20%light lightbrown brownweathering weathehgferroan ferroancarbonate carbonateininblobs blobsand andseamlets, seamlets,lesser lessersmall small masses of dark green euhedral euhedral chlorite, chlorite, and rare rare small small blobs blobs of of very very late late stage stage black tourmaline. tourmaline. Interstitial to the quartz veins, veins, the the other 50% 50% of of the the boulder boulder is is made made up up of of highly highly foliated foliated "horses" "horses" of of chloritic greenstone, showing an impressive impressive internal internal continuity continuity of of foliation throughout carbonate-altered cblontic with oblique tensional development in a boulder. The vein g", consistent with the boulder. The style style of veining is "ladder veining", sheared sheared rock. rock. chalcopyrite, and abundant malachite The quartz veins contain contain patchy blobs of pyrite with lesser chalcopyrite, staining. Bill Bill Bodwell's Bodwell'sinitial initialgrab g a bsample sampleof ofthe thesulfide-bearing sulfide-bearingquartz quartz gave gave .267 ,267oz/ton odton Au; Au; two later later 10,000 ppm Cu, samples odton and .006 01/ton, odton, respectively. All All of of these these samples samples yielded ++lO,OOO samples yielded .036 oz/ton Ch showing that copper, although obviously mineralogically associated with gold here, does not necessarily have a direct assay correlation (Bodwell, 1988, written written communication). communication). Our grab sample sample of the quartz.006 odton oz/ton Au. Au. Our greenstone yielded 005 sulfide gave ,006 Our sample sample of of the the barren-looking host greenstone ,005o1/ton odton Au. Au. 80 �This This wide range of gold gold assay results demonstrates the "nuggety" distribution dihbution of gold gold within within this this boulder, boulder, aa phenomenon phenomenon that that requires requires special special assaying assaying techniques techniquesto toobtain obtainaarepresentative representativevalue. value. However, Carp However, the the main point of of this this field fieldtrip trip stop stopisisthat that this this boulder boulderlikely lkeiy caine cameeither eitherfrom from the the Carp River from a similar zone nearby. It's River Falls Falls shear zone or &om It'sinteresting interestingto to note notethat that glacial glacialstriae striae on on the the pillowed greenstone greenstone near near the USGS USGS benchmark benchmark at at the eastern eastern end end of of the theStop StopSG-5 SG-5outcrop outcrop across across the the pillowed highway highway are are nearly nearly east-west, east-west, paralleling the shear zone. The Thestrongest strongestinference inferencefrom h m the theevidence evidenceatat both both this this stop stopand and the the preceding preceding one one isis that that the the Carp CarpRiver River Falls Fallsshear shear zone zone isis in in itself itself aagold goldexploration exploration target. target. Stop StopSG-7: SG7: Basal Basal Proterozoic Proterozoic Enchantment EnchantmentLake Lakeconglomerate conglomeratein in contact contact with Carp Carp River River Falls Falls shear shear zone zone in in Archean Archean metabasalt. metabasalt. (Location (Locationmap, map,Figure Figure9). 9). This This spot spot has has been been aa classic classic field field trip trip stop stop for for seeing seeingthe the features features of of the the Mesnard Mesnard and and Ajibik Ajibk quartzites U.S 41 41roadcut. roadcut.But Butour ourinterest interestlies liesthither furtherdown-section down-sectionininthe theProterozoic, Proterozoic,atatits its quartzites in the US. contact contact with with the Archean. This Thislocality localitywas waslast lastmapped mappedby byPuffett hffett(1974), (1974),who whoshowed showedthe theArchean Archean rocks rockshere here as as Mona Mona Schist, Schist, now now included included in in the the informal informal lower lower basalt flow flow unit unit of of the Mona Mona Formation Formation of of Bornhorst Bomhorst and and Johnson Johnson (1993). (1993).Puffett's Puffett'smap map(P1. (PI.1)1)shows showsthe theCarp CarpRiver RiverFalls Fallsshear shearzone zoneasasaaline line passing passingabout ahoutaa half half mile mile north north of ofhere, here, but but he hestated statedin in his his text text (p.43), (p.431, "The "The zone zoneisis indicated indicatedon on the the map map as asaanarrow, narrow,well well defmed defmedstructure, structure,but but the the symbol symbolmarks marks only only the the north north limit limit of of aa broad broad zone zoneof of sheared sheared and andaltered alteredlower lowerPrecambrian Precambrianrocks." rocks." After M e rparking parking at atthe the intersection intersectionof of U.S. U.S. 41 4 1and andChippewa ChippewaDrive, Drive, walk walk about about100 100feet feetnorthwest northwest past pastthe thebillboard billboardto to aaseries seriesof oflow lowoutcrops outcropsininthe thewoods. woods.The Thefirst fistone oneencountered encounteredisisglacially glaciallypolished, polishe4 and andexposes exposesthe theCarp CarpRiver RiverFalls Fallsshear shearzone zoneinincontact contactwith withthe theoverlying overlyingbasal basalconglomerate conglomerateofofthe the Enchantment EnchantmentLake L&e Formation. Formation.Both Botheast eastand andwest westofofhere herethere thereare arenumerous numerousnearby nearbyexposures exposuresofofthe the shear shearzone zonelying lyingnorth north of of this this contact. contact. AAwidth widthofofabout about200 200feet feetofofthe theshear shearzone zoneisisexposed exposedininthe the immediate immediatevicinity. vicinity. Shearing Shearingintensity intensity isis variable; variable; relict relict pillow pillow textures texturesare are present present in in exposures exposuresabout about 150 150yards yardsto to the the east. east. Here Hereatatthis thisexposure, exposure,the theArchean Archeangreenstone greenstoneshows showsstrong strongfoliation foliationstriking striking280°, 280° 85° 85' S. S.AAparallel parallelfoliation foliationalso alsoaffects a f k t sthe thelowermost lowermostpart partofofthe theoverlying overlyingconglomerate. conglomerate. The Theconglomerate conglomerateisisabout about55feet feetthick, thickbut butisissomewhat somewhatpatchy patchyand anddiscontinuous, discontinuous,grading grading intermittently intermittentlyboth bothupwards upwardsand andlaterally laterallyinto intocoarse coarsegrained gainedquartzite quartzitecontaining containingonly onlyoccasional occasionalsmall small 81 �cobbles or pebbles. The Theentire entireunit, unit, including includingthe the quartzite, quartzite,isis20-50 20-50 feet feetthick, thick forming formingan an erosionally erosionally resistant E-W ledge. South South of of it, it, aa 100-foot-wide 100-foot-widelow lowswale swaleoccupies occupiesthe theinterval interval presumed presumed to to represent represent erosionally recessive sericite slate that constitutes the upper part of erosionally of the the Enchantment Enchantment Lake Formation Fornation in in this area (Puffett, 1974); 1974); the very uppermost uppermost part part of of this thislithology lithologycan canbe beseen seenbelow belowthe theMesnard Mesnardquartzite quartzite back at the the highway. highway. The basal conglomerate conglomerate can be traced traced westward westward from fromhere here at at the the initial initial outcrop outcrop for forabout about250 250feet. feet. layers of of itit consist consist of of +80% The coarsest layers +8O% white vein qquartz u a cobbles. ItIt bears bears aa striking striking physical resemblance to the low-pyrite varieties of the Witwatersrand resemblance Witwatersrand conglomerate conglomerate of of South South Africa, Afiica, and and occurs occurs in in a similar geologic setting. setting. We We took tookthree threegrab grabsamples samplesof of conglomerate ffom from these these outcrops. outcrops. Two of them retumed returned detectable gold: gold: ,003 .003 odton ozlton and and ,005 .005 odton. or/ton. These These two two were were re-analyzed by Chemex and returned retumed 65 ppb and 37 ppb Au, respectively. respectively, These Theseresults resultssuggest suggestaa problem problem with with nugget nugget effect effect at the low end of the detectability scale, which would not be surprising surprising in the case of placer gold. No sulfides sulfides are are megascopically visible in this rock, nor were any found found under under the the binocular binocular microscope microscope in in an an examination examination crushed rejects rejects from from our our grab grabsamples, samples. We of the cmshed Wehave havenot not done doneany any further further testing to ddetermine e t d e the internal domains hosting these low but anomalous gold values. intemal Discussion Diicussion Although it may tum turn out that the the traces traces of gold gold in this rock are caused solely by the foliation event it, aa paleoplacer paleoplacer origin originseems seemstotous ustotobe be much more more likely. likely. For economic concentrations of of that affects it, paleoplacer gold to be found found in in the the Enchantment Enchantment Lake Lake conglomerate, conglomerate, the first fust consideration consideration would be be deposits in the Archean tmane terrane were actually in existence prior prior to to the erosional events whether or not gold deposits deposition of of the the conglomerate. conglomerate. The in that led to the deposition Theonly onlyknown known significant significant gold mineralization in region occws occurs in veins at the Champion iron mine; the Proterozoic rocks in this region the Proterozoic Proterozoicisis otherwise otherwise notable for its paucity of gold showings. Bornhorst Bomhorst and and others others(1998) (1998) have have attempted attempted to constrain constrain the dates for some some of the mineralization in the Archean rocks by lead isotope studies, obtaining obtaining a model model age age 2,455 to to 2,510 2,s 10Ma Ma for forgalena galenathat thatoccurs occurswith with gold goldin inthe theRopes Ropesmine, mine, but but also alsomentioning mentioningstructural stn~ctural of 2,455 evidence suggesting that that the the Ropes Ropes gold gold was was deposited deposited at at about about 2,690 2,690 Ma. Ma. They also pointed out that ages are poorly constrained for the timing timing of the the rifting that that initiated initiated the earliest Marquette MarquetteRange RangeSupergroup Supergroup sedimentation that this conglomerate represents. Whatever the absolute age(s) of the thegold-bearing g o l d - b e ~veins gveinsin in the the Archean Archean rocks rocks of of the the Ishpeming Ishpeming belt, this this conglomerate conglomerateprobably probablypost-dates post-datesthem. them. Evidence for this is is the the high high preponderance preponderance greenstone belt, 82 �of vein quartz within it at this this locality, locality, the the presence presenceof of anomalous anomalous gold gold in in it, it, and its apparently unconformable relationship with the Carp River Falls shear zone, which was demonskated demonstrated to be goldpaleoplacer-typegold golddeposit depositwithin withinthis this mineralized at Stop SG-5 Whether or or not not a paleoplacer-type SO-S of of this field field hip. trip. Whether for exploration exploration is is another another matter. There Thereare arevery veryfew fewexposures exposuresofofthe theEnchaniment Enchantment unit is a prime target for Lake Formation, and especially few hin conglomeratic few of of this this tthin conglomeraticphase. phase. The many samples needed needed for for assaying, provenance provenancestudies studiesand andthe thelike likewould would nearly nearly all all have have to to be be obtained obtainedby byexpensive expensivesubsurface subsurface assaying, means means over over aa wide wide area. area. Stop Stop SC-8: SG8: Lithology-seleetive Lithology-selectiveductile ductile shearing s h e a ~ with g boudinage i in n the Carp Carp River River Falls F a h shear shear 12). zone. (Location (Locationmap, map,Figure Figure12). This This locality locality was last mapped mapped by Cannon and and Klasner Klasner (1977), (1977), shown shown as as part part of of their their Precambrian Precambrian mafic-uleamafic complex. complex. The Therevised revisedstratigraphy stratigraphyof ofthe theArchean Archeanrocks rocksof ofthe theIshpeming Ishpeminggreenstone greenstone W mafic-ultramafic belt (Bomhorst (Bomhorst and and Johnson, Johnson, 1993) 1993)assigns assignsitit to to the the informal informal basalt basalt flow flow unit unit of of the the Kitchi Kitchi Formation. Formation. Beginning about us 118 mile mile east east of of here, Cannon and Klasner mapped a large area area of of Precambrian W serpentinite, serpentinite, now considered considered part of the Deer Lake peridotite. About About1/4 I14 mile to the northeast are a number of outcrops outcrops of of aa very very fresh fiesh looking, looking, nearly nearly unfoliated biotite biotite tonalite tonalite intrusion inhusion that we informally refer to as the "Mockler tonalite", named named for for an an adjacent adjacent small gold gold prospect; Cannon Cannon and and Klasner Klasner mapped mapped that as Only a few hundred feet south of here Cannon and Klasner's outcrop area as Precambrian W felsic rocks. rocks. Only Klasner's map shows shows a fault fault contact contact between the Archean and the Proterozoic. Bornhorst Bomhorstand andJohnson Johnson(1993) (1993) included included this this in the Carp Carp River River falls falls shear shear zone. zone. This expowe was was not not available available to previous workers. ItItwas wascreated createdonly onlyvery very recently, recently, when when the This exposure Marquette Marquette County County Road RoadCommission Commissionstraightened straightenedthe the approach approachto tothe therailway railwayunderpass underpassimmediately immediately south of of us. The TheRoad RoadCommission Commissiondumped dumpedaavery very large large pile pile of of excess excess blasted blasted rock from fiom this new south roadcut roadcut in aa gravel pit that lies a couple of hundred hundredyards yardssoutheast. southeast. Figure 13 13 is a detailed detailed map of of this this exposure. exposure. ItItshows showsaawide widevariety varietyof ofrock rocktypes, types,which which are are affected affected by by an an east-west east-west zone zoneof ofductile ductileshearing shearingthat that varies varies from fiom weakly weakly to to intensely intenselydeveloped, developed, dependiig on the rock type. There Thereisisevidence evidencehere here for formultiple multiple deformation: deformation: aa nearly nearly horizontal horizontal 52 S2 depending crenulation crenulationcleavage cleavageisis superimposed superimposedon onaavertical verticalS1 S, cleavage, and and is is mimicked mimickedatatall allscales scalesby bynearnear- horizontal horizontal boudins boudinsof offoliation-resistant foliation-resistantveins veinsand androck rockunits units (see (seephoto, photo,Figure Figure15). 15). 83 �___ _____ Figure 12. Location map for Stops SG-8, 9 and 10. 32'30' -______ 16/8 I ii I ." •- -: r a H o ?& 0 "N 7r"X)r 0 002 —C S 0 1000 - 60 - —-—— 2000 0 — ,g) 45 3000 I -5 I— - 2/± - —. T. 48 N. T. 47 W 1 MILE 3 601)0 7000 FEET i KILOHErER CONTOUR INTERVAL 20 FEET 47'JO' GREENWOOD 1.2 ML I,rrrnlOB—GE0LOGICAL SUSVEV - WASHING TON, Oj._ISSS—NS SI 5,3565 84 46030) 87°45' �I Figure Figure 13. 13. Plan Planmap map of of Marquette Marquette County Highway 8. Higbway "CL" roadcut, Stop SGSO-S. AT noMttrEtY $$(AC merA&454Lr .2 tocM1, LI/E4%'Y rot,4r6) o — 4u•rt1 E . yo Sd' m'Ms.4Lr ed fri 6Th 54$4tr So uOiW3 p0SN}fRY — -. 'tI—.& /tt1 c. A cm.' "/ ftttt H ti7t,t $4F1c r.mb4/c ch(orb'è jAta.rtd ..,&caJt -J 4 0 iay .cwt#4e6D MErA34re4. r >- L o I piEr I 'U mer4 ,nE.'r5 x .45S0-q SancpI' wI'ok rock sQflpI& T 0 50 5' Pit 1-owib flttT$ &4At- wE'Y C.npast and flp'. JA /0/98 C) 85 �Figure IS. 50-8. Near Figure 15.Looking Lookingeastward eastwardat at roadcut roadcut exposure, Stop SG-8. Nearcenter centerof of photo photo is is mega-boudined blocky tonalite porphyry with with brecciated south south margin margin of of tonalite tonalite fragments, fragments, quartz, chlorite and tourmaline. tounnaline. Tonalite Tonalitemega-boudin mega-boudinisisenveloped envelopedin in highly highly sheared sheared basalt basalt that also hosts horizontally horizontally boudined boudined quartz-carbonate quartz-carbonatevein veinnear nearleft leftside sideof ofphoto. photo. Highly sheared talcose ultramafic ultramafic is is at far far right. right. This exposure exhibits lithologic and structural features too numerous to be described described in detail in will be be briefly briefly mentioned. mentioned. Near the south end, end, a 15-foot this paper; the highlights will %foot layer of virtually piliowed metabasalt and undeformed graywacke and minor pink chert lies between weakly foliated pillowed moderately sheared metabasalt. rnetabasalt The not clear. clear. The southern Thegraywacke grayacke has graded bedding, but tops are not contact of the sediments sediments with the basalt appears to be conformable, conformable, but the northern contact contact with the by pyritic pyritic slickensides. slickensides. Moving northward past a mbbly rubbly interval of moderately sheared basalt is marked by near-outcropping sheared sheared basalt, shearing becomes progressively more intense, and seems to be centered on a 4-foot none can be be found at the 4-foot zone of talcose. talcose,papery-thin papery-thin sheared sheared ultrarnafic ultramafic rock. Although none outcrop itself, aapiece pieceof ofthis thisrock rock found foundin in the the gravel gravel pit pit waste waste pile pile contained contained cross-fiber cross-fiber chrysotile. On On the Jensen Jensen cation cation plot plotof ofour ourwhole wholerock rockanalyses analysesfrom fromthis thisexposure, exposure,the thesample samplefrom from this talcose material material 86 �plots in the peridotitic komatiite field (see Figure 14). This This rock rock isis either either an apophysis apophysis of the Deer Lake peridotite, or a tectonically emplaced slice slice of it; it; it exhibits exhibits vertical vertical rodding rodding but but horizontal horizontal slickensides. slickensides. Because of the structural deformation here, it's problematic problematicwhether whether the the boudined bondined tonalite tonalite porphyry is a dike or a sill. This Thisisisaafme fmegrained grained dark dark pinkish pinkish gray gray rock with up to about 20% small phenoctysts, which which in in thin thin section sectionare areall allhighly highlysericitized sericitizedalbite-oligoclase. albite-oligoclasa The feldspar phenocrysts, The groundmass composition is: a few few percent opaques, opaques, (about (about ¾ % rutile rude pseudomorphing pseudomorphing ilmenite ilmenite and ¼ '/4 porphyroblastic porphyroblastic cubic pyrite); one third anhedral quartz; quartz; one one third third sericitized sericitized albitic albitic plagioclase; plagioclase;and andone onethird thirdinterstitial interstitial chlorite, sometimes as pressure shadows of pyrite, defining a clear thin section-scale foliation. This This isis an an albitic rock that yielded yielded 6.04% 6.04% Na20, Na20, the study. A the highest highest of any of the whole rock analyses done for this study. A K20 content of 1.39% K20 1.39% is is probably probably entirely entirely due due to to sericite; sericite; no no K-spar K-spar was was found. found. A zone of of interest interest in in the the sheared sheared metabasalt metabasaltand and marked marked on onthe themap mapisisaathin thininterval intervalrich richinin disseminated disseminated coarse coarse magnetite magnetite coexisting coexisting with randomly randomly oriented oriented coarse coarsecubic cubicpyrite pyrite that thatappears appearsto tohave have developed porhyroblastically porhyroblastically without pressure shadows in a low strain environment. Another Another isis aa few few feet feet of sheared sheared greenstone greenstone with minor minor iron iron carbonate, carbonate, aa trace trace of of fine finedisseminated disseminatedpyrite pyriteand andrare raremalachite malachite spotting. spotting. This exposure has been sampled for gold more than once by MPC; MPC; the locations locations of of the latest three grab samples are shown on the map. None None of of the the samples samples yielded yielded gold above above detection limits. Despite Despite the favorable-looking favorable-looking shearing, shearing,the the lack lack of of significant significantaccompanying accompanyingcarbonate carbonatealteration alterationmay maybe hean an important reason for the lack of of detectable detectablegold gold in in it, it, even even where where copper copperminerals mineralsare arepresent. present. Figure 14, 14, the Jensen Jensen plot plot for for the the whole whole rock rock samples samplestaken takenfrom fromthis thisexposure, exposure,illustrates illustratesthat thatthe the greenstone samples, samples,regardless regardless of of degree degreeof of shearing, shearing, plot plot closely closely together together in in the the high iron tholeiite tholeiite field. Our sample of the tonalite porphyry from here is shown repeated on the Jensen plot of Figure 16 for the purpose of comparison comparison with with two two other other felsic felsic intrusive intrusive bodies bodies in in this this vicinity, vicinity, the the Mockler Mockler tonalite tonalite(sample (sample "MOCK") mine (sample (sample"PG-1"). "PG-I"). (Note: "MOCK) and andthe the tonalite tonalite porphyry at the Peninsula Peninsula mine (Note: Accessory Accessory zircon zircon was noted in thin sections sections of all of of these these rocks). rocks). The shearing be traced westward only shearing seen here cannot be Iraced traced eastward, and can he only a few few hundred feet, where it is partially exposed in the old highway highway cut. Beyond Beyond that that point, point, scattered scatteredoutcrops outcrops in in the the hills to the west are of unfoliated metabasalt. The Theductile ductileshearing shearingseen seen at at this this stop stop might might represent represent only only a branching splay of the Carp Carp River River Falls Falls shear shear zone, whose whose main expression expression may may well well lie lie south southof of here here at at the Proterozoic Proterozoiccontact. contact. 87 �FeO* + 1102 SAMPLES Cation % Cation YO Jensen Jensen (1976) (1 976) • PC-B-i • PC-B-2 £ PC-8-3 V PC-UM • PC-PFWO AJ203 MgO Figure 114: 4: Stop Stop SG-8 SG-8 Fe0* FeO*++1102 m02 Cation Cation % % Jensen Jensen (1976) ( 1 976) . w SAMPLES • MOCK K C K • RC-PI-WO m K-RtNO £ PJ203 A203 PG-I MgO Figure 6 Figure116 88 �Stop SG9: SG.9: Peninsula Peninsula gold gold deposit (Location (Location map, map, Figure Figure 12). 12). In In contrast to the broad anastomosing anastomosing ductile shear shear zones seell seen so far on this field trip, the Peninsula gold deposit occurs in a discrete brittle-ductile structure. Also Alsoin in contrast contrast to to the the nearly nearly east east -west regional shear zones seen so so far, the Peninsula Peninsula structure structure strikes strikes north north -- northeast. northeast. This structure structure cuts a by Cannon Cannou variety of host hostrocks, rocks, regionally regionally mapped mapped as as Precambrian Precambrian W massive massive and layered felsic rocks by and Klasner (1977) and subsequently subsequently assigned to the informal basalt flow flow unit of the Kitchi Formation (Bornhorst 1993). At (Bomhorst and Jobnson( Johnson(l993). At aa scale scale useful usefbl for exploration, exploration, the the geology geology is is quite quite complex. complex. History Gold was discovered at the Peninsula in the 1880's, 1 8 8 0 ' but ~but ~ there there was was never never any any commercial commercial production. All Allinformation informationon onthis thisperiod periodconsists consistsof ofold oldnewspaper newspaperarticles articleswith withvery verylittle littleuseful useful technical data except the probable depths of the two old main shafts on the property, 69 feet for the North shaft and 80 feet for the South Shaft (Fountain, (Fountain, 1992). 1992). There Therewas wasno nomodem-day modem-dayactivity activityat at the the Peninsula Peninsula by Callahan Miing Mining Corp. in 1981. MPC until it was purchased by MPCpurchased purchasedthe thetracts tractsencompassing encompassingthe the Peninsula and the nearby Michigan gold mine mine from from Callahan Callaban in in 1995; 1995;included includedin inthis thisacquisition acquisitionwere wereall all reports on these properties. properties. The following of Callahan's Callahan's drill d d l core, core, exploration data data and internal rqorts following synopsis part of a of the work done by Callahan is based on an analysis and summary of this acquired data in p~ detailed report for MPC (Duskin, (Duskin, 1997). 1997). detailed mapping, rock sampling and and Between 1981 1981 and 1984 1984 Callahan conducted surface reconnaisssance recomaisssance mapping geophysics. An An early early phase, phase,called calledthe the "granitoid "granitoid program" program'' was wasfocused focusedon onintensive intensivechip chipand and channel channel sampling of the tonalite porphyry, thought to be a pluglike intrusion with potential for large tonnage, tonnage, open inmsion with open pittable gold mineralization. Disappointing pittahle Disappointingresults resultsled led to to aare-focus re-focus on on the the steeply steeplydipping dipping"siliceous "siliceous exhalite" originally tested by the oldtimers, termed tenned the "Target exbalite" "Target Zone" by Callahan. Callahan. The The subsequent subsequent testing No detailed mapping or trenching Irenching were were done. done. Three program consisted entirely of angle core drilling. No mee shallow test holes under the old workings workings in 1984 1984returned returned sub-ore sub-oregrade gradeassay assayresults resultsbut but encouraging encouraging Shaft, returned returned 15.6 slant feet feet grading grading .216 thicknesses. In In 1985 1985the the fourth fourth hole, under the old South Shak ,216 oz/ton odton Au. Intensive Intensiveclose close spaced spaced drilling drillingwas wasthen then carried carried out out through through 1987, 1987, resulting resulting in about 20,000 feet of core in a total of 37 37 holes. boles. During D U Mthe the ~ course courseof ofthis thisdrilling drillingaapresumed presumedblind bliid en enechelon echelon termed the the "Back Zone", was was discovered. stratabound zone zone of of mineralization, mineralization, tenned The purpose purpose of of the the drilling drilling was was to to quickly quickly prove prove up up aa ramp-minable ramp-minableshallow shallowtonnage tonnageof ofhigh higb grade grade ore to augment augment or eventually eventually replace the ore being fed to the mill by the Callahan's mining operation 89 �o -. + • 441+ .7, -c - +- '"ir' '.4 .+ _+4'4 ,.—r' + 4 ++ + - ++ 4 5 + + 4 *4, - - - : 4 + - +4 + : -J 4 + • + + 4 4 + '4 4 , • + 4 + 4 + + 4* 4 o 4 4 .:-:+ ';* 55*4., 44 4 4 + •4 4 'i, 4 v-I i' +',. ,.' -4, 4 + 4 '"Mbc+ - " : + + 4 4 + + + I + + 44 4* ,1 V t -4+- '1-c-ct 7-c'? ++44•V +44 V 4,1-c-c 4 '4 -, 'ç+-c," "v' 414+ +4 "4 v,'ç.,'ç'v,'çc,v,vvv. v.vV'+ 744 +VT+ vvvV'?41vc,# 4', vvvuv c,'?c, :++ + SVV"V+IZQPQV 43'? '+24 WV. v tIn''? Vt ct -. +_.: _..., c,t 'Vt WV' 4 ' :- I \ 441*4 V14V 4 +444+4 ,'1vvvu vvvVvVtvv'?cvVtIc, Vvtv+,+-vvvVvtv,-V 'VVYVU" + Ct.'. 4 • + +-'. 44 4+-.' \\ c,t —': :'47—WãWet ,c-c1 +444+' 4; .>VQ,V+ 4 -: 4 + ' -'v-ct'-c-c VVvr+v +WtVVv V VWWVV WVV'?" V vcVvvvv V-c VvvV W4,VVv" 4' + ;+, 4 '.,tc':::4.'c:: Qc,vvvvVv'?M'?%4V?(,+ '—_.,.i,,,, + + jI V" '+++4I* '4*'• 4 wv,,-+ 9FtV++ 14 V4+- ..''?.t,,' "-cv — 43 ,, -'4" 0 .c(V4,VVV vc'vo vwt V-c 4-c vW+4.4..,v++% •-cfl-c ' Vt''? vwv 554,4 4 -' C" 'C 44+4* +44 4. 4444 +4 ',1W'-4-4-4'-4 w +44444444 '''.,.'.' t+* ' * 4 + 4 ++ +'+ 4+4+4+ -i B Zârie 1'+ 7+44. J -.f+JTh 4, .r+ -r 4 4 4 444''' ++ 4-- 4 + + -u'1°'' 'inC cm:. (.,U,4w vc, 1 •-'..C•0 0 7449?V 4* *4 r ' U'OO 4i4444'4+5 44_•+ .' C>>t>000( wvvv ,'', • +4.4+4+ + + 4 54+•4.'+ 1+4 ,I+ 44+4+4+5 — +4' 4-474 + 4- 4+ + 4 f'- I:$4f] ., 4+44+4+44.4 t. mafic intrusive 200 feet Geology Peninsula Gold Project Minaals Processing Corporation 100 Trench Outcrop Fault Gold—bearing zone Laminated felsic tuf I Greenstone Metagabbro Magnetic Figure 17: Stop SG-9 0 r Tonalite porphyry �at the the Ropes Ropes deposit. deposit. There Therewas wasno noattempt attemptatatstepout stepoutdrilling, drilling,and andthe the deposit deposit remains remains open open at at depth depth and and at in both both directions directions along along strike. strike. Callahan Callahan eventually eventually calculated calculated a reserve of 51,700 5 1,700tons tons grading grading .141 ,141 01/ton odton in in in the the outcropping outcropping Target Target Zone Zone segment segment of of the the structure, structure, and and an an additional additional 41,200 41,200 tons tonsgrading grading.082 ,082 oz/ton asfar far as as obtaining obtaining aa mining mining permit in 1988 1988 from from the first fust odton in in the the Back Zone. Mining Miingplans planswent went as level level of of authority, authority, Marquette County. But Butthe thedeclining decliningfortunes fortunesof of the the Ropes Ropes mine mine and and ofofthe the corporationitself itself led ledtotoaasuspension suspensionofofactivity activityatatthe thePeninsula Peninsulafrom fromthen thenuntil untilthe thesale saletotoMPC. MPC. corporation Taking in the the early early Taking aa new new approach approach not influenced influencedby bythe thestratabound strataboundgold goldmodels modelsin in vogue vogue in 1980's, MPC MPCbegan began its its re-evaluation re-evaluation of of the the property property by rock sampling sampling and mapping mappingon onaagrid gridat atl"=lOO' l"=lOO' 1980's, in in 1996. 1996.This Thisled ledtotothe thediscovery d i s w v wof ofthe theBack BackZone Zoneininoutcrop outcrop(now (nowrenamed renamed the the "B "B Zone"), Zone"), and and the the recognition recognition that that itit is is simply simply aa fault fault offset offset of of the the Peninsula Peninsula structure. structure. Further Furtherwork workincluded includeddigging diggingand and channel "=20' mapping channel sampling sampling 11 11backhoe backhoe trenches, trenches, detailed detailed11"=20' mappingalong alongthe theentire entireexposed exposedstructure, strncture, petrographic petrographic and polished section studies studies of mineralized core intervals, complete re-logging of many of the thecore coreholes, holes,and andcorrelation correlationof ofthe therevised revisedcore corelog loggeology geologywith withthe thesurface surfacemapping. mapping. Figure Figure17 17isisaa geologic geologicmap mapcompiled compiledfrom fromthis thiswork. work. Lithology Lithology The The oldest oldest of of the the rocks rocks hosting hosting the the deposit deposit area area appear appear to to be be an an interlayered interlayered sequence sequence of of greenstones greenstones and a laminated felsic felsic tuft'fragmental tuWfiagmental unit. unit. The Thetuff'fragmental tuWEapentd isisnon-magnetic non-magnetic and and erosionally one very v q small outcrop outcrop just east of the North Shaft Shaft can be found found on on surface; snrface; it erosionallyrecessive. recessive. Only one was wasalso alsoencountered encounteredin in Trench Trench 77 northwest northwest of of there. there. InIndrill drillcore corethis thisgray grayrock rockisisextremely extremelywell wellbanded banded and andoften oftencarries canies coarsely coarselyfragmental kagmental heterolithic heterolithic layers. layers. ItItexhibits exhibitsgraded gradedbedding, bedding,but buttops topsand andbottoms bottoms in inthis thissequence sequencehave have not not yet yet been worked worked out. out. The Thegreenstones greenstonesare aretypical typicalmetabasalts metabasaltsand andoften oftenexhibit exhibit amygdules amygdulesin in drill drill core. core. The Themany manystructural structuraldislocations dislocationsininthe theimmediate immediatePeninsula Peninsulavicinity vicinitymake makeitit difficult difficultto todetermine determineaastrike striketrend aendfor forthese theseunits, nnits,but butaadistinctive distinctivebedded beddedchert cherthorizon horizonwithin withinthis this sequence sequencethat that outcrops outcropsabout about1000 1000feet feetnorthwest northwestgives givesan anattitude attitudeof of035°, 035",72°SE. 72"SE. The Thecoarse coarsegrained grainedmetagabbro metagabbrowest westofofthe theNorth NorthShaft Shaftappears appearstotobe beaasmall smallplug plugororsill sillintruding inin~diig the thegreenstone; greenstone;itit contains containslarge large angular angular fragments Eagments of of greenstone. greenstone.This Thismetagabbro metagabbroisisnon-magnetic non-magneticand and completely completelyamphibolitized, amphibolitizedwith withpseudomorphs pseudomorphsofofcalcic calcicamphibole amphiboleafter afterorthopyroxene orthopyroxenefaintly faintlypreserved. presewed. ItIt contains contains 2-5% 2-5Yo coarse coarse cubic cubic porphyroblastic porphyroblastic pyrite pyrite that that often often hosts microscopic inclusions inclusions of of 6 chalcopyrite; chalcopyite; tiny tinyfree Eeegrains grainsof ofchalcopyrite chalcopyriteare arealso also present present in in traces. The Therock rockcontains containsabout about5% 5% chlorite chloritereplacing replacing amphibole, amphibole, indicating indicatingretrograde retrogrademetamorphism. metamorphism. 91 �The porphyry. This The most most erosionally erosionally resistant resistant of of the the Peninsula Peninsula structure structure host rocks is the tonalite porphy~~. This rock rock has has been been affected affectedby by both both metamorphism metamorphismand andhydrothermal hydrothermalprocesses, processes,especially especiallywhere whereititlies liesclose close to the the auriferous auriferous structure, structure, where gold values ranging from fiom a few to a few hundred ppb can often be found to in init. it. In In mapping mapping near near this this structure, structure, itit is is often often difficult diff~cultto todistinguish distinguishaadivision divisionbetween between the the two two alteration alteration effects, effects, but but one one of of the the principal principal hallmarks hallmarks of of the thehydrothermal hydrothermalalteration alterationisis an an increase increasein in chlorite chloriteas as replacements, replacements, seamlets, s e d e t s ,enhanced enhanced foliation foliation partings p d g s and and slickensides. Other Other such such effects effects are are elevated elevated content content of of fme fine grained grained disseminated disseminatedpyrite, pyrite,carbonate carbonatereplacement replacementof ofthe thegroundmass, groundmass,and andwhite whitequartz quark veining. veining. Strong Strongalteration alterationseldom seldompersists persistsfor formore morethan thanaafew fewfeet f& from fromstructural structuralcontacts. contacts. The Theporphyritic porphyriticnature natureof ofthis thisrock rock isisoften oftentoo toosubtle subtletotoreadily readilydiscern discernininhand handspecimens, specimens,even even in in relatively relatively fresh fiesh samples. In Inthin thinsections sectionsof ofthese, these,the thephenocryst phenocrystcontent contentvaries variesfrom from5% 5%to to 30%, 30%, and and these these are are all all heavily sericitized, sericitized, corroded albite-oligoclase albite-oligoclase crystals. The The groundmass groundmasshas has about about 20% 20% anhedral anhedral quartz, quark, within within aa very very fme fme grained grained mixture mixtureof ofbiotite biotitealtering alteringto to chlorite, chlorite, chlorite, chlorite,albite, albite, muscovite/sericite, primarily of of rutile rutile and and pyrite. Very muscovitelsericite, and opaques consisting primarily Very rare rare tiny tiny grains grains of of probable thin probablemolybdenite molybde~tehave been found in a few hand specimens. In In one polished t hin section of altered altered tonalite, tonalite,microscopic microscopicinclusions inclusionsof ofmixed mixedchalcopyrite-pyrrhotite chalwpyrite-pymhotitewere werefound foundininpyrite. pyrite. Because Becauseof ofits itsrelative relativeerosional erosionalresistance, resistance,this thisunit unit has hasbeen been "overmapped" "overmapped"ininthe thepast, past,and andisis probably probablyalso alsosomewhat somewhatovermapped overmappedas asdepicted depictedon onFigure Figure 17. 17. InInseveral severaldrill drillholes holespassing passingunder under outcrops outcropsof oftonalite, tonalite, none none was was encountered encountered in the subsurface. subsnrface. In Insome someof ofthe thetrenches trenchesitit was was found foundthat that low by outcrops outcropsof oftonalite tonalitewere wereunderlain underlamby bysubcrop subaopof ofthe theolder oldergreenstone-tuff greenstone-tuff lowareas areassurrounded surroundedby sequence sequencethat thatthis thishypabyssal hypabyssalintrusive intrusiveinvades. invades. In In drill drillcore coreintercepts, intercepts, its itscontacts contactswith withthis thissequence sequence are areusually usuallybrecciated brecciated and/or and/or slickensided, slickensided, but butaafew fewof ofthem themshow showinjections injectionsof ofthe thetonalite tonaliteinto intothe the greenstone. greenstone. The Thetonalite tonaliteporphyry porphyryisisnot notaamassive massiveplug, plug,but butrather ratheraacluster cluster of of dikes/sills. diiedsills. The Theyoungest youngestrock rock unit unitisismapped mappedas as"magnetic "magneticmafic mafic intrusive", intrusive", but butititisisprobably probablyaametadiabase. metadiabase. This Thisblack blackrock rockisisvery veryweakly weaklyfoliated foliated(except (exceptimmediately immediatelyadjacent adjacenttotocontacts), contacts),exhibits exhibitsan an equigranular equigranular texture, texture,and andcontains containsmegascopic megascopicfresh fieshbiotite. biotite. ItItcarries carriesaafew fewpercent percentcoarse coarseeuhedral euhedralpyrite, pyrite,asaswell wellasas ubiquitousdisseminated disseminated magnetite, magnetite, sometimes sometimes up up to to 10%. 10Y0.InIndrill drillcore coreititcontains containstrains bainsand andscreens screensof of ubiquitous angular fragmentsofofthe thetonalite. tonalite. angularfragments 92 �Structure Mineralization Structure and and Mineralization The Peninsula Peninsula fault fault structure structure affects affects all of of the the rock rock types, types, inclusions inclusionsof ofwhich whichcan canbe be found foundwithin within it. We Werecognize recognize two two basic basic lithotypes within the structure: quartz-carbonate quartz-carbonate ("q-c"), ("q-c"), and chlorite("ccpy"). Angular carbonate-pyrite ("copy"). Angular breccias are common in the q-c lithotype. Host Hostrock rock fragments fragments are are less abundant, but sometimes ccpy lithotype, usually as boudins. The sometimes present present in the copy Theq-c q-clithology lithology predominates Target Zone; Zone; itit exhibits predominates where the fault fault structure structure intersects tonalite, primarily in the Target exhibitsmostly mostly brittle brittle texures and has abundant abundant albite as veinlets and breccia matrix. The Theprimary primary carbonate carbonate is is dolomite, dolomite, with lesser ankerite, rhodochrosite and and late late calcite. calcite. Silica content is highly variable. variable. The q-c usually contains chioritic slip planes planes,,and contains chloritic and sometimes sometimes lenses lenses or intetfingering interfmgering layers of copy. Megascopic Megascopic metallic minerals in the q-c are pyrite, very minor chalcopyrite, minerals chalcopyrite, and, and, rarely, visible visible gold. gold. There Thereisis aa strong strong conelation correlationof ofgold gold assays assays with with pyrite, but it is not 1:1. 1:1. In Inmicroscope microscopeexamination examinationof of high high gold gold -- high pyrite samples, gold gold is is found found as as tiny tiny inclusions in pyrite, either alone or with sphalerite. Other Otherinclusions inclusions in pyrite samples with visible gold, the pyrite are are argentiferous argentiferous galena, galena- pyrrhotite pyrrhotite and and chalcopyrite. chalcopyrite. In low pyrite samples gold appears appears to to be be later later than than pyrite, pyrite, occurring occurring as as free freegrains grains in in chlorite chloriteand and carbonate, carbonate,associated associatedwith with chalcopyrite. chalcopyrite. characteristically displays The dominant mineral in the copy ccpy lithology is chlorite, and this rock characteristically ductile textures. This Thislithology lithologyseems seemsto to dominate dominatethe the fault fault zone zone where where itit intersects intersects greenstone or and in in the the deeper deeper levels levels of of the the Target Target Zone Zone segment. segment. There is metadiabase, both in the B Zone segment and albite in the matrix of this rock, rock, but but virtually virtuallyno noquartz. quartz. In the B Zone, Zone, most most of which which involves involves faulting adjacent to the metadiabase, much of the chlorite can be be seen in thin thin section to to be be replacing replacing biotite. biotite. The The ccpy is generally much higher in pyrite than the q-c, and also contains copy contains several several percent percent magnetite in the B Zone segment, probably probably derived derived directly from the metadiabase. In Inpolished polished section sectionmagnetite magnetite and and pyrite pyrite exhibit coexisting mutual mutual textures. textures. Chalocopyrite in this thislithology. lithology. Gold, Chalocopyrite also occurs as aa minor sulfide in where found so far, occurs occurs as as inclusions in pyrite, and in quartz and and carbonate carbonate veinlets. that the the composition composition of of the the Peninsula Peninsula gold gold structure's structure's gangue is is very very host host The clear impression is that rock-dependent. ItIt appears appearsthat that aa great great deal deal of of host host rock has has been been assimilated assimilated into into the structure, with the the metatonalite metatonalite contributing contributingto tothe thequartz quartzin inthe theq-c q-clithology. lithology. Similarly, the the availability of free silica in the of ferromagnesians fenomagnesians in more mafic host rocks promoted the lack of free silica and the abundance of rocks were were intersected. intersected. The abundance of dolomite in the q-c and of development of chlorite where those rocks chlorite cepy indicates introduction of magnesium chlorite in the copy indicates a very strong introduction magnesium into into the the hydrothermal system system that that operated within the operated the Peninsula Peninsula fault fault structure. structure. 93 �Zone strikes 020' 020° and dips steeply SE. On The Target Zone Onthe thesouthwest southwestititisisoffset offsetby by aa later laterhigh high angle fault which also rotates it into Zone). into an an orientation orientation trending trending 050°, 050°still stilldipping dippingsteeply steeplySE SE(the (theBBZone). Vertical movement on on this this cross crossfault faulthas has exposed exposedthe thegold goldstructure structurehere hereatataadifferent differentdepth depthlevel, level, porphyry. Where involving mostly mostly the the magnetic magnetic metadiabase in its footwall instead of the tonalite porphyry. Where intersected of breccia. These intersected in drilling, late faults such as this one consist of narrow zones of Thesefaults faults form form an an interconnecting pattern. Their interconnecting Their traces traces in in some somecases cases yield yield anomalous anomalous gold gold in in grab grab sampling, sampling, but it's not not clear whether this represents a later later mineralizing mineralizing event or mineralization mineralization remobilized remobilized from from the the Peninsula Peninsula structure. structure. SG-1O: Michigan Michigan Gold Mine Mine (Location Stop SG10: (Location map, map, Figure Figure12). 12). MPC has done only a limited amount of work so far on this gold occurrence, MFC occurrence. ItItisisincluded included as as an an optional field trip stop stop if time permits. There Thereare arevery veryfew fewoutcrops outcropsin inthe theimmediate immediatemine mine vicinity; vicinity; most most of them are metabasalts metabasalts of the the Kitchi Kitchi Formation Formation informal informal basalt basalt flow flowunit, unit, cut cutby by tonalite tonaliteporphyry porphyrysimilar similar to that at the Peninsula mine. These Theserocks rocksare are cut cut by by at at least least five five parallel, east-west, nearly vertical quartz veins. Compared Comparedto toother othergold golddeposits depositsininthis thisarea, area, the theMichigan Michigan veins veins are are very very low low in in pyrite, and represent a low sulfide sulfide hydrothermal system. There Thereisis no no particular particular correlation correlation of of gold gold with with pyrite, and and this deposit represents a case of severe nugget nugget effect. effect. These These veins veins are are famous famous for for carrying carrying free free gold, which can only be be found today today through through very verydiligent diligenteffort efforton onthe theold oldmine minedump. dump. Examination of of the the dump rocks and three core holes drilled by Callahan in the the 1980's 1980's shows shows that the theveins veinsrepresent representbrittle brittle structures. Angular are open open space space filling filling textures. Black Blacktourmaline tourmalineisisaacommon common Angular breccia breccia is is common, common, as as are vein mineral here; other exotic exotic minerals minerals found found here include include coarse coarse molybdenite, molybdenite, powellite, powellite, scheelite, scheelite, chalcopyrite chalcopyrite and a bismuth telluride. This Thismineralogy mineralogy is is typical of of the the igneous igneous assemblage often found in the roots roots of of porphyry porphyry copper copper deposits. deposits. Recorded 19th 19&Century production from from here was 856 856 ounces ounces of gold. Most Most of ofthis this appears appears to have come come from from the the No. No. 66 Shaft Shafton onthe the "main" "main"vein, vein,which whichwas wasmined minedfrom fromthe the55-foot 55-footlevel levelupwards. upwards. the property property by by MPC, MPC, nothing According to records inherited with the nothing happened at at this this mine again until the 1930's, when aa financially financially struggling strugglingsmall local stock company company deepened deepened the the No. No. 66to to 250 250feet feetand and drifted laterally east and west along the the vein. vein. The blocked-out ore was never mined except for bulk sample sample tests. tests. It is not clear exactly exactlywhere where in in the the mine the bulk samples came from. from. The Thereason reasonthat thatthe the bulk tests were done done is that the company's company's underground underground grab grab and and channel channelsamples samplesall allshowed showedextreme extreme 94 �assay variability. variability. Two Two bulk tests, tests, first first of of aa 1-ton 1-ton sample sample and and then of a 10-ton 10-ton sample, were done in Floughton by by Michigan Michigan Tech., Tech., which which determined determined aa grade grade of of approximately approximately .3 odton oz/ton Au. Au. A Houghton A third third test test was was done in 1937 at a flotation flotation mill SI! on-site Tech.. This on-site under under the the supervision supervision of Michigan Tech.. This also indicated a oziton. At Atthis this point point the the stock stock company company tried tried to to pay pay its its debts debts and move to commercial mining grade of .3 odton. by floating a new stock issue in a difficult fmancial financial and regulatory environment. The The various variousrecords records and and correspondence in MPC's files files show showthat that this this company companywas was still still frying trying to get approval to market its stock the summer of of 1941. As began, the the War War Production Production Board Board prohibited all as late as the Assoon soonas asWorld WorldWar War11 TI began, gold nothing apparently apparently ever ever happened happenedat atthe the Michigan Michigan after afterthat thatexcept exceptthe thethree threecore core gold mining in the U.S.; nothing holes by Callahan. Callahan. holes drilled drilled by 95 �References References Cited Cited Bornhorst, Bornhorst, T.J., T.J., Thorpe, Thorpe, R.I. R.I. and and Johnson, Johnson,R.C., R.C., 1998, 1998,Lead LeadIsotope Isotopestudy studyof ofveins veinsin inthe theArchean Archean Ishpeming Ishpeming(}reenstone GreenstoneBelt, Belt,Michigan: Michigan:Economic EconomicGeology, Geology,vol.93, vol.93,p.102-107. p.102-107. Cannon,W.F., W.F., and and Klasner, Klasner, J.S., J.S., 1977, 1977,Bedrock BedrockGeologic Geologicmap mapof ofthe thesouthern southernpart part of ofthe theDiorite Diorite Cannon, and Champion 7 Vz-minute quadrangles, Marquette County, Michigan: U.S. Geological and Champion 7 %-minute quadrangles, Geological Survey Survey Miscellaneous MiscellaneousInvestigations InvestigationsSeries SeriesMap Map1-1058, 1-1058,scale scale1:24,000. 1:24,000. Duskin, D.J., D.J.,1997, 1997,Peninsula Peninsula gold gold prospect: prospect: private privatereport reportfor forMinerals MineralsProcessing Processing Corporation, Corporation, Duskin, 21p. 2lp. in the the Upper Upper Peninsula: Peninsula: Lake Lake Superior Superior Port Port Cities Cities Fountain, W., 1992, 1992,Michigan Michigan gold gold mining mining in Fountain, Press, Press, l68p. l68p. Gair, Gair, J.E., and and Thaden, Thaden, R.E., R.E., 1968, 1968,Geology Geology of of the the Marquette Marquetteand and Sands SandsQuadrangles, Quadrangles, Marquette Marquette County, Tip., scale County, Michigan: Michigan: U.S. US. Geological GeologicalSurvey SurveyProfessional Professionalpaper paper 397, 397,77p., scale1:24,000. 1:24,000. Gleason, Gleason, R.J., R.J., 1986, 1986,Extended Extended Phase Phase 11Exploration Explorationof of the the Dead Dead RiverRiver- Ishpeming Ishpeming Greenstone Greenstone Belt, CallahanMining Mining Corp. Corp. private privatereport, report, 57p. 57p. Belt,Marquette Marquette County, County, Michigan: Michigan:Callahan Grunsky, E.C., 1981, 1981, No.16No. 16- An algorithm algorithm for for the classification classification of subalkalic subalkalic volcanic rocks Grunsky, using 1using the the Jensen Jensen cation cationplot: plot: Ontario OntarioGeological GeologicalSurvey SurveyMiscellaneous MiscellaneousPaper Paper100, 100,p.6 p.6165. 65. subalkalicvolcanic volcanicrocks: rocks: Ontario Ontario 1976, A new cation plot for classifying Jensen, L.S., 1976, c1assi'ing subalkalic Division 66,22p. 22p. Division of of Mines Mines Misc. Misc.Publication Publication##66, Johnson, Johnson, R.C., R.C., and and Bornhorst, Bomhorst, T.J. 1991, 1991,Archean Archean geology geology of of the the northern northern block of of the Ishpeming Ishpeming greenstone belt, Marquette County, Michigan: U.S. Geological Survey Bulletin 1904-F, greenstone belt, Marquette County, Michigan: US. Geological Survey Bulletin 1904-F, 20p. 20p. Puffet, Puffet, W.P., W.P., 1974, 1974,Geology Geologyof ofthe theNegaunee NegauneeQuadrangle, Quadrangle,Marquette MarquetteCounty, County,Michigan: Michigan:U.S. U.S Geological Geological Survey Survey Professional Professional Paper Paper 788, 788,53p., 53p.,1:24,000. 1:24,000. Van Van Hise, Hise, C.R., C.R., and and Bayley, Bayley ,W.S., W.S.,1897, 1897,The TheMarquette Marquetteironiron-bearing bearingdistrict districtof ofMichigan: Michigan:U.S. U.S. Geological 6O8p. Geological Survey SurveyMonograph Monograph28, 28,608~. Williams, G.H., 1890, 1890, The greenstone greenstone schist areas of the Menominee and Marquette regions of Michigan: 62, 2'llp. Michigan: U.S. Geological Survey Bulletin 62,241~. 96 �Examples of of Gold Gold Mineralization in the N orthern Mineralization in Northern Block of of the the Isbpeming Ishpeming Greenstonc Greenstone Belt Thomas 0. 0. Quigley and A. Mnhin Mahin and Robert Robed A. Minerals Minerals Processing Corporation, Champion MI Corporation, Champion 97 �Minerals Processing Corporation's High High Point, Point., Silver Silver Creek West, and Gold Bluff Bluff gold properties properties the in in the the northern northern m arm of of the the Ishpeming Jshpeminggreenstone greenstonebelt. belt. The field trip stops are intended to to all lie in the illudrate Host lithologies, structure, illustrate the the various various styles styles of of gold gold mineralization mineralization found found in in this thispart part of of the the belt. belt. Host mineralization, and alteration discus^ and and compared. compared. controls of mineralizatioq alteration will be discussed High Point Gold Prospect The High Point prospect was discovered diswvered by by MPC MPC during duringreconnaissance rewnnaissanceexploration explorationactivities activities from Callahan Callahan Mining Corp's working out fiom Corp's Silver SilverCreek CreekWest Westoccurrence occurrencelocated located1500 1500ft. ft.totothe thesoutheast. southeast, High grade surface mineralization at High Point is hosted by aa prominent knob knob of of intrusive intrusive felsic felsic porphyry porphy~~ escarpment of the the Dead Dead River Shear Zone Zone (DRSZ). (DRSZ). Subsequent along the topographic escaynent Subsequent exploration activities at the prospect included detailed mapping and and sampling, sampling, geochemical surveys, trenching, and diamond drilling. Figures Figures 11and 22 show show the the geology geology of of the the High High Point Point prospect. prospect. Lithology Rock types rocks, types at the High Point Point prospect prospect consist wnsist of of felsic, felsic, porphyritic porphy5ticintrusive in-ive rocks, within within aa sheared sheared of matic mafic flows and tuffacwus tuffaceous rocks and minor interfiow sequence of interflow sediments sediments corresponding correspondingto to the the Lighthouse Point Basalt of Johnson and Bomhorst Bornhorst (1991). The TheHigh High Point Point intrusive intrusiveis is aa fme fme to to medium medium grained, massive to weakly foliated foliated feldspar feldspar porphyry porphyq stock stock consisting consisting of of small small phenocrysts phenoaysts of of albite albitein in aa matrix of quartz, albite, potassium feldspar and carbonate. In thin In addition additionto to the the main main stock, stock, numerous numerous thin stringers of pporphyry o ~ h y r yof similar composition composition are are present present in the surrounding mounding volcanics. These mafic volcanic volcanic rocks consist of fine h e grained, chlorite, chlorite, sericite, sericite, and and amphibole amphibole schists, schists, and and are are probably probably altered altered basalts and related kff"wus tuffaceous rocks that have been variably sheared and deformed. Structure types defonnation related All rock t ypes at the High Point prospect have been subjected to shearing and deformation related to to the DRSZ. Mafic units exhibit steeply dipping shear related foliations striking NW-SE, parallel to the Mafk units exhibit steeply dipping shem foliations the ancillary shearing oblique obliqueto tothe themain main DRSZ DRSZtrend. trend. This shearing is main DRSZ, as well as E -- W striking ancillaq~ through 33 (see Figure 21, 2), which expose the flanking volcanic d section well exposed in backhoe trenches 11 &rough o n to the High High Point Point iintrusive. and dikes exhibit exhibit adjacent to n h i v e . The The High High Point Point Intrusive I n h i v e body and related sills and intense brittle deformation deformation manifested manifested by irregular stockwork fracturing, quartz -- carbonate carbonate veining, veining, and and brecciation. Irregular Irregularcontacts contactsof ofthese these felsic felsicunits unitsobserved observedin indrill drillcore, core,as aswell weU as as aa lack lackof ofcontinuity continuity between pporphyry units have been o r p h y ~units ~ in outcrops, drill holes, and trenches, kenches, suggest that these felsic units extensively disrupted and possibly rotated as as large competent wmpetent blocks within this portion of the DRSZ. Alteration Alteration Ubiquitous Ubiquitous carbonate carbonate alteration alteration consisting consisling of of calcite calcite and dolomite-ankerite is present throughout the the High High Point Point P Prospect, pervasive replacement replacement of of rock rock matrix, and as sheared section at the r o s p q occurring as a pmasive discrete fillings in both mafic and felsic muscovite, as discrete veins and fracture fiacture mlings felsic units. Coarse, secondary muswvite, as well as black shiny carbon mineral are wmmonly commonly associated with with carbonate carbonate veining veining in in the the High High an unknown black Point area. Examples of the carbon mineral mineralcan be readily readily found in the talus slope below the the mineralized that mineral is present present throughout throughout the the ha! this mineral outcrops of High Point intrusive, intrusive, and drilling has revealed t 98 �________ VVVVVVV vVVVVvVVVVVVvVVvVVVvyvVVtVVtvvVVvVvvVVVVVVVVVflVVVVVVVVVVV V V V V 9 V V V V V 9 V V V V V V V V V V VV V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V VVVVVVVVVV VV VVVWVVVVVVVVVVVVVVVVVVVVVVVVVVVVWVVVVVVVVVVVVVVVVVVVVVVVVVVVV VVVVVVVVV VVVVVVVVVVVVVVVVVWWWVVGVVV v VVVVVVVVVVVVVV V VVVVVV MINERALS PROCESSINGv' VcVVVVVVVV VVVVVVVVVVVVVVV74VVVVVVVV 9VVVVVVVVVVVVVVVVVVVVVVVV 7VVVVVVVVVV VVVVV CORPORATION Geology of the High Point Prospect ala t'ia eei.Iila Pi 11aM Rnjn 4n %0 — .'J — dd tone ci shearing. Strike and dip of inflation. 0 ¼0 Stzika end dip *1 .i or joint. VWVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVWVVVVVVVVVVVVWVVVVWVVVVVVV VVVVI V cv V V V V V V V V V V V V V V V V V V V V 9 V V V V V V V V V V V V V V V V V WV V V V V V V V V V V V V V WV 49 V V V ' V V V flY V V V V V V V V V V V VV V V V V V V V V V V cv c V V V iii VVVVr '' ea',,T, V igure narge VVVVVVVVVVVVVVV EVVVV 4VVVV VVV V r' I VVVVVVVVVVVVVvVVVVVVTwwVVVVVVVVVV VVVVVVVVVVVVVVVVVV VVVVVVVVVV - Thvv44 cv?,y1j.t,t÷ V VVV - 'VWVWVV&V \r.VVV*1 \74 ttt 4 V + 4 4 + % i " 4 4 V + + 4 4 4, • c + +* Hiab Point Intrusive Porpbyiy, Slice to madimu pained, reddish brown porphyriuo rock p,mpo.ed of 1 to 5 = sibite pbgiooryat. in a matrix of elba.. K—feitpar. a + * t '+ . VVVV VVVVVVVVVVVV VVV VVWVVVVVVV VVVVVVVVVVVV VV VVVVVVVVVV VVVVVVVVVVVV3'VV VVVVVVVVVV VVVVVV 3VVVVw. 9VVVVVVVVV + + * -€ - VVVWiVtI4 VVVSq4/VV9tN44 IVVVV4'W4iVV VVVVVVVVVV 9 VVVVVrVnVVVVV VVVVVVVVVV + VVVVVVVVVVVV t 9 1 4\VVWVWVV9VVVVVVWVVVVVV tt"VJPV?VVVVVVVVVWVVVVVVVVVVV 'V9JryV VV"?.flVV9VVVI "VW VVV V V V V 9' Fgpa_r V quarts, otuacovite and carbonat.. Parnitvely franturod, end veined with quartz, ten-can dolornito. ankorita. end en action black carbon minaret. liii j4j4j }li.h Point Intrusive Bericit. end cerbonata alias-ed porph1ry, cut by bieguler etockwork Veina and mesas of gray quartz. iron carbonates, minor pyrita, minor guiana, bismuth tafluride., and gold. VVVV VVV VVWVVV VVr,4VV.W VVVVVVVVVV rVVVV)_J,tc%.VV 44 VVVVVVVV t 4vvvc-vint VVr%nV gVVVVVVVVV VVt VVVVVVVVV VVWVVVVVVVV VVVVVVVVVV * 'VVVVV VVVt VVVVVV' VVVVVVVVV VVVVVVVVVV VVVV$t.'V-M, VVVVV VVVVVVVVVV VVVVVVVVVV flVVVVVV-t -VtflVWttt$VVV V%VPVVVWVVV VVVVVVVVVV VVVVVSVq VVVVVVVVVV t'Q.b7J VØ V VVV V 499 Vt V VVvVV-yg.VVVlV LVuvv',aVareVvVVVVVVVVVV VVVVVVVVVV 4 tVtV4VV-, VVVVVV 44 V' t.%fl Vflfi-VV Fj.+*9 + VVVVVVW V V; t$VVVY,VVVVV4V . tV,r-VVVVVV%V V uVVVVVVVVVV9V VVVVWVVVVVVVVW VVVVVVtVVVVVVV tI4SVVVVVVVVVV.aL \ViVVVVVVVVI V'VVVVVVVV \VLVVVVVfl VVV'VW WVVVVVVVVV Id WVVVVVVVVV VVT/V V 4LVVV V V VV'V VVVVVV VVVVVVV Ii V V - - 4 9 ÷ 9+ 9 -r 9 VVVVV + + -4 - wVr' -. - t - 'LV'kVV VV 1 t - - + 9 4 4 V4kVJV 'tJLVvN V VVV 4 9 V / tV VVV/ V '%VLVVVV V VVVVVVVVVVVVVVVVVV T''VVVVVVVVV1 VVVVVVVV' VVVVVVVVVV N o 25 - rVV -, V VVVVVVVV V V V V V V 44 V V V VV VVVVVVV V V V V V V V V VVV 50 Scala In S'bet Basalt. Indesita EJ - Fine grelnad chlorite, earlclt carbonate ecbi.te. Massive to roustad end fractured with atockwork carbonate — carbon mineral yams and dissemlatatad pyrtte where .haared, Locaily containing gray quarts veining ecd gold inlnarellsauon, Sequence contains minor mntarfior shexty. pyritln sediments- I Figure Figure 1. 1. Geology of High High Point Point �0 0 '4 + 4 4 4 4 4 4-4-4 MPC Trench in ppb. 7 4+4 444 1 + + ÷ + -1- -4- ± +4- —E 'Intt. 4 4 4 ——3— 4. ± Gold Values (ppb) CORPORATION Oda\E.ctMc Psat Geel 0 25 0 IT I Scale in Feet 0 Channel Chip and Trench Samples Figure 2. Detailed Geology of High Point 4 44 tt* 4+4444 4 44444444 * 4 rTTI Channel sample with gold value Basalt, Andesite 4 4 +t.tt.t-,-ttttt4 444 4-4+4 4 4 T:] High Point Intrusive IThrfl vfl C 4+44 Trench 1 50 MINERALS PROCESSING __ �flanking volcanic section as well. Within Withinthe themineralized mineralizedportion portionof ofthe theHigh HighPoint Pointintnisive, intmsive,microprobe microprobe analysis has shown that zoned zoned dolomite-ankerite dolomite-ankeriteis isintimately intimatelyintergrown intergrownwith with barium bariumbearing bearingK-feldspar K-feldspar Tourmaline is also locally present in quartz veins, in the matrix matrix of brecciated porphyry, and muscovite. Tourmaline and intergrown intergrown with chlorite chlorite along along fracture ffacture surfaces surfacesin in sheared sheared volcanic volcanicrocks. rocks. Mineralization Mineralization gray Surface mineralization at High Point is confmed to the porphyry, and consists of irregular gray quartz veining in altered porphyry porphyry on on the the southeast southeast side sideof ofthe themain mainknob. knob. Here channel chip chip sampling sampling of of exposed exposed outcrops outcrops (Chip (Chip Samples Samples A, A, B, B, and and C) C) returned retumed significant significant gold gold values values including 28 ft. &. of of .09 .09 ozlton, .35 oz/ton odton including including 4 ft of 1.25 1.25 ozlton odton (Figure 2). The Themineralized mineralized quartz quartz from ffom these odton, and 14 14 ft. of .35 exposures gay, cut cut by by iron ironcarbonate carbonateveinlets, veinlets, and andcontains containssmall smallamounts amountsof ofpyrite, pyite, chalcopyrite, chalcopyrite, exposures is dark dark gray, galena, sphalerite, galenq sphalerite, and electrum electnun as as well well as as an an exotic exoticsuite suiteof of bismuth bismuth tellurides, tellurides,lead leadbismuth bismuth tellurides, tellurides, and an unknown lead-bismuth-silver sulfide. The Thegeometry geometryof ofthis thismineralized mineralizedzone zonehas has not not yet yet been been defined, and defmed, although although its its extent extent has has been been partially patially confined confmedby by trenching ~~enching andwide widespaced spaceddrilling. drilling. Silver Creek Creek West Fiver Silver Creek West is a gold occurrence variably altered and and foliated foliated mafic mafic rocks. rocks. In occmnce within variably In 1988 1988 million tons @O.O37optAu @0.037optAu for Silver I. 1 &ion Silver Creek Callahan Mining Corporation calculated a resource of 1.1 controls. Surface West but never exploited it because of unresolved concerns over gold continuity and coneols. Surface trenching exposes exposes gold mineralization eenching mineralidon in in ductile ductile sheared sheared and and carbonate-chlorite-sericite-pyrite carbonate-chlonte-sericite-pyritealtered altered basalt near the margin of a felsic porphyry. In Indrill drillhole hole intersections, intersection&mineralization mineralizationappears appears to to be stratabound seatabound within 170 170 foot foot section section of ofmoderately moderatelycarbonate carbonatealtered, altered,massive massivemedium mediumgrained grainedmafics. mafics, Mineralization in both trenches eenches and and drill drill core core will be be observed observed at at this this stop. stop.The Thegeneral general geology geologyof ofSilver Silver Creek West is 3. is shown shown in in Figure Figure3. Lithology The lithologies in the immediate vicinity of the Silver Creek Creek West West prospect prospect consist consist of of aa number number of of generally generally northwest striking, striking steeply dipping dipping units, largely largely of the Archean Lighthouse Lighthouse Point Basalt (Johnson and Bornhorst, largeexpanse expanseof offine finegrained, graind Bomhorst, 1991). 1991).To Tothe thenortheast northeastof ofthe theSCW SCWprospect prospectisisaalarge pillowed basalt. Nearer Nearerto tothe theprospect prospectoccurs occursaamedium mediumto tofine finegrained grainedequigranular equigranularchiorite-albitechlorite-albitecarbonate carbonate unit, variously interpreted interpreted as as an ophitic ophitic basalt, aa sheared sheared carbonated carbonatedbasalt, basalt, and and aa hypabyssal hypabysd mafic pyrrhotite and hosts gold mafic intrusive intrusive or sill. The Theunit unit isisgenerally generally massive, massive, contains contains significant significant pynhotite mineralization mineralization at depth in drill core. The Thenext nextunit unit to to the the southwest southwestis is aa narrow narrow band of of chlorite-albitechlorite-albitephyllite interpreted interpreted as as aa ductile ductile sheared shearedbasalt. basalt. This unit hosts hosts gold mineralization mineralization sericite-carbonatephyllite trenches. This exposed in surface trenches. Thisbasalt basalt is is bounded bounded to to the the southwest southwest along along the cliff cliff face face by aa rhyodacite rhyodacite porphyry which which consists consists of of quartz, q w feldspar, feldspar,and andchlorite chloritephenocrysts phenocrystsin in aa felsic felsicgroundmass. groundmass.Drill Bill intercepts show an additional sequence sequence of chiorite-albite-sericite chlonte-albite-sericite phyllite and quartz-feldspar quartz-feldspar intrusive intrusive to the southwest. In Inatatleast least one onehole holethe the latter latter felsic felsic is is in in fault fault contact contact with Proterozoic Proterozoic sediments sediments which have have been down-thrown dom-thrown to form form the the basin basin to to the the southwest. southwest. 101 �_ __ ___ ____ VVVVVVVVVVV VVVVVVVVVP VVVVVVVV VVVVVV VVVV MINERALS PROCESSING CORPORATION --vvwVvvVvVt VVVnVflVVV vVVVVVVVVVVV VVVVVVVVVVVVV. uqVVVVVVVVVVVVV VVVV VV VV Vt Vt Vt V VV 1 —— V V V V V V V Vt PVV VVV % V V V V VVV VPVVV VVVV Silver Creek West — a'—.- 1, 1VVVVVVVV VVVVVVVPV 'VVVVVVVV Dt V V V V V V V V V V V V V V V 'VVVVVVVVVVVVVV V V V V V V V V V V V V V V V V! V V V V V V V V V V V V V V rt' °o°bZj V V V V V VP VVV V VY V V Geology — ni-la VVVVVVVVVVVVVW%R%i - VVVVVVVVVVVVV0 p V V V V V V V V V,S V V V V V V VVVVVVVV•&. qa4VV LV V VV V Vt VS%E VVVVV VVVVVV9V '1 r VVVVV Me Reversely polarized 0 a N441 Sedimantan rock. S*cii4 Undifferentiated. Berega Group V÷A FeolnaiRocks I Mafic Volcanic Rook. lv • Hvnabvsai Vafic Intnstve Rocks • Enterwediate Vo4genãc ggçp SedimoctmHoon • — Fault ihowing downthron aide Outcrop Shearing Trench — 200 0 Figure 3. 3. Geology Geology of of Silver Silver Creek Creek West West Figure 200 Scale in feet 400 V Vi �Structure and mineralization mineralization At the surface, gold mineralization exposed exposed in trenches by Callahan occurs within a ductile ductile sheared mafic mafic volcanic volcanic near the margin of of aa felsic felsic porphyry. This Thisshearing shearingstrikes strikes300° 300' and andmineralization mineralization is is considered C-type replacement. In Incontrast contrastto tosurface surfaceexposures, exposures,mineralized mineralizedintervals intervalsin in drill drill core core are are in in an unfbliated, weakly altered altered medium medium grained grained mafic maficunit; unit; there thereisislittle littleresemblance resemblanceto to mineralization mineralizationin in unfoliated, weakly depth to to the the easthortheast east/northeast from from the sheared basalt. Gold-bearing intervals that in drill intercepts occur at depth the trenched intervals intervals do not project project upwards upwards along alongobvious obviousstructural structuralplanes planesto tothe thesurface surfaceworkings. workings. The exact controls to the mineralization at at depth depth have havenot not been beenproved. proved. Intersection lineations lineations of of plunge down to to the east and offer offer one possible explanation for joining joining surface various structural features plunge and drill-hole gold (Johnson, 1991). MF'C has hasshown shownthat thatanomalous anomalousmineralization mineralization fJohnson 19911Limited Limitedwork workby bvMPC . occurs in outcrop outcrop to to the the east eastof o fthe thehigh gradetrenches trenchesatatthe theup-dip up-dip(along (alongSSlfoliation) projection of of the the occurs high grade 1 foliation) projection mineralized drill core mineralized core intervals, intervals, suggesting suggesting that the trench and and drill drill core core intercepts interceptsare are not connected. connected. Alteration The mineralized zone The mineralized zone is is associated associated with with weakly weakly disseminated disseminatedcalcite+chlorite+sericite+pyrite calcite+chlorite+sericite+pyrite alteration. Locally, Locally,minor minorFe-carbonate Fe-carbonateisisobserved observedatatsurface surfaceand andin infelsic felsicunits units encountered encountered in in drilling. drilling. Additionally, Additionally, Callahan Callahan geologists geologists identified identified an an early early epidote-pyrrhotite epidote-pynhotite(spilite) (spilite)event eventin in the the basalts. basalts. Gold Gold Bluff BluffProspect Prospect Gold Bluff Bluff is one of Minerals Processing Corporation's Corporation's active gold properties properties (see (see Figure Figure4). 4). Gold Bluff trending, 1000 foot wide shear zone in mafic mafic volcanics. volcanics. A A 100 to to 200 foot Bluff is is located located within a 3000 300' trending, wide wide felsic felsic porphyry porphyry (the (the GB GBporphyry) porphyry) intrudes intrudesthe theshear shearzone. zone.Within Withinthe thebounding boundingshear shearoccur occureasteastwest and northeast striking mineralized subsidiary shear zones. zones. Outcrop Outcropsampling sampling routinely yields yields gold in the Oppm range. range. Trenching the lppm lppmto to1lOppm 1998 intersected intersected significant significant widths of disseminated Trenching and drilling drilling in 1998 low low grade gold gold mineralization mineralization the GB porphyry and higher grade gold in mafic host rock. Mineralization in both mafic felsic hosts hosts in in different different structural structural orientations orientations will will be be seen seen at at Gold Gold Bluff. Bluff. mafic and felsic Lithology Three lithologies are found at Gold Gold Bluff: Bluff:fine-grained fine-grained mafic mafic volcanic; volcanic; medium medium to tocoarse-grained coarse-grained mafic volcanic, referred to as aa gabbro; volcanic, referred gabbro; and andfelsic felsicporphyry. porphyry. The The mafic maficunits units are aremetamorphosed metamorphosed to to facies and both both can be massive massive to to strongly strongly foliated. foliated. They greenschist fades They belong belong to to Lighthouse Lighthouse Point Point Basalt Basalt as as described by by Johnson and Bonthorst (1991). The felsic unit described Johnson and Bornhorst (1991). unit isis aarhyodacite rhyodacite porphyry porphyry interpreted interpreted as as intrusive. Where unit that that divides the the two two mafic mafic units, units, itit is is dubbed dubbed the the GB intrusive. Where it appears appears to be aa continuous continuous unit throughout the theproperty. property. Contacts porphyry. Smaller Smallerfelsic felsic dikes dikes are are also observed in various orientations throughout Contacts strike northwest and have have steep dips. A Areversely reverselypolarized polarized dike dikeof ofKeeweenawan Keeweenawan age age is is interpreted interpreted from from data to lie just just to the north of the outcropping rocks. rocks. The magnetic data The only only other other unit unit of of significance significance in in the the area is the Reany Lake Pyroclastic (Johnson (Johnson and and Bomhorst, Bomhorst, 1991) which which occurs occursjust just off off the Gold Bluff property to the the north and and west west in in association association with with gabbro gabbro flows. flows. 103 �104 Bluff Gold of Geology — .tgnlflcnt I thoy Figure 4. soda- tat wits. — .siclt. flax. Isyaxat a .aanta acp.alUon. .od.duo to basaitia pobabi. of rook mle4 and The.. u4—eet.d rse,. patoad. o.tdf to Ito. Rnnko Vnlnin MaNe Locally 33 Sec 28 Sec — — foto gr4. inn to coax.. iocr.iln .44 sonata. &aiztt.). (t. t.rbcats S44h .lnd .04 1.t.d broesalad. fr.osr.d. locally qwtL and/ot Mltpc or pb.toetyM. otth pakUo to SqWjnmiIar bO4a th04o .04 — dfr. rflo]a to t.Itth rot to wtittt nedja to vest jeus. Rocks Intrusive Feisic palnb.d Vfl 0 4 Ir' 4 0 0 • 44 + 4 V H '-•t• 01' 4t ciw g- flçf -, V V '7 VVVVV V V S÷ '4 :÷. V '-——V c'flu V — :rn7t; a-+-.. -. ?bfl ?V fl) t;vytV - • - w 4 VV +, 4 VVV o' -t 4 4 4 47 4÷ — 4 fl3 V 01 •vv-r 4_, , .4_ .4, 4__4 t hJt& + • 0 1çJ •lC. t9-ç, VV +, 4 ¶VV1.V • V9VVfl' C VW C" 1'- - + VVVVV C) flt * 4 2 4 vVVW VVV9? q feet in 300 200 .—Iy 9U Scale 100 4Sa 0 100 —I 0*t4M. GEOLOGY Project Bluff Gold Corporation Processing Minerals —. S WE N �Structure The orientation orientation of of brittle brittle and and ductile ductile shear shear structures, structure&felsic felsicporphyries, porphyries, and and quartz quartzveins veinsisis with a system of of conjugate shears shears that that control control gold gold mineralization, mineralization. Bounding geometrically consistent with shear features, mostly penetrative foliation in mafic rocks rocks and along felsic contacts, contacts, strike strike 300' 300°. . Within this, subsidiary stnctures structures and a variety of of mineralization mineralization styles are are observed. observed. For For example, example, the the GB GB trends 3200 and appears porphyry m d s 320' appears to occupy an oblique shear shear position (probably R-type Reidel). Mineralization 300 °and and is C-type Mineralization in Trench 5 and DDH GB-3, and along felsic contacts, strikes 300' replacement veining. R'-type R'-typeshears shearsare arepresent presentas asnortheast northeaststriking strikingductile ductilemicro-shears micro-shears and and as as numerous numerous mineralized quartz veins. Numerous Numerousductile ductileshears shearsand and minor minor felsic felsic porphyries porphyries that that strike strike 080° 080' to 1000 100' or S-type S-type structures. structures. may be either either P or quartz-carbonate-tounnaline veins White quartz-carbonate-towmaline veins with with fibrous fibrousstructure structnreperpendicular peqendicular to to the the vein vein walls walls are are interpreted features. These intqreted as extensional fmtures. Thesetypically typically dip dip in in the the 30° 30' to to40° 40' range rangeand andindicate indicateaahigh highangle angle component veins. Gray Gray quartz quartz veins veins are are often often mineralized, component to the shearing event responsible for these veins. defonned, deformed, and andcross-cut cross-cutby bywhite whitequartz quartzveins veinsindicating indicatingmultiple multipleshearing shearingand andvein veindeposition depositionevents. events. Alteration Alteration A zoned carbonate alterationhalo halo occurs occursat atGold GoldBid. Bluff Distal Distalalteration alterationin in the the mafic ma& volcanics consists cousists of of disseminated disseminated calcite calciteand and weak weak Fe-carbonate, Fe-carbonate, (ankerite-dolomite). (ankerite-dolomite). As As the the GB GB porphyry porphyryisis approached, Fe-carbonate approached, Fe-carbonate increases increases and can can be pervasive to the point point of of flooding floodingand and the theassemblage assemblage sericite+white quartz+pyrit&tourmaline quartz+pyrite+tounnaline appears, sencitewhite appears, largely largely in in the the felsics. felsics. Lithologic Lithologic textures texturesare are generally generally intact. Within Withinthe theGB GBporphyry poxphyryaazone zoneof ofstrong saongsericite+pyrite+Fe-carbonate sericite+pyrite+Fecarbonate occurs occurswith with porphyritic porphyritic sometimes completely completely replaced by fine textures sometimes fine grained gained sericite. sericite. Mineralization Mineralization occurs in all three lithologies lithologies and consists consists of quartz+gold+pyrite+Ag&Bi-tellurides. qm?z+gold+pyrite+Ag&Bi-tellurides. mineralization (i.e., In the metabasalts C-type replacement mineralkalion (i.e., highly silicified and sulfidized sulfidized zones wnes with with is generally generally confined confined to thin thin ductile ductile shears shears at at or or narrow foliation-parallel foliation-parallel quartz quartz veins, lenses lenses and pods) is proximal proximal to to felsic felsic contacts. contacts.Similar, Similar, although althoughoften oftenhigher higher grade, grade, mineralization minerahation occurs occursat atthe thegabbro/felsic gabbro/felsic contact. Significant SignificantC-type C-typevein vein mineralization mineralizationnot associated associated with a felsic contact also occurs within sheared gabbro south of the GB porphyry (S.7'@O. 188opt optAu Auand and17'@0.077 l7'@0.077 opt sheaxed (S.T@O. 188 opt including including 7.5'@0.1480pt w/VG). wNG). 7.5'@0.l4Sopt In In the GB porphyry, mineralization mineraIizatiou is is found found in in quartz quartz vein vein stockwork stockwork and and tends tends to to be be associated associated with disseminated pyrite and strong alteration. Gold-bearing Gold-bearing veins veins are gray g a y colored compared compared to to barren veins, although although white whitequartz quartzveins veinsare arean animportant importantindicator. indicator. One ggray ay white quartz-carbonate-tourmaline veins, quartz vein 0.4 feet wide assays 20-50 opt Au and has yielded impressive impressive visible visible gold gold specimens. Recent Recent drilling in the GB porphyry by MF' MPC significant m mineralization (224'@0.Ol8opt including C intersected sigificant i n e r h t i o n (224'@0.018opt including 1l'@O,l78 and 3'@0.l22 3'@0.122 opt). opt). ll'@O.178 105 �References R.C., 1991. proposal: Stage Johnson, KC., 1991. Silver Creek West drilling proposal: Stage III. 111. Western Western Mining CorporationlCallahan CorporatiodCallahanMining Corporation Corporation unpublished unpublished report, report, February, F e b m ~1991. 1991. , R.C., and Bodorst, Bornhorst, T.J., Johnson, R.C., T.J., 1991, 1991, Archean geology geology of of the northern northern block of of the Ishpeming Greenstone belt, Marquette Marquette County, County, Michigan: Michigan:U.S. U.S.Geological GeologicalSurvey SurveyBulletin Bulletin1904-F, 1904-F,2Op. 20p. 106 �Field Field Trip Trip33 Tilden Marquette Iron Tilden and and Empire EmpireMines Mines of the Marquette Iron Range, Range,Michigan Michigan Leaders: Leaders:G.W. G.W.Scott, Scott, P.M. P.M. Nordstrom Nordstrom and andH.M. H.M. Lukey Lukey 107 �Setting of of the the Tilden Tilden and and Empire Empire Mines, Michigan Michigan Geologic Setting Theodore Theodore J. Bornhorst, Bornhorst, Department Department of of Geological Geological Engineering Engineering and and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, Houghton, MI MI 49931 4993 1 Introduction Introduction The Tilden and Empire Mines are located in the Marquette Iron hon Range Range of Michigan's Michigan's Upper Upper Peninsula (Figure (Figure 1). 1). Mining Miningbegan beganatatthe theEmpire EmpireMine Minein in 1963 1963and and at at the the Tilden TildenMine Minein in 1974. This This is is the the first first Institute Institute of of Lake Lake Superior Superior Geology Geology field trip to either of these iron mines. The TheMarquette Marquette hon IronRange Rangehas hashad had aalong long and and varied varied mining history (Boyum, (Boyum, 1988). 1988). reserves are are sufficient sufficient to to sustain iron mining Iron mining began in the mid-1800's and current reserves until at at least least 2030. 2030. Stratigraphic Setting Stratigraphic Marquette Marquette Range Range Supergroup Supergroup The Tilden and Empire Mines produce iron ores from the Early Proterozoic rocks of the Marquette Range Supergroup (Figure 2). The The Marquette Range Supergroup consists of sedimentary sedimentary rocks with minor minor amounts amounts of cf volcanic volcanic rocks and is is subdivided subdivided into into three three groups: groups: to youngest. youngest. The Chocolay, Menominee and Baraga Groups, from oldest to The rocks rocks of of the the on older older Archean Archean basement. basement. Marquette Range Supergroup were unconformably deposited on are separated separated by by minor minor angular angular The three groups of the Marquette Range Supergroup are and informal informal units. units. The unconformities. The The groups groups are are subdivided subdivided into formal formations and The from the base upward, of conglomerate Chocolay Group Group consists, consists, from conglomerate (Enchantment (EnchantmentLake Lake Formation), quartzite quartzite (Mesnard (Mesnard Quartzite), Quartzite), dolomite dolomite (Kona (Kona Dolomite), Dolomite),and and slate slate (Wewe (Wewe Slate). Slate). The TheMenominee MenomineeGroup Groupunconformably unconformably overlies overlies the the Chocolay Chocolay Group Group and and consists, consists, from the base upwards, upwards, of local local conglomerate, conglomerate, quartzite quartzite (Ajibik (Ajibik Quartzite), Quartzite),slate slate (Siamo (Siamo Slate), and iron formation (Neguanee Iron IronFormation). Formation). The Baraga Group is is the the youngest youngest of of Menominee Group. Group. The the three groups and unconformably overlies the Menominee The Baraga Baraga Group Group includes a variety of stratigraphic units. In In the the Marquette Marquette area area itit consists, consists,from from the the base base upwards, of quartzite quartzite (Goodrich (Goodrich Quartzite), Quartzite), slate slate (Lower (Lower Slate Slate of the the Michigamme Formation), iron formation (Greenwood Iron hon Formation), Formation), Formation), mafic pyroclastics (Clarksburg (Clarksburg Volcanics), Volcanics), iron formation, formation, slate slate (Upper (Upper Slate Slate of the Michigamme Michigamme Formation), Formation),and and iron iron formation (Bijiki Iron Formation). hon Ironore orehas has been been mined mined from from iron formations within the Menominee and Baraga Groups. However, However, most most production production has has come come from from the the Negaunee Negaunee hon Formation Iron Formation of of the the Menominee Menominee Group, Group, including the Tilden and Empire Mines. Diabase Dikes Dikes and and Sills Sills stratified units of the Marquette The stratified Marquette Range Supergroup Supergroup are commonly commonly intruded intruded by Early Early the form form of of dikes dikes and and sills. sills. Early Proterozoic diabase (metamorphosed) in the Early Proterozoic Proterozoic diabase dikes and sills sills are particularly particularly common in vicinity of the Tilden and and Empire Empire Mines. Mines. Volcanics of of the the Baraga Baraga Group, Group, 10 to to 20 20 km km Diabase is also associated with the Clarksburg Volcanics 108 �% LAKE SUPERIOR srow or EXPLANATION EXPLANATION Paleozoic Paleozoic Undifferentiated Paleozoic Undifferentiated Paleozoic Rocks Rocks Keweenawan Keweenawan UndifferentiatedKeweenawan Keweenawan Rocks Rocks [----1 Undifferentiated Early Proterozoic Early_Proterozoic ji Undifferentiated UndifferentiitedEarly EarlyProterozoic ProterozoicRocks Rocks Archean Archean Undifferentiated Undifferentiated Archean Rocks Rocks I I Marquette iron Figure 1: Geologic setting of the Marquette Figure iron range. range 109 �Explanation Explanation Archean Proterozoic Proterozoic Middle Proterozoic Early Proterozoic Archean Metadiabase Undifferentiated Keweenawan sandstone ItLIMI Undifferentiated Keweenawan sandstone Metadlabase I and diabase diabase Marquette Range Supergroup Marquette Range Supergroup Baraga Group Group Baraga rc::.i Undifferentiated Undifferentiated Menominee Group Group Menornmee Negaunee Iron Negaunee Iron Formation Formation Siate I>'">I Siamo Slate Quartzite LL.Jj.JI Ajibik Quartzite Chocolay Group Group Chocolay Undifferentiated Undifferentiated 1++1 0 I !1 Generalized geology in vicinity Figure 2: Generalized vicinity of the Tilden Tilden and and Empire Empire Mines. Mines. 110 �west of the mines. Several Severalgeologists geologists have have suggested suggested that Early Proterozoic Proterozoic diabase diabase intrusions intrusions throughout the Marquette region are the same age as the Clarksburg Clarksburg Volcanics Volcanics of of younger than than the theNegaunee NegauneeIron hon Formation. Formation. However, some of the the Baraga Group and younger diabase sills at the Tilden and Empire Mines may have been lava flows (Scott (Scott and Lukey, Lukey, this volume). This Thisinterpretation suggestsmultiple ages of Early Proterozoic Proterozoic diabase diabase and interpretation suggests multiple ages of deposition of of iron iron formation. formation. The Hemlock Formation, mafic magmatism during the time of Formation, south of the Marquette area in the Iron hon Mountain area, consists of mafic volcanics that is (Morey, 1996). This supports correlative with the Menominee Group (Morey, supports the interpretation interpretation of mafic magmatism during the Menominee Group in the Marquette area. metamorphosed) UKC> dikes also {UUL LLLCLUWL~LLUXAI, uu cut LUL the rocks rocks diabas~(not Later Middle Proterozoic Proterozoic Keweenawan diabase and cut cut the the Negaunee Negaunee Iron hon Formation at the Tilden and of the Marquette Range Supergroup and Empire Empire Mines. Mines. Negaunee Fonnation Negaunee Iron Formation The Neguanee hon Iron Formation Formation consists consists of of aa variety of iron rich rocks in the Marquette Marquette area (Figure 2). The Themajor major types types of of iron iron formation formation are are carbonate iron-formation (iron carbonate carbonate and chert with minor magnetite), oxide iron formation (hematite or magnetite and chert), magnetite-banded iron formation (laminated magnetite and chert), hematite banded iron formation (laminated hematite and chert), silicate iron formation (iron silicate minerals formation minerals and types (Gair, (Gair, 1975). The TheNegaunee NegauneeIron hon Formation is chert) and combinations of these types described in detail by Scott and Lukey (this volume), Nordstrom (this volume), and Gair (1975). The Theorigin originof of the the iron iron minerals minerals in in the the Negaunee hon Iron Formation Formation isis aa complex complex processes. combination of primary sedimentary depositional, diagenetic, and metamorphic processes. The The maximum maximum thickness thickness of of the the Negaunee Negaunee Iron Formation is about about 1150 1150meters, meters, although although to assess assess (Gair, (Gair, 1975). 1975). The Negaunee hon folds and faults make thickness difficult to Iron Formation is thickest thickest in in vicinity vicinity of the Tilden and Empire Mines where is occurs occurs in in the the nose nose km across across (Figure (Figure2). 2). of a regional west plunging plunging syneline synclineabout about 66 km Age of the Marquette Range Supergroup Morey (1996) has provided a stratigraphic synthesis of the Marquette Range Supergroup. Supergroup. Supergroup is Although the age of the onset of sedimentation of the Marquette Range Supergroup 2,219+1-4Ma. Ma. The age uncertain, he has suggested that the Chocolay Group is younger than 2,219+/-4 age the Menominee Menominee Group Groupisis 1,910+/-10 1,910+/-10Ma. Ma. Deposition of the of volcanic rocks correlated with the Baraga Group Baraga Group ended endedby by1,852+1-6 1,852+/-6Ma. Ma. Depositional and and Tectonic Tectonic Setting Setting The Marquette Range Supergroup is interpreted to have been deposited in several stages (Morey, 1996; Schulz and and others, others, 1993). 1993). The Thesediments sedimentsof of the the Chocolay Chocolay Group Groupwere were deposited or intrarift intrarift stage stage (Figure (Figure3). 3). The sediments deposited during a late intracratonic or sediments of the Menominee Group were deposited on a passive continental margin in normal listric fault bounded rift basins (Cambray, 1991). The The Negaunee Negaunee hon Iron Formation Formation mined mined at at the the Tilden Tildenand and 111 �Late lntracratonic Intracratonic or Intrarift lntrarift Stage Stage Chocolay Group Archean Basement Basement Rift Stage Rift Stage Menominee Group Group Spreading Spreading Center Archean Basement Foredeep Foredeep Basin Basin Stage Stage Archean Basement Continent-arc Continent-arc Collision matic Oceanic Crust Figure Figure 3: Depositional Depositional and and tectonic tectonic setting of the Marquette Marquette Range Range Supergroup Supergroup (modified (modified from from Morey, Morey, 1996). 1996). 112 �Empire Mines was deposited deposited during this stage stage and some some faults faults at the mines may may be be related related to to this stage (Scott and Lukey, this volume). Elsewhere, Elsewhere, and and perhaps perhaps in in the Marquette Marquette area area too, too, tholeiitic basaltic basaltic magmatism also also accumulated in these rift basins. The Negaunee Negaunee Iron Iron Formation basin(s) are are located along the Great Great Lakes tectonic tectonic zone, zone, aa late late Formation depositional depositional basin(s) others, 1980). Passive margin deposition transitioned into Archean suture zone (Sims and others, deposition deposition of sediments sediments and and minor volcanic rocks in a foredeep foredeep basin stage stage that that formed formed as as aa result of Penokean collision collision of the Wisconsin Wisconsin magmatic arc with the edge edge of the the continent continent (Morey, 1996). The The continent-arc continent-arcsuture suture zone zone approximately approximately follows the MichiganWisconsin border. The TheBaraga BaragaGroup Groupwas was mostly mostly deposited deposited during during the foredeep foredeep stage stage as as turbdites. turbdites. The Marquette Range t h s t belt of the 1850 1850Ma Ma Penokean Penokean Range Supergroup Supergroup is is within the fold and thrust orogen (Sims, 1996). The The Tilden Tilden and and Empire Empire Mines are located on the south limb of the Marquette Synclinorium, an east-west trending, west plunging syncline that is about 6 km km across and 55 lun km long long parallel parallel to tothe thefold foldaxis. axis. The synclinorium, like likethe theNegaunee NegauneeIron hon Formation depositional basin(s), may have been controlled by the Archean Great Lakes tectonic zone. The Archean structures structures were subsequently folded during The iron iron formation formationand and Archean the Penokean Orogeny. The The Penokean Penokean orogenic orogenic event produced complex folds and faults and greenschist facies metamorphsim metamorphsim of the rocks at the Tilden and Empire Mines Acknowidegments Acknowldegments for comments comments on on aa version versionof ofthis thispaper. paper. Shannon Bair I thank Rod Johnson and Glenn Scott for and Chris Pascoe Pascoe helped helped with with drafting draftingof of the the figures. figures. References References Boyum, B.H., 1988, 1988, Marquette Marquette Mineral District of Michigan Mining History and Geology: Geology: Meeting, Institute on Lake Lake Superior Superior Geology Geology Proceedings, Proceedings, 34th 3 4 Annual Annual ~ Meeting, Marquette, Marquette, MI, MI, v. v. 34, part 2, p. B1-B33. Bl-B33. Cambray, F.W., Mancusco, J.J., J.J., and Slitor, W., 1991, 1991, Detachment faulting and the origin of asymmetric depositional depositional pattern of the Marquette trough (abstract): Institute on Lake Clalre, WI, v. 37, part 1, Superior Superior Geology Geology Proceedings, Proceedings, 337th7 Annual Annual ~ Meeting, Eau Claire, 1, p. 17-18. 17-18. Gair, J.E., J.E., 1975, 1975, Bedrock Bedrock geology and ore deposits of the Palmer Quadrangle, Quadrangle, Marquette Marquette County, Michigan: U.S. U S Geological Survey Professional Paper 769, l59p. 159p. Continental Margin Assemblage: Morey, G.B., 1996, Assemblage: 1996, Early Early Proterozoic Proterozoic Penokean Orogen - Continental U.S. U S . Geological Geological Survey Survey Professional Professional Paper Paper 1556, 1556,p. p. 30-44. 30-44. Sims, P.K., Card, K.D., Morey, G.B., and Peterman, Z.E., Z.E., 1980, The Great Lakes tectonic major crustal crustal structure structure in in central central North North America: Geological Society -A major Society of zone —A v.91, p.690-698. America Bulletin, v. 91, Pt. pt. 1, p. 690-698. Structure of the Continental Sims, P.K., 1996, Continental Margin: Sims, 1996,Early Early Proterozoic ProterozoicPenokean Penokean Orogen Orogen -- Structure U.S. p.44-51. U S . Geological Survey Professional Paper 1556, p. 44-51. 113 �GEOLOGIC GEOLOGIC FIELD TRIP TRIP TO THE THE TILDEN MINE Engineering Department, Tilden Mining Glenn W. Scott and Helene M. Lukey, Mine Engineering Mining Company, P.O. Box 2000, Ishpeniing, MI 49849 Ishpeming, Introduction Introduction This geologic primary structural and geologic field trip to the Tilden Mine is designed to show the primary stratigraphic features of the iron ore bodies and the implication implication of these geologic stratigraphic geologic features features in mine planning and ore control. The The interaction interaction of sedimentation sedimentation and and diagenesis diagenesis within within and supergene oxidation oxidation has has resulted resulted in in aa growth fault controlled basin, metamorphism and complex suite of ore types, each with specific, specific, if not entirely entirely objective, blending blending characteristics and problems. Although the mining operation tends toward characteristics Although the mining operation tends toward "brute "bruteforce", force", some of the blending concerns can be quite subtle and sensitive. sensitive. For the purpose of mine modeling, the deposit has been divided divided into into geologic geologic domains domains 3;Table Table1) 1)based based in in part part on on lithology lithology but, more importantly importantly on the (Figures 1,2 1 , 2and and3; bench tests tests and and in in the the processing processing plant plant (Table (Table 2). 2). The metallurgical response based on bench The primary p r i m w ore/waste orelwaste parameters are weight recovery (the percentage of each ton of ore that is turned into concentrate concentrate and pellets; i.e. the value of that ton of ore) and grade grade (does (does the the ore contain sufficient sufficient iron and silica silica grade). Other factors which can effect the plant operation and pellet quality are mineralogy (as related to total oxides and loss on ignition); trace chemical ignition); chemical composition (in particular phosphorous but also also Mn and and alkalis); alkalis); crude, magnetic and slime iron; and autogenous grinding feed. It should be noted that essentially all based on rather involved bench tests that may not directly these data are essentially directly reflect the plant response. response. Structural Geology Geology Ththis thisregion, region,the the Marquette Marquette Range Range Supergroup Supergroup is is in in aa narrow narrow east east west trending basin In basin known as the Marquette Synclinorium. This basin lies along the Great Lakes Tectonic This lies along originally defined by Sims and others (1980) as a Late Archean crustal scale Zone as originally suture with Superior Superior Province Province granite-greenstone granite-greenstone terrain to the north and older older Southern Southern Complex gneiss gneiss to the the south. south. The The northern northern margin displays a more or less complete complete stratigraphic stratigraphic succession from the base of the Chocolay Group through to the top of the Menominee Group. The Thesouthern southernmargin margin is is truncated; truncate& the the Negaunee Iron Formation Formation at Menominee group abuts directly against the high grade Archean Gneiss. Gneiss. the top of the Menominee This sharp sharp contact contact is is marked marked by outcrops outcrops of the Palmer Gneiss, Gneiss, described described as as a "comminuted, sericitised sericitised and partly silicified phase of the lower Precambrian gneiss" "comminuted, gneiss" use and (Van Hise andBayley, Bayley, 1897). 1897). since that time time has exposed a large face (Stop2) (Stop2) of the chioritic chloritic schists schists Mining activity since that form part of the Palmer Gneiss. ItIt displays displays mega-shear mega-shear bands, the spacing spacing between 114 �NORTH INTRUSIVE 4-- - 35 I.A±J -, — — -4' - HEI'l �F1 : H lN 1 rC it. 4. CDIII PIT MAGNETIU CD-Ill I 420 L?1AIN /3 1/ — a H 1420 / / H DOOIAIN vii Jat 2 7/ / (_ CROSS SECN' 'N iT I OOP$A1S1 V 2 zi IIAIH 'F 7- CN- N, L — 3 JF -' 'H' 1 (i11T"fH ,-_ -! - IZO F — — TILDEN MINE Figure 1-21.000 DATE: 1 3/11/99 " IDSnAINJ: v1 '' - .1 400 0 I = *ivwW C:: g - 000 I ) .( 1 — 20 - ' PIT F = 800 I 1000 C w OanoIa BoeIdorIts :: flT Me Tot �TILDEN HEMATITE NORTH-SOUTH CROSS-SECTION -13,100 -13,10( - TILDEN MAGNETITE MAGNETITE EAST-WEST CROSS-SECTION CROSS-SECTION -16,000 WES WE' — �________ _________ PIT PIT I LOOKING WEST WEST LOOKING NORTIOWEST DOMAIN (500) HANGINGWALL ZONE (470) L MAGP11TITI DOMAIN 1(420) x4 rooTwALi. ZONE Li ri (410) HEMATITh DOMAIN $NOWAU. CONTACT 20111 DOMAIN INTRUSOVE (200) (230)(240) I_____ L CLAY ZONE (350) HEMATITE - MARTIn DOMAIN (350) MAIN PIT CARIONATE IRON FOMIATIOII (340) FOOTWALL CLASTICS (480) FOOTWALI. IRON FOM4ATIOII DOMAIN — I (310) FOOTWAU. AND MANOINOWALI. (12Q(250) 200 400 600 800 L FIGURI 2 CDIII PIT PIT CDIII LT LnqKING NORTH NORTH LOOKING I -. - ORIGINAL GR0tMD r I CDIII HANGINGWALL AND FOOTWALL E-:J (230) (250) ,/ HEMATITE r' / (440) 1 INTRUSIVE (460) HAGNETITE (420) Figure 2 HANGING WALL ZONE (470) 0 200 I I 400 I 600 I 800 I FIGuRE 5 000 FT. 1000 F �North North S outh South coolly UT PIT .tt I FT NW UUVU 600 rT EAST PIT +1200 FT a DIAGRAMATIC STRATIGRAPHIC STRATIGRAPHIC SECTION SECTION OF OF TILDEN DIAGRAMATIC T I L D E N MINE MINE West Looking Lookin9 est - W Refer R e f e r to t o tcxbIe t ~ k d e11 Figure 33 �Mine. The Table 1: 1: Geologic domains domains and subdomains at the Tilden Mine. The domains domainsare arebased based on on lithology and metallurgical response. The numbers for each domain correspond to those lithology metallurgical The numbers for each domain correspond to those shown on Figures 1, 2, and 3 and are used as drill core codes and in modeling of the deposit 1,2, using MEDSYSTEM. MEDSYSTEM. NORTHWESTDOMAIN DOMAIN 500 NORTHWEST The Northwest Domain is stratigraphically above CD IIll/West I W e s t pit hanging wall metadiabase metadiabase (250) and below North Intrusive Intrusive (270); (270); this this domain domain includes includes numerous numerous dikes dikes and and one one mappable igneous igneous horizon, horizon, the the West Intrusive Intrusive (260). (260). 550 West Hematite 550 Hematitedomain, domain,restricted restrictedto tothe theFar Far West West Extension, Extension, is dominantly 40% and and variable variable but but elevated elevated hematite chert with mixed goethite, recoveries around 40% and metallurgical metallurgical phosphorous. Contact Contact with with 530 530 domain is defined by a thin intrusive and change. change. 530 (Hematite)-Goethite (Hematitel-Goethitedomain domainincludes includesflot flot"ore" "ore"(531) (531)and and WIF WIF (532). (532). 531 Plot Flot"ore" "ore"that thatisisdominantly dominantlygoethite-chert goethite-chert with with weight weight recovery recovery of of iron iron in in the the low 30 to -mid 40 40 %; %; variable, but generally generally high silica silica and and phosphorous. phosphorous. 532 WIF WIF"ore" "ore"isisoxidized oxidizedmartite/goethite; martitelgoethite;low low weight weight recovery, recovery,high high silica silica and and phosphorous; low heads indicate original iron formation may have been carbonate(?). heads formation have been carbonate(?). Sulfates Sulfates are are locally locally common common in in bench bench faces. faces. 520 Magnetite horizons. This Magnetitedomain domainisisdominantly dominantlymagnetite-carbonate magnetite-carbonate with silicate horizons. may be flot and/or andor mag ore in part depending on liberation. liberation. 510 Clastic horizon is at the contact with top of 5 10 Clastic horizon is at the contact with top of the the CDffl/West CDIIT/West pit pit hanging hanging wall (250) syncline.This This horizon horizon isis in in part part flot lot ore. in a local ('1) (?) syncline. ore. 400 CDIII-WEST CDIII-WESTPIT PITDOMAIN DOMAIN This domain is stratigraphically stratigraphically between CDIIJIWest C D W e s t pit hanging wall metadiabase metadiabase (250) (250) and and Thisdomain domainincludes includesnumerous numerous small small dikes dikes and and sills, sills, aa Keweenawan Keweenawan CDIII footwall (230). This dike and the West Pit Marker horizon (240). Footwallclastic clasticzone zonealong alongMain Mainpit pit footwall footwall (100). (100). Consists of dominant martite 480 Footwall clastics with coarse coarse quartzite/conglomerate quartzitelconglomerate and interbedded martite-hematite martite-hematitechert. chert. 470 Hanging Hangingwall wallzone zonealong alongbase baseofofCDIII/West CDIIIlWestpit pithanging hangingwall wallmetadiabase metadiabase(250). (250). WIF Defined as W F due to very fine grain size andlor andor oxidization. Dikedomain domainisisdefined definedasasaanortheast northeasttrending trendingzone zone of of chioritic chloritic dikes dikes and and 460 Dike associated oxidized associated oxidized and unoxidized iron formation. 450 South South Hematite Hematitedomain domainoccurs occursininthe thesouth southpart part of of CDffl CDIII and and the the West pit. It contains flot oreof of variable variablemetallurgy metallurgy and and WIF and is dominantly thin bedded, fine lot ore grained hematite-martite chert although some zones may be oxidized oxidized carbonate. carbonate. 451 Goethite Goethitezones zoneswithin withinhematite hematitedomain. domain.These Thesezones zonesare areassociated associatedwith with folding folding and faulting. A goethite zone along the footwall is present but not broken out as A goethite zone along the footwall as aa domain domain at at this this time. time. 452 Goethite Goethitezone zonealong alongCDIII CDIIIfootwall footwallsouth southof ofKeweenawan Keweenawan dike. This This zone zone typically typically has high slime slime Fe, Fe, may be oxidized oxidized Carbonate Carbonate (430) (430) domain domain along along intersection of dike and footwall. dike footwall. 118 �440 North Northhematite hematitedomain domainconsists consistsofoffine finegrained grainedoxidized oxidizedmartite-hematite martite-hematite chert with numerous dikes. The Theboundary boundary between between this this domain domain and the Magnetite Magnetite domain domain (420) trends northeast and dips steeply Plot ore in part. steeply south. Flot Carbonatedomain domainisiscarbonate carbonateflot flotore orewith withlow lowmagnetite magnetite content, high weight 430 Carbonate recovery and low concentrate grade. Fault Fault bounded bounded on on north and south south but apparently apparently gradational down dip to the west into magnetite domain (420). gradational (420). 420 Magnetite Magnetitedomain domainconsists consistsofofmagnetite-carbonate magnetite-carbonateand and magnetite magnetite silicate-chert silicate-chert with variable variable oxidation and grain size. size. This domain has relatively sharp sharp boundaries boundaries with with other domains. Domain Domaingenerally generallydefined defined by by magnetite magnetite content, content, not ore type, so so it contains potential flot contains flot ore. ore. 421 West Westpit pitmagnetite magnetitedomain domainisisananisolated(?) isolated(?)zone zoneof ofhigh highgrade grademagnetite magnetite in the west pit. It is defined defined by drilling drilling and and blast blast pattern pattern data. data. Footwallzone zoneisisdefined definedasasthe themagnetite-silicate magnetite-silicate horizon horizon at at the contact contact with the 410 Footwall CDIII Footwall metadiabase metadiabase (230). (230). It is typically waste or low grade grade due to low low magnetite content or poor liberation. content or poor liberation. MAIN PIT PIT DOMAIN DOMAIN 300 MAIN The Main Pit Pit Domain Domain contains contains iron iron formation formation units stratigraphically stratigraphically below the the CDffl CDIII footwall metadiabase (230) and/or the East pit hanging wall metadiabase (200). (200). This domain domain includes numerous includes numerous small small mafic mafic intrusives. intrusives. 370 Hanging Hangingwall wallcontact contactincludes includeszones zonesof oferratic erratic metallurgy metallurgy along along the base of the CDffl footwall CDIII footwall (230) (230) or or East East pit pit hangingwall hangingwall(200). (200). 360 Transition Transitionzone zonebetween betweenCDffl CDIIIfootwall footwall(230) (230)and and East East pit hanging wall (200). This zone consists consists of variably variably oxidized oxidized hematite hematite iron formation formation and mafic intrusives. intrusives. Restricted to north side side of East East pit. 350 Hematite-martite Hematite-martitedomain domainininEast Eastpit pitconsists consistsofofvarious varioustypes types of of martite martite chert. This domain includes includes horizons of magnetite-carbonate iron formation and thin dikes. Gradational transition over 20-50 feet to Carbonate iron formation (340). Gradational 340 Carbonate is is stratigraphically Carbonateiron ironformation formation stratigraphicallybelow belowthe thehematite-martite hematite-martitedomain domain It consists of martite-carbonate-chert with variable in East pit. (350) (350) East pit. consists martite-carbonate-chert variable magnetite/martitelFe silicate content. This magnetite1martiteFe This unit is defined by magnetic Fe, weight recovery and total oxides. ItIt has has lower lower weight recovery and higher concentrate grade than CDIII CDIII carbonates carbonates (430) (430) and and may may be be magnetite magnetite ore ore in in part. part. 330 Clay Clayzone zoneisisdefined definedasasthe thehorizons horizonsof of iron ironformation formationoutlined outlinedas as waste waste due due to to high high silica from montmorillonite (or other) interference. interference. This does not differentiate differentiate nonliberating hematite material. This zone may be stratigraphically stratigraphically controlled. controlled. Includes nonliberating Includes some some flot flot ore ore within within boundaries. boundaries. 320 East East pit pitclastics clasticsare aremixed mixedsiliceous siliceous clastics clastics and iron formation. This This unit unit includes includes oxide and carbonate horizons. ItIt may may be be the the stratigraphic stratigraphic equivalent equivalent of carbonate domain (340) down plunge to the west (7). (340) down plunge to the west (?). 321 Clay similar Clay zone zone in in clastics.is c1astics.i~ similarto to clay clay zone zone (330) (330) but in clastic clastic domain. domain. Footwalliron ironformation formationdomain domainconsists consistsofofvariably variablyoxidized oxidizedoxide oxide iron iron 310 Footwall by erratic metallurgy. formation and coarse clastics. This domain is typified by 311 31 1 Earthy Earthyfines finesare arehigh highgrade grade (>50 (>50 weight recovery recovev and >50 head Fe) oxidized zones zones are are controlled controlledby structures structures within within the the footwall footwall domain. domain. 119 �200 INTRUSIVE INTRUSIVEDOMAINS DOMAINS These domains are used for correlations of the iron formation domains, and structural trends. They appear to be conformable at the the scale scale of of the the ore orebody. body. These rocks are generally which vary vary from from diabasic diabasic to to porphyritic porphyritic interpreted as intrusives, they consist of mafic rocks which to aphanitic. All horizons appear to thin to the west and south. Contacts tend to be All horizons appear Contacts tend to be sheared sheared if and locally oxidized. Contact Contact metamorphism metamorphism of the iron formation is minimal and, if present, results in finer grained iron iron formation. Synclinal structures and intersections with Synclinal dikes have focused oxidation of the iron formation. formation. 270 North intrusive is a poorly defined North intrusive is a poorly definedhorizon horizonatatthe thetop topof of the the Northwest Northwest zone zone (500). (500). West intrusive 260 West intrusiveisisaapoorly poorlydefined definedbut but mappable mappable horizon within the Northwest zone zone (500). (500). CDIIIIWest pit 250 CDIII/West pithanging hangingwall wallisisaarelatively relativelyeasily easilymappable mappablehorizon horizon and and along along principle horizons for stratigraphic with the CDIII footwall footwall (230) (230) is one of the principle stratigraphic correlations between the CDffl correlations CDIII pit and the the Main Main pit. 240 West Westpit pitmarker markerisisa athin thinbut butcontinuous continuoushorizon horizon within within the the CDIII/West CDin/West pit stratigraphy (300). ItIt isis interpreted interpreted to to extend extend from from the the Foster Foster Lake Lake slot slot through through the the West West pit. 230 Top Topof ofthe theCDIII CDIIIfootwall footwalldefines definesthe thebase baseofofthe theCDIIIfWest CDIO/West pit pit domain domain (400) (400) while the base defines the top of the Main pit east domain (300). (300). 220 Chloritic Chloriticand anddiabase diabasedikes dikesand andthin thinsills sillsoccur occurininall alldomains. domains. This Thisunit unitincludes includes east-west trending 30+ foot thick Keweenawan Keweenawan dike in CDIII. 200 East Eastpit pithanging hangingwall wallisisseparated separatedfrom fromthe theCDffl CDIIIfootwall footwall (230) (230) by the Transition zone (360) iron formation. This Thisunit unit occurs occurs along along the the north north side side of of the the East East pit, pit, the the base base Main pit pit East East domain domain (300) (300) for for mining mining and and planning planning of this horizon marks the top of the Main purposes PIT FOOT WALL DOMAIN 100 MAIN MAIN PIT FOOTWALL 100 rocks which which are are separated separated from from the the iron iron This domain consists of Archean metamorphic rocks formation formation domains domains by an an east-west east-west trending, north-dipping north-dipping high angle angle fault. fault. 121 Chloritic Chloriticschist schistisisthe thedominant dominantfootwall footwallrock rocktype typeexposed exposed within within the the pit pit and and in in of the the CDIII CDffl footwall horizon horizon (230) within the drill holes. This rock may the extension of the fault zone. zone. 111 111 Granite Granitegneiss gneissoccurs occurssouth southofofthe thechloritic chloriticschist schist(121) (121)but but isisonly onlypoorly poorly exposed exposed in the pit. This Thisdomain domainhas hasnot not been been used used in in the the drill drill hole hole codes. codes. 999 OVERBURDEN OVERBURDENDOMAIN DOMAIN This domain domain consists consists of of Quaternary Quaternary overburden, overburden, rock rock fill fill and and broken broken bench bench material. material. 120 �Table Table 2: Glossary Glossary of terms terms and and abbreviations. abbreviations, Natural The amount of material recovered from the material fed Natural Weight Weight Recovery Recovery -- The fed into into the the concentrator In other words, words, it's the tons of concentrate concentrate made made (measured (measuredas as filter filter concentrator circuit. circuit. In cake) from tons of crude crude ore ore used (measured (measured by #3 belt scale). scale). Metallurgical Metallurgical Weight Weight Recovery Recovery (Met. (Met. Wt. Wt. Rec.) Rec.) - Calculated Calculated by comparing comparing the iron losses losses (as tailings) tailings) with the iron iron content content of the crude crude ore fed into into the concentrator concentrator circuit circuit (i.e., (i.e., the the head Fe). The formula formula used for for this this calculation calculation is called the iron balance balance formula, formula, or or sometimes sometimes called called the the concentration concentration formula. formula. (Head Fe - Tail Fe) Wt. Rec. = x 100 (Grade - Tail Fe) Grade Grade -- Also Also called the concentrate grade, is a chemical measurement (assay) of the total total iron oxide oxide of the concentrate. Iron oxide oxide is found in iron minerals such such as hematite hematite (Fe203), (Fe203), magnetite magnetite (Fe304), (Fe304),geothite geothite(Fe203 (Fez03** OH), OH), and iron iron carbonate carbonate(FeCO3). (FeC03). Concentrate Silica Grade Grade - The chemical Concentrate chemical measurement measurement (assay) (assay)of of the the % % SiO2 Si02in the the concentrate. concentrate. When When aalower lowerconcentrate concentratesilica silicagrade grade is is achieved, achieved, the losses losses in iron units (tailings) (tailings) increases. increases. content of the crude ore fed into the concentrator concentrator circuit. circuit, Grade -- The assayed iron content Head Grade concentrator's ability Iron Iron Recovery Recovery(Fe (FeRec.) Rec.) -- A calculation of the efficiency of the concentrator's ability to recover the iron available. This is calculated by comparing the Met. Wt. Rec., at some iron available. grade, with the head Fe of the crude crude ore. For example, (Met. Wt. Rec. x Grade % Fe) Grade % % = .................................. % Fe Rec, Rec. = (Head (Head % Fe) Percent Percent Magnetic Magnetic Iron Iron Recovered Recovered (% (% Mag. Fe Rec.) - The calculation calculation of the efficiency of recovering recovering the magnetic magnetic iron that was in the feed (crude ore). The Met. Wt. Rec., Rec., at at some some iron grade, is compared compared with the magnetic potential (i.e. (i.e. head) of the crude crude ore. For example, example, (Met. Wt. WI Rec. % Fe) Rec. xx Grade Grade % Rec = .................................. % Mag Fe Re (Head Mag % Fe) Tailings Tailings -- The The product lost in the process. Tailings always includes iron, because iron is always associated with many other minerals (silica, phosphate, carbonate, etc.). 121 �Flot (flotation) -- Flot ores are are the martite, martite, hematite, hematite, geothite geothite and and carbonates, carbonates that are are treated treated The final stage of the by selective chemical chemical processes to achieve Fe and silica grade. The magnetite process magnetite process is is flotation flotation to to achieve achieve target target silica silica grade. grade. to low low weight weight recovery recovery andlor and/or high WIF (waste iron formation) formation) -- hon Iron formation that due to silica cannot be treated in the plant to produce economic economic concentrate. concentrate.Rarely, Rarely, phosphorous phosphorous levels are too high to be treated. treated. The percent of the crude iron that that is concentrated concentrated in in the the Davis Davis Magnetic Magnetic Magnetic iron - The Tube Test (DMTT). (DMTT). %MagFe %MagFe == DMTT Wt. Rec. Rec. x DMTT Grade Grade However, in in the the Tilden Tilden ores ores an The assumption assumption is that all of this occurs as magnetite. However, appreciable and is is carried carried into the DMTT appreciable amount of hematite is up locked with the magnetite and Fe content by by 1-2% points points and concentrate. This tends to over estimate the magnetic Fe therefore therefore the over over estimate estimate weight weight recovery. Satmagan susceptibility and and is is the the Satmagan - The satmagan magnetic iron content is measured using susceptibility actual magnetite content content of of the the crude crude or or concentrate. concentrate. Domain - The The deposit deposit is divided into volumes of rock with similar similar metallurgical metallurgicalresponse. response. These are usually stratigraphic stratigraphichorizons horizons but may be fault fault bounded bounded or or nonconformable nonconfonnable alteration/oxidation alteratiodoxidation zones. The The domains domains are are the basis for for the economic economic and and planning planning models. models. 122 �CIstructures structuresisison onthe theorder orderofof2.5 2.5meters, meters,most mostcommonly commonlysuch suchstructures structuresare arehand hand Cl specimen specimentotomicroscopic microscopicininscale. scale.They Theyindicate indicatethe thepresence presenceofofa alarge, large,reverse reversedip dipslip, slip, ductile ductileshear shearzone zonewith withaaNNE NNEtotoSSW SSWtransport transportdirection. direction.The Thefact factthat thatthe theNegaunee Negaunee hon IronFormation Formationisisthrust thrustup upon ontotothe theolder olderArchean ArcheanGneiss Gneissindicates indicatesthat thatthere theremust musthave have been beenprior priorlocal localsubsidence subsidencehere heretotoform formthe thesedimentary sedimentarybasin, basin,aaclassic classicbasin basininversion inversion pattern pattern(Gillchrist (Gillchristand andothers, others,1987). 1987). Folds Foldsmeasured measuredwith withininthe theNegaunee NegauneeIron IronFormation Formationhave haveaxial axialsurfaces surfacesand andhinge hingelines lines that WNW,indicating indicatingaasimilar similarstrain strainenvironment environmenttotothat thatdetermined determined thattrend trendeast-west east-westtotoWNW, from the shear zone. The folding and shearing are thought to have occurred at from the shear zone. The folding and shearing are thought to have occurred atthe thesame same time. time. The Theiron ironformation formationisismostly mostlyaachemical chemicalor or biochemical biochemical deposit. deposit. The Theclastic clasticlenses lensesthat that in the south, thinning and occur occurininthe theformation formationare arethickest thickestand andmost mostnumerous numerous in the south, thinning and becoming becomingless lessfrequent frequentto tothe thenorth north (Breithart, (Breithart, 1983). 1983). The Thepattern patternsuggests suggestsan an asymmetric asymmetricrift riftbasin basinwith withaabreakaway breakawayfault faulton on the thesouthern southernmargin margin and andaarollover rolloveron onthe the north side. The principal source of clastic sediments would have been derived from the north side. The principal source of clastic sediments would have been derived from the southern southernmargin marginthat thatwas wasbeing being uplifted uplifted along along the the fault. fault. This Thisepisode episodeisisrelated relatedto tothe the development of a passive margin during the early Proterozoic. Subsequent compression development of a passive margin during the early Proterozoic. Subsequent compression during duringthe thePenokean PenokeanOrogeny Orogenyinverted invertedthe thebasin basinand andinitiated initiatedreverse reversefaulting faultingthat thatgave gave rise to the shear zone (Cambray, 1978). To the east, in the Harvey Quarry, a similar rise to the shear zone (Cambray, 1978). To the east, in the Harvey Quarry, a similar pattern patternof ofyounger youngerover overolder olderthrusting thrustingisisobserved observedsuggesting suggestingthat that this thisrelationship relationshipisis rift and later thrusting common commonalong alongthe theSynclinorium Synclinoriumand andconfirms confirmsthe theearly early rift and later thrustingpattern. pattern. Mining Mining Ore 50'x50'x45' Orereserve reserveand and long long range range mine mine planning is done in MEDSYSTEM using 5O'x50'x45' blocks based primarily on development drill holes which are on a nominal 300 blocks based primarily on development drill holes which are on a nominal 300foot foot spacing. spacing.Weekly Weeklyplans plansand anddaily dailyore orepredictions predictionsare arebased basedon onblast blastpattern patternsamples, samples, which which are areon on about about 90 90 foot foot centers. centers. Reconciliation Reconciliationof of ore, ore,waste wasteand and pellet pellet production production between betweenthe the'model" "model"and andactual actualproduction productionshows showsless lessthan than1% 1%difference. difference. The Theannual annualmining miningtask taskisisto tomove moveapproximately approximately38 38million million long longtons, tons, about about20 20million million long longtons tonsof ofore oreand and18 18million millionlong longtons tonsof ofstripping strippingwaste, waste,to to produce produce 7.8 7.8million millionlong long tons tonsof of flux fluxpellets pellets per per year. year. Production Productionsince since1974 1974has hasbeen been 126 126million million long longtons tonsof of pellets pellets from from355 355million million long long tons tons of of ore ore at at aa stripping stripping ratio of 0.94. As As of of January January1,1, 1999, 1999,the the proven proven and and probable probablelong longrange range (30 (30year) year) mine mine plan plan reserve reservewas was628 628million million long long tons tons of of ore ore containing containing233 233 million million long long tons tons of of pellets pellets at at aa stripping strippingratio ratio of of 0.77. 0.77. The P&H 2800 2800(38 (38 cubic cubic yard) yard) cable cable shovels, shovels, three three P&H P&H Theloading loadingfleet fleetconsists consistsof of two twoP&H 2100 2100 (l7cubic (17cubicyard) yard)cable cableshovels shovelsand andtwo two994 994(21 (21cubic cubicyard) yard)Caterpillar Caterpillarwheel wheel loaders. loaders. The The hauling haulingfleet fleetconsists consistsof of three three 793 793 (240 (240 ton) ton) Caterpillar Caterpillar trucks, trucks, seven seven 789 789 (190 (190 ton) ton) Caterpillar trucks and six Haulpack 630E (170 ton) trucks. Drilling is done with one trucks. Drilling is done with one Caterpillar trucks GD120 120drill. drill. P&H and and one oneGD P&H 123 �Field Trip Trip Stops Stops - . stops to be visited and their locations cannot he be determined determined until until iust just urior prior to The actual stoos the field trip. The generic stop descriptions are provided in this guide and the actual The generic stop descriptions are provided in this guide and the actual localities to be visited will be provided provided to participants on on the the day day of the the field field trip. trip. Stop 1 - Pit Service Building Before beginning the tour of the Tilden pit, the mine safety rules will be reviewed and and aa short video of the Tilden Tilden Mine Mine operation operation will be shown. shown. The The video, not not particularly particularly geologic, describes pelletizing processes that have describes the mining cycle, milling and pelletizing have aa major major impact on the ore quality determinations. determinations. Stop 2 -- Main Main Pit Footwall Shear Shear Zone Zone Chlorite schist defines the footwall of the Tilden ore body. body. This This chlorite chlorite schist schist is is described described in the literature literature (Van Hise and Bayley, 1897; 1897; Gair, 1975) 1975) as part of the Palmer Palmer Gneiss and marks the boundary between the Archean Compeau Creek gneiss gneiss of the the Southern complex and the early Proterozoic sediments. This This contact contact extends extends for for approximately seven miles east from the the Tilden Mine. Gair Gair and Simmons Simmons (1968) (1968) made madeaa complete complete study study of this rock and proposed three possible modes of origin: 1) 1)alteration alterationand and shearing shearing of Precambrian rock during during faulting; faulting; 2) migration of fluids fluids along along the contact contact between lower and middle Precambrian rocks; and 3) alteration of a regolith during lower Precambrian alteration regolith during folding. folding. At Atthe theTilden TildenMine, Mine,there thereappear appearto to be be two two varieties varieties of of gneiss, gneiss, aa southern southern sericitic phase related to a granitic protolith and a northern chloritic phase with a diabasic diabasic protolith. protolith. At this locality surface cut by the the more more locality one one can see see the dominant, dominant, steep steep north dipping dipping S surface gently north dipping Cl 4). The C/ surface (Figure 4). The intersection intersection between the S and Cl C/ plunges plunges WNW. The gently to the WNW. The movement movement plane plane on the shear shear zone is at right angles to this intersection and the intersection of this plane and the boundary of the shear zone (determined from drill records) gives the direction of movement (marked with a filled (determined filled triangle on Figure 5). The Thepattern patternof of the the SS surfaces surfaces and and shear shear bands bands give the sense sense of movement (Figure 4). Chemical Chemical analyses analyses indicate that the protolith for the shear zone was most likely to have been one of the diabase bodies found interlayered with the banded iron formation. formation. (-60') foliation foliation in the chlorite schist creates a bench and slope slope The steep steepnorth northdipping dipping(—60°) stability concern. This 45° final wall slope with 35 Thisisis controlled controlled by by triple triple benching to a 45" 35 foot catchers. Proper Properclean cleanup up along alongthe the toe toe line line is is critical critical to avoid "undercutting" the the foliation. foliation. 124 �West 2.5 Shear Zone (Palmer IPaImrGness) GneW Figure Figure 4: 4: Footwall Footwallshear shearzone, zone,Tilden TildenMine. Mine. Pole Poleto to mean mean C-foliation C'-foliation S * U Pole poleto tomean meanS-foliation ~-fo~atim Slip direction Mean ~ e a S-C S-C. n intersection intersection S-C intersections S-foliafion plane Top of shear zone ' .C-foliation C'-foliation plane p4ane "Nonnal intersection \ N o m d totoS-C' S-C/intersection Figure5: 5: Stereo Stereo projection projection of of shear shearzone zonestructures. structures, Figure 125 �Stop 3 -- Martite and Main Pit Pit Carbonate CarbonateDomains Domains The Martite and main pit Carbonate Carbonatedomains domains lie lie stratigraphically stratigraphically below below the the CDffl CDEI Footwall and Main Pit Hangingwall intrusives. This This is is metallurgically metallurgically "good "good ore" ore" and and isis typically characterized characterized by high weight recovery (35-45+%), (35-45÷%), low phosphorous, low slime slime iron and good grinding media. With Withcrude crudeFe Fe around around 35%, 35%, iron iron recovery recovev averages averages over over 70%. The The'best' 'best'ore oreisiscentered centeredon onthe theMain MainPit Pitanticline anticlineand andconsists consistsof of thick thick bedded bedded (2(24 cm) chert with variable variable martite martite and magnetite magnetite plus subordinate subordinatecarbonates carbonatesand and silicates. silicates. The boundary between the Martite and Carbonate domains is based on higher magnetite Carbonate domains higher magnetite content; content; the Carbonate Carbonate domain domain contains contains low calculated calculated total oxides oxides that that may may be be due due to to iron silicates. silicates. The Thevariation variationin inmagnetite magnetitecontent content may may reflect reflect either either the the environment environment of of deposition deposition or or diagenesis; diagenesis;itit is is unlikely unlikely to be due due to supergene supergene effects. This domain comprises reserve. The mine plan comprises about 56% of the ore reserve. The~mine plan attempts attempts to to control control the blend percentages to about 50% of this domain. This This has has been been only only partially partially successful due to pellet quality concerns when blending with other types of ore. The successful planned final final depth depth of of the the Main Main pit pit is is about about sea sea level level so so the the pit will will be be about about 1000 1000feet feet deeper. deeper. As the base of the iron formation is not exposed at the Tilden Mine, the stratigraphic stratigraphic thickness is unknown. The Thethickness thickness exceeds exceeds 1000 1000feet feet and and is probably underlain by and is gradational into undifferentiated clastics and iron formation formation of the Empire Empire Mine. "Intrusive" Igneous Horizons Stop 4 - Mafic "Intrusive" formation and the rapid Due to the lack of clear stratigraphic markers within the iron formation rapid facies changes in the iron formation, several igneous horizons are used for stratigraphic stratigraphic and structural correlation correlation(Figure (Figure 1). 1). The term 'intrusive' 'intrusive' or or'dike' 'dike'isisused usedfor forgreen greenand andgray-green gray-green mafic mafic igneous igneous rocks, which vary from (semi) (semi) conformable sill-like sill-like horizons to obviously crosscutting crosscutting bodies. bodies. Since the fabric varies from diabasic diabasic to porphyritic to aphanitic, the conformable conformable bodies bodies are usually interpreted as synsedimentary sills sills but but may maybe beflows. flows. The sills range in thickness thickness from a few tens of feet to at least 600 600 feet with the thicker horizons horizons thinning thinning to to the south. Dikes, typically 55 to to 20 20 feet feetthick. thick. The Dikes,obviously obviously crosscutting crosscutting bodies, are typically dikes may be feeders. feeders. The dikes and thinner parts of the sills are commonly altered altered to chlorite and carbonate retain primary primary igneous igneoustextures. textures. Contacts cabonate while the thicker parts retain Contacts with the iron formation are variably sheared and altered. the iron formation are variably sheared and altered. The principal principal sills sills are are the the Main pit pit hangingwall, hangingwall, CDffl CDEI footwall footwall and the CDffl CDEI hangingwall. hangingwall. The Thesills sillsand andmajority majorityof of the the dikes dikes appear appear to be of early Proterozoic Proterozoic age but, there are several dikes that are interpreted to be of Keweenawan age based on the and fracture fracture zones. zones. The igneous event magnetic signature. Dikes Dikes commonly fill faults and Clarksburg, that emplaced emplaced the sills sills and majority of the dikes may be related to the Clarksburg, Hemlock and Emperor Volcanics. 126 �Dilution from dikes, especially along shallowly dipping contacts, is the most common internal waste. waste. kcipient type of internal Incipientrecrystallization recrystallization due due to to contact contact metamorphism metamo~hismand hangingwall. quartz overgrowing magnetite results in high silica waste along the CDIII hangingwall, Stop 5 - West West Pit/CDIJI Pit/CDZZZ Hematite Hematite Domain The West Pit/CDffl PivCDIII Hematite Hematite domain domain in in the the west pit is is stratigraphically stratigraphicallybetween between the the CDffl hangingwall and footwall. This domain extends from CDffl along the north limb CDIII This domain extends CDIII pit anticline. In contrast to the martite domain, this is and over the crest of the Main pit metallurgically 'poor' ore orewith with higher higher slime slime iron, iron, phosphorous and poor grinding. Fe), due to the the high crude Fe Although weight recoveries are relatively good (about 36% Fe), below 60%. 60%. Mineralogically of 40%, the iron in this domain is below Mineralogically and texturally, this domain differs from the martite domain in being dominantly platey hematite with thin (mm scale) chert laminae. Presumably, the bedding thickness reflects the original sedimentary sedimentary features but it is unclear as to the nature of the oxidation event that produced the hematite hematite (related (related to to deposition, deposition,diagenesis diagenesisor or supergene supergenealteration). alteration). With a thickness thickness of about about 600 600 feet, this domain contains contains 27% of the ore reserve but, due due to blending concerns for phosphorous, slimes or grinding, it is often difficult to maintain phosphorous, maintain that percentage percentage in in the the blend blend going going into into the the processing processing plant. plant. Stop 66 -- Magnetite Domain The Magnetite PitJCDffl hematite hematite Magnetite domain domain is the stratigraphically equivalent of the West PivCDIII but is essentially essentially restricted to the CDffl CDIII syncline (basin?). Magnetite Magnetiteore orequality qualityisis determined (magnetic determined by the percentage of the crude iron that occurs as magnetic iron (mapetic concentrate determined by the Davis Magnetic Magnetic Tube TubeTest). Test). On average, the Magnetite domain contains 27% magnetic iron with 37% total total crude crude iron. iron. With about 90% magnetic magnetic iron recovery recovery in the plant, weight recoveries are 34-36% iron. Mineralogically, Mineralogically, the ore consists primarily of magnetite-siderite-chert with variable hematite and silicates. consists primarily silicates. This This mineralogy, along along with the thin laminations, laminations, appears to indicate a restricted basin and a reduced environment environment of deposition. deposition. respect to to the There is some scientific scientific controversy as to the role of diagenesis with respect hematite and and siderite. siderite. Within the Magnetite domain relationship between magnetite, hematite there is a faultldike-bounded faulvdike-bounded zone of low magnetite siderite ore; it is uncertain whether this is the protolith of the magnetite ore. The The southern southern extension of the CDffl CDIII magnetite into the hematite domain contains the highest highest grades grades (-30 (-30 magnetic iron). The The sharp sharp contact, not structural, structural, indicates indicates that this is some sort of redox front but it is unknown unknown whether it is is of of diagenetic diageneticor or supergene supergene origin. origin. Approximately reserves are are in in magnetite. magnetite. Development of the Approximately 23% of the Tilden ore reserves of pushbacks pushbacks along along the thewest westwall wallininthe theintrusive. intrusive. The The wall is reserve involves a series of planned planned to move move back about about 800 800 feet and the pit is to be he deepened about 600 feet. 127 �Acknowledgments Acknowledgments We thank Bill Cambray Cambray and Cheryl Webster for their contribution of the Structural Stmctural Geology section in the Introduction and structural structural discussion in Stop Stop 2. References References Cambray, F. W., 1978, 1978, Plate Tectonics as a model for the environment environment of deposition deposition and and deformation Northern Michigan: Michigan: deformation of the the early early Proterozoic Proterozoic (Precambrian X) of Northern Geological 7, p. 376. 376. Geological Society Society of America Abstracts with Programs, Programs, v.10, no. 7, Breithart, M. S., S., 1983, 1983,Significance Significanceof of the the distribution distribution of of clastic clastic lenses lenses within within the the Breithart, Negaunee Iron Formation Formation at the eastern end of the of the Palmer Basin, Marquette Marquette Synclinorium, Synclinorium, Northern Michigan: Masters Masters thesis, Michigan Michigan State State University. University. Gair, J.E., J.E., 1975, 1975,Bedrock Bedrock geology geology and ore deposits deposits of the Palmer Palmer Quadrangle, Quadrangle, Marquette Marquette County, Michigan: U.S. U S . Geological Geological Survey Survey Professional Professional Paper 769, lS9p. 159p. Gair, J. E. and and G. G. C. C. Simmons, Simmons, 1968, 1968,Palmer Palmer Gneiss Gneiss -- an an example of retrograde retrograde metamorphism metamorphism along along and and unconformity: U.S. US. Geological Geological Survey Survey Professional Professional Paper, Paper, 600-D, 600-D, p. D186D186- D194. D194. Gillchrist, Gillchrist, Ralph, Ralph, Mike Mike Coward Coward and and Jean-Louis Mugnier, Mugnier, 1987, 1987,Structural Structural inversion inversionand and its controls: controls: examples examples from from the the French French Alpine foreland foreland and and the the French French Alps: Alps: Geodinamica Acta (Paris) v.1, no. 1, p. p.5-34. 5-34. Sims, P.K., Card, K.D., Morey, G.B., and Peterman, Z.E., 1980, The Great Lakes tectonic zone A major crustal cmstal structure structure in central North America: Geological Society of zone -- A America bulletin, V. V.91, 91, Pt. pt. 1, 1, P.690-698. p. 690-698. Van Hise, C.R., and C.R., and Bayley, W.W., 1897, 1897, The Marquette iron-bearing district of Michigan: Michigan: U.S. U.S. Geological GeologicalSurvey Survey Monograph Monograph 28, 2 8 ,608p. 608~. 128 �Geologic Field Field Trip Trip to the Empire Empire Mine Mine , M. Nordstrom, Nordstrom, Empire Empire hon IronMining MiningPartnership, Partnership,P.O. P.O. Box Box 38, 38, Palmer, Palmer, MI MI 49871 49871 Paul M. Introduction Introduction Empire mine commenced operations in 1963; 1963; over the past thirty-five years the operation The Empire has produced nearly 200 200 million long tons of pelletized iron concentrates. The TheEmpire EmpireMine Mine represents repr&ents a partnership partnekhip of steel making m G n g and iron iion mining interests and is partially oowned h e d and operated by the Cleveland-Cliffs Iron hon Company. The Thereserve reserveis is about about 600 600 million million long long tons tons of magnetite magnetite ore. ore. The Thecurrent currentannual annualproduction productionisis8.4 8.4million million long longtons tonsof of pellets pelletsfrom from27.5 27.5 million long tons of ore. Han hon Han (1975) (1975)provides provides aa detailed description of the Negaunee Iron Formation at at the the Empire Empire Mine. Mine. Stratigraphic hon Formation Stratigraphicrelationships relationships within the Negaunee Iron Formation in in the the vicinity vicinity of of the the Empire Empire Mine Mine are: are: • Upper UpperUndifferentiated UndifferentiatedSeries Series(+ (+1500'): 1500'):intermixed intermixedsequence sequenceof ofcarbonate, carbonate,silicate, silicate, clastic clastic and "lean" "lean" carbonate carbonateassemblages. assemblages. • Clastic Clastic horizon (200-300'); (200-300'); graywacke graywackeand and feldspathic feldspathicquartzite quartzite interbedded interbedded with with chert, iron carbonate carbonate minerals minerals and and magnetite. magnetite. • Carbonate Carbonate horizon horizon (350-500'): (350-500'): alternating alternating bands bands of of magnetite-chert magnetite-chert and and chert, chert, with with siderite siderite or or ankerite ankerite distributed distributedthroughout. throughout. Local, Local, minor minor beds beds of of riebeckite riebeckiteand and aegerine-augite aegerine-augite are present contact. present near near the the upper upper contact. .. • Silicate Silicate horizon horizon (400-500'): alternating alternating laminae laminae of of magnetite, magnetite, carbonate, carbonate, greenish greenish microstilpnomelane), and chert. micro- to to sub-microscopic sub-microscopiciron iron silicate silicateminerals minerals(principally (principally stilpnomelane), and chert. - . • Lower h w e r Undifferentiated undkferentiated Series Series (700-1500'): (700-1500'): intermixed intermixid sequence sequence of carbonate, carbonate, silicate silicate minerals and and clastics clastics (clastics (clasticsincrease increasetoward toward base base of of interval). internal). The The basal basal contact contact of of the the Lower Lower Series Series is is transitional with the underlying Siamo Slate. The The Siamo Slate is represented in the mine area by quartz-arkose and graywacke. Siamo Slate is represented in the mine area graywacke. A A geologic geologicmap map and and section sectionof of the theEmpire EmpireMine Mine(Figure (Figure11and and 2) 2) illustrate illustratethe therelationships relationships between between the the various variouslithologic lithologicunits. units. hon Ironformation formationatatthe theEmpire EmpireMine Mineisistransected transectedby by aa number number of of near-vertical, near-vertical, chioritized chloritized metadiabase are metadiabase dikes. dikes.The Thedikes dikesoccupy occupyfaults, faults,believed believed to to be be of of early earlyProterozoic Proterozoicage, age,which which are probably related related to to basin basin development. development. The Thedikes dikeshave havehad hadaasignificant significantlocalized localizedimpact impact on on ore ore probably processes. processes. The Thefine finegrain grainsize sizeofofmagnetite magnetite(5 (5p.) p)in in iron iron formation formationadjacent adjacentto tothe thedikes dikes represents represents aa "selvage" "selvage" which which was was apparently apparently impervious impewious to subsequent subsequent processes that influenced influenced growth of of the the magnetite magnetite grains grains in in other portions of the iron formation. Effective Effectiveliberation liberationof of growth magnetite in in these these"fine-gralned" "fine-grained"rocks rockscan canrarely rarelybe beachieved. achieved. magnetite The iron iron content content of of the the iron iron formation formation at at the Empire Empire mine is fairly uniform, about 32-35%. The The The amount amount and and grain-size grain-size of of magnetite magnetite determines determines ore quality. Ore-forming Ore-formingprocesses processescontributed contributed and remobilized remobilizediron ironby bydiagenetic diageneticor orlow-grade low-grademetamorphic metamorphicreactions reactionsof of recrystallization recrystallizationand and and replacement. Oxidation Oxidationofofsiderite sideritehas hasresulted resultedininlarge-scale large-scalereplacement replacementby by magnetite, magnetite,but but replacement. 129 �N N N N P1010ED 04/05/99 Formation Iron Fine—Grained 2000 Horizon Carbonate UOji.OWtiOJ Iron UOJI Oxidized PdZlplXn Formation Horizon Ctastics Series Undifferentiated Upper Siamo 1 Figure Series Undifferentiated Lower Horizon Silicate \ Dike Diabase Keweenawan SiLt/Dike Mc-taciiobase - LEGEND GEOLOGIC —- '9tfV.K 's.-.) ' Eevation) Bench (+940 —22000 ---r- ç—1j . - \(iJ l — -. GEOLOGY MINE EMPIRE —18000 (7bt -- 20 t 'tion _J 'A' -- —14000 Resource IV CD —10000 Cu 0 0 0 Li 00 0 nJ o o o Li Li EIIJ ��of the the magnetite magnetite in in these these enriched enriched chert layers are also replaced by magnetite; the grain size of zones is coarser than magnetite in zones not effected by replacement. coarser magnetite zones effected replacement. the Empire Empire Mine. Mine. NonSecondary oxidation has a profound impact on ore quality at the Non- or or weakly weakly characteristic of of oxidized oxidized zones zones are are typically magnetic iron minerals (e.g., martite, hematite) characteristic rejected during primary magnetic separation. Incipient Incipient or or partial partial oxidation oxidation of of magnetite magnetitegrains grains then in flotation flotation stages. may cause them also to be rejected, if not in magnetic separation, then extent of of oxidation oxidation and and predict predict its its impact impact on on plant plant However, it is often difficult to recognize the extent recovery. The Theoxidation oxidationisisthought thoughtto to be be largely, largely,ifif not not entirely, entirely, the the result result of of supergene supergene processes. processes. Circulation Circulationof ofthe theoxidizing oxidizingfluids fluidswas wascontrolled controlled by by faults, faults,dike dikecontacts contactsand andclastic clastic beds and lenses. However, the boundaries of oxidized zones are very irregular and difficult to However, the boundaries of oxidized define. define. all Empire Empire iron iron ores, ores, including including the the Due to the very fine grain size of magnetite in virtually all carbonate ores, extremely carbonate extremely fine fine grinding grinding (93-95% (93-95% passing 500 500 mesh) is is required required to to achieve achieve sufficient sufficient liberation of magnetite for product specifications. Process Process control control is is dominated dominated by by the the specification for Si02 Si02 in the final product. product. Smaller Smalleraverage average grain grain size size of magnetite magnetite in in silicatesilicateliberation. In type ores means that they must be ground finer to achieve acceptable liberation. In general, general,the the becomes significantly significantly more finer grain size also implies increased work index so that grinding becomes costly. costly. Field Trip Trip Stops Stops be determined determined until untiljust just prior prior to the field The actual stops to be visited and their locations cannot be trip. The Thegeneric genericstop stopdescriptions descriptionsare areprovided provided in in this this guide guideand and the the actual actual localities localities to to be be visited will be provided to to participants participants on on the the day day of the the field field trip. trip. Stop Overlook Stop 11 -- Dispatch Overlook Mining development pit, with with significant contributions contributions from development at Empire has focused on the Main pit, satellite satellite pits to the north north (CD-I), (CD-I), east east (Section (Section 20) 20) and and west (Southwest (Southwest Extension), Extension),and and expanding expanding development development to the northwest (CD-V). The The bottom bottom bench bench of of the the Main Main pit pit is is approximately pit will will ultimately ultimately be be developed approximately 1,000 1,000 feet below the dispatch overlook, and the pit 750 feet below the present mining mining level. level. entirely in in the the Carbonate Carbonate and and Silicate Silicate The bottom bench of the Main pit is developed almost entirely horizons. horizons. The The iron iron formation formation in in this this area area strikes strikes about about N35°E N35"E and and dips dips 30-35° 30-35' to to the the northwest. northwest. Stop 2 -- First Class Carbonate Carbonate The Carbonate i) Carbonate unit is gray to dark gray, relatively coarse-grained (magnetite grain size: 20-30 p) and characterized characterized by "thick" (5-25 mm), indistinct magnetite-rich and chert-rich layers with subordinate The term term "carbonate" "carbonate" is is utilized utilized at at the the Empire Empire Mine Mine to to subordinate siderite and ankerite. The c 10) 10) with very good liberation characteristics (low concentrate of indicate soft ores (work index < Si02). These high-grade ores ores have havebeen beenthe the"life-blood" life-blood' of Si02). of Empire's Empire's production. production. 132 �Stop 33 -- First Class Silicate Class Silicate Silicate iron ironformation formationconsists consists thin laminae (2 mm) of magnetite (minor tominor very minor of of thin laminae (2 mm) of magnetite (minor to very amounts greenish or or brownish-gray brownish-gray mixtures mixtures of of amounts of silicate, carbonate, chert, and clastics) and greenish silicate minerals, siderite, magnetite, chert and clastics. The The silicate silicate minerals minerals are are dominantly dominantly stilpnomelane stilpnomelane and and minnesotaite. The TheSilicate Silicatehorizon horizoncommonly commonlyhas has aa greater greaterabundance abundanceof of carbonate p) is finer carbonate minerals minerals than the Carbonate Carbonate zone. The Thegrain grainsize sizeof of the the magnetite magnetite(5-20 (5-20 L') than in the Carbonate-type. The term "silicate" at the Empire Mine is applied to ores Carbonate-type. The term "silicate" at the Empire Mine is applied to oreswith withwork work index> 10and andliberation liberationcharacteristics characteristicsthat thatare areinferior inferiorto to carbonate carbonateores; ores; silicate silicate or or yield yield index >10 higher higher concentrate concentrate of of Si02. Si02. Stop4Stop 4 -CD-V CD-V Future development in two areas: the the "pillar" "pillar" between the development of the mine will be principally focused in Main Main pit and and the the Section Section 20 20 pit pit (west (west wall), wall), and and the the north north and and northwest northwest areas areas of of the the Main Main pit pit termed CD-V. CD-V. Development Developmentof ofthe thewest westwall wallincludes includesrelocation relocation of of the the existing existing rail rail lines linesaround around the the east side side of the Section Section 20 pit; the "pillar" area will then be excavated to expose ores in the wall and, and, more more importantly, importantly,below below the the bottom bottom of of the the present present pit. pit. The The CD-V CD-V pit pit is is being being developed developed in in the the Upper Upper Series Series horizon, horizon, characterized characterizedprincipally principallyby by carbonate-type ores and clastic bands and lenses. Much of the yellowish carbonate material carbonate-type Much of the yellowish carbonate material contains contains very very little little magnetite magnetite ("lean" ("lean" carbonate), carbonate),consisting consistingdominantly dominantlyof of siderite sideriteand andchert. chert. However, very very rich rich carbonate carbonate ores ores are are also also present present in in the the push-back of of the the Main Main pit pit wall. wall. However, Current Current development development is is just below below aa large large diabase diabase sill sill that that is is 200-400 200-400 feet feet thick. thick. Several Several of of these these large, generally generally conformable, conformable, tabular tabular diabase diabase bodies bodies intrude intrude the the Negaunee Negaunee Iron Iron Formation Formation in in this this large, area of the mine. Predictably, Predictably, "fine-grained" "fine-grainer effects effectsare are extensive extensiveadjacent adjacentto to these these large largeigneous igneous bodies. bodies. In In the the CD-V CD-V area areaof of the themine, mine, iron ironformation formationand and interlayered interlayeredsills sillshave have been been folded foldedinto intoseveral several smallsmall- to moderate-scale moderate-scale anticlinal anticlinal and synclinal features. Fold Fold axes axes plunge plunge 10-20° 10-20' toward toward the the northwest. northwest. Bounding BoundingCD-V CD-V to tothe thenorth northisisaalarge largearea areaunderlain underlain by by magnetite-bearing magnetite-bearingiron iron formation formationthat, that, because because of of its its extreme extremehardness hardness (work (workindex index18-20) 18-20)and and poor poor liberating liberatingqualities, qualities,isispresently presently regarded regarded as as aa resource, resource, not not aa reserve. reserve. The Thenature natureof ofthe themetallurgical metallurgicalproblems problemsin in processing processing these these ores ores isis under under investigation investigationby by Cleveland ClevelandCliffs' Cliffs'research researchgroup. group. Stop 5- CD-I CD-I CD-I has has been been an an important importantsource sourceof of very veryhigh high quality quality(high (high weight weight recovery, recovery,low lowconcentrate concentrate Si02)carbonate carbonatematerial materialfor forblending blendingwith with lower lowerquality qualityores ores from from other otherlocations locationsin in the themine. mine. Si02) Ironformation formationininCD-I CD-Istrikes strikesnorth-south north-southand anddips dipsabout about30° 30' to to the the west. west. Two TwoKeweenawan Keweenawan hon age (1.1 (1.1 Ga) Ga) diabase diabase dikes dikes cross the pit in a westerly to southwesterly direction. These two two dikes dikes age direction. These are are coarser-grained coarser-grainedand and fresher fresherin in appearance appearancethan than the the other, other, older older early early Proterozoic Proterozoic diabase diabase dikes. dikes. 133 �The current phase of pit development development in CD-I will be completed in 1999. High High quality qualitycarbonate carbonate but its potential potential development development is is hindered hindered by by the the large large ore extends to the west beneath the pit wall but amount of stripping required. About About 750 750feet feet of of overlying overlying waste waste rock rock would would have have to to be be mined mined in in order to access access the ore. ore. References References Han, Tsu-Ming, 1975, Petrology of of Iron-Formation hon-Formation at the Empire 1975, Lithology, Stratigraphy, and Petrology Deposits of of the the Palmer Palmer Quadrangle, Mine, in Gair, Jacob E., Bedrock Geology and Ore Deposits Marquette Marquette County, County, Michigan, Michigan, U.S.G.S. U.S.G.S. Prof. Prof. Paper Paper 769, 769, pp. pp. 76-106. 76-106. 134 �Field Trip Trip 4 and Glacial Geology Geology from from Au Au Train Train to Paleozoic and Grand Marais, Grand Marais, Michigan Leaders: and J. J. Anderton Anderton Leaders: R.S. Regis and �______ ______ ____ ______ _____0144 ____On ______________________________________ ___________ ____________________________ ________ Pt(ISIOCENE NOMENCLATURE SYSTEM ERA a S z STAGE SERIES RRCMI U w_ i QUATERNARY kRISTOCINR EM STRATIGRAPHIC IN MICHIGAN MICHIGAN STFUTIGRAPHIC SUCCESSION SUCCESSION IN PPAUOZOIC ~ Z C Mmmi U THkOl &E4T 8 m . •• — I________ I__________ ——— DNI 3 DNR CSD I OUTCROP NOMENClATURE SUSSURFAa NOMtNCLATURE IECWW SCPtI11CJTOfflThI*tItSOOflS IWF 0. L GROIOGIC ITIMnTRAIIGAAPHFCI TIME F &LF4UFU& ORUET 0IT FORMATION MEMBER - R T44 kpl, — •.s — -19- .4- - coaflflI INFOPJI&AI. TERMS •fl 9 942 —fl — —d — — I....a — 4.4 04.44 •— •Afl •SC4MAL l1LU SILATGEAWIIC poslifli 4- 09,4 —. I-—. — 4-1 1, 1=- — ii 0._a. Rh 4.. b.,,Cs0L4 04442* 021 442 Tt 1Ja' ...u_o ._0fl4 — .4 S. — Os.— -.4-S— — ____._....__O4 4 ca hød5.S.. 44-,— .1 4-2 *4 —_____ - w.—9 89- -, — '4— 02S4 4I Go 04 SR. _•4_ — 0— O'la EXPLANATION C- — — — -' I flICMdfl p—,.— %%,— 4- 0-4.4 — waaflø fl.,O —. —, — — — —. a — .- 4d 4—— —, — # . . . — —I 42 --- CHART CHART 11 1964 ¶964 2071 em �ILSG Field Field Tdp Trip ##4from 1999 ZLSG 4 -Paleozoic Paleozoic and andPleistocene Pleistocene Geology Geologyfrom Au Train Train to Grand Grand Marais, Michigan Road log log Overview Ovewiew - - Au Train Train channel Profile of Au Stop 11 stop -- Au Au Train Train Falls Falls Stop stop 22 - - Beach Beach ridges and and Stop stop 33 -- Au Train-Whitefish Train-Whitefish Channel Channel Grand Grand Island Overlook Overlook Stop stop 44 -- Stop stop 55 -- Stop 6 -- Stop 77 stop -- Break Stop 88 stop -- Stop 9 stop Stop 10 stop 10 Stop 11 stop 11 ---- Stop 12 stop 12 -- US4 US41I S. (view to east at 2.3-3 ml.) mi.) continue 16.2 ml to M94, F. then E. 16.2 mi 18.2 mi. ml. to Forest Forest Lk. Rd. Rd. Return to Forest Lk. Rd. N 7.4 mi. to M28 M28 F. 2.5 mi. to H58, then to M28 E. Washington St. St. (1.2 mi.), to Munising Munising Falls (0.55 (0.55 mi.) mi.) Munising Munising Falls Falls Return to H58 (0.55 mi.), E to Miners Castle Rd (3.7 mi.), then N to Miners Castle Castle (4.9 mi.) mi.) Miners Miners Castle Castle Return to H58, continue continue F E to to Bear Bear Trap Inn 9 (3.6 mi.), mi.), keep keep left left and and continue on H58 (end of pavement another 4.3 mi.) to Kingston Corner Comer (11.2 (1 I .2 mi. beyond pavement end) Kingston Kingston Outwash Outwash Plains Plains N on H58 to 2-track on left (7.1 mi.) Proceed on 2 track 0.1 mi. & park park mi. & Walk due W 400 yds (strenuous) (strenuous) Turtle Return to H58,2.1 H58, 2.1 mi. to dropoff Turtle Lake Kettle into channel, @ 6.7 mi. is edge of upper outwash terrace, @ @ 8.7 mi. turn left on Log Slide Slide Rd.. Continue Continue to Log Slide Slide (0.75 ml.) mi.) Picnic area area @ Grand Sable @ NW side Grand Sable Lk. Log Slide Slide Return to to H58. H58. FE on on H58 H58 to to parking lot for Sable Creek falls and Ghost forest (5.6 mi.). Ghost Ghost Forest Sable Sable Falls Falls To Grand Marais (1.7 (1.7 mi.) Grand Harbor Grand Marais Harbor Nipissing Bluff E-W M77 to M28 (22.6 E-W channels channels crossed crossed by by M77 M77 (22.6 mi.) To Munising (22.4 mi.) To Marquette (44 mi.) 137 �Detailed Detailed Road Road Log. Log. of Au Au Train Train Whitefish Channel Overview of From the WashingtonfBaraga Washingtonmaraga St. St. intersection in downtown Marquette travel S on baraga St St US41). Along (turns into US4l). Along U.S. U S . 41 41 at at about about 2-3 2-3 miles miles south south of Marquette, a view to the east reveals a profile of channel cut by proglacial meltwater that flowed eastward along the margin of the Marquette (Grand Marais) ice. ice. The the Onota The feature feature was referred to by Hughes (1971) as the outlier. Water Waterspilled spilledinto intothe theAu Au Train TrainWhitefish Whitefish channel channel southward southward to to (present) (present) Lake Lake Michigan after passing through this channel. Continue on U.S. 41 south 16.2 miles to M94, turn east. Continue 16.2 Travel to 29.9 29.9 mi. to to Chatham, Chatham, turn turn SS at at stopsign, stopsign, travel travel to 30.9 30.9 mi and and turn FE on on M94, M94, continue continue to 34.4 34.4 mi and and turn N N on on Forest Forest lake lake rd., travel 0.1 mi to dirt road on right, follow to to gated gated parking area. Walk Walkto to falls. falls. Au Train Train Formation Formationand andAu AuTrain-Whitefish Train-WhitefishChannel, Channel,Beach Beachridge ridgecomplex complex Return to Forest Forest lake lake Rd., Rd., turn N. Follow Follow Forest Forest Lake Rd. At 6.3 miles and all the way to M28, note the beach ridge complex. Turn TurnEE on on M28 M28 and and travel travel to to the Grand Island overlook parking lot on the N side side of M28. M28. Grand Island Island Overlook Overlook From the Grand Island overlook, return return to M-28 and and travel travel east east 2.5 2.5 miles milesto toMunising. Munising. Turn on Dogpatch restaurant restaurant is on Ge the right at H-58 after passing the Holiday gas station on the left (the Dogpatch the intersection...excellent vittles! In In aa rustic, Li'l Abner Abner setting). setting). Continueon on H-58 H-58 an an additional additional intersection ...excellent vittles! . Continue 0.55 miles to to Washington Washington St., St., turn turn left left and and proceed to Munising Munising Falls Falls visitors visitors center center parking lot lot (0.3 miles). miles). Munising Falls Return to H-58 from the parking lot and and proceed proceed north north 3.7 3.7miles milesto toMiners MinersCastle CastleRoad. Road. Turn left. Travel Travel 4.9 4.9 miles miles to to the the Miners Miners Castle Castle parking parking lot. Miners Castle turn east (left). (left). Travel 5.9 miles to the Bear Trap Inn, veer left to to Return to H-58 (4.9 miles) and turn stay on H-58. End End of of pavement pavement 4.4 4.4 miles miles from the Bear Trap Inn. Continue Continueto to Kingston Kingston Corner Comer junction (11.2 (1 1.2 miles). Kingston Plain Travel north on H-58 7.1 miles to the small 2-track road on the left. Proceed Proceed about about50 50yards yardson on the road and park. Walk Walk about about 55 minutes minutes due due west (this (this walk may be strenuous for some). We We will remain at this stop for about ½ hour to allow time to walk to the bottom of the kettle. stop ?h NOTE: At 2.1 miles miles drop-off drop-off onto ontosurface surfaceB B (Hughes). (Hughes). NOTE: At 6.7 miles miles steep steephill hill marking markingedge edge of of surface surface C. C. Turtle Lake Return to H-58 and continue north. north. Travel 8.75 miles to the the Log Log Slide SlideRoad. Road. Turn north. Travel Travel 0.75 miles to the the Log h g Slide Slide parking lot. 139 �Log Slide Slide Return to H-58. Proceed Proceed east. east. NOTE: At 3.7 miles, the Grand Grand Sable Sable dunes dunes are areon onthe theleft left(north). (north). At At the the intersection intersection of of Newburg and William Hill roads, turn north on William Hill road and travel 0.7 miles to the Sable Falls parking lot. Walk Walkto tothe theGhost Ghostforest forest then then to to Sable Sable Falls. Falls. Ghost Forest and and Sable Sable falls Return to parking parking lot lot and and travel travel to to Grand Grand Marais Marais (east). (east), harbor Grand Marais harbor Follow M77 to M28, M28, turn turn e, e, follow follow to to US41, US41, N N to to Marquette. Marquette. Meitwater Meltwater channels channels Observe the outwash channels along M-77 appearance M-77 as as we we proceed proceed south. south. The "terrace"-like appearance of the topography is due due to M77 M77 crossing crossing proglacial meltwater meltwater terraces at right angles. angles. Streamfiow was to the east. Note Streamflow Note the the gentle gentle southward southward slope slope of individual individual terraces, marked by drained, swampy swampy areas areas near near their their southern southernedge. edge. poorly drained, 98 miles to Marquette. Sleep! Sleep! Grand Marais to M-28 M-28 south south on on M-77 M-77 West on M-28 M-28 to to U.S. U.S. 41 41 North on U.S. 41 to to Marquette Marquette 140 �—— — o — .r HIAWATHA InKEe - sera I. HP a Cenle 33 . FOREST 1 C —;-__--_---- NATIONAL -p /t t jIIu —H- -, _\_ 1 / LftlIaReavat - _ — . S -H ogon '° I-vanM -' t9 Ø4jfrurcShk . . -- a I I C C •— Ct-p I ft jt" rLi /' (\ "]' ' U\ In SI q Visitot Information Center a.0suadUtFI 0eSS— Mlnerecautle Stop 5 ta ° :1* diiiL ayeH ml - 4:) - r..r° ra TSI — tC Pu,u4LS.u.Hur '55d F PISM urea. LAKESUPERIOR UP Huu.p.flntS M,nuIee Falls 6*8.0 W5.0. wtt MUNISING HRHO 32*3)4* A re,pr'..d rt°t:d unttt _ _____ 3 C — ' 1 t / ( . C '>' - S I I C a - IA -- SUPERIOR C C -. S . STATE '\' A.a.uPuH . - . .- . FOREST '. .u Stop 9 -- s__s I 23 --— . j. ___1iS I. ¼ H- - -- I C / SIeP.IIS o 0LE' Ø1 "C-\' Log SI' ;r . S'.. ,CCk . SENEY NATIONAL WILDUFE REFUIE H LAKE r-t. ( 4' Hurricane River Stop 8 ___________________________________ jSop7 / 4)-Stop6 '— 'a CO&1 IWulvurulle Beach _____ — -- - STATEFOREST uurwPa.Heef - A 3 Sane 3 _eSdue lAKE SUPERIOR EuThHuth — -C. .H 5-' top 11 nterStop 12 Grand Sable GRAND t3ais rfiIrnCTMUSeUnt _______ �and Pleistocene Geology Geologyfrom fromAu AuTrain Trainto toGrand Grand Marais, Marais, Michigan Michigan Paleozoic and (FIELD TRIP #4) (FIELD TRIP#4) by Robert S. Regis and John B. B. Anderton Anderton Northern Michigan University University The geological history of the Pictured Rocks National Lakeshore (PRNL) (PRNL) is limited limited to to intervals of geologic two intervals geologic time; time; the Pleistocene Pleistocene epoch epoch when glaciers reworked reworked and and mantled mantled the the underlying underlying bedrock bedrock with with aa nearly nearly continuous continuous veneer veneer of drift, drift, and the the late late Proterozoic, Proterozoic,Cambrian Cambrian and early Ordovician periods when sediments deposited in shallow seas became the the sandstones sandstones that form the "pictured rocks" section section of of the the lakeshore. lakeshore. Late the Central Upper Late ProterozoiclCambrian/Ordovician Proterozoic/Cambrian/OrdovicianHistory of the Peninsula Peninsula including including PRNL PRNL Hamblin (1958), who who performed performed a Most material for this section was compiled from Hamblin detailed study of the Cambrian rocks outcropping in the PRNL and elsewhere elsewhere in northern Michigan. Michigan. The The Paleozoic Paleozoicgeologic geologic history history of of the the PRNL PRNL is is best described described as as aa period period of of eroding eroding highlands highlands and sedimentary sedimentary deposition deposition into into transgressing transgressing empeiric empeiric seas. seas. The The Northern Northern Michigan Michigan Highlands Highlands and the the Wisconsin Wisconsin Arch Arch stood stood as as eroding erodingremnants remnants of of former former highlands highlandsand and mountains, trending east-west across northern Michigan and more north-south across Wisconsin, trending east-west across northern Michigan and more north-south across Wisconsin. respectively. Encroaching respectively. Encroachingshallow shallowseas seas(the (theSauk Sauk transgression) transgression) during during the late Proterozoic Proterozoic and and throughout the Cambrian were depositional journey's end for of eroded sediments. the journey's most the sediments. Bedrock Bedrock is is best best exposed exposed in in the the pictured pictured rock rock section section where where bluffs bluffs rise rise up up to to 200' 200' above above short Lake Superior and extend seventeen miles from Munising to to the the Beaver Beaver Basin. Basin. For aa short distance distance inland from from the the escarpment, escarpment, usually usually no more than several several hundred hundred yards, bedrock may may occasional outcroppings. outcroppings. Elsewhere Elsewherein in the the National National Lakeshore Lakeshore bedrock is is only only found found be seen in occasional in the vicinity of the the Grand Grand Sable Sable bank, where where it forms a low bluff around around the the north north and and east east side side of Au Sable Point, Point, and and in in the the gorge gorge at at Sable Sable Falls. On this field trip, we will observe the rock rock formations formations in in reverse reverse order. order. The first rocks we will see are the youngest youngest exposed in the the park (western (western end) and last rocks we see see are are the oldest (eastern end). The TheJacobsville Jacobsvillesandstone, sandstone,of of questionable questionablelate-Proterozoic late-Proterozoicto to lower lower and and age, is is the the oldest oldest formation formation in in the the lakeshore lakeshore (more (more than 520,000,000 520,000,000years years old). old). middle Cambrian age, It is a feldspar-rich, quartz quartz sandstone, sandstone, deep deep red in color color with white mottlings. Although Although the the Jacobsville has a thickness thickness of of 1100 1100feet, feet, only only the top several several feet rise above above lake level, level, and and only only Jacobsville Onthis thistrip, trip,we we will will see see the the Jacobsville Jacobsville at at Sable Sable Falls Falls (Stop (Stop 10). 10). in the eastern part of the park. On The early-to-middle early-to-middle Cambrian-age Cambrian-age Munising- formation underlies most of the the lakeshore, lakeshore, mostof and forms most of the significant bedrock outcroppings in in the the park. park. It lies unconformably on top of the Jacobsville Jacobsville sandstone. The TheMunising MunisingFormation Formation isis divided divided into into two two members, members, the the lower lower and 5) 5) members members (500 (500 -Chapel Rock Rock (Stops (Stops 10 10and and 5) 5) and and the the upper upper Miners Miners Castle Castle (Stops (Stops 44 and 520,000,000 520,000,000 years old). old). Except Except where where the friable Miners Castle member is being rapidly rapidly undermined by wave action it forms slopes rather than cliffs. undermined forms slopes rather cliffs. In the western half of the "pictured rocks" the late Cambrian Au Train formation formation cropscropsout only along the top edge of the cliff (480 The Au Au Train Train is is aa light light along edge (480 500,000,000 500,000,000 years old). The brown or white, hard, dolomitic dolomitic sandstone sandstone usually highly present, it forms forms a highly glauconitic. glauconitic. Where present, - 142 �cap cap rock rock on on the the weaker weaker Miners Miners Castle Castle member. We Wewill will observe observethe the"type "type locality" locality" of ofthe theAu Au Train Trainformation formationatatAu AuTrain TrainFalls Falls(stop (stop1)1)on onthis thisfield fieldtrip. trip. All All formations formationsdip diptoward towardthe thesouth southaadegree degreeor ortwo twoas as shown shownin in the thephoto photohere here(view (viewisis toward toward the the east). east). All Allthe theformations formationsalso alsoarise ariseeastward eastwardso sothat thatthe theAu Au Train Trainformation formationisismissing missing east of of Miners MinersCastle castlebut but east the the Jacobsville, Jacobsville,which whichisis below below lake lake level levelat atMiners Miners Castle, Castle,carries carriesabove abovelake lake level. East Eastof ofMiners Miners level. beach, it is well exposed beach, it is well exposed beneath beneath the the conglomerate conglomerateof of ChapelRock Rockand andin inthe the Chapel gorgeat atSable SableFalls. Falls. gorge Thereare aremany many There waterfalls along along the the waterfalls escarpment escarpmentformed formed mostly mostly by the the Au Au Train Trainformation, formation, by but all all are arefed fedby by small small but streamswith with small small streams watersheds and and are are only only watersheds imposingin in the the spring springand and imposing during wet wet periods. periods. during MunisingFalls Falls(stop (stop4) 4) isis Munising view View along along the thePictured PicturedRocks Rocksshowing showing the the Munisiug Munisine formation formation dipping dipping to to the the the most most unusual unusual and and the south south at at aalow lowangle. angle. interesting of the the falls. falls. ItIt isis interesting - of an an extremely extremelywell-developed well-developedcap-rock cap-rockwaterfall waterfall with withthe the Au Au train train Formation Formation forming forming aa shelf shelf that that overhangs overhangs the the Miners Miners Castle Castle member member by by 25 25 to to 30 30 feet feet permitting observers observers to walk behind behind the the torrent torrent which which falls falls from fromthe the center center of of the the overhang overhang as as aa concentrated concentrated stream stream and then then descends descends another another 30 30 to to 40 40 feet feet in in aa series series of cascades. AArecent recent collapse collapseof of aa section section of this formation formation onto onto the walkway prompted Park officials to close a part of the walkway. Some well developed the walkway officials of the walkway. Some potholes potholes may may be seen seen in the cataract section. Miners MinersFalls Falls has has developed developed where where the Miners Miners River River drops from the upper to the broad lower valley. The fall is vertical and about 30 feet high. drops from the upper to the broad lower valley. The fall is vertical and about 30 feet high. Chapel Chapel Falls Falls isis fed fed by by aa tributary tributary to to Chapel Chapel Lake Lake that courses down the valley slope where there is no cap rock. The fall is a long cascade, about The fall is a long cascade, about 90 90 feet feet high that broadens fan-like from ten feet at the top top to to 30 30 feet feet at at the the bottom. bottom. Bridalveil Bridalveil Falls Falls and Spray Spray Falls are formed where streams streams fall, fall, about 90 feet, directly into Lake Superior, adding greatly to the beauty of the Pictured Rocks. At about 90 feet, directly into Lake Superior, of At Sable Sable Falls, Falls, the the stream stream draining draining Grand Grand Sable Sable Lake Lake cut into the Chapel Rock and Jacobsville Jacobsville formations formations where where they they lie lie beneath beneath sand sand dunes. dunes. The Thedeeply deeplywooded woodedsetting settingisisexceptionally exceptionally beautiful beautiful and and is is but but aa short shortwalk walk from from the the lakeshore lakeshore and and the the parking lot. The The Pictured Pictured Rock Rock escarpment escarpmenthas has been been carved, carved, by frost action and wave erosion erosion of the the present present lake, lake, as as well well as as higher higher stages, stages,into into aa variety variety of shore shore cliff features features such as: stacks, stacks, caves, caves, sea arches, and promontories. These Thesefeatures features have have been named: named: Lovers LoversLeap, Leap,Rainbow RainbowCave, Cave, Grand Grand Portal, Portal, Miners Miners Castle, Castle, Chapel Chapel Rock, Rock, The The Battleships, Battleships, Flower Vase and Indian Drum Cave. Cave. Most Most of of the the features features can can be be reached reached by hiking but only Miners Castle is accessible accessible by automobile. The The best way to appreciate appreciate the cliffs cliffs is by boat tour. Increased Increased accessibility accessibilityby by land land will will not not diminish diminish the the advantage advantageof of viewing viewingthe thecliffs cliffsfrom fromthe thewater. water. 143 �Late Quaternary QuaternaryHistory Historyof of the the Central CentralUpper UpperPeninula Peninulaincluding includingPRNL PRNL The Great Lakes region experienced experienced repeated glaciations glaciations and concommittant concommittant inundation inundation The the Quaternary. Quaternary. For by proglacial lakes throughout the For the the purposes purposes of of this fieldtrip, the final major (i.e. 11,800 BP) BP) marks marks the the beginning beginning of of deglaciation of the area during post-Twocreekan times (i.e. is most most relevant. relevant. Between 11,800 the portion of Late Quaternary history that is 11,800and 11,500 11,500 the Superior covered the the Upper Peninsula (Farrand and Drexler 1985). Superior Ice Lobe nearly completely covered 1985). By about 11,500 11,500 BP, retreating retreating glacial ice, followed followed closely by the high stands stands of Glacial Lake Lake Futyma, 1981). 1981). The retreat of ice continued, Algonquin, had nearly left the region (Larsen, 1987; Futyrna, opening up large portions of the Lake Superior basin in what is large portions the Lake Superior is known as as Glacial Glacial Lake Lake Duluth Duluth (Phases A and B), allowing allowing discharge discharge from from Glacial Glacial Agassiz during during Post Algonquin Algonquin times times (ca. (ca. 10,700 BP); however, evidence of this period was largely obliterated by a final readvance of ice into the Lake Superior Superior basin. The Theglacial glacialreadvance readvance is is known known as as the the Marquette Marquette advance advance (Drexler (Drexler et al. 1983). 1983). Shoreline features created by these earlier lake stages in the Lake Superior Superior basin were Shoreline largely destroyed during during the Marquette Marquette Advance (Hughes, 1978; Drexler, 1981; 1981; Farrand and and Drexler, 1985). 1985). By Byabout about9800 9800BP, BP, the theice icehad had begun begun to to retreat retreat again, again, resulting in a stepwise stepwise drop in lake lake levels levels which initiated initiated the the Post Post Duluth Duluth Phase Phase lakes lakes (Farrand (Farrand and and Drexler Drexler 1985). 1985). After about 9,800 BP, Marquette Advance ice had retreated far enough to the north to 9,800 Marquette Advance ice north to allow allow lake lake water from the western part part of Superior Superior basin to drain eastward and southward, southward, eventually eventually However, catastrophic catastrophic discharge discharge creating the Main Minong Phase (Farrand and Dexler, 1985). However, from Lake Agassiz early in the Nipigon Phase is thought to have breached a till barrier at at the the east east end of the Lake Superior Superior basin, basin, causing causing aa decline decline in Lake Minong resulting in at least least five five or or six six Teller and and Thorleifson, Thorleifson, 1983). The The post-Minong levels levels in the Superior Superior basin (Farrand, 1960; Teller lowering was finally finally stopped stopped as resistant resistant bedrock at the Sault Sault outlet outlet was reached, reached, culminating culminatingat at the Houghton Houghton Low around around 8000 8000 BP, BP, the the lowest lowest lake lake phase in the Superior Superiorbasin. basin. Finally, Finally, as as the the ice left the south south shore shore of of the the basin, basin, Glacial Glacial Lake Lake Minong formed formed along the margins margins of the the retreating glacier reaching its maximum expression by about 9500 BP; however, shortly reaching expression 9500 shortly afterwards afterwards the retreating retreating ice ice front front in the eastern eastern Great Lakes revealed the isostatically depressed depressed known as as the the Houghton HoughtonLow. Low. During this North Bay outlet, resulting in falling lake levels known period, lake lake levels levels in the the Superior Superiorbasin dropped to their their all all time time lowest lowest elevation, elevation, which which may may their valley valley channels. channels. By about 8000 BP the bedrock have allowed many rivers to deeply incise their sill at the Sault Sault acted acted to to halt halt falling falling lake lake levels levels in in the the Lake Superior Superior basin; however, however, by then isostatic isostatic uplift had had acted acted to to raise raise the the elevation elevation of of the the North Bay outlet, outlet, resulting resulting in rising rising lake lake levels in the southern southern basins. Eventually, Eventually, the the rising rising lake lake levels levels reached the elevation elevation of the Sault Sault Outlet Outlet and and lake lake levels levels in the Superior Superior basin began to gain in elevation. During During this this period, period, known as as the the "Nipissing "Nipissing Great Lakes," water in the basins basins of Lake Superior Superior and Lakes Huron and Michigan joined together to create create one one huge lake, lake, which which was controlled controlled by the North Bay outlet. Notwithstanding, Notwithstanding, the the North North Bay Bay outlet outlet continued continued to to rise rise and and eventually eventually lower lower drainages drainages to to the the south became active active commencing commencing the three-outlet (Chicago, (Chicago, Port Huron, and North Bay) phase of Lake Nipissing (Nipissing (Nipissing I), I),which reached its maximum elevation between 4700 and 4000 BP BP (Hansel et al. 1985). 1985). During Duringthe the Nipissing Nipissing Maximum, Maximum, flooding flooding of many tributary river valleys embayments along the coastal areas of the Upper Peninsula (Anderton 1993a). created large embayments 1993a). The Nipissing II IIphase, marking a slight drop in levels, was attained about 4000 years BP as continued continued isostatic isostatic uplift uplift raised the North Bay outlet above the altitude of the two southern southern II phase, lake-levels began to outlets (Hansel et al. 1985, 1985, Larsen 1985b). Following Following the the Nipissing II w �fall as as downcutting downcuttingprogressively progressively lowered lowered the Port Huron outlet and water volumes fluctuated fluctuated in in the the basins. basins. AAshort shortpeak peakininlake-levels lake-levelsatatabout about3200 3200BP BPresulted resulted in in the the Algoma Algoma phase, phase, but but by by about 2200 2200 BP BP lake-levels lake-levels in in the the Lake Lake Michigan-Huron basin had fallen below the elevation elevation of of the the rebounding rebounding sill sill at at the theSault, Sault,separating separatingthe the Superior Superiorbasin basin from from the the lower lowerGreat Great Lakes Lakesand and initiating 1960). Modern Modem lake-levels lake-levels in in both the the Lake Superior Superior and Lake initiating the Sault Sault level (Farrand 1960). Michigan-Huron Michigan-Huronbasins basinswere werefinally finallyattained attainedby byabout about2000 2000years yearsago. ago. Larsen Larsen (1985), (1985), working working in the the southern southern portions of the Lake Michigan-Huron basins, has has also also proposed an an alternative alternativemodel model of of Holocene Holocene lake-level lake-level fluctuations, fluctuations, which suggests suggests aa complex record of climate-related changes that lasted between 200 and 300 years complex record of climate-related changes that lasted between 200 and 300 years each each and and fluctuated fluctuated with with an an amplitude amplitudeof of 11to to 22 meters above the apparent mean lake level. In In the the last last 7000 7000 years at least least eight eight episodes episodes of high water periods separated by intervening low water periods are are recognized recognized (Larsen (Larsen 1985). 1985). periods Stop 1. Au Au Train TrainFormation Formationat atAu Au Train TrainFalls Falls At At Au Au Train Train Falls, Falls, aa 30 30 meter meter thick thick section section of the 100 100 meter thick early Ordovician Ordovician Au Train Formation (aka Trempealeau Formation) is exposed. exposed. The The formation consists consists of 2 parts, the upper and lower members. At Atthis thisstop, stop,we we will will examine examine the the lower lower section section at the lower lower falls, falls, and walk to to an overview overview of of the the upper upper section, section, which is is exposed about 200 200 meters upstream, upstream, but is is relatively inaccessible. inaccessible. The TheAu Au Train TrainFormation Formation lies lies unconformably unconformably upon the Munising Formation, Formation, and and is is representative representative of of the the continued continued Sauk Sauk sea sea marine marine transgression transgression that that began began in in the the late late Proterozoic. The environment of The environment of depositionwas was aa shallow shallow shelf shelf deposition platform platform with with fluctuating fluctuatingsea sea levels. levels. Paleogeographically, Paleogeographically,the theregion region was was equatorial with with the the equator equatortrending trending equatorial nearly north-south north-south compared compared to to nearly modern modem orientation. orientation. Note the the step-like step-like character character of falls (also (also in in the the upper upperfalls) falls) the falls created by the alternating alternating layers layers of of dolomite, dolomite, shale, shale, and and sandstone sandstoneof of varying varyingdegrees degrees of of resistance. Near areaaseries seriesof ofthin thinbeds bedsof of glauconitic glauconiticsandstone sandstone Nearthe thebase baseofofthe thelower lowerfalls fallsare (hydrous (hydrous silicate silicate of iron iron and potassium) potassium) and shale. Glauconite Glauconiteisisdisseminated disseminatedas asflakes flakes throughout the sandstone. sandstone.Glauconite Glauconite comprises comprises as much as 35% of some beds in the lower lower Individual beds Individual beds vary vary section and imparts a speckled green to dark green color to the formation. section and imparts a speckled green to dark green color to the formation. from pure sandstone sandstone to pure dolomite (Hamblin, 1958). Dolomitic Dolomitic beds are are bluish gray in color. An intraformational conglomerate(?) with pebbles of sandstone and dolomitic intraformational conglomerate(?) dolomitic sandstone sandstone are are found in a few of the units near the base of of the section (see (see cross cross section sectionon onnext nextpage). page). At the base of the lower lower Au Au Train, Train, the the contact contact with the underlying Miners Castle member of the Munising Formation is easy to recognize because the friable sandstone is quite quite different in Munising appearance from the hard, resistant dolomitic sandstone sandstone of the Au Train. Fossils are rare in the formations. Following deposition of the Au Train Au Train but become abundant in later formations. Formation was was aa minor minor regression regression that that formed formed an an unconformity. unconformity. 145 �eq a. a Cl) I- a a Cl) �Footage Footage Section section - top Upper Train rep of of ~ m Au AU s~ r r i nr7.11. a n Sandy grayi.h..blu. to to dark 4-10 Inch*. inches [hick. thick, some M d y dolomite, dtilmnitq, grayi#h-blu. dark blue, h h à §b.ds bed# 4-10 miu interbedded buff fin., ttoo mediurn.grained 1 iwft finemedium-grained sandstone Â¥andçtounits. ualte, .everal ¥¥vr horizons contain contain abundant • '/. 120 120 Description Detcription of of lithology lithology ,1auconite and and a uthl'enic pyrite authigenic pyrite Iglauconit. Olagco.ddc Gl.ueonldc . Sand.tone bed6""thick, S u d i t o i r bed thick, buff buff to to light gray, medium- to flne-grain.d, fine-grxincd, well wellrounded rounded well sorted and well sorted Sand.tone bed, same above S a d i t o n e bad, #Â¥mas above 110 110 Sandstonebed, bed, mame same ,a.iabove Suidçton above Ito 110 Authigenic pyrite filling vu ge Pure dolomite I::.: • 90 90 - :1 Highly glauconitic Authigenic pyrite filling wg. 80 80 70 70 - Sandstoneb ibed thick,finefine-totomedium-(rained, medium-grained,buff bufftotolight light gny, gray, well rounded thick, rounded Skndatonà d 8"8" sad well a dw e l l sorted sorted _ Abundant tuthigenic pyrite -: • - 60 60 Highly glauconitic of Uppç Upper An Au Train Train FP41. 1Base !am ef dln interysi (Covered :overed interval - 50. 50 40 40 - betweenUpper Upperaud andLowr LowerAu AuTrain Train fills Falls between -2 and" dolomite thick,generally generally Sandy dolomit,to todolomitic dolomiticsanditone, sandstone,buff bufftotobluish-#ray, bluieh-gray,bçd beds2"-t" 2"-" thick, separated by thin thin !.me* lenses of of silt silt or c p r t t e d by or clay, clay, bedding bedding planes plane* are ere undulatory, undulatory, percent of sand sand b e ' à § r lthroughout throughout à the section, #action, glauconite gluuconit. extremely extremelyabundant abundant mmpeclaily vane, the especially near the base Glauconità Glauconit. and clay galls Crest of of 1.ow.r lower Au Train Train Falls Crçs Fall. 30 30 Olauconit. concentrated along several horizons, sandy units ezhitat email-scale croci bedding, thin shale lense. separate unite 20 20 10 10 00 - _ _ Clauconite is is extremely 10-30 percent percent of of many many extremely abundant abundant as iitt conslitutee Gl*ucÈnit coirtltu1.m between bçtwç10-30 unit. thin uaite Had, weather, dark brown, beds Iron. thick, several horizons contain pebbles of .and.tone and dolomitic .sndstone which ,.pparently constitute an intraformational conglomerate IBase of Lower Au Train F'41s Columnar Columnarsection sectionofofthe theAu AuTrain TrainFormation FormationatatAu AuTrain Trainfalls falls(1-tamblin, [Hamblin, 1958) 1958) 147 147 �Stop Stop 2. Au Au Train-Whitefish Train-WhitefishChannel, Channel, Barrier, Barrier,and andBeach BeachRidge RidgeComplex Complex Train Whitefish Whitefish Channel Channel Au Train The The Whitefish-Au Whitefish-Au Train Train Channel Channel isis aa former formerproglacial proglacial lake lake spillway spillwaythat that drained drainedacross across the the central central Upper Upper Peninsula. Peninsula. From FromLittle LittleBay BayDe DeNoc, Noc,north northto toAu Au Train TrainBay Bay on on Lake Lake Superior, Superior, kilometers the channel is over 60 kilometers (36 miles) in length and ranges between about 2.5 the channel is over 60 kilometers (36 miles) in length and ranges between about 2.5 kilometers (1.5 miles) to 6.7 6.7 kilometers kilometers (4 (4 miles) miles) in width. The TheWhitefish WhitefishRiver, River,aatributary tributaryto to Little LittleBay Bay De De Noc, Noc, drains drains the the southern southerntwo-thirds two-thirds of of the the Channel. Channel. The Thenorthern northernthird thirdisisdrained drainedby bythe theAu Au Train Train River, River, aa tributary tributary to to Lake Lake Superior. Superior. Most Mostof ofthe thechannel channelbottom bottomisisunderlain underlainby by thin thin deposits of of gravel gravel or or till till over over bedrock. bedrock. deposits The The lowlands lowlands of of the the Au Au Train-Whitefish Train-WhitefishChannel Channel were were first first noted notedby by Foster Fosterand andWhitney Whitney (1851), (1851), but itit was was Winchell Winchell (1871) (1871) who who interpreted interpreted the feature as a meltwater spillway. Russell Russell (1904), (1904), however, identified identified the the channel channel sides sides as as kame kame terraces terraces having having been been deposited deposited by by aa thin thin lobe of ice that had stretched stretched across the Upper Peninsula. The The channel channel has has since since been been studied studied by by a number (1929), Hough Hough (1958), (1958), Drexler Drexler et et al. al. (1983), (1983), Farrand Farrand and and number of workers workers including including Leverett Leverett (1929), Drexler (1985), (1985), and Hughes Hughes (1990). (1990). Incidently, Incidently,Leverett Leverett (1929) (1929) indicates indicates that during during the 1920s, 1920s, government government engineers engineers considered considered cutting cutting aa ship ship canal canal through through the the Au Au Train-Whitefish Train-WhitefishChannel Channel and connecting connecting Lake Lake Superior Superior to to Lake Lake Michigan, thus avoiding avoiding the Sault Sault Locks. According to Hughes (1990), (1990), the Au Train-Whitefish Channel reached its its full expression expression According during during the Marquette Marquette Advance Advance about 10,000 10,000 BP. At At this this time, time, lake lakelevels levels in in the the Lake Lake MichiganMichiganHuron basins as retreating retreating ice ice had revealed revealed the the basins were were extremely extremely low low (Chippewa-Stanley (Chippewa-Stanley Low) as isostatically isostatically depressed depressed North North Bay Bay outlet, outlet, allowing allowing water water to nearly drain from the southern southern basins. basins. Before, Before, during, during, and, and, for for an an unknown unknown period period after after the the Marquette Marquette Advance, Advance, proglacial proglacial lake lake water water drained across the central Upper Peninsula to the lower lakes, creating the Au Train-Whitefish central Upper Peninsula lakes, creating Train-Whitefish Channel. Hughes Hughes(1990) (1990)has hassuggested suggestedthe the Channel Channel extends extends under Little Bay De Noc and Green Bay to a large, Chippewa-level off the east east side side of of the the Door Door Peninsula. Peninsula. The Chippewa-level delta submerged off The Channel was abandoned abandoned at at around around 9700 9700 BP when retreating retreating ice allowed allowed lake water to reach the the Sault Outlet Outlet on the the east east end end of of the the Superior Superior basin. Barrier Au Train Barrier During Nipissing Nipissing times, times, lake lake water water flooded flooded some some 66 kilometers kilometers (3.6 miles) miles) into into the the northern end of the the Au Train-Whitefish Train-Whitefish Channel Channel creating creating Au Train Relict Relict Bay, which is is one one of of Nipissing II wave-cut bluffs the largest Nipissing embayments in the central Upper Upper Peninsula. Peninsula. Nipissing and cliffs, cut cut in bedrock bedrock and and unconsolidated unconsolidated sediments sediments at at 192 192meters, meters, rim much much of of the the east east and and west sides of the former embayment; however, in places along the southeast fringes, the shoreline sides the former embayment; southeast fringes, the shoreline is less developed, appearing by eolian eolian activity. activity. In fact, small relict appearing to have been modified by along the the southeast southeast side of Au foredunes may be present along Au Train Lake. Lake. A massive mid-bay barrier extends extends from from northwest northwest of of Paulson Paulson Lake, Lake, east east to to Joel Joel Creek, Creek, forming forming the the northern northern boundary boundary of of modern Au Train Lake. The Thebarrier, barrier, having having an an elevation elevation of 186 186 meters on its north side side and 189 189 its south south side, side, reaches reaches an an elevation elevation at at its its crest crest between 195 195 and and 192 192 meters meters and and aa meters on its maximum elevation dune remnant. remnant. In elevation of 201 meters on what appears to be a dune In places, places, the barrier severely eroded eroded by by the the Au Au Train Train River. River. has been severely The barrier barrier created created aa huge huge lagoon lagoon between the barrier proper and the southern southern rim of of the the The bay, now occupied occupiedby byAu Au Train TrainLake, Lake, Paulson Paulson Lake, Lake, and surrounding surrounding wetlands. Based on the depth of Au Train Train Lake Lake (USDA, (USDA, 1938), 1938),during during Nipissing II times, times, the lagoon would have have had had aa maximum maximum depth depth of of at at least least7.5 7.5 meters meters (25 (25feet), feet), an an average average depth depth of 33 to to 44 meters meters (9.8 (9.8 to to 13 13feet), feet), miles). Drainage may have exited from the and covered about 6 square kilometers (2 square miles). 148 148 �Au Train Lake $Iapnck Cr. AU TRAIN- CisySand Cliffs Baa n SPI LLWAY Cr. WhIt.fish P. SCALE SCALE kilomstsrs I a , j I 0 -I $ IQ Ovation In ff11 vs Little Bay Do Noc AuTrain-Wiifeflsh Spiliway AuTrain-Whitefish Spillway (Hughes, (Hughes, 1971) 1971) 149 �D Moraines and channels in the Marquette area and the Eben-Chatham channels (Hughes, 1971) �SUBMARINE VALLEY IN IN THE THE FLOOR FLOOR OF GREEN GREEN BAY BAY I 11 SCALE I. I. ItI• KIlO S•I SI I SSIk,Ic lIt,SI - S S4—• 151 �lagoon on its its northeast northeast corner comer near near the the eastern eastern end end of of the the Au Au Train Train Barrier Barrier or or at at some somemidmidposition breach in the barrier, where the Au Train River runs through today. today. Nipissing Nipissing II IIlevels levels may have modified the the northern northern edge edge of the the barrier, which is is at an an elevation elevation of of 186 186meters. meters. Au Train TrainBeach BeachRidge Ridge Complex Complex The The Au Train Train Beach Beach Ridge Ridge Complex Complex occupies occupies the the area area between between the the barrier barrier and and the the modern shoreline of Lake Superior. The complex is composed of some 50 separate recessional modem shoreline Superior. The complex is composed of some 50 separate recessional ridges which form a compact, arcuate shaped "corrugated plain" plain' as first first termed by Bergquist Bergquist (1936). The rIdges, which range in elevation between 186 and 184 meters, are currently being (1936). The ridges, which range in 186 184 eroded eroded by Lake Lake Superior, Superior, which has has created created an irregular irregular line of actively forming coastal coastal foredunes on the northern end of the complex. The The Au Au Train Train River has also also meandered through the ridges ridges resulting resulting in in erosion erosion and and truncation, truncation, suggesting suggesting that that the the river's river's present present course course isis relatively recent. The Theridges ridgesare areparallel parallel to toeach each other, other, and and there there is is no no evidence evidence of cross-cutting cross-cutting relationships, relationships, indicating indicatingfluctuating fluctuatinglake lake levels. levels. Grand Island/Powell Stop 3. Grand Island/PowellPoint Point Scenic Scenic Overlook moraine. The This stop stop is on the crest of a Marquette Advance moraine. The overlook overlook affords affords aa view view of Grand Island, Island, Grand island Island Harbor, Harbor, Murray Bay, and Sand Point. Sand Point, a large cuspate spit, is visible in the east channel of Grand Island Harbor. Harbor. The The spit, spit, which ranges in elevation elevation between 185 185 and 183 183 meters, appears appears to to have formed in post-Nipissing times, times, and and is is still still being being actively modified by wave-action wave-action from from Lake Lake Superior. Superior. It is composed of a number of lesser bathers that deve]opment of of the the spit. A sandy barriers that appear appear to to have have created smaller smaller lagoons during the development A massive Nipissing I, wave-cut bluff at 192 meters is present along the southeast side of the spit, 192 southeast side the spit, Nipissing I, which extend extend to the the northeast northeast from marking the start of the modem cliffs of the Pictured Rocks, which Sand Point. Point. On Grand Island, Island, Nipissing Nipissing I wave-cut bluffs developed in bedrock at 192 192 meters meters rim rim much of the southern portions of island. Wave-cut Wave-cut caves, caves, shoreline shorelinestacks stacks and and arches, arches, and pocket pocket shoreline along beaches are present along the Nipissing I shoreline along the west side of Murray Bay. WaveWavecut bluffs at 192 192 meters meters rim portions portions of the the Island's Island's western high ground, known locally as as the the Thumb. Thumb. AAwell-developed well-developedsystem systemof ofstream streamgullies gullieshas has dissected dissected the the eastern eastern hillsides hillsides of of the the main lobe of the island, as well as much of the hillsides on on the the Thumb. Thumb. These These narrow, narrow, deep deep incised valleys end abruptly at the Nipissing I shoreline, indicating that they formed in preabruptly shoreline, Nipissing, Houghton Low times Nipissing, times when stream stream base levels were extremely extremely low. Cuspate Cuspate barriers barriers grading grading from the Nipissing I bluffs to about 186 186 meters are are also also visible visible on Grand Island. The Cuspate Bather, Barrier,which which isis located located Themost most obvious obvious of of these is the Duck DuckLake Lake Cuspate on the east side of the main lobe of the island. ItIt isis composed composed of of a number number of large ridges ridges that trend east to west on the south side, and north to south on the east east side of of the the barrier. barrier. Duck Duck Lake, Lake, a small inland lake, lake, is is aa lagoon lagoon remnant remnant associated associated with the the barrier. The The Muskrat Muskrat Point Point Cuspate Cuspate Bather, Barrier, formed formedoff off the the southwestern southwestern end end of of the the Thumb, also contains a lagoon remnant, now a small swampy pond. Wave Waveaction actionfrom fromLake Lake Superior Superiorhas has eroded the southeastern southeastern tip of the the Duck Lake Cuspate Cuspate Barrier, the the southern southern limb limb of the the Muskrat Muskrat Point Point Cuspate Cuspate Barrier, Barrier, and and the the southeastern southeastern tip tip of of the the Williams WilliamsLanding Landing Spit, Spit, exposing exposing imbricated imbricated gravel gravel and and cobble cobble beds beds in in both cases. These Theseeroded erodedareas areasshow showup upas ashigh, high, sandy sandy bluffs bluffs along along the modern shoreline. The Grand Island Beach Ridge Complex, a complex of at least 25 beach ridges ranging ranging in tombolo between the Thumb Thumb and and the the main main part part elevation between 186 186 and 183.5 183.5 meters, meters, forms a tombolo of the island. 1i Inplaces placeson onthe thesouthern southernedge edgeof of the the complex, complex, beach beach ridges are submerged by 152 1 52 �Stops 3 & 4 Stop 5 153 �Lake Superior, Superior, while while the the northern northern edge edge is is currently currently being eroded eroded by the modern modem lake, lake, creating creating small coastal foredunes foredunes along along Trout Trout Bay. of Grand Island Island presents presents an an enigma. enigma. Some A steep cliff visible high on the west side of Some workers (Don and Eschman, 1971) have suggested it is a wave-cut bluff from Lake Algonquin. (Dorr and Eschman, 1971) have suggested it is a However, such such aa feature feature would would have have been been destroyed destroyed during during the the Marquette Marquette Advance. Advance. Alternatively, the escarpment may be a remnant of an ice marginal stream channel Alternatively, escarpment may stream channel created created during during the retreat of Marquette Marquette Advance Advance ice ice or or itit may may have been created created by headward headward erosion erosion and and retreat retreat of a caprock on the the highest highest portions portions of of Grand Grand Island. Island. Stop 4. Munising Munising Falls Falls At Munising falls, the Au Train Formation (see (see stop stop 11for for a more complete complete description) description) meters thick. Conformably forms a resistant resistant caprock caprock of of dolomitic dolomitic sandstone sandstoneabout about 55 meters Conformably below is the weaker Miners Castle member of the Munising Formation, which has has been been undercut undercut to to form form a steep high-walled valley. Munising MunisingCreek Creek plunges plunges 10 10meters meters over over the the falls falls in in its its short short journey to to Lake Superior. At plunge pools. pools. They were At the the base base of of the the falls falls are are several potholes and plunge abraded into the sandstone sandstone by by hard cutting cutting tools tools carried from from the overlying overlying caprock caprock and and from from glacial drift. Visitors Visitorsused usedtotowalk walkbehind behindthe thefalls, falls,underneath underneath the the overhanging overhanging caprock, caprock, but but aa recent collapse collapse of aa section section onto onto the the walkway walkway prompted prompted park officials officials to to close close that that part part from from the the general general public. public. The Munising Munising formation formation represents represents aa transgression transgression of of the the shallow shallow Sauk Sauk sea sea onto ontothe themidmidcontinent region in Cambrian Cambrian time. The Theupper upper Miners MinersCastle Castle Member Member isis aa light light gray gray to to white white colored, poorly poorly sorted, sorted, cross-bedded sandstone sandstone that comprises comprises the the upper upper 30 30 meters meters of of the the Munising Formation. In the lower part of the member, thin thin lenses lenses of of blue blue shale shale are are common, common, but but become scarce scarce in the the upper upper portions. portions. Quartz Quartz grains grains dominate dominate the the lithology lithology (>95%) (>95%) of of the the Miners Miners Castle member, member, with feldspar comprising most of the remainder. Most Most quartz quartz grains grains exhibit exhibit straight extinction and are likely of igneous origin. origin. ItIt is is not not uncommon to find find 1-3 1-3 cm cm thick thick beds beds of shale alternating with 10cm 10 cmthick thickbeds bedsof of coarse coarsesandstone sandstoneand and even even conglomerate! conglomerate! Especially Especially in the lower parts of the Miners Castle member. Higher Higher up in the member, member, fewer beds of shale and conglomerate conglomerate are are found, found, and and beds beds consist consist mostly mostly of well-sorted, well-sorted, cross-bedded sandstones sandstones with a greater degree of mineralogical and textural textural maturity. maturity. Some Some individual individual beds are are quartz quartz arenites, but in sum the formation formation is poorly sorted. Quartz Quartzisis also also the the dominant dominant cementing cementing agent, agent, but with only only slight slight secondary secondary enlargement of the detrital detrital grains, grains, it is porous porous and and friable. friable. Authigenic Authigenic pyrite pyrite is is common common enough enough in in some some of the middle middle beds that it is is megascopically megascopically discernable. Discussion Discussionof ofthe theMiners MinersCastle Castlemember member continues continuesat at the the next next stop. stop. Stop Stop 5. 5. Miners Miners Castle This stop stop examines examines the the type locality locality of the Miners Castle member of the Munising Munising formation (see description in stop 4). Sedimentary structures such as mud cracks (mostly Sedimentary structures as (mostly in the shale beds), ripple marks marks and cross cross bedding bedding (as seen at this stop) suggest an alternating alternating fluvialllacustrine environment of deposition. Significantly, fluvial/lacustrine Significantly,the ripple marks and cross bedding in the Miners Castle Castle member member indicate indicate aa transport transport direction direction from the east-northeast, east-northeast, as as opposed opposed to to the northwesterly transport direction direction measured in the older Chapel Rock member (see (see figure figure illustrating cross-bedding directions). The The abrupt abrupt change change in in transport transport directions directions in the two members provides provides further further evidence evidence of an unconformity that separates separates them. The change change in transport direction also also suggests suggests that that the the Wisconsin Arch and the the Northern Michigan Michigan highlands, highlands, 1544 15 �Miners Castle Castle Member Member of the Munising Formation Au Train Train Formation Formation dolomitic, yellow-brown, coarse-and coarse-and medium medium grained with much 148 'Sandstone, very very dolomitic, 148 ' -152' 152' Sandstone, very coarse and little fine, fine, scattered scattered very veryfine fineand andfine finequartz quartzpebbles. pebbles. Some irregularly bedded. bedded. Some large zones conglomeritic. Massive Massive bedded and irregularly sandstone sandstone pebbles. pebbles. Munising Formation, Miners Munising Formation. Miners Castle Castle Member Member 144' - 148' 148' Sandstone, 144' Sandstone, light light yellow gray, medium grained grained with much fine fine and and aa little little fine, fine, even bedded and thin-medium thin-medium beds. Another bed as above above 140' - 144' haccessible 122' - 140' Inaccessible Light yellow-gray sandstone, coarse and very coarse grained with a trace of 121'- 120' granules. Cross-bedded Cross-beddedin inmedium-thin medium-thin beds. beds. Light yellow-gray sandstone medium to fine grained with traces traces of granules. granules. 115'- 121' bedding. Poorly sorted with much fine Medium - thick bedded with cross bedding. material in lower foot foot of bed. 112' - 115' coarse to to medium medium grains. grains. Trace Light yellow gray sandstone, coarse Trace of granules. Massive, cross cross bedded. 111' -112' Light yellow gray sandstone, poorly sorted with sizes ranging from silt silt to to granules. Abundant Abundant limonite limonite staining. Appears Appears to to be be burrowed. Narrow Narrow ledge. ledge. 108' - 111' Light brown gray sandstone. Medium to coarse grained grained with much much fines. fines. Massive. Trace Traceof of granules. granules. Light yellow gray sandstone. Poorly Poorly sorted sorted with grains grains ranging from silt silt to to 106' - 108' granules. Abundant Abundantburrows burrowsbest bestseen seenfrom from overhangs. overhangs. 103' - 106' Light yellow brown sandstone. Medium Medium to to coarse coarse grained grained with with few few granules. granules. Massive bedded. Massive bedded. Same as above above except except more silty and abundant abundant burrows. 99' - 103' 95' - 99' gray sandstone. sandstone. Silty Light yellow gray to gray Silty medium to fine grained with thin beds of red, blue and green shale. Poorly Poorly sorted. sorted. 40' - 95' gray sandstone. sandstone. Poorly sorted to well well sorted beds. beds. The Light yellow gray The upper upper part, part, of medium to fine grained beginning at the top of Miners Castle pinnacle, consists of wed wee1sorted sortedbeds beds of of sandstone, sandstone,interbedded interbedded with with poorly poorly sorted sorted beds beds of of sandstone sandstone containing abundant silt and thin beds of silty shale, and conglomeritic beds with silty shale pebbles. The The upper upper 66 feet contains burrowed beds. At At 10-12 10-12feet feet below the top, are prominent poorly sorted, shaly, conglomeritic and cross are prominent conglomeritic and cross bedded bedded sandstones. sandstones. 20' - 40' Gray sandstone. Poorly Poorlysorted, sorted,medium medium grained grained with with abundant abundant thin thin blue blue shale shale partings. Some conglomerate. Cross bedded. Some conglomerate. Cross bedded. 10' - 20' Light yellow gray sandstone, coarse coarse grained, grained, well well sorted. sorted. Contains Contains clay pebbles. pebbles. Formation, Chapel Munising Formation, Chapel Rock Member Light yellow gray sandstone. Medium 0' 0' -- 10' 10' Medium to to fine fine grained grained with with aa trace trace of of coarse, coarse, wellwellsorted sandstaone. Cross Cross bedded. bedded. Lake Level 183 m (602') Level == 183 (602') 155 �+ Inland—0Prairie du du Chlen Chien inland PJI members arise to to the the east east so that that JacobsvllIe All members Jacobsville is above lake Is above lakelevel levelat atGrand GrandMarais Maraisand andthe theAu AuTrain Train fornialion formationIsismissing missingfrom fromThe the top top of ofcliffs, cliffs. — 7 a —— —— - - Unconformity - -I- —- —— Light brown, hard, dolomilic sandstone. Giauconillc. Au Train Formation Resistant Resistant A Upper 5-12 5-12 meters meters Upper Moderate Moderateto tovery vewdoiomitlc doiommcwttti with O L O gronJies ~ on0 pebDie5. qUarlz granuies and pebbles. Burrowed br the ELnowea "for tnebirdC Diros" i Soft riable ,,poorly pooW sorted sorted Soft, ffriable silty silly, shaM shov, sandstone, often often cross-bedded. cross-bedded, Light yellow-gray color Light yellow-gray color imparted importedby bylimonite. llmontte.(In (In varying varying amounts amounts Miners Castle Member C 0 About 3Dm to lake 0 U- 0) C Cl, C 0' A ——— _Uo9rmjy_ —— Pink. light Pink, Ughtbuff buffto to brown, brown, medium medium omoquommcsandstone. sandstone. grainedorthoquartzWc grained Thin blue shale shale beds beds 2-3 2-3cm Thin blue cmthick. thick. Mudcracks Mudcrocksininshale shalebeds. beds. ""bdsôh"é'(°h€ri Uórtz quartzite, and chert w/minor amounts of siate, BiF, basalt and granite) Chapel Rock Memberô a —————a—— c b a Jacobsville Jacobsville Formation Formation I - —a——— a I Nigular unconformity Nkosic to Arkosic quartz quartz sandstone. sandstone. Red Redto red-brown abundant mottles red-brownwith abundant mottles and where on0sireaks, s ~ ~ o < sespecially es~ecioirv . wnere permeable. Th cmessvaries vanesgrecztts greatly, Denneooie.Thickness from > 1m to 500 m, from>lmtoSOOm. �____________________________________________________________________________________ Ga rat Zircon looter, 5.çtton Dcecflptioaotltthotogy ntis 0 I DeIsmilic ttnd.tae. light brown, Very resistant 3ssso1 kU TRAIN formation tencanlormity • • ISO ''.•.' Top of MUNISINC t.rmatlea Miner's C..tj. nwmb.r teStIsa. .Mte, m.dlwn-grasn.4, friable, ma.!,. badtsg (I' tot thick), fonti vertical di/l. — Details of ..dimtntsry strvcttr.s ob•c,and hyw.ath.riag; ataytadte appnrt be cr*tt.b.dd*d 120 Sandstone wMt. mSwm.praintd. ..U coned, masal,. bedding (I' tel thick). email cavee and arch... friable N'&marc'aa tat;. tcrsdeaa along bedding pta. Smelt—scale crass bedding to,. 11.4 stains ales; certain hastens .... b6. i" bed. very resistant. contains abtaadaat n.atris Sandstone. pr.tn,iaaatly poorly sorted ttt. is gray. tniaor streak. .1 red, blee and grssn, 5... of Mint's Castle piradle 55 Coarse .and.sene conc.atrat.d along cantata bedding p1.... Abundant day pail.;. deposited parallel to the cro.* bedding cbann*I. and Ian... shine cflgtOrnhrstO iO Small ceagiarat. lens.. So. Coarse eand and conglomerate I..... S Slut, grita, red, and yells'. colorado. foflo.tn bedding ,a.'... S.ndst.. gray to grayteh'.bl.a., m.tum,grain.d, pearly .on.d amall_.caIa crosa bedding 4".,i" thick ..parat.d by thin blue hal. I.n.e. l14"-t" thick '4 3° (approalmaisly 2030 percent .hal*), torn, coarse and fin. coagloanarat. / 20 ''i L'&3c 10 , & ¶cat.r t*v.l of bk. r / y I, ( 1 pa.' of Itt.,'0 tail. m..r unonntor Top of Chapel Rock rna,.bor 5aad.tots, pink, coors.-grainsd, nil sorted, rounded, abundant clay pellet. Mud cracks 4"-S' In tonnetar dontloped in beds of bIn. shale ines than I' thick. Clay pellet. sandseont light brown to buff well carted large •cale cross bedding It thick j - Superior Columnar Columnarsection sectionof ofthe theMiners Miners Castle Castle member memberof ofthe theMunising MunisingFormation Formation at atMiners MinersCastle Castle(after (afterHamblin, Hamblin,1958) 1958) 157 157 �Paleogeography member of Paleogeographyduring duringdeposition depositionof of the the Miners Miners Castle member of the the Munising Munising Formation Formation(after (afterHamblin, Hamblin, 1958) 1958) £IPLSNAtION bSSJ V tsuSe ndI.* d— - — •_N_ •m Caib — — fl4 —*• lö? I— I*aj •f — t* un—*. _*._ cni .4 * t tS3a, La - is 0 iG it sai—. t— '0 •0S.iii Cross bedding bedding directions MinersCastle Castlemember member of the the directions in the Miners Munising (after Hamblin, Homblin, 1958) Munising FormatHon Formatiion (after 1958) 158 158 �which which provided providedthe thesource sourcefor forsediments sedimentsduring duringthe the Jacobsville Jacobsvilleand and Chapel Chapel Rock Rock deposition, deposition,had had eroded erodedenough enoughthat thatthe thetransgressing transgressingSauk SaukSea Seasubmerged submerged most most of of the the Upper Upper Peninsula peninsula and and Wisconsin. Wisconsin. Stop6. 6. Kingston Kingston Plain Plain Stop Stop Stop66 isison onthe theKingston KingstonPlain, Plain,an an extensive extensiveoutwash outwashplain plain that that isislocated locatedbetween betweenthe the towns towns of of Munising Munising and and Grand Grand Marais. Marais. The ThePlain Plainpresents presentsaaunique, unique,prairie-like prairie-likesetting setting compared compared to to much much of of the the more more heavily heavily forested forested areas of the Upper Peninsula. The The multitude multitude of of pine pine stumps stumps preserved presemed on on the the Kingston Kingston Plain Plain serve serveas as testimony testimony to to the the intensity intensity of of historic historic clear-cut clear-cut logging. logging. A (Leverett,1911, 1911, A number numberof of workers workershave havestudied studiedthe the geology geology of of the the Kingston Kingston Plain Plain (Leverett, 1929; 1929;Bergquist, Bergquist, 1936; 1936;Martin, Martin, 1957; 1957;Hughes, Hughes, 1968; 1968;Drexler, Drexler, 1981, 1981, Drexler Drexler et et al., al., 1981; 1981;Blewett Blewett and and Rieck, Rieck,1987; 1987;Blewett, Blewett,1994), 1994),which which has has resulted resulted in in aa wide wide range range of of theories theories concerning concerningits its formation formationhistory. history.Largely, Largely,the thecontroversy controversyhas hasfocused focusedon onthe theinterpretation interpretationof ofthe theMunising Munising Moraine, which the Kingston Plain is part of (Blewett, 1994). According to Hughes Moraine, which the Kingston Plain is part (Blewett, 1994). According to Hughes (1968 (1968and and unpublished unpublishedwork), work),and andlater laterby by Blewett Blewett (1994), (19941,whom whom has has done done the the most most current currentQuaternary Quaternary geology geology research research in in the the area, area,the the Plain Plain initially initially formed formed when when Marquette Marquette Advance Advance ice ice probably probably reached reached an an equilibrium equilibriumand andsouthward southwardflowing flowingmeltwater meltwater streams streamsbuilt built the the Upper Upper Kingston Kingston Outwash I). Ice Outwash Plain Plain surface surface at at about about 10,000 10,000 BP (Phase 0. Ice retreated retreated somewhat somewhat from this position, opening opening up drainage drainage to to the the east east between between the the ice ice front front and higher ground to the south, south, creating creating aa channel M-77. The channel at at 283 283 m m that that currently currently parallels state highway M-77. The upper upper portions portions of of the the Kingston Kingston Lake Lake Kettle KettleChain Chainformed formedatatthis thistime. time. Next Next (Phase (PhaseII), lI), the the ice ice margin margin retreated to a new position along along the Lower Kingston Kingston Plain, opening even lower drainage outlets from the west. Consequently, water flowing to the Plain, opening even lower west. Consequently, water east east between between the the ice ice front front and and the the now now abandoned abandoned Upper Upper Kingston ice-contact ice-contact slope, slope, formed formed aa broad, broad, kame kame terrace terraceatatabout about285 285m, m,which whichslopes slopestotothe theeast. east. Marginal Marginal retreat retreat of of the the ice ice from from highlands highlands south south of Grand Grand Marais Marais allowed allowed still still lower lower outlets outlets to to open open (Phase (PhaseIII), I Q ,which which resulted resulted in in the the incision incision of a channel channel at 250-253 m, into the the Lower Lower Kingston Plain Plain surface. surface. The TheHurricane Humcane River River currently currently follows this channel. Also Alsoatatthis this time, time, some some meitwater meltwaterspilled spilledsouthward southward from from the the Lower Lower Kingston Kingston ice-contact ice-contact slope slope south south of of Beaver Beaver Lake, Lake, forming forming the the Long Long Lake Channel. The Thelower lowerportions portionsof ofthe theKingston KingstonLake LakeKettle Kettle Chain, Chain, including includingKingston KingstonLake Lakebasin basinmust musthave haveformed formedduring duringthis thisphase. phase. IV,and and55 of of Blewett, 1994), 1994), the ice withdrew to a position position several several Eventually(Phase (PhaseIV, Eventually kilometers kilometers north north of of the the Lower Lower Kingston Kingston ice-contact ice-contact slope, slope, allowing allowing meltwater meltwater drainage drainage across across aa broad terrace heading at 230 m, known as the Beaver Basin surface. Further retreat of ice broad terrace heading at 230 m, known as the Beaver Further retreat of ice allowed allowed even even lower lower channels channelsat at 225 225 and and 215 215 m m to to be be incised incised into into the the Beaver Basin surface. surface. Finally, the glacier retreated to a position just south of Portal Point, but eventually Finally, glacier eventually further retreat retreat allowed allowedlake lake water water in in the the western western Superior Superiorbasin basin to to flow flow eastward, eastward, abandoning abandoning the the Au Au Train-Whitefish Channel, into the eastern basin, forming an early version of Lake Minong. Train-Whitefish Channel, into the eastern basin, forming an early of Lake Continual Continual retreat retreat allowed allowed Lake Lake Minong Minong to expand, expand, eventually eventually filling the entire Superior Superior basin. 159 �- :'-——".. T't"- -: J. i r- P B - Phdse I Surface —'P. s5QfcEIev.: go RE -. - / "<k, -\' ;. 41t' -<k - Y - I Stops Stops66&&77 160 160 *An �a' — 'I', GoS 90 930 Pr-e dank7 k" //ey 'P. Pre C/ezcjaf L'a//ey? Grand Sa6/ Lke 1' '9 The Kingston Outwash Plain and meltwater channels near Grand Marais, Michigan Ti, '7 C 4 Ml g5 "V.. �ice 5 cc' a'icsA .rr lace 0 a-s tn1 art ordj-/o,a4y Chaewst2ng O7 eat La r i' 0 ,C7Ma,/ack.. I A '4 - - C /aives eat teverd . .noph-ig cc' tciiorh .ntrt.ct - Pi-erent level lake So,ntyor ,,v—*_5- rect;oAt vieai ea..rt ,s,i-tA end 07C sc (a SorjCacej 'lope ecjt'ora - .c4,,tt.n fan .&9nt5' iwein) -Present lake 4/fC 0 -I- 2 -.1. -A. 162 - 3 -I-- �0' Mosaic Mosaic of of digital digital elevation elevationmodels models(DEM) (DEM)processed processedtotoshow showrelief relief(illumination (illuminationfrom fromSE) SE) �; .—.I 0 / I,I) Stop 7.7.Turtle Lake (actually an unnamed pond, soso called stop lbrtle Lake (actually an unnamed pond, calledononthis thistrip tripbecause becauseon on previous previous visits itit was observed observed that many many turtles turtles make make itit their their home) home) occupies occupies aa deep deep kettle kettle in in the the Kingston KingstonOutwash Outwash Plain. The kettle kettle is is the the deepest deepest (though (though not not the the largest) largest) in in aa south-southeast/north-northwest south-southeasthorth-northwesttrending trending chain of kettles that (presumably) were formed as ice stagnated in aa now-buried now-buried bedrock bedrock valley. valley. A from bedrock bedrock and a minimum minimum seismic study conducted by Regis in the 1980's revealed no reflection from sediment thickness of 60 meters. The kettle is several hundred meters in diameter diameter and and is is at at least least 40 40 meters deep. deep. Because Because the the kettle kettle chain chain extends extends across across (cuts) (cuts) each each of of the the outwash outwash and and drainage drainagesurfaces, surfaces, the stagnant Marais) ice was was building building stagnant ice must have been in place from &om the time the Marquette (Grand Marais) surface, and was buried by sediments sediments as the main ice ice mass mass retreated. retreated. the upper Kingston outwash surface, 00 m m hike hike through through the the woods, woods, and and ifif descending descending into into the the kettle, kettle, aa strenuous strenuous This stop requires a 2-3 2-300 return hike. 164 164 �Stop 8. Log Log Slide Slide From the to the the east. east. Two the Log Slide, the Grand Sable complex is visible to Two geomorphic geomorphic features, in this this view: view: The features, the "Banks" "Banks" and the "Dunes" are prominent in The Grand Sable Sable Banks consist of a steep, north-facing exposure of glaciofluvial sediments ranging in thickness consist of a steep, north-facing exposure of glaciofluvial sediments ranging in thickness from from 30 30 to to 100 100 meters, meters, rising rising directly directly above above the the shoreline shoreline of Lake Superior. Superior. To Tothe thesouth southaway awayfrom fromLake Lake Superior, Superior, the Banks form form aa high high terrace terrace surface, which is overlain by the Grand Sable Dunes, a dune dune field field "perched" "perched"up up to to 100 100meters meters above above the the lake lake and and covering covering about about 10 10square square kilometers. kilometers. The The deposit deposit that that underlies underlies the the dune duneplateau, plateau, exposed exposed in in the the Grand Grand Sable Sable Banks, Banks, has has been been variously variously interpreted interpreted as as aa crevasse crevasse filling filling or or kame kame terrace terrace that incorporated incorporated heterogeneous heterogeneous glaciofluvial glaciofluvialdebris debris transported transported by by rivers rivers flowing flowing west to east east along along an ice marginal channel channel (Drexler, (Drexler, 1981; 1981;John D. D. Hughes, Hughes, personal communication). Within Within the the central central portion portion of of the the Banks, Banks, stratigraphy stratigraphy of the the lower lower third third of of the the section section is obscured by colluvial and aeolian aeolian sand; sand; at at the the east and and west ends ends of the banks, the section is better exposed. Upper Upper portions portions of of the the banks banks are several thin thin gravel gravel beds. beds. thterbedded are dominated dominated by coarse, coarse, cross-bedded cross-bedded sand and include several Interbedded silt silt and and sand sand comprise comprise the the middle middle third of the deposit. The Thelower lower third third is is dominated dominated by by fine fine textured textured material, material, primarily primarily silt. silt. AAsurface surfacegravel gravel layer layer is is presently partially exposed in a "stripped "stripped plain" in the central plateau. This This layer layer is is often iron-stained and contributes contributesto toaalag lag that that periodically periodically armors armors the the bluff bluff crest crest as as the the slope slope retreats retreats southward southward (Farrell and Hughes, Hughes, 1985). 1985). The The Grand Grand Sable SableDunes Dunescontain contain evidence evidence of of buried buried soils, soils, which which record record episodes episodes of of geomorphic geomorphic change change consisting consistingof of soil soil profile profile development development followed followed by soil profile profile burial burial (Anderton (Anderton and Loope, Loope, 1995). 1995). In Inmost mostcases, cases,an an entire entire episode episode is is preserved presewed as a buried soil profile or or organic organic accumulation, accumulation,capped capped by by relatively relatively finer sediments, sediments, such as silt and very fine to fine sand, which is capped by medium to coarse eolian cross-bedded sand. The contact between the sand, which is capped cross-bedded sand. upper upper soil soil horizon, horizon, usually usually an an 0/A OIAhorizon, horizon,isisoften oftenvery verysharp, sharp,suggesting suggestingrelatively relativelyrapid rapidburial. burial. Such Such sedimentary sedimentaryand andpedological pedologicalevidence evidencestrongly stronglysuggests suggeststhat that periods periodsof ofstability stabilityare are represented represented by by forest forest vegetation vegetation colonizing colonizing landscape landscape surfaces surfaces within the Dunes, while while periods periods of of instability instabilityare are characterized characterizedby by the the burial burial of trees and associated soil profiles and organic organic accumulations. accumulations. A A soil soil catena, catena, consisting consistingof of aa sequence sequenceof of buried Spodosols, Spodosols, may be found found outcropping outcropping in in various various places places throughout throughoutthe the Dunes, Dunes, especially especially at at the Log Slide Slide locality. The Thecatena, catena,referred referredto to as as the the Sable Sable Creek Creek Soil Soil(Anderton (Anderton and and Loope, Loope, 1995), 1995),is is traceable traceable across across much of the the Bluff top top and and outcrops outcrops sporadically sporadicallywithin within the the Dunes Dunes reflecting reflecting the preservation presemation of a past soilscape soilscape which began forming forming immediately immediatelyafter after deglaciation deglaciation about about 10,000 10,000 years ago, but was isolated from further further surface surface weathering weatheringunder under eolian eolian sediments sediments beginning about 5000 5000 years ago. The Theburial burial event event seems seems to to have have been been initiated initiatedby by the the massive massive destabilization destabilization of the the Bank Front Front during during the the high lake levels of the Nipissing Great Lakes. high lake levels of the Nipissing Great Lakes. While While there there may may have have been been some some eolian eolian activity activity immediately following deglaciation, deglaciation, the evidence tends to support the hypotheses of Farrell and Hughes (1985) who suggest evidence tends to support the hypotheses of (1985) suggest that the Grand Grand Sable Sable Dunes Dunes are are no no older older than 5500 5500 BP. This Thisisisin in contrast contrast to to Marsh Marsh and and Marsh Marsh (1990) (1990) who who argue arguethat that the the Grand GrandSable SableDunes Dunes began began forming forming as as lake lake levels levels rose from from the pre-Nipissing pre-Nipissing lows lows sometime sometimearound around 9000 9000 BP. BP. Marsh Marshand andMarsh Marsh(1990) (1990)maintain maintain that that sand sand nourishment nourishment to to the the Dunes until around around 3500 3500 BP. BP. However, Dunes increased increased from from 9000 9000 BP BP to to 5500 5500 BP and remained high until However, the the presence presenceof of the theSable SableCreek CreekSoil, Soil,which which isis developed developed into into glaciofluvial glaciofluvialsediments, sediments,suggests suggests that that the the Bluff Bluff top topwas wasaastable, stable,forested forestedenvironment environment from from deglaciation deglaciationuntil about about 5000 5000BP BP when when eolian eoliansand sandbegan began to to cover coverthe the upper upper surface. surface. Rising Risingpost-Houghton post-Houghtonlevels levelsapparently apparentlyhad hadlittle little 165 165 �a. t 0 0 2 0) 0) 0 D C 0 0 KN 0' a. 166 �effect on the Banks until well into into the the mid-Holocene, mid-Holocene, suggesting that wave action did not begin to modify the bluff front until lake levels were relatively high during the Nipissing Great Lakes. Stop 9. Ghost Forest Subsequent, Subsequent, post-Nipissing post-Nipissing fluctuations fluctuations in lake level also also seem to have influenced influenced the the Bank front, causing changes in the sediment available for eolian transport on the upper surfaces causing upper surfaces of the Grand Sables, Sables, resulting in a discontinuous discontinuous occurrence occurrence of buried soils soils and organic organic layers layers of various ages within the Dunes. In In addition addition to to the the major major burial event event that covered the Sable Creek Soil at least as early early as around 4500 BP, radiocarbon dates from the Ghost Forest profile also more recent recent burial burial at at about about 100 100years yearsago. ago. Also a record a burial event at about 3500 BP and a more radiocarbon date from other localities localities in the Dunes suggest that eolian activity also took place at about 1500 1500BP, BP, and and at at about about 700 700years years ago. ago. While, these these data data may not be conclusive, an analysis of radiocarbon dates from the Grand Sable Dunes strengthens strengthens interpretations. Beginning Beginning with the investigations investigations of Bach (1978), (1978), researchers working in the Grand Sable Dunes have been collecting and radiocarbon dating Sable collecting the study study area. area. In general, the dates seem to preserved wood, bulk soil, and charcoal from the roughly delineate delineate major times of increased eolian activity, documenting burial events within the Grand Sable Sable Dunes, and likely likely recording fluctuations in the lake levels of the Lake Superior Superior basin. Based on the available available data, data, episodes of increased eolian activity occurred at about about 5300, 5300, 2100, 1500, 500, and 4600, and 3500 3500 RCYBP, RCYBP, and and may also also have occurred at about 2500, 2500,2100, 1500, 1000, 1000,500, and RCYBP. The 100 RCYBP. The first first three three episodes episodesseem seem to to coincide coincide well well with with rising rising Nipissing, Nipissing, Nipissing NipissingI,I, and Nipissing II II phases, which are recognized throughout the southern Great Lakes (Larsen, 1985). The other, The other,later laterepisodes episodesalso alsocompare compare favorably favorably to to previous research research which which indicates indicates fluctuating fluctuating lake levels levels in in the the Lake Lake Michigan basin during the last 3000 years (Larsen, 1985). 1985). Larsen (1985) (1985) has suggested suggested that Holocene lake level fluctuations are linked to climatic climatic changes changes that affected the the temperature temperature and moisture moisture patterns influencing the water balance of the lakes. lakes. Holocene climate of proxy proxy indicators suggest climate changes changes in the the Great Great Lakes, as revealed by a varity of alternating alternating episodes episodes of cool, cool, moist moist and and warm, dry conditions (Swain, 1978; 1978; Bernabo, Bemabo, 1981). 1981). Comparison of burial burial events events within within Grand Grand Sable Sable system system with lake level and climate climate data data from from the the Great In general, general, Great Lakes Lakes region for for the the last last 3000 3000 years indicate a general correlation of events. In of cool, wet climatic increased eolian activity in the dunes appears to correlate with periods of conditions, conditions, while while periods periods of of relative relative stability stability and soil development development are are associated associated with times times of of of shore-zone warm, dry climatic conditions. These These findings findings do not fit Larsen's (1985) model of changes during rising and falling lake levels. In the Larsen model, increased precipitation In the Larsen model, increased precipitation and and lowered temperature result in high lake levels that cause tributary stream aggradation, marsh establishment, and soil profile development in in eolian eolian sands. sands. Decreased precipitation and raised establishment, temperatures cause temperatures cause low lake levels that result in tributary stream erosion, marsh extinction, and soil profiles becoming buried by eolian sands. While While Larsen's model seems to work for most coastal areas, perched dunes, dunes, such as the Grand Sable Sable system, appear to be reacting differently to climatically-induced climatically-induced changes changes in in lake lake level. level. been a nearly nearly constant constant rain rain of of eolian eolian sediments sediments with with In general, there seems to have been relatively short-lived periods of soil development and forest colonization within the Dunes since about 3000 BP. The Thedistinct, distinct,buried buried soil soil profiles profiles of different ages within the Dunes argues for the Bank Bank front. front. Otherwise, the fact that only relatively high lake levels are influencing the Otherwise,ifif the the of stability, but rather a Bank front was continually being undercut, there would be no evidence of 157 �homogeneous deposit of eolian sands. Thus, Thus,the the evidence evidence of of geomorphic geomorphic changes changes from from the the Grand Sable Dunes seems shore of seems to to be be an an indicator indicator of lake lake level changes changes along along the the south southshore of Lake Lake Superior. Th In sum, the buried soil profiles reflect fluctuations fluctuations in the amount amount of sediment sediment available available Hughes, 1985). The for eolian transport within the Dunes (Farrell and Hughes, The availability availability of sediment sediment Bank face face (Marsh (Marshand andMarsh, Marsh,1987) 1987).. High depends on the condition of the Bank High lake levels result in increased wave action, which undercuts the bank toe slope, slope, causing mass mass wasting, wasting, destabilizing destabilizing for wind wind deflation. deflation, If enough sediment is available the Bank face and presenting a fresh surface for on the the high high terraces. terraces. Low lake for a long enough period of time the result is dune development on lake levels allow the Bank face to stabilize stabilize and and perhaps perhaps become become vegetated, vegetated, resulting resulting in in aa reduction reduction or or near elimination of available sediment. Thus, Thus, dune dune building building on the the high high terraces is retarded, retarded, - on - terraces allowing stabilization stabilization and surface surface weathering to begin, as well as forest vegetation vegetation to to colonize colonize the fresh landscape surfaces. Thus, Thus, soil soil profiles profiles formed formed in in the the Grand Grand Sable Sable Dunes during during periods periods basin. These of low lake levels in the Lake Superior basin. These soil soil profiles profiles and in many cases the forests themselves were, however, buried by eolian sediments, sediments, eliminating further soil development development and and forest growth, the result of high lake levels destabilizing the Bank front. result lake destabilizing Stop Stop 10. 10. Sable Falls At Sable Sable Falls, Falls, the the Jacobsville Jacobsville Sandstone Sandstone forms forms the the base of the the section section exposed exposed in in the the gorge. The The Jacobsville Jacobsvillesandstone sandstoneisisaa redbed redbed deposit deposit of of questionable questionable late Proterozoic-early Proterozoic-early Cambrian age named by Lane and Seaman (1907) after the Keweenaw Peninsula town of Jacobsville. There, There,the the"Portage "PortageSandstone" Sandstone"that thatwas was used used as as ornamental ornamental and and construction construction stone stone was quarried. ItIt isisexposed exposedall all along alongthe the southern southern shoreline shoreline of Lake Superior Superior from the Keweenaw Peninsula to Munising. However, However, from from Munising Munising to Beaver Bay, it is below lake level, spare for a few occurrences slightly above above water. water. At Sable Falls and south of Grand Marais, good exposures are found. Thickness Thicknessof of the the Jacobsville Jacobsville appears appears to be extremely extremely variable variable and largely controlled by the underlying Precambrian topography, upon upon which which the Jacobsville unconformably for the most part. For example, rests unconformably example, Hamblin (1958) (1958) cites an instance instance of aa 22 wells, one of which drilled loot of of Jacobsville Sandstone, and the other well drilled drilled through 11100' through only 46' 46 of and the wells are only of the the same same rock rock before before reaching Precambrian quartzite, and 10 miles apart (T47N, (T47N, R1E). RlE). The Jacobsville can be easily recognized recognized by by its its striking striking red redto to red-brown red-browncolor. color. Much of the Jacobsville is mottled with white reduction splotches and streaks. The The color color change change is is abrupt abrupt and distinct. Most of the mottles are related to variations in permeability of the beds. That is, Most of the mottles are permeability of the beds. is. where the beds have the greatest permeability, leaching and white coloration is the greatest. greatest. Most fine grained beds and shale lenses in the Jacobsville are are not not leached leached at at all. all. Leaching most joints, and and cross-bedding. cross-bedding. Spherical often ffollows o l l o k bedding planes, fractures such as joints, Spherical spots spotiofof leaching appear to be controlled controlled by a dark grain or pebble at occurs at the center of the spots. The grains are probably of some some lithology that have a composition sufficient to produce a reducing reducing environment. environment. Texturally, Texturally, the the Jacobsville Jacobsville Formation Formation ranges from conglomerate conglomerate to a fine grained grained siltstone. The by Hamblin Hamblin (1958). (1958). The Theformation formationhas has 44 different different facies, as described by conglomerate conglomerate facies facies occurs occurs mostly at the base of the formation, formation, especially especially where it lies unconformably unconformably on Precambrian rocks (Presque Isle near Marquette, for example), but may also be found found scattered scatteredthroughout throughoutthe theyounger younger beds. beds. Thickness of these beds can be as great as 5 meters. The Themost mostcommon commonof of the the44 facies facies(laterally (laterally and vertically) is a red to reddish brown, medium-grained, medium-grained, lenticular lenticular bedded sandstone. In In some some places, places, lenticular lenticular bedded sandstones sandstones are are 168 �over meters in thickness. Trough over 100 100 meters Troughcross cross bedding bedding and and ripple marks are are common in this this facies. facies. bedding in in the the formation formation accentuate accentuatethe thestructures. structures. The Selective leaching along cross bedding occurrence environment of occurrence of ripple marks, mud cracks cracks and clay pebbles clearly indicate a fluvial environment deposition. AAmassive deposition. massivefacies faciesof of the theJacobsville Jacobsville is is characterized characterized by persistent, thick beds of relatively structureless structureless sandstone, sandstone, many over 3 meters in thickness. At Victoria Falls, a measured measured section of 200 meters of Jacobsville Jacobsville consists consists almost almost entirely entirely of 3 meter thick beds of sandstone. sandstone. Some laterally persistent oscillation ripple marks are found in the beds and support support a lacustrine lacustrine environment of of deposition. deposition. Finally, Hamblin Hamblin recognized recognizedaared redsiltstone siltstonefacies. fades. Though not not common (except (except at Laughing Fish Point and Agate Falls), beds of siltstone siltstone and shale occur occur interfingered with other facies and is interpreted as a quiet-water lacustrine environment facies environment of deposition. deposition. Paleogeographically, the Jacobsville Sandstone represents a continental red bed sandstone sandstone from the the Northern NorthernMichigan Michiganhighlands. highlands. As shown in the deposited by streams flowing northward from paleocurrent (cross (cross bedding and ripple marks) map produced by Hamblin (1958) there is very little deviation in trend (of indicators) indicators) from the mean. An unconformity, in some some places a disconformity, but as on Grand Island, an angular unconformity, separates separates the Jacobsville Jacobsville from the overlying Chapel Rock Member of the Munising Formation. At At Grand Grand Island Island the the Jacobsville Jacobsville dips a few degrees northward, and the Chapel Rock member of the Munising Munising Formation dips a few degrees southward, but at this stop, stop, bedding appears appears to to be be parallel parallel or or nearly nearly parallel parallel at at the the contact. contact. The lower two to fifteen foot section of the Chapel Rock member is a basal conglomerate, fifteen foot conglomerate, formation 90% vein quartz, quartzite quartzite and chert with lesser amounts of slate, basalt, granite, iron formation and sandstone. The Theupper upper 49 49to to 60 60feet feet isis pink pink to to light bluff to brown, medium grained orthoquartzitic sandstone blue-clay and and silty siltyshale shalebeds. beds. The beds in the top 20 orthoquartzitic sandstone with several thin, blue-clay very dolomitic dolomitic and andfrequently frequently"burrowed." "burrowed." Limonite imparts a light or 40 feet are moderately or very yellow-gray color to the member member and occasionally occasionally red to some some thin beds. beds. Northern Michigan The (lower) Chapel Rock member represents a period when the Northern Highlands (to the south) were eroding and shedding their sediments into a shallow empeiric sea south) to the north (see page). The (see the figures on the next page). The Chapel Chapel Rock member is composed composed almost entirely of quartz (mostly of igneous origin; Hamblin, 1958) with minor amounts of feldspar. (mostly minor of tourmaline, and abundant zircon Heavy minerals in the member include well-rounded grains of (20-50% of the total heavies, both altered and unaltered), magnetite, hematite, and ilmenite. Silica is the predominant cement in most places and occurs as secondary overgrowths of varying degrees. Farther Farthereast, east,near nearTahquamenon TahquamenonFalls, Falls, porosity porosity in in the the Chapel Chapel Rock Rock member member isis reduced reduced to almost zero due to the silica cement. Texturally, Texturally, the Chapel Rock member is well-sorted, medium-grained sandstone. Most Most grains grainsare are 1/4 114to 1/2 112 mm diameter. Color Colorgradually graduallyranges ranges sedimentary from white to buff to red. Large Large scale scale trough cross bedding is the most abundant sedimentary The size size of these troughs range from I1 to to nearly nearly 200 200 structure in the Chapel Rock member. member. The meters in width (mean about about 10 10 meters). Megascopically, Megascopically,they they are are useful useful for for differentiating differentiatingthe the Miners Chapel Rock Member Member from the underlying Jacobsville Formation and the overlying Miners Castle member. At At Miners MinersCastle, Castle, they they are are abundant. abundant. They Theyrepresent represent deep deep erosional erosional channels channels that were cut into the older units. Near Near the the base base of the Chapel Rock member, pebbles become abundant in the cross-beds that fill the troughs. Hamblin cross-beds Hamblin(1958) (1958)suggests suggeststhat thatthey theyare areindicative indicative along aa cuspate cuspate shore. shore. Ripples marks are less abundant and of marine deposition in embayments along are both current-formed and oscillatory. Where Wherecurrent-formed, current-formed,they they indicate indicate aa mean mean transport transport direction to the northwest with little little standard standard deviation about that mean (see figure illustrating illustrating cross-bedding directions directions in the the U.P.). This Thisindicates indicatesaafairly fairlysteep steepgradient gradientwith with little little cross-bedding 169 �11 UPLI6*TION S V •t•*d O$Iø *1 — bs#' an a4 — biSS d.ttli. 4 A'SM I.l.. s4 I 474 t1 isa— ii—.— ii I——— iii ii. *i• tsis. 0 G••t_ — .9 0 •? to Cross bedding bedding directions directions in in the the Jacobsville Jacobsville Sandstone Sandstone (after (after Hamblin, Hamblin, 1958) 1958) Paleogeographyduring during deposition depositionof of the theJccobsville JacobsvilleSandstone Sandstone(after (afterHamblin, Hamblin, 1958) 19581 Paleogeography 170 170 �1 Cflt*N*?IO V — •Iadad — ..d at d.(i.IIa I tetIa .1 n. - g*.• •.n k..—.' - • ••—' I— 4, t%St fr.at If SpI —a. Tnqt.....q P•fIi t — — Mtt • ft !a.f •— If so I-. Is ma'.. Cross Crossbedding beddingdirections directionsininthe theChapel ChapelRock Rockmember member ofofthe theMunising MunisingFormation Formation(affer (afterRamblin, Hamblin,1958) 1958) Paleogeography Paleogeographyof ofNorthern NorthernMichigan Michiganduring during deposition deposition of the the Chapel ChapelRock Rockmember member 958) ofthe theMunising MunisingFormation Formation(after (afterHamblin, Hamblin, 1958) of 171 171 �meandering. meandering.InInthe theupper upperpart partofofthe theChapel ChapelRock Rockmember, member,mudcracks mudcracksare arefound foundininthe thefinefinetextured cm in in diameter diameterand and the theintervening intervening textured sandstone sandstoneand andthe theshale shalebeds. beds. They Theyare areabout about55cm cracks cracksare arefilled filled with with sand. sand. Paleogeographically Paleogeographicallyand andenvironmentally, environmentally,they theyindicate indicatedeposition depositionin in aa shallow shallowwater, water, subaerial subaerialenvironment environmentwith with the the sea sea regressing regressing northward. These Thesebeds bedsgrade grade directly into the Miners Castle Member and suggest a minor regression of the Chapel Rock directly into the Miners Castle Member and suggest a minor regression of the Chapel Rocksea. sea. Compact Compact till till isis found found overlying overlying the the bedrock in this valley. The Thetill tillisisreddish reddishin incolor, color,and and texturally ranges from clay to cobbles. It is likely Marquette age (about 10,000 YBP) and was texturally ranges from clay to cobbles. It is likely Marquette age (about 10,000 YBP) and was deposited deposited as as the the Munising Munisingmoraine moraineand and Kingston Kingston outwash outwash plain were being deposited (Phase I1of of thi previous previousdiagrams). diagrams). the Grand Marais Marais Harbor Harbor Stop 11. Grand Grand Grand Marais Marais Harbor Harborisisthe theonly only Harbor Harbor of of Refuge Refuge between between Marquette Marquetteand and Sault SaultSt. St. Marie. Native Americans. Americans. Later, Marie. Originally, Originally,the theprotected protectedbay bay was was aa summer summer camping place for Native French voyageurs used the bay as stopping place to either prepare for, or recuperate French voyageurs used the bay as stopping place to either prepare for, or recuperate from, from, the the dangerous dangerouspaddle paddle along alongthe thecliffs cliffsof of the the Pictured Pictured Rocks Rocksduring during their their travels travelsalong alongthe thesouth southshore shore of of Lake Lake Superior. Superior. The Thetown townitself itselfwas wasestablished establishedininthe the1860's 1860'sby by the the fishing fishing and and lumber lumber industries industriesas as aa boom boom town. town. However, However,by by1910, 1910,the thelumber lumberindustry industrydeclined declinedand and Grand Grand Marais Marais became became mainly mainly a commercial commercial fishing fishing port. Eventually, Eventually,this thisindustry i n d u s e also also declined declined and and the the community community became became all all but aa ghost ghost town. Today, Today,Grand Grand Marais Maraisis is seeing seeing aa renaissance renaissance as as aa summer and and winter winterrecreation recreation town. town. summer Recent, Recent, soon-to-be-published soon-to-be-publishedresearch research at at the the Drexler-Carter Drexler-Carter(D-C) (D-C)site site(Anderton, (Anderton,in in progress), fill section section exposed exposed along along the the front front of of the the eastern eastern portion portion of of the theGrand Grand progress), aa paleo-valley paleo-valleyfill Sable Banks, suggests that prior to the Nipissing transgression, the Grand Marais area may Sable Banks, suggests that prior to the Nipissing transgression, the Grand Marais area may have have consisted consisted of of extensive extensive lagoon. lagoon. Evidence Evidencefor forthe thelagoon lagoonconsists consistsof of extremely extremelythick. thick. Compressed Compressed peat peat deposits, deposits,dated datedatatbetween betweenapproximately approximately7000-6000 7000-6000BP, BP, which which have have been been found foundatatthe theD-C D-C site, site, on on the the floor floor of of Grand Grand Marais Marais Harbor Harbor by by divers, divers, and and during during drilling drilling of wells wells to to the the east east of of the the Harbor. Harbor. The Thepre-Nipissing pre-Nipissinglagoon lagoonwas waslikely likelyprotected protectedbehind behindananextremely extremelylarge largebay baybarrier, barrier, which which may have have extended extended from from as as far far west west as as the the ancestral ancestral Grand Sable Sable Banks Banks or or Au Au Sable Sable Point. Point. The The high high ground groundand andassociated associateddune duneforms, forms,which which begin begin at at Lonesome LonesomePoint Point and andextend extendto tothe the east for for several several kilometers, kilometers, may may be be remnants remnants of of this this older older barrier, bamer, which was was apparently apparently breached breached during rising Nipissing levels. Much Muchfurther furtherwork work isis needed needed to to verify verify these these interpretations. interpretations. The The Nipissing Nipissing transgression transgressioninundated inundated the the Grand Grand Marais Marais area, area, flooding flooding the the mouth mouth of of the the Sucker Sucker River River and and extending extending inland inland for for several several kilometers kilometers south south of of the the high high ground ground that that begins begins at at Lonesome Point. Steep, Nipissing-age, wave-cut bluffs at an elevation of about 195 m (640 ft) Lonesome Steep, Nipissing-age, wave-cut bluffs at an elevation of about I95 m (640 ft) rim the the southern southern edges edges of the town and harbor. Much Much of of the the town town appears appears to to have have been been built built on on aa Nipissing wave-cut wave-cut platform. platform. Nipissing Recently, Recently, Grand Grand Marais Marais Harbor Harbor has has been been the the focus focus of a great great deal of concern by local local residents West Bay. Bay. From residents in regard to the condition of West Fromthe thetime time of of the the earliest earliest written written records and and maps maps of of Grand Grand Marais, Marais,the the bay bay was was originally originally portrayed as relatively relatively deep water lagoon, protected protected behind behind aa low, low,sandy sandybaymouth baymouth barrier barrier that that extended extended from from the the west west side side of of the the current current town, town, east east to to Lonsome Lonsome Point. Point. AAsmall smallchannel, channel,which whichallowed allowedwater waterto to pass pass from from the the bay bay into into the to the harbor. harbor. This the waters waters of of lake lake Superior, Superior, provided provided the only navigable entrance to This natural natural channel, channel, adequate adequate for for several several centuries centuries for for Native Americans Americans and Voyageurs in canoes, was was prone to sand sand bar development, development, which which interfered interfered with commercial shipping shipping associated associated with with the the lumber 800ts. Consequently, various harbor lumber and and fishing fishing industries industries that that began began in in the the late late 11800's. protection protection structures, structures, including includingeventually eventually aa large large breakwater, were built beginning beginning as as early early as as 172 17 2 �L Stop 1 — jt/ioravel Pita - et; Grav4f+t I -. - 'a $k — 3__'_ RM868 - — r -. 3 87O •1 lIlT H V-- -. — Eastward-slopingmeliwater meltwaterdischarge dischargechannels channels southofofGrand Grand Marais Easiword-sloping south Morals 17 3 �1883 1883 to stop sand bars from from blocking blocking the the entrance entrance to the bay (USCOE, (USCOE, 1980). 1980). , Over Over the the years, years, the the harbor harbor protection protection structures structureshave have effectively effectively blocked blocked coastallycoastallytransported transported sand, sand, that that would would have have otherwise otherwisebeen been conveyed conveyed by by littoral littoral drift drift processes, processes,from from replenishing the eastern portion of the original bamer. Consequently,this this part part of of the the barrier barrier has has replenishing barrier. Consequently, been removed removed by by wave wave erosion, erosion, exposing exposing nearly nearly the the entire entire east east end end of the the bay bay to to Lake Lake Superior. Superior. On the west side side of of the the structures, structures,sand sand eroded erodedfrom from the the Grand Grand Sable Sable Banks Banks and and transported transportedto to the the east east has has been been deposited. deposited. Since Since 1961 1961the the beach beach in this area has been growing at a rate of 38,000 cubic m per year (USCOE, 1980). According (1990),the the beach beach has has widened widened by by 1980). Accordingto to Marsh Marsh (1990), 2500-3000 2500-3000 m, m, and, and,ifif left leftunchecked, unchecked,will willeventually eventuallywiden widen to to the thepoint pointwhere wherethe thebeach beach effectively cuts off wave-contact wave-contact with the Grand Sable Banks. ifIf this thishappens, happens,the thesand sandsupply supplyto to effectively the the Grand Grand Sable SableDunes, Dunes,which which isisultimately ultimately tied tied to to lake lakelevels levelsand andbluff bluff recession, recession,will willbe be artificially reduce reduce dune dune nourishment nourishment rates. In Ineffect, effect,the theDunes Dunesmay may cease cease to to exist. exist. artificially Stop stop 12 12 Stop Stop 12 12is is not not really really aa stop, stop, but but an an overview ovewiew of of channels channels as as we we leave leave Grand Grand Marais Marais southward southward on on M-77. M-77. Eastward Eastwarddischarging dischargingstreams streamscut cutchannels channelsatatsuccessively successivelylower lower elevations elevations as the the Marquette Marquette (Grand (Grand Marais) Marais) ice ice retreated retreated into the Lake Superior basin. At least least 88channels channels as basin. At are are recognized recognized from from 207 207 meters meters to 271 meters. Leverett Leverett(1929) (1929)and andothers othersmistakenly mistakenlyinterpreted interpreted these these surfaces surfaces as as Lake Lake Algonquin wave-cut platforms. Hughes Hughes (1968), (19681,through through use use of of aneroid aneroid barometers and and topographic topographicmaps, maps,determined determined they they slope slopeeastward eastward and and asserted assertedthat that they theyare are barometers glacial glacial spillways. spillways. Further, Further,Hughes Hughesrecognized recognizedthe thefact factthat, that, in in profile, profile, the the surfaces surfacesactually actually slope slope southward southward toward toward the the next next escarpment escarpment(characterized (characterized by by poorly poorly drained drained swampy swampyregions regions at at the the south theywere werewave-cut wave-cutterraces, terraces,the the slope slope in in profile profile would would be be in in the the south edge edge of of the the surfaces). surfaces). ifIfthey opposite direction. opposite direction. 174 �REFERENCES Bach, Bach, D.P. 1978. 1978.Plant Plant Communities, Communities,Habitats Habitatsand and Soil Soil Conditions Conditionsof of Grand Grand Sable SableDunes, Dunes, Pictured Rocks National Lakeshore, Michigan. Unpublished Masters Thesis, Michigan Pictured Rocks Lakeshore, Unpublished Master's Thesis, Michigan Technological Technological University, University, 180 180p. p. Bergquist, Bergquist, S.C. S.C. 1936. 1936.The The Pleistocene Pleistocenehistory history of of the the Tahquamenon Tahquamenon and and Manistique Manistique drainage drainage region of hblication 40, 40, of the the northern northern peninsula peninsula of of Michigan. Michigan. Michigan Michigan Geological Geological Survey Survey Publication Geological GeologicalSeries Series34, 34,part part11pp.7-148. pp.7-148. Blewett, Blewett, W.L. W.L. and and R.L. R.L. Rieck. Rieck. 1987. 1987. Reinterpretation Reinterpretationof aa portion of the the Munising Munising Moraine Moraine in in northern northern Michigan. Michigan.Geological GeologicalSociety Societyof ofAmerica AmericaBulletin Bulletin98:169-175 98: 169-175 Blewett, Blewett, W.L. 1994, 1994,Late Late Wisconsin Wisconsin History History of Pictured Rocks Rocks National Lakeshore Lakeshore and Vicinity. Vicinity. National Park Park Service Service PIRO P R O 94-01, 94-01,8 p. National 8 p. Carey, L. 1993. 1993. Interim Interimsoil soilsurvey surveyof ofPictured PicturedRocks RocksNational NationalLakeshore, Lakeshore,Alger AlgerCo., Co.,Michigan. Michigan. USDA, USDA, Soil Soil Conservation ConservationService, Service,Marquette, Marquette,MI. MI. Drexler, Drexler, C.W. C.W. 1981. 1981.Outlet Outletchannels channelsfor for the the post-Duluth post-Duluth lakes lakes of of the the Upper Upper Peninsula Peninsula of of Michigan. PhD PhD dissertation, dissertation, University University of of Michigan, Michigan, Ann Ann Arbor. Arbor. 295 295 p. p. Michigan. Ells, Ells, G.D., G.D., 1967, 1967,Correlation Correlationof of Cambro-Ordovician Cambro-Ordovician Rocks Rocks in in Michigan. Michigan. in in Correlation CorrelationProblems Problems of the Cambrian and Ordovician Outcrop Areas, Northern Peninsula of Michigan, Michigan Cambrian and Ordovician Outcrop Peninsula Basin Geological } pp. Geological Society SocietyAnnual Annual Field FieldExcursion, Excursion,M.E. M.E. Ogstrom Ogstromand andA.E. A.E.Slaughter, Slaughter,{eds. {eds.] pp. 42-57. Farrell, Farrell, J.P. and and J.D. J.D. Hughes Hughes 1985. 1985. Long Long Term Implications, Implications, From a Geomorphological Geomorphological Standpoint, Location at at Grand Grand Sable SableLake. Lake. Contract Report Standpoint, of Maintaining Maintaining H-58 in its Present Location PX60000-4-0839, PX60000-4-0839, submitted submittedto tothe theNational NationalPark ParkService, Service,78 78p.p. Hamblin, Hamblin, W.K., 1958, 1958,Cambrian Cambrian Sandstones Sandstonesof of Northern Michigan. Michigan Michigan Dept. of Natural Natural Resources Pub. 51, 51, 146 146p. p. Resources Larsen, Larsen, C.E. 1985. 1985.Lake Lake Level, Uplift, Uplift, and Outlet Incision, The Nipissing and Algoma Great Lakes. In Quaternary Calkin. Quaternary Evolution Evolution of of the the Great GreatLakes, Lakes, edited edited by by P.F. P.F. Karrow Karrow and and P.E. P.E. Calkin. Geological GeologicalAssociation Associationof of Canada CanadaSpecial SpecialPaper Paper30. 30. Leverett, U.S. Geological Survey Leverett, F. 1929. 1929.Moraines Moraines and and shorelines shorelines of the Lake Superior region. U.S. Prof. Paper Paper 154-A. 154-A.72 72 p. p. Levin, H.L., H.L., 1996, 1996, Earth Earth Through Through Time. Time. 5th 5~ ed., Saunders, Saunders, 568 568 p. Marsh, W.M. 1990. 1990.Nourishment of Perched Sand Sand Dunes and the Issue of Erosion Control in the Great Lakes. Environ. Environ.Geol.Water GeoLWaterSci. Sci.16(2): 16(2):155-164. 155-164. 175 �Marsh, W.M. and B.D. Marsh 1988. 1988. Wind Erosion and Sand Dune Formation Formation orj on High Lake Superior Bluffs. Geografiska GeografiskaAnnaler Annaler 69A 69A (3-4):379-391. (3-4):379-391. Schaetzl, R.J. and D.L. Mokma 1988. 1988. A Numerical Index of Podzol and Podzolic Soil Development. Development. Physical Physical Geography Geography 9(3):232-246. 9(3):232-246. USCOE, 1980, 1980, Final Detailed Detailed Project Project Report on Shore Shore Damage of Grand Grand Marais Harbor, Harbor, Section ifi, in, Detroit, Detroit, MI MI Detroit Detroit District. Michigan, Section 176 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1999 Description An account of the resource Institute on Lake Superior Geology. Marquette, Michigan. May 4-8, 1999. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1999 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/c95bde6817524fac0b7a49791755d404.pdf 8b20a8aef357cb8f905e7b7c0b74dba7 PDF Text Text 4 FORTY-SIXTH ANNUAL MEETING St ON LAKE SUPERIOR : SINSTITUTEGEOLOG S — Si h1*r Bay,Ontario — S May. 08-13,2000 44 '1 44 . 4. ••r :4 .tssi.:. S S S S PROCEEDINGS VOLUME 46 45 /4 4 /4 /4 4/4 PARfl: PROGRAMAND ABSTRACTS �46th I.L.S.G. rogram & Abstracts 2000 May 8-13, 8-13,2000 Hosted at at Lakehead University Universi by the Geology Department Thunder Bay, Ontario Canada �46thAnnual Annual Meeting Meeting 46th 1 II INSTITUTE ON LAKE SUPERIOR GEOLOGY U Volume 46 contains the following parts: parts: Part 1: 1: Program and Abstracts Part 2: Field Trip Guidebook — Geology of the Mesoproterozoic Sibley Group 1 -Geology 22 — PGE-Cu-Ni Mine - Geology Geology of the Lac Lac des des Ties Iles PGE-Cu-Ni Mine 33 — Geoarcheology and deglaciation history the Thunder Thunder Bay Bay area - Geoarcheology history of the 44 — - Geology Geology of the Paleoproterozoic Gunflint Formation 55 — - Glacial Glacial history and regional till sampling sampling in the Archean Shebandowan Shebandowan Greenstone Greenstone Belt 6— Finlayson Lake Greenstone Greenstone Geology of of the Archean Archean Steep Steep Rock Rock Lake Lake - Finlayson 6 -Geology Belt - Reference ce to the material material in in this this volume volume should should follow follow the the example examplebelow: below: A., 2000. Chemistry and mineralogy of Lower Chowlay Chocolay G roup rocks, Dickinson Dickinson Argast, A,, County, Michigan, Michigan, [abstract]: [abstract]: Institute Institute on on Lake Lake Superior SuperiorGeology GeologyProceedings, Proceedings,46th 46* Annual Meeting, Meeting, Thunder Thunder Bay, Bay, ON, ON, 2000; 2000; v.46, v.46, Part Part 1, 1, p. p. 1-2. 1-2. Volume 46 is published by the Institute on Lake Superior Geology and distributed by the Institute Institute Secretary-Treasurer. Secretary-Treasurer. Jirsa (term (term 1994-2000) 1994-2000) Mark Jirsa Minnesota Minnesota Geological Geological Survey Survey 2642 University Avenue St. Paul, MN USA 55114-1057 55 114-1057 (612)-627-4780 (6 12)-627-4780 email: jirsaOO iirsa00liätc.umn.edu 1(Sitc.umn.edu http://www.ilsgeology.org ILSG website: website: htto://www.ilsgeologv.org All volumes are are available available at at the the cost costofphotocopying ofphotocopyingfrom from Michigan Michigan Technical TechnicalUniversity UniversityArchives. TSSN 1042-9964 1042-9964 ISSN �INSTITUTE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON ON LAKE CONTENTS Proceedings Proceedings Volume Volume 46 46 Part Part 1—Program I-Program and Abstracts Abstracts Editor: Stephen Editor: StephenA. A. Kissin Kissin Institutes on Institutes on Lake Lake Superior Superior Geology, Geology, 1955-2000 1955-2000 ..... . ...... iii ... By-Laws of the Institute Lake Superior Geology .... By-Laws of the Institute on on Lake Superior Geology . . . .v Constitution of Constitution of the the Institute Institute on on Lake Lake Superior Superior Geology Geology Goldich Goldich Medal Guidelines Guidelines Past Goldich Medallists Medallists ................... ..... . . . vivi ... ..... viii Vlll Goldich Medal Committee ............... ... viii ..... Vlll Citation Recipient....... Citation for 2000 2000 Goldieh Goldich Medal Recipient ...... ix . ................. . . . xi ... .............. . . . . . . xii ... xiii . . . . . . Xlll Student Paper Student Paper Awards Awards Committee Committee ..... ... . . . . . . Xxiii lll Student Travel Travel Awards Awards Student Travel Travel Award Application Application Form Form Student Paper Student Paper Awards Awards Board of Directors Directors ............. Xiv . . . . . . xiv Local Committees Committees ..... . . . . . . xiv ................................. Report of the the Chair Chair of of the the 45th 45th Annual Annual Institute Institute Meeting ...... Program ........................................ Banquet Speaker Banquetspeaker Abstracts Abstracts .... xv .......XV ...... xvi ...... Xix xix ... 1 . 1 �ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY, GEOLOGY, 1955-2000 1955-2000 INSTITUTES ON # DATE PLACE CHAIRS 1 1955 1 1955 Minneapolis, Minneapolis, Minnesota Minnesota Floughton, Michigan 1956 1956 Houghton, 3 1957 1957 East Lansing, Lansing, Michigan Michigan 44 1958 1958 Duluth, Duluth, Minnesota Minnesota 5 1959 1959 Minneapolis, Minneapolis, Minnesota Minnesota C.E. Dutton Dutton A.K. Sneigrove Snelgrove B.T. Sandefür Sandefiir R.W. Marsden Marsden G.M. Schwartz & C. Craddock Craddock (note (note Schwartz & 2 2 66 77 88 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 27 28 29 30 30 31 31 32 32 33 33 34 34 35 35 36 37 38 1960 1960 Madison, Madison, Wisconsin 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 Port Arthur, Arthur, Ontario Ontario Houghton, Michigan Houghton, Michigan Duluth, Duluth, Minnesota Minnesota Ishpcming, Ishpeming, Michigan St. Paul, Minnesota Minnesota Sault Ste. Marie, Michigan Michigan East Lansing, Michigan Superior, Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Marquette, Marquette, Michigan Michigan Minnesota St. Paul, Minnesota Thunder Thunder Bay, Ontario Ontario Wisconsin Milwaukee, Wisconsin Minnesota Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Kenora, Ontario Ontario Wisconsin Rapids, Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Michigan Marquette, Duluth, Minnesota Minnesota Thunder Bay, Ontario Ontario Eau Claire, Claire, Wisconsin Wisconsin Hurley, Wisconsin I correction) correction) E.N. Cameron Cameron E.G. Pye Pye A.K. Snelgrove Snelgrove H. Lepp Lepp A.T. Broderick Broderick P.K. Sims & R.K. Hogberg R.W. White W.J. Hinze H i e A.B. Dickas A.B. G.L. LaBerge LaBerge M.W. Bartley & E. Mercy M.W. D.M. Davidson Davidson Kalliokoski J. Kalliokoski M.E. Ostrom Ostrom P.E. Giblin Giblin J.D. Hughes Hughes M. Walton Walton M.M. Kehienbeck Kehlenbeck U. Mursky G. D.M. Davidson Davidson P.E. Myers Myers W.C. Cambray W.C. D.L. Southwick Southwick D.L. Bomhorst T.J. Bornhorst LaBerge G.L. LaBerge Blackburn C.E. Blackburn J.K. Greenberg J.K. Greenberg Sage E.D. Frey & R.P. Sage J. S. Klasner J.C. Green Green M.M. Kehlenbeck Kehlenbeck P.E. Myers Myers A.B. Dickas Dickas �39 40 41 42 43 44 45 1993 1994 1995 1996 1997 1998 1999 46 2000 D.L. Southwick Southwick T.J. Borithorst Bornhorst M.C. Smyk L.CI.Woodruff Woodruff L.G. R.P. Sage, W. Meyer J.D. Miller, M.A. Jirsa T.J. Bornhorst, R.S. Regis S.A. Kissin, P. Fralick Eveleth, Minnesota Minnesota Houghton, Houghton, Michigan Michigan Marathon, Ontario Ontario Cable, Wisconsin Wisconsin Sudbury, Ontario Ontario Minneapolis, Minnesota Marquette, Marquette, Michigan Michigan Thunder Bay, Ontario Ontario 11 �CONSTITUTION CONSTITUTION LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY OF THE INSTITUTE ON LAKE (Last amended by the the Board—May Board-May 8, 1997) 1997) Article II Article Name The name of the organization organization shall be the "Institute on Lake Superior Geology". Geology". Article II Article I1 Objectives Objectives The objectives objectivesof of this this organization organizationare: are: A. To Toprovide provideaameans meanswhereby whereby geologists geologists in in the the Great Great Lakes Lakes region region may exchange ideas and scientific scientific data. B. To Topromote promotebetter better understanding understanding of of the geology of the Lake Superior Superior region. region. C. To Toplan plan and and conduct conduct geological geological field field trips. Article III Article 111 Status && No part of of the income income of the organization organization shall shall insure insure to the benefit benefit of of any any member or individual. In the event of dissolution, the assets of the organization shall organization shall be distributed distributed to to _________(some free (some tax free organization). organization). (To avoid Federal and State income taxes, the organization should be not educational, but only "scientific" or "educational, but also also "non-profit") "non-profit") Anno. 290.01, 290.01, subd. subd. 44 Minn. Stat. Stat. Anna. Minn. Stat. Stat. Anno. 290.05(9) 290.05(9) 1954 1954 Internal Revenue Revenue Code Code s.501(c)(3) s.501(~)(3) Article IV Article Membership Membershir The membership of the organization shall consist of persons who have registered for an annual meeting within the past three three years, and those who indicate interest in being a member according to guidelines approved by the Board of Directors. Directors. Article V Article Meetings Meetings The organization shall meet once aa year. year. The The place and exact date of each meeting will will be be designated designated by by the the Board Board of of Directors. Directors. Article VI Directors Directors The Board of Directors shall consist of the Chair, Secretary-Treasurer, and the last three past Chairs; but if the board should at at any any time time consist consist of of ... I"I ll �fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be be filled by the Chair so as to bring the membership of the board to five members. members. Article ArticleVII VII Officers Officers The The officers officers of of this this organization organization shall shall be be aa Chair Chair and and Secretary-Treasurer. Secretary-Treasurer. A. A. The TheChair Chairshall shallbe beelected electedeach eachyear year by by the the Board Board of of Directors, Directors, who shall give due consideration to the wishes of any group that shall give due consideration to the wishes of any group that may may be be promoting the next annual His/her term of office as Chair will promoting the meeting. Hisher term of office as Chair will terminate terminate at at the the close close of of the the annual annual meeting over over which which he/she helshe presides, or or when when his/her hisiher successor shall have been appointed. He/she Helshe will then then serve serve for for aa period period of of three three years years as as aa member member of of the the Board Boardof ofDirectors. Directors. B. The Secretary-Treasurer shall be elected at the annual B. The Secretary-Treasurer shall be elected at the annualmeeting. meeting. His/her Hisiher term term of of office office shall shall be four four years, or until his/her hisher successor successor shall shall have been appointed. have been appointed. Article ArticleVIII VIII Amendments Amendments This This constitution constitutionmay may be be amended amended by by aa majority majority vote vote (majority (majority of of those those voting) voting)of of the the membership membershipof ofthe theorganization. organization. iv �BY-LAWS OF THE INSTITUTE ON LAKE LAKE SUPERIOR GEOLOGY I. Duties Dutiesof of the the Officers Officers and Directors A. ItItshall shallbe bethe theduty dutyof ofthe the Annual Annual Chairman Chairman to: 1. Preside Preside at at the the annual annual meeting. meeting. 2. Appoint Appointall allcommittees committeesneeded needed for for the the organization organizationof of the the annual annual meeting. meeting. 3. Assume Assumecomplete completeresponsibility responsibility for forthe the organization organizationand and financing financing of of the the annual meeting over which he/she presides. helshe B. ItItshall shallbe bethe theduty dutyof ofthe theSecretary-Treasurer Secretary-Treasurerto: 1. Keep Keep accurate accurateattendance attendance records records of of all all annual annual meetings. meetings. 2. Keep Keepaccurate accuraterecords records of of all all meetings meetings of, and correspondence correspondence between, the Board of Directors. Directors. 3. Hold Holdall allfunds fundsthat that may may accrue accrue as as profits profits from from annual meetings meetings or field field organization and operation trips and to make these funds available available for the organization operation of future future meetings meetings as as required. required. C. ItItshall shallbe bethe theduty dutyof ofthe the Board Board of of Directors Directorsto to plan locations locations of of annual annual meetings meetings and to advise advise on the organization organization and financing financing of all meetings. II. Duties 11. Duties and and Expenses Expenses A. Regular $5.00or or less less on on an an annual annual basis basis shall shall be assessed assessed Regularmembership membershipdues duesof of $5.00 each each member member as as determined determined by by the the Board Boardof of Directors.. Directors.. B. Registration Registrationfees feesfor forthe the annual annual meetings meetings shall shall be determined by the Chair in Directors. The consultation with the Board of Directors. The registration registration fees fees can include include determined by expenses to cover operations outside of the annual meeting as determined the Board of Directors. ItItisisstrongly recommended that registration strongly recommended that registration fees fees be be kept at a minimum minimum to to encourage encourage attendance attendance of of students. students. III. Rules 111. Rules of of Order The rules contained contained in Robert's Rules of Order shall govern this organization organization in in all all cases cases to which which they they are are applicable. applicable. IV. Amendments Amendments by aa majority majorityvote vote (majority (majorityof ofthose thosevoting) voting)of of These by-laws may be amended by the membership membership of of the organization; organization; provided provided that such such modifications modifications shall shall not not conflict with the constitution as presently adopted or subsequently amended. constitution v �GOLDICH GOLDICH MEDAL MEDAL GUIDELINES GUIDELINES (Adopted (Adopted by the the Board Board of of Directors, 1981; 1981;amended amended 1999) 1999) Preamble Preamble The The Institute Institute on on Lake Lake Superior Superior Geology Geology was born in 1955, 1955, as documented documented by the fact fact that that the 27th annual meeting was held in 1981. The Institute's continuing objectives are to 27th annual The Institute's continuing objectives are deal with those those aspects aspects of of geology that are related geographically geographically to Lake Superior; Superior; to encourage encourage the discussion discussion of of subjects subjects and sponsoring sponsoring field trips that will bring bring together together geologists geologists from from academia, academia, government surveys, surveys, and industry; and to maintain an an informal informal but but highly highly effective effectivemode modeof ofoperation. operation. During During the the course course of of its its existence, existence, the the membership membershipof of the the Institute Institute (that (that is, is, those those geologists who indicate an interest in the objectives of the ILSG by attending) geologists indicate an interest objectives attending) has has become become aware aware of of the the fact fact that that certain certain of of their their colleagues colleagues have made particularly noteworthy noteworthy and and meritorious meritoriouscontributions contributionsto to the the understanding understanding of of Lake Lake Superior Superiorgeology geology and and mineral mineral deposits. deposits. The The first first award awardwas was made made by by ILSG ILSG to to Sam SamGoldich Goldich in in 1979 1979for for his his many many contributions contributionsto to the the geology geologyof of the the region regionextending extendingover over about about 50 50 years. years. Subsequent Subsequent medalists medalists and and this this year's year's recipient recipientare arelisted listedin inthe thetable tablebelow. below. Award Award Guidelines Guidelines 1) 1) The Themedal medalshall shallbe beawarded awardedannually annuallyby bythe theILSG ILSGBoard Boardof ofDirectors Directorsto toaageologist geologist whose whose name name is is associated associated with a substantial substantial interest in, and contribution contributionto, to, the the geology geology of the Lake Superior region. of the Lake Superior region. 2) The TheBoard Boardof ofDirectors Directorsshall shall appoint appoint the Goldich Medal Committee. The The initial initial appointment appointment will will be be of of three three members, members, one one to to serve serve for for three three years, one one for for two two years, years, and and one one for for one one year. year. The Themember memberwith withthe thebriefest briefestincumbency incumbencyshall shallbe be chair chair of of the the Nominating Committee. After the first year, the Board of Directors shall appoint Nominating Committee. After the first year, the Board of Directors shall appoint at at each each spring years. In histher third third year year this this spring meeting meeting one one new new member member who will serve for three years. In his/her member member shall shall be be the the chair. chair. The TheCommittee Committeemembership membershipshould shouldreflect reflect the the main main fields fieldsof of interest interestand andgeographic geographicdistribution distributionofofILSG ILSGmembership. membership. 3) 3) By Bythe theend endofofNovember, November,the theGoldich GoldichMedal Medal Committee Committeeshall shall make make its its recommendation recommendationto to the theChair Chairof ofthe the Board Board of of Directors, Directors, who who will will then then inform inform the the Board Board of the nominee. of the nominee. 4) 4) The TheBoard BoardofofDirectors Directorsnormally normallywill willaccept acceptthe thenominee nomineeof ofthe theCommittee, Committee,inform inform the the medallist, medallist,and andhave haveone onemedal medalengraved engravedappropriately appropriatelyfor for presentation presentation at at the the next next meeting meetingof ofthe theInstitute. Institute. vi �I sources, such 5) ItIt isisrecommended recommendedthat that the the Institute Institute set set aside aside annually from whatever sources. funds as will be required to support the continuing continuing costs of this award. award. Nominating Nominatine Procedures Procedures 1) The The deadline deadline for for nominations nominations is November 1. Nominations shall be taken at any time by the Goldich Medal Committee. Committee Committee members members may themselves themselves nominate nominate candidates; however, Board members may not solicit for or support individual candidates; individual nominees. 2) Nominations Nominationsmust mustbe bein inwriting writing and and supported supported by by appropriate appropriate documentation documentation such such as as letters of recommendation, lists of publications, curriculum vita's, and evidence of lists curriculum evidence contributions contributions to Lake Superior Superior geology and to the Institute. Institute. 3) Nominations Nominationsare arenot notrestricted restricted to to Institute Instituteattendees, attendees, but are open to anyone anyone who has worked on and contributed to the understanding of Lake Superior Superior geology. Selection Selection Guidelines Guidelines 1) Nominees Nominees are are to to be be evaluated evaluated on on the the basis of their contributions contributions to Lake Superior geology (sensu (sensu lato) lato) including: including: geology a) importance importanceof ofrelevant relevantpublications; publications; b) promotion promotionof ofdiscovery discoveryand andutilization utilizationof of natural natural resources; resources; c) contributions contributionsto tounderstanding understandingof of the the natural natural history history and and environment environmentof of the the region; region; d) generation generationof ofnew new ideas ideas and and concepts; and e) contributions contributionsto to the the training training and and education education of geoscientists geoscientists and the public. 2) Nominees Nomineesare areto tobe beevaluated evaluatedon ontheir their contributions contributionsto to the the Institute Institute as as demonstrated demonstrated by attendance at Institute meetings, presentation of talks and posters, and service attendance at Institute of talks service on on Institute Institute boards, committees, committees, and and field field trips. trips. 3) The Therelative relativeweights weightsgiven givento to each each of of the foregoing foregoing criteria must remain flexible and at the discretion discretion of of the the Committee Committee members. members. 4) There Thereare areseveral severalpoints pointsto tobe beconsidered consideredby by the the Goldich Goldich Medal Medal Committee: Committee: a) An attempt should be made to maintain a balance of medal recipients from An attempt should be made to maintain a balance of from each each of the the three three estates—industry, estates-industry, academia, and government. government. b) ItItmust mustbe benoted notedthat thatindustry industrygeoscientists geoscientistsare are at at aa disadvantage disadvantage in that much of of their work in not published. 5) Lake Canada. This LakeSuperior Superiorhas has two two sides, sides, one one the U.S., U.S., and the other Canada. This is is undoubtedly undoubtedly one of the Institute's great strengths and should be be nurtured nurtured by by equitable equitable recognition recognition of of excellence excellence in in both both countries. countries. vii �GOLDICH MEDALISTS MEDALISTS 1979 Samuel Samuel5. S.Goldich Goldich 1990 Kenneth C. Card Card KennethC. 1980 not not awarded awarded 1980 1991 William Hinze 1991 1981 1981 Carl E. Dutton, Jr. 1992 William William F. F. Cannon 1982 Ralph RalphW. W. Marsden Marsden 1993 Donald Donald W. W. Davis Davis 1983 Burton BurtonBoyum Boyum 1994 Cedric CedricIverson Iverson 1984 Richard RichardW. W. Ojakangas Ojakangas 1995 Gene GeneLaBerge LaBerge K. Sims Sims 1985 Paul Paul K. 1996 David David L. L. Southwick Southwick 1986 G.B. G.B.Morey Morey 1997 Ronald P. Sage Sage Ronald P. 1987 Henry HenryH. H. Halls Halls Petennan 1998 1998 Zell Peterman 1988 Walter WalterS. S.White White 1999 Tsu-Ming Tsu-Ming Han 1989 Kalliokoski 1989 Jorma Jorma}Calliokoski 2000 John 2000 John C C. Green Green GOLDICH MEDAL COMMITTEE COMMITTEE1999-2000 1999-2000 members (Committee (Committeemembership membershipextends extendsthrough throughthe the meeting meeting year year shown; shown; replacement replacement members that year. year. Note will be selected during the Board of Directors' annual meeting of that Note that that the the 1999 Board of Directors) Directors) term of each each committee committee member was extended 11 year by the 1999 John Klasner John Klasner(2000) (2000) Western Illinois Illinois University, Macomb, Illinois Illinois Mark Mark Smyk Smyk(2001) (2001) Ontario Ontario Geological Geological Survey, Survey, Thunder Thunder Bay Bay Johnson (2002) Rod Johnson (2002) Rod Johnson and Associates, Associates, Negaunee, Michigan viii viii �CITATION John C C.Green, Green, Medal Recipient 2000 Goldich Medal John C. C. Green, Green, Professor Professor Emeritus Emeritus of of the the Department Department of ofGeological GeologicalSciences, Sciences, University of Minnesota-Duluth, has had a long, distinguished, and on-going career has distinguished, and on-going careerin in the the Lake Superior Superior region. He received his B.A. B.A. Degree Degree in in Geology Geology from from Dartmouth DartmouthCollege Collegeinin 1953. 1953. He at the the University University of of Oslo Osloon onaaFulbright FulbrightFellowship. Fellowship. He then spent a year amid Norskies at Ph.D. in 1960, both both from from Harvard Harvard University. University. With received his M.A. in 1956 1956 and his Ph.D. With his his dissertation on Appalachian geology of an area in New Hampshire/Maine not quite dissertation on Appalachian geology of in New Hampshire/Maine not quite finished, New Englanders Englanders John and Jan moved to Duluth in 1958 1958 when John accepted the position at UMD. position UMD. Most Mostofofhis hissubsequent subsequentsummers summers were were spent spent mapping mapping in in northern northern He did the Archean portion of the Minnesota for the Minnesota Geological Survey. the the Minnesota Geological Survey. the Archean Gabbro 1966), the first first detailed map map Gabbro Lake 15' 15' Quadrangle Quadrangle(Green, (Green, Phinney, Phinney, and Weiblen, 1966), in the that was undertaken by the MGS the remapping remapping of the the Precambrian Precambrian that undertaken by MGS under under the the leadership of Paul Sims. Whereas Minnesota has been his primary working domain, Whereas Minnesota has been his primary working domain, he he has taught at the Wasatch-Uinta Wasatch-Uinta Geology Field Camp in Utah for six summers, has spent a year year as as aaNASA-NRC NASA-NRC Senior Senior Research Research Associate Associate at the the Johnson Johnson Space Space Center Center in in including study Houston, and has traveled widely — Japan, Iceland, and Namibia — to Iceland, and Namibia - to study and has traveled widely - including volcanic volcanic rocks. rocks. John has served as Head of UMD's Department Department of Geology, has served served on on dozens dozens of university committees, and has chaired several of them. them. He Hewas wason onthe theAll-University All-University Council has chaired chaired the the Board of of Directors Council on Environmental Environmental Quality for eight years. He He has of the Lake Superior Basin Studies Center. He has taught 20 different courses, including Superior Studies He has taught 20 different courses,including several that that deal with geology, one one of of his many He has several with environmental environmental geology, many interests. interests. He has supervised 13 supervised 13 M.S. theses theses and has served served on on 61 61 M.S. and and 55 Ph.D. examining examining committees. committees. He has has authored authored or or co-authored co-authored more more than than 100 100publications, publications, maps, maps, field field guides, guides, and and abstracts. abstracts. John's has been been the theNorth NorthShore ShoreVolcanic VolcanicGroup Group—John's main main scientific scientific interest interest has physical volcanology, stratigraphy, physical volcanology, structure, structure, petrology, petrology, and and chemistry chemistry—- and and the the in general. general. Indeed, the name of John C. Green is synonymous Midcontinent Rift System in with with the NSVG. NSVG. He is a most careflil geologist. Today, careful and observant field geologist. Today, at the the age age of of 68, 68, long long would have have hung hung up up their field boots after many geologists would boots and settled for writing the paper about about their their glory glory days, he is still out their leading field trips, umpteenth summary paper beating the bush and the bugs, and hunting for the outcrops that that will will bring bring him him a little beating John doesn't just look at the rocks! He is the rare "complete closer is the rare "complete closer to the the truth. truth. John doesn't just look at the rocks! naturalist", for he knows every species of flora and and fauna fauna as as well. well. And, And, he he isis very very active active in preservation preservation ooff nature for the enjoyment enjoyment of all. His foresight, initiative, and drive resulted in in the the preservation preservation of of Sugarloaf Sugarloaf Cove/Point CoveIPoint near Schroeder on the North Shore, Shore, with its unique geology, geology, flora, flora, and cultural cultural history, as aa protected protected Natural and and Scientific Scientific ix �Site. Site. He was was instrumental instrumental in the the founding founding and and continuance continuance of SICA, SICA, the Sugarloaf Sugarloaf Interpretative Center Association. Interpretative Center Association. One of his his more more recent recent accomplishments accomplishments is his book on on the the geology geology and and natural natural history of the state parks of the North Shore, entitled "Geology on Display". history state parks of the North Shore, entitled "Geology on Display". It was was published by the 1996. published the Minnesota MinnesotaDNR DNR in in 1996. John has been one one of of the the strongest strongest supporters supporters of the the Institute Institute on on Lake Lake Superior Superior Geology over the last several decades. decades. He presented his first talk there in 1959, 1959, and has added 28 abstracts abstracts since since then. then. It is because of the dedication and support of people people like like John, that the ILSG has remained such a viable and healthy organization for nearly half remained such a viable and healthy organization for nearly half aa century. century. geologist, the the laboratory John C. Green Green—- the the tireless tireless field field geologist, laboratory scientist, scientist, the John C. demanding teacher, teacher, the knowledgeable and and cooperative colleague, the educator of the cooperative colleague, the the most deserving deserving of the public, the complete complete naturalist, naturalist, and and the the advocate advocateof ofILSG ILSG—- is is most Goldich Medal! Medal! All of us us assembled assembled here, as well well as as wife wife Jan, Jan, daughters daughters Martha Martha and and Sarah, sons-in-law Joe and Richard, and five grandchildren, are proud of you! and five grandchildren, are proud of you! Congratulations, J.C.! Congratulations, J.C.! x �4 EISENBREY EISENBREYSTUDENT STUDENTTRAVEL TRAVELAWARDS AWARDS The The 1986 1986Board Board of ofDirectors Directorsestablished established the the ILSU ILSG Student Student Travel Travel Awards Awards to to support support student Institute. The student participation at the annual meeting meeting of the Institute. Thename name "Eisenbrey" "Eisenbrey" was was added Eisenbrey(1926-1985) (1926-1985)and andutilize utilize added to to the theaward awardinin1998 1998totohonor honorEdward EdwardH.H.Eisenbrey contributions contributions made made to to the the 1996 1996Institute Institutemeeting meetingininhis hisname. name. "Ned' "Ned"isiscredited creditedwith with discovery of significant massive sulfide sulfide deposits deposits in in Wisconsin, significant volcanogenic volcanogenic massive Wisconsin, but his his talents as scopewas was much muchbroader—he broader-he has been described as having unique talents as an an ore ore finder, finder, scope geologist, geologist, and and teacher. teacher. These Theseawards awardsare areintended intendedtotohelp helpdefray defraysome someof ofthe thedirect directtravel travel costs costs of of attending attending Institute Institute meetings, meetings, and include include a waiver waiver of of registration registration fees, fees, but but exclude exclude expenses expenses for for meals, meals, lodging, lodging, and and field field trip registration. registration. The Thenumber numberofofawards awards and and value value are aredetermined determined by by the theannual annualChair Chairininconsultation consultationwith withthe theSecretarySecretaryTreasurer. Treasurer.Recipients Recipientswill willbe beannounced announcedatatthe theannual annualbanquet. banquet. The The following followinggeneral general criteria criteria will will be be considered considered by the annual annual Chair, Chair, who who is is responsible responsible for forthe theselection: selection: 1) 1) The Theapplicants applicantsmust musthave haveactive activeresident resident(undergraduate (undergraduate or or graduate) graduate)student studentstatus statusatai the thetime timeof ofthe theannual annualmeeting meetingof ofthe theInstitute, Institute,certified certifiedby by the thedepartment departmenthead. head. who are the senior author author on on either either an oral or poster 2) Students who poster paper paper will be be given given 2) favored favoredconsideration. consideration. 3) 3) ItItisisdesirable desirablefor fortwo twoorormore morestudents studentsto tojointly jointly request requesttravel travel assistance. assistance. 4) 4) InIngeneral, general,priority prioritywill willbebegiven giventotothose thoseininthe theInstitute Instituteregion regionwho whoare arefarthest farthestaway away from from the the meeting meetinglocation. location. 5) Each Eachtravel travelaward awardrequest requestshall shallbe bemade madeininwriting writingtotothe theannual annualChair, Chair,arid andshould should explain need, student and author status, and other significant significant details. details. The The form form below is is optional. optional. Students Students can can use use the the form form below, below, or or consult consultthe the Institute's Institute's web webpage page(ilsgeology.org) (ilsgeology.org) to to apply. apply. Successful Successful applicants should contact the meeting chair to receive receive their their awards awards during during the the meeting. meeting. xi �- p INSTITUTE SUPERIOR GEOLOGY INSTITUTE ONLAKE ONLAKE SUPERIOR GEOLOGY flTenbrey Eisenbrey Student Student Travel Travel Award Award Application Application Student StudentName: Name: Date: Date: Address: email: _____________________ Department DepartmentHead-Typed Head-Typed Department DepartmentHead-Signature Head-Signature Educational Educational Status: Status:________________________ Are the senior seniorauthor authorofofanan oral or poster paper? NO_._ oral or poster paper? Y YES— E S NOAre you the Will Will any any other otherstudents studentsbe betraveling travelingwith withyou? you? Who? Who? ________________ Statement Statementof of need need (use (useadditional additionalpage pageififnecessaiy) necessary) to: Pleasereturn returnto: Please xl' xii �STUDENT PAPER AWARDS ., Each year, the Institute selects the best of the student presentations and honors presenters Funding for for the award registrations of the with aa monetary monetary award. award. Funding award is generated from registrations annual meeting. The TheStudent StudentPaper Paper Committee Committeeis is appointed appointed by by the the annual annual meeting meeting Chair Chair in such a manner as to represent a broad range of professional and geologic expertise. manner as to represent a broad range of professional and geologic expertise. Criteria for Criteria for best best student studentpaper—last paper-last modified by the Board Board in in 1997—follow: 1997-follow: 1) The contribution contribution must be demonstrably demonstrably the work of the student. student. 2) The student student must present the contribution contribution in-person. 3) The Student Student Paper Committee Committee shall shall decide decide how many awards to grant, and whether or not to give give separate separate awards awards for for poster poster vs. vs. oral oral presentations. presentations. 4) In cases of multiple senior author, author, or or multiple student student authors, the award will be made to the senior * the award will be shared equally by all authors authors of the contribution. contribution. 5) The The total amount of the awards is left to the discretion of the meeting Chair and typically is about Secretary-Treasurer, but typically about $300 $300 US. US. 6) The Secretary-Treasurer Secretary-Treasurer maintains, and will supply supply to the Committee, Committee, a form form for for the the numerical ranking of presentations. This This form form was was created created and modified modified by Student Student Paper Committees Committees over several several years in an effort to reduce the difficulties difficulties that may arise from selection background. The selection by raters of diverse background. The use of the form is not required, but is required, is left left to the the discretion discretion of the Committee. Committee. 7) The names of award recipients shall Chair's report report shall be included as part of the annual Chair's that appears appears in in the the next volume of the Institute. Institute. Student Student papers papers will will be be noted noted (*) (*)on onthe the Program. Program. STUDENTPAPER PAPER AWARDS AWARDS COMMITTEE COMMITTEE 2000 STUDENT Manfred M. Kehlenbeck, Chair Chair Manfred Lakehead Univers University, Thunder Bay, Ontario Terrence TerrenceS. J. Boerboom Boerboom Minnesota Geological Survey, St. Paul, Minnesota Graham C. Wilson son Turnstone urnstone Geological Geological Ltd., Campbellford, Campbellford, Ontario Ontario ... xiii Xlll �2000 BOARD 2000 BOARD OF DIRECTORS meeting year shown in parentheses) parentheses) (Board membership extends through the meeting Stephen Stephen A. Kissin, Chair Chair(2003) (2003) Lakehead University, Thunder Thunder Bay, Ontario Ontario Theodore J. Bornhorst Bornhorst(2002) (2002) Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan James James D. D. Miller Miller (2001) (2001) Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, Minnesota Minnesota Ronald Ronald P. P.Sage Sage(2000) (2000) Ontario Geological Geological Survey Survey Mark Mark Jirsa Jirsa(2000) (2000) Institute Institute Secretary-Treasurer Secretary-Treasurer Minnesota Geological Survey, St. Paul, Minnesota LOCAL COMMITTEES LOCAL COMMITTEES 2000 GENERAL GENERAL CO-CHAIRS: CO-CHAIRS:Stephen StephenA.A.Kissin Kissinand andPhilip PhilipW. W. Fralick Fralick PROGRAM PROGRAMAND AND ABSTRACTS ABSTRACTS EDITORS: EDITORS:Stephen StephenA. A. Kissin Kissin FIELD FIELD TRIP TRIPCOORDINATOR COORDINATORAND AND GUIDEBOOK GUIDEBOOKEDITOR: EDITOR:Philip PhilipW. W. Fralick Fralick Assistance to Assistance to the thelocal localcommittee committeewas wasprovided by by the thefollowing individuals: individuals: Karen Karen Farther Farrier - Lakehead Lakehead University Manuscript preparation, accounting accounting and communications Sam Lakehead University Sam Spivak Spivak -- Lakehead Graphics Graphics Becky Rogala Lakehead University Rogala - Lakehead Manuscript preparation Manuscript preparation and and audio-visual audio-visual Mark Smyk Northern Development Developmentand arid Mines Mines Smyk -- Ministry of Northern Organization Organization xiv �SESSION CHAIRS (in order order of appearance): appearance): Wed. AM Manfred Kehlenbeck Lakehead Lakehead University University— - Thunder Thunder Bay Dick Ojakangas University University of of Minnesota Minnesota— -Duluth Duluth Wed. PM Bornhorst Ted Bornhorst Houghton Michigan Technological TechnologicalUniversity University— - Houghton Mike Mudrey Wisconsin Geological Wisconsin Geologicaland and Natural NaturalHistory HistorySurvey Survey— -Madison Madison Thurs. Thurs. AM AM Andrew Mitchell Andrew Mitchell Thunder Bay DST DST Consulting ConsultingEngineers Engineers— - Thunder Bay Tony Naldrett Naldrett Consultant — Toronto Consultant - Toronto Thurs. Thurs. PM PM Mark Mark Smyk Smyk Bay Ontario Ontario Geological GeologicalSurvey Survey— - Thunder Thunder Bay Jim Jim Miller Miller Minnesota Minnesota Geological GeologicalSurvey Survey— - Duluth BANQUET SPEAKER SPEAKER 2000 2000 Bruce Bruce Simonson Simonson Oberlin Oberlin College College "Depositional "Depositional settings settings and and Early Diagenesis Diagenesis of Large Precambrian Precambrian Iron Formations" Formations" xv �REPORT MEETING OF REPORTOF OF TilE THE45"' 4SthANNUAL ANNUAL MEETING OF THE THE INSTITUTE INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Marquette, Marquette, Michigan Michigan REPORT ON MEETING OF THE INSTITUTE INSTITUTE REPORT ON THE THE 45TH 45TH ANNUAL MEETING SUPERIOR GEOLOGY, MARQUETTE, ON LAKE SUPERIOR MARQUETTE, MICHIGAN MICHIGAN The 45th Annual Annual Meeting Meeting of the Institute Institute on on Lake Lake Superior Superior Geology Geology was held in in Marquette, Marquette, Michigan May 4-8, 1999 at the Ramada Inn. The meeting was co-sponsored by Michigan May 4-8, 1999 at the Ramada Inn. was co-sponsored by Northern Northern Michigan University Michigan Technological Technological University. University. Robert S. Regis and Theodore J. University and Michigan Bornhorst co-chaired the annual meeting. meeting. The The meeting was well attended with 120 geoscientists registering from 10 provinces, and and Switzerland. Switzerland. The registering from 10 different states, states, three Canadian Canadian provinces, The meeting meeting consisted of two pre-technical session and two post-technical session field trips, two days of of consisted pre-technical session and two post-technical session field hips, two days technical sessions, sessions, and and an an evening evening banquet. banquet. The Proceedings Volume 45 was published 1- Program Program and and Abstracts Abstracts was was Proceedings Volume published in two two parts. parts. Part 1Theodore J. J. Bornhorst. Bornhorst. There edited by Robert S. Regis and Theodore There were were 33 published abstracts for the 22 oral Part 22 -- Field Trip Trip 22 oral and and 11 11poster posterpresentations presentations given given in in the the technical technical sessions. sessions. Part Guidebook, was Guidebook, was edited edited by by Theodore Theodore J. Bornhorst. There There were were 44 field field trips hips and and for for two two of ofthem them there were were separate separate papers papers with with supplementary supplementary information. information. The Theguidebook guidebookcontained contained several several colored maps and cross-sections. Field hips trips continue to be an important component component of of the the annual annual meeting meeting of ILSG ILSG evidenced evidenced by by 76% of attendees participating in 11 or more field hips. trips. The Theguidebook guidebook contains contains44field fieldtrips: hips: Field trip 11 was titled titled "Early "Early Proterozoic Proterozoic strata of the Marquette iron range, Michigan" and was lead W.F. Cannon. Cannon. This one-day one-day field field trip hip had had 30 30 participants participants who visited classic classic lead by by W.F. geologic localities in in the Marquette Marquette area. area. Field trip "ArcheanIshpeming Ishpeming greenstone greenstone belt belt and and gold goldmineralization, mineralization, Field trio 22 was wastitled titled"Archean Michigan" and and was was lead by T.O. Michigan" T.O. Quigley, Quigley, R.A. R.A. Mahin, Mahin, D.J. D.J. Duskin, Duskin, R.C. Johnson, Johnson, T.J. Bornhorst, and G.W. Scott. This two-day field trip had 28 participants and visited localities This two-day field hip had localities focused on lithology, New data focused lithology, structure, structure, and and gold goldmineralization. mineralization. New data on on several several gold gold prospects were presented. Field trip 3 was Field was titled titled "Tilden "Tilden and and Empire Empire Mines of the the Marquette Marquette iron iron range, range, Michgian" Michgian" and was lead by G.W. Scott, P.M. Nordstrom, Nordstrom, and H.M. H.M. Lukey. Lukey. This This one-day one-day trip trip was was very very well attended with 45 participants. We Wethank thank the the Tilden Tilden Mining Mining Company Company and and the the Empire Empire Partnership for for allowing allowingaccess accesstotothese thesetwo twoiron ironmines. mines. Participants of this Iron Mining Mining Partnership Participants of one-day field trip visited localities within the open-pit mines. This was the first time trip visited localities This was the first timeILSG ILSG has visited either of these two mines. mines. The The last last time time aa Michigan Michigan iron iron mine mine was visited by an ILSG field trip hip was was 27 27 years years ago ago in in 1972. 1972. Field Field trip 44 was wastitled titled"Paleozoic "Paleozoic and and glacial glacial strata shata from from Au Au Train Train totoGrand Grand Marais, Marais, field trip Michigan" and was lead by R.S. Michigan" and R.S. Regis Regis and and J.J. Anderton. Anderton. This one-day one-day field hip had 16 16 This is the first participants. This first time time ILSG ILSG has had had a field field trip hip in in the the Munising Munising area area and and participants were able to see participants were see and and learn learn about about the the geology geology of ofthe thePictured Pictured Rocks RocksNational National Lakeshore. xvi �by 99 out of of the the 120 participants participants at at the the annual annual meeting. meeting. Nelson Ham The banquet was attended by along the the southern edge of the of St. St. Norbert College gave an excellent talk on glacial processes along Laurentide ice sheet. A Ahighlight highlight of of the the banquet banquet was was the awarding of the 1999 1999 Goldich medal to Tsu-Ming Han for his contributions contributions to the North American iron ore industry. It is is interesting interesting to note that Tsu-Ming delivered a paper at the first ILSG annual meeting in in 1955 1955and and another another at at this this meeting some 45 years later. meeting some years later. The technical sessions sessions included two invited papers: "Cross "Cross Margin Transport Transport in in Lake Lake Superior" Superior" presented by by Sarah presented Sarah Green Green and and 'A "ANew NewApproach ApproachtotoHistorical HistoricalReconstruction: Reconstruction: Combining Combining Descriptive and Experimental Paleolimnology" presented presented by by Charlie Charlie Kerfoot. Kerfoot. We We are are grateful grateful to to associated with Cliffs Mining Services, the solicited presentations made by industry industry personnel associated Services, Company and and Empire Iron Iron Mining Mining Partnership. Partnership. Two students were selected Tilden Mining Company selected for Ulrich Puschner (Basel, Switzerland) was awarded awarded $150 for his outstanding presentations. presentations. Ulrich Puschner (Basel, Switzerland) was his paper on metamorphism of the the Portage Portage Lake Lake Volcanics Volcanics in in Michigan Michigan and and Joy Loughry poster paper metamorphism of (Univ. Minnesota-Moms) Minnesota-Morris) was was awarded awarded $150 $150 for for her oral presentation presentation on the Crowduck Crowduck Lake David Ams (Kent State Univ., Group, Kenora, Kenora, Ontario. Ontario. Three students, David Univ., Ohio), Ohio), Dyana Dyana Czeck Czeck (Univ. Minnesota), and Ulrich Puschner were awarded Eisenbrey Eisenbrey Student Travel Travel Awards Awards for a total of $800. All Allof ofthese thesestudents studentspresented presented papers papers at at the meeting. The Institute's Board of Directors met on May 6, 1999 1999 and the following is an overview overview of the meeting. meeting. 1. 1. Accepted the Report Report of of the the Chairs Chairs for for the the 44th 44th ILSG. ILSG. 2. 2. Accepted the 1998-99 1998-99 ILSG financial report. There was discussion on methods to encourage student attendance through monetary and other means. A lower cost for encourage students students to attend field field trips, just like like meeting registration, was acceptable. acceptable. 3. 3. Discussed guidelines guidelinesfor for the the Goldich Goldich Award. Award. Committee for one year. 4. 4. Maintained the composition composition of the Goldich Medal Committee 5. Discussed Discussed recasting of the Goldich Goldich Medal. 6. Discussed and approved 2000 meeting location in Thunder Bay with Kissin and Fralick 6. Fralick as co-chairs. co-chairs. 7. Discussed the possibility of a 2001 meeting in Sault 7. Sault Ste Marie, Michigan. Michigan. 8. 8. Discussed defraying defraying the meeting meeting expenses expenses for the secretary-treasurer. secretary-treasurer. The The Board Board (registration, field trips, and approved waiving registration for all meeting events (registration, banquet). 9. Approved a Corporate Resolution for the secretary-treasurer to conduct investments. 9. 10. Reaffirmed Reaffirmed Board commitment to the ILSG Newsletter Newsletter and Web Web page. page. The The Web Web page page Bomhorst. will be reorganized reorganized by Laurel Laurel Woodruff Woodruff and and Ted Ted Bornhorst. 11. Agreed that only one of the two co-chairs co-chairs would continue continue as as primary primary board boardmember. member. Ted Bornhorst will will be be the the representative representative from from the the 1999 1999meeting. meeting. We wish to thank all of the people the field trips and made people who lead and prepared materials for the presentations. While field trips continue continue as as the the traditional traditional strength strength of of ILSG, ILSG, the the presentations presentations provide a forum for discussion of Lake Superior geology. Of Of course, course, there there are are many many others others who who to the success of aa meeting we acknowledge for contributing to meeting including including the session session chairs, chairs, best best student paper paper award award committee, committee, ILSG ILSG Board Boardmembers, members,and andthe the staff staff of of the the Ramada Ramada Inn. Inn. We We volunteer help help with with registration. registration. Last we thank all of especially thank Suki Smaglik for all of her volunteer those who attended attended the the 45th 45th annual annual ILSG ILSG meeting, meeting, for for without without them there there would would not not be be an an JLSG. ILSG. Our "break pre-meetinginterest. interest. As a result "break even" even" budget budget model was based based on indicated indicated pre-meeting result of of xvii �than expected expected and and some some unexpected unexpected additional additional monies, monies, the meeting generated higher attendance attendance than generated cash flow flow of a few thousands of dollars dollars for for ILSG. !LSG. aa positive cash thousands of personally satisfied satisfied with the overall We are personally overall outcome outcome of of the the meeting meeting and and feel feel ititwas was aa success. success. waswell well worth worth the the effort. effort. We While itit is is aa lot lot of of work work to toput put on on the the ILSG ILSG annual annual meeting, meeting, itit was We encourage others to consider being chair or co-chairs of the ILSG annual meeting. encourage others to consider being chair or co-chairs of the ILSG Regis Ted Bornhorst Bornhorst and and Bob Bob Regis Co-Chairs of the 45th Co-Chairs 45th Annual ILSG xviii �CALENDAR PROGRAM CALENDAR OF OF EVENTS EVENTS AND PROGRAM MONDAY, 2000 MONDAY. MAY MAY 8. 8.2000 I I I 0800-1800 0800-1800 PRE-MEETING FIELD FIELDTRIPS TRIPS PRE-MEETING All field trips trips leave leave and and return returneach eachevening eveningto to Lakehead Lakehead University University Alifleld 1) 1) MESOPROTEROZOIC MEsoPRoTERozoIc SIBLEY SIBLEYGROUP GROUP(Day (DayOne) One) Leaders: Philip Philip Fralick, Fralick, Mark Smyk Smyk TUESDAY. 2000 TUESDAY. MAY MAY 9. 9.2000 I 0800-1800 0800-1800 PRE-MEETING PRE-MEETING FIELD FIELDTRIPS TRIPS 1) MESOPROTEROZOIC MESOPROTEROZOIC SIBLEY SIBLEYGROUP GROUP(Day (DayTwo) Two) Leaders: Leaders: Philip Philip Fralick, Fralick, Mark Mark Smyk Smyk 2) LAC LAC DES DES ILES ILES MINE MINE (I) (I) Leader: Moe Lavigne Moe Lavigne 3) 3) GEOARCHEOLOGY GEOARCHEOLOGY OF OF THE THUNDER THUNDER BAY AREA Leaders: Brian Phillips, Phillips, Scott Scott Hamilton, Hamilton, Joe Stewart, Stewart, Pat Julig, Julig, Bill Bill Ross Ross I 1700-2200 1700-2200 REGISTRATION AT LAKEHEAD UNIVERSITY POSTER POSTER SESSION/CASH SESSIONICASH BAR MIXER Agora/Faculty AgoraPaculty Lounge Lounge xix xix �WEDNESDAY. 2000 WEDNESDAY. MAY MAY 10. 10.2000 0800-1200 0800-1200 REOISTRATION/PRE-REGISTRATION REGISTRATION/PRE-REGISTRATIONPACKET PACKETPICK-UP PICK-UP I: GEOLOGICAL PROVINCE Session I: GEOLOGICAL OVERVIEW OF THE WESTERN SUPERIOR PROVINCE University Centre Theatre Theatre 0900-0915 0900-0915 WELCOME AND OPENING OPENING REMARKS REMARKS 0915-0945 091 5-0945 Kehlenbeck, Kehlenbeck, M.M. M.M. Rocks of ofthe theQuetico QueticoSubprovince Subprovinceand andAdjacent AdjacentTerranes Tenanes A Review of Structures in Rocks 0945-10155 0945-101 Davis, Davis, D.W. D.W. Western Superior Province: Geochronologic GeochronologicAspects Aspects 1015-1040 1015-1040 COFFEE COFFEE BREAK AND AND POSTER POSTER SESSION SESSION 1040-1110 1040-1 110 Tomlinson, Tomlinson, K. K. Western Superior Superior Province: Province: Volcanological Volcanological Aspects Aspects 1110-1140 1110-1140 Fralick, P.W. P.W. Fralick, Western Superior Superior Province: Province: Sedimentological Sedimentological Aspects Aspects 1140-1200 1140-1200 Czeck, D.M.* and Hudleston, P.J. P.J. A Sequence Transpression in the the Seine River River Conglomerates Conglomerates Sequence of Folding and Dextral Transpression 1200-13 1200-1310 10 LUNCH BREAK 1310-1330 1310-1330 R.R. Davis, D.W., Amelin, Y., V., Nowell, Nowell,G.M. G.M. and and Parrish, Parrish, R.R. Hf Isotope Study Study on on Zircons Zircons from from the the Western Western Superior SuperiorProvince Province 1330-1350 1330-1350 Pettigrew, N.T.*, Hattori, Hattori, K.H. and and Percival, Percival, J.A. Intrusion: a POE-bearing Samuels Lake Intrusion: PGE-bearing Quetico-type Quetico-type Intrusion Intrusion in in the the Central, Central, Western Quetico Subprovince, Subprovince, Northwestern Ontario 1350-1410 1350-1410 Wilson, A.C. Archean Diamond Exploration Targets in the Michipicoten Greenstone Greenstone Belt, Wawa, Ontario Ontario 1410-1430 1410-1430 R.P. and and Crabtree, Crabtree, D.C. Morris, T.F., Sage, R.P. Kimberlite, Base Metal, Gold and Carbonatite Exploration Targets, Derived from Overburden Heavy Mineral Data, Killala Lake Area, Northwestern Northwestern Ontario Ontario xx �1430-1450 Karkkäinen, N. and Bornhorst, Bornhorst, T.J. Karkkainen, Small Mafic Intrusions of the Lake Superior Region: Targets for Titanium Titanium Exploration 1450-15 10 COFFEE BREAK AND POSTER SESSION 1510-1530 Bajc,A.F. Bajc, A.F. Results of Regional Till Sampling Sampling in the Western Part of the Shebandowan Shebandowan Greenstone Belt, Northwestern Ontario Greenstone Northwestern Ontario 1530-1550 Cannon, W.F. and Cannon, and Woodruff, Woodruff, L.G. Some Some Factors That Control the Distribution of Mercury in the Near-surface Environment of Isle Royale National Park, Michigan-earth, Wind and Fire 1550-1610 Larson, P.C. Larson, P.C. and andMooers, Mooers, H.D. H.D. Commination Commination and Dilution of Glacial Indicators: Rate Estimates Estimates from from Field Field Data Data 1610-1630 Peterson, D.M. Peterson, D.M. Geometry Between Gold-rich Gold-rich Subsidiary Subsidiary Shear Shear Zones Zones and Major Geometry Between Major Structures: Structures: Implicationsfor Archean Lode-Gold Mineral Exploration Implicationsfor 1630 ILSG Business Business Meeting Meeting 1800-1930 MIXER (Residence Cafeteria) Cafeteria) MIXER Cash Bar 1930-2130 ANNUAL BANQUET BANQUET AND AWARDS PRESENTATION Residence Cafeteria Cafeteria • Announcement Announcementofof47th 4T11 Annual Meeting location location • Banquet BanquetSpeaker: Speaker: Dr. Dr. Bruce BruceSimonson, Simonson,Oberlin Oberlin College College "Depositional Settings Settings and Early Diagenesis Diagenesis of Large Precambrian Iron Formation" xxi �THURSDAY. MAY 11.2000 GEOLOGICAL OVERVIEW OF THE WESTERN SUPERIOR PROVINCE II; Session 1 1: University Centre Theatre Theatre 0900-0930 0900-0930 Lavigne, M.J. The Lac Mine, Northwestern Ontario Lac des des Ties lies Mine, Ontario 0930-1000 0930-1000 Fralick, Fralick, P.W. Western Western Superior Superior Province: Province: Proterozoic Proterozoic Sediments Sediments 1000-1030 1000-1030 Kissin, Kissin, S.A. S.A. Vein-type Deposits of the Thunder Bay Area 1030-1050 1030-1050 COFFEE BREAK AND POSTER POSTER SESSION SESSION 1050-1110 Pueschner, U.* and Schmidt, Pueschner, U.* and Schmidt,S.T. S.T. the Keweenawan Keweenawan Portage Portage Lake Lake Volcanics Volcanics on Low-grade Metamorphic Zonation of the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan 1110-1130 Rampe, .LS.* Rampe, J.S.* and Holm, Holm, D.K. Modelling the Effect of Intermediate Intermediate Temperature Temperature (350°-500°C) (350'-500°C Mazatzal-Age Mazatzal-Age Thermal Overprinting Superior Region Thermal Overprinting on Argon Diffusion from the Southern Lake Superior 1130-1150 Hudak, G.J., Hudak, G.J., Morton, Morton, R.L. RL. and and Dahlberg, H. Preliminary Volcanology and PreliminaryVolcanology and Hydrothermal HydrothermalAlteration AlterationStudies Studiesat at the the Five Five Mile Lake, Eagles Nest, and Quartz Hill Hill Prospects: Prospects: Implications Implications for forVMS-Style VMS-StyleMineralization Mineralization Eagles in Northeastern Northeastern Minnesota Minnesota 1150-1300 LUNCH LUNCH 1300-1320 Green, Green, J.C. J.C. Mystery Faults Faults of the Cascade River, North Shore, or What Is this Granite Doing Doing Here? Here? 1320-1340 K.J. and Schulz, KJ. and Nicholson, Nicholson, S.W. Lithogeochemistry Lithogeochemistry and and Paleotectonic Paleotectonic Setting Setting of the Bend Massive Massive Sulfide Sulfide Deposit, Deposit, Northern Wisconsin 1340-1400 Van Schmus, Schmus, W.R., W.R, MacNeill, MacNeill, L.C., Holm, and HoIm, D.K., D.K., Boerboom, Boerboom, T.J. and xxii �Jirsa, M.A. Jirsa, M.A. The 1787-1772 1787-1772 Ma Ma East-Central East-Central Minnesota Minnesota Batholith: Batholith: Precursor Precursor to to Crustal Crustal Stabilization in the Lake Superior Region Superior Region 1400-1420 Schweitzer, D.J.*, Schnieder, D.A., and Schweitzer, D.A., Boerboom, Boerboom,T.J., T.J., Holm, Hoim, D.K. BK. and Van Schmus, Schmus,W.R. Assessing the Extent of Assessing the of Early Early Proterozoic Proterozoic Penokean Penokean Versus Versus -A770-1760 -1770-1760 Ma Ma Metamorphism Metamorphism in East-Central East-Central Minnesota Minnesota 1420-1440 HoIm, D.K.. D.K., Hodees. Hodges, K.V. K.V.and and Hurtado, Hurtado, J. Holm. Results of40Ar/39Ar Laser Microprobe Mapping of of~Muscovite from Precambrian ~ e s u l tof s40k~9i~& ~ iec r o ~ r o~~e bAge e Mapping u s c o v i t from e ~recambrian Bedrock of the Southern Lake Superior Region 1440-1500 Kissin, S.A., Okamoto, RG. Okamoto, M., Addison, W.D. W.D. and and Brumpton, Brumpton, R.G. A Possible Sudbury Ejecta Layer in the Gunflint Formation, Northwestern Ontario Sudbury Ontario 1500-1520 COFFEE BREAK AND POSTER POSTER SESSION SESSION 1520-1530 STUDENT AWARDS STUDENT AWARDS 1530-1550 North, J. North,J. Nature of Logan Nature and Distribution Distribution of Logan Diabase Diabase Sills and Gabbro Gabbro Channels in the the near Thunder Thunder Bay, Bay, Ontario: Ontario: Brief BriefComparison Comparisonto toNoril'sk Noril'sk Keweenawan Rift near 1550-1610 Jr. Medaris, L.G. Jr. The Barren Barron Saprolite: Confirmation Confinnation of of Mature Mature Chemical Chemical Weathering Weathering in the Source Source Paleoproterozoic Quartz Arenites in the Lake Superior Region for Paleoproterozoic 1610-1630 Argust,A. Argust, A. Chemistry Chemistry and Mineralogy of Lower Chocolay Group Rocks, Dickinson Dickinson County, County, Michigan Michigan 1630-1650 Simonson, B.M. Simonson, Conglomerates and Intraformational Intraformational Breccias The Distinction Between Flat Pebble Conglomerates Breccias in Precambrian Precambrian Iron Formations Iron Formations xxiii �POSTER PRESENTATIONS POSTER PRESENTATIONS B.R.* and Saini-Eidukat, Saini-Fidukat, B. Bandli, B.R* B. Nomarski DIC Microscopy Analysis of of Plagioclases Plagioclases from from the Duluth Microscopy and Structural State Analysis Complex, Minnesota .J andHavholm, H~VUUIII!, K.G. Beaster, K.F.*, Kohn, J.D.* J.D.t and K.G. Wind or Water? Water? Paleoenvironment of the Proterozoic oterozoic Hinckley Sandstone, Sandstone, Northeastern Minnesota Minnesota Harris, Harris, E.C.A.* E.C.A.* and Wirth, Wirth, K.R. K.R region, eastern eastern Mesabi Mesabi Range, Range, Minnesota Petrogenesis of granitic rocks of the Dunka River region, Hauck, S.A., S.A., Bite, A. and Severson, M. Hauck, and Severson, Copper Pyroxene Homfelsed Homfelsed Archean Archean Giants Giants Range RangeBatholith Batholith Footwall Footwall of of opper Mineralization of Pyroxene thee Keweenanwan South Kawishwi Intrusion, Duluth Complex, NE Minnesota -- Archean Archean orr Keweenawan Mineralization? Mineralization? Jerde, E.A. Jerde, E.A. Magmatic for Nathan's Series: An Initial of the Magmatic Origins Origins for Nathan's Layered Layered Series: Initial Reassessment Reassessment of the or Plutonic Materials Midcontinent Rift's First FirstMaj Major Materials Kean, Kean. W.F. and Luther, Luther. F. F. Additional Paleomagnetic PaleoniagneticStudies Studiesofof aa Proterozoic Proterozoic Diabase DiabaseDike, Dike, in in Pifher Pifher and Irwin Irwin Townships,,Lake Nipigon District, District, Ontario Wirth, K.R. Kennedy, B.C.*, Wirth, K.R and and Vervoort, Vewoort, J.D. Petrogenesis Petrogenesis of the Midcontinent Midcontinent Rift Granophyric Granophyric Complexes Complexes of Northern Minnesota Minnesota Luther, Luther, F.R. Low-grade Metamorphismofofan an Archean Archean Debris Debris Flow, Flow, Irwin, Irwin, Pither Low-grade Metamorphism Pifher and and Meader Meader Townships, Lake Nipigon Region, Ontario Jr. and Medaris, L.G. Jr. and Fournelle, Fournelle, J.H. Tourmaline-bearing QuartzVeins Veinsin in the the Baraboo Baraboo Quartzite: Quartzite: A A New New Occurrence Tourmaline-bearing Quartz Occurrence of the Alkali-deficient Tourmaline, Foitite Morris, R.P. and Crabtree, Morris, T.F., Sage, Sage, RP. Crabtree,D.C. D.C. Kimberlite, Base Metal, Gold and Kimberlite, and Carbonatite Carbonatite Exploration Exploration Targets, Targets, Derived Derived from from Heavy Heavy Mineral Data, Killala Killala Lake Lake Area, Northwestern Ontario Ontario Peterson, Peterson, D.M. Geologic and GIS-based Geologic GIS-based Lode-gold Lode-gold and Volcanogenic Volcanogenic Massive Sulfide Sulfide (VMS) (VMS) Mineral Mineral xxiv xxiv �Potential Maps Maps of aa Portion Potential Portion ofofthe theArchean ArcheanVermillion VermillionGreenstone GreenstoneBelt, Belt,Northeastern Northeastern Minnesota Minnesota E.H.*, Wirth, Wirth, K.R. and Phillips, EX.*, and Morey, Morey, G.B. G.B. Petrogenesis of the Enigmatic Aurora Sill, Mesabi Range, Minnesota Petrogenesis Enigmatic Minnesota Sage, Sage, R.P. The "Sandor" Diamond Diamond Occurrence, Occurrence, Michipicoten Michipicoten Greenstone Greenstone Belt, Belt, Wawa, Wawa, Ontario Ontario Stott, Stott, G. and and Berdusco, Berdusco, B. B. Precambrian Features under the James Bay and Hudson Bay Lowlands Vervoort, Vewoort, J.D., Wirth, Wirth, K.R. and andKennedy, Kennedy, B.C. Isotopic Constraints Constraints on on the Origin of Granophyre in the Midcontinent Isotopic Granophyre Complexes Complexes in Midcontinent Rift Ritt of nNortheastern or the astern Minnesota Wilson, Wilson, A. A. Archean Diamond Exploration Targets in the Michipicoten Greenstone Belt Wolbers, Wolbers, J.A.* and and Seifert, Seifert, K.E. K.E. Petrogenesis of the Silver Creek Midcontinent Rift Petrogenesis Creek Dike: a 1.1 Ga Intrusion in the Midcontinent L.G., Attig, Attig,J.W. J.W.and andCannon, Cannon,W.F. WI. Woodruff, L.G., Geochemical Impacts of an Undisturbed Mineral Deposit -- Results from the Bend Deposit, Chequamegon Chequamegon National Forest, Forest, Wisconsin xxv XXV �FRIDAY. 2000 FRIDAY. MAY 12. 12.2000 0800-1800 0800- 1800 POST-MEETING FIELD TRIPS TRIPS All field field trips leave and and return returneach eachevening eveningto to Lakehead Lakehead University, University,except exceptfor Field an overnight stay in Field Tr4p Trip 6, which will involve an in Atikokan on May 12 (at (at the the participant's expense). participant's expense). 4) PALEOPROTEROZOIC PALEOPROTEROZOIC GUNFLINT GUNFLINTFORMATION FORMATION Leaders: Pier Pufahi and Philip Fralick Pier Pufahl and Philip 5) 5) QUATERNARY QUATERNARYGEOLOGY, GEOLOGY,SHEBANDOWAN SHEBANDOWANBELT BELT Leader: Andy Andy Bajc Bajc - - 6) 6) STEEP STEEPROCK ROCK - FINLAYSON FINLAYSON - LUMBY LUMBY BELTS BELTS (Day (Day One) One) Leaders: Denver Stone, Kirsty Tomlinson, Ray Bernatchez Denver Stone, Kirsty Tomlinson, Ray Bematchez and Philip Philip Fralick Fralick 7) 7) LAC LAC DES DES ILES ILES MINE MINE(II) (11) Leader: Moe Lavigne Moe Lavigne SATURDAY. 2000 SATURDAY. MAY MAY 13. 13.2000 0800-1800 0800- 1800 FIELD FIELD TRJP TRIP66(Day (DayTwo) Two) xxvi xxvi �Chemistry Group Rocks, Chemistry and and Mineralogy Mineralogy of Lower Chocolay Group Dickinson County, Michigan Michigan ARGAST, Anne, Department of Geosciences, Geosciences, Indiana-Purdue Indiana-Purdue University University Fort Fort Wayne, Wayne, Fort Wayne, Wayne,IN IN46805-1499, 46805-1499,argast(%ipfw.edu argastipfw.edu Fort Rocks of the Chocolay Dickinson County, County, Michigan. Michigan. Most Most Chocolay Group rest on Archean basement in Dickinson likely accumulated accumulated in the interval 1.9-2.1 Ga. ago, the Group consists of the basal, partly 1.9-2.1 consists partly conglomeratic, Fern Creek Formation, overlain conglomeratic, overlain by Sturgeon River Quartzite Quartzite and and Randville Randville Dolomite. Chocolay Group likely represents deposition terrigenous and shallow deposition in temgenous shallowmarine marine environments with later environments later units of the Marquette Range Supergroup Supergroup (Menominee (Menominee and and Baraga Baraga Groups) transitioning upwards into deeper water, more active and isolated environments. environments. There are two alternate alternate views for the origin origin of the Fern Creek Creek Formation. Some Some interpret interpret the the Fern Creek (or its putative equivalents of Reany Creek and Enchantment Lake Formations putative equivalents Lake Formations farther north in Michigan) as examples examples of glaciogenic glaciogenic sediments, possibly synchronous synchronous with with Gowganda glaciation (e.g., Pettijohn, 1943; Gair, 1981; Young, 1983; Ojakangas, 1984). Gowganda glaciation Pettijohn, 1943; 1981; 1983; 1984).Others Others interpret the Fern Creek as originating, originating, for for example, in fluviatile, fluviatile, occasionally occasionally torrential torrential environments (e.g., environments (e.g., Bayley et al., 1966; 1966; Larue, 1981; 1981; Mattson Mattson and Cambray, Cambray, 1983). 1983). This This is is an an important determination, determination, affecting affecting aspects aspects of regional and interregional interregional correlation correlation on on aa significant scale (e.g. Ojakangas, 1988). 1988). This study focuses focuses on on the bulk and and mineral chemistries chemistries of the Fern Fern Creek Creek Formation Formation and and Sturgeon Sturgeon River Quartzite Quartzite exposed exposed along an an access access road road to aa hydroelectric hydroelectric dam dam located located about about33 km northeast of Loretto, Loretto, Michigan. The purpose is to further further evaluate evaluate the glaciogenic glaciogenic vs. vs. fluviatile origins fluviatile origins of the Fern Fern Creek Formation, Formation, and to characterize characterize the materials materials to to constrain constrain possible source source areas. Fern Creek rocks are dominated by quartz, sodic sodic plagioclase, K-feldspar, antiperthite, antiperthite, and and micas micas of di- and trioctahedral trioctahedral composition. Sturgeon River is predominantly quartz with minor illite. composition. Sturgeon River quartz with minor illite. Zircon, tourmaline, tourmaline, fluor-hydroxy fluor-hydroxy apatite, apatite, pyrite, rutile, mtile, fluorite, fluorite, monazite, huttonite huttonite and and aa fluorfluorREF mineral occur Zircon and tourmaline tourmaline dominate in the hydroxy REE occur in the Fern Creek Formation. Zircon Sturgeon Sturgeon River River Quartzite. Quartzite. The tourmaline compositions compositionsvary systematically systematically with with vertical vertical position position throughout throughout the the Fern Fern Creek/Sturgeon CreekBturgeon River River sequence. sequence. This This suggests suggests a gradual gradual denudation denudationof of the the source source area areaover over an an extended length of time. extended length Bulk chemistries chemistries for for the the Sturgeon SturgeonRiver River Quartzite Quartzite are are consistent consistent with with an an origin origin as as aa well well sorted sorted sediment in a nearshore marine environment. Fern Creek chemistries are typical of unsorted chemistries unsorted materials materials that have have not undergone undergone hydraulic hydraulic differentiation, differentiation,and and are are similar similarto to chemistries chemistriesfrom from the underlying Carney Lake Gneiss. underlying Carney Lake Gneiss. I �REE distributions distributions are highly highly variable in the Fern Creek Formation, ranging from nearly flat (normalized to PAAS) to extremely steep (e.g. chondrite normalized LdYb La/Yb of 101.5). (normalized 101.5). These These distributions result from enrichment in LREEand Tb-rich minerals. distributions Th-rich The bulk chemistry and presence of REE minerals are consistent with proximal derivation derivation from the underlying (pegmatite-rich) Carney Lake Gneiss. The trends in tourmaline composition composition suggest association association with a process capable of deep erosion over an extended period of time. The similarity similarity of the Fern Creek to stratigraphically equivalent rocks at some distance north suggests suggests a process of significant significant areal extent. Taken together, these results strongly support support the origin origin of the Fern Creek Formation as a proximal till derived from the underlying gneiss. References References iron-bearing Bayley, R.W, Dutton, C.E., and Lamey, C.A., 1966, Geology of the Menominee iron-bearing Counties, Wisconsin: district Dickinson County, Michigan and Florence and Marinette Counties, 96 pp. U.S. Geological Survey Professional Professional Paper Paper 513, 513,96 Gair, J.E., 1981, Lower Proterozoic Proterozoic glacial deposits deposits of Northern Michigan, in Hambrey, M.J., University and Harland, W.B., eds., Earth's pre-Pleistocene glacial record: Cambridge University 803-806. Press, p. 803-806. Lame, D.K., 1981, 1981, The The Chocolay Chocolay Group, Group, Lake Superior Superior region, U.S.A.: Sedimentologic Sedimentologic evidence for deposition deposition in basinal and platform settings settings on an Early Proterozoic Proterozoic craton: Geological v. 92, 92,p. p. 417-435. 417-435. Geological Society Society of of America America Bulletin, Bulletin, Part Part 1,1, v. F.W., 1983, The The Reany Reany Creek Creek Formation: Formation: aa mass-flow mass-flowdeposit deposit of of Mattson, S.R. and Cambray, F.W., possible post Menominee possible Menominee age age [abs.], [abs.], in in Proceedings, Proceedings,29th 29' Annual Institute Institute on Lake Lake Superior Superior Geology, p. 27. 27. Ojakangas, R.W., 1984, 1984, Basal Lower Proterozoic glaciogenic formations, formations, Marquette Marquette Range Annual Supergroup, Upper Peninsula, Michigan [abs.]: in Proceedings, 30th Institute Upper Peninsula, Michigan [abs.]: in Proceedings, 30' Institute on Lake Superior Superior Geology, Geology, Wausau, Wausau,WI, WI,p.p. 43. 43. Ojakangas, R.W., 1988, 1988, Glaciation: Glaciation: An uncommon "mega-event" "mega-event" as a key to intracontinental intracontinentaland and intercontinental intercontinental correlation correlation of Early Proterozoic basin fill, North American and Baltic Baltic New perspectives in basin analysis: Cratons, in Kleinspehn, K.L., and Paola, C., eds., New Springer-Verlag, p. 431-444. 43 1-444. Pettijohn, F.J., 1943, 1943, Basal Basal Huronian Huronian conglomerates conglomerates of Menominee and Calumet Calumet districts, districts, Michigan: Journal of. Geology, v. 51, p. 387-397. Michigan: Geology, 51, 387-397. Young, G.M., 1983, Tectono-sedimentary history of Early Proterozoic Proterozoic rocks of the northern Proterozoic geology of the Great Lakes Great Lakes region, in Medaris, L.G., Jr., ed., Early Proterozoic Lakes region: Geological Society of America Memoir 160, p.15-32. 2 �RESULTS OF REGIONAL TILL TILL SAMPLING IN THE WESTERN PART OF THE SHEBANDOWAN GREENSTONE BELT, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO THE GREENSTONE BELT, Bajc, A.F., Sedimentary Geoscience Section, Ontario Geological Geological Survey, Survey, Ministry Northern Development and Mines, 933 Ramsey Lake Lake Road, Road, Sudbury, ON of Northern P3E 6B5 6B5 A project of Quaternary Quaternary geological geological mapping mapping and regional till sampling sampling was was undertaken undertaken over the western part of of the Shebandowan Shebandowan greenstone greenstone belt during during the the 1999 1999field field season. season. Quaternary Quaternary mapping helped to characterize characterize the surficial surficial materials materials present within within the the study area and to reconstruct the ice flow history associated with with these these deposits. deposits. This This information information provided a framework framework by which which the regional materials materials compositional compositional datasets could be interpreted. interpreted. The Theregional regional sampling sampling program program provided provided information informationon on the background concentrations concentrations of various elements elements in in till as as well as as on on the the number number and and character character of gold grains grains and base metal indicators indicators in in till. The study area contains a relatively simple record of Quaternary events. events. Most Most deposits deposits were laid down during the final retreat of ice from the the area. Ice flow indicators Ice flow indicatorssuggest suggest aa consistent consistent pattern of flow flow towards towards the south south across across the eastern eastern half half of of the the study study area, area, becoming more westerly towards the west. Till cover is generally thin and discontinuous Till cover is generally thin and discontinuous over most parts of the study area. Thicker, Thicker, more more extensive extensive till till is is present present within within Hagey, Hagey, Conacher Conacher and Blackwell townships. Till Tillsamples samplescollected collected from from these these townships townships are are less less representative representative of local local geology geology than are are samples samples collected collected from from areas areas of of very very thin thin till. till. Geochemical Geochemical and mineralogical mineralogical interpretations interpretations should should consider consider these these local local variations variationsin in till character. character. The till sampling sampling program program has has clearly clearly identified identified aa number number of of precious precious and and base base metal metal exploration belt. Higher exploration targets within the western Shebandowan greenstone belt. Higher density density follow-up follow-up sampling sampling surveys surveys are are recommended recommended for for these these areas areas to to determine determinethe the the anomalies and more more precisely precisely define define potential potential source sourcerocks. rocks. The significance of the regional character character of this this survey survey will assist assist with with the the interpretation interpretationof of local, local, property-scale property-scale geochemical datasets by placing results results into into context context with with respect respect to to regional regional background. background. geochemical datasets The results of this survey survey clearly clearly support support the the use use of of till compositional compositional surveys surveysfor for mineral mineral exploration. exploration. The Theapproach approachfor forfollow-up follow-upsampling samplingprograms programs will will be be dictated dictated by by the the type type of mineralization mineralization sought sought and and the the local local conditions conditionswithin within aa given given property. property. 3 �NOMARSKIIDIC DICMICROSCOPY MICROSCOPY AND AND STRUCTURAL STRUCTURAL STATE ANALYSIS ANALYSIS OF NOMARSKI OF PLAGIOCLASES FROM THE PLAGIOCLASES THE DULUTH COMPLEX, MINNESOTA MINNESOTA BANDLI, Bryan R., Department of Geosciences, Geosciences, North Dakota Dakota State Statc University, University,Fargo, Fargo, ND 58105-5517 USA. (Bryan_Bandli@ndsu.nodak.edu). (Bryan.Bandli@ndsu.nodak.edu). SAINI-BIDUKAT, SAINI-EIDUKAT, Bemhardt, Department Bernhardt, Department of Geosciences, North Dakota State University, Fargo, ND 58105-5517 58 105-5517 USA. (sainieid@badlands.nodak.edu) (sainieid@badlands.nodak.edu) Nomarski Differential Differential Interference Interference Contrast Contrast (DIC) (DIC) and and structural structural state state XRD XRD analyses analyseswere were carried out on samples of Duluth Complex Anorthositic Series rocks. rocks. Nomarski DIC is a reflected light technique technique which uses aa double-crystal double-crystal prism prism to to split split plane-polarized plane-polarizedlight lightto to produce a dark-light shading that highlights microrelief. To use the method on mineral in acid to to produce produce microtopography. microtopography. Anderson Anderson specimens, polished sections are etched in (1983), Pearce and Kolisnik (1990), (1990), and Pearce Pearce (1994) (1994) discuss the the importance importance of of interference interference imaging in showing that high-resolution high-resolution mineral mineral zonation patterns, patterns, that that are are correlatable correlatable with with varying An content, record complicated complicated dissolution dissolution and reaction reaction events events that that occurred occurredduring during crystal growth. growth. Polished block and thin sections sections were prepared from three three samples samples of of the the anorthositic anorthositic series taken near its contact with the Duluth Layered Series, Series, along along Skyline Skyline Parkway Parkway in in Duluth above Oneota Cemetary (Stop 1-5 of Miller, 1995). Sample 1 is an inclusion containing more than 95% plagioclase; plagioclase; sample sample 22 is the the host host gabbroic gabbroic anorthosite, anorthosite, and and sample sample three is from the outcrop used for zircon zircon age age dating dating (Paces (Paces and and Miller, Miller, 1993). 1993).Polished Polishedthin thin sections were prepared on orthogonal orthogonal axes axes to expose expose a variety variety of of crystallographic crystallographic orientations, etched in 48-50% HBF4 HBF4 for approximately seven minutes (adapted from the method of Anderson, 1983), 1983), and then imaged imaged using aa Nomarski Nomarski mirror mirror cube cube and and prism prism slider slider on an Olympus Olyrnpus BX-60 petrographic petrographic microscope. Although some some oscillatory oscillatory zoning was was observed, observed, the the most most common common zoning zoning observed observed was was patchy. This type of zoning zoning could be considered considered a hiatus hiatus type type of of discontinuity discontinuityas as defined definedby by Castro and de la Rosa (1994). Irregular Irregular zoning zoning of of plagioclase plagioclase is is common common in in the the Anorthositic Anorthositic Weiblen, 1990) 1990)and and could could indicate indicate significant significant disruptions disruptions of of the the Series (Miller and Weiblen, crystallizing surface surface due to dissolution dissolution and and reaction events events as as the the crystal crystal mush mush moved moved from from deep to shallow chambers. chambers. Plagioclase Plagioclase structural structural analyses analyses were were carried carried out out on on the the three three samples samples plus plus one one additional additional plagioclase separate separate from from the the Duluth Duluth Anorthositic AnorthositicSeries Series (Sample (SampleD-12) D-12) and and one onefrom from the the plagioclase Gabbro Lake area area (sample (sample BL-27). BL-27). Samples Samples were were crushed crushed and and plagioclase plagioclasewas was hand-picked, hand-picked, powdered, and diffraction patterns collected on a Philips Automatic Vertical Diffractometer Characterization Laboratory at the Materials Characterization Laboratory at NDSU. Scans Scans were were made made from from 6.0 6.0 to to 65 65 degrees 20 using using a step step of of 0.02° 0.02' 28, 20, Cu Ka Karadiation radiation (X= (\= 1.54184 1.54184 angstroms), angstroms), a diffracted diffracted 4 �beam beam monochrometer, monochrometer, and and aa sealed sealed proportional proportional counter. counter. Patterns were were matched matched to to aa plagioclase in the PDF reference file and refined using Garvey's Gamey's (1986) (1986) implementation implementation of the program of Appleman and Evans (1973). Refined A131 and yvalues yvalues were used to determine (1983). Despite determinethe the structural structuralstate state based based on on figures figures from from Kroll Kroll(1983). Despite the the potential potential difficulties difficultieswith with refining refining zoned zoned minerals, minerals, the the results results (with (with the the exception exception of of sample sample 3-99, 3-99, for for which are in in "low" "low' (lowwhich An An content content is yet to be measured) indicate that all the samples are (lowtemperature, temperature,or orordered) ordered)structural structuralstate state(Table (Table1). 1). samnie 1-99 90.180 (-i-I- An 65* 0.084) 2-99 90.247 (+1- 0.204) 62* 3-99 90.299 BL-27 89.843 D-12 90.213 (+1- 0.130) (+1- 0.190) (÷1- 0.218) n.m. 55 63 Table Refinedgamma gamma and values plagioclase separates of Duluth Complex Anorthositic Series rocks. Table 1. Refined and AnAn values for for plagioclase separates of Duluth Complex Anorthositic Series rocks. *from *from Miller Miller (1995); (1995);n.m. n.m. not not measured. measured. Errors Errors reported reported as two standard standard deviations, deviations, because no internal standard wasused. used. standardwas References Referencescited: cited: Anderson, Anderson, A.T., A.T., Jr., Jr., 1983, 1983,Oscillatory Oscillatoryzoning zoning of of plagoclase: plagoclase: Nomarski Nomarski interference interferencecontrast contrast microscopy microscopy of of etched etched polished polished sections: sections: American AmericanMineralogist, Mineralogist,v. v. 68, 68, p. p. 125-129. 125-129. Appleman, Appleman,D.E. D.E. and andEvans, Evans, H.T., H.T., Jr., Jr., 1973, 1973,Job Job 9214: 9214: indexing indexingand and least-squares least-squaresrefinement refinement of 67 pp. 20,67 pp. (NTIS (NTIS of powder powder diffraction diffraction data. data. U.S. U.S. Geological GeologicalSurvey, Survey, Computer Computer Contrib. Contrib. 20, Doc. Doc. PB2-16188) PB2-16188) Castro, A,,and and de dela laRosa, Rosa,J., J., 1994, 1994,Nomarksi Nomarksi study study of of zoned zoned plagioclases plagioclasesfrom from granitoids granitoidsof of Castro,A., the the Seville SevilleRange Range batholith, batholith, SW SW Spain. Spain. Petrogenetic Petrogenetic implications: European European Journal Journalof of Mineralogy, Mineralogy,v.v.6,6,p.p.647-656. 647-656. Garvey, Garvey,R.G., R.G., 1986, 1986,LSUCRIPC LSUCRIPCLeast Leastsquares squaresunit unitcell cellrefmement refinementwith with indexing indexingon onthe the personal personalcomputer. computer.Powder PowderDiffraction, Diffraction,v. v.I1no. no.1., I.,p.p.114. 114. Kroll, Kroll,H., H.,1983, 1983,Lattice Latticeparameters parameters and anddeterminative determinativemethods methods for for plagioclase plagioclaseand andternary ternary feldspars, ed., Reviews Reviews in in Mineralogy, Mineralogy,v.v.2, 2 ed., feldspars, in in Ribbe, P.H., P.H., ed., 2, 2nd ed., p. p. 101-119. 101-119. Miller,J.D., J.D., Jr., Jr.,1995, Duluth Complex Complex at at Duluth, Duluth, in in Miller, Miller, J.D. J.D. Jr., Jr., ed., ed., Field FieldTrip Trip Miller, 1995, The Duluth Guidebook Guidebookfor forthe theGeology Geologyand andOre OreDeposits Depositsof of the theMidcontinent MidcontinentRift Riftin in the the Lake Lake Superior SuperiorRegion. Region.Minnesota MinnesotaGeological GeologicalSurvey SurveyGuidebook GuidebookSeries, Series,no. no. 20, 20,p.p.123-169. 123-169. Miller,J.D., J.D., Jr., Jr., and andWeiblen, Weiblen, P.W., P.W., 1990, 1990,Anorthositic Anorthositic rocks rocks of of the the Duluth DuluthComplex: Complex: Miller, Examples Examplesof of rocks rocks formed formed from from plagioclase plagioclase crystal mush: Journal Journalof of Petrology, Petrology,v.v.31, 31,p.p. 295-339. 295-339. Paces,J.B., J.B., and andMiller, Miller,J.D., J.D., Jr., Jr., 1993, 1993,Precise PreciseU-Pb U-Pb ages agesof of Duluth DuluthComplex Complexand andrelated related Paces, maficintrusions, intrusions,northeastern northeasternMinnesota: Minnesota:Geochronological Geochronologicalinsights insightsto tophysical, physical, mafic petrogenetic,paleomagnetic paleomagneticand andtectono-magmatic tectono-magmaticprocesses processesassociated associatedwith withthe the1.1 1.1Ga Ga petrogenetic, Midcontinent Midcontinentrift rift system: system: Journal JournalofofGeophysical GeophysicalResearch, Research,v.v. 98, 98,p. p. 13,997-14,013. 13,997-14,013. Pearce, Pearce,T.H., T.H., 1994, 1994,Recent Recentwork workon onoscillatory oscillatoryzoning zoningin in plagioclase, plagioclase,in inParson, Parson,I., I.,eds., eds., Feldsparsand andTheft TheirReactions: Reactions:Dordrecht, Dordrecht,Kluwer, Kluwer,p.p.3313-349. Feldspars 13-349. Pearce,T.H., T.H., and andKolisnilc, Kolisnik, A.M., A.M., 1990, 1990,Observations Observationsof of plagioclase plagioclasezoning zoningusing using Pearce, interference EarthScience ScienceReviews, Reviews,v.v.29, 29,p.p.9-26. 9-26. interferenceimaging: imaging:Earth Grierguided guidedus usinincarrying carryingout outthe theplagioclase plagioclasestructural structuralanalyses. analyses.BSE BSE Acknowledgements:Dean DeanGrier Acknowledgements: gratefully NDEPSCoR EPSCoRthrough throughNSF NSFgrant grant#OSR-9452892. #OSR-9452892. gratefullyacknowledges acknowledgesfinancial financialsupport supportfrom fromND 5 �Wind or Water? Paleoenvironment Paleoenvironmentof the Proterozoic Proterozoic Hinckley Sandstone, Sandstone, Northeastern Minnesota Northeastern Beaster, K.F., Geology K.F., Kohn, Kohn,J.D., J.D.,and andHavholm, flavholm,K.G., K.G.,havholke@uwec.edu, havhoIkwuwcc.edu, Geology Department, University of Claire, Eau Claire, WI 54702-4004 o f Wisconsin-Eau Wisconsin-Eau Claire, The Proterozoic Hinckley Sandstone is a mineralogically mature, fine-grained quartz (Tryhorn & arenite representing late stage Keweenawan rift fill sedimentation. Previous work (Tryhom Ojakangas, 1972) interpreted the Hinckley Sandstone as a shallow-water lacustrine deposit. 1972) shallow-water Recent recognition of adhesion structures, formed by sand blown onto a damp surface, suggest be partially partially eolian eolian (wind-deposited). (wind-deposited). The purpose of this project was to that this formation may he reevaluate the environment(s) of deposition environmentfs) of deposition of of the the Hinckley Hinckley Sandstone. Sandstone. The study area is located in Pine County, MN, near the town town of Sandstone, where five sections along the Kettle River were measured and described in detail. Four major facies were identified: planar-bedded sandstone (PS), cross-stratified sandstone (CSS), trough crossstratified sandstone sandstone (TCS), and pebbly trough cross-stratified sandstone (PTS). The planarbedded facies comprises a complexly interbedded sequence of crinkly and mottled strata, preserved ripple forms, and packages of thin (2-6 mm.), planar, inversely graded laminae. Crinkly and mottled strata are interpreted as adhesion structures (Hunter, 1973, 1980). 1980). Ripples have low ripple indices (<10) ( 4 0 ) and steep, normally graded foresets, indicating a subaqueous origin (Hunter, 1977). Planar (Hunter, Planar laminae laminae are are identified identified as as climbing wind-ripple laminations (Hunter, 1977). Therefore, the planar-bedded facies represents an environment where where conditions conditions alternated from wet to damp to to dry. Fine nature of Fine grain grain size, large set size, and the compound nature large sets suggest a large-scale eolian dune dune origin origin for for the the cross-stratified cross-stratifiedsandstone sandstonefacies. facies. In addition, wind-ripple and adhesion lamination were identified in tangential dune apron toe-sets. Trough cross-strata cross-strata and pebbly trough cross-strata facies contain predominantly medium-grained sandstone; pebbles cm.are arecommon commonininthe thepebbly pebbly trough trough cross-stratified cross-stratified facies. facies. pebblesup uptoto44cm. Adhesion and wind-ripple laminae are absent in these relatively small (up to 2 m. wide and 20 cm. thick), simple trough cross-strata. cross-strata. Coarse Coarse grain grain size and nature of strata suggest a subaqueous subaqueous origin origin for for these these facies. facies. Exposures of the Hinckley Sandstone are incomplete and widely separated, limiting detailed correlation of sections. The m. for The thickest thickest exposure exposure measures measures 30 m., whereas a thickness of 150 m. this formation is reported from a well in the the area area (Morey, (Morey, 1977). 1977). However, using a regional regional structural dip of 50 (Tryhorn and Ojakangas, Ojakangas, 1972) the the measured measured sections sections stack stack to to give a 5' or less, (Tryhom sediment sequence sequence that alternates alternates from depositon in subaqueous to subaerial and back to subaqueous conditions several times. Small Small (mm.(mm.- to cm-scale) cm.-scale)extensional extensional faults faultsand andcm.cm.-to to dm.-scale fluid-escape structures are associated associated with with the the subaqueous subaqueousto tosubaerial subaerialtransition. transition. This vertical sequence sequence suggests suggests a rift setting setting with a shifting mosaic of eolian and fluvial, and possibly lacustrine, environments. lacustrmne, environments. Reference Reference cited: cited: by climbing climbing adhesion adhesionripples. ripples. Journal of Sedimentary Sedimentary Hunter, R.E., 1973, Pseudo-crosslamination formed by Petrology, v. v.43, p. 1125-1127. 43, p. 1125-1 127. R.E., 1977, Basic types types of of stratification stratificationininsmall smalleolian eoliandunes. dunes.Sedimentology, Sedimentology,v.v.24, p.361-387. Hunter, R.E., 24, p. 361-387. 6 �- I I I - Hunter, — an Hunter,R.E., R.E., 1980, 1980,Quasi-planar Quasi-planaradhesion adhesionstratification stratification an eolian eolian structure structure formed in wet sand. Journal Journal of of Sedimentary SedimentaryPetrology, Petrology, v. v. 50, 50, p. p. 263-266. 263-266. Morey, Morey, G.B., G.B., 1977, 1977,Revised Revised Keweenawan Keweenawan subsurface subsurface stratigraphy, southeastern Minnesota. Minnesota Minnesota Geological 2lpp. Geological Survey SurveyReport Report of of Investigations Investigations 16, 16,27pp. Tryhorn, Tryhorn, A.D. A.D. and and Ojakangas, Ojakangas, R.W., R.W., 1972, 1972,Sedimentation Sedimentation and petrology of the Upper Precambrian Hinckley Hinckley Sandstone Sandstoneof of east-central east-central Minnesota. In, In,P.K. P.K. Sims Simsand andG.B. G.B. Morey, Morey,eds., eds., Geology Geologyof of Minnesota: Minnesota: AACentennial CentennialVolume, Volume,Minneapolis, Minneapolis,Minnesota MinnesotaGeological GeologicalSurvey, Survey,p. p. 431-435. 431-435. 7 �Some factors factors that control the distribution of mercury in the near-surface environment National Park, Park, Michigan-earth, Michigan—earth, wind, and fire environment of Isle Royale National W.F. W.F. Cannon, Cannon,U.S. U.S. Geological GeologicalSurvey, Survey,Reston, Reston,VA VA L.G. U.S.Geological GeologicalSurvey, Survey,St. St.Paul, Paul,MN MN L.G. Woodruff, Woodruff,U.S. The The concentration concentrationof of mercury mercury in in soils soils on on Isle Isle Royale Royale is is highly variable variable in in response response to to many understood. Our Our studIes studies during during the many factors factors whose affects and interplay are poorly understood. past them. Interest past three three years years have helped to clarify some of them. Interest in in mercury mercury distribution distribution on on the island was heightened in the mid 1990's when potentially dangerous mercury levels the island was heightened in the 1990's when potentially dangerous mercury levels were were discovered discovered in in game game fish fish from from six six of of the island's island'sinland inlandlakes. lakes.Because Becausethese thesesix six lakes were clustered in the north central part of the island, whereas lakes on other parts lakes were clustered in of the whereas lakes on other parts of of the the island island showed showed lower lower mercury mercury levels levels in in game game fish, fish, we initially initially suspected suspected that that previously previously unrecognized unrecognized bedrock bedrock mercury concentrations concentrationswithin within the the watersheds watersheds could could be be aa cause. cause. Small Smallnative nativecopper copperdeposits depositswith withsignificant significantmercury mercury content content are are distributed distributed throughout throughout the the island. island. To Totest testthis thishypothesis hypothesiswe we sampled sampledsoils soilsaround around the the Minong Minong Copper 19&century century mining mining operations, operations, and and within within the the watershed watershed CopperMine, Mine,the thelargest largestofofthe the19th of of Sargent SargentLake, Lake, one one of of the the mercury mercury impacted impacted lakes. lakes. Results Results presented presented last last year year (Cannon (Cannon and and Woodruff, Woodruff, 1999) 1999)showed showed that that aa bedrock bedrock source source for for mercury mercury to to the the impacted impactedlakes lakesisis unlikely. The TheMinong Minongcopper copperdeposit depositproduces produces aa very very pronounced pronounced copper copper anomaly anomaly in in soils, Lake watershed. watershed. We soils, but a comparable comparable anomaly anomaly is absent within the Sargent Lake We did did find, find, however, however, that that a-horizon a-horizon soils soilsin in the the Sargent Sargent Lake Lake watershed watershed contain contain very very high high mercury mercury concentrations. concentrations. Because Because aa bedrock bedrock source source is is unlikely unlikely we we concluded concludedthat that mercury mercury concentrations concentrationswere were largely largelyfrom fromairborne airbornedeposition. deposition. Additional Additional sampling samplingand and analyses analyses have have been been conducted conducted in in the the past past year year to to address address the the question ~uestionof of why whv mercury mercurv concentrations concentrationsare are so so variable variable in in soils soils ifif the the source sourceof of mercury mercurv is atmospheric atmospheric pollution. pollution. There There isis aa very very high high correlation correlationbetween between organic organiccarbon carbonin in soils soils and total mercury content (R=0.9). Thus, it appears that factors that control carbon and total mercury content Thus, it appears that factors that control carbon sequestration sequestrationin in soils soils also also control mercury sequestration. One One factor factorthat that could could influence influence both bothisis the the history history of of forest forest fires. fires. During Duringaafire firemuch muchof ofthe thecarbon carbonon onthe theforest forestfloor floorand and in in surface surface soil soil layers layers may may be be burned, burned, thus thus liberating liberating adsorbed adsorbed mercury mercury as as aa gas gas or or fine fine particles that would be transported out of the area. After a fire, the gradual accumulation particles that would be transported After a fire, the gradual accumulation of of organic organic carbon carbon and and mercury mercury can can require require decades decades or or longer longer to to reestablish reestablish pre-fire pre-fire concentrations. A large portion of Isle Royale burned in 1936, including part concentrations. A large portion of Isle Royale burned in 1936, including partof ofour ourstudy study area, burned in in historic historic times. times. Soils area, whereas the remainder of our study area has not burned Soils within within the the 1936 1936burn burn area area invariably invariably have low carbon and mercury content. All Allsamples samples are are below the mean concentration concentration for the island. Some Somesoils soilsoutside outside of of the the bum burn have have comparably comparably low low values values but most are significantly higher. Further Further sampling samplingis is being being conducted fire to to conducted to to seek seek additional additionalconfirmation confirmationof of the the importance importance of of this this 64-year-old 64-year-old fire current currentmercury mercurydistribution. distribution. is Finally, Finally,the thedistribution distributionof ofmercury mercuryin ingeological geologicalmaterials materialsas asaa possible possiblefactor factorinin controlling controllinemercury mercurv accumulation accumulation in in the aquatic aauatic food web needs to be addressed. High Hi& mercury mercuryconcentrations concentrationsin ingame gamefish fishare arethe theend endresult result of ofsuccessive successiveaccumulations accumulations through various steps in the food web. Mercury concentrations inngame gamefish fishtissue tissuemay maybe be - - .. 8 �as lake water. water. Furthermore, as much as one one million times higher than in the ambient lake Furthermore, mercury mercury enters enters the food food web web as as an an organic organic compound, compound, mostly mostly dimethyl dimethyl mercury, mercury, rather rather than the more common inorganic forms. As a result, may researchers discount the than As a result, may researchers discount the concentrations concentrationsof of mercury mercury in in the the terrestrial terrestrial environment environment as as aa factor factor controlling controllingmercury mercuryin in fish. Rather, the efficiency of methylation processes within a lake and its watershed and fish. Rather. the efficiency of methvlation orocesses within a lake and its watershed and complexities complexitiesin in the the food food web web are are commonly commonly cited cited as as causes causes for for widely widely variable variablemercury mercury content Ourresults resultsnow now show showthat that there there are aremuch much higher higher content of of fish fish between nearby lakes. Our mercury mercury concentrations concentrationsin in soils soilsin in the the watersheds watershedsof of Sargent SargentLake Lake (high (highmercury mercury in in fish) fish) than than in in soils soils around around nearby Lake Richie (low mercury in fish). Although Althoughthese theseresults results address address only only two two lakes, lakes, we we suggest suggestthat that itit would would be be premature prematureto to discount discountvariations variationsin in mercury mercury in in watershed watershed soils soilsas as aa factor factorin in determining determiningthe the intensity intensityof of mercury mercury accumulation accumulationin in related related aquatic aquaticecosystems. ecosystems. . < 4. SARGENT LAKE4J MINONG MINE .:•—. LAKE RICHIE 6 6 0 l2MiIes East half of soil thickness) thickness)in inaaof Isle Isle Royale. Royale. Relative Relative mass mass of of mercury mercury (concentration (concentrationxx soil horizon shown fire. Native Native shown by black squares. White White area areawas was burned burned in in 1936 1936forest forest fire. copper copper mines mines and and prospects prospects shown shown by pick and and hammer hammer symbol. symbol. '. a 7 3 Reference Reference Cannon, W.F., W.F., and and Woodruff, Woodruff, L.G., 1999, 1999,Mercury Mercury distribution distribution in in bedrock, bedrock, native native copper copper Cannon, ore and soils—Isle soils-Isle Royale National Park, Michigan (abs): Institute on Lake Superior Superior Geology Proceedings, 45, p.9-10. p.9-10. Geology Proceedings, v. v. 45, 9 �A SEQUENCE OF FOLDING AND DEXTRAL TRANSPRESSION IN THE SEINE RIVER CONGLOMERATES. Peter J., J., Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of CZECK, Dyanna M. and HUDLESTON, Peter Minnesota, 310 3 10 Pillsbury Drive SE, Minneapolis MN, 55455, 55455, czecO019@tc.umn.edu czec0019@tc.umn.edu GEOLOGICAL INTRODUCTION The Superior Province is subprovinces that that are are is comprised of of approximately approximately east east -- west trending subprovinces defined by lithological contrasts, metamorphic grade, and structural boundaries (Card and Ciesielski, 1986). A A popular popular tectonic tectonic model for for this this province province is is the the successive successive accretion accretion of of island island arcs arcs and and their their associated sediments sediments(Floffluan, (Hoffman, 1989). 1989). metavolcanic Wabigoon Wabigoon and the This study focuses on the boundary between the metavolcanic metasedimentary Quetico subprovinces near Mine Centre, Ontario. The Quetico contains mostly amphibolite facies metasediments, and the Wabigoon contains greenschist facies metavolcanics. Distinctive rocks found along this boundary are the Seine River Metasedimentary Metasedimentary Group including the conglomerates. From River conglomerates polymictic Seine River conglomerates. From stratigraphic evidence, the Seine River deposition of of the the volcanic volcanic sequences sequences(Poulsen (Poulsenetetal., at., 1980). 1980). Preliminary formed late following the deposition attempts at absolute absolute dating dating have have confirmed confirmed this this (Davis (Daviset et al., al., 1989). 1989). Previous structural work along this boundary described a dominant subvertical foliation (Poulsen, 1986; Tabor Tabor and and Hudleston, Hudleston, 1991). 1991). These features are interpreted interpreted to to transecting large folds (Poulsen, have formed during dextral transpression. STRUCTURAL INTRODUCTION The term "transpression" was first introduced by Harland (1971) to describe motion that is obliquely convergent, or motion motion partitioned partitioned into into both both convergent convergentand andstrike-slip. strike-slip. In In Harland's original obliquely convergent, described the development development of of folds folds and and strike-slip strike-slip structures structuresdue duetotooblique obliqueconvergence. convergence. A A paper, he described Marchini (1984). This specialized case of transpression was introduced by Sanderson and Marchini This idealized idealized definition of transpression has been used to describe homogeneous deformation consisting of orthogonal simple shear and pure shear components with constant volume and confined deformation deformation boundaries, possibly corresponding to the strain in deep ductile shear zones that accommodate oblique convergence. Quetico boundary seems to be related to this more specific The dominant foliation along the Wabigoon - Quetico type of transpression transpression based based on on the flattening flattening fabrics fabrics and asymmetric features indicating simple simple shear shear in in subhorizontal plane. the subhorizontal One of the questions addressed by this study is the relationship between the folds and the dominant foliation. Clearly, Clearly,itithas hasbeen beendemonstrated demonstratedthat that folds foldscan canform formin intranspression transpression Flarland Harland transpression fabric, or are they an (1971). Are Are the the folds folds at at this this boundary boundary consistent consistent with the rest of the transpression earlier structural feature? FOLIATION/ BEDDING INTERSECTIONS The Seine Group has well defined bedding indicated by fine grained layers interbedded with the recognized pebble conglomerates. conglomerates. In In this this analysis, analysis, the the major major fold fold in in the Seine River conglomerates was recognized on the basis of of structural structural facing facing between between bedding bedding and and the the dominant dominant foliation foliation(Shackleton's (Shackleton'srule rule—- see Borradaile (1976)). This Thisfold foldisisconsistent consistent with with the the observed observed 'way "wayup" up" indicators indicators in in the the conglomerates conglomerates based on graded bedding. bedding. 10 �If this fold were to have formed as a result of the transpression, transpression, the foliation! foliation1 bedding throughout the the field field area. area. In fact, the plunge of the intersection varies intersections should be consistent throughout throughout the field area. The The intersection intersection angle angle is is generally small because both foliation and bedding throughout are steep; steep; however, however, locally the the angle angle is is quite quite large large nearing nearing 75" 75°atatthe thehinge. hinge. This suggests a more history, and that the folding occurred prior to the major transpressive event. complex history, TECTONIC IMPLICATIONS As described elsewhere in the Superior province, the sequence of initial folding followed by homogeneous transpression (and possibly later stage amplification of the strike- slip slip shear shear component component reasonable for for the the WabigoonWabigoon-Quetico Queticoboundary. boundary. It remains an along discrete shear zones) seems reasonable interesting question whether the folds and the homogeneous transpression were two entirely abrupt, separate events or rather an evolution of structural styles during different stages of the same same oblique oblique collisional event. The fact that the initial folding folding is seen in the Seine Group has important implications for for the the relative timing between this change in in structural structural style style and and Seine Seinedeposition. deposition. Some researchers have pull-apart basins formed as suggested that the Seine Group could have been syntectonically deposited in pull-apart as (Poulsen, 1986). The a result of wrenching (Poulsen, The early folding folding of the Seine seems to indicate that it was deposited earlier in the deformation sequence, prior prior to to at at least least some some of ofthe thefolding. folding. Additionally, the overall geometry of the interconnected faults faults seems seems to indicate that during dextral wrenching, the the Seine Seine Group's "basin" "basin" would would have have been been in in aa compressive compressive rather rather than than an an extensional extensional regime regime required required of ofaapullpullbasin. This apart basin. Thissuggests suggests that that aa different different sedimentation/ sedimentation,tectonic model for the Seine Group is needed. J., 1976. the Palaeozoic Palaeozoic rocks rocks of of the the Malaguide Malaguide Complex Complex Borradaile, G. J., 1976. "Structural "Structural facing" (Shackleton's rule) and the nederlandse akademie akademie van van wetenschappen wetenschappen 79B, 798, near Velez Rubis, SE Spain. Proceedings, Koninklijke nederlandse 330330336. 336. A., 1986. the Superior Province Province of of the the Canadian Canadian Shield. Shield. Geoscience Geoscience Card, K. D., Ciesielski, A,, 1986. DNAG Subdivisions of the Canada 13, 5-13. 13,5-13. Davis, D. W., Poulsen, Poulsen, K. H., Kamo, Kamo, S. S. L., L., 1989. 1989.New New insights insightsinto into Archean Archean crustal crustaldevelopment developmentfrom from geochronology 97, 379-398. geochronology in the Rainy Lake area, area. Superior Superior Province, Canada. Journal of Geology 97,379-398. 8., 1971. 27-42. Harland, W. B., 1971.Tectonic Tectonictranspression transpressionin in Caledonian Caledonian Spitsbergen. Spitsbergen. Geological Magazine 108, 108,27-42. Hoffman, P. F., 1989. America. In: In: Bally, Bally, A. A. W., W., Palmer, A. A. R R. ( Hoflinan, 1989. Precambrian geology geology and tectonic history of North America. Eds.), The geology geology of of North America; an overview. The geology of North America A, pp. 447-512. Poulsen, K. Fl., example of of an an Archean Archean Subprovince Subprovinceboundary boundary in inNorthwestern Northwestern H., 1986. 1986. Rainy Lake Lake Wrench Zone: An example Ontario. (Eds.), Tectonic evolution of greenstone greenstone belts belts Technical Report Ontario. In: de Wit, M. J., Ashwal, L. D. (Eds.), 86-10, pp. 177-179. 177-179. Poulsen, K. H., Borradaile, Archean succession succession at at Ramy Rainy Lake, Lake, Borradaile, G. J., Kehlenbeck, M. M., 1980. An inverted Archean Ontario. Canadian Journal of Earth Sciences 17, 17,1358-1369. 1358-1369. D., 1984. Transpression. Transpression. Journal Journal of of Structural Structural Geology Geology 6,449-458. 6,449-458. Sanderson, D. J., Marchini, W. R. D., Tabor, J. R., Hudleston, P. J., 1991. Deformation at an Archean subprovince boundary, northern Minnesota. 1991. Tabor, Hudleston, Canadian Journal of E Earth Sciences 28,292-307. arth 28,292-307. 11 �A A Hf Hf isotopic isotopic study study on zircons from from the the western western Superior Superiorprovince province D.W. D.W.Davis, Davis,Y. Y.Amelin, Amelin,Earth EarthScience ScienceDept., Dept.,Royal RoyalOntario OntarioMuseum, Museum,100 100 Queen's Queen's Park, dond(drom.on.ca, G.M. G.M. Nowell Nowelland andR.R. R.R. Parrish Parrish Park. Toronto, Toronto. ON, ON. M5S 2C6 dond@,rom.on.ca. NERC NERC Isotope Isotope Geoscience GeoscienceLaboratory, Laboratory,Kingsley Kingsley Dunham Dunham Centre, Centre, Keyworth, Keyworth, Nottingham, Nottingham, NG12 NG12 5GG 5GGUK UK U-Pb U-Pb dating datingof of zircon zirconhas hasprovided provided some someof of the the most most important importantconstraints constraintson on geological geological interpretations interpretationsininthe theSuperior Superiorprovince. province.Zircon Zirconalso alsocontains containsHf, Hf,whose whose176Hf "'Hf isotope isotopecan can be beused used to toinfer inferolder oldercrustal crustal provenance provenance of of the magma from which it crystallized. crystallized. Early Hf studies by Corth and Stott (1993, 1996) in the Uchi subprovince show a distribution studies by Corfu and Stott (1993, 1996) in the distribution of EHf EHf values valuesthat thatrange rangebetween betweendepleted depletedmantle mantleand and aa3.0 3.0Ga Gacrustal crustalgrowth growth curve, curve, reflecting reflecting contamination contaminationfrom fromthe theNorth NorthCaribou Caribouterrane terraneand andsupporting supportingthe themodel modelof ofan anAndean-type Andean-type tectonic tectonicsetting. setting.These Thesestudies studiesused usedthermal thermalionization ionizationmass massspectrometry, spectrometry,which whichisis laborious laboriousand andrequires requireslarge largequantities quantitiesof ofzircon. zircon.The Therecent recentdevelopment developmentof ofmulti-collector multi-collector inductively inductivelycoupled coupledmass massspectrometry spectrometrynow nowpermits permitsprecise precisemeasurement measurementof ofHf Hfisotopic isotopic analyses analyseson onsingle singlezircon zircongrains grainsas assmall smallas as22micrograms microgramswith withanalysis analysistimes timeson onthe the order order of 10 minutes per sample. of 10 minutes per sample. Using Usingthe thePlasmaS4 Plasma54instrument instrumentatatthe the NERC NERC lab, lab,Hf Hf isotopes isotopeswere weremeasured measured on on dated datedzircons zirconsfrom from62 62separate separaterock rockunits unitsin inthe thewestern westernSuperior Superiorregion regionplus plus25 25detrital detrital zircon zircongrains grainsfrom fromthe theca. ca.2700 2700Ga GaQuetico Queticometasediments metasedimentsand andpre-2800 pre-2800Ma Maquartz quartz arenites. arenites.The Themass massspectrometer spectrometeranalyses analyseswere weredone doneover overaafour fourday dayperiod. period.This Thisexpands expands the available Hf database in the transect area by a factor of four. the available Hf database in the transect area by a factor of four. Most Mostdata datafrom fromthe theSW SWWabigoon Wabigoonsubprovince subprovincecluster clustertightly tightlyaround aroundaadepleted depleted mantle value of +6S. +6.5. This confirms that assemblages south of the Wiimipeg mantleEHf Enfvalue Winnipeg River River subprovince subprovincewere weremagmatically magmaticallyemplaced emplacedininan anoceanic oceanicenvironment. environment.Analyzed Analyzedzircons zircons from fromthe theSturgeon-Savant Sturgeon-Savantarea areashow showaatrend trendof ofincreasing increasingcontamination contaminationby byolder oldercrust crust with younger age (decreasing Eflf down to +2). with younger age (decreasing Ein-down to +2). Younger Youngerplutons plutonsand andvolcanics volcanicsfrom fromthe thecentral centralWabigoon Wabigoonsubprovince subprovince(2693-2750 (2693-2750 Ma) mostly scatter around values of +4 ± 1, showing the possibility of slight Ma) mostly scatter around values of +4 1, showing the possibility of slight contamination contaminationby byolder oldercrust. crust.Zircons Zirconsfrom fromthe theolder older3000 3000Ma Maold oldrocks rocksininthe theLumby Lumby Lake Lakebelt beltcluster clustertightly tightlyaround aroundaadepleted depletedmantle mantlevalue value(at (at3.0 3.0Ga) Ga)ofof+5.5. +5.5.Zircons Zirconsfrom from ca. ca.2.9 2.9Ga Gaplume-derived plume-derivedrocks rocksgive giveslightly slightlymore moreenriched enrichedvalues valuesdown downtoto+4. +4.The Theresults results from fromLumby LumbyLake Lakeoverlap overlapwith withthose thosefrom fromsimilar similaraged agedrocks rocksininthe theNorth NorthCaribou CaribouLake Lake area of the Sachigo subprovince, supporting the suggestion that the Lumby Lake and area of the Sachigo subprovince, supporting the suggestion that the Lumby Lake andNorth North Caribou Caribouterranes terranesare arecorrelative. correlative. The TheHf Hfdata datafield fieldfrom fromthe theWabigoon Wabigoonand andSachigo Sachigosubprovinces subprovincesoverlaps overlapsclosely closely with withthat thatofofCorfu Corfuand andStott Stott(1996) (1996)from fromthe theUchi Uchisubprovince. subprovince.InIncontrast contrastzircons zirconsfrom fromthe the Winnipeg WinnipegRiver Riversubprovince subprovinceare arenoticably noticablymore moreenriched, enriched,with withEHf EHfvalues valuesof ofabout about00toto -2 over an age range of 2721 Ma to 3225 Ma. An EHf value of—2 value found on 3.2 Ga Ga -2 over an age range of 2721 Ma to 3225 Ma. An Eufvalue of -2 value found on3.2 zircons zirconsfrom fromthe theCedar CedarLake Lakegneiss gneissimplies impliesaaca. ca.3.5 3.5Ga Gacrustal crustalprotolith, protolith,ininagreement agreement with withresults resultsofofNd Ndwhole wholerock rockisotopes isotopes(Henry (Henryetetal. al.1997). 1997). AAsingle singleanalysis analysisfrom fromthe thewidespread widespread2722 2722Ma Mavolcanics volcanicsininthe theShebandowan Shebandowanbelt belt shows showsaadepleted depletedsignature, signature,asasdoes doesaa2726 2726Ma Mavolcanic volcanicfrom fromthe theMelchett MelchettLake Lakebelt, belt,ininthe the middle middleofofthe theEnglish EnglishRiver Riversubprovince. subprovince.However, However,2723 2723Ma Mavolcanic volcaniczircons zirconsfrom fromthe the Separation SeparationLake Lakegreenstone greenstonebelt, belt,which whichmay mayunderlie underlieEnglish EnglishRiver Rivermetasediments, metasediments,show showaa * 12 �more enriched enriched value value of of -2, -2, suggesting suggesting that that itit is is contaminated contaminatedby by much much older olderWinnipeg Winnipeg River-type River-type crust. crust. Results Results on on detrital detrital zircons zirconsfrom from quartz quartz arenites arenites in in the the North North Caribou Caribouterrane terranegenerally generally overlap An analysis analysis from from 3250 3250 Ma Ma old old zircon zirconin inthe the overlap the the data data field field from from rocks rocks in in this this area. area. An Jutten Jutten quartz quartz arenite arenitein in the the northern northern Wabigoon Wabigoon subprovince subprovinceshows shows still still older oldercontamination contamination (E1 ( h fof of 0), 0), suggesting suggestingthat that 3.0 3.0 to to 3.3 3.3 Ga Ga detrital detrital zircons zircons in this unit were derived derived from from the adjacent adjacent Winnipeg Winnipeg River River subprovince. subprovince.Ca. Ca. 3.2 3.2 Ga Ga zircons zircons from from the the Quetico Quetico metasediments metasediments also show enriched values down to —3, while the youngest zircons at ea. 2.7 also show enriched values down to -3, while the youngest zircons at ca. 2.7 Ga show variable variableenrichments enrichmentsfrom from+5 +5 to to +0, +0, again againsuggesting suggestingaa source sourcepartially partiallyin inthe theWinnipeg Winnipeg River subprovince. River subprovince. The values at at ca. ca. 2.7 2.7 Ga Ga and and 3.0 Ga provides The general general coherence coherenceof ofthe thehighest highestEHf Enfvalues reasonable reasonable constraints constraintson onthe theevolution evolutionof ofthe thedepleted depletedmantle mantlereservoir reservoirduring duringthe thelate late Archean. These results agree with the linear growth trend defined by other Hf Archean. These results agree with the linear growth trend defined other Hf measurements measurements from from younger younger rocks rocks and and from from early early Archean Archean rocks rocks in in Greenland Greenland (Vervoort (Vervoort and Blichert-Toft 1999). They give evidence for a major depletion of the mantle or and Blichert-Toft 1999). They give evidence for a major depletion of the mantle atator before 4.0Ga. Ga.IfIfcontinental continentalcrust crustwas wasthe thecomplimentary complimentaryenriched enrichedreservoir, reservoir,this thisimplies implies before 4.0 that that such suchcrust crustwas wasof ofan anextent extentcomparable comparableto to the thepresent present during duringthe theearly earlyArchean. Archean. Otherwise, Otherwise, the the enriched enriched reservoir reservoir may may have have been been oceanic oceanic crust crust that that was was subducted subductedand and stored Archean. stored in in the the deep deep mantle mantle until until the the end end of of the the Archean. Continuing Hf isotopic studies on precisely Continuing Hf isotopic studies on precisely dated dated zircons zirconspromise promiseto to be beaapowerifil powerful tool tool for forresolving resolvinglocal localand andglobal globalproblems problemsininEarth Earthhistory. history. REFERENCES REFERENCES Corfu, Corfu, F. F. and and Stott, Stott,G. G. 1996. 1996. Hf Hf isotopic isotopic composition composition and and age age constraints on the evolution evolution of of the the Archean Archean central central Uchi subprovince, subprovince, Ontario, Canada. Precamb. Res. 78: 535363. 63. Corfli, Corfu,F. F. and and Stott, Stott,G. G.1993. 1993.Age Ageand andpetrogenesis petrogenesisof oftwo twolate lateArchean Archeanmagmatic magmaticsuites, suites, northwestern northwesternSuperior Superiorprovince, province,Canada: Canada:Zircon ZirconU-Pb U-Pb and andLu-Hf Lu-Hf isotopic isotopicrelations. relations. Jour. Petrol. 34: 8 17-838. Jour. Petrol. 34: 817-838. Henry, Henry,P., P., Stevensen, Stevensen,R., R., Larbi, Larbi,Y., Y.,and andGariepy, Gariepy,C. C.1997. 1997.Use Useof ofNd Ndisotopes isotopestotoquantify quantify 700 in the 700 Ma Maof ofcrustal crustalgrowth growthfrom from3.4 3.4to to2.7 2.7Ga Gain thewestern westernSuperior Superiorprovince province (Ontario, (Ontario,Canada). Canada).Western WesternSuperior SuperiorTransect TransectWorkshop WorkshopReport Report#63: #63:27-36. 27-36. Vervoort, Vervoort,J.D. J.D. and andBlichert-Toft, Blichert-Toft,J.J.1999. 1999.Evolution Evolutionof ofthe thedepleted depletedmantle: mantle:Hf Hfisotope isotope evidence from juvenile rocks through time. Geochim. Cosmochim. Acta evidence from juvenile rocks through time. Geochim. Cosmochim. Acta63: 63:533533556. 556. 13 �MYSTERY FAULTS FAULTSOF OFTHE THE CASCADE RIVER, RIVER, NORTH NORTH SHORE, MYSTERY SHORE, OR, OR,WHAT WHATIS IS THIS THIS GRANITE DOING HERE? HERE? GREEN, GREEN,John JohnC., C., Department DepartmentofofGeological GeologicalSciences, Sciences, University University of Minnesota Duluth, Duluth, MN 55812, jgreen@d.umn.edu jpreen@d.umn.edu Duluth, MN 55812, The The Cascade Cascade River in Cook County, MN, exposes exposes a homoclinal section section about about 13 13km km long longacross across normal-polarity rocks rocks of of the the North North Shore Volcanic Volcanic Group. Group. With normal-polarity With an an average dip of about 12 degrees, this this amounts amounts to a thickness of about 2.4 km. In degrees, Inits itslowest lowest mile mile and and aa major major tributary, tributary, it cuts across several faults faults that that involve the the great, great, cuesta-forming cuesta-forming Terrace Terrace Point Point basalt flow and the thick, underlying Good Good Harbor Harbor Bay Bay sandstone. sandstone. red sandstone and the At the top of of the the cascades, cascades, the conformable contact between the big red also visible visiblefour four miles miles to to the the east at the big Good overlying flood basalt flow, also GoodHarbor HarborBay Bayhighway highway fault. As the the river river starts starts cut, is dropped down to to the the north northaafew fewfeet feetalong alongaa high-angle, hii-angle, east-west fault. cascades,the the top top of of the sandstone can be seen under the to enter enter the the gorge and plunge down the cascades, 100m m into intothe thegorge, gorge,the thebasalt basaltisis interrupted interruptedby byaaremarkable remarkablebreccia brecciaof ofpink, pink, basalt. But Butless less than than 100 apparent fault contact medium-grained granite that occurs in apparent contact with the the volcanic volcanic rocks. rocks. Locally, Locally, fragments of of basalt basalt and and perhaps perhaps sandstone are caught up up in the breccia, but but most of it is granite. On uncontaminated granite. Onthe thedownstream downstreamside, side,abundant abundantjoints joints in in the the adjacent adjacent basalt imply aa upstream, but but itit isis covered. covered. On steep fault contact dipping upstream, On the the upstream upstream side, side, the bounding bounding fault apparently dips much apparently much more more gently gently downstream, downstream,implying implying aa wedge of of granite granite emplaced emplaced mechanically mechanically flows. A fault contact a kilometer or or so to to the northeast between the sandstone into the lava lava. flows. sandstone and aa rhyolite may be related to this event. event. There are two conceivable sources for this granite, granite, which which must must be be far far from from its original original site siteof of There crystallization. related to to the roof zone zone of crystallization. If itit is Keweenawan, and related of the the Duluth Duluth Complex Complexthat thatisis Eagle Mountain, Mountain, ititwould would have havemoved movedupward upward at at least least2.4 2.4km. km. Otherwise exposed up-dip (inland) at Eagle it could be part of the the Archean Archean basement, basement, in in which case it would have come up much farther, perhaps 10 km. ItItisismedium-grained, medium-grained,hypidiomorphic hypidiomorphicwith with minor minor micrographic micrographic patches patches and and its its ferromagnesian silicate is is Fe-rich biotite, which is rare in Keweenawan granites. Petrographically Petrographically itit rocks of of is not a good match for for either either the the Eagle Eagle Mountain Mountain granophyre granophyre or or typical typical Archean granitic rocks the region. Its from, but but not not how it Itsabundant abundantzircons zircons should should solve solve the problem of where it came from, got to to its its present present position. position. x---- ----- Geologic sketch map from from Green, Green, 1996, Geolom Diswlav: Geology Geology Geology on Display: Minnesota's North and Scenery of Minnesota's Shore State Parks, MN Dept. of of Nat. Nat. Resources, Resources. St. St. Paul Paul . .. . ............... ............... .... - Fault 880 Sandstone I 14 �PETROGENESIS OF RiVER REGION, PETROGENESIS OF GRANITIC GRANITIC ROCKS ROCKS OF OF THE THE DUNKA RIVER REGION, EASTERN EASTERNMESAI3I MESABI RANGE, MINNESOTA MINNESOTA HARRIS, Emily HARRIS, Emily C. C. A., A,, Macalester Macalester College, College, St. St. Paul, Paul, MN 55105, 55105, eharris@macalester.edu; eharris@macalester.edu; Wirth, Wirth, Karl Karl R., R., Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN MN 55105, 55105, wirth@macalester.edu throughout the the Midcontinent Midcontinent Rift (MCR) Middle Proterozoic felsic igneous rocks are exposed throughout and the eastern Mesabi Range of northern northern Minnesota. Minnesota. Many of these are considered to be Keweenawan (1,100 Ma) in age. However, However,recent recent studies studies suggest suggest that some some early Middle Proterozoic felsic magmatism may have have occurred occuned in the region region as as well well (Phillips (Phillipset. et.al., al.,this thisvolume). volume). To better understand understand the history of felsic magmatism in northern Minnesota, samples from the Dunka River Region, which is situated along the base of the Duluth Complex, have been collected and studied. Felsic Felsicrocks rocksthat thatintrude intrudegabbros gabbrosof of the the Dunka Dunka River River Region Region have have coarse coarse graphic graphic textures, textures, chemically distinct complexes in the Midcontinent Midcontinent Rift. and are chemically distinct from granophyre complexes Granitic rocks were were collected collected from from along along the the eastern eastern Mesabi Mesabi Range Range between between Babbitt Babbitt and and Aurora, Minnesota. Granite with coarse graphic texture was collected from stockpiles within the Granite with coarse graphic within the Biwabik Iron Iron Formation Fonnation and gabbro mining operations operations along the contact between metamorphosed Biwabik gabbro withingabbro gabbroand andiron ironformation formation(Strandlie, (Strandlie,pers. pers. of the MCR. These Thesegranites granitesoccur occuras assmall smalldikes dikeswithin conimunication). They communication). Theyare arecommonly commonly pegmatitie, pegmatitic, and are composed of potassium feldspar or sodic %), and biotite biotite (5-10 (5-10 %). %). Feldspars Feldspars are variably altered altered to plagioclase (40-50 %), quartz (35-45 %), clay minerals and biotite is altered to chlorite. These Thesegraphic graphic granites granites are are mineralogically mineralogically and and texturally comparable comparable to some some felsic felsic granophyres of the Midcontinent Rift (Kennedy (Kennedy et al., this vol.). Other vol.). Othergranitic graniticrocks rocks were were collected collected from ____________________________________ IS 15 nearby outcrops of the eastern eastern margin of of the the Archean Aurora Sill Archean Giants Giants Range Range batholith batholith for for comparison. comparison. MCi felt The Archean granites are finefine- to to mediummediumgnnophyres 10 s 10 grained, and consist consist of of plagioclase plagioclase (20-40%), (20-40%), amphibole amphibole (<15%), (<15%), quartz quartz (10-40%), (10-40%), potassium potassium S. C feldspar feldspar (5-20%), (5-20%), biotite biotite (5-10%), (5-lo%),and andFe-Ti Fe-Tioxox- % ides ides (<5%), (<5%), and and commonly commonlyexhibit exhibitstrained strainedquartz quartz C+ Giants Range bathofith and weakly foliated textures. These These granites granites are are 9a MCRmalIc texturally texturally and and compositionally compositionallysimilar similarto to grangrangnnophyrs gra=ophy= ites of the western Giants Range batholith (e.g., Boerboom and Zartman, 1993). 1993). 60 70 80 o 40~ " " " " 50 SO" " " " " (50 ' 70 80 The graphic graphic granite granite dikes dikes from from the the Dunka Dunka SiO.* drt. %). o) St02(wt. . characterized by a greater Pit are characterized greater silica silica content Figure Figure 1. Plot of Na20+K20 Na 20+1(20 (total (totalalkalis) versus (Si02=70.8-78.7 wt. (Si02=70.8-78.7 wt. %) %) than than isis observed observed in in MCR MCR SiO2 comparing Dunka granites (open Dunks graphic granites (open gi02 wt. %; Kennedy et al., this this ggranophyres r a n o ~ h ~ r(66-76 es circles) with rocks from the Giants Range Giants Ranee vol.) and and the Aurora Aurora Sill Sfflsyenites syenites (54.6-60.7 (54.6-60.7 wt.%; W.%; batholith (Boerboom and Zartman,1993), Zartman,l993), the the Potassium,sodium, sodium,and and Phillips et al., this vol.). Potassium, Aurora Silt Sill (Phillips et at., al., this vol.), and granogranocalcium concentrations of the granite phyre complexes of the MCR (Kennedy granite dikes dikes (Kennedy et et al., al., (K20=2.98-5.16 wt. wt.%; %; Na2O=3.20-6.48 Na20=3.20-6.48wt, wt, %; %; this vol.). this vol.). (1(20=2.98-5.16 * 1 - - - I - - ~~~ ~ 15 �CaO=O.28-1 .09wt. wt.%) %)are aresimilar similar to to those those of of Ca0=0.28-1.09 the MCR granophyres and the Aurora Sill (Figgranophyres ure 1). 1). However, However,most mostof ofthe thegraphic graphic granites granites have high high A1203 Al203 concentrations concentrations and are are have peraluminous, similar to those of the Aurora Sill; MCR granophyres are peraluminous to metaluminous. The metaluminous. Thegraphic graphicgranites granites also have Ti02than than rocks rocks of of the the MCR MCR and and the the AuAuless Ti02 ron Sill. The graphic granites are compositionS i l l . The graphic granites are compositionrora ally similar to those of of the the Giants Giants Range Range batholith, although although they have slightly slightly higher higher 59 Si02 concentrations Si02 valSi02 concentrations (Giants (Giants Range Si02 ppm) ues %). ues range from 52.9-73.6 wt. %). 2. Plot PlotofofNb Nbversus versusY Y comparing comparing Dunka On On trace element element diagrams diagrams (e.g. ZrITiO2 Zr/Ti02 Figure 2. circles) with other graphic granites (open circles) other felsic felsic Nb/Y) the graphic graphic granites granites are are distinct distinct from from vs. Nb/Y) Minnesota; Figure 1 for data rocks of northern Minnesota; see 1 Aurora Sill syenites syenites (Phillips (Phillips et al., al., this this vol.), references. and references. but plot with the Duluth Complex Complex granophyres granophyres ((Kennedy ~ e k e et d al., ~ this vol.). However, However, whereas whereas major element concentrations of Dunka graphic granites are similar similar to those of felsic rocks of the MCR granophyre granophyre complexes, complexes, their trace trace element element compositions are more similar to those of mafic rocks of the MCR granophyres. A plot of Nb vs. Y compositions similar mafic rocks of the MCR granophyres. of (Figure 2) reveals the depletion in graphic granites of both Nb and Y with respect to MCR granogranoY/Nb and and ThfNb ThINb ratios ratios of of the the graphic graphic phyres and Aurora Sill Sill syenites. syenites. Furthermore, Furthermore, the the greater greater Y/Nb batholith and and suggest suggest that that these these rocks rocks contain contain granites are most similar similar to those of the Giants Range batholith a more significant crustal crustal component component than do the MCR granophyres and Aurora syenites. similar in mineral and major element element composicomposiGraphic granites of the Dunka River Area are similar lions to felsic granophyres associated with with the the Midcontinent MidcontinentRift. Rift. However, the low trace element tions concentrations of the concentrations the Dunka Dunka graphic graphic granites granites are are more more similar similar to the the mafic mafic rocks rocks of of the the granophyre granophyre complexes. Therefore, Therefore,we weconclude concludethat thatthe thegraphic graphicgranites granites of of the the Dunka Dunka Region Regionare areunrelated unrelatedto to Midcontinent Rift Rift and and to to the theAurora Aurora Sill. Sill. Alternatively, they the other felsic granophyres of the Midcontinent sirnimight be partial melts of country rock along the base of the Duluth Complex. The The chemical chemicalsimilarity between the Dunka graphic granites and the Giants Range Range batholith batholith granite granite suggests suggests that have produced produced the themelts meltsfor forthe thegraphic graphicgranite. granite. Alternapartial melting of Archean granites could have tively, the graphic graphic granites might be the melting products of nearby argillite, argillaceous siltstone, (e.g., Morey, Morey, 1972). 1972). and fme-grained fine-grained feldspathic feldspathic graywacke graywackeof of the the Virginia Virginia Formation Formation (e.g., j References Zartman, Robert E., E., 1993. Geology, geochemistry, and and geochronology geochronology of the central Boerboom, Terrence J. and Zartman, Giants Range batholith, batholith, northeastern Minnesota. Minnesota. Canadian Canadian Journal Journal Earth Earth Science, Science,v. 30, 30, p. p. 2510-2522. 2510-2522. Kennedy, Bryan Bryan C. wirth, Wirth,K., K., and andVervoort, Vervoort,J,J,this thisvolume. volume.Petrogenesis Petrogenesisof ofthe theMidcontinent MidcontinentRift Riftgranophyric granopbyriccomcomplexes of northern Minnesota. P.K. and and Morey, Morey, G.B., GB., Morey, GB., G.B., 1972. 1972.Mesabi MesabiRange. Range.A A Centennial CentennialVolume, Volume, Minnesota Geological Survey, Sims, P.K. editors, Minnesota Minnesota Geological Geological Survey, Survey,p. 204-217. 204-217. Phillips, Phillips, Erin Erin H. and and Wirth, Wirth, K., K., this this volume. volume. Petrogenesis Petrogenesisof of the the Enigmatic EnigmaticAurora AuroraSill, Sill,Mesabi MesabiRange, Range,Minnesota. Minnesota. 16 �Pyroxene Homfelsed Copper Mineralization in the Pyroxene Hornfelsed Archean Giants RangeBatholith Range Batholith Footwall Keweenawan Footwall of the Keweenawan Intrusion, Duluth South Kawishiwi NE Minnesota - Archean or Keweenawan Mineralization? South Intrusion, Dnlnth Complex, Complex, NE - Steven Miller Trunk Trunk Steven A. A. Hauck, Hauck, Natural Resources Resources Research Research Institute, Institute, University University of of Minnesota, Duluth, Duluth, 5013 Miller Andy Wallbridge Mining Company Fielding Road, Hwy., Duluth, MN, 5581 1, Bite, Wallbridge Mining Company Ltd., 129 129Fieldiing Road, Lively, Ontario, 55811, 5013 P3Y 1L7, 1L7, and Mark Severson, Natural Resources Research Institute, University of Minnesota, Duluth, Duluth, 5013 55811. Hwy., Duluth, MN, 1. Miller Trunk Hwy., MN, 5581 Copper sulfide mineralization mineralization in Ga)Giants GiantsRange RangeBatholith Batholith(GRB) (GRE)footwall footwallofthe of theSouth SouthKawishiwi Kawishiwi Copper sulfide in the the Archean Archean (—2.7 (-2.7 Ga) intrusion the Keweenawan intrusion (SKI) (SKI) of ofthe Keweenawan (1.1 Ga) Ga) Duluth Duluth Complex Complex (DC) (DC) of of northeastern northeastern Minnesota Minnesotawas was first first discovered discoveredby by exploration companies 960s and 1970s, exploration companiesdrilling drillingin in the the I1960s 1970s, and and was was recently reported reported in in outcrop outcropin in the the Spruce SpruceRoad Roadarea area E.. H.. H.. Dahlberg, 1998). The firstdescribed (pers. corn., E.. The Cu mineralization was first described by by Bonnichsen Bonnichsen et et al. al. (1980) and and further further described Severson (1994). According occurs as disseminatedsulfides disseminated sulfides described by Severson Accordingto to Severson Severson (1994), the copper mineralization occurs within the uppermost 330 ft. of the ORB, GRB, although in some some drill drill holes holesthe thefirst first 100 100ft. ft.may maybe bebarren. barren. Chalcopyrite Chalcopyrite is the dominant sulfide. However, pynhotite is However, in in the the overlying overlying SKI rocks pyrrhotite is the dominant dominant sulfide. Also, Also, at at or or just just above above the basal contact contact of of the SKI SKI and within the upper 100 100 ft. of the GRB, semi-massive to massive sulfides sulfides can occur, occur, e.g., drill holes BL-95-1, BL-95- I, K-1. K-I. These Thesesulfides sulfidesare aregenerally generallypyrrhotite-rich, pyrrhotite-rich, and andmay may have have Ni>Cu N i X u values values exceeding exceeding1% 1%Ni Ni and/or contain sulfides GRE, that these andlor Cu. Cu. Severson Severson(1994) (1994)suggests, suggests,based basedon onthe thelinearity linearityof ofthe the drill drill holes holes that contain sulfides in the GRB, drill northeast-trending belts drill holes define define two northeast-trending belts or or faults. Also Alsocoincident coincidentwith withthese theselinear linearzones zonesare areelevated elevatedplatinumplatinummineralizationin inthe theoverlying overlyingSKI. SKI. Bonnichsen Bonnichsen et et al. al. (p. (p. 563,1980) 563,1980) state state these Cugroup element (PGE) and Cr mineralization enriched enriched zones zones in the the GRE ORB "probably "probably resulted resulted because because fractional fractional crystallization crystallizationcaused caused Cu Cu enrichment enrichmentin in the the melts melts as as they trickled downward through a decreasing decreasing thermal thermal gradient beneath the complex". AAsimilar similarmodel modelfor forCu-PGE Cu-PGE mineralization has been proposed for the footwall mineralization in the Sudbury Complex Complex (Naldrett, (Naldrett, et et al., al., 1999) mineralization In 1997, Nickel,began beganaa new new exploration explorationprogram programon ontheir theirSpruce SpruceRoad Road INCO's U.S. U.S. subsidiary, subsidiary,American AmericanCopper Copper&&Nickel, 1997, INCO's Cu-Ni deposit east of Ely, MN. Based copper intercepts Based on on their previous drilling, drilling, INCO identified fifteen s 1% 1% copper interceptsin in the footwall, footwall, which suggested suggested footwall footwall copper copper exploration potential. Recently Recentlyat at Spruce SpruceRoad, Road, several several 1960-era 1960-eradrill drill holes holes geophysical surveys. surveys. Two drill holes (13648,34889) (13648,34889) were probed using a 3D Borehole Borehole Pulse were found to be open for geophysical geophysical survey, was identified identified at at 375131 375m (1,230 (1,230 ft.;Ravenhurst, ft.;Ravenhurst, 1997). EM geophysical survey, and in hole 13648, 13648, a footwall conductor was In 1999, injoint drilled DDH WM-lto WM- ito 1,754 ft. ft. At 183 1999, Wallbridge Mining Mining Company, in joint venture venture with INCO, drilledDDH 183 ft. and 330 footwall copper mineralization was intersected, ft. beneath the basal contact contact of the Duluth Complex Complex (919 ft.), footwall intersected,i.e., i.e., 79.5 79.5 ft. of 1.91% Cu and and 10.5 10.5 ft. ft. of of 0.55% 0.55% Cu. Cu. Nickel, PGEs, and Au ft. of 0.17% Cu, which includes includes 1.1 1.1 ft. 1.91% Cu Au are are minor minor constituents. constituents. The footwall to the DC DC is is generally generally composed composed of of felsic, felsic,intermediate, intermediate, mafic, hybrid hybrid rocks, and and scattered scattered homfelsed homfelsed inclusions of which which may maybe berelated relatedtotothe theGRB. GEE. In the Spruce Road area, Green (1970) inclusions (Severson, (Severson, 1994), 1994), some or all of of granitic rocks, rocks,i.e., i.e.,porphyritic porphyriticandnon-porphyritic. andnon-porphyritic. Both types types are are composed composed ofhomblende-biotite ofhornblende-biotite reports two types ofgranitic adamellite, monzonite, gabbroic adamellite, monzonite,granodiorite, granodiorite,and andseveral severalmafic maficrocks. rocks. All Allrock rocktypes typesare arecut cut by a variety of dioritic and gabbroic dikes, which may have been metamorphosed by the SKI. In In the the vicinity vicinity of of the the Spruce Spruce Road Cu-Ni Cu-Ni deposit, deposit, the the GRB ORB metamorphosed (Green, (Green, 1970). 1970). The has been contact metamorphosed The GRE ORB rocks rocks intersected intersected in WM-linclude WM-Iinclude several several of of these these rock rock types, e.g., porphyritic porphyritic quartz quartz monzonite, monzonite, quartz quartz monzonite, monzonite, granodiorite, granodiorite, monzonite, monzonite, possible Archean Archean Knife Knife Lake Lake Group homfels inclusions, norites, which which are are less lesscertain certainin inorigin. origin. All of these rock types inclusions, as well as melanorites and norites, have undergone pyroxene homfels hornfels (opx+cpx+amphibole) (opx+cpx+amphibole)contact contactmetamorphism. metamorphism. Of primary interest, however, is mineralization within itself. mineralization within the the footwall footwallmelanorites/norites, melanorites/norites, and and the the footwall footwallGRB GRB itself. The melanorites with the the granitoid granitoid rocks, rocks, and and include include rounded rounded fragments fragments of of melanorites and norites have sharp intrusive contacts with them. Petrographically, the melanorites are composed of opx and cpx (30-60%), amphibole (—1-80%), zoned and Petrographically, the melanorites are composed of opx and cpx (30-60%), amphibole ( -1-SO%), uuzonedplagioclase (10-60%),biotite biotite(4-8%), minorquartz(1-3%), oxides(<1-2%), (4-2%), unzoned plagioclase (10-60%), minor quartz (1-3%), apatite(<!%), apatite (<1%), muscovite muscovite (4-3%), (<1-3%), oxides (<1-3%). Opx early. Amphibole and sulfides (4-3%). Opx and and cpx cpx are are subhedral subhedral to euhedral and crystallized early. Amphibole generally rims the pyroxenes, Anhedralto to subhedral, subhedral,zoned zoned pyroxenes, and in some some instances instances corrodes corrodes the pyroxenes producing anhedral crystals. Anhedral 17 �and unzoned plagioclase may show show undulose extinction, extinction, occur occur as equant grains, and are often altered altered to clay clay minerals. Anhedral to subhedral flakes of biotite follow the crystallization of plagioclase and can be porphyroblastic. suhhedral flakes porphyroblastic. Quartz Quartzisis the last silicate to crystallize. Apatite occurs as euhedral rods, both very early and late in the sequence. last silicate to crystallize. Apatite occurs as euhedral rods, both very early and late in the sequence. Oxides (magnetite> ilmenite) and and sulfides sulfides are are last last to crystallize. The The oxides oxides and and sulfides sulfides are are often associated with alteration (magnetite >ilmenite) of the pyroxenes pyroxenes to to biotite, biotite, muscovite, muscovite,talc talc(?), (?),and andchlorite chlorite(?) (?)along alongfractures fracturesand andalong alongthe therims rimsininthe theopx. opx. The sulfides, in order of appearance, appearance, are are millerite, millerite, sphalerite, sphalerite,and andhomite bomiteandlor and/orchalcopyrite. chalcopyrite. The The sulfides sulfides also also occur occur as as interstitial to net-textured net-textured grains that surround surround opx. opx. The melanorites also contain net-textured magnetite. The A similar sulfide and silicate mineralogy occurs in the footwall footwall host host rocks. rocks. These These rocks rocks can can have have feldspar feldspar phenocrysts phenocrysts with a plagioclase plagioclase matrix matrix and minor minor quartz quartz ((5%), amphibole, opx, biotite, oxides (magnetite, ilmenite), ~ 5 % )amphibole, , opx, biotite, oxides (magnetite, ilmenite), and andsulfides sulfides (chalcopyrite, hornite, bomite, millerite, pentlandite, sphalerite). The blebs and anddiscontinuous discontinuous veins, veins, generally generally The sulfides occur as blebs associated with biotite, plagioclase, opx, ±amphibole ±amphibole, ±quartz ±quartz, and oxides. The The plagioclase plagioclase in in these these zones zones is equant and equigranular, and exhibits sutured contacts with the larger plagioclase. The copper mineralization in the granitoid and noritic rocks have Cu:Ni ratios of 8-32:l, 8-32:1, compared to the 3.3:1 3.3: 1 in the overlying DC. The Pd:Pt ratio is these rocks is 1-15:1, compared to the 3:1 in the overlying DC. Data from The Pd:Pt ratio is these rocks is 1-15:1, compared 3: 1 Data fromSeverson Severson (1994) on other footwall intercepts give Cu:Ni and Pd:Pt ratios of 2-9:1 and 2-7:1, respectively, indicating footwall intercepts give Cu:Ni and Pd:Pt of 2-9:1 and 2-7:1, respectively, indicating that thatCu Cuisis enriched, and Ni and PGEs are depleted in WM-1 when compared to other footwall samples. Comparison Comparisonof ofCu:Ni Cu:Niinin all GRB samples indicates a tendency for Cu enrichment and Ni depletion with depth beneath the the basal contact. contact. geology. Possible The origin of this this mineralization mineralization opens opens new and and exciting exciting aspects in Duluth Complex geology. Possible emplacement scenarios scenarios include: include: I) A relict of Archean emplacement. The 1) Themodel model isis supported supported by both sharp contacts contacts and net-textured sulfides sulfides and oxides in the mafic rocks rocks of the footwall. Duluth Complex Complex sulfide. sulfide. The observed depletion of nickel and enrichment enrichment 2) Keweenawan fractionation of Duluth depth below below the the footwall-Duluth footwall-Duluth Complex Complex contact, contact, and andthe theassociation associationof ofnet-textured net-texturedand anddiscontinuous discontinuous of copper with depth biotite-muscovite-talc(?)-chlorite(?) alteration support this possibility. vein sulfide with biotite-muscovite-talc(?)-chlorite(?) feeder-dike' totothe 3) Proximity to a "feeder-dike" theDuluth DuluthComplex. Comvlex.This Thiscase caseisissupported supportedby bythe thepresence presence of ofmagmaticmagmatichigh-grade sulfide intersections intersections not not unlike unlike those those from from Voisey's Voisey's Bay and Sudbury. These looking high-grade Theseintersections intersections are are associated with mafic assemblages not normally part of granitoid intrusions. Regardless ofpreferred genetic model, developments indicate significant new exploration exploration potential Regardless ofpreferredgenetic model, these recent developments potential for the Duluth Complex. Y., 1980, Geologic setting, mineralogy, mineralogy, and geochemistry of magmatic Bonnichsen, B., Fukui, L. M., and Chang, L. L. Y., magmatic D., ed., ed., Proceedings Proceedings ofthe of the fifth fifth quadrennial quadrennial IAGOD IAOOD symposium, symposium, sulfide deposits, Duluth Complex, U.S.A, in Ridge, J. D., Alta, Utah, 1978: Stuttgart, Schweizerbart'sche Schweizerbart'sche Verlagsbuchhandlung, Verlagsbuchhandlung, v. v. 1, p. p. 545-565. Snowbird, Aka, 3. C., C., 1970, Lower Precambrian rocks of the Gabbro Green, J. Gabhro Lake Quadrangle, Quadrangle, northeastern northeastern Minnesota: Minnesota: Minnesota Minnesota Geological Survey, Special Special Publication Series, Series, SP-13, SP-13, 96 96 p. Naldrett, A. J., Asif, M., Schandl, E., Searcy, T., Morrison, G G.. G., Binney, Binney, W. P., P., and and Moore, Moore, C., C., 1999, Platinum-group Platinum-group to the the origin origin of of different different ore ore zones zones and and to to the the exploration exploration for for elements in the Sudbury ores: Significance with respect to orebodies: Economic Economic Geology, Geology, v.v.94, footwall orehodies: 94, no.2, no. 2, p. p. 185-210. 185-210. Ravenhurst, B., 1997, 1997, Geophysical Geophysical survey survey report report for for American American Copper Copper & & Nickel Nickel Inc., Inc., Spruce SpruceRoad Road project: project: Division Division of Lands and Minerals, Minnesota Minnesota Department Department of of Natural Resources, Resources, Open-File Report, 26 26 p. p. of the South South Kawishiwi Kawishiwi Intrusion, Intrusion,Duluth DuluthComplex, Complex,northeastern northeastern Minnesota: Minnesota: Severson, M. J., 1994, Igneous stratigraphy ofthe 210 Duluth, Natural Resources Research Research Institute, Institute, Univ. Minnesota, Minnesota, Duluth, Duluth, Technical Technical Report NRRI/TR-93/34, NRRIITR-93/34,2 10p. p. 18 �An Archean age argument is supported by by::I)1)sharp sharpintrusive intrusivecontacts contactswith with xenoliths xenolithsof ofhost host rock rock in in the the melanorites; melanorites; and 2) magmatic-looking net-textured sulfides and oxides in the melanorites. A Keweenawan argument magmatic-looking sulfides the A Keweenawan argument includes includesthe the previous examples and is also supported by: 1) depletion ofNi and enrichment of copper with depth beneath 1) ofNi and enrichment of copper with depth beneath the the basal basal previous examples and is contact of the DC (as might be expected of a downward differentiating differentiating sulfide sulfidemelt meltthrough through fractures fractures and and faults); faults); 2) 2) association of net-textured and discontinuous vein sulfides with biotite-muscovite-talc (?)-chlorite (?) alteration; and (?) net-textured discontinuous sulfides 3) possible emplacement Keweenawan"feeder "feeder dike" dike" to the DC. Evidence Evidencewould wouldinclude includethe thepresence presenceof ofmagmatic magmatic emplacementof of aa Keweenawan pyrrhotite-pentlandite-chalcopyrite mineralization not unlike that of the Sudbury and Voisey's Bay, as well as the pyrrhotite-pentlandite-chalcopyritemineralization not unlike that of the Sudbury and Voisey's Bay, as well association of mafic assemblages not normally part of the granitoid intrusions. In In any any event, event, the the presence presenceof of Cu-rich Cu-rich well below the basal contact of the SKI (300-425 ft.) ft.) is interesting and suggests a new exploration mineralization well potential for potential for the the DC. DC. Table I. WM-l 1. Footwall Footwall Copper Copper Intersections in WM-1 Interval Ni Interval Feet Cu Cu Ni Co Ag Au Pt Pd ppm ppm ppb ppb ppm ppm (ft.) (ft.) (ft.) (ft4 P P ~P P ~P P ~P P ~P P ~P P ~ppb P P ~ 1102.0-1 107.3 15 2.7 54 152 1102.0-1107.3 5.3 5.3 4872 237 15 2.7 54 59 152 1251.6-1252.7 1.1 19100 592 23 5.7 154 1251.6-1252.7 1.1 19100 592 23 5.7 99 69 69 154 1251.6-1262.1 1251.6-1262.1 10.5 10.5 5496 5496 1249.0-1328.2 1249.0-1328.2 79.2 79.2 1655 1655 421 421 144 144 19 22 22 12 12 2.7 2.7 0.9 0.9 43 43 21 21 23 23 99 69 37 �Results of ^ArP9Ar 40ArP9Ar laser laser microprobe microprobe grain-scale grain-scale age mapping Results of mapping of of muscovite muscovite from from Precambrian bedrock Precambrian bedrock of the southern Lake Superior Superior region HOLM, Daniel Daniel K., K., Department of Geology, HOLM, Department of Geology, Kent State University, University, Kent. Kent, OH OH 44242; 44242; V., and HURTADO, Jose, both at Department of Earth, Atmospheric, and HODGES, Kip V., Cambridge, MA, 01239 Planetary Sciences, Massachusetts Institute of Technology, Cambridge, 01239 step-heating mineral mineral ages collected collected in the 4OArP9Ar step-heating the The results results of of over over 100 100conventional conventional40Ar/39Ar 1990's 1990's from the southern Lake Superior region have greatly increased our understanding of the thermal and deformational deformational history of the crust crust following following the the Paleoproterozoic PaleoproterozoicPenokean Penokean Step-heating experiments, experiments,however, however,may may not not effectively effectively reveal reveal the internal orogeny. Step-heating distribution of radiogenic radiogenic argon within crystals, distribution crystals, but instead can mask mask important importantdetails details of of the the GCA). samples thermal history (Hodges (Hodges et al., 1994, 1994, Geology; Geology; Hodges Hodges and and Bowring, Bowring, 1995, 1995,GCA). step-heating experiments experiments on four We compare results of of previous previous conventional conventional 40Ar/39Ar 40ArP9Ar step-heating muscovite grains grains with with new new results results from from in in situ spot analyses analyses using using the Ar-ion Ar-ion laser laser muscovite microprobe (see table below; age in Ma, uncertainties at two sigma). Samnle s ?A!u2k 97CM7 97CM7 97CM13 97CM 13 96DR8 96DR8 97DR7 97DR7 Location LQ&Qll Republic, MI Dunbar, inb bar, WI Little Falls, WI Neillsville, WI Step-heating ae stemheathe .@g 1716±5 171 6 s plateau olateau 1366±6 iear-plateau near-plateau 1366&6 plateau 11614±5 6 1 4 s plateau 1518 total gas Age gradient 1707-1660 1373-1327 1373-1327 1652-1563 1652-1563 1923-1414 1923-1414 The form 97CM7suggests suggestsincorporation incorporationof ofexcess excess40Ar ^Ar form of of the the age agegradient gradient of of sample sample97CM7 along the grain boundaries. boundaries. Core Core spot spot ages ages of of 1660-1680 1660-1680 Ma Ma are are consistent consistent with a nearby nearby biotite plateau spectrum age (Schneider (Schneider et et al., al., 1996, CJES). CJES). Laser Laser microprobe microprobe results results from the other three samples samples reveal varying degrees degrees of age gradients gradients (see (see Figure Figure 11for forexamples). examples). Sample 96DR8, which yielded an excellent plateau age of 1614±5 1 6 1 4 s Ma, revealed a >90 m.y. my. age gradient. gradient. The The weighted weighted mean mean of the the 10 10 spot spot fusion fusion ages ages is is close close to to the the plateau plateau age. age. Step-heating therefore appears to have homogenized age gradients present in in this this sample. sample. 97CM13 gives gives aa near plateau plateau age of 1366±6 The spectrum of sample 97CM13 1 3 6 6 s Ma, but shows age increasing from from 1334 Ma Ma to to 1383 Ma. Ma. In increments generally increasing I n situ spot spot laser analyses analyses allow us to verify the existence of an age gradient (from at least 1373±12 1373k12 Ma to to 1327±9 1327BMa) Ma) with with significant clarity. Sample Sample97DR7 97DR7yielded yielded aa saddle-shaped saddle-shapedage age spectra spectra with with aa minimum minimum age age increment of 1484±2 Ma (Fig. I). increment of 1484zk2 Ma (Fig. 1). Ar-ion Ar-ion laser microprobe data reveals a spectacular 500 500 m.y. age gradient from core (oldest) to to rim. rim. The my. The youngest youngest ages ages preserved (down to 1414±21 1414±2 Ma) are are obtained from what what is probably a real grain boundary. A difficult problem in in interpreting interpreting 40ArP9Ar 4OArP9Ar age gradients is whether they formed formed during during slow cooling or resulted resulted from from superimposed, superimposed, episodic episodic reheating. reheating. If the entire core to to rim rim south transect, transect, Fig. Fig. 1) 1)reflects reflectssimple simpleslow slow gradient of sample 97DR7 (along the center to south then the implied implied cooling cooling rate rate is is about about 0.3 0.3 K1m.y. K/m.y. This cooling with volume diffusion, then This rate rate is is remarkably similar to the integrated cooling rate estimated for the Proterozoic terrain of the southwest United United States (Hodges et al., southwest a]., 1994). 1994). However, However, consideration consideration of the overall overall geologic context within which these dated samples exist suggests suggests aa more more complex complex episodic episodic thermal history. Case studies studies (i.e., (i.e., Hames Hames and and Cheney, 1996, 1996, Los) Bos) suggest that the form of history. Case grain-scale 'chrontour' 'chrontour' maps maps should should help help to distinguish between between simple and more detailed grain-scale complex thermal histories. histories. Whatever Whatever their their mechanism mechanism of of formation, formation, the the documentation documentation of large and quantifiable quantifiable age gradients gradients in this this study study indicates indicates promise promise for forobtaining obtaining more more detailed information about the Proterozoic thermal evolution of the the southern southern Lake Lake Superior Superior region. 20 �97DR7 Muscovite Muscovite 10000 C-) C, 0 '5 1550 C 0) 1500 1450 0 20 60 40 80 100 % Ar cumulative O h ^Ar cumulativereleased released , - , r , I . I 1 . , , , s 10000 10000 9GDRBMuscovite Muscovite 96DR8 100 100 10 10 I - , I I , , , . 1 , , , , I I . , , 8 , , , I I 96-DR-8 96-DR-8 Muscovite Muscovite - 1650 1 6~0 1600 1600 , I * s - I1, = 1614±5 Ma 1550 t91615Ma 1500 I 0 20 40 60 80 lao % cumulative released released % 30Ar ^Ar cumulative Figure 1. Figure 1.Spot Spotfusion, fusion,single singlecrystal crystalage agedata data(this (thisstudy) study)and andcorresponding corresponding conventional conventional incremental-release data (after Romano, Kent State M.S. thesis, incremental-release data Romano, thesis, 1999) 1999) for fortwo twomuscovite muscovite 97DR7 is coarse samples samples from from the southern southern Lake Lake Superior Superior region. region. 97DR7 coarse muscovite muscovite from from a muscovite gneiss of probable Archean age collected at Sylvan Lake west of Neillsville, muscovite gneiss of probable Archean collected Sylvan Lake west of Neillsville, Wisconsin. 96DR8 Wisconsin. 96DR8 isis muscovite muscovite from from aa late late pegmatite pegmatite dike dike collected collected at at Little Little Falls Falls south of Eau Claire, Wisconsin. Wisconsin. Grain images are video stills of individual (001) cleavage fragments Grain images are video stills of individual Ar-ion laser fusion micron-diameter (outlined), and the dots indicate the position of ca. 100 (outlined), and position 100 fusion pits, each labeled with its measured age (age uncertainties are variable but generally less age (age uncertainties are variable but generally lessthan than Unlabeled pits pits in in 96DR8 too little gas 10 Ma at two two sigma). sigma). Unlabeled 96DR8 produced produced too gas for for effective effective measurement. 21 �PRELIMINARY HYDROTHERMAL ALTERATION PRELIMINARY VOLCANOLOGY VOLCANOLOGY AND HYDROTHERMAL ALTERATION STUDIES STUDIESAT AT THE THE AND QUARTZ QUARTZHILL HILL PROSPECTS: PROSPECTS: FIVE MILE LAKE, EAGLES NEST, AND IMPLICATIONS IMPLICATIONS FOR FOR VMS-STYLE VMS-STYLE MINERALIZATION MINERALIZATION IN NORTHEASTERN MINNESOTA GEORGE .1. HUDAK GEORGE J. HUDAK Department 54901 Departmentof of Geology, University iversityof of Wisconsin Wisconsin Oshkosh, Oshkosh, Oshlcosh, Oshkosh, WI WI 54901 RONALD L. MORTON MORTON Geology Duluth, MA' MN 55812 55812 Geology Department, Department, University Universityof of Minnesota Minnesota—Duluth, -Duluth, Duluth, HENK DAHLBERG Minnesota Department MN Department of of Natural Natural Resources, Resources, Minerals MineralsDivision, Division, Hibbing, Hibbing, MN The Five The Five Mile Mile Lake, Lake, Eagles Eagles Nest, Nest, and and Quartz Quartz Hill Hill prospects prospects occur occur ininArchean Archean metavolcanic metavolcanic and and metasedimentary rocks rocks the the western western half half of the Vermilion District District of northeastern northeastern Minnesota. Minnesota. The metasedimentary TheFive FiveMile MileLake Lake prospects occur within the lower member of the Ely Greenstone Sequence, whereas the Quartz and the Eagles Nest prospects Hill prospect Detailed diamond relogging, Hill prospect occurs within the the Bass Bass Lake LakeSequence Sequence (Peterson, (Peterson, 1999). 1999). Detailed diamond drill core core relogging, petrography, and lithogeochemistry lithogeochemistry have have been been recently recently completed completed at at these these prospects prospects (Hudak (Hudak and and Morton, Morton, 1999) to: petrography, a) better understand the geology (in particular, particular, the physical physical volcanology) volcanology) associated associated with with these these prospects; prospects; b) b) identify identi& and evaluate the metamorphosed hydrothermal alteration mineral assemblages that occur at each of of these these prospects; prospects; and c) evaluate the potential for volcanogenic massive sulfide (VMS) and/or gold mineralization in in these these areas. areas. During our investigation, investigation, a total of eight eight diamond diamond drill drill holes holes from from the the three threeprospects prospects listed listedabove abovewere were and sampled sampled for petrographic petrographic and and lithogeochemical lithogeochemicalanalysis. analysis. Four diamond drill holes from the Five Mile relogged and Lake prospect prospect (SXL-1, (SXL-l, SXL-2, SXL-4), two two diamond diamond drill drill holes holes from from the the Eagle's Eagle'sNest Nestprospect prospect(EN-4 (EN4 SXL-2, SXL-3, SXL-3, and and SXL-4), EN-7), and two diamond diamond drill holes from the Quartz Hill prospect (QH-84-2 and QH-85-4) were relogged with and EN-7), an emphasis emphasis on identi'ing identifyinglithology, lithology,volcanic volcanicfeatures featuresand andtextures, textures,metamorphosed metamorphosedhydrothermal hydrothermal alteration alteration mineral assemblages, assemblages, and syn-volcanic thin sections (33 from Five syn-volcanic and post-volcanic post-volcanic fault zones. Sixty-four thin Five Mile Mile Lake, 18 from Eagles Nest, Nest, and 13 Lake, 13 from from Quartz Quartz Hill) Hill) were were evaluated evaluated for lithology, lithology, alteration alteration types, primary primary and textures, mineral modal analysis, and fragment secondary textures, fragment modal analysis. In In addition, addition, thirty-eight thirty-eight lithogeochernical lithogeochemical (both major and trace element) were were also also performed performed (22 (22 from from Five Five Mile Mile Lake, Lake, 10 from Eagles Nest, and 6 analyses (both from Quartz Hill). Hill). andesite/basalt lava flows and scoriaThe Five Mile Lake region is composed of massive to amygdaloidal andesitehasalt rich volcaniclastic deposits, locally quartz-phyric dacitic to rhyolitic lavas and flow breccias, and and volcaniclastic volcaniclastic and and chemical sedimentary sedimentary rocks. rocks. Quartz-feldspar Quartz-feldspar porphyry porphyry and and diahase diabase dikes are also present throughout chemical throughout the the volcanic volcanic and sedimentary sequence. textures indicate indicate that that these these rocks rocks likely sequence. Volcanic Volcanic textures likely were formed within a deep deep water water Hydrothermal alteration alteration minerals minerals include include epidote, epidote, iron-rich chlorite, magnesium-rich (>500meters) environment. Hydrothermal magnesium-rich Stringer and and semi-massive sulfide mineralization mineralization are are associated associated with with two chlorite, and quartz quartz (silicification). (silicification). Stringer semi-massive sulfide chlorite, assemblage, and and b) an epidote - iron distinct alteration assemblages: a) an early early iron-rich iron-rich chlorite chlorite - sericite sericite - quartz assemblage, iron carbonate assemblage assemblage associated associatedwith with late late sulfide sulfide remobilization. remobilization.The TheFive FiveMile Mile Lake Lake prospect prospect appears appears to to be be a carbonate "Noranda-type" VMS system based on on the criteria discussed by Morton and Franklin (1987). (1987). Two diamond drill holes in the Two diamond drill holes investigated investigated in the Eagles Eagles Nest Nest region region comprise comprise massive massive to toamygdaloidal amygdaloidal andesite/basalt lava flows and associated flow andesiteibasalt flow breccias/hyaloclastite, breccias/hyaloclastite, mafic mafic to to intermediate intermediatevolcaniclastic volcaniclasticsediments, sediments, Algoma-type mixed mixed facies facies (sulfide, (sulfide, oxide, oxide, silicate) silicate) iron iron formations Algoma-type formations and associated associated chert horizons, horizons, interbedded interhedded semi-massive to massive sulfide deposits, deposits, and rhyodacite rhyodacite to rhyolite tuffs and/or siltstone and debris flow deposits, semi-massive tuffaceous volcaniclastic porphyry intrusions intrusions and and diabase diabase dikes dikes are also volcaniclastic sediments. sediments. Quartz Quartz feldspar feldspar porphyry also present. present. textures suggest that the rocks in the area were also formed in a deep water Volcanic textures water (>500 (>500 meters) meters) environment. environment. A A massive sulfide is overlain overlain by by approximately approximately 2 meters (6 feet) of sulfide four meter thick intersection of pyrite-rich massive approximately 22 22 meters meters (73 (73 feet) feet) of of mixed mixedfacies faciesAlgoma-type Algoma-typeiron iron (py)-chert exhalite, which is overlain in turn by approximately formation. The The host host and and footwall footwall rocks rocks to to the sulfide sulfide mineralization mineralization comprise sericite-, iron-rich chlorite-, kaolinitecarbonate- (dolomite (dolomite andlor and/or ankerite) ankerite) and and locally chlorite-alteredfelsic felsic ash ash tuffs tuffs or tuffaceous carbonatelocally magnesium-rich magnesium-rich chlorite-altered tuffaceous volcaniclastic sediments. sediments. Based Based on on the volcanology alteration present, present, the Eagles Nest prospect volcaniclastic volcanology and hydrothermal hydrothermal alteration prospect represent aa "Noranda-type" also appears to represent "Noranda-type" VMS VMS system. system. - 22 - �The two diamond diamond drill holes investigated investigated at the Quartz Quartz Hill Hill prospect prospect comprise comprise amygdaloidal amygdaloidal to massive massive basalt/andesitelava lava flows, flows, mixed mixed volcaniclastic and chemical (including chert, chert, silicate-fades basaltlandesite volcaniclastic and chemical sediments sediments (including silicate-facies iron iron formation, oxide-facies iron formation), and felsic tuffs and/or andlor tuffaceous volcaniclastic sediments. sediments. Massive Massiveto tosemisemimassive sulfide sulfide mineralization mineralization occurs occurs between between 89 89 and and 150 feet feet in exploration diamond drill drill hole QH-84-2, exploration diamond QH-84-2, and is hosted within felsic felsic ash tuff or tuffaceous tuffaceous sedimentary sedimentary rocks. rocks. The relative abundance of felsic tuffs and The and tuffaceous tuffaceous material, coupled with hydrothermal alteration assemblages comprising andalusite, chloritoid, and hon-rich iron-rich chlorite, chlorite, suggests that that the the Quartz Hill mineralization suggests mineralization may represent represent either either a) aa "Mattabi-type" "Mattabi-type" VMS VMS system system (Morton (Morton and and Franklin, 1987); or or b) an ancient shallow subaqueous or subaerial high-sulfidation high-sulfidation system (White and Hedenquist, Franklin, Mattabi-type VMS VMS systems systems are characteristic 1990, Sillitoe et al., al., 1996). 1996). Mattabi-type characteristic of shallow shallow water water 1990, 1995; 1995; Sillitoe, Sillitoe, 1995; Sillitoe meters water water depth) depth) hydrothermal hydrothermal systems, systems, reflect reflect extreme extreme acid acid leaching leaching of the rocks by ((<500 6 0 0 meters by the the hydrothermal hydrothermal fluids, and and may he be analogous to "high fluids, "high sulfidation" sulfidation" epithermal epithermal systems within shallow water environments. environments. Such Such hydrothermal systems may produce gold-rich massive sulfide deposits (Hannington et et al., 1997). 1997). The results of this study indicate that the Vermilion region of northeastern Minnesota contains at least least two examples (Five (Five Mile Lake and Eagles examples Eagles Nest) Nest) of ofdeep deepwater, water,flow-dominated flow-dominated VMS VMSsystems systems(Noranda-type). (Noranda-type). The The Quartz Hill prospect may represent either a volcaniclastic dominated, shallow water "Mattabi-type" VMS system, or Continued re-evaluation re-evaluation of of a shallow subaqueous subaqueous or possibly possibly subaerial subaerial high high sulfidation-type sulfidation-type epithermal epithermal system. system. Continued mapping, diamond these these prospects prospects via detailed detailed field mapping, diamond drill core core relogging, petrographic analysis, analysis, and lithogeochemical studieswill willbe be performed performedduring duringthe the next next year year to further evaluate lithogeochemical studies evaluate and better better understand understand these potentially ore-forming hydrothermal systems. References References Hannington, M., Poulson, K. H., Thompson, J., & Sillitoe, R. H., (1997): Volcanogenic gold gold and and epithermal-style epithermal-style environment. In In Barrie, Barrie, C. C. T., T.,and Hannington, M. D. (Eds.), (Eds.), Volcanic mineralization in the VMS environment. Associated Massive Sulfide Deposits: Processes and Examples in Modern Modem and and Ancient Settings: Settings: GACGACMDD-SED Short Course Volume, 183-214. 183-214. J., & Morton, R. L., (1999): Bedrock and glacial drift Hudak, G. J., drift mapping for for VMS VMS and and lode lode gold gold alteration alteration in in the the Vermilion — Big Fork Greenstone Belt: Part A: Discussion of Vermilion -Big of lithology, lithology, alteration, alteration, and and geochemistry geochemistry atatthe the Five Mile Lake, Eagles Nest, Nest, and Quartz Hill Hill Prospects. Prospects. Minnesota Department of Natural Resources Project 326 Open File Report, 136 136 pages. L., & & Franklin, Franklin, J. J. M., M., (1987): (1987): Two-fold Two-fold classification of Archean volcanic-associated massive sulfide Morton, R. L., Geol., 82, 1057-1063. 1057-1063. deposits. Econ. Geol., D. M., (1999): Economic geology and lode gold and volcanogenic massive sulfide Peterson, D. sulfide prospects prospects of ofthe the western Vermilion District, St. Louis and Lake Counties, northeastern Minnesota. Minnesota Minnesota Exploration Exploration Conference 1999, Lode Gold and Massive Sulfide Sulfide Prospects Prospects in in the the Archean Archean Western Western Vermilion Vermilion District District of of Northeastern Minnesota, Abstracts Abstracts Volume, Volume, 3-5. 3-5. Fl., (1995): (1995): The influence of magmatic-hydrothermal models on exploration strategies Sillitoe, R. H., strategies for volcanoSillitoe, Deposits, Mineralogical In Thompson, Thompson, 3. J. F. H., H., (Ed.), Magmas, Mamas. Fluids, Fluids. and Ore Deoosits, Mineralogical Association Association plutonic arcs. In of Canada Short Course Volume 23,511-525. Sillitoe, R. H., H., Hannington, Hannington, M. M.D., & Thompson, Thompson, J.J. F. F. H., H.,(1996): (1996): High High sulfidation deposits in the volcanogenic D., & massive sulfide environment. Econ. 204-2 12. Econ.GeoL, Geol.,91, 91,204-212. White, N. C., &Hedenquist, 3. W., (1990): Epithermal environments and styles of mineralization: variations and J. W., and their causes, and guidelines for exploration. Jour. 445-474. Jour.Geochein. Geochem.Res., Res., 36, 36,445-474. N. C., & Hedenquist, J. 3. W., W., (1995): Epithermal gold deposits: deposits: styles, characteristics, and Exploration. SEG White, N. Newsletter, 23,9-13. Newsletter, 23, 9-13. 23 �MAGMATIC ORIGINS ORIGINS FOR FOR NATHAN'S NATHAN'S LAYERED SERIES: AN INITIAL REASSESSMENT REASSESSMENT OF OF MAGMATIC THE MIDCONTINENT RIFT'S FIRST FIRST MAJOR PLUTONIC MATERIALS JERDE, Eric JERDE, Eric A. (e.jerde@morehead-st.edu), (e.jerde@morehead-st.edu),Dept. Dept. of ofPhysical Physical Sciences, Sciences, Morehead MoreheadState State University, Morehead, KY 40351 Morehead, 4035 1 In recent years, great greatstrides strideshave havebeen beenmade madein indeciphering decipheringdetails detailsof ofthe the evolution of of the the Midcontinent MidcontinentRift Rift (MCR.),and andthe theemplacement emplacementof ofthe theDuluth DuluthComplex Complexintrusions intrusionsand andassociated associatedlavas. lavas. The The vast vast majority majority of of System (MCR), Ripley, 1996), material produced by the MCR was between 1099 1099and 1095 1095Ma Ma (Miller (Miller and Smyk, 1995; 1995; Miller and Ripley, an indication of how vigorous the system was. The Theearliest earliestmaterials, materials,however, however, were wereproduced producedininexcess excessofof88 years previously, previously, and and because because of their relative rarity are incompletely understood. understood. million years One of the most interesting period of rifting is is known known informally informallyas asNathan's Nathan's Layered Layered interesting intrusions of this early period Series after after the the work of Nathan (1969). HIs still stands as the most intensive study of the rocks, comprising His still stands as the most intensive study of the rocks,comprisingfield field descriptions, petrographic petrographic analysis, and some microprobe and optical determinations of m mineral compositions. No ineral compositions. No work has has been been performed performedon on any anyrocks rocksof ofthis thisseries. series. A U-Pb zircon date of 1106.9  ± .6 .6 Ma has been geochemical work obtained for one (Paces and Miller, 1993), confirming its antiquity in in the the MCR MCR. Nathan one of of the the units units of this series series (Paces Nathan (1969) identified 27 separate the letter designations A-Z and AA in their inferred separate units, which are given the the discordancies discordancies observed. observed. Nathan's chronological order based on the Nathan'sown owninterpretation, interpretation,plus plus those thoseof ofsubsequent subsequent observers, gradational variations, whBe while others others may be sparse dikes or observers,offers that many of the separate separate units may be gradational "sport" varieties, Nathan (1969). varieties, to to use use the theterminology terminology of ofNathan (1969). In terms of major magma bodies, bodies, the the series seriescomprises comprisesfour fourprincipal principalunits: units:A-B A-B(troctolites (troctolitestotogabbronorites), gabbronorites),G0 (oxide-rich olivinegabbro), gabbro),M M (gabbronorite), (gabbronorite), and andP-Q P-Q((troctolites troctolites to to gabbros). gabbros), These (oxide-rich olivine These units units are are present present in in amounts amounts great enough great enough to to permit permit their their being assigned as the principal events in the evolution of the series. Typical Typicalmodal modal abundances and m mineral compositionsfor forthese thesegroups groupsare aregiven givenininTable Table1.1. One One of of the the more more interesting interestingaspects aspects of of ineral compositions the presence of large amounts of of Fe-Ti oxides in many many of of the the units. units. There Thereare areseveral severalunits units that that this series is the occasionally have have in in excess excess of of 30% 30% Fe-Ti Fe-Ti oxides. oxides. Among Among the the major major units, only only Unit 0Gisisnotable notablefor foraahigh high abundance of oxide phases, in some locations exceeding 60%. 60%. This abundance Thisoccurs occursin in aa fairly fairly primitive magma (forming abundant olivine of of Fo.io.50 Fo,0 and andlittle littlequartz quartzororgranophyre), granophyre),resembling resemblingthe theother othermajor majormagmas magmasin inother otheraspects. aspects. 1. TyDical Tvoical Mineral Abundances Abundancesfor for NLS NLS and and Model ModelResults. Results. Table 1. Model g ! Q l & g Q e & & g fl IEli Q! AizQn&Qa Eiz Li! u A-B P-Q 42 42 53 53 Fo AAn6.e lien,; FRY? 58 58 33 An,4 Fo Feat 3 Mg9 Mg*4,9 -—- ~ % 4 3 M 59 --- 62 An555 32 Mg71 M&wl 13 _ 77 24--- Mg53 Mg An55.43 G 22 3 5 8 Fo 11 —- -_ 6kb 6kb 47 io, 10% An Afl63 .. — 46 Fo62 FO(Q 22 6kb 6kb 49 49 14 14 Fo F06o 4 An62 &2 51 6 5 1kb i 14 Mg3 !izAnQ -15% 6kb 2 Q Qi l An Fo 48 6 An54 Fo45 55 Mg, M ~È-~ 33 33 Mg --- M~ Mg5g 343 --2816 Mg.57 Petrographic data data from Nathan (1969). Petrographic (1969). Modelling of magma crystallization was was made made to to explore possible possible scenarios scenarios for for the the unusual unusual abundance abundance of of oxide oxide in the the material material comprising comprisingUnit UnitG. 0. This Thismodelling modelling was was done donewith with the the MAGFOX MAGFOX program program(J. (1.Longhi, Longhi, pers. pa. minerals in comm.). AAtypical typicalcomposition compositionof ofaa Logan Logansill sill (Table (Table 2) 2) was was used used as as aa parent parentsince sinceitit represents representsthe theonly onlycommon common composition in the region that is even remotely remotely coeval coeval(the (theLogan Loganssills havebeen beendated datedatat1108 1108-1./.2 composition that is ills have ; by Davis and and Sutcliffe, 1985). 1985). constraints are poor Nathan's series, series,some someinteresting interesting Although the constraints poor since since no liquid compositions are known for Nathan's features features of of the the modelling are present. Using Usingthe theLogan Logancomposition compositionofofTable Table2,2,materials materialsresembling resemblingthose thoseof ofunits units P-Q, can to 6 kb. In A-B, can be generated generated through through crystallization crystallization at depths depthscorresponding corresponding to Inthis, this, A-B A-B and and P-Q A-B, M, and P-Q, P-Q 24 �I I I   I M after crystallizatiow These shown in can can be be formed fanned after after 10-15% 10-15% crystallization, crystallization, and and M after —25% -25% crystallization Theseresults results are are shown in Table Table I1 adjacent to the the petrographic petrographic observations of Nathan Nathan (1969). (1969). In adjacent to observations of Inthis thismodel, model,the theoxide oxidephases phasesappear appear after after28% 28% crystallization, are moderately moderately abundant abundantthereafter, thereafter,consistent consistentwith withthe thefe few percentofofoxides oxidespresent presentininP-Q P-Q.ItIt crystallization, and and are w percent is interesting interesting to to note existed at at 66 kb, kb, then then the the P-Q P-Q magma must mustbe beolder olderthan thanM, M, in in that ififonly onlyone onemagma magma chamber chamber existed is note that contradiction to the or that that contradiction to the original original mapping. mapping. IfIfNathan Nathan(1969) (1969)isiscorrect, correct,ititimplies impliesthat thatmultiple multiplechambers chambers existed, existed, or recharge was was taking taking place, place, both both of of course course plausible. plausible. At recharge At 66kb, kb,oxides oxidesdo donot notform formininabundances abundancesakin akintotothose thoseseen seen in in >50% crystallization, that point, the 0 until until >SO% crystallization,and and at at that point, the the liquid liquid isis far far more moreevolved evolved than than could could have have produced produced the Unit G responsible for for the the smaller intrusive dikes to other other minerals other minerals seen. seen. Such Such liquids may be be responsible smaller intrusive dikes and and sills sills assigned assigned to other units units enlarge the stability field for and modelling at I kb showed oxide phases, by Nathan. However, lower pressures by However, lower pressures enlarge stability field for oxide and modelling at 1 suggested by by the model 0 are ilmenite appearing appearing after afterless less than than 20% 20% crystallization. crystallization. Materials Materials akin akin to those of Unit G are suggested ilmenite crystallization, Thus 0 may evolution in shallower magma chamber. after after approximately 40% crystallization Thus Unit G may reflect evolution in aa shallower chamber. The tremendous variation and the the gradational gradational nature nature of the rocks is The tremendous variation in in cumulate cumulate textures on on aa small small scale, and rocks is of (and presage) the the later later Anorthositic Anorthositic Series Duluth Complex reminiscent reminiscent of (and in in this this case case may presage) Series rocks rocks of the the Dulutb Complex suggested suggested to to have formed formed as asinjections injectionsof of plagioclase plagioclasecrystal crystalmushes mushes(Miller (Millerand andWeiblen, Weiblen,1990). 1990). Thus, Thus, the the rocks rocksof of Nathan's Nathan's have Layered Series representmaterial material (of (of Logan Logan composition?) in the Layered Series may represent composition?) that that was was emplaced emplaced at at several several levels levels in the crust crust in in the initial phases of rifting. Evolution in these disparate chambers would lead to some magmas having unusual the initial phases of rifting. Evolution in these disparate chambers would lead to some magmas having unusual amounts amount's of nxidm ..--- of -.oxides. -.----. It composition similar It isis interesting interestingto to note note that that the the models models produced produced a liquid composition similar to to the the Grand Grand Portage Portage dikes (composition given Green al., 1987) after after35-40% 3540% crystallization 0. (composition given by G reen etetal., crystallization at at 1kb, lkb, roughly roughly equivalent equivalent to that of Unit G. Perhaps theGrand Grand Portage PortageDikes Dikes are arethe thehypabyssal hypabyssalsibling siblingofofthe theplutonic plutonicUnit Unit G 0 seen further inland. Perhaps the seen farther inland. may - F Table 2. Paren t ('am nnsitinn IIwit in M odelling and one result I wt nerrenti MnO MaO Na,O !c22 un!! 1Q2 1122 A1223 1Q fzQs Logan Login 49.0 49.0 3.40 3.40 13.1 13.1 15.6 15.6 0.22 0.22 5.60 7.45 2.52 2.52 1.16 1.16 0.38 40% 53.9 2.49 13.3 15.1 0.25 2.11 7.07 2.96 1.82 0.62 Grand 52.5 Grand 52.5 Portage Portage 2.48 13.4 13.4 13.3 '13.3 0.19 0.19 3.68 3.68 6.72 6.72 3.17 1.79 1.79 0.48 0.48 @1kb Logan composition from from Geul Logan composition Ged (1970). (1970). Grand of 17 Grand Portage Portage isis an average of 17dikes dikes (Green (Greenet al., 1987). 1987). Citedi References Cited: ItH.,1985, U-Pb Davis, D.W. and Sutclift'e, Sutcliffe, RH.,1985, U-Pb ages ages from the Nipigon Plate and and northern northern Lake Lake Superior: Superior: Geological Geological Society of Davis, AmericaBulletin, 96,1572-1579. 1572-1579. America Bulletin, v. 96, of Mines, Mines, Geological Geological of Devon Location: Ontario Geul, J.J.C., J.J.C., 1970, 1970, Geology of Devonand and Pardee Panfee Townships and Stuart Location: Ontario Department of Geul, Report 52p. Rewrt 87, 87.520. RE., Pesonen, and Wilband, Green,k., Bomhocst, Ti., T.J.,Chandler, Chandler, V.W., Mudrey, Mudrey, MJ., Mya-s, P.E., PisaKtt.LJ., Wilband,J .T., 1987, 1987, Mi., Jr., Myers, Li,, aud iC., Bomhorst IT., Region: Evidence Evidencefor forevolution evolutionof of the the Middle Middle Proterozoic Proterozoic Midcontinent Mideontinent Rift Rift in Keweenawan Keweenawan Dykes of the Lake Superior Region: in 289-302. North America, in Halls, North Halls, H.C. KC.and and Fahrig, Fahrig,W.F., W.F., eds., cds., Mafic MaficDyke DykeSwarms: Swarms:Geol. Geol.Soc. Soc. Canada Camda Spec. Spec. Paper Paper 34, 34,289-302. examples of Wieblen, P P.W., Anorthositic rocks of the D Duluth Miller, J.D., Jr. and Wieblen, .W.,1990, Anorthositic ulufliComplex: Complex: examples of rocks rocks formed formed from &omplagioclase plagioclase Miller, 3D., Jr. Petrology, v. v. 31.295-339. 31,295-339. crystal crvstalmush: mush: Journal of Prtrolotv. Trip Guidebook for in Field Tnp Miller, M.,,1995, Gabbroic intrusions M ~ I IJ.D., ~D. JJrJr. and Smyk, St& M 1995,Gabbroic mmisioiis of the the international mieniatid boundary area, in forthe die region: Minnesota Geoloacal Geological Survev Swvey Guidebook geology deposits of of the Midcontinent emloev and ore dcoosits Mdcooement Rift Rift in m the Lake Lake Superior Suoenorrefflon, ~Series e r iNo. e ~20,171-181. 20, ~ o171-181 . USA, In 1996, Layered intrusions Miller, J.D., J.D., Jr. and bley, intmions in in the Duluth Duluth Complex, Complex,Minnesota, Minnesota, USA, in Cawthorn, Cawthoin, KG., ed., Miller, Ripley,EM., EM., 19%. ItO., ed., Layered Intrusions: Amsterdam. Amsterdam, Elsevier, Uvered Intrusions: Elsevier, 257-301. 257-301. Cook County, The geology geology of a portion portion of the the Duluth Duluth Complex, Cook County,Minnesota: Minnesota: Ph.D. Ph.D. dissertation, dissertation.University University ~ a t h a H.D., n . - ~1969, . ~ . , The Nathan, Minneapolis, l9Sp. of Minnesota, Minnesota. Minueawlls. 1980. related mafic mafic intrusions, northeastern J,D., U-Pb ages Paces,J.B. and ~Miller, i e rJ.D.: , Jr., 1993, 1993"Precise Precise U-Pb ages of ofDuluth Dulufli Complex and related intrusions, northeastern Paces, Minnesota: Minnesota:Geochronological Geochronologicalinsights insightstotophysical, physical,petrogenetic, petrogenetic,paleomagnetic paleomagncticand andtectono-magmatic tectono-magmaticprocesses processes associated associated Midcontinent Rift System: of Geophysical GeophysicalResearch, Research,v.v,98,l3,997-14,013. withthe with the 1.1 1.1Ga MidcontinentRift System:Journal of 98,13,997-14,013. . I . - 25 - �INTRUSIONS OF OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION: REGION: TARGETS TARGETS FOR FOR SMALL MAFIC INTRUSIONS TITANIUM EXPLORATION KARKKAINEN, Nub, Geological -E N, Niilo, Geological Survey Survey of Finland, 02150 Espoo, Espoo, Finland; Finland; BORNHORST, BORNHORST, Theodore, J., Department of Geological Engineering and Sciences, Michigan Technological University, University, Houghton, oughto on, MI MI 49931 4993 1 - magmatic ilmenite deposits are often in or closely associated with Globally, high-grade magmati anorthosite complexes. Large layered mafic intrusions host Ti-rich magnetite in Fe-Ti oxide anorthosite rocks. There There are are many mafic intrusions intrusions throughout throughout the Lake Superior Superior region that range in in age age from Archean to Proterozoic. However, most of these intrusions are not associated with However, many are are relatively relatively small. small. Despite these characteristics, small mafic anorthosite complexes and many amounts of Ti, based intrusions of the Lake Superior Superior region have the potential to host significant amounts on analogy with a recently documented documented occurrence occurrence in in Finland. Finland. The Finnish Koivusaarenneva Koivusaarenneva gabbro is a small mafic intrusion, not associated with an anorthosite complex, that contains inferred resources of 44 Mt with 15 % ilmenite and 5% V-rich magnetite 50m (an (an additional additional 44 44 Mt Mt are arepossible possible to to aa depth depth of of magnetite (0.7 (0.7 wt. wt. % % V) V) to aa depth depth of of 1150m 300m). The Thefeasibility feasibilityof of mining mining this this ore ore body body is is currently currently being investigated by a Finnish mining mining company. company. Koivusaarenneva gabbro is an elongated sill-like intrusion, 0.5 to 1 km thick and 3 The Koivusaarenneva km long long parallel to strike. strike. The Theintrusion intrusionproduces produces aa 44 mGal mGal gravity gravity anomaly anomaly and a clear clear NE-SWNE-S oriented aeromagnetic anomaly anomaly in the low-intensity low-intensity background. The intrusion was emplaced at 1881 Ma Ma into tonalitic bedrock and is part of a gabbro province province interpreted to to have formed in tensional zones zones in in the the vicinity vicinity of of or or marginal to to convergent convergent plate boundaries. boundaries. The The Koivusaarenneva gabbro is part of a 12 km long chain of intrusions that were emplaced along along a Koivusaarenneva 12 krn NE-SW oriented oriented fault fault zone. The The intrusion intrusion is is mostly composed composed of of modally modally layered layered mediummediumgrained and metamorphosed metamorphosed gabbro and gabbronorite. The magmatic layers have been tilted to a subvertical orientation and faults faults segment segment the intrusion. The intrusion is divided into into three three zones zones on the basis of geochemistry geochemistry and petrography. Fe-Ti oxide-rich layers are common in the lower middle zones. ratioisisconstant constantfor forall allrock rocktypes types in in the the lower zone at and middle zones. The TheTi02/Fe2O3TOT Ti02/FezOsToT ratio about 0.2. The Themiddle middlezone zonecontains containsthe the 22 km km long long ilmenite ilmenite ore body that grades between 8 and an ratioofofthe themiddle middlezone zoneisisbetween between0.25 0.25and and0.50. 0.50. The The upper upper 48% ilmenite. ilmenite. The TheTiO2/Fe2O3TOT Ti02/Fe203ToT ratio zone consists consists of P-rich gabbro and leucogabbro. gabbro The genetic genetic model model of the intrusion intrusion and ore body begins with primary tholeiitic tholeiitic mafic mafic magma emplaced emplaced in a deep deep magma chamber at or near the base of the crust. In the deep chamber, crystal-liquid crystal-liquid fractionation, fractionation,under under conditions conditionsof ofvery verylow lowf02, fm, generated Ti-enriched parent magma averaging about 3.3% TiOz. Ti02. This parental magma was was successively successively injected injected into into each each of of the three zones zones of the the intrusion. intrusion. Variation Variation within the lower lower and upper zones is consistent consistent with with closed-system closed-system crystal-liquid crystal-liquid fractionation fractionation of two separate separate batches of magma magma from the deep deep chamber. chamber. The middle zone contains the voluminous voluminous ilmenite ore. The overall composition of nonnon non-mineralized gabbro mineralized gabbro from the middle zone is compositionally compositionally similar to non-mineralized gabbro 26 �from the lower zone, however, the weighted average composition composition of the middle zone is Fe than than the the weighted weighted average averagecomposition compositionof ofthe thelower lowerzone. zone. The considerably higher in Ti and Fe volume of magma magma in the the middle middle zone zone is is far far too small small to yield the the large large mass mass of of ilmenite ilmeniteunless unless the parent magma had extreme extreme Ti and Fe. Instead, the extreme excess excess of Ti and Fe Fe in in the the middle middle zone can be explained explained by a parent magma with elevated, but rather normal Ti and Fe Fe (like (like the the lower and upper zones) that flowed through the partly crystallized magma chamber. After an zones) crystallized chamber. After an oxide-rich immiscible immiscible liquid was was extracted from the magma this this dense dense material material sank sank to to the the floor floor of the shallow magma chamber to form a Fe-Ti oxide rich matrix between a silicate framework. shallow magma chamber form oxide silicate framework. The Ti and Fe depleted depleted magma magma was then replaced by a new batch of parent magma magma and and so so on. on. . The middle middle zone zone represents represents a channel channel for for magma flow with multiple multiple episodes episodes required required for for accumulation accumulation of the large mass mass of of oxides. A similar similar magma magma flow flow through through model model has has been been proposed to generate generate gabbro-hosted gabbro-hosted Ni-POE Ni-PGE sulfide sulfide mineralization mineralization at Norilsk, Norilsk, Russia Russia (Naldrett (Naldrettet et al., 1996) 1996) and Voisey's Bay, Canada Canada (Evan-Lamswood (Evan-Lamswood et al., 1998). 1998). an For Ti-deposits in small mafic intrusions, an open magma flow through system system is is an essential essential genetic genetic component component to produce produce economic economic size size deposits. Continuity Continuity of of gabbro gabbro intrusions intrusions as a chain or along a fault zone is a favorable geologic geologic setting. setting. An An overall overall elevated elevated Ti Ti content content of of non-mineralized non-mineralized gabbros gabbros is is another another favorable favorable characteristic characteristic indicating elevated elevated Ti in in the the parent parent magma. Small mafic intrusions of the Lake Superior region can be tested for potential to Small mafic intrusions of the Lake Superior can tested for potential to host host Ti Ti resources using an an exploration exploration model based on the Finnish Koivusaarenneva Koivusaarenneva gabbro gabbro intrusion. intrusion. 27 �ADDITIONAL PALEOMAGNETIC STUDIES OF OF A A PROTEROZOIC PROTEROZOIC DIABASE DIABASE DIKE, PIFTIER AND ANDIRWIN IRWINTOWNSHIPS, TOWNSHIPS,LAKE LAKE NIPIGON NIPIGON DISTRICT, DISTRICT, ONTARIO IN PIFHER Kean, W. F., Department Department of of Geosciences, Gwsciences, University University of of Wisconsin-Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, WI WI 53201, and Luther, F., Geology Geology Department, UW UW Whitewater, Whitewater, Whitewater, Whitewater, WI WI 53190 53190 An approximately 50 m wide porphyritic diabase dike outcrops outcrops in and Pither in western westernIrwin Irwinand Pier Townships in the Nipigon district and is locally known as greenspar. The dike has a characteristic Townships the Niigon district and is locally known as greenspar. characteristic outcrop as a result of saussaritized greenish mottled appearance in outcrop saussaritizedplagioclase glomerophenocrysts in in aadiabase diabasegroundmass groundmass(Luther, (Luther, 1997). 1997). The dike strikes due north and dips dips vertically, and is is found foundas assegments, segments,off-set off-setby byeast-west east-westfaulting faulting(Mackasey, (Mackasey,1975). 1975). There There are are no radiometric this rock or radiometric dates dates on this or associated associated rocks, rocks,although, although,itit isiscut cutby by aalarge largemiddle middle or or late late Proterozoic sill Proterozoic sill in Irwin Township (Mackasey, 1975). 1975). We previously reported reported palco magnetic studies on on four sites f from (Thomas and paleomagnetic rom this area (Thomas others 1998). Five additional sites were collected in the summer of 1999, primarily others 1998). Five additional sites were collected in the summer of 1999, primarily from from locations locations Pither Township. The The nine nine sites sites span span approximately approximately27km. 27km.of ofthe thedike. dike. Samples Samples from each in Piflier location were subjected suljected to (A.F.) and thermal demagnetization demagnetization. The to both both alternating alternating field (A.F.) The samples samples demagnetization temperatures show one one primary magnetic direction which is removed at demagnetization temperaturesof of 5100 570 C. A.F. A.F. demagnetization demagnetizationof ofsamples samplesup up to to60 60mT, mT,also alsogives givesonly onlyone onedirection directionof ofmagnetization.. magnetization the magnetometer the samples are quite viscous and require a long wait time in the However, the between measurements. All All but two two locations locationsshow shownormal normal polarity polarity with with northwesterly northwesterly declinations (200°-300°) and inclinations of 40° to 80°. One site in southern declinations (200"-300") and inclinations 40" to 80'. One site in southernPifher PifterTownship Township appears 100°, and appears to to be be reversally reversallymagnetized magnetizedwith withdeclinations declinationsof of90° 90"totolOOo, andinclinations inclinationsof of -75°. -75'. The The southern southern most location near Beardmore produces producesinconsistent inconsistentresults. results. Overall, the themagnetic magnetic directions directions are are consistent with Keweenawan paleomagnetic paleomagnetic directions directions in the Lake Superior SuperiorRegion. Region. References References Luther, F., 1997, Pither. 1997,The The Petrology Petrology of of Greenspar: Greenspar: A A Proterozoic Proterozoic Porphyritic Diabase Dike; Pifher and Irwin Townships, Lake Nipigon Nipigon District, District, Ontario., Ontario., [abstract]: [abstracti: Institute on Lake Superior Geology Proceedings, Proceedings,v.v.43, Part l,p. 43, 1,p. Macjçasey, W.O., 1975, Gwlogy Geology of of Dorothea, Dorothea, Sandra, and Irwin Townships, District of Thunder Mackasey, W.O., Bay; Ontario division of Mines, rpt rpt 122 2294, 83 p. 122 with map 2294,83 Kean, W., W.,and and Luther, Luther, F., F., 1998, 1998,Paleomagnetic Paleomagnetic Studies Studiesof ofaaProterozoic ProterozoicPorphyritic Porphyritic Thomas, C., Kean, Diabase Dike, Pifher Nipigon District, District, Ontario.,[abstract]: Ontario.,[abstractj: Institute P i i and Irwin Townships, Lake Nipigon Institute on on Lake Superior Part 1 l,p. ,p. 119. 119. Superior Geology Proceedings,v.44, Part 28 �PETROGENESIS PETROGENESIS OF OF THE THE MIDCONTINENT MIDCONTINENTRIFT RIFTGRANOPHYRIC GRANOPHYRICCOMPLEXES COMPLEXESOF OF NORTHERN NORTHERNMINNESOTA MINNESOTA ---- - - Kennedy, & Wirth, Kennedy,Bryan Bryan C., C., (bkennedy@macalester.edu) (bkennedy@macalester.edu) & Wirth,Karl Karl R., R., Geology Department, Macalester College, St. Jeff D., St. Paul, MN (wirth@macalester.edu); Vervoort, Vervoort,Jeff D., Department Department of Geosciences, University (vervoort@geo.Arizona.edu) University of of Arizona, Arizona, Tucson, Tucson, AZ AZ (vervoort@geo.Arizona.edu) The The hypabyssal hypabyssal granitic granitic rocks rocks of northeastern Minnesota, Minnesota, commonly commonly referred referred to to as as granophyres, granophyres, are are an an important important component component of of the the Midcontinent Midcontinent Rift Rift (MCR) (MCR)of of northeastern northeastern Minnesota. Minnesota. InInthis thisstudy study we we examine examine eight eight intrusive intrusive complexes complexes associated associated with the the rift, rift, including including detailed detailedtransects transects across across the the Misquah Misquah Hills Hills and and Greenwood Greenwood Lake Lake granophyres. Evidence Evidence from petrographic, major and trace element element data data suggest suggest a combination of of magma magma mixing, chemical differentiation, and partial melting melting of of MCR MCR and and older granophyrecomplexes. complexes. older crust crust to to form form the thegranophyre The in 30to to150 150km km in The granophyre granophyre complexes complexes are generally concordant intrusions intrusions that thatrange rangefrom from 30 surface area and are up up to to 1000 meters metersthick. thick. The The complexes basaldiorite, diorite, monzodiorite, monzodiorite, complexes typically consist of basal and quartz monzodiorite monzodiorite and and upper uppergranite graniteand andgranodiorite. granodiorite. The The contact contact zones zones between the mafic and felsic rocks are are compositionally compositionally and and structurally structurally heterogeneous; heterogeneous; evidence evidence of ofmutual mutual intrusive intrusive relationships relationships between between the mafic mafic and and felsic felsic rocks can often be found within the the same same outcrop. outcrop. Porphyritic Porphyriticrhyolire rhyolite overlies granitic of the the complexes complexes (e.g., (e.g., Misquah Misquah Hills, Hills,Greenwood Greenwood Lake, Lake, Eagle EagleMountain, Mountain, granitic rocks rocks of several of and Lima Lima Mountain). Mountain). Thus Thusfar, far,only onlyone oneof ofthe thecomplexes complexeshas has been been dated dated (Swamper (SwamperLake=Greenwood Lake=Greenwood Lake granophyre, granophyre, 1107 1107 Ma Ma ±Â1.1, reversed magnetic polarity; Davis and Green, 1.1, reversed magnetic polarity; Davis Green, 1997); 1997);the the other othercomcomplexes are undated but are generally considered considered to to have have normal normal magnetic magnetic polarity, polarity,with withthe the exception exception of of the the Misquah MisquahHills Hillsbody bodywhich whichisispossibly possibly reversed. reversed. The monzodiorite, monzodiorite, monzodiorite, and diorite) diorite) are The mafic maficrocks rocks of the complexes complexes (e.g., quartz monzodiorite, are distindistinguished by by abundant (15-35 vol.%) significant (1 (1-3 vol.%) apatite. apatite. The -3 vol.%) Thefelsic felsic vol.%) interstitial pyroxene and significant rocks sodic plagioclase plagioclase (30-40 (30-40 vol.%), vol.%), orthoclase orthoclase (25-35 vol.%), and quartz (20-30 (20-30 vol.%). rocks are composed of sodic vol.%). Plagioclase Plagioclase commonly exhibits exhibits normal normal and andoscillatory oscillatorycompositional compositionalzoning; zoning;many manyplagioclase plagioclasegrains grainsare are mantled mantled by by thin thinrims rimsof ofsodic sodicplagioclase. plagioclase. Anhedral Anhedral pyroxene pyroxene and andsmall smallFe-Ti Fe-Ti oxides oxides make make up up less less than than 10% 10% of the rock. All All of of the the rocks rocks in in the the complexes complexes are characterized characterized by granophyric intergrowths of alkalifeldspar feldspar and and quartz. quartz. Intergrowths Intergrowths are are interinter_________________________________________________ 10.0 stitial or more commonly .. stitial between between plagioclase plagioclase or more commonly radiate radiate from from euhedral euhedral plagioclase phenocrysts. phenocrysts. -quartz monzodiorite, monzodiortie, and diorite n monzodiorite, diorite • 8 0 lntergrown quartz ranges from coarse and Intergrown quartz ranges from coarse and mimioo -granophyric -granophyricgranite graniteand and granodiorite granodiorite 7.0 crographic crographiccuneiforms cuneiformsto to fine fine and andradially radiallygragranophyric $ 6.0 6.0 o O nophyricshapes. shapes. The granophyre complexes Thegranophyre complexesdisplay displayaa wide wide 5.0 5Q5.0 0 S silica ino 0 o b $ ' % As %). As inSiO2 (47-76 wt range of range of Si02 (47-76 wt %). cc$°°o 4Z 4.0 4.0 creases, TiOz, MnO, MgO, CaO, and creases, 1107, Fe203, CaO, and 33.0 0 2 0 increases. There P20sdecrease, whereas K P205 K20 There 20 2.0 • m • hare notable compositional "gaps" in lincompositional "gaps" in the lin• .^ ~ ~ 10 l . •~ % ear trends on Harker variation variation diagrams diagrams be0.0 tween the the mafic mafic and and felsic felsic portions portions of each each of of 65,0 55.0 60.0 55.0 60.0 65.0 70.0 75.0 50.0 the complexes (Figure 1). Although rocks in (Figure 1). Although rocks S (w - .i n- 7 (wt,%) .. r... % .,l Si02 the lower complexes have have relalower portions of the complexes relaFig. II - K20 K 2 0(wt. (wt.%) %) versus versusSi02 (wt.%) %)diagramfor diagramforall allsamples Si02 (wt. samples tively low Si02 (47-62 wt. /o) most are tively Si02 (47-62 wt.%) are silica silica illustrating the compositional compositional from the granophyre ganophyre complexes, complexes, illustrating over-saturated over-saturated and all but two two samples samples congap between the rocks of ofthe the intrusions. intrusions. Note the mafic and felsic felsicrocks Note tam normative quartz. The granitic rocks tain The granitic rocks in trend of the major element element variation variation with increasing the linear trend the the upper portions of the complexes are SiO the upper portions of the complexes are SiO z2SiOz.Full Fulldata dataset setin inKennedy Kennedy (2000) (2000) Si02. 1 - ~ Za?aj o & +',PQJ .-• •• ~ - - \ . . . 29 �rich (66-76 wt.%), and and are are slightly to metaluminous metaluminous to slightly 2.0 2.0 1.8 0 1,8 peraluminous. peraluminous. The The mafic mafic and and felsic felsic 1.6 0 - rocks plot along linear — linear trends trends on on most most —— F 1.4 incompatible incompatible trace trace element elementdiagrams diagrams .975 0 0 (e.g., U, U, Nb, Ce, (e.g., Ce, and and Zr Zr vs. vs. SiO SiO2); 2); Q 1.2 0 LZ .950 compositional compositional"gaps" "gaps" between between the the mamaI.0 • -quartz -quartz monzodiorite, monzodiorite,monzomonzofic evident in fie and and felsic felsic rocks rocks are also evident in 0.8 diorite, and diorite these these plots. plots. The Themafic maficand andfelsic felsicrocks rocks o granophyric granite and 0.6 0-6 from from all of the granophyre granophyre complexes complexes granodiorite exhibit -mixing 0.4 trend; exhibit negative negative Nb-anomalies Nb-anomalies on on 0.4 mixing trend; values values at at tick tick ,— marks indicate the fraction of multi-element variation variation diagrams. diagrams. o,7 marks indicate the fraction of 0.2 felsic component component The Th/Nb and The small small variation variation in in the the Th/Nb and ______________ 0.0 M 50.0 £00.0 150.0 200.0 250.0 M 50.0 100.0 150.0 200.0 250.0 Ce/Nb ratios between the the mafic mafic and Ce/Nb felsic rocks suggests that the source of S iO 2/C aO felsic rocks that the source SiOzICaO the hyperbolic Fig. Fig. 22 - KzO/Fe203* KzO/FeaO3* versus versus SiO2/CaO SiOdCaO diagram showing the hyperbolic the the Nb Nb depletion depletionisis common common for both mixing trend for all samples from the granophyre concordant mixing trend for all from the granophyre complexes, concordant the mafic and felsic rocks. the mafic and felsic rocks. withhmixing mixing model. The Themixing mixingmodel model isis based based on on two two end endmember member Although , ~ ~ the the~major ~ ~ ~with majorh element parental compositions (triangles), Sonju Lake (M) and parental compositions (triangles), the intrusion (M) and an an variation variation might mightbe beexplained explainedby bycryscrysaverage of the three most felsic granitic samples (F). (F). The dashed line isis The dashed line average three most tal tal fractionation fractionationofofaatypical typicalMCR MCRmamathe the NSVG the mixing model with the NSVG olivine olivinetholeiite tholeiiteasasthe themafic maficcompowmpofic fie component, component, itit seems seems unlikely that nent, nent,which which isis not not concordant concordantwith with the the data. data. fractionation fractionationofofmafic maficmelts meltscould couldacaccount 10.15% of the intrusive rocks countfor for the theformation formationof of this this large large volume of granitic rock (approximately 10-15% of SiO 27(e.g., (e.g., of the the MCR MCR exposed exposed in northeast northeast Minnesota). Minnesota). Furthermore, Furthermore,on onplots plotsof ofmajor major elements elements versus versus SiO K20; change during during thetrend trendof ofthe thedata datashould shouldchange changein inslope slope as as the the fractionating fractionatingassemblages assemblages change K20;Figure Figure 1) 1) the crystallization. of SiO SiO 22 concentrations concentrations which crystallization. Instead, Instead, the thedata dataplot plotalong alonglinear lineartrends trends over over aa wide range of may may indicate mechanical mixing. mixing. On Ondiagrams diagrams of of major element ratios, the themafic maficand andfelsic felsic rocks rocks plot along vs.SiOz/CaO, SiO2/CaO,Figure Figure2). 2). These These trends trends can be modeled modeled by along hyperbolic hyperbolic trends trends (e.g., (e.g., K2O/Fe2O3* K2O/FezOj* vs. mixing of a mafic mafic (Miller (Miller &Chandler'scomposite & Chandler's composite Sonju Sonju Lake intrusion intrusion parental parental magma (1997)) (1997)) and and felsic felsic (average (average of the the most most evolved evolved samples samples from the granophyre complexes) end-members. IfIf aa more more primitive primitive olivine olivinetholeiite tholeiitefrom fromthe theNSVG NSVGisisused usedas asthe themafic mafic end end member, member, the the resulting resulting model does not fit fit the the data data for for the the granophyre granophyre complexes. complexes. Samples Samplesthat thatdo donot notplot plotalong alongthis thismixing mixingline linelikely likely evolved evolved from mixing products SiO2/CaO z/CaOand andK1O/Fe2O3. K20/Fe203. productsby by fractional fractionalcrystallization, crystallization,which whichwould wouldincrease increaseSiO An A n origin origin for for the the granophyre granophyre complexes complexes by mixing is consistent with the field relationships relationships and and linear trends trends on on major major element elementdiagrams. diagrams. However, However,although although aa combination combinationof ofmagma magma mixing mixing and and fracfractionation tionationmay may explain explainthe theorigin originof ofthe thegranophyre granophyrecomplexes, complexes,itit does does not not explain explainthe thesource sourceof of the thelarge large volume of felsic end-member necessary for mixing. Nd isotope data from the granophyre complexes volume of Nd isotope data from the granophyre complexessugsuggest that that the thefelsic felsic component component may may be be the the result result of of fractionation fractionation or or melting melting of of contemporaneous crustal materials (Vervoort, (Vewoort, this volume). Further Further examination examinationisisneeded neededto todetermine determinean anultimate ultimatesource sourcefor for the the felsic material material and and it's it's relationship relationshiptotothe thegenesis genesisof ofthe thegranophyres. granophyres. * ,-- - References References Davis, Green, J. C. 1997. North American 1997. Geochronology Geochronology of the North American Midcontinent MidwntinentRift Riftininwestern westernLake LakeSu Su Davis, D. W. & Green, perior perior and andimplications implicationsfor forits itsgeodynamic geodynamicevolution, evolution,Can. Can.J.J. Earth EarthSci. Sci.34: 34:476-488 476-488 Kennedy, Kennedy, B.C. 2000. 2000. Petrogenesis Petrogenesisofofmidcontinent midcontinentrift riftgranophyres: granophyres:evidence evidencefrom fromgeochemistry geochemistryof ofKeweenawan Keweenawan granitic northern Minnesota. MacalesterCollege, College, graniticigneous igneous complexes complexes of northern Minnesota. Senior SeniorHonors HonorsThesis, Thesis,Macalester Saint SaintPaul, Paul,MN. MN. Miller, J.D. & Chandler, V.W. Miller,J.D. &Chandler, V.W. 1997. 1997.Geology, Geology,petrology, petrology,and andtectonic tectonicsignificance significanceofofthe theBeaver BeaverBay BayComplex, Complex, northeastern, 3 12. northeastern,Minnesota. Minnesota.Geological GeologicalSociety SocietyofofAmerica AmericaSpecial SpecialPaper Paper312. 30 �A A POSSIBLE POSSIBLESUDBURY SUDBURY EJECTA EJECTA LAYER LAYER IN IN THE THEGUNFLINT GUNFLINT FORMATION, FORMATION,NORTHWESTERN NORTHWESTERNONTARIO ONTARIO Stephen Thunder Bay, Ontario, Stephen A. A. Kissin, Kissin,Department Departmentof ofGeology, Geology, Lakehead University, Thunder Ontario, Makoto International University, Makoto Okamoto, Okamoto,Faculty Facultyof ofEconomical Economical Sciences, Sciences, Kyushu International University, Kitakyushu, Kitakyushu, Japan, Japan,William William 0. D.Addison, Addison,Thunder ThunderBay, Bay,Ontario Ontarioand andGreg GregR. R.Brumpton, Brumpton, Thunder ThunderBay, Bay, Ontario Ontario Previous Previous studies studiesrevealed revealed that that the the Gunflint Gunflint lapilli lapilli tuff tuffunit, unit, located located in in the the Kamistiquia KamistiquiaGorge Gorgenear near Thunder Bay, Ontario, is unlikely to represent an ejecta layer from the Sudbury impact event. Thunder Bay, Ontario, is unlikely to represent an ejecta layer from the Sudbury impact event. Euhedral unit have 878±2Ma (Fralick tuffunit haveyielded yieldedaadate dateof of11878i2Ma (Fralicket et al., al., Euhedralzircons zirconsextracted extractedfrom fromthe thelapilli lapillituff 1998) 1998) presumed presumed to to be be the the age age of of sedimentation sedimentation based based on on aa volcanic volcanic source source for for the the zircons, zircons,too tooold old to 4Ma (Krogh to be be associated associatedwith withthe theSudbury Sudburyevent eventatat1836±1 1836il4Ma (Kroghet et al., a1.J1984) 984) However, However,aadistinct distinctash ash layer higher in section has been layer approximately approximately lOOm loom stratigraphically higher been recently recently discovered discovered and and investigated. investigated. A A grey greyash ashlayer layer11.5 11.5cm cm thick thick isis exposed exposed in in two two locations locationson on the southern southernside side of of the the Kaministiquia Kaministiquia Gorge. Gorge. The Thelayer layerisiscomprised comprisedmostly mostlyofoffriable fiableillite illiteand andmontmorillonite, montmorillonite, but but separation separation of of particulate mudball lapilli, lapilli, crystal crystal fragments fragmentsand and particulatefractions fractionsrevealed revealedthe thepresence presenceof of lithic lithic fragments, fragments, mudball green spherules spherules with a glassy appearance. The The latter latter were were found to be glauconite, glauconite, which also has has been described The crystal crystalfragments fragments described in in the the Gunflint Gunflint lapilli tuff unit (Hassler & Simonson, 1989). The are are mostly mostly pure pure potassium potassium feldspar, feldspar, with with minor minor quartz, quartz, calcite calcite and and various various other other minerals. minerals. The proximal The glauconite glauconitepellets pelletsand andpotassium potassiumfeldspar feldsparclasts clasts have have been been interpreted interpreted as as indicative indicativeof of aaproximal submarine submarine volcanic vent (Hassler & Simonson, 1989). In Inparticular, particular, the the sodium-free sodium-free potassium potassium feldspar feldspar clasts have have been bee; interpreted interpreted as as the theproduct productofofmetasomatic ietasomatic replacement replacement of i f igneous igneous plagioclase. Also present are quench-textured basaltic clasts and occasional devitrified vesicular plagioclase. Also present are quench-textured basaltic clasts and occasional devitrified vesicular glass glass fragments. fragments. However, However,large, large,unstrained unstrainedquartz quartzclasts clastsand and fresh fresh plagioclase plagioclase clasts clasts suggest suggest that aa somewhat somewhat more more felsic felsicvolcanic volcanic source sourcehas has also alsocontributed contributedto to the the particulate particulateassemblage. assemblage. Analyses enclosing shales Analysesof of samples samplestaken taken at at various variousintervals intervals in in the the layer, layer, as as well as as of the enclosing shales at one of of the locations, locations,revealed revealed the the presence presenceof of anomalous anomalousJr Ir (1.9 ppb) ppb) as well as other other PGEs PGEs and and Au. Au. On On the Ni are in the the ash ash layer layer as as compared compared the other other hand, hand, the the chalcophiles chalcophilesCo, Co,Cr Crand andNi are significantly significantly depleted depletedin to which have to the enclosing enclosing shales. AAstrong strongenrichment enrichmentin in Zr Zr indicates indicates the presence of zircons, which have opportunitiesfor for dating dating of of the the material been been separated separated and and should should again again provide provide opportunities material as well well investigation for shock features. features. Shock Shock features features in in the the particulate particulate fraction have not so far far been been identified, and the depletion depletion of of chalcophiles chalcophiles is contrary contrary to expectations expectations in an an ejecta ejecta layer layer(e.g. (e.g. Hildebrand, 1993). However, However, Simonson Simonson et et al. al. (1998) (1998) noted noted that that the the Acraman Acraman impact impact layer layer in in Australia Australia lacks lacks this this enrichment. enrichment.This Thislayer layeras aswell well as as aa layer layer seen in the Hammersley Basin can be explained explained as as the result of submarine impact. As As the the Sudbury Sudbury Structure Structureis is believed to have formed formed in in aa marine marine shelf shelf environment, environment, the the possibility possibilityof of an an impact impact origin origin for for the the Gunflint Gunflintash ash layer layer remains remains open. open. To To date, date, however, however, the evidence evidence is in favor favor of of aa volcanic volcanic source source for for the the ash ashlayer, layer,but but geochronology geochronology will will be be needed neededin inorder orderto to exclude excludethe the possible possible impact impact origin originof of the the layer. layer. 31 �References References Kissin, S.A. Fralick, P.W., Kissin, S.A. and Davis, D.W. (1998) (1998) The age and provenance of the Gunflint Gunflint lapilli lapilli Inst. tuff. Program and Abstracts, 44th Lake Superior Geol, Minneapolis, 66-67. Program and Abstracts, 441hInst. Minneapolis, 66-67. vocaniclastic strata in two Hassler, S.W. and Simonson, B.M. (1989) Deposition and alteration of vocaniclastic Proterozoic iron-formations in Canada. Can. J. Earth Sci. 26, 1574-1585. 1574-1585. lare, early Proterozoic Cretaceous/Tertiary boundary boundary impact impact (or (or the the dinosaurs dinosaurs didn't didn't have a Hildebrand, A.R. (1993) The CretaceousITertiary Roy. Astronom. Astronom.SOC. Soc.Can. Can.g, $, 77-118. chance). J.J. Roy. 77-1 18. Krogh, T.E., T.E., Davis, D.W. and Corfu, F. (1984) Precise U-pb U-pb zircon and baddeleyite ages for the Sudbury area, -446 in The Deposits ofthe of the Sudbury Sudbury Structure, Sudbury area, p.431 p. 43 1-446 The Geology Geology and Ore Deposits Structure,edited editedby by E.G. E.G. Pye, A.J. Naldrett and P.E. Giblin, Ont. Geol. Surv. Spec. Vol. 1, 6O3p. and P.E. Giblin, Ont. Geol. Surv. Spec. Vol. 1 , 6 0 3 ~ . Reeves, S. S. and Hassler, S.W. (1998) anomalybut but Simonson, B.M., Davies, Davies, D., Wallace, Wallace,M., Reeves, Simonson, B.M., Hassler, S.W. (1998) Iridium Iridium anomaly nor shocked quartz quartz from fromLate LateArchean Archeanmicrokrystic microkrysticlayer: layer:Oceanic Oceanicimpact impact ejecta? Geology , ejecta? Geology 2 , 1 19595198. 198. 32 �COMMINUTION COMMINUTION AND AND DILUTION DILUTION OF GLACIAL GLACIAL INDICATORS: INDICATORS: RATE ESTIMATES ESTIMATES FROM FROM FIELD FIELD DATA DATA LARSON, LARSON, Phillip Phillip C., C., and and MOOERS, MOOERS, Howard D., Department D e p m e n t of Geological Sciences, University of Minnesota,Duluth, Duluth,MN MN55812, 55812,plarson2@d.umn.edu plarson2@d.umn.edu Minnesota, Introduction: Introduction: Tracing Tracing glacial glacial indicator indicator trains has long long been been recognized recognized as as being being fundamentally fundamentally a problem problem of of interpreting of an an indicator indicator with with increasing increasingtransport transportdistance distancefrom fromits itssource, source. The interpreting the diminishing diminishing concentrations concentrations of dispersal dispersal pattern of of an an indicator indicator is is aa function function of of the the processes processes of dilution dilution and comminution acting on that indicator indicator during during transport. transport, Numerous Numerousstudies studieshave haveestablished establishedempirically empiricallythat thatdispersal dispersalpatterns patternstypically typicallytake a ethe theform formofofan an exponential exponential decay curve. However, However,while while an anindicator indicator ideally ideally comprises comprises all debris debris with with aa particular particular lithologic lithologic or or geochemical geochemical signature signature derived from a unique source, source, in practice most indicator studies examine only a portion portion of of the the size sizefractions fractionsof ofaatill. till. This This approach approach precludes precludes precise precise quantification quantification of the the systematics systematics of of indicator indicator transport, transport, ininparticular particular quantification quantification of dilution dilution and and comminution comminution rates. This Tbis is due due to to aanumber numberofoffactors; factors;previous previousindicator indicatortracing tracing studies studies have have often often been been limited limited to to examination examination of of only only aa portion of the size size fractions containing containiig an indicator, and in in many many cases cases recognition recognition of of aa unique unique indicator indicator derived derived from from aa specific specific bedrock bedrock source source has has proven proven difficult. dificult. The Thelack lack of due to to dilution (largely a function of specific specific data data relating relating the the relative relative changes changes in in indicator indicator concentrations concentrations due dilution (largely function of interaction interaction with the bed) bed) and and comminution comminution (largely (largely a function function of the the material material properties properties of of the tbe indicator) indicator) have have precluded precludedsatisfactory satisfactoryquantitative quantitativemodeling modelingofofglacial glacialdebris debristransport. transport. The The present present study study attempts attempts to address address these these questions questions by examining examining dispersal dispersal of clasts derived from from aa quartz-epidote District, Minnesota. Minnesota. Bedrock qum-epidote altered basalt unit in the Vermilion District, Bedrock within the study area consists consists of of aa metavolcanic-dominated E-W. Glacial Glacial drift in the area area isis thin thin (0-10 (0-10 m), m), and and metavolcanic-dominated greenstone belt belt striking striking roughly roughly E-W. records advance moving moving from from the the W NNE. records aa single single advance advance of the Rainy Rainy Lobe, with the last glacial advance E . Samples Samples were were collected from basal basal tills, tills, and screened to separate separate ibree three adjacent adjacent size size fractions fractions(1-2, (1-2,2-4, 2-4, and and 4-16 4-16 mm). mm). The collected from screened to The quartz-epidote altered basalt basalt indicator indicator is is visually quartz-epidote altered visually distinct distinct and was was easily easily separated separated from from each eachsize sizefraction; fraction; concentrations represent mass proportions, proportions. A A transport transport distance distance for each each sample sample was was calculated calculated by measuring measuring the the distance distance from from each eachsample samplelocation locationalong alongthe theflow flowpath pathto tothe thesource sourcearea. area. Dispersal: Dispersal: The The concentration concentration of an an indicator indicator in in aa particular particular size size fraction fraction of of till till is is aa function function of of the the change change in in concentration due due to to dilution, dilution, and and the the change change inin concentration concentration due due to to comminution. comminution. The The relationship relationship concentration between dispersal, dispersal, dilution, dilution, and and comminution comminution can can be be between expressed expressedas: as: CD1SJ = (I) Grs~ = CDm CDTLCCOM ' CCOM (1) C Dispersal Dispersal curves cuwes for for the the indicator indicator inineach eachparticle particle 0 size size fraction fraction in in the the study study area areawere weregenerated generatedby byplotting plotting C indicator indicator concentration concentrationagainst againsttransport transportdistance distance(T, (T,inin1cm) !an) 5 of the largest (Fig, 1). I). Concentrations Concentrations of largest clasts clasts (4-16 (4-16 mm) mm) C (Fig. 0 decreased with transport transport distance distance at the the fastest fastest rate, rate, while while 0 decreased medium-sized (2-4 (2-4 mm) mm) clast clast concentrations concentrations decreased decreased at aa medium-sized rate. Dispersal Dispersal of of the the smallest smallest clasts clasts (1-2 (1-2 mm) mm) has has aa lower rate. curious km curious form; form;concentrations concentrationsincrease increaseduring duringthe thefirst fust—5 -5 km transport, then then decrease decrease with with increasing increasing transport transport of transport, 0 4 12 distance. distance. 3 Dilution: Dilution Dilution reduces reduces indicator indicator concentration concentration by by Tmnsporl Distance Distance(km) (km) Dilution: eroding erodiig and incorporating incorporating material from from the the bed bed downflow downflow Figure I . Dispersal Dispersal Curves Cuwes Figure 1. from the mdicator indicator source. source, AAdilution dilutioncurve curveshould should ideally ideally QE doler Allered Basalts Quarlz-Epidote Altered Basalts take a e the form fonn of of aapower power function, function, with with the the exact exact slope slope of of the dilution dilution curve curve at any any given given point point in in space space and and time time aa the function function of of distance distance from from the the source source and and the instantaneous instantaneous rate of erosion and entrainment. These 'hese are aredependent dependent on on a number and the the basal basal thermal thermal regime. regime. Deviations number of of variables, variables, including including bed bed roughness, roughness, bed composition, composition, and Deviations of of aa Trans - 33 �dilution curve from from a power function of represent deviations deviations from from uniform uniform conditions. conditions. However, over relatively short distances on a bed of uniform composition it is short distances on a bed of uniform composition it is , 0.04 reasonabletoto assume assume aa uniform rate of erosion reasonable uniform rate erosion and and S incorporation. incorporation. An estimate of the in the An estimate of the dilution dilution rate rate in 0.03 Vermilion District was obtained by calculating calculating the the total total =05 S proportion of indicator Ct indicator material in the the 1-16 1-16mm nun fraction fraction 5 (Fig. 1). of the total sample pig. I). Regression Regression analysis analysisof of these these E0,02 a> C, S C data results in the following equation equation for dilution: 0 C) CD = O.O348e)2T (2) S S too Clearly, this dilution rate represents non-ideal 2 conditions. This Thisisisdominantly dominantlyan anartifact artifactof of not not Transport Distance Qan) TrawxtDi&nce (km) the—I mm and and +I6 +16mm including the -I nun mm size size fractions in the Figure 2. Dilution Curve Figure 2.Dilution Curve calculations, calculations, however however itit represents represents aa reasonable reasonable Quartz-Epidote Altered Altered Basalts Quartz-Epidote Basalts estimate. estimate. Comminution: Comminution:Comminution Comminutionalters altersthe theconcentration concentrationofofan anindicator indicatorwithin wifimaaparticular particularsize sizefraction hction as asparticles particlesare are than broken down by by clast-on-clast clast-on-clast and andclast-on-bed clast-on-bed interactions. interactions. Larger clasts tend to comminute comminute more more rapidly rapidly than smaller clasts. Larger Largerclasts clastsare arenot notlost lost to to the the system system as as they break down, but are transferred to smaller smaller size size classes. classes. The concentration of an indicator in a particular size fraction hction at a given transport distance is thus a function of of the the of larger larger clasts, clasts, and the rate at rate at which particles are being Kmg added to the size size class class by comminution comminution of at which which particles are leaving the size particles size class class by by comminution comminution to $asmaller smaller clasts. clam. + Comminution rates for indicator Comminution rates indicator clasts in the the OM' I j4no • 1-zm + by rearranging Vermilion Dislxict District were were calculated calculated by Vermilion rearranging • 2-4mm 2-4equation (I) CCOM equation (1)and andsolving solvingforfor CcoM at at each sample sample m' • 4-18mm 4.16location using the 3). CCoM the model modelCDIL CDL (Fig. 3). CCOM for the largest particles showed poor poor correlation correlation with with transport transport F EM,4 e + distance; this is is probably probably aa result result of of significant significantvariation variation 0 S in indicator boulder concentrations in indicator concentrations along along individual individual flow lines resulting from variable rates of addition addition by boulder comminution to this size size class. class. Medium-sized particles showed increase in in CCOM CcoMwith particles showedaarelatively relativelysharp sharp increase om transport distance, reflecting the higher rate transport rate of Transport TtansprlDistance D i m(km) (h) comminution of the comminution the coarsest coarsest particles. particles. The smallest smallest Figure 3. Comminution ComminutionCurves Cu~es particles showed a lower rate of of increase increase reflecting reflecting the Quartz-Epidote Altered Basalts Quartz-Epidote Altered Basalts lower rate at which coarser comminuted to coarser particles are comminuted this size size class. class. Conclusions: Conclusions: Results of indicator indicator tracing in in the the Vermilion Vermilion District District illustrate illustrate the importance importance of segregating sepgating the effects of dilution and comminution comminution to modeling the concentration of an indicator at a particular transport distance. Dilution affects affects the concentration Dilution concentration of each each particle particle size s i z equally, equally, however however comminution comminution rates rates strongly strongly and and differentially influence influence indicator indicator concentrations concentrationsin in differing d i f f e ~size g sizeclasses. classes. Since clast comminution is controlled controlled by by grain size and and material material properties, the the concentration concentration of an indicator indicator at aa particular particular transport transport distance distance can can be be seen seento to be dominantly dominantly aa function function of of the the initial initialparticle particle size sizedistribution distribution and and the the material material properties properties of of the the indicator. indicator. basalts. However, This study focused on dispersal of quartz-epidote qnartz-epidote aaltered l t e d hasalts. However, several severalother otherdispersal dispersaltrains trains were recognized in the the Vermilion Vermilion District Dislxict during during the course course of of the thestudy, study,including includingankerite-sericite ankerite-sericite lode lode goldgoldassociated alteration, and iron formation, associated formation, each each displaying displaying aa unique unique dispersal dispersalpattern. pattern. Given an identical identical glacial glacial of the the differing material material properties properties of of the the indicator. These environment, these differences must be a reflection of Thesedata data underscore that may accompany application of of a general underscore the potential potential problems problems that accompany application general regional regional dispersal dispersal model model to to interpreting particular localized interpreting localized glacial glacial indicator indicator trains. 6 4 0 . 12 10 + + 0A4 + !03it !! Em' :: 2 34 4 6 $ 10 12 �1 Low-grade Low-grademetamorphism metamorphismof of an anArchean Archeandebris debrisflow, flow, Irwin, Irwin, Pifher, Pifher, and and Meader Meader Townships, Lake LakeNipigon NipigonRegion, Region,Ontario Ontario 1 I I Frank FrankR. R.Luther, Luther,Geography Geographyand andGeology GeologyDepartment, Department, UW-Whitewater, hitewater, Whitewater, Whitewater, WI 53190 lutherf@mail.uww.edu lutherf@mail.uww.edu This hisextensive extensivebody bodyof of volcanic volcanic breccia brecciaisislocated locatedeast eastof of Lake LakeNipigon Nipigoninin northern northernIrwin, Irwin, southeastern southeasternMeader, Meader, and and aa large largepart partof of southern southernand andeastern eastern Pifher PiiherTownships. Townships. ItItisis10-25 10-25km kmeast eastof ofLake LakeNipigon Nipigonand and17-28 17-28km kmnorthnorthnortheast northeastofofBeardmore. Beardmore. Mapping Mappingby byMackasey Mackasey(1975), (19751,Kresz Kreszand andZayachivsky Zayachivsky (1989), (1989),and andas as aapart partof of this thisstudy studyshows showsthis thisrock rockto tobe beenclosed enclosedininaathick thick sequence sequenceof of typical typicalgreenstone greenstoneassemblage assemblagerocks. rocks. Metamorphism, Metamorphism,probably probably caused causedby by large large granitic granitic intrusives intrusivesin in Pifher Piiher Twp, increases thenortheast. northeast. increases totothe The Thebreccia brecciawas was thoroughly thoroughly described described and andan anorigin originas asaasubaqueous subaqueous debris debrisflow flowwas wasdocumented documentedby byLuther Luther(1998). (1998). In Inbrief, brief,the the breccia brecciaconsists consistsof of rounded roundedrock rock fragments fragments ranging rangingfrom from <1 e l mm mmto toover over11mmininaavery veryfine-grained finegrained matrix. matrix. Larger Larger fragments fragments tend tend to to be besimilar similar to tothe thematrix matrixinincomposition compositionwhile while smaller smaller fragments fragmentsvary vary in incomposition compositionfrom from that that of of the thematrix matrixto tomafic maficto toultramafic ultramafic to tocarbonate-rich. carbonate-rich. The The matrix matrixof of the thebreccia brecciawas wascomposed composedof of quartz quartzgrains, grains, euhedral euhedral and and broken brokencrystals crystals of of plagioclase, plagioclase, aa glass glassshard/pelitic shardlpelitic fraction fraction (now (now replaced below), and replaced by by the the greenschist greenschist metamorphic assemblage described below), and pyroxene pyroxene and/or andlor hornblende hornblende (now (now chlorite) chlorite) up up to to 0.5 0.5 mm. mm. Representative Representativewhole whole rock rock analyses analyses of of the the portion portionof of the thebreccia brecciaaffected affectedby bylow-grade low-grademetamorphism metamorphism are are presented presented in in Table Table 1; 1;these these analyses analyses show show the the average average (igneous (igneous rock rock equivalent) equivalent) composition compositionof of the thebreccia brecciato tobe bedacitic. dacitic. A A metamorphic metamorphic assemblage assemblage of of Mg-Fe Mg-Fechlorite, chlorite, high-Al high-A1to to high-Fe high-Feepidote, epidote, aluminous aluminous actinolite, actinolite, phengitic-paragonitic phengitic-paragoniticsericite, albite, albite, high-Fe high-Fe biotite, biotite, and and minor minor KK feldspar feldspar over-prints over-printsthe the primary primarytexture textureand andreplaces replacesthe the glass/pelitic glasslpelitic fraction; fraction; EMPA EMPAanalyses analysesof of the themore morevoluminous voluminousmetamorphic-origin metamorphic-originminerals mineralsare are given givenininTable Table2. 2. Most Most of of the the metamorphic metamorphic minerals, minerals, as as isisto to be beexpected expectedinin greenschist greenschist facies faciesrocks, rocks, show showminor minorvariation variationininindividual individualminoral mineralcompositions; compositions; two two minerals, minerals,plagioclase plagioclaseand andepidote, epidote, show showmajor majorcompositional compositionalvariation. variation. Plagioclase varieties: — an5 an5and and— an40. a m . The Thelarge largeplagioclase plagioclase Plagioclaseisispresent presentinintwo two varieties: crystals an40and and are are partially partially sausuritized; saussuritized; these these grains grains crystalshave haveaacomposition compositionofof— anw are are interpreted interpretedas as relict relictigneous igneousplagioclase. plagioclase. The The small small matrix matrix grains grains of of plagioplagioclase an5;these thesegrains grains are are interpreted interpreted as metamorphic metamorphic plagioclase plagioclase generatgeneratclase are are —ans; ed of the the breccia brecciamatrix. matrix. The The variation variation in inepidote epidotecomposition composition ed by by recrystallization recrystallizationof probably probably represents represents crystallization crystallization of of epidote epidote over over aa range rangeof of temperatures; temperatures;high-Al high-A1 epidote epidote usually usually crystallizes crystallizes at at aahigher highertemperature temperaturethan thanthe thehigh-Fe high-Feepidote. epidote. - - - 35 - �In Insummary: summary: aa classic classic greenschist greenschistfacies faciesmineralogy mineralogyof of albite, albite,epidote, epidote, muscovite, muscovite, biotite, biotite, actinolite, actinolite, and and chlorite chlorite overprints overprints the the primary primarymineralogy mineralogyof of the the debris debris flow flow which whichincluded includedfinely-crystalline finely-crystallinequartz, quartz,glass glassand andaltered alteredglass glass(pelite), (pelite), and anddetrital detrital quartz, quartz, plagioclase, plagioclase, and and mafic mafic minerals minerals grains. grains. Table Table1.1. Whole Whole rock rock analyses analyses of of the the samples samples of of the thevolcanic volcanicbreccia brecciawhich whichwere were affected by low-grade metamorphism. Analyses by XRAL. affected by low-grade metamorphism. Analyses by XRAL. S102 AL203 CAO NA2O K20 K20 FE203 T102 P205 P205 LOl S102 AL203 CAO MOO MGO NA20 FE203 FEO FEO MNO MNO TI02 LO1 SUM SUM 0.58 0.15 3.20100.3 3.40 1.72 6.25 4.30 0.08 16.0 3.84 4.00 LN97-3-1A 61.0 61.0 16.0 3.84 4.00 3.40 1.72 6.25 4.30 0.08 0.58 0.15 3.20100.3 LN97-3-1A LN97-6-1B LN97-6-19 63.2 63.2 16.5 16.5 6.03 99.8 6.03 2.15 2.15 3.53 3.53 1.49 1.49 5.30 5.30 3.10 3.10 0.07 0.07 0.51 0.51 0.11 0.11 0.85 0.85 99.8 Table Table2.2. Chemical Chemical analyses analyses of major major greenschist-facies greenschist-facies minerals minerals in in the the volcanic volcanic breccia. breccia. Analyses Analysesby byelectron electronmicroprobe microprobeat atUW-Madison. UW-Madison. hi-Al epidote biotite chlorite 37.9 35.2 25.3 0.3 1.7 0.1 23.9 23.9 28.0 16.8 20.9 10.6 10.6 10.9 10.9 5.6 20.2 23.2 MnO MnO 0.2 0.2 0.2 0.2 0.2 0.3 MgO MgO 13.4 13.4 10.3 16.3 CaO CaO 11.3 11.3 actinohte actinolite b-Al lo-AIeDidote eoidote 5102 Si02 55.5 55.5 37.0 37.0 1102 Ti02 0.0 0.0 ----- A1203 A1203 5.1 5.1 FeO FeO Na20 Na20 K20 K20 TOTAL TOTAL 1.6 1.6 0.1 23.1 23.I 24.3 ----- 0.2 0.2 = 97.9 97.9 96.2 95.1 95.1 0.1 0.1 0.4 9.9 0.1 94.4 86.7 REFERENCES REFERENCES Kresz, D.U. and Zayachivsky, B., 1989, Precambrian geology, Barbara, Meader and Rfher Pifher Townships; 2536-2537,91 p. Townships; Ontario Ontario Geological Geological Survey, Survey, rpt 270 with maps 2536-2537,91 Mackasey, Mackasey, W.O., 1975, 1975, Geology of Dorothea, Sandra, and Irwin Townships, District of Thunder 2294,83 p. Thunder Bay; Bay; Ontario Ontario Division Division of Mines, rpt 122 with map 2294,83 1998,An An Archean Archean subaqueous subaqueous heterolithic heterolithic debris debris flow, flow, Irwin, Irwin, Pifher, and Meader _______ ,1998, Townships, 44thAnnual Annual Institute Instituteon on Townships,Lake Lake Nipigon Nipigon Region, Region, Ontario Ontario(extended (extendedabstract): abstract):44th Lake 44. Lake Superior Superior Geology Geology meeting, meeting, Minneapolis, Minneapolis,Minnesota, Minnesota,v. v. 44. 36 �ThE THEBARRON BARRONSAPROLITE: SAPROLITE:CONFIRMATION CONFIRMATIONOF OF MATURE MATURE CHEMICAL WEATHERING IN IN THE THE SOURCE SOURCE FOR FOR PALEOPROTEROZOIC PALEOPROTEROZOIC QUARTZ QUARTZ AREMTES ARENITESIN INTHE THELAKE LAKE SUPERIOR REGION SUPERIOR REGION MEDAMS, MEDARIS,L.G., L.G., Jr., Jr.,Dept. Dept.ofofGeology Geology&&Geophysics, Geophysics,Univ. Univ. of ofWisconsin-Madison, Wisconsin-Madison, 1215 W. W. Dayton Dayton Street, Street,Madison, Madison,WI, WI,53706, 53706,medaris@geology.wisc.edu medarisgeology.wisc.edu It It has has long long been been inferred inferred that that the the post-1760 post-1760 Ma Ma supermature supennature Baraboo, Bamboo, Sioux, Sioux,Barron Barren and and related related quartz arenites were derived from sources that experienced mature chemical weathering, due quartz arenites were derived from sources that experienced mature chemical weathering, dueto to the in the the near near absence absence of of feldspar feldsparin in the the arenites arenites and and predominance predominance of of kaolinite kaolinite and and pyrophyllite pyrophyllite in the -- - argillaceous 1983; Ojakangas Weber, al., 1986). Paleosols argillaceous strata strata (Don, (~ott,1983; Ojakangas and ~ e b e r1984; , Southwick et al., Paleosols have been recognized recognized beneath beneath the the Baraboo, Baraboo, Sioux, Sioux, and and Barron Barren quartzites quartzites (Medaris (Medaris et et al., al., 1997; 1997; Southwick of aa continuing continuing investigation investigationto to Southwick and and Mosler, 1984), 1984), and and the the present present report report is is part of determine determine the chemical chemical maturity maturity of such such paleosols paleosols and to evaluate evaluate the climatic climatic conditions conditions associated associated with genesis genesis and and deposition deposition of the supermature supennature sedimentary sedimentary rocks. rd- ,xL ------rA-A large large outcrop outcrop of of red saprolite saprolite occurs occurs beneath beneath the A Barton Ban-on Quartzite Quartzite on on the the south southbank bank of of Weirgor Weirgor Creek, Creek, —lOOm east of Reichel Road, in Rusk County (NWI/4, -100m east of Reichel Road, in Rusk County (NW114, R7W). The closest basement Sec 9, 9, T36N, R7W). basement exposure exposure SWll4,Sec SWI/4, is milesouth, south,where wheremetatonalite metatonalite crops out on is —J/2 -% mile on both both sides of Reichel Road. Although Althoughthe the saprolite saprolite and and metametamile apart, tonalite tonaliteoutcrops outcropsare areV2 %mile apart, the the close close similarity similarityin in their textures textures (Fig. 1) 1) makes the metatonalite metatonalite a reasonable reasonable protolith orotolith candidate. The Themetatonalite metatonalitehas has inequigranular ineauimular - texture, texture, in in which which large large quartz quartz grains grains are are surrounded surrounded by aa medium- to fine-grained fine-grained granoblastic granoblastic assemblage assemblage of quartz, Figure 1. Polished Barron polishedslabs slabsof ofBarron plagioclase, hornblende, homblende, epidote, and opaques. opaques. The texture of metatonalite metatonalite protolith protolith and and saprolite; saprolite; metatonalite has has been preserved preserved in in saprolite, saprolite, in which which large large light light grains grainsare are quartz. quartz. the metatonalite relict quartz grains are surrounded by a matrix of finer-grained quartz grains are surrounded finer-grained Table 1. 1. Chemical Chemical Analyses Analyses quartz, quartz, kaolinite-rich kaolinite-rich domains domains (after (after feldspar), feldspar), hematite-rich hematite-rich domains domains % (2) (3) (2) (3) (1) 70.25 67.85 -10 Si02 (after (after hornblende), hornblende), traces traces of of sericite sericiteand tiny, euhedral euhedral crystals of Sioz ~i02 67." 0.24 70.25 0.29 -10 0 crandallite-florencite(aluminophosphate (aluminophosphateminerals). minerals). A1203 14.00 16.15 o crandallite-florencite AIQs 7.05 +9 5.63 Fe203 The The most striking strikingfeature featureof of the the saprolite saprolite chemical chemical composition composition $;FMnO 0.00 0.07 -100 0.09 -97 Mgo 2.41 is the virtual absence absence of of MnO, MnO, MgO, MgO, CaO CaOand andNa2O Na20 and the low MOO 2.41 0.09 -97 concentration concentration of K20 K20 (Table 1). 1). The Thechemical chemicalindex indexof ofalteration alteration o3 -100 -lE 0:58 57 1.17 (CIA) for the saprolite is 95.7, illustrating the high degree x2o (CIA) for the saprolite is 95.7, illustrating the degree of of KSJ 1.17 0.58 -57 ',05 m5 maturity maturity attained attained by by chemical chemical weathering weathering of of the saprolite saprolite [CIA [CIA == I'% LO1 0.70 5.53 100.06 99,91 100*A1203/(AI2O3+CaO+Na2O+K2O) on a molar basis]. The isocon Sum lOO*Al203/(Al203+CaO+Na~0+K20) on a molar basis]. The isocon sum 99.91 1m.w method (Grant, 1986) 1986) has been used to evaluate evaluate the magnitude magnitude of ppm ..à 14 8 -52 8 -52 Rb 14 chemical changes associated with weathering, taking metatonalite chemical changes associated mitatonalite as Sr 321 90 -76 Sr protolith for for the saprolite. saprolite. When Whenoxides oxidesand andelements elementsin insaprolite saprolite Ba 251 31 -89 Ba 91 00 80 91 Zr 80 and and protolith protolith are areplotted plottedagainst againsteach eachother other(Fig. (Fig.2), 2),A1203, A1203,TiO2 Ti02 and and Barron metatonaliie metatonalite protolith (1) Barren pmtoli Zr lie on a straight straight line, line, an an isocon, isocon, along along which the relative concenBarron sapmliie saprolite (2) Barren trations of trations of the defining defining constituents constituents remained remained constant constant dunng during % change relative (3) %change relativeto to isocon isocon r ,. 37 : ;5 7: ;3 4: i:: �weathering. The Therelatively relativelysmall smalldeviation deviationof ofFe203 Fe203 40 40 / from the isocon may be he due to an unrepresentative unrepresentative concentration of Fe203 in the the assumed assumed protolith, rather o 5*SiO: concentration Fez03 in < / O.5'5i02 30 than than its mobility. The The isocon slope of 1.15 1.15 <D 30 + .corresponds corresponds to a 13% 13% mass mass decrease decrease during during 0. weathering, weathering, when MnO, MnO, MgO, MgO, CaO CaO and and Na20 Na20were were 20 2o effectively effectively completely completely removed, removed, and and K20, K20, P205, P20s, Rb, Rh, Sr Sr g and Ba were substantially substantially removed from from metatonalite metatonalite 5 m (Table 1). 1). 0 . m (Table 10 -Fe2%'".2oow2o5 •OPSr The Baraboo Barahoo Quartzite Quartzite is is also also underlain underlain by by aa 7 •SOl'Rb saprolite saprolite on Baxter Baxter Hollow Hollow granite granite (Medaris (Medaris et et al., al., e° • ,'lo*T102 I!•• 00 1997), and application application of the the isocon isocon technique technique to to the the 1997), 00 10 20 30 40 10 20 30 40 Baraboo saprolite yields Barahoo saprolite yields an an isocon isocondefined definedby byAl203 A1203 Barron protolith protolith and Ti02 Ti02with a slope of 1.14, 1.14,corresponding corresponding to to aa 12% 12% diagram for Barron Figure 2. Isocon mass decrease, similar similar to to that that for for the the Barron Barron saprolite. saprolite. protolith saprohte; oxides in wt%, protolith and saprolite; oxides m Chemical maturity matunty of of Baraboo Barahoo saprolite saprolite is comparable comparable to that elements elements in ppm. of Barron saprolite, as as indicated indicated by the "" levels of depletion in in MnO, MnO, MgO, M ~ O CaO, :C~O, 6 60 60 - A % Na20, Sr Sr and and Ba Ba (Fig. (Fig. 3). Depletion Depletion of Si02 Si02 ".. % 40 both saprolites, is --'10% -10% in both saprolites,and and—'30% -30% Fe203 Fe203 § 40 : A A - 20 20 Baraboo. Following was removed at Barahoo. Following 9 weathering of the the Baraboo Barahoo saprolite, saprolite, K20 £2 2-rn 00 Rb were reintroduced by hydrothermal -20 and Rh hydrothermal -20 fluids, which were channeled channeled along along the the §' sub-Baraboo unconforrnity unconformity during suh-Barahoo 60 metamorphism. metamorphism. -80 The Barron and other other contemporaneous contemporaneous b00 . " m " m . n saprolites exhibit a high degree of &  ¡ & m0 Q0 ' &a ' 0S , Q Q Q Q ° mineralogical mineralogical and and chemical chemical maturity, maturity, x g ~ us s a ~ + similar Figure 3. Comparison of similar to that found found in in present-day o f chemical changes changes in in Bàrron Barren and Baraboo saprolites; s~prolites;elements and oxides arranged arranged weathering zones zones in in humid, humid, warm warm climates, climates, in order order of decreasing ionic ionic radius. radius. where intense chemical chemical leaching leaching is is characteristic, characteristic, in demonstrating the existence of a tropical environment in the Lake Superior region at thereby demonstrating -4750-1650 Ma. -1750-1650 Ma. Such Suchaaclimate, climate,combined combinedwith withaastable stabletectonic tectonicsetting, setting,was wasessential essentialfor for supermature features of the Baraboo, Barron and Sioux quartzites. generating the supennature Acknowledgments Acknowledmzents I'm indebted to Mike Mudrey, who drew my attention to the Barron saprolite saprolite and provided a locality map, and to Jim Grant, who enlightened me regarding the isocon method. References Dott, Don, R.H. Jr. (1983) (1983) Geol. Soc. Soc. Amer. Memoir 160, 160, 129-141; 129-141; Grant, J.A. (1986) (1986) Econ. Econ. Geol., Geol., v. 81, 1976-1982; 1976-1982; Medaris, L.G. Jr. eta!. et al. (1997) (1997)43rd 43rd Inst. Inst. Lake Lake Superior Superior Geol., Geol., 39-40; 39-40; Ojakangas, R.W. and Weber, R.W. (1984) Minn. Geol. Sun'., Surv., Rept. Rept. Inv. Inv. 32, 32, 1-15; 1-15;Southwick, Southwick, Mossler, J.H. D.L. et al. (1986) Geol. Soc. Amer. Bull., v. 97, 1432-1441; 1432-1441; Southwick, D.L. and Mossier, (1984) Minn. Geol. Sun'., Surv.,Rept. Rept.Inv. Inv. 32, 32, 17-44. 17-44. - - / - - 7 - - I • • . . . . . 0 - 38 - �TOURMALINE-BEARING VEiNS IN THE BARABOO QUARTZITE: A NEW TOURMALINE-BEARING QUARTZ VEINS OCCURRENCE OCCURRENCE OF THE ALKALI-DEFICIENT TOURMALINE, TOURMALINE, FOITITE FOITITE MEDA1US, L.G., Jr.and FOURNELLE, J.H., Department of Geology & Geophysics, Geophysics, MEDARIS, L.G., Jr.and FOURNELLE, J.H., Department University University of Wisconsin-Madison, 1215 1215 W. Dayton Street, Madison, WI, 53706; 53706; medarisgeology.wisc.edu; johnfgeology.wisc.edu medaris@geology.wisc.edu; johnf@geology.wisc.edu Tourmaline Tourmaline has long long been known to occur in quartz veins in the Baraboo Baraboo Quartzite, Quartzite, but its its chemical composition and geological significance have have never neverbeen been assessed. assessed. The present investigation was undertaken to characterize this tourmaline, as part of an ongoing project to establish the mineralogical and chemical composition of Proterozoic rocks in the Baraboo Bamboo Range. Three samples of tourmaline-bearing tourmaline-bearing quartz quartz veins from low in the Bamboo Baraboo stratigraphic stratigraphic section section on the south limb limb of the Baraboo Baraboo syncline syncline were were selected for investigation: investigation: sample I) 1)aa folded, folded, 1.5 1.5 cm thick quartz quartz vein in in the the regolith regolith of of the the Baraboo Baraboo paleosol from drill core 613 in Baxter Hollow; sample 2) a 3 cm thick quartz vein in quartzite in the SE ¼ 'A Sec. 29, Baxter Hollow; and sample 3) 3) a 3 mm nun thick, tourmaline-rich tourmaline-rich quartz vein in quartzite and metapelite in the NW ¼ 'A Sec. 35, Pine Hollow. All All three samples samples are mineralogically mineralogically simple, consisting of quartz, quartz, specular specular hematite hematite and and tourmaline. tourmaline. Tourmaline Tourmaline occurs in clusters clusters of small, randomly Figure 1. Photomicrograph tourmaline, Photomicrograp~of oftourmaline, oriented oriented pleochroic pleochroic crystals crystals (Fig. (Fig. 1), l), in in which which sample 3, plane polarized light = pale o= 0 pale to medium medium grayish grayish blue blue and and EE == colorless. colorless. Tourmaline analyses Tourmaline analyses were obtained obtained by wavelength Table Electron microprobe Table 1. Electron microprobe analyses analyses 5X50 instrument, quartz veins dispersive tournialine from quartz of tourmaline veins in in dispersive spectrometry on a Cameca SX50 using instrument, using Baraboo Quartzite Barabw Quartzite a 15 kV accelerating voltage, a 10 nA beam current, a beam 15 accelerating voltage, a 10 nA beam current, a beam 2 3 sample 1 2 3 sample p.m.the the(bpZ pZ reduction diameter of 1 pm, reductionsoftware, software, and a wt% combination of natural and synthetic combination synthetic minerals minerals as as standards. standards. 35.14 Si02 35.14 35.23 35.18 35.18 tourmalme by electron Analysis of tourmaline Analysis electron microprobe microprobe presents presents aa 34.86 2O3 35.05 A ~ O S 34.00 34.00 35.05 34.86 14.59 challenge because 13.98 FeO 13.98 12.35 12.35 14.59 to measure measure Li Li and and H H directly, directly, FeO challenge because of of the inability inability to 1.11 0.00 MgO 0.49 0.49 1.11 0.00 MgO the difficulty in determining B and 0 0 precisely, and the Na20 0.62 0.55 0.47 uncertainty in valency of transition elements. Nevertheless, Nevertheless, 8 Sum 84.23 84.29 85.09 results are achieved by normalizing acceptable acceptable results achieved normalizing cations cations to to 24.5 cations p.fu. cationsp.~u. 5.96 6.00 5.96 Si 6.00 5.96 5.96' Si oxygens HzO- and and B203-free B203-free basis and assuming assumingaa oxygens on an H206.85 6.98 6.96 Al 6.96 6.85 6.98 A1 B atoms atoms and and 331 0 atoms stoichiometric formula containing 33 B 10 1.75 2.07 Fe 2.00 2.07 Fe 2.00 1.75 ofF). (in the absence of F). Tourmaline Tourmalinewas wasanalyzed analyzed for for Si, Si, Ti, Al, Mg 0.12 0.28 0.00 Fe, Mn, Mg, Ca, Na, K, F, and Cl, but only Si, Al, Fe, Mg, and Na 0.20 0118 ohs N~ 0.20 0.18 0.15 occupancy are Fe-rich, Fe-rich, site occupancy TheBamboo Baraboo samples samplesare Na were detected (Table 1). The 5.96 6.00 5.96 T(6) 6.00 5.96 5.96 T(6) the Y-site is effectively effectively filled filled with Fe and Al A1 (means (means and 6.00 &00 6.00 Z(6) z(6) 6.00 6.00 6.00 standard deviations are 2.96±0.05, 2.96±0.08 and 2.98±0.06 2.96+0.05,2.96+0.08 2.98L0.06 3.01 3.03 y(3, 2.97 for the three samples), samples), indicating indicating the absence of Li, and the o.is 0120 0.18 0.18 0.15 X(O-1) 0.20 x(0-1) X-site is largely vacant, containing containing subordinate subordinate amounts of Na. ,. 1 r° 39 �Thus, Thus, the the composition composition of of Baraboo Barabootourmaline tourmalineisis close close to type foitite and lies in a field near the foitite corner type foitite and lies in comer of a plane defmed definedby by the the tourmaline tourmaline end-members, end-members, , foitite foitite [O(Fe2+2A~)Aksi60~~(Bo3)3(oH)3(oH)], foitite[D(Fe22Al)Al6SioOia(BO3)3(OH)3(OH)J, schorl 8(B03)3(OH)3(OH)J, schorl[Na(Fe2s)AloSisOj paCFe2+~)A&O~s@O~)3(0I^OH)], and and their their Mg Mg counterparts counterparts(Fig. (Fig. 2). 2). >c All three Baraboo Baraboosamples samplesare arealkali-deficient, alkali-deficient,with with All three A cores 0.5<X0c0.9, 0.5<X60.9, although althoughthey theyeach eachoccupy occupyaadifferent different field field in Fig. 2. The TheFe Fe##ininsample sample33isis99-100 99-100 and and in in sample is 90-95, 90-95, but but sample sample22isismore moremagnesian, magnesian, sample 22 is with the Fe# of rims being 70-85 and of cores, the Fe# of rims being 70-85 and of cores, 35-55. 35-55. The The effective effectiveoperation operationof of the thecoupled coupledexchange, exchange, 90 100 60 70 60 50 40 30 X(D) Fe# Y(A1) ==X(Na) X(Na) + + Y(Fe+Mg), Y(Fe+Mg), is is illustrated illustrated by by X(D) ++Y(Al) F& 4 schorl schorl the linear linear covariance covariance of of Al A1 and and Fe+Mg Fe+Mg (Fig. (Fig. 3). 3). Figure 2. Fipe 2-Compositional variation of Most analyses extend from the theoretical composition of analyses extend from theoretical composition Baraboo tourmaline Bamboo tourmalineininterms termsof ofX-site X-site foitite (6 Al, foitite (7 Al, Al, 22 Fe+Mg) Fe+Mg) toward toward that that for forschorl schorl(6 Al, 33 vacancy, 0, and Fe#, I 0O*Fe/(Fe+Mg) vacancy, 0, and Fe#, 100*Fe/(Fe+Mg) Fe+Mg), although although the the cores cores of of tourmaline tourmaline in in sample sample33 are are 3.C more more aluminous, aluminous,extending extendingtoward toward88Al Aland and11Fe+Mg, Fe+Mg, * type fofte \.... 0 sanplel which, which, in in the the absence ofF of Fand andLi, Li, suggests suggeststhe the presence presence of of A sample2 \.. 4 . an [D(Fe2Al2)Al6Si6O13(BO3)3(OH)3O]. anoxy-foitite oxy-foititecomponent component [D(Fe2+A12)A16S&O18(B03)3(OH)30]. • b. 2.5 25 Foitite Foititeisis aa relatively relativelyuncommon uncommonvariety varietyof oftourmaline tourmaline %Nq : t that has been described from late-stage hydrothermal veins that has been described from late-stage hydrothennal veins ? ?jk associated associatedwith with granitic granitic pegmatites pegmatites and and from from metasomatized metasomatized If wall wall rocks rocks in in areas areas of of Pb-Zn mineralization. Such Suchfoitite foitite "- 2.0 2o : differs differs from from that that at at Baraboo Barabooin incontaining containingappreciable appreciable quantities quantities of of Ti, Ti, Mn, Mn,Ca, Ca, Li Li and and F, F, depending dependingon onlocality, locality, A and andin in being beingassociated associatedwith withaavariety varietyof ofsilicate silicateminerals, minerals, 1.5 6.0 6.5 7.0 7.5 6o 65 7o 75 includingalbite, albite,adularia, adularia,micas micasand andzeolites, zeolites,among amongothers. others. including Al, A aptu am In In contrast, contrast,the theBaraboo Baraboofoitite foititeisischemically chemicallysimple, simple, 3.0 30 1Vs8mp183 containing containingonly onlySi, Si,Al, Al,Fe, Fe,Mg Mgand andNa Na(+ (+B+O+H), B+O+H),and andisis •\\ accompanied accompanied solely solely by quartz quartz and hematite. The Thechemical chemical . \ 2.5 25 constitution constitutionand andalkali alkalideficiency deficiencyof ofBaraboo Barabootourmaline tourmalineare are •.•.c,,v "\..v %.. V V, consistent consistentwith with its its environment environmentof of formation formationin in hydrohydroÈ. a t 2.0 thermal thermal veins veinswithin withinBaraboo Baraboometasedimentary metasedimentaryrocks. rocks. a, & 20 + During post-Penokean folding and low-grade metaDuring post-Penokean folding and low-grade metae U. LL. 3%. morphism, morphism, hydrothermal hydrothermalfluids fluids migrated migrated through through the the 15 -\\ 1.5 v chemically chemicallymature mature Baraboo Baraboo sequence, sequence, which which consists consists almost almost +... V\ B entirely entirelyof of5i02, SiOa,Al203 A1203and andFe203, Fe203, where where they theyscavenged scavengedBB % .1 1.0 10 and and the the few fewother otherelements elementsnecessary necessaryto toprecipitate precipitatequartz, quartz, 60 65 7o 75 8o 6.0 6.5 7.0 8.0 7.5 Al, apfu am hematite, hematite, and and alkali-deficient alkali-deficient tourmaline. Thus, Thus,the the Figure 3. Covariance Covarianceof ofFe+Mg Fe+Mg Figure3. chemical chemicaland and mineralogical mineralogicalcompositions compositionsof ofhydrothermal hydrothermal (Y-and and Z-sites) Z-sites) (Y-site) and and Al A1(Y('V-site) quartz quartzveins veins in in the the Bamboo Baraboo range range are are inherited inherited in in part part from from in Bamboo tourmaline; scale in in Baraboo tourmaline; scale in Proterozoic Proterozoicweathering weatheringand andsedimentation sedimentationprocesses. processes. . & I . , . '%. . t\;\\ \\ .  % ¥. ! atomsper performula formulaunit unit atoms 40 �Metal, Gold Gold and and Carbonatite Carbonatite Exploration Kimberlite, Base Metal, Exploration Targets, Derived From Overburden Overburden Heavy Mineral Data, Killala Lake Area, Northwestern Ontario. MORRIS, MORRIS, T.F., SAGE, SAGE, R.P., Ontario Ontario Geological Geological Survey, 933 933 Ramsey Ramsey Lake Lake Road, Road, Sudbury, ON. P3E tom.morris(ändm.gov.on.ca; CRABTREE, D.C., D.C., Ontario Geoscience Sudbury, ON. P3E 6B5, tom.morrisfaindm.gov.on.ca; P3E 6B5. Laboratories, 933 Ramsey Lake Road, Sudbury, Sudbury, ON., P3E ABSTRACT Since Since 1993, 1993, the Ontario Ontario Geological Geological Survey Survey (OGS) (OGS) has has conducted conducted aa series series of of Quaternary Quaternary mapping mapping and overburden overburden sampling sampling programs programs to assess assess the diamond potential of the the Kapuskasing Kapuskasing Structural Structural A suite suiteof of heavy heavy Zone (KSZ). Kimberlite Kimberlite is is recognized as as the primary host host rock for for diamond. diamond. A minerals (Cr-pyrope minerals (Cr-pyrope garnet, garnet, chromite, cbromite, Mg-rich ilmenite, ilmenite, Cr-diopside Cr-diopside and and forsteritic forsteriticolivine) olivine)are are commonly KIMs). commonlv associated associated with kimberlite kimberlite and and are are referred referred to to as as kimberlite kimberlite indicator indicator minerals minerals(KIMs). The typeiand types and distribution distribution of of KIMs KIMs recovered recovered from from these these programs programs clearly clearly demonstrate demonstratethat that the the KSZ has excellent potential for hosting diamond-bearing kimberlite. kimberlite. To To date, date, 22 occurrences occurrences of of diamond-bearing rock and diamond-bearing and kimberlite kimberlite have have been been discovered discovered in in the the Wawa Wawa area area (KWG (KWG Resources Resources 1nc.ISpider Resources Resources Inc., Inc., Press Press Release, Release, 20/08/97; 20108197; Canabrava Canabrava Diamond Corporation, Corporation, Press Press Inc./Spider Band-Ore Resources Release, 09/12/97; 09/12/97; Band-Ore Resources Ltd., Press Press Release Release 10/02/00; 10102100;Pele Pele Mountain Resources Resources Release, Inc., Press Release, Release, 10/02/00). 10/02/00). Following the success success of the KSZ Quaternary Quaternary mapping mapping and overburden overburden sampling sampling programs, programs, plans to assess similar structures in other parts of Ontario were made. One such assess similar structures in other parts of Ontario were made. One sucharea, area, the the TransTransfrom Michigan Michigan north-northeast north-northeast into intoOntario, Ontario,west west of of Superior Tectonic Zone (TSTZ), extends from Marathon. Marathon. Kimberlites Kiberlites straddle straddlethe the structure structurewithin within Michigan Michigan and and ultramafic ultramafic lamprophyres, lamprophyres, which may belong "clan", are recognized in association with the TSTZ in belong to the kimberlite "clan", Ontario. Ontario. The The TSTZ TSTZ represents represents aa fault fault system system that that has has accommodated accommodated emplacement emplacementof of upper upper mantle derived derived material. material. To To evaluate evaluate the the kimberlite kimberlitepotential potential of of the the TSTZ TSTZ in in Ontario, Ontario,an an area area between the towns of Marathon and Terrace Terrace Bay was chosen for Quatemary Quaternary mapping mapping and and stream stream sediment and till sampling. Collected overburden samples were processed to determine KIM sampling. Collected overburden samples determine KIM signatures. signatures. In addition addition to KIMs, KIMs, overburden overburden samples samples were were processed for for metamorphic metamorphic or or magmatic magmatic gold grains and carbonatite indicator massive sulphide indicator minerals (MMSIM ), ), gold indicator minerals. minerals. The MMSIMs MMSIMs are are associated associated with with 33 main types types of of base base metal deposits: deposits: 1) 1)volcanosedimentary volcanosedimentary massive sulphides sulphides in in high grade grade regional regional metamorphic metamorphic terrain; terrain; 2) skarn skarn and and greisen greisen deposits; deposits; and and 3) magmatic Ni-Cu sulphides. The composition of gahnite, a rare and important MMSIM magmatic sulphides. The composition of gahnite, a rare and important MMSIM associated with metamorphosed associated metamorphosedvolcanosedimentary volcanosedimentarymassive massive sulphide sulphide deposits, deposits, can can also also be used used to indicate indicate the presence presence of of rare-element rare-element pegmatite. pegmatite. The The presence presence and and distribution distribution of of MMSIMs MMSIMs and gold grains grains recovered recovered from from overburden overburden sampling samplingprograms programs completed completed over over the the KSZ KSZ defined defined several several important important base base metal, metal, rare-element rare-element pegmatite pegmatite and and gold gold exploration exploration targets. targets. This presentation presentation provides provides data data and preliminary preliminary interpretations interpretations on the types types and and distribution distribution of kimberlite kimberliteheavy heavy mineral mineral indicators indicators(KIMs), (KIMs), metamorphic metamorphicor or magmatic magmatic massive massive sulphide sulphide indicator minerals (MMSIMs), gold grains grains and carbonatite carbonatite indicator indicator minerals minerals from from modern modem Registered Trademark, Trademark, Overburden Overburden Drilling Drilling Management Management Drilling Drilling Limited Limited 41 �alluvium and till samples collected in the Killala Lake area, northwestern Ontario. This data can be used to focus exploration efforts for kimberlite (diamonds), base metal, gold and carbonatite (rare earth )) deposits. A total of 230 modern alluvium and 82 till samples were collected from across the study area. modern alluvium and till samples, 8 bedrock samples were collected In addition to the modem and processed to characterize their heavy mineral composition. Orientation surveys surveys were were completed over the Prairie Lake Lake Carbonatite, Carbonatite,Major MajorGeneral GeneralResources ResourcesLtd.'s Ltd's Spider Spider Lake Lake base base metal deposit and Cameco Gold Inc.'s Inc.'s Empress EmpressHill Hill gold gold deposit. deposit. These Thesesurveys surveysdefined defined overburden heavy mineral signatures signatures associated with each deposit type. Bedrock and overburden overburden data obtained from the orientation surveys surveys were used to help interpret heavy mineral signatures signatures derived from the regional overburden sampling program. From the overburden samples, samples, a number of kimberlite indicator minerals, base metal indicator minerals, carbonatite iiidicator minerals, carbonatite indicator minerals and a few gold grains were recovered. This data will be released in number 6013, 6013,April April2000. an Ontario Geological Survey Open File Report, number 2000. 42 �Nature and distribution distribution of ofLogan Logandiabase diabase sills sills and and gabbro gabbro channels channelsin inthe the Keweenawan Rift near Thunder Thunder Bay, Bay,Ontario: Ontario: Brief Brief comparison comparison to to Noril'sk Noril'sk - Jon NorthAtlantic AtlanticNickel NickelCorp. Corp. Jon North North- North Flat-lying Flat-lyingLogan Logandiabase diabasesills, sills, vertical verticaldiabase diabasedikes, dikes, and andlayered layeredgabbro gabbrocomplexes complexes intrude intrudelower lowerProterozoic Proterozoicand andArchean Archean rocks rocksin inthe thenorthwest northwestcorner cornerof ofthe theKeweenawan Keweenawan Rift. These 1108 Ma plutonic and hypabyssal rocks are broadly contemporaneous Rift. These 1108 Ma plutonic and hypabyssal rocks are broadly contemporaneouswith with thick thick sequences sequences of of flood flood basalt basaltof of the the North NorthShore ShoreVolcanic VolcanicGroup Groupand andOsler OsierGroup Groupinin northern northernLake LakeSuperior Superiorand andthey they ostensibly ostensibly represent representthe themagma magmapathways pathwaysfor forthe theflood flood basalts. basalts. South Southof of Thunder ThunderBay, Bay,aarugged, rugged,upland uplandarea areaof ofdiabase-capped diabase-cappedcuestas cuestas occupies occupies aa 70 70 km km by by30 30km kmnortheast-trending northeast-trendingtopographic topographicfeature feature--the the"Logan "LoganBasin" Basin"-between betweenThunder ThunderBay Bayand andthe theMinnesota Minnesotaborder. border. The The Keweenawan Keweenawan diabase diabase caps caps of of the above valleys valleys and and canyons canyons thecuestas cuestas(i.e. (i.e. the theLogan LoganSills) Sills) commonly commonly rise rise 15Cm 150 mabove underlain underlainby by deeply deeply eroded erodedflat-lying flat-lying sedimentary sedimentaryrocks rocksof of the the lower lowerProterozoic ProterozoicRove Rove Formation Formation of of the the Animikie Animikie Group. Group. Northwest Northwestof ofthe theLogan LoganBasin BasinArchean Archeangranitoid granitoidrocks rocks of of the the southern southernSuperior SuperiorProvince Provinceform form low low rolling rolling hills. Southeast Southeastofofthe theLogan LoganBasin Basin the thetopography topographyisisaarugged ruggedupland uplandarea areaof ofnortheast-trending, northeast-trending,linear linearridges ridgesformed formedby by vertical verticaldiabase diabaseand andgabbro gabbrodikes dikesintruded intrudeddiscordantly discordantlythrough throughthe theflat-lying flat-lyingstratigraphy stratigraphy of ofthe the Animikie AnimikieGroup. Group. Geological Geologicalmaps mapsofofthe thearea area(e.g. (e.g.Smith Smithand andSutcliffe Sutcliffe1987;1989, 1987;1989, Pye and Fenwick 1963) tentatively illustrate NE-trending faults on the NW and Pye and Fenwick 1963) tentatively illustrate NE-trending faults on the NW andSE SEsides sides of the Logan Basin. of the Logan Basin. The I), high TheLogan LoganBasin Basinhas hasrelatively relativelyhigh hightotal totalmagnetic magneticintensity intensity(TM (TMI), highmagnetic magneticrelief, relief, and andlong longwavelength wavelengthmagnetic magneticanomalies anomaliescaused causedby bythe theflat-lying, flat-lying,magnetic magneticdiabasediabasecapped cappedcuestas. cuestas. North Northofofthe theLogan LoganBasin Basinaadomain domainofoflow lowTMI TMIand andlow lowrelief reliefcoincides coincides with Archeancrust crustand andsoutheast southeastof ofthe theLogan LoganBasin Basinhigh highTMI, TMI,high highrelief, relief,and andhigh high with Archean frequency magnetic anomalies coincide with the area of northeast-trending diabase frequency magnetic anomalies coincide with the area of northeast-trending diabase dikes. dikes.Northeast Northeastand andeast-trending east-trendingfaults faultscan canbe beinterpreted interpretedas asthe theboundaries boundariesofofthe the Logan LoganBasin. Basin. The Thejuxtaposition juxtapositionofofthe thedomain domainofofsills sillsofofthe theLogan LoganBasin Basinagainst againstthe thedomain domainofofdikes dikestoto the thesoutheast southeastcan canbe bereconciled reconciledininan anhypothetical hypotheticalcross crosssection sectionififthe theLogan LoganBasin Basinisis interpreted interpretedas asaagraben grabenwhere wherethe thetransition transitionfrom fromvertical verticaldikes dikesto tohorizontal horizontalsills sillsisis preserved preservedat atdepth. depth.The Thenortheast-trending northeast-trendingdikes dikestotothe thesoutheast southeastare arevertical verticalconduits conduits to tothe theLogan Logansills sillsunroofed unroofedby byerosion erosionininaahorst-like horst-likefeature. feature. In In1995 1995aalocal localprospector prospectordrilled drilledaa499 499mmvertical verticalhole holeinto intothe theLogan LoganBasin BasinininBlake Blake Township Townshipand anddiscovered discoveredan anunusual, unusual,131 131m-thick m-thicksulphide-bearing sulphide-bearinggabbro gabbrobelow belowthe the Logan Sills. Lighifoot and Lavigne (1995) compared the geology and texture of the Logan Sills. Lightfoot and Lavigne (1995) compared the geology and texture of the gabbro gabbroto tothe thefertile fertileNi-Cu-PGE Ni-Cu-PGEbearing bearingsub-horizontal sub-horizontalgabbro gabbrochannels channelsbelow belowthe theflood flood basalt basaltsequence sequenceatatNoril'sk, Noril'sk, Siberia, Siberia,the theworld's world'slargest largestnickel nickeldeposit. deposit. North NorthAtlantic AtlanticNickel Nickelsubsequently subsequentlydetermined determinedthat thatthe thegabbro gabbrowas wasaaflat-lying, flat-lying, northeast-trending, northeast-trending,taxitic-textured taxitic-texturedintrusion intrusionup upto to130 130mmthick thickwhich whichpinches pinchesdown downtotoaa normal-looking normal-lookingLogan Logandiabase diabasesill sillless lessthan than20 20mmthick thickwithin within300 300mmofofthe thecentre centreofofthe the intrusion. intrusion.An Aninterpretation interpretationisisthat thatthe thetransition transitionfrom fromvertical verticaldikes dikestotohorizontal horizontalsills sillsinin the theLogan LoganBasin Basinisisaccompanied accompaniedby byhorizontal horizontalmagma magmachannelling. channelling.This Thisdiscovery discovery underscores underscoresthe thepotential potentialfor forNoril'sk-type Noril'sk-typeNi-Cu-PGE Ni-Cu-PGEconcentrations concentrationsininthe thebasal basalpart partofof the Rift theflood floodbasalt basaltsequence sequenceofofthe theKeweenawan Keweenawan anidea ideathat thathas hasbeen beendeveloped developed Rift—-an and andadvanced advancedby byseveral severalworkers workersininthe thepast pastdecade. decade. 43 �References Lightfoot, P.C., and Lavigne, M.J., M.J., 1995. Nickel, Nickel, copper, and platinum group element mineralization in Keweenawan intrusive rocks: new targets in the Keweenawan mineralization Keweenawan intrusive Keweenawan of the Thunder Bay Bay region, northwestern Ontario. Ontario Ontario Geological Geological Survey Survey Open Open File File Report Report 5928, 32 32 p. p. Fenwick, K.G., KG., 1963. Pye, E.G., and Fenwick, 1963. Atikokan-Lakehead Atikokan-Lakehead Sheet, Map Map 2065, Ontario Department of Mines, Geological Compilation Series, scale 1:253,440. Smith, A.R., and Sutcliffe, R.H., Smith. A.R., R.H., 1987. Keweenawan Keweenawanintrusive intrusive rocks rocks of the Thunder Bay Bav area, in in Summary of Fieldwork, 1987. Ontario OntarioGeological Geological Survey Survey Miscellaneous Miscellaneous Paper paper 137, p. 248-255. A.R., and Sutcliffe, R.H., R.H., 1989. Precambrian Smith, A.R., Precambrian geology of Keweenawan Keweenawan intrusive intrusive River area; area; Ontario rocks in the Crystal Lake-Pigeon River Ontario Geological Survey, Map P. 3139, Geological Series - Preliminary Preliminary Map, Map, scale scale 1:50,000. 1:50,000. Geology 1987. 44 �GEOMETRY BETWEEN GEOMETRY BETWEEN GOLD-RICH GOLD-RICHSUBSIDARY SUBSIDARY SHEAR SHEAR ZONES ZONES AND MAJOR MAJOR STRUCTURES: STRUCTURES: IMPLICATIONS IMPLICATIONS FOR FOR ARCHEAN ARCHEAN LODE-GOLD LODE-GOLD MINERAL MINERAL EXPLORATION EXPLORATION DEAN M. PETERSON Department of Geology, University Minnesota -- Duluth University of Minnesota Detailed GIS-based spatial spatial analysis analysis of of the three Detailed GIs-based three largest largest Archean Archean lode-gold lode-gold mining mining camps camps in in Canada Canada has led led to to the thedevelopment developmentof ofsome someseemingly seeminglyfundamental fundamentalgeometric geometric relationships relationships between major structures, subsidiary subsidiary structures, structures, and and gold gold mineralization. mineralization. The lode-gold between lode-gold mining camps included in the Lake, and Hemlo Hemlo the analysis analysis are arethe theTimmins, Timmins,Kirkland KirklandLake Lake—- Larder Lake, districts, which together have produced approximately 115 million ounces of gold. Additional analysis of the Noranda, Cadillac, and Malarctic analysis Malarctic gold camps camps of northwestern northwestern Quebec Quebec corroborate corroborate the original original findings, and add strength to the implications implications of the model. The relationships relationships link the location and and size size of gold location gold mines mines with with the the sense sense of ofshear, shear,stress stressregime regime(compression (compression verses verses extension verses parallel), and and distance to to the the major major structures structures in in each each camp. camp. Additional analysis doduments the the relationship relationship between between the the location location and size of gold gold mines mines to to the the orientation orientation and and distance distance to subsidiary subsidiary shear zones in the the camps. camps. These relationships allow the the exploration exploration geologist to quickly develop specific lode-gold lode-gold structural structural targets targets based based on on the the simple simple analysis anaiysis of of geologic maps. geologic maps. For this study, study, the major major shear shear zones zones were were divided divided into into compressional, compressional, extensional, and shear parallel segments based on regional maps and and literature literature review review (see (see inset map of parallel segments based regional geological geological maps Figure 1). GIS GIs analysis analysis has has shown shown that that essentially essentially all all of of the the gold gold in in the the camps camps has has been been mined mined a). In within 6 kilometers of major major shear shear zones zones (Table (Table 1la). In addition, addition, greater greaterthan than 98% 98%of of the the gold gold in in the three camps has been mined from zones of regional compression (Table (Table lb). ib). Together, these facts lead to the conclusion conclusion that lode-gold lode-gold mineral exploration programs should be targeted upon areas areas within 6 kilometers kilometers of compressional compressional zones zones of of major major shear shearzones. zones. Inset H .4P N\ 1St Order Shear Shear Zone Zone. 1st Order '\\ yP&IeI 212T 21.27' - \' \ 163.670 163.67' Figure 11 Figure , 59.700 \_ * — -- \ Order Shear Compression Compression Zone 1st Order Zone 7 Regional shear shear zone zone classification classification(inset (insetmap) map)and androles rulesfor forclassifying classiing the geometry of Regional geometry of associated with with major major structures. Angles subsidiary shear zones spatially associated Angles are are measured measured along along arcs from points, in the same direction as the major structures ares Son) inferred intersection points, structures sense of shear. shear. 45 �Proximity (A) (A) and and structural structural (B) (B) relationships Table I1 Proximity relationships between between lode-gold lode-gold mines mines and and major major structures structuresfor for Timunins, Kirkland Lake-Larder Lake, and Hemlo gold the T iins,K i a n d Lake-Larder gold camps, camps, Ontario. Ontario. - A) Proximity Proximity Analysis A) Analysis Distance to Major Structure <3 < 3Kilometers Kilometers 33—6 - 6 Kilometers Kilometers >6 > 6Kilometers Kilometers B) Structural Structural Analysis Analvsis Mined Gold (million Oz) (million Oz) Structural Structural Setting Selling Mined Mined Gold Gold Gold (million Oz) (million Oz) Gold Gold 83.108 83.108 32.100 32.100 0.235 0.235 72.0% 72.0% 27.8% 27.8% 0.2% Compressional Extensional Extensional Parallel 113.539 113.539 1.877 1.877 0.027 98.35% 1.63% 1.63% 0.02% 0.02% ((%) %) Table Table 22 Proximity Proximity (A) and structural structural (B) relationships relationships between lode-gold mines and subsidiary subsidiary structures for the T Timmins, structures i i n s , Kirkland LakeLarder Lake, Lake, and Hemlo Hemlo gold gold camps camps A) Proximity Analysis A) Proximity Analvsis Distance to Subsidiary Shear <200 < 200meters meters 200—250 - 250 meters meters 200 Mined Gold 1%) ('%) (millionOz) Oz) (million Gold 108.417 108.417 5.869 5.869 0.5 10 0.510 1.157 93.91% 93.91% 5.08% 5.08% 0.44% 0.44% 1.00% 250—300 250 - 300 meters > 300 meters Bl Structural Analvsis (250 m Buffer1 Subsidiary Shear Mined Gold t%> (%) Gold Angle ~ n & (million Oz) (million Oz) 106.252 106.252 160° - 180 180° 160¡ 140°- 160° 120°- 140° 1.398 100° - 120° 80° - 100° 0.000 0.400 0.000 60° - 80° 400 - 60° 20° - 40° 0° - 20° 0.006 0.860 4.170 1.200 92.97% 92.97% 1.22% 0.00% 0.35% 0.00% 1.05% 0.01% 0.75% 3.65% (%) 1%) - For this study, the relationship between the major and has been defined and subsidiary subsidiary structures structures has defined by by measurements along an arc in the same same direction as the the dominant dominant sense sense of shear shear of the the major major structure (Figure (Figure 1). 1). Each structure Each subsidiary subsidiary shear zone segment has has an an associated angle to the major segment associated angle major structure stored in its associated GIS database. structure stored its associated GIs database. The location of gold mines and their production records in each camp were spatially records spatially linked linked with shear zone. zone. The the nearest subsidiary subsidiary shear The outcome outcome spatial analysis analysis isis given 2. of this this spatial given in in Table Table 2. Approximately 99% of the gold in the camps has Approximately been mined been mined within within 250 meters meters of of aa subsidiary subsidiary In addition, (Table 2a). 2a). addition, subsidiary subsidiary shear zone (Table high-angle (160°-180°, Figure 1) 1) structures structures in the (1600-180°Figure compressional zones of of the major compressional zones major structures structures account for ofall all gold gold mined mined in the camps -93% of for —93% (Table 2b). Table 33 display the Area calculations in Table usefulness of this analysis usefulness analysis for gold gold exploration. exploration. Programs that that would would be targeted upon the highhighPrograms subsidiary in in regional regional compresangle (160°-l80°) (160"-1800) subsidiary sional zones would would reduce reduce the the total total area to be sional zones be Similar targeting criteria in explored by 99%. explored by 99%. lode-gold exploration programs would greatly lode-gold exploration programs greatly lower lower cost, cost, reduce reduce time, time, and and would would quickly quickly vector the program vector program into areas areas of of high high lode-gold lode-gold mineral potential. - Table 33 Tabulation Table Tabulation of of the the total total GIS GIS map map area, area,areas areaswithin withm 250 250meters metersof ofhigh-angle high-anglesubsidiary subsidiaryshears, shears, and explorationwould wouldbe be targeted targetedonly onlyinin and percentage percentage of of the the map map area area reduced reduced ifif exploration the most favorable favorable areas areas of of the the three three mining mining -camps. . ~Mining Camp Camp Hemlo Hemlo Timmins Timmins Kirkland GIS Map 2 Area ( ~ m ) Area (Km2) 2280.00 4106.00 2414.00 ~~ 5 Buffer Around Hi-angle0 Percentage Reduced from ~ Area (Km2) of2SOm Total Map Area Area (> 1607 Subsidiary Shears Shears Total Map 160°) Subsidiary " 5.55 5.55 19.04 19.04 24.94 24.94 46 99.70% 99.70% 99.42% 99.42% 98.70% 98.70% �GEOLOGIC GEOLOGICAND AND GIS-BASED GIs-BASED LODE-GOLD LODE-GOLD & & VOLCANOGENIC VOLCANOGENICMASSIVE MASSIVE SULFIDE SULFIDE(VMS) (VMS) MINERAL MINERAL POTENTIAL POTENTIALMAPS MAPS OF OFA A PORTION PORTION OF OFTHE THEARCHEAN ARCHEAN VERMILION VERMILIONGREENSTONE GREENSTONEBELT, BELT, NORTHEASTERN NORTHEASTERNMINNESOTA MINNESOTA DEAN M. PETERSON Department Departmentof ofGeology, Geology,University Universityof of Minnesota Minnesota -- Duluth Duluth Lode-gold Lode-gold and VMS VMS mineral mineral potential potential maps maps of of aaportion portionofofthe theArchean ArcheanVermilion Vermiliongreenstone greenstone belt belt in in northeastern northeastern Minnesota Minnesota have have been been developed developed from from the the digital digitalincorporation incorporationof ofthe thelodelodegold and VMS ore deposit models into spatial analysis of a new 1:100,000 1:100,000 scale geologic map of the the study study area. area. The TheGIS-based GIs-basedmineral mineralpotential potentialmodels modelsincorporated incorporatedfuzzy-logic fuzzy-logic techniques techniques of of map map combination combination using using variations variations of of knowledge-driven knowledge-driven (ore deposit deposit model) model) and and data-driven data-driven (analog (analog mining camp analysis) techniques. Inference Inferencenets nets depicting depictingthe the mineral mineral potential potential models models are presented in Figure 1 (lode-gold model) and Figure 2 (VMS model). are presented in Figure 1 (lode-gold model) and Figure 2 (VMS model). .a STEP I Weld Spatial STEP 2 Dab Ptocasmg a Collect Spatial Date and Input into GIS GEOLOGIC GEOLOGIC STRUCTURES STOUCTURES Extraction of GIS Features Relevant to the VMS Ore 2. Cetass burg — I. Recteifr —— ladoeda I.tOtder Prolimhiaiy Maptof Selected GIS Peanuts PoId 3rd Ott Aalt Shass l.ExwtRoekTypa 2. Crate baea I. Babies mapped eats 2. Qeeiy Database 3. C* 3. Ct.att Baits —I S Aakarile SandIa SadISt —I— ASisli' QFP Pynte Afida — Sa GOLD GOLD ANOMALIES ANOMALIES COMPETENCY COMPETENCY CONThASTS CONTRASTS LthSse I. Emct C-to 2. Reclassify Types LCeateBaff froesG ____________________ Tails —— tabs. .a S0 ALTERATION ALTERATION ASSOCIATED ASSOCIATED HOST ROCKS HOSTROCKS it Soils !ssa)cael s_ — Wth_ of Evidence Fany tut(O.lI Map Overlay %Overlay STEP STEP33 to Peedsice = * Intenuedisee Factor Maps STRUCTURAL STRUCTURAL F- Integration i i HOSTROCK HOSTROCK ALTERATION ALTERATION Factor F- Factor 1 GEOChEMICAL GEOCHEWCAL Factor Facto' i ROCK RHEOLOGY ROCKRHEOLOGY Factor Factor Modelling UwkOsss Overlay of Intermediate Factor Maps to Pyodece the Final Predictive Map 04 Map Weightings Map Woifligs - LODE MAY LODEGOLD GOLDMINERAL MINERALPOTENTIAL POTBtTTUU. MAP Figure Figure1.1. Inference Inference net for for the the three-step three-step GIS GIs model model of ofthe thelode-gold lode-gold mineral mineral potential potential of of the theArchean Archean Vermilion Minnesota. The Vermilion greenstone belt, Northeastern, Minnesota. The three three steps stepsare: are:1)1)Detailed Detailedgeologic geologic mapping Conversion of all all data datainto intoprimary primary mapping and compilation compilation of of all all available available geologic geologic data. data. Conversion GIS datasets;2) 2) Extracting Extractingand and enhancing enhancingthe the features featuresof ofthe theprimary primarydatasets datasetsthat thatare areimportant important GIs datasets; for predicting deposits; and and 3) Integration predicting lode-gold lode-gold deposits; Integration of the the preliminary preliminary maps maps using using GIS GIS modeling modeling techniques techniques that that predict predict mineral mineralpotential. potential. 47 �Build Build Collect Collect Spatial Spatial Inpul Data and Input Data Spatial Spatial into into GIS GIs Database Extraction Extractionof of GIS GIS Features Features Relevant Relevan to to ±e theVMS VMS Ore Ore Deposit Deposit Model Model . . sTEP 1 • S MAPPED BEDROCK 13EDROCK GEOLOGY GEOLOUY ALTERATION Al.Tf-RATION ZONES ZONES ROCK, ROCK.CORE, CORE.SOIL SOIL REGIONAL REGIONAL & LAKE MAGNETICS A LAKk SEDIMENT SEDIMENT MAGNI-IlCS GEOCHEMISTRY GEOCHEMISTRY . AIRBORNE & GROUND EM GROUNDFM CONDUCTORS CONDUCTORS ————t——t——±—H— , II . ~Reclaatij e~la~~ify 2 Extract 2. EM contacts con3. Create Cteate buffers buflrs I. I. ~Classi . ~ExtractAitTypes x t r a c t A l ~1~classifyinterval~ ~ ~ intervals 2. Create buffers 2. Grid soil & lakes 3. Buffer rock Ctassifr 3. Classify rock & & core core II. .CompileTF C . & T FMae M ~ ~1.IExtractEM .E~~~~~~EM 2. Reduce pole Claaai' Reduce to topole 2. Classify 3. Calculate Calculate 2VD 2VD 4. Extract Polygona ExtractPolygons STEP 22 STEP Data Data Processing roccssiog Preliminary Preliminary Maps Maps of of Selected GIs GIS Selected Features Features contacts contacts 1 Quattz- contacts contacts Epedote Volcanic-Sedsment contacts Greenstone Subvolcanic Sequences Inmiatotia Msnerattzed Intxut,ves * -Na20 ChIotite Pyrite Cu Zn Soila Cu Zn Lake Cu Zn Rocks Core 2"VD Ground Aithonse Mag EM EM Assign Weights Weights Assign Evidence of Evidence Fair weights to - I) Fuzzyweighs(0-1) Map Overlay MapOverlay STEP 3 STEP Integration itegration Modelling toddling to Produce Produce to Intermediate Intermediate Factor Maps 1 Overlay of Intermediate Intermediate Factor Maps to Produce Produce the Final Predictive Predictive Map 1 1 STRATIGRAPHY STRATIGRAPHY HEAT HEAT Factor Factor Factor Factor 1 ALTERATION ALTERATION Factor Factor rILiTt 1 GEOCHEMICAL GEOCHEMICAL Factor Factor VVMS M S MINERAL POTENTIAL MAP 1 MAGNETIC Factor Factor  EM Factor 0.20 VMSTARGETSI TARGETS !____rIVMS GIS modeling of the VMS potential of the mineral mineral potential of of Figure 22 Inference network for the 3-step GIs the Archean Vermilion greenstone belt. belt, Northeastern, Northeastern, Minnesota. Minnesota. The The three three steps steps in in the thestudy study are: 1) 1) Detailed Detailed geologic geologic mapping mapping and compilation compilation of of all all available available geological, geological,geochemical, geochemical,and and geophysical data. data. Conversion Conversion of of all all data data into into primary GIS GIs datasets; datasets; 2) Extracting and enhancing the features of the primary VMS deposits; and 3) the primary datasets that are important important for predicting predicting VMS Integration of of the preliminary Integration preliminary maps maps using GIS GIs modeling modeling techniques techniques that predict predict mineral mineral potential. Unlike similar greenstone belts of the Canadian Shield in Canada, the Vermilion greenstone belt Minnesota remains remainsunder-explored. under-explored. One One of the main reasons reasons that the area has of northeastern northeastern Minnesota seen little mineral exploration was was due due to to the the discovery of of the the great great iron iron deposits in in the the 1870's. Iron companies acquired great tracks of land and essentially prevented precious and base land and essentially prevented precious and base metal metal exploration for over a century. Recent Recentmapping mappinghas hasshown shownthe thepresence presenceof ofvery verylarge-scale large-scaleVMS VMS alteration systems (> 19 19km km strike strikelength lengthofofsemi-conformable semi-conformable quartz-epidote quartz-epidote alteration) alteration) and and gold-mineralized shear systems analogous to Archean gold camps camps in Canada. The mineral potential potential maps maps integrate integrateimportant important geological, geological, geochemical, geochemical, and and geophysical geophysical data data mapped and compiled by the author with ore deposit models. The Theore oredeposit depositmodels modelshave havebeen been largely developed developed from from the the study study of mines within the Canadian Shield and western Austrailia. largely Areas on the the maps maps with with high high modeled modeled VMS VMS and and lode-gold lode-gold mineral mineral potential potential should shouldbe beexamined examined in detail by or in by exploration exploration geologists geologists because because they they possess possess geologic geologic features features indicative indicative of ofmaj major districts. mining districts. 48 �Samuels Lake Intrusion: Intrusion: A PGE-bearing Quetico-type Intrusion Intrusion in the Central, Western Western Quetico Quetico Central, Subprovince, Northwestern Ontario Ontario •I 2 Keiko H. ~ Hattori Neil T. Pettigrew pettigrewl,, Kbiko a t t o r iand and ' John John A. Percival perciva12 I I. Ont Canada, 1. Dept Dept.of ofEarth EarthSciences, Sciences, University University of Ottawa, Ont. Canada,KIN KIN 6N5 6N5 Survey of of Canada, Canada, Ont. Canada, Canada, KIA 0E8 2. Geological Survey OE8 An array of mafic-ultramafic mafic-ultramafic bodies known as the Quetico Quetico intrusions intrusions occur occur along alongthe the northern boundary of the Quetico Quetico subprovince subprovince adjacent adjacent to the Wabigoon Wabigoon belt (Fig. (Fig. 1). 1). This This study study identified two previously has identified previously unrecognised unrecognised Quetico-type Quetico-type intrusions, intrusions, the Samuels SamuelsLake Lake and and Redhorse Lake intrusions, intrusions, in the central central western Quetico Quetico subprovince subprovince (Fig. (Fig. 1). 1). The The Redhorse Redhorse the westernmost westernmost identified identified example example of of this this type type of of Lake intrusion near the US-Canada border is the intrusion. intrusion. The Quetico Quetico intrusions intrusions characteristically characteristically contain contain hornblendite, hornblendite, clinopyroxenite, clinopyroxenite, minor minor appinite and are accompanied appinite accompanied by Cu-Ni-PGE mineralization. mineralization. Larger intrusions intrusionsalso also contain contain wherlite, gabbro, diorite diorite and syenite. syenite. They are distinguished distinguished from from the mafic-ultramafic mafic-ultramafic intrusions intrusions in the Wabigoon Wabigoon and Wawa Wawa greenstone greenstone belts, such such as as the Bad Vermilion Vermilion Lake, Lake, Grassy Grassy Portage, Portage, and Shebandowan Shebandowan complexes, complexes, by their their lack lack of of associated associated komatiities komatiities and and anorthosites. anorthosites. The 1999 1999 field field season season consisted consisted of reconnaissance reconnaissance work on on the Quetico Quetico intrusions intrusionsalong along the subprovince subprovince boundary boundary and alkaline alkaline intrusions intrusions surrounding surrounding the Samuels SamuelsLake Lake intrusion. intrusion. Grid Grid mapping and sampling were conducted on the Samuels Lake intrusion which was chosen for sampling conducted Samuels Lake intrusion which was chosen for detailed work due to recent recent exploration exploration activity activity and a lack of previous previous work. The Samuels Lake intrusion has an NE-SW elliptical form, displaying Samuels Lake intrusion an elliptical displaying weak weak concentric concentric zoning with a wehrlite wehrlite core core partially surrounded surrounded by hornblendite hornblendite and and completely completely surrounded surrounded by by marginal clinopyroxenite. clinopyroxenite. These These units units are are cut cut by small small dikes dikes and and plugs plugs of of diorite. diorite. The The wehrlite wehrlite and clinopyroxenite clinopyroxenite phases show show aa gradational gradational change change in modal modal abundance abundance of of constituent constituent and clinopyroxene clinopyroxene (Mg# (Mg# =0.83) =0.83) with with minerals. The wehrlite is composed primarily of olivine and minor phlogopite. Sulphides % Sulphides(pyrrhotite, (pyrrhotite,chalcopyrite chalcopyriteand and pentlandite) pentlandite) constitute constitute up up to to 30 30 vol vol % with olivine olivineand andclinopyroxne clinopyroxne suggest suggest the the separation separation of of . The intergrowth textures of sulphides with inuniscible (<0.06 immisciblesulphide sulphide melt melt from fromthe the parental parental silicate silicate magma m a m a .. Low Ni f< 0.06 wt%) wt%)in in olivine suggests suggests sulphide sulphide saturation saturation prior prior or or during during olivine olivine crystallization. crystallization. The The clinopyroxenite clinopyroxenite contains contains clinopyroxene (Mg#= 0.84) variable amounts of olivine (Fo76) and minor phlogopite with clinopyroxene (Mg#= variable amounts of olivine (Fojyj) and minor phlogopite with trace trace sulphides. sulphides. Homblendite Hornblendite isis composed composedof of euhedral euhedralpargasite pargasite to to magnesio-hornblende, magnesio-hornblende,phlogopitic phlogopitic biotite, and plagioclase plagioclase with with trace trace titanite, titanite, pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite, and and ilmenite. ilmenite. Diorite Dioriteconsists consists of plagioclase, magnesio-hornblende, biotite, quartz, and microcline with trace pyrrhotite, magnesia-hornblende, biotite, quartz, and microcline with trace pyrrhotite, chalcopyrite, ilmenite, magnetite, ilmenite, magnetite, titanite, titanite, and and zircon. zircon. .. intrusion has undergone The Samuels Samuels Lake ~akeintrusion undergone high temperature, deuteric deuteric processes processes and and lowlowtemperature temnerature retrograde retrograde alteration. alteration. The The deuteric deuteric phase chase resulted resulted in in the the formation formation of of hornblende hornblende after clinopyroxene, clinopyroxene, and andthe theformation formationof oflow-Ti low-Timagnetite. magnetite.ItIt may may have have been been accompanied accompanied by by serpentinization of olivine. temperature alteration Low temperature alteration produced tremolite-actinolite tremolite-actinolite alteration of homblende, hornblende, chlorite after hornblende homblende and biotite, and carbonate alteration. Alteration style and biotite, and carbonate alteration. Alteration style and and intensity intensity vary vary between between phases phases and and appear appear to to partially partially control control Cu-PGE Cu-PGE mineralization. mineralization.In In the the clinopyroxenite clinopyroxenite - . - 49 �phase, Cu-POE Cu-PGE mineralization mineralization occurs occurs in areas areas of intense intense alteration alteration of the border border phase phase with with associated associated chalcopyrite-rich chalcopyrite-rich blebs, inter-fingered with actinolite actinolite and calcite. In wehrlite, wehrlite, high high levels of POE mineralization occur in chalcopyrite-rich zones instead of pentlandite-pyrrhotite levels PGE mineralization occur chalcopyrite-rich pentlandite-pyrrhotite rich zones. Small veinlets in wehrlite wehrlite may contain significant significant amounts amounts of of apatite apatite and and Small chalcopyrite chalcopyrite veinlets with elevated POE contents. POE mineralization in the wehrlite phase is associated with the elevated PGE contents. PGE mineralization associated with the immiscible immiscible sulphide sulphide liquid, liquid, indicating indicating a magmatic origin. In the clinopyroxenite clinopyroxenite border border phase, phase, POE mineralization PGE mineralization is is associated associated with apatite, carbonate carbonate and Cu enrichment enrichment suggesting suggestingthat that volatile-rich PGEs. volatile-rich fluid, fluid, most most likely likely deuteric deuteric in origin, origin, were responsible responsible for for concentration concentration of of PGEs. The The Quetico-type Quetico-type intrusions intrusions may not be restricted restricted to the Quetico Quetico belt. The The east-west east-west trending array array of of intrusions intrusions may be extended extended eastward into the Wabigoon Wabigoon subprovince subprovince to to include include Lac Des Milles Lac, Demar Lake, Lake, Taman Taman Lake, Legris Legris Lake, Lac Des Iles, Iles, and and Tip Tip Oabbro Gabbro mafic-ultramafic 1). These These intrusions intrusions have similar similar lithological lithological assemblages assemblages to to the the mafic-ultramafic intrusions intrusions (Fig. (Fig. 1). Quetico Quetico intrusions. intrusions. The The mineralization mineralization observed in Samuels Samuels Lake and other other Quetico Quetico intrusions intrusions are also also similar similar to to that that in in the the clinopyroxenite clinopyroxenitephase phaseof ofthe theRoby Robyzone zoneininthe the2692 2692+41-2 +4/-2 Ma Ma Lac Lac Des Ties mafic-ultramafic complex. If this correlation is supported by geochronology lies mafic-ultramafic geochronology in in progress, progress, it will establish 2692 Ma. establish that that the the Quetico Quetico and and Wabigoon Wabigoon subprovinces subprovinces were proximal proximal by 2692 Figure Figure1.1.Simplified Simplifiedgeological geologicalmap mapof ofWestern WesternWabigoon, Wabigoon, Quetico, Quetico, and Wawa subprovinces. Solid, finely dashed line outlines the distribution of similar subprovinces. Solid, finely dashed line outlines distribution similar mafic-ultramafic mafic-ultramafic intrusions intrusions across across the the Quetico-Wabigoon Quetico-Wabigoonsubprovince subprovince boundary. 50 �PETROGENESIS PETROGENESISOF OFTHE THEENIGMATIC ENIGMATICAURORA AURORASILL, SILL, MESABI MESABI RANGE, RANGE, MINNESOTA MINNESOTA PHILLIPS, PHILLIPS,Erin ErinH. H.(ephillips@macalestetedu); (ephillips@macalester.edu);Wirth, Wirth,Karl KarlR., R.,Geology GeologyDepartment, Department, Macalester Macalester St. Paul, Paul, MN MN 55105 and Morey, G.B., Minnesota Geological 55105 (wirth@macalesteiiedu); (wirth@macalester.edu); and College, St. 2642 University Ave., Ave., St. St. Paul, Paul, MN MN 55114 Survey, 2642 syenitic Aurora Sill intrudes the Biwabii Biwabik Iron-formation Iron-formation of ofthe the Mesabi Mesabi Range Range in in northern northern MmMinThe syenitic nesota. Since the work of White (1954), (1954), the sill sill has has commonly commonly been assigned assigned aa Mesoproterozoic Mesoproterozoic (Keweenawan) because of its resemblance to "red rocks" associated associated with the Midcontinent Midcontinent Rift in the (Keweenawan) age because Duluth region. The Theage ageof ofthe thesill sillisisimportant important to to understanding understanding the the timing timing of of ore ore formation formation in in the Mesabi Mesabi Range. In In1999, 1999,Morey Moreyproposed proposedaaconceptual conceptualmodel model in in which which the the high-grade high-grade ores ores formed formed in in aa regional regional ground-water Strandlie (1999) argued that ground-water system system during during Paleoproterozoic Paleoproterozoic time. Subsequently, Subsequently,Graber Graber and Strandlie nearby appears nearby high high grade grade ores ores must must have have formed formed in Mesoproterozoic Mesoproterozoic or or later later time, because the the Aurora Sill appears to have controlled controlledore-forming ore-forming processes processes in nearby mines. New New data datafrom from this this study study imply imply that that the the Aurora Aurora mineralogically and Sill is quite different, both mineralogically and geochemically, geochemically,from from known known felsic felsic rocks rocks in in the Midcontinent Midcontinent Rift. Thus, Thus,the the age ageof of the the sill sillremains remains uncertain uncertain and the possibility exists that it was intruded soon after deposition of the Biwabik deposition Biwabik Iron-formation Iron-formation in in the the Paleoproterozoic Paleoproterozoic(ca (ca 1878 1878Ma; Ma; Fralick, Fralick,1998). 1998). The Aurora The Aurora Sill Sill extends extends approximately approximately 5.6 5.6 km km along along the the Mesabi Mesabi Range Rangenorth northof ofthe thetown townof ofAurora and ranges in thickness thickness from 6 to 37 m m (White, (White, 1954). The sill was recently exposed exposed during during mining operaoperations in the NW 1/4, NE 1/4, T58N, R15W. RISW. Due to the inaccessibility inaccessibility of the exposures 114,NE 114, sec 3, T58N, ofthe exposuresalong along vertical vertical walls in the mine, samples were collected collected from from large largeblocks blocksalong alongaabench benchimmediately immediatelyabove abovethe thesill. sill. In In all, ten samples samples were studied from this locality along with seven samples from core (16.4-38.1 m in depth) studied locality in see 2, T58N, R15W. R15W. Fine-grained, porphyritic porphyritic syenite syenite from from the the margin margin of of 114, NE 1/4, 114, sec drilled in the NW 1/4, the sill exhibits exhibits trachytic trachytic texture; texture; mediummedium- to to coarse-grained coarse-grained syenite syenite in in the the interior interior of of the sill sill lacks lacks aligned aligned microcrysts (0.2-1.0 (0.2-1.0 mm) mm) plagioclase. Sodic Sodicplagioclase plagioclase(albite) (albite)occurs occurs as as phenoerysts phenocrysts (3.0-7.0 (3.0-7.0 mm) and microciysts Maiic minerals minerals in in finefineand is extensively altered. Mafic ' ' ' ' # ' ' ' ' # ' ' ' ' ' ' ' ' ' I15s grained samples include grained include small small (0.1-0.3 (0.1-0.3 mm) mm) and and euhedral aegirine; euhedral aegirine;fibrous fibrousamphibole amphiboleand andchlorite chloriteare are common in the coarse-grained samples. Other Otherminminerals oxides, Fe sulfide, sulfide, and zirerals are are K-feldspar, K-feldspar, Fe-Ti oxides, 3 ,oI0 con. con. The presence presence of two two feldspars feldspars indicates indicates $ 1 w subsolvus crystallization at at high highPH2@ H2Q 0 Coarse-grained Coarse-grained samples samplescontain contain50 50 modal modal per- S Mideontinent Rift sodic plagioclase plagioclase and modal percent cent sodic and 5-20 5-20 modal percent K-feldK-feld1 Granophyre Complexes Complexes 4: 5 Graaopbyre spar and are classified as syenite syenite and alkali-feldspar alkali-feldspar a? Lester Lester River Sill Sill these rocks insyenite. CIPW CIPW norm norm compositions compositions of ofthese clude 68-82 percent alkali alkali feldspar feldspar (Or (Or ++ Ab), 5-10 Endion Sill sill o 4o , , , , , , , , , , I , , , , percent plagioclase (An), and as much as 5 percent 50 60 70 SO 60 70 80 nepheline; they are are classified classified as as nepheline-bearing nepheline-bearing Si02 %) Sio, (wt. %) alkali syenite or or nepheline-bearing nepheline-bearing syenite. syenite. FineFinegrained samples from along the margin ofthe sill congrained from margin ofthe con- Figure Figure1. 1 Na20+K20 NaO+K20(total (totalalkalis) alkalis) versus Si02 SiO comparwmpartain 74-84 percent normative alkali feldspar (Or + + ing Aurora Sill rocks rocks with with those ofthe of the Endion Endion Sill, Lester Lester (<4%) normative quartz quartz and River Sill (Green, 1972; JJerde, Ab) with small amounts (<40h)n0rmative 1991), Midwntinent Midcontinent Rift d e , 1991), are classified classified as alkali alkali feldspar feldspar syenite. granophyre complexes complexes (Kennedy (Kennedy et al., this volume), volume), and granophyre Samples from from the Aurora Sill exhibit granophyric dikes of the Dunka River region (Harris exhibit little little granophyric (Harris and and percent; Wirth, this this volume). volume). Symbols: inverted geochemical inverted triangles triangles == drill geochemicalvariation variation(SiO2 (SO2= = 54.6-60.7 wt. percent; (open = = fine-grained; Y= = 9-19 Mg# mine (open fine-grained;half-filled half-filled== core; diamonds diamonds == mine 9-19 ppm) suggesting suggesting that that the core; Mg# == 0.40-0.75; Y filled = coarse-grained). = warse-grained). medium-grained; filled medium-grained; intrusion has undergone relatively little intrusion little internal frac- 1.0 6 , 51 �tionation. Al 203 con159 so tionation.All Allofofthe thesamples samplesexhibit exhibithigh highA120i concentrations centrations and andare areperalurninous peraluminous to tometaluminous. metaluminous. There There appears appears to tobe beno nocorrelation correlationbetween betweenstrucstructural tural position position in in the the sill silland andcomposition. com~osition.Marked Marked 00 0 differences differencesexist existininthe theconcentrations concentrationsofofsome someeleelements drillcore coreand and I (e.g., K20 K 2 0and and Si02) SO2) between between drill ments(e.g., mine minesamples samples.Such Suchdifferences differencescould couldreflect reflectdifferdiffer- S-S ent entdegrees degreesof ofalteration alterationororfractionation fractionationalong alongthe the & I length the sill. lengthof ofthe sill.Alternatively, Alternatively,the thedifferences differencesmight might reflect reflectthe thepresence presence of oftwo twoseparate separateintrusions, intrusions, but but this thisisisconsidered consideredunlikely unlikelybecause becausethese thesesample sampletolocalities are well within the 5.6 km expanse of the sill calities are well within the 5.6 km expanse ofthe sill o 0 as 10 15 asdefined definedby by'White White(1954). 0954). "(}"') yhmm) The Aurora Sill is distinct from the felsic com~ h e ~ & o sillis r a distinct from the felsic comFigure2.2.Nb Nbversus v a ~Yplot Yplot s comparing comparingAurora AuroraSill Sillsamples samples plexes plexesofofthe theMidcontinent MidcontinentRift Riftininseveral severalrespects. respects. Figure withanalyses analysesofofMidcontinent MidcontinentRift Riftgranophyre granophyrecomplexes complexes The andquartz with Thesill silllacks lacksthe thegranophyric granophec textures texturesand (Kennedyetetal.5 flmvolume). volume).Symbols SymbolsasasininFigure Figure1.1. al., this that thatare an.typical typicalofoffelsic f&iC rocks r o c kofofthe theMidcontinent Midcontinat (Kennedy $ I - I I Rift. Rift.The Thesill sillisisweakly weaklysaturated saturatedtotoundersaturated undersaturated ininsilica silicaand andcontrasts contrastssharply sharplywith withthe thesilica-saturated silica-saturatedrift-related rift-relatedgranophyres. granophyres. Furthermore Furthermorethe theAurora Aurora Sill Sillisischaracterized characterizedby byhigh hightotal totalalkalis alkalis(Figure (Figure1),I),Nb/Y NbN(Figure (Figure2), 2).and andCe/Zr CeIZrcompared comparedwith withfelsic felsicrocks rocks of ofthe theMidcontinent MidcontinentRift. Rift. The Thesill sillalso alsolacks lacksthe thenegative negativeNb Nbanomalies anomaliesthat that are arecharacteristic characteristicof ofthe the MidcontinentRift Riftgranophyres. granophyres.This Thisproperty propertysuggests suggeststhat thatthe thesill sillwas wasderived derivedfrom fromaamantle mantlemelt meltthat thatdid did Midcontinent Nband andRb, Rb,low-Y low-Ycomposition compositionof ofthe thesill sillisis notinteract interactsignificantly significantly with withcrustal crustalmaterials. materials. The Thehigh highNb not theAnimikie Animildeforelandbasin. foreland basin. typicalofofwithin plategranites m i t e s(Pearce, (Pearce,1984), 1984).consistent consistentwith withemplacement emplacementininthe typical within plate Nd Ndisotope isotopeand andU-Pb U-Pbzircon zirconstudies studiesare areininprogress progressand should provide additional constraints on the petrogenesis genesisand andage ageofofthe theAurora AuroraSill Sill(Phillips, (Phillips,ininprep). prep References ReferencesCited Cited D.W.Davis, Davis,1998, 1998,The TheAge Ageand andProvenance Provenanceofofthe theGunflint Gunflimt LapilliTuff. Tuff.Institute Instituteonon Fralick.P.W., P.W.,S.A. SA.Kissin, Kissin,and and11W. Fralick, Lapilli Lake LakeSuperior SuperiorGeology, Geology,Proceedings Proceedingsand andAbstracts, Abstracts,p.p.66-67. 66-67. Strandlie,1999, 1999,Where Whereace arethe theMetamorphosed MetamorphosedNatural NaturalOrebodies Orebodiesofofthe theMesabi Mesabi Graber,Ronald RonaldG. G.and andAlan AlanI.J.Strandlie, Graber, Range? ononLake 17-19. Range?Institute Institute LakeSuperior SuperiorGeology, Geology,Proceedings Proceedingsand andAbstracts, Abstracts,p.p.17-19. Green,J.C., J.C.,1972, 1972,North NorthShore ShoreVolcanic VolcanicGroup: Group:ininAACentennial CentennialVolume, Volume,Minnesota MinnesotaGeological GeologicalSurvey, Survey,Sims, Sims,P.K. P.K. Green, and andG.B. G.B.Morey, Morey,editors, editors,p.p.294-332. 294-332. andK.R. K.R.Wirth, Wirth,this thisvolume, volume,Petrogeneis Petrogeneisofofgranitic graniticrocks rocksofofthe theDunka DunkaRiver Riverregion, region,eastern easternMesabi Mesabi Harris,E.E.and Harris, Range, Range,Minnesota. Minnesota. Jerde,Eric EricA., A,,1991, 1991,Geochemistry Geochemistry andPetrology PetrologyofofHyuabyssal RocksAssociated Associatedwith withthe theMidcontinent MidcontinentRift, Rift,NorthNorthJerde, and 1-lypabyssal Rocks easternMinnesota. Minnesota.Unpublished Unpublished Ph.D.Thesis, Thesis, UniversityofofCalifornia, California,Los LosAngelas. Augelas. eastern Ph.D. University W i d ,and andJ.J.Vervoort, Vervoort,this thisvolume, volume,Petrogenesis PetrogenesisofofMidcontinent MidcontinentRift RiftGranophyres: Granophyres:EviEviKennedy,Bryan BryanC., C.,K.K.Wirth, Kennedy, dence dencefrom fromgeochemistry geochemistryofofKeweenawan Keweenawangranitic graniticigneous igneouscomplexes complexesofofnorthern northernMinnesota. Minnesota. — Product Morey,G.E., G.B.,1999, 1999.High-Grade High-GradeIron IronOre OreDeposits Depositsofofthe theMesabi MesabiRange, Range,Minnesota MinnesotaProductofofaaContinental-Scale Continental-Scale Morey, Proterozoic 133-142. ProterozoicGround-Water Ground-WaterSystem. System.Economic EconomicGeology, Geology,VV94, 94,p.p.133-142. Pearce,l.A., J.A.,NEW. N.B.W. Harris, Ymdle, 1984, Trace element discrimination diagrams tectonic intetprePearce, Harris, and8ndA.G. AG. Tindle, 1984, Trace element discrimination diagrams forfor thethe tectonic interpretation rocks. Journal of Petrology, V 25, p. 956-983. tationofofgranitic granitic rocks. Journal of Petroloev. V 25. D. 956-983. . , Phillips, Aurora Phillips,Erin ErinH., Hi,ininprep, prep,Petrogenesis Petrogenesisofofthe theEnigmatic Enigmatic AuroraSill, Sill,Mesabi MesabiRange, Range,Minnesota, Minnesota,Unpublished Unpublishedhonors honors thesis, MN. thesis,Macalester MacalesterCollege, College,St.St.Paul, Paul.MN. White, Geological White,David DavidA., A.,1954, 1954,The Stratigraphy Stratigraphyand andStructure Structureofofthe theMesabi MesahiRange, Range,Minnesota. Minnesota.Minnesota Minnesota Geological Survey University ofofMinnesota SurveyBulletin Bulletin38. 38.Minneapolis: Minneapolis:The The University MinnesotaPress, Press.p.n.63-66. 63-66. -. . 52 �I I I Low-grade metamorphic o the Keweenawan Portage Low-grade metamorphic zonation zonation of Lake Lake Volcanics Volcanics on on the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan U. U. PUESCHNER* PUESCHNER* and and S. S. Th. Th. SCHMIDT SCHMIDT Mineralogisch-Petrographisches Mineralogisch-PetrographischesInstitut Institut Universitaet Universitaet Basel/Switzerland BaseWSwitzerland *UPUESCITNER@l1njbch *U.PUESCHNER@unibas.ch The The metamorphic-hydrothermal metamorphic-hydrothermal alteration and mineral assemblages assemblages of the the Portage Portage Lake Lake Volcanics Volcanics (PLV) (PLV) on onthe theKeweenaw KeweenawPeninsula Peninsulain in Michigan Michigan have been been studied studiedover overthe thelast last - have ten decades due to the occurrence of native copper deposits. Jolly & Smith (1972) ten decades due to the occurrence of native copper deposits. Jolly & Smith (1972) illustrated illustrated for for the the first firsttime timethe theexistence existenceofofa asystematic systematiczeolite-prehnite-pumpellyite zeolite-prehnite-pumpellyite sequence in the PLY. In their Eagle Harbor drill core profile sequence the PLV. In their Eagle Harbor drill core profilethey theyidentified identifiedaazonation zonation from from zeolite zeolite facies facies in in the the upper upper part part of of the thesection sectiontotoaaprehnite-pumpellyite prehnite-pumpellyite facies facies in in stratigraphically lower parts. In this study, three diamond-drill core profiles (Fig. A) A) stratigraphically lower parts. In study, three diamond-drill through through the the PLY PLV were were re-examined re-examined using using aa combination combination of of different different techniques techniques such such as as electron electronmicroprobe microprobeanalysis analysisand and special specialX-ray X-ray powder powder diffraction diffraction techniques. techniques. The Theprofile profile include the Ahmeek, the Copper Harbor, and the Eagle Harbor profile and penetrate penetrate 5000 5000 include the Ahmeek, the Copper Harbor, and the Eagle Harbor m m of of vertical vertical section section in in the the PLY, PLV, and and are are spaced spaced over over aa distance distance of of 50 50kin. km. The Theprofiles profiles were were correlated correlatedusing usingcharacteristic characteristicinterfiow interflowsediments sedimentsand and selected selectedlava lavaflows flowsas asmarker marker horizons. horizons. Macroscopic of 614 samples indicate at least three Macroscopic and microscopic microscopic examination examination of samples indicate three and and possibly possibly up upto tofive fivedifferent differentstages stagesofofalteration alterationbased based on onthe thevarious variousamygdule amygduleinfilling infilling sequences sequences that that can canbe bedifferentiated differentiatedduring duringthe thedeposition depositionand andsubsequent subsequenttilting tiltinghistory history of of the the PLY. PLV. AA vertical vertical as as well well as aslateral lateral zonation zonation is observed observed in the PLY PLV on on the the Keweenaw Keweenaw Peninsula. Peninsula. From From the the approximately approximately southwest southwest to to the the northeast, northeast, three three different different low-grade metamorphic zones can be observed. In the vicinity of the former low-grade metamorphic zones can be observed. In vicinity the former copper copper mining mining region region and andadjacent adjacenttotothe theKeweenaw KeweenawFault, Fault,aapumpellyite-prehnite pumpellyite-prehnitefacies, facies,also also with abundant epidote is observed. Further to the north and stratigraphically below the with abundant epidote is observed. Further to the north and stratigraphically below the Greenstone Greenstone Flow Flow aapumpellyite-prehnite pumpellyite-prehnite facies facies isis present. present. The The flows flows above above the the Greenstone to the the northeast northeast toward toward the the Keweenaw Keweenaw Tip Tip show show aa zeolite zeolite Greenstone Flow and and thrther further to facies facieswith with laumontite, laumontite,phyllosilicates phyllosilicates(mainly (mainlyclinochlore) clinochlore)and andcalcite. calcite. I I I I I I The The alteration alterationof of the the PLY PLV starts startswith withthe thefilling fillingof ofsmall small(<3 (<3 mm) mm) vesicles vesicles and and the the lining lining of 1). During During deposition deposition and and of larger largervesicles vesicleswith withphyllosilicates phyllosilicates(alteration (alterationstage stage 1). subsequent subsequent burial burial metamorphism metamorphism of the the sequence sequence (alteration (alteration stage 2), 2), Section Section CC and andDD (Fig.: A ++ B) B) experienced experienced conditions conditions of ofthe thepumpellyite-prelmite pumpellyite-prehnitefacies facies(assemblage (assemblage (Fig.: A pumpellyite-prehnite-epidote-albite) which the sequence. sequence. The The pumpellyite-prehnite-epidote-albite) which is the highest observed in the beginning beginning thrusting-event thrusting-event of of the the PLY PLV combined combined with with the theformation formationof ofthe theKeweenaw Keweenaw Fault Fault tilts tilts the thePLV. PLV. AAnew newalteration alterationstage stage33with withaafluid fluidprobably probablyoriginating originatingfrom fromthe the Lake LakeSuperior Superiorsyncline synclinenow nowcrosscuts crosscutsand andoverprints overprintsthe the earlier earlierburial burialmetamorphic metamorphicstage stage 53 �2, especially especially in in the the Section SectionAAand andB.B.Afterwards Afterwardsa anew newNINW-SSE NNW-SSE directed directed fracture fracture system was set up on the Keweenaw Peninsula. Along these fracture zones a hyper salinar ore containing containing fluid deposited deposited in open open pore pore space space quartz, quartz, native native copper copper and and calcite calcite conditions similar to the the temperature temperature conditions conditions of of alteration alteration (alteration stage 4) under conditions stage 3. The low-grade history of of the the Keweenaw Peninsula ends ends with with a low-grade metamorphic metamorphic history Keweenaw Peninsula meteoric, cold and low salinity fluid that precipitates the final calcite and late zeolites in veins veins and and still still open open amygdules amygdules(alteration (alterationstage stage5). 5). Differentiation of of Jolly, W. T. a. a. S., S., Raymond Raymond E., E., 1972, 1972, Degradation Degradation and Metamorphic Metamorphic Differentiation the Keweenawan Journal of the Keweenawan Tholeiitie Tholeiitie Lavas Lavas of of Northern Northern Michigan, Michigan, U.S.A.: U.S.A.: Journal Petrology, v. 13, 13, p. p. 273-309. 273-309. Paces, 1988, Magmatic Magmatic processes, processes, evolution and and mantle mantle source characteristics characteristics Paces, contributing to the petrogenesis contributing to petrogenesis of the the Midcontinent Midcontinent Rift basalts: basalts: Portage Portage Lake Lake Volcanics, Keweenaw Peninsula, Michigan [Ph.D. thesis]: Michigan Michigan Technological Technological University, 413p. 4l3p. 54 �A: SW NE [m] -o Top of Portage Lake Volcanics -1000 Hancock Congi. Calumet & Hecla Congl. - 2000 3000 Bohemia Congi. - 4000 Keweenaw Fault - 5000 0 n n. Portage Portage Lake Lake Volcanics Volcanics b q 1- 1 I—-i [ 1 1 1 D57 1 I D57I bigger single flows in in the the PLV PLV Interflow sediments used as marker horizons Interflow horizons other interfiow interflow sediments sediments with with in inthe the PLV PLV sampled drill cores Figure: A: :Back ~ ~ a rotated c k stratigraphic cross-section cross-sectionof of the the Portage PortageLake LakeVolcanics Volcanics (PLV) (PLV) along along strike strike from from Houghton in the southwest to the Keweenaw Point in the the northeast. With With the the sampled sampled drill cores Houghton appropriate marker and appropriate marker horizons. horizons. (Modified (Modifiedfrom from Paces Paces1988) 1988) Simplified sketch of cross-section B: Simplified cross-sectionfor easy easy reference. reference. 55 55 �Modeling Modeling the effect of intermediate intermediate temperature temperature(350°-500°C) (350'-500°C Mazatzal-age Mazatzal-age thermal thermal overprinting on on argon argon diffusion in hornblende from the southern Lake Superior Superior region. region. RAMPE, RAMPE, J.S., and and HOLM, HOLM, D.K., D.K., Dept. Dept. of of Geology, Geology, Kent Kent State State University, University,Kent, Kent,OH OH44242 44242 Mica Ar/Ar ArIAr ages from the southern Lake Superior region leave little question that that much much of of the the Penokean Penokean orogenic belt was thermally and deformationalty deformationally overprinted by Mazatzal (ca. (ca. 1650 1650 Ma) orogenic activity to the south (Holm et al., 1998; 1998; Romano et al., 2000; Loofboro Loofboro and and HoIm, Holm, 1998). Complete Complete resetting resetting of of mica mica argon argon systematics systematics from from bedrock bedrock samples samples beneath beneath 1750-1630 1750-1630 Ma deformed heating to temperatures deformed quartzites quartzites suggests suggests widespread widespread heating temperatures above 350°C 350° during during Mazatzal-related metamorphism. Hornblende Ar/Ar ages ages from within the Mazatzal-related metamorphism. Hornblende ArIAr the deformed deformed region region (Romano, 2000) are predominantly (Romano, 1999; Mancuso, Mancuso, 2000) predominantly younger younger than the the Penokean Penokean Orogeny, Orogeny, scattering from 1800-1638 1800-1638 Ma (Fig. (Fig. 1). 1). Three of of the the hornblende hornblende separates separates analyzed analyzed were were completely completely reset, probably by localized localized hydrothermal fluid-related activity associated with the the Mazatzal postRomano et et al. al. (2000) (2000) have have postulated postulated that the the scatter scatter of of the the other other postMazatzal Orogeny. Orogeny. Romano Penokean Penokean hornblende hornblende ages ages (over (over aa 70 70 m.y. m y . interval) interval) reflect reflect variable variable retention retention of of radiogenic radiogenic argon argon associated associated with episodic episodic loss loss after after initial initial closure closure during during Penokean Penokean time. time. In In order order to to test test this this hypothesis, hypothesis, we we have have modeled modeled various various thermal thermal histories histories by by imposing imposing peak peak temperature temperature excursions excursions from over orogenic orogenic timescales timescales (20-80 (20-80 my.). m.y.). The from 350°-600°C 350'-600° over The effectiveness effectiveness of diffusion diffusion in in resetting ArIAr ages is primarily a function of the the peak peak temperature temperature and its its duration; duration; the the model model resetting Ar/Ar results results are are fairly insensitive insensitive to choice of initial and final conditions (Lootboro (Loofboro and and Holm, Holm, 1998). 1998). The suggests that the distribution of hornblende Ar/Ar ArIAr ages ages (Fig. (Fig. The results of modeling modeling (Fig. (Fig. 2) suggests 1) 1) is consistent with the the partial partial resetting resetting of of argon argon systematics systematics at at ca. ca. 1650 1650Ma Maby bythermal thermalpulses pulses reaching temperatures between between 350' 350° and and 460°C 460°C. A recent petrologic investigation of reaching maximum temperatures the the deformed deformed Baraboo Baraboo quartzite quartzite indicates indicates metamorphic metamorphic temperatures temperatures of of 320°-390°C 320'-39O0C (Medaris (Medarisetet al., 1998). 1998). We Wedo donot notconsider considerititimprobable, improbable, therefore, therefore, that that bedrock bedrock regions regions underlying underlying the the deformed deformed quartzites quartzites reached reached even higher higher temperatures temperatures (between (between 400° 400' and and 460°C) 460°Cduring during Mazatzal-age Mazatzal-age overprinting. overprinting. The Themodeling modelingsuggests suggeststhat thataacombination combinationofofelevated elevatedtemperatures temperatures (350°-460°C (350'-460° with with gradients gradients in inTmax) Tmax)and and localized localized fluid-activity fluid-activity associated associated with withMazatzal Mazatzal deformation deformation provide provide the simplist simplist explanation explanation for preservation preservation of of the the scattered scatteredPenokean, Penokean, intermediate, intermediate, and and Mazatzal Mazatzal hornblende hornblende age agedata data(Fig. (Fig.1). 1). We We present present aa conceptual conceptual model model for for Mazatzal Mazatzal orogenic orogenic overprinting overprinting of of the thesouthern southernLake Lake Superior Superior region (Fig. 3). The Thegeometry geometrywe wedepict depictfor forcollision collisionof ofthe theMazatzal Mazatzalprovince province isisinin concert concert with with that that recently recently proposed proposed for for Mazatzal Mazatzal collision collision in in the thesouthwest southwestU.S.A. U.S.A. (Selverstone (Selverstone et al., 1999) 1999)and and accounts accounts for for southward southward vergence vergence of of folds folds in in the the Baraboo Baraboo quartzite quartzite (Dalziel (Dalziel and and et al., Dott, 1970). 1970). Our Ourresults resultscorroborate corroboratethe thehypothesis hypothesisproposed proposed nearly nearly 20 20years years ago agoby by Dott Dott(1983) (1983) Dott, that that the the severity severity of of quartzite quartzite deformation deformation in in Wisconsin Wisconsin was was related related to tocollision collisionfrom fromthe thesouth southatat —1630 -1630 Ma. Ma. References References Dalziel, Wisc.Geol. Geol.and andNat. Nat.Hist. Hist.Surv. Surv.Inf. Inf.Circ. Circ.14, 14,164 164p.p. Dalziel, I.W.D., I.W.D., and and Dott, Dott, R.H. R.H.,Jr., Jr.,1970, 1970,Wisc. Dott, Dott, R.H., R.H., Jr., Jr., 1983, 1983,Geo. Geo.Soc. Soc.Am. Am. Mem. Mem. 160, 160,129-141. 129-141. Holm, D.K., D.K., Schneider, Schneider,D., D., and and Coath, Coath,C.D., C.D., 1998, 1998,Geology Geology 26, 26,907-910. 907-910. Hoim, Loofboro, 1-82. Loofboro, J.J. and andHolm, Holm,D.K., D.K.,1998, 1998,Inst. Inst.Lake LakeSuper. Super.Geo. Geo.44, 44,881-82. Mancuso, C., 2000, 2000, Kent Kent State StateUniversity University MS MS thesis, thesis,97 97p. p. Mancuso, C., Medaris, L.G., L.G., Jr., Jr., Brown, Brown, PB., P.B.,and andBunge, Bunge,R.J., R.J.,1998, 1998,Inst. Inst.Lake LakeSuper. Super.Geo. Geo.44, 44,89-90. 89-90. Medaris, Romano, Romano, D., D., 1999, 1999,Kent KentState StateUniversity University MS MSthesis, thesis,92 92p.p. K.A., 2000, 2000, Precambrian Precambrian Geology Geology(in (inpress). press). Romano, D., D., HoIm, Holm, D.K., D.K., and and Foland, Poland, K.A., Romano, Selverstone, J., J., Pun, Pun, A., A,, and and Condie, Condie, K.C., K.C., 1999, 1999, Geol. Geol. Soc. Soc. Am. Bull. 111,590-606. I l l , 590-606. Selverstone, 56 �Partial resetting Partial resetting associated associated with with Mazatzal Mazatzal deformation deformation A> i 0'/ dBiW3-0 a Y 7 -'9Q Inu Li Penokean metamorphism /\ Penokean metamorphism (not reset) reset) (not \ c' 500 500 6- complete resetting Locally complete resetting associated associated with with Mazatzal Mazatzal deformation deformation 'S \ Age of Age of metamorphism metamorphism \ \ 2 \ \ a E C) H 4 /1 v 100• 100 25 25 -- 'L \ 300 0 and deformation of quartzites Toward localized localized younger — — D Toward resetting associated associated resetting with with 1100 1100Ma Ma rifting rifting 9 I , 1850 1850 I I P P 1550 1650 1650 1550 Age Age (Ma) (Ma) south of of the the Mazatzal-age Figure 1. Summary Summary of from bedrock bedrock south Figure 1. of hornblende hornblendeAr/Ar ArIAr dates dates from Mazatzal-agethermal thermal front front Romano et al. (after Flomano, Romano, 1999, 1999, and and Mancuso, Mancuso,2000). 2000).Temperature-time Temperature-timepath pathmodified modifiedafter after Romano eta\. (after (2000). Note gap gap in spread of ofhornblende hornblendedates datesbetween between 1733 1733 and and 1646 1646 Ma. (2000). Note in spread Ma. 1850 1750 1750 0 Hornblende — .5 (C S 1750 20 Ma excursion intervals C) 0) S (0 0 PC 0) 1650 80 Ma excursion intervals C S S 5'—— mica ages 2 PC C. C. araooo — < 1550 metamorphism metamorphism I I I I I I I I I I 600 400 500 200 300 200 300 400 500 600 Maximum thermal excursion excursion Maximum temperature reached during thermal (°C) PC) Figure 2. Results Resultsof of modeling modelingaa Mazatzal-age Mazatzal-age (1650-1600 (1650-1600 Ma) thermal overprinting on minerals which the Penokean orogeny orogeny (1850-1830 (1850-1830Ma). Ma). Dashed Dashed curves show effect on initially cooled shortly after the apparent age data for for 20 m.y. m.y. temperature temperature excursions excursionsat atvarious variouspeak peaktemperatures. temperatures. Solid lines for 80 m.y. m.y. excursions. Squares Squaresrepresent represent hornblende hornblende age age data data as in figure 1. Stippled Stippledregion regiondepicts depictsthe thetemperature temperature range necessary to thermally reset reset hornblende hornblende to the degree degree indicated indicated by the the hornblende hornblendeage age data. data. N undeformed Barron undeformed Barren quartzite \ quartzite deformed quartzites sS 1650-1630 0 Ma Ma Mazatzal Orogeny Orogeny C Figure 3. Conceptual Conceptualmodel model(no (no scale) scale) for the Mazatzal orogeny and andits its effects effectsin inthe the southern southernLake Lake Superior region. Modified Modifiedafter after Romano Romano et al., 2000. Collision Collisioncauses causescrustal-scale crustal-scaledeformation, deformation, south-verging of the the Penokean orogenic orogenic belt. belt. CM is continental south-vergingfolds, and heating of much of continental margin, MT is Marshfield Marshfield terrane, MP is Mazatzal Mazatzai province, NFZ is Niagara Niagara fault zone, WMT WMT is is Wisconsin Wisconsin magmatic terrane. magmatic 57 �THE 'SANDOR' 'SANDOR' DIAMOND DIAMOND OCCURRENCE, OCCURRENCE, MICHIPICOTEN MICHIPICOTEN GREENSTONE GREENSTONEBELT, BELT, WAWA, WAWA, preliminary study) ONTARIO study) ONTARIO ( a preliminary SAGE, R.P., R.P., Ontario Geological Survey, Survey, 933 933 Ramsey Lake Road, Sudbury, Sudbury, Ontario, P3E 6B5 (705-670SAGE, 5949; ron.sage@ndm.gov.on.ca) ron.sagendm.gov.on.ca) The "Sandor" diamond occurrence is is the first discovery of a bedrock diamond source in the Michipicoten region since since veteran prospector "Mickey" "Mickey" Clement reported in 1993 1993 the presence of alluvial diamond diamond in the the Michipicoten River to the Ontario Geological Survey. River to the Ontario Geological Survey. A xenolith-bearing lamprophyre dike Surmacz and and Geologist Geologist dike was observed by veteran prospector Sandor Sumiacz Marcefle Marcelle Hauseux along highway 17 17 in Lalibert Township north of Wawa, Ontario on June 22, 1993 1993 (S. ( S. Surmacz, Prospector, personal communication, 1997). area 1997). Exploratory work was being conducted in the area under an Ontario Prospector Assistance Program (OPAP) grant. Diamond indicators were not found but a sample for geochemical analysis returned results interpreted as unfavorable for the presence of diamond diamond (S. Prospector, personal personal communication, communication,1997). 1997). Surmacz, Prospector, Surmacz resampled the the Wawa Wawa dike dike in in 1995. The The sample was was sent to the Saskatchewan Surmacz and and 1-lauseux Hauseux resampled Research Council's diamond recovery laboratory and 6 gem diamonds recovered (press release, KWG Resources Inc., June 6, 1996; 1996; S. S. Surmacz, Sunnacz, Prospector, personal communication, 1997). 1997). The ground was claimed from the Algoma Central Railroad and optioned to Spider Resources Inc. (S. Surmacz, Prospector, 1997). personal communication, 1997). The occurrence represents a unique discovery  42 Ma, L. Heaman, discovery of diamond in Archean (2703 ± University of Alberta, unpublished data) rocks of non-kimberlite composition. The dikes are commonly data) non-kiiberlite of characterized by rounded mafic xenoliths up to 11 metre in size set in a fme fine grained groundmass. The The xenoliths are commonly widely spaced spaced throughout the lamprophyre dike but hut in some dikes the xenoliths may be densely packed. The The xenoliths weather in in positive relief and commonly are enveloped in a dark biotite-rich reaction rim up up to to several several centimeters centimeters in in width. The dikes have been subjected to regional metamorphism and tectonism and actinolite-talc-carbonateassemblage. Primary and the xenoliths altered altered to an actinolite-talc-carbonate mineralogy and texture are are not preserved in in the matrix or xenoliths. Geochemically the dikes dikes approximate aa basalt or or mildly alkalic basalt magma and the xenoliths pyroxenite. These diamoniferous dikes dikes are are concentrated concentrated in in the northwest-central region of the Michipicoten Greenstone Belt largely restricted to to aa synformal anticline anticline centered in Lalibert Township. The dikes are concentrated near and east of of the Dickenson Dickenson Lake Lake syenite syenite stock, but a genetic relationship between the stock and dikes dikes remains to be firmly firmly established. established. The The dikes are are both conformable and crosscutting to the deformed supracrustal supracmstal stratigraphy. The The lamprophyre lamprophyre dikes are are up to 5 m in width and cannot be traced any great great distance in the bush % of of the bush covered terrain. Diamond Diamond is is distributed erratically in the dikes and only 10 10 % dikes have yielded diamond. diamond. The dikes likely source source for for dikes do do not contain contain mineral mineral compositions compositions characteristic of kimberlite and are not a likely the kimberlite kiiberlite indicator indicator minerals found found in in the region. Geophysical Geophysical methods have proven ineffective in in locating the dikes. The presence of actinolite and anomlous Cr and Ni contents in the soils are the most effective prospecting techniques. 58 �Lithogeochemistry Lithogeochemistry and and Paleotectonic Paleotectonic Setting Setting of the Bend Northern Wisconsin Massive Sulfide Deposit, Northern Klaus J. Schulz Nicholson Schulz and Suzanne W. Nicholsov U.S. Geological Geological Survey Survey 954 National National Center Center Reston, VA 20192 20192 The Bend massive sulfide sulfide deposit deposit is is located located in in Taylor Taylor County, County, Wisconsin, Wisconsin, approximately approximately miles north-northwest north-northwest of Medford, Medford, in in the the Chequamegon ChequamegonNational NationalForest. Forest. Exploration 19 miles conducted between 1985 1985and and 1994 1994by by the the former former Jump Jump River River Venture, Venture, and and more more recently recently by by Sharpe Sharpe Energy Energy and and Resources, Resources, identified identified 3.9 3.9 million million short short tons tons of of ore ore grading grading 1.87% 1.87% copper, copper, 0.09 0.09 opt gold, and 0.39 opt silver (DeMatties and Rowell, RowelI, 1996). We conducted a geochemical study conducted of the volcanic section section hosting hosting the the massive massive sulfide sulfidedeposit deposit using using 90 90 samples samplescollected collected from from drill drill core. The (e.g., REE, REE, Zr, Hf, Ta, Ti) to Thestudy studyemphasized emphasizedinterpretation interpretationof ofstable stabletrace traceelements elements(e.g., help determine determine primary primary magmatic magmaticaffinities affinitiesand and the the tectonic tectonic setting settingof of the the volcanic volcanic section section hosting the Bend deposit. deposit. massive sulfide The Bend massive sulfide deposit deposit occurs occurs in a felsic felsic volcanic-dominated volcanic-dominatedsequence, sequence,located located along the southern flank of a mafic volcanic succession (DeMatties, 1994). The felsic volcanic (TDeMatties. 19941. alone sequence is up to 2000 feet thick, steeply dipping, south facing, andlow&greenschist and lower greenschist facies. facies. The stratigraphic footwall consists of bedded felsic tuffs tiffs (sericite stratieraohic (sericite schist) schist) with with interbedded interbedded quartztiffs (quartz-sericite crystal tuffs (quartz-sericiteschist) schist)overlain overlain(stratigraphic (stratigraphichangingwall) hangingwall)by mafic rnafic to felsic feisic fine tuffs tiffs and sediments. feldspar-phyric lava flows, felsic volcaniclastic layers, and associated fine sediments. Alteration, consisting sericitization, and and sulfidation, sulfidation, is is most most intense intense near near the the Alteration, consisting of of silicification, silicification,sericitization, massive sulfide, particularly in the footwall sericite and quartz-sericite schist. Mafic Mafic to to intermediate dikes intermediate dikes and and sills sills (?) (?) are are present present locally. locally. The Bend volcanic sequence volcanic sequence ranges ranges from from basalt basalt through through andesite andesite to to dacite-rhyodacite dacite-rhyodacite with dacite-rhyodacite most abundant. Both Boththe the mafic mafic and and felsic felsic rocks rocks are are calc-alkaline calc-alkaline in FeOt and and high high La/Yb LdYb (>15) (>IS) and and Th/Yb Th/Yb (>0.65) ratios (i.e., Barrett and character with decreasing decreasingFeOt MacLean, 1999). 1999). Mafic Maficrocks, rocks,mostly mostlyandesite andesitewith with minor minor basalt, basalt, are are characterized characterized by enriched enriched 6), relatively flat heavy-REE, prominent depletion of Ta, Zr, Hf, and Ti, ([La/Yb]n 6), relatively flat prominent depletion light-REE light-REE ([LaIYb]n and enriched Th on a primitive primitive mantle mantle normalized normalizedplot plot(Fig. (Fig.la). la). Relatively unaltered Relatively hangingwall felsic hangingwall felsic volcanic volcanic rocks rocks partly partly overlap overlapcompositionally compositionallywith with the the most most evolved evolved andesites andesites 3-4 vs -2-3 --2-3 for the andesites) light-REE(i.e., (i.e.,[La/Sm}n [LaISmln— 3-4 andesites) but have have slightly slightlygreater greaterenrichment enrichmentininlight-REE and no to small negative negative Eu anomalies. On Onaaprimitive primitive mantle mantle normalized normalized plot the the hangingwall patterns similar Nb,Ta, and Ti, felsic rocks show patterns similar to the the andesites andesiteswith with prominent prominent depletions depletions in Nb, lesser lesser depletion depletion of Zr-Hf, and enriched Th (Fig. la). la). The Thehangingwall hangingwalldacite-rhyodacite dacite-rhyodacitewas was plagioclase+pyroxene+Fe-Ti oxide oxide from from the the andesite. andesite. probably derived derived through throughfractionation fractionationof of plagioclase+pyroxene+Fe-Ti Footwall sericite sericite and and quartz-sericite quartz-sericite schist schist show show compositional compositional effects effects of of alteration alteration with with more variable Si02,higher higher K20/K20+Na20, K20/K20+Na20,and andhigher higherSScontent contentthan thanmost mosthangingwall hangingwallfelsic felsic variable Si02, rocks; footwall footwallsamples samplesalso alsoshow showincreasingly increasinglypositive positive Eu Eu anomalies anomalieswith with increasing increasingSScontent. content. felsic rocks rocks mostly mostly have have depleted depleted heavy-PEE heavy-REEand and generally generallylower lowertrace traceelement element The footwall felsic abundances than hangingwall felsic rocks (Fig. ib). lb). Although Althoughthe theheavy-REE heavy-REEdepletion depletionin in the the footwall samples samples could could be be aa result result of of alteration, alteration,some some samples samples with with depleted depleted heavy-PEE heavy-REEshow showno no compositional evidence of significant alteration (e.g., no high S content and/or high K20/K20+ compositional evidence of significant alteration (e.g., no high S content andlor high K20/K20+ Na2Oratio). ratio). Also, studies Na20 studies of of PEE REE mobility mobility associated associated with alteration below massive sulfide deposits have identified deposits identified mobility mobility of of lightlight- and and middle-PEE middle-REE but but general general stability stability of the heavy-PEE heavy-REE (Barrett and MacLean, 1999). (Barren 1999). Thus, Thus,the thecompositional compositionaldifference difference between footwall and hangingwall felsic hangingwall felsic rocks rocks may may reflect reflect primary primary differences. differences. ~ - -~ - - 59 �''JIlT Roc4P.imwve RoWPrirnitiveMantle Mantle 1000 1000 RocWPrlmiffve Mantle Rock/Primit!ve Mantle 1000 1000 b. 100 100 100 Hangingwall Felsic Rocks Hangingwall Felsic Rocks 10 10 10 1 1 Footwall Felsic Rocks .1 .1 I .1 II,, ThNbTsLaCeNdZr HfSmTiGdTbDy Y HoErTmYbLu Figure I.1. Primitive Primitivemantle mantlenormalized normalized(Kerrich (Kemchand andWyman, Wyman,1997) 1997)trace traceelement element plots plots for for Bend a) a) basalt-andesite basalt-andesite and hangingwall b) hangingwall hangingwalland and footwall footwallfelsic felsicrocks. rocks. hangingwall felsic felsic rocks rocks and and b) The Bend volcanic rocks plot as as a typical orogenic caic-alkaline calc-alkaline basalt-andesite-daciterhyodacite suite suite on on various various compositional compositionaldiscrimination discriminationdiagrams diagrams(e.g., (ex., Th-Hf-Ta; Th-Th-Ta; Th-Tb-Ta: . - . Th-FIf-Ta; Th/Yb-TaIYb). the T l k - T ~ I Y ~Further, Further, ). theenriched enrichedlight-REE light-REEand andhigh highTh T bof o fthe theBend Bend suite suiteare arecharacteristic characteristic Acontinental continental setting setting of orogenic sequences in continental settings settings (Barrett (Barren; and MacLean, 1999). 1999). A volcanic rocks rocks in in the the Bend Bend sequence. sequence. In is also supported by the abundance of felsic calc-alkaline volcanic addition, the volcanic rocks hosting the Bend massive sulfide deposit are similar compositionally to those in the Monico Monico area area in in north-central Wisconsin Wisconsin that that host the Pelican deposit (Sims (Sims and and have others, 1989). Neodymium Neodymium isotope isotope data data for for felsic felsic volcanic volcanic rocks in the Monico area have contribution from from an an enriched enriched crustal crustal source. source. The negative epsilon Nd indicating a contribution lithogeochemistry suggests that the Bend deposit deposit and probably other massive sulfide deposits associated with felsic centers in northern Wisconsin (e.g., (e.g., Flambeau, Pelican, Crandon) evolved in an extensional continental setting, possibly a continental back-arc back-arc basin in a southwarddirected subduction system. References cited: lithogeochemistry, and and hydrothermal hydrothennal Barrett, T.J. and MacLean, W.H., 1999, 1999, Volcanic sequences, lithogeochemishy, alteration in some bimodal volcanic-associated massive sulfide sulfide systems: systems: in in Bame, Bathe, C.T. C.T. and alteration Hannington, M.D., editors, Hannington, editors, Volcanic-Associated Volcanic-AssociatedMassive Massive Sulfide SulfideDeposits: Proceeses Proceeses and and Examples in Modem v.8, 8, p. p. 101-131. 101-131. Examples Modem and and Ancient Ancient Settings: Settings: Reviews in Economic Geology, v. DeMatties, T.A., 1994, 1994,Early Early Proterozoic Proterozoicvolcanogenic volcanogenicmassive massive sulfide sulfide deposits depositsin in Wisconsin: Wisconsin:an an overview: Economic Economic Geology, Geology, v. 89, 89, p. 1122-1151. 1122-1151. DeMatties, T.A. and Rowell, W.F., Wi., 1996, 1996,The TheBend Benddeposit: deposit:an an Early Early Proterozoic Proterozoic copper-gold VMS deposit: in LaBerge, LaBerge, G.L., G.L., editor, editor,Volcanogenic Volcanogenicmassive massive sulfide sulfidedeposits depositsof of northern northern Wisconsin: Wisconsin; aa commemorative volume: commemorative volume: Institute Institute on onLake LakeSuporior SuperiorGeology Geology Proceedings, Proceedings,v. v. 42, 42, Part Part 2, 2, p. p. 143143159. 159. Kenich, R. Kemch, R. and andWyman, Wyman,D.A., D.A., 1997, 1997,Review Reviewof of developments developmentsin in trace-element trace-element fmgerprinting fingerprinting of geodynamic geodynamic settings settingsand and their theirimplications implicationsfor formineral mineralresources: resources: Australian AustralianJournal Journalof of Earth Earth 465-487. Sciences, v. 44, p. 465-487. inthe theevolution evolutionof ofthe thePenokean Penokeanorgogen: orgogen:isotopic isotopic Schuiz, K.J. and and Ayuso, Ayuso, R. R. A., A,,1998, 1998,Crustal Crustalrecycling recyclingin Schulz, evidence evidence for for Archean Archean contributions contributionsto tocrustal crustalgrowth growthin inthe the Pembine-Wausau Pembine-Wausau terrane, terrane,northern northern Wisconsin Wisconsin [abstracti: [abstract]: Institute Instituteon onLake LakeSuperior SuperiorGeology GeologyProceedings, Proceedings,44th 44&Annual Annual Meeting, Meeting, Minneapolis, MN, 1998; v. 44, p. p. 113-114. 113-114. v.44, Sims, P.K., Schmus, W.R., Schulz, Schulz, K.J., and and Peterman, Z.E., 1989, 1989,Tecton-stratigraphic Tecton-stratigraphicevolution evolution of P.K., Van Schmus, the Early Proterozoic ProterozoicWisconsin Wisconsin magmatic magmatic terranes terranes of of the the Penokean Penokean Orogen: Orogen: Canadian Canadian Journal Journal of of Earth Sciences, Sciences, v. 26, 26, p. 2145-2158. 2145-2158. 60 �Assessing the extent of Early Proterozoic Mametamorphism metamorphism Proterozoic Penokean Penokeanversus versus—1770-1760 -1770-1760Ma in east-central east-central Minnesota Schweitzer, Kent, OH; OH; Schneider, Schneider, D.A., Schweitzer, D.J., DJ., Dept. Dept. of of Geology, Geology, Kent State University, Kent, DA., Dept. of Earth and Environmental Sciences, Lehigh Lehigh University, University,Bethlehem, Bethlehem,PA, PA;Boerboom, Boerboom, TJ., T.J., Minnesota Geological Survey, Survey, 2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul,MN, MN;Holm, iloIm,D.K., D.K.,Dept Dept of Geology, Kent State University, Kent, Kent, OH; OH; and and Van Van Schmus, W.R., W.R., Dept. Dept. of of Geology, Geology, University of Kansas, Lawrence, KS. Combined field, field, geophysical, geophysical, and and drill drill core core data from the internal zone Combined zone of of the the Penokean Penokean orogen in Minnesota Minnesota have have greatly greatly increased increased our our knowledge knowledge of of this this orogen's orogen's architecture, architecture,allowing allowing new correlations with the Wisconsin Wisconsin magmatic magmaticterranes terranesto to the the east east (Jirsa (Jirsa et et a]., al., 1995). Lowcorrelations with Lowgrade, greenschist structural panels panels have been identified as greenschist metamorphic, metamorphic, structural as arcuate, arcuate, imbricate imbricate thrust sheets in the poorly exposed, southeast portion of of the zone (Jirsa and Chandler, 1997). To To the west and and north, north, these these structural structural panels panels have have been been intruded intruded by bv abundant abundant post-tectonic vost-tectonic granitoids granitoids that make up aa physically physically continuous continuous mass of bedrock bedrock over over 7000 7000 km2 k d (Figure (Figure 1). 1). Holm et al. al. (1998) (1998) have have documented documentedwidespread widespread post-Penokean post-Penokean (1770-1760 (1770-1760 Ma) Ma) amphibolite amphibolite metamorphism in in the the plutonic plutonic region. region. Our goal is facies metamorphism Ourgoal is to to determine determine the the extent extent of of Penokean Penokean and/or —1760 Mametamorphism metamorphismwithin withinthe the lower-grade lower-grade terranes terranes to the southeast. andlor -1760 Ma We have have dated dated five five mineral mineral separates separates from from recently recently obtained obtained drill core housed housed at at the the Minnesota Geological Geological Survey. Survey. Sample Minnesota Sample localities localities and and associated associated dates dates are are plotted plotted on on figure figure11 (Southwick, 1994; Holm Holm and Lux, together with results from prior thermochronologic thennochronologic studies (Southwick, HoIm et et al., a!., 1998). 1998). Biotite from a biotite-hornblende 1996; Holm biotite.-hornblende granodiorite (EC-8) intruded by the post-tectonic Foley batholith batholith yielded yielded aa plateau plateau age age of 1846±6 post-tectonic Foley 1846k6 Ma Ma (four (four age age increments increments 75% of of the gas released). released). In constituting over 75% In spite spite of of its its proximity proximity to to the the Foley Foley intrusion, intrusion, this this unaffected by by it thermally. thermally. Biotite rock was apparently unaffected Biotite from from aa biotite biotite schist schist(EC-22) (EC-22)sampled sampled east of the Foley batholith yielded a plateau age of 1863±7 1863k7 Ma (eight age increments constituting over 72% of the gas released). Biotite Biotitefrom from aa tonalitic tonalitic orthogneiss orthogneiss (EC-27) yielded a plateau age increments, 81% 81% of of total total gas gas released). released). A 1820± Ma (seven increments, A hornblende hornblende separate separate from the of 1820±7 same drill core sample of orthogneiss yielded a plateau age of 1831±6 1831k6 Ma (seven (seven increments; from a meta-quartzdiorite (EC-l6) yielded 64% of total gas gas released). released). Lastly, hornblende hornblende from meta-quartzdiorite (EC-16) yielded aa 81% of of total total gas gas released). Only plateau hornblende date of 1838±5 1838k5 Ma (seven increments, 81% Only one one other Penokean Penokean Ar/Ar ArIAr age age on hornblende hornblende has been reported from east-central Minnesota Minnesota (1854±5 (1854s Ma plateau plateau date date on on the thePhilbrook Philbrook pluton; pluton; Southwick, Southwick, 1994). 1994). Five previously previously published published hornblende Ar/Ar ArIAr dates dates from from the theplutonic plutonicterrane terreneall allyielded yieldedpost-Penokean post-Penokeandates datesofof—1760 -1760 Ma Ma (Holm et al., 1998). 1998). This is the ArIAr cooling cooling ages ages in in east-central east-central the first first study study totodocument document biotite biotite Penokean Penokean Ar/Ar Minnesota. These Thesedata datafirmly firmlyestablish establishaaPenokean Penokean age age of ofmetamorphism metamorphism for for the the lower lower grade grade structural panels panels described described by by Jirsa and Chandler Chandler (1997). (1997). While While preliminary, preliminary, these these data data also also indicate thermal overprinting overprinting atat either either ca. ca. 1760 Ma Ma (as documented indicate no significant significant thermal documented to the northwest in the plutonic terrane) or at ca. 1630 1630 Ma (as (as long documented documented in adjacent adjacent parts of the the orogen in Wisconsin). ItItappears appearsthe the1770-1760 1770-1760Ma Ma barrovian barrovian amphibolite amphibolite metamorphism metamorphism in in the the internal zone of east-central east-central Minnesota may be restricted restricted to to the the deepest deepest exposed exposed region region which which also contains contains abundant abundant post-tectonic post-tectonic plutons. plutons. If so, so, this this would would be be consistent consistent with with the the interpretation of Holm et al. (1998) (1998) that the deepest deepest exposed region was probably the thickest thickest portion portion of the the Penokean Penokean orogenic orogenic belt belt which which became became unstable unstable and and rapidly rapidly collapsed collapsed (i.e., (i.e., unroofed) at —1760 Ma. The temporal and spatial association of post-tectonic plutons, barrovian -1760 Ma. —1760 Mametamorphism, metamorphism,and andmidcrustal midcrustal unroofing unroofing suggest suggest aa genetic link between -1760 Ma between thermal thermal softening of the overthickened overthickened crust and post-orogenic collapse in the hinterland of the Penokean Penokean orogen. 61 �QiDKeweenawan Supergroup Paleoproterozoic C:) LIWe Falls Fonnation Mixed supraaustai rot and shearS granitic rocks. Mets.plutomc rocks may be Archean an part 0 HilIman tonalite (may be Archean in part) c1 Archean/Proterozoic? Undiffetentiated — Minnesota. Filled Figure 1. 1.Generalized Generalized bedrock bedrockgeology geology map map of of east-central Minnesota. Filled circles circles represent localities Lux, 1996; HoIm etal., (after HoIm Holm and Lux. 1996;Holm etal.. 1998) 1998)which reoresent localities of of prior crior results results (after yielded ca. 1760-1750 Ma dates onmica on mica and hornblende. Also plotted the 1854 1854Ma M a Ar/Ar Arlk clotted is is the vikded 1760-1756% plateau age on hornblende from the Penokean Philbrook Philbrook pluton pluton (southwick, (Southwick, 1 1994). Open 994). Open circles from study. LF circles represent localities localities and results f rom this study. LF is is Little Little Falls, SC SC is St S tCloud. Cloud . ~ ~ ~ - ~ ~ - ~ ~~~~ References References HoIm, D.K.,and D.K.,and Lux, Lux, D.R., DR., 19%, 1996,Core Corecomplex complexmodel model proposed for gneiss dome development Holm, Paleoproterozoic Penokean Penokean omgen, orogen, Minnesota: Minnesota Geology, 24,343-346. 24,343-346. during collapse of the Paleopmteromic D.K., Darrah, K.S., K.S., and Lux, Lux, D.R., DR., 1998, -1760 Ma Holm, D.K., 1998,Evidence for widespread -1760 Ma metamorphism and 870-1820 Ma) morphism and rapid rapid crustal crustal stabilization stabilizationof ofthe theEarly EarlyProterozoic Proterozoic(1 (1870-1820 Ma) Penokean Penokean Orogen, Minnesota: Minnesota American 60-81. 298,60-81. Omgen, AmericanJournal Journalof ofScience, Science,298, M. and Jirsa, M., andChandler, Chandler,V., V,1997, 1997,Scientific Scientifictest testdrilling drillingand andmapping mappingin ineast-central east-centralMinnesota, Minnesota, 1994-1995: Sununary Summaryof oflithologic lithologicresults: results:M~M. Mlnn.Geol. Geol.Smv. Suit Info. Circular 105 pp. 1994-1995: Circular42, 42,105 .,Chandler, Chandler, V, V, and andBoerboom, Boerboom,11, T., 1995, 1995,Extension Extension of of the the Wisconsin Wisconsin magmatic terranes Jim, M Jirsa, lvi, into the Minnesota Minnesota segment of the Penokean omgen: orogen: Institute Institute on on Lake Lake Superior Superior Geology, 4 1st Annual Meeting, 41st Meeting, Marathon, ON, 42.25-26. 42,25-26. D.L., 1994, geochronologic studies studies of of Precambrian Precambrianterranes terranes in inMinnesota: Minnesott Southwick, D.L., 1994,Assorted geochronologic A potpourri of timely information: information: in in Short Short Contributions Contributions to the the Geology Geology of of Minnesota, Minnesota, 1994, 1994, Investigations 43, 1-19. edited by D.L. Southwick, Minnesota Geological Survey Report of Investigations 43,l-19. 62 �THE THE DISTINCTION DISTINCTION BETWEEN BETWEEN FLAT FLAT PEBBLE PEBBLECONGLOMERATES CONGLOMERATES AND AND INTRAFORMATIONAL INTRAFORMATIONALBRECCIAS BRECCIASIN INPRECAMBRIAN PRECAMBRIANIRON IRONFORMATIONS FORMATIONS Bruce BruceM. M.Simonson Simonson Geology GeologyDepartment Department Oberlin OberlinCollege College Oberlin, USA Oberlin,01144074-1044 OH 44074-1044USA Iron Ironformation, formation,aa distinctive distinctivetype type of of rock rock restricted restricted largely to the Precambrian, Precambrian, consists consists mainly of oi silica (in the form of ehert) and such iron-rich minerals as hematite, magnetite, siderite, andlor silica (in the form of chert) and such iron-rich minerals as hematite, magnetite, siderite, and/or greenalite. greenalite. Lamination Laminationand andthin thinbedding beddingare arecommonplace commonplacein inthese theserocks rocksas asevidenced evidencedby by the the near-universal use of the term BIF (for "Banded Iron Formation"), but a substantial minority near-universal use of the term BIF (for "Banded substantial minority of of iron iron formations formations(particularly (particularlythose thosein inNorth North America) America)are are actually actually GIF GIF(for (for "Granular "GranularIron Iron Formation"). Formation"). Such Suchunits unitshave havecoarsely coarselyclastic clastictextures textures(analogous (analogousto tothose thoseof ofcarbonate carbonate grainstones and oolites) and display structures such as cross-bedding rather than grainstones and oolites) and display structures such as cross-beddmg rather thanbanding. banding. CentimeterCentimeter-to todecimeter-scale decimeter-scalelayers layersrich richin insiliceous, siliceous,flat, flat,pebble-size pebble-size fragments fragmentsare areminor minor constituents of both BIF and GIF. The fragments are clearly intraformational in origin constituents of both BIF and GIF. The fragments are clearly intraformational in originand andare are frequently bothsettings, settings, frequentlycited citedas asevidence evidenceof ofdeposition depositionin inshallow, shallow,high-energy high-energyenvironments environmentsininboth but but they they have have very very different differentorigins. origins.The Thefragments fragmentsin in GIF GIFoccur occurin in flat flatpebble pebbleconglomerates conglomerates where where they they generally generally have havewell-rounded well-roundedends, ends, form formaa grain-supported grain-supported framework, framework,and andoriginated originated via via erosion erosionand and reworking reworkingatatthe the sediment-water sediment-waterinterface. interface.In In contrast, contrast,the the fragments fragmentsin inBIF BIF occur in breccias where they are generally much more angular, isolated in a matrix of less occur in breccias where they are generally much more angular, isolated in a matrix of less siliceous siliceousmaterial, material,and andoriginated originatedafter afterdeposition depositionand andatatleast leastshallow shallowburial burialvia viapartial partial liquefaction. liquefaction.The Thedominance dominanceof ofeherty chertyfragments fragmentsin inboth bothbreccias brecciasand andconglomerates conglomeratesindicates indicates that thansilica-poor silica-poorones onesin inboth bothBIF BIFand and that silica-rich silica-richlayers layerswere weresignificantly significantlymore morecohesive cohesivethan GIF. GIF. Many Manv of of the the flat flat pebbles nebbles in in GIF GIF are are identical identical to to nodular nodular masses masses known known as aschert chertpods in -podsin underlying sediments, suggesting they are exhumed nodules. Petrographic evidence such as underlying sediments, suggesting they are exhumed Petrographic evidence such as large differences in minus-cement porosity inside large differences vorositv vs. outside the pods and dramatic thinning- of . individual individuallayers layersas as they they exit exitpods podsindicates indicatesthe the pods podsformed formedvia via early earlysilica silicacementation. cementation.This This widespread widespread early early cementation cementationisis probably probably due dueto to high high silica silicaconcentrations concentrationsin inPrecambrian Precambrian seawater seawater which, which, unlike unlike today, today, caused caused silica silicato to difftise diffuse into into (rather (rather than than out out of) of) sediment sedimentpore pore waters (Siever, 1992, Geochimica et Cosmochiiica Acta 56,3265-3272). waters (Siever, 1992, Geochimica et Cosmochimica Acta 56, 3265-3272). . 63 �PRECAMBRIAN FEATURES UNDER THE THE JAMES JAMES BAY BAY AND HUDSON BAY BAY LOWLANDS LOWLANDS PRECAMBRIAN Geological Survey, Ontario Geological Lake Rd, Rd, Sudbury, Sudbury, ONP3E ON F3E 6B5 Greg Stott, Brian Survey, 933 Ramsey Lake Brian Berdusco, Ontario stottg(ägov.on.ca ;brian.berdusco)ndm.gov.on.ca stottgf%~ov.on.ca brian.berdusco@ndm.eov.on.ca Large cover of of both both the James Bay and and Hudson Large parts parts of the the Superior Superior Province Province underlie underlie the Phanerozoic Phanerozoic cover James Bay Hudson Bay lowlands. This, This, plus plus the the poor poorbedrock bedrockexposure exposureininthe theeastern easternand and northernmost northernmostexposed exposed Sachigo Sachigo Subprovince, Subprovince,has has permitted only limited with permitted limitedsuccess success to date date in correlating correlating the regional geology of of the the Uchi-Sachigo Uchi-Sachigo superterrane superterrane with parts project is planned number of geological the Superior Superior Province Province in in northwestern northwestern Quebec. Quebec. AA project planned to examine examine aa number parts of the problems in addition addition totoregional regionalcorrelations correlations by byreprocessing reprocessing the the ODMJGSC ODMIGSC aeromagnetic aeromagnetic data the 1960s 1960s problems data of of the covering the region mainly north of of Latitude Latitude 510. 51'. This will willbe be done done in in co-operation co-operation with with Regional Regional Geophysics Geophysics staff of under the the lowland cover of the the GSC. GSC. This This poster poster isis intended intended to to outline outlinesome some of of the the Precambrian Precambrian features under cover that might might be he enhanced when the reprocessing is completed. Features and Interpretive Interpretiveissues: issues: the substrate substrateof of the the northern northern Hudson Hudson Bay 1) The complex, broad high magnetic magnetic susceptibility susceptibility that that characterizes characterizes the I) [HBL] isissimilar Lowlands [HBL] similartotothat thatofofthe thePikwitonei Pikwitoneigranulite granulitedomain domainand and adjacent adjacent domains domains in Manitoba. We suspect that that this this region region of old broad range range of of Archean Archean ages ages including includingpre-3.8 pre-3.8 Cia Ga crust crust (cf. (cf. suspect old crust, crust, containing containingaa broad B6hm Geology, JanIOO), JanIOO), continues and underlies underlies the early early BOhm et et al., Geology, continuesinto intothe the northernmost northernmostpart partof of Ontario Ontario and Inlier. Proterozoic Sutton Inlier. Orogen [THO] [THO] are in parts parts of of Manitoba and the the HBL. Re-interpretation 2) Elements of the Trans-Hudson Orogen are exposed exposed in Re-interpretation of the aeromagnetic aeromagnetic patterns patterns that that characterize characterize this this region region suggests suggests several points to to consider: consider: 3) 3) River Belt BeltofofManitoba Manitobadoes doesnot notappear appeartotocontinue continueeastwards eastwards across across the northern northern a) The Proterozoic Fox River HBL but border and and probably probably links links to the hut continues continues north north to to Hudson Hudson Bay Bay near near the the Manitoba-Ontario Manitoba-Ontario border the Internides of the main THO linear gravity gravity anomaly just just offshore, north north of Ontario. Strata seem to reappear reappear as of Strata from from the Trans-Hudson Orogen Orogen offshore offshore in Hudson Bay seem asfolded folded units units north of b) h) the Sutton Inlier the Inlier and anddiscontinuously discontinuouslyextend extend southwards southwards towards the inlier. inlier.These These features features need need further further discrimination to to establish establish their full extent. discrimination full extent. as aa single, single, continuous continuous package packageof of rock rock as as currently c) The Sutton Sutton Inlier Inlier has has for formany manyyears years been been treated treated as c) portrayed on on geological maps maps (compiled (compiled from from the the original original work by H. Bostock GSC Paper Paper 70-42). But a portrayed Bostock -- GSC closer examination of patterns in in its its vicinity vicinity suggests the Sutton Inlier Inlier is of the the aeromagnetic patterns suggests the is not not aa single single large large domain but aa set set of ofsouthward-convex-shaped southward-convex-shaped inliers resemble "klippe-like" domain inliers strung strung along along aa line. They resemble features comprising shallow shallow water platform sedimentary depositsincluding including iron iron formation, and features comprising sedimentary deposits and gabbroic gahhroic sills that southwardsonto ontothe theArchean Archeancraton cratonfrom from the the main main THO belt that might might have have been been transported transported southwards belt offshore. Smaller of the currently defined aeromagneticallyapparent apparent to the north and east east of defined Smaller "klippe" "klippe"are arealso alsoaeromagnetically Sutton Inlier. The the Nastapoka NastapokaFormation Formationon onthe the eastern easternshore shoreofof Hudson HudsonBay Bay (cf. (cf. Sutton The strata strata resemble resemble the Chandler Res.1989) 1989)and andpart partofofthe thePovungnituk PovungnitukGroup Group of of Cape Cape Smith Smith Belt. Chandler and and Parrish, Prec. Res. Beneath the James JamesBay BayLowlands Lowlands [JBL], [JBLJ,there thereisis aa strong strong likelihood likelihood that that the Beneath the the English English River River and and Quetico Quetico metasedimentarysuhprovinces subprovincesconverge converge underthetheJames JamesBay BayLowland Lowlandcover cover and and that that the metasedimentary under the Wabigoon Wabigoon Subprovince pinches pinches out out eastwards. eastwards.Discrimination Discriminationof of this this has hasimportant importanttectonic tectonic implications implications for the original Subprovince original that the converging nature of these these subprovinces. subprovinces. It is compelling compelling to to suggest suggest that converging English English River River and and Quetico Quetico nature resemble telescoped telescoped inter-arc inter-arc basins basins that that wrap wrap around the the east eastend endof of aa Wabigoon Wabigoon microcontinent microcontinent and and continue continue 'basins in Quebec. The merged merged English English R R - Quetico R. and and Opinaca Opinaca R. R. "basins" Quebec. The Quetico isis on-line with with the the Nemiscau Nemiscau R. on-line conceptually conceptually analogous analogous to to the the modern modem basins basins of of the the Solomon Solomon and and Coral Coral seas seas respectively north north and and south south of of east east Papua-New Papua-New Guinea. Guinea. The Sachigo and Uchi Uchi subprovinces to merge merge under under the the eastern easternHBL HBL and and JBL JBL suhprovinces of northwestern Ontario appear appear to and continue as aa single single domain domain and and emerging emerging as asthe theMinto Minto domain domain of northern Quebec. continue eastwards eastwards as Quehec. the eastern easternHBL, HBL,flanked flankedto tothe thewest westby byaafault faultsimilar similar in orientation A major major indenter-like indenter-likefeature feature occurs occurs under the to the the Miniss Miniss Fault. Fault. This Thisfeature, feature, like likeother other"indenters" "indenters"ininnorthwestern northwestern Ontario Ontario (e.g., (e.g., at Savant Savant Lake, Lake, Shebandowan and Manitouwadge), Manitouwadge), closes closesnorthwards northwardsand andborders bordersaa"bow-tie" "bow-tie" aermagnetic aermagneticpattern patternon on its its north Shehandowan and flank, which flank, whichappears appears to to reflect reflectshortening shorteningand andexhumation exhumationofofdeeper deepercrust. crust. - 4) 4) 5) 5) 64 �THE THE 1787-1772 1787-1772MA MAEAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA BATHOLITH: BATHOLITH: PRECURSOR TO TOCRUSTAL CRUSTALSTABILIZATION STABILIZATION IN IN THE THEL.L.SUPERIOR SUPERIOR PRECURSOR REGION REGION - - VAN both bothatatDept. Dept.of ofGeology, Geology,Univ. Univ.ofof VAN SCHMUS, SCHMUS, W.R., W.R.. and andMacNEILL, MacNEILL,L.L.C.,C., ofofGeology, Kansas,Lawrence, Lawrence,KS, KS,55045 55045(rvschmus@ukans.edu); (rvschmus@ukans.edu);HOLM, HOLM.D.K., D.K.,Dept. Dept. Geology,Kent Kent Kansas, both at Minnesota BOERBOOM, JIRSA. M.A, M.A. both at Minnesota State Univ., State Univ.,Kent, Kent,OH; OH; BOERBOOM,T.J. T.J.and and JIRSA, Geological MN GeologicalSurvey, Survey,2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul,MN The Thecause causeofof—1760 -1760 Ma magmatism in the the southern southernL. L.Superior Superiorregion regionhas hasbeen beenconsidered considered considerable amagmatic enigmatic because of its apparently abrupt nature and the enigmatic because of its apparently abrupt nature and the considerable amagmatichiatus hiatus(—60 (-60 m.y.) m.y.) that that separates separates itit from from Penokean Penokean orogenesis. orogenesis. The Theage age of of post-Penokean post-Penokeanmagmatism magmatisminin Wisconsin, Wisconsin,commonly commonlyreferred referredtotoasas"1760 "1760Ma", Ma",was wasobtained obtainedby by dating datingmg-sized mg-sizedfractions fractionsfrom from here new U-Pb data rhyolites and and epizonal epizonal granites granites (Van (Van Schmus, Schmus, 1980). 1980). We Wereport report here new U-Pb datafrom fromthe the rhyolites recently recentlycharacterized characterizedmidcrustal midcrustalplutonic plutonicterrane terraneinineast-central east-centralMinnesota. Minnesota. This Thisportion portionofofthe the exposed exposed Penokean Penokean orogen orogencontains containsnumerous numerouspost-tectonic post-tectonicplutons plutonsof ofvarying varyingcomposition compositionand and Based on field, drill-core, geometry(Jirsa (Jirsaetetal., al.,1995; 1995;Boerboom Boerboometetal., al.,1995; 1995;1998). 1998). Based on field, drill-core,petrologic, petrologic, geometry and andgeophysical geophysicalstudies, studies,about about20 20separate separateintrusive intrusivebodies bodieshave havebeen been identified identifiedand andcategorized categorized granites; into 1)granodioritic granodioritic to todioritic dioriticrocks; rocks;2)2)gray gray granites; 3) 3)red redgranite granite into four four separate separate groups: groups: 1) quartzofeldspathic dikes. plutons, plutons,dikes dikesand andsills; sills;and and4)4)late laternafic maficplugs plugsand anddiabasic diabasictoto quartzofeldspathic dikes. 0.34 Richmond Granite Intercepts at 4 grains 'N f?2- 0±0&1772.3±1.OMaI MSWD= 1.6; P = a16J 0.32 1 grain 1720 0.30 0.28 600 TV" .1 grains 0.26 0.24 3.5 3.7 3.9 4.3 4.1 201 207 4.5 4.7 4.9 p y 235 U(J Pb!235 Fiyure 1.1. Plot Plotof ofzircon zircondata datafrom fromthe theyounger youngerand andolder olderends endsof ofthe theage agespectrum spectrumfor forthe theEastEastFigure Central CentralMinnesota Minnesotabatholith. batholith.Data Datafor forother otherunits unitsfall fallininbetween betweenthese thesetwo twopopulations. populations. 65 �Our new results are mostly U-Pb isotope dilution analyses from single zircons zircons weighing weighing 11 to to 5 micrograms, with with several several hand-picked, hand-picked,air-abraded air-abradedgrains grainsselected selectedfor foreach eachrock rockunit. unit. For the most part the analyses are not influenced by by xenocrystic cores, cores, although in a few cases they may be present. All units of the post-tectonic suite, the "East-Central All units of the post-tectonic suite, the "East-Central Minnesota Minnesota batholith" (ECMB), (ECMB), yield ages within the range 1772±1 Ma (Richmond Granite) to 1787±3 1772i1 to 1787i3 Ma (Warman (Wannan Granite). The relative relative ages within this range correlate with relative relative ages based based on on field fieldrelationships relationships known). Thus, (where known). Thus, all all units units of of the the ECMB ECMB (St. Cloud Cloud Red Granite, Granite, Reformatory Reformatory Granodiorite; Granodiorite; Rockville Granite, Freedham Tonalite, Anne Lake Lake Granite, Granite, plus plus others) others) were emplaced within 15 15 m.y. are determining determining ages from from surrounding surrounding basement rocks, using using m.y. In Inaddition additionto to the the ECMB, ECMB, we we are outcrop and and drill core samples; preliminary results resultsyield yield an an age age of of 1800±8 Ma for a foliated samples; preliminary 1800± Ma foliated tonaiite tonalite within the Hillman migmatitecomplex. We are are also also redetermining redetermining U-Pb U-Pb ages ages of of several several units of the "1760 Ma" suite in Wisconsin using using single-crystal single-crystal analyses, analyses, but but at at this this time our data definitive. are not definitive. Our results suggest that the "1760 Ma" magmatic event is only only the the last last stage stageof ofaa—25 -25 m.y. m.y. episode of post-tectonic magmatism. These post-tectonic magmatism. These data data significantly significantlyreduce reduce the the time-lag time-lagbetween between the the end of Penokean orogenesis and the onset of post-tectonic plutonism, bringing it into into line line with with thermal and physical physical models which which predict predict characteristic characteristic time-lags time-lags of of only only 20-40 m.y. m.y. (England thermal Thompson, 1984; and Thompson, 1984;Turner Turneret et aL, al., 1992). 1992). Intrusion of the Intrusion of the ECMB ECMB was was associated associated with withwidespread widespread midcrustal midcrustal amphibolite amphibolite and directly preceeded preceeded rapid rapid exhumation exhumation (i.e., (i.e., collapse?) collapse?) and and crustal crustal stabilization metamorphism and In some (Holm al., 1998). 1998). In some regions regions of incipient incipient collapse collapse (i.e., (i.e., India-Asia India-Asia today), today), the the (Holm et al., overthickened crust crust contains contains aa partially partially molten molten layer layer ponded ponded in in its mid-section (Nelson et al., overthickened al., 1996). manner we suggest the overthickened overthickened Penokean crust was was invaded invaded by by 1996). In analagous manner midcrustal melts melts which which probably probably affected affected its its rheological rheologicalbehavior. behavior. Vast magma midcrustal magma intrusion intrusion may may dramatically decreased crustal viscosity and and promoted promoted collapse (as recently proposed for have dramatically the Canadian Cordillera; Cordillera; Vanderhaeghe Vanderhaeghe et et aL, al., 1999). 1999). References Boerboom, T., T., Jirsa, Jirsa, M., M., and Holm, Hoim, D.K., D.K., 1998, Early Early Proterozoic Proterozoic Intrusive Intrusive Rocks of EastBoerboom, Superior Gwl. Geol. Fieldtrip Fieldtrip Guidebook, Central Minnesota: Institute on L. Superior Guidebook, v. 44, 44, p. 3-30. 3-30. Boerboom, T.J., T.J., Setterholm, D.R., D.R., and Chandler, V.W., V.W., 1995, Bedrock geologic map, plate 2 G.N., Project Project Manager, Manager,Geologic Geologicatlas atlasofofSteams SteamsCounty, County,Minnesota: Minnesota: Minnesota of Meyer, G.N., SurveyCounty CountyAtlas AtlasSeries, Series,C-10, C-b, Part A, Geological Survey scales 1:200,000 and l:lOO,000.England, P.C., and and Thompson, A.B., 1984, scales 1:200,000 and l:lOO,OOO.England, P.C., Thompson, A.B., 1984, PressurePressuretemperature-time paths paths of of regional regional metamorphism metamorphism I.I. Heat Heat transfer transfer during during the evolution of temperature-time regions of thickened continental crust: Journal of Petrology, v. 25, p. 894-928. 894-928. Holm, Darrah, K., K., and and Lux, Lux, D.R., D.R., 1998, 1998,Evidence Evidence for forwidespread widespread—1760 -1760 Ma Ma Holm, D.K., D.K., Darrah, metamorphism and and rapid crustal stabilization of the Early metamorphism Early Proterozoic Proterozoic (1870-1820 (1870-1820 Ma) Ma) Penokean orogen, Minnesota: American American Journal Journal of Science, Science, v. 298, p. 60-81. 60-81. Jirsa, M.A., 1995, Bedrock geologic map of easteastM.A., Chandler, V., V., Cleland, J., J., and Meints, J., J., 1995, central Minnesota: Minnesota Minnesota Geological Geological Survey Survey Open-File Open-File Report Report 95-1. Nelson, K.D., K.D., and 27 others, 1996, Nelson, 1996, Partially molten middle crust beneath beneath southern southern Tibet: Tibet: Synthesis of project INDEPTH results: Science, v. 274, p. 1684-1688. 1684-1688. and Foden, Foden, J., J., 1992, 1992,Some Some geodynamic geodynamic and and compositional compositional Turner, Sandiford, M., Turner, S., S., Sandiford, M., and constraints on "postorogenic" magmatism: 1-934. constraints magmatism:Geology, Gwlogy,v.v.20, 20,p.p.93 931-934. Vanderhaeghe, O., 0., Teyssier, Vanderhaeghe, Teyssier, C., and and Wysoczanski, Wysoczanski, R., 1999, 1999, Structural Structural and and geochronologic geochronologic constraints on the role of partial melting during during the formation formation of the the Shuswap Shuswapmetamorphic metamorphic Thor-Odin dome, British Columbia: Columbia: Can. J. Earth Sci., core complex at the latitude of the Thor-Odin 17-943. v. 36, 36, p. p. 9917-943. W.R., 1980, Van Schmus, W.R., 1980, Chronology of igneous rocks associated with the Penokean orogeny orogeny in Wisconsin: Geol. Geol. Soc. Soc.America AmericaSpec. Spec. Paper Paper 182, 182,p. p. 159-168. 159-168. 66 �ISOTOPIC CONSTRAINTS CONSTRAINTS ON THE ORIGIN ORIGIN OF GRANOPHYRE GRANOPHYRE COMPLEXES COMPLEXES IN IN THE THE MIDCONTINENT RIFT OF NORTHEASTERN MINNESOTA. MIDCONTINENT OF NORTHEASTERN MINNESOTA. Vervoort, Jeff D., Department Department of of Geosciences, Geosciences, University of of Arizona, Tucson, Tucson, AZ AZ Vewoort, JeffD., (ve~oor@,geo.arizona.edu); Wirth,K.R., K.R.,(wirth@macalester.edu) (wirth@macalester.edu) & & Kennedy, Kennedy,B.C., B.C., (vervoort(geo.arizona.edu); Wirth, (bkennedy@macalester.edu). Macalester College, St. Paul, MN (bkennedy@macalester.edu). The magmatism of the Midcontinent Midcontinent Rift (MCR) (MCR) is dominantly dominantly mafic in composition compositionin in both both the volcanic In some someportions portionsof of the the MCR, MCR, volcanic sequences sequences as well as the underlying intrusive rocks. In however, the magmatism magmatism is strongly strongly bimodal with significant significant volumes of rhyolite rhyolite and and granite granite in in [1]. This This is is particularly true true for for the northeast northeast limb of the North association with basalt and gabbro [I]. km thick thick volcanic volcanic stratigraphy stratigraphy Shore Volcanic Group Group (NSVG) (NSVG) where where approximately approximately 25% 25% of of its its 6.4 6.4 km other evolved evolved lavas lavas 121. [2]. Evolved intrusive rocks rocks are also also prominent prominent in in is composed of rhyolite and other the northwest flank of the MCR and occur in compositionally stratified complexes. Although these stratified complexes. Although northwest flank are dominantly granitic (granite-granodiorite) (granite-granodiorite) in composition, composition, intermediate intermediate rocks rocks (monzodiorite(monzodioritein the the lower lower portions portions of ofthese thesecomplexes. complexes. Collectively these quartz monzodiorite) predominate in granophyres because of their their characteristic characteristic gmophy& granophyrictextures. textures. The field relahave been termed graniphyres tions, petrography, and geochemistry of these complexes are described by Kennedy petrography, and geochemistry of these complexes are described by Kennedyet et al. al.[3]. [3]. similarities to to the the overlying overlying volcanic volcanic rocks. rocks. Both The granophyres granophyres have striking geochemical similarities 8-67% SiO2 S i O (Fig. 1). 1). have a strong bimodal character illustrated by the compositional gap at 558-67% The chemistry of the rhyolites and the granites are similar in many many respects (e.g., (e.g., major and trace elements, REE patterns) which begs the interpretation elements, interpretation that the granophyric granophyric complexes complexes represent represent the magma chambers chambers that supplied supplied the large rhyolitic rhyolitic eruptions. eruptions. The NSVG lavas are isotopihe NSVG i&topi7 (Fig. 2). 2). Most cally heterogeneous (Fig. Granophyre ~ r a u ~ p ~Complexes Complexes qm values close close basalts e.,, values basaltshave haveinitial initial£Nd • Greenwood 6 1 &wood Lake Lake [4, 5]. 51. to zero or slightly negative negative [4, A A Misquali MiquahHills Hilh The rhyolites, <)Eagle The rhyolites, in in contrast, contrast, typically typically 5 @ EagleMountain Mountain • Pine 0 PineMountain Mountain eNd have strongly strongly negative negativeinitial initial8Nd 4 o Finland values (down values (down to -15) - 15)indicating indicatingthey they were formed formed in in large large part by the the par- 1(20 4 t 3 a NSVG Rhyolites melting and tial melting and assimilation assimilation of of older (most Archean) crustal crustalrocks. rocks. (most likely likely Archean) C> 2 In contrast contrast to to the the NSVG lavas, lavas, the granophyres are more isotopi1I NSVG transitional baaalia b:alts cally homogenous both individually cally homogenous individually 0 and and collectively collectively (Fig. 2). With one one 60 65 75 80 exception hiexception all all granophyres granophyres have have iniSi02 similar to most values 0 tiale., 0 to to -5, -5, similar tial aNd values Figure 1. Si02 S i Ovs. vs. 1(20 K,0 plot illustrating illustrating the linear array basalts in the MCR [7]. [7]. The The isotoisotoand bimodal distribution of of and bimodal distribution of the the granophyre granophyre pic homogeneity of individual gracompositions. Also shown are data for NSVG tholeiitic Also shown are data for tholeiitic nophyres is demonstrated by the and and transitional basalts [5] rhyolites [6]. Few samples Few samples transitional [5] and compositions of two granophyre (4 of 5 are from the Finland granophyre) plot in the SiO2 from Finland granophyre) plot in the Si02 complexes (Misquah complexes (Misquah Hills and and gap (58% to 67%). (58% to 67%). Greenwood Lake) Greenwood Lake) located located in in central central - n .I - 455055 67 �Cook County. The The Greenwood Greenwood Lake Lake granophyre granophyre ranges from monzodiorite to granite ((Si02 S i O 52% to 72%) but has initialENd values of-0.7 of -0.7to to -1.9 -1.9 (Fig. (Fig. initial 2), an extremely extremely small small range considerconsidering analytical analytical reproducibility reproducibility (±0.3 (±0.to to 0.4&Nd G units). The Greenwood Lake ENd 0.4 NSVG Rhplites granophyre was emplaced emplaced during during the the early stage stage of the MCR MCR (1107 (1 107Ma; Ma; [8]). [8]). A Misquah Hilb granophyre The Misquah Hills granophyre has not Misquah granophyre been dated but is likely of similar age because it intrudes because intrudes a sequence sequence of older, 45 50 55 60 65 70 75 reversed polarity lavas. These new isotopic data, in in conconFigure 2. 2. Si02 Figure S i O vs. vs. initial initial EENd of the granophyre junction with major and trace-element chemistry and previously published Nd complexes. Also Also shown shownare are data data for for NSVG NSVG tholeiitic tholeiitic results from 6 other granophyres [6], basalts [5] and rhyolites [6]. Note the Nd isotopic basalts and rhyolites [6]. Note the isotopic [6], homogeneity of the Misquah Hills and Greenwood provide important constraints on the origin of the granophyre Lake granophyres granophyres over over a wide wide range range of of Si02. SiO. granophyre complexes. complexes. First, the granophyres graniphges are isotopically i~ot6~icall~ distinct from the rhyolites. Although Althoughtwo twoof ofthe theCook Cook County County rhyolites rhyolites(Kimball (KimballCreek, Creek,Red Red Rock) Rock) about -5, this is more negative (Eagle have initial G~ values than all but one of the granophyres ENd genetically related to Q = = -7.7). -7.7). This indicates that the granophyres are probably not genetically Mtn., initialENd Mm., initial the rhyolite flows and do not represent the the magma magma chambers chambersfrom fromwhich whichthe therhyolites rhyoliteswere werefed. fed. It is important to note, however, that the granophyres most thoroughly studied thus far (Misquah likely older older(-1 (l 107 Hills, Greenwood Lake) are likely 107Ma). Ma). ItItisisnot notuntil untilthe themain mainstage stageof of the the rift rift (<1100 ( 4 100 &Nd values were erupted erupted in in the the NSVG. NSVG. Ma, [9]) [9]) that thatthe thelarge largerhyolites rhyoliteswith withthe thehighly highlynegative negative Secondly, homogeneity. This Secondly, the two granophyres granophyres examined thus far show remarkable isotopic homogeneity. This implies that these complexes have been derived from a single parental parental magma magma or or from from magmas magmas that are isotopically similar. In In the the case case of of the the granophyre granophyre complexes, complexes, the high silica portions could not have been derived to a significant significant extent from melting or assimilation of older crust. Rather, Rather,ititisis complexes were were produced more probable that the limited isotopic variations within the granophyre complexes minor assimilation. assimilation. It remains by fractionation and mixing processes with only minor remains possible possible that that the the granitic rocks have been derived by partial melting and cannibalization cannibalization of crystallized crystallized MRS magmas lower in the crust, but this seems unlikely considering the refractory nature of such rocks and the availability of less refractory older crust present in the lower crust, especially during early stages stages of of rifling. rifting. sd - sd References: References: [I] [1] J.C.Green, 1982, Geol. Soc. Soc. Am. Am. Mem., Mem., 156,47. 156, 47. [2] J.C.Green and T.J.Fitz, J. Volcan. Geotherm. Geothenn. Res., 54, 177 177 (1993). [3] [3] B.C.Kennedy, B.C.Kennedy, K.R.Wirth, K.R.Wirth, and and J.D.Vervoort, J.D.Vervoort, this this vol[4]J.C.Brannon, J.C.Brannon, Ph.D. Ph.D. thesis, thesis, St. St. Louis Univ. (1984). [5] L.Dosso, L.Dosso, Ph.D. thesis, Univ. ume. [4] (1984). [5] (1984). [6] [6]J.D.Vervoort J.D.Vervoortand andJ.C.Green, J.C.Green, Can. Can. J. Earth Earth Sci.,34, Sci.,34,521 [7]S.W.Nicholson, S.W.Nicholson, Minn. (1984). 521 (1997). [7] K.J.Schulz, and and J.C.Green, J.C.Green,Can. Can.J.J.Earth EarthSci., Sci.,34,504 34, 504(1997). (1997). [8] D.W.Davis and S.B.Shirey, K.J.Schulz, J.C.Green, Can. J. Earth Sci., Sci., 34,476 [9] J.D.Miller J.D.Millerand andJ.D.Vervoort, J.D.Vervoort,ILSG ILSG abstr, abstr, (1996). (1996). J.C.Green, 34, 476 (1997). [9] 68 �ARCHEAN DIAMOND EXPLORATION EXPLORATION TARGETS IN IN THE THE MICHIPICOTEN MICHIPICOTEN GREENSTONE GREENSTONE BELT, BELT, WAWA, ONTARIO WILSON, A. A. C., C., Ministry Ministryof ofNorthern NorthernDevelopment Development and and Mines, Mines, Ontario Ontario Government Government Complex, Complex, Highway 101 101 East, East. WILSON, Porcupine, Ontario, P0N 0. Bag IHO (705-235-1614; (705-235-1614;ann.wilsonfiindm.gov.on.ca ann.wilson(ndm.gov.on.ca Bag 3060, 3060, South South Porcupine, PON 1HO P. 0. Traditionally, diamond exploration Traditionally, exploration in Ontario Ontario has focussed focussed on following following KIM dispersion dispersion trails trails and and on on examining geophysical targets believed to be related related to to kiiberlite kimberlite pipes. pipes. However, the 1993 announcement 1993 announcement of the discovery of three three alluvial alluvial diamonds diamonds recovered recovered from the the Michipicoten Michipicoten River River area area south south of of Wawa Wawa has has led led to tothe the search for much different diamond diamond sources. sources. Surmacz and the frst first discovery discovery of of Archean-aged Archean-agedbedrock bedrock occurrence occurrence of of In 1995, 1995, S. Sunnacz and M. Hauseux made the diamonds in Ontario kilometers north of the town of Wawa. Following diamonds Ontario in Lalibert Lalibert Township, Township, approximately approximately 20 kilometers Following this this discovered nine the same geographic geographic region region in announcement, Spider announcement, Spider Resources Resources discovered nine more diamondiferous dikes in the 1997. Early Earlythis this year, year, Ban-Ore Resources Ltd. announced the discovery of at least one more diamondiferous diamondiferous dike dike Township. To date, commercial stones, 42 macrodiamonds (the GQ Occurrence), macrodiamonds and in Musquash Musquash Township. date, 55 commercial and 338 338 Occurrence), this this time time in microdiamonds have microdiamonds have been recovered recovered from from bedrock bedrock in in an an area area approximately approximately30 30 square square kilometers in size. size. Presently, bedrock in in the the area. The Presently, there there appear appear to to be two two types types of Archean diamond-bearing bedrock The "Sandor"Sandoractinolite+talc+carbonatexenoliths xenolithsranging ranging type" dikes dikes are are mafic mafic in in composition compositionand and contain contain up up to to 35% 35% spectacular spectacular actinolite+talc+carbonate up to 11 metre in size. The fine-grained matrix is foliated. These These cocks rocks have been classified as lamprophyres. These These dikes are detailed P. Sage Sage of of the the Ontario Ontario Geological GeologicalSurvey Surveyin in Sudbury. Sudbury. detailed in in another another featured featured poster poster by by R. R. P. The second type of dike, the GQ-type, is more strongly strongly foliated than the first frst type and and very very closely closely resembles the intennediate intermediate to to felsic felsic tuffs tuffs that host them. The Thematrix matrixisisfute-grained, fme-grained,actinolite-rich actinolite-richand andup up to to 60% 60% subangular, supracrustal xenoliths have been observed in the the dikes. dikes. These rocks have yet to be classified. These Both maximum length length is is unknown. unknown. The 10 m wide) and their maximum Both types typesof ofdikes dikesare aretypically typicallynarrow narrow(0.1 (0.1— 10 dikes trend both northeast northeast and and northwest northwest and, and, as as yet, seem seem to to display display no no readily readily recognizable recognizablegeophysical geophysicalsignature. signature. Both types types of of dikes dikes are are metamorphosed metamorphosedand and are are presumed presumed to to be be slightly slightlyolder older than than the the supracrustal supracrustalrocks rocksthat thatthey they diopsides or KIM signature signatureassociated associatedwith with these these occurrences occurrences is unusual in that there are no chrome diopsides intrude. The TheKIM chrome chrome pyrope gamets garnets related related to the dikes. Chromite Chromiteand andilmenite ilmeniteare are the the only only two two indicator indicator minerals minerals presently presently thought to be associated associated with with these these occurrences. occurrences. These dikes are concentrated concentrated in the central part of the Michipicoten Michipicoten greenstone greenstone belt and and are are related related to to aa synfonnal anticliiie centred on Leclaire Township. These dikes appear to be related to a nappe structure lying synformal anticline centred These dikes appear to be related to a nappe structure lying on on the the northwest shoulder of the Kapuskasing Structural Zone. northwest shoulder of the Kapuskasing Structural Zone. The recent discovery discovery of Archean-aged diamondiferous diamondiferousdikes dikes within the Kapuskasing Kapuskasing Structure Structurein in Ontario Ontario has significantly significantlyinfluenced influenced diamond diamond exploration explorationin in the the province. province. - 69 �DIAMONDS AND AND DIAMOND DIAMOND EXPLORATION EXPLORATION IN IN NORTHERN NORTHERN ONTARIO ONTARIO WITH WITH A FOCUS ON THE MICHIPICOTEN MICHIPICOTENGREENSTONE GREENSTONE BELT, BELT, WAWA, WAWA, ONTARIO WILSON, C., Ministiy Ministryof ofNorthern NorthernDevelopment Development and and Mines, Mines, Ontario Ontario Government Complex, Highway 101 101 East, East. WILSON, A. A. C., P. 0. 0.Bag Bag3060, 3060,South SouthPorcupine, Porcupine,Ontario, Ontario,PON PON1HO 1HO(705-235-1614; (705-235-1614;ann.wilson(1iindm.gov.on.ca) ann.wilson@,ndm.eov.on.ca) Since 1899, it has been postulated that the source of the alluvial diamonds found south of Lake Superior originated east or west of James Bay. Blue Blue (1899) (1899) made this suggestion based on the fact that many of the gravels and boulders found in the glacial drift of Wisconsin, Michigan and Ohio, for example, are identical in composition and structure to the materials north of the Great Lakes. The first in hedrock, bedrock, in in Ontario, Ontario,was wasin in 1914. 1914. Microscopic diamonds were f i r t reported occurrence of diamond in reported by the Ontario Department of Mines in a sample collected from the claims of D. O'Connor in inReaume Reaume Township, located approximately 32 kilometers north of Porcupine. Exploration for diamonds in Ontario began in earnest in about 1960 1960 when the presence of of diamond indicator minerals (KIMs) (KIM5) was was discovered discovered by by Selco SelcoExploration Explorationininthe theMoose MooseRiver Riverdrainage drainagebasin. basin. The first confirmed kimberlite kimherlite was discovered in Hogg Township by Aquitaine Company of Canada iii in 1974. 1974. The James Bay Lowlands have been a diamond exploration hotspot since the late 1980's 1980's and andhas hascontinued continued up to to the the present. present. Exploration has involved companies such as KWG Resources, Resources, to be a favourite exploration target up Spider Resources, Ashton Mining of Canada, Continental Precious Metals, Garde Mining Exploration, B. B. P. Ltd. Exploration kimberlite clusters, the Resources Canada Ltd. and Monopos Ltd. Exploration has led to the discovery of several kiiherlite most notable being the cluster situated in the the Attawapiskat Attawapiskat River Riverarea. area. During the winter winter of 1999-2000, Monopros Monopros Ltd. has been in the process of extracting a 10,000 10,000 tonne bulk hulk sample from the Victor kimberlite kimherlite pipe. Traditionally, diamond exploration has focussed on following KIM dispersion trails and on examining examining related to kimberlite kimberlite pipes. pipes. However, the 1993 announcement announcement of the discovery of geophysical targets believed to be related three alluvial diamonds recovered from the Michipicoten River area south of Wawa has led to the search for for much much different diamond sources. In 1995 Surmacz and M. Hauseux made the first discovery of Archean-aged bedrock occurrence of of 1995 S. Surmacz diamonds in Ontario in Lalibert Township, approximately approximately 20 20 kilometers kilometersnorth northof ofthe thetown townof ofWawa. Wawa. Following this announcement, Spider Resources discovered nine more diamondiferous dikes in the same geographic geographic region in in 1997. Early Early this this year, year, Ban-Ore Ban-OreResources ResourcesLtd. Ltd.announced announcedthe the discovery discovery of of at at least leastone onemore more diamondiferous diamondiferous dike dike Township. To (the GQ Occurrence), this time in Musquash Township. To date, 5 commercial commercial stones, 42 macrodiamonds and 338 from bedrock hedrock in an area area approximately 30 square kilometers in in size. microdiamonds have been recovered from Archean diamond-bearing diamond-bearingbedrock bedrockin inthe thearea. area. The "SandorPresently, there appear to be two types of Archean actinolite+talc+carhonate xenoliths ranging ranging type" dikes are are mafic in in composition composition and and contain contain up to 35% 35% spectacular actinolite+talc+carbonate fme-grained matrix matrix is foliated. foliated. These rocks have been classified as lamprophyres. lamprophyres. up to 11 metre in size. The fine-grained The second type of dike, the GQ-type, is more strongly foliated than the first type and very closely tuffs that that host host them. them. The matrix is fine-grained, actinolite-rich actinolite-rich and up up to 60% resembles the intermediate to felsic tuffs been observed observed in in the the dikes. dikes. These rocks have yet to be classified. classified. subangular, supracrustal xenoliths have been their maximum maximum length length is is unknown. unknown. The 10 m wide) and their The Both types types of ofdikes dikesare aretypically typicallynarrow narrow(0.1 (0.1—- 10 dikes trend both northeast and northwest and, as yet, seem to display no readily recognizable geophysical signature. Both types of dikes are metamorphosed and are presumed to be he slightly older than the supracrustal rocks rocks that they they intrude. The TheKIM KIMsignature signatureassociated associated with with these these occurrences occurrences is unusual in that there are no chrome diopsides or chrome pyrope garnets related to the dikes. Chromite presently ilmenite are the only two indicator minerals presently Chromite and and ilmenite thought to be associated with these these occurrences. occurrences. The recent discovery of of Archean-aged Archean-aged diamondiferous dikes within the Kapuskasing Structure Structure in in Ontario Ontario will significantly influence influence the way that future future diamond exploration is conducted in the province. 19-124. in Report of the Ontario Ontario Bureau Bureau of of Mines Mines 1900, 1900,p.1 p.119-124 Blue, A. 1899. 1899. Are Arethere there diamonds diamondsin inOntario?; Ontario?; in Gibson, T. W. 1914. 1914. Statistical StatisticalReview Review of of the the Mineral Mineral Industry Industry of Ontario for 1913; 1913; in Ontario Bureau of Mines Annual Report 1913, v. v.23, p.47. 23, pt. pi. 1, 1, p. 47. 70 �PETROGENESIS OF THE SILVER SILVER CREEK DIKE: A 1.1 1.1 Ga INTRUSION IN THE MIDCONTINENT MIDCONTINENT RIFT RIFT SEIFERT, Karl Karl E., E., Department Departmentof ofGeological Geological& &Atmospheric Atmospheric WOLBERS, Jennifer A., and SEIFERT, State University, Ames, Iowa 50011 50011 Sciences, Iowa State The Lake Superior at Silver The Silver Creek dike is a mafic intrusion exposed along Lake Silver Creek cliff north of Duluth, Minnesota. Silver Creek cliff is comprised of several lava flows of the North Shore Silver Creek cliff is comprised Volcanic Group, which the the dike dike intrudes, intrudes,and andaathin thinoverlying overlyingsill. sill. Previous Previous misinterpretations misinterpretations of of the result result of of an an unseen unseen upper upper contact, a contact that is Silver Cliff as a single sill were the is now clearly exposed as the result of of aa tunneling tunneling project project in in the the early early 1990s. 1990s. Samples from field work and drill cores taken during the tunneling project have been analyzed for both maior major and trace trace elements. elements. Major Maior element data from both XRF analysis analvsis and microprobe work indicate that that the Silver Creek dike is is aa diabase consisting predominantly of of labradorite, augite, olivine, and Fe-Ti oxides. The The rare rare earth earth element (REE) pattern of the dike's upper chill zone mimics that that of the the overlying flows flows suggesting suggestingcontam&tion contamination inthe theupper upperpart part of of be aa primitive primitive olivine olivine tholeiite the dike. REE REEpatterns patternsofofthe thelower lowerchill chillzone, zone, however, however, show show itit to to be dataindicates indicatesthat that the theSilver SilverCreek Creekdike dikeformed formed from from with no significant contamination. Isotope Isotopedata a relatively primitive and uncontaminated 0. uncontaminated mantle magma with eNd values near near 0. in 71 �Geochemical Impacts of An An Undisturbed Undisturbed Mineral MineralDeposit Deposit— - Results From the Bend Deposit, Chequamegon National Forest, Wisconsin Laurel G. Woodruff, Woodruff, USGS, USGS,St. St.Paul, Paul,MN MN55112 55112(woodruff@usgs.gov), (woodruffusgs.gov), John John W. W. Attig, Attig, Wisconsin Geological and Natural History Survey, Madison, WI 53705, 53705, and William F. F. Cannon, USGS, Reston, VA 22092 The Bend copper-gold massive sulfide deposit in the Medford District District of of the Chequamegon National Forest, Taylor County, Wisconsin, is hosted by Early Proterozoic volcanic rocks. Pre-Pleistocene Pre-Pleistocene saprolite and 100-120 100-120 feet of Quatemary Quaternary materials materials cap cap the mineralized horizon. Ore Oreconsists consists of of massive massive pyrite with varying amounts amounts of bornite, arsenopyrite, chalcocite, and rare gold-silver chalcopyrite, tetrahedrite-tenantite, bornite, tellurides. The ore zone at Bend contains significant concentrations of arsenic, significant concentrations arsenic, bismuth, bismuth, mercury, tellurium, thallium, and antimony antimony in addition to the principal ore metals, metals, copper copper and gold. Because Because these these elements elements are atypical of surrounding bedrock, the Bend deposit was selected selected to examine examine natural elemental dispersion from a buried massive massive sulfide sulfide in in aa glaciated region. The The influence influence of the Bend mineralization on its environment is characterized using a geochemical characterized geochemical database database that that includes: includes: 1) bedrock, sulfide bedrock, massive sulfide provided by Sharpe Energy and Resources and saprolite obtained from diamond drill core provided and the Jump River Joint Venture; 2) regional samples samples of Quaternary Quaternary materials materials from from Taylor County (Attig, subsurface Quaternary Quaternary material and weathered weathered (Attig, 1993); 1993); and 3) subsurface bedrock from the area of the Bend deposit obtained by rotasonic drilling. The USGS drilled five rotasonic rotasonic drill holes through the Quaternary deposits deposits along along aa 0.5 0.5 mile the strike strike of of the the Bend Bendmineralized mineralizedzone. zone. Nearly mile linear transect that crossed the Nearlv continuous core was recovered from every borehole, including up to several feet of weathered weathered bedrock. The core reveals a complex Quatemary Quaternary section section that that consists consistsof of two two till sheets, several intervals of gray, clay-rich lake sediments, and several several areas areas of of outwash. The older till is gray, carbonate-rich carbonate-rich till of the Marathon Marathon Formation Formation and and the the younger is reddish brown till of the Copper Falls Falls Formation. Formation. The Marathon Marathon Formation Formation both underlies and overlies lake sediments and and outwash. outwash. Bedrock Bedrock in the area area of the Bend deposit is directly overlain by the lowermost outwash outwash unit, whereas the Marathon Marathon Formation Formation is draped over metagabbro metagabbro that forms a bedrock high to the south south of of the the deposit. Detailed Detailed geochemical geochemical analyses analyses of the different units show that in addition to obvious color and grain size distinctions, higher average Ca content also distinguishes the Marathon Marathon Formation Formation from from the the Copper Copper Falls Falls Formation. Formation. As much as 20 meters of saprolite saprolite is preserved over massive sulfide sulfide at the Bend Bend deposit. deposit. Saprolite is leached of most metals that are concentrated in unweathered massive sulfide. Cu, Zn, Au, As, Se, and Te concentrations all decline sharply across the transition from massive sulfide sulfide to saprolite, saprolite, whereas whereas Ba, Mn, Ti, Cr, Ni, and V increase increase markedly. Anomalous Anomalous concentrations concentrations of those elements elements within the massive sulfide sulfide are are mostly mostlv lacking in overlying glacial deposits suggesting that the saprolite saprolite cap prevented physical rock by by glacial glacial movement. movement. However, in the glacial deposits directly dispersal of sulfide rock relatively high high values valuesof ofHg Hgand andxAu arefound. found. This over the Bend mineralization, relatively u are of these these elements elements from frommassive massivesulfide. sulfide. In the downsuggests hydromorphic dispersion of 72 �ice direction from the Bend deposit, gold concentrations are found increasingly increasingly higher in the Quaternary section (Figure 1). The The overall pattern for Hg is less distinct, although Hg values found in both Marathon Formation and Copper Falls Formation tills from rotasonic core are markedly higher than Hg values measured in regional subsurface subsurface samples from the same formations. same formations. This study shows that although regional background geochemical values in glacial glacial deposits can be influenced by anomalous concentrations of elements in bedrock, the nature of both the sources and the sinks for various elements controls the dispersion dispersion subcrop of a massive patterns. ItIt also alsoshows showsthat that understanding understanding the character character of the subcrop sulfide and the intervening surficial stratigraphy is critical in geochemical exploration exploration in In the the case caseof of the the Bend Bend deposit, deposit, metal-depleted saprolite caps the deposit this terrane. In and has protected massive sulfide from glacial dispersion, so sulfide-bearing boulders boulders and traditional metal (such as Cu and Zn) anomalies have not developed even in till near the bedrock surface. However, However, more more subtle subtle dispersion dispersion patterns of other elements elements may indicate the presence of sulfide mineralization. sulfide mineralization. North Ta-4 Ta-4 Ta-3 1350 South South Ta-5 I—...—- Ta-2 1330 Ta-i rr L.r CF 1310 . — •• 1290 — —— C I 'S — A I 0 'U — - C) C — Ow . 1270 ow a) w 1250 1230 •-- -. ailay S.----- ls. t Bedrock surface - OH. . , - —___ - -S d deposit 1210 Figure 1: Cross-section of Bend Bend deposit. deposit. CF = Cross-section of of the the surficial surficial section in the area of = Copper = outwash, Falls Formation, MA = = Marathon Marathon Formation, ow = outwash, ls Is == lake lake sediments, sediments, Ta drill hole. hole. Striped designates each rotosonic drill Striped areas areas show locations locations of samples with greater than .01 .O1 ppm Au. Vertical Verticaland andhorizontal horizontaldimensions dimensionsare are not not to to scale. scale. Reference: Attig, Attig,J.1.W., W., 1993, 1993, Pleistocene Pleistocene geology of Taylor County, Wisconsin: Wisconsin Wisconsin Geological Geological 27 p. and Natural History History Survey Survey Information InformationCircular Circular65, 65,27 p. 73 � https://digitalcollections.lakeheadu.ca/files/original/632fe39ce4815072b1d96ab2bd49fbae.pdf 99b9247da40b34d2229b67c16bf62343 PDF Text Text FORTY-SIXTH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR .GEOLOGY. thunder Bay, Ontario May 08-13; 2000 * 4 1 PROCEEDINGS VOLUME 46 4 PART 2: FIELD TRIP GUIDE BOOKS S �46th I.L.S.G. 46th I.L.S.G. ield Guide May 8-13, 2000 �46thANNUAL ANNUAL MEETING MEETING INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY Volume 46 consists of Part Part 1:1:Program Programand and Abstracts Abstracts Part Part 2: 2: Field FieldTrip Trip Guidebook Guidebook References References to to material material in in this this volume volume should shouldfollow follow the the example examplebelow: below: Ams, Holm, D., 2000, Characterization Characterization and timing constraints of Arns, D. and Hoim, post-Penokean meso-scale structures structures in the Watersmeet and Republic gneiss Institute on Lake Superior gneiss domes domes of northern Michigan (abst.): Institute Superior, Geology 46"' Annual Annual Meeting, Meeting, Thunder Bay, Ontario, Ontario, GeologyProceedings, Proceedings,46th v.46, p.2. part 1, 1, p. 2. v. 46, part Volume Volume 46 46 Published Published and and distributed distributedby by Institute Institute on on Lake Lake Superior Superior Geology Geology Mark Jirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer, I.L.S.G. I.L.S.G. Minnesota Minnesota Geological Survey Survey 2642 University Avenue Avenue St.Paul,MN USA 55114-1057 551 14-1057 St. Paul, MN USA (612) 627-4780 627-4780 (612) email: jirsa00ltc.unm.edu email:jirsaOOl0,tc.urnn.edu ILSG ://www.Qeo.mtu.edulgreat lakes/ilsg/ ILSG website: website:httn httw://www.geo.mtu.edu/great lakedilsd ISBN ISBN 1042-9964 1042-9964 All volumes are available availablefor photocopying photocopying costs costs from Michigan Michigan Technological TechnologicalUniversity UniversityLibrary Library Archives �INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS Volume 46 Field Trip Guidebook Compiled by: Philip Fralick �TABLE OF TABLE OF CONTENTS CONTENTS The trip description coded to to aid aid The first first page page of of each each field field trip description is is colour colour coded finding it finding it in in the the book. book. Field Trip Field Trip 1) 1) Mesoproterozoic Sibley Sibley Group Group (yellow) Mesoproterozoic (yellow) Field Trip Field Trip 2) 2) Lac des des Iles Iles Mine Mine (purple) (purple) Lac Field Trip Field Trip 3) 3) Geoarcheology of of the the Thunder Thunder Bay Bay Area Area (red) (red) Geoarcheology Field Trip Field Trip 4) 4) Paleoproterozoic Gunflint Gunflint Formation Formation (blue) (blue) Paleoproterozoic Field Trip Field Trip 5) 5) Quaternary Geology Shebandowan Belt Belt (orange) (orange) Quaternary Geology Shebandowan Field Trip Field Trip 6) 6) Steep Rock-Lumby Belts Belts (green) (green) Steep Rock-Lumby �GEOLOGY OF THE MESOPROTEROZOIC SIBLEY SIBLEY GROUP GROUP Philip Fralick, Lakehead University Mark Smyk, Ontario Geological Survey This of a This trip trip will will examine examine the depositional depositional architecture architec playa-alluvial playa-alZuvialsuccession successiondeveloped developed in in an an intracratonic intra basin. The pristine sequence records the effects basin. The pristine sequence records the effectsof ofboth both climate climateand andtectonics tectonicson onsediment sediment character. character. �Geology and and Stratigraphy Stratigraphy of the Mesoproterozoic Sibley Group Group by Philip Mark Smyk2 and Mariah Mariah Mailman' Philip Fralick1, ~ralick',Mark smyk2 and ail man' 1 a Amethystine stromatolite, Rossport Rossport Formation, Formation, Dorion, Dorion, Ontario Ontario Amethystine stromatolite, 1 'Department of '~e~artrnent of Geology, Geology, Lakehead LakeheadUniversity, University,Thunder ThunderBay Bay ON ON P7B P7B 5E1 5E1 2Ontwio '0ntario Geological Survey, Survey, Resident Resident Geologists Geologist'sProgram, Program,Ministry Ministryof ofNorthern NorthernDevelopment Development and 435 S. and Mines, Mines, Suite SuiteB002, B002,435 S. James James St., St., Thunder Thunder Bay ON ON P7E P7E 657 6S7 �FOREWORD FORE WORD This field of the This field guide guide is is intended intended to to provide provide aacomprehensive comprehensive overview overview of the Sibley Sibley Group Group Trip stops have been sedimentary rocks, their stratigraphy and associated mineral deposits. sedimentary rocks, deposits. Trip selected on on the basis of representivity many other key and noteworthy sites selected representivity and accessibility; accessibility; many cannot be easily accessed but are described in the text. This guide follows in the footsteps of a number of previous field trips that have focused on the Proterozoic geology geology of the Thunder Bay area. Field stop descriptions have incorporated Proterozoic incorporated and built upon and Kustra Kustra et et al. (1972), Kustra built upon those found in guide guide books written written by Franklin Franklin and Kustra (1972), aL (1982) and Kissin (1990), as as well as other, unpublished unpublished reports. (1977), Franklin ci et al. contact the staff of the Please contact the Resident Resident Geologist's Geologist's Office, Thunder Bay South District, (807) 475-1331, 475-133 1, for current information regarding regarding permitted permitted access access to private and staked properties. A CKNO WLEDGEMENTS ACKNOWLEDGEMENTS The authors would like like to thank Scott for for assistance in the the scanning of The authors would thank J. J. Scott assistance in scanning 1I digitization digitization of K. Farrier Farrier and and S. Warren photographs and maps. S. Spivak drafted some of the the diagrams. diagrams. K. Warren photographs the Ruby Lake quarry was permitted permitted by Ruby Lake provided word processing support. Access to the Marble Ltd. Ltd. Discussions with J. Franklin, Marble Discussions with Franklin, H. Poulsen, Poulsen, other other geologists geologists and prospectors prospectors are appreciated. appreciated. �INTRODUC HON INTRODUCTION Sedimentaryrocks rocksof of the the Sibley discontinuouslyoutcrop outcropon on the the north north shore shore of Lake Sedimentary Sibley Group Group discontinuously Lake Superior and around Lake Nipigon (Figure 1). The flat-lying to gently dipping, elastic-carbonate Superior and around Lake Nipigon (Figure 1). The flat-lying to gently dipping, clastic-carbonate succession oval area disconfonnably overlying succession occupies occupies aa broad broad oval disconformably to unconformably unconformably overlying Mesoproterozoic, Paleoproterozoic and Neoarchean rocks. Mesoproterozoic, Paleoproterozoic and Neoarchean rocks. Sibley Group rocks are located located in in the the Southern Southern Province Province of of northwestern northwestern Ontario. Ontario. The first first documentation of these red beds was by Logan (1863). Hunt (1873) divided Logan's Upper documentation of these red beds was (1863). Hunt divided Logan's "Upper Copper-Bearing Series" into the Animikie and Keweenaw groups; the Sibley was assigned to the latter. descriptions of of the the Sibley Group were were provided provided by by Bell (1870), Parks (1901) and latter. Other descriptions Wilson (1910) who compared the Sibley Sibley (then called "Nipigon "Nipigon Series") Series") to to similar similarKeweenawan Keweenawan and Paleozoic rocks rocks elsewhere. elsewhere. Despite similarities to these younger rocks, the Sibley Sibley Group Group rocks were different enough to preclude assigning them a definite Precambrian age. Subsequently, they were were given given the the name name "Sibley by Tanton Subsequently, they "Sibley Group" Group" by Tanton (1931) (1931) after after the the Sibley Sibley Peninsula on on which which they they are are well-exposed. well-exposed. The Peninsula The Sibley Sibley Group Group rocks were studied studied by Hawley Hawley (1930) and Moorhouse (1960), but they were not mapped comprehensively comprehensively until Coates Coates (1972). (1972). Mcllwaine (1971a,b; (1971a,b; 1975) 1975) also also studied studied the the Sibley Group Mcllwaine Group rocks. Franklin Franklin (1970) pursued pursued a doctoral thesis thesis regarding regarding the the metallogeny of Proterozoic rocks in the doctoral metallogeny of Proterozoic rocks the Thunder Thunder Bay Bay District, District, including the Sibley Group. Thereafter, he described the stratigraphy and depositional setting of the Sibley Group (Franklin et al. 1980). 1980). The Thetectonic tectonic setting, setting, source source areas, areas, and and environments environments of deposition Keweenawan strata strata in in the the Lake Lake Superior region were were published published by by Morey Morey and deposition of Keweenawan Superior region and A doctoral thesis by Cheadle (1985) was executed on the "lower Ojakangas (1982). the "lower Ojakangas (1982). A doctoral thesis by Cheadle (1985) was executed Keweenawan" Sibley Sibley Group. Group. In all of of these these studies studies the Sibley Sibley Group Group rocks are presented as Rift. ift. This Thisnotion notionwas was refuted refuted by by Fralick Fralick and and Kissin Kissin being genetically related to the Keweenawan R (1995). (1995). Outcrop exposure and drill core lithologies provide evidence that the Sibley Sibley Group Group sedimentary sedimentary rocks are continuous, near-horizontal strata there were deposited in an an extensive, extensive, low-lying low-lying area. area. For this reason, the structure structure in in which which the the sediments sedimentsaccumulated accumulated will will be be called called the the Sibley SibleyBasin. Basin. The Sibley Basin is elongate elongate in a northwesterly northwesterly direction, extending extending from from the north north shore shore of of Lake Lake It Superior in the south, along the western mar margin of Lake Nipigon, to Armstrong in the north. in Nipigon, It discontinuouslywithin withinaa15 15000 000km km area area (Franklin et eta?. crops out discontinuously al. 1980). 1980). The Theexposed exposed basin basin is now 175 175 km wide and and 400 400 km km long. long. 5 The fluvial fluvial and and lacustrine lacustrine strata strata of of the the Sibley SibleyGroup Groupare aredivided dividedinto intothree threesubhorizontal subhorizontal formations: 1) the the lowermost is the Pass Lake Formation; 2) the Rossport Formation overlies it, formations: followed by 3) 3)the the Kama KamaHill Hill Formation. Formation. The Pass Lake Formation varies from 0 to 50 50 m in in thickness thickness and and consists consists of of basal basal conglomerate conglomerate It was and beds of quartz arenite. arenite. It was deposited deposited in in aashallow shallowlacustrine lacustrine and upward-thinning upward-thinning beds of quartz 135 m thick Rossport Formation is composed The 135 thick Rossport composed of a a!. 1980). environment (Franklin et a!. 1980). lower, arenaceous, red red dolomite unit, a central and stromatolitic unit, and an lower, arenaceous, dolomite unit, central chert-carbonate chert-carbonate and stromatolitic unit, upper, argillaceous, argillaceous, red red dolomite dolomite unit. unit. These These beds were were laid down in aa shallow, shallow, saline saline basin basin of of Fifty metres of purple shale constitute the Kama Hill fluctuating size (Franklin et a!. fluctuating a!. 1980). constitute Kama Hill 1980). Fifty metres �Formation. Formation. Desiccation Desiccationcracks, cracks,evaporite evaporiteclasts, clasts,and and mud mud chip chip conglomerates conglomerates in this purple purple shale were formed on mudflats that were subaerially exposed and dried out periodically (ibid). formed on mudflats that were subaerially exposed dried periodically (ibid). The The lack lack of of fossils fossils in in the the Precambrian Precambrian presents problems in age determination and in interpreting that are are present present in in the Sibley Group rocks the environment environment of of deposition. deposition. The stromatolites stromatolites that (Hoffman (Hoffinan 1969) 1969) can can occur occur in in both marine and fresh water, but the red beds are characteristic of a continental setting (Morey (Morey and Ojakangas Ojakangas 1982). 1982). The thick dolomite and gypsum gypsum sequences sequences formed formed during during intermittent, intermittent, arid arid periods. 33 Ma, to 1537 Historically, has been been postulated postulated that that the the Sibley SibleyBasin Basin(1339 (1339+1+/- 33 1537 Ma; Franklin Historically, itit has 1978a; Davis and Sutcliffe 1985, respectively) developed because of crustal attenuation Sutcliffe 1985, attenuation caused caused described itit as a failed by the Keweenawan Rift System. System. Franklin Franklin et et aL al. (1980) described Keweenawan Midcontinent Rift arm, radial radial to aa paloplume palasoplumeininrelation relationthe theKeweenawan Keweenawan Rift. Rift. Morey Morey and Ojakangas (1982) described a sedimentary-tectonic framework for the Sibley Basin that is is related related temporally temporally and and sedimentary-tectonic framework for the Basin that spatially Rift; the Sibley subsidence of of the Sibley Basin developed developed as renewed renewed subsidence spatially to the Keweenawan Keweenawan Rift; Conversely, Cheadle (1986) described Animikie Animikie Fault Block Block Basin Basin (2200-2000 (2200-2000 Ma). Ma). Conversely, Cheadle (1986) described the tectonic framework of the Sibley Basin as broad, subsiding sag where significant fault control is lacking at the Sibley Group red beds are representative of the the margins. margins. It was thought that the Sibley earliest evidence Event. However, evidence of the Keweenawan Rift Event. However, this this interpretation interpretation is problematic. The oldest igneous activity that that isis related relatedtoto rifting riflingisisdated datedatat-1l 109 igneous activity 109 Ma Ma (Davis (Davis and and Sutcliffe Sutcliffe 1985) aa minimum minimum of of -230 230 My Myafter afterthe theSibley SibleyGroup Groupwas was deposited. deposited. Conceptually, Conceptually, aa thermal thermal dome precedes rifting, rifling, and erosion will will occur. occur. It is reasonable to presume that volcanism can be be that volcanism can is preceded by sedimentation on this this time time scale, scale,but butthe thepalasodrainage palodrainage system sedimentation on system will will develop develop away away from the dome. This palocurrent work This conflicts conflicts with the palasocurrent workdone doneby by Cheadle Cheadle (1986) (1986) in which the palodrainage palasodrainagesystem systemflowed flowedtoward towardthe thethermal thermal welt. welt. It is unreasonable to hypothesize that the pre-rifi pre-rift basin was was overlying overlying the the thermal thermal welt. welt. Thus, the presumed presumed relationship relationship of the Sibley Sibley Basin with the Keweenawan Rift must must be be reappraised. reappraised. The two events are not related directly Keweenawan Rift the Sibley Sibley Basin Basin may may be be genetically linked to the Kissin 1995). 1995). Alternatively, Alternatively, the genetically linked (Fralick and Kissin heating event represented by the igneous complex formed at Redstone Point, Lake Nipigon heating represented igneous complex formed Redstone Point, (1537 Ma; Davis SibleyGroup Group Davis and and Sutcliffe Sutcliffe 1984) 1984)as as these these igneous igneous rocks rocks lay lay directly directly under under the the Sibley Basin (Fralick (Fralick and Kissin 1995). 1995). In Inthis thisscenario, scenario,mantle mantle upwelling upwelling would cause partial melting of the lower crust, forming the Redstone Point Point felsic felsic magmas. magmas. The higher heat heat flow flow would would cause cause thermal doming the dome. dome. Upon relaxation of the crust an infracratonic infracratonic doming with erosive stripping of the This basin basin, basin, the Sibley Sibley Basin, Basin, would would be be created. created. This basin would would be be saucer-shaped saucer-shaped without without pronounced pronounced boundary boundary faults. faults. This Thiscorresponds correspondsto to the theactual actual basin basin geometry. geometry. REGIONAL REGIONAL GEOLOGY GEOLOGY The Sibley Group rocks rest unconformably on the Paleoproterozoic Animikie Animikie Group Group (Rove (Rove and and Gunflint Formations) and Ojakangas 1982). Formations) and Neoarchean granitic and volcanic rocks (Morey and The Sibley Formation, a series of trough crossSibley Group Group possibly correlates correlates with the Puckwunge Formation, crossstratified, medium-grained, lensoid sandstones occurring in northeastern Minnesota (Mattis medium-grained, lensoid sandstones occurring northeastern Minnesota (Mattis overlies Paleoproterozoic Rove Formation Formation shales shales and 1972). This formation formation unconformably unwnformably overlies Paleoproterozoic Rove 1972). �represents braided fluvial fluvial channel channel deposition, deposition, exhibiting exhibiting strong, strong, represents South South Saskatchewan Saskatchewan River-type, River-type, braided unimodal flow to the southeast. unimodal flow to the southeast. The and sandstone unit, the the Pass The Sibley Sibley Group Group consists consists of of aa lower lower basal basal conglomerate conglomerate and sandstone unit, Pass Lake Lake Formation, and an Formation, aa middle middle unit unit of of red red and and buff buff dolomitic dolomitic mudstone, mudstone, the the Rossport Rossport Formation, Formation, and an upper unit, unit, the to siltstone to upper the Kama Kama Hill Hill Formation, Formation, consisting consisting of of purple purple shale shale and and buff-coloured buff-coloured siltstone fine has subdivided the Sibley to the fine sandstone. sandstone. Cheadle Cheadle (1986) (1986) has subdivided the Sibley Group Group according according to the different different sedimentary facies. From sedimentary facies. Frombottom bottom to to top: top: Pass Lake Lake Formation Formation Pass Loon Loon Member Member (basal (basal conglomerate conglomerate facies) facies) Fork Bay Member (plane-bedded Fork Bay Member (plane-bedded facies facies and and cross-bedded cross-beddedfacies) facies) Rossport Formation Rossport Formation Channel facies and Channel Island Island Member Member (cyclic (cyclic facies and mudstone mudstone facies) facies) Middlebrun Bay Bay Member Middlebnm Member (stromatolite (stromatolite facies) facies) Fire Hill Hill Member Fire Member (chalcedonic (chalcedonic mudstone mudstone facies) facies) Kama is constituted wholly by by aa laminated shale facies facies and and thus, Kama Hill Hill Formation Formation is constituted wholly laminated shale thus, is is not not subdivided. subdivided. PASS FORMATION PASS LAKE LAKE FORMA TION The Loon Lake Member Member is is best best exposed exposed at at Pass Pass Lake Lake in in aa cliff, The Loon Lake cliff, consisting consisting of of the the Pass PassLake Lake At the Formation, which which runs runs parallel parallel to to the the Canadian Canadian National National Railway. Railway. At the north north end end of of the the Formation, outcrop, the the Paleoproterozoic Rove Formation Formation is is visible visible where where the the lowermost lowermost beds beds of of the the Pass outcrop, Paleoproterowic Rove Pass Lake Formation disconformably overlie overlie it. it. The The Pass Pass Lake Lake Formation Formation ranges ranges in in thickness thickness from from Lake Formation disconformably The Loon facies, consists consists of of thin, 18 thin, lensoid lensoid 18 to to 50 50 m. m. The Loon Member, Member, the the basal basal conglomerate conglomerate facies, conglomeratic sediment. sediment. ItItisisthickest near the the basin basin margin margin and and it it thins thins down to conglomeratic thickest(-'-15 (-15 m) near to about about Animikie taconite, taconite, jasper, jasper, and and shale one metre in the the basin basincenter center(Cheadle (Cheadle 1986). 1986). Animiie shale clasts clasts one metre in predominate in in the over Animikie rocks whereas predominate the conglomerate conglomerate deposited deposited over Animikie rocks whereas vein vein quartz quartz vein, vein, granite, and metavolcanic rock clasts dominate where an Archean basement is present clasts dominate an Archean is present (Cheadle (Cheadle and are are < 5 30 30 cm cm in in diameter diameter (Morey (Morey and and Ojakangas Ojakangas 1982) 1982) and are in in matrixmatrix1986). The The clasts clasts are 1986). The polymictic polymictic matrix matrix isis brick-red brick-red (Franklin (Franklinetet aal. and it support (Cheadle 1986). 1986). The t. 1980) 1980) and it is is composed of of medium medium to to coarse coarse grains grains of of quartz, quartz, hematite, hematite, and and mudstone mudstone(Cheadle (Cheadle1986). 1986). The The composed conglomerate has has calcareous calcareous cement. cement. The with deeper and conglomerate The lenses lenses have have scour scour and and fill fill structures structures with deeper and They are narrower channels channels cut proximal narrower proximal to the the source. source. They are cross-bedded cross-bedded with with rare rare dolomite dolomite mudstone layers. layers. At with the the lower lower half half of of the the bed bed in in clast clast mudstone At Silver Silver Islet, Islet, the the lensoids lensoids are are graded graded with support that changes into matrix support in the upper half (Cheadle 1986). support that changes into matrix support in the upper half (Cheadle 1986). The Fork Fork Bay Bay Member Member is is dominated dominated by by medium-grained medium-grained sandstones sandstones which which are are subdivided subdivided into into aa The lower plane-bedded plane-bedded facies facies and an an upper cross-bedded facies. ItItoverlies overliesthe theLoon LoonMember. Member. Plane Bedded Facies: 20 Plane Bedded Fades: 20 to to 80 80m mofofplaneplane-totocross-bedded cross-bedded quartz quartz arenite arenite overlie overlie the the basal basal conglomerate (Cheadle 1986). This buff-coloured sandstone consists of well-sorted, rounded to This buff-coloured well-sorted, �well-rounded, coarse-grained, mature subarkose to sublitharenite sublitharenite well-rounded, finefine- to to coarse-grained, mature quartz quartz arenite arenite to to subarkose and Ojakangas Ojakangas 1982). Minor quartzfragments fragmentsare arepresent. present. As (Morey and Mmor chert and polycrystalline quartz layers that that separate the 5 cm well, there are thinly interbedded dolomitic mudstone and siltstone layers to 11 m thick thick sandstone sandstone beds. The Theupper upper 55to to 10 10cm cmof ofsome somesandstone sandstonebeds beds contain contain mud mud chips. chips. The plane-bedded facies hosts an array of sedimentary structures plane-bedded facies hosts an array of sedimentary structures including including horizontal laminations and and parting laminations parting lineations, lineations, isolated isolated planar planar cross-beds, cross-beds, straightstraight- to to sinuous-crested sinuous-crested oscillation ripples, rare current ripple laminations, rare sand volcanoes and dewatering tubes, and and oscillation volcanoes and dewatering tubes, desiccation desiccation cracks cracks and halite halite clasts clasts in thinly interbedded mudstone (Cheadle 1986). Cross Bedded Fades: Facies: The Thecross-bedded cross-bedded facies facies is is 55 to to 10 10m m thick, thick, with with mediummedium- to large-scale, large-scale, cross-bedded arenite intercalated beds at cross-bedded intercalated with with 1 m thick thick planar, planar, cross-stratified cross-stratified sandstone sandstone beds Rossport, Red Rock, Channel Island, contains scoured scoured bases and Rossport, Island, and Pass Lake. Lake. This facies contains The ripple-marked ripple-marked and and mud-cracked mud-crackedquartz quartz arenite arenite beds beds have have pebbly (Cheadle 1986). 1986). The pebbly infill (Cheadle horizontal to to wavy wavy stratification stratificationwith withminor minortrough troughcross-beds. cross-beds.The Thepalaeocurrents palocurrents of the crosshorizontal beds at Pass Lake and the Enterprise Mine are scattered, with predominantly south-southeast and east-southeast directions, east-southeast directions, respectively (Morey and Ojakangas 1982). aL (1980) logged the 50 m m cliff cliff exposure exposure at at Pass PassLake. Lake. Twenty metres of of buff arenite Franklin et al. rest on the basal lensoid conglomerate. This This buff buff arenite arenite thins upward from 1 m thick beds at the base to to 1 to 22 cm The sequence alternates alternates upwards upwards from from dolomite dolomite to cm thick thick beds beds at at the the top. top. The base arenite. They recorded 1 m of red dolomitic arenite to 13 m of buff arenite; 1 m of thinly bedded They recorded 1 m of red buff arenite; 1 m of thinly bedded m of of buff buff arenite; arenite; 1 m m of ofred reddolomitic dolomiticarenite; arenite;and and 77m mof of red dolomite and dolomitic arenite; 10 m thickly bedded buff arenite. arenite. AAsharp sharpincrease increase in inthe thedolomite dolomite content, content, aa pigmentation pigmentation change, and a gradual decrease in clastic content mark the upper boundary of the Pass Pass Lake Lake Formation Formation et aL al. 1980). 1980). (Franklin (Franklin et At Redstone Point, along the At the Lake Lake Nipigon Nipigon shoreline, shoreline, the Pass Pass Lake Lake Formation Formation overlies an anorogenic, felsic intrusive-extrusive granitoid suite (Fralick and Kissin 1996, unpublished data) dated at 1537 One metre below the dated 1537 Ma Ma (Davis (Davis and and Sutcliffe Sutcliffe 1985). 1985). One the volcanic-sedimentary volcanic-sedimentary contact, the the igneous rocks rocks are weathered weathered and and the the feldspar feldspar exhibits exhibits aa chalky, chalky, cream cream to to salmon contact, colouration. There There is aa 30 colouration. 30cm cmthick thickvolcanic volcanic breccia breccia with with caliche caliche overlying overlying the the weathered weathered rocks. The igneous rocks. ThePass PassLake LakeFormation Formation isis lacking lacking the the basal basal conglomerate conglomerate at Redstone Redstone Point. Point. Instead, there are fine-grained, red sublithareniite to subarkosic sandstones with massive or Instead, fine-grained, sublitharenite to subarkosic sandstones with massive or parallel-laminated beds. beds. Trough These strata contain very angular, Trough cross-stratification cross-stratification is rare. These volcanic clasts clasts with with oxidized oxidizedrims rimsand andweathered weathered granular to pebble to small cobble-sized, felsic volcanic pebbles. feldspars. There Thereare arealso alsoless lessabundant abundant clasts clasts of of hematitic hematitic mudstone, chert, and caliche pebbles. The basal pebble sandstone sandstone is poorly sorted with subrounded to rounded sand and small angular grains. The hascarbonate carbonatecement cement with with clay filling between the grains. The beds range from from 11 to pebbles. ItIt has 80 cm thick, with a mean thickness of 15 cm. They They are are laterally laterally continuous continuous over several metres with rare, 1 m wide channels. Tightly Tightlypacked packed quartz quartzarenite arenite overlies the basal pebbly sandstone. contains minor minor clay clay in the matrix, The quartz arenite is well-sorted, well-sorted, subangular to subrounded, contains and has quartz cement. The Thearenites arenitesare are folded folded slightly slightly and and plunge at <15° <15' to the east east (Fralick (Fralick and Kissin 1996, 1996, unpublished data). �ROSSPORT FORMA FORMATION ROSSPORT TION The The Rossport Rossport Formation Formation consists consists of of red, red, fine-grained, fine-grained, arenaceous arenaceous and and clayey clayey dolomite. dolomite. It It lies lies disconformably on the the Pass Pass Lake Lake arenite arenite (Franklin (Franklin et et at. al. 1980) disconformably on 1980) and and it it has has aamaximum maximum vertical vertical outcrop of 134 m at marker bed bed (Morey and outcrop of 134 m at its its type type locality locality where where it it is is lacking lacking the the stromatolite stromatolite marker (Morey and Ojakangas 1982). North Ojakangas 1982). North of of Nipigon Nipigon and and north north of of Dorion Dorion there there have have been been 300 300 m m and and 180 180 m m of of the et aL al. (1980) (1980) logged logged and and subdivided subdivided the the the Rossport Rossport Formation Formation drilled, drilled, respectively. respectively. Franklin Franklin et Rossport Formation, Formation, starting starting with with aa lower, lower, argillaceous argillaceousred reddolomite dolomiteunit. unit. They recorded 11 m m of Rossport red through the the sequence, there is red conglomerate conglomerate at at the the base. base. Upwards Upwards through sequence, there is 96 96 m mof ofwell-bedded, well-bedded, brick and arenaceous dolomite intercalated intercalatedwith withbuff buff to to white white arenite, arenite, 11 to to 22 m m of brick red red dolomite dolomite and arenaceous dolomite of black chert, gray chert, and buff calcite that alternate from 0.5 to I cm thick laminae with a lowblack chert, gray chert, and buff calcite that alternate from 0.5 to 1 cm thick laminae with a lowamplitude is topped amplitude crinkle crinkle structure. structure. The The sequence sequence is topped with with 37 37 m m of ofmassive massive red reddolomite dolomite and and arenaceous and irregular arenaceous dolomite dolomite that that fractures fracturesconchoidally. conchoidally. Spherical Spherical and irregular reduction reduction spots spots are are noted throughout the the upper upper and and lower lower units. units. The noted throughout The top top of of the the Rossport Rossport Formation Formation is is marked marked by by aa change as it gradually to to zero. zero. The change in in the the dolomite dolomite content content as it decreases decreases gradually TheRossport Rossport Formation Formation rests rests unconformably on Archean Archean rocks rocks at at Kama Kama Bay. Bay. At unconformably on At this this location, location, as as well well as as at atPass PassLake, Lake, Red Red Rock, and Moseau Mountain, the Rossport's basal, basal, red red conglomerate conglomerateis is not not present. present. Cheadle has divided Cheadle (1986) (1986) has divided the the Rossport Rossport Formation Formation into into four four facies facies from from base base to to top: top: Channel Island Member (cyclic and mudstone facies) Channel Island Member (cyclic and mudstone facies) Middlebrun Middlebrun Bay Bay Member Member (stromatolitefacies) facies) (stromatolite Fire Fire Hill Hill Member Member (chalcedonic (chalcedonic mudstone mudstone facies) facies) Cyclic of the Member isis 77 to It has has Cyclic Facies: Fades: The The cyclic cyclic facies facies of the Channel Channel Island Island Member to 30 30 m m thick. thick. It rhythmic layering of mudstone and dolomite couplets or mudstone and sandstone sandstone couplets. The The couplets couplets range range from from 5 5 to to 160 160 cm cm in in thickness. thickness. The Thesandstone sandstoneand anddolomite dolomiteare areend endmembers members that that have throughout the the sequence. sequence. The have various various degrees degrees of of mud mud interlayering interlaye~g throughout The dolomitic dolomitic mudstone mudstone is is red, massive, friable, and tabular. ItIt isis common common to to both both cycles. cycles. The Themudstone mudstoneoften oftencontains containssilt silt or or sand sand and and rounded, rounded, reworked reworked pebble-sized pebble-sized carbonate carbonate clasts clasts (Cheadle (Cheadle 1986). 1986). Red Red Rossport Rossport Formation Formationmudstones mudstones with with diagenetic diagenetic evaporite evaporite minerals minerals formed by by precipitation precipitation in in aa clastic-dominated, clastic-dominated, sabkha sabkha setting setting Mudstone The Mudstone Facies: Fades: The mudstone mudstone facies facies has has �red red and and buff, buff, dolomicritic dolomicritic mudstone mudstone and and claystone claystone that that are are dominantly dominantly massive massive and and friable, friable, but but have local desiccation cracks and adhesion ripples, and small, scattered gypsum and anhydrite have local desiccation cracks and adhesion ripples, and small, scattered gypsum and anhydrite nodules. One to nodules. One to two two metre metre thick thickfinefine-totomedium-grained, medium-grained, poorly poorly sorted, sorted, subarkose subarkose and and sublitharenite with 10% matrix are sporadically introduced into the dolomicritic mudstone. matrix are sporadically introduced into the dolomicritic mudstone. sublitharenite with These subarkose and sublitharenite beds have powering-down powering-down sequences: scoured scoured bases, bases, planeplanebedded laminations, ripple cross-laminations, and horizontal, suspended load laminations bedded laminations, ripple cross-laminations, and horizontal, suspended load laminations (Cheadle 1986). (Cheadle 1986). Stromatolite Facies: Fades: The Stromatolite Thestromatolite stromatolitefacies, facies,or or the the Middlebrun Middlebrun Bay Member, which is located in the middle of the Rossport Formation, is 80 to 140 cm thick. The Thegray graychert-carbonate, chert-carbonate,cryptcryptalgal laminate is laterally laterally extensive, extensive, but but commonly commonly brecciated. brecciated. The base of this this marker marker bed bed has has alternating layers of light gray dolomite, dark gray chert, and crinkly laminae. Moving upwards, Moving upwards, there is a thin thin chert-carbonate chert-carbonate breccia, a layer layer of of laterally laterally linked linked and and domical domical single single parabolic - parabolic stromatolites, and a dark gray chert band (Cheadle 1986). stromatolites, gray chert band (~headle1986). I 1 I I I I Plan Plan view view section of stromatolitic marble garganicus), (Conophyton garganicus), Wolatko Lake Mudsione Facies:. Facies:. The upper Rossport Rossport Formation is is composed composed of of the the chalcedonic chalcedonic Chalcedonic Mudstone mudstone facies. At the base, there are local lenticular, intraformational, paraconglomerate mudstone facies. the base, there are local lenticular, intraformational, paraconglomerate wedges that that contain contain subangluar subangluar mudstone mudstoneclasts clastsup uptoto22 m m in in diameter. diameter. Reduction Reduction spheres spheres are wedges comnon. Red of common. Redand andbuff, buff,dolomicritic dolomicriticmudstone mudstone and and claystone claystone are the dominant constituents constituents of this sequence. They lack the coarse silt and sand that is present in the Channel island mudstone They lack the coarse silt and sand that is present in the Channel Island mudstone and claystone. Dolomite Dolomitepartially partially replaces replaces 22 cm cm diameter diameter chalcedony chalcedony nodules that are are found found in in weathering horizons. resistant weathering horizons. I �KAJVL4 HILLFORMATION FORMATION KAMA HILL The The Kama Kama Hill Hill Formation Formation consists consists of of aa single single (laminated (laminated shale) shale) facies, facies, and and thus thus is is not not subdivided subdivided into constituent members. The original thickness of the Kama Hill Formation is unknown into constituent members. The original thickness of the Kama Hill Formation is unknown as as the the top top is is truncated truncated by by the the Logan Logan diabase diabase sills. sills. The The Kama Kama Hill Hill laminated laminated shale shale has has aa minimum minimum thickness of 46 46 m m (exposed at Kama Kama Hill), Hill), and and this this varies, varies, depending dependingon onthe the location. location. At thickness of (exposed at At Red Red Rock, Island, and and Stewart StewartLake Lakeititisis 20 20 m m thick, thick, and and at at Albert Albert Lake Lake itit is is 45 Rock, Channel Channel Island, 45 m m thick thick (Franklin et a!. (Franklin et al. 1980). 1980). The Thehorizontally horizontallylaminated, laminated, buff buff arkosic arkosicsiltstone siltstoneto to fine finesandstone sandstoneare are exposed in aa cliff exposed in cliff face face along along the the shore shore of of Kama Kama Bay, Bay, east east of of Nipigon Nipigon (Franklin (Franklin et et aL al. 1980; 1980; Cheadle 1986). The base base is istransitional transitional over over 11 to to 22 mmand andcontains containsvery verylittle littlecarbonate. carbonate. 1986). The Reduction spots are common, as are mud cracks and ripple marks on bedding surfaces Reduction spots are common, as are mud cracks and ripple marks on bedding surfaces(Franklin (Franklin et et al. al. 1980). 1980). Breccia Brecciadikes dikesare arepresent presentand andmud-chip mud-chipconglomerates conglomeratesare are associated associated with with the the siltsiltdominated layers (Morey and Ojakangas 1982; Cheadle 1986). The siltstone layers contain dominated layers (Morey and Ojakangas 1982; Cheadle 1986). The siltstone layers containthe the following ripple cross-laminations, low amplitude ripple following sedimentary sedimentary structures: structures: erosional erosional bases, bases, ripple cross-laminations, low amplitude ripple marks, normal grading, marks, centimetre centimetre to to decimetre decimetre fining-upward fining-upward sequences, sequences, normal grading, and and suspensate suspensate caps caps (Cheadle This formation formation locally locally contains contains (Cheadle 1986) 1986) evaporite evaporite casts casts and andraindrop raindropimpressions. impressions. This carbonate algal stromatolites stromatolites at at the the base base of of the carbonate algal the facies facies in in the the north north half half the the basin basin (Morey (Morey and and Ojakangas Ojakangas 1982; 1982; Cheadle Cheadle 1986). 1986). Enigmatic mudcracks(?) in distal bar Formation bar sequences sequences of of the Kama Hill Formation �.1 I I I I LEGEND L EGEND Conglomerate Basal Conglomerate Dolomite lolomite Sandstone Sandstone Gypsum Siltstone __jshale p Mud Chip Conglomerate Mud 1 Stromatolites , Diabase Magnetic Granite Granite Magnetic Gneiss �DEPOSITIONAL SYSTEM DEPOSITIONAL SYSTEM The Sibley were laid The Sibley Group Group sediments sediments were laid down down in in aa broadly broadly subsiding, subsiding, ovoid ovoid basin basin during during the the Mesoproterozoic. There is no evidence of high relief along any exposed segments of Mesoproterozoic. There is no evidence of high relief along any exposed segments of the the basin basin margin. At the margin. At the time time of of deposition, deposition, the the Sibley Sibley Basin Basin was was situated situated very very close close to to the theequator equator (unpublished paleomagnetic paleomagnetic results, results, Dr Dr G. G. Borradaile) Borradaile) and and was was subjected subjected to to an an arid arid to (unpublished to semiarid semiarid climatic regime. These These factors factors combined combined to to dictate dictate the the types climatic regime. types of of depositional depositional systems systems which which developed the basin's developed during during the basin's active activelifetime. lifetime. The large-scale The large-scale depositional depositional patterns patterns are are quite quite clear clear and and will will be be discussed discussed in in the the following followingpages. pages. However, superimposed on this are complex, and sometimes conflicting, data provided smallHowever, superimposed on this are complex, and sometimes conflicting, data provided by by smallscale structures. This complexity scale structures. This complexity is is aa result result of of the the excellent excellent preservation preservation on on minute minute structures structures in in both outcrop outcrop and and core. the field trip we we will will investigate possible solutions solutions to to some some of of the the both core. During During the field trip investigate possible conflicting data, data, and and hopefully conflicting hopefully gain gain further further insight insight into into how how aaMesoproterozoic, Mesoproterozoic, low-relief, low-relief, interior drainage interior drainage depositional depositional system system operated. operated. Pass Lake Formation Disagreement exists exists as as to to the the depositional depositional setting setting of of the the Pass Pass Lake Formation Disagreement Pass Lake Lake Formation. Franklin et al. Formation. Franklin al. (1980) (1980) believed believed that that the the sandstones sandstones and and conglomerates conglomerates were were deposited deposited in a shallow shallow lacustrine lacustrine environment, environment, whereas Cheadle (1986) put forward an alluvial fan-fluvial fan-fluvial model. This controversy model. This controversy may may be be due due to to different differentdepositional depositional processes processes operating operating in in different different places. The The sequences of powering-down beds,such such as as at at Pass places. sequences of powering-down beds, Pass Lake, Lake, appear appear to to represent represent lacustrine sheet sheet sandstones sandstones laid laid down down during during the the waning waningphases phases of of storm storm events events in in aa shallow lacustrine shallow lacustrine environment. environment. The The lensoid, planar and lacustrine lensoid, large-scale large-scale planar and trough trough cross-stratified cross-stratified sandstones, sandstones, present on present on Channel Channel Island Island and and neighbouring neighbouring islands, islands, probably probably represent represent transverse transverse bar bar sand sand flats flats in aa braided they may may be be aeolian. in braided fluvial fluvial system. system. However, However, they aeolian. The The rapid rapid lateral lateral variations variations in in thickness of of the the unit, thickness unit, not not related related to to position position relative relative to to the the basin basin margin, margin, reflect reflect infilling infilling of of basement depressions depressionsrather rather than than clastic clastic wedges wedges advancing advancing from from sediment sediment entry points. points. A A picture picture arises than sands sands evening evening the the topography topography arises of of the the Pass Pass Lake Lake Formation Formation representing representing first first gravels gravels than by by infilling infilling basement basement valleys valleys through through braided braided stream stream transport transport to to a a shallow shallow lacustrine lacustrine environment. environment. In with In the the upper upper portion portion of of the the Pass Pass Lake Lake Formation, Formation, the the sheet sheet sandstones sandstones become become interbedded interbedded with red, red, silty silty shales. shales. This This represents represents aa more moreoffshore offshoredepositional depositional setting setting where where muds muds deposited deposited between storm events events are are not not eroded by the the next as is between storm eroded by next storm, storm, as is the the case case in in the the nearshore nearshore multimultistorey sandstones. The upward decrease in the sand-to-mud ratio indicates deepening sand-to-mud deepening water water and and culminates in the siltculminates silt- and and mud-dominated mud-dominated Rossport Rossport Formation. Formation. The the Pass The contact contact between between the Pass Lake Lake Formation Formation and and the the Rossport Rossport Formation is is gradational, with the the name Formation gradational, with name change change occurring occurring where where the the mudstone mudstone begins begins to to dominate. Upward Upward through through the the sequence, indicationsofof dessication dessicationbegin begin to to appear dominate. sequence, indications appear (eg. (e.g. mudcracks and and early, authigenic gypsum growth). at this point, growth). Commonly at point, interlayering, interlayering, with with mudcracks millimetre- to to centimetre-scale dolomite laminae, laminae, begins begins to to occur. In drill millimetrecentimetre-scale dolomite occur. In drill cores cores from from areas areas closer to to the of dolomite closer the basin basin center, center, an aninterlaminated, interlaminated, decametres decametres thick, thick, succession succession of dolomite and and gypsum occurs gypsum occurs at at this this stratigraphic stratigraphic position. position. The The dessicated dessicated mudstones mudstones probably probably represent represent periodically exposed exposed mudflats mudflats surrounding surrounding the the lake. lake. This This necessitates necessitates aa regressive regressive phase phase in in the the periodically lower Rossport Rossport Formation, Formation, for for which there is friable siltstone lower which there is some some evidence evidence (e.g. (e.g. brick-red, brick-red, friable siltstone at at Rossport Formation �The dolomite-mudstone horizon). horizon). The dolomite-mudstone interlayered interlayered sequence represents represents aa shallow shallow offshore offshore environment. Muds Muds were were washed washed in during rainy periods and dolomite environment. dolomite precipitated during dry periods as the saline lake shrank. The deeper offshore only received clastic elastic input during the latter stages off this depositional episode. It was probably dominated by chemical depositional was probably dominated chemical precipitation precipitation of dolomite during the wetter periods when the lake salinity decreased, and by rainout of of gypsum gypsum crystals on the bottom during dry intervals with increasing salinity. Alternatively, both may have precipitated during dry intervals with hiatuses representing wet periods. The control in this model is the MgICa Ca2 inhibits dolomite precipitation and a period of removal MgKa ratio. The presence of ca2+ of Ca2 ca2+via viagypsum gypsumprecipitation precipitationisisneeded needed before before dolomite dolomite will will begin begin to precipitate. precipitate. Thus, first gypsum then dolomite would precipitate during the dry intervals in this scenario. gypsum then dolomite would precipitate during the scenario. Oxygen Oxygen and and carbon stable isotope analysis is needed to choose between the two alternatives. Sandstone beds beds appear interbedded with the upper dolomite-mudstone sequence or overlie it. Sandstone interbedded with dolomite-mudstone sequence These are interbedded with red mudstone and the unit is laterally extensive is laterally extensive throughout throughout the the basin. basin. Closer to to the southern Closer southern edge edge of of the thebasin, basin,repetitive repetitivesandstone sandstone assemblages assemblages occur occur (metre(metre- to to decametre-scale thicknesses) with intervening intervening decametre-scale, decametre-scale, dolomite-mudstone dolomite-mudstoneassemblages. assemblages. Here, trough trough cross-stratification and channelling channellingare are much much more more evident evident in the Here, cross-stratification and the sandstones. sandstones. in this unit show higher variability than in the Pass Lake Formation. They appear Paleocurrents in to have a southern southern source as opposed to the northern source for the Pass Lake. Lake. The The sandstones sandstones appear to represent renewed renewed tectonism tectonism and basin tilting, resulting resulting in sediment influx from the south, with sand dunes migrating through scour scour channels channels during duringhigh-discharge high-dischargeevents. events.Whether Whether this was was subaerial subaerial or or shallow shallow subaqueous subaqueous deposition deposition is difficult difficult to determine determine as as strandline strandline position is position is obscure. obscure. Metres to decametres of mud-chip mud-chip conglomerates conglomerates overly the sandstones, sandstones, either interbedded interbedded with Mudstone the upper sandstones sandstones or interbedded interbedded with with siltstones siltstones overlying overlying the upper upper sandstones. sandstones. Mudstone fragments are up to metres in diameter, although this is rare, and have variable compositions. metres in diameter, although is rare, and have variable compositions. This unit appears appears to thicken thicken towards towards the the basin basin center centerand and may mayrepresent representupraising upraisingand andrecycling recycling (cannibalization) of basin margin lithofacies; perhaps a further stage of the north-down (cannibalization) of basin margin lithofacies; perhaps the north-down basin basin tilting, represented by the sandstone sandstone wedges, upraising upraising the southern southern basin margin. The mudblock conglomerate is succeeded in some areas by red mudstones mudstones with mudcracks mudcracks and abundant gypsum veins veins and nodules nodules representing representing clastic clastic sabkhas. sabkhas. In In other otherareas, areas, aabrecciated brecciated and and stromatolitic stromatolitic carbonate occurs at this this horizon. horizon. This Thisrepresents representssubaqueous, subaqueous,shallow shallowlacustrine lacustrine deposition, with teepee teepee structures reflecting reflecting periodic periodic drying. drying.These These units units are are overlain overlain by by the deposition, with Kama Hill Formation. Formation. The Kama Hill Formation consists of red to Kama Hill Formation: to purple purplemudstones mudstones with with Formation: sandstones. The ripple-laminated, coarse-grained siltstones to fine-grained interlayered, coarse-grained siltstones fine-grained sandstones. The interlayered, ripple-laminated, abundance of rippled units increases upward until they are replaced by sandstones, which abundance of rippled increases upward are replaced by sandstones, which continue the coarsening- and thickening-upward trend. The sandstones sandstones and and all all stratigraphically stratigraphically higher units are only present in core. The Kama Hill mudstones represent subaqueous in core. The Kama Hill mudstones represent subaqueousdeposition deposition in a non-saline lake. The coarseningcoarsening- and and thickening-upward sequence sequence reflects reflects delta delta progradation progradation and eventual establishmentof of aa fluvial delta delta top environment, forming the the base base of the next environment, forming next and eventual establishment formation. formation. �This is This is a a new new unit unit which which has has not not been been formally formally named. named. It It is is present present only in drill core from under Nipigon Bay. At some localities, the coarsening-upward only in drill core from under Nipigon Bay. At some localities, the coarsening-upward delta delta Nipigon Bay Bay Formation: Formation: Nipigon sequence of planar cross-stratified, sequence of the the Kama Kama Hill HillFormation Formationisisoverlain overlainby bylarge—scale, large-scale, planar cross-stratified, mediummediumgrained sandstones of the Nipigon Bay Formation. These reach approximately 500 m m in grained sandstones of the Nipigon Bay Formation. These reach approximately 500 in thickness. Mudstone Mudstone and and siltstone siltstone interlayers interlayersare are almost almost totally totally absent absent with with the thickness. the entire entire unit unit consisting of of multi-storey multi-storey sandstones. sandstones. Colour Colour varies varies from red to consisting from red to white, white, with with the the white white sandstones sandstones containing gypsum gypsum grains grains and containing and aa gypsum gypsum cement. cement. Research Research continues continues on on this this formation, formation,with with the the present data data indicating indicating an an aeolian aeolian origin origin with with possibly possibly some some braided braided fluvial fluvial reworking. reworking. present At other other locations, locations, aa different different assemblage the one one described described above the Kama At assemblage separates separates the above from from the Kama Hill Hill Formation. This assemblage overlies the coarsening-upward sequence of the delta and is Formation. This assemblage overlies the coarsening-upward sequence of the delta and is composed of of finingcomposed fining- and and thinning-upward, thinning-upward, multi-storey multi-storey sandstones, sandstones, metres metres to to decametres decametres thick, thick, separated by by friable red mudstones In some some places, places, minor minorcarbonate carbonate separated friable red mudstones and and fissile fissile green green mudstones. mudstones. In layers are layers are associated associated with with the the green green mudstones. mudstones. The The sandstones sandstones are are fluvial fluvial channels; channels; the the intervening mudstones mudstonesrepresent representaa rare intervening rare example example of of a apreserved preservedPrecambrian Precambrianfloodplain floodplain succession with with sun-baked, poorly developed succession sun-baked, poorly developed soils, soils, friable friable units, units, and and small, small, open-water open-water ponds. ponds. The possibly possibly aeolian The aeolian sandstones sandstones lie lie sharply sharply on on top top of of this this unit. unit. �FIELD TRIPROAD TRIP ROAD LOG Stop Number Locality Road Lop Loe (kin) (km) DAY DAY ONE STOPS 1-1 1-1 Remote Drill Core Storage Facility (Generalized (GeneralizedStratigraphy) Stratigraphy) 1-2 1-2 Thunder North (Downtown) Thunder Bay Bay North (Downtown) (Architectural Stone) (Architectural Stone) Junction JunctionHighways Highways 11-17 11-17 and and 587 587 0.0 km (Reset) (Reset) 1-3 Pass Pass Lake Lake (Railway) (Railway) (Animikie/Sibley disconformity; disconformity; Pass PassLake Lake Fm. Fm. Type Type section) section) 5.9 to 6.1 km 1-4 Pass Pass Lake Lake (Highway) (Highway) (Lacustrine (LacustrineSheet Sandstones, Sandstones, Rossport Rossport Fm.) 8.6 km 1-5 Pass Pass Lake Lake (Highway) (Highway) (Lacustrine (LacustrineChannel ChannelSandstones, Sandstones,Rossport Rossport Fm.) Fm.) 9.9 km Pass Pass Lake Lake Crossroad Crossroad 10.3 km Pass Pass Lake Lake (Highway) (Highway) (Subaerial (SubaerialSiltstone-Caliche, Siltstone-Caliche,Rossport RossportFm.) Fm.) 10.7 km Junction JunctionHighways Highways11-17 1 1 - 17and and587 587 0.0 0.0 km km (Reset) (Reset) Turn-off Turn-off(Pipeline (Pipelineroad) road) to to Enterprise Enterprise Pb-Zn Pb-Zn Mine Mine 14.5 14.5 km km 1-6 1-7 �DAY TWO TWO STOPS STOPS DAY Stop Number Stop Number Locality Road Lou Road Loe (kin) (km) Junction of Junction of Highways Highways 11 11 and and 17, 17, east of Nipigon east of Nipigon 0.0 km km (Reset) 0.0 (Reset) 2-1 Gurney (Highway) Gurney (Highway) (Archean-Sibley (Archean-Sibley Unconformity, Unconformity, Debris Debris Flows, Flows, Pass Pass Lake Lake Fm.) Fm.) 39.9 km km (east of 39.9 (east of junction) junction) 2-2 Kama Kama Hill Hill (Highway) (Highway) junction) junction) (Interbedded (Interbedded Dolostone-Siltstone, Dolostone-Siltstone, Rossport Fm.) Fm.) 21.4 km (east of (east of 21.4 km 2-3 Ruby Ruby Lake Lake Marble Marble Quarry Quarry (Turn-off from Highway Highway 17; 17; (Turn-off from 4.1 4.1km km into into site) site) 6.8 km (east of (east of 6.8 km junction) junction) 2-4 2-5 2-6 Junction Junction of of Highways Highways 11 11and and 17, 17, east of Nipigon east of Nipigon 0.0 km (Reset) (Reset) Junction Junction of of Highways Highways 11-17 11-17and and 585 585 4.0 km Turn-off Turn-off to to Moseau Moseau Mountain Mountain 5.0 5.0 km km 17.5 17.5-- 18.5 18.5 km Moseau Moseau Mountain Mountain (Pass Lake Fm. & Evaporite Breccias, Rossport Fm) (Pass Lake Fm.& Evaporite Rossport Fm) Junction Junction of of Highways Highways11-17 11-17and and 628 628 0.0 km km (Reset) (Reset) Pull-off Pull-off parking parking lot; lot; start start of of hiking hiking trail trail 6.3 6.3 km km Lloyds Lloyd's Lookout Lookout q'Shales &Rippled RippledSiltstones, Siltstones, Kama Kama Hill Hill Fm.) Fm) (Shales & (walk (walk trail trail 0.8 0.8 km) km) Junction Junction of of Highways Highways 11-17 11-17 and and 628 628 0.0 km (Reset) (Reset) Big Big Squaw Squaw Creek Creek Road Road Cut Cut (Hornfelsed Rossport Fm.) Fm.) (Hornfelsed 10.2 10.2 km km �(JAY (((UNDER I Rossport Fm 0 0: 12 LAKE Map 2232 NIPIGON-SCHREIBER SHEET, MNDM Miles I P (CO (V 2-5 Lloyd's — (IV4 /.k fACQ,' r Thunder Bay, Ontario a a C I Ic-i -t 1. CD -a. ij 0 CD c-) C/D 0 0 0 0 C/D I-I I ILSG 2000 Sibley Group Field Trip �FIELD FIELD TRIP TRIP STOP STOP DESCRIPTIONS DESCRIPTIONS STOP Y REMOTE GE SITE, SITE, CONMEE STOP 1-1: 1-1: THUNDER THUNDERBA BAY REMOTE DRILL DRILL CORE CORESTORA STORAGE CONMEE TOWNSHIP TO WNSHZP This This stop stop presents presents an an opportunity opportunity to to view view stratigraphic stratigraphic sections sections of of the the Sibley Sibley Group Group in in diamond diamond drill drill core core donated donated to, to, or or collected collected by, by, the the MINDM from private MNDM from private sector sector mineral mineral exploration exploration projects. projects. Core Core from from three three drill drill holes holes has has been been selected selected from from different of different parts parts of the the Sibley Sibley depositional basin to provide depositional basin to provide geographically and stratigraphically geographically and stratigraphically distinct of the distinct sections sections of the constituent constituent formations formations and and their their characteristic characteristic lithologies. lithologies. The The latest latest drilling drilling was was completed completed by by Falconbridge Falconbridge Limited Limited and and joint-venture joint-venture partners, partners,Canmine Canmine Resources Corporation and and Red Red Engine Engine Resources, Resources, in in 1997 1997 from from the the ice ice of of Nipigon Nipigon Bay Bay as as part part Resources Corporation of an exploration program designed to evaluate the area's nickel potential (Assessment files, of an exploration program designed to evaluate the area's nickel potential (Assessment files, Thunder Thunder Bay Bay South South District, District, Thunder Thunder Bay). Bay). Falconbridge Falconbridgebecame becameinterested interestedin inthe thearea areainin1991 1991 and started a compilation and regional reconnaissance program which delineated a 23 km k m long long and started a compilation and regional reconnaissance program which delineated a 23 magnetic anomaly adjacent adjacent to to the the North Airborne and and ground ground magnetic anomaly North Shore Shore fault fault (see (see map map below). below). Airbome geophysical geophysical surveys, surveys, geological geological mapping, mapping, soil soil sampling sampling ensued, ensued, culminating culminatingin in the thedeep deepdrilling drilling program program (ibid). (ibid). No Nosignificant significantnickel nickelnor norcopper coppervalues values were were returned returned from fromthe thedrilling drillingand andthe the Exploration Licence of of Occupation on Lake was allowed allowed to to lapse lapse in Exploration Licence Occupation on Lake Superior Superior was in 1999. 1999. Despite Despite the the disappointing results, the the drilling disappointing results, drilling provided provided aa plethora plethora of of new new stratigraphic stratigraphic information information on on the the Sibley Sibley Group Group in an an area area where where no no drilling drillinghad had previously previously taken taken place. place. Most Most remarkable remarkable of of these these results were the unexpectedly thick sections (up to 850 m) that dwarfed previously measured results were the unexpectedly thick sections (up to 850 m) that dwarfed previously measured sections total thickness thickness on on the the mainland, mainland, as well well as as the the presence presence of of upper upper units units of of sections and and estimated estimated total the the Sibley Sibley Group Group which which had had not notpreviously previously been been recognized recognized (i.e. (i.e. proposed proposed Nipigon Nipigon Bay Bay Formation). Formation). Drill Drill Hole Hole CYP 96-01 CYP 96-01 NB NB 97-02 97-02 NB NB 97-03 97-03 NB NB 97-04 97-04 NB NB 97-05 97-05 (m) Overburden (m) Overburden Sibley Group (m) Sibley Group (m) 2.0 2.0 22.7 22.7 30.0 28.6 28.6 73.2 73.2 62.56 62.56 452.5 452.5 75.0* 75.0* 858.2 858.2 635.1* 635.1* Total Length (m) Total Length (m) 464.5 464.5 677.8 677.8 105.0 105.0 1015.6 1015.6 744.2 744.2 Table showing thicknesses of Sibley Sibley Group Group intersected intersected by Falconbridge Falconbridge Limited's Limited'sdrilling. drilling. (*hole did not reach reach Archean Archean basement) basement) �Vert Island Black Bay Peninsula Osler Osier Group Group FZ1 0 5 km LI Loqari Logandiabase diabase / North Shore / North ShoreFault Fault 1 Archean Archean I 'High" 1 Magnetic 'High" r] Sibley Group Group D -Sibley I/ Map of of Nip Nipigon drilling Map igon Bay, Bay, showing showing location location of Falconbridge Falconbridge Limited's drilling The sedimentary rocks unconformably overlieaa red red granite which has been sedimentary rocks unconformably overlie granite which been subjected subjected to to Mesoproterozoic, equatorial equatorial weathering. weathering. Mesoproterozoic, Two drill holes, completed Noranda Inc., Inc., will also be examined at this stop. completed by Noranda stop. These holes were drilled drilled north of of Dorion Dorion on on aa north-south north-south line, line, with with one one lying lying approximately approximately 15 15 km km closer closer to to Thus, the three holes examined will show basin margin basin center center than than the the other. other. Thus, three holes examined will show basin margin the basin (Falconbridge), (Falconbridge), medial medial (Noranda) (Noranda) and and basin basin center center (Noranda) (Noranda) lithofacies lithofacies assemblages. assemblages. The basin-center drill hole bottoms out in diabase which is overlain by millimetre- to centimetrescale layers layers of dolomite and gypsum. This This assemblage assemblage is is approximately approximately 40 m thick and contains pink to to red, red, clay-rich clay-rich interlayers interlayers near near its its top. top. This is overlain overlain by by aashale-siltstone shale-siltstone sequence sequence containing containing abundant abundant layers layers of of intraformational intrafonnationalconglomerate conglomerate(mud-chip (mud-chipconglomerates). conglomerates). �The The medial medial drill drill hole holeoverlies overliesa agneissic gneissicbasement. basement. An An upward-fining, upward-fining, conglomerate conglomerate to to sandstone sandstone to to siltstone, siltstone, trend trend is is well well developed developed in in the the Pass Pass Lake LakeFormation Formation present present in inthis thishole. hole. Approximately 50 m m of and red Approximately 50 of inter-laminated inter-laminated dolomite dolomite and red mudstone mudstone overlie overlie the the Pass Pass Lake Lake siltstone containing layers of mud-block succeeded by a Formation. in is turn, This, Formation. This, in turn, is succeeded by a siltstone containing layers of mud-block conglomerate. conglomerate. AAbrecciated brecciatedand andstromatolitic, stromatolitic,white whitecarbonate carbonateunit unitoverlies overliesthe theclastic clasticrocks rocksand and this this is is succeeded succeededupwards upwards by by siltstones siltstonesof of the the Kama Kama Hill Hill Formation. Formation. The drill hole hole is is similar The basin-marginal basin-marginal drill similar to to the the medial medial hole hole except: except: 1) 1) the the basal basal Pass Pass Lake Lake is is almost entirely missing; 2) the upper carbonate unit is not present; 3) it contains approximately almost entirely missing; 2) the upper carbonate unit is not present; 3) it contains approximately 550m Sibley strata strata not not previously previously discovered discovered elsewhere elsewhere in in the thebasin. basin. The The upper upper 550m of of overlying overlying Sibley strata consist of a coarsening-upward, deltaic sequence at the top of the Kama Hill Formation. strata consist of a coarsening-upward, deltaic sequence at the top of the Kama Hill Formation. This This is is overlain overlain by by aawell-developed well-developedfluvial fluvialsystem systemwith withmulti-storey, multi-storey, powering-down, powering-down, channel channel sandstone sandstone assemblages assemblagesimbedded imbedded with with floodplain floodplain fines. fines. Overlying Overlyingthis thisisisaasandstone sandstonesuccession succession hundreds dry aeolian aeoliansystem. system. hundreds of of metres metres thick thick which which was was probably probably deposited deposited in in aa dry We We will will spend spend the the morning morning in in the the core coreyard yardexamining examining the the various variouslithofacies lithofacieswhich whichare arepresent present in in each each of of these these lithofacies lithofacies assemblages. assemblages. For Foraa more more detailed detailed description descriptionof of the the sequence sequence see see the the section section on on "Depositional "Depositional Environment". Environment". STOP(S) STOP(.) 1-2A,B,C: 1-2 A,B.C: THUNDER THUNDERBAYNORTH(DOWNTOWN) BAY NORTH (DOWNTOWN) This This series series of of stops stops is is designed designed to to show showexamples examples of of rough rough and and cut cutdimension dimensionstone stonethat thatwas was quarried quarried from three different different sites sites around around the turn turn of of the the century. century. Sibley Sibley Group Group stone stone quarries quarries are are listed listed below below (summarized (summarized from from Hinz Hinz et et al. al.1994): 1994): Quarry Rock Type Cooke Point George George Point Point La Grange Island Nipigon River Quarry Ouarrv Island Island Ruby ~ u bLake ~ yake Simpson SimpsonIsland Island Vert Vert Island Island Wolf Wolf River River Marble Gray Gray sandstone sandstone Red sandstone Variegated marble White White sandstone sandstone Variegated Variegated marble marble Buff Buff sandstone sandstone Red Red sandstone sandstone Buff Buff sandstone sandstone . - Years of Operation 1931-1 940(?) Late 800s(?) Late 118001s(?) 1882-1 1882-1883(?) 883(?) 1883-1910(?) 1883-l910(?) Late 800's(?) Late11800's(?) 1998-present 1998-present 1904-1912 1904-1912 1881-1912 1881-1912 1913-15; 1913-15;1921-31 1921-31 �These three three architectural stops along along one one of Thunder These architectural stops Thunder Bay's major arteries provide an opportunity see aa Bay's major arteries provide an opportunity toto see variety of of Sibley Sibley Group Group stones stonesand and note note the the effects effects of of variety The architectural of exposure. almost a century of exposure. The are taken website descriptions are taken from from aa walking walking tour tour website developed and and maintained by the developed maintained by the Local Local Architecural Architecural Conservation Advisory Committee conservation Advisory Committee (L.A.C.A.C.) (L.A.C.A.C.) (http://www.city.thunder-bay.on.caltbwalkingtourf). (http://www.city .thunder-bay.on.ca/tbwalkingtour/). STOP 1-2A: 432 432 RED RED RIVER RIVER ROAD retaining wall wall is constructed with distinctive, brickThis retaining red Vert red Vert Island Island sandstone sandstone (Nipigon (Nipigon Bay Bay Formation?). Formation?). was aa popular stone used in the construction of many many This was grand homes and other buildings in Fort William grand homes and other buildings in Fort William (now (now Thunder Bay South). PORT ARTHUR STOP 1-2B: PORT ARTHUR INSTITUTE (401 INSTITUTE (401 Red Red River Road) COLLEGIATE COLLEGIATE This building, building, constructed constructedin in 1909 1909of ofSimpson SimpsonIsland Island buff buff sandstone (Nipigon Bay Formation?), is an example of the Queen Anne Anne style that that was was in in common common use use from from the the 1880s l880s I to the 191 Os.wWhen the school school board board made made the initial to 1910s. h e n the initial planning for the building, it was decided that it should be "erected for posterity, and and not not be be of the 'shack' order", resulted in the shack' order", so so they they chose chose the the stately stately Queen Queen Anne style. style. Alterations in 1925 resulted addition of four more classrooms, and more renovations to the north and south in 1953 south 1953 and 1962 1962 created other other rooms. rooms. These These alterations alterationsused usedstone stoneinin an an attempt attempt to to blend created blend into the original original building, but a gynmasium gymnasium planned in 1964 1964 and completed in 1974, 1974, provoked controversy as its design was incompatible incompatible with the rest of the school. school. ' �Port Arthur after its Port Arthur Collegiate _. ..sgiate Institute, Institute, shortly rtly after its construction co ..-.. ~ c t i o n STOP J-2C: South) STOP 1-2C:TRINITY TRINITYUNITED UNITEDCHURCH CHURCH(30 (30Algoma Algoma Street Street South) This building, building, constructed constructed in in 1906, was formerly known as as the This 1906, was formerly known the Trinity Trinity Methodist Methodist Church, Church, and and became the Trinity United Church after the United Church of Canada was formed became the Trinity United Church after the United Church of Canada was formed in in 1925. 1925. Constructed of of rough rough cut, Constructed cut, Simpson Simpson Island Island buff buff sandstone sandstone (Nipigon (Nipigon Bay Bay Formation?), Formation?), this this structure is is an an example 890s to to the the that was was popular popular from from the the 11890s structure example of of the the Late Late Gothic Gothic Revival Revival style style that 1 940s.The Theunusual unusualtower tower features featuresvery very narrow narrow windows, windows, four four buttresses, buttresses, each each capped capped with with aa 1940s. pyramid shaped shaped finial, finial, and and an an extremely extremely sharp sharp hexagonal hexagonalspire. spire.The The rest rest of of the the building also pyramid building also features very very steeply pitched roofs, features steeply pitched roofs, and and arched arched windows windows in in the the Gothic Gothic style. style. �TrinityUnited UnitedChurch Church Trinity STOPI-2D: I-2D:MASONIC MASONICHALL HALL(262-270 (262-270Red RedRiver RiverRoad) Road) STOP Builtinin1910 1910and andalso alsoknown knownas asShuniah ShuniahLodge, Lodge,this thisstone, stone,brick brickand andconcrete concretebuilding buildingreplaced replaced Built the 1909.The Thefirst firstfloor floorisismade madeof ofcut cutNipigon Nipigon theold oldMasonic Masonictemple templethat thatwas wasdestroyed destroyedby byfire fireinin1909. River Rivermarble marble(Rossport (RossportFormation) Formation)and andthe theentrance entrancefeatures featurescarved carvedmarble marblepilasters pilastersand and decorative decorativepanels. panels.Originally Originallythere therewas wasaadome domeon onthe theroof roofover overthe theentrance, entrance,which whichhas hassince since been been removed. removed.The Thecentral centralportion portionof ofthe thebuilding buildinghas hasaaMansard Mansardroof roofof ofFrench Frenchdesign. design.The The building's building'swindows windowsare aredecorated decoratedwith withalternating alternatinground roundand andtriangular triangularpediments pediments above above them. them. Conmercial Commercialspace spaceoccupies occupiesthe theground groundfloor, floor,while whilethe thelodge lodgeisislocated locatedabove. above. �STOP STOP 1-3: 1-3:PASS PASS LAKE LAKE (RAILROAD (RAILROADCUT) CUT) j ' Ill 4 I A A cliff cliff on on the the far far side side of ofthe therailroad railroad tracks tracks contains the type type section of the contains the section of the Pass Pass Lake Lake A Formation. disconformity Formation. A low-angle low-angle disconformity separates the the basal separates basal conglomerates conglomerates of of the the Pass Pass lake Formation from the underlying, —1.9 Ga lake Formation from the underlvin~. -, -1.9 Ga Rove Formation shales (lower photo). The Rove Formation shales (lower r>hoto\. The maroon maroon and and green green shales shales exhibit exhibit extensive extensive weathering. evidence of Mesoproterozoic weathering. evidence of Mesooroterozoic The The basal basal conglomerate conglomerate thins thins and and thickens thickens laterally, laterally, pinching pinching down down to to pebbly pebbly sandstone sandstone in in places. places. Clasts Clastsare are generally generally surrounded surrounded and and by dominated local Gunflint dominated by local Gunflint formation formation lithologies. lithologies. The The matrix matrix is is poorly poorly sorted. sorted. The The conglomerates are overlain by a conglomerates are overlain by a thinningthinningupward of sandstone (ohoto at at uoward sequence seauence of sandstone beds beds (photo laterally left). left). Individual ~ndividualbeds beds are are reasonably reasonablylaterally continuous though sometimes sometimes lens lensout. out. They continuous thoueh They are by upper are dominated dominated bv uover flow flow regime regime parallel oarallel lamination with occasional lamination with occasional ripples ripples and and smallsmallscale scale dunes dunes on on their their tops. tops. . - ~ - A - ~ - of this this depositional environment of depositional environment Both alluvial fansequence is continuous. atuuence is continuous. Both alluvial fanThe braided fluvial and and shallow shallow lacustrine lacustrine (Cheadle (Cheadle 1986; 1986; Franklin Franklin 1980; 1980; respectively) respectively) While examining examining the the lithofacies lithofacies in in the the field depositional environments ments have have been been proposed. proposed. While field we we depositional em will discuss the merits incuts of of each each interpretation. interpretation. between the the Disconformity between Disconformity conglomerate basal basal conglomerate of of the the Pass Pass Lake Lake Formation Formation (cgl) (cgl) Rove and weathered and weathered Formation shales at Pass Pass Formation shales (reg) (reg) at Lake. A Lake. A concretion concretion (con) (con) is is shown at lower right. right. �STOP 1-4: (HIGHWA!) 1-4: PASS LAKE (HIGHWAY) This This is aa roadside roadside exposure exposure of of the the transition transition zone zone between between the Pass Pass Lake Lake and and Rossport Rossport Formations. Laterally Laterally continuous continuoussandstone sandstone beds interlayer in a red silty mudstone assemblage. The sandstones are often massive, though though one bed at this this location location contains contains low angle, angle. wispy, wisvv. trough trough cross-stratification. cross-stratification. Here again, two two possibilities possibilities exist exist for for the theenvironment environment of of deposition. deposition. The sandstones could represent crevasse fines during during flood-stage flood-stage failure failure crevasse splay sand sheets spread out on the floodplain fines of fluvial levee systems. Alternatively, Alternatively, the the sand sand sheets sheets may may represent represent shallow lacustrine storm deposits caused by rainfall event-driven fluvial sand delivery delivery to to a lacustrine system and storm event-driven fluvial surge ebb plus river river mouth mouth density density current current transport of sand offshore into a fair fair weather weather siltsiltdominated area. The merits of both interpretations will be discussed in the field. The merits of both interpretations will be discussed in I �STOP 1-5: WA 17 STOP 1-5:PASS PASSLAKE LAKE(HIGH (HIGHWAT) This This stop stop contains contains aa variety variety of of lithofacies. lithofacies. Large Largesandstone sandstonelenses lensescap capthe the outcrop, outcrop, overlying overlying siltstones, siltstones, a fairly continuous, continuous, non-silty, non-silty, purple purple shale shale and and aa massive, massive, lensoid lensoid dolomite. dolomite. tQ — .1 .: C :- :-A' - r1.a ff !$ ... . S . — ,. . . ',r - -. .1 .. ., Layer geometry geometry and and contact contact relations relations in in this this exposure exposure are are perplexing perplexingat at first first glance. glance. Take Layer Take some some time to to trace time trace out out the the geometries geometries of of the the various various lithologies. lithologies. Hopefully Hopefully we we will will be be able able to to answer answer the the following following questions questionswhile whileat at this thisstop: stop: Is the dolomite dolomite really lensoid? Is the lensoid? Is this this caused by structural disturbance? disturbance? How does does the the dolomite How dolomite correlate across across the road? Are any intraformational intraformational conglomerates present? What is their geometry? geometry? How could have this small small sequence sequence of various lithologies have formed? • STOP 1-6: WA 17 STOP 1-6:PASS PASSLAKE LAKE(HIGH (HIGHWAY) This is is aa small, small, crumbly crumbly outcrop outcrop of of red, red, friable friable silty-mudstone. silty-mudstone. Although Although it it is is not not impressive, impressive, its its This brick-red colour and friable nature are important. important. Commonly, outcrops such as this this one are brick-red interpreted as highly highly sunbaked that is is probably probably what what this this outcrop outcrop represents. represents. interpreted sunbaked soils soils / caliche, and that �1-7: ENTERPRISE STOP 1-7: ENTERPRISE MINE Peter MeKellar discovered aa lead-copper-mineralized veinatatthis thislocation locationinin 1865 1865 that that was was Peter McKellar discovered lead-copper-mineralized vein subsequently developed as as the the Enterprise Enterprise Mine Mine (Tanton (Tanton 1931). 1931). Between 1870 and 1876, subsequently developed 1876, two two shafts were sunk. No. 1 shaft reached a depth of 180 feet (55m); levels were run easterly 76 feet No. 1 shaft reached a depth of 180 feet and westerly westerly 66 feet feet at at aa depth depth of of 60 60 feet. feet. A A stope stope was made in the west drift and a winze was sunk in the east drift about 50 feet from the the shaft. shaft. A crosscut was driven from the the bottom bottom of the the shaft 115feet 5feetsouth. south. Shaft No. 2 was sunk 60 feet at a point approximately 300 feet west of No. 11 of shaft (ibid). The total total recorded productionfrom fromthe themine minewas wasaa single single shipment shipmentofof 167 167 tons tons made made to to The recorded production Swansea, Wales, in in 1875 (ibid) (ibid) that that averaged averaged37.4% 37.4%Pb. Pb. Although no no other metal metal credits credits are Swansea, Wales, listed, appreciable copper, copper, silver silver and and gold gold were were reported reportedin in some somesamples. samples. Analyses conducted by Dr. E.J. Chapman Chapman in in 1874 1874include include one of a large, large, average average sample sample of the vein near surface surface that that returned 41.84% Pb, 5.40% Cu, 3.2 ounce Ag per ton and 0.33 0.33 ounce Au per ton (Tanton 1931). Hawley (1930) reported Chapman's Chapman's estimate estimate of of part part of of the ore body near surface as 47.5% Pb, Hawley Pb, 10.0% Cu, 17 17 dwt. 12 12 grammes grarnrnes (sic) Au and 2 ounces ounces 22 dwt. Ag per ton. ton. Mining operations ceased ceased in in 1876; fire destroyed destroyed the the mine mine buildings buildings aa few few years years later (Tanton (Tanton Mining 1931). New owners dewatered and sampled the workings in 1884 but no ore was produced. 1931). New owners dewatered workings in but produced. 927(ibid). Dewatering, examination and subsequent suspension took place between between 1926 1926and and11927(ibid). The mine site was initially rehabilitated in 1926 and 1927 and is now monitored and maintained by the Canadian CanadianNational ~ a t i o n Railway. al~ailwa~. have described describedthe thelocal localgeology. geology. Ore-bearing Ore-bearingveins veinsoccupy occupyaa Hawley (1930) and Tanton (1931) have breccia breccia zone in in dolomitic dolomitic siltstones siltstones of the the Rossport Rossport Formation Formation that extends extends down into into the the has basement. This Archean granitic basement. This breccia breccia zone strikes 065° 065' and dips 70° 70' SE to vertically. ItIt has been traced traced over over 60 m and has an average width width of 1.2 m. Fracture-controlled offshoots and and been Fracture-controlled offshoots branch veinlets may occur in a metre-wide envelope envelope or or "shatter "shatter zone" zone" around aroundthe themain mainvein. vein. The veins tend to pinch-and-swell; pinch-and-swell; mineralized zones over 4 m wide have been noted (ibid). The veins consist consist of the the ore oreminerals minerals galena, galena, low-Fe low-Fe sphalerite sphalerite pyrite pyrite and chalcopyrite chalcopyrite in a Malachite has gangue assemblage of of quartz / amethystine gangue assemblage amethystine quartz, quartz, calcite calcite and and pink pink barite. barite. Malachite precipitated on chalcopyrite-rich, chalcopyrite-rich, weathered dump material. First synopsized by Hawley Hawley (1930) (1930) and and further further described described by Tanton Tanton (1931), (1931), "lead-zinc-barite "lead-zinc-barite termed, were were reported reportedas asearly earlyas as1866. 1866. Of Of the the approximately approximately veins" (LZBV), as they are locally termed, only the Dorion, Ogema and and Enterprise Enterprisedeposits depositswere weremined minedtotoany anydegree. degree. As 30 deposits, only Dorion, Ogema noted by Franklin Franklin and and Mitchell Mitchell (1977), (1977), these these small small deposits deposits comprise comprise a distinct distinct metallogenetic metallogenetic and is is spatially spatially confined confined to to the the group that has a consistent, simple vein mineralogy and structure, and basin. Although Sibley Group depositional basin. Although temporally temporally similar, similar, they are are clearly clearly distinguishable distinguishable from silver-bearing veins that occur near Thunder Animikie Group Group from silver-bearing veins Thunder Bay in in Paleoproterozoic Paleoproterozoic Animikie sedimentary rocks and Logan diabase. �Franklin Franklinand andMitchell Mitchell(1977) (1977)subdivided subdividedthese theseLZBV LZBVdeposits depositsinto intothree threeclasses: classes: (1) those that have the Sibley Group as at least one wall rock (1) those that have the Sibley Group as at least one wall rock(e.g. (e.g.Dorion DorionMine); Mine); (2) those that are entirely enclosed within Sibley Group rocks (e.g. Enterprise (2) those that are entirely enclosed within Sibley Group rocks (e.g. EnterpriseMine); Mine);and and lie within the Archean basement but near the unconformity with (3) those (3) those lie within the Archean basement but near the unconformity withbasal basal sandstones sandstonesof ofthe theSibley SibleyGroup Group(e.g. (e.g.Ogema OgemaMine). Mine). Wall Wall rock rockalteration, alteration,typically typicallybest best manifested manifested in in dolomitic dolomiticrocks, rocks, isistan tanto togrey greyinincolour colourand andisis characterized characterized by by enrichment enrichmentin in 5i02 Si02and andCaO, CaO,slight slightenrichment enrichmentin inFeO FeOand andMnO MnOand anddepletion depletion of ofMgO, MgO,CO2 CO2and andA1203. A1203.(ibid). (ibid). This This indicates indicates silicification, silicification, the the conversion conversion /I replacement replacement of of dolomite dolomite by by calcite, calcite, removal removal of of feldspar feldspar and and mica mica and and pyritization. pyritization. Metal Metalenrichment enrichmentis is noted noted in in altered alteredwall wallrock. rock. Archean K-Arages, ages,indicating indicatingthat thatvein-forming vein-formingfluids fluidswere were Archean wall wall rocks rockshave havereturned returnedArchean ArcheanK-Ar Sulphur-isotopic data not hot enough to re-equilibrate the argon in the analysed mica. not hot enough to re-equilibrate the argon in the analysed mica. Sulphur-isotopic dataindicate indicate equilibrium equilibrium between between galena galena and and sphalerite sphalerite yielding yielding aa depositional depositional range range of of35°-135°C, 35O-l35OC, and and disequilibrium disequilibriumbetween between sulphide-sulphate sulphide-sulphate pairs pairs (ibid). (ibid). Haynes Haynes(1988) (1988)noted notedthat thatfluid fluidinclusions inclusions in wt.%NaCI NaCl±+ in quartz quartzand andsphalerite sphaleriteindicate indicatedeposition depositionfrom fromNa-Ca Na-Cachloride chloridebrines brines(26-33 (26-33wt.% CaCl2 equiv. equiv. salinity) salinity)atattemperatures temperaturesofof90°-200°C. 9O0-20O0C. He He also alsosuggested suggestedthat thattwo twoisotopically isotopically CaCl2 distinct CaCl2 >> >> Theinclusion inclusionfluids fluidscontain containNaC1 NaCl>>CaCl2 distinctbrines brines were were involved involvedin invein veinformation. formation.The brines and Mississippi Valley-type present-day basinal to KC1, compositionally compositionally similar similar to present-day basinal brines and Mississippi Valley-type KCl, mineralizing mineralizingsolutions. solutions. High ratios 30.7) from from vein vein galena galena (Franklin (Franklin and and Mitchell Mitchell 1977) 1977)likely likelyreflect reflect 2 0 6 ~ b / 2 wratios ~ b ((s 30.7) High206Pb/2°4Pb radiogenic lead associated with the radioactive, Archean, Bowker granite. As noted radiogenic lead associated with the radioactive, Archean, Bowker granite. As notedby byFranklin Franklin (l978b), (1978b),the theEnterprise Enterprise Mine Mine has hasthe thedistinction distinction of ofbeing being the theonly onlyLZBV LZBVdeposit deposittotocontain contain appreciable U)portions portionsof ofthe theEnterprise Enterpriseveins veins appreciable amounts amounts of of uranium. uranium. U-enriched U-enriched(up (upto to540 540ppm ppmU) (Ruzicka (Ruzicka1976) 1976)are areapparently apparentlyspatially spatially associated associated with with galena galena and and likely likely reflect reflectproximity proximityto toaa uraniferous, uraniferous, basement basement source source rock. rock. Lead Leadisotopes isotopesare arehighly highlyanomalous, anomalous,yielding yieldingaa secondary secondary isochron isochron that that likely likely indicates indicatesaamixed mixedArchean-Paleoproterozoic Archean-Paleoproterozoic lead lead source source (Franklin (Franklin and and Mitchell Mitchell 1977). 1977). These These anomalous anomalous and and very very radiogenic radiogenic leads leads are are more more uranogenic uranogenic and and less less thorogenic thorogenic than than leads leads found found in insilver-bearing silver-bearing veins veins near near Thunder Thunder Bay Bay (Franklin (Franklinet et al. al. 1986) 1986)to to which they are temporally and tectonically similar. The LZBV mineralization is most which they are temporally and tectonically similar. The LZBV mineralization is mostlikely likely related 110 Ma). related to to dewatering dewateringof of the the Sibley Sibleybasin basin during during Keweenawan Keweenawanrifting rifting(ca.1090-l (ca.1090-1110 Ma). Franklin Franklin and and Mitchell Mitchell (1977) (1977) suggested suggested that that the the vein vein metals metals were were either either leached leached from from basement basement rocks rocks anchor andlor the breakdown breakdown of of Sibley Sibleysandstone sandstonematrix. matrix. Metals Metals and and sulphate sulphatemoved moved through through permeable permeable Pass Pass Lake Lake Formation Formation sandstone sandstoneas as chloride chloride complexes complexes (Haynes (Haynes 1988) 1988)in in aa very very saline saline brine, brine, and and precipitated precipitated in in veins veins at at the thesandstone sandstone pinch-out, pinch-out, at at or or near near the the Archean Archean unconformity. unconformity. Isotopically Isotopically light light sulphur, sulphur,perhaps perhapsof oforganic organicderivation, derivation,may mayhave havebeen beenlocked lockedinina aH2S-bearing His-bearing gas gas trap trap at the the pinch-out, pinch-out, and and caused caused the the metals metals to to precipitate. precipitate. �- - -s-- -:-ccc: H . . .. - .1.1.II.__•t ,'.' • - • - - • • . - . - . . , 1' .;•.'•• - - —- — — - KAMA HILL-FM-L-.. — I— H S accumulates ROSSPORT FM. pinch-out trap • ' • PASSLAKE FM : , f :.:c:::::::::I.:4;. Tt0Itso •,e.:,.f_.e_•._ . -,.•s• 4—BASEMENT '_.,—,-,—;.-; — 4-t4t'+ + + . + + - • + t + + + • • _ __ — — — Schematic formation of LZBVdeposits from Franklin Franklin and and Mitchell Mitchell (1977); fl977); scale is Schematic model model of of the formation ofLZBV depositsfrom is variable. variable. Amethyst The The largest largest deposits depositsof of amethyst, amethyst,Ontario's Ontario's provincial provincial mineral mineral emblem, emblem, occur occur in in the the Thunder Thunder Bay Bay area. area. Nearly Nearlyall allof ofthe themost mostextensive extensiveand andrichest richestdeposits depositsoccur occur in in aa 10 10km-long, km-long, northeastnortheasttrending trending belt belt near near the the margin margin of of the the Sibley SibleyGroup Group outcrop outcrop where where itit is is underlain underlain by by Hilma Hilma Lake Lake granite granite (Kissin (Kissin 1990; 1990; Garland 1994; 1994; Vos 1976). 1976). Other Otheroccurrences, occurrences,mainly mainly hosted hosted in in granite, granite, are also also spatially spatially related related to to Sibley Sibley outcrop. outcrop. These amethystine quartz, quartz, with minor calcite, calcite, barite and sulphide sulphide These deposits depositsconsist consist of of quartz quartz ++ amethystine minerals minerals (e.g. (e.g. pyrite, pyrite, chalcopyrite, chalcopyrite, bomite). They Theytypically typicallyoccupy occupyfaults faultsand and related related fracture fracture zones zones where where brecciation brecciation and open-space-filling open-space-filling are common (ibid). The The similarities similarities in in geologic geologic setting setting between between amethyst amethyst and and LZBV LZBV led led Kissin Kissin (1990) (1990) to to suggest suggest that that these these two two types types of of vein vein deposits in McArthur McArthur and deposits are are cogenetic. cogenetic. Fluid Fluidinclusion inclusionstudies studiesby by McArthur McArthur (1988), (1988), reported reported in Kissin Kissin (1988), (1988), indicate indicate that that most most amethyst amethyst formed formed near near the the surface, surface, at at temperatures temperatures ranging ranging from from 60' to 90' C. Kissin (1990) suggested that they may be low-temperature derivatives of LZBV, 60" to 90" C. Kissin (1990) suggested that they may be low-temperature derivatives of LZBV, poorer in in sulphides sulphidesand and richer richer in in quartz. quartz. The The presence presence of of aa uraniferous uraniferous basement granite granite (Franklin 1978) was probably crucial in the formation of local amethyst deposits (Kissin 1990), (Franklin 1978) was probably crucial in the formation of local amethyst deposits (Kissin1990), because radioactivity radioactivity is is essential essential in in causing causingelemental elemental substitution substitutionand and defects defectsin in the the quartz quartz crystal crystal that that impart impart the the purple purple colour colour (Garland (Garland1994 1994and and references referencestherein). therein). In In the vicinity vicinity of of the the Enterprise Enterprise Mine, Mine, amethyst amethyst veins veins and and breccia breccia zones zones occur occur in in basement basement granitoids granitoids and and in in overlying overlyingclastic clastic and and stromatolitic stromatoliticSibley Sibley Group Group rocks rocks at at or or near near the the unconformity. paper) basemetal-mineralized metal-mineralizedstromatolites stromatolites(see (seefrontispiece, this this paper) unconformity. Amethyst Amethyst± base the Ontario Gem Welch's Farm occurrence occurrence (C. Anderson, Anderson, pers. comm., 1999), 1999), at occur at the Welch's Company Company Amethyst Amethyst Mine Mine (Garland (Garland 1994) 1994)and in other other places places east east of of Ancliff Ancliff station station (Tanton (Tanton + �1931; J. Scott, Scott, pers. pers. comm., comm., 1999; Mcllwaine 1971 a,b). They They typically typically occur occur on on top top of of 1931; J. 1999; Mcllwaine 1971a,b). prominent granite granite knobs knobs which which may mayreflect reflectpaleotopographic paleotopographic"highs". 'highs. prominent The nearby nearby rockcut rockcut produced produced by the railway railway exposes exposes the the basal basal contact contact of the Sibley The by the of the Sibley Group Group with with underlying Archean Archean granitoids. A regolith regolith makes makes identification identification of of the the contact contact difficult difficult in places. underlvine eranitoids. A in vlaces. Unconformity betweenArchean Archeangranite granite (Gr) (Gr) and and trough Unconformity between trough crossbedded, crossbedded, Pass Pass Lake Lake Formation Formation quartz arenite (s.s.), Enterprise Mine quartz arenite ( i s . ) , Enterprise Mine Medium-grained,trough trough cross-stratified cross-stratifiedsandstones sandstoneslie lie directly directly on on the Medium-grained, the regolith. regolith. The The lensoid, lensoid, cross-cutting bed bed geometry the sandstone discernable. Flow cross-cutting geometry of of the sandstone units units is is easily easily discernable. Flow was was to to the the southeast southeast (Cheadlel986). Again the the exact these units units were were laid laid down (Cheadlel986). Again exact depositional depositional environment environment these down in in is is difficult to to ascertain. difficult ascertain. Without Without fossil fossil evidence evidence to to rely relyon onnear-shore, near-shore,trough troughcross-stratified, cross-stratified, sandstone sandstone sequences sequencesare aredifficult difficultto to differentiate differentiate from from South South Saskatchewan-type, Saskatchewan-type, braided braided fluvial, fluvial, channel channel sandstones. sandstones. Overall Overall unit unit geometry geometry can can give give some some clues, clues, as as can can variability variability of of paleocurrent paleocurrent directions and directions and associated associated minor minor lithofacies, lithofacies, but, but, thick, thick, laterally laterally persistent, persistent, monolithic monolithic successions successions assigning a depositional in serious problems of trough cross-stratified sandstone pose of trough cross-stratified sandstone pose serious problems in assigning a depositional environment. Are Are there there any any clues which would would help help in environment. clues in in this this assemblage assemblage which in deciding deciding between between the the two aforementioned two aforementioned environments? environments? �STOP GH WA 17 STOP2-1: 2-1:GURNEY GURNEY(HI (HIGHWAY) The basal unconformity between the Sibley Group and underlying granitoids is exposed at at this this location. A channel is eroded into basement, and containing matrix-supported visible, eroded into basement, and containing matrix-supported location. A channel is visible, conglomerates overlain by by cross-stratified sandstones. This This sequence sequence differs differs from the conglomerates overlain cross-stratified sandstones. the other other coarse-grained, basal sediments we have examined, as itit represents episodes of subaerial debris represents episodes of subaerial debris flow flow activity activity interspersed intersversed with with normal normal flash flashflood flood runoff. runoff. Unconformity between betweenweatheredArchean weatheredArchean granite (Gr) flows (Gr) and and Pass Pass Lake Lake Formation Formationdebris debrisjlows and Highway 17 17 at at Gurney Gurney and sandstones, sandstones,Highway Archean granitic granitic rocks are altered altered at the unconformity and likely represent a pre-Sibley weathered regolith. This weathered weathered regolith. This weathered paleosol, noted noted by Gill Gill (1926) (1926) and and Moorhouse Moorhouse(1960), (1960),was was locally described by Scott (1987). Friable, locally described Friable,blotchy, blotchy,red redand andgreen greengranite granitehosts hostsquartz-carbonate quartz-carbonate veins between exfoliation exfoliation blocks. Feldspars Feldsnarshave havebeen beenhematitized hematitizedand/or and/ordestroyed; destroyed:. ferromagnesian ferromagnesian minerals minerals have have been been chloritized chlohtized(ibid). (ibid). Limited sampling sampling of of drill drill core core from from the the Black Sturgeon Lake area area cited by Scott (1987) (1987) suggests suggests that this alteration may typically involve marked increases H20 and decreases in NazO, Na20, CaO and perhaps KiO. K20. increases in Fe203, MgO, H2O Paleomagnetic data suggest suggest that this weathering was equatorial (G. Borradaille, unpublished data, 1999). 1999). data, . As (1987) number of As noted noted by by Franklin Franklin(1 (1 978b), Scott (1 987) and Tanton (1948), (1 948), a number of uranium uranium occurrences occurrences are rocks within within the Sibley Sibley are associated associated with with altered altered Archean Archean granitoids granitoids and and overlying overlying sedimentary sedimentary rocks basin, basin, prompting prompting comparisons comparisonswith with the the Athabasca Athabasca basin basin in in Saskatchewan. Saskatchewan. Favourable Favourablelocal local parameters parameters for for supergene supergeneuranium uranium deposits depositsinclude: include: (i) (i) uranium-enriched uranium-enriched basement rocks rocks (quartz monzonites, (ii) onlaps onlapsof ofbasal basal Sibley Sibleysandstones sandstoneson onArchean Archeanpaleotopographic paleotopographic monzonites, pegmatites); pegmatites); (ii) "highs'; "highs";and and(iii) (iii)Keweenawan(?) Keweenawan(?)faults faultsthat thatextend extendto tothe thebasement basement(ibid). (ibid). �STOP 2-2: HILL STOP 2-2:KAIMA KAMA HILL Diabase-capped Kama Hill Hill provides Diabase-capped Kama provides an an excellent excellent roadside roadside exposure exposure of of the theRossport RossportFormation. Formation. The sequence is dominated by interlaminated dolostone and red shale with The sequence is dominated by interlaminated dolostone and red shale with layer layer thicknesses thicknesses ranging from from millimeters millimeters to to ten ten centimeters. There is is some ranging centimeters. There some cyclicity cyclicity in in layer layer thickness thickness variation variation up through the sequence, but it is not a strong trend. Some carbonate layers up through the sequence, but it is not a strong trend. Some carbonate layers contain contain coarsecoarse- to to medium-grained sand sand grains. grains. Dessication medium-grained Dessication cracks cracks are are present, present, but but not not common. common.Synsedimentary Synsedientary deformation manifests manifests itself itself as deformation as small small to to large large slump slump folds folds and and brecciation brecciation of of units unitsin inplaces. places.The The sequence is is intruded sequence intruded by by diabase diabase dykes dykes which which bake bake immediately immediately adjacent adjacent sediments. sediments. Some Some evidence has been been put put forward evidence has forward that that the the diabase diabase intruded intruded watery watery sediment, sediment, but but we we have have not not seen seen clear indications of of this. this. Structural clear indications Structural controls controls on on the the emplacement emplacement of of local local sills sills were were suggested suggested by by Antonellini and and Cambray Cambray (1992). (1992). AAchert-carbonate Antonellini chert-carbonate unit unit (Middlebrun (Middlebmn Bay Bay Member; Member; Cheadle Cheadle 1986) locally hosts hosts stromatolites 1986) locally stromatolites and and hydrocarbons. hydrocarbons. The Kama below the the upper The Kama Hill Hill sequence, sequence, exposed exposed below upper diabase diabase sill, sill, was was laid laid down down in in the theshoreshoreproximal region of a playa lake. Pieces accessible in a pile of excavated talus display proximal region of a playa lake. Pieces accessible in a pile of excavated talus display ripple ripple rainy periods, periods, water marks, mudcracks influx into into the the marks, mudcracks and and rare rare raindrop raindrop impressions. impressions. During During rainy water influx lake lake brought brought and and deposited deposited hematite-rich hematite-rich clays. clays. In In dry dry periods, periods, evaporation evaporation from from the the internal internal drainage system system resulted resulted in in lake contraction, hypersalinity hypersalinity and and the the precipitation drainage lake contraction, precipitation of of dolomite. dolomite. This This requires aa high high MgICa Mg/Ca ratio ratio in in the the lake lake water water and and may may have have been been the the result result of of the the precipitation precipitation of of requires gypsum in in the the central this is is unlikely are expected in the the gypsum central lake. lake. However, However, this unlikely as as higher higher salinities salinities are expected in shallower, marginal marginal areas areas then then the shallower, the lake lake center, center, and and thus, thus, gypsum gypsum precipitation precipitation should shouldbe be initiated initiated in triplets. The The lack in the the shallows, shallows, producing producing shale-gypsum-dolomite shale-gypsum-dolomite triplets. lack of of these these means means that that gypsum gypsum precipitation was was not not necessary necessary to to increase increase the the MgKa Mg/Ca ratio. ratio. The The ambient ambient ratio ratio in in the the lake lake water water precipitation itself must have been high enough for the precipitation of dolomite. itself must have been high enough for the precipitation of dolomite. Interlaminated red formed Interlaminated red shales shales and and dolostone, dolostone, formed by climatic cycling cycling in in aa semi-arid, semi-arid, playa playa lake by climatic lake environment, Rossport Rossport Formation, Formation, Kama environment, Kama Hill. Hill. I Reduction spheres in Reduction suheres in hematitic hematitic siltstone, siltstone. Kama Kama Hill, with black, carbonaceous, locally "",z,.-"*;.," """*""" radioactive centers. �STOP STOP2-3: 2-3:RUBYLAKEMARBLELTD. RUBY LAKE MARBLE LTD.QUARRY QUARRY The The Ruby Ruby Lake Lake Marble Marble Ltd. quany quarry isis owned owned and and operated operated by by Don DonMacAlpine MacAlpine and Gerald Gerald Landry. Landry. Variegated, Variegated, multimulticoloured, coloured, banded banded marble marble is is quarried quarried for for landscaping landscaping stone. stone. Approximately Approximately 175 175 tonnes tonnes of of marble marble were were quarried quarried and and shipped shipped in in 1998 1998(D. (D. MacAlpine, MacAlpine, personal personal communication,1999). 1999). The dimensions dimensions communication, of of the the largest, largest, transported transported block block was was 1.8 1.8 by by 0.50 0.50mm(= ( 1.8 1.8 tonnes) tonnes) (ibid). (ibid). by 0.75 0.75 by Approximately 398 tonnes Approximately 398 tonnes of of marble marble were were quarried quarried and and shipped shipped in in 1999 1999(D. (D. MacAlpine, MacAlpine, pers. pers. comm., comm., 2000). 2000). Additional Additional information information is provided orovided on on their their World World Wide Wide Website Website(http://www.rubylakemarble.com). (http://www.mbylakemarble.com). . This This marble marble consists consistsofofcontact contactmetamorphosed, metamorphosed,Mesoproterozoic, Mesoproterozoic, Rossport Rossport Formation Formation contact sedimentary rocks in the (Sibley (Sibley Group) Group) dolostone dolostone and and other, other, calcareous calcareous sedimentary rocks in metamorphic metamorphic aureole aureole of of Keweenawan Keweenawan diabase diabase sills. sills. It has previously been termed termed Nipigon Nipigon River from 1883 1883 to to ca. ca. 1910 at at a site on the River marble and was quarried quarried from the eastern eastern side side of of the the cxl. 1994). A Nipigon River, approximately km west west of the Ruby approximately 66 km Ruby Lake Lake quarry quarry (Hinz (Hinz et et al. similar, similar, hornfelsed homfelsed unit is is described described in more detail detail at Stop Stop 2-6. all Calcite, and opaque minerals were were noted noted in in thin section by Hinz Him et et al. Calcite, dolomite, epidote epidote and opaque minerals (1994) from the Nipigon Nipigon River River quarry. quarry. The The following following chemical analyses analyses for for Nipigon Nipigon River River (1994) - chemical marble also provided (wt.%)were werialso provided (ibid): (ibid): marble (wt.%) Sample Sample S102 SiO; 89MCK 35.21 35.21 89MCK 1 MgO MgO Ti02 A1203 A1203 Ti02 0.20 0.20 8.20 8.20 Fe203 Fe203 FeO FeO MnO MnO 2.04 2.04 0.05 0.05 23.56 23.56 CaO 26.74 Na20 0.00 1(20 2.38 P205 1.53 1.53 0.10 2.04 0.00 0.03 27.63 35.32 0.00 0.41 0.07 0.09 -09 -09 89MCK 29.19 5.20 -10 Shallow Shallow exploration explorationtrenches trenches on on the side side of the road leading to the top of Ruby Mountain (i.e. (i.e. top of marble. Fine-grained, of the the upper upper sill) sill)have have exposed exposed copper-mineralized copper-mineralized marble. Fine-grained, disseminated disseminated blebs blebs of of native native copper copper (0.1 (0.1 to to 1.0 1.0 mm mm occur occur along along calcite-coated, hairline fractures parallel to fractures are are most easily planes. Mineralized Mineralized fractures easily recognized recognized where where secondary secondary bedding planes. just formed. The top of the the adjacent adjacent (middle?) sill is exposed just (supergene) malachite has formed. Polygonal cooling coolingjoints joints (seen (seen in in plan plan view) view) and and the chilled, upper upper farther along along the the road. road. Polygonal are evident. evident. margin are Similar, calcareous units units have have been been noted noted near near a diabase sill contact at Similar, copper-mineralized, calcareous all Hughes Point, 2.5 km krn to the south-southwest south-southwest by Schnieders et al. (1996). At At this this location, location, 2 to 55 cm cm wide wide calcite calciteveins veinscontain containdisseminated disseminated covellite covellite (after (after chalcocite?) chalcocite?) and and malachite. malachite. �The Theorientation orientationof ofthe theveins veinsare areroughly roughlyparallel parallelto tojoints joints developed developedin inthe theadjacent adjacentsill. sill.Grab Grab samples have returned up to 3.065% Cu, nil Au and nil Ag (ibid). samples have returned up to 3.065% Cu, nil Au and nil Ag (ibid). Franklin Franklin (1970) (1970)described describedcopper-mineralized copper-mineralized stromatolitic stromatolitic units units near nearDisraeli DisraeliLake. Lake. AA variety varietyof ofcopper copperminerals, minerals,including includingdigenite, digenite,cuprite, cuprite,covellite, covellite,chalcopyrite, chalcopyrite,native nativecopper copper and and malachite, malachite, were were identified identified as as open-space open-space fillings fillings in in the the vuggy vuggy host hostrock. rock. Franklin Franklin (1970) (1970)suggested suggestedthat thatthe thecopper copperwas wasintroduced introducedepigenetically epigenetically from fromaagabbro gabbrototoperidotite peridotite The close spatial association plug plug that thatintruded intrudedthese theseSibley SibleyGroup Grouprocks. rocks. The close spatial associationofofcoppercoppermineralized mineralizedrocks rockswith withdiabase diabasesill sillcontacts contactsininthe thevicinity vicinityof ofRuby RubyLake Lakesupports supportsthis thistheory. theory. The Themarble marble isisstromatolitic, stromatolitic, though though this this is is difficult difficult to to ascertain ascertain in in most most places places due due to tothe the alteration. The stromatolites are best seen on the tops of beds where they protrude, causing alteration. The stromatolites are best seen on the tops of beds where they protrude, causing the thecontact contactto tobecome becomewavy. wavy. Hints Hintsof ofthe thepresence presenceofofstromatotactis stromatotactisare arevisible, visible,giving givingthe the impression impression that that aa large largeamount amount ofofthe thehorizontal horizontallayering layeringisisstromatolitic stromatoliticS-mat. S-mat. This This sequence sequence was was deposited deposited in inaastrandline strandlineproximal proximalposition positioninin the the playa, playa, as asdenoted denotedby bythe the horizon at other locations. This infers that lake size presence presenceof ofteepee teepeestructures structuresininthis this horizon at other locations. This infers that lake sizehad had stabilized stabilizedduring during this thisinterval, interval,eliminating eliminatingthe theseasonal, seasonal,large-scale large-scalefluctuations fluctuationsin inshoreline shoreline positioning. positioning. r . - - - - .— t - - — 4T : TI - - - -- Lz.L .. . Parallel-laminated ininpossible Parallel-laminatedcarbonate carbonatewith withvariable variableamounts amountsofofhematitic hematiticclays ...~, 'a possibleS-mat stromatolite, Ruby Lake Quarry �U MOUNTAIN MOUNTAIN STOP 2-4: 2-4: MOSEA MOSEAU The Moseau stop consists consists of of a number Moseau Mountain Mountain stop number of of small small outcrops outcrops extending extending from from the the granitic basement basement to to the middle granitic middle portion portion of ofthe theRossport RossportFormation. Formation. Cross-stratified sandstones of the Pass Lake multiLake Formation Formation overlie basement. The lower lower sandstones sandstones are multistorey, but as we proceed upwards mudstone mudstoneinterbeds interbedsbegin begin to to appear. appear. Above Above this thiszone zonethe the sandstones are replaced by siltstones, continuing the general upward-fining trend. trend. Higher Higher in the siltstone mudblock conglomerates conglomeratesbegin begintoto appear. appear. These, These, in in turn, turn, are are the siltstone succession succession mudblock upwardly transitional into evaporite block conglomerates, with gypsum and dolomite clasts. and dolomite clasts. Diabase intrusions intrusions occur occur above above this this zone. zone. The lower portion of of the sequence is similar to the one observed The lower portion sequence is similar to observed at Pass Pass Lake, Lake, where where a and conglomerates to to the the siltstones thinning and fining trend exists from the basal sandstones and of the basal Rossport Formation. This again represents expansion expansion of a playa playa lake lake system. system. The The intraformational conglomerates which which overly overly this this sequence may may have have been produced by two intrafonnational mechanisms. Dissolution Dissolution of of an evaporitic layer causing collapse of the overlying mechanisms. overlying units, units, or or tectonic raising of the basin margin margin resulting resulting in inthe theerosion erosionand and resedimentation resedimentation in in aa more more basin-center environment of the upper marginal sediments. The latter explanation explanation is preferred as this unit is regional in extent, occurring where it is unlikely that underlying evaporites ever existed. existed. STOP 2-5: S LOOKOUT 2-5: LLOYD LLOYD'S LOOKOUT This stop, located on the Nipigon-Red Rock hiking trail, features exposures of Kama Hill Formation shales and siltstones siltstones underneath a Logan diabase sill which caps the prominent mesa and provides the vantage point over Nipigon Nipigon Bay Bay known known as as Lloyd's Lloyd'sLookout. Lookout. From one can can view view the themouth mouthof ofthe theNipigon NipigonRiver Riverand andNipigon NipigonBay. Bay. The this vantage point, one locations of the quarries 1-2 are shown in the photograph photograph below. quarries mentioned in STOP 1-2 Viewfrom fromLloyd's Lloyd's Lookout, Lookout, looking looking east east over Nipigon Bay View I �This This is is one oneof ofthe thefew fewaccessible accessibleexposures exposuresof ofthe theKama KamaHill HillFormation. Formation.This ThisFormation Formationisis homogeneous, consisting of brick-red mudstones with interlayered, current-rippled, homogeneous, consisting of brick-red mudstones with interlayered, current-rippled,coarsecoarsegrained grained siltstones siltstones and and very veryfine-grained fine-grained sandstones. sandstones. The The rippled rippled layers layers are are usually usually centimeters centimetersto to aa few fewdecimeters decimetersthick. thick.The Themudstones mudstonesare arecommonly commonlymudcracked. mudcracked. Cheadle believed that that this this unit unit was was deposited deposited as as subaerial subaerialmudflats, mudflats, representing representing the the Cheadle (1986) (1986) believed final final stage stageof of infilling infilling of of the the lake lake basin. basin. However, However, new new drill drill core core data dataindicate indicate that that the the Kama Kama Hill Hill Formation Formation is is overlain overlain by by aaprograding, prograding,deltaic deltaicsequence. sequence. This Thisinfers infersa asubaqueous subaqueous position position for for the the Kama KamaHill HillFormation Formationwith withthe thesediments sedimentsrepresenting representingprodelta prodeltato todistal distalbar bar sequences. In core, core, these these are are overlain overlain by by distributary distributary mouth mouth bar bar and andfluvial fluvialchannel channel sequences. In sandstones. The mudcracks are problematic. They may be syneresis cracks, sandstones. The mudcracks are problematic. They may be syneresis cracks, formed formed subaqueously subaqueously through through differential differential swelling swelling of of clays, clays, or or they they may mayrepresent representlarge-scale, large-scale,water water level level fluctuations. fluctuations.Neither Neither of ofthese theseexplanations explanationsappears appearsadequate. adequate. The The view view over over Nipigon Nipigon Bay Bay isistowards towardswhere wherethe thedrillcore drillcoreexamined examinedthe theprevious previousday daywas was drilled. 20 m m of ofwater, water, drilled. During During Kama Kama Hill Hill time time we we would would be be standing standing in in approximately approximately 20 looking looking towards towards aa horizon horizon where where aa delta delta system system would would be be located, located, building building towards towards us. us. STOP STOP 2-6: 2-6:BIG BIGSQUAW SQUAWCREEK CREEKROAD ROAD CUT CUT This This stop stop presents presents the the opportunity opportunity to to view view stoped stoped blocks blocks of of Rossport Rossport Formation Formation dolostone dolostone in in aa diabase diabase sill, sill, as as well well as asthe theattendant attendantmetamorphic metamorphic and andmetasomatic metasomaticeffects. effects. Pale Pale green green to to buff, buff, thinly thinly bedded bedded dolostones dolostonesare are preserved preserved as as rafted rafted xenoliths xenolithsup up to to several severalmetres metres thick. thick. Rafied Formation in Rafted xenoliths of hornfelsed Rossport Formation in Logan diabase diabase sill, sill, Highway Highway 11-17 11-1 7 at at Big Squaw Creek Creek I I I I �Thin section Thin section petrography petrography reveals aa recrystallized, recrystallized, granoblastic granoblastic texture texture predominated predominated by epidote. Subhedral to euhedral, epidote porphyroblasts are typically 0.05 to 0.10mm size, mm in size, Subhedral porphyroblasts are typically 0.05 to 0.10 but they may reach 0.25 mm, in a fine-grained matrix of vermicularly intergrown quartz and feldspar. Large Large (<0.75 (<0.75 cm), cm), optically optically continuous, continuous, decussate, decussate, acicular biotite porphyroblasts Radiating, sheaf-like sheaf-like aggregates aggregates have have been are also overgrown are overgrown by by epidote. epidote. Radiating, been tentatively tentatively Minor sericite sericite and and calcite were were also noted. Epidote persists into the identified as chlorite. chlorite. Minor margin of of the the diabase. diabase. Joints fine-grained, chilled margin Joints and and fractures fractures surfaces may be coated coated with Large, consp conspicuous, lime-green clots of prehnite occur in epidote-calcite veins muscovite. Large, within the diabase. Little work has been done done on on contact contact metamorphic metamorphic effects in vicinity of the diabase diabase sills. sills. (1986) noted noted that that such metamorphism occurs in in calcareous calcareous rocks rocks over over a zone Sutcliffe (1986) Sutcliffe metamorphism occurs zone several metres metres thick, thick, where where bleaching bleaching is is its its most obvious manifestation. manifestation. Fine-grained, Fine-grained, calcmineral-bearing assemblages assemblages identified identified by by Sutcliffe Sutcliffe (1986) (1986) include include calcite, plus (in silicate mineral-bearing (in order of increasing metamorphic grade): talc, tremolite, serpentine (after forsterite) and increasing metamorphic grade): tremolite, serpentine (after forsterite) and Calculations by by Sutcliffe Sutcliffe (1986) (1986) suggest suggest that that the diabase sills were emplaced at diopside. diopside. Calculations shallow crustal crustal levels, levels, near near the the Archean-Proterozoic Archean-Proterozoicunconformity, unconformity,atataalithostatic lithostaticload loadof of shallow <0.4 adjacent 88OSC,while adjacent 0 . 4 kbars. The Thesills sillscrystallized crystallizedover over aa temperature temperature range of 1100° 1100" to 880°C, wall rocks may have experienced 665°C (ibid). experienced temperatures temperatures ranging ranging from 540° 540' to 665'C hornfels at Big Squaw Creek may may reflect simple The mineral assemblage in the calc-silicate hornfels significant recrystallization of sedimentary units without of the impure, impure, calcareous sedimentary units without significant compositional or compositional or volumetric volumetric changes changes (ci'. (cf. Hall and and MacKevitt MacKevitt 1962). 1962). �REFERENCES REFERENCES Antonellini, Antonellini, M.A. M.A. and and Cambray, Cambray, F.W. F.W. 1992. 1992. 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McTavish McTavish Township Township (West of north north halt), half), District District of ofThunder ThunderBay; Bay; Ontario Ontario Department Department of of Mines Mines and and Northern Northern Affairs, Affairs, Preliminary Preliminary Map Map P.720, P.720, scale scale 1:15 1:15 840. 840. . 1975. 1975. McTavish McTavish Township Township (south (south half), half), District District of of Thunder Thunder Bay; Bay; Ontario Ontario Department Department of of Mines Mines and and Northern Northern Affairs, Affairs, Preliminary Preliminary Map Map P.990, P.990, scale scale 1:15 1:I5 840. 840. Moorhouse, W.W. 1960. The Gunflint Moorhouse, W.W. Gunflint iron range in the the vicinity vicinity of ofPort PortArthur; Arthur;Ontario Ontario Department Department of of Mines, Mines, Annual AnnualReport, Report,v.69, v.69, pt.7, pt.7, p.1-40. p.1-40. Morey, Morey, GB. G.B. and andOjakangas, Ojakangas, R.W. R.W.1982. 1982.Keweenawan Keweenawan sedimentary sedimentary rocks rocks of ofeastern eastern Minnesota and northwestern northwestern Wisconsin; Wisconsin; in Tectonic Tectonic history of of the the Lake LakeSuperior Superior basin, Geological Geological Society Society of of America, America, Memoir Memoir 156, 156, p.135-146. p.135-146. Parks, W.A. 1901. 1901. Report of 1901 1901 on on the the geology geology and and natural natural resources resourcesof ofthe thesoutheastern southeastern Nipigon district; Geological Survey of Canada, Report. Nipigon district; Geological Survey of Canada, Report. Ruzicka, V. 1976. in Report 1976. Assessment Assessment of some some Canadian Canadian uranium uranium occurrences; occurrences; in Report of Ruzicka, V. Activities, Part A, Geological Survey of Canada, Canada, Paper Paper 76-IA, 76-lA, p.341-342, p.341-342. �Scott, J.F. J.F. 1987. Uranium occurrences of the Thunder Bay-Nipigon-Marathon area; Ontario Ontario Bay-Nipigon-Marathon area; l58p. Geological Survey, Open File Report 5634, 158p. Sutcliffe, R.H. R.H. 1986. The The petrology, mineral chemistry chemistry and and tectonics tectonics of Proterozoic Sutcliffe, petrology, mineral Proterozoic riftrelated igneous rocks at Lake Nipigon, Ontario; unpublished Ph.D. related igneous rocks Lake Nipigon, Ontario; unpublished Ph.D. thesis, thesis, The The University of Western Ontario, London, 325p. Tanton, T.L. T.L. 1931. Fort William and Port Arthur, and Thunder Cape map-areas, Thunder Tanton, map-areas, Thunder 222p. Bay District, Ontario; Geological Survey of Canada, Memoir 167, 167,222~. Radioactive nodules nodules in in sediments sediments of of the Sibley series, Nipigon, Ontario; 1948. Radioactive . 1948. Ontario; III, section IV, p.69-75. Transactions of the Royal Society of Canada, v.XLII, series 111, Wilson, A.W.G. 1910. 1910. Geology of the Nipigon Basin, Ontario; Canada Department of Mines, Geological Survey Branch, Memoir Memoir No. No. 1, 152p. l52p. 1 �GEOLOGY GEOLOGY OF OF THE THE LAC LAC DES DES ILES ILES PGE-Cu-Ni PGE-Cu-Ni MINE MINE Moe Lavigne, Lavigne, Matawin Matawin Mineral Mineral Exploration, Exploration, and and Moe Staff, Lac Lac des des lies lies Mines Mines Ltd. Ltd. Staff, North American American Palladium Palladium Limited's pit Lac Iles North Limited's open open pit Lac des des lies Mine Archean Lac Lac des des lies Iles mafic-ultramafic mafic-ultrama/Ic Mine is is hosted hosted by by the the Archean intrusive complex. This trip on PGE intrusive complex. This trip willfocus will focus on PGE mineralization mineralization as structure and and alteration. as it it relates relates to to intrusive intrusive lithology, lithology, structure alteration. �PaHadurn Geology Geology of the the Lac Lac des lies lles Palladium Deposit Regional Regional Geology Geology The age rocks rocks (2.6 (2.6 ttoo 3.0 The Lac Lac des des lies lles area is underlain by the Archean age 3.0 billion billionyears) years) of ofthe theCanadian CanadianShield.These Shield.These rocks are overlain and and intruded intruded by by Proterozoic Proterozoic age agerocks rocks(0.9 (0.9t o to 2.2 2.2billion billionyears) years)that thatformed formedduring duringrifting riftingof of the mafictto or have the continent, continent,centered centeredon onLake LakeSuperior.Archean Superior.Archean age. age. mafic o ultramafic intrusions that host, host. or have the potenpoten- tial are dispersed dispersedthroughout throughoutNorthwestern Northwestern 0ntario.These Ontario.These intrusions are are concentratconcentrattial to t ohost hostPGE PGE mineralization, mineralization,are ed malor faults.The 20km km south south of Lac Lac ed within within granite-greenstone granite-greenstone terrain, terrain, and and along major faults.The Quetico Quetico Fault, Fault, which passes passes 20 des lles, lies, is is coincident coincident with with a 180km southwesterly trend trend of PGE bearing intrusi0ns.A intrusions.A particular particular high high concentraconcentral80km southwesterly PGE bearing tion circular feature feature with with a 30 km tion of ofintrusions intrusionsoccur occurininthe theLac Lacdes des lies llesarea, area,aa number of intrusions define a circular diameter.These major crustal sutures are are important important as that can can only only originate originate from diameter.These major as they allow allow PGE PGE rich magma magma that the the earths earths mantle, mantle, ttoo move move upwards upwards into into the the crust. crust Proterozoic mineralization isis not not as as common common in northwestern northwestern Ontario. Ontario.However, However,potential potentialPGE PGE hosting hosting Proterozoicage age PGE PGE mineralization Proterozoic mafic tto voluminous.Gabbro Gabbrocovers coversor or intrudes intrudes most most of the Proterozoic age mafic o ultramafic intrusions are much more voluminous. Lake Superior Superior area, area, no no less lessthan than 20,000 20,000km2.A km2.A recent 8 g/t lies at Wolf Wolf g/t Pd+Pt Pd+Pt discovery discovery made made east of Lac Lac des lles Mountain in a Proterozoic ultramafic intrusion intrusion is testament testament tto o its its potential. potential. Proterozoic age age ultramafic The known knownmafic mafic to t oultramafic ultramaficintrusions intrusionsininthe theLac Lacdes deslIes llesarea area consists consists of of the the following; following; . • Lac des lles lies Complex Complex (—30km2) (-30km2) (Company ownership; ownership;100%) 100%) • Tib TibLake LakeIntrusion Intrusion(—25km2) (-25km2) (Company (Company ownership; ownership;65%) 65%) ..,~ ~, ~:~ ,. • Legris 2km2) (Company ownership; LegrisLake LakeIntrusion Intrusion(—.1 (-1 2km2) ownership; 0%) 0%) • Demars DemarsLake LakeIntrusion Intrusion(-.(-1I km2) km2)(Company (Companyownership; ownership;100%) 100%) . . • Taman Taman Lake Lake Intrusion Intrusion (CI (C Ikm2 km2 (Company (Company ownership; ownership;0%) 0%) DogRiver RiverIntrusions Intrusions(<I (< lkm2) km2) • Dog (Company (Company ownership; ownership;0%) • Buck BuckLake LakeIntrusion Intrusion(—Skm2) (-5km2) (Company (Company ownership; ownership;90%) 90%) • Wakinoo WakinooLake LakeIntrusion Intrusion(--II (-1 kni2) lkm2)(Company (Companyownership; ownership;100%) 100%) w) These intrusion intrusion are are similar similar in in that that they theyare arelate latetectonic tectonicand andintrude intrudetonalite tonalitegneiss, gneiss,have have tholeHtic tholeiitic affinity and contain rangingfrom from ultramafic ultramafic peridotitic contain phases phases ranging peridotiticand andpyroxenitic pyroxeniticcummulates cummulatestot omagnesian magnesiangabbro-norite gabbro-noriteand and iron-rich Taman and Dog Dog River intrusions. is found found in in all all except except the theTaman intrusions. iron-rich gabbro. gabbro. PGE PGE mineralization mineralization is des lles lies Complex consist of three The Lac des three distinct distinct lithological lithologicalpackages; packages; tto o the north, north, ultramafic ultramafic intrusions intrusionscencentered gabbroic intrusions intrusions immediately south of the lake and a horntered on on Lac Lac des des lies, lles, complex gabbroic lake (Mine Complex), Complex),and blende gabbro southwest southwest of of Camp Camp Lake Lake (Camp (Camp Lake Lake lntrusion).These three threesegments segments are are partially partiallyseparated separated by by tonalite of which consist of several septums.The ultramafic ultramafic intrusions intrusions consist consist of of two twocoalescing coalescingcentres, centres, each each of tonalite septums.The It conconintrusive phases.The northern ultramafic centre is nearly circular in plan with a diameter of nearly 4 km. It phases.The northern sist of interlayered interlayered dunite dunite and and wehrlite, wehrlite,olivine-clinopyroxenite olivine-clinopyroxeniteand andclinopyroxenite. clinopyroxenite.and and websterite websteritewhich whichdefine define aa �Palladium concentric concentric inward inward dipping dipping pattern.These pattern.These lithologies lithologies occur occurininseveral several cycles cycles which which probably probably represents represents fractional fractional crystallization of pulses.ItItalso alsorepresents representsrepeated repeatedopportunities opportunities tto concentrate PGE's. This crystallization of separate separate magma magma pulses. o concentrate PGE's. This part of sulphide rich rich horizons, occurrences (>1 part of the thecomplex complexdoes doeshave haveseveral several PGE's PGE's bearing bearing sulphide horizons, and and 55 PGE PGE occurrences (>I g/t g/t Pd+Pt) were discovered 999.The elliptical elliptical southern southern ultramafic wehrlite core Pd+Pt) were discovered in in I1999.The ultramafic centre centre consist consist of of aamassive massive wehrlite coresursur- rounded websterite.These two gabbronorite wedge on the the east side of of the the rounded by by websterite.These two centres centres are are partially partiallyseparated separated by by aa gabbronorite wedge on east side complex..This area PGE occurrences, occurrences,S 5 discovered discovered in in 1999. 1999. complex..This area contains contains 77 PGE The had been been considered considered tto a relatively homogenous hornblende hornblende be a relatively homogenous The Camp Camp Lake Lake Intrusion, Intrusion, south south of of Camp Camp Lake, Lake, had o be gabbro and barren barren of of PGE mineralization. Historically, Historically, itit had had been been subjected subjected tto minimal exploration. exploration. Stripping gabbro and PGE mineralization. o minimal Stripping along its northern northernmargin margininin1999 1999revealed revealedunexpected unexpectedcomplexity complexityand andsampling samplinggenerated generatedlow lowgrade gradePGE PGEassays. assays. along its The mineralcompositionally, texturally texturallyand and structurally structurallycomplex, complex,contains contains abundant abundant PGE PGE mineralThe Mine Mine Complex, Complex, which which isis compositionally, ization. Its Its composition composition ranges rangesfrom from anorthosite anorthosite to ization. t o clinopyroxenite, clinopyroxenite,gabbronorite gabbronoriteto t omelanonorite melanonoriteand andincludes includes magnetite rich rich gabbro.Textures gabbro.Textures include include equigranular equigranularfine fine to to coarse coarse grain, grain, porphyrytic, porphyrytic, pegmatitic. pegmatitic, varitextured varitextured magnetite units three textural units and and heterolithic-gabbro-breccia.These heterolithic-gabbro-breccia.Theselast last three texturaltypes typescoincide coincidewith withallallmineralized mineralizedzones. zones. Fragments in in these these breccias, breccias,which whichvary varyfrom fromaafew few centimeters centimeters tto Fragments o tens tens of of meters metersininsize, size, are are representative representative of of most most of of the the lithologies lithologiesininthe thearea.The area.Thebreccias breccias were were created created as as the result result of of an an energetic energetic influx influxof of aa volatile volatile charged, PGEbearing bearing magma, magma,which whichassimilated assimilatedofofaalarge largevolume volumeof of rock rock and disrupted Iayering.The charged. PGE and disrupted layering.The PGE PGE bearing bearing magma, typically aa melanogabbro, melanogabbro,isisthe the matrix matrix to magma, typically t o the thebreccia brecciaand andcontains containshigh highgrade gradePGE PGEvalues.The values.The accompanyaccompany- ing volatiles, volatiles, migrating migrating through through the altered the the chamber, chamber, produced varitextured varitexturedand andpegmatitic pegmatiticgabbro, gabbro,altered thesilicates, silicates, mobilized produced sulphide poor poor mineralization.The mineralization.The varitextured varitexturedgabbro gabbrothat thatdefines definesthe theoval ovalshape shape mobilized metals and produced of the to the the Roby Roby Zone.The Zone.The occurrence occurrenceof ofthese these key key rock rock types types and and mineralization mineralization the Mine Mine Complex, Complex, is host to throughout the it in throughout the Mine MineComplex Complexisisevidence evidence that thatthe themineralizing mineralizingprocess process affected it in its its entirety. entirety. POE Mineralization of PGE Mineralization of the the Mine Mine Complex Complex Zones of PGE PGE mineralization with delineated resources in the Mine Complex Complex consists consists of the Roby Roby Zone,Twilight Zone, Moore Zone. from 0.7 0.7 e/t g/t to Zone. Baker Zone and Moore Zone. Other Othermineralized mineralizedareas, areas, with values values from to 23 23 g/t g/t Pd Pd have have had limited amounts of surface sampling and anddiamond diamond drilling drilling and and require require follow-up. follow-up. Roby Zone Roby Zone The Roby Zone is is a bulk bulk mineable deposit with aa minimum minimum strike strike length length of of 850 850 meters, meters, width width achieving achieving 365 meters and aa depth depth of 500 meters.The zone and tto and potential exist for zone remains remains open at depth, and o the southeast and for new mineralization mineralization ttoo the the west. west. Ore (7.6% North Roby The Roby Zone contains three three distinct distinctore oretypes; types; Shear Shear Ore (7.6% of volume), North Roby Ore Ore(5.3% (5.3%of ofvolume) volume) and Breccia 1% % of volume). volume). Breccia Ore Ore(87. (87.1 Shear Ore Ore Shear Ore is is confined confinedtto portion of a IS Shear Ore o aa portion 15 to t o25 25meter meterthick thicklayer layerof ofpyroxenite pyroxenitethat thatisisthe thehanging hanging wall in the central portion Only aa 400 400 metre metre portion portion of portionof ofthe theRoby RobyZone, Zone,inincontact contactwith withaabarren barrengabbro gabbrohangingwall. hangingwall. Only of the the �Palladium mineralized, the the strike pyroxenite pyroxenite is is mineralized, strike extensions extensionsare are barren.The barren.Thepyroxenite pyroxeniteisisplanar, planar,trends trendsatat3410, 3 ~ ,is sis subvertical subvertical to t o aa depth depth of of 250 250metres metresand and shallows shallows to to the theeast eastat at greater greaterdepth. depth Higher grades(6 (6tto g/t Pd) are achieved achievedin inthose thoseportions portions o off the Higher PGE PGE grades o 12 12 g/t Pd) are the pyroxenite pyroxenite that that are arealtered alteredto t oaaschisschistose assemblage of actinolite-talc-chlorite (Shear Ore).The sulphide content of the pyroxenite, including the conconlose assemblage of actinolite-talc-chlorite (Shear Ore).The sulphide content of the pyroxenite, including the tained shears, shears,isis 1% 1%t oto3% 3%with with local localpatches patchesofofnet nettexture texture with with up tenor is tained up to to10% 10% sulphide. sulphide. The The PGE PGE tenor is not notproproportional to the sulphide content.The dominant sulphides are pyrrhotite, chalcopyrite and pentlandite. PGM are portional t o the sulphide content.The dominant sulphides are pyrrhotite, chalcopyrite and pentlandite. PGM are vysotskite (Pd,Ni)S Sb2As2 , kotulskite sperrylite PtAs2 ,and aa vysoiskite (Pd.Ni)S , isomerticite isomerticitePd PdIII ISb2As2 kotulskitePd(Te,Bi), Pd(Te.Bi). sperrylite PtAs2 , Merenskyite Merenskyite PdTe2 PdTe2 .and Pd arsenide,either either Stillwaterice Stillwaterite or segment of of the the pyroxenite pyroxenite is is juxtaposed juxtaposed Pd arsenide, o r Palladoarsenide. Palladoarsenide. The The higher-grade higher-grade segment with the higher grades found in the adjacent breccia ore.The PGE tenor of the pyroxenite declines with the higher grades found in the adjacent breccia ore.The PGE tenor of the pyroxenite declines dramatically dramatically ttoo the the south southwhere wherethe thedegree degreeof oftalc talcalteration alterationisisdiminished. diminished.ItI talso alsodeclines declines in in the theadjacent adjacent breccia breccia ore.The ore.The pyroxenite and and iits contained shears shears pinch pinch out out tto to pyroxenite t s contained o the the northwest.The northwest.TheShear Shear Ore Orehas has been been drilled drilledsystematically systematically rn a depth of 500 mecers.The pyroxenite separates the two other major ore types. a depth of 500 meters.The pyroxenice separates the two other major ore types. . . . North Roby Ore Ore N o r t h Roby North ofofthe Roby Ore is a zone whose gradual boundaries are It North thepyroxenite, pyroxenite,the theNorth North Roby Ore is tabular a tabular zone whose gradual boundaries aredefined definedby byassay. assay. It is 20 20 to to 40 The zone zone strikes strikes aatt 20' 20° with with its is 40 meters meters thick, thick, and and 200 200 meters meters long. long.The its footwall footwalldipping dippingto t othe theeast eastat at45° 45wall steeper. steeper.ItIt isishosted hostedby byaawide wide variety variety of of lithologies.At lithologies.At surface, it is is dominated dominated by by surface, it tto o 60° 60Âand and the the hanging hanging wall coarse grain Ieucogabbro containing irregular irregular masses massesof ofvari-textured van-textured gabbro gabbro and and medium medium tto gabbrocoarse grain leucogabbro containing o coarse coarse grain grain gabbronorite.The proportion with depth.The content of of this this norite.The proportionof ofnoritic noriticrock, rock,and andheterolithic heterolithicbreccia brecciaincreases increases with depth.The suiphide sulphide content mineralization ranges from trace amounts to 4%, and typically is less than 0.25%.The sulphide poor mineralization mineralization ranges from trace amounts t o 4%. and typically is less than 0.25%.The sulphide poor mineralization cannot visually visually be be distinguished distinguished from from the the barren cannot barren wallrock.The wallrock.The dominant dominantsulphides sulphides are are pyrrhotite, pyrrhotite.pentlandite. pentlandite,chalchalcopyrite and distribution isis erratic 1616 g/teft Pd) and weakens copyrite and pyrite.The Pd) and weakensininaaNE N Edirection. direction.Systematic Systematic pyrite.The PGE PGE distribution erratic(I( Itot o drilling of a maximum maximum depth depth of of 250 drilling of this this zone zone has has only only attained attained a 250 metres. metres. Breccia Ore Breccia O re Southwest of the Southwest of the Shear Shear Ore, Ore, Breccia Breccia Ore Ore isis contained containedwithin withinaamineralized mineralizedcomplex complexthat thatmeasures measures550 550by by350 350 meters.This complex complex contains contains intrusive intrusive lithologies lithologies that that range range in in composition composition from from clinopyroxenite clinopyroxenite tto meters.This o anorthosite anorthosite van-textured and tto o norite.Textures norite.Texturesinclude includeequigranular equigranular fine fine to t ocoarse coarsegrain, grain, porphyrytic, porphyrytic.pegmatitic. pegmatitic.vari-textured and heterolithheterolithic-gabbroic-breccia. Mineralization is concentrated in these last three textural types, but it is also commonly ic-gabbroic-breccia. Mineralization is concentrated in these last three textural types, but it is also commonlyfound found in medium grain grain norite norite and coarse grain grain gabbro-norite.All gabbro-norite.All of in clinopyroxenite, clinopyroxenite.melanogabbro, melanogabbro, medium and medium medium and and coarse ofthese these rocks types rocks types occur occur as as discontinuous, discontinuous, irregularly irregularlyshaped shaped pods pods with with rnaxiryium maximum dimensions dimensions of of 60 60 meters metersthat, that,when when viewed are in viewed on on aa map, map, are in fact fact aa larger largerscale scale of ofbreccia. breccia. The boundary tto the central portion of the sub-vertical contact with with the the The east east boundary o the central portion of the theBreccia Breccia Ore Ore is is defined defined by by the sub-vertical contact pyroxenite.The southeast extension of of the pyroxenite.The southeast extension the Breccia Breccia Ore Ore remains remains open.The open.The southern southern and and western western boundaries boundaries of of the Breccia Ore are all defined by a gradual decline in PGE content.As defined by the 0.7 g/t Pd assay cutoff, the the Breccia Ore are all defined by a gradual decline in PGE content.As defined by the 0.7 g/t Pd assay cutoff, the western and the the southern southern boundary boundary dips dips steeply steeplyt to the north. north. Due Due tto nature is sub-vertical sub-vertical and o the o the the gradual gradual nature western boundary boundary is distribution, these assaycutoff.The cutoffThe greatest potential of the PGE PGE distribution, these boundaries boundaries are subject to t o changes changes in assay potential for forexpanexpansion of of resources assuming similar similar continuity continuity of the extent extent of sion resources at at the the Roby Roby Zone, Zone.assuming of grade, grade, is is deepening deepening the of the the Breccia Breccia Ore. Ore. �Palladium The The most mostdefinitive definitive lithological lithologicalcontrol controlon onPGE PGEgrade gradewithin withinthe theRoby RobyZone Zoneisisthe thepresence presenceoro rabsence absenceof ofhetheterolithic-gabbro-breccia erolithic-gabbro-breccia and andaccompanying accompanying varitextured varitexturedgabbro.The gabbro.Thebreccia brecciaisisalways always ore, ore, and and other otherlithologies lithologies are are only only ore oregrade gradewhen when in inproximity proximitytot obreccia. breccia.However, However,mineralized mineralized breccia breccia on o n the the margin margin of of the theRoby RobyZone Zone can contain less than 0.7 g/t Pd.Also, with the exception of post mineralization dykes. every lithology can either can contain less than 0.7 g/t Pd.Also. with the exception of post mineralization dykes, every lithology can either be orwaste. waste.I-Ieterolithic-gabbro-breccia Heterolithic-gabbro-brecciaisiscomposed composedof offragments fragmentsaafew fewcentimetres centimetrestotoseveral severalmetres metresinin be ore oreor size area, size that that are are representative representative of ofmost mostof o fthe thelithologies lithologiesininthe the area.as aswell wellas asaafew fewexotic exoticclast.This clast.Thisbreccia brecciahas hasaa wide spectrum of characteristics. It can consist of sub-angular fragments crowded together with very little matrix wide spectrum of characteristics. It can consist of sub-angular fragments crowded together with very little matrix and to aa breccia of 10% sub-rounded fragments fragments (digested (digestedxenoliths) xenoliths) and and 90% 90%matrix. matrix. A A trantranbreccia consisting consisting of 10% sub-rounded and can can grade grade to sition matrix rich breccia is is observed in in the southern Breccia Ore. Melanogabbro matrix rich breccia observed the southern Breccia Ore. Melanogabbroisisthe the sition from frommatrix matrixpoor poortoto matrix Observed gabbroic gabbroic composition composition for for the matrixand andthe theintrusive intrusivemagma magma creating creating the the breccia. breccia. Observed the matrix matrixin inmany many localocations selectively assayed, tions isisinterpreted interpretedas asaacomposition compositionchange changedue dueto t odigestion digestionofofless lessmafic maficxenolithsWhere xenoliths.Where selectively assayed, the gltPd, Pd,and andthe thefragments fragments0.08 0.08 g/t g/t Pd.This Pd.This explains explains the the observation observation that that matrix matrixpoor poor the matrix matrixwill willcontain contain8 8g/t breccia is usually low grade. Pegmatitic gabbro occurs on the rims of the fragments, as irregular patches and breccia is usually low grade. Pegmatitic gabbro occurs on the rims of the fragments,as irregular patches andveinveinlets lets throughout. throughout. Breccia is transitional transitional into Breccia is into varitextured varitextured gabbro gabbroand and lacks lacks distinct distinct xenoliths.Varitextured xenoliths.Varitextured gabbroic gabbroic rock rock range range in in composition from leucocratic to melanocratic, and some varieties are fine grain with medium grain patches and composition from leucocratic t o melanocratic, and some varieties are fine grain with medium grain patches and veinlets, grain with with pegmatitic veinlets, medium medium grain grain with withcoarse coarseand andpegmatitic pegmatiticpatches patchesand and veinlets, veinlets. and and coarse coarse grain pegmatitic patches patches and Pegmatitic rock rock is occursas asconvex convexmultiple multiplelaylayand veinlets. veinlets. Pegmatitic is more more abundant abundant in in the the central central Breccia Breccia Ore. Ore.Here Hereititoccurs ers, and lenses lensesup upto to several severalmetres metresin inwidth width but but not not laterally ers, dykes dykes and laterally continuous.The continuous.The common common pairing pairing of of the the brecbreccia pegmatitic gabbro gabbro nnot cia and and varitextured varitextured gabbro, gabbro, and and its its associated associated pegmatitic o t only only key key to t o interpreting interpretingthe theprocess processthat that created the the ore, ore. but butalso alsoserves serves as as an important importantassociation association that that guides guides exploration. exploration. The 5%chalcopyrite. chalcopyrite.pentlandite. pentlandite,pyrrhotite pyrrhotiteand andpyrite. pyrite.ItItoccurs occursas asfine fine grain grain The Central CentralBreccia BrecciaOre O r econtain containup uptoto5% disseminations throughout. and as coarse blebs interstitial to pegmatitic clinopyroxene and plagioclase.The fine disseminations throughout, and as coarse blebs interstitial t o pegmatitic clinopyroxene and plagioclase.The fine sulphides are contained contained as asstreaks streakswithin within the the clinopyroxene clinopyroxene pseudomorph pseudomorph that that are are now now composed composed of of actinolite, actinolite, sulphides are chlorite chlorite and and talc.This talc.This late late introduction introductionof ofsulphide sulphideisis synchronous synchronous with with the the alteration alteration of ofpyroxene pyroxene to t oactinolite. actinolite. Twilight TwilightZone Zone The Twilight Zone TheTwilight Zone is is aa new new zone zone in inthe theprocess processof ofbeing beingdelineated delineated by by diamond diamond drilling.This drilling.This zone zone isisseparated separated from the Roby Zone on its western boundary by a 50 to 70 metre thick unit of massive homogenous from the Roby Zone on its western boundary by a 50 t o 70 metre thick unit of massive homogenousbarren barrengabgabbro from the broand and separated separated from the southeastern southeastern extension extension of of the theRoby RobyZone Zoneby byaa50 50metre metrethick thickbarren barrendyke.Twentydyke.Twentytwo t w odiamond diamonddrill drillholes holestotodate datehave havedelineated delineatedaazone zone 100 100 metre metrewide. wide, 200 200 metre metredeep deep and and 200 200 metre metrelong.The long.The zone remains open to the east, and south.This area has the same style of lithological complexity as the Roby zone remains open t o the east,and south.This area has the same style of lithological complexity as the Roby Zone, pegZone, but but isis dominated dominatedby byaaless less heterolithic heterolithicgabbronorite-breccia, gabbronorite-breccia,and and does does not notcontain containvaritextured varitexturedand andpegmatitic matitic gabbro.The gabbro.The most mostsignificant significant mineralization mineralization discovered discovered in in this this area area to t odate datewas was intersected intersectedby byholes holes99-040 99-040 and 99-I 71 This mineralization, containing 0.25% to 0.5 % pyrrhotite and chalcopyrite. assayed 2.38 g/t Pd over and 99-1 71 .This mineralization,containing 0.25% to 0.5 % pyrrhotite and chalcopyrite,assayed 2.38 g/t Pd over I I II 6 metres. metres. �North American America:Palladium Palladium Ltd Baker Z Zone Baker one The Baker surface is one one kilometer kilometereast eastofofthe theRoby RobyZone. Zone.Detailed Detailed surfacesampling samplinghas has defined defined aa mineralized mineralized The Baker Zone Zone is zone that that is wide and traced continuously continuously for for 250 meters. This defined by by is 100 100 meters meters wide and traced 250 meters. This northeast-striking northeast-strikingzone zone is is defined zone assaysgreater greaterthan than0.68 0.68g/t g/t Pd Pdand andgenerally generallycontains containsless lessthan than 11% sulphides.The Themineralized mineralizedrock rockconsists consistsof of assays % sulphides. gabbro, varitexcured varitextured gabbro. and heterolithic-gabbro-breccia.To heterolithic-gabbro-breccia.To date, date, the the highest highest grades are associated gabbro, gabbro, pyroxenite, and with aa pyrrhotite-chalcopyrite samplesover overaa 115 meter length with pyrrhotite-chalcopyriterich richarea areaat ataabreccia/gabbro breccWgabbro contact. contact. Channel samples 5 meter assayed4.69 4.69g/t g/tPd, Pd,0.27 0.27g/t g/tAu. 0.48g/t g/tPC. Pt.0.43% 0.43%Cu Cuand and0.39% 0.39% Ni.A3500 3500metres metres(20 (20holes) holes)diamond diamonddrilling drilling Au, 0.48 Ni.A assayed program conducted conducted during during the the winter winter of program of 1998-99 1998-99 tested tested the the zone zone over over aa 250 250 metre metre strike strikelength, length, tto o aa maximum maximum 200 metres, metres, at 50 50 metre metrespacing. spacing. depth of of 200 Moore Moore Zone Zone area 600 600 metres metres south south of of the the Roby Zone poorlyexposed exposedmineralized mineralized area area in in aa swampy area The Moore Moore Zone Zoneisis aapoorly Mineralization has hasbeen beenuncovered uncoveredin inan anarea area 100 100by by200 200meters metersand andappears appearstotohave havea aNW NW strike strike boundary. Mineralization basedon on the the alignment alignmentof of aa sulphide sulphiderich rich zone. zone. Where Where best exposed the the mineralization consist of of heterolithicheterolithicbased best exposed mineralization consist with less less than than 1% 1%disseminated disseminatedpyrrhotite pyrrhotiteand andchalcopyrite.An chalcopyrite.Aninterval intervalofofnorice norite within within the the gabbro-norite-breccia with breccia contains contains 22 to to 5% 5% pyrrhotite pyrrhotite and interval generated generatedfrom from diamond diamond drilling drilling is is and chalcopyrite.The chalcopyrite.The best best assay assay interval 24.3 meters meters grading I .39 g/t g/t Pd+PC+Au, Pd±Pt+Au, 0.29 0.291% Ni, and and 0 0.3 I 2%Cu. Cu.On Onthe the basis basisof of 17 diamond diamond drill drill holes, 24.3 grading 1.39 1% Ni, .3 12% holes, itit is is interpreted that interpreted that the theMoore MooreZone Zoneisisrod rodshaped, shaped,and and has has maximum maximum dimensions of 22m x 45m x 90m 90m deep. deep. �LH r Palladium Pafladium Ltd Northi American Geology of of the the Lake Lake Superior Superior Region Region , _ r -' • BuKkflr pN a 'i . Tc' ,\&wt3 çfra q Wi 80 km radius "( tii2f' t 'fl (Ii. 1 . . . . . . . . . . . METAL> FOR CLEAN AIR PAGE 7 . . ... . . . . .. .. . . . . .. .. . .. : �.. .,.. . . .. . . .. . . . . . C) cf 3 F EL SO D n (D -J .. Ct- North American . . PalladiumLt / .... Geology and mining claims of the Lac des lies area . .. ... . . . . . PAGE:a . . . . . .. . . . . . . . , ... . . . . .. ... . . . . .... . . . . . . . . . . . E T A L S F O R CLEAN A m . .. ... . ,,. . �. .. .. . . . North American Ltd. North ~ m e r i c Pallad:ium aPalladium ~ Ltd., Geology of the Lac des lies complex ...... ... . .. . �. . . Geology of the mine complex . . . ...... . North American Palladium Ltd. 1 �r a N Geology of the Roby Zone ......... 9 .. .. . it r Th / North American Palladium Ltd. �P Norite; equigranular Gabbro-norite; equigranular Meianogabbro-norite (10-35% plag) Ilelerolithic gabbro-norite breccia Gabbro; varitexiured Gabbro;equigranular Incipient heterolithic gabbro breccia Heterolithic qabbro breccia Leucogabbro/East Gabbro Anorthosite (<10% matics) Leucogabbro; porphyrltic Leucogabbro; varitextured Mine Sequence Felsic Dyke Folsic Plutonic Rocks U 025 U 04 Pyroxen lie Heterolithic melanogabbro breccia Melanogabbro Breccia Dykes •I Matic dykes (minor, narrow) lJ LI n 9 EEl lCd •J_ Archean LI Diabase Diabase Breccia Prot€iozolc 0 meters 12.5 Detailed geology, South Roby Zone 25 tit E 2 01 a In -J > if 7 North American Palladium Ltd. �I Surface South Roby RobyZone Zone (overlay (overlay on on "Detailed "Detailed geology, South Roby Zone") SurfacePd Pdassay, assay, South geology, South Roby Zone") Pd Grade 5 >5.0 g/tonne 5 2.50 to 5.0 g/tonne 5 0.70 to 2.50 g/tonne 5 0.35 to 0.70 g/tonne S <0.35 g/tonne z 0-5 > 0 12.5 meters w S mi U 0 00 25 SOUTH ROBY PIT (0 -5 n CM C, 31750 N 1) B �a F as -Q > 7 2 -J c3j fl 3 1 Roby Pit Level Plan Grade Model 0 North American Palladium Ltd 1' . . . PAGE'1.4 . . . .. . . . . . . ' . . . . .... ... . . . . .., .. + O K CLEAN A I R . .METALS . .... .. ..... . . . . .... . . . ., �-r Oeet burden ODD-i collar with driltitole taco downhote 0 25 SC. metera 15 . . . . . '---ft Oetirie 01 Proposed Pit Oetbne ot Current Pit and SurDace Pd Grade - 035 Do 0.70 gltortne Pd Grade - 0.70 to 2.50 g'tonne Pd Grade - 2.50 to 5.0 ylronne Pd Grade >5.0 gilcoine ' LEGEND ' e 0 0 . 20Dm 0 2 z 0 1 . . . .. . . . . 30Dm 400,0 A Roby Zone Grade Model Cross Section 509 N > IT North AmericanPallad:i.umLtd. F n (D 3 -I . . . . . . . . .. . . . .. . . . . �GEOARCHAEOLOGY AND DEGLACIATION GEOARCHAEOLOGY HISTORY OF AREA HISTORY OF THE THE THUNDER THUNDER BAY BAY AREA Brian Phillips, Lakehead University Scott Hamilton, Hamilton, Lakehead Lakehead University Joe Stewart, Lakehead University University Joe Stewart, Lakehead Pat Julig, Larentian University Pat Julig, Larentian University Bill Ross, Ross, Ontario Ontario Ministry Ministry of of Citizenship, Citizenship, Culture and Culture and Recreation Recreation Soon after after deglaciation, deglaciation, native nativepeoples peoples established established habitation habitation Soon examine how how the the local local geomorphology geomorphology will examine sites. This trip will these sites sites and and the the nature nature of of controlled the location of these human activities. activities. �Forty-Sixth Annual Meeting Forty-Sixth Meeting Institute on Lake Superior Geology Thunder Bay, Ontario, May 8-13th, 2000 PRE-MEETING FIELD TRIP 3 PRE-MEETING - Geoarchaeology of the Thunder Bay area - Field Guide Dr. Brian Phillips, Department Department of Geography, Geography, Lakehead Lakehead University. with Dr. Joe Joe Stewart, Stewart, Department of Anthropology, Anthropology, Lakehead University. Hamilton, DeDartment Department of Anthro~oloav, Anthropology, Lakehead Dr. Scott Hamilton. Lakehead University Universitv Dr. Pat Julig, Julig, ~ Department of Anthropology, Laurentian University e ~ a r t m e n t~ n t h r o ~ o lLurentian o~~, Mr. Bill Ross, Regional Archaeologist, Ministry Ministry of Culture Culture and and Recreation. Recreation. - Objectives: Objectives: field trip tripwill willfocus focuson onthe thedeglaciation deglaciationand and lake lake level level history history of of Thunder The field Bay and the area immediately to the west of of the thecity city -the the Kaministiquia Kaministiquia river river valley, Kakabeka Falls Falls and and the Marks Moraine. evidence of of Paleoindian Kakabeka Moraine. In particular, particular, evidence presence associated with the abandoned shorelines, river mouths and deltas associated with shorelines, river deltas of the 9.5 ka ka B.P.) will be examined examined (Figure (Figure 1). 1). Lake Minong stage of Lake Superior Superior (circa (circa 9.5 The trip trip will will start startby byaa visit visit to to the the former former mouth mouth of of the the Current Current River River at at the the north north end of the city, where the Simmonds and McDaid McDaid sites, both surface sites, are located. Then Then the trip will head head west, west, up valley, to the more famous Cummins site, a site,part partofof which which is is preserved preserved within aa fenced area. area. The third area to be be stratified site, the western extent of Lake visited will be the Rosslyn delta, on the Kam river, visited Rosslyn delta, the Kam river, the western extent of there the the trip trip will will travel travel west west to toKakabeka, Kakabeka,where whereearlier earlierLake Lake Beaver Beaver Minong. From there Bay features will be examined. Finally, the trip will mount the Marks moraine, features examined. Finally, trip will mount the Marks moraine, that will place the days observations in context with pre pre and post providing a view that Marquette ice marginal events and Paleoindian Paleoindian presence. - Introduction strongthough though not notexclusive exclusiverelationship relationshipofof Paleoindian Paleoindian habitation habitation There is aa strong in the Thunder Bay area areawith with the the shoreline shoreline features features of of the the post-glacial post-glacial lakes of of the Superior basin, particularly those those of of Lake Minong, established about 9.5 ka ka B.P. B.P. This is perhaps illusory in that they they occupied occupied aa number number of of habitats, habitats, some some far far from from aa lakeshore, but but in geomorphological mapping of of these these shorelines, it is these sites lakeshore, which have been most commonly found and reported. have been most commonly since early early excavations excavations by by MacNeish MacNeish (1952) (1952) by by both Evidence accumulated since amateur and professional archaeologists (Fox 1975, 1980: amateur archaeologists (Fox 1980; Dawson 1983; Julig, Julig, PIano Indians migrated north eastwards from from the the area area of of Dakota Dakota 1984) suggest that Piano cul-de-sac formed formed between between Lake Lake Agassiz, Agassiz, which which covered and Minnesota into the cul-de-sac of Manitoba and parts of Northwestern Ontario at at its maximum Northwestern Ontario maximum extent, extent, the most of lakes of of the Superior basin and the retreating margin of of the Laurentide ice sheet. These people, people, derived derived from from plains plains cultures cultures characterised characterisedby byaa fluted fluted point point lithic These �Sturgeon Pt u4ittgleton I _ p. uneII 1: Keeter T hn,e,r 250,000 tIIand .- B atne .t--- Li CT 1.tAdcKeIIAr Greenetone Pt T ARTHUR r 165 are Pt - S ç1\, - �technology, probablyfollowed followedgame gameinto intothe the area area as as hunters, technology, probably hunters, but but in in staying, staying, to form and in their diversified diversified in in their economic economic activities activities and their tool-kit tool-kit design, design, to form a a recognisable "Interlakes Composite" Composite"(Ross, (Ross,1994) 1994)characterised characterisedby byaa parallel recognisable "Interlakes flaked making particular particular use use of of the flaked point point lithic lithic technology, technology, making the red red (jasper) (jasper) taconite taconite material material found in the siliceous Gunflint Gunflint formation that outcrops in the Thunder Bay Bay area. area. Deglaclation Deglaclatlon HIstory History The broad details of of the the deglaciation of the the Superior Superior basin basin are are shown shown in deglaciation of Figure 2. As ice central of the the Rainy Rainy River River and and Superior Superior lobes lobes withdrew withdrew from from central Figure 2. ice of Minnesota, series of of recessional moraines were were left left in in place. recessional moraines place. The The Vermilion Vermilion Minnesota, aa series moraine, trending northwest northwest to southeast, southeast, across northeastern northeastern Minnesota, Minnesota, was was followed on the Canadian Canadian side of the border, and and the followed by by the Steep Steep Rock Rock moraine on Brule moraine (Figure (Figure 3). 3). Guided Guided by by these these ice Brule moraine ice marginal marginal positions, positions, Lake Lake Agassiz Agassiz found found an an early early eastern eastern outlet outlet through through the Arrow/Whitefish ArrowiWhitefish lakes corridor (circa (circa 11 11 ka and, shortly after, after,through throughthe theShebandowan Shebandowan lake corridor, corridor, ultimately ultimately using ka B.P.) B.P.) and, the Lake Lake Nipigon Nipigon spillways spillways around around 10.4 10.4 ka ka B.P. B.P. (Figure (Figure 2a) to enter enter Early Early Lake Lake Minong Minong (Teller, 1985) which occupied occupied the Superior Superior basin. basin. There is no to believe did not There is no reason reason to believe that that the the warming warming climate climate did not permit permit environmental conditions conditions to to become become suitable suitable for for the the immigration immigration of of animal animal herds and prehistoric peoples into the Thunder Bay region at this time. Only tenuous prehistoric peoples into the Thunder Bay region at time. evidence of such early occupation has been reported (Phillips, 1993: Ross, occupation reported (Phillips, 1993: Ross, 1994), 1994), evidence though corridor has has confirmed confirmed aa number of sites though recent recent work in in the Arrow/Whitefish ArrowIWhitefish corridor sites that most likely represent earlier Paleoindian presence. (McLeod and Phillips, represent an earlier Phillips, 1999). pers. communication, 1999). A major event in the the deglaciation deglaciation history of ofthe the Lake Lake Superior Superior basin basin was the the Marquette readvance readvance (9.9 (9.9ka ka B.P.), B.P.),during duringwhich whichthe the basin basin and and its margins were briefly reoccupied by ice (Figure 2b). Recessional of the Brule Recessional moraines northeast of moraine formed in in their their place. This event moraine were destroyed destroyed and and more more recent features formed of archaeological implications, implications, since since any also also has has considerable considerable archaeological any evidence evidence of occupation prior to to the the Marquette Marquettereadvance readvanceisislikely likelytoto have have been been buried buried or or occupation prior destroyed destroyed completely completely by by the the new new ice ice cover. cover. Hudson Bay ice pushed southwestward southwestward into into the the Lake LakeSuperior Superior basin, basin, to to halt on its southern shore (Drexler, (Drexler, Farrand Farrand and and Hughes, Hughes, 1983). 1983). Only in in aa small small portion of Whitefish Bay near near Sault Sault Ste. Ste. Marie, corner of of the basin, did Whitefish Bay Marie, in the southeast corner did Early an open 1985). The Early Lake Lake Minong Minong remain remain an open lake lake (Farrand (Farrand and andDrexler, Drexler, 1985). Marquette lobe pushed westward against against the the steep steep Minnesota shore shore and, and, where flowed northwest up up the the Kaministiquia Kaministiquia valley valley to the Marks moraine less obstructed, flowed moraine (Figure (Figure 3). This Thisprominent prominentridge, ridge,rising risingto to over over 470 470 m m (1550') (1550') in in places, places, curves curves from Lappe through and around around the the northwest of Kakabeka towards the the through Mokomon Mokomon and northwest of Kakabeka towards Pigeon River (Zoltai, l965b; Burwasser, 1977, 1980; Burwasser and and Pigeon (Zoltai, 1963, 1963, l965a, 1965a, 1965b; Ferguson, 1980). Contemporaneously, to the the west west of of the the Lake Lake Superior Superior basin, the Patricia ice lobe pushed district and and halted to to deposit the pushed towards the Rainy Rainy River district Dog Dog Lake moraine. This This runs runs northwest northwest from Lappe and holds up Hazlewood, One of Lappe, Lappe, where where the two moraines meet, a Hawkeye and and Dog Doglakes. lakes. East of Island, Hawkeye line of glacial debris known as the Mackenzie interlobate moraine can be known Mackenzie be traced traced �Figure Figure 22 The TheGlacial GlacialPeriod Periodand andEarly EarlyPeoples Peoples d) km Figure 1: The retreat of the glaciers in the Superior region nbetween between10,400 10,400and and9,500 9,500year yearago. ago.(from (from Phillips, Phillips, 1993, p. 95) �Figure Figure33 - -.... o0 • to . .-..- . . .. . .. . .. . . . .-... .... ....- . -. . . . - ... . . ... 4 0ma.. mile 40 I area showing moraines moraines and Mapof ofthe theQuetico—Nipigon Quetico-Nipigon area and direction direction of of ice ice movement movement FIG.5.5. Map Fm. duringvarious variousphases. phases. during - from from ZoItal, Zoltai, 11965a) 965a) �through Pearl and and on to through Pearl to the the Black Black Bay Baypeninsula. peninsula. A glacial glacial lake, lake, Lake Kaministiquia, was formed formed between between the the two two ice margins 1985) and, and, at Kaministiquia, was margins (Teller, (Teller, 1985) Lappe, off the the Lappe, a huge sand sand and gravel gravel delta delta was was built built by bysediment sediment pouring pouring off interlobate of debate, however, and and there there interlobate moraine. moraine. This Thisscenario scenarioisisstill stillthe the subject subject of is some the Marks and Dog may be older some field field evidence evidence that that the Marks and Dog Lake Lake moraines moraines may older features that that were were simply reoccupied reoccupied by ice ice ofofthe theMarquette Marquetteadvance advance(Jul19, (Julig, Lake McAndrews and Mahaney, Mahaney, 1990; 1990; Tickle, Tickle, 1996; 1996;Noble, Noble,pers.comm.1999). pers.comm.1999). Lake Agassiz, deprived advance of of the the ice, ice, expanded expanded in area area deprived of its its eastern outlets by the advance and depth (the Emerson phase), and flooded catastrophically through depth Emerson phase), and flooded catastrophically through the the Clearwater Saskatchewan and the Clearwater and and Athabasca Athabasca valleys valleys in in Saskatchewan and Alberta into the Mackenzie Mackenzieriver river and and the the Arctic Arctic ocean ocean (Smith (Smithand andFisher, Fisher,1993). 1993). The of Lake Lake The Marquette readvance obliterated evidence of the earlier phase phase of Superior's shoreline history in most of the basin. Shoreline sites that prehistoric basin. Shoreline sites that prehistoric most people people might might have have occupied in in the area of Thunder Bay before 9.9 ka B.P. B.P. may lie lie buried beneath Marquette deposits. In the four hundred years between 9.9 and 9.5 buried beneath Marquette deposits. the four ka B.P., about which which much more is known, B.P., aa period about known, ice withdrew from from the Lake Lake Superior basin (Figure 2c/2d). Then, again, Paleoindian people followed game up 2cl2d). Then, again, Paleoindian up Superior basin the Interlakes this time time to to settle, settle, in in part at Interlakes corridor and into the Thunder Bay region, this least, on the shores shores of of Lake Beaver Bay (Stuart, 1993) and Lake Minong Minong (Phillips, (Phillips, 1988). 1988). Shoreline Shoreline History History At At the peak peak of of Wisconsinan Wisconsinan glaciation, glaciation, the the northeastern northeastern margin of the the Lake Lake Superior was depressed by the the weight to a ice (isostatic (isostatic depression) depression) to Superior basin was depressed by weight of ice greater degree than the less heavily ice-loaded southwestern side. As a result, than the less heavily ice-loaded southwestern side. result, "rebound" (isostatic (isostatic recovery) since that time has been greater on the north north shore shore of the Lake Lake Superior Superior basin basin than than on on the the south south shore. shore. Lake shorelines which had had been originally originally horizontal horizontal became became progressively progressively tilted tilted along along an an approximate approximate northeast such that that aa shoreline shoreline of of the the same same chronological age increases in northeast axis, axis, such altitude northeast along along the western western shore shore of of Lake Lake Superior. Superior. AA altitude from from southwest to northeast theoretical archaeological site at Grand Marais, Marais, Minnesota, found at 184 184 metres, metres, just theoretical site just above abovethe the present present storm beach, will be of similar age to another theoretical site in contour (1 (117 in Terrace Terrace Bay, Bay, Ontario, Ontario, at the 300 metre contour 17 metres above the the present present lake), lake), with with both both sites sites lying lying on on the the same tilted tilted shoreline shoreline (Figure (Figure 4). As As the the Marquette Marquette ice ice lobe lobe wasted wasted back, the eastern and western sides sides of of the the basin (Figure 2c). 2c). On basin were exposed as separate entities (Figure On the eastern eastern side, a fairly fairly stable Mary's River outlet at Sault stable Lake Lake Minong, controlled by the height of the St. Mary's Ste. Marie, extended northwards up the Ontario shore and westwards along the the Michigan (Farrand and and Drexler, Drexler, 1985). 1985). Michiganshore shore as as they were exposed by by melting melting ice ice (Farrand In succession of of ever ever larger but In the enclosed western end of the basin, a distinct succession progressively lower level progressively lower level lakes lakes formed formed (Lakes (Lakes Duluth, Duluth, Highbridge, Highbridge, Moquah, Moquah, Washburn, Manitou, and and Beaver Beaver Bay), each extending Washburn, Manitou, Bay), each extending further further northeast northeast up the the Minnesota Minnesota - Ontario Ontario shore shore and east east along along the the Wisconsin Wisconsin shore shore (Farrand (Farrand and and Drexler, of these these water bodies bodies were formed Drexler, 1985). Along Along the the land-based land-based margins margins of various features, such as bluffs and beaches, by which the shorelines can various coastal features, can be ice vacated vacated the basin, basin, the the eastern eastern and and western western lakes lakes were were be traced tracedtoday. today. As ice �Figure Figure44 Shoreline ShorelineDiagram Diagramfor forthe thePigeon PigeonRiverlThunder RiverKhunderBay BayArea Area 1400 a; S I H (fromFarrand, Farrand,1960) 1860) (from FIgure Figure 55 ofpotential Figure pre-Nipissing transgression Figure10: 10:The Thepre-Nipissing transgressionand andthe theresulting resulting loss loss ofpotential archaeological archaeologicalsites sitesalong alongthe theshores shoresof ofLake Lake Superior Superior,(from (fromPhillips, Phillips, 1993, 1993, p. P. 100) 100) �united and the single shoreline of Lake Minong was formed around around the the basin basin about about (Figure2d). 2d). For the the next next 1,500 1,500years, years,water-levels water-levelsininthe the Lake Lake Superior Superior 9.5 ka B.P. (Figure basin declined as the St. St. Mary's Mary's sill sill was was eroded eroded down down to to bedrock. bedrock. A staircase of of Post-Minongshorelines shorelineswere wereformed, formed,the thelast lastand and lowest lowest ofof which which was was Lake Post-Minong Lake Houghton, about 8.0 ka B.P. Houghton, about 8.0 ka B.P. By 8.0 8.0 ka B.P., due to isostatic uplift, the the rising levels of of Lake Huron Huron had had By B.P., due isostatic uplift, flooded into the St. St. Mary's Mary's River River and and reversed reversed the the flow flow (Larsen, (Larsen, 1987). 1987). This backThis backflooding led Lake Superior Superior basin basin and and culminated culminated flooding led to slowly rising water-levels in the Lake in the Nipissing lake stage around 5,000 years years B.P.. B.P.. Known as the pre-Nipissing pre-Nipissing transgression, this rise in in water-level water-level was was imposed imposedupon uponaastill-tilting still-tiltingbasin. basin. On On the the north shore, shore, east east of of Dorion, Dorion,the therate rateofofisostatic isostaticuplift upliftremained remained more more rapid rapid than than the waters of of the the pre-Nipissing pre-Nipissing period, period, with with the the result result being being that that the the shoreline rising waters marking the Nipissing lies at at a lower all older older marking Nipissing maximum maximum level level lies lower altitude altitude than than all shorelines, including that of of Lake Lake Houghton. Houghton. On the south shore the pre-Nipissing pre-Nipissing transgression was more rapid than isostatic recovery, and wave action "inherited" rapid isostatic "inherited" the features of older older shorelines, shorelines, modifying modifying and and destroying destroying portions portions of them, them, the features of including pre-existing pre-existing shoreline shoreline archaeological archaeological sites sites(Phillips, (Phillips,1977). 1977). This This causes causes a chronological discontinuity which which is at its its greatest greatest near Duluth Duluth and and decreases decreases towards Dorion where the Houghton shoreline shoreline appears appears above above the the present waterlevel (Figure (Figure 5). 5). Thunder Bay, Bay, evidence evidence of of Paleoindian would normaliy Paleoindian activities activities would normally have have In Thunder been traced as aa continuum continuum from the high high Minong Minong shoreline shoreline to to the the Houghton Houghton (which lies just (which just below below present present water-level), water-level), but but the the pre-Nipissing pre-Nipissing transgression transgression reoccupied the the lower lower and and later later part part of of that that record record and and cut cut a prominent reoccupied prominent bluff on on which the General St. Joseph's Joseph's Hospital, Hospital, and Lakehead General Hospital, the Court House, St. Lakehead University are are built. built. The Nipissing shoreline can be traced traced up up the valley valley towards University Thus, the the later later part part of of the Mapleward road and across across towards towards Mount Mount McKay. McKay. Thus, record, the the important important transition transition into into the the Archaic Archaic period, period, and and aa good Paleoindian record, portion of the early Archaic is is missing missing in in Thunder Thunder Bay. Bay. portion Local HIstory History an interpretation of of the the detailed detailed history of of the the withdrawal withdrawal Figure 6 represents an of Superior (Marquette) ice from from the Thunder Thunder Bay area, area, based on currently known information, though though subject to As ice wasted information, to revision. revision. As wasted back back from from the Marks Marks Moraine, shorelines shorelineson onthe thesouth southside sideofof the the moraine moraine show show that that aa body body of of water water Moraine, between the the moraine moraineand andthe theice icefront front(Figure (Figure6a). 6a).This This proglacial proglacial lake lake collected between and there there is is tenuous tenuous evidence evidence has been named Lake Cedar Creek (Jahnke, 1993), and that with high high level level lakes Lake Duluth Duluth that it connected connected with lakes to the the south, south, perhaps perhaps of Lake Kaministiquia embayment embayment aa small equivalence. As ice equivalence. As ice withdrew withdrew from from the the Kaministiquia small The higher higher levels of of lake readvance to the Intola Moraine occurred (Figure (Figure 6b). The been traced traced into into this this moraine moraine (Stuart, (Stuart,1993), 1993),and andititisis likely likely that that Beaver Bay have been Paleoindian time, probably using the Marks Paleoindian peoples peoples entered entered the area at about this time, Marks causeway. As As ice ice withdrew withdrew further further and and water water level level declined declined to to the moraine as a causeway. of lake Beaver Bay (Figure 6c), the possibility of Paleoindian lower lower levels levels of lake Beaver Bay (Figure 6c), the possibility Paleoindian in the the occupation increases, increases,and and by by the the time Lake occupation Lake Minong Minong was was established established in Kaministiquia embayment, embayment,there thereisisplenty plentyofof evidence evidenceto to prove prove their their presence presence Kaministiquia �Figure Figure 66 An history in in the Bay area. area. An interpretation Interpretation of of post-Marquette post-Marquette history the Thunder Thunder Bay (a) Marquette toe and Proglaciat Lakes area 9,800 years 8.P (b) Intola Moraine Moraine and Upper Upper Lake Beaver Bey Bay circa circa ( bl irrtola 9,700 years years B,P. 9.700 B.P. Hudson Bay t.obe - KaWA7 M s—ar S.—, * — ;8.s'.a.yr — Uporlor Lobe'. 1= ,1-..t22i (c) Lower Cc) LowerLake LakeBeaver BeaverBay Baycirca circa9.600 9.600years yearsB.P. 89. Cd) Lake Minong, 9,500 years B.P. (from Phillips, Hill, Fralick Fralick and Ross, Ross, 1994) 1994) I �(Figure 6d). 6d). The withdrew from The shoreline shoreline diagram diagram (Figure (Figure 4) shows that only as ice withdrew sequence of post-glacial the Thunder Bay region did the sequence post-glacial takes lakes extend into the area. Beaver Bay shorelines shorelines can can be be found found at at Kakabeka, Kakabeka,but butonly onty the the lower tower levels levels extend eastwards eastwards through through the the city towards the Mackenzie Mackenzie River. River. A few notable sites associated with the Minong shorelineare arethe the Simmonds Simmonds A few notable sites associated with the Minona shoreline sites at at the the mouth mouth of of the the Current Current ~ River, Catherine and and McDaid sites i v e r the ,the Biloski, Biloski, Catherine Cummins sites sites along along the north side side of of the Kam embayment, embayment, and and the the collection of on the the Rosslyn Rosslyndelta deltaat atthe themouth mouthof ofthe the Kaminsitiquia Kaminsitiquia River, River,though though here here the the sites on association is less simple and deserved more analysis (Hamilton, 1996). Some association analysis (Hamilton, Paleoindian sites unrelated to to shorelines shorelines occur occur at at High High Falls Falls on on the the Pigeon river, 1982), at at Harstone Harstone Hill, Hill, near near the the junction junction of of the Whitefish on Dog Lake (McLeod, (McLeod, 1982), rivers and and near near Kakabeka Falls where where the the Kaministiquia Kaministiquia river river and Kaministiquia Kaministiquia rivers Kakabeka Falls might have been most logically logically crossed. crossed. The Crane site near Kakabeka, found The Crane found in a garden, provides providesaa rich richcache cacheofofbeautifully beautifullycrafted crafted10 10cm cmbiiaces bifacesin in aa vegetable garden, location apparently unrelated unrelated to to any any topographic topographic feature, feature, though though on on the the surface of of Beaver Bay Bay terraces. one of the higher Beaver Because of their antiquity and the acidic Because of their acidic nature nature of of the the Boreat Boreal forest forest soils, soils, (Figure 7), 7), though though itit is is very very only the lithic materials remain to be found at these sites (Figure likely that many other natural materials would have been been used used by these peoples. Field Excursion Stops - Stop 11 - Hillcrest Stop Hillcrest Park Park Lookout. from the the University will will be down Oliver Road and, and, just just below betow the The route from bluff, left left on on High High Street Streetand and up upthe thehill hill for for aa brief visit to Hillcrest Nipissing bluff, Hillcrest Park Park from where where the the city city can can be seen and Lake from seen in in context context with with local local topography topography and Superior. Superior. - Boulevard Park, Park, the the Bluffs Bluffs and and CentennIal Centennial Park Park Rd. Rd. Stop 2 and 3 - Boulevard will head northeast on on High High St., St., over overthe theSt.Joseph/Hillcrest St.Joseph/Hillcrest island island The route will lefton on Balsam BalsamSt, St,right righton onHudson HudsonAve Aveand and onto onto Arundel Arundel St. from from of Minong times, left which a left turn before Black which Black Bay bridge will lead lead to to the the Bluffs Bluffs Scenic Scenic Lookout. Lookout. Walk down to Simmonds site. Then board to cross Black Black Bay Bay bridge bridge and and turn turn left left on on Walk Centennial Park roadway. Centennial Park Rd Rd to visit the McDaid McDaid site, adjacent adjacent to the roadway. Simmonds (DcJh-4) and arid McDaid McDaid (DcJh-16) (DcJh-16) Sites Sites The Simmonds present Current Current river riverruns runsin in aa channel channel incised incised into into a gently lakeward The present formationthat thatfronts frontsaa bounding bounding rock rock wall, wall, a structural dipping shelf shelf of of Gunflint Gunflint formation structural feature, which now forms the 'bluffs' In the Minong feature, which 'bluffs' scenic scenic lookout lookout (Figure (Figure 8). 8). In Minong river carried carried much muchwater waterand andsediment sedimentfrom frominland inlandproglacial proglaciallake lake flows flows period, the river of coastal coastal history, a series and here evidence evidence supports supports a major 'bar building' building' phase phase of spits or or bars being being formed formed on on both both sides sides of of the the river riveras as water water level of river mouth spits generally declined. generally The highest lay against the bounding at The highest Minong Minong shoreline shoreline lay against the bounding rock rock wall at approximately the the 252 252 m m (827') (827') level level but but between between 240 240 and and 236 236 m (787-774') (787-774') a approximately of sand sand bars bars formed formedparallel parallel to to the the wall wall on on the the west west bank bank of of the the river river and and a series of matching series seriesofofbars barson on the the east east side side curve curve sharply sharply into into the the then then river mouth matching �Figure Figure 7 7 Paleolndlan bifaces from the Paleoindian blfaces the Thunder Thunder Bay Bay region. region. THE LAKEHEAD LAKEHEAOCOMPLEX COMPLEX —REFINED -REFINED BTFACES BIFACES — - DaJn—7 DfJg—1 Quetico Park Oliver O l t v e rLake Lake DeJj-6 DcJi—1 4% I'" OdJf—I tT;.rJTH:::i;:::tc:: OdJn— 7 DdJn—7 1995) (from Ross, 1995) �Figure 88 MOUTh Figure 9: The The changing changing geography geography and and present present characteristics characteristics of Figure of the and sites. (fivm Phillips,1988, 1988, p. p. 135) ~Simmonds i k n d and s ~McDaid c ~ asite; i d (from~hillips, LATER 4O RE LINE A. UPPER MINONG 250fl!m F .SLAOOO\ R.POSTMINONG SERIES OF MAJOR •ARS + FLAT SWALE • EASTERN 'US FORMEDPOST MINONG 217215n, 'F ALLUVIUM .&rMARSH C —Cr— CREST Pr CUFF u,4. DIRECTION OF SLOPE MODIFIED �from aa source source on on the thesame same rock rockwall wall east east of of the the point point where where itit is It from is cut cut by by the the river. river. It appears that the river entered Lake Minong along the rock wall, forming offshore appears that the river entered Lake Minong along the rock wall, forming offshore and beach and beach bars bars which which extend extend south south eastwards eastwards across across the the shallow shallow McVickers McVickers embayment to the southwest. Simultaneously, longshore transport embayment to the southwest. Simultaneously, longshore transport from from the the east east built bars partially across the river mouth at times, only to be later truncated by built bars partially across the river mouth at times, only to be later truncated by fluvial fluvial action. action. The Simmonds site site on on the the west west side, side,occurring occurringon on the the parallel parallel bars bars at at about about The Simmonds 236 m is matched in elevation and position position by by the the McDaid site on on the 236 m (774') (774') is matched in elevation and McDaid site the eastern curving bars bars (Figure (Figure 9). 9). Neither Neither site site is is aa long long term term habitation habitation site site but but show show eastern curving evidence of activity typical typical of of aa river river mouth mouth camping evidence of activity camping and and fishing fishingsite. site. Interestingly, Interestingly, the to have to the the the major major bar bar building building episode episode appears appears to have been been just just subsequent subsequent to occupation of these these two two sites, sites,two twolarge largecurving curvingbars bars being being formed formed at at 231 231 and and 227 227 occupation of m (758-745') flat topped one largely m (758-745') on on the the east east bank, bank, the the latter latter flat topped one largely aa subaqueous subaqueous feature that that was was probably probably contemporaneous contemporaneous with with the the supra-aqueous supra-aqueous ridge ridge form form of of feature the first. On the west bank a very long bar, now unfortunately truncated at its river the first. On the west bank a very long bar, now unfortunately truncated at its river mouth In south west, west, in in places places broadening broadening to over 100 (328') in end, runs mouth end, runs south to over 100 m m (328') in width. width. In almost text-like manner, the mean grain size and sorting characteristics along its almost text-like manner, the mean grain size and sorting characteristics along its length out from from the length confirm confirm that that itit prograded prograded out the mouth mouth across across the the McVickers McVickers embayment, probably mostly in subaqueous form. Some evidence of Paleoindian embayment, probably mostly in subaqueous form. Some evidence of Paleoindian activity has has been been found found on on the the crests crestsofofthese thesenewer newerbars barsbut butno no sites sites equivalent equivalent to to activity those those named. named. - Stop 4 Stop 4 - Mapleward Mapieward Road, Road, the the Cummlns Cummins Site. Site. The route to Balsam The route will will retrace retrace to Balsam and and join join the the Expressway Expressway heading heading southwest. Just Just beyond beyond the the John John St. St. traffic lights the the route southwest. traffic lights route crosses crosses the the Mcintyre Mclntyre River. On On the the north north side side the the low bluff will will be River. low Minong Minong bluff be seen, seen, with with aa housing housing development on on top. top. The The Biloski Biloski site siteoccupies occupiesthis thissurface surfaceand andaa small small sand sand bar bar at at development the bluff bluff foot, foot, where where a a small small embayment embayment and the and secondary secondary river river channel channel once once existed. existed. As the the Expressway Expressway curves curves to to the the south, south,the thearea areaon on the the right right holds holds a As a lengthy lengthy baymouth bar on the end of which lies the Catherine site, unseen from the baymouth of the road. On the summit summit of of Rabbit RabbitMMt (275m, 902'), 902'), which which rises t. (275m, rises behind behind the the embayment, embayment, lies lies the the the Irene site, a lookout lookout site. site. The route route turns turnswest weston on Oliver Oliver Road Road and and within within 22 km km rises The rises up up the the distinct distinct Minong bluff. A left turn on Mapleward Road sees a gentle descent to the Minong bluff. left turn on Mapleward Road sees a gentle descent to the Minong Minong shore again, and and the the Cummins Cummins site. site. Cummins Site 1) The Curnmins Site(DCJi(DCJi-l) By far far the Paleoindiansite site isis that that of of the By the most most significant significant Paleoindian the Cummins Cummins site site (Figure 10). Reported the site site has has been been excavated excavated and and Reported by by a local local collector collector in in 1962, 1962, the considered a has been the focus of thorough thorough examination. examination. Initially Initially considered a typical typical surface surface site, Julig Julig et et al. al. (1986) (1986) concluded concluded that that itit is is a a rare deeply stratified site, stratified Paleoindian Paleoindiansite, site, under use over over a under continued continued use a long long period periodof ofchanging changingenvironmental environmentalconditions. conditions. Though the the basic basic tool tool kit Though kit is is that that of of Plains PlainsPiano Pianoculture culture(Dawson, (Dawson, 1983; 1983; Julig, Julig, 1984), the the wide wide range range of of artefacts artefacts imply imply a a diversification diversification into into woodworking, woodworking, fishing fishing 1984), and beaver trapping in in addition addition to to the and beaver trapping the regular regular hunting hunting of of caribou caribou and and perhaps perhaps bison (McAndrews, (McAndrews, 1982). 1982). The The Cummins Cummins Site Site was was a major regional tool tool making making �Figure 9 tHE MCDAID SITE — geamorphologicl basis and archaeological test and transect locations PT — Pathway V metres • — Shovel • - Excavation in path U — Feature 'Ill' — Culling leil I sites — ((napping 'lotion - Spot height (in metre,) S Beach ridge axis —— — — Swale axis 236.6 236 6? baseline conlrol pabst — Elevation 0236 .7 transect A a I (from Stewart, Ross and Phillips, 1984) �and the the presence of of exotic exotic lithic components components implies implies aa broad geographical centre and interaction interaction with other groups in in the region region (Julig, 1984). 1984). While the the archaeological archaeological value value of of the Cummins Site was being While being revealed, revealed, broader questions questions remained remainedconcerning concerningthe thechoice choiceofofthis this and and other other sites sites for broader habitation, habitation, especially especially in in relation relationto to lake lake margin margin history. history. The Cummins CumminsSite Site occurs occurs across across the the surface surface of of several several large large sand sand and The which trend trend northeastwards from from the the then then Neebing river mouth across gravel bars which southerly gentle gentledip dip slope slopeof oflocal localGunflint Gunflintshales, shales,overlain overlain by by aa thin thin water water a broad southerly washed silty these shales shales occurs occurs jasper jasper taconite, taconite, the the major major source source of of tool till. In these silty till. making material. Figure I10 of the the site and and the the material. Figure 0 shows shows the the fenced fenced area of morphological details (Julig et al., 1990). Figure I 11 1990). Figure I shows the paleogeographic reconstructionofof events events believed believed to to have have formed formed the the area area (Phillips, (Phillips, 1982). reconstruction 1962). Longshore transport from from the the Neebing Neebing rivermouth rivermouth built built aa series series of of progressive bars bars Longshore across the shallow shallow water water rock rock shelf, shelf, recurving recurving into into aa minor across the minor river river valley valley which which sheltered embayrnent embaymentto tothe thewest westofofa arock rockisland. island. AA further further bar bar was was built built formed a sheltered front of of existing existing ones eventually crossed along the front crossed the the embayment embayment in in tombolo-Jike tombolo-tike form to to enclose enclose a small lagoon, the Cummins Pond, after after which which lower lower and and later later form Cummins Pond, the established established plan plan shape. shape. A pollen shoreline features mimicked the pollen core taken in the pond suggests etal., al., 1986). 1986). pond suggests this enclosure enclosure took place place before before 8.1 8.1 ka ka B.P. B.P. (Julig et of the the bars bars is not compatible with with a declining The plan shape and structure of water level indeed the the accumulation and building building up up of of these water level margin, margin, indeed accumulation and these large large features shelf slope slope is unlikely unlikely without without transgressive transgressivewave waveaction. action. Even features on a gentle shelf so, such action across across aa gentle gentle shore shoreslope slopewould would not notordinarily ordinarilybuild build up up a large so, large supra-aqueous bar without some initial encouragement to accumulate sediments supra-aqueous bar without some initial encouragement to accumulate sediments sheet. The along a line line rather rather than disperse them in a sheet. The key key to the existence of these bedrock control. control. While Julig (1984) determined bars in this location is underlying bedrock and ground ground radar studies that that variation variation in sediment through resistivity resistivity and sediment character character irregularities could could be be traced, traced, aa more of the and bedrock bedrock irregularities more simple reconstruction reconstruction of possible. By surveying surveying down downthe theexposed exposed bedrock bedrock dip dip slope bedrock profile is also possible. of the the site, site, the the trend trend (see inset, Figure showed that that beneath beneath the site must north of Figure111) I ) showed must typical of of many that that occur occur in in the the present present topography topography of of these these lie a marked marked rock step, typical flat-lying shales, and often sharpened by wave action. Accumulation of of sediments took place place firstly firstly against against this this rock rock step step and and subsequently subsequently over over the the top top of of it. ItIt is took possible that some till till remained remained in the the angle angle of ofthe thestep. step. To To the the west west of of Mapleward possible Road an an exposure exposure of of coarse coarse sand sand and and gravel gravel with with angular angular shale inclusions at the rear of the bar bar in contact contact with with bedrock bedrock suggests suggestsoverwash overwashof ofthe thetype typethat thatwould would be expected in this scenario (Figure 12). Once the linear feature was established, scenario (Figure 12). Once the established, longshore sediment supply would extend its length and add add to to the the lakeward lakeward face. face. overwash and and building building in elevation is characteristic characteristicof of wave wave action action either either However, overwash storm event eventor or aa transgressive transgressivelake lakemargin. margin. Again, Again,aa 'bar 'bar building' building' in an extreme storm evident at at Cummins. Cummins. Julig Julig (1984) (1984) found found confirmatory evidence of of period seems seems evident confirmatory evidence of these these bars bars during during the the process process of of their their accumulation, accumulation, aa buried buried layer of habitation of water worn being associated associated with with aa period of water worn taconite taconite artefacts artefacts being of overwash overwash and and construction. construction. While occupation of of the site when a lakeshore location offered advantages While of longshore of longshore access, access, lagoon fishing and perhaps perhaps water water transport, transport, a cremation cremation �(1982) Phillips by mapping morphological on based (1990), Mahaney and McAndrews, Julig, scions. sod aandarsi of Figure Onurio Superior. Lake nartbwzern size, UChSeCIOiS Cummins 5. 1don sad Quarry nct'ottons edge 3-Bog acovah1s Minwtg Z.Lower section DI & excavations Main I. pit Growl % cliff — Govt Ontero by purchased site of gortion Fenced ponns undisturbed Sot',. ridges beach Mong tower and middle at grawl-remoct) s.c destnjction site totol to severe of Areas ,-. — ridge beach Minong middle of limits Aggrazimate —— viSit7. the in elevatton Spot pit Gravel xe' zidg bcb and r.n*4 'ccc terrace wove or Bluff —.-, ridge beach Removed ridge Beach — Ouzailo, Supeñor, Lake oorthwzern she, Cummins 4. Fsguzt 500 9 NCThCS PMPOOSIGC1 OF TWP eat TIC$OCR OF CITY 10 Figure �Figure 11 Figure 11 + FLAT SWAtS '1 ALUWIUM MARSH CREST CUFF S ...d. DIRECTI ON OF 5LOFE MOCIFIED C. MAJOI •AR FORMATION FIIOFILE ACROSS CUMMINS Sits EAST OF MAPLEWARD ROSS ri,cit 0. POST MINONsMIN0R EARS FORMED MIMICKING PLANE SHAPE OF MAIN EAR 0—n.. Nh Figure 8: p. Fisure 8:The Thechanging changinggeography geographyand andpresent presentcharacteristics characteristicsofofthe theCummins Cummimsite. site. (from (from Phillips, PhiZlips, 1988, p. 133) 133) �Figure 12 12 Schematic representation representationofofthe the cliff cliff face at the the Cummins site. Schematic site W Wind wi nd Deflation -flation Lag Lag Fbviai Deposits 0—I 00 - Rich Berm Berm Gravel —Rich Magnetite — Rich Magnetita -Rich Foreshore Beach Foreshwe 8each Sands Sands .. . Foreshore Beach cc! Talus Slope Sands Backbeach Backbeach I—.zkl Bioturbated Sands Sands Massive, Heavily Massive, Bioturbated Dune Dune Sands Sands + +.. • 4+ + Bedrock Bedrvk Sedimentology Sediment010 y A wellwell-developed, exposed at the Cummins site. site. Figure30 30shows shows a eveloped, beach deposit is exposed schematicrepresentation representationofofthe thesandy sandy dii cliffface face where where the the strandline strandlinedeposits deposits are are visible. schematic cross-stratified sands sands of of the the foreshore foreshore dominate dominatethe the exposure. exposure. individual Low-angle, planar cross-stratified Individual Iarninae dipping 3' 3° to 12° 12' lakeward lakeward (original swash-backwash surfaces) are arranged atranged into into laminae dipping one another anotheratatvery verylow low angles. angles. The packets which erosively truncate one Theplanar planarcross-stratified moss-stratified both laterally laterally and and vertically vertically into massive sands through a bioturbated sands are transitional both bioturbated zone. the zone. thebioturbated bioturbatedarea area represents represents a sparsely sparsely vegetated vegetatedbackshore backshore environment environment while while massive sands the massive sands were were deposited depositedas asaeoliari aeolian dunes. foreshore sands sands are areerosively erosivelytruncated truncatedininthe theeastem easternportion portionofofthe the dii cliff by by The foreshore magnetite-richsands. sands. Internal internalstructures structuresindicate indicatethat thatthey theyare arealso alsoforeshore foreshoredeposits. deposits. The The magnetite-rich magnetite-richforeshore foreshorelaminae laminaewere wereformed formedduring duringregression regressionwhen whenstorm stormwave wave activiv activity magnetite-rich During the the lower portion of the beach, erosively erosivelytruncating truncating the older older deposits. During reworked the intervening periods periods of fair events sand was removed storm events removed and stored in offshore bars. In inte~ening weather, sand sand moved fmm fromthe theoffshore offshorebars barsback backonto ontothe thebeach beachand andwas waswinnowing winnowing by by weather, waves, producing small waves, produangthe themagnetite-rich magnetite-richlag lag deposits depositsfilling fillingscour scour truncations. truncations. The beach assemblage is is overlain overlainby by erosively erosively based, trough cross stratified stratified sands. sands. Major rainfall rainfallevents events caused after subaereal subaereal exposure exposure of of the area. fomed after area. Major These were formed to flow flow off the adjacent rock knoll knot!dissecting dissectingand and reworking reworkingthe theupper upper layer of beach streams to beach deposits. deposits. 3 Phillips, Fralick Fralick and and Ross, Ross, 1987. Phillips, C-12, From INQUA Field Guide GI 2, Eds. Geddes, Geddes, Kristjansson Kristjansson and and Teller. Teller. Eds. �burial site on on the the rock rock island (Dawson, (Dawson, 1983) was was dated to to 8,480 8,480 + 390 years BP. both just just below below the the aeolian aeolian sands sands that that characteristically characteristically Julig (1984) found artefacts both modified the topography of the the shoreline shoreline features features once once the offshore offshore shelf shelf was modified the topography of exposed by by lower exposed lower lake lake levels levels (circa (circa 8.0 8.0 ka ka BP) BP) and and in in peat peat that that accumulated accumulated in in Cummins Pond, Indications are are that that long longafter afterthe the lake lake ceased ceased to to lap the beach Cummins Pond. Indications beach face, the site remained remained used, used, at at least least until until 7.5 7.5 ka ka BP BP (Julig (Julig et et al., 1986). 1986). - Stop 5 Stop 5 (several) (several) - The The Rosslyn Rosslyn Delta Delta will retrace to to Oliver Oliver Road Roadand and continue continue west, west, turning turning south at the The route will towards Twin Twin City City Crossroads. Crossroads. Immediately Immediatelysouth south of of the the driving driving range, Golf Course towards the road road descends descends aa gentle gentle bluff bluff around around the the 268m 268m (880') (880') contour contour that that is is aa Beaver Beaver the Bay shoreline, shoreline, and and then, then, beyond beyond two two turns turns in in the the road, the descent down the the Bay road, the descent down shoreline arrives flat surface of the offshore shelf and offshore shelf Minong shoreline arrives on the extensive, extensive, flat surface of the Kaministiquia Kaministiquia River River where where it entered Lake Minong. This surface, 222m delta of the (729') at the mainly of sandy with boggy sandy silts, silts, with boggy areas (729') the crossroad, crossroad, is composed composed mainly the crossroads crossroads the the route route will will turn turn west west along underlain by more clayey silts. From the Hwy 11-17, Minong bluff, forming an abrupt rise at 11-17, where, within 2 kms, is again the Minong Hwy at the Weighscales. Weighscales. Turning Turning left, left,once once on on the the terrace, terrace, the the road leads south to several several fields in which the Dairy fields which lithic lithic material material has has been been found. found. These These sites, sites, the Dairy Farm, Farm, Breukelman Evergreen and and Halow A, A, B B and andC, C,will willbe beviewed viewed (Figure (Figure 15) 15) and and then of the Kaministiquia River River towards towards Stanley. Stanley. En the route will follow the north side of route the upper and lower Drezecky sites sites will will be seen (Figure (Figure 17), 17), as as well well as the Pawlick site site which whichcan canbe be seen seen on on the the south south side side of of the river. From Stanley Stanley the the river. From Pawlick Stanley delta and return return to Hwy 11-17. 11-17. route will climb the terraces of the Stanley The following extract extractofof text textand and figures figuresderives derivesfrom fromaa paper paper by by Scoff The following Scott Hamilton, that that has has been been submitted submitted for forpublication publication review review to to the theCanadian Canadian Journal Journal Archaeology. Entitled Entitled"Archaeological "ArchaeologicalPredictive PredictiveModelling Modellingininthe theBoreal BorealForest: Forest of Archaeology. No Easy the paper paper addresses addresses the the difficult difficult problem problem of of developing No Easy Answers", Answers", the developing archaeological predictive models to aid in Forest Class Class environmental environmental assessment. assessment archaeological Among the many many challenges challenges is is the issue of development sensitive Among development of temporally temporally sensitive palaeo-environmental reconstructions, and also models of land use that are are palaeo-environmental reconstructions, and also models of land use that relevant to the political economy and social organization of the ancient peoples relevant political economy and social organization of the ancient peoples under consideration. consideration. "The apparent apparent correlation correlation between between relict relict shorelines shorelines and Piano archaeological archaeological well known in the Thunder Bay area where landscape evolution has been sites is well been of some somestudy study(Figure (Figure 13). 13).While While many many Piano Piano shoreline shoreline archaeological archaeological the subject of documented,the thebest best known known ones ones are are lithic quarry and workshop sites sites are documented, such as the and McDaid Sites (Julig 1984, the Cummins, Cummins, Biloski, Simmonds, Simmonds, and 1984, 1994; 1994; MacNeish 1952; 1952; Hinchelwood Hinchelwood 1990; 1990; Phillips 1988, These large large sites sites are MacNeish 1988, 1993). 1993). These well removed shorelines, but but are are associated associated with with the the late late Pleistocene removed from modern shorelines, shorelines of Glacial Lake Minong Minong and and Gunflint Gunflint Formation Formation bedrock exposures that are suitable suitable for lithic lithic tool tool production production (Figure (Figure 13) 13) (see (see Julig, Julig, McAndrews McAndrews and and Mahaney 1990; Phillips Phillips 1988, 1988, 1993). 1993). However, However, these these special-purpose special-purpose sites sites do do not not characterize the full Paleo-Indian settlement pattern. Rather, the dense recoveries Paleo-Indian Rather, the dense recoveries �from, and ready visibility visibility of, of, these these sites has resulted in their over-representation over-representation in in the published literature. Archaeological Archaeological reconnaissance reconnaissance upon the published archaeological archaeological literature. agricultural fields fields within within the Kaministiquia River River delta delta has has revealed revealed a number number of PIano or or probable probable Plano Piano sites sites in a wide of landscape landscape contexts contexts (Hamilton Plano wide range range of 1996) (Figure (Figure 14). 14). Many Manyofofthese thesesites sitesare arefound foundatatorornear nearLake LakeMinong Minong shoreline shoreline elevations (i.e. 750 750 feet feet or or 228.6 A.S.L). When elevations (i.e. 228.6 metres metres A.S.L.). When placed in aa hypothetical hypothetical Minong- environmental Lake Minong environmentalcontext, they are found associated with: flowing into into sheltered sheltered coves coves of Lake Minong (Figure 15: 1) springs flowing 15: Breukelman Breukelman Evergreen); Evergreen); 2) on points of land that protruded protruded out out into Lake Minong to the the northeast northeast and and southeast of the Breukelman Evergreen site cluster (Figure 15); Breukelman Evergreen site cluster (Figure 15); well-drained sandy knolls surrounded surrounded by by poorly drained 3) upon low, low, well-drained sandy knolls poorly drained 3) upon floodplain/deltaic sediments floodplainldeltaic sediments (Figure (Figure 15: 15: Halow Halow C); 4) along deltaic deltaic backwater backwater channels (Figure 16: DbJi-8, DbJi-7, DcJi-28, DcJi32); 32); or 5) on sandy storm storm beaches beaches developed upon relict deltas (Figure (Figure 16: 16: DcJi-30, DcJi-30, DcJi-31). DcJi-31). Other sites were found upon: upon: 6) raised raised Pleistocene Pleistocene terraces terraces overlooking overlooking the the present present Kaministiquia Kaministiquia River River channel (Figure channel (Figure 17: 17: Pawlick); Pawlick); 7) on high high valley valley rims rims that offer panoramic views (Figure 17: Drezecky E); the Lake Minong shores shores (Figure (Figure 16: 16: Halow Halow A A 8) along draws leading down to the and B); and B); well removed from from late Pleistocene shorelines (Figure 9) along upland upland streams well (Figure 17: DcJj-12, DcJj-13); and 10) upon well-drained upland knolls knolls on what likely were formerly discontinuous permafrost uplands permafrost uplands (Figure (Figure 18: 18: Breukelman BreukelmanField: Field:lithic lithicscatters scatters AA to to E). E). Probable Plano Piano lithic lithic scatters scatters have have also also been been found found upon isolated bedrock Probable controlled knolls knolls offering offering panoramic panoramicviews viewsofof floodplains floodpiainsadjacent adjacenttoto the the Lake controlled Thisrange range of of landscape landscape characteristics Minong shoreline (Figure 19: 19: BeIluz Belluz Farm). This is certainly not exhaustive, but is sufficient to demonstrate demonstrate the the diverse diverse microhabitats microhabitats frequented by frequented by Piano Piano people. people. Lakehead Complex sites in terms of of a very These sites are consistent with other Lakehead preference for Gunflint Gunflint Formation Formation lithic lithic materials materials (Hamilton 1996). However, strong preference virtually all all of of these are well well removed are virtually these sites sites are removed from from bedrock bedrock exposures, exposures, are �Figure Figure 13 13 Late Rolocene watere Cuminins Site Bioski Site Brohn. Site .r Julig, MscAndr..,s nit Maimmy (l900tfl) Figure Figure66The The Correlation Correlationbetween betweenLakehead Lakfcu-u Complex bxinplexsites, sites, Minong Minong beaches beachesand andGunflint GunflintFormation Formationoutcrops outcrops(Hamilton (Hamilton1996:34) 1996:34) �Figure 14 Figure 14 Some Archaeological Sites associated with the Kaministiquia River Delta • Modern Hydrological System U Lake Minong water levels * Lakehead Complex Site SModern Community ..-M fl f Lake Superior distribution of confirmed confirmed or Figure 7 The distribution or probable probable Lakehead LakeheadComplex Complex sites sites on on the the Kaministiquia River (Hamilton1996: 1996:36) 36) Kaministiquia Riverdelta delta(Hamilton �Figure Figure 15 15 Figure or probable welldrained drained sediment sediment near near Figure 88 Confirmed or probable Piano Piano sites on well (750feet feetASL) ASL)(Hamilton (Hamilton 1996:59) 1996:59) LakeMinong Minongshorelines shorelines(750 Lake �1996:65). (Hamilton channels backwater deltaic along and beaches, storm Minong on Sites Piano probable and Confirmed 9 Figure 16 Figure �1). 1996:5 (Hamilton terraces river Holocene early and Pleistocene late along sites Piano possible and Confirmed 10 Figure 17 Figure �Figure 18 18 3ntour Interval = 10 metres AN 1 Figure PIano sites located located upon upon well-drained well-drained knolls knolls in in upland upland Figure11 11 Possible Piano regions (Hamilton1996:47). 199647). regions well well removed removedfrom fromLake LakeMinong Minong(Hamilton �Figure Figure 19 19 Figure Figure12 12Probable ProbablePiano Pianosites siteson on aa bedrock bedrock controlled controlledknoll knoll overlooking overlookingPleistocene Pleistocenefloodplain floodplainzone zone(Hamilton (Hamilton1996:57). 1996:57). �significantly smaller smaller than than the the quarry-workshop quarry-workshop sites sites (such (such as as the the Cummins Site), When compared compared to to the the quarry/workshop quarry/workshop sites, sites, these these and yield many fewer artifacts. When small sites also yield a much higher relative frequency of tools, preforms tools, preforms and small sites also a much higher relative frequency to debitage debitage (Hamilton (Hamilton 1996). This indicates that the small utilized flakes compared to sites represent represent encampments, encampments,hunting hunting stands stands and and food procurement procurement sites, rather than lithic extraction extraction and reduction stations. Such Such observations than lithic reduction stations. observations are hardly surprising, but they do serve as cautionary tales regarding surprising, but they do serve as cautionary tales regarding the dangers dangers of of predicting site distribution on the basis of our current incomplete heritage heritage inventory. inventory. predicting in that that they theydemonstrate demonstratethat thatmodelling modelling ancient ancient These examples are also important in human behaviour requires ongoing ongoing refinement, an understanding of human human human behaviour requires refinement, an understanding of forager behaviour, and a well-developed sense sense of of the the nature nature and and structure structure of of the forager behaviour, ancient landscape landscape and and its its microhabitats." microhabitats." As one leaves delta (Minong, (Minong, 9.5 9.5 ka ka B.P.) B.P.) and and moves As leaves the Rosslyn Rosslyn delta moves up the the present Kaministiquia valley, valley,one one is is in in effect effect travelling travelling back back in time. time. The Stanley delta was built into Lake Beaver Bay (9.7 ka ka B.P.), B.P.), the the first first Superior Superior lake to occupy occupy the area recently recently vacated vacated by Marquette Marquette ice ice retreating retreating from from the the Marks Marks moraine. moraine. Though perhaps less less conspicuous, conspicuous,Paleoindian Paleoindiansites sitesofofthis this period period are are also also Though perhaps present. present. The larger step back in paleogeography paleogeography is is to consider consider the area that lies lies to to the the west of the maximum of the Marks maximum position position of Marks moraine, moraine, an area area which which remained remained west of unglaciated by the Marquette readvance and and which which was was freed freed from from ice icearound around 11.0 unglaciated B.P. Figure Figure 20 20 shows shows the the projected projected maximum maximum position position of ofthe the Marquette Marquettelobe lobe and and ka B.P. the large area covered of aa pre-Marquette pre-Marquette lake lake (Early (Early Lake Lake Minong) , covered by the waters of by the the 1400' contour. contour. On Onthe thebasis basis of of some some long known sites, now approximated by both in the interior Phillips and and Hill (1995) both interior and and on on the the Minnesota Minnesota northshore, northshore, Phillips proposed that a Paleoindian Paleoindian routeway routeway along the Minnesota Minnesota shore turned inland of Judge Judge C. C. Magney MagneyState StatePark, Park,towards towardsNorth Northand andSouth South Fowl Fowl lakes lakes and and just east of in the the Whitefish number of more more recently recently discovered discovered sites in Whitefish Lake region. region. A number Whitefish -- Arrow Arrow Lake Lake corridor corridor supports supports the the contention contention that that Paleoindian peoples peoples Whitefish the Marquette advance, and were present in the area perhaps before and during the Marquette advance, that corridor continued continued to to be used into periods of of Lake that the corridor into the the post-Marquette post-Marquette periods Though conjectural, conjectural, there there is is the possibility that after Beaver Bay and Lake Minong. Though the retreat of of Marquette Marquetteice ice had hadbegun, begun,the the Marks Marks moraine moraine itself itself provided provided aa high ground from the the Whitefish Whitefish Lake Lake area area along along the north of the ground routeway routeway from north side side of Kaministiquia valley of Thunder Thunder Bay. Bay. Kaministiquia valley and andinto intothe the area areato to the the north northand andeast eastof - Stop 6 - Kakabeka Falls Just west west of of the the junction junction of of Hwy Hwy 11-17 and the Stanley turn off, off, the the huge Just structure of the Stanley delta is seen (Figure 21). This delta was formed as the structure of the Stanley delta seen (Figure 21). This delta was formed as Kaministiquia River Beaver Bay. Bay. A A well welt formed formed bluff representing a River entered Lake Beaver lower Beaver Bay phase of 260m (853'), runs along the north north side side of of the main main lower Beaver Bay phase of 260m (853'), runs along the highway, and the surface below below itit (250-2401% (250-240m;820-787') 820-787')is is heavily heavily exploited exploited by the sand and gravel industry. The present Kaministiquia river river has has incised incised deeply into into the delta, creating a terraced valley side. �Figure 2200 Figure -- 1 Kaminisliqili R. Valley 2 Whilefish Lake 4 N & S Fowl Lake 5 Pigeon R.Valley 6 Silver Mountain km SW99 (Alter Phillips and Hill Hamilton 1996) (After Phillips and Hill 1995:22-24, 1995:22-24, HuDUton 1996 Figure 13 Siteson onthe theUplands Uplands west westof ofThunder Thunder Bay Bay Figure 13 Some Piano Archaeological Sites �-4 ( Shorelines - Terraces - -1 r (from Grootenboer, 1972) — -C - Lower Beaver -4 cirumlinoid -r Upp, N N Beaver 88y N ( Figure 21 �Kakabeka Kakabeka village village is is built built on on the the floor (277m; (277m; 909') 909') of of an an old old distributary distributaryof of the the Kaministiquia Kaministiquia river which cut through a higher terrace still (Figure 21). Remnants of this at around around 300m 3Com(984') (984')overlook overlookthe the village. village. They They represent represent the this terrace surface at highest Lake and highest level level of of the Stanley delta, as asitit formed into Upper ~ a k eBeaver ~ e a v e Bay, r and on on the of the the Kaministiquia KaministiquiaRiver, River, the Crane Crane site was found. the one one on on the the west west side side of Kakabeka Falls is aa major major scenic scenic attraction. attraction. ItIt is is formed formed as as aa result of of a very was just just this sort of resistant chert bed that caps the the underlying, underlying, softer softer shales. shales. It was rock material material that was desired desired for tool making. Today, a fairly spectacular gorge lies lies below the falls (Figure 22). There has been some debate concerning the age of the below the falls (Figure gorge, since unless inherited and exhumed from from a previous stage of of river river incision to prior to there is only post to the the Marquette Marquette readvance, readvance, there post Beaver Beaver Bay Bay time time for it to develop its current grandeur. grandeur. An An interesting interestingabandoned abandonedfalls falls and and plunge plunge pool on the west side of the gorge lies lies aa short short walk walk from from the the Park Park Information Information Centre, and represents 'horseshoe' fall that would have been more spectacular than the represents a wide 'horseshoe' present present falls. falls. - Stop 7 (several) (several) - The The Marks Marks Moraine. Moraine. The route will turn on Hwy 590 just just west of of Kakabeka, Kakabeka, run run across across the the High Beaver Bay terrace terrace remnant remnant (look (lookfor forthe thecemetery cemeteryon onthe the right) right) and and due due west west until turning Moraine. As Asthe thedirt dirtroad road rises rises up up the the outer outer face face of of turning north north towards the Marks Moraine. the Marks (1400') and 442m Marks moraine it crosses crosses two distinct distinct benches at 42Gm 426m (1400') (1450'). These shorelines shorelines of of pro-glacial pro-glacial Lake Lake Cedar Cedar Creek Creek have been traced all (1450'). These along of the theMarks Marksmoraine moraine (Jahnke, (Jahnke, 1993) 1993) and and represent represent along the outer outer slope slope of stillstands in a lake earlier than and isolated of the the Superior Superior basin. isolated from the lakes of The Marks Marks Moraine. Moraine. Stopping on the 46Cm (1510'), (1510'),the the view view south south over over the Stopping on the crest crest around around 460m Whitefish valley and the the rugged rugged borderland borderland country country of of the mesa-like NorWesters Norwesters is spectacular. It is not hard hard to to envisage envisage ice ice pushing pushing its its way way up to the Marks Marks moraine, moraine, nor is it hard to imagine pro-glacial Lake Cedar Creek occupying the narrow strip hard imagine pro-glacial Lake Cedar between between the the moraine moraine and and the the retreating retreatingice icemargin. margin. The moraine is not a simple structure. structure. Although Although characterised characterised by by aa till which contains diagnostic pieces of Sibley red red sedimentary sedimentary rocks, along much its length the Marks joins and Marks moraine moraine joins and smothers smothers isolated isolated rock rock outcrops outcrops which which probably probably greatly top of of the the moraine greatly influenced influencedthe the extent to which the ice pushed inland. The top kettles. Spillway remarkable flat flat in many many places places and and is pockmarked pockmarked with with kettles. is remarkable Lake at one channels channels cross cross the the feature feature in in places suggesting suggesting that at one point point Lake Kaministiquia to the north was a few metres higher than Lake Cedar Creek to the south. The moraine moraine appears appears to to have have briefly briefly existed existedas as aa narrow south. The narrow ridge between between these two water bodies, and a possible post-Marquette routeway for animals routeway for animals and water Paleo-lndian Arrow/Whitefish region region and and Paleo-Indian people, from the unglaciated unglaciated (Marquette) ArrowIWhitefish Interlakes corridor. corridor. Interlakes The Conmee Pit and and spiliway. spillway. Conmee Pit Continuing north across across the the moraine and then turning east brings Continuing north moraine and brings the the excursion to to a distinct south across across the moraine excursion distinct channel cutting from from north to south surface. Here Conmee Township has has several several gravel gravel pits. from the huge surface. Here Conmee Township pits. Apart Apart from huge boulder beds that that suggest suggest high high discharges discharges down down this this spillway spillway at at times, times, the the pit boulder beds �Figure 22 (from Grootenboer, 1972) �reveals another another key key fact fact in in understanding local deglaciation. deglaciation. Figure Figure 23 23 shows shows a understanding local rare occasion occasion when when the the western western pit pit face rare face was cleanly cleanly exposed. exposed. Tickle Tickle (1996) (1996) interpreted the the sequence sequence as as consisting consisting of of two two tills separated interpreted separated by by fluvioglacial fluvioglacial sediments. However, However,while while one one till till was was of of diagnostic diagnostic Sibley Sibley origin, origin, the the underlying sediments. lobes. one was of a northern provenance typical of the Patricia or Rainy River lobes. Elsewhere, at several several places places along along the the Marks Marks moraine moraine aa thin thin Sibley till Elsewhere, at till is p'astered over over fluvioglacial fluvioglacial sediments. sediments.The The observation observationsuggests suggeststhat thatthe thebulk bulk of of plastered the Marks moraine may may in in fact fact be be pre-Marquette pro-Marquettein inorigin, origin,with with thin thin Marquette Marquette ice the moraine. moraine.This Thishas hasbeen beenthe the growing growing opinion opinion of another local field field reoccupying the Figure 3, 1999) and and looking the worker (T. (T. Noble, Noble, pers.communication, pers.communication, 1999) looking at Figure worker 3, the possibility of the Marks moraine moraine being being the the result result of of pushing pushing the the eastward eastward part part of of the the possibility former Brule moraine till contorted till former moraine is not not unreasonable. unreasonable. Several exposures exposures of contorted structures also support this idea. idea. Moraine scenic Marks Moraine scenic lookout. lookout. outofofthe thepit pitand andagain againatatthe thecrossroad crossroadbrings bringsone oneto toaa point point in in Turning left out the road from from which which a view east over the Kaministiquia Kaministiquia valley, valley, Thunder Thunder Bay city the distant distant Sleeping Sleeping Giant Giant is is obtained. obtained. The The stop stop is useful only to to impress impress and the of things. It is easy to imagine ice viewers with scale of ice grinding grinding past past Mt. Mt. McKay McKay and and flowing up to imagine imagine that that aa slight slight tilt tilt of of the the present lake flowing up the valley, just as it is easy to would bring the margin of the lake lake right right up up into into the the Kaministiquia Kaministiquia and and Whitefish Whitefish valleys. valleys. 1I I I ii I to the the crossroad, crossroad, the the route routewill will turn turn left leftdown down the the face face of of the Marks Marks Returning to road is is straight, straight,save savefor foraajog jogaround aroundaakettle kettlehole, hole, and, and, lower lower down, down, moraine. The road fields and along the stream stream beds. beds. Turning Turning right rightat at Hwy Hwy 11 11-17 rock is exposed in the fields -17 back to to Kakabeka Kakabeka Falls. Falls. From Fromhere herethe theroute routewill will take take Oliver Oliver brings the excursion back Road back back to to the the University. University.The The road road climbs climbs out out of of Kakabeka over the the Upper Kakabeka over Beaver Bay terrace remnant and then runs due east to Lakehead University. University. One landform of of note note on on the theway wayisis aa crag crag and and tail tail feature, feature, showing the flow up the the Kaministiquia Kaministiquiavalley. valley.The The'Old 'Old Barn' Barn' restaurant restaurantlies lieson on the thetail tail and and on on of ice up farmhouse, open open for for bed bed and and breakfast breakfast (another (another time, time, eh!). ehl). Just east the crag is the farmhouse, the north north of of Oliver Oliver Road Roadisisthe theMurillo Murillodrumlin drumlinfield, field, aa series series of of long of Murillo but to the narrow forms parallel to the the strike strike of ofthe theGunflint Gunflintshales, shales,suggesting suggestingaagood good deal deal of bedrock control. bedrock The The excursion excursion is over. over. We We hope that that participants participants obtained obtained an informed informed glimpse of of the the deglaciation deglaciation history history and and Paleoindian presence in in the area, and glimpse Paleoindian presence and enjoyed enjoyed doing doing so. so. I �Figure Figure23 23 . , Figure Figure1.1 1.1 The TheStudy StudySite Site--Conmee Cn-mee Township Townshipgravel gravelpit pi SOUTH Note: Note: Vertical Vertical sections sectionstaken takenatatnumbered numberedlocations. locations. (from Tickle, 1996) �References and and Bibliography Bibliography References Arthurs, D. 1979. 1979. An Archaic Archaicsite siteon onthe thewestern westernLake LakeSuperior Superiorshore. shore.Report Reporton onfile filewith withthe the Planning and Research Historic Planning Research Branch, Ontario Ministry of of Culture Culture and and Histonc Branch, Ontario Communication, Toronto, Toronto, 35 pp. pp. S. 1985 1985 Deglaciationchronology chronology and and revegetation revegetation in in northwestern northwestern Ontario. Bjorck, S. Ontario. Canadian Canadian Journal of of Earth EarthScience Science 22,850-871. 22, 850-871. G.J. 1977 1977 Quaternary Geology of the City of Thunder Bay Ministry of of Bay and and Vicinity. Ministry Burwasser, G.J. Natural Resources, Resources, Ontario Ontario Geological Survey Report 164. Geological Survey Report OR GR164. Burwasser, G.J. G.J. 1980 1980 Quaternary Quaternarygeology geology of of the the Onion Lake of Burwasser, Lake and Sunshine Sunshine area, area, District of Thunder Bay. Ministry of of Natural Resources, Ontario Ontario Geological Geological Survey Survey Report Report Bay. Ministry Natural Resources, MP94. MP94, Burwasser, G.J. G.J.and andFerguson, Ferguson,A. A.1980 1980Quaternary Quaternarygeology geologyof ofthe theOnion Onion Lake Lakeand andSunshine Sunshine Burwasser, area, District of of Thunder Bay. Ministry of of Natural area, District Bay. Ministry Natural Resources, Resources, Ontario Geological Geological MapP.2203, P.2203, Geological GeologicalSeries, Series, 11:50,000. :50,000. Survey Preliminary Map Clayton, L. L. 1983 1983 Chronology Chronologyof ofLake LakeAgassiz AgassizDrainage Drainage Lake Superior: jTeller, J.T., J.T., and and totoLake Superior: in.Teller, Clayton, Lee, Agassiz, Geological Geological Association of Canada Lee, eds., eds., Glacial Glacial Lake Agassiz, Canada Special Special 26, 291-307. Paper 26,291 -307. Clayton, L L. 1984 Pleistocene Pleistocenegeology geologyof of the theSuperior Superiorregion, region, Wisconsin, Wisconsin, Information InformationCircular No. 46, Wisconsin Geological Geological and Natural History HistorySurvey, Survey, Madison, Madison, Wisconsin. Wisconsin. N O. 46, Clayton, 5. 1982 Clayton, L. and Moran, Moran, S. 1982 Chronology Chronology of of Late LateWisconsin Wisconsin glaciation glaciation in middle North North America, Quaternary Science Science Reviews, vol. vol. 1, pp. pp. 55-82. 55-82. Dawson, K.C.A. K.C.A. 1983a Prehistory of Northern Bay Historical Historical Museum Museum Dawson, Northern Ontario. Ontario. Thunder Bay Society. Society. ite at Thunder Bay, Bay, Dawson, K.C.A. K.C.A. 1983b Cummins Site: A Late Palaeo-lndian (Piano) Site Dawson, Archaeology 39,3-31. 39, 3-31. Ontario. Ontario Archaeology Drexler, C.W., C.W., Farrand, Farrand,W.R. WA. and and Hughes, J.D. .J.D. 1983 1983 Correlation of Glacial Lakes in the Drexler, Correlation of Glacial Lakes the with Eastward EastwardDischarge DischargeEvents Eventsfrom fromLake LakeAgassiz AgassizjnTeller, j. Teller,J.T., J.T.,and and Superior Basin with Agassiz, Geological Geological Association Association of Canada Clayton, Lee, eds., Glacial Glacial Lake Agassiz, Canada Special Special 26, 309-329, Paper 26,309-329. Dudzik, M.J. M.J. 1993 1993 The State Archaeology Archaeology The Paieoindian Paleoindian tradition in northwestern northwestern Wisconsin, Wisconsin, State Regional Program, Siren, Siren, Wisconsin. 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ProteinResidues Residuesin inLithic Liihic Artifacts Artiactsfrom a Stratified Boreal Forest Forest Site. Site. Canadian CanadianJournal JournalofofArchaeology Archaeology 13, 119-132. 119-132. Nordeng, S.C., S.C., A.P. A.P. Ruotsala, Ruotsala,S.A. S.A.Nordeng Nordeng1987 1987Buried Buriedbog bogdates datesthe the time time of of the Nordeng, establishment of postglacial post-glacial Lakes Lakes Houghton Houghton and Nipissing in inthe the western western arm armof of the the Section Geological Society of America Lake Superior basin, North-central Section America Abstracts Abstracts with Program,vol. vol. 19, 19, no. no.4, 4, p. 237. Phillips, B.A. BA. M. Science 195, 11-16. 11-16. Coastal Histories, Science M.1977 1977Shoreline ShorelineInheritance Inheritancein in Coastal Phillips, B.A.M. B.A.M. 1982 Morphological Mapping and and Palaeogeographic Reconstruction of of Phillips, Morphological Mapping Palaeogeographic Reconstruction Former Shorelines Shorelines between between Current Current River Riverand and Rosslyn, Rosslyn, Thunder Thunder Bay, Former Bay, Ontario, Ontario, Including Cummins CumminsSite SiteDcJi-1. DcJi-1. Report Report on file with Historical Historical Planning and Research Research of Citizenship Citizenship and Culture, Culture, Toronto, Toronto, Ontario. Branch, Ontario Ministry of Ontario. Phillips, B.A.M. Phillips, B.A.M. 1988 1988 Palaeogeographic Palaeogeographic reconstruction of shoreline shoreline archaeological archaeological sites sites around Thunder Bay, Ontario. Geoarchaeology: An International Journal, 3, 2, 127138. Phillips, 3A.M. 1993 A Time-Space Model for the Distribution of Shoreline Archaeological the Lake Superior Superior Basin. Basin, Geoarchaeology: An International Journal, 8, 8, 2, 2, 87Sites in the InternationalJournal, 107. 107. Phillips, B.A.M. 3A.M. and C. 1994 History and Glacial and and Shoreline and 1994 The The Geology, Geology, Glacial Shoreline History Phillips, and Hill, Hill, C. Archaeological Potential Potential of of the Lake Superior: Superior: a Archaeological the Minnesota Minnesota North North Shore Shore of Lake background paper paper for for Geomorphologial and Archaeological ArchaeologicalStudies Studies of of Individual background Gwmorphologial and Individual State Parks Report for for Minnesota State Parks on the North North Shore. Shore. Report Minnesota Department Department of Natural Natural and Recreation, Recreation, St. St. Paul, MN. MN. Resources, Division Division of Parks and SAM. and P.W. 1994. 1994. A Transgressive Event on Lake Minong, Northshore Northshore Phillips, B.A.M. andFraiick, Fralick, P.W. of Lake Superior Superior -- Possible Possible Evidence Evidence of of Lake Agassiz Inflow,circa circa9.5 9.5 KA KA BP. BP. Agassiz Inflow, of Journalof ofEarth EarthScience, Science,v.v.31, pp. 1638-1 1638-1641. Canadian Journal 31, pp. 641. Phillips, B.A.M., B.A.M., Hill, Hill, C.L., CL., Fralick, P.W. and and W.A. WA. Ross Shorelines and Ross 1994 1994 Post-Glacial Post-Glacial Shorelines Phillips, Fralick, P.W. alongthe the Northwestern Northwestern Shore Shoreof of Lake LakeSuperior, Superior,Guidebook Guidebookfor for Paleoindian Migration along Fieldtrip E, E, 13th Biennial Meeting Meeting of AMQUA, AMQUA, Minneapolis, Mn. . : 8A.M. and Hill, C.L. CL. 1995 The Phillips, B.A.M. Thedeglaciation deglaciation history history and and geomorphological character a partof ofthe the region region of ofthe the 'Interlakes 'InterlakesComposite' Composite' -some - somenew newevidence. evidence. Symposium Symposium of apart Paleoindian Occupations Occupations of of on 'Archaeology, geomorphology and Paleoenvironmet: Paleoindian Great Lakes, Lakes, 60th 60th Annual of the the Western Western Great Annual Meeting Meeting of the Sociaety Sociaety for for American American Archaeology, Minneapolis, Archaeology, Minneapolis,MN. MN. May May 3-7. W. 1980 AAPalaeo-lndian Oliver Lake Lake Area. Area. Wanikan, 80, 33. Ross, W. Palaeo-Indian Refined Refined Biface Biiace from the Oliver Wanikan, 80, Society. Thunder Bay Bay Chapter, Ontario Archaeological Society. �Ross, Composite:aa re-definition re-definitionofof the the initial settlement of of the Ross, W. W. 1995 The Interlakes Interlakes Composite: initial settlement Agassiz-Minong 76, 3-4. 3-4. Agassiz-Minong Peninsula. Wisconsin Wisconsin Archaeologist, 76, Sharp, Sharp, R.R R.P. 1953 1953 Shorelines Shorelines of the the glacial glacial Great Great Lakes Lakes in in Cook Cook County, County, Minnesota: Minnesota: American Science,251, 251,109-139. 109-139. AmericanJournal JournalofofScience, Smith, TO. 1993 Lake Agassiz: The northwestern outlet and Smith, D.G. D.G. and Fisher, Fisher, T.G. 1993 Glacial Glacial Lake Agassiz: The northwestern outlet and paleoflood, 9-12. 21,9-12. paleoflood, Geology 21, Stewart, Ross, W.A. W.A.and and B.A.M. SAM. Phillips Stewart, J.D., Ross, Phillips1984 1984Investigations Investigationsatatthe theMcoaid McDaidSite Site(DcJh(DcJh16), 16), Thunder Thunder Bay, Bay, Report Reportto to the theOntario OntarioHeritage HeritageFoundation. Foundation. Stewart, A.S. Kissin 1989 1989 Two Isolated Isolated Biface Biace Finds Finds from the the Stewart, JO., J.D., Ross, Ross, W.A. W.A. Faykes, Faykes, A and AS. . Thunder Thunder Bay Bay Area, Area, Wanikan, Wanikan, 89, 89, 3, 3, 4-6, 4-6, Thunder Ontario Thunder Bay Bay Chapter, Chapter, Ontario Archaeological ArchaeologicalSociety. Society. Stuart, 1993 Paleogeographical Paleogeographical reconstruction reconstruction of of Lake LakeBeaver BeaverBay Bayraised raisedshorelines shorelines Stuart, A.J, A.J. 1993 with correlation correlation to possible possible Paleoindian Paleoindian settlement, settlement. Thunder Bay Bay region, region, Ontario. Ontario. HBSc. HBSc. dissertation, dissertation,Dept. Dept.of of Geography, Geography,Lakehead LakeheadUniversity, University,Thunder ThunderBay, Bay,Ontario. Ontario. Taylor, on the the north north Superior shore, American Geologist, vol. Taylor, F.B. 1895 The Nipissing beach on 15, 304-314. 15, p. 304-314. Teller, Agassiz and its fts Influence Influence on on the the Great Great Lakes. Lakes. fi Karrow, Teller, J.T. J.T. 1985 1985Glacial Glacial Lake Agassiz Karrow, P.F., P.F., and Calkin, Calkin, P.E. P.E. eds., eds., Quatemary Quaternary Evolution Evolution of the Great Great Lakes, Lakes, Geological Geological Association Associationof of Canada CanadaSpecial Special Paper Paper 30, 30, 1-16. 1-16. Teller, Thorleifson, L.H. 1983. The - LakeSuperior Superiorconnection. connection. In Teller, J.T. and Thofieifson, The Lake Lake Agassiz -Lake In J.T. Teller and LakeAgassiz, Agassiz,pp. pp.261-290, 261-290, Geological Geological Association Association and L. Clayton, eds., Glacial Glacial Lake of 26. of Canada, Canada, Special Special Paper Paper26. Tickle, Tickle, R. R. 1996. 1996. Depositional Depositional Systems Systems developed developed during during Deglaciation:Evidence D8glaciation:Evidence from from aa portion of the Mats ON., NBA. Dept. of MarksMoraine, Moraine, Conmee Conmee Township, Township, ON., HBA. dissertation, dissertation, Dept. Geography, Geography, Lakehead LakeheadUniversity, University, Thunder Thunder Bay, Bay, Ontario. Ontario. Van Rise, CR. and C.K. Leith 1911 of the the Lake Lake Superior Superior Region, Region, United States States 1911 The Geology of Hise, C.R. Geological Survey, Washington. Washington. Geological 1901, Glacial Glacial Lakes America Bulletin, Bulletin, vol. vol. Winchell, N.H. 1901, Lakes of of Minnesota, Geological Society of America 12, 12, p. p. 108-128. 108-128. Wright, H.E., F-I.E.,1972a 1972aPhysiography PhysiographyofofMinnesota, Minnesota,ininSims, Sims,P.K. P.K.and andG.B. GB.Morey, Morey,eds. eds.Geology Geology of Minnesota: aCentennial volume, 561- 578. Minnesota: acentennial volume, Minnesota MinnesotaGeological Geological Survey, p. 561- Wright, history of of Minnesota, in Sims, Sims, P.K. P.K. and and G.B. GB. Morey, Wright, H.E. H.E. 1972b Quaternary Quaternary history Minnesota, in Morey, eds. eds. Geology of Minnesota: Centennial volume, Minnesota Survey, p. 515515Minnesota: aacentennial Minnesota Geological Survey, 547. 547. Wright, HE. HE. Tunnel hydrology of of the Superior Tunnelvalleys, valleys, glacial glacial surges and subglacial subglacial hydrology Superior lobe, lobe, Minnesota, 136, p. 251-276. 251-276. Minnesota, Geological Geological Society Society of America Memoir 136, �Wright, J.V. 1963 Survey along alongthe the North North Shore Shore of of Lake Wright, J.V. 1963 An An Archaeological Archaeological Survey Lake Superior. Superior. Anthropology Papers, of Canada3, Canada 3,Department Departmentof of Northern Northern Affairs Affairs Anthropology Papers, National National Museum of pp. and National National Resources, Ottawa, 99 pp. Wright, HE., Cushing 1973 Moines Lobe, Geological H.E., C.L. C.L. Matsch, Matsch, and and E.J. Gushing 1973 Superior Superior and and Des DesMoines Geological Society 136, p. 153-1 153-185 Society of America Memoir 136, 85 Wright, Wright, HE. H.E. WA. W.A.Watts Watts1968 1968Glacial Glacialand andvegetational vegetational history of northeastern Minnesota, Minnesota Minnesota Geological Society Survey Survey Special Special Publication Publication11. 11. - Zoltai, S.C. 1963. Glacial features of the Canadian Lakehead, Canadian Geographer Geographer 7, 7, 101 101ead, Canadian 115 Zoltai, S.C. 1 965a. Glacial features of the Quetico-Nipigon area, area, Ontario. Ontario. Canadian CanadianJournal Journal of of Earth Science Science 2, 247-269. 2,247-269. - Zoitai, Thunder Bay Surficial Geology, Geology, 1:506,880, 1:506,880, Map S265, Ontario Zoltai, S.C. S.C. 1965b. 1965b. Thunder Bay - Surticial Ontario Department of Lands and Forests. ! �TIlE PALEOPROTEROZOIC GEOLOGY OF THE GUNFLINT FORMATION Peir Pufahi, Pufahl, University University of British Columbia Fralick, Lakehead Philip Fralick, Lakehead University John Scott, John Scott, Ministry Ministry of of Northern Northern Development Development & Mines Formation records records a chemically dominated shelf shelf The Gunflint Formation silica- and iron-rich iron-rich precipitates precipitates predominate. predominate. sequence in which silicathe role role that both physical physical and and chemical chemical This frzp trip will examine the This processes played in invarious variousshelf shelf environments. environments. �FIELDTRIP 4 DEPOSITIONAL ENVIRONMENTS OF THE PALEOPROTEROZOIC GUNFLINT FORMATION Pier Pufahl and Philip Fralick INTRODUCTION INTRODUCTION Paleoproterozoic many other other important important Paleoproterozoiciron ironformations formationshost host most mostof of the the world's iron ore and many Consequentlythey theyhave havebeen beenthe the focus focus of of hundreds hundreds of of mineral deposits deposits (Simonson, (Simonson, 1985). 1985). Consequently mineralogical, geochemical investigations. However, in in spite spiteof ofthis immense mineralogical, geochemical and sedimentological investigations. this immense amount of data no consensus has ever ever been been reached reachedas asto totheir theirorigins. origins. Some Some of of this this controversy controversy stems accumulated stems from a poor understanding of the sedimentological environments in which they accumulated (Simonson, 1985). They were deposited during a unique interval of earth history when grossly They were deposited during a unique interval different prevailed (Cloud, 1973), and therefore therefore lack lack precise precise different atmospheric atmosphericand and hydrologic hydrologic conditions conditions prevailed modem analogues (Simonson, 1985; Fralick and Barrett, Barrett, 1995). Modem subaqueous hot-spring Modem subaqueous hot-spring activity has provided sediments, but but the provided clues to understanding understanding the precipitation precipitation of iron-rich sediments, mineralogy and deposits is not not comparable comparable to tothe thelarge largePaleoproterozoic Paleoproterozoic iron iron mineralogy and areal areal extent extent of modem deposits formations deposited during during the the Earths Barren, 1995). 1995). Detailed formations deposited Earth's early early history history (Fralick (Fralick and and Barrett, petrographic to interpreting the the paragenesis paragenesis of of petrographic investigations investigations of iron formations formations have contributed to syndepositional, diagenetic and metamorphic mineral mineral assemblages, assemblages, but but they they have done little to provide detailed, reliable information information regarding regarding iron iron formation formationdepositional depositionalprocesses. processes. Minerals Minerals and and provide detailed, textures are are commonly commonly altered altered to to secondary secondary assemblages, and when primary minerals minerals are are present present theoretical has been been limited in in its its ability to explain explain their genesis genesis (Fralick (Fralick and and theoretical chemical chemical modelling modelling has Barrett, Barren, 1995). 1995). Paleoenvironmental Paleoenvironmentalinferences inferencesfrom fromgrain-size grain-sizedistributions distributionsin in iron iron formations formationsare are also plagued with with uncertainty uncertainty because because they they are are commonly commonly indurated, indurated, diagenetically &genetically altered, altered, and and frequently fine-grained fine-grained (Simonson, (Simonson, 1985). 1985). Fortunately, these problems can be overcome by combining a regional basin analysis analysis of clastic clastic and and volcanic volcanicrocks rocks surrounding surroundingiron iron formations formations with detailed detailed examination examination of vertical and lateral facies trends within chemical sedimentary successions (Fralick and Barrett,1995). 1995).Associated Associated lateral faciestrends withinchemical sedimentary successions(Fralick and Barren, sedimentary settings. Sedimentary structures sedimentary and volcanic rocks provide data on depositional settings. structures and lithic processes, and lithic associations associationswithin within iron iron formations formationsgive give information on physical sedimentary processes, regional basin analysis analysis provides a framework framework within which to to view view iron ironformation formationgenesis. genesis. Combining these techniques techniques makes makes paleogeographic paleogeographic reconstruction reconstruction and depositional depositional modelling modelling Barrett, 1995). 1995). This is the same same approach approach used by sedimentologists sedimentologists and possible (Fralick and Barrett, stratigraphers to reconstruct clastic depositional systems. stratigraphers reconstruct clastic depositional systems. Location Location The United States, The main main portion portionofthe of theGunflint Gunflintiron ironrange rangeextends extends170 170km km northeast northeast from from the United States, at Gunflint Lake, to Loon Lake, Ontario (Figure 1). In Minnesota the Gunflint forms a narrow belt Gunflint 1). In narrow belt �Figure 1. Distribution Figure Distributionof ofPaleoproterozoic Paleoproterozoic iron iron formations in the Lake Superior region. Ontario f GUNFLINT — —— — -S. — — 1 4+( 41-4 i2H-' •4.* 4+4+444443+ +4. A . —. MESABI Cf 'of MARQUETTE t,++ •+ 4j 4+4+ 4 + 4 : 444 +44 CUYUNA F rocks younger than early Proterozoic Proterozoic early _____ Penokean plutonics L and volcanics early Proterozoic early ____ rocks, BIF in black Archean greenstone -::.:;:; Archean granite terrane .: +'4" + ... +44 . . . 444+ •831 •44 GOGEBIC .... .... . ..... . __ A . 44+ 44 4.44 4+ L5r '; I, Ii II.— / i/pt/li/I p/il, '1/ LEGEND — I, Archean Archean gneiss gneiss terrane terrane I / t t - . - Minnesota I- ON R1VE - Wisconsin. C. L100km I . �20 the southwest southwest by bythe theDuluth DuluthComplex. Complex. Erosional remnants 98 km 20 km long which is truncated to the northeast Ontario, suggest suggest apre-erosional apre-erosional continuation continuation of the the chemical chemical northeast of of Thunder Thunder Bay at Schreiber, Ontario, sedimentary rocks to the east. sedimentary rocks to the east. Previous Previous Work Work The Gunflint was discovered discovered in in 1850. 1850. The Gunflint iron formation was The earliest earliest recorded recorded geological investigation of the Gunflint by E. D. Ingall in 1887 (Ingall, 1888), who briefly briefly Gunflint was conducted by described the iron-bearing and Whitefish Whitefish Lake. Lake. Other early accounts iron-bearing strata near Silver Mountain and accounts were made by general by Smith Smith (1905) (1905) and Silver Silver (1906). (1906). Van VanHise Hiseand and Leith Leith in in 1911 1911presented presented aa general overview of the iron bearing rocks rocks in in the the Thunder ThunderBay Baydistrict. district. In 1924 J. E. Gill was was the the first to to describe its stratigraphy stratigraphynortheast northeastof ofSilver SilverMountain. Mountain. In 1927 describe the Gunflint in detail, and in 1926, its Gill published the chemical chemical sediments. sediments. T. L. Tanton described the published again, this this time on the origin of the iron prospects at at Mink Mink Mountain Mountain in in 1923, 1923, and in 1931 1931 gave an overview of the general geology in the vicinity vicinity of of Thunder Thunder Bay. Bay. In 1956 formation was divided by Goodwin Goodwin (1956) (1956) into six major sedimentary sedimentary facies 1956the iron formation facies representing Conglomerate Member, Member, 2) Lower Lower representingtwo twodepositional depositionalcycles cyclesand and four four members, members, a 1) 1)Basal Conglomerate Gunflint Member, 3) Upper Gunflint Member and 4) Upper Limestone Member; which are largely Gunflint Member, 3) Gunflint Member correlative with Broderick's (1920) four-fold division of of the Gunflint Gunflint iron iron range range in northeastern Minnesota and Wolff Wolffss (1917) subdivision of the the Biwabik Biwabii iron iron range range in in east-central east-central Minnesota Minnesota (Figure 2). He He also alsodrew drewattention attentionto to evidence evidence of widespread volcanism associated with deposition of the chemical sediments and suggested the iron iron and and silica. silica. In 1960 Goodwin of the chemical sediments and suggested a volcanic source for the 1960Goodwin and Moorehouse published the first detailed geological maps of the region (scale 1:31 1:31 680) 680) and and reported on the economic potential, mineralogy and chemistry of the iron bearing strata, and reported the economic potential, mineralogy and chemistry of the bearing modified modified Gunflint Gunflintstratigraphy stratigraphyinto intoaaLower Lowerand and Upper Upper Gunflint Gunflint depositional depositionalcycle cycle composed composedof of 10 10 members; a Basal Lower Taconite, Taconite, Local Local Lava Lava Basal Conglomerate, Conglomerate, Lower Algal Chert, Lower Shale, Lower Flows, Upper Algal Chert, Chert, Upper Jasper, Upper Shale, Shale, Upper Upper Taconite and an an Upper Limestone Limestone member. Fralick and Barrett Barrett (1995) (1995) have have recently recently redefined redefined Gunflint Gunflint stratigraphy stratigraphy as as simply simply member. consisting oncolitric cherts, cherts, and and cherty cherty consisting of of 22 members; members; aa lower lower member member comprised comprised of of basal algal and oncolitric They grainstones, and an upper member similar in stratigraphy to the lower member. grainstones, upper member similar in stratigraphy to the lower member. They have interpreted interpreted this this succession successionas as representing representing aa wave- and and tide-dominated inner shelf shelf sequence. Floran Lougheed (1983) (1983) and and Simonson Simonson Papike (1975), (1975), Randazzo Floran and and Papike Randazzo and Markun (1980), Lougheed (1987) mineral assemblages comprising comprising the the ~Gunflint (1987) have have given givendetailed detkled petrographic ietro&aphicdescriptions descriptionsof ofmineral unflint iron formation. The iron formation. TheGunflint Gunflintvolcanics volcanics(Goodwin, (Goodwin,1956,1960) 1956,1960)have havebeen been petrographically petrographically described described by Hassler and Simonson by Kissin and REE geochemistry geochemistry has been determined by Simonson (1989). Their TheirREE Fralick exhalative origin Fralick (1994). (1994). Carbon Carbonand andsulfur sulfurisotopic isotopicstudies studieshave have indicated a hydrothermal exhalative geochemical source for for the the iron iron (Cameron, (Cameron, 1983; 1983; Carrigan Camgan and as the source and Cameron, Cameron, 1991). 1991). Other geochemical investigations investigations(Kronberg (Kronbergand and Fralick, Fralick,1992) 1992)have have attributed attributedthe the alteration alteration of the Archean basement to the penetration penetration of Gunflint-derived fluids diagenetic or low-grade metamorphic metamorphic conditions. conditions. of Gunflint-derived fluids under under diagenetic Detailed accounts accounts of of The overlying Rove Formation Formation was was described described by Morey Morey (1967, (1967, 1969). 1969). Detailed microfossils preserved and Barghoorn (1 (1954), Barghoorn microfossils preservedwithin withinGunflint Gunflintchert chertare arerecorded recordedby Tyler andBarghoom 954), Barghoom and Tyler (1965a,b), Awramik (1976). (1976). (1965a,b), Edhom Edhom(1973) (1973) and and Awramik �S. I .... Basal con glomeraté Iron Formation Gunflint . . Formatin Pokagama Quartzite Biwabik Iron Formation 0 a = Dunham Formation Glen Township Formation lJttie Falls Formation Trout Lake Formation Mahnomen Formation Trommaid Formation Formation Rabbit Lake Virginia Formation Rove Morey, 1978 White, 1954 Goodwin, 1958 Cuna range Mesath range Gunflirite Northwest segment S a a Sunday Quartzite Bad River Dolomite Palms Formation Formation Iron- Ironwood Formation Tyler Aldrich, 1929 Blair / Ajibik Quartzite Siamo Slate Negaunee Iron Formation Goodrich Quartzite Michigamme Formation Cannon, 1986 Marquette range Archean rocks, undivided Bad River Dolomite Palms Formation Creek Formation Emperor Volcanic Compl Formation copp NFormation N Michigamrne GogeLNcrage For mation Reany Creek Enchantment Lake Formation Mesnard Quartzite Kona Dolomite Wewe Slate Quartz ite Ajibik Siamo Slate Formation Iron- Negaunee Goodrich Quartz ite Thaden, 1968 Marquette range Saunders Hemlock Formation Amasa and Fence River Formations Michigamme Slate Green stone Badwater Cannon, 1986 A7uPhft - Southeast segment Hemlock Formation Amasa and Fence River Formations Mithigamme Slate Dunn Creek Slate Badwater Greenstone Riverton Iron Formation Fortune Lakes Slate Stambaugh Formation Hiawatha Graywacke Cannon, 1986 ta Figure 2. Proposed correlations ofAnimikie Group sediments in the Lake Superior region. Fern Creek Formation Qua rtzite Sturgeon Randville Dolomite Fetch Formation Formation Iron- Vulcan Michigamme Slate Badwater Greenstone ratttn 2 j a a 0 0 C E a 0 0. = I! a d. 0 a = I 0 0, = 0 a = 2 2' 0 a = �Figure 3. Gunflint sediments sediments outcropping outcropping at at the spiiway Photographs of of Gunflint spillway section section near Figure 3. Photographs Kakabeka Falls. A) Trough Kakabeka Troughcross-stratified cross-stratified"lapihi" 'Tap(Â¥//i"tuff'(reworke volcaniclastic tuff (reworked rip-ups). rip-ups). ofseqAence. B) Large Largealgal algalbioherm biohermdraped drapedby by shales shales at at the the base of sequence. I A C! __ - -— , -: r' a -a / - - / - ;1 '. , - 2 - - I — _----1-_ - ft /; - I .-;C f �Several isotopic investigations investigations have have constrained constrainedthe the depositional depositionalage ageof of the the Gunflint Several isotopic Formation between between 1.6 1.6 and and 2.0 2.0Ga. Ga. Hurley Hurley et et al. at (1962) minimum age age of of deposition depositionof of (1962) obtained aa minimum about K-Ar methods, methods, to to which which they theyapplied appliedan anempirical empiricalcorrection correction factor, factor, about 1.6 1.6 Ga Ga by both Rb-Sr and K-Ar which allowed age of ofapproximately approximately 1.9 1.9Ga Ga(Stille and Clauer, Clauer, 1986). 1986). Faure and which allowed them to propose an age (Stille and approximately 1.6 1.6 Ga. Ga. More Kovach (1969) also obtained a Rb-Sr isochron age of approximately More recently, recently, Stille Stille Clauer (1986) obtained about 2.08 2.08 Ga Ga for forvolcanic volcanicslates slatesinterbedded interbedded and Clauer obtained a Sm-Nd isochron age of about with iron-bearing iron-bearing strata strata of the Guntlint Gunflint Formation. The absolute age age of of the the Gunflint Formation Formationwas wasdetermined determinedby byFralick Fralicketetal. a. (1998) by conducting U-Pb, single zircon geochronology on a sample population from reworked tuffs conducting U-Pb, single zircon geochronology on a population from reworked tuffs outcropping near Kakabeka Kakabeka Falls Falls (Figure (Figure3), 3),aaeuhedral euhedralzircon zircongave gaveaaconcordant concordantage ageof of1878 1878zE2 ± outcropping (Figure 4) which Fralick et al. at (1998) (Figure (1998)argue argueis is the the depositional depositional age of this unit. I KB-TUFF Brown euhedral zircons .34 .338 .336 .334 .332 5.2 5.25 5.3 5.35 5.4 5.45 fromthe theupper upperGunflint GunflintFormation Formation (Fralick, (Fralick,etetal, at 1998) 1998) Figure 4. Concordia Concordiadiagram diagramfor zirconsfrom Animikie Basin Paleoproterozoic sedimentary Animikie Basin Basin form a southwardsouthwardThe Paleoproterozoic sedimentaryrocks rocks deposited deposited in in the Animikie thickening wedge province, which truncated in in eastthickening wedge covering coveringthe the southern southernmargin marginof of the the Superior Superiorprovince, which is truncated central Minnesota and northern Wisconsin by the 'Penokean" magmatic terranes". Sedimentation Minnesota by the "Penokean" terranes". Sedimentation began approximately prior to to or during during approximately 2.1 2.1 Ga Ga ago ago and and ceased ceased roughly 1.85 1.85 Ga ago (Morey, 1983), prior the Penokean orogeny of Goldich et al. at (1961). The nature of the sediment varies considerably, The nature of the sediment varies considerably, (1961). ranging the thick thick successions successions of of ranging from from volcanic volcanic and and clastic to the chemical precipitates which form the iron formation. The Thetermination terminationof ofthe thePenokean Penokeanorogeny orogeny marked marked the onset onset of an intrusive igneous phase plutons into into the theAnimikie Animikiesediments sediments emplaced subduction subductionrelated related tonalitic tonalitic and granitic plutons phase which which emplaced related volcanics volcanics of the the Wisconsin Wisconsin magmatic magmatic terranes. terranes. The the basin basin was was The present form of the and the arc related �achieved around1.1 1.1 Ga Gaago achieved around ago (Silver (Silver and Green, 1972; 1972; Hanson, Hanson, 1975;Wanless Wanless and and Lovebridge, Lovebridge, 1978) 1978) System (King (King and Zietz, 1971) when a north-northwest trending trending branch of the Midcontinental Rift System Zietz, 1971) separated the Animikie Animikie sediments southeastern segment (Morey, 1983). separated sediments into a northwestern and southeastern 1983). of the Animikie Animikie Group unconformably unconformably overlays overlays the the Superior The northwestern segment of Province Malinomen Formation), Province and and consists consistsof a basal sandstone-siltstone (Pokegama (Pokegama Quartzite, Mahnomen Formation), (Gunflint, Biwabik, Biwabii, Trommald iron formations), and a thick, upper, formation (Gunflint, iron formation upper, shale-siltstone shale-siltstone sequence (Rove, Virginia and Rabbit Rabbit Lake Lake Formations). Formations). In east-central Minnesota the the Thomson Formation Rove, Virginia Virginia and and Rabbit Rabbit Lake Lake Formations, Formations, has has also also Formation which has similar similar lithology to the Rove, considered correlative and Ojakangas, Ojakangas, 1970). However, been considered correlativeto the Animikie Group (Morey and However, recent recent structural interpretations have complicated complicated the the correlation interpretations have correlation of these units units (Ojakangas, (Ojakangas, 1995); 1995); northward Penokean Orogeny Orogenyhas hasjuxtaposed units of ofdiffering differingEarly EarlyProterowic Proterozoic juxtaposedunits northward thrusting thrustingduring during the Penokean ages in east-central Minnesota (Southwick et al., 1991; Hemming, Hemming, Minnesota at, 1988; Southwick and Morey, 1991; 1994). Similar within the the southeastern southeastern segment segment in in Similarstructural structuralcomplexities complexities also hinder correlation within northern Wisconsin 1991 ; Gregg 1993). northern Wisconsin and and the the Upper Upper Peninsula Peninsula of Michigan (Klasner et al., at, 1991; 1993). The were deformed deformed during during the the Penokean Penokean orogeny, orogeny, The sedimentary sedimentary rocks rocks of the Animikie Basin were and Archean Archean rocks rocks along along the the forming a zone zone of of deformed deformed and and metamorphosed metamorphosed Paleoproterozoic and southern margin of the Superior Province Province (Sims, (Sims. 1991). It is thought to to have have occurred occurred between between 1.9 1.9 southern margin and Bickford, Bickford, 1985). In the Great Lakes region it and 1.76 Ga (Van Schmus, 1976; Van Schmus and forms the Late Archean crust crust of the the Superior Superior Province Province and and the the forms the transition transition between between the Late Archean Paleoproterozoic Paleoproterowic continental crust of the Mazatzal Mazatzal and Yavapai Yavapai provinces of the southwestern southwestern Deformation along United United States States(Sims (Simsand and Petennan, Peterman,1986; 1986;Hoffman, Hofflnan, 1989; 1989;Barovich Barovich et al., at, 1989). Deformation this thrusting and development of basement basement gneiss gneissdomes domes(Southwick (Southwicket etal., this tectonic tectonic front front involved involved thrusting at, Minnesota, northern northern Wisconsin Wisconsin and and the the 1988). Rocks of the orogeny are exposed in east-central Minnesota, 1988). Upper Peninsula Peninsulaof of Michigan. Michigan. The orogeny Animikie strata strata and and a southern orogeny consists consists of a northern northern zone of deformed deformed Animikie southern assemblage plutonic rocks rocks of of the the Wisconsin Wisconsin assemblageof of arc-related arc-related volcanics volcanics and synorogenic, calc-alkaline plutonic magmatic terranes, separated by by the Niagra Fault Zone Zone in in northern northern Wisconsin Wisconsin and the the Upper Upper Peninsula 1989) and by the Malmo Discontinuity in east-central Minnesota 1989) and by the Malmo Discontinuity in east-central Minnesota Peninsulaof of Michigan Michigan(Sims (Sims et al., at, (Southwick and and Morey, Morey, 1991). 1991). (Southwick The earliest sedimentological for the the Animikie Animikie Basin Basin relied relied on on the the work work of of James James sedimentological models for (1954) successions evolved from from aa "miogeosynclinal" "miogeosynclinal" sequence sequence (1954) who concluded concluded that iron formation successions to a "eugeosynclinal" during Paleoproterowic Paleoproterozoictime. time. James' James original ideas were then "eugeosynclinal" assemblage during discarded in the mid sediments in in aa rift-like rift-like basin basin discarded mid 1970's 1970's in in favour favour of of deposition deposition of Animikie Animikie sediments (Cambray, 1978). 1978). In Inthis thismodel modelrifling riftingwas wasfollowed followedby by the theultimate ultimateclosure closureof of the the basin basin with with the the and Penokean orogeny. orogeny. In the early early 1980's 1980's Young Young (1983), (1983), by analogy analogy with other Phanerozoic and Proterozoic tectonic and sedimentary history history of ofProterozoic Proterozoicdepositional depositionalbasins, basins, interpreted interpretedthe the tectonic Proterozoic rocks in the northern Great Lakes region in terms of an aulacogen model. model. Unfortunately, Unfortunately, there was no general consensus on the driving force which which caused caused the the basin basin to to form and the characteristic characteristic sediments analogous to rift/aulacogen depositional systems are absent. In In the mid 1980's 1980's continued sediments analogousto rifVaulacogen depositional systems research lead to to significant significant advancements advancements in understanding understanding the tectonics associated with basin development. These Thesestrides strideslead leadHoffman Hofflnan(1987) (1987)to tosuggest suggestdeposition depositionof ofchemical-sediments chemical-sediments �Icr\, member 2 member member!1 member member 4 member 3 member member S member 5 , I. p..) : I 20m C ra'< I I C) t ININ coarsening upwards sequence transgression basal transgression middle transgression upper transgression Stratigraphk section from holes Figure 5. Stratigraphic sectionthrough throughthe theGunflint GunflintFormation Formationbased basedon on drill drill core corefrom Figure is aafew few kilometres kilometres north north of the the US US border. barrfcr.A A detailed detailed discussion discusshn of the lithofacies is - - L (sen/o/In the tort 'ft Up vorlion graillsizg changes in water 4 tR1 In4n-nt clianees trends.,, L [_Z L L �occurred crustal loading occurredin inaamigrating migratingperipheral peripheralforeland forelandbasin basinwhich whichformed formedin in response response to crustal loading during during the thePenokean Penokeanorogeny. orogeny.Southwick Southwicketetatal.(1988) (1988)and andSouthwick Southwickand andMorey Morey(1991) (1991)then thenreinterpreted reinterpreted the at, 1960) 1960)in in Minnesota. Like LikeHoffman, Hoffinan,(1987) (1987) thesegment segmentof ofthe thePenokean Penokean orogeny orogeny (Goldich, et al., they peripheral foreland theyalso alsoconcluded concludedthat thatthe theAnimikie AnimikieGroup Groupaccumulated accumulatedin inaaperipheral forelandbasin basinand andthat thatiron iron formation formationdeposition depositionoccurred occurredin inthree threedistinct distincttectonic tectonic settings settings as as the orogeny evolved. evolved. Recently, Recently, Pufahl (1995, 1996) 1995) have Pufahl(1995, 1996)and andHemming Hemming(1994, (1994,1995) have demonstrated demonstrated that this tectonic tectonic model model is is no no longer 1995) contends longervalid. valid. Hemming Hemming(1994, (1994,1995) contendsthat thatnedodimium nedodimiumand and lead lead isotopic isotopic evidence evidence for for the provenance provenanceof ofthe theAnimikie AnimikieGroup Groupis isconsistent consistentwith with the the tectonic tectonic evolution evolution of of the Animikie Animikie Basin Basin beginning telescoped back arc basin basin that that beginningas asaapassive passivemargin marginwithin withinaaback backarc arc basin, basin, and and ending ending as a telescoped closed closedas asaa result resultof ofaa change change in in relative relative plate convergence convergence direction. Nevertheless, Nevertheless,in in recent recentyears years the theforeland forelandmodel modelhas hasreached reachedwidespread widespreadacceptance acceptancebased basedon on high high resolution resolution aeromagnetic data, aeromagneticdata, exploratory exploratory drilling drillingthrough through structurally structurally complex complex regions, and sedimentological sedientological investigations investigations of clastic (Hoffman, 1987; 1987;Southwick Southwicketal. etat,,1988; 1988; Southwick clasticunits unitsabove aboveand and below below iron-bearing strata (Hoffman, Southwick and andMorey, Morey,1991; 1991;Ojakangas, Ojakangas,1995). 1995). GUNFLINT GUNFLINTIRON IRONFORMATION FORMATION PALEOGEOGRAPHIC PALEOGEOGRAPHICRECONSTRUCTION RECONSTRUCTION Interpretations Interpretations presented presented here here are are based based on on the the study study of of core core drilled drilled through through the the Gunflint Guntlint Formation. Formation. The The Formation Formation has has been been divided divided into into five five members members based based on on distinct distinct lithofacies lithofacies associations associationsand andcontrolled controlledby bytransgressive-regressive transgressive-regressivecycles cycles(Figure (Figure5). 5). The The strand strand proximal proximal succession fine-grained, chemical chemical sediments sediments successionpresent presentin inNorthwestern NorthwesternOntario Ontarioofflaps offlapsto to the south as fine-grained, of 6 and and 7). 7). This of the the slope slopeare are approached approachedin in the the Cuyuna Cuyuna Iron Iron Range Range (Figures (Figures 6 Thischapter chapterwill will give give detailed detailed interpretations interpretations of the the depositional depositional environment environment of each each of of these these members; members; but but first first an an overview overviewof ofnearshore nearshoresedimentation sedimentationisispresented. presented. Lateral Lateral and and vertical vertical facies facies changes changes within within the the Gunflint Gunflint Formation Formation indicate indicate deposition deposition occurred on a shallow, non-barred, microtidal, storm-enhanced shelf with little influx. occurred on a shallow, non-barred, microtidal, storm-enhanced shelf with little clastic clasticinflux. Bedforms Bedformsand andinternal internalsedimentary sedimentarystructures structurescomposing composingGunflint Guntlintstrata strataare are directly directly comparable comparable to to those found in modern nearshore-to-shallow marine clastic and carbonate depositional those found in modern nearshore-to-shallow marine clastic and carbonate depositionalsystems. systems. These These facies facies trends trendsrecord recordenergy energytransformations transformationsfrom fromdeep deep water, water, offshore offshorewaves waves to to nearshore, nearshore, shoaling conditions. Minor shoaling waves waves under under fairweather fairweather and storm conditions. Minor mafic mafic flows (Goodwin, 1960) 1960) and extensive extensivetuffaceous tuffaceoushorizons horizons(Hassler (Hassler and and Simonson, Simonson,1989) 1989)within within the the Gunflint Gunflint indicate indicate that that the the region region was was volcanically volcanicallyactive activeat at the the time time of of basin basin formation formationand and subsidence subsidence (Fralick (Fralick and Barrett, Barren, 1995). 1995). The Themain mainmorphological morphologicalelements, elements,bedforms bedformsand andinternal internal sedimentary sedimentary structures structures along along aa typical typical beach-shoreface-offshore beach-shoreface-offshore profile profile are are shown shown in in Figure Figure 8. 8. The Thefollowing followingsummary summary of of these these features and Clifton Clifton et. et. al. at (1971). features is is taken taken from from Walker and Plint (1992), Einsele (1992) and (1971). The foreshore, also portion above above the the low low tide tide line line alsosynonymous synonymouswith with beach, beach, consists consistsof of the the portion Theforeshore, In the the foreshore foreshore zone zone the the most most and and is is dominated dominatedby by the theswash swashand andbackwash backwash of of breaking breakingwaves. waves. In high characteristic dipping seaward. seaward. On characteristicfeature featureis is parallel parallel to to low-angle low-angle cross-bedding cross-bedding dipping On non-barred non-barred high inner (upper foreshore), planar zone and energy an energyshorelines, shorelines,two twoplanar planarlaminated laminatedzones zonesoccur, occur,an an inner (upper foreshore), planar zone and an outer (lower foreshore) planar zone within the zone of breaking waves. waves. In between these outer (lower foreshore) planar zone within these two two zones zones depositional features. the the bedding beddingsurface surfacebecomes becomesrough roughdue dueto to dotted dotted and andirregular irregularerosional erosionaland and depositional features. �Figure 6. Figure 6. Location of driliholes depicted on Figure 7. �G-1 MGS-8 Mahnomen Fm (Cs) 18290 Rabbit Lake Fm (Vs) SW Is. • -.4 MGS-7 MGS-2 20m Figure 7. 30f TB0642 4 Gp,GIICS TB0218 Rove Fm (Vs) NE slope. The green units are fine-grained volcaniclastics. Other units are described in the text. sections are from logged driliholes (for locations see Figure 6). Sc and Si arc fine-graincd chemical sediments of the Lithofacies distribution across the Gunflint, Mesabi and Cuyuna shelf to slope depositional system. Stratigraphic Kakabeka Conglomerate (Cp) GF-3 ftp Pokegama Quartzite (Cs) MGS-5 Virginia Fm (Vs) �Morphological elements, and internal Figure & elements, bedforms bedforms and internal sedimentary sedimentary structures structures along along aa Figure 8. Morphological typical beach-shoreface-offs bore profile. @pica1beach-shoreface-offshoreprofile. - ZONE ZONE OF OF SHOALING SHOALING WAVES SURF ZONE fairweather wave base !Sn'9 P2 stormwave wave storm basebase S SHOREFACE SHOREFACE SHELF INNER SHELF (subtidal) (subtidal) Beciforms Bedforms Grain Grain size size - parallel - laminated laminated mud facies fades silt and and clay clay —I I lunate lunate outer assymetric HCS HCS assYmetric dune planar dune planar fades facies facies rippled facies facies fades facies facies fine sand sand - silt silt - - fine fine medium medium sand sand FORE FORE BACK BACK SHORE SHORE SHORE SHORE (supratidal) (intertidal) (supratidal) (intertidal) inner inner rough rough facies facies inner inner planar planar fades facies coarse coarse fine sand sand - fine mediurr fine fine mediur sand gravel sand gravel - - �In tidally tidally dominated dominated systems systems the the foreshore foreshore and and upper upper shoreface shoreface is is comprised comprised of of flaser, wavy, and In lenticular lenticular bedded bedded sands sands and and muds muds typical typical of of sedimentation sedimentation on inter- and subtidal, sand-mud subtidal, mixed sand-mud flats. The shorefacelies liesbelow belowlow lowtide tidelevel leveland andisischaracterized characterized by by day-to-day day-to-day sand transport transport Theshoreface above fairweather fairweather wave wave base. base. The above Theshoreface shoreface normally normally has has a concave-upward profile, which is is in in equilibrium with with the the waves waves that that shape On the the lower at depths equilibrium shape it. it. On lower shoreface, shoreface, at depths near near or or below below produced by storm fairweather wave base (10 (10 to 20 m), are long crested symmetrical symmetrical wave ripples, produced storm waves. Landward, Landward, on onthe themiddle middleshoreface, shoreface,these these inactive inactive ripples ripples pass into into active active ripples ripples which which become increasingly increasingly asymmetric, trough cross become asymmetric, irregular, and short-crested. Larger, trough cross stratified, stratified, lunate lunate zone. All dunes are frequently observed on the upper shoreface in the breaker zone. All these these bedforms bedforms are are associated with small-scale or larger-scale cross bedding which is is predominantly oriented oriented toward toward continuous agitation, the deposition of mud the land. Because Becausethe thesediments sedimentsof of this this zone zone are are under continuous base and has a lower istypically typically below below fairweather wave base is prevented. The The mud-dominated mud-dominated shelf is depositional slope foreshore and shoreface. Muds typicallyparallel parallel laminated laminated and and highly highly thanthe foreshore Muds are typically depositional slope than bioturbated bioturbated in in modem modem shallow-marine shallow-marinedepositional depositionalsystems. systems. In storm In storm enhanced enhanced shallow shallow marine marine non-barred, non-barred, environments environments the the shoreface shoreface processes processes described thus described thus far, far, as as well well as as processes processes in in deeper deeper regions regions of of the the inner inner and and outer outer shelves shelvesare are strongly strongly affected and and modified modified by by storm storm events events (Davis, (Davis, 1992; 1992; Einsele, Einsele, 1992). 1992). Storms affected Storms can can deposit deposit sandy sandy material in in the material the supra supra tidal tidal zone, zone, as aswell well as asgenerate generatespecial specialnon-channelized non-channelized flow flow conditions conditions in in deeper water. water. These deeper Thesehigh highenergy energyevents eventsfrequently frequently produce produce characteristic characteristic sheet-like sheet-like sand sand and and mud mud beds, called tempestites, of considerable lateral extent (Johnson and Baldwin, Baldwin, 1986; Morton, 1988; Nummedal, 1991; Einsele, 1992). Storm-generated bed forms show a the beach beach Nummedal, 1991; E i e l e , 1992). Storm-generated bed forms show adistinct distincttrend trend from fromthe into deeper water. The upper shoreface (surf zone) displays dunes oriented parallel to the shoreline. into deeper water. The upper shoreface (surf zone) displays dunes oriented parallel to the shoreline. When flow becomes channelized longshore erosively scour scour fairweather fairweather sediments, sediments, longshore and rip currents erosively depositing mediumand coarse-grained, trough and planar, cross stratified sands. The middle depositing medium- and coarse-grained, trough and planar, cross stratified sands. The middle shoreface is dominated dominated by both bedfonns with horizontal or shoreface both flat and swaley bedforms with nearly horizontal or low-angle low-angle swaley swaley cross cross stratification. stratification. Because Becauseof ofthe thecontinual continual agitation agitation of of sediments sediments through through wave wave action action on on the the upper middle shoreface record of of heavy heavy storms storms is isusually usuallydestroyed. destroyed. On the lower lower shoreface shoreface upper and and middle shorefacethe the record On the (5 to 20 20 m m water water depth), depth), the ebb currents currents reaches reaches about about the the same same magnitude magnitude as (5 to the stress stress of of storm storm surge surge ebb as the oppositely oppositely directed the directed storm-wave storm-waveinduced induced oscillatory oscillatory flow flow (Einsele, ( E i e l e , 1992). 1992). Thus, Thus,for foraashort shorttime, time, both currents both currents may stir stir up up sand sand and and mud, mud, which which are are redeposited redeposited as as parallel parallel and and hummocky hummocky crosscrossstratified fine-grained,graded gradedbeds bedsatat the the same same location location or or nearby nearby (Einsele, (Einsele, 1992; 1992; Dott Doll and stratified fine-grained, and Bourgeois, 1982). On inhigh-energy high-energy Bourgeois, 1982). Onthe theinner innershelf shelfand andparts partsof ofthe theouter outershelf, shelf,particularly particularly in environments, environments, storm-induced combined flow may still still generate HCS or thin, graded, graded, sandy sandy beds beds resulting from If the the suspension suspension originates originates from from storms storms and and resulting from laterally laterally flowing flowing suspension suspension currents. currents. If the sandy the sandy layers layers alternate alternate with with shelf shelfmuds, muds, the thestorm storminduced inducedbeds bedsrepresent represent distal distaltempestites tempestites (Aigner, Einsele, the current current component component of of the the (Aigner, 1985; 1985; E i e l e , 1992). 1992). At At greater greater water water depths depths on on the the shelf, shelf, the combined storm beds combined storm flow flow becomes becomes dominant, dominant,leading leadingto to current currentrippled, rippled, offshore, offshore, fine fine sand sand and and silt silt beds and graded graded rhythmites rhythmites (Aigner, and (Aigner, 1985; 1985;Einsele, Eisele, 1992). 1992). Since Sinceonly onlythe thelargest largeststorms stormscan canaffect affectthe the mud deposition. quiescence and mud deposition. storm events events are are followed followed by long long periods of quiescence sea floor in this zone, storm Paleogeographic interpretation interpretation Paleogeographic The following following discussion discussion has divided into into three three sections. sections. Each The has been been divided Eachdeals deals with with interpreting interpreting the vertical and lateral facies trends comprising the basal transgressive, middle regressive and upper upper the vertical and lateral facies trends comprising the basal transgressive, middle regressive and transgressive depositional cycles of the Gunflint Formation in detail. transgressive depositional cycles of the Gunflit Formation in detail. �Kakaheka Conglomerate Conglomerate ,tidal roB Figure 9. Figure 9. Paleogeographic reconstruction reconstruction of of the thedepositional depositional system system which which produced produced the Gunflint Formation. Formation. AAdetailed attributes of this this system system isispresented presented detaileddiscussion discussionof of the the attributes Gunflint -in &the iB &L text. - ?UOPtE �Basal transgression Basal transgression extends from from the the base base of ofthe theAnimikie Animikie Group Group to to the the This 20 m thick, upward fining cycle extends middle of base of the cycle a middle of member member 2. 2. The base cycle is is characterized characterized by the Kakabeka Conglomerate, a backshore, pebbly pebbly beach beach deposit deposit preserved preserved as as aa transgressive pebble lag lag (Figure This backshore, transgressive pebble (Figure 9). 9). This intraformational conglomerate conglomeratewas was formed formedby bythe the localized localizedweathering weatheringof ofthe thepeneplain. peneplain. Then, intraformational tirough subsequent intraclasts were reworked reworked (swash/backwash) these these intraclasts through subsequentstorm-generated storm-generatedwave waveaction action(swashlbackwash) crudely stratified, tidal, beach beach deposits. deposits. Ojakangas into crudely stratified, matrix supported, supported, pebbly, supra tidal, Ojakangas (1983) (1983) has similar interpretation conglomeratic unit forming the the base base of of the the Pokegama Pokegama quartzite quartzite made a similar interpretation of the conglomeratic Mesabi iron range in the Mesabi range in east-central Minnesota. Minnesota. As the basal transgression progressed these coarse beachface beachface sediments sediments were were on-lapped on-lapped by by the fineparallel laminated laminated grainstones grainstones(GP (GP facies) facies) of of member member 1. The the fine- and and medium-grained, medium-grained, parallel 1. The hematite-enriched transition from member I may indicate a change in the redox state of of the hematite-enriched transition from member 1 may indicate a change in the redox state the depositional system level or, or, more more simply, simply,ititmay mayrepresent representoxidation oxidationof of depositional system accompanying accompanying a rise in sea level iron-bearing sediments by late phase oxygen-rich meteoric waters percolating along this lithologic sediments meteoric waters percolating along this lithologic boundary. Deposition boundary. Deposition of of this this thin, thin, parallel parallel bedded bedded grainstone unit marks the onset of intertidal intertidal sedimentation on the the foreshore foreshore (Figure (Figure 9). 9). Member Member l's m) and and apparent apparent lack lack of of sedimentation 1'srelative relative thinness thinness (5 m) desiccation features features suggests suggests that that the the intertidal zone was was not well developed Animikie desiccation intertidal zone developed on the Animikie (tidal range range <2 <2 m) m) (Reineck (Reineck and and shoreline, a situation typical of modem, microtidal environments (tidal Singh, may have have developed developed LLHstromatolitic stromatoliticbioherms bioherms(Ad (Ad facies) facies)at at the base of member 1 may Singh, 1975). 1975). LLH modem, colunmar in much the same way modem, columnarstromatolites stromatolitesand and crypt crypt algal algal knolls knolls form form in the low energy Here columnar intertidal flats flats of intertidal of Shark Shark Bay, Bay, Australia Australia (Hoffman, (Hoffinan, 1976; 1976; Schreiber, Schreiber, 1986). 1986). Here columnar stromatolites develop in the lower intertidal zone in response response to to strong strong wave wave action. action. An oncolitic stromatolites oncolitic mats marks the the transition transition into into the the subtidal subtidal (Figure (Figure horizon (Ao facies) facies) above these intertidal, algal mats Ginsburg (1960) (1960) compared compared modem modern 9) (1 (Logan al.,1964; 1964; Ginsburg, Ginsburg, 1960, 1960, Sellwood, Sellwood, 1986). 1986). Ginsburg ogan et aT, oncolites from Devonian, Permian and Precambrian Precambrian examples examples and oncolites from the the Florida Florida and and Bahama Bahama Banks to Devonian, found they formed I1 to or near near the the subtidal subtidaltransition. transition. Oncolites to 88 feet below mean water level at or from the Paris Paris Basin, Basin, aa non-barred, non-barred, shallow shallow epeiric epeiric sea sea covering covering much much of of northwestern northwestern Europe Europe during the Middle Jurassic, were also determined to characterize this transition (Seliwood, Middle Jurassic, were also determined (Sellwood, 1986). 1986). The overlying flaser and wavy bedded grainstones(Gf, (Gf, Gw Gw facies) of bedded chert-carbonate chert-carbonate grainstones member 2 represents represents subtidal deposition on a shallow, shallow, storm stormenhanced, enhanced,non-barred non-barred shoreline shoreline (Figure (Figure member subtidal deposition 9). 9). Similar Similar Middle Middle and and Upper Upper Cambrian, Cambrian, cyclic, cyclic, peritidal, peritidal, carbonate, carbonate, tempestites tempestites compose compose the the Elbrook Virginia Appalachians Appalachians (Demicco, (Demicco, 1985, 1985, Koerschner Koerschner Elbrook and Conococheague ConococheagueFormations Formations in the Virginia This 1.6 and Read, 1989). krn thick thick carbonate carbonate sequence sequence formed formed on on the the Cambro-Ordivician Cambro-Ordivician 1989). This 1.6 km continental shelf; aggraded, rimmed, mature, passive passive continental continental margin margin (Koerschner (Koerschner and and Read, Read, continental shelf; an aggraded, 1989). Cycles thickness, possess possess aa sharp sharp basal basal transgressive transgressive 1989). Cyclestypically typically range range between between 11 and and 7 7m m in in thickness, surface, are overlain overlain by aa subtidal subtidal unit unit passing passing into into aa tidal tidal flat flat cap, and record regional changes changes in time (Koerschner and and Read, Read, 1989). 1989). Three types of cycles are sea level over very short intervals of time recognized, thin-based cycles. The been recognized, thin-basedcycles, cycles,thrombolitic-based thrombolitic-basedcycles, cycles,and and thick thick based based cycles. The latter latter has has been divided into three grainstone-based and and digitate-algal-bioherm-based,grainstone-based three subcycles, subcycles, those which are digitate-algal-bioherm-based, Ribbon-carbonate-basedcycles cyclesmost most closely closely resemble resemble member member 33 and ribbon-carbonate-based. and ribbon-carbonate-based. Ribbon-carbonate-based therefore will will be be the the only only cycle cycle fully fully reviewed reviewedin inthe thefollowing followingdiscussion. discussion. For Foraafull fulltreatment treatmentof of these cyclic, peritidal carbonates carbonates the reader is referred to Koerschner and Read (1989). �Ribbon-carbonate-based cycles are composed Ribbon-carbonate-based cycles composed of 11 to to 55 m m thick thick fining fining and andcoarsening coarsening upwards upwards sequences sequencesof of flaser flaserbedded beddedcoarse-grained coarse-grainedcarbonate carbonate grainstones/packstones grainstonedpackstones which are are comprised of wavy and lenticular bedded finer-grained pelletal carbonates and rare lime comprised wavy and lenticular bedded finer-grained pelletal carbonates rare lime conglomerates dolomitic mudstones. The conglomeratesintimately intimately interbedded interbedded with with parallel laminated dolomitic The term term comes comes from the field appearance ofthe alternating thin-beds (ribbons) of differentially weathered limestone from the field appearanceofthe alternatingthin-beds (ribbons) of differentially weathered limestone and are and dolostone dolostone (Demicco, (Demicco, 1983). 1983). The Thecoarse-grained coarse-grainedribbon ribboncarbonates carbonatesand and pellet pellet packstones packstones are most similar to the flaser bedded, chert-carbonate grainstones (Of facies) of member 3 in the similar to the flaser bedded, chert-carbonate grainstones (Gf facies) of member 3 Gunflint Gunflintchemical chemicalsedimentary sedimentarysuccession. succession.Coarse-grained Coarse-grainedribbon ribboncarbonates carbonatesare areunlayered unlayered or or have have low-angle cross bedding with weakly graded foreset laminae. Pellet packstones have horizontal low-angle cross laminae. Pellet packstones horizontal laminations, ripple cross-lamination. cross-lamination. Mud-poor pelletlaminations,climbing climbingwave-ripple wave-ripple lamination and wave ripple rich ribbon ribbon carbonates carbonates and and mud-and-pellet mud-and-pellet rich ribbon ribbon sequences sequences most most closely closely resemble resemble wavy wavy bedded, bedded, chert-carbonate chert-carbonategrainstones grainstones(Gw (Gwfacies). facies). Mud-poor, Mud-poor, pellet-rich pellet-rich ribbon ribbon carbonates carbonatesare are planar laminated; pellet laminated;mud-and-pellet-rich mud-and-pellet-richribbon ribbonsequences sequencesare arecomprised comprisedofwavy of wavyand andlenticular lenticular bedded pellet layers interbedded interbedded with with form-discordant form-discordant wave ripples, ripples, starved ripples and and parallel parallel laminated laminated dolomite mudstones mudstones(Koerschner (Koerschnerand and Read, Read, 1989). 1989). dolomite Demicco Demicco (1983) (1983) and Koerschner Koerschner and Read (1989) (1989) interpret these ribbon sequences as recording storm-influenced subtidal settings floored floored by byinterlayered interlayered recordingshallowing shallowingby by aggradation aggradationfrom from storm-influenced Coarsening-upward lime muds muds and and sands, sands, to to subtidal subtidal sand sand flats flats on on aa mature, mature, rimmed rimmed shelf shelf. Coarsening-upward sequences sequencesrecord record low lowenergy, energy, subtidal subtidalconditions, conditions,followed followedby upward-shallowing upward-shallowinginto into high high energy energy shallow zone). Koerschner contend these these shallowwater water settings settings (ie. surf zone and breaker zone). Koerschner and Read (1989) contend coarse-grained coarse-grained ribbon ribbon carbonates carbonatesformed formed on on sand sand flats, flats, where coarse layers were reworked during storms and stormitidalenergy energy waned. waned. The rare lime lime and less less common common fine fine layers layerssettled settledout outasasstorm/tidal conglomerate conglomerate interbeds interbeds were deposited deposited during storms storms which swept semi-lithified, peloidal sands from transgressive from shallow shallowsubtidal subtidaland and intertidal intertidal settings. settings. Fining Finingupwards upwards ribbon ribbon sequences sequences record transgressive high-energy conditions that gave way way to low energy energy conditions conditionsas asthe theplatform platform shallowed. shallowed. Finegrained response grained peletal, peletal, ribbon ribbon carbonates carbonatesformed formed on lower energy, subtidal, mixed sand flats in response to wave wave action action and and grade gradelandward landward into into mixed mixed sand-mud sand-mud flats flats (Koerschner (Koerschner and Read, 1989). 1989). Fairweather with deposition of of thick thick storm layers of Fairweather reworking of wave rippled beds alternated with pelletal pelletal sediment sedimentwith withamalgamated amalgamatedhurnmocky hummocky cross cross stratification, stratification, and wave and current ripples (Koerschner (Koerschnerand and Read, Read, 1989). 1989).Similar Similarclastic, clastic,shallow, shallow,tidal tidal marine marine sequences sequences occur occur in the modem North Sea (Demicco, 1983). North Sea (Demicco, 1983). Unlike wavy Unlike the the Cambrian Cambrian ribbon ribbon carbonates carbonatesof the Virginia Appalachians these flaser and wavy bedded bedded chemical chemicalsediments sedimentsdid didnot notform formby by aggradation aggradationof of upward upward shoaling shoaling grainstone grainstonesequences. sequences. Instead, vertical changes reflect a rate of relative sea level level rise which which changes in iron formation facies reflect consistently consistently outpaced outpaced that that of of sedimentation. sedimentation. Middle regression regression Middle This extends to This minor, minor, 20 20 m m thick, regressive regressive phase begins in the middle of member 2 and extends 3. It records the gradual onset of shallowing from the middle shoreface to the the top top of of member member 3. the lower lower foreshore. foreshore. The Thesubtidal subtidalmixed mixedgrainstone-chemical grainstone-chemicalmud mud flats flats of member 2 coarsen upwards to packages) of flaser bedded chert-carbonate grainstones. grainstones. These to 33 m thick packages) These coarse coarse packages packages formed formed during duringregressive regressiveofflap offlapof oflower-middle lower-middleshoreface shorefacefacies faciesand, and,like likethe theflaser flaser bedded bedded package packageat atthe the base base of of this this member, member, represent represent dune dunedevelopment development in in the the surf surf zone zone of of the upper shoreface. shoreface. �As level continued continued to these flaser flaser and and wavy wavy bedded bedded chert-carbonate chert-carbonate grainstones As sea sea level to fall fall these grainstoneswere were transgressed by the coarser, higher energy, stromatolitic and oncolitic, chert-carbonate, transgressed by the coarser, higher energy, stromatolitic and oncolitic, chert-carbonate,grainstones grainstones of member member 3. 3. These Thesestorm stormenhanced, enhanced,crypt cryptalgal, algal, lower lower foreshore foreshoredeposits depositsmark mark the the regressive regressivepeak peak of of this middle cycle. Like the Gf facies chert-carbonate grainstones of member 2, those of this middle cycle. Like the Gf facies chert-carbonate grainstones of member 2, those comprising comprising member 3 3 also member also record record lunate lunate dune dunedevelopment developmenton onaasubtidal/lower subtidal/lowerintertidal intertidalchert-carbonate chert-carbonate grainstone flat. grainstone flat. The 6 6 cm cm thick, thick, Gi Gi facies grainstone bed bed at at the the base base of of member member 33 in in O'Connor O'Connor township township is is facies grainstone The interpreted as being a proximal tempestite deposited in this shallow, high energy environment. This interpreted as being a proximal tempestite deposited in this shallow, high energy environment. This coarse, storm storm generated lag is coarse, generated lag is thin, thin, possesses possesses aa base base which which appears appears to to erosively erosively scour scour the the flaser flaser bedded chert-carbonate 2, contains contains abundant abundant magnetitemagnetite- and and hematite-rich hematite-rich bedded chert-carbonate grainstones grainstones of of member member 2, rip ups ups and and pinches pinches laterally laterally towards rip towards Blake Blake township; township;all all are are characteristics characteristicsof of nearshore nearshoresheet sheetstorm storm deposits (Einsele, deposits (Einsele, 1992). 1992). With Withaareturn returnto tofairweather fairweatherconditions conditionsthis this storm stormbed bed provided provided an an ideal ideal substrate for stromatolites to colonize. ItIt was not easily easily reworked reworked by by normal normal shelf shelf currents currents substrate for stromatolites to colonize. was firm firm and and not (Fralick, 1988). was however however not not (Fralick, 1988). Development Developmentof of crypt crypt algal algal knolls knolls on on this this intraformational intraformational lag lag was widespread as they they colonized colonized only only the the most most stable stableregions regions sheltered shelteredfrom from fairweather fairweatherreworking. reworking. widespread as The thin, thin, discontinuous, discontinuous, stromatolitic which developed developed above above this this basal, basal, crypt crypt The stromatoliticand and oncolitic oncolitichorizons horizons which algal layer layer suggests suggests subtidal, on aa substrate substrate that that underwent underwent periodic, periodic, algal subtidal, stromatolitic stromatolitic growth growth occurred occurred on fairweather reworking. reworking. The LLH and and SS SS fairweather The development development of of these these poorly poorly formed, formed, discontinuous discontinuous LLH stromatolitic on shallow, shallow, high high energy, energy, subtidal subtidal sand sand sheets sheets stromatolitic bioherms biohermsis is typical typical of of crypt crypt algal algal growth growth on of the the upper upper shoreface (Pratt et et a al., of shoreface and and lower lower foreshore foreshore (Pratt !., 1992). 1992). Upper transgression transgression possibly The upper transgressive member 3, through through member member 5, The upper transgressivecycle cycleextends extendsfrom fromthe thetop top of of member 5, possibly to the top of the Rove Formation; Formation; a vertical distance of almost 700 m. m. Its onset is rapid and Its onset is rapid and records records the those of of the the lower lower shoreface. shoreface. The the progressive progressive onlap onlap of of offshore offshore facies facies over over those The thin thin package package of of hummocky cross stratified chertand hematite-rich grainstones (GHCS facies) at the base of of hummocky cross stratified chert- and hematite-rich grainstones (GHCS facies) at the base member 4 in O'Connor township marks this transition. Modern hummocky-cross-stratified sands member 4 in O'Connor township marks this transition. Modem hummocky-cross-stratified sands occur below wave base base on of storm dominated, shallow shallow marine marine occur below fairweather fairweather wave on the the lower lower shoreface shoreface of storm dominated, depositional systems transition to the the inner inner shelf shelf (Hamblin (Hamblin and and Walker, Walker, 1979; Dott and depositional systemsat ator or near near the the transition 1979; Dott and Binsele, 1992; Davis, Davis, 1992). The Bourgeois, 1982; 1982; Aigner, Aigner, 1985; 1985; Walker and Plint, 1992; Emsele, The parallel parallel bedded, hematite-rich, (Gp facies grainstone) to to which which this this basal basal bedded, hematite-rich,slaty slatyand and cherty chertyiron iron formation formationbeds beds (Gp facies grainstone) hummocky-cross-stratified unit of storm storm deposition deposition near near this this change change hummocky-cross-stratified unit grades grades are are also also characteristic characteristic of They are (Figure 9). 9). They are identical identical to to modern, modem, proximal proximal offshore, offshore, storm-sand storm-sand layers layers (proximal (proximal tempestites) and their their more distal equivalents, rhythmites (distal (distal tempestites) tempestites) (Reinick (Reinick and and tempestites) equivalents, graded rhythmites Singh, Aigner, 1985). these storm 1985). Like Likethe theparallel parallel bedded bedded chemical chemical sediments sediments these storm beds beds also also Singh, 1972; 1972; Aigner, posses a sharp instances may may grade grade upward upward into into plane planelaminated laminatedmud mud layers. layers. In In posses sharp base, and in some instances modern tempestites laminated rhythmites, rhythmites, in modem tempestitesthe the sand sandlayers layersare are either either evenly evenly laminated laminated or or are laminated in which which the lower lower laminae grade upwards upwards into into thinner thinner and and finer-grained finer-grained the laminae are thicker thicker and coarser-grained coarser-grainedand grade laminae (Reinick (Reinick and and Singh, 1972). marine, storm storm laminae 1972). They They are are the the result result of of deposition deposition from shallow marine, generated turbidity currents Finsele, 1992; generated currents (Reinick (Reinick and Singh, 1972; 1972; Walker, 1984; Einsele, 1992; Davis, 1992). 1992). The fine- and medium-grained chert- and hematite-rich hematite-rich grainstone grainstone beds beds comprising comprising this this member member represent episodic development of storm-generated, chemical sedimentary beds. Thicker, episodic development Thicker,graded, graded, coarser beds developed during the most severe storms. The hematite-rich slaty The hematite-rich slaty iron iron formation formation packages between fairweather sedimentation sedimentation on lower packages between storm-grainstones storm-grainstonesrepresents representsthe the return return to fairweather on the lower �Figure precipitation of iron-rich iron-rich sediments on ontheAnimikie theAnimikie shelf. shelf Figure10. 10. Depositional modelfor modelfor the theprecipitation The model is based on data from the Gunflint and Gogebic data collected collectedfrom Gogebic iron ranges. Samples from these areas were Samples from were examined examined in thin section section under under a petrographic petroeraphic - microscope and using aa scanning scanningelectron electronmicroscope microscope with an an energy dispersive dispersive systent rock analysis was also performed performed using an system. Whole Whole rock an inductively inductively coupled plasma. plasma. During Duringthe thePaleoproterozoic Paleoproterozoicthe theworld world ocean ocean contained much less oxygen than enabledFeu FC and thanatatpresent present(Cloud, (Cloud,1973). 1973). This enabled and MC Mnutotostay stayininsolution. solution. Oxygen present in appreciable quantities in the Oxygen would only be present the shallow, near shore environment environmentwhere wherereasonable reasonablelevels levelsof of light light penetration penetrationtotothe thebottom bottomwould would allow allow the cyanobacteria colonies in this area to thrive, and thus release oxygen (1). During the cyanobacteriacolonies in this area to and oxygen (1). During storm pressure system system over overthe the area area storm events events the the combined combined effects of an extreme low pressure and forcing caused the buildup of water in in aa strand-proximalposition. strand-proximal position. Upon and wave waveforcing Upon waning this water would be returned returned to the mid and and outer outer shelfvia shelf via waning of of the the storm storm event event this aa storm storm surge surgeebb ebbflow. flow. The Thedeliverance deliveranceof ofmore morehighly highlyoxygenated oxygenated waters waters to to the the deeper deeper shelf would would cause the the rapid rapid precipitation of iron iron oxide oxide (probably (probably as as iron iron hydroxyoxide) (2). At high high Fe/Mg FdWg ratios ratios itit isis likely likely that that precipitation precipitation of iron iron hydroxyoxide)(2). compounds during this rapid precipitation phase. phase. As oxygen and/or compoundswould would dominate dominate during this rapidprecipitation and/or iron iron is/are Mare depleted depleted precipitation precipitation rate slows slows and silica silica gel, gel, which which isis slowly slowly but but constantly from seawater, seawater, increases increases in in importance importance as as aa constituent constituent of of constantlyprecipitating from the phase due the layer. layer. Finally, Finally,with withdepletion depletionof of iron iron in in the the aqueous aqueousphase due to to precipitation, and a resu king decrease in Fe/Mg ratio, manganese anda resultingdecrease in the the FdWgratio, manganesebegins beginsto to effectively effectivelyscavenge oxygen forming MnO-rich Mn 0-rich tops some layers. layers. If another another storm occurs before oxygenforming tops to some storm event occurs the the Fe/Mg F e w ratio ratioof of seawater seawater has hasdecreased decreased to to the thepoint point manganese manganeseprecipitation precipitation becomes sign jficant the the upper upperportion portion of of the thelayer layer will willnot notform. form. Smaller Smaller storms storms are are becomes significant able precesses to operate in the mid-shelfarea, mid-shelf area, whereas ableto to cause causethe theabove aboveprecesses whereasonly only large large storms shelf Thus, storms effect effect the outer shelf. Thus,manganese manganeseconcentrations concentrationsare are much much higher higherin in rocksformed environment A) sequencefound rocksformed in inthe theouter outershelf-slope shelf-slope environment. A) Typical Typicalsequence found in in the mid-shelf (1cm) cm) chemical chemical sediment sediment laminae laminae directly directly overlay overlay storm mid-shelf where where thick thick (1 generated from the outer mid-shelf. mid-shelf C) B)Typical Typical laminae from C)Thin, Thin, generated granule granule lenses. lenses. B) complete laminae deposited in the outer helf complete laminae deposited helf. �- 1. Fairweather FairweatherPeriod Period - Stratified Stratified Water Water Body Body 02 02 020202 F' 02 — PC' — Mn PC' PC' PC' PC' Mn" -I- FC' 2. Storm - Destratitied Water Body 4 ÷+ PC' Fe' Fe" cmC cm 20 C.mm - mm -5 Ca fl • 'e3'•4 + 5102 Massive Fe304 Granular -o 1e304 2MnO Fe304 + Si02 Massive Fe304 0 Trough Trough Cross-Stratified Fine to Medium Grained Sand Grained - Ripple Laminated d and Massive Very FineS Fine Grained Sand to Coarse - Grained Grained Silt Silt Coarse - - Thinly to Thickly Laminated Mud �shoreface. storm layers lay directly shoreface. In In Blake Blake township township these chemical sedimentary storm directly on the the grainstones grainstonesof ofmember member2. 2. The The pulse pulse of of volcanism volcanism preserved preserved in in the the middle middle of member member 4 as a 6m thick volcaniclastic volcaniclastic horizon deposition. Its (Vsfacies) facies) occurred occurred swiftly, swiftly, outpacing iron formation deposition. Its sharp sharp bottom bottom contact contact horizon(Vs indicates indicatesrapid rapid influx influxof of volcaniclastic volcaniclasticmaterial material into into the depositional depositional system. Its Its gradational gradational upper contact waned gradually gradually over overtime. tuff contactsuggests suggestsdelivery delivery of of volcaniclastics volcaniclastics to the basin waned time. The The lapilli lapillituff (Vt reworked and deposited deposited (Vtfacies) facies)which whichcharacterizes characterizesthe thebase baseof ofmember member 55 is is interpreted interpreted as being reworked by by storms stormsfrom from more more proximal, proximal, nearshore nearshore settings. settings. The Themassive, massive,mediummedium-to tocoarse-grained coarse-grainedchertchertcarbonate grainstone bed (Gi facies) characterizing its base is similar to the (Gi facies) characterizing stromatolitic,storm storm carbonate grainstone stromatolitic, generated itslower lowerbounding boundingsurface surfaceisiserosive erosiveinto intothe thetop topof of member member44 and and itit also also generatedlag lagin inmember member3;3;its pinches laterally towards Blake Township. beds within the Gunflint pinches laterally towards Blake Township. Similar Similar volcaniclastic volcaniclastic beds Gunflint Formation Formation have have also alsobeen been interpreted interpreted by by Hassler Hassler and and Simonson Simonson(1989) (1989) as being being reworked reworked and and redeposited by turbidity currents. redeposited by turbidity currents. The The coarsening coarsening upwards, upwards, massive massive and andcross-stratified, cross-stratified, chert-carbonate, chert-carbonate, grainstone grainstone successions onlapof ofinner innershelf shelffacies facies over those of successions(Gc (Gcfacies) facies)of ofmember member55mark markthe theprogressive progressiveonlap the GHCS thelower lowershoreface shorefaceparallel parallel laminated laminated and and hummocky cross-stratified grainstones (Gp and GHCS facies) facies)(Figure (Figure9). 9).Similar Similarsuccessions successionsdeposited depositedinincoastal coastaland andopen openmarine marineenvironments environmentscomprise comprise the Sussex and and Shannon Shannon sandstones sandstones of the Powder Powder River River Basin Basin in in northern northern the Upper Upper Cretaceous, Cretaceous, Sussex Wyoming. Wyoming.InInWyoming Wyomingcycles cyclescoarsen coarsenfrom fromsilty siltyoffshore offshoremudstones, mudstones,through throughthin thin bedded, bedded, stormstormand and tide-generated tide-generated sandstones sandstones to to cross cross stratified stratified sandstones sandstones with with abundant abundant clay clay rip-ups. rip-ups. The The depositional depositionalmodel modelproposed proposedfor forthe theShannon Shannonand andSussex Sussexsandstones sandstonesconsists consistsof ofmigrating, migrating,offshore offshore bar Hobson barcomplexes complexesthat thathave havetheir theirsurfaces surfacescovered coveredby bysand sandwaves waves(Berg, (Berg,1975; 1975;Brenner, Brenner,1978; 1978;Hobson etetal., al.,1982; 1982;Davis, Davis, 1992). 1992).With Withsome somemodification modificationthis thismodel modelmay may also also be be applied applied to to the the coarsercoarsergrained, grained,shoaling shoalingupwards upwardssequences sequencescomprising comprisingmember member55 of of the the Gunflint GunflintFormation. Formation. Like Like bar bardevelopment development in inclastic clasticsystems systemsgenesis genesisof ofchemical chemicalsedimentary, sedimentary, offshore offshorebar bar complexes 2)the the complexesdepends dependson, on,1)1)the theavailability availabilityof ofcoarse coarsesediment sedimentto to offshore offshore environments environments and and 2) presence presenceof ofcurrents currentscapable capableof ofshaping shapingthis thissand sandinto intowell well defined, defined, migrating, migrating, sand sandbodies. bodies. In In elastic, clastic,shallow shallowmarine marinedepositional depositionalsystems systemscoarse coarsedetritus detritusisissupplied suppliedtotooffshore offshoreareas areasby bystorm storm Tillmanand andMartinson, Martinson,1984) 1984)and andtide tide(Spearing, (Spearing,1976; 1976;Brenner, Brenner,1978; 1978; (Berg,1975; 1975;Walker, Walker,1984; 1984;Tillman (Berg, Seeling, 1978) generated currents. However, unlike their clastic counterparts, bar genesis Seeling, 1978) generated currents. However, unlike their clastic counterparts, genesis in in chemical chemicalsedimentary sedimentarysystems systemsrelies relieson onoffshore offshoreprecipitation precipitation of of iron iron oxides oxides and and silica silica gel gel from from upwelled 1993),and andsubsequent subsequent upwelledenriched enrichedbottom bottomwaters waters(Borchert, (Borchert,1950; 1950;Drever, Drever,1974; 1974;Morris, Moms,1993), current currentreworking reworkingof ofthe thesubstrate substrateinto intorip-up rip-upgrains grains(Simonson (Simonsonand andGoode, Goode,1989) 1989)(Figure (Figure10). 10). Consequently this process does not depend on systems tracts capable of delivering coarse detritus Consequently this process does not depend on systems tracts capable of delivering coarse detritus to development in in a chemical sedimentary, tothe theshelf shelf.Bar Bar development a chemical sedimentary,shallow-marine shallow-marinedepositional depositionalsystem systemisis therefore governed by the position of areas on the shelf with high, primary chertlcarbonate therefore governed by the position of areas on the shelf with high, primary chert/carbonategrain grain production production and and the the presence presence of ofcurrents currentsable abletotorework reworkthese thesechemical chemical precipitates precipitates into into bar bar complexes. The relative stratigraphic position of member 5, over facies characteristic of the lower complexes. The relative stratigraphic position of member 5, over facies characteristic of the lower shoreface graingenesis genesis were were below below shoreface(Gp (Gpand andGHCS GHCSfacies), facies),suggests suggeststhat thatregions regionsofofprimary primarygrain fairweather wave base and that storm-generated, oscillatory flow was responsible for reworking fairweather wave base and that storm-generated,oscillatory flow was responsible for reworkingthe the substrate substrateinto intorip-up rip-upgrains. grains. Finer-grained, Finer-grained,shoaling shoalingupwards, upwards,chemical chemicalsedimentary sedimentarysuccessions successionsfrom fromthe theGogebic GogebicIron Iron Range in Wisconsin (Figure 11) (Pufahl, 1994) are identical to the coarsening upwards successions Range in Wisconsin (Figure 11) (Pufahl, 1994) are identical to the coarsening upwards successions �comprising comprising the Sussex Sussex and Shannon Shannon sandstones in Wyoming. They They are regarded regarded as as being being the distal equivalents equivalentsto to the the coarse coarse offshore offshore bars bars of of the the Gunflint Gunflint(Pufahl, (Pufahl, 1994). 1994). Cycles in Wisconsin Wisconsin coarsen from parallel laminated, magnetite-rich slaty iron formation in much much the the same same way way the the Cretaceous Cretaceous upwards shoaling shoaling cycles coarsen from shelf mudstones. 4 Sm.g 0*4. Dunes 400, 'S 4% 44. ) O4 Figure 11. Figure 11. Development Development oof f coarsening- and thickeningcoarseningthickening- upwards sequences in sequences in Wisconsin Wisconsinwere were related related to progradation of lunate dune offshoreprogradation dominated sand sand sheets. sheets. In a broad sense these offshore In offshore regions of primary grain genesis are similar to the "subtidal carbonate factories" factories" responsible responsible for for grain grain production production on on modem modem and some carbonate some ancient ancient carbonate carbonate platforms (James and Kendall, 1992). The upwards cycles cycles The coarse coarse nature of the Gunflint shoaling upwards suggests bar bar development developmentoccurred occurredatator or near near aa "grainstone "grainstone in Blake and O'Coimor O'Connor townships suggests factory. As with shoreline shoreline retreat retreat factory". Asthe thetransgression transgressionprogressed progressedthese thesefactories factoriesmigrated migrated in step with resulting in the deposition complexes further ftrther from regions of primary deposition of slightly finer-grained bar complexes production. The absence of of aa mud mud grain production. Theexistence existenceof of these these offshore offshore factories factories would account for the absence dominated offshore, offshore, which is so clastic shallow-marine shallow-marine depositional systems dominated so characteristic characteristic of of clastic (Walker and Plint, 1992). 1992). Alternatively, these coarsening upwards, upwards, GGc fades grainstone c facies grainstone successions successions may represent paracycle development (Vail et al., aL, 1977) in regions regions of high high primary primary grain grain genesis genesis during during relative relative sea level rise. Paracycles form in response to a punctuated rise in overall sea level. They record a Paracycles form in response sea level. period of rapid, relative sea level rise rise and still stand, followed by another another relative relative rise rise with with no no period followed by �significant that accumulates accumulates is is coarsening coarsening upwards, upwards, significantfall fall intervening intervening (Vail (Vail et aL, al.,1977). 1977). The sequence that suggestive of mediumsuggestive of continued continued shoaliñg shoaling as sediments sediments accumulate accumulate to sea level. In In this this scenario scenario the the medium-- as grained, chert-carbonate grainstonesatat the the base base of coarsening upward cycles would represent chert-carbonate grainstones grainstone deposition deposition during during rapid rapid sea level level rise as regions of primary primary grain grain genesis genesis migrated migrated shoreward. The coarse-grained tops of cycles would represent accumulation of grainstones shoreward. The coarse-grained tops of cycles would represent accumulation of grainstonesnear near to to base level where breaking waves were able to winnow the substrate during an interval of relative calm. At Atthe thepresent presenttime timedata dataisisinsufficient insufficient to to choose choose whether whether an autocyclic autocyclic (depositional) or allocyclic allocyclic (sea (sea level) level) mechanism mechanism governed governed cycle cycle genesis. - The transitional facies into the the The Gi Gi facies facies chert-carbonate chert-carbonategrainstone erainstonebeds which characterize transitional overlying Rove in Blake township are interpreted as representing deposition from suspension clouds overlying Rove in Blake township are interpreted representing suspension generated generated by either either storms storms or or tectonism tectonism during during basin subsidence. subsidence. OVERVIEW OVERVIEW OF OF THE THEANIMIKIE ANIMIKIEBASIN BASIN The iron-bearing iron-bearing rocks in Ontario and Minnesota Minnesota form form aachemical chemicalsedimentary sedimentary wedge wedge which which fines fines and and thickens thickens from from coarse, coarse, wave wave reworked, reworked, nearshore deposits of the Gunflint Formation to offshore, offshore, parallel-laminated, chemical mudstones of the Trommald iron formation in east-central Minnesota. to those those observed observed in in Minnesota. Lateral Lateral and and vertical vertical facies facies transitions transitions are directly comparable to modem They record modem shallow shallow marine marine clastic clastic and and carbonate carbonate depositional depositional systems. systems. They record energy energy transformations nearshore, shoaling shoaling waves waves under under fairweather fairweather and transformationsfrom fromdeep deepwater, water, offshore offshorewaves waves to nearshore, storm storm conditions. conditions.Paleocurrent Paleocurrentdata datasuggests suggestsdeposition depositionof of chemical chemical sedimentary sedimentaryrocks rocks occurred occurred on on a southward southward facing facing paleoslope. paleoslope. Nearshore rocks consist Nearshore chemical chemical sedimentary sedimentary rocks consist of of successions successions of ofstrand-proximal strand-proximal stromatolites, flaser and wavy and parallel parallel bedded stromatolites, flaser wavy bedded bedded chert-carbonate chert-carbonate grainstones, grainstones, and bedded and hummocky non-barred, microtidal, microtidal, hummocky cross cross stratified stratified hematite-rich cherty grainstones deposited on aa non-barred, storm-enhanced storm-enhancedshoreline shorelinewith with little little clastic clastic influx. Deposition Depositionon on the the inner shelf was dominated by accumulation accumulationof of coarse-grained, coarse-grained,shoaling shoalingupwards, upwards, chert-carbonate chert-carbonategrainstone grainstone successions, successions,possibly possibly associated with offshore bar development. development. Their Their genesis is believed to have been the result of a unique physiological conditions Animikie unique interplay interplaybetween betweenthe the chemical chemicaland and physiological conditionswhich which prevailed prevailed in in the Animikie Basin Basin during during iron iron formation formation deposition. deposition. They Theyformed formedin in proximal proximal offshore offshore areas areas where iron oxide and precipitating, and precipitates into and silica silicagel gel were actively precipitating, and where currents could rework chemical precipitates into rip-up grains grains and redistribute redistribute them. The Theshoaling shoalingupwards upwards successions successions replace replace a mud dominated offshore, offshore, which which is is so so characteristic characteristicof of modern modem shallow-marine shallow-marine depositional depositional systems. systems. Distally, finer-grained and less lesswell welldeveloped. developed. They They Distally, coarsening coarsening upwards upwards sequences sequencesbecome become finer-grained coarsen medium-grained, massive massive and and coarsen from from parallel parallel laminated, laminated, magnetite-rich chemical slates to medium-grained, cross offshore crossstratified, stratified,chert-carbonate chert-carbonategrainstones, grainstones,and andare areinterpreted interpretedas as recording recording progradation of offshore bar complexes of high high primary primary complexeson on the the middle middle shelf shelf below below fairweather fairweather wave base, away from areas of grain paracycledevelopment developmentduring during an an overall overall rise rise grain genesis. genesis. These Thesesuccessions successionsmay mayalso alsorepresent representparacycle in in relative relative sea sealevel. level. Monotonously parallel and slatescharacterize characterizedeposition deposition Monotonouslyinterbedded interbeddedparallel and wavy wavy bedded chemical slates of of iron iron formation formation on on the the outer outer shelf shelfand and slope-break. slope-break. The Thepresence presence of ofrare, rare, massive massive and and cross cross �stratified, magnetite-rich slaty slaty laminations laminations indicates indicates that that stratified, chert-carbonate chert-carbonate grainstones grainstones and graded, magnetite-rich storm-generated storm-generatedturbidity turbiditycurrents currentsoriginating originatingon onthe theinner innershelf, shelf,where where grain grain production productiontook tookplace, place, were for moving moving sediment sediment onto ontothe thedistal distalshelf. shelf The were an an important important mechanism for The existence existenceof of iron iron formation 1963) in in the the Cuyuna Cuyunanorth north range suggests that mass mass flow flow processes processes formation breccia breccia (Schmidt, (Schmidt, 1963) generated the distal distal shelf shelf were important generatedby by large-scale large-scalerotational rotationalslumping slumpingand and sliding sliding on the important in moving sediment sediment from from the the slope slope to to the the rise. rise. Sedimentological Sedimentologicaland andstratigraphic stratigraphicdata datado do not not provide provide definitive definitiveanswers answers to to the the question question of of plate plate tectonic tectonic setting settingof of the the Animikie Animikie Basin. However, However,paleogeographic paleogeographicreconstructions reconstructionsbased based on vertical vertical and and lateral lateral facies facies transitions transitions present within the Gunflint, Gunflint, Biwabik, and Trommald iron formations, and clastic units above and below strata indicate indicate that that it is is doubtful doubtful formations, and below iron-bearing iron-bearing strata deposition migrating peripheral depositionof ofthe theAnimikie AnimikieGroup Groupoccurred occurredwithin withinaamigrating peripheral foreland foreland basin basin (Figure (Figure 12). 12). There There is is an an apparent apparentlack lackof ofcoarse coarseturbiditic, turbiditic, deltaic, deltaic, and and fluvial fluvial sediments, adjacent to the fold thrust thrustbelt, belt, and and paleocurrent paleocurrentdata data from from clastic clastic and chemical sedimentary rocks are are opposite opposite to what should formation was shouldbe be observed observed if if deposition deposition took took place in a foreland basin. Also, Also, if if iron iron formation was to have accumulated accumulated in aa foreland foreland setting setting it it should should be be restricted restricted to the distal distal shelf shelf as as weathering weathering of the peripheral peripheralbulge bulgewould wouldshed shedclastics clasticsinto intonearshore nearshoreregions regionseffectively effectivelypreventing preventingdeposition depositionof ofiron iron formation. formation. Facies Faciestransitions transitionswithin withiniron-bearing iron-bearingmembers membersindicate indicatethe the contrary, contrary, a complete complete shelf shelf sequence, sequence, not not just just the the distal distalportion portionis ispresent. present. Although Animikie Basin Basin in Although data datais is insufficient insufficient to to reconstruct reconstruct the the tectonic tectonic evolution evolution of the Animikie detail, detail,some somegeneral generalinferences inferencesregarding regarding the the depositional depositionalhistory history of of the the Paleoproterozoic Paleoproterowic strata stratain in Ontario Ontarioand and Minnesota Minnesotacan canbe be made. made. Sedimentation Sedimentationwithin withinthe thebasin basinbegan beganwith withan anoverall overallmarine marine transgression the transgressiononto ontothe thesouthern southernmargin marginof ofthe the peneplained peneplainedSuperior Superior province province and deposition deposition of the Pokegama Mahnomen Formation. Formation. The PokegamaQuartzite Quartzite and and Mahnomen ThePokegama PokegamaQuartzite Quartziteaccumulated accumulated in in nearshore, tidally tidally influenced influencedsettings settingswhile whilethe theMahnomen Mahnomen Formation Formation was deposited deposited simultaneously in more distal shelf regions by pelagic settling and waning turbidity currents. This clastic deposition deposition distal shelf regions by pelagic settling turbidity This phase of clastic was probably associated with the early history of basin development. Through time, the continuing was probably associated with the Through continuing erosion erosionof of the the source sourceterrain terrainresulted resultedin in aa reduction reduction of of clastic clastic supply supply to to the the basin, basin, to to aa point pointwhere where iron iron formation formation began to accumulate accumulate on the the shelf, shelf, away away from from the the land-derived land-derived clastics clastics still still accumulating iron formation formation was accumulatingin inthe thenearshore. nearshore.Once Oncethe thehighland highlandwas wasreduced reducedto to near near base base level level iron then then able ableto to accumulate accumulatein inthe thenearshore, nearshore, and anddirectly directlyonlap onlapthe the Superior Superiorprovince. province. Deposition Deposition of of iron ironformation formation occurred occurred during during an anoverall overalltransgressive transgressive marine marine event event punctuated punctuatedby by two twominor minorregressions. regressions.Lateral Lateralfacies faciestransitions transitionswithin withiniron-bearing iron-bearingunits unitsrecord recordaa complete reworked nearshore nearshore deposits deposits completeshelf shelfsequence sequencewhich which fines finesand and thickens thickens from from coarse, coarse, wave wave reworked to the distal distal shelf. shelf. The to parallel-laminated parallel-laminated chemical chemical mudstones mudstones of of the The existence existence of of minor minor mafic mafic flows flows and three volcaniclastic volcaniclastic horizons horizons in in the the and tuffaceous tuffaceous horizons horizons in in the the Gunflint, Gunflint, and andthe thepresence presence of of three Ounflint Gunflintand andMesabi Mesabiiron ironranges rangesindicate indicatethat that the the region region was was volcanically active active during during subsidence subsidence in in this this phase phaseof of basin basin development. development.The Thethickest thickestvolcaniclastic volcaniclastichorizon horizonforms formsthe thebase baseof ofthe theRove, Rove, Virginia, Virginia, and and Rabbit Rabbit Lake Lake Formations, Formations, and and marks marks the the transition transition from from chemical chemical to to clastic clastic sedimentation. sedimentation.This Thisvolcanic volcanicepisode episodestopped stoppediron ironformation formationgenesis genesisby bychoking chokingthe thedepositional depositional system with volcaniclastics. As relative sea level continued to rise deposition within system with volcaniclastics. As relative sea level continued to rise deposition within the the Animikie Animikie Basin Basin was wasdominated dominatedby byaccumulation accumulationof of clastics clasticsderived derived from from the the north north by by southward southward flowing flowing turbidity turbiditycurrents. currents. �Figure asaamigrating migratingperipheral peripheralforeland basin. Arguments Figure 12. 12. The TheAnimikie Animikie Basin Basin modelled modelled as foreland basin. against this tectonic interpretation are presented in the text. SOUTH SOUTH NORTH - - FOLD THRUST BELT FOLD - AND AND - THRUST BELT I FORELAND FORELAND BASIN I migrating to north PERIPHERAL PERIPHERAL BULGE • •iiui sediment sediment eroded eroded from from fold fold -- and and thrust thrust belt belt mmmm — ---- Â¥I - fluvio deltaic flu I sedts .N sediment eroded eroded from sediment from peripheral bulge N SUPERIOR PRO VINCE nearshore clastics ff011 formation and coarse turbidites 0 20km 10 I I I �FIELD TRIP FIELD T R I P STOPS STOPS ITINERARY ITINERARY Stop 11 Stop Stop 22 Stop Stop 33 Stop Stop 44 Stop Stop S5 Stop Stop Stop 66 Stop 77 Stop Stop 88 stop Stop 99 Stop Stop 10 Stop 10 Stop Stop11 11 Stop 12 Stop 12 V V V V V V V V V V V V V V V V V V V V VV V V V V V Basal stromatolites; Nolalu Nolalu turnoff turnoff Basal unconformity, unconformity, stromatolites; Basal unconformity, unconformity, stromatolites; stromatolites; Kaministikwia Kaministikwia Riven Riverr Basal TufTs,volcaniclastic volcaniclastic sediments; sediments; Kakabeka Kakabeka Falls Tuffs, Falls Ribbon chert-carbonate; chert-carbonate; Kakabeka Kakabeka Falls Falls Ribbon Basal Basal pebbly pebbly sandstone; sandstone; Oliver Oliver Road Road Stromatolites, beachrock; beachrock; Rupert Rupert Street Stmmatolites, Collapse breccia; breccia; base basc of High Street Park Collapse of High Street Park Grainstones, stromatolites; Current River Slumped ribbon ribbon chert-carbonate; chert-carbonate; road road to to Pass Pass Lake Lake Slumped Rippled Rippled siltstones; siltstones; Transcanada Transcanada Highway Highway Grainstones with volcanic volcanic sherds; sherds; Terry Teriy Fox Fox Lookout Lookout Grainstones with Grainstones; Transcanada Transcanada Highway Highway near near Current Cunent River Grainstones; River V V V V pa Thunder V o 00 V Bay 000 0 hwy. 1h17 ÷ g —- Lake Superior LEGEND ARCHEAN PROTER OZOIC PROTEROZOIC km km V V 111 0 0 V V V 'I ++ V V V 5 5 Rove Rove Formation Formation Eorniation Gunflint Formation 10 0021 Gunflint Figure 13. Geology Geology of the Thunder ThunderBay Bay area. area Figure 13. Rocks ~ ~ +1 ~ Granitic a ? i Rocks + i c I ~olcanics IV V VJ Volcanics �STOP STOP 11 Proceed west weston onHighway Highway 11/17 11/17(the (the Transcanada) Transcanada) (Figure 13)past Kakabeka Falls and over the Kaministikwia Kaministikwia River. A A few few hundred metres metres past this bridge there is a turn off to Nolalu. Take outcrop Takeitit and and proceed proceed approximately approximately100 100metres, the main outcrop is is on on the the right. right. Chemical Archean granitoids granitoids at Chemical sediments sedimentsof of the Gunflint Gunflint Formation rest directly on Archean this location. This thin conglomeratic conglomeratic Thishighlights highlightsthe the sporadic sporadicdevelopment development ooff the the thin veneer comprising the Kakabeka Conglomerate Conglomerate in inthis thisarea. area. Stromatolites, Stromatolites, including including veneer comprising some these basal basal cherty cherty carbonates. carbonates. The some large forms, are developed in these The stromatolitic stromatoliti; ribbon carbonates carbonates are are abruptly abruptly overlain overlain by aa grainstone grainstone succession. succession. STOP STOP22 Proceed Proceed back to to the the Transcanada Transcanada Highway turn right and cross the Kaministiquia Bridge. Turn park to to end end of Turnleft lefton onroad road immediately immediately after after bridge bridge and drive through park road. road .AApath pathleads leadstotothe thefirst firstset setofofrapids rapidsabove abovethe the bridge. bridge. The The rapids rapids are are formed by Archean granitoids. The The slow-water slow-waterarea area to to the the south southisis underlain Gunflint Formation. Formation. River Riverlevel level will will govern govern what can can be observed observed underlain by the Gunflint at at this this stop. stop. The Kakabeka Kakabeka Conglomerate Conglomerate is patchily developed overlying the Archean Archean at at this stop. stop. Silicified Silicifiedstromatolites stromatolitesare aredeveloped developedon on the the Conglomerate Conglomerateor or directly directly on on the granitic granitic basement. This Thisisis the the location location from from which samples collected in cyanobacteria described in in the theliterature. literature. The in the 1950's 1950's yielded the first Gunflint cyanobacteriadescribed samples samples were were from from the the silicified silicified stromatolites stromatolites and were described by Tyler and and Barghoom (1954). (1954). Barghoorn STOP STOP33 Proceed back to the Transcanada Highway Highway and andturn turn left. left. Turn Turn right right into into the the main main park entrance entrance and and park in in the parking lot. Walk Walkto tothe theobservation observationplatform. platform. The The river river gorge gorge is is composed composed of of aa sequence sequence of of volcaniclastic volcaniclastic shales shales (less (less resistant, darker darker units) units) and and tuffs tuffs (more (moreresistant, resistant, lighter lighter coloured coloured units). units). This sequence sequence represents the ma] or volcaniclastic horizon present in the upper Gunflint Formation represents the major volcaniclastic horizon present the upper Formation and and is is traceable traceable to to the thesouth souththrough throughthe theMesabi MesabiRange. Range. Basalts outcropping outcropping approximately probably correlatable this unit. approximately30 30kilometres kilometresto tothe the southwest southwestare are probably correlatablewith withthisunit. Unpublished Unpublishedgeochemistry geochemistry(major, (major,trace, trace, REE REEanalysis) analysis)performed performedon onsamples samplesof of the the basalt basalt indicate indicate aa tholeiitic tholeiiticcomposition composition with a deep deep mantle source source (plume). STOP STOP44 Walk Walk back back to to the the southeast southeastside sideof ofthe the parking parking lot. lot. An forms this this cut. cut. Folds An outcrop outcrop of of ribbon ribbon chert-carbonate (ankerite) forms Folds and faults faults are present deformation. Commonly, present and and probably probably represent soft sediment deformation. Commonly, past studies studies of of the the Gunflint GunflintFormation Formationhave havedescribed describedthis thistype typeof ofsediment sedimentas asforming formingin inaadeep, deep, quiet quiet water water environment environment and and this this may may be becorrect. correct. However, similar carbonate carbonate sequences intertidal or or lagoonal lagoonal subtidal subtidal sequences are often often attributed attributed to deposition deposition in intertidal environments. environments.The Theevidence evidencesupporting supportingaadeep deepor or aa shallow shallow setting setting will be discussed at at this thisstop. stop. �a tS-s -:. - 4 ., - . -A ..r!'efl j _ Figure wave rip-up rip-up Figure 14. 14. Stop Ston6. 6.A) A)Intraformational Intraformationalbeachrock beachrockconglomerate conglomerateformed by by storm wave of partially partially cemented cementedsurficial surficial layers layers of of medium-grained medium-grainedsand sandin in the the upper upper beach beach of environment B) stromatolites with withmedium-grained medium-grainedan and B)Plan-view Plan-viewof of cabbage-sized cabbage-sizedstromatolites environment. granule sand sand layers layers banked bankedup upagainst againstthem. thea granule 1 �STOP STOP 55 Turn right onto the Transcanada and turn left onto Oliver Road. Turn Turn left on Turn Transcanada and Road and and right right on on Dawson DawsonRoad. Road. Drive 7.4 km km to to aa small small dirt dirt pull pull off off Mapleward Road on the left and park. Walk down the path for a few minutes until you see a small, Walk down rounded outcrop. belonging to to the the Kakabeka Kakabeka Conglomerate. Conglomerate. It This is an outcrop of pebbly sandstone belonging overlies Archean granitic rocks and represents gris (angular, granitic debris), probably probably @tic debris), overlies Archean granitic rocks and represents surrounding basement. weathered from surroundiig STOP 66 STOP Turn left left on Dawson Turn right right on the Turn Dawson Road Road and and proceed proceed to to Thunder Thunder Bay. Bay. Turn onthe Oliver Road. Road. Continue down Oliver Road Turn right right at at Hill Hill Transcanada and left on Oliver the comer corner with with Queen Queen Street. Street. This Street and stop at the This is private property so stay on the outcrop. outcrop. the base base of of the the This is a no hammer stop. The The middle middle stromatolitic stromatolitic unit forming the the Gunflint Gunflint Formation Formationoutcrops outcropsatatthis thislocation. location. The carbonate upper member of the stromatolites are excellently preserved and are visible visible in in both both cross-section cross-section and and plan plan stromatolites forms Carbonate sands sands are are banked up against the cabbage-sized forms view (Figure 14). Carbonate and eventually eventually overwhelm overwhelmthem. them. The stromatolites established themselves themselveson on aa and stromatolites established silicified horizon horizon which at other other locations locationsshows showsevidence evidenceof ofsubaerial subaerialexuosure. exposure.This This silicified provided the necessary hard substrate substrate to to allow allowthe thestromatolites stromatolitesto todevelop. develop. The unit providedthe maj or stromatolitic horizon is overlain by beachrock which has been disrupted by a major stromatolites have been been ripped ripped up up along along with with storm event. Pieces Pieces of of the underlying stromatolites overlying partially cemented carbonate sands. The beachrock formed in inthe theupper upper the overlying beach environment beach environment due to salt salt spray spray from from breaking breaking waves waves depositing depositing meniscus meniscus cements at grain grain contacts contacts of the sand. This partially cemented cements This partially cemented sand sand layer layer on the upper disrupted into slabs when when a large storm caused waves waves to to break in this tbis beach was dismpted environment. environment. STOP STOP 77 Proceed back back to to Oliver Oliver Road. Road. Turn right. Turn the Turn left left on Crown Street (at the junction with near where where it bends bends right right and and &s turns into into Dixon Dixon junction with John John Street) Street)and and drive drive to ;ear Street. Drive one block northwest on a small lane to the base of the High Street Park Drive one block northwest to the base of the High Street Park hill. outcrop forming forming the base of the hill bill is composed composed of carbonate carbonate breccia breccia with with some The outcrop chert clasts. Wavy laminated dripstone forms discontinuous layers blanketing some Wavy laminated dripstone discontinuous of the the roof roof of a of the breccia piles. This Thisisisaacollapse collapse breccia breccia formed by failure of cavern in the ankerite. A number of failures occurred as denoted by the the ankerite. A number of failures occurred as denoted by cavern which were were deposited depositedon ondebris debrispiles pileson onthe thecavern cavernfloor floor interlaminated dripstones, which by roof leakage. This Thisunit unit forms forms the the upper layer of the Gunflint Formation's lower correlatable with with STOP STOP 6. 6. Maximum Maximum member and is often overlain by stromatolites comelatable regression of the Animikie sea occurs at this internal interval leading to to subaerial subaerial exposure exposure Gunflint sediments sediments in the the Thunder ThunderBay Bayregion. region.Evidence Evidenceof ofsubaerial subaerialexposure exposurehas has of Gunflint not been obserned observed in drill core examined from south of the U.S. border. �A) Sills jfied stromatolitic stromatolitic reef reef overlain ales Figure 8.8. A) Siliszjied overlain by by black blackvolcaniclastic volcanicIasticsit shales Figure I15. S . Stop Sto~ (background). plane of ankeritic grainstones. grainstones. -' B) -' Hummocky Hummoc'- bedding ' ?ddingplane of ankeritic �STOP 8 Drive turn left. left. Proceed to its end and andturn turnleft leftonto onto Cumberland. Cumberland. Drive to Oliver Road and turn Continue River. Turn Continue driving driving on on Cumberland Cumberland to to Current Current Ever. Turnleft left onto onto Arundel Arundel Street Streetand and proceed to the cement bridge across the Current Rver. River. Immediately Immediately before crossing crossing the onto Lyon Blvd. Pull to the right into one of the the parking parking m the bridge bridge turn turnleft onto Pull off offto as. areas. Walk to the river then then down down river river to to the the end end of of the the outcrop. outcrop. You are standing on the Paleoproterowic Paleoproterozoic sea sea floor. floor. The The uneven topography of the ankerite ankerite grainstones grainstones reflects reflects the presence of dunes and hummocks produced by the storm which moved moved thi the carbonate sands over over the the bottom 15). carbonate sands bottok (Figure (~igure-15). storm events events which Silicified dot this this irregular irregularseascape. seascape. This forms forms the the lower lower Silicified colonies of stromatolites dot unit of of a tripartite assemblage. Large Large silicified silicifiedstromatolites stmmatolites occur occur on the other side of directly overlying overlying these is aavolcaniclastic volcaniclastic silty silty shale. shale. A description description of the the bridge and directly of this this sequence sequence and and its itsinferred inferreddepositional depositional environment environment follows (taken from Fralick, 1989). Fralick, 1989). Major Major Subdivisions Subdivisions Coalesced domal stromatolites form the microbial bioherms bioherms present present in the outcrops outcrops on on Current underlain by by parallel parallel CurrentRiver. River. They Theyrepresent representaaportion portionof ofthe the upper upper stromatolitic stromatoliticzone and are underlain laminated complicated laminatedand and hummocky hummocky cross-stratified cross-stratified carbonate carbonate grainstone which has undergone a complicated history and dolomitizition-ankeritizition. dolomitization-ankeritization. The bioherms history of of silicification, silicification, neomorphic neomorphic spar growth and are are draped draped by by graded, graded, centimetre-scale centime&-scale beds beds of of dark grey siltstone siltstone and shale shale (Figure (Figure 16). 16). Carbonate Carbonate Grainstone Grainstone The grainstone grainstone is divisible divisible into into three three types: types: 1)1)hummocky hummocky cross-stratified; cross-stratifie4 2) parallel parallel laminated; 3) massive, massive, highly highly silicified. silicified.Flummocky Hummockycross-stratification cross-stratificationgenerally generally has has wavewavelaminated; and and 3) lengths, lengths,between between0.5 0.5 and and 11m. ItItcommonly commonlycontains containsoval oval and and rectangular rectangular rip-up rip-up clasts clasts which, which, when when abundant, abundant,fine fineupwards upwards in in individual individualbeds. beds. Often Oftensilicified silicifiedrip-ups rip-upsor or mixtures mixtures of of silicified silicified and and nonsilicified silicified rip-ups rip-ups are arepresent present in in non-silicified non-silicified beds. beds. Parallel they are less less abundant. The The Parallellaminated laminated grainstone grainstone also also contains rip-up clasts, but they appearance of these units is nodules. The is complicated complicated by the presence of silicified nodnles. Thegrainstone grainstone develops bend around around silicified silicified areas. areas. The compaction compaction developsaa wavy wavy lamination laminationwhere where the the parallel laminae bend deformed but can be deformed laminae laminae are similar similar in inappearance appearance to tohummocky hummocky cross-silicification, cross-silicification, but be distinguished distinguishedby by the thepresence presence of of low-angle low-angleerosive erosive truncations truncationsin in the latter. Silicification is very verycommon. common. One bed bed near near the the base base of of Silicificationof of layers layers and patches within layers is the silicification, culminating, culminating, at at its its top top in the measured measured section section exhibits exhibitsaa marked upward increase in silicification, aa layer layer of of massive massive chert. chert. Another Anotherhighly highlysilicified silicifiedzone zonedirectly directlyunderlies underlies the the stromatolite stromatolitebearing bearing horizon. horizon. Silicified Silicifiedlaminae laminaepresent presentin inother other beds beds have have sharp, sharp, flat top surfaces and sharp irregular bottom bottomsurfaces. surfaces.Water Waterescape escapestructures, structures,common commonthroughout thoughout the the hummocky hummocky cross-stratified cross-stratifiedunits, units, sometimes brittlelydeform deformthese thesesilicifled silicifiedlayers, layers, forming forming cross-cutting cross-cutting carbonate carbonate dikes dikes which rotate sometimesbrittlely plug-like, plug-like,angular angularchert chertblocks blocksto toone oneside. side. �Figure 16. of1 the stromatolitic sequence on Current Current Figure 16. Stratigraphic Stratigraphic sections sections at at varying vafying scales scales 0 the stromatolztzc sequence on River. LEGEND L EGEND I: m Limestone I 90 - Dolomite Dolomite ____ wavy Lamination Hum mocky Cross Cross -Hummocky Stratification Stratification El V / 1 I F / F F / I F F / F so - II, __________ Section A Intrabasinal lntrabasinal Rip—up Clasts Rip-up Clasts Escape Fluid Escape Fluid Structures structures 0 ARCHEAN BASEMENT SECTION B SECTION SECTION A SECTION m I F F Pyrite Lenses % Lenses ___ Pyrite .tr I / / / I / 1' / / 1 I I 1 / / II / I / / I F Hemispherical Hemispherical ___ .Stromatdi+es Stromatolites :° I I 60 - Chert Light/Dark Chert LightIDark e0 I / Parallel to rj Parallel Wavy Lamination Co I F = Interbedded flTInterbedded Siltstone and Siltstone and Shale Shale t1 ''I'll - — — — -JROVE FORMATION -- m m 12 — I--- . -- - - -- - - -I - 7' i/i .9 — 6 17 / ., '.-1 //I ,—. / •6 3 .3 0 0 A PAP SpA P A p PAPA PA P A P A ASASASSA AS P �Microbial Bioherms Bioherm The base of of the thebioherm biohem bearing bearing layers layers isiscomposed composed of ofparallel parallellaminated laminated carbonate carbonate containing isolated isolated centimetre centimetre to todecimetre-scale decimetre-scale (maximum (maximum grainstone, wavy silicified in patches, containiig 20cm 20 cmhigh high xx 50 50 cm cm wide) wide) domal domal stromatolites. stromatolites. They They represent represent the the SH-C/LLH-C SH-CLLH-C type of Logan et aL mounds. Some 01. (1964). Grainstone Grainstonelaminae laminae are are banked banked up against the sides of the microbial mounds. Some mounds are buried by the grainstone while others, after being partially covered, re-established by the grainstone while others, after being p d a l l y covered, re-established themselves. stromatolites begin themselves. The Theamount amountof ofgrainstone grainstonedecreases decreasesupward upward and and the cabbage sized stromatolites laterally merging. This trend resulted in the development of up to 1 m high, sometimes overlapping, This trend resulted in the development of up to 1mhigh, sometimes overlapping, microbial mounds scattered oover bottom. In v e ~the bottom. In areas areas where where early stromatolites stromatolites flourished raised platforms were built (up to 0.5 m above the surrounding bottom) on which large, coalescing. coalescing, domal domal platforms were built (up mounds grew, grew, giving giving aa total total relief reliefabove abovethe the adjacent adjacentarea area of of well well over over1I m. m. All stromatolites stromatolites have internal structures poorly preserved. presewed. have been extensively silicified silicified and internal structuresare are poorly Lamination in the strornatolites, when visible, is caused by the alternation of light and dark stromatolites, caused by the alternation of light and dark chert chert bands. bands. Pyrite layers and irregular blobs are present in the mounds, in places forming up to 20% of the rock. A A stratiform, stratifom,discontinuous discontinuouspyrite pyritelayer layeralso also drapes drapes some some mounds; the larger ones. Lenses Lenses in this unit attain attain thicknesses thicknesses up to to 10 I0 cm. Siliciclastics Siliciclastic, microbial biohems. bioherms. Centimetre-scale beds Siliciclastic, fine f i e grained Centimetre-scale graded graded beds -grained rocks drape the microbial comprising this comprising this unit unit are are internally internally composed composed of of alternating altemating matrix-rich and and matrix-poor, millimetremillimetrescale laminae. The angular qtmtz quartz Thematrix-rich matrix-richlayers layerscontain containfine fine grained, grained, sand-sized sand-sized clasts clasts of very angular and orthoclase containing orthoclase floating floating in aa matrix m&ix composed composed of 02very very fine finegrained graineddark darkmaterial mat-erial-cont&ng disseminated pyrite and 1I to 2% non-carbonate carbon. Matrix-poor layers are composed 2% non-carbonate Matrix-poor layers are composedof of very very (maximum size size 0.1 0.1 mm). mm). The The angular quartz, orthoclase, biotite and muscovite in clast support (maximum thinly bedded rocks are overlain by an indistinctly laminated unit which fills in hollows between thinly bedded rocks are overlain by an indistinctly laminated unit which fills in hollows between the the stromatolite stromatolite mounds. mounds. It is aapoorly poorly sorted, sorted,matrix matrix supported supported silty silty shale shale with bedding bedding parallel muscovite flakes muscovite flakes up up to to 55 mm in length. Shallow, Shallow,saucer saucershaped shapedscours scoursoccur occur in in its its upper upper portion. portion. The scours carbonate grainstone laminae thick. The scours are overlain overlain by carbonate laminae up to 1 cm thick. The grainstone grainstone unit unit is is 10 10 cm in thickness and is interbedded with and overlain by well laminated silty shale similar to the silty similar to thickness and is interbedded lower lower unit. unit. DEPOSITIONAL ENVIRONMENT DEPOSITIONAL ENVIRONMENT AND HISTORY HISTORY Sta2e A -- Storm Dominated Sheq Stage Shelf The presence presence of hummocky hummocky cross-stratified cross-stratifiedcarbonate carbonate grainstone grainstone with with the the absence absence of of wavewaveripple weather wave-base wave-base ripple reworked reworkedtops topsindicates indicatesthat thatthe thesand sandblankets blankets were were deposited depositedbetween between fair fair weather and stom storm wave-base in arelatively a relatively silicicIastic-free siliciclastic-free environment environment (Figwe (Figure 17). The The carbonate, carbonate,or or its its precursor was likely precipitated, eroded and abraded in shallow water areas and transported into deeper water during storm events. Silicified Silicifiedrip-up rip-up clasts clasts and and crusts cmstsdenote denote that that silicification silicificationwas was syndepositional (as degree of silicification increasing towards the syndepositional (asproposed proposed by by Simonson, Simonson,1986); 1986);the the degree bed indicates indicates that that seawater seawater(sensu (sensulato) lato)was wasprobably probablythe thesilicieing siliciing agent. top of the bed �/ - ...: . , .. D. sediments present at Stop 8. Figure Figure17. 17. Developmentalphases DeveIopmentaIphasesofofthe theenvironment environmentrepresented represented by by sedimentspresent atS-. Each text. Each stage stage is is discussed discussed in in the the text. I �- Stare B - Stabilization Siii4fication of Stabilization and Siliczfication Stase of the Substrate If seawater seawater was the the agent agent causing causing alteration alteration of of the the carbonates carbonatesthen then silicification silicification should should increase with length of time the unit was positioned close to the water-sediment interface. increase with length of time the unit was positioned close to the water-sediment interface. This This scenario implies implies that that the the stromatolites formed by by alteration of scenario the massive massive chert chert underlying underlying the stromatolites formed alteration of carbonates during an interval of lowered deposition rate. This is best explained by increasing the carbonates during an interval of lowered deposition rate. This is best explained by increasing the water depth depth so so that that the the bottom bottom sinks sinks below below storm storm wave-base wave-base and and slower slower deposition deposition rates rates ensue. ensue. - Stage C Stase C - Stromatolite Stromatolite Development Development Stromatolites grew on the silicified, silicified, stabilized stabilized substrate, substrate, forming forming inverted-bowl shaped mounds on the Some mounds the bottom. bottom. The lack of of wave wave agitation agitation and and firm firm substrate substrate proved proved ideal. ideal. Some stromatolites were occasionally buried by grainstone laminae brought in by seaward flowing bottom stromatoliteswere occasionally buried grainstone laminae seaward bottom currents generated during storm events. storm Stage D D --Large Large Microbial Bioherm Stase Bwherm Growth Growth Individual stromatolite Individual stromatolitecolonies coloniescoalesced coalesced upwards, upwards, forming forminglarge large mound mound shaped shapedstructures structures irregular bottom bottom topography. topography. Little and creating an irregular Little sediment sediment accumulated accumulated between between the stromatolite stromatolite mounds mounds as as storm storm events events became became less less capable capableof of supplying supplyingdetritus detritusto to the the area. area. - State E - Volcaniclastic VolcaniclasticBurial Growth of of the bioherms was abruptly terminatedby bythe the deposition depositionofof aa series Growth bioherms was abruptly terminated series of volcaniclastic sediment blankets. The Thedraping drapingof of these these blankets blankets over the mounds rather than their than sedimentation from bottom ponding in intermound intermound areas indicates indicates rain out from above rather than currents. currents. feldspars) and and sorting sorting (large The composition (fresh detrital biotite), angularity (subhedral feldspars) well formed crystals floating in a dark fine grained groundmass) all point to little or no reworking floating a dark fine grained of pyroclastic pyroclastic material. asrain rainout outfrom fromash ash landing landingon on material. The Thelayers layersmay mayhave havebeen beendeposited depositeddirectly directlyas the water's surface or as storm deposited layers. The latter is preferred, as the microlaminations can surface or as storm The latter is microlaminations can then be explained explained by fluctuations fluctuationsin in the the energy energy level. level. The Thepresence presenceof of significant significantquantities quantitiesof ofnonnoncarbonate carbon in the groundmass of these rapidly deposited units units may may reflect reflect the the settling settling of of the the volcaniclastics a composition similar siinilarto vegetable soup. soup. The occasional occasional volcaniclasticsthrough throughaa sea sea with acomposition to microbial vegetable large storm event eroded saucer shaped scours into the the fine fine grained grained material material and andtransported transported minor minor amounts of carbonate amounts carbonate in in from from the the shore-proximal shore-proximal zone. zone. Lateral Implications As water depth depth increased, increased, the bottom changed changed from from a wave dominated dominated condition condition to to aa zone zone sedimentation and of slow sedimentation and thus pervasive silicification. silicification.This Thisled ledto to stabilization stabilizationof of the the sediment sedimentand and stromatolites began to develop. With time (increasing water depth) large domal structures grew. With time (increasing water depth) domal structures stromatolites stromatolitic zone of the Gunflint Formation by This succession succession was was brought brought to an end in the upper stromatolitic pyroclastic eruptions eruptionsand and volcaniclastic volcaniclasticdeposition depositiondrastically drastically altering altering bottom bottom conditions. conditions. STOP 99 STOP Turn left on Lyon Blvd. Blvd. Then Arundel. Turn nodder Ave Then right on Anmdel. Turn left on Hodder Ave and and drive drive Transcanada. Turn to the Transcanada. Turnright righton onthe theTranscanada Transcanadaand anddrive driveto to the the Pass Pass Lake Laketurnoff. turnoff. Turn right here and proceed till you encounter encounter a large outcrop of contorted contorted ribbon ribbon chert-carbonate on chert-carbonate on your your left. left. �Figure 18. ribbon chedearbonate chert-carbonate layers. B) SStop Chert-carbonate silt to1 ~11. 1. Chert-carbonate A)-.Ston 9. Disrupted ribbon Figure 18. A) to pebbly pebbly grainstone grainstone with rip-ups of volcaniclastic sediment and fingernail-sized volcaniclastic sediment and fingernail-sized, shards. shards. 1 ____ - :' F&: . 1; _ �a- Jrrce —— _____ w L a: r Ia r TTTT 'a — , -a / 't* ;c •- 5'4 '1r * J * a a : s A .1-1 — at' Efl C_ - \ ' - — — * — a- a- I a -, Figure 19. A) internal laminations medium-grained sandstone stormlayer. layer. The Figure A)Close-up Close-upof internal laminations in a medium-grainedsandstonestorm one third third of of the thelayer layercontains containsupperflow upperfiowregime regimeparallel parallellaminations. laminations. The bottom one two thirds thirds Ic hummockycross-stratified cross-stratjfiedwith withlow lowangle angletruncation truncationsurfaces surfaces upper two is hummocky B) Outcrops Outcropsat at Stop Ston 12. 12. clearly visible. B) �Laterally chert and and ankerite ankerite layers layers occur occur in Laterally continuous continuous interlaminated interlaminated chert in this this outcrop outcrop (Figure 1 8A). These layers are intensely folded and disrupted in places. The outcrop outcrop (Figure 18A). These layers are intensely folded and disrupted in places. The provides an excellent opportunity to discuss if the deformation is synsedimentary, provides an excellent opportunity to discuss if the deformation is synsedimentary, why the the ribbon ribbon chert-carbonates preferentially exhibit exhibit this this type type of of deformation deformation and and why chert-carbonates preferentially what type type of depositional environment what of depositional environment is is represented represented by by these these sediments. sediments. STOP 10 STOP 10 Proceed back back to Bay. Drive Proceed to the the Transcanada Transcanada and and turn turn left, left, towards towards Thunder Thunder Bay. Drive approximately 1.8km road on on the the right. right. Turn approximately 1.8km until until you you reach reach the the small small side side road Turn right right onto onto the the dirt dirt road road and and park. park. Volcaniclastic, Volcaniclastic, very very fine-grained fine-grained sandstones, sandstones, siltstones siltstones and and mudstones mudstones occur occur at at this this location. These location. Theseare areprobably probably correlatable the gorge gorge at correlatablewith with the the interval interval examined examined in the Kakabeka Kakabeka Falls. Falls. The Thevery veryfine-grained fine-grainedsandstones sandstonesand and coarse-grained coarse-grained siltstones siltstonesare are ripple ripple laminated laminated with with well well preserved preserved internal internal structure structure (see (see polished polished hand hand samples). samples). Again possible depositional Again the the possible depositionalprocesses processes which which may may have have operated operated to to form form this this unit unit will be discussed in the field. will be discussed in the field. STOP STOP11 11 Turn right onto onto the the Transcanada Transcanada and and proceed proceed towards towards Thunder Thunder Bay. Bay. Turn Turn right Turn right right at at the the access road to the Terry Fox lookout. Park in the parking lot and walk to the large access road to the Terry Fox lookout. Park in the parking lot and walk to the large outcrop outcrop on on the the highway; highway; watch watch out outfor forcars. cars. A the Gunflint Gunflint Formation Formation at at this this location. location. The A large large diabase diabase sill sill overlies overlies the The Gunflint Gunflint grainstones present here contain large rip-up fragments and both small grainstones present here contain large rip-up fragments and both small and and large large sherds of of volcanogenic volcanogenic origin origin(Figure (Figure 18B). l8B). Volcaniclastic present near near Volcaniclastic shales shales are are present sherds the top of the sedimentary this has has been been described described by by some some workers workers as as the top of the sedimentary sequence sequence and and this However, interbedding interbedding of of volcaniclastic the the Gunflint-Rove Gunflint-Rove contact. contact. However, volcaniclastic shales shales and and chemical sediment the upper upper portions portions of of the the Gunflint Gunflint Formation, Formation, and chemical sediment is is common common in in the and if more sediment occurs occurs at at aa higher higher level level this this cannot cannot be be defined defined as as the the if more chemical chemical sediment contact. contact. STOP STOP 12 12 Turn Turn right right on on the the Transcanada Transcanada and and drive drive across across the the bridge bridge over over the the Current CurrentRiver. River. Proceed up hill on the other Proceed up the the hill on the other side. side. A Arock rock cut cutoccurs occursat at the the top top of of the the hill hill and and there there is a dirt dirt pull-in. pull-in. Park is a Park here. here. This grainstone those examined on the the Current Current River This grainstone sequence sequence is is similar similar to to those examined on River (Figure (Figure 19). There may be metre-scale thinning-upwards cycles present here 19). There may be metre-scale thinning-upwards cycles present here hut but they they are are indistinct. indistinct.Thin, Thin, discontinuous discontinuouschert chertlayers layersoccur occurat at the the tops tops of of these these possible possible cycles. cycles. In places this this chert very carbon-rich, carbon-rich, possibly possibly denoting denoting aa slowing slowing of of the the deposition deposition In places chert is is very rate allowing accumulation of organic carbon. This outcrop provides an opportunity rate allowing accumulation of organic carbon. This outcrop provides an opportunity to discuss to discuss some some of of the the possible possible process process which which could could drive drive deposition deposition of of this this type type of of assymetric cycle (Figure 20). assymetric cycle (Figure 20). Turn right Turn left left on on Turn right on on the the Transcanada Transcanada and and proceed proceed to to Oliver Oliver Road. Road. Turn Oliver Road Road and and turn turn right right at at the the road road leading leading to to the the main main entrance entrance of of Lakehead Lakehead Oliver University. University. �Figure modelfor for nonbarred nonbarred portions portions of Figure 20. 20. Generalized Generalized depositional depositional model of the the strand-proximal strand-proximal Gunflint shelf during deposition of upper Gunflint chemical sediments. Gunjlint shelf during deposition of upper Gunflint chemical sediments. 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G , cd , Early Proterozoic ProteroxoicGeology Gcolog) of ofthe thc Great Great Lakes Lakes Region: Region Geological Geological Society Socicty of of America America Memoir Memoir160, 160,p.p 15-32. 15-32 �GLACIAL GLACIAL HISTORY AND REGIONAL TILL SAMPLING SAMPLING IN THE THE ARCHEAN SHEBANDO WANGREENSTONE GREENSTONE BE BELT SHEBANDOWAN I Andy Bajc, Ontario Geological Survey , Shebandowan Greenstone Belt, Belt, host host to to aa variety variety of of The Shebandowan precious and andbase basemetal metal deposits, deposits, is is aa bedrock-dominated bedrock-dominated terrain, terrain, typically typically having having thin thin till cover. Till Till sampling sampling techniques and resultant grain and resultant gold grain and other other heayy heavy mineral results will be examined in an exploration context context. �INTRODUCTION INTRODUCTION The Shebandowan Shebandowan greenstone greenstone belt, which is located located immediately north and west of the city of Thunder exploration and mining spanning well over 100 Thunder Bay, has a rich history of mineral exploration 100 years. The belt is host to a variety of precious and base metal mineral deposit types. Past producers The mineral deposit types. include the Inco Inco Limited Shebandowan Shebandowan Ni-Cu-PGE mine, the the North Coldstream Coldstream Cu-Au-Ag Cu-Au-Ag mine mine include and the Ardeen Au mine which which was was northern northernOntario's Ontario's first first gold gold producer. producer. Exploration activity activity within response to the depressed prices of precious precious and within the belt has has currently currently subsided, subsided, largely largely in response base metals and the inability ofjunior mining companies to raise hinds for exploration. metals of junior mining companies to raise funds for exploration. In response to this this recent decline decline in mining mining and mineral mineral exploration exploration activity activity within the belt, the Ontario and drift drift geochemistry geochemistry Ontario Geological Geological Survey Survey initiated a 2 year program of Quaternary geology and to further evaluate potential of of the the Shebandowan belt. belt. This was accomplished evaluate the mineral resource potential by detailed (1:50 (1 :50 000 000 scale) scale) Quaternary geology mapping and regional humus and c-horizon till sampling. sampling. Quaternary Quaternarymapping mapping was was undertaken undertaken to to document document the the distribution distribution and character of the various Quaternary deposits within the study area and to reconstruct various Quaternary deposits within the study area and to reconstruct the the ice ice flow flow history history associated associated with with these these deposits. deposits. This Thisinformation informationisis essential essentialfor forthe thesuccessful successfulimplementation implementationof ofmineral mineral exploration drift prospecting prospectingtechniques techniquesand and surficial surficialgeochemistry. geochemistry. explorationprograms programsutilizing utilizing drift During During the the 1998 1998field field season, season, Quaternary Quaternary mapping mapping and and regional regional humus humus and and c-horizon c-horizon till till sampling sampling were conducted conducted over the eastern half of the belt within within the area area covered by the Sunshine Sunshine (52A/l2) (52N12)and andKakabeka KakabekaFalls Falls (52A/5) (52N5) 1:50 1:50000 000scale scaleNational NationalTopographic Topographic System System (NTS) map sheets sheets (Figure (Figure 1). 1). The Theresults resultsof ofthis thiswork workare aresummarized summarizedin in Ontario OntarioGeological Geological Survey Survey Open File Report (Bajc 1999a). 1999a). Mapping Mappingand andsampling samplingwas wasextended extendedwestward westward into into the the Shebandowan Shebandowan Report 5993 5993 (Bajc (52B/9) (52B19) and and Burchell Lake (52B/10) (52B110) 1:50000 1:50 000scale scaleNTS NTS map map areas areas during during the 1999 1999 field season. An OGS OGS preliminary preliminary map map containing containing information information on on the the regional regional distribution distribution of of gold gold grains grains in in till till within was released during the fall of 1999 1999 (Bajc 1999b). The The complete complete mineralogical mineralogical and within this this area area was geochemical geochemicaldatasets datasetsfor for the the western western half half of of the the belt belt were were released released in in the the spring spring of of 2000 2000 (Bajc (Bajc 2000). 2000). BEDROCK BEDROCK GEOLOGY GEOLOGY A A comprehensive comprehensivesummary summaryof of the the bedrock bedrock geology geology of of the the study study area area is is contained contained in papers by Sutcliffe Sutcliffe (1991), (1991), Williams Williams (1991) (1991) and Williams Williams aetall al.(1991) (1991)as aswell wellas asininnumerous numerousOntario Ontario Geological Geological Survey Survey maps maps and reports. The Thestudy studyarea areacontains contains33 distinct distinct bedrock domains domains (Figure (Figure 2). 2). The Thecentrally-located centrally-locatedWawa WawaSubprovince, Subprovince,within withinwhich whichthe the Shebandowan Shebandowan greenstone greenstone belt occurs, occurs, is is fault-bounded fault-boundedto to the the north north by by metasedimentary metasedimentaryand and felsic felsic intrusive intrusive rocks rocks of of the the Quetico Quetico Subprovince Subprovinceand and unconformably unconformably overlain overlain to to the the south southby by Paleoproterozoic Paleoproterozoicmetasedimentary metasedimentaryrocks rocks of Animikie Group Group(Gunflint (Gunflintand and Rove Roveformations). formations). of the the Animikie Metasedimentary Metasedimentaryrocks rocks of of the the Quetico QueticoSubprovince Subprovinceconsist consistprimarily primarily of of turbiditic turbiditic wackes, wackes, arkoses migmatites. PostQuartzarenites arenites and and their their associated associated paragneisses varaeneisses and miematites. Post- to to arkoses and and quartz - syndepositional syn&msitiorkl felsic felsicplutons plutonsconsisting consistingof offeldspar-megacrystic feldspar-megacrysticgranite, granite, granodiorite granodiorite to to tonalite tonalite and and monzonite monzonite comprise comprise aa notable notable proportion proportion of this domain. Narrow, Narrow, elongate elongatelenses lensesof of tholeiitic, tholeiitic, �PROTEROZOIC Jacobsville Gp.- sandstone, shale, wnglomerate [_\j Keweenawan mafic intrusive rocks Sibley Gp.-conglomerate,sandstone,shale I Animikie Gp.-wacke, shale, iron formation, limestone, minor volcanics Oskr Gp.- basalt, wn@omerate, a h s e a ARCHEAN Fekic lntmsbe ro& 0 Queliw Subpvinm mtasedimnta~yrocks UI tig goon Subpvince supracrustal rocks Wawa Subprovince supramstat rocks [S3 1998 Survey Area 19gg suwey Area Figure 1. Figure 1.Location Locationmap mapofofstudy studyarea areaincluding includingregional regionalbedrock bedrockgeology. geology. mafic metavolcanic the Quetico metavolcanic rocks and associated gabbroic rocks occur locally within the Subprovince (Brown 1995, 1995, Osmani Osmani 1997). 1997). Metasedimentary rocks of the Gunflint Gunflint and Rove formations (Animikie Group) were deposited Metasedimentary Minnesota, Wisconsin Wisconsin and and Michigan Michigan(Sutcliffe (Suteliffe 1991). 1991). The within a large basin that extends into Minnesota, Gunflint Formation unconformably on the Archean Formation contains a basal unit of conglomerates conglomerates that rest unconfommbly jasper, basement and are overlain by interbedded argillites, argillite tuffs, cherts, algal cherts, jasper, carbonates, hematite, hematite, magnetite magnetitetaconite taconiteand andsilicate silicate(aconite. taconite. The carbonates, ferruginous carbonates, consists of black, locally pyritic shales and grades upward upward into into overlying Rove Formation consists interbedded black shale and arkosic greywackes. greywackes. Mesoproterozoic "Logan" diabase sills intrude the the Mesoproterowic diabase sills intrude resistant cap rocks of large mesas in the southern part of the map Rove Formation Formation and form the resistant area. Silver Silvermineralization mineralizationoccurs occurslocally locally along along normal normal faults faults that intersect the contact between Rove Formation shales and Logan diabase diabase sills. sills. Notable silver silver deposits deposits occur in the southeastern corner of the Kakabeka Falls NTS map area, in the vicinity of Badger and Beaver mountains mountains comer Mountain group group of of deposits) deposits) and and Silver SilverMountain. Mountain. Accessory minerals minerals in in these these (Creswel or Rabbit Mountain calcite; quartz; quartz; barite; barite; and and fluorite fluorite deposits include: acanthite; pyrite; sphalerite; marcasite; galena; calcite; (Franklin eta/. 1986). et at 1986). �Figure 2. Bedrock geology of the study area, Archean metasedimentary rocks (Wawa Subprovince) Aichean mafic intruswe rocks Archean felsic4ntennediate intrusive rocks Archean meta volcanic rocks * CmsweuRabbit Mtn. Ag deposits Snodgrass Lake Au deposit Shebandowan Ni-Cu-POE mine North Coidsiream Cu-Au mine Animikie Op. Metasedimentaiy rocks Archean metasedirnentary rocks (Quetici, Subprovince) Ardeen Au mine Keweenawan malic intrusive rocks �can be be subdivided into into 2 contrasting Supracrustal rocks of the Shebandowan greenstone belt can packages of metavolcanic metasedimentary rocks: 1) metavolcanic and metasedimentary 1) an older suite of mafic to felsic metavolcanic metavolcanic rocks rocks belonging to the Greenwater Greenwater assemblage; and 2) a younger suite of metasedimentary to the the Shebandowan Shebandowan assemblage. assemblage. The metasedimentary and metavolcanic rocks belonging to Greenwater assemblage consists primarily of tholeiitic basalts with intercalated intermediate to Greenwater assemblage felsic and Stott 1998). Mineralization felsic metavolcanic metavolcanic rocks and minor komatiites (Corfu and Mineralization at the Shebandowan, North Coldstream and Ardeen mines are all contained within Greenwater assemblage Ni-Cu-Pt-Co mineralization mineralizationatatthe theShebandowan Shebandowanmine mineisishosted hosted by by aa gabbrogabbroassemblage rocks. Ni-Cu-N-Co peridotite sill. Cu-Au-Ag mineralization at the North Coldstream mine is hosted by a highly peridotite Cu-Au-Ag mineralization at the North Coldstream mine is hosted silicified silicified gabbro. Gold Goldmineralization mineralizationatatthe the Ardeen Ardeen mine mine occurs occurs in in composite composite quartz veins developed along the Pete and Ardeen fault systems. Advanced exploration developed Pele exploration in the form of a decline ramp ramp and and bulk sample sample was was undertaken undertaken at the Snodgrass Snodgrass Lake Au prospect in central Moss Township mid-i 980s. Gold Township during the mid-1980s. Gold mineralization mineralizationoccurs occurs in in sheared sheared felsic felsic metavoicanic metavolcanic rocks and in sheared and fractured diorite, gabbro and and quartz-feldspar quartz-feldsparporphyries. porphyries. The Haines gabbroanothosite within the the belt. belt. The intrusion, anothosite complex complex represents one of the larger mafic intrusions within which occurrences. which is is crudely layered, is host to a number of Ni-Cu-PGE occurrences. The overlies (i.e., (i.e., fault contact) and The younger, Shebandowan Shebandowan assemblage assemblage both unconformably overlies intrudes intrudes the Greenwater Greenwater assemblage. ItIt consists consists of of alkalic alkalic metavolcanic metavolcanic and intrusive rocks (tuff, breccia, breccia, syenite, syenite, lamprophyre, lamprophyre, quartz quartz and and feldspar feldspar porphyry, granodiorite and diorite) as well as metasedimentary metasedimentaryrocks rocks (arkoses, (arkoses, wackes, conglomerates conglomeratesand oxide-facies oxide-facies iron iron formation) formation) at 1998). This assemblage is interpreted as representing an intracratonic (Schneiders ci' This assemblage is interpreted as representing an intracratonicbasin basin (Schneiders et al. assemblage assemblagesimilar similarto to the the Timiskaming Timiskamingassemblage assemblageof of the the Abitibi Abitibi subprovince. subprovince. Most Most gold gold occurences occurencesin in the the eastern eastern portion portion of of the the Shebandowan Shebandowangreenstone greenstone belt display display a close close spatial association with rocks of the Shebandowan assemblage. The style of gold mineralization is spatial association The style of not unlike and Kirkland Lake. Lake. Gold i m m i nand i I&kland unlike that which occurs in such such prolific mining camps as ~Tinimins mineralization mineralizationisiscommonly commonly associated associatedwith with both both large large scale scale and and subsidiary subsidiarystructures structures and structurally-controlled en echelon echelon quartz veins, structurally-controlledintrusions. intrusions. Mineralization Mineralizationoccurs occursin in sheeted sheetedand and en stockwork stockworkzones zones and and vein vein breccias breccias as as well well as as in in stocks, stocks,dikes dikes and and sills sillsof of felsic felsicto to mafic mafic composition. composition. Gold Goldisisalso alsocommonly commonlyassociated associatedwith: with: sulphide-rich, sulphide-rich,quartz-veined quartz-veined replacement replacement zones zonesin in oxide oxidefacies faciesiron iron formation; formation;silica-flooded, silica-flooded,hydrothermally-altered hydrothermally-altered zones; and and ironcarbonate with shear shear and and permeable permeablezones. zones. Associated carbonate and and pyrite-rich zones commonly associated with alteration alteration and and accessory accessory minerals minerals thclude: include: iron iron carbonate; carbonate; silica; silica; potassic potassic feldspar; feldspar; sericite; sericite; arsenopyrite; tourmaline; tourmaline; and and green green mica (Schneiders (Schneiders et aL al. 1998). 1998). hematite; chlorite; chlorite; calcite; calcite; pyrite; pyrite; arsenopyrite; hematite; Notable Notable exploration explorationprograms programs within within the the current currentstudy study area area are are highlighted highlighted in the last 55 annual annual volumes volumes of of the Resident Resident Geologist's Geologist's Report Report of of Activities. Activities. as GLACIAL GLACIALGEOLOGY GEOLOGY The The study study area area isis characterized characterizedby by several several contrasting contrasting physiographic physiographic regions, each defined by a unique unique suite suite of of overburden overburden conditions. Most Mostof ofthe theBurchell BurchellLake Lakeand and Shebandowan Shebandowan NTS map areas areas as as well well as as parts parts of of the the Sunshine Sunshineand and Kakabeka Kakabeka Falls Falls NTS NTS map map areas areas are are characterized characterized as as bedrock-dominated drift occur occur in in morainic morainic belts, bedrock-dominated terrains. Local Localaccumulations accumulationsof of thick thick drift glaciofluvial glaciofluvial complexes complexesand and narrow, narrow, structurally-controlled structurally-controlleddepressions depressions within within these these uplands. �Thicker within g. Thicker deposits deposits of of till and/or andlor glaciofluvial glaciofluvial and glaciolacustrine sediments occur within#? isolated isolatedbasins basins(Figure (Figure3). 3). AAnorthern northernlowland, lowland,here herereferred referredtotoasasthe the"Kaministikwia "Kaministikwiabasin", basin", occupies Kaministikwia rivers. AA occupies the the valleys valleys of of the the Oskondaga, Oskondaga, Matawin, Shebandowan and Kaministikwia southern In the the northern northern southern basin is centred centred on the valleys of the Whitefish and Kaministikwia rivers. In basin, basin, thick thick deposits deposits(several (several tens tens of of metres) of of glaciofluvial glaciofluvial and glaciolacustrine glaciolacustrine sediments sediments drape a rugged surface rolling landscape landscapewith with sporadic sporadicbedrock bedrock rugged Archean ~ r c h e bedrock bedrock k surface producing producing aa gently rolling outcrops. The low relief observed within the southern basin is a reflection of not only outcrops. The low relief observed within the southern basin is a reflection of not onlythe theflat-lying flat-lying Proterozoic glaciolacustrine deposits that ~roterizoicsediments sedimentsthat that underlie underlie the the region, but the extremely extremely thick glaciolacustrine have have infilled infilled deep deep valleys valleys along the Whitefish Whitefish and Kaministikwia Kaministikwia rivers. Overburden Overburdenthicknesses thicknesses along along these these valleys valleysexceed exceed 60 60m m in in places. places. The The erosional erosionaland and depositional depositionalfeatures features preserved within the study area record a complex history history of of ice ice flow flow events events associated associated with the Wisconsinan glaciation ( T i m 44).1 The Theentire entirestudy study -daciation (Figure area area was was initially initially affected affected by southward flowing "northern" "northern" ice. Striae striaeassociated associatedwith with this thisevent event generally 220° Az. In In the the southern southernhalf half of of the the Sunshine Sunshinemap map area, area, there there is is generally range between 190° 190Âand 220' widespread evidence for an older ice flow event towards 160° Az. The age and significance of this widespread evidence for an older ice flow event 160" significance event event is is not not known. known. Pauses Pauses in in the the general general retreat retreat of of the the "northern" "northern" ice ice lobe lobe resulted resulted in in the the formation formationof oflarge, large, which traverses arcuate, arcuate, recessional recessional moraines moraines in northwestern Ontario. The TheBrule Brule Creek CreekMoraine, Moraine, Aldina A l d i and Marks Marks townships townships in the west-central portion of the Kakabeka Falls NTS map area, represents represents one one of these stilistand stillstand positions (Figure 4). This Thismoraine morainehas hasbeen beentraced tracedwestward westward into the Shebandowan by aa discontinuous discontinuous belt belt of Shebandowan and and Burchell Lake map areas where it is defined by morainic associated ice-contact ice-contact stratified stratifieddeposits. deposits. West of the stud study morainic ridges composed of till and associated with the Eagle Finlayson Moraine (Zoltai area, the Brule Creek Moraine has been correlated area, the Brule Creek Moraine has been correlated with the Eagle Finlayson Moraine (Zoltai 1965). 1965). A A large large ice-contact delta delta built off of this moraine along the south shore of Burchell Lake is graded to to an an upper upper level level of of glacial Lake Agassiz. The Theupper uppertopset topsetsurface surfaceof of the the delta deltaoccurs occursat at an an elevation as1 (1500-1550 feet aasl). s h To To the east of Marks Township, the Brule elevation of 457 to 472 m asl Creek Creek Moraine Moraine has has been been overridden overridden and obscured obscured by by aayounger younger glacial glacial advance advance (Figure (Figure 4). Isolated deposits of northern provenance and Isolated buried deposits denosits of of ice-contact ice-contact stratified stratified glaciofluvial elaciofluvial dewsits possibly associated and associated with with the the Brule Creek Moraine occur in south-central Conmee A d west-central Oliver Olivertownships. townships. - A second major moraine of northern affinity (Dog Lake Lake Moraine) Moraine) is is situated situated in in the the northeastern northeastern corner 4). Unlike comer of of the Sunshine Sunshine map map area area in the vicinity of Dog Lake (Figure 4). Unlike the Brule Creek Moraine, this moraine was constructed following a minor readvance of the "northern" ice lobe. Moraine, this moraine was following Glaciolacustrine readvance. In In the the vicinity vicinity Glaciolacustrine sediments sediments underlying till north of the moraine support aa readvance. of Dog Lake, the moraine is fronted by a lobate, flat-topped, flat-topped, glaciofluvial glaciofluvial plain plain believed believed to to be be deltaic deltaic in origin. The Theelevation elevationof ofthis thisplain plain(460 (460m masl) as]) defines definesthe the level level of of Glacial GlacialLake Lake Kaministikwia, a large large glacial lake which occupied the Kaministikwia basin. Distinctive Distinctivered red clays, clays, associated with this to, but not above, this this glacial lake can be found throughout the basin up to, elevation. �IA r— I' - - r- — C— Figure 3. Digital elevation model of the Shebandowan greenstone belt and surrounding region. ,1 c— r-— C —- — - — -- r - �f(i ij Figure4.4. Ice Ice flow flowpatterns, patterns, major major moraines moraines and and surface surface tills tills of of the the study study area. area. Onlapping Onlappingpattern pattern of ofarrows arrowsindicates indicates age age relationships relationships Figure of ice flow events. Light grey zone indicates area where older, northern till exposed on surface. Dark grey zone indicates of ice flow events. Light grey zone indicates area where older, northern till exposed on surface. Dark grey zone indicates area affected by Marquette readvance (southern area by Superior lobe; northern area by northern lobe). area affected by Marquette readvance (southern area by Superior lobe; northern area by northern lobe). �Kaministikwia was was topographically-supported topographically-supportedon on its its southern southernflanks flanksby by an anupland upland Glacial Lake Kaministikwia in the northwestern corner of the Kakabeka Falls NTS area area (Figure (Figure 3) 3) as as well as as by glacial glacial ice ice advancing out of the Superior basin and whose terminal position is defined by the Marks moraine TheMarks Marksand andDog DogLake Lake moraines moraines are are correlative correlative and and merge merge east east of of the the study study area area (Figure 4). The Striaeassociated associatedwith withthe theadvance advanceof of the the Superior Superiorlobe lobe along the McKenzie interlobate Moraine. Striae range from from 3400 340ÂAz in the northeast to 240 240° Az in the southwest attesting to the lobate nature of the Thisadvance advanceisiscorrelated correlatedwith withthe theMarquette Marquettestadial, stadial,aalate-glacial late-glacial surge surgeevent event that that Superior lobe. This resulted in much of the Superior basin being reoccupied by glacial ice about 9.9 ka With the the ka BP. BP. With corner of the Kakabeka Falls area, the Superior lobe advanced into a exception of the northeast comer glacial lake, referred to as "Glacial Lake OtConnortt Numerous sections sectionsalong along the the O'Connor" (Zoltai (Zoltai 1963). Numerous Whitefish River expose thick sequences of glaciolacustrine rhythmites beneath a fine-textured Superior lobe till. Shorelines Shorelinesof ofthis thisglacial glaciallake lakehave havenot notbeen beenidentified. identified. Superior (Patrician) provenance has been observed throughout the the entire study area. area. On Till of northern (Patrician) On less than than aa few metres metres Archean terrane, beyond the limits of the Superior lobe, the till is generally less thick and has a silty sand texture with low to to moderate moderate stone-content. stone-content. Till cover is significantly more extensive thicknesses of 5 extensive over over the east-central part of the Shebandowan Shebandowan NTS map area where thicknesses to 10 m m are are not not uncommon. uncommon. Unoxidized till generally has an olive-grey olive-grey to to buff-grey buff-greycolour. colour. The contains a high proportion of clasts clasts that are locally-derived. Faceted Faceted and andstriated striatedclasts clasts till often contains within the till indicate deposition by ice flowing towards towards the the south-southwest. south-southwest. Many exposures of this northern till contain remnant clasts Sibley Group metasediments. These Thesedistinctive, distinctive,reddishreddishclasts of Sibley coloured siltstones occur most commonly east of Thunder Bay on the Sibley Peninsula and on the Peninsula and to to aa Nipigon basin. basin. Sibley Sibley Group Group clasts clasts in in northern northern lesser extent, northeast of the study area in the Lake Nipigon till are likely derived from the Nipigon basin, 70 km to the northeast. The Thenon-magnetic non-magneticheavy heavy mineral concentrates concentrates of northern tills are rich in clinopyroxenes derived from Nipigon diabase within this same same area. area. Northern till is buried beneath variable thicknesses of glaciolacustrine deposits deposits and Superior Superior lobe till within the Whitefish-Kaministikwia Whitefish-Kaministikwia lowland. lowland. InInthis thisarea, area,the thetill tillisissignificantly significantlyfinerfinertextured owing owing its fineness fineness to the underlying shales shales and argillites argillites of the Rove and Gunflint formations. formations. Stony Stonytill, till,of ofpresumed presumednorthern northernprovenance, provenance,exposed exposedatatwater waterlevel levelalong alongWhitewood Whitewood Creek in east-central O'Connor Township, contains abundant striated and faceted boulders boulders indicating ice ice flow flow toward toward the the southwest. southwest. Superior Lobe till is easily recognized recognized by its fine-texture fine-texture and and high high proportion proportion of of Animikie Animikie Group Group metasedimentary clasts in the pebble fraction. Even Evenin inareas areasunderlain underlainby by Archean Archean terrane, terrane, as occur in the northeast corner comer of the Kakabeka Falls area, Superior lobe till contains only a small proportion of the underlying rock rock types types in in the the pebble pebble fraction. fraction. This has important implications for programs of mineral exploration utilizing till as a sample medium. medium. The The colour of the unweathered till ranges from dark grey, to brown to reddish-brown. Sections Sectionsof oftill, till,containing containinglayers layerswith with all all 33 reflect the the melting melting out out of of colours have been observed in Oliver and Gillies townships and probably reflect debris bands derived from different bedrock sources. Superior Superiorlobe lobetill till also alsovaries varies markedly markedly in in texture. In InOliver OliverTownship, Township,near nearthe thecommunity communityof ofMurillo, Murillo,Superior Superiorlobe lobetill tillisissilty siltyand andcharged charged with shales shales of the Gunflint Formation. The The till till in in this this region region is is fluted fluted and has been observed to reach thicknesses thicknesses of 7 to 8 m. Similarly, Similarly,to to the the south south in in Scoble Scoble and Gillies Gillies townships, Superior �Lobe till is silty and charged with clasts of Rove Formation shale and Logan diabase. diabase. Along Along the the Whitefish contains less less than than 5% 5% clasts. clasts. This Whitefish River valley, the till is silty to clayey and contains This is is primarily primarily due due to to the the thick thick deposits depositsof ofglaciolacustrine glaciolacustrinesilts siltsand andclays claysthat that were overridden overridden and and incorporated incorporated into the basal debris layers of the advancing Superior lobe. into the basal debris layers of the advancing Superior lobe. OVERVIEW OVERVIEWOF OFFIELDTRIP FIELDTRIPAGENDA AGENDA The landforms, landforms, deposits depositsand and features featureswe we will will be be visiting visitingtoday today will will provide provide an an overview overviewof of the the The important belt. An important elements elements of of the Quaternary Quaternary geology of the Shebandowan greenstone belt. An attempt attempt will willbe be made madeto toillustrate illustratehow howthe thevarious variousQuaternary Quaternarydeposits depositscan canbe beutilized utilizedfor forprograms programs of of mineral mineral exploration. Figure Figure55 shows showsthe the locations locations of of the the fieldtrip fieldtrip stops. The Thefieldtrip fieldtripwill willbegin begin in in the anderosional erosional thecentral centralpart part of ofthe thebelt beltwhere wherewe wewill willhave havean anopportunity opportunitytotoview viewdeposits depositsand features features associated associated with the advance and retreat of northern ice. Some Sometime timewill willbe be spent spent demonstrating demonstratingsampling samplingtechniques, techniques,discussing discussingthe thepros prosand andcons consof ofvarious varioussample samplemedia, media,and and finally, reviewing strategies for property-scale surficial geochemical surveys. We will proceed finally, reviewing strategies for property-scale We will proceed easterly easterlyinto intothe the centre centreof ofthe thenorthern, northern,Kaministikwia Kaministikwiabasin basinwhere wherewe wewill willhave havean anopportunity opportunitytoto view deposits of glacial Lake Kaministikwia and discuss the glacial lake history of this view deposits of glacial Lake Kaministikwia and discuss the glacial lake history of thisand andother other proglacial proglacial water water bodies bodies within within the the region. region. From Fromhere, here,we wewill willproceed proceedsouth southand andwest westwhere wherewe we will have an opportunity to view deposits and landforms associated with the advancing Superior will have an opportunity to view deposits and landforms associated with the advancing Superior lobe. lobe. Stops Stopswill willinclude: include:1)1)aasection sectioncut cutinto intoice-marginal, ice-marginal,subaquatic subaquaticdebris debrisflows flowsdeposited depositednear near the the outer outer limit limitof of the the Superior Superiorlobe; lobe; 2) 2) aa Superior Superiorlobe lobe ice-contact ice-contact delta delta which which has has been overridden overridden by by the the advancing advancingSuperior Superiorlobe; lobe;3) 3) an anexposure exposureof ofSuperior Superiorlobe lobetill tilloverlying overlyingnorthern northerntill; till;4) 4)aa panoramic panoramicview viewof ofthe thelowland lowlandinto intowhich whichthe theSuperior Superiorlobe lobeadvanced; advanced;and and5)5 )aastop stoptotoview viewthe the morphology morphologyof of the the Marks Marks Moraine. Moraine. At Atseveral severalofofthese thesestops, stops,we wewill willhave havean anopportunity opportunityto to discuss discussthe thesuitability suitabilityof ofSuperior Superiordrift driftas asaasample samplemedium mediumfor forprograms programsofofmineral mineralexploration. exploration. The The trip trip will will conclude concludeby by travelling travellingsouthward southwardinto intothe theWhitefish WhitefishRiver Riverlowland lowlandwhere wherewe wewill willlook look at ataa couple coupleof ofexposures exposuresthat thatillustrate illustratethe thedrastic drasticfacies facieschanges changesthat thatoccur occurininboth boththe theSuperior Superiorand and northern northernlobe lobetills tillsas asyou youproceed proceedinto intothe thelowland. lowland.The Thesignificance significanceofofglaciolacustrine glaciolacustrinedeposits deposits exposed exposedatateach eachof ofthe thesites siteswill willbe bediscussed discussedasaswell. well. The proceed westward The bus bus will will depart depart the the Lakehead Lakehead University Universitycampus campus and andproceed westwardalong alongHighway Highway 102 102 towards Kaministikwia where it will meet Highway 11/17 at Sistonens Corners. Turn right onto towards Kaministikwia where it will meet Corners. Turn right onto Highway Highway 11/17 11/17and andproceed proceed west west 16.0 16.0k,ns. kms. Turn Turnleft left on on aasmall small sideroad sideroadsituated situatedapproximately approximately 150 m before before (east (eastof) of)aa sign sign on on the the north northside side of of the the highway highway marking marking "Bylund "BylundPit Pit Road". Road". 150to to 200 200 m Follow Follow the the main mainroute route on on this this sideroad sideroadfor approximately approximately 300 to 400 m. Park Park vehicle vehicle at aa large large area areaofofstripped strippedoutcrop. outcrop.This Thisisisthe theBylundAu Bylund Auoccurrence. occurrence. �Figure 5. Location map of fieldtrip stops. S- C S r r— C - S——-- 5-- - - �Stop 1: Bylund Trenches 1: Property-Scale Sampling Programs: Programs: Bylund Regional and property-scale property-scale surficial sampling sampling programs programs have been been widely used in in the the mineral mineral Unfortunately, aa significant significant proportion of of the surveys exploration sector for many years. Unfortunately, surveys Clearly, many many of of the failures failures undertaken within glaciated terrain have met with mixed results. Clearly, some effort been put forth forth in in understanding understanding the the nature nature of of the the could have been avoided had some development of of sampling sampling strategies strategiesand and Quaternary deposits present within a given area prior to the development At this thisstop, stop,discussion discussionwill will focus focuson on the the various various sampling sampling implementation of sampling programs. At media that are available to the explorationist explorationist for for aa surficial surficial geochemical geochemical perspective, perspective, how how they they are are collected and at what density and finally, the analytical techniques employed for their analysis. Trenches exposed adjacent to the Bylund Au occurrence occurrence will be used to demonstrate demonstrate the the various various media and sampling techniques. The Bylund Au property is located at the west end of the Dawson Road Lots and is is jointly operated by Freewest Resources Resources & & Co. Co. Inc. Inc. and and Greater Greater Lenora LenoraResources ResourcesCorp. Corp. Mineralization is contained within a 125 125 m wide, east-trending east-trending zone zone of of carbonate-altered, carbonate-altered, mafic mafic to to ultramafic ultramafic metavolcanic rocks transected by a stockwork stockwork of northeast-trending northeast-trending quartz-carbonate quartz-carbonate veins veins (Schneiders et al. 1998). 1998). Finely Finelydisseminated disseminatedarsenopyrite arsenopyriteis is commonly commonly associated associated with with Theauriferous auriferousdeformation deformationzone zoneoccurs occursatator ornear near the theunconformable unconformablecontact contact mineralization. The between Greenwater assemblage metavolcanics metavolcanics to the south south and and Shebandowan Shebandowanassemblage assemblage metasedimentary rocks to Channel sampling sampling over over the the main main Bylund occurrence occurrence has to the north. north. Channel 14 m. Outcrops Outcropsexposed exposedin intrenches trenchessituated situatedboth both east eastand and returned values of up to 4.1 g/t Au over 14 showing have have returned returned values values typically typically in in the the range range of of 11 to to 22 g/t g/t Au Au over over several several west of the main showing metres. Notable Notableintersections intersectionsinclude includeaa 0.54 0.54m m section, section,just west west of of the the main main showing, showing, assaying assaying 123 123 g/t Au (C. Bishop, Freewest Resources, personal communication, communication, 1998). 1998). The trenches west of the main Bylund occurrence occurrence were opened to investigate investigate Au and As anomalies in soil. They They expose expose aa variety of material types. Two Two facies facies of till have been recognized; buff-grey, stone-poor, silty sand till till of of semi-local semi-local composition composition and and aa stony, stony, silty siltysand sandtill tillof of a light, buff-grey, local composition. The Thelower, lower,local localtill till contains containsabundant abundantclasts clastsof of mineralized, mineralized, iron-carbonate iron-carbonate altered sericite schist. ItIt isis restricted restricted to to the the up-ice up-ice side side of of aa prominent prominent bedrock bedrock ridge ridge where erosive erosive forces beneath the advancing ice were greatest. Compressive Compressive subglacial subglacial forces forces resulted in the the till till section. This lower, local till being sheared up into the upper parts of the This till till contains contains anomalous concentrations concentrations of gold gold grains grains and appears appears to reflect reflect local local mineralization mineralization along along aa major major break. The Thebuff-grey buff-grey till till reflects reflects semi-local semi-local bedrock bedrock sources sources and and was was probably derived from the melting out of debris bands in the basal portions of the glacier. Red Red glaciolacustrine glaciolacustrine clays clays overlie overlie the till in low-lying ground to the north. Drift Drift thickness thickness diminishes diminishes to to less less than than aa metre metre at at the the crest crest of the hill consists of deeply deeply weathered weathered till. till. Soil samples collected for mineral exploration exploration bill and consists from this area returned anomalous Au and As values. The The bedrock bedrock surface surface drops drops off off abruptly abruptly to the south and is overlain by deposits of different character. Stratified Stratified deposits depositsare are intimately intimately associated associated with the till and were probably deposited in a leeside cavity beneath beneath the the glacier. glacier. These deposits deposits have been modified by glaciolacustrine processes. A A thin thin layer layer of of red clay overlies overlies the till package gravel. This and is capped by nearshore deposits of sand and gravel. This example example clearly clearly demonstrates the variabilty that that can can occur occurover oversuch suchaashort shortdistance. distance. Clearly, Clearly, an understanding of complexity and variabilty the origin of samples samples collected is required required for for the the successful successful interpretation interpretation of of geochemical geochemicaldatasets. datasets. �Sample Media Four distinct media types are commonly sampled for programs of mineral exploration utilizing These include: include: 1) 1) vegetation; 3) b-horizon b-horizon soil; and 4) surficial geochemistry. These vegetation; 2) 4) c-horizon c-horizon humus; 3) 2) humus; till. till. Vegetation Vegetation consists of the leaves, needles, twigs, twigs, cones cones or or bark bark of ofplants. plants. The premise behind behind sampling plant tissue for mineral exploration exploration is that the root systems of the plants will absorb metals contained in groundwater, overburden and bedrock at a given sample site. The The geochemical geochemical response of the plant tissue will therefore provide information on the chemistry of the the substrate on which the plant is growing. Vegetation Vegetationsampling samplingisisbest best utilized utilized in interrains terrainswhere where overburden overburdencover cover is thin (less than 3-4 m) and locally locally derived derived and and where where root root systems systems are are able able to to penetrate penetrate fractures fractures and joints Inareas areasof of thick, thick, exotic exoticoverburden, overburden,vegetation vegetation sampling samplingmay may fail fail to to evaluate evaluate joints in bedrock. In local mineral potential. For Foraaregional regionalor orproperty-scale property-scale sampling sampling program, program, itit is is important important to to collect collect samples of the same organ from plants plants of of the the same same species, species, size size and and outer outer appearance. appearance. Humus is a black to brownish-black, organic-rich material derived from the decomposition of forest lifter. litter. It consists of unidentifiable remains of leaves, roots, needles, bark, etc. that that have have been been Humus sampling sampling broken down into a fine-grained, amorphous material by by organisms and and bacteria. bacteria. Humus is, in many respects, similar to that of vegetation sampling. Being Being aa first first derivative derivative of of vegetation, vegetation, geochemical results geochemical The same same basic basic rules apply to humus resultsshould shouldmimick mimick those of vegetation. The sampling as well. Drastic changes changes in vegetation type could different well. Drastic could produce humus with different Bothhumus humusand andvegetation vegetationare aresusceptible susceptibleto tocontamination contaminationfrom fromanthropogenic anthropogenic compositions. Both 11117 between between the the Shebandowan Shebandowan Nisources of metal. Humus Humussamples samplescollected collectedalong alongHighway Highway 11/17 Cu-PGE mine and the hamlet of Sunshine are strongly contaminated. Hauling Hauling of of Ni-Cu concentrate concentrate in aa corridor corridor aa few few hundered hundered metres metres on on either eitherside sideof of the the highway highway within within along the highway resulted in values are enriched in humus. The Thec-horizon c-horizontill tilldata datawithin withinthis thiscorridor corridorhighlights highlights which metal values the true geochemical geochemical signature signature for for this this area. area. B-horizon soil soil is usually usually the the dark, dark, orange-brown orange-brown material material encountered encounteredat at aa depth depth of of 5-10 5-10 cm cmin in immediately below the humus layer. Often Oftenthere therewill willbe be aathin thinhorizon horizon of ofgreyishgreyishthe soil profile immediately Thislayer layer(Ae) (Ae)has has been been coloured mineral matter (Ae horizon) between the humus and B-horizon. This leached of most metals by the downward percolation of groundwaters rich in humic and fulvic downward percolation of groundwaters rich in humic and fulvicacids acids derived from the decomposition of the overlying organic organic debris. debris. The B-horizon is the the zone of of accumulation accumulation of of clays clays and and iron iron and and manganese manganese oxides oxidesderived derivedfrom fromthe theweathering weatheringof ofunstable unstable mineral grains. They Theyare are excellent excellentscavengers scavengers of metals. B-horizon B-horizonsoils soilscan can be be developed developed on on parent materials of local to non-local composition. For For the successful successful implementation of b-horizon soil sampling surveys, surveys, it is critical that the the parent parent materials materials be be composed composed of of till, till, that that they they have have characteristics and that they be of a local provenance. provenance. ItIt is similar grain size characteristics is also also important important that the till cover not exceed 2 to 3 m in thickness. C-horizon till is the relatively unaltered sediment that underlies the B-horizon. In In well-drained well-drained upland environments, oxidation can extend down several meters meters into into the theprofile. profile. Metals contained within sulphide sulphide minerals in this zone zone of of weathering weathering are generally liberated by oxidation and �hydromorphically dispersed downwards The upper part of the c-horizon will often often be downwards in in the the profile. profile. The enriched in metals compared surveys are compared to to the the b-horizon. b-horizon. C-horizon till sampling surveys are best best undertaken undertaken in areas where till thicknesses are less than The till till will will often often exhibit exhibit aa local local than aa few metres. metres. The signature under these In areas areas where where till cover is thicker, more more expensive expensive sampling sampling these conditions. In methods, such as reverse circulation drilling, are required to obtain till samples from the bedrockloverburdeninterface. interface. bedrock/overburden Analytical Methods explorationutilizing utilizing drift drift prospecting prospecting Analytical methods employed for programs of mineral exploration techniques and surficial geochemistry geochemistry vary depending upon the commodity commodity sought sought and and the sample sample media collected. collected. For the Shebandowan Shebandowan regional sampling sampling survey, 2 samples samples of of screened screened c-horizon c-horizon mm) were collected for analysis. A A 10 10kg kg sample sample was was collected collected for for heavy mineral till (-5 mm) concentration and subsequent subsequent gold grain, kimberlite indicator indicator mineral mineral (KIM) (KIM) and and metamorphic/magmatic massive sulphide indicator mineral Heavy mineral (MMSIM) determinations. determinations. Heavy minerals were separated from the -2 mm fraction of these these samples samples by wet gravity gravity tabling, producing producing a "table concentrate", then further concentrated to >3.2 B3.2 S.G. using density-dependent density-dependent settling settling in in methylene iodide. Magnetic Magneticminerals minerals were were removed removed from from the the methylene iodide heavy mineral concentrate (HMC) using an automagnet. automagnet. At the tabling stage, a preliminary count of gold grains, including size size and shape shape determinations determinations Thegold goldgrain graincontent contentof ofthe thetable tableconcentrates concentrateswas was further further refined refined using using aa was undertaken. The secondary panning samples containing greater panning procedure procedure to to obtain obtain more more exact exact grain grain counts. counts. Only samples 10 gold grains at the tabling stage were panned. The Thesize sizeand and shape shape of of the the panned panned gold gold grains grains than 10 table concentrate. concentrate. were recorded before they were returned to the table A second 2 to 3 kg sample of screened screened c-horizon till was was also also collected collected for for -63 -63 micron micron fraction fraction geochemical determinations. A A 30 30gg split split of of the the -63 -63 micron micron (silt (silt and and clay) clay) size size fraction fraction of this till (1NAA). The neutron activation activation matrix was sent for instrumental neutron activation analysis (INAA). dataset provides excellent information information on on the the Au, As, As, Sb Sb and and REE REE content of the samples. A second 20 to 25 g split was sent for Pt-Pd-Au determinations by by Pb Pb fire fire assay1ICP-MS assay/ICP-MS finish. finish. A third split was sent for geochemical geochemical determinations determinations by ICP-OES and ICP-MS following following aa standard standard aqua regia digestion. These Thesemethods methods produce produce high high quality quality data data on on the the base metal content of the samples. Similar Similaranalytical analyticalmethods methodsshould shouldbe be employed employedfor for vegetation, vegetation, humus humus and and b-horizon b-horizon sampling sampling programs programs as as well. well. For Forhumus, humus,the the—177 -1 77 im pmfraction fractionisisanalyzed analyzedrather ratherthan thanthe the—63 -63 .tm pm fraction. Humus Humussamples samples are are briquetted briquetted prior to neutron activation analysis. Vegetation Vegetation samples are either macerated and briquetted or ashed prior to analysis. analysis. Sampling Strategies The density at which samples samples are collected collected is dependent dependent upon the the style style of of mineralization mineralization sought. sought. Dispersal trains originating from lode gold type mineralization are significantly smaller than those originating from mineralization are significantly smaller than those originating from volcanogenic massive sulphide-type mineralization. mineralization. The The surface surface area area of mineralized rock available for erosion is probably the the most most important factor that that effects effects the the scale scale of of the dispersal train produced. The Theorientation orientationof ofthe themineralized mineralizedstructure structureor or horizon horizon with with respect respect to to �regional ice ice flow flow is is parallel parallel to to regional ice flow also effects the geometry of the the dispersal trains. trains. IfIf regional the strike of mineralization, the resulting dispersal train will be long, narrow and difficult to identify. IfIf regional regional ice ice flow flowisis perpendicular perpendicular to to the the strike strikeof of mineralization, mineralization, then then the the resulting resulting Theposition positionof ofmineralization mineralizationwith withrespect respectto toregional regionalice iceflow flowisisalso also dispersal train will be wider. The important. For For example, example, ifif the the mineralized mineralized horizon is shear-hosted and situated within a deep ravine perpendicular to ice flow, the advancing glacier may not not actively actively erode erode the the mineralized mineralized rock rock and therefore not produce a dispersal plume from mineralization. Dispersal trains originating from lode gold deposits of northern Ontario are typically less than than 200 to 300 m in length. Sampling Samplingprograms programs aimed aimed at at locating locating these types of deposits should Asample samplespacing spacingof of200 200m mand and therefore be designed to be able to identify a train of this length. A 100 m, staggered on 100 100 m lines, is recommended to recognize a potential target of this preferable 100 Onceaadispersal dispersaltrain trainisisidentified, identified,the thedensity densityatatwhich whichsamples samplesare arecollected collectedshould shouldbe be type. Once increased to to 25 25 m or 50 m spacing to more clearly define the source of the Dispersal increased the gold gold anomaly. anomaly. Dispersal arising from base metal targets can reach several kilometres in length. AAsampling samplingprogram program trains arising aimed at identifying this type of dispersal train could involve collecting samples initially at 500 m spacing then increasing the density to to 100 m in anomalous areas to to further refine refine exploration exploration targets. targets. Bylund Case Case Study High density, property-scale property-scale soil soil sampling sampling was was undertaken undertaken over over and and adjacent adjacentto to the theBylund Bylund Au Au occurrence at the west end of Dawson Road Lots. Fifty-three Fifty-threeb-horizon b-horizon soil soilsamples sampleswere were collected collected at 100 100 m centres centres on 6 grid lines spaced 100 100 m apart. The Theproperty propertyisischaracterized characterizedas asaa bedrockbedrockaccumulations of drift drift (till and stratified deposits) deposits) in low-lying areas. dominated upland with local accumulations Most soils soils are developed in till, however, a small small proportion have stratified sands sands and pebbly sands as their parent material. These These samples sampleswere were included included in in the geochemical dataset since most of them were derived from the washing and sorting of of the the underlying underlyingtill. till. Soil samples were not collected from a poorly drained drained wetland wetland that that occurs occurs along along the the west-central west-centraledge edgeof ofthe the property. property. The sample grid is oriented at 150° 150' Az and extends extends approximately 500 m south of the mineralized zone into unaltered Keewatin mafic metavolcanics. The Thesilt siltand andclay clayfraction fractionof ofthe thesoil soilsamples samples were extracted extracted and and geochemically geochemically analyzed analyzed by instrumental instrumental neutron neutron activation activation analysis analysisand and ICPICPfollowing a standard aqua OES following aqua regia digestion. digestion. Contoured plots of Au and As content derived by neutron activation analysis are presented in Figures 6. Other Otherelements elementsdid did not not show show aa close close spatial spatial association with mineralization. The The patterns depicted by Au and As clearly delineate the position of mineralization with little or no evidence for down-ice down-icedispersal dispersalbeyond beyond aa few few hundred metres. Similar Similarscales scalesof of glacial glacial dispersal dispersal have been previously documented at the Matachewan Consolidated Mine in northeastern Ontario (Bajc 1997) as well as at numerous other gold properties within the province. Gold Gold values values quickly quickly 100 to 200 metres down-ice (south-southwest) decline to below detection limit (<2 ppb) within 100 from the Bylund occurrence. Arsenic Arsenic values values display display aa slightly slightly more more diffuse diffuse pattern. L1W west of of the the documented documented Au Au W and L2W, immediately west Elevated Au and As values along L1 zones suggests a possible possible westerly westerly extension extension of ofmineralization. mineralization. A sample on L1 L1W that returned W that returned aa �1280 ppb and an As value of of 88.4 88.4 ppm was was collected collected from from the the fringes fringesof of aa poorly poorly gold value of 1280 This anomaly anomaly may have been drained wetland and contained significant amounts of organic matter. matter. This A produced by hydromorphic dispersion from from mineralized mineralized till till and and rock rock on on the the upland upland to to the the north. north. A anomalous Au and As response response was was obtained, obtained, however, however, from from an an upland upland soil soil 100 100metres metresto to similar anomalous the east. These These22anomalies anomaliesmay may suggest suggest aa second second auriferous auriferous structure structure is is present to the south; south; this warrants further investigation. A A strong strong Au Au and and As As anomaly anomaly along along the the central portions of lines lines 2E and 3E suggest suggestthe the potential potential for for another, another, as as yet yet undiscovered, undiscovered, zone zone of of mineralization. mineralization. recommendations can be drawn drawn from from the the Bylund Bylund soil soil sampling sampling Several conclusions and recommendations orientation survey. orientation survey. 1. Soil geochemistry is a viable exploration tool for shear-hosted 1. shear-hosted gold gold in in the the eastern eastern portion of the Shebandowan Shebandowan greenstone belt. The Thetechnique techniqueisisbest best suited suitedto to upland upland properties with thin till cover and abundant abundant outcrop. outcrop. 2. AAsample samplespacing spacingofof100 100mmstaggered staggeredon onadjacent adjacentlines linesappears appearsto to be be sufficient sufficient for for the the delineation delineation of potential potential mineralized mineralized zones. zones. 3. Gold and arsenic appear to be the elements elements best suited suited for for target delineation delineation at at the the Bylund occurrence. Neutron fraction (-63pm) (-63tm) of Neutron activation activation analysis of the silt and clay fraction of soil provides excellent contrast between background and anomalies. anomalies. 4. 4. There is very little little evidence evidence in in support support of of down-ice down-ice dispersal dispersal of of gold gold greater greater than than 100 100to to 200 m from mineralization. Ultra-high Ultra-highdensity densitysampling sampling(i.e. (i.e.20 20to to 25 25 m m spacing) spacing)would would be required to more more clearly clearly define define glacial glacial dispersal dispersal patterns. patterns. Turn vehicles vehicles around around and proceed proceed back out to the highway. highway. Turn Turn right, right, drive 3.1 km km east along Highway 11/17 and stop at aa rockcut rockcut along alongthe the sides sidesof of the the highway. highway. �A *C) • <2 • <2 Auu mineralization mineralization 5' •<2 • <2 Au (ppb) • <2 • <2 .3 • <2 .3 100 m .3 • • <2 .3 13 • <2 B .1.8 / .2.9 100 m •2O .19 4.6 S /.12 Figure Figure6. 6.Geochemical Geochemicalresponse responseofofb-horizon b-horizonsoils soilsover overand andadjacent adjacentto to the the Bylund Au contoured Au data: B: contoured occurrence, Dawson Road Lots. A: occurrence, Lots. A: data: B: contoured As As data. data. �Stop 2: Crossing Crossing Striation Striation Site Site At this stop, we will have an opportunity to look at an outcrop outcrop of of Shebandowan Shebandowanassemblage assemblage The striation striation metasediments that are well striated and flanked by red, glaciolacustrine clay clay and and till. till. The displays a consistent consistent pattern pattern of of flow flow towards towards the the south south record for the western half of the belt displays There is, is, however, however, evidence evidence for an older becoming progressively more westerly westerly towards towards the the west. west. There ice flow event towards the the southeast in the the southwestern comer corner of of the the Sunshine Sunshine map map area. area. The significance of this event is There are are several several examples examples of of southeasterly-oriented southeasterly-oriented (160° (160' is not not known. known. There Az) striae striae crossed by south-southwesterly south-southwesterly (200-210° (200-2 10' Az) striae striae on on the the outcrop outcrop surface surface (Figure (Figure 7). 7). This older older event event is is In most cases, the older striae are preserved on faceted, protected protected surfaces. surfaces. This krn since it has been observed observed at many sites sites spanning spanning aa 30 30 km recognized as regionally significant since The till till overlying overlying the bedrock surface is distance and is not apparently related to topography. The deposited by ice flowing flowing towards towards the the south-southwest south-southwest (latest (latest ice ice fow fow direction). direction). believed to be deposited on the the southeast southeast end end of of the the roadcut roadcut have have striated striated upper upper surfaces surfaces Faceted boulders within the till on indicating flow towards the south-southwest. This Thisinformation informationisis critical critical for for the the successful successful followfollowanomalies obtained obtained from from this this area. area. up of till anomalies Figure Figure7. 7. Crossing Crossingglacial glacialstriae striaewere werefrequently frequentlyencountered encounteredin in the the Dawson Dawson Road Lots area. In In this example, example, an an older older set set of of striae striaeoriented oriented at at 160° 160' Az Az are are crossed crossed by by aa main main set set oriented oriented at 210° Az. 210' Az. Proceed 11/17 to to Sunshine Sunshine Cross Cross Rd. Rd. Turn left left (north) onto onto sideroad sideroad and Proceed 9.8 9.8km krn east on Highway 11/17 stop by the railway railway tracks. tracks. �Stop 3: Contamination and and Implications for Mineral Exploration 3: Humus Contamination At this stop, we will have an opportunity to discuss humus sampling and potential problems that may arise with contamination. This This site site was chosen for the stop because it is located adjacent to to aa railway siding that was used by 1NCO INCO for for loading loading Ni-Cu Ni-Cu concentrate from the Shebandowan mine onto railway cars. During Duringthe the early early days days of of production production at at the the Shebandowan Shebandowanmine mine site, site, Ni-Cu Ni-Cu concentrate was hauled by dump truck from the mill to the railroad siding at Sunshine, a distance of Thedispersal dispersalof offine fineparticulate particulate suiphides sulphidesby by wind wind from from these these trucks trucks approximately 50 km. The resulted in a strong Ni-Cu geochemical anomaly in humus following the Highway 1117 corridor Highway 111/17 corridor and extending several hundred metres in from the highway. The The Ni-Cu Ni-Cu geochemical geochemical datasets datasetsfor for Sunshine and Kakabeka Kakabeka Falls Falls map areas areas clearly illustrate illustrate this contamination (Figure 8). The The the Sunshine geochemical datasets c-horizon till are are drastically drastically different different from from those those portrayed portrayed by by the the humus humus datasets for c-horizon and reflect the primary geochemical geochemical signature signature associated associated with with local local variations variationsin in bedrock bedrock source source and 7). 7). It would appear appear that there is no signal of contamination within c-horizon rocks (Figures (Figures 66 and rocks till. till. All humus sampling programs should consider the potential for problems associated with contamination. Contamination Contaminationcould couldarise arisefrom fromaavariety varietyof ofsources sourcesincluding including road road dust dust from from local local logging operations, wind-blown tailings dust and airborne fallout from smelters. In In the the Sudbury Sudbury area, there is a strong geochemical signature in humus associated with the smelting operations. The The element associations associations closley mimmick those of the ore mined in Sudbury. Fine Finecolloidal colloidalsulphide sulphide element particles particles are dispersed by wind and quickly oxidize in the surficial environment where they are available for adsorption by humic and falvic fulvic acids acids present present within withinthe thehumus. humus. Should a potential source of contamination be identified within a given area, it is recommended that the explorationist avoid sampling humus and that c-horizon till be considered considered as the preferred sampling medium for surficial geochemical geochemical surveys. surveys. Proceed back back out out to to Highway 11/17. Turn Turnleft left (east) (east)and anddrive drive 3.0 3.0km krn to the intersection intersection of Proceed Highways 11/17 and and 102 102 (Sistonens (Sistonens Corners). Corners).Turn Turnleft leftonto ontoHighway Highway102 102and andproceed proceed7.0 7.0kms krns before turning left into a sand sand and and gravel gravel pit pit owned owned and andoperated operatedby byTowland-Hewitson Towland-Hewitson Construction Ltd. Construction Ltd. �Figure 8. Comparison of humus and c-horizon till geochemical datasets for nickel, Note the strong anthropogenic signature in humus along the Highway 11/17 corridor. This anomaly is attributed to the haulage of Ni-Cu concentrate from the Shebandowan mine to a railway siding near the village of Sunshine. �Stop 4: Glacial Lakes of the Shebandowan Shebandowan Area Portions of of the the Shebandowan Shebandowan study study area were inundated by glacial lakes. These Theseinclude: include:1) 1) Portions glacial Lake Agassiz Agassiz in in the the extreme extreme western western part part of of the the study study area; area; 2) glacial glacial Lake Kaministikwia Kaministikwia glacial and high high level level Superior Superiorbasin basin lakes lakes within the Sunshine Sunshine map area; area; and 3) glacial lakes O'Connor and within Thedeposits depositsof ofthese theseglacial glaciallakes lakes are are considered considered aa Kakabeka Falls map area (Figure 9). The within the Kakabeka hinderance to to programs programs of ofmineral mineralexploration explorationutilizing utilizingsurficial surficialgeochemistry geochemistryininthat thatthey theyconceal conceal hinderance and prevent access to deposits of till till and the the underlying underlying bedrock. bedrock. The composition of glaciolacustrine deposits deposits does does not not closely closely reflect reflect the the composition compositionof ofthe theunderlying underlyingbedrock bedrockand and glaciolacustrine should should therefore not be sampled for mineral exploration purposes. Expensive Expensiveoverburden overburdendrilling drilling techniques must must be be utilized utilized to to sample sample the the glacial glacial tills tills that that underlie underlie these these deposits. deposits. techniques Glacial Glacial Lake Lake Agassiz Agassiz was was the the largest largestof ofseveral severalwater waterbodies bodieswhich whichbordered borderedthe thesouthern southern margin margin of of the the Laurentide Laurentide Ice Sheet Sheet during Late Wisconsinan glaciation. ItItinundated inundatedan anarea areaof of approximately11million million square squarekilometres, kilometres,although althoughatatno noparticular particulartime timedid didititoccupy occupythis thisentire entire approximately area. The Thelake lakeformed formedapproximately approximately12.0 12.0ka kaBP BPwhen whenice iceof ofthe theDes DesMoines MoinesLobe Loberetreated retreatednorth north area. of the the continental continental drainage drainage divide divide in in eastern eastern North Dakota Dakota and northwestern northwestern Minnesota ponding of water water within within the the Red Red River River valley. valley. Progressive Progressiveexpansion expansionofofthe thelake lakeinto intoManitoba, Manitoba,Ontario Ontarioand and parts of of Saskatchewan Saskatchewan occurred occurred with with further further retreat of the ice margin. Glacial GlacialLake LakeAgassiz Agassiz parts extended into into northwestern northwestern Ontario, Ontario, fronting fronting the the retreating retreating ice margin in low-lying areas. Deposits Deposits extended of glacial glacial Lake Lake Agassiz Agassiz occur occur in in the the southwestern southwesterncorner cornerof ofthe theBurchell BurchellLake Lakearea areaalong alongthe the of Obadinaw Obadinaw River River valley. The Thedeposits depositsare aremainly mainlycoarse-textured coarse-texturedwithin withinthis thisregion, region,however, however, varved clays clays have been reported from the banks of Tilly Creek. An Anice-contact ice-contactdelta deltabuilt built off off of ofthe the Brule Creek Creek Moraine Moraine south southof ofBurchell BurchellLake Lakegrades gradesto to an anupper upper level levelof ofLake LakeAgassiz Agassiz(Herman (Herman Brule level) at at 457 457 to 472 m m asl. asl. All Allareas areassouth southofofthis thismoraine moraineand andbelow belowthis thiselevation elevationwould wouldhave have level) been been inundated inundatedby by Lake LakeAgassiz. Agassiz. Glacial Glacial Lake Lake Kaministikwia Kaministikwiaoccupied occupiedthe thevalleys valleysof ofthe theOskondaga, Oskondaga,Matawin, Matawin,Shebandowan Shebandowan and Kaministikwia Kaministikwiarivers riverswithin within the the Sunshine SunshineNTS NTS map maparea. area. The Thelake lakewas wasbordered borderedon onits its and northeastern northeasternand andsoutheastern southeasternflanks flanksby byglacial glacialice iceof ofthe thenorthern northernand andSuperior Superiorlobes, lobes,respectively. respectively. High High ground ground bordered bordered the the lake lake to to the the north, north, west west and and southwest. southwest. The TheDog DogLake Lakeand andMarks Marks moraines morainesmark mark the thepositions positionsofofthe thenorthern northernand andSuperior Superiorlobes, lobes,respectively respectivelywhile whileLake Lake Kaministikwia Anice-contact ice-contactdelta deltaconstructed constructedoff offofofthe theDog DogLake LakeMoraine Morainejust just Kaministikwiawas was in in existence. existence. An south of Dog Lake and whose upper surface occurs at 460 m as! defines the glacial Lake south of Dog Lake and whose upper surface occurs at 460 m as1 defines the glacial Lake Kaministikwia Kaministikwiawater water plane. plane. The Thelake lakeformed formedwithin withinthe thestudy studyarea areaapproximately approximately10.0 10.0ka kaBP BPwhen when the northern and Superior lobes readvanced into the study area during a late-glacial surge event the northern and Superior lobes readvanced into the study area during a late-glacial surge event (Marquette (Marquetteadvance). advance). The Theextent extenttotowhich whichnorthern northernand andSuperior Superiorice iceretreated retreatedprior priortotothis thisevent eventisis not not known. known. Meltwaters Meltwatersinitially initiallydrained drainedfreely freelysouthward southwardoff offofofthe theretreating retreatingnorthern northernice icemargin margin depositing depositingthick thicksequences sequencesof ofglaciofluvial glaciofluvialsands sandsand andgravels gravelswithin withinthe thevalleys valleysofofthe the Kaministikwia Kaministikwiaand and Oskondaga Oskondagarivers. rivers. Progressive Progressiveincision incisionofofthe thefluvial fluvialdeposits depositsoccurred occurredasasbase base levels levelsdropped dropped within within the the lower lowerreaches reaches of of the the valleys. valleys. Thick Thicksections sectionsofofglaciofluvial glaciofluvialsand sandand and gravel gravelare areclearly clearly visible visible from from Highway Highway 102 102within within the the Kaministikwia Kaministikwia river valley. These Thesedeposits deposits are are terraced terraced and and draped draped by by distinctive, distinctive,red red clays clays associated associated with with glacial glacial Lake Kaministikwia. The The red red clays clayswhich whichcan canreach reachthicknesses thicknessesof ofseveral severaltens tensofofmetres, metres,are aretypically typicallyfaintly faintlylaminated laminatednear near the the base base and and become become progressively progressively more more massive massive upwards. upwards. The Thered redpigmentation pigmentationofofthe theclay clayisis �showing the locations of the major moraines and glacial lake basins. Figure 9. Digital elevation model of the Thunder Bay area �derived from Sibley Group metasedimentary source source rocks rocks eroded eroded by bythe the Superior SuperiorLobe. Lobe. Glacial Lake Kaministikwia probably probably lasted no no more more than than aa few few hundred hundred years. years. The lake overflowed westward into the Glacial Lake Agassiz basin via a narrow lowland lowland through through Shebandowan ShebandowanLake. Lake. Red clays within the eastern Lake Agassiz basin attest to this influx influx of of sediment sediment from from Lake Lake GlacialLake LakeAgassiz Agassizmust musthave havefallen fallenfrom fromaa Herman Herman to to aa lower lower level level prior prior to to the the Kaministikwia. Glacial development Kaministikwia. development of Lake Kaministikwia. occupied the the valleys valleys of the Whitefish Whitefish and Kaministikwia Kaministikwia rivers within Glacial Lake 0'Connor O'Connor occupied the Kakabeka Falls map area. The Thelake lakefronted frontedthe the advancing advancingSuperior Superiorlobe lobe during during the the Marquette Marquette the Whitefish Lake Lake basin. basin. Shorelines advance and probably drained westward through the Shorelines associated associated with this glacial lake have not been identified. Fine Finetextured textured glaciolacustrine glaciolacustrinedeposits depositshave have 0'Connor occur both however been observed beneath till up to 350 350 m asl. Deposits Deposits of of glacial glacial Lake O'Connor above and below till of the Superior lobe. This Thissequence sequenceisistypical typical of of an an ice ice advance-retreat advance-retreat cycle cycle within a glacial lake basin. Thick Thicksequences sequencesof ofsilty siltyto to clayey clayey grey grey rhythmites, in places exceeding 30 m in thickness, occur beneath fine-textured Superior lobe till within the Whitefish River lowland. Excellent Excellentexposures exposuresof ofthese thesedeposits depositsoccur occurin inlarge largesections sectionsalong along the the Whitefish Whitefish River River valley and its tributaries. Grey, Grey, rhythmically rhythmically laminated laminated clays clays associated with Lake O'Connor overlie Superior lobe till. These Thesedeposits depositshave havebeen been observed observedto to exceed exceed several several metres metres in in thickness. thickness. As the Superior lobe continued to withdraw from the Whitefish-Kaministikwia lowland, low-level outlets to the Superior Superior basin were uncovered resulting in the termination of glacial Lake Lake O'Connor. O'Connor. Superior basin waters inundated low-lying areas up to This represents represents the the to approximately 260 260 m m asl. asl. This approximate level of glacial Lake Minong, the highest water water body body to to occupy occupy the the entire entire perimeter perimeterof of the Lake Superior basin. Very Verylittle littleisisknown knownabout aboutthe thelate-glacial late-glacialhistory history of of glacial glacial lakes lakes within within Clearly,additional additional studies studiesare are required. this southern basin. Clearly, At this fieldtrip stop, we will look at a section of glaciolacustrine deposits associated with glacial Lake Kaministikwia. These Thesered, red, clay clay rich rich deposits depositsare are unusual unusual in in that that they were deposited in the ice ice margin. margin. The approximately 100 m of water less than a few kilometres from the The clays clays are rhythmically rhythmically laminated laminated at at their their base, where where they they overlie overlie glaciofluvial glaciofluvial deposits depositsof of sand sandand and gravel, gravel, and quickly become massive upwards. There Thereisis very very little little indication indication of of aa proximal proximal ice ice margin. margin. That is, there are very few dropstones and few few indications indications of of seasonal seasonal variability variability in in sediment sediment load. load. Proceed Proceed back back to to Highway 11/17 (Sistonens Corners) and turn left (south). Travel Travel 5.2 5.2km south along along Highway 11/17 and turn turn left on Teitto Road. The The next stop consists of aa road cut on the southeast ofthis this intersection. intersection. southeast corner cornerof Subaquatic Flow Till and Stop 5: Subaquatic and Glaciolacustrine Glaciolacustrine Sediment Sediment of the Superior Superior Lobe Lobe lobe. This At this site, we begin to see the first direct evidence of the advancing Superior lobe. This 22 m m well exposure is located less than a few kilometres from the Marks Moraine and consists of well overlying massive massive dark dark grey grey silty siltytill. till. These sediments were laminated, gritty, pebbly silt and clay overlying likely deposited at the bottom of of Lake Lake Kaministikwia Kaministikwia as as bottom-hugging bottom-hugging density density currents currents and and as as ice-rafted debris (rainout) in water depths of about 50 m. Red Red Sibley SibleyGroup Group siltstones siltstonesand and dark dark grey shales derived from the Gunflint Formation Formation are are clearly clearly recognizable recognizable in in the pebble pebble fraction fraction and and provide direct evidence for a Superior lobe provenance. Red, Red, massive massive clays clays associated associated with with glacial glacial �Lake Kaministikwja Kaministikwia occur less less than a few few kilometres kilometres to Clearly, the to the the north north of of this this site. site. Clearly, the composition of the Superior Superior lobe lobe flow flow tills tills and and glaciolacustrine glaciolacustrine deposits do not reflect the composition deposits do not reflect the This material material should should not not be be sampled sampled for for mineral mineral composition of the underlying Archean bedrock. bedrock. This exploration purposes. purposes. exploration Turn vehicles around and and turn turnleft left onto onto Highway Highway 11/17. 11/17. Proceed south 5.3 5.3 km krn to Proceed south to Briggs Briggs Drive Drive and and turn right (east) (east) into into Conmee Township sand and gravel pit. Park vehicle at gate i f locked. sand and gravel pit. Park vehicle at gate j/locked. OverriddenSuperior SuperiorLobe LobeDelta Delta and and Conmee Conmee Base Stop 6: Overridden Base Metal Metal Float Float exposed sequence sequence At this stop, we will be looking at aa section of of Superior Superior lobe lobe drift. drift. The exposed consists of approximately 6 to 7 m of well sorted, steeply-dipping sand and gravel of Superior consists Clastsin in the the lower lower provenance overlain by 2 to 3 m of silty Superior lobe till till (Figure 10). Clasts glaciofluvial unit consist primarily of Proterozoic Proterozoic metasedimentary metasedimentaryrocks. rocks. Numerous cobbles and Numerous cobbles and Gunflint Formation Formation and and Sibley Sibley Group Group are are recognizable. Foreset beds dip boulders belonging to the Gunflint recognizable. Foreset beds dip The delta delta was steeply to the north and are likely of deltaic origin. origin. The was probably probably built built proglacially proglacially into into an early phase of glacial Lake Kaministikwia. The feature therefore represents a location at which Lake Kaministikwia. The feature advancing Superior Superior Lobe Lobe stalled stalled prior prior to to reaching reaching its its maximum maximumposition positionatatthe theMarks MarksMoraine. Moraine. the advancing The delta is actually located within only 3 km krn of the Superior Superior lobe limit limit and and occurs at an elevation was of about 375 m asl, asi, 85 m below below the the maximum maximum elevation elevation of of Lake LakeKaministikwia. Kaministikwia. The delta was overridden by the Superior lobe resulting in the truncation of the foreset unit and removal of the overridden Superior resulting in the truncation of the foreset unit and removal of the Severalmetres metresof ofsilty, silty,Superior SuperiorLobe Lobe subglacial subglacialtill till was was deposited deposited on on top top of of the the sands sands topset beds. Several and gravels. gravels. of large large angular angular to rounded boulders boulders on on the the pit pit floor. floor. significanceis the occurrence occurrence of Of particular significance from the lower lower glaciofluvial glaciofluvial unit unit and, and, in in some some cases, do not appear to The boulders were extracted from have been transported very far. Some Someof of the the larger larger boulders boulders measure measure several several metres across and still still display striated surfaces. The The boulders boulders are are derived derived from from both both Archean Archean and and Proterozoic Proterozoic source source rocks. Several Severalboulders bouldersof ofsuiphidized sulphidizediron ironformation formationand andmassive massivepyrite pyriteof ofArchean Archeanage agewere were discovered in the boulder piles. One Oneof ofthe theboulders bouldersmeasured measuredover over11m min indiameter diameterand and consisted consisted of massive pyrite and magnetite with 10 to 15% sphalerite disseminated in pyrite-rich sections. 10 15% sphalerite disseminated in pyrite-rich sections. throughout the Sphalerite was also concentrated concentrated along along fractures fractures and and adjacent adjacent to to quartz quartz veinlets veinlets throughout the rock. rock. 18 pprn ppm Cu, Cu, 19 ppm Two samples samples from from the pyrite-rich pyrite-rich zones zones returned returned values values of: of: 1) 1)5.13% 5.13% Zn, Zn, 18 19 pprn 16 ppm Cu, 20 ppm Pb, 245 ppb Au and Pb, 260 ppb Au and 0.5 pprn ppm Ag; and 2) 2)2.85% 2.85% Zn, Zn, 16 pprn Cu, 20 pprn Pb, 245 ppb Au and 0.5 0.5 magnetite-rich zone returned values of 850 ppm Zn, 25 ppm Cu, ppm Ag. A sample from the pprn A sample from magnetite-rich zone returned values of 850 pprn Zn, 25 pprn Cu, 55 ppm <0.2 pprn ppm Ag. Ag. A second second sulphidized sulphidized iron iron formation formation boulder boulder measuring measuring pprn Pb, 25 ppb Au and <0.2 pyrite, returned of pyrite, returned values approximately 0.5 m in diameter and consisting almost exclusively of values of of 140 140 ppb Au Au and ppm Zn, 8 pprn ppm Cu, 11 ppm Pb, 710 ppb 1 1 pprn and <0.2 <0.2 ppm pprn Ag. Ag. pprn There are two possible source source areas areas for for the the boulders. boulders. Superior Superior lobe lobe striae striae in in the the immediate immediate eroded and transported vicinity of the pit are oriented at 320 to 330' 330° Az. IfIf the the boulders boulderswere were eroded and transported by by from they could have been Superior ice, then there is a 5 km window towards the southeast from which which they could have been beyond the the 55 krn km limit. limit. Alternatively, derived. Proterozoic derived. Proterozoic metasedimentary metasedimentary rocks rocks outcrop outcrop beyond Alternatively, the the �Figure 10. Figure 10. Steeply-dipping Steeply-dippingforeset foresetbeds beds of of aa delta delta constructed constructed along the margin of the advancing Township). Silty Superior lobe (Conmee Township). Silty Superior Superior lobe lobe till caps the sequence. boulders could have initially been eroded by northern ice from a source source to the north-northeast north-northeast of of the the pit then remobilized by the Superior lobe. remobilized Superior Exploration work during 900s along the lower reaches of Brule Creek, 4 to 5 km during the early 11900 Sulphur Company and General General north-northeast of the gravel pit, by B.L. Morrison, the Davis Sulphur Chemical Company resulted in the discovery discovery of "seven "seven lenticular masses of brecciated, brecciated, banded iron iron formation, in which pyrite has replaced replaced aa considerable considerable part part of of the the rock" rock" (Carter (Carter 1990b). 1990b). The largest of these masses has a maximum width of 23 m and is 244 m long. Other Other discoveries discoveriesinclude includeaa 21 21 magnetite and and pyrrhotite pyrrhotite and andaa99m mwide wideby by 15 15m mlong longzone zoneof of m wide body of pyrite containing magnetite magnetite-pyrite-jasper ironstone. ItIt is is possible possible that that the the boulders boulders found found within the gravel pit were derived from this area and that sphalerite was was not not recognized recognized in in the the rock. rock. It is is not yet clear whether sulphides indicate proximity to to a VMS style zone zone of of mineralization. mineralization. Further the sulphides Further work is is required required to assess the mineral potential of this area. assess south on onHighway Highway111/I 0.5km. k,n. Turn Turn left leftatatHolland HollandRoad Roadand andproceed proceedeastward eastwardfor for Continue south 1 4 77for for 0.5 roadcut at 2.6 km to a roadcut at the the top top of of aa steep steep decline. decline. �7: Superior Northern Till Stop 7: SuperiorLobe Lobe Till Overlying Northern The purpose of this stop is to compare and contrast contrast tills tills of Superior and and northern northern provenance provenance programs. Exposed with respect to drift prospecting programs. Exposed in in the the road cut cut on on the the south south side side of of the the road road is is approximately fairly high approximately 2 to 3 m of brown, blocky, silty Superior lobe till containing aa fairly from the the Gunflint Gunflint Formation, Formation, 2.5 2.5 km km to to the the southeast. southeast. Despite concentration of platy clasts derived from Despite its apparent subglacial origin, this this till till contains few clasts clasts of of Archean Archean supracrustal supracrustal or or intrusive intrusive composition. An olive grey, silty sand till of northern provenance is exposed in a few An olive grey, silty sand of northern provenance few places beneath the the Superior Superior lobe lobetill. till. Most of the clasts in this this lower till till are are of of an an Archean Archean directly beneath affinity. A quartz-feldspar porphyry is exposed in outcrop further down the slope and probably A quartz-feldspar porphyry is exposed in outcrop underlies the northern till in this exposure. exposure. lobe till till as as aa sample medium medium for for mineral mineral Under discussion is the suitability of Superior lobe exploration programs over Archean terrain terrain in in the the eastern eastern portion portion of of the the belt. belt. Compositionally, Compositionally, lobe till till overlying overlying Archean Archean bedrock bedrockdoes doesnot notreflect reflectlocal localbedrock bedrocksources. sources. This is likely Superior lobe attributed to the fact that the Superior lobe was was surging into into aa glacial glacial lake, lake, overriding overriding fine-grained fine-grained glaciolacustrine deposits and shales. The fine-grained substrates and proglacial lakes faciltated The fine-grained substrates proglacial lakes faciltated the process. Subglacial erosion close to the the ice ice margin margin was wasreduced reduceddue dueto toaafloating floatingice iceshelf shelf surging process. and reduced subglacial pressures caused by buoyancy. subglacial pressures caused by buoyancy. The background concentrations of gold grains grains and and elements elements in in Superior Superior lobe lobe till till are are different from those of northern tills. It is therefore advisable to treat datasets significantly different containing information from both tills as separate populations populations for anomaly anomaly recognition. recognition. Even more more importantly, it is recommended that only the the lower lower northern northern till till be be sampled sampled in in Archean Archean areas areas affected by the the Superior lobe. In In areas areas of of thick thick overburden, overburden, it may be necessary to employ expensive drilling techniques to sample the the lower till. till. Alternatively, Alternatively, itit may may be be possible possible to access access by backhoe backhoe trenching trenching off offof ofoutcrops outcropsininthe thearea. area. To To the the south south of of the the Whitefish Whitefish River River the lower till by lowland, Superior lobe till till is exposed exposed on on the the flanks flanksof ofthe theLogan Logandiabase diabasesills. sills. The The till till in in this this area area appears to reflect local variations in bedrock geology geology and and may maybe be suitable suitablefor for exploration exploration programs programs for such commodities commodities as as silver silver or or the platinum group group elements. elements. the vehicles vehiclesaround around andproceed and proceed back to to Highway Highway 11/17. 11/17. Drive Drive straight through Turn the through Highway down Holland Holland Road Roadfor for 3.2 Ion. kin. Stop at top of hill adjacent to aa microwave 11/17 down microwave tower on on the side of of the the road. road. Proceed pit adjacent adjacent to the south side Proceed to to the the north north edge edge of the sand and gravel pit microwave tower. microwave tower. 8: Scenic Brule Creek Moraine Stop 8: Scenic Lookout and Extension of the Brule this site provides provides the the fieldtrip fieldtrip participant participant an an excellent excellent view view of of the the lowland lowland The view afforded at this advanced during during the the Marquette MarquetteAdvance. Advance. Thunder Bay is located into which the Superior Lobe advanced km to to the the east east and and the the Logan Logandiabase diabasesills sillstotothe thesouth southare areapproximately approximately12 12km kmaway. away. Our over 30 km point is is situated situated approximately approximately 120 120mm above the Whitefish Whitefish River River lowland lowland to tothe the south southand and vantage point the east. east. The 230 m above Lake Superior to the The upland upland on which we stand stand clearly clearly affected the Superior Lobe causing it to halt less than 3 km to the northeast of this advancing Superior this location. location. �-s- —— — -- - - - — - _ - - ____________ -- - _ — — _ - --- - ---j -- -c 1--: -t.... -: _ r— -- - C *S- - — Cr----: I Ic- - ___ - 1- - ____ T_i_± - —- - C --S-- 2__ _ - Figure 11. Figure 11.Oblique Obliqueaerial aerialview viewofofthe theWhitefish-Kaministikwia Whitefish-Kaministikwialowland lowlandinto intowhich whichthe theSuperior Superior the Marquette Marquette stadial. stadial. Mesas of Proterozoic diabase are visible lobe advanced during the in the distance. distance. Exposed in the sand and gravel pit before us is a sequence of glaciofluvial sand and gravel of northern provenance which is in turn overlain by a unit of glaciolacustrine sand and finally by m of silty silty Superior Superior Lobe Lobetill. till. Paleocurrents in the lower glaciofluvial unit suggest approximately 3 m flow towards the the south-southwest. south-southwest. This is consistent with with aa northward northward retreating retreatingice icemargin. margin. The The glaciolacustrine sands glaciolacustrine sands are likely associated associated with with an an early early phase phase of of glacial glacial Lake Lake Kaministikwia. Kaministikwia. A number of buried sand and gravel deposits of northern provenance occur in southern and and adjoining adjoining Oliver Oliver Township. Township. It is possible that these deposits southeastern Conmee Township and Brule Creek Moraine, a significant ice-marginal feature represent the eastern extension of the Bmle the retreating northern northern ice ice lobe. lobe. The eastern extension of the Brule Creek Moraine associated with the beyond the Marks Moraine was obscured by Moraine obscured the the advancing advancing Superior Superiorlobe. lobe. The next next stop stop is is optional optional depending depending upon upon the the condition conditionof ofthe theroad road intothe intothe site. site. Continue Continue west kmdown downHolland HollandRoad RoadtotoSovereign SovereignRoad. Road Turn Turn right right and and drive drive north north 800 800 m. m. Turn another 1. 1.77 km logging road road and follow follow ititfor for approximately approximately600 600m. m. Turn right right at at vv in in road road and andfollow follow road road left on logging (-1 kin,). km). Park Parkvehicle vehicleatatcrest crestofofhilL hill. to the north until you reach reach aa clearcut clearcut('-4 �9: Marks Moraine Stop 9: This fieldtrip stop is located on on the the crest crestof ofthe theMarks MarksMoraine, Moraine,aaterminal terminalmoraine moraineassociated assoiated 9.9 to 10.0 10.0ka ka BP, BP, with the advancing Superior lobe. The The moraine moraine was was constructed constructed approximately approximately 9.9 during the Marquette Stadial. ItIt has has been been traced traced across across the study study area area from the southwestern southwestern corner comer of Marks Township to the southeastern comer corner of of Ware Ware Township. Township. Mapping is required toward Mapping is required toward the the its position. position. Where it is best developed, the moraine consists consists of of multiple multiple till till southwest to determine its ridges within a zone 11 to 2 km wide (Figure 12). It is composed primarily of fine-textured till and 12). It is composed primarily of fine-textured till and relatively low low profile. profile. In other areas, the moraine consists of a stacked therefore displays a relatively sequence of flow tills tills and glaciolacustrine deposits deposits with with no no apparent apparent geomorphic geomorphic expression. expression. The moraine here is assymetrical in cross-section, displaying a steeper slope on the ice-contact side. side. Fine-textured glaciolacustrine sediments sediments interbedded interbeddedwith with Superior Superior southeastern, ice-contact tills occur bevone beyong themoraine morainetotothe thenorthwest. northwest. To To the the southwest southwest are areaa series seriesof of lobe flow tills . the that follow follow the the ice ice margin margin and and terminate terminate in in the the Kaministikwia Kaministikwia basin basin to to northeast-trending channels that the northeast. Paleocurrents flow towards towards the the Paleocurrentsof of cross-bedded cross-bedded sands within these channels indicate flow Kaministikwia basin. Kaministikwia basin. - Drive back out to the intersection of of Sovereign SovereignRoad Roadand andHolland HollandRoad Roadand andproceed proceedsouth south on on Sovereign Road for for 4.9 km km till tillyou youreach reach Highway Highway 590. 590. You have have now now descended descended into into the the Whitefish-Kaministikwialowland, lowland,aavertical verticaldrop dropof ofover over100 100in. m. Sovereign SovereignRoad Roadchanges changes into into Whitefish-Kaministikwia Highway 595 595 beyond beyond Highway Highway590. 590. Continue south on Highway 595 595for for an an additional 4.9 Highway 4.9 km. km. Smith Road Road and and drive drivefor for 3.0 km km till tillyou you reach reach a bridge crossing Turn left on Smith crossing Whitewood Whitewood Creek. Creek. Park the far side Park the vehicle vehicle on the right on on the far side of of the bridge. bridge. Stop 10: 10: Whitewood Creek Section At this stop, we will be looking at a section along the banks of Whitewood Creek that exposes 2 glaciolacustrinedeposits. deposits. The section has has not not been been studied studied tills with intervening and superimposed glaciolacustrine in detail. however, demonstrate demonstrate the the drastic drastic changes changes that that occur occur in in till till character character as as one one detail. It does, however, Archean upland upland to tothe thenorth northinto intothe theWhitefish-Kaministikwia Whitefish-Kaministikwialowland. lowland. At At this this proceeds off of the Archean stop, we will concentrate on on the the lower lower till till unit. unit. The steepness of the section makes makes itit difficult difficult to to units. These units will be viewed at the next fieldstop. view the upper stratigraphic units. At river level is exposed a dark grey, sandy silty silty subglacial subglacial till till presumed presumed to to be be of of northern northern its subglacial subglacial origin. origin. A affinity. The The till till contains contains numerous numerous faceted and striated clasts supporting its stone line or boulder pavement is clearly visible visible aa few metres metres above above water water level level when when the the section section is is towards the the well exposed. Striations Striationson on the the upper upper surfaces surfaces of the boulders indicate ice flow towards southwest. Most Shales, wackes, wackes, ironstones ironstones Mostof of the the clasts clasts are are derived from the Gunflint Formation. Shales, jaspers are commonly seen in the the river river bed. bed. Only and oolitic jaspers Only aa small small proportion proportion of of the clasts clasts are are derived from Archean terrain terrain to to the the north. north. Oxidation of sulphide minerals contained contained within within Gunflint Formation shales has caused a rusty appearance appearance to to the the till till up up to to the the high high water water line line in in the the section. The that which which is is observed observed over over Thecharacter character of of this this lower lower northern till is quite different from that to the the north. north. The owing its its fineness fineness to to the the texture texture Archean terrain to The till is significantly finer textured, owing displays aa much much darker darker colour. colour. It is similar of the underlying source rocks and displays similar in that it appears appears to �:Jw •w&w • fl LjflMj f'? 2 Figure 12. Figure 12. Aerial Aerialphoto photoof ofthe thearea areasurrounding surrounding Stop Stop 9. 9. The Themorainie morainicridges ridgesform form part part of of the the Marks Moraine. Moraine. The Theesker eskerridge ridgewas wasdeposited depositedby bysouthward southwardflowing flowingnorthern northernice. ice. Superior lobe till flanks flanks the eastern eastern margin of of the the esker. esker. �reflect local bedrock sources sources and and therefore is is aa suitable suitable sampling samplingmedium medium for for programs programs of of mineral mineral exploration exploration within within this thisarea. area. The The lower, lower, northern northern till till is is overlain overlainby by aa sequence sequence of of silty silty glaciolacustrine glaciolacustrinesediments sedimentswhich which were were likely deposited within glacial Lake O'Connor. These sediments have likely deposited within glacial Lake O'Connor. These sediments have not not been been looked lookedat at in in any any detail. There Thereare arenumerous numeroussections sectionsalong alongthe thevalley valleyof ofthe theWhitefish WhitefishRiver Riverand andtributaries tributariesthat that expose Lake O'Connor sediments. These sections require detailed examination to expose Lake O'Connor sediments. These sections require detailed examination to assist assist with with unravelling unravelling the the history history of of this this glacial glacial lake. lake. Higher toclayey clayey Higher up up in in the the section, section, immediately immediatelyabove abovethese these stratified stratifieddeposits depositsisisaamassive massivesilty siltyto diamicton pebbles. This diamicton with with aa few few grits grits and and pebbles. Thisunit unitisisinterpreted interpretedto tobe beaatill tillderived derivedfrom fromthe the Superior Superior lobe. lobe. The Thetill till owes owesits itsfine fine texture texture to to the the incorporation incorporation of of large large volumes volumes of of glaciolacustrine deposits into the base of the advancing Superior lobe. This till barely glaciolacustrine deposits into the base of the advancing Superior lobe. This till barelyresembles resembles other other examples examples of of Superior Superior lobe lobe till which we we have have seen seen earlier earlier in this fieldtrip. fieldtrip. The Thepebbles pebbleswithin within this till are easily recognized as derived from the Animikie and Sibley Group metasediments to the this till are easily recognized as derived from the Animikie and Sibley Group metasediments to the northeast and east. This till does not carry a signature of local geology because the ice that northeast and east. This till does not cany a signature of local geology because the ice that deposited deposited it it did did not not have have access access to to the the bedrock bedrock surface. surface. The The upper, upper, Superior Superior lobe lobe till till is is overlain overlainby by aa second secondsequence sequenceof ofglaciolacustrine glaciolacustrinedeposits. deposits. These These sediments sedimentswere were probably probably also also deposited deposited within within glacial glacial Lake O'Coimor O'Connor as as the the Superior Superiorlobe lobe ice ice margin margin retreated retreated eastward eastwardout out of ofthe thelowland. lowland. Turn vehicles around around and and go go back back to to Highway Highway595. 595 Turn for 3.3 km. Turn Turn the the vehicles Turnleft left and and drive drive south southfor 3.3 km. Turn left on Blaikie Rd and Bluikie Rd. anddrive drive east eastfor for 1.8 1.8kin. km.The Theexposure exposurewe wewill will be belooking lookingat atisiscut cutinto intothe the River valley valley and and is is located located on on the southwest southwest side side of the the road. road walls of the the Whitefish Whitefish River Stop Stop 11: 11: Whitefish WhitefishRiver RiverSection. Section. At At this this stop, stop, we we will will have have an an opportunity opportunityto to look look at, at, in in detail, detail, aa section section through through glacial glacial lake lake O'Connor anupper upper sequence sequenceof of glaciolacustrine glaciolacustrineand and fluvial fluvial O'Connor sediments, sediments,Superior SuperiorLobe Lobetill till and and an deposits. deposits. The Thelower lower33toto44mmconsists consistsofofdark darkgrey, grey,well welllaminated laminatedsilt siltand andclay claylikely likelydeposited deposited with are the the Rove Rove and and with glacial glacial Lake Lake O'Connor. O'Connor. The Theclays claysare areclark dark grey grey because because their their source source rocks rocks are Gunflint Gunflint Formations. Formations. Glacial GlacialLake LakeO'Connor O'Connorformed formedproglacially proglaciallywhen when the the Superior Superiorlobe lobe advanced advanced into intothe the Whitefish WhitefishRiver Rivervalley valleyproducing producingaaclosed closedbasin basinsupported supportedon onits itsnorthern northernand andsouthern southern flanks flanksby by high high ground. ground. The Thelake lakemust musthave havedrained drainedwestward westwardout outthrough throughthe theWhitefish WhitefishLake Lakebasin. basin. Eventually Eventually the the advancing advancingSuperior Superiorlobe lobeoverrode overrodethese thesedeposits depositsproducing producingaafine-textured, fine-textured, clayey silt till with few pebbles. This till is very similar to that exposed clayey silt till with few pebbles. This till is very similar to that exposedatatnear nearthe thetop topof ofthe the section at Stop 10. The till is massive, dense, compact and was probably deposited subglacially section at Stop 10. The till is massive, dense, compact and was probably deposited subglacially under of under active active ice. ice. The Thefineness finenessof ofthe theunderlying underlying deposits deposits would would have have prevented prevented the the infiltration infiltration of subglacial meltwater into the substrate. This would help to promote the development of a thin layer subglacial meltwater into the substrate. This would help to promote the development of a thin layer of of water water at at the the glacier glacier sole sole which which would would have have facilitated facilitated the the rapid rapid advance advance of of ice ice into into the the basin. basin. As As mentioned earlier, the base of the advancing Superior lobe was isolated from the bedrock surface by mentioned earlier, the base of the advancing Superior lobe was isolated from the bedrock surfaceby �several tens tens of of metres metres of of intervening intervening sediment. sediment. As this ice not several As aa result, result, the the till till deposited deposited by by this ice does does not display a signature of local bedrock within the Whitefish River valley. display a signature of local bedrock within the Whitefish River valley. Superior Superior lobe lobe till till is is abruptly abruptlyoverlain overlainby by approximately approximately22m mof ofdark darkgrey greyclay clayand andsilty siltyclay. clay. This sediment was deposited proglacially beyond the retreating margin of the Superior lobe. The This sediment was deposited proglacially beyond the retreating margin of the Superior lobe. The dark grey grey colour colour of of this this sediment sediment suggests deposition within dark suggests deposition within aa closed closed basin basin (i.e. (i.e. aa basin basin not not linked linked with Lake with Lake Superior). Superior). This overlain by by approximately approximately 11 m m of of pebble pebble gravel. gravel. The This unit unit is is abruptly abruptly overlain The gravel gravel is is wellwellmoderately sorted and probably of fluvial character. A low-water phase is implied by this unit. unit. moderately sorted and probably of fluvial character. A low-water phase is implied by this Perhaps the the eastward eastward retreat retreat of of Superior Perhaps Superior ice ice beyon beyon d d Stanley Stanley Hill Hill in in southwestern southwestern Paipoonge Paipoonge Township resulted resulted in in the the drop drop of of glacial glacial Lake Lake O'Connor O'Connor to to aa lower Township lower level. level. This Thiswould wouldhave have resulted resulted in the influx of coarse sediments from uplands east of the site (Little Pig and Badger Mountains) in the influx of coarse sediments from uplands east of the site (Little Pig and Badger Mountains) resulting resulting in in the the superposition superposition of of fluvial fluvial sands sands and and gravels gravelsover over clay. clay. The fluvial fluvial unit unit is abruptly overlain overlain by reddish-coloured glaciolacustrine The is abruptly by reddish-coloured glaciolacustrine deposits deposits of of silt, silt, very very fine minor clay. clay. The fine sand sand and and minor Theupper upper surface surfaceof of this thisglaciolacustrine glaciolacustrineplain plain occurs occurs at at approximately approximately 275 275 m m asl, as], well well above above the the highest highest elevations elevations reported reported for for Superior Superiorbasin basin lakes lakesin in the theThunder ThunderBay Bay area. area. These Thesedeposits depositswere werelikely likelylaid laiddown downwithin withinaa confined confined basin basin with with aa configuration configurationsimilar similarto to that of of glacial glacial Lake Lake O'Connor. O'Connor. The of the the sediment sediment that Thesignificance significanceof of the the colour colour and and textural textural change change of is is unclear. unclear. Clearly, Clearly,additional additionalwork work is isrequired requiredto to obtain obtainaa better better understanding understanding of of the the glaciolacustrine history glaciolacustrine history of of this this region. region. �REFERENCES REFERENCES Baje, Bajc, A.F. A.F. 1997. 1997. A Aregional regionalevaluation evaluationof ofgold goldpotential potentialalong alongthe the western western extension extensionof of the the Larder Larder Lake-Cadillac Break, Matachewan area: results of regional till sampling; Ontario Lake-Cadillac Break, Matachewan area: results of regional till sampling; OntarioGeological Geological Survey, Open Open File File Report Report 5957,50 5957, Sop. Survey, p. Bajc, A.F. 1999a. 1999a.Results Resultsof ofregional regionalhumus humusand andtill tillsampling samplingin inthe theeastern easternpart part of of the the Bajc, A.F. Shebandowan greenstone greenstone belt, belt, northwestern northwestern Ontario; Ontario; Ontario Shebandowan Ontario Geological Geological Survey, Survey, Open Open File File Report W2p. Report5993, 5993,92p. Baje, Ak'. 1999b. Bajc, A.F. 1999b. Gold Goldgrains grainsin intill, till,western western Shebandowan Shebandowan greenstone greenstone belt, belt, northwestern northwestern Ontario; Ontario; Ontario Geological Geological Survey, Survey, Preliminary Preliminary Map Map 341 3417, 000. Ontario 7, scale scale 1:100 1:100 000. Bajc, A.F. 2000. Bajc, A.F. 2000. Results Resultsof ofregional regionaltill tillsampling samplingin inthe thewestern westernpart part of ofthe the Shebandowan Shebandowan greenstone northwestern Ontario; Ontario; Ontario greenstone belt, belt, northwestern OntarioGeological GeologicalSurvey, Survey, Open Open File File Report Report 6012, 6012, 82p. 82p. Brown, Brown, G.H. G.H. 1995. 1995. Precambrian Precambriangeology, geology, Oliver Oliverand and Ware Ware townships; townships;Ontario Ontario Geological GeologicalSurvey, Survey, Report 294, 'tSp. Report 294,48p. Carter, Carter, M.W. M.W. 1990b. 1990b. Geology Geologyof ofForbes Forbesand and Conmee Conmeetownships; townships;Ontario OntarioGeological Geological Survey, Survey, Open Open File Report 5726, 158p. File Report 5726, 188p. Corfu, F. and and Stott, Stott, G.M. G.M. 1998. 1998.Shebandowan Shebandowangreenstone greenstonebelt, belt,western westernSuperior SuperiorProvince: Province: U-Pb U-Pb Corfu, F. ages, tectonic implications, and correlations; Geological Society of America, ages, tectonic implications, and correlations; Geological Society of America, v.110, v.110, no.11, no. 11, p. 1467-1484. p.1467-1484. Franiclin,J.M., J.M.,Kissin, Kissin,S.A., S.A.,Smyk, Smyk,M.C. M.C.and andScott, Scott,S.D. S.D. 1986. 1986. Silver Silver deposits deposits associated associated with with Franklin, Proterozoic rocks rocks of of the the Thunder Thunder Bay Bay District, District, Ontario; Ontario; Canadian Proterozoic Canadian Journal Journal of of Earth Earth Sciences, v.23, No. No.10, 10, p.1576-1591. p. 1576-1591. Osmani, LA. l.A. 1997. Osmani, 1997. Geology Geologyand andmineral mineral potential: potential:Greenwater GreenwaterLake Lake area, area, West-Central West-Central Shebandowan Greenstone Greenstone Belt; Belt; Ontario Ontario Geological Geological Survey, Survey, Report Report 296, 296, 135p. l35p. Shebandowan Schneiders, B.R., Scott, Scott, J.F. J.F. and and Smyk, M.C. 1998. Schneiders, B.R., Smyk, M.C. 1998. Report Report of ofActivities, Activities,1997, 1997,Resident ResidentGeologist Geologist Program, Thunder Thunder Bay Bay South South Regional Regional Resident Resident Geologist's Geologist's Report: Program, Report: Thunder Thunder Bay Bay South South District; Ontario District; Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5971, 5971, 56p. 56p. Sutcliffe, R.H. 1991. Sutcliffe, R.H. 1991. Proterozoic Proterozoicgeology geologyof ofthe the Lake Lake Superior Superiorarea; area; in in Geology Geology of of Ontario, Ontario, Ontario Ontario Geological Geological Survey, Survey, Special Special Volume Volume 4, Part Part 1, 1, p.627-660. Williams, H.R. H.R. 1991. Quetico in Geology Geology of of Ontario, Ontario, Ontario Ontario Geological Geological Survey, Survey, QueticoSubprovince; Subprovince;in Special Special Volume Volume 4, Part Part 1, 1, p.383-404. p.383-404. �Williams, T.L. and and Sage, Sage, R.P. R.P. 1991. Wawa Subprovihce; Williams, H.R., H.R., Stott, Stott, G.M., Heather, K.B., K.B., Muir, T.L. in in Geology Geology of of Ontario, Ontario, Ontario OntarioGeological Geological Survey, Survey, Special Special Volume Volume 4, Part Part 1, 1, p.485-542. Zoltai, Zoltai, S.C. S.C. 1963. 1963.Glacial Glacialfeatures featuresof ofthe theCanadian CanadianLakehead Lakeheadarea; area; Canadian Canadian Geographer, Geographer, v.7, p.101-115. p.101-115. Zoltai, Zoltai, S.C. S.C. 1965. 1965.Glacial Glacial features featuresof of the the Quetico-Nipigon Quetico-Nipigonarea, area, Ontario; Ontario; Canadian Canadian Journal Journal of of Earth Earth Sciences,v.2, v.2, p.247-269. p.247-269. Sciences, �GEOLOGY OF STEEP GEOLOGY OF THE THE ARCHEAN ARCHEAN STEEP ROCK LAKE FINLAYSON LAKE LAKE ROCK LAKE - FINLAYSON GREENSTONE BELT GREENSTONE BELT Denver Denver Stone, Stone, Ontario Ontario Geological Geological Survey Survey Kirsty Tomlinson, Survey of of Canada Canada Kirsty Tomlinson, Geological Geological Survey Ray Ray Bernatchez, Bernatchez, Atikokan Atikokan Resources Resources Inc. Inc. Philip Fralick, Fralick, Lakehead Philip Lakehead University University 3.0 Ga Ga assemblage qfIc tofelsic fr/sic This 3.0 assemblageconsists consistsof ofu/tram ultramaflc metavolcanic rocks and metavolcanic and chemical-clastic chemical-clasticsedimentary sedimentaryrocks. rocks. This trip will will examine examine the the structural, structural, petrographic, petrographic, sedimentaological sedimentaologicaland andeconomic economicaspects aspectsof ofthese theserocks. rocks. �FIELDTRIP 2B FIELDTRIP 2B MESOARCHEAN GEOLOGY GEOLOGY OF OF THE THE STEEP STEEP ROCK ROCK MESOARCHEAN LUMI3Y LAKE LAKE TERRAINS TERRAINS LUMBY INTRODUCTION INTRODUCTION The various Mesoarchean Mesoarchean sequences sequencesin in the Canadian Canadian Shield are remarkably similar, being composed metabasalt-quarta areniate-iron areniate-iron formation formation association association or a 2) 2) metavolcanicmetavolcanic:1) a metabasalt-quartz composedof of either either :1) shallow water carbonate association (Thurston and Chivers, 1990; Erikisson et al, 1994). Worldwide shallow water carbonate association (Thurstonand Chivers, 1990;Erikisson Worldwide examples of these associations associations typically overlie overlie granitoids granitoids or volcanic volcanic successions successions intruded by granitoids and include theoleiitic basalt and komatiite, quartz arenite, iron formation, pelite and/or include theoleiitic quartz andlor stromatolitic carbonate. carbonate.Conglomeratic Conglomeraticintervals intervalstypically typicallyare arepresent presentatat the the base base of stromatolitic of these these successions. Included in this association successions. association are the Manjeri Formation at the base of the Ngezi Group in Zimbabwe, the Paddy Market in the the Pilbara Zimbabwe, Paddy Market Supersequence Supersequence in Pilbara Block, Block, and and numerous numerous local local occurrences in in Superior Province Province (Erikisson (Erikissonetet al, al, 1994; 1994; Erikisson Erikisson et et al, al, 1996). Of the various occurrences various examples examplesof of this this association associationthe the carbonate carbonatedominated dominatedSteep SteepRock Rock assemblage assemblagehas has received receivedthe the most most detailed analysis. Thurston and Chivers (1990) and Erikisson et al (1994, (1994, 1996) 1996)concluded concluded that that associations associations of of this this type type are areformed formedas asaa stable stableplatform platform undergoes undergoesrifting. rifting. Data amassed in recent years on these Mesoarchean sequences Data amassed in recent years on these Mesoarchean sequenceshas, has, in in some some cases, cases, led led to to an an elaboration of of preexisting preexisting tectonic tectonic models, models, while while in in other other cases cases has has caused new models to be elaboration be proposed. This new data on the Steep Rock-Lumby Lake Terrains is briefly reviewed at the end of proposed. This new data on the Steep Rock-Lumby Lake Terrains this article, with the the new article, with with the aim aim of of familiarizing familiarizing the field field trip participants participants with new ideas on Mesoarchean tectonics being developed in this area. First we will stan with an introduction to and Mesoarchean tectonics developed First we will start with an description of the the belt. belt. General Geology General Geology The Steep Steep RockRock- Lumby Lumby Lake within the the District District of of Rainy Rainy River, River, extending extending Lake Terrain Terrain is located within Atikokan to the northeast, northeast, and approximately 200km Thunder Bay, Ontario 200km to the west of Thunder from Atikokan and lying approximately TheSteep SteepRock RockGreenstone GreenstoneBelt Beltlies liesimmediately immediatelyto tothe thenorth north of of Atikokan, near the (Figure 1). The (Figure 2). 2). It was first described by Smyth (1891) as a Quetico-Wabigoon subprovince boundary (Figure vertical succession ferruginous strata strata and and volcanics. volcanics. The The belt vertical succession of conglomerate, conglomerate, limestone, limestone, ferruginous belt unconformably overlies the 3003-+5Ma (Davis and Jackson, 1988) tonalitic Mannion Marmion batholith (Wilks, 1986; Stone et al., 1992). 1992). The The greenstone greenstone Belt comprises comprises the following following five Formations defined (1959),Wilks Wilksand andNisbet Nisbet(1986) (1986)(Figure (Figure3) 3)and andStone Stoneetetal. al.(1992). (1992). defined by Jolliffe Jolliffe (1959), 1. quartzo-feldspathic conglomerates 1. Basal quartzo-feldspathic conglomeratesand andsandstones sandstonesof ofthe theWagita WagitaFormation Formation(up (upto to 150 150 m thick) thick) representing representing alluvial alluvial fan fan deposits deposits on on fault fault scarps scarps (Wilks, 1986); 2. Stromatolitic limestones of the Mosher Carbonate Formation(up (uptoto 500 2. Stromatolitic limestones of the Mosher Carbonate Formation 500 m m thick) thick) representing deposition deposition in in aa shallow shallowsea; sea; 3. Iron formation formation and carbonate-Mn-Fe-rich carbonate-Mn-Fe-rich mudstones mudstones of the the Jolliffe Ore Ore zone zone Formation Formation (up to 400 m thick) representing representing deposition deposition in a subsiding subsiding basin (Wilks, 1986); 1986); 4. an unusual high-Mg, predominately pyroclastic komatiitic unit named the Dismal Ashrock 4. predominately pyroclastic komatiitic Formation (50-400 m thick) representing Formation representing shallow water volcanism; and �n -.4 I n t —. —. Location (if nit itihohan /Steep Ruck area in relation to the belt structure of Superior Province. �p.. * N e Geology of the Steep Rock (a and south-east of A), Finlayson Lake (B) and Lumby Lake (C,S, E) areas. t :!lj Figure 2. �5. . aa sequence the Witch Witch Bay Bay Formation Formation (ca. (ea. 55 sequence of mafic and minor felsic metavolcanics called the km km thick) thick) representing representingsubaqueous subaqueousvolcanism. volcanism. T 200 nil] 200 m .1. B. B. Metosedirnents Metosediments WITCH WITCH BAY BAY FORMATION FORMATION (( rnetavolcanics metavolconics , metasedirnents) metosediments I Possible Possible Tectonic break Tectonic break Lovas LOWS ? DISMAL DISMAL ASHROCK ASHROCK JOLLIFFE JOLLIFFE ORE ORE ZONE ZONE Pyrite Pyrite lenses lenses Buckshot Buckshot ore ore Mammil lose Mommillose St ro m a to ites Stromatolites ./ / / Fault MOSHER CARBONATE 1 WAGrTA FORMATION i clostics I unconformity MARMtON COMPLEX MOSHER MOSHER CARBONATE CARBONATE WAGITA WAGITA FORMATION FORMATION clastics ( ctostics) I MARMION MARMION COMPLEX COMPLEX Giant Columnar Columnar Stromalolites Oncolites Strotiform Stromatolites Pseudomorphs otter Gypsum (Atikokania) Branching & Hemispherical Stromotolites Xenoliths Xenoliths Eorly Early Mofic Mafic Dykes Dykes Figure Rock area. area. The sedimenta,y units Figure3.3. A) A) Geology Geology of the Steep Rock Thewhite white area area south south of of the the sedimentary unitsisis mostly mafic volcanics. B) Stratigraphy of the Steep Rock succession. (Mod j/ied mostly B) Stratigraphy of the Steep Rock (Modified afterWllks Wilksand andNisbet, Nisbet,1986).. 1986).. after The The age ageof ofthe theSteep SteepRock Rock Group Group isis fairly fairly well well constrained. constrained. Six Sixdetrital detritalzircons zirconsfrom fromthe the basal basal sandstones sandstonesare areca. ca. 2999 2999 Ma Ma (reported (reported by by Fralick Fralick and and King, King, 1996 1996 as as D. D. Davis, Davis, personal personal communication). The Dismal Ashrock Formation contains zircons which are 2997 Ma, and these communication). The Dismal Ashrock Formation contains zircons which are 2997 Ma, and these may Davis, personal personal communication, communication,1998). 1998). Sphenes Sphenes in in the the Marmion Mannion (D. Davis, may also alsototobe bedetrital detrital(D. batholith batholithhave havebeen beendated datedatatca. ca.2950 2950Ma, Ma,possibly possiblyreflecting reflectingthe theage ageof of hydrothermal hydrothermalactivity activity that that generated JolliffeOre Orezone zoneFormation Formation(D. generatedthe theJolliffe (D. Davis, Davis,persona personacommunication, communication, 1998). 1998). The TheFinlayson FinlaysonLake LakeGreenstone GreenstoneBelt Beltajoins ajoinsthe theSteep SteepRock RockBelt Belttotothe thenorthwest northwestand and extends extendstotothe thenortheast. northeast.ItItisisapparently apparentlyan anextension extensionof ofthe theSteep SteepRock Rock sequence, sequence, but with with the the sedimentary sedimentaryassemblage assemblageon ontop topofofthe thevolcanic volcanicpile pilerather ratherthan thanbelow belowit, it,as asisisthe the case case with with Steep Steep Rock. Rock. The thanthe theSteep SteepRock Rockgreenstone greenstonebelt belt and andthe therocks rocks are are atat The belt belt isismore moredeformed deformedthan greenschist greenschistto toamphibolite amphibolitefacies. facies.The Thebelt beltisisthought thoughttotooverlie overliethe theMarmion Marmionbatholith batholith(Stone (Stone et., et., 1992) 1992)but butthe thecontact contacthas hasbeen beenintruded intrudedby bysynsyn-to to post-volcanic post-volcanic tonalite tonaliteand and granodiorite granodiorite(Stone (Stoneand and Kamineni,1989). 1989).The Thebelt beltisisdominated dominatedbybysheared, sheared,pillowed pillowedand andmassive massivemafic maficlava lavaflows flowsand and Kamineni, banded bandedamphibolites. amphibolites.Thin Thinunits unitsofoffelsic felsictuff tuffand andmetasedimentary metasedimentarvrocks rocksare are intercalated intercalatedwith with the the mafic maficvolcanics volcanicsapproximately approximatelyhalfway half waythrough throughand andatatthe thetop topofofthe thesequence sequence(Fralick (Fralickand andKing, King, 1996). Six detrital zircons from the upper sedimentary sequence give an age range of 3002 to 2997 1996). Six detrital zircons from the upper sedimentary sequence give an age range of 3002 to 2997 �Ma Ma (Fralick (Fralick and and King, King, 1996) 1996)and and aa rhyolite rhyolite near near the the top top of of the the volcanic volcanic sequence sequencehas has been beendated datedat at 2932± 2 Ma (Davis, 1993). 2932  2 Ma (Davis, 1993). The The Luinby LumbyLake LakeGreenstone GreenstoneBelt Beltextends extendseastwards eastwardsfrom fromthe thenorth northend endof of the the Finlayson Finlayson belt (Jackson. (Jackson, l985a, belt 1985a,b). b). The Thesouthern southernmargin margin of ofthe the belt belt is is in in faulted faulted contact contact with with the the Marmion Marmion batholith (Sage (Sage et et al., al., 1974). pillow batholith 1974). The Thebelt beltisisdominated dominated by by mafic mafic volcanic volcanic rocks, rocks, particularly particularly pillow lavas, but but also of komatiite komatiite flows flows and and pyroclastics, pyroclastics, felsic felsic volcanic volcanic units units and and lavas, also contains contains sequences sequences of chemical the chemical and and clastic clastic sediments. sediments. The Thenorthern northernhalf half of of the the belt belt generally generally youngs youngs to to the the south south and and the southern the belt belt dipping dipping steeply. steeply. Jackson a,b) suggested southernhalf half to to the the north, north, with with both both halves halves of of the Jackson(1985 (1985a,b) suggested that represented aa syncline along the the sedimentary sedimentary units units at the centre centre of of the the that the the belt belt represented syncline with with the the fold fold axis axis along at the belt. This model model appears to be belt. This appears to be oversimplified oversimplified as as there there are are reversals reversals in in younging younging direction direction and and because the the stratigraphy stratigraphy in in the the two two halves halves of of the the belt belt is is rather rather different. different. We because We suggest suggest that that these these opposing tectonic boundary simple synclinal synclinal axis, opposing sequences sequencesmay may be be separated separatedby by aa tectonic boundary rather rather than than aa simple axis, but but do not not discount do discount that that the the two two halves halves of of the the belt belt are are related. related. A felsic of the the southern southern half half of of the the belt belt contains contains 2999 2999 Ma Ma tuff unit unit low low in in the the stratigraphy stratigraphy of A felsic tuff zircons and and aa felsic felsic tuff tuff slightly slightly higher higher in the stratigraphy stratigraphy contains range 2999 zircons in the contains zircons zircons in in the the range 2999 to to 2903 2903 Ma (Davis (Davis and and Jackson, Jackson, 1988). 1988). However the 2999 2999 Ma Ma component component in in each eachof ofthese these felsic felsic units units is is Ma However the thought to be be detrital detrital (D. (D. Davis, 1998). This higher felsic felsic unit unit is thought to Davis, personal personal communication, communication, 1998). This higher is also also along 1 50-m-thickunit unit(Jackson, (Jackson, 1985a) 1 985a)ofofsandstones, sandstones,carbonates carbonatesand and chert chert along strike strike from from aa ca. ca. 150-m-thick thought to thought to have have formed formed in in aa shallow shallowwater water environment environment (lower (lower sedimentary sedimentary sequence; sequence; Fralick Fralick and and King, 1996). 1996). A thick thick felsic the belt belt contains contains zircons zircons that that give give aa maximum maximum felsic tuff unit in the northern northern half of the U-Pb age age of of 2973 2973 ma ma (D. (D. Davis, An upper upper sedimentary sedimentary sequence sequence U-Pb Davis, personal communication, communication, 1997). 1997). An described by Fralick and King (1996) m of chert-rich chert-rich iron formation formation and elastic described (1 996) comprises comprises 500-700 500-700 m clastic sedimentary rocks rocks that that occur The upper part of sedimentary occur along along the the centre centre of of the the greenstone greenstone belt. belt. The upper part of the the upper upper sedimentary sequence sedimentary sequence comprises comprises elastic clastic turbidites turbidites with conglomeratic conglomeratic intervals intervals (Fralick (Fralick and King, 1996). 1996). The mafic rocks of of the belt are The mafic and and ultramafic ultramafic volcanic volcanic rocks the Lumby Lurnby Lake Lake greenstone greenstone belt are at at amphibolite the northen northen margin margin of of the the greenstone greenstone amphibolitegrade grade close close to to the the Norway Lake Lake pluton and along along the belt, but but otherwise otherwise they they are are generally generally at at greenschist greenschist facies. facies. They belt, They are, are, in places, places, well well exposed exposed and, and, although original stratigraphic stratigraphic and textural features features are frequently frequently very well preserved, preserved, although often often sheared, sheared, original and textural particularly in particularly in the the northern northern half half of of the the belt. belt. Steep Rock Rock Group Group Steep Smyth (1891) was the the first first to to describe describe the the Steep Steep Rock Rock succession succession which which he he interpreted interpreted as as aa Smyth (1891) was monoclinal assemblage monoclinal assemblageof ofnine nineformations formationsthat that unconformably unconformablyoverlie overlieaa granitic graniticbasement basementcomplex. complex. The unconformable basal (1912), though he reduced reduced Smyth's Smyth's nine 912), though Lawson (1 The unconformable basal contact contactwas was confirmed confirmedby Lawson formations formationsto to four four by eliminating eliminatingthe the dubious dubious upper upper units. units. Moore Moore (1939), (1939), Jolliffe Jolliffe (1966), (1966), Shklanka Shklanka (1972) and Wilks Wilks and Nisbet (1988) (1972) andNisbet (1988)all all redefined redefined the constituents constituents of of the Steep Steep Rock Rock Group, Group, with with the the presently accepted presently accepted definition definitionbeing being the thelatter. latter. Intrusive Igneous Atikokan area Intrusive IgneousRocks. Rocks.The The Atikokan areastraddles straddlesan anelongate elongatebelt beltof ofmetasediments metasedimentsto to the the (Quetico Subprovince) south (Quetico Subprovince)and andmixed mixedmetavolcanic, metavolcanic,gneissic, gneissic,and andfelsic felsicplutonic plutonicrocks rocksto tothe the north north tonalite and and "old" 'old" tonalite (Wabigoon Subprovince). PrePre- to to synvolcanic synvolcanic intrusions intrusions include mafic tonalite tonalite �(which predate the the Marmion Marmion batholith batholith and and Lefteye Lefteye stock stock as as well wellas astonalite tonalite (which predate the Steep Steep Rock Rock Group) Group) in in the and Syn-to postvolcanic postvolcanic intrusions and mafic mafic tonalite tonalite gneisses gneisses of of the the Dashwa Dashwa gneiss gneiss complex. complex. Syn-to intrusions encompass a broad range of felsic to mafic magmas. "Young" tonalite, which postdates postdates some some encompass a broad range of felsic to mafic magmas. "Young" tonalite, which supracrustal the Nevison, Nevison, Righteye, Righteye, Wasp, Wasp, Bow, Bow,and andHardtack Hardtackintrusions. intrusions. The TheLittle Little supracrustal rocks, rocks, occupies occupies the Eye stock is composed of homblendite and diorite. Granodiorite and granite occur in the Diversion, Eye stock is composed of hornblendite and diorite. Granodiorite and granite occur in the Diversion, Margaret, Margaret, Bewag, Bewag, Eye-Dashwa, Eye-Dashwa, and and White White Otter Otterfelsic felsic intrusive intrusive centres. centres. 'Old" tonalite is so-named because it is the dominant " O l d tonalite is so-named because it is the dominant lithology lithology of of the the basement basement complex complex upon which rocks of the Steep Rock Group were deposited. Along northeastern margins upon which rocks ofthe Steep Rock Group were deposited. Along northeastern marginsof of the the Steep Steep Rock of several metres to to metasandstone metasandstone and and Rock belt, belt, the the "old" "old" tonalite tonalite is is gradational gradational over over distances distances of several metres meaconglomerate at the base of the Steep Rock Group. Here the plutonic basement is tan-brown in meaconglomerate at the base of the Steep Rock Group. Here the plutonic basement is tan-brown in colour, shear zones zones and and abundant abundant metagabbro metagabbro dykes. dykes. colour, schistose, schistose, highly highly fractured, fractured, and and transected transected by by shear The dykes are are fewer fewer and and the the "old" in the The metagabbro metagabbro dykes " o l d tonalite tonalite is is less less intensely intensely foliated foliated in the central central Marmion this tonalite, tonalite, collected collected near the Ontario Ontario Hydro Marmionbatholith batholith(Marmion (MarmionLake Lakearea). area).A Asample sampleof ofthis generating station, has has aa U/Pb generating station, Ma (Don (Don Davis, Davis, Royal Royal Ontario Ontario Museum, Museum, U/Pb titanite titanite age age of of 2953 2953 Ma pers.comm., 1987). Granodiorite of the Margaret and Diversion stocks intrudes the northern northern and and pers.comm., 1987). Granodiorite of the Margaret and Diversion stocks intrudes the southern southern margins margins of of the the Marmion Marmion batholith. batholith. "Old" "Old" tonalite tonalite is is typically typically mediummedium- to to coarse-grained, coarse-grained, foliated, foliated, and and inequigranular inequigranular to to porhpyritic. quartz (25%), (25%), and andbiotite biotite(20%). (20%). Plagioclase Plagioclase and porhpyritic. It is composed composed of plagioclase (40%), quartz biotite are extensively altered to epidote, sericite, and chlorite in shear zones and biotite are extensively altered to epidote, sericite, and chlorite in shear zones and adjacent adjacent to to the the Steep Steep Rock Rock belt. belt. Sedimentary SedimentaryRocks Rocks The Rock Group Group and and consists consists of of pebble pebble and and cobble cobble The Wagita Wagita Formation Formation forms forms the the base base of of the the Steep Steep Rock conglomerates interbedded with with poorly poorly sorted sorted sandstones sandstones conglomerateswith withangular angularto to subrounded subrounded igneous igneous clasts clasts interbedded and fine-grained chioritic in thickness thickness from from 0 0 to to 150 chloritic layers. The clastic clastic sequence varies in 150 m and and is is overlain overlain by by carbonates. carbonates. The by dark dark kerogen The Mosher Mosher Carbonates Carbonates are are well well banded banded with with the the layering layering accentuated accentuated by kerogen streaks silica-rich ridges ridges at at some some locations. locations. The The laminated laminated carbonates carbonates streaks or millimetre-scale elevated silica-rich are are commonly commonly brecciated brecciated where where they they are are spatially spatially associated associated with with fault fault zones zones and and mafic mafic dykes. dykes. Calcite, and brecciated brecciated units, units, although although the the ankerite and dolomite dolomite are are present in both the laminated and Calcite, ankerite breccias Stromatolites are breccias often often have have an anadditional, additional,late-stage late-stagedolomitic dolomiticpore-filling pore-filling cement. cement. Stromatolites common forms dominating dominating in in the the lower lower portions portions and common throughout the carbonate carbonate unit, with smaller forms larger mounds, 33 m m in in diameter, diameter, becoming becoming abundant abundant near the upper contact (Wilks and Nesbit, 1988). very irregular irregular upper upper contact contact 1988).The Theentire entirecarbonate carbonateassemble assembleisisup upto to 500 500 m m in thickness with a very which which may may be be karstified. karstified. A rock" overlies the A 100 100to to 300 300 m m thick thick succession successionof of manganiferous manganiferous strata strata termed termed "paint "paint rock" overlies the Mosher Jolliffe Ore Zone, Zone, consists Mosher Carbonates. Carbonates. This Thissuccession, succession,which whichforms formsthe thelower lower unit of the Jolliffe consists of of an an of of an earthy, earthy, poorly poorly consolidated consolidated mixture mixture of of goethite, goethite, hematite, hematite, chert, chert, kaolinite, kaolinite, illite, illite,calcite, calcite, gibbsite gibbsite and and pyrolusite pyrolusite (Huston (Huston 1956). 1956). The Thepaint paintrock rockisisoverlain overlainby by the the upper upper unit unit of of the the Jolliffe Jolliffe Ore Ore Zone, Zone, the the Goethite GoethiteMember, Member, which, like like the paint rock, is composed of of goethite goethiteand and hematite, hematite, but versus 5%, 5%, respectively). respectively). The Goethite Goethite Member, Member, which which but has has aa lower lower manganese manganesecontent content(3.8% (3.8%versus is is 50 50 to to 100 100m m thick, thick,occurs occursboth bothas asbrecciated brecciatedmasses masses and and alternating alternating layers layers of goethite goethite and and chert chert (McIntosh mafic to ultramafic pyroclastics and minor (Mclntosh 1972). 1972).The The Goethite Goethite Member is is overlain by mafic thin thin flows flows of of the the Dismal Dismal Ashrock. Ashrock. �and Nisbet Nisbet (1 (1988) suggest the the depositional depositional environment environment of ofthe small Wilks and 988) suggest the basal basal clastics elasticsis is a small alluvial fan fan with alluvial with aa fluvial fluvial system system that that has has incised incised and and backfilled backfilled channels channels into into the the underlaying underlaying Marmion Complex. Complex. As Marmion As clastic clastic deposition deposition in in the the area area ended, ended, carbonate carbonate began to accumulate in a shallow marine setting. setting. The depth is indicated indicated by byprobable probablegypsumpseudomorphs, gypsum pseudomorphs,possible possible shallow The shallow shallow depth desiccated ripples, ripples, and and polygonal polygonal cracks cracks on on large (Wilks and and Nisbet, desiccated large stromatolites stromatolites (Wilks Nisbet, 1988). 1988). Stromatolite sabkha to Stromatolite morphology may reflect adaptations to various water depths ranging from sabkha subtidal (Wilks (Wilks and and Nisbet Nisbet 1988). 1988). The of the the carbonate carbonate assemblage assemblage suggests suggests an an subtidal The karstified karstified surface surface of interval of subaerial exposure that caused dissolution of the upper units. It is also possible that acidic interval subaerial exposure dissolution upper units. It is also possible that acidic pile and and dissolved dissolved the the carbonates. carbonates. In solutions moved downward through the sediment pile In either either case case the manganiferous manganiferous paint represent residual residual deposits deposits left leftbehind behindafter after carbonate carbonate dissolution. dissolution. paint rock may represent published concerning concerning the the origins origins of ofthe theoverlying overlyingJolliffe JolliffeOre OreZone. Zone. The The alternating alternating layers layers Little is published unit is a classic classic iron iron formation; formation; modified modified through through dissolution dissolution or or as as of chert and Goethe suggest this unit paleosol. aa paleosol. Volcanic Rocks Formation has has been been Volcanic Rocks The Thestratigraphy stratigraphyand andpetrography petrography of of the the Dismal Dismal Ashrock Ashrock Formation Komatiiticlapilli lapillituff tuff makes makesup up over over 80% 80% of of the the described by by Schaefer described Schaefer and Morton Morton (1991). (1991). Komatiitic formation, the remainder comprising comprising lenses lenses of komatiitic komatiitic volcanic volcanic breccia, breccia,komatiitic komatiiticvolcaniclastic volcaniclastic formation, sandstone and siltstone, and mafic to to ultrarnafic ultramafic lava lava flows. flows. The rocks are classified classified as as komatiites komatiites as defined defined by by Arndt Arndt and and Nisbet Nisbet (1 (1982) although spinifex spinifex texture texture is is rare. rare. Wilks (1986) recognized recognized as 982) although possible pseudomorphs after spinifex layering layering' in in one one lava lava flow, flow, and and Schaefer Schaefer and Morton Morton (1991) (1991) possible described lapilli fragments. The nvroclastic pyroclastic rocks of of the the Dismal DismalAshrock Ashrock described micro-spinifex micro-sninifex texture in lanilli Formation thought to have formed by explosive explosive volcanism volcanism caused causedby byultramafic ultramaficmagma magmaentering entering Formationare are thought water-saturated sediments Formations (Schaefer water-saturated sedimentsof of the the Mosher Mosher Carbonate Carbonateand and Jolliffe Ore Zone Formations (Schaeferand Morton, 1991). 1991). The Thetop topof ofthe the Dismal Dismal Ashrock Ashrock Formation Formation is in most places tectonised or invaded original stratigraphic stratigraphic relation-ship relation-ship occurs between between the the Dismal Dismal Ashrock Ashrock Formation-and Formation-and by sills but an original al., 1992; Tomlinson Tomlinson ct ct al., al., 1996% 1996a; TomlinTomlinthe Witch Bay Formation near Strawhat Strawhat Lake (Stone et al., son, 1996). 1996). The Witch Witch Bay Formation dominates Rock greenstone greenstone belt belt and and is is aa sequence sequence of of The dominates the Steep Rock mainly mafic mafic lavas lavas comprising comprising up up to to 80% pillow pillow lavas. lavas. Flyaloclastite and massive massive lava lava flows flows also also mainly Hyaloclastite and beds of of felsic felsic pyroclastic pyroclastic volcanics. volcanics. The occur along with rare beds The volcanics volcanics have have in places been highly suggested that the original thickness thickness was was likely likely to to approach approach 55km kmbased based folded. Stone et al. (1992) suggested of pillow pillow lavas lavas at at the the south south end end of of Steep SteepRock RockLake. Lake. The Witch Bay on a homoclinal sequence of Formation is is overlain by by intermediate to felsic felsic volcanics volcanics whose whose age age and and contact contact relationship relationship with with Formation intermediate to the underlying predominantly mafic mafic sequence sequence is unknown. - A. Finlayson and and Lumby Lake Greenstone Belts Finlayson Early reconnaissance surveys surveys were were conducted conducted in in the the Lumby Lumby Lake Lake area area by by the the Geological Geological Early Canada in the late andthe thearea areareceived receivedconsiderable considerableattention attentionfrom fromprospectors prospectors Survey of Canada late 18001s, 1800's, and 890ts.L. L.F.F.Kindle Kindletraversed traversedthe thearea areain in 1937 1937for forthe theG.S.C. G.S.C.and andthe therocks rocksof ofthe thebelt belt were were in the 11890's. by Jackson (1985). mapped for the Ontario Ontario Geological survey by Woolverton (1960) and again by Volcanic Rocks Volcanic mafic lava lavaflows flowspredominating. predominating. These These Volcanicrocks rocks dominate dominate the belts, with mafic commonly have massive lower portions and pillowed upper portions and are rarely capped by commonly have massive portions and pillowed upper portions and are rarely capped by brecciated flow flow tops. tops. Individual flows (ca. (ca. 44 m ni thick) by thin thin units thick) are are often often separated separated by units of of iron iron brecciated Individual flows �formation and and iron iron rich rich material material is is also also common commonbetween betweenpillows. pillows. Variolitic Variolitic lavas lavas are are found found in in the the formation upper portion of the stratigraphy. upper portion of the stratigraphy. Two komatiite komatiite horizons horizons occur occur in in the the northern northern half half of ofthe thebelt. belt. The The main main komatiitic komatiitic sequence sequence Two is 120 m thick and includes numerous komatiite flows, pillowed and hyaloclastite portions of flows, flows, is 120 m thick and includes numerous komatiite flows, pillowed and hyaloclastiteportions of variolitic intervals, subordinate mafic flows and inter-flow sediment comprising chert and iron variolitic intervals, subordinate mafic flows and inter-flow sediment comprising chert and iron formation (Tomlinson et al., 196b). Komatiite flows are 4 to 13 m thick with cumulate bases and formation (Tomlinson et aL, 196b). Komatiite flows are 4 to 13 m thick with cumulate bases and spinifex-textured tops. tops. This can be be traced traced for for ca. ca. 13 13 krn km along along spinifex-textured This predominantly predominantly ultramafic ultramafic sequence sequence can strike and and occurs occurs on pluton but but itit thins thins to to the This main main strike on either either side side of of the the Van Van Nostrand Nostrand pluton the east. east. This komatiite overlain by by further further mafic maficflows flowsand andiron ironformation. formation. An An upper upperkomatiitic komatiitic unit unit komatiite sequence sequence is is overlain is present east east of of the the Van Van Nostrand Nostrandpluton, pluton, near near the the top top of of the the stratigraphy. stratigraphy. This upper komatiitic komatiitic is present This upper unit varies varies along along strike. 20 m m thick thick bedded beddedpyroclastic pyroclasticunit unit(similar (similar unit strike. To Tothe the east east itit comprises comprises aa Ca. ca. 20 to the the Dismal Dismal Ashrock Ashrock Formation) Formation) interbedded interbedded with with thin thincarbonates carbonatesand andiron ironformation. formation. West West of ofthis this to is ca.20 20m mthick thickcoarse-grained, coarse-grained,unsorted unsortedand andmassive massiveultramafic ultramaficpyroclastic-flow pyroclastic-flowunit. unit. Both Both units units is aa ca. overlie a prominent prominent ca. l0-m-thick, chert-rich chert-rich iron iron formation formation and and are are themselves themselves overlain overlain by by further further overlie a ca. 10-m-thick, amygdaloidal amygdaloidal mafic mafic lavas. lavas. The main sequence in the the southern southern half half of of the the belt belt isis less lesswell wellknown. known. Fine-grained Fine-grained pillow pillow The main sequence in lavas are common but the exposure is not good enough to establish flow thickness or lavas are common but the exposure is not good enough to establish flow thickness or flow flow stratigraphy. phenocrysts up upto to22cm cmacross. across. Poorly Poorly exposed exposed stratigraphy. Some Somelava lava units units contain contain plagioclase plagioclase phenocrysts komatiite flows unknown extent near the the top top of ofthe thestratigraphy stratigraphy(which (whichwere werefirst firstrecorded recorded komatiite flows of of unknown extent occur occur near by Jackson, I 985a). Thin felsic tuff units (10-20 m) occur intermittently in the southern stratigraphic by Jackson, 1985a). Thin felsic tuff units (10-20 occur intermittently in the southern stratigraphic sequence. sequence. Sedimentary Rocks Sedimentary RocksAAthin thinsuccession successionofoffelsic felsicmetavolcanic metavolcanicunits units and and matasediments matasediments occurs occurs approximately halfway halfway through through the the volcanic volcanic sequence sequenceand and aa thicker thicker assemblage assemblage of of elastics clastics and and approximately chemical sediments caps the In the the Finlayson Finlayson Lake Lake area area the the lower chemical sediments caps the assemblage. assemblage. In lower clastic clastic wedge wedge thickens and and coarsens coarsens to to the the southwest, and is is gradational in this this direction to aa felsic thickens southwest, and gradational in direction to felsic volcanic volcanic assemblage (Figure (Figure 4). Beds vary in thickness assemblage 4). Beds vary from from centimetre-to centimetre-to metre-scale metre-scale in thickness averaging averaging approximately 70 Coarse-grainedsand sand with with felsic felsic volcanic-clast pebble bands bands approximately 70 centimetres. centimetres. Coarse-grained volcanic-clast pebble dominates, except except in in volcanic volcanic proximal proximal areas areas where units gain gain in in importance. importance. dominates, where the the conglomeratic conglomeratic units Clastic mud drapes drapes and and mafic centimetre-scaleinterbeds. interbeds. The The sandstones sandstones are are Clastic mud mafic tuffs tuffs rarely rarely form form centimetre-scale massive and and nongraded. nongraded. Bed the metasedimentary massive Bed thicknesses thicknesses decrease decrease to to the the northeast northeast where where the metasedimentary succession thin and sporatically present. succession is thin �Little Falls! Little Falls 1Finlayson Finlayson Lumby Lumby i V A . . "V V v v Oo:,.. . V " "V V v v V oO...... A . VV . VV V V v v v v v + ++ + +±± + 500 m V V V V V V V V V v V v VV v v V v ; .. v v V V V V vV vV v V V V v Scale V V V V V V V vV V v ±±+ V vV vV ±± ± ± ++± + + + V V IV V V ~ v v v v l'V " V " V v Vv Vv v v I V vV I , 61 Iv V V v Vv V v v V V V V v v .....:::...: .... ...-.... V V V v V V v V V V V V v v v vv v v. v v vV vV "V v V " V v V v V v V vV "V "V vV v V vV v V v V v V v V v vv v v v v v v v vV vV vV vV vV vV vV vV vV vV v v V v K\"+";;v:v V v v V v v v v + + v + + + + + v v v v v v + + + + + + + V V V + + + + + + + v+ v + + + + + Figure Figure 4. 4. V ~ I" vV vV vV vV vV vV vV vV vV vV vV vV vV vV vV v ~ v V v V v V v V v V v V v V v V v V v V vV vV vV vV vV v ~ lv vv vv vV vV vV vV vV vV vV vV vV vV vV vV vV v l v v v v v v v v v v v v v v v v I lYlafic Volcanic Volcanic Mafic Rocks Rocks AA Felsic Volcanic Faisic Volcanic Rocks Rocks 1+ +1 Intrusive lntruslveRocks Rocks IV V '' v IV ±1 4 km Iron Iron Formation Formation Carbonate 11111111111 Carbonate Lo0oal Conglomerate Conglomerate Pf1 Sandstone/Siltstone Sandstonepiltstone A J Agglomerate Agnlomerate .. l;".;,vvy .:,.v V + + - " - V V V v A V V v + V " " v + v+ + Reconstruction of Finlayson andLumby -.sect;anal Reconstruction of the the units unitsin in the Finlayson andLumbyLakes Lakesarea areain incross trim-sectional view. view. The The stratigraphy stratigraphyisIs discussed discussedin in the thetext. text. These sediments sediments represent represent aa clastic clastic debris apron formed adjacent to, and deriving sediment These sediment Sedimenttransport transport was was via via subaqueous subaqueous sediment-water sediment-water dispersions dispersions from, a felsic volcanic centre. Sediment with to keep keep material material in in suspension. suspension. This with dispersive dispersivepressure pressure probably acting acting as an important force to This requires a high slope, slope, possibly higher higher than 10 in the the area areathe theflows flowswere weregenerated. generated. Subarial Subarial requires 10 degrees, in mafic mafic volcanism volcanism was was also also active activeduring during this this depositional depositional interval. interval. The Lake area area is is also also laterally laterally transitional transitional metasedimentary belt belt present present in the Lumby Lake The lower lower metasedimentary to felsic centimetres, and felsic volcanics. volcanics. Sandstones Sandstonespresent presenthere hereare are more more thinly bedded, averaging 15 centimetres, do mafic ash interbeds. They nongraded varieties exist. do not contain containmafic ashinterbeds. Theyare aremassive, massive,and and both both graded graded and andnongradedvarieties exist. The elastic with cherts cherts and and carbonates. carbonates. The cherts are laminated laminated on on the the clastic sequence is intercalated with centimetrerecrystallized with with fractures, fractures, which may centimetre-and and subcentimeter-scale subcentimeter-scaleand and the the carbonates carbonates are recrystallized represent represent original original bedding, bedding, spaced spaced on on the the decimeter-scale. decimeter-scale. This provides very little information information on ondepositional depositionalenvironment. environment. The sandstones sandstones This sequence sequence provides suggest imply aa water water suggest deposition depositionby by grain grainflows flows and and high-density turbidity turbidity currents, currents, but this does not imply depth. Personal Personalexperience experienceindicates indicatesthat thatArchean Archean carbonates carbonates associated with cherts usually form in shallow shallow water water environments, environments, though though this this remains remains speculative. speculative. The capping cappingsedimentary sedimentarysequence sequencepresent present at Finlayson The Finlayson Lake conformably conformably overlies overlies pillowed and massive mafic volcanic pile in the volcanic rocks in the the southern and central area and an agglomeratic pile north. Basal by centimetre centimetre thick thick DE DE Basalcherts chertsand andoxide oxidefacies faciesiron iron formation formation are are succeeded upwards by turbidites. turbidites. These gradually gradually thicken and coarsen coarsen up sequence sequence to decimeter decimeter thick, graded graded beds beds Above this this zone zone internal, internal, scallop-shaped scours, composed of medium-grained sand. Above scours, filled filled with coarse-grained sand, appear in the beds. These Theseare areoverlain overlainby by pebble pebble and and cobble cobble conglomerates conglomerates with sandstone sandstone interbeds interbeds and lenses lenses (Figure (Figure 5). 5). The coarsening coarsening upward upward trend trend in in this this zone is interrupted grainsize to medium-grained medium-grained turbidites, turbidites, which again gradationally gradationally interruptedby by abrupt abruptdecreases decreasesin grainsize coarsen coarsen upwards upwards to to conglomerates. conglomerates. + + v �m. F-6 200 S. s. graphite graphite sulfides sulfides C. C. ch e ii chert 9. 9. 150 F-5 1I-I- +H Diabase Diabase 1 Conglomerate Conglomerate Sandstone with with lil Sandstone L°o°o°S! I.E I.F. Iron IronFormation Formation ________ [i.cJ j1 - ________ L: fl—El :1 L _______ H 1 bc?ed ________ 100 Al I scours scours Sandstone Sandstone ( turbidites ) (turbidites) Siltstone Siltstone Slate SlateCouplets Couplets Slate Slate MaficVolcanic Volcanic Mafic Rocks Rocks Agglomerate Agglomerate F-4 F-2 F-i c.Is. ___ oJ c..,g.js. 0 FigureS. sections through Figure 5. Stratigraphic Stratigraphicsections throughthe theuppersedimentary uppersedimentaryunit unitononFinlayson FinlaysonLake. Lake.Section Section F-i logged other F-1was was loggednear nearthe thenorth-east north-eastend endofofthe thelake. lake.The The othersections sectionsare arespaced spaced along approximately iO10 km alonga aline linerunning running approximately krntotothe thesouth-west south-westand andending endingwith withF-6 F-6inin the lake. system braidedfault systemlongitudinally longitudinallycutting cuttingthe thebelt belt thesouthern southernportion portionofthe of the lake.AAbraidedfault inintwo twonear nearitsitscenter centerdownsteps downstepsthe thestratigraphy stratigraphyininaanorth-east north-eastdirection. direction. 1 I < 1 I �3,000 Ma 2,925 Ma ?7 A v V V v Vv v V v " V V .—C?\ 1 Little LittleFalls FallsI1Finla Finlayson yson V I? I? — —— r fle?.o.o.c?1o.? OOoooo C v ?1 ? I V v V v V v Lumby Lumby vV / Iron Iron Formation Formation IJJJfflJJCarbonate Carbonate J'I Conglomerate Conglomerate Sandstone Slate % H I Agglomerate Siltstone I/Slate Agglomerate ..... Sandstone ____ ____ Siltstone IAAI Felsic F e M cVolcanic VolcanicRocks Rocks Mafic VolcanicRocks Rocks l"I Mafic Volcanic Figure for the Figure6.6. Sequential Sequential environmental environmental reconstruction reconstruction of of the the depositional depositional environments environments for the lower sedimentary units of the the Finlayson Finlayson and lower sedimentary sedimentary units units(A) (A) and and upper uppersedimentary units (B, C) of and Lumby Lumby Lake greenstone greenstone belts. Processes Processes are arediscussed discussedin in the the text. text. Il �This After cessation cessation of of mafic This succession succession represents represents shoreline shoreline progradation progradation (Figure (Figure 6). 6). After mafic volcanism a starved succession of chemical sediments was deposited. The first clastics delivered volcanism a starved succession of chemical sediments was deposited. The first clastics delivered to silts transported transported by by low-density low-density turbidity turbidity flows. flows. This This probably probably represents represents to the the area area were were clays clays and and silts prodelta debris, though sediment transport via storm currents is possible. Shoreline progradation prodelta debris, though sediment transport via storm currents is possible. Shoreline progradation caused caused the the coarsening coarseningupwards upwardssuccession successionto to form, form, culminating culminatingin in deposition depositionin in depths depthseffected effectedby by wave induced scour. Delta top sands and gravels cap the sediment pile and show the effects lobe wave induced scour. Delta top sands and gravels cap the sediment pile and show the effects of of lobe outbuilding outbuildingand andabandonment, abandonment,with withsubsequent subsequentsubsidence subsidenceinduced induced flooding floodingand and aa return return to to deeper deeper water water conditions. conditions. This Thisisisfollowed followedby byaaminor minorcoarsening coarseningupward upward sequence sequenceformed formedby by another anotherstage stage of is capped capped by by aa final final flooding flooding event. event. of delta delta lobe lobe outbuilding outbuildingin in the the area area and and the the entire entire sequence sequence is The The sedimentary sedimentary sequence sequence capping capping the the assemblage assemblage of of mafic mafic volcanic volcanic rocks rocks in in the the Lumby Lumby Lake thick sequences sequences ofboth ofboth clastic and chemical chemical units units (Figures (Figures 5). 5). WayLake greenstone greenstonebelt belt consists consistsof of thick clastic and up up directions directionsare are ambiguous ambiguous though though itit is is more more likely likely that that the the iron iron formation formation and and chert chert assemblage assemblage overlies overlies the the elastic clastic assemblage. assemblage. AAthin thinzone zoneof ofchert chertand andiron ironformation formationseparates separates the the volcanic volcanic sequence sequence from from the the clastic clastic sediments. sediments. The Theclastics clasticsconsist consistof of decimeter-scale decimeter-scaleturbidites turbiditeswith with metremetrescale the map map area. area. Structural scale conglomeratic conglomeratic interbeds interbeds in in the the western western portion portion of of the Structural complexities complexitiesand and scarcity if aa coarsening coarsening upwards upwards trend trend exists. exists. In scarcity of of outcrops outcrops prohibited prohibited ascertaining ascertaining if In the the west west the the elastic clasticsuccession successionis isoverlain overlainby by thinly thinly laminated laminatedcarbonates carbonates with with submillimeter-scale submillimeter-scale clay clay drapes drapes commonly commonly developed developed between between laminations. A Avery very chert-rich chert-rich iron formation formation assemblage assemblage overlies the carbonates in the west, lies on clastics in the central area and directly overlies the carbonates in the west, lies on clastics in the central area and directly overlies the the volcanic volcanic succession successionin inthe theeastern easternoutcrop outcroparea area(Figure (Figure4). 4). Scarcity of outcrop Scarcity of outcrop in in this this belt belt inhibits inhibits aa detailed detailed reconstruction reconstruction of of depositional depositional environments. environments.After Aftercessation cessationof ofvolcanic volcanicactivity activityaaclastic clasticsediment sedimentstarved starved interval interval was was followed followed by by deposition depositionvia via high high and and low low density density turbidity turbidity currents. currents. Conglomeratic Conglomeraticunits unitsprobably probably represent represent the the most most strand-proximal strand-proximaldepositional depositional events. events. This Thisisisfollowed followedby bythe thesequence sequencebecoming becomingrapidly rapidly sediment sedimentstarved starvedwith withcarbonates carbonatesdeposited deposited in in the the shallower shallower areas, areas, in in the the west west where where the the strandstrandproximal and cherty cherty iron iron formation formation in in deeper deeper areas. areas. With proximal conglomerates conglomerates are are located, located, and With increasing increasing water migrated westward westward until until iron iron formation formation diachronouscontact contactwith with the the iron iron formation formation migrated water depth depththe the diachronous was was being being deposited depositedthroughout throughoutthe theentire entirearea. area. Structure Structure The from mainly mainly The east-trending east-trending Quetico-Wabigoon Quetico-Wabigoonboundary boundary separates separatesturbidites turbiditesto the south from volcanic rocks to the north and is a first order lithostrnctural feature in the area. Regional volcanic rocks to the north and is a first order lithostructural feature in the area. Regional juxtaposition subduction-related accretion accretion of ofthe juxtapositionof ofthe thecontrasting contrastinglithologies lithologieshas has been been attributed attributed to subduction-related the Quetico sedimentary prism against the Wabigoon volcanic arc about 2695 Quetico sedimentary prism against the Wabigoon volcanic arc about 2695 Ma Ma ago. ago. Quetico Quetico metasediments metasedientshave have pervasive pervasive easterly easterly structural structural trends trends and and isoclinal, isoclinal, mainly mainly easteast- facing facing folds folds possibly possibly generated generated by by strong strongdextral dextraltranspression transpression after after accretion. accretion. In contrast, contrast, Wabigoon WabigoonSubprovince Subprovinceshows showsmegascopic megascopicoval ovalstructures structuresdefined definedby by concentrically concentricallyzoned zoned structural structural trends trends in in gneisses gneissesand and supracrustal supracrustal rocks rocks that that envelope envelope felsic felsic plutons. plutons. Metavolcanic belts are are situated situatedbetween between some someoval oval structures. structures. This Thisstructural structuralpattern pattern may may have have originated originated due to rise of granites overlying granitesand and gneisses gneissesin incentral centralparts parts of of oval oval structures structures attendant attendant with slumping of dense overlying supracrustal supracrustalrocks rocksinto intomarginal marginaltroughs troughs(metavolcanic (metavolcanicbelts). belts). The Theaxes axesof ofsix sixmajor majorfolds foldsextend extendalong alongthe the central central Finlayson Finlayson belt belt whereas whereas the the Steep SteepRock Rock belt belt shows showsfewer fewerfolds foldsand andaa thick thick east-younging east-youngingsequence sequenceof of pillow pillow lavas lavas that that may may be be aa deformed deformed lava lavacone. cone. �A complex system system of of oblique-slip and and normal normal faults faults and and metagabbro metagabbro dykes dykes transect transect the the A Marmion batholith. batholith. The Samuel fault fault appears appears to to have have The dip-slip, dip-slip, probably probably reverse reverse displacement displacement Samuel uplifted a segment segment of the batholith batholith into into the the central central Steep SteepRock Rockbelt. belt. Displacements Displacements of of reverse reverse sense sense uplifted are also likely to have occurred on the Atikokan fault, which is conformable conformable with the the upper upper ashrock ashrock transcurrent fault fault in in the the vicinity vicinity of of contact in the Steep Rock Mine area. Clear Clear evidence evidence of a major transcurrent the Quetico-Wabigoon Quetico-Wabigoon boundary has not been found. Metamorphism Metamorphism Supracrustal belts of Metavolcanic belts belts have Supracrustal belts of the the Atikokan Atikokan area areaare aremetamorphically metamorphically zoned. zoned. Metavolcanic greenschist assemblages (chlorite-epidote-plagioclase-calcite+actinolite) and and greenschist assemblages at their cores (chlorite-epidote-plagioclase-calcit&actinolite) amphibolite assemblages assemblages at the margins margins (hornblende-plagioclase-biotite-ilmenite-sphene). (hornblende-plagioclase-biotite-ilmenite-sphene). amphibolite Metamorphic grade grade does does not not change but increases Metamorphic change abruptly abruptly at at the the Quetico-Wabigoon Quetico-Wabigoon boundary boundary but increases garnet, and and staurolite staurolite isograds. isograds. Pressuresteadily southward as defined by biotite, Ca-amphibole, garnet, Presswetemperature conditions conditions in in the the garnet garnet zone zone of of Quetico Quetico metasediments metasediments fall fall in in the the upper upper greenschist greenschist temperature facies facies (P-230-430 (P230-43O MPa, MPa,T-419-577T). T4l9-577°C). Except for greenschist greenschist assemblages assemblages in the Marmion Marmion batholithadjacent batholith adjacent to to the the Steep Steep Rock Rock belt, belt, Except tonalites and gneisses show amphibolite conditions (P=560 (P=560 MPa, MPa, T=7OO0C). T=700°C). tondites The high metamorphic grade of of gneisses gneisses within within oval oval structures structures is is attributed attributedto totheir theirhaving having risen from deeper crustal levels, as well as proximity to felsic plutons. Thermal anomalies risen from deeper cmstal levels, as well as proximity to felsic plutons. Thermal associated with oval structures associated structures and and plutons, plutons, superimposed superimposed on regional burial metamorphism, metamorphism, may may be responsible responsible for the metamorphic zonation of these supracrustal belts. metamorphic zonation supracrustal Tectonic Environment Environment Tectonic Nisbet (1988) were were the the first first to to attempt attempt to to define definethe the tectonic tectonic environment environment that that Wilks and Nisbet Mesoarchean Mesoarchean strata strata in the Atikokan Atikokan area area formed in. They believed that a rift, formed by extension extension of the Marmion Marmion block, is the most most probable probable tectonic setting for the the Steep Steep Rock Rock Group. Group. This explains explains the outcrop outcrop patterns patternsof of the the Steep SteepRock Rock and and nearby nearby Lumby Lumby Lake Lake successions successionsas as having having formed formed on on two two adjacent tilted tilted blocks. blocks. Alternatively, may have have taken taken place place on on aa stable stable divergent divergent adjacent Alternatively, sedimentation sedimentation may continental margin with all or only the lower lower part of of the the Wagita Wagita Formation Formation representing synrift symift deposits and the remainder of the succession up to and including the Joliffe Ore Zone reflecting deposition on a post-fift post-rift stable shelf. shelf. If the overlying Witch Bay Bay volcanics volcanics are areautochthonous, autochthonous,they they deposition record renewed extension. extension. A study by Thurston and Chivers (1990) put the Steep Rock and Lumby Lake Belts into a A * group they they termed sequences. These These consist, consist,from frombase basetoto top, top, of of quartz group termed platform platform sequences. quartz arenite arenite ± carbonate, oxide facies iron formation and komatiitic to tholeiitic volcanic rocks. They strornatolitic strornatoliticcarbonate, oxide facies formation komatiitic to tholeiitic volcanic rocks. They compare these with plateform sequences at modern passive margins. compare sequences at modem at the the base base of of the the Steep Rock Fralick and King (1995) correlate the sedimentary sequence at Group with sediments at the top of the Finlayson-Lumby Lake Lakevolcanic volcanicsuccession. succession. This implies chronologicallyseparated separatedby byaasedimentation sedimentationevent. event. They They also also two periods of mafic volcanism chronologically record subsidence of of an an oceanic oceanic plateau plateauand andthe thelong longperiod period stress that the sedimentary sequences record plume driven volcanism is consistent consistent with with coupling coupling of ofthe thearsenosphere arsenosphereand andlithosphere. lithosphere. If If they they of plume are correct this would plate tectonics during the the early are would negate negate the the operation operation of of modern-style modem-style plate tectonics during Mesoarchean. Mesoarchean. �Hollings et a1 a! (1998) agree with Fralick and and King's King's (1995) stratigraphic interpretation but advance a more elaborate model model to to explain explainthe thegeochemistry geochemistryof ofvolcanic volcanicand andintrusive intrusiveunits. units. They They which is mainly mainly represented represented by by the the believe that an arc arc developed, developed, due to subducting lithosphere, which deformed and eroded remnants of the intrusive tonalites. tonalites. Failed subduction of an ocean plateauridge complex al, 1998). complex juxtaposed the the arc arc intrusives intrusives with the metavolcanics (Hollings et a], 1998). Kusky and Hudleston (1999) agree with with Hollings Hollings et et d al (1998) (1998)that thatthe thetonalites tonalitesrepresent representan an sedimentary succession formed formed aa shallow shallow water water carbonate carbonate eroded arc remnant, but suggest that the sedimenw platform during arc rifling and the Dismal Ashrock is an allochthonous melange overridden by rifting Dismal allochthonous ovemdden by structurally structurally emplaced emplaced arc arc volcanics volcanics of of the the Witch Witch Bay Bay Formation. Formation. Based on extensive geochemical analysis of volcanic units Tomlinson et al(1999) al (1999) propose that the unfractionated high-Mg basalts basalts represent represent high unfractionated basaltic basaltic komatiites and spinifex-textured spinifex-textured high-Mg degree partial melts of the upper mantle. These are geochemically similar to lavas erupted forming empted forming degree These the modem Ontong-Java Ontong-Java oceanic plateau. Enriched Enriched basaltic basaltic komatiites represent a deep mantle plume source that has not been mixed with depleted Volcanism in in the the Steep Rock, has not been mixed with depleted mantle. mantle. Volcanism Rock, Finlayson and Lumby Lake belts most likely occurred in a continental setting and was probably proceeded by rifling rifting of of the continental continental crust. The Thestratigraphy stratigraphyof of the greenstone greenstone belts and evidence of magmatism may 70 Ma) Ma) indicates indicates that more than one pulse of plume magmatism of protracted protracted volcanism volcanism (ca. (ca. 70 have been involved (Tomlinson et a!, 1999). have been involved (Tomlinson et al, 1999). Obviously opinions tectonic setting the the succession succession developed developed in. The fieldtrip Obviously opinionsdiffer differas as to the tectonic will provide a form where these ideas can be discussed on the outcrop. provide a form where these �REFERENCES: REFERENCES: - Antevs, E.,l951, E.,l951, Glacial Glacialclays claysininSteep SteepRock RockLake, Lake, Ontario, Ontario,Canada; Canada; Geological Society Sooiety of America Bulletin, Bulletin,v. v.62, 62,nono.ID, 10,p. p. 1223-1262 1223-1262 Brain, Canadian Mining JJournal, v. 61, 61, p. p. 573.574. 573-574. 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Lithopmk Secretarm, Unwcrs8ty Rrilish Columbia. Colurnbi&PP. pp 29-35 . Hardy, R.M., R.M.. and R.F.,1960, Boulder in vvarved at Steep SteepRock RockLake, Lake,Ontario, Ontario,Canada; Canada;Geological GeologicalSociety SocietyofofAmerica AmericaBulletin, Bulletin,v. v. m c d clay at Hmdy, and Legget, L e ~ e tR.F.,1960, , Boulder 71,no. 71, no. I,1,p. p. 93-94. 93-94. of Steep RockImn Iron Mines Mines Limited; Limited; The kPrecambrian, 8-tO. Steep Rock m b r i a n , v.v.23, 23, P. p. 8-10. Hicks, H.S., 1950, 1950, Geology of the iron deposits of Huston, WI., Queen's University, Kii@ton, Kingston, Ontario. H u s t o ~W.J., ~ , 1956, 1956,The TheSteeprock St-pmck Manganiferous Manganifmus Foot-wall Foot-wall Paint; Paint; M.Sc. MSc. thesis. thesis. Q m e d s University, Indares. A, and Martignole, J.,1985, J..l985, Biotite-garnet geothermometryininthe thegranulite granulitefacie: fades: the the influence influenceof of Ti Ti and and Ai Al in Indares. A, and Martignole. 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Jolliffe, A,W,, Rock Lake, Lake, Ontario: Ontario: in in The The relatiomhip relationship of of rnineralimion mineralization to ofthe the Steep Sleep Rock Rock Group, Group, Steep Steep Rock lo Precambrian Prccmb"an Jolliffe, A.W., 1966, 1966,Stratigraphy Stratigraphy of stratigraphy in certain m mining ofOntario and Quebec, PrecambrianSymposium, Symposium,edited editedby byA.M. A.M.Goodwin, Goodwin,Geological Geological Association Association smtigraphy i n i n gareas m m of Ontarioand Qmebeo, Precambrian Paper No. No. 3, 3, p. p. 75-98. 75-98. of Canada, Special Paper Jolliffe, A.,W., oresof ofSteep Steep Rock Rock Lake: Lake: Economic Economic Geology, G d o g y , v.50, v. 50,no.4, "0.4. p.373-398. p.373-398. Jolliffe, A..W., 1955, 1955,Geology Geologyand andiron imnores c h e a n granitic updm K m i n m i , D.C.. D.C., Thivierge. Thivierge, R.H., RH.. and and Stone, Stone, D., Kaminent. D., 1988, Development Developmentof of aa camlwtic cataclasticfault faultmne zoneininan ankArchean graniticplulm pluton of of the the SSuperior structural, geochemical geochemical and andgeophysical geophysicalcharacte"stics: characteristics:AAmerican JournalofofScience, Science, v.v.288, 288, p.p.458.494. 458494. Province: smclural, mdJournal Lakespluton, ploton, Atikokan, Alikokan,northwestern norlhwestern Ontario, Canada; Canada; Kmineni, D.C., 1982,AAstudy sNdyofofrock mckalteration alterationininthe theEye-Dashwa Eye-Dmhwa Lakes Kansineni, D.C.. and and Dugal, Dugal, J.J.B., JIB., 1982, ('heroical Geology, v. 36, 36, p. p. 35-57. 35-57. Chemical Geology, v. Kmineni, D.C., and andStone, Stone, D.,1983, D.,1983, The The ages ages of fmcturos in tlse the Eye-Dmhwa o Mineralogy Kamineni, D.C., of fractures Eye-DashwaLakes Lakespluton. pluton.Atikokan, Atikokan, Canada; Canada;Contribuliom Contributionstto Mineralogy and Petrology, Petrology, v. v. 83, p. 237-246. and D., 1983, granite kKamineni, i n m i , D., 1983, Sulphur-isotope Sulphur-isolop~geochemistry gco~hemistryof fracture-filling xiacNre-filling gypsum mpaum in in an an-'Archean --A~chean granitenear near Atikokan, Atikokan,Ontario. Ontario.Canada: Canada: Chemical Geology Geology v.39.p.263-272. Chemical v.39.p.263-272. Kimberley, M.M.,and andSorbara, Sorbma,J.P., J.P..1976, Post-Archean weathering of pmceedings of of the the 1976 1976Geotraverse Geomve-=Kimberley, MM., 1976, Post-Arehean of Steep Steep Rock Rock Gmup GroupIron Iron Fornation: Formation: proceedings Conference, University University of Conference, of Toronto, Tomnto, Toronto, Toronto, Ontario, Ontario, p. p. 128-136. 128-136. �Lawson, AC., Lake, Ontario Canada, Canada, Memoir28, Memoir 28, P. P 7-15. A.C., Geological GeologicalSunYey SunYey011912, of 1912,The TheGeology Geologyof of Steeprock SteepmckLake, 7-15 Legget, MW., 1953, Ontario, Canada: Canada: Economic Economic Geology, Geology, v.v. ha% R.F., R.F., and and Bartley, B d e y , M.W., 1953,An An engineering engineering study study of of glacial glacialdeposits dewsits at at Steep Steep Rock Rock Lake, Lake, Ontario, 13-540. 48, 48. p. p. 5513-540. Miller, v. I2,p. 12,p. 304-317. 304-317 Miller, Wa., W.G.,1903, 1903.Iron lmnranges rangesofofnorthern northernOntario; Ontario;Ontario OntarioBureau Bureauof ofMines, Mines, v. Moore, Mcare, ES., E X , 1939, 1939,Geology Geologyand and ore oredeposits depositsof ofthe theAtikokan Atikokan area: area: Ontario Ontario Department Department of Mines, Mines, v. 48, 48, Pt. pt. 2, 2, P.p. 1-34 1-34(published (pblished 1940). 1940). Accompanied 48a, scale scale 1I inch inch to to II mile. Accompanied by by Map Map 48% mile. Moore, ES., Canada, Transaction Section 4,3rd 4,3rd series, v.32, E X ,1938, 1938,The TheSteeprock SteepmckSeries: Series: Royal Royal Society Society of ofcanada, series, v. 32,p. p. 11-23. 11-23, Morris, M.V., 1986, Geochemistry and tectonic seuing setting of the Steep Rock Rock greenstone greenstone belt, belt,Atikokan, Atikokan,Canada; Canada;BSc. B.Sc.thesis, thesis,Carleton CarletonUniversity, University, 1986, Geochemistry Ottawa, Oltawa,Ontario, Ontario,162p. l62p. Roberts, T,L. and Bartley, replacement in in deep deep seated seated iron iron ore deposits Lake Superior Superior region; Economic hnomic B d q . M.V, M.V, 1943, 1943. Hydrothermal Hydmthennal replacement dewsits of the Lake Geology, v' 38. Geology, v 38. p. p. 1-24. 1-24, their geology, geology, ppetrography, Schaefer, 5.J., S.J.. Morton, Morton, P., P., 1991, 1991. Two Two komatiitic komatiiticpyroclastic pymclastic units, units, Superior Superior Province, Fmvince, northwestern northwestern Ontario: their e m p p h y , and correlation. Canadian CanadianJournal Journal of of Earth EatthScience Science 28, 1455-1470. 1455-1470. Schaefer, Schaefer, S.J., 1989, 1989, AAcomparison comparisonofoftwo twoultramafic ultramaticpyroclastic pyroclasticrock rock units, units, northwestern northwestem Ontario: Ontario: Institute Institute of of Lake Lake Superior SuperiorGeology Geology Proceedings, v. 35, p. 77. Proceedings, Shklanka, Shklanka, R., 1972, 1972, Geology Geology of of the the Steep SteepRock RockLake Lakearea, area,District DistrictofofRainy RainyRiver; River;Ontario OntarioDepartment Department of ofMines Minesand andNorthern NorthernAffairs, Affiirs, Geological Report93, Report 93, I l4p. Smith, Sheet. Geological Survey of Canada, sscale Smith, W.H.C., W.H.C., and Mclnnes, W., 1897, Seine River Sheet. Suwey ofcanada, a l e I1:253 12.53440. 440, of America Bulletin, v. v.4, Smith, 4, p. p. 333-348. 333-348 Smith, W.H.C., 1893, 1893, The Archean Archean rocks rocks west of of Lake Superior; Geological Geologicd Society Society ofAmerica Smith, Smith, F.G., 1942, 1942, Notes Notes on on the the iron iron ores ores of of Steeprock Steepmck Lake, Lake, Ontario; Ontario; University Universityof of Toronto Toronto Studies, SNdies, Geological Geologid Series, Series, No. 47, Contributions Contributions to 1-75. to Canadian CanadianMineralogy, Mineralogy,p.p.771-75, Sniyth, Lake, Ontario; Ontario;American AmericanJournal JournalofofScience, Science,v.v.42, 42, p.p.317-331. 3 17-331 Smyth, H.L., H.L., 1891, 1891, Structural Structural geology of Steep Rock Lake, Stone, Stone, D., Kamineni, Kamineni, D.C., D.C., Brown, Brow, A., A., and and Everitt, Eveflit R.A., R.A., 1989, 1989. A A comparison comparisonof of fracture h t u r e styles stylesin in two two granitic graniticbodies bodiesof ofthe theSuperior Superiorprovince; province; Canadian Journal of Earth Sciences. Sciences. v. 26, p. 387-403, 387403. Canadian Stone, 1982, Fractures and fracmre fracture in in fillings fillings of of the the Eye-Dashwa Fye-Dashwa Lakes Lakes pluton, pluton, Atikokan, Atikokan, Ontario; Ontario; Canadian Canadian Journal Journal of of Stone, U.. D., and and Kamineni, Kamineni,D.C., D.C.,1982, Earth Sciences, Sciences, v 19, 19, p. 789-803. Stone, the Atikokan Canada, Map 1666A, Stone, D., Kamineni, Kamineni, D.C., D.C., 1989, 1989,Geology Geologyof ofthe Atikokan area, area, Ontario Ontario Geological Geological Survey Suwey of ofCanada, 1666A, scale 1:50,000. 1:50,000, Precambrian geology geology of of the Atikokan m area, Ontario. Geological Survey of Stone, Stone. D., D., Karnineni, Kamineni. D.C., D.C., Jackson, Jackson,M.C., M.C., 1992, 1992, Precambrian a, northwestern northwestern Ontario. Bulletin 405, 106 Canada, Bulletin I06 pp. 35, p.p. 131-141, 1941,Origin Tanton,T.L., 1941, Origin to the hematite deposits at Steep Rock Rock Lake, Lake, Ontario; Ontario;Royal RoyalSociety Societyof ofCan* Canada,Transactions, Transactions,v.v.35, 131-141. Tanton,T.L., Lake, Ontario; Ontario; Royal Royal Society Society of of Canada, Canada,Transactions, Transactions,Section Section4,4,v.v.20, Tanmn,T.L., 1926, 1926, Recognition Recognition of the Coutchiching near Steep Rock Lake, 20, p. 39-49. 3949. Tanton,T.L., of Canada, Canada,Transactions, Transactions,v.v.40. p. 103-112 103-112. Steep Rock Lake; Royal Society of 40. p. Tant0n.T.L.. 1946, 1946. The iron iron ore at Steep Tanton,T.L., 1927, 1927, Mineral Mineral deposits deposits of of Steep Steep Rock Rock Lake Lake map-area, maparea, Ontario; Ontario; Geological Survey Swwey of of Canada, Canada, Summary Summay Report, 1925, 1925,Pt. pt. C, C, p. p. Tanton,T.L., IC-lIC, IC-IIC. Secular variation variation in greenstone Canada. P.C., Chivers, Chivers, K.M., K.M., 1990, 1990, Secular Thurston, P.C., greenstone sequence development development emphasizing Superior Province. Province. Canada. Research 46,2148. 46,21-58. Precambrian Research and Chivers, Chivers, K.M., K.M., 1990, 1990,Secular Secular variation variation inin greenstone greenstone sequence sequence development development emphasizing cmphmizing Superior Province, Canada: Canadc Thurston, P.C., and Research:v.v.46, p.21 Precambrian Research: 46, p. 21 -58. -58. 'Tomlinson, K.Y., Thurston, P.C., P.C., Hughes, Hughes, D.J., D.J., Keays, R.R., 1996%The central Wabigoon Wabigom region: pemgenesis of mafic-ultramafic matic-ultram&k rocks Tomlinson, KY.. Thurston, R.R., l996a, region: petrogenesis rocks in in the Steep Rock, Lumby Lake and O h n g a Lake greenstone In: Harrap, Harap, R.M., RM., Obonga greenstone belts belts (continental (continental rifIing rifting and drifIing drifting in in the Archean). Archean). In: Helmstaedc e p m #53. Helmstaedt, H. Fds.), (Eds.), Western Superior Transect Transect Second SecondAnnual AnnualWorkshop Workshop(Oci (Oct.20-2l,l995), 20-21,1995),Lithoprobe LithoprobeRReport #53.Lithoprobe Lithoprobe Secretariat, University of British Secretariat British Columbia, pp. 65-73. �Tonilinson, KY., 1996,The belts, northem northern Ontario, Ontario, Canada: Canada: unpublished Tom1ins.m. K.Y., 1996,megeochemistry geochemisryand andtectonic tectonicsetting sewingofofearly earlyPrecambrian Precambriangreenstone greenstone belts, unpubliihd PhD thesis. University University of PhD thesis, of Portsmouth, P o ~ m o u t hUK, U& , pp.287. pp.287. Tomlinson, K.Y., KY., Hughes, I) the Hughes, Di., D.J.,Thurston, 'Ibumton,P.C., P.C., 1996b, 1996b,Metavoleanic Metavolcanic rocks rocks of of the the central c e n d Wabigoon Wabigmn Subprovince: Subprovince: 1) the Lurnby Lumby Lake Lake Tomlinson, greenstonebelt. belt.1": In: Summary Summas'yofofFicidwork other Activities, 1996. Geological Survey pp. 60-63. 60'63. greenstone Fieldwork and and otherAdvities. 1996. Ontario OntarioGeological SurveyMiscellaneous MiscellaneomPaper Paper 166. 166, pp. tJgIow, vicinity of Rook No. No. 8, 12th IInternational I, 12th n t m d o n a l Geological GeologicalCongress, Congress,issued iswed Uglow, W.L., W.L.. 1913, 1913, Geology Geology of of the the vioinity ofSteep Steep Rock Rock Lake: Lake: in in Guide Guide Rook 8, Pt. pt. I, by the Canada, p. by the Geological Geological Survey S w e yof ofCanada p. 46.53. 46-53. Walcott, Ontario. CanadCanada;Geological GeologicalSurvey Surveyof ofCCanada. Memoir 28, 28, p. p. 16onfossils fos?.ils from tiomlimestone limestoneof o fSteeprock Steeprock Series, Series, Ontario, d a . Memoir 16W d w C CD,, C.D.,1912, 1912,Notes Noteson 23. 23. Wilks, ME., NorthwesternOntario: Ontario:aaMajor Major Archean ArcheanUmwfonnity Unconformity an an Archean Archean Swomatolites, Stromatolites, TheGeology Geologyof ofthe theSteep Steep Rock Rock Group Group Norrhwestem Wilks, M.E..1936, 1986,The MSc thesis. Saskatchewan, MSG thesis. University University Saskatchewan.Saskatoon, Saskmon,Saskatchewan, Saskatchewan, 206 206 pp. pp. Wilks, unconformity and Wilb. ME,, M.E.,and andNisbet, N i s ME.G., E.G.,1988, 1988,Stratigraphy Stratigraphyofofthe theSteep SteepRock Rock Group, Group, northwestern northwestern Ontario: Ontario: aa major major Archean Amhean unwnfomity and Archean Amhem stromatolites: smmatolites: Canadian Canadian iournal l o ~ aofoflEarth EaOhSciences. Sciences,v.v.25, 25,P. p. 370-391. 370-391. Wilka, ME., major Archean Wilks, M.E., 1986, 1986,The Thegeology geologyofofthe theSteep SteepRock RockGroup, &up, northwestern mxthwestem Ontario: Ontario: a a major Archem unconformity unwnfomity and and Archean Archean stromatolites; smmmliies; M.Sc. thesis, MSe. thesis,University UnivmityofofSaskatchewan, Saskatchewan,Saskatoon, Stskmon,Saskatchewan, Saskatchewan,206 206P. p. Wilks, ME,, ofofthe Wilb, M.E.,Nisbct, Nisbet,E.G., E.G.,198$, 1988,Stratigraphy Shati-hy theSteep SteepRock RockGroup, Group,northwestern norrhwestmn Ontario Ontario major major Archean Archean unconformity unwnfomity and and Archean Archean stromatolites. 370-391, smmatoliies. Canadian Canadian iournal JournalofofEarth EarthScience:25, Scimce:25,370-391. Wright, CM,, the Steeprock Queen'sUniversity, University,Kingston, Kingston, Ontario. Ontario. zonesininthe thehangingwall hangingwallofofthe Steeprock Ore %Zone; Zone; M.Sc. M.SG thesis, thesis, Queeds Wright, C.M.,1959. 1959,Pyrite Pyritezones I I �Day 1 Field Field Trip Tnp Stops Stops Field stops in the Lumby Lake Lake greenstone greenstone belt. From Thunder Bay travel NW to to Upsala Upsala on onTrans-Canada Trans-Canada Highway Highway 17. 17.Approximately Approximately 15-16 km further west of Upsala at the Graham road, turn left (west) onto the Graham logging logging road, gravel road to Sapawe. This road initially follows the Firesteel Sapawe. follows Firesteel River (Provincial Series Pakashkan Lake sheet). After approx. approx. 24-25 24-25 km you come to aa junction junction map 52G15E, 52G/SE, Pakashkan where the main gravel Sapawe-Upsala road turns south (left), continue ahead (right gravel Sapawe-Upsala south (right hand hand fork) and after km you you come come to to aabridge bridgecrossing crossingBrush Brush Creek Creek (Provincial (Provincial Series Series map map after 22 km 520/SW, Gulliver River sheet). You are at the eastern extent of the greenstone belt and 52G/SW, Gulliver eastern within the northern half of the stratigraphy (Figure 1). 1). This generally east-west bush road runs across most of the length of the Lumby Lumby Lake Lake greenstone greenstone belt (at a low low angle angle to to the the strike) before turning turning south near Lumby Lake and joining the gravel north-south Premiere south joining Lake road (near km 33), main Sapawe-Upsala Sapawe-Upsala road (between km 33), which which later later rejoins rejoins the main 12 and 13). 13). Stop 643340E 5435920N: 5435920N:BIF, BIF,ultramafic ultramafic fragmentals, fragmentals, mafic Stov 1: 1: UTM UTM zone zone 15, 15,643340E maficlavas. lavas. reachthe thefirst firststop stop(Figure (Figure 1). 1).ItIt is is on the From Brush Creek Creek continue continue another another —2km -2km totoreach left side of the road next next to to aa clearing clearing for for parking, parking, and opposite opposite aa road road heading heading off off on on the the right hand side. The area area was was burnt burnt over over in in 1995 1995but but new new trees have been planted and are are growing Om thick growing fast. fast. A A large largeoutcrop outcropofofbanded-iron banded-ironformation formationisisclose closetotothe theroad road(—4 (-10m unit) and then further from the road (south) is an ultramafic fragmental sequence then further from the road (south) is an ultramafic fragmental sequence(—20m (-20m thick). South of this are are mafic mafic amygdaloidal amygdaloidal flows, followed by mafic pillow lavas. The ultramafic fragmental ultramafic fragmental sequence sequence is unusual unusual and and ofofdebatable debatable origin. origin. It comprises comprises predominantly ultramalic ultramafic lithic, lithic, lapilli-sized lapilli-sized fragments fragments within an an ultramafic ultramafic matrix matrix (bulk (bulk composition 12 to 21 wt. % MgO, 38-45 wt. % Si02). a ranges from ungraded to graded 12 21 wt. % MgO, % Si02). It ranges from ungraded to graded and would be breccia. In places it shows be classified classified un-genetically un-genetically as aa volcaniclastic volcaniclastic breccia. shows evidence and quenched but was was itit generated evidence of hyaloclatite hyaloclatite textures textures and quenched fragments fragments but generated by by predominantly pyroclastic or autoclastic processes and has it been resedimented? predominantly pyroclastic or autoclastic processes and has it been resedimented? in high-field strength strength Geochemically these are Al-depleted komatiites komatiites which are enriched in elements and light rare earth earth elements elements (REE) (WE) but depleted depleted in in heavy heavy REE. See See Tomlinson Tomliison (l999a) for et al. (1999a) foraadetailed detaileddescription descriptionof of the the chemistry chemistry and and petrogenesis. petrogenesis. Stop 2: UTM 637750E 5437300N: 5437300N: komatiite komatiite flows, interflow interfiow BIF BIF and and chefl. Stov UTM zone zone 15, 15,637750E chert. From stop I continue a further —6 km west along the road to a small turn off on the right. stop 1 continue a further -6 km west Follow Follow this thistrail trailfor for—200 -200 m then then turn turn left leftonto ontoanother anotherfrail trailand andafter after—300 -300 m you you come cometo to the outcrop or a large, flat, flat, glacially glacially polished polished outcrop. outcrop. ItIt may may be be possible possible to drive drive right right to outcrop the trails may be too too muddy. muddy. At this this stop stop (Stop (Stop 2, Figure Figure 1) 1) there there are are several several large large �mapof ofthe theLumby LumbyLake Lake greenstone greenstone belt belt showing showing trip trip localities Figure 1: GeoLogical Geological map Jackson, 1985 (geochronology from Davis and Jackson, 1985 and and Tomlinson Tomlmson et et a!., al., 1999b). 1999b). -t Norway Lake Pluton Ma 3014 Ma A Red Paint /3014 -t , /, Irene-Eltruit me-Eltruit Lakes ikes Complex Complex Lake -s - — .1 Gargoyle Lake 4' Norway A Lake V 'Bar 1 2 Divers ion W 1 T 1 -- L - 2997 r'---a 0,-1c,11', Jefferson Lake !U..::A - Stnç * Sapawe4 Post-tectonic granite Post-tectonic granite Pre-tectonic tonalite-gabbro intrusive complex Pre-tectonic granodioritegranodioritetonalite gneiss I . ) - r. Marmion Batholith 3003. Ma Sedimentary edimentary rocks - Brush Brush Creek I Lake -1 .4 - <2963 ~ 2 9 6 3Ma 6 kilometers h/f. ' Sapawç * Komatiitic ir Komatiiticrocks rocks Intermediate felsic ..a. ~termediateto felsic A pillow ~nging Pillow p younging volcanic rocks direction direction * volcanicrocks rocks * U-Pb U-Pbage age Mafic volcanic --f-i— 4 4- 1 Faults Faults Fold axis: Fold . axis: . syncline anticline, anticline, Q Trip @ Triplocality locality Roads Roads ala �komatiite outcrops that have been stripped by a prospector (Ray Bernatchez) and hence the rocks are well exposed with beautifully preserved textures and field relationships visible. The first large outcrop contains komatiite flows, some are thin (<lm thick) with thin pillowed flow tops (sequence youngs to the SW\ Spinifex texture is rare on this outcrop. Spherules are common as are ancient cracks that facilitated devitrification. Walk through the bush towards the NW and several outcrops occur along the way, the first on a small scarp shows wonderful spinifex texture. Several small outcrops show banded iron formation (BIF) and evidence of komatiite lava flowing into water-laden sediment. Peperite textures, evidence of autobrecciation, ultramafic pillows etc. are all beautifully preserved. Continue to the NW and a large outcrop of spinifex textured komatiite occurs. Flows are separated by thin units of cherty BIF. A 9m thick flow contains randomly orientated pyroxene crystals (altered to actinolite) which in the top 3m of the flow are spinifex textured with branching acicular blades. Generalized log of these outcrops shown in Figure 2 (from Tomlinson et al., 1996 and 1999b). Compositionally many of these flows are basaltic komatiites (18-13 wt. % MgO) and spinifex textured high-Mg basalts (9-12 wt. % MgO). Chemically they differ from the ultramafic fragmental units and are Al-undepleted with REE profiles that are generally unfractionated (Tomlinson et al., 1999a). Stons 3 and 4: UTM zone 15, 0637345E 5437130N, and further along the road: Mafic lava flows. Return to the east-west road that runs across the greenstone belt, reset the odometer and continue driving west. Many outcrops along the road between the komatiite locality and the culverts at Pinecone and Cryderman Lakes (2 large lakes either side of the road after a -7.5 km stretch) show well preserved mafic lava flows. This lithology (having undergone various states of strain) makes up the majority of the greenstone belt stratigraphy. We will stop at a couple of localities before Pinecone and Crydennan Lakes. In the first (just -300 m from where we rejoined the road, Stop 3, Figure I), flow top breccia is overlain by a massive flow base, which is in turn overlain by pillowed lava, which is capped by thin hyaloclastite. The complete flow is 3.8 m thick with 80 cm of pillowed flow. Further along the road several outcrops show undefonned pillows where younging direction is easy identified (any of these outcrops are suitable for stop 4). Pillows are small with convex upward tops and bases that project downwards into the interstices between the underlying pillows. 4 S t o 5: ~ UTM zone 15,633266E 5435600N: view. Continue along the "main" road until reaching the culverts at Pinecone and Cryderman Lakes (Stop 5, Figure 1, -7-7.5 km from Stop 3), reset the odometer again. These lakes occur at the central east-west axis of the belt within sedimentary units that separate the northern and southern halves of the belt. Unfortunately the sedimentary units are poorly exposed but the view is nice and so is the water if its warm enough for swimming! �Figure 2. Lower komatiite unit, northern assemblage, Lumby Lake greenstone belt (after Tomlinson et al., 1999a). Metres SW Pyroxene cumulate Pillowed and spherultitc flows Komatiite flow Ultramafic hyaloclastite Komatiite flow Ultramafic hyatoclastite Interbedded komatiite flows, iron formation and chert Komatiite flow Komatiite flow Gabbro with increasing proportion of tremolite needles towards the top �Stoo 6 (if time allows): UTM zone 15,628130E S433850N: mafic lavas. Continue following the road through the belt. The road heads predominantly west and is now cutting the southern stratigraphy at a low angle to the strike. Unlike the northern half of the belt (which youngs southwards), the southern half youngs predominantly to the north. Mafic pillow lavas again make up the majority of the stratigraphy and an outcrop 6 km further on shows good younging to the north (Stop 6, Figure 1). - Stoo 7: UTM zone 15,624000E 54323SON: felsic volcanics a t S margin of the belt. Continue on this "main" road for a further -6 lan as the road eventually turns south into the felsic volcanic sequence at the base of the greenstone belt. Close to Lumby Lake itself a large property has been cleared by Ray Bernatchez and the felsic sequence is well exposed (Stop 7, Figure 1). Felsic volcanic rocks make up a relatively thick sequence here. They have been dated at 3 localities along the southern margin of the belt (including this site) and range from 3001 to 2997 Ma which is within error of the age of the Marmion tonalite. The felsic volcanics are quartz porphyritic and range from fragmental units to massive rhyolite flows. Continue south and this road rejoins the main gravel logging road down to Sapawe (Provincial Series map 52B/NW, Marmion Lake sheet). A few km south of Sapawe the road rejoins Trans-Canada Highway 11. To the right is Atikokan and to the left is Thunder Bay. References Davis, D.W. and Jackson, M.C., 1988. Geochronology of the Lumby Lake greenstone belt: a 3 Ga complex within the Wabigoon Subprovince, northwest Ontario. Geol. Soc. Am. Bull., 100, 818-824. Tomlinson, K.Y., Hughes, D.J., Thurston, P.C. and Hall, R.P. 1999a. Plume magmatism and crustal growth at 2.9 to 3.0 Ga in the Steep Rock and Lumby Lake area, western Superior Province. Lithos, 4611, 103-136. Tornlinson, K.Y., Davis, D.W., Thurston, P.C., Hughes, D.J. and Sasseville, C. 1999b. Geochemistry, Nd isotopes and geochronology from the Central Wabigoon Subprovince and North Caribou Terrane: regional correlations leading towards a Mesoarchean reconstruction; in Harrap, R.M. and Helmstaedt, H. (eds.). Western Superior Transect 1999 Annual Meeting, Lithoprobe Report #70. Lithoprobe Secretariat, University of British Columbia, p 136-146. Tomlinson, K.Y., Hughes, D.J. and Thurston, P.C. 1996. Metavolcanic rocks of the central Wabigoon subprovince: 1) the Lumby Lake greenstone belt. Summary of Fieldwork and Other Activities, 1996. Ontario Geological Survey Misc. Paper 166: 6063. �Day 2. Atikokan area Day 2 features several unique geologic features spanning 300 My of Archean crustal evolution in the southern Wabigoon and adjacent Quetico Subprovinces. Stops include the early Mannion tonalite batholith, a rare Archean unconformity, the Steep Rock Group (a platform sequence) and contiguous metavolcanic and metasedimentary rocks (Figure 1). An attempt is made to examine the structural relation between these rocks. Most stops are in vicinity of the abandoned Steep Rock Iron Mine from which approximately 100 Mt of ore were removed from 1944 to 1979. Starting from the junction of Highways 622 and 11B in Atikokan, proceed west on Highway 11B turning north on Mercury or O'Brien Streets. Continue past the Atikokan airport in the direction of the abandoned Steep Rock Iron Mine. After passing under the Canadian National Railway overpass, follow the paved perimeter road along the west side of the mine area. The perimeter road curves around the north end of the mine area and crosses back and forth beneath a power line. Stop where the road crosses the power line for the second time approximately 1 1 km from the start and walk west to low, rounded outcrops interspersed with grassy areas. The Marmion batholith -The Marmion batholith is a large oval tonalitic intrusion extending at least 50 km east of Atikokan. Dated at 3003+5 Ma (Davis and Jackson 1988) it is among oldest felsic intrusions in the western Superior Province and together with the pre 2900 Ma Dashwa Gneiss Complex and Finlayson and Lumby greenstone belts (Davis and Jackson 1988) is part of the enigmatic older volcanoplutonic terrane in the central Wabigoon Subprovince. The Marmion batholithformed a mature erosional surface on which the Steep Rock Group was unconformably deposited at an unknown but probably early stage in tectonic evolution of the area. Although rare in central parts of the Marmion batholith, metagabbro dikes are voluminous near the Steep Rock belt; some dikes seem topredate whereas others postdate the Steep Rock Group. Although the tectonic environment at the time of Steep Rock Group deposition is speculative, the dikes imply extensional conditions, possibly in a rifted continental margin setting (Wilks and Nisbet 1988). Felsic and mafic varieties of tonalite are mapped in the Marmion batholith near the Steep Rock belt. These are typically medium-grained, weaklyfoliated and inequigranular to porphyritic rocks composed of essentially plagioclase, quartz and biotite and up to 20% hornblende in the mafic variety. The Marmion batholith is cut by ductile-brittlefaults and primary minerals are extensively converted to sericite, carbonate, chlorite and actinolite within a few kilometers of the Steep Rock belt. Stop 6-1 The Marmion batholith adjacent to the Steep Rockgreenstone belt Exposures in the power line right-of-way are somewhat poor due to an intense brown weathering rind but consist of tonalite interspersed with about 30% metagabbro dikes. Dikes are irregular in shape and are mainly north-northeast trending. All rocks are well foliated to friable and intensely altered to greenschist minerals. A few hundred meters south of this locality the Marrnion tonalite is overlain by the Steep Rock Group. �Figure 6-1 : Geologic map of the Atikokan area shown field-trip stops 6-8 and 6-9. See Figure 63 for other stops. �From the power line, follow the perimeter road south for a distance of about 1 km where the pavement ends at an abandoned railway crossing. Park in the grassy area near the end of the paved perimeter road and walk west along the tom-up railway roadbed. Unconformity at the base of the Steep Rock Group - Greenstone belts are interspersed with voluminousfelsic plutonic rocks throughout the Superior Province and in the majority ofplaces the boundaries between the two are marked by sharp contacts where plutonic rocks intrude and contact metamorphose greenstone belts. Rarely is the base of an Archean greenstone belt preserved although in recent years, an increasing number of localities have been identified where the bases of greenstone successions lie unconformably on felsic plutonic rocks. Most arc: found in remote northwestern parts of the Superior Province. The Steep Rock Lake locality represents an extremely rare, well-preserved and accessible example of an Archean unconformity and is featured in several stops on this trip. Stop 6-2 Unconformity at the base of the Steep Rock Group Outcrops at this locality illustrate the gradational nature of the unconformity at the base of the Steep Rock Group. After walking about 200 m along the tom-up railway line past outcrops of mainly tonalite, you will see a large vertical rock-cut on the east side. Foliated, relatively fine-grained dark metagabbro makes up most of the vertical rock-cut and, at the north end of the vertical rock-cut, is transitional to friable, buff, gritty metasandstone (Wagita Formation). The metasandstone is poorly bedded, but locally shows clasts, and is well foliated, possibly indicating enhanced shearing at the unconformity. The metasandstone can be traced north from the large vertical rock-cut through a series of small exposures to a rounded outcrop of metaconglomerate that lies opposite piles of mine-waste placed on the railway line. Boulders of the conglomerate are mainly tonalite and a dark rock that is probably metagabbro. Beyond the metaconglomerate, rock-cuts show carbonate breccia, tonalite and metagabbro. Outcrops at the obstructed tunnel entrance are metamorphosed pelite and sandstone. The section along the railway line passes back and forth through the unconformity at the base of the Steep Rock Group. Rarely is the unconformity sharply defined as the transition from tonalite to sandstone takes place gradually over distances of a few meters. Return to the vehicle and drive .9 km south along the gravel perimeter road past remains of the head frame of the Hogarth shaft and a branch road (east) to the former concentrator plant area. Turn right and proceed .2 krn down the pit access ramp. Turn right at the first side-road and proceed .15 km and park at the outside of a sharp bend overlooking the pit. Walk down the gravel slope following an erosional channel past several rusty, jagged outcrops of tonalite and gabbro. Follow a flagged trail from the base of the gravel slope about 100 m westerly through a wooded area and emerge onto a north-facing slope interspersed with outcrops, boulders and �Mafic Metavolcanii rocks Dismal Ashroch Jolliffe Ore Zone Mosher Carbonate Wagita Formation (elastics) Stromatolites Unconforrnity Marrnion Batholith Early Mafic Dikes Figure 6-2: Schematic diagram (after Wilks and Nisbet 1988) showing the Steep Rock Group and contiguous supracrustal rocks of the Steep Rock belt. See legend of Figure 6-1.The upper ashrock contact is locally faulted and may represent a depositional time-gap. �small trees. The Steep Rock Group -The Steep Rock Group was extensively studied over the past century (see reviews in Stone et at. 1992) and although early workers offered diverse structural and stratigraphic interpretations, later studies showed the Group to be a homoclinal succession of 4 formations totalling about 1000 m thickness. These include,from the base up, the Wagita Formation (conglomerate, sandstone), Mosher Carbonate Formation (limestone, dolostone), Jolliffe Ore Zone Formation (goethitic ironformation) and Dismal Ashrock Formation (ultramafic pyroclastic rocks) as shown in Figures 6-2 and 6-3. The lower boundary of the Steep Rock Group is defined by an unconformity at the base of the Wagitaformation. Although sheared locally (e.g. Stops 6-2, 6-3) other exposures of the unconformity (e.g. Stop 6-5) show little deformation and preclude tectonicjuxtaposition of the Steep Rock Group onto the Marmion batholith. The upper contact of the Dismal Ashrock Formation is highly deformed in the Steep Rock Mine area and is widely cited as the upper boundary of the Steep Rock Group (e.g. Jolliffe 1955). The Steep Rock Group is cited as a prime example of a platform sequence (Thurston and Chivers 1990); platform sequences typically comprise a succession of quartz arenite and conglomerate, stromatolitic carbonates, iron formation and komatiitic rocks unconformably overlyingfelsic plutonic rocks. Most are concentrated in the Sachigo Subprovince and arepre 2.8 Ga in age having preceded the mafic, mafic tofelsic and "Timiskaming-type" volcanic sequences that make up many greenstone belts. Geologic evidence suggests platform sequences developed in shallow water in a tectonically stable environment, involving initial erosion of widespread older sial followed by rift-related volcanism (Thurston and Chivers 1990). Stop 6-3 Marmion tonalite; Wagita Formation; Mosher Carbonate Formation; stromatolites The outcrop at the end of the trail is made up of buff, gntty, poorly bedded Wagita Formation and altered friable tonalite that gives way westerly over a distance of about 10 m to grey, bedded Mosher Carbonate Formation. Note that the contact between clastic metasedimentary rocks and Mosher Carbonate Formation is sharp; rocks are strongly foliated possibly due to shearing at this locality. About 10 m north at the low end of the outcrop, spherical and pseudocolumnar stromatolites, typically .1 m in diameter are exposed in bedded Mosher Carbonate Formation. A west-sloping face of the outcrop provides a lateral section showing the concentric domical shape of stromatolites. Apexes of the stromatolite domes indicate a westerly younging direction. Continue down the slope to a level area and turn west toward the edge of the Hogarth open pit. Observe large domical stromatolites exposed on the west-facing wall of the upper bench. Rather than returning to the vehicles by the way in which you came, proceed northerly from the level area along a steep access ramp to the perimeter road. Walk along the perimeter road to the vehicles and drive .1 km up the hill and park in a level place at the observation area. Walk to the west side of the observation area. Stop 6-4 Scenic lookout and overview of the Steep Rock Group The partly flooded Hogarth pit can be seen to the north and the Roberts pit to the extreme �Figure 6-3: Detailed geologic map of the Steep Rock Mine area showing l o c a t i o n s o f field-trip stops 6-1 to 6-7. Dlsmel Ashrook Formatton Pyrite Zones JoIHffe Ore Zone Formati Moaher Carbonate Format! Wagita Formation ~onai~te - ./--ROÈ -Railway, ..... - ' abandoned railws Water lavç*l1 9 8 8 ) Geological contact / Fault ^%/Aautt + zone synctirr outcrop �south. Looking west, the west arm of Steep Rock Lake can be seen beyond a concrete retaining dam. This stop provides an overview of the west-facing Steep Rock Group and adjacent, eastfacing mafic metavolcanic sequences in the Mine area (Figure 6-3). The scenic lookout is situated on Marmion tonalite at the base of the Steep Rock Group. The Wagita Formation is not well exposed and can be either absent or else thin at this locality. In either case, the base of the Steep Rock Group extends along the foot of the slope immediately in front of you. Grey outcrops underlying the tree-covered hill 200 to 300 m west, and the rusty jagged bluff to the northwest are Mosher Carbonate Formation. The Jolliffe Ore Zone Formation is almost completely flooded; a few reddish outcrops at the northwest end of the Hogarth pit may be remnants of the ore-zone. Dark grey-greenish outcrops on the west side of the pit near the centre of the mine area are Dismal Ashrock Formation. The sides of large heaps of waste rock on the west side of the mine area also appear to be mainly ashrock. The upper bench road that runs nearly fill1 length of the west side of the mine area approximately marks the contact between Dismal Ashrock Formation and adjacent mafic metavolcanic rocks. East-facing pillow lavas and metagabbro dikes underlie most of the tree-covered ridge beyond the upper bench road. The failed slope at the northwest end of the Hogarth pit is in metagabbro and tonalite. Proceed back down the side-road, turn right and continue 1 km down the main access ramp. Park at the junction with the first bench road to the left and walk about 300 m south along the bench road. Stop 6-5: Unconformity; Wagita Formation; Mosher Carbonate Formation The large bluff east of the bench road is composed of tonalite cut by thick, inclined metagabbro dikes. Near the top and at the south end of a small talus slope about 300 m from the parking area, steep-westerly dipping beds of rusty Mosher Carbonate Formation lie in unconformable contact with tonalite along the face of the bluff. Normally grey crystalline tonalite becomes buff, friable and altered possibly reflecting development of a regolith at the unconformity. Mafic minerals and plagioclase are altered to chlorite, sericite and carbonate however, the rock retains a relict igneous texture shown by unaltered quartz grains dispersed throughout the medium. The unconformity is marked by a transition over a distance of 1 to 2 m from altered tonalite through gritty sandstone (Wagita Formation) to bedded Mosher Carbonate Formation. Quartz content increases up-section in the sandstone; quartz grains are nresent in the lower carbonate beds. The unconformitv is relatively unfaulted at this locality. Proceed back up the main ace of Dismal Ashrock in the west wall of the Hogarth pit Stop 6-6:Dismal Ashrock Formation mine to exposures �The soft, dull, dark green rock is representative of Dismal Ashrock Formation. The ashrock is composed of dark, poorly sorted, subrounded lapilli and is essentially a lapilli tuff that rarely shows stratification. Some lapilli are zoned possibly due to accretionary growth under subaerial conditions. Although Jolliffe (1955) noted thin lava flows in this unit, the ashrock is dominantly pyroclastic and in this regard is rare among Archean komatiites. Continue north on the upper bench road along the west side of the mine area. Turn right and proceed .3 km down a pit-access ramp turning right at an ensuing junction and continue .2 km down toward the flooded Hogarth pit. Park by two power poles mounted in cement-filled tires. Walk north along the access road curving up-hill to the west. From the end of the road follow a flagged trail north over heaps of mine waste to the edge of the pit. Supracrustal assemblages and the structure of greenstone belts - Although originally interpreted as homoclinal successions, geochronology has shown in recent years that many greenstone belts are composites of supracrustal assemblages differing in age by up to 300 Ma (e.g. Corfu and Andrews 1986; Ayres and Corfu 1991). Although assemblages are major structural components of greenstone belts, mapping of assemblages has proven difficult because many contain similar types of volcanic and sedimentary rocks and all have been affected by late metamorphism and deformation. Boundaries between assemblages tend to be poorly exposed and can be either depositional time gaps orfaults with large possible displacements. In certain well-studied areas such as the Favourable Lake greenstone belt, assemblage boundaries appear to be mainly thrust faults (Ayres and Corfu 1991). At the present locality, the boundary between the Dismal Ashrock Formation and contiguous mafic metavolcanic rocks could possibly be an assemblage boundary. Favourable evidence includes the major lithologic and structural transition from the west-facing Steep Rock Group to a thick sequence of east-facing mafic lava flows and gabbro. The boundary isfaulted in the mine area (Figure 6-3; Stop 6-7),which implies that the mafic sequence could have been tectonically juxtaposed with the Steep Rock Group. Since neither the Steep Rock Group or metavolcanic rocks of the Steep Rock belt are dated, the depositional time gap at their mutual contact is unknown. Stop 6-7: Deformation at the contact between the Dismal Ashrock Formation and mafic metavolcanic rocks The pale green to white outcrops west of the upper bench road are pillowed mafic flows. East of the flooded Hogarth pit are bluffs of rusty Mosher Carbonate Formation. Approximately where the trail ends, the Steep Rock Group curves abruptly west and is cut off by a large metagabbro dike and the Bartley fault at the northwest end of the Hogarth pit. Metagabbro and tonalite make up most of the large bluff beyond the northwest end of the pit; a large rock slide in this area forced the mine to close prematurely in 1979. Provided that the slope of waste rock to the north is not flooded, carefully move down the �slope. Observe the pale-green to white friable rock that shows good pencil structure in the bench wall to your left. The pale green rock is probably a deformed mafic metavolcanic flow. Moving farther down the slope you pass beside soft, crumbled and crenulated, variably rusty to dark green rock of uncertain type. Upon reaching the lower bench level, go west along the bench to apoint where it is overrun with talus. The darkgreen deformed rocks in the pit wall behind the bench are Dismal Ashrock Formation and metagabbro. A rusty zone, which is possibly a pyrite lense, can be seen high on the pit wall. Several subvertical, north-trending mesoscopic faults cut up through the ashrock and are eroded back into the pit wall. The area illustrates severe deformation at the upper ashrock contact in the mine area, Mineral lineations plunge down-dip westerly implying a dominant component of dip-slip faulting. Proceed back up the ramps to the upper bench road and go south on to the paved perimeter road in the direction of Atikokan. Turn right on the road leading to the seaplane base on Steep Rock Lake and continue up a steep hill and around several curves for .4 km. Park in a turn-out on the left side of the road and walk east about 50 m through small trees to low outcrops in an abandoned gravel pit. Stop 6-8 (optional) Pillowed mafic metavolcanic flows This outcrop lies within the Canadian Charelston Gravel Pit that was strip-mined for ironore gravel in 1960 to 1965. Pillowed mafic metavolcanic flows that underlie the western half of the Steep ~ o c belt k are represented in this outcrop. Pillows typically have a pale-green, homogeneous interior and very-fine-grained, dark-green rims. Several varieties of pillows ranging from large "mattress" to small spherical types occur together. The younging direction derived from pillow shapes in this outcrop and elsewhere in the western Steep Rock belt is east. A massive flow occurs at the extreme west end of the outcrop. The rock is calc-alkaline basalt. Proceed back to Atikokan and south to the junction of Highway 11B and Highway 11. Turn west on Highway 11 and continue for 1.2 kilometers turning north on a forest access road just before Kemuel Lake. Drive about 200 m into a clear-cut and reforested area, park at the first turn-out and walk to a low outcrop on the east side of the road. Stop 6-9 (optional) Quetico metasedimentary rocks This outcrop shows several types of bedding and sedimentary features. Thick beds (up to 1. m) of fairly homogeneous metawacke occur at the north side of the outcrop. Bed thickness is generally .05 to .2 m; many beds are graded from a coarse sandy base to a grey, laminated, silty top. Truncated beds and crescentic scour channels filled with coarse material are present. Clasts (up to .2 m) of fine-grained, white chert or possibly �felsic volcanic material fill some scoured channels. Grainsize gradation and scour channels indicate that the local younging direction is south. The outcrop is cut by quartz veins, fractures and small-displacement faults. The mafic mineral is mainly biotite. Metamorphic grade increases south with the appearance of amphibole and garnet about 1. krn distant. End of Day 2. Return to Atikokan or Thunder Bay. �References Ayres, L.D. and Corfu, F. 1991. Stacking of disparate volcanic and sedimentary units by thrusting in the Archean Favourable Lake greenstone belt, central Canada; Precambrian Research, v. 50, p. 221-238. Corfu, F. and Andrews, A.J. 1987. Geochronological constraints on the timing of magmatism, deformation, and gold mineralization in the Red Lake greenstone belt, northwestern Ontario; Canadian Journal of Earth Sciences, v. 24, p. 1302-1320. Davis, D.W. and Jackson, M.C. 1988. Geochronology of the Lumby Lake greenstone belt: a 3 Ga complex within the Wabigoon Subprovince, northwest Ontario; Geological Society of America, Bulletin, v. 100, p. 818-824. Jolliffe, A.W. 1955. Geology and iron ores of Steep Rock Lake; Economic Geology, v. 50, p.373-398. Stone, D., Kamineni, D.C. and Jackson, M.C. 1992. Precambrian geology of the Atikokan area, northwestern Ontario; Geological Survey of Canada, Bulletin 405, 106p. Thurston, P.C. and Chivers, K.M. 1990. Secular variation in greenstone sequence development emphasizing Superior Province, Canada; Precambriari Research, v. 46, p. 21-58. Wilks, M.E. and Nisbet, E.G. 1988. Stratigraphy of the Steep Rock Group, northwestern Ontario: a major Archean unconformity and Archean stromatolites; Canadian Journal of Earth Sciences, v. 25, p. 370-391. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 2000 Description An account of the resource Institute on Lake Superior Geology. Thunder Bay, Ontario. May 8-13, 2000. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 2000 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English